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

Abstract

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.