Motion Control Of Pneumatic Muscle Actuator : Experimental Setup And Modeling.

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“I hereby declare that I have read through this report entitle “Motion Control of Pneumatic Muscle Actuator : Experimental Setup and Modeling” and found that it has comply the partial fulfillment for awarding the degree of Bachelor of Mechatronic Engineering ”

Signature : ... Supervisor’s Name: Dr. Chong Shin Horng

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MOTION CONTROL OF PNEUMATIC MUSCLE ACTUATOR: EXPERIMENTAL SETUP AND MODELING

VASANTHAN A/L SAKTHI VELU

A report submitted in partial fulfillment of the requirements for the degree of Mechatronic Engineering

Faculty of Electrical Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

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I declare that this report entitle “Motion Control of Pneumatic Muscle Actuator: Experimental Setup and Modeling” is the result of my own research except as cited in the references. The report has not been accepted for any degree and is not concurrently submitted in candidature of any other degree.

Signature: ... Name : Vasanthan A/L Sakthi velu

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ACKNOWLEDGEMENT

First and foremost, I would like to thank god for His blessing. Without gods’ bless I will not able to complete this research as required. Besides, the help and support from certain groups and individual has encouraged me to finish up this project.

In conjunction, my deepest appreciation and thank you to Dr. Chong Shin Horng, my supervisor who had given me endless help, guidance, and support me to make up with the standard as required as a Mechatronic Engineer student during the final year project. Her words and kindness have kept me in moving forward and made this project a valuable experience. Even though I have to gone though many difficulties during the process to complete the project, I have successfully finished my project. I also would like to say special thank to my parent because of their support in term of financial, motivational and advice.

Last but not least, thank to all my friends who gave me support to achieve the objective of this project and sparing their time to share their knowledge and information related to my project. The idea and opinion shared by them are very useful and effective to develop and finish this project successfully.

All the knowledge gained at Universiti Teknikal Malaysia Melaka presented here in my project report. Finally, I am indebted to all those people who have directly or indirectly helped to make my final year report stint an incredible journey of knowledge and self improvement.

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ABSTRACT

In recent times, the Pneumatic Muscle Actuator (PMA) has achieved popularity in the field of research, robotics and industrial application due to its advantages such as light weight actuator, dynamic, powerful and resistant to dust and clean. The muscle actuator is capable of mimicking behaviour of human muscle like actuator where it contracts and generates force in non-linear manner when it is activated (pressurized). Due to its nonlinear dynamics, the muscle actuator is difficult to be controlled because changes in the system occur due to the presents of compressed air (pressure). In order to present its dynamic and for effective motion control purpose, an effective experimental setup has to be developed in this project. The prime interest of this project is to develop a pneumatic muscle actuator experimental setup and model its dynamic system. The study in this project has been continued by validating the effectiveness of the proposed model in positioning control via experimental and simulation. The result achieved for the muscle actuator static load study and open loop experiment has been presented in this project with graphical aid. Finally, a good conclusion of the pneumatic muscle actuator experimental setup and dynamic system modeling is explained and recommendation for further research has been proposed.

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ABSTRAK

Sejak kebelakangan ini, penggerak pneumatik seakan otot manusia telah mencapai populariti dalam bidang penyelidikan, robotik dan bidang perindustrian oleh kerana kelebihannya seperti penggerak yang ringan, dinamik, kuat dan tahan kepada habuk dan operasinya yang sangat bersih. Penggerak otot ini mampu meniru tingkah-laku seakan otot manusia kerana penggerak ini mampu mengerak dan menjana tenaga dalam keadaan tidak “linear” apabila ia diaktifkan (tekanan angin). Oleh kerana pengerak ini mempunyai dinamik tak linear, penggerak otot adalah sukar untuk dikawal kerana perubahan sentiasa berlaku dalam sistem kerana ia membentangkan udara termampat (tekanan). Untuk membentangkan dinamik dan bagi maksud kawalan pergerakan yang berkesan, satu alat uji kaji akan yang berkesan akan dihasilkan dalam projek ini. Fokus utama projek ini adalah untuk memhasilkan meghasilkan satu alat uji kaji yang merangkumi pneumatik otot penggerak sebagai bahagian utama dan modelkan dinamik sistem tersebut. Kajian dalam projek ini telah diteruskan dengan mengesahkan keberkesanan model matematik yang dicadangkan dalam kawalan otot pengerak pneumatic melalui kaedah eksperimen dan simulasi. Keputusan dicapai untuk sistem otot penggerak dalam kajian beban statik yang dibuat dan percubaan gelung terbuka (Open-Loop) telah dibentangkan dengan jelas dalam projek dengan bantuan grafik pada bahagian keputusan projek. Akhirnya, satu kesimpulan yang baik daripada otot penggerak pneumatik kaedah uji kaji dan model matematik yang dibangunkan dijelaskan dan cadangan untuk penyelidikan selanjutnya pada masa akan datang dibentangkan dalam projek ini.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES ix

LIST OF FIGURES x

LIST OF SYMBOLS xi

1 INTRODUCTION 1

1.1 Problem Statement 2

1.2 Objectives of project 2

1.3 Scope of Project 3 2 LITERATURE REVIEW 4

2.1 Pneumatic Muscle Background 4 2.1.1 Description of pneumatic muscle 4 2.2 Types of pneumatic muscle 6

2.3 Pneumatic muscle Operation Methods 7 2.4 History of Pneumatic Muscle 8 2.5 Applications for Pneumatic Muscle Actuator 9 2.6 Modeling of Pneumatic Muscle Actuator 10

2.6.1 Phenomenological models 11

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CHAPTER TITLE PAGE

3 EXPERIMENTAL HARDWARE AND SETUP 15

3.1 Experimental Setup 15

3.2 Three-Element Phenomenological Pneumatic Muscle Actuator modeling 21

4 DYNAMIC MODEL AND NONLINEAR ANALYSIS OF PMA 25

4.1 Characterization of Phenomenological Modeling for Commericial Festo Fluidic Muscle Actuator MAS-20-250N 25

4.1.1 Experimental Method for Static Load Study 25

4.1.2 Open Loop Test 28

4.2 Static Load Study result 28

4.3 Open Loop Test result 29

4.4 Pneumatic Muscle Actuator percentage contraction result 31

4.5 Festo Fluidic Muscle Isobaric Characterization simulation result 32

4.6 Simulation Result by using three-element phenomenological modeling 33

4.7 Experimental equipments calibration result 35

4.7.1 Proportional pressure regulator calibration result 35

4.7.2 Pressure Transducer calibration result 36

4.7.3 Infrared Sensor calibration result 37

4.7.4 Load cell calibration result 38

4.8 Analysis 39

4.8.1 Open Loop test analysis 39

4.8.2 Repeatability 42

4.8.2.1 Open Loop test for PMA displacement Analysis 42

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CHAPTER TITLE PAGE

5 MODEL ACCURACY AND PMA PERFORMANCE

CHARACTERIZATION 49

5.1 Mathematical Model Accuracy Test 5.2 PMA Performance Characterization 51

5.2.1 Characterization of three element phenomenological modeling for Festo fluidic Muscle MAS-20-250N 51

5.2.2 Nonlinear characteristics 52

5.2.3 Need of a mathematical modeling in pneumatic muscle actuator system 52

5.2.4 Need of a controller for pneumatic muscle actuator system 52

6 CONCLUSION AND FUTURE WORKS 54

6.1 Conclusion 54

6.2 Future Works 55

6.2.1 Experimental Setup 55

6.2.2 Further advancement 55

6.2.3 PMA system Modeling (PMA contraction study, PMA relaxation study and PMA static load study) 56

6.2.4 Improvement in PMA Control System 56

REFERENCES 57

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LIST OF TABLES

NO TITLE PAGE

3.1 Summary table of calibration equations 16

4.1 Open Loop test result analysis 39

4.2 Repeatability test for open loop test of the pneumatic muscle

actuator 42

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LIST OF FIGURES

NO TITLE PAGE

2.1 Illustration of pneumatic muscle operation 5

2.2 Commercially used PMA Festo fluidic muscle 5 2.3 McKibben Muscle/Braided Muscle, (b) Pleated Muscle, (c) Yarlott Muscle, (d) Robotic Muscle Actuator (ROMAC) Muscle and IPaynter Hyperboloid Muscle 6

2.4 PMA operation at constant load 7

2.5 PMA operation at constant pressure 8

3.1 Schematic view of the experimental setup 16

3.2 Schematic view of the experimental setup 17

3.3 Experimental setup photograph 17

3.4 Experimental setup photograph with load cell 18

3.5 Three element phenomenological model free body diagram 22

4.1 Static Load study experimental setup photograph 26

4.2 Open Loop test setup photograph 27

4.3 Show the mean contractile force coefficient (Fce) as a Function of pressure denoted in blue and the red line denotes the linear line plot for contractile force and pressure dependent equation 28

4.4 Pressure versus tau value result from open loop test 29

4.5 Pressure versus Contraction result from open loop test 30

4.6 Pressure versus percentage contraction result 31

4.7 Screen Shot of Festo MuscleSim Version 2.0.1.5 software 32

4.8 Isobaric characteristic for Festo fluidic muscle type MAS-20-250N 33

4.9 Simulation result from three- element phenomenological model 34

4.10 PPR calibration graph 35

4.11 Pressure Transducer Calibration graph 36

4.12 IR sensor calibration graph 37

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NO TITLE PAGE

5.1 Pressure versus contraction (Measured data and simulation by using 3 element phenomenological model via experimental

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LIST OF SYMBOLS

PMA – Pneumatic muscle actuator

P _ Pressure

v _ Volume

V _ Voltage

PID _ Proportional, Integral, and Derivative

Fce – contractile force coefficient of phenomenological modeling P – Pressure

K – Spring Coefficient B – Damping Coefficient h – Percentage Contraction lo -- Original Length

l _ contracted muscle length Fr -- Frictional Force

F _ Force

L _ Load

kPa _ kilo pascal

kg _ Kilogram

TF _ Transfer Function mm _ millimeter

N _ Newton

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LIST OF APPENDICES

APPENDIX TITLE PAGE

A Experimental Setup Photograph 60

B Experimental Setup Equipments Calibration Result 65 C Mathematical Derivation of Phenomenological Model Governing

Equation 67

D Matlab/Simulink block diagram 69

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CHAPTER 1

INTRODUCTION

1.1 Introduction

Nowadays, pneumatic muscle actuator (PMA) has become one of the most widely-used fluid-power actuators which yield remarkable muscle-like properties such as high force to weight ratio, soft and flexible structure, minimal compressed-air consumption and low cost. Pneumatic muscle actuator (PMA) is made mainly of a flexible and inflatable membrane. This actuator is used to convert pneumatic power to pulling force. Due to the advantages, the use of this muscle like actuator has increased in the factory floor automation, robotics and many more. Lately, PMA is been used as a main motion power source. One of the major attractions about pneumatics is the low weight and inherent compliant behavior. Compliance is due to the compressibility of air and, and it can be overcome by controlling the inlet pressure into PMA. Pneumatic system is extensively used in the industrial environment mainly for its advantages. The nonlinear characteristics of PMA are caused by the existence of pressurized air, elastic-viscous material and the geometric features. Due to this, the task to obtain an accurate mathematical modeling is a prime challenge. Better positioning performance depends on how precise or accurate the parameter of the modeling. However, the nonlinear characteristics of the actuator made it difficult in controlling. This project will focus on developing a pneumatic muscle actuator motion control system experimental setup and model its dynamic characteristic for a commercially used muscle actuator.

2 1.2 Problem Statement

Pneumatic system is extensively used in the industrial environment mainly for simple repetitive tasks due to their compactness, power to weight ration and simplicity. The use of pneumatic muscle technology has spread into many different fields including robotics, human power assisted robot (exoskeleton) and mobility assistance, therapy and rehabilitation. Besides that, to define an accurate mathematical modeling to represent the PMA system dynamics is a difficult task as well. The main scopes of this project will mainly focus in the experimental setup and mathematical modeling of the dynamic system. The experimental and simulation results will be used in the performance validation.

Motivation: - The use of pneumatic muscle technology has spread into many different fields including robotics, human power and mobility assistance, therapy and rehabilitation. The design and development of this project will help in the research of applicability/effectiveness of pneumatic muscle actuator positioning system in robotics applications; especially for a set-up with very non-linear characteristics and very difficult to be controlled.

1.3 Objective of Project

1. To develop the pneumatic muscle actuator system and model its dynamic system. 2. To validate the effectiveness of the proposed modeling in positioning control via

3 1.4 Scope of Project

In order to achieve the objective of the project, several scopes have been outlined:-

 Necessary, research on the field of pneumatic muscle actuator will be done at first.  An accurate mathematical modeling to present the dynamic behavior of the pneumatic

muscle actuator will proposed.

 An experimental setup with effective position control setup will be designed and developed.

 The pressure range for the PMA experimentation were set to 0-6bar(max) and maximum load tested were 65kg.

 The resolution of infrared sensor was 0.01 Volts per step from ADC.

 The effectiveness of the proposed mathematical modeling will be validated via experiment and simulation result.

 A brief conclusion of the effectiveness of the system and the adaptability of PMA into industrial application will be presented.

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CHAPTER 2

LITERATURE REVIEW

2.1 Pneumatic Muscle Background 2.1.1 Description of pneumatic muscle

A pneumatic muscle actuator (PMA) is a mechanical apparatus that copies the conduct of skeletal muscle where it contracts and creates drive in a nonlinear way when activated [1]. PMAs could be found in common elastic tube, wrapped inside man-made mesh, for example Kevlar, at predetermined angle. Defensive elastic covering encompasses the fibber wrapping and fitting metal fittings are connected at every close [2]. The filament wrapping gives uphold and upgrades incitation. PMA is an actuator which changes over pneumatic (or water driven) vigor into mechanical structure by exchanging the force connected on the internal surface of its bladder into shortening tension. When the PMA is pressurized, the hose expands in its peripheral direction, thus generating a tensile force and a contraction motion of muscle longitudinal direction. The level of contraction and constrain preparation is reliant on the pulling constrain against the PMA (load). Figure 2.1 represents the operation of a PMA and Figure 2.2 shows the Festo fluidic muscle.

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Figure 2.1: Illustration of pneumatic muscle operation [2]

Figure 2.2: Commercially used PMA Festo fluidic muscle [11].

This type of actuator has several unique characteristics, some of its characteristics which have made it as an ideal actuator for applications involving human interaction. Pneumatic muscles are capable of producing a high force output. They have higher power/weight and power/volume ratios about 1 W/g and 1W/cm3 _{than electric motors or}

hydraulic actuators [3]. They have a higher force output than a pneumatic cylinder of equal volume [4]. Pneumatic muscles are cost effective, clean, highly dynamic movements, no slip effect; intermediate positions can be set easily by regulating the pressure, compact, and can be used in harsh environments because they do not have moving parts such as pistons or guiding rods [5]. There are also a safe alternative to other actuators. The main disadvantage of this actuator is that its motion is difficult to be controlled due to its nonlinear characteristics. This is due to the need of controlling the both PMA displacement and PMA force by only varying the inlet pressure to the muscle actuator.

6 2.2 Types of pneumatic muscle

There are many types of artificial muscle actuator in the field of research. Figure 2.3 shows the picture of the famous muscle actuators and the names are listed below:-

i. McKibben Muscle ii. Braided Muscles

iii. Sleeved Bladder Muscle iv. Pleated PAM

v. Netted Muscles vi. Yarlott Muscle vii. ROMAC

viii. Paynter Hyperboloid Muscle

Figure 2.3: (a) McKibben Muscle/Braided Muscle, (b) Pleated Muscle, (c) Yarlott Muscle, (d) Robotic Muscle Actuator (ROMAC) Muscle and Paynter Hyperboloid Muscle [2].

7 2.3 Pneumatic Muscle Operation Methods

The basic principles of the PMA‟s operation can be categorized in two cases: i) Under a constant load and with varying gauge pressure. ii) Under a constant gauge pressure and a varying load.

To illustrate this operation a PMA operations a standard and dynamic configuration has to be prepared. Figure 2.4 one illustrates the PMA configuration in real world, one end of the PMA is fixed and the other end is loaded with constant mass. During this type of operation the PMA:

i) The PMA will shorten its length by increasing its enclosed volume, and ii) It will contract against a constant load if the pneumatic pressure is increased.

Figure 2.4: PMA operation at constant load [2].

The second type of PMA‟s operation, which is the case of operation under constant gauge pressure, is illustrated in Figure 2.5. During this type of operations the PMA:

i) At constant pressure the PMA will decrease its length when the load is removed, and

ii) Its contraction has an upper limit/maximum contraction at which it develops no force and its internal bladder volume is at maximum level.

8

Figure 2.5: PMA operation at constant pressure [2].

For these two principal operations, for given pressure and load, the PMA has an equilibrium length. This characteristic makes pneumatic muscle actuator unique from pneumatic cylinder where the developed actuation force depends on only the pressure and the piston surface.

2.4 History of Pneumatic Muscle

In the earliest Pneumatic Muscle Actuator also known as the McKibben Pneumatic Artificial Muscle (PAM), fluidic muscle or a Biomimetic Actuator, was first invented in 1950s by the physician, Joseph L. McKibben and was used as an orthotic appliance for polio patients [6]. In the early 1960s, Schulte published details of the braided pneumatic muscle which he called McKibben artificial muscle along with mathematical analysis included in Gaylord‟s patent. Due to challenges controlling the pneumatic muscle and the large gas tank required for its activation, use of pneumatic muscles remained limited [7]. In 1980s, pneumatic muscles resurfaced in the robotics industry. Brigestone developed a commercial version of the pneumatic muscle called Rubbertuator and used it in industrial robotic arms [8]. Work on the Rubbertuator ended by the 1990s, but others have continued working on pneumatic muscle due to advantageous features including high force generation, high power to weight and power to volume ratios, and soft-actuation (allowing safe pneumatic muscle-human interaction). In 2002, Festo Corporation patented a more robust pneumatic muscle design, called the fluidic

9 muscle [9]. At the present time, companies such as Festo and Shadow are producing commercially available pneumatic muscles in many sizes and configurations [11].

2.5 Applications for Pneumatic Muscle Actuator

The use of pneumatic muscle technology has spread into many different fields due to their advantages including robotics, human power and mobility assistance, and therapy and rehabilitation. Pneumatic muscle also utilized in several industrial applications. Example of pneumatic muscle use in selected applications is given.

The use of pneumatic muscle in robotics has increased lately due to the advantages such as light weight. Whole body humanoids, robotic arms, bipedal robots, and other robots modeled after the lower limb have been developed or are currently under development. A climbing robot has been developed as well as robots inspired by animals and insects. Robotic arms have been created by many groups of researchers around the world. The robotic arm is considered to be something more complicated than a one link or one segment manipulator. Several devices have been designed to provide power and mobility assistance for humans (exoskeleton). Many researchers and undergraduates have incorporated pneumatic muscle into these devices because of the inherent safety and high to weight ratio provided by the pneumatic muscle. Several upper body assistance devices have been developed, both exoskeleton devices worn by the operator and manipulators that only interact with human operator.

Pneumatic muscles have been used for several industrial applications including nuclear waste retrieval, construction machinery, a video-probe, and nozzle positioning device. Underwater applications have also studied, in some underwater applications; water can be used to activate the pneumatic muscle instead of air (medium of actuation).

10 2.6 Modeling of Pneumatic Muscle Actuator

The aim of the modeling is to relate the pressure and length of the pneumatic actuator to the force it exerts along its axis accurately. A highly accurate model that can be applied to different muscles has yet been developed. In the process of deriving the dynamic behavior of PMAs in the mathematical equation, variable such as pulling force, actuator‟s length, air pressure, diameter and material properties, plays an important role and the mathematical model relates all this in an equation. In order to control it, the dynamics behavior should be understand first. Many researchers have worked on creating geometric model where pneumatic muscle properties are in some way based on the construction geometry of the actuator. Biomimetic models describing pneumatic muscle behavior have been developed using models of skeletal muscle. Phenomenological model have used visco-elastic parameters to describe the behavior of pneumatic muscle. Other pneumatic muscle models have used fluid flow theory, neural networks and finite element theory. The types of modeling which have been widely used are:-

1) Geometrical Models. 2) Phenomenological Models. 3) Mathematical Models. 4) Empirical Models.

Based on the reading, phenomenological model is selected and only will be discussed in this chapter.

Figure 2.1: Illustration of pneumatic muscle operation [2]

Figure 2.2: Commercially used PMA Festo fluidic muscle [11].

This type of actuator has several unique characteristics, some of its characteristics which have made it as an ideal actuator for applications involving human interaction. Pneumatic muscles are capable of producing a high force output. They have higher power/weight and power/volume ratios about 1 W/g and 1W/cm3 _{than electric motors or} hydraulic actuators [3]. They have a higher force output than a pneumatic cylinder of equal volume [4]. Pneumatic muscles are cost effective, clean, highly dynamic movements, no slip effect; intermediate positions can be set easily by regulating the pressure, compact, and can be used in harsh environments because they do not have moving parts such as pistons or guiding rods [5]. There are also a safe alternative to other actuators. The main disadvantage of this actuator is that its motion is difficult to be controlled due to its nonlinear characteristics. This is due to the need of controlling the both PMA displacement and PMA force by only varying the inlet pressure to the muscle actuator.

2.2 Types of pneumatic muscle

There are many types of artificial muscle actuator in the field of research. Figure 2.3 shows the picture of the famous muscle actuators and the names are listed below:-

i. McKibben Muscle ii. Braided Muscles

iii. Sleeved Bladder Muscle iv. Pleated PAM

v. Netted Muscles vi. Yarlott Muscle vii. ROMAC

viii. Paynter Hyperboloid Muscle

Figure 2.3: (a) McKibben Muscle/Braided Muscle, (b) Pleated Muscle, (c) Yarlott Muscle, (d) Robotic Muscle Actuator (ROMAC) Muscle and Paynter Hyperboloid Muscle [2].

2.3 Pneumatic Muscle Operation Methods

The basic principles of the PMA‟s operation can be categorized in two cases:

i) Under a constant load and with varying gauge pressure. ii) Under a constant gauge pressure and a varying load.

To illustrate this operation a PMA operations a standard and dynamic configuration has to be prepared. Figure 2.4 one illustrates the PMA configuration in real world, one end of the PMA is fixed and the other end is loaded with constant mass. During this type of operation the PMA:

i) The PMA will shorten its length by increasing its enclosed volume, and ii) It will contract against a constant load if the pneumatic pressure is increased.

Figure 2.4: PMA operation at constant load [2].

The second type of PMA‟s operation, which is the case of operation under constant gauge pressure, is illustrated in Figure 2.5. During this type of operations the PMA:

i) At constant pressure the PMA will decrease its length when the load is removed, and

ii) Its contraction has an upper limit/maximum contraction at which it develops no force and its internal bladder volume is at maximum level.

Figure 2.5: PMA operation at constant pressure [2].

For these two principal operations, for given pressure and load, the PMA has an equilibrium length. This characteristic makes pneumatic muscle actuator unique from pneumatic cylinder where the developed actuation force depends on only the pressure and the piston surface.

2.4 History of Pneumatic Muscle

In the earliest Pneumatic Muscle Actuator also known as the McKibben Pneumatic Artificial Muscle (PAM), fluidic muscle or a Biomimetic Actuator, was first invented in 1950s by the physician, Joseph L. McKibben and was used as an orthotic appliance for polio patients [6]. In the early 1960s, Schulte published details of the braided pneumatic muscle which he called McKibben artificial muscle along with mathematical analysis included in Gaylord‟s patent. Due to challenges controlling the pneumatic muscle and the large gas tank required for its activation, use of pneumatic muscles remained limited [7]. In 1980s, pneumatic muscles resurfaced in the robotics industry. Brigestone developed a commercial version of the pneumatic muscle called Rubbertuator and used it in industrial robotic arms [8]. Work on the Rubbertuator ended by the 1990s, but others have continued working on pneumatic muscle due to advantageous features including high force generation, high power to weight and power to volume ratios, and soft-actuation (allowing safe pneumatic muscle-human interaction). In 2002, Festo Corporation patented a more robust pneumatic muscle design, called the fluidic

muscle [9]. At the present time, companies such as Festo and Shadow are producing commercially available pneumatic muscles in many sizes and configurations [11].

2.5 Applications for Pneumatic Muscle Actuator

The use of pneumatic muscle technology has spread into many different fields due to their advantages including robotics, human power and mobility assistance, and therapy and rehabilitation. Pneumatic muscle also utilized in several industrial applications. Example of pneumatic muscle use in selected applications is given.

The use of pneumatic muscle in robotics has increased lately due to the advantages such as light weight. Whole body humanoids, robotic arms, bipedal robots, and other robots modeled after the lower limb have been developed or are currently under development. A climbing robot has been developed as well as robots inspired by animals and insects. Robotic arms have been created by many groups of researchers around the world. The robotic arm is considered to be something more complicated than a one link or one segment manipulator. Several devices have been designed to provide power and mobility assistance for humans (exoskeleton). Many researchers and undergraduates have incorporated pneumatic muscle into these devices because of the inherent safety and high to weight ratio provided by the pneumatic muscle. Several upper body assistance devices have been developed, both exoskeleton devices worn by the operator and manipulators that only interact with human operator.

Pneumatic muscles have been used for several industrial applications including nuclear waste retrieval, construction machinery, a video-probe, and nozzle positioning device. Underwater applications have also studied, in some underwater applications; water can be used to activate the pneumatic muscle instead of air (medium of actuation).

2.6 Modeling of Pneumatic Muscle Actuator

The aim of the modeling is to relate the pressure and length of the pneumatic actuator to the force it exerts along its axis accurately. A highly accurate model that can be applied to different muscles has yet been developed. In the process of deriving the dynamic behavior of PMAs in the mathematical equation, variable such as pulling force, actuator‟s length, air pressure, diameter and material properties, plays an important role and the mathematical model relates all this in an equation. In order to control it, the dynamics behavior should be understand first. Many researchers have worked on creating geometric model where pneumatic muscle properties are in some way based on the construction geometry of the actuator. Biomimetic models describing pneumatic muscle behavior have been developed using models of skeletal muscle. Phenomenological model have used visco-elastic parameters to describe the behavior of pneumatic muscle. Other pneumatic muscle models have used fluid flow theory, neural networks and finite element theory. The types of modeling which have been widely used are:-

1) Geometrical Models. 2) Phenomenological Models. 3) Mathematical Models. 4) Empirical Models.

Based on the reading, phenomenological model is selected and only will be discussed in this chapter.