Research On The Digital Holographic Accurate Measurement Method Of The Three-dimensional Topography Of Object Surface

With the rapid development of life sciences,mechanical micromachining,microelectronics,and material sciences,higher requirements are put forward for the measurement of geometric features of three-dimensional objects,and there is an urgent need for high-resolution,fast and high-precision measurement methods.In the field of optical measurement,digital holography is a three-dimensional information expression technology based on interference recording and diffraction reconstruction.It can record the wavefront information of objects well,and can meet the above requirements while also having reasonable sensitivity and dynamic measurement Range.It is an ideal technique for measuring the three-dimensional topography of objects.In this paper,theoretical analysis,computer simulation and experimental verification are used to study the digital holographic measurement method of 3D surface topography.In the summary and analysis of the domestic and foreign research status of digital holographic topography measurement,it is found that factors such as the wavelength of the laser,the illumination angle and the observation direction will all affect the phase,but the current methods are mostly based on the method of multiwavelength and rotating illumination light.The method of changing the observation vector has not been reported in the digital holographic profile measurement.According to the geometric relationship between the reconstruction phase of digital holography and the height of the object surface,a mathematical model of digital holographic three-dimensional profile measurement is established,and a threedimensional profile measurement method is proposed to change the observation vector by rotating the CCD.In this method,two single-wavelength digital holograms of different observation vectors are recorded by rotating CCD with a precision rotating stage at a small angle during digital holographic recording.After the reconstructed phase difference is unwrapped and the tilt component is subtracted,the threedimensional surface topography information of the object can be obtained by substituting the relationship equation between phase difference and height.Firstly,detailed theoretical analysis and numerical simulation are carried out for the research method.Then,a calibration method which can calibrate the CCD receiving plane on the rotating axis of the rotating stage is presented.Based on off-axis digital holography,two acquisition schemes for changing the observation vector are designed,one is the two-time shooting scheme with single CCD rotation,and the other is the single real-time shooting scheme with double CCD.Finally,the experimental setup of a rotating single CCD is built to measure the topography of a hemispherical workpiece with a radius of 16 mm.The calculated results are in good agreement with the real value of the object,and the experiment verifies the feasibility and accuracy of the proposed digital holographic topography measurement method based on rotating CCD.As the application and promotion of the proposed method,the surface topography of the dental crown used in the biomedical field was measured.The measured results well reflect the contour information of the dental crown surface,which can provide guidance for dentists in the process of repairing teeth and making dentures.