Digital Force Controlled Grinding And Polishing Technology For Complex Surfaces

The profile accuracy and surface quality of aero-engine blades directly affect the aerodynamic performance of the engine.At present,more than 90% of the edges of blades are still grinded and polished manually in China,which causes the consistency is poor,the quality cannot be guaranteed,and the machining efficiency is low.The blade profile is complex,the edge features are small,the contour and surface precision requirements are high,the removal margin is small,and the distribution is uneven.At present,there is an urgent need for an automatic grinding and polishing method with precise force and position control.Although CNC grinding machine can significantly improve the processing efficiency and quality,the cost is high and the programming is complicated.Because industrial robot has a large moving space,is intelligent,low in cost,and can be quickly and flexibly converted,it has significant advantages in achieving multi-variety and small-batch aero-blade grinding and polishing.However,the industrial robots have poor openness,slow response and severe force coupling.The traditional robot grinding and polishing system only plans toolpath,and lacks precise control of the positive force.It is difficult to achieve the compliant processing of specified material removal.In summary,research on high-performance force-controlled grinding and polishing unit is of great significance,which can achieve the decoupling control of force and position in robot belt grinding and polishing system,and complete precise grinding and polishing through coordinated control of force and position.In this paper,the high-bandwidth precise force control problem of robot grinding and polishing system is studied.Based on decoupling of force and position,a rigid-flexible digital force-controlled abrasive belt grinding and polishing unit is designed.Force control algorithms during contact transition state and steady state are studied.And supporting interactive control software was written,and grinding verification of aero-engine blades was carried out.The main research contents are as follows:1 Overall design of force controlled grinding and polishing unit.Based on the practical requirements of decoupling of force and position,structural modularization,fusion of active and passive compliance,systematically designing rigid-flexible coupling structure,a flexible open electronic control system,position-force double closed-loop control algorithm,easy-to-use interactive control software that enables data visualization named ForceControlDesk of the grinding and polishing unit which could polish the full features of aero-blades in this paper.2 Force shock and vibration suppression algorithm in contact transition state.Input signal is shaped by the offline-feedback input shaping technology to guide the system vibrations to cancel each other.The simulation results show that contact stabilization time is shortened by about 84.2%,and maximum force overshoot is reduced by about 94.7% after using ZV shaper.On this basis,Nonlinear tracking differentiator(NTD)automatic shaping technology is proposed to increase the adaptability and robustness of system to the unstructured environment.The NTD method reduces contact stability time by about 72.3% and maximum force overshoot by about 87.5.%.3 Adaptive force tracking and compensation algorithm in contact steady-state.within impedance control framework,an environmental stiffness and position observer with Lyapunov stability is proposed to generate the adaptive reference trajectory,and iterative learning control method is adopted to compensate force tacking error due to position tracking error.The compensation strategy made force tracking steady-state error is reduced by about 96.4% in actual experiment.4 System integration,test and polishing verification.Least squares method is used to identify the dynamic model of the device.A control software is written in Visual Studio with Qt plugin using mixed programming method,and various debugging and testing experiments are carried out.The grinding test was carried out on the blade,trailing edge and leading edge of various aero-engine blades.The grinding force control accuracy was ±0.5N.After grinding,blade edges rounding was obvious,and blade profile roughness Ra reached 0.1263μm.