| 摘要 |
A position sensor has a detector fixed to a first body, the detector having sensitive elements defining a track (10) of such elements. A scale being e.g. the optical image of a part of a second body, is caused to impinge on the detector. The scale has a track (6) of indicia (i.e. a bar pattern) and the sensitive elements of the track (10) of the detector detect their overlapping with a corresponding one or more of the indicia and generate an output depending on that overlapping. The indicia of the track (6) of indicia define two patterns (A, B) arranged in a plurality of successive sections (8). One pattern (A) is fixed for all sections (8) and the other pattern (B) varies according to a predetermined rule (e.g. cyclically) from section (8) to section (8). The track (10) of the detector detects a length of the track (6) of indicia corresponding approximately to the length of a section (8), as a result, the output of the detector can be processed to determine the relative positions of the first and second bodies, from detection of the relative position of the detector and the fixed pattern together with the relationship between the two patterns. |
