| Surface strengthening of Aero-engine blades is very important,it can not only improve the working life and work efficiency of the engine,but also improve the aviation safety of the aircraft.The titanium alloy material of the aviation blade has the characteristics of high specific strength,so it needs ultrasonic strengthening transducer with large amplitude and stable output.In addition,in order to achieve the improvement of the automation level of ultrasonic strengthening and the high-precision strengthening of the aviation blade surface,the industrial robot need to be used to load strengthening devices to automatically complete the process.In addition,the industrial robot need specific motion planning and compliant control of contact force during operation.The research content of this paper includes four parts.(1)The development of ultrasonic surface strengthening transducer that provides large amplitude output.As for the ultrasonic strengthening of the TC4 titanium alloy,transducers shall be needed to provide continuous and large amplitude and stable output.Rare-earth giant magnetostrictive materials can replace the piezoelectric ceramics to develop ultrasonic transducers.And With Terfenol-D rod as the core element of composite vibrator,the ratio of front and rear vibration velocity and vibration stability can be improved.After the modal analysis of the composite vibrator,the natural frequency with good vibration mode and large amplitude output have been obtained.At the same time,the finite element magnetic field analysis of the rare-earth giant magnetostrictive transducer has verified the closed overall magnetic field and reasonable distribution.After testing,it can be found that under the condition of 20 k Hz and square wave,the amplitude of 11.3?m can be output.The surface quality distribution of the strengthening area is uniform,which can reflect the continuous and stable output of the effective amplitude of the transducer.(2)Robotic motion planning based on dynamic response of ultrasonic enhancement surface.On the one side,the dynamic response model of TC4 titanium alloy ultrasonic surface enhancing has been constructed,and the information of tool head movement state and pressing depth in the strengthening process has been obtained.On the other side,based on this response model,the path points of ultrasonic enhancing on aviation blade surface are reasonably extracted.And the overall path distribution can be adaptively adjusted with the blade surface curvature,which can not only ensure the strengthening quality but also improve the efficiency.In order to achieve the description of the pose of the tool head in the robot task space,the joint kinematics model of the robot and the end ultrasonic strengthening device has been established,and the quaternion spherical interpolation method has been used to construct a smooth pose trajectory of the tool head.The simulation results show that the robotic motion planning method is suitable for the ultrasonic strengthening of the aviation blade surface.(3)Compliance control of contact force for robotic ultrasonic surface strengthening.After the position control and force control of the robot has been decoupled,the intelligent control method is adopted to control the output force of the compliant force control device,and the problem of constant contact force control under multi impact and vibration conditions can be solved.The time domain method has been adopted to identify the parameters of the compliant force control system model so as to obtain the experimental measurement model.The fuzzy PID controller and RBF neural network have been combined to control the output contact force of the compliant force control device.The controller is adaptive and intelligent,and the regulation performance and follow-up robustness of the system has been improved.The compliance control strategy can realize the control optimization of the compliance device,thereby effectively improving the static and dynamic characteristics of the compliance controller.(4)The experiment of robotic ultrasonic surface strengthening for aviation blades.After the analysis of the response function,control accuracy and following robustness of the compliance force control system,the fuzzy RBF neural network PID control method can be verified to effectively improve the response performance of the output force of the compliance force control device and the dynamic characteristics of the system,so as to realize the high-speed regulation of the system.The experimental method of Response Surface Methodology(RSM)has been designed,and the interaction of the main process factors on the surface roughness and surface hardness has been studied.The optimal combination of processing parameters has been obtained from the experimental results.After robotic ultrasonic strengthening,regular and uniform strip-texture is formed on the surface of titanium alloy blade.And the surface roughness of blade is reduced from Ra 2.7 ?m to about Ra 0.8 ?m,the surface hardness is increased from 585 HL to about 672 HL.The maximum residual compressive stress on the blade surface can reach 841 MPa,and the depth of the compressive stress layer is close to 1.2 mm.Therefore,it provides a feasible reference for the practical application of robotic motion planning and compliance control technology for ultrasonic strengthening of aviation blade surface. |
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