Research On Phase Coding Fringe Projection Profilometry

Structured light 3D measurement technology is widely used in scientific analysis,industrial control,bioengineering,biomedicine,and materials science due to its characteristics of non-contact,high efficiency,non-destructiveness and large working range.Among them,the digital fringe projection technology with high resolution and high accuracy is the most widely used technology in structured light 3D measurement.During the measurement,the projector projects a sinusoidal fringe pattern or a group of sinusoidal fringe patterns onto the surface of the measured object.The camera captures the modulated fringe pattern on the surface of the object,and obtains the phase distribution based on the collected fringe pattern for three-dimensional reconstruction.The basic principle of this method is to use phase information to establish a correspondence relationship,so it is highly robust to the texture changes of the measured object.The purpose of this paper is to study the phase coding fringe projection profilometry,which aims to lay a theoretical foundation for broadening the practicality of phase coding fringe projection profilometry.The following three aspects have been studied for this method:1.The principle of fringe analysis and phase unwrapping is studied in detail.Fringe analysis technology can be divided into two categories: Fourier transform profilometry and phase shift profilometry.Fourier transform profilometry can be used for three-dimensional measurement with fewer stripes,so it is suitable for scenes with higher measurement speed requirements.Dual-wavelength and multi-wavelength algorithms can greatly increase the fringe frequency,thereby improving the robustness of the system.2.The principle of phase coding method is studied in detail.The existing three-dimensional measurement methods of fringe projection profilometry can be divided into two categories: intensity-based and phase-based coding methods.However,studies have shown that the phase encoding method is intrinsically superior to the intensity encoding method,which is less sensitive to object surface contrast,ambient light and camera noise because it uses the phase rather than the intensity to determine code word.In order to solve the problem that the traditional phase coding has low measurement accuracy due to the small number of code words,segmented phase coding method is proposed,which can enlarge the number of code words and improve the measurement accuracy.Due to the large number of fringe patterns required for segmented phase coding,it is difficult to achieve rapid measurement.To this end,improved phase coding measurement methods are proposed,such as color phase coding,phase coding based on geometric constraints,and so on.3.An S-shaped segmented phase coding method is proposed.This method has three advantages.First,use Gray code to encode the number of phase-encoding segments,which simplifies the phase unwrapping algorithm,and greatly reduces the error rate in the solution process.Second,a design method of the s-shaped segmented phase encoding is proposed by adding constraints.Improved the accuracy of fringe order judgment.Finally,the number of code words is expanded by using the idea of segmentation,and the measurement accuracy is improved.In summary,this method can measure complex and isolated objects with high accuracy.The experimental results also prove the superiority of this method in measuring complex and isolated objects.