Abstract:
A linear drive mechanism comprising a moveably guided output member ( 12 ). The output member ( 12 ) is guided on a supporting device ( 15 ) in a supporting area ( 13 ) of the housing ( 1 ). A position determining device ( 54 ) protrudes laterally from the output member ( 12 ). The position determining device moves along a position determining area ( 55 ) during the axial movement of the output member ( 12 ). The support device ( 15 ) extends only over part of the perimeter of the output member ( 12 ), wherein the output member ( 12 ) is exposed along a section of the perimeter so that an open space ( 67 ) is provided, thereby forming part of a position determining area ( 55 ) which can be traversed by the position determining element ( 54 ). This makes it possible to combine effective guidance with a compact linear drive design.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a linear drive comprising a rod-like rotationally locked output drive part guided for axial movement in relation to a housing using a bearing means cooperating with its outer periphery, said bearing means being provided in a bearing portion of said housing, at least one position preset element, extending to the side, being provided on the output drive part, such preset element being shifted on axial movement of the output drive part along a position preset space extending alongside the output drive part. 
     2. Description of the Prior Art 
     Linear drives of this type are predominantly utilized in assembly and handling operations and are disclosed for instance in the European patent publication 0 219 439 A1. In this known case an output drive part adapted to be driven by the action of fluid to perform a linear movement is provided, which in a bearing portion lying in the front section of a housing, is encircled by a bearing means and is therefore is guided for movement in the longitudinal direction with lateral support. In order to be able to position the output drive part in a predetermined axial position a laterally projecting position preset element is provided laterally projecting from the output drive part, which runs along a lead screw, which is arranged in a position preset space arranged adjacent to the output drive part. Moreover several sensors are arranged in the position preset space adapted to respond to the position preset element and which cooperate with a brake means associated with the lead screw. If during the axial movement of the output drive part the position preset element draws close to one of the sensors, the brake means will be operated by a brake signal so that the lead screw is locked against rotation and a further axial movement of the position preset element and of the output part connected with same will be prevented. 
     The section, projecting from the housing, of the output drive part is extremely frequently subjected to high transverse forces during operation. For instance the output drive part may be provided with a gripping means, which is to convey heavy loads. It is furthermore possible for further linear drives to be mounted in order to produce a multi-axial handling system. It is therefore necessary to guide the output drive part in relation to the housing along a relatively long bearing portion and to support it in the transverse direction. This leads to a correspondingly larger overall size of the housing. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a linear drive of the type initially mentioned, which while ensuring reliable bearing of the positionable output drive part has a compact overall length. 
     In order to fulfil this object there is a provision such that the bearing means extends for at least one section of its overall length over part of the periphery of the output drive part and the output drive part is exposed in the bearing portion along a section of the periphery not cooperating with the bearing means so that in the bearing portion to the side adjacent to the output drive part there is a free space extending in its longitudinal and peripheral direction, such free space constituting a component, which is available for motion of the position preset element, of the said position preset space. 
     This means that there is a linear drive, in the case of which the axial shift path available for the position preset element extends into the bearing portion. The axial movement of the position preset element is hence no longer limited by the start of the bearing portion. The position preset space, into which the position preset element extends, and along which such position preset element is moved during the linear movement of the output drive part, is now at least partly extended to include the bearing portion, because the bearing means provided there only extends over a part of the periphery of the output drive part and the output drive part is exposed along a section of the periphery located in the path of movement of the position preset element so that there is a free space in the bearing portion, wherein the position preset element may move without hinderance. The position preset element may therefore be shifted past the effective bearing means into the bearing portion. There is accordingly the possibility of selecting a comparatively long axial bearing portion without thereby overly increasing the overall length of the position preset space, since the position preset space and the bearing means may overlap axially without impeding each other. 
     Further advantageous developments of the invention are defined in the dependent claims. 
     If the bearing means extends for its entire overall length over only a part of the periphery of the output drive part, it is possible for a free space increasing the overall length of the position preset space to be provided, which occupies the entire length of the bearing portion. 
     The bearing means is preferably constituted by at least two diametrally oppositely placed and for instance cassette-like bearing units, which on sides, which are diametrally opposite as related to the longitudinal axis of the output drive part, cooperate with the outer periphery of the output drive part for bearing same. Several such pairs of bearing units can be set in positions distributed in the longitudinal direction of the output drive part on the housing. 
     Preferably the bearing means simultaneously serves for preventing rotation of the output drive part. If diametrally oppositely placed bearing units are present, the output drive part will preferably have a longitudinally extending guide groove in each of the corresponding potions, into which the respectively associated bearing unit fits in an interlocking manner. 
     The housing of the linear drive is preferably so designed that in cross section it possesses a rectangle-like configuration. In order in this respect to make optimum use of the overall volume, it is an advantage for the free space for the position preset element to move in is so placed in relation to the transverse and vertical axis of the housing that it has an oblique alignment, it facing obliquely to the side and at the same time downward or upward. 
     Preferably the bearing means is set on a covering body connected with the base. 
     It is convenient for the bearing means to be set on main body, having a generally L-shaped cross section, of the housing, the peripheral part of the output drive part facing away from the two L-limbs forming the free space, which is preferably covered over by a cover body connected with the main body, such cover body furthermore covering over the position preset space. 
     In accordance with a convenient form of the invention the position preset element is designed in the form of an abutment, which cooperates with at least one counter-abutment for presetting the position, such counter-abutment being a component of a position preset means arranged in the position preset space. For position presetting the abutment runs up against a counter-abutment arranged in its path of motion. 
     The counter-abutments present are conveniently arranged on a holding rod extending in the position preset space in parallelism to the longitudinal axis of the output drive part. 
     Conveniently the counter-abutments are adapted to be adjusted in the longitudinal direction in order to be able to preset the position as required. In order to ensure optimum centering of the acting force, the abutment is preferably so designed that it at least partly fits around the holding rod more particularly in the manner of a fork. 
     A modification of the position preset is possible without axially resetting the counter-abutments, if the position preset means has at least one counter-abutment, which may be switched over, using an associated switch-over means, between an active position extending into the path of travel of the abutment and an inactive position located clear of such path of travel of the abutment. It is preferred for the switch-over means to cooperate with the holding rod bearing the counter-abutments, positioning of a respective counter-abutment being implemented by turning the holding rod about its longitudinal axis. In this respect it is preferred for the holding rod to be able to be positioned in at least two different angular settings. The number of the selectable angular settings depends to a significant extent on the number of counter-abutments which may be switched over. If in addition to the two predetermined end settings in the case of need a further or single intermediate setting, as for example a center setting, is to be preset, it is sufficient to have one counter-abutment and two selectable angular settings in order to set the counter-abutment selectively in the active or in the inactive setting. In order to preset as greater number of intermediate settings a correspondingly larger number of counter-abutments is provided which may be shifted into the active setting by positioning the holding rod in steps. 
     In order to reduce the load on the individual components of the linear drive and more especially to prevent jerks, the position preset means is preferably provided with a shock absorber means, which possesses at least one moving damping member, which is kinematically coupled with the holding rod. In this case the holding rod is so movingly mounted that it is able to be moved along a predetermined damping path to a limited extent. In this case the terminal setting of the counter-abutments is preferably so performed that same will assume their position preset setting when the holding rod arrives at the end of the damping path at a permanently settable end position. The damping path is then defined by the distance which is traveled by the counter-abutment, acted upon by an abutment, as far as the said end position. It is in this manner that there will be, irrespectively of which counter-abutment is active, a reliable shock absorbing function, it not being necessary to associate a separate shock absorbing means with each counter-abutment, and in fact it is sufficient to provide a single shock absorbing means cooperating with the holding rod. 
     The shock absorbing means preferably comprises only two shock absorbers, which are respectively active in one direction of stroke and are more especially located functionally at the two axial end parts of the holding rod. Accordingly for positioning shock absorbers are required able to be set in two or more settings and preferably in only two. 
     In the following the invention will be described with reference to the accompanying drawings in more detail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a preferred design of the linear drive in accordance with the invention in a side view and partially in section or broken away. 
     FIG. 2 shows the two terminal sections of the linear drive of FIG. 1 on a larger scale. 
     FIG. 3 shows the linear drive in accordance with FIGS. 1 and 2 in cross section taken on the line III—III. 
     FIG. 4 shows the linear drive of FIGS. 1 and 2 in a cross section taken on the line IV—IV. 
     FIG. 5 shows a perspective view of part of the linear drive, the bearing portion being visible and the position preset means not being illustrated in detail. 
     FIG. 6 is a separate view of the position preset element employed in the linear drive and designed in the form of an abutment. 
     FIG. 7 shows the portion marked VII in FIG. 2 on a larger scale in order to make clear the action of the shock absorber means, the holding rod being illustrated in its home setting. 
     FIG. 8 shows the arrangement of FIG. 7 with the terminal position assumed by the holding rod after moving along the damping path. 
     FIG. 9 shows part of a cross section taken through the linear drive adjacent to the switch-over means, only indicated in chained lines diagrammatically, on the line IX—IX, the holding rod having assumed a first angular setting. 
     FIG. 10 shows the switch-over means of FIG. 9 in the actuated state, the holding rod being positioned in a second angular setting. 
     FIG. 11 shows a cross section through part of the linear drive at a switching counter-abutment, indicated in chained lines and diagrammatically in FIGS. 1 and 2, on the line XI—XI, the counter-abutment being in an inactive setting corresponding to the first angular setting as in FIG.  9 . 
     FIG. 12 shows the arrangement of FIG. 11 with the counter-abutment moved into the active position, which corresponds to the second angular position of FIG. 10, of the holding rod. 
     FIG. 13 diagrammatically shows a view, corresponding to FIG. 9, of a further embodiment of a switch-over means, which permits a positioning in steps of the holding rod into more than two different angular positions. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The linear drive of the example comprises a housing  1 , which possesses a main body  2  extending in the longitudinal direction and as seen in cross section in FIG. 4 with a generally L-like configuration, on which in the portion delimited by the two limbs of the L-like configuration, has a covering body  5  detachably mounted thereon, such body  5  having a similar L-like cross section so that in cross section there is an external shape of the housing  1  which is essentially rectangular. on the two end faces the housing  1  is closed off by a front ( 6 ) and a rear ( 7 ) terminal wall, the terminal walls  6  and  7  being attached to the main body  2  by means of attachment elements  8 , said covering body  5  for its part being detachably secured to the main body  2  and to the two terminal walls  6  and  7 . 
     The linear drive possesses an output drive part  12  able to be moved axially in relation to the housing  1 , such output drive part having a rod-like shape and in the example being tubular. The output drive part  12  extends partially in the interior of the housing  1 , it extending through a bearing portion  13 , which is predetermined in the housing  1 , and through a front terminal wall  6 , and having an external longitudinal section  14  extending out of the housing  1 . The bearing portion  13  is preferably located in the front section, associated with the front terminal wall  6 , of the housing  1 . 
     In the bearing portion  13  a bearing means  15  is arranged, which is solid with the housing and which cooperates with the outer periphery of the output drive part, the output drive part  12  only being laterally supported and simultaneously axially guided thereby. The bearing means  15  may conveniently serve furthermore for fixing the output drive part  12  to prevent relative rotation thereof around its longitudinal axis  16  in relation to the housing  1 . At the free end of the outer longitudinal part or section  14  a force output element  17  is aranged, which is able to be connected with something to be moved. The means preventing relative rotation ensure a constant angular alignment of the force output element  17  so that the linear drive is more particularly suitable for applications in assembly and materials handling, in which case inter alia articles must be conveyed and positioned with a predetermined alignment. 
     The output drive part  12  is provided with a fluid operated drive means  18 , with whose aid the output drive part  12  is able to be driven to and fro by fluid power axially along its longitudinal axis  16 . This drive means  18  is preferably accommodated in the interior of the housing  1 . 
     It is preferred for the drive means  18  to be constituted by a separate fluid operated drive cylinder  22 . This cylinder possesses a cylinder housing  21  set in a fixed manner at the back on the rear terminal wall  7  of the housing  1  of the linear drive, such cylinder housing being arranged parallel to the output drive part  12 . The attachment to the housing is preferably with the use of a rear terminal body  24 , on which the rear end of a cylinder tube or barrel  23  is secured, and which for its part possesses a screw connection  25 , indicated in chained lines, or some other type of attachment means holding it on the rear terminal wall  7 . 
     On its front side the cylinder barrel  23  of the cylinder housing  21  is closed off by a front terminal body  26 , through which a piston rod  27  extends in a sealed manner, the inner end thereof being secured on a piston  28  which is axially guided for running in the interior of the cylinder barrel  23 . The piston  28  divides up the external space of the cylinder barrel  23  into two working spaces  32  and  33  of variable volume, which on the opposite axial side are delimited by respective terminal bodies  24  and  26  in a sealing manner. 
     The overall axial length of the drive cylinder  22  is less than that of the housing  1 . The front side, facing the front terminal wall  6 , of the cylinder housing  21  ends axially within the front terminal wall  6  and in the example it ends in the bearing portion  13 . 
     The output drive part  12 , which in the embodiment is tubular, is designed in the form of a component separate from the cylinder housing  21  and the entire drive cylinder  22 . It is arranged coaxially to the cylinder barrel  23  and slipped onto same from the front side axially so that it surrounds the cylinder barrel  23  for at least a part of its overall length. In this respect the output drive part  12  is able to be shifted axially in relation to the cylinder housing  21 , which is solid with the housing, it extending to a larger or smaller extent past the front side of the cylinder housing  21  so that there is a corresponding change in the length of the outer section  14  of the length of the output drive part  12 . The piston rod  27  emerging from the front terminal body  26  toward the front terminal wall  6 , of the drive cylinder  22  extends into the outer space  34 , placed axially in front of the cylinder housing  21 , of the tubular output drive part  12  and extends forward as far as a point adjacent to the force output element  17 , at which it is secured to the output drive part  12  jointly. 
     Each working space  32  and  33  of the drive cylinder  22  communicates with a connection port  35  and  36  provided for it, via which as required a fluid pressure medium and more particularly compressed air, may be supplied to the working spaces  32  and  33  and removed therefrom. Dependent on which working space  32  and  33  is supplied with pressure medium, the piston  28  will be moved in the one or the other direction axially, its motion being transmitted with the aid of the piston rod  27  to the output drive part  12  fixedly connected with same. In the course of the resulting axial movement of the output drive part  12  the same is, in the present example, exclusively guided by the bearing means  15 . More particularly there is no transverse supporting action for the output drive part  12  on the cylinder housing  21  made up of the cylinder barrel  23  and the two terminal bodies  24  and  26 . In the example there is a cylindrical annular gap  37  with the same length as the said section of the length, such gap being radially present between the cylinder housing  21  and the said section, surrounding same, of the length tubular output drive part  12 . This leads to the advantage that the cylinder barrel  23  may be made with an extremely thin wall, because it does not have to perform any guiding function. The drive cylinder  22  is practically mounted at its rear terminal body  24  and its piston rod  27 , which extends at the front side, in an exposed manner between the housing  1  and the output drive part  12  and does not need to resist any transverse forces. 
     The connection portion between the rear end of the drive cylinder  22  and the rear terminal wall  7  may in case of need be manufactured to be resilient to a limited extent and/or be adapted to be pivoted in order to automatically allow for errors in alignment, due to manufacture or assembly, of the longitudinal axes of the drive cylinder  22  and of the output drive part  12 . FIG. 1 shows this diagrammatically by indicating a pivot axis  38  in chained lines. 
     Since the cylinder barrel  23  is not subjected to any transverse loading by the output drive part  12  it may with advantage be employed for transmission of the pressure medium required for the operation of the drive cylinder  22 . For this purpose a connection duct  42  extends in the interior of the cylinder barrel  23  in the longitudinal direction thereof, such duct communicating with a first connection duct  43  at the rear side or end of the cylinder barrel  22  and extending through the rear connection body  24  and leading to the first connection port  35 . At the front end of the cylinder barrel  23  the connection duct  42  is connected with a transfer duct  45 , formed in the front connection body  26 , and for its part the transfer duct  45  opens into the adjacent front working space  33 . It is in this manner that the front working space  35  may be charged with compressed air through the purely static connection ducts, or be vented. Because at the periphery of the drive cylinder  22  no pressure medium ducts are necessary, which would otherwise interfere, all in all extremely compact transverse dimensions of the linear drive are possible. 
     It is convenient for the second connection port  36  to be located in the vicinity of the first connection port  35  and more especially on the rear terminal wall  7 . It communicates with a second connection port  44  also extending through the rear terminal body  24 , such second connection duct  44  opening into the directly adjacent working space  32 . It is in this manner that fluid control and drive of the linear drive is made possible from a central point. 
     In order to be able to design a cylinder barrel  23  having a minimum wall thickness while still providing a maximum flow cross section in the connection duct  42 , the connection duct  42  is in the example designed in the form of an annular duct  46  arranged concentrically in the internal space  32  and  33  or bore in the cylinder barrel  23 , such annular duct  46  having an annular cross section as may be seen from FIG.  4 . The radial dimensions of this annular duct can be minimized, because due to the large size of the periphery there is a sufficiently large flow cross section. 
     It is convenient for the annular duct  46 , as in the illustrated embodiment of the invention, to be composed of an inner tube  47  of small diameter and a coaxial outer tube  48  surrounding the inner tube  47  with a clearance all the way around. The inner tube  47  delimits the working spaces  32  and  33  and constitutes the running face for the piston  28  and the surrounding intermediate space between the two tubes  47  and  48  constitutes the annular duct  46 . The concentric alignment of the two tubes  47  and  48  is ensured by suitable attachment to concentrically set back attachment sections  51  and  52  on the two connection bodies  24  and  26  so that in the interior of the annular duct  46  there are no obstructions to flow. 
     The linear drive is preferably provided with a position preset means  53 , which extends in the housing to the side adjacent to the output drive part  12  and, respectively, the drive cylinder  22 . It cooperates with a position preset element  54 , which in a part of the output drive part  12  is secured to same for ganged movement therewith, such part being located axially within the housing  1  independently of the axial position of the output drive part  12 . In the embodiment it is axially clear of both ends of the output drive part  12  on the outer periphery of the output drive part  12 . It is convention for it to be located in the vicinity of the inner end of the output drive part  12 . It extends laterally from the output drive part  12  and in a receiving space  55 , termed in the following the position preset space, arranged adjacent to the output drive part  12  and the drive cylinder  22 , the position preset means  53  being arranged in such receiving space. If the output drive part  12  is shifted axially, the position preset element  54  will be displaced as indicated by the double arrow  56  in the longitudinal direction of the position preset space  55 . 
     Owing to cooperation with the position preset element  54  the position preset means  53  is able to preset different axial positions of the output drive part  12 . It is in this manner that the output drive part  12  may be positioned during its operation as required in preset positions. 
     In order to render possible simple and at the same time reliable positioning of the position preset element  54  is in the example designed in the form of an abutment body, herein termed an abutment  57 , extending away from the output drive part  12  in the transverse direction. It is able to cooperate with one or more counter-abutments  58 , same being components of the position preset means  53  secured in relation to the housing. Should the abutment  57  strike one of the counter-abutments  58  set on its path  56  of travel, the motion of the output drive part  12  will be arrested. 
     In order to ensure a minimum overall length of the housing  1  while at the same time having a large positioning range and a firm means for supporting the output drive part  12 , the arrangement in the embodiment herein is such that the position preset space  55 , wherein the abutment  57  moves along, extends from the rear side of the housing  1  into the bearing portion  13  axially. This means that the abutment  57  may run past the bearing means  15  without being hindered by same. The range of movement of the abutment  57  and the bearing portion  13  consequently overlap each other in the axial direction with the result that a foreshortened overall length is possible. 
     This is rendered possible because the bearing means  15  extends at least along a section of its overall length and preferably—as in the working embodiment—along the entire length of the bearing portion  13 , only over part of the periphery of the output drive part  12 . The output drive part  12  is hence not completely surrounded by the bearing means  15  and there is only a bearing function in a certain part. In the illustrated working embodiment the bearing function is limited to two diametrally opposite parts of the outer periphery of the output drive part  12 , such parts appearing in cross section as being restricted to points. The corresponding bearing portions are referenced  62  in FIGS. 4 and 5. The bearing means  15  in this case comprises two pairs, following each other in the longitudinal direction of the output drive part  12 , of diametrally opposite and more particularly cassette-like bearing units  63  and  64 , which in the bearing portions  62  rest on the outer face of the output drive part  12  so that same is guided for axial sliding movement and at the same time is supported in the transverse direction. Since the two pairs of bearing units  63  and  64  are arranged with an axial distance between them, there is a transverse supporting action distributed along a considerable length, something which results in an extremely precise and sturdy guiding action for the output drive part  12 . 
     The number of bearing units  63  and  64  is basically freely selectable. It would for example be possible to have only one pair of bearing units  63  and  64 , if there were a sufficient length. The bearing units  63  and  64  may as desired be in the form of plain bearings or anti-friction bearings and more particularly in the form of bearings with recirculating balls or rollers. 
     The bearing means  15  conveniently at the same time constitute a means for preventing rotation of the output drive part  12 . For this purpose in the embodiment there is a provision such that the output drive part  12  possesses a longitudinally extending guide groove  61  in its bearing portions  62 , such groove being machined into its outer periphery and having the associated bearing units  63  and  64  interlocking with it. This latter feature is made clear in FIG.  4 . 
     The bearing units  63  and  64  extend respectively only over a part of the periphery of the output drive part  12 . This means that there are two sections  65  and  66  of the periphery of the output drive part  12 , which do not cooperate with the bearing means  15 . Along one of these sections of the periphery  65  the output drive part  12  is exposed or uncovered in the bearing portion  13  with the result that laterally to the side of the output drive part  12  there is a free space  67  extending in the longitudinal direction and simultaneously in the circumferential direction. Such free space is so aligned that it lies in the path  56  of travel of the abutment  57  and accordingly constitutes a part of the position preset space  55 . Its peripheral extent is in the working example of the order of 180° and, owing to the overall width of the bearing units  63  and  64 , is somewhat less than 180°. 
     When the output drive part  12  is located in the retracted position indicated in FIGS. 1 and 2, wherein it surrounds the drive cylinder  22  for preferably its entire length, the abutment  57  will be in the interior of the housing  1  axially spaced from the bearing portion  13 . It is however able to moved into the above mentioned free space  67  when the output drive part  12  is moving outward, it laterally moving past the bearing means  15 . The position of the abutment  57  is indicated in FIG. 5 in chained lines at  68  when it is moved into the free space  67 . 
     As measured in the direction as considered in the plane extending through the output drive part  12  and the position preset space  55  the overall width of the housing  1  is larger than in the direction at a right angle thereto. The corresponding alignment is therefore spoken of as the vertical axis  72  and the alignment extending at a right angle thereto is termed the transverse axis  73 . In order to make the best possible use of this cross sectional form for the accommodation of the free space  67 , the free space  67  is preferably so placed in relation to the transverse and vertical axis  73  and  72  that it is obliquely aligned, the uncovered section  65  of the periphery of the output drive part  12  facing obliquely to the side in the transverse direction and simultaneously in the vertical direction downward or upward. In order to design with this constructional form the main body  2 , at least in the bearing portions  62 , possesses the above mentioned L-like cross sectional shape, its two L limbs  3  and  4  covering the one peripheral section  66  of the output drive part  12 —preferably without having to perform any guide function—and an exposed section  65  of the periphery is left, which has the free space  67  associated with it. 
     The free space  67 , as in fact like the entire position preset space  55 , could, as a matter of principle, be open to the side. In order to avoid injury, it is convenient to provide for a covering function by the above mentioned covering body  5 . 
     The position preset means  53  provided in the embodiment of the invention extends over approximately all the length of the housing between the front and the rear terminal wall  6  and  7 . It comprises two holders  74  and  75  arranged adjacent to the terminal walls  6  and  7 , such holders being set more particularly on the inner face of the longer L-like limb  3 . For attachment the main body  2  may have at least one longitudinally extending anchoring groove  76 , on which the holders  74  and  75  may be anchored in an axially adjustable manner using commercially available anchoring runners. 
     The two holders  74  and  75  bear a holding rod  77  extending between them and aligned with the longitudinal axis  16  of the output drive part  12 . On the holding rod  77  a plurality of the above mentioned counter-abutments  58  are mounted at an axial distance apart in a manner preventing rotation thereof. In the example two terminal counter-abutment  58 ′, arranged in the vicinity of one of the two holders  74  and  75  and furthermore an intermediate counter-abutment  58 ″ are provided. The abutment  57  extends as far as the holding rod  77 , which it at least partly fits round, this being indicated in FIGS. 11 and 12. In this case the abutment  57  extends into the axial intermediate space between the two terminal counter-abutments  58 ′, which are so arranged and designed that they are always in the path  56  of travel of the abutment  57 . They serve to preset the terminal positions of the output drive part  12 , the abutment  57  being shown in FIG. 1 as having run onto the rear terminal counter-abutment  58 ′ in the terminal position reached on moving into the terminal position, while in the case of reaching the terminal position by moving out (not illustrated) it runs onto the front terminal counter-abutment  58 ′. 
     The terminal counter-abutments  58 ′ are mounted on the holding rod  77  so that they may be adjusted and refixed in the longitudinal direction and there is a more particularly stepless possibility of adjustment for the terminal positions. For this purpose the holding rod  77  may be designed in the form of a lead screw, on which the counter-abutments  58  are screwed with a complementary female screw means  78  with the result that they may be shifted axially by screwing and on reaching the desired point may be detachably set using a lock nut. 
     The counter-abutment  58 ″ additionally provided in the working example additionally renders possible the presetting of an intermediate position of the output drive part  12  as required. This intermediate position may be set as required as a preliminary, if the intermediate counter-abutment  58 ″ for example is able to be adjusted in the axial direction in a manner comparable with the terminal counter-abutment  58 ′. 
     Unlike the terminal counter-abutment  58  and  58 ′, which are essentially like disks in form and are seated coaxially on the holding rod  77 , the intermediate counter-abutment  58 ″ has a shape which is not symmetrical in relation to the longitudinal axis  85  of the holding rod  77  and particularly is not radially symmetrical. A possible design by way of example is illustrated in FIGS. 11 and 12. This configuration renders it possible to change over between an active position (FIG. 12) extending into the path  56  of travel of the abutment  57  and an inactive position (FIG. 11) outside the path  56  of travel of the abutment  57 . The switching over operation is in the example performed by a switching over means  84 , which cooperates with the holding rod  77  and is able to turn the latter about its longitudinal axis  85  into preselected angular positions and to set it in such position. Dependent on which switching position is set, it is possible for the abutment  57  to move past the intermediate counter-abutment  58  and  58 ″ without hindrance or to be halted by it so that the output drive part  12  is halted in an intermediate position. 
     In the embodiment of the invention the intermediate counter-abutment  58 ″ is slipped coaxially on the holding rod  77 , but however in its outline departs from the form of a disk or from a radially symmetrical shape. It does for instance have two diametrally opposite counter-abutment regions  86  on a common imaginary circle  87 , such regions more particularly extending to the outside like wings. The intermediate portions  88  placed between the counter-abutment region  86  are free. 
     For adaptation to this configuration the section, partially extending around the holding rod  77 , of the abutment  57  is provided with two abutment regions  89 , which are also diametrally opposite as related to the longitudinal axis  85  of the holding rod  77 , and which extend into the periphery  87  centered of the longitudinal axis  85 . The remaining intermediate portions lying of the periphery  87  between the abutment portions  89  are free. Preferably the abutment portions  89  are adjacent to the free end of a section, surrounding the holding rod  77  like a fork, of the abutment  57 . 
     In the inactive position the intermediate counter-abutment  58 ″ has been moved into such an angular position that its counter-abutment portions  86  are outside the axial path of travel of the abutment portions  89 . In order to set in the active position, the intermediate counter-abutment  58  and  58 ″ is turned using the switching over means  84  until its counter-abutment portions  86  are, as seen in FIG. 12, in the path of axial movement of the abutment portions  89  provided on the abutment  57 . 
     Because the counter-abutment portions  86  and the abutment portions  89  are arranged opposite to each other as related to the longitudinal axis of the holding rod  77 , there is on impact a centered transfer of force to the holding rod  77 , something which extends the length of the working life of the individual components. 
     In order to ensure a reliable rotational locking of the intermediate counter-abutment  58  and  58 ′ on the holding rod  77  it is possible, as a modification of the above mentioned embodiment, to provide a special type of attachment. Thus in the example the holding rod  77  designed in the form of a lead screw, has a square cross section as indicated in FIGS. 11 and 12, only the corner parts having threads so that the terminal counter-abutments  58 ′ and the lock nuts  83  therefor may be screwed together without any trouble. On the contrary the intermediate counter-abutment  58 ″ possesses a central square opening  90  corresponding in cross section to the holding rod  77 , permitting the counter-abutment  58 ″ to be slipped in an axially sliding manner, while at the same time being rotationally locked, on the holding rod  77 . Axially to either side of the intermediate counter-abutment  58  and  58 ′ it is then convenient to provide a respective attachment nut  92  so that the intermediate counter-abutment  58 ″ may be held tight at the desired axial position. 
     In the case of the embodiment described by means of the switching over means  85  the holding rod  77  can be positioned in two different angular settings, which correspond to the active and in active setting of the intermediate counter-abutment  58  and  58 ′. A switching over means  84  suitable for this purpose is indicated diagrammatically in FIGS. 9 and 10. It comprises a holding body  82 , via which it is attached to the main body  2  of the housing  1 , for example at the anchoring nut  76 . On the holding body  82  a force applying means  97  is arranged having a force applying element  93 , the latter cooperating with a switching latch  94  rotationally locked with the holding rod  77 . By means of a spring means  95  the switching latch  94  is biased into an initial setting, in which the holding rod  77  assumes an angular position corresponding to the inactive setting (FIG.  9 ). By operation of the force applying element  93  the switching latch  94  is turned against the force of the spring means until it assumes the actuated position indicated in FIG. 10, in which the holding rod  77  is shifted into an angular position corresponding to the active setting of the intermediate counter-abutment  58  and  58 ′. For adjustably presetting the actuated position of the switching latch  94  it is appropriate to provide an adjustment element  96 , which in the embodiment is constituted by a screw. During the following de-activation of the force applying element  93  the switching latch  94  is swung back into the initial position by the spring means  95 . 
     In the illustrated working embodiment the force applying element  93  is a component of a fluid operated force applying means, for instance in the form of a drive cylinder. Here it would however be possible to conceive of any other possible type of actuation, as for example an electrical actuating means. It would also be possible to do without a return spring, if a double acting actuating means were provided for the force applying element  93 . 
     It would also be perfectly possible to provide a plurality of intermediate counter-abutments  58  and  58 ′ on the holding rod, of which one respective counter-abutment could in case of need be switched into the active position in order to preset a greater number of intermediate positions. In this respect it would also be advantageous to design the switching over means  84 , for example in accordance with the configuration illustrated in FIG. 13, as a step drive, with which the holding rod  77  could be set in more than two predetermined angular positions by rotation in steps. 
     In the case of the switching over means  84  as illustrated in FIG. 13 there is again the provision of a force applying means  97  provided with a force applying element  93 , such means  97  cooperating with a switching latch  94  associated with the holding rod  77 . Once again the switching latch  94  is urged by a spring means  95 , not illustrated, into the depicted initial position. Unlike the configuration illustrated in FIGS. 9 and 10 the switching latch  94  is however arranged freely rotatably on the holding rod  77  and provided with at least one or more moving detent latches  98 , which may cooperate with detent portions  99 , distributed in the peripheral direction, of a switching body  100  connected in a rotationally locked manner on the holding rod  77 . If the switching latch  94  is deflected into its actuated position, the detent latches  98  will come into detent engagement with the detent portion  99  coming next in the peripheral direction so that with the switching latch  94  turning back into the initial position, the switching body  100  will be moved on further through one angular step together with the holding rod  77 . 
     FIG. 6 shows an abutment  57  having a preferred design by itself. The reader will see the fork-like section  102  with the two abutment portions  89  provided thereon. It is convenient to provide a further fork portion  103  placed in front of and at a distance from the front terminal counter-abutment  58  and  58 ′. On reaching the inner terminal position of the output drive part  12  the rear fork-like section  102  of the abutment  57  will run onto the inner end counter-abutment  58  and  58 ′, whereas on reaching the outer end position its fork portion  103  will run onto the front end counter-abutment  58  and  58 ′. There is now the possibility of putting a single intermediate counter-abutment  58 ″ out of operation by screwing same tightly against the front counter-abutment  58  and  58 ′. The abutment  57  is then able to be moved so that its fork portion  103  runs onto the front end counter-abutment  58  and  58 ′, the intermediate counter-abutment  58  and  58 ′ running into the fork recesses without taking effect. The slot-like intermediate space  104  facilitates the accessibility of the one attachment nut  92 , when the abutment  58  is put on the intermediate counter-abutment  58 ″ for adjustment purposes. 
     In order to deaden the impact of the abutment  57  on the counter-abutments  58 , the position preset means  53  is preferably provided with a shock absorber means  105 . It comprises at least one and in the example two moving damping members  106  and  106 ′, with which the holding rod  77  is kinematically coupled axially. The shock absorber means  105  is hence associated with all counter-abutments  58  in common, with which it cooperates via the holding rod  77 . 
     As regards details it will be seen that the holding rod  77  is mounted on the housing  1  via the shock absorber means  105  for motion to a limited extent axially along a path termed the damping path s. This is made possible in the embodiment because at both ends of the holding rod guide members  107  and  107 ′ are provided which are preferably designed like pistons, by means of which the holding rod  77  is guided axially for sliding motion in guides  108  and  108 ′ provided on the holders  74  and  75 . Each respective guide member  107  and  107 ′ at the same time constitutes an abutment element, axially opposite to which, at a distance corresponding to the damping path s, a stroke limiting portion  109  and  109 ′ is arranged which is provided on the associated holder  74  and  75 . 
     Normally the holding rod  77  will assume a home position, at which its guide members  107  and  107 ′ are spaced apart from both stroke limiting portions  109  and  109 ′ by the damping path s. This is shown in FIGS. 1,  2  and  7 . This home position is stabilized by the above mentioned damping members  106  and  106 ′ of two fluid-type shock absorbers  110 , which are arranged on either side of the holding rod  77  as an extension thereof. They are so attached by means of their damper housing  11  on the respective holder  74  and  75  that their damping member  106  and  106 ′ is turned toward the holding rod  77  and acts on same with a resilient loading action. This means that the holding rod  77  is stabilized in its home position axially. This biasing force is caused by a spring means, not illustrated, which is accommodated in the associated damper housing  111 . The damping members  106  and  106 ′ are constituted by plungers extending away from the damper housing  111  and on which the in the damper housing  111  a damping piston is arranged, each damping member  106  and  106 ′ being able to be shifted toward the damper housing  111  with the displacement of damping fluid. Shock absorbers of this type, be they gas shock absorbers, hydraulic shock absorbers or hybrid shock absorbers are known as such so that a more detailed description thereof is unnecessary here. 
     If when the holding rod  77  is in its home position the abutment  57  strikes against one of the counter-abutments  58  (this instant being illustrated in FIG.  7 ), the respective counter-abutment  58  will be displaced together with the holding rod  77  by the impact along the damping path s until the guide member  107 , which is to the fore in the direction of motion, runs up against the associated stroke limiting portion  109  and the holding rod  77  accordingly reaches a terminal position. Since then the associated damping member  106  is displaced, there is a shock absorbing action, in which the energy of the impact is reduced to a commensurate level. 
     The individual counter-abutments  58  are preferably so set here that same exactly assume the desired position preset positions, when the holding rod  77  has reached the end position at the end of the damping operation. 
     In order to be able to adjustably set the intensity of damping without affecting the end position of the holding rod  77  and accordingly the position preset settings of the counter-abutments, the damping path s is preferably permanently set. The path limiting portions  109  and  109 ′ are arranged separately from the respective shock absorber  110  on the associated holder  74  and  75 . On the contrary the shock absorbers  110  are mounted on the associated holder  74  and  75 , the axial distance apart of the damper housing  111  and the associated stroke limiting portion  109  and  109 ′ being able to be reset. The possibility of adjustment is preferably ensured by a screw connection. In the example the damper housings  11  are provided with an external screw thread allowing them to be screwed a predetermined degree of insertion into a holding recess  113  provided with an internal screw thread. A lock not can be provided for fixing the position set. 
     In order to render possible the detection of predetermined axial positions of the holding rod  77 , it is convenient to provide at least one guide member  107 ′ with an actuating element  118 , for example with a permanent magnet, for which at least one sensor  119  is provided, which is located at the outer periphery of the associated guide  108 ′.