Seagate Technology Incorporated

Alain M Cassat

Laurent Cardoletti

Gunter Karl Heine

Robert Michael Pelstring

Donald J MacLeod

Greg Zariphopoulos

A circular magnetizer is disclosed comprising circular insulating inset holding pans of axially disposed wires, each pair carrying a current oppositely directed from the adjacent pair, the insert being disposed within and facing a back iron across a circular gap of sufficient width to allow a circular magnet to be disposed therein and spaced by a gap from the insert and/or back iron. The pan's of wires are arranged to create flux lines which will establish alternating magnetic poles separated by null zones in the magnet.

Magnetizing apparatus

A brushless DC motor control apparatus and method for regulating the speed of a motor at a nominal speed. The apparatus maintains a nominal motor speed without the use of conventional rotor position location devices such as Hall sensors. The current speed of the motor is determined using the back EMF zero-crossing measured only on complete rotor revolutions to mitigate motor dissymmetry errors. A control system compares the current speed to a desired speed and adjusts the total motor current to attain the desired speed. As a result, highly accurate speed control is maintained.

Closed loop control of a brushless DC motor at nominal speed

The present method and apparatus detects the position with an accuracy of .pi./m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to be able to start in the correct direction with certainty. 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 difference between the induced voltage 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. Additionally, a method and apparatus is presented which uses the static position detection method to accelerate the motor to a medium speed. The method shortens the duration of the drive pulse as the motor accelerates ensuring a smooth acceleration without the possibility of back oscillation.

Closed-loop control of a brushless DC motor from standstill to medium

The present method and apparatus detects the position with an accuracy of .pi./m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to be able to start in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, starting the rotor in the correct direction, the 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 difference between 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 when polarity currents should be applied to each phase to reliably and certainly start the motor in the proper direction.

Position detection for a brushless DC motor

The present method and apparatus detects the position with an accuracy of .pi./m electrical radians (where m=the number of motor phases) within one electrical period, and provides enough information to be able to start in the correct direction with certainty. After starting the motor in an open loop mode of one or two steps, starting the rotor in the correct direction, the 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 difference between 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. The present invention includes a method and apparatus for optimizing the duration of the short current pulses used in determining the rotational position of the rotor.

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Pully, Switzerland

Alain M Cassat