Design and ATEX-Aware Kinematic Analysis of a Multi-Body Robot for Gas Pipeline Inspection

This paper presents the design and theoretical validation of a multi-body in-pipe inspection robot intended for operation in natural gas pipelines under the ATEX Directive 2014/34/EU. The proposed platform adopts a three-module architecture with passive joints and conical wheels, enabling compliant traversal of straight sections and 90° elbows in 8-inch pipelines while satisfying conservative design-stage mechanical and thermal constraints. The main novelty is the definition and evaluation of ATEX-feasible motion: an ATEX-aware kinematic feasibility framework in which ignition-risk constraints are embedded directly into the motion feasibility definition. Unlike conventional passability analyses that treat feasibility as primarily geometric (collision avoidance and joint-limit satisfaction) and handle ATEX considerations as a downstream hardware check, our formulation couples continuous kinematics and collision checking with explicit regulatory bounds on contact/rolling velocity, slip, power dissipation, and localized friction-induced heating. Consequently, trajectories classified as feasible by the proposed framework are collision-free and compatible with the imposed ATEX-aware design-stage bounds under conservative modeling assumptions. Simulation-based evaluations demonstrate collision-free navigation, continuous wheel–pipe contact, and bounded joint angles throughout elbow traversal. The analysis further shows that, under conservative design-stage assumptions, operational limits are dominated by tribological and slip-related constraints rather than by available actuation power or global thermal dissipation. A conservative ATEX-aware screening velocity is therefore introduced within the Ignition Hazard Assessment framework for non-electrical equipment. Overall, the proposed methodology provides a conservative design-stage foundation for the design and virtual assessment of in-pipe robotic systems intended for explosive atmospheres, and supports future experimental validation and conformity assessment.