Concrete dreams

3D printers are showing great promise in building construction, printing prefabricated components that are then transported to the construction site. A research project at the Technical University of Liberec in the Czech Republic aims to create a mobile robot that can print buildings directly on site. The team is using B&R controls, drives, HMI and software solutions to control the ground-breaking robot's sophisticated print head.

The first 3D printers used in architecture played a supporting role in the design process: producing plastic models for displays and presentations. Now, larger printers are beginning to fabricate concrete components used in the construction of actual buildings. At the Technical University of Liberec (TUL) in the Czech Republic, however, a team of researchers is already preparing for the next step in this evolution: mobile robots that will do the printing right at the construction site.

3D printing promises exciting benefits in the field of building construction. Building components are now being printed from a mix of concrete and reinforcing materials. The new design possibilities are inspiring architects' creativity, and the components are considerably more economical to produce. Since they don't require the extensive formwork needed for conventional monolithic structures, they also result in less waste.

Exciting as these experimental methods are, however, the current state of the art still has a number of drawbacks. The components are fabricated in a production hall and must then be transported to the construction site. The vehicles used for transport place constraints on component dimensions and generate considerable logistical costs and environmental impact. Current systems also print only the vertical elements of the building, while the horizontal slabs for the floors and ceilings are created using conventional methods.

The TUL research team aims to overcome these drawbacks and print entire multistory buildings – floors and ceilings included – directly on the construction site. The mobile 3D printing robot will be called Printing Mantis, due to the robot arm's resemblance to the elongated forelegs of the praying mantis insect. The project is being conducted in cooperation with the Institute of Information Theory and Automation of the Academy of Sciences of the Czech Republic and the Klokner Institute of the Czech Technical University in Prague and will feature controls, drives, HMI and software from B&R.

Jiří Suchomel, from the TUL Faculty of Arts and Architecture, predicts that on-site printing with the Printing Mantis will allow architects even greater creativity to implement intricate shapes with unprecedented accuracy of 2-3 millimeters. The robot will assemble multistory buildings on site like large Lego pieces. "Horizontal slabs will be printed on the ground and hoisted into place, while the vertical walls will be printed directly in their final location," describes Suchomel. "All directly on site."

Cement production has a significant environmental impact, and the aggregates and gravel added to make concrete are in limited supply. "That's why we want to build light, thin-walled concrete structures with unconventional reinforcements," explains Suchomel. "That will significantly reduce material consumption."

The 3D printers most of us are familiar with use powders and plastics. Adapting the design to print a house, on the other hand, involves quite a bit more than simply replacing these materials with conventional concrete. The cement mix alone is a major challenge. It must be flexible enough to work with, yet also solidify fast enough to support subsequent layers. Ordinary concrete matures for 28 days, but the printed structure must be able to hold itself up immediately.

Another key challenge is giving the robot the ability to print walls of virtually any curvature, including inflection points, and to implement sharp angles and interruptions. "That's important, so that we can give architects maximum freedom," says one of the Con4Bot's lead designers, Associate Professor Václav Záda from the TUL Institute of Mechatronics and Computer Engineering. Thanks to the Con4Bot's design, when the end effector stops printing briefly, for example to leave space for a door or window, the rest of the robot can continue moving. "The large robot is able to retain its considerable kinetic energy," says Záda, "and that's something other machines can't do."

When it is complete, the Printing Mantis will be a rotating and sliding robotic arm with a horizontal reach of up to 5.6 meters and a vertical reach of 3.3 meters. The project is being conducted using two test setups. The first is a SCARA robot. Currently being tested at 1:4 scale, the full-scale version will later be transported by a standard construction truck. The second is a Cartesian robot at the Klokner Institute in Prague, where researchers are testing and developing the print head along with different building material mixtures.

After a decade of cooperation with B&R, the research team knew the automation components would deliver not only the necessary performance, but also the scalability to grow along with the robot through future phases of development and implementation. "We put together an automation solution that can handle whatever new requirements appear down the road," says B&R engineer Tomáš Kohout.

The drive system includes axes with absolute multiturn encoders, servo motors, a modular control system and advanced safety functions. "The integrated B&R motion control system made the solution very pleasant to work with, both for designers and for future operators," says Leoš Beran from the TUL Institute of Mechatronics and Computer Engineering. "The solution is exceptionally scalable for the future, which is especially important for a cutting-edge research project like this."

The robot's print head end effector is operated by a B&R control system. The core of the 3D printing software is based on standard B&R CNC components. Additionally, B&R's mapp Technology toolkit provided ready-made software components that saved the team from having to program basic functions such as recipe handling and user management.

The control software runs on a powerful industrial PC from B&R's Automation PC series. "In addition to the control software, the Automation PC will also run the web-based HMI application," says Kohout. The HMI application is displayed on a swing-arm-mounted Automation Panel 5000 with custom operating elements. "The high-end HMI offers a high degree of flexibility and control ergonomics," notes Kohout, "and the web-based HMI application can just as easily be viewed on a PC, smartphone or tablet."

When and where the Printing Mantis will create its first multistory building on site remains to be seen. Among other things, that depends on the progress of building regulations for printed structures. One thing is certain, however: with B&R as an automation partner, the research team has access to a broad portfolio of flexible, scalable solutions – and can quickly and easily adapt the Printing Mantis to whatever challenges it encounters printing the buildings of the future.