Browse Prior Art Database

Controlling the Gripping Force in Hydraulic Gripper

IP.com Disclosure Number: IPCOM000089829D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Brennemann, AE: AUTHOR [+2]

Abstract

A system for program control of the gripping force on the fingers of a manipulator is described wherein the gripping force is developed as a function of preset or programmed force values and not in accordance with any real-time finger sensor value.

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Controlling the Gripping Force in Hydraulic Gripper

A system for program control of the gripping force on the fingers of a manipulator is described wherein the gripping force is developed as a function of preset or programmed force values and not in accordance with any real-time finger sensor value.

An analog servo system is shown in the figure for controlling the spacing and force values between a pair of parallel manipulator fingers by varying the power provided to a hydraulic control valve 1.

The fingers are commanded to operate from a computer program which outputs two digital words. The first word represents the finger spacing for the fingers and is fed to a digital to-analog converter 2 (DAC 1). The second word represents the desired force value and is applied to digital-to-analog converter 3 (DAC 2).

Two-position servo modes of operation to be described include a first mode wherein a "position" digital word is applied to DAC 1 while the "force" word into DAC 2 is zero. When the position is requested, a voltage Vin appears at the DAC 1 output. A position potentiometer 4 provides a voltage Vs in accordance with the separation of the gripper fingers. Both voltages Vin and Vs are subtracted via a pair of resistors R1 and R2 and the result applied to an operational amplifier 5. The output V1 of amplifier 5 is connected to one side of the coil of the hydraulic control valve 1, while the other coil side is connected to receive the output V2 of an operational amplifier 6 associated with DAC 2.

If Vin -Vs does not = 0, then the servo loop operates the hydraulic valve 1, moving the gripper fingers until Vs approximately = Vin. The finger spacing should now be "S", the requested spacing. During this move, V2=0 while V1=A (Vin-Vs). If Vin-Vs is large enough, V1 will reach a saturated value depending on the type of operational amplifier. As the position potentiometer 4 reaches position "S", V1 decreases to ne...