| The SCARA robot is a planar assembly robot that combines with other mechanical or electronic devices,which have the advantages of high speed,high accuracy,and good flexibility.It is widely adopted in machinery,electronics,automotive industry,and it mainly realizes automatic assembly,testing,welding and other related work.With the vigorous development of the electromechanical industry in China,the development of the automatic assembly industry have been correspondingly promoted.SCARA robots have also undertaken more assembly tasks.The positioning accuracy of the end effector of the SCARA manipulator have a very important significance in the field of automatic assembly,which affects the reliability of the assembly.Therefore,it is very important to improve the positioning accuracy of the end effector of the SCARA manipulator.There are many factors that affect the accuracy of the end effector,but the most important ones are the mechanical structure design and the visual processing technology.Mechanical structure: Firstly,the basic bionics theory was expounded,and the structural characteristics and geometric shapes of the stems and veins were analyzed.The bionic I were designed based on the feature of the veins and Bionic II were designed based on the feature of the stem-veins,which a manipulator stiffener structure as a T-shaped structure as the research object.Then 3D modeling was performed using the Proe/E software and imported into the ANSYS Workbench software for static analysis,modal analysis and specific stiffness performance analysis.The bionic II type,which was the most determined,was selected according to the results of simulation,and its ring size was optimized by the multi-objective optimization based on optimized numerical model.Finally,the low-speed and high-speed repeat positioning accuracy test of the SCARA robot end effector was performed,and the rationality of the bionic II structure was verified by test,and it increased the repeat positioning accuracy of the end effector to 0.015 mm.Visual processing: The visual processing technology study was conducted on a motor-gasket assembly machine using the SCARA robot manipulator with bionic design.Firstly,the work flow of the motor-gasket assembly equipment was described.The LED lamp with blue light and the coaxial illumination and the Basler ac A2500.14 gm Gig E camera with CMOS sensor was selected based on the small size and reflective feature of the motor and the gasket.Then camera's internal,external parameters and distortion coefficients was obtained by non-linearly calibrated of camera.The relationship matrix of the camera relative to the end were obtained by hand-eye calibration.Then the image of the motor and gasket collected by the end effector was processed,and the center of the gasket and the center of the motor were identified and positioned based on the template features of gasket and motor.A motor coordinate calculation method,which motor image was processing three times was proposed based on the geometry of the motor mold.Finally,the positioning accuracy control test of end effector was performed and the feasibility of this motor coordinate calculation method was verified,and it increased the assembly accuracy of the end effector from 0.2259 mm to 0.1526 mm.In summary,the bionic design of the mechanical structure and the new coordinate calculation algorithm both improve the accuracy of the SCARA robot end effector.It provides some theoretical support and technical support for the subsequent SCARA robot optimization and visual processing. |
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