Researchers at MIT have made significant steps toward creating swarms of robots that could practically and economically assemble nearly 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), has demonstrated that both assembler robots and the components of the structure being built can all be made of the same subunits, and that the robots can move independently in large numbers to accomplish large-scale assemblies quickly.
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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, said CBA’s director, Neil Gershenfeld, but the new work makes important strides toward that goal, including working out the complex tasks of when to build more robots and how big to make them, as well as how to organise swarms of bots of different sizes to build a structure efficiently without crashing into each other.
As in previous experiments, the new system involves large, usable structures built from an array of tiny identical subunits called voxels (the volumetric equivalent of a 2D pixel). But while earlier voxels were purely mechanical structural pieces, the team has now developed complex voxels that each can carry both power and data from one unit to the next. This could enable the building of structures that can not only bear loads but also carry out work, such as lifting, moving and manipulating materials – including the voxels themselves.
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‘When we’re building these structures, you have to build-in intelligence,’ Gershenfeld said. While earlier versions of assembler bots were connected by bundles of wires to their power source and control systems, ‘what emerged was the idea of structural electronics – of making voxels that transmit power and data as well as force.’ Looking at the new system in operation, he pointed out, ‘There’s no wires – there’s just the structure.’
The robots themselves consist of a string of several voxels joined end-to-end. These can grab another voxel using attachment points on one end, then move inchworm-like to the desired position, where the voxel can be attached to the growing structure and released there.
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Gershenfeld explained that while the earlier system demonstrated by members of his group could, in principle, build arbitrarily large structures, as the size of those structures reached a certain point in relation to the size of the assembler robot, the process would become increasingly inefficient because of the ever-longer paths each bot would have to travel to bring each piece to its destination. At that point, with the new system, the bots could decide it was time to build a larger version of themselves that could reach longer distances and reduce the travel time. An even bigger structure might require yet another such step, with the new larger robots creating yet larger ones, while parts of a structure that include lots of fine detail may require more of the smallest robots.
As these robotic devices work on assembling something, said CBA doctoral student Amira Abdel-Rahman, they face choices at every step along 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 been focusing on is creating the algorithms for such decision-making.
‘For example, if you want to build a cone or a half-sphere,’ Abdel-Rahman said, ‘how do you start the path planning, and how do you divide this shape’ into different areas that different bots 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 that need to be traversed.
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There are thousands of papers published on route-planning for robots, Gershenfeld said. ‘But the step after that – of the robot having to make the decision to build another robot or a different kind of robot – that’s new.’
While the experimental system can carry out the assembly and includes the power and data links, in the current versions, the connectors between the tiny subunits aren’t strong enough to bear the necessary loads. The team is now focusing on developing stronger connectors. ‘These robots can walk and can place parts,’ Gershenfeld said, ‘but we are almost – but not quite – at the point where one of these robots makes another one and it walks away. And that’s down to fine-tuning of things, like the force of actuators and the strength of joints, but it’s far enough along that these are the parts that will lead to it.’
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The research has been published in Nature Communications Engineering.