Patent GB-1174161-A (GB)
Title: Electric motor arrangement having acceleration control
IPC: B66B1/26
Filed: 1967-03-15
Abstract: 1,174,161. Control of D.C. motors. WESTINGHOUSE ELECTRIC CORP. 15 March, 1967 [28 March, 1966], No. 12147/67. Heading H2J. [Also in Division G3] In a system for accelerating a lift according to a predetermined pattern the means for producing the pattern comprises a circuit which includes a capacitor 501 arranged to reduce the accelerating signal initially to provide a smooth transition from standstill. The drive comprises a Ward Leonard system, the generator field GF of which is connected across a bridge consisting of rectifiers 253, 256 and resistors 239R, 241R which are progressively short circuited by the up or down movement of a pivoted arm 215. The arm is moved for acceleration by an electromagnetic " pattern motor" PM, this motion being opposed by the reaction between permanent magnets 237 on the arm and a conductive disc 231 coupled to the drive motor 1. The "pattern motor" has a main winding PM1 which carries the accelerating signal and a stabilizing winding PM2 which carries negative feedback proportional to the rate of change of armature voltage, via capacitor 345, and positive feedback proportional to generator field current measured across resistor 341. In addition, when the lift has stopped, contacts FK1, FK2 close to apply this residual armature voltage in a negative sense to PM1 so that the arm 215 moves sufficiently to cancel it. The accelerating pattern signal comprises a current produced by transformer 363, rectified at 359, and regulated by back-to-back controlled rectifiers 371, 373, which are triggered by a circuit comprising a capacitor 411 which is charged through transistor 377 and discharges through unijunction transistor 379 and triggering transformer 375. Conduction of 377 is controlled by a current I c , through resistor 388 from rectifier 391, which is opposed by a feedback current I F  proportional to the rate of change of voltage across PM1, derived by differentiating capacitor 399. A second capacitor 415 is connected in parallel to reduce the acceleration when the voltage on 399 reaches the Zener value of diode 383. Control resistor 388 is shunted by capacitor 501 which is uncharged at switch on, thus producing the required smooth initial change in acceleration. A Zener diode 419 provides protection should power be applied with PM1 open circuited. Slow down is effected by reducing the voltage applied to PM1, by " slowdown transducer " (autotransformer) 311 and by the increase of impedance of coils UMC, UMD as cores UMA, DMA are moved into them. These coils and cores are mounted on a lift selector moving synchronously with the cage. The feedback I F  causes maximum conduction of 371, 373 during slowdown. For final location PM1 is switched over contacts TR4, TR5 to the system at the top of Fig. 4A, in which a shaped plate P1 fixed to the shaft moves between the windings of differential transformers EU1, EU2. Load sensitive switches LG1, LG2 cause some energization of PM1 before take off to tend to balance the load before the mechanical brake 7d is released. The relay controlling this brake is time delayed so that it is applied after the cage has come to rest.