Path Planning For Grinding And Polishing Based On Shape Of Aero-Engine Blades And Research On Force Control Technology

The surface accuracy and quality of aero-engine blades directly affect the life and performance of the engine.Grinding and polishing,as the last process in the blade processing process,greatly determine the blade surface quality.Therefore,ensuring the quality of grinding and polishing of aero-engine blades(groups)is a key link in the development of the aviation industry.However,for small features and complicated curved surfaces,manual grinding and polishing are still used for small blades and blade edges.Combined with multi-axis CNC machining technology,it can effectively overcome the problems of poor consistency of manual grinding and polishing,low efficiency,high scrap rate,and long training period of technical personnel.However,it also has the following problems:(1)the equipment cost is high and the processing mode is single;(2)the flexibility is poor,it is difficult to expand the perception function such as vision and force perception;(3)the tool path planning is more Because of the principle of curved surface engagement,it is easy to cause the phenomenon of gnawing at the front and rear edges of the blade;(4)Without high-bandwidth adaptive contact force control,it is easy to cause the blade to be under/over grind,and the surface quality consistency is poor.In response to the above problems,this article uses robots as the equipment body,expands the intelligent grinding and polishing unit and visual detection unit with precise force control,and forms a process closed loop.According to the shape characteristics of aero-engine blade profile,a full-featured tool path planning method for abrasive belt compound wide-line conformal grinding and polishing blade profile is proposed,which not only improves the processing quality of the blade edge area but also improves the profile grinding Toss efficiency.Based on the accurate estimation of the contact environment parameters(position,stiffness,etc.)of the "grinding unit-blade",a precision impedance control with adaptive reference track generation was proposed to achieve precise control of the contact force.The details are as follows:1.The robot blade self-adaptive "machining-detection" system is built.A six-axis industrial robot is used to hold the blade for posture adjustment.The force-controlled grinding and polishing unit is used as the seventh axis to adjust the contact positive pressure and the linear speed of the abrasive belt.The visual inspection technology has formed a process closed loop of " machining-detection".The simulation and experimental verification of the motion modeling of the six-axis robot and the force-controlled grinding and polishing unit were carried out on MATLAB and the assembly prototype.The accuracy of the latter’s transfer function for the system response prediction under the same set of inputs was 98.72%,respectively,98.66%.The coupled seven-axis linkage CNC abrasive belt grinding and polishing system can ensure that the positive contact pressure is consistent with the direction of the main normal of the knife contact,which not only improves the force on the tip of the grinding tool but also ensures that the grinding tool surface is not processed.The interference on the surface provides an important technical guarantee for improving the machining accuracy and efficiency of the blade.2.Path planning for grinding and polishing based on shape of aero-engine blade.Aiming at the shape characteristics of different regions of the blade profile,a tool path planning method for the full-featured abrasive belt composite wide-line conformal grinding and polishing aero-engine blade is proposed: the blade wheel and the blade back adopt the contact wheel type abrasive belt for transverse grinding,using equal residual height method and equal chord height step method to obtain the machining line spacing and machining step length,and carry out the tool path planning;on this basis,the discrete tool contacts obtained on the front and rear edges of the blade are based on the principle of arc fitting curve carry out enveloping wide-row horizontal and vertical mixed grinding toolpath planning.Based on the UG and MATLAB platforms,the simulation examples of the aviation blades are carried out,and the above-mentioned seven-axis CNC platform is used to experimentally verify the high-pressure III blades using the planned tool path.The proposed strategy not only obtains a larger processing bandwidth and step size but also reduces the number of blade contacts by more than 78.8% in the blade edge area and effectively avoids the edge of the blade.phenomenon.3.Machining unit-environmental contact impedance parameter estimation.Based on the fact that the rubber material of the contact wheel and the base material of the abrasive belt is super-elastomers,the non-linear "spring-damping" model that is more in line with the physical reality is selected to drive the contact process of the constrained environment characterized by the polishing unit and the blade.According to the description,an online parameter estimator with double Kalman filter interconnection was designed to realize real-time estimation of contact impedance parameters,and its stability was analyzed.Finally,the simulation and experiment of the parameter estimation and contact force prediction of the high-pressure Ⅲ blades on platforms such as MATLAB and grinding and polishing unit.The results show that the parameter estimator can ensure the estimated value is fast(about 0.2s)and accurately converges to the true value,the contact force prediction error in the stationary phase is less than ±0.15 N,and the contact force prediction error in the moment of speed commutation is not greater than 11.2%,thus providing a solid foundation for the effective design of the desired contact force controller.4.Precise impedance control with reference track adaptive generation.Given the problem that the environmental contact impedance parameters and position parameters are unknown or their a priori knowledge is inaccurate,which will lead to limited force tracking accuracy during processing,which will affect the surface quality and consistency of the workpiece,a precision impedance adaptively generated by reference trajectory is proposed Control Strategy.It integrates environment(contact)parameter estimator,reference trajectory adaptive generator,and motion tracking controller based on optimization function tuning in the basic framework of position-based impedance control.Simulation and experimental verification of the strategy on a sinusoidal curved surface and a high-pressure class III blade show that the optimized impedance control strategy can ensure that the force tracking error is less than ±0.38,and the surface roughness(Ra)of the blade It reaches 0.175μm with good consistency.