Dynamics and control of pneumatic actuators

Pneumatic actuators are, with hydraulic and electrical ones, a large class of actuators today in use in industrial or technical domains to satisfy the very broad range of constraints corresponding to the domains of working parameters. In marked difference with the two other classes, these actuators are extremely simple in their structure, with very low price, easily repairable, are basically non-polluting and can be used in hazardous environments. They also self-adapt to exterior load due to the elasticity of the compressed air acting as an automatic and continuous speed clutching, and they adapt to a large set of working conditions. Despite these qualities, these machines are limited to low level tasks, and are for instance in the push-pull case not used for precise positioning which is preferably left to the other classes. So they are not in this case as much technically advanced, do not have any control system, and generally suffer from large friction effects which hampers their performances, though it proves to be useful. For higher level applications, various types of control structures have been studied previously, but they all lead to oscillatory behavior around a nominal value, making the fine positioning problem still unsatisfactorily solved. It is shown here that with proper adapted control associated to better technology for significantly lowering internal losses, these actuators are able at low extra cost to perform comparably to other ones, with the advantage of their intrinsic quality of simplicity and robustness