The Research Of Fast Three-dimensional Shape Measurement Based On Phase Extraction

Fast measurement is one of the research hotspots in the field of optical three-dimensional shape measurement,and it has high application value in the field of non-static shape measurement such as dynamic process analysis and online detection.For the measurement of dynamic objects,inter-frame motion of objects is the main factor affecting the measurement accuracy.The solution to this problem mainly relies on the following two ways.One is to improve the phase calculation algorithm to reduce the deformed fringes number required in phase retrieval,and the other is to improve image acquisition speed of the measurement system.In this paper,a fast measurement method is studied based on the above two methods.In this paper,an improved phase measurement method is proposed.Based on the advantages and limitations of traditional four–step phase shifting method and Fourier transform profilometry,an improved algorithm for fast measurement is proposed.By accurately extracting the mean envelope of the fringe in time domain and simply filtering in frequency domain,the fringe can be pre-processed.Combined with the two-step phase-shift algorithm based on 90~o phase shift,an accurate phase value can be obtained from two fringe patterns.At the same time,the background removal method can effectively suppress the Fourier zero-frequency component,thus expanding the Fourier transform measurement range and improving the measurement accuracy.The absolute phase of the object can be retrieved from four deformed fringe patterns by combining the two above-mentioned methods.Under the general experimental conditions,the root mean square error is within 0.015rad.Based on the improved phase calculation method,a multi-channel fast measurement system is built in this paper.An infrared projector and a visible projector constitute a four-channel projection system by the use of a beamsplitter mirror changing the light path of the projectors.Four-channel stripes will be obtained at the same time by a 2CCD camera,so as to complete the three-dimensional shape measurement through a single-shot acquisition process.At the same time,a new six-degree-of-freedom fringe projection simulation system is established for analyzing the deviation of the two projectors and the measurement system's performance.Based on the simulation system and projector calibration,a software solution to correct spatial position deviation of two projectors by fringe pattern pre-deformation method is proposed.Experiment results show that by using the fast measurement method proposed in this paper,the detection time is reduced to 1/12 of the traditional method,and the measurement accuracy is high,which can meet the requirement of rapid measurement.