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Research into a new flexible actuator from PNOPAM gels to replace piezoelectric actuators in Braille displays

Currently, visually impaired people use Braille displays equipped with piezoelectric actuators, which are costly and bulky. The major challenge in designing a more suitable Braille device lies in the integration of a large number of milimeter-scale actuators. As part of the Ability project, we are focusing on developing a 2D Braille display that innovates by replacing piezoelectric actuators with a novel technology to active the pins. However, numerous reserchers are exploring different technologies to make Braille displays accessible to a wider audience.

A recent article introduces a new technology using a poly(N-isopropylacrylamide)(PNIPAM) thermosensitive gel as a flexible actuator. Macroporosity is introduced into the gel, accelerating the response time from several hours to a few seconds. At temperature above 34°C, PNIMAM undergoes reversible contraction with a significant swelling ratio up to 1000%. This volume change is attributed to a modification in PNIPAM solubility, leading to water transfer into/out the polymer matrix and a slow response to stimuli. The authors combined two recent developments to overcome these limitations. The first is the synthesis of a mechanically robust hydrogel, and the second is the synthesis of a fast-reacting gel with a macroporous structure. Combining these scientific advances results in an intelligent gel suitable for flexible actuation.

To demonstrate the capabilities of the new actuation technology, a one-pin Braille prototype was constructed. It consists of a central part with a 3D-printed containment unit for the gel and water, and a small rod placed above that can move vertically through a hole. An electrolysis device (placed under the gel) and a nichrome wire (wrapped around the gel) were used to cool and heat the system, respectively. The initial results are promising, as the prototype effectively lifted a pin. Further work is planned to develop a prototype with a set of 8 pins to display letters and even images.

(Left Image representing the principle of the thermosensitive PNIPAM gel, and right image representing the pin activation, with its different parts).

Article: (images from the article)

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