Tendon-Based Proprioception in an Anthropomorphic Underactuated Robotic Hand with Series Elastic Actuators

Anthropomorphic underactuated hands are widely employed for their versatility and structural simplicity. In such systems, compact sensing integration and proper interpretation aligned with underactuation are crucial for realizing practical grasp functionalities. This study proposes an anthropomorphic underactuated hand that achieves comprehensive situational awareness of hand-object interaction, utilizing tendon-based proprioception provided by series elastic actuators (SEAs). We developed a compact SEA with high accuracy and reliability that can be seamlessly integrated into sensorless fingers. By coupling proprioceptive sensing with potential energy-based modeling, the system estimates key grasp-related variables, including contact timing, joint angles, relative object stiffness, and finger configuration changes indicating external disturbances. These estimated variables enable grasp posture reconstruction, safe handling of deformable objects, and blind grasping with proprioceptive-only recognition of objects with varying geometry and stiffness. Finger-level experiments and hand-level demonstrations confirmed the effectiveness of the proposed approach. The results demonstrate that tendon-based proprioception serves as a compact and robust sensing modality for practical manipulation without reliance on vision or tactile feedback.