Knee-Inspired Hinge Absorbs Longitudinal Impacts to Enhance Robot-Environment Interaction Safety

As robots integrate into human society, ensuring safe robot-environment interaction, particularly in the event of collisions, has emerged as a growing design priority. A promising solution is introducing proper compliance into existing rigid robots, akin to musculoskeletal systems, to absorb impacts in various directions. However, mimicking longitudinal compliance seen in biological joints to absorb compressive impacts along limbs, such as the role of cartilages like menisci, remains a challenge shadowed by the complexity of joint architecture. Here, exploring and adapting the elastic longitudinal movement structure of knee, we incorporated traditional mechanical hinges with a compact buffer structure to enable both simple rotational motion and effective longitudinal impact absorption. Under longitudinal loading, the buffer structure functions as a mechanism transmitting the limited compression to amplified deformations of elastic elements, thus producing resistance against load. The resistive load-displacement relationship is tailorable by tuning diverse elastic components, allowing for a high-static-low-dynamic stiffness to improve energy absorption efficiency. Drop tests and walking robot demonstrations confirm that the proposed knee-inspired hinge not only mitigates acceleration transmitted to the robot’s main body but also reduces ground reaction forces, thereby improving robot-environment interaction safety. This work highlights the design paradigm of adapting natural solutions to mechanical systems, and holds potential for direct integration into diverse robots, exoskeletons, and prostheses.