Patent GB-664687-A (GB)
Title: Electric motor control system
IPC: B66B1/44
Filed: 1948-11-25
Abstract: 664,687. Control of motors. WAYGOODOTIS, Ltd. Nov. 25, 1948. [Nov. 25, 1947] Class 38 (iii). [Also in Group XXXVIII] Apparatus for compensating for the load in the car of an elevator system in which an electric hoisting motor is provided for the elevator car and in which the stopping means for the car is controlled in accordance with the load on the motor to obtain an accurate stop of the car at a landing is characterized by the provision of a condenser which is charged in accordance with the load on the motor, and in that the condenser discharge, after the discontinuance of the charging thereof, is utilized to control the stopping means to compensate for load in stopping. The application to a system for automatically controlling a lift motor is illustrated, actuation of a push-button, either in the car or at a landing, starting the car which is decelerated and stopped at landings for which push-buttons, corresponding to the direction of car-travel have been pressed. The car is automatically re-started after each stop so long as calls remain to be responded to. The control circuit for four floors are shown, car-buttons being provided for each of the floors. There is also a button at the top and bottom floors, and an "up" and "down" button at each of the intermediate floors. The lift motor is of the polyphase induction squirrel cage type having stator windings MO1, MO2, MO3, and rotor MOR. The car gate and hatchway doors are operated by a squirrel cage motor, having stator windings DM1, DM2, DM3, and rotor DMR, which is carried in the car. A part of the control circuit is energised through a rectifier RE. When the lift is idle at the second floor and the third floor hall button 3UH, for example, is actuated and latched up, a relay 3U is operated to close contacts whereby a reversing relay AU and an "up" reversing switch A are energised through a cam section CU and direction switch FH3 of a floor controller. A stopping-switch S is energised and latched up to close a main line switch P, so that the lift motor is started in the appropriate direction, the brake coil BR being energised simultaneously. As the brake releases, contacts BR1 are opened to insert resistor BRR1, a rectifier REB preventing current-flow through resistor BRR2. An accelerating relay K engages contacts, after a time-delay, to remove resistors from the stator circuit of the liftmotor. As the car approaches the third floor, brushes UCS and UHS of the floor controller engage stationary contacts CAC3 and UHC3 respectively, there-setting coil of the stopping- switch S being energised. As the car continues its movement, switch FH3 moves from cam section CU, and thereafter switches UMS1, UMS2, are opened to disconnect the lift-motor and apply the brake. A switch DO is energised to operate the door-opening motor until limit switches DOL1 and DOL2 are actuated respectively to open the switch DO and to de-energise a time-delay relay Z. The latter allows time for a passenger to enter the car and press the car-button for the desired direction of travel. When the time-interval has expired, the hall-buttons are again rendered effective and a door-closing relay DC is energised. The operation for downward travel is similar to that described, the car being stopped during downward travel in response to the actuation of "down" hall-buttons. Stops in response .to car-buttons are made during either direction of travel. If buttons have been actuated for floors ahead of the car when travelling upwardly, for example, the switches AU and A are maintained operated until the highest floor, for which a button has been pressed, is reached. If, during upward travel, no button has been actuated for a higher floor, a stop may be made in response to a "down" button. To obtain accurate stopping of the car at the landings, the action of the brake is controlled through a switch Q to compensate for the load on the lift-rotor. A condenser CQ, which maintains the coil of the switch Q energised for a period according to the charge thereon, is connected in the secondary circuit of a transformer TRQ, the primary winding of which is connected in one of the supply-lines to the motor. It is arranged that the secondary voltage of the transformer is substantially in phase with its primary current, the resultant voltage applied to the condenser being in accordance with the vector sum of the said secondary voltage and one of fixed phase which is derived from the supply through resistor QR1. As the load on the motor becomes greater, the phase of the voltage derived from the secondary winding of the transformer TRQ is advanced and the voltage applied to the condenser through rectifiers REQ1, REQ2, increases. The switch Q is operated when the car is started, the condenser is re-charged after each starting-operation, and the ultimate charge is determined just before the motorcircuit is broken prior to stopping. The motor is disconnected and the brake-circuit is broken at a fixed distance from each landing, the condenser discharges, the switch Q being held operated to close contacts Q1 and connect discharge resistor BRR2 across coil BR, so holding off the brake until the car is at the appropriate distance from the floor for correct levelling. Specification 415,931, [Group XXXV], is referred to.