| 摘要 |
A rotary encoder has a scale 22 which rotates relative to a pair of readheads 14. Each of the readheads projects light onto the scale and generates at an analyser grating 40, a periodic light pattern, such as interference fringes. The interference fringes and the analyser grating interact to produce a series of resultant Vernier fringes which are incident upon a structure detector array 100. In one embodiment the analyser grating is configured to interact with the angularly extending interference fringes to generate linear resultant fringes. It has been found that phase errors due to eccentric rotation of the scale 22 reduce with decreasing pitch of the resultant fringes. <IMAGE> |
