GB741841A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

741.841. Control of motors; controllers. GENERAL ELECTRIC CO., Ltd., and' FRIEDLANDER, E. S. April 14, 1954 [April 16, 1953], No. 10434/53. Class 38(3) When a load 10-is driven by an electric motor 13 in an upward direction and reaches a predetermined position 1, a switch 17 is closed to energize a self-holding relay 32 so that a constant-speed pilot motor 30 moves a contact arm 31 in the clockwise direction. Upon the load reaching a second predetermined position 2, a. relay 33 is energized and the first relay is de-energized, thereby reversing the pilot motor 30. When the arm 31 reaches a position, during its reverse movement, in :which a contact which it carries touches a stationary contact 35, a signal for the application of a mechanical brake 14 is given. Thereafter, the motor 30 continues to rotate until the arm 31 reaches its initial position wherein the pilot motor is halted bymeans of adjustable stop 36 and limit switch 34. The extent of movement of the arm 31 during the passage of the load between positions 1 and 2 is inversely proportional to the speed of the load so that the time interval between the instant at which the load passes position 2 and that at which the signal for brake application is given is also dependent upon the load-speed, the arrangement being such that, if the load is moving faster than normal, the brake-application is advanced. This variation in the time of application of the brake thus compensates for the speed of the load which is stopped in a prescribed position. The endstop 36 can be adjusted to. allow for the delay in the full application of the brake after the initiating signal is given and to provide an allowance for braking from the normal speed of the load. The pilot motor may be of the three phase or the direct-current type, and its speed may be controlled in dependence upon load and other conditions influencing the precise point at which brake application should be made. The pilot motor may run in one direction only, the arm 31 being reversed by means of electromagnetic clutches. In an alternative system, a capacitor is charged at a definite rate when the load is between the first and second positions, the brake being energized as soon as the capacitor voltage has dropped below a predetermined rate after the load has passed the second position.