Eglin 1 Design of Acoustic Sensor Eye Housing Eglin 1 Design of Acoustic Sensor Eye Housing Group...

Eglin 1Eglin 1Design of Acoustic Design of Acoustic

Sensor Eye HousingSensor Eye Housing

Group Group Members: Members:

Erik Erik FernandezFernandez

Kevin GarveyKevin GarveyWilliam William HeffnerHeffnerBrian Brian

McMinnMcMinn

AcknowledgementsAcknowledgements

We would like to extend our sincere We would like to extend our sincere thanks and appreciation to the thanks and appreciation to the following contributors to the success following contributors to the success of our project:of our project:

Dr. Henry PfisterDr. Henry Pfister Eglin AFRL/MNEglin AFRL/MN Keith LarsonKeith Larson

Agenda Agenda

Design BackgroundDesign Background ConstraintsConstraints Material SelectionMaterial Selection Vibration Control Vibration Control Actuation SystemActuation System T-Base ArrayT-Base Array Testing and ResultsTesting and Results ConclusionConclusion

Acoustic Eye Sensor (Courtesy Dr. Pfister, Eglin AFRL)

Design BackgroundDesign Background Acoustic Eye Sensor Acoustic Eye Sensor

Frame DesignFrame Design Integrate an acoustic Integrate an acoustic

eye sensor into NASA eye sensor into NASA RDS robot. RDS robot.

Also integrate acoustic Also integrate acoustic eye sensor into VEX™ eye sensor into VEX™ robot. robot.

NASA RDS Robot

Background Cont.Background Cont. RDS (Robot Demonstration System)RDS (Robot Demonstration System)

Multiple sensor integration into test Multiple sensor integration into test bed processor.bed processor.

Acoustic Eye SensorAcoustic Eye Sensor 4 Microphone array that processes 4 Microphone array that processes

sound signals to determine location to a sound signals to determine location to a sound source.sound source.

Constraints (Tetrahedral Constraints (Tetrahedral Array)Array)

Tetrahedral Array ConstraintsTetrahedral Array Constraints Tetrahedral GeometryTetrahedral Geometry Adapt to NASA RDS RobotAdapt to NASA RDS Robot Microphone Spacing of 20 inchesMicrophone Spacing of 20 inches Collapsible remotelyCollapsible remotely Damp Mechanical VibrationsDamp Mechanical Vibrations Low Cost and LightweightLow Cost and Lightweight Utilize off-the-shelf componentsUtilize off-the-shelf components

Tetrahedron

Constraints (T-Base Constraints (T-Base Array)Array)

T-Base ConstraintsT-Base Constraints Tetrahedral GeometryTetrahedral Geometry T-base configurationT-base configuration Adapt to VEX™ RobotAdapt to VEX™ Robot Microphone spacing of 10 inchesMicrophone spacing of 10 inches Damp Mechanical VibrationsDamp Mechanical Vibrations Low Cost and LightweightLow Cost and Lightweight Utilize off-the-shelf componentsUtilize off-the-shelf components

T-Base Part

Materials SelectedMaterials Selected

Four deciding factors for material selection:Four deciding factors for material selection: Price, Availability, Weight, and Sound Conduction Price, Availability, Weight, and Sound Conduction

Materials ChosenMaterials Chosen• UHMW-PE (Ultra High Molecular Weight- Polyethylene)• ABS (Acrylanitrile Butadiene Styrene)

Materials Considered Price of Material ($/ft) for 1 inch diamterDensity of Material (lb/in 3̂) Speed of Sound Through Material (ft/s)

ABS 5.2 0.04 4254.163UHMW-PE 4.56 0.0336 2679.871

Vibration Substrates Vibration Substrates SelectedSelected

Sorbothane® Visco-elastic Sorbothane® Visco-elastic polymerpolymer Durometer 30Durometer 30 Vibration IsolationVibration Isolation

Acoustic FoamAcoustic Foam Low DensityLow Density Vibration AbsorptionVibration Absorption

http://www.sorbothane.com/

Vibration Isolation Vibration Isolation Floating BoltFloating Bolt

Sorbothane® Bushings

Flat Metal Washer

¼” Nut

¼” Bolt

Flat Metal Washer

Compressed Bushings Create Damping Region

Floating Bolt OperationFloating Bolt Operation

Shock Impact Energy In

Heat Energy Out

Heat Energy Out

Sorbothane® Bushings change mechanical energy into heat. The effect is that the input energy is displaced by an approximate 90º phase shift.

Vibration Absorption Vibration Absorption Septum BoardSeptum Board

Mic Board

Mic Adapter PlateAbsorption Foam Layer

Mic to Rod Adapter Board

Microphone Sensor Isolation Setup

Septum Board OperationSeptum Board Operation

Acoustic foam absorbs the incoming vibration impulse and acts as a filter to the frequency wave that passes to the microphone sensor.

Shock Impulse

Frequency Filtering/Absorption

Impact Impulse Impact Impulse PropagationPropagation

Microphone Sensor

Shock Impulse

Damped Impulse

Actuation SystemActuation System Stepper Motor Stepper Motor Dual Slider Track SystemDual Slider Track System

Z-2684X-V Bipolar Stepper Motor

Interior slider

Guide Pin

Lead Screw

Guide Track

External Slider

Tetrahedral Array Tetrahedral Array SystemSystem

Septum Board Slider

Guide Track

External Slider

Stepper motorFloatin

g Bolt

T-Base Array SystemT-Base Array System

Half Size Extending Rods

Half Size Center Shaft

Sorbothane® Bushing

T-Base

Floating Bolt Design

Actual Size Robot Mounting Plate

TestingTesting Vibration had to be characterized for the Vibration had to be characterized for the

RDS RobotRDS Robot 3 Tests were utilized to characterize 3 Tests were utilized to characterize

different types of vibrations:different types of vibrations: DC Motor TestDC Motor Test Rod Impact TestRod Impact Test Base Impact Base Impact

RDS Robot Test Frame

DC Motor TestDC Motor Test

Characterize the vibration Characterize the vibration propagation from the 3 DC motors propagation from the 3 DC motors attached to the RDS robot.attached to the RDS robot.

Simulated RDS base with DC motors

6 Volt DC Motors

Rod Impact TestRod Impact Test

Characterization of impulse Characterization of impulse vibration caused by a direct vibration caused by a direct extension rod obstruction impact.extension rod obstruction impact.

Simulated RDS base with Extension Rod Attached

Microphone Sensor mount

Extension Rod

Base Impact TestBase Impact Test Characterizes general vibration Characterizes general vibration

propagation through the RDS robot propagation through the RDS robot base itself.base itself.

Simulated RDS Base

RDS Test Base

DC Motor TestsDC Motor TestsMotor Vibration Test Baseline

2.75

2.8

2.85

2.9

2.95

3

3.05

3.1

0 100 200 300 400 500

Time (Scans)

Vo

ltag

e O

utp

ut

(V)

No DampingComplete System DampingBaseline = 2.95 Volts

Motor Vibration Test Baseline

2.75

2.8

2.85

2.9

2.95

3

3.05

3.1

0 100 200 300 400 500

Time (Scans)

Vo

ltag

e O

utp

ut

(V)

No DampingComplete System DampingBaseline = 2.95 Volts

500 Scans = 71.42 ms

Motor Test ResultsMotor Test Results

Design Parameter No Damping System Damping % Reduction

Microphone Excitation 1802.5 Hz 422.8 Hz 76.5 %Resonance Impulse

Magnitude 3.096 Volts 2.988 Volts 74 %

ABS Rod Impact TestsABS Rod Impact Tests

Rod Impact Test (4 Ounce Weight)

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200 1400

Time (Scans)

Vo

ltag

e O

utp

ut (

V)

No Damping Impact

Complete System Damping

Baseline = 2.95 Volts

500 Scans = 71.42 ms

Rod Impact Test (4 Ounce Weight)

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200 1400

Time (Scans)

Vo

ltag

e O

utp

ut (

V)

No Damping Impact



500 Scans = 71.42 ms

Rod Impact ResultsRod Impact Results(Critical Damping (Critical Damping

Coefficient)Coefficient)Test Type Critical Damping Coefficient

No Damping 205.2 kg/s

System Damping 1039.3 kg/s

Advantage 5 Times Better

• Critical Damping coefficient characterizes the rate at which an impulse will be damped out.

Rod Impact ResultsRod Impact Results(Settling Time and Impulse (Settling Time and Impulse

Magnitude)Magnitude)Test Parameter Settling Time Impulse Magnitude

No Damping 185.7 ms 5.457 Volts

System Damping 124.98 ms 5.361 Volts

% Reduction 33 % 4 %

• Settling time is the time it takes for an impulse wave to return to equilibrium.

• Impulse magnitude is the actual strength that an impulse imposes upon the system.

RDS Base Impact TestsRDS Base Impact TestsBase Impact Test (4 Ounce Weight)

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200Time (Scans)

Vo

ltag

e O

utp

ut (

V)

No Damping



500 Scans = 71.42 ms

Base Impact Test (4 Ounce Weight)

0

1

2

3

4

5

6

0 200 400 600 800 1000 1200Time (Scans)

Vo

ltag

e O

utp

ut (

V)

No Damping



500 Scans = 71.42 ms

RDS Base Impact ResultsRDS Base Impact Results(Critical Damping (Critical Damping

Coefficients)Coefficients)Test Type Critical Damping Coefficient

No Damping 866.5 kg/s

System Damping 1978.8 kg/s

Advantage 2 Times Better

• This characterizes the rate at which the impact is mitigated through the structure before it reaches the microphone sensor.

RDS Base Impact ResultsRDS Base Impact Results(Settling Time and Impulse (Settling Time and Impulse

Magnitude)Magnitude)Test Parameter Settling Time Impulse Magnitude

No Damping 160.8 ms 5.073 Volts

System Damping 72.4 ms 3.701 Volts

% Reduction 55 % 65 %

• The majority of the vibration will be through the RDS structure itself and testing has shown a significant result in the impulse magnitude.

Rod Impact Test (Acrylic vs. Rod Impact Test (Acrylic vs. ABS)ABS)

Rod Impact Tests (Multiple Materials)

0

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0 200 400 600 800 1000Time (Scans)

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lta

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Ou

tpu

t (V

)

Baseline = 2.905 VAcrylicAluminumBrassWoodComplete System


0

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0 200 400 600 800 1000Time (Scans)

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)


Rod Impact Test (Aluminum Rod Impact Test (Aluminum vs. ABS)vs. ABS)


0

1

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3

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5

6

0 200 400 600 800 1000Time (Scans)

Vol

tage

Out

put (

V)



0

1

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0 200 400 600 800 1000Time (Scans)

Vol

tage

Out

put (

V)


Rod Impact Test (Brass Rod Impact Test (Brass vs. ABS)vs. ABS)


0

1

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0 200 400 600 800 1000Time (Scans)

Vo

lta

ge

Ou

tpu

t (V

)



0

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0 200 400 600 800 1000Time (Scans)

Vo

lta

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)


Rod Impact Test (Pine Rod Impact Test (Pine vs. ABS)vs. ABS)


0

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0 200 400 600 800 1000Time (Scans)

Vo

lta

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Rod Impact ComparisonRod Impact ComparisonRod Impact Tests (Multiple Materials)

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t (V

)


Material Comparison Material Comparison ResultsResults

Material Material AcryliAcrylicc

AluminAluminumum

BrassBrassWood Wood (Pine)(Pine)

ABS ABS SysteSyste

mm

Settling Settling TimeTime

114 114 msms

50.7 ms50.7 ms 110 110 msms

100 100 msms

72.4 72.4 msms

Impulse Impulse MagnitudMagnitud

ee

5.308 5.308 VV

5.308 V5.308 V 5.308 5.308 VV

5.303 5.303 VV

3.701 3.701 VV

Overall Major ResultsOverall Major Results Mitigated impulse shock Mitigated impulse shock

magnitude by 65%.magnitude by 65%. Increased Damping coefficient by Increased Damping coefficient by

80%.80%. Decreased Settling time by as Decreased Settling time by as

much as 55%.much as 55%.

ConclusionConclusion Successfully designed and built working Successfully designed and built working

prototype arrays to Eglin AFRL prototype arrays to Eglin AFRL constraints. constraints. Collapsible Tetrahedral ArrayCollapsible Tetrahedral Array

Low Cost (~$250)Low Cost (~$250) Lightweight (~2 lbs.)Lightweight (~2 lbs.) Considerably Mitigates Vibration (As described Considerably Mitigates Vibration (As described

previously)previously) Full RDS AdaptabilityFull RDS Adaptability Complete remote actuation collapsibility Complete remote actuation collapsibility

T-Base ArrayT-Base Array Considerably Lower Cost (~$25)Considerably Lower Cost (~$25) Full VEX robot adaptabilityFull VEX robot adaptability Vibration Control and LightweightVibration Control and Lightweight

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