Research Of 3-D Shape Measurement Technology Based On Dithered Fringe Defocused Projection

High speed and high precision real-time 3D shape measurement has an important significance in modern measurement.In a variety of 3D measuring technology,as the fringe projection technique has the advantages of non-contact operation,full-field acquisition,and easy information processing,it has been one of the main technology.Traditional fringe projection technique gets information through the projected sinusoidal grating.There are usually two aspects of the problem: Because of the 8 bits sinusoidal fringe,measurement speed is restricted(120HZ);Owing the nonlinear effect of projector?the control of camera and projector and the control of the exposure time,the projected sinusoidal fringe is no longer meet the standard sine distribution,thus affecting the speed and accuracy of the measurement system.How to solve these problems is an important research topic in the area.This article uses the binary fringe defocused projection to overcome above problems.Because the binary fringe only has two kinds of gray value(0 and 255),the measurement speed increase,and the nonlinear response of the projector is no longer sensitive.The experimental results have show that the method used in this paper improved the speed and precision of system compared the traditional method.Due to the method based on defocused projection,the camera doesn't need strictly synchronous to the projector,and the exposure time of the camera doesn't need to precise control,so this method can be well applied in real-time measurement.Most of the existing correction technologies are based on focused projection,and when large cycle fringes are protected,it is difficult to obtain high quality fringes.Based on hereinbefore problems,we use dithering algorithm to process the sinusoidal fringe to binary fringe,coupled with defocused projection for measurement.This paper uses different representative filters of ordered dithering and error diffusion dithering in measurement,the measurement results show that using dithering algorithm approves the measurement accuracy,and error diffusion dithering method is better than ordered dithering method moresuitable for defocused projection.On the basis,we use optimized dithering algorithm and scanning paths to the 3-D measurement,experimental results proved that the optimized dithering methods improve the speed and accuracy of the real-time measurement.