Kinematics and Singularity Analysis of an Underwater Electric Manipulator

Abstract

An underwater electric manipulator is a key operational tool for unmanned underwater vehicles. The control of this manipulator demands kinematic models, but for arms of different structures, these models differ. Furthermore, underwater electric manipulators encounter certain singular positions; at these positions, minor changes at the manipulator's endpoint may yield substantial alterations in joint positions, potentially causing damage to the manipulator. Therefore, avoiding these singular positions in control is crucial. This paper focuses on an underwater electric manipulator and utilizes an enhanced Denavit-Hartenberg parameter method to derive forward and inverse kinematic equations, establishing its kinematic model. The Jacobian matrix of the manipulator was calculated, followed by an analysis of the manipulator's singular positions, using the condition number to gauge the current operational status of the manipulator's joints. Simulation experiment results demonstrate that the kinematics model developed in this study accurately calculates endpoint poses based on joint positions and inversely determines joint positions based on endpoint poses. As the manipulator nears singular positions, the condition number exponentially increases, indicating its effectiveness as a tool in avoiding these singular positions of the underwater electric manipulator.

Keywords

• underwater electric manipulator
• forward kinematics model
• inverse kinematics model
• jacobian matrix
• singularity
• condition number