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120 Ioana Petre et al.
by a pneumatic muscle versus the enveloping angle and feed pressure (Fig. 3)
[5].
The advantages of the pneumatic muscles utilization are: power to weight
ratios in excess of 1 kW/kg; a varying force-displacement relation at constant
gas pressure, an adjustable compliance; the absence of friction and hysteresis;
the ability to operate at a wide range of gas pressures, and thus to develop both
very low and very high pulling forces; the possibility of direct connection to a
robotic joint; cheaper to buy and install than other actuators and pneumatic
cylinders; smooth and natural movement; fast -full contraction.
Disadvantages are: the force which can be applied is only tensile in nature;
its total displacement is only about 20% to 30% of its initial length; friction
between the netting and the tube leads to a substantial hysteresis in the forcelength
characteristics; rubber is often needed to avoid the tube from bursting;
rubber deformation will lower the force output of this type of muscle up to 60%
[8].
3. Industrial Applications of Pneumatic Muscles
Pneumatic muscles were, lately, used in many applications especially in the
field of industrial robots, because of the evolution of the technology.
The major application of pneumatic muscles is in the field of industrial
robots, usually in those that mimic human actions. Because of their analogy
with human skeletal muscles, they are able to perform many functions specific
to human hand.
As example in this area we can specify the stepping robot WAP-1 is the first
biped robot designed in 1969 by Ichiro Kato from Waseda University of Tokyo.
(Fig. 4a)
a b
Fig. 4 a – WAP-1(source www.androidworld.com) ; b - Humanoid robot manufactured
by Shadow robotic company (source www.shadowrobot.com)