Human Mimetic Forearm Design with Radioulnar Joint using Miniature Bone-Muscle Modules and Its Applications

TL;DR

This work tackles the challenge of creating a human-like forearm with a radioulnar joint that preserves body proportion, weight balance, muscle arrangement, and joint performance within a compact, maintainable hardware design. It introduces miniature bone-muscle modules that integrate dual actuators with the bone structure and employs heat-dissipation strategies to sustain high tension, enabling a radioulnar forearm on the Kengoro humanoid. The authors demonstrate a four-module, eight-muscle forearm capable of multiple DOFs and show skillful motions such as soldering, page-turning, screw-turning, and rapid badminton swings that leverage the radioulnar geometry, including a slanted axis for extended reach and speed. The results indicate that the approach can yield high-DOF, human-mimetic actuation with improved maintainability, suggesting a path toward small tendon-driven humanoids and broader deployment of miniature bone-muscle modules.

Abstract

The human forearm is composed of two long, thin bones called the radius and the ulna, and rotates using two axle joints. We aimed to develop a forearm based on the body proportion, weight ratio, muscle arrangement, and joint performance of the human body in order to bring out its benefits. For this, we need to miniaturize the muscle modules. To approach this task, we arranged two muscle motors inside one muscle module, and used the space effectively by utilizing common parts. In addition, we enabled the muscle module to also be used as the bone structure. Moreover, we used miniature motors and developed a way to dissipate the motor heat to the bone structure. Through these approaches, we succeeded in developing a forearm with a radioulnar joint based on the body proportion, weight ratio, muscle arrangement, and joint performance of the human body, while keeping maintainability and reliability. Also, we performed some motions such as soldering, opening a book, turning a screw, and badminton swinging using the benefits of the radioulnar structure, which have not been discussed before, and verified that Kengoro can realize skillful motions using the radioulnar joint like a human.

Figures (16)

• Figure 1: Forearm of Kengoro, composed of newly developed miniature bone-muscle module.
• Figure 2: Details of the newly developed miniature bone-muscle module.
• Figure 3: General versatility of the newly developed bone-muscle module. Left: various arrangements of ultra tiny tension measurement unit. Right: various connections of muscle modules.
• Figure 4: The principle of ultra tiny tension measurement unit. Left: the principle of tension measurement. Right: the result of calibration.
• Figure 5: Comparison of motor heat transition, with and without heat transfer sheet. 20 [kgf] and 40 [kgf] weights are lifted with the newly developed miniature bone-muscle module.