Research On End Effector Capturing Dynamics And Its Hybrid Simulation

With the space station of China constructing,robot arm will be used to conplete on-orbit services tasks,such as on-orbit assembly,on-orbit maintence, on-orbit handing.On-orbit capturing is the basis of on-orbit service technology.robot arm is a effective mean to realize on-orbit capture,by the connection with the end effector and the target adapter.The success of on-orbit capturing depends on the reliable work of end effector.Because of high investment and risk for the space activities,on the ground the integrated performance of end effecor is need to be tested and the boundary conditions of successful capturing are checked,before put into use.So simulating the end effector capturing process is necessary.In order to simulate the end effector capturing process,the end effector dynamics model is built in the paper,and then a end effector capturing hybrid simulation system is proposed,based on the model.Its working principle is that the collision force measured by the 6-DOF force sensors are input to capturing dynamics model,and then the relative motion between the end effector and the target adapter which is calculated by the dynamics model,drives the Stewart platform and the target adapter which is fixed on the platform move.About the end effector capturing dynamics and its hybrid simulation,there are the details of research contents as the followings:With analysis the relative motion of the end effector and the target adapter, the end effector capturing dynamics model is respectively based on rigid robot arm and based on flexible robot arm.After verified by simulation,the end effector capturing dynamics model can more accurately describe the relative motion,compared with the model based on rigid robot arm.By the analysis of collison force,the stiffness and damping of robot arm,the mass of the spacecrafts and postion vector effecting the relative motion,and combining with the characteristics of the structure of the robot arm,the effective way to reduce the relative motion is reducing the contact collision force,which have guiding significance to improve the probility of successful capturing.Keeping stable is the primary condition of the end effector capturing dynamics hybrid simulation system.In order to study the stability of system,the model of end effector capturing dynamics hybrid simulation system in 1-DOF is built.Through the analysis of the stiffness and damping of snare cable,the speed gain of the Stewar t platform,the stiffness and damping of robot arm,the mass of spacecrafts effecting the stability of the system,the damping of robot arm will be ignored,in order to simplify the model of hybrid simulation system And then the stable condtion can be get by Routh criterion.After snare cable seeing as the spring_damper,the hybrid simulation system in 1-DOF is built,and then is used to validate the stability condtion of the system.After being verified by simulation,the stability of the system conditions are correct.To successfully build the end effector capturing dynamics hybrid simulation system,the capturing dynamics calulating unit.the servo control unit and motion simulator are detailly designed,and the working process of the hybrid simulation system is researched.According to the preliminary simulation on the virtual prototype, the hybrid simulation system can simulate the process of end effector capturing,but with poor precision.The error of hybrid simulation system is due to the hysteresis characteristics of interface(the interactive media between the real model of end effector and capturing dynamics calculating unit).Through the analysis of the transfer function of interface,when the system working on the hybrid simulation bandwidth,the interface transfer function matrix equal to unit matrix,the error of hybrid simulation system is zero.Lag compensation method is proposed to eliminate interface lag,and the conditions of lag compensation method are given.The simulation of the end effector capturing dynamics hybrid simulation system show that the lag compensation can greatly improve the accuracy of hybrid simulation.To verify the end effector capturing dynamics hybrid simulation system is feasible and the conclusions get by above analysis,the virtual pro totype of the hybrid simulation system is bulit by the ADAMS and Simulink.The simulation results of virtual prototype show that the capturing dynamics unit is correct and the virtual prototype of the system can simulate the process of end effector capturin g,compared to the results of ADAMS capturing model.on the different conditons of capturing initial conditions,the stiffness of robot arm and the mass of spacecrafts,the simultion are run on the virtual prototype. The results shows that end effector capturing dynamics hybrid simulation is feasible, lay the foundation on acutal building of space capturing dynamics hybrid simulation and test research.