Abstract
The main requirements of low-speed, dc power servomotors used as drive members of director control systems are for fast speed of response coupled with optimization of size and weight for a given torque output. It can be shown that the over-all time constant of such a dc machine is inversely proportional to the gap density squared; thus, where physical size and temperature rise of the field windings are important design limitations, the use of modern, high-energy permanent-magnet materials becomes advantageous. This paper describes the conversion of a conventional 6-pole, 1-hp, 100-rpm machine to one having permanent magnet excitation employing Columax (Alnico VB, DG) poles. Difficulties associated with machining, and magnetizing and demagnetizing the 6-pole stator in situ are discussed, and a study of the maximum demagnetization forces existing in such a machine, carried out with the aid of Hall plates, is given. A comparison of both the dynamic and the steady-state performance of the conventional machine and the permanent magnet machine, shows the feasibility of using modern permanent magnet materials for such an application.
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