Study Of The Loading Performance And Control Of A Friction Based Electro-hydraulic Load Simulator

Aerodynamic electro-hydraulic load simulator(EHLS)is mainly used to simulate the aerodynamic load spectrum acting on the steering engine system of flying aircraft e.g.,missile and fighter,to simulate the real working condition in the laboratory for the steering engine system.Since the performance requirements of the key defense weapons such as missiles,fighters are increasing,the loading performance of the aerodynamic EHLS need to be improved further badly.Since traditional EHLS is rigidly connected with the tested steering engine,therefore the active movement of the steering engine will have strong ineradicable disturbance on the EHLS.The disturbance is the so-called extra torque.The extra torque seriously reduce the performance of the EHLS.To eliminate the extra torque,then improve the overall performance of the EHLS,a friction based high frequency response and high accuracy electro-hydraulic torque loading method is proposed,then a multi friction pair load mechanism is proposed to improve the loading amplitude of the method.Using the method,a friction based electro-hydraulic load simulator(FEHLS)prototype is developed.To validate the feasibility of the method and solve its key problems,then lay a solid foundation for the high performance FEHLS,the main research works are done as follows.First,to validate the feasibility of the method,the control model of the prototype is established and the FEHLS's basic control performance is studied.Under the control of a PID plus feed-forward controller,the FEHLS's loading performance is experimentally studied,the results indicate the method has no extra torque.Besides,the impact of the friction disks' friction coefficient on the FEHLS's loading performance is studied.The results indicate that the friction coefficient uncertainty has quite serious disturbance on the loading performance and should be compensated.To improve the loading performance,the system's uncertain parameters is considered,then a robust H ? controller is designed,the loading simulations and experiments have been carried out under the control of the designed controller,the results indicate the effectiveness of the designed controller and that the control performance of the FEHLS can be improved by a controller with higher control performance.Although the proposed method has no extra torque,as an electro-hydraulic servo system,the FEHLS has strong nonlinearity.To obtain high accuracy control in high frequency,the servo valve's dynamics should be considered,however the spool displacement and velocity cannot be measured by the sensors directly,in addition,the system has uncertain parameters.To improve the FEHLS's control performance further,considering the nonlinearity,the valve's dynamics i.e.,the un-measurable state variables,the uncertain parameters and etc,a nonlinear adaptive backstepping-flatness controller based on an adaptive state observer is designed.The designed adaptive state observer is used to on-line real-time observing the un-measurable state variables of the system with uncertain parameters,based on the observer,an backstepping-flatness controller is designned.The controller's effectiveness is then validated by the simulation and experimental results.In practical control systems especially the nonlinear systems,since the feedback state variables usually measured by the sensors,thus the state variables always contain measurement noise.However,most of the reported nonlinear controllers always have a lot of feedback state variable derivatives and high order derivatives,therefore in practice,those controllers will amplify the measurement noise.The amplified noise will have great disturbance on the systems' control performance.For the FEHLS,especially,for the low frequency,high loading amplitude FEHLS,the current controllers can hardly obtain high loading performance.To suppress the noise amplification and compensate for the uncertain parameters,then obtain high accuracy torque loading for the FEHLS,an indirect nonlinear adaptive flatness controller is proposed.The indirect parameter estimation law with a low-pass filter can suppress the disturbance of the noise on the parameter estimate performance to a maximum extent,based on the estimation law an adaptive flatness controller with no feedback state variable derivatives is designed,then the measurement noise amplification is avoided.The feasibility of the proposed control algorithm is validated by the simulation and experiment results.In order to highly improve the loading amplitude of the FEHLS under compact structure by using the current friction materials,based on the proposed multi friction pair friction disk loading mechanism,a loading mechanism prototype is designed and developed.According to the real working conditions,using the finite element software ABAQUS,the feasibility of the designed mechanism is validated by the simulation results,in addition,through simulation the dynamic thermal-mechanical coupling behavior of the mechanism is studied,the friction heat production characteristics and the impact of friction heat on the force-friction torque conversion performance of the mechanism are analyzed,then provide the theoretical basis for the real torque loading.Using the developed mechanism,the original developed FEHLS is transformed into a multi friction pair FEHLS.Based on the transformed FEHLS,the torque loading experiments are conducted and the experimental results indicate the feasibility of the designed mechanism and that the transformed FEHLS has higher torque loading performance than the traditional EHLS.