Robots simultaneously 3D-printed from both solids and liquids

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Hexapod robot with all mechanical parts fabricated in a single step(Credit: MIT)

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Robots have a tremendous potential, but if a way can't be found to manufacture them quickly, cheaply, and in large numbers, that potential may remain exactly that. To that end, MIT's Computer Science and Artificial Intelligence Lab (CSAIL) has come up with a new way to make soft, hydraulically-powered robots in one step using commercial 3D printers that can print solid and liquid parts simultaneously.

The problem with the anticipated robotic industrial revolution is that robots tend to be very complex machines that require a lot of assembly. This is not only time-consuming and a general bottleneck, but it makes it very difficult when many robots are needed for a specific task. 3D printing can help, but so long as it's confined to making only discrete parts, its utility is only limited. What the CSAIL engineers are working on is a way to make complex robots without the need to assemble them.

Using a commercial 3D printer, the CSAIL team has come up with a novel technique for printing fully-functional robots in one go. The idea is that by printing active, integrated systems instead of static parts, it will be possible to create bespoke design templates that can produce different sizes, shapes, and functions on demand.

MIT says that the key is what the team calls "printable hydraulics." This means that instead of printing or otherwise fabricating discrete parts and then assembling them, a 3D inkjet printer with multiple printing heads forms solid, flexible, support, and liquid parts at the same time. For the process, individual droplets 20 to 30 microns in diameter are deposited layer-by-layer to build up legs, gears, pumps, and bellows, in a variety of solid and liquid substances.

These substances are made up of a photopolymer which is cured by high-intensity UV light, or of liquid polyethylene glycol as a hydraulic fluid, which the printer has been modified to use. The eight printing heads allow the printer to deposit different materials next to one another with enough resolution to print complex, pre-filled fluidic channels.

The team says that the process overcomes the messy nature of printing with liquids by using different test geometries and resolutions to make sure that the liquids are added at the appropriate times to fill the cavities properly, and that they don't interfere with the hardening of the solid components. The finished robot only needs a battery and a motor stuck on after printing.

The CSAIL team has already applied the concept in a number of test robots. One is a small six-legged robot powered by 12 hydraulic actuators inside the body. It weighs about 1.5 lb (680 g) and is less than six inches (15 cm) long. It's powered by a DC motor running a crankshaft that feeds a set of fluid-filled bellows pumps, which move the legs. Another version uses a 3D-printed gear pump for continuous flow.

In addition, the team has made a soft silicone-rubber robotic manipulator (seen below) for the Baxter robot, that was fabricated in less time than a conventional one would require. Currently, the six-legged prototype robot takes 22 hours to print, but the team believes that with more advanced printers it should be possible to improve on this time.

According to MIT, the printing process has a number of applications. It can not only make robots quickly and cheaply, but also makes it possible to alter the design in minutes for specific purposes with fewer electronic components. This is especially useful in high-radiation areas where robots have a very limited lifespan and need to be replaced regularly.

"Building robots doesn't have to be as time-consuming and labor-intensive as it's been in the past," says CSAIL Director Daniela Rus. "3D printing offers a way forward, allowing us to automatically produce complex, functional, hydraulically-powered robots that can be put to immediate use."

The CSAIL team's results will be presented in a paper at the 2016 IEEE International Conference on Robotics and Automation (ICRA).

The video below shows the printable robots in action.

Source: MIT

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