Development Of Large Size Workpiece Measurement System Based On Machine Vision And Linear Driven Precision Positioning Aerostage

With the development of science and technology,the continuous development of photoelectric technology,computer technology,automatic control technology,and with the development of aerospace and marine engineering,the size of the components of different equipment has become larger and more complex,the detection environment has also been restricted,the traditional large size work-piece detection methods have already been used.It is unable to meet the requirements of large size work-piece detection.Visual inspection has been used more and more in modern industrial testing because of its characteristics of non contact,high flexibility,fast detection speed,high automation and high precision.Through the organic combination of visual measurement and motion control,the feature information of large size work-piece can be taken in different places through the movement of the motion platform,and the high precision measurement of large size work-piece can be realized.In this paper,a large size work-piece is selected and a visual system is set up according to the requirement of measurement.And motion control platform is set up according to the motion requirements of the system,and a complete visual measurement system is set up with the visual system and the motion control platform.Then the image is processed according to the requirement of image detection,the feature information in the image is obtained.Finally,the measurement of the work-piece is completed by the measurement scheme,and the measurement results are compared with the actual requirements.The main contents of the research are as follows:Firstly,the main component of a visual system is introduced,and the camera,lens and light source in the visual system are selected according to the measurement requirements of the large size work-piece.A visual system is set up,and the calibration coefficient of the camera is obtained by the corresponding calibration method then the calibration of the camera is completed.Secondly,according to the movement requirement and motion control principle of the visual inspection system,a motion control platform is built.In order to achieve high precision motion control,a powerful PMAC controller and its supporting driver areselected,and the linear motor and marble guide are used,the grating ruler and the laser ruler are used as feedback elements.After building a suitable platform,the factors affecting the motion accuracy of the platform are analyzed,and the straightness and positioning accuracy of the platform are measured by experiments.The range of less variation of the straightness is found as the measuring range.The pitch error and clearance compensation for the platform are carried out to make the positioning precision higher and less change.Thirdly,according to the requirement of extracting feature points,different filtering algorithms,threshold processing and edge detection operators are analyzed.Finally,the image is processed by using the algorithm,adaptive threshold processing,median filter,Canny edge detection algorithm to process the image,and then adapt Hof.Transform to find straight line information and the circular hole information in the image.Finally,model of the whole visual measurement system is built up,and the transformation matrix of the work-piece size from the motion platform component Y to the camera image is established through the model,and the image information is converted.Through the whole visual measurement system and image processing technology,a software with visual processing and motion control is written,and a flowchart is written to measure a large size piece of work.The accuracy of the visual measurement system is verified by measuring the size of the feature points of large size pieces and the actual size and reliability.