While these EAPs can be made to bend, their low capacities for torque motion currently limit their usefulness as artificial muscles.
[7] Ionic EAPs are polymers that can be actuated through the diffusion of ions in an electrolyte solution (in addition to the application of electric fields).
A (untwisted) polymer fiber, such as polyethelene fishing line or nylon sewing thread, unlike most materials, shortens when heated—up to about 4% for a 250 K increase in temperature.
One application of thermally-activated artificial muscles is to automatically open and close windows, responding to temperature without using any power.
[1][12] It has also been demonstrated that a coiled vanadium dioxide ribbon can twist and untwist at a peak torsional speed of 200,000 rpm.
As such, the following examples should not be treated as an exhaustive list of the variety of control systems that may be employed to actuate a given artificial muscle.
Electro-Active Polymers (EAPs) offer lower weight, faster response, higher power density and quieter operation when compared to traditional actuators.
Pneumatic artificial muscles, while lightweight and inexpensive, pose a particularly difficult control problem as they are both highly nonlinear and have properties, such as temperature, that fluctuate significantly over time.
As these parts come into contact with each other during actuation, the PAM's temperature increases, ultimately leading to permanent changes in the structure of the artificial muscle over time.
As for closed-loop control, a passivity-based approach analyzing SMA closed loop stability has been used (Madill and Wen, 1994).
A large variety of supramolulecular recognition elements can be introduced into gel-forming polymers, which can bind and use as initiator metal ions, different anions, aminoacids, carbohydrates, etc.
Artificial muscle technologies have wide potential applications in biomimetic machines, including robots, industrial actuators and powered exoskeletons.
EAP-based artificial muscles offer a combination of light weight, low power requirements, resilience and agility for locomotion and manipulation.
[2] Future EAP devices will have applications in aerospace, automotive industry, medicine, robotics, articulation mechanisms, entertainment, animation, toys, clothing, haptic and tactile interfaces, noise control, transducers, power generators, and smart structures.
[20] Thermal actuators such as SMAs have various military, medical, safety, and robotic applications, and could furthermore be used to generate energy through mechanical shape changes.