GB1190846A - Analog-to-Digital Code Converter - Google Patents

Abstract

1,190,846. Shaft encoders. WARNER & SWASEY CO. 14 April, 1967 [6 June, 1966], No. 61787/69. Divided out of 1,190,845. Heading G4H. The description is identical to that of the Specification 1,190,845 but the invention claimed is a shaft encoder comprising a coded disc. Fig. 4, of which tracks 1, 2 and 3 are sensed by a plurality of slits through which light passes to cause photo-cells to provide signals from which an indication is derived of the shaft angle, the track 3 and the co-operating phase-displaced slits F+ and G+ giving precisely defined signals and the tracks 1 and 2 and the co-operating phase-displaced slits A+ to E + providing a number of imprecisely defined signals which have a larger tolerance than the precisely defined signals and which, in logical dependence on the precisely defined signals, define a cyclically coded value for the shaft angle. The signals A-G for 20 steps are shown in Fig. 5. They are combined in a decoder circuit which is such that only signals F and G need be accurate. For example the beginning (or end) of signal A could occur anywhere in the space corresponding to steps 8 and 9. For sensing the track 3 there may be groups of three photo-cells reading equivalent parts of adjacent scale markings. All the slits may be complemented by antiphase slits A - to G - which are combined in push-pull fashion to improve the switching operation of the decoding circuitry. The direction of movement is indicated by the order of occurrence of the F and G signals. Tracks 4-7 defining the decimal digit of the next decade are each sensed by lead and lag slits 20d, 20g; 40d, 40g; 80d, 80g; 100d, 100g. The lead or lag signal is selected in dependence upon the signals A-G, an output from the decoding circuit serving to open appropriate gates.