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Browse Prior Art Database

Stepping Motor Control System

IP.com Disclosure Number: IPCOM000087577D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 51K

Publishing Venue

IBM

Related People

Black, MJ: AUTHOR [+2]

Abstract

This system (Fig. 1) controls the magnitude or level of the average current applied to the windings of a stepping motor, thereby allowing the motor to operate at the same lead angle while generating varying amounts of torque. A stepping motor controlled with the circuit shown above exhibits some of the desirable characteristics of a servo motor.

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Stepping Motor Control System

This system (Fig. 1) controls the magnitude or level of the average current applied to the windings of a stepping motor, thereby allowing the motor to operate at the same lead angle while generating varying amounts of torque. A stepping motor controlled with the circuit shown above exhibits some of the desirable characteristics of a servo motor.

Operating with a lead angle of one-half step to one and one-half steps generally provides the maximum balanced torque per step. The above circuit maintains a lead angle in the one-half to one and one-half step range even though the required torque varies. This is accomplished by varying the magnitude or level of the average current applied to the motor. If the motor slows down, the magnitude of the current is increased, and if the motor is moving too fast, the magnitude of the current is decreased, thereby maintaining the lead angle in the desired range irrespective of the amount of torque required. It is noted that the average current supplied to the motor can be changed by either changing the duty cycle or the magnitude of the pulses applied to the motor.

Fig. 2 shows the amount of torque produced for various amounts of current when the lead angle is between 1/2 and 1-1/2 steps.

The system shown includes a conventional stepping motor 10, the coils of which are activated by drive circuits 11. The magnitude or level of the average current supplied to the motor coils is controlled by digital/analog converter (DAC) 12 and DAC counter 13. The sequence in which the coils of motor 10 are activated is controlled by sequencer 14. Feedback circuit 16 produces one pulse for each step the motor moves, and escapement counter 18 compares the desired amount of motion with the number of pulses received from feedback circuit 16. DAC counter 13 and sequencer 14 are controlled by logic 20, which receives inputs from feedback circuit 16, escapement counter 18, and two timers 21 and 22.

The values loaded into timers 21 and 22 determine the speed and the range of lead angles at which the motor operates. For any particular move, the desired time perio...