Adjusting the Interdigital Space and Hybrid Fingers of an Adaptive Gripper Utilizing a Single Motor

The exceptional dexterity of human hands in grasping objects across a wide range is attributed not only to the fingers but also to the adaptable interdigital space facilitated by the palm. Drawing inspiration from this unique functionality and aiming to minimize external driving sources, we present an innovative adaptive gripper that can passively adjust its interdigital space and hybrid fingers based on the shape and size of objects using a single motor. The gripper consists of three dual-stage spring sets (D3Ss) and three hybrid fingers. With these D3Ss, the interdigital space between fingers can be adjusted without any additional drivers. Through a design incorporating rigid-soft coupling, the hybrid finger exhibits a 33-fold increase in reverse bending stiffness and a 3.1-fold increase in lateral stiffness compared to its counterpart without the rigid layer. In addition, its torsional stiffness can increase by two to four times depending on the torsion angle. We have developed a mathematical model to quantitatively assess the gripper's configuration in relation to cable length variation, which has been validated by predicting sphere diameters post-grasping. Through experiments, we consistently demonstrate that our adaptive gripper outperforms fixed-finger-distance grippers in terms of grasping forces when handling spheres of varying diameters. In addition, we demonstrate the gripping capability of our gripper in successfully grasping objects with a size ranging from 35–160 mm, and effortlessly lift a lead ball weighing 3 kg by passively adjusting its interdigital space and finger bending amplitude. Notably, our design can be extended to accommodate more fingers while still utilizing only one motor-driven mechanism as exemplified by our five-fingered gripper prototype presented toward the conclusion of this study. By seamlessly integrating D3Ss and hybrid fingers into a single motor-driven mechanism, our gripper presents an elegant solution that not only simplifies grip technology but also enhances its capabilities.