Conference article

This paper presents a positioning system of a linear double acting pneumatic cylinder commanded by two proportional pressure regulator valves. The advantages presented by pneumatic systems make this technology reason for constant research in the scientific field. But, the nonlinearities related to the use of compressed air and the involved frictions in the movement make the control complex. In many researches about this subject, the authors adopted proportional valves to control the air mass flow directed to the rear and front chambers of the pneumatic cylinder. In the present research, the proportional valves controlled the air pressure instead of air mass flow. The pneumatic cylinder was equipped with an internal linear resistive transducer and the proportional pressure regulator valves were set to work in double loop mode, monitoring and controlling the input and output signals of the process. Each valve was equipped with an onboard proportional integral (PI) controller which were tuned according to the second technique proposed by Ziegler-Nichols. To make possible the execution of simulations, mathematical models were developed taking into account the piston dynamics, the compressed air behavior inside the front and rear chambers, the static and dynamic frictions and the valves dynamics. To validate the mathematical model proposed, comparisons between the experimental data, collected from a prototype connected to the software Labview, and the computational simulations results, that were performed in the software Matlab / Simulink, were done. The results obtained from the experimental data returned a maximum position error of 4,48mm for positive steps inputs, which was considered satisfactory for industrial applications. The comparison between simulated and experimental responses shows that the mathematical model presents a satisfactory approximation from the real system, although the experimental results have a faster stabilization time than the simulation, the transient response and the errors were similar.

Positioning system, pneumatic actuator, proportional pressure regulators, PID control, pressure control

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