Direct Visual Servoing Using Wavelet Coefficients

This paper focuses on the design of a 6 degrees of freedom visual servoing control law. Instead of using geometric visual features in standard vision-based approaches, the proposed controller makes use of wavelet coefficients as control signal inputs. It uses the multiple resolution coefficients representing the wavelet transform of an image in the spatial domain. The main contributions are the definition of the multiple resolution wavelet interaction model that links the time-variation of wavelet coefficients to the robot spatial velocity and the associated task function controller. The proposed control law was tested and validated experimentally using a commercial micromanipulator in an eye to hand configuration. To be able to judge the efficiency of the control law, several validation tests were carried out under different conditions of use i.e., large illumination variations, noisy images, partial occlusions, and using unknown three-dimensional scenes. It is also demonstrated experimentally that the proposed approach outperforms, the well-known photometry visual servoing as well as a feature-based visual servoing, namely in unfavorable conditions of use.