Design of a Robotic Water-Pipe Rehabilitation System by Yip Fun Yeung Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Science and Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2019 © Massachusetts Institute of Technology 2019. All rights reserved.
Sigatue edacted A uthor ...... I f Department of Mechanical Engineering May 19, 2019 Signature redacted Certified by.. Kamal Youcef-Toumi Professor Thesis Supervisor Signature redacted Accepted by ...... Nicolas Haijiconstantinou FTEO Chairman, Department Committee on Graduate Thesis JUN 13 2019 LIBRARIES H
2 Design of a Robotic Water-Pipe Rehabilitation System by Yip Fun Yeung
Submitted to the Department of Mechanical Engineering on May 19, 2019, in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Science and Engineering
Abstract Corrosion in water pipeline causes leak and forms tubercle at the vicinity of leaks. Various in-pipe robots have been developed in recent years for locomotion and in- spection along the pipeline. Not much focus is put on in-pipe operations such as pipe maintenance and rehabilitation. This thesis presents an in-pipe robotic system for minimal particle contamination obstruction removal operation of corroded water pipes. It proposes a robotic system with a Manipulation Module and a Compliant Surface Adaptation Module. The Manipulation Module contains a 4-Degree of Free- dom robotic manipulator that is able to remove tubercle in 102mm diameter pipes. The Compliant Surface Adaptation Module contains optimized designs to enclose a watertight volume on a macroscopically rough surface. This robotic platform is the first in-pipe robot designated to rehabilitate water pipe with minimal contamination.
Thesis Supervisor: Kamal Youcef-Toumi Title: Professor
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Acknowledgments
I am honored to express my deepest thank to my advisor, Prof. Kamal Youcef-Toumi, for guiding me with extensive knowledge and patience through my first two years at MIT. His vision in future and persistence in details set everyone in Mechatronics Research Laboratory a good model. It is a pleasure for me to learn from and work with such a great professor. I would also like to take this time to thank our sponsor, Mathearth.Inc. Without their proficient resource and technology guidance, this project wouldn't have been possible. I am also grateful to Boston Water and Sewer Commission, for providing us with valuable samples of water pipes and practical advice in water network. I am very thankful to my colleagues on this project, Tyler Okamoto, Xiaotong Zhang and Elizabeth Mittmann for our daily collaboration. They are also excellent mates outside the lab. I really enjoy our time supporting each other. My deepest gratitude towards my friends at MIT and Harvard, especially Chen, who stood by me days and nights for the last two years. Best of luck in your future work. Last but not least, I wish to thank my family members for providing me with consistent love and mental support. I would like to dedicate this thesis to my pet, Sam, who passed away last week after being my dearest friend for 12 years. Rest in peace brother.
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Contents
1 Introduction 17 1.1 Motivations for Water Pipe Rehabilitation ...... 17 1.2 Background of Water Pipe Rehabilitation ...... 18 1.2.1 Rehabilitation Process ...... 18 1.2.2 Robotic In-Pipe Solution ...... 19 1.3 Thesis Outline ...... 21
2 System Overview 23 2.1 Proposed System Layout ...... 23 2.2 Design and Work-flow ...... 24 2.3 Sum m ary ...... 26
3 Compliant Surface Adaptation Module - Design 27 3.1 Background of seals ...... 27 3.1.1 Dynamic Seal ...... 28 3.1.2 Static Seal ...... 29 3.2 CSAM Functional Requirement ...... 29 3.3 Design Overview ...... 30 3.4 Modelling and Analysis ...... 31 3.4.1 Objective and Review 31 3.4.2 Silicone Cross-section Optimization ...... 32 3.4.3 Compression Spring Suspension Optimization 42 3.5 Sum m ary ...... 46
7 4 Compliant Surface Adaptation Module - Implementation 47 4.1 Silicone Cushion ...... 47 4.1.1 Material Selection ...... 48 4.1.2 Substrate Surface Roughness ...... 50 4.1.3 Design Process ...... 51 4.1.4 Finalized Design ...... 54 4.2 Compression Spring Suspension ...... 55 4.3 Fabrication ...... 56 4.4 Design Process Summary ...... 57 ...... 4.5 Chapter Summary ...... 57
5 Manipulation Module 59 5.1 Functional Requirement ...... 59 5.2 Mechanical Design ...... 60 5.2.1 Assumption ...... 60 5.2.2 Design Description ...... 60 5.2.3 Forward Kinematics ...... 62 5.2.4 Force Analysis ...... 64 5.3 Controller Design ...... 66 5.4 Material Selection ...... 67 5.5 Summary ...... 68
6 System Integration 69 6.1 System Prototype ...... 69 6.2 Experiment Overview ...... 71 6.2.1 CSAM Test ...... 71 6.2.2 Kinematics Test ...... 72 6.2.3 Maneuverability Test ...... 74 6.2.4 Corroded Pipe Surface Treatment 75 6.3 Summary ...... 77
8
q1 11R111" "W-W-1 7 Conclusion and Recommendation 79 7.1 Thesis Summary and Contribution ...... 79 7.2 Recommendations for Future Research ...... 80
A Persson Contact Theory 81 A.1 Persson Contact Theory Key Equations ...... 81 A.2 Surface Roughness Parameters from PCT ...... 82
B Concept Validation for CSAM 85
9 10 List of Figures
1-1 Illustration of the leak detection method using a suction force caused by a pressure gradient...... 1 9 1-2 Karso Working Robot...... 20
2-1 Proposed work flow for each sub-system of MRL pipe rehabilitation robot ...... 24 2-2 Demonstration of the Manipulation Module ...... 25
3-1 Demonstration of a dynamic seal...... 28 3-2 Mildly corroded water pipe...... 30 3-3 Severely corroded water pipe section obtained from Boston Sewer and Water Commission...... 31 3-4 Final design of CSAM...... 32 3-5 Exploded view of CSAM...... 33 3-6 Demonstration of CSAM application...... 34 3-7 Demonstration of self-affine surface...... 35 3-8 Dimensional analysis of two H2 values...... 38
3-9 Dimensional analysis with 14/U15...... 39 3-10 Grooved CSAM silicone cross-section...... 40 3-11 Grooving the cross-section significantly reduces 11,...... 40 3-12 Experimentally determine aspect ratio to maintain structural rigidity. 41 3-13 Change in pipe wall profile statistically affect average height of the tub ercle...... 42 3-14 Simplified model of silicone-spring assembly...... 43
11 3-15 Compression spring suspension materials and critical dimensions. .. 45
4-1 Experimental setup for Compression Experiment I...... 48 4-2 Compression Stress-Strain curve for Ecoflex 00-30...... 49 4-4 Topology of 3d-printed rough surface to simulate tubercles...... 50 4-5 Height distribution of the 3d-printed rough surface...... 50 4-3 Power spectrum for the 3d-printed rough surface...... 50 4-6 Dimensionless H groups for the 3d-printed substrate...... 51 4-7 Dimensions of cylindrical specimens...... 52 4-8 Leak experiment setup...... 52 4-9 Leak pressure pi for the cylindrical tests...... 53 4-10 Experimental and theoretical result represented in dimensionless H group ...... 54 4-11 Finalized design of silicone cross-section...... 55 4-12 Fabricated CSAM ...... 56
5-1 Demonstration of MRL pipe rehabilitation robot and global coordinates. 60 5-2 Robot kinematics and D-H notation for robotic platform...... 61 5-3 Workspace for the spindle and the CSAM when in contact with 102mm diameter pipe surface...... 63 5-4 End effector workspace for the 22mm tool head...... 64 5-5 Bench-top tubercle removal experiment...... 65 5-6 Force analysis of MPCOR...... 65 5-7 Schematic for automated tubercle removal task...... 66
6-1 Prototyped CSAM with modifications to connect with Manipulation M odule...... 69 6-2 Prototyped MPCOR. A: 2-DOF Manipulator; B. CSAM; C. CSAM attached to Manipulation Module; D: Full assembly of MPCOR. . . . 70 6-3 Mock rough surface board with obstructions and height drops corre- sponding to tubercle and pipe profile change...... 71
12 6-4 Experiment demonstrates the good sealing performance of CSAM with grooved design and compression spring suspension...... 72 6-5 Step response of each joint of Manipulation Module given a simulated deploym ent task...... 73 6-6 Prototyped MPCOR is tested in a 102mm pipe with 3d-printed tubercle. 74 6-7 MPCOR in maneuverability test...... 75 6-8 MPCOR in maneuverability test...... 76
A-1 Energy equilibrium of Persson Contact Theory...... 82
B-1 Surface contact FEA of hyperelastic material...... 86
13 14 List of Tables
3.1 Unit for each parameter in fundamental dimensions...... 37 3.2 H group representation for the silicone cushion analysis...... 37 3.3 Modified H group representation for the compression spring suspension analysis...... 38
5.1 D-H parameters for MPCOR Manipulation Module...... 63 5.2 Range of motion of each joint...... 63 5.3 Actuator and gearbox selection for each joint...... 67
15 16 Chapter 1
Introduction
1.1 Motivations for Water Pipe Rehabilitation
Water pipe leak is causing significant losses in natural and human resources around the world. In the United States and Canada, there is an approximately 10% loss due to pipeline leakage before water reaches its consumer, and over 240,000 water mains break per year. In developing countries, water loss rate can be up to 40% [1][2][3]. The world spends trillions of dollars annually for water pipe maintenance and compensating leaked water. Under such pressing conditions lie great opportunities in water pipeline rehabilitation and protection. The two major failures faced by water pipelines are pipe leakage and tubercles. Both problems can be traced down to corrosion [4]. The corrosion process first starts with the attachment of aerobic and anaerobic bacteria onto pipe wall [5]. The anaero- bic bacteria need to build a shelter to block oxygen, thus reduction-oxidation reaction takes place on the pipe wall. The reaction slowly removes elements from the pipe wall and builds shelters around the bacteria. At the anode site, these shelters eventually become tubercle. At the cathode site, as more elements are taken, the thickness of the pipe wall decreases and eventually leads to a leak. In some extraordinary cases, more than 50% of pipe diameter can be obstructed by tubercles. Although tubercles have negligible impact on consumer health, they significantly reduce flow rate, place an extra burden on water station and increase the risk of water pipe outburst.
17 Although water pipeline failure is a tremendous issue worldwide, rehabilitation of water pipes seems to be a neglected area. Contrary to the blooming technol- ogy developments in robotics, artificial intelligence and Internet of Things, the most commonly used pipe rehabilitation 'technology' is still digging out and replacing the entire pipe. Such conventional methods are extremely labor-intensive, usually includ- ing an extensive amount of manpower in digging and setting up temporary pipelines. Water service needs to be shut down and neighborhood around the area end up with muddy flood everywhere. Such situations make technology development in water pipe rehabilitation a must.
1.2 Background of Water Pipe Rehabilitation
1.2.1 Rehabilitation Process
There are three steps for a successful pipe rehabilitation job. They are removing tu- bercles, fixing leakage and post-treatment. No matter the rehabilitation is performed by a human or a robot, the process still entails the exact three steps, unless the entire pipe is replaced. First, tubercle along the pipe, or at least, at the vicinity of leaks should be removed. This process is normally called 'pigging'. The goal of pigging is to provide clear access to the device or adhesive that is going to be used to fix the leak. For pipes with larger diameters, workers are sent in to remove the tubercle. Faster and more efficient pigging techniques include mechanical pigging, ice-pigging and metal-scrapping the entire pipeline. The second and third steps are fixing the leak and doing the post-treatment. The goal is to get rid of any leak along the pipeline and prevent future corrosion from reoccurring. Aside from replacing the entire pipe, Nu-Flow [6] and UV curing repair are the latest technologies into pipeline rehabilitation. Corrosion resistant chemicals or UV adhesives are blown along the pipe wall to seal leaks after the pigging process. Without sufficient post-processing of pipe wall, tubercles and leaks are likely to return in a more intense manner.
18 1.2.2 Robotic In-Pipe Solution
In-pipe robots (IPR) provide an alternative solution to pipe rehabilitation. Compar- ing to conventional rehabilitation techniques, robotic solutions possess advantages in all aspects. First, the covered pipe.length for a single rehabilitation job is increased. Previously, even with trenchless repair techniques such as UV curing and Nu-Flow, only a few meters of pipes can be repaired in a single run. With untethered robots in pipe network, hundreds of meters of pipes can be repaired with a single deployment. Additionally, in-pipe robots can reduce human labor to a minimal amount. Another advantage of in-pipe robots is that they can focus on local defects along the pipeline. In case when there's only one 2mm pinhole leak along a 5m pipe, IPRs are able to repair only the leak site while conventional methods need to repair a much larger por- tion of the pipe, wasting time and resource. In the near future, swarms of IPRs can form pipeline networks. The entire water pipe system can be built into an ecosystem. IPRs with various functions such as leak detection, pipe rehabilitation and communi- cation patrol along its designated pipes, talk to each other and distribute tasks based on data gathered from each other.
outsie the pipe suchonforce low pressure region leak pipe wal _ _ _ _J ic force mm
Mw bie motion Inside the pipe pusurmdbuId envtrment
Figure 1-1: Illustration of the leak detection method using a suction force caused by a pressure gradient [7].
Such a huge potential shifts the focus of numerous research labs and companies towards In-Pipe Robots (IPR). Saga et al. [8] proposed an IPR with inchworm driving mechanism. Kakogawa et al. [9] developed a crawler IPR that utilizes underactuated
19 four-bar linkage to overcome obstacles. Pratama et al. [101 designed an automatic wheeled driving robot using fuzzy control logic to fit various pipe diameters. Nayak et al. [11] put focus on pipeline inspection. Chatzigeorgious et al. [12] proposed reliable sensing techniques inside pipelines. Most of these works focus on the locomotion and sensing modules of IPR. Despite the prosperity in locomotion module and pipe- adaptation module of In-pipe Robots, few are designed for pipe rehabilitation. Wu et al. [7] designed a passive in-pipe leak sensor that utilizes a suction force, caused by a pressure gradient at the vicinity of the leak, as shown in Fig.1-1. This concept provides a possibility for future research direction. On the commercial side, KA-TE [13] developed a series of intelligent robot that repairs pipe joints with Ultraviolet (UV) adhesives. ProKarso [14] proposed a 2 Degree-of-Freedom (DOF) manipulator installed on a locomotion module that is able to remove obstructions with a Direct Current (DC) motor driven grinder, demonstrated in Fig.1-2. Such robots are by far the most advanced ones in pipe rehabilitating.
Figure 1-2: The Karso Working robot contains a 2-DOF manipulator and a DC motor grinder [14].
In-pipe robot is a promising pathway for water pipe rehabilitation, yet quite a few challenges exist. Pipe size is one of the challenges. Even as advanced as KA-TE and ProKarso, neither robot targets small pipes, i.e, pipes under 100mm in diam- eter, which are very common in urban pipe networks. The absence of IPR dealing with small diameter pipes is caused by the complexity of arranging multiple actuators compactly while maintaining maneuverability. Another consideration lies in the con- tamination made by IPRs during the tubercle removal process. IPR tubercle removal process generates a huge amount of particles and chemical waste. It is crucial for
20 IPRs to contain all contamination so that they are able to operate with the pipeline in service. To the author's knowledge, there hasn't been any effort made in this area. Other challenges include communication, power consumption and localization [15].
1.3 Thesis Outline
In this study, the Minimal Particle Contamination Obstruction Removal system (MP- COR) is designed and implemented. This is a major sub-system of the Mechatronics Research Laboratory (MRL) pipe rehabilitation robot. There are two major break- throughs in this robot. First, it is the first IPR that takes care of particle contamina- tion during the pipe rehabilitation process and it is, in fact, one of the few pioneering pipe rehabilitation robots. Second, it is the first high-DOF rehabilitation robot that can operate in pipes under 100mm diameter. The MRL pipe rehabilitation robot is designed to be deployed in both in-service and dry pipelines. As mentioned previously, an important function required for IPR to operate in such pipelines is to be able to contain the contamination generated by tubercle removal. The designed robot carries a Compliant Surface Adaptation Module (CSAM) to create a completely enclosed volume on tuberculated pipe walls to collect all the debris. It combines optimized geometries and mechanical components to minimize actuator burden to seal corroded pipe surface and is the pioneering device in such application. The main body of the MPCOR is a Manipulation Module(MM). The challenge is due to the confined in-pipe environment. Most IPRs either have a very limited workspace, low Degree-of-Freedom or can only operate in large diameter pipes. The study presents an arrangement for a 4-DOF manipulator that can operate in 102mm diameter pipes. This manipulator also includes an integrated spindle for tubercle removal process. This robot is also highly modularized to satisfy the needs of various tasks. This thesis is organized as follows: Chapter 2 describes the overview of the MRL Pipe Rehabilitation Robot system. Chapter 3 includes the theoretical work behind
21 CSAM module. Chapter 4 contains experiments and design process of CSAM. Chap- ter 5 describes the design of the robotic Manipulator Module. Chapter 6 illustrates the integrated robot and performance tests. Chapter 7 summarizes this thesis and provides recommendations for future work.
22 Chapter 2
System Overview
In this chapter, we provide an overview of the of MRL pipe rehabilitation robot. In Sec.2.1, the system layout of the robot is presented. In Sec.2.2, the robot working procedure is described.
2.1 Proposed System Layout
A successful pipe rehabilitation task involves three steps, removing tubercle, fixing leak and post-treatment. To accomplish this, MRL pipe rehabilitation robot contains at least four sub-systems, a Locomotion system, a Leak and Obstruction Detection system, a Minimal Particle Contamination Obstruction Removal system and a Leak Repair system. This study focuses on the Minimal Particle Contamination Obstruc- tion Removal system and its two modules. The overall functionality of each sub-system is presented in Fig.2-1. In the begin- ning, the robot patrols along the water pipe with its Locomotion system. Its Leak and Obstruction Detection system alerts the operator with the existence of a leak. Information such as surrounding tubercle height, leak location and size are recorded or sent to the operator. The Locomotion system embraces the robot rigidly to the pipe wall. After this step, the rehabilitation process takes place. Minimal Particle Contamination Obstruction Removal system is first activated. The function of the MPCOR is to create a completely enclosed environment around the leak. Tubercle
23 around the leak is removed by the MPCOR while no tubercle debris is released out of the sealed environment. After the removal process is completed, the MPCOR collects the debris. When the leak is successfully repaired, the robot re-starts the patrolling sequence and moves on to the next leak site.
Leak-a------Leak andI Locomotion Obstruction MPCOR Leak Repair Detection
Seal Surface Debris Formation Treatment Collection I
L E
Figure 2-1: Proposed work flow for each sub-system of MRL pipe rehabilitation robot.
The MRL robot is a pipe rehabilitation robot designed to work in both in-service and dry water pipes. As a first step towards in-pipe robotic rehabilitation, this study focuses on the dry deployment scenario. However, during the design process, the limitation of in-service deployment is considered and space for future mechanical upgrades is held. The difference between the two working environments lies in the debris collection sequence. In both scenarios, the debris should be flushed out of the pipe through the leak site. For a dry environment, the robot carries an appropriate flushing system. After the tubercle is completely removed, a water pump rinses the sealed environment and flush out the debris. In case the robot is operating in an in-service water pipe, a water valve is used to control the flushing process. The complexity lies in water-proofing electronics and high power requirement to fight against water pressure.
2.2 Design and Work-flow
The MPCOR system includes a Compliant Surface Adaptation Module, discussed in Chapter 3 and 4 and a Manipulation Module, presented in Chapter 5. The Manip- ulation Module is made up of a serial 4-DOF robotic manipulator and a spindle as an end effector. It robotic manipulator consists of two revolution (R) joints and two
24 prismatic (P) joints in series, as shown in Fig.2-2. The Compliant Surface Adaptation module is made up of a silicone cushion and a compression spring suspension. The spindle is mounted on the last link and the CSAM is mounted on the second link. For the dry water pipe scenario, a cleaning system is attached to CSAM. It ejects rinsing fluid through a nozzle installed on the silicone cushion.
Link 4, Joint-Z Link 3, Joint-R Link 2, Joint-4Bar Link 1, Joint-Theta
Figure 2-2: Demonstration of the Manipulation Module
The Manipulation Module and Compliant Surface Adaptation Module work to- gether to finish the task. The first and second joints of the manipulator are controlled to press the CSAM against the pipe wall to create a completely enclosed environment around the spindle. The third and fourth joints then control the position of the spin- dle for it to grind or drill. The debris generated is contained in the CSAM. After the tubercle within the spindle's workspace is removed, the nozzle mounted on the sili- cone cushion wall flushes cleaning fluid to collect the debris and rinse the treated pipe wall. Finally, the first and second joints re-position the spindle for another tubercle removal process.
25 2.3 Summary
In this chapter, the work-flow for MRL pipe rehabilitation robot and required system layout is proposed. MRL pipe rehabilitation robot should contain a Locomotion system, a Leak and Obstruction Detection system, a Minimal Particle Contamination Obstruction Removal system and Leak Repair system. This study focuses on the design of the MPCOR, which contains two modules, the Manipulation Module and the Compliant Surface Adaptation module. The major components for each module are described and the coordination between the two modules is illustrated. The detailed designs are contained in Chapters 3, 4 and 5.
26 Chapter 3
Compliant Surface Adaptation
Module - Design
There are two critical modules for the MPCOR. The Manipulation Module operates an end-effector to clean off any obstructions at the vicinity of the pipe leak. During this process, the Compliant Surface Adaptation Module encloses a watertight sur- rounding for the spindle to prevent any debris from falling out and contaminating the pipeline. In this chapter, the Compliant Surface Adaptation Module is introduced. It is designed to minimize force requirement. Modeling and theoretical analysis of CSAM components are introduced. Step-by-step guidance for future designers is also presented.
3.1 Background of seals
In this section, we briefly review the sealing device that is currently used in human activities. Reviewing state-of-the-art seals facilitate understanding why these seals cannot function in the CSAM application and reveal the importance of CSAM. Seals can be divided into two main categories, dynamic seals, normally referred to as me- chanical seals, and static seals. Different types of dynamic seals are presented along with current static seals.
27 3.1.1 Dynamic Seal
Dynamic seals are sealing devices that are installed on machines to prevent leak when two mating parts are in reciprocal or rotational motion. Depending on its arrange- ment, there are pusher/non-pusher, hydrodynamic/hydrostatic, balanced/unbalanced and single-spring/multi-spring type. They are commonly used on the shaft of fluid pumps.
Sal - 1br leod,g
Seal (oflower
Mal
Sprin Rer
Figure 3-1: Demonstration of a dynamic seal [16].
Dynamic seals consist of two major components, a primary seal that is used to seal the relative motion and secondary seals such as o-rings to seal the components of the primary seal. For example, on a water pump, the primary seal is made up of a rotor that rotates with the shaft and a stator that is fixed on the pump body. The two parts are pressed against each other with different spring arrangements. The major challenge for dynamic seals is to seal the mating surface between the rotor and the stator while maintaining enough lubrication. Both sealing and lubricating are either achieved by filling the mating gap with working fluid or specialized sealing liquid. The secondary seals are static seals. O-rings are used in almost every case. Obviously, the primary seal is not applicable in CSAM application because there is no relative motion once the manipulators are in place. The only applicable reference for CSAM is the static seal.
28 3.1.2 Static Seal
Static seals possess many forms. Heat seal and induction seal are used in production lines to wrap products. These seals include special types of machinery and application scenarios are very limited. Face seal is the most common type of static seal. Gaskets and o-rings both belong to this category. This type of seals is placed in between two mating parts. Under compression, the seal fills in the irregularities on the mating surfaces and prevent fluid or gas leakage. A common application is head gaskets in car engines. It is used to seal the upper and lower half of the combustion chamber to ensure no coolant or engine oil is leaked into the engine cylinder. The two keywords of face seals are compression and rough surface. This is very similar to the MPCOR application. The CSAM is pressed against the corroded pipe surface by a robotic manipulator to create a completely sealed volume on that surface. For corroded water pipes, the rough surface can display peak-valley height difference up to centimeters. Current gaskets or o-rings cannot be applied to the CSAM application because they are used to seal machined surfaces, which only possess microscopic roughness. 0- rings and gaskets also require high compression pressure, on the scale of MPa, to operate. Given compact space in water pipes, it is very challenging to carry actuators that are able to deliver such power. In the CSAM application, the thickness of the sealing device can be no more than 2 - 3cm. With tubercle height in mm or cm, this means that the sealing device needs to endure extreme strain. The CSAM uses hyperelastic material such as silicone to solve this challenge. By optimizing sealing device's material, geometry, and supporting method, the CSAM requires minimal compression force to create a complete seal. The details are discussed in this chapter and Chapter 4.
3.2 CSAM Functional Requirement
Corroded pipe wall is extremely rough, with tubercles of arbitrary heights. The CSAM is designed to accommodate uneven surface as an approach to avoid particle contamination introduced by cutting or grinding the obstructions. Tubercles inside
29 corroded water pipes possess various sizes and shapes depending on the stage of corrosion. For example, Fig.3-2 demonstrates an early-stage corroded pipe section. The severity of such corrosion should be covered by the CSAM. In cases of extremity, shown in Fig.3-3 is a 152mm (6-in) diameter corroded water pipe sample that is obtained from the Boston Water and Sewer Commission (BWSC). The corrosion is very intense, covering more than 50% of the pipe cross-section. The maximum tubercle height from the pipe wall is over 20mm. This extreme kind is not considered in this study.
Figure 3-2: Mildly corroded water pipe. [171
The CSAM is designed and implemented to create a sealed environment for the spindle to operate on such rough surfaces. Based on the deployment scenario, it should be highly deformable when it is pressed against a rough pipe surface. More specifically, the CSAM should be able to operate inside 101mm (4-in) diameter corroded water pipe. The maximum obstruction height CSAM can accommodate should be at least 5mm. CSAM should not interfere with spindle operation on any occasion. The design should be scalable for water pipes with various diameters.
3.3 Design Overview
The finalized design of CSAM consists of three components, an elastic cushion, a compression spring suspension, and a supporting base, as shown in Fig.3-5. When it
30 A*
Figure 3-3: Severely corroded water pipe section obtained from Boston Sewer and Water Commission. is pressed against a pipe wall under applied pressing force, the cushion is in direct contact with the tubercle and the compression spring assembly act as a floating support for the cushion. The entire design is optimized so that the minimum applied pressing force is needed for the CSAM to create a completely sealed environment.
3.4 Modelling and Analysis
3.4.1 Objective and Review
The objective of the CSAM is to optimize the cross-sectional shape of the silicone cushion and design of compression spring suspension so that it can create a fully enclosed environment on the pipe wall with minimal pressing power. Theoretical modeling of the design is divided into two parts. We first investigate and optimize the silicone cross-section, then the effect of compression spring suspension is analyzed.
31 Figure 3-4: Final design of CSAM.
3.4.2 Silicone Cross-section Optimization
Surface Contact Mechanisms
Sealing rough surfaces with elastic components, such as o-ring and gaskets, is one of the most common applications in hardware design. However, despite its popularity, theoretical analysis of o-rings and gaskets are not broadly studied. The sealing ap- plication can be categorized as a surface contact problem. Surface contact theories describe analytically the deformation of a surface when it's pressed against a sub- strate. Quite a few contact theories have been developed since the 1 9 th century. The pioneering work is done by H.Hertz in 1880s [18], in which he described the contact between 'flat' surfaces as contacts between very small elastic solids with parabolic shapes. The work is based on the assumption that these solids are spherical bumps with equal radius. Greenwood and William published the first rough surface contact model in 1966 [19], in which the elastic solids are modeled with equal radii and at different heights. Starting from 1975 [20], more advanced multi-asperity contact the- ories are studied. A widely used model is the Bush, Gibson, and Thomas (BGT) model, which considers asperities at various length scales. Despite the abundance of contact theories, few are applicable to this study. All mentioned contact theories are suitable for 'machined' surface, where there's no macroscopic bumps or dents. In water pipes, the condition is not similar. Simply observing the corroded water pipe wall, it can be seen that tubercles have arbitrary
32 Figure 3-5: Exploded view of CSAM. A. Elastic Cushion; B. Compression Spring Suspension; C. Supporting Base.
profiles, not even close to a parabolic shape. Nonetheless, a novel contact mechanics being developed by Persson [21][22][231 since 2000s serves as a good reference for this study. Persson did not approach the surface contact problem by assuming the shape of the asperities, instead, he looked at the overall surface roughness power spectrum density (PSD). The advantage of utilizing the power spectrum density is that the PSD does not assume the shape of the substrate a priori. In addition, it not only evaluates the vertical difference of a rough surface, but also the horizontal distribution of height difference [24]. Some important details of Persson's Contact Theory are presented in Appendix.A.
Design Parameters
The simplified model of the CSAM application can be seen as a long rubber block bonded to a rigid plate is pressed against to a rough surface by pressure, as indicated in Fig.3-6. Intuitively, the applied compression pressure pa on the silicone is dependent on surface roughness of the substrate, silicone material, silicone geometry and the
33 amount of deformation experienced by the silicone. In this sub-section, we present dimensionless analysis for this relationship.
HMaterial Property: E
Pa P.
Figure 3-6: Demonstration of CSAM application.
Corroded water pipe walls have randomly distributed height and shape at different length scale, the most scientific and widely-applied method to describe the surface is through power spectrum C(q), where q is the roughness wavevector [25]. It is very similar to the power spectrum density widely applied in signal processing, where the power for each frequency is calculated using Fourier Transform. In a 2-D space, the wavevector space is denoted as q (q2, qy) and q = g2 + q2. The power spectrum is calculated with Eqn.(3.1),
C(q) =(2)2 (h(x)h(O))e -iTxd2x (3.1) where (... represents the ensemble average, x = (x, y) is the coordinate of the surface and h(x) is the height at x above the average height h(x) = 0. Since it is impossible to get the continuous height for a real surface, the power spectrum is always calculated discretely. The equations are presented in [26]. Further, the corroded water pipes can be described as self-affine fractal. As shown in Fig.3-7, self-affine fractal surfaces have the property that when a part of it is mag-
34 Imedium
smaul
Figure 3-7: Demonstration of self-affine surface [22].
nified at different magnification (, the profile is roughly the same and the statistical properties are invariant [22]. For self-affine fractal surfaces, Persson extracted two independent parameters # and uO from PSD in [27][281. The two values do not have defined physical meanings, but one can interpret that a greater # or smaller uo repre- sents a rougher surface. Calculating # and uo is very complicated and the equations are attached in Appendix.A. The last important parameter for the surface roughness is the maximum peak-valley height difference of hmax. The information of hma, is indeed contained in C(q). However, it is treated as an independent parameter due to its importance and trivial dependence with # and uO.
Now that the information from the substrate is extracted, the silicone properties are investigated. For the Compliant Surface Adaptation Module, the designed silicone rubber block has a rectangular cross-section with a height of H and thickness of T. The penetration of rubber block into the substrate is given the term w, as shown in Fig.3-6. Assume that the selected silicone has a compression modulus E and Poisson's ratio v. Since the silicone cushion is rigidly bonded to the base, i.e., no slip relative to the base. Under this condition, the effective modulus is dependent upon shape factor S [29][30], which is determined by the dimension of the rubber block. Gent and Lindley [31] introduced the equations to approximate apparent Young's modulus
35 Ea for compression of bonded rubber blocks
Ea = E( + 4 S2) (3.2) 3 3 for infinitely long rubber blocks. Shape factor can be calculated with S = where T is the rubber width and H is the rubber height. The shape factor is derived as the ratio of loaded surface area over force-free area. For cylindrical disks, the apparent Young's modulus is approximated with
Ea = E(1 + 2S 2 ) (3.3) where S = and r is the cylinder radius. An extra term effective shape factor
Se = Ea/E is defined as a more straightforward expression.
In conclusion, we have eight independent parameters to evaluate the applied com- pression pressure Pa; for surface roughness, three parameters, 3, uo and hmax; for the silicone geometry, H and T, the cross-section; for silicone material, the compression modulus E and Poisson's ratio v; and the silicone's penetration w in to substrate.
Dimensional Analysis
Due to the massive amount of independent variables, it is clearer and more convenient to express the relationship in a group of dimensionless terms, i.e., Buckingham's II groups. It is a common approach in fluid mechanics to express complex terms in a compact and economic form. Furthermore, relating dimensionless parameters expedites scaling laws especially in this study when various designs are compared. Persson [27][28] derived an explicit expression
pE(U) = a 2 e u/uo (3.4) 1e- v
where u is the separation between silicone's bottom surface and deepest point of
36 the substrate when silicone is compressed into the substrate. The applied force is
Fa = PaA (3.5)
where A is the area in contact with the substrate. Eqn.(A.2) can be further derived into a more intuitive form with penetration as an input, as shown in Eqn.(3.6). Here, the bonding effect is also accounted for.
Ea e(w-hmax)/Uo 2 (IV2p E (w-hmax)/Uo (3.6) -v2 3 3 H 1 -v2
For hyperelastic material used in this study, it is assumed that v = 0.5 for all cases. In this relationship, there are eight independent parameters with units listed in Table.3.1. For Buckingham's l Theorem to stand, the fundamental units in this study are chosen to be [Force] and [Length]. Rigidly following Buckingham's 11 Theorem, w and E are selected as the fundamental parameters, forming six dimensionless EUs. The H group is defined in Table.3.2.
Parameter Pa / Uo hmax W T H E
Unit [2 1 L [L] [L] [L] [L] [F]
Table 3.1: Unit for each parameter in fundamental dimensions.
Ui1 H2 113 H 4 15 16
Pa u-Q hmax T H E w w w w
Table 3.2: H group representation for the silicone cushion analysis.
Since in the CSAM applications, the only interested scenario is hmax = w, meaning that silicone rubber fully penetrates the deepest valley of the substrate. This is set as the standard to evaluate if silicone fully seals the substrate. As a result, hmax/W can be simplified as unity and removed from H groups. The new H group
37 is shown in Table.3.3. Further, accounting for both physical meaning and clarity of representation, H6 is defined as the ratio of H4 and 15 and is used in the following analysis. It can be interpreted as the aspect ratio of the silicone cross-section or 2S, twice the shape factor. The relationship between the dimensionless 1 groups are demonstrated in Fig.3-8.
UIl 112 113 4 15
E w w w
Table 3.3: Modified 11 group representation for the compression spring suspension analysis.
022 0.7 o .34B33r4.OSas .. P2as,..1 o w3.OSrUw-1 021 0.03 o 02= - -+- .3 407336.4=1.5 -e- r34S.733.a=.5
-+- 4.s -4i0.4.1S 0.18 - 0 s.1Ases..4.1 - - .45=1466ed=1 -A-- tA46.4d1.5 0.16- .A-s~41834,.4=1 4 .41334.,4.1.6 4 e la.o~m.":_ 0.14
., 0.12 OA -4 A-- Ww-.
0.2
ak 0- - ~ 2_2-o -A- --4D-~A O.W, ~ ~ A - -
0.2 0.5 1I 1.5 0.A 1.6 2 9S 56
Figure 3-8: Dimensional analysis of two 112 values.
As indicated in Eqn.(3.6), 12 is simply a scaling factor. 111 is positively correlated with 114 and negatively correlated with l15 and 113. In Fig.3-9, aspect ratio of cross- section, 116, is included. This can expedite design when dimensional constraints are imposed.
38 r2 = 0.026, r3 = 0.45 0.12 w w4=0.5 A i4=0.75 0.11 - A- 74=1- --- r4/r5=0.1 ----v4/76=0.55 0.1 . - r4/r5=1
0.09
£~ 0.08
0.07
0.06
0.05
0.04 0.8 1 1.2 1.4 1.6 1.8 2 7r 5
Figure 3-9: Including H6 can expedite the design when dimensional constraints are imposed.
Geometric Optimization
As mentioned in previous sections, the ultimate goal of optimizing silicone geometry is to reduce the magnitude of applied compression pressure. In Fig.3-8 and Fig.3-9, this is directly reflected as a lower value of 11 . In a real-world scenario, the substrate surface roughness is given, meaning that the designer cannot optimize 112 and 113- Thus, setting up the best 14 and 15 is of top priority. In the CSAM application, the rectangular silicone cross-section contains a groove that divides the cross-section in the thickness direction, as shown in Fig.3-10. Adding the groove helps to reduce the value of 114 while keeping 115 constant. In consequence, H value is lowered. More technically speaking, adding the groove reduces the effect of traverse shear stress in the thickness direction, thus lowers the value of shape factor and apparent compression modulus. As demonstrated in Fig.3-11, adding one bisecting groove lowers 1 from 0.075, red dot, to 0.056, green dot, while maintaining all other parameters the same. As long as the split cross-section follows the design constraint discussed below, a groove in the cross-section is a significant way of reducing
39 the compression pressure.
Groove
Figure 3-10: CSAM silicone cross-section are grooved to lower applied compression pressure.
7 2 = 0.026,,,3 = 0.45 0.12 A r4=0.5 0.11 - -A r4=0.75 - 4=1
0.1
0.09 F
0.08 F roove
0.07 I
0.06,
0.05 -
0.04 0.8 1 1.2 1.4 1.6 1.8 2
7r 5
Figure 3-11: Grooving the cross-section significantly reduces II1 .
Design Constraints and Procedure
Every design process is an optimization process given certain constraints. For the
CSAM, the first constraint is that IH5 should always be greater than unity so that
40 silicone can fully penetrate to the deepest point of the substrate valley. The second constraint is the silicone material. For applied compression pressure to be as low as possible, the selected silicone material should possess a low compression modulus E. Meanwhile, there is an important consideration for 116, the aspect ratio of the cross- section. For hyperelastic materials such as silicone, the structural rigidity should be considered. As illustrated in Fig.3-12, each wall of the silicone cushion can be modeled as a thin-plate with thickness T, lengths H and L. The critical buckling stress is proportional to f2 and buckling coefficient k, which has a positive correlation with . The full analytical relationship for various boundaries can be found in Timoshenko and Gere [32]. In conclusion, the selection of aspect ratio IH6 and E is dependent on each other. It is more practical to determine the relationship experimentally than analytically. Designers should first determine the silicone material, and then conduct an independent experiment with that silicone material to decide an acceptable range
of aspect ratio, 116 -
HL
Figure 3-12: Experimentally determine aspect ratio to maintain structural rigidity.
The third constraint is the range of applied compression pressure that falls in the load capacity of the Manipulation Module. The next constraints are the dimensional constraint is actual cross-section thickness and height. Such constraints depend on the details of the deployment scenario. Last but not least, add a groove to the silicone cross-section while ensuring the split cross-section follows all the previous constraints. In summary, the overall objective is to minimize the applied compression pressure. Several constraints should be imposed by designers. First, silicone material should be
41 determined. Second, based on the selected silicone material, empirically determine the range of aspect ratio H6. Third, narrow down the design based on the range of accepted IU1l. Fourth, further sort out designs that do not fall in the geometric constraints. Last but not least, add groove to the cross-section and ensure the previous constraints are still satisfied. The design process of CSAM cross-section is presented in Chapter 5.
3.4.3 Compression Spring Suspension Optimization
Problem Statement
The second component of the CSAM is the compression spring suspension. It is used to ameliorate change of water-pipe geometries, which is very common at pipe joints and valves. Shown in Fig.3-13 is a corroded pipe intersection. Buried the tubercle is a pipe-joint intersection. The pipe and joint have a height difference of 6h.
Pipe Wall
hA Cj S oint
C h(q)
Figure 3-13: Change in pipe wall profile statistically affect average height of the tubercle.
There are two ways of characterizing the surface roughness at this intersection. The surface roughness of region A and region B can be defined as CA and CB, respec- tively. Assuming an ideal situation where all hydrodynamics and bacterial conditions are the same, CA = CB. This is because the PSD only contains the information of a rough surface relative to its average asperity height h(x) = 0 while no information about the absolute average height is provided. On the other hand, the PSD for the combined region A+B can be defined as C,. However, C, does not contain the cor-
42 rect surface roughness information because it is an averaged roughness calculation over both regions A and B and it's statistically inappropriate to be applied. Silicone cross-section designs that follow Co would not work. The average height difference in region A and region B is assumed to be identical to the pipe geometry difference, i.e, hA - hB = 6h. The compression spring suspension is used to deal with this situation.
Theoretical Modelling
The compression spring suspension act as a mobile and discretized support for the- oretical modeling of compression spring suspension is presented in this sub-section. Assume that each compression spring is in charge of supporting a portion of silicone cushion of length L, indicated in Fig.3-15. The silicone-spring assembly can then be modeled as two compression springs with stiffness k,pring and effective stiffness ksilicone installed in series. Assume two silicone-spring assemblies, A and B, are mounted on a board which is pressed against a stepped surface with height difference 6h, as shown in Fig.3-14.
ah
ksicone Assembly A Assembly B
F,
Figure 3-14: Simplified model of silicone-spring assembly.
Each of the silicone needs to deflect at least w = hmax under compression force
Fsiicone for a complete seal. The compression force can be calculated as Fsiicone = paTL, and the effective stiffness as ksiiicoe = Fs"gone. For a longer length, L, of silicone, the total force needed to deformation it, Fsiiicone, is greater, so as the effective
43 stiffness of silicone. From Sec.3.4.2, Pa and hmax can be obtained given silicone and substrate information. When silicone A is fully compressed, FA = Fsiicone = Fspring. The stiffness for one spring-silicone assembly is
kA = kB = kspringksilicone(37) L% kspring + ksiiicone The total amount of deformation for assembly B is simply expressed in Eqn.(3.8). The force exerted on assembly B is then
6 XB = 6XA + 6h (3.8)
FBB = kBEBB = kA EA + 6h] = Fic 6h ksiliconekspring (3.9) ] sikicone + hsiicone + kspring
Since for a given scenario, Fsiiicone, ksiicone and 6h are constant values, the total force exerted on the rigid board is F = FA + FB = f(kspring). In this case, F can be simply minimized by minimizing the equivalent stiffness kA = kB by choosing a very low stiffness spring.
lim Fo = 2Fsiticone (3.10) kspring-+0
2 lim Fo = Fsiiicone + 6h x ksiicone (3.11) kspring-+00
Physically interpreting, when the assembly contains a very stiff spring, the silicone is in charge of all the step difference Sh. When silicone height, H, is small, two situations could happen. First, just due to dimensional limitation, the silicone might not be able to reach the farther rough surface. The second case is when silicone height is enough to penetrate into the farther surface, the portion of silicone at the closer surface need to penetrate 'more' into the substrate by a virtual distance 6h. Given in
Fig.3-8, this decreases II 4 and H15 , thus significantly increases 1 1. On the other hand, with a small stiffness spring, the height difference is primarily absorbed by the spring instead of silicone. In conclusion, a spring with minimal stiffness provides the CSAM with the best performance to deal with a height difference at pipe intersections.
44 Design Constraints and Procedure
Unlike the design of silicone cushion, most constraints for the compression spring suspension comes from hardware dimensions. As shown in Fig.3-15, single silicone- spring assemblies consist of the following components: silicone cushion, compression spring, pushrod, spring base, silicone base, shaft, linear bearing or sleeve and retaining ring.
Silicone Cushion
-ilienne Ra
Push Rod
CompressionSSpring
Linear Sleeve
dsleeve Spring Base
Retaining Ring
Figure 3-15: Compression spring suspension materials and critical dimensions.
Given h, the designers can minimize L, or k,,,ing to minimize the pressing force on the spring base, F,. From the dimensionless analysis it is inferred that FB can be reduced by decreasing L,. In the design, it means that each spring should be in charge of supporting a shorter portion of the silicone cushion. Thus, the minimum L, is set as the largest value between the outer diameter of compression spring, retaining ring and sleeve, denoted as d,pring, drr and dsieeve, respectively. In order for the assembly to
45 function, the length of spring L,pring needs to be greater than 6h, otherwise, it cannot fully penetrate silicone into the farther surface. The maximum length of spring is
only determined by the allowable length for the hardware design. Notice that ksp,ing is inversely proportional to Lpring,, so normally longer spring is a less stiff spring, which is ideal for optimization. Once the material selection is completed, FB should be experimented and ensured that it does not exceed the designated load capacity limit of the power source, in CSAM application, an actuator.
In conclusion, given 3h, the designers can minimize L, and k,pring to minimize
the pressing force on the spring base. The minimum value of L, is determined by the diameters of spring, sleeve and retaining ring. The minimum L,pring should be
greater than 6h. Satisfying all dimensional constraints, the value of k,pring should be the lowest among the available options. Last but not least, FB should not exceed the actuator force limit.
3.5 Summary
The Compliant Surface Adaptation Module is a module that is used to enclose the workspace of the robotic end-effector so that no contamination is introduced to the water stream during the pipe rehabilitation process. The CSAM consists of three parts, a silicone cushion, a compression spring suspension, and a supporting base. This chapter focuses on the theoretical modeling silicone cushion and suspension system. This chapter investigates the sealing effect of silicone rubber on obstructions in the same size scale and is a pioneering research topic in this area. Persson Contact Theory and Buckingham's 11 Theorems are used to predict the performance of the sealing for silicone cross-section. A novel compression spring suspension is introduced to accommodate the change in pipe geometry. Dimensionless guidance for future designers is configured. The design and fabrication process and experiments are included in Chapter 4 and 6.
46 Chapter 4
Compliant Surface Adaptation Module - Implementation
In this chapter, the CSAM module for a tuberculated 102mm-diameter pipe is de- signed and fabricated based on theoretical and experimental optimization. The opti- mization process for silicone cushion is first presented. Then the design and material selection for compression spring suspension system is demonstrated. Finally, a CSAM prototype is fabricated. The CSAM consists of three main components, the silicone cushion, compression spring suspension and supporting base. The silicone cushion is designed in the first place as it is the primary compliance provider. The compression spring suspension is designed based on the hardware constraints after the silicone cushion dimensions are determined.
4.1 Silicone Cushion
In this study, the CSAM module is deployed in a 102mm-tuberculated pipe with.
Since the pipe surface is set, three parameters for surface roughness, /3, hma, and nO can be specified. The compression modulus for silicone, E, is fixed once a certain silicone material is selected. The design narrows down into the investigation between applied compression pressure and dimensions of the rectangular cross-section.
47 The design, fabrication and experiment processes for silicone cushion is arranged as follows. First, the silicone material is selected and experimented to obtain compres- sion modulus. Second, the surface roughness information of the substrate is collected and calculated. Third, silicone cross-sections with various dimensions are fabricated and tested. Last but not least, combining experimental and theoretical result, the cross-section for CSAM is finalized.
4.1.1 Material Selection
For both experiment and implementation, Ecoflex 00-30 by Smooth-On is selected as the silicone material. It is a platinum-catalyzed super-soft silicone rubber with Shore Hardness 00-30. For small strain, the tensile modulus for Ecoflex 00-30 is 69kPa(10psi) while the compression modulus is missing. Since for a hyperelastic material, its tensile modulus can differ significantly from compression modulus, an experiment to obtain the compression modulus is necessary.
Experimental Setup
Figure 4-1: Experimental setup for Compression Experiment I. The specimen is pressed on a flat substrate.
The experimental setup is shown in Fig.4-1. The base is a press bench. A Mitu-
48 toyo 500-196-30 Digital Caliper, a Vernier Dual Range Force Sensor and a pressing plate are rigidly mounted onto the press bench. A 20mm diameter and 12mm height cylindrical Ecoflex 00-30 specimen is made and rigidly bonded to the pressing plate. The specimen is squeezed against a flat substrate by the pressing plate. The force sensor is able to collect compression and tension force up to 50N with 0.03N reso- lution. The digital caliper can measure the displacement of the pressing plate with 0.01mm resolution. The operator controls the displacement of the pressing plate in an increment of 0.1mm and the corresponding compression force is recorded.
Result and Discussion
As demonstrated in Fig.4-2, the compression stress-strain relationship is almost lin- ear and can be approximated by apparent compression modulus Ea = 135kPa. Since the top surface of the specimen is bonded, the original compression modulus can be calculated by taking the inverse of Eqn.(3.3) with shape factor S = 10 ~ 0.42. The
calculated compression modulus E = 101kPa and is used in the following experi- ments.
9 x10 4
8
7-
6-
5
CO, 3-
2
0 0.1 0.2 0.3 0.4 0.5 0.6 Strain
Figure 4-2: Compression Stress-Strain curve for Ecoflex 00-30.
49 Topology of Simulated Tubercle -101 Histogram of Specimen Tubercle Height
Euhne DiMboonn - ruk Nomurl Oftibum 3 1200 Mon HeigM Valm -10-3 5- 1000 2
800 0 9 600
400 -0.0 ' 02 0.03 -1
200 0.01 -2 0.02 0.01 y[m] 0.03 0 x [m] -5 -4 -3 -2 -1 0 1 2 3 4 Tubercle Height [mm] x10~3
Figure 4-4: Topology of 3d-printed Figure 4-5: Height distribution of the rough surface to simulate tubercles. 3d-printed rough surface.
4.1.2 Substrate Surface Roughness
A 3d-printed rough surface is made and used during the experiments as a mock cor- roded pipe. It is 75mm x 75mm in length and width, made up by nine 25mm x 25mm board with topology shown in Fig.4-4. The height distribution is nearly Gaussian, as shown in Fig.4-5, with maximum height difference of hmax = 6.87mm.
Power Spectrum of Specimen 10-10
10-11
1 0-12V
10-13
10~14 F
L.- 10-6 3 101 102 10 10 4 q [m~1]
Figure 4-3: Power spectrum for the 3d-printed rough surface.
The 3-d topology information from CAD contains information of surface height h(x) at coordinate x = (x, y). The power spectrum density can be calculated with
Eqn.(3.1) and is plotted on a log-log scale in Fig.4-3. The calculated # and uo for this surface are 0.072 and 0.006, respectively. With surface roughness information,
50 the dimensionless 1 groups are plotted in Fig.4-6
72 0.072, r - 0.873
-- -- r4=0.5 0.26 -_- - ,r4=0.75 w4=1 r4=1.25 - 4=1.5 0.24 .----r4hr5=0.1 ---- r4/5=0.325 ------r4/r5=0.55 ------r4/7r5=0.775 ---- r4/75=1
0.2 - -
0.16 -
0.14 1 1.2 1.4 1.6 1.8 2 7r 5
Figure 4-6: Dimensionless H groups for the 3d-printed substrate.
4.1.3 Design Process
Leak Experiment
In this experiment, the relationship between H1, 114 and 115 is investigated. As a reminder, U1 is a dimensionless parameter accounting for the applied pressure over silicone compression modulus; H4 and H5 is the silicone cross-section thickness T and height H over penetration w, respectively." The specimens are pressed against the 75mm x 75mm 3d-printed rough substrate. The chamber is a cylindrical com- partment, as indicted in Fig.4-7. The compartment interior diameter is 40mm, with circumference c = 125.7mm. The cross sections have wall thickness T = 2, 4, 6, 8mm, and H = 5, 6, 8, 10, 12mm. Since c >> T and c >> H, the silicone seal can be approximated as an infinitely-long block and the shape factor can be calculated with Eqn.(3.2). The specimens are named in the form of T4H6, representing 4mm wall thickness and 6mm compartment height.
51 Figure 4-7: Leak pressure for silicone cushions with cylindrical compartment are tested.
The experimental setup is demonstrated in Fig.4-8. The compartment is filled with water of 0.2m depth, corresponding to 1.96kPa water pressure. The specimen is squeezed with the pressing plate so that no water leakage from the compartment is observed. The applied pressing force is slowly reduced at 0.03N decrements until a clear leak is observed and the force is recorded as leak force F. The specimens are squeezed against the four corners and the middle of the rough substrate. In total, 180 tests are conducted. The applied pressing forces are recorded and corresponding leak pressures p, are calculated and demonstrated in Fig.4-9.
Figure 4-8: Leak experiment setup.
52 Pressure Test for Cylindrical Chambers
x.104 8,
6 (D 4,
0 12 8
10 8 6
64 Height [mm] 4 2 Thickness [mm]
1 Failed Seal ---* Successful Seal
Figure 4-9: Leak pressure p, for the cylindrical tests.
Result and Discussion
Leak pressure result for cylindrical specimens is indicated in Fig.4-9. Among the failed tests, a 'x' and a 'o' symbol indicates that the specimen fails one and two out of the five tests, respectively. For further investigation, the leak pressure for failed experiments are excluded and the average leak pressure for each silicone cross-section is calculated. Experimental and theoretical result for each geometry is computed and expressed in dimensionless H groups, as shown in Fig.4-10. The theoretical analysis successfully predicts the negative correlation between 15 and 1. Similarly, it predicts the positive correlation between H1 and H4 . It is observed that for 11 >
1, the theoretical analysis predicts the values very well. As H5 decreases below 1,
H 1 significantly increases. Theoretically, no specimen should work when H 5 < 1. However, under high compression load, the specimen is deforming in an injection molding manner. It deforms to fill up the prescribed volume around it, instead of deforming freely when lateral deformation can be approximated.
Specimens with large r1 and low 14 values also fail the seal the gap. This is
53 0.5 r2= 0.072, 7r3 =0.873 0.5 r2 0.072, 7r3 =0.873 -e-----r4 = 0291 - 7r4 = 0291 0.45 + r4 = 0.582- 0.45 - 4 = 0.582 0r4 = 0.873 - 74 = 0.873 0.4 -O- r4 = 1.16 -0.4 - ,r4 = 1.16
0.3 0.35 #* Failed Seal - 0.3503
0.3 0.3
0.25 0.25
0.2 0.2
0.15 0.15
0.1 0.1
0.05 0.05 0.6 0.8 1 1.2 1.4 1.6 1.8 0.6 0.8 1 1.2 1.4 1.6 1.8
7r5 7r5 Figure 4-10: Experimental and theoretical result represented in dimensionless H group. caused by the aspect ratio problem mentioned in Sec.3.4.2. For example, the only reason T2H12 specimens are able to seal is that they are too soft to maintain shape. Even with very small compression pressure, the specimens deform in all directions instead of by pure compression, filling up the gaps on the rough surface. In this experiment, it is shown that the specimen should have an aspect ratio of 1H15 > 0.25 to retain structural rigidity enough for the CSAM application.
4.1.4 Finalized Design
In this study, the CSAM silicone cushion should have a total thickness of 4mm. This is a comprehensive result dependant on many factors such as water pipe diameter, tubercle height, workspace and sizes of other modules, etc. Given the total thickness, there are two silicone arrangement options for the cross-section. The options are: directly using a T4 (4mm thickness) section, or combining two T2 (2mm thickness) sections, corresponding to no groove or one groove. As discussed in Sec.3.4.2, adding the groove significantly reduces required applied pressure to seal the leak. Referring to Fig.4-10, for U5 = 1.17, i.e., H8 (8mm height) specimens, adding one groove reduces H 1 from 0.15 to 0.10. Theoretical value simultaneously shows adding the groove could reduce H1 from 0.17 to 0.15. In the experiment, the T2H8 cross-section
54 also demonstrates the best sealing performance not only among its group but among all specimens. As a result, a 2 x T2H8 configuration is selected. The finalized CSAM cross-section is demonstrated in Fig.4-11. The two sections are placed 2mm apart to remove mechanical coupling and is modified based on the curvature of 102mm diameter pipe.
H6
Figure 4-11: Finalized design of silicone cross-section.
4.2 Compression Spring Suspension
The second procedure is to design the compression spring suspension. As mentioned in Sec.3.4.3, the design parameters of the compression springs are constrained by hardware dimensions. Once pipe height difference 6h is specified, the performance of compression spring suspension is only dependant on the spring stiffness k,,p,ig and the length of silicone each spring is supporting, L,. To determine the two values, the hardware constraints are listed. The selected push rod has 3mm diameter and 12mm length. For this diameter, the smallest available retaining ring has a diameter of 8mm and the smallest linear sleeve has 4mm diameter and length. To provide enough space for the reciprocal motion of push rod and retaining ring, L, is set to be 9.8mm. On the other hand, at the joint
55 M
section of a 102mm diameter pipe, there is a typical profile change of 6h = 2.5mm. So the minimum spring length is 2.5mm. The length of spring cannot exceed 8mm or MPCOR would be too bulky to operate in the corroded pipe. In conclusion, the
compression spring needs to satisfy the following dimensions: 2.5mm < L,,,in, 8mm, 3mm < dspring < 9.5mm. Eventually, a 7mm in length and 6mm in diameter
spring with stiffness k,pring =0.068N/mm is selected.
4.3 Fabrication
The fabricated CSAM is shown in Fig.4-12. The silicone used in the experiments, Ecoflex 00-30 is used for the fabrication. The interior of the silicone chamber has 78mm and 49mm length and width and is modified to fit the curvature of the pipe wall. The silicone is injected into a 3d-printed female mold and placed in 65°C(150°F) for 20 minutes to cure. There are 26 compression springs in total. The silicone base and spring bases are 3d-printed. With this design, referring back to Fig.4-6, an applied force of 3.28N is sufficient to create a complete seal. The enclosing effect is demonstrated in Chapter 6.
Figure 4-12: Fabricated CSAM.
56 4.4 Design Process Summary
In conclusion, to create a fully functional CSAM, the following steps need to be completed. First, obtain surface data including surface roughness and 6h to determine
112 and 13. Second, set the silicone material. This provides the designer with a fixed compression modulus E. The next step is to experimentally determine the aspect ratio (thickness/ height) range of the cross-section for the selected silicone. Based on components dimensional constraint, determine the cross-section thickness and height.
This step determines 114 and 15 for the design and thus 111 can be extracted from the dimensionless rI groups analysis. To further lower H 1 , add a groove to the cross- section while ensuring the aspect ratio does not fall out the experimentally determined range. The required applied pressure can thus be determined by multiplying 111 by E. The selection of compression spring depends on dimensional constraints. Given length and spring radius, select the spring with lowest stiffness and length greater than 6h that is available. With the silicone and compression spring design finalized, the compression force for the CSAM application can be calculated with Eqn.(3.5) and Eqn.(3.9). This compression force is the minimum force to guarantee the full functionality of CSAM.
4.5 Chapter Summary
In this chapter, we simulate a 3d-printed rough substrate. Based on the surface rough- ness information and Ecoflex 00-30 silicone properties, we combine two T2H8 (2mm thickness and 8mm height) sections. The compression spring assembly contains 26 compression springs with stiffness ks,pring = 0.068N/mm. The theoretical calculation indicates that a minimal force 3.28N is needed to create a fully enclosed seal. The CSAM is fabricated and the experiments are performed in Chapter 6.
57 58 Chapter 5
Manipulation Module
5.1 Functional Requirement
The second critical module for the MPCOR is the Manipulation Module. It collabo- rates with CSAM to complete a tubercle removal task with minimal contamination. The Manipulation Module should satisfy the following functional requirements:
" include a manipulator with at least 3-DOF
" include an actuated end-effector for tubercle removal task
* include space for the installation of the CSAM
" deliver enough power for the CSAM to function
* capable of manipulating the CSAM and end-effector independently
" maneuverable inside a 102mm diameter pipe
" scalable across various pipe diameters
Despite the required functions listed above, there are several optional consid- erations that are taken into account during the design process. For example, the Manipulation Module is preferred to be as modularized as possible to satisfy various deployment and installation of new gadgets. The module should also leave space for potential water-proofing upgrade.
59 5.2 Mechanical Design
5.2.1 Assumption
In the design of the Manipulation Module, several assumptions are made based on prior art. The water pipe is straightforward to express in both Cartesian Coordinate system and Cylindrical Coordinate, with the direction along the pipe as the Z-axis. The two Coordinates are used interchangeably in the following analysis, as shown in Fig.5-1. It is assumed that the Locomotion system is fully developed, so the Manipulation Module is always rigidly grounded and centered relative to the pipe wall at [0, 0, z, 0, 0, 0]. The maximum tubercle height is 5mm relative to the pipe wall. It is assumed that leak and obstruction locations are both known.
Figure 5-1: Demonstration of MRL pipe rehabilitation robot and global coordinates.
5.2.2 Design Description
The finalized Manipulation Module consists of a 4-DOF serial manipulator and a quick-release spindle. As demonstrated in Fig.5-2. The manipulator is in arranged in serial Revolute-Revolute-Prismatic-Prismatic form. The four DOFs are named as
60 Joint-Theta, Joint-4bar, Joint-R, and Joint-Z. In a Cylindrical Coordinate, Joint-
Theta controls 6-axis of the manipulator. The spindle, denoted with a subscript ". , is mounted on Link 4 and the CSAM, denoted with a subscript "c", is mounted on Link 2. For the dry water pipe scenario, a cleaning system is attached to the CSAM. It ejects rinsing fluid through a nozzle installed on the silicone cushion.
Z3 1
Link 4, Joint-Z yD Link 3, Joint-R z3 xs Link 2, Joint-4Bar Link 1, Joint-Theta z xZ.
2
Xo
Figure 5-2: Robot kinematics and D-H notation for robotic platform.
Joint-Theta and Joint-4bar are used to set the CSAM position and spindle workspace. Link 1 is directly driven by Joint-Theta for compactness and a full range of motion in Theta direction. Link 2 is a four-bar mechanism driven by Joint-4bar so that
X2 is always in Z-direction. Joint-4Bar controls R and Z-coordinate, respectively, for both the CSAM and the spindle. Joint-R and Joint-Z are decoupled from the CSAM and only control the spindle. Joint-R is a prismatic joint consists of a pair of lead-screw assemblies, Link 3, and it controls spindle's R-coordinate. It is in a lead-screw arrangement because it provides high load capacity for the spindle to drill through tubercle and is non-backdrivable. The only requirement for this Joint-Z is compactness, so Joint-Z is a prismatic joint with rack and pinion assembly to control Z-coordinate of the spindle. At the beginning of Minimal Particle Contamination Obstruction Removal pro- cess, Joint-Theta and Joint-4bar thrust the Compliant Surface Adaptation Module
61 against pipe wall to create a completely sealed environment around the spindle. Joint- R and Joint-Z then control the position of the spindle for it to grind or drill. The debris generated is contained in the CSAM. After tubercle within the spindle's workspace is removed, the nozzle mounted on the silicone cushion wall flushes water to collect the debris and rinse the treated pipe wall. Finally, Joint-Theta and Joint-4bar re-position the spindle for another tubercle removal process.
5.2.3 Forward Kinematics
The manipulator's forward kinematics is calculated using the Denavit-Hartenberg (D- H) parameter. The homogeneous transformation matrix from Joint i to Joint j and is given as Eqn.(5.1) where 6i, ai, ai, di are determined by Joint i and Link i. The transformation matrix from the base to the end effector, T is calculated by Eqn.(5.2).
cos6i - sin i cos a sin O0 sin ai a2 cos 0;
sin 9, cos 9, cos a,i - cos 9, sin a, a sin O0 (5.1)
0 sin a cos a2
0 0 0 1
- A 1A 2 Aendef°fector T 0 l endef f ector -I (5.2)
Table.5.1 lists the D-H parameters for the 4-DOF manipulator. The range of motion for each joint is listed in Table.5.2. Notice that 0 in the transformation matrix denotes a D-H parameter while E denotes the angular displacement of each joint.
62 D-H Parameters and Motor Specifications
Joint Name Theta 4Bar R Z Name
a [mm] 0 20 + 35 cos(E 4Bar) 0 0
a [rad] - 22 - --a2 - 2
d [mm] 22 35 sin(E 4Ba,) 10 + dr 5 + d,
6 [rad] ETheta 0 -E 0 - 11 1 1 2
Table 5.1: D-H parameters for MPCOR Manipulation Module.
Range of Motion
Oracta[rad] (-2(
E4Ba,[rad] [0, ]
d,[mm] [0,22]
d,[rad] [0,15]
Table 5.2: Range of motion of each joint.
Spinde Woiapem n 100nv4e Pipe WOD Besc Chmber Woospc on 100m-O. Pe Wal .*5A- E16 MfiCI, 0- so so
y
.0 1 .0 15 S0 soso 0 150
z (mmJ -50 0 y m) Z Irnmn) 40 Y(mmn]
Figure 5-3: Workspace for the spindle and the CSAM when in contact with 102mm diameter pipe surface.
63 mi
Fig.5-3 illustrates the workspace of the CSAM and the spindle when they are in contact with a 102mm diameter pipe wall. The CSAM is constantly covering the workspace of the spindle during the operation. Assuming fixed ETha and e4Ba, values, the manipulator is grounded at the origin and a 22mm long grinding head is attached to the spindle, Fig.5-4 illustrates the workspace of the grinding head. Any obstruction inside the red area can be removed by the grinder.
End Efbctor WorkSpace - 2D with 22mm tool length
40 - 30
20 10
E On& X -10
-20 -
-30 -
-40 -
-501 0 10 20 30 40 50 60 z (mm)
Figure 5-4: End effector workspace for the 22mm tool head.
5.2.4 Force Analysis
There are two major power sinks in the MPCOR dry-deployment application. Illus- trated in Fig.5-6, FCSAM is the amount of force needed to deform CSAM to form a complete seal around the spindle. In Sec.3.4.2, the design of CSAM is specified.
For the dual-T2H8 silicone cushion design, area in contact ACSAM with tubercle is 272mm 2 . Referring to Fig.4-10, the average leak pressure pi required for this design is
1.2 x 104pa. Taking a safety factor of SF = 2.5 leads to FCSAM = SF x ACSAM x Pi a 8.2N.
The other power sink is the thrust force comes from the spindle, Fp,,indle. Without enough reference, a bench-top experiment is conducted to determine this force, as shown in Fig.4-10. To drill through and collapse an area of tubercle, the maximum
64 force needed is 9.6N. The required torque for Joint-4Bar is approximately 0.89Nm to hold CSAM and thrust the spindle. The actuator selection is included in Sec.5.4.
Figure 5-5: Bench-top tubercle removal experiment indicates maximum required spindle Fpiedl = 9.6N.
174Ra0
ENIMM
Figure 5-6: Force analysis of MPCOR.
65 5.3 Controller Design
The controller for each joint is Proportional Integral Derivative (PID) control. PID control is expressed as
d Control Effort = Kpe(t) + Ki e(t)dt + KD-e(t) (5.3) / dt
e(t) = 0 ref - 9 actual (5.4)
where Kp, Ki, and KD are the gains; e(t) is the error between reference displace- ment and actual displacement. The control effort is the output of the controller. With a rotary encoder, the angular displacement of the DC motor is recorded. Inside the microcontroller, since the computation is discrete, angular velocity is computed by dividing step angular displacement over a step period. The products of step angular displacement errors and step period are summed up and put into Integral control. In case Integral control diverges over time, an anti-integral-windup is added. Control effort is sent as Pulse Width Modulation (PWM) into the motor driver. Advantages of PID control includes fast response and inexpensive computation.
Micro- controller
Control Effort
Motor Encoder T iw mcontt ler i Motor Driver DC Encoder Reading
Encoder Reading iure 5:: ShMicfo r aum atdtbrleoa ak
Micro- controller
Figure 5-7: Schematic for automated tubercle removal task.
Two types of control methods are designed for the platform. First, manual control
66
I - 11 lmm- is used for testing and experiment. A joystick or other analog input device sends an angular reference to the microcontroller. The microcontroller calculates control effort and drives the actuator. An automated control adds Simulink into the control loop, as shown in Fig.5-7. In this case, the microcontroller only acts as an encoder reader and motor driver. It transfers encoder readings through the serial port to Simulink. The control effort is calculated by Simulink and is transferred back to the microcontroller. With automated control, multiple microcontrollers can be operated at one and trajectories can be planned. Additionally, the computational burden on each microcontroller is lowered and computation speed can be increased. In Chapter 6, the step responses for each joint are analyzed.
5.4 Material Selection
Actuator selection is very limited due to compact in-pipe space and power consump- tion consideration. Each actuator consists of a DC motor and a gearbox. The links are driven by the gearbox output shaft. The motors are all driven by DRV8838 dual motor drivers. Each motor driver is capable of driving two motors with 1.7A current and is controlled by an Arduino UNO Table.5.3 lists the specifications for each joint.
Actuator Specification for each Joint
Joint Name Theta 4Bar R Z
Motor Power[W] 1.0 1.0 1.5 1.5
Gear Ratio 1000:1 1000:1 210:1 150:1
Transmission Lead Rack- Screw Pinion
Quantity 1 2 2 1
Table 5.3: Actuator and gearbox selection for each joint. Note - For joints with two motors, PID control is implemented for synchronization.
67 On the DC motor output shaft attaches a 12 Count per Revolution (CPR) mag- netic encoder, i.e., with 1000:1 gear ratio, the gearbox output shaft receives a reso- lution of 0.030. Since the encoders are incremental, a Force Sensor Resistor (FSR) with a voltage divider circuit is installed on each joint and is incorporated with pin- change-interrupts to zero encoder reading. A 9V battery supplies each motor driver. The links are 3d-printed with polylactide.
5.5 Summary
In this chapter, the Manipulation Module of the MPCOR is presented. It includes a 4-DOF serial manipulator and a quick-release spindle. The forward kinematics and force analysis are conducted. Material selection for both mechanical components and electronics are done based on the analysis. PID controller is implemented for each joint. In Chapter 6, the Minimal Particle Contamination Obstruction Removal system is integrated and experimented.
68 Chapter 6
System Integration
In this chapter, the two modules, the Manipulation Module and the Compliant Surface Adaptation Module are fabricated and implemented. Experiments are conducted to test the effectiveness of both modules.
6.1 System Prototype
Ecoflex 00-10
Spindle hamber Inlet Connector
Chamber Outlet
Figure 6-1: Prototyped CSAM with modifications to connect with Manipulation Module.
The completed MPCOR system is presented in Fig.6-2, including a Compliant Surface Adaptation Module and a Manipulation Module. Demonstrated in Fig.6-
69 2.A-B, the CSAM can be snapped directly onto the 4-DOF manipulator without an extra fixture.
Micro-Motors driven by PID control for DRV8838 motor motor driver each A
LM3UU I Linear 12 CPR Parallelogram Bearing incremental four bar linkage encoder
Figure 6-2: Prototyped MPCOR. A: 2-DOF Manipulator; B. CSAM; C. CSAM attached to Manipulation Module; D: Full assembly of MPCOR.
The two prismatic joints on the Manipulation Module contains two LM3UU 3mm linear bearing each to minimize friction. The onboard electronics include a 12CPR
70 incremental encoder and a Force Sensor Resistor for each motor. The power supplies, DRV8838 motor drivers and microcontrollers are installed on external fixtures are connected to the motors via 6-pin header. As illustrated in Fig.6-1, to prevent any debris from falling into the manipulator, a thin film of silicone is added to the base of the CSAM. The spindle can directly slide into the connector installed in the thin film for easy installation. For dry deployment of the MPCOR, an external cleaning system is installed rinse cleaning fluid.
6.2 Experiment Overview
To evaluate the overall performance of the MPCOR, four experiments are conducted. The first experiment is to evaluate the water-sealing capability of the CSAM. The second experiment tests the kinematics of the Manipulation Module and manipulation performance of each joint. The third experiment demonstrates the maneuverability of the MPCOR inside a 102mm pipe with simulated tubercle. In the last experiment, the MPCOR is dry-deployed in a corroded pipe section for a complete operation.
6.2.1 CSAM Test
Height DropsSh = 2.5mm
Figure 6-3: Mock rough surface board with obstructions and height drops corresponding to tubercle and pipe profile change.
71 Water sealing ability of the Compliant Surface Adaptation Module is tested. As shown in Fig.6-3, a 3d-printed tubercle board is made. It has the same profile as the simulated substrate used for the experiment in Sec.3.4.2. Its base curvature is modified according to 102mm pipe curvature. There are grooves with step height difference 6h ~ 2.5mm along the tuberculated board to simulate the sudden change of water pipe profile. Theoretically according to the dimensional analysis in Chapter 3, CSAM require at least 4.91N for a complete seal if no groove or compression spring suspension is added. During the experiment, the CSAM is pressed onto the board with a constant force of 3.23N. Water is filled inside the chamber. The applied pressing force is held for 10 minutes. Over the course of the experiment, there is no visual water leakage from the chamber. This experiment validates the optimized design of the CSAM as a whole. It also demonstrates good enclosing capability of the CSAM even with very low applied pressing force.
Figure 6-4: Experiment demonstrates the good sealing performance of CSAM with grooved design and compression spring suspension.
6.2.2 Kinematics Test
The experiment is to test the performance of PID tuning and kinematics of the MPCOR. During the test, a simulated deployment task is input to MPCOR. A rect-
72 angular area with 10mm width and 20mm length is projected onto the pipe wall as the grinding area. The tool head for the spindle is set to be a 5mm diameter grinding bit. Based on tool size, projected grinding area, the gear ratio of each actuator and link length of each joint, reference angular displacements are calculated. Reference displacement is sent to each microcontroller. Encoder readings for each actuator are collected and compared with step inputs, as shown in Fig.6-5.
Joint-Theta Joint-4Bar 500 700
600 400 500
300 400
200 300 200 100 010
00 10 20 30 10 20 30
Joint-R Joint-Z
w 2500 600 2000
1500 400
1000 200 500
0 0 0 10 20 30 0 10 20 30 Step Response Time [s] - -- Reference Input Figure 6-5: Step response of each joint of Manipulation Module given a simulated deployment task.
All four joints are able to follow step inputs very well. For Joint-R, despite the settling time is longer than other joints, its rise time is still within 0.4s. The step responses imply that the tuning of PID is sufficient to accurately and quickly control the robotic platform. The joints are capable of reaching designated positions. For Joint-Z, the actuator settles at 12 counts away from the step input after three steps,
73 corresponding to a 2.4° error. This indicates that there is minor dissatisfaction in the hardware.
6.2.3 Maneuverability Test
The experiment simulates a repair operation conducted in a 102mm diameter clear PVC pipe, as demonstrated in Fig.6-7. The black object on the pipe wall is a 20mm long 3d-printed PLA section with tubercles of 5mm maximum height. The MPCOR is installed to a fixture placed into the pipe. The spindle is manually operated to test the maneuverability of the Manipulation Module.
Figure 6-6: Prototyped MPCOR is tested in a 102mm pipe with 3d-printed tubercle.
Fig.6-6.A-C demonstrate the platform at various positions by controlling Joint- Theta, Joint-4Bar, and Joint-R. The test demonstrates satisfying maneuverability of the Manipulation Module in a compact workspace. By manually controlling Joint-R and the spindle, the operator successfully drills a 2mm hole on the 3d-printed tubercle, as indicated in Fig.6-6-D. Since PLA hardness is orders of magnitude greater than
74 real tubercle, the experiment shows MPCOR's confidence to satisfy a real tubercle removal job.
Figure 6-7: MPCOR in maneuverability test. A-+ B: Controlling Joint-4Bar and Joint-R; B-C: Controlling Joint-Theta; D: Manipulation Module successfully drilled a 2mm hole on a 3d-printed tubercle.
6.2.4 Corroded Pipe Surface Treatment
Finally yet importantly, the MPCOR is experimented in a corroded cast iron pipe as a dry-deployment demonstration. The iron pipe is 102mm in diameter. Over 6 months period of soaking and oxidation, tubercle of 3mm maximum height is formed on the pipe surface. A repair operation is manually conducted. Since neither the pipe wall nor CSAM chamber is transparent, the spindle position is interpreted with encoder reading. Manipulation module controls the spindle to clean a 15 x 15mm projected area on the pipe wall as shown in Fig.6-8-D. During the operation, each joint is capable of reaching and holding its respective position. In Fig.6-8-B, the CSAM successfully creates a complete seal on the pipe wall around the spindles. No particle caused by the removal process escape from the
75 Figure 6-8: [MPCOR in maneuverability test.]] A: Corroded pipe wall with 3mm maximum tubercle height; B: MPCOR after tubercle removal process; C: MPCOR after rinsing CSAM compartment. D: Cleaned 15 x 15mm projected area.
chamber. After the tubercle removal process, the external water pump and container rinsed the interior of the CSAM. During the rinsing process, there is no observable leak from the silicone cushion, as indicated by the dry groove in Fig.6-8-C. An external vacuum pump and container are connected to CSAM to collect rinsed water. The real world test validates the overall functionality of the MPCOR.
76 6.3 Summary
In this chapter, the MPCOR is fabricated and four experiments are conducted to test the performance. The MPCOR is deployed in a simulated tuberculated pipe and a real corroded cast iron pipe. The experiments demonstrate the satisfying performance of the MPCOR and its two modules. Room for improvement is discussed in Chapter 7.
77 78 Chapter 7
Conclusion and Recommendation
7.1 Thesis Summary and Contribution
In this thesis, the MRL pipe rehabilitation robot is presented. Depending on the deployment scenario of the robot, it should involve the following sub-systems, in- cluding a Locomotion system, a Leak and Obstruction Detection system, a Minimal Particle Contamination Obstruction Removal System and a Leakage Repair Section. This thesis main focus is the MPCOR sub-system. This sub-system consists of two modules, a Manipulation Module and a Compliant Surface Adaptation Module. For the CSAM, the goal is to create a completely sealed compartment on water pipe tubercle. The challenge lies in the comparable size of obstruction and thickness of the silicone compartment. The relationship between silicone material compartment geometry, substrate surface roughness and applied pressing pressure is investigated. A comprehensive research based on Persson Contact Theory and experimental results are combined to configure guidance for future designers when they encounter similar problems. For the Manipulation Module, a compact and powerful 4-DOF manipulator is configured. It is the first high-DOF robotic manipulator targeting obstruction removal for pipes under 102mm diameter. A MPCOR is fabricated and the prototyped. Experiments are conducted to val- idate the CSAM performance, kinematics, and maneuverability of the Manipulation Module. For the fully integrated MPCOR, a dry-deployment operation is conducted
79 in a corroded cast-iron pipe and. The experiments demonstrate the full functionality of the MPCOR.
7.2 Recommendations for Future Research
There is a lot of room for future research in in-pipe rehabilitation robots. More specifically, take the MPCOR as an example, the current version satisfies the IPR size limits presented in [12]. However, if other sub-systems are integrated, this whole robot will inevitably become too bulky to turn in the pipe network. This can be resolved by shrinking the robot dimensions with more powerful actuators and more rigid links. In- service deployment is also a potential upgrade for the MPCOR. Controlling robotic manipulator under high water pressure is a challenging topic and can become an investigation topic.
80
I Appendix A
Persson Contact Theory
A.1 Persson Contact Theory Key Equations
The key concept in PCT is that when an elastic block is pressed against a rough surface, the elastic energy stored inside the deformed block is equal to the amount of work done by the pressing force [28]. In Eqn.(A.1), p denotes the applied pressing pressure; Uei denotes the stored elastic energy and u denotes the average surface separation, which is defined as the distance between the lower surface of the block and the average height of the substrate [33]. The energy equation is expressed in
p(u) = 1 dUej (A.1) Ao du
Through a series of deduction [21][23][28], the relationship can be further derived
E 2 e "/uo (A.2) p(u) = # 1-v2 where # and uo are intrinsic properties that can be directly calculated given C(q); v is the Poisson's ratio and E is the compression elastic modulus for the elastic block. By assuming v ~ 0.5 for rubber and p = a F/AO, a linear relationship can be acquired
log =(A.3)
81 ......
Figure A-1: Elastic energy stored by the block equals to the work done by the pressing pressure [28].
Accounting for the apparent elastic modulus introduced in Sec.3.4.2, the finalized equation is
log( ) = B + (s - d (A.4) Ea no Ea where B = log(4Ea#/Ea) -h-.
A.2 Surface Roughness Parameters from PCT
The two parameters # and uO are very important in the CSAM theoretical work, the following section present the equations to calculate these values based on Persson Contact Theory given surface roughness PSD [21][23][28].
2 fg q C(q)w(q) log[w(q)]dq 2 # = E~^ f1 q C(q)w(q)dq (A.5) where e = 4.047. The derivation of e is included in Persson's work. The value qo and qi can be directly observed or calculated when PSD C(q) is plotted on a log-log plot. uo is given as
82 8
(9w) lbJ 84 Appendix B
Concept Validation for CSAM
The design concept of pressing an elastic material against a rough surface is studied and validated. The elastic cushion is in the form of a loop of silicone, a hypere- lastic material suitable for large deformation. Isotropic hyperelastic material can be characterized with various models, such as Mooney-Rivlin Model (MR), neo-Hookean Model, Odgen Model and so on [34][35]. In this study, silicone is characterized with 5-Parameter Mooney Rivlin Model. It is widely used to pre-study concepts due to its simplicity and efficiency. The strain energy function for 5-parameter MR is given with Eqn.B.1,
IF = Cio (1- 3) +Coi (I2-3)+Cl(-11--3)(12-3)+C20(I1-3)2 +C02 (12- 3)2 + I(j-1)2 (B.1) where C10,C0 1,C20,C0 2 and C11 are the material constants; I1 and 12 are the deviatoric first and second principal invariant; d is the incompressibility parameter and J is the Jacobian. Static structural Finite Element Analysis (FEA) is conducted in ANSYS to val- idate the feasibility of the concept. As illustrated in Fig.B-1, the tubercle is rep- resented by an arbitrarily shaped surface and the silicone rubber is represented by an 8 x 8 x 10mm cuboid. The surface contact is set to be bonded. The bottom of the silicone rubber is fixed. A 0.iN pressing force is constantly applied to the
-y-direction. For this simulation, the MR parameters are set as C10 = -3.20kPa,
85 Total Dforman 2 Downward Force Type: Total Deform~ton Lhitmm
209/2/28 1713
2.5193 2.2044 lAWS 1.5746 12596 0.94473 0.62982 0.1491
Figure B-1: FEA of hyperelastic material pressed by tubercle is conducted to test feasibility of silicone deforming over rough surface.
Co 1 = 4.24kPa, C20 = 0.62kPa, C02 = 4.37kPa, C1 = -2.63kPa and d = 0. The result demonstrates that silicone rubber can considerably deform with a small force input to adapt to a rough surface, validating the design concept.
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