Centering device

1. A centering device for centering flat workpieces comprising a centering station having at least a first and a second gripping device for gripping the workpiece, and conveying device for conveying workpieces in a conveying direction to the centering station, where the first and the second gripping device can each be moved horizontally by a first and a second guiding device, respectively, and wherein the first and the second gripping device can each rotate freely about a different vertical axis when the first and the second gripping device grip a workpiece and are moved horizontally by the first and the second guiding device.

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

3. The centering device as claimed in claim 2 , characterized in that the conveyor belt comprises a plurality of parallel conveyor belt strips which are spaced apart from one another, wherein a lifting unit 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 can lie exclusively on the workpiece support surface.

4. The centering device 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.

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

6. The centering device as claimed in claim 1 , characterized in that the centering station further comprises a third and a fourth gripping device, wherein the third and the fourth gripping device can each rotate freely about a different vertical axis and can each be moved horizontally by means of a third and fourth guiding device, respectively.

7. The centering device as claimed in claim 1 , characterized in that one of the guiding devices comprise a first linear guide for moving the corresponding gripping device in the conveying direction and a second linear guide for moving the first linear guide at a right angle to the conveying direction.

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

9. The centering device as claimed in claim 7 , characterized in that 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.

10. The centering device as claimed in claim 7 , characterized in that the first and the second gripping device can be lowered and raised.

11. The centering device as claimed in claim 10 , characterized in that the first and the second gripping device can be pneumatically raised counter to a restoring force.

12. The centering device as claimed in claim 11 , characterized in that the first and second gripping device can be pneumatically raised counter to a spring force.

13. The centering device as claimed in claim 10 , characterized in that the first and second gripping device can be lowered and raised relative to the first linear guide.

14. The centering device as claimed in claim 10 , characterized in that the first and second gripping device can be pneumatically raised and/or lowered.

15. The centering device as claimed in claim 1 , characterized in that the first and the second gripping device comprises a sucker for gripping the workpiece.

16. The centering device as claimed in claim 1 , characterized in that it comprises a detection device for detecting a position and an orientation of a conveyed workpiece.

17. The centering device as claimed in claim 16 , characterized in that the detection device comprises a line camera which is arranged upstream of the centering station with respect to a conveying direction.

18. The centering device as claimed in claim 17 , characterized in that the centering device further comprises a control device which is designed in such a way that the centering station can be controlled on the basis of measurement data of the line camera in such a way that a desired orientation of the workpiece can be achieved.

19. The centering device as claimed in claim 1 , characterized in that the flat workpieces are sheet metal blanks to be processed in a press.

20. A method for centering a flat workpiece as claimed in claim 1 comprising the following steps:

a) determining a current position and an orientation of the workpiece conveyed on the conveying device by means of a detection device;

b) conveying the workpiece to the centering station;

c) gripping the workpiece by the first and the second gripping device which can rotate freely about the vertical axes;

d) orienting the workpiece on the basis of the current position and of a desired position by the first and second guiding devices.

21. A centering device for centering flat workpieces comprising a centering station having at least a first and a second gripping device for gripping the workpiece, and conveying device for conveying workpieces in a conveying direction to the centering station, where the first and the second gripping device can each be moved horizontally by a first and a second guiding device, respectively, and wherein the first and the second gripping device can each rotate freely about an a different vertical axis, wherein the first and second gripping device are each mounted on the first and second guiding device, respectively, so as to be each exclusively freely rotatable, that is exclusively passively rotatable about a different vertical axis.