Design and Modeling of a Bioinspired Flexible Finger Exoskeleton for Strength Augmentation

Hand strength augmentation is significant for rehabilitation exercise and activities of daily living (ADL) assistance. However, designing a portable exoskeleton robot with sufficient fingertip force for ADL remains challenging. A bioinspired wearable flexible finger exoskeleton for hand strength augmentation is proposed in this article based on a two-layered nonparallel spring structure. The stiffness of the flexible nonparallel fingers is analyzed, and the effects of the slope magnitude on the stiffness of the finger are obtained. Considering the friction and external fingertip force, a variable-curvature kinematic model of the flexible finger is proposed by recursively calculating the force and moment of each finger module. Experiments are performed to validate the stiffness performance and the variable-curvature kinematic model of the nonparallel finger. Based on the experimental results, compared with the parallel finger, the stiffness and load-to-mass ratio of the nonparallel finger can be improved by 63.8% and 147%, respectively. Finally, the flexible finger exoskeleton is demonstrated to have the potential for wearable ADL assistance.