| 摘要 |
PROBLEM TO BE SOLVED: To prevent malfunctions in detecting adjacent sections associated with scale detection errors when performing absolute detection over sections N-times the wavelength of two sets of scales with different wavelengths by the phase difference between phase modulation signals outputted from the two sets of scales. SOLUTION: Each relative amount of displacement of the first scale 1 of a wavelengthλm and a first detecting head 2 and the second scale 7 of a wavelengthλa and a second detecting head 8 is extracted by first and second displacement amount detecting parts 3 and 9 as the phase modulation signals epm and epa. A pulse string SAPm of a resolutionλm/M corresponding to the absolute location of the first detecting head 2 within the wavelengthλm is created from the phase modulation signal epm, and a pulse string SAPa corresponding to the phase difference between the phase modulation signals epm and epa is created. Through the use of a quotient and a reminder obtained by dividing a count value of the pulse string SAPa by a pulse number M/N obtained by converting the amount of phase corresponding to one section of the wavelengthλm, aλm address in a section N-times the wavelengthλm in which the first detecting head 2 is located is specified, and combined with an absolute location within the wavelengthλm obtained by counting the pulse string SAPm by an absolute location composing part 6.
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