Patent GB-664263-A (GB)
Title: Improvements in control systems of the correspondence kind for movable members
Inventor: LIVERSIDGE JOSEPH HORACE
IPC: G05D3/12
Filed: 1949-02-07
Abstract: 664,263. Electric follow-up systems. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd., Feb. 27, 1950. [Feb. 7, 1949] No. 3354/49. Addition to 610,029. Class 40 (i). [Also in Group XXXV] The follow-up system according to the parent Specification, wherein backlash or resilience in the drive between the motive equipment and the controlled member effects a control action on the motive equipment, is modified by deriving the control quantity dependent on the displacement of the motive equipment by approximate integration of the velocity thereof, so that the control is transient. As shown, Fig. 1, the controlled member 4 is driven by a reversible motor 9 through a mechanical drive, having backlash or resilience represented at 10, to follow up the movements of a control handle 3. The control handle and the controlled member 4 drive directly i.e. with no backlash, selsyn rotors 5, 8, respectively. The error voltage from the rotor 8 is fed through a transformer 19 having two secondaries 16, 16a to a phase sensitive amplifier 14, which in known manner drives the motor 9 in the followup sense. A D.C. tachometer generator 11 driven directly by the motor 9, i.e. without backlash, feeds a voltage proportional to the velocity of the motor 9 to an integrating circuit, 12, 13, the output of which, a voltage approximately proportional to the displacement of the motor 9, is fed through a potentiometer 15 to the amplifier input to modify the error signal control, but only during transient conditions i.e. during change of position of the motive equipment. The relative proportions of the two control signals are adjustable by tappings 17, 18 on the potentiometer 15. First derivative control of the motor 9 may be introduced in the amplifier 14 as in the parent Specification or by tachometer generators as in Specification 611,046. The time constant of the integrating network 12, 13, is made large enough to ensure good integration at the frequencies at which the system would otherwise tend to oscillate. At lower frequencies the integrator output approximates to a velocity feedback which serves to stabilize the system. Such feedback however introduces velocity errors, which may be eliminated in known manner or as in Fig. 2. Here a further tachometer generator 20 driven directly by the controlled member 4, i.e. without backlash, is series connected with the generator 11, the two generator outputs being equal and in opposition when the motor 9 and controlled member 4 are moving together so that a resultant input to the integrating circuit arises only when the motor 9 moves relatively to the controlled member 4 as permitted by the backlash 10. The voltages produced by the tachometer generator 20 may, alternatively, be greater or less than that of the generator 11 for corresponding velocities to correct velocity errors or to produce a stabilizing derivative voltage as the case may be. The generator 20 may, alternatively, be driven by the control member 3. In a further modification, Fig. 3 (not shown), the integrating network is arranged so as to become effectively a differentiating circuit at very low frequencies so as to eliminate steady state velocity errors. In cases where the motor 9 has constant field excitation the control action dependent on the velocity of the motor may be derived from the motor armature voltage instead of a tachometer generator e.g. by a compensating circuit according to Specification 580,005, [Group XXXV].