Exploration of Tensile Structures in Context of Ergonomics

Samantha C Ho
May 16, 2018 · 5 min read

This is a documentation my process for a final project for 24–672 Special Topics in Design, DIY, and Fabrication in Carnegie Mellon’s College of Engineering.

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This project began as a continuation of the previous assignment about resin casting — for context, read about it here.

As I approached this final project, I wanted to test myself in the fabrication of a product, without sacrificing form and design.

Emerging from a successful cast of the “seahorse,” I knew I wanted to deeper explore artifacts at this scale; thus I began thinking about ergonomics and different types of grips.

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Moodboards for manufacturing inspiration in addition to ideal demographic

Additionally, I considered different types of structures I could apply to the “grip” I was developing. As I fell deeper and deeper into a research hole, I needed to accept that this project was going to be more form and concept driven rather than solving a specific problem.

Immediately I thought of Frei Otto and his work with lightweight, membrane-like structures —on such a small scale, I wondered if the “tensile-structure” approach could afford an interesting interaction.

It became clear to me that the form itself was going to take on a rather organic and complex shape — thus when it came time to CAD, I decided to try out Fusion360.

Having only been familiar with Solidworks before this, taking on Fusion was certainly a challenge.

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building faces to build in three dimensions

After a horrifying amount of time spent sitting in front of Fusion, I was able to sculpt a form that resembled what I was looking for. This solid form would serve as my base model for the rest of my process. Upon finishing, I extruded a lighter shaped cut and sent it to the printer so I could move on with prototyping.

Still interested in tensile structures, I needed to face my next challenge — figuring out how to stretch string across the “valleys” to achieve an elastic interaction. After some thinking, I applied the Voronoi algorithm and how its cell based structure could act as the skeletal structure to string a net across. Thus, I pulled the part back into Fusion and played around in the sculpt environment. However, after investing more hours into the program, I realized there was no conceivable way I could achieve the cell pattern I needed with solely the sculpt environment. Upon further reading, I discovered an alternate program online called MeshLab that had the Voronoi algorithm built into the program.

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Meshlab

I imported my .stl file and began experimenting with different ratios of poisson-disk sampling till I found what I liked, then I sent it to the printer as well.

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The first batch of prints on the Form2
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After the first batch came out of the printer, I felt rather satisfied, but was still bothered by the fact that ergonomically, the grip wasn’t comfortable to hold yet. Considering I had guessed my way through the proportions on the 3D model, I wasn’t surprised that some of the “valleys” were much too small. Luckily, at this point, I was rather familiar with the program so I adjusted the model and prepared it to print again.

As for the testing of the tensile structures, I took a cordless drill and drilled holes along the contours of the form. While this was rather risky, I was able to drill through with minimal damage to the solid structure. I figured that the holes themselves would not take on an exorbitant amount of stress and the force due to tension on the strings would disperse along the entire form.

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grip studies + first batch of printed grips in different materials (clear +flexible)

Upon completing the first iteration, I pulled in some of the angles on the model and tested the string on other forms. From an orthographic standpoint, the grip I had originally modeled was rather jarring and frankly, uncomfortable to look at.

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The grip needed to take on a more recognizable form, so I took in the angles and resolved some outstanding curves. I considered what makes people want to click on lighters — what about their shape and semantics make people want to interact with lighters?

After an excruciating iterative process, I landed on final form. It is printed out of tough resin on the Form2 printer and strung with waxed thread to create a tensile structure. The elastic interaction allows for a more comfortable grip that accommodates different hands.

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