Research On On-machine Measurement Technology Of Rotation Angle Of Large Diameter Parts

Angle measurement is an important branch of geometric measurement of mechanical products,and it is widely used in fields such as military equipment,automated control,machine manufacturing,and medical equipment.The accuracy of its processing and detection directly affects the quality and life of the product.The measurement characteristics of the rotation angle of large diameter parts is considered,a on-machine large diameter parts rotation angle measurement based on machine vision technology is proposed.Double telecentric imaging system,lighting system and Angle measuring reference board are used to form the machine measuring system for large diameter parts.The main contents are as follow:(1)Research on the existing rotation angle measurement technology at home and abroad is consulted.Based on the characteristics of rotary angle measurement of large diameter parts,the principle and method of rotary angle measurement of large diameter parts are proposed.Combined with the image acquisition requirements of the measurement system,the imaging equipment,light source equipment and mechanical structure of the measurement system are formulated.Because of the large diameter of the part to be measured and the limited camera field of view,binocular camera is used to collect the image of the feature markers.The reference plate of angle measurement is used as the feature marker,which can avoid the shortcoming of using single large scale calibration plate.By studying its calibration method,the unification of image coordinate system under binocular camera in measurement coordinate system is realized.(2)The machine measurement algorithm of rotation Angle of large diameter parts is studied.Firstly,Gaussian filtering algorithm is used to smooth the image edges,and Sobel edge location algorithm is used to locate the pixel-level edges of the calibrated circle image.Secondly,the sub-pixel edge location algorithm based on logistic regression is used to locate the sub-pixel edge of the image.The least square circle fitting method is used to fit the pixel coordinates of the center of the calibration dot.Finally,the view center coordinates are converted from the image coordinate system to the measurement coordinate system by the calibration algorithm of the reference plate of angle measurement.The rotation angle of large diameter parts is obtained by changing the slope of physical coordinate line of the center point of the field of vision of binocular camera before and after rotation.(3)The calibration experiment of the reference plate for angular measurement and the analysis of angular measurement error are completed.The transformation parameters from image coordinate system to measurement coordinate system are determined by calibration experiments on the reference plate of angular measurement.Based on the transformation parameters,the measuring point error caused by the positioning errors of feature points of the center point of visual field after coordinate transformation is analyzed.And the measurement accuracy of rotation angle caused by the measuring point error is analyzed.The feasibility of the measurement method is verified by simulation experiment.