Research On 3D Profile Measurement Of Objects Based On Sinusoidal Fringe Projection

At present,digital technologies such as artificial intelligence and computer vision are in the ascendant,and the application prospects of three-dimensional shape measurement technology have more potential.Among the many measurement methods,the three-dimensional shape measurement technology based on the optical measurement principle has many advantages such as non-contact,high precision,high speed,and automation.Optical three-dimensional measurement technology has been widely used in machine vision,reverse engineering,industrial inspection,biomedicine,entertainment and commercial applications and other fields.Optical measurement methods can be divided into active optical measurement methods and passive optical measurement methods.The active optical measurement method has higher accuracy and measurement speed.The method completes the profile measurement by actively projecting structured light patterns to the measured object,and the sine fringe projection is a very widely used structured light measurement method.In the process of measuring the object,the phase information needs to be calculated from the fringe information,and then the height information of the object is calculated from the phase information.In this paper,based on the fringe projection principle,a three-dimensional optical measurement system is built using DLP projectors,CCD cameras,etc.,and the four-step phase shift method and phase unwrapping algorithm are used to calculate the phase and simulate the folding phase unwrapping process.In order to obtain the three-dimensional shape information of the object in the world coordinate system according to the phase information,the system needs to be calibrated according to the internal and external parameters of the system.The system calibration includes depth calibration and lateral calibration.Through depth calibration,the phase information of each pixel in the fringe image is converted into object height information.After obtaining the internal and external parameters of the system through horizontal calibration,the horizontal position of each pixel in the world coordinate system can be determined and the lens distortion can be determined.After the system calibration is completed,the three-dimensional topography of the object can be reconstructed.Not all the surface of the measured object is the standard diffuse reflection situation.When measuring the surface of smooth materials such as metals,the surface reflectivity varies greatly.When using the conventional fringe projection method to measure such high-reflectivity changing surfaces,the results of the phase calculation will produce obvious errors.The fringe brightness in the area with high reflectivity on the surface of the object is too high,and local saturation will occur,leading to distortion of the phase information.Areas with low reflectivity on the surface of the object will be affected by ambient light,resulting in a low signal-to-noise ratio and a significant increase in errors.In this paper,the method of fringe fusion is used to accurately measure such objects.For objects with large differences in diffuse reflection colors,the grouping method of the exposure time and modulated intensity of the fringe fusion method is improved.In the experiment,the fringe projection was performed on the two diffuse reflection surface objects,and the higher and lower camera exposure time were set respectively,and more accurate 3D reconstruction results were obtained.It shows that the built three-dimensional measurement system can effectively realize the three-dimensional measurement function of the object,and the moderate reduction of the exposure time of the diffuse reflection object will not cause the ambient light to significantly reduce the signal-to-noise ratio.In order to investigate the surface with high reflectivity,fringe projection was performed on metal products.The results showed that accurate fringe phase information could not be obtained under conventional methods.By comparing the two sets of phase calculation results under the conventional method and the phase calculation results obtained by using the fringe fusion method,it can be found that only the fusion fringe method will not cause information loss and large errors.This confirms the feasibility of the fusion fringe method for the measurement of highly reflective surfaces.Finally,the fringe fusion method is improved for the diffuse reflection surface with large color difference,which is the surface object with high reflectivity change.The improved grouping method can reduce the number of exposure time and modulated light intensity setting groups,and there is no need to preset grouping parameters,which saves time and cost and is more universal.