The world's first wheel and mobile robot technology that can overcome various obstacles in daily life, such as stairs or rocks, by changing the stiffness of the wheel in real time has been developed. It is expected to be widely applied to all mobile devices that utilize wheels that are important for overcoming obstacles on the road.

The Korea Institute of Machinery and Materials (President Ryu Seok-hyun) under the Ministry of Science and ICT announced on the 2nd that it has developed the world's first morphing wheel whose rigidity can be freely changed by simulating the surface tension principle of liquid droplets, and successfully applied it to an actual moving object.

The morphing wheel, developed by a team led by Song Seong-hyeok, a senior researcher at the Advanced Robotics Research Center of the Korea Institute of Machinery and Materials (Director Park Chan-hoon), and Park Dong-il, the head of the Advanced Robotics Research Center, is a wheel and modular system that can easily change its rigidity by simply changing the surface tension applied to the smart chain block without any complex mechanical devices or sensors. During normal driving, it operates as a solid cylindrical wheel, but when going over an obstacle, the wheel becomes soft and can freely transform depending on the height or shape of the obstacle.

The technology to construct the inside of a wheel with a flexible structure, like a non-pneumatic tire, already existed. Existing technology has limitations in that it causes continuous, large deformation of the wheel even when driving on flat surfaces, which reduces driving efficiency and stability and increases noise.

On the other hand, the wheel developed by the Korea Institute of Machinery and Materials research team can adjust its stiffness as desired, so it maintains the same stiffness as a normal wheel when driving on flat surfaces at high speeds, and only changes to a softer wheel in real time when there is an obstacle, allowing it to overcome the obstacle. This is the biggest difference.

The morphing wheel developed by the research team of the Korea Institute of Machinery and Materials consists of a smart chain block and a flexible structure. The outermost part of the wheel consists of a smart chain block, and the wire spoke structure that controls the surface tension of the smart chain block is connected to the hub structure of the wheel. When the hub structure rotates or the distance changes, the wire spoke structure connected to it is pulled strongly or loosely, which changes the surface tension of the smart chain block structure.

When the blocks are strongly pulled inward using wire spokes, the force increases in the direction of bringing the smart chain structures on the outermost side of the wheel closer together. In this process, an effect similar to the strong attraction between the outermost molecules in a liquid droplet with high surface tension occurs, and a stable circular shape is maintained. On the other hand, when the wire spoke structure becomes loose, it changes to low rigidity.

The research team completed verification of the change mechanism of these variable stiffness wheels in October of last year, and recently developed modularization technology that can be easily applied to various mobile devices. The mechanism that changes stiffness was made small and lightweight, inserted into the internal space of the wheel, and modularized to apply it to various mobile devices such as two-wheel wheelchairs.

The two-wheel-based wheelchair system not only allows stable movement by changing the stiffness of the wheels in real time, but is also advantageous for movement in narrow spaces, such as changing direction in place. It can overcome rocks and 18cm high stairs. In addition, the obstacle overcoming performance was tested by applying it to a four-wheel-based vehicle, and it was confirmed that it could stably overcome obstacles up to 1.3 times the wheel radius in height.

“In the case of quadruped and biped walking robots that are designed to overcome obstacles, there was a problem that their movement efficiency on flat ground was low and that shaking inevitably occurred when moving,” said Senior Researcher Song Seong-hyeok. “The significance of the newly developed morphing wheel lies in the fact that it maintains the high movement efficiency, which is the advantage of existing wheels, while also being able to overcome obstacles, which was the limitation of wheels,” he explained.

Dong-il Park, director of the Advanced Robot Research Center at the Korea Institute of Machinery and Materials, said, “The surface tension-mimicking wheel technology is a technology that can overcome the limitations of complex mechanical devices such as existing obstacle-overcoming robots and wheel clusters,” adding, “It is expected to be widely used in the future in wheelchairs that can overcome obstacles, various mobile robots, and ride-on transportation.”

Meanwhile, this study was published as the cover paper in the August issue of 'Science Robotics,' a sister journal of 'Science,' and the number one journal in the field of robotics, and was conducted with the support of the 'Robots for Independent Living of Lower Extremity Disabled Persons (Project Manager: Center Director Dong-il Park)' project of the Basic Project of the Korea Institute of Machinery and Materials.