CAD-based probing and localization method for arbitrarily fixed workpiece

A major difficulty associated with applying existing localization algorithm to practical manufacturing task is the need of having to identify the home surface of each measurement point. Furthermore, even though computationally efficient localization algorithms now exist, probing process is still done manually, at least for 3-dimensional workpiece. In this paper, an efficient method for automatic probing and localization of 3D workpiece arbitrarily fixed to the machine table of a five-axis milling machine is presented. First, by formulating localization problem as minimizing a least-square question, an explicit solution is obtained. Based upon this solution and sensitivity analysis, we present some guidelines and develop a CAD-based automatic probing strategy. By means of the knowledge about the approximate location of workpiece computed by 3D localization algorithm as estimator, together with CAD model of workpiece, we then on line generate a new collision free probing trajectory to probe additional point on a neighborhood of the previous sampling point. Utilizing the newly measurement point, we improve the Euclidean transformation which in turn is used together with the CAD model, to generate another collision free probing path to probe more points on the surfaces of workpiece. This process continuous until the workpiece is accurately localizated. This algorithm has been implemented in HKUST Machine Centre, in which the CAD model of workpiece is modelled as sculpture surface using NURBS. Experimental results show that this algorithm overcomes the need of home surface identification process, and is thus suitable for real-time implementation in manufacturing or inspection process.