Absolute Planar Position and Full Angle Orientation Sensor Using a 2-D Color-Coded Binary Scale

Abstract

A multi-axis position sensor using a 2-D color-coded binary scale (CCBS) is proposed for measuring absolute 2-D planar position and orientation in a full angle range. Since a color-encoding method provides higher information density with multiple color channels, two absolute position codes and incremental scale patterns could be encoded in the 2-D CCBS using three color channels. Therefore, the absolute position value was obtained with high efficiency and robustness by processing three color channel images of the CCBS separately, and the measurement range of orientation was also extended to 360° using the relationship of two absolute position codes. The proposed method was implemented as a sensor module composed of an imaging lens, a board-level camera, and the CCBS on a flat panel display. The performance of the prototype sensor was evaluated by comparing with a laser interferometer and an angle encoder. The position sensor could measure 0.5-μm linear and 0.005° angular displacements clearly. The repeatability was smaller than 0.13 μm,, but the positional error of the CCBS increased the measurement errors up to 3.1 μm when the sensor was evaluated over 24 mm $\times24$ mm range. The full angle orientation was measured successfully with the accuracy of 0.02°.