Patent GB-863262-A (GB)
Title: Improvements in and relating to electric control systems for winders, hoists and thelike
Inventor: RUSSELL DEREK BARRY
IPC: B66B1/28
Filed: 1956-03-27
Abstract: 863,262. Control of A.C. motors. ENGLISH ELECTRIC CO. Ltd. March 27, 1957 [March 27, 1956], No. 9604/56. Class 38 (3). [Also in Groups XXXIV and XXXV] In an electric control system for maintaining the speed of an electric motor-driven winder or hoist in accordance with the setting of a control member, motor torque controlling means cause the motor to produce a torque greater than that required to maintain the winder speed in accordance with the setting of the control member for all settings within a predetermined low range and a braking torque varying in accordance with the excess of a speed dependent quantity over a speed reference quantity is applied to maintain the winder speed in accordance with the setting of the control member. Induction motor 10, Fig. 2, is controlled during full speed running in accordance with the difference between the voltage on potentiometer wiper 24a, Fig. 1, and output of tachometer generator 23 by resistors R1-R14 which are switchable into the rotor circuit and dynamic braking by D.C. applied to the stator circuit over contacts 19, and at speeds of less than 20% full speed by friction brake 12 which is fully applied with zero input to its actuator 13 and fully lifted at maximum input. A saturating limiting device is included in speed/reference comparator 28 and an acceleration responsive device 30 applies to a magnetic amplifier 29 a signal opposing the output from comparator 28 which controls both braking, and resistor insertion, the latter through polarized relays 31-33. The operation of forward drive pushbutton 39a, Fig. 3, energizes a forward directional relay 40 which operates a stop relay 38 to provide lock up, release a relay 37, energize a positional motor (not shown) to move potentiometer wiper 24a and cam follower (also not shown) to full speed, and energize forward stator reversing contactor 15 to energize motor 10 and " start " relay 44. Relay 44 completes a circuit for a rotor contactor RC1 whereby resistor R1 is short circuited to increase the motor torque, operated relays 43 and 46 are maintained, a hold circuit is established for the contactor over contact 47a of a decrease relay 47, and a path is prepared for the operation of a further rotor contactor RC2. If the driving torque is insufficient to react on the brake 12 to close auxiliary contacts 12a further rotor contactors are similarly and sequentially operated until the contacts 12a close and energize selflocking relay 36 to connect amplifier 35 to actuator 13. Contacts 12a which are simultaneously opened release relay 44. At 2% of full speed, switch 48a energizes motion relay 45 which isolates relay 44, and actuates relay 34 to connect magnetic amplifier 35 to the output of 29. Acceleration is limited by the accelerationresponsive device 30 which at a predetermined acceleration reduces the output of amplifier 29 to zero so that the brake is fully applied. This braking torque is reduced as speed increases and contacts 13a in the actuator 13 are closed when it reaches a predetermined low level, to actuate relay 50 and thereby actuate the next rotor contactor to increase the winder torque. The braking torque again gradually decreases and further rotor contactors successively remove more resistances from the rotor circuit until at 20% full speed switch contacts 49a release relay 34 and the brake is taken off. Polarized relays 31-33 for subsequently controlling the rotor contactors are connected to the output of amplifier 29 by contacts 49b and with the acceleration responsive device 30 control acceleration until the actual speed approaches the required speed relay 31 controlling increase relay 50, and relay 32 decrease relay 47. The system is arranged so that all contactors are energized at full speed under normal hoisting load and the reference speed is made slightly above synchronous speed so that regenerative braking occurs if the load should drive the motor above synchronous speed. Deceleration when the reference voltage is dropped by cam is controlled by an auxiliary decrease relay 32 and decrease relay 47 to insert resistance as the speed is desired to fall. The rotor contactors RC1- RC14b and RC1-RC14d contacts of which are delayed prevent rapid insertion of the sequence and at 20% of full speed switch 49 operates to disconnect the contact circuit of rotor resistances by relay 32 and reconnect brake control, the rotor resistance controlled by an auxiliary contact 13b on the brake actuator when an upper limit of braking is reached. Relay 38, which is de-energized by track switch contacts 42a at the pit bottom operates drop-out relay 37 which clears the rest of the rotor contactors and deenergizes relays 40, 15 and 36, the latter causing the application of brake gear 12. If the insertion of all the resistors does not produce the desired deceleration RC1d releases relays 46 and 43 which releases relay 15 and energizes dynamic braking relay 19. Relay 15 is isolated, the supply to relays 31-33 is reversed and the connections between contacts 13a, 13b and relays 50 and 47 are crossed over. On reversal, relay 32 drops off, releases relay 47 and operates relays 46, 43. Relay 31 operates due to the changeover, and resistance is cut out to increase the braking torque until it is limited by device 30. When the deceleration torque is reduced by the deceleration device 30 speed relay 31 operates again to take out further resistance and at 20% of full speed control by brake 12 is reapplied by the speed switch 49. At the pit bottom the relays are cleared by the stop relay as before. Excessive negative output of amplifier 29 operates relay 33 to drop out all contactors by energizing relay 37. A reverse wind is initiated by reverse button 39b energizing reverse directional relay 41 and reverse contactor 16. Torque limiting means applicable to both drive and dynamic braking, open-circuits the increase negative supply line 22d to prevent energization of further rotor contactor. In an alternative arrangement, device 30 may be responsive to motor torque and further means may be provided to prevent the control system changing when acceleration or deceleration exceeds a predetermined value. In a still further arrangement, device 30 may be responsive to rate-of-change of speed error with means to prevent change in the control system when torque and acceleration or deceleration exceeds predetermined values. For close and continuous speed control within a low-speed range, movement of the driver's lever from zero, causes the simultaneous energization of a number of contactors. Speed may in another arrangement be controlled over the whole range by brake gear 12 with changes in rotor resistance by contacts 13. With a liquid resistance induction motor, speed may be controlled by brake gear at low speeds and manually at higher speed or by a speed-responsive device at higher speed. Rotor contactors may be relay controlled and contacts 13 may be operated by brake or actuator or by relays across the output of amplifier 35. Polarized relays 31, 32 may be replaced by a single relay. Specification 863,263 is referred to.