Research On Three Dimensional Shape Measurement Technology Based On Projection Moiré Method

Three-dimensional(3D)shape measurement technology based on optical method has extensive application prospect in many fields,such as reverse engineering,product testing and quality control,aerospace,medical care,cultural relics’ protection and biometrics.To realize precise measurement of 3D shape on object surface,this article proposes a 3D shape measurement technology based on projection moiré method.For the key technologies related to this method,including system model creation,moiré image processing,phase extraction,system calibration and so on,in-depth study is carried out.Firstly,a novel system model of projection moiré 3D shape measurement system is proposed.Compared with the existing traditional system model,projection system and receiving system are arbitrarily arranged in new model which corresponds with the status in actual measurement and it is more universal and flexible at the same time.Based on the new model,the conversion relationship between moiré fringe phase and object surface height is derived theoretically.The concept of full-field sensitivity coefficient matrix is proposed for the first time.Three sensitivity coefficient matrixes are used to describe the conversion relationship between moiré fringe phases and object surface height.The imaging relationship of projection moiré system is studied to establish the relationship between the 3D coordinates of spatial point on object surface and its corresponding pixel coordinates in image.By combining the conversion relationship between moiré fringe phase and object surface height,a novel method for 3D shape measurement based on projection moiré is proposed.Secondly,methods for removing the high frequency grid noise from original moiré image are investigated.The removal consequents of mean filtering,Gaussian filtering and discrete grid averaging are compared.As a result,discrete grid averaging is recommended.Phase extraction method of moiré fringe is studied by comparing the calculation accuracy of four step phase-shifting algorithm,Carré’s,Stoilov’s and Sun’s algorithm.Carré’s phase-shifting algorithm is selected to calculate the phase of moiré fringes.An absolute phase acquisition method with wrapped phase and unwrapped phase is proposed.Thirdly,calibration method of full-field sensitivity coefficient matrixes is proposed and the principle of calibration is elaborated in detail.The full-field sensitivity coefficient matrixes calibration is realized by the calibration experiments.The calibration precision is studied and analyzed as well.In addition,the imaging system of projection moiré system is calibrated with Zhang’s calibration method.Finally,3D shape measurement experiments are conducted using the technology proposed in this article which demonstrates the feasibility and reliability.The root mean square vale of measurement error of a 2D flat plane is less than 4μm under a measurement range of 174mm×132mm.When measuring a 3D sphere with the diameter of 117.40 mm,the measurement error is only 0.19%.3D shape reconstruction of human face plaster and model fish with complex surface topography are also achieved successfully.Comparing with traditional projection moiré method,the measurement accuracy and resolution of the method proposed in this paper is increased significantly.