Computational analyses of pinching dynamics of a finger exoskeleton composed of IPMC actuators

Abstract

There is an increased demand for hand exoskeletons that are light weight, low profile, and flexible, and that consume less power. In order to replace the rigid actuators such as motors and pneumatic cylinders, an ionic polymer metal composite (IPMC) actuator may be a good candidate. Because of the limited forces generated by IPMC actuators, prediction of the IPMC actuation force for the required fingertip force is important in designing and improving the performance of a finger exoskeleton. Anthropomorphic data on index fingers and the stiffness of a finger joint were measured, and a standard index finger model was established. Electromechanical characteristics of IPMC actuators were experimentally measured and mathematically modeled. These were incorporated into the dynamics of an index finger actuated by IPMC, and the dynamics of tip pinching were simulated. The arrangement of IPMC actuators at the initial position significantly affected the required actuator force to hold a given load. The maximum actuator force required to hold 0.98 N of fingertip load decreased by 50% for IPMC actuators that were arranged straight at the initial pinching position as compared to straight at the initial open position.