Development and validation of a rigid-flexible hybrid robotic leg with structural compliance and intrinsic contact sensing capability

Elastic elements in robotic legs offer benefits in terms of adaptability, energy efficiency, and robustness. This paper presents a novel concept of a robotic leg with a fully elastic arc-shaped link that serves as both a structural component for motion transmission and a leaf spring. This unique design endows the robotic leg with structural compliance, which is particularly advantageous for impact absorption during interactions with the environment. Furthermore, the deformation of the elastic link enables intrinsic contact sensing capability. A compact deflection sensor capable of measuring large-scale deformations was developed and integrated with the elastic link. A contact sensing model was derived using a discretization-based approach to predict the foot contact force and position by leveraging elastic deformation and hip motor torque. Various experimental validations were performed using the fabricated prototype. The results demonstrate a 35% reduction in the impact loads compared to those of a rigid counterpart. Moreover, foot contact force sensing and control in both static and dynamic scenarios were achieved, and useful terrain information was obtained using the sensed force. • Novel rigid–flexible hybrid robotic leg with a fully elastic arc-shaped link. • Intrinsic contact sensing model leveraging elastic deformation and motor torque. • Impact load absorption capability owing to structural compliance. • Validation of force sensing and control in static and dynamic scenarios.