GB884367A - Improvements in or relating to servo-mechanisms - Google Patents

Abstract

884,367. Electric control systems. GENERAL PRECISION Inc. Nov. 29, 1957 [Nov. 29, 1956], No. 36305/57. Class 40 (1). In a servo-system comprising a motor for producing a mechanical output in response to input quantity signals, with feedback from the output to the input of the motor so that it operates in accordance with the difference between the input and feedback quantities, the input signal is modified by the addition of components representing its first derivative, or its first and second derivatives, with the object of improving the overall transfer function of the system. The invention is described with reference to particular position and velocity servo-systems. Position servo-system, Fig. 2.-An input quantity 0i, representing e.g. an acceleration, is fed to an integrator 10 to produce a Oi quantity which is further integrated with respect to time at 20 to provide a 0i quantity, representing a position, which forms the input to servo-means 40 comprising an amplifier and a motor, a quantity #o representing the output of the servomeans being fed back and compared with #i in a comparator 30. The overall transfer function of the system, which is expressed by the equation where A is servo-loop gain, T is the combined time constant of the motor and amplifier, and p is the Heaviside differential operator, is improved by the application of #i and #i components to the comparator 30, the composite input quantity being #i(K 11 + K 12 p + K 13 p<SP>2</SP>), where K 11 , K 12 , K 13 are proportionality constants which, by correct scaling, can be made equal to 1, 1/A, T/A respectively, so that the overall transfer function, which is now becomes substantially equal to unity. Fig. 3 shows an electrical embodiment in which the output of integrator 20 is combined in amplifier U103 with the #i component via amplifier U102, and the #i component, the output of U103 being supplied via a magnetic amplifier 102 to the control winding of a 2-phase motor 105. The #i term is taken from the integrator 10, and may be synthesized with a #o signal from a tachometer generator 107 driven by motor 105. Amplifier U103 has a variable feedback impedance R104 adjustable to provide the desired loop gain. Where the time constant is small the #i to U103 may be omitted. In a system where #i is not derived by integration, differentiating means may be used to provide first and second derivative signals. Velocity servo-system, Fig. 6.-The overall transfer function of a system, wherein the input #i is compared at 280 with the rate feedback #o of a tachometer generator 270 driven by the servomotor 260, is given as #o/#i = A/p(T + p). A quantity representing #i/A is added to the input so that #o/#i becomes 1/p. If the #i quantity is derived by integration, the #i/A term may be taken, with suitable scaling, from the input of the relevant integrator; otherwise a differentiating device may operate on the input quantity.