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Stepper Motor Angular Velocity Detection Circuit

IP.com Disclosure Number: IPCOM000037190D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Burke, EJ: AUTHOR [+2]

Abstract

This article describes a circuit and method of connection that senses the back EMF of a permanent magnet (PM) stepper motor to detect the angular velocity of the motor shaft. This is done when the motor's chopped current driver is off and the motor is being driven as a generator. Velocity detection is achieved using a voltage threshold detection circuit connected directly across the motor windings.

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Stepper Motor Angular Velocity Detection Circuit

This article describes a circuit and method of connection that senses the back EMF of a permanent magnet (PM) stepper motor to detect the angular velocity of the motor shaft. This is done when the motor's chopped current driver is off and the motor is being driven as a generator. Velocity detection is achieved using a voltage threshold detection circuit connected directly across the motor windings.

The intended application is to measure ribbon velocity in a dual motor bidirectional ink ribbon drive for a printer. Here, ribbon is fed from one spool to another as one motor drives and the other motor is off. This information is used for ribbon velocity feedback control and to detect the end of a spool of ribbon. Other applications include robotics and tape equipment.

A preferred embodiment is shown in the figure. In the velocity detecting mode, the upper drive transistor 10 and lower drive transistors 1 and 2 must be off. When these conditions are met, the motor coil windings 5, 6 are isolated from the noisy ground. The inputs of the detection circuitry 13 are connected as shown across both motor coil windings in a series circuit so that true differential amplification is possible. The detection circuit may instead be connected across just one motor phase only.

As the motor's shaft is turned, the motor acts as a generator and a back EMF is developed across the motor coil windings 5 and 6. The circuit converts the moto...