| Design Theory and Method |
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| Research on singularity of pipeline creeping parallel mechanism based on screw theory |
| ZHU Jin-yi, ZHANG Chun-yan, LU Chen-hui |
| School of Mechanical and Automotive Engineering， Shanghai University of Engineering Science， Shanghai 201620， China |
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Abstract The pipeline creeping mechanism based on 3-(P)URU(P) parallel mechanism can realize the creeping in the pipeline by alternately releasing the moving and fixed platform and 3 URU branch chains connected to the two platforms, so it can be applied to the monitoring and flaw detection of industrial and agricultural transportation pipeline. The singularity of the mechanism will affect its efficiency and engineering quality, so a singularity analysis method of mobile parallel mechanism was proposed, and the singularity of the mechanism was studied. Firstly, according to the screw theory and the line geometry method, the configurations of branch chain singularity, constraint singularity and drive singularity were analyzed; then, the singularity of the mechanism in the creeping process in the pipe was analyzed. The results showed that the branch chain singularity of the mechanism occurred in the elbow pipe, which led to the reduction of the degree of freedom and even the blockage in the pipe, and the constraint singularity occurred in the straight pipe, which led to the uncontrollable creeping; finally, the constraint equations were established according to the constraint relationship of mechanism singularity, and the respective singular trajectories were obtained by numerical simulation. The research results provide an important theoretical basis for the follow-up design and engineering application of the mechanism control system.
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Received: 17 July 2020
Published: 28 June 2021
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基于螺旋理论的管道蠕动并联机构的奇异性研究
以3-（P）URU（P）并联机构为主体的管道蠕动机构通过交替移动动定平台及连接两平台的3条URU支链实现在管道内的蠕动，从而可以应用于工农业运输管道的监测和探伤等。机构的奇异性会影响其使用效率和工程质量等，因此提出了一种移动并联机构的奇异分析方法并对该机构进行奇异性研究。首先，根据螺旋理论并结合线几何法分析了支链奇异、约束奇异和驱动奇异的位形； 然后，分析了机构在管道内蠕动过程中的奇异性，结果表明，机构在弯管内会发生支链奇异且导致自由度减少甚至在管道内卡死，在直管内会发生约束奇异导致其蠕动不可控；最后，根据机构奇异的约束关系建立了约束方程，并通过数值仿真得出各自的奇异轨迹。研究结果对后续机构控制系统的设计及其工程应用提供了重要的理论基础。
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