Preliminary Detailed Design Review Emeka Akpaka Kayla Cole Lindsay Johnson Justin LaMar Christine Lochner Nick Stewart 11132014 Preliminary Detailed Design Review 1 Engineering Requirements ID: 778961
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Slide1
P15043: Smart Cane Systems IntegrationPreliminary Detailed Design Review
Emeka AkpakaKayla ColeLindsay JohnsonJustin LaMarChristine LochnerNick Stewart
11/13/2014
Preliminary Detailed Design Review
1
Slide2Engineering Requirements11/13/2014
Preliminary Detailed Design Review2
Importance
Source
Function
Engr. Requirement (metric)
Unit of Measure
Ideal Value
Comments/Status
9
CR1
System Operation
Provide 90 degree detection range in front of user
Degrees
90
Will be achieved by a combination of the user's sweeping motion and 2, 25 degree range sensors
9
CR1
System Operation
Signal detection of obstacles via haptic feedback (motion in handle)
Binary
Pass
3
CR2
System Portability
Adds no more than 1
lb.
to standard white cane
Lbs.
1
3
CR3
System Assembly
Decrease amount of visible hardware by 50% compared to P14043
Pieces
10
Less small parts would improve the manufacturability of the product
3
CR4, CR5
System Operation
8 hour rechargeable battery (minimum battery life)
Hours
8
3
CR6
System Portability
Collapsible into 8-10" sections
Inches
8
3
CR7
System Cost
Manufacturing cost $125 or less
USD
125
3
CR9
System
Usability
Keep cane collapse/re-open time less than 1 minute
Minutes
1
9
CR10
System Operation
Horizontal detection range
Feet
10
3
CR12
System Operation
Maximum pressure
psi
5
Didn’t
want to stall motor
3
CR12
System Structure
Handle contents fit within handle mock up envelope
Binary
Pass
9
CR12
System Structure
Maximum handle grip diameter
in
1.3
Research on typical cane diameters
Slide3Critical Design Parameters11/13/2014
Preliminary Detailed Design Review3
Slide4System Level Proposal: Actuated Buttons In Handle
Pros:Easy learning curveFeedback awarenessPotential to have versatile cane handlingConcerns:Handle must be designed carefully to ensure versatile cane handling
More moving parts
10/2/2014
P15043 Systems Design Review
4
Slide5Subsystems
MotorButtonsMicrocontrollerAccelerometerBatterySensor11/13/2014
Preliminary Detailed Design Review
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Slide6Subsystem Risk Breakdown
SubsystemRisk
MotorMedium
ButtonsMedium-high
Microcontroller
High
Battery
Medium
Sensor
Low
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Preliminary Detailed Design Review
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Slide7Handle Repair Feasibility11/13/2014
Preliminary Detailed Design Review7
Goal:
Make handle repair simple and easy for user or technician
Analysis:
Main parts of system: Sensor, Battery, Micro-controller and Motor
Instead of replacing the entire cane, small sections of the cane can be replaced instead
Solution:
Design parts of the cane to be detachable or easily accessible. One of the main parts that could break due to weathering is the sensor. The current design was made with that in mind making sure that it could be easily accessed for repair or replacement
**Examples of these design considerations will be shown in later slides**
Slide811/13/2014Preliminary Detailed Design Review
8Linear Motor Research
A solenoid motor turned out to be the only type of linear motor we could find within our price range and close to our dimension specifications.
Pros:
Cost Effective
Enables us to use original button design
Concerns:
Constant current draw (will drain battery)
Excessive heat build-up
Solenoid housing is slightly larger than or preferences, so the handle design would need to be slightly modified.
Conclusion:
Using a linear motor is not feasible,
and
the motor type and button motion must be re-designed.
Slide9Motor Selection & Design Change
11/13/2014Preliminary Detailed Design Review9
Original
Change
Button oscillation is in and out of the cane (pressing motion)
Button Oscillation is side to side (sliding motion)
Linear Actuator
Gear Motor (From P14043’s Design)
Slide10More on Design Change
11/13/2014Preliminary Detailed Design Review10
This new button motion will be similar to P14043’s cane during the middle sensor feedback simulation:
Click above for video of feedback
Motor Selected:
298:1 Micro Metal
Gearmotor
HP
Slide11Button Placement Feasibility
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Goal
:
Place buttons in a way to
maximize tactile feedback
feeling transmitted to the user
Background:
How the Blind Hold Their Cane
The blind hold their cane with their pointer finger extended down the flat side of the handle with the rest of their fingers curled around it.
Mechanoreceptors
Mechanoreceptors specialize in sending tactile information to the brain.
Meissner’s Corpuscles:
Directly beneath epidermis of fingers and palms
Have rapidly adapting action potentials for shallow skin depression
Suited for detecting low frequency vibrations and detecting textures moving across skin
Accounts for 40% of sensory nerves in human hand
Slide12Button Placement Feasibility Continued
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Figure 1: Distribution of Meissner’s
Corpuscles in the human hand. Image
taken from source 3.
Figure 2: Two Point Discrimination Chart. Image
taken
from source 3.
Figure 3: Indentation threshold for different areas of the hand. Image taken from source 3.
Slide13Button Placement Feasibility Continued
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Sources:
[1] Dario, 2012, “O&M – Orientation and Mobility. Lesson #1: The long white cane.” From URL:
http://www.noisyvision.com/2012/03/27/om-orientamento-e-mobilit%C3%A0-lezione-1-il-bastone-bianco-lungo-2/?lang=en
[2]
Purves
D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA):
Sinauer
Associates; 2001. Mechanoreceptors Specialized to Receive Tactile
Information.Available
from:
http://www.ncbi.nlm.nih.gov/books/NBK10895/
[3] Gardner, E.P., Martin, J.M.,
Jessell
, T.M., “The Bodily Senses.” From URL:
http://fisica.cab.cnea.gov.ar/escuelaib2014-neurociencias/restricted/BOOKS/Principles%20of%20Neural%20Science%20-%20Kandel/gateway.ut.ovid.com/gw2/ovidweb.cgisidnjhkoalgmeho00dbookimagebookdb_7c_2fc~28.htm
[4] Johansson, R.S.,
Vallbo
, A.B., “Detection of tactile stimuli. Thresholds of afferent units related to psychophysical thresholds in the human hand.”
The Journal of Physiology.
1979 Dec. 297: 405-422. [PubMed]
[5]
Tustumi
, F.,
Nakamoto
H.A.,
Tuma
Junior
.
P.,
Milcheski
D.A., Ferreira, M.C., “
Prospective study on tactile sensitivity in the hands of a Brazilian population using the pressure-specified sensory device.”
Revista
Brasileira
de
Ortopedia
,
2012, 47(3). From URL:
http://www.scielo.br/scielo.php?pid=S0102-36162012000300011&script=sci_arttext&tlng=en
Information Learned to Help Guide Design:
Meissner’s Corpuscles make up 40% of sensory nerves on hand.
Meissner’s Corpuscles have a high density in finger tips and an even distribution on other areas
of
the hand.
Meissner’s Corpuscles are good at detecting moving textured surfaces (consider textured buttons)
Two point discrimination for the human palm is around10mm.
Two point discrimination for human fingers is around 5mm.
Fingers have a lower indentation threshold compared to the palm
.
Slide14Handle Button Mock-Up and Demonstration
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Slide15New Design Diagram11/13/2014
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Bearing chosen for rollers
Slide16Spatial Considerations
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Handle Motors
Micro controller
Battery
Slide17Material Considerations and Selection
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Slide18Proposed Design11/13/2014
Preliminary Detailed Design Review18
Front View of Cane Handle
Back View of Cane Handle
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Wire Housing
Bottom View of Wire Housing
Slide2011/13/2014Preliminary Detailed Design Review
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Front View of Sensor Cover
Back View of Sensor Cover
Slide21Going ForwardAdd pilot holes and stand-offs for hardware
Remove material in certain spaces to reduce material cost and weightDiscuss with SME about our final detailed design11/13/2014
Preliminary Detailed Design Review
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Slide22Sensor Selection Analysis
Based on rough measurements, the max sensor range length must be at least 8.75 ft. Thus, EZ3 and EZ4 were immediately ruled out.Based on rough measurements of cane sweeping, the maximum angular displacement during a cane sweep was determined to be about 45°.
Thus, the sensor range angle can be no more than 45°.The angles of the sensors’ ranges were determined, using half of the max range width and the length at which said width is reached.
Using one sensor on the cane, EZ0 provides a sensor range angle of 25°, which is desirable for the lateral detection range. However, the height of the sensor range is about 7.5 ft.,
which provides a range that is much too tall.
Thus
, EZ0 was ruled out.
EZ2
provides a sensor range angle of 22°, and a sensor range height of about 4 ft. This is a desirable height.
Using two sensors, the EZ2 allows the sensor range angle to vary between
φ
min
= 22°;
φ
max
= 44°. The optimal sensor range angle is assumed to lie within those values.
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Slide23Sensor Test PlanRead data from sensors using a development board
Compare results using an oscilloscopeVary the detection object width/height and distanceTesting of implemented algorithm using a cane (MSD II)11/13/2014
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Slide24Essential Microcontroller Functionality
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Slide25High-Level Circuit Schematic
High level designEmphasis on the input/output of the uControllerUART serial communication for SensorsGPIO pins for Motors and Accelerometer
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Slide26Decision to design a Printed Circuit Board (PCB)
Meeting with Carlos cemented the pre-production prototype ideaAdvantages:Cheaper in the long runEasy to modify/control all aspects of the uController functionalityDisadvantages:
TimelyNo previous experience
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Slide27MicroController Selection
Key Selection Criteria:Low CostMinimum of 8-bit core size5 V input voltageAnalog-to-Digital Converters
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Manufacturer
Unit Price(USD)
Core Processor
Core Size
Speed (MHz)
Number of I/O
Program Memory Type
Voltage Supply (V)
Data Converters
Microchip Technology
4.34
PIC
16-Bit
32
65
FLASH
2 - 3.6
A/D 16x10b
Texas Instruments
0.64
MSP430
16-Bit
16
10
FLASH
1.8 - 3.6
Slope A/D
Atmel
0.59
AVR
8-Bit
12
28
FLASH
1.8 - 5.5
A/D 8x10b
Atmel
0.86
AVR
8-Bit
20
16
FLASH
1.8-5.5
A/D 11x10b
Atmel
2.1
AVR
8-Bit
16
23
FLASH
4.5-5.5
A/D 8x10b
Selection: #5 – Atmel’s ATMEGA8
Meets all of the selection criteria
Chip commonly used for popular Arduino boards
Troubleshooting resources readily available
Slide28Microcontroller Schematic11/13/2014
Preliminary Detailed Design Review28
Slide29Battery Selection
Inheriting P14043’s TENERGY Lithium Ion batteries, Li-18650 3.7V 2600mAh, recharging circuitry built-inReducing the number of batteries from two to one; using a boost converter to meet voltage requirements.This solution should have the system running for around 10 hours.2600 mAh/ 300 mA ~ 9 h200 ma is the maximum predicted current draw, also at full operating power
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Slide30Power ManagementPowering:
Two Motors, two Sensors, uController, and an Accelerometer Output of 5V and 150 - 200 mA for ~ 8 hoursChoice of One battery with a boost converterTwo batteries with a buck converter
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Slide31Buck/Boost Decision
Buck Converter (decreases input voltage)Has large parts and takes up space on a PCBHaving two batteries is not ideal (due to handle space)Boost Converter (increases input voltage)Also takes up room on a PCBOnly needs one battery to operateBoth provided the necessary power to components.
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Slide32Boost converter it is!
Condensing the real estate in the cane to as little as possible is invaluableHaving one less battery also decreases the manufacturing cost11/13/2014
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Slide33Power Management Test PlanPlug 3.7 V power supply into converter
Monitor the current draw from power supply (multimeter)Monitor the voltage output (oscilloscope)Monitor the current output (multimeter)Verify outputs match nominal values/simulations
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Slide34Accelerometer Selection
Kionix KXD94Small package
Low NoiseLow Power Consumption
Analog voltage output
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Slide35Accelerometer Test PlanRead data from accelerometer using a developmental board
Compare the data using an oscilloscopeVary the acceleration of the cane to determine the accuracy11/13/2014
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Slide36Proposed DesignOne battery with a Boost converter to power all of the devices
Two EZ2 sensors to acquire data from the environmentAccelerometer to determine cane position relative to user’s directionUsing an AtmegA8 embedded system to implement our algorithm and automate the entire system11/13/2014
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Slide37Tentative PCB Layout
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Slide38Going ForwardShift focus towards programming
Acquire development board to test the functionality of our concepts in both programming and hardwareInclude a USB interface to charge the batteriesTest components, verifying functionality/qualityDiscuss with SME to finalize PCB designMinimization of physical size main priority
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Slide39Manufacturing Costing
Requirement: Manufacturing Costs < $125
Manufacturing Cost=
Materials + Labor+ Overhead + Misc. (fixtures, G&A)Manufacturing “Elements”:
Electronics (PCB, sensors)
Handle (Handle production, motor and electronics assembly)
Entire cane
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Slide40ABVI Manufacturing CostingStandard Labor Rate=$10.50/hr
Manufacturing Cost = (Material Cost + Labor*) + 11%*Time required as determined by time studies11% is the assumed general and administrative rateExcludes fixtures, overhead and waste factors
Materials from an ABVI standpoint would be:
Handle assemblyCollapsible Cane
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Slide41Collapsible Cane Research11/13/2014
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Slide42Tentative Bill of Materials11/13/2014
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Slide43Risk Mitigation and Analysis11/13/2014
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Risk Item
Effect
Cause
Likelihood
Severity
Importance
Actions to Minimize Risk
General
R1
Battery contact is compromised
Loss of power
Deflection of wire connection
2
3
6
Make sure all components that house wires are rigid and secure wires sufficiently for cane movement
R2
User Muscle Fatigue
Pain/discomfort to user
•How hand grips on handle
•Weight distribution of cane
2
2
4
Ergonomics considered in design
R3
Over heating
Damage to system
Harm to user
Insufficient heat dissipation
1
3
3
Perform thermal analysis
R4
Cane malfunction
No feedback delivered to user
Component malfunction or damage
1
3
3
Design for redundancy
R5
Misplaced parts
User frustration
Multiple unconnected in the system
2
1
2
•Make system all one piece
•Create a way separate components can be stored together when not in use
Sensors
R6
Sensors relay incorrect information to feedback
Confusion and/or danger to user
•Sensor malfunction
•Broken connection
•Problem with program
1
3
3
Test prototype extensively
R7
Sensors hit obstacles when cane is sweeping
•Damage to sensor
•Shift in sensor position
•Sensor falls off
Location of sensors on the cane
2
2
4
Attach sensors in the top region of the cane
R8
Sensors get dusty/dirty
Malfunction
Environment encountered
1
2
2
State in user manual that sensors should be cleaned frequently
Handle
R9
Water damage
Ruined components
Not waterproof
2
3
6
•Minimize openings
•Put waterproof cover over feedback
R10
Loss haptic motion (when signal is send from sensors, feedback does not respond with motion)
Feedback not given to user
•Disconnection of feedback mechanism and motor
•Burnout of motor
2
3
6
•Sufficiently secure roller to motor
•Do analysis to make sure torque is not too high for motor
R11
Haptic motion is unclear and not intuitive
•User confusion
•Learning curve to use cane
Haptic motion design
2
2
4
Do thorough testing to make sure haptic feedback relays information clearly to users
R12
Feedback is obstructed by clothing or jewelry (ex. Gloves)
Decreased feeling of feedback
Location where feedback comes in contact with the user
1
2
2
Brainstorm ways to minimize clothing/jewelry obstruction
R13
Motor vibrations harm user
Nerve damage
Magnitude of motor vibration (mm/s)
1
2
2
Do research on effects of vibration magnitude versus time of exposure. Ensure the motor ordered is below the limit.
R14
Degree of serviceability and ease part replacement
Defines if the handle can be fixed if a part breaks or if the user needs to go out and buy a whole new cane
•Lack of access to inside components
•Can not remove/replace one part without removing/replacing another
2
3
6
•Design handle with an easily removable insert that contains an organized array of all handle components
•Use commercially available parts so that they can be ordered separately
Slide44Budget Breakdown11/13/2014
Preliminary Detailed Design Review44
Slide45Schedule
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Slide46Next StepsDetailed design completion
Systems level test planFinalized BOMPrepare for parts procurement11/13/2014
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Slide47Questions?
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