Abstract:
In a transfer arrangement and method for transferring a workpiece between first and second spaced locations along a guide rail with a carriage movably supported on the guide rail, a transfer arm is pivotally supported on the carriage and carries at its free end a workpiece holder which is accelerated by the carriage with the arm essentially stretched out in the movement direction out of, and decelerated into, the end positions, and, in an intermediate position, the carriage movement is slowed down or even reversed while the workpiece holder is moved along by a pivot movement of the arm.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a transfer arrangement, particularly for a transfer press and to a method for transporting workpieces by means of a transfer arrangement including a guide track on which a carriage is movably supported. 
   The transport of workpieces between individual presses has been mechanized for some time in connection with different press installations, workpiece conveyor lines from press-to-press and similar devices. Particularly for presses arranged closely adjacent one another and for the handling of smaller sheet metal parts, so-called gripper track transfer equipment has been used as shown for example in DE 43 10 057 A1. With this kind of equipment, the workpieces are transferred by means of two parallel gripper rails which are moved in the rhythm of the presses so that one is moved toward and below the workpiece on other gripper rails and then raised to support the workpiece and then, with the workpiece supported thereon is moved away from the other gripper rails, and then again downwardly to deposit the workpiece on another set of rails or other support device. During the press stroke, the gripper rails are again returned to the start-out position. 
   The transport of larger sheet metal parts is facilitated by the so-called suction transfer devices as they are described in DE 195 06 518 A1. They include suction bridges which are arranged transverse to the transport direction and are supported at their two ends by carriages disposed on guide rails. Raising and lowering of the guide rails results in raising and lowering the suction bridges and consequently the workpieces. For moving the suction bridges, so-called push rods are provided on the guide rails which are operated by electric motors. 
   For individual presses which are to be interlinked and which are set up at a certain distance from each other, transfer arrangements are known which operate individually between two press stages. DE 195 21 976 A1, for example, discloses in one of the shown embodiments a transfer arrangement which includes a vertically adjustable carriage. The carriage is provided with a parallelogram-arm structure at the lower end of which a two-element pivot arm is arranged. The pivot arm may have vertical or horizontal pivot joint axes. In the arrangement with a horizontal pivot axis, the parallelogram arm structure operates like a pendulum. The arm can be extended in one direction toward an upstream workpiece or in another direction toward a downstream workpiece. The joints pivot in the process about a horizontal axis. 
   With such a drive arrangement, large distances between presses can be bridges and the transfer of the workpieces can be arranged to be reasonably flexible. For example, the distances between the presses of a transfer set up do not need to be uniform. 
   The height required for the pivot movement is substantial. This means that the tools must be opened wide to permit the pivot movement of the arms. To overcome this disadvantage arms with vertical pivot axes are disclosed in the same reference. Such arrangements however, with long arms, suffer from bearing inaccuracies resulting in inaccurate positioning of the workpieces. 
   Furthermore, the power required for the transport of the workpieces and the movement of the arms and the engagement structures must be provided by pivot drives which require high torques. If the drives are positioned at the various joints of the arms, these drives must be relatively large in order to generate the required torques and they too must be moved. 
   It is therefore the object of the present invention to provide an improved transfer arrangement and method of operating such a transfer arrangement. 
   SUMMARY OF THE INVENTION 
   In a transfer arrangement and method for transferring a workpiece between first and second spaced locations along a guide rail with a carriage movably supported on the guide rail, a transfer arm is pivotally supported on the carriage and carries at its free end a workpiece holding means which is accelerated by the carriage, with the arm essentially stretched out in the movement direction, out of, and decelerated into, the end positions, and, in an intermediate portion, the carriage movement is slowed down or even reversed while the workpiece holder is moved along by pivot movement of the arm. 
   The transfer arrangement according to the invention includes a guide rail and a carriage supported thereon so as to be movable along the guide rail. On the carriage, a preferably two-element arm is supported which can be pivoted in the transport direction and opposite thereto. Its upper member, which is connected to the carriage, is pivotable by 180°. Its lower member, which is connected to the support device, is pivotable preferably in the opposite direction by 360°. A control arrangement at least for controlling the carriage drive can cause the arm with support device to extend in its stretched state to move into the at least partially open tools. In this way, a certain relatively small plunger opening is sufficient for the insertion and for the removal of the workpiece. In other words, with an approximately sinus-shaped plunger movement, a large part of the plunger stroke and consequently a relatively long time span can be used for the workpiece transport. The pivoting of the arm from the rearwardly oriented to the forwardly oriented position does not occur in synchronism with the forward movement of the carriage but basically, is concentrated within an available pivot volume or operating space between the presses or plungers of adjacent tools. The control unit controls the carriage in such a way that, during pivoting of the arm, the carriage is at least slowed down but preferably moves backwardly for a short distance. This is energetically advantageous. The carriage and the carriage drive which is preferably stationary can be used in this way to accelerate the essentially stretched arm and the workpiece held thereby out of the tool. The pivot drives of the arm then only need to provide the force required to hold the arm in a stretched state that is, they only must accommodate the weight force. When the arm and the workpiece have been accelerated by the carriage, they can continue to move in the direction of acceleration while the strong carriage drive moves the carriage in the opposite direction or at least decelerates the carriage while the pivot drives then operate the pivot movements of the arm joints. The movement of the carriage in the opposite direction supports the movement of the pivot drives. When the arm is again stretched, the carriage can than again be moved forward to insert the workpiece into the open adjacent press. Little space is needed for that procedure. The retarding energy is again provided solely by the carriage drive, not by the pivot drives. 
   As a result, the carriage drive provides most of the power needed for the transfer of the workpieces. It can be large and rugged. Its weight is of no consideration since it is stationary. The pivot drives on the other hand do not need to be powerful so that the moving parts of the transfer arrangement, that is, the arms and the parts supported thereby can be very lightweight. 
   The transport arrangement described so far can move very rapidly because of the energetic and power-based optimization. If the workpiece support structure, (the suction bridge) is introduced into the tool and removed therefrom with the arms essentially stretched, the transfer arrangement requires, as initially mentioned, only a small opening of the tool for the insertion of the workpiece. A large press angle (corresponding to the stroke of the press drive) can therefore be utilized for the transport of the workpiece. Both advantages combine to permit the provision of a modular transport arrangement which is lightweight and can be activated rapidly so that high press stroke rates can be achieved. 
   The invention will become more readily apparent from the following description thereof on the basis of the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows schematically two presses interconnected by a transfer arrangement according to the invention, 
       FIG. 2  shows the transfer arrangement according to  FIG. 1  in a schematic perspective view, 
       FIG. 3  shows the transfer arrangement of  FIG. 2  in a schematic side view, 
       FIG. 4  shows an alternative embodiment of the transfer arrangement in a schematic side view, 
       FIGS. 5 to 16  show the transfer arrangement according to the invention in various operating states, 
       FIGS. 17 and 18  show two alternative movement diagrams for the carriage of the transfer arrangement indicating the carriage speed and the support structure speeds, 
       FIG. 19  shows diagrammatically the locations of the transfer arrangement over time, 
       FIG. 20  shows schematically two presses which are interconnected by a transfer arrangement and have additional lift shafts, 
       FIG. 21  shows the presses in a horizontal cross-sectional view, 
       FIG. 22  shows the presses of  FIG. 20  as seen in the transport direction, 
       FIG. 23  shows an alternative embodiment of the transport arrangement also the transport direction, and 
       FIG. 24  shows the presses of  FIG. 23  in a horizontal cross-sectional view. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
     FIG. 1  shows an arrangement of two presses  1 ,  2  of a setup of presses  3  which are interconnected by a workpiece transfer system. The workpiece transfer system comprises individual transfer arrangements of which one transfer arrangement  4  is schematically shown in  FIG. 1 . It is used for transferring metal sheet workpieces  5  from the press  1  to the press  2 . The transfer arrangement  4  can be used, as shown, for the interconnection of individual presses or for the transport of workpieces n hybrid press installations or in transfer presses. The transfer arrangement  4  is shown separately in  FIG. 2 . It is arranged between adjacent columns  6 ,  7 ,  8 ,  9  of the adjacent presses  1 ,  2 . Spaced parallel guide rails  13 ,  14  are supported on, or between, the columns  6 ,  7 , and  8 ,  9  and beams  11 ,  12  extend transverse to the transport direction T. Guide carriages  15 ,  16  ( FIGS. 1 and 2 ) are supported on the guide rails  13 ,  14  so as to be movable in the transport direction T. Although it would be possible in principle to use arc-like curved guide rails  14  straight guide rails  13 ,  14  are preferred. The two carriages  15 ,  16  are arranged in a mirror-reversed manner relative to each other. They form, together with other elements, symmetrical transfer components which are movable synchronously in order to tilt workpieces in a predetermined way. 
   Below, the transfer component group connected to the guide rail  14  and the carriage  16  will be described. This description also applies to the opposite transfer arrangement which is disposed on the guide rail  13  and the carriage  15 . For that reason, the same reference numerals are used. 
   As shown particularly in  FIGS. 3 and 4 , the arrangement includes a carriage drive  17  for the carriage  16  capable of moving the carriage  16  back and forth in the transport direction T. The carriage drive  17  may be a stationary servo motor  18  as symbolically indicated in the figures which, via a pull member  19  such as a toothed belt, is connected to the carriage  16 . With the servomotor  18  preferably mounted at one end of the guide rail  14 , a redirecting roller  21  is provided at the opposite end of the guide rail around which the pull member  19  extends. Alternatively, a gear rack drive arrangement may be provided with the servomotor arranged on the carriage  16  and the gear rack being stationary and mounted on the guide rail  14 , a screw spindle drive with a threaded nut disposed on the carriage  16  and extending along the guide rail  14  and connected at one end to the servomotor  18 , or another linear drive including a position-controlled hydraulic drive for driving the carriage  16 . The carriage  16  can be driven, particularly in the latter case, by way of hydraulic or pneumatic cylinders without piston rods. 
   The carriage carries an arm  24  comprising two elements  22 ,  23  and is supported on the carriage  16  pivotally about a pivot axis  25 . Pivot movement of the arm  24  is provided for by a drive motor  26  or another controlled drive mounted on the carriage  16 . The drive motor  26  determines the pivot positions of the element  22  of the arm  24 . 
   The elements  22 ,  23  of the arm  24  are joined by a pivot joint  27  whose pivot axis  28  extends parallel to the pivot axis  25  of the arm  22  that is in a direction transverse to the transport direction T. The pivot axis  28  and the pivot axis  25  extend preferably horizontally. It is pointed out however, that the pivot axis  25  and the pivot axis  28  may be vertically or otherwise oriented, any orientation being within the scope of the present invention. 
   The joint  27  is provided with a joint drive  29 , which, in the embodiments shown in  FIGS. 2 and 3 , is a servomotor  31  as indicated in  FIG. 3 . In this way, the element  23  can be pivoted independently of the pivot movement of the element  22 . 
   The element  23  is in all embodiments somewhat longer than the element  22 . As a result, its lower end reaches below the carriage  16 . It is connected to an attachment device for carrying a suction bridge  33 —see FIG.  2 —which serves as support means for the transport of the sheet metal parts  5  ( FIG. 1 ). Another servomotor  34  schematically indicated in  FIG. 2  at the lower end  32  of the lower element  23  is adapted to rotate the suction bridge  33  about its axis transverse to the transport direction T. In this way, the sheet metal workpiece  5  can be kept in a horizontal orientation during pivoting of the arm  24  and the workpiece can be tilted into any desired position. 
   The description provided above applies equally to the embodiment of  FIG. 4 . Other than in  FIG. 3 , however, the drive  29  for the joint  36  is not provided by a motor arranged at the joint but a drive structure  30  including for example a toothed belt sprocket wheel mounted on the carriage  16  concentrically with the pivot axis  25  so as to be stationary and over which a toothed belt  35  extends. The toothed belt  35  extends around a smaller toothed sprocket  36  which is firmly connected to the element  23  and is concentric with the pivot axis  28 . With this arrangement, pivoting of the element  22  about the pivot axis  25  results at the same time in an opposite pivotal movement of the element  23  in an opposite sense at a transmission ratio depending on the relative sizes of the sprocket wheels. 
   The transfer arrangement described so far is controlled by a control arrangement which is described below on the basis of its operation. Under the control of the control arrangement, the transfer arrangement  4  operates as follows: 
   In the  FIGS. 5 to 16 , various movement states of the transfer arrangement during a completion of a transfer stroke are shown schematically as to the kinematics thereof. 
   In  FIG. 5 , the transfer arrangement  4  is shown in a rest position. The tools  37 ,  38  of the two adjacent presses  1  and  2  are closed, that is, the respective top parts  37   a ,  38   a , are disposed on the bottom parts  37   b ,  38   b  of the respective presses. In the rest position, the carriage  16  is disposed closer to the tool  38  than to the tool  37 . A workpiece is to be transferred from the tool  37  to the tool  38 . The arm  24  is angled toward the tool  37 . The element  22  extends upwardly at a relatively steep angle whereas the element  23  is angled downwardly toward the tool  37 . The position represents the start-out position for the subsequent transfer cycle. In  FIG. 19 , the carriage position along the guide rail  14  (x-direction) is shown depending on time. For the situation as shown in  FIG. 5 , the carriage  16  is positioned on the right of a center line  39  disposed in the center between the centers  41 ,  42  of the tools. The tool center lines  41 ,  42  represent the center of the workpiece  5  and the end of the arm  24  at the starting and the end points. 
   After completion of a press stroke, the tools  37 ,  38  are being opened as indicated in  FIG. 6 . The servomotors  18 ,  31  controlling the arm  24  are beginning to stretch the arm  24  as shown in  FIG. 6 . At the same time, the carriage  16  starts to move toward the tool  37 . This carriage movement is indicated in  FIG. 19  by the reference to  FIG. 6 . 
   When the tool  37  is sufficiently opened, the transfer arrangement  4  with the suction bridge  33  can move into the tool  37 . During change of the positions of the arm  24  and the carriage  16  from those shown in  FIG. 6  to those shown in  FIG. 7 , first the arm  24  is stretched and then the carriage  16  is moved to its end position closest to the tool  27  (line A in  FIG. 19 ). Line A marks the start-out point A for the transfer movement of the carriage  16  in the transfer step. In this position, the workpiece  5  is picked up by shortly lowering the arm  24  and then raising it again. 
     FIG. 8  discloses the transfer arrangement wherein the arm  24  is slightly raised but still stretched. As indicated by the arrow, the carriage  16  is moving at full speed toward the tool  38  after having accelerated the carriage  16 , the arm  24  and the workpiece  5  together with the suction bridge  33  toward the tool  38 . This acceleration is accomplished essentially by the carriage drive motor  18 —without any contribution by the other motors. The speed of the carriage  16  on its way from the left extreme end position (line A in  FIG. 19 ) toward its right end position (line B in  FIG. 19 ) is shown in  FIGS. 17 and 18  for different embodiments. The line B represents the end point for the carriage movement during the transfer of the workpiece to the tool  38 . The carriage is accelerated in either case, that is following the curve I as well as the curve II, from the speed zero to a positive speed value, whereby the workpiece  5  reaches so to say “travel speed”. 
   After the acceleration phase with the arm  24  essentially stretched the carriage  16  reaches the position shown if  FIG. 9  and specifically marked in  FIG. 19  in which the carriage  16  stops and is then accelerated in the opposite direction while the workpiece  5  with the arm element  23  continues to move toward the tool  38 . The arm  24  is moved in this process from the position shown in  FIG. 9  over to the position shown in  FIG. 10  toward the tool  38 . The servomotors  26 ,  31  which cause the pivot movements of the elements  22 ,  23  require only small drive moments for this movement since the workpiece and the suction device have already been accelerated by the carriage  16  and the carriage is now moving in the opposite direction. The servo motors  26 ,  31  can therefore be relatively small and lightweight. 
   From the left intermediate position as shown in  FIG. 10  and in  FIG. 19 , the carriage  16  is then again moved toward the tool  38  after the arm  24  has been essentially stretched toward the tool  38  so that, as shown in  FIG. 11 , it extends into the open tool  38 . The carriage moves the suction bridge  33  with the workpiece with the arm  24  stretched out to the tool center  42  while it is decelerated. The deceleration of the suction bridge  33 , the workpiece supported thereby and the arm  24  is then again provided by the drive for the carriage  16 . The workpiece is then deposited in the tool which is closing while the stretched out arm  24  is moved back out of the tool  38  as the carriage  16  is moved back preferably beyond the center line  39 . 
   As indicated in  FIG. 18 , the speed of movement of the carriage  16  can become negative in the center area that is the carriage moves backward as shown also in  FIG. 19 .  FIG. 17  relates to an embodiment wherein the speed of the carriage  16  during the flipping over of the arm in the transfer from  FIG. 9  to  FIG. 10  is only reduced and its direction of movement is not reversed. Such an intermediate speed reduction on the way from the end point A to the end point B still provides for a load reduction of the servo drives of the arm. It may be used for example if the presses are arranged at larger distances from each other, that is if there are larger travel distances for the workpiece from one press to the other. The speed of the suction bridge remains positive in any case as indicated by the dashed line III; it is always positive, also in the center area between the presses. 
   After completion of the transfer stroke, the suction bridge  33  and the arm  24  are moved out of the closing tool  38 , while the arm  24  is stretched whereby the carriage  16  again moves past the centerline  39  as shown in  FIG. 14  and is decelerated. The kinetic energy of the arm available during deceleration of the arm  24  can be used to flip the arm over as shown in  FIGS. 14 and 15 . The carriage  16  is then moved to a rest position nearer to the tool  38  and the arm  24  assumes a waiting position in which it is pivoted toward the tool  37 . The position as shown in  FIG. 16  shows the rest position as it is also shown in  FIG. 5 . An operating cycle is then completed. 
     FIG. 20  shows an embodiment of a transfer arrangement  4  based essentially on the transfer arrangement according to  FIG. 1 . Here, however, the guide rails  13 ,  14  (see also  FIG. 21 ) are height adjustable. To this end, lifting units  44 ,  45 ,  46 ,  47  are provided which support the guide rails  13 ,  14  together at their ends. The lifting units  44 - 47  may include weight compensation units ( 48 ,  49 ,  51 ,  52 ). The lifting units  44  to  47  like all the other drives of the transfer arrangement  4  such as the servomotors  18 ,  26 ,  31 ,  34  are subject to a central control unit which control at least the transfer arrangement  4 . The control unit addresses the various motors in a way that the desired transfer curve is obtained. 
   The lifting units  44 ,  45 ,  46 ,  47  can be controlled synchronously in pairs so that the guide rails  13 ,  14  are raised or lowered while remaining in a horizontal orientation. However, the guide rails  13 ,  14  can also be raised or lowered independently of each other. In this way, the workpiece can be tilted in a transverse direction also in the center position between the two presses  1 ,  2 . In addition, the orientations of the guide rails  13 ,  14  can be adjusted other than horizontally if needed. As shown in  FIGS. 21 and 22 , the units supported on the guide rails  13 ,  14  are arranged mirror symmetrically. But their movements do not need to be synchronized. By controlling the two units differently, the suction bridge  13  can be pivoted or inclined with respect to the horizontal longitudinal direction (transport direction T), with respect to the transverse direction and with respect to the vertical direction. 
     FIGS. 23 and 24  shows a simplified and presently preferred embodiment of the transfer arrangement  4 , wherein only a single guide rail  13  is used. The guide rail  13  is arranged outside a center line  53 , which, in the transport direction T, extends in the center between the pair of columns  6 ,  8  and  7 ,  9 . This guide rail  13  is again supported by lifting units  44 ,  45 . In a particular embodiment, the columns can be omitted. However, generally, when present they are adjustable by the control unit for the adjustment of the transfer arrangement  7  which is possible thereby also during operation of the presses. The suction bridge  33  is supported at the center thereof by the element  23  of the arm structure  24 . The joint provided at the support includes at least one pivot axis and a control motor for rotating the suction bridge  33  around its longitudinal axis with respect to the element  23  of the arm  24 . Other pivot structures with the respective drive motors may be provided. The advantage of such an arrangement resides in the small numbers of control motors required while providing a large degree of freedom of movement and pivotability of the suction bridge  33 . Any pivot position of the workpiece can be maintained during the transfer step without the need for adjusting guide rails  13  or  14  as it is required in connection with the other embodiments. 
   It is apparent from  FIG. 23  that the suction bridge is preferably supported in the center thereof and the transfer arrangement  4  is arranged at one side of the center plane M. 
   The explanations given with respect to the earlier figures supplement the description concerning the embodiments shown in  FIGS. 23 and 24 .