Brushless d.c. motor with precise speed control
First Claim
1. A brushless d.c. motor comprisinga permanent magnet rotor;
- a stator having a winding;
means supplied with d.c. current and connected to said stator winding for producing an alternating magnetic field in said stator and having a speed control circuit;
means for deriving, from said motor, signals synchronized with the rotation of said rotor;
means for generating pulses of a predetermined length;
means for triggering the generation of said pulses by said pulse generating means in response to said signals;
analog circuit means for phase-shifting and smoothing said pulsesfor deriving from said pulses a smoothed voltage having a d.c. component and a superimposed a.c. component, andmeans for feeding said smoothed voltage to said speed control circuit for controlling the speed of said motor by said d.c. component of said voltage while the a.c. component serves to control the armature current and torque cycles as the motor turns.
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Accused Products
Abstract
Speed control for a brushless d.c. motor is made independent of the effects of temperature and aging on the magnetic structure by triggering a rectangular wave pulse generator by voltages produced by the rotation of the motor through a coupling network that makes the trigger time correspond to a certain portion of the rise of voltage so that the influence of the amplitude of the signal on the trigger time will be negligible. The square waves are phase-shifted and integrated to produce a d.c. signal proportional to motor speed on which is superimposed a practically sinusoidal ripple and this signal is fed into a comparator to produce both an error signal from the d.c. component and a commutation control from the a.c. component. The speed is switched between desired precise values by an electronic circuit that controls the duration of the rectangular pulses and makes corresponding adjustments in the integrator and phase shifter.
28 Citations
13 Claims
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1. A brushless d.c. motor comprising
a permanent magnet rotor; -
a stator having a winding; means supplied with d.c. current and connected to said stator winding for producing an alternating magnetic field in said stator and having a speed control circuit; means for deriving, from said motor, signals synchronized with the rotation of said rotor; means for generating pulses of a predetermined length; means for triggering the generation of said pulses by said pulse generating means in response to said signals; analog circuit means for phase-shifting and smoothing said pulses for deriving from said pulses a smoothed voltage having a d.c. component and a superimposed a.c. component, and means for feeding said smoothed voltage to said speed control circuit for controlling the speed of said motor by said d.c. component of said voltage while the a.c. component serves to control the armature current and torque cycles as the motor turns. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification