High speed visual motion control applied to products with repetitive structures

This paper focusses on direct dynamic visual servoing at high sampling rates in machines used for the production of products that consist of equal features placed in a repetitive pattern. The word direct means that the system at hand is controlled on the basis of vision only. More specifically, the motor inputs are driven directly by a vision-based controller without the intervention of low level joint controllers. The product in view consists of a repetitive pattern, which is used as an encoder purely on the basis of vision. The considered motion task is to position the repetitive structure in order to align the tool with respect to the features. The vision based controller is designed using classical loop shaping techniques. Robustness with respect to imperfections of the repetitiveness is investigated. The combination of fast image processing and a Kalman-filter-based predictor results in a 1 kHz visual servoing setup capable of exploiting the repetitive pattern as an encoder with an accuracy of 2 μm. The design approach is validated on an experimental setup.