Predicting the response of a tendon-driven prosthetic finger with hyperelastic joints

• Many prosthetic and robotic fingers are tendon-actuated. • These fingers use hyperelastic joints to provide spring action. • A model relating tendon tension to finger flexion is presented. • This model was experimentally verified. • Experiment to model error was <5.5 % under different loads. Properly designed prosthetics hands can enhance the quality of life for those suffering from limb loss. Recently, 3D-printed prosthetic hands are becoming common. In these prostheses, fingers flex through the tendons that are activated by motion of the wrist. To provide spring action, thermoplastic polyurethane (TPU) hyperelastic joints are used to connect digits to each other as well as to the wrist. While these designs are common, no model for the relationship between tendon tension and joint flexion is available. This work has developed a quasi-static virtual work-based model to predict the relationship between tendon forces and the flexion of the digits of a prosthetic finger with TPU joints. The equivalent spring stiffnesses of the joints were determined based on the results of flexural tests. The proposed model was verified experimentally to model errors <5.5 % under different loads. The proposed model can be used to design tendon-actuated fingers with TPU joints effectively.