Researchers are developing a new kind of gripper that mimics the ability of a gecko to grip and release surfaces, an advance that may allow climbing robots to move across a range of rough and smooth surfaces.
Geckos can stick to sheer surfaces due to complex structures on the pads of their feet. Like the gecko, the new gripper has "tunable adhesion," which means that its effective stickiness can be tuned from strong to weak.
Unlike the gecko and other artificial imitators that rely on structures with complex shapes, the gripper developed by the University of Pennsylvania uses a simpler, two-material structure that is easier to mass-produce.
At their current millimetre-scale size, the grippers can be used for moving smooth, fragile components, like silicon wafers or glass sheets.
Scaled down, they could be used in arrays to grip to a range of rough and smooth surfaces, making them useful for climbing robots and other larger-scale applications.
The research was conducted by Kevin Turner, the Gabel Family Term Associate Professor in the School of Engineering and Applied Science's Department of Mechanical Engineering and Applied Mechanics, and Helen Minsky, a graduate student in his lab.
"When it comes to tunable adhesion everyone is familiar with the gecko, and everyone tries to copy it. The problem is that it's really hard to manufacture complex structures as well as nature," Turner said.
"We've come up with a strategy that can achieve similar adhesion behaviour but is much easier to make," Turner said.
The structures in the geckos' feet are sticky because of a phenomenon known as van der Waals adhesion, a force which is present at all times between two surfaces in close contact; the closer the contact, the stronger is the attraction.
Van der Waals forces generally are not noticeable in everyday life, as even two seemingly smooth, flat surfaces are rough enough at the microscopic scale to make them ineffective.
But with many angled, flared-tip fibres lying flush with this rough terrain, van der Waals forces are strong enough for the gecko to stick to a wall.
Changing the angle of their feet is what makes the gecko's adhesion "tunable" and what allows them to detach from the wall to take each step.
"Other researchers have mimicked these structures to achieve tunable adhesion, but they are tough to make," Minsky said.
"You can make a few of these structures, but, if you want to make larger arrays of them, it becomes much tougher. The angles and the flared tip means you can't just slip them out of a mold," Minsky said.
The team's approach to realising tunability and to address this manufacturing problem relies on a gripper with a fundamentally different structure.
Rather than being angled or flared, they are simple cylindrical posts. The secret is in their composite construction - a hard plastic core surrounded by a softer silicone rubber shell.
