Research On Compensation Method Of Analog Coding Structured Light Phase Error

In recent years, with non-contact optical measurement technology researched extensively and deeply, the level of this technology has developed rapidly. And the application of this technology is also increasing, like in industrial, military, medical, aerospace and other fields. One of the most development potential and practical three-dimensional measurement is the analog coding structured light measurement technology. Analog coding structure light three-dimensional measurement technology has many advantages, such as non-contact and simple operation, fast measurement, high sampling density. However, with the use of camera and projector system for three-dimensional measurement, the measurement accuracy is influenced by many factors, and the accuracy is not high. In order to reduce the error of analog coding structured light measurement system, this paper proposes a method to reduce the intensity ratio deviation. This method could simplify calculation, and improve the accuracy of three-dimensional measurement.Firstly, this paper describes, in the analog coding structured light measurement, the basic principles of phase shift profilometry measuring method, the composition of three-dimensional measurement system, derived triangulation, a brief description of the basic steps of analog coding structured light three-dimensional measurement, and described the basic method of system calibration. Then, this paper analyzes the sinusoidal phase-shifting algorithm. The sinusoidal phase-shifting algorithm computed the unwrapping phase containing three-dimensional information of the object surface by collecting multiple fringe images with a certain phase-shifting. Use temporal phase unwrapping method to expand the unwrapping phase, establish the mapping relationship between phase difference and height, and get the three-dimensional information of the object. But there is a phase error, and do analysis with it. Since the phase calculation in sinusoidal phase-shifting algorithm would have a complex arctangent operation. This paper uses triangular phase-shifting algorithm, projects triangular phase-shifting fringe pattern, defines intensity ratio information instead of phase information, and expands the acquired unwrapping intensity ratio, establishes the mapping relationship of intensity ratio difference and height. The algorithm also exists a large number of phase error. To analysis the existing error, first build two triangular phase-shifting coding pattern with the initial intensity ratio difference is T/6. Then use the traditional three-step triangular phase-shifting algorithm twice to obtain two unwrapping intensity ratio. Finally, using the discipline founded in phase error analysis of phase-shifting algorithm, and combine with the characteristics of intensity ratio deviation, this paper proposes a method which can reduce the intensity ratio deviation.Based on the theoretical analysis, this paper builds a three-dimensional measurement system. Hardware system includes CCD cameras, projector, computer and other infrastructure, and calibrated the system. Through the simulation experiment, verified the effectiveness of the double three-step triangle phase-shifting algorithm. The experimental results show that the proposed method, double three-step triangle phase-shifting algorithm, can effectively improve the accuracy of analog coding structured light in three-dimensional measurement.