Tokyo researchers create forearm with accurate human proportions

In a recent breakthrough highlighted by Interesting Engineering, researchers have achieved a significant advance in robotics by developing a robotic forearm that closely mimics human anatomy.

Researchers have created a robotic forearm designed to replicate human body proportions, weight, muscle configuration, and joint functionality. 

A team from the JSK Lab at the University of Tokyo engineered two muscle motors integrated into a single module, which functions as both the muscle system and the bone structure. This design maximizes space efficiency and incorporates miniature motors, with a system developed to manage heat dissipation through the bone structure.

This innovative approach has resulted in a forearm featuring a radioulnar joint that closely mimics human anatomy and performance. The robotic forearm successfully demonstrated its capabilities by performing tasks such as soldering, opening books, and executing badminton swings, showcasing its ability to replicate human-like movements through the radioulnar structure. In recent years, the field of humanoid robotics has advanced significantly, with early models like ASIMO focusing on mimicking human movement.

Research has since progressed to tendon-driven musculoskeletal robots that aim to replicate human proportions, joint configurations, drive systems, and muscle arrangements. However, while many studies have focused on duplicating human joint structures, the radioulnar joint has received limited attention. 

Existing models with this joint often rely on pneumatic actuators, which present challenges in terms of control and muscle arrangement. Replicating the radioulnar structure of the human forearm—comprising the radius and ulna—presents challenges for robotic design due to muscle arrangement constraints. Previous tendon-driven humanoid robots, such as Kojiro and Kenzoh, faced difficulties achieving accurate joint structures.

To overcome this, researchers developed a new miniature bone-muscle module that integrates two actuators into the bone structure, optimizing space and enhancing proportional accuracy. This module features miniature motors with efficient heat dissipation to maintain high muscle tension, and an ultra-compact tension measurement unit that reduces the overall volume by 39 per cent. 

This innovative approach allows for a linear connection of muscle modules, enabling a more precise and maintainable radioulnar structure in next-generation tendon-driven robots. The human forearm's radioulnar joint facilitates unique movements such as writing, turning doorknobs, and swinging rackets. The newly developed compact forearm uses miniature bone-muscle modules to mimic human proportions, with two modules for the radius and ulna, housing a total of eight muscles. 

These muscles control six degrees of freedom (DOFs), including the radioulnar joint, radiocarpal joint, and finger movements. The compact design preserves accurate body proportions and weight ratios while offering greater muscle-driven freedom compared to other robots. Researchers tested Kengoro, a robot equipped with this human-mimetic radioulnar forearm, in tasks such as soldering, opening a book, turning a screw, and swinging a badminton racket, demonstrating its ability to replicate human-like motion with precision.

The radioulnar joint enabled Kengoro to perform precise, human-like movements, such as steady hand motions with minimal rigidity and effective torque transfer. The angled joint enhanced the range and speed of movements, showcasing its potential for tasks requiring both accuracy and agility. 

Future efforts will center on developing a compact tendon-driven humanoid robot incorporating the newly designed miniature bone-muscle modules, which can be applied to the forearm as well as other robot components. Additionally, researchers plan to investigate the biological significance of the radioulnar joint and identify more refined motions that leverage this joint's capabilities.