| Robots are widely used in industry because of their high precision,high flexibility,high reliability,programmability and competitive cost.However,the series robot has the problem of weak rigidity,and chatter easily occurs in the processing,which affects the processing quality.The thesis focuses on the relationship between the posture of the robot and the stiffness of the end operation,and optimizes the machining stiffness of the robot system under a given grinding condition.The main contents of this thesis include the following aspects:(1)Taking the IRB6700 robot of ABB Company as the research object,the composition of the robot grinding system is introduced with the help of the titanium alloy grinding project,and the kinematics equation of the robot with this structure type is deduced.The forward kinematics equation of the structure type robot is deduced by D-H method with pre-coordinates.The inverse kinematics solution of the structure type robot is obtained by separating variables.The Jacobian matrix of the robot is obtained by vector product method and differential transformation method,which lays a foundation for the establishment of the rigidity matrix of the robot.The above results are validated in solidworks,MATLAB and robotstudio software,which proves the correctness of the results.(2)The stiffness model and task space of grinding robot are established.Based on the simplification of robot joint stiffness,the traditional static stiffness model of robot is established.The tool coordinate system is established at the end point of the robot,and then the transformation relationship between the tool coordinate system and the robot base coordinate system is deduced.The force of the tool is transformed to the origin of the flange coordinate system,which is described in the base coordinate system.The reachable task space of the robot's terminal position and the reachable task space of the robot's terminal posture are discussed,and the reachable judgment model of the robot's posture is established.Based on posture reachability judgment,a feasible solution model for a given posture of the robot is established,and an algorithm is written in MATLAB software to solve the feasible solution model.The correctness of the solution model is verified by robot studio software,which is used to prepare for the posture optimization algorithm of the robot.(3)The processing stiffness of the robot is discussed and optimized.The influence of each part of the flexibility matrix on the end deformation of the robot is studied to find out the most influential factors,and then the flexibility matrix is simplified.Based on the simplified flexibility matrix,the Cartesian flexibility ellipsoid of the robot is studied in depth,the anisotropy of the manipulation stiffness of the end of the robot is obtained,and the distribution of the relationship between the deformation vector and the force vector in the manipulation space is found.Taking the volume of the flexible ellipsoid as the stiffness performance evaluation index,the influence of the inverse solution of the position and posture of the robot on the end operating stiffness is discussed.For a specific working condition,based on known operating force,the processing stiffness performance index of the direction of operating force is proposed.Taking the stiffness performance index as the optimization objective,the optimal inverse configuration model of the unit pose point and the optimization model of the unit pose point considering the redundancy of machining are established.Based on the optimization of the unit posture point,the optimal grinding model of the robot trajectory is obtained by optimizing multiple target points on the robot-processing trajectory.In matlab software,the algorithm is written to solve the above optimization model,and the optimal posture of the robot at a given target point is obtained.The results before and after optimization are simulated in ANSYS software.The correctness of the optimization results is verified by analyzing the deformation and stress nephograms.The posture optimization method is used to improve the rigidity of the robot.It does not need to change the body structure of the robot.It only needs to change the joint configuration of each target point in off-line programming or on-line trial teaching.The analysis results show that the stiffness of the optimized end-effector is improved,which has important guiding significance for improving the machining accuracy,reducing the machining chatter and improving the processing quality of the robot. |
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