To ensure the safe operation of complex systems such as aircraft engines and refinery equipment, their piping needs to be inspected from time to time.
It is worth noting that the diameter of the pipeline to be inspected varies from a few millimeters to several tens of centimeters. Most of the existing pipeline robots use electromagnetic motors and gear transmission systems, including wheeled, walking, and crawler robots, which are more suitable for detecting large-diameter pipelines. When the diameter of the pipeline is less than 1 cm, if the size of such robots Further reduction is more difficult, and the applicability will be greatly reduced.
Recently, scientists from the Modern Mechanism and Robotic Equipment Laboratory of the Department of Mechanical Engineering of Tsinghua University have developed a robot that can be used for sub-centimeter (between 1 cm and 0.1 cm) pipeline inspection. It weighs only 2.2 grams and has a diameter of less than 1 cm, 4.7 cm long.
The results of this research make up for the deficiencies in the field of micro-pipe detection to a certain extent.
The related paper was published under the title “A Pipeline Inspection Robot for Subcentimeter-Scale Tubular Environment Navigation”. Tang Chao, a postdoctoral fellow in the Department of Mechanical Engineering of Tsinghua University, is the first author of the paper, and the corresponding author is Zhao Huichan, an associate professor of the department.
It is understood that the sub-centimeter-scale detection robot uses an intelligent driving material dielectric elastomer actuator as an artificial muscle.
Compared with small-sized electromagnetic motors, dielectric elastomer actuators have higher power and are more likely to be scaled to small sizes, and in practice, they have been attempted to be applied to small mobile robots. The dielectric elastomer actuator used in this work also has a long service life and a fast response speed, so it shows a unique advantage in the pipeline movement.
In small pipes, a reliable interaction between the robot and the pipe wall is required, and it is necessary to design a soft robot for agile navigation and efficient inspection.
Currently, such pipeline inspection tasks remain challenging due to the complexity of some pipeline environments (curved and filled with media).
One of the challenges comes from the choice of robot-driven method. For example, pneumatically driven soft robots are usually driven by mass transfer of pressurized air, which is not good for long-distance pipeline inspection, and the speed of the robot will be greatly slowed down.
DEAs rely on the transfer of electric charge for driving, so they have higher power density and have great potential in the fabrication of small pipeline inspection robots.
In addition, in order to verify the real pipeline inspection capability of the robot, the researchers installed a miniature camera in front of the robot to observe the situation inside the pipeline. Under human control, it successfully completed the scheduled inspection tasks at different speeds.
”At the same time, the sub-centimeter-scale robot we developed can move in pipes with different geometries such as S-shaped and spiral, and it works well even if the pipes contain oil, gas and other media. It is also suitable for different pipes such as glass, metal or carbon fiber. material.” Tang Chao said.
It is understood that in order to be able to move efficiently and quickly in pipes of different shapes, the soft robot can achieve rapid assembly through a variable number of magnetic units. Due to the high degree of freedom of the low-modulus materials that make up the robot, it can passively accommodate changes in pipe size and shape.
Another challenge is to design and fabricate the robot’s body structure for efficient movement in small pipes. To draw an analogy between mollusks and mammals, mammals have evolved bone structures for rigid support and muscles for soft actuation, which greatly enhanced their motor abilities.
Compared with pure soft robot design, the introduction of rigid components can also greatly improve the motion performance of the robot. The anchoring unit of the robot developed this time is based on the smart composite microstructure (SCM) technology, which can overcome the limitations of micromachining technology and has been widely used in the structural design of microrobots.
”In this work, the locomotion principle of the robot was inspired by the crawling behavior of earthworms”.
Tang Chao added, “In addition, considering the requirements of pipeline inspection robots, SCM technology has become an ideal choice for designing and manufacturing a small robot with efficient force transmission and mobility.” After modeling and analysis, some special characteristics (such as viscosity and resonance characteristics) driven by soft materials were regulated and utilized, and finally the rapid movement of the robot in all directions in sub-centimeter-sized pipes was realized.
Overall, the researchers demonstrate the feasibility of using smart materials to build a sub-centimeter-diameter-scale pipe inspection robot. And the robot has stronger environmental adaptability in terms of pipe diameter (especially on the sub-centimeter scale), material and filling medium changes.
In the future, the researchers will also explore more flexible actuators with active bending capabilities. At the same time, since the robot is currently powered by cables outside the pipeline, the wired cables will be cancelled in the future and replaced by small high-voltage power supplies and high-energy-density batteries, thereby reducing the travel resistance for more in-depth pipeline exploration.