Patent GB-970039-A (GB)
Title: Improvements in or relating to transmission mechanisms
IPC: B66B1/16
Filed: 1959-09-08
Abstract: 970,039. Control of D.C. motors. BENNIE LIFTS Ltd., and M. GODWIN. Dec. 8, 1960 [Sept. 8, 1959], No. 11911/59. Heading H2J. [Also in Divisions B8 and F2] A transmission mechanism comprises a rotary output member connectable by a magnetic particle clutch to a motor and by a second magnetic particle clutch to braking means, the energization of both clutches being variable to vary the torque applied to the output member. As applied to a lift car driven by a D.C. motor 12 of a Ward-Leonard set 11, an electric motor M1 is connected by a magnetic particle clutch 23 to a flywheel 22 and to the armature 17 of an auxiliary D.C. generator which feeds signals to the field winding 16 of the D.C. generator of the Ward - Leonard set, the armature 15 of which is connected to the armature 12 of the lift motor. The armature 17 of the auxiliary D.C. generator is also connectable by a magnetic particle clutch 25 and through an irreversible gear 26 to a creep motor M2. The lift is started by operating a call button closing one of contacts 1F . . . TF corresponding to the various floors. This energizes the motor M1 and a timing motor (not shown). The timing motor causes a waveform generator 32 to be driven through half a revolution by a motor M3, the potential picked off the generator 32 being fed through an amplifier 31 to the control winding 24 of the magnetic clutch 23 so that the armature 17 is progressively coupled to the motor M1 At the completion of the half-revolution the armature has reached the terminal velocity of the motor M1 and a negative voltage is applied through contacts CC1 to the amplifier 31 to maintain the clutch 23 fully energized, so that the armature 17 continues to run at the speed of the motor M1. As the lift starts moving a tachometer generator TG1 is driven from the low speed shaft of the lift driving gear. The output from the generator TG1 is fed through an amplifier 33 to a motor M4 which drives a linear potentiometer PV3 and a square law potentiometer PV4. The output from the linear potentiometer PV3 is fed back to the amplifier 33 so that the motor M4 stops when the outputs of the tachometer generator TG1 and the potentiometer PV3 balance. The output of the linear potentiometer PV3 is also fed through a tachometer generator TG2 to a servo amplifier 35 energizing a servomotor SM which drives the tachometer generator TG2. The outputs of the potentiometer PV3 and the tachometer generator TG2 are in opposition so that the servomotor SM turns at a speed proportional to that of the lift car. As soon as the servomotor SM begins to turn the timer motor closes, and subsequently opens, a contact T4 so that for this period, corresponding to half the acceleration time of the lift car, a magnetic particle clutch 38 is energized and the servomotor SM drives a field rheostat 37. The field rheostat is initially set at zero so that the current supplied to the field winding 13 of the lift motor is a maximum, and as the rheostat is driven the current in the field winding is decreased. The power output of the lift motor is therefore a maximum to get the lift car moving and it is subsequently decreased to a value determined by the lift loading. At a predetermined distance before the floor at which the lift car is to stop is reached, a high speed relay having contacts HSRX is actuated, de-energizing the motor M1 and earthing the floor selector line. When this occurs the potential picked off from a resistor R5 in accordance with the position of the lift car is fed to a high speed relay unit RC1, to which a steady potential is fed by the square law potentiometer PV4. When these potentials balance, the relay unit RC1 is actuated and a contact HR1 in the energizing circuit of a magnetic clutch 39 is closed. The clutch 39 is thereby energized and drives a waveform potentiometer PV2 through half a revolution. The output of the potentiometer PV2 is fed through an amplifier 41 to the energizing winding 27 of the magnetic clutch 25. The armature 17 is thus progressively coupled to the irreversible gear 26 and thereby retarded as determined by the signal to the amplifier 41. The potential picked off from the resistor R5 is also fed to a high-speed relay RC2. When the lift car reaches the desired floor this potential reaches earth potential, and the unit RC2 operates, energizing the lift brakes. When the lift car comes to rest the main contactor drops out, energizing the timing motor and the creep motor M2. The creep motor compensates for variations in the distance travelled by the lift car during retardation, and the timing motor resets the system to accept another call. In a modification, instead of the signal indicative of the position of the lift car being picked off the resistor R5, a signal can be obtained as described in Specification 891,667.