Research Of3-D Shape Measurement Technology Based On Binary Fringe Defocused Projection

The3D shape measurement of objects has an important significance in modern measurement. In a variety of3D measuring technology, as the fringe projection profilometry has the advantages of non-contact operation, full-field acquisition, and easy information processing, it has been one of the main technology. The fringe projection profilometry has wide application background in many fields, for example, medical field, heritage conservation areas, aerospace field, social security and so on.The intersecting-axis measuring system is used for traditional fringe projection profilometry, access to information through the projected sinusoidal grating. There are usually two aspects of the error:the one is the nonlinear gamma error of projector, and the other is the error caused by broadening fringe cycle.Owing the nonlinear effect of projector, the projected sinusoidal fringe is no longer meet the standard sine distribution, thus affecting the accuracy of the measurement system.We will adopt the binary fringe defocused projection to overcome the nonlinear gamma error of the projector. Because the binary fringe only has two kinds of gray value(0and255), the nonlinear response of the projector is no longer sensitive. Because appropriate degrees of defocusing can be the binary fringes streaks into sinusoidal fringes, it can overcome the error brought by the effect of gamma and improve the precision of the measurement system. This article will use Fourier transform profilometry for plaster hand measurement when the measurement is binary defocused projection. The experimental results have show that the method used in this paper improved the precision of system compared with the traditional method, and the measuring range of Fourier transform profilometry is increased1.5times. Due to the Fourier transform profilometry based on defocused projection just need to project two gratings,the CCD camera doesn’t need strictly synchronous to the projector, and the exposure time of the CCD camera doesn’t need to precise control, so this method can be well applied in real-time measurement.When the projector oblique projection, the cycle of fringe that on the reference plane will be broadened, the value of fringe period is not a contrast value. The fringe cycle along the X axis is gradually changing trends, brings to the error of measurement system and reduces the measurement accuracy. In the face of larger objects measured, the broadening of the cycle is more serious, the measurement error is more serious. Based on the mathematical theory model that plane phase and coordinates which is derived by our group combined with threshold judgement, this paper will use reverse non-uniform binary fringe based on defocused projection to overcome the errors of the broadened period and the nonlinear of projection. The results show that the combination of binary defocused projection and cycle correction achieved high measurement accuracy, small measurement error, the effectiveness of fast measuring speed when measured the three-dimensional shape measurement of objects.