Vibration Analysis And Control Of Space Deployable Truss Arm

In recent years,due to the gradual complex trend of space missions,the space structures have gradually developed in the direction of large scale and flexiblility.Space deployable trusses are often used as supporting structures for working platforms of spacecrafts due to their light weight and high expansion-to-retract ratio.However,spacecrafts are often affected by external factors such as space gravity gradient,temperature variation and solar light pressure in space environment.In addition,during active working process such as position and attitude changes or space operations,low-frequency vibration of the extended truss structure is easy to be caused,which decays very slowly in space environment with low damping.If the vibration energy is not controlled,it may adversely affect the entire system.In this paper,a concentratedly driven articulated deployable truss containing scissor-like elements that can be used for space support is preliminarily designed.Considering the unfolded and locked state of the truss structure,simplified model is established in ANSYS.And the model of the truss structure is established with the second Lagrange equation based on finite-element-method.Compared with the modal analysis results of ANSYS,the accuracy of the established model is verified.Then the energy criterion is used to preliminarily truncate the modal of the structure,and the number of the controlled modes is determined by the dynamic response performance of the truncated modes under the excitation of external load.In order to suppress the vibration of the truss structure,the piezoelectric ceramic stack and the piezoelectric film(PVDF)are used as the actuators and sensors.The actuators and sensors are mechanically modeled based on the piezoelectric constitutive equation,and combined with the dynamic model of the truss structure,the electromechanical coupling dynamic equation of the intelligent truss is established.The criteria of position optimization of actuators and sensors is constructed using Gramian matrices that can describe the controllability and observability of the control system.The optimization is realized with an improved adaptive genetic algorithm.A linear quadratic(LQR)controller is designed.Through the simulation of vibration control of the structure excited by the external pulse,the effectiveness of the position optimization of the actuators is verified by comparing the control effect of the random-placed actuators with that of the optimized-placed actuators.Considering the process and observation noise,a Kalman filter is introduced to design the LQG controller.Considering the situation where the output voltage of actuators is limited,the control results of simulation show that the excitation of a large load can cause serious control input saturation.In this case,the stability and the efficiency of the control system decrease.To solve this problem,an anti-windup compensator is designed with the linear matrix inequality method.According to the simulation analysis of the vibration control of the structure excited by pulse and periodic load,it is shown that the anti-windup compensator can effectively improve the efficiency of vibration control and the controller is prevented from being in dead zone for a lot of time,which improves the stability of the control system.