Variable-Stiffness Joint Enabling Multiple Adhesion and Detachment Strategies for Climbing Robots

Abstract

Quadruped dry-adhesive climbing robots require ankle joints to meet conflicting demands in adhesion and detachment. The ankle should be compliant to form conformal contact during adhesion, yet stiff to transmit peeling moments during detachment. Wall-angle uncertainty and varying peeling difficulty make fixed-stiffness ankles and passive compliance alone insufficient. This paper presents a miniaturized variable-stiffness ankle joint (VSAJ) that integrates a Kresling origami pneumatic actuator with granular jamming to enable rapid stiffness switching and active rotation for wall-angle compensation. Within an approximately 1 cm form factor, VSAJ achieves 2.4× tuning in bending stiffness, 2.6× tuning in torsional stiffness, and up to 0.16 rad of active rotation. Two adhesion strategies and two detachment strategies are developed and validated through single-leg experiments and full-robot climbing demonstrations. The results show robust, versatile, and high-performance adhesion and detachment.