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Integrating Strings and Fibers into Additive Manufacturing Designs
- 1. harnettlab.org Integrating Strings and Fibers into Additive Manufacturing Designs C. J. Kimmer, Indiana University Southeast C. K. Harnett University of Louisville
- 2. harnettlab.org 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= 46m22s Bicycle helmet assembly: https://youtu.be/DVzoognroCY?t=28s . Toy assembly: https://youtu.be/pEerHkxMN2w?t=9m22s
- 3. harnettlab.org Functional fibers will create new kinds of integrated devices How can we install fibers in 3D printed and machined parts? High tensile strength Optical waveguiding Fluid flow in hollow fibers Capacitive touch sensing Electrical conductivity Actuation Examples of functional fibers from www.rle.mit.edu/fabric Embroidery machine = sewing machine + x-y translation stage.
- 4. harnettlab.org Embroidery approach: Use a soluble stabilizer sheet to install 2D fiber layers in and around 3D parts
- 5. harnettlab.org Strings make flexible, versatile hinges Tightly spaced hinges for folding to a final shape Loose hinges for motion and draping
- 6. harnettlab.org 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.
- 7. harnettlab.org 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:
- 8. harnettlab.org 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
- 9. harnettlab.org A state-detection switch for a bistable beam, made from conductive thread
- 10. harnettlab.org
- 11. harnettlab.org Switches capture the bistable behavior
- 12. harnettlab.org 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
- 13. harnettlab.org 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
- 14. harnettlab.org Fibers move the 3D printed pointer Dissolving the stabilizer in water Device in motion
- 15. harnettlab.org Fiber layers could snap or drop in during a 3D print
- 16. harnettlab.org 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.
- 17. harnettlab.org 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?
Editor's Notes
- Abstract: Flexible switching sensors for passive shape monitoring Power consumption has to be considered at the beginning of the sensor design process for passive wireless sensors. Pervasive, low-maintenance, battery-free wireless sensing will be realized with sensor elements that match the power resources of RF-powered and other energy-harvesting systems. This presentation will discuss the development of electromechanical switches on flexible substrates. The goal is a passive wireless sticker that can monitor the shape of deployable structures in aerospace applications. These bistable devices hold their state without power, so they can report on the shape of a structure even if polling rates are slow because of energy harvesting system constraints. Topics to be covered are: Design rules for creating these bistable sensor elements for a given bend angle/size/weight range. A power-efficient method for scanning these flexible switch arrays with the microcontroller on WISP, a RFID-based sensor platform. MEMS and larger-scale fabrication methods for these devices. Algorithms for reconstructing a shape from an array of digital switch
- Applications: Circuits, articulated parts that currently require hand threading
- Because some other part pops out. There are a couple of local minima, however.
- “Geometrical frustration” commonly used at the molecular scale, in magnetism etc. Basically, you can’t get all parts of an object to the lowest energy state Because some other part pops out. There are a couple of local minima, however.