| 摘要 |
PURPOSE:To improve resolution by comparing respective signals outputted by two detectors with plural reference voltages, and checking whether digital signals outputted as a result are coincident or not and obtaining and inputting two rectangular waves to a decoder. CONSTITUTION:The output signal of a photodetector 3a is inputted to a comparator 7 and compares with the reference voltages E/8, 3E/8, 4E/8, 5E/8, and 7E/8 and converted into logic signals X1-X5. Then whether or not the signals X1, X2, X4 and X5 are coincident is checked to obtain a signal X. The output signal of a photodetector 3b, on the other hand, is compared with voltages 2E/8, 4E/8, and 6E/8 and converted into logic signals Y1-Y3 and whether or not they are coincident with a signal X3 is checked to obtain a signal Y. The signals X and Y become rectangular waves which have frequencies four times as high as the signals outputted by the photodetectors 3a and 3b. Then the signals X and Y are inputted to the decoder 8, which outputs pulses synchronized with the edges of the two rectangular waves and those pulses are counted 9 to detect the rotational angle of a shaft.
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