Patent GB-966974-A (GB)
Title: Binary scale reader
Inventor: KLIEVER WALDO HAROLD
IPC: G05B19/29
Filed: 1960-11-01
Abstract: 966, 974. Binary scale readers. CLEVITE CORPORATION. Nov. 1, 1960, No. 37491/60. Heading G4H. A reader for a natural binary coded scale comprises a plate 21, Fig. 2 divided into strips which correspond in number and location to the tracks of the scale to be read, each strip having an ordered series of reader areas of two distinct types e.g. transparent and opaque, the areas of one type 21A2-21A5 and 21B2-21B5 for the more significant tracks being symmetrically disposed about a centre line CL and occurring in the same cyclic sequence as the corresponding areas on the scale, whereas the areas 21A1 and 21B1 for the least significant track, although occurring in the same cyclic sequence as the corresponding areas on the scale, may be assymmetrically disposed about the centre line. The plate 21 co-operates with two sets of photo-cells illuminated by light transmitted through the scale and the respective portions A, B of plate 21. In Fig. 11 plate 21 is shown superimposed upon the scale with centre line CL lying on the transition between the positions "31" and "0". The widths of the transparent areas in the plate 21 may be varied, the widths of the transparent areas for the more significant tracks preferably being one half that of the corresponding scale areas. In Fig. 20 the scale reader is shown in a machinetool control system. Light transmitted through the least significant track of the plate 21 and scale 20 falls on photo-cells A1, B1, and light transmitted through the more significant tracks (not shown) falls on respective pairs of cells A2, B2-An, Bn- The following conditions are assumed: 1. Least significant track, (a) if A1 is brighter than B1, binary 0 is read. (b) if B1 is brighter than A1, binary 1 is read. 2. For any other track, (a) A is read if the digit in the preceding order is 0. (b) B is read if the digit in the preceding order is 1. The cells A1, B1-An, Bn are connected in respective bridge circuits 25, 39, 40, 41, the output from the bridges being positive if cell A is brighter than cell B, negative if cell B is brighter than cell A, and zero if the cells are equally illuminated. The bridges control respective bi-stable circuits 28, 43-45 which in turn control respective change-over relays R1-Rn-1 so as to fulfil the above conditions. The binary coded signal thus read from scale 20 denoting the position of rack 38 is supplied to an analogue-to-digital converter and comparator 33 which is also supplied with command signals from a punched or magnetic tape unit 34 and produces an error signal to drive servomotor 35. Further accuracy is obtained by interpolating the signals from cells A1, B1, for example by means of the system shown in Fig. 21. The Specification shows that the outputs VA1, VB1 of cells A1, B1 can be regarded as the quadrature components of a vector V. The circuit comprising summing networks 88, 92, differential amplifier 89 and resolver potentiometers 90, 91 is arranged so that the output V<SP>1</SP> of amplifier 89 is maintained equal to the voltage V represented by VA1, VB1, any difference in the respective components of V, V<SP>1</SP> being detected by differential amplifiers 95, 93 which supply resolver potentiometers 94, 96 which in turn provide an error voltage for servomotor 105. The output shaft of motor 105 is thus driven to an angular position determined by VA1, VB1 and besides driving the wipers of the resolver potentiometers, produces relative movement between a further coded scale 120 and reader 121. Photo-cells (A), (B) to nA1, nB1 corresponding to the respective tracks of scale 120 produce a binary coded output representing the fine position of scale 20 of Fig. 20. The fine-position-signal is converted to an analogue voltage at 133 and relay R1 is operated when this voltage attains a predetermined value instead of being operated by the output of bi-stable circuit 28 of Fig. 20. The fine-position-signal is also supplied to comparator 33.