Feasibility Study of a Gripper with Thermally Controlled Stiffness of Compliant Jaws

Guangbo Hao,Mehdi Riza

doi:10.3390/app6110367

Abstract

This paper proposes a simple and compact compliant gripper, whose gripping stiffness can be thermally controlled to accommodate the actuation inaccuracy to avoid or reduce the risk of breaking objects. The principle of reducing jaw stiffness is that thermal change can cause an initial internal compressive force along each compliant beam. A prototype is fabricated with physical testing to verify the feasibility. It has been shown that when a voltage is applied, the gripping stiffness effectively reduces to accommodate more inaccuracy of actuation, which allows delicate or small-scale objects to be gripped.

Highlights

The ability to handle delicate/fragile or small-scale objects is very useful, but challenging, since such materials are either very sensitive to the gripping force or too small to control the tiny actuation
Creating a gripper mechanism that applies exactly the right amount of force to grip such an object without breaking it can be done in several ways: one active approach is to use force sensing technology to accurately control actuation displacement [1,2], and another method is to use preloading displacement to generate a constant force from the jaw mechanism over a relatively large displacement range to accommodate the actuation inaccuracy [3]
Electrothermal control-based shape memory alloy actuators were proposed for force tracking control of a flexible gripper in [7]

Summary

Introduction

The ability to handle delicate/fragile or small-scale objects is very useful, but challenging, since such materials are either very sensitive to the gripping force or too small to control the tiny actuation. The proposed method aims to manipulate (reduce) the gripping stiffness of the gripper’s jaw (rather than actively controlling the motion of jaws by thermal actuation), which allows the human user to roughly control the gripping force of the system based on the strength property of the objects. In such a way, there is no need to have precise control/sensing of the force applied on the object, but this is enough to avoid (or reduce the risk of) exceeding the breaking force.

Theoretical

Prototype Fabrication and Testing

Further Discussions