Patent GB-844511-A (GB)
Title: Improvements in or relating to elevator systems
IPC: B66B1/36
Filed: 1958-05-14
Abstract: 844,511. Control of D.C. motors; controllers. WESTINGHOUSE ELECTRIC CORPORATION. May 14, 1958 [May 29, 1957], No. 15457/58. Class 38 (3). After a fully loaded elevator car is registered with a landing and the car is being unloaded so that the car rises above the landing due tc contraction of the cables, re levelling of the car is deferred until the load has decreased, so avoiding the operation of levelling a heavy load in an overhauling direction. The driving motor MO is supplied from generator GE which is controlled in part by regulating exciter RG having pattern field windings RGP1, RGP2, and auxiliary windings RGL1, RGL2, which boost the excitation of the machine during levelling operations. The exciter has a field winding RGS which compensates for the armature resistance of the motor-MO, and a differential field winding RGD for limiting the output of the main generator. Assuming that the car is fully loaded (load-responsive switches WA, WC2 being opened and contacts WB1, WB2, WC1 closed) and that the car is moving downwardly, adjustment of a car switch CS to prepare for stopping de-energizes relays DR, 80 and GR6. The introduction of a portion of resistor R7 reduces the excitation of the main generator to decelerate the car, the coils of inductor relays 1UL-3L being energized to assist in the landing operation. As the car approaches a landing, the inductor relays cooperate with inductor plates whereby progressively greater portions of resistor R7 are introduced until bridge circuit 21 is disconnected from its supply lines and brake 5 is applied, a resistor R6 being selected to provide gentle braking operation. Just as the car comes to rest, a portion of resistor R2 is shunted to increase the excitation of the differential field winding RGD and reduce the output voltage of the main generator to zero. If the car overruns the landing, inductor relay 1UL energizes uplevelling relay LU, so completing a lowresistance discharge circuit for brake coil 5a and preventing setting of the brake before the car is reversed. The bridge 21 is connected for uptravel, until the car approaches the landing and the relay LU is de-energized to disconnect the bridge and to interrupt the circuit of the brake coil, a substantial portion of resistor R6 being included for quick braking action. The driving motor is finally disconnected under the control of a timing relay. After the fully loaded car has reached the landing and is being unloaded, the car rises until the inductor relay 1DL operates the levelling relay LD to close contacts LD4. The downswitch D cannot be energized, however, to correct for cable-contraction until the load decreases sufficiently for closure of contacts WC2. When the switch D does operate, the bridge 21 is connected for down -travel and the exciter RG has its field windings RGL1, RGL2 effective and the whole of resistor 21g in circuit for rapid increase of the main generator voltage. In addition, a substantial portion of resistor 7 is shortcircuited. The driving motor is connected to the main generator and the brake is released, undue car movement being avoided since the load is substantially balanced. When the voltage applied to the motor reaches a sufficient value, the car starts to move downwardly, a voltage-responsive relay BL adjusting resistor R7 for low-speed return of the car. As the car reaches the landing, the switch D is opened and the brake quickly applied. Further reduction of the load to a predetermined low value leads to automatic re-levelling, a relay B energizing brake relay BA to release the brake when the generator voltage becomes sufficient to support the car unaided. The relay BL, which is now re-calibrated, again holds the landing speed to a low value. When an empty car is stopped at a landing and loading commences, the car drops to energize levelling relay LU, an up-switch U being energized when load contacts WB2 close. If the car continues to receive load after it has been registered with the landing, the contacts WA, WC2 open and contacts WBI, WB2, WC1, WD close whereby release of the brake is prevented. The motor assists the brake in supporting the load but its torque is held to a value insufficient to produce motion, this condition being maintained until the load is reduced or movement of the car initiated by car switch CS. The contacts WD shunt the contacts of an overcurrent relay RE during the period in which the motor assists the brake. Specification 697,046 is referred to.