Shape Memory Polymer taxels

Shape Memory PolyUrethanes are the most common type of thermo-responsive shape memory polymers available on the market. A key SMP feature is their ability to memorize an initial shape, to be deformed and held in a temporary shape under specific conditions of temperature and stress, and to then relax to the initial shape upon thermal command. During this thermal cycle, the SMP material we use has a 100 fold change in Young’s modulus.

To make a haptic displays, we take advantage of this enormous change in Young’s modulus with temperature (up to 100 times) to intrinsically implement latching and to selectively actuate individual taxels in the array. Our unique and novel concept, which enables large scale manufacturing and faster refresh rate, is to integrate a stretchable microheater on each taxel and to use a common pneumatic source to move all taxels (i.e. one pump drives all the taxels, but only those that were heated move). As illustrated below, there are two stable taxel states when the membrane is cold: “UP” or “DOWN”; with taxel motion obtained uniquely when the global pneumatic actuation and the local Joule heating are synchronized.

Movie showing the flexible version of our 24×32 element active skin: i) displaying different patterns, ii) device operating principle, and iii) dynamic thermal imaging showing selective taxel heating. Published in Advanced Materials Technologies 2017.

Operating principle for a single SMPs taxel. Synchronizing the global pneumatic actuation and the Joule heating switches the taxel from up to down, or vice versa.