Compact 3-degrees of freedom absolute position sensor based on a CCD chip

In this paper, we present a new concept of 3 Degrees Of Freedom (3-DOF) sensors, which are capable of measuring the absolute position X-Y with a resolution less than 0.16μm (defined here as 4σ and σ denotes the standard deviation) and the orientation θz (over 360°) with a resolution of 0.48'. The principle of this low-cost and small-size 3-DOF sensor relies on a target with a specific pattern that includes periodic absolute position information that can be used to enhance the position resolution by statistical analysis. Efficient image processing algorithms are applied to improve both the reliability and the resolution of the target positioning and are optimized in term of processing complexity (i.e., time of processing).