kb/data/en.wikipedia.org/wiki/Artificial_muscle-1.md

title	chunk	source	category	tags	date_saved	instance
Artificial muscle	2/2	https://en.wikipedia.org/wiki/Artificial_muscle	reference	science, encyclopedia	2026-05-05T13:54:53.431748+00:00	kb-cron

=== Pneumatic control === Currently there are two types of Pneumatic Artificial Muscles (PAMs). The first type has a single bladder surrounded by a braided sleeve and the second type has a double bladder.

==== Single bladder surrounded by a braided sleeve ==== 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. PAMs generally consist of rubber and plastic components. 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. This problem has led to a variety of experimental approaches. In summary (provided by Ahn et al.), viable experimental control systems include PID control, adaptive control (Lilly, 2003), nonlinear optimal predictive control (Reynolds et al., 2003), variable structure control (Repperger et al., 1998; Medrano-Cerda et al.,1995), gain scheduling (Repperger et al., 1999), and various soft computing approaches including neural network Kohonen training algorithm control (Hesselroth et al.,1994), neural network/nonlinear PID control (Ahn and Thanh, 2005), and neuro-fuzzy/genetic control (Chan et al., 2003; Lilly et al., 2003). Control problems regarding highly nonlinear systems have generally been addressed through a trial-and-error approach through which "fuzzy models" (Chan et al., 2003) of the system's behavioral capacities could be teased out (from the experimental results of the specific system being tested) by a knowledgeable human expert. However, some research has employed "real data" (Nelles O., 2000) to train up the accuracy of a given fuzzy model while simultaneously avoiding the mathematical complexities of previous models. Ahn et al.'s experiment is simply one example of recent experiments that use modified genetic algorithms (MGAs) to train up fuzzy models using experimental input-output data from a PAM robot arm.

==== Double bladder ==== This actuator consists of an external membrane with an internal flexible membrane dividing the interior of the muscle into two portions. A tendon is secured to the membrane, and exits the muscle through a sleeve so that the tendon can contract into the muscle. A tube allows air into the internal bladder, which then rolls out into the external bladder. A key advantage of this type of pneumatic muscle is that there is no potentially frictive movement of the bladder against an outer sleeve.

=== Thermal control === SMA artificial muscles, while lightweight and useful in applications that require large force and displacement, also present specific control challenges; namely, SMA artificial muscles are limited by their hysteretic input-output relationships and bandwidth limitations. As Wen et al. discuss, the SMA phase transformation phenomenon is "hysteretic" in that the resulting output SMA strand is dependent on the history of its heat input. As for bandwidth limitations, the dynamic response of an SMA actuator during hysteretic phase transformations is very slow due to the amount of time required for the heat to transfer to the SMA artificial muscle. Very little research has been conducted regarding SMA control due to assumptions that regard SMA applications as static devices; nevertheless, a variety of control approaches have been tested to address the control problem of hysteretic nonlinearity. Generally, this problem has required the application of either open-loop compensation or closed-loop feedback control. Regarding open-loop control, the Preisach model has often been used for its simple structure and ability for easy simulation and control (Hughes and Wen, 1995). As for closed-loop control, a passivity-based approach analyzing SMA closed loop stability has been used (Madill and Wen, 1994). Wen et al.'s study provides another example of closed-loop feedback control, demonstrating the stability of closed-loop control in SMA applications through applying a combination of force feedback control and position control on a flexible aluminum beam actuated by an SMA made from Nitinol.

=== Chemical control === Chemomechanical polymers containing groups which are either pH-sensitive or serve as selective recognition site for specific chemical compounds can serve as actuators or sensors. The corresponding gels swell or shrink reversibly in response to such chemical signals. 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. Some of these polymers exhibit mechanical response only if two different chemicals or initiators are present, thus performing as logical gates. Such chemomechanical polymers hold promise also for targeted drug delivery. Polymers containing light absorbing elements can serve as photochemically controlled artificial muscles.

=== Applications === 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. 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. Pneumatic artificial muscles also offer greater flexibility, controllability and lightness compared to conventional pneumatic cylinders. Most PAM applications involve the utilization of McKibben-like muscles. 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.

== See also == Artificial cell Electronic nose Electronic skin

== References ==