Multi-line laser structured light fast visual positioning system with assist of TOF and CAD

Abstract

As a reliable and high-precision three-dimensional (3D) vision method, line laser structured light vision has been widely used in the engineering field. However, to obtain overall 3D shape of target to be measured, scanning mechanisms need to be added. Multi-line laser structured light vision can obtain multi-line array 3D shape of workpiece without scanning; however, the encoding of multi-line lasers is a difficult task. This paper proposes a composite vision system, which is composed of time-of-flight(TOF) camera, color camera and vertical cross multi-line laser structured light. Color camera and multi-line laser form a multi-line array 3D vision system, while the coded signal of multi-line laser stripes is provided by TOF camera and corresponding coding algorithm is also proposed in this paper. Based on this system, automatic positioning of welding seam is realized by registration of CAD data and multi-line laser 3D data. The registration is divided into two steps, which are coarse registration and precise registration. Coarse registration is performed by using CAD point cloud data and original point cloud data of multi-line laser; while precise registration is performed with CAD welding seam point cloud data and welding seam point cloud data of multi-line laser. This paper also analyzes accuracy of vision system based on constructing structured light vision model. The measurement accuracy of vision system in x, y and z directions is 0.25, 0.06 and 0.29 mm respectively. This composite vision system can realize precise positioning of target within a single exposure time, which provides possibility for positioning under movement.