A Fabrication Method Of High Quality Sinusoidal Grating For Structure Fringe Projection System

Structured-Light Three-Dimension Measuring System is primarily composed of projection system and the receiving system. The quality of the grating which is projected by the projection system is key to achieve hight-precision measurements, and the grating component is the core of the projection system. In this paper, a fabrication method of high quality grating components is proposed to meet the demand Structured-Light Three-Dimension Measuring System, among them, the production of sinusoidal grating of a group of coding elements is the focus of this article.There are many ways to produce sinusoidal grating. Weighing the special requirement of the sinusoidal, we choose space filter imaging process to make high-precision sinusoidal grating. The basic theory and optical parameters of making gray sinusoidal grating are described. In this way, the required frequencies can be easily adjusted and we can on-line observe fringe quality. It can produce grating fringe with high parallelism and uniformity reliably, control grating constant accurately with very small distortion and obtain favorable sinusoidal fringe distribution efficiently. To improve the shortcoming of optical path, pairs of speckle screen is introduced in the light path to eliminate the laser's strong coherence which effects on image quality, and a background light is introduced to expose the image so that the intensity distribution of the sinusoidal interference fringes can reach the linear region of the characteristic curve of holographic plane.During the experiment,first, we produce high-quality Ronchi grating which we put on object plant of the imaging system. Sinusoidal grating image in the image plane is recorded on holographic plane with high-quality under different experimental conditions. Second, the grating is projected in the optical projection system, after the processing date of the picture shot by CCD, we obtain the transmittance curve of holographic plane. By comparing the difference between the transmittance curve and the standard sinusoid which we fit with the actual curve, is or no and the contrasting degrees of the picture are obtained. At last, according to test results we obtain optimal experimental conditions of producing favorable sinusoidal fringe distribution, high contrasting degrees, high-quality sinusoidal grating.Experimental results show the we can obtain a higher frequency sinusoidal grating with lower frequency binary grating, adjust grating constant conveniently, and finally obtain the sinusoidal grating's projection imaging with accurate frequency, high parallel, as well as very small coherent noise distribution. In order to ensure liner recording and linear imaging, appropriate light exposure of the background and total exposure are introduced, and we control the sinusoidal interference fringes exposure in the linear region of the characteristic curve of holographic plane and develop the holographic plane in Water-soluble ratio of 10:1 DEVELOPER, then we can make contrasting degrees to meet the requirement of high-quality gray sinusoidal grating.