Geometric Analysis of a Multi-fingered Robotic Hand Involving an Iris Mechanism

Abstract

In this study, we propose a multi-finger robotic hand with an iris mechanism that positions the blades of the hand, with fingers extending perpendicular to the blades attached to the blade tips, using a swing mechanism external to the iris mechanism. A single actuator drives the hand, which can concentrically grasp objects at multiple points while maintaining a regular polygonal shape around the entire circumference. The proposed structure can use the same mechanism to realize a hand with an arbitrary number of blades. Furthermore, the gears can be arranged in a planar configuration within the iris mechanism, thereby enabling adjustments to the grasping torque and speed by changing the gear ratio. This study examines the appropriate number of fingers for this iris multi-finger robotic hand, along with the cross-sectional shape of those fingers, according to the object to be grasped. We perform a geometric analysis of the relation between the rotational angle of the blades and the sizes of graspable objects, considering both the circumferential multi-point grasping of cylindrical objects and the multi-point pinching of rectangular objects. By comparing the analysis results of these different grasping methods, we consider how differences in the number of fingers and their cross-sectional shapes affect the size of graspable objects. The findings provide specific guidelines on the selection of an appropriate iris multi-finger robotic hand configuration for specific target objects.