GB948941A - Electrical automatic speed control system - Google Patents

Abstract

948,941. Clutch control. PYE Ltd. Nov. 3, 1960 [Nov. 6, 1959], No. 37747/59. Heading F2L. [Also in Division G3] A winch drum is driven by a constant speed motor through induction couplings 2, 3, which are adapted to rotate an output shaft in opposite directions, the arrangement being such that, when one coupling is energized to transmit the drive, the other coupling is energized to act as a dynamic brake if the speed of the shaft exceeds a predetermined value. A hoist control circuit 9 comprises thyratrons V 1 , V 2 , which are biased by A.C. derived from transformer T 1 and also by a D.C. error signal which represents the difference between the voltage from tachometer generator 8, driven by the output shaft, and a reference voltage from potentiometer P 1 . The lowering control circuit 11 is similar to the circuit 9 and comprises thyratrons V 3 , V 4 . Balance potentiometers P 3 , P 2 are provided for each control circuit 9, 11, respectively, a balance potential being applied to that circuit which at any time is controlling the coupling functioning as a brake. In this manner, braking action of the associated coupling is initiated when the driving torque of the other coupling approaches zero. Relays 10, 12, ensure that the output shaft is locked by a magnetic brake 7 unless one of the couplings is energized. A single controller may regulate change-over switch contacts SA-SF and also adjust the potentiometer P 1 . During the hoisting operation, an error signal indicating underspeed causes increased excitation of coupling 2, the same signal being applied to thyratrons V 3 , V 4 , with opposite polarity to prevent torque being generated by coupling 3. If the potentiometer P 1 is moved to a lower tapping, the thyratrons V 1 , V 2 are cut-off and the thyratrons V 3 , V 4 become fully conductive so that coupling 3 provides dynamic braking. When a light.load is being lowered, the coupling 3 provides the driving torque, whereas, with substantial loads, the coupling 2 is always energized to provide a braking torque. If the load tends to overhaul, further driving by the coupling 3 is prevented and the coupling 2 provides a negative torque to maintain a set lowering speed. Specification 871,437 is referred to.