GB849902A - Improvements in and relating to control systems for electrically operated winders, hoists, and the like - Google Patents

Abstract

849,902. Control of motors; controllers. BRITISH THOMSON-HOUSTON CO. Ltd. Dec. 10, 1957 [Dec. 21, 1956], No. 38961/56. Class 38 (3). [Also in Group XXXV] A winding CW controls the speed of a winder motor according to the difference of voltages derived respectively from a tachometer generator TG and a reference potentiometer RP which is continuously adjusted to provide a desired speed for any point in the wind. The current in the control winding CW is limited to a predetermined value, irrespective of the error signal, by means of a polarized rectifier 3. A braking relay BR is connected in series with a rectifier 8 and responds when the current in resistor 7 is in a direction resulting from the voltage of the tachometer generator being greater than the reference voltage, the relay being actuated when the excess voltage reaches a predetermined value. The relay BR may control the regulating valve of an hydraulic braking engine, and the arrangement may be such that, after the brake has responded, its application is maintained until the end of the wind, the motor providing a driving torque when required. Alternatively, the brake is applied and released intermittently so that the mean effective braking effort is sufficient to hold the motor speed at a required value. In another arrangement, the braking relay is of the moving-coil type and the braking torque varies continuously in accordance with changes in the excess speed. The moving coil displaces a floating lever in opposition to a spring, one end of this lever being coupled to the piston rod of an hydraulic brake engine which is controlled by a pilot valve also coupled to the lever. The braking force is thus proportional to the degree of energization of the braking relay. The coil of the relay is connected to a magnetic amplifier having a biasing control winding opposed by a control winding which is excited when excessive speeds are obtained, so that the amplifier passes a current to energize the braking relay when the excess speed reaches a predetermined value, and the magnitude of the current is increased with further increases in speed, Fig. 3 (not shown). The brake may be of other than the mechanical type, such as an eddy-current brake. The driving motor may be an induction motor adapted for direct-current braking, or it may be a direct-current motor supplied from a Ward-Leonard generator or through rectifiers. Specifications 588,209 and 849,901 are referred to.