Nikon Corporation

Koh Ohno

Tsuyoshi Matsumoto

Motokatsu Imai

Yuji Yamazaki

An absolute encoder has a code plate formed with an absolute pattern and an incremental pattern. A first detector detects the absolute pattern, and outputs an absolute signal. A second detector detects the incremental pattern, and outputs an incremental signal. The absolute encoder stores the absolute signal according to an external input signal, and forms a corrected absolute signal on the basis of the incremental signal input after the absolute signal is stored.

Absolute encoder

An absolute encoder device comprises a code plate having a 1-track type absolute pattern whose minimum reading unit length is .lambda., a first incremental pattern with a pitch .lambda., and a second incremental pattern with pitch 2.sup.-n .lambda.. The device also comprises a detector section, which is movable relative to the code plate, which includes a detector detecting the absolute pattern and obtaining an absolute pattern signal, a detector detecting a first incremental pattern and obtaining a first incremental signal, and a detector detecting a second incremental pattern and obtaining a second incremental pattern signal. A shorter cyclic incremental signal is generated from the first incremental signal by interpolating and the shorter cyclic signal is synchronized with the second incremental signal. The absolute pattern signal, the second incremental signal and the synchronized first incremental signal represent the relative positional relationship between the code plate and the detector section.

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Zama, Japan

Koh Ohno