Research On The Key Technologies Of Vision Measurement System For Cover Glass

Smart terminals such as mobile phones and tablet computers are the main interfaces to achieve human-computer interaction.The cover glass are the outermost layer of the intelligent terminals,which not only protect the inner screen,but also affect the appearance and touch of the whole machine.Traditional cover glass measurement mainly uses industrial micrometer as a tool,which has low measurement efficiency and can only carry out partial quality control by offline sampling.In order to ensure production quality,all products need to be tested efficiently.The measurement of intelligent terminal cover glass has the requirements of large size range,high precision,fast detection speed and strong cost limitation.In view of these requirements,this paper designed a machine vision system for cover size measurement,analyzed the key factors of vision measurement,and studied the error source and compensation method.Specific research work includes:Firstly,based on the cover glass manufacturing process and measurement requirements,the components of the cover glass vision measurement system are analyzed.The physical structure of the cover glass edge,the selection of the imaging lens,the divergence Angle of the light source,the position of the ink and other key factors on the edge imaging were verified by Zemax simulation experiments.Then,a simulation measurement system was built through Zemax to simulate the changes of actual imaging conditions and design and verify the feasibility of the vision measurement scheme.Secondly,according to the selection parameters verified by the simulation experiment and other important reference indexes of the actual selection,the cover glass size measurement system is built,and the corresponding installation mechanism and movement mode are designed at the same time.The imaging model and calibration principle were analyzed,and the calibration method based on the checkerboard saddle point coordinate mapping was designed to achieve fast calibration.Thirdly,the influence of the edge detection method on the edge location and measurement of the cover glass was studied.According to the gray expression form of the edge of the cover glass in the image,the edge location method based on gray stretch and the edge location compensation method based on the neural network were proposed.At the same time,according to the multi-camera and cross-image measurement methods of the measurement system,the image Mosaic algorithm based on checkerboard and the image Mosaic compensation algorithm based on the feedback of Mark point position are designed.In addition,in view of the measurement error caused by the deformation of the platform caused by temperature change,the shape variable of the platform was verified by ANSYS analysis,and the error compensation method based on the feedback of the position and posture of the inflatable steel was proposed.Finally,the measurement repeatability(3sigma)of the measuring system designed in this paper is 0.005mm.By comparing with the standard microscopic measuring instrument,the maximum measurement deviation of the system is no more than 0.01mm within the measuring range of 280mm,and the relative linearity is 0.004%.The measurement accuracy and detection time meet the actual production requirements.