Reflective optical rotary encoder disc

摘要

A reflective optical rotary encoder device detects an angular speed or position of a rotatable member with a light beam applied to and reflected from a reflective optical encoder disc. The reflective optical rotary encoder disc has an annular encoder track for reflecting the light beam, the encoder track being composed of an annular pattern of angularly spaced pit units each including a plurality of radially spaced arcuate pits, and a pit-free annular focus servo track for focusing the light beam onto the encoder track, the focus servo track extending along and being disposed radially substantially centrally in the annular encoder track. The reflective optical rotary encoder disc further includes at least one arcuate reference pit for reflecting the light beam to produce a reference signal, the reference bit being positioned in the focus servo track and radially aligned with one of the pit units, and an annular tracking servo pit for keeping the light beam applied thereto, the annular tracking servo pit extending along and being disposed radially substantially centrally in the annular focus servo track.