Design of an Underactuated Gripper with a Floating Differential Actuator

Abstract

Underactuated grippers are developed to grasp objects of varying shape and sizes without the need to rely on sensors and feedback systems. This main aspect makes underactuated grippers efficient in their ability to automatically distribute the actuation force to multiple outputs. Besides actuating multiple phalanges by the actuation principle, it is also possible to drive multiple fingers. An interesting approach is to give the actuator a spatial degree of freedom and suspend it such that it can provide its power both to the shaft as to the unconstrained degree of freedom. There already exist designs that apply this working principle to distribute a force to two and four fingers, without the need for additional differential mechanisms. In both cases the fingers are divided into two pairs, where one pair is connected to the rotor and the other to the stator. When the actuator is activated a force is transferred to the fingers connected to the rotor. The reaction force, caused by the actuation force, is acting on the stator and this force is transferred to the fingers connected to the stator. The aim of this report is to determine how the floating actuator principle can best be implemented such that the number of outputs is as high as possible. The theoretical maximum number of outputs a floating actuator differential can achieve is seven, namely six spatial degrees of freedom and the actuated shaft. In this report it was found that it highly unlikely that this system can provide seven outputs for a sufficient workspace, due to kinematic restraints introduced by dependencies between the orientation and the position of the actuator. For the concept with a maximum of six outputs the floating actuator principle can provide ample torque for a sufficient range of motion for the fingers. The prototype, as developed in this report, shows that the floating actuator principle works for a system with six outputs.