External Enclosure

External Enclosure

• Needs– The external package should be lightweight/ robust/ water resistant– The devices should be competitive with current devices– The device should fit into a small pouch and be comfortable for user

and be comfortable for the user– The external package should resist minor splashing– The device should survive a fall from the hip

• Risks– Housing for the electronics is too heavy/large/uncomfortable– Water can enter the external package and harm the electronics– The housing fails before the electronic components in drop tests– The electronic components can not survive multiple drop tests

Concept Generation- Materials/Manufacturing Process

Concept Generation- Material and Manufacturing Processes

Manufacturing Processes

Rapid Prototyping (ABS

Plastic) Stereolithography Injection Molded Machine Metal or PolymerSelection Criteria Weight Rating Notes Score Rating Notes Score Rating Notes Score Rating Notes ScoreCost 9 4 36 1 9 1 $30k for mold 9 2 18Feasibility within timeline 10 5 50 4 long lead time 40 1 10 3 30Strength 6 4 37 MPa 24 5 58 MPa 30 5 35-70 MPa 30 5 ~580 MPa 30Material Interaction with water 4 2 8 4 resin based 16 5 20 4 16Ease of Manufacturing 3 5 15 5 15 3 9 3 9 0 0 0 0 20 wires 0 10 wires 0 3 wires 0 3 wires 0Net Score 133 110 78 103Rank 1 2 3 4

Continue? yes No no noweight 1- low importance

10- high importancerating 1- does not meet cirteria

5- meets cirteria

Rapid Prototyping• Machinable

– Material can be drilled and tapped (carefully)

• Accepts CAD drawings– Complex geometries can be created easily – Ideal for proposed ergonomic shape

• Builds with support layer– Models can be built with working/moving

hinges without having to worry about pins• Capable of building thin geometries

• ABSplus– Industrial thermoplastic

• Lightweight - Specific gravity of 1.04• Porous

– Does not address water resistant need

http://www.dimensionprinting.com/

ABS Plastic

Mechanical Property Test Method Imperial Metric

Tensile Strength ASTM D638 5,300 psi 37 MPa

Tensile Modulus ASTM D638 330,000 psi 2,320 MPa

Tensile Elongation ASTM D638 3% 3%

Heat Deflection ASTM D648 204°F 96°C

Glass Transition DMA (SSYS) 226°F 108°C

Specific Gravity ASTM D792 1.04 1.04

Coefficient of Thermal Expansion

ASTM E831 4.90E-5 in/in/F

• Important Notes• Relatively high tensile strength• Glass Transition well above body temperature• Specific Gravity indicates lightweight material

Feasibility- Water Ingress Test• Need: The external package should

resist minor splashing• Specification: Water Ingress Tests

– Once model is constructed, (user interface, connectors sealed, lid in place) exclude internal electronics and perform test

– Monitor flow rate (length of time and volume) of water

– Asses the quality to which water is prevented from entering case by examining water soluble paper

• Risk: Water can enter the external package and harm the electronics

• Preventative measures:– Spray on Rubber Coating or adhesive– O-rings around each screw well and around the

lid– Loctite at connectors

• Preliminary Tests without protective coating show no traceable water ingress

Spray on Rubberized CoatingLoctite

Feasibility- Robustness Testing• Need: The device should survive a fall from the hip• Specification: Drop Test

– Drop external housing 3 times from 1.5 m, device should remain fully intact

– Specify and build internal electrical components– Identify the “most vulnerable” electrical component(s) which may

be susceptible to breaking upon a drop– Mimic those components using comparable (but inexpensive and

replaceable) electrical components, solder on point to point soldering board

• Goal– Show the housing will not fail – Show electronics package will not fail, when subjected to multiple

drop tests• Risks

– The housing fails before the electronic components in drop tests (proved unlikely with prototype enclosure)

– The electronic components can not survive multiple drop tests• Preventative Measures

– Eliminate snap hinges from housing (tested and failed)– Test the housing first– Design a compact electronics package

Feasibility- Heat Dissipation of Internal Components

• 130°C is absolute maximum for chip junction temperature in order to function properly• Goal- comfort for the user• Assumed steady state, heat only dissipated through 3 external surfaces• Maximum heat dissipation ~25W• Actual heat dissipation ~5W

t, k

Q

TinTout

h

0 5 10 15 20 25 30 35 400

50

100

150

200

250

Tout= RoomTout = BodyAbsolute Max Temperature

Heat Generation, Q [W]

Inte

rnal

Tem

pera

ture

[°C]

Prototype Enclosure• Survived drop test• Water resistant• Plastic is machinable

– Drilled, tapped, milled• Helicoils should be used to tap

holes– Constant opening and screwing and

unscrewing of lid will result in stripped threads

• Approximate wall thickness (6mm)• Distance between center of holes

and wall needs to be increased– Some cracking occued

• Latches are not feasible

User Interface

Components:Indication of battery life (3x LED)Indication of Fault (LED and Buzzer)Indication of levitation (LED)DisplayIncrease/Decrease Speed (2x Button)Menu (Button)

-

+SpeedBattery Life

Fault Indication

BATTERY

OK ERROR

MENUTo

BatteryFrom Pump

To/From Computer

To Battery

Connectors:26- pin LEMO connectorUSB connectorBattery Terminals (x2)

OK: Indication of levitationERROR: No Levitation, connection errors

User Interface- ComponentsLED Backlit display with waterproof bezel and o-ring

G/R/Y LEDs with O-ring and waterproof bezel

Waterproof buttons with O-ring

User Interface- ConnectorsCurrent Model: Part # EGG 2K 326 CLL Proposed: Part # EEG 2K 326 CLV

Pin Layout

User Interface- IP CodesIP Ingress Protection

First Number Protection against Solid Objects0 - No protection (Sometimes X)1 - Protected against solid objects up to 50mm³2 - Protected against solid objects up to 12mm³3 - Protected against solid objects up to 2.5mm³4 - Protected against solid objects up to 1mm³5 - Protected against dust, limited ingress (no harmful deposit)6 - Totally protected against dust

Second Number Protection against liquids0 - No protection (Sometimes X)1 - Protection against vertically falling drops of water (e.g. condensation)2 - Protection against direct sprays of water up to 15 degrees from vertical3 - Protection against direct sprays of water up to 60 degrees from vertical4 - Protection against water sprayed from all directions - limited ingress permitted5 - Protected against low pressure jets of water from all directions - limited ingress permitted6 - Protected against low pressure jets of water, limited ingress permitted (e.g. ship deck)7 - Protected against the effect of immersion between 15cm and 1m8 - Protected against long periods of immersion under pressure

Display IP 67

Buttons IP 67

LEDs IP 67

USB IP 68

Connector IP 68