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Force to Deviation Conversion Table For Gripping

IP.com Disclosure Number: IPCOM000050614D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Kennedy, TG: AUTHOR

Abstract

In robotic manipulators, gripping devices are used to grasp objects. The gripping force applied to an object must be closely monitored so that the object is not damaged. This is achieved by mounting pinch force sensors on the gripping device, as shown in Fig. 1.

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Force to Deviation Conversion Table For Gripping

In robotic manipulators, gripping devices are used to grasp objects. The gripping force applied to an object must be closely monitored so that the object is not damaged. This is achieved by mounting pinch force sensors on the gripping device, as shown in Fig. 1.

In Fig. 1, the gripping device 10 surrounds a 3-inch object. The gripping device, opened to 4 inches, has force sensors 12 between the device and the object. In order to pick up the 3-inch object, the gripper must grasp the object until the force sensors detect a pressure high enough to work with the object and light enough to keep it from damaging the object. The disadvantage of the above method is that the force sensors are expensive and easily damaged.

The force sensors can be eliminated by making use of the error signal generated by the servo mechanism. The error signal indicates the deviation of the commanded position from the actual position. For example, if the gripping device in Fig. 1 were commanded to move 2.5" and the 3" object was non- deformable, the error signal (in volts) would indicate a .5" deviation. The servo uses that .5" deviation to drive the gripping device to continue applying a (pinch) force. The relation ship between the deviation and the error signal is shown in Fig. 2.

Fig. 2 shows that, for a limited range, the error signal decreases monotonically as the deviation increases. When the deviation is zero, the error signal is zero.

Servos apply a corrective force which is related to the error signal. This is shown in Fig. 3. The servo corrective forcs monotonically increases as the error signal increases. The corrective force is zero when the error signal is zero.

A conversion table can be generated which will translate each deviation into a unique corrective force and each corrective force into a unique deviation. Corrective

Deviation Force

0.0 in 0 grams

-.2 100

-.3 300

-.4 500

-.7 700

-1.6 1000

FIG. 4

Fig. 4 shows the table to convert between deviation (commanded position minus actual position) and the corrective force applied by the...