Patent GB-896487-A (GB)
Title: Improvements in numerical positioning control system
IPC: G05B19/35
Filed: 1960-12-14
Abstract: 896,487. Electric positional control systems. GENERAL ELECTRIC CO. Dec. 14, 1960 [Dec. 16, 1959], No. 42996/60. Class 40 (1). Apparatus for measuring the position of, e.g., a work-table, comprising a series of cylindrical iron pins assembled side-by-side to be moved through the gaps in four pairs of wound U-shaped cores spaced so that the changes in the gaps of each of adjacent cores of each pair are 180 degrees out of phase, and the pairs are 90 degrees out of phase with each other, to produce a combined A.C. signal from the interlinked bridge circuits whose phase is indicative of the position of the pins relative to the coils over one pin diameter, is characterized in the addition of computing apparatus to enable the combined signal to be zero at a preselected position within onethousandth of a pin diameter. As shown (Fig. 1), four pairs of coils 12-15 are located in a parallel arrangement for an assembly of cylindrical iron pins 11 to be moved through the gaps. Coil pairs 12, 13 and 14, 15 each form a bridge with a centre-tapped energized winding 33 (Fig. 2), the unbalance voltage e A  and e B  of the two bridges being added to produce an error voltage which is used to position the pin assembly. It is shown that a displacement of R produces a zero error voltage signal produced by adding e A  cos R and e B  sin R, and can be made to have a positive slope at this point by applying a suitable sign to e A  and e 5 . Thus the distance represented by one pin diameter can be divided into ten equal parts by giving R successively values of multiples of 36 degrees. The signals e A  and e B  are therefore fed into coupled resolvers whose shafts are rotated through the desired angle R, to produce outputs of e A  cos R and e B  sin R, which are added together and fed to a servomotor which moves the pin assembly until the signal e A  cos R + e B  sin R is zero. In an embodiment (Fig. 8) providing finer control of the movement of the pin assembly, the voltages e A  and e B  are fed to transformers 52, 56 each having a group of tapped secondary windings producing the voltages e A  cos R and e B  sin R for values of R which are integral values of 36 degrees. The voltage combination for a required displacement is selected by rotor 87 of a ten-position switch 84, the rotor 85 of a ganged switch 83 selecting the next decimal value. The voltage between the rotors 85, 87 is subdivided into tenths by tapped potentiometers 89, 91 to provide the next decimal digit of the displacement, and a further tapped potentiometer 98 provides a third decimal digit. The output voltage at terminals 82, 102 is zero when the displacement of the pin assembly is equal to that set up on control-knobs 86, 90, 100. Alternative methods for producing e A  cos R + e B  sin R are also described (Figs. 9, 10, not shown). Selection of the desired displacement of the pin assembly may be effected manually or by means of a data storage medium. A coarse position indicating device may be included in the system, which counts the number of pins 11 over which the mechanism is traversed, and stops the relative motion at a predetermined number. Specification 889,578 is referred to.