Clamping Force Sensor Fault Analysis and Fault-Tolerant Control of the Electromechanical Brake System

In rail transportation, electromechanical brake (EMB) technology is seen as the next generation of the braking system. Due to the deplorable working conditions (such as wading, impact vibration, and voltage surge), the clamping force sensor can encounter bridge-cut-off, zero shift, cable transmission faults, and other problems. Hence, the reliability of the clamping force sensor is greatly challenged. For the thorny problem, this paper proposed a novel clamping force sensor fault-tolerant control strategy that can be a backup control loop to enhance the reliability of the system. Firstly, the paper describes the working principle of the EMB system and establishes its nonlinear mathematical model. Combined with the piezoresistive sensor working principle, the cause of clamping force sensor failure is analyzed. Meanwhile, the corresponding relationship between motor output torque and the braking process is explained, and a gap adjustment control strategy without a clamping force sensor is proposed. Then, a clamping force estimation method is presented under strong coupling conditions, considering the different hysteresis characteristics between foreign clamping forces. In addition, the designed enhanced extended state observer (ESO) utilizes the sigmoid function to solve the high-frequency chattering phenomenon of the conventional nonlinearity ESO. With the enhanced ESO, the power fast terminal sliding-mode (PFTSM) control can ensure the dynamic response and improve the anti-interference ability of the system. Finally, compared with a conventional method, a static experimental platform verifies the effectiveness of the proposed control strategy.

Automated summary

This paper proposes a novel fault-tolerant control strategy for the clamping force sensor in the electromechanical brake system, aiming to enhance the system reliability. By analyzing the causes of clamping force sensor failure, the relationship between motor output torque and braking force, and considering the hysteresis characteristics of external clamping forces, a clamping force estimation method is presented. Combined with an enhanced extended state observer and power fast terminal sliding-mode control, the proposed strategy achieves dynamic response and improved anti-interference ability.