Precision Shaft-Position Encoders

An extremely compact, direct-reading, shaft-position encoder is described. A cyclical-binary code, expressed as clear and opaque areas in concentric rings, is printed photographically on a glass disk. A gas-discharge lamp placed radially to cover all channels is flashed periodically. The radiation transmitted through the disk causes voltage pulses, treated as binary ONEs, to be generated by those elements of a multielement PbS cell on which the light falls. Cell elements shielded by opaque areas of the code disk give no signal, a binary ZERO. Methods are described for serializing and converting the output to binomial-binary code. Sine-cosine codes are also described.