Research On A Three-dimensional Measurement Method Based On A Stereoscopic Target

In the industrial fields like mechanical manufacturing, electronics, automotive and aerospace, high-precision three-dimensional measuring device is commonly used to test the surface contour and its geometry of the workpiece. However, in the process of online measuring, the existing three-dimensional measuring device often appears measurement insufficiency、low efficiency、difficulty of automated measurement and so on. Therefore, combined with the characteristics of various types of measurement system, this article researched a three-dimensional measurement approach which is based on stereoscopic target to solve the three-dimensional measurement of the complex surfaces of mechanical parts, automatic measurement in coordinating with robot and other issues. It has important engineering value.Specific work is as follows:(1)This paper presents the principle and method of a three-dimensional vision measurement based on a stereoscopic target, designs the corresponding binocular vision measurement system and a mathematical model of the system. It describes the coordinate systems which the measurement systems involved and the mathematical transformations between the coordinate systems are given, provides sufficient mathematical basis for measuring the three-dimensional coordinate of the space measured point.(2)The advantages and disadvantages of the existing flat light pen have been analyzed. Then, we designed a stereoscopic target which has four measuring surface, each measuring surface pasted with four symbols, each symbol has a landmark. Put forward a kind of coding rule for landmark, according to the rules, we design a kind of coding landmark. The measuring probe was designed under the stereoscopic target, and a sample of the stereoscopic target was produced.(3)The related experiments based on the binocular vision measurement system were completed, and the algorithm for measuring three-dimensional coordinate of the measuring head was designed. Using a binocular camera to obtain the stereoscopic target images, segment a measuring surface of the stereoscopic target from the image, to extract the center of the coding landmark and the encoded digital of coding landmarks, complete the matching of the same landmark in binocular images, calculate the three-dimensional coordinates of each coding landmark center to obtain the three-dimensional coordinate of the corresponding measuring head.(4)The measure precision of the measurement system is verified based on displacement method, and the experimental results show that within the scope of the measuring distance is 1150 mm, the measuring accuracy of the binocular vision measurement system based on stereoscopic target is of + /- 0.21 mm, this kind of binocular vision measurement system based on stereoscopic target provides a new method for on-line measurement in industrial field.