Patent GB-728912-A (GB)
Title: Improvements in and relating to electrical winding and like gear
Inventor: EVANS OWEN THOMAS
IPC: B66B1/12
Filed: 1952-05-12
Abstract: 728,912. Automatic speed-control systems. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. April 29, 1953 [May 12, 1952], No. 11982/52. Class 38 (4). [Also in Group XXXVII] The speed of an induction motor 1 driving winding equip ment is measured by tachometer generator 13 the output of which is compared with signal voltages derived from a potentiometer 14, means being provided for automatically selecting the lesser of the signal voltages and for controlling the winder speed in accordance with the magnitude of the selected voltage. A movable contact 17 of the potentiometer is mechanically coupled with a cam follower 18 cooperating with cam 19 the angular position of which is representative of the position of the cage, the profile of the cam being such that the voltage derived from the potentiometer 14 is proportional to the maximum permissible speed of the drum at any point of the wind. The voltages derived from the tachometer generator 13 and potentiometer 14 are applied in opposition to an amplifier 20 the output circuit of which includes a torque motor 22 for controlling the electrodes of a rotor rheostat 8. A driver's lever 106 is coupled to a shaft 105 carrying brushes bd, be; bf, as well as contact 17a which co-operates with potentiometer 14, the shaft being displaced in the same direction for any direction of movement of the lever 106. A shaft 103 is coupled to the cam follower 18 and carries slip-rings a-f2. When the lever 106 is moved to initiate winding in the forward direction, contacts MF are closed to energize contactor OCF and supply current to the stator winding of the motor. Since the contact 17a has moved ahead of the contact 17, the signal voltage derived from the driver's lever is greater than that obtained from the cam gear. Directional contacts DR, LF, are closed to energize accelerating relay OCAC which opens contacts ACb and closes contacts. ACa whereby the voltage derived from contact 17a is effective to determine the speed of the winder, the camoperated contact. 17 being ineffective. When contacts LF are opened by cam 112, the accelerating contactor is de-energized so that the contacts ACa, ACb are changed over, and, upon the winder reaching a required retarding point, the cam 19 is progressively returned to the zero position. If the driver's lever is left in the " full-speed " position " the signal voltage produced thereby is no longer effective and the voltage derived from the cam 19 controls the winder. If, during the retardation period, however, the driver's lever is returned towards the "off " position so that contact 17a occupies a lower voltage position than that of contact 17, then the effective signal voltage is that obtained from the contact 17a. This selection of the lower voltage occurs automatically by the movement of brushes bd, be, off segments d, e, and the engagement of brush bf with segment f2. If the tachometer output exceeds the selected reference voltage a rectifier 39 conducts and magnetic amplifier 38 actuates a dynamic braking relay. OCD for connecting the stator to a rectifier 11. In order to prevent the torque from exceeding a predetermined value during both motoring and braking, a resistor T1 is energized through rectifier 34 and current transformer 33 in accordance with the rotor current. A resistor T3 provides a redetermined reference voltage so that, when the torque exceeds the set value, rectifier T6 conducts and amplifier 20 becomes effective for increasing the rotor resistance. A capacitor A is connected in series with resistor A2 across the tachometer generator 13. If the acceleration of the winder exceeds a predetermined value, rectifier A4 conducts and the amplifier 20 operates to prevent reduction of rotor resistance. The rectifier 11 is controlled during dynamic braking operation in accordance with the rotor current of the motor. In a modification, Fig. 6 (not shown), the contacts 17, 17a co-operate with separate potentiometers, and the amplifier 20, which is of the magnetic type, has one winding energized in accordance with the difference between the voltage from contact 17a and that of the tachometer generator. Another control winding of the amplifier is connected between contacts 17, 18a, in series with a rectifier. If the contact 17a is moved ahead of the contact 17, the second amplifier winding is energized to oppose the first winding for motoring or to assist it for braking, so preventing excessive speed in each case. In a further arrangement, the potentiometers are replaced by induction regulators, Fig. 7 (not shown). An audible or visible warning may be given when the speed permitted by the cam becomes less than that represented by the displacement of the driver's lever. Specifications 690,035 and 690,090 are referred to.