Implementation

The cord-like nature and power density of SCP lend themselves well to applications with limited space. They can be assembled together in fabric-like sheets or braids (see Design Principles) and are inherently flexible, letting them wrap and curve around non-flat surfaces.

Wearable Robotics

A wearable sheath-like design has been demonstrated by a Japanese development group at Panasonic. They describe a variant of SCP using high-end materials that can contract at relatively low temperatures (approx. 60 C), and have integrated the SCP actuator with common fabric, wrapped around a finger model.

One potential application for this is in pain relief, especially around joints and fingers. Pressure applied by the SCP can be controlled in a way that mimics a massage, relaxing tensed muscles. The heat generated by the SCP can also be taken advantage of -- warm temperatures will cause blood vessels to expand in diameter, and improve blood flow in pained areas.

In some cases, SCP's may also be appropriate for assisted movement devices. While they do not generate much force on their own, their flexible nature and relatively small size allows them to be less obtrusive than a pneumatic-driven exoskeleton (such as those driven by McKibben actuators). For the finger and wrist joint especially, flexibility will be far more important than raw force output, and the SCP is a strong candidate for wearable assistance devices of this nature.

SCP's developed by Maki Hiraoka, et. al., demonstrating the these actuators wrapped around a fabric glove.

A) Completed robotic limb design, by M. Yip and G. Niemeyer, detailing attachment points for each two-ply SCP coil.

B) Actuation of the robotic limb. Note the red-hot glow of the SCP's -- thermal expansion at work!

Limbs and Prosthetics

Another great use case for SCP actuators is in the field of general robotic limbs and prosthetics. Purely synthetic in nature, a biomimetic or prosthetic limb must be built to mirror natural muscle as much as possible. Being flexible, and able to be braided together into bundles that mimic human muscle fibers, SCP's are a great fit for those seeking to build a robotic limb that can flex, tense, and relax much like a human's.

One such robotic limb design by Dr. Yip (UCSD) and Dr. Niemeyer (MIT/Caltech associate) uses two SCP's coiled around one another, creating a "two-ply" coil. A number of these two-ply coils are then hooked up from fingertip to base of the palm, and the base of the palm to the forearm limb. Contraction of each network of SCP's will cause individual fingers or the wrist to roll inwards.

An even more elaborate variant of this design could introduce yet more SCP's to mimic twisting of the forearm. or better mimic the wide range of motion of the thumb joint. This is an emerging field, and in the pursuit of mimicking evolution's own designs with man-made materials, there will always be room for improvement!

References

Hiraoka, M. et al. Power-efficient low-temperature woven coiled fibre actuator for wearable applications. Sci. Rep. 6, 36358; doi: 10.1038/srep36358 (2016).
M. C. Yip and G. Niemeyer, “High-performance robotic muscles from conductive nylon sewing thread,” in Proc. IEEE Int. Conf. Robot. Autom., 2015, pp. 2313–2318.

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