New Bio-Inspired Joint Model to Create Better Robotic Exoskeletons

Robotic exoskeletons are a set of different robotic parts that work together to become a wearable shell, with recent technological advancements allowing for more sophisticated and controllable robot parts.

Imitating Arthropods for Better Robot Hinges

Researchers from the Xi'an Jiaotong University in Xi'an, China, have reported the design for a new joint model that could lead to more robust and more stable exoskeletons. With details published in the journal IEEE Access, reports how the design takes inspiration from nature, specifically arthropods - invertebrates mainly characterized by exoskeletons, segmented bodies, and jointed appendages. It includes insects (ants, bees, dragonflies, grasshoppers), arachnids (spiders, scorpions), crustaceans (shrimps, lobsters, crabs), and myriapods (millipedes, centipedes.)

"A common way to realize bionic motion is with an n-bar linkage mechanism within bearings, but the resultant joints can become complex," researchers noted in the paper. "Herein, we propose a joint model based on the anatomy of grasshopper joints that consists of a pair of conjugate surfaces and a flexible connection body."

The particular model detailed in the study takes inspiration from grasshoppers. However, comparative anatomical studies reveal that it is similar to how lobsters and crabs move their appendages, suggesting broad similarities for most arthropods subgroups.

In designing the joint, researchers used an optimization algorithm they also developed to create the prototype joint for robotic exoskeletons. After coming up with a prototype, they tested its performance through a series of experiments to assess its kinematic characteristics.

Researchers used a conjugate surface hinge and a flexible connecting body attached to two parts in their design for the arthropod-inspired joint.

Robotic Exoskeletons: From Industrial Applications to Medicine

Current robotic exoskeletons have their designs based on a fixed-axis rotating hinge as the part that allows movement between the robot parts. Despite proving simple and effective, it remains restrictive. It does not perfectly capture human movements, resulting in a difference between the user's expected movements and the actual movements the robot parts can deliver.

"However, as the rotation axis of human joints is not constant - i.e., it is polycentric - the monocentric rotation model causes inconsistencies between human limbs and the exoskeletons during movement," researchers noted in the paper.

This restriction led to further studies concerning possible alternative joint designs. Among the proposed options include using n-bar linkages to join robotic sections and offering more mobility compared to fixed-axis hinges. However, while it is closer to emulating human movements, its excessive use could lead to loose and often unstable exoskeletal designs. This problem with n-bar linkages makes it unsuitable for rehabilitating patients suffering from injuries, trauma, or paralysis.

The discovery and implementation of more human-like robotic exoskeletons would revolutionize a number of fields. For more industrial applications, exoskeletons have been used to amplify the user's strength and stability in performing physical tasks such as lifting or moving heavy objects. Additionally, research for more sensitive and flexible exoskeletons has been geared towards rehabilitating injuries and paralyzed limbs.