Patterned Structure Muscle : Arbitrary Shaped Wire-driven Artificial Muscle Utilizing Anisotropic Flexible Structure for Musculoskeletal Robots

TL;DR

This work introduces Patterned Structure Muscle (PSM), a flexible, wire-driven artificial muscle designed for musculoskeletal robots that can realize diverse shapes and operate under environmental contact. By embedding a sparse anisotropic lattice inside a TPU pattern and routing wires through a defined path, PSM achieves controlled contraction via bending and compression deformation phases, enabling simple 1-DOF, multi-DOF, joint-covering, and branched muscles. The authors fabricate four PSM shapes and an upper-arm assembly, demonstrating 10 kg lifting, robust performance under contact, and coordinated multi-muscle motion across eight postures. The approach is scalable and fabrication-friendly through FDM 3D printing, with potential extensions to tactile sensing and humanoid robots that move more naturally in complex environments.

Abstract

Muscles of the human body are composed of tiny actuators made up of myosin and actin filaments. They can exert force in various shapes such as curved or flat, under contact forces and deformations from the environment. On the other hand, muscles in musculoskeletal robots so far have faced challenges in generating force in such shapes and environments. To address this issue, we propose Patterned Structure Muscle (PSM), artificial muscles for musculoskeletal robots. PSM utilizes patterned structures with anisotropic characteristics, wire-driven mechanisms, and is made of flexible material Thermoplastic Polyurethane (TPU) using FDM 3D printing. This method enables the creation of various shapes of muscles, such as simple 1 degree-of-freedom (DOF) muscles, Multi-DOF wide area muscles, joint-covering muscles, and branched muscles. We created an upper arm structure using these muscles to demonstrate wide range of motion, lifting heavy objects, and movements through environmental contact. These experiments show that the proposed PSM is capable of operating in various shapes and environments, and is suitable for the muscles of musculoskeletal robots.

Figures (16)

• Figure 1: The overview of this study: On the left, the structure of PSM, the process of making PSM using 3D printing, and the four types of PSM are shown. On the right, the upper arm structure driven by PSM is shown.
• Figure 2: Comparison between human muscle structure and the concept of PSM. While human muscle maintain their shape through the integration of small actuators during movement, PSM realizes similar movements through the combination of wire and flexible pattern structure.
• Figure 3: The three directions of characteristics required for PSM. In x-direction, flexibility and range of motion are required to realize contraction. In y-direction, strength is required to support the structure and allow x-directional contraction in the presence of external load. In z-direction, a certain degree of strength is required to maintain the positional relationship of wire and structure.
• Figure 4: PSM is composed of the following four structures: 1. inner pattern structure, 2. outer structure, 3. wire path, and 4. end points.
• Figure 5: The inner pattern structure of PSM utilize the lattice structure. (a) illustrates the unit structure, (b) illustrates the deformation during compression, and (c) shows actual images of the deformation.