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Integrating Strings and Fibers into Additive Manufacturing Designs

C. J. Kimmer, Indiana University Southeast

C. K. HarnettUniversity of Louisville

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Feasible for individuals making one item, but not sustainable for mass production

Strings and fibers: laborious to install

. e-Nable Raptor Hand assembly: https://youtu.be/5HVwC3RnWXk?t=46m22sBicycle helmet assembly: https://youtu.be/DVzoognroCY?t=28s. Toy assembly: https://youtu.be/pEerHkxMN2w?t=9m22s

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Functional fibers will create new kinds of integrated devices

How can we install fibers in 3D printed and machined parts?

High tensile strengthOptical waveguiding

Fluid flow in hollow fibersCapacitive touch sensing

Electrical conductivityActuation Examples of functional fibers from www.rle.mit.edu/fabric

Embroidery machine = sewingmachine + x-y translation stage.

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Embroidery approach:Use a solublestabilizer sheetto install2D fiber layersin and around3D parts

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Strings make flexible, versatile hingesTightly spaced hinges for folding to a final shape

Loose hinges formotion and draping

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Alignment is important but cheap machines don’t offer many controls

Lowest cost consumer machine has:•1 degree angle increments•0.5 mm translation increments

Instead, we measure the location of two points on the part and calculate a rotated/translated embroidery pattern. Most machines can resolve 0.1 mm stitch positions.

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What if the sewing thread is a “functional” fiber?• Fibers with functions like high

tensile strength, conductivity or waveguiding are not designed with machine sewing in mind

• Conductive thread works ok as needle thread; breaks often

• BUT most are too thick or fragile. Some of them work as bobbin thread.

• If a thick bobbin thread is used, it usually stays on one side of the material:

https://youtu.be/v/ML8CMNzW6Tg

Sewing animation: watch the different paths of the needle (black) and bobbin (blue) threads. Source:

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Conductive fibers carry signals from soft sensors to a Bluetooth board

• First the needle has to be aligned to two holes on the printed circuit board

• Thread: Silver-plated nylon• Holes: Copper on top, bottom and sides,

1.5 mm diameter

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A state-detection switch for a bistable beam, made from conductive thread

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Switches capture the bistable behavior

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Switch threshold is adjustable by beam compression ratio

Switching angles follow the calculated curve for rectangular cross-section beams

This means you could integrate a limit switch into a piece of flex circuit and use circuit length to adjust the limit angle

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Embroidered cables in a 3D printed structure

• Cables deflect the needle• The structure is 3D

printed in PLA directly on water-soluble stabilizer (sticky side up)

• Alignment marks too.• Then cables are added

using the embroidery machine

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Fibers move the 3D printed pointer

Dissolving the stabilizer in water Device in motion

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Fiber layers could snap or drop in during a 3D print

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Design rules

• Holes in solid parts have to be greater than needle diameter; needles range from 0.6 to 1.5 mm on consumer machines

• Avoid designs that put holes in a line, watch out for “perforating” your part

• Make the functional fiber the underlying bobbin thread (usually) to minimize damage.

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Acknowledgments

This work is supported by Kentucky Science and Engineering Foundation award KSEF-3503-RDE-019 and a travel supplement from the University of Louisville.Thanks to Amer Beharic for test-driving the 3D printing methods, and Tim Gillespie for cutting PCBs at FirstBuild.

Questions?