Organisms in nature, after hundreds of millions of years of evolution, have shown us their amazing survival wisdom with their unique structure and mechanism. The fine structure, high performance, and outstanding adaptability of these organisms continue to provide inspiration for the development of robotics, driving the evolution of robots towards higher performance, more precise operation, and greater environmental adaptability. This nature-inspired innovation is particularly evident in the field of soft robotics.
Compared to organisms in nature, soft robots tend to exhibit inferior dynamic performance and agility during movement and interaction, especially for untethered insect-scale soft robots. Whether it's high-performance drive mechanisms, agile control strategies, or co-design of collaborative functions, all severely limited by their very limited size, researchers have been trying to achieve better motion controllability and dynamic performance to address these technical challenges.
In the field of soft microrobots, many researchers have tried to improve the motion controllability and dynamic performance of soft robots, and have developed robotic achievements such as insect-scale robots based on catalytic artificial muscles, magnetic millimeter robots, and microrobots based on the Maragoni effect, which have effectively expanded the range of movement forms and capabilities of soft microrobotsUnfortunately, the controllability and dynamic performance of soft microrobots are still not comparable to those of natural organisms.
Not long ago,Researchers from the research team of Professor Wu Zhigang, Academician Ding Han, School of Mechanical Engineering, Huazhong University of Science and TechnologyOnce again, challenge this conundrum. Inspired by the Rove beetle's rapid swinging abdomen, ducts for secretion transport, and body bristle system of body structure, combined with magnetic induction to rapidly change posture, the research teamIn this paper, a fast, agile and unfettered millimeter-scale soft thruster uni-sopros that can be propelled on water is proposed.
Figure 1Fast, agile and untethered insect-grade soft thrusters (uni-sopros) inspired by the Rove beetle
The thruster body length (bl) 36 mm, achieving a staggering speed of 201 times the body length per second (bl s) and 8,372 times the body length per square second (bl s). Its comprehensive dynamic performance far exceeds several orders of magnitude of the previous thrusters of the same scale.
Figure 2Recently, the research results were published in the journal Nature Communications under the title "Stenus-Inspired, Swift, and Agile Untethered Insect-Scale Soft Propulsors". Ph.D. student Ke Xingxing is the first author, doctoral student Yong Haochen, and master's student Xu Fukang are co-authors.
Next, let's explore this research result in depth with the Robotics Lecture Hall!
Biomimetic and integrated co-design of thrusters
Through countless rounds of evolution and natural selection, organisms have developed elegant and efficient cross-scale structures that give them superior adaptability and kinematic performance in their environment. In the case of the Rove beetle, the insect's high-speed mobility on the surface of the water is achieved through its unique body structure and mechanism, allowing it to effectively evade predators.
Inspired by the biological structure and mechanism of the Rove beetleResearchers have designed a new type of thruster – uni-sopros. This design not only mimics the flexible and flexible abdomen of the Rove beetle on a macroscopic scale, but also borrows its structural characteristics on the microscopic and mesoscopic scales.
On a macro scale,Uni-Sopros uses a magnetic material that achieves movement along the main axis by mimicking the swinging abdomen of a rove beetle. Using magnetic manipulation technology, researchers can manipulate the movement of the thrusters with a high degree of dynamics, allowing them to generate propulsion on demand.
Figure 3Systematic biological inspiration from the Rove beetle, and co-design for detailed characterization of the soft body thruster.
On a microscopic scale,The researchers observed that there are countless tiny conduction ducts in the glandular system of the Rove beetle that are used to transport the surfactant. Inspired by this feature, the researchers introduced a similar surfactant subdivision transport mechanism in uni-sopros, optimizing delivery by inserting aligned fibers at the tip of the tail.
On a mesoscopic scale,In order to mimic the surface structure of the rove beetle, the researchers introduced microstructural morphology on the body surface of the uni-sopros to obtain a superhydrophobic**, thus avoiding sinking and guaranteeing its stability on the water surface.
To improve real-time maneuverability, the researchers also integrated a pair of magnetic steering chips for the uni-soprosFor fast and stable steering control. In addition, the UNI-SOPROS features a naturally decoupled design and maneuvering mode for independent operation of propulsion and steering control.
In order to pursue the ultimate optimization of the performance and functional perfection of the thruster uni-sopros, the research team also conducted a thorough investigation and characteristic analysis of the relevant biomimetic structures. This process provides valuable guidelines for the co-design of the entire system.
The researchers studied the basic properties of the magnetic particle powder and magnetized film used, established the performance benchmark of these building materials, and focused on the analysis and study of the magnetron tail, driving force, and main surface of the thruster uni-sopros.
In terms of magnetically controlled tails,The researchers analyzed how the content of magnetic particles and the size of the magnetic tail affect their bending behavior, which in turn acts on fuel delivery and water surface disengagement behavior. The results show that magnetic tails with high magnetic particle content exhibit better bending behavior, effectively enabling fuel delivery to the water surface and cutting off fuel when needed**. The researchers also looked at the effects of different attitudes and the underwater length of the magnetic tail on steering behavior (see Supplementary Figure 7) and found that over-immersed magnetic tails impaired steering ability. Therefore,Selecting the right magnetized tail, considering its magnetic particle content, tail size, and tail immersion length is critical to improve maneuverability.
Figure 4Characterization of magnetization and response characteristics of magnetic particles and magnetic films.
Figure 5The effects of different attitudes and immersion tail lengths on their steering behavior.
In terms of driving force,Maintaining the necessary surface tension gradient is critical to Istituto Marangoni's advancement. By precisely adjusting the amount of surfactant delivered to the surface, researchers were able to prevent rapid surfactant diffusion and maintain the necessary tension gradient. By mimicking the natural mechanism of the rove beetleThe researchers introduced polypropylene microfibers to the artificial tail tip, achieving a uniform distribution of the fuel with a gentle Marangoni flow. In addition, the researchers also verified by comparing the direct contact of fuel with and without fibers with waterFiber insertion improves the ability to adjust local surface tension, resulting in enhanced controllability and consistency of motion.
Figure 6Inspired by the receiving conduction duct, fibers are inserted at the tip of the tail section of the uni-sopro.
Figure 7Comparison of the release of magnetic tail fuel (surfactant, NOP) without insertion fibers.
Figure 8Characterization of the local surface tension adjustment ability of the magnetic tail without insertion fibers.
In terms of the surface of the main body,The researchers mimicked the bristles on the row beetle. By creating a superhydrophobic microstructure morphology on the surface of the body with laser surface treatment, the researchers ensured the stability of uni-sopros on the water surface. At the same time, by integrating the magnetic steering chip (SC), the researchers also improved the real-time control of the UNI-SOPROS, achieving fast and stable steering control.
Figure 9Surface hydrophobic treatment and its characterization.
Figure 10Crafting process.
Through the comprehensive investigation and characterization of the bionic structure, and on this basis, the co-design improvement of the system, the uni-sopros propeller not only approached the roof beetle in nature in terms of kinematic performance, but also demonstrated excellent agile behavior.
Kinematic performance testing of thrusters
The uni-sopros thruster, which has undergone extensive biomimetic research and has been carefully designed, not only mimics the elegant mobility of the Rove beetle in nature, but also shows excellent athletic performance in experimental tests. This thruster can be triggered by a single three-dimensional magnetic field to achieve kinematic performance at the biological level and beyond.
Figure 11Kinematic performance, power optimization management, and trajectory programming.
During the analysis of the kinematic characteristics of uni-sopros, the researchers extracted:Characteristic size 36 mmReal-time velocity and acceleration data of uni-sopros. The results show that the thruster is capable of rapidly reaching a peak acceleration of -30 m s 2 or 8,372 bl s 2 in a short period of time (-20 ms) and a maximum movement speed of -725 mm s or -202 bl s after about 250 ms.
At the same time, in the braking test, the uni-sopros also showed excellent deceleration performanceThe deceleration reached -5,010 bl s 2. These tests not only demonstrate the great power of the Uni-Sopros, but also their excellent control ability in high-speed movements.
Figure 12Detailed velocity and acceleration curves of uni-sopros in scale effect characterization and braking tests.
Furthermore, the researchers experimentally investigated the effect of external loading on the performance of uni-sopros. The test results showed that even after withstanding 1At a load of 5 times its own weight (-12 mg), the performance of uni-sopros is also similar to that of no load, except that the peak velocity is reduced from -230 mm s to -200 mm s, and the acceleration is slightly reduced. This result proves that Uni-SOPROS has good load capacity and stability in practical applications.
Figure 13Characterization of the load capacity of uni-sopros.
In order to gain insight into the kinematic properties of uni-sopros, the researchers also studied a series of uni-sopros of different sizes and observed their scale effects when in motion. Observations show a monotonic downward trend in peak velocity as the size increases, especially in the smaller size range. This finding provides valuable guidance for researchers to optimize the performance and design of uni-sopros at different scales.
Figure 14Design and production parameters of various uni-sopros.
Figure 15Simulated flow velocity mapping of uni-sopros at peak velocity in horizontal attitude of each size.
Figure 16Dimensional analysis.
Previous studies have shown that the improved conveying strategy can effectively slow down the attenuation of the propulsion velocity, and then prolong the maintenance time of the expected trajectory during the propulsion process. Based on this, the researchers also performed a comparative analysis of uni-sopros with and without fiber inserts, and performed a comparative test of 10 unidirectional cyclic propulsion under the same magnetic trigger. The test results showed that the uni-sopros inserted fibers were able to significantly slow down the velocity decay and maintain an almost constant velocity trend during the test. Inspired by the structure of conduction tubing in a beetle gland system, this innovative design minimizes velocity drops and simplifies trajectory planning during continuous triggering by precisely regulating fluid delivery.
Figure 17Numerical simulations were used to compare surfactant release under different strategies.
Finally, a feature size of 5The 4 mm uni-sopros utilize a variable external magnetic field to enable complex trajectory planning. As shown in Figure 3f and supplementary video 5, the uni-sopros is able to accurately execute a pigeon-patterned trajectory with multiple sharp turning points, demonstrating its ability to decelerate, steer and accelerate quickly as needed.
Thanks to the precise fuel release mechanism and the precise control of the start and brakes, combined with the nimble steering ability, the uni-sopros thrusters demonstrate excellent trajectory planning performance. Special size is 5The 4mm uni-sopros are capable of being pre-programmed using a variable external magnetic field to execute a complex pigeon-patterned trajectory with multiple sharp turning points, demonstrating its ability to decelerate, steer and accelerate quickly as needed.
After the above experimental tests, the uni-sopros propeller has not only been deeply studied in the bionic structure, but also has been rigorously verified by experiments in terms of motion performance, showing excellent dynamic performance and precise control ability.
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