# Magnetic Levitation Belt Conveyor Control System Based on Multi-Sensor Fusion
## 1 Introduction  
Belt conveyors have been widely used in modern high-yield efficient mines owing to their long conveying distance, large transportation volume, high productivity, and stable operation [1]. However, the energy consumption related to idlers in traditional belt conveyors accounts for approximately 70% [2] of the total energy consumption of the entire conveyor system. With the emergence of intelligent construction in coal mines, the intelligence degree of the belt conveyor--the key equipment of the main coal transportation system--directly affects the efficiency of coal transportation and the level of intelligent construction in coal mines [3]. Therefore, a magnetic suspension belt conveyor that uses magnetic suspension support instead of a roller support is proposed herein. The structural diagram of the magnetic levitation belt conveyor is shown in Figure 1.  
Owing to its advantages of no contact, no friction, and long service life, magnetic levitation technology has been widely used in various industries, such as magnetic levitation trains, magnetic levitation bearings, and high-speed magnetic levitation motors [4; 5; 6]. Compared with permanent magnet suspension, electromagnetic levitation has the advantage of easy control. The real-time operation and the accuracy of the air gap displacement signal are crucial for controlling the magnetic levitation system stability. To date, eddy-current, capacitive, and photoelectric displacement sensors have been often used to measure the magnetic suspension air gap. However, they have some shortcomings, such as a large volume, poor stability, and poor linearity. Therefore, in order to overcome the limitations of sensor-based approaches, numerous researchers have devoted their efforts to sensorlessmagnetic levitation systems [7; 8; 9; 10; 11; 12]. For instance, [PERSON] et al. [7]. addressed the state observation problem in sensorless control of magnetic levitation systems by only measuring the voltage and current of the power supply to adjust the position of the levitated object. [PERSON] [11] proposed a solution to the position stabilization problem in nonlinear magnetic levitation systems using only position measurements. However, it is evident from the aforementioned sensorless research that sensors still need to be employed in conjunction with complex mathematical models. To reconcile the contradiction between sensorless approaches and the complexity of model solving, we adopt a multi-sensor scheme that exhibits transitional characteristics. Compared with a single sensor, multi-sensor fusion [13; 14; 15] has advantages, such as fault tolerance, complementarity, real-time performance, and economy. This approach is therefore used in various fields, such as robotics, medical applications, and target tracking. With the advancement of machine vision measurement technology, its application [16; 17; 18] in dimensional measurement provides high measurement efficiency. Meanwhile, industrial cameras are small, easy to install and display, and have no special requirements for the detection surface, which thus resolves some of the limitations of traditional sensors. Industrial cameras can not only assist in detecting clearances but also transmit a wealth of measurement information, including material flow and other conveyor measurements. Furthermore, even the replacement of sensors could be achieved in the future. Therefore, the integration of multiple sensor information from traditional displacement sensors and industrial cameras not only effectively addresses the aforementioned issues but also enhances the stability and reliability of the system, laying the foundation for the intelligent and diversified development of conveyors  
Due to their strong nonlinearity and open-loop instability, electromagnetic levitation systems typically require displacement sensors to detect the suspension air-gap displacement in real-time and perform closed-loop feedback control.