Patent GB-637092-A (GB)
Title: Improvements in or relating to speed regulating system for electric motors
IPC: H02P7/34
Filed: 1946-11-04
Abstract: 637,092. Automatic speed control systems. IGRANIC ELECTRIC CO., Ltd. Nov. 4, 1946, No. 32671. Convention date, Nov. 3, 1945. [Class 38 (iv)] [Also in Group XXXVII] A direct-current motor is supplied from a generator, a normally open main switch establishing a low resistance supply circuit between the motor and the generator. An adjustable field regulator is movable out of a given normal position to strengthen the field of the generator for acceleration of the motor and is returnable to the normal position to weaken the field of the generator for deceleration of the motor by regenerative operation. Means, operative upon closure of the main switch, control the field regulator for operation of the motor at a selected speed and means, associated with the last-mentioned means, temporarily arrest operation of the field regulator during accelerating or decelerating operations thereof in response to predetermined high current conditions in the supply circuit. Upon actuation of a push-button 20 a relay winding 1CR<1> is energized to energize a starting switch winding MS<1> so completing the connection between the armatures of a motor M and a generator G. A resistor 11a is connected in series with the generator field winding, a resistor 10a being excluded from the field winding circuit of the motor which operates at low speed. Actuating windings 18a and 18b of a relay 15 are connected in series between a tachometer generator TG and the slider of a potentiometer 9. If the potentiometer is set for full speed or an intermediate speed, the relay 15 will be so energized that an arm 16 engages a contact 16b and a relay winding F1 is energized to operate a pilot motor 13 in such direction that a rheostatarm is moved towards the right to accelerate the main motor. Upon release of the button 20 relay windings 1CR<1> and MS<1> are maintained energized. At a predetermined high value of the main motor armature current a relay winding 1AR<1> is energized to open contacts 1AR<2> and de-energize the winding F1 to halt the rheostat arm 12, which is re-started when the armature current decreases. However, a timing relay which is de-energized simultaneously with the starting of the main motor, and drops out after a time interval to close contacts TR2 bridging contacts 1AR<2>, transfers the control of the relay winding F1 to contacts 2AR<2>. These last contacts are under the control of a relay winding 2AR<1> which responds to a still higher value of armature current and provides a higher rate of acceleration. When the motor M reaches the speed pre-set on potentiometer 9 the relay 15 is de-energized and the rheostat arm is stopped at a position corresponding to such speed. If the motor M is operating at a preset speed and the potentiometer 9 is adjusted to a higher speed position, the relay 15 is energized as before to move the arm 12 to the new position. If the motor M is operating at a pre-set speed and the potentiometer 9 is set to a lower speed position, the relay 15 is so energized that the arm 16 engages contacts 16a and a relay winding S1 is energized to operate the pilot motor 13 and move the arm 12 towards the left. A relay coil DR1 is energized to open contacts DR2 at a predetermined high value of regenerated current to halt the movement of the arm 12 while such high current persists. To break the motor regeneratively, a push-button 21 is depressed to de-energize the relay winding 1CR<1>. The relay windings MS<1> and S1 are energized to return the arm 12 towards the " off position, the coil S being controlled by the contacts DR2 as before. When the arm 12 reaches the " off " position, the coil MS<1> is de-energized by disengagement of contacts 14 and 14c, and the limit switch SL is opened to de-energize coil S1. In order that the motor M may coast to rest, a push-button 22 is depressed to de-energize coils MS<1> and 1CR<1>. A voltage relay winding 2VR<1> is included in the main motor circuit and the relay 15 is disconnected. When the back electromotive force of the motor M falls below the voltage of the generator G, the coil 2VR<1> is energized to energize the coil S1 and cause the pilot motor 13 to return the arm 12 towards the " off " position until the motor and generator voltages are balanced. During coasting, a relay coil 1VR<1>, connected across the armature of the motor M, is energized, and upon depression of a push-button 23 a relay coil 2CR<1> is energized, through contacts 1VR<2>, to energize coil MS<1>. The regenerative braking circuit is re-established, the coil S1 being again controlled by the contacts DR2. Prior to the return of the arm 12 to the " off " position, an additional coasting period may be initiated by actuation of button 22.