Patent GB-598573-A (GB)
Title: Improvements in or relating to electric motor drives
IPC: H02P7/03
Filed: 1945-07-17
Abstract: 598,573. Control of motors. BEECHING, G. H., and ROBSON, J. M. July 17, 1945, No. 18344. [Class 38(iii)] [Also in Groups XXXV and XXXVIII] Travelling between predetermined limits; continuous reversals.-A reversible electric motor for repeatedly traversing a driven element is arranged and excited to reduce displacement of the element from a predetermined position and is additionally excited according to its speed so that the driven element repeatedly over-swings said pre-determined position. The invention is applied to a directional radio aerial which is repeatedly swung through an angle adjustable in mean direction and magnitude. The aerial and associated circuits are mounted on a rotor unit which is coupled to a driving motor by mechanical gearing and selsyn machines. The rotor unit is also coupled to the alternating-current fed rotor of a transmitting selsyn the stator windings of which are connected to similar windings of a coincidence selsyn of which the rotor is manually adjustable to a reference position and carries a winding in which is induced a voltage proportional to the displacement angle between the rotors of the selsyns. This voltage is applied to a phase-sensitive rectifier unit 12 to yield a direct voltage which is applied to a differential power amplifier 15 to excite opposed field windings 16 of the driving motor which is driven to reduce the displacement. A feed-back generator is coupled to the motor and produces a voltage, the sign and magnitude of which depends on the direction of rotation and speed of the motor, which is applied to the differential power amplifier unit and which reduces or increases the hunting of the system according to the sense in which it is injected. The alternating displacement voltage is applied in opposite sense to the grids of two valves V1 and V2 and an alternating reference voltage is applied across the valves by a transformer T2. When the displacement voltage on the grid of the valve V1 is in phase with the reference voltage this valve passes current which negatively biases the valve V2. Reversal of phase reverses the operation of the valves. The rectified voltage appears across resistors R4 and R5 of the differential amplifier unit comprising valves V3 and V4. According to the sign of the rectified voltage, one valve is more positively biased than the other, and in passing more current biases the other more negatively. One of the field windings is strongly excited and operates the motor to reduce the displacement. The feed-back voltage is fed through the leads 18 and 19 and a reversing switch S to a potentiometer P from which an adjustable fraction is taken and applied between the grids of valves V3 and V4. According to the position of the reversing switch this voltage damps or reduces the damping of the operating motor. When the reversing switch is adjusted so that the feed-back increases the motor speed, the aerial scans a sector of amplitude determined by the voltage taken from the potentiometer P and of mean bearing determined by the setting of the coincidence selsyn.