Research Of Grating Fringe Cycle Correction Method In Fringe Projection Method

In modern measurement, the3D shape measurement of objects has an important significance. With the more and more widely use of the three-dimensional shape measurement of the object using non-contact techniques in automatic control, on-line testing, reverse engineering, complex3D modeling of objects, medical diagnosis, engineering design, machine vision, and many production process. The demand of three-dimensional shape measurement increasingly higher, its applications have also been expanded. As fringe projection profilometry offers the advantages of non-contact operation, full-field acquisition, high resolution, and easy information processing, it becomes the ideal method for the three-dimensional shape measurement, and has an important significance in the three-dimensional shape measurement. The intersecting axis measurement system is widely used, but this system has several limitations. First, the original standard sinusoidal grating is deformed after oblique-angle projection, and the cycle of the grating fringe on the reference surface is non-uniform and broadening. The fringe cycle is not a fixed value and is always obtained by the average method. Error is expected, and measurement accuracy is reduced. In measuring large objects, measurement accuracy becomes lower as a measurement deviates more from the origin. Second, fringe cycle broadening on the reference surface is not considered in the traditional phase shift method. The fringe phase shift on the projection surface is probably the same as that on the reference surface. However, they are not the same because of oblique-angle projection. Thus, an accurate phase shift method must be developed.According to the grating cycle variation on the reference plane, a new correction method with advantages of good applicability, small amount of computation, and conveniences proposed. According to the idea, a grating generation software is designed. The software can generate a grating whose grating cycle and phase variation is contrary to the variation of grating obtained in the reference surface tilt project using grating with uniform cycle to the projection reference surface. After tilt project the grating generated, a grating with uniform cycle is obtained on the reference plane. Finally, carry out a measurement experiment by projecting the corrected grating onto the object, and reconstruct the three-dimensional shape of the object. In the system calibration process, in order to overcome the limitations of level, perpendicularity in traditional system calibration technology, a calibration combine with system calibration method and least squares method is used to calibration the measurement system parameters L, d. On this basis, a detailed analysis of calibration method which calibrate the internal and external parameters of the CCD camera is carried out.Experiment result shows that, the three-dimensional shape measurement of objects using the grating corrected by the method proposed in this paper has the advantages of high measurement speed, high precision, low error.