| Miniaturization and intelligentizing is an important development direction of future unmanned air vehicles(UAVs).The micro air vehicles(MAVs)and smart ammunitions are two representative products developed in recent years.Micro rudder actuator is one of the key technologies in this field.At present,the traditional sub-scale electromechanical actuators are most widely used on UAVs.However,they cannot fit in with the requirements for future miniature UAVs' servo actuators due to their various defects,such as narrow bandwidth,low accuracy,and large number of auxiliary parts and so on.By contrast,piezoelectric smart structures have the advantages of wide bandwidth,high precision,fewer auxiliary parts and high power density,thus have become a promising alternative for UAVs' servo actuators,but the limited strain is a major drawback.Therefore,in this thesis,based on the post buckled pre-compression(PBP)bimorph actuator which can not only increase the output of displacement but also enhance the output torque,the performance of PBP bimorph actuators was studied in detail,including their mechanical behaviors,hysteresis control,etc,and their feasibility of application in guided aerogun bullets and the methods to further improve the actuation performance were also studied systematically.The main contributions and innovations of this thesis are listed as following:1.The static and dynamic characteristics of PBP actuators were studied by theoretical analysis and experiments.It showed that for static cases,the output angle of a PBP actuator would be increased by more than three times and the output torque would be increased by 25% when it is compressed by an axial force being 70% of its critical buckling force.As a result,the design space of bimorphs in enlarged by about four times.For a PBP actuator in dynamic cases,with the increasing axial load,its first order frequency was reduced;the relative damping ratio was increased;and the electromechanical conversion efficiency was improved.With the increasing inertial mass added at the end,the PBP actuator's first order frequency was reduced.2.The rate-dependent hysteresis nonlinear properties of PBP actuators were studied.The model parameters were identified by analytic method and genetic algorithm.On this basis,the parameters of dynamic discrete linear block were obtained by least square method.The Hammerstein rate-dependent hysteresis model was established based on Bouc-Wen model.The sweep and fixed frequency experiments showed that the rate-dependent hysteresis nonlinear characteristics of PBPs can be well predicted by this model.3.Based on the rate-dependent hysteresis feedforward controller,a composite controller,consisting of an adaptive single neural net PID and a feedforward controller,was designed for the linearization control of PBP actuators.Then,displacement tracking experiments of control loop under various single and multi-frequency signals were carried out,showing that controller have a good versatility and the tracking precision meets the engineering requirements well.Besides,the second order transfer function of PBP actuators was obtained through control loop sweep frequency test.Moreover,the change laws of with and without the controller were acquired accordingly.4.The structure of a new-style 30 mm caliber guided aerogun bullet and its PBP actuator subassembly were designed.The static and dynamic performance of the PBP actuator was studied;the aerodynamic characteristics of the bullet were calculated;and the control system of the bullet was designed.The longitudinal plane attitude trajectory simulations of the bullet for maneuvering targets were carried out.The results showed that,the control bandwidth of PBP actuator is large enough for the bullet.In the case of modest maneuvering targets,the bullet could be guided by this PBP actuator to hit the target accurately;however,for the high maneuvering targets,the ability of current PBP actuator is insufficient.5.To further improve the actuation capability of PBP,two schemes of the PBP actuator were proposed,namely the PBP actuator with a connection rod mechanism to magnify output angular and the multilayer PBP actuator to increase output torque.The results showed that the PBP actuators with connection rod mechanism could increase the output angle up to 30°,while the output torque would be decreased;for the multilayer PBP actuators,the output torque could be increased proportionally.Then,for the actuator of guided aerogun bullets,a new-type PBP actuator was proposed by combining the advantages of the above two schemes.Further research on static,dynamic analyses and the longitudinal plane attitude trajectory simulation showed that the new-type PBP actuators could satisfy the requirements for the guided aerogun bullet. |
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