Pneumatic actuators: a comparison of energy-to-mass ratio´s

In literature a high power to weight ratio is mentioned among the assumed advantages of pneumatic artificial muscles over other types of actuators. In this paper a comparison was made between pneumatic artificial muscle type actuators and cylinder actuators on the basis of energy to mass ratio. When compared to standard industrial cylinder actuators, it is shown that pneumatic artificial muscles have a somewhat better [≈30%] energy to mass ratio for short stroke applications [s < 20 mm] and are up to a factor of 2 better at longer strokes [s ≥200 mm]. However, a redesign of piston in cylinder actuators shows the energy to mass ratio of these cylinder actuators to be superior to pneumatic artificial muscles and to standard industrial cylinder actuators. The energy to mass ratio is a factor of 30 better at a stroke of s = 10 mm, declining to a factor of 4.8 for a stroke s = 900 mm. The standard industrial cylinders are over-dimensioned, thus initiating the euphoria about pneumatic artificial muscles. However, for many applications a more careful design of piston in cylinder actuators provides a far better energy to mass ratio. Therefore, the use of pneumatic artificial muscles is questionable, especially in applications where the energy to mass ratio is important, like (autonomous) robotics, rehabilitation, etc.