EP2921260B1 - Pneumatically operable working machine - Google Patents

Description

The invention relates to a pneumatically operable working device, in particular for use in the bodywork of the motor vehicle industry, with a cylinder having a cylinder housing, a displaceable in this piston and a connected thereto, linearly displaceable and led out of the cylinder housing, not variable-length piston rod, and with a connected to the cylinder housing head housing, wherein a projecting into the head housing portion of the piston rod with at least one toggle lever for pivoting a toggle associated arm, in particular gripping arm or clamping arm cooperates, said arm in the head housing stored and pivotable between a closed position and an open position.

Such a working device, which includes the features of the preamble of claim 1, is known from DE 296 15 157 U1 known. In this two toggle lever pivotally engage directly on the located in the head housing end of the piston rod. Here, two gripping arms between a closed position and an open position are pivotable. In the closed position, the gripping arms are arranged parallel to each other. A arranged in the region of the free end of the piston rod bearing axis for the two toggle lever is provided at the end with bearing rollers, which are guided in guide grooves of the head housing. - Due to the direct connection of the toggle lever to the piston rod, the opening angle of the gripper arms is not adjustable.

Pneumatically operated equipment having gripping or clamping arms, and in which a non-variable-length piston rod is used, are further from the DE 10 2004 040 606 B3 . EP 2 241 402 A1 and US RE 41,223 E known.

In the EP 2 548 700 A1 a pneumatically operable working device is described in which a piston of a cylinder is positioned in the open position of a clamping arm in the region of a bottom of the cylinder housing. In order to adjust the opening angle of the clamping arm, the piston rod is designed variable in length and has piston rod parts with threaded portions, wherein the piston rod parts are screwed together. By turning the bottom of the cylinder housing facing the piston rod part arranged in the region of the bottom piston can be changed by externally accessible means for rotating this piston rod part, the length of the piston rod and thus the opening angle of the clamping arm can be adjusted continuously.

Object of the present invention is to develop a working device of the type mentioned so that this, with structurally simple design, with respect to the open position of the arm is infinitely adjustable.

The object is achieved by a pneumatically operable working device, which is designed according to the features of patent claim 1.

In the pneumatically operable working device according to the invention, the open position of the arm, in particular of the gripping arm or clamping arm, is infinitely adjustable. In this case, the piston rod has a threaded portion and receives in the region of the threaded portion an adjustable in the longitudinal direction of the piston rod stop member. The stop member is in the open position of this arm to a stationary relative to the head housing system. The piston rod is rotatable with respect to its longitudinal axis. It takes in the region of the knee lever end facing a bearing element for the toggle. The piston rod is rotatable with respect to this bearing element.

Due to this design of the working device, the stop member can be changed in its position relative to the piston rod, based on the axial direction of the piston rod, whereby by adjusting the abutment portion of the opening angle of the arm is infinitely adjustable. At this opening angle, the stop member contacts the station relative to the head housing stationary.

The working device may be designed such that the cylinder and the head housing constitute separate structural units or a common structural unit.

The stop member is in particular rotationally fixed in the head housing positioned. If the piston rod is rotated with respect to its longitudinal axis, and thus changes the position of the stop member in the direction of the longitudinal axis of the piston rod to this, therefore, the stop member is not rotated and displaced only in the axial direction of the piston rod. This positioning of the stop member in the head housing can be achieved in different ways, for example by a guide of the stop member in the direction of the longitudinal axis of the piston rod in the head housing, or by a non-circular design of the stop member, wherein the non-circular outer contour of the stop member cooperates with a correspondingly shaped inner contour of the head housing.

The relative to the head housing stationary system can be designed in different ways. The stationary system has the task to form the bearing surface for the stop member, which prevents further contact with the abutment member on the stationary system further axial displacement of the stop member and thus defines the open position of the arm. In particular, it is provided that the contact surface extends orthogonal to the longitudinal axis of the piston rod. In this case, a contact surface of the abutment part extending orthogonally to the longitudinal axis of the piston rod interacts with the abutment surface upon contact of the abutment part.

To ensure that during operation of the implement no adjustment of stop member and piston rod, thus no adjustment of the open position of the arm, it is provided that the thread between the piston rod and connector is self-locking.

Structurally particularly easy adjustment of the position of the stop member is possible when a head housing facing away from the bottom of the cylinder housing means for rotating the piston rod in the closed position of the arm has arranged in the region of the bottom piston. These means in particular pass through the floor and can preferably be displaced in the direction of the longitudinal axis of the piston rod to be brought into engagement with the piston rod. It is then possible to rotate the piston rod from outside the cylinder housing. If the stop member is in the desired set position, the means are again disengaged from the piston rod. This takes place, for example, when the cylinder is pressurized by the pressure medium.

It is also considered advantageous if a head housing facing away from the bottom of the cylinder housing means for axially displacing the piston rod in the closed position of the arm with arranged in the region of the bottom piston in order to move out the toggle lever from an over-center position. This means for axially displacing the piston rod in the closed position of the arm is provided so as to allow, in the closed position of the arm, the supply of fluid to the cylinder to allow fluid-independent release of the arm from the over-center position of the toggle lever. To achieve this, it is only necessary to exert a force on the piston rod via the means for axial displacement of the piston rod, whereby the piston rod is moved slightly axially and the toggle lever is pivoted from the over-center position. In general, the pivot angle of the toggle lever from the dead center position in the over-center position is a fraction of an angular degree, so that it is only necessary to move the toggle from the over-center position to move the piston rod by means of the axial displacement of the piston rod by a small distance, which corresponds to this small angle.

It is considered particularly advantageous if the means for axial displacement of the piston rod have the means for rotating the piston rod. The means are in the simplest manner as in the bottom of the cylinder housing slidably and sealed to the bottom of the plunger formed, which has a receptacle for a tool for rotating the plunger outside of the cylinder housing and within the cylinder housing a receptacle for rotationally fixed engagement in a receptacle of this facing the end of the piston rod. When inserted into the piston rod ram, the piston rod can be moved axially by applying a striking force on the plunger and thus the toggle lever can be moved from the Übertotpunktstellung. Regardless of this, the plunger has the task of rotating the plunger by means of the tool, the piston rod about its longitudinal axis and thus adjust the stop member with respect to the piston rod.

The pneumatically operated implement has in particular a toggle for pivoting an associated arm, or in particular two toggle lever, each of the two toggle lever is used to pivot an arm associated with this toggle. The arm is in particular a gripping arm.

The toggle lever or the toggle lever are arranged in the closed position of the arm or the arms, in particular in an over-center position. A further pivoting of the respective toggle lever on the Übertotpunktstellung addition is prevented by a stop, which can be arranged arbitrarily and has the task to prevent axial displacement of the piston rod or with this piston rod cooperating components in the direction of the bottom of the cylinder housing.

According to a preferred embodiment of the invention it is provided that the bearing element has on opposite sides receptacles for the pivotable mounting of two hinge connectors which are pivotally connected in the region of the bearing element facing away from the ends with the two arms at a distance from the pivot axes of the arms, wherein the pivot axes the joint connector and the arms are arranged parallel to each other. On the respective side of the bearing element, thus laterally with respect to the longitudinal axis of the piston rod, the receptacles are thus provided for the pivotable mounting of the two joint connectors. This design allows a structurally simple connection of the two joint connectors, which interact with the arms.

If only one arm is present in the implement, the same bearing element can be used for the sake of standardization of the implement, in which case only one articulated connector will be connected to the bearing element for connection to one arm, while the other receptacle of the bearing element does not receive a hinge connector.

If the bearing element accommodates the two joint connectors, it is considered to be particularly advantageous if the bearing element, the joint connectors and the arms are arranged symmetrically with respect to a plane passing through the longitudinal axis of the piston rod. This results in a symmetrical design of the implement in the region of the head housing and the two arms, which introduced into the two arms gripping or clamping forces when contacting the working device associated component, such as a body panel, are symmetrically introduced into the implement.

It is considered to be particularly advantageous if the bearing element is guided in a guide of the head housing in the direction of the longitudinal axis of the piston rod. This guide is important not only under the aspect of the actual leadership of the bearing element in the head housing, but also under the aspect of the introduction of the forces acting on the arm or the arms, from the bearing element in the head housing. This guided bearing of the bearing element makes it possible to carry out the implement both in the variant with one arm and in the variant with two arms. In the variant with one arm forces are introduced unbalanced over the arm in the head housing. This is due to the leadership of the bearing element in the head housing readily possible, because the forces are introduced directly through the bearing element and the guide associated therewith in the head housing.

It is considered from a structural aspect and from the point of view of wear as particularly advantageous if the bearing element is mounted by means of a sliding and / or roller bearing in a guide of the head housing. In particular, in the rolling bearing, the use of rolling bearings in the form of roller or Tönnenlagern is considered advantageous.

The guide has in particular mutually parallel guide surfaces, which are arranged parallel to the pivot axis of the arm.

Further features of the invention are described in the dependent claims, the description of the figures and the figures themselves, wherein it is noted that all individual features and all combinations of individual features are essential to the invention.

Fig. 1

ein erstes Ausführungsbeispiel eines pneumatisch betreibbaren Arbeitsgerätes, das einen einzigen Arm aufweist, veranschaulicht in einer Schnittdarstellung bei einer eingestellten geöffneten Stellung von 30°,

Fig. 2

das Arbeitsgerät gemäß Fig. 1 in einer geöffneten Zwischenstellung,

Fig. 3

das Arbeitsgerät gemäß der Fig. 1 und 2 in der geschlossenen Stellung,

Fig. 4

das erste Ausführungsbeispiel des Arbeitsgerätes in einem Schnitt durch eine Kolbenstangenachse des Arbeitsgeräts, senkrecht zur Schnittdarstellung gemäß der Fig. 1 bis 3 geschnitten, veranschaulicht für eine veränderte eingestellte geöffnete Stellung,

Fig. 5

das erste Ausführungsbeispiel des Arbeitsgerätes, veranschaulicht bei einer eingestellten geöffneten Stellung von 50°,

Fig. 6

das Arbeitsgerät gemäß Fig. 5 in einer geöffneten Zwischenstellung,

Fig. 7

das Arbeitsgerät gemäß der Fig. 5 und 6 in der geschlossenen Stellung,

Fig. 8

ein zweites Ausführungsbeispiel eines pneumatisch betreibbaren Arbeitsgerätes, das zwei Arme aufweist, veranschaulicht in einer Schnittdarstellung bei einer eingestellten geöffneten Stellurig von 90°,

Fig. 9

das Arbeitsgerät gemäß Fig. 8 in einer geöffneten Zwischenstellung,

Fig. 10

das Arbeitsgerät gemäß der Fig. 8 und 9 in der geschlossenen Stellung,

Fig. 11

das zweite Ausführungsbeispiel des Arbeitsgerätes, veranschaulicht bei einer eingestellten geöffneten Stellung von 160°,

Fig. 12

das Arbeitsgerät gemäß Fig. 11 in einer geöffneten Zwischenstellung,

Fig. 13

das Arbeitsgerät gemäß der Fig. 11 und 12 in der geschlossenen Stellung,

Fig. 14

eine vergrößerte Schnittdarstellung durch den Bodenbereich des Zylinders bei nicht in Wirkstellung befindlichem Stößel,

Fig. 15

eine Schnittdarstellung gemäß Fig. 14, bei in Wirkstellung befindlichem Stößel,

Fig. 16

eine vergrößerte Schnittdarstellung der Anbindung eines Lagerelements an einen Arm.

In the figures, the invention is illustrated with reference to two preferred embodiments, without being limited thereto. It shows:

Fig. 1

a first embodiment of a pneumatically operable working device having a single arm, illustrated in a sectional view at a set open position of 30 °,

Fig. 2

the implement according to Fig. 1 in an open intermediate position,

Fig. 3

the implement according to the Fig. 1 and 2 in the closed position,

Fig. 4

the first embodiment of the implement in a section through a piston rod axis of the implement, perpendicular to the sectional view according to the Fig. 1 to 3 cut, illustrated for an altered set open position,

Fig. 5

the first embodiment of the working device, illustrated at a set open position of 50 °,

Fig. 6

the implement according to Fig. 5 in an open intermediate position,

Fig. 7

the implement according to the Fig. 5 and 6 in the closed position,

Fig. 8

a second embodiment of a pneumatically operable working device having two arms, illustrated in a sectional view at a set open Stellurig of 90 °,

Fig. 9

the implement according to Fig. 8 in an open intermediate position,

Fig. 10

the implement according to the Fig. 8 and 9 in the closed position,

Fig. 11

the second embodiment of the implement, illustrated at a set open position of 160 °,

Fig. 12

the implement according to Fig. 11 in an open intermediate position,

Fig. 13

the implement according to the Fig. 11 and 12 in the closed position,

Fig. 14

an enlarged sectional view through the bottom portion of the cylinder when not in operative position plunger,

Fig. 15

a sectional view according to Fig. 14 , with the ram in operative position,

Fig. 16

an enlarged sectional view of the connection of a bearing element to an arm.

figure description

The figures show a pneumatically operable implement 1, which is used in particular in the bodywork of the automotive industry. The implement 1 is as Handfingsgreifer with a single arm 2 - gripper arm - according to the embodiment of the Fig. 1 to 7 - or with two arms 2 - two Gripping arms - according to the embodiment of the Fig. 7 to 13 educated. Both embodiments have a similar structure. In this respect, the presentation of the Fig. 1 to 4 the first embodiment described.

As shown by the Fig. 1 to 4 the working device 1 has a cylinder 3. With a cylinder housing 4, a head housing 5 is connected via not illustrated fastening means. The cylinder housing 4 receives a displaceable in this piston 6 and a connected thereto, linearly displaceable and sealed out of the cylinder housing 4 brought out, not variable-length piston rod 7. An area of the piston rod 7 projecting into the head housing 5 cooperates with at least one toggle lever 8 for pivoting the arm 2 associated therewith. This arm 2 is mounted in the head housing 5 via an axis 9 and about this axis 9 between an open position ( Fig. 1 ) and a closed position ( Fig. 3 ) pivotable.

The open position of the arm 2 is infinitely adjustable. For this purpose, the piston rod 7 has a threaded portion 10 and receives in the region thereof an adjustable in the longitudinal direction of the piston rod 7 stop member 11. The stop member 11 is in the open position of the arm 2 to a stationary relative to the cylinder housing 4 system, which is formed as an annular contact surface 12 of the head housing 5, which surrounds the piston rod 7 and is arranged orthogonal to the longitudinal axis 13 of the piston rod 7. The cooperating with the contact surface 12 of the head housing 5, also annular contact surface of the stop member 14 is designated by the reference numeral 14. This contact surface 14 is arranged parallel to the contact surface 12.

The stop member 11 is rotatably positioned in the head housing 5, specifically via a not-shown groove which extends parallel to the longitudinal axis 13 of the Kolberistange 7 and in which the stop member 11 engages. The thread in the Area of the threaded portion 10 between the piston rod 7 and stop member 11 is self-locking.

The piston rod 7 is rotatable with respect to its longitudinal axis 13 and takes in the region of the knee lever 8 end facing a bearing element 15 for the toggle lever 8. The piston rod 7 is rotatable about the longitudinal axis 13 with respect to the bearing element 15. For this purpose, the piston rod 7 is inserted into a receptacle 16 of the bearing element 15 and connected by means of a form-locking ring 17 in the extension of the longitudinal axis 13 fixed to the bearing element 15. By this connection, a rotation of the piston rod 7 about the longitudinal axis 13 with respect to the receptacle 16 and thus of the bearing element 15 is possible.

A head housing 5 facing away from the bottom 18 of the cylinder housing 4 has means 19 for rotating the piston rod 7 in the closed position ( Fig. 3 ) of the arm 2 at in the region of the bottom 18 arranged piston 6. This means 19 is a plunger which is mounted sealed in the bottom 18 and slidable in the longitudinal axis 13 of the piston rod 7. The outside of the cylinder housing 4 arranged end of the plunger 19 has a hexagonal recess 20 for receiving a tool, not shown, for rotating the plunger 19 about the longitudinal axis 13, wherein the tool is inserted with a hexagonal end in the hexagonal recess 20. The arranged within the cylinder housing 4 end is provided with a projection 21 with hexagonal cross-section. These details are the representation of Fig. 13 to remove when not engaged plunger 19. Fig. 14 shows the engagement of the plunger 19, wherein the projection 21 is inserted in the closed position of the arm 2 in a hexagonal recess in cross section 22 of the facing end of the piston rod 7. By rotating the plunger 12 by means of the tool can thus rotate the piston rod 7 and consequently change the position of the stop member 11 to the piston rod 7. Fig. 14 illustrates that when inserted in the bottom end position of the piston rod 7 in the recess 2 plunger 19, an axial gap 23 between a head 24 of the plunger 19 and the bottom 18th remains so that upon application of an external force or impact force on the plunger 19 in the region of the head 24 is an axial displacement of the plunger 19 to a consequently mechanically induced axial displacement of the piston rod 7 slightly away from the bottom 18 away.

The bearing member 15 is formed symmetrically with respect to a plane passing through the longitudinal axis 13 of the piston rod 7. In the bearing element 15, two axes 25 are mounted, wherein the respective axis 25 on both sides of the bearing element 15 roller-shaped rolling bearing elements 26 receives, which are guided in a bearing groove 27 extending in the longitudinal axis. As a result, the bearing element 15 is guided substantially without play in the direction of the longitudinal axis 13. On opposite sides, the bearing element 15 has tabs 28 formed as tabs. Each tab 28 is intended to receive a plate-shaped hinge connector 29 in the region of an axis 30. In the embodiment having only one arm 2, only one tab 28 is tied while the other tab 28 remains free. This other tab is connected only in the event that a second arm 2 is present.

The hinge connector 29 is pivotally connected to the arm 2 in the region of the end facing away from the bearing element 15 in the region of an axis 31. This axis 31 is positioned at a distance from the axis 9 of the arm 2. The axis 9 and the axes 30 and 31 are arranged parallel to each other. The axes 9, 30 and 31 are constructed so that the axes 30 and 31 and 9 and 31 form the toggle lever 8, wherein in the open position according to Fig. 1 the connecting line between the axes 30 and 31 occupies an angle of less than 90 ° with respect to the line connecting the axes 9 and 31 with respect to their centers, while in the closed position of the arm according to Figs Fig. 3 this angle is slightly greater than 90 °, so that there is a slight Übertotpunktsteilung in which the bearing element 15 is fixed in the direction of the longitudinal axis 15 and in the direction of the piston rod 7 by the piston rod side roller bearing elements 26 in the region of the end of the Storage groove 27, which faces the piston rod, abut at this end 32 of the bearing groove 27.

Fig. 15 shows a detail of the mounting of the joint connector 29 in the arm 2. Here, the axis 31 is extended and engages in a substantially over a quarter circle extending guide groove 33 of the head housing 5 a.

The operation of the implement 1 according to the embodiment of the Fig. 1 to 4 is as follows:

The cylinder housing 4 is divided by the piston 5 into two working spaces 34 and 35 of the fluid. Starting from the open position of 30 ° of the arm 2 with respect to the longitudinal axis 13, in which the arm 2, based on the set position of the stop member 11 is in the maximum open position, the working space 34 is acted upon in a known manner with fluid so that the piston 6 is moved in the direction of the bottom 18. In this case, the stop member 11 reaches in the region of the contact surface 14 out of contact with the contact surface 12 of the head housing 5. The piston 6 and the piston rod 7 pull the bearing member 15 and it is about the toggle lever 8 of the arm 2 with its in the region of the free end of the Armes 2 arranged gripping element 36 moves in the direction of a mounted in the head housing 5 gripping member 37. - The intermediate position is in Fig. 2 illustrated.

In the further movement of the piston 6, this finally reaches its end position adjacent the bottom 18, in which the two gripping elements 36 and 37 contact each other or a sheet metal arranged between them is gripped by means of the gripping elements 36 and 37. When the arm 2 is closed, the toggle lever 8 is in a slight over-center position in which the connecting line of the two axes 30 and 31, based on the center, is arranged at an angle slightly different from 90 ° to the longitudinal axis 13 of the piston rod 7, such that the center The axis 30 is located slightly closer to the ground than the center of the axis 31. Since in this closed Position of the arm 2 also a stop position is formed, in which the piston rod side roller bearing elements 26 abut the end 32 of the guide groove 33, the toggle lever 8 can be moved from this over-center position only by actively applying the other working space 35 out in accordance with the fully open position Fig. 1 upon contact of the stop member 11 on the head housing.

If the supply of the fluid to the working device 1, in particular to the working space 35, has failed, this over-center position of the toggle lever 8 can be released by the above-described mechanical loading of the tappet 19. Here, the axial displacement of the piston rod 7 and thus the corresponding axial displacement of the bearing element 15 is achieved, that the hinge connector 29 is slightly pivoted, so that the center of the axis 30 is further away from the ground than the center of the axis 31. In this position, a pivoting of the arm 2 mechanically possible by the arm 2 is gripped.

As before, concerning the presentation in particular of Fig. 13 and 14 clarified, the position of the stop member 11 can be changed by turning the piston rod 7. Here, the plunger 19 is inserted into the recess 22 of the piston rod 7. The plunger 19 is moved back when pressure is applied to the cylinder 3 to transfer the piston 6 from the closed position of the working device, wherein pressure medium is supplied to the working space 35 and also acts on the facing end face of the plunger 19. Even with the mechanical loading of the plunger 19 for transferring the toggle lever from the over-center position, the subsequent return movement of the plunger 19 takes place due to the working space 35 supplied pressure medium (after the pressure medium is available again).

In Fig. 4 is denoted by the reference numeral 38 an interrogation device which is mounted in the head housing 5 and the interrogation of the position of the bearing member 15 and the stop member 11 is used.

The Fig. 5 to 7 show for the previously discussed operating conditions according to the Fig. 1 to 4 a with respect to the opening angle adjusted working device 1 with an opening angle of 50 °. This adjustment is evident, for example, in that the contact surfaces 12 and 14 have a different distance from each other when the arm 2 is closed, the change in the distance corresponding to the change in the position of the abutment part 11 relative to the piston rod 7.

The embodiment according to the Fig. 8 to 13 corresponds largely to that of Fig. 1 to 7 , To avoid repetition, reference is made to the detailed description of the first embodiment.

In the embodiment according to the Fig. 8 to 13 2 two arms 2 are provided instead of an arm. The connection of the second arm is identical to the one arm according to the first embodiment, whereby the bearing element 15, the hinge connector 29 and the arms 2 are arranged symmetrically to the plane passing through the longitudinal axis 13 of the piston rod 7 level. In this respect, reference is made to the above description, concerning the connection of one arm 2.

The second embodiment also differs from the first embodiment in that the respective arm 2 is modified and, moreover, the gripping element 37 is part of the second arm 2.

Fig. 8 shows the implement 1 with the two arms 2 in an open position of 90 °, Fig. 9 the intermediate position and Fig. 10 the closed position in which contact the two gripping elements 36 and 37.

Fig. 11 shows for the execution of the implement 1 with the two arms 2 an adjusted position of the stop member 11, so that an open position of 160 ° according to Fig. 11 reveals Fig. 12 the intermediate position is illustrated and Fig. 13 the closed position shows.

The two embodiments illustrate that can be converted to the variant with an arm 2 or two arms 2 by simply retooling or supplementing the implement 1. It is only necessary, starting from the variant with the one arm 2 to use a modified head housing 5, which has no receptacle for the gripping member 37 and instead to store in this modified head housing 5, the two arms 2 on the knee lever 8 and to the To connect bearing element 15.

LIST OF REFERENCE NUMBERS

1

implement

2

poor

3

cylinder

4

cylinder housing

5

head case

6

piston

7

piston rod

8th

toggle

9

axis

10

threaded portion

11

stop part

12

contact surface

13

longitudinal axis

14

contact surface

15

bearing element

16

admission

17

Positive engagement ring

18

ground

19

Medium / plunger

20

hexagonal recess

21

head Start

22

recess

23

axial gap

24

head

25

axis

26

Rolling element

27

bearing groove

28

Recording / tab

29

Adjustable connector

30

axis

31

axis

32

The End

33

guide

34

working space

35

working space

36

gripping element

37

gripping element

38

interrogator

Claims (15)

1. Pneumatically operable work tool (1), in particular for use in body construction in the motor vehicle industry, with a cylinder (3) which has a cylinder housing (4), a piston (6) moveable therein and a piston rod (7) which is connected to said piston, moveable linearly, guided out of the cylinder housing (4) and not variable in length, and with a head housing (5) connected to the cylinder housing (4), wherein a region of the piston rod (7) protruding into the head housing (5) cooperates with at least one toggle lever (8) to pivot an arm (2) assigned to the toggle lever (8), in particular a gripper arm or clamping arm, wherein this arm (2) is mounted in the head housing (5) and is pivotable between a closed position and an opened position, characterized in that the opened position of this arm (2) is fully adjustable, wherein the piston rod (7) has a threaded portion (10) and in the region of the threaded portion (10) receives a buffer part (11) which is adjustable in the length direction of the piston rod (7) and, in the opened position of this arm (2), lies on a support (12) that is stationary relative to the head housing (5), and the piston rod (7) is rotatable relative to its longitudinal axis (13) and, in the region of its end facing the toggle lever (8), receives a bearing element (15) for the toggle lever (8), wherein the piston rod (7) is rotatable relative to the bearing element (15).
2. Work tool according to Claim 1, characterized in that the buffer part (11) is positioned rotationally fixedly in the head housing (5).
3. Work tool according to Claim 1 or 2, characterized in that the stationary support (12) is formed as a support face of the head housing (5).
4. Work tool according to Claim 3, characterized in that the support face (12) extends orthogonally with respect to the longitudinal axis (13) of the piston rod (7).
5. Work tool according to one of Claims 1 to 4, characterized in that the thread of the threaded portion (10) between piston rod (7) and buffer part (11) exhibits a self-locking action.
6. Work tool according to any of Claims 1 to 5, characterized in that a base (18) of the cylinder housing (4) facing away from the head housing (5) has means (19) for rotation of the piston rod (7) in the closed position of the arm (2) when the piston (6) is arranged in the region of the base (18).
7. Work tool according to any of Claims 1 to 6, characterized in that a base (18) of the cylinder housing (4) facing away from the head housing (5) has means (19) for axially displacing the piston rod (7) in the closed position of the arm (2) when the piston (6) is arranged in the region of the base (18), in order to move the toggle lever (8) out of an over-dead-center position.
8. Work tool according to Claim 6 or 7, characterized in that the means (19) for axially displacing the piston rod (7) comprise the means (19) for rotation of the piston rod (7).
9. Work tool according to any of Claims 1 to 8, characterized in that it has a single toggle lever (8) for pivoting an assigned arm (2), or two toggle levers (8, 8), wherein each of the toggle levers (8, 8) serves to pivot an arm (2) assigned to this toggle lever (8).
10. Work tool according to Claim 9, characterized in that on its sides facing away from each other, the bearing element (15) has recesses (28) for pivotable mounting of two hinge connectors (29) which, in the region of their ends facing away from the bearing element (15), are connected pivotably to the two arms (2) at a distance from the pivot axes (9) of the arms (2), wherein the pivot axes (9, 30, 31) of the hinge connectors (29) and the arms (2) are arranged parallel to each other.
11. Work tool according to Claim 10, characterized in that the bearing element (15), the hinge connectors (29) and the arms (2) are arranged symmetrically to a plane running through the longitudinal axis (13) of the piston rod (7).
12. Work tool according to any of Claims 1 to 11, characterized in that the bearing element (15) is guided in a guide (27) of the head housing (5) in the direction of the longitudinal axis (13) of the piston rod (7).
13. Work tool according to Claim 12, characterized in that the bearing element (15) is mounted in a guide (27) of the head housing (5) by means of a plain bearing and/or roller bearing.
14. Work tool according to Claim 12 or 13, characterized in that the guide (27) has parallel guide faces which are arranged parallel to the pivot axis (9) of the arm (2).
15. Work tool according to any of Claims 1 to 14, characterized in that in the closed position of the arm (2) or arms (2), the toggle lever (8) or toggle levers (8) is/are arranged in an over-dead-center position.

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