Soft Robotics Joint Actuator (2020)
This project principally was a test of my prototyping skills, especially since I had never worked with molding processes or polymer compounds before it.
This was made as part of a research project, aiming to find a cheap way to actuate exoskeletons. The idea to use soft robotics for such a purpose was once I came to after considering several alternatives, including traditional mechanical solutions such as servomotors.
Working Principle
The working principle of a PneuNet actuator is simple. When 2 surfaces of different stiffnesses are combined, the structure will bend when subject to equal pressure. It is similar to a bimetallic strip bending under heat.
This idea was initially conceptualized by Harvard University and I decided to perfect it for my purpose.
Mold Making
So I set about making the CAD design for the mold on PTC Creo. I exported it as an STL file and sent it for 3D printing.
Prototyping
The next step was to essentially prototype the actual device. This included:
1) Mixing the 2 chemical compounds to make the polymer
2) Pouring it into the mold, conjoined
3) Adding a strip of paper into the mold of the baseplate, which will be used to make a stiffer base. Alternatively, a different proportion of polymers can be used to make it.
4) Putting the mold in a vacuum chamber to ensure the final product has no air bubbles
5,6) Topping it up with mold, essentially due to how the volume will decrease from the vacuum suction
7) Placing them in the oven for the chemical reaction to properly take place so that the polymer will be formed
8) Lastly, the final top layer is layered over the base plate and set in the oven again
9) That is essentially the finished product and we’ll now subject it to testing
Testing
Finally, we tested the finished actuator. The actuator works pneumatically, by pumping in air through the central core . The tip of the actuator was used to measure the amount of force it can apply. A strain gauge was used to measure the force.
Pressure of the air supplied was monitored through a pressure valbe. On the left, the lines with dots shows the results and the red line approximates it into a parabolic curve. The device finally ruptured at a pressure of 221kPa (Gauge Pressure). It took about 64kPa for the the actuator to reach maximum acutation value when subject to 0 resistance in an STP environment.
Video of it working
A video of the acutation in progress.