Development of Orthros, A Thickness Evaluation System for Free Curved Plate-Basic Performance Based on the Measurement Principle

Abstract

At present, for thickness inspection of sheet metal processed product having free curved surface in a manufacturing process, some typical points are selected experientially by operator. The selected points are generally measured with a point micrometer for accuracy and practicality. In this case, it is difficult to measure the thickness of whole range with non-destructive method. The study deals with an automatic measurement and evaluation system for free curved plate thickness using an industrial robot and two laser displacement sensors, called Orthros. The robot is used as a workpiece positioning device and the static dual-head thickness measuring unit composed of faced two displacement sensors measures the thickness of the workpiece with non-destructive method. The measuring procedure comprises three steps. First, the workpiece shape is measured by the system to acquire the shape data as a point cloud. Then, a thickness measuring path including the surface normal vectors and the measurement forwarding vectors is generated from the acquired shape data. Finally, the thickness is measured when the robot moves to match the calculated normal direction and the laser irradiation direction at each measuring point. The thickness data is displayed in relation to the shape data according to the needs of operator as a color map, etc. In this paper, the measurement principle and the basic performance of Orthros is described. In addition, the result of the actual thickness measurement is presented and discussed.