Skin for Robots and Why It’s Crucial
By: Florian Geiser
Tags: Sensors, Robotics, Technology, Data Science, Science

Skin for Robots and Why It’s Crucial

Photo by Lyman Gerona on Unsplash

Good old C-3PO is, according to Star Wars, a stunning example of how humanoid robots could look like in the future. But this poor guy has a huge handicap: his skin!

Skin is the human’s largest organ, so why are we giving it that little relevance when designing robots? Sorry Star Wars, this is not how humanoid droids will look like in the future!

The relevance of Skin for Humans

Skin is crucial for every being, but only a few scientists seem to realize its importance when it comes to a robot’s appearance. Besides giving living things the ability to interact with the environment in a sensing way, temperature regulation is one of the most important things our skin is made for [1]. Sweating is a brilliant mechanism nature designed for creatures, while local sweating is a progression humans can count on nowadays.

Another great feature is the ability to provide a barrier against the external environment. The skin prevents us from water loss and protects us from foreign chemicals and micro-organisms [2]. This can be achieved due to various skin-layers with different functions. Of course, our body gets strength and stiffness, too, thanks to the largest organ of the human body.

Benefits for Robots

Human skin is composed of several layers. Each layer has a unique structure and function, but when it comes to design robots, it often has just a cosmetic purpose.

To enable robots to sense their environment, scientists at TU Munich developed artificial skin cells for the robotic purpose [3]. In addition, a self-organizing network builds a kinematic model of the robot, and the skin was attached to it. With multi-modal sensor signals, scientists try to design safer robots that are capable of identifying contact as well as pre-contact interactions.

The image was taken by Astrid Eckert, TUM

The H-1 robot shown in the image above is equipped with 1260 cells and more than 13000 sensors. The cells themselves can measure:

vibrations (acceleration sensor)

pressure (capacitive force sensors)

pre-touch (proximity sensor)

temperature (temperature sensor)

Then, the microcontroller samples and filters sensor data on each cell and prepares the information for distribution.

Implementing these hexagonal skin cells can not only make humanoid robots huggable. Even robots’ feet are equipped with sensors to make them more responsible for uneven floors and thus improves their ability to walk enormously, as shown in the TED Talk.

Scientists working on e-skin figured out similar needs for artificial skin [4]. Various types of sensors need to be distributed over different areas. Appropriate placement of the sensors is important, similar to the different areas of sensitivity on a human body. Sensors need to be embedded within a soft and stretchable material while the components are fast response and low-power. Nevertheless, strong processing capabilities are necessary to handle large generated data sets. The skin itself should benefit from a set of different sensors, like touch, temperature, gas, and electrochemical sensors.

Challenges to Overcome

One of the biggest challenge Gordon Cheng’s team has to deal with is handling the amount of data the hexagonal skin cells are producing. Multi-modal tactile signals of over 1200 cells need a large communication bandwidth and a lot of processing power. Different implementation frameworks allow a reduction of information load but a redundant cell network is still crucial for its operation.

In essence, applying more cells is not necessarily the better choice. Scientists and engineers still need to find a trade-off between benefits skin cells can enable to important robotic parts while areas with lower importance need to compromise.

Conclusion

Human skin is made out of cells, so why shouldn’t we try to apply skin-cells for robots too? A metal skin like C-3PO’s one is obviously not made for sensing. To overcome this problem, scientists are working on similar approaches.

Cheng’s team created a self-calibrating artificial skin made out of hexagonal cells, which can work autonomously. The biggest advantage of this skin would be the improved security aspect with various features provided by different sensors. Robots could finally sense their environment and prevent harming humans (or even themselves) thanks to pre-contact detection.

Even though some features of the human skin are not covered in the current field of research yet, first concepts lead to plenty of new opportunities and can enable human-robot interaction more safely.