| 摘要 |
PURPOSE:To measure the moving distance of a grating pattern highly accurately by forming a code plate having plural grating patterns, sensor arrays for detecting respective grating patterns, driving circuits, and a phase measuring circuit. CONSTITUTION:Electric signals generated from the code plate having three or more grating patterns are outputted from three of more photodiodes and inputted to signal processing circuits 51-53 through switch driving circuits 31-33. These input signals are shaped into square waveforms by the signal processing circuits 51-53 and alternate signals having repeat corresponding to the scanning periods of the switching circuits 31-35 are generated. The phase differences of the alternate signals outputted from the signal processing circuits 51-53 are measured by a phase difference measuring circuit 6. On the basis of an input signal from the circuit 6, a signal related to an absolute displacement position is generated by an arithmetic circuit 7 and outputted to a display device 8. Consequently, the minimum measuring limit is expanded and the moving distance of the grating patterns can be measured highly accurately.
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