Patent GB-833968-A (GB)
Title: Control systems for electric lift motors
Inventor: BRUNS WILLIAM HENRY
IPC: B66B1/30
Filed: 1958-07-01
Abstract: 833,968. Control of D.C. motors. OTIS ELEVATOR CO. July 1, 1958, No. 21050/58. Class 38 (3). [Also in Group XXXV] When a D.C. motor MA for driving a lift is started in the upward direction, a portion of resistor MFR is short-circuited to bring the strength of the motor field MF up to full value, circuits then being completed for the main and auxiliary field windings GMF, GLF, of a generator GA which supplies the motor. A portion of resistor GMFR is short-circuited to accelerate the motor, and, after a time-delay, the motor field excitation is reduced to provide full-speed operation. As the car approaches a floor at which a stop is to be made, resistor GMFR is reinserted to decelerate the lift motor, and arrival at the levelling-zone causes the engagement of contacts FLV, ULV, a selector switch SLS then opening to disconnect the field winding GMF. The circuit for field winding GLF is maintained, and, as contacts FL1 of relay FL are now engaged, the motor runs at fast levelling speed. As the car further approaches the floor, contacts FLV separate to reduce the excitation of winding GLF. Finally, contacts ULV open to disconnect the generator auxiliary field winding and to apply the brake. When the car is initially started in the up-direction and attains a certain speed, a latching-switch IR is operated by the generator voltage whereby resistor IGSFR is connected in parallel with the field winding GLF, this condition continuing during the levelling operation. If the car over-runs the floor, the field winding GLF is reversed and resistor IGSFR is connected in parallel with resistor GLFR, the amount of excitation being such as to compensate for the residual flux of the generator field in effecting the return of the car to the landing-level. When the car is initially started in the down-direction and attains a certain speed, switch IR is re-set, and resistor IGSFR is again connected in parallel with field winding GLF. If the car over-runs the floor, the field winding GLF is reversed and residual flux is compensated for in the manner described. The completion of circuits for starting the car causes the energization of a rope-stretch compensation time relay LXT and a two-coiled rope compensation switch LX, whereby contacts LXY2 close to shortcircuit a portion of resistor IGSFR. This condition is maintained during the operation of returning the car to a floor after over-run, thus increasing the speed of the return operation. If a change of load causes stretching or contracting of the hoisting ropes when the car is stopped at a floor, the car is re-levelled and residual flux compensation is effected by exciting the field winding GLF, as described. Since the contacts LXT2 are not closed under these conditions, a more gradual return of the car is effected. When the car is brought to an initial stop, contacts open to disconnect the field winding GLF but further contacts then close to establish a reverse circuit for the field winding and to balance the effects of residual magnetism in the final stopping operation. This arrangement also provides quick electrical braking action. A second switch 2R, operating at a higher voltage than the switch 1R may be provided for compensating the residual flux of the generator. During up-travel, the switch 2R closes contacts 2R2 to short-circuit resistor 3GSFR to compensate for the increased effect of residual flux, these contacts remaining closed when the car over-runs the floor and is returned in the downward direction. The switch 2R is reset when the car is started in the downward direction, contcts 2R1 being closed to shortcircuit resistor 2GSFR unless the initial start involves a one-floor run. The establishment of a connection of field winding GMF across the generator armature with a polarity to oppose the residual flux is delayed until the car has been brought to a final stop. Specification 721,988 is referred to.