Prof. Dr. Patrick Baudisch

AirTied: Automatic Personal Fabrication of Truss Structures

Lukas Rambold, Robert Kovacs,Conrad Lempert, Muhammad Abdullah, Helena Lendowski, Lukas Fritzsche, Martin Taraz, and Patrick Baudisch

We present AirTied, a device that fabricates truss structures in a fully automatic fashion. AirTied achieves this by unrolling a 20cm-wide inflatable plastic tube and tying nodes into it. AirTied creates nodes by holding onto a segment of tube, stacking additional tube segments on top of it, tying them up, and releasing the result. The resulting structures are material-efficient and light as well as sturdy, as we demonstrate by creating a 6m-tower. Unlike the prior art, AirTied requires no scaffolding and no building blocks, bringing automated truss construction into the reach of personal fabrication.

As illustrated by the following figure, users start by modelling a truss structure using our custom editor. Its exporter converts the model into executable instructions and sends them to the AirTied device (a). (b) In order to fabricate the structure, AirTied device starts by unrolling some tube. (c) AirTied pushes the first tube segment into a physical bracket, which we will refer to as a bookmarkingslot since it marks the start of a segment. (d) AirTied now unrolls more tube and holds on to it using a second bookmarking slot. AirTied continues this process and fills another two bookmarking slots (the double tetrahedron requires a minimum of three bookmarking slots). (e) When AirTied re-encounters the second node bookmarked earlier, AirTied inserts the tube again into the second bookmarking slot, forming a second layer, (f) wraps a wire-tie around both tube layers, and (g) ejects the completed node from the bookmarking slot. After similarly constructing the remaining five nodes, the AirTied system ejects the last node, completing the model. (h) The user now cuts off the tube, attaches a compressor using a hose clamp, sealing off the tube (as shown in Figure 8), and (i) inflates the structure.

The following figure shows the AirTied device. Its central element is a mechanism that allows it to “bookmark” and tie tube segments.

AirTied achieves this with the help of two major functional groups. We reveal them by removing the tube unroller, i.e., two actuated rubber rollers that the spool rests on. (b) Group 1: A set of (here, five) bookmarking slots are organized in a rotationally symmetric arrangement around the perimeter of the device. Each slot features a lock, i.e., asmall servo-actuated lever that allows fixating the tube in the slot. (c) Group 2: The rotary mechanism rotates the components located at the center of the device, i.e., the tube unroller, the tube pusher, and the wire tie gun.

To evaluate the functionality of the system, we fabricated five models of varying complexity, tube length, scale, and bookmarking slot requirements, i.e., the three models from the water polo scene: