JPWO2019181847A1 - Chuck mechanism and its manufacturing method - Google Patents

Abstract

It is an object of the present invention to provide a chuck mechanism and a method for manufacturing the same, which can avoid spoiling the appearance even if a chamfered portion for improving safety is formed.
A chuck mechanism provided with a chuck body, wherein the chuck body has a front surface, a first chamfered portion, an outer peripheral surface, and a groove portion, and the work is grasped on the front surface. A jaw is installed, the first chamfered portion is formed in a curved surface shape, the first chamfered portion is formed between the peripheral edge portion on the front surface and the outer peripheral surface, and the groove portion is the first. A chuck having a groove portion, the first groove portion is formed on the front surface side of the first chamfered portion, and the first groove portion extends along the circumferential direction of the chuck body to form a ring shape. A mechanism is provided.

Description

The present invention relates to a chuck mechanism for grasping a workpiece and a method for manufacturing the chuck mechanism.

The chuck mechanism includes a chuck main body and a plurality of jaws that are movably installed on the front surface of the chuck main body in the radial direction and grasp the work.

The chuck body has a cylindrical shape made of metal, and from the viewpoint of safety, the boundary portion between the peripheral edge portion and the outer peripheral surface of the front surface of the chuck body forms a chamfered portion having a planar shape (for example). , Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-172172

However, even if a flat chamfered portion is provided at the boundary portion, the chamfered portion itself is still sharp in the case of a chamfered portion having a small size. On the other hand, even in the case of a chamfered portion having a large size, the corners at both corners are sharpened. Therefore, the chuck mechanism may be manually replaced and attached, and in that case, the chuck mechanism may hit the chamfered portion and cause injury or the like.

Therefore, the inventors of the present application have paid attention to providing a curved chamfered portion at the boundary portion in order to further enhance safety.

However, in the manufacturing process of the chuck mechanism, the finishing process is generally performed after the molding process is performed. At that time, the chamfered portion having a curved surface shape is formed in the molding process, but when shifting from the molding process to the finishing process, it is generally carried out by replacing the chamfered portion with another machine. That is, it is inevitable that a small amount of misalignment due to misalignment of the work center or a slight amount of inclination will occur due to reattachment at the time of machining setup. Then, in order to shift to the finishing process in such a state, the boundary line between the curved surface-shaped chamfered portion and the front surface of the chuck body, or the curved surface-shaped chamfered portion and the outer peripheral surface is largely deviated depending on the location. Chamfer. For example, the boundary line between the finished surface on the front surface of the chuck body and the chamfered portion having a curved surface may be eccentric with respect to the center of the chuck body. Further, the boundary line between the finished surface on the outer peripheral surface of the chuck body and the chamfered portion having a curved surface may be oblique with respect to the axial direction of the chuck body.

In this way, even if the boundary line between the finished surface and the chamfered portion of the curved surface shape on the front surface and outer peripheral surface of the chuck body is a small amount of positioning deviation due to reattachment, a large deviation may occur depending on the location. There is a problem that it occurs and the deviation of the boundary line becomes conspicuous in appearance.

The present invention has been made in view of this point, and provides a chuck mechanism and a method for manufacturing the same, which can avoid spoiling the appearance even if a chamfered portion for improving safety is formed. I am aiming.

According to the present invention, the chuck mechanism is provided with a chuck body, and the chuck body has a front surface, a first chamfered portion, an outer peripheral surface, and a groove portion on the front surface. A jaw for grasping the work is installed, the first chamfered portion is formed in a curved surface shape, and the first chamfered portion is formed between the peripheral edge portion and the outer peripheral surface on the front surface. The groove portion has a first groove portion, the first groove portion is formed on the front surface side of the first chamfered portion, and the first groove portion extends along the circumferential direction of the chuck body and is a ring. A shaped chuck mechanism is provided.

Preferably, the groove portion has a second groove portion, the second groove portion is formed on the outer peripheral surface side of the first chamfered portion, and the second groove portion extends along the circumferential direction to form a ring shape. No chuck mechanism is provided.
Preferably, the first chamfered portion and the groove portion are formed of a molded surface of the chuck body.
A chuck mechanism is provided in which the front surface and the outer peripheral surface are finished surfaces.
Preferably, the chuck body has a back surface and a second chamfered portion, the back surface is formed on the chuck body on the side opposite to the front surface, and the second chamfered portion has a curved surface shape. And is formed between the peripheral edge portion and the outer peripheral surface on the back surface, the groove portion has the third and fourth groove portions, and the third groove portion is on the back surface side of the second chamfered portion. It is formed and extends along the circumferential direction to form a ring shape, and the fourth groove portion is formed on the outer peripheral surface side of the second chamfered portion and extends along the circumferential direction to form a ring shape. A chuck mechanism is provided.
Preferably, the groove portion is provided with a chuck mechanism having an arc shape or a V shape in a cross-sectional view.
According to another aspect of the embodiment, it is a method of manufacturing a chuck mechanism in which a jaw for grasping a work is installed on the front surface of the chuck body, and the peripheral portion of the chuck body on the front surface. A molding process in which a portion between the chuck body and the outer peripheral surface is formed to form a curved chamfered portion in the portion, and after the molding process, the front surface and the outer peripheral surface are formed. The molding process includes a step of forming a groove in the chamfered portion formed therein, and in the step of forming the groove, the groove portion is the chamfered portion of the chamfered portion. Provided is a method for manufacturing a chuck mechanism, which is formed on the front surface side and extends along the circumferential direction of the chuck body to form a ring shape.
Preferably, a method for manufacturing a chuck mechanism is provided in which the groove portion is formed in an arc shape or a V shape in a cross-sectional view.

According to the present invention, the first groove portion is formed on the front surface side of the first chamfered portion, and the first groove portion extends along the circumferential direction of the chuck body to form a ring shape. Since such a first groove portion is formed in the chuck body, the connection position (boundary line) between the front surface and the first groove portion is sharp. Here, when the front surface is finished, the deviation directions of the connection positions between the front surface and the first groove portion are the direction orthogonal to the front surface and the radial direction of the front surface. It is divided into. In the present invention, since the connection position between the front surface and the first groove portion is sharp, the amount of deviation of the connection position in the radial direction of the front surface is small. In other words, since the connection position between the front surface and the first groove is sharp, it is possible to prevent the connection position (boundary line) between the front surface and the first groove from shifting before and after finishing the front surface. Will be done. As described above, according to the present invention, even if the first chamfered portion for improving safety is formed on the chuck body, the connection position (boundary) between the front surface and the first groove portion before and after the finishing process. The deviation of the wire) is suppressed, and as a result, the appearance of the chuck body is prevented from being spoiled.

It is a perspective view which showed typically the structure of the conventional general chuck mechanism. It is an enlarged side view of the vicinity of the boundary portion between the peripheral edge portion on the front surface of the chuck body and the outer peripheral surface of the chuck body, and is a view showing a state in which a curved chamfered portion is formed at the boundary portion. It is a figure which showed the state which finished the front surface of the chuck body after forming the chamfered part shown in FIG. It is a front view which showed the boundary line between the front surface of a chuck body and a chamfered part after finishing processing. It is a perspective view which showed the boundary line between the outer peripheral surface of a chuck body and a chamfered part after finishing processing. In the chuck mechanism according to the embodiment of the present invention, it is an enlarged side view of the vicinity of the boundary portion between the peripheral edge portion on the front surface of the chuck body and the outer peripheral surface of the chuck body. It is an enlarged view which showed the state which the front surface of the chuck body was finished in the chuck mechanism in this embodiment. It is a perspective view which showed typically the structure of the chuck mechanism in this embodiment. FIG. 8 is a front view of the chuck mechanism shown in FIG. 8 as viewed from the top jaw side. It is a partial side view of the chuck mechanism shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments. In addition, changes can be made as appropriate without departing from the range in which the effects of the present invention are exhibited.

FIG. 1 is a perspective view schematically showing the configuration of a conventional general chuck mechanism.

As shown in FIG. 1, the chuck mechanism 1 includes a chuck main body 10, a plurality of master jaws 20 movably installed on the front surface 11 of the chuck main body 10, and each master jaw 20. A top jaw 30 that can be detachably attached is provided on the front surface.

The chuck body 10 has a metal cylindrical shape. The boundary portion 13 between the peripheral edge portion of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10 is sharpened by forming a flat chamfered portion having a small size.

FIG. 2 is an enlarged side view of the vicinity of the boundary portion 13 between the peripheral edge portion of the front surface 11 of the chuck main body 10 and the outer peripheral surface 12 of the chuck main body 10, and the boundary portion 13 has a curved chamfered portion (hereinafter referred to as a chamfered portion). It shows a state in which 40 (referred to simply as a chamfered portion) is formed. Here, reference numeral P indicates a boundary line between the front surface 11 and the outer peripheral surface 12 of the chuck body and the chamfered portion 40.

As described above, in the manufacturing process of the chuck mechanism, the chamfered portion 40 is formed in the molding process, and then the front surface 11 and the outer peripheral surface 12 of the chuck body are finished in the finishing process. At that time, when shifting from the molding process to the finishing process, it is common to transfer the chuck body to another machine. Therefore, by reattaching the chuck body, a slight misalignment or a slight tilt may occur. Due to this, it is inevitable that the finishing process will be misaligned.

FIG. 3 is an enlarged view illustrating a state in which the boundary line P between the front surface 11 of the chuck body and the chamfered portion 40 is displaced when the finishing process is displaced. Here, an example will be illustrated in which a slight finishing misalignment D occurs on the finishing surface 11 and 11'of the front surface of the chuck body due to a slight misalignment when the chuck body is reattached.

As shown in FIG. 3, even if the finishing processing deviation D is small, a large deviation L1 will occur at the boundary lines P and Q between the front surface 11 of the chuck body and the chamfered portion 40. This is because the finished surface of the front surface 11 of the chuck body is substantially parallel to the tangent line of the chamfered portion 40 in the vicinity of the boundary line.

Such a large deviation L1 also occurs at the boundary line between the outer peripheral surface 12 of the chuck body and the chamfered portion 40. Further, such a large deviation L1 is also generated by a slight tilt at the time of reattaching the chuck body.

As a result, as shown in FIG. 4, there arises a problem that the boundary line Q1 between the front surface 11 of the chuck body 10 and the chamfered portion 40 after the finishing process is eccentric with respect to the center O of the chuck body 10. Further, as shown in FIG. 5, there arises a problem that the boundary line Q2 between the outer peripheral surface 12 of the chuck main body 10 and the chamfered portion 40 after finishing is inclined with respect to the axial direction of the chuck main body 10. Note that, in FIG. 5, the boundary line Q1 between the front surface 11 of the chuck body 10 and the chamfered portion 40 after finishing is shown in a state where it is not eccentric with respect to the center O in FIG.

As described above, when the positions of the boundary lines Q1 and Q2 between the finished surface on the front surface 11 and the outer peripheral surface 12 of the chuck body 10 and the chamfered portion 40 are largely deviated depending on the location, the boundary lines Q1 and Q2 The misalignment of is noticeable, which is not preferable in appearance.

The present invention has been made to solve such a problem. Hereinafter, the configuration of the chuck mechanism in the present invention will be described with reference to the drawings.

FIG. 6 is an enlarged side view of the vicinity of the boundary between the peripheral edge of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10 in the chuck mechanism according to the embodiment of the present invention.

As shown in FIG. 6, a curved chamfered portion 40 is formed at the boundary between the peripheral edge portion of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10. The chamfered portion 40 is a surface (molded surface) formed by molding. Further, the front surface 11 and the outer peripheral surface 12 of the chuck body 10 are surfaces (finished surfaces) that have been finished after the chamfered portion 40 has been formed.

In the present embodiment, in the chamfered portion 40, groove portions 50A and 50B are provided on the front surface 11 side of the chuck body 10 and the outer peripheral surface 12 side of the chuck body 10, respectively. That is, the front surface 11 and the outer peripheral surface 12 of the chuck body 10 are connected to the chamfered portion 40 via the groove portions 50A and 50B, respectively. The groove portions 50A and 50B are each formed in a ring shape along the circumferential direction. Further, the groove portions 50A and 50B are formed in the molding process in the same manner as the chamfered portion 40. The chamfered portion 40 on the front surface 11 side of the chuck body 10 corresponds to the first chamfered portion. Further, the groove portion 50A on the front surface 11 side of the chuck body 10 corresponds to the first groove portion, and the groove portion 50B on the front surface 11 side of the chuck body 10 corresponds to the second groove portion.

In the present embodiment, since the groove portions 50A and 50B are connected to the front surface 11 and the outer peripheral surface 12 of the chuck body 10, the boundary between the front surface 11 of the chuck body 10 and the groove 50A and the chuck body 10 A boundary line appears at the boundary between the outer peripheral surface 12 and the groove portion 50B.

FIG. 7 is an enlargement showing the deviation of the boundary line between the front surface 11 of the chuck body and the groove 50A when a deviation occurs in the finishing process, as shown in FIG. 3 in the present embodiment. It is a figure. Here, an example will be illustrated in which a slight finishing misalignment D occurs on the finishing surface 11 and 11'of the front surface of the chuck body due to a slight misalignment when the chuck body is reattached.

As shown in FIG. 7, even if the finishing process deviation D occurs, only a slight deviation L2 occurs at the boundary lines P and Q between the front surface 11 of the chuck body and the groove portion 50A. Specifically, the amount of deviation from the boundary line P to the boundary line Q is divided into a deviation in the direction orthogonal to the front surface 11 and a deviation in the radial direction of the front surface (corresponding to the deviation L2). .. When FIG. 3 showing the conventional configuration and FIG. 7 showing the configuration of the embodiment are compared, in the embodiment, the radial deviation of the front surface (corresponding to the deviation L2) is suppressed. Such an effect is obtained because the connecting portion between the finished surface of the front surface 11 of the chuck body and the groove portion 50A is sharp. In other words, this is because the angle formed by the finished surface of the front surface 11 of the chuck body and the tangent line (the line connecting P and Q) of the groove portion 50A in the vicinity of the boundary line is large.

As shown in FIG. 7, a boundary line R also appears in the chamfered portion 40 and the groove portion 50A, but the position of this boundary line R is lower than the surface S corresponding to the maximum deviation in finishing (finishing direction side). ) Is preferable. As a result, since the boundary line R is not finished, it is possible to prevent the boundary line R from being displaced.

Similarly, even if the finishing processing deviation D occurs, only a slight deviation occurs at the boundary line between the outer peripheral surface 12 of the chuck body and the groove portion 50B. Further, even if a finishing process deviation occurs due to a slight inclination when the chuck body is reattached, only a slight deviation occurs at the boundary line between the outer peripheral surface 12 of the chuck body and the groove portion 50B.

According to the present embodiment, a curved chamfered portion 40 is provided at the boundary between the peripheral edge portion of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10, and the chamfered portion 40 is provided with a chuck. By providing ring-shaped groove portions 50A and 50B along the circumferential direction on the front surface 11 side of the main body 10 and the outer peripheral surface 12 side of the chuck main body 10, respectively, the front surface 11 and the chuck main body 10 are provided. When finishing the outer peripheral surface 12, even if a finishing processing deviation occurs, it is possible to prevent a large deviation from occurring at the boundary line between the front surface 11 and the outer peripheral surface 12 of the chuck body 10 and the groove portions 50A and 50B. can do. Therefore, such a boundary line may be eccentric with respect to the center of the chuck body 10 in the front view, or may be slanted with respect to the axial direction of the chuck body 10 in the side view, and may be conspicuous in appearance. Can be solved. As a result, it is possible to provide the chuck mechanism 1 provided with the chuck body 10 which is safe and has a chamfered portion having an excellent appearance shape.

In the present embodiment, the shapes of the groove portions 50A and 50B are not particularly limited, but as shown in FIG. 7, it is preferable that the grooves have an arc shape or a V shape in a cross-sectional view. As a result, sharp angles are not formed at the boundary between the groove 50A and the front surface 11 and the boundary between the groove 50B and the outer peripheral surface 12. It also makes it harder for chips to get caught. Furthermore, the appearance will be beautiful.

The "arc shape" includes an "elliptical arc shape", and the "V shape" includes a boundary portion between the groove portion 50A and the front surface 11 and a boundary portion between the groove portion 50B and the outer peripheral surface 12. However, it also includes those having an R shape.

FIG. 8 is a perspective view schematically showing the configuration of the chuck mechanism in the present embodiment.

As shown in FIG. 8, the chuck mechanism 1 in the present embodiment includes a chuck main body 10, a plurality of master jaws 20 movably installed on the front surface 11 of the chuck main body 10, and each master. A top jaw 30 that can be detachably attached is provided on the front surface of the jaw 20.

The chuck body 10 has a cylindrical shape made of metal, and a curved chamfered portion 40 is provided at a boundary between the peripheral edge of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10. Has been done. Then, as shown in FIG. 6, the chamfered portion 40 has a ring-shaped groove portion 50A on the front surface 11 side of the chuck body 10 and the outer peripheral surface 12 side of the chuck body 10, respectively, along the circumferential direction. , 50B is provided.

FIG. 9 is a front view of the chuck mechanism 1 shown in FIG. 8 as viewed from the top jaw 30 side.

As shown in FIG. 9, when the appearance of the chuck mechanism 1 is viewed from the front, a ring-shaped groove 50A is visually recognized on the peripheral edge of the front surface 11 of the chuck body 10, but the front of the chuck body 10 The boundary line between the surface 11 and the groove 50A does not deviate significantly depending on the location. Therefore, such a boundary line is not eccentric with respect to the center of the chuck body 10 and does not stand out in appearance.

FIG. 10 is a partial side view of the chuck mechanism 1 shown in FIG.

As shown in FIG. 10, when the appearance of the chuck mechanism 1 is viewed from the side, a ring-shaped groove portion 50B is visually recognized at the end portion of the outer peripheral surface 12 of the chuck body 10, but the outer peripheral surface 12 and the groove portion of the chuck body 10 are visible. The boundary line with 50B does not deviate significantly depending on the location. Therefore, such a boundary line is not obscured with respect to the axial direction of the chuck body 10 and is not conspicuous in appearance.

In the present embodiment, a curved chamfered portion 40 is also provided at the boundary between the peripheral edge of the back surface 14 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10, and the chamfered portion 40 includes the chuck body 10 Ring-shaped groove portions 50A and 50B are provided along the circumferential direction on the back surface 14 side and the outer peripheral surface 12 side of the chuck body 10, respectively. The chamfered portion 40 on the back surface 14 side of the chuck body 10 corresponds to the second chamfered portion. Further, the groove portion 50A on the back surface 14 side of the chuck body 10 corresponds to the third groove portion, and the groove portion 50B on the back surface 14 side of the chuck body 10 corresponds to the fourth groove portion. Since the back surface 14 of the chuck body 10 is rarely seen as an external appearance, it is not necessary to provide the groove portion 50A.

According to the present embodiment, a curved chamfered portion 40 is provided at the boundary between the peripheral edge portion of the front surface 11 (further, the back surface 14) of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10. In the chamfered portion 40, ring-shaped groove portions 50A and 50B are provided along the circumferential direction on the front surface 11 (further, the back surface 14) side of the chuck body 10 and the outer peripheral surface 12 side of the chuck body, respectively. It is possible to provide a chuck mechanism 1 provided with a chuck body 10 having a chamfered portion that is safe and has an excellent appearance shape.

Further, the chuck mechanism 1 in the present embodiment can be manufactured by the following method.

First, a curved chamfered portion 40 is formed at the boundary between the peripheral edge of the front surface 11 of the chuck body 10 and the outer peripheral surface 12 of the chuck body 10. The chamfered portion 40 is formed in a molding process in which the front surface 11 and the outer peripheral surface 12 of the chuck body 10 are formed (rough processing leaving a finishing allowance).

Next, after the molding process, the front surface 11 and the outer peripheral surface 12 of the chuck body 10 are finished (finishing process).

In the present embodiment, as shown in FIG. 6, in the molding process, both ends of the chamfered portion 40 (the front surface 11 side of the chuck body 10 and the outer peripheral surface 12 side of the chuck body 10) are subjected to the circumferential direction. Along the same, ring-shaped groove portions 50A and 50B are formed.

The grooves 50A and 50B are preferably formed in an arc shape or a V shape in a cross-sectional view. Here, the "arc-shaped" includes the "elliptical arc-shaped", and the "V-shaped" includes the groove portion 50A and the front surface 11, and the boundary portion between the groove portion 50B and the outer peripheral surface 12 is R. Including those in shape.

Although the present invention has been described above in terms of preferred embodiments, such a description is not a limitation, and of course, various modifications can be made. For example, in the above embodiment, the specific shape of the chamfered portion 40 is not particularly limited as long as it has a curved surface shape. For example, in cross-sectional view, it may be arcuate or elliptical arcuate.

Further, in the present embodiment, the molding process includes turning process, machining process, press process, three-dimensional molding, mold molding and the like. Further, the finishing process includes high-precision cutting process, grinding process, polishing process and the like.

In addition, the dimensions shown in each of the above drawings have been appropriately changed for the sake of clarity of explanation, and do not represent actual dimensions.

In the present embodiment, both the groove portion 50A (first groove portion) and the groove portion 50B (second groove portion) are formed on the chamfered portion 40 (first chamfered portion) on the front surface 11 side of the chuck body 10. The form has been described, but the present invention is not limited to this. Only the groove portion 50A (first groove portion) may be formed on the chamfered portion 40 (first chamfered portion) on the front surface 11 side of the chuck body 10. Also in this case, an effect corresponding to the effect produced in the embodiment can be obtained.

1 Chuck mechanism
10 Chuck body
11 Front surface of chuck body
12 Outer peripheral surface of the chuck body
14 Back side of chuck body
20 Master Joe
30 Top Joe
40 Chamfer
50A, 50B groove

Claims (7)

It is a chuck mechanism equipped with a chuck body.
The chuck body has a front surface, a first chamfered portion, an outer peripheral surface, and a groove portion.
A jaw for grasping the work is installed on the front surface.
The first chamfered portion is formed in a curved surface shape, and the first chamfered portion is formed between the peripheral edge portion of the front surface and the outer peripheral surface.
The groove portion has a first groove portion and has a first groove portion.
A chuck mechanism in which the first groove portion is formed on the front surface side of the first chamfered portion, and the first groove portion extends along the circumferential direction of the chuck body to form a ring shape. The chuck mechanism according to claim 1.
The groove has a second groove and has a second groove.
A chuck mechanism in which the second groove portion is formed on the outer peripheral surface side of the first chamfered portion, and the second groove portion extends along the circumferential direction to form a ring shape. The chuck mechanism according to claim 1 or 2.
The first chamfered portion and the groove portion are formed of a molded surface of the chuck body.
A chuck mechanism in which the front surface and the outer peripheral surface are finished surfaces. The chuck mechanism according to any one of claims 1 to 3.
The chuck body has a back surface and a second chamfered portion.
The back surface is formed in the chuck body on the side opposite to the front surface.
The second chamfered portion is formed in a curved surface shape, and is formed between the peripheral edge portion on the back surface and the outer peripheral surface.
The groove has third and fourth grooves.
The third groove portion is formed on the back surface side of the second chamfered portion and extends along the circumferential direction to form a ring shape.
The fourth groove portion is a chuck mechanism formed on the outer peripheral surface side of the second chamfered portion and extending along the circumferential direction to form a ring shape. The chuck mechanism according to any one of claims 1 to 4.
The groove portion is a chuck mechanism having an arc shape or a V shape in a cross-sectional view. This is a manufacturing method of a chuck mechanism in which a jaw for grasping the work is installed on the front surface of the chuck body.
A molding process of forming a portion between the peripheral edge portion of the front surface of the chuck body and the outer peripheral surface of the chuck body to form a curved chamfered portion on the portion.
After the molding process, a finishing process for finishing the front surface and the outer peripheral surface is provided.
The molding process includes a step of forming a groove in the chamfered portion formed therein.
In the step of forming the groove portion, the groove portion is formed on the front surface side of the chamfered portion and extends along the circumferential direction of the chuck body to form a ring-shaped chuck. Manufacturing method of the mechanism. The method for manufacturing a chuck mechanism according to claim 6.
A method for manufacturing a chuck mechanism, wherein the groove portion is formed in an arc shape or a V shape in a cross-sectional view.