Patent GB-627095-A (GB)
Title: Electric motor control system
IPC: B66B1/44
Filed: 1947-03-10
Abstract: 627,095. Control of motors. CRANE, H. C. March 10, 1947, No. 6651. Convention date, March 14, 1946. [Class 38(iii)] [Also in Group XL(b)] A system for controlling an electric motor-driven conveyer structure of the kind adapted to move along a guiding structure comprises a circuit element of variable impedance mounted on one structure, means mounted on the other structure for varying, in accordance with the position of the conveyer structure, the impedance of said circuit element and, in accordance with the velocity of the conveyer structure, the rate of change of the impedance of said circuit element, means controlled by the circuit element for creating a controlling electrical response which is a function of the impedance and of the rate of change of impedance of the circuit element and hence is a function of the position and velocity of the conveyer structure, and means controlled by the controlling electrical response for varying the speed of the conveyer. As shown, means for levelling a lift-car at a desired floor comprises photo-electric control units 22 and 23 which are mounted on the car and which co-operate with 26, fixed to the side-wall of the lift-shaft. The photo-electric cell of the control unit 22 is effective only when the car is moving stationary vanes 24, having notches 25 and downwardly, the other cell being likewise effective in the opposite direction of travel. When the car is moving upwardly and approaches a floor at which it is desired to stop, the vane 24 passes through slots 30 and 31 and the light from an electric lamp 33 is gradually cut off from a photo-electric cell A which is included in a circuit controlling the supply of current to the coil of a contactor for stopping or starting the motor. If the lift-car is in a stationary position just below a floor-level, the tube A will conduct a current the value of which is dependent upon the amount of light passing through the slot 26, and a voltage representative of the distance of the car from the floor will be developed across a resistor R1, an amplifier valve B being biassed to cut-off so as to allow a valve D to pass current through a relay-coil UR. Energization of the main driving motor to move the car upwardly is thereby initiated or maintained. With the car moving upwardly, the light beam passing through the slot 26 is reduced and a voltage is developed across a resistor R3, which is shunted by a condenser C, which is representative of the rate of change of the current passing through the resistor R1 and therefore the car-velocity. This voltage opposes that developed across the resistor R1 in the grid circuit of the valve B and has the effect of allowing that valve to conduct, de-energize the relay UR, and stop the motor at an appropriate moment for levelling. If the car overshoots the floor, a photo-cell A<SP>1</SP> is activated by the light from a lamp 32 passing through the notch 25, this cell now being effective to energize a relay and reverse the motor until the car is re-levelled. Different methods of connecting resistors R1 and R3 in the grid circuit of the valve B are shown. The resistor R3 may be connected to a tapping of a resistor in series with the tube A. An additional circuit, similar to that comprising the resistor R3 and the condenser C, provides a voltage component in the grid circuit of the valve B which compensates for acceleration or deceleration of the lift-car. Fig. 10 (not shown) illustrates the application to a variable voltage system. The output of the tube D, instead of being applied to the relay-coil UR, is used to energize an extra field winding of a generator which supplies the working-motor. The speed of the motor is normally regulated by adjustment of the excitation of a main generator field winding, the extra field winding, which is controlled by the photo-electric circuit, producing a correcting-effect so as to level the car accurately.