p13002: ankle-foot orthotic un-tethered, mechanical

P13002: Ankle-Foot Orthotic Un-Tethered, Mechanical

Detailed Design Review

Team Members:◦Pattie Schiotis – Team Manager (ME)◦Shane Reardon – Lead Engineer (ME)◦Dana Kjolner (EE)◦Robert Ellsworth (EE)◦Sam Hosig (CE)◦John Williams (CE)

•Faculty Guide: Dr. DeBartolo

The Team

Introduction Project Background System Architecture Locking Mechanism Power Characterization Sensor Characterization Microcontroller/ Coding Progress Component Testing Bill of Materials Budget Breakdown Updated Risk Assessment

Agenda

Lasting side effect of a stroke: foot drop◦ Inability to dorsiflex the foot

Ankle Foot Orthotics (AFOs) currently used to aid dorsi-flexion.◦ Passive devices don’t allow for movement when

walking on ramps and stairs Foot is always pointed upwards

Project Background

User will have no ability to either plantar-flex or dorsi-flex their foot

Side to side stability of the foot will be ignored

Worst case will be analyzed:◦ 95 percentile male having heavy foot.◦ Fast walker – gait cycle less than 1 second.

Device may not use air muscles as an actuation source

Assumptions & Constraints

Key Customer NeedsPrimary Needs: Secondary Needs:

Safety Portable

◦ Lasts all day without charging/refueling

◦ Lightweight◦ Tolerable to wear all day

Reliable Accommodates Flat Terrain Accommodates Special

Terrain◦ Stairs◦ Ramps◦ Obstacles

Comfortable◦ Aesthetically Pleasing

Durable◦ Water Resistant◦ Corrosion Resistant

Salt & Environment Biocompatibility

Convenient◦ Easy to put on and take

off

Key Engineering Specifications

Engineering Specification

Number

Engineering Specification Description

Units of Measure

Preferred Direction

Nominal Value

Method of Validation

Stems From Customer Need

s1 torque on Foot N-m Up ≥±3.0 Test FT1,2,4,ST1,5

s2 system response time (sensing terrain to actuating device) ms down <400 Test ST3

s4 predicts step down yes/no - yes Test ST1,2,4s5 predict flat yes/no - yes Test FT1,ST5s7 predicts ramp down yes/no - yes Test ST1,2,4

s10 allowable range of motion between foot and shin degrees range 70 to 135 Test FT1,3,CF8,9,ST1

s12 untethered usage time hrs/steps up 8 hrs or 3000 steps P1,2,D1

s17 force to secure constraints N down < 80 Test C4s18 force to remove constraints N down < 80 Test C3s23 radius of edges/corners on AFO mm up 0.5 - S4,CF1,2s24 weight of entire device lb down ≤2.2 Test FT6

s28 Operates in environment temperature range °C range -17.8 to

37.8Component

Ratings D2

s31 Minimum life until failure steps up 5.5 million test D1

Characterizations used for calculations

Average # of steps per day: 10,000 # steps on stairs: 100 # steps on ramps: 100 Time for rotation: ~0.6 seconds

Walking Patterns

CAD modelSystem Architecture

Sensors

Piston/Cylinder

Mounting Bracket

Valve

Battery

Processor

Reservoir

CAD Model: DOF Analysis

1

2

34

Component #

Component Description

Connected to Joint Type # of

Constraints

1 Bottom of AFO Ground Fixed 6

2 Piston Bottom of AFO Pin 5

3 Cylinder Piston Slide 4

4 Top of AFO Cylinder Pin 5

4 Top of AFO Bottom of AFO Tamarack 4

4 Components 24 DOF Total: 24

Locking Mechanism:Selection Matrix

Concepts A B C D E E Hydraulic

LockingPiston/

Cylinder (Air)

Piston/ Cylinder

(Oil)

Socket Linear ratchet

Fluid Brake (benchmark)

Selection Criteria Rating Rating Rating Rating Rating Rating

weight 0 1 1 -1 -1 -1ease of design (electrical) 1 1 1 0 0 -1ease of design (mechanical) 0 1 1 -1 -1 -1response time (electrical) 1 1 1 -1 -1 0response time (mechanical) 1 -1 1 0 0 0locking force 1 -1 1 0 0 1attachment to orthotic 0 0 0 0 0 0safety -1 1 -1 0 0 0reliability 1 1 1 0 0 0Range of Motion 1 0 0 0 0 1Energy consumption 0 0 0 -1 -1 0

Total Score 5.00 4.00 6.00 -4.00 -4.00 -1.00Rank 2 3 1 4 4 4

Cylinder Selection

In order to swing foot, joint must apply ~2.75Nm

If locking device is 1.5” (3.81cm) away from joint,

Round up to 9/16” to be safe

lbfNm

NmFl 1718.72

0381.0

75.2

4,

2DA

A

FP

"416.0

)125(

)17(44min

psi

lbf

P

FD

Cylinder Benchmarks

BIMBA HL Original Line Bimba "500" Series MAXIM Hyd CylinderBore 9/16" 1+1/16" 1+1/2"

Stroke 3" 3" 4"Weight 0.09 lbs 0.5 lbs 7 lbs

PSI Rating 250 500 3000Cost $21.80 $61.90 $104.75

Material 304 Stainless Steel 304 Stainless Steel Iron/Steel

Picture

Valve Selection Criteria Capable of 125 Psi #10-32 or 1/8” NPT threads Allows max flow rate of 0.6213 in3/s

◦ Cv > 0.013◦ Assuming laminar, incompressible flow

min1618.06213.06.0

"5.1

2

"169 3

2

GALs

in

st

lA

t

VQrequired

0145.0125

11618.0

P

SGQCv

Valve Selection

•Cv=0.035•Solenoid Powered•Normally Closed (solenoid opens valve)•12 or 24 VDC•1/8” NPT threaded•~3 ms response time

Locking Mechanism: Stress Calculations

1

NOV 1 201213:29:30

ELEMENTS

1

X

Y

Z

NOV 1 201213:05:35

VOLUMES

TYPE NUM

UROTF

HD Polyethylene•E=125,000 Psi•Yield Strength=4,600


1

MX

.024902

581.9071163.79

1745.672327.55

2909.433491.32

4073.24655.08

5236.96

NOV 1 201213:35:57

NODAL SOLUTION

STEP=1SUB =1TIME=1SEQV (AVG)DMX =.485218SMN =.024902SMX =5236.96

1

.024902

581.9071163.79

1745.672327.55

2909.433491.32

4073.24655.08

5236.96

NOV 1 201213:35:07

NODAL SOLUTION


Stress at Joint:5000 Psi

Stress at Bolt Locations:

2000 Psi


1

X

Y

Z

NOV 1 201217:17:34

ELEMENTS1.67”

F

M

F=17 lbfM=22.695 in-lb


Stress at Joint:1500 Psi

Stress at Piston Connection:

1250 Psi

1

MX

X

Y

Z

.136886

179.46358.783

538.106717.428

896.7511076.07

1255.41434.72

1614.04

NOV 1 201217:11:41

NODAL SOLUTION


What we plan on buying:◦ Piston/Cylinder◦ Valve◦ Fluid Reservoir, 0.72 in3

◦ Pivot bracket to mount cylinder to top of AFO What we need to make

◦ Bracket to mount piston to bottom of AFO

Locking Mechanism:Component Breakdown

Power Calculations

Total Power Consumption

Steps TakenActuation (mWhr)

Sensing System (mWhr)

Total Power (mWhr)

200 1311 590 1902

Sensing System Power Consumption

SystemTime Hours

Duty Cycle Seconds Current Voltage mWhr QTY

Total Power (mWhr)

Sensor 8 0.2 5760 0.03 5 240 2 480Micro Controller 8 1 28800 3.00E-04 5 12 1 12 80% Efficiency 590

Chemistry Cost Weight Temp ( °C) Cycle Life Volts per cell

Lead Acid $13.50 4 lb -65 to 80 300 2.0

Nickel Cadmium $37.95 1.6 lb -20 to 65 500+ 1.2

Nickel Metal Hydride $49.95 1.36 lb -10 to 65 500 1.2

Lithium Ion $64.95 0.65 lb -20 to 60 500 3.7

Lithium Polymer $61.95 0.825 lb -20 to 60 500 3.7

Battery Selection

Circuit Design

Charger ConnectorD 1

D 1 N 4 0 0 2

Micro Controller and SensorsM 1

I R F 5 3 0

V 11 2 V

V B S D 1 -S I P

6

24

V O U TVIN

GN

D

U 31 2

D 2

D 1 N 4 0 0 2

C 1

1 0 0 u F

R 2

1 0 k

C 2

1 0 0 u F

Solenoid

Sensor Characterization Measure the output when compared to a

known distance. Yardstick or tape measure required.

Initial comparisons indicate strong correlation between expected and measured characterization curves.

Short range IR sensor: 10-80 cm (4-31 in) Long range IR sensor: 20-150 cm (8-59 in)

Calibration with Paper

Multiple Surface Testing

Placement of the Sensors: Top

10.25 in31.63 in

30 in

Lower SensorHeel Strike:

~15 cm (5.9 in)

Lift-Off: >~15 cm (5.9

in)

Tolerance: +/- 2 cm (.79 in)

Angle of Lower Sensor: ~20° from vertical

Placement of the Sensors: Bottom

15

cm

Functions written for determining upcoming terrain based on sensor readings

Function written to read sensor values Working on what needs to be written for SD

card Working on function calculation for gait

cycle time

Coding Progress

System UML

Price: $5 for each model◦ TI-MSP430G2553◦ Stellaris

Memory capability◦ MSP430 16KB flash memory◦ Stellaris 256KB flash memory

Speed◦ MSP430 16 MHz◦ Stellaris 80 MHz

No need to create separate PCB Ability to connect SD card for writing out data

Microcontroller Selection

Currently using 2 MSP430

For final assembly: will be using 1 Stellaris*If not enough memory, will add 1 MSP430

NOTE: Stellaris due to come in mid-December

Component Testing

Subsystem/ Function/ Feature Name: Locking Mechanism- ReservoirOwner: Shane/Pattie

Subsystem/ Function/ Feature Name: Locking Mechanism- CylinderOwner: Shane/Pattie

Subsystem/ Function/ Feature Name: Locking Mechanism- ValveOwner: Shane/Pattie

Engr. Spec. #

Specification (description)Unit of

MeasureMarginal

Value

Recorded Value Comments/Status

ES10Allowable range of motion between foot and shit º

94.5 to 137.7

ES24 Weight of entire device Kg 1 Will weigh when arrived

Force to move piston (fluid, valve closed) Lbf 17 Force to move piston (no fluid, valve open) lbf minimize Leak rate of cylinder In3/s minimize Stroke In 3

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device Kg 1 Will weigh when arrived Volume In3 >=0.7456

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device kg 1 Will weigh when arrived

Opens/closed in prototype circuit - Must open

Flow rate through open valve In3/s maximize

Component TestingSubsystem/ Function/ Feature Name: SensorsOwner: John/Dana

Subsystem/ Function/ Feature Name: MicrocontrollerOwner: Sam/John

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device kg 1 Will weigh when arrived ES3 Predicts step up - ES4 Predicts step down - ES5 Predicts flat -ES6 Predicts ramp up -ES7 Predicts ramp down -ES8 Predicts speed of person m/s ±0.1

ES28Operates in environment temperature range ºC

-17.8 to 37.8 Verify component specs

Verify distances with calibration curve cm

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device kg 1 Will weigh when arrived ES8 Predicts speed of person m/s ±0.1ES22 Error status - Yes



Memory KB 16/256

Component TestingSubsystem/ Function/ Feature Name: Battery/ Electrical componentsOwner: Rob/Dana

Subsystem/ Function/ Feature Name: OrthoticOwner: Shane/Pattie

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device Kg 1 Will weigh when arrivedES13 Charging time for full discharge Hours 8



Output voltage V 24Test in circuit - Yes

Engr. Spec. #


MeasureMarginal

Value


ES24 Weight of entire device kg 1

ES10Allowable range of motion between foot and shit Degrees

94.5 to 137.7

ES32 Allowable toe extension/flexion degrees 0-50 ES26 Noise level (at ears of user) dB 60

Bill of Materials/Budget Breakdown

Projected budget usage: $235.49 Total estimated weight: 0.51 kg

Updated Risk Assessment

What’s Next

Questions?

p13002: ankle-foot orthotic un-tethered, mechanical

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