Design and one-shot fabrication of a 2-DOF tendon-driven robotic finger via additive manufacturing using continuous CFRP

This paper proposes a design and one-shot fabrication method for a tendon-driven robotic finger utilizing continuous carbon fiber-reinforced polymer (CFRP) as the tendon material. Although additive manufacturing (AM), particularly material extrusion (MEX), enables the fabrication of compliant mechanisms, the integration of complex actuation elements usually requires manual assembly or multi-step processes. To address this challenge, we developed a fabrication process using a dual-nozzle MEX system that embeds continuous carbon fibers into a thermoplastic-compliant structure. Furthermore, this study introduces a novel two-degree-of-freedom design for this multi-material fabrication. Routing the distal tendon along the neutral axis of the proximal flexural beams enabled functionally decoupled two-degree-of-freedom actuations and complex planar deformations. Moreover, we developed a theoretical model based on beam theory to predict deformation and grasping force. Experimental results with the fabricated one-shot robotic fingers confirm successful monolithic fabrication of fingers with embedded tendons and validate the effectiveness of the theoretical model. Furthermore, a dual-tendon finger was integrated into a robotic hand to demonstrate the grasping of objects with various geometries and the execution of complex manipulation tasks, specifically “pull-in” and “push-out” operations. This study highlights the potential of continuous fiber materials in AM to serve not only as structural reinforcements but also as functional actuation elements in soft robotics.