# Study of a Small Robot for Mine Hole Detection
## 1 Introduction
Tracked pipeline robots have a large support area, slight ground-specific pressure, resistance to slip, good traction adhesion performance, and good passability. [PERSON] designed a tracked pipeline robot in 2021 that innovatively used a flexible articulated permanent magnetic track to generate local adhesion force, which allowed the robot to be adsorbed to the pipe wall for movement and solved the passability problem of non-clearable pipes. However, this kind of magnetic track only works in ferromagnetic pipes, and the robot's crawling performance in non-magnetic orifics is significantly weakened [24]. [PERSON] and colleagues designed a tracked pipeline robot with three tracks uniformly distributed on the outside of the body 120 degrees apart and an electric actuator, which can independently adjust the radius of the tracks to adapt to different pipeline sizes and adjust the pressure between the tracks and the pipe wall to regulate the traction force and pressure wall. It can adjust the traction force by adjusting the pressure between the tracks and the pipe wall, and the method of pressing the wall makes it suitable for pipes made of various materials; however, the tracks of the pressure-wall tracked pipeline robot cannot be retracted inside the body, which makes the space utilization rate low and difficult to miniaturize, and it is not suitable for pipes under 100 mm [25]. Wheeled pipeline robots are the most widely used because of their excellent maneuverability and high efficiency. A simple wheeled pipeline robot only relies on the crawling wheel and the lower side of the pipe wall contact to travel. However, the structure is simple, the traction force is insufficient. [PERSON] designed a six-wheeled pressure-wall pipeline robot with each of the two ends of the three wheels distributed at 120\({}^{\circ}\). The ball screw forms the two sides of the wheels, which can be retracted and released to regulate the pressure between the crawling wheels and the pipe wall, thus allowing the robot to adapt to the diameter of a pipe from 100 mm to 200 mm. The robot is flexible and stable,but the structure is too exposed to adapt to a waterlogged environment [26; 27]. [PERSON] designed an articulated wheeled pipeline robot that is flexible in its movement, strong in obstacle avoidance, and easy to miniaturize. However, its structure and control method are too complex, and its performance is unstable [28]. In summary, although the pipeline robot technology has matured, the existing pipeline robots are often designed for specific environments, and simple modifications cannot adapt these robots to new environments. In 2006, the rescuers for the U.S. West Virginia Pressure Coal Mine Rescue Operation used conventional rescue robots to enter the underground to detect the situation, but the robot could not continue to move forward in the wells stuck in the mite. In 2010, on the New Zealand island west of the Atyrau Pike River, the rescuers for a coal mine gas explosion accident attempted to detect the underground situation with a simple spark-proof modification to a pipeline robot. However, the robot short-circuited underground due to waterproofing problems. Therefore, pipeline robots in particular environments must be specialized according to specific conditions [29]. The main task of the coal mine hole-detection robot is to carry a camera with various types of sensors to photograph the coal mine stratum and detect the environmental parameters in the hole. Considering the task requirements and the actual mine hole environment, the robot's diameter should not be too large, and it should have a specific adaptability to changes in the hole diameter and an excellent crawling ability. The robot should also be waterproof and explosion-proof and should be able to run smoothly in the mine hole in order to ensure the effect of filming and detection. To address the above needs, a small-wheeled robot is proposed in this paper.