Position Control of a Floating Ball in a Vertical Air Stream

Quantitative Feedback Theory (QFT) control theory was used to design a control loop in order to provide stability and tracking ability for a ball floating in a jet stream of air. Due to nonlinearity of the system governing equations, a set of linear transfer functions was derived to capture the dynamics of the system. Using this set, a controller and a prefilter were designed that met the stability and tracking performances. The feedback loop was also implemented in an experimental setup consisting of a DC motor, an axial fan, an expansion tank, and a nozzle. The experimental data showed some differences with the simulation results, but the closed-loop system response was satisfactory and the design criteria were met.