The joint‐limits and singularity avoidance in robotic welding

Abstract

Purpose -The aim of this paper is to develop a redundancy-resolution (RR) algorithm to optimize the joint space trajectory of the six-rotation-axis industrial robot as performing arc-welding tasks. Design/methodology/approach -The rotation of the tool around its symmetry axis is clearly irrelevant to the view of the task to be accomplished besides some exceptional situations. When performed with a general 6-degrees-of-freedom (DOF) manipulator, there exists one DOF of redundancy that remains. By taking advantage of the symmetry axis of the welding electrode, the authors decompose the required instantaneous twist of the electrode into two orthogonal components, one lying into the relevant task subspace and one into the redundant task subspace, respectively. Joint-limits and singularity avoidance are considered as the optimization objectives. Findings -The twist-decomposition algorithm is able to optimize effectively the joint space trajectory. It has been tested and demonstrated in simulation. Originality/value -A new RR algorithm is introduced for the six-rotation-axis industrial robot performing welding tasks. A new kinetostatic performance index is proposed on evaluating the kinematic quality of robotic postures. It can also be used in other applications like milling, deburing and many other tasks requiring less than 6-DOF in tool frame.

Integrated sliding-mode algorithms in robot tracking applications

“…laser engraving, where the reference for the tool orientation can be relaxed within a cone of allowable values. 6 The Z -axis of the reference frame is aligned with the first joint of the robot and its origin is located at the same height of the second joint, i.e., the shoulder joint.…”

“…In this sense, this work presents an integrated solution for robotic trajectory tracking based on three sliding-mode algorithms recently proposed by the authors 1 for speed autoregulation [2], path conditioning [3] and redundancy resolution [4] in order to fulfill velocity, workspace and C-space constraints, respectively. These constraints may be due to different reasons such as joint speed limits [5], joint angle limits [6], obstacle collision avoidance [7], etc.…”

Manipulator Performance Measures - A Comprehensive Literature Survey

“…In ( [38], [39]) Baron defined the following objective function to maintain the manipulator joints close to the mid-range position:…”

A supervisory loop approach to fulfill workspace constraints in redundant robots

“…Similar indexes of quadratic forms in the robot configuration q have been considered in the literature together with the robot manipulability [20] or the condition number of the Jacobian matrix [21] in order to avoid singular configurations. Furthermore, a performance index based on artificial potential fields [5] could also be considered to keep the robot away from the obstacles.…”