Browse Prior Art Database

Use of Stepper Motor As Variable Load

IP.com Disclosure Number: IPCOM000088008D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Barnett, JA: AUTHOR

Abstract

A stepper motor provides a readily variable load by suitably switching on control windings or changing supply voltages. In certain applications such as maintaining tension on a spooled web having a continually changing radius, the stepper motor easily lends itself as an adjustable drag device.

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Use of Stepper Motor As Variable Load

A stepper motor provides a readily variable load by suitably switching on control windings or changing supply voltages. In certain applications such as maintaining tension on a spooled web having a continually changing radius, the stepper motor easily lends itself as an adjustable drag device.

Referring to Fig. 1, a ribbon drive is schematically shown in which each spool is driven by its individual stepper motor. It is desirable that the tension in the ribbon between spools be maintained as nearly constant as possible to provide uniform winding and that the ribbon direction be reversible. Either stepper motor can be used as the driving motor while the other is used to provide drag torque.

An example of a control circuit for a motor is shown in Fig. 2. A pedestal control and pedestal driver have been added to a typical driving circuit. When the stepper motor is driving, the pedestal control turns on the pedestal driver to shunt R1. Drivers A, A, B, and B are toggled on and off by the winding sequence control to provide clockwise or counterclockwise rotation.

This same control circuit may be used to apply a smooth transition drag torque. Considering only the drag control, the pedestal driver is turned off by the pedestal control. Current is limited to the windings by R1, RA, RB, the winding resistance and supply voltage. With one or more drivers turned on and a force applied to displace the rotor, a resultant opposing torque is created that is determined by the motor characteristics, the power circuit and the effective winding current. The number of energized windings and the stepping rate determine the smoothness of the drag torque curv...