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Fingertip Pressure Sensor for Dextrous Machines

January 08, 2021 by Luke James

Researchers from the University of Tokyo have developed a fingertip pressure sensor that doesn’t affect the touch sensitivity of real skin. They believe that the intricate technology, which was fabricated by electrospinning, may be able to train machines to carry out tasks with more fidelity.

To measure the amount of force required for a person’s hand to grasp an object, naturally, sensors must first be placed on that person’s fingertips. However, such sensors, due to the effects that they have on touch sensitivity, can influence how much force ends up being applied by the user. This means that traditional measurement technologies have kept us from being fully capable of understanding the natural sense of touch.

Now, researchers at the University of Tokyo claim to have developed a fingertip pressure sensor that has a minimal influence on the users’ touch sensitivity and ability to grip objects. Sunghoon Lee and his colleagues describe, in their journal paper in Science, their new ultra-thin pressure sensor, which is made from multiple layers of conductive and dielectric nanomesh structures.


Precise Measurement of Finger Manipulation

To fully understand and reproduce the sense of natural touch—something which is critical if we’re ever to realise the full potential of fields such as prosthetics and robotics—we need a way to monitor finger manipulation without disturbing its inherent functionalities.

And although significant advances in measuring and examining the human sense of touch have come from the likes of instrumented gloves, optical-based estimation of finger forces based on nail colour, and force sensor-integrated objects, there still exists an element of sensory loss and degradation when it comes to natural touch, which researchers want to avoid.

In their research paper, the Tokyo-based scientists reported that, after a quantitative investigation on the effect of their sensor on human skin, they found that the grip forces of a sensor-applied finger exhibited comparable grip forces with those of a person’s bare finger. This is despite their 2-micrometre-thick polymeric film sensor—leading to a 14% increase in grip force after adjusting for friction.

The fingertip pressure sensor, held in-between a person’s thumb and forefinger.

Image credit: the University of Tokyo.

“Our fingertips are extremely sensitive. So sensitive, in fact, that a superthin plastic foil just a few millionths of a metre thick is enough to affect somebody’s sensations,” said Sunghoon Lee. 


Fabricating the Sensor

Using the fabrication method known as electrospinning, Lee and his research team designed two types of layer for their sensor.

The first layer is an insulating polyurethane mesh with fibres of roughly 200 to 400 nanometres in thickness. The second layer is a stencil-like network of lines that forms the functional electronic component of the sensor. Such a layer is made from gold and uses a supporting polyvinyl (materials made from polymers of vinyl compounds) alcohol frame. This is then washed away after the fabrication process to leave only the gold traces behind. These layers all combine to form a functional sensor that can measure pressure and movement.

“We performed a rigorous set of tests on our sensors with the help of 18 test subjects,” Lee said in a statement. He added that these tests confirmed that the sensors were both imperceptible and had no effect on the ability to grasp neither objects nor touch sensitivity. “This is exactly the result we were hoping for.”


The Promise Shown by the Fingertip Pressure Sensor

Sunghoon Lee and his researchers’ work marks the first time that a fingertip-mounted pressure sensor with no effect on skin sensitivity has been reported and demonstrated. In view of such a breakthrough, the research team would like to see their sensor used in the digital archiving of the works of artists, surgeons, and other specialists who use their hands—so that, one day, machines can be trained on how to perform complex tasks with improved reliability.

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