| With the function of adjusting the position and attitude,the air rudder system should meet the requirements,such as the high accuracy,fast response speed,good stability,and so on,to ensure that the aircraft has good flying quality during the flight mission.The contact-impact phenomenon appears in the joint due to the existence of the clearance,which is liable to cause the deviations of position and period of the moving links,and the contact-impact force of the joint compared with the expected values.To accurately analyze and predict the dynamic characteristics of the air rudder system with revolute joints,the static and dynamic contact processes in the joints should be analyzed and the dynamic characteristics of the air rudder system should be analyzed based on the mechanism dynamics model considering the joint clearance.Aiming to the common revolute joint in the air rudder system,the static contact characteristics of the revolute joint with a small clearance was researched under heavy load.The mathematical model for the static contact characteristic of the revolute joint was established by both the varying distance between contact points and the elastic deformation of the material: the function of the distance between the contact points which possess the same arc length in the outlines of pin and the hole was established according to the geometrical constraint condition;The elastic deformation function was derived based on elastic foundation model and elastic half space theory respectively.With image measuring technique,the static contact experiment for the pin and the hole was carried out to verify the computational accuracy of the proposed model.The influence of elastic layer thickness on the static contact properties of the shaft and hole was analyzed to obtain the non-linear characteristics of the parameters(such as the semi-contact width,the contact depth,the maximum contact stress)with the increasing external load.The study of static conformal contact characteristics of joints can provide a certain theoretical basis for the dynamic contact characteristics of the joint in the air rudder system.Considering the dissipated energy by the damping of the joint material,the normal dynamic contact force model of the revolute joint was established by fitting the parameters of the proposed static contact force model,which can provide an effective approach to describe the dynamic characteristics of the revolute joint in the air rudder system.The contact-impact process that a free falling pin impacts with a cylindrical groove at the initial speed was analyzed by the dynamic contact force model to investigate the parameters(such as the indentation,the contact velocity and the contact acceleration)as the contact time increases and to obtain the damping,the intial contact velocity and the external force influence on the dynamic contact characteristics of the clearance revolute joint.Considering the friction in the joint,the dynamic model of a simple pendulum with a clearance revolute joint was built to analyze the trajectory of the pendulum and the influence of the friction.The dimension parameters of the rods were optimized based on the principle of the maximum efficiency of the two common connecting rod type air rudder transmission mechanisms.Considering the influence of the joint clearance and the rod flexibility,the analysis method can be presented to effectively evaluate the dynamic characteristics of the air rudder transmission mechanisms: the normal dynamic contact force model was compiled into the multi-body dynamics software;the rods were transformed into flexible bodies by the finite element software,which can be imported into the multi-body dynamics software.The dynamics test platform for the air rudder system was built to carry out the dynamic experiments and the simulations were also executed to verify the dynamic contact force model of revolute joint with a small clearance under heavy load and the effectiveness of the assessment method for dynamic characteristics of the air rudder transmission mechanism.The simulations and verification experiments for the dynamic characteristics of the rudder system were carried out to study the influence rule of the joint clearances and the external loads on the dynamic characteristics of the system.The test platform was established to gain how the clearance and the loads influence on the band width of the air rudder system and the frequency response characteristics can be obtained based on the frequency sweeping method. |
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