JP2010179429A - Clamp cylinder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a clamp cylinder, which is excellent in reliability and durability by reducing risks of operation failure by cutting powder or the like and breakage by deterioration of strength. <P>SOLUTION: In the clamp cylinder 1, a piston rod 7 and a clamp arm 13 are connected by first and second links 21 and 23. The clamp arm 13 is rotated to an unclamp position through the second links 21 and 23 according to contracting operation of the piston rod 7, and a biasing means (a push rod 29 and a coil spring 30) for rotationally biasing the first link 21 toward the unclamp position of the clam arm 13 is provided within the piston rod 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a clamp cylinder used for fixing an object such as a workpiece to a table or the like.

A clamp cylinder is known that includes a piston that moves in the axial direction by pneumatic pressure, hydraulic pressure, and the like, and a clamp arm that performs a clamping / unclamping operation according to the movement of the piston. For example, in Patent Document 1, a clamp arm is pivotally attached to a rod cover that holds a piston so that one of the oscillating ends of the clamp arm is engaged with the piston. Arm movement is obtained. Particularly here, the engagement surface of the clamp shaft and clamp arm at the tip of the piston that is projected and biased by a spring is a chamfered inclined surface, thereby generating a wedge effect and releasing the pressure from the drive source. Even if it is done, the clamp state by a clamp arm is maintained.
In addition, a torsion spring that urges the clamp arm to the unclamping position and avoids interference with the object during unclamping is provided at the shaft attachment portion of the clamp arm in the rod cover.

Japanese Utility Model Publication No. 2-63942

  However, in the clamp cylinder of Patent Document 1, since the torsion spring is provided in a shape exposed in a notch formed in the clamp arm, chips and the like are likely to adhere to cause malfunction. In addition, the strength of the clamp arm is reduced due to the formation of the notch, and there is a possibility that the clamp arm may be damaged by repeated use over a long period of time.

  Therefore, the present invention is excellent in reliability and durability by reducing the risk of malfunction due to chips or the like and damage due to strength reduction even if the clamp arm is configured to urge the clamp arm to the unclamping position. The object is to provide a clamp cylinder.

In order to achieve the above object, according to a first aspect of the present invention, a piston rod and a clamp arm are connected by a link mechanism, and the clamp arm is moved to an unclamping position via the link mechanism as the piston rod contracts. A biasing means for rotating and biasing the link mechanism to the unclamping position side of the clamp arm is provided in the piston rod.
According to a second aspect of the present invention, in the configuration of the first aspect, the link mechanism includes a first link having a base end connected to an end portion of a shaft member rotatably provided to the piston rod, and the first link. The urging means is provided so as to be capable of moving forward and backward with respect to the pressing portion formed at the eccentric part of the shaft member. The second link is formed with one end connected to the tip and the other end connected to the clamp arm. The push rod and the elastic member that presses the push rod toward the shaft member are formed.
According to a third aspect of the present invention, in the configuration of the first or second aspect, the holding member is located on the opposite side of the clamp arm with the piston rod slidingly contacting the rod cover and sandwiching the piston rod at the clamp position of the clamp arm. It is formed.
According to a fourth aspect of the present invention, in the configuration of the third aspect, the sliding surface of the piston rod in the holding portion is a curved surface that bulges along an arc locus centering on an axis orthogonal to the piston rod. It is a feature.
According to a fifth aspect of the present invention, in the configuration of any one of the first to fourth aspects, a taper-inclined shape that presses the clamp arm to the clamp position in accordance with the extension operation of the piston rod is provided at the extension side end of the piston rod. A wedge surface and a chamfered portion that is located on the tip side of the wedge surface and has a larger inclination angle than the wedge surface and that the clamp arm contacts at the unclamping position are formed. .
According to a sixth aspect of the present invention, in the configuration of any one of the first to fifth aspects, the contact portion of the clamp arm with the piston rod is an arc locus centering on an axis parallel to the swing axis of the clamp arm. It is characterized by being a curved surface portion that bulges along.
According to a seventh aspect of the present invention, in the configuration of any one of the first to sixth aspects, the clamp arm rotates at the abutting portion with the piston rod in accordance with the expansion / contraction operation of the piston rod, and the piston rod on the extension side end A key for relatively sliding the part is provided.
According to an eighth aspect of the present invention, in the configuration of the seventh aspect, a rotation urging means for urging the key to the sliding position at the unclamping position of the clamp arm is provided.
According to a ninth aspect of the present invention, in the structure according to any of the third to eighth aspects, the abutting portion of the piston cover at the clamp position with the holding portion is lubricated with respect to the piston rod at the unclamp position. A lubricating member is provided.

According to the first aspect of the present invention, the biasing means is not exposed to the outside, and there is no possibility of malfunction due to adhesion of chips or the like. Further, since it is not necessary to provide a notch for the torsion spring in the clamp arm, the strength of the clamp arm can be secured, and the possibility of breakage even during long-term repeated use is reduced. Therefore, a clamp cylinder excellent in reliability and durability can be obtained.
According to the second aspect of the present invention, in addition to the effect of the first aspect, it is possible to easily obtain a biasing means that is not easily affected by chips, cutting oil or the like in the piston rod.
According to the invention described in claim 3, in addition to the effect of claim 1 or 2, it is possible to prevent the piston rod from collapsing in the clamped state.
According to the invention of claim 4, in addition to the effect of claim 3, even if the piston rod tilts, the piston rod does not contact the edge of the holding portion, and the piston rod is damaged. Does not occur.
According to the fifth aspect of the invention, in addition to the effect of any one of the first to fourth aspects, the clamping force is increased by the wedge effect due to the wedge surface, and the clamp arm holding (locking) at the clamping position is increased. While the reliability increases, the clamp arm comes into contact with the chamfered portion at the unclamping position and the retraction amount increases, so that interference between the clamp arm and the workpiece is effectively avoided. In addition, the operation of the clamp arm becomes smooth and the contact surface pressure with the chamfered portion is lowered, so that wear of the clamp arm is suppressed.
According to the invention described in claim 6, in addition to the effect of any one of claims 1 to 5, it becomes possible to reliably engage with the wedge surface corresponding to the variation in the clamp height (workpiece height), The reliability of the clamp becomes higher.
According to the seventh aspect of the invention, in addition to the effect of any one of the first to sixth aspects, it is possible to suppress wear of the piston rod and to cope with variations in the height of the clamp position.
According to the eighth aspect of the invention, in addition to the effect of the seventh aspect, the use of the rotation urging means makes it possible to smoothly operate the clamp arm.
According to the ninth aspect of the present invention, in addition to the effect of any one of the third to eighth aspects, the use of the lubricating member can surely lubricate the contact portion of the piston rod with the holding portion, thereby reducing wear. can do.

It is explanatory drawing of the clamp cylinder of the form 1, (A) shows a plane, (B) shows a back surface, (C) shows a side surface, respectively. It is an AA line sectional view, (A) shows a clamp position and (B) shows an unclamp position, respectively. It is a BB sectional view. It is CC sectional view taken on the line. It is an expanded sectional view of a holding part. It is explanatory drawing of the clamp state by the dispersion | variation in the height of a workpiece | work, (A) shows an intermediate position, (B) shows an over clamp position, respectively. It is an enlarged view which shows the upper end part of the piston rod in the clamp cylinder of form 2, and the rear end part of a clamp arm. It is explanatory drawing of clamp operation | movement, (A) shows an unclamping position, (B) shows an intermediate position, respectively. It is explanatory drawing of clamp operation | movement, (A) shows an intermediate position, (B) shows a clamp position, respectively.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Form 1]
A clamp cylinder 1 shown in FIGS. 1 and 2 has a bottomed cylindrical cylinder body 3 fixed to a lower surface of a rod cover 2 installed on a table or the like of a machine tool with bolts 4 and 4 and a cylinder chamber 5 inside. Is forming. In the cylinder chamber 5, a piston 6 is provided so as to be movable in the vertical direction of FIG. 2, and a piston rod 7 integrally formed on the upper portion thereof protrudes upward through the rod cover 2. In addition, a holding portion 8 is formed on the upper rear side of the rod cover 2 (the right side in FIG. 1 is the front side) so as to contact the rear side surface of the piston rod 7 and guide the expansion and contraction operation of the piston rod 7. As shown in FIG. 5, the sliding contact surface 9 of the piston rod in the holding portion 8 is a curved surface that bulges along an arc locus centering on an axis orthogonal to the piston rod 7. 10 is a dust seal provided on the upper surface of the penetrating portion of the piston rod 7 in the rod cover 2, and 11 is a lubricant holding ring as a lubricating member having a lubricant holding function (a fiber aggregate material in which synthetic fibers are fused with a rubber elastic body). Impregnated with oil such as grease).

Further, a connecting portion 12 is formed upward in front of the upper portion of the rod cover 2, and a clamp arm 13 is connected to the upper end of the connecting portion 12. The clamp arm 13 has an inverted L-shape in which a downward end portion 14 is pivotally mounted by a left-right swing shaft 15 so as to be swingable in the front-rear direction. A clamp bolt 17 having a lower end protruding downward through 16 is screwed.
Further, as shown in FIGS. 3 and 4, a through hole 18 is formed in the left-right direction at the upper part of the piston rod 7, and the shaft member 19 is rotatably accommodated in the through hole 18. The lower ends of the pair of left and right first links 21 and 21 are respectively fitted to the fitting sections 20 and 20 having a square cross section projecting from both ends, and both the first links 21 and 21 are integrated with the shaft member 19. It can be rotated. At the center of the lower surface of the shaft member 19, a pressing portion 22 that is chamfered at an eccentric portion and inclined so as to open the gap with the through-hole 18 in a rearward state with the first link 21 in a vertical posture is formed. Yes.

One ends of the second links 23 and 23 are rotatably connected to the upper ends of the first links 21 and 21 by pins 24, respectively, and the other ends of the second links 23 and 23 are the swing shafts in the clamp arm 13. A pin 24 is rotatably connected to an upper portion of the motor 15. The first link 21 and the second link 23 are the link mechanism of the present invention.
The front surface of the upper end of the piston rod 7 is formed with an inclined wedge surface 25 that recedes upward and a chamfer 26 that is continuous from the upper end of the wedge surface 25 and has a larger inclination angle than the wedge surface 25. A curved surface portion 27 that bulges along an arc locus centering on an axis parallel to the swing shaft 15 is formed on the rear surface of the upper end of the clamp arm 13. When the piston rod 7 extends, the wedge surface 25 comes into contact with the curved surface portion 27, so that the clamp arm 13 is pressed forward and rotated to the right.

  On the other hand, a shaft hole 28 that communicates with the through hole 18 and communicates with the lower cylinder chamber 5 is formed in the axial center of the piston rod 7. A push rod 29 is accommodated in the shaft hole 28 so as to be movable up and down, and a coil spring 30 is accommodated below the push rod 29. Reference numeral 31 denotes a screw that is screwed into the lower end of the shaft hole 28 and supports the lower end of the coil spring 30. Therefore, the push rod 29 is urged upward by the coil spring 30, and the upper end of the push rod 29 is brought into contact with the pressing portion 22 of the shaft member 19, whereby the push member 29 is attached to the shaft member 19 and the first links 21, 21 in the left rotation direction. Power will be granted. The push rod 29 and the coil spring 30 as an elastic member serve as the biasing means of the present invention.

  In the clamp cylinder 1 configured as described above, the rod cover 2 is fixed in a state where the lower surface of the rod cover 2 is in contact with the upper surface of the table T or the like of the machine tool on which the workpiece W is set, and provided on the rear surface of the rod cover 2. A drive source of pressure fluid (oil or air or the like) is connected to the push side port 34 and the pull side port 35 via a pipe (not shown). Therefore, when the pressure fluid is supplied from the drive source to the push-side port 34, the piston rod 7 extends, and the lower wedge surface 25 abuts on the curved surface portion 27 of the clamp arm 13 as described above, and the clamp arm 13 Rotate forward. Then, as shown in FIG. 2A, the clamp bolt 17 at the front end comes into contact with the upper surface of the workpiece W to clamp the workpiece W.

  At this time, a reaction force to the rear is applied to the piston rod 7 via the clamp arm 13, but since the rearward movement is restricted by the holding portion 8, the clamp arm 13 can clamp the workpiece W in a stable state. . In this clamped state, the upper end of the piston rod 7 is press-fitted between the holding portion 8 and the curved surface portion 27 of the clamp arm 13, so that a so-called wedge effect occurs and the supply of pressure from the drive source is cut off. Even if it happens, the clamped state by the clamp arm 13 is maintained. Further, since the sliding contact surface 9 of the holding portion 8 with the piston rod 7 is a curved surface, even if the piston rod 7 is inclined due to the component force of the wedge, the piston rod 7 is attached to the edge of the holding portion 8. Will not touch.

  Further, the wedge effect in the clamped state is exhibited in the range where the curved surface portion 27 of the clamp arm 13 contacts the wedge surface 25 even if the height H of the workpiece W varies. That is, as shown in FIG. 6A, when the height of the workpiece W is large (H + α), the wedge effect is exhibited at an intermediate position where the lower side of the curved surface portion 27 comes into contact with the upper side of the wedge surface 25. When the height of the workpiece W is small (H−α) as shown in FIG. 9, the clamping can be performed at the over-clamping position where the lower side of the curved surface portion 27 contacts the lower side of the wedge surface 25. The same applies between the intermediate position and the over clamp position.

  On the other hand, when releasing the clamping of the workpiece W (unclamping), when the pressure fluid is supplied from the driving source to the pulling side port 35, the piston rod 7 contracts downward, and the curved surface portion 27 of the clamp arm 13 by the wedge surface 25. Release the pressure. However, since the clamp arm 13 is connected to the piston rod 7 via the first and second links 21 and 23, the clamp arm 13 rotates counterclockwise as the piston rod 7 descends, and the piston rod 7 shown in FIG. At the bottom dead center, the clamp arm 13 reaches a position where the curved surface portion 27 comes into contact with the chamfered portion 26 of the piston rod 7. Therefore, the workpiece W can be taken out and replaced.

Since the clamp arm 13 including the clamp bolt 17 does not protrude forward from the front surface of the rod cover 2 at this unclamping position, the workpiece W is connected to the clamp arm 13 when replacing the workpiece W or the like. The possibility of interference is reduced. In particular, when the clamp arm 13 is released, the push rod 29 exerts a rotational biasing force on the shaft member 19, and the first link 21, 21 biases the clamp arm 13 counterclockwise via the second link 23, 23. Therefore, in the unclamped state, the clamp arm 13 does not accidentally rotate to the clamp position side due to its own weight or the like.
In the piston rod 7, the portion (S portion in FIG. 2) where the lubricant holding ring 11 provided on the rod cover 2 contacts at the unclamping position is the portion where the sliding contact surface 9 of the holding portion 8 contacts the clamping position. The position setting is Therefore, the sliding contact surface 9 that receives a large surface pressure by the piston rod 7 is lubricated by the oil content of the lubricant retaining ring 11, and wear of the sliding contact surface 9 is suppressed.

  As described above, according to the clamp cylinder 1 of the first aspect, the piston rod 7 and the clamp arm 13 are connected by the first and second links 21 and 23, and the first and second are coupled with the contraction operation of the piston rod 7. The clamp arm 13 is rotated to the unclamping position via the two links 21 and 23, and the urging means (push rod) is configured to rotate and urge the first link 21 toward the unclamping position of the clamp arm 13 in the piston rod 7. 29 and the coil spring 30), the biasing means is not exposed to the outside, and there is no possibility of malfunction due to adhesion of chips or the like. Further, since it is not necessary to provide a notch for the torsion spring in the clamp arm 13, the strength of the clamp arm 13 can be ensured, and the possibility of breakage even during long-term repeated use is reduced. Therefore, the clamp cylinder 1 excellent in reliability and durability can be obtained.

  In particular, here, the link mechanism includes a first link 21 having a base end connected to an end of a shaft member 19 rotatably provided to the piston rod 7, and one end connected to the tip of the first link 21. A push rod 29 provided with a second link 23 whose end is connected to the clamp arm 13, and a biasing means provided so as to be movable back and forth with respect to the pressing portion 22 formed in the eccentric part of the shaft member 19; By forming the push rod 29 with the coil spring 30 that presses the shaft member 19 toward the shaft member 19, an urging means that is not easily affected by chips, cutting oil, or the like in the piston rod 7 can be easily obtained.

Further, the piston rod 7 is slidably contacted with the rod cover 2, and the holding portion 8 is formed on the opposite side of the clamp arm 13 with the piston rod 7 sandwiched at the clamp position of the clamp arm 13. The rod 7 is prevented from falling.
Furthermore, since the sliding contact surface 9 of the piston rod 7 in the holding portion 8 is a curved surface that bulges along an arc locus centering on an axis orthogonal to the piston rod 7, the piston rod 7 may tilt. However, the piston rod 7 does not contact the edge of the holding portion 8, and the piston rod 7 is not damaged.

  On the other hand, a taper-inclined wedge surface 25 that presses the clamp arm 13 to the clamp position in accordance with the extension operation of the piston rod 7 at the extension side end of the piston rod 7, and the tip end side of the wedge surface 25. By forming the chamfered portion 26 which has a larger inclination angle than the wedge surface 25 and the clamp arm 13 abuts at the unclamping position, the clamping force increases due to the wedge effect by the wedge surface 25, and the clamping position While the clamping arm 13 is reliably held (locked) at the unclamping position, the clamping arm 13 abuts against the chamfered portion 26 at the unclamping position, and the retraction amount increases, so that the interference between the clamping arm 13 and the workpiece W occurs. Is effectively avoided. In addition, the operation of the clamp arm 13 becomes smooth and the contact surface pressure with the chamfered portion 26 is lowered, so that wear of the clamp arm 13 is suppressed.

The portion of the clamp arm 13 that contacts the piston rod 7 is a curved surface portion 27 that bulges along an arc trajectory centered on an axis parallel to the swing axis 15 of the clamp arm 13. Corresponding to the variation in the height (the height of the workpiece W), the wedge surface 25 can be reliably engaged, and the reliability of the clamp becomes higher.
In addition, by providing the rod cover 2 with a lubricant holding ring 11 that lubricates the piston rod 7 in the unclamping position with the contact portion S with the holding portion 8 in the piston rod 7 in the clamping position, The contact part S can be reliably lubricated and wear can be reduced.

[Form 2]
Next, another embodiment of the present invention will be described. However, the same reference numerals are given to the same constituent portions as those in the first embodiment, and redundant description is omitted.
In the clamp cylinder 1a shown in FIG. 7, a groove 36 having a semicircular cross section that opens to the rear surface is formed in the left-right direction at the rear end of the clamp arm 13, and the groove 36 is notched more than the groove 36. A key 37 having a semi-circular cross-section in which the portion is small and the chamfered portion 38 protrudes from the rear surface of the clamp arm is accommodated coaxially with the groove 36 and rotatable. In addition, a notch 39 is formed at an eccentric portion with respect to the center of rotation on the upper peripheral surface of the key 37.

  On the other hand, an insertion hole 40 communicating with the groove 36 and opening on the upper surface of the clamp arm 13 is formed above the key 37 and can be moved forward and backward with respect to the notch 39 of the key 37 in the insertion hole 40. A pressing pin 41 and a coil spring 42 that urges the pressing pin 41 toward the cutout portion 39 to contact the cutout portion 39 are provided. Reference numeral 43 denotes a screw that is screwed into the opening of the insertion hole 40 to position the upper end of the coil spring 42. Therefore, the key 37 is urged in the counterclockwise direction by the pressing pin 41 and the coil spring 42 serving as a rotation urging means.

In the clamp cylinder 1a configured as described above, in the unclamping position, as shown in FIG. 8A, the piston rod 7 is at the bottom dead center and the clamp arm 13 is also biased to the left rotation position. . At this time, the chamfered portion 38 of the key 37 is in contact with the chamfered portion 26 of the piston rod 7.
When the piston rod 7 is raised from here, the clamp arm 13 is also pressed through the key 37 and rotates to the right as shown in FIG. Therefore, the state in which the chamfered portion 38 is in contact with the chamfered portion 26 is maintained.

When the rotation of the clamp arm 13 proceeds, the contact position of the chamfered portion 38 of the key 37 is switched to the wedge surface 25 as shown in FIG. 9A, and a wedge effect is generated. When the piston rod 7 moves up as it is, the chamfered portion 38 of the key 37 slides relatively downward on the wedge surface 25 to press the clamp arm 13 to the clamping position of the workpiece W, as shown in FIG. Will do.
When the piston rod 7 is lowered from the clamp position, the clamp arm 13 is rotated to the unclamp position of FIG.

Thus, also in the clamp cylinder 1a of the above-described form 2, the urging means is not exposed to the outside, there is no possibility of malfunction due to adhesion of chips and the like, and the strength of the clamp arm 13 can be secured and reliable. The effect similar to the form 1 that is excellent in property and durability is obtained.
Here, in particular, a key 37 that rotates in accordance with the expansion and contraction of the piston rod 7 and relatively slides on the end portion on the extension side of the piston rod 7 is provided at a contact portion of the clamp arm 13 with the piston rod 7. As a result, wear of the wedge surface 25 and the chamfered portion 26 of the piston rod 7 can be suppressed, and variations in the height of the clamp position can be accommodated.

  Further, by providing a rotation urging means for urging the key 37 to the sliding position at the unclamping position of the clamp arm 13, the chamfered portion 38 of the key 37 and the wedge surface 25 on the piston rod 7 side are chamfered. The operation of the clamp arm 13 when switching between the portions 26 can be performed smoothly.

In the first and second aspects, the number of links of the link mechanism is not limited to two, and for example, one L-shaped link may be used, or conversely, three or more links may be used. Further, each link is not necessarily a pair of left and right, and a configuration in which the links are arranged at the center across the slits formed in the piston rod and the clamp arm is also conceivable.
Further, the biasing means of the link mechanism is configured to press the pressing portion formed by chamfering the shaft member with the push rod in the above embodiment, but may be configured to press the pressing piece protruded from the shaft member. is there.
In addition, the upper end shape of the piston rod can also be changed in design, such as omitting the chamfered portion to have only a wedge surface, or making the wedge surface and the chamfered portion a continuous curved surface portion.
On the other hand, the key shape of form 2 is not limited to the pressing piece protruding from the key, not the notch, and the rotation urging means is not limited to the pressing pin and the coil spring. It is possible to urge rotation using only the member.

  1, 1a ··· Clamp cylinder, 2 ·· Rod cover, 3 · · Cylinder body, 5 · · Cylinder chamber, 6 · · Piston, 7 · · Piston rod, 8 · · Holding part, 9 · · Sliding contact surface, 11 .... Lubricant retaining ring, 13 .... Clamp arm, 15 .... Oscillating shaft, 19 .... Shaft member, 21 ... First link, 22 .... Pressing part, 23 ... Second link, 25 ... Wedge surface, 26 ·· Chamfered portion, 27 ·· Curved portion, 28 · · Shaft hole, 29 · · Push rod, 30 · · Coil spring, 36 · · Groove, 37 · · · Key · 41 · · Pressing pin, W ..Work, T..Table, S..Contact part.

Claims (9)

A piston rod that expands and contracts by the supply of external pressure fluid, a rod cover that guides the expansion and contraction of the piston rod, and is connected to the rod cover so as to be swingable between a clamp position and an unclamp position, A clamp arm that includes a clamp arm that rotates to the clamp position as the piston rod extends,
The piston rod and the clamp arm are connected by a link mechanism, and the clamp arm is rotated to the unclamping position via the link mechanism in accordance with the contraction operation of the piston rod, and the link mechanism is inserted into the piston rod. And a biasing means for biasing the clamp arm to the unclamping position side of the clamp arm. The link mechanism includes a first link having a base end connected to an end of a shaft member rotatably provided to the piston rod, one end connected to the tip of the first link, and the other end connected to the clamp arm. While forming from the second link to be connected,
The urging means is formed of a push rod provided so as to be movable back and forth with respect to a pressing portion formed at an eccentric portion of the shaft member, and an elastic member that presses the push rod toward the shaft member. The clamp cylinder according to claim 1, wherein   3. The holding portion located on the opposite side of the clamp arm is formed on the rod cover so that the piston rod is in sliding contact with the piston rod at the clamp position of the clamp arm. Clamp cylinder as described.   The clamp cylinder according to claim 3, wherein the sliding contact surface of the piston rod in the holding portion is a curved surface that bulges along an arc locus centering on an axis orthogonal to the piston rod.   A taper-inclined wedge surface that presses the clamp arm to a clamp position in accordance with the extension operation of the piston rod at the end of the piston rod on the extension side, and the wedge surface that is located on the tip side of the wedge surface The clamp cylinder according to any one of claims 1 to 4, further comprising a chamfered portion that has a larger inclination angle and abuts the clamp arm at the unclamping position.   The contact portion of the clamp arm with the piston rod is a curved surface portion that bulges along an arc locus centering on an axis parallel to the swing axis of the clamp arm. The clamp cylinder according to any one of 5.   The clamp arm is provided with a key that rotates in accordance with the expansion / contraction operation of the piston rod and relatively slides on an extension side end of the piston rod at a contact portion with the piston rod in the clamp arm. The clamp cylinder in any one of Claims 1 thru | or 6.   The clamp cylinder according to claim 7, further comprising: a rotation urging unit that urges the key to a sliding position at an unclamping position of the clamp arm.   9. A lubricating member that lubricates a contact portion of the piston rod at the clamp position with the holding portion with respect to the piston rod at the unclamp position is provided on the rod cover. A clamp cylinder according to any one of the above.

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