GB1080675A - Analog to digital encoder - Google Patents

Abstract

1,080,675. Measuring angular displacements. D.H. BALDWIN CO. July 21, 1965 [July 27, 1964], No. 31050/65. Heading G4H. Phase displaced signals 12, 14 from a plurality of photo-cells sensing markings on a disc rotating with a shaft are converted in a wave synthesizor 20 to five signals phase displaced by 36 degrees before being passed to triggers 32, 38, 44, 50, 56 which convert the signals to square wave form and also form their complements. The ten signals are then fed to a logic unit which examines the phase relationship of pairs of signals phase displaced by 72 degrees to determine the direction of movement of the shaft, a train of positive or negative pulses being sent to a reversible counter, the counter receiving ten pulses for each marking on the disc. To prevent errors due to incorrect centring of the disc four photo-cells are positioned on each side of the disc. To compensate for any change in the direct current level of the signals produced by the photo-cells, each photo-cell assembly gives out four signals phase displaced by 90 degrees and these are subtracted in pairs, the R 180 signal from the R 0 signal, the R 270 signal from the R 90 signal and vice versa.