Soft-exoskeleton Part 1: Exoskeleton (of a kind) – Introducing


Time for some news and there’s plenty of it! This should probably have been posted as many separate posts to follow the progress but it so happened that I wasn’t really good at updating continously so here goes the retrospect until I catch up.

During the past 4 months I’ve been super busy on a super fun project. We are building a soft-robotic system for upper-limbs actuation (I don’t want to call it an exoskeleton given that it implies a rigid outer structure, which this one hasn’t)

Our project is based on an idea I had last year on approaching exoskeletons from a slightly different angle.

To begin from the beginning, here is a little intro:

As a Mechanical Engineering student at DTU, the 4th semester is where you have your mid-term project. This is supposed to concern developing something mechanical of your own choosing, involving topics from a minimum of 2 of our mandatory courses. It’s furthermore a team effort and involves a course in project management alongside the product development. The project is set for 10 ECTS point meaning 1/3 of the semester.

Given that I had about a billion different ideas for such projects,  I immediately started investigating which ideas would be most interesting.
About the same time it so happened that my grandmother fell and hurt her shoulder quite bad. Due to old age and a damaged Rotator Cuff, she ended up not being able to lift her left arm above 10 degrees’ish from vertical. This meant that she couldn’t reach out for he rolator too well, could bring her left hand to her head and many other issues that seem insignificant until you’re in the situation.

Anyway, I thought I’d give it a shot at helping her out by building a wearable system that could help her lifting her arm when she desired.

The more I thought about it the more the idea seemed to fit right in with the mid-term project. Eventually I started talking to a few of my friends from my class about potentially doing it and in no time we were 5 guys ready and all super excited about getting started.

In this way I had prepared an idea for the project as well as gathered a team already before Christmas. With the project not starting before February I still had some time to play around with further ideas.
For several weeks I was investigating existing exoskeletons, how we could potentially build one ourselves, what it would require and so on. I quickly concluded that exisiting systems are super expensive as it requires quite sophisticated machinary to augment movement when required whilst aiming to be non-invasive. I found that we probably shoudn’t aim for a fully-fledged exoskeleton Iron-Man’ish suit but instead see how we could hack something together, approaching functionality from the bottom-up instead. My Grandmother didn’t require much and merely allowing her to lift her arm forward to horizontal in an intuitive way would be an enormous help.

With this in mind and some other arbitrary trail of thought that I cannot remember, I started thinking of the way tubes tend to straighten out when inflated. From that I started wondering if you could strap such a tube to a person and using a that straightening force to actuate an arm.

After a bit of back and forth-ing with thought experiments I concluded that it could potentially work. Consider a long tube strapped to a person above the hip on the back, going up and over the shoulder and down along the upper-arm where it attaches again at the elbow. This would give it a bend over the shoulder and when inflating it, which would make it straighten, the only way to do so would be by lifting the arm (or detaching at the back but that’s a matter of strapping it down more tightly)

Showing my initial idea of strapping a tube down, bending over the shoulder. Inflating the tube should theoretically lift the arm

Showing my initial idea of strapping a tube down, bending over the shoulder.
Inflating the tube should theoretically lift the arm

Using a tube in this way could potentially eliminate a lot of the issues with needing rigid structures to counter reaction-forces from motors pulling or rotating.
I quickly found many other potential benefits with using this method for less needy actuations. These included much cheaper production cost, light weight and flexible which would allow it to follow the shape of the body naturally without having to include multiple mechanical joints.
I found that this approach was much more my style and while it definitely has it’s drawbacks I saw great potential in investigating further.

I told the rest of the team about my new idea and while they had initially thought of a more mechanical exoskeleton, they were very keen on this idea as well. Only problem now was the chance of getting going with a project which was based on some very strong assumptions on many points.

…To be continued in Explorations of Wearable Soft Robotics – 3 Week Course


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