Research On Displacement Measurement System Of Laser Dual Reverse Perspective Mapping

With the large-scale construction of Bridges in China,bridge structures are all over the country,but the long-term accurate monitoring of bridge pier settlement cannot be effectively guaranteed.Many Bridges are in inconvenient areas for measurement,and the intelligent and portable requirements of measurement methods and measuring equipment are high,so the traditional displacement measurement methods are greatly limited.Laser diffraction measurement technology is a high precision and high efficiency measurement technology,has significant advantages for small displacement measurement.The method is simple and easy to use,high precision,high degree of automation,good long-term monitoring stability,and can be connected with a microcomputer to realize automatic data acquisition and storage operation,which has been widely used in many high-precision,real-time online measurement fields.In this paper,based on the principle of laser diffraction technology to amplify the small displacement,a measuring device for pier settlement is invented,which can effectively realize the long-term high-precision automatic monitoring of pier settlement.Firstly,the principle of laser diffraction is studied and analyzed,Fresnel diffraction and Fraunhofer diffraction formulas are derived,and related formulas are simplified according to the actual engineering background of the device.According to the key conditions in the design,the prototype device was successfully designed and improved by using the principle of reflection increasing optical path and double reverse perspective mapping technology.The theoretical simulation modeling process based on the prototype device is described.Based on the actual application conditions,the Form of Fourier transform under Fresnel approximation condition is simplified.Through matlab simulation analysis,clear diffraction images are obtained.Combined with the actual characteristics of Fresnel near-field circular hole diffraction pattern,an improved circle center fitting algorithm was developed as the optical spot center recognition algorithm,and the identification results of diffraction images were processed to obtain the relationship between the settlement amount of bridge structure and the optical center displacement amount.At the same time,the problem of diffraction spot and alignment error caused by the keyhole alignment state in outdoor experiment conditions was simulated,and the influence of translation alignment error,tilt error and other common error states on the accuracy of the device was analyzed.The experimental system of the laser diffraction high-precision measurement device is built,and the settlement displacement curve is obtained.The results show that when the settlement is less than 0.5mm,the settlement and the vertical displacement of the optical center show a significant linear relationship,indicating that the device can achieve about 10 times the amplification effect.Paper analyzes some error of experimental process and put forward the corresponding improvement measures,including spot acquisition error,laser reverse error,receive,screen the vertical installation error,error caused by the laser structure,camera lens distortion error and correction,the installation error and correction of camera,etc.,effectively ensure the accuracy of practical application.This paper combines laser diffraction technology with reverse perspective mapping technology and proposes a remote settlement observation device based on laser double reverse perspective mapping technology to achieve high precision measurement.The measuring device consists of a laser and a receiver,and the displacement amplification of about 10 times is achieved under experimental conditions,which proves that it can be used effectively for highprecision monitoring of pier settlement displacement.The device does not need extra assistance,the measuring equipment and the measuring process is simple,high precision,fast measuring speed.This research has engineering application value for long-term observation of real-time fixed point settlement of pier.