Structural Design of a Bionic Bone-Contraction Variable-Diameter Pipeline Robot
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Abstract
To improve the adaptability and structural efficiency of pipeline robots in small and medium variable-diameter pipelines, a bionic bone-contraction variable-diameter pipeline robot is proposed. The so-called bone-contraction mechanism is an engineering abstraction of feline shoulder-thorax compliance rather than literal bone shortening: the cat scapula is mainly constrained by muscle-ligament tissues and can slide relative to the thoracic wall, allowing the effective body width to decrease when passing through narrow gaps. This biological mechanism is transformed into a six-leg radial support system composed of a flexible spine, spherical/universal joints and spring-preloaded support legs. Static and dynamic models are established for diameter-changing conditions, and the main load-bearing components are verified by finite element analysis and SIMP-based topology optimization. The main innovations are: a biologically consistent shoulder-thorax-to-flexible-spine mapping, an active-passive variable-diameter support principle, a theoretical model for contact force, spring preload, driving torque and energy consumption, and a topology-based structural weight-reduction scheme. The robot can adapt to pipe diameters of 200–440 mm. Under the worst working condition, the maximum Von-Mises stress is 186.4 MPa and the first-order natural frequency is 42.6 Hz. After topology optimization, the main-frame mass decreases from 2.84 kg to 2.17 kg, corresponding to a 23.7% reduction relative to the initial frame of the proposed robot. This result is defined as within-design structural weight reduction rather than a claim of product-level lightweight superiority over a commercial robot. The results provide a feasible route for adaptive cleaning and inspection robots in variable-diameter pipelines.
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