Control Methods for Energy-Efficient Pneumatic Servos Employing Asymmetric Cylinders

Pneumatic drives or actuators are most widely used in industry, in comparison to their hydraulic and electrical counterparts. However, they are low in energy efficiency and have typically been used in performing simple actuation tasks. This paper investigates the use of pneumatic actuation for point-to-point positioning applications in the context of employing asymmetric cylinders. The focus of this research is to study appropriate control methods, aiming for improved energy efficiency in the use of pneumatic servo positioning system. Relevant mathematical models and stability analysis will be presented in this paper, with results from simulation and experimental verification. In particular, a hydraulic circuit (rapid motion circuit) is adopted in the case for pneumatic actuation. For point-to-point positioning application, in the forward moving phase, the inlet and outlet chambers will be connected via by-pass valve allowing exhausted compress air to be reused. In comparison with the conventional way in controlling the motion of an asymmetric pneumatic cylinder, a portion of the compressed can be re-used leading to an enhancement in energy-efficiency. The results show that some 15% saving in energy use can be acquired with improved stability while the settling time of the positioning system is maintained. Relevant design and applications issues will be outlined and discussed in this paper as well.