Handling: hand and hoist-line implements – Utilizing fluid pressure – Frames
Reexamination Certificate
1999-04-15
2003-01-07
Cherry, Johnny D. (Department: 3652)
Handling: hand and hoist-line implements
Utilizing fluid pressure
Frames
C294S064200, C294S907000, C901S040000, C901S046000
Reexamination Certificate
active
06502877
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a gripper system having at least two mutually independent gripper elements, and to a vacuum gripper system having at least one independent gripper element.
BACKGROUND OF THE INVENTION
In handling workpieces, it is currently unavoidably necessary for the workpiece to have a defined outset position or a defined position in space, so that the workpiece can be grasped exactly with a gripper system that is secured to a robot hand. The permissible positional deviations are as a rule in the range of ±0.2 mm. Such exactly positioned workpieces can be grasped blind by a robot and can be handled and joined together blind. However, it has been found that large workpieces in particular, such as molded sheet-metal parts, while exactly positioned still cannot be grasped without error, for instance because they are warped or deformed. There is also the danger that because of its warping, a workpiece once grasped cannot be joined or can be joined only defectively. Such a handling system therefore requires permanent monitoring.
It also requires relatively expensive workpiece receptacles that assure that the workpieces will have a defined position of repose. Another problem is considered to be that if a gripper crashes, the gripper may become deformed. The gripper then moves onward, thus deformed, which can lead either to an inaccurate reception of the workpiece and/or an imprecise or defective joning operation.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to furnish a gripper system which requires less monitoring and with which even workpieces that are positioned outside the tolerance range can be grasped and nevertheless joined exactly.
This object is attained according to the patent invention with a gripper system which has at least two mutually independent gripper elements, and each gripper element is provided with at least one force sensor for ascertaining a force in a predetermined direction. This object is also attained according to the patent invention with a vacuum gripper system which has at least one independent gripper element that is provided with at least one force sensor for ascertaining a force in a predetermined direction.
In the first of these embodiments, the two mutually independent gripper elements enable secure grasping of the workpiece, and the quality of the gripping operation is ascertained via the force sensors. For instance, if a gripper element is located correctly on the workpiece or if this gripper element engages the workpiece in accordance with the specifications, then the value ascertained by the force sensor is also within the predetermined tolerance range. If the workpiece is incorrectly positioned, however, then the gripper element engages the workpiece out of line. As the workpiece is being lifted, the force sensor ascertains a value that is outside the tolerance range. The possibility now exists of putting down the workpiece and grasping it again, with the gripper system now shifted slightly, and in particular as a function of the force values ascertained by the force sensors. This can be done with recourse to the data stored in a data memory. From the forces ascertained, however, the positioning of the workpiece can also be calculated.
The gripper system can advantageously be secured to a robot hand. Another option is for the workpiece, despite being grasped wrong, to be transported onward, with the robot hand triggered via the values of the force sensors in such a way that the gripping error is compensated for, so that the workpiece is nevertheless joined exactly.
The gripper system according to the present invention has the substantial advantage that even workpieces that are outside the specified tolerance of ±0.2 mm can be grasped. In other words, this means that with the gripper system of the present invention a substantially greater positional tolerance for the workpieces can be specified; it can be in the range of ±2 cm, or in other words can be higher by a factor of 100.
Another advantage is considered to be that in handling the grasped workpiece, that is, in swiveling the workpiece that is grasped, the forces acting on the gripper elements, the force of gravity, and the dynamic mass or centrifugal forces in all the degrees of freedom, can be ascertained, and as a result the position of the workpiece at the gripper elements or in the gripper system can be determined. The robot hand or arm can also be braked, if the forces acting on the workpiece exceed limit values, and hence the workpiece will not come loose from the gripper elements. Because of the possibility of ascertaining dynamic mass forces or centrifugal forces, the possibility also exists of grasping a workpiece that has been positioned rotationally incorrectly, detecting the misrotated position, and correcting it. Both position error detection and rotary position detection are possible. The rotary position error can also be ascertained, in one embodiment, directly from the measured forces.
In order to grasp a beam, for instance, two gripper elements can be used, with which the force and the X position of the beam are ascertained. If three gripper elements are used, then both the introduced force at right angles to the X-Y direction and the X-Y position of the workpiece can be ascertained. If four gripper elements are used, the force of gravity, the X-Y position, and the position angle or in other words the rotary position of the workpiece can be ascertained.
The gripper system of the present invention furthermore has the substantial advantage that with it, different workpieces can be grasped, and that the gripper system can tell which workpieces have been grasped. If a gripper element is grasping empty air, for instance, or if its overall force deviates from the norm, then for instance it can be assigned to a particular component or workpiece.
In a further refinement, it is provided that the force sensor is disposed on the gripper element in such a way that with it, the force component acting in the receiving direction of the gripper element can be ascertained. As a result, in a simple way, the optimal contact of the gripper system with the workpiece to be grasped is ascertained. Via the ascertained force component in the receiving direction, the contact force of the gripper system on the workpiece can also be detected, so that the workpiece on being grasped is not damaged even if the workpiece is not in its intended position. It is furthermore possible in joining to monitor the requisite joining forces, that is, a controlled pressing of a front panel onto a passenger car body, or to monitor a force path, for instance in snap-in operations, and as a result integrated monitoring of successful joining is achieved.
An especially advantageous embodiment provides that the gripper elements are embodied as modules, and in particular as plug-in modules. Plug-in modules can be put together relatively simply and in a way secure against mistakes, so that the gripper system can be constructed quickly and without problems by putting the individual components together. Furthermore, modules have the particular advantage that because of their identical design they can be manufactured relatively inexpensively, and virtually any desired configuration can be created with them.
To make it possible to grasp large components or workpieces, the gripper elements are connected to one another via connecting components. The connecting components are either embodied rigidly, for instance as straight or curved connecting pieces, corner pieces or shunts. Furthermore, the components may have their own code for their shape and size. These connecting components make it possible to construct different structures, so that the gripper system can be optimally adapted to the shape of the workpiece. All the gripper elements, however, have identical connection hookups.
However, the connecting components can also be variable in their three-dimensional structure and can for instance be embodied as a two- or three-dimensional joint
Eisele Thomas
Schick Jens
Schmalz Kurt
Schmalz Wolfgang
Cherry Johnny D.
J. Schmalz GmbH
Jones Tullar & Cooper P.C.
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