OPTO-ELECTRONIC ROTARY ENCODER

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.