Measurement Of 3D Shape For Optical Surface Based On Structured Light Projection

Noncontact, high-precision, high-speed optical 3D sensing, which is based on structured light projection, has been widely used since being presented in 1980's. It is mainly used to measure complex 3D object with diffuse-reflected surface. On the other hand, the interferometry as a high-precision technique has been widely used to detect optical surface. But almost all interferometers require a coherent illumination, a precise and complex mechanical system, and almost all are expansive. Therefore, the further wide use of the interferometries is limited.A simple and novel method for optical surface measurement is presented in this paper, which is based on optical 3D sensing by structured light projection.The basic of this method is to display a computer-generated sinusoid gray fringe pattern on a computer monitor, which links with a dual-imaged PC card. And the pattern is imaged in a CCD camera. A distorted pattern will be recorded, while the tested object is placed in the ray path. Compared with the standard pattern recorded, the changed phase could be worked out. The vertical and horizontal changed phases could be calculated respectively, when the directions of the computer-generated fringe pattern are correspondingly adjusted. The measured face might be constructed by numerical integration, after the gradients of the face are calculated according to the equations between the gradients of the measured face and the changed phase, which is established by the principle of incoherent imaging. The computer-generated fringe pattern leads the capability of adjusting the directions andperiods of the fringe conveniently, and avoiding the problems in phase shift by mechanical parts.Experiments and computer simulating of two kinds of optical surfaces, which are these of transparent object and reflector, prove the feasibility of this method in this paper. The critical problems, including phase unwrapping algorithm and surface construction algorithm, have also been discussed.Compared with those present interferometries, this setup is simpler, cheaper and more versatile, especially being used to measure the aspheric optical surface and the wide changed surface. Moreover, the improvement of the precision of this method could be estimated, while the resolution of the monitor increases, and the wide use can also be expected.