Robust H-Infinity Control of Feeding Speed in Coal Seam Drilling Process With Uncertain Hardness

The hardness of the coal seam significantly influences the relationship between feeding speed and resistance at the drill bit. Due to the compressive deformation of the drill string, maintaining a stable feeding speed during drilling remains challenging. In this article, we propose a robust H-infinity dynamic output feedback controller, formulated to explicitly address uncertainties in formation hardness, thereby ensuring stable feeding speed and improved dynamic performance of the feed system under diverse drilling conditions. First, we develop a bitrock interaction model that incorporates the uncertainties in formation hardness and the rock-breaking threshold, which are key factors affecting drilling performance. By integrating this model with a finite element representation of the drill string, the feeding system is recast as a norm-bounded uncertain system. On-site data is utilized to replicate drilling conditions and validate the accuracy of the model. Subsequently, considering the uncertain parameters and industrial performance requirements, a dynamic output feedback controller is designed using robust H-infinity optimization with tailored weighting functions. This controller maintains stable feeding speed across varying formation hardness, effectively suppressing the impact of hardness fluctuations by attenuating resonance peaks. Both simulation and field experiments confirm that the proposed controller substantially reduces feeding speed fluctuations and achieves the desired robustness and control performance.