The term 'rapid prototyping' has been synonymous with three-dimensional (3D) printing ever since the additive manufacturing technique began moving into just about every industry imaginable, over a decade ago. Whether it is being used to make plastic kitchenware, a steel hinge for the pressurized door of an airliner, or even a titanium nozzle for a rocket engine, 3D printers can rise to the challenge of making it.
There is a problem with 3D printing, however: by its very nature, it is a slow additive process in which solid items are built up painstakingly in a layer-by-layer fashion. However, help is at hand: certain classes of flexible electronic devices could soon be prototyped at much greater speed using some newly developed desktop cutting techniques, as the ACM CHI Conference on Human Factors in Computing Systems (CHI 2019) will hear in Glasgow, Scotland, this week.
At CHI 2019, digital manufacturing researchers Jürgen Steimle and Daniel Groeger of the HCI lab at Saarland University in Saarbrücken, Germany, will demonstrate LASEC, a system they have devised that lets them fabricate two-dimensional (2D) stretchable devices, including the necessary electronic circuitry, using a computer-controlled laser cutter.
In addition, a joint Massachusetts Institute of Technology (MIT)/University of Tokyo team led by Junichi Yamaoka and Stefanie Mueller, both of MIT's Computer Science and AI Laboratory (CSAIL), will unveil a 3D prototyping system called FoldTronics, which uses a bladed, computer-controlled desktop device called a cutting plotter to fabricate 2D plastic sheets that can be folded, origami style, into honeycomb-like 3D structures populated with circuit connections.
The overarching aim of both LASEC and FoldTronics is to allow interaction designers to make prototypes of devices, like stretchy, body-hugging quantified-self wearables, or ultra-flexible game controllers, in a very short time.
Because the methods are quick, the hope is that designers will get more chances to iterate with still more prototype variants before they commit to a full 3D design. It's something HCI really needs, says Floyd Mueller of the Exertion Games Lab at the Royal Melbourne Institute of Technology in Australia. "We definitely need more tools like these, as rapid prototyping is key for good designs, but current personal fabrication devices, especially 3D printers, do not support iterative processes well."
Enter LASEC. Short for Laser-fabricated Stretchable Circuits, it has two chief aims, Steimle said. "We are doing two things that are hard to achieve on today's 3D printers: first, creating surfaces that are very stretchable, with a defined degree of stretchability. And second, we are integrating conductive circuit tracks inside them. And both are done simultaneously, in a single fabrication step, and very rapidly, within a few minutes, whereas 3D printing typically requires many hours."
The technique is based on the laser cutter, a device used for slicing thin, 2D shapes out of paper, cardboard, wood, or steel, perhaps making beautiful folding paper models in arts and craft applications, or in industry to create replacement parts for machines, like flat metal gaskets. What is notable is their speed: "They are characterized by their high precision and high speed of fabrication," says Steimle.
So how does it work? LASEC takes as its input material a flexible polyester plastic layer coated with a conductive layer, such as a thin layer of carbon paint. Unlike additive 3D printing, the process is then subtractive: driven by design software running on a PC, the laser cuts away some of the combined material, making slits in it where the material needs to be stretchable. "These slits allow the surface to stretch when tensile force is applied," according to the researchers. Next, the laser is used to ablate, or burn away, just the top conducting layer where it is not needed, leaving conducting tracks where components like switches, LEDs, and batteries will need to connect.
The resulting circuits, says Steimle, are stretchable in the directions in which they need to be—with rigid, non-stretching islands where connected components are situated—and allow for the multi-version prototyping of devices in which he says stretchability has become increasingly important. "Many real-world surfaces are stretchable. Think of clothing and the many applications that are emerging in the field of wearables, such as continuous monitoring of health parameters, or tracking the movements of athletes to give personalized feedback," he says.
"The human body itself is stretchable, so devices that more closely integrate with our skin will have to be stretchable, too," Steimle says.
Limited as LASEC is to single-layer circuit boards, however, the Saarland duo are not pretending complex circuits are possible yet, though standalone nonstretchable islands containing microchip-laden modules could be implemented, Steimle says. And it is also currently limited to 2D designs.
FoldTronics, in contrast, allows prototyping in structures that can be folded into 3D shapes.
The FoldTronics development, says MIT's Yamaoka, is in part based on origami, the Japanese art of paper folding. FoldTronics can be used to fold a flat plastic sheet into a strong honeycomb-shaped 3D structure which, unlike LASEC, can be used to provide large volumetric prototypes of simple electronic gadgets.
To make these, the FoldTronics team reveal in their research paper that they have written design software that allows a device called a cutting plotter to guide a thin, sharp blade (instead of a laser cutter's powerful light source) to score, cut, or perforate a 2D sheet to make it foldable, origami style. "A cutting plotter is a machine tool that can cut and engrave paper and plastic into a desired shape. It is mainly used for DIY, crafting, and creating stickers," says Yamaoka. His main reason for using it instead of a laser cutter, he says, is its very low cost.
Once the plastic sheet is scored (but before folding it), users will place it back in the plotter with a thin layer of copper sheeting on top of it, allowing electronic connections to be written on the plastic, as can be seen in the team's CHI2019 demo video. Once those are written, the components can be soldered on before the folding operation is completed.
The MIT/University of Tokyo team has already constructed some imaginative FoldTronics prototypes, such as a smartwatch with a vertically expanding display peppered with LEDs. They also prototyped a sensing test tube holder matrix that has built-in light sensors to measure fill levels in an array of test tubes, and measure the color of the chemicals in the tubes, too. They now plan to prototype a number of Internet of Things devices using it, says Yamaoka.
Speed is everything
The two new prototyping methods vary widely in cost. The LASEC team's laser cutter is a piece of industrial equipment costing $10,000 (although some next-generation laser cutters will soon be available for around $2,000, says Gröger).
In contrast, the cutting plotter used in the FoldTronics project sells for a mere $300. Pitch that against typical maker lab 3D printers that come in anywhere between $500 and $2,000 typically, and $10,000 at the top end, and it's clear there are trade-offs to be made.
Yet the main imperative driving all this is iteration speed, not cost-cutting, says Yamaoka. "We could make a simple prototype with one LED and a battery within 18 minutes. A 3D printer would take between one and two hours to make the same-sized object," he says.
It's a capability that has impressed one observer who is very familiar with the capabilities of maker technologies: Patrick Baudisch, chair of the Human-Computer Interaction Lab at the Hasso Plattner Institute in Potsdam, Germany. At CHI2019, Baudisch and his research team will be revealing Kyub (pronounced 'cube'), a design system that uses laser cutters to create components for "sturdy structures"—anything from shelving to coffee tables and desks.
With his deep laser cutter experience in mind, Baudisch says he is impressed with both new electronic prototyping methods based on fabrication technology. "LASEC and FoldTronics both look like great ways of saving time on projects where you are prototyping devices rather than making durable products, especially as they both have integrated design tools to make it all work."
The way both methods create inbuilt conductive interconnections will avoid the need for the nest of dangling wires that are common in most breadboarded prototypes, Baudisch says. He also applauds FoldTronics' use of a low-cost cutting plotter: "That type of cutter is an under-appreciated option," he says.
Both the LASEC and FoldTronics teams plan further development of their techniques. The Saarland team wants to develop a 3D version of LASEC, while Yamaoka says he has plans to take the FoldTronics concept to different scales entirely: "We would now like to apply this prototyping technology to various fields, such as architecture and nanotechnology."
Paul Marks is a technology journalist, writer, and editor based in London, U.K.
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