A Model-Based Vision System for Manipulator Position Sensing

The task and design requirements for a vision system for manipulator position sensing in a telerobotic system are described. Model-based analysis-by-synthesis techniques offer generally applicable methods with the potential to meet the system's requirement for accurate, fast and reliable results. Edge-based chamfer matching allows efficient computation of a measure, E, of the local difference between the real image and a synthetic image generated from arm and camera models. Gradient descent techniques are used to minimize E by adjusting joint angles. The dependence of each link position on the position of the link preceding it allows the search to be broken down into lower dimensional problems. Intensive exploitation of geometric constraints on the possible position and orientation of manipulator components results in a correct and efficient solution to the problem. Experimental results demonstrate the use of the implemented prototype system to locate the boom, stick and bucket of an excavator, given a single video image.