CENTERING DEVICE

Description

Technical area

[0001] The invention relates to a centering device for centering flat workpieces, in particular for sheet metal blanks to be processed in a press, comprising a centering station with at least a first and a second gripping device for gripping the workpiece, as well as conveying means for conveying workpieces in a conveying direction to the centering station. State of the art

[0002] In a press (e.g., a multi-station press or press line), pre-punched sheet metal parts, known as blanks, are often further processed. Before the actual processing in the press begins, the fed blanks must usually be stacked or separated, washed, and, if necessary, oiled. To ensure precise further processing in the press, the blanks must be precisely positioned and oriented in a specified direction after the aforementioned operations before being inserted into the press.

[0003] The workpieces to be centered are typically sheet metal blanks. These can lose a predefined position during transport or during a cleaning process, especially if transported improperly. To minimize this risk, it has been known to grasp, lift, and center the workpieces at several locations simultaneously using robot arms and grippers. However, such devices are expensive to purchase, and the corresponding processes are very complex and expensive to convert to new workpieces.

[0004] Further known positioning and alignment methods involve centering with mechanical slides and stops. However, these have the disadvantage that they require complex retooling when changing the blank type, requiring the slides and stops to be repositioned and reoriented. When machining irregularly shaped or multiple small sheets, a large number of slides and stops are also necessary to ensure correct positioning. Furthermore, mechanical slides have the disadvantage that they can damage the blank during centering.

[0005] JP 2003326327 A (Hitachi Zosen Fukui Corp) discloses a centering device according to the features of the preamble of patent claim 1.

[0006] The known solutions either have a complex structure or are difficult to convert to a new workpiece type, i.e. they cannot be easily used for any workpiece. Description of the invention

[0007] The object of the invention is to create a centering device belonging to the technical field mentioned at the outset, which can be used universally with a compact and simple design.

[0008] The solution to the problem is defined by the features of claim 1. According to the invention, the first and the second gripping devices are each horizontally movable with a first or a second guide device, and the first and the second gripping devices are freely rotatable about an axis.

[0009] This creates a particularly simple centering device with a technically simple solution. Gripping devices for gripping workpieces as well as guide devices for moving the gripping devices are known to those skilled in the art and are also particularly easy to implement technically. Furthermore, guide devices can be controlled particularly easily and precisely, especially in contrast to the driven balls of a ball table or ball plate.

[0010] The fact that the workpiece is gripped for centering by at least two freely rotatable gripping devices enables particularly simple centering. Especially when using exactly two gripping devices that can rotate freely about an axis, centering can be achieved via a particularly simple control system. To center a workpiece, the latter is preferably gripped by at least two gripping devices. After the workpiece has been gripped by the gripping device, the guide devices are actuated to center the workpiece. Since the gripping device is now rotatably mounted, rotations of the workpiece generated by the two guide devices can be easily absorbed.Due to the free rotation of the gripping devices, it is only necessary to ensure during centering that the distances between the gripping devices remain constant, while the rotations occurring during centering can be absorbed by the freely rotatable gripping devices.

[0011] Preferably, the gripping device is mounted on the first guide device so that it can rotate freely, preferably exclusively freely, about a vertical axis. However, it is also conceivable in principle for the gripping device to be actively rotated in addition, thus actively supporting centering. This means that the gripping device can be designed such that both active rotation and free rotation can be achieved. If the gripping devices are pivotable, the axis of rotation can also be non-vertically aligned.

[0012] The centering device allows workpieces to be rotated through an angle of more than 90°, making it particularly suitable for a wide range of applications. It is also conceivable to guide the gripping devices in such a way that they can overlap each other, for example, in the conveying direction, which would also allow rotations through an angle of more than 180°.

[0013] The term "centering" is understood below to mean a change in the position and / or orientation of the workpiece in the plane. Typically, centering is performed via translation, rotation, or both. Preferably, during centering, the workpiece is transferred from an actual position to a desired position by a superimposed translation / rotation. Typically, the actual position is the orientation of the workpiece in which it is conveyed to the centering station, and the desired position is the orientation of the workpiece in which it is to leave the centering station.

[0014] In a method for centering a flat workpiece, with a centering device according to claim 1, in particular for centering a sheet metal blank to be processed in a press, the following steps are carried out: a) Determining a current position and orientation of the workpiece conveyed on the conveyor by means of a detection device; b) Conveying the workpiece to a centering station; c) Gripping the workpiece with a first and a second gripping device freely rotatable about an axis. d) Aligning the workpiece based on the current position and a target position by the first and second guide devices, respectively.

[0015] These process steps create a particularly simple method for centering a workpiece. By determining the position of the workpiece before reaching the centering station, the latter can be designed particularly compactly and simply. In particular, the centering station and the detection device can be designed independently of each other and, for example, maintained, upgraded, or repaired, thus simplifying the operation and maintenance of the centering device.

[0016] The conveying means preferably comprise at least one conveyor belt. This allows the workpieces to be transported quickly and precisely. A conveyor belt can be designed, for example, as a magnetic belt, which can be used to secure a workpiece during transport. Instead of magnetic belts, other conveyor belts known to those skilled in the art, such as vacuum belts, can also be used. With a suitable choice of conveyor belt surface, the workpiece can also be secured to the conveyor belt via the friction between the workpiece and the conveyor belt.

[0017] In variants, other conveying means can also be provided, for example conveyor plates, support rollers, ball plates, etc.

[0018] In a particularly preferred embodiment, the centering device is designed such that the workpiece rests on a support surface during the centering process thanks to the gripping devices and the guide devices. This allows particularly large or deformable workpieces, such as large metal sheets, to be aligned gently. The workpiece does not necessarily have to rest on the conveyor belt for this purpose. In a preferred embodiment, the workpiece rests on a support surface that differs from the support surface of the conveyor belt during centering (see below). Alternatively, the workpiece can also be lifted or raised completely or partially from the conveyor belt for centering.

[0019] The conveyor belt preferably comprises a plurality of parallel and spaced-apart conveyor belt strips, wherein a lifting unit with a workpiece support surface is arranged in a space between two conveyor belt strips, wherein a workpiece rests exclusively on the workpiece support surface when the workpiece support surface is raised. This allows a workpiece conveyed on the conveyor belt to be lifted easily. Lifting the workpiece is particularly advantageous for centering the workpiece when centering on the conveyor belt itself is not suitable. This is typically the case when the conveyor belt is designed such that the orientation of the workpiece does not change during transport.Typically, the aim is to ensure that the orientation of the workpiece does not change during transport; in particular, the orientation of the workpiece after centering should not change, for example, during further transport. The lifting unit is preferably pneumatically operated, i.e., it comprises pneumatic cylinders with which the workpiece support surface can be raised and lowered directly or indirectly. Instead of pneumatic cylinders, the lifting unit can also comprise other drives, for example, a spindle drive, hydraulic cylinder, or the like.

[0020] In some variants, the lifting unit between the conveyor belt strips can be omitted. In this case, the workpiece can rest on the conveyor belt for centering or be gripped, lifted, and centered from above by a gripping device.

[0021] During operation, the gripping device is preferably lowered at the same time as gripping a workpiece (see below) and the workpiece is lifted from the conveyor belt by means of the lifting unit.

[0022] In some variants, the gripping device can also be lowered first to secure the workpiece, after which the lifting unit moves upwards together with the workpiece and the gripping device. In this case, the gripping device can be moved upwards actively or passively together with the lifting unit.

[0023] Preferably, the workpiece support surface has a coefficient of friction that is lower than the coefficient of friction of a workpiece support surface of the conveyor belt strips. This ensures that, when the workpiece support surface is raised, the workpiece now resting on the workpiece support surface can be moved, in particular centered, against less frictional resistance. This allows the workpiece to be centered precisely and efficiently, with greater acceleration and a lower risk of damage.

[0024] In variants, the different friction coefficients can also be omitted.

[0025] Preferably, the surface of the lifting unit comprises a ball plate, which is arranged such that, when the lifting unit is raised, a workpiece rests on the balls of the ball plate. For this purpose, the balls of the ball plate are mounted for free rotation, so that the workpiece can be moved, in particular centered, by the gripping device with as little resistance as possible.

[0026] In some variants, other means can also be provided to reduce resistance during centering between the support surface and the workpiece. Instead of a ball plate, for example, an air cushion or similar device can be provided.

[0027] The centering station preferably further comprises a third and a fourth gripping device, wherein the third and fourth gripping devices are each horizontally movable by means of a third or fourth guide device, respectively. Particularly for large-surface workpieces, it is particularly advantageous if more than two gripping devices are available. This reduces the load on individual gripping devices, thus enabling an efficient method for centering larger workpieces. Depending on the arrangement of the gripping devices, it is also possible to simultaneously center several individual workpieces lying next to one another or one behind the other, which in turn increases the efficiency of the workpiece centering process.

[0028] In some variants, the third and fourth gripping devices can be omitted. However, it is also conceivable to provide three or more than four gripping devices, for example, five, six, seven, eight, or more guide devices. The preferred number of guide devices ultimately depends on the type of application, in particular the size, stability, weight, maximum load capacity of the gripping device, the number of workpieces to be processed in parallel, and other factors.

[0029] Particularly preferably, exactly two gripping devices are used in the process to center a workpiece.

[0030] Preferably, one of the guide devices comprises a first linear guide for moving the gripping device in the conveying direction and a second linear guide for moving the first linear guide at right angles to the conveying direction. This creates a particularly simply constructed and therefore cost-effective Cartesian guide. Cartesian guide devices have the advantage of being cost-effective, easy to control and also low-maintenance. The alignment of the first linear guide at right angles to the conveying direction has the advantage that the centering device as a whole can be constructed compactly. In particular, this essentially makes it possible to dispense with a large overhang of the centering station over the conveyor belt width at the centering station. In particular, the second linear guide can be designed such that two or more second linear guides are guided on this first linear guide.

[0031] In variants, the guide devices can comprise a first linear guide for moving the gripping device at right angles to the conveying direction and a second linear guide for moving the first linear guide in the conveying direction. It is also conceivable for the first and second linear guides to not run parallel to each other. For example, the rails for the first linear guides of the first and second guide devices can be perpendicular to each other. Finally, one or more of the guide devices can also be designed as robots, which can in particular have four, five, six, or more axes.

[0032] Preferably, the first linear guides of the first and second guides are arranged parallel to one another, and the second linear guides of the first and second guides are arranged in alignment with one another. Particularly preferably, the first linear guides of the first and second guides comprise one, preferably a single rail guide transverse to the conveying direction, on which the first linear guides can be moved transversely to the conveying direction. The aligned rail guides or the shared rail guide of the first linear guides of two guide devices can in turn achieve a compact and cost-effective design of the centering device. The two first linear guides can be moved via their own drives, so that they can be controlled independently of one another. However, it can be accepted that the two first linear guides cannot cross each other.

[0033] In variants, the first linear guides can also be guided on separate rail guides and, in particular, arranged offset parallel to one another.

[0034] Preferably, the first linear guide comprises a belt drive for moving the gripping device and / or the second linear guide comprises a belt drive for moving the first linear guide. Particularly preferably, the first and second linear guides each comprise a belt drive. The use of belt drives has the advantage that high accelerations and rapid movements can be carried out with great precision. Belt drives are also cost-effective to purchase and maintain. However, it is also conceivable for only the first or only the second linear guides to comprise a belt drive, while the other linear guides comprise another drive, for example a spindle drive, a pneumatic or hydraulic drive, a rack and pinion drive, a linear motor, etc.

[0035] In variants, drives other than a belt drive can also be provided for the first and second linear guides. Even in this case, the drives do not have to be identical for the first and second linear guides. For example, a first linear guide could comprise a spindle, while the second linear guide is driven by a linear motor.

[0036] The gripping device can preferably be lowered and raised, preferably pneumatically raised and / or lowered, in particular relative to the first linear guide. This allows the gripping device to be easily guided to the workpiece so that the workpiece can be gripped. For this purpose, the gripping device comprises a lifting device, wherein a lifting direction is preferably oriented vertically, preferably at right angles to a support surface of the conveyor belt. The lifting device can be designed such that the workpiece can be held forcelessly with respect to a lifting direction. In this case, the workpiece would be pulled over the support surface of the conveyor belt or the ball plate for centering. This design is particularly advantageous for large and / or flexible workpieces, in particular those deformable under their own weight, since it can prevent deformation of the workpiece and thus distortion of the alignment after setting it down.On the other hand, the lifting device can also be designed in such a way that the workpiece can be actively raised and lowered. This allows, in particular, smaller or dimensionally stable workpieces to be centered without friction. The lifting device can also be designed in such a way that both forceless holding in the vertical direction and active lifting of the workpieces are possible.

[0037] In variants, the gripping device can be raised and lowered relative to the first linear guide without the ability to do so. Furthermore, instead of the gripping device being raised and lowered relative to the first linear guide, the first linear guide, together with the gripping device, can be designed to be raised and lowered relative to the second linear guide. Finally, the guide as a whole can also be designed to be raised and lowered.

[0038] The gripping device can preferably be raised pneumatically, in particular against a restoring force, preferably against a spring force. The gripping device is thus lowered in the de-energized state. This arrangement is advantageous because it allows the gripping device to be moved downwards with a constant force while the spring is relaxed. The force can be easily preset by selecting a spring with the desired spring constant. Particularly preferably, the gripping device is lowered exclusively via the spring force. This makes it easy to control the pressure exerted on the workpiece. The gripping device is preferably raised pneumatically. This enables particularly fast movements to be carried out, i.e. the gripping device can be raised quickly after centering. This results in shorter centering cycles, creating a particularly efficient process.

[0039] In variants, the gripping device can also be designed to be raised and lowered in other ways. Lowering can also be achieved by gravity. Furthermore, in principle, lifting can also occur against a spring force instead of lowering. This prevents damage to the centering device in the event of a malfunction of the lifting device, for example, in the event of a leak in the pneumatic system. Furthermore, both raising and lowering can be achieved pneumatically, using a so-called pneumatic spring. Rack and pinion drives, hydraulic drives, and, especially for short strokes, magnetic drives, etc., can also be used instead of pneumatics.

[0040] The gripping device preferably comprises a suction cup for gripping the workpiece. Especially with a pneumatically operated lifting device, the existing infrastructure can be better utilized. For example, the conveyor belt could also be designed as a vacuum belt. Suction cups also allow workpieces to be gripped particularly gently. Furthermore, gripping workpieces with suction cups is particularly easy, since essentially only a surface of the workpiece needs to be present that corresponds to the suction cup diameter.

[0041] In variants, the gripping device can also be designed differently. For example, the gripping device can comprise an electromagnet. Furthermore, the gripping device can also comprise actively actuated clamps. Hooks can also be provided, which can, for example, grip behind an edge area of ​​the workpiece. Other possible gripper designs are also known to those skilled in the art.

[0042] The centering device preferably comprises a detection device for detecting the position and orientation of a conveyed workpiece. Based on this detected information, the position and orientation of the workpiece can then be corrected by the centering device. The detection device is thus arranged upstream of the centering station so that the actual position can be determined before centering.

[0043] In some variants, the detection device can also be integrated into the centering station. In this case, the actual position can be detected using the centering station itself, for example, by the grippers grasping predefined points on the workpiece.

[0044] The detection device preferably comprises a line scan camera, which is arranged upstream of the centering station with respect to a conveying direction. The line scan camera is thus arranged in the feed path of the workpieces and preferably extends transversely across a feed track for the workpieces. The position and orientation of the workpieces are thus detected by the line scan camera during their feed. The line scan camera can be designed simply, enables precise detection of position and orientation, and, unlike other detection devices such as cameras, does not require complex image processing.

[0045] In variants, however, another detection device may also be provided, for example a camera, a sensor grid or the like.

[0046] In a preferred embodiment, the line scan camera is arranged in the transition, particularly in a gap between two conveyor belts, and comprises a scanner, which is preferably located vertically below the support surface of the workpieces, and a reflector, which is located vertically above the space through which the workpieces are conveyed. The workpiece is thus scanned from below.

[0047] In variants, the workpiece can be scanned from above. For this, the scanner would be positioned vertically above a workpiece support surface. A photo can also be taken from above to record the actual position of the workpiece. In principle, the device can also include a detection device downstream of the centering station in the conveying direction to compare the position of the workpiece after centering with the target position. However, this detection device can also be omitted.

[0048] The centering device preferably comprises a control device configured to control the centering station based on measurement data from the line scan camera in such a way that a desired alignment of the workpiece can be achieved. Preferably, the line scan camera determines a light-dark profile of the workpiece. This provides easily processable data that allows for precise positioning and orientation of the workpiece.

[0049] The recorded profile can be compared with a target profile, which represents the position and orientation expected by the subsequent processing station. Deviations between the light-dark profile and the target profile are evaluated by the control system in a conventional manner and converted into necessary corrections, e.g., corrections to the angle of rotation, longitudinal, and transverse directions. The corrections are then implemented by the guide devices so that the finally positioned and oriented workpiece corresponds to the target profile.

[0050] Further advantageous embodiments and combinations of features of the invention emerge from the following detailed description and the entirety of the patent claims. Short description of the drawings

[0051] The drawings used to explain the embodiment show: Fig. 1: a schematic representation of a side view of a centering device transverse to the conveying direction; Fig. 2: a schematic representation of a side view of a centering device in the conveying direction with the gripping devices lowered; Fig. 3: a schematic representation of a side view of a centering device in the conveying direction with the gripping devices raised; Fig. 4: a schematic representation of a top view of a centering device; Fig. 5: a sectional representation through a Cartesian guide device in the conveying direction; Fig. 6: a sectional representation through a Cartesian guide device transverse to the conveying direction with the gripping device raised; Fig. 7: a sectional representation through a Cartesian guide device transverse to the conveying direction with the gripping device lowered; Figs. 8 - 12: schematic representations of top views of Cartesian guide devices with four gripping devices when handling different workpieces; Fig.13 a schematic representation of a top view of a Cartesian guide device with six gripping devices during the handling of three workpieces; Fig. 14 - 16 schematic representations of top views of Cartesian guide devices with eight gripping devices during the handling of different workpieces; Fig. 17 a schematic representation of a top view of a Cartesian guide device with four gripping devices, wherein two workpieces are rotated through an angle of 90°; Fig. 18 a schematic representation of a top view of a Cartesian guide device with four gripping devices, wherein two workpieces are centered from a side-by-side arrangement to a one-behind-the-other arrangement.

[0052] In principle, identical parts in the figures are provided with identical reference symbols. Ways to implement the invention

[0053] The Figure 1shows a schematic representation of a side view of a centering device 1 transverse to the conveying direction.

[0054] The centering device 1 comprises a conveyor belt 400 for conveying workpieces (in Figure 1 (not shown). The conveyor belt 400 comprises a plurality of conveyor belt strips 410, which are oriented parallel in the conveying direction. The conveyor belt 400 comprises a substructure 420 on which the conveyor belt strips 410 are mounted. The conveyor belt strips 410 are driven by a drive (not shown), in particular one or more electric motors. During operation, the individual conveyor belt strips 410 are driven at the same speed (meters per second), particularly in straight sections.

[0055] Furthermore, the centering device 1 comprises a second conveyor belt 500 as a component of the centering station 100. The conveyor belt 500 also comprises several conveyor belt strips 510 oriented parallel in the conveying direction, which are driven in a similar manner to the conveyor belt 400. The support surfaces of the conveyor belts lie essentially in the same plane, so that a workpiece can be transferred from the conveyor belt 400 to the conveyor belt 500.

[0056] A gap is provided between conveyor belt 400 and conveyor belt 500, across which a workpiece can be conveyed in one direction from conveyor belt 400 to conveyor belt 500. The gap is thus perpendicular to the conveying direction. A line scan camera 600 is mounted below a support surface of the conveyor belts, in the area of ​​the gap, with which a workpiece guided across the gap can be detected and its orientation and position can be determined. A reflector 601 is positioned above the support surface of the conveyor belts to reflect the light emitted by the line scan camera 600. The positioning below the support surface of the conveyor belts 400, 500 allows for a particularly compact design of the centering device 1.

[0057] The centering station 100 further comprises a Cartesian guide device 200, of which Figure 1two second linear guides 250, 251 extending perpendicularly to the image plane and parallel to it. On the two second linear guides 250, 251, a first linear guide 210 with a gripping device 300 and a first linear guide 212 with a gripping device 302 are arranged transversely to the conveying direction and horizontally movable. The gripping devices 300, 302 are movable along the two first linear guides 210, 212 in the conveying direction and can be raised and lowered relative to the second linear guides 210, 212 (see below, Figures 5 - 7 ).

[0058] The Figure 2 shows a schematic representation of a side view of a centering device 1 in the conveying direction with lowered gripping devices 210, 211. The Figure 2 now shows in particular the individual conveyor belt strips 510, which are parallel in the conveying direction and with respect to the Figure 2orthogonal to the plane of the page. Therefore, the individual conveyor belt strips 510 are shown as essentially square.

[0059] Additional shows the Figure 2 a lifting unit 530, with which a workpiece 700 can be lifted through gaps between the conveyor belt strips 510. The lifting unit comprises several ball plates connected by a base plate 533 (see Figures 5 - 7 ), which can be guided through the gaps between the conveyor belt strips 510, creating a support surface for the workpiece 700 that is higher than the support surfaces of the conveyor belt strips. The ball plates 531 can be lifted by means of one or more pneumatic cylinders (not shown).

[0060] In the Figure 2the workpiece 700 is gripped by the gripping devices 210, 211 and the lifting unit 530 is in an upper position in which the workpiece 700 is not in contact with the conveyor belt strips 510. The details are described in more detail in the Figures 5 - 7 described. In this configuration, the workpiece 700 can now be centered using the Cartesian guide 200. For this purpose, the individual linear guides 210, 211, and 250 (the linear guide 251 is not visible and is located behind the linear guide 250) are moved based on the actual position determined by the line scan camera 600 and the known target position in order to transfer the workpiece 700 to the target position.

[0061] The Figure 3shows a schematic representation of a side view of a centering device in the conveying direction with raised gripping devices 210, 211. After the workpiece 700 has been transferred to the desired position, on the one hand the lifting unit 530 is moved downwards and on the other hand the gripping devices 300, 301 are moved upwards, whereby the workpiece 700 rests again on the conveyor belt 500 and can be transported further by the same, in particular for example to a press for further processing of the workpiece 700.

[0062] The Figure 4 shows a schematic representation of a plan view of a centering device 100, wherein a workpiece 700 is guided on the conveyor belt 400 and in the conveying direction after the Cartesian guide devices 200 - 203. Thus, the Figure 4a state in the transition period in which a workpiece 700 has just been aligned and another workpiece 700 is about to enter the centering station 100. The centering station 100 in this case has a Cartesian guide device 200 with two second linear guides 250, 251 offset parallel to the conveying direction. The two second linear guides 250, 251 each comprise two first linear guides 210, 211 and 212, 213, respectively, on each of which a gripping device 300, 301 and 302, 303 is held. With the second linear guides 250, 251, the first linear guides 210, 211 and 212, 213 can be moved transversely to the conveying direction. With the first linear guides 210, 211 and 212, 213, the gripping devices 300, 301 and 302, 303 can be moved in the conveying direction.

[0063] The following Figures 5 to 7show the Cartesian guide device 200 and in particular the gripping device 300 in detail.

[0064] The Figure 5 shows a sectional view through a Cartesian guide device 200 in the conveying direction. This view shows the second linear guide 250 in cross-section. The first linear guide 210 is mounted on it for movement via the drive belt 260. The second drive belt 261 is provided for the first linear guide 211, which is not visible in this figure. The first linear guide 210 also includes a drive belt 220, with which the gripping device 300 can be moved in the conveying direction.

[0065] The gripping device 300 comprises a base plate 311, to which a holder 312 for connection to the drive belt 220 is attached at one end. At the other, opposite end of the base plate 311, a cylinder 313 is attached, in which a piston 314 is mounted for vertical movement. The piston 314 is connected to a piston rod 317, which comprises a suction cup 315 at a vertically lower end. A compression spring 316 is arranged vertically below the piston, which drives the piston 314 and thus also the suction cup 315 upwards. To lower the suction cup, the space in the cylinder 313 vertically above the piston 314 is pressurized with compressed air. This causes the piston 314 to move downwards against the spring force, whereby the suction cup 315 is lowered. In the present Figure 5The spring 316 is essentially relaxed (apart from the weight acting on it), and the suction cup 315 is in the raised state. The suction cup 315 is actively actuated by negative pressure (vacuum). The compressed air or vacuum connections are not shown in the figures; their arrangement is sufficiently clear to a person skilled in the art. The suction cup 315 is freely rotatable, so that a workpiece can also be rotated for centering.

[0066] The Figure 6shows a sectional view through a Cartesian guide device 200 transverse to the conveying direction with the gripping device 300 raised. In particular, based on the first linear guide 210, it is clearly visible that the viewing direction is now in the conveying direction. In the area of ​​the conveyor belt 500, two individual conveyor belt strips 510 are visible, with the lifting unit 530 being arranged between these two conveyor belt strips 510. The lifting unit 530 comprises a ball plate 531, which can be raised or lowered by means of one or more lifting cylinders. The ball plate 531 is connected via supports 532 to a base plate 533 (see Figures 2 and 3), which in this case is pneumatically actuated. In order to center a workpiece 700 located in the centering station 100, the gripping device 200, i.e., the suction cup 315, is simultaneously lowered and the workpiece 700 is lifted from the conveyor belt strips 510 by the lifting unit 530 with the ball plates 531.

[0067] The Figure 7 shows a sectional view through a Cartesian guide device 200 transverse to the conveying direction with the gripping device 300 lowered and the lifting unit 530 raised. In this state, the workpiece 700 can now be aligned using the Cartesian guide device 200. For this purpose, all of the gripping devices 300-303, in this example, can be moved independently of one another in the plane to reach the desired position of the workpiece 700.

[0068] Depending on the configuration, the centering device 1 can perform different centering operations, possibly on multiple workpieces simultaneously. The number of linear guides can be varied for this purpose.

[0069] The Figures 8 - 12 show schematic representations of top views of Cartesian guide devices 200 with four gripping devices during the handling of different workpieces 700-706, which are all rectangular in shape, by way of example. However, it is clear to a person skilled in the art that any conceivable shape of workpiece can be centered with the centering device, as long as there is a surface on which a gripping device 300 can grip the workpiece.

[0070] The Figure 8shows an arrangement of four gripping devices 300-303, with only two opposing gripping devices 301 and 302 gripping the workpiece 700 at diagonally opposite ends. In this orientation, the workpiece 700 essentially occupies the full width of the conveyor belt 500.

[0071] The Figure 9 shows an arrangement according to Figure 8 , wherein each workpiece 701 is gripped at diagonally opposite ends by pairs of opposing gripping devices 300, 302 and 301, 303, respectively. The two workpieces 701, lying next to each other in the transverse direction, essentially occupy the full width of the conveyor belt 500 in the present orientation. This illustrates that several workpieces 701 can also be centered simultaneously with the centering device 1.

[0072] The Figure 10 shows an arrangement according to Figure 8, wherein a workpiece 702 is gripped centrally opposite one another by pairs of opposing gripping devices 300, 302 and 301, 303, respectively. The workpieces 702 are small in size compared to the workpieces 701. This demonstrates that the centering device is essentially independent of the workpiece size.

[0073] The Figure 11 shows an arrangement according to Figure 8 , wherein a workpiece 703 is gripped by two adjacent gripping devices 300, 301 and 302, 303, respectively. This shows that several workpieces 703 arranged one behind the other can also be centered simultaneously by the centering device 1.

[0074] The Figure 12 shows an arrangement according to Figure 8, wherein a workpiece 704 or 705 is gripped at diagonally opposite ends by pairs of opposing gripping devices 300, 302, or 301, 303. The workpieces 704 and 705 have different dimensions transverse to the conveying direction. This illustrates that differently dimensioned workpieces 704, 705 can also be centered simultaneously with the centering device 1.

[0075] The Figure 13 shows a schematic representation of a top view of a Cartesian guide device 200 with six gripping devices 300-305 handling three identical workpieces 705. With pairs of opposing gripping devices 300, 302, or 301, 303, or 304, 305, each workpiece 705 is gripped centrally at opposite ends. This demonstrates that even three adjacent workpieces 705 can be centered simultaneously.

[0076] The Figures 14 - 16show schematic representations of top views of Cartesian guide devices 200 with eight gripping devices 300 - 307 during the handling of different workpieces. Figure 14 are analogous to Figure 13 Workpieces 705 are gripped, whereby instead of three, four are now centered simultaneously. Figure 15 shows essentially analogous to the Figure 14 that of the four workpieces 705 to be centered, not all of them necessarily have to have the same orientation. In this case, two workpieces 705 are aligned with their longitudinal direction transverse to the conveying direction and two are aligned in the conveying direction. Figure 16 also shows four workpieces 705, which are now all aligned transversely to the conveying direction.

[0077] The Figure 17shows a schematic representation of a top view of a Cartesian guide device 200 with four gripping devices 300-303, wherein two workpieces 706 are rotated by an angle of 90°. In the state before centering, the workpieces 706 are each oriented with their longitudinal direction transverse to the conveying direction. The first workpiece 706 is gripped diagonally offset by the gripping devices 300, 302, and the second workpiece 706 is gripped diagonally offset by the gripping devices 301, 303. To execute the rotation, the gripping devices 300, 302 and 301, 303, respectively, are moved toward each other by means of the first guide devices 250, 251. At the same time, the gripping devices 300, 302 and 301, 303 are moved away from each other so that the distance between the gripping devices 300, 302 and 301, 303 remains constant.If the travel path of the first linear guides 210-213 is sufficiently large, or the workpiece can be gripped with a sufficiently small distance between the gripping devices, a rotation through an angle of more than 90° is also possible. If the gripping devices 301 and 303, or 300 and 302, can intersect in the conveying direction (for example, the gripping devices would have to be guided with the linear guides along a center line transverse to the conveying direction between the second linear guides 250 and 251), a rotation of the workpieces 706 through an angle of more than 180° is possible.

[0078] The Figure 18shows a schematic representation of a top view of a Cartesian guide device 200 with four gripping devices 300-303, wherein two workpieces 705 are centered from a side-by-side arrangement to a one-behind-the-other arrangement. In the state before centering, the workpieces 705 are each oriented next to one another with their longitudinal direction transverse to the conveying direction. The first workpiece 705 is gripped by the gripping devices 302, 303 in the region of a front edge in the conveying direction, and the second workpiece 705 is gripped by the gripping devices 300, 301 in the region of a rear edge in the conveying direction. To execute the movement, the gripping devices 302, 303 are moved in the conveying direction and the gripping devices 300, 301 are moved against the conveying direction by means of the first linear guides 212, 213 and 210, 211, respectively.They are then moved towards each other by means of the first guide devices 250, 251 until they are arranged one behind the other with respect to the conveying direction.

[0079] It should be noted that one or more workpieces can be gripped multiple times for centering purposes, which means that any positioning of several workpieces among each other is possible.

[0080] The conveyor belt 400 does not necessarily have to have conveyor belt strips 410, but can also comprise a single conveyor belt that has the full transport width. Instead of the conveyor belt 400, another feed conveyor can also be provided, for example, a roller conveyor or the like.

[0081] Although the first linear guides 210-217 and the second linear guides 250, 251 are driven by drive belts in the present case, they can also comprise other drives, for example, a spindle drive, a rack and pinion drive, or the like. Further variants are known to those skilled in the art.

[0082] The line scan camera 600 can also be positioned differently. Instead of a line scan camera 600, other detection means can also be provided to determine the position and orientation before centering.

[0083] While the present embodiments exclusively depict Cartesian guide devices, it will be clear to those skilled in the art that other guide devices may also be provided. In particular, individual or all of the Cartesian guide devices may be replaced by robots or the like in a known manner.

[0084] In summary, it can be stated that according to the invention a centering device is created which can be used particularly variably despite its simple construction.

Claims

1. A centering device (1) for centering flat workpieces (700-706), in particular for sheet metal blanks to be processed in a press, comprising a centering station (100) having at least a first and a second gripping device (300, 301) for gripping the workpiece (700-706), and conveying means for conveying workpieces (700-706) in a conveying direction to the centering station (100), where the first and the second gripping device (300, 301) can each be moved horizontally by a first and a second guiding device (200, 201), respectively, characterized in that the first and the second gripping device (300, 301) can rotate freely about an axis, wherein wherein the centering device is configured such that, for centering the workpiece, the latter is gripped by the first and second gripping devices (300, 301) and, after gripping the workpiece, the guide devices (200, 201) are actuated such that the workpiece is centered.

2. The centering device (1) as claimed in claim 1, characterized in that the conveying means comprise at least one conveyor belt (500).

3. The centering device (1) as claimed in claim 2, characterized in that the conveyor belt (500) comprises a plurality of parallel conveyor belt strips (510) which are spaced apart from one another, wherein a lifting unit (530) having a workpiece support surface is arranged in an interspace between two conveyor belt strips, with the result that, with the workpiece support surface raised, a workpiece (700-706) can lie exclusively on the workpiece support surface.

4. The centering device (1) as claimed in claim 3, characterized in that the workpiece support surface has a coefficient of friction which is less than a coefficient of friction of a workpiece support surface of the conveyor belt strips (510).

5. The centering device (1) as claimed in claim 4, characterized in that the surface of the lifting unit (530) comprises a ball plate (531) which is arranged in such a way that, with the lifting unit raised, a workpiece (700-706) can lie on balls of the ball plate (531).

6. The centering device (1) as claimed in one of claims 1 to 5, characterized in that the centering station (100) further comprises a third and a fourth gripping device (302, 303), wherein the third and the fourth gripping device (302, 303) can rotate freely about the axis and can each be moved horizontally by means of a third and fourth guiding device (200-203), respectively.

7. The centering device (1) as claimed in one of claims 1 to 6, characterized in that one of the guiding devices (200-203) comprise a first linear guide (210) for moving the gripping device (300) in the conveying direction and a second linear guide (250) for moving the first linear guide (210) at a right angle to the conveying direction.

8. The centering device (1) as claimed in claim 7, characterized in that the first linear guides (210, 211) of the first and of the second guiding devices are arranged parallel to one another, and the second linear guides (250) of the first and of the second guiding devices (210, 211) are arranged in alignment with one another.

9. The centering device (1) as claimed in either of claims 7 and 8, characterized in that the first linear guide (210, 211) comprises a belt drive for moving the gripping device, and / or the second linear guide (250) comprises a belt drive for moving the first linear guide.

10. The centering device (1) as claimed in one of claims 7 to 9, characterized in that the gripping device (300) can be lowered and raised, preferably can be pneumatically raised and / or lowered, in particular relative to the first linear guide (210).

11. The centering device (1) as claimed in claim 10, characterized in that the gripping device (300) can be pneumatically raised, in particular counter to a restoring force, preferably counter to a spring force.

12. The centering device (1) as claimed in one of claims 1 to 11, characterized in that the gripping device (300) comprises a sucker (315) for gripping the workpiece (700-706).

13. The centering device (1) as claimed in one of claims 1 to 12, characterized in that it comprises a detection device for detecting a position and an orientation of a conveyed workpiece (700-706).

14. The centering device (1) as claimed in claim 14, characterized in that it comprises a control device which is designed in such a way that the centering station (100) can be controlled on the basis of measurement data of the line camera (600) in such a way that a desired orientation of the workpiece (700-706) can be achieved.

15. A method for centering a flat workpiece (700-706) as claimed in one of claims 1 to 15, in particular a sheet metal blank to be processed in a press, comprising the following steps: a) determining a current position and an orientation of the workpiece (700-706) conveyed on a conveying means by means of a detection device; b) conveying the workpiece (700-706) to a centering station (100); c) gripping the workpiece (700-706) by a first and a second gripping device (300, 301) which can rotate freely about an axis; d) orienting the workpiece (700-706) on the basis of the current position and of a desired position by the guiding devices.