Robust Phase-Based Decoding for Absolute (X, Y, Theta) Positioning by Vision

Computer vision is a convenient noncontact tool for position control and thus constitutes an attractive multidirectional alternative to widely used single-direction sensors. However, to meet actual industry requirements, vision-based measurement methods must be sufficiently robust to comply with industrial environments. This article explores the robustness of an in-plane position measurement method based on a pseudoperiodic pattern and allowing a 10(8) range-to-resolution ratio in displacement and a 1-mu rad angular resolution over 2 pi rad. This article shows how the pattern phase can be used to maintain reliable measurements despite defocus, discrepancies in local contrast, nonuniform illuminations, or occlusions. The proposed method can be implemented at different size scales with unique capabilities combining high resolution, large measurement range, and robustness to diverse kinds of disturbances.