Artificial Skin: How to Teach the Robot to Feel and What to Do

Monday, August 12th, 2013

For us, it has become customary that robots can see and hear better than humans. Depending on the tasks they have access to the different spread spectrum perception and processing data often come from dozens of cameras and microphones. At the same time with the tactile sensitivity of the situation it is extremely important. Leatherette capable touch, it has become a real challenge for experts in the field of robotics. Commercially fabric and coating are comparable with the human skin is not available until now. At the same time the latest news from the laboratories looks very reassuring.

The problem of imitation of human perception with the help of electronics has become one of the most difficult. Today it is a major stumbling block in the creation of artificial intelligence systems and the development of human-machine interfaces. From robots all want greater flexibility and participation in search and rescue operations.

The ability to accurately handle different objects requires rapid determination of the nature of their surface and the allowable pressure on them. One thing – to clear a blockage of debris, and quite another – to pull out of his wounded men, some of them unconscious. For the first task is suitable and a bulldozer, but the second involves the utmost caution. One camera can not do: the robot (or operator) should be constantly aware that he is holding in his hands, and precise dosing effort.

What more can be required to teach a robot to feel? At the time, the answer to this question is depicted by the artist Franz Steiner (Franz Steiner). Let us recall here only one of his famous paintings.

The problem of the lack of tactile feedback has repeatedly faced and NASA experts during rovers control. In the picture it was difficult to determine the nature of the planet’s surface in the upcoming section of the route. Rovers move on centimeters, but still tied in a pliable soil, and the “Spirit’s” after another accident were blocked wheel.

In general, the transmission of tactile technology requires fabrication of a large array of sensors with high sensitivity, resolution and low return time to its original state.

After years of experiments, researchers from the Georgia Institute of Technology were able to develop a sensor device that converts the energy of the weak mechanical pressure directly into light signals. The latter are easily transferred to any transparent medium, to fix at a considerable distance, and process on the existing principles in optoelectronics.

For the first prototype achieved an effective resolution of 2.7 micron. In the usual terminology of the users of graphic tablets is the equivalent of 6350 dpi. The sensor is suitable for reading the fingerprint on the finger pads and other moth-eye structures.

In addition to the analysis of fingerprint processing of handwritten signatures, and other biometric applications, this technique can be used to develop new microelectromechanical (MEMS) circuits of different purposes. The most important task is to simulate the touch skin for robots. The resulting prototype to have sensitivity comparable to that of man.

Earlier, independent signal processing of microsensor has been reached in the working prototype artificial skin, placed at a distance of about two to three millimeters. Syntouch company already manufactures such sensitive fingers series BioTac for robot manipulators. They react to distinguish between surface temperature and over a hundred different textures. Because of the relatively low density of the location of sensitive elements of the “feeling” sometimes takes considerable time. To get closer to the average person’s skin indicators needed to increase resolution to 50 microns – that is sixty times.

Until now, the main research efforts have focused on various embodiments, changes in capacitance and resistance of the chain of small plots, which were nanowires, organic transistors or multilayer structure with piezoelectric effect.

“Computerra” already wrote last year about the achievements of the research team of the National University in South Korea. They created an artificial skin with a variety of polymer hairs also considered more sensitive than human. However, it was only on registration of the fact of touching, without recognition of its detailed characteristics. Scanning papillary lines and other microrelief with its help it would be impossible.

It is much more advanced, scientists from Stanford University. In the group under the leadership of Chzhenan Bao was established elastic material, at the same time acting as a flexible solar panel and touch sensor. Tactile sensitivity was added due to the transistors, the recording current changes.

Created in the Georgia Institute of Technology sensor continues this trend by adding optoelectronics components for ease of simultaneous recording of signals. It is an array of nanowires made of zinc oxide, orderly placed on a thin film. To save a specific pattern of laying the space between conductors is filled with polymethyl methacrylate (organic glass). The common electrode on the upper part of the array formed by a transparent layer of indium tin oxide.

Each pixel is represented by one touch surface of the zinc oxide nanowire (n-type semiconductor) and organic LED (p-type semiconductor). The intensity of the radiation depends on the last degree of deformation and due to a combination of photovoltaic and piezoelectric effects.

When mechanical pressure appears nanowires are compressed and create a negative piezoelectric potential, while the uncompressed conductors have zero potential.

As a result of the sensor creates an electronic mechanical pressure distribution map. It is performed by reading parallel signals from all of electroluminescent pixels, which recharge time is about 90 ms. In other words, such an artificial skin are recognized not only simple single and multiple touch, and vibration with a frequency of 11 Hz.

According to the results of tests on the stability of the sensor showed good results. Deviations signal levels twenty thousand pixels prototype did not exceed five per cent in a series of twenty-five experiments.

Used sensors ensure the development of robotics and bionics. Sensitive artificial limbs need not only robots, but also to people who have lost their own. Also, the sensors will contribute to the creation of new human-machine interfaces, and will be widely used in the field of security.

By Андрей Васильков

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