Published on Apr 17, 2020
Air muscle is essentially a robotic actuator which is replacing the conventional pneumatic cylinders at a rapid pace. Due to their low production costs and very high power to weight ratio, as high as 400:1, the preference for Air Muscles is increasing. Air Muscles find huge applications in biorobotics and development of fully functional prosthetic limbs, having superior controlling as well as functional capabilities compared with the current models.
The Air Muscle consists of an inner rubber tube, which is often made from pure rubber latex. It is surrounded by a braided mesh.
The header at each end of the muscle consists of an Aluminium ring, and a Delrin plastic bung, with a female thread. This thread can be used as a means of attachment, and to allow air into or out of the muscle. The muscle is supplied with two Delrin fittings also.
The inner rubber tube is inflated by entering air at a pressure, usually limited to 3.5 bar. The movement of this tube is constrained by the braid. When the tube gets inflated it experiences a longitudinal contraction. This would create a pull at both ends of the tube. Usually one end of the tube will be attached to somewhere so that force can be applied from one end. This pull when effectively utolised could provide the necessary motion. The working of the Air Muscle closely resembles that of the natural muscle and hence the name Muscle given to it along with Air. The figure below shows the physical appearance of the muscle at different stages of its working.
Advantages of Air Muscles
1.Power to weight ratios in excess of 1 kW/kg, by way of comparison, electric drives typically has some 100 W/kg
2.A varying force-displacement relation at constant gas pressure, contrary to pneumatic cylinders, which results in a muscle-like behavior; an adjustable compliance, due to gas compressibility and the dropping force-displacement characteristics
3.A maximum displacement or stroke of up to 50% of initial length
4.The absence of friction and hysteresis, as opposed to other types of PAMs
5.The ability to operate at a wide range of gas pressures, and thus to develop both very low and very high pulling forces
6.The possibility of direct connection to a robotic joint, i . e . without having to use any gears, because of their high output forces at all speeds
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