Structured Light Vision Measurement Of Three Dimensional Object Surface

Structured light three-dimensional measurement system consists of camera,projector,and other equipments.It works by projecting encoded image onto the surface of the measured object through projector,and then capture the image modulated by the surface of the measured object.By decoding the deformed image and matching with the projected image,the matching points of the two images can be found out.Finally,the three-dimensional information of the measured object can be calculated,and the three-dimensional reconstruction of the measured object can be achieved.Through continuous development,structured light measurement technology has become a measurement technology with very high reliability and stability.And a variety of measurement methods have been proposed.However,this method still has some short comings,for example,it can't work well when measure the moving object,and also can't make fast and stable decoding on the image captured by the camera.The study of this paper is based on the method of using sinusoidal fringe raster image for the process of encoding.Sinusoidal fringe image can be generated by using a four-step phase shift method.Then the sinusoidal fringe image can be projected from horizontal and vertical directions.Using camera to capture the distortion fringe image modulated by the surface of the measured object.Then according to the four-step phase shift method,the phase diagram of the captured image can be calculated.The absolute phase diagram can be obtained by unwrapping them.Finally,according to some features of the absolute phase diagram,the corresponding match point can be found out,and the three-dimensional reconstruction of the object can be completed.As sinusoidal fringe raster image can be affected by many factors during the process of measurement,the distortion will occur.So the captured the image may doping noise or other interference,this will make the three-dimensional information of the object inaccurate,and thus affect the measure accuracy.Therefore,the correction and compensation on nonlinear gamma measurement error were studied in this paper to improve measurement accuracy.The main study contents are as follows:Firstly,describe the basic principles of three-dimensional measurement technology and several commonly used methods of measurement.Specially introduced the structured light measurement method based on sinusoidal fringe image.And,the factors affecting measurement accuracy of sinusoidal fringe gratings were analyzed and summarized.Secondly,the gamma correction method based on the phase shift method is studied in this paper.This method analyzes the wrapped phase which doesn't have gamma distortion,and then the non-linear gamma model is established.By using four step phase shift method to project fringe raster images having different initial phase shift to the standard plate,which can cancel the phase error and achieve phase error correction generated by gamma distortion.Thirdly,the gamma correction method based on phase iterative method is studied in this paper.This method also uses the four-step phase shift method to project sinusoidal fringe raster images to the standard plate.Then analyze the nonlinear phase error,using an phase iterative method,the wrapped phase of the captured image is iterated several times,in order to reduce the phase error and achieve phase error correction generated by gamma distortion.Finally,the basic principles and the reconstruction methods of three-dimensional reconstruction are studied in this paper.The three-dimensional reconstruction image of the measured object is obtained through reconstruct experiment,and by analyzing and comparing the results,the effectiveness of the proposed algorithm is validated.