Browse Prior Art Database

Stepper Motor Speed Control

IP.com Disclosure Number: IPCOM000089026D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Walrath, LE: AUTHOR

Abstract

A combination of both closed loop and open loop operation for a stepper motor aids in maintaining constant velocity with variable load.

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Stepper Motor Speed Control

A combination of both closed loop and open loop operation for a stepper motor aids in maintaining constant velocity with variable load.

During open loop operation, outside forces can cause a stepper motor to shift phase sufficiently to produce a stall, but in the absence of such forces speed variations are slight. On the other hand, with closed loop operation, small variations in outside forces cause large variations in the constant speed; stalls, however, are unlikely because the phase shift is kept within the bounds of the feedback system.

The above timing diagram of feedback pulses and advance pulses indicates how the closed and open loop systems of operation may be combined for a ratio of one closed loop and four open loop advance pulses. The advance at A1 is delayed from the first positive edge of the feedback signal a predetermined time for a closed loop advance. The next four advance pulses B1-B4 are spaced equally in time at a frequency which will produce the correct velocity of the motor. After the fourth open loop advance, the controlling system looks for the next negative edge of the feedback signal and times closed loop advance pulse A2 from that point, then provides open loop pulses B5-B8. The procedure continues in that manner.

As outside forces attempt to change the velocity, the open loop advances bring the motor back to nominal velocity, and the closed loop advances bring the motor in synchronism. It is, of course, evi...