Underactuated Robotic Finger: Dynamic Modeling and Experimental Validation of Passive Adaptive Grasping

Abstract

This work presents the design and analysis of a tendon-driven underactuated robotic finger capable of adaptive grasping without individual joint control. The mechanism is actuated by a single input force while joint motion emerges from the interaction between stiffness distribution, inertia, and tendon transmission geometry. A dynamic model based on second-order rotational systems was developed to describe the behavior of each passive joint and predict the closing sequence. The finger was designed using CAD tools and fabricated through additive manufacturing using carbon fiber PLA and TPU materials. Experimental tests were performed to evaluate the closing behavior under constant actuation. Results show that the joints reach equilibrium at different settling times, producing a progressive grasping motion consistent with the dynamic model. The study demonstrates that adaptive grasping can be achieved through passive mechanical dynamics, reducing sensing and control requirements in robotic and prosthetic applications.