Hi, I'm Lea Albaugh, and I'm presenting an exploration of spacer fabrics as a tunable
metamaterial. This is work done with Jim McCann, Lining Yao, and Scott Hudson at Carnegie Mellon
University. Spacer fabrics are a layered fabric structure
that can be produced on a v-bed weft knitting machine.
They have a characteristic sandwich structure with two face fabrics and this puffy 'filler'
area between them. When the filler is made from a semi-stiff
yarn such as nylon monofilament, otherwise known as fishing line,
the whole structure can act as a soft mechanical linkage.
Or, the same structure can have one face removed
and be turned into a sort of open-faced sandwich, which we call a bristle structure.
This can be for applications including high-surface area
friction attachment points, or in other words, "velcro,"
and biasing motion inputs; so, in this case, the
bristles are acting as a kind of ratchet to converta pneumatic expansion and retraction cycle
into forward locomotion.
In this work, we characterize several useful properties of a spacer fabric,
and we identify the construction parameters which underlay them.
For example, the thickness of a spacer fabric
might be a surprise to those of you who know what a v-bed knitting machine looks like,
because at knitting time, the two faces of the fabric are constructed at a set distance
apart -- that's the distance between the needle beds; it's a property of the knitting machine itself and can't be changed.
To produce a *thick* fabric, like these spacers, the faces are knit with an elastic under tension; after
knitting, the elastic causes the faces to shrink laterally, and the semistiff filler
yarn acts as a jacks mechanism that pushes the faces apart.
Therefore, the final distance between the faces of fabric is influenced by the width of those zig zags.
We can vary that distance by increments of needle spacing, with, as we found,
stable spacer knits resulting with tuck distances up to five needles apart.
And because the thickness of an assembly affects its bending moment,
that spacing or thickness parameter also affects the stiffness of the material overall
which we measure here by loading the swatches until their bending point at 45°.
Of course, other parameters also affect the stiffness of the overall assembly.
So here, we’re charting the stiffness effects of the density of the filler, as measured in
number of filler rows added for every bit of face fabric height. In this chart, we’re
keeping the zigzag spacing constant -- it's 4, from the previous chart --
and the stiffness range here is actually very similar
to the previous chart, which means we can achieve a comparable stiffness differential
through *either* the spacing of the faces or the density of the infill,
which means we can use whatever parameter better suits our other goals.
Altogether, thickness and stiffness are two of the characteristics we track in the paper,
as well as the shearing bias which you saw in the linkage example before. These characteristics
ultimately arise out of both material properties, such as the friction, stiffness, and thickness of the yarns,
as well as construction parameters such as the ratio of filler material to face material.
As such, a spacer fabric is an engineered metamaterial
which emerges from the both material and structural properties.
With computational weft knitting, a spacer fabric can be assembled computationally.
So instead of knitting yardage and post-processing it into what we want, we can tune those characteristics to
a particular area of an overall assembly right within the knitting process.
So for example we can incorporate conductive yarns for sensing, and use small local bumps
of thicker spacer material as tactile cues: a soft button panel.
Or the spacer fabric can be a fully knit-in stiffener for a soft mechanical gripper.
As you see, the fabric part of this assembly is entirely machine-knit.
There was no hand finishing of the soft component.
Our investigation into the spacer fabric structure
pushes the bounds of machine knitting as a fabrication technology.
We detangle material and structural concerns
in order to reintegrate them as tunable metamaterial structures with
interactive, robotic, and other technically engineered applications.
Thanks for listening!
Please reach out with any questions.