Modeling soft actuators

Last summer I worked in the Insect Robotics Lab and got introduced to soft robotics via the maggot robot that is in development there. I worked on C. Elegans movement analysis which led me to the OpenWorm project but the idea of soft robots and soft actuators in particular stuck in my mind. The potential for developing better robot joints was very interesting and given that the field is still in its infancy, quite exciting!

So, just last week the idea occurred to me that it might be interesting to model soft robots. But, where to start? I contacted Adam Stokes, who once worked in the Whiteside lab at Harvard which originated the idea of soft robots, and he referred me to Dylan Ross of the Insect Robotics Lab. After brain-storming with Dylan today we came to the conclusion that it might not be a bad idea to start with modeling soft actuators.

-soft actuator illustration taken from Cornell University

A soft actuator(aka PneuNet) basically has three parts:

  • a pressure-pump that injects
  • fluid into a
  • visco-elastic container(often made of silicon)

Now, this leads to interesting questions that engineers in this field haven’t looked into much detail yet such as:

i) How does the PneuNet behave with variable pressure and/or variable number of cycles?
ii) How does the PneuNet behave with variable material properties(elasticity, viscosity…) assuming fixed pressure?
iii) Assuming a well-defined goal for the PneuNet how can we optimize the energy use and material cost?

These are not easy questions to answer and in fact it turns out that I have a lot of reading to do. Assuming that I’m going to use fine mesh models to describe the theoretical dynamics of this system I would need to read a book on elasticity like Theory of Elasticity by Landau and Lifschitz. And, in order to model the fluid I’ll have to read a book on computational fluid dynamics. Then I’ll need to take into account the fact that the material properties will change over time with the growing number of cycles. This means that I’ll need a tight feedback loop.

The ideal setup would have a webcam which would analyze the variation in the geometry of the visco-elastic container when inflated in real-time, sensors to detect variation in temperature and pressure of the fluid, and of course a supercomputer to solve numerical differential equations. This might be the most challenging project that I have yet to take on.

My goal for next week is to 3D print the visco-elastic container to begin simple experiments and finish reading half of Theory of Elasticity which isn’t a very thick book to be honest.

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