Method and apparatus for improving the regulation of the speed of a motor

Abstract

An automatic braking and speed control for a device driven by an electric motor. A controller provides a pulsed output voltage having a pulse width dependent upon the load seen by the motor (16). When the drive pulses are present two diodes (52,54) and a transistor (66) serve to maintain a power transistor (56) in the off condition. When the controller is not providing drive pulses and the motor (16) is being turned by the momentum of the mechanical device or by some outside force, such as gravity, the motor (16) functions as a generator and turns on two transistors (56,67) so that two resistors (51a,51b) apply a load to the generator (16). This provides a braking action between the output pulses so that the net speed of the motor (16) and its associated mechanical device is more dependent upon the output pulses provided by the controller. A shunting diode (42), in conjunction with two resistors (51a,51c) provides a braking mechanism in the event that the motor (16 ) should begin turning in a direction reverse to that desired. A switch (64) allows reversing the polarity of the voltage provided to the motor (16) so that the motor (16) may be made to run in a clockwise or a counterclockwise direction, as desired. The result is an apparatus which can be easily retrofit onto existing systems so as to provide for automatic braking and improved speed control for a device driven by an electric motor.