This paper describes a novel approach to the problem of reaching an object in space under visual guidance. The approach is characterized by a great robustness to calibration errors, such that virtually no calibration is required. Servoing is based on binocular vision: a continuous measure of the end-effector motion field, derived from real-time computation of the binocular optical flow over the stereo images, is compared with the actual position of the target and the relative error in the end-effector trajectory is continuously corrected. The paper outlines the general framework of the approach, shows how visual measures are obtained and discusses the synthesis of the controller along with its stability analysis. Real-time experiments are presented to show the applicability of the approach in real 3-D applications.

The role of vision in two-arm manipulation is investigated in order to suggest a qualitative approach for the solution of coordinated manipulative actions. The visuomotor behavior proposed, although partially supported by experimental results, differs from more geometrical approaches based on explicit 4D measures and trajectory estimation in that it is based on direct visual information, such as stereo disparity or the 2D image motion field. The experiment is limited to analysis of the optical flow information extracted from manipulative actions performed by a human operator. These experiments demonstrate that the qualitative approach proposed is not in contrast with human behavior and that the two-arm manipulation task proposed can be seen as a testbed for qualitative and geometrical approaches.>