Nowadays, businesses cannot work without stationary robotic systems. Nevertheless, people also want helpful and collaborative robots that can work in both organized and unstructured settings. Animals do well in these kinds of places in part, because they have embodied intelligence, which means that their bodies have changed over time to do certain jobs. Forty years ago, the metallic Raibert Hopper was the first machine to use legs for moving around. Robots with legs today are made up of rigid metal frames with separate links. These systems can already walk on rough surfaces, like hiking trails in the mountains, and electromagnetically powered platforms with legs are being used to keep an eye on high-security areas. However, systems with legs still are not as flexible and quick moving as animal systems.
In the pursuit of creating versatile robots capable of navigating unstructured environments, researchers at ETH Zurich and the Max Planck Institute for Intelligent Systems have developed an innovative robotic leg design that takes inspiration from the musculoskeletal architecture of animals. This groundbreaking study, led by Thomas J. K. Buchner, Toshihiko Fukushima, and Robert K. Katzschmann, introduces a bio-inspired leg driven by antagonistic pairs of electrohydraulic artificial muscles, offering a new paradigm in robotic locomotion.
Conventional legged robots, while capable of traversing uneven terrains, often struggle to match the agility and adaptability exhibited by animals in natural environments. To address this challenge, the researchers hypothesized that musculoskeletal robots powered by electrohydraulic artificial muscles could pave the way for a new class of versatile robots capable of navigating and operating in unstructured natural environments.
The key innovation of this robotic leg lies in its use of antagonistic pairs of electrohydraulic muscles, which replace the traditional electromagnetic motors and rotational encoders found in conventional legged systems. These artificial muscles, known as Peano-HASEL (hydraulically amplified self-healing electrostatic actuator), contract linearly and can self-sense their contraction state, providing inherent proprioception without the need for joint angle encoders.
The researcher Christoph Keplinger, emphasizes the significance of this design, stating, “The electrohydraulic leg features a low cost of transport (0.73), and while squatting, it consumes only a fraction of the energy (1.2 %) compared to its conventional electromagnetic counterpart. Its agile, adaptive, and energy-efficient properties would open a roadmap toward a new class of musculoskeletal robots for versatile locomotion and operation in unstructured natural environments.”
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The robotic leg, named PELE (Peano-HASEL driven leg), consists of a carbon fiber backbone with 3D printed joints (hip and knee) and four sets of electrohydraulic artificial muscles attached via tendons. The tendon routing over each joint creates a nonlinear moment arm, resulting in a suitable torque output from the contracting muscles.
One of the key advantages of PELE is its inherent adaptability, which allows it to hop over various terrains using only open-loop force control. Thomas J. K. Buchner the lead authors of the study, explain, “PELE also exhibited tunable stiffness via voltage regulation and inherent adaptability, which allowed it to hop over grass, sand, gravel, pebbles, and even larger rocks using only a single set of open-loop force control commands.”
In addition to its adaptability, PELE displays impressive agility, capable of performing powerful and agile gait motions beyond 5 Hz, linear motions beyond 10 Hz, and high jumps up to 40% of the leg height. The researchers also demonstrate PELE’s energy efficiency, with a low cost of transport ranging from 1.79 to 0.73 depending on the type of locomotion, outperforming most systems based on electromagnetic motors. Furthermore, PELE utilizes its capacitive self-sensing capabilities to detect and overcome obstacles by switching its actuation mode. This feature allows the leg to hop on varying terrain using its inherent proprioception without relying on joint angle encoders.
The development of PELE represents a significant step forward in the field of legged robotics, opening up new possibilities for versatile and efficient locomotion in unstructured environments. As Robert K. Katzschmann aptly states, “The electrohydraulic leg features a low cost of transport (0.73), and while squatting, it consumes only a fraction of the energy (1.2 %) compared to its conventional electromagnetic counterpart. Its agile, adaptive, and energy-efficient properties would open a roadmap toward a new class of musculoskeletal robots for versatile locomotion and operation in unstructured natural environments.”
With its impressive performance in agility, adaptability, and energy efficiency, PELE represents a significant advancement in the quest for creating robots that can navigate and operate in natural environments with the same ease and versatility as animals. The innovative use of electrohydraulic artificial muscles and the bio-inspired musculoskeletal design have the potential to revolutionize the field of legged robotics, paving the way for a new generation of versatile and efficient robotic systems.
For citation visit: https://doi.org/10.1038/s41467-024-51568-3
