# Study of a Small Robot for Mine Hole Detection
## 1 Introduction  
Coal is a vital fossil energy source and the foundation of China's energy system. China is rich in coal resources, but the complex geological conditions of coal mines and the difficulties in mining have led to frequent coal mine production accidents in China, and there is a significant gap in the safety situation of coal mines compared with that of developed countries [1; 2; 3; 4; 5; 6]. According to relevant statistics, between 2008 and 2021, the total number of coal mine accidents in China reached 1157, causing a large number of casualties and property losses, of which roof accidents and water damage accounted for 44.43%, resulting in 514 deaths; this represents a severe hazard [7; 8]. These accidents are closely related to local hydrogeological conditions, and the use of mine hole-detection technology can determine the stratigraphic conditions of coal mines, which can effectively reduce the risk of coal mining. A coal mine borehole is usually up to 60 m long, with a particular slope, slight and uneven borehole diameter, slippery borehole, and the presence of flammable and explosive gas. The existing mine borehole-detection technology uses the manual pushrod jacking probe method, using the internal environment of the borehole to shoot and subsequent image processing recognition and other work to assess the condition of the stratum. The manual advancement of this method of operation is cumbersome, the jacking depth is insufficient, the speed is difficult to regulate, and the imaging results are poor. Therefore, the development of a small mobile robot integrating various detection functions is of great engineering significance for safeguarding safe production in the mineral industry. The mine hole-inspection robot belongs to the pipeline robot category. Pipeline robots represent electromechanical integrated systems capable of navigating through and operating inside or outside boreholes. Pipelines constitute critical components of modern industrial transportation, necessitating regular inspections as a crucial safety measure. Scholars worldwide have designed various pipeline-inspection robots catering to different pipeline structures and usage environments, laying the foundation for developing mine borehole-inspection robots [9; 10; 11; 12]. Different driving methods divide pipeline robots into two categories: external load-driven and self-driven robots. External load-driven robots mainly refer to PIGs, which are now widely used in the oil and gas industry and are based on the principle of utilizing rubber discs that move under the pressure of fluids in the pipeline. [PERSON] and colleagues (2019) designed a novel foam smart PIG for oil and gas pipelines with good pass-through capability to detect pipeline defects while performing pipeline cleaning. However, such robots' particular power source limits their application environments to sealed pipelines filled with flowing media [13; 14; 15; 16; 17]. Self-driven pipeline robots have their own power source and are categorized into serpentine robots, crawler robots, wheeled robots, and other types, depending on how they move [18; 19; 20]. Serpentine pipe robots have strong crawling ability and can adapt to complex environments. [PERSON] designed a serpentine pipe robot named PipeTron, whose main body is divided into several parts; each part has an active wheel and uses the wall-pressing method of walking. The parts are connected with each other via deflector joints, which possess good crawling and traction ability; however, the robot's energy consumption is large, and it is complicated to operate [21]. [PERSON] and colleagues improved the structure of the snake robot to allow for traveling in a rolling fashion, which grants the robot a strong obstacle avoidance capability; however, this robot has limiting requirements concerning the pipe diameter, meaning it cannot adapt to small caliber pipes [22; 23].