Mitutoyo Corporation

Norihito Hikawa

Wataru Ishibashi

A reference light transmission window is provided in the vicinity of a sub grating disposed on a usual index scale, and a light transmitted by the reference light transmission window is photoelectrically converted to a reference signal. When a main scale is of an optical transmission type, a light transmitted through a reference light transmission window of a second index scale, which is provided on the opposite side to the usual index scale so as to put the main scale between the second index scale and the usual index scale, or a light among those modulated by the main grating and by the sub grating, which light is not used for displacement detection, is photoelectrically converted to a DC level detection signal. The reference signal or DC level detection signal is used to correct DC level variations of the displacement detection signal.

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Yokohama, Japan

Norihito Hikawa