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Brushless DC motor system with optically scannable member for commutation

  • US 4,803,408 A
  • Filed: 02/11/1987
  • Issued: 02/07/1989
  • Est. Priority Date: 02/11/1986
  • Status: Expired due to Fees
First Claim
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1. A brushless DC motor system, comprising:

  • a DC motor which includes a plurality of stator coils to receive commutation current, a rotatable member having an optically scannable code, and a plurality of permanent magnets, fixedly positioned with respect to the scannable code, mounted along a circular path in the rotatable member opposite the coils so that the coils and magnets are spaced apart by gaps;

    fixed scanner means with respect to the stator coils for scanning the code to generate scanner signals having phase positions; and

    control means for evaluating the scanner signals with respect to their phase positions to determine the moment of commutation, and for supplying the commutation current to the coils,wherein the motor requires n commutation steps during each revolution, n being an integer greater than 1,wherein the rotatable member is composed of a rotationally symmetrical light-transmitting plastic element which includes a ring with an edge bearing the scannable code, the scannable code including a plurality of light-impermeable equidistant zones on the ring, the light-impermeable zones being distributed around the circumference of the ring, each light-impermeable zone corresponding to respective commutation step, andwherein there are n-1 first light-impermeable zones and one second light-impermeable zone, the second light-impermeable zone being shaped differently than the first light-impermeable zones.

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