| 摘要 |
PCT No. PCT/GB88/01110 Sec. 371 Date Aug. 15, 1989 Sec. 102(e) Date Aug. 15, 1989 PCT Filed Dec. 15, 1988 PCT Pub. No. WO89/05964 PCT Pub. Date Jun. 29, 1989.An optical electronic scale reading apparatus comprising a scale read by a read head to determine the relative displacement therebetween. The read head comprises reflective surfaces so arranged that light from a source is reflected therefrom and interacts with the scale at first, second and third positions. At the third position, a fringe field is developed which has the same pitch as the scale. A detector is provided to receive light modulations during relative movement of the scale and read head as the fringe field interacts with the scale at the third position. These modulations are counted to determine the relative displacement between the scale and read head.
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