Research On 3D Measurement Technology Of Elevator Rail Based On Binocular Vision

With the building floor gets higher and higher,the demand for elevators is increasing.Elevator rail is an important component of the elevator,which plays an important role in ensuring the quality of elevator operation.Therefore,it is very important to detect the processing quality of the elevator rail.In recent years,the requirement of quality inspection in the elevator rail industry is getting higher and higher.Because of its own limitations,the two-dimensional measurement is gradually replaced by the three-dimensional measurement.Three-dimensional measurement is to perform a full range of measurements on the workpiece to be measured and calculate its three-dimensional coordinates.The instrument developed according to the principle of three-dimensional measurement includes visual three-dimensional scanner,laser three-dimensional scanner and three coordinate measuring machine.Among them,binocular vision has become the focus of research in recent years because of its advantages of non-contact,simple structure and high precision.In this paper,the elevator rail was taken as the object of measurement,and the binocular vision three-dimensional measurement technology based on grid projection was studied deeply.The main contents of this paper include:(1)Aiming at the problem of low contrast and few feature points of elevator rails,a three-dimensional measurement method based on grid projection was proposed.In this method,the intersection of the laser grid projected on the surface of the elevator rail was taken as the feature point.And according to the principle of binocular vision measurement,the design of the image processing algorithm and the construction of the hardware and software platform were completed.On the software platform,the servo motor control program,the image acquisition program,the image processing program and the geometric error calculation program were completed based on Visual C++ integrated development environment.Finally,the precision experiment and error analysis of the three-dimensional measurement system were completed on the platform.(2)Aiming at the problem of large amount of stray light noise in grid projection images,this paper simulated and compared various spatial domain and frequency domain image enhancement algorithms.On this basis,a filtering algorithm for elevator guide image was proposed,which partially suppressed some noise.Then,an image preprocessing algorithm based on the analysis of the laser grid was proposed by using the characteristics of high brightness contrast between the laser grid and stray light noise.This method further suppressed the stray light noise and improved the signal-to-noise ratio of the image.(3)Grid projection line has a certain width.The gray value of the central pixel in the width direction of the line is the largest,and the gray value of the pixel on both sides decreases.In this case,the RANSAC fitted line will be skewed.Therefore,this paper proposed a processing method of pixel weighting to improve the accuracy of fitting lines.When the RANSAC algorithm is used for feature extraction,the efficiency is low.In order to solve the problem,this paper proposed a method of hypothesis model pre checking.At the same time,RANSAC was applied to multi-line fitting by making appropriate improvements to the traditional RANSAC algorithm.(4)In order to solve the problem of low efficiency and high mismatch rate of the traditional stereo matching method,this paper proposed a simple and efficient stereo matching algorithm.Based on the special location information of grid intersection,the method realizes the accurate matching of grid intersection points.In order to solve the problem of false matching,an improved RANSAC algorithm was proposed,which was used to eliminate false matching points.(5)Aiming at the problem that the world coordinate systems of two groups of cameras are inconsistent,a camera graft model was proposed based on the existing stereo vision model.The model makes the two groups of cameras in the same world coordinate system.In this paper,the hardware and software of the three-dimensional measurement system was built according to the measurement requirements of the elevator rail.The system realizes the automatic measurement of the geometrical error of the end of the elevator rail.The experimental results show that the system has good robustness and accuracy,and has strong theoretical significance and engineering practice value.The repeatability of the system is less than 0.01 mm.