3D Shape Precision Measurement And Application Based On Non-diffracting Light Projection

3-D shape measurement can provide direct information about the measured object, which has potential application in modern life and many industry applications, such as production inspection, quality control, machine vision, plastic and artificial limb, and etc. With the rapid development of digital projection equipment, image sensor and image process tools,3-D shape measurement with digital fringe projection is widely researched as a nod-contact, whole field measurement approach. There are many problems about 3-D shape precision measurement to be solved. The existing fringe projection technique for 3-D shape measurement can not satisfy precision measuring and testing application because of the limitation of projection equipment and system measurement model. How to improve the measurement range, measurement accuracy and universality is an important research orientation.In this dissertation, a 3-D shape precision measurement system is presented, which uses non-diffracting grating structure light with high contrast, sinusoidal intensity distribution as projection source. The major techniques about 3-D shape precision measurement, such as, realization of projection fringes, camera calibration, projection system calibration, algorithm of fringes image process and 3-D shape reconstruction, are in-depth studied. The prospect application of this measurement system is given in the dissertation. The main outlines and innovations of this dissertation are as follows:Model of 3-D shape precision measurement based on non-diffracting grating fringes projection is proposed, which is consist of camera model, fringe phase obtaining, height-phase relationship mode. There is no approximation in this model, which can satisfy the precision measurement.Implementation method to generate non-diffracting grating structure light using biprism is presented. The generated fringe features such as fringe space, intensity distribution, the maximum nondiffraction distance, are analyzed by geometric optics method. Non-diffracting property of grating structure light is confirmed by Diffraction theory and numerical simulation. The diffraction effect of biprism edge aperture is also discussed. Utilize the approved Mach-Zehnder interferometer and 488nm Diode Pumped Solid State (DPSS) laser to project wild field grating structure light. The light with 488nm wavelength can make laser induced fluorescence.The calibration approaches suitable for small field camera and grating structure light projection system are investigated. The relationship between phase and function of the non-diffracting structure light is obtained by calibration. The actual calibrate experiments prove the veracity of the proposed calibrate approach.The property of speckle on the captured fringe image is analyzed and an effective speckle reduction algorithm based on power spectrum intensity (PSF) of fringe image is described. The PSF of speckle is small enough than the carrier wave. Speckle index is induced to evaluate the result of filter. Wrap phase of fringe is calculated by FFT and unwrap phase is obtained by whole period phase compensation algorithm, which can restain the error inducded by noise.Set up a 3-D shape precision measurement system according to the proposed technique and conduct some real measurement experiments. Resolution and error of the system is discussed and give some error reduction methods. The surface coated by Fluorescein Sodium is measured and the result shows the potential application of the presented system. A good 3D shape of rabbit cornea is obtained by the system to further the biomedical application.