When you grab a balloon, the pressure to hold it is different from what you would exert to grab a jar. And now engineers at MIT and elsewhere have a way to accurately measure and trace these subtleties of tactile dexterity.
The team has designed a new touch-sensitive glove that can “feel” pressure and other tactile stimuli. The inside of the glove is lined with a system of sensors that detects, measures and maps small pressure changes through the glove. Individual sensors are highly tuned and can detect very faint vibrations in the skin, such as from a person’s pulse.
When subjects wore the glove while picking up a balloon against a beaker, the sensors generated specific pressure maps for each task. Holding a balloon produced a relatively uniform pressure signal across the palm, while grabbing a beaker created a stronger pressure on your fingertips.
Researchers say the touch glove could help recycle motor function and coordination in people who have suffered a stroke or other fine motor condition. The glove can also be adapted to enhance virtual reality and gaming experiences. The team plans to integrate pressure sensors not only into tactile gloves, but also into flexible stickers to track dust, blood pressure and other vital signs more accurately than smart watches and other portable monitors.
“The simplicity and reliability of our detection structure is a great promise for various healthcare applications, such as pulse detection and sensory capacity recovery in patients with tactile dysfunction,” says Nicholas Fang, professor of mechanical engineering from MIT.
Fang and his collaborators detail their results in a study published today in Nature Communications. Co-authors of the study include Huifeng Du and Liu Wang at MIT, along with the group of Professor Chuanfei Guo at the Southern University of Science and Technology (SUSTech) of China.
Glove pressure sensors are similar in principle to sensors that measure humidity. These sensors, which are found in HVAC systems, refrigerators, and weather stations, are designed as small capacitors, with two electrodes or metal plates, that include a rubber “dielectric” material that carries electrical charges between the two electrodes.
In humid conditions, the dielectric layer acts as a sponge to absorb charged ions from the surrounding moisture. This addition of ions changes the capacity, or amount of charge between the electrodes, in a way that can be quantified and converted into a measure of humidity.
In recent years, researchers have adapted this capacitive sandwich structure for the design of thin, flexible pressure sensors. The idea is similar: when a sensor is removed, the charge balance of its dielectric layer changes, so it can be measured and converted to pressure. But the dielectric layer of most pressure sensors is relatively bulky, which limits their sensitivity.
For their new touch sensors, the MIT and SUSTech team ended up with the conventional dielectric layer in favor of an amazing ingredient: human sweat. Because sweat naturally contains ions such as sodium and chloride, they reasoned that these ions could serve as dielectric substitutes. Instead of a sandwich structure, they imagined two thin, flat electrodes, placed on the skin to form a circuit with a certain capacity. If pressure were applied to a “sensing” electrode, ions from the skin’s natural moisture would accumulate at the bottom and change the capacity between the two electrodes by an amount they could measure.
They found that they could increase the sensitivity of the sensing electrode by covering the bottom with a forest of conductive, tiny hairs. Each hair would serve as a microscopic extension of the main electrode, so that if pressure were applied, for example, to one corner of the electrode, the hairs in that specific region would bend in response and accumulate ions from the skin, and the location of which could be accurately measured and mapped.
In their new study, the team made thin-core detection electrodes coated with thousands of gold or “micropillar” microscopic filaments. They showed that they could accurately measure the degree to which groups of micropiles bent in response to various forces and pressures. When they placed a sensing electrode and a control electrode at a volunteer’s fingertips, they found the structure to be very sensitive. The sensors were able to pick up subtle phases in the person’s pulse, such as different peaks in the same cycle. They could also maintain accurate dust readings, even when the person wearing the sensors was shaking hands as they walked across a room.
“The pulse is a mechanical vibration that can also cause skin deformities, which we can’t feel, but the pillars can get caught,” Fang says.
The researchers applied the concepts of their new micropillar pressure sensor to the design of a highly sensitive tactile glove. They started with a silk glove that the team bought on the shelf. To make pressure sensors, they cut small squares of carbon fabric, a textile made up of many fine filaments similar to micropiles.
They turned each square of fabric into a sensing electrode by spraying it with gold, a natural conductive metal. They then glued the fabric electrodes to various parts of the inner lining of the glove, including the fingertips and palms, and threaded conductive fibers along the glove to connect each electrode to the wrist of the glove, where the researchers glued an electrode. control.
Several volunteers took turns with the touch glove and performed various tasks, such as grabbing a balloon and grabbing a glass beaker. The team collected readings from each sensor to create a pressure map through the glove during each task. The maps revealed different and detailed pressure patterns generated during each task.
The team plans to use the glove to identify pressure patterns for other tasks, such as writing with a pen and manipulating other household objects. Ultimately, they anticipate that these tactile aids could help patients with motor dysfunction calibrate and strengthen hand dexterity and grip.
“Some fine motor skills require not only knowing how to handle objects, but also how much force must be exerted,” says Fang. “This glove could provide us with more accurate measures of grip strength for control groups versus patients recovering from a stroke or other neurological condition. This could increase our understanding and enable control.”
This research was supported, in part, by the Joint Center for Mechanical Engineering Research and Education at MIT and SUSTech.