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Dynamic Modeling and Grasp Characteristics Analysis of an Underactuated Prosthetic Finger

A dynamic model was established using the virtual spring approach for the underactuated prosthetic finger containing the closed kinematic chains and holonomic constraints. The dynamic model was verified by grasp simulation. The virtual spring is used to approximate the constraint force and differential algebraic equations are converted into ordinary differential equations which are ideal for simulation and real-time control. The grasp characteristics of the underactuated finger were studied based on the model with the stiffness of the linear springs as variables. By properly increasing the stiffness of springs, the grasp stability of underactuated finger could be improved and ejection phenomenon would be reduced. However, self-adaptive capability would be reduced with large stiffness. A characteristic index was used for estimating grasp stability and self-adaptive capability. The simulation results show that setting the stiffness of the linear springs between 1N/mm and 2N/mm is the best choice for the underactuated finger.