Design Considerations and Design Considerations and Preliminary Evaluation for an Preliminary Evaluation for an off-the-visor wide field of view off-the-visor wide field of view

HMDHMDRussell S. Draper, Charles D. Balogh

Night vision Electronic Sensors Directorate

Steven J. Robbins

Kaiser Electronics, San Jose, CA

IntroductionIntroduction

• Purpose– Performance evaluation of a prototype

binocular, WFOV, “off-visor” HMD– Army’s interest in a “Jet Fighter” HMD?

• Directed development for Objective Force Warrior– Multi-spectral head worn sensor system

– Possible form: binocular/see through vision system

• Maintain expertise in “state-of-the-art” HMD technology

IntroductionIntroduction

• Purpose– Test key performance attributes

• FOV

• Resolution

– Test key ergonomic attributes• Eye box

• Binocular alignment/stability

• Head borne weight/CG

IntroductionIntroduction

• Test Methods– NVESD Near Eye

Display Test Station employed for all tests except system weight and CG

– Weight/CG• CG determined by

analysis

WFOV HMD GoalsWFOV HMD Goals

• Risk mitigation effort– Binocular+off-visor

• Stability/alignment

• Profile

– 4.1 lb+Binocular• Stability/alignment

– Eye relief+FOV• Profile/CG

• Platform demo of emerging technology– LCD vs. CRT

Parmeter GoalDisplay presentation Binocular/BiocularCombination technique Off-visorHead borne weight 4.5 lbs w/O2 maskObscurations minimizedIPD Range 59-74 mmMonocular eye box 15 mmEye relief 75 mmFOV >40° horizontalMinimum overlap >30°Resolution 0.5 cy/mrBinocular divergence -0.5 to +0.2 prism dioptersBinocular dipvergence +/- 0.1 prism diopters

System EvaluationSystem Evaluation

• Description– Display unit (DU)

• Binocular optical support structure (BOSS)

• Relay optics assemblies

• Visor/combiner

– Helmet unit (HU)

– Electronics Unit (EU)

Display unit Helmet unit

System EvaluationSystem Evaluation

• Description- Display unit

Visor/combiner

BOSS

Relay optic assembly(right)

System EvaluationSystem Evaluation

• Description- Helmet unit

Helmet shellRetention/retraction

LCD cables

Interface PCB

Suspension fit latches

Main cable

System EvaluationSystem Evaluation

• Performance test results: FOV– Methods

• Display active area driven to full “on” condition

• Digital image frame captured with NEDTS WFOV CCD array sensor

• Unique edge detection algorithm applied to captured image– Edge detection starts at center and propagates outward

• Edge pixel values converted to angle space using NEDTS WFOV lens mapping.

• Test performed on right and left channels, 3 IPD settings each with sensor located at IPD setting design eye position.

System EvaluationSystem Evaluation

• Performance test results– FOV

30 20 10 0 10 20 3020

10

0

10

20

Azimuth Angle (degrees)

Ele

vatio

n A

ngle

(de

gree

s)

20

20

ELNomR

ELNomL

ELWidR

ELWidL

ELNarR

ELNarL

3030 AZNomR AZNomL AZWidR AZWidL AZNarR AZNarL

System EvaluationSystem Evaluation

• Performance test results– FOV

• Inscribed rectangular areas

30 20 10 0 10 20 3020

10

0

10

20

Azimuth Angle (degrees)E

leva

tion

Ang

le (

degr

ees)

20

20

ELNomR

ELNomL

ELWidR

ELWidL

ELNarR

ELNarL

3030 AZNomR AZNomL AZWidR AZWidL AZNarR AZNarL

IPD Setting Sens IPD Horiz.(°) Vert.(°) Horiz.(°) Vert.(°) Horiz.(°) Vert.(°) Horiz.(°) Vert.(°)

Nominal 66 mm 48.5 27.3 39.0 29.3 39.0 21.9 35.0 26.3Wide 74 mm 46.8 26.3 38.8 29.1 38.7 21.8 34.6 26.0Narrow 59 mm 42.8 24.1 38.0 28.5 35.2 19.8 33.9 25.4

R-Mono4X3Test Condition Binocular 16X9 Binocular 4X3 R-Mono16X9

System EvaluationSystem Evaluation

• Performance test results: Resolution– Methods

• Maximum contrast measured with NEDTS PMT sensor.• Display active area driven with 50% duty cycle square wave

grid at Nyquist sample rate, ½, ¼, 1/8 Nyquist rate• Digital image frame captured with NEDTS NFOV CCD array

sensor• Localized distortion correction (3rd order warping horizontal or

vertical) applied to captured image.• Row/column averaging performed.• Average cycle Michelson contrast computed for all viewable

cycles.

System EvaluationSystem Evaluation

• Performance test results: Resolution– Methods

Raw data: Distortion correction applied:

System EvaluationSystem Evaluation

• Performance test results: Resolution

Right channel Left channel

System EvaluationSystem Evaluation

• Performance test results: Eye box– Methods

• 2D scan of eye left and right side design eye location +/-12 mm vertical and +/-15 mm horizontal

• 3 parameters measured at each scan position– Luminance

– On/off contrast

– Nyquist rate contrast

• Plotted 50% contour of normalized data

System EvaluationSystem Evaluation

• Performance test results: Eye box

Units in mm

Luminance DC contrast Nyquist contrast

System EvaluationSystem Evaluation

• Performance test results: Alignment/Stablity– Methods

• Visor removal/replacement– Single 5 mr spot at approximately 0,0 field position

displayed in each channel

– Visor removed and replaced 20 times

– Field location of test spot measured with each trial

– Relative change between right and left channels recorded.

System EvaluationSystem Evaluation

• Performance test results: Alignment/Stablity– Methods

• IPD adjustment– Single 5 mr spot at approximately 0,0 field position

displayed in each channel

– IPD adjusted on single channel through all three settings for 10 trials

– Field location of test spot measured with each trial for each channel

– Relative change between right and left channel recorded

System EvaluationSystem Evaluation

• Performance test results: Alignment/Stablity– Methods

• Eye position shift– 2-D Grid of 5 mr points displayed at approximately 4°

increments– Sensor position moved in eye box from design eye location

at nominal IPD +/- 2 mm horizontally and vertically– Field location of test spot measured with each trial for each

channel– Relative change between right and left channel for

corresponding spots within the binocular overlap region recorded

System EvaluationSystem Evaluation

• Performance test results: Alignment/Stablity– Methods

• Visor See through deviation– Collimated “plus” symbol generated with bright line

theodolite outside of visor at specific field angle relative to DU.

– NEDTS sensor with digital cross hair oriented to view collimated image until digital cross hair overlaped “plus” symbol

– Visor removed– Theodolite adjusted to re-position “plus” symbol on cross

hair– Theodolite change in azimuth/elevation recorded

System EvaluationSystem Evaluation

• Performance test results: Alignment/Stablity

Test parameter samples Divergence Dipvergence Divergence Dipvergence

Visor removal/replacement 20 0.62 0.55 1.14 1.21IPD adjustment right channel (center) 10 0.54 0.75 1.28 2.01IPD adjustment right channel (wide) 10 0.91 0.42 2.43 1.30IPD adjustment right channel (narrow) 10 0.76 0.53 2.66 1.90+/- 2 mm shift in eye box 86 0.29 0.24 1.71 1.59Visor see-through deviation 10 0.19 0.29 0.55 1.04

RMS (mr) Peak-to-peak (mr)

System EvaluationSystem Evaluation

• Performance test results: Weight/CG– Methods

• Shell, fit system, electronics,1 ft. cable weighed

• Display unit weighed with visor and relay optics

• Visor weighed separately

• Right channel relay optics weighed separately

• Total head borne weight computed from actual component weights

• CG estimated from CAD data and actual component weights.

System EvaluationSystem Evaluation

• Performance test results: Weight/CGDescription wt (g) wt (lb)

WFOV BOSS assembly 741.9 1.63HGU-56P special Helmet 741.7 1.63

(includes fit and pads) Video board, cover, 1' cable 109 0.24

MEASURED SUBTOTAL 1593 3.51 z (in) y (in)ESTIMATED SUBTOTAL 2088 4.60 -1.33 2.46

O2 mask MBU-12/P 273 0.60 1.44 -3.50TOTAL 1866 4.11 -0.92 1.59

Misc Subassemblies wt (g) wt (lb)Visor 96.3 0.21

Optics assy 130.2 0.29(includes backlight,IF board)

estimated Center of Gravity from

Tragion Center1 mm inforward (z) 41 1.63

above (y) 54 2.141 Uses measured weights, does NOT include Head wt./CG

CG from pupil center

ConclusionsConclusions

• WFOV prototype HMD incorporates several innovative design elements– Flexible optical mounts for durability

– 3-point visor interface for improved visor positional repeatablity

– Bifurcated v-shaped visor for narrow profile and visor stability

– Integrated small footprint binocular optical support for stability

– 3 position IPD adjustment with kinematic interface

ConclusionsConclusions

• WFOV promising performance attributes:– FOV >40° horizontal and 30° vertical for

binocular viewing with approximately 30° overlap

– Resolution nominally 0.75 cy/mr (currently display source limited)

– Stability of binocular alignment better than 0.75 mr RMS and 2.5 mr worst case.

ConclusionsConclusions

• WFOV performance concerns:– Notable FOV vignetting occurs for narrow

IPDs– IPD adjustment mechanism has no apparent

effect on eye box position.– Notable resolution loss over small area of

design eye box– Visor bifurcation causes small amount of image

doubling at joint