| 摘要 |
A scale is provided with a plurality of marks or slits arranged in a first direction such that a distance between centers of adjacent marks or slits in the first direction assumes a first length. An encoder is opposing the scale and includes: a photo emitter, operable to emit light; and a plurality of photo detectors, each of which has a light receiving region adapted to receive the light emitted from the photo emitter and transmitted by way of the marks or slits, and is operable to output a detection signal in accordance with a quantity of the light received by the light receiving region, so that the detection signal has a first cycle corresponding to the first length. A control signal generator is operable to generate a control signal having a second cycle which is (½<SUP>n1</SUP>) of the first cycle. A controller is operable to estimate a rotation speed of a motor based on a third cycle which is defined by subsequent (2<SUP>n1</SUP>) second cycles. Here, n1 is an integer no less than one.
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