Tri-axis Differential Drive Unit Of In-Pipe Robot Design And Its Reliability Research

Different kinds of in-pipe robot have been developed for various pipeline environments in the world. Among them, in-pipe robot with tri-axis differential drive unit can thorough solved the complex problem of contact situation between the driving wheels and the inside wall of the pipeline and can realized self-differential of every wheel by itself, in this way solved the key technique issue of in-pipe robot with travelling wheels without set up system model of complicated robot. A mathematic model to describe the traveling–capability of drive unit of tri-axis differential in-pipe robot in elbow is presented, which include its differential velocity and mechanics property in elbow. The theoretical analysis indicates that the drive unit of tri-axis differential in-pipe robot has automatic differential velocity property without autoeciousness power, furthermore its drive-wheels produce sufficient drawing force and with automatic mechanical adaptability. The mathematic model with its differential velocity property and mechanics equilibrium equation in elbow is fundamental to mechanical adaptability theory of tri-axis differential in-pipe robot. A proto type which is based on the tri-axis differential drive principle was made and before it was used in the practice the examining and research to the reliability must be done to ensure its reliable and provide useful reference for the reliability research of similar products. Design and research on tri-axis differential drive unit of in-pipe robot and its reliability in this article has been done as follow:1. To guarantee a better adaptability to the environment of the pipeline the in-pipe mobile robot which constitutes differential drive unit and diameter accommodating mechanism a tri-axis differential drive unit has been developed and its differential velocity and mechanics property both in the straight and elbow pipe had been analyzed theoretically. Tri-axis differential drive unit performs no differential velocity in straight pipe, while automatic differential velocity in elbow pipe according to in-pipe topological environment and its wheels moving with pure rolling without autoeciousness power. Tri-axis differential drive unit of in-pipe robot is fundamental to theoretical research of differential in-pipe robot with mechanical adaptability.2. While patrolling at elbow the real distance passing by each walking wheel has some difference. To describe the traveling–capability of the unit in elbow a mathematic model is presented, which includes its differential velocity and mechanics property, this also shows that it can perform automatic differential velocity in elbow and without autoeciousness power. At the meantime the driving wheels supplied sufficient dragging force and had better self accommodating property. The locomotion and equilibrium equation of the unit is the fundamental to the theory of the mechanical self accommodating.3. In-pipe robot with tri-axis differential drive unit is a product of non-standardization designing, during its proto type testing a fault tree analysis measure had been introduced to solve the complex issue of this system according to the malfunctions, every probability importance of the basis events in the fault tree to the upper event been calculated by means of minimal cut-sets and pass-sets. Economical and effective fault controlling scheme to design the robot is depending the number of the basis events in the minimal pass-sets, difficulty in technical, working time and financial consumed, this provided the gist for quantitative analysis the fault of the robot later on.4. It's difficult to collect the failure data at present due to the robots is less and its developing period is shortter but its life-span is longer. A new method to accelerate the reliability test research of in-pipe robot is been bring forwarded in this article, mathematic models of Weibull distributing probability density function based on the inverse power law and accelerated factor is been built up. The tests proved that the accelerate stress is suitable, and easily extrapolate the accelerated factor under different stresses. It can deduce the character of the reliability under the test which similar to the practice result by using the mathematic model of accelerating life test; the mean time between failures concluding from the test can satisfied the demand of the robot in the practice. 5. Although the theoretical analysis shows that as long as the structure of the driving unit is symmetry it can guarantee to realized performing differential function, but it still can meet the problems like malfunction of differential and power depleting and so on caused by improper designing, manufacturing and assembling. So from the point to enhance the transmission precision and optimized the technics, typical parts and its structure has been analyzed. To reduce the technics difficulty of the parts, partial differential method is been used to solve the issue of tolerance distribution, this ensure the machining quality of the parts under the common machine tools, this saved the money and the time for scientific research. Meshing quality between the bevel gears and adjusting clearance in the direction of the axis which are influenced by the uprightness error of the gimbal were analyzed in detail and the relation function of them had been set up, this can be used to analyzed the transmission precision of the tri-axis differential drive unit during quantitative analyzing the robot in the reliability.Finally, this paper has addressed the innovation achievement and research findings, and pointed out the deficiency.