Robotic Vacuum Cleaner Design to Mitigate Slip Errors in Warehouses

By

Benjamin Fritz Schilling

Bachelor of Science in Mechanical Engineering New Mexico Institute of Mining and Technology, New Mexico, 2016

Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of

Master of Engineering in Advanced Manufacturing and Design at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY

September 2017

© 2017 Benjamin Fritz Schilling. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created.

Signature of Author: Department of Mechanical Engineering August 11, 2017

Certified by: Maria Yang Associate Professor of Mechanical Engineering Thesis Supervisor

Accepted by: Rohan Abeyaratne Quentin Berg Professor of Mechanics & Chairman, Committee for Graduate Students

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Robotic Vacuum Cleaner Design to Mitigate Slip Errors in Warehouses

By

Benjamin Fritz Schilling

Submitted to the Department of Mechanical Engineering on August 11, 2017 in partial fulfillment of the requirements for the degree of Master of Engineering in Advanced Manufacturing and Design

Abstract

Warehouses are extremely dusty environments due to the concrete and cardboard dust generated. This is problematic in automated warehouses that use robots to move items from one location to another. If the robot slips, it can collide with other robots or lose track of where it is located. Currently, to reduce the amount of dust on the floor, warehouses use industrial scrubbers that users walk behind or ride. This requires manual labor and a regular scheduled maintenance plan that needs to be followed to mitigate the dust accumulation. Therefore, an industrial robotic vacuum cleaner that can continuously clean the warehouse floors is proposed. The five key parts to a vacuum are inlet duct, brush roller, filtration, storage, and suction. This thesis will discuss in detail the design and development of the filtration, storage, and suction of the robotic vacuums that were developed in this project. The thesis will go through design considerations and computational fluid dynamics that were conducted to validate and improve the design. Then, it will discuss the experimental results of the robotic vacuum cleaners.

Thesis Supervisor: Maria Yang Title: Associate Professor of Mechanical Engineering

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Acknowledgements

I would like to take this opportunity to express my gratitude to the people that have been supportive throughout my educational experience here at MIT and throughout my life. First, I would like to thank my family for their continuous support, encouragement, and unconditional love. I would especially like to thank my parents, Scott and Lori Schilling, and my brother Isaac Schilling, for their insurmountable support throughout my life. Without them, I would not have been able to accomplish or do the things that I have done thus far. Thank you for pushing me to pursue my dreams.

I would like to thank my thesis advisor, Professor Maria Yang, who has provided helpful guidance throughout my thesis project. I would also like to thank Jose Pacheco and Professor David Hardt, who gave me the opportunity to be a part of the Master of Engineering in Advanced Manufacturing and Design.

I would like to express my gratitude to the company for providing me with a fabulous experience and an enjoyable project. I would especially like to thank Jude for his insightful engineering guidance, patience, and mentorship of our group at the company. I would also like to thank Peter for supporting, guiding, and providing engineering guidance throughout the project. Thanks to Craig for doing the electronics and making the firmware work for our prototypes. Thanks to Dragan, Gabriel, Jennifer, and Allan for providing their engineering expertise and assistance. I am thankful to Ron and Mark for assisting in fabricating parts in the machine shop and allowing us to use the machine shop to build our prototypes. Finally, I would like to thank everyone at the company who helped my team and I with the project and made it a rewarding experience.

Last, but definitely not least, I would like to thank my wonderful teammates, Barbara Maia Araujo Lima, Jody Fu, and Youngjun Joh for their excellent collaboration and engineering ideas. I had a fabulous time working with this group, and without this team we would not have been able to accomplish what we did.

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Table of Contents

Abstract ...... 3 Acknowledgements ...... 5 List of Figures ...... 9 List of Tables ...... 10 Definition of Key Terms ...... 11 Chapter 1 : Introduction ...... 14 1.1 Motivation ...... 14 1.2 Objective ...... 15 1.3 Functional Requirements...... 15 1.4 Scope ...... 15 1.5 Task Division ...... 15 Chapter 2 : Background Information ...... 17 2.1 Current Robotic Vacuums on the Market ...... 17 2.2 Inertial Separation ...... 19 2.3 Blower Selection ...... 19 2.4 Scroll Design ...... 21 Chapter 3 : Mechanical Design of Vacuum Bin and Blower Assembly ...... 23 3.1 Bin ...... 23 3.2 Trapdoor ...... 24 3.2.1 Finite Element Analysis to Determine O-Ring Compression on Trapdoor ...... 25 3.3 Filters and Filter Plate ...... 27 3.4 Blowers...... 29 3.5 FEA to Determine the Theoretical Compression on the O-Rings ...... 30 3.5.1 Front Plate FEA ...... 31 3.5.2 Filter Plate FEA ...... 33 3.5.3 FEA Blower Cover Plate ...... 35 3.5.4 Theoretical Percent Compression ...... 36 3.5.4.1 Force Required to Compress AS568A-280 O-Rings with a Shore A Hardness of 50A ...... 36 3.6 Second Prototype Bin and Blower Assembly ...... 38 3.7 Blower Housing...... 39

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3.8 Cleaning Hatch ...... 40 3.9 Filter ...... 41 3.10 Piston Seals ...... 41 Chapter 4 : Experimental Results and Analysis ...... 42 4.1 Particle Separation...... 42 4.1.1 Computational Fluid Dynamic Setup...... 42 4.1.2 CFD Results ...... 44 4.1.3 Experimental Particle Separation Results ...... 46 4.2 Velocity Measurements ...... 47 4.2.1 Cut Plot Velocity Measurements ...... 47 4.2.1.1 Experimental Velocity Measurements ...... 48 4.2.1.2 Velocity Measurement at the Inlet to the Bin ...... 49 4.2.1.3 Experimental Velocity Measurements Along the Inlet of the Bin ...... 50 4.3 Filter Experiment...... 51 4.3.1 Velocity Measurements with a Clogged Filter ...... 51 4.4 CFD Results for Improving Separation ...... 52 4.4.1.1 Experimental Results with Triangular Separator ...... 54 4.4.2 CFD Flow Trajectories and Particle Simulation with a Triangular Member and Straight Walls in Front of the Filter ...... 55 4.4.2.1 Experimental Results with Triangular Member and Straight Walls in Front of the Filter ...... 57 4.4.3 Circular Bin Design for Inertial Separation ...... 58 4.4.3.1 Cylindrical Bin Experiment ...... 59 4.5 Blower Placement ...... 61 4.6 Particle Study and Flow Simulation of Cylindrical Bin ...... 63 4.6.1 Experimental Results of Cylindrical Bin ...... 66 4.7 Scroll Housing and Blower CFD ...... 66 4.7.1 Open-Walled Blower Housing ...... 67 4.7.2 Scroll Housing CFD ...... 70 4.7.3 Peripheral Discharge Design CFD ...... 73 4.7.4 Blower Housing with Large Exhaust Ports ...... 77 4.7.5 Conclusions on Scroll Housings ...... 80 Chapter 5 : Conclusions and Future Work ...... 81

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5.1 Summary ...... 81 5.2 Future Work ...... 81 Bibliography ...... 83

List of Figures

Figure 1: Key components of robotic fulfillment [1] ...... 11 Figure 2: Main components of the robotic vacuum system ...... 12 Figure 3: Cyclone separator [13] ...... 19 Figure 4: Characteristic Performance of different blade types [16] ...... 20 Figure 5: Scroll design [19] ...... 22 Figure 6: Main components of bin and blower assembly ...... 23 Figure 7: Trapdoor diagram ...... 24 Figure 8: FEA displacement of the lid ...... 25 Figure 9: FEA on acrylic lid ...... 26 Figure 10: Filter and filter plate diagram ...... 27 Figure 11: Blower assembly diagram ...... 29 Figure 12: Diagram showing the different O-Ring grooves and surfaces ...... 30 Figure 13: Compression load for 1/8-inch O-Ring [20] ...... 31 Figure 14: FEA setup for the front plate ...... 32 Figure 15: FEA deflection results for the front plate ...... 32 Figure 16: FEA setup for filter plate ...... 33 Figure 17: FEA deflection results for the filter plate ...... 34 Figure 18: FEA setup for blower cover plate...... 35 Figure 19: FEA deflection results for blower plate ...... 35 Figure 20: O-Ring Compression Picture...... 37 Figure 21: Assembly of the second prototype bin and blower ...... 38 Figure 22: Exploded view of blower housing ...... 39 Figure 23: Two different blower designs ...... 39 Figure 24: Cleaning hatch door...... 40 Figure 25: Filter assembly ...... 41 Figure 26: CFD setup ...... 42 Figure 27: Fan curve for RER 120-26/14/2 TDP fan [22] ...... 43 Figure 28: RER 120-26/14/2 TDP fan inputs in Solidworks ...... 43 Figure 29: Particle simulation ...... 44 Figure 30: Flow trajectory and velocity profiles...... 45 Figure 31: Experimental test for picking up Splenda ...... 46 Figure 32: Cut plot in the middle of the bin showing the velocities ...... 47 Figure 33: Velocity plot in the middle of the bin...... 48 Figure 34: Experimental setup to measure the velocity ...... 48 Figure 35: Cut plot of the inlet of the bin ...... 49 Figure 36: Velocity plot along the inlet of the bin ...... 50

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Figure 37: Filter after flour experiment ...... 51 Figure 38: CFD flow trajectories with triangular separator in the bin ...... 52 Figure 39: Particle simulation with triangular separator...... 53 Figure 40: Experiment using triangular separator ...... 54 Figure 41: CFD flow trajectories with a triangular separator ...... 55 Figure 42: Particle simulation with triangular separator and walls in front of the filters ...... 56 Figure 43: Experimental results with triangular separator and a wall in front of the filter ...... 57 Figure 44: CFD flow trajectories in a multi-bin design ...... 58 Figure 45: Cylindrical bin experimental setup...... 59 Figure 46: Flour separation experiment ...... 60 Figure 47: Blowers placed in the back of the bin ...... 61 Figure 48: Blowers placed on top of the bin ...... 61 Figure 49: Blowers placed on the side of the bin...... 62 Figure 50: Flow simulation setup with cylindrical bin ...... 63 Figure 51: Flow trajectories in a cylindrical bin ...... 64 Figure 52: Midplane cut plot of the cylindrical bin ...... 64 Figure 53: Cylindrical bin particle study ...... 65 Figure 54: Cylindrical bin separation ...... 66 Figure 55: Open-walled blower housing CFD setup ...... 67 Figure 56: CFD velocity results from open-walled blower housing...... 68 Figure 57: CFD pressure results with open-walled housing ...... 69 Figure 58: CFD setup with scroll housing ...... 70 Figure 59: CFD pressure cut plot of scroll housing ...... 71 Figure 60: CFD velocity cut plot of scroll housing ...... 72 Figure 61: Peripheral discharge housing CFD setup ...... 73 Figure 62: Peripheral discharge housing velocity cut plot...... 74 Figure 63: Peripheral discharge blower housing pressure cut plot ...... 75 Figure 64: Flow trajectories of the peripheral discharge housing...... 76 Figure 65: CFD setup for blower housing with large exhaust ports ...... 77 Figure 66: Velocity cut plot of blower housing with large exhaust ports ...... 78 Figure 67: Pressure cut plot of housing with large exhaust ports ...... 79

List of Tables Table 1: Commercially available robotic scrubbers ...... 17

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Definition of Key Terms

Figure 1: Key components of robotic fulfillment [1] Pod (A): Stores products and is manipulated by the robotic drive Robotic Drive (B): Carries pods around the fulfillment center Fiducials (C): Fiducials are stickers placed on the ground to help the robot navigate to its intended destination

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Figure 2: Main components of the robotic vacuum system Bin: Container that holds the debris that is sucked up Duct: Component that the debris travels through to get into the bin Brush: Agitates the debris so that the blower can suck it up or imparts kinetic energy onto heavier objects to fling them through the duct Blower: Creates a constant stream of air that runs from the intake port of the vacuum (the bottom part of the duct) to the exhaust ports Filter: Allows air to pass through, but has small enough particle size to capture the debris so that the debris stays inside the bin Back Chassis Connectors: Connects the front and back chassis together Caster Wheel Mount: A mount that holds the front caster wheel in place Chassis Plate: A plate that holds all of the components

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Chapter 1: Introduction

1.1 Motivation

Automated Fulfillment Centers have a significant amount of cardboard and cement dust in their warehouses. The reason there is so much dust is because the floors are made out of concrete. Over time, the cardboard and cement dust creates a slippery environment for the robotic drives that are used throughout the Automated Fulfillment Centers. The reason that slip errors are a problem is because if the robot slips too much, it could collide with other robots that are carrying pods with products. This leads to the pods falling over, and products strewn across the floor. If this happens, then a portion of the robotic floor has to be shut down. A human associate then has to clean up the mess and re-sort the products, which is a very time-consuming process. Also, the products could be damaged or broken.

Currently, most automated warehouses use a walk-behind automatic scrubbing machine to clean the warehouse. The floors are scheduled to be cleaned every three months, but that does not always happen because it requires shutting down the robotic floor. During the peak season, it is very difficult to shut down the floor for cleaning since there is a plethora of orders that need to be fulfilled. If the maintenance schedule is neglected, more slip errors occur.

Therefore, it is proposed that a robotic vacuum cleaner should be designed to continuously clean the fulfillment center without having to shut down the floor.

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1.2 Objective The main objective for this project is to design and develop a robotic vacuum cleaner that can be used in Automated Warehouses to mitigate slip errors caused by debris on the floor, especially dust.

1.3 Functional Requirements

• Ensure that the noise level is 90 decibels or below. This complies with OSHA standards for a normal work day. OSHA states that the permissible exposure limit for noise is 90 decibels for an 8-hour time-weighted average [2] • Easy to use, less than 5 minutes to empty holding bin o Ideally, the robot would dock and get emptied without human interaction • Run time: One hour • Able to pick up, at a minimum, cardboard and cement dust o Ideally, can pick up liquids and screws along with dust

1.4 Scope

The scope of this project is to design a proof of concept robotic vacuum cleaner. If the concept proves to be useful, then future development can be embarked upon. The scope of this thesis is the design of the bin assembly on the robot. This includes the consideration for blowers, filters, seals, and the bin, which holds the debris that is sucked in.

1.5 Task Division

There are five main components that make up a vacuum cleaner. They include the brush, duct, bin, blower, and filter. Barbara Maia Araujo Lima focused on the duct and brush design, her thesis is Optimization of head and duct design for a warehouse vacuum robot using computational fluid dynamics [3]. This thesis focuses on the components of the bin assembly. This includes filters, blower selection, blower housing, and bin design. Besides the main components for a vacuum cleaner, there are several other tasks that need to be completed to make the robotic vacuum cleaner work. Youngjun Joh designed and performed FEA (finite

15 element analysis) on the chassis plate, caster wheel mount, and connections to the back chassis. Jody Fu designed the roller brush assembly, and Barbara and Jody worked together on the first head duct design. Barbara also designed the head assembly for the second prototype.

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Chapter 2: Background Information

2.1 Current Robotic Vacuums on the Market

There are several commercially available robotic vacuum cleaners on the market. Most of the robotic vacuums that are on the market are for personal use in the home, such as the iRobot vacuum cleaners. These vacuums are not designed for massive industrial warehouses because they have small storage capacity for debris, and their brushes are designed for carpet and hardwood floors; not for concrete floors which are common in fulfillment centers. Therefore, this thesis will look at industrial robots that have a larger storage capacity for debris and are designed for cleaning warehouses and large public places, such as malls and hospitals. Some of the commercially available industrial vacuums that are on the market include the Makita DRC200Z Industrial Robotic Vacuum, SWINGOBOT 1650, DUOBOT 1850, Robo 40s, and Navi 660.

Table 1: Commercially available robotic scrubbers

Model DuoBot 1850 Swingobot Makita Robo 40s Navi 1650 DRC200Z 660 Price $31,600.00 [4] $30,445.00 [4] $1346 [5] $16,931 [6] N/A Run Time on Single 4 [7] 4 [8] 3.33 6 [9] 2.5 Charge (hrs) [10] Machine Length 48 48 21.3 27.55 36.5 (inch) Machine Width 32 32 21.3 27.55 33.5 (inch) Machine Height 43 43 11.1 27.55 34.6 (inch) Scrubbing Width 25 29 18 15 26 (inch) Scrubbing Force 50 100 N/A N/A N/A (lbs) Solution Tank 14 14 None 7.4 11.88 (gallon) Debris Tank 1.15 1.15 0.625 8.1 11.88 (gallon) Cleaning Rate 10000 10000 1640 12917 12917 (sq ft/hr)

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The disadvantage of all of these commercially available robotic vacuum options is that they need someone to empty the debris tank and plug them into a charger. An additional issue with the floor scrubbers is that they dispense a liquid solution onto the ground that can potentially leave the ground slightly damp. This can make the robots loose traction and slip.

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2.2 Inertial Separation

When developing a bin to hold debris, it is important to keep the filters as clean as possible to ensure that the flow rate does not decrease too much. One way to keep the filters clean is though inertial separation. Cyclone separation is the most commonly used inertial separation technique [11]. A cyclone separator separates the denser particles from the air stream via a centrifugal force field. This force pushes the particles that are denser than the fluid to the outside walls, and forces the particles to fall into a holding bin [12]. Figure 3 shows the main elements of the cyclone separator. The dirty air enters tangentially to the cyclone body and flows from a nozzle at the top of the cyclone causing the fluid within the cyclone chamber to rotate [12]. The heavy particles follow the conical shape of the body downward until they exit at the bottom of the cyclone. Then, the clean air gets sucked out of the top of the cyclone separator.

Figure 3: Cyclone separator [13]

2.3 Blower Selection

The blower creates a constant stream of air from the bottom of the head duct (intake port) to the outlet port. This creates a slight pressure differential, which helps the dust particles get

19 sucked into the bin. This pressure differential is very small and, therefore, it is more important to have large amounts of airflow to pick up particles. The name vacuum cleaner is slightly misleading because the definition of a vacuum is “a space entirely devoid of matter” [14]. A name that is more fitting would be “suction cleaner” because the main purpose of a vacuum cleaner is to move particles from one place into a holding container. Axial and centrifugal fans are the two most common fans on the market. Axial fans draw the air in parallel to the axis of rotation, and the air leaves in the same direction. These fans create a large volume of airflow, but the airflow that they create is at low pressure. Centrifugal fans, which are sometimes called blowers, increase the pressure of the air coming into the impeller eye and move the air radially away from the middle of the impeller [15]. Therefore, the best fan for a vacuum application is a centrifugal fan. There are three main blade types for a centrifugal fan. The three main types are forward curved, backward curved, and radial blades. The forward curved fan delivers high air volumes against pressure, but when it is at a state of high free delivery, it requires a lot of horsepower and can overload the motor if there are variations within the airflow [16] (see Figure 4). Backward curved impellers are used to deliver high airflow under pressure. Backward curved impellers also have a non-overloading characteristic. Looking at Figure 4, it can be seen that the horsepower curve of the backward curved blades hits a maximum when the free delivery increases. This means that variations in the systems airflow will not burn out the motor. Also, backward curved impellers have an efficiency of about 90% [16]. Radial fans are the simplest to manufacture for centrifugal fans because the blades are straight and do not have a unique curvature. Radial fans are used in high static pressure conditions, and deliver low air volumes [16]. They also exhibit an increasing horsepower curve as the free delivery increases.

Figure 4: Characteristic Performance of different blade types [16] 20

Considering the different blades types that can be used in the impeller design, backward curved blades seemed to be the best for a vacuum application because of the non-overloading condition, high efficiency, and ability to operate under high pressure conditions. Since one of the functional requirements is to use the preexisting batteries, it is essential that the blowers that are selected can run for an hour on the batteries charge. This means that it is not possible to use a massive blower that consumes a significant amount of power, such as an industrial vacuum cleaners motor. The blowers that were selected for the robotic vacuum were S-Force RER 120-26/14/2 TDP. These blowers are centrifugal fans with backward-curved blades. They spin at 6100 RPM and are 24-volt DC fan that has a power consumption of 78 watts. Since most of the pressure build-up takes place in the impeller, this fan does not require a scroll housing. The motor of the fan is positioned in the impeller of the centrifugal fan, which provides optimal cooling of the motor. The motor also has PWM (pulse width modulation) control input, which allows the user to adjust the speed for testing purposes [17].

2.4 Scroll Design

Most centrifugal fans have a scroll housing. In a centrifugal fan, the air enters in the axial direction and then the deflects the airflow radially away from the center axis. The scroll housing’s purpose is to combine all the air streams back into a single air stream and discharge it tangentially. The air velocity is greatest at the blade tips, and when the air stream gets collected in the scroll, the velocity slows down as the air leaves the housing. The deceleration of the air creates a decrease in the velocity pressure, and some of that pressure is converted into static pressure, per Bernoulli’s principle [18].

One way to design the scroll casing is to draw a spiral shape that has radii of 72.2%, 83.7%, and 96.2% of the wheels diameter. The center of these three circles are located off the centerlines by 6.25% of the wheels diameter. The width of the housing is 75% the diameter of the wheel, and the outlet height is 112% the diameter of the wheel [18]. Near the housing outlet, there is a piece that protrudes into the housing outlet by 35% of the wheel diameter. The piece that protrudes is called the cutoff. The cutoff, which can also be called a recirculation shield, prevents bypassing air which causes loss in air volume and efficiency [19]. The cutoff should be

21 located very close to the fan to stop the bypassing air, but typically a 5 to 10% clearance is designed in between the cutoff and the fan. The purpose for the clearance is to reduce the noise caused by having a small clearance between the impeller and the cutoff, but creating this gap does decrease the efficiency [18]. This design methodology is convenient because everything is based on the diameter of the centrifugal fan.

Figure 5: Scroll design [19]

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Chapter 3: Mechanical Design of Vacuum Bin and Blower Assembly

Figure 6: Main components of bin and blower assembly

3.1 Bin

The bin was designed to maximize the area on the preexisting robotic drive. The reason for this was to ensure that the robot could dock at the current charging stations and still tunnel under the pods, while maximizing the debris storage capacity of the robotic vacuum. For ease of manufacturability for this prototype, the bin was constructed out of acrylic. Acrylic is an easy material to laser cut and it is transparent. Constructing it out of a transparent material made it easier to visually see what was happening during testing, and allowed the user to see when the bin was full.

The acrylic members were glued together using Weld-On 4 Acrylic Adhesive. The adhesive is a solvent which slightly melts the acrylic and create a strong bond. To ensure that the bin was air tight, hot glue was distributed along all the seams. For ease of assembly, the acrylic

23 panels were made with square holes so that the panels would snap together and would stay in situ when the bin was getting glued together.

3.2 Trapdoor

Figure 7: Trapdoor diagram

The trapdoor was 3D printed out of ABS plastic, with an O-Ring slot designed into the part. The slot was designed using the specifications out of the Parker O-Ring Handbook. The door was mounted using two acrylic hinges, and was adhered to the bin using Weld-On 4 Acrylic Adhesive. Acrylic hinges were used because acrylic adheres well to acrylic using a solvent, but most other materials do not adhere well to acrylic. If a different hinge material was used, it would need to be screwed into the bin. This could lead to potential leak sites. The door was secured using an adjustable draw latch. The adjustable draw latch makes it easy to adjust the force that is applied to the trap door to ensure there is compression on the O-Ring so that it would seal to the bin.

The hole in the acrylic is 2.5 inches in diameter, which is the size of a standard industrial vacuum cleaner hose. The idea was to use an industrial vacuum cleaner to suck out the debris

24 inside the bin when the robot docks to charge. The problem with this method is that a 6.5 HP industrial vacuum cleaner was not capable of sucking out the debris because the vacuum was not able to generate enough suction. This was due to the fact that the duct and filter openings are exposed to the environment. Therefore, to make this method work, one would need a way to close off the duct from the environment or close off the filters from the environment to generate enough suction.

3.2.1 Finite Element Analysis to Determine O-Ring Compression on Trapdoor

FEA was conducted to understand how much the O-Ring would be theoretically compressed between the 3D printed plate and the acrylic plate.

Figure 8: FEA displacement of the lid The trapdoor is fixed where the hinges are located and where the draw latch connector is attached. The fixed constraints are the green arrows on the door. A pressure of 5 psi was applied to the O-Ring groove because, according to the Parker O-Ring Handbook ORD 5700, for an O- Ring with Shore A hardness of 50, a 5-psi load has to be applied to obtain 20% compression [20].

Figure 8 show that the maximum displacement occurs in the middle of the plate and displaces 0.109 mm.

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Figure 9: FEA on acrylic lid

The acrylic plate was fixed on the sides (indicated by the green arrows) and a pressure of 5 psi was applied to the O-Ring groove (indicated by the red arrows). As is shown in Figure 9, the acrylic plate deflects 0.0039mm in the middle of the plate.

Total deflection from trapdoor and acrylic plate = 0.1091+0.0039 = 0.14893 mm = 0.0059 inch

Recommended gland depth from Parker O-Ring book is 0.107 inches and a 1/8” O-Ring has a diameter of 0.139”.

Equivalent gland depth= 0.107 + 0.0059in=0.1129 in % Theoretical Compression= (0.139-0.1129)/0.139 *100% = 18.8% compression

Therefore, 1.2% of the compression is lost due to the deflection of the trapdoor and the acrylic plate.

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3.3 Filters and Filter Plate

Figure 10: Filter and filter plate diagram

The filters that were used were 053200200 BUSCH filters. In a vacuum, it is essential to maximize the surface area of the filter because the instant that at filter is clogged, the flow rate drastically decreases. When selecting a filter, the main consideration is having a large filter to keep the flowrate decent for as long as possible. The first filters that were selected were Briggs & Stratton 798897 because they had a large surface area and fit into the bin well. The only problem with these filters is that the diameter that interfaces with the filter plate was small, which constricts the airflow. Therefore, the BUSCH filter was selected because it had a larger opening that interfaced with the filter plate. The BUSCH filter is also nice because it has a metal mesh that protects it from large objects such as nails and screws.

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Filter plate (A): The filter plate was 3D printed with ABS plastic. The ABS plastic was then brushed with acetone. Acetone melts the ABS and creates an airtight plastic part. The purpose of the filter plate is to attach the filter to the bin and make it easy to replace the filter if it gets damaged or extremely dirty.

Heat sets (B): There are three heat sets used to secure the filter cage to the filter plate. Since ABS is a thermoplastic, heat sets work great and provide a simple way to secure the filter cage while still allowing for easy removal of the filter.

Filter holder (C): This component makes sure that the filter is sealed against the O-Ring, and holds the filter in place.

Attachment holes (D): The attachment holes secure the filter plate (A) to the front plate (F). The attachment holes are designed to have a bolt go through the filter plate and the front plate. Then, a wing nut is attached to the bolt to hold the whole assembly together. Using a wingnut to hold the two plates together makes it easy to take off the filter assembly and allows the user a convenient way to tighten the two plates together to compress the O-Ring between the plates.

Clearance holes for a hex drive rounded hex screw (E): When the blower is pushed against the filter plate, the rounded hex screws interfere with the plate and therefore, clearance holes had to be made to ensure that there is a seal between the blowers and the filter plate.

Front Plate (F): The front plate was 3D printed out of ABS plastic and acetone was painted on the part to ensure it was airtight. The front plate holds the acrylic members in place when they are glued. It also has a handle so that the bin can be easily removed.

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3.4 Blowers

Figure 11: Blower assembly diagram Since centrifugal fans are not required to have a scroll housing, a simple open housing was initially designed. The housing is 3D printed from ABS plastic and heat sets were placed in the plastic blower housing for an easy way to fasten the cover plate. The slots that are placed on the side members are designed to fasten the blower housing to the chassis plate. Having the slots allows for adjustability and provides the user the ability to firmly press the blower housing against the filter plate to ensure that there is an air tight seal between the two components.

The cover plate was designed using the same external housing that was used to obtain the fan curves in the specification sheets [17]. The specification sheets state that the cover plate is 140 x 140 mm, and the air inlet opening has a diameter of 94.4 mm. The radius on the intake cover is 16 mm, and the radius of the air inlet opening is inserted 2 mm into the centrifugal fan. The cover was designed in the exact same way as the specification sheets to ensure that the fan curves were relevant when they were incorporated into the CFD (computational fluid dynamics) models that were performed on the robotic vacuum. The cover plate also acts as a venturi inlet,

29 which can improve the airflow by 6 percent [18]. Also, according to the Fan Handbook [18], the design follows the recommended radius of 0.14D for the inlet bell, which means that the airflow is improved compared to having a straight inlet with no radius. If you do not have a venturi inlet, then a vena contracta exists which reduces the flow rate [18].

3.5 FEA to Determine the Theoretical Compression on the O-Rings

To determine how much compression would be on the O-Rings on the bin, an FEA study was conducted. The FEA was run to determine the deflection of the different sealing surfaces. By knowing the deflection from the FEA, the groove depth designed into the members, and the size of the O-Ring, a percent theoretical compression could be calculated.

Figure 12: Diagram showing the different O-Ring grooves and surfaces In all of the following FEA setups, there was a 5-psi pressure applied to the O-Ring groove. According to the Parker O-Ring Handbook, an O-Ring with a Shore A hardness of 50

30 requires about 5 psi to have a 20% compression on the O-Ring (see Figure 13). Also, according to Quality Seals, it is recommended that an O-Ring is squeezed a minimum of 0.005 inches and a maximum of 30% of the O-Rings diameter [21]. The material property for all the members was ABS plastic.

Figure 13: Compression load for 1/8-inch O-Ring [20]

3.5.1 Front Plate FEA

To determine how much deflection there would be in the front plate, a 5-psi load was applied to the O-Ring groove, which is depicted by the red arrows in Figure 14. The green arrows depict where the member was fixed. The front plate was fixed along the edges where the acrylic members mate and where the screw holes are located. The major assumption that is being made in this study is that there is a 5-psi pressure being applied along the whole O-Ring. When the bin and blower assembly is assembled, the user just pushes as hard as they can against the blower housing and then tightens the wing nuts to hold it in place. There is no measurement of how much force is applied and, therefore, there is no way of knowing how much force is applied

31 at the O-Rings. This study is to ensure that the O-Rings could potentially be compressed and make a seal in this current assembly configuration.

Figure 14: FEA setup for the front plate

Figure 15: FEA deflection results for the front plate

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The deflection FEA results show (Figure 15) that the O-Ring grove deflects 0.00019 inches and it occurs in the areas that are the least supported.

3.5.2 Filter Plate FEA

Figure 16: FEA setup for filter plate The filter plate was fixed at the bottom where the blower housing presses against the bottom of the plate. Since the blower housing is bolted down to the chassis, the assumption was made that the bottom of the plate would be relatively secure and not be able to deflect very much. At the top of the plate, there is nothing fastening the blower housing and the filter cover together so both the blower housing and the filter plate could deflect. A 5-psi pressure was applied to the O-Ring groove that mates with the blower cover plate and a 5-psi pressure was applied to the back of the filter plate where it makes contact with the O-Ring from the front plate.

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Figure 17: FEA deflection results for the filter plate

With a 5-psi pressure applied to the O-Ring groove and the back of the plate, the filter plate deflected 0.00004 inches. Figure 17 is showing an exaggeration of the deflection. This makes sense that there is almost no deflection because there is an equal pressure applied to the front and the back of the plate in approximately the same spot and, therefore, the forces almost cancel each other out.

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3.5.3 FEA Blower Cover Plate

Figure 18: FEA setup for blower cover plate

Since the blower plate is secured by the blower housing, fixed constraints were applied to the four corners that made contact with the plate and a 5-psi pressure was applied to the surface that the O-Ring presses against.

Figure 19: FEA deflection results for blower plate

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As can be seen in Figure 19, the plate deflects 0.0039 inches in the locations that have the least support.

3.5.4 Theoretical Percent Compression

This calculation is to see if it is possible to compress all of the O-Rings with a Shore A hardness of 50A to the recommended compression percentage. Assuming that there is a 5-psi pressure applied to all of the O-Rings, the following calculations were made.

3.5.4.1 Force Required to Compress AS568A-280 O-Rings with a Shore A Hardness of 50A

Area of the O-Ring grooves is 2.709 in2 퐹표푟푐푒 = 푃푟푒푠푠푢푟푒 ∗ 퐴푟푒푎 = 5푝푠𝑖 ∗ 2.709𝑖푛2 = 13.55 푙푏푓

Consequently, if the O-Ring was making contact with the whole groove, then a 13.6 lbf is required to compress the O-Ring. In reality, it would be less force than this because the O-Ring contact area is smaller than the O-Ring groove. If the area is decreased, then the force needed is also decreased.

For all of the calculations, the groove depth that was designed into the part was 0.101”, which is what Parker O-Ring book recommends for the O-Rings that were used. The O-Rings that were used were AS568A -280.

퐹푟표푛푡 푃푙푎푡푒 푡표 퐹𝑖푙푡푒푟 푃푙푎푡푒 퐷푒푓푙푒푐푡𝑖표푛 = 1.815 ∗ 10−4 + 0.4018 ∗ 10−4 = 2.22 ∗ 10−4 𝑖푛 퐸푞푢𝑖푣푎푙푒푛푡 퐺푙푎푛푑 퐷푒푝푡ℎ = 0.101 + 2.22 ∗ 10−4 = 0.1012 𝑖푛 Equivalent gland depth is the depth of the O-Ring groove plus the deflection that was obtained in the FEA.

푂−푅𝑖푛𝑔 푑𝑖푎푚푒푡푒푟−퐸푞푢𝑖푣푎푙푒푛푡 퐺푙푎푛푑 퐷푒푝푡ℎ 0.139−0.1012 % 퐶표푚푝푟푒푠푠𝑖표푛 = = = 27% 푂−푅𝑖푛𝑔 퐷𝑖푎푚푒푡푒푟 0.139 퐵푙표푤푒푟 퐶표푣푒푟 푡표 퐹𝑖푙푡푒푟 푃푙푎푡푒 퐷푒푓푙푒푐푡𝑖표푛 = 3.889 ∗ 10−3 + 0.4018 ∗ 10−4 = 3.93 ∗ 10−3 𝑖푛 퐸푞푢𝑖푣푎푙푒푛푡 퐺푙푎푛푑 퐷푒푝푡ℎ = 0.101 + 3.93 ∗ 10−3 = 0.1049𝑖푛 푂 − 푅𝑖푛푔 푑𝑖푎푚푒푡푒푟 − 퐸푞푢𝑖푣푎푙푒푛푡 퐺푙푎푛푑 퐷푒푝푡ℎ 0.139 − 0.1049 % 퐶표푚푝푟푒푠푠𝑖표푛 = = 푂 − 푅𝑖푛푔 퐷𝑖푎푚푒푡푒푟 0.139 = 24.5%

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So, in both of these cases, the percent compression is within the recommended range for AS568A-280 O-Rings, which is 20-30% [20].

Figure 20: O-Ring Compression Picture

Looking at Figure 20, the O-Ring that is compressed between the front plate and the filter plate is being well compressed because the plates are almost flush. However, the blower plate and the filter plate do not appear to be compressing the O-Ring enough. Using ImageJ, the measured gap for the front plate to the filter plate was 0.009 inches and the measured gap between the filter plate to the blower plate was 0.032 inches. Therefore, the % compression for the filter plate to the front plate is about 20.8% and the compression between the filter plate and the blower plate is about 4.3%.

The O-Ring between the blower plate and the front plate is within the recommended percent compression, while the O-Ring between the blower and the filter plate is well below the recommended percent compression. One reason that there could be poor compression on the O- Ring between the blower plate and the filter plate is because there was not 13.6 lbf applied to the blower housing. The other reason that there could be poor compression is because the blower housing is deflecting. In all of the FEA’s, it assumed that the blower housing was rigid and that the plates would deflect a lot more than the housing.

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3.6 Second Prototype Bin and Blower Assembly

Figure 21: Assembly of the second prototype bin and blower

A second robotic vacuum was designed and developed and modifications were made based on the lessons learned from the first prototype. In the second iteration of the robotic vacuum cleaner, a circular bin is being used. This bin is a polycarbonate tube that has the correct features machined out of it. The reason that a cylindrical tube was chosen for this prototype is because it reduces the number of members that have to be joined together, and makes the bin more leak resistant. This is due to the fact that many of the pieces do not need to be glued together. The round bin shape also increases the swirling motion due to the inherent shape of the bin, which helps with inertial separation.

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3.7 Blower Housing

Figure 22: Exploded view of blower housing

The blower housing for the second robotic vacuum was designed so that there is a good seal between the filter and the blower. This design eliminates the multiple face seals that were needed in the first robotic vacuum because the filter mates directly to the blower housing.

Figure 23: Two different blower designs

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Picture A is a blower housing design the has large openings for the air to easily escape. Picture B shows a blower housing which resembles a peripheral discharge vacuum blower housing. The advantage of having the larger opening (picture A) is that it will not impede the airflow very much. The advantage of having the small ducts (picture B) is that the static pressure will be increased and the suction will be slightly better.

3.8 Cleaning Hatch

Figure 24: Cleaning hatch door

The cleaning hatch door is constructed out of acrylic because it is an easy material to laser cut. The bottom base is 3D printed from ABS plastic and is brushed with acetone to make it airtight. The base also has four heat sets placed in it for screwing down the lid to ensure good compression on the O-Ring, if the draw latch is not capable of providing the pressure needed to compress the O-Ring. The bottom base is then glued onto the polycarbonate bin using Weld-On 4. The adjustable draw latch is used to apply compression on the O-Ring and make it easy to open and close.

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3.9 Filter

Figure 25: Filter assembly

The filter is the same one used in the first prototype. This filter has a large surface area and fits inside of the geometry of the bin. For this prototype, the filter slips onto a tapered cone and makes a tight seal with the cone. The filter plate and standoffs are to ensure that the filter does not fall off as the robotic vacuum cleaner is driving around. This design is an improvement over the first prototype because it eliminates another seal and ensures that the filter is engaged well with the blower housing.

3.10 Piston Seals

In the first prototype, several O-Ring seals were used, which have a potential to leak. During experimentation, it appeared that the O-Rings were not sealing very well because there was flour residue on the outside of the O-Ring. To mitigate this problem, piston seals were used for the second prototype. The glands were designed to ensure a 20% compression on the O-Rings when they are slid into the polycarbonate tube. Two O-Rings are being used to ensure there is a good seal with the polycarbonate tube.

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Chapter 4: Experimental Results and Analysis

4.1 Particle Separation

To see, theoretically, where the particles would go, a CFD was run using Solidworks Flow Simulation.

4.1.1 Computational Fluid Dynamic Setup

Figure 26: CFD setup Figure 26 shows how the CFD was set up in Solidworks Flow Simulation. To make the flow simulation run, the body must be air tight. To make the model air tight, lids have to be created at the inlets and the outlets. The lids for the inlets were placed on the bottom of the head duct. Since there is a brush in the middle of the head duct, lids were created on both sides of the brush to make it resemble the actual design. At the outlets, lids were created where the blowers are attached. The entrance to the head duct was set to an environmental pressure of 101325 Pa and the side fans were set as external outlet fans. The goal was to maximize velocity at the edges

42 of the duct. The fans that were used for the robotic vacuum were RER 120-26/14/2 TDP. Curve number 2 of Figure 26 shows the RER 120-26/14/2 TDP fan curve. This fan curve was inputted into the SolidWorks Flow Simulation.

Figure 27: Fan curve for RER 120-26/14/2 TDP fan [22]

Figure 28: RER 120-26/14/2 TDP fan inputs in Solidworks 43

Figure 28 shows the exact parameters that were used to create a user defined fan in Solidworks Flow Simulation. The fan curve comes from Figure 27, and the fan type, rotor speed, outer diameter, and direction of rotation come from the specification sheet for the given fan.

4.1.2 CFD Results

Figure 29: Particle simulation

Figure 29 shows the results of a particle simulation that was run in Solidworks Flow Simulation. The particles that are dark blue have approximately zero velocity, and the particles in red have the highest velocity, which is 5.878 m/s. The particle was defined as cement dust that has a 10 μm diameter. According to a MERV (Minimum Efficiency Reporting Value) rating chart, the particle size of cement dust is 1-50μm [23]. Therefore, 10μm seemed like a reasonable diameter for the cement particle.

As can be seen in Figure 29, there is accumulation of cement dust in the corner of the bin, and there are slow-moving particles in the middle of the bin.

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Figure 30: Flow trajectory and velocity profiles

Figure 30 shows the velocity profiles of the air moving in the bin. Looking at the figure, there is a circular motion. This vortex is created by the rotating centrifugal fans that were used. The red arrows represent the maximum theoretical velocity of the air, and the dark blue represents the minimum velocity of the air. The maximum velocity of the air occurs near the fan opening because the air is getting constricted into a 2” diameter hole which causes the velocity to increase. The slowest velocity happens in the middle of the bin, but because both blowers are trying to suck the air in, the air is confused which blower to go to. This results in a low velocity in the middle of the bin.

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4.1.3 Experimental Particle Separation Results

Figure 31: Experimental test for picking up Splenda

Figure 31 shows how the particle settled in the bin. For this experiment, Splenda was placed on the ground, as can be seen in picture B, and the robotic vacuum cleaner was driven over it. Picture A shows that the Splenda settled in the middle of the bin and in the corners of the bin near the filters. The experimental result is consistent with the results from the particle study and the flow simulation. The particle study (Figure 29) showed that there would be build up in the corners of the bin near the filters, and this was exactly what happened in the actual experiment. The accumulation of Splenda in the middle of the bin can be explained by the simulations, which showed very low velocity in the middle of the bin, which means that the particles would settle in that location.

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4.2 Velocity Measurements

Velocity measurements were conducted to determine how well the simulation compared to the measured values.

4.2.1 Cut Plot Velocity Measurements

Figure 32: Cut plot in the middle of the bin showing the velocities

Figure 32 shows a cut plot of the velocity in the middle of the bin. The blue represents low velocity and red represents high velocity. As can be seen in the plot, there is high velocity at the head and low velocity as it enters the bin. This makes sense because as the area goes from a small area to a large area, the velocity decreases according to the continuity equation (A1*v1=A2*v2, A is the cross-sectional area and v is the velocity).

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w Figure 33: Velocity plot in the middle of the bin

Figure 33 shows the velocity along a line that was drawn in the middle of the bin from the duct wall side to the back of the bin. This plot shows that as the air goes from the duct to the back of the bin, the velocity decreases. The minimum velocity happens almost in the middle of the bin. This is due to the fact that a vortex is formed, and in the middle of the vortex there is low velocity.

4.2.1.1 Experimental Velocity Measurements

Figure 34: Experimental setup to measure the velocity An Extech Mini Thermo-Anemometer was used to measure the air velocity inside the bin. The anemometer was taped to the bottom of the bin and adjusted to approximately the

48 middle of the bin. The filters were cleaned and the brush was turning at about 3,000 RPM. The blowers were set at maximum speed, which is approximately 6100 RPM. The measurement was taken when the velocity was at a steady state.

Three measurements were taken and the velocity was 4.43 ± 0.31 푚/푠. The percent error compared to the simulation was:

|4.43 − 3| %푒푟푟표푟 = ∗ 100 = 32.3% 4.43

There could be several reasons that the percent error is fairly large. The first reason could be that the place that the velocity was measured with the anemometer was in a different place than where the simulation velocity was measured. As can be seen in Figure 32, it makes a big difference where the anemometer is measuring. If the anemometer is slightly higher than the middle of the bin and closer to the duct, the velocity increases significantly and would yield a velocity similar to the measured velocity. The second reason that the measurement could be off is that the anemometer has a 1-inch diameter. If the center axis of the fan blades is in the middle of the bin, then the tips of the fan blades are 0.5” above that center axis and are capturing the airflow at that height.

4.2.1.2 Velocity Measurement at the Inlet to the Bin

Figure 35: Cut plot of the inlet of the bin

Figure 35 is a cut plot where the duct mates to the bin. As can be seen in the figure, the velocity is very constant across the bin opening and increases as it gets to the sides. The reason

49 that the velocity is high at the sides is because there is probably a vena contracta on both sides. This is due to the fact that the air is getting squeezed at the sides since the duct tapers out.

Figure 36: Velocity plot along the inlet of the bin

The velocity plot in Figure 36 is a plot that was taken along the inlet of the bin across the duct. The plot shows that the velocity is about 6 m/s along most of the duct, and increases as it approaches the edges.

4.2.1.3 Experimental Velocity Measurements Along the Inlet of the Bin

The velocity was measured using the same technique that was described in 4.2.1.1 except the anemometer was placed flush with the bin wall and the axis of the anemometer was placed in 푚 the middle of the cutout. Three measurements were taken and the velocity was 5.4 ± 0.1 . The 푠 percent error compared to the theoretical result is 11%. This result is much better than the result in section 4.2.1.1. The reason this result is better than the first experiment is due to the fact that it is easier to control the experimental setup. Since the anemometer was placed in the middle of the duct and pressed against the wall, it was easier to ensure that where the velocity was being measured corresponded to approximately the same location where it was measured in the simulation.

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4.3 Filter Experiment

Figure 37: Filter after flour experiment

An experiment was run where 50 grams of flour was spread on the ground, similar to Figure 31 picture B, and the robotic vacuum was driven over the flour to see how much flour would be picked up. Figure 37 shows the filter after it was removed from the bin after the experiment. As can be seen in the picture, there is a significant amount of flour that gets trapped in the filter. This is not desirable because it impedes the airflow.

4.3.1 Velocity Measurements with a Clogged Filter

After several experiments were run and the filters were clogged with flour, velocity measurements were taken. An Extech Mini Thermo-Anemometer was used to measure the air velocity inside the bin. Three air velocity measurements were taken in the middle of the bin and 푚 in the middle of the cutout for the duct. The velocity was 1.85 ± 0.07 . This is a percent 푠 decrease of 65.74% compared to the velocity when the filters are not clogged.

This measurement shows that having clogged filters drastically decreased the velocity of the airflow. This leads to poor vacuum performance.

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4.4 CFD Results for Improving Separation

Looking at section 4.3, it is obvious that research needs to be conducted to figure out a way to reduce the debris build up in the filters. Several particle separations were conducted to see if adding certain geometry to the bin would help reduce the number of particles that accumulate at the filters.

Figure 38: CFD flow trajectories with triangular separator in the bin

Figure 38 shows the flow trajectories when a triangular member is placed in the center of the bin. The simulation was setup in the same way that was described in section 4.1.1. The reason to add a triangular piece in the middle was to help direct the airflow to each respective blower. Without the triangular piece, the airflow in the middle of the bin was behaving strangely because each blower was competing for the air in the middle of the bin, which caused a dead zone (see Figure 30). Examining Figure 38, it can be seen that the flow is divided in half. Half of

52 the flow goes to one blower and the other half goes to the other blower. Also, looking at the figure, it shows that there are vortexes mainly in the x-direction.

Figure 39: Particle simulation with triangular separator

A particle simulation was run with the triangular separator in the middle of the bin. From the simulation, it can be seen that there is accumulation of particles in the front corners of the bin and there is also accumulation near the triangular piece. Since the triangular separator is in the middle of the bin, one would expect to see the accumulation on both sides of the triangle. This is most likely due to an inaccuracy in the simulation. Looking at Figure 38, there appears to be voids in the air trajectories near the triangle. Therefore, it makes since that there would be some accumulation at the leading edge of the triangle, and it probably should be on both sides of the triangle.

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4.4.1.1 Experimental Results with Triangular Separator

Figure 40: Experiment using triangular separator

To see if the particle study results were reasonable, a triangular member was placed in the center of the bin. The robot was then pushed over Splenda to see where the particles ended up. Picture A is with the filter still in the bin and picture B is when the filter is removed from the bin after the experiment. As can be seen in Figure 40, the particles accumulated at the triangular piece and by the filter. These results are very similar to the particle study that was done with the triangular separator in the bin.

This is not an improvement from the initial bin that had no internal geometric members because it accumulates most of the particles at the filter, which is what is trying to be mitigated.

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4.4.2 CFD Flow Trajectories and Particle Simulation with a Triangular Member and Straight Walls in Front of the Filter

Figure 41: CFD flow trajectories with a triangular separator

Figure 41 shows the flow trajectories when a triangular piece is placed in the middle and side walls are placed in front of where the filters are located. The simulation was setup in the same way that was described in section 4.1.1. The walls were added in front of the filters to attempt to mitigate the particles that initially blew straight into the filters.

As can be seen in Figure 41, the air seems to create vortices on each side of the triangle. The vortices seem to be moving more in the z-direction than in the x-direction. This is an encouraging result because it means there is potentially some cyclone separation occurring.

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Figure 42: Particle simulation with triangular separator and walls in front of the filters

Figure 42 shows a particle study with the triangular separator and the walls in front of the filters. The blue particles are at low velocity and the red and green particles are at higher velocity. This study shows that there is particle build up in the corners of the bin next to the walls that are in front of the filters. It also looks like there is a slight concentration of particles near the triangular separator. Both of these accumulation areas are desirable because they are away from the filters, which means that not as many particles will get to the filter. The problem with the accumulation near the walls is that if the buildup increases a significant amount, then the debris could spill over into the duct cutout, which could make the debris fall back onto the ground.

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4.4.2.1 Experimental Results with Triangular Member and Straight Walls in Front of the Filter

Figure 43: Experimental results with triangular separator and a wall in front of the filter

A triangular cardboard member was placed in the middle of the bin and a straight cardboard member was placed alongside the filter. Splenda was positioned in front of the robotic vacuum and the vacuum was pushed over the Splenda. Picture A shows the location of the particles after the experiment was conducted and the filter was removed. Picture B shows where the particles are resting after the experiment. As can be seen in Figure 42, the particles accumulated near the triangular member and around the filter.

These results are slightly different than the particle study that was conducted because in the particle study the wall in front of the filter was a solid impermeable member that air could not flow under or over. Since there is a hole in the bin, it was difficult to get a large enough member inside the bin to make a wall where air could not go under or over. This is why, in the simulation, there is accumulation in front of the wall and in the experiment, there is no accumulation. Other than that detail, the simulation shows very slow-moving particles near the triangular piece and in the experiment, there is also accumulation near the wall.

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This result is better than having a triangle in the middle of the bin, but is still not ideal because there is a large number of particles that build up near the filter.

4.4.3 Circular Bin Design for Inertial Separation

Figure 44: CFD flow trajectories in a multi-bin design

Inspired by woodshop dust separators, a multi-bin separator was studied. For the setup, a blower was placed in the middle bin. The openings on the bins furthest from the middle were set to environmental pressure. The reason that there are so many bins is because there is a height constraint on the robotic vacuum, and it is ideal to maximize the storage capacity so the robot does not need to be emptied constantly. Figure 44 shows vortices that form in the outer bins and there is very low velocity in the center bin. The vortices show that there is a centrifugal force pushing the particles against the bin walls. This simulation show that this design is a great way to separate out the particles before they get to the filter. This would ensure that the filter would not get clogged so quickly, and the airflow would stay more constant.

Even though this design is great at separating out the dust particles so that the filter does not clog, it is not advantageous for picking up larger objects such as screws and nails. The reason it is not good at picking up screws and nails is because it requires a significant amount of suction or a good brush roller that imparts kinetic energy onto the screw to throw it into the bin. With a duct that spans the whole bin, it is easy to fling the screws into the bin from the brush roller. In this design, the screws would have to go through a small opening and probably would not be able to make it into the bin.

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4.4.3.1 Cylindrical Bin Experiment

Figure 45: Cylindrical bin experimental setup

An experiment was conducted to test particle separation using a cylindrical bin. The cylindrical bin was made with a 2-liter soda bottle. There was a hole cut in the top and the side of the bin. The hole in the top of the bin allowed the air to travel from one bin to the next, and a hose was attached to the side hole. Before attaching the hoses to the cylindrical bin, the bin was weighed. 100 grams of flour was placed on the ground and then sucked up. After all of the flour was vacuumed off the floor, the cylindrical bin was weighed again. The final weight was then subtracted from the initial weight of the bin to determine how much flour was trapped in the cylindrical bin.

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Figure 46: Flour separation experiment

Picture A is a picture taken during the experiment, and picture B is after the 100 grams of flour was vacuumed up. As can be seen in picture A, the flour is circulating around the inside of the bin and there is a large spot of flour across from the inlet. Picture B shows that there is very little accumulation in the bin with a vacuum attached to it. Three experiments were run, and the percentage of flour that was in the first cylindrical bin was 80.67 ± 2.52 %. This result indicates that the first cylindrical bin separates a significant amount of the flour before it reaches the vacuum. Even though it is not 100%, it still means that the filter will stay clean for a longer amount of time. If multiple cylindrical bins were in series, like the simulation that was run in 4.4.3, there would be less particles that make it to the filter because there would be two stages of cyclone separation before getting to the filter.

To improve the separation, the duct on the side of the bin should enter tangentially. This would help direct the particles into the vortex motion that is already being created in the bin.

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4.5 Blower Placement

Figure 47: Blowers placed in the back of the bin

To determine the best placement for the blowers, a CFD was conducted. Figure 47 shows the blowers placed in the back of the bin. The flow trajectories in the figure show that the air enters the duct opening and then goes almost straight into the fan. This is not ideal because this would mean that the dust particles would go straight into the filters.

Figure 48: Blowers placed on top of the bin

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If the blowers are placed at the top of the bin, then the air trajectories have a slightly more chaotic path that they must take due to the vortex motion that the fans create. This placement of blowers is still not desirable because the debris goes almost straight into the filter.

Figure 49: Blowers placed on the side of the bin

When the blowers are placed on the side of the bin, there is a nice vortex motion inside the bin. This helps to separate the particles as they enter into the bin. Therefore, placing the blower motors on the side of the bin seemed the most advantageous.

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4.6 Particle Study and Flow Simulation of Cylindrical Bin

Figure 50: Flow simulation setup with cylindrical bin

A flow study was conducted on the second prototype bin design to understand the flow and particle behavior. Figure 50 shows how the flow simulation was set up. The inlets to the ducts were set to an environmental pressure of 101325 Pa, and the external fans were set to user defined RER 120 fans.

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Figure 51: Flow trajectories in a cylindrical bin

Figure 51 shows the trajectories of the airflow in the bin. The flow has a vortex pattern due to the centrifugal fans. The maximum velocity is at the inlets of the blowers because the air is being constricted into a small orifice. There is a void in the trajectories near the middle of the bin. The reason for this dead zone is because the cleaning hatch disturbes the flow pattern.

Figure 52: Midplane cut plot of the cylindrical bin

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Figure 52 shows the velocity and velocity vectors in the middle of the cylindrical bin. Looking at the velocity vectors, one can see that the airflow gets split in the middle of the bin. Some of the air goes to the right blower, and some of the air goes to the left blower. In the middle of the bin, there is a slow velocity zone because it is the furthest away from the blowers. Also, the division of the air in the middle of the bin contributes to the slow velocity.

Figure 53: Cylindrical bin particle study

A particle study was conducted on the cylindrical bin to understand where the particles might settle. The particles were defined as cement dust with a diameter of 50 휇푚. There is a circular pattern in the middle of the bin due to the fact that each blower is competing for the air. This is also a large accumulation of particles near the left blower. This particle buildup might be a result of the cleaning hatch. The cleaning hatch obstructs the airflow and could be forcing the air towards the bottom left corner of the bin.

To make the flow more uniform across the bin, the cleaning hatch should be placed in the middle, but if the hatch is located in the middle, it interferes with another part of the robot. This is why the hatch is asymmetric.

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4.6.1 Experimental Results of Cylindrical Bin

B

A

Figure 54: Cylindrical bin separation

Looking at Figure 54, the flower accumulated near the pipe in the middle (A). This is exactly what the simulation showed. When the experiment was conducted, there was swirling motion around the bin. “B” shows streaks where the swirling motion was most noticeable.

4.7 Scroll Housing and Blower CFD

To understand how the different blower housings behave with airflow, a CFD was conducted on each type of blower housing designed.

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4.7.1 Open-Walled Blower Housing

Figure 55: Open-walled blower housing CFD setup To understand the flow behavior in the open-walled blower housing, a CFD was run. Figure 59 shows the setup that was used to conduct the CFD. A tube was mounted to the blower housing Venturi inlet. The purpose of this tube was to create a steady flow into the blower housing. The simulation that was run was an internal rotational analysis using Solidworks Flow Simulation. The top of the tube was set to environmental pressure, and the three side walls that are exposed to the environment were also set to environmental pressure. The reason that the bottom wall was not placed at environmental pressure is because the chassis plate is blocking the flow on the bottom. To conduct a rotational analysis, a “dummy part” had to be created that was the shape of the impeller. That dummy part was used as the rotational body and was set to 638 rad/s. This is the speed that the RER 120-26/14/2 TDP fan rotates at. The fan blades on the impeller had a boundary condition of 638 rad/s also.

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Figure 56: CFD velocity results from open-walled blower housing

Figure 56 shows a cut plot that was taken in the center of the impeller blades displaying the velocity and the velocity vectors. As the figure shows, the air is greatest at the tips of the impeller. This makes sense because they are the furthest point from the axis of rotation. The blue part in the middle can be ignored because there is a plastic impeller piece that would be taking up that space. As the velocity moves radially away from the tips of the impeller, the velocity quickly goes to zero as it disperses into the atmosphere. Another interesting phenomenon that happens with this blower housing design is that the air at the bottom has to squeeze out the sides and this creates a high velocity stream where all of the air is converging on the bottom plate. This is not ideal because it is most likely creating back pressure which decreases the efficiency of the blower. It could be useful to have a cutout in the bottom of the plate that allows the radially discharged air to escape, but having that cutout might make the blowers blow the dust away before the vacuum sucks it up.

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Figure 57: CFD pressure results with open-walled housing

Figure 57 shows a cut plot of the pressure in the same location that it was taken for the velocity plot in Figure 56. Looking at the figure, it can be seen that there is a low-pressure region around the middle of the impeller. This means that the impeller is creating a slight pressure differential which helps to suck the air in. It can also be seen that there is a high-pressure region on the front side of the impeller blade. At the bottom of the blower housing, there is a high- pressure region caused by the fact that the air is trying to escape, but the chassis plate is pinching the airflow. This is not good because this creates backpressure which decreases the performance of the blower.

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4.7.2 Scroll Housing CFD

Figure 58: CFD setup with scroll housing

A CFD simulation was performed on a scroll housing that was designed for the robotic vacuum cleaner. The scroll housing was designed using the principles in section 2.4. To stay within the height requirement of the robotic vacuum, the scroll housing was decreased, but kept the same curvature of the recommended scroll housing design.

Figure 58 shows how the CFD was set up in Solidworks Flow Simulation. The large tube that is attached to the scroll housing inlet and the rectangular tube that is attached to the scroll housing outlet ensure that the flow entering the system is at steady state. The top of the cylindrical member and the top of the rectangular member were set to environmental pressure. Since this was a rotational analysis, there was “dummy part” that was the rotational member and it was the same size as the impeller. The rotational member was set to a rotational speed of 638 rad/s and the impeller blades were set to have that same angular velocity.

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Figure 59: CFD pressure cut plot of scroll housing

Figure 59 shows a cut plot of the pressures inside the scroll housing. The cut plot was taken in the middle of the impeller blades. The figure shows that there is high pressure along the walls and a low pressure in the middle of the impeller. The low pressure in the eye of the impeller causes a pressure differential and helps suck in more air.

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Figure 60: CFD velocity cut plot of scroll housing

Figure 60 shows a cut plot of the velocity and velocity vectors in the scroll housing. As can be seen in the figure, the vectors are pushed radially against the walls and then collect into a single air stream as it leaves the scroll housing. This is the main purpose of a scroll housing, so it is promising that the results show the vectors all traveling in the same direction at the outlet. Also, notice that the cutoff seems to be working decently. It does not appear that the airflow is bypassing the cutoff and going around the impeller again. This means that the cutoff is located in a reasonable spot.

Even though the scroll housing increases the static pressure and creates more suction, for the robotic vacuum that was designed in this thesis, airflow is more important than suction. The reason that airflow is more important is because the cutout for the duct is so large that there is no need for a lot of suction. Instead, having a large amount of airflow that brings the dust in is more advantageous for this robotic vacuum design. According to the Fan Handbook, having no scroll housing decreases the maximum static pressure by 15%, but almost doubles the air volume at low static pressures [18].

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4.7.3 Peripheral Discharge Design CFD

Figure 61: Peripheral discharge housing CFD setup

The setup for the peripheral discharge housing is shown in Figure 61. All of the outlet ducts and the inlet duct were set to environmental pressure. This was an internal rotational analysis. The rotating region was set to 638 rad/s.

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Figure 62: Peripheral discharge housing velocity cut plot

Looking at Figure 62, the velocity is greatest near the tips of the impeller and is the least in the middle of the impeller. Since there is no opening at the bottom of the housing, there is a larger velocity as the air traverses the distance in the bottom to exit the blower housing. Also, since the outlets for the impeller are not very big, the air might recirculate inside the housing which might be causing the high-speed velocity behind the impeller blades.

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Figure 63: Peripheral discharge blower housing pressure cut plot

With the peripheral discharge blower, there is a low pressure in the middle of the impeller and higher pressure in each of the discharge ducts. Since the air is not able to escape out of the bottom of the duct, there is a high-pressure zone and there is an increase in pressure on the bottom impeller blade. This increase in pressure at the bottom of the unit is probably causing back pressure and could be reducing the efficiency of the blower. However, having the smaller discharge ducts creates a larger static pressure and helps with the suction.

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Figure 64: Flow trajectories of the peripheral discharge housing

Figure 64 shows the flow trajectories of the peripheral discharge housing. In the figure, it can be see that the flow trajectories follow a circular pattern and that only some of the flow is escaping from the discharge ducts. When the flow simulation is animated, it can be observed that the air gets trapped inside and makes several loops around the inside of the housing. This is an adverse result because it probably decreases the airflow through the vacuum bin. It most likely decreases the efficiency of the blower as well.

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4.7.4 Blower Housing with Large Exhaust Ports

Figure 65: CFD setup for blower housing with large exhaust ports

Figure 65 shows how the blower housing with large exhaust ports was set up. The outlets and inlet were set to environmental pressure, and the impeller region was set as a rotational body with an angular velocity of 638 rad/s. To make this simulation work, the exhaust ports had to have a cylindrical body with a lid. This is why there are seven cylindrical ducts. The real design does not have the ducts, it only has the elliptical cutouts (see Figure 23 picture A).

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Figure 66: Velocity cut plot of blower housing with large exhaust ports

Figure 66 shows the velocity and velocity vectors of the blower housing with large exhaust ports. The highest velocity is at the tips, which is what would be expected because the tips of the blades have the largest angular velocity. It can also be seen that there is a high velocity circle depicted in orange. This is an indication that some of the flow is circling around the inside of the housing several times. This phenomenon is not as pronounced in the open-walled blower or the scroll housing. In both of those designs, most of the air escapes on the first pass.

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Figure 67: Pressure cut plot of housing with large exhaust ports

Figure 67 shows a cut plot of the pressure and pressure vector field. There is a low- pressure zone in the eye of the impeller and higher pressure on the back surfaces of the impeller blades. The high-pressure zone on the top duct near the wall would not happen in reality because the actual design does not have the tubes extending out. The orange pressure zone would probably occur. This is due to the fact that the air smacks against the walls, and is abruptly stopped.

This design looks better than the peripheral discharge design because the air had an easier time escaping from the blower housing.

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4.7.5 Conclusions on Scroll Housings

The best design for the scroll housing for the application of the robotic vacuum cleaner is the open walled blower housing. Even though this is the simplest and least visually appealing, it is the appropriate design for the robotic vacuum. It is the easiest and cheapest to manufacture, and it allows the air an easy escape path. All of the other designs create a slightly better suction because of the conversion of velocity pressure into static pressure. But, in the case of the robotic vacuum cleaner, the most important aspect is having a significant amount of airflow. The reason that suction is not as important is because the duct opening is very large and very little pressure differential will be created because of the large openings. Also, with the large duct openings, all that is needed is airflow, so that the particles can follow the trajectory through the duct and into the bin.

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Chapter 5: Conclusions and Future Work

5.1 Summary

The purpose of this project was to develop a robotic vacuum cleaner that could provide preventative maintenance by cleaning up dust and debris on the floor of industrial warehouses. This goal was achieved through a collaborative effort of Barbara Maia Araujo Lima, Jody Fu, Youngjun Joh, Jude Jonas, and Benjamin Schilling.

This thesis focused on the storage bin to collect the debris, the filtration interface with the blowers, and the blower housing design. To accomplish this goal, several iterations of the design were made. Computational fluid dynamics were performed to assess the different designs and to determine which designs seemed the most promising for the application at hand.

From the experiments that were conducted, the robot was able to pick up debris very well and keep it in the bin. The experiments also showed that a large amount of debris gets clogged in the filter, which then drastically decreases the air velocity. By adding different geometric components inside the bin, it altered the airflow, but did not significantly reduce the number of particles that ended up at the filter.

Several housing designs were developed and tested. It was concluded that the best design is the open blower housing, since it provides the air an easy exit and allows for more flow rate, according to the Fan Handbook. The most important characteristic of the blower is to provide sufficient airflow, and the suction generated by the blower is not as important.

5.2 Future Work

To improve the robotic vacuum cleaner, there would need to be more investigation done on inertial separation to ensure a large airflow. A larger blower motor could be used, but there would need to be a trade study that compares the amount of suction generated by that motor with how long the robot can run before going back to the charging station. Also, research would need to be conducted to figure out an elegant and efficient solution for picking up liquids and large

81 objects. Since these designs are proof of concept, more design for assembly and design for manufacturability would need to be done in order to make large numbers of these robotic vacuums. Currently, the designs rely heavily on 3D printing and would be difficult to manufacture using other techniques.

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