Mechanism Design And Property Study Of In-pipe Robot Based On Self-locking Principle

With the development of modern industrial technology, plenty of pipelines withvarious diameters and shapes have formed a complex system which successfullyoccupied every corner of human daily life, even in petrochemical industry, refrigeratingindustry and nuclear power plant. The development of in-pipe robot technique providesin-service pipelines with a potential possibility to perform inside surveillances andmaintenances. Many achievements have been reported in the in-pipe robot researchdomain, but there are still many unacceptable shortages remained as the robot worksunder tough environment. Therefore, many researchers are devoting themselves toimproving the in-pipe robot performance, aiming at accelerating its application toreality.The request of powerful and fast moving in-pipe robot is urgent from theapplication areas like the nuclear reactor evaporator and the horizontal petroleum well.By utilizing functions and properties of self-locking mechanism, this thesis makesresearch on the telescopic in-pipe robot based on self-locking principle. It performedconcept design, parameter optimization, property analysis, virtual simulation andprototype developing, which as a result breaks through the traditional constraint ofmaximum friction imposed on in-pipe robot traction ability, and makes the movingvelocity and transaction ability individually adjustable. The referred self-locking can beexplained as, the in-pipe robot could get locked with the pipeline automatically, withoutany help of control. Main contributions and innovations of this thesis are summed up as:(1) Present various in-pipe robots are summarized, and a contact style basedclassification method is proposed. It is not easy to make contrast and analysis amongdifferent in-pipe robots with diverse styles and varying dimensions, while relatedresearches are focusing on actuating systems. The thesis divides in-pipe robots intothree groups depending on different contact styles with pipeline, which makes it moreconvenient to compare different in-pipe robots. One group has faces contacted withpipeline, one has lines or points, and the left one has nothing.(2) For the first time the Axiomatic Design (AD) method is introduced into thedesign process of in-pipe robot that has been explored, and the concept of telescopicin-pipe robot based on self-locking principle is proposed. The traction ability of presentin-pipe robot is limited by the constant maximum friction between pipeline and therobot supportive mechanism, and can’t be adjusted without putting influence on itsmoving velocity. The concept design and coupling analysis are carried out following theAD theory. As a contrast, the wheeled and pneumatic telescopic in-pipe robots are bothmade coupling analysis with the results of coupled design and decoupled design,separately. (3) The in-pipe robot construction is deliberately designed, which embodies theproposed concept. A series of guide specifications and optimization theories arepresented, as well as the bending rigidity of compression spring. With varying diameter,the long and thin pipeline raises new requirement for in-pipe robot construction design,linkage design and security design. Focusing on two proposed mechanisms, it derivesthe self-locking requirement relationship, optimizes the cam contact profile, simulatesand gets the repelling force between two sets of permanent magnets, calculates theminimum required force and minimum action time. As the flexible linkage of thein-pipe robot, the spring is investigated and its bending rigidity calculation formulas arefound out based on the thin elastic rod theory. The security clutch has been developedfor the application in pipelines.(4) The property of self-locking mechanism is explored. After successful validityof partial assembly and the whole robot, the formulation relationships for calculating themaximum driving ability and the mechanically localization accuracy are built up. Theshortage of traction ability is one of the main reasons that blocks the application ofin-pipe robots in reality, meanwhile its local ability heavily depends on various sensors.The thesis takes inertia impulse in-pipe robot as an example to make analysis on itstraction ability, and then deduces related calculation formulas about the maximumtraction ability and localization accuracy for the proposed two mechanisms. The resultshows that the traction ability of the self-locking mechanism can increase automaticallywith the rise of outside payload.(5) The geometry constraint is explored as the in-pipe robot passes through anelbow, and theoretical rules are proposed to guide the design of supportive legdeflection. With a proper deflection, the elastic legs remain contact with the pipeline allthe time when moving in a pipeline, thus avoiding discontinuous motions and leavingrobot body with enough space. However, reported researches have merely establishedthe constraint relation about the outline dimension. The thesis obtains the formulas ofreal-time deflection of supportive legs by setting up the mathematical model for in-piperobot inside pipelines, gets the maximum and needed deflection with the help of Matlab,and reveals how the deflection effected by different fabric parameters.(6) About the self-locking in-pipe robot, the prototype is developed, thecomprehensive test platform is set up, and the principle test is conducted, as well as theperformance test. Guided by the deduced design rules, two prototypes are developed.On the specialized test platform, the validity of self-locking mechanism is carried out,as well as its performance of climbing, traction ability, moving velocity and decoupling.The concept of ratio of traction ability to space is invented for quantifying the tractionabilities of different in-pipe robots. The experimental results indicate that two types ofself-locking mechanism can help in-pipe robot achieve a fast and stable moving ability,and a accuracy localization ability inside pipelines. The prototype with diameter of 16mm is proved to be capable of climbing vertically set pipelines, carrying a maximumload of15.2N, speeding up to13.72mm/s, pushing the ratio of traction ability to spaceto9.364with normal ones under1, and realizing the uncouple design between movingvelocity and traction ability.