Research On 3D Measurement System Of Mobile Phone Shell Based On Structured Light Vision

In three-dimensional(3D)system for measuring geometry of the mobile phone shell,there are have some problems such as high price,low efficiency and low precision and so on.In order to solve the problem which is difficult to detect the mobile phone shell in the production line,this paper designs a 3D system for measuring mobile phone shell based on structure light vision.The 3D system composes of a projector and a camera and a computational unit.In the measurement system,the projector project the grating images to the shell surface,and then the modulated gratings are captured by the camera.The modulated gratings include the phase information of the shell.Combining with calibration,phase calculation,3D reconstruction and other technologies to achieve accurate geometry of the shell.The main researches and the results are as follows:1)The paper studies a 3D method of objects based on structured light vision,analyzes the research background of mobile phone shell 3D measurement methods,designs a measurement system suitable,and analyzes the principle of system measurement.In addition,the relation between the pixel coordinates of the shell image obtained by the camera and the corresponding world coordinate system are derived in this paper.2)This paper studies many calibration methods whose merits and shortcomings are analyzed.Because its simplicity and high accuracy,Zhang's algorithm is used as the calibrated method for the camera.And this paper deduces the expressions of the internal and external parmeter for the camera,the reverse camera calibration method are selected to calibrate the projector,and the red and blue checkerboard calibration board with higher calibration accuracy are selected for experiment.3)This paper studies and compares a variety of approaches of calculating wrapped phase and phase unwrapping whose advantages and disadvantages are analyzed.This paper uses the four-step phase-shifting algorithm to calculate the wrapped phase and the three-frequency unwrapping in heterodyne method to phase unwrapping,and then solve the absolute phase by these algorithms.Combing with calibrated parameters and triangle method,the 3D point cloud and shell size can be solved.4)Three different sizes of mobile phone shell are selected for testing.And the sizes of the mobile phone shell obtained by the measurement system are compared with the data obtained by a coordinate measuring machine.Experimental results show that the measurement system has a measurement error of ?0.38% which meets expected requirements,and the factors affect accuracy are analyzed.5)At last,the paper analyzes the shortcomings of the measurement system,and the futuregoals of the measurement system are also prospected,with a view to getting better results in the future.The paper designs a measurement system experimental platform,verifies the size of three different sizes mobile phone shells.The test results show that the system has high speed,high accuracy,low cost.The measuring system can be extended to measure other products in the production line,in order to improve the efficiency.