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We next want to present a useful model for the dynamic behavior of the popular stepping motor. This class of motors also has several versions and corresponding analysis models,8 and we choose one of the simpler descriptions9 for our presentation. Figure 5-20 shows a simple permanent-magnet stepping motor. The rotor is a permanent magnet with a single pair of poles. The stator has four windings (electromagnets) which can be independently energized by connected them to electrical power supplies (voltage or current sources). By reversing the voltage polarity or current direction of the electromagnets, we can create either north or south poles at the ends of the electromagnets facing the rotor. By properly energizing all four electromagnets, we can create a stator magnetic field which will attract the rotor into specific angular positions. By switching the windings in the proper sequence, we can

8 A. Leenhouts, The Art and Practice of Step Motor Control, Intertec International Inc., 1987; A. Leenhouts, Step Motor System Design Handbook, Litchfield Engineering Co., 1991; C. Raskin, Stepper motion ... What's it all about? Motion Control, January 1993, pp. 17-22; C. K. Taft and R. G. Gauthier, Stepping motor selection for point-to-point positioning systems, PCIM, October 1985, pp. 22-33; P. G. Krause and 0. Wasynczuk, Electromechanical Motion Devices, McGraw-Hill, New York, 1989, chap. 8.