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Stepping Motor Drive Insensitive to Noise

IP.com Disclosure Number: IPCOM000079392D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 102K

Publishing Venue

IBM

Related People

Kulterman, RW: AUTHOR

Abstract

Stepping motor systems normally operate by obtaining pulses from an emitter. Such pulses are applied to a logic system to generate voltage levels capable of starting, running, and stopping a stepping motor according to some predetermined scheme. Stopping or reversing is usually accomplished by providing a series of single-shot pulses of controlled duration, which must be adjusted to match the speed of the motor for a given load and inertia of the system. Noise pulses can upset electronic logic which keeps track of the motor position and changes in speed, and can require frequent readjustment in the single-shot pulse systems for proper operation. The following circuit and method describe a system that is insensitive to noise, and does not employ single-shots for stopping or reversing s stepping motor.

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Stepping Motor Drive Insensitive to Noise

Stepping motor systems normally operate by obtaining pulses from an emitter. Such pulses are applied to a logic system to generate voltage levels capable of starting, running, and stopping a stepping motor according to some predetermined scheme. Stopping or reversing is usually accomplished by providing a series of single-shot pulses of controlled duration, which must be adjusted to match the speed of the motor for a given load and inertia of the system. Noise pulses can upset electronic logic which keeps track of the motor position and changes in speed, and can require frequent readjustment in the single-shot pulse systems for proper operation. The following circuit and method describe a system that is insensitive to noise, and does not employ single-shots for stopping or reversing s stepping motor.

The described system uses an emitter to derive pulses from the actual position of the stepping motor, utilizing sensors that are position sensitive only. Emitter sensor systems of this type which are satisfactory are of the RF energy transmitter and receiver pair type, the optical source and sensor type, or of the magnetic type. The RF or optical systems are preferred. In the system described below, a three-phase reluctance type stepping motor is defined and the details are unique to a three-phase motor and principle of operation, but could be easily extended to control an N-phase stepping motor configuration.

Specific tasks to be described are the controlling of a three-phase, 15 degrees per step, reluctance type stepping motor, so that the motor can be run alternately clockwise or counterclockwise or be stopped at any time during its continuous motion.

Fig. 1 is a typical plot of torque (produced by a current Io flowing in a phase winding) versus angle of rotation for the three phases of a three-phase stepping motor. The plot is drawn with triangular shaped phase-torque functions to simplify the discussion, although somewhat more rounded curves would more accurately describe the actual torques generated in stepping motors. However, the triangular curves have the characteristics needed for the discussion.

In this discussion, torque above the horizontal axis of the chart is taken to drive the motor in a counter-clockwise direction, and torque below the line drives the motor in a clockwise direction. If any two phases of the motor are energized simultaneously with a current Io, the torque experienced will be approximately that of the superposition of the torque curves for the two phases that were energized. Superposed torque phase combinations AB, BC, and AC, are illustrated in Fig. 2.

In Fig. 3, the torque curve illustrates the resultant if current in the three phases is alternately turned off and on as illustrated, starting at the left where there is no current in phases A and C and there is a current Io in B. The motor experiences phase B torque only, which causes it to move in a clockwise d...