05028852 is referenced by 82 patents and cites 9 patents.

The present method and apparatus detects the rotor position of a brushless DC motor with an accuracy of .pi./m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to enable starting the motor in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, a closed loop mode may be switched on, using a dynamic indirect position detection as is already well known in the technology. More specifically, the position at start is determined by the injection of short current pulses in different motor phases, each phase or pair of phases being energized first by a pulse of one polarity and of the opposite polarity. The sign of the time difference between the rise times of the induced voltages is detected. By performing a succession of these tests on different phases or pairs of phases of the standing motor, a table of results is established which clearly defines the position of the rotor relative to the motor phases. The same table then defines what polarity currents should be applied to each phase to reliably and certainly start the motor in the proper direction.

Title
Position detection for a brushless DC motor without hall effect devices using a time differential method
Application Number
7/541583
Publication Number
5028852
Application Date
June 21, 1990
Publication Date
July 2, 1991
Inventor
John C Dunfield
Santa Cruz County
CA, US
Agent
Flehr Hohbach Test Albritton & Herbert
Assignee
Seagate Technology
CA, US
IPC
H02P 6/02
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