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118 Ioana Petre et al.
The utilization of the pneumatics offers many advantages, the most important
being the low weight and the inherent compliant behavior of its actuators.
Compliance ensures a soft touch and safe interaction. In contrast with
pneumatic muscle actuator, hydraulic and electric drives have a very rigid
behavior and can only be made to act in a compliant manner through the use of
relatively complex feedback control strategies. [1]
2. Pneumatic Muscle
2.1. History
Pneumatic muscle is an actuator system based on an inflatable and flexible
membrane operated by pressurized air (Fig. 1).
Fig. 1 – Pneumatic muscles and their function principle
(source http://www.festo.com/hm2001/eng/1001.htm).
Pneumatic muscles were first conceived in 1930 by G a r a s i e v, a Russian
inventor [2]. According to B a l w in [3], J. L. McKibben introduced it to
motorize pneumatic arm orthotics for helping control handicapped hands: due to
the similarity in length-load curves between this artificial muscle and skeletal
muscle, it seemed an ideal choice for this purpose [4], [5].
The artificial muscle, which construction is simple, was made of a rubber
inner tube covered with a shell braided according to helical weaving. The
muscle was closed by two ends, one being the air input and the other the force
attachment point. When the inner tube was pressurized, the muscle inflated and
contracted [6].
The Bridgestone rubber company (Japan) proposed a redesigned and more
powerful version of the pneumatic muscle in the 1980s under the name of
Rubbertuators and used them to power an industrial use robot arm, Soft Arm.
At the present, McKibben-like muscles are being brought to the market by
Festo Ag. & Co.