Suppressing stick-slip oscillations in drill-strings by Modified Integral Resonant Control

This paper presents development of a novel control scheme for suppressing stick-slip oscillations of drill -strings. This scheme utilises a Modified Integral Resonant Control (MIRC) with tracking in order to meet a desired drilling velocity. A low-dimensional two degrees-of-freedom drill-string model incorporating bit-rock interactions adopted for an open-loop control, clearly demonstrate presence of unwanted stick-slip responses. Next a detailed design of the MIRC-based damping scheme (without tracking) capable of eliminating this undesired behaviour is presented. Then in order to enhance efficacy, the MIRC-based scheme is combined with an integral tracking controller to show that this combined damping and integral tracking control scheme is not only capable of eliminating stick-slip oscillations but also maintaining the desired drill-bit angular velocity. To highlight the benefits of the proposed combined scheme, it is compared with the recently proposed Sliding-Mode Controller (SMC). Its inherent simplicity, robustness to parameter uncertainty and excellent performance of the proposed combined scheme propels it to be a leading candidate for stick-slip mitigation in drill-strings. To further showcase the efficacy of the proposed control scheme, its closed-loop performance when implemented on an 8-DOF system, has also been discussed.