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The field of robotics has come a long way since Hanson Robotics' Sophia was activated back in 2016. Now we have humanlike and expressive robots such as Engineered Arts' Ameca and the Russian robot Alex. But we also have animal-like robots, such as AIRO's AI fish MIRO which can swim in water, and Hengbot's robotic dog Sparky which has musculoskeletal limbs.

Now, a group of researchers from DePaul University in Chicago have developed a soft-limbed robotic seal by studying the locomotion of pinnipeds. Pinnipeds are a group of marine mammals, such as sea lions and seals, which use flippers for movement.

Soft-limbed robots can perform several tasks that traditional robots can't, such as maneuvering through narrow spaces and handling delicate objects. Additionally, they are more adaptable to changing environments as they can tolerate falls which makes them safer to work with around humans.

Due to these advantages, they have several potential applications, such as surveillance, search and rescue, and deep-sea or planetary exploration. However, the current technology has many drawbacks, such as restricted payload, low limb dexterity, minimal gait trajectories, and limited degrees of freedom.

Dimuthu D. K. Arachchige et al./arXiv

The researchers were motivated by these drawbacks to build a soft-limbed robot inspired by the movements of pinnipeds. Their robot has two front limbs and one hind (or back) limb for terrestrial movement, like walruses, sea lions, or seals.

Each of the robot's limbs is 9.5 inches (~ 24.1 cm) long and 1.5 inches (~ 3.8 cm) wide, driven by pneumatic muscle actuators (PMAs). PMAs are soft, flexible devices that use pressurized air to generate movement and are inspired by the structure and function of biological muscles.

The limbs of the robot seal can be filled with liquid to make them stiff and then drained to make them more flexible. This is how it moves and changes directions. The entire structure is covered by a strong shell and backbone to protect it.

The exact movements of the soft robot can be seen in this video shared by the study's first author Dimuthu D. K. Arachchige.

As can be seen, the soft-limbed robot shows many different gaits, including forward and backward crawling, leftward and rightward crawling & turning, turning in place (both clockwise and anti-clockwise), and aggressive turning in both directions.

This wide range of movements allows it to jump over uneven terrain and jump over obstacles, which traditional robots based on four-legged creatures can't do. The researchers plan to work on dynamic gaits in the future.

Study abstract:

Legged locomotion is a highly promising but under-researched subfield within the field of soft robotics. The compliant limbs of soft-limbed robots offer numerous benefits, including the ability to regulate impacts, tolerate falls, and navigate through tight spaces. These robots have the potential to be used for various applications, such as search and rescue, inspection, surveillance, and more. The state-of-the-art still faces many challenges, including limited degrees of freedom, a lack of diversity in gait trajectories, insufficient limb dexterity, and limited payload capabilities. To address these challenges, we develop a modular soft-limbed robot that can mimic the locomotion of pinnipeds. By using a modular design approach, we aim to create a robot that has improved degrees of freedom, gait trajectory diversity, limb dexterity, and payload capabilities. We derive a complete floating-base kinematic model of the proposed robot and use it to generate and experimentally validate a variety of locomotion gaits. Results show that the proposed robot is capable of replicating these gaits effectively. We compare the locomotion trajectories under different gait parameters against our modeling results to demonstrate the validity of our proposed gait models.