Research On Three-dimensional Contour Measurement Method Based On Fringe Projection

With the continuous development of the digital age,three-dimensional measurement method based on fringe projection technology has been deeply studied by a large number of researchers.It has the advantages of simple hardware configuration,fast measurement speed and high measurement accuracy,so it has been widely used in various fields of human production and life.In this paper,the establishment of system model,phase calculation of fringe pattern,system calibration,solution of three-dimensional coordinates and three-dimensional measurement of objects with different depth of field are studied deeply in the measurement technology based on fringe projection,and the corresponding three-dimensional measurement system is built.The specific research content mainly includes the following aspects:(1)A triangulation model was established to obtain the relationship between the height of the measured object and the phase,and two methods of calculating the wrapping phase were compared and studied: phase shifting profilometry and fourier transform profilometry.Then phase shift profilometry was used to calculate the wrapping phase.The phase unwrapping methods of classical pruning method and multi-frequency heterodyne method are compared.The experimental results show that the multi-frequency heterodyne method has the characteristics of avoiding error propagation and solving phase accurately.(2)The mathematical model of the system is established based on the imaging principle of the camera,and the calibration principle and method of the system are analyzed.Finally,the calibration method of Zhang Zhengyou is used to calibrate the camera.The projector is regarded as an inverted camera,and the internal and external parameters of the system are calibrated.(3)Select the appropriate hardware equipment to build the three-dimensional measurement system and carry out the measurement experiment of the three-dimensional contour of the object.The results show that the system has a better measurement accuracy and this system can meet the needs of some practical applications.However,when objects with different depth of field are measured at the same time,the system cannot obtain the high precision measurement results of multiple objects with different depth of field.In order to verify the influence of depth of field on measurement accuracy,a6-layer gypsum standard step model is selected for measurement experiment.By comparing the measurement accuracy of each step plane,the influence of depth of field on measurement accuracy of the system can not be ignored.(4)A fringe projection measurement method based on mirror assisted is proposed.By building mirrors part assisted to increase the optical path of the camera from objects with small depth of field,the camera can collect clear images of the 3D contour surface,thus realizing the high precision measurement of multiple objects with different depth of field simultaneously.The three dimensional contour surfaces of two standard ping-pong balls(100mm apart)were measured synchronously and simultaneously by the three dimensional measurement method based on fringe projection and the mirror assisted fringe projection,respectively.The relative errors of fitting radius of the ping-pong balls measured by the three dimensional measurement method based on fringe projection are 2.9% and 34.3%,respectively.The relative errors of fringe projection method based on mirror assisted measurement are 2.7% and 5.3%,respectively.Experiments show that the proposed method can reduce the error caused by the depth of field,so the fringe projection measurement method based on the mirror assisted is feasible in the simultaneous measurement of objects with different depth of field.