JP7815082B2 - chair - Google Patents

Description

The present invention relates to a chair.

Various chairs with backrests that can be tilted backward have been known (see, for example, Patent Document 1).

In recent years, the industrial sector has been calling for the development of environmentally friendly products, particularly in line with efforts to achieve the SDGs. The chair sector is no exception, and one example of this is a design that allows for easy disassembly.

In addition, in order to curb the spread of infectious diseases such as COVID-19, many users are using chairs at home to work, and there is a demand for chairs that can be easily disassembled by individuals.

However, most conventional chairs require the removal of multiple screws to disassemble, or require the application of dangerously large amounts of force when removing components, so they are not something that anyone can easily disassemble.

In particular, the reaction force generator, which generates a reaction force when the backrest is tilted backward, is inherently dangerous when disassembled, and until now it has been extremely difficult to do so without using specialized tools.

Patent No. 5386071

The present invention was made in light of the above circumstances, and aims to provide a chair in which at least the reaction force generating body can be conveniently attached to and detached from the support base.

In other words, the present invention has the following configuration:

The invention described in claim 1 is a chair comprising legs, a support base supported by the legs, and a back support supported on the support base so as to be rotatable between a normal position and a backward position tilted further back than the normal position. A reaction force generator is provided between the support base and the back support, which can urge the back support toward the normal position. The reaction force generator is a compression spring type having one end attached to the support base via a support member and the other end attached to the back support. The support base is provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member. The support member can be moved to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and can be moved toward a counter-fixed position while engaging with the inclined surface by rotating the screw in a second direction. The inclined surface is configured to gradually move away from the other end as it moves from the fixed position toward the counter-fixed position.

The invention described in claim 2 is the chair described in claim 1, in which a mounting portion to which the support member is attached is provided at the rear of the support base.

The invention described in claim 3 is the chair described in claim 2, in which the mounting portion includes at least a bottom wall portion having the first screw insertion hole, and a rear wall portion extending upward from the rear end of the bottom wall portion and having the inclined surface on its front surface.

The invention described in claim 4 is the chair described in claim 2, wherein the mounting portion comprises a bottom wall portion having the first screw insertion hole, a rear wall portion extending upward from the rear of the bottom wall portion and having the inclined front surface, and left and right side wall portions extending upward from both left and right sides of the bottom wall portion and having rear portions connected to the rear wall portion.

The invention described in claim 5 is the chair described in claim 4, wherein the support member is surrounded by the bottom wall portion, the rear wall portion, and the left and right side wall portions at the fixed position.

The invention described in claim 6 is the chair described in claim 1, in which the support member includes a support member main body and a nut disposed inside the support member main body, the support base includes a bottom wall portion having a second screw insertion hole through which the screw is inserted, and a peripheral wall portion extending upward from the peripheral edge of the bottom wall portion, and the nut threads onto the screw inserted through the first and second screw insertion holes.

The invention described in claim 7 is the chair described in claim 6, in which the nut engages with the peripheral wall portion so as to restrict left-right movement and horizontal rotation, and engages with the peripheral wall portion so as to allow forward-backward movement.

The invention described in claim 8 is the chair described in claim 1, in which the first screw insertion hole is an elongated hole extending in the front-to-rear direction.

The invention described in claim 9 is a chair comprising legs, a support base supported by the legs, and a back support supported rotatably with respect to the support base between a normal position and a backward tilted position tilted further back than the normal position, wherein a reaction force generating body is provided between the support base and the back support, which is capable of urging the back support toward the normal position, the reaction force generating body being a tension spring having one end attached to the support base via a support member and the other end attached to the back support, the support base being provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member, the support member being capable of moving to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and the support member being capable of moving in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction,
The inclined surface is set so as to gradually approach the other end portion as it moves from the fixed position toward the anti-fixed position.

As described above, the present invention provides a chair in which at least the reaction force generating body can be conveniently attached to and detached from the support base.

1 is a perspective view showing an embodiment of the present invention; FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 15 is an enlarged view of the lower part of FIG. FIG. FIG. 2 is a rear view of the back upholstery in the same embodiment with a portion thereof broken away. FIG. 2 is a front view of the back upholstery in the same embodiment with a portion thereof broken away. FIG. 2 is a perspective view of first and second belt-shaped members in the embodiment. FIG. FIG. FIG. FIG. 4 is a plan view illustrating the operation of the operating member in the embodiment. FIG. 4 is a plan view illustrating the operation of the operating member in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the operation of the operating member in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the operation of the operating member in the embodiment. 5 is a view taken in the direction of the arrow X in FIG. 4 . FIG. FIG. FIG. 4 is an enlarged perspective view of a rear portion of the seat support in the embodiment. FIG. FIG. FIG. FIG. FIG. 2 is a perspective view of the seat body from below in the same embodiment. FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. FIG. 4 is a cross-sectional view illustrating the attachment of the seat body to the seat receiver in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat receiver in the embodiment. FIG. 4 is a cross-sectional plan view illustrating the attachment of the seat body to the seat receiver in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. 5A to 5C are explanatory views of a method for forming an opening in the embodiment. FIG. 10 is an enlarged view of the embodiment after the openings are formed. FIG. FIG. FIG. FIG. FIG. 10 is a left side view of the support base in the same embodiment. FIG. FIG. FIG. FIG. FIG. FIG. 2 is a partially enlarged vertical cross-sectional view of a leg and support base in the embodiment. FIG. 2 is a partially enlarged vertical cross-sectional view of a leg and support base in the embodiment. FIG. 2 is a partially enlarged vertical cross-sectional view of a leg and support base in the embodiment. FIG. 3 is a partially enlarged vertical cross-sectional view of a reaction force generating body and a support member in the embodiment. FIG. 68 is a partially enlarged longitudinal cross-sectional view corresponding to the cutting position of FIG. 67 in the same embodiment. FIG. 2 is an exploded perspective view of a reaction force generator and a support member in the embodiment. FIG. 4 is a perspective view of the support member in the same embodiment, seen from the rear. FIG. 2 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in the embodiment. FIG. 2 is a cross-sectional view illustrating the legs, the support base, and the lifting operation lever in the embodiment. 3 is a cross-sectional view taken along line AA in FIG. 2. FIG. 74 is a longitudinal cross-sectional view of the same embodiment when the seat back is tilted backward, corresponding to the cutting position of FIG. 73. FIG. 74 is a longitudinal cross-sectional view of the same embodiment when the seat is in a forward tilted position corresponding to the cutting position of FIG. 73. Cross-sectional view taken along line BB in Figure 29. FIG. 77 is a cross-sectional view of the same embodiment when the seat is in a forward tilted position, corresponding to the cutting position of FIG. 76 . FIG. FIG. 79 is a longitudinal cross-sectional view of the same embodiment when the seat is in a forward tilted position corresponding to the cutting position of FIG. 78. Cross-sectional view of line CC in Figure 84. FIG. 81 is a cross-sectional view of the same embodiment when the seat is in a forward tilted position corresponding to the cutting position of FIG. 80 . FIG. FIG. FIG. FIG. FIG. FIG. 87 is a central vertical cross-sectional view corresponding to the cutting position in FIG. 86 for explaining the process of removing the intermediate member in this embodiment. FIG. FIG. FIG. FIG. FIG. FIG. FIG. 79 is a longitudinal cross-sectional view of the seat in the lifted position corresponding to the cutting position of FIG. 78 in the same embodiment. 79 is a longitudinal cross-sectional view of the seat in a pop-up position corresponding to the cutting position of FIG. 78 in the same embodiment, and the seat in a state where it has been detached from the support base.

One embodiment of the present invention will be described below with reference to Figures 1 to 95.

The chair comprises legs A, a support base B supported by legs A, a seat C supported by support base B, a back support L supported by support base B, and a backrest M supported by back support L.

The seat C is disposed on a support base B and is configured to be able to assume three positions: a normal position (ps), a forward-leaning position (pf) that is more forward than the normal position (ps), and a backward-leaning position (pr) that is more rearward than the normal position (ps). Between the support base B and the back support L, a reaction force generator R is provided that can bias the back support L in the direction of the normal position (ps).

The backrest M is supported on the support base B via the back support L so that it can tilt backward. In other words, the backrest M and back support L can take two positions relative to the support base B: a normal position (ps) and a backward tilted position (pr) that is tilted further back than the normal position (ps).

The chair is equipped with a weight-sensing rocking mechanism that can lift the front and front-to-rear center of the seat C upward in response to the backward tilting movement of the back support L linked to the backrest M, and can also tilt and move the entire seat C backward.

The chair is equipped with a seat forward tilting mechanism that shifts the seating load to the front of the seat C, i.e., the portion of the seat C in front of the front axis j2, thereby rotating the seat C forward around the front axis j2 and transitioning it to a forward tilting posture (pf).

The following describes in detail each component of the chair in this embodiment.

<<Leg A>>
The leg A has a plurality of leg blades a1 with casters at their lower ends, and a leg support a2 that stands up from the part where the upper ends of the leg blades a1 gather.

In this embodiment, the leg A constitutes an obstructing member that can obstruct rotation in a predetermined direction relative to the support base B, preventing the lifting/lowering lever V, which extends and retracts the leg support a2 in the vertical direction, from assuming a detachable position (SR) in which it can be detached from the support base B.

<Leg support a2>
The leg support a2 is configured to be extendable and contractible in the vertical direction.

The leg support a2 extends vertically. The leg support a2 includes a gas cylinder ag that allows the vertical position of the seat C to be adjusted.

The gas cylinder ag is of a known configuration, comprising a cylinder portion a21 attached to the bottom of the leg support a2, a lifting rod a22 that can be raised and lowered relative to the cylinder portion a21, and an actuating member a23 that protrudes from the upper end of the lifting rod a22 so that it can be extended and retracted in the vertical direction. When pressed downward, it allows the gas sealed inside to flow, thereby enabling the lifting rod a22 to be raised and lowered.

The lifting rod a22 is cylindrical. The outer circumferential surface of the upper part of the lifting rod a22, which is the upper part of the leg support a2, is tapered. In other words, the upper part of the lifting rod a22 is formed so that the diameter gradually decreases toward the top.

The upper part of the lifting rod a22 is designed to fit into the fitting hole Ba, which is the leg connecting part of the support base B. The fitting hole Ba of the support base B, into which the lifting rod a22 is fitted, is shaped to fit tightly around the upper part of the lifting rod a22.

The actuating member a23 can be pressed downward by the lifting/lowering lever V, which is an operating lever rotatably supported on the lever support b13 of the support base B.

<<Support base B>>
A support base B is attached to the top of the leg A.

Support base B is supported by legs A so that it can be moved up and down and rotated. Support base B is molded as a single piece from metal. Overall, support base B is box-shaped, elongated in the front-to-back direction and open at the top.

The support base B comprises a bottom wall 2 having a downward surface and integrally formed with a mounting portion 2T for supporting the rear end of the reaction force generator R; left and right side walls b1 extending upward from both the left and right ends of the bottom wall 2; a rear wall b2 erected at the rear end of the bottom wall 2 and connecting the rear ends of the left and right side walls b1; and extending flanges b3 extending outward from the rear of the left and right side walls b1.

<Bottom wall portion 2>
The bottom wall portion 2 comprises a foundation bottom wall 21 having a substantially horizontal bottom surface and a fitting hole Ba, which is a leg connecting portion that fits into the upper part of the leg support a2; an inclined bottom wall 22 extending diagonally upward and rearward from the rear end of the foundation bottom wall 21; a front bottom wall 23 extending forward from the front end of the foundation bottom wall 21 so as to be positioned gradually higher as it moves forward; and a rear bottom wall 24 extending substantially horizontally from the rear end of the inclined bottom wall 22 toward the rear.

The bottom wall 2 is provided with a rising structure 2S that rises near the fitting hole Ba, and a mounting portion 2T to which a support member W that engages with the rear end of the reaction force generator R is attached.

[Foundation bottom wall 21]
A boss portion 211 is provided on the base bottom wall 21, and has a fitting hole Ba formed therein that penetrates vertically and fits onto the upper portion of the leg support b2.

[Slanted bottom wall 22]
The inclined bottom wall 22 is provided at an angle so as to be positioned gradually upward toward the rear from the rear end of the foundation bottom wall 21. Because the inclined bottom wall 22 extends at an angle upward and rearward from the foundation bottom wall 21, it is possible to suitably provide the rear bottom wall 24, on which the mounting portion 2T is disposed, at a position higher than the foundation bottom wall 21.

[Front bottom wall 23]
The front bottom wall 23 extends forward from the front end of the base bottom wall 21. A front shaft j2 is disposed on the front bottom wall 23 and inserted into the long holes b12 in the left and right side walls b1.

[Rear bottom wall 24]
The rear bottom wall 24 extends rearward and substantially horizontally from the rear end of the inclined bottom wall 24. The left-right intermediate portion of the rear bottom wall 24 forms the bottom wall portion of the mounting portion 2T for mounting the support member W.

The rear bottom wall 24 is positioned higher than the base bottom wall 21. The rear bottom wall 24 is provided with an attachment portion 2T for a support member W that supports the rear end of the reaction force generator R.

In other words, by positioning the rear bottom wall 24 higher than the base bottom wall 21, a configuration can be suitably adopted for arranging the reaction force generator R in a horizontal position.

[Rising structure portion 2S]
The rising structure 2S is configured to include a screw hole n4 having a screw groove disposed above the fitting hole Ba.

The rising structure 2S is located adjacent to and rises in front of the fitting hole Ba. The rising structure 2S is made of metal and is formed integrally with the boss portion 211 of the foundation bottom wall 21 that forms the fitting hole Ba.

The rising structure 2S comprises rising portions 25 that rise to partially surround the front of the fitting hole Ba in plan view, and horizontal portions 26 that are installed between the rising portions 25 so as to be positioned directly above the fitting hole Ba.

The upright portion 25 is integrally connected to the front of the boss portion 211, which has the fitting hole Ba formed in it. The upright portion 25 has a shape in which the rear side's central portion in the left-right direction is recessed forward.

In other words, the rear of the upright portion 25 is shaped so that a space is provided directly above the fitting hole Ba, and the horizontal portion 26 can be integrally disposed above that space.

The horizontal portion 26 has a screw hole n4 that penetrates it in a substantially vertical direction. The horizontal portion 26 is integrally connected to the upright portion 25.

The rising structure 2S provided on the chair in this embodiment is provided solely to enable the worker to safely separate the leg A from the support base B.

Using standard tools, an operator can insert a screw v4 of a size that matches the screw threading hole n4 from above downward into the screw threading hole n4 provided in the horizontal portion 26 of the rising structure 2S.

The upper part of the leg support b2, which is located directly below the screw hole n4, is configured to be pressed downward by a screw v4 that threads downward while using the rising structure 2S, which is integral with the support base B, as a foothold.

More specifically, the screw v4 threaded into the screw hole n4 is guided by the thread groove of the screw hole n4 and rotates and descends, so that the lower end of the screw v4 can press downward against the outer periphery of the upper end of the lifting rod a22 that constitutes the leg support b2.

The rising structure 2S is used when detaching the leg A from the support base B. When the chair is completed, the fitting hole Ba in the support base B and the upper part of the lifting rod a22, which is the upper part of the leg support a2, are firmly fitted together.

In this embodiment, the pressing force of the screw v4, which can thread into the screw-receiving hole n4 of the rising structure 2S, is used to release or relax the tight fit between the fitting hole Ba and the lifting rod a22.

The screw v4, which rotates and descends along the thread groove, can apply a strong and continuous pressing force to the lifting rod a22, effectively eliminating or alleviating the tight fit between the fitting hole Ba and the lifting rod a22.

In other words, the chair of this embodiment is provided with a fit relaxation structure that relaxes the fit between the leg support a2 and the support base B. The fit relaxation structure has a screw threaded hole n4 disposed above the fit hole Ba in the support base B, and allows a screw v4 threaded into the screw threaded hole n4 to press the upper part of the leg support a2 downward.

Note that the screw v4 may be any type that meets the specifications for the screw insertion hole n4 and has a certain length in the vertical direction. In this embodiment, when disassembling the chair, for example, the screw v5 used to secure the support member W to the mounting portion 2T of the support base B is removed, and then the screw v5 can be reused as the screw v4 to thread into the screw threading hole n4 of the rising structure portion 2S.

[Mounting portion 2T]
The mounting portion 2T is provided at the rear of the support base B. The mounting portion 2T is a portion to which a support member W that supports the rear end of the reaction force generator R is attached.

The mounting portion 2T includes a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole v5 through which a screw v5 for mounting the support member W is inserted; a rear wall portion 27 extending upward from the rear of the rear bottom wall 24 and having a rearwardly inclined front surface nm; and left and right side wall portions 28 extending forward from both left and right ends of the rear wall portion 27 and extending upward from both left and right sides of the rear wall 24.

The rear bottom wall 24 is a generally horizontal plate. A first screw insertion hole h51, which is a screw insertion hole that penetrates vertically, is provided in the rear bottom wall 24 in the center in the left-right direction. The first screw insertion hole h51 is formed as an elongated hole that is elongated in the front-to-rear direction.

The rear bottom wall 24 is abutted against the bottom wall portion w11 of the support member W, which is pulled toward the rear bottom wall 24 by the movement of the hexagonal nut n5 threaded onto the screw v5.

The rear wall portion 27 is shaped like an upright plate and is erected so as to be tilted backward relative to the rear bottom wall 24. The front surface of the rear wall portion 27 forms an inclined surface nm against which the rear wall portion w13 of the support member W abuts.

The inclined surface nm is designed to gradually move away from the other end of the reaction force generator R, i.e., the front end of the front member r2, as it moves from the fixed position (lower position) tightened against the rear bottom wall 24 toward the anti-fixed position, i.e., upward from the lower position.

The left and right side wall portions 28 are erected on the rear bottom wall 24 and connected at their rear portions to the rear wall portion 27. The left and right side wall portions 28 serve to determine the left-right position of the support member W and also to ensure the strength of the rear wall portion 27, which serves as a foothold for receiving the biasing force of the reaction force generator R.

<Left and right side walls b1>
The left and right side walls b1 are erected from the left and right end portions of the bottom wall portion 2, i.e., the base bottom wall 21, the inclined bottom wall 22, the front bottom wall 23, and the rear bottom wall 24. The left and right side walls b1 extend substantially linearly in the front-to-rear direction.

The left and right side walls b1 are each equipped with a shaft hole b11 penetrating in the left-right direction, located at a position corresponding to the rear of the base bottom wall 21, for rotatably holding the main shaft j1; a long hole b12 penetrating in the left-right direction, located at a position corresponding to the front of the front bottom wall 23, for holding the front shaft j2, which supports the front portion of the seat C, so that it can slide forward and backward and up and down; a lever support b13, located only on the left side wall b1, for rotatably supporting the lift operation lever V for raising and lowering the seat C; a groove b14, located in front of and along the long hole b12 and opening outward; and a shaft movement restriction b15, located at the upper end of the middle portion in the front-to-back direction so as to protrude in a mountain shape, and which prohibits downward forward movement of the seat engagement shaft j3, which is attached to the back support L.

[Shaft hole b11]
The shaft hole b11 is for supporting the main shaft j1 that supports the back support L rotatably relative to the support base B.

Boss-like portions b4 that protrude outward and form part of the shaft hole b11 are integrally formed on the left and right side walls b1. By providing the boss-like portions b4 on the left and right side walls b1 in relation to the shaft hole b11, a left-right area capable of directly supporting the main shaft j1 is ensured that is longer than the width of the left and right side walls b1. The boss-like portions b4 are connected to the front end of the extension flange b3.

[Long hole b12]
The long hole b12 extends obliquely so that its lower end is located forward of its upper end in side view. A sleeve member gs made of synthetic resin is fitted into the long hole b12 to allow easy sliding on the front axle j2. The front axle j2 is supported by the long hole b12 via the sleeve member gs.

In other words, the support base B is provided with a long hole-shaped front shaft support portion that is composed of a long hole b12 and a sleeve member gs with excellent sliding properties that is attached to the long hole b12 and can slidably support the front shaft j2.

[Lever support portion b13]
The lever support b13 pivotally supports the lift control lever V so that it can perform a flap operation. The lift control lever V acts on the gas cylinder ag to extend and retract the leg support a2 in the vertical direction.

The lever support portion b13 includes a pair of front and rear support walls b15 that protrude outward from the left side wall b1, generally perpendicular to the left side wall b1, and a pair of shafts j4 that protrude toward each other from the inner surfaces of the pair of supporting walls b15 that face each other.

A space is formed between the pair of front and rear support walls b15 in which the lifting operation lever V is located.

The pair of shaft portions j4 protrude in opposite directions, i.e., in directions approaching each other with their axes aligned. The shaft portion j4 has a narrow portion j41 that is narrow in the left-right direction, which is a direction perpendicular to the axis, and a wide portion j42 that is wide in the up-down direction, which is a direction perpendicular to the axis (wider than the narrow portion j41). In other words, the horizontal width of the shaft portion j4 is shorter than its vertical width.

[Groove b14]
The groove b14 extends in the same direction as the long hole b12, that is, in a diagonal direction so that the lower end side is positioned forward of the upper end side in a side view.

A restricting protrusion 1t on the seat support body 1 is arranged in the groove b14 to restrict the position of the seat support body 1 relative to the support base B.

<Back wall b2>
The rear wall b2 extends from the rear end of the rear bottom wall 24. The rear wall b2 connects the rear ends of the left and right side walls b1. A left-right intermediate portion of the rear wall b2 forms a rear wall portion 27 of the mounting portion 2T for mounting the support member W.

<Extended tsuba b3>
The extending flanges b3 extend outward beyond the left and right side walls b1.

The extension b3 is provided with a damper mounting portion b31 for mounting a damper gx against which the back support base 4 abuts when the back support L is tilted backward. The damper gx mounted on the damper mounting portion b31 can be engaged with an engaging protrusion 41c that protrudes inward from the upper end of each of the left and right arm bodies 411.

The lower front portion of the support base B, which is configured as described above, is covered by a support base cover X1 made of synthetic resin.

<<Lifting operation lever V>>
The lifting operation lever V is a single unit made of synthetic resin and is configured to be attachable to the lever support portion b13 of the support base B without using fasteners such as screws.

The lifting operation lever V is rotatably supported on the support base B. More specifically, the lifting operation lever V is rotatably supported on the lever support portion b13 provided on the left side wall b1 of the support base B.

The lifting/lowering lever V can be operated by the user to make the leg support a2 of the leg A extendable and retractable in the vertical direction in order to raise and lower the seat C.

When the user moves the operating end vc side of the lifting control lever V upward, the bearing vb rotates around the shaft j4 of the support base B, with which the bearing vb engages, and the rotating end va moves downward, pressing down on the operating member a23 located at the upper end of the leg support a2.

The lift control lever V comprises a lever body vh in the shape of a plate extending laterally and having an operating end vc at its tip; a base end erection portion vi extending upward from the base end of the lever body vh; an inward extension portion vm extending inward from the upper end of the base end erection portion vi and having a pivot end va at its tip that can abut against the leg support a2; and a bearing portion vb provided between the base end erection portion vi and the inward extension portion vm.

<Lever body vh>
The lever body vh is curved to fit the outer surface of the seat support body 1, i.e., curved in a partial arc shape that convexly extends downward when viewed from the front. The tip of the lever body vh is the operating end vc that primarily receives the operating force from the user's fingers. When not receiving the operating force from the user, the operating end vc is configured to be located at its lowest position due to its own weight.

<Base end standing portion vi>
The base end erected portion vi is a generally square pillar-shaped member erected from the base end portion of the lever main body vh.

<Inward extension part vm>
The inward extending portion vm is cantilevered by the base end erecting portion vi. The base end portion of the inward extending portion vm has substantially the same width as the base end erecting portion vi, and the width gradually decreases toward the tip end side located inside the support base B.

The tip of the inward extension vm is a pivotable end va that can press down on the actuating member a23 attached to the leg support a2.

<Bearing part vb>
The bearing portions vb are provided at the front and rear of the boundary between the base end erect portion vi and the inward extending portion vm so as to face in opposite directions.

The bearing portions vb are provided in pairs on both sides of the lift control lever V, i.e., on the front and rear. One of the bearing portions vb faces forward, and the other faces rearward. The bearing portions vb are provided near the inner edge of the boundary between the base end upright portion vi and the inward extension portion vm.

The pair of front and rear bearing portions vb are recessed in opposite directions. The pair of front and rear bearing portions vb engage with a pair of front and rear shaft portions j4 that protrude in directions toward each other on the lever support portion b13 of the support base B, allowing the entire lift control lever V to rotate around the shaft portions j4.

The pair of front and rear bearing portions vb are provided with cutout portions vd, which serve as escape passages through which the pair of front and rear shaft portions j4 can escape by moving the lift control lever V, only when the lift control lever V is in a predetermined releasable position (SR).

The notch vd of the bearing portion vb is set to a width that allows the narrow portion j41 of the shaft portion j4 of the lever support portion v13 to pass through. On the other hand, the notch vd is set to a width that does not allow the wide portion j42 of the shaft portion j4 to pass through.

In this embodiment, the notch vd is located at a position that allows the shaft j4 to move linearly relative to the bearing vb in the vertical direction and disengage from the bearing vb to the outside when the lift control lever V is in the releasable position (SR).

<<Attaching the lift control lever V to the support base B>>
The mounting structure of the lifting operation lever V for mounting the lifting operation lever V to the support base B that constitutes the chair will now be described.

In this embodiment of the chair, the lifting operation lever V can take a detachable position (SR) in which it can be detached from the support base B, and a non-detachable position (SH) in which it cannot be detached from the support base B.

<About the SH (Short-Handed Posture)>
The lifting operation lever V can only take a non-detachable position (SH) in which it cannot be detached from the support base B when the leg A, which is an obstructing member, is fitted inside the support base B.

In other words, the lifting operation lever V cannot assume the detachable position (SR) when the leg A is properly attached to the support base B.

The chair supports the lift control lever V on the lever support b13 of the support base B, and then attaches the leg support a2 of the leg A, which acts as an obstructing member, to the support base B. This restricts the range of rotation of the lift control lever V by the presence of the upper part of the leg support a2.

The lift control lever V can only be rotated within the range of the non-releasable position (SH) by the upper part of the leg support a2, and as a result, any further rotation is prevented, preventing it from assuming the releasable position (SR).

In other words, when leg A is attached to support base B, the pivot end va of lift control lever V abuts against the upper part of leg support a2 in the non-detachment position (SH), and further downward movement of said pivot end va is prevented by the presence of leg support a2. For this reason, lift control lever V cannot be detached from support base B unless leg A is removed from support base B.

<About the ready-to-remove attitude (SR)>
The lifting/lowering operation lever V can take a detachable position (SR) in which it can be detached from the support base B only when the leg A, which is an obstructing member, is not fitted inside the support base B.

The chair is configured so that by removing the leg support a2 of the leg A from the support base B on which the lift control lever V is supported, the rotational range of the lift control lever V is no longer restricted by the upper part of the leg support a2, and the lift control lever V can be changed to the releasable position (SR).

In other words, when the leg A is detached from the support base B, the rotation end va of the lift control lever V can enter the inside of the fitting hole Ba until it can assume the detachable position (SR).

When the lift control lever V in the detachable position (SR) is moved by the user relative to the support base B (upward vertically), the narrow portion j41 of the shaft j4 can pass through the notch vd of the bearing vb, allowing the lift control lever V to detach from the support base B.

<<Reaction Force Generator R>>
The reaction force generating body R is also called a reaction force spring, and is interposed between the support base B and the back support body L. The reaction force generating body R is arranged so as to be expandable and contractible in the front-rear direction.

The reaction force generator R is a compression spring type whose one end, i.e., the rear end, is attached to the support base B via the support member W, and whose other end, i.e., the front end, is attached to the seat engagement shaft j3 of the back support L.

The reaction force generator R is capable of directly biasing the seat engagement axis j3 forward. The reaction force generator R is set to assume a substantially horizontal position extending in the front-to-rear direction when the seat C and back support L are in the normal position (ps). In the normal position (ps), the reaction force generator R assumes a horizontal position between the support base B and the seat engagement axis j3 of the back support L.

In this embodiment, the reaction force generator R uses the support base B as a foothold to bias the left-right center of the seat engagement shaft j3 forward. The seat engagement shaft j3 abuts against the shaft movement restricting portions b15 on the left and right side walls b1 of the support base B, preventing further forward and downward movement.

In other words, when the seat engagement axis j3 comes into contact with the support base B, the spine support L is prevented from rotating forward around the main axis j1, thereby defining the normal position (ps) of the spine support L.

In addition, as the back support L and seat C transition from the normal position (ps) to the rearward tilted position (pr), the seat engagement shaft j3 moves rearward and upward, causing the reaction force generator R to be gradually compressed in the front-to-rear direction and tilt backward.

The reaction force generating body R is mainly composed of a metal coil spring r1 (compression coil spring), which is a spring material.

In this embodiment, the seat occupant's weight-sensing locking mechanism presses the seat engagement shaft j3 forward and downward via the seat C, and the occupant's weight assists in generating a reaction force in the direction of the normal posture (ps) in response to the backward tilting of the backrest M. For this reason, a relatively small and lightweight coil spring r1 is used as the reaction force generator R in this embodiment.

The reaction force generator R comprises a metal coil spring r1, a front member r2 attached to the front of the coil spring r1, a rear member r3 attached to the rear of the coil spring r1, and a position-holding shaft r4 whose front portion is inserted into a holding hole provided in the front member r2 and whose rear portion is inserted into a holding hole provided in the rear member r3, thereby maintaining the positions of the front member r2 and the rear member r3.

The tip of the front member r2 is connected to the seat engagement shaft j3 so that it can rotate relative to it. The tip of the front member r2 has an engagement recess r21 that extends in the left-right direction so that it can fit onto the cylindrical seat engagement shaft j3.

The rear end of the rear member r3 is supported on the support base B via the support member W. The rear end of the rear member r3 is connected to the support member W so that it can rotate relative to the support member W. The rear end of the rear member r3 is provided with an engagement recess r31 extending in the left-right direction, and a pair of upper and lower vertical engagement recesses r32 that are aligned with the upper and lower parts of the engagement recess r31 in the left-right direction.

The engagement recess r31 of the rear member r3 is designed to engage with a pair of left and right shaft protrusions w15 protruding from the vertically middle portion of the front wall portion w12 of the support member main body w1. The pair of left and right shaft protrusions w15 protrude forward to form a partial disk shape in side view.

The vertical engagement recess r32 of the rear member r3 is designed to engage with a mountain-shaped protrusion w16 protruding from the left-right center of the front wall portion w12 of the support member main body w1. The mountain-shaped protrusion w16 is designed to extend in the vertical direction.

Note that although the front member r2 and rear member r3 have different postures, they each have the same shape.

<<Support member W>>
The support member W comprises a support member body w1 formed from synthetic resin, having a portion on the front side that can engage with the reaction force generating body R and having an inclined back surface portion wm on the rear side, and a hexagonal nut n5 which is a nut arranged freely inside the support member body w1.

The support member W is fixed to the mounting portion 2T, which has a first screw insertion hole h51 provided at the rear of the support base B, using a screw v5.

When the support member W is fixed in a predetermined position, it is surrounded by the rear bottom wall 24, which is the bottom wall portion of the mounting portion 2T of the support base B, the rear wall portion 27, and the left and right side wall portions 28.

<Support member body w1>
The support member main body w1 has a bottom wall portion w11 having a second screw insertion hole h52 through which the screw v5 is inserted, and a peripheral wall portion ws extending upward from the peripheral edge of the bottom wall portion w11 and having a nut arrangement space wk inside which a hexagonal nut n5 is accommodated.

[Bottom wall part w11]
The bottom wall portion w11 has a second screw insertion hole h52 in the center in the left-right direction, the second screw insertion hole h52 being elongated in the front-rear direction. The lower surface of the bottom wall portion w11 is adapted to abut against the rear bottom wall 24 of the mounting portion 2T in the fixed position.

[Peripheral wall ws]
The peripheral wall portion ws comprises a front wall portion w12 that engages with the rear member r3 of the reaction force generating body R, a rear wall portion w13 having an inclined back surface wm that can slide against the inclined surface nm of the rear wall portion 27 of the support base B, and left and right side wall portions w14 that connect the left and right side portions of the front wall portion w12 and the rear wall portion w13.

The front wall portion w12 has a pair of left and right shaft protrusions w15 protruding from the vertically intermediate portion so as to be able to engage with the engagement recesses r31 of the rear member r3, and a mountain-shaped protrusion w16 protruding from the horizontally intermediate portion so as to be able to engage with the vertical engagement recesses r32 of the rear member r3.

The rear wall portion w13 is tilted backward in side view. The rearward-facing inclined back surface portion wm of the rear wall portion w13 is tilted upward so that it gradually becomes more rearward.

The left and right side wall portions w14 each have an outer wall wa and an inner wall wb located inside the outer wall wa. The nut placement space wk is formed by the front wall portion w12 and rear wall portion w13 of the peripheral wall portion ws, and the inner walls wb of the left and right side wall portions w14.

The hexagonal nut n5, which is disposed in the nut placement space wk of the peripheral wall portion w12, engages with the inner peripheral surface of the peripheral wall portion w12 so as to restrict left-right movement and horizontal rotation. Furthermore, the nut placement space wk is formed so that its front-to-rear dimension gradually increases upward, allowing for front-to-rear movement of the hexagonal nut n5.

<Hexagonal nut n5 (nut)>
The hexagonal nut n5 has a known configuration and is held by the support base main body w1. The hexagonal nut n5 has a threaded groove and is threaded onto a screw v5 inserted into a first screw insertion hole h51 provided in the support base B and a second screw insertion hole h52 provided in the bottom wall portion w11 of the support member main body w1.

Hexagonal nut n5 engages with peripheral wall portion w12 to restrict left-right movement and horizontal rotation, and also engages with peripheral wall portion w12 to allow forward-backward movement.

<Operation of the support member W for mounting the reaction force generating body R>
The support member W for mounting the reaction force generating body R is attached to the attachment portion 2T in the following manner.

First, engage the front member r2 of the reaction force generator R with the seat engagement shaft j3, and then engage the rear member r3 with the front wall portion w12 of the support member main body w1.

Next, screw v5 is inserted from bottom to top through the first screw insertion hole h51 of support base B and the second screw insertion hole h52 of support member main body w1, and then connected (threaded) to the hexagonal nut n5 disposed inside support base main body w1.

At this time, the support member W is connected to the rear of the reaction force generator R, which is not compressed in the front-to-rear direction. In other words, the support member W is positioned above and behind the fixed position. The screw v5 inserted through the first and second elongated screw insertion holes h51 and h52 can easily assume a rearward tilted position in order to thread into the hexagonal nut n5.

After going through the above steps, the worker can complete the installation work simply by rotating the screw v5, without directly touching the reaction force generating element R, which can be dangerous, or the support member W connected to the reaction force generating element R.

Next, rotate the screw v5 threaded into the hexagonal nut n5 in the first direction (tightening direction).

When the screw v5 is rotated in the first direction, the hexagonal nut n5 held by the support member body w1 moves downward along with the support member body w1. In other words, the support member W moves toward the rear bottom wall 24 of the mounting portion 2T when the worker rotates the screw v5.

At this time, as the support member W moves downward, it is biased rearward by the reaction force generator R with gradually increasing force. In other words, as the support member W descends, it is guided by the inclined surface nm of the mounting portion 2T and moves downward and forward, so that the reaction force generator R is gradually compressed between the seat engagement shaft j3 and the support member W, and the biasing force gradually increases.

As the screw v5 continues to rotate, the support member W is guided along the inclined surface nm against the biasing force of the reaction force generator R and moves smoothly forward and downward, eventually reaching the predetermined fixed position.

In this way, the attachment of the support member W to the attachment portion 2T is completed.

Removing the reaction force generating body R and support member W can be done extremely safely by reversing the procedure described above.

In other words, by rotating the screw v5 in the second direction, the support member W can be moved (raised) in the direction opposite to the fixed position while being guided and engaged with the inclined surface nm. At this time, the support member W moves upward and rearward while being guided by the inclined surface nm, weakening the biasing force of the reaction force generator R as the hexagonal nut n5 rises.

The operator can complete the initial step of disassembling the reaction force generator R and support member W, which can be dangerous, by simply rotating screw v5 in the second direction without touching the reaction force generator R or support member W.

＜＜Location C＞＞
The seat C is supported by a support base B disposed on the legs A. The lower surface of the support base B and the outer peripheral surface of the seat C are configured to be smoothly continuous when viewed from the front.

Seat C comprises a seat support 1 and a seat body D, which has an upward-facing seat surface and is detachable from seat support 1.

The outer peripheral surface of seat C, i.e., the outer peripheral surfaces of seat support body 1 and seat body D, are smoothly continuous to form a partial sphere.

<Regarding the forward tilting configuration of the seat C>
The front part of the seat C is supported via a front axis j2 so as to be rotatable and movable up and down relative to the support base B. The rear part of the seat C is supported by a seat engagement axis j3, which is a seat engagement part of the back support L, a structure supported by the support base B in the normal posture (ps). Here, the "rear part of the seat C" supported by the back support L means "behind the front part of the seat C."

The seat C is configured to be tiltable around a front axis j2 supported by the support base B between a normal position (ps) and a forward-tilted position (pf) that is tilted further forward than the normal position (ps).

The seat C has an engaged portion 1k that can abut against the seat engagement shaft j3, which is the seat engagement portion provided on the support base B.

The engaged portion 1k of the seat C engages with the seat engagement axis j3 so that it rests on the seat engagement axis j3 when the seat is in the normal position (ps) or the leaning-back position (pr). The engaged portion 1k of the seat C is configured to move upward away from the seat engagement axis j3 when the seat is in the leaning-forward position (ps).

<Seat support body 1>
The seat support 1 supports the seat body D. The upper surface of the seat support 1 is adapted to engage with the shell body 3 that constitutes the seat body D. In other words, the shell body 3 is adapted to be placed on the upper surface of the seat support 1.

The seat support 1 is made of synthetic resin and has a shell-like shape. The seat support 1 has a partially spherical shape. The outer surface of the seat support 1, which is visible to the user, is formed to have a spherical surface.

The outer peripheral surface of the front part of the seat support body 1 is configured to smoothly connect with the underside of the front part of the support base B. The outer peripheral surface of the seat support body 1 is also configured to smoothly connect with the outer peripheral surface of the seat body D.

The seat support body 1 is provided with a front axle holder 1m that can hold both ends of the front axle j2 supported by the support base B.

The seat support body 1 has a recess 11 that is open downward and in which the support base B and back support L are disposed, a shell body mounting portion 12 that is provided on the top surface and serves as the seat body mounting portion, a recess 13 that is open upward and provided in the left-right center and in which the intermediate member U and coil spring Y are disposed, and an arm passage hole 14 that is provided between the recess 13 and the recess 11 and is a vertical communication hole through which the arm portion u2 of the intermediate member U can pass.

<Recess 11>
The recess 11 is provided in the lower part of the center of the seat support body 1 in the left-right direction, and is open downward so that the support base B can be disposed therein.

The recess 11 forms a recessed space in which the support base B and back support L are arranged.

At a location on the seat support body 1 facing the recessed space of the recess 11, there is a front axle holding portion 1m capable of holding the front axle j2, an engaged portion 1k arranged behind the front axle holding portion 1m and engaging with the seat engagement shaft j3 in the normal position (ps) and rearward tilt position (pr) and separating from the seat engagement shaft j3 in the forward tilt position (pf), and a restricting protrusion 1t arranged in a groove b14 provided in the support base B.

The recess 11 comprises a recess top wall 111 whose underside faces the recess space and has an engaged portion 1k with which the seat engagement shaft j3 engages; a recess front wall 112 and a recess rear wall 113 extending downward from the front and rear of the recess top wall 111, respectively; and left and right recess side walls 114 extending downward from the left and right side portions of the recess top wall 111, respectively.

The distance between the inner surfaces of the left and right recess side walls 114 is set to be longer than the left-right dimension of the seat engagement shaft j3.

[Front shaft holding part 1m]
The front axle holders 1m protrude downward from the front of the recess top wall 111. The front axle holders 1m are provided in pairs on both the left and right sides of the recess top wall 111. The left and right front axle holders 1m are shaped to hold both the left and right ends of the front axle j2. Adjacent to the left and right front axle holders 1m are shaft passages 1r through which the front axle j2 can pass when attaching or detaching the front axle j2.

[Engaged part 1k]
The engaged portions 1k are engaged with the seat engaging shaft j3 of the back support L pivotally supported on the support base B. The engaged portions 1k are provided on the recess top wall portion 111. The engaged portions 1k are provided in pairs on the left and right sides of the front lower portion of the recess 13.

The engaged portion 1k has an upper contact portion 1ku that can contact the upper portion of the seat engagement shaft j3 and a rear contact portion 1kr that can contact the rear portion of the seat engagement shaft j3. The left and right engaged portions 1k are roughly L-shaped.

The engaged portion 1k is configured to be able to move toward and away from the seat engagement axis j3 as the position of the seat C changes.

The engaged portion 1k engages with the seat engagement shaft j3 when the seat C is in the normal position (ps) or the backward tilted position (pr), and is designed to separate from the seat engagement shaft j3 only when the seat C is in the forward tilted position (pf). In other words, the engaged portion 1k is not designed to constantly hold the seat engagement shaft j3 so that it does not come off, but is instead designed to be able to come into and out of contact with the seat engagement shaft j3.

[Regulation protrusion 1t]
The restricting protrusion 1t is intended to prevent the seat body 1 from separating from the front axis j2 unless the seat support body 1 assumes the jump-up position (ph), which is the position for separating the seat support body 1 from the front axis j2.

In other words, the restricting protrusion 1t engages with the groove b14 of the support base B, and can restrict the forward movement of the seat body 1 relative to the front axis j2 when the seat body 1 is in a position other than the specified bounced-up position (ph).

The restricting protrusions 1t are provided in pairs on the left and right in front of the recess 11 of the seat support body 1. The restricting protrusions 1t protrude inward at locations on the seat support body 1 that correspond to the grooves b14 of the support base B. The restricting protrusions 1t are inclined so that they gradually rise upward toward the rear. The restricting protrusions 1t protrude from the inside of the left and right front axle holders 1m.

<Shell body installation section 12>
The shell body mounting portion 12 has a connecting portion with the shell body 3 of the seat main body D, and is provided in the upper portion of the seat receiving body 1, i.e., the portion of the seat receiving body 1 facing upward.

A notch 122 is provided at the rear end of the shell body mounting section 12 to avoid interference with the operating lever k2 provided on the shell body 3.

As will be described in detail below, the shell body mounting section 12 is provided with shaped components that form a detachable engagement structure (central positioning section G, vertical engagement mechanism H, horizontal engagement mechanism I, and reverse restriction mechanism K) that allows the seat body D to be detached.

The outer peripheral edge 1e of the seat support body 1 is formed so that it gradually decreases (concaves downward) from both the left and right ends toward the center in the left-right direction when viewed from the front and back. Furthermore, the outer peripheral edge 1e of the seat support body 1 is formed so that it gradually increases (convex upward) from both the front and rear ends toward the center in the front-to-rear direction when viewed from the side.

The upper end of the seat support peripheral wall portion 121, which is erected inward from the outer peripheral edge 1e of the seat support 1, is configured to extend substantially horizontally when viewed from the front, back, and side.

<Recess 13>
The recess 13 is provided in the upper part of the seat receiving body 1 for arranging the intermediate member U and the coil spring Y. The recess 13 is provided in the vicinity of the engaged portion 1k that engages with the seat engaging shaft j3.

The recess 13 is recessed downward relative to the central ceiling wall portion 123, which is the upper surface of the seat support body 1 that constitutes the shell body mounting portion 12. The recess 13 is open upward and includes the other spring support portion 13a, which faces upward and receives the lower part of the coil spring Y.

The recess 13 defines an arrangement space 13s in which the intermediate member body u1 and coil spring Y are arranged.

The recess 13 comprises a bottom wall 131 on whose upper surface the other spring bearing portion 13a facing upward is provided, a front wall 132 connecting the front end of the bottom wall 131 to the central ceiling wall portion 123, a rear wall 133 connecting the rear end of the bottom wall 131 to the central ceiling wall portion 123, and an outer wall 134 connecting the outer end of the bottom wall 131 to the central ceiling wall portion 123.

The bottom wall 131 of the recess 13 is spaced apart on the left and right so that the arm portion u2 of the intermediate member U can be positioned on the recess 11 side. In other words, the bottom wall 131 of the recess 13 is spaced apart on the left and right via the arm passage hole 14.

<Arm passage hole 14>
The arm passing hole 14 allows the arm portion u2 of the intermediate member u2 to pass through. The arm passing hole 14 is provided between the recess 13 and the recess 11. The arm portion u2 of the intermediate member U is arranged in the arm passing hole 14. The arm passing hole 14 allows the intermediate member U held in the recess 13 to move in the up and down direction.

<Configuration for easily attaching and detaching the seat support body 1 to and from the support base B>
The seat support 1 is rotatable around the front axle j2 so that its rear end portion bounces up after the intermediate member U is released. The front axle holding portion 1m is configured to be detachable from the front axle j2 only when the seat support 1 is changed to a predetermined bounced-up position (ph).

A pair of grooves b14 extending vertically and opening outward are provided on the front of the left and right side walls b1 of the support base B.

The seat support body 1 is provided with a pair of inward-protruding restriction protrusions 1t on the left and right at locations corresponding to the grooves b14 of the support base B. The restriction protrusions 1t protrude from the inner portions of the left and right front axle holders 1m provided on the seat support body 1.

When the seat support body 1 is restricted from disengagement by the intermediate member U (i.e., when the intermediate member U is interposed between the seat support body 1 and the seat engagement shaft j3), the restricting protrusion 1t is positioned within the groove b14, preventing the front axle holding portion 1m from disengaging forward from the front axle j2.

Even if the intermediate member U is not interposed between the seat receiving body 1 and the seat engagement shaft j3, if the specified jump-up posture (ph) is not taken, the restricting protrusion 1t and groove b14 will engage, preventing the front axle holding portion 1m from disengaging from the front axle j2.

When the seat support body 1 assumes a predetermined jump-up position (ph), its position is changed so that the restricting protrusion 1t is positioned outside the groove portion b14, allowing the front axle holding portion 1m to disengage forward from the front axle j2.

In other words, this embodiment is configured so that the seat body 1 can be easily separated from the front axis j2 (support base B) by placing it in a predetermined jump-up position (ph) without using any special tools. On the other hand, the seat body 1 cannot be separated from the front axis j2 (support base B) unless it is placed in the predetermined jump-up position (ph), resulting in a configuration in which the seat body 1 is stably supported.

<Intermediate member U>
The intermediate member U is made of synthetic resin and is provided between the seat receiving body 1 and the seat engaging shaft j3 which is the seat engaging portion of the back support body L.

A pair of coil springs Y, which are spring members, are installed on the left and right between the seat support body 1 and the intermediate member U.

The intermediate member U is disposed between the seat engagement axis j3 of the back support L, which is rotatably supported on the support base B, and the rear of the seat C, i.e., the area near the engaged portion 1k.

The intermediate member U has a portion that engages with the seat engagement shaft j3 and a portion that engages with the seat support body 1 via the coil spring Y. The intermediate member U can limit the distance between the engaged portion 1k and the seat engagement shaft j3 in the forward tilted position (ps).

The intermediate member comprises an intermediate member body u1 having a spring support portion u11 that supports the upper end of the coil spring Y, and a pair of left and right arm portions u2 that extend from the intermediate member body u1 and can engage with the seat engagement shaft j3, which serves as the seat engagement portion.

[Intermediate member body u1]
The intermediate member body u1 is a horizontally long rectangular plate-like member. The intermediate member body u1 is provided with one spring receiving portion u11 that faces downward.

That is, a pair of spring bearing portions u11 are provided on the underside of the intermediate member main body u1, one on each side, to receive the upper ends of the pair of left and right coil springs Y.

[Arm section u2]
The arm portion u2 has a downward extension portion u21 that extends downward from the front of the intermediate member main body u1, and a hook-shaped portion u22 that extends from the lower portion of the downward extension portion u21 so as to curve forward and can engage with the lower portion of the seat engagement shaft j3.

<Coil spring Y (spring member)>
The coil springs Y are interposed between the seat support body 1 and the intermediate member U. The coil springs Y are arranged in pairs on the left and right. The coil springs Y are in a position that allows them to expand and contract in the vertical direction.

The coil spring Y biases the intermediate member U upward, using the seat support body 1 as a foothold. In other words, the coil spring Y biases the intermediate member U in the direction of engagement with the seat engagement shaft j3.

<Attachment/detachment structure of intermediate member U>
The intermediate member U can restrict the separation of the seat support body 1 from the back support body L. In other words, the intermediate member U is interposed between the back support body L and the seat support body 1 so that the rear part of the seat support body 1 does not move away from the seat engagement axis j3 by more than a certain distance.

The arm portion u2 of the intermediate member U engages with the lower portion of the seat engagement shaft j3 on the back support L, and the intermediate member body u1 of the intermediate member U engages with the seat support body 1 via the coil spring Y.

The intermediate member U is configured to be detachable at a predetermined position between the back support L and the seat support body 1 without using any fasteners.

In other words, the intermediate member U can be disengaged from the seat engagement shaft j3 by being pressed in a direction against the biasing force of the coil spring Y, and is configured to be able to separate from between the seat engagement shaft j3 and the seat support 1 when the engagement is released.

Furthermore, by following the above-described procedure in reverse, the intermediate member U can be placed in a predetermined position between the back support member L and the seat support body 1 without using a fastener.

<Seat body D>
The seat body D includes a seat cushion Dq, a cushion-supporting shell body 3 that is a support member attached to the underside of the seat cushion Dq, and a seat upholstery Dh that covers the upper and peripheral edge of the seat cushion Dq and also covers the peripheral edge of the shell body 3. The seat body D has a seat surface on the upper surface that is approximately circular in plan view.

[Seat cushion Dq]
The seat cushion Dq is made mainly of urethane foam, which is a foam material. The seat cushion Dq is formed so that its width gradually increases toward the top. The underside of the seat cushion Dq is attached to the shell body 3.

The seat cushion Dq is shaped to fit over the shell body 3 from above. When viewed from the bottom, the seat cushion Dq is larger than the shell body 3. The front-to-back and left-to-right dimensions of the seat cushion Dq are set longer than the front-to-back and left-to-right dimensions of the shell body 3.

[Shell body 3]
The shell body 3 is a generally disk-shaped body attached to the underside of the seat cushion Dq. The shell body 3 is integrally formed from synthetic resin.

The shell body 3 comprises a shell body main body 31 having a disk-shaped portion whose upper surface is adhered to the underside of the seat cushion Dq; a support wall portion 33 that extends downward from the peripheral edge of the shell body main body 31 and whose outer surface abuts against the inner surface of the peripheral edge of the seat cushion Dq; an end wall portion 34 that extends diagonally upward and outward from the lower end of the support wall portion 33 and supports the lower end of the peripheral edge of the seat cushion Dq; and a peripheral wall portion 32 that hangs down from the underside of the peripheral edge of the shell body main body 31, inside the support wall portion 33.

The lower end of the peripheral wall portion 32 extends substantially horizontally when viewed from the front, rear, and side.

The shell body 3 is integrally provided with a cantilevered operating lever k2 having a protrusion kt that engages with the seat support body 1 to prevent relative rotation from the mounting position (F).

The shell body main body 31 has a central protrusion g1 that protrudes downward from the center in the front-to-back and left-to-right directions. The shell body main body 31 also has multiple locking projection engagement portions hk that are spaced at regular intervals in the circumferential direction, inside the peripheral wall portion 32.

The central protrusion g1 constitutes the central positioning portion G, and the locking projection engagement portion hk constitutes the vertical engagement mechanism H, which will be described in detail later.

The peripheral wall portion 32 is disposed on the periphery of the shell body 3. More specifically, the peripheral wall portion 32 is disposed closer to the center than the support wall portion 33 of the shell body 3. The peripheral wall portion 32 has an outward surface 32m against which the edge portion de of the seat upholstery Dh that encases the seat cushion Dq can abut.

The peripheral wall portion 32 is arranged in a generally circular ring shape when viewed from the bottom. In other words, the peripheral wall portion 32 is arranged continuously on a circular path, with the exception of one location at the rear where the operating lever k2 is located, so that it is located on an imaginary circumferential line that forms a perfect circle centered on the central protrusion g1 when viewed from the bottom.

The peripheral wall 32 is provided with outward extensions 321 that extend outward and restrict downward movement of the edge de of the seat upholstery Dh. The outward extensions 321 are multiple protruding pieces arranged at regular intervals around the periphery of the peripheral wall 32.

Inwardly bulging inward protrusions it are provided on the inner surface of three locations on the front end and both left and right end portions of the peripheral wall portion 32, namely the inner surface of the center portion of the front portion of the peripheral wall portion 32 in the left-right direction, and the inner surface of the center portion of the front-rear direction on both left and right sides of the peripheral wall portion 32. The inward protrusions it constitute the horizontal engagement mechanism I, which will be described in detail later.

Ribs rv are connected to the inner surface of the peripheral wall portion 32. The ribs rv are perpendicular to the shell body main body 31 and extend outward from the center of the shell body main body 31. The ribs rv are arranged radially on the underside of the shell body main body 31.

The operating lever k2 is supported in a cantilevered manner on the shell body main body 31. That is, the shell body 3 is provided with the operating lever k2, which is a cantilevered lever member that engages with the seat support body 1. The operating lever k2 has a wall-like portion k21 that forms part of the peripheral wall portion 32 and extends from the base end portion of the operating end portion k22.

The operating lever k2 is disposed at the rear of the shell body main body 31. The base end ke of the operating lever k2 is integrally connected to the shell body main body 31, and the outer end is provided with an operating end k22 that receives the operating force from the user's fingers.

A protrusion kt projects downward between the base end ke and the operating end k22 of the operating lever k2. This protrusion kt can engage with an upward recess k1 provided in the seat support 1. The recess k1 of the seat support 1 and the protrusion kt of the operating lever k2 form the reverse movement prevention mechanism K, which will be described in detail later.

The lower edges 3e of the support wall portions 33 of the shell body 3 are formed so that they gradually decrease in size (so as to be convex downward) from both the left and right ends toward the center in the left-right direction when viewed from the front and rear. Furthermore, the lower edges 3e of the support wall portions 33 of the shell body 3 are formed so that they gradually increase in size (so as to be convex upward) from both the front and rear ends toward the center in the front-to-rear direction when viewed from the side.

The lower edge 3e of the support wall portion 33 of the shell body 3 is set to align with the outer peripheral edge 1e of the seat support body 1 when the seat body D is in the mounting position (F).

[Zoom area Dh]
The seat upholstery Dh is mainly made of a stretchable fabric that covers the seat cushion Dq.

The seat upholstery Dh has a ring-shaped edge portion de. The seat upholstery Dh is configured in a bag-like shape that is open downward. The seat upholstery Dh is provided with a string-like member (not shown) that reduces the diameter of the edge portion de and causes the edge portion de to abut against the outward surface 32m of the peripheral wall portion 32 of the shell body 3.

<<Attachment/detachment structure of seat body D to seat support 1>>
The seat body D is configured to be horizontally rotatable around a common axis cj relative to the seat support 1 between a retracted position (E) in which it can be detached from the seat support 1 and an attached position (F) in which it is attached to the seat support 1.

The chair of this embodiment is designed so that the seat body D can be easily attached and detached to the seat support 1 without the use of tools, by both the manufacturer and the end user, to facilitate maintenance such as cleaning and replacement, as well as storage and transportation.

Between the seat support 1 and seat body D are provided a central positioning section G, which positions the seat support 1 so that its axis coincides with that of the seat body D; a vertical engagement mechanism H, which tightly engages the seat support 1 and shell body 3 in the vertical direction when the seat body D is in the mounting position (F); a horizontal engagement mechanism I, which tightly engages the seat support 1 and shell body 3 in the horizontal direction when the seat body D is in the mounting position (F); and a return restriction mechanism K, which restricts the seat body D in the mounting position (F) from returning backward toward the retracted position (E).

<Central positioning part G>
The central positioning portion G is capable of positioning the seat receiving body 1 and the shell body 3 of the seat main body D so that they can approximately coincide with the common axis cj.

The central positioning portion G is cylindrical and includes a downwardly protruding central protrusion g1 located in the center of the shell body 3 of the seat main body D, and a hole-shaped central protrusion engagement portion g2 located in the center of the seat support body 1, with which the central protrusion g1 engages to allow relative rotation.

<Vertical direction engagement mechanism H>
The vertical engagement mechanism H engages the seat support 1 and the shell body 3 of the seat main body D in the vertical direction so as to draw them together.

The vertical engagement mechanism H has a locking protrusion hp, which is a first engagement part provided on the seat support body 1, and a locking protrusion engagement part hk, which is a second engagement part provided on the shell body 3 and can engage with the locking protrusion hp of the seat support body 1.

The seat body D can assume the mounting position (F) by tightly engaging the locking protrusion hp and the locking protrusion engagement portion hk.

The locking projections hp on the seat support body 1 and the locking projection engagement portions hk on the shell body 3 are arranged at regular intervals along an imaginary circumferential line centered on the common axis cj.

[Lock projection hp (first engagement portion)]
The locking projections hp constitute a protruding structure that protrudes in a direction intersecting the common axis cj. The locking projections hp protrude approximately horizontally inward, i.e., toward the center of the common axis cj, from the seat support peripheral wall 121, which is an upright wall that is erected so as to form an approximately annular shape in a plan view on the periphery of the seat support 1.

The locking protrusion hp can engage vertically with the guide inclined surface hm provided on the locking protrusion engagement portion hk. More specifically, the locking protrusion hp can press downward against the guide inclined surface hm of the locking protrusion engagement portion hk. In other words, the locking protrusion hp moves the seat body D downward as it pivots from the retracted position (E) to the attached position (F).

[Latching protrusion engaging portion hk (second engaging portion)]
The locking projection engaging portion hk has an upwardly inclined guide surface hm with which the locking projection hp can engage. The locking projection engaging portion hk is provided to protrude downward from the shell body main body 31, which is in the shape of a circular plate.

The locking projection engagement portion hk comprises a support wall hs that hangs downward from the shell body main body 31, and an engagement portion main body hg that is supported by the support wall hs and has an upwardly facing guide slope hm on its upper surface.

The support wall hs comprises a first support wall portion ha extending in the circumferential direction and a second support wall portion hb connected to the first support wall portion ha and extending in a direction substantially perpendicular to the first support wall portion ha.

The first support wall portion ha is connected to the inner edge of the engagement portion main body hg, which extends in the circumferential direction. The second support wall portion hb has a width dimension shorter than that of the first support wall portion ha and is connected to the base end edge, which is one circumferential edge of the engagement portion main body hg.

The engagement body hg is a plate-like member that is in a laid-down position and extends in the circumferential direction. The inner edge and base edge of the engagement body hg are connected to the support wall hs. The upward guiding slope hm provided on the engagement body hg is sloped so that it gradually rises from the tip end toward the base end. Here, the tip end side of the engagement body hg refers to the edge side that forms the tip of the direction of travel when pivoting from the retracted position (E) to the attached position (F).

The locking projections hp and guide inclined surfaces hm of the vertical engagement mechanism H configured as described above are configured to gradually increase in degree of contact as the seat body D pivots from the retracted position (E) to the attached position (F).

The procedure for attaching the seat body D to the seat support body 1 is as follows:

First, as shown in Figure 43, the seat body D is moved downward from a position spaced above the seat support 1 while its horizontal position is positioned on the common axis cj using the central positioning part G.

Next, as shown in Figure 44, the seat body 43 that has been moved downward is rotated around the common axis cj.

Then, as shown in Figure 45, when the seat body D reaches the mounting position (F), the locking protrusion hp and the locking protrusion engagement portion hk engage closely in the vertical direction.

<Horizontal engagement mechanism I>
The horizontal engagement mechanism I engages the seat support 1 and the shell body 3 of the seat main body D in the horizontal direction.

The horizontal engagement mechanism I comprises an inward protrusion it, which is a second engagement portion provided on the shell body 3, and an outward guide inclined surface im, which is a first engagement portion provided on the seat support body 1 and can engage with the inward protrusion it, which is a horizontal protrusion on the shell body 3.

The inward protrusions it of the shell body 3 and the outward inclined guide surfaces im of the seat support body 1 are arranged at regular intervals along an imaginary circumferential line centered on the common axis cj.

[Inward protrusion part it (second engaging part)]
The inward protrusion it constitutes a protruding structure protruding in a direction intersecting the common axis cj. The inward protrusion it protrudes inward, i.e., in the direction of the common axis cj, from the peripheral wall portion 32, which is a hanging wall-like wall erected on the shell body 3 so as to form a substantially annular shape in a plan view.

In addition, from the portion of the peripheral wall 32 where the inward protrusion it is provided, an outward extension 321 extends in the opposite direction, i.e., outward, to engage with the edge de of the seat upholstery Dh.

The inward protrusion it can horizontally engage with the outward inclined guide surface im provided on the seat support 1. More specifically, the inward protrusion it can press inward against the outward inclined guide surface im provided on the seat support peripheral wall portion 121 of the seat support 1.

[Outward guide inclined surface im (first engagement portion)]
The outward inclined guide surface im is provided on the outer peripheral surface of the seat support peripheral wall portion 121, which is an upright wall erected on the peripheral edge portion of the seat support 1. The outward inclined guide surface im faces outward, which is the horizontal direction in which it can engage with the inward protrusion it. The outward inclined surface is inclined so as to be positioned gradually outward as it moves clockwise.

The inward protrusion it and outward inclined guide surface im of the horizontal engagement mechanism I, configured as described above, are configured to gradually increase in tightness as the seat body D pivots clockwise from the retracted position (E) to the attached position (F).

<Reverse regulation mechanism K>
The reversal prevention mechanism K is provided between the seat body D and the shell body 3 of the seat support 1, and prevents the seat body D in the mounting position (F) from reversing toward the retracted position (E).

On the other hand, the reverse restriction mechanism K can release the state in which the seat body D cannot rotate relative to the seat support body 1 by operating the operating lever k2 so that it deforms upward against the elastic return force of the shell body 3, allowing the seat body D to rotate from the attached position (F) to the retracted position (E) and separate from the seat support body 1.

The reverse restriction mechanism K comprises a recess k1 provided on the upper surface of the rear end of the seat support body 1, and an operating lever k2 provided on the shell body 3 with a protrusion kt that can engage with the recess k1 only in the mounting position (F).

The protrusion kt of the reverse movement prevention mechanism K is provided on a cantilevered operating lever k2 attached to the shell body 3. By using the elastic deformation of the member to move the operating end k22, which receives the operating force from the user's fingers, upward, the protrusion kt of the operating lever k2 disengages from the recess k1 provided in the seat support body 1, allowing the seat body D to rotate from the attached position (F) to the retracted position (E).

In addition, a guide sloped surface km is provided on the upper surface of the rear end of the seat support body 1, adjacent to the recessed portion k1, which can engage with the protruding portion kt of the operating lever k2. The guide sloped surface km is sloped so that it gradually rises as it approaches the recessed portion k1. The top of the sloped surface is set to be located above the bottom of the recessed portion k1.

When the seat body D is in the retracted position (E), the protrusion kt of the operating lever k2 is located at the lowest position on the inclined surface. When the seat body D pivots from the retracted position (E) toward the attached position (F), the protrusion kt is gradually pushed upward by the guide inclined surface km against the elastic return force of the operating lever k2.

When the seat body D moves from the retracted position (E) to the attached position (F), the convex portion kt overcomes the guide slope km and engages with the concave portion k1 due to the elastic return force of the operating lever k2.

In this embodiment, when the reverse prevention mechanism K moves from the retracted position (E) to the attached position (F), the pivoting movement of the shell body 3 causes the convex portion kt to rise up the inclined guide surface km of the seat support body 1, eliminating the need to apply operating force to the operating lever k2. Once the convex portion kt of the operating lever k2 has climbed up the inclined guide surface km, the elastic return force of the operating lever k2 automatically engages with the concave portion k1. In other words, no special operation of the operating lever k2 is required when the reverse prevention mechanism K moves from the retracted position (E) to the attached position (F).

In addition, downward protrusions 32t are provided on both sides of the peripheral wall 32 of the shell body 3 adjacent to the operating lever k2, extending downward to the same position as the lower end of the operating lever k2.

These downward protrusions 32t are designed to prevent the operating lever k2 from being pushed upward by the placement surface when the seat body D or shell body 3 is placed independently on a placement surface such as the floor for purposes such as replacement parts.

In other words, the downward protrusions 32t provided on the left and right sides of the operating lever k2 prevent the operating lever k2 from being pushed up by the placement surface, thereby effectively preventing the operating lever k2 from developing a bending tendency that would impair its intended elastic deformation.

The back support L of this embodiment is described in detail below.

<<Back support L>>
The back support L is interposed between the support base B and the backrest M. The back support L can operably support the backrest M between a normal position (ps) and a backward tilted position (pr) that is tilted further back than the normal position (ps).

The backrest M supported by the back support L is biased in a direction that allows it to assume the normal position (ps) by a reaction force generator R located between the support base B and the seat engagement axis j3 of the back support L.

The back support L is also interposed between the support base B and the seat C. In other words, the back support L also functions as a seat support that supports the seat C. The back support L is equipped with a seat engagement shaft j3 that extends in the left-right direction and engages with the engagement portion 1k provided on the seat receiving body 1 of the seat C.

The spine support L comprises a spine support base 4, which is a metal structure rotatably supported on the support base B via the main shaft j1, a spine support main body 5 attached to the spine support base 4, and a cover member 6 attached to the spine support main body 5.

The back support L supports left and right operating members p1, which can be changed between an engagement position (U) in which they engage with the backrest M and a retracted position (N) in which they are retracted from the backrest M. The left and right operating members p1 constitute a release prevention mechanism P, which will be described in detail later.

<Back support base 4>
The back support base 4 comprises a pair of left and right arms 41 each having an upright plate shape extending in the front-to-rear direction and rotatably supported on the support base B via a main shaft j1, an upright plate-shaped connecting member 42 connecting the rear portions of the pair of left and right arms 41, and a seat engagement shaft j3 extending in the left-to-right direction and supported at a position forward of the main shaft insertion hole 41a of the pair of left and right arms 41.

[Left and right arms 41]
The left and right arms 41 are made of metal and have left and right arm bodies 411 that extend longitudinally in the front-to-rear horizontal direction, forming an upright wall shape. The left and right arms 41 are disposed outside the left and right side walls b1 of the support base B.

The left and right arms 41 comprise left and right arm bodies 411 that extend in a generally linear fashion in the front-to-rear direction and can support the main shaft j1 at their front ends; left and right forearm sections 412 that extend diagonally upward and forward from the front ends of the left and right arm bodies 411 and support, at their upper ends, the seat engagement shaft j3 that engages with the seat C; and a main shaft insertion hole 41a that is provided between the left and right arm bodies 411 and the left and right forearm sections 412 and penetrates in the left-right direction to hold the main shaft j1.

The rear ends of the left and right arm bodies 411 are connected by a connecting member 42. The rear ends of the left and right arm bodies 411 protrude rearward beyond the connecting member 42. The rearward protruding portions 41b of the left and right arm bodies 411 that protrude rearward beyond the connecting member 42 are designed to fit into the fitting holes 5b of the back support base connecting parts 5a provided at the base end 51 of the back support body 5.

The left and right forearm sections 412 extend diagonally upward and forward from the front ends of the left and right arm bodies 411. A seat engagement shaft j3 extending in the left-right direction and capable of engaging with the seat C is rigidly connected to the distal ends, i.e., the upper ends, of the left and right forearm sections 412.

[Connecting member 42]
The connecting member 42 is made of metal and has an upright plate shape that extends in the left-right direction. The left and right ends of the connecting member 42 are rigidly connected to the inner sides of the left and right arm bodies 411 by welding.

The connecting member 42 has a nut portion n3 onto which a screw v3 for attaching the back support body 5 is threaded. Attached to the back side of the connecting member 42 is a connecting wall 5c of the back support body base connecting portion 52 provided at the base end 51 of the back support body 5, which is fastened with the screw v3.

[Seat engagement axis j3]
The seat engagement shaft j3 extends in the left-right direction and is connected to the upper ends of the left and right forearm portions 412. The seat engagement shaft j3 is located above the left and right side walls b1 of the support base B and extends outward beyond both sides of the support base B.

The seat engagement shaft j3 is positioned in front of and above the main shaft j1. The seat engagement shaft j3 pushes up and rearward the middle portion of the seat C in the front-to-rear direction as the back support L tilts backward. In other words, this chair is configured so that when the back support L tilts backward, the seat engagement shaft j3 pushes up the seat C, causing the front portion of the seat C to lift upward.

The seat engagement shaft j3 is directly pressed forward by the reaction force generator R. The seat engagement shaft j3 is directly connected to one end of the reaction force generator R, which is positioned using the support base B as a foothold. The seat engagement shaft j3 is pressed forward by the reaction force generator R.

Here, we will explain the movement of the back support base 4 when the backrest M is tilted backward.

When the backrest M tilts backward due to the weight of the seated person, the back support L7 supporting the backrest E rotates around the main axis j1 supported by the support base B.

At this time, the left and right arm bodies 411 on the back support base 4 move downward and forward, and the left and right front arm portions 412 on the back support base 4 move upward and backward.

The seat engagement shaft j3, which is connected to the upper part of the left and right forearm sections 412, moves upward and backward in the same way as the left and right forearm sections 412 move.

The seat engagement shaft j3 moves upward and rearward, lifting the seat C upward against the seating weight of the seated person.

[Back support body 5]
The back support body 5 comprises a base end portion 51 fixed to the back support body base 4, left and right standing frame portions 52 connected to the base end portion 51 and extending in the vertical direction in pairs on the left and right, and an upper frame portion 53 extending in an approximately horizontal direction and connected to the upper ends of the left and right standing frame portions 52.

The base end 51 includes a back support base connector 5a that connects to the back support base 4, and left and right arm sections 5d that form inward channels extending linearly forward from both the left and right sides of the back support base connector 5a and that can restrict outward movement of the main shaft j1 at the front.

The back support base connecting portion 5a is provided with a pair of left and right fitting holes 5b that are open forward and fit into the rearward protruding portion 41b protruding from the rear end of the back support base 4, and a connecting wall 5c that is arranged between the pair of left and right fitting holes 5b and is attached to the connecting member 42 of the back support base 4.

The connecting wall 5c has a screw insertion hole h3 that penetrates in the front-to-rear direction. The back support body 5 is attached to the back support body base 4 by threading a screw v3 inserted into the screw insertion hole h3 into a nut n3 provided on the connecting member 42.

The left and right arm portions 5d extend in the front-to-rear direction along the outer sides of the arm body 411 of the back support base 4. The front portions of the left and right arm portions 5d are located outside the axial center of the main shaft j1, which protrudes outward from the left and right side walls b1 of the support base B. The left and right arm portions 5d also prevent the main shaft j1 from slipping out of the support base B.

The main shaft j1 is simply a cylindrical member extending in the left-right direction. In this embodiment, the main shaft j1 is not directly provided with a positioning device (for example, a retaining ring attached to the end of the shaft, or a flange-like portion formed on one end of the shaft). Instead, the arm portion 5d of the spine support body 5 of the spine support L is used to position the main shaft j1 relative to the support base B.

A recess q2 that constitutes the positioning mechanism Q is provided on the front side of the upper end of the left and right standing frame sections 52, i.e., on the front side of the connection between the left and right standing frame sections 52 and the upper frame section 53. The recess q2 will be described in detail later.

The upper frame portion 53 has a partially annular shape that curves convexly backward in plan view. The upper frame portion 53 cooperates with the cover member 6, which forms the upper half of the upper frame portion 53, to form a circular shape with both left and right end faces facing forward, and the overall outer shape is a partially annular, curved cylinder.

In other words, the upper frame portion 53 forms the lower half of a cylindrical outer shape that is curved in a partially annular shape. In other words, the upper frame portion 53 and cover member 6 have circular forward end faces at both the left and right ends, are curved in a shape that convexly curves rearward in a plan view, and form an upper frame body 5a that, as a whole, has a roughly cylindrical shape that is curved in a partially annular shape.

The upper frame portion 53 has multiple screw insertion holes h1 that penetrate vertically and through which screws v1 are inserted to attach the cover member 6 to the upper frame portion 53.

The rear side of the upper frame portion 53 is provided with a rear biasing member engaging portion 532 having a recessed shape that supports the rear portion of a coil spring p3, which is a biasing member that biases the operating member p1 forward, i.e., in the direction of the engaged posture (U).

A boss portion 533 is provided on the upper frame portion 53. A screw member v2 is threadedly attached to the boss portion 533, which can regulate the vertical movement of the operating member p1. The boss portion 533 and the screw member v2 constitute the vertical movement regulation portion 53k.

The boss portion 533 is disposed within the elongated hole portion p14 provided at the rear of the engagement portion p11 of the operating member p1. The head of the screw member v2 can engage near the upper opening edge of the elongated hole portion p14 of the operating member p1 to prevent the operating member p1 from moving upward.

[Cover member 6]
The cover member 6 constitutes approximately the upper half of the curved cylindrical upper frame body 5a. The cover member 6 is attached to the upper frame portion 53 with screws v1 so as to cover the left and right operating members p1.

The cover member 6 covers the operating member p1 so that only the engaging portion p11 and the operated portion p13 provided on the operating member p1 are exposed to the outside.

The cover member 6 is provided with a window frame portion 6w that surrounds the engagement portion p11 of the operating member p1, which can be protruded and retracted from the upper frame portion 53. The window frame portion 6w has an upper wall portion 61 that partially covers the upper side of the engagement portion p11 of the operating member p1, and side wall portions 62 that partially cover both the left and right sides.

The window frame portion 6w cooperates with the outer peripheral wall q21 that constitutes the recess q2 of the positioning mechanism Q to form a rectangular window frame-shaped portion when viewed from the front.

In addition, a notch 6k is provided on the front side of the cover member 6 to expose the operated portion p13 of the operating member p1. The notch 6k is located adjacent to the inside of the window frame portion 6w.

The back support L configured as described above is covered by a front back support cover X2 and a rear back support cover X3, both made of synthetic resin.

The front and back support cover X2 primarily covers the lower and outer sides of the back support base 4. The front and back support cover X2 is attached to the arm portion 5d of the back support body 5.

The rear support cover X3 is attached so that the screw v3 for attaching the back support body 5 to the back support base 4 is not exposed on the rear side. The rear support cover X3 covers the rear of the back support base connecting portion 5a, which is attached to the base end 51 of the back support body 5 and located between the left and right upright frame portions 52. Both side ends of the rear support cover X3 are designed to connect to the rear ends of the front support cover X2.

The backrest M of this embodiment is described in detail below.

<<Backrest M>>
The backrest M has a generally horizontally elongated rectangular shape with rounded left and right ends. The backrest M has a backrest surface on the front surface against which the back of a seated person can rest. The backrest M in this embodiment is configured to be detachable from the back support L with a simple operation by the user. The backrest M has a backrest main body 7, which is the structural main body, and a back upholstery 8, which is a covering that can cover the backrest main body 7.

<Backrest body 7>
The backrest main body 7 comprises a backrest base 71 made of synthetic resin and having a substantially horizontally elongated rectangular shape, and a back cushion 72 attached to the front surface of the backrest base 71. A single storage groove 7m that opens downward and extends in the left-right direction is provided at the lower end of the backrest base 71 of the backrest main body 7.

The storage groove 7m is composed of a pair of front and rear groove-forming walls 7f, 7r arranged so that their inner surfaces face each other in the front-to-rear direction. The single storage groove 7m is designed to accommodate insertion of first and second strip-shaped members 81, 82 attached to the lower edge of the back upholstery 8 that covers the backrest body 7.

A number of engagement protrusions t(f), t(r) are provided inside the accommodation groove 7m, i.e., on the inner surfaces of the pair of groove-forming walls 7f, 7r. Both of the pair of groove-forming walls 7f, 7r are provided with engagement protrusions t(f), t(r) that protrude forward or backward.

In this embodiment, the engagement protrusions t(f), t(r) are provided alternately on both groove-forming walls 7f, 7r, which are arranged facing each other from front to back along the extension direction of the storage groove 7m. In other words, the engagement protrusions t(f) on one groove-forming wall 7f and the engagement protrusions t(r) on the other groove-forming wall 7r are provided alternately from one longitudinal end to the other longitudinal end of the storage groove 7m so that they do not collide.

The back side of the backrest base 71, which constitutes the backrest main body 7, is provided with an engaging portion p2 and a protruding portion q1, which are connecting structures for connecting to the back support L. The engaging portion p2 constitutes the detachment prevention mechanism P. The protruding portion q1 constitutes the positioning mechanism Q.

<Back upholstery 8 (covering body)>
The back upholstery 8 comprises a bag-shaped back upholstery main body 80 that is open downward and includes a front covering portion 8f that covers the front side of the backrest main body 7 and a back covering portion 8r that covers the back side of the backrest main body 7, and first and second belt-shaped members 81 and 82 arranged at the lower opening end of the back upholstery main body 80.

The back upholstery 8 comprises a front covering portion 8f that covers the front side (the front side) of the backrest main body 7; a back covering portion 8r that covers the rear side (the back side) of the backrest main body 7; a first belt-shaped member 81 that is attached by sewing to the lower end of one end of the front covering portion 8f and inserted into the storage groove 7m of the backrest main body 7; and a second belt-shaped member 82 that is attached by sewing to the lower end of one end of the back covering portion 8r and inserted into the storage groove 7m of the backrest main body 7.

The back upholstery 8 exposes the engaging portion p2 and protruding portion q1, which are connecting structures on the backrest main body 7, to the outside through a pair of openings 8s on the left and right sides of the back side.

[Back upholstery body 80]
The back upholstery body 80 is formed into a bag-like shape that is open downwards by sewing together the peripheral edges of the front covering portion 8f and the back covering portion 8r, which are made of stretchable fabric, except for the lower ends.

A space capable of accommodating the backrest main body 7 is formed inside the back upholstery main body 80. A lower opening 8k is formed at the bottom end of the back upholstery main body 80, i.e., between the bottom end of the front covering portion 8f and the bottom end of the back covering portion 8r, and is open downwards, allowing the backrest main body 7 to be inserted into the internal space.

In this embodiment, the back side of the back upholstery main body 80, i.e., the back covering portion 8r, is provided with a pair of openings 8s on the left and right sides that expose the engaging portion p2 and protruding portion q1 of the backrest main body 7 to the outside.

The opening 8s is primarily composed of a through-hole 8t provided in the back covering portion 8r, which is made of fabric material; a through-hole rim portion 8e, which is the peripheral area of the through-hole 8t in the back covering portion 8r; and a continuous ring-shaped synthetic resin annular member T, which is attached by sewing to the through-hole rim portion 8e.

Through holes 8t are formed in two locations on the left and right of the rear covering portion 8r, at positions corresponding to the protrusions q1 protruding from the rear side of the backrest main body 7.

The annular member T is formed into a square frame shape from a flexible synthetic resin sheet material with a hole th in the center. The annular member T is configured to be flexible and deformable. The annular member T is sewn to the through-hole periphery 8e of the backside covering portion 8r. In the completed installation position (Ta), the annular member T is covered by the backside covering portion 8r so that everything except the hole th is invisible from the outside.

In this embodiment, the entire outer surface t1, the entire inner end t2, and at least a portion of the inner surface t3 of the annular member T in the installation completion position (Ta) are covered by the through-hole periphery 8e adjacent to the through-hole 8t in the back cover 8r, and the through-hole periphery 8e is fixed only to the inner surface t3 of the annular member T in the installation completion position (Ta).

[First and second belt-shaped members 81, 82]
The first and second belt-shaped members 81, 82 are made of synthetic resin and have a belt-like shape extending in the left-right direction. In this embodiment, the first and second belt-shaped members 81, 82 have substantially the same structure. Each of the first and second belt-shaped members 81, 82 has a plurality of through-holes 81a, 82a arranged in a row, into which the engaging protrusions t(f), t(r) can engage.

[Regarding the engagement between the first and second belt-shaped members 81, 82 and the accommodation groove 7m of the backrest main body 7]
A first belt-shaped member 81 sewn to the lower end of the front covering portion 8f and a second belt-shaped member 82 sewn to the lower end of the back covering portion 8r are adapted to be inserted into a single storage groove 7m provided at the lower end of the backrest main body 7.

The first and second belt-shaped members 81, 82 are inserted together into the storage groove 7m in a stacked state.

When the first and second belt-shaped members 81 and 82 are inserted to a predetermined position within the storage groove 7m, the engaging protrusions t(f) and t(r) protruding from the groove-forming walls 7f and 7r of the storage groove 7m can engage with the through-holes 81a and 82a formed in the respective belt-shaped members 81 and 82. More precisely, only the through-holes 81a and 82a located at positions corresponding to the engaging protrusions t(f) and t(r) of the inserted first and second belt-shaped members 81 and 82 can be engaged with the engaging protrusions t(f) and t(r).

As a result, once the first and second strip-shaped members 81, 82 that make up the edge of the back upholstery 8 have penetrated to a specified depth within the single storage groove 7m, their downward movement (reverse movement/slip-out) is restricted by the engaging protrusions t(f), t(r), making them less likely to slip out to the outside even when subjected to a pulling force from the back upholstery main body 80.

In addition, the engagement protrusions t(f) protruding from one groove-forming wall 7f and the engagement protrusions t(r) protruding from the other groove-forming wall 7r are arranged alternately along the extension direction of the storage groove 7m, so the first and second strip-shaped members 81, 82 can be inserted smoothly and effortlessly into the storage groove 7m without being excessively obstructed by the engagement protrusions t(f), t(r).

<<Method for forming opening 8s in back upholstery 8 (covering body)>>
An opening 8s is provided in the back upholstery 8. The opening 8s includes a back covering portion 8r, which is a fabric material having a through hole 8t, and a continuous annular member T that is attached to the through hole periphery 8e and is arranged so as not to be visible from the outside without impairing the front-to-rear communication function of the hole th.

In this embodiment, the opening 8s in the back upholstery 8 is formed through the following steps: preparation process S1, outer surface attachment process S2 of the annular member, first annular member inversion process S3, and second annular member inversion process S4.

<Preparation process S1>
As shown in Figure 48, the preparation process S1 involves preparing a back upholstery main body 80, which is the fabric material that constitutes the back upholstery 8 in which the opening 8s is to be formed, and a ring-shaped member T in the initial position (Tb).

Through holes 8t are provided in the rear covering portion 8r of the back upholstery main body 80 using an appropriate method. The annular member T is a flexible thin plate frame that can be sewn to the back upholstery main body 80. In this embodiment, the annular member T is made of synthetic resin and is formed into a roughly rectangular ring shape.

<Annular member outer surface side mounting step S2>
Following the preparation process, as shown in Figures 49 and 50, a process of attaching an annular member T in the initial position (Tb) to the outer surface side of the through-hole peripheral portion 8e of the back side covering portion 8r, which is the base material, is carried out (annular member outer surface attachment process S2).

In this embodiment, the annular member T in the initial position (Tb) is sewn to the through-hole periphery 8e while in contact with the outer surface of the through-hole periphery 8e. In other words, the annular member T in the initial position (Tb) is fixed to the outer surface of the through-hole periphery 8e via the sewn portion tx.

In other words, the annular member outer surface attachment process S2 involves sewing the annular member T to the outer surface of the through-hole periphery 8e, which is the edge of the through-hole 8t.

<First annular member inversion step S3>
After the annular member mounting process, as shown in Figure 51, the annular member T in its initial position (Tb), which is attached to the outer surface of the through-hole peripheral portion 8e, is flexibly deformed so that its inner peripheral edge rotates toward the inner surface of the back-side covering portion 8r, and the annular member T is inverted back and forth to be disposed on the inner surface of the back-side covering portion 8r (first annular member inversion process S3).

<Second annular member inversion step S4>
After the first annular member inversion process S3, as shown in Figure 52, a process (second annular member inversion process S4) is performed in which the annular member T in the intermediate position (Tc) is inverted back and forth while further bending and deforming the inner edge side toward the inner surface of the back covering portion 8r, so that the entire annular member T is covered from the outer surface side by the back covering portion 8r.

In this embodiment, by using the method for forming the opening 8s in the back upholstery 8 (covering body) that includes each of the steps described above, an opening 8s is formed in the rear covering portion 8r of the back upholstery 8, reinforced by the annular member T in the completed installation position (Ta), which is inverted 360° from the initial position (Tb).

The first and second annular member inversion steps S3 and S4 are carried out smoothly and continuously due to the flexural deformation of the annular member T.

<<Attachment/detachment structure of the backrest M to the back support L>>
The chair of this embodiment is configured so that the backrest M can be easily attached and detached to the back support L without the use of tools, not only by the manufacturer but also by the end user, to facilitate maintenance such as cleaning and replacement, as well as storage and transportation.

The attachment/detachment structure of the backrest M includes a positioning mechanism Q that positions the backrest M relative to the back support L, and a detachment prevention mechanism P that prevents the backrest M, once positioned in the correct attachment position by the positioning mechanism Q, from detaching from the back support L.

<Positioning mechanism Q>
The positioning mechanism Q positions the backrest M at a predetermined mounting position relative to the back support L.

The positioning mechanism Q has a protrusion q1 on the backrest M and a recess q2 on the back support L with which the protrusion q1 can engage. The protrusion q1 on the backrest main body 7 and the recess q2 on the back support L can engage in the vertical direction.

[Protrusion q1]
The protrusions q1 are provided in pairs on the left and right sides of the backrest M. The protrusions q1 protrude from the back side of the backrest main body 7 and are exposed to the outside through openings 8s in the back upholstery 8.

The protrusion q1 includes a wall-shaped engaging portion q11 that extends vertically in rear view, gradually narrowing in width as it moves downward, and is positioned gradually further rearward as it moves downward in side view, and a connecting portion q12 that connects the backrest main body 7 and the left-right middle portion of the wall-shaped engaging portion q11, and gradually increases in length in the front-to-rear direction as it moves downward. The upper end of the wall-shaped engaging portion q11 is connected to the backrest main body 7.

Protrusion q1 is located below engaging portion p2, which constitutes the anti-detachment mechanism P, recessed into the backrest body 7.

[Recess q2]
The recess q2 is provided on the front side of the upper end of each of the left and right upright frame portions 52 that constitute the back support L. The recess q2 is open upward and is designed to fit over the protrusion q1 of the backrest M inserted from above.

The recess q2 is provided inside the outer peripheral wall q21, which protrudes forward from the upper ends of the left and right upright frame portions 52. The recess q2 is composed of the outer peripheral wall q21, which has a bottom wall portion qt and left and right side wall portions qs erected upward from both left and right edges of the bottom wall portion qt, and a pair of left and right front wall portions q22 erected in front of the bottom wall portion qt.

The recess q2 has a pair of left and right front wall portions q22 erected on the bottom wall portion qt so as to be spaced apart from each other, and a front recess portion qm is provided between the pair of front wall portions q22, with a first space qa in which the connecting portion q12 of the protrusion q1 is disposed.

The recess q2 also has a rear recess qr formed behind the front recess qm, i.e., behind the pair of front wall portions q22, and between the left and right side wall portions qs erected on the bottom wall portion qt, where a second space qb is provided in which the wall-like engaging portion q11 of the protrusion q1 is disposed.

In this embodiment, the protrusion q1 of the backrest M, which constitutes the positioning mechanism Q, moves vertically, or more precisely, from a diagonally upper-front direction to a diagonally lower-rear direction, while engaging with the recess q2 of the back support L. The load of the seated person's backrest acts upward, backward, and downward, but hardly acts forward. Therefore, by configuring the protrusion q1 to be inserted into the recess q2 from a diagonally upper-front direction to a diagonally lower-rear direction, the backrest M is less likely to come off the back support L, and the backrest M can be securely fixed to the back support L.

<Release prevention mechanism P>
The separation prevention mechanism P is provided between the back support L and the backrest M and prevents the backrest M from separating from the back support L.

The detachment prevention mechanism P comprises an operating member p1 that is attached to the back support L and can be reversibly operated by human operation, i.e., rotated forward and backward, between an engagement position (U) that prevents the backrest M from detaching and a retracted position (N) that allows the backrest M to detach, and an engaged portion p2 that is attached to the backrest M and can engage with an engaging portion p11 on the operating member p1 when in the engagement position (U).

[Operation member p1]
The operating member p1 prohibits the up-and-down movement of the backrest M relative to the back support member L in the engaged position (U). The operating member p1 is rotatably supported by the upper frame portion 53 of the back support member main body 5. The operating members p1 are arranged in pairs on the left and right sides of the back support member L.

The operating member p1 is provided with an axial hole pa at the inner end (base end) that penetrates vertically and is inserted into the axial portion 531 erected on the upper frame portion 53; an engagement portion p11 that protrudes forward from the outer end (tip end); a biasing member engagement portion p12 that is provided on the rear side between the axial hole pa and the engagement portion p11 and engages with the front portion of the coil spring p3 that serves as a biasing member; an operated portion p13 that is provided on the front side between the axial hole pa and the engagement portion p11 and directly receives a human operating force, i.e., a rearward pressing force applied by a finger, when moving from the engaged position (U) to the retracted position (N); and an elongated hole portion p14 that is provided behind the engagement portion p11 and engages with a vertical movement regulating portion 53k provided on the upper frame portion 53.

The operating member p1 is constantly biased toward the engaged position (U) by a coil spring p3. The user can change the position of the operating member p1 to the retracted position (N) by pressing the operated portion p13 of the operating member p1, which is in the engaged position (U), against the biasing force of the coil spring p3 toward the retracted position (N) (the direction in which the engaging portion p11, which is the rotation end, moves rearward).

The operating member p1 can be changed from the engaged position (U) to the retracted position (N) by pressing the operated part p13 backward with the user's finger. In other words, the user can move the operating member p1 to the retracted position (N) by pressing the operated part p13 backward like a push button.

As shown in Figure 27, a space sp is provided between the back support L and the backrest M into which fingers can be inserted. The operated part p13 is disposed in a position facing the space between the back support L and the backrest M. This allows the user to easily press the operated part p13 like a push button.

Furthermore, only the outer surface of the operated portion p13 of the operating member p1 in the engaged position (U) is exposed between the back support L and the backrest M. In other words, the outer surface of the operated portion p13 and the outer surface of the cover member 6 are configured to be substantially flush. Therefore, although the operated portion p13 is arranged so that it can be operated from the outside, it is arranged in an inconspicuous location and is substantially flush with the cover member 6 so as to be less noticeable.

[Engaged part p2]
The engaged portion p2 is a portion that can be engaged with the engaging portion p11 of the operating member p1 supported by the back support L. The engaged portion p2 is adapted to be engaged with the engaging portion p11 of the operating member p1 in the engaging posture (U).

The engaging portions p2 are provided in pairs on the left and right sides of the backrest M. The engaging portions p2 are recessed and open to the rear on the back side of the backrest main body 7. The engaging portions p2 recessed in the backrest main body 7 are exposed to the outside through openings 8s in the back upholstery 8.

The engaged portion p2 is provided on the protruding portion q1 that constitutes the positioning mechanism Q, which protrudes from the backrest main body 7.

After the backrest M is positioned in the correct mounting position by the positioning mechanism Q, when the engaging portion p11 of the operating member p1 engages with the engaged portion p2, the backrest M cannot move upward relative to the back support L, and as a result, is prevented from detaching from the back support L.

<<Weight-sensing locking mechanism>>
The weight-sensing rocking mechanism is configured to be able to tilt the backrest M in accordance with the weight of the occupant sitting on the seat C. The weight-sensing rocking mechanism is configured to move the seat C backward in response to the backward tilting of the backrest M, while lifting the seat C against the weight of the occupant.

The weight-sensing rocking mechanism includes a mechanism that lifts the seat C upward against the weight of the occupant, so a backward tilt load proportional to the occupant's weight is required to tilt the backrest M backward.

The weight-sensing rocking mechanism is primarily composed of a support base B supported by legs A, a seat C disposed on top of support base B and supported at its front by support base B via front axle j2, a back support L rotatably supported on support base B via main axle j1 and having a seat engagement axle j3 disposed in front of and above main axle j1 that can engage with the front-to-rear center of seat C and is urged forward by a reaction force generator R, a backrest M supported on back support L, and a reaction force generator R disposed between support base B and back support L that can apply a reaction force to the backward tilting movement of backrest M.

＜＜Seat forward tilting mechanism＞＞
The seat forward tilting mechanism is capable of changing the position of the seat C, which is rotatably supported on the support base B via the front axis j1, between a normal position (ps) and a forward tilted position (pf).

The seat forward tilt mechanism is primarily composed of a support base B supported by legs A, a seat C disposed on support base B with its front portion supported by support base B via front axis j2, a back support L having a seat engagement axis j3 that engages with the engaged portion 1k of seat C in the normal position (ps), and an intermediate member U whose lower portion engages with seat engagement axis j3 and whose upper portion engages with seat C via coil spring Y, limiting the distance between the engaged portion 1k and seat engagement axis j3 in the forward tilt position (pf).

The above-described embodiment provides a chair with a suitable configuration that allows the backrest M to be easily attached and detached from the back support L using the operating member p1, which can be reversibly operated by a human operating force.

Furthermore, in the above-described embodiment, the seat body D is configured to be able to rotate horizontally around the common axis cj relative to the seat receiver 1 between a retracted position (E) in which it can be detached from the seat receiver 1 and an attached position (F) in which it is attached to the seat receiver 1. This makes it possible to provide a chair with a suitable configuration that allows the seat body D to be easily attached and detached from the seat receiver 1 without the use of special tools.

In addition, in the above-described embodiment, the shell body 3 is provided at its peripheral edge with a peripheral wall 32 that has an outward surface 32m against which the edge de of the seat upholstery Dh can abut, and that is arranged in a generally annular shape when viewed from the bottom. This makes it possible to provide a chair that allows the edge de of the seat upholstery Dh covering the seat cushion Dq to abut against the peripheral wall 32 of the shell body 3 with a generally uniform pressing force.

In addition, in the above-described embodiment, the backrest main body 7, which is the main structure, is provided with a storage groove 7m with engaging protrusions t(f) and t(r), and the back upholstery 8 is provided with first and second belt-shaped members 81 and 82 with through-holes 81a and 82a that engage with the engaging protrusions t(f) and t(r) of the storage groove 7m. This makes it possible to provide a chair with a configuration that allows the edge of the back upholstery 8 to be easily and reliably attached to the storage groove 7m of the backrest main body 7, which is the main structure.

The above-described embodiment also provides a method for suitably forming reinforced openings 8s with a desirable appearance in the back upholstery 8, which is a covering that can encase a component. The above-described embodiment can be applied to the back upholstery 8, etc., and can provide a chair with a covering that has reinforced openings 8s with a desirable appearance.

Furthermore, in the above-described embodiment, the front part of the seat C can rotate relative to the support base B so that it can assume a normal position (ps) and a forward-leaning position (pf), and an intermediate member U is provided between the back support L supported by the support base B and the rear part of the seat C (the part behind the front part of the seat C) to limit the distance between them.

This makes it possible to provide a chair that allows the seat C to suitably assume either the normal position (ps) or the forward-leaning position (pf) without providing a complex mechanism at the front of the seat C.

In addition, in the above-described embodiment, a reaction force generating body R is disposed between the seat engagement shaft j3 and the support base B, which can directly bias the seat engagement shaft j3 forward, and this reaction force generating body R is set to assume a substantially horizontal position extending in the front-to-rear direction in the normal position (ps). This makes it possible to provide a chair that can rock between the normal position (ps) and the reclining position (pr), with excellent design freedom for reducing the size of the support base B and seat C.

Furthermore, in the above-described embodiment, the intermediate member U, which can prevent the seat support body 1 from separating from the back support body L, is detachably arranged without using a fastener. This makes it possible to provide a chair in which the seat support body 1 can be easily attached and detached from the support base B.

Furthermore, in the above-described embodiment, when the support member W supporting one end of the reaction force generator R is removed from the support base B using the screw v5, the reaction force generator R moves while being guided by the inclined surface nm while gradually weakening its biasing force, thereby providing a chair that allows the reaction force generator R to be conveniently attached to and detached from the support base B.

In addition, in the above-described embodiment, a screw threaded hole n4 is disposed above the fitting hole Ba in the support base B, and a screw v4 threaded into the screw threaded hole n4 can press the upper part of the leg support a2 downward. This makes it possible to provide a chair with a configuration that can suitably release the fitting state between the upper part of the leg support a2 and the fitting hole Ba in the support base B.

In addition, in the above-described embodiment, the leg support a2 of the leg A, which is an inhibiting member that prevents the lift operation lever V, which is an operating lever, from taking the releasable position (SR), is attached to the support base B, and the lift operation lever V can only take the releasable position (SR) when the leg support a2 is detached from the support base B. This makes it possible to provide a chair in which the lift operation lever V can be suitably attached to the support base B.

As described above, the chair according to this embodiment comprises legs A, a support base B supported by the legs A, and a back support L supported rotatably with respect to the support base B between a normal position (ps) and a backward tilted position (pr) that is tilted further back than the normal position (ps).

A reaction force generator R is provided between the support base B and the back support L, which can bias the back support L in the direction of the normal position (ps).

The reaction force generator R is a compression spring type whose rear end is attached to the support base B via a support member W and whose front end is attached to the back support L.

The support base B is provided with a first screw insertion hole h51 through which a screw v5 for attaching the support member W is inserted, and an inclined surface nm that engages with the support member W. By rotating the screw v5 inserted into the first screw insertion hole h51 in a first direction, the support member W can be moved to a predetermined fixed position while engaging with the inclined surface nm, and by rotating the screw v5 in a second direction, the support member W can be moved in the direction opposite to the fixed position while engaging with the inclined surface nm.

The inclined surface nm is configured to gradually move away from the front end of the reaction force generating body R as it moves from the fixed position toward the anti-fixed position.

For this reason, when the support member W, which supports the rear end, one end of the reaction force generator R, is removed from the support base B using the screw v5, it is guided by the inclined surface nm and moves while gradually weakening the biasing force of the reaction force generator R.

As a result, this embodiment can provide a chair with a configuration that allows the reaction force generator R to be suitably detached from the support base B.

Conversely, this embodiment can provide a chair configured so that the reaction force generator R can be suitably attached to the support base B.

A mounting portion 2T to which the support member W is attached is provided at the rear of the support base B.

This allows the support member W to be attached to a suitable location on the support base B.

The mounting portion 2T comprises at least a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole h51, and a rear wall portion 27 extending upward from the rear end of the rear bottom wall 24 and having an inclined front surface nm.

As a result, the support member W is suitably supported by the rear bottom wall 24 and rear wall portion 27 having the inclined surface nm that constitute the mounting portion 2T.

The mounting portion 2T comprises a rear bottom wall 24, which is a bottom wall portion having a first screw insertion hole h51; a rear wall portion 27 extending upward from the rear of the rear bottom wall 24 and having a sloping front surface nm; and left and right side wall portions 28 extending upward from both the left and right sides of the rear bottom wall 24 and having their rear portions connected to the rear wall portion 27.

As a result, the support member W is suitably supported by the rear bottom wall 24 that constitutes the mounting portion 2T, the rear wall portion 27 having the inclined surface nm, and the left and right side wall portions 28 that support the rear wall portion 27. In particular, because the rear wall portion 27 having the inclined surface nm is urged rearward by the reaction force generator R, the rear wall portion 27 is suitably reinforced by the left and right side wall portions 28.

When in the fixed position, the support member W is surrounded by the rear bottom wall 24, the rear wall portion 27, and the left and right side wall portions 28.

As a result, the support member W is surrounded by the rear bottom wall 24, rear wall portion 27, and left and right side wall portions 28 when in the fixed position, thereby ensuring optimal support for the mounting portion 2T.

The support member W includes a support member main body w1 and a hexagonal nut n5 disposed inside the support member main body w1. The support base W includes a bottom wall portion w11 having a second screw insertion hole h52 through which the screw v5 is inserted, and a peripheral wall portion ws extending upward from the periphery of the bottom wall portion w11.

The hexagonal nut n5 is threaded onto the screw v5 that passes through the first and second screw insertion holes h51 and h52.

For this reason, the support member W comprises a support member body w1 and a hexagonal nut n5, and is configured so that the support member body w1 can move appropriately along the inclined surface nm.

Hexagonal nut n5 engages with the peripheral wall portion ws to restrict left-right movement and horizontal rotation, and engages with the peripheral wall portion ws to allow forward-backward movement.

In other words, the hexagonal nut n5 is arranged to be able to move freely in the front-to-rear direction relative to the support member main body w1. As a result, the hexagonal nut n5 can adopt an appropriate inclined position inside the support member main body w1, which moves up and down along the inclined surface nm, so that it can be threaded onto the screw v5.

The first screw insertion hole h51 in the support base B is an elongated hole extending in the front-to-rear direction.

As a result, the screw v5 inserted into the first elongated screw insertion hole h51 can adopt an appropriate tilted position in response to the support member main body w1 and hexagonal nut n5, which move up and down while tilting along the inclined surface nm.

Note that the present invention is not limited to the embodiments described above.

The reaction force generator may be a tension spring type, with one end attached to the support base via a support member and the other end attached to the back support. In this case, the inclined surface is designed to gradually approach the other end as it moves from the fixed position toward the anti-fixed position. Even with this configuration, the intended purpose can be achieved.

The other end of the reaction force generator may be attached to the back support via some other separate member.

The support base must have at least a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member. In other words, as long as the nut portion is integrally formed with the support member W, it does not have to have a screw insertion hole. Furthermore, the inclined surface may be formed on one surface of the block-shaped portion, and does not have to be formed on one surface of the upright wall-shaped portion.

The mounting portion to which the support member is attached may be provided at a portion other than the rear portion of the support base.

The mounting portion must have at least a bottom wall portion with a first screw insertion hole and a rear wall portion extending upward from the rear end of the bottom wall portion and having an inclined front surface. In other words, the mounting portion may not have left or right side wall portions.

The support member may be configured such that the support member body and the nut are integrally formed. In other words, the support member does not have to be configured such that the nut is freely movable relative to the support member body.

The first screw insertion hole in the support base does not have to be an elongated hole extending in the front-to-rear direction.

Furthermore, the specific configuration of each part is not limited to the above embodiment, and various modifications are possible within the scope of the present invention.

A...Leg B...Support base R...Reaction force generator W...Support member L...Back support (structure)
2T...Mounting part

Claims (9)

A chair comprising legs, a support base supported by the legs, and a back support supported rotatably with respect to the support base between a normal position and a backward tilted position tilted further backward than the normal position,
a reaction force generating body is provided between the support base and the back support body, the reaction force generating body being capable of urging the back support body in the direction of the normal posture;
the reaction force generating body is a compression spring type having one end attached to the support base via a support member and the other end attached to the back support body,
the support base is provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member,
the support member can be moved to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and can be moved in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction,
The inclined surface is set so as to gradually move away from the other end as it moves from the fixed position toward the anti-fixed position. The chair of claim 1, wherein a mounting portion to which the support member is attached is provided at the rear of the support base. A chair as described in claim 2, wherein the mounting portion comprises at least a bottom wall portion having the first screw insertion hole, and a rear wall portion extending upward from the rear end of the bottom wall portion and having the inclined surface on its front surface. The chair of claim 2, wherein the mounting portion comprises a bottom wall portion having the first screw insertion hole, a rear wall portion extending upward from the rear of the bottom wall portion and having the inclined surface on its front surface, and left and right side wall portions extending upward from both left and right sides of the bottom wall portion and having their rear portions connected to the rear wall portion. A chair as described in claim 4, wherein the support member is surrounded by the bottom wall portion, the rear wall portion, and the left and right side wall portions at the fixed position. The support member includes a support member body and a nut disposed inside the support member body,
the support base has a bottom wall portion having a second screw insertion hole through which the screw is inserted, and a peripheral wall portion erected upward from a peripheral edge portion of the bottom wall portion,
2. The chair according to claim 1, wherein the nut is threaded onto the screw inserted through the first and second screw insertion holes. A chair as described in claim 6, wherein the nut engages with the peripheral wall portion so as to restrict left-right movement and horizontal rotation, and engages with the peripheral wall portion so as to allow forward-backward movement. The chair of claim 1, wherein the first screw insertion hole is an elongated hole extending in the front-to-rear direction. A chair comprising legs, a support base supported by the legs, and a back support supported rotatably with respect to the support base between a normal position and a backward tilted position tilted further backward than the normal position,
a reaction force generating body is provided between the support base and the back support body, the reaction force generating body being capable of urging the back support body in the direction of the normal posture;
the reaction force generating body is a tension spring type having one end attached to the support base via a support member and the other end attached to the back support body,
the support base is provided with a first screw insertion hole through which a screw for attaching the support member is inserted, and an inclined surface that engages with the support member,
the support member can be moved to a predetermined fixed position while engaging with the inclined surface by rotating the screw inserted into the first screw insertion hole in a first direction, and can be moved in a direction opposite to the fixed position while engaging with the inclined surface by rotating the screw in a second direction,
The inclined surface is set to gradually approach the other end as it moves from the fixed position toward the anti-fixed position.