GB436309A - Improvements in controlling the speed of electric motors, particularly lift driving motors - Google Patents

Abstract

436,309. Automatic regulation. POLLARD & CO., Ltd., E., 159, St. John Street, and HAMMOND, E. N., 26, Fordhook Avenue, Ealing Common, both in London. May 1, 1934, No. 13119. [Class 38 (iii)] In a control system for a lift &c. motor which runs at various speeds means are provided for obtaining a fixed crawl speed comprising a rotating member 4, Fig. 1, driven at a constant speed and another member 11 driven in the same direction at a speed corresponding to the speed of the motor to be controlled, the members actuating contacts in a circuit which effects control of the motor. Two contacts 6, 7 are mounted on the member 4, between which a third contact 10 loosely mounted on the shaft is situated. This contact is in friction engagement with the member 11. Fig. 3 shows the circuit diagram, assuming that the controls are set to crawl speed, the contactor coil 25 is open circuited causing the eddy current brake 26 to be applied. According to the direction of movement of the lift either switch 20<a> or 21<a> will be closed. If the motor is too slow contact 10 moves out of engagement with contact 6 and contactor coil 30 is de-energized to short circuit a resistance in the rotor circuit of the motor. If the motor speed still remains low the contact 10 engages the contact 7 to energize contactor coil 32 and remove further resistance from the motor circuit. The reverse action takes place to lower speed. The eddy current brake 26 and electromechanical brake 33 are de-energized when the lift is stationary by contactors 20b and 21b. The contacts 20<a>, 21<a> serve as a reversing switch to change over the connections of the contacts 6, 7 when the action of the lift reverses. A reversing switch is also provided to reverse the rotation of the motor driving the disc 4. Specification 424,994 is referred to.