Dynamic model for modern air powered servodrives

The successful marriage of digital electronic sensing and control to air powered actuations has rekindled interest in the use of air powered servodriives for industral applications, as a rival technology for electronically controlled hydraulic and d.c. electric servodrives. For automation machines which use servodrives, such as inductrial robots, there is an increasing requirement that the drives be fast, stiff, accurate and predictable. A dynamic model of generral use for predicting the responses of air motor (rotary motion) and air cylinder (rectilinear motion) powered servodrives is developed and presented. A linear control volume approach is used initially to provide a transfer function model for small perturbation analysis, and for broad understanding of the dynamic nature of such systems. To provide a more accurate and detailed model for digital simulation of proposed designs of air powered servos, the bond graph approach is used. This allows inclusion of nonlinearities required for a model to be readily usable in the system design situation. Current use of the model, involving both motor and cylinder powered servos, electropneumatic servovalve control, digital control via a set of electrically controlled on-off valves, and adaptive control, is outlined.