Giving machines a fine sense of touch

Tuesday, September 14th, 2010 by Robert Cravotta

Two articles were published online on the same day (September 12, 2010) in Nature Materials that describe the efforts of two research teams at UC Berkeley and Stanford University that have each developed and demonstrated a different approach for building artificial skin that can sense very light touches. Both systems have reached a pressure sensitivity that is comparable to what a human relies on to perform everyday tasks. The sensitivity of these systems can detect pressure changes that are less than a kilopascal; this is an improvement over earlier approaches that could only detect pressures of tens of kilopascals.

The Berkeley approach, dubbed “e-skin”, uses germanium/silicon nanowire “hairs” that are grown on a cylindrical drum and then rolled onto a sticky polyimide film substrate, but the substrate can be made from plastics, paper, or glass. The nanowires are deposited onto the substrate to form an orderly structure. The demonstrated e-skin consists of a 7x7cm surface consisting of an 18×19 pixel square matrix; each pixel contains a transistor made of hundreds of the nanowires.A pressure sensitive rubber was integrated on top of the matrix to support sensing. The flexible matrix is able to operate with less than a 5V power supply, and it has been able to continue operating after being subjected to more than 2,000 bending cycles.

In contrast, the Stanford approach, sandwiches a thin film of rubber molded into a grid of tiny pyramids, packing up to 25 million pyramids per cm2, between two parallel electrodes. The pyramid grid makes the rubber behave like an ideal spring that supports compression and rebound of the rubber that is fast enough to distinguish between multiple touches that follow each other in quick succession. Pressure on the sensor compresses the rubber film and changes the amount of electrical charge it can store which enables the controller to detect the change in the sensor. According to the team, the sensor can detect the pressure exerted by a 20mg bluebottle fly carcass placed on the sensor. The Stanford team has been able to manufacture a sheet as large as 7x7cm, similar to the Berkeley e-skin.

I am excited by these two recent developments in machine sensing. The uses for this type of touch sensing are endless such as in industrial, medical, and commercial applications. A question comes to mind – these are both sheets (arrays) of multiple sensing points – how similar will the detection and recognition algorithms be to the touch interfaces and vision algorithms that are being developed today? Or will it require a completely different approach and thought process to interpret this type of touch sensing?


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