Patent GB-782378-A (GB)
Title: Improvements in or relating to electric motor control systems
Inventor: FRIEDLANDER ERICH SIEGFRIED
IPC: B66B1/12
Filed: 1955-01-28
Abstract: 782,378. Control of motors; controllers. GENERAL ELECTRIC CO., Ltd. Jan. 2, 1956 [Jan. 28, 1955], No. 2672/55. Class 38 (3). Relates to a control system for a mine winder wherein the load driven by a motor is stopped substantially in a predetermined position by means which control the initiation of dynamic braking in accordance with the load. Braking is introduced under the control of a timer 1 driven by a constant speed A.C. motor 3, and, when the winder is started, the timer arm 2 is at its zero position in which contacts 15, 16 are closed. The closure of contacts 23 allows power to be supplied to the winder motor, and the removal of the mechanical brakes closes contacts 20 to energize relay 10 whereby the timer motor is energized to drive the arm 2 in the clockwise direction. When the winder has reached a predetermined fraction of its full speed, a relay 6 is actuated by a tachometer generator 8 driven by the winder so that the motor 3 is de-energized and the arm 2 is stopped. The timer arm remains in this position until the load reaches a predetermined distance from the bank, whereupon a position-responsive switch 24 closes to actuate a relay 13 for energizing the timer motor in the reverse direction and for driving the arm 2 back towards its zero position. When the arm reaches this position, the relay 18 is energized to open the driving contacts 23 and to close contacts 22 for developing a dynamic braking torque on the winder. The opening of contacts 19 on the relay 18 prevents the timer motor from driving its arm in the clockwise direction when the winder-speed falls sufficiently to de-energize the relay 6. The arm 2 is halted at its zero position by means of a slipping clutch and end-stop. Should the timer fail, the relay 18 is energized, to introduce dynamic braking, by relay 25 controlled by a position-responsive switch 26 which responds when the winder is approaching its desired stopping-position. The D.C. supply 21 is disconnected and the mechanical brakes applied at the end of the winding operation. For reverse operation, the switches 24, 26 are respectively replaced by suitably-positioned switches 29, 126. The amount of clockwise movement of the arm 2 at starting is a measure of the load, being greater with a heavier load, and dynamic braking is initiated at a time dependent upon the measuring-position of the arm so that, with a maximum positive load, braking is delayed for the greatest period. The winder motor may be of the three-phase type or of the D.C. type using Ward-Leonard control. In another arrangement, Figs. 4, 5 (not shown), the measuring-position of the arm 2 is determined by the power taken by the winder motor when driving the load at constant speed. For this purpose, two torque motors are mounted on a driving shaft for the arm 2, one acting as a brake and return motor, the other as a power motor, and the arm is coupled directly with an induction regulator for controlling the brake motor. The windings of the torque motors and of the induction regulator are supplied from transformers responsive to the current or voltage of the main supply to the winder motor.