Abstract:
The motor-actuable coupler is used for connecting workpiece grippers with a manipulating device, in particular a robot, which passes on workpieces from one stamping press to the next. The coupler consists of a fixed element ( 12, 66, 80, 38 ) on the drive side and a connecting element ( 10, 54 ) on the gripper side. Since normally a very large number of different workpiece grippers are employed and the connecting elements on the gripper side entail great costs, it is proposed that the fixed element of the coupler has a collet chuck ( 66, 74, 80, 38 ), and that the connecting element ( 10, 54 ) is a tube section, which can be centered in the fixed element ( 12, 66, 80 ) spaced apart from the clamping area (at  68, 76 ) located at the front end of the collet chuck. The tube section ( 10 ) is preferably centered by clamping faces ( 70, 78 ) and/or by cone surfaces ( 58 ) at its end which can be inserted into the collet chuck ( 14 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a motor-actuable coupler for connecting workpiece grippers with a manipulating device, in particular for the interlinking of stamping presses, consisting of a fixed element on the drive side and a connecting element on the gripper side. 
     BACKGROUND OF THE INVENTION 
     The workpiece grippers of manipulating devices, or respectively robots, must be individually matched to the workpieces. In connection with sheet metal parts, for example for motor vehicles, they normally have the form of a tube-shaped boom of, for example, 2 m length, with several boom extensions, to which suction grippers and/or clamping grippers are attached. Since the sheet metal parts are being deformed in several stamping presses, which are linked with each other, until they have their final shape, and since a specially designed workpiece gripper in accordance with the respective intermediate stage is required for a transfer to the next stamping press, 120 different workpiece grippers are required in order to produce 20 different sheet metal parts for a defined vehicle model on a line with, for example six stamping presses. So that the stocks of sheet metal parts can be kept as low as possible, the press tools are mostly exchanged in the course of only a few hours. Accordingly, in one work day it is often necessary to change the workpiece grippers of all transfer robots at the stamping presses ten times. 
     There are simple connections, which can be manually made by attachment screws, between the boom of a workpiece gripper and the portion of the robot supporting it, which is driven in a controlled manner. However, in view of the very high capital cost of a stamping press line per unit of time, a rapid exchange of the workpiece grippers must be relied upon. This requires quick acting couplers, which are motor-actuated when automatic gripper changing systems are used. 
     Such known couplers of this kind typically consist of a housing-like fixed element on the drive side, into which a matched connecting element coupled with the boom can be inserted and locked in place by means of interlocking connecting elements, for example stop bolts or hooks extending behind transverse pins. Since all workpiece grippers must be equipped with such a connecting element, considerable total costs result because of the multitude of grippers. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is the object of the invention to create a motor-actuable coupler of the type mentioned at the outset, which permits very rapid coupling and uncoupling, but which has a very simple structure. 
     The above object is attained in accordance with the invention in that the fixed element of the coupler has a collet chuck and the connecting element is a tube section, which can be centered in the fixed element spaced apart from the clamping area located at the front end of the collet chuck. 
     Collet chucks are used, for example, for clamping workpieces during lathe operations. In that process only comparatively low bending moments occur, because the cutting tools act on the workpiece at a short distance from the chuck. 
     In contrast to this workpiece grippers have to absorb considerable moments in particular at stamping presses. At the same time very high demands are made on accuracy. In spite of a long boom, large load stresses and great accelerations, a very narrowly delimited repetitive accuracy of the positioning movements is demanded. For this reason comparatively large connecting elements are provided on the gripper side of known quick change couplers, through which all forces are transferred from the boom to the robot arm, and which must be produced with several fitting surfaces in order to assure exact seating in the fixed element. In contrast to this, with the proposed coupler the structure can be much simpler, since no additional connecting element and no fitting surfaces are required at the point where the collet chuck of the fixed element of the coupler grips a tube section of the boom and clamps it. On the gripper side, a bezel on the front face of the end of the boom which can be inserted into the coupler is sufficient for centering the two coupler elements at a place spaced apart from the clamping place. Alternatively or additionally it is possible to use a collet chuck with two clamping areas arranged at a distance from each other. In both cases no additional connecting element is needed on the gripper side. The frontmost tube section of the boom is simply used as such. 
     In a preferred embodiment, on the gripper side the conical centering surface is provided on a cover, which is fitted or pressed into the end of the tube section which can be inserted into the collet chuck. This embodiment has the advantage that the cover can support the plug connector elements for compressed air or other power or control connections of the workpiece gripper on the gripper side. 
     In a further preferred embodiment of the invention, the collet chuck consists in a manner known per se of a bushing, which is conically widened on a longitudinally slit end, of a fitted inner cone on a housing receiving the slit bushing, and of a power cylinder for the axial movement of the slit bushing in relation to the housing. The centering cone surface is located on the side of the fixed element on a holder connected with the slit bushing and the portion of the power cylinder, which can be moved in relation to the housing. Usefully the piston of the power cylinder slides directly in a bore of the housing, so that no additional part is required for the cylinder. A very simple construction of the fixed element of the coupler as a whole is obtained if the housing has a stepped, continuous bore, which is closed at the rear end by a cover and into which a tight separating wall is inserted between the piston of the power cylinder and the holder. 
     Surprisingly, neither the coupling process nor the centering function is negatively affected if in an advantageous embodiment of the invention the conical centering surface on the side of the fixed element of the coupler is formed on the holder or on another part which is moved in the course of tightening the collet chuck. The reason for this is on the one hand the radial guidance of the holder or another part in the cylinder bore of the housing, on the other hand that a comparatively short axial displacement path of the longitudinally slit bushing of the collet chuck and the holder connected with it is sufficient for causing the clamping and the release of the tube section inserted into the collet chuck. During the short axial displacement it is possible to assure the mutual contact of the conical centering surfaces by means of a force exerted on the boom, if not anyhow after the insertion of its end into the collet chuck the boom is taken along by friction in the course of the axial movement of the slit bushing. 
     It has been found that it is advantageously possible to connect power-carrying lines, and possibly even control lines, with the holder, in spite of the necessary movements of the holder for tightening and releasing the collet chuck. In a further preferred embodiment of the invention it is therefore provided that the holder is equipped with several compressed air and/or vacuum connections, which extend outward through holes in the housing, which holes are of sufficient size for making the axial movements of the holder in the housing possible. Axially oriented plug connectors, which suitably are furthermore provided on the holder are connected with the compressed air and/or vacuum connections and in the course of inserting the connecting element into the collet chuck can be tightly connected with counter plug connectors arranged on the closing cover of the boom, which are connected with pneumatically actuable elements on the workpiece gripper. 
     Exemplary embodiments of the invention will be explained in more detail in what follows by means of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 represents an axial longitudinal section through a coupler of a workpiece gripper with a robot arm, 
     FIG. 2 is a cross section along the section line II—II in FIG.  1  and 
     FIG. 3 shows an axial longitudinal section through another embodiment of a coupler. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Only the outermost tube section  10  of the boom of a workpiece gripper for sheet metal parts is represented in FIG.  1 . In the individual case, and depending on the size of the workpiece and the spatial conditions in the stamping presses, from which the workpieces are to be removed, or respectively in which they are to be inserted, the tube section can have a length of more than 2 m. Other workpiece grippers which are to be fastened by means of the same coupler on the robot arm possibly only have a short tube section  10 . It is understood that the tube-shaped ends of all workpiece grippers intended to be held by means of the same coupler must have the same exterior diameter and a sufficient length, so that they can be exchangeably inserted into the coupler in defined positions. 
     While the tube section  10  constitutes the connecting element of the coupler on the gripper side, its fixed element attached on the drive side, i.e. at the end of a robot arm, essentially consists of a housing  12 , which receives a collet chuck  14 . The housing  12  has the shape of a cylinder provided with a radial flange  16  on its rear end and is reinforced by means of several exterior ribs  18  extending over its length. The rear end of the cylindrical housing  12  is tightly closed by means of a cylinder cover  20 , which is screwed on the flange  16  from the rear. So that the same coupler can be attached to the differently designed ends of different robots, fastening takes place via an adapter disk  22 , which is matched on the one side with the fastening surface of the respectively associated robot, and on its oppositely located surface to the outside of the cylinder cover  20 . Following the fastening of the adapter disk  22  on the end of the robot arm, the coupler is screwed to the adapter disk  22  by means of screws which are inserted through holes  24  in the flange  16  and the cylinder cover  20 , and is centered by means of centering bores  25 . 
     The housing  12  preferably is a cast part made of an aluminum alloy. Since this material is comparatively soft, a ring-shaped insert  26  of steel, whose inner circumferential surface conically widens from the inside to the outside, has been placed on the inside of the front end of the cylindrical housing  12 . It cooperates with the front end  28  of the collet chuck  14 , which is conically and radially outwardly widened at the front. Otherwise, this has the form of a bushing of hardened steel with several slits distributed over the circumference and extending over the larger portion of the length. This bushing is screwed with its rear end into a holder  30 , which is connected by means of a fastening screw  32  with the piston rod  34  of a piston  38 , which is guided in an axially displaceable manner in the cylinder bore  36  of the housing  12 . The cylinder chamber receiving the piston  38  is limited at the front by a separating wall  40 , which has been fixedly end tightly inserted into the cylinder bore  36 . The piston  38  is displaced in the one or the other direction by means of compressed air, which is let into the cylinder chamber either by means of a compressed air connector  42  in its rear portion or by means of a further compressed air connector  44  in its front portion. The cylinder cover  20  and the separating wall  40 , along with a disk  46  resting against the rear of the latter, are used as end stops. The maximum stroke of the piston  36  between these two end stops is only approximately 3 to 5 mm in this example. 
     Respectively three air connections  48  are screwed into the holder  30  at the top and bottom in a parallel arrangement (also see FIG.  2 ). Each of them is connected with one of six circularly arranged hollow bolts  50 , which are tightly inserted into the holder  30 , protrude at the front and constitute plug connectors. They sealingly cooperate with matching counter plug connectors  52  in the form of bores in a cover  54 , which is pressed into the frontmost end of the tube-shaped boom. Air connections  56  have been screwed into the bores  52  on the inside and are connected via air supply lines, not represented, with gripper and other elements on the workpiece gripper, which can be actuated by compressed air or vacuum. The plug connections between the hollow bolts  50  and the counter plug connectors  52 ,  56  are created when the front tube section of the boom  10  is inserted into the collet chuck  14 ,  28 . If it is desired that the two coupler elements can always be connected only in a defined relative rotational angular position, this can be done in a simple manner in that in accordance with FIG. 2 one of the plug connectors, in the example the one identified by  50 ′, is not arranged on the same radius as the remaining air guide bolts  50 . 
     In the exemplary embodiment of FIG. 1, the cover  54  has an outer flange edge, which covers the front face of the boom  10 , and whose circumferential face forms a centering cone  58  with a pitch of 20°, for example. When the front end of the boom  10  is inserted into the collet chuck, the centering cone  58  comes to rest against a corresponding inner cone of the holder  30 . Care must be taken that the mutual contact between the cone faces remains intact when the piston  38  is subsequently displaced to the right by means of compressed air being supplied through the air connector  44 , and in the process takes the holder  30  and the longitudinally slit bushing  14  along for tightening the collet chuck. In the clamped state, the front tube section of the boom then is held in a centered manner on the one side within the clamping area of the collet chuck, i.e. in the area of the conical widening  28 , and on the other side spaced apart from this clamping place by the centering cone  58  at the frontmost end. For releasing the coupler it is only necessary to displace the piston  38  by means of a compressed air supply through the air connector  42  toward the left in respect to FIG.  1 . The perfect displacement of the holder  30  is assured by a slide ring insert  60 , made of plastic, in the sliding surface of the cylinder bore of the housing  12 , and inserting holes  62  of sufficient length in the axial direction in the cylindrical housing  12  permit the axial movement of the air connectors  48  together with the holder  30 . So that the holder  30  is secure against rotation relative to the housing  12 , it is provided with a longitudinal groove on its circumference, which, in accordance with FIG. 2, is engaged by the pin-like end of a securing screw  64 . 
     In the exemplary embodiment of FIG. 3, many elements have the same function or even the same form as in the exemplary embodiment of FIGS. 1 and 2. These elements have been identified in FIG. 3 with the same reference numerals as in FIGS. 1 and 2. They need not be discussed in further detail. 
     One essential distinction of the embodiment of FIG. 3, over the exemplary embodiment described above, is that it uses a collet chuck  66  with two faces  68 ,  70  that widen conically toward the front. The two conical outer faces  68 ,  70  have a relatively great axial spacing, which is preferably greater than half the length of the collet chuck  66 . 
     Such a collet chuck  66  expediently comprises segments to be made by axial severing cuts; these segments would coincide if they were not retained, on a radius which is somewhat greater than the radius of the tube section  10 , by elastic, split snap rings  72 , such as Seeger rings, which are seated in inner grooves of the segments of the collet chuck  66 . 
     In a manner corresponding to the two conical outer faces  68 ,  70 , a bushing-like insert  74  fixed in the housing  12  cooperates with the collet chuck  66  by way of two conical inner faces  76 ,  78  that have the same spacing as the outer faces  68  and  70 . All the conical faces have at least two regions of different pitch. If to tighten the tube section  10  the collet chuck  66  is pulled to the right in terms of FIG. 3, then at first steeper conical faces cooperate and bring about a rapid radial tightening motion of the collet chuck  66 . Upon further axial motion of the collet chuck  66  toward the right in terms of FIG. 3, the flatter regions of the conical faces come into action, so that tightening can be done no longer with the same radial speed but on the other hand with substantially greater force. 
     In the exemplary embodiment of FIG. 3, the piston rod  34  of the drive piston  38  is not solidly joined directly to the holder  30  but instead via a screw  79  it is joined to a cage  80 , on which the holder  30  is supported in axially displaceable fashion. The end on the left, in terms of FIG. 3, of the substantially bushing-like cage  80  is provided with an inner annular groove, which is engaged by an annular rib  82  on the right-hand end of the segments of the collet chuck  66 , so that upon an axial displacement of the cage  80  by means of the piston  38 , the collet chuck  66  is carried along as well. The engaged connection between the segments of the collet chuck  66  and the cage  80  is embodied such that in the substantially radial tightening and release motion of the segments of the collet chuck  66 , the annular rib  82  can execute a radial motion in the annular groove receiving it, and/or the segments of the collet chuck  66 , beginning at their radially inner tightening position contacting the tube section  10 , can execute a limited pivoting motion radially outward about their right-hand end. 
     As also seen in FIG. 3, the conical face  58  on the fixed part is provided not on the holder  30  but rather on the cage  80 . The cage is guided in the bore of the housing  12 . The right-hand end of the cage  80  forms a cylinder  84 , in which a second piston  86  is guided axially displaceably. This piston is solidly connected via a screw  88  to the holder  30 , whose left-hand side, in terms of FIG. 3, is formed by a damping plate  90 . Because of the displaceability of the holder  30  together with the piston  86  relative to the cage  80 , the air connections  48  extend not only through the holes  62  in the housing  12  but also through suitably long holes  92  in the circumferential wall of the cage  80 . The displaceability of the holder  30  relative to the cage  80  makes it possible that after the introduction of the tube section  10  into the fixed part of the coupler, in a first step the tube section is precentered by means of the conical faces  58  and then the tube section  10  is tightened and thus centered by the segments of the collet chuck  66 , before the plug connection between the hollow bolts  50  and the counterpart plug connectors  52 ,  56  is made. The construction of FIG. 3 has the advantage that whenever the tube section  10  is not introduced in a precisely centered position into the collet chuck  66 , the cover  54  abutting the hollow bolts  50  displaces the holder  30  toward the right in terms of FIG.  3 . 
     Once the collet chuck  66  has been tightened and the tube section thus centered, the cylinder  84  is acted upon by compressed air via an air connection  94 , so that the piston  86  and the holder  30  are displaced to the left in terms of FIG. 3, and in the process the hollow bolts  50  penetrate into the counterpart plug connectors  52 ,  56 . Because the plug connections are not made until after the tube section  10  is centered, damage to the seals and other contacting parts is averted. 
     A further improvement in the version of FIG. 3 over the exemplary embodiment of FIGS.  1  and  2  comprises the retention of the cover  54  on the end of the tube section  10  by means of one or more elastic disks  96 , which are connected in the center to a threaded bush  98  and have a diameter which is somewhat greater than the inside diameter of the tube section  10 , so that they flex on being pressed into the tube section, as shown in the drawing. A threaded bolt  100  that can be screwed into the threaded bush  98  tightens the cover  54  against the elastic disks  96  clamped in place in the tube section  10 . To loosen the cover  54  from the tube section  10 , the screw bolt  100  need merely be unscrewed. The elastic disks  96  are provided with holes for carrying the air and signal lines laid in the tube section  10 . 
     Finally, as a further special feature of the version of FIG. 3, a spring  102  can be mentioned which seeks to urge the drive piston  38  toward the right, or in other words tends to tighten the collet chuck. This assures that the collet chuck will remain tightened even if the pressure in the compressed air connection  44  drops. 
     It is understood that the components of the fixed element and the connecting element of the coupler represented in the drawings and described above can be designed differently in detail. If no internal connectors for compressed air or vacuum are needed, parts  48  to  56  can be omitted, and the front face of the boom  10  could be provided with the centering cone  58 . In both embodiments, with and without the cover  54 , the connecting element of the coupler is considerably more simple and cost-effective to produce than with the power-operated couplers customary up to now. In place of a motor drive of the collet chuck by means of a linearly acting power cylinder, it would also be possible to employ a rotary drive which generates a linear movement, for example via a screw gear. 
     For making electrical connections, male plugs  104  and female plugs  106  can be mounted on the outside of the housing  12  and of the tube section  10 . Upon the insertion of the tube section  10  into the collet chuck  66 , the male and female plugs are brought into contact with one another.