Patent GB-740257-A (GB)
Title: Improvements in or relating to control systems for electric motors
IPC: H02P3/24
Filed: 1953-04-24
Abstract: 740,257. Automatic speed-control systems. GENERAL ELECTRIC CO., Ltd., FRIEDLANDER, E. S., and PARTON, K. C. April 22, 1954 [April 24, 1953], No. 11383/53. Class 38 (4). [Also in Group XXXVII] A winder is driven by an induction motor 10 having a wound rotor, and means are provided for controlling the rate of deceleration of the motor in accordance with its electrical loading at a predetermined point prior to the commencement of deceleration, so that the load is stopped in a predetermined position. As shown, the present system is applied to arrangements disclosed in Specifications 738,310 and 740,256. The system comprises a circuit for comparing the voltage output of a potentiometer 47, which is adjusted by slider 44 coupled to speed-setting lever 40, with the voltage derived from a motordriven tachometer generator 33. The error voltage is applied to a winding 70 of a saturable reactor whereby the speed of the motor is automatically maintained at a value dependent upon the setting of the lever 40 during both motoring and dynamic braking operation. The voltage derived from the potentiometer 47 is modified by means of an adjustable tapping 210 which is coupled to a spring-biased shaft 211 driven by a torque motor 215. Means indicated at 221 are arranged to de-energize solenoid 220 and release a brake 218 when the winding cage reaches a predetermined position during full-speed operation of the induction motor. If the winding cage is being driven by the motor 10 when the cage reaches the said predetermined position, the windings of the torque motor are respectively energized in accordance with the primary current and voltage of the winder motor, the torque of the motor 215 being thus proportioned to the power input to the motor 10. When the tapping 210 has thus been adjusted in dependence upon the electrical loading of the winder motor, the brake 218 is again applied so as to hold the shaft 211 fixed during the decelerating operation. The speed of the cage at the end of the decelerating period is therefore rendered substantially independent of load conditions thereby reducing errors in the stopping-position of the load. If the load is overhauling when the predetermined position of the cage is reached at which the brake 218 is released, dynamic braking operation will be in force, and the torque of the motor 215 is made dependent upon the degree of braking required and hence upon the electrical loading of the winder motor. The brake 218 is again released when the control lever 40 is moved through the " off " position, the tapping 210 assuming a " no load " position in which the shaft 211 is locked during the earlier part of the wind. Regenerative braking may be provided by means of a single resistance step in the last section of the control lever movement. In an alternative arrangement, a fixed bias tapping is provided on the potentiometer 47 in addition to the tapping 210. Further modifications relate to a winder-driven cam for controlling the slider 44, and another torque motor for replacing the spring 212. Specification 717,253 also is referred to.