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Counter Preset and Modified Index Pulse for Use in Incremental Encoder Support Robotic Circuitry

IP.com Disclosure Number: IPCOM000039425D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Alewine, NJ: AUTHOR [+6]

Abstract

A technique is described whereby a counter preset and a modified index pulse is used in incremental encoder support circuitry. A course "Home" switch, a modified index pulse, and an eight-bit preset feature is added to the counter circuitry so as to attain the necessary flexibility to adapt a wider range of robotic configurations. Incremental encoders, used to track the position of a motor shaft, require support circuitry to interpret their signals. A counter circuit is usually used to provide the interface between the encoder and the microprocessor controlling the motor. At start-up, the system is set to an initial value so that, as the motor rotates, signals are generated by the encoder and fed to a counter circuit. Two signals are usually used to determine the direction and distance traveled by the motor shaft.

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Counter Preset and Modified Index Pulse for Use in Incremental Encoder Support Robotic Circuitry

A technique is described whereby a counter preset and a modified index pulse is used in incremental encoder support circuitry. A course "Home" switch, a modified index pulse, and an eight-bit preset feature is added to the counter circuitry so as to attain the necessary flexibility to adapt a wider range of robotic configurations. Incremental encoders, used to track the position of a motor shaft, require support circuitry to interpret their signals. A counter circuit is usually used to provide the interface between the encoder and the microprocessor controlling the motor. At start-up, the system is set to an initial value so that, as the motor rotates, signals are generated by the encoder and fed to a counter circuit. Two signals are usually used to determine the direction and distance traveled by the motor shaft. This in turn provides the information needed regarding the relative displacement of the robot joint. Since incremental encoders are only able to supply relative position, the joint positions are redefined each time the robot is turned

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on. The technique described herein implements a course "Home" flag, generated by an external switch, and an index pulse from the encoders so as to locate the "Home" position. The course "Home" switch is open for part of the work path of the joint operation and closed for the other part. The point where the switch opens and closes identifies the course location of the "Home" position. The "Home Sequence" involves the finding of the modified index pulse after the course home switch changes from a logical "0" to a logical "1", or vice versa per convention, and presetting the counter to the actual position of the robot joint. To illustrate how the encoder positions operate, signal lines "A" and "B" of the encoder and the index signal "I" are ANDed to generate an interrupt, as shown in the two examples in Fig. 1. In order to provide uniformity between the several different types of encoders, which could be installed on the robot manipulator, the logical AND function of the three lines provides the interrupt and marks a unique position when the encoder is rotated in either direction. The counter circuit will count either up or down, based on the state changes of the "A" and "B" signals. The unmodified index pulse of example #1 will not generate a signal during a single counter value, but instead it generates a signal over several values. As a resul...