Scientists from Nanyang Technological University, Singapore (NTU Singapore) have developed a technology whereby two robots can work in unison to 3-D-print a concrete structure. This method of concurrent 3-D printing, known as swarm printing, paves the way for a team of mobile robots to print even bigger structures in the future. Developed by Assistant Professor Pham Quang Cuong and his team at NTU’s Singapore Centre for 3-D Printing, this new multi-robot technology is reported in Automation in Construction. The NTU scientist was also behind the Ikea Bot project earlier this year, in which two robots assembled an Ikea chair in about nine minutes.
Using a specially formulated cement mix suitable for 3-D printing, this new development will allow for unique concrete designs currently impossible with conventional casting. Structures can also be produced on demand and in a much shorter period.
Currently, 3-D-printing of large concrete structures requires huge printers that are larger in size than the printed objects, which is unfeasible since most construction sites have space constraints. Using multiple mobile robots that can 3-D print in sync means large structures and specially designed facades can be printed anywhere, as long as there is enough space for the robots to move around the work site.
The NTU robots 3-D-printed a concrete structure measuring 1.86m x 0.46m x 0.13m in eight minutes. It took two days to harden and one week for it to achieve its full strength before it was ready for installation.
“We envisioned a team of robots that can be transported to a work site, print large pieces of concrete structures and then move on to the next project once the parts have been printed,” explained Asst Prof Pham from NTU’s School of Mechanical and Aerospace Engineering.
“This research builds on the knowledge we have acquired from developing a robot to autonomously assemble an Ikea chair. But this latest project is more complex in terms of planning, execution, and on a much larger scale.”
Printing concrete structures concurrently with two mobile robots was a huge challenge, as both robots have to move into place and print their parts without colliding with each other. Printing the concrete structure in segments is also not acceptable, as joints between the two parts will not bond properly if the concrete does not overlap during the printing process. This multi-step process starts by mapping the design to be printed and assigning a specific part of the printing to a robot. It then uses a special algorithm to ensure that each of robot arms do not collide during the concurrent printing.
Using precise location positioning, the robots then move into place and print the parts in good alignment, ensuring that the joints between the separate parts are overlapped. Finally, the mixing and pumping of the specialised liquid concrete mix have to be blended evenly and synchronised to ensure consistency. Professor Chua Chee Kai, executive director of the Singapore Centre for 3-D Printing, said disruptive Industry 4.0 technologies like additive manufacturing can be advanced even further when combined with other innovative technologies like robotics, AI, materials science and green manufacturing techniques.
“This multiple-robot printing project is highly interdisciplinary, requiring roboticists to work with materials scientists to make printable concrete. To achieve the end result of a strong concrete structure, we had to combine their expertise with mechanical engineers and civil engineering experts. This innovation demonstrates to industry what is feasible now, and proves what is possible in the future if we are creative in developing new technologies to augment conventional building and construction methods.”
Moving forward, the NTU research team will look at integrating even more robots to print larger scale structures, optimising the printing algorithm for consistent performance and improving the concrete material for faster curing.
Xu Zhang et al, Large-scale 3D printing by a team of mobile robots, Automation in Construction (2018). DOI: 10.1016/j.autcon.2018.08.004