| 摘要 |
<p>A scale has a first incremental track with first incremental patterns including first light and dark patterns formed at equal intervals in first periods, an absolute track with absolute patterns representing absolute positions, and a second incremental track with second incremental patterns including second light and dark patterns formed at equal intervals in second periods longer than the first periods. A light source emits a measurement light to the scale. A photodetector receives the measurement light reflected at or transmitted through the scale. A signal processing circuit processes the received light signal of the photodetector to detect an absolute position of the scale.
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