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Project P12016

Project P12016. Multi-Disciplinary Senior Design I Detail Design Review November 11, 2011. Agenda. Meeting Goals Project Background Objectives Specification Functional Analysis Final Design Analysis Risk Assessment Bill of Materials Preliminary Test Plan MSD II Proposed Schedule.

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Project P12016

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  1. Project P12016 Multi-Disciplinary Senior Design I Detail Design Review November 11, 2011

  2. Agenda • Meeting Goals • Project Background • Objectives • Specification • Functional Analysis • Final Design • Analysis • Risk Assessment • Bill of Materials • Preliminary Test Plan • MSD II Proposed Schedule

  3. Meeting goals • Is attachment method feasible? • What thickness of housing snaps is necessary? • Will they fail? • Is the design truly inconspicuous? • Will bottom of housing hold up to fastener loads? • Where do we stand on our specifications?

  4. Project Background Requirements • Creating a navigation system aid for blind and deaf people walking in an unfamiliar building. • Need to allow the user to continue to use a cane or guide dog. • Navigate a person from any point on the 2nd floor of the Gleason Building (09) • Without the use of Braille. • No hands should be used to carry system

  5. Project Background Summary of Major Specifications (page 4)

  6. Final Design External Overview (page 6) Highlighted numbers indicate BOM designation Battery Door Housing Top 3 Keypad Rear Vibrational Motor Mini-USB Charging Port 4 Housing Bottom Tie-Downs to Housing/Elastic Wiring Feed Hole 8 Front Vibrational Motor (Left) 4 On/Off Slide Switch 17 Foam Padding 19 Front Vibrational Motor (Right) 4 Elastic Sleeve 8 Thumb Hole (Approximation of Actual Use)

  7. Final Design External Dimensions, inches [mm] 3.7 [93] (thumb hole) 1.4 [35] 2.2 [56] 2.4 [60] 0.9 [24] (vib motors) 7.8 [200] 2.4 [60]

  8. Final Design Exploded View Housing Components Fasteners & Spacers Electronic Components Ergonomic Attachment

  9. Final Design Plastic Snaps & Fasteners 2X Snaps Front Section: 4X Snaps 4X Holes Shim + Adhesive 20, 21 5X Snaps 4.5mm Hex Nut 16 M3 Cap Screw, 12mm Long 12 14.4mm 2X Holes 6mm Nylon Spacer 13 2mm Nylon Spacer 15 4X Connections

  10. Final Design Electronics and Internals PCB Bottom: RFID/PCB Connection Right Side Section: Connections for Front Vibrational Motors Printed Circuit Board (PCB) Battery Antenna Connection 5 RFID Reader 6 PCB Bottom: Mini USB Charging Port Connections for Front Vibrational Motors

  11. Analysis Weight & Volume vs Specifications (page 8) Engineering Specifications Max Volume: 8 in3 Max Weight: 4 oz * PCB weight based on anticipated volume times material density ** Housing weight based on volume taken from CAD model times material density

  12. Analysis Manufacturing Method • What: 3D Printer • Where: RIT Brinkman Machine Labs • How Much Material: Approximately 1.5 cubic inches total • What Kind of Material: ABS Plus (industrial thermoplastic polymer) • How Much Money: $10/inch^3 -- roughly $15 total • How Long: About 8-15 hours per part • Method: • Geometry imported to 3D printer • 3D Printer builds model layer-by-layer with resin • 2. Cantilevered, floating parts supported by soluble secondary material, washed away in ultrasonic bath

  13. Analysis Assembly Method 1 2 • Insert cap screws through holes in bottom housing. Place 2mm spacers on screws. • Insert RFID Reader, place 6mm spacers on top of reader. Snap power switch in place. • Insert PCB. Bond shims to top of hex nuts and tighten components in place. • Bond Foam Padding to bottom of housing • Snap keypad in place on top half of housing 3 4 5

  14. Analysis Assembly Method 6 • Loop elastic straps through slits in bottom half of housing. Attach external motors to PCB. • Loop elastic straps through top half of housing and snap together the two halves of the housing. • Connect battery to PCB and insert in to enclosure. • Snap battery door in to place. 8 7 9

  15. Analysis Battery Replacement • Battery door is removed via pressing snaps into housing until they clear mating holes: • Battery (still wired) is removed from cradle: • Disconnect battery from connections on PCB: • Insert connectors from new battery: • Place new battery in cradle: • Snap battery door back into place: 1 2 (Connectors) (Cradle) 3 4 5 6

  16. Analysis Attachment Method • Elastic creates tight fit, fits broad range of sizes • Thumb holes orient device, prevent rotation • Elastic is inexpensive, can be found locally • Elastic is reinforced near housing, stabilizes interface there • User slides arm through elastic sleeve, inserts thumb through hole • Vibrational motors align with two sides of wrist, rear motor rests on upper-middle arm • Vibrational motors are sewn into pockets on elastic sleeve, wiring is routed through pockets to prevent tangling 5.9 [115] 1.4 [35] 2.0 [50] *Inches [mm]

  17. Analysis Structural Durability • After visiting the Brinkman Lab we determined a wall thickness of 1.5mm (~0.06”) should provide an adequate balance of strength, weight and flexibility • Testing will be necessary to confirm durability of housing and snaps. We have room in the weight budget to add material if necessary. • Current Material Volume of ~1.7in3. A total cost of about $17 for the housing leaves room in the budget for multiple iterations if necessary. • Design considerations to strengthen housing include: increased wall thickness, adding ribs or adding patches of extra material at weak points • Shims at the top of internal screw columns will contact the bottom of the keypad to provide structural support as buttons are pressed. Force of user input Shim

  18. Analysis Structural Analysis – Housing Stress • Results: • Largest stress is 2.09e5 Pa; < rated Tensile Strength of 3.7e7 Pa • Educated assumption that plastic will survive shock (i.e. heavily simplified drop condition) • Largest stresses occur in corners of opening where keypad will actually add support Fixed Load

  19. Analysis Structural Analysis – Stress in Snaps 4 σ max = 257 Pa σ max = 428 Pa 3 • Results: • All stresses in snaps < rated Tensile Strength of 3.7e7 Pa 1 2 1- Keypad side 2- Keypad rear σ max = 397 Pa σ max = 1661 Pa Setup 3- Top body 4- Battery door

  20. Analysis Heat Dissipation QSide QTop Specifications • Max air temperature inside: 120°F • Max RFID Reader Operating Temp: 158°F QSide Assumptions • Bottom surface is well insulated • Housing is rectangular • All electronics lumped as a single heat source the size of the RFID Reader • Heat source is a plate floating in the box • Free convection on a vertical plate outside the housing • Free convection in an enclosure inside housing • Halve calculated values for convective coefficients • RFID Reader running on high 100% of the time (worst case) • RFID Reader running on high 100% of the time (average case) QSide QSide

  21. Analysis Heat Dissipation Calculations • Used equations and tables from Heat Transfer text to calculate convective coefficients inside and outside of the housing • Modeled problem as steady state 2D heat transfer through 5 walls • Using known values for the power source and ambient temperature, solved equations for temperature throughout the housing • Calculated results using MatLab Results • Worst Case: • Inside Air Temp: 107.2°F • RFID Reader Temp: 181.5°F • Average Case • Inside Air Temp: 80.7°F • RFID Reader Temp: 99.8°F Qsource Tcomp Tair,i Twall,i Twall,o Tair,o

  22. Analysis Human Factors Keypad • Rotate keypad to ease pressure on wrist • Tactile feedback “Bump-Dots” on Keypad • Input data twice Correct Orientation • Asymmetrical housing • Thumb hole 1 2 3 # 4 5 6 * 7 8 9 0

  23. Analysis Motor Placement 98% 100% 100% 92% 90% 98%

  24. Analysis Output Testing • Testing concluded that it was very difficult to distinguish between different pulse lengths. • Based on test results, altering the time between vibrational pulses will result in distinguishable outputs.

  25. Risk Assessment Major Risks (Page 9)

  26. Bill Of Materials (page 10)

  27. Preliminary Test Plan One time Tests (page 12) • Number of hands needed to place/carry device (S20, S21): • No hands should be used to carry device • One hand should be used to place and use device • Impact resistance (S19) • Device is functional after 3 ft. drop • Internal housing Temperature (S27) • Less than 120 degree F • Device Attention Test • Noise Generated (S18) • Noise generated from the device should be < 50 db.

  28. Preliminary Test Plan Statistical Analysis Needed 95% Confidence Interval • Input Reliability (S17) • Number of input mistakes made by user • H0: μInput ≤ 1/100 • Output Reliability (S10, S11, S26) • Number of outputs not properly understood • H0: μOutput ≤ 1/100 • Training Time (S24) • H0: μTraining ≤ 60 min • Attachment/detachment time (S22, S23) • H0: μAttachment ≤ 60 sec • H0: μdetachment ≤ 60 sec • Change battery time (S7) • H0: μChange Battery ≤ 60 sec • User Comfort (S25) • Wear time without user discomfort • H0: μComfort> 8 hrs

  29. MSD II Proposed Schedule Gantt Chart (page 14) • Go to Schedule

  30. Questions

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