Transport method for transferring workpieces

In a transport method for transferring workpieces between a plurality of successive stations of a processing device, especially a forming device, workpieces are in each case transported from one station to the respective next station of the processing device simultaneously by means of a plurality of gripping tools which are movable jointly in a transport cycle. In the event of a process disturbance, the transport cycle is suspended and the gripping tools with the workpieces are moved into a waiting position in which the workpieces are outside the operating range of processing tools of the stations of the processing device. Once the process disturbance has been eliminated, the transport cycle of the workpieces is resumed. By virtue of the movement of the gripping tools into a safe waiting position outside the operating range of the processing tools of the stations, consequent damage resulting from the process disturbance can be prevented.

This application is the United States national phase of International Application No. PCT/EP2017/059724 filed Apr. 25, 2017, and claims priority to Switzerland Patent Application No. 000562/16 filed Apr. 28, 2016, the disclosures of which are hereby incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a transport method for transferring workpieces between a plurality of successive stations of a processing device, especially a forming device.

Description of Related Art

In mass-forming and also in other forming operations or processing operations generally workpieces often pass through a number of stations of a processing device in succession, the workpieces being transported on from station to station. In a forming device, the stations are typically a loading station and various forming stations. To transport the workpieces from station to station there are usually used transport apparatuses which are equipped with tongs-like gripping tools and which operate in time with the rhythm of the processing device, the gripping tools simultaneously grasping the workpieces, withdrawing them from a station and supplying them to the respective next station, where they release them.

In the case of the known processing devices, especially forming devices, the transport movements and the operation of the gripping tools are coupled to the power train of the processing device see, for example, CH 595 155 A.

EP 2 233 221 A2 discloses a stamping apparatus for a progressive stamping press in which stamped parts are transported from one processing station to the next by means of gripping tools on a star-shaped rotating arm arrangement. The star-shaped rotating arm arrangement is rotated alternately in the clockwise direction and the anti-clockwise direction by a drive motor.

A transport apparatus for transferring workpieces in a forming device is described in EP 1 048 372 B1. In this known transport apparatus, a plurality of gripping tools configured as gripping tongs, each with a dedicated gripping tool drive which is decoupled from the power train of the forming device, are arranged on a common tong support which is movable in the longitudinal direction and transversely thereto and by means of which all the gripping tongs are jointly transported back and forth in each case between two adjacent stations of a forming device. The gripping tongs comprise two pivot arms which are driven by a servo motor via kinematic coupling members so as to be pivotable towards one another and away from one another. EP 1 048 372 B1 relates essentially to the configuration of the gripping tongs and the drives thereof; the drive of the tong support for carrying out the transfer movements of the gripping tongs is not specifically described.

In forming devices, especially hot forming devices, the raw material is usually supplied in the form of bars from which pieces of the required length are then cut off. The beginnings and ends of the bars are not permitted to enter the forming process and have to be discarded. Those discarded portions are missing from the forming process and create individual empty forming stations in the forming device. On account of the absence of forming force at those locations, the deformation of the machine body is altered, which has an adverse effect on the geometry of the formed parts. Depending upon the requirements, such parts cannot then be used and have to be manually sorted out from the finished parts or separated out by means of suitable separating devices. Since mechanical separation is not so accurate, it may happen that good formed parts are also separated out. In addition, an empty forming station undergoes greater cooling by cooling water, which has an adverse effect on the wear to the forming tools. This problem is described in detail, for example, in EP 1 848 556 B1.

EP 1 038 607 A2 discloses a transport apparatus and a transport method for transferring workpieces between a plurality of successive stations of a forming device, in which the workpieces are in each case transported from one station to the respective next station of the forming device simultaneously by means of a plurality of gripping tools which are movable jointly in a transport cycle. At the end of each transport cycle the gripping tools without workpieces are moved into a home position. If a device for monitoring the supply of workpieces to the first station of the forming device detects the absence of a fresh workpiece, the gripping tools wait in the home position until a workpiece is supplied to the first station again. In this way empty forming stations during the forming operation are avoided.

A further problem of conventional transport apparatuses and of the transport methods performed therewith is that in the event of process disturbances, which are caused, for example, by empty gripping tools or by workpieces incorrectly inserted into the gripping tools or by damaged parts, such as, for example, broken-off gripping tools or fractured punches etc., it is not possible to react immediately and so workpieces are not shaped as desired or often even considerable consequent damage can be caused to the transport apparatus or to the processing device.

Against this background a problem underlying the invention is to improve a transport method of the kind mentioned at the beginning and a corresponding transport apparatus to the effect that it is possible to react easily and quickly to process disturbances, so that consequent damage can be avoided. A particular objective is to be able to avoid empty locations in the stations of the processing device.

SUMMARY OF THE INVENTION

That problem is solved by the transport method according to the invention and by the transport apparatus according to the invention.

In respect of the method, the core of the invention lies in the following: in a transport method for transferring workpieces between a plurality of successive stations of a processing device, especially a forming device, the workpieces are in each case transported from one station to the respective next station of the processing device simultaneously by means of a plurality of gripping tools which are movable jointly in a transport cycle. In the event of a process disturbance, the transport cycle is suspended and the gripping tools with the workpieces are moved into a waiting position in which the workpieces are outside the operating range of processing tools of the stations of the processing device. Once the process disturbance has been eliminated, the transport cycle of the workpieces is resumed.

By virtue of the movement of the gripping tools into a safe waiting position outside the operating range of the processing tools of the stations, consequent damage resulting from the process disturbance can be prevented.

The method is especially advantageous if the process disturbance has been caused by a missing workpiece or by a workpiece unsuitable for processing in a loading station of the processing device, because it is thus possible to avoid empty processing stations and the disadvantages associated therewith.

The method is also advantageous if the process disturbance has been caused by a missing workpiece or by a workpiece incorrectly inserted into a gripping tool, because it is thus likewise possible to avoid empty processing stations or further disturbances caused by the incorrectly inserted workpiece.

The method is also advantageous if the process disturbance has been caused by a damaged part of a gripping tool or by a damaged part of the processing device, because it is in that way possible to avoid further consequent damage.

Advantageously the absence of a workpiece or the presence of a workpiece unsuitable for processing is detected by means of a sensor device, in which case the movement of the gripping tools into the waiting position is initiated by the sensor device. This allows the gripping tools to be moved automatically into the waiting position in the event of a process disturbance caused by the absence of a workpiece or the presence of a workpiece unsuitable for processing.

Advantageously the absence of a workpiece or the presence of a workpiece incorrectly inserted into a gripping tool is detected by means of a gripping tool controller of a gripping tool drive, in which case the movement of the gripping tools into the waiting position is initiated by the gripping tool controller. This allows the gripping tools to be moved automatically into the waiting position in the event of a process disturbance caused by the absence of a workpiece or the presence of a workpiece incorrectly inserted into a gripping tool.

In respect of the transport apparatus for simultaneously transferring workpieces between a plurality of successive stations of a processing device, especially a forming device, the core of the invention lies in the following: the transport apparatus comprises a movably mounted gripping tool support on which there are arranged a plurality of gripping tools, each for gripping one workpiece, a motor-driven gripping tool support drive for back and forth movement of the gripping tool support with the gripping tools between the stations of the processing device, and a support controller for the gripping tool support drive, which controller is configured to control the movement of the gripping tool support and, as a result of a control command supplied thereto, to move the gripping tool support with the gripping tools into a waiting position by means of the gripping tool support drive. The gripping tool support drive and the support controller are configured to move the gripping tool support with the gripping tools with workpieces into the waiting position and to suspend the transport of the workpieces.

By means of the transport apparatus according to the invention, the transport of workpieces can easily be suspended in the event of a process disturbance and the gripping tool support with the gripping tools can easily be moved into a safe position, so that consequent damage can be avoided.

Advantageously the gripping tool support is, on the one hand, mounted so as to be movable in a linearly guided way and, on the other hand, mounted so as to be displaceable transversely with respect to its linearly guided movability by means of a parallelogram guide arrangement. Furthermore, the gripping tool support is advantageously movable by means of a gripping tool support drive comprising two crank gear arrangements each having an associated gripping tool support drive motor, wherein each crank gear arrangement has a crank, which is drivable in rotation by the associated gripping tool support drive motor, and a drive rod which is articulatedly connected on the one hand to the crank and on the other hand to the gripping tool support.

By virtue of the dedicated gripping tool support drive, the transport apparatus is decoupled from the power train of the processing device. The decoupling and the displaceability of the gripping tool support transversely with respect to its linear back and forth movement enables the gripping tool support to be quickly moved into a safe position in the event of a disturbance. The kinematic coupling of the gripping tool support to the gripping tool support drive motors via two crank gear arrangements allows simple control of the movement sequences solely by corresponding actuation of the gripping tool support drive motors.

Advantageously the gripping tool support with the gripping tools is movable by means of the gripping tool support drive in a forward movement along a first linear path of movement and in a return movement along a second linear path of movement parallel to the first linear path of movement. As a result of the spacing between the two linear paths of movement, the gripping tools can in a simple way be moved out of the operating range of processing tools in the stations of the processing device.

Very especially advantageously the transport apparatus has a sensor device for detecting a process disturbance caused by a missing workpiece or by a workpiece unsuitable for processing, and for signalling that disturbance to the support controller. As a result, the support controller can be automatically caused to move the gripping tools into the waiting position.

Advantageously the gripping tools are each assigned a gripping tool drive, which is arranged on the gripping tool support, for individual operation of the gripping tools, and a gripping tool controller which is configured to control the opening and closing movements and preferably also the clamping force of the individual gripping tools individually and to recognise a process disturbance caused by an empty gripping tool or by a workpiece incorrectly inserted into a gripping tool and to signal that disturbance to the support controller. As a result, the support controller can be automatically caused to move the gripping tools into the waiting position.

DESCRIPTION OF THE INVENTION

The following observations apply in respect of the description which follows: where, for the purpose of clarity of the drawings, reference signs are included in a Figure but are not mentioned in the directly associated part of the description, reference should be made to the explanation of those reference signs in the preceding or subsequent parts of the description. Conversely, to avoid overcomplication of the drawings, reference signs that are less relevant for immediate understanding are not included in all Figures. In that case, reference should be made to the other Figures.

The diagrammatic overviews ofFIGS. 1-6show the parts of the processing device according to the invention that are relevant for understanding the present invention, in this case using the example of a forming device. WhileFIG. 1is a view from the front according to line I-I inFIG. 2,FIG. 2is a sectional view according to line II-II inFIG. 1. Correspondingly,FIGS. 3 and 5are views from the front andFIGS. 4 and 6are associated sectional views.

In the exemplary embodiment shown, the forming device, indicated as a whole by reference sign M, comprises five stations110,120,130,140,150, arranged one next to the other, of which a first station110is a loading station and the other stations120,130,140and150are forming stations. The forming stations120,130,140and150comprise four forming dies121,131,141and151arranged in a common die holder101, four forming tools in the form of punches122,132,142and152and four ejection elements123,133,143and153, with which workpieces W that have been shaped in the forming dies by means of the punches can be ejected from the forming dies. The loading station110comprises a shearing device112for shearing off a workpiece W from a bar material (not shown, supplied by means of a bar material feed device, likewise not shown) and an ejection element113, with which a workpiece W can be ejected from the shearing device112. A transport apparatus, indicated as a whole by reference sign T, serves for transferring the workpieces from one station to the respective next station of the forming device M. Of the transport apparatus T,FIGS. 1-6each show only gripping tools, each having a pair of tong arms32aand32b.

During operation of the forming device, in a starting position the tongs-like gripping tools of the transport apparatus T, which are formed by the pairs of tong arms32aand32b, each pick up a workpiece W which is held in readiness in the loading station110or has been ejected from the forming dies121,131,141and151of the forming stations120,130,140and150(FIGS. 1 and 2) and then transport those workpieces W simultaneously to the respective next station of the forming device M, the finished shaped workpiece W picked up from the last forming station150being released so that it can be discharged from the forming device.FIGS. 3 and 4illustrate this. In forming stations120,130,140and150, the workpieces W are inserted into the forming dies121,131,141and151and subjected to forming by means of the punches122,132,142and152. The transport apparatus T then returns the (empty) gripping tools to the starting position shown inFIGS. 1 and 2. There the gripping tools each pick up a fresh workpiece W which is held in readiness in the loading station110or has been ejected from the forming dies121,131,141and151of the forming stations120,130,140and150and again transport those workpieces to the next station of the forming device, as shown inFIGS. 3 and 4. The entire sequence takes place in a transport cycle in time with the rhythm of the forming to device M.

It is clear from the above brief description of the transfer operation that in each transfer cycle each gripping tool transports a different workpiece and each pair of adjacent stations of the processing device is served by a different gripping tool. In the context of the present invention the transfer of workpieces from station to station of the processing device by means of a plurality of gripping tools is to be understood in this sense.

Thus far the processing or forming device M shown corresponds in structure and mode of operation to conventional processing or forming devices of this kind, so that the person skilled in the art requires no further explanation in this regard.

The transport apparatus of the processing or forming device M is explained in detail below with reference toFIGS. 7-17. The transport apparatus, indicated as a whole by reference sign T, comprises a fixed frame10, a plate-like gripping tool support20, which is arranged to be movable in or on the frame10and which in the example herein supports five gripping tool units30, and a gripping tool support drive. The gripping tool units30are all arranged at the same distance from a common reference plane E (FIG. 7). A front face of the plate-like gripping tool support20, facing towards the gripping tool units, is aligned parallel to the reference plane E. The gripping tool support drive comprises two gripping tool support drive motors55and56, which are each configured as servo motors having rotary encoders and gearing and are rigidly mounted on the frame10. Furthermore, the tool support drive comprises two crank gear arrangements which each have a crank51,52and a drive rod (connecting rod)53,54, respectively. The cranks51and52are each rigidly mounted on a rotatable part of the gearing of the gripping tool support drive motors55and56, respectively, and are drivable in rotation thereby. In practical use, the frame10is mounted on the machine body (not shown) of the forming device M so as to be detachable or pivotable away, so that access can easily be gained to the forming dies and to the forming tools.

In the frame10there are arranged two parallel guide rods11and12(FIGS. 7-10), the axes of which define the reference plane E (FIG. 7). Two link rods13and14are guided along or on those guide rods11and12so as to be linearly movable in the longitudinal direction of the guide rods. In addition, the two link rods13and14are each pivotally articulated about a respective one of the two guide rods11and12. At their ends remote from the guide rods, the link rods13and14are pivotally attached to the gripping tool support20by means of journal pairs15and16(FIGS. 9 and 10). The distance between the two journal pairs15and16is the same as the distance between the two guide rods11and12. The distance between the journal pair15and the guide rod11is the same as the distance between the journal pair16and the guide rod12. The two parallel guide rods11and12and the two link rods13and14together with the gripping tool support20accordingly form a parallelogram guide arrangement for the latter, the gripping tool support20being displaceable in both directions (upwards and downwards in the Figures) transversely with respect to the longitudinal direction of the guide rods11and12. InFIG. 7this is symbolised by the double-headed arrow25. At the same time, via the slidably mounted link rods13and14, the gripping tool support20is movable back and forth along the guide rods11and12in the longitudinal direction thereof in a guided way, this being indicated inFIG. 7by the double-headed arrow26. Therefore the gripping tool support20is, on the one hand, guided so as to be linearly movable parallel to the reference plane E and, on the other hand, mounted so as to be displaceable substantially parallel to the reference plane transversely with respect to its linear movability.

Each of the drive rods (connecting rods)53and54is rotatably articulated by one end on the crank51and52, respectively, and by its other end on the gripping tool support20. By corresponding rotation of the two cranks51and52by means of the two gripping tool support drive motors55and56, the gripping tool support20can be moved as desired (within predetermined limits) in the direction of the double-headed arrow26and/or the double-headed arrow25.

An advantage of the parallelogram guidance is that the gripping tool support20, during its transverse displacement (pivoting movement about the guide rods), performs only a small movement perpendicular to its displacement movement, that is to say perpendicular to the reference plane E.

FIG. 19shows in diagrammatic form a typical path of movement of the gripping tool support20and accordingly of the gripping tool units30attached thereto. The closed, cyclically followed path of movement21comprises four movement path sections21a-21d. The two linear movement path sections21aand21ccorrespond to the linearly guided sliding movement of the gripping tool support20along the guide rods during the forward movement and return movement between the stations of the forming device, while the two movement path sections21band21dresult from the displacement of the gripping tool support20by means of the parallelogram guide arrangement. The points22and23mark the starting position of the gripping tool support20shown inFIG. 1and its position displaced by one station shown inFIG. 3, respectively. AsFIG. 19shows, the forward movement of the gripping tool support20takes place along a first linear path of movement (movement path section21a), while the return movement of the gripping tool support20takes place along a linear path of movement (movement path section21c) parallel to the first linear path of movement. The distance between the two linear paths of movement resulting from the displacement of the gripping tool support20is selected so that at the level of the second linear path of movement the gripping tool units30arranged on the gripping tool support20, or rather the gripping tools thereof, are located outside the engagement range of the forming tools122,132,142,152in the forming stations120,130,140,150, as can be seen fromFIG. 5. Reference sign27marks a waiting position, which will be discussed further hereinbelow.

The gripping tool units30arranged one next to the other on the gripping tool support20are all identically constructed. Their structure will be apparent fromFIGS. 11-17.

Each gripping tool unit30comprises a tong body31, a pair of movable tong arms32aand32bforming gripping tongs, and a gripping tool drive in the form of an (electric) servo motor33having a rotary encoder and gearing, the servo motor being shown only inFIGS. 9 and 14. The tong body31and the servo motor33, including the gearing, are each mounted on the gripping tool support20. The two tong arms32aand32bare movably arranged on the tong body31.

In the tong body31, two tong carriages35aand35bare displaceably mounted on three guide rods34a,34band34c. The tong carriages35aand35bare each kinematically connected to a respective toothed rod37aand37bvia a drive rod36aand36b, respectively, so that a movement of the toothed rods brings about a concomitant movement of the tong carriages and vice versa. The two toothed rods37aand37bare in engagement with a drive pinion38on diagonally opposite sides thereof, which drive pinion is drivable in rotation by the servo motor33(via the gearing thereof), so that on rotation of the drive pinion38the two toothed rods37aand37bmove in opposite directions and accordingly the two tong arms32aand32bare moved towards one another or away from one another. The opening and closing movement of the gripping tongs formed by the tong arms32aand32bis therefore effected by the servo motor33or the drive pinion38driven thereby.

The gripping tool drive can alternatively also be in the form of a servo-controlled (having servo valves) hydraulic drive. What is important in that case is that, on the one hand, the movement of the gripping tongs can be effected very quickly and, especially, with position control and, on the other hand, the clamping force of the two tong arms can be precisely adjusted or controlled and fed back, as is also true in the case of the above-described gripping tool drive having the electric servo motor.

At the free ends of the two tong arms32aand32bthere are arranged tong shoes39aand39bwhich serve for gripping the workpieces and are exchangeably attached, so that the gripping tongs can easily be matched to the shape of the workpieces being gripped (FIG. 11). The tong shoes need not be configured and/or arranged in the same way on all the gripping tongs. Preferably on each tong arm there are arranged, as shown, two tong shoes which together form an especially advantageous four-point holding arrangement for the workpieces being gripped. Such a four-point holding arrangement on the one hand enables the workpieces to be held securely and on the other hand reduces the risk of the workpieces tilting, especially when being introduced into closed gripping tongs.

The tong arms32aand32bare each releasably connected to the tong carriages35aand35bvia a pair of serrated plates40aand40b, respectively (FIGS. 15 and 17). In this way the tong arms32aand32bcan easily be adjusted laterally or in height relative to the respective tong carriages35aand35bin order, for example, to adapt the gripping tongs to the particular workpiece.

It will be understood that in the transport apparatus according to the invention, instead of gripping tongs it is also possible to use gripping tools of some other configuration. For example, the gripping tools could also be in the form of vacuum grippers. For use in a forming device, however, gripping tools in the form of gripping tongs are customary and proven.

As shown diagrammatically inFIG. 18, the transport apparatus T also comprises a support controller60for the gripping tool support drive motors55and56and also a gripping tool controller70for actuating the gripping tool drive motors33of the individual gripping tool units30. The gripping tool controller70is configured to control the opening and closing movements and the clamping force of the individual gripping tools, here gripping tongs32aand32b, individually. The support controller60calculates the rotated positions of the two cranks51and52necessary for travelling along the path of movement21of the gripping tool support20and controls the servo motors55and56accordingly. Moreover, the support controller60co-operates with a sensor device65which is configured to recognise a process disturbance caused, for example, by an unprocessable or missing workpiece W′ in the loading station110and to signal that disturbance to the support controller60.

The sensor device65, which is indicated only symbolically inFIGS. 2, 4 and 6, is assigned to the afore-mentioned bar material feed device (not shown) and can be, for example, a light barrier arrangement. Such sensor devices on bar feed devices are known per se and are described, for example, in EP 1 848 556 B1. The sensor device65is capable of recognising the beginnings and ends of bars. When the sensor device65recognises the beginning or end of a bar, it signals this to the support controller60, so that the support controller knows that the next bar section is defective and must be discarded, that is to say is not permitted to enter the forming process. The support controller60then reacts to that process disturbance in the way explained in greater detail below.

The support controller60and the gripping tool controller70co-operate with a higher-level controller80which inter alia also makes the connection to the processing device and specifies at which position of the path of movement the gripping tool support or the gripping tools thereof should be located. By means of the higher-level controller80, an operator can also input or modify settings, for example relating to the movement of the gripping tool support or to opening and closing movements of the gripping tongs. It will be understood that the functions of the support controller60, the gripping tool controller70and the higher-level controller80can also be realised in some other configuration, for example they can be combined in a single controller.

As already mentioned at the beginning, in forming devices, especially hot forming devices, the raw material is usually supplied in the form of bars from which pieces of suitable length are then sheared off. The beginnings and ends of the bars are not permitted to enter the forming process and have to be discarded. Those discarded portions are missing from the forming process and create empty forming stations in the forming device, which should be avoided for the reasons explained at the beginning.

Because the drive of the gripping tool support20, or of the gripping tools32a,32barranged thereon, is independent and decoupled from the power train of the forming device, the above-described transport apparatus according to the invention makes it possible to avoid empty forming stations in a forming device.

If, for example, the mentioned sensor device65detects a process disturbance caused by a missing workpiece or by a workpiece W that is unsuitable for further processing and is to be discarded (FIGS. 5 and 6), the sensor device65sends a corresponding control command to the support controller60for the gripping tool support drive. The support controller60then causes the gripping tool support20with the gripping tool units30to depart from its customary path of movement21(FIG. 19) and instead causes the gripping tool support20with the workpieces W located in the gripping tool units30to be moved into a waiting position27(FIG. 20). The waiting position is located, for example, on the upper movement path section21cof the gripping tool support20, the tong arms32aand32bof the gripping tool units30being located above and between the tools112,122,132,142and152, so that they are out of range of the latter. This situation is shown inFIGS. 5 and 6. The forming tools then perform an empty stroke, but this has no adverse consequences because all the forming stations are empty. Preferably, the cooling of the tools is suspended during this phase, so that the tools and the workpieces located in the waiting position are not cooled. The defective workpiece W′ is discarded (in a manner known per se). As soon as the sensor device65reports that a workpiece W suitable for the forming process is to arrive in the loading station110again, the support controller60causes the gripping tool support20to return to its original path of movement, the workpieces being transferred to the respective forming stations and the gripping tool support20then following its normal path of movement21into its starting position22shown inFIGS. 1 and 2in order to pick up workpieces W in that position and then transport them to the respective next forming station.

FIG. 20illustrates in graphic form the movement sequence of the gripping tool support20just described in the event of a process disturbance. The movement of the gripping tool support20into the waiting position27takes place along a movement path section24aand the movement of the gripping tool support20from the waiting position27to position23takes place along a movement path section24b. The overall path of movement from position22via the waiting position27to position23is denoted by reference sign24. The movement path sections24aand24bneed not necessarily follow the course shown inFIG. 20. The movement of the gripping tool support20can also take place, for example, along alternative movement path sections24a′ and24b′ which correspond to movement path sections21dand21c, and21cand21b, respectively, of the normal path of movement21.

Decoupling the transport apparatus from the power train of the forming device enables the duration and route for transporting, lifting and gripping to be adjusted and varied independently of the stroke of the forming tools. “Lifting” is to be understood herein as the vertical displacement of the gripping tool support20, the lifting stroke corresponding to the vertical distance between the two movement path sections21aand21c. The adjustment of the lifting and gripping movement decoupled from the stroke of the forming tools allows individual adaptation to the particular workpieces, with the result that wear to the machine is reduced. In addition, in the event of issues in the tool chamber, for example if a formed part has not been fully pushed out of the forming die or a broken punch is stuck in the forming die or a formed part has been lost from a gripping tool, it is thereby also possible to react to the situation and move the gripping tool support20with its gripping tool units30into a safe position, for example the mentioned waiting position27, and to stop the forming device until the disturbance has been resolved. It is thereby possible, for example, to prevent gripping tools from being broken off or other consequent damage from being caused to the transport apparatus.

As already mentioned, the gripping tool units30are individually controllable by means of the gripping tool controller70. As a result, the timepoint for opening and closing can be adjusted individually for each gripping tool unit. The opening stroke of the tong arms32aand32band the duration of the movement can also be adapted to the workpiece in question. The same applies to the lifting movement. That movement can also be optimised for each workpiece in respect of stroke and duration, with the aim of keeping acceleration and accordingly load on the structure of the apparatus low. In contrast thereto, known transport apparatuses with control curves must always be designed for the maximum possible stroke, with the result that the components are subjected to maximum loading and accordingly maximum wear in the case of every workpiece or formed part.

In order to compensate for defects in the shape of the blank section or to achieve an off-centre predistribution of material, for example in the production of cams, it is necessary for the first gripping tongs or another gripping tongs to be positioned off-centre. In known transport apparatuses, eccentric adjusting elements are utilised for that purpose or the tong shoes are adjusted by trial and error so that the centre of the workpiece is shifted from the centre by the desired amount. The transport apparatus according to the invention enables the gripping tool support20to be moved out of the centre (zero position) by the desired amount by means of the gripping tool support drive motors55and56simply by inputting the desired values at the higher-level controller80. The relevant gripping tongs are then aligned with a central adjusting element and then the gripping tool support is moved into its zero position again. In this way it is possible for one or more gripping tongs to be positioned off-centre. The remaining gripping tongs are adjusted when the gripping tool support20is central (in the zero position) again.

The clamping or holding force of each gripping tool unit30is controlled by means of the gripping tool controller70via the torque of the associated servo motor33and can in this way be simply adapted to the workpiece being held and optionally also varied over the movement cycle of the gripping tool support. The clamping force can be adjusted so that, for example, it is smaller when the workpieces are being introduced into the gripping tongs than it is for transport. The loading on the mechanical components is therefore only as high as necessary.

Servo motors usually have a rotary encoder for feeding back the current rotated position to its controller. Using the rotary encoder the gripping tool controller70can easily establish whether a gripping tool is loaded or empty, for example if a workpiece has been lost from a gripping tool, by comparing the actual rotated position with the desired rotated position, so that if necessary the forming device can be stopped. By suitable configuration of the gripping tool controller70it is thus possible also to recognise process disturbances caused, for example, by crookedly positioned workpieces in the gripping tools or by gripping tools tearing open. In that case this is signalled to the support controller60by the gripping tool controller70in a suitable way, and the support controller60then causes the gripping tool support20with the gripping tool units30to be moved into a safe position, for example the mentioned waiting position27, where it is stopped until the process disturbance has been resolved. A gripping tool is at risk of tearing open when, for example, a workpiece is incompletely ejected from the die or if the punch breaks and sticks in the workpiece. On attempting to transport the workpiece, the gripping tool would tear open. The gripping tool controller70recognises this at an early stage, however, and, via the support controller60, brings about a return movement of the gripping tool support, so that the gripping tool in question is prevented from tearing open. The gripping tool support20with the gripping tool units30is then moved into a safe position, for example the mentioned waiting position27, where it is stopped until the process disturbance has been resolved. The forming device is of course stopped during that time. In this way it is possible to react immediately to a process disturbance before greater damage occurs. The co-operation of the gripping tool controller70with the support controller60is symbolised by arrow71inFIG. 18. The gripping tools or gripping tongs of the described transport apparatus have parallel tong arms32aand32bwhich are moved linearly towards one another and away from one another. Such gripping tongs have the advantage over gripping tongs with pivotable tong arms that the tong shoes reach uniformly into the gripping diameter. If the tong shoes engage the workpiece at the same angle on both sides, on introduction of the workpiece they are pressed against it by the same amount. This reduces the risk of a workpiece being pushed crookedly into the gripping tongs.