An Unified Approach to Model-Based and Model-Free Visual Servoing

Standard vision-based control techniques can be classified into two groups: model-based and model-free visual servoing. Modelbased visual servoing is used when a 3D model of the observed object is available. If the 3D model is completely unknown, robot positioning can still be achieved using a teaching-by-showing approach. This modelfree technique needs a preliminary learning step during which a reference image of the scene is stored. The objective of this paper is to propose an unified approach to vision-based control which can be used with a zooming camera whether the model of the object is known or not. The key idea of the unified approach is to build a reference in a projective space invariant to camera intrinsic parameters which can be computed if the model is known or if an image of the object is available. Thus, only one low level visual servoing technique must be implemented at once.