| Industrial robot has become an important part of modern industrial automation production equipment because of its excellent performance,especially in automobile,electronics,food packaging and other industries.The absolute and repetitive positioning accuracy of robots are important guarantees of robots' working accuracy,improving the working accuracy of robots is of great significance to the development of industrial automation and intelligence.This paper takes SCARA robot as an object,and studies the influence of rotating joint error on the accuracy of robot end positioning.It is of great significance to improve the working accuracy of robots.The main research contents are as follows:(1)The error analysis model of robot rotary joint is established by analyzing the structural characteristics of the robot's rotary joint.Regarding the rotation joint motion of the robot as six-degree-of-freedom motion between rigid bodies,the relationship between the spherical image curve and waistline and the geometric axis of the robot joint motion is discussed by introducing the spherical image theory and waistline theory of linear discrete trajectory of space motion,and the solution method of joint motion axis is given.the working clearance of the rotary joint is further analyzed,and the solution method of the clearance extremum is given.(2)The influence model of joint error and joint clearance on end positioning of SCARA robot.Firstly,the kinematics model considering the geometric axis error of revolving joint is established.Secondly,considering the randomness of joint clearance size and direction,a Monte Carlo model of the relationship between joint clearance and repetitive positioning accuracy of the SCARA robot is established,the distribution of repetitive positioning accuracy of the end of the robot under the influence of multi-variables is analyzed.This relationship can provide constraints for joint clearance allocation in the design of repetitive positioning accuracy for robots.(3)Then,the experimental study on the errors of rotary joint,joint clearance and the end-repetitive-positioning of robot is carried out.The errors of SCARA robot rotary joints are measured innovatively with double-ball artifact.Firstly,taking the kinematics model of the measuring device as basis,the principle of measuring six-degree-of-freedom motion parameters of rotary joint is expounded.Then,a method for measuring the joint clearance of SCARA robot with single-ball-bar is presented.It is proved that the installation error of the ball-bar and the joint structure error have no influence on the measurement results.The clearance of the robot's rotary joint and the repetitive positioning accuracy is measured by a single-ball-bar.(4)The effects of joint errors on the absolute and repetitive positioning of the end of the robot are analyzed based on the experimental data.There are fixed errors between the rotation axis and the theoretical axis of the joint,which will result in regular position errors of the end.The influence of joint clearance on the accuracy of the end can not be ignored.In the design of the repetitive positioning accuracy of the robot,the joint clearance can be constrained by the accuracy to guide the design and assembly of robot. |
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