Pneumatic artificial muscles

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

PAMs were first developed (under the name of McKibben Artificial Muscles) in the 1950s for use in artificial limbs. The Bridgestone rubber company (Japan) commercialized the idea in the 1980s under the name of Rubbertuators.

The actuation function of PAMs are dependent on the braid angle of the relaxed actuator state. PAMs which utilize a weave with a braid angle smaller than the critical locking angle (54.7°) will contract when pressurized, while PAMs utilizing a braid angle greater than the critical locking angle will extend when pressurized.

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.

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