Abstract
The kinematic reliability of robots, defined as the probability that the end-effector falls inside the specified safe boundary, is of great significance in predicting the accuracy achieved in reality. This work selects the 7 degrees-of-freedom (7-DOF) redundant robot as an example to conduct reliability analysis by utilizing the envelope method against time-related issues in this work. Since variables in industrial robots are very small relative to their means, the motion error functions are commonly linearized by the first-order Taylor’s formula to simplify calculation, and the failure models in all directions and attitude angles are then established through the probability method over the entire input interval. As a result, the actual accuracy of the robot in each pose component will be displayed, instead of merely considering the position error like other scholars. The principle of the proposed method is to transform a time-dependent problem into a time-independent one with the help of the failure extreme points and endpoints, so as to enhance the operation efficiency under the premise of ensuring accuracy. Finally, the simulation results verify that the relative error of the envelope method is less than 6.0% compared with that of the Monte Carlo simulation method, and the computational efficiency is higher than that of the Monte Carlo method, which demonstrates that the envelope method has better comprehensive performance.
Highlights
Industrial robots are critical components of modern manufacturing because they offer low production costs, high stability, and high efficiency [1–3]. e 7 degrees-of-freedom (7-DOF) redundant robot serves as a current research hotspot, famous for its tremendous flexibility in completing multiple tasks like avoiding singularity, avoiding obstacles, and optimizing pathways
Since errors universally exist in the manufacturing, assembly, and joint rotation processes [4,5], the actual pose of the end-effector may differ from the predetermined one where the precision is in perfect condition. erefore, kinematic reliability, which is widely used in mechanical structures, is proposed as a method of uncertainty evaluation to quantify the impact of multiple factors on accuracy
For the inverse kinematics of 7-DOF redundant robots, studies have shown that some algorithms can make the pose of the manipulator almost identical to the ideal state
Summary
Industrial robots are critical components of modern manufacturing because they offer low production costs, high stability, and high efficiency [1–3]. e 7-DOF redundant robot serves as a current research hotspot, famous for its tremendous flexibility in completing multiple tasks like avoiding singularity, avoiding obstacles, and optimizing pathways. Intelligent welding work performed by robots in conjunction with vision systems has been progressing apace in recent years [9], whose kinematic error can be effectively predicted based on the reliability theory. Pendey and Zhang [25] effectively computed the fluctuation range around the intended motion, and the probability density function of the extreme value distribution points is derived in terms of the principle of maximum entropy Whereas this method requires a large amount of sample data, its stability may be insufficient for widespread adoption. E main contributions are threefold: (1) compared with planar mechanisms or 6-DOF manipulators, the 7-DOF redundant robot involves more input variables and higher coupling in motion function, whose time-dependent reliability problem has not been studied yet. Kinematic Reliability Model e kinematic reliability of a robot can be defined as the probability that the actual output trajectory of its end-effector in the specified interval falls within the allowable error
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