DE9114837U1 - Hydraulically operated swing clamp - Google Patents

Description

Hydraulically operated Shoe spanner.

The invention relates to a hydraulically actuated clamping device, in particular for clamping a workpiece or tool on a processing machine, with a clamping calender that can be moved axially in a first cylinder chamber of a housing, the calender rod of which is firmly connected to it and carries a clamping arm at its end protruding from the housing, with a control piston arranged coaxially to the clamping calender in a second cylinder chamber of the housing, axially displaceable and rotatable therein, which carries a control piston rod that projects into a cavity of the clamping calender and the clamping piston rod, which is connected to the clamping calender in a rotationally fixed but axially displaceable manner, and with at least one control cam connected to the control calender, which has a helical section adjacent to the control calender and into which at least one control ball mounted in a ring fixed in the housing engages.

In a known swing clamp of this type (�Egr;&Rgr;-31�THgr; 2D A2), the clamping calves in the first cylinder chamber can be acted upon from both sides. A part of the control calves protrudes into the first cylinder chamber and can thus be acted upon in one direction of displacement from the first cylinder chamber and in the other direction of displacement from the second cylinder chamber. Both sides of the control piston can be acted upon over the entire piston surface, so that relatively high pressures act on the control calves, which move the control piston and cause the control calves to rotate around their axis via the helical section of the control curves. Since the control piston is connected to the clamping calves in a rotationally fixed manner via its control calves rod, which is described in more detail below,

piston, when it rotates it also turns the clamping calves and the clamping arm provided at the end of the clamping piston rod. If the clamping arm encounters any resistance, the well-known swing clamp can be damaged. For this reason, an overload protection device must be provided at a suitable location, which disengages when the clamping arm is blocked. However, if such a disengagement has occurred, the clamping arm must be manually rotated back to its original position relative to the control piston after the fault has been rectified, which requires a corresponding amount of work. The well-known swing clamp also has a relatively complicated structure. In order to connect the control piston rod to the clamping piston in a rotationally fixed but axially movable manner, the control piston rod has a hexagonal cross-section and engages in a guide sleeve fixed in the clamping piston with a recess that is also hexagonal. These parts are expensive to manufacture. In addition, the known swing clamp has two helical control curves on a projection that is located on the side of the control piston opposite the control piston rod. These helical control curves can therefore only be manufactured in a separate operation. So that the known swing clamp can be supplied with pressure media via just two connections, it also has a hydraulically unlockable check valve in its housing. Due to the design of the known swing clamp and its hydraulic circuit, the piston seal of the clamping piston is pressurized in its extended position. This creates considerable friction between the piston seal and the cylinder wall of the first cylinder chamber.

to overcome this, a considerable force must act on the control piston. This is also a reason why the surface area of the control piston cannot be reduced in size and makes overload protection necessary. It is also necessary to provide a large number of control balls so that the required high torque is generated by the helical control grooves. In addition, the known swing clamp can malfunction because when the clamping piston is extended, pressure can build up in the second cylinder chamber via the check valve, which is opened at the same time, as a result of the dynamic pressure, which also shifts the control piston during the extension movement of the clamping piston and thus causes both pistons to swivel unintentionally.

The invention is based on the object of creating a hydraulically operated swing clamp of the type mentioned at the beginning, which is simpler in construction and in which an overload protection device can be omitted.

This is achieved according to the invention in that the control piston rod has an annular piston sealed against it at its free end protruding into the cavity, that the control curve is incorporated into the outer surface of the control piston rod, which has an axially extending section adjacent to the annular piston in its area protruding into the cavity, to which the screw-shaped section is directly connected towards the control piston, that a guide ball is mounted in a stationary, rotatable manner in the tensioning piston, which exclusively engages in the axially extending section, that the ring is arranged between the tensioning piston and the control piston and the control ball is mounted in a stationary, rotatable manner in the tensioning piston.

_-I4-

is rotatably mounted, which alternately engages in the axial and the screw-shaped section, that the control calves have a tube extension on their side facing away from the control calves rod, which can be moved in a sealed manner in the housing, and that in order to extend the clamping calves rod, only the part of the cavity located between the clamping arm and the ring piston can be pressurized with pressure medium via the tube extension and a central axial bore that passes through the control piston and the control piston rod.

The new swing clamp is constructed with a few, easy-to-manufacture components. In particular, the parts required to guide the control piston rod against rotation relative to the clamping calves and the parts required to pivot the control calves are particularly easy to manufacture. The control groove, which has an axial section and a helical section immediately adjacent to it, can be manufactured in one operation ^and fulfils two functions. On the one hand, it serves to prevent rotation but to provide an axially movable connection between the control piston rod and the clamping calves, and on the other hand, it also serves to rotate the control piston relative to the housing. The guide ball engaging in the control groove and the control ball are commercially available components. They can each be mounted in a simple manner in a radial bore in the clamping piston or in the ring so that they can rotate in a fixed position. The ring piston used to pivot the control piston back to its starting position has a relatively small effective ring area, since the ring calves are arranged inside the clamping calves rod. This ensures that the force that actuates the control piston is significantly smaller than the actual clamping force, so that the destruction of the swivel mechanism is prevented when the clamping arm is blocked.

therefore, no overload protection is required and the manual alignment of the clamping arm relative to the control piston, which is required when using an overload protection, is no longer necessary.

A particularly advantageous embodiment of the invention consists in the fact that the valve stem clamp has only two connections for supplying pressure medium, of which the first connection is connected to the pipe socket via a first connecting line, and the second connection is connected to the side of the first cylinder chamber facing the clamping arm via a second connecting line, that a hydraulically releasable check valve is arranged in the second connecting line, the spring-loaded valve ball of which in its first closed position blocks a first passage to the side of the second cylinder chamber facing away from the clamping arm as long as the pressure in the first connecting line is below a predetermined value, that the hydraulically releasable check valve has a switching piston which can be acted upon by the pressure in the first connecting line and which acts on the valve ball via a tappet, that an additional spring arrangement is arranged on the switching piston and holds it in its rest position corresponding to the first closed position of the valve ball as long as the pressure in the first connecting line is below the predetermined value, and that opposite the first passage a second passage leading to the first cylinder chamber is provided, which can be closed by the valve ball under the action of the switching piston and the tappet as soon as the pressure in the first connecting line exceeds the predetermined value.

This design has the advantage that the second cylinder chamber assigned to the control piston can only be pressurized when the clamping cylinder is in its fully extended position.

This prevents malfunctions of the swing clamp. In addition, the piston seal of the clamping piston is not subjected to pressure in its fully extended position. This means that the torque required by the control piston to pivot the clamping calves can be

1D. This also contributes to a simplification of the structure. The lower torque also contributes to the fact that the piston area required to extend the control cylinder can be kept smaller, which means that less force is exerted on the swivel mechanism and damage to the swivel mechanism can be avoided even better in the event of the swivel arm becoming blocked.

Further advantageous embodiments of the invention are 2G characterized in the remaining subclaims.

The invention is explained in more detail below using an embodiment shown in the drawing.
25

Figure 1 shows a longitudinal section of the swing clamp in the rest position with the clamping arm retracted, Figure 2 shows a longitudinal section with the clamping arm fully extended.

tension piston rod,
3G Figure 3 is a longitudinal section with fully extended,

clamping piston rod rotated by 90°, Figure k shows a longitudinal section in clamping position, Figure 5 shows a cross section along the line UW of Figure it,

Figure 6 Details of the switchable check valve

in longitudinal section,

Figure 7 is a view of the swing clamp in the direction Uli of figure U.

The housing 1 has a first cylinder chamber 2 in which the clamping piston 3 can be moved. The clamping piston 3 is firmly connected to the clamping piston rod U , which carries the clamping arm 5 at its free end. In a second cylinder chamber of the housing 1, a control piston 7 is arranged so as to be movable coaxially to the clamping piston 3 and rotatable about its axis. This control piston 7 has a control piston rod 8 on one side, which projects into a cavity 9 of the clamping piston 3 and the clamping piston rod U. On the other side, the control piston 7 carries a tubular extension 10 which is sealed off from the housing 1 by means of the seal 11 and is movable in it.

The control piston rod θ carries an annular piston 12 sealed against the cavity 9 at its end protruding into the cavity. A control cam 13 is incorporated into the surface 8a of the control piston rod 8, which has an axially extending section 13a adjacent to the annular piston 12 in its area protruding into the cavity 9. This axially extending section 13a is directly connected to a helical section 13b towards the control piston 7. In the clamping collar 3, a guide ball 15 is mounted in a radial bore 1^+ so that it can rotate in a fixed position relative to the clamping piston 3 and engages exclusively in the axially extending section 13a of the control cam 13. A ring 16 is arranged between the clamping collar 3 and the control collar 7 or between the two cylinder chambers 2 and 6 and is fixed in the housing 1. In a

A control ball 1Θ is mounted in a stationary, rotatable manner in the radial bore 17 of this ring, which, depending on the position of the control piston Θ, alternately engages in the axial section 13a or the helical section 13b of the control curve 13.

Furthermore, it is advantageous to provide a second similar control curve 13 ¹ in the control piston rod 8, diametrically opposite to the control curve 13, in which

^)Q before a guide ball 15' and a control ball 18' engage in a corresponding manner. The diametrically opposed arrangement of two control curves 13, 13' prevents transverse forces on the control piston rod 8. If necessary, additional control grooves can also be provided in the control piston rod 8.

The control piston 7 and the control piston rod 8 also have an axial bore 19 which passes into the pipe extension 1G. The part 9a of the cavity 9 located between the clamping arm 5 and the annular piston 12 can be pressurized with pressure medium via this axial bore 19.

The swing clamp has only two connections A, B for the pressure medium supply. The first connection A is connected to the pipe socket 10 via a first connecting line 2D. The second connection B is connected to the side of the first cylinder chamber 2 facing the clamping arm 5 via a second connecting line 21a, 21b, 21c. In this second connecting line

3Q device 21a - 21c is provided with a hydraulically releasable check valve 22 with a valve ball 2k loaded by the spring 23. Under the action of the spring 23, the ball 2k normally blocks a first passage 25 to a line 26 which opens on the side of the second cylinder chamber 6 facing away from the clamping arm 5.

The hydraulically releasable check valve 22 also has a switching valve 27 which is connected to a tappet 2Θ and can act on the valve ball Zk via this. This switching valve 27 is located in the area of the first connection A or the first connecting line 2G and is acted upon by the pressure prevailing in A or 2D.

Furthermore, an additional spring arrangement 29 is provided which acts on the switching cylinder 27 and holds it in its rest position, shown in Figure 6, corresponding to the closed position of the check valve 23, Zk , as long as the pressure in the first connecting line 20 is below a predetermined value. The spring force of the second spring arrangement 29 is expediently dimensioned such that the switching cylinder 27 is held in the rest position until the pressure in the first connecting line has reached approximately a quarter of the operating pressure, the operating pressure being, for example, 20 °C bar.

Opposite the first passage 25, the check valve 22 has a second passage 30 which leads to the part 21c of the second connecting line. This second passage 30 can be closed by the valve ball Zk as soon as the pressure in the first connecting line 20 exceeds the predetermined value and the switching piston 27 is thereby raised against the force of the second spring arrangement 29. As a result, the tappet 28 presses the valve ball Zk upwards according to Figure 5, whereby the second passage 30 is closed.

The swing clamp works as follows:

In the initial position, the parts of the swing clamp assume the position shown in Figure 1, with the clamping arm 5 completely sunk into the housing 1. If the clamping arm 5 is now to be used to clamp a tool

(- a of the workpiece are extended, then connection A is pressurized. This pressure is initially less than a quarter of the operating pressure, i.e. less than 100 bar, whereby the hydraulically releasable check valve 22 in its position shown in Figure 1 and

/|r> remains in the position shown. The pressure prevailing at connection A is propagated via the first connecting line 20, the pipe extension 10, the axial bearing 19 into the upper part 9a of the cavity 9, and acts on the surface bordering the cavity 9a towards the clamping arm 5.

-I5 9b and the surface 12a of the ring piston 12. As a result, the tensioning piston rod k is extended upwards out of the housing, whereby the tensioning piston 3 displaces the pressure medium contained in the first cylinder chamber 2 via the part 21c of the connecting line. Since at the same time the

2Q ring surface 12a of the ring piston 12 is subjected to pressure, the control piston 7 is held in the rest position shown in Figure 1. When the clamping piston rod k is extended relative to the control piston rod 8, the guide ball 15 moves in the axial section 13a of the control curve 13, whereby a twisting of the clamping piston relative to the control piston rod 8 is avoided and the clamping piston rod k is extended linearly. The pressure medium contained in the cylinder chamber 2 or part 2c is pressureless or is under the so-called dynamic pressure.

3Q In hydraulic systems, dynamic pressure is understood to be the pressure that is created by frictional resistance in pipes, valves, etc. The pressure medium escaping through the connecting pipe 21c could, in the position of the check valve shown in Figures 1 and 5,

tiles 22 via part 21b and part 21a into the tank. However, since the dynamic pressure in these line parts 21b, 21a may be too high, a bypass check valve 31 can be provided, through which the pressure medium can escape more easily from the line part 21c.

When the tensioning piston rod U is fully extended as shown in Figure 2, the tensioning piston 3 rests on the upper end 2a of the cylinder chamber 2 via the needle bearing 32. As a result, the pressure in the connecting line 2G rises above the predetermined value of approx. 100 bar and pushes the switching piston 27 into its upper position. The tappet 28 pushes the valve ball CLOSED upwards, opening the first passage 25 and closing the second passage 30. The second connection B is then also pressurized, which is propagated via the line parts 21a, 21b, the first passage 25 and the line 26 to the second cylinder chamber s. As a result, the lower annular surface 7a of the control cylinder 7 facing away from the tensioning arm 25 is pressurized. Since this ring surface 7a is larger than the ring surface 12a of the ring piston 12, the control cam is pushed upwards into its position shown in Figure 3. The control ball 18 held in the ring 16 enters the helical section 13b of the control cam 13. Under the effect of the helical section 13b, the control cam rod 8 is rotated about its axis and also takes the clamping piston _with the clamping piston rod k with it. The clamping arm 5 is thereby pivoted by 90° into the position shown in Figure 3. In this position, the clamping arm is now above the tool or workpiece to be clamped. During the axial movement of the control piston 7 and

By rotating the control cylinder 7 and the tensioning piston 3, the tensioning piston rod k is held in its fully extended position by the pressure acting on the surface 9b. Since at the same time the second passage 3D <- is closed by the raised valve ball 2h ,

This prevents the upper piston surface 3a of the clamping calve 3 from being subjected to pressure via the line part 21c. This ensures that the clamping piston rod remains in its fully extended position during the swinging and is not moved into the clamping position during the swinging.

As soon as the clamping arm 5 has been pivoted into its clamping position

-]5, both connections A and B are depressurized. As a result, the switching piston 27 is pushed back into its rest position shown in Figures U and 6 under the action of the spring arrangement 29. The valve ball Zh can now also be moved back into its rest position under the action of the spring 23.

2Q return to the initial position. It closes the first passage 25 and opens the second passage 3D. If the second connection B is now subjected to pressure, this pressure can be propagated via the line parts 21a, 21b and 21c to the upper part of the first cylinder chamber and act on the upper ring surface 3a of the clamping piston 3 facing the clamping arm 5. The latter moves downwards under this pressure until its clamping arm 5 rests against the tool or workpiece to be clamped and pulls it firmly towards the housing 1. The clamping process is thus completed. During the downward movement of the clamping calender 3, the control calender remains in its upper position shown in Figure h . Since during the downward movement of the clamping piston 3 the guide ball 15 engages in the axial section 13a of the control curve 13 and the stationary

Since the control calender rod B is secured against rotation by the control ball 18, the tension calender 3 cannot twist during its downward movement.

To release the tension, pressure is again applied to connection A, whereby pressure is again applied to part 9a of cavity 9 via axial bore 19. Under the influence of the pressure acting on surface 9b, the tensioning piston rod U is moved upwards

ig until it has reached its upper end position. A corresponding pressure now builds up in connection A, which also acts on the ring surface 12a of the ring calve 12 and pushes the control piston down into its starting position. In this case, under the influence of the

-] 5 screw-shaped section 13b and the control ball the control piston rod 8 is rotated back to its starting position. It also rotates the clamping piston 3, which causes the clamping arm 5 to be pivoted back from its clamping position to its rest position. The parts

2Q now return to the position shown in Figure 2. If connection A is then depressurized again, the switching piston 27 returns to its lower position and the valve ball 2k also returns to its initial position shown in Figure 6.

When pressure is applied to connection B, the pressure can propagate through the now opened passage 30 to the annular surface 3a of the clamping piston 3 and the clamping piston is thereby pressed downwards into its rest position. A rotation of the clamping piston 3 relative to

3Q of the control piston rod 8 is prevented in the manner described by engagement of the guide ball 15 in the axial section 13a.

The extension and retraction of the clamping calves 3 and the pivoting movement caused by actuation of the control calves 7 can also be reversed in any position of the clamping device according to the invention if this is necessary for any reason.

In the above considerations, it was initially ignored that when pressure is applied to connection A, the annular surface 10a of the pipe extension 10 is also subjected to pressure.

ig. This exerts a force on the control piston 7 which is opposite to the force which acts on the ring surface 12a of the ring piston 12 when pressure is applied to connection A. However, since the ring surface 12a is larger than the ring surface 10a, when pressure is applied to connection A, the control piston rod ß is always subjected to a pressure directed away from the clamping arm 5, i.e. downwards, which pushes the control piston rod B and thus also the control piston 7 into its starting position.

The check valve 21 used in the tensioner according to the invention acts like a 3/2-way valve 1 thanks to the second spring arrangement 29 and thanks to the second passage 30 which can be closed by the valve ball CLOSED, which always directs the pressure medium flow from the second connection B, depending on whether the connection A is pressurized or not, only to the annular surface 3a of the tensioning piston or to the annular surface 7a of the control piston 7. In addition, the check valve 22 switches thanks to the spring

3Q arrangement 29 only switches at a predetermined higher pressure of, for example, 100 bar. This prevents malfunctions and in particular ensures that the switch from linear movement of the clamping piston 3 to swivel movement only takes place when

the tensioning piston 3 is in its extended end position.

Since the effective area 9b when the clamping calve 3 is extended is significantly smaller than the ring area 3a that causes the clamping calve to retract, it is ensured that the pressure for extending the clamping calve 3 is always greater than any dynamic pressure that may be present in connection B and the connecting line 21a - 21c. If this dynamic pressure were greater, then this dynamic pressure could possibly cause swiveling during the extension movement (with the passage 25 open). It is advisable for the pressurizable area 9b that delimits the cavity 9 towards the clamping arm 5 and/or the ring area 12a of the ring calve to be smaller by a factor of about 6 than the ring area 3a of the clamping piston.

In addition, the ring surface 7a of the control piston 7 adjacent to the pipe extension 10 should advantageously be twice as large as the difference between the ring surface 12a of the ring calve 12 minus the ring surface 10a at the free end of the pipe extension 10. This ensures that the retraction force and extension force acting on the control piston rod B and thus also the torque generated thereby to pivot the clamping calve 3 are the same in both directions of rotation.

V/an V/arteil is also when the difference between the annular surface 12a of the annular piston 12 minus the annular surface 10a of the pipe extension 10 is equal to the product of the diameter of the annular surface 3a of the clamping calve 3 facing the clamping arm 5 multiplied by 5.

Since in the tensioner according to the invention the control piston 7 and the control piston rod &thgr; are provided with an axial bore 19 this axial bore can also be provided with a

to accommodate a central control rod 33 which is firmly connected to the upper end of the clamping rod k . The control rod 33 is guided through the axial bore 19 and the pipe extension 1D, with a sufficient distance between these parts to allow pressure medium to pass through. The control rod 33 is also sealed off from the housing 1 by the seal 3k . At the end protruding from the housing, the control rod 33 carries a switching cam 35 which interacts with several switching elements 36, 37. The switching elements 36, 37 are arranged at mutual axial and circumferential distances according to the respective end positions of the clamping arm 5. In this way, it can be determined via the switching elements 36, 37 whether the clamping arm 5 is in its rest position shown in Figure 1 or in its clamping position shown in Figure 3.

Claims (1)

- 17 claims 1. Hydraulically actuated clamping device, in particular for clamping a workpiece or tool on a processing machine, with a clamping piston which is axially displaceable in a first cylinder chamber of a housing, the piston rod of which is firmly connected to it and carries a clamping arm at its end protruding from the housing, with a control piston arranged coaxially to the clamping piston in a second cylinder chamber of the housing, axially displaceable and rotatable therein, which carries a control piston rod which projects into a cavity of the clamping piston and the clamping piston rod and which is connected to the clamping piston in a rotationally fixed but axially displaceable manner, and with at least one control cam connected to the control piston, which has a helical section adjacent to the control piston and in which at least one control ball mounted in a ring fixed in the housing engages, characterized in that the control piston rod (8) carries at its free end protruding into the cavity (9) an annular piston (12) which is sealed relative to the latter, that in the jacket surface (8a) of the Control piston rod (8) is incorporated with the control cam (13, 13'), which has an axially extending section (13a) adjacent to the ring piston (12) in its area projecting into the cavity (9), to which the helical section (13b) is directly connected towards the control calve (7), that a guide ball (15, 15') is rotatably mounted in the clamping calve (3) in a fixed manner, which guide ball extends exclusively into the axially extending section 3Q (13a) engages, that the ring (16) is arranged between the clamping calves (3) and the control piston (7) and the control ball (18, 18') is rotatably mounted in it, which alternately engages in the axial (13a) and in the helical section (13b), that the Control calves (7) have a tubular extension (1G) on their side facing away from the control piston rod (8) which can be moved in a sealed manner in the housing (1), and in that in order to extend the clamping calves rod ( k ) only the part (9a) of the cavity (9) located between the clamping arm (5) and the annular piston (12) can be pressurized with pressure medium via the tubular extension (1G) and a central axial bore (19) passing through the control piston (7) and the control piston rod (8). 2. Schuenk clamp according to claim 1, characterized in that two similar control grooves (13, 13') are arranged diametrically opposite each other on the control piston rod (8) and that a corresponding number of guide and control balls (15, 15'; 18, 18') are mounted in the tensioning piston (3) and the ring (16). 3. Schüjenk clamp according to claim 1, characterized in that the pressurizable surface (9b) delimiting the cavity (9) in the direction of the clamping arm (5) and/or the annular surface (12a) of the annular piston (12) is smaller than the annular surface (3a) of the clamping piston (3) facing the clamping arm (5). h. Schüjenk clamp according to claim 3, characterized in that the pressurizable surface (9b) delimiting the cavity (9) towards the clamping arm (5) and/or the annular surface (12a) of the annular piston (12) is smaller by a factor of approximately 6 than the annular surface (3a) of the clamping piston (3). 5. Swing clamp according to one of claims 1 - h , characterized in that the annular surface (7a) of the control piston adjacent to the pipe extension (1Q) is twice as large as the difference of the annular surface (12a) of the annular piston (12) minus the annular area (10a) at the free end of the pipe extension ( 10) . 6. Schüjenk clamp according to claim k and 5, characterized in that the difference between the annular area (12a) of the annular piston (12) minus the annular area (1Da) of the tubular extension (10) is equal to the product of the square root of the annular area (3) of the clamping piston facing the clamping arm (5) multiplied by 5. 7. Swing clamp according to one of claims 1-6, characterized in that the swing clamp has only two connections (A, B) for its pressure-IG medium supply, of which the first connection (A) is connected to the pipe extension (10) via a first connecting line (20) and the second connection (B) is connected to the clamping arm via a second connecting line (21a, 21b, 21c). (5) facing side of the first cylinder chamber (2), that in the second connecting line (21a, 21b, 21c) a hydraulically releasable check valve (22) is arranged, the spring-loaded valve ball (.Zh) of which in its first closed position blocks a first passage (25) to the side of the second cylinder chamber (6) facing away from the tensioning arm (5) as long as the pressure in the first connecting line (20) is below a predetermined value, that the hydraulically releasable check valve (22) has a switching piston (27) which can be acted upon by the pressure in the first connecting line (20), which acts on the valve ball (2U) via a tappet (28), that an additional spring arrangement (29) acts on the switching piston (27) and in its first closed position of the valve ball (2^t) corresponding rest position as long as the pressure in the first connecting line (20) is below the predetermined value, and that opposite the first passage (25) a second passage (30) leading to the first cylinder chamber (2) is provided, which is The valve ball (2U) can be closed under the action of the switching valve (27) and the tappet (28) as soon as the pressure in the first connecting line (20) exceeds the predetermined value. &THgr;. Swing clamp according to claim 7, characterized in that the spring force of the second spring arrangement (29) is dimensioned such that the switching piston (27) is held in the rest position until the pressure in the first connecting line (20) has reached approximately a quarter of the operating pressure. 9. A clamp according to one of claims 1 - &THgr;, characterized in that a central roller rod (33) is firmly connected to the clamping piston rod (U) , which is guided through the central axial bore (19) of the clamping piston rod (8), as well as of the clamping calves (7) and the tubular extension (10) and is guided out of the housing (1) in a sealed manner, and that 2G the end protruding from the housing interacts with several switching elements (36, 37) which are arranged at mutual axial and circumferential distances according to the respective end positions of the clamping arm (5).