Abstract:
In a drive system of a forming press for driving the plunger with a crank mechanism controllable by a servomotor, the torques of the servomotors that are required to achieve a high pressure force for the plunger by means of intermediate gearing, preferably with a double gear transmission, to the cam or crank mechanism, wherein the symmetrically configured drive arms of multipoint presses for the right and the left pressure points of two-point presses or the pressure point groups of four-point presses are optionally mechanically synchronized with one another in such a way that each of the intermediate gears of the first or of one of the first gear transmissions is effectively connected to the others.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a drive system for a multi-point forming press. 
     Known according to DE 10 2004 009 256 is a mechanical multi-servo-press in which the servo-motors with associated pinions as a single-stage gear at spaced apart locations each drive an eccentric wheel for driving a slide having two pressure points. At great pressing forces, high torques for the servo-motors are necessary due to the limited transmission ratio of the single-stage gear. In this regard, the document discloses that the load on the servo-motors can be reduced by using the momentum of the mass moment of inertia of the gear. Since this effect can only be used at elevated speeds, at low speeds the servo-motors would be underdimensioned for applying the installed pressing force, especially in set-up mode. 
     The intermediate gears that connect the eccentric wheels and that are also necessary for mechanical synchronization in the gear result in increased complexity. 
     Brake motors are suggested for braking and stopping the slide. Due to the limited transmission ratio of the single-stage gear, elevated braking torques are necessary, which increases the mass moment of inertia. Not disclosed are means required for attaining a safety category necessary for press operation, including possible locking of the slide. 
     Known in accordance with WO 2004/056559 is another pressing device having a pressure point, in which device a direct drive, in the form of a frequency-controlled AC motor, which is arranged directly on the eccentric shaft, controls the movement of the slide. The limited available torques of the servo-motor enable relatively low pressing forces without any intermediate gearing. 
     For operational on/off movements for the press device, emergency off devices are provided via the motor control and/or mechanical devices, but the structure required for satisfying safety requirements and their functions is not disclosed. 
     JP 2006061974 describes a drive system for a multi-point forming press, each of the crank wheels of which can be driven via a two-stage transmission by means of a separately controllable servo-motor, the first gear stage being embodied as a flexible drive, the traction means of which have different lengths between the front and rear pressure point group in a four-point press. 
     In another multi-point forming press in accordance with JP 2005271070, each drive wheel separately associated with each pressure point and connected to a crank is driven via one or two single-stage toothed wheel gears by a servo-motor, in the case of a four-point press it being possible for the drive for the two drive wheels belonging to one pressure point group to come from one or alternatively two common single-stage gears. 
     The last two documents cited do not disclose means required for attaining a safety category necessary for press operation, including possible locking of the slide. 
     Known from DE 199 32 990 is a slide locking and slide release device, for a conventional mechanical press equipped with a flywheel and a clutch/brake combination, in which device a non-positive fit additional brake that is controlled independently of the main brake is arranged on a central shaft, the function of which is monitored cyclically and redundantly for satisfying safety requirements and is integrated into the press safety control unit. 
     Known from DE 199 10 965 is another locking device for a press slide, in which device the stepless locking of a main drive shaft, which where necessary acts on a plurality of slides simultaneously, is attained using outer and inner teeth that can be caused to engage by means of a positioning device. 
     DE 101 35 663 describes a positive fit mechanical restraint device that is on a brake device and in which a gear ring is borne rotation-fast in the mutual guide of the outer disks of a multi-disk brake and can be longitudinally displaced in a counter-gear ring, said counter-gear ring being able to perform a rotary movement for positive-fit coupling. 
     None of these last three publications cited discloses applications in servo-presses that are largely free of flywheels and clutches. 
     Known from DE 102 44 318 is a press having a servo-spindle drive, the drive movement of which can be braked using a brake motor and/or using a mechanical brake device. 
     JP 2003290997 discloses a single-point forming press, the drive wheel of which is connected to a crank and can be actuated via a single-stage gear by a servo-motor, a brake borne on the frame side being provided between the servo-motor and the drive wheel. 
     The measures of the last two publications cited are not adequate for satisfying engineering and personnel safety requirements for presses in order to be classified in a defined safety category. 
     SUMMARY OF THE INVENTION 
     The underlying object of the invention is to configure a drive system for a multi-point forming press such that on the one hand high pressing forces can be attained using the available torques of servo-motors and on the other hand to reduce the technical complexity both in the design of the drive having a plurality of mechanically synchronized pressure points and also in the design of the drive having pressure points that can be controlled independent of one another. The intent of the latter design is in particular spatial tilt control for the slide in two planes when using a forming press embodied with four pressure points. Moreover, the mechanical and personnel safety requirements for the press that can be controlled by one or a plurality of servo-motors are to be satisfied. 
     The core idea of the invention is to transfer the torques required for high pressing force for the slide from the servo-motors via intermediate gears, preferably dual gear transmissions, to the eccentric or crank mechanisms, in multi-point presses the symmetrically configured drive arms for the right-hand and left-hand pressure points on two-point presses or pressure point groups on four-point presses being selectively mechanically synchronizable with one another such that the intermediate gears of the first gear transmission or of one of the first gear transmissions are mechanically linked. It is likewise conceivable to drive each eccentric or crank mechanism, which belong separately to one pressure point of a four-point press, using a single gear transmission, so that spatial tilt control of the slide is possible in two planes. 
     In addition, in a first design type the pinion shafts, which are allocated separately to each crank wheel and can be controlled by means of a servo-motor, are arranged radially offset to one another such that the pinion shafts on the one hand are connected to a servo-motor borne on the frame side and on the other hand to a retention device borne on the frame side. The servo-motors and retention devices can each be arranged together on one side or preferably in a mirror-image of one another with regard to the adjacent, successive pressure points. 
     Moreover, it is conceivable to use a single gear transmission to drive separately crank wheels jointly allocated to the two pressure point groups of a four-point press so that tilt control for the slide is only possible in one plane. 
     If tilt control that can be controlled by the slide drive is omitted, this embodiment can be converted to a forming press with alternative positioning of the drive shafts in the longitudinal direction in that a single gear transmission drives a crank wheel jointly allocated to the two pressure points of a two-point press. 
     In a second design type each crank wheel is driven by a first servo-motor-driven pinion shaft, mechanical synchronization of the right and left pressure points, or pressure point groups, belonging to a multi-point press being possible by means of the intermediate gears arranged coaxially on the pinion shafts. 
     For higher outputs, in a third design type a second gear transmission is mechanically linked on the one hand to each servo-motor-driven first gear transmission and on the other hand via a second pinion shaft to the associated crank wheel. The intermediate gears that belong to the first gear transmission and that are each arranged coaxially on the second pinion shaft can be mechanically linked for the purpose of selective mechanical synchronization of the pressure points. In a fourth design type, in order to divide the torque introduced into the crank wheel, it is possible to employ, per crank wheel, two second pinion shafts, the intermediate gears of which are arranged coaxially and belong to the first gear transmission and are spaced apart such that they can be driven jointly by a servo-motor-driven first pinion shaft. In this case as well, the coaxially arranged intermediate gears of one of the pressure points adjacent to the second pinion shaft can be mechanically linked to one another for the purpose of mechanical synchronization. 
     In one advantageous embodiment, axially displacing these intermediate gears and the associated pinion can select and deselect the mechanical link between the pressure points. 
     In a fifth design type, the crank wheels of the adjacent pressure points or pressure point groups can be centrally driven via a single or preferably dual gear transmission by one or a plurality of servo-motors with a power split via an intermediate gear that mechanically synchronizes the crank wheels. In one advantageous design, in a single gear transmission the pinion shaft, which acts on the one hand on one of the two crank wheels and on the other hand on the intermediate gear that synchronizes the crank wheels, can be driven by a servo-motor borne on the first end, the associated retention device being borne on the second end. 
     In another embodiment of this design type having dual gear transmissions, the pinion shaft of the embodiment described in the foregoing is driven by a first gear transmission such that the first pinion shaft belonging to the first gear transmission is mechanically linked on the one hand to a servo-motor and on the other hand to a retention device. 
     Moreover, it is possible for the pinion shaft of the first gear transmission to be connected to opposing servo-motors borne on the frame side and for the associated retention device to be mechanically linked to the pinion shaft of the second gear transmission or of the intermediate gear. 
     Likewise, it is conceivable for the torque introduced into the second gear transmission to be divided in that two first pinion shafts arranged radially offset to one another act jointly on the toothed wheel that belongs to the second gear transmission, the first pinion shafts being connected on the one hand to a servo-motor borne on the frame side and at least one first pinion shaft on the other hand being connected to a retention device borne on the frame side. 
     For further reducing the drive torque it is possible to arrange between the crank wheels and pressure points of the slide a lever mechanism that creates a transmission. 
     For satisfying the engineering and personnel safety requirements for servo-presses, which compared to conventional presses do not have any clutch/brake combination between motor and transmission, it is furthermore essential to the invention that the servo-motor or servo-motors are mechanically linked to a combination made of a mechanical retention device and a device for electrical torque isolation. Either two independently acting non-positive fit safety brakes in the form of rotation and/or linear brakes or at least one non-positive fit safety brake and one positive fit blocking device in the form of a rotation and/or linear blocking unit are used for the mechanical retention devices. Depending on design type, the rotation brake and rotation blocking unit can advantageously be arranged coaxially on the free shaft end that opposes the servo-motor, it advantageously being possible to use the position on the high-speed shaft allocated to the servo-motor for reducing the braking and blocking torque. In contrast, linear brakes and linear blocking units can be arranged between the frame and the slide that can be moved linearly. 
     The electrical torque isolation unit is necessary to prevent the servo-motors from starting up in an uncontrolled manner. To this end, in a first embodiment a line contactor that can be turned off is provided in the servo-converter system. A power contactor that can be turned off and that is in the motor line can be used in a second embodiment. In a third embodiment, a turn-off element for the control energy for the semi-conductor valves of the motor inverter is used for the torque isolation unit. 
     Depending on the categorization of the press in a defined safety category, the devices in each embodiment can be redundant, it also being conceivable to combine a plurality of these embodiments. 
     The invention is explained in greater detail in the following using exemplary designs and associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a drive system for a forming press in accordance with a first design type in a first embodiment having four electronically synchronizable pressure points; 
         FIG. 2  depicts a drive system for a forming press in accordance with a second design having two mechanically synchronizable pressure point groups; 
         FIG. 3  depicts a drive system for a forming press in accordance with a third design having two electronically synchronizable pressure point groups; 
         FIG. 4  depicts a drive system for a forming press in accordance with a third design having two mechanically synchronizable pressure point groups; 
         FIG. 5  depicts a drive system for a forming press in accordance with the third design for variable pressure point spacing; 
         FIG. 6  depicts a drive system for a forming press in accordance with the third design having selectively mechanically and electronically synchronizable pressure point groups; 
         FIG. 7  depicts a drive system for a forming press in accordance with a fourth design having two mechanically synchronizable pressure point groups; 
         FIG. 8  depicts a drive system for a forming press in accordance with a fifth design having a central drive for adjacent pressure point groups and dual gear transmissions with two first pinion shafts; 
         FIG. 9  depicts a drive system for a forming press in accordance with a fifth design having a central drive for adjacent pressure point groups and dual gear transmissions with a first pinion shaft; 
         FIG. 10  depicts a safety device that is a combination of a retention device and a device for torque isolation in accordance with a first design; 
         FIG. 11  depicts a safety device that is a combination of a retention device and a device for torque isolation in accordance with a second design; 
         FIG. 12  provides a detail view of the device for torque isolation from  FIGS. 10 and 11 ; 
         FIG. 13  depicts a drive system for a forming press in accordance with a first design type in a second embodiment having two electronically synchronizable pressure point groups; 
         FIG. 14  depicts a drive system for a forming press in a longitudinal shaft arrangement having a mechanically synchronized pressure point group; 
         FIG. 15  depicts a drive system for a forming press in accordance with a fifth design having a central drive for adjacent pressure point groups and a single gear transmission. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a first exemplary embodiment of the first design type,  FIG. 1  depicts a four-point forming press, the drive  2  of which occurs on the four pressure points  4  of the slide  1  by means of a crank mechanism  3 , each pressure point  4  being driven separately. The crank mechanism  3  for each pressure point  4  comprises a crank wheel  6  that is borne in the head piece  27  and that is connected on the output side via an eccentrically attached connecting rod  28  to the pressure point  4  of the slide  1  and on the drive side to a first pinion shaft  8 . In the second exemplary embodiment of the first design type in accordance with  FIG. 13 , a common crank wheel  6  that is connected on the drive side to a first pinion shaft  8 . 1 ,  8 . 2  is allocated to the two pressure points  4  in a pressure point group  5 . What these two exemplary embodiments have in common is that the first pinion shaft  8  borne in the head piece  27  can be controlled by a freely programmable servo-motor  7  arranged at the first shaft end thereof. (By “controlled” is meant directly controlled or driven.) The servo-motor is advantageously embodied as a hollow shaft motor. The second shaft end is mechanically linked to a retention device  9  borne on the frame side. In accordance with  FIG. 1 , the first pinion shafts  8  of the crank wheels  6  that are placed one after the other and that are allocated to each pressure point group  5  are arranged radially offset to one another such that the servo-motors  7  for the drive of the front pressure points  4  are borne on the front side and the retention devices  9  are borne on the back side of the head piece  27 . For the back pressure points  4 , the servo-motors  7  are borne on the back side and the associated retention devices  9  are borne on the front side of the head piece  27 . The retention devices  9  are embodied as rotation brakes  14 , preferably as non-positive fit safety brakes  12 . 
     The separately controllable servo-motors  7  can on the one hand produce a synchronous movement of the slide  1  using electronic coupling and on the other hand, using an asynchronous movement, can equalize tilting of the slide  1  due to the elastic resilience given an eccentric load or can produce a target tilt position, spatial tilt regulation of the slide  1  in two planes being possible using the four-point embodiment. 
     The exemplary embodiment in accordance with  FIG. 14  describes a forming press with a longitudinal shaft arrangement having two pressure points  4  that are driven by a common, centrally arranged crank wheel  6  via a pinion shaft  35  for a servo-motor  7 . The associated retention device  9 , in the form of a non-positive fit double brake  36  arranged axially successively, is borne on the opposite end of the pinion shaft  35 . 
     In the second exemplary embodiment in accordance with  FIG. 2 , the adjacent crank wheels  6  each act on the pressure points  4  in the case of a two-point forming press or on the pressure point group  5  in the case of a four-point forming press. In the case of a four-point forming press, it is also possible for a separate crank wheel to be allocated to each pressure point. The crank wheels  6  are each driven via a first pinion shaft  8 . 1 ,  8 . 2  by means of a servo-motor  7 , mechanical synchronization of the adjacent pressure points  4  or pressure point groups  5  being possible by means of the intermediate gears  10 . 1 ,  10 . 2  arranged coaxially on the pinion shafts  8 . 1 ,  8 . 2 . 
     The retention devices  9  on the front side that are coaxially mechanically linked to the first pinion shafts  8 . 1 ,  8 . 2  are opposite the servo-motors  7  arranged on the back side on the head piece  27 . The retention device  9  is embodied on the first piston shaft  8 . 1  belonging to the left-hand crank wheel  6  as a non-positive fit or non-force fit (the two terms being used interchangeably herein) safety brake  12  and on the first pinion shaft  8 . 2  belonging to the right-hand crank wheel  6  as a positive-fit rotation blocking unit  16 , preferably as a positive fit blocking unit  13 . Compared to the safety brake  12  with the non-positive fit active principle, the positive fit active principle of the blocking device  13  can be realized for instance using outer and inner teeth that can be caused to engage. 
       FIGS. 3 and 4  depict a third embodiment of the drive system in which embodiment, by means of a dual gear transmission, a second pinion shaft  11 . 1 ,  11 . 2  mechanically linked to the associated crank wheel  6  is driven via a coaxially arranged intermediate gear  10 . 1 ,  10 . 2  by a first pinion shaft  8 . 1 ,  8 . 2  that can be controlled by means of a servo-motor  7 . The intermediate gears  10 . 1 ,  10 . 2  that are mechanically linked to one another in the embodiment in accordance with  FIG. 4  satisfy the additional function of mechanically synchronizing the adjacent pressure points  4 . 
     Furthermore, in the case of a four-point forming press it is possible for a separate crank wheel to be allocated to each pressure point and for the second pinion shafts  11  to act jointly on two crank wheels  6  that are disposed one after the other. 
     Analogous to the exemplary embodiment in accordance with  FIG. 2 , the servo-motors  7  that are mechanically linked to the first pinion shafts  8 . 1 ,  8 . 2  are each disposed on the back side and the retention devices  9  are disposed on the front side of the head piece  27 . The retention device  9  associated with the pinion shaft  8 . 1  is embodied as a non-positive fit safety brake  12  and the retention device  9  associated with the pinion shaft  8 . 2  is embodied as a positive-fit blocking device  13 . If the mechanical link between the intermediate gears  10 . 1 ,  10 . 2  is eliminated, according to the embodiment in accordance with  FIG. 3  the adjacent pressure points  4  are electronically synchronized. One non-positive fit safety brake  12  is allocated as a retention device  9  to each pinion shaft  8 . 1  and  8 . 2 . 
     In order to create different spacing between the adjacent pressure points  4  as a function of the structural size of the press, the second pinion shafts  11 . 1 ,  11 . 2  allocated to the crank wheels  6  can be arranged rotated in the same direction about the same angle on a common circular path  29  as in  FIG. 5 . In the embodiment, alternative to rotating systems, depicted as exemplary retention devices  9  are systems in the form of a linear brake  15  and a linear blocking unit  17  that act linearly on the movement of the slide. 
     The dual gear transmission described in the foregoing can furthermore be employed in the drive system having the longitudinal shaft arrangement in accordance with  FIG. 14 . 
     The third embodiment in accordance with  FIG. 4  can advantageously be modified with the option to switch between mechanically and electronically synchronizing the pressure points  4  in that corresponding to  FIG. 6 , by means of a pushing device  33  for instance the pinion  34  belonging to the second pinion shaft  8 . 2  and the intermediate gear  10 . 2  mechanically linked thereto are relatively displaceable on the second pinion shaft  11 . 2  such that the mechanical link between the intermediate gears  10 . 1  and  10 . 2  can be eliminated. 
     In order to optimize the addition of force to the crank wheels  6 , corresponding to the fourth design in accordance with  FIG. 7  it is possible with the drive  2 , depicted for half a machine, to divide the torques introduced into the crank wheels  6  in that two second pinion shafts  11 . 1 ,  11 . 3  (depicted) and  11 . 2 ,  11 . 4  (not depicted) that are arranged radially offset engage with the respective crank wheel  6 . Arranged coaxially on the second pinion shafts  11  are the intermediate gears  10 . 1 ,  10 . 3  (depicted) and  10 . 2 ,  10 . 4  (not depicted), the intermediate gears  10 . 1 ,  10 . 3  being jointly controllable by the first pinion shaft  8 . 1  and the intermediate gears  10 . 2 ,  10 . 4  by the first pinion shaft  8 . 2  (not depicted). The intermediate gears  10 . 1 ,  10 . 2  that are mechanically linked to one another assume the additional function of mechanically synchronizing the adjacent pressure points  4 . The first piston shafts  8 . 1 ,  8 . 2  can be controlled by the servo-motors  7  arranged on the back side of the head piece  27 . Borne on the front side of the head piece  27  are the retention devices  9  that belong to the first pinion shafts  8 . 1 ,  8 . 2  and that are embodied on the first pinion shaft  8 . 1  as a non-positive fit safety brake  12  (depicted) and on the first pinion shaft  8 . 2  as a positive-fit blocking device  13  (not depicted). 
       FIGS. 8 and 9  describe a drive system in accordance with a first design having a central drive that acts jointly on the adjacent crank wheels  6 . To this end, in accordance with  FIG. 9 , one, or as depicted preferably two, servo-motors  7  arranged coaxially and opposing one another on the first pinion shaft  8 , via a gear transmission  32 , drive a second pinion shaft  11 , the pinion of which is mechanically linked on the one hand to the right-hand crank wheel  6  and on the other hand via an intermediate gear  10  borne separately in the head piece  27  to the adjacent left-hand crank wheel  6 . The pressure points  4  are mechanically synchronized via the intermediate gear  10 . The non-positive fit safety brake  12  and positive-fit blocking device  13 , acting as retention devices  9 , are borne on the head piece  27  connected to the second pinion shaft  11 . 
     Compared to the embodiment in accordance with  FIG. 9 , in order to reduce the torques to be transmitted by the retention devices  9 , in the alternative exemplary embodiment in accordance with  FIG. 8  the retention devices  9  are arranged on the high-speed motor shafts. Two first pinion shafts  8 . 1 ,  8 . 2  that are arranged offset to one another jointly drive the gear transmission wheel  32  that is disposed on the second pinion shaft  11 . Each of the first pinion shafts  8 . 1 ,  8 . 2  is controlled by a servo-motor  7  that is borne on the back side of the head piece  27 . The associated retention devices  9  are each borne coaxially on the first pinion shaft  8 . 1 ,  8 . 2  opposite the servo-motors  7  on the front side of the head piece  27 . The retention device  9  of the pinion shaft  8 . 1  is embodied in the form of a rotation brake  14  as a non-positive fit safety brake  12  and that of the pinion shaft  8 . 2  is embodied in the form of a rotation blocking unit  16  as a positive-fit blocking device  13 . Analogous to  FIG. 9 , the pinion of the second pinion shaft  11  is on the one hand mechanically linked to the left-hand crank wheel  6  and on the other hand via the intermediate gear  10  borne separately in the head piece  27  to the adjacent right-hand crank wheel  6 . For reducing the torques on the retention devices it is likewise possible, analogous to the embodiment in accordance with  FIG. 9 , in addition to the first pinion shaft  8  that can be controlled using two servo-motors  7 , to arrange the non-positive fit safety brake  12  belonging to the retention device  9  and the positive-fit blocking device  13  coaxially and opposing one another on another first pinion shaft, both first pinion shafts being mechanically linked to the gear transmission wheel  32  arranged on the second pinion shaft  11 , analogous to the embodiment in accordance with  FIG. 8 . 
     In another embodiment of the fifth design, in accordance with  FIG. 15  the drive system with central drive for adjacent pressure point groups is embodied with a single gear transmission. The pinion shaft  35  is mechanically linked on the one hand to the right-hand crank wheel  6  and on the other hand to the intermediate gear  10  synchronizing the two crank wheels  6 . The pinion shaft  35  is driven by a servo-motor  7 . The associated retention device  9 , in the form of a non-positive fit double brake  36  that is arranged axially successively is borne on the opposite end of the pinion shaft  35 . 
     Moreover, in the case of a four-point forming press it is possible for a separate crank wheel to be allocated to each pressure point and for the pinion shaft  11 ,  35  to act with associated pinions jointly on two crank wheels  6  that are disposed one after the other. 
     In this case, for mechanically synchronizing the adjacent pressure points, the two pinions arranged on the pinion shaft  11 ,  35  are each mechanically linked with an intermediate gear  10 . 
     In all of the embodiments, the servo-motors  7  attain flexible path and speed profiles for the movement of the slide  1 , the target positions of the slide  1  preferably being produced using guidewave-controlled electronic cam disks. In terms of the path profile, it is possible to choose between a 360° cycle movement, a reversible movement at an angle &lt;360° with passage through the bottom reversal point, or a movement at an angle &lt;180° with reversal in the area of the bottom reversal point. The latter operating mode can preferably be used in conjunction with the tilt control for the slide  1 , which is possible with electronic synchronization of the pressure points  4 , in one plane for a two-point forming press or in two planes for a four-point forming press. 
     It is also true of all of the embodiments that for satisfying the personnel safety requirements the slide  1  is securely retained using a combination of a retention device  9  and a device for torque isolation  18 . For the mechanical retention devices  9 , either two independently acting non-positive fit safety brakes  12  can be used in accordance with the exemplary embodiments according to  FIGS. 1 ,  3 ,  6 ,  7 , or at least one non-positive fit safety brake  12  and one positive fit blocking device  13  can be used in accordance with the exemplary embodiments according to  FIGS. 2 ,  4 ,  5 ,  8 , these securely locking and unlocking the slide  1  in any desired position without a time delay. The functioning of the retention devices  9  is monitored cyclically and redundantly and they are integrated into the press safety control unit. To this end, in the non-positive fit, preferably spring-actuated safety brakes  12  on the one hand, for controlling the spring force, the braking force on the servo-motor actuated with a defined drive torque when idle is controlled using current measurement and on the other hand the final position of the brake piston in the brake pitch is monitored in the unlocked position. The safety control unit compares the monitoring signals to prespecified limiting values. 
     To supplement the measures described in the foregoing for stopping and retaining the slide  1 , for satisfying engineering safety requirements, in particular for preventing impermissible loads, it is possible on the one hand to limit the torque of the servo-motors  7  with or without direct force measurement and on the other hand to provide overload elements in the gear chain. In addition to the overload safety devices that are equipped with a hydraulic cushion and that are in the pressure points  4  of the slide  1 , where needed at least one rotationally acting overload element can be provided in the rotating part of the gear chain. The overload safety device is linked via the safety control unit  26  to the control for the servo-motors  7  in order to provide additional braking for the drive if there is an overload. 
       FIG. 10  depicts the safety device in a combination of a retention device  9  and a device for torque isolation  19  in accordance with a first design corresponding to the drive system for instance according to the exemplary embodiment having electronically synchronizable pressure points according to  FIG. 1  or  3 . The crank wheels  6  can be controlled independently of one another via the first pinion shaft  8 . 1 ,  8 . 2  by the respective servo-motor  7 . A non-positive fit safety brake  12  is allocated to both pinion shafts  8 . 1 ,  8 . 2  as the retention device  9 . 
     The second design for the safety device in accordance with  FIG. 11  is essentially distinguished from the first design in that, corresponding to the exemplary embodiments described in the foregoing that have mechanically synchronizable pressure points according to  FIG. 2 ,  5 ,  7 ,  8 , or  9 , the first pinion shaft  8 . 1  is mechanically linked to a non-positive fit safety brake  12  and the second pinion shaft  8 . 2  is mechanically linked to a positive-fit blocking device  13  as the retention device  9 . In both designs the servo-motors  7  are controlled via the servo-converter system  18 , fed by the power supply  23 , with the integrated device for torque isolation  19 . 
     For satisfying the personnel and engineering safety requirements, the mechanical retention devices  9  and the devices for electrical torque isolation  19  act in combination and are controlled and monitored jointly by the safety control unit  26 . The torque isolation unit  19 , which is necessary for preventing uncontrolled start-up of the servo-motors  7 , can be created using the following measures that can be seen in  FIG. 11  individually or in combination. In addition to the line contactor  20 . 1  that can be embodied to be turned off and that is in the servo-converter system  8  in a first embodiment, a power contactor  20 . 3  that can be turned off can be used in the motor line in a second embodiment. A turn-off element  20 . 2  for the control energy of the semi-conductor gates of the motor AC converter  25  can be used for torque isolation in a third embodiment. It is also conceivable to short-circuit the motor line, by means of a short circuit protection unit  21 , in conjunction with load resistors  22 .