Model free sliding mode stabilizing control of a real rotary inverted pendulum

Inverted pendulum systems, because of highly nonlinear, coupled, and unstable dynamic behaviour, are excellent experimental platforms for testing new developed control algorithms. This study explores nonlinear modelling, simulation and sliding mode stabilizing control of a real rotary inverted pendulum in detail. For simulation purposes only, the system was modelled in a nonlinear state space form including the servomotor dynamics. In the light of the simulation results, a rotary inverted pendulum system was designed and manufactured. For a certain quality level of desired output, benefits of the sliding mode control of the system without using an equivalent control signal by selecting a proper smoothing function were shown. This model free approach can be used to satisfy a need especially for practical control applications in industry to a certain level, encouraging practical control engineers to use sliding mode control, who have no ability to model a system or no sufficient time for this, or encounter very complex nonlinear system models in many cases. Comparisons of the theoretical and experimental results demonstrate that the state equations describe the dynamics of the system satisfactorily, and that robust and accurate balancing of the pendulum can be achieved by using model free sliding mode control with sigmoid smoothing function.