| Industrial robots are the irreplaceable important equipment and means in the development of advanced manufacturing.In recent years,robots are used in repetitive tasks at a fixed time sequence at high speed,high quality,and high precision in laborintensive applications such as welding,spraying,and handling.At the same time,robots equipped with high-speed spindles also perform a rapid development trend in the field of metal cutting.Compared with the traditional CNC machining centers,robots have absolute advantages in completing large-size,customized,and medium-to-small batch processing tasks with the characteristics of a wide area,high dexterity,high reconfigurability,and low cost.However,the robot's service environment is harsh in the milling process.The high-frequency,time-varying,and impact loads generated by the high material removal rate and intermittent cutting characteristics further lead to extremely complex static and dynamic mechanical behaviors,affecting product quality and production efficiency.With the continuous development of the aviation industry,advanced CNC machining technology has become the main forming method of the aviation components.The false boss provides a stable and reliable clamping solution for the CNC machining process.Cutting off the connection structure of the false boss and the workpiece along the side wall should be conducted in the end of the machining process("cutting off the false boss").CNC machining centers and manual technology are the two methods for cutting off the false boss.Long occupation time,high production cost,and limited working space are the main disadvantages of the CNC machining centers.Meanwhile,the drawbacks of manual technology are poor quality stability,strong experience dependence,and harsh operating environment.A robotic system for cutting false boss of aviation components is developed to break through the "short board effect" constraints that restrict the manufacturing capacity and level of aviation components.The relevant theories,methods,and technologies are researched around the scientific issues involved in robotic stiffness characteristics and chatter suppression in the process of false boss cutting.The main research contents are as follows:Based on the demand-driven system design scheme,the development and integration of software and hardware in the robotic system are carried out.The robotic man-machine interactive flexible force control technology is developed,and the man-machine interactive flexible force control programming method oriented to the process of false boss allowance milling is proposed.The D-H kinematics model for the COMAU SMART5 NJ 165-3.0 robot is established based on the transition angle conversion strategy.Then the nonlinear multivariate function optimization model for solving the characteristic length of the robot is constructed,and the Jacobian matrix can be normalized based on this length.Using Adams simulation analysis software to analyze the force characteristics of the robotic body structure reveals the law of the external wrench and joint torque transmission of this type of robot.The basic principles and methods of joint stiffness identification based on the least square method are clarified,and our research focuses on the mechanism of the influence of system disturbance on identification accuracy.A quantitative characterization method for identification accuracy based on the uncertainty of the joint stiffness identification is proposed,and the correlation between the uncertainty of the joint stiffness identification and the condition number of the observation matrix is deeply revealed.For the existing identification conditions of the system,a novel index considering both the dexterity and the condition number of the observation matrix is presented.The theory and method of variable posture to anti-disturbance are formed that improves the joint stiffness identification accuracy.A numerical simulation is carried out to prove the effectiveness of the theory of variable posture to anti-disturbance.Developed the theory of Conservative Congruence Transformation stiffness analysis,a multi-matrix norm-based index to evaluate the influence of complementary stiffness matrix is proposed that reveals the pose dependence of the stiffness characteristics of the robot.Given the system constraint conditions of the joint stiffness identification experiment loading/measuring process,the anti-disturbance comprehensive pose optimization model considering the influence of the complementary stiffness matrix is constructed.The postures with strong robustness and little influence of the complementary stiffness matrix are selected based on this model.The joint stiffness identification experiment is carried out to prove the validity of the model,and the robot joint stiffness is obtained.It is difficult to ensure that the tool axis is perpendicular to the clamping plane(parallel to the sidewall of the workpiece)in the process of the false boss allowance milling.A novel guide-milling integrated cutter is developed to solve this "misalignment"problem.The study on the identification of cutting force coefficients based on variablefeed full-tooth milling experiment is carried out,and the six cutting constants of the cutter are obtained.The two-degree-of-freedom dynamic model of the system for the milling conditions of the ordinary cutter without/guide-milling integrated cutter with active contact force is constructed.Then the conversion relationship between the workpiece coordinate system model and the stiffness coordinate system model is clarified,obtaining the characteristic roots of the system.The stability of the system is determined based on the distribution of the characteristic roots.Aiming at the "instability" problem of the milling process caused by the interaction of multiple sources of chatter during the process of false boss allowance milling,an innovative theory and method of mode coupling chatter suppression based on the active contact force between the cutter guidance and the workpiece sidewall is proposed.The relationship between the active contact force and the system stability of the milling process is revealed.It clarifies the mechanism of the active contact force on the mode coupling chatter suppression.Furthermore,the system stability study of the milling process driven by the characteristic root distribution characteristics of the system is carried out,forming the active contact force selected criterion of the guide-milling integrated cutter.The feasibility and effectiveness of this method are verified base on the experiments. |
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