Volume 20 Issue 11 - Publications Date: 1 November 2001
Visual Servoing Based on Image Motion
A. Crétual IRISA/INRIA Rennes, France and F. Chaumette
The general aim of visual servoing is to control the motion of a robot in order that visual features acquired by a camera become superimposed with a desired visual pattern. Visual servoing based upon geometrical features such as image points coordinates is now well set on. Nevertheless, this approach has the drawback that it usually needs visual marks on the observed object to retrieve geometric features. The idea developed in this paper is to use motion in the image as input of the control scheme, since it can be estimated without any a priori knowledge of the observed scene. Thus, more realistic scenes or objects can be considered. Two different methods are presented. In the first one, geometric features are retrieved by integration of motion,which allows to use classical control laws. This method is applied to a 6 d.o.f. positioning task. We show that, in such a case, an affine model of 2D motion is insufficient to ensure convergence and that a quadratic one is needed. In the second method, the principle is to try to obtain a desired 2D motion field in the image sequence. In usual image-based visual servoing, variations of visual features are linearly linked to the camera velocity. In our case, the corresponding relation is more complex and we describe how it is possible to use this relation. This approach is illustrated with two tasks: positioning a camera parallel to a plane, and trajectory following.
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