Hand held variable speed drill motor and control system therefor

Abstract

A high speed hand held polyphase motor and a control system therefor is disclosed. The motor is of the induction type, designed for use in oral surgery and the like. The control system includes a bridge type inverter having a separate pair of solid state switching devices such as transistors connected in a bridge configuration across a pair of direct current power supply conductors for each phase winding of the motor. A switch control circuit is connected between the solid state switches and a variable frequency clock signal generator for turning the switches of each pair on and off in a given phase sequence to provide three phase current for the motor windings. The speed of the motor is proportional to the clock signal frequency. A voltage regulating circuit is connected between the power supply conductors and a source of direct current voltage to supply a direct current voltage across the supply conductors which varies in accordance with the clock signal frequency over a pre-established range. The control system further includes a torque demand adjustment circuit coupled to the voltage regulating circuit to permit the voltage across the supply conductors to be independently adjusted over a preset range of clock signal frequency.