Linear scale reader for reading position of workpiece, has length measuring units to read upper and lower score mark value data and circuits for producing quadrant signals to correct counter output

摘要

The reader has two length-measuring units (31) detecting a score mark measured length value of a linear scale and reading upper and lower data of the scale. A comparator (39) for comparing quadrant signals from a latching circuit and a quadrant determination circuit and upper counter output is corrected within the range of +1 to -1 in response to comparator result. The two length-measuring units have an analog-to-digital converter (ADC) (36). The composite data is obtained from an adder (43) that adds two data. The latching circuits (35) latch the polarities of two-phase output signals. The quadrant determination circuit (38) identifies the lower data output based on 90 degree phase shift and issues it to four-phase area.