The Kinematic Parameters Identification Of Constant Velocity Spherical Wrist Based On Dual Numbers

Robots are widely used in field of manufacture,medical treatment,rescue,services and space exploration,which have a profound impact on the development and progress of human society.Robot wrist is the key component that connects the manipulator and the end-effector.In order to adapt to the development of high-performance robots,the robot wrist should have the feature of high flexibility,high precision,miniaturization,strong torque and modularization.Since during the process of manufacturing,assembling and working of the robot wrist,there will be errors which could lead to the change of kinematic parameters and model,affects the wrist and even the overall positioning accuracy of the robot.The aim of this paper is to identify the kinematic parameters of the constant velocity spherical wrist whose structure is compact and closed,and the kinematics parameters are difficult to be determined.An identification method based on dual numbers is proposed,which can identify the kinematic parameters of the wrist based on the end trajectory of the wrist,achieve the accurate kinematic parameters.The main research contents are as following:Firstly,the error of the constant velocity spherical wrist is analyzed.The kinematic model is built with geometrical method according to the wrist structure,and solves the working space of wrist Monte Carlo method.The joint errors of the wrist were analyzed.The influence of the errors on the positional accuracy of the wrist end was analyzed separately based on whether the wrist meets the structure decoupling condition.The meaning of the constant transmission and decoupling feature and the requirements of an identification method are insured.After that,the identification method of kinematic parameters based on dual numbers are proposed.The concept of dual numbers and Plücker coordinates are introduced.Based on the spatial circle recognition method,the Plücker coordinates of the position of the joint axis are obtained according to the end trajectory of the wrist.The spatial linear relationship is determined with dual numbers.Based on the specific definition of the standard DH parameters and the modified DH parameters,the kinematic parameters and link frames identification process of two models based on dual numbers are discussed.The fifth parameter introduced by Hayati is identified considering the problem of approximate parallel of the adjacent axis of the robot.The correctness of the above method is verified by Puma560 robot model in the MATLAB environment.Finally,a simplified model of the wrist is built in the Inventor,the possible errors of constant velocity spherical wrist are simulated and the end trajectories of the wrist are obtained.The identification method based on dual numbers is implemented to identify the kinematic parameter,which proves the validity and the adaptability to the wrist.