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Closed Loop Stepper Control With Auto Synchronization Of Encoder Feedback

IP.com Disclosure Number: IPCOM000048721D
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 27K

Publishing Venue

IBM

Related People

Cavill, BR: AUTHOR [+3]

Abstract

Traditionally, stepper drive systems are either 'open loop', in which the motor phase advances are timed, or 'closed loop', in which there is a physically fixed relationship between the motor and the attached encoder system. This relationship is set by adjustment of the emitter system phasing to match the motor phasing. After the emitter is adjusted, it can then be sensed and used to trigger motor phase changes. This adjustment is required because normal assembly of motor and encoder components does not guarantee synchronization.

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Closed Loop Stepper Control With Auto Synchronization Of Encoder Feedback

Traditionally, stepper drive systems are either 'open loop', in which the motor phase advances are timed, or 'closed loop', in which there is a physically fixed relationship between the motor and the attached encoder system. This relationship is set by adjustment of the emitter system phasing to match the motor phasing. After the emitter is adjusted, it can then be sensed and used to trigger motor phase changes. This adjustment is required because normal assembly of motor and encoder components does not guarantee synchronization.

The present drive system is physically the same as a standard closed-loop system except that there is no requirement for manual adjustment of the encoder. A manual adjustment involves presetting the motor in a known phase by locked rotor, or a known phase sequence by an open-loop run. The encoder can then be rotated relative to the motor until encoder phasing matches motor phasing. One method is to observe the command pulse train and compare it to the encoder pulse train on an oscilloscope.

The proposed system uses a microcomputer 11 which measures the differences in phase relation between the motor 12 and encoder 13, and automatically adjusts its command sequence and timing to match that of the encoder.

The microcomputer is commanded to perform the synchronizing function, and drives the stepper motor in open-loop mode at a specified rate. The feedback sequence (encoder phase) is compared to the command sequence (motor phase), and the difference noted and stored in memory. Additionally, the timing difference between command transitions and encoder transitions is computed and stored as a synchronizing data value. The microcomputer is then commanded to run closed loop. Using the synchroni...