Abstract
This paper describes a surface encoder, which consists of a sensor unit and a sinusoidal grid, for precision positioning of a sawyer motor–driven stage over a long stroke. The 2D local slopes of two points on the grid surface are simultaneously detected by the two angle sensors of the sensor unit. The positions and directions of movement in the X– and Y–directions can thus be detected by the two–phase sensor outputs with a phase difference of 90 degrees in each direction. To generate quadrature encoder outputs, the collimated light from the laser diode of the sensor unit is passed through an aperture plate on which two apertures are generated in such a way that the two beams output from the apertures are exactly projected onto the desired positions on the grid surface.
