Dielectric elastomer minimum energy structure ring

A minimum energy structure (MES) is a soft mechanism based on the two related design principles of differential growth and transfer of elastic energy. Elastomeric minimum energy structures are created when a thin rubber is stretched and adhered to an inextensible, but pliant planar frame (i.e. the frame begins flat and can bend, but not stretch). Because the film is stretched, it wants to shrink; being bound to the frame which cannot shrink, the whole system bends into 3D. Similarly we could think about this as the transferring of elastic energy from the film to the frame (i.e. from stretching energy to bending energy). This process was completed for two identical frames--which bent into pseudo-half circles and were glued together at the edges, forming the rest state shown at the start of the video.

The white frame in the video is laser-cut from a 75 micron thick ABS plastic. There are two identical frames adhered at their edges. The black film is 250 micron thick VHB tape from 3M (F9473PC VHB) biaxially prestretched 6x and coated on each side in carbon grease from MG Chemicals.

Coating a thin film dielectric elastomer (read: insulating rubber) with electrodes (read: conductive material) creates a dielectric elastomer actuator (DEA) (read: compliant capacitor). Applying a voltage across the film causes positive and negative charges to build on opposite sides, creating an electrostatic pressure, causing the film to decrease in thickness and increase in area. When a dielectric elastomer is used as the elastomeric film in a minimum energy structure (DEMES), we have the ability to transition between the 3D conformation and a more planar conformation as can be seen in the video.

In the video a voltage of 1.2 kV (1200 volts) is applied across the dielectric elastomer film to create the motion seen.

This work was completed by Michael Thomas Petralia (petralia@seas.harvard.edu) and Robert J. Wood, Ph.D. at the Harvard Microrobotics Laboratory (micro.seas.harvard.edu). The Microrobotics Lab is part of the Harvard University School of Engineering and Applied Sciences (seas.harvard.edu) and the Wyss Institute for Biologically Inspired Engineering (wyss.harvard.edu).

It was supported by the Defense Sciences Office (DSO) of the Defense Advanced Research Projects Agency (DARPA) as part of the Chemical Robots (Chembots) project, Contract No. W911NF-08-C-0060. Michael was supported by the Department of Defense (DoD) through a National Defense Science and Engineering Graduate (NDSEG) Fellowship.

It was presented at the International Conference on Intelligent Robots and Systems (IROS) 2010 and is published under "Fabrication and analysis of dielectric-elastomer minimum-energy structures for highly-deformable soft robotic systems." The prezi for this talk can be found here: http://bit.ly/cvcN0G .

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