Research On Dynamic Characteristics Of Planetary Roller Screw Electromechanical Actuator With Rough Contact Surface Clearance

The electric actuator is the executive component of hypersonic aerocraft.Its dynamic characteristics are significant for hypersonic aerocraft.The planetary roller screw is widely used in new type of electric actuator as the transmission device for its high stiffness,light mass and heavy capacity.However,the transmission model of planetary roller screw is multipoint non-conformal contact,it is hard to establish the dynamic model of planetary roller screw.The small clearances are inevitable in electric actuator because of the machining accuracy and constantly attrition.The electric actuator has very high request of kinematic accuracy.The clearance has great influences on the dynamic characteristics of electric actuator,which makes the modeling accuracy of continuous contact model for the revolute joint clearance to be a key point of electric actuator dynamic modeling.All influencing factors that could be a possible factor affecting the contact force should be considered in the contact model,such as the roughness.This paper takes electric actuator system as the research object.Aiming at the problems of dynamics modeling for planetary roller screw and modeling of contact model for the revolute joint clearance,the dynamics model for electric actuator is established.And the study is carried out based on the dynamics model.The main content of this work include:Aiming at the multipoint non-conformal contact issue of planetary roller screw,the planetary roller screw axial static stiffness is established based on Hertz contact theory and differential geometry.The influences of contact angle,roller number,roller eccentricity and roughness on planetary roller screw axial static stiffness are analyzed.The test rig of planetary roller screw axial stiffness is designed.The model of planetary roller screw axial stiffness is verified.To study the dynamic characteristics of planetary roller screw,the dynamic model of planetary roller screw is established based on the axial stiffness model.The influences of contact angle,roller diameter and roller number on planetary roller screw natural frequencies are studied.The test rig of planetary roller screw dynamic stiffness is set up.The dynamic model of planetary roller screw is verified.Aiming at the issues of lack consideration of contact surface topography on traditional contact model for revolute joint clearance,a new contact model for rough surface revolute joint clearance is set up.The influences of impact velocity,roughness and recovery coefficient are analyzed.And the contact model is introduced to a slider-crank mechanism.Compared the simulation results and experimental results from other researchers with the theoretical results from this paper,the contact model accuracy of this paper is verified.Aiming at the servo electric actuator with the transmission of planetary roller screw,the dynamics model of servo electric actuator with small revolute joint clearance is established.The simulation results show the planetary roller screw enhances kinematic accuracy,stability and response speed of the servo electric actuator system.The influences of contact surface topography and clearance on servo electric actuator dynamic characteristics are studied.The test rig of servo electric actuator dynamic characteristics is set up.The experiments for joint clearances and impact velocities on servo electric actuator are conducted.The experimental results are compared with the theoretical analysis,the theoretical analysis are validated.