IN SITU FABRICATOR

What if, instead of building factories to prefabricate building components, we could fabricate entire buildings by digitally controlled machinery directly at the construction site? Can we redefine conventional construction processes, augment them with the use of robots and develop alternative tectonics to improve structural performance and minimise material waste, and increase worker safety on construction sites? The In situ Fabricator (IF) – a context-aware mobile construction robot for fabricating building elements directly on construction sites – is the answer to this challenge. Its integrated on-board sensing and computation system is developed to enable autonomous repositioning procedures, localisation of the endeffector and the adaptation of fabrication data according to unforeseen material behaviour and fabrication-related tolerances – without the need for external measurement devices.

At DFAB HOUSE, the IF facilitated the on-site fabrication of a doubly curved steel rebar mesh for a load-bearing reinforced concrete wall featuring the Mesh Mould technology. Two complementary vision-based sensing systems provided the feedback necessary to accurately build the undulated structure: For the robot’s localisation, the site was equipped with markers. During build-up, the robot moved along the length of the fabricated mesh structure, while a camera on the end effector measured the positions of the markers to situate the robot relative to its surroundings. The mesh was fabricated by the IF through continuous bending and welding of 6-mm rebar in vertical layers. Two additional cameras monitored this process to enable compensation on the fly for unpredictable springback behaviour and deformation of the fabricated rebar mesh. In this way, the steel rebar mesh was successfully built as a free-standing structure without any additional support.

The 12-m-long undulated steel mesh on the ground floor of DFAB HOUSE consists of 335 layers and more than 20,000 welding nodes. The overall production time took 125 hours, during which the robot was repositioned eight times.

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