Synchronization of tool tip trajectory and attitude based on the surface characteristics of workpiece for 6-DOF robot manipulator

• Published in: Robotics and computer-integrated manufacturing 2019-10, Vol.59, p.13-27
• Main Authors: Chen, Chin-Sheng, Chen, Shih-Kang
• Format: Article
• Language: English
• Subjects: Attitudes; B-splines; Curve fitting; Degrees of freedom; Feature extraction; Interpolation; Machining; Manipulators; Mathematical analysis; Matrix algebra; Matrix methods; Robot arms; Rotating machinery; Rotation; Surface characteristics; Surface properties; Synchronism; Tool reference trajectory; Tool tip trajectory; Trajectories; Workpieces
• ISSN: 0736-5845; 1879-2537
• DOI: 10.1016/j.rcim.2019.01.016

•Propose a method to extract surface characteristics for B-spline curve fitting.•Reduce the calculation complexity and obtain a smooth fitting curve.•Use the tool tip and corresponding attitude to get the tool reference at each sampling.•Use a rotation matrix and the direction to synchronize the pose with position. This study proposes a method to extract feature points from the surface characteristics according to the machining accuracy of a 6-Degrees-of-Freedom (6-DOF) robot manipulator, which makes the fitting of the B-spline curve easier and decreases the amount of calculation for the approximation process. The tool tip trajectory is defined via B-spline curve fitting. Many robotic controllers use two Non-Uniform Rational B-Spline (NURBS) curves to represent the trajectories of the tool tip and tool axis but these double trajectories are not synchronous. In order to synchronize the orientation with the tool tip trajectory, this study uses a rotation matrix and a machining direction vector to plan the attitude of the tool. Before the attitude is planned, interpolation is used to generate the motion command for the tool tip using the S-Curve feedrate profile. The trajectory of the tool tip is further used to calculate the synchronized tool reference using a rotation transformation. Finally, the tool tip trajectory and the corresponding synchronized tool reference are used to determine the machining position and the orientation information. One of the experimental results shows that the proposed method can simultaneously sustain a 10 μm machining accuracy with a significant decrease in the computation load from 1113 s to 31 s.