Model-based Friction Compensation for the the Furuta Pendulum using the LuGre Model

Friction is present in all mechanical systems and causes a wide range of problems for control. The development of friction models and methods to account for friction in control has been an active research area for many years. A promising friction model that is capable of describing a wide array of observed friction phenomena is the LuGre model. This thesis deals with the application of friction compensation based on the LuGre model for the unstable Furuta pendulum. LuGre friction compensation schemes and a model of the plant are implemented quasi-continuous and tested in simulation. An identification of LuGre friction parameters for the Furuta pendulum is carried out, showing the limitations due to the sensor equipment of the device. The LuGre friction compensation schemes are tested with hardware in the loop, evaluated and compared with friction compensation schemes based on the Dahl and Coulomb model. Further the influence of velocity observation on the control and friction compensation performance is elucidated. Friction compensation based on the LuGre model, discretized as proposed by Freidovich [2], is a suitable method to compensate for friction offering several advantages in comparison to other tested friction compensation schemes. Due to the used sensor equipment the full potential of the LuGre model cannot be tapped and the proposed friction observers require further modification before being applicable for the Furuta pendulum.