Wire driven Robotic hand with two-paired Crossed flexural hinge

Abstract

Robotic hands which is made up of rigid links and pin joints, have been studied a lot because they can be precisely controlled to implement complex movements, and because of their great mechanical strength, they can hold high payloads. However, the rigid body-based robotic hand is vulnerable to impacts because it cannot absorb the impact in an unspecific direction. To solve this problem, researches have also been actively con-ducted to create robotic hands with flexible materials. In the case of soft robots, the ability to absorb impact is excellent thanks to the compliance of the material itself, but the disadvantage is that they cannot grasp heavy objects because they are limited to make high grasping forces. In this paper, an anthropomorphic robotic hand with the advantages of rigid-based robot hand and soft robot hand simultaneously, was produced using a new structure called curved 2 paired CFH. Prior to the man-ufacture of the Curved 2 paired CFH, the stiffness analysis was carried out for the conventional CFH first. If a robotic hand is manufactured using 1 paired CFH of a conventionally shaped shape, the out of plane compliance causes the fingers to twist and prevent proper grasping motion. To solve this problem, we designed 2 paired CFH, which is made by two symmetrically shaped 1 paired CFH, and checked how much stiffness increase is present compared to 1 paired CFH, theorecically, and validated it by experiments. For practical application of the 2 paired CFH with enhanced stiffness to the robotic hand, the shape was modified to produce the curved 2 paired CFH. When we use the CFH as robotic hand’s joints, the load bearing capacity is drastically decreased due to the decrease of supporting stiffness according to the finger bending. In addition, the supporting stiffness is so large that if the robot is impacted, there is a risk of permanent deformation in the joint. However, using the newly proposed curved 2 paired CFH, the supporting stiffness increases as the fingers are bent, allowing heavy loads to be supported and external shocks are absorbable when the robot is not operating. In this paper, an underactuated wire mechanism, suitable for the robotic hand was used to maximize the advantages of a CFH. The manufactured robotic hand was able to grasp objects of various shapes using curved 2 paired CFH and underactuated wire mechanism, and was able to hold a cylindrical object of up to 4.04kg when it supplied power close to its rated voltage and current. In addition, we also validated ability to absorb impacts through an experiment.