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Step Motors With High Cogging Torque

IP.com Disclosure Number: IPCOM000044239D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Chai, HD: AUTHOR [+2]

Abstract

A polyphase rotary step motor has a permanent magnet rotor and stator poles having single or bifilar windings. Fig. 1 shows a three-phase step motor 10 with permanent magnet rotor 11. Stator 12 has poles I, II, and III wound with single windings A, B, and C. For clockwise rotation, the pulsing sequence is B-A-C-B where the current direction produces south polarity. An initial motion can be enhanced by pulsing both A and B windings to start the motion where winding B is pulsed to produce a south polarity in pole II and winding A is pulsed to produce a north polarity in pole I. Fig. 2 shows a three-phase step motor 13 having a rotor 14 with a square core 15 made of soft iron coupled between permanent magnet poles 16 and 17.

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Step Motors With High Cogging Torque

A polyphase rotary step motor has a permanent magnet rotor and stator poles having single or bifilar windings. Fig. 1 shows a three-phase step motor 10 with permanent magnet rotor 11. Stator 12 has poles I, II, and III wound with single windings A, B, and C. For clockwise rotation, the pulsing sequence is B-A-C-B where the current direction produces south polarity. An initial motion can be enhanced by pulsing both A and B windings to start the motion where winding B is pulsed to produce a south polarity in pole II and winding A is pulsed to produce a north polarity in pole I. Fig. 2 shows a three-phase step motor 13 having a rotor 14 with a square core 15 made of soft iron coupled between permanent magnet poles 16 and 17. Permanent magnets 16 and 17 have circular arc pole faces with flat sides coplanar with the sides of core 15. This construction of rotor 14 provides a stiffness around the detent position. It also provides a lower reluctance path for the ac flux and a better fringing pattern in the repulsive mode of operation. Stator poles I, II, and III are wound with bifilar windings A through F. Fig. 3 shows the motor circuits with windings A - F connected in series with drive transistors 18 - 23. Fig. 4 shows the timing and winding switching sequence for clockwise rotation of motor 13. From the initial position in Fig. 2, transistor 18 is energized momentarily and transistor 23 is energized for a time sufficient to drive r...