GRIPPING DEVICE, ROBOT AND CONTROL METHOD

Abstract

A gripping device for a robot for gripping objects, including at least two gripping units each having a gripping finger and being transferable by a controlled movement between a release position and a gripping position gripping an object, the gripping units each having gripper elements which, in the gripping position, can be brought into contact with the object to be gripped, in which the gripper elements are rotatably mounted on the gripping fingers of the gripping device.

Claims

1. A gripping device for gripping objects comprising at least two gripping units each comprising a gripping finger and being transferable by a controlled movement between a release position and a gripping position gripping an object, the gripping units each comprising gripper elements which, in the gripping position, can be brought into contact with the object to be gripped, wherein the gripper elements are rotatably mounted at distal ends of the gripping fingers.

2. The gripping device according to claim 1, wherein the gripper elements are configured to rotate towards each other and away from the object to be gripped when the gripper elements come into mutual contact upon reaching the gripping position.

3. The gripping device according to claim 2, wherein the gripper elements comprise a first section, an outer contour of which is configured with respect to its axis of rotation in such a way that a contact between the gripper elements takes place linearly.

4. The gripping device according to claim 2, wherein the outer contour of the first section with respect to the axis of rotation (D) partially follows a shape of a mathematical spiral.

5. The gripping device according to claim 3, wherein the gripper elements comprise a second section, an outer contour of which in relation to its axis of rotation is designed in such a way that, when the gripping position is completed, a further rotation of the gripper elements is prevented.

6. The gripping device according to claim 5, wherein, when the gripping position is completed, the gripper elements lie at least partially flat opposite one another with engagement of the object.

7. The gripping device according to claim 1, wherein the gripper elements are biased.

8. The gripping device according to claim 1, wherein the gripper elements comprise means arranged to prevent rotation of the gripper elements when these are not in contact with each other.

9. The gripping device according to claim 8, wherein the device is further adapted to cause the gripper elements to rotate away from each other when there is no longer contact between the gripper elements.

10. The gripping device according to claim 1, wherein at least one of the gripper elements is rotatably drivable.

11. The gripping device according to claim 10, wherein the gripping fingers comprise a gear mechanism for driving the gripper elements.

12. The gripping device according to claim 1, wherein an outer surface of the gripper elements comprises a friction-enhancing coating and/or structure.

13. A robot comprising the gripping device according to claim 1.

14. A method of gripping an object by means of a robot having the gripping device according to claim 1, comprising steps of: moving the gripping device by the robot towards the object until the gripper elements come to rest on the object; moving the gripping fingers towards each other until the gripper elements come into mutual contact; and further moving the gripping fingers towards each other in such a way that the gripper elements are set in rotation while gripping the object.

15. The method according to claim 14, comprising the further a step of: further moving the gripping fingers towards each other until the gripper elements come into abutment with their sections under engagement of the object, which sections are configured not to allow further rotation of the gripper elements.

16. The method according to claim 14, wherein the steps are performed by an impedance-controlled and/or sensitively controlled robot.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Further features and advantages of the invention will become apparent from the description of the embodiments illustrated by the accompanying drawings, in which

[0037] FIG. 1 exemplifies a gripping device according to the prior art;

[0038] FIGS. 2 to 5 show a first embodiment of a gripping device according to the invention, each figure representing a gripping step of the method according to the invention;

[0039] FIG. 6 schematically shows a second embodiment of a gripping device according to the invention; and

[0040] FIGS. 7a and 7b exemplarily show a gripping process by means of the second embodiment.

DETAILED DESCRIPTION

[0041] FIG. 1 shows an example of a prior art gripping device that can be attached to a distal end of a multi-link manipulator of an impedance-controlled robot.

[0042] The gripping device consists of a base 1, in which a drive mechanism and a guide for the gripping fingers 4 are located, with a flange 2 for attachment to a robot arm, which is not shown, and a connection 3 for controlling the drive of the gripping fingers 4, which can be moved linearly towards each other and comprise gripper jaws 5 at their distal ends. As can be seen, these gripping fingers 4 only permit a parallel grip, with which flat, soft objects, such as textiles, arranged on a flat surface cannot be gripped.

[0043] FIGS. 2 to 5 show a first embodiment of a gripping device according to the invention, with which gripping of such objects can be realized in a simple manner.

[0044] In FIG. 2, a gripping device is shown in a first embodiment according to the invention, wherein the condition in which the gripping device comes to rest on the flexible object to be gripped is shown, as indicated by the vertical arrow.

[0045] The soft and flat object 7 to be gripped, a textile fabric, is placed on a flat support 6.

[0046] The gripping device also comprises two gripping fingers 8 that can be moved parallel to each other, as indicated by the horizontal arrows.

[0047] At their distal ends, both gripping fingers 8 each comprise a rotatably mounted gripper element in the form of rotary jaws 9, which are provided with a friction-enhancing coating 10 on their outer surface intended to come into contact with the object 7.

[0048] In order to prevent the rotary jaws 9 from already starting to rotate when they move towards each other as a result of the parallel movement of the gripping fingers 8, a means 11 is provided which prevents rotation and is designed, for example, as an appropriately dimensioned one-way spring.

[0049] As can be seen, movement of the rotary jaws 9 towards each other causes the object 7 to pile up slightly between them due to compression.

[0050] By exceeding the force in vertical direction by the robot system (not shown) and closing the rotary jaws 9, the flexible object 7 is already compressed and accumulated between the rotary jaws 9. In this state, the two torsion springs 11 prevent the rotation of the rotary jaws 9.

[0051] As can be seen in all FIGS. 2 to 5, the outer contour in a first section 9.1 of the rotary jaws 9 follows the line of an Archimedes spiral, so that as the linear motion progresses, the rotary jaws 9 come into mutual contact at a point K which lies above a common plane formed by the pivot points D of the bearings of the rotary jaws 9.

[0052] This, according to the invention, as shown in FIG. 3, causes the rotary jaws 9 to begin to rotate as soon as they contact each other at point K, and thereby, as a result of friction and adhesion, more and more material of the object 7 is picked up between the rotary jaws 9 as they continue to rotate and their sections 9.1 roll on each other with intermediate support of the object 7, as shown in FIG. 4, which is induced by further linear movement of the gripping fingers 8 towards each other.

[0053] FIG. 5 shows a condition in which the gripping fingers 8 have finally reached their closed position and the rotary jaws 9 have reached their final gripping position. Following their first section 9.1, as seen in the direction of rotation, the rotary jaws 9 comprise a second section 9.2, which is of linear design, as indicated in FIG. 4.

[0054] In the final gripping position, these sections 9.2 lie flat opposite each other, enclosing the object 7 at this point. This results in a two-dimensional load with increased frictional engagement, whereby the object 7 can be held securely. In this gripping position, the object 7 can now be lifted by means of the robot and transferred to a target position, where it is then released by the gripping fingers 8 moving apart linearly and the rotary jaws 9 rotating in an opposite direction back to their starting position, if necessary supported by the spring means 11.

[0055] The shown mechanism of gripping by the gripping device according to the invention takes advantage of the flexibility of the object 7. It does not rely on precise gripping positions and is therefore more robust against visual errors, for example if additional optical sensors are to be used in conjunction with the robot. Correct and non-destructive gripping of flexible objects of any, preferably planar, design is carried out according to the invention predominantly by force control with respect to the linear movement of the gripping fingers 8.

[0056] Alternatively, however, it may also be provided that the gripper elements at the distal ends of the gripping fingers are actively actuated. For this purpose, FIGS. 6 to 7b schematically show a second embodiment according to the invention.

[0057] Here, a gear and drive mechanism 12 is used, which can be designed in any desired way inside at least one gripping finger 13 and the base 14 of the gripping device.

[0058] For example, as shown in FIG. 6, the rotary jaw 15 can be driven by a belt drive 16 arranged inside the gripping finger 13, which in turn is actuated by a gear 17 rolling on a rack 18 inside the base 14, thereby causing it to rotate when the gripping fingers 13 themselves are moved linearly toward or away from each other.

[0059] As FIGS. 7a and 7b show, the linear movement of the gripping fingers 13 towards each other and the simultaneous rotary movement of the rotary jaws 15, as indicated in each case by the arrows, causes a flexible object 19 to be accumulated at a corresponding point and to be pulled upwards between the rotary jaws 15 and thereby gripped. This design of the gripping device is suitable for heavier objects 19 of this type, whereby the gripping device as such can also be dimensioned accordingly larger.

[0060] Here, too, the advantage is exploited that the object to be gripped has flexible properties. By pulling the object between the rotary jaws of the gripping fingers through a rotating surface with high friction, the mechanism ensures correct and non-destructive gripping. The rotational motion of the rotary jaws 15 is coupled to the linear motion of the gripping fingers 13, so no additional motor is required. The object 19 is deformed between the rotary jaws 15 and the actual gripping force is controlled by the linear motion of the gripping fingers 13. By controlling the distance between the gripping fingers 13, failed gripping attempts can be easily detected and responded to.

[0061] The above-described embodiments of a gripping device are particularly suitable for use with an HRC-robot that has a corresponding impedance-control that is capable of implementing such “sensing” gripping of a flat, filigree object, for example, by the gripping device and the robot.