Design and Analysis of a Bio-inspired Leg-ilaw System With Active-passive Coupling for Aerial Grasping and Perching

Reliable physical interaction with unstructured natural environments remains a fundamental challenge for aerial robots, particularly in grasping and perching tasks. This paper presents a bio-inspired leg-claw system with active-passive coupling, enabling rapid passive perching and controllable active grasping. Inspired by the avian Tendon Locking Mechanism (TLM) and Automatic Digit Flexion Mechanism (ADFM), the proposed system integrates an independent digit self-locking mechanism based on a knot-ratchet-sprocket configuration with a leg-driven tendon actuation architecture. A rigid-soft gradient digit design is further adopted to enhance impact tolerance and surface adaptability. To evaluate system-level perching stability, a quasi-static slip model is developed to estimate the critical slip/tipping boundary under varying branch diameters. A quadrotor-mounted prototype is developed, and comprehensive experiments are conducted, including grasping adaptability, static load capacity, cyclic actuation and load-retention tests, response time, slip stability testing and calibrated trend-level model comparison, and flight demonstrations. Under the dry rigid mm branch load test, the proposed claw achieved an average static load capacity of 12.03 kg, corresponding to a single-side leg-claw-module-normalized load-to-weight ratio of 140.5. The cyclic actuation and load-retention test showed repeatable tendon actuation, while the fixed-load retention ratio decreased after 200 cycles owing to adhesive-interface failure between adjacent carbon-fiber plates of the ratchet-sprocket. Passive grasping and mechanical locking are completed within 48 ms. Together, these results demonstrate a compact aerial grasping and perching solution that combines rapid passive engagement, controllable release, and high load retention, while also identifying adhesive-interface failure of the current ratchet-sprocket as a structural limitation.