Patent ID: 6313601
Filing Date: 2001-11-06
Classification: G11B,H02P

Abstract:
A speed control system for a brushless d.c. motor of the type having a stator with three-phase stator windings, a rotor rotatable relative to the stator, and magnetoelectric converter means for providing a first, a second and a third rotor position signal with phase differences of 120 degrees therebetween, each rotor position signal being indicative of the angular position of the rotor relative to the stator, the motor speed control system comprising:(a) differentiating circuit means for differentiating the first, the second and the third rotor position signal from the magnetoelectric converter means and providing a first, a second and a third output signal in a prescribed phase relationship with the first, the second and the third rotor position signal, respectively;(b) binary signal forming circuit means for translating the first, the second and the third rotor position signal into a first, a second and a third binary signal having a prescribed phase relationship with the first, the second and the third rotor position signal, respectively, each binary signal having a first and a second prescribed state;(c) a first switch connected to the differentiating circuit means and the binary signal forming circuit means for passing the first output from the differentiating circuit means when the third binary signal is in the first prescribed state;(d) a second switch connected to the differentiating circuit means and the binary signal forming circuit means for passing the second output from the differentiating circuit means when the first binary signal is in the first prescribed state;(e) a third switch connected to the differentiating circuit means and the binary signal forming circuit means for passing the third output from the differentiating circuit means when the second binary signal is in the first prescribed state;(f) adder means connected to the first, the second and the third switch for adding outputs therefrom and thereby providing a motor speed signal representative of an actual speed of rotation of the motor;(g) a target speed signal generator for generating a target speed signal representative of a desired speed of rotation of the motor;(h) arithmetic means connected to the adder means and the target speed signal generator for providing a speed control signal representative of a difference between the motor speed signal and the target speed signal; and(i) a motor excitation circuit responsive both to the first, the second and the third rotor position signal from the magnetoelectric converter means and to the speed control signal from the arithmetic means for causing the motor to rotate at the desired speed.