GB754105A - Improvements in and relating to position-control systems - Google Patents

Abstract

754,105. Electric follow-up systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 11, 1953 [Dec. 11, 1951], No. 29011/51. Class 40(1) [Also in Group XL(c)] In a position control system having a controlled element supplying a signal representing its instantaneous position to a mixing circuit to which is also fed a signal representing its required position the output of the mixer circuit which is a signal proportional to square root of error magnitude and of the same sign as the error, is applied together with a signal proportional to velocity of the element, to a high gain amplifier controlling the element, e.g. through a servomotor. The amplifier is saturated by low input signals and the servomotor therefore runs under full forward torque until the amplifier input becomes zero at a position midway between the initial and required positions of the element, when full reverse torque is applied to bring it to rest. The signal proportional to velocity is obtained from a tachometer generator or an equivalent signal proportional to the first derivative of error signal is produced by the anode follower circuit of Fig. 5. The square root signal is generated from the error signal in the circuit of Fig. 6 in which valves V1 1 and V1 2 are worked on non-linear parts of their characteristics to produce outputs proportional to the square roots of negative inputs while having positive input signals short circuited by diodes 6 and 7 respectively. V1 1 , fed directly with the error signal therefore gives an output only for negative error signals, while V1 2 which is fed through inverter V2 gives an output only for positive errors, which is inverted by V3 so that the input to mixer V4 changes in sign with the error. The output of V4 is inverted by V5 and amplified in variable gain amplifier V6, the output of which, together with the velocity dependent signal is fed to the servomotor controlling amplifier which saturates at low inputs. The invention may be used in the system described in Specification 750,294 in which the movable element carries a pick-up member close to a series of insulated segments to which are applied pulse signals intercollated in time. Because of capacity between the pick-up and segments a signal representing position is derived, which with signal predicting a desired position is fed to a circuit as shown in Fig. 6, the output of which is fed with a first derivative of error signal to a saturable amplifier supplying current to a coil on the element moving in a magnetic field. In this system the square root signal may be obtained by suitable shaping of the pickup member. Specification 687,520 [Group XXII] also is referred to.