Robot “Swarm” 3D-Prints Concrete Structure

For the first time, researchers have 3D-printed a structure using two mobile printers at the same time.

A team of researchers, led by NTU’s Assistant Professor Pham Quang Cuong, show off the structure their robots printed. (Image courtesy of NTU Singapore.)

A team of researchers, led by NTU’s Assistant Professor Pham Quang Cuong, show off the structure their robots printed. (Image courtesy of NTU Singapore.)

Tiny ants working in a coordinated team can create some incredibly complex structures. A new study from the Nanyang Technological University of Singapore paves the way for a future in which robots can 3D print buildings in much the same way, working together in a cooperative “swarm.”

Currently, 3D-printed structures suffer from scale problems. It’s difficult to print a structure much larger than the printer. Typically, the way around it is to have robots print pieces one after the other and join them together later. Sequential printing means that there will be joints between fresh and hardened concrete, weakening bond strength.

To solve the construction scale problem without resorting to piecemeal printing, a team led by NTU Singapore’s Assistant Professor Pham Quang Cuong began looking into the possibility of printing a structure with two or more robots at the same time.

“We envisioned a team of robots that can be transported to a worksite, print large pieces of concrete structures and then move on to the next project once the parts have been printed,” Pham said in the university’s press release.

The team developed robots with a mobile holonomic base. This means that the controllable degrees of freedom are the same as the total degrees of freedom, allowing it to move more flexibly. The robots were equipped with a six-axis robotic arm with a print nozzle at the end to apply concrete. Having a greater number of axes than a conventional gantry-printing system, which typically has three or four, allowed them to print smoother transitions between layers.

To create the paths the robots would follow, and ensure they didn’t bump into each other while printing, the team divided the 3D CAD model of the structure into thin slices and formatted the robots’ paths as an optimization problem. They then used this “sliced” model to program a path for each robot to follow. As they were printing, the robots used a stereo camera and set of sensors and scanners to develop an environmental map to ensure they were on the right path. The researchers set up ArUco markers around the printing area to aid the robots in this task.

Using their maps and sensors, the robots were able to print a structure measuring 1.86m x 0.46m x 0.13m (6.10ft x 1.5ft x 0.43ft) in eight minutes, twice as fast as working with sequential printing. The structure hardened in a day and was at full strength in a week.

The team has several directions they want to pursue with their technology. They plan to develop a better mobility-planning system for rough terrain, as most construction sites have, and add more sensors to the nozzle to determine how it should move to offset terrain changes. They would also like to further optimize their layer joining techniques.

They are excited about what their robots might mean for the future of construction.

“Such an innovation demonstrates to the 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,” said Professor Chua Chee Kai, executive director of the Singapore Center for 3D Printing.