Stefanie Pender

Large-format additive · 2022

Dar Smart Bridge

Engineering a bridge that designs and builds itself. Video by Autodesk Research.
A person walking across the printed bridge on an exhibition floor, with a live digital-twin readout of the structure on a screen beside it
The finished span in use at Autodesk University, with the live sensor model running alongside it.

Two 3D-printed pedestrian bridges, a 2 metre prototype and a 5 metre single-cantilevered span, built with the engineering firm Dar. Both were printed from recycled PETG and glass fibre as large-format extrusions on a six-axis arm riding a linear track, instrumented with embedded strain and fibre-optic sensors, and exhibited as structures the public actually walked across.

Role
  • Designed and set up the work cells
  • Integrated the Strangpresse extruder onto the arm
  • Integrated the safety systems
  • PLC programming
  • Toolpath generation
  • Material analysis
  • Robot and sensor programming
  • Fabrication supervision
Team
Dar, with the Autodesk Technology Center, Boston
Stack
ABB IRB 4600 on an IRBT linear track, Strangpresse extruder, RobotStudio, PowerMill, Faro Focus scanning, Project Dasher
Timeline
Scope agreed June 2020 · 2 m printing March 2021 · 2 m debut at IRF November 2021 · 5 m printing July 2022 · 5 m debut at Autodesk University September 2022
Read more
Engineering a Bridge that Designs and Builds Itself · Putting the “Smart” into the Dar Smart Bridge · Dar · VoxelMatters

Printing it

The spans were printed in continuous beads on an ABB IRB 4600 riding a linear track, with a Strangpresse extruder on the flange. Parts of the geometry were printed on an angled bed rather than flat. That keeps the bead perpendicular to the surface where the structure curves, at the cost of a much harder setup.

Material selection was its own research track: tensile strength along and across the print direction, melt and glass-transition temperature, maximum extrusion speed, UV and ageing behaviour, recyclability, and bead quality all had to land at once.

An ABB robot arm with a pellet extruder printing the bridge structure, lit in red by the heated end effector
Printing in progress on the six-axis arm.
The robot arm extruding the curved deck surface of the bridge, lit orange by the heated nozzle
Laying down the deck surface.
A printed bridge abutment section bolted to an aluminium base plate, showing the cellular internal geometry
An abutment section on its base plate.
The printed bridge structure viewed end-on, showing the internal cellular ribs beneath the deck
The cellular rib structure under the deck, where the generative geometry pays for itself.

Designing for the process

The geometry was generatively designed against what the printer could actually do, not the other way round: a maximum overhang angle of 45°, a minimum element thickness of 32 mm, and a fixed print direction. Toolpaths came out of the Fusion manufacture workspace through a robotics add-in that emitted native robot code.

An ABB robot printing onto a steeply angled print bed in the shop, with an operator monitoring from a workstation
Angled printing. Tilting the bed keeps the bead square to the surface where the structure curves.

Instrumenting it

Sensors went in during the print rather than being bonded on afterward: strain gauges and fibre Bragg grating (FBG) sensors placed at structurally meaningful points, feeding a live model of the span.

Interlayer temperature was monitored throughout the print, because bond strength depends on how hot the previous layer still is when the next one lands. Above 110 °C was the target; 80–110 °C a warning band; below 80 °C a risk of a weak interlayer bond.

The completed bridge installed in a landscaped exhibition set with plants and rocks
Installed and open to foot traffic.
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