Optimal Design of Ground-Penetrating Robotic Arms Using RFT-Based Ground Resistance Analysis

In recent years, robotic systems, including robotic arms, have been increasingly investigated for lunar and planetary exploration. Robotic arms are particularly important for tasks such as sample collection and subsurface exploration. Since the surfaces of the Moon and Mars are covered with soft granular materials, the design of robotic-arm link lengths that reduce energy consumption while considering ground reaction forces and required motions is important for ground penetration tasks. In this study, ground reaction forces acting on a robotic arm during ground penetration were estimated using Resistive Force Theory (RFT). Based on the estimated reaction forces and the force manipulability ellipsoid, an evaluation index R was introduced to evaluate the actuator load, and a method for determining energy-efficient link lengths was proposed. A two-link robotic arm with the link lengths determined by the proposed method was fabricated and experimentally evaluated. The experimental results showed that the link-length combinations determined by the proposed method exhibited the lowest RMS current for all tested trajectories, demonstrating the effectiveness of the proposed method for determining energy-efficient robotic-arm link lengths.