SCUBA Pressure Regulator for Prosthetic Limb Volume II

Aaron Hatlevoll

Travis Hulbert

Justin Lerbakken

Peter Swift

Adam Trulen

Table of Contents

1. Problem Definition Supporting Documents………………………………………………………………………...1 1.1 Annotated Bibliography……………………………………………………………………………………………..1 1.2 Patent Search…………………………………………………………………………………………………………….3 1.2.1 Objective……………...………………………………………………….………………………………….3 1.2.2 Search Criteria…………………………………………………………………………………………….3 1.2.3 Findings……………………………………………………………………………………………………...3 1.3 User Needs Research…………………………………………………………………………………………………5 1.4 Concept Alternatives………………………………………………………………………………………………….5 1.5 Concept Selection………………………………………………………………………………………………………7 2. Design Description Supporting Documents……...…...……………………………………………………………...8

2.1 Manufacturing Plan………………………………………..…………………………………………………………..8 2.1.1 Manufacturing Overview………………........………………………………………………………..8 2.1.2 Part Drawings…………………………….......……………………………………………………………9 2.1.3 Bill of Materials……………………………..…………………………………………………………...12 2.1.4 Manufacturing Procedure…....………..……………………………………………………………13 3. Design Evaluation Supporting Documents……….....……………………………………………………………...17

3.1 Evaluation Reports…………………………………………………………………………………………………..17 3.1.1 Activation Pressure Evaluation…………………………………………………………………..17 3.1.2 Cost Estimate……………………………….....…………………………………………………………19 3.1.3 Adaptability to Existing SCUBA Configuration Evaluation ……………........………...20 3.1.4 Ergonomic Evaluation…………………………………………………………..........………………22

3.1.4 Pressurization and Impact Failure Evaluation….......…….....................………23 3.2 Environmental Impact Statement………………………………………………………......…………......…..27

3.2.1 Purpose and Need………………………………………………………...........................…………..27 3.2.2 Impact to Environment……………………………………………................……………………..27

3.2.3 Alternatives to Design…………………………………………………...................………………..27

3.2.4 Discussion……………………………………………………………..........................................……..27

3.3 Regulatory and Safety Considerations....................................................................................................28

1

1. Problem Definition Supporting Documents

1.1 Annotated Bibliography

The following sources are a mix of SCUBA and prothesis literature. They detail the technology relevant in each field and include history, design and usability discussion, and safety considerations. These sources aided this project by providing important context for the design of a prosthesis regulation system. [1] Kin M. Norton, 2009, “A Brief History of Prosthetics”,

http://www.amputee-coalition.org/inmotion/nov_dec_07/history_prosthetics.html

Norton provides historical context for the field of prosthesics, from 300 B.C. to present day. [2] Christine Dell’Amore, 2007, “Photo in the News: Mummies’ Fake Toes could be first

Prosthetics”, http://news.nationalgeographic.com/news/2007/07/070727-egypt-toe.html

Dell'Amore describes an archeological find of an ancient prosthetic. [3] Denise Wang, 2011, “Types of Sleeves for Prosthetic

Legs”, http://www.livestrong.com/article/38182-types-sleeves-prosthetic-legs/ Wang describes the multiple types of protective sleeves used in prosthetics. [4] Lawrence Martin M.D., 1997, “A Brief History of Diving From Antiquity to the Present”

http://www.lakesidepress.com/pulmonary/books/scuba/frames.htm Martin provides historical context for SCUBA diving, from ancient pearl divers to modern equipment. [5] “Scuba Unit” http://www.padi.com/scuba/scuba-gear/scuba-gear-descriptions-

tips/scuba-unit/default.aspx PADI, an international SCUBA training organization, details the various pieces of equipment used in recreational SCUBA diving. [6] “Scuba Tanks” http://www.padi.com/scuba/scuba-gear/scuba-gear-descriptions-

tips/scuba-unit/scuba-tank/default.aspx PADI, an international SCUBA training organization, details the various features of tanks used in recreational SCUBA diving. [7] 2002, “SCUBA Valves, Regulator Fittings, and Cylinder Neck Threads” http://

www.divegearexpress.com/library/valves.shtml

2

Dive Gear's article addresses common questions regarding SCUBA valve options and includes important pressure values and part numbers. [8] “Difference Between Din and Yoke Scuba Tank Valves”

http://www.scuba.com/video/23/Differences-between-Din-and-Yoke-tank-valves.html

This video shows the differences between the two standard types of SCUBA tanks. [9] Eric Hanauer, “Regulator Basics, Part 1: the First Stage”

http://www.dtmag.com/Stories/Dive%20Equipment/02-00-feature.htm Hanauer describes the inner workings of a first stage regulator. [10] Lisa Porter, 2010, “How Does Scuba Equipment Work?”

http://www.livestrong.com/article/117152-scuba-equipment-work/ Porter gives a basic overview on the practical implementation of SCUBA equipment. [11] scubanetwork, 2010, “How its work - Scuba Dive Regulator 2nd Stage –

www.Scubatraveller.com”,http://www.youtube.com/watch?v=mnd-nhmgHaM This animated video shows the inner workings of the second stage regulator. [12] Bob Rutlegde M.D., “Regulators?”, http://www.dogndive.com/dive/reg/publ.html Rutledge covers the mechanisms in a regulator in great detail. [13] Pedemonte, S., 2004, “Second-stage regulator for scuba divers,” U.S. Patent 8166974 This is a patent for a second-stage regulator, which includes part drawings. [14] Hart, D.L., 1991, “Divers first stage adjustable regulator,” U.S. Patent 5184609 This is a patent for a first-stage regulator, which includes part drawings. [15] Fundora, R.A., Pomerantz, M.P., 1992, “Breathing regulator having air injector feature,”

EP Patent 0534741 A1 This is a patent for a second-stage regulator, which includes part drawings. [16] Roberts, R.E., 1971, “Inflatable vest having a quick-release hose connection to supply tank,” U.S.Patent 3747140 This patent includes quick connect fittings.

3

1.2 Patent Search

1.2.1 Objectives

One of the many functions of SCUBA equipment is the regulation of pressure as the diver ascends and descends underwater. Because of this, many existing products could regulate the pressure of an airtight prosthesis, which is the main objective of this project. This project’s design is a smaller regulator that is connected from the buoyancy control device to the prosthesis, adding air to the prosthesis as the pressure of the surrounding environment changes. The housing of the regulator, as well as the Y-valve that will connect the regulator to the BCD will most likely be patentable. 1.2.2 Search Criteria

The database that was used to search for patents related to this project was Google Patents. This proved to be a better search engine than USPTO, which was used initially. The main class that was searched was A62B7/04, which is a classification of air flow devices, such as SCUBA regulators, respirators and pressure support systems. The keywords “SCUBA regulator,” “SCUBA diaphragm,” and “pressure regulator” were also used. 1.2.3 Findings

The patent with the most risk was found to be a second stage demand breathing regulator manufactured by APEKS, which uses a diaphragm to regulate the pressure when the diver breathes into the scuba system, patent number EP 0278598 B1. The diagram from the patent is shown in the Figure 1. This patent poses a risk because it regulates pressure for the person breathing in the air, while the proposed design would regulate pressure in the prosthesis. The current project will use a similar diaphragm configuration, but will design a new apparatus around the diaphragm. This patent was issued in 1991, so the parts of this apparatus can be used in the prosthesis pressure regulator. Another patent that poses some risk is another second stage pressure regulator, this one manufactured by U.S. Divers Co., patent number EP 0499507 B1. The diagram from the patent is shown below in Figure 2. This poses a threat because it performs a similar function to our product, but it regulates the pressure of the person breathing. The current product will regulate the pressure inside a prosthetic limb. Also, a pressure regulator has never been used in this fashion, which suggests that the housing of the regulator, as well as any other custom parts that we design for this apparatus are patentable.

4

Figure 1: APEKS 2nd Stage Regulator, Top View (Fig.1) and Side View

Figure 2: U.S. Divers Co. 2nd Stage Regulator (Side View)

5

1.3 User Needs Research

User needs research was conducted using multiple methods, mainly utilizing direction from the team’s project advisors, who will likely be the first customers for the device. User needs were also determined by asking local dive shops for information and opinions on pressure mechanics, existing products, and possible implementation of the device. The team also conducted ergonomic evaluations for different configurations with existing SCUBA equipment in order to determine the most comfortable ways to incorporate the device into the diver’s equipment. The user needs were then interpreted by the design team and given a rank of general importance on a scale of one to five. A summary of these user needs is shown in Table 1.

Table 1: User needs research results.

No. Need Imp

1 The regulator reduces pressure as needed 5

2 The regulator increases pressure as needed 5

3 The regulator operates automatically 5

4 The regulator operates without electronics 4

5 The regulator allows for personal adjustment 2

6 The regulator is lightweight 3

7 The regulator stays dry on the interior 5

8 The regulator is inexpensive 3

9 The regulator is non-corrosive with seawater 5

10 The regulator is easy to install 4

11 The regulator works with many SCUBA configurations 4

12 The regulator is non-obtrusive to the diver 3

13 The regulator does not interfere with other diving equipment 3

14 The regulator is safe 5

15 The regulator does not interfere with emergency diving procedures 5

16 The regulator does not significantly decrease dive time 2

17 The regulator is comfortable to wear while diving 3

18 The regulator is easy to clean and maintain 4

19 The regulator is able to be reached by the diver during a dive 5

1.4 Concept Alternatives

A number of concept alternatives were considered during the development process. A concept generation brainstorm session yielded many promising ideas. Many more were discarded for not meeting the specific design criteria. One possible concept that emerged was a pressure regulation system that utilized bladders which could fill with ocean water as the diver descended. Figure 3 shows this concept. On dry land, the bladders within the prosthetic would deflate, allowing normal comfort for the

6

Figure 3: Diagram bladder

pressure regulation concept

user. When the diver began his/her descent, these bladders would fill with ocean water. The inflation would regulate pressure within the prosthetic, while maintaining a dry

environment to prevent loss of adhesion to the user. Ideally, this concept would work without any input from the user. It would also require no connection to the diver’s equipment, and likely maintain normal comfort during use on dry land. This idea was discarded during the concept selection process when it was discovered that the cost of modifying an individual’s prosthetic would greatly deter casual SCUBA divers from buying the product. Other concepts involved direct connection to the diving equipment. A button valve connected to the air cylinder would allow on-demand air addition to the prosthetic for pressure regulation. It was determined that this solution would be relatively easy to implement. As a similar design, the team considered a diaphragm valve, similar to a conventional second-stage regulator, which would achieve the same result but without constant attention of the user. This was the final design chosen. After this decision had been made, new concepts were introduced regarding the ergonomics of the system. SCUBA diving is an inherently dangerous activity, and direct connection to the diving equipment introduced

several safety concerns. The design could not interfere with normal operating maneuvers of a diver. In addition, the entire apparatus needed to easily and entirely disconnect from the dive equipment in case of an emergency. The regulator style design uses SCUBA hoses connected to the air cylinder, which needed to navigate the user’s body in a comfortable, ergonomic fashion. The initial outline for this was to split the low pressure hose from the BCD inflator line, and run this new line left along the diver’s ribcage and down to the hip. The hip would hold the regulator valve, where another hose would run down the user’s thigh and into the prosthetic. This concept was discarded when research uncovered the need for divers to raise the BCD controller above his/her head when purging air from the BCD, an action of done during the dive’s descent. It became apparent that a new hosing strategy was needed. As a result, an ergonomics feasibility session was conducted, which compared possible hosing solutions. The hosing solution needed to supply low pressure BCD air to the regulator system. As a design requirement, it also needed to work for both right and left leg amputees. The BCD controller is conventionally placed on the left of the diver’s chest, which presented a problematic non-symmetry.

7

The concepts presented mostly included running a hose over the diver’s shoulder parallel to the BCD inflator line. This configuration fixed the earlier described problem of not allowing the diver to raise the controller. At this point, the choice lay between running the hose behind the neck, near the first stage regulator and above the air cylinder, or below the tank and near the diver’s lower back. Both concepts held inherent strengths and weaknesses. 1.5 Concept Selection

The concept selection process weighed the pros and cons of each solution in a matrix. This method allowed the team to objectively compare the benefits of each concept. Table 2 shows one such elimination matrix. The matrix includes the bladder system described earlier, as well as both regulator valve types. Selection criteria included ease of installation, ease of manufacture, durability, ease of operation, comfort, activation differential, and cost. The ease of installation category refers the difficulty of attaching the system on a dive boat to the equipment, and also attaching the system to existing prosthetics. The water bladder concept scored low in this category because in order to maintain

Table 2: Selection matrix for choosing final design.

Selection Criteria Weight Rating

Weighted

Score Rating

Weighted

Score Rating

Weighted

Score

Ease of installation 0.2 4 0.8 3 0.6 1 0.2

Ease of Manufacture 0.05 3 0.15 3 0.15 3 0.15

Durability 0.15 3 0.45 3 0.45 3 0.45

Ease of operation 0.2 5 1 2 0.4 5 1

Comfort 0.2 4 0.8 4 0.8 3 0.6

Activation differential 0.05 3 0.15 3 0.15 4 0.2

Cost 0.15 4 0.6 4 0.6 1 0.15

Total Score

Rank

Continue? NoNoDevelop

3.95 3.15 2.75

321

A

Diaphragm

Regulator

B

Push-Button

Regulator

C

Water Bladder

Concept

comfort, each prosthetic would require a custom fitting. Ease of manufacture was considered equal among the concepts. Durability was a major concern, in large part because of the corrosive nature of seawater. It was determined that each concept could be manufactured using corrosion resistant materials, so this category did not differentiate the designs. The ease of use and comfort categories were weighted heavily because they were the ultimate end-goal for the design. The push-button design scored low in this category

8

because it required user input to function. Activation differential refers to the pressure differential between ambient water pressure and that within the prosthetic. This category was weighted as relatively unimportant because most designs were well within the 15 psi threshold. Most were closer to a 1-3 psi differential. The diaphragm regulator design was chosen because it successfully accomplished pressure regulation without active user input. The regulator design was similar to existing second-stage regulators, which meant existing technology could be repurposed. Existing designs for second-stage regulators were already designed to be corrosion resistant and work well in a scuba environment. A similar metric was used to determine the ergonomics of the hosing. It was decided that the best solution was to run the hosing from the BCD inflator over the shoulder and down to the hip. For right leg amputees, the line would run above the air cylinder and behind the neck. The final solution was chosen because it best accomplished comfortable pressure regulation within the prosthetic. It allowed the user to move easily while diving, and made connecting and disconnecting on the dive boat easy. The design chosen is safe, and can be removed quickly in any emergency regardless of the dive equipment types used by the diver. 2. Design Description Supporting Documents

2.1 Manufacturing Plan

2.1.1 Manufacturing Overview

The design incorporates two different models: a working prototype, and a finished part. The finished part was not able to be made during this semester due to budget and machine issues; because of this, two prototypes were made. The prototype was 3D printed looks similar to the final model, but because of the 3D printing process it will be porous and unable to sustain the pressures needed. The prototype was 3D printed as stated earlier. The manufacturing process for this is very simple. A .STL file will be uploaded into the 3D printer and printed out. This is the same process used to make the intermediate prototypes. A .STL file is a file format used by both Solid Works and Pro E. This is read by the 3D printer and then the printer is able to make the part. 3D printing is an additive process where a layer is created and the layer above is created, each layer a section of the geometry of the part. The 3D printed part was then coated in an epoxy to assist with the unwanted porous nature of a 3D printed part.

The final model was not made in this project. This is because the best way to produce the part in the long run is to use an injection modeling process. This allows for the use of the complex geometry of the aesthetic and ergonomic prototype, while gaining the ability to be made out of a non-porous stronger material. The process would be cheaper in the long term, but if only one part is produced, cost of creating the die and then injection molding

9

one part would be very expensive. In order manufacture an injection molded part, the die must first be milled using the negative geometry of the final product. Two plates would need to be created. The injection modeling machine then injects liquid plastic into the die which, when cooled, would be the finished part.

2.1.2 Part Drawings

An overall assembly of the prosthetic regulator system is shown in Figure 4. The regulator system is made of many components that can be supplied by manufacturers that specialize in SCUBA equipment, predictably at a cheaper cost than Pongratz Engineering could manufacture the parts. However, two parts that Pongratz Engineering would need to manufacture are the regulator body and regulator cap, shown in Figure 5 and Figure 6, respectively. Both of these pieces require detailed drawings in order to create the die used in the injection molding process to produce them.

Figure 4: Assembly drawing of the prosthetic regulator system.

10

Figure 5: Detailed drawing of regulator body used to create future injection die.

Figure 6: Detailed drawing of regulator cap used to create future injection die.

11

In addition to the parts and dies required to put the prosthetic regulator system into production, another avenue of design was considered. Originally, it was thought that the FDM material used by the 3D printer would not hold up to the pressures required to test the regulator concept. This spurred the design of a regulator prototype that could be easily manufactured with minimal tooling, while still maintaining functionality. A rendering of this functional prototype is shown in Figure 7. Fortunately, the FDM material was able to fulfill the requirements for the scope of this project and the functional prototype was never needed, saving money for Pongratz Engineering and time for the design team.

Figure 7: Renderings of unused prototype designed for testing purposes.

12

2.1.3 Bill of Materials

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13

2.1.4 Manufacturing Procedure

Operation 1: 3D Printing body

Machine: Stratasys SST 768 3D printer

Time: 30 hours

Step 1: Send file to printer

Tool: Computer & Stratasys SST 768 3D printer

Procedure: Send regulator.STL file to the printer

Time: >1 min

Step 2: Print body

Tool: Stratasys SST 768 3D printer

Procedure: Start printer and let it complete

Time: 15 hours

Step 3: Bath

Tool: Ammonium sulfate and water solution

Procedure: Place part in bath

Time: 15 hours

Operation 2: 3D Printing cap

Machine: Stratasys SST 768 3D printer

Time: 25 hours

Step 1: Send file to printer

Tool: Computer & Stratasys SST 768 3D printer

Procedure: Send cap.STL flie to the printer

Time: >1 min

Step 2: Print cap

Tool: Stratasys SST 768 3D printer

Procedure: Start printer and let it complete

Time: 10 hours

Step 3: Bath

Tool: Ammonium sulfate and water solution

Procedure: Place part in bath

Time: 15 hours

14

Operation 3:

Epoxy

Regulator

Machine:

Loctite

Epoxy

Time: 25 mins

Step 1: Mix Epoxy

Tool: Popsicle stick

Procedure: Mix resin & hardener on a cardboard, stir to assure good mixture

Time: 5 mins

Step 2: Epoxy Regulator

Tool: Paint brush

Procedure:

Paint on the epoxy with a brush paying special attention to edges,

epoxy only exterior, up to threads.

Time: 20 mins

Step 3: Dry

Tool: None

Procedure: Let part sit out over night

Time: <12 hours

15

Operation 4: Tap Regulator

Machine: Hand

Time: 10 mins

Step 1: Tap Regulator inlet

Tool: 9/16" -18 TPI Tap

Procedure: Tap Inlet 1" deep

Time: 5 mins

Step 2: Tap Regulator inlet

Tool: 9/16" -18 TPI Tap

Procedure: Tap Outlet 1" deep

Time: 5 mins

16

Operation 5:

Machine

couplings

Machine: Lathe

Time: 35 mins

Step 1: Face Part

Tool: Triangle Insert

Procedure: Face Part

Time: 1 mins

Step 2: Machine OD

Tool: Triangle Insert

Procedure: Machine OD to 9/16" 1.25" long

Time: 5 mins

Step 3: Center Drill

Tool: Center Drill

Procedure: Center drill

Time: 3 mins

Step 4: Drill first hole

Tool: .173" drill

Procedure: Drill part to 1.25" depth

Time: 5 mins

Step 5: Drill second hole

Tool: 3/8" drill

Procedure: Drill part to .5" depth

Time: 5 mins

Step 6: Thread OD

Tool: 9/16" -18 TPI die

Procedure: Remove bar from lathe and place in vice, thread entire OD with Die.

Time: 5 mins

Step 7: Cut off

Tool: Cut off tool

Procedure: Cut off part at 1.25"

Time: 5 mins

Step 8: Face opposite edge

Tool: Triangle insert

Procedure:

Place cut off tool in machine backwards, do not tighten as to not harm

threads, face part for smooth surface

Time: 1 mins

17

Operation 6

: Assembly

machine: Hand

Time: 15 mins

Step 1: Inserting spring mechanism

Tool: Pliers

Procedure

:

Insert spring, valve piston, and piston spacer into inlet. Screw on

lock nut

Time: 10 mins

Step 2: Insert lever

Tool: Hand

Procedure

: Push valve piston and place lever behind lock nut

Time: 3 mins

Step 3: Insert couplings

Tool: Hand

Procedure

:

Insert coupling into inlet until it hits the valve piston, insert coupling

into outlet.

Time: 2 mins

3. Evaluation Supporting Documents

3.1 Evaluation Reports

3.1.1 Activation Pressure Evaluation

Introduction

One of the important design aspects of the regulator is the automatic pressure regulation between the prosthetic and the surrounding water, resulting in a characteristic of the regulator called activation pressure. The activation pressure of the regulator is the required pressure difference between the air inside the regulator (acting on the inner side of the diaphragm) and the ambient pressure of the water (acting on the outer side of the diaphragm) needed to depress the diaphragm and valve lever and start a flow of air into the prosthetic. This aspect of the design is important because it determines how large of a change in depth is required to activate the regulator and equalize the pressure between the inside of the prosthetic and the water, effectively easing the diver’s discomfort. As the diver descends the ideal activation pressure should be as small enough to not cause the diver discomfort between equalization, but not so small as to have the regulator injecting air on a nearly-constant basis. The ideal range for the activation pressure of the diaphragm is 1-2 psi, which corresponds to approximately a 2-4 foot change in depth. .

18

Method

To test the activation pressure of the regulator, a weight test was conducted using a set of weights and a scale. An increasing amount of weight was added to the top of the diaphragm until air was exhausted out the outlet. When air was released, the weight was removed from the diaphragm and measured. From the weight measured, the required activation pressure in psi was calculated using the equation Pressure = Force/Area. The average value of the activation pressure was calculated with some uncertainty. The data is shown in Table 4.

Results

The conclusion from the activation pressure test was that an average of 0.29 psi is required to activate the regulator, which equates to about 0.66 feet of water. This result reveals that the diver does not have to descend too far for the ambient water pressure to be large enough to activate the regulator. Once the ambient pressure of the water increases enough, it will depress the diaphragm and cause the lever to open and deliver the air to the prosthetic limb.

Table 4: Activation pressure test data

Weight

(lb)

Area

(in2)

Pressure

(psi)

0.45 1.20 0.38

0.33 1.20 0.28

0.35 1.20 0.29

0.34 1.20 0.29

0.27 1.20 0.23

0.34 1.20 0.29

0.35 1.20 0.29

0.33 1.20 0.28

0.34 1.20 0.28

0.33 1.20 0.28

Average 0.29

Std Dev 0.03

average w/o outliers 0.28

CI 95% 0.02

Discussion

With an average activation pressure of 0.29 psi, the diver’s discomfort would be non-existant. About 15-30 feet of water causes a large amount of pain and discomfort for the diver. With an activation pressure equivalent to 0.66 feet, the diver will have air pumped into the prosthetic limb long before any discomfort would be experienced.

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3.1.2 Cost Estimation

Introduction

The cost of the regulator plays a key role in determining if the device is a viable option for amputees who wish to SCUBA dive. Whether the end user is a casual or avid diver, a high price point would deter many potential customers from buying the prosthetic regulator. The cost of the purchased components, machined parts, materials, and labor must all be considered when determining the retail price of the device in order to make the investment worthwhile by Pongratz Engineering. In order to establish the final retail price the price of each component must be taken into account. The concept of economies of scale may also be taken into account when items can be bought in bulk. While the prototype produced for this design report was a one-off design, many of the parts used in fabricating the prototype would still apply if production were scaled to a larger level. Additionally, a large-scale operation would make use of different manufacturing procedures than those used to make the prototype. Method

To determine the retail cost of the regulator if it were to be put into production, the cost of materials, machining, and labor must all be taken into account. A large-scale production of the regulator would most likely utilize an injection molding process to produce the plastic regulator housing as well as SCUBA equipment manufacturers to provide the appropriate fittings, valves, hoses, and other miscellaneous parts. Labor and marketing also play a key role in setting a final price for the regulator system. The price of manufacturing the regulator housing is dominated by the price of the die used for the injection molding process. The cost of having a die machined for this use can cost several thousand dollars, a cost that needs to be made up over the production life of the regulator. While the die used for injection molding has a high up-front cost, the materials used in injection molding are relatively cheap and benefit from being bought in large quantities. The prices for fittings, valves, and hosing are generally controlled by the manufacturer, although cheaper prices are available when buying large quantities. To estimate the total cost of the regulator, each one of the components used to make the prototype must be analyzed and estimated what a large-scale cost of the component would be.

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Results

Table 5: Estimates for component costs of prosthetic pressure regulator

Volume

(in3) Density (lb/in3)

Weight (lb)

cost per 1 (USD)

main body 3.35

lid 0.85

regulator 4.2 0.03791 0.159222 0.206989

hose 60

internal assembly 5 diaphragm and exhausted valve 60

couplings 10

total cost 135.207

From this, the estimated cost for materials to produce the regulator can be assumed to be about $150. The cost of the material of the actual regulator is very cheap and the main cost comes from the SCUBA equipment obtained from third-party SCUBA manufacturers. Another large cost comes from the diaphragm which could be cheapened by self-manufacturing, but at the moment no plans are made to manufacture this component. The next component of cost comes from the die which will be used for the injection molding process. A die could cost as much as $10,000. While the initial cost is high, the more parts produced by the die, the less the die will cost per part. If enough parts are manufactured and sold, the cost of the die is paid back, making future production comparatively cheap. The final consideration for cost is labor and marketing. Since the product will initially be produced and manufactured by Pongratz, the cost of packaging and marketing the regulator would add to the retail price dramatically. Also because our product is a specialty part this could drive the cost up more due to it being a niche market, although the price customers are willing to pay for the product may be higher due to the lack of alternatives in the market. An estimate for the retail price of the regulator system would range between $300-$500, a price well within the target range of $1500-$2000. 3.1.3 Adaptability to SCUBA Configurations Evaluation

Introduction

The requirement that the device is adaptable to many different SCUBA configurations stems from the many levels of experience that divers have with their equipment. While some divers own items such as regulators and BCDs, many novice and intermediate level divers end up renting dive equipment from rental shops when they wish to go on a dive. For this reason, the device has the option of attaching to directly to the 1st-stage regulator (a semi-permanent attachment that requires the use of tools) or attaching to the end of the

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BCD inflator hose using quick-disconnect fittings (a non-permanent option for divers renting equipment). The connection directly to the 1st-stage regulator has been a set standard thread size for many years, resulting in nearly every regulator and hose manufacturer to use the same threaded connection. The quick-disconnect attachment on the BCD has also been standardized over the years, although there is more variation with the connection due to different desired flow rates from the 1st-stage regulator to the BCD. Since the connection directly into the 1st-stage regulator is nearly uniform for all different makes and models of regulators, the main focus of the evaluation will be on the connection using the BCD inflator hose.

Methods

The criteria of adaptability to different SCUBA configurations will be evaluated by determining the average time it takes for a person to attach the regulator and hosing to an existing set of SCUBA equipment. This experiment is meant to replicate the situation of a diver attempting to assemble their equipment while en route to a dive location. This test also evaluates how easily the system is implemented if the person using the regulator is unfamiliar with the equipment they are given in the case that they do not own the equipment.

The experiment consists of giving several different people a BCD with a filled air tank and regulator already attached (a common situation found on a dive boat). The person was then instructed to put the equipment on and attach the additional prosthetic regulator after only a brief bit of instruction. The person was timed on how long it takes to attach the prosthetic regulator and additional hosing to the BCD and get the regulator situated comfortably on their body. Additional notes were made if there is confusion regarding certain aspects of the equipment or if the person was unable to assemble the system. The different trials were then evaluated to determine the average time-to-assemble.

Results

The results of the adaptability testing showed that the prosthetic regulation system could be attached to the diver reasonably quickly after only a brief bit of instruction. The results of the trials are shown in Table 6. The average time to assemble the system was around 50 seconds, with a 95% confidence interval of ±11.7 seconds, making a reasonable estimate of the maximum time to assemble 61.6 seconds.

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Table 6: Test results for adaptability testing showing time required to assemble the

prosthetic pressure regulation system.

Trial Assembly Time (sec) 1 51.8 2 52.7 3 44.7 4 66.1 5 95.0 6 40.4 7 44.6 8 30.6 9 31.4 10 41.8

Average: 49.9 Std Dev: 19.0 95% Interval: 11.7 Results: 49.9 ± 11.7 seconds

Discussion

The results of the test show that attaching the prosthetic regulation system to the diver using quick disconnect fittings is fast and effective. Minimal instruction was required of the participants and all participants were able to completely attach the system. The results also show that the system is easily assembled within two minutes, meeting the design criteria for the regulator’s ease of use.

3.1.4 Ergonomic Evaluation

Introduction

A major consideration for the project was the comfort and ergonomics of the system. A diver is unlikely to use the system if it would present more impairments than it solves, so ease of use was a primary goal of the design. It was determined early that the hosing layout of the final product must not interfere with any of the possible basic maneuvers a diver may attempt. The design must also be comfortable while on a dive boat, while swimming on the surface, and while diving underwater. An ergonomics study was conducted to determine whether the design would satisfy these needs. The study needed to test comfort and usability in all relevant environments for diving and identify weaknesses of the design to be addressed. The hosing layout is easily modifiable so it was expected that some comfort issues could be addressed and remedied during the test.

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Method and Results

To test the usability of the system, an ergonomics prototype was fitted to a diver. The ergonomics prototype was nonfunctional, and did not include interior mechanics necessary to actuate any pressure regulation. It included a printed regulator model, and two Miflex hoses which were used in the final design. The prototype was fitted to the diver's gear with plastic clips and a fabric strap fitted to the diver's leg. The diver was asked to run through several common maneuvers while wearing SCUBA equipment, and comment on the comfort and usability of the system as a whole. Two expert divers were also on hand to comment on the system. The system's hoses were somewhat long for the diver, so the extra slack coiled and secured with plastic clips. This also allowed the diver freedom of movement since the bights flexed with the diver's joints. Several important maneuvers were tested, including raising the buoyancy compensator hose over the head to bleed air, which also raises the upstream hose of the prototype. Because the prototype hose parallels the BC line over the shoulder, the process was unimpeded. Another important action tested was a regulator retrieval, wherein the diver's mouthpiece is pulled from the mouth. A large sweeping motion of the arm collects the mouthpiece hose, and brings the breathing apparatus back to the diver. It had previously been a concern that extra hosing may tangle in the retrieval process, but the prototype hoses were well clear of the diver's arm. The regulator valve part was clipped to a metal ring on the compensator near the waist of the diver. Though the prototype used did not include a manual button, it could be easily reached and activated when the feature is included to the system. Discussion

Overall the test was a resounding success, and proved that the hosing layout and regulator ergonomics were sound. The test diver claimed, "I didn't even notice it." A weakness of the test may be that the diver was not wearing a wetsuit, where it is expected that most users of the product would be. For a wetsuit diver, a fabric loop could be sewn to the wetsuit instead of using fabric strapped to the leg. An asset of the system is that the layout is largely customizable by the user, who may prefer a sewn loop to the strap or vice versa. The ergonomics test proved that the system was not a hindrance to the diver, and further customization could only improve upon the comfort achieved. 3.2.5 Pressurization and Impact Failure Evaluation

If the outlet port of the regulator is blocked, and the mushroom valve on the regulator is blocked, a large pressure could be experienced inside the regulator. To ensure that the regulator doesn’t explode and cause injury to the person wearing this regulator, a maximum pressure simulation was performed using ANSYS Static Structural analysis. The mesh used in this analysis is shown in Figure 8. The most pressure that would be experienced inside the regulator would be the amount of pressure coming from the SCUBA

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tank, which is 150 psi. This pressure was applied to all faces inside the regulator model. Another test was performed in ANSYS to ensure that the regulator can survive being dropped from five feet, testing the durability of the product. A force of 50 lb. was applied to the outside faces and edges of the regulator to simulate a fall and impact with a hard surface from 5 feet. The regulator was simulated with polycarbonate as its construction material

The results of both of these tests are shown below. For the failure test, the maximum deformation was 0.0004 inches and the maximum stress was 70 psi. The contour plots for each of these values are shown in Figures 9 and 10, respectively. According to these results, if the regulator fails or is blocked, the part will not explode and cause harm to the diver wearing the regulator. For the impact test, the deformation of the part reached no more than 0.0001 inches, and the maximum stress of the regulator was 50 psi. The contour plots of each of these values are shown in Figures 11 and 12, respectively. According to these results, if the regulator falls from a normal distance, the regulator should survive the fall and maintain its structural integrity.

Figure 8: Mesh of regulator geometry

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Figure 9: Deformation contour plot of failure testing

Figure 10: Stress contour plot of failure testing

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Figure 11: Deformation contour plot of impact testing

Figure 12: Stress contour plot of impact testing

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3.2 Environmental Impact Statement

3.2.1 Purpose and Need

The prosthetic regulator provides a comfortable experience while SCUBA diving for an individual with a prosthetic limb. This service is valuable because it adds a whole new group of people into the SCUBA market who will rent or buy their own equipment along with this product.

3.2.2 Impact to Environment

The materials used to create this product are the same materials used to create existing SCUBA equipment. In its final stage, the regulator housing will be injection molded out of polycarbonate, a common plastic used in most plastic SCUBA components. Plastic is harmful to the environment because it doesn’t decompose and could potentially pollute the ocean if lost or discarded. The injection molding machine uses large amounts of energy, depending on the machine and mold process used. The inner components of the regulator are made of rubber and steel, and the SCUBA fittings and hoses used in the apparatus are made of brass and carbon fiber, respectively. These components are made by other companies, so suppliers should be chosen based on their environmental consciousness.

3.2.3 Alternatives to Design

One way to better design the prosthetic regulator for the environment would be to use a recyclable plastic to manufacture the regulator housing. This would enable the plastic used to make the product to be reused if the regulator gets damaged beyond repair or is discarded for a newer model. Another way to better design the prosthetic regulator for the environment would be to use another manufacturing method other than injection molding that uses less energy. Such methods include blow molding, rotational molding and thermoforming. The other components that need to be ordered from other manufacturers should be ordered from companies with a high environmental consciousness.

3.2.4 Discussion

The above design alternatives should be pursued if they are cost effective. Recycled plastic is a good way to design for the environment, but the process to recycle plastic is more expensive than just manufacturing a non-recyclable plastic. However, in the long run, this may prove to be a cost effective strategy if the plastic used to make new products came from the older products, saving money on materials. This would be a good process to research more for future versions of the regulator. Injection molding has a high initial cost, but is less expensive to make more products once the initial mold is created. In the long run, this is a less expensive option than other processes. The amount of energy used to run the injection molding machine is larger than other processes, but the cost outweighs this factor. Using an injection molding process is still recommended, unless a less expensive alternative that uses less energy is found.

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3.3 Regulatory and Safety Considerations

From research and information gathered from SCUBA equipment vendors, there is no central regulatory and certification agency of SCUBA equipment. The industry is mostly self-regulated, with certification and regulatory agencies for SCUBA trainees and instructors, such as PADI and NAUI. SCUBA equipment vendors have their own set of standards and technical requirements that would need to be passed to distribute this product in their shops. Following SCUBA vendors testing and technical requirements would ensure the trust of the vendors as well as the customers. From a safety standpoint, this product, as well as the apparatus around the device, has been designed to follow the same procedures while diving to ensure a safe experience while SCUBA diving. To address any safety concerns, it is recommended to follow all regular SCUBA safety precautions to prevent injury and ensure the safety of other divers.