Fascination of Technology More Sensitivity for Robots

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In our "Fascination of technology" section, we present impressive research and development projects to design engineers every week. Today: how a sensitive artificial skin gives robots an almost human sense of touch.

Robots are becoming increasingly powerful in terms of vision and movement, but touch remains one of their greatest weaknesses. Now researchers at the University of Cambridge have developed a miniature touch sensor that could give robots a sense of touch that is much closer to the human sense of touch.

Almost Like Human Fingertips

Human fingers use multiple types of mechanoreceptors to perceive pressure, force, vibration and texture simultaneously. Reproducing this multidimensional tactile perception in artificial systems is a major challenge, especially for components that are both small and robust enough for practical use. 

The technology now developed is based on liquid metal composites and graphene—a two—dimensional form of carbon. The 'skin' enables robots to detect not only how hard they are pressing on an object, but also the direction of the forces exerted, whether an object is slipping and even how rough a surface is—all at a scale small enough to rival the spatial resolution of human fingertips.

Most existing tactile sensors are either too bulky, too sensitive, too complex to manufacture, or unable to accurately distinguish between normal and tangential forces. This has been a major obstacle to the development of truly sophisticated robotic manipulation.

Professor Tawfique Hasan, Cambridge Graphene Centre

Tiny Pyramids—Inspired By Human Skin

To solve this problem, the research team developed a soft, flexible composite material that combines graphene sheets, malleable metal microdroplets and nickel particles in a silicone matrix. Inspired by the microstructures of human skin, the researchers formed the material into tiny pyramids, some of which are only 200 micrometers (0.008 in) wide. These pyramid structures concentrate the load at their tips, allowing the sensor to detect extremely small forces while covering a large measuring range.

Tactile Sensor Detects Grain of sand

The result is a tactile sensor that is sensitive enough to detect a grain of sand. Compared to existing flexible tactile sensors, the new device improves the size and detection limits by about an order of magnitude, according to the researchers. The sensor also distinguishes shear forces from vertical pressure, allowing it to detect when an object starts to slip so that the gripper can readjust.

In demonstrations, the team integrated the sensors into robot grippers. The robots were able to grasp fragile objects such as thin paper tubes without crushing them. 

Multimodal Artificial Skin Possible

Beyond robotics, this technology could also have a significant impact on prosthetics. Artificial limbs are increasingly reliant on tactile feedback to provide users with a sense of touch. Highly sensitive, miniaturized 3D force sensors could enable more natural interaction with objects, improving user control, safety and confidence. 

Looking to the future, the researchers believe the sensors could be miniaturized even further, possibly to below 50 microns, which is close to the density of mechanoreceptors in human skin. Future versions could also integrate temperature and humidity sensors, moving closer to a fully multimodal artificial skin.

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