Mathematical Modeling with Friction of a SCARA Robot Driven by Pneumatic Semi-rotary Actuators

This article approaches the problem of the modeling of a SCARA (Selective Compliance Assembly Robot Arm) manipulator designed by two semi-rotating pneumatic servo-actuators in the presence of friction in view of the precise control for a future application of a non-linear controller. Even though pneumatic systems are widely used in industry, it is found that the robustness of pneumatic servo-positioning solutions is limited by the positioning accuracy of the system controllers, that is, these controllers require complete knowledge of the system because they depend on sophisticated algorithms which should contemplate the highly non-linear nature of the operation of the pneumatic system. As precise model of Scara pneumatic driven robots are not found in the bibliography, present study deal with such task, being continuation of a modeling procedure executed for an isolated semi-rotary pneumatic actuator, where the dynamic relationship among the pressures in the semi-rotary actuator chambers, the rotational piston position and velocity, and the flow mass rate, was achieved. In that work, the friction was expressed through the LuGre model and curves of mass flow rate, pressures and control signal of the servovalve were obtained by means of experimental identification procedures. Therefore, current article uses the modeling of the same semi-rotary pneumatic actuator to consolidate a mathematical model of a SCARA manipulator consisting of two semi-rotary pneumatic actuators and a linear pneumatic actuator that will support the future development of non-linear controllers. Open loop validation was performed through comparisons between experimental and simulation results.