| 摘要 |
A scale ( 10 ) has magnetic incremental scale marks in a track ( 10 a), and a pseudo-random code sequence in a reference mark track ( 10 b). Sensors ( 2,3 ) feed the pattern of the code in the track ( 10 b) into a bi-directional shift register ( 18 ). So that a user can select any desired position for use as a reference mark, a memory ( 24 ) is provided, into which any selected code value can be pre-stored. A comparator ( 26 ) then compares the code value in the shift register ( 18 ) with the code value in the memory ( 24 ) and outputs a reference mark signal (Ri) when they match. |
