Hybrid fuzzy sliding mode for stick-slip suppression in drill string systems

Stick-slip vibration is one of the main factors that contribute greatly to reducing the service life of drill string equipment and decreasing the efficiency of the overall drilling system. Thus, it would be very desirable to overcome the challenge of stick-slip vibration via an effective control strategy. This paper proposes a new robust active controller based on the fuzzy sliding mode approach to suppress stick-slip vibration and to maintain the angular velocity of the drill components at the desired references. A discontinuous lumped parameter torsional model of a vertical drill string based on four degrees of freedom is used in this study. In addition to the drill bit and rotary table, the drill pipes and drill collars are included in the model. Moreover, nonlinear interactions between the drill bit and the rocks, including friction torque and the mud drilling effect, are considered. The proposed hybrid controller is based on a combination of artificial intelligence and a discontinuous first-order sliding mode control approach. A comprehensive numerical analysis was conducted by means of MATLAB and Simulink software. Real-time implementation of the system was conducted using dSPACE control board. The proposed controller has been tested under severe weight on bit variation and at different angular velocities. The results of the simulation and the real-time implementation are presented to demonstrate the good performance and feasibility of the proposed controller.