Researchers in Switzerland brought out a less traditional, but perhaps fitting instrument to test their 4-centimeter, bug-like soft robot: the fly swatter.
The team at the École polytechnique fédérale de Lausanne institute, or EPFL, whacked the very flat, half-millimeter-thick "DEAnsect" robot a good ten times, in fact.
The robotic bug, tethered to an external power supply by ultra-thin wires, can be folded, squashed with a shoe, or, yes, hit repeatedly with a fly swatter without impacting its ability to move.
"We wanted to make a soft robot that could be fast and robust like insects and yet carry its own power supply and control electronics," lead researcher Herbert Shea told Tech Briefs.
The "DEA" in DEAnsect refers to the hair-thin artificial muscles propelling the robo-insect forward: dielectric elastomer actuators.
Each of the DEAnsect's three legs – one front, one left, and one right – is driven by one artificial muscle.
The artificial muscles consist of an elastomer membrane sandwiched between two soft electrodes. When a voltage is applied, the electrodes are attracted to one another and compress the membrane. When the voltage is turned off, the membrane returns to its initial shape.
Movement is generated by switching the voltage on and off very quickly. The muscle can push each leg forward and backward rapidly – over 400 times a second.
By reducing the thickness of the artificial muscle's elastomer membrane and by creating very-thin, highly conductive soft electrodes, the DEAs operate at relatively low voltages and require less power.
The DEAnsect survived the flurry of attacks, for the most part.
A second version of the robot, an untethered model, did not fare as well as its wired counterpart. A good swat to the wireless model breaks the connection between the onboard electronics and the body, preventing further movement.
The untethered, autonomous DEAnsect weighs less than 1 gram, despite all electronic components, including the battery, on its back. Equipped with a microcontroller and photodiode "eyes," the intelligent bug recognizes black and white patterns and can follow any line drawn on the ground.
This second version of the robot will stand a better chance, says Shea, as electronic components like batteries and circuits also become softer and more flexible.
In a Q&A with Tech Briefs below, Shea reveals how the innovative design opens up new possibilities for the broad use of DEAs in robotics, search-and-rescue efforts, and inspection.
Tech Briefs: Did you really swat this bug? What happened when you did so?
Soft Transducers Laboratory (LMTS) Director Herbert Shea: Glad you asked. Yes, we really swatted the bug! The DEAnsect version without the integrated electronics survives being repeatedly swatted about 10 times.
We power up a DEAnsect, let it zip along, and then swat it, flattening it against the table, keeping the power on. As the body is pushed down, the legs are forced up, stretching the artificial muscles. We then peel the DEAnsect off the table, and it starts moving along again. Swatting the insect turned out to be a fun way to show how robust soft robots can be.
The DEAnsect version with the complete electronics does not survive being flattened as the electrical contacts break; making all electronics parts, including the battery, soft is planned for a future version.
Tech Briefs: How realistic of an idea are soft batteries and soft electronic parts?
Shea: Several groups have reported soft lithium based batteries. Zhenan Bao’s team at Stanford has published fully stretchable transistors and capacitors for e-skins ; others have published reports about liquid-metal based inductors.
It will not be an easy task to pull it all together, but it is certainly feasible. Soft electronic parts might be more realistic in the medium term. You could keep some small, mm-sized silicon integrated circuits, for example, and only have the PCB and battery be truly soft.
Tech Briefs: Help us visualize this DEAnsect. What does it look like?
Shea: DEAnsect is 4 centimeters long (1.5 inches) and very flat; its body is only 0.5 mm thick. From the top it looks like three ovals bonded to a central mm-wide stalk, with a little leg sticking out from under the center of each oval. The legs are angled backwards, so that they push the DEAnsect forward when they are vibrated back and forth using thin artificial muscles. DEAnsect scoots along at 3 cm/s, similar to a fast insect.
The DEAnsect “body” weighs 200 mg. It carries a flexible printed circuit board, weighing 780 mg, that includes a rechargeable battery, microcontroller, photodiodes to “see,” and the control electronics to move each leg 500 times per second. As each leg is independently controlled, DEAnsect can actively steer itself. The onboard computer allows it to perform a variety of tasks, for example, autonomously following a line or recognizing simple gestures.
Tech Briefs: What is special about this robot insect? What can this robot do that others cannot?
Shea: We wanted to make a soft robot that could be fast and robust like insects and yet carry its own power supply and control electronics. In contrast to DEAnsect, nearly all soft robots are tethered to a compressor or to a power supply, especially at insect scale, where it is particularly challenging to make artificial muscles that can deliver high enough power to carry the entire robot. Our goal was to show that artificial muscles, when coupled to the right low-mass electronics, allow for untethered autonomous walking robots.
We developed two versions of DEAnsect. The "wired" version is fully soft. It consists of the robot body without the printed circuit board. Since it is made only of flexible and stretchable materials, it can survive being bent, twisted, and even being hit with a fly swatter, and then keep on moving with agility. This wired version shows the sort of resilience we see in bugs or insects, something rarely seen in mobile robots.
The “integrated” DEAnsect includes the battery and electronics, making it both untethered (no wires) and autonomous, meaning it can sense the environment, and react on its own, namely turning as needed to follow a line, and stopping at the end. DEAnsect is not only untethered and robust, but also fast, weighs less than 1 gram, and can be programmed for other tasks.
Tech Briefs: What kinds of applications do you envision for the DEAnsect?
Shea: The applications are inspired by how insects collaborate. We envisage DEAnsects working together to solve complex problems, similar to how colonies of ants or bees build elaborate structures and ingeniously defend their colony.
Such emergent behavior, or swarm intelligence, builds on many simple individuals with limited processing power and communication abilities. Swarms are extremely robust, as they do not depend on any one individual. We imagine a collective of dozens of next-generation DEAnsects crawling down pipes, exploring a disaster site, sending back pictures. As they move, they will develop skills to explore ever more challenging terrains, for instance using their bodies to build bridges for each other, as ants do.
Tech Briefs: What are “artificial muscles,” and how important are these components to what makes the robot special?
Shea: The artificial muscles we use are extremely thin (18 µm thick) soft and stretchable devices that expand when a voltage is applied. More technically, they are "dielectric elastomer actuators (DEAs)," hence the DEAnsect moniker. Our DEAs consist of a soft silicone elastomer film sandwiched between two extremely soft carbon nanotube electrodes. When a voltage is applied between the electrodes, they compress the silicone membrane, which expands in-plane as is becomes thinner out-of-plane. When the voltage is removed, the muscle returns to its original shape.
The DEAs are crucial to DEAnsect for several reasons: i) DEAs are soft and stretchable, unlike electrical motors, allowing for a soft and deformable robot body. ii) Our DEAs are very fast and have very high power-density: despite weighing less than one mg, they can propel the DEAnsect robot weighing 1000x more. iii) A main obstacle for the widespread adoption of DEAs has been the high drive voltages (typically several thousand Volts). We succeeded here in reducing the DEA drive voltage to below 500V, which allows for sub-gram control electronics.
Tech Briefs: What was the most challenging part of the design to get right?
Shea: The most challenging aspect was developing the stretchable nanotube electrodes for the artificial muscles, as the electrodes must be good electrical conductors, yet extremely stretchable and soft. We fabricate those electrodes one molecular layer at a time, by floating nanotubes on ultra-pure water, gently lining them up, and finally transferring the nanotubes to the silicone elastomer, then repeating the process three times per DEA. It took about 2 years to get this method right.
Designing the DEAs to move the legs efficiently while simultaneously finding the best leg shape and leg stiffness was an important achievement, as was addressing the well-known challenge of electrical and mechanical integration between soft and rigid elements.
As often happens in research, understanding and optimizing the processes took several years, but a new PhD student in our lab can now make a DEAnsect in a morning.
Tech Briefs: What’s next? What kinds of development and tests are on the horizon?
Shea: We are planning a new generation of DEAnsects that can collaborate as a swarm. For this we will add bi-directional wireless communication between the little robots, improved articulated legs to handle more varied terrain with more sophisticated artificial muscles, as well as an electrostatic “hook” so that DEAnsects can lock together, thus allowing them to build complex and reconfigurable structures with their bodies, allowing for much more advanced functionality as one smart system than as a collection of individual robots.
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