GB1035910A - Improvements in or relating to variable speed drives for machine tools - Google Patents

Abstract

1,035,910. Automatic speed control. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Oct.23, 1963 [Nov.5, 1962], No.41764/62. Heading G3R. [Also in Division H2] A lathe chuck 3 is driven by D.C. motor 25 coupled to gear box 27 having low-speed and highspeed output shafts 29, 31, associated with clutchcoils LSCS, HSCS, and gear box 39. Tachometer generator 51 controls relay circuits 53, 57, which in turn control the clutch-coils, and also supplies a speed-regulating circuit 55 energizing a pilot motor 61 for adjusting field-regulator 63. A second input to circuit 55 is provided by potentiometer 65 which is positioned in accordance with the traversing of the tool radially of the work-piece piece. For constant cutting-speed operation, switch N/CCS is set to position CC, contacts LTSA, LTSB, being closed for leftward traverse. Actuation of start button SS energizes relay LSR to operate clutch-coil LSCS. A positive bias is applied to resistor 97, bridge 85 being connected to resistor 87 and to earth. The resultant voltage applied to terminal 89 is initially positive, but, as the speed of the motor 25 increases, a negative voltage at terminal 89 causes relay VR to pick-up. Potentiometer 79 provides a reference voltage corresponding to the proper cutting-speed, voltages derived from the potentiometers 65, 79, being applied to centre-stable circuit 75 for controlling the pilot motor 61. Inward movement of the tool reduces the voltage from potentiometer 65 so that relay 75 is unbalanced and motor 61 is energized to reduce the current in field winding 25F, whereby motor 25 accelerates. Relay VR is energized when the motor 25 reaches full speed, relay CR being energized to de-energize relay LSR whereby clutch solenoid LSCS is de-energized to uncouple motor 25 from the chuck. Relay GUR is also energized to de-energize contactor 69C which disconnects armature 25A from the supply and introduces braking resistor 70. Contactor 73C by-passes resistor 63 to increase the field excitation. During this braking operation, the circuit 75 is rendered inoperative, the motor 61 driving slider 63S to the other extreme of its travel. As the speed of the motor 25 decreases, the relay VR drops out to energize the high-speed clutch solenoid HSCS, resistor 78 being inserted in circuit with potentiometer 79, and the circuit 75 rendered effective again. Further inward movement of the tool unbalances the circuit 75 and the field of the motor 25 is weakened to cause an increase of speed sufficient to maintain constant cutting-speed. When the tool has finished its inward traverse, the supply to bridge 85 is reversed, the motor 25 continuing to drive the chuck through the high-speed gear train. The speed of the motor is progressively decreased until relay VR picks-up to uncouple the motor from the chuck. The field 25A is weakened to accelerate the motor to its upper limit until relay VR is deenergized. The low-speed clutch solenoid is then energized and continued movement of the tool is accompanied by progressive reduction of the speed of the motor 25.