Patent GB-406655-A (GB)
Title: Improvements in and relating to electric control systems for electric elevators
IPC: B66B1/38
Filed: 1932-07-28
Abstract: 406,655. Control of D.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Eaton, J.; Rosendale Road, Schenectady, New York, U.S.A.) July 28, 1932, No. 21346. Convention date, July 28, 1931. [Class 38 (iii).] Travelling to predetermined limits.-A motor for a lift is controlled by means of three cathode ray tubes mounted on the car two of which operate to slacken the speed of the motor when the cage approaches within a predetermined distance of a selected landing from above or below respectively, and the third to slacken it still further at an intermediate distance from the landing, the first two again acting to stop it at the landing ; contact devices operated from the lift provide a preliminary slackening of the speed and prepare the circuits of the cathode ray tubes, which are finally actuated by a metal plate on the frame of the lift disturbing the balance of an inductance in their circuits ; a starting handle on the car must be returned to its off position before the tubes can function, a signal being given to warn the operator to do this. In the arrangement shown the motor 11 is arranged in Ward - Leonard connection with a generator 14 and the speed is regulated by inserting resistances 20 ... 25 in circuit with the field-winding 16 of the generator. The fieldcircuit of the generator 14 is controlled by up and down contactors 9, 19, interlocked as shown and operated through relays controlled by its switch 17 and the cathode ray tubes 48<1>, 55, 62. In the grid and plate circuits of the tubes 48<1>, 55, 62 are interposed inductances 53, 52, 60, 59 and 67, 66 respectively, so balanced that the discharge normally takes an oscillating form which will not pass a relay coil, but when the balance is disturbed the plate currents of the tubes pass through the coils of the relays 45, 46, 47 respectively. To effect this a metal plate 75 is mounted on the frame of the lift and arranged to pass between the pairs of coils as shown in Fig. 2. The plate is so arranged that when the car arrives within, e.g., twenty-nine inches from a landing the plate 75 passes between the coils 52, 53 if the car is rising or between the coils 59, 60 if the car is sinking ; when the car is about fifteen inches from the landing it passes between the coils 66, 67 and clears the other pair of coils as the car reaches the landing. When the plate is between any pair of coils it disturbs the balance in that pair and allows current to pass from the tube to the corresponding relay. The device for setting the apparatus to stop at the required floor comprises a bar 27 operated from the lift cable 13 by the gearing shown and carrying conductors which bridge sets of contacts 31, 31<a> ... 33-33<a> for rising and a corresponding set for descending. The set required is put in circuit by a switch 39 operated from the first contact point of the control-switch 17, through a relay 95 or 105 as the car is to rise or descend, and the contact corresponding to the required floor is put in action by switches 34, 35 controlled by push buttons. The further operation will be described when the lift is rising, the descent taking place similarly. When the switch 17 reaches the second contact point the contactor 19 is closed and the generator winding 16 energised through the resistance 22, in series with the resistance 23 and in parallel with the resistance 20. At the same time the brake relay 106<1> is energized to remove the brake 48 from the motor. The contactor 86 is also closed and breaks the circuit of the relay 47, thus energizing the relay 118 and closing an additional circuit for the contactor 19. As the switch 17 reaches its third and fourth points the resistances 25 and 26 are added in parallel to the resistances 20 and 22. When the switch reaches its fifth contact point it energizes the relay 123 thus short circuiting the resistances 20, 22, 24 and 25 and allowing the back e.m.f. of the motor to act through the relay 125, to short circuit the resistance 23 through the contactor 126, and to break the circuit of a relay 130 and partly close the circuit of a relay 131. The back e.m.f. then causes the relay 89 to break the circuits of the relays 45, 46, 47. The car then continues until it is about two floors below that at which it is to stop, when the bar 27 bridges the contacts 31, 31<a> corresponding to that floor and energizes the relay 131. This energizes the relay 135 which causes the relay 113 to break the circuits of the relays 123 and 86 and close a holding circuit for itself, but also closes an alternative circuit for the relays 123, 86. As the circuit through the contacts 31, 31<a> is broken by the further motion of the car the relay 135 opens, breaking the circuits of the relays 123, 86 and replacing the resistances 20, 22, 23, 24 and 25 in circuit. The relay 123 also partially completes a circuit for the relay 130, which is fully completed when the bar 27 bridges the contacts 33, 33<a> appropriate to the required floor. This operates the gong 75<1> and warns the operator to return the switch 17 to the off position. The relay 130 also operates the contactor 115 which cuts the resistance 26 out of parallel with the other resistances and also establishes a holding circuit for itself. The weakening of the generator field produced by reintroducing the resistances allows the relay 89 to re-establish the circuits of the relays 45, 46, 47 and when the plate 75 upsets the balance of the tube 48<1> it closes relay 45, which through a contactor 80 puts the resistance 21 in series with the resistance 20 and also completes a further holding circuit for the contactor 19. When the plate 75 upsets the balance of the tube 62 the relay 47 breaks the circuit of the relay 118 and removes one of the holding circuits for the contactor 19. It also operates a contactor 140 to cut out resistance 20 from its parallel connection with the resistances 21, 22. When the car reaches the desired landing the balance of the tube 48<1> is re-established and the relay 45 de-energized, cutting out the last holding circuit for the contactor 19 and so breaking the circuits of the generator and applying the brake 48 and returning all contacts to their original position. If the car overshoots the floor the tube 55 comes into action and returns it. When the car has only to move to the second floor from its starting point the bar 27 by bridging the contacts 32, 32<a> establishes a separate circuit for the contactor 131 and thus prevents the car from reaching its full acceleration before the slackening operations begin. Specification 316,193, [Class 38 (iii)], is referred to.