Research On Scanring Measurement Method Of Doubly Curved Hull Based On Binocular Vision

The 3D Ship Hull Plate Bending Machine is a hull plate automatic forming processing equipment jointly developed by Wuhan University of Technology and Shandong Shuoli Machinery Manufacturing Co.,Ltd.Based on the non-counter-pressing technology of flexible square indenter,the hull panel can be stamped by variable dies.In the process of processing,it is necessary to measure the shape of the plate at any time,and solve the springback problem by gradually approaching,so as to achieve the desired shape.The current measuring equipment is laser-point scanning measuring device,which can complete the measurement of ship hull curved plate and meet the needs of automation development.But the measuring efficiency is low and the edge of plate can not be measured.Therefore,it is urgent to improve the measuring speed on this basis.In this paper,a laser-line scanning measurement system composed of binocular vision sensor and three-dimensional numerical control platform is built.Based on binocular stereovision,the system uses laser-line to scan the double-curved hull plate,and combines the laser stripe matching method based on polar constraint to complete the measurement of the stamped double-curved hull plate.The main contents of this paper include:1)By consulting relevant literatures at home and abroad,the existing free-form surface measurement methods are investigated,and the contact measurement and non-contact measurement in surface measurement methods are compared.The research status of measurement methods for ship hull curved plates and the development of stereo vision measurement technology in surface measurement are described.The status of camera calibration technology and stereo matching technology is briefly introduced.2)Understanding the principle of camera calibration and several solving methods,comparing direct linear calibration,radial constrained calibration and Zhang Zhengyou calibration method.Based on calibration accuracy and economic considerations,choose Zhang Zhengyou calibration method to achieve camera calibration and obtain accurate Stable calibration results.3)In view of the characteristics of the hull hyperbolic plate and the measuring environment,the digital image processing methods such as color space conversion,image segmentation,morphological processing and image thinning are used to extract the center line of the structured light,and the binocular stereo matching is completed by using the method of polar constraint to realize the three-dimensional reconstruction of the structured light and obtain the spatial shape of the hull hyperbolic plate.4)According to the requirement of the experiment,the hardware parameters are determined,the hardware equipment is selected,and the measurement experiment platform consisting of binocular vision sensor and three-dimensional numerical control platform is built.Considering the measurement accuracy and the field of view,the structure and physical size of the experimental platform are designed.The software program is designed according to the functional requirements,and a complete laser-line scanning measurement system is obtained.5)The saddle-shaped plate is measured by the experimental platform,and the measurement results and edges of the plate are obtained.At the same time,the metal welding piece and a platform were measured,and the visual measurement results and the vernier caliper measurement results were compared.Experiments show that the accuracy of the vision measurement system is 0.04 mm in the X and Y directions and the error in the Z direction is less than 0.5mm,which can meet the requirements of engineering application and lay a foundation for the application of the vision measurement system in the bending machine.