| 摘要 |
PURPOSE:To obtain the title apparatus having higher resolving power, by converting two signals different by 90 deg. in a phase to frequency modulation signals and digitally reading phase displacement quantity changing on the basis of the relative movement of scales. CONSTITUTION:Moire fringes formed by scales 1, 2 are applied to photoelectric converter parts 6A, 6B and detected as an A-phase signal and a B-phase signal different by 90 deg. in a phase from said converter parts 6A, 6B to be inputted to a modulation adder part 8. Herein, the output of a clock oscillator 9 having frequency higher than that of each of the A-phase signal and the B-phase signal is subjected to frequency dividing by a frequency divider 10 to obtain signals as carrier waves and both signals are modulated by the A-phase signal and the B-phase signal and added to generate a modulated signal. Further, the high frequency component in this signal is removed to perform waveform shaping by a wave from shaping part 11. Next, a pulse counter 12 detects one cycle of the signal from the wave form shaping part 11 and counts the reference clock contained therein. The reference clock is applied to a comparing part 14 through a comparing counter 13. The number of reference clocks at the stop time of the scales 1, 2 are preset in the comparing part 14 as reference values and compared with the counting result of the counter 12 to detect the relative moving direction and distance of the scales 1, 2.
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