Mathematical modeling of pneumatic semi-rotary actuator with friction

In this paper, the problem of modeling a pneumatic semi-rotary actuator for precise control in the presence of friction for future robotic manipulator applications is addressed. Precise commercial pneumatic components have become increasingly available and are widely applied in the processes and manufacturing industry. The robustness of pneumatic actuator solutions is limited by the precision of the system controller positioning, which depends on sophisticated algorithms that must deal with the highly nonlinear nature of the pneumatic system operation by means of the use of controllers that require suitable system knowledge. In this study, aiming at obtaining such a suitable model for a class of pneumatic semi-rotary actuator, the pressure dynamics in its chambers is modeled. The overall modeling task involves a detailed experimental identification of the curves of the mass flow rate related to the control voltage of the servovalve and its relationship with the pressures in the piston chambers. Moreover, friction was formulated with the LuGre model on account of its ability to represent different effects that comprise friction phenomena, including Coulomb, viscous and static friction effects, resulting in a comprehensive mathematical model for supporting future development of a nonlinear controller. Finally, validation in open loop was performed with comparisons between experimental and simulation results.