| 摘要 |
PROBLEM TO BE SOLVED: To make the measuring resolution fine by taking the sum of a travel distance equal to an integer multiple of a grating pitch detected by a grating moving counter and a travel distance less than a pitch detected by a grating stop position detector for the travel distance. SOLUTION: A flashing controller 13 blinks a light source 10 at fixed time intervals to intermittently illuminate a grating. A lighting pulse counter 15 detects and stores the light pulse number during moving of the grating by a pitch length in a specified section, and a lighting pulse counter 16 detects and stores a fist lighting pulse number from the grating stop position to a next grating reference position and a second lighting pulse number from a grating reference position just before stopping to a stop position. A grating stop position detector 17 compares both lighting pulse numbers to obtain a grating stop position and a travel distance less than one grating pitch length. A grating moving counter 19 counts up-/down of the moving unit number according to the moving direction to obtain the travel distance equal to an integer multiple of the grating pitch length, and, from the sum of both, the travel distance of a moving scale 11 is obtd.
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