Rotational speed control system of coal mine automatic drilling rig based on extended state observer

Maintaining a stable rotational speed and ensuring accurate tracking of the optimal value during automated underground coal mine drilling is essential for achieving intelligent drilling, and forms the foundation for improving both drilling safety and efficiency. To address the problem of fluctuating drilling loads caused by coal-bearing stratum geological uncertainties—which makes precise control of drill rig rotational speed challenging—an automatic rotational speed control system in coal mines based on an Extended State Observer (ESO) is designed and implemented. First, a dynamic model of the electro-hydraulic rotary drive system is established based on its operating principles. Considering the step-response characteristics of the system, it is simplified to a first-order model. Then, the least squares method is adopted to identify the system parameters, and the mathematical model of the slewing system is obtained. Subsequently, the steady-state relationship between the input control signal and the rotational speed was fitted using a piecewise function, and the steady-state models of the slewing system under different control signals were established. This provides a theoretical basis for overcoming the dead-zone effect during system startup and improving the response speed. Second, A composite control scheme is designed by integrating an ESO, a PI controller, and a dead-zone compensator. The ESO treats the rotary load torque as an extended state, and mitigates the impact of rock stratum hardness variations on rotational speed through real-time observation and feedforward compensation. The PI controller dynamically adjusts the control signal based on the speed deviation to achieve high-precision speed tracking. The dead-zone compensator provides an initial control signal based on the steady-state model and the desired speed, enabling the system to quickly overcome the dead-zone effect and improve response performance. Finally, closed-loop simulation experiments and on-site actual drilling tests of the slewing system were carried out under different scenarios. The results show that the proposed control system exhibits good dynamic performance, stabilizing the rotational speed to the setpoint within 3 s and meeting the on/off control requirements of the rotary system under complex working conditions. The steady-state error is maintained within ±3 r/min, significantly enhancing the uniformity of the drilling process and the operational stability and safety of the rotary system. It provides strong theoretical and practical support for safe, efficient, and intelligent drilling under complex conditions in underground coal mines.