# A Scraper Conveyor Coal Flow Monitoring Method Based on Speckle Structured Light Data
## 2 Literature Review  
At this stage, the methods used for the amount of coal transported by scraper conveyors mainly include electronic belt scales, nuclear scales, visual ranging, and laser scanning methods. These methods can be divided into contact and non-contact categories.  
The traditional coal instantaneous flow detection mostly adopts contact methods such as electronic tape scales and nuclear scales. The contact method is usually installed on a single weighing device on a long conveyor belt frame, and the structure includes a weighing frame, a load cell, a speed sensor, and a totalizer meter. The advantages of this  
Figure 2: Scraper conveyor coal flow: (**a**) Normal coal flow; (**b**) Abnormal coal flow.  
method include low-cost, simple and convenient installation, and no need to make too many changes to the original equipment infrastructure [10; 11; 12; 13]. Scholars have used the discrete element method (DEM) to study the interaction between scraper conveyors and coal flow [14]. Traditional contact methods often have the following disadvantages:  
1. When the environment around the sensor is humid, the sensor is prone to short circuit.
2. Due to the long transportation distance of the scraper conveyor, the accuracy of this type of method is insufficient.  
To overcome the above problems, scholars have successively proposed coal flow calculation methods based on non-contact scraper conveyors with ultrasonic technology, laser technology, and computer vision [15]. Ultrasonic technology is a high-efficiency, high-precision, real-time measurement of the physical height of the object to be measured. It has the advantages of non-contact measurement, less influence by coal texture characteristics and coal dust resistance and is widely used in coal mine production [16]. The ultrasonic range finder detection method uses the principle of ultrasonic detection to realize the detection of coal flow through the reflected sound waves, but there are problems such as poor anti-interference performance and accuracy  
Laser measurement technology is an important means of geometric measurement. It is based on the principle of photoelectric technology, and the product is added together by means of mechanical instrument measurement. Using computer technology, it can be measured quickly and accurately with high precision. Due to its high accuracy, clear imaging, non-contact, and other advantages, it is widely used in modern industrial estimation. Although lidar can accurately extract the coal flow of the scraper conveyor, it cannot be widely promoted due to its high cost and redundant data processing problems in the later stage [17; 18].  
Vision measurement technology is a new type of measurement technology based on machine vision. Its advantages are high precision, strong real-time performance, large amount of information and non-contact measurement. With the reduction of implementation costs and the development of related software and hardware performance, the advantages of visual measurement technology have gradually emerged, and it has become one of the methods to solve measurement problems in the industrial production process [19; 20; 21; 22]. In view of the huge potential safety hazards of nuclear scale radiation, scholars [23] have proposed a coal quantity detection method based on machine vision and deep learning classification. This method uses an industrial camera to capture a dynamic coal volume image transmitter that laser illuminates the conveyor belt. However, due to the gravity of the coal, the scraper conveyor belt will bend to different degrees than when it is empty, resulting in errors in the data predicted by the visual measurement method.