Research On Multi-Harmonic Active Control Of Helicopter Fuselage Vibration Driven By Piezoelectric Stack Actuators

The vibratory loads of helicopter are mainly form the rotor exciting loads which are forces in three directions and moments in three directions containing harmonics at rotor hub center.Those vibratory loads transfer to the helicopter fuselage and can cause large,steady and harmonic vibration responses at fuselage.Many approaches have been adopted to minimize the vibration of helicopter fuselage,in which active vibration control based on fuselage has better vibration reduction performance,better adaptability and no influence to rotor aerodynamics,therefore has become the most promising way for helicopter vibration reduction.The two cores of active fuselage vibration control are high-performance control algorithm and efficient actuators.The control algorithm should be able to accommodate the complex vibration environment of helicopter and have good adaptability.Actuators are required to have light weight,fast response speed,large actuating force and the feasibility to install.Piezoelectric Stack Actuator(PSA)has large output force,rapid response speed,wide working frequency and light weight,therefore has become a promising actuator for active control of helicopter fuselage vibration.According to the characteristics of helicopter vibration,a Multi-Input Multi-Output and MultiHarmonic(MIMOMH)feed-forward adaptive filtering algorithm is presented in this paper by combining harmonic coefficient identification based on Least Mean Square(LMS)algorithm and adaptive filtering control algorithm.And a new method for MIMOMH active control of helicopter fuselage vibration driven by PSAs is established.By using a frame structural model scaled from the Z-11 helicopter fuselage floor structure which has a similar dynamic character as Z-11 helicopter fuselage,simulations are conducted under various excitations.The simulation results indicated that the MIMOMH adaptive filtering algorithm can achieve more vibration reduction effect than filtered X-LMS algorithm when controlling multi harmonic vibration and good adaptability to the changes of phases,amplitudes and frequencies of vibration.The results indicate that the presented algorithm is very suitable to control the complex multi harmonic vibration of helicopter fuselage.To verify the performance of the algorithm comprehensively,a PSAs driven active control experimental system of helicopter fuselage vibration is established to conduct experimental investigations.In the experimental system,the experimental object is a manufactured experimental frame model scaled form Z-11 fuselage floor structure,PSAs are integrated into the structure of experiment object,and a Digital Signal Processor(DSP)is used as the controller.MIMOMH feed-forward adaptive filtering algorithm is compiled in the controller of the control system and active vibration control experiments are conducted.The results show that the MIMOMH adaptive filtering algorithm have better vibration reduction effect than filtered X-LMS algorithm when controlling multi harmonic vibration.The results also show that the presented algorithm has good adaptability and can follow the variations of real measured acceleration response of helicopter,therefore is an ideal algorithm for active control of helicopter fuselage vibration.The results also illustrated that PSA can satisfy the unsteady and multi-harmonic requirements of helicopter vibration control,thus is an efficient actuator for active control of helicopter fuselage vibration.The hysteresis nonlinearity of piezoelectric material will lead to the unsynchronization between the actuating voltage and output displacement of the PSA.When PSAs are used as the execution units of active vibration control,higher harmonic vibration response will be produced at the controlled structure,worsening the control effect.Therefore the hysteresis nonlinearity of PSA should be compensated.The usually used model based hysteresis compensation methods have difficulty to precisely compensate the asymmetric nonlinearity of piezoelectric actuator,and very few investigation focus on PSA’s nonlinearity when actuated by multi harmonic signals.Neural network has strong fitting ability for nonlinear system,and has data-driven adaptability and generalization ability,therefore is a very suitable for modelling and compensating the hysteresis nonlinearity of PSA.In order to eliminate the influence of hysteresis nonlinearity of PSA on active control of helicopter fuselage vibration,a hysteresis nonlinear model and a hysteresis compensation model of PSA has been presented based on neural network in this paper.Through the experiments,the PSA’s driving voltages and output displacement under the excitation of two harmonic signals with the same harmonic frequency and various total amplitude,amplitude ratio and phase difference are acquired to train the neural networks of hysteresis model and compensation model,enabling the hysteresis model and compensation model to fit and compensate any two harmonic actuating signals with the same harmonic frequency.The results of nonlinearity compensation experiments show that the nonlinear compensation neural network can well compensate the hysteresis nonlinearity of PSA and have good adaptability.By integrating the compensation neural network into the controller of the PSAs driven active vibration control system,the active vibration control experiments with PSA nonlinear compensation are conducted.Experimental results show that the proposed compensation method can improve the vibration reduction effect of PSA driven active helicopter vibration control and have good adaptability to the vibrations of various total amplitude,amplitude ratio and phase differences.