Swarms of assembly robots show potential for building larger structures

Swarms of assembly robots show potential for building larger structures

MIT researchers have made significant strides toward creating robots that can practically and economically assemble almost anything, including things much larger than themselves, from vehicles to buildings to larger robots.

The new work, from MIT’s Center for Bits and Atoms (CBA), builds on years of research, including recent studies showing that objects like a deformable airplane wing and a functional racing car can be assembled from small identical lightweight pieces—and that robotic devices that would perform some of this assembly work. Now, the team has shown that both the assembly robots and the components of the structure being built can all be made from the same subunits, and the robots can move independently in large numbers to quickly perform large-scale assemblies.

New work is featured in the journal Nature Communications Engineeringin a paper by CBA PhD student Amira Abdel-Rahman, CBA Professor and Director Neil Gershenfeld, and three others.

A fully autonomous self-replicating robot assembly system capable of both assembling larger structures, including larger robots, and planning the best construction sequence is still years away, Gershenfeld says. But the new work takes important steps toward that goal, including working out the complexities of when to build more robots and how big to make them, as well as how to organize swarms of robots of different sizes to efficiently build a structure without bumping into each other.

As in previous experiments, the new system involves large, usable structures made of a series of small, identical subunits called voxels (the volumetric equivalent of a 2-D pixel). But while earlier voxels were purely mechanical structural elements, the team has now developed complex voxels, each of which can transmit both energy and data from one unit to another. This could make it possible to build structures that not only carry loads, but also do the work of lifting, moving and manipulating materials – including the voxels themselves.

“When we build these structures, you have to build in intelligence,” says Gershenfeld. While earlier versions of assembly robots were connected by bundles of wires to their power source and control systems, “the idea of ​​structural electronics—creating voxels that carry energy and data as well as power—emerged.” Looking at the new system in action, he notes, “There are no wires. There’s just structure.”

The robots themselves consist of a chain of several voxels connected end-to-end. These can grab another voxel using the attachment points at one end, then move like an inchworm to the desired position where the voxel can be attached to the growing structure and released there.

Gershenfeld explains that while the earlier system demonstrated by members of his group could in principle build structures of any size, as the size of these structures reached a certain point relative to the size of the assembler robot, the process would become increasingly inefficient due to the increasingly long paths each robot would have to travel , to deliver each piece to its destination. At that point, with the new system, the robots could decide it was time to build a larger version of themselves that could reach longer distances and reduce travel time. An even larger structure may require another such step, with new larger robots creating even larger ones, while parts of the structure that contain a lot of fine detail may require more of the smallest robots.

As these robotic devices work to build something, Abdel-Rahman says, they face choices every step of the way: “It could build a structure, or it could build another robot of the same size, or it could build a bigger robot. Part of the work the researchers have focused on is creating algorithms for making such decisions.

“For example, if you want to build a cone or a hemisphere,” he says, “how do you start with path planning and how do you divide that shape” into different areas that different robots can work on? The software they developed allows someone to input a shape and get an output that shows where to place the first block and each one after that, based on the distances to cover.

Gershenfeld says there are thousands of articles published on route planning for robots. “But the next step, where the robot has to decide to build another robot or a different kind of robot – that’s new. There’s really nothing before that.”

While the experimental system can be assembled and includes power and data lines, in current versions the connectors between the small subunits are not strong enough to support the necessary load. The team, including graduate student Miana Smith, is now focused on developing stronger connectors. “These robots can walk and they can place parts,” says Gershenfeld, “but we’re almost—but not quite—at the point where one of these robots creates another one and it goes away. And that’s for fine-tuning things like the power of the drives and the power of the joints. … But it’s far enough that these are the parts that will lead to it.”

Ultimately, such systems could be used to construct a wide variety of large, high-value structures. For example, the way airplanes are built today involves huge factories with gantries much larger than the components they’re building, and then “when you make a jumbo jet, you need jumbo jets to carry the parts of the jumbo jet to make it,” Gershenfeld he says. A system like this, assembled from small parts assembled by small robots, makes “the final assembly of the aircraft a single assembly”.

Similarly, he says, when building a new car, “you can spend a year tooling” before the first car is actually built. The new system would bypass this entire process. Such potential efficiencies are why Gershenfeld and his students work closely with car companies, aerospace companies and NASA. But even the relatively low-tech construction industry could potentially benefit.

While there is growing interest in 3D printed houses, these today require printing machines as large or larger than the house being built. Again, the potential for such structures to be assembled by a swarm of tiny robots instead could bring benefits. And the Defense Advanced Research Projects Agency is also interested in working on the possibility of building structures to protect the coast against erosion and sea level rise.

Aaron Becker, an associate professor of electrical and computer engineering at the University of Houston who was not associated with the research, calls the paper a “home run” [offering] an innovative hardware system, a new way of thinking about swarm scaling, and rigorous algorithms.”

Becker adds, “This paper explores a critical area of ​​reconfigurable systems: how to rapidly expand a robotic workforce and use it to efficiently assemble materials into a desired structure. … This is the first work I’ve seen that attacks the problem from a radically new perspective—using a raw set of robot parts to create a set of robots whose sizes are optimized to build the desired structure (and other robots) as quickly as possible .”

The research team also included MIT-CBA student Benjamin Jenett and Christopher Cameron, who is now at the US Army Research Laboratory. The work was supported by NASA, US Army Research Laboratory, and CBA consortium funding.

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