GB798193A - Automatic position-control system - Google Patents

Abstract

798,193. Electric selective signalling; electric correspondence control systems. HILGER & WATTS, Ltd. Nov. 16, 1956 [Nov. 18, 1955], No. 33113/55. Class 40 (1). A shaft control arrangement includes two different control systems: an analogue system using two identical tapped potentiometers P1, P2, Fig. 1, a servomotor M being adapted to bring a slider OS to a balanced position approximately corresponding to that of a control slider IS and a digital system in which cam-controlled contacts IC, Fig. 2, provide signals on a combination of lines, the servomotor also driving a coded commutator C to energize a combination of relays Ra-Rd the contacts MC of which are connected to contacts IC so that when the shaft controlled arrives at the precisely correct position a relay RLS is energized to switch off the servomotor and apply braking. The slider IS, Fig. 1, is set by a knob K which also sets the cams Ca-Cd controlling the contacts ICa-ICd. The servomotor is controlled by an error indicator EI in dependence on the error signal, i.e. the difference of potential between the tappings contacted by the sliders IS and OS. The servomotor would tend to overshoot the balanced position and oscillate about it if the digital system did not apply a positive stopping control. In another form the two systems are combined by replacing the servomotor-controlled slider OS by a decoding network of relay contacts, the relays for which are controlled through the coded commutator C. At each position of the controlled shaft the commutator picks up a combination of relays the contacts of which apply to the error indicator EI a voltage from a corresponding one of the tappings of potentiometer P2 for comparison with the voltage on the tapping selected by the control slider IS. Both systems operate in the same manner as before. Where selection on more than one digit is required an analogue and digital system is provided for each digit and automatic means are provided to bring them into operation in succession, e.g. starting with the thousands digit and ending with the units digit. In this case the coding commutator may be replaced by photo-responsive devices controlled by a transparent coded disc.