Steer-by-wire control method for underground load-haul-dump vehicles based on smoothed inverse dead-zone compensation

Aiming at the problem that the input dead-zone of the electro-hydraulic proportional valve in the steer-by-wire system of underground load-haul-dump (LHD) vehicles makes the steering cylinder fail to respond effectively under small control signals, leading to delayed articulation angle response and poor low-speed small-angle tracking accuracy, a steer-by-wire control method based on smoothed inverse dead-zone compensation is proposed. A steer-by-wire steering system using the EPEC3724 controller as the core, a single-turn absolute encoder for feedback, and an electro-hydraulic proportional directional valve as the actuator was built. Based on duty-cycle versus articulation-angle tests on a real vehicle, the system dead-zone characteristics were identified, an asymmetric dead-zone model considering different left/right boundaries was established, and a smoothed inverse dead-zone compensation function was constructed. The compensation term was superimposed on the output of an incremental PID controller to obtain the steering control law with dead-zone nonlinearity handling. Dead-zone compensation comparison tests, continuous step and sinusoidal trajectory tracking tests, as well as variable-load tests under no-load, light-load and heavy-load conditions were carried out on a LH410 underground LHD. The results show that the identified positive and negative dead-zone boundaries are 223 and ?211 respectively, exhibiting obvious asymmetry. After introducing the smoothed inverse dead-zone compensation, the response starting time of the steering system was shortened from 0.621 s to 0.476 s, a reduction of 23.3%, and the cumulative control-effort variation J_Δu decreased by approximately 38%; the articulation-angle tracking error was kept within ±3° under both continuous step and sinusoidal trajectory conditions; the steady-state tracking accuracy under step conditions was hardly affected by load variations under the proposed controller, while under heavy-load condition the dynamic response delay increased by 0.46 s and the maximum tracking error increased by about 53% compared with the no-load case. The proposed method effectively reduces the response delay caused by the hydraulic dead-zone, improves steering accuracy and smoothness, and provides underlying actuation support for autonomous trajectory tracking control of underground LHD vehicles.