Pneumatic artificial muscles (PAMs) are contractile or extensional devices operated by pressurized air filling a pneumatic bladder. In an approximation of human muscles, PAMs are usually grouped in pairs: one

agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ag ...

and one

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, ri ...

. PAMs were first developed (under the name of '' McKibben Artificial Muscles'') in the 1950s for use in artificial limbs. The

Bridgestone is a Japanese multinational tire manufacturer founded in 1931 by Shojiro Ishibashi (1889–1976) in the city of Kurume, Fukuoka, Japan. The name Bridgestone comes from a calque translation and transposition of , meaning 'stone bridge' in Japa ...

rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...

company (

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

) commercialized the idea in the 1980s under the name of Rubbertuators. The retraction strength of the PAM is limited by the sum total strength of individual fibers in the woven shell. The exertion distance is limited by the tightness of the weave; a very loose weave allows greater bulging, which further twists individual fibers in the weave. One example of a complex configuration of air muscles is the Shadow Dexterous Hand developed by the Shadow Robot Company, which also sells a range of muscles for integration into other projects/systems.

Advantages

PAMs are very lightweight because their main element is a thin membrane. This allows them to be directly connected to the structure they power, which is an advantage when considering the replacement of a defective

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

. If a defective muscle has to be substituted, its location will always be known and its substitution becomes easier. This is an important characteristic, since the membrane is connected to rigid endpoints, which introduces tension concentrations and therefore possible membrane ruptures. Another advantage of PAMs is their inherent compliant behaviour: when a force is exerted on the PAM, it "gives in", without increasing the force in the actuation. This is an important feature when the PAM is used as an actuator in a

robot A robot is a machine—especially one programmable by a computer—capable of carrying out a complex series of actions automatically. A robot can be guided by an external control device, or the control may be embedded within. Robots may be ...

that interacts with a human, or when delicate operations have to be carried out. In PAMs the force is not only dependent on pressure but also on their state of inflation. This is one of the major advantages; the mathematical model that supports the PAMs functionality is a non-linear system, which makes them much easier than conventional pneumatic cylinder actuators to

control Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controlli ...

precisely. The relationship between force and extension in PAMs mirrors what is seen in the length-tension relationship in biological muscle systems. The compressibility of the gas is also an advantage since it adds compliance. As with other pneumatic systems PAM actuators usually need electric valves and a compressed air generator. The loose-weave nature of the outer fiber shell also enables PAMs to be flexible and to mimic biological systems. If the surface fibers are very badly damaged and become unevenly distributed leaving a gap, the internal bladder may inflate through the gap and rupture. As with all pneumatic systems it is important that they are not operated when damaged.

Hydraulic operation

Although the technology is primarily pneumatically (gas) operated, there is nothing that prevents the technology from also being

hydraulically Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...

(liquid) operated. Using an incompressible fluid increases system rigidity and reduces compliant behavior. In 2017, such a device was presented by

and the

Tokyo Institute of Technology is a national research university located in Greater Tokyo Area, Japan. Tokyo Tech is the largest institution for higher education in Japan dedicated to science and technology, one of first five Designated National University and selected as ...

,Development of a Hydraulic Drive High-Power Artificial Muscle through the Cabinet Office Tough Robotics Challenge
/ref> with a claimed

strength-to-weight ratio The specific strength is a material's (or muscle's) strength (force per unit area at failure) divided by its density. It is also known as the strength-to-weight ratio or strength/weight ratio or strength-to-mass ratio. In fiber or textile appli ...

five to ten times higher than for conventional electric motors and hydraulic cylinders.

Notes

External links

{{Wikibooks, Robotics/Components/Actuation Devices/Air muscle
Pneumatic Artificial Muscles: actuators for robotics and automationBas Overvelde's ballooning muscles Biped robot powered by pneumatic artificial musclesSoft Robot Manipulators with McKibben musclesAir Muscles from Shadow Robots
Robotics hardware Pneumatic actuators

Advantages

Hydraulic operation

See also

Notes

External links