JPH0551401B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a spindle structure applied to a rotatable spindle that removably holds a tool in a machine tool such as a machining center.

(b) Prior Art Conventionally, in this type of rotatable main shaft, a tool attachment/detachment means such as a drawbar for attaching/detaching a tool and a drive means for the said attachment/detachment means such as a hydraulic cylinder are arranged in series in the axial direction of the main spindle. The drive motor for rotating the main shaft is installed on the side of the main shaft and is independent of the main shaft, and the drive motor and the main shaft are usually connected via a power transmission mechanism such as a gear train or a belt. It was connected.

(d) Measures to solve the problem However, with this method, a power transmission mechanism is interposed between the drive motor and the spindle, which increases the weight of the spindle head, making it difficult to move the entire spindle head to a specified position. There are drawbacks such as a decrease in positioning accuracy when moving the machine to a certain position for machining, and heat generated from the power transmission mechanism increases thermal displacement of the spindle, which adversely affects machining accuracy.

As a countermeasure for this, a system in which the drive motor is directly connected to the main shaft may be considered, but it is possible to achieve good loading and unloading operation of the tool by connecting the tool attachment/detachment means, its driving means, and the drive shaft that transmits the rotational force from the drive motor to the main shaft. The question of what kind of structure to arrange them while adjusting them remained an unresolved issue.

Furthermore, in Japanese Patent Application Laid-Open No. 59-53136, a drive motor is directly connected to a main shaft through a hollow connecting member, a driving piston is attached to the outer circumference of the connecting member, and a frame is provided outside the connecting member. The tool is movable and driven on the member, and the drive piston reciprocates the drawbar provided in the main spindle through a connecting plate that penetrates the inside and outside of the connecting member, so that the tool can be freely attached to and removed from the main spindle. A main shaft structure configured as follows is disclosed. In the main shaft structure,
When connecting the connecting member to the main shaft, a cap nut placed in a hollow portion within the connecting member is used to fasten the connecting member to the outer peripheral portion of the main shaft.

With this structure, the driving force of the drive motor is certainly transmitted to the main shaft via the connecting member, and tools can be attached and detached, but the cap nut, connecting member, connecting plate, driving piston, and frame member are inseparable. Because the rotor is arranged radially with respect to the spindle center in the shape of , the diameter of the rotor that is rotated by the drive motor increases, making it easier for runout to occur during high-speed rotation, which not only deteriorates machining accuracy. , all the components are arranged inside the drive piston provided on the outermost periphery, so when inspecting the drawbar inside the main shaft, etc. It is not possible to inspect it without disassembling all the parts, which makes work extremely difficult.
In addition, the connecting member and the main shaft are connected and the drawbar is held through a cap nut provided within the connecting member, and a connecting plate is also provided to transmit driving force to the drawbar within a narrow space within the connecting member. Since it is provided in series with the drawbar, it is difficult to assemble it, and it is difficult to maintain assembly accuracy.

In order to eliminate the above-mentioned drawbacks, the present invention allows the tool to be smoothly attached to and detached from the main shaft.
Moreover, it is an object of the present invention to provide a main shaft structure in which a drive motor can be directly connected to the main shaft.

In addition, the present invention enables high-speed rotation of the main shaft by reducing the size of the rotating body portion in the diametrical direction of the main shaft.
High-precision machining is possible, drawbars, etc. can be inspected easily without disassembling the drawbar drive means, and the drawbars and parts for transmitting driving force to the drawbars can be assembled with high precision and easily. The second purpose is to provide a main shaft structure that can be used for various purposes.

(d) Means for Solving the Problems That is, the present invention provides a rotatable main spindle provided with a tool holding portion capable of holding a tool, and a tool holding means is provided inside the main spindle at the tool holding portion. The tool holding means is provided such that the tool can be held and released from holding, and a drawbar is provided inside the main spindle, and the tool holding means can be freely driven by moving the drawbar in the axial direction of the main spindle with respect to the main spindle. In the main shaft structure, a drive shaft connection part having a first diameter is formed on the opposite side of the main shaft where the tool holding part is provided, and a connection surface is provided on an end surface of the drive shaft connection part. A drive shaft having a hollow connection hole formed at the end thereof is rotatably supported, an abutting connection surface is formed in the hollow connection hole, and a drive shaft of the main shaft is connected to the hollow connection hole of the drive shaft. the abutment connection surface of the drive shaft and the connection surface of the main shaft are fitted and engaged in the axial direction of the main shaft such that the abutment connection surface of the drive shaft outer circumference and the drive shaft are in contact with each other. A rod-shaped fastening member, which has fastening member mounting surfaces formed at positions facing each other in the axial direction, and is installed to penetrate the drive shaft and the main shaft in the main shaft axial direction via the fastening member mounting surface, the abutment connection surface, and the connection surface. The drive shaft and main shaft are separably fastened together from the abutment connection surface and the connection surface, a drawbar contact surface is formed in the hollow connection hole of the drive shaft, and the tool holding means of the drawbar is provided. A bracket member is connected to the opposite end of the drawbar, and a bracket member is connected to the bracket member of the drive shaft. A connecting hole is provided at a corresponding position so as to communicate the hollow connecting hole with the outer circumference of the drive shaft, an arm portion is formed in the bracket member, and the arm portion is connected to the hollow connecting hole through the connecting hole of the drive shaft. The arm part of the bracket member is made to protrude from the connection hole to the outer peripheral part of the drive shaft, and the outer diameter of the arm part of the bracket member is smaller than or equal to the first diameter of the drive shaft connection part of the main shaft, and the arm part of the outer peripheral part of the drive shaft A reciprocating drive means is positioned at a position aligned with the drive shaft axis direction of the drive shaft, and a contact member capable of abutting and engaging with the arm part to move the arm part in the spindle axis direction is aligned with the drive shaft axis direction. A drive motor is directly connected to the end of the drive shaft opposite to the side where the hollow connection hole is formed.

(e) Effect With the above-described configuration, the present invention drives the reciprocating drive means when the tool is attached to and detached from the main shaft, transmits the reciprocating driving force to the drawbar by the bracket part through the connection hole, and attaches to and removes the tool from the main shaft. The main shaft is driven by transmitting the rotation of the drive motor to the main shaft via the drive shaft and the drive shaft connection part fitted and engaged with the hollow connection hole.

Further, in the present invention, the drive shaft, which is directly connected to the main shaft and the drive motor, is connected by a rod-shaped fastening member through the drive shaft connection portion of the main shaft and the hollow connection hole of the drive shaft,
The drawbar acts so as to be held in contact with a drawbar abutment surface that is an inner end surface on the inner diameter side of a plane perpendicular to the drive shaft axis of the drive shaft in which the hollow connection hole is formed.

(f) Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a cross-sectional view showing an embodiment of the main shaft structure according to the present invention, FIG. 2 is a three-dimensional cross-sectional view showing essential parts of the main shaft structure according to the present invention, and FIG. 3 is a view taken in the direction of the arrow in FIG.

As shown in FIG. 1, a spindle head 1 in a machine tool such as a machining center has a cylindrical frame 2, and a cylindrical main bearing 3 is fitted on the right side of the frame 2 in the figure. has been done. A cylindrical main shaft 6 is rotatably supported by the main bearing 3 via a plurality of bearings 5, and a tapered tool holding portion 6a is formed at the right end of the main shaft 6. A sleeve 7 is fitted on the left side of the tool holding portion 6a, and the sleeve 7 and the main shaft 6
A draw bar 9 is provided movably in the direction of the main shaft axis, that is, in the directions of arrows A and B. A piston portion 9a that slides into engagement with the main shaft 6 is formed at the left end of the drawbar 9, and a plurality of disc springs 10 are provided between the piston portion 9a and the sleeve 7 to constantly bias the drawbar 9 in the direction of arrow A. Furthermore, a collet 11 is provided at the right end of the drawbar 9 so as to be openable and closable in a radial direction with respect to the axis of the main shaft 6.

On the other hand, a ring nut 8 for holding the bearing 5 is screwed onto the outer periphery of the main shaft 6, and the left end of the ring nut 8 in the figure is a driving nut having a diameter of D2, as shown in FIG. A shaft connecting portion 6b is formed, and the connecting portion 1 of the drive shaft 13 is connected to the driving shaft connecting portion 6b via a key 12 and a plurality of bolts 14.
3a is connected. The drive shaft 13 extends to the left in FIG. 1 and is directly connected to the output shaft 15a of the drive motor 15. As shown in FIGS. 2 and 3, the drive shaft 13 is a solid medium with a small diameter. It has a connecting portion 13a consisting of a solid shaft 13b and stepped shafts 13c and 13d that have a larger diameter than the solid shaft 13b and have a hollow portion 13f formed inside. The stepped shaft 13d, which has the largest outer diameter, has a main shaft connection hole 13i inside.
is formed by drilling, and the second hole of the spindle connection hole 13i
At the left end of the figure, an inner end surface 13g is formed in an annular shape in a plane perpendicular to the axis of the main shaft (drive shaft).
The main shaft connection hole 13i has a drive shaft connection portion 6b of the main shaft.
However, a connecting surface 6c formed in an annular shape on the left end surface in the drawing of the drive shaft connecting portion 6b of the main shaft 6 is fitted into engagement with the inner end surface 13g from the right side in FIG.

In addition, the inner end surface 13g of the outer peripheral part of the drive shaft 13
A bolt fastening surface 13j is formed in an annular shape in a plane perpendicular to the main shaft (drive shaft) axial center at a position facing the axial center direction (arrow A, B direction) of the drive shaft 13. , the aforementioned plurality of bolts 14 are attached to the bolt fastening surface 13j, the inner end surface 13g of the main shaft connection hole 13i, and the connecting surface 6c of the main shaft 6.
It is fastened and installed in such a way that it penetrates in the directions of arrows A and B, which are the axial directions of the main shaft. Note that by loosening and removing the bolt 14, the main shaft 6 can be removed from the main shaft connection hole 13i of the drive shaft 13.

The stepped shafts 13c, 13d have two connection holes 13e elongated in the direction of the six main shaft axes at a pitch of 180° with respect to the main shaft axis.
13d is provided in a form that penetrates toward the spindle axis side (that is, a form that communicates between the hollow part 13f and the outside of the connecting part 13a).

Further, as shown in FIGS. 2 and 3, a connection bracket 1 is attached to the piston portion 9a of the drawbar 9.
6 are fixed by bolts 18 through hollow portions 13f of the stepped shafts 13c and 13d, and two arms 16a are attached to the connecting bracket 16 in an L-shape, and their tips are connected to the connecting bracket 16 through connecting holes 13e. is provided so as to protrude outward from the solid shaft 13b.

In addition, the outer diameter D1 of the two arms 16a, 16a
As shown in FIGS. 1 and 2, the diameter D2 of the drive shaft connection portion 6b of the main shaft 6 is smaller than or equal to the diameter D2.

Further, a space 13h is formed on the right side of the drive shaft 13 in FIG. 2 to prevent interference between the bolt 18 and the drive shaft 13, and the drawbar is Due to the elasticity of the disc spring 10, the piston portion 9a of 9 is provided within the hollow connection hole of the drive shaft in the same vertical plane as the inner end surface 13g and on the inner diameter side of the drive shaft axis.
It is in abutting engagement with s.

As shown in FIG. 1, a piston 17 is located outside the solid shaft 13b at a position on the left side of FIG. are fitted and engaged so as to be movable in the directions of arrows A and B, and a cylinder block 19 on which a cylinder 19a is formed is attached to the frame 2 corresponding to the outer circumference of the piston 17.
A piston 17 is slidably engaged with the piston 9a. In addition, number 20 is drive shaft 1
This is a bearing that supports 3.

Since the spindle head 1 has the above configuration,
When the tool 21 is mounted on the tool holding portion 6a of the main shaft 6, pressure oil is supplied to the cylinder 19a of the cylinder block 19 to move the piston 17 in the direction B along the drive shaft 13. Then, piston 17
and the arm 16 of the connecting bracket 16.
a comes into contact with each other, and as the piston 17 moves in the B direction, the arm 16a slides in the B direction within the connection hole 13e of the drive shaft 13, and thereby the connection bracket 16 also moves in the B direction. do.
When the connection bracket 16 moves in the direction B, the drawbar 9 is released from the engagement with the drive shaft inner end surface 13s and moves inside the main shaft 6 through the piston portion 9a against the elasticity of the disc spring 10. Collet 1 sliding in direction B and provided at the right end of drawbar 9
One engaging claw 11a is opened outward with respect to the six axes of the main shaft. In this state, the tool 21 is inserted and set so that its taper shank portion 21a is inserted into the tool holding portion 6a, and then the piston 17 is moved back in the A direction via the cylinder 19a. Then, the contact and engagement relationship between the tip 17a of the piston 17 and the arm 16a is released, the connection bracket 16 and the drawbar 9 move in the direction A due to the elasticity of the disc spring 10, and the engagement claw 11a of the collet 11 also moves toward the main shaft 6.
The pull stud 2 of the tool 21 converges in the axial direction.
1b is gripped and engaged. Even after the engaging claw 11a grips the pull stud 21b, the drawbar 9 moves in the direction A, so the tool 21 grips the pull stud 21b.
The taper shank portion 21a contacts the tool holding portion 6a with a predetermined contact pressure, and the tool 21 is reliably held on the main shaft 6. (In this state, the drawbar 9 and the inner end surface 13s of the drive shaft have a predetermined distance, so the elasticity of the disc spring 10 is
It acts effectively to hold the tool 21 on the spindle 6 via the . ) When the tool 21 is held on the main shaft 6, the drive motor 15 is driven to rotate. Then, the drive shaft 13 is rotationally driven via the output shaft 15a, and the main shaft 6 is further rotationally driven via the connecting portion 13a, the key 12, and the like. As a result, the tool 21 mounted on the tool holder 6a also rotates together with the collet 11, drawbar 9, connection bracket 16, etc., making it possible to perform predetermined machining.

When machining with the tool 21 is completed and the tool 21 is replaced, the cylinder 1 of the cylinder block 19 is
Pressure oil is supplied to 9a to move the piston 17 to the drive shaft 1.
3 in the B direction, the tip 17a of the piston 17 and the arm 16a of the connection bracket 16 come into contact with each other, and as the piston 17 further moves in the B direction, the arm 16a is connected to the drive shaft 13.
The connection bracket 16 also moves in the B direction by sliding in the connection hole 13e in the B direction. When the connection bracket 16 moves in the direction B, the drawbar 9 also slides in the direction B inside the main shaft 6 through the piston portion 9a against the elasticity of the disc spring 10, and the collector provided at the right end of the drawbar 9 slides in the direction B against the elasticity of the disc spring 10. The engaging claws 11a of 11 are opened outward with respect to the axial center of the main shaft 6, and the tip 9b of the drawbar 9 comes into contact with the pre-stad 21b of the tool 21, pushing the tool 21 in the direction B, and the tool holding part 6a Then, the tightly held state of the taper shank portion 21a is released.
Therefore, the tool 21 is removed from the tool holder 6a, and the tool 21 to be used next is removed from the tool holder 6a.
, install it according to the procedure already described and continue machining.

(g) Effects of the Invention As explained above, according to the present invention, the main shaft 6 is provided with the tool holding portion 6a capable of holding a tool.
is rotatably provided, and a collector 1 is provided inside the main shaft.
A tool holding means such as No. 1 is attached to the tool holding portion of the tool 2.
A drawbar 9 is provided inside the spindle, and the drawbar drives the tool holding means by moving in the axial direction of the spindle, such as in the direction of arrows A and B, with respect to the spindle. In the spindle structure configured to be freely connected to the tool holding means, a drive shaft connection portion 6b having a first diameter such as diameter D2 is formed on the opposite side of the spindle from where the tool holding portion is provided. At the same time, a connecting surface 6c is formed on the end surface of the drive shaft connecting portion, and a main shaft connecting hole 13i, a hollow portion 13f, and a space 13h are formed at the end.
A drive shaft 13 having a hollow connection hole formed therein is rotatably supported, and an abutment connection surface such as an inner end surface 13g is formed in the hollow connection hole, and the hollow connection hole of the drive shaft is used to drive the main shaft. The shaft connecting portion 6b is fitted and engaged in the direction of the spindle axis in such a manner that the abutment connection surface of the drive shaft and the connection surface of the main shaft are in contact with each other, and the abutment connection surface of the drive shaft outer periphery A fastening member mounting surface such as a bolt fastening surface 13j is formed at a position facing the drive shaft axial center, and the drive shaft and the main shaft are connected to the main shaft center via the fastening member mounting surface, the abutment connection surface, and the connection surface. fastening the drive shaft and the main shaft in a manner that allows them to be separated from the abutment connection surface and the connection surface by a rod-shaped fastening member such as a bolt 14 installed through the direction;
A drawbar contact surface such as an inner end surface 13s is formed in the hollow connection hole of the drive shaft on the inner diameter side of the drive shaft axis in the same vertical plane as the inner end surface 13g, and The provided opposite portion is provided in the hollow connection hole so as to be able to freely abut against the drawbar contact surface, and a bracket member such as the connection bracket 16 is connected to the opposite end of the drawbar, and the drive Connecting holes 13e, 13e are provided on the shaft at positions corresponding to the bracket members.
are provided in such a way that the hollow connection hole communicates with the outer circumference of the drive shaft, and the arms 16a, 1 are attached to the bracket member.
6a, the arm portion is made to protrude from the hollow connection hole to the outer periphery of the drive shaft through the connection hole of the drive shaft, and the outer diameter D1 of the arm portion of the bracket member is set to the above-mentioned diameter. A piston 17 and a cylinder 19a are formed to have a diameter equal to or smaller than the first diameter of the drive shaft connecting portion of the main shaft, and are located on the outer periphery of the drive shaft at a position aligned with the drive shaft axis direction of the arm portion.
A contact member such as a piston 17 that can abut and engage with the arm portion and move the arm portion in the axial direction of the main shaft can be freely moved in the axial direction of the drive shaft. of the drive shaft;
Since the drive motor 15 is directly connected to the end opposite to the side where the hollow connection hole is formed, the bracket member transfers the driving force of the reciprocating drive means provided on the outer periphery of the drive shaft 13 to the connection hole 13e. can be transmitted to the drawbar provided inside the main shaft 6 through the
Therefore, it is possible to smoothly attach and detach the tool, and it is also possible to provide the drive motor 15 directly connected to the axis of the main shaft 6, so that there is no gear train between the main shaft 6 and the drive motor 15 as in the conventional case. There is no need to provide a power transmission mechanism such as a belt or a belt, and the influence of thermal displacement of the main shaft 6 due to heat generated from such a power transmission mechanism is eliminated, making it possible to perform highly accurate machining.
Further, since there is no need to provide a power transmission mechanism, the weight of the spindle head 1 can be reduced accordingly, and the positioning accuracy when moving and positioning the entire spindle head 1 can be improved.

In addition, the main shaft and the drive shaft are connected by a rod-shaped fastening member provided in the direction of the main shaft axis, and the drawbar is held without using a cap nut by the drawbar contact surface provided on the drive shaft side, and the drawbar is held by the drawbar contact surface provided on the drive shaft side without using a cap nut. The reciprocating drive means for driving the drawbar is provided on the outer circumferential side of the drive shaft, which is aligned with the arm part of the bracket member that drives the drawbar, which is formed below the outer diameter of the drive shaft connection part of the main shaft. This avoids lamination in the diameter direction, makes it possible to make the outer diameter of the rotating body between the main shaft and the drive motor as small as possible, and prevents runout even when the main shaft rotates at high speed. This makes it possible to achieve high machining accuracy.

Further, the drive shaft connection portion of the main shaft is fitted and engaged in the hollow connection hole of the drive shaft in the direction of the main shaft axis with the abutment connection surface of the drive shaft and the connection surface of the main shaft in contact with each other, A fastening member mounting surface is formed at a position opposite to the abutment connection surface in the drive shaft axial direction on the outer circumference of the drive shaft, and the drive shaft and the main shaft are connected to the fastening member mounting surface,
The drive shaft and the main shaft are fastened in such a manner that they can be separated from the abutment connection surface and the connection surface by a rod-shaped fastening member that is installed through the abutment connection surface and the connection surface in the direction of the axis of the main shaft. a drawbar abutment surface is formed in the hollow connection hole, a portion of the drawbar opposite to the tool holding means is provided in the hollow connection hole such that it can freely abut against the drawbar abutment surface; A bracket member is connected to the opposite end of the drive shaft, a connection hole is provided at a position corresponding to the bracket member of the drive shaft so as to communicate the hollow connection hole with the outer circumference of the drive shaft, and the bracket member is connected to the drive shaft. An arm portion is formed, and the arm portion is made to protrude from the hollow connection hole to the outer circumferential portion of the drive shaft through the connection hole of the drive shaft, and the outer diameter of the arm portion of the bracket member is aligned with the drive shaft of the main shaft. Since the connecting portion is formed to have a diameter equal to or smaller than the first diameter, by releasing the fastened state by the rod-shaped fastening member, the drive shaft and the main shaft are separated by relatively moving in the direction of the main shaft axis through the main shaft connection hole. In addition, when the drawbar is separated, the drawbar can be exposed immediately, which eliminates the need for complicated work such as disassembling the reciprocating drive means each time the drawbar is inspected, making maintenance and inspection work smoother. And it can be done easily.

Furthermore, since the outer diameter of the arm part of the bracket member is formed to be less than the outer diameter of the drive shaft connection part of the main shaft, even when the main shaft is attached to and detached from the drive shaft, the main shaft is simply connected to the drive shaft through the hollow connection. Simply pull out or insert it relatively from the hole in the direction of the spindle axis.
Both the drawbar and the bracket member can be removed or inserted, making it extremely easy to work with.In addition, when assembling the drawbar, the bracket member is attached to the drawbar before connecting it to the main shaft of the drive shaft, and the drawbar and bracket are assembled in that state. Assembling is possible by inserting the component into the hollow connection hole of the drive shaft together with the main shaft, which eliminates the difficulty of assembly within the narrow space inside the hollow connection hole that occurs when the bracket component is attached after the drive shaft has been connected. The bracket member can be reliably attached to the drawbar, and assembly accuracy can be easily maintained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the main shaft structure according to the present invention, FIG. 2 is a three-dimensional cross-sectional view showing essential parts of the main shaft structure according to the present invention, and FIG. 3 is a view taken in the direction of the arrow in FIG. 6...Main shaft, 6a...Tool holding part, 9...Draw bar, 13...Drive shaft, 13a...Connection part, 1
3e... Connection hole, 15... Drive motor, 16...
Bracket member (connection bracket), 17... Reciprocating drive means (piston), 19a... Reciprocating drive means (cylinder), 21... Tool.

Claims (1)

[Scope of Claims] 1. A spindle provided with a tool holding portion capable of holding a tool is rotatably provided, and a tool holding means is provided inside the spindle so that the tool can be held and released from holding in the tool holding portion, A main spindle structure comprising a drawbar inside the main spindle and connected to the tool holding means so that the drawbar can freely drive the tool holding means by moving in the axial direction of the main spindle with respect to the main spindle, A drive shaft connection portion having a first diameter is formed on the opposite side of the main shaft where the tool holding portion is provided, and a connection surface is formed on an end surface of the drive shaft connection portion, and a hollow connection hole is formed in the end portion. The formed drive shaft is rotatably supported, and an abutment connection surface is formed in the hollow connection hole, and the drive shaft connection portion of the main shaft is connected to the hollow connection hole of the drive shaft, and the drive shaft is abutment connected to the drive shaft. A fastening member is fitted and engaged in the axial direction of the main shaft with the surface and the connecting surface of the main shaft in contact with each other, and a fastening member is placed on the outer circumference of the drive shaft at a position opposite to the abutting connection surface in the axial direction of the drive shaft. The abutment connection surface and the connection surface are formed by a rod-shaped fastening member that forms a mounting surface and is installed to penetrate the drive shaft and the main shaft in the main shaft axis direction via the fastening member mounting surface, the abutment connection surface, and the connection surface. the drive shaft and main shaft are separably fastened to each other, a drawbar contact surface is formed in the hollow connection hole of the drive shaft, and a portion of the drawbar on the opposite side where the tool holding means is provided is connected to the hollow connection hole of the drive shaft. a bracket member is provided in the connection hole so as to be able to freely come into contact with the drawbar contact surface, a bracket member is connected to the opposite end of the drawbar, and a connection hole is provided at a position corresponding to the bracket member of the drive shaft, and the connection hole is provided in the hollow The connection hole is provided in a form that communicates with the outer circumference of the drive shaft, and an arm portion is formed in the bracket member, and the arm portion is protruded from the hollow connection hole to the outer circumference of the drive shaft through the connection hole of the drive shaft. At the same time, the outer diameter of the arm portion of the bracket member is formed to be less than or equal to the first diameter of the drive shaft connection portion of the main shaft, and the outer peripheral portion of the drive shaft is aligned in the direction of the drive shaft axis of the arm portion. A reciprocating drive means is provided at the position, and a contact member capable of abutting and engaging with the arm portion to move the arm portion in the axial direction of the main shaft is provided in a form capable of being freely moved and driven in the axial direction of the drive shaft, A main shaft structure in which a drive motor is directly connected to an end of the drive shaft opposite to the side where the hollow connection hole is formed.