Performance of interferometric rotation encoders using diffraction gratings

High resolution optical encoders take advantage of diffraction and interference properties of light. In such components, the scale is a phase grating that diffracts light into several orders; an optical reading system makes two of them to interfere. In state of the art systems, the orders interfere after they have been spatially separated from other orders; this leads to cumbersome reading heads. A compact, fully diffractive optical reading system was designed and realized. This reading system was used for the realization of rotation encoders. Using the competences of the Eureka EU 922 FOTA project partners, the encoder phase gratings were successfully realized and the reading system was implemented in standard rotation encoder housings. Without interpolation the encoder gives 480'000 pulses per revolution with a repeatability of 2.5 pulses.