Research On The Key Techniques Of An Autonomous Lockup Creeping Micro In-Pipe Robot

Thin-wall inverted "U" type heat transfer pipelines with inner diameters ranging from 15~20 mm, are extensively used in nuclear reactor evaporators. After a long running, they are prone to corrosion, fatigue failure, or damage to cause leakage accidents, etc. Therefore, it has become a key to monitor, diagnose, clean and maintain for the sake of safety, smoothness and efficient operations of the nuclear reactor system. However, due to their complex structure, constrained internal space, and poisonous environment, repair and maintenance of the pipelines are very difficult. So it is very important to develop a new type of micro in-pipe robot applicable to such special cases, to realize non-destructive testing on the heat transfer pipelines in nuclear reactor evaporators.Based on the urgent need of automatic detection of micro heat transfer pipelines in nuclear reactor evaporators, this thesis carries out the design and research of a new type micro in-pipe robot supported by the "Eleventh Five-Year Plan" Ministry Pre-research Project and the Hi-Tech Research and Development Program (863) of China. Aiming at technological breakthrough of "microminiaturization, large traction, fast, long-distance movement" for in-pipe robot, this thesis is focused on the structure design, theoretical modeling, motion stability analysis and multi-objective optimization and other key issues of the robot. The research efforts mainly include the following points:1. A new type of creeping micro in-pipe robot with autonomous lockup function is designed. Aiming at the issues of microminiaturization, diameter adaptation and elbow trafficability, and based on the analysis of the advantages and disadvantages of the existing driving schemes, an autonomous lockup creeping micro in-pipe robot is proposed. Then the body structure is designed and optimized. As a result, innovative design of self-regulating supporting mechanism, flexible holding mechanism and flexible-shaft driving mechanism is presented. The virtual prototype simulation shows that the optimized micro in-pipe robot possesses the advantages of autonomous lockup and improved diameter adaptability, and efficiently solves the problems of rigid braces and elbow trafficability.2. The mechanical characteristics of the micro in-pipe robot are researched systematically. Based on the principles of mechanical equilibrium and virtual displacement, the mechanical properties of self-regulating supporting mechanism are discussed in respect of diameter adaptability. Then the driving characteristics of the robot are analyzed, and mathematical models of closed-force, traction and climbing ability are established. As a result, the monotonically decreasing law of the traction changing with the diameter is discovered. Using integral theory and motion synthesis, the movement resistance and the "autorotation" problem are discussed. After the mechanism of robot's "autorotation" analyzed, the spherical design of supporting and holding wheels is presented to efficiently restrain the "autorotation". At last, the mechatronics dynamic equations of the robot's drive system are established. The above-mentioned established mathematical models and the conclusions provide theoretical basis for structure design and optimization of the micro in-pipe robot.3. Motion stability of micro in-pipe robot with frictional contacts is studied in depth. With sliding and rolling friction contacts considered, the limited rigid body dynamics model is established in respect of the robot's restricted movement, which is based on the first Lagrangian equation for holonomic system. Using linear complementarity theory, the existence and uniqueness of dynamic equation is discussed. Combining Kelvin's contact model, using singular perturbation and Layapunov's stability theory, the additional conditions of stability of constrained rigid body are given. With the stability conditions of the robot movement in straight pipes simulated, the flexible holding mechanism is presented, which efficiently solves the instability problem of micro in-pipe robot moving in pipelines.4. Based on the genetic algorithm, the multi-objective optimization problem of micro in-pipe robot is studied. According to characteristics of the robot's movement, the speed calculation model is established. Using energy balance, the least square method and extremum principle, the power model for the robot transmission system is established. On this basis, the multi-objective optimization model is established, where some sizes of the robot are taken as the variables, and traction, kinematic velocity and system power consumption are taken as the objective functions. Using genetic algorithm, optimization solution to the multi-objective model of the micro in-pipe robot is obtained. The results show that the theoretical value of robot's traction is 11.47 N, with velocity of movement up to 12.7 mm/s, well conformed to the design specifications.5. Two-generation test prototypes and motion control box of the robot are developed successfully. Then the test system is established with experiments conducted. The experimental result shows that the optimized second-generation prototype can smoothly run in 15~20 mm diameter pipelines, pass the elbow with radius of curvature no less than 80 mm, move bidirectionally with a speed of 8.7~12 mm/s, climb the oblique pipelines angled 0~90o, and carry load about 9.95 N. And the load weight ratio is up to 6.77:1, which well meets the design goals of "microminiaturization, large traction, fast, long-distance movement" for the pipeline robot.