In a recent article published in the journal Nature Communications, researchers introduced an innovative method for creating thin-soft robots (TS-Robots) that can move in solid and liquid environments and transition between them. This technology addresses the challenge of accessing hard-to-reach areas, such as narrow gaps and confined spaces in industrial and civil engineering.
a Type-A TS-Robot (left) and Type-B TS-Robot (right), targeting for navigation in narrow gaps on horizontal or vertical surfaces (“Energy” scenario); b Asymmetric configuration of Type-A TS-Robot, targeting for the hybrid solid-liquid environment (“Chemistry” scenario); c Twin Type-A TS-Robot, targeting for transitions between horizontal and vertical surfaces (“Security” scenario); d Serial Kinematics TS-Robot, targeting for transitions between horizontal and vertical surfaces (“Aerospace” scenario); e One example of TS-Robots collaborating with other types of robots—Flying-TS-Robot, targeting for Transitioning between surfaces by using a carrier (“Security” and “Energy” scenario). Image Credit: https://www.nature.com/articles/s41467-024-50598-1
Background
Navigating built environments is a significant challenge for robots of all sizes. Obstacles like doors, stairs, and narrow gaps often block their path, restricting their ability to explore effectively. While there are different types of robots—humanoid, wheeled, and quadruped—they frequently struggle in tight spaces. To address this, researchers have developed smaller robots inspired by worms, insects, and origami, which offer more flexibility. However, these designs typically depend on external magnetic fields for movement, which can be impractical in real-world settings due to their size and potential interference from ferromagnetic materials.
About the Research
In this paper, the authors focused on developing a new approach to overcome the limits of existing robots for navigating tight spaces. They proposed TS-Robots powered by Thin Soft Dielectric Elastomer Actuators (TS-DEAs) and equipped with Electrostatic Adhesive Pads (EA-Pads). The TS-DEAs are the main movement mechanism, generating displacement and driving force. At the same time, the EA-Pads anchor the robots to surfaces, allowing them to move on various materials and orientations.
The researchers created three types of TS-Robots: Type-A (zero Poisson's ratio), Type-B (negative Poisson's ratio), and Type-C (silicone-based). Type-A TS-Robots, with a zero Poisson's ratio TS-DEA, can extend/contract and bend in one direction. Type-B TS-Robots, with a negative Poisson's ratio TS-DEA, can extend/contract and steer in two directions. Type-C TS-Robots, using silicone-based elastomers and directional friction feet, are designed for fast movement.
Research Findings
The study explored the static and dynamic properties of TS-DEAs and EA-Pads, highlighting their capabilities in generating displacement, output force, and adhering to various surfaces. The TS-Robots were tested for a range of movements, including crawling, climbing, steering, swimming, and landing, showcasing their ability to navigate narrow gaps, vertical walls, and liquid environments.
The results indicated that the Type-A TS-Robot achieved a maximum speed of 2.3 mm/second on horizontal surfaces and 1.7 mm/second on vertical surfaces at a driving frequency of 4 Hz. The Type-B TS-Robot, which can steer in two directions, effectively navigated a 2 mm high tunnel with multiple obstacles, demonstrating its obstacle-avoidance and directional-change capabilities. Notably, the Type-A TS-Robot swam in silicone oil at an average speed of 45.5 mm/second—about 20 times faster than its crawling speed—illustrating its versatility.
Additionally, the authors developed a Serial Kinematic TS-Robot (SK-TS-Robot) by connecting a Type-B TS-Robot and a Type-A TS-Robot via an active hinge joint. This hybrid system could perform four distinct gaits, allowing it to cross narrow gaps, steer, transition between surfaces, and function as a manipulator. The SK-TS-Robot demonstrated its cross-domain locomotion potential by carrying a commercial drone, navigating a two-floor test rig, reconnecting a "damaged" electric circuit, and executing complex tasks in tight spaces.
Applications
The TS-Robots have significant potential for various real-world uses, particularly in inspecting and maintaining industrial equipment like aero-engines, aircraft, and nuclear facilities, where accessing tight spaces is a major challenge. The researchers also demonstrated a TS-Robot inspecting magnetic field degradation in an electrical generator for aircraft propulsion, showcasing the technology's versatility.
Beyond industrial uses, these robots could assist in search and rescue operations by navigating collapsed structures or disaster zones to locate survivors. In biomedical fields, their small size and flexibility could enable them to navigate delicate environments, potentially aiding in targeted drug delivery or minimally invasive surgery. Additionally, TS-Robots could be used for environmental monitoring, such as assessing water quality or air pollution in hard-to-reach areas. Their adaptability also makes them suitable for underwater exploration, allowing them to inspect shipwrecks or underwater pipelines.
Conclusion
In summary, the TS-Robots, capable of multimodal movement in solid and liquid environments, proved effective for accessing narrow and confined spaces. This technology could revolutionize various industries, from infrastructure inspection to hazardous environment exploration. The combination of TS-DEAs and EA-Pads allowed the creation of highly versatile and adaptable robotic systems.
The authors also introduced a new method for adjusting the resonant frequency of dielectric elastomer actuators by mechanically altering the stiffness of the tensioning mechanism. This approach could save time tuning DEA properties to achieve the desired resonant frequency, offering a fundamentally new way to enhance DEA performance. Moving forward, they suggested developing untethered TS-Robots with improved actuation abilities and exploring their use in other challenging environments, such as underwater exploration and medical applications.
Journal Reference
Wang, X., Li, S., Chang, JC. et al. Multimodal locomotion ultra-thin soft robots for exploration of narrow spaces. Nat Commun 15, 6296 (2024). DOI: 10.1038/s41467-024-50598-1, https://www.nature.com/articles/s41467-024-50598-1