Innovative Mobility Real-Time Stiffness: Morphing Wheel Conquers Stairs and Rocks with Ease

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A new technology for wheels and mobile systems, necessary for overcoming various obstacles in daily life such as stairs or rocks by adjusting the stiffness of the wheel in real time, has been developed for the first time in the world. This technology is anticipated to find wide applications in various moving vehicles equipped with wheels, where overcoming terrain obstacles is essential.

The Korea Institute of Machinery and Materials (Kimm) has announced a groundbreaking innovation in wheel technology: the world's first variable-stiffness morphing wheel inspired by the surface tension dynamics of a liquid droplet. This cutting-edge technology, developed by a research team led by Principal Researcher Sung-Hyuk Song and Dong Il Park, Head of the Advanced Robotics Research Center at KIMM’s Research Institute of AI Robotics, has been successfully applied to various mobile systems.

The newly developed morphing wheel and its modularization system represent a significant leap forward in mobility technology. Unlike traditional wheels that maintain a fixed structure, this innovative wheel can alter its stiffness by adjusting the surface tension applied to smart chain blocks, eliminating the need for complex machinery or sensors. The wheel can operate as a rigid, circular wheel on flat surfaces, ensuring efficient and stable driving, and can switch to a softer, deformable state to roll over obstacles of varying heights and shapes.

Overcoming the Limitations of Conventional Wheel Technologies

While flexible-structure wheel technologies, such as non-pneumatic tires, have existed, they come with limitations. These wheels often remain in a deformed state even on flat surfaces, which can reduce driving efficiency, compromise stability, and generate noise. In contrast, the variable-stiffness morphing wheel developed by Kimm can seamlessly transition between a rigid state for flat terrain and a soft, adaptable form to navigate obstacles. This dual capability enhances both the versatility and functionality of vehicles equipped with this technology.

The morphing wheel's design incorporates a smart chain block and a flexible structure. The outermost edge of the wheel consists of a smart chain block connected to a wire spoke structure, which in turn is linked to the wheel’s hub. The rotation or distance changes of the hub structure affect the tension of the wire spokes, which either tighten or loosen the smart chain blocks, thereby altering the wheel's surface tension.

The principle behind this innovation draws inspiration from liquid droplet dynamics. When the wire spokes pull the smart chain blocks inward, the traction force increases, akin to the increased surface tension in a liquid droplet that helps maintain a stable circular shape. Conversely, loosening the wire spokes reduces the wheel's rigidity, allowing it to adapt to uneven surfaces and obstacles.

Versatile Applications in Mobility Systems

KIMM's research team has also achieved a breakthrough in the modularization of this technology, making it adaptable to a wide range of mobile systems. A miniaturized, lightweight version of the variable-stiffness mechanism has been successfully integrated into the wheel's interior, enabling its application to different vehicles, such as a two-wheeled wheelchair.

The incorporation of this wheel into a two-wheeled wheelchair system demonstrates its practical advantages. The wheelchair can dynamically adjust its wheel stiffness in real time, allowing for stable movement and agile maneuvering even in confined spaces. It can also navigate over obstacles like rocks or stairs up to 18 centimeters high. Furthermore, when applied to a four-wheeled mobile system, the wheel can overcome obstacles up to 1.3 times its radius, confirming its superior adaptability and robustness.

Principal Researcher Sung-Hyuk Song of the Kimm commented: “One of the problems associated with quadrupedal and bipedal walking robots for overcoming obstacles is that movement efficiency is relatively low on flat surfaces, and that shaking inevitably occurs in the moving state.” Song added, “The newly developed morphing wheel is significantly meaningful in that it is capable of overcoming obstacles while at the same time maintaining high movement efficiency comparable to conventional wheels.”

Dong Il Park, Head of the Kimm’s Advanced Robotics Research Center, said: “This new technology for morphing wheels inspired by surface tension can help to overcome the limitations of conventional mechanical devices such as leg-type robots and wheel clusters for overcoming obstacles.” Park added, “It will likely find applications in a wide range of fields including wheelchairs, mobile robots, and personal mobility capable of overcoming obstacles.”

Original Article: Variable-stiffness–morphing wheel inspired by the surface tension of a liquid droplet; Science Robotics; DOI:10.1126/scirobotics.adl2067

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