Electromechanical chopper for speed control of battery powered devices

A speed control system for a cordless portable electric motorized tool having a tool housing including a handle portion comprising:

• a portable D.C. power supply comprising battery cells mounted within said housing;
• and a self-enclosed, trigger-controlled electro-responsive chopper mounted in said handle portion with the trigger extending out therefrom for actuation by the user to control the motor speed, said chopper comprising:
• a pair of contacts;
• an electromagnet comprising a coil and a movable armature arranged to open a first one of said contacts from the second contact;
• means connecting said contacts in circuit with said motor and said coil and being effective when closed to apply a voltage pulse from said battery cells to said motor and also to said coil to cause said electromagnet to open said contact;
• and an operating spring controlled by said trigger for applying variable resilient closing force to said first contact to vary the closed-to-open time ratio of said contacts thereby to correspondingly vary the width of the voltage pulses applied to the motor, the average voltage applied to the motor and the speed of the motor.

A speed control system for a portable electric motorized device comprising:

• a portable D.C. power supply comprising a storage battery;
• and a self-enclosed, manual actuator controlled electroresponsive chopper with its manual actuator extending out from its housing for actuation by the user to control the motor speed, said chopper comprising:
• a pair of contacts;
• an electromagnet comprising a coil and a movable armature arranged to open said contacts;
• means connecting said contacts in circuit with said motor and said coil and being effective in closed condition to apply a voltage pulse from said storage battery to said motor and also to said coil to cause said electromagnet to open said contacts;
• and means comprising an operating spring controlled by said actuator for initially closing said circuit and for applying variable resilient closing force to said contacts to vary the closed-to-open ratio of said contacts thereby to correspondingly vary the width of the voltage pulses applied to the motor, to proportionally vary the average voltage applied to the motor and the motor speed.