Research On Key Techniques Of Phase Measurement Deflectometry For Three-Dimensional Measurement Of Specular Surface

The non-contact and high-precision measurement of specular surface has become an important scientific problem in the field of three-dimensional optical measurement.The structured light measurement method for diffuse reflectance object is no longer applicable because it can not obtain the feature information of the measured mirror surface.The phase measurement deflectometry(PMD)has become a research hotspot because of its simple principle,low cost,large dynamic measurement range and fast full-field measurement.In this paper,the measurement model of PMD,corresponding phase solution,system parameters calibration and gradient integration are studied.Achievements have been made in respect-s of high-precision phase solution,high-precision calibration methods and high-precision measurement methods.Specifically as follows:1.Aiming at the problem of repeated calibration in the conventional mobile screen deflectometry,a deflectometry measurement method of single-camera monitoring is pro-posed.The two positions of LCD screen are monitored by an auxiliary camera;the po-sitional relationship of the LCD screen relative to the main camera is determined by the Perspective-n-Point(PnP)method and the coordinate system transformation.The incident light is determined by two homonymy phase points on the LCD screen at two positions through absolute phase tracking.Finally,the normal and gradient information are deter-mined and the mirror surface is reconstructed accurately through the radial basis function interpolation.The two cameras,which do not have a common field of view,are calibrated using the mirror calibration method.Therefore,the incident light and reflected light are unified into the main camera coordinate system by transformation.The calibration work is just needed to be implemented once,and the repeat errors are eliminated.2.Aiming at the problem of limited field of view and complex structure in conven-tional phase measurement deflectometry with spatial structure,the spatial biplane phase measurement deflectometry is proposed.The biplane structure for determining inciden-t light is constructed by using transparent surface light source instead of spatial reuse of ordinary surface light sources.Transparent light source is modeled as a transparent glass with uniform thickness and refraction index.The propagation path of incident light is ac-curately described by thickness and refraction index parameters.The refraction parameters of transparent light source are calibrated by multi-stereo vision method,and the system pa-rameters are calibrated by the improved mirror calibration method.After calibration,the measurement accuracy of the system can reach micron level.3.In order to improve the accuracy and efficiency of the phase measurement deflec-tometry system calibration,a parallel mirror calibration method is proposed.The rotation matrix is calculated directly by PnP method and mirror principle with one parallel mirror position.The translation matrix is determined by two calibration modes:single camera mode and dual camera mode.In the single camera calibration mode,the translation matrix is determined by solving linear equations with two parallel mirror positions.In the dual camera calibration mode,the translation matrix solution is converted to one-dimensional search for the optimal distance between the mirror and the camera.The dual camera cali-bration mode of parallel mirror calibration method can be used for automatic calibration of posed relationship of the system in stereo deflectometry.4.The line-planes deflectometry is proposed.The intersection between the reflected light and incident light is transformed into the intersection between the reflected light and the plane containing the incident light,and the line-plane model is constructed.Based on the mirror calibration method,calibration methods for the line-plane deflectometry system parameters are proposed.The system can be used for mirror measurement after calibration.There are two measurement modes for line-planes deflectometry:line-1-plane mode and line-2-planes mode.In line-1-plane mode,the maximum error is 0.25mm,the root mean square error(RMS)is 0.073mm.In the line-2-planes mode,the measurement accuracy of the system can reach micron level.