On Sliding Mode Control for Stick Slip Rejection in Drilling Systems

Drilling systems have enormous economic potential, although there are many practical challenges that can be solved by automated control. Mathematical models need to be developed, sources of disturbance and error identified, and control laws calculated to achieve the desired performance. This article deals with the control of drill string dynamics, focusing on stick-slip vibrations. A two-degree-of-freedom drill string model with friction modelling representing the interaction between the rock formation and the drill bit was used, and then a control law based on a sliding-mode control scheme was applied. This approach suppresses torsional vibrations and maintains the required angular velocity of the drill bit. To highlight the performance of the proposed controller, several sliding surfaces were selected and compared in terms of robustness and load specifications.