Development Of A High-accuracy Interferometry System And The Metrological Traceability Of Pavement Profilometry

This paper develops a pavement profilometry system based on laser interference,proposes a traceability system of pavement profilometry,and realizes its metrological traceability.This research has filled the vacancy of the traceability system of pavement profilometry in China,and has completed the establishment of a standard equipment in a new field.Standard metrical instruments are standard equipments used for value transfer in metrological systems of different fields.Developing standard metrical instruments for pavement profiles is an important means to achieve value transfer.In the field of pavement engineering,standard instruments used for value transfer has not been established yet,and more attention is paid to the establishment of pavement profilometry devices that meet the national metrological standards.This research can greatly improve the accuracy of traditional measurement methods,ensure engineering quality,and save measurement costs.The establishment of related metrological calibration techniques and traceability systems based on laser interference fringe will improve the value transfer and traceability in the field of pavement engineering,and provide an important technical basis for 3D pavement profilometry.This topic combines theoretical analysis,indoor and outdoor experiments based on interference fringe profilometry,explores the method of improving its measurement accuracy,and applies the method to pavement profilometry,designs and builds a pavement profilometry system,and then conducts the metrological traceability to the proposed device based on national standard components,which provides a basis for the calibration of the pavement profilometry devices from different institutions in China.On the basis of the existing researches,this research has carried out a systematic study on 3D pavement profilometry based on interference fringe.The main contents and results are as follows:1)The influences of various system parameters(such as incidence angle of interference fringe,fringe spatial frequency and fiber core distance,etc.)on the measurement accuracy of interference fringe profilometry is analyzed via experiments.The results show that when the incident angle is 13°,the 3D reconstruction results are better.This parameter can not only reduce the influence of noise on the 3D measurement results,but also limit the scanning blind area within a suitable range;With the increase of the fringe spatial frequency,the measurement accuracy of the system gradually improves,but when the fringe spatial frequency is too high,the fringe is extremely sensitive to the influence of noise,thereby the measurement accuracy is reduced;when the fiber core distance is 0.75mm,the fringe generator can project interference fringes with higher spatial frequency,and can ensure the recognizability of interference fringes,so that high measurement accuracy can be maintained when projecting at a long distance(500mm-1800mm).2)According to the conclusion of the factors affecting the accuracy of the interference fringe profilometry,the structure of the fringe generator is improved,and a metering device suitable for measuring the pavement profile is designed and built.The device mainly includes a frame system,a scanning system,a transmission system,a walking system,and an electronic control system.The frame system is used to support the scanning system and the transmission system.The scanning system can be moved to any position of the lane through the transmission system to scan the pavement surface being measured,and the measurement height can be changed.The diameter of the interference pattern is in the range of 45.98-165.52mm.3D measurement accuracy of the device can reach ±0.1 mm,and the resolution can reach 0.053mm.It fills the lack of interference fringe metrological technology in the field of pavement profilometry.3)From the perspective of image post-processing,the factors that affect the quality of fringe images are analyzed,methods to reduce interference information are explored,and the reconstruction algorithm is improved to compensate for the error induced by the beam divergence angle,thereby the system's 3D reconstruction accuracy is improved.The results show that the use of single-component method,piecewise linear transformation,construction of inverse Gaussian function,wavelet denoising,etc.to process the original fringe image can effectively repair the cosine distribution characteristics of the fringe image,filter out the interference information,and realize 3D pavement profile.The optimization on the original algorithm also makes the acquired 3D data more accurate.4)The differences between the measured values and the standard values are explored,the error source is analyzed,and system error at different measuring heights is explored.The key link of the pavement profilometry in the metrological traceability system is completed:The pavement profilometry system is traced to the metrological standard,and the standard uncertainty of the pavement profilometry system is calculated;the new pavement crack standard component is calibrated with this system,and the standard uncertainty of the pavement crack standard component is calculated.Then the profiles of the actual asphalt pavement surfacse are reconstructed in three dimensions,and the results show that the system can accurately represent 3D morphology of the asphalt pavement profile.