Flexible In-Pipe Leak Detection Sensor Module
ARCHIVES
Design and Fabrication
MASSACHSET LNSTITUTE
OF TECHNOLOGY
by
OCT 012015
David Donghyun Kim
LIBRARIES
BASc., University of Waterloo (2013)
Submitted to the Department of Mechanical Engineering
in partial fulfillment of the requirements for the degree of
Master of Science in Mechanical Engineering
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
September 2015
Massachusetts Institute of Technology 2015. All rights reserved.
Signature
redacted.
A u th o r ................................................................
Department of Mechanical Engineering
June 19, 2015
Certified by....
Signature redacted ......
Kamal Youcef-Toumi
Professor
Thesis Supervisor
Accepted by............
Signature redacted
UA
David E. Hardt
Chairman, Department Committee on Graduate Theses
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Flexible In-Pipe Leak Detection Sensor Module Design and
Fabrication
by
David Donghyun Kim
Submitted to the Department of Mechanical Engineering
on June 19, 2015, in partial fulfillment of the
requirements for the degree of
Master of Science in Mechanical Engineering
Abstract
Recent pipe bursts and explosions have caused not only financial losses but also a
threat to public safety. Due to the recent incidents, governments have imposed strict
laws with an increase in inspection regulation requirements. Large size networks
make manual inspection of an entire complex system almost impossible. The need for
autonomous automatic inspection systems is evident. A robust autonomous in-pipe
leak detection robot was developed and reported in [1-5]. The developed system is
able to accurately detect leaks in both pressurized gas and water pipes. This however
was limited to 101.6mm (4in) internal diameter pipes. In practice, fouling of water
pipes makes the internal pipe surface irregular. This thesis presents an analysis, design
and experimental evaluation of a flexible detection system for pipes with large inner
pipe diameter variation (80mm to 120mm). The system performance is evaluated
through simulations and experiments. Experimental results show that the flexible
sensor can detect leaks in pipes with simulated limescale. In addition, experiments
were conducted to evaluate the effects of detector shift from the pipe centerline along
with the effective area coverage of the leak by the sensor. The results show robust
performance under large variations.
Thesis Supervisor: Kamal Youcef-Toumi
Title: Professor
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Acknowledgments
I would like to thank my advisor Professor Kamal Youcef-Toumi for taking me into
his lab and guiding me through the entire degree program. He has inspired me to
look over and beyond as a researcher.
I also want to thank my project team. Dr. Dimitris Chatzigeorgiou guided me
through this project. His experiences and knowledge was essential for me to proceed
with this project. His past experimental data and setups were essential for the success
of this project. I would like to thank You Wu as well for giving me design advice and
helping me with electronics.
Last, but not the least, I would like to thank my family and friends who supported
me from around the world. They were there for me when I was down and always
cheered me up to stand back up again and move forward.
This project was supported by Kuwait Foundation for the Advancement of Sciences and Kuwait-MIT Center for Natural Resources and the Environment.
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Contents
Pipe Leak Detection and Society
. . . . . . . . . . . . . . . . . . .
15
1.2
Available Inspection Technologies
. . . . . . . . . . . . . . . . . . .
16
1.3
Summ ary
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16
.
.
17
Mechanical Design
Functional Requirements . . . . . . . . . . . .
. . . . . . .
17
2.2
Conceptual Designs . . . . . . . . . . . . . . .
18
.
.
2.1
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2.2.1
Non-Interference Multiple Sensor Design
. . . . . . .
18
2.2.2
Flexible Membrane Single Sensor Design
. . . . . . .
20
2.2.3
Rigid Pivoting Membrane Sensor Design
. . . . . . .
21
Conceptual Design Evaluation . . . . . . . . .
. . . . . . .
23
2.4
Conceptual Design Modules
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24
2.4.1
Flexible Membrane . . . . . . . . . . .
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25
2.4.2
Gimbal Mechanism . . . . . . . . . . .
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26
2.4.3
Wheel Assembly
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.
Summ ary
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2.3
2.5
29
Flexible Membrane Sensor Design
Range of Measured Force . . . . . . . . . . . .
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29
3.2
Membrane Free End Deflection Analysis
. . .
. . . .
32
3.3
Membrane Buckling Analysis
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34
3.4
The Final Membrane Design . . . . . . . . . .
35
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3.1
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3
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1.1
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2
15
Introduction
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1
7
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36
3.5.1
Design Options . . . . . . . . .
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36
3.5.2
Design of Wheel Assembly . . .
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38
3.6
Performance Enhancement . . . . . . .
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39
3.7
Summary
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41
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Prototype
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43
4.2
Force Sensing Resistor Circuit Design .
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43
4.3
Experimental Setup . . . . . . . . . . .
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46
4.4
Leak Detection Experimental Results .
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4.5
Summary
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48
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4.1
51
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5.1.1
Magnetic Experimental Setup . . . . . . . .
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52
5.1.2
Compressed Air Experimental Setup
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53
5.2
Magnetic Experimental Results and Discussion . . .
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5.3
Compressed Air Experimental Results and Discussion
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5.4
Summ ary
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59
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Experimental Setup . . . . . . . . . . . . . . . . . .
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Sensor Performance Analysis
5.1
6
43
Leak Detection Experiment
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5
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4
Wheel Assembly Design
.
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3.5
61
Conclusion & Recommendations
63
A CAD Drawings
8
List of Figures
2-1
The non-interference multiple sensor design . . . . . . . . . . . . . . .
18
2-2
(a): Positive membrane structure, (b): Negative membrane structure
19
2-3
A non-interference carrier with arrows indicating the degrees of freedom 19
2-4
The non-interference carrier motion, red shows the example displacement of membrane carrier
. . . . . . . . . . . . . . . . . . . . . . . .
20
. . . . . . . . . . . . . .
21
2-5
The conceptual design of flexible membrane
2-6
(a): The conceptual deployed and collapsed mode of pivoting membrane design, (b): The conceptual assembly of the pivoting membrane
design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22
2-7
The carrier details for pivoting membrane sensor . . . . . . . . . . . .
22
2-8
A flexible membrane design with 600 membrane section overlap
. . .
25
3-1
Free body diagram of leak force on membrane
. . . . . . . . . . . . .
30
3-2
Gimbal structure with green and yellow circles indicating the possible
FSR placements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3-3
(a):Force components measured by FSR1 , (b):Isometric view of the
gimbal mechanism
3-4
30
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
31
A sectioned membrane FEA model. The red arrow indicates gravity
direction and the green arrows indicate the fixed surface of the membrane base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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33
3-5
FEA results for a membrane supporting its own weight (a): 60' membrane, (b): 90' membrane, (c):
180' membrane, The legend on the
right shows red being the largest deflection (1.790mm) while blue being no deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
33
3-6
Summary of deflection at the tip of the membranes due to gravity . .
34
3-7
Finite elements buckling simulation results for 600 membrane design:
(a): Mode 1, (b): Mode 2. Red on the legend shows large membrane
deformation while blue corresponds to no displacement
3-8
. . . . . . . .
34
Finite elements buckling simulation results for 180' membrane design:
(A): Mode 1, (b): Mode 2. Red on the legend shows large membrane
. . . . . . . .
35
. . . . . . . . . . . . . . . . . . . . . . . . .
36
3-10 (a): Swing leg wheel concept, (b): Telescopic wheel concept . . . . . .
37
deformation while blue corresponds to no displacement
3-9
Overlap angle definition
3-11 (a): Configurations for 80mm pipe operation and 120mm operation,
(b): The completed wheel assembly . . . . . . . . . . . . . . . . . . .
39
3-12 (a): Teflon coating on membrane surface to prevent membranes from
attaching to each other, (b): Addition of tape to prevent buckling . .
40
3-13 Swing arm attachment to regulate irregular friction pipe forces . . . .
41
. . . . . . . . . . . . . . . . . .
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3-14 Swing arm contact force components
4-1
A prototype of the sensing module
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4-2
The circuit diagram for FSR . . . . . . . . . . . . . . . . . . . . . . .
45
4-3
Labview interface to measure FSR values . . . . . . . . . . . . . . . .
45
4-4
Labview block diagram for reading the FSR values . . . . . . . . . . .
46
4-5
(a): Experimental setup for compressed air, (b): Robot placed inside
the setup.......
4-6
47
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(a): Inside view of the clean pipe experimental setup, (b): Inside view
of the simulated limescale pipe experimental setup . . . . . . . . . . .
47
. . . . . . . . . . . .
48
. . . . . .
51
4-7
Leak detection result from 101.6mm (4in) pipe
5-1
(a): Definition of center shift, (b): Definition of vector tilt
10
Sensor fixture for performance analysis experiments . . . . . . . . .
52
5-3
The membrane performance verification experimental setup . . . . .
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5-4
Assembled center shift and vector tilt experiment setup . . . . . . .
54
5-5
The magnet in place to produce simulated leak force
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54
5-6
(a): The center shift cases, (b): The vector tilt with center pivot, (c):
The vector tilt with front pivot, (d): The vector tilt with back pivot
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5-2
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Effective area control of the membrane
5-8
Summary of experimental results from performance analysis of flexible
56
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5-7
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58
A-1
Sensor assembly drawing . . . . . . . . . . . .
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A-2
Center axis for sensor . . . . . . . . . . . . . .
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A-4 Gimbal small ring 131 . . . . . . . . . . . . . .
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A-5
Wheel assembly drawing . . . . . . . . . . . .
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A-6
Wheel assembly base plate . . . . . . . . . . .
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A-7
Linkage joint for wheel assembly . . . . . . . .
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A-8
Spring fork for wheel assembly . . . . . . . . .
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A-10 Swing arm assembly base . . . . . . . . . . . .
.... . . . . . . . . .
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A-14 Wheel holders for the experimental fixture . .
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A-15 Coordinate stage for the experimental fixture .
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A-16 Universal joint base for the experimental fixture . . . . . . . . . . . .
79
A-17 Universal joint center piece for the experimental fixture . . . . . . . .
80
A-18 Universal joint end (sensor side) piece for the experimental fixture
81
A-19 Universal joint carriage piece for the experimental fixture . . . .
82
.
.
m em brane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.................
A-11 Swing arm for irregular pipes
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A-9 W heel [31
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A-3 Gimbal drum [31
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A-13 Experimental fixture center piece
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A-12 Assembly drawing for the experimental fixture
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12
List of Tables
2.1
The conceptual design evaluation
. . . . . . . . . . . . . . . . . . . .
23
4.1
Summary of leak detection results . . . . . . . . . . . . . . . . . . . .
49
5.1
Summary of results for center shift experiments
. . . . . . . . . . . .
57
5.2
Summary of results for vector tilt about the center pivot
. . . . . . .
57
5.3
Summary of results for vector tilt about the front pivot . . . . . . . .
57
5.4
Summary of results for vector tilt about the back pivot . . . . . . . .
57
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Chapter 1
Introduction
1.1
Pipe Leak Detection and Society
Water leaks in pipelines cause not only a waste of a valuable resource but also a danger
to the public. The Canadian Water Research Institute reported that 20% of water is
lost during delivery [6]. This loss is mainly caused by small leaks in the pipe network.
In water stressed regions, water loss due to leaks has a greater impact on society.
In normal situations, water leaks out of a pipe through a crack. However, there are
also conditions when the outside pressure becomes higher than the in-pipe pressure
and consequently, contaminated water moves back into the pipe. For example, in
2010, a water main break occurred in the Boston area.
The contaminated water
supply affected approximately 2 million residents and required boiling water before
drinking [7]. Water leaks can thus be detrimental in certain regions of the world.
Pipelines with low integrity can also lead to gas explosions as in the case of
San Bruno, California. The 2010 accident caused 8 deaths, 66 injured and damage
to 38 residential properties [8].
Such explosions with serious implications caused
governments to impose new strict inspection and reporting laws. The Commonwealth
of Massachusetts, for example, now requires from the utility companies to report all
leak information. This annual report includes the number of gas leaks, their locations,
and risk level of each leak [9]. Reliable autonomous robotic systems will make such a
task feasible.
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1.2
Available Inspection Technologies
Existing leak inspection solutions show limitations in performance.
A common in-
spection method uses a listening device for leak detection in pipes [101. This acoustic
method requires trained operators and has limited application to plastic pipes [1.
In the United States, there are about 2 million kilometers of natural gas pipes and
about 240 thousand kilometers of pipes for petroleum product [111. Manual inspection methods for such large and complex pipeline networks are not practical. The
Smartball is an autonomous tool that flows inside a pipe and detects small leaks [121.
The Smartball is used in a single pipe at a time since it has no maneuvering ability.
An operator controls the valves inside a facility or a pipe network to constrain the
navigation path of the Smartball. Reference [131 introduces an autonomous robot capable of not only navigating inside water pipes but also to follow defined trajectories.
Multiple robotic inspection technologies were presented in [141.
1.3
Summary
This thesis presents an analysis and design of a flexible mechanism for in-pipe robotic
leak detection. This new sensing module can be attached to a propulsion system such
as the one in [13,151. It is also based on the same fundamental detection method
developed in [1-51. Such a method, however, cannot operate in pipes with varying
diameters but only in pipes with internal diameter close to 101.6mm (4in). Water
pipes are fouled over time and consequently their internal surfaces become irregular.
The detector introduced in this thesis is able to operate in pipes with diameters in
the range 80mm-120rmm.
A flexible mechanism allows the detector to operate in
pipes with irregular diameters. This thesis first introduces a design of the flexible
mechanism and then a prototype. Various experimental results verify that the new
system is able to detect leaks inside pipes with different diameters.
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Chapter 2
Mechanical Design
This chapter describes how the conceptual designs for the flexible sensor module were
developed. First, the functional requirements for the sensor were identified. Based
on the identified functional requirements, the three feasible conceptual designs were
proposed and evaluated. The best conceptual design was selected and divided into
design modules which were discussed in further detail in section 3.
2.1
Functional Requirements
The goal of this project is to design a sensor module that can operate in realistic pipe,
which has irregular internal surfaces. As discussed in section 1.3, the real water pipes
that operated for long period accumulate limescales.
The limescales form smooth
deviations in the diameter of the pipes. The existing in-pipe leak detection sensors
are not able to operate in such pipe conditions. Two key functional requirements were
derived to meet the project goal as described below.
The first functional requirement was that the sensor module should be able to pass
through smooth changes with the diameter of the pipes. This functional requirement
also included cases when the sensor has to go through real water pipes with limescale
accumulated. The design has to reduce any chances of the sensor module deviating
far from the center of the pipe. For the purpose of this thesis, it was assumed that
the sensor module is pulled by the propulsion module in the center.
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The second functional requirement was that the design should move the membrane
location based on the pipe wall's location changes. As the membrane is placed closer to
the pipe walls, the sensor's sensitivity to small leaks increases. Ideally, the membrane
is placed with gaps in order of few millimeters. The membrane may be placed so
it maintains constant contact with the pipe wall. The constant contact membrane
going through irregular pipe surfaces may cause false detection. The enhancement
techniques may be needed for different types of membrane designs.
2.2
Conceptual Designs
Three different conceptual designs for the sensor module were proposed. They were
all designed to meet the functional requirements, but each design had different performance predictions. In the next section, the conceptual designs were evaluated to
determine which design can meet the functional requirement best.
2.2.1
Non-Interference Multiple Sensor Design
Figure 2-1: The non-interference multiple sensor design
The general overview of the non-interference multiple sensor design is shown in Fig.
2-1. The non-interference design utilizes 8 membrane structures, which are composed
of 4 positive membrane structure shown in Fig.
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2-2a and 4 negative membrane
structure shown in Fig.
2-2b. Each of the membrane structures in Fig. 2-2 will
have flexible membranes attached to the top curved surface and will be carried by
the carrier as shown in Fig. 2-3.
The non-interference carrier in Fig. 2-3 can move
(a) Positive Membrane
(b) Negative Membrane
Figure 2-2: (a): Positive membrane structure, (b): Negative membrane structure
Figure 2-3: A non-interference carrier with arrows indicating the degrees of freedom
up and down as shown in Fig. 2-4. The up and down motion was limited only by
the leg extension limit in the overall design. The positive and negative membrane
structures do not interfere.
The up and down motion of the membrane structure
allows the membrane to be placed close to the pipe walls. The carriers are given two
degrees of freedom as shown in Fig. 2-3. The two degrees of freedom for each carrier
allows the membrane structures to align itself to the irregular pipe surfaces. The four
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wheels on the carrier allowed the carrier to place the membrane so the membrane was
not contacting the pipe walls. The FSR sensor was placed inside the positive and
negative membrane structures as indicated in Fig. 2-2. The leak induced force tilts
the membrane structure while the entire sensor assembly is traveling inside the pipe.
Figure 2-4: The non-interference carrier motion, red shows the example displacement
of membrane carrier
2.2.2
Flexible Membrane Single Sensor Design
The flexible membrane concept is shown in Fig. 2-5. The flexible membrane design
utilizes the flexible membrane, which deforms upon contact to the interior pipe walls.
The truncated cone shaped membrane structure will support its own weight.
As
the sensor module passes through irregularities inside the pipe, the membrane will
deform itself while contacting the irregularities. The wheel assembly is independent
of the membrane location, which is different compared to the other two conceptual
designs. By making the membrane positioning independent of the wheel's location
inside the pipe, the design became simplified. In addition, the non-interference design
and pivoting arm design used 8 FSRs, the flexible membrane design only needed 2
FSRs, which could simplify the electronics design as well.
20
Membrane
Giibal Mechanisn-\
pp
WTceel Assgnibly
Figure 2-5: The conceptual design of flexible membrane
2.2.3
Rigid Pivoting Membrane Sensor Design
The pivoting membrane design is shown in Fig. 2-6. The pivoting membrane design
uses pivoting arm attached to the central base. Each arms carry a membrane structure
similar to the non-interference design. The membrane can be deployed to fit inside
bigger pipe as shown in Fig. 2-6a. The collapsed membrane structure is shown in Fig.
2-6b. Each membrane structures are carried by the carriage as shown in Fig. 2-7. The
unique pivoting arm motion requires the carrier to move in circumferential direction
to the pipe simultaneously with the entire sensor moving along through the pipe. As
a result, fixed wheels similar to non-interference design and flexible membrane design
cannot be utilized in this design. Spherical ball transfers as shown in Fig. 2-7 is used
to solve this problem.
21
.Collapsed
Deployed
(b) Conceptual assembly
(a) The pivot arm deployment
Figure 2-6: (a): The conceptual deployed and collapsed mode of pivoting membrane
design, (b): The conceptual assembly of the pivoting membrane design
Membrane Structure
Ball Transfer
Carriage
Spring Placement Hole (FSR can be
place in one side)
Figure 2-7: The carrier details for pivoting membrane sensor
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2.3
Conceptual Design Evaluation
In order to select the best design for the sensor module, the three conceptual designs
described above were evaluated. To evaluate the conceptual designs, three criteria
were set. The three criteria were: estimated leak detection performance, ease of fabrication and the ability to overcome irregularities inside the pipe. The first criteria was
evaluated mainly by predicting how the conceptual designs can place the membrane
close to the varying diameters of pipe. The design that can adapt better to irregular pipes. The ease of fabrication was evaluated by considering how many parts are
required to make the sensor module. The complex design generally will have more
components, which makes the fabrication difficult. The last criterion was evaluated
by estimating how the conceptual design may react to obstacles inside the pipe. If
the sensor is likely to get stuck inside the pipe with small obstacles, the design is not
optimal for this project's purpose.
The above three conceptual designs were evaluated relative to each other with
the described criteria and results are shown in Table 2.1. Criterion 1 in Table 2.1
Table 2.1: The conceptual design evaluation
Criterion 1
Criterion 2
Criterion 3
Non-Interference
Design
Medium
Poor
Poor
Flexible Membrane
Design
Good
Good
Good
Rigid Pivot
Design
Poor
Medium
Medium
represents the leak detection performance while Criterion 2 represents the ease of fabrication and Criterion 3 represents the sensor performance in going through obstacles.
For the first criterion, the flexible membrane design was expected to have the
best performance. For the design with rigid membrane structures (non-interference
and pivot design), there always exist a gap between larger diameter pipes and the
membrane structure as shown in Fig. 2-6a. Through design optimization, the gap
between the pipe internal walls and the membrane structure can be minimized but the
rigid structure cannot perform better than flexible membrane. The non-interference
design performs relatively better compared to pivot arm design as the positive and
23
negative membrane structures' locations are independent of each other.
The flexible membrane design was also the easiest to fabricate compared to other
conceptual designs. The non-interference design and the pivoting membrane design
both require separate carriers which carries the membrane structure.
design contains many components and are complex to fabricate.
The carrier
The number of
components required to build the flexible membrane design was significantly smaller,
which made the design easy to fabricate. The pivoting membrane design was easier to
build compared to the non-interference design. The number of components shown in
Fig. 2-1 and Fig. 2-6b shows that the non-interference design needs many components
just to move the carrier. This makes the flexible membrane design most suitable for
fabrication.
For the final criterion, the flexible membrane design was most likely to have less
trouble while going through irregularities inside the pipes. The non-interference design utilizes fixed wheels similar to the flexible membrane design. The non-interference
design may fail if one carrier slows down and collide with adjacent carriers. The collision may cause false detection. The pivoting membrane design is less likely to have
false detection issues, but the ball transfers may cause unexpected complications.
The flexible membrane design is the better solution compared to the other two
designs because the other two design utilized the rigid membrane structure.
The
rigid membrane structure may collide with the irregular surface with smaller radius
compared to the membrane structure. The flexible membrane design may get stuck
inside the pipe only when the irregularities make the pipe diameter smaller than the
designed performance limit.
2.4
Conceptual Design Modules
The flexible detector's conceptual design is shown in Fig. 2-5. The system consists
of 3 subsystems (i) a flexible membrane, (ii) a gimbal mechanism, and (iii) a wheel
assembly. These subsystems are indicated in Fig. 2-5. The flexible membrane transfers the leak-induced force to the gimbal mechanism. This force is generated due to
24
-
Cover Membrane
Base Membrane
Figure 2-8: A flexible membrane design with 600 membrane section overlap
a pressure gradient that pushes the membrane radially in the presence of a leak [4].
The membrane is attached to the gimbal mechanism that allows the assembly to
rotate about 2 orthogonal axes. The gimbal base is equipped with 2 sensors whose
signals determine the leak-induced force. The leak force is detected when it pulls on
the membrane momentarily, while the sensor passes by the leak. Finally, the wheel
assembly guides the whole sensor as it moves through pipes. This design allows for
the detection of leaks and the ability to maneuver in pipes with irregular surfaces.
2.4.1
Flexible Membrane
The design uses a flexible membrane to satisfy 3 functional requirements.
These
requirements are (i) conforming to large pipe diameter variations, (ii) maintaining
close contact to small surface variations, and (iii) transferring the leak-induced force
to a sensing base.
The flexible membrane is designed with overlapping sections to meet large pipe
diameter variations. This is shown in Fig. 2-8. The range addressed in this thesis
is 80mm to 120mm. Key issues of geometry, kinematics and material properties are
discussed in section 3. In addition, proper membrane material and support mechanism
allow the free end of the membrane to stay close to the pipe inner walls. Finally, the
flexible membrane serves as a means to transfer the leak-induced force to the gimbal
mechanism. The radial pressure pulls the membrane towards the leak and against
25
the pipe wall, as shown in Fig. 3-1. The friction force, between the membrane and
the pipe wall, is transferred to the gimbal. The membrane will detach from the wall
as the whole detector moves downstream with the flow.
The details of the design
methodologies along with a performance enhancement techniques are described in
section 3.
2.4.2
Gimbal Mechanism
A gimbal mechanism is used to sense the leak-induced force. This force is in fact the
friction force between the membrane and the pipe wall. It occurs only in the presence
of a leak as part of the membrane, closest to the leak, gets attached to the wall by
suction.
The membrane transmits this force to a gimbal mechanism consisting of
two orthogonal rotary axes. The drum mounted on the gimbal of Fig. 3-2 rotates
in response to the force and thus changes the pressure on 2 force sensing elements
located behind the springs.
In the current design, the sensing elements are Force
Sensing Resistors (FSR). The springs are preloaded so positive and negative force
effects can be sensed by the FSRs. The FSRs generate electrical signals in response
to the drum rotation, which are related to leak information. This includes estimates
of the leak size, leak flow rate, leak location around the pipe circumference and along
the pipe.
The gimbal mechanism is designed based on the minimum operational
diameter requirement. In this thesis this minimum diameter is 80mm.
2.4.3
Wheel Assembly
The wheel assembly carries the entire sensor module inside the pipe. The two wheel
assemblies, shown in Fig. 2-5, are designed to operate with six wheels on each assembly. The objective is to have the wheels contacting the pipe walls continuously. To
this end, the wheel holders are preloaded with torsional springs so as to keep them
open and maintaining the wheels in permanent contact with different pipe diameters.
The wheel assembly is also used to maintain the mobility module along the pipe centerline. The mobility module hosts the propulsion, computing/electronics modules,
26
along with the detection system.
2.5
Summary
This chapter presented three different conceptual design and reasoning why the final
design was selected. First, the goal of the machine was defined. The designed machine should be able to operate and detect leaks inside a realistic water pipe with
irregular internal surfaces. From the goal, the two functional requirements were identified. The first functional requirement was that the machine should be able to pass
through smooth transitions from different cross-sectional diameters inside the pipe.
The second functional requirement was that the machine should adjust the location
of the leak-sensing membrane according to the internal shapes of the pipe. After the
functional were identified, the three different conceptual designs were derived. The
conceptual designs were evaluated with three criteria: leak detection performance,
ease of fabrication and ability to go through obstacles. The best design, which was
flexible membrane design was selected.
27
28
Chapter 3
Flexible Membrane Sensor Design
The design of a flexible membrane is presented in this section. The study covers range
of measured forces, deflection behavior of the membrane free end, membrane behavior
under loading, and performance enhancements solutions. Finally, a membrane design
is proposed. The results reported in this thesis are obtained using Finite Element
Analysis (FEA). The design and performance enhancement techniques were based on
FEA simulations results.
The completed CAD drawings with the key dimensions of
the sensor are included in Appendix A.
3.1
Range of Measured Force
The FSR specifications are necessary for an optimal leak detection design. For this,
the range of measured forces in terms of the leak induced force need to be established.
Then the specifications are identified. Fig. 3-1 shows the operating pressure P, the
normal force F., the friction force Ff, and the leak diameter D. The figure also shows
the membrane pushed against the pipe inner wall due to the pressure P. In this study,
D is set to 3.5mm and P to 68.9kPa (10psi) . The normal force F, acting on the
membrane, from an assumed circular leak, is calculated using the following equation,
F = ()2
29
. 7F2P
(3.1)
D
PIPE WALL
MEMBRANE
Ff
P
GIMBAL
Fn
Figure 3-1: Free body diagram of leak force on membrane
:ROTATION
ROTATION AXIS 1
Figure 3-2: Gimbal structure with green and yellow circles indicating the possible
FSR placements
(3.2)
The friction force Ff is given by the Equ. (3.2). The coefficient of friction A is between
the polyurethane membrane and the inside pipe wall. The static coefficient of friction
was found experimentally, in 131, to be p = 3.0. And the resulting Ff is calculated
to be 1.990N. This analysis assumes that the leak edge effects do not influence the
friction force calculation.
The relationships between the different forces associated with the drum are now
derived. The principal function of the gimbal mechanism is transferring the friction
30
AXIS 2
DRUM
0
F1, FSPR.ING
SPACER
RSET
SCREW
D
AXIS 1
R,
p-FLeak
FI
---- ------------
-
(a)
F2
(b)
Figure 3-3: (a):Force components measured by FSR1 , (b):Isometric view of the gimbal mechanism
force to the FSRs. Fig. 3-2 shows this drum module. The drum has two rotary axes
namely one rotation about axis 1 and the second about axis 2. In addition, the Figure
shows 4 sockets as potential locations for the FSRs. The 2 FSRs used in this design
are located in the solid green and yellow circles. The 2 remaining dashed circles are
alternative locations. The total leak force induces, in general, rotations about the
two axes. FSR1 and FSR2 measure force components of the total leak force.
The definition of key parameters and variables is now presented. In Fig. 3-3, R is
the pipe radius and D9 is the gimbal diameter. The parameter R, is the distance from
the gimbal central axis to the FSR location. Fp is the FSRs preload force. The actual
prototype uses parameter values of 20mm and 75mm for R, and Dg respectively. The
maximum value of Dg is chosen to be less than the minimum pipe diameter, 80mm
in this study.
The forces F and F2 are components of the leak-induced force. These forces are
applied onto FSR1 and FSR2 . Assuming a condition where the components F and
F2 are applied onto FSR1 and FSR2 , then the total applied forces for the 2 sensors,
labeled by Flt and F2 t, are given by,
Fi = Fp + F
(3.3)
F2t = F ,+ F 2
(3.4)
31
Therefore, each FSR measures the total forces F1 and F12 t. Under an instantaneous
static condition, one can write the following moment balance equations about the
rotation axes in Fig. 3-3.
0 = -F.
R cos(O) - (Fp - F1 ) Rs+ Fu R,
(3.5)
0 = -F
R -sin() - (Fp - F
2 )- R + F2 t- Rs
(3.6)
The Fp value is constant and the range of Fit and F2t depends on the changes in F
and F2 . Equations (3.5) and (3.6) can be rearranged to lead to,
F,F
-
R - cos(O)
2 - RS
(37)
F
R - sin(O)
2. R.5
(3.8)
Each leak force is dependent on the radial distance R and the angular displacement
and related to different FSR readings F and F2 . The analysis reveals that the F
and F2 ranges are between -3N
and 3N. The FSR model used in the prototype is
TekScan FlexiForce® A301. The FSR supplier Tekscan Inc. manufactures 3 different
FSR models (FlexiForce@ A301) with standard force of 4N, 11IN and 445N. The
predicted force with sufficient preload force Fp can easily go beyond 4N. As a result,
the TekScan FlexiForce@ A301 FSR with 111N specification was used.
3.2
Membrane Free End Deflection Analysis
The design of the flexible membrane involves material and geometric properties. The
membrane system consists of overlapping adjacent membrane sections as shown in
Fig. 2-8. The section sizes and material properties are chosen appropriately so as to
eliminate possibilities of buckling. The behavior of the membrane system is analyzed
using SolidWorks with a simulation model shown in Fig. 3-4. For each membrane, the
root of the membrane is fixed and gravity acts downwards. Different size membranes
were analyzed. It was found, for example, that 45' and 30' membranes cannot provide
32
Diameter:
120mm
Diameter:
751mn
Gimbal Attachment:
6mm
Fixed End
Figure 3-4: A sectioned membrane FEA model. The red arrow indicates gravity
direction and the green arrows indicate the fixed surface of the membrane base
(a)
(b)
(c)
Figure 3-5: FEA results for a membrane supporting its own weight (a): 600 membrane,
(b): 90' membrane, (c): 1800 membrane, The legend on the right shows red being
the largest deflection (1.790mm) while blue being no deflection
proper support to their own weight. The ideal membrane deflects due to leak-induced
pressure, during operation, but springs back to its original shape. Such membrane
can be setup with overlapped sections to form a circular overall shape as shown in
Fig. 2-8.
Selected results of the FEAs are now presented.
results for a membrane supporting its own weight.
Figure 3-5 shows some FEA
The associated angles are 60',
900 and 1800. The red color on the scale represents the largest deflection (1.790mm)
and blue for no deflection. Figure 3-6 summarizes the deflection of the membranes
at the free end.
The blue color of Fig.
3-5 and Fig.
3-6 indicate that the 90'
membrane will have a distinct drop in the center. This drop of the membrane near its
center eliminates the 900 design option since it does not lead to a successful system.
Another issue is that the membrane drop affects the distance to the pipe walls. The
ideal membrane section supports its own weight and exhibits the least deflection at
its center.
33
Deflection of Segmented Membranes Due to Gravity
2
Dr
--
- -90 Degree Segment Membrane
1 .5-~
-. 180 Degree Segment Membrane
0 .5
-
0
S IembIane
60 Degree Segment Membrane
-60
-40
20
-20
0
Seqment Circumferencial Location (mm)
40
60
Figure 3-6: Summary of deflection at the tip of the membranes due t o gravity
150
(b)
(a)
Figure 3-7: Finite elements buckling simulation results for 600 membrane design: (a):
Mode 1, (b): Mode 2. Red on the legend shows large membrane deformation while
blue corresponds to no displacement
3.3
Membrane Buckling Analysis
Satisfying the buckling condition is a required characteristic for any feasible membrane
design. Buckling analysis is performed to check this condition. The previous section's
simulation results concluded that only the 600 and the 180' membrane designs were
feasible options.
The simulation setup is similar to that of the static deflection analysis.
The
boundary conditions along with the gravity effects are similar to the ones shown in
Fig. 3-4. This buckling analysis, which uses gravity as a reference load, is reasonable.
Such an analysis reveals whether a membrane's deformation under higher loads will
result in a separation from the pipe wall. The ideal membrane supports its own weight
and exhibits the least deflection at its center.
The buckling simulation results are shown in Figures 3-7 and 3-8. They show two
34
I"V"MI
)
(a)(
Figure 3-8: Finite elements buckling simulation results for 1800 membrane design:
(A): Mode 1, (b): Mode 2. Red on the legend shows large membrane deformation
while blue corresponds to no displacement
modes of buckling. Each figure shows both mode 1 and mode 2 for two membrane
designs, namely the 600 and 180' configurations. Mode 1 corresponds to the lowest
safety factor. While mode 2 corresponds to the second lowest factor of safety. Mode 1
is the most likely configuration that the membrane exhibits under the gravity load of
Fig. 3-4. Figure 3-8 indicates that the 1800 membrane will have a wavy form when it
is compressed. This buckling behavior is detrimental to the sensor performance. The
wavy condition implies that there will be both high and low regions on the membrane.
The membrane low regions may be too far from the leak and consequently the sensor
may miss detecting the leak. As a result, the 600 membrane was selected for the final
design.
3.4
The Final Membrane Design
The overlap angle plays a crucial role in the membrane assembly performance. All of
the overlapping membrane sections are assembled to form the complete membrane.
This will then be attached to the gimbal mechanism. It is worthy to note that the
concept of overlapping sections is used not only for large diameter adjustment but
also for minimizing the membrane drop especially near the free ends. One key issue
in the assembly of the overlapping sections is determining the overlap angle.
The 600 selected design option also shows some membrane edge drop. This is
highlighted in red in Figure 3-7. A closer look at the membrane overlapping sections
is shown in Figure 3-9. The overlap angle plays a crucial role and was selected as 150
35
%S
Figure 3-9: Overlap angle definition
based on the results of the buckling simulations. This angle is indicated by the green
arrows near the base of the membrane in Figure 3-7. Mode 1 and 2 bucking results
show that all of the red regions are within the 15' edge. The final membrane design,
shown in Fig. 2-8, is composed of 4 cover 600 membranes and 4 base 600 membranes
with 150 overlap.
3.5
Wheel Assembly Design
The wheel assembly carries the gimbal mechanism and membrane inside the pipe.
The wheel assembly was designed to go over the irregularities inside the pipe and
operate in the pipe diameters ranging from 80mm to 120mm
3.5.1
Design Options
For the purpose of mechanical design, two different design options were considered for
the wheel assembly. The first design option was called the swing leg design and it is
shown in Fig. 3-10a. The leg swings about the base pivot point. The telescopic wheel
design is shown in Fig. 3-10b. The telescopic wheel design was composed of base
with hole which the leg can linearly move in and out to accommodate for different
36
(
diameters of pipes. For both design options, the range of actuation for each legs (la)
*1
Div
lb
Db
(b) Telescopic vwheel
(a) Swing leg wheel
Figure 3-10: (a): Swing leg wheel concept, (b): Telescopic wheel concept
is defined by:
la =
Drn-j p
Driax p
-
(3.9)
2
2
Where the Dinaa p is the maximum operational internal diameter of the pipe and
Dinin
pis
the minimum operational internal diameter of the pipe.
The swing leg
design does not have strict dimensional limit as long as reasonable structural rigidity
is guaranteed from the selected dimensions. On contrary, the telescopic wheel design
has limited application range. For the case with the wheel diameter being defined as
Dw, the base length (1b) in Fig. 3-10b can at most be length
lax t.
The lina, can
be calculated by:
Maximum lb
D
-
2
'p
- DV
Using equation (3.10) and the D, = 19.3306mm, the
lb
(3.10)
= 20.6694mm. From equation
(3.9), the la = 20mm. It was expected that fabricating a telescopic wheels with the
maximum base length almost similar to the required actuation distance would be
a challenge.
This was because for the telescopic design, there has to be at least
three legs in an assembly to center the sensor. The legs at the minimum diameter of
operation will interfere with each other. In addition, the space for placing the springs
would be limited. As a result, the swing leg wheel design is selected for final design.
37
3.5.2
Design of Wheel Assembly
The operational pipe diameter range and wheel diameter were considered to design
the wheel assembly. The wheel assembly using the swing leg concept was designed as
shown in Fig. 3-11. The wheel assembly was designed based on the operation pipe
diameter range of Dmin p = 80mmn to
Dmax p
=120mm. The diameter of the wheel
was set to D, = 19.33mm. The arm was preloaded with torsional spring.
The number of wheels were determined to allow the robot to stay in the center of
the pipe. The 3 wheels can ensure stable robotic motion inside the clean pipe. The
previous robot presented by Chatzigeorgiou used 3 wheels along the circumference of
the pipe [3]. For the flexible sensor, two wheels are placed in the same plane. This
helps the wheels to center the sensor better when it encounters bumps. As a result,
6 wheels spaced equally along the circumference of the pipe were designed.
The detailed analyses were conducted to determine the key dimensions for the
wheel assembly. The absolute limits of the key dimensions were first defined. The
diameter of the base
Db
in Fig. 3-10a has to be less than the Dmin p. The Db has to
also consider the amount of extra material added to surround the pin joint. The
Db
was set to be 48mm. The length of the leg is defined as i. The absolute minimum
length of the l was determined by:
Di,ax
p-
-
Db
(3.11)
2
For this thesis, the minimum i was calculated using equation (3.11) to be 26.3347mm.
There was not a limit to the maximum value of 1i. The only problem that long 1i
may cause was that the wheel assembly will become too large. The leg length i was
set to be 31.25mm. The angle of the leg A in Fig. 3-10a during the operations were
investigated.
A = sin 1 (
2
2
i
2
)
The Dp was the diameter of the pipe that the wheel assembly was placed.
(3.12)
From
equation (3.12), the A for selected dimensions ranged from 11.70" in Dmin p = 80inm
38
to 57.430 in Dmax
p
=120mm. This proves that torsion spring with 900 original angle
would be able to cover the entire range of leg swing motion. The maximum A being
less than 90" also means that when the wheel assembly is not in the center of the
pipe, the wheels will still contact the pipe walls. From the set dimensions, the design
as shown in Fig. 3-11 was produced. The drawings for the wheel assembly is included
in Appendix A.
120mni Configuration
Torsion Spring
Somm Configurat
io
(b)
(a)
Figure 3-11: (a): Configurations for 80mm pipe operation and 120mm operation, (b):
The completed wheel assembly
3.6
Performance Enhancement
Design enhancements were necessary to resolve problems of adhesion, buckling and
friction. These problems limited the performance of the assembled membrane. This
section suggests solutions to enhance the sensor's performance.
The polyurethane
membrane strips exhibited adhesion. It occurs between adjacent membrane sections
and prevented their relative motion. Consequently, the membrane strips, attached to
each other, inhibit the sensor from changing shape and adapt to a new pipe diameter.
Liquid state Teflon was coated on the opposite sides of the membrane-sensing surfaces.
When dried, it forms a thin Teflon layer. This is shown in the Fig. 3-12 (a). This
eliminated the adhesion issues and allowed the sensor to adjust to different diameters.
39
Circumferential Direction Tape
Axial Direction Tape
Tefion Coating
Structural Tape
_
(b)
(a)
Figure 3-12: (a): Teflon coating on membrane surface to prevent membranes from
attaching to each other, (b): Addition of tape to prevent buckling
Membrane buckling can be detrimental to the sensor performance. The membrane
proximity to the pipe wall assures proper function.
However, buckling caused the
membrane to deflect in a wavy form near its free end.
A larger gap between the
membrane and the pipe wall can result and thus making the pressure gradient action
inappropriate in pushing the membrane towards the leak. Adding two strips of Kapton
tape on each membrane surface, as shown in Figure 3-12, removed this issue. Higher
structural rigidity allows the membrane to stay in close proximity to the pipe wall.
In addition, the circumferential direction tape maintains the membrane's flatness,
preventing the wavy forms from appearing.
Friction, on the other hand, between the membrane and the pipe walls turned
out to be non-uniform.
The friction irregularity is mainly due to the pipe surface
fouling. Such irregular walls may cause an excessive friction force on the membrane
and identify the irregularity as a leak.
Swing arm assemblies relieve such friction
problems. They contact the pipe internal walls before the membrane and adjust the
membrane location with radial forces on the membrane. This reduces the effect of
irregular friction with the pipe. Figure 3-13 shows how the swing arm is attached to
the sensor module. The gimbal detects the effect of a friction force, in the pipe's axial
direction, acting on the membrane. The swing arm contact with the pipe generates a
force component in the axial direction and a force normal to the pipe wall, as shown
40
ABn
wwing
Meimbranle
Figure 3-13: Swing arm attachment to regulate irregular friction pipe forces
Irregular
Friction Force
i-vot
Figure 3-14: Swing arm contact force components
in Figure 3-14.
This normal force acts on both the swing arm and the membrane.
The membrane deforms and thus reducing the membrane's normal force and consequently reducing the axial friction force Ff. This reduction in the axial force prevents
false sensor readings. These types of friction issues are -non-existent when the sensor
operates inside a clean pipe, such as gas pipes.
3.7
Summary
This chapter discussed the details in designing the flexible membrane leak detection
sensor. The gimbal mechanism developed by Chatzigeorgiou was re-evaluated. The
41
new leak force estimations were performed for varying diameter pipes and required
FSR's force ratings were specified.
The segmented flexible membrane design was
completed based on static analysis, which checked if the membrane can withstand
gravity. After the static analysis, the buckling analysis was performed to check if the
membrane segments will wrinkle. The 60' segment was selected as the final membrane
size. The segmented membranes are overlapped to reduce the effect of the edges of
the membrane deforming. The three main performance enhancement techniques were
applied after the sensor is designed to enhance the sensor performance.
The swing
arm leg reduces the chance of false leak signals. The membrane coatings with Teflon
and Kapton tape allows the consistent sensor performance.
42
Chapter 4
Leak Detection Experiment
This section discusses the leak detection experiments using the prototype sensor.
The leak detection experiments are performed inside a pipe filled with compressed
air.
The first three leak detection cases were performed inside a clean pipe with
different diameters. The last leak detection case was done inside a pipe with simulated
limescale.
4.1
Prototype
The prototype of the flexible sensor was fabricated and is shown in Fig. 4-1. The
prototype was built with two wheel assemblies and a gimbal mechanism. The performance enhancements including swing arms, tape and Teflon are included in the
prototype. Teflon tape was also wrapped around the swing arm to reduce any friction
that the swing arm would induce on the sensor module.
4.2
Force Sensing Resistor Circuit Design
The electronic circuit had to be designed for the FSRs. The basic application circuit
of the FSRs can be found in the FSR data sheet [16].The field resistor value, Rf
determines the sensitivity of the FSR reading. The data sheet also provided equation
(4.1) [16]. Equation (4.1) shows the relationship between the negative voltage supplied
43
Figure 4-1: A prototype of the sensing module
to the FSR and the value of the Rf. The final output from the circuit was sent to
Arduino. The Arduino measures the voltage value,
Vaduino.
The FSR measurement can be linearized by using an Operational Amplifier(OpAmp).
For this project, the chip MAX1044 was used to invert 5V supply voltage to Vinverted
-5V.
The
=
The manufacturer provided the circuit diagram for the voltage inverter 1171.
Varduino
in equation (4.1) is the value that will indicate the force on the FSR.
The resistor value is selected based on the leak force analysis result. From the leak
force analysis in section 3.1, the range of the force change that needed to be sensed
was from -3N to +3N. The Rf was set to be 330kQ. According to calibration data
from Chatzigeorgiou's Ph.D. thesis, Rf = 330kQ will have VArduino to be 1.733V with
3N of load
131.
By preloading the FSR to steady state voltage of 2.5V, the
VArduino
should always be under 5V limit set by the voltage inverter's supply voltage.
Varduino = -Vinverted
-
Rf
Rf sr
(4.1)
An Arduino Pro Mini and Labview interface were used to display the real time
signal. Combining the Arduino with Labview allows the sensor operators to observe
44
Rf
10pF
CAP+
Vsp*
CAP-
MAX1 044
+5V
VINVERTED
-VA
lTpF
10pF
+
+5V
GND
Figure 4-2: The circuit diagram for FSR 116,171
Figure 4-3: Labview interface to measure FSR values
45
rdui
10pF
the sensor reading in real time. The waveform chart in Fig. 4-3 will show the sensor
readings from the two FSRs. The block diagram is shown in Fig. 4-4. The block
diagram first initializes the Arduino by setting port, Baud rate, processor specification
and connection type.
The Arduino then goes to while loop. Inside the loop, the
analog read command reads data from pin number 0 and 3, which are the pins that
are attached to the FSR circuits. The output from the read command is sent into
the median filter. The median filter helps reduce the noise in the signal from the
environment. Finally, the output of the median filter is sent to the waveform chart,
which displays the FSR values in real time.
Waveform Chart
COM Port
Baud Rate (115200)
Stop
Dimuelanove w/Atmeqa 328
Connection Type (USB/Serial
Median Filter (2nd Order)
Figure 4-4: Labview block diagram for reading the FSR values
4.3
Experimental Setup
The experiments for the leak detection sensor were set up in a pressurized pipe similar
to the setup shown in Fig. 4-5a. Fig. 4-5b shows the robot placed inside the pipe.
The pipe setup was also shown in our previous publications [3,5]. For the experiments,
all of the pipes were pressurized to in 68.9kPa (10psi) with circular leaks having a
3.5mm diameter.
Clay was used to create a simulated surface fouling experiment, shown in Fig.
46
(a)
(b)
Figure 4-5: (a): Experimental setup for compressed air, (b): Robot placed inside the
setup
(a)
(b)
Figure 4-6: (a): Inside view of the clean pipe experimental setup, (b): Inside view of
the simulated limescale pipe experimental setup
4-6b. The simulated fouling was attached to standard schedule 40 plastic pipes. The
original clean pipes are shown in Fig.
4-6a.
The clay was attached manually to
allow the formation of non-uniform surfaces. After the layer of clay was attached,
the internal clearance was checked by inserting an 80mm diameter cylinder.
This
clearance check ensures that the experiment setup is created within the boundary of
the sensor module's operational range.
4.4
Leak Detection Experimental Results
The experimental results show that the sensor was able to detect the simulated leaks
in all cases.
Fig. 4-7 shows the experimental result of the test case using a clean
47
101.6mm (4in) Leak Detection Data
I
-Sensor
- Sensori
1.6F
i
r
1.25
1.1-
0
0.5
1
1.5
2
2.5
Time (s)
4
3.5
3
4.5
5
Figure 4-7: Leak detection result from 101.6mrm (41'n) pipe
101.6mm (4itn) internal diameter pipe. It is noted that distinct jumps in the FSR
readings were observed at the leak location. All experiments showed distinct signal
change at the site of the leak as shown in Fig.
sensor experimental measurement results.
4-7.
Table 4.1 summarizes the
The first column lists the pipe internal
diameters for the 4 cases considered. The second and third columns show the sensor
measurement values. They are the absolute values of the voltage differences between
the peak of the leak signals, and the average steady state voltages before the leak
signal.
The metric column combines the voltage differences from sensors 1 and 2
together using the root mean square method, given by [2,
Sf + S.,
Metric =
31
(4.2)
With this metric, the experimental data shows that the 101.6mm (4in) pipe with
simulated limescale has the most distinct leak signal.
4.5
Summary
This chapter described the experimental procedures to verify the sensor module's
ability to detect leaks in variable setups. There were total of 4 different experimental
setups for leak detection. The 3 experiments were conducted in the clean pipe with
48
Table 4.1: Summary of leak detection results
Pipe Internal
iaeters
Diameters
Sensor 1
Measurement
1 , (V)
Sensor 2
Measurement
S2, (V)
Metric
82.55mm (3.25in)
101.6mm (4in)
120.65mm (4.75in)
101.6mm (4in)
0.324
0.1225
0.093
0.088
0.2303
0
0.336
0.261
0.093
0.9348
0.4598
1.042
Limescale
different internal diameters. The last experiment was conducted in the 4in internal
diameter pipe with a layer of clay inside to simulate the accumulated lime scale in
water pipes. The experimental results show that the sensor can detect leaks in all
the experimental setup. The leak signal was most distinguishable inside a pipe with
irregular internal surface.
49
50
Chapter 5
Sensor Performance Analysis
This chapter presents experimental studies in evaluating the effects of detector shift
from the pipe centerline along with the effective area coverage of the leak by the
sensor. In practice, the sensor module may not always be in the center of the pipe
due to disturbances. Another aspect is when the contact area of the flexible membrane is affected due to pipe irregularities or some other reasons. The leak detection
capabilities were confirmed in the previous section, now the performance limits of the
sensor system are investigated.
Central Axis
.
Center Shift
Sensor Axis
ipe Wall
(b)
(a)
Figure 5-1: (a): Definition of center shift, (b): Definition of vector tilt
The detection performance is evaluated in terms of the sensor shifting and/or
titling. A center shift away from the pipe centerline and a vector tilt are described
in Figure 5-1.
The center shift is defined as an axis shift from the pipe central
51
inear Rail
Distance
Indicator
Figure 5-2: Sensor fixture for performance analysis experiments
axis while remaining parallel to it. The sensor vector tilt is defined as p. It is the
sensor's axis being tilted out of parallel with the pipe's central axis. A special fixture
with adjustment mechanisms was designed and built in order to conduct controlled
experiments. This setup allows a precise evaluation of the sensor's performance.
5.1
Experimental Setup
In order to conduct controlled experiments, a special fixture with adjustment mechanisms was designed and built. The experimental setup was also created with a custom
sensor fixture, shown in Figure 5-2. This fixture holds the sensor module as shown
in Figure 5-3. Two fixtures were attached to the ends of the sensor module's central
axis. To facilitate the sensor positioning, a linear graduated rail in Figure 5-2 shows
preset positions every 5mm. The experiments though were conducted without the
wheel assemblies and swing legs to eliminate the performance enhancing elements.
The 101.6mm. pipe setup, of section 4, was used with compressed air.
5.1.1
Magnetic Experimental Setup
The experiments were set up to identify the center shift and vector tilt limits. The
experiment used fixture shown in Fig. 5-2 with complete sensor. The resulting sensor
52
Figure 5-3: The membrane performance verification experimental setup
module set up for these experiments is shown in Fig. 5-4. To identify the limits, a
magnetic force was used to simulate a leak. The magnets are set up as shown in Fig.
5-5. The experimental cases that the setup is used for are listed in Fig. 5-6.
5.1.2
Compressed Air Experimental Setup
A set of experiments dealt with the effect of the membrane's effective area associated with the leak. The exposed controlled area shown in Figure 5-7 is the effective
area relevant for leak detection. These experiments considered 6 different effective
areas. The exposed areas varied in width by 1mm increments from 1mm exposure.
The length of the exposed area was fixed to 13.17mm. For each effective area, the
center shift values were varied. A total of 5 different center shifts were used, namely:
-10mm, -5mm,
0mm., +5mm and +10mm. Preliminary results indicated that a low
coefficient of friction between the Kapton tape and the pipe walls. In fact, in one of
the experiments, where Kapton tape covered completely a section of the membrane,
the sensor was unable to detect any leaks with. This is due to the very low coefficient
of friction.
53
Z
Figure 5-4: Assembled center shift and vector tilt experiment setup
Membrane
101.6ni (4in) Pipe
12.7mm (0.51n)
Cube Magnet
Taped 6.35mm (0.25n)
Cube Magnet
Figure 5-5: The magnet in place to produce simulated leak force
54
Center Shift Cases
Vector Shift CasesCenter Pivot
22-
W
2D
10
im5
2
11% 160
2
5
...
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(b)
(a)
Vector Shift Cases Rear Piot
Vector Shift Cases Front Pivot
16
-W
10e
Q
Fask
1
140
IA 22
o On aw f
(d)
(C)
Figure 5-6: (a): The center shift cases, (b): The vector tilt with center pivot, (c):
The vector tilt with front pivot, (d): The vector tilt with back pivot
55
t
Figure 5-7: Effective area control of the membrane
5.2
Magnetic Experimental Results and Discussion
The experiments showed that the center shift and vector tilt could influence the
performance of the sensor. Table 5.1 shows that with center shift of -15mm,
the
sensor failed to detect the leak. The experimental results for changing p (central axis
tilt angle) are summarized in Tables 5.2 to 5.4. It is noted that for the vector tilt
cases, the sensor was able to detect leak in all cases.
The center shift experiments showed that the sensor placed closer to the leak
performs better. In Table 5.1, the metric increases as the center shift value decreases.
The vector tilt experiments showed the same trend as the center shift cases. In
Tables 5.2 and 5.3, the metric increases as the membrane is placed closer to the leak.
The Table 5.4 shows that the metric is higher when the front offset is negative. In
summary, the membrane placement closer to the leak allowed the same leak force to
be measured with higher metric value.
The values of p for the limits can be calculated using the fixture spacing.
The
distance between the universal joints in the fixture was measured to be 178.73mm.
From the length of the sensor's central beam, the tilt angles are calculated.
center pivot has maximum allowable tilt angle of
has maximum allowable tilt angle of
4.80'.
56
The
9.53'. The front and back pivot
Table 5.1: Summary of results for center shift experiments
Center Shift (mm)
0
5
10
15
-5
-10
-15
Sensor 1 Difference (V)
Sensor 2 Difference (V)
Metric (V)
1.1079
0.6910
0.3430
0.0440
0.8379
0.9653
N/A
0.8130
0.6380
0.5240
0.0740
0.7595
0.7399
N/A
1.3742
0.9405
0.6263
0.0861
1.1309
1.2162
Table 5.2: Summary of results for vector tilt about the center pivot
Front Offset (mm)
Back Offset (mm)
Differnsore(V)
Differne 2(V)
Metric (V)
5
10
15
-5
-10
-15
-5
-10
-15
5
10
15
0.2744
0.2205
0.5292
0.5390
0.5341
0.4214
0.4704
0.4900
0.6762
0.6076
0.5439
0.4802
0.5446
0.5373
0.8587
0.8122
0.7623
0.6389
Table 5.3: Summary of results for vector tilt about the front pivot
Front Offset (mm)
Back Offset (mm)
Differnce1(V)
0
0
0
0
0
0
-5
-10
-15
5
10
15
0.5537
0.7644
0.8722
0.5978
0.4214
0.2205
Dif erensore2
Metric (V)
0.6076
0.6468
0.6272
0.4459
0.4312
0.4116
0.8220
1.0013
1.0743
0.7458
0.6029
0.4669
Table 5.4: Summary of results for vector tilt about the back pivot
Front Offset (mm)
Back Offset (mm)
Differnce (V)
Differne 2(V)
Metric (V)
-5
-10
-15
5
10
15
0
0
0
0
0
0
0.7938
1.0094
0.9653
1.1270
0.2793
0.2352
0.7546
0.8820
0.8624
0.8379
0.5292
0.3528
1.0952
1.3405
1.2944
1.4044
0.5984
0.4240
57
Membrane Performance Analysis: Effect of Distance and Exposed Area
R
-e-Exposed Ratio 0.29
0.-
-0-Exposed RPto 0.57
+-Exposed
Ratio 0.86
0.8
-- Exposed Ratio 1.14
-+-Exposed Ratio 1.43
-*-Comp"eel Exposed
c0.6
0.7
--
20.3
0.44
--
0.2-
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Normalized Distance Between Membrane and Leak
0.8
0.9
1
Figure 5-8: Summary of experimental results from performance analysis of flexible
membrane
5.3
Compressed Air Experimental Results and Discussion
The experiments showed that larger exposed areas provide better sensor performance.
The data also indicates that the sensor measurement voltage differences increase, as
the exposed ratios are increased. The exposed ratio is obtained by dividing the width
of the exposed membrane by the leak diameter. In these studies, the leak diameter
was set to 3.5mm. The sensor was able to detect such size leaks with an exposed
membrane area of 13.17mm 2 and a center shift ranging from 0mm to -10mm.
The results for different exposed membrane areas and center shifts are summarized
in Figure 5-8. The distances from the leak are normalized. A 0 value represents the
-10mm
central shift while 1 represents the +10mm central shift. Figure 5-8 shows
that the measured voltage increases as the sensor is moved closer to the leak. The
outliers in the Figure are likely due to experimental errors.
These include manual
pressure valve control, alignment error of the membrane exposed area relative to the
leak.
58
5.4
Summary
This section presented two different experiments to analyze the performance of the
sensor. The first set of experiments used a pair of magnets to simulate leak forces.
The purpose of the first set of experiments were to identify the sensor's limit in terms
of center shift and vector tilt. The sensor can operate with center shift of t10mm.
The sensor can operate with p =
can operate up to p =
9.53' when pivoting about the center. The sensor
4.80' when pivoting about front or back.
The second set of experiments used compressed air, similar to the leak detection
experiments.
The purpose of the second set of experiments were to observe the
relationship between the sensor performance and the effective area of the membrane
and the center shift.
It was found that larger effective area of the membrane and
center shift towards the leak yields better performance.
59
60
Chapter 6
Conclusion & Recommendations
A flexible in-pipe leak detection sensor was developed for pipes with varying diameters and with irregular inner walls.
The prototype performance was validated in
pipes with internal diameters of 82.55mm (3.25in), 101.6mm (4i'n) and 120.65mm
(4.75in). In addition, the prototype was also tested with irregular pipe surfaces due
to fouling. Limescale was simulated using clay inside a 101.6mm (4in) pipe. Leaks
were successfully detected in these different types of pipes.
The detection performance of the .sensor was also analyzed.
The sensor shift
from the pipe centerline and effective membrane area influenced the performance.
Experimental results showed that the leak signal is amplified with center shift moving
towards the leak. The performance also improved with a larger effective area of the
membrane. This sensor module can be attached to a propulsion robot such as the
ones described [13,15].
For the future, the sensor module described in this thesis can be attached to
propulsion robots described in previous literature [131.
The propulsion module of
the robot developed in [13] has major diameter of 85mmrn which cannot operate in
the 80mm pipe.
A new propulsion robot using the motor developed in [151 can
be created for this task. The addition of an autonomous propulsion module to the
flexible membrane sensor module would allow the inspection of water pipelines with
accumulated limescales. In addition to developing an integrated propulsion and sensor
system, more effort could be directed towards studying the performance of the sensor
61
module when attached to a swimming type propulsion system.
62
Appendix A
CAD Drawings
This appendix shows the technical drawings of the flexible leak detector.
The completed assembly drawing is shown in Fig. A-1. The assembly drawing
contains gimbal mechanism and wheel assembly. The drawing also shows the swing
arm assembly.
Figures A-2 to A-4 show the components for the gimbal mechanism. The gimbal's
samll ring in Fig. A-4 is fixed to the main shaft in Fig. A-2 with pins. The drum in
Fig. A-3 is then fixed to the gimbal ring using pins.
The wheel assembly components are shown in Fig. A-5 to A-9.
The Fig. A-5
shows the completed wheel assembly. The balloons in the Fig. A-5 indicates how
each components are assembled together.
The swing arm assembly is constructed with two different components. The Fig.
A-10 shows the swing arm assembly base. The assembly base is where the swing arms
are attached. The swing arms are fabricated according to Fig. A-11. The swing arm
assembly base is slided on to the main shaft in Fig. A-2.
Finally, the experimental fixture assembly drawing is shown in Fig. A-12. All the
components that are required to build a single fixture is listed in the bill of materials
chart in Fig. A-12. The component drawings are shown in figures A-13 to A-19.
63
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