/ D O M 
DEVELOPMENT OF PNEUMATIC ROBOT ARM 
CONTROLLER FOR INDUSTRIAL 
APPLICATION 
A thesis submitted to the 
Department of Electrical Engineering, University of Moratuwa 
in partial fulfillment of the requirements for the 
Degree of Master of Science 
by 
PATHIRANAGE GUMINDA SANJEEWA 
PRIYADARSHANA 
Supervised by: Dr. Lanka Udawatta 
C)\\b3 
Department of Electrical Engineering 
University of Moratuwa, Sri Lanka 
April 2008 
University of Moratuwa 
91163 
91163 
DECLARATION 
The work submitted in this thesis is the result of my own investigation, except where 
otherwise stated. 
It has not already been accepted for any other degree, and is also not being 
concurrently submitted for any other degree. 
£ 
P.G. S. Priyadarshana 
(Candidate) 
Date: O ^ j o ^ - |;2£>m 
I endorse the declaration by the candidate. 
Dr. Lanka Udawatta 
(Supervisor) 
CONTENTS 
Declaration 
Abstract 
Acknowledgement 
List of Figures 
List of Tables 
1. Introduction 1 
1.1 Robotics actuators 1 
1.2 Pneumatic artificial muscle 4 
1.2.1 Braided muscle 5 
1.2.2 Netted muscle 5 
1.2.3 Embedded muscle 5 
1.3 Simple application of pneumatic artificial muscle 6 
1.3.1 Lifting and lowering masses 6 
1.3.2 Antagonistic setups 7 
1.3.3 Bicep and tricep configurations 7 
1.4 Industrial applications of pneumatic artificial muscle 9 
1.5 Research objective 12 
1.6 Dynamic behavior of pneumatic artificial muscle 13 
2. Hardware development 14 
2.1 Pneumatic muscle 14 
2.2 Pressure regulator valve 15 
2.3 Hall effect sensor 16 
2.4 Current control circuit 16 
2.5 Complete hardware assembly 17 
3. Theoretical development 18 
3.1 Dynamic analysis of pneumatic artificial muscle 18 
3.2 Mathematical model 25 
3.2.1 Mathematical model for pneumatic muscle 25 
3.2.2 Mathematical model for pneumatic robot arm 26 
3.3 State space model 27 
3.3.1 State space model for pneumatic muscle 27 
3.3.2 State space model for pneumatic robot arm 28 
ii 
4. Proposed solution 30 
4.1 Develop state space model 30 
4.2 Inverse based control approach 31 
4.3 Applications of inverse based control approach 32 
5. Prototype realization 33 
5.1 Practical results 33 
5.2 Comparison of theoretical and practical situations 42 
5.3 Summary 43 
6. Results 44 
6.1 Tracking a triangular waveform 44 
6.2 Tracking a sinusoidal waveform 47 
7. Conclusion and Future Directions 49 
7.1 Conclusion 49 
7.2 Suggestions for Future directions 50 
References 51 
Appendix A: (Data logging Program) 55 
Appendix B: (Hall effect sensor data sheet) 59 
Appendix C: (MCP4250 Digital potentiometer) 63 
Appendix D: (PIC 16F877A Microcontroller) 64 
Appendix E: (Micro C Program code) 65 
Appendix F: (MATLAB Program) 70 
iii 
Abstract 
This research study focuses on developing a pneumatic robot arm for industrial 
applications, where the discussion here is narrowed down to the application of 
Pneumatic Artificial Muscles (PAM) on bicep configuration. When compared with 
other robotic actuators Pneumatic muscles have several advantages such as lower 
power to weight ratios, high strength, lightweight and easiness of employment. Hence 
pneumatic artificial muscles have become more attractive actuators in industrial 
robotics applications. A pneumatic muscle analysis was carried out with the help of 
practical results which were obtained with a prototype experiment. It was realized that 
the muscle behaves in a non-linear manner which is the main disadvantage. The 
system equation is linearised in order to derive the state space model. With this the 
system would be linearised only within a small range of inputs, where it is impossible 
to use it as a general model with whole range of inputs. 
A simulation study has been carried out for the system using Matlab/Simulink 
environment for various categories of inputs and it is experienced that the system 
responded to linear input signal, as per anticipated output of the theoretical analysis. 
Even though the above paradigm is discussed for single pneumatic sub-systems, it is 
emphasized, that the same approach can effectively be extended without any major 
conceptual breakthrough to any number of muscles. Depending on the application the 
pneumatic muscle may require different contraction profiles, where the controlling 
task of the muscle contraction would be vital. 
To obtain the desired tracking of the actual performance, Inversion Based Control 
(IBC) concept has been employed. Simulated results showed the proposed 
methodology could be effectively applied. Further, investigations need to be carried 
out to model the complete system with other perturbations and apply the inversion 
based control concept for precise control of the tip of the arm. 
iv 
Acknowledgement 
I specially thank my supervisor, Dr. Lanka Udawatta for his unwavering guidance, 
support and advice for carrying out this research work successfully. I am also very 
appreciative for his extensive help in fulfillment of some publications related to this 
research work, in some prestigious international forums. 
I am indebted to my parents for constant support and encouragement for successfully 
carrying out this work. My gratitude is also due to Prof. H.Y.R. Perera, 
Head/Electrical Engineering, for the support given with my studies. My sincere 
thanks to the chairman and the committee members of the SRC grant committee, 
University of Moratuwa, for the grant provided, which existed as an extensive support 
in my research studies. Dr. N Munasinghe and his staff, at the Engineering Post 
Graduate Unit, are also thanked for all assistance extended. 
I would like to take this opportunity to extend my thanks to Dr. Thrishantha 
Nanayakkara, Dr. Palitha Dassanayaka and Dr. Sisil Kumarawadu for being the 
members of the review committee for my research. If not for their guidance and 
advice this work wouldn't have been a success at the end. 
I have been assisted extensively by Mr. Pasidu Pallewella , Mr. Gamini Jayasinghe 
Mr. Geeth Jayendra, in developing the prototypes for the research work which I 
should greatly appreciate. I would also like to thank Mr. Buddhika Jayasekera, Mr. 
Dharshana Prasad, Ms. Imali Hettiarachchi and Mr. Chang Jong Baek, who have been 
my colleagues at the Departmental Research Lab, for helping me in various ways for 
successfully carrying out this work. 
Finally, my thanks go to various other personnel without whose help this work 
wouldn't be a success. Understandably, their individual names cannot be mentioned 
here due to being large in number. 
v 
List of Figures 
Figure Page 
Figure 1.1 Braided muscle 5 
Figure 1.2 Embedded muscles 6 
Figure 1.3 Lifting and lowering masses 6 
Figure 1.4 Antagonistic setups 7 
Figure 1.5 Muscle configuration in the human arm 8 
Figure 1.6 Pneumatic robots 9 
Figure 1.7 Pneumatic muscle applications (Drive for a tab punching) 9 
Figure 1.8 Pneumatic muscle applications (Emergency stop for rollers) 10 
Figure 1.9 Pneumatic muscle applications (Drive for a vibrating Hopper) 10 
Figure 1.10 Pneumatic muscle applications (Fatigue failure test bench) 11 
Figure 2.1 Pneumatic muscles 14 
Figure 2.2 Pressure regulator valve 15 
Figure 2.3 Hall effect sensor 16 
Figure 2.4 Current control circuit 16 
Figure 2.5 Complete hardware assembly 17 
Figure 3.1 Solid tube with two end closed rubber end cap 18 
Figure 3.2 Pressures vs. Volume 20 
Figure 3.3 Forces vs. Contraction 20 
Figure 3.4 Spring mass damper system 21 
Figure 3.5 Transfer function 22 
Figure 3.6 Step response 23 
Figure 3.7 Pneumatic muscle system 24 
Figure 3.8 Pneumatic muscle states 24 
Figure 3.9 Pneumatic muscle in bicep configuration 26 
Figure 4.1 Concepts of inverse based tracking 31 
Figure 4.2 System transfer.. 31 
Figure 4.3 Inverse based control 31 
vi 
Figure Page 
Figure 5.1 Area Vs. Contraction (No Load) 34 
Figure 5.2 Area Vs. Pressure (No Load) 34 
Figure 5.3 Area Vs. Contraction (2.5 kg) 35 
Figure 5.4 Area Vs. Pressure (2.5 kg) 35 
Figure 5.5 Area Vs. Contraction (5 kg) 36 
Figure 5.6 Area Vs. Pressure (5 kg) 36 
Figure 5.7 Area Vs. Contraction (7.5 kg) 37 
Figure 5.8 Area Vs. Pressure (7.5 kg) 37 
Figure 5.9 Area Vs. Contraction (10 kg) 38 
Figure 5.10 Area Vs. Pressure (10 kg) 38 
Figure 5.11 Voltage input to the controller 39 
Figure 5.12 Muscle contraction Vs. Time 41 
Figure 5.13 Muscle velocity Vs. Time 41 
Figure 5.14 Muscle acceleration Vs. Time 42 
Figure 5.15 Theoretical and Practical results 43 
Figure 6.1 Tracking application with out pole replacement 44 
Figure 6.2 Desired output waveform for T=1 Seconds 45 
Figure 6.3 Triangular tracking application for T=1 Seconds 45 
Figure 6.4 Desired output waveform for T=0.1 Seconds 46 
Figure 6.5 Triangular tracking application for T=0.1 Seconds 46 
Figure 6.6 Desired output waveform for T=0.1 Seconds (Sinusoidal waveform) 47 
Figure 6.7 Tracking application for T=0.1 Seconds (Sinusoidal waveform) 47 
Figure 6.8 Desired output waveform for T=1 Seconds (Sinusoidal waveform) 48 
Figure 6.9 Tracking application f o r T = l Seconds (Sinusoidal waveform) 48 
List of Tables 
Table Page 
Table 5.1 Practical results (No Load) 33 
Table 5.2 Practical results (2.5 kg) 35 
Table 5.3 Practical results (5 kg) 36 
Table 5.4 Practical results (7.5 kg) 37 
Table 5.5 Practical results (10 kg) 38 
Table 5.6 Hall effect sensor output results 39 
Table 5.7 Summary of Practical results 43 
viii