I've been interested in soft robotics for a long time. When I was working in the FX industry about 10 years ago I had a phone conversation with Barry Trimmer at Tufts' Biomimetic Technologies Lab. We talked about ways to use the many mold making and casting techniques used to manufacture movie monsters int the production of laboratory soft robots. That conversation stuck with me.
A few years later I was part of the fabrication crew on the series Prototype This! It was similar to Mythbusters (in fact, made by the same production company) in that a team of experienced designers and fabricators all got together to solve an engineering problem under a tight deadline. Instead of busting myths, they were building strange machines like pizza delivery helicopters and water slide carousels. I was brought on to help them build devices that would let people climb walls like Spider-Man.
We explored two methods: van der Waals-based directional adhesion, and insectile tarsi-based spring-loaded hooks. The first is employed by geckos, and leverages the tiny intermolecular force atoms experience when very close to one another. In a rough-and-ready way: if you can get two surfaces to touch without an air gap or water between them, they will feel a very slight attractive force. The more surface area you've got, the stronger the force. Geckos have tiny spatula-like fibers on the pads of their feet called spatulae, which are arranged like feathers on a feather duster on the ends of hairs called setae. These offer boatloads of surface area for contact and can conform to surface features from the 1mm scale all the way down to 1um. The other adhesion method we used is very similar to how flies stick to walls. Flies have hook-like hairs on their legs that are biased to grip when the leg is raked across a surface in a particular direction. As long as that leg is putting pressure on the wall in that direction, the hairs engage with the surface and the fly is stuck.
We made versions of the geckoadhesive gripper using pressure casting and machined molds. The most difficult part of getting successful pulls from our molds was how fine the hairs were, and how likely they were to just tear off the silicone pad and simply stick in the mold. Eventually we found a solution that produced spatulated hairs pretty reliably.
[This video showcases the tarsi gripper method, as well as the engineering of JPL mech-e Aaron Parness, who I worked with on the Prototype This! devices.]
What was even more fascinating was the manufacturing method behind the tarsi gripper. This involved facing a huge block of wax, etching temporary molds, casting these molds with a two part urethane, machining features into these parts (still locked in the mold) for placing hooks and casting in a second layer of softer urethane. The resulting spring mechanism was sincerely brilliant. It was biased to change the hook's angle based on the force applied and bouncing it up out of whatever feature it was clutching when pressure was removed. It was a simple part with a very simple manufacturing process that exhibited a complex behavior.
That concept has influenced a large portion of my work: the right manufacturing process can simplify even the most complex mechanism. I realized how powerful compliant mechanisms can be and how nature has employed them everywhere to solve mechatronics problems.
I didn't start seriously experimenting with soft robots myself until I met Jim Bredt. Jim is one of the founders of Z-Corp and runs a 3d powder printer research lab in Summerville. He offered to queue up some designs on his printers in exchange for some help around the shop and time evaluating some of his experimental manufacturing processes.
I started producing simple pneumatic actuators like tubular tentacles and inflating patches that would bend with pressure. Soon, I established some reliable manufacturing techniques like lost wax casting for creating interior geometry in seamless silicone forms. I made the Glaucus as the capstone project for all this manufacturing research. I created a robot that integrated a lot of complexity using multiple molding techniques in a seamless casting.
So, where do you go once you're confident soft robots are reliable and manufacturable enough to be applied to engineering problems just like any other engineered material or actuator? The short version is I asked a lot of people what problems there were in their field that might be a good fit for the properties native to a soft robot. I'd like to do a larger post on what that process looked like, but in the interests of time I landed on therapeutic exoskeletons based on the advice of my father, an orthopedic surgeon, and my robotics mentor, a 10 year veteran of medical device development.
Given how well a soft actuator can distribute force evenly across a large area and can conform to a huge variety of situations without disturbing its essential function, we decided that it was a good fit for Cerebral Palsy therapy. Once we landed on this it was a pretty short process to print some molds for simple actuators and stitch them on to a hacked-up athletic elbow brace.
I began working with Kari Love, who helped refine the form, choose athletic gear to pull apart as a starting point, and fabricated the initial prototype. That early prototype showed promise, so I decided to push forward and develop a more sophisticated version. It isn't perfected, yet, but the potential is very exciting.