JP2970461B2 - Weight balance device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the use of a spring to force a heavy object such as an X-ray tube or an image intensifier provided in various medical diagnostic devices or the like, or a top plate on which a subject is mounted. The present invention relates to an equilibrium weight balance device.

[0002]

2. Description of the Related Art As shown in FIG. 7 (a), for example, a conventional weight balance device of this type has an object (heavy object) attached to a distal end of an arm 102 to which two parallel link mechanisms 100 and 101 are connected. ) The WP is supported, the base end is supported by the base B, and the weight W1 of the heavy object WP can be balanced by the tension springs 103, 104 provided in each link mechanism 100, 101. .

According to this apparatus, as shown in FIG. 7 (b), it is possible to displace the heavy object WP in the horizontal and vertical directions while maintaining the balance of the heavy object WP.

[0004]

However, the prior art having such a structure has the following problems. That is, in the conventional apparatus shown in FIG.
The tension springs 103 and 104 are used in order to maintain the balance between the tension springs 103 and / or 10.
4 breaks, the weight WP moves in the direction of gravity (vertical direction)
There is a problem that it is dangerous because it falls down.

[0005] Further, in the above-described conventional apparatus, two springs (tensile springs) must be provided in order to take a wide range of displacement of the heavy load WP, and there is also a problem that the cost is increased.

[0006] The present invention has been made in view of such circumstances, and has as its object to provide a safe and inexpensive weight balance device.

[0007]

The present invention has the following configuration to achieve the above object. That is, the present invention is a weight balance device capable of balancing the weight of an object (heavy object) supported by a base with the force of a spring,
(A) a first arm, a second end having a base end rotatably connected to a front end of the first arm and supporting the heavy object at a front end, and a second arm parallel to the first arm; A third arm having a base end rotatably connected to an intermediate portion of the second arm and an intermediate portion rotatably connected to and supported by the base; and a third arm parallel to and parallel to the second arm. A fourth arm having a base end rotatably connected to the distal end of the first arm, and a fourth end rotatably connected to the base end of the first arm; and the first arm and the fourth arm A length between a 4-arm connecting portion (hereinafter, referred to as a connecting portion P1) and the third arm and a fourth-arm connecting portion (hereinafter, referred to as a connecting portion P2);
The length between the tip of the second arm (hereinafter, referred to as a connecting portion P3) supporting the heavy object and the connecting portion (hereinafter, referred to as a connecting portion P4) between the second arm and the third arm. The ratio is L
_2: L _1, and the intermediate portion of the third arm which is connected to and supported on the base (hereinafter referred to as connecting portions P5) and the connection portion P2
The ratio of the length L ₂ between the length, and the connecting portion P5 and the connecting portion P4 between: and L ₁ parallel becomes linkage,
(B) The connecting portion P1 is connected, has guide means for guiding the connecting portion P1 in the horizontal direction, and moves up and down while maintaining the guide state of the connecting portion P1 in the horizontal direction by the guide means. (C) a base end portion rotatably connected to the base and a tip end portion rotatably connected to a predetermined connection portion PX of the movable member; Shaft, a first spring seat rotatably connected to the base, and a distal end portion rotatably connected to a connection portion PX of the movable member, and a second spring seat to a base end portion. A rod slidably fitted to the first spring seat in a state inclined with respect to the vertical direction, the first spring seat and the second
And a weight balance portion including a compression spring provided between the spring seats.

[0008]

The operation of the present invention is as follows. In the parallel link mechanism, an intermediate portion (connecting portion P5) of the third arm is rotatably connected to the base, and the connecting portion P1 is vertically movable and horizontally displaceable with respect to the base via a movable member and guide means. It is connected and supported. The base end of the third arm is connected to the middle part of the second arm. That is, from the middle part (connection part P4) of the second arm to the tip part (connection part P3)
Are protruded from the parallelogram formed by the first to fourth arms, and a heavy object is supported at the tip of the second arm. Therefore, by appropriately displacing the first to fourth arms, the heavy object can be displaced in the horizontal and vertical directions. With the displacement of the heavy object, the connecting portion P1 is guided by the guide means in the horizontal direction with respect to the movable member, and the movable member is moved up and down with respect to the base while maintaining the guide state in the horizontal direction. Is done.

In addition, the parallel link mechanism is composed of a line segment P1-P
2): (length of line segment P3-P4) = L ₂ : L
_1, (the length of the line segment P5-P2) length of :( segment P5-P4) = L _2: is L _1. Therefore, irrespective of the displacement of the heavy object (position of the heavy object), the line segment P1-P5-P3 is straight, and the triangle having the connecting parts P1, P2, and P5 as vertices, and the connecting parts P3, P4, and P5 as vertices. The triangle
L ₂ : always similar to L ₁ .

A heavy object exerts a force in the direction of gravity (vertically downward). The rotational moment of the heavy object around the connecting portion P5 is the weight of the heavy object (W1) × (the connecting portion P5).
5, the length of the horizontal component between P3: La).
Therefore, if a predetermined weight (referred to as W2) acting in the direction of gravity is applied to the connecting portion P1 which is a pair of the connecting portion P3 with the connecting portion P5 interposed therebetween so as to cancel the rotational moment of the heavy object around the connecting portion P5. Maintains weight balance. The balance formula of the rotational moment around the connecting portion P5 is W1 × La
= W2 × (Length of horizontal component between connecting portions P5 and P1: Lb
). Here, regardless of the displacement of the heavy object (position of the heavy object), the line segment P1-P5-P3 is a straight line,
A triangle having the connecting portions P1, P2, and P5 as vertices and a triangle having the connecting portions P3, P4, and P5 as vertices are always L ₂ :
Since a similar figure of L _1, the ratio between La and Lb is always constant, therefore, the W2 is, W1 is determined uniquely if Kimare.

Further, as described above, the guiding state of the connecting portion P1 in the horizontal direction is always maintained. Therefore, a force corresponding to the weight W2 in the direction of gravity applied to the connecting portion P1 may be applied to the movable member itself, and this is performed by the weight balance portion.

That is, a compression spring provided between the first and second spring seats exerts a force in a direction in which the second spring seat is separated from the first spring seat, so that the tip end of the movable member is moved. The rod connected to the connecting portion PX pulls the movable member in the vertical diagonal direction, and thereby the weight W2 in the direction of gravity
Is applied to the movable member.

Here, when the heavy object is displaced, the movable member is appropriately raised and lowered. The weight balance portion always exerts a force corresponding to the weight W2 in the gravitational direction on the movable member. There is a need. Therefore, in the weight balance portion according to the present invention, the base end portion of the shaft rotatably connected to the base and the first end portion rotatably connected to the base.
And a distal end of a rod slidably mounted on a spring seat of the movable member and inclined with respect to the vertical direction.
Are connected rotatably. As a result, the weight W around the base end of the shaft (the portion rotatably connected to the base) is obtained.
If the spring constant of the compression spring is appropriately determined so that the rotation moment by the rotation spring 2 and the rotation moment by the compression spring around the base end of the shaft are balanced, the weight in the direction of gravity can be obtained regardless of the vertical displacement of the movable member. A force corresponding to W2 can always be applied to the movable member.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. <First Embodiment> Referring to FIG. The device of the first embodiment includes a parallel link mechanism 1 including first to fourth arms 11 to 14, a movable member 2, and a weight balance unit 3 including one compression spring 31. I have.

With the first arm 11 and the third arm 13 and the second arm 12 and the fourth arm 14 being parallel to each other, the distal end of the first arm 11 and the proximal end of the second arm 12, The intermediate part of the arm 12 and the base end of the third arm 13, the distal end of the third arm 13 and the base end of the fourth arm, the distal end of the fourth arm and the base end of the first arm 11 are respectively turned. The parallel link mechanism 1 is movably connected to each other.

The weight W is attached to the tip of the second arm 12.
P is supported, and an intermediate portion of the third arm 13 is rotatably supported by, for example, a base B installed on the floor surface, and a roller 15 rotates around a connecting portion between the first arm 11 and the fourth arm 14. It is movably mounted.

Further, the first arm 11 and the fourth arm 14
P1, the connection between the third arm 13 and the fourth arm 14 is P2, the tip of the second arm 12 supporting the heavy object WP is P3, and the connection between the second arm 12 and the third arm 13 is P1. P4, the third arm 1 rotatably supported by the base B
3 of the intermediate portion when the P5, (line segment length of P1-P2) :( length of the segment P3-P4) = L _2: in L _1, (length of the segment P5-P2): (Length of line segment P5-P4) = L
_2: L at _1, each arm 11 to 14, the parallel link mechanism 1 each connecting portion is determined is constructed.

A roller 15 attached to the connecting portion P1 is connected to the movable member 2, and a guide groove 21 for guiding the roller 15 in a horizontal direction along a guide line 21a is provided. Also, they are arranged in parallel, and each base end is
Each of the distal ends of the links 22 and 32 rotatably supported on the movable member 2 is rotatably attached to the movable member 2. By the links 22 and 32, as shown in FIG. 2B described later, while maintaining the guide line 21a of the guide groove 21 in the horizontal direction (maintaining the guide state of the roller 15 in the horizontal direction),
It is configured to move the movable member 2 up and down. Note that the rollers 15 and the guide grooves 21 constitute guide means in the present invention.

The weight balance section 3 includes a link 32 corresponding to a shaft, a rod 35 having a first spring seat 33 and a second spring seat 34, a compression spring 31, and the like. As described above, the link 32 has its proximal end rotatably connected to the base B, and its distal end rotatably connected to the connecting portion PX of the movable member 2. Here, the connecting portion between the base end of the link 32 and the base B is PY.

The first spring seat 33 is rotatably connected to a connecting portion PZ of the base B. Second spring seat 34
Is provided at the base end of the rod 35. This rod 3
Reference numeral 5 has a distal end portion rotatably connected to the connection portion PX of the movable member 2 and slidably fitted to the first spring seat 33 in a state inclined with respect to the vertical direction. Also, the first
Compression spring 31 between the spring seat 33 and the second spring seat 34
Is provided.

Next, the operation of the embodiment apparatus having the above-described configuration will be described. First, the displacement of the heavy object WP will be described. As described above, the parallel link mechanism 1
The intermediate portion (connection portion P5) of the arm 13 is rotatably connected to the base B, and the connection portion P1 (roller 15) is displaced via the movable member 2 and the guide groove 21 in the horizontal direction along the guide line 21a. The base B is connected and supported so as to be vertically movable and horizontally displaceable. Further, an intermediate portion of the second arm 12 and a base end of the third arm 13 are connected by a connecting portion P4. That is, the arm portion between the middle portion (connection portion P4) and the tip portion (connection portion P5) of the second arm 12 is
The second arm 12 protrudes from the parallelogram formed by the first to fourth arms 11 to 14, and a heavy object WP is supported at the tip of the second arm 12.

Accordingly, as shown in FIG. 2, by appropriately displacing the first to fourth arms 11 to 14, the heavy object WP can be moved in the horizontal and vertical directions (or in a combination of the horizontal and vertical directions). Can be displaced. 2A shows a state of displacement of the heavy object WP in the horizontal direction, and FIG. 2B shows a state of displacement of the heavy object WP in the vertical direction. With the displacement of the heavy object WP, the roller 15 of the connecting portion P1 is guided by the guide groove 21 in the horizontal direction with respect to the movable member 2, and the movable member 2 is moved while maintaining the guide state in the horizontal direction. It is displaced up and down with respect to the base B.

By the way, the parallel link mechanism 1 is provided with a line segment P
Length) length of :( segment P3-P4 of 1-P2) = L _2:
In L _1, (length of the segment P5-P2) :( segment P5-P4
Length) = L ₂ : L ₁ . Therefore, regardless of the displacement of the heavy object WP (regardless of where the heavy object WP is located), the line segment P1-P5-P3 is a straight line, and a triangle having the connecting portions P1, P2, and P5 as vertices, Connection part P
A triangle having vertices at 3, P4 and P5 is always L ₂ : L
_It is similar to ₁ (see FIG. 3).

The weight WP exerts a force in the direction of gravity (vertically downward). As shown in FIGS. 1 and 2, the rotational moment of the heavy object WP around the connecting part P5 is represented by the weight of the heavy object (W1) × (the length of the horizontal component between the connecting parts P5 and P3: La). Do). This is because, as shown in FIG. 1, a rotational moment of a predetermined weight (referred to as W2) acts vertically upward around the connecting portion P5 on the connecting portion P1 which is paired with the connecting portion P3 with the connecting portion P5 interposed therebetween. Will be. Therefore, if a rotational moment that cancels the rotational moment due to the weight W2 is generated at the connecting portion P1 (when the weight W2 acts vertically downward on the connecting portion P1), the balance of the heavy object WP is obtained.

The balance equation of the rotational moment about the connecting portion P5 is as follows: W1 × La = W2 × (Length of the horizontal component between the connecting portions P5 and P1: Lb), so that W2 is: W2 = W1 × La / Lb.

Here, irrespective of the displacement of the heavy object (position of the heavy object), the line segments P1-P5-P3 are straight, and the triangle having the connecting portions P1, P2, and P5 as vertices and the connecting portion P3,
A triangle having vertices P4 and P5 is always a similar shape of L ₂ : L ₁ .

Therefore, for example, FIGS. 3 (a) and 3 (b)
(C) (FIG. 3 (a) shows the state of FIG. 1, FIG. 3 (b)
(C) shows the state in which the heavy object WP is displaced in the horizontal direction with respect to the state of FIG. 3 (a). In this case, La is (line segment P3-P5) and Lb is (line segment P1- P5), the ratio (La: Lb) is always constant at L ₁ : L ₂ .

FIGS. 3 (d) and 3 (e) (FIG. 3 (d),
(E) shows a state in which the heavy object WP is displaced in the vertical direction with respect to the state of FIG. 3 (a), respectively, where La is (line segment P5-P6) and Lb is (line). Minutes P5-
Here, the triangle having vertices of P3, P5, and P6 and the triangle having vertices of P1, P5, and P7 are always similar to L ₂ : L _1. ,
La: Lb is always constant at L ₁ : L ₂ . Note that P
6 is an intersection of a horizontal line passing through P5 and a vertical line passing through P3, and P7 is an intersection of a horizontal line passing through P5 and a vertical line passing through P1.

Therefore, regardless of the displacement of the heavy object WP (no matter where the heavy object WP is located), La: Lb is always constant, that is, La / Lb is always constant. Therefore, the W2 is uniquely determined by the weight W1 of the heavy load WP.

Here, as described above, the guiding state of the connecting portion P1 in the horizontal direction is always maintained. Therefore, a force corresponding to the weight W2 in the vertical direction applied to the connecting portion P1 may be applied to the movable member 2 itself. That is, a force equivalent to the weight W2 is applied to the movable member 2 vertically downward, and through the guide line 21a of the guide groove 21 and the roller 15,
A force corresponding to the weight W2 may be applied to the connecting portion P1. This is performed by the weight balance unit 3.

That is, the first and second spring seats 33, 34
The compression spring 31 provided between them applies a force in a direction to separate the second spring seat 34 from the first spring seat 33, so that the tip end of the rod 35 is connected to the connection portion PX of the movable member 2. Pulls the movable member 2 in the vertical diagonal direction, whereby a force corresponding to the weight W2 in the vertical direction is exerted on the movable member 2.

Here, as described above, when the heavy object WP is displaced, the movable member 2 is appropriately displaced up and down by the links 22 and 32 (in this embodiment, the movable member 2 is displaced obliquely to the right in FIGS. 1 and 2). However, even for this displacement, the weight balance unit 3 needs to always exert a force corresponding to the weight W2 vertically downward on the movable member 2.

Therefore, in this embodiment, each member of the weight balance unit 3 is configured as shown in FIG. This allows
If the spring constant of the compression spring 31 is appropriately determined such that the rotation moment due to the weight W2 around the base end portion (connection portion PY) of the link 32 and the rotation moment due to the compression spring 31 around the connection portion PY are balanced. Regardless of the vertical movement of the movable member 2, a force corresponding to the vertically downward weight W2 can always be applied to the movable member 2. This will be described with reference to FIG.

In FIG. 4A, the rotational moment MF acting counterclockwise on the connecting portion PY by the force of the compression spring 31 is obtained by the following equation. MF = C × m × r where C is the spring constant of the compression spring 31 and m is the connecting portion P
The length r of the center line (indicated by a dotted line) CL of the rod 35 between X and PZ, and r is the length of a perpendicular line (indicated by a one-dot chain line) HL lowered perpendicularly to the center line CL from the connecting portion PY.

On the other hand, the vertical upward weight W shown by the dotted line in the figure
2, the rotational moment MG acting clockwise on the connecting portion PY is obtained by the following equation. MG = W2 × b × sin θ where b is the length between the connecting portions PX and PY (the length of the link 32), and θ is (line segment PX−PY) and (line segment PY−PZ)
Is the angle between the two.

In FIG. 4A, applying a force corresponding to the weight W2 vertically downward to the movable member 2 by the force of the compression spring 31 means that the MF and MG are balanced (M
F = MG).

That is, C × m × r = W2 × b × sin
θ, and C = (W2 × b × sin θ) / (m × r) is obtained.

Here, m × r corresponds to the area of the parallelogram PX, PY, PZ, PY ′ in FIG. 4B, and this area can also be represented by a × b × sin θ. Therefore, the above equation is expressed as C = (W2 × b × sin θ) / (a ×
b × sin θ), and C = W2 / a is obtained.

When the movable member 2 is displaced obliquely to the right, as shown in FIG. 4C, when PX is displaced obliquely to the right (PY and PZ are fixed), the distance between PX and PZ is reduced. The length of the rod 35 (m) is displaced (the force of the compression spring 31 is displaced). At this time, r is also displaced, so that the MF is always constant. Therefore, even in such a case,
With the force of the compression spring 31, a force corresponding to the vertically downward weight W2 can always be applied to the movable member 2.

That is, the spring constant of the compression spring 31 is set to W2
(Or compression spring 3
When the spring constant C of 1 is predetermined, by adjusting the length of a), the force corresponding to the vertically downward weight W2 is applied by the force of the compression spring 31 regardless of the vertical displacement of the movable member 2. It can always work on the movable member 2.

Since the weight of the movable member 2 is also applied to the connecting portion P1, the vertically downward force on the movable member 2 generated by the compression spring 31 is actually from W2 described in FIG. The spring constant C is determined as a force corresponding to the weight obtained by subtracting the own weight of the movable member 2.

As described above, in this embodiment, the heavy load WP can be displaced in the horizontal and vertical directions, and the balance of the heavy load WP is always maintained by one compression spring 31 against this displacement. Can be.

According to this embodiment, the compression spring 31
Even when is broken, the compression spring 31 pulls the movable member 2 vertically downward, so that the heavy load WP does not fall.

<Second Embodiment> An apparatus according to a second embodiment will be described with reference to FIG. The device of the second embodiment has a configuration in which the device of the first embodiment is turned upside down. That is, the base 1
Are placed on the ceiling, for example, to support the heavy object WP.

Since the basic structure and operation of the second embodiment are the same as those of the first embodiment, FIG.
The same reference numerals are used, and the detailed description is omitted.
Also in the embodiment device, the spring constant of the compression spring 31 and the connecting portion P
By determining the length between Y and PZ (the above-mentioned a) using the same calculation formula in the first embodiment, this distance is always obtained regardless of the displacement (displacement in the horizontal and vertical directions) of the heavy load WP. The balance of the weight WP can be maintained.

<Third Embodiment> The configuration of the third embodiment will be described with reference to FIG. In the third embodiment, the movable member 2 is vertically moved using a linear guide mechanism.
The tip of the link 32 and the tip of the rod 35 are
The roller 41 is configured to be freely displaceable in the horizontal direction along the guide groove 42 of the movable member 2.

In the linear guide mechanism, a rail 43 provided on the side of the movable member 2 is slidably attached to a guide member 44 fixed to the base B, and the movable member 2 is moved up and down (in this case, (Displacement in the vertical direction). Thereby, the guide state of the connecting portion P1 (the roller 15) in the horizontal direction is maintained. Further, since the length of the link 32 is fixed, the roller 41 is horizontally displaced along the guide groove 42 in accordance with the vertical displacement of the movable member 2. In this embodiment, the connecting portion between the distal end of the link 32 and the distal end of the rod 35 corresponds to the connecting portion PX in the first embodiment, and the compression spring 31 is connected to the movable member 2 via the connecting portion PX.
Is pulled vertically downward with a force corresponding to the weight W2.
The other configuration is the same as that of the first embodiment, so that it is denoted by the same reference numeral as in FIG. 1 and its detailed description is omitted.

With such a configuration, the heavy load WP can be displaced in the horizontal and vertical directions as in the first embodiment, and the spring constant of the compression spring 31 is set to the same value as in the first embodiment. , The balance of the heavy object WP can be always maintained by the force of the compression spring 31 regardless of the displacement of the heavy object WP.

Note that, as in the second embodiment, the third
The embodiment may be modified so as to be upside down (the base B is installed on the ceiling, for example).

The mechanism of the weight balance device has been described in detail in each of the above embodiments and the modifications thereof. However, the weight balance device can be used for weight balance of the heavy load WP in various devices.

For example, in the first and third embodiments, the weight balance can be achieved by using the displaceable X-ray tube of the X-ray tube device in which the base B is supported on the floor surface as the heavy load WP.
Similarly, a displaceable X-ray tube or image intensifier of an X-ray fluoroscope is used as a heavy object WP, or a top plate for mounting a subject provided in various medical diagnostic devices is used as a heavy object, and the weight of the object is determined. You can also balance.

For example, in the apparatus of the second embodiment, an X-ray tube is suspended from the ceiling, and the X-ray tube in the ceiling-suspended X-ray tube device capable of displacing the X-ray tube in an arbitrary direction is heavy. W
P can be used for weight balance.

Further, the present invention is not limited to devices in the medical field, and can be used for weight balancing of predetermined heavy objects in devices in various fields.

[0054]

As is apparent from the above description, according to the present invention, the balance of the heavy object is maintained by the force of the compression spring. Is safe from falling in the direction of gravity.

Also, in the present invention, since a parallel link mechanism and a movable member capable of taking a wide displacement direction of the heavy object are provided, the balance of the heavy object is maintained by one compression spring via the movable member. The number of springs used is small, and the cost can be reduced accordingly.

Further, since the structure is such that the balance of the heavy object is maintained by the spring force of the compression spring, the weight and size of the device can be reduced as compared with a device for maintaining the balance of the heavy object with a corresponding weight. Can be planned.

[Brief description of the drawings]

FIG. 1 is a front view showing a schematic configuration of a weight balance device according to a first embodiment of the present invention.

FIG. 2 is a view showing a state of displacement of a heavy object of the first embodiment.

FIG. 3 is a diagram for explaining a similarity relationship between (the length of the horizontal component between the connecting portions P5 and P3) and (the length of the horizontal component between the connecting portions P5 and P1) with respect to the displacement of the heavy object. .

FIG. 4 is a diagram for explaining a method of calculating a spring constant of a compression spring.

FIG. 5 is a front view showing a schematic configuration of the second embodiment apparatus.

FIG. 6 is a front view showing a schematic configuration of an apparatus according to a third embodiment.

FIG. 7 is a diagram showing a schematic configuration of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Parallel link mechanism 2 ... Movable member 11 ... 1st arm 12 ... 2nd arm 13 ... 3rd arm 14 ... 4th arm 15 ... Roller 21 ... Guide groove 22 ... Link 31 ... Compression spring 32 ... Link 33 ... 1st Spring seat 34… Second spring seat 35… Rod B… Base WP… Heavy

Continuation of front page (58) Fields investigated (Int. Cl. ⁶ , DB name) F16F 15/28 A61B 6/00 300 A61B 6/00 310 B66F 19/00

Claims (1)

(57) [Claims] 1. A weight balance device capable of balancing the weight of an object (heavy object) supported by a base with the force of a spring,
(A) a first arm, a second end having a base end rotatably connected to a front end of the first arm and supporting the heavy object at a front end, and a second arm parallel to the first arm; A third arm having a base end rotatably connected to an intermediate portion of the second arm and an intermediate portion rotatably connected to and supported by the base; and a third arm parallel to and parallel to the second arm. A fourth arm having a base end rotatably connected to the distal end of the first arm, and a fourth end rotatably connected to the base end of the first arm; and the first arm and the fourth arm A length between a 4-arm connecting portion (hereinafter, referred to as a connecting portion P1) and the third arm and a fourth-arm connecting portion (hereinafter, referred to as a connecting portion P2);
The length between the tip of the second arm (hereinafter, referred to as a connecting portion P3) supporting the heavy object and the connecting portion (hereinafter, referred to as a connecting portion P4) between the second arm and the third arm. The ratio is L
_2: L _1, and the intermediate portion of the third arm which is connected to and supported on the base (hereinafter referred to as connecting portions P5) and the connection portion P2
The ratio of the length L ₂ between the length, and the connecting portion P5 and the connecting portion P4 between: and L ₁ parallel becomes linkage,
(B) The connecting portion P1 is connected, has guide means for guiding the connecting portion P1 in the horizontal direction, and moves up and down while maintaining the guide state of the connecting portion P1 in the horizontal direction by the guide means. (C) a base end portion rotatably connected to the base and a tip end portion rotatably connected to a predetermined connection portion PX of the movable member; Shaft, a first spring seat rotatably connected to the base, and a distal end portion rotatably connected to a connection portion PX of the movable member, and a second spring seat to a base end portion. A rod slidably fitted to the first spring seat in a state inclined with respect to the vertical direction, the first spring seat and the second
A weight balance unit including a compression spring provided between the spring seats.