| 摘要 |
PURPOSE:To detect an absolute position characterized by high resolution and high accuracy by using a pair of detected signals having the 90-degree phase difference for each of binary coded patterns in a plurality of degrees, and sequentially limiting detected regions with said detected signals. CONSTITUTION:Higher third-order gray binary coded patterns (a)-(c) and lower third-order binary coded patterns (d)-(f) are formed on a code plate 4. Binary coded patterns a'-c' and d'-f' whose phases are different by 90 degrees with respect to the phases of above described patterns are formed, respectively. For example, when the position of a point P is to be detected, a pair of the detected signals having the 90-degree phase difference is obtained based on the highest patterns (a) and (a'). A detected region A' is limited under the state which includes an error E based on the detected signals. The detected regions are sequentially limited as B, B', C, C'... based on the detected signals obtained by (b) and b, (c) and (c')... by the same way. Finally, it is judged that the detected region is present in a region F'. |
