Smart thumb sensor provides cost-effective accuracy

April 1, 2022
Max Planck researchers add fingertip sensitivity to robotics with a new thumb-shaped sensor.

Using computer vision and a deep neural network to infer haptic contact information inside a thumb-shaped sensor (see figure), researchers at the Max Planck Institute for Intelligent Systems (MPI-IS; Stuttgart, Germany) are adding a desirable layer of sensitivity to robots.

Known as Insight, the sensor is constructed around an internal monocular camera, with only a single layer of elastomer over-molded onto a stiff frame to guarantee sensitivity, robustness, and soft contact. This design allows it to continually provide a directional force-distribution map over its entire conical sensing surface.

Insight is also the first system to combine photometric stereo and structured light using a collimator to detect 3D deformation of its flexible and replaceable skin. It generates a 3D force map when the thumb is touched, which estimates where objects meet the sensor and the amount of force applied.

Much like biological systems, robots need touch-sensitive skins to provide practical benefits. Previous touch sensors are mostly in the concept-designing phases, such as creating functional materials and testing flat-sheet-shaped sensors. These designs only offer small sensing areas, are delicate and hard to fabricate, and cannot often feel contact parallel to the skin.

“In our research, we invented a soft and durable sensor shaped like a 3D cone with an extremely large contact surface; it can feel force distributions of multiple contacts with different force magnitudes and directions,” says primary researcher Huanbo Sun. “The research could significantly break the bottleneck of current haptic perception in robotic applications.” Insight is surprisingly straightforward to manufacture and quite modularized, explains Sun. Plus, all the components are low cost with online accessibility or could be easily 3D-printed. The sensor is also robust and durable for long-term use—two years so far without visible performance drop.

The team also designed the sensor with the imaging and sensing surface as separate systems. “If the sensing surface is damaged by collision and extremely high force impact, its effortless to replace it by unscrewing the old one at the cost of around 2 to 5 Euro,” he says. “And the sensor is data-driven in its current state. Weve found that our machine-learning algorithm is very general and robust to use.” Flexibility is key as this technology develops. While Insight is designed to be very sensitive, robust, and high resolution, its shape can be changed; the sensor size can be rescaled; the data processing method can be quickly adapted or modified according to application requirements; and the sensor can also work using a raw camera image. “We hope every robotic lab can access our sensor at a meager cost with our open-access research philosophy,” says Sun. Of course, like human skin, multiple types of cells (mechanoreceptors) are responsible for contact with different speeds and temperatures. The current sensor cannot measure temperature and runs at 10 frames per second (fps), but Sun is currently working on improving the speed and integrating temperature-sensing modularity.

“Different components are involved in our sensor design, such as materials, cameras, lighting systems, 3D printing techniques, data collection procedures, data processing methods (machine-learning algorithms),” says Sun. “We’re exploring ways to optimize the design from the above-listed aspects and integrate more functionalities in our sensor.

About the Author

Peter Fretty | Market Leader/Group Editorial Director, Laser & Military

Peter Fretty began his role as the Market Leader, Laser & Military in June 2023; the group encompasses the Laser Focus World, Military & Aerospace Electronics, and Vision Systems Design brands. He also serves as Group Editorial Director, Laser & Military (effective spring 2023) and served as Editor in Chief of Laser Focus World since October 2021. Prior to that, he was Technology Editor for IndustryWeek for two years.

As a highly experienced journalist, he has regularly covered advances in manufacturing, information technology, and software. He has written thousands of feature articles, cover stories, and white papers for an assortment of trade journals, business publications, and consumer magazines.

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