Bio-Inspired Compliant Systems

One body, lots of possibilities

If you compare human-engineered machines to mechanisms found in nature, you can easily find fundamental differences in how they are made, work and perform. Human-contrived mechanical devices typically employ a collection of rigid parts and joints that must be assembled, aligned and lubricated in order to function. Compare this to nature’s designs – 90 % of all creatures are invertebrates. Unlike human-made machines, they are actually quite “monoform” in that there are no separate parts in their makeup. Their organic components either grow out of one another or are bonded together with strong, self-regenerating living interfaces. Although they appear to have “rigid” exoskeletons, they are remarkably flexible, suitably compliant, comparatively strong, and offer a tremendous range of shape adaptability to live out their lives.

Study of how nature’s monoforms combine movement and structure can help us design and build machines that require no assembly, and how they may even be constructed at micron-scale sizes using novel construction means.

Adaptability on the fly

Nature’s machines operate with the utmost efficiency largely because they can adapt the shape of their structural geometry in real time in response to differing conditions, needs and desires. Contrast this to the fixed geometries of the engineered world: automotive drivetrains, airplane wings, engines, motors, compressors, fans, ships hulls, etc. Practically all conventionally designed machines operate most efficiently at a specific median condition, and almost always less efficiently at any other time. Birds, on the other hand, take off, land, hover and dive by adjusting the shape of their wings on demand. In nature’s model a complaint design is strong and flexible enough to morph from one shape to another and back again with ease.

Compliant mechanisms are particularly useful for shape morphing adaptation. By using a selected material’s flexibility, and by applying minimal forces to deform and displace adaptive portions of the device, it is possible to optimize performance in ways not otherwise possible.

Elasto-fluidic mechanisms without joints

The most flexible natural machines on earth have no apparent skeletons at all. These more otherworldly life forms include Mollusks, particularly squids, octopi and snails, as well as Annelid and Nematode worms and other lesser-known phyla. Through an elasto-fluidic arrangement of connective tissue fibers and muscles, interacting with a pressurized liquid-filled elastomeric enclosure, they create an effective “hydrostatic skeleton” through which they are able to extend, contract, rotate, bend, and even create helical corkscrew motions. The way the device moves is determined by the fiber angles used in each discrete arrangement and is controlled by selectively pressurizing the fluid within them. Such assemblies can be used singly or in parallel to form devices that have a wide range of possible motions.

The CSDL is exploring soft robotic devices and orthotic devices with fiber-reinforced elastomeric enclosures that use elasto-fluidics to move in ways similar to soft-bodied animal or even botanical archetypes, and likely be scalable to a much smaller profile than current rigid-element designs.