Control of a slender rotary system subjected to dry friction and rub

The objective of this study is to present the results of implementing a robust tracking control strategy for a rotating and slender system, subject to dry friction and rubbing. This system corresponds to a physical model defined from the rotary drilling system used in the oil and gas industry. In the simulations, the system to be controlled is modeled using finite element, while for the control design, a lumped parameter model with adjustments is used. The control law is based on the sliding mode technique with a dynamic boundary layer. An important result is that the use of the boundary layer enabled the system to track the desired trajectory with a permanent error within acceptable limits, while also eliminating the high switching frequency at the input, a typical issue of the sliding mode method. Additionally, auxiliary functions are recursively defined to incorporate a smooth friction model into the control law, aiming to treat the friction torque not as a perturbation and to minimize the required actuation force. Another significant outcome is the proposal of a general methodology for representing the internal dynamics of the torsion system. Finally, the physical model served as the basis for the design and construction of a prototype, which is described throughout this study.