Abstract: To address the problem that conventional quadruped robots for fuel tank inspection can hardly traverse an in spection opening, this paper firstly introduces a linear guide rail and combines it with hip flipping to reconfigure the leg degree-of-freedom layout. The swing leg can thus complete the traversal in stages within the limited clearance without taking the inspection opening frame as a supporting point. Secondly, the overall structure and the leg mechanism are designed, and a kinematic model is established. Under identical link dimensions and joint limits, the reachability of footholds on the far side of the inspection opening and the configuration redundancy are then analyzed before and after the prismatic joint is introduced. Finally, the traversal trajectory is planned under a fixed stage sequence, and the candidate traversal sequence is audited frame by frame. The results show that, af鄄 ter the prismatic joint is introduced, the average reachability rate of discrete footholds of the four legs increases from 50.0% to 92.9%. The area coverage of the far-side foothold region of the inspection opening increases from about 26% to about 96%. Configuration switching can provide posture redundancy for the same foothold. For the 696-frame candidate traversal sequence, the minimum clearance from the inspection opening frame is 26.989 mm, and the minimum static stability margin (SSM) is 9.034 mm. The self-collision distance remains positive, indicating that the staged traversal path is numerically feasible under the digital model and nominal working conditions adopted in this study. The results can provide a basis for the leg mechanism design and traversal planning of aircraft fuel tank inspection robots that traverse inter-bay inspection openings with low contact risk.

Key words: aircraft fuel tanks, quadruped robot, prismatic-revolute-revolute-revolute (PRRR) mechanism, foothold reachability