Kinematic Accuracy Analysis Of Youbot And Experimental Research Based On The Exponential Product Formula

With the development of science and information technology,in the field of aviation,medical and electronic product manufacturing,people pay more attention to the accuracy and size of the robot.In the manufacturing process of industrial production,the high precision of the robot determines the quality of the process product.Robot as the main body of production,by the influence of various factors,such as environment change,assembling deformation,gear transmission,wear and tear,and resulting the nominal value of the internal geometric parameters of the robot can’t accurately express end position of the actual robot and the relationship between the various joints.Therefore,the robot’s kinematics parameters need to be calibrated regularly.nowadays,robot model is used on the market,mainly using D-H model calibration method,although this method is easy to implement,the D-H model does not have the characteristics of integrity,continuity,parameter minimality,with great impact on the performance of the robot operation.Besides,the realization and application of parameter calibration methods are also restricted when the kinematics parameters are identified.This paper,begining with the theory of spin,reveals the essential properties of robot movement,which is an effective complement to classical methods.The exponential modeling approach is a good way to overcome these shortcomings.Therefore,based on Kuka-Youbot robot,which is in the laboratory of nanjing university of posts and telecommunications,robot error distribution problems and calibration methods for the robot error sources are developed in this paper.The main research contents are as follows:First of all,based on the theory of lie algebra,mechanical arm kinematics relationship is described.it sets up robot kinematics characteristics for the five degrees of freedom for joint type with a global exponential product and local exponential product to improve the index kinematic error model of product.Secondly,the robot kinematics model is applied to the robot kinematics error distribution,using the global exponential product,the local exponential product and the improvement exponential product.Then based on the kinematic relationship,the Jacobi matrix is established,and numerical simulation is carried out by matlab.It is concluded that the first-order linear error of composition and the influence of the second order error component.Thirdly,based on the traditional parameter calibration method,the corresponding homogeneous transformation error model was established using the POE kinematic model.And the space between two points of distance error is defined to describe absolute positioning accuracy at the end of the robot actuator,integrated the homogeneous transformation of kinematic error model is established,deduced the kinematic calibration model based on distance error.With singularity phenomenon of Jacobi matrix in the process of identification,QR decomposition and schmidt orthogonal method are used for redundancy parameter modification.Finally,it is realized for all parameters identification.Finally,in the experimental part of the project,the method of measuring each joint markers is adopted by the OKIO scanning machine.The 3d scanner can guarantee the accuracy of measurement to industrial level of micron level.To ensure the accuracy of the data acquisition,the end poses are analyzed before and after the calibration.In the process of experiment,due to the 3d scanning instrument can only determine the relative position of marked points,and the 3d scanner measurement range is small,it needs to be repeatly measured.the coordinate system should be transformated.In order to accurately express the space position of the robot end point relative to the robot coordinate system,it will be collected into the distance error model of robot pose information for identification.In the end,calibration experiment is carried out for Kuka-Youbot robot,the results show that the absolute and repeated precision is obviously increased with the improved method of direct identification method,the calibrated robot could be meeting the industrial requirements.