Piston for fluid pressure cylinder

Abstract

To provide a technique for improving the durability of a piston in a fluid pressure cylinder.SOLUTION: The piston for the fluid pressure cylinder includes a piston body arranged in a cylinder chamber movably along a cylinder tube, and a piston rod connected to the piston body, extending in the axial direction of the piston, and inserted into a through-hole formed in a rod cover. A piston end opposed to a head cover, out of both axial ends of the piston, includes a protrusion protruding in the axial direction of the piston. The protrusion is formed to reduce the width as extending from the base end to the top, and the top of the protrusion is located at the tip end of the piston in the axial direction of the piston and formed where the center axis of the piston passes.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a piston for a fluid pressure cylinder. [Background technology]

[0002] Conventionally, as a means for transporting a workpiece or the like, for example, a fluid pressure cylinder that uses fluid pressure to reciprocate a piston has been widely used. The piston of a fluid pressure cylinder is generally an aluminum piston body fixed to the end of a piston rod by crimping, fastening, or the like. In contrast, in order to reduce the number of parts and the number of assembly steps, a technology is known in which the piston rod and the piston body are integrally formed by insert molding the piston body made of synthetic resin into the piston rod (for example, Patent Document 1).

[0003] Incidentally, some fluid pressure cylinders are provided with a damper made of an elastic material such as rubber to prevent the piston from being damaged by the impact when the piston abuts (collides) against the cylinder body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-2416 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, efforts have been made to reduce the weight and size of fluid pressure cylinders, and it is desirable for the fluid pressure cylinder to have a piston that is lightweight and compact while also having high durability.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a technique capable of improving the durability of a piston in a fluid pressure cylinder. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention employs the following means. That is, the present invention relates to a piston of a fluid pressure cylinder, which is inserted into a cylinder body having a cylindrical cylinder tube, a head cover closing one end of the cylinder tube, and a rod cover closing the other end of the cylinder tube. The piston includes a piston body disposed in a cylinder chamber defined by the cylinder tube, the head cover, and the rod cover so as to be movable along the cylinder tube, and a piston rod connected to the piston body, extending in the axial direction of the piston, and inserted into an insertion hole formed in the rod cover, and one of both axial end portions of the piston, which faces the head cover, includes a convex portion protruding in the axial direction of the piston, and the convex portion is formed so as to decrease in width from the base end portion toward the apex portion in the axial direction of the piston, and the apex portion of the convex portion is formed at a position located at the forefront of the piston in the axial direction of the piston and where the central axis of the piston passes through the apex portion.

[0008] With the piston according to the present invention, when the piston body reaches the end stroke on the head cover side, the top of the convex portion first comes into contact with the head cover. Then, as the convex portion is deformed (crushed) by the impact load, the convex portion collides with the head cover while gradually expanding the contact area with the head cover from the top. This allows the impact energy to be dispersed and absorbed by the piston end, reducing the impact stress. As a result, damage to the piston end can be prevented. do.

[0009] In the present invention, at least a part of the piston end portion may be made of resin.

[0010] In the present invention, the convex portion is formed as a rotating body with the center of rotation being the central axis of the piston, and when the diameter of the convex portion is D1 and the inner diameter of the cylinder tube is D2, 0.075≦D1 / D2≦0.995 is satisfied, and when the distance in the axial direction of the piston between a point on the surface of the piston end portion, which is located at a distance of D1 / 2 radially outward from the central axis of the piston, and the top of the convex portion is H, 0.0024 <H / (D1 / 2)<0.075であってもよい。

[0011] In the present invention, the surface of the convex portion may be spherical.

[0012] In the present invention, the surface of the convex portion may be curved.

[0013] In the present invention, the convex portion may be formed in a tapered shape.

[0014] The present invention may also be configured as a piston for a pneumatic cylinder. Effect of the Invention

[0015] According to the present invention, it is possible to improve the durability of the piston in a fluid pressure cylinder. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of an air cylinder including a piston according to an embodiment; [Diagram 2] 1 is a cross-sectional view of the vicinity of a piston end of an air cylinder according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a cross-sectional view for explaining details of a convex portion. [Figure 4] FIG. 4 is a cross-sectional view of the vicinity of a piston end of an air cylinder according to a comparative example. [Diagram 5] 10 is a cross-sectional view showing the vicinity of a piston end portion of a piston according to a first modified example of the embodiment. FIG. [Figure 6]11 is a cross-sectional view showing the vicinity of a piston end portion of a piston according to a second modified example of the embodiment. FIG. [Figure 7] FIG. 11 is a cross-sectional view showing the vicinity of a piston end portion of a piston according to a third modified example of the embodiment. [Figure 8] FIG. 13 is a diagram showing an analysis result of impact stress. [Figure 9] 1 is a graph showing the relationship between H / (D1 / 2) and maximum impact stress. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment described below, the present invention is applied to an air cylinder (pneumatic cylinder) using compressed air as a driving source, as an example of a fluid pressure cylinder. However, the fluid pressure cylinder to which the piston according to the present invention can be applied is not limited to an air cylinder. The piston according to the present invention may be applied to a hydraulic cylinder using compressed oil as a driving source, or a fluid pressure cylinder using other pressure fluids. Furthermore, unless otherwise specified, the configurations described in the following embodiments are not intended to limit the technical scope of the invention to only those configurations. Furthermore, in the drawings referred to below, for convenience of explanation, some shapes may be exaggerated and not drawn to scale.

[0018] FIG. 1 is a cross-sectional view of an air cylinder 100 including a piston 20 according to an embodiment. FIG. 1 is a diagram for illustrating a schematic structure of the air cylinder 100. In FIG. 1, a portion indicated by reference symbol A A cross section along the central axis of a piston 20, designated 1, is shown.

[0019] [composition] First, the configuration of an air cylinder 100 according to an embodiment will be described. As shown in FIG. 1, the air cylinder 100 includes a cylindrical cylinder body 10 with both ends closed, and a piston 20 inserted into the cylinder body 10. The cylinder body 10 includes a cylindrical cylinder tube 1, a head cover 2 attached to one axial end of the cylinder tube 1, and a rod cover 3 attached to the other axial end of the cylinder tube 1. The head cover 2 closes an opening on one end side of the cylinder tube 1. The rod cover 3 closes an opening on the other end side of the cylinder tube 1. A cylinder chamber 30 is defined in the cylinder body 10 by the cylinder tube 1, the head cover 2, and the rod cover 3. The inner peripheral surface (inner peripheral wall) of the cylinder tube 1 that forms the cylinder chamber 30 is cylindrical.

[0020] A first supply / discharge port 101 is formed in the cylinder tube 1 at a position closer to the head cover 2, and a second supply / discharge port 102 is formed in the cylinder tube 1 at a position closer to the rod cover 3. In addition, an insertion hole 31 is formed in the rod cover 3.

[0021] The piston 20 is formed in a generally cylindrical shape extending along the cylinder tube 1, and is inserted into the cylinder body 10 so that one end is accommodated in the cylinder chamber 30 and the other end protrudes outside the cylinder chamber 30. Of both axial ends of the piston 20, the end facing the head cover 2 is referred to as a piston end 201. The piston 20 includes a piston body 4 disposed in the cylinder chamber 30 so as to be movable along the cylinder tube 1, and a piston rod 5 connected to the piston body 4, extending in the axial direction of the piston 20, and inserted into an insertion hole 31 formed in the rod cover 3.

[0022] 1, the cylinder chamber 30 is divided by the piston body 4 into a first pressure chamber 301 on the head cover 2 side and a second pressure chamber 302 on the rod cover 3 side. The first pressure chamber 301 communicates with the outside of the cylinder chamber 30 via a first supply / exhaust port 101, and the second pressure chamber 302 communicates with the outside of the cylinder chamber 30 via a second supply / exhaust port 102.

[0023] FIG. 2 is a cross-sectional view of the vicinity of the piston end 201 of the air cylinder 100 according to the embodiment. As shown in FIG. 2, the piston rod 5 is a cylindrical shaft body extending along the axial direction of the piston 20. The central axis of the piston rod 5 coincides with the central axis A1 of the piston 20. The piston rod 5 is formed of a metal material such as SUS or steel. However, the shape and material of the piston rod 5 are not limited to those described above. Here, the end of the piston rod 5 on the piston end 201 side among both axial ends is referred to as the rod end 51. As shown in FIG. 2, the rod end 51 is covered by the piston main body 4. The end face of the rod end 51 (i.e., the tip end face of the piston rod 5) is formed as a flat surface perpendicular to the axial direction of the piston 20. The tip end face of the piston rod 5 may be formed in a convex shape. On the outer circumferential surface of the piston rod 5, an annular engagement groove 5a for mounting the piston main body 4 to the piston rod 5 is formed extending in the circumferential direction. In this case, in the piston rod 5, a portion located axially opposite to the rod end portion 51 across the engagement groove 5a is referred to as a rod main body portion 52. As shown in FIG.

[0024] 2, the piston body 4 is formed in the shape of a cylindrical cap with a bottom so as to cover the rod end portion 51. The piston body 4 is formed from a resin material such as PPS (polyphenylene sulfide), POM (polyacetal), PA (polyamide), etc. However, the shape and material of the piston body 4 are not limited to those mentioned above. The piston body 4 may be formed from a metal material such as aluminum, an aluminum alloy (A6061, etc.), titanium, etc.

[0025] The piston body 4 has a cylindrical portion 41, a cover portion 42, a piston outer peripheral portion 43, and an engagement portion 44. The cylindrical portion 41 is formed in a cylindrical shape and covers the outer peripheral surface of the rod end portion 51 of the piston rod 5. The cover portion 42 closes one end of the cylindrical portion 41 and covers the tip surface of the rod end portion 51. The piston outer peripheral portion 43 protrudes from the outer periphery of the cylindrical portion 41 and faces the cylinder tube 1. An annular mounting groove 4a is formed on the outer peripheral surface of the piston outer peripheral portion 43 and extends in the circumferential direction. A rubber piston packing 6 is mounted in the mounting groove 4a, which seals between the first pressure chamber 301 and the second pressure chamber 302 by sliding against the inner peripheral surface of the cylinder tube 1. The engagement portion 44 protrudes from the inner periphery of the cylindrical portion 41 and engages with the engagement groove 5a of the piston rod 5. The engagement portion 44 engages with the engagement groove 5a, thereby connecting the piston body 4 and the piston rod 5.

[0026] The piston 20 is formed, for example, by insert molding a piston body made of synthetic resin into a piston rod. However, the manufacturing method of the piston according to the present invention is not limited to insert molding. For example, when the piston body is made of metal, the piston body and the piston rod may be joined by screwing.

[0027] 2, in the piston 20, a piston end portion 201 is formed by the cover portion 42 of the piston body 4. In addition, an annular groove 7 extending in the circumferential direction is formed around the piston end portion 201. Note that the annular groove 7 is not an essential component in the present invention.

[0028] As shown in FIG. 2, the piston end 201 includes a convex portion C1 protruding in the axial direction of the piston 20. In the figure, a dot pattern is applied to the range of the convex portion C1. In the piston 20, the convex portion C1 is formed by a part of the piston body 4 made of resin. In addition, the convex portion C1 according to this example is formed as a rotating body having a circular arc cross section, which is formed by rotating a convex arc around the central axis A1 of the piston 20 as the center of rotation. Therefore, the convex portion C1 is formed in a spherical shape, and the surface S1 of the convex portion C1 is curved in a spherical shape. Here, the part of the convex portion C1 closest to the head cover 2 side (i.e., the tip) is referred to as the apex T1. At this time, as shown in FIG. 2, the apex T1 of the convex portion C1 is located at the tip of the piston 20 in the axial direction of the piston 20, and is formed at a position where the central axis A1 of the piston 20 passes. The convex portion C1 is formed so as to decrease in width (diameter) from its base end toward the apex T1. The term "reduced width" here means, more specifically, that the width in a direction perpendicular to the axial direction of the piston 20 is narrowed. The shape of the convex portion according to the present invention is not limited to the spherical shape (R-shape) described above. The convex portion C1 may be, for example, tapered (conical or pyramidal). The convex portion C1 may be trapezoidal with a flat apex T1 as in Modification 1 described later. The surface of the convex portion C1 may be a curved surface with a uniform R or a curved surface with an uneven R. In the present invention, it is not essential that the central axis of the piston and the apex of the convex portion completely coincide with each other, and a mode in which the apex of the convex portion is eccentric to the central axis of the piston within a small range is also acceptable.

[0029] 2, the diameter of the convex portion C1 is defined as D1. More specifically, the diameter D1 is the diameter of the base end portion of the convex portion C1 where the outer diameter is maximum. The inner diameter of the cylinder tube 1 is defined as D2. In this example, 0.075≦D1 / D2≦0.995.

[0030] FIG. 3 is a cross-sectional view for explaining the details of the convex portion C1. As shown in FIG. 3, the height (protrusion amount) of the convex portion C1 in the axial direction of the piston 20 is H. More specifically, the height H is the distance in the axial direction of the piston 20 between point P1 and the top T1 of the convex portion C1. Point P1 is a point on the surface of the piston end portion 201, located at a position away from the central axis of the piston 20 radially outward by D1 / 2. Point P1 is located at the base end portion of the convex portion C1. At this time, in this example, <H / (D1 / 2)<0.075となっている。

[0031] Returning to Fig. 2, the diameter of the rod end portion 51 of the piston rod 5 is defined as D3. In this example, 1.03 ≤ D1 / D3 ≤ 1.99.

[0032] [Operation] Next, the operation of the air cylinder 100 according to the embodiment will be described with reference to Fig. 1. Note that the description will be given assuming that the state in which the piston body 4 abuts against the head cover 2 shown in Fig. 1 is an initial position.

[0033] First, when compressed air is supplied from a compressed air supply source (not shown) to the first pressure chamber 301 via the first supply / exhaust port 101 in the initial position, the piston body 4 pressed by the compressed air starts to move toward the rod cover 3. Then, the air in the second pressure chamber 302 is discharged to the outside via the second supply / exhaust port 102, and the piston body 4 moves until it reaches the stroke end on the rod cover 3 side. As a result, the piston rod 5 moves in a direction protruding from the cylinder tube 1. When the piston body 4 reaches the stroke end on the rod cover 3 side, it collides with the rod cover 3.

[0034] Next, when compressed air is supplied to the second pressure chamber 302 via the second supply / exhaust port 102, the piston body 4 pressed by the compressed air starts to move towards the head cover 2. Then, the air in the first pressure chamber 301 is discharged to the outside via the first supply / exhaust port 101, and the piston body 4 moves until it reaches the stroke end on the head cover 2 side (i.e., the initial position). As a result, the piston rod 5 moves in a direction to retract into the cylinder tube 1. When the piston body 4 reaches the stroke end on the head cover 2 side, it collides with the head cover 2.

[0035] [Actions and Effects] Hereinafter, the action and effect of the piston 20 included in the air cylinder 100 according to the embodiment will be described in comparison with a comparative example. FIG. 4 is a cross-sectional view of the vicinity of the piston end 401 of the air cylinder 200 according to the comparative example. As shown in FIG. 4, the piston 40 according to the comparative example is different from the piston 20 according to the embodiment in that the convex portion C1 is not formed on the piston end 401. In the piston 40 according to the comparative example, the end surface S2 of the piston end 401 is a flat surface perpendicular to the axial direction of the piston 40. Therefore, in the piston 40, when the piston body 4 reaches the end stroke on the head cover 2 side, the entire end surface S2 of the piston end 401 collides with the head cover 2 at approximately the same time. As a result, a high impact stress (instantaneous maximum stress) is generated in the piston end 401, and there is a risk that the resin piston body 4 constituting the piston end 401 may be damaged.

[0036] In contrast, as shown in FIG. 2, the piston end 201 of the piston 20 according to the embodiment includes a convex portion C1 protruding in the axial direction of the piston 20, and the convex portion C1 is formed so as to narrow from its base end portion toward the top portion T1. And the top portion T1 of the convex portion C1 is formed at the foremost end of the piston 20 in the axial direction of the piston 20 and at a position through which the central axis A1 of the piston 20 passes. According to this, when the piston body 4 reaches the end stroke on the head cover 2 side, the top portion T1 of the convex portion C1 first contacts the head cover 2. Then, when the convex portion C1 is deformed (crushed) by the impact load, the convex portion C1 collides with the head cover 2 while gradually expanding the contact area with the head cover 2 from the top portion T1. Thereby, the impact energy is dispersed and absorbed by the piston end 201, and the impact stress is reduced. As a result, breakage of the piston end 201 can be prevented.

[0037] As described above, according to the present embodiment, it is possible to improve the durability of the piston 20. This is particularly suitable for the piston 20 in which the piston end 201 is formed by the resin piston body 4. Note that in the present invention, at least a part of the piston end may be made of resin. However, in the present invention, it is not essential that the piston end is made of resin. In addition, in the present embodiment, by setting 0.075 ≦ D1 / D2 ≦ 0.995 and 0.0024 < H / (D1 / 2) < 0.075, the impact stress when the piston end 201 collides with the head cover 2 can be more preferably reduced. Further, by setting 1.03 ≦ D1 / D3 ≦ 1.99, the impact stress when the piston end 201 collides with the head cover 2 can be more preferably reduced. Also, as shown in FIG. 2, when the diameter of the rod main body portion 52 of the piston rod 5 is D4, D3 ≦ D4 may be satisfied. However, the present invention is not limited to these conditions.

[0038] Moreover, in the present embodiment, by setting 0.075 ≦ D1 / D2 ≦ 0.995 and 0.0024 < H / (D1 / 2) < 0.075, the impact stress when the piston end 201 collides with the head cover 2 can be more preferably reduced. Further, by setting 1.03 ≦ D1 / D3 ≦ 1.99, the impact stress when the piston end 201 collides with the head cover 2 can be more preferably reduced. Also, as shown in FIG. 2, when the diameter of the rod main body portion 52 of the piston rod 5 is D4, D3 ≦ D4 may be satisfied. However, the present invention is not limited to these conditions.

[0039] [Modification Example] A piston according to a modified example of the embodiment will be described below. In the description of the modified example, differences from the piston 20 described in Figures 1 to 3 will be mainly described, and detailed description of the same points as the piston 20 will be omitted.

[0040] [Variation 1] Fig. 5 is a cross-sectional view showing the vicinity of the piston end portion 201 of the piston 20A according to the first modified example of the embodiment. As shown in Fig. 5, the convex portion C1 of the piston 20A has a top portion T1 formed as a flat surface. As a result, the cross section of the convex portion C1 is bowl-shaped with curved both sides. The cross section of the convex portion C1 may be trapezoidal with straight both sides.

[0041] In the piston 20A according to the first modification, similarly to the above-described piston 20, the convex portion C1 is formed so as to narrow toward the apex T1, and the apex T1 is formed at a position where the central axis A1 passes through the apex T1 and is located at the forefront of the piston 20. This makes it possible to improve the durability of the piston 20A in the first modification as well.

[0042] [Variation 2] FIG. 6 is a cross-sectional view showing the vicinity of the piston end 201 of the piston 20B according to the second modified example of the embodiment. As shown in FIG. 6, the piston body 4 of the piston 20B does not have a cover portion 42 that covers the rod end 51 of the piston rod 5. Therefore, the end face of the rod end 51 is exposed at the tip of the piston 20B. As a result, in the piston 20B, the piston end 201 is formed by the cylindrical portion 41 of the piston body 4 and the rod end 51 of the piston rod 5. As in the piston 20 described above, the piston end 201 of the piston 20B also has a convex portion C1 that protrudes in the axial direction of the piston 20. In the piston 20B, a spherical convex portion C1 is formed by a part of the piston body 4 made of resin and a part of the piston rod 5 made of metal.

[0043] In the piston 20B according to the second modification, similarly to the above-described piston 20, the convex portion C1 is formed so as to narrow toward the apex T1, and the apex T1 is formed at a position that is located at the forefront of the piston 20 and through which the central axis A1 passes. This makes it possible to improve the durability of the piston 20B in the second modification as well.

[0044] [Variation 3] Fig. 7 is a cross-sectional view showing the vicinity of a piston end portion 201 of a piston 20C according to Modification 3 of the embodiment. As shown in Fig. 7, the piston 20C does not have an annular groove 7, unlike the piston 20 shown in Fig. 2 and the like.

[0045] <Analysis and Evaluation> A stress evaluation of the piston according to the embodiment was performed by finite element analysis using analysis software. In the stress evaluation, the distribution of impact stress in the piston body and the maximum value of the impact stress when the piston collides with the head cover of the air cylinder were obtained. The materials of the members used in the analysis model were PPS for the piston body, S45C for the piston rod, and A6061 for the cylinder body. In addition, the mass of the piston including the piston body, piston rod, and piston packing was set in consideration of the weight equivalent to the overload test, and the piston speed was set to 0.3 [m / s].

[0046] As Examples 1 to 10, the piston 20 according to the embodiment was evaluated. Also, as Comparative Examples 1 to 3, the piston 40 according to the comparative example was evaluated. Table 1 shows D1, H, H / (D1 / 2), and the maximum impact stress ratio in Examples 1 to 10 and Comparative Examples 1 to 3. The maximum impact stress ratio is the ratio of the maximum value of the impact stress (maximum impact stress) in Examples 1 to 10 and Comparative Examples 1 to 3. The maximum impact stress ratio is expressed as a ratio to the maximum impact stress of Comparative Example 1. In Table 1, when comparing the maximum impact stress ratio between Examples 1 to 10 and Comparative Example 1, it can be seen that the maximum impact stress of Examples 1 to 10 is lower than that of Comparative Example 1. Thereby, the stress reduction effect by forming a convex portion at the piston end was confirmed. Also, FIG. 8 is a diagram showing the analysis result of the impact stress. FIG. 8 shows the distribution of the impact stress in the piston bodies of Example 3, Example 10, and Comparative Example 1. In FIG. 8, the horizontal half of the cross section of the piston body is shown.

Table 1

[0047] Next, based on the above analysis, the range of H / (D1 / 2) was evaluated. FIG. 9 is a graph showing the relationship between H / (D1 / 2) and the maximum impact stress derived from the analysis result. The maximum impact stress is expressed as a ratio to the maximum impact stress when H / (D1 / 2) = 0. In the graph, the solid line indicates the maximum impact stress ratio, and the broken line indicates the tensile strength of the piston body. As shown in FIG. 9, it can be seen that in the range of 0.0024 < H / (D1 / 2) < 0.075, the maximum impact stress becomes lower than the tensile strength of the piston body. Thereby, it was confirmed that by setting 0.0024 < H / (D1 / 2) < 0.075, the impact stress can be suitably reduced.

[0048] As described above, the preferred embodiments of the present invention have been described, but the various forms described above can be combined as much as possible.

Explanation of Reference Numerals

[0049] 1: Cylinder tube 2: Head cover 3: Rod cover 4: Piston body 5: Piston rod 10: Cylinder body 20: Piston 100: Air cylinder (an example of a fluid pressure cylinder)

Claims

1. A piston of a fluid pressure cylinder is inserted into a cylinder body having a cylindrical cylinder tube, a head cover that closes one end of the cylinder tube, and a rod cover that closes the other end of the cylinder tube, a piston body disposed within a cylinder chamber defined by the cylinder tube, the head cover, and the rod cover so as to be movable along the cylinder tube; and a piston rod connected to the piston body, extending in an axial direction of the piston, and inserted into an insertion hole formed in the rod cover, a piston end portion facing the head cover among both axial end portions of the piston includes a convex portion protruding in the axial direction of the piston, The convex portion is formed so as to decrease in width from its base end portion to its apex portion, The apex of the convex portion is located at the tip of the piston in the axial direction of the piston and is formed at a position through which a central axis of the piston passes. piston.

2. At least a portion of the piston end is made of resin. The piston of claim 1.

3. The convex portion is formed as a rotating body having a center axis of the piston as a center of rotation, When the diameter of the convex portion is D1 and the inner diameter of the cylinder tube is D2, 0.075≦D1 / D2≦0.995, When the distance in the axial direction of the piston between a point on the surface of the piston end portion, which is located at a position D1 / 2 away from the center axis of the piston in the radial direction outward, and the top of the convex portion is H, 0.0024<H / (D1 / 2)<0.075; A piston according to claim 1 or 2.

4. The surface of the convex portion is spherical. A piston according to claim 1 or 2.

5. The surface of the convex portion is curved. A piston according to claim 1 or 2.

6. The convex portion is formed in a tapered shape. A piston according to claim 1 or 2.

7. It is formed as a piston for a pneumatic cylinder, A piston according to claim 1 or 2.

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