Development of Underactuated Geometric Compliant (UGC) Module with Variable Radial for Robotic Applications

TL;DR

This work addresses the challenge of creating underactuated, compliant robotic modules capable of reshaping their geometry while using few actuators. It develops a library of semi-rigid geometric joints fabricated with easy-to-print PLA, characterized by stiffness and recovery behavior; it then employs Gaussian Process Regression to model stiffness $F_b$ and return angle $\theta_r$ as functions of thickness $T$ and bend angle $\theta$, and validates these models on a circular, multi-joint module. A five-section ring actuated by a single motor achieves radius reduction to 80-85% of the original, guided by torque and geometry considerations. The study highlights design trade-offs, limitations of the current GP data range, and prospects for integrating UGC into snake-like robots and varied materials.

Abstract

This paper introduces a novel underactuated geometric compliant (UGC) robot and investigates the behaviors of underactuated compliant modules with variable radial stiffness, aiming to enhance the versatility and functionality of UGC robots. We initiate the study by designing and fabricating various compliant semi-rigid geometric joints, each tailored to a specific design objective. These joints undergo physical testing to validate their stiffness characteristics and returnable angles as durability factors. Subsequently, we develop a mathematical model based on Gaussian process regression to incorporate the different geometric joint characteristics, including thickness, facilitating the development of fully functional prototypes with easy-to-3D print models. After analyzing individual joints, we present various configurational combinations to construct the overall UGC module for robotics applications. Our final prototype UGC can dynamically alter its radius, reducing to 80-85\% of its original value while maintaining structural integrity and operational efficiency. This study discusses potential abilities, challenges, and limitations associated with employing UGC modules, offering valuable insights for future research and developments in UGC robotics.

Figures (14)

• Figure 1: Series of designed geometric compliant joints.
• Figure 2: (a) The measurement of each joint for testing stiffness and return angle,(b) The force (blue line) and return angle (red line) versus the deformation angle for the straight joint.
• Figure 3: The force (blue line) and return angle (red line) versus the deformation angle for $T=$ 0.4 mm curve joint.
• Figure 4: The force (blue line) and return angle (red line) versus the deformation angle for $T=$ 0.8 mm curve joint.
• Figure 5: The force (blue line) and return angle (red line) versus the deformation angle for $T=$ 1.6 mm curve joint.