# Design and Analysis of Independently Adjustable Large In-Pipe Robot for Long-Distance Pipeline
## 1 Introduction  
Pipelines are widely used due to their convenience and economy. As demand for oil and gas is increases across the globe, we can expect pipeline networks will increase in length in the near future. However, as the service life increases, problems with pipelines will inevitably arise, such as aging, cracks, corrosion or external damage--especially for large oil and natural gas pipelines. Leak-detection methods based on detection of vibration are widely used because of their advantages, such as wide range, high-precision and good expandability. This system ensures safe operation of pipelines over a wide range [1, 2]. However, the pipeline structure itself cannot be inspected until it is too late to maintain after leaking [3, 4]. The in-pipe robot has been a growing interest by reducing operator intervention from a dangerous work environment and improving work accuracy and efficiency in enclosed space. After more than 20 years of development, in-pipe robot field is gradually becoming mature; meanwhile, the ILI (in-line Inspection) technology has made considerable progress. In-pipe robots can be classified into nine different robotic systems, such as PIG, wheels, crawler, inchworm, helical, etc. [5, 6]. We focus on wheeled, cylindrical and crawler types because they have more controllability over their movements and stronger stability than others. There have been many studies done on these types of in-pipe robots [7, 8] as these small robots have excellent motion control, enabling them to pass t-tubes, elbows and obstructions. However, we hope to make a comprehensive and accurate NDE (non-destructive evaluation) with MFL (magnetic flux leakage testing) and UT (Ultrasonic Testing) equipment [9]. Because of the strength and weight of the materials involved, small in-pipe robots cannot simply be scaled up to accommodate large pipes. There are many studies on large-scale in-pipe robots. [PERSON] (2011) focused on designing an optimal pipe navigation mechanism with a driving unit to overcome the various situations encountered inside steel pipes (' 600-' 800) [10]. [PERSON] (2012) presented another concept. Their robot consisted of six wheeled-legs that support the structure along the center of the pipe which enables cleaning and sealing tools to work properly by rotating around the inner circumference of the pipe, thus covering the entire 3D in-pipe space (' 800-' 1000) [11; 12]. Most large and long-distance steel pipelines are straight, and the curved parts are smooth with large-angle bending. If the bending angle is too small, it causes water-hammer and wastes much energy. Robots are making new demands in this environment. On one hand, robots must get rid of the cable (the cable increases the robot's running friction), work alone in oily long-distance pipes and store information. On the other hand, large pipelines have heavy manufacturing and operating costs. Once they start operation, they will be filled with high-pressure oil sources. Therefore, any means of inspection into the pipeline must be carried out under the condition of fluid empties, and comprehensive testing data should be obtained. Visual equipment alone--like CCD--for inspecting inside a tube cannot find the defects inside the steel structure, which is an uneconomical investment. The robot itself should be used as a platform for testing and processing information. Moreover, it can carry other testing equipment into the pipeline for inspection [13; 14; 15; 16]. This study focuses on the design of a large-scale robot with novel track-driving modules and independent pantographs controlled by the pressure sensors, encoder and laser radar. Three track driving modules (crawlers) are radially connected with an interval of 120. Each crawler structure can expand and contract independently by an electric putter. To make the robot run stably in the long-distance pipeline, we established a mechanical model and differential rotation model to active control the robot attitude.