Efficient Structure-Based Models for the McKibben Contraction Pneumatic Muscle Actuator: The Full Description of the Behaviour of the Contraction PMA

Alaa Al-Ibadi,Steve Davis,Samia Nefti-Meziani

doi:10.3390/act6040032

Abstract

To clarify the advantages of using soft robots in all aspects of life, the effective behaviour of the pneumatic muscle actuator (PMA) must be known. In this work, the performances of the PMA are explained and modelled with three formulas. The first formula describes the pulling force of the actuator based on the structure parameters; furthermore, the formula presented is the generalised contraction force for wholly-pneumatic muscle actuators. The second important model is the length formula, which is modified to our previous work to fit different actuator structures. Based on these two models, the stiffness of the actuator is formulated to illustrate its variability at different air pressure amounts. In addition, these formulas will make the selection of proper actuators for any robot arm structure easier using the knowledge gained from their performance. On the other hand, the desired behaviour of this type of actuator will be predefined and controlled.

Highlights

An interaction between a robot arm and humans represents an important issue in industrial and medical applications, which has to be safe and compliant during all probable situations, such as control failure, human error, or any unexpected error in the robot arm itself
10 of ratio increases as a pressure increase, and the highest rubber stiffness sr leads to the lowest stretchable where: the parameters a, b, c, d, and e are constants for each L0 and they represent the coefficients of ability, : To present an efficient length formula that isL able α to track the actual length of the pneumatic muscle actuator (PMA), the initial
Since the McKibben artificial muscle is applicable for structure differences, the most effective model has to be based on the structure coefficients, such as initial length, initial inner diameter, the thickness of both the inner rubber tube and the braided sleeve and the stiffness of the rubber tube or, in other words, its ability to extend

Summary

Introduction

An interaction between a robot arm and humans represents an important issue in industrial and medical applications, which has to be safe and compliant during all probable situations, such as control failure, human error, or any unexpected error in the robot arm itself. The pneumatic muscle actuator (PMA), which is the base of such types of robots, has numerous positives over ordinary pneumatic cylinders, such as the high force in comparison to its weight, low workspace requirement, high flexibility to construct [6,7], adaptable installation possibilities, minimum consumption of compressed air, accessibility of different measurements, low cost, and being safe for human use [6,8]. For these exceptional features, the PMA has been considered as an appropriate actuator to use behind electrical and hydraulic actuators. The variable stiffness of the inner tube has been clarified it is it is influencing to the stiffness the PMA at variety pressurised conditions

Structure ofof the Pneumatic

Presented Force Formula

Equation

Structure-Based

The Stiffness of the Contraction PMA

Conclusions