Research And Design Of A Surface Topography Visual Measurement System

Measurement of surface topography is important to many techniques like defect detection of industrial products,surface detection of cultural relics and artwork,3-D printing technology.Traditional surface topography measurement methods(Such as using coordinate measuring machine)use contact probe to measure every point of the surface.The accuracy is at the micron level.But the method has poor efficiency and is low-density.It's difficult to be NDE.Visual measurement is appropriate to be used in the measurement of surface topography because of its non-contact characteristic,high efficiency and high adaptability.Projecting coded pattern by using a projector as the scheme of structured light projection has the advantages of high spatial resolution and uncomplicated matching method.Based on these advantages,this paper mainly focuses on the single projectorsingle camera measurement model and designs a surface topography vision measurement system which has high spatial resolution and measuring efficiency.It has following sections:1)Based on camera's imaging principle,projective principle of the projector(considered as a reverse camera),the correspondence of point's 3-D coordinates in the world coordinate system and it's 2-D coordinates in the projector and camera's photo coordinate systems can be obtained.Every characteristic point's 3-D coordinates in the world coordinate system can be calculated by the correspondence and the extrinsic parameters of the projector and the camera.2)A new projection scheme which combines time domain method and space encoding method is designed after comparing different schemes: First,the projector projects multizone pattern to partition the pattern projected by the projector.Secondly,the projector projects multizone gray code pattern.A new method combined with gray centroid method is designed to determine the center point of the pixels which have the same code and the same row.Then the horizontal correspondence between a column of projector's pixels and pixels of the camera.Finally,the correspondence between every characteristic point's 2-D coordinates in the projector and it's 2-D coordinates in the camera can be determined by the vertical correspondence established by epipolar constraint.3)The measurement system uses checkerboard and plane method to calibrate the camera's and the projector's internal,external and distortion parameters.4)The calibration experiments and the surface topography measurement experiments of the system were carried out and the errors of the calibration and the measurement experiments have been analysed.Average error of the measurement system is less than 0.1mm,as shown from the experiment results.