| 摘要 |
Scale reading apparatus is described that comprises a readhead (12) that is moveable relative to a scale (10). The readhead (12) comprises an incremental channel from which a series of reference mark pulses (56) are produced as the readhead (12) is moved relative to the scale (10). A reference mark channel is also provided that produce a reference mark gating pulse (58) when the readhead (12) passes a predetermined (absolute) position mark (22) on the scale. Alignment detection means monitor, during use, phase alignment of the reference mark gating pulse (58) and reference mark pulses (56). The alignment detection means is arranged to monitor the phase of the leading and trailing edges (68) of said reference mark gating pulse (58) relative to the phase of the reference mark pulses (56). The apparatus may be used in position encoders and the like.
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