Design Considerations and
Preliminary Evaluation for an
off-the-visor wide field of view
HMD
Russell S. Draper, Charles D. Balogh
Night vision Electronic Sensors Directorate
Steven J. Robbins
Kaiser Electronics, San Jose, CA
Introduction
• 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
Introduction
• Purpose
– Test key performance attributes
• FOV
• Resolution
– Test key ergonomic attributes
• Eye box
• Binocular alignment/stability
• Head borne weight/CG
Introduction
• 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 Goals
• Risk mitigation effort
•
Parmeter
– Binocular+off-visor Display presentation
• Stability/alignment Combination technique
Head borne weight
• Profile
Obscurations
– 4.1 lb+Binocular
IPD Range
• Stability/alignment Monocular eye box
Eye relief
– Eye relief+FOV
FOV
• Profile/CG
Minimum overlap
Resolution
Platform demo of
Binocular divergence
emerging technology Binocular dipvergence
– LCD vs. CRT
Goal
Binocular/Biocular
Off-visor
4.5 lbs w/O2 mask
minimized
59-74 mm
15 mm
75 mm
>40° horizontal
>30°
0.5 cy/mr
-0.5 to +0.2 prism diopters
+/- 0.1 prism diopters
System Evaluation
Display unit
• Description
– Display unit (DU)
• Binocular optical
support structure
(BOSS)
• Relay optics assemblies
• Visor/combiner
– Helmet unit (HU)
– Electronics Unit (EU)
Helmet unit
System Evaluation
• Description- Display unit
BOSS
Visor/combiner
Relay optic assembly(right)
System Evaluation
• Description- Helmet unit
LCD cables
Retention/retraction
Interface PCB
Helmet shell
Suspension fit latches
Main cable
System 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 Evaluation
• Performance test results
Elevation Angle (degrees)
– FOV
20
ELNomR
20
10
ELNomL
ELWidR
ELWidL
0
ELNarR
ELNarL
10
 20 20
30
 30
20
10
0
10
20
AZNomR  AZNomL  AZWidR  AZWidL  AZNarR  AZNarL
Azimuth Angle (degrees)
30
30
System Evaluation
• Performance test results
– FOV
• Inscribed rectangular areas
Elevation Angle (degrees)
20
ELNomR
20
10
ELNomL
ELWidR
ELWidL
0
ELNarR
ELNarL
10
 20 20
30
 30
Test Condition
IPD Setting
Sens IPD
Nominal
66 mm
Wide
74 mm
Narrow
59 mm
20
10
0
10
20
AZNomR  AZNomL  AZWidR  AZWidL  AZNarR  AZNarL
Azimuth Angle (degrees)
30
30
Binocular 16X9
Binocular 4X3
R-Mono16X9
R-Mono4X3
Horiz.(°) Vert.(°) Horiz.(°) Vert.(°) Horiz.(°) Vert.(°) Horiz.(°) Vert.(°)
48.5
27.3
39.0
29.3
39.0
21.9
35.0
26.3
46.8
26.3
38.8
29.1
38.7
21.8
34.6
26.0
42.8
24.1
38.0
28.5
35.2
19.8
33.9
25.4
System 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 Evaluation
• Performance test results: Resolution
– Methods
Raw data:
Distortion correction applied:
System Evaluation
• Performance test results: Resolution
Right channel
1
Left channel
1
1
0.75
Modulation
Modulation
0.75
M odRH
M odRV
0.5
M odLH
M odLV
0
0.5
0.25
0.25
0
1
0
0
0
0.2
0.4
FreqRH  FreqRV
Cycles/ mr
0.6
0
0.8
0
.8
0
0.2
0.4
FreqLH  FreqLV
Cycles/ mr
0.6
0.8
.8
System 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 Evaluation
• Performance test results: Eye box
Units in mm
Luminance
DC contrast
Nyquist contrast
System 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 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 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 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 Evaluation
• Performance test results: Alignment/Stablity
Test parameter
Visor removal/replacement
IPD adjustment right channel (center)
IPD adjustment right channel (wide)
IPD adjustment right channel (narrow)
+/- 2 mm shift in eye box
Visor see-through deviation
samples
20
10
10
10
86
10
RMS (mr)
Peak-to-peak (mr)
Divergence Dipvergence Divergence Dipvergence
0.62
0.55
1.14
1.21
0.54
0.75
1.28
2.01
0.91
0.42
2.43
1.30
0.76
0.53
2.66
1.90
0.29
0.24
1.71
1.59
0.19
0.29
0.55
1.04
System 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 Evaluation
• Performance test results: Weight/CG
Description
WFOV BOSS assembly
HGU-56P special Helmet
(includes fit and pads)
Video board, cover, 1' cable
wt (lb)
1.63
1.63
109
0.24
MEASURED SUBTOTAL
ESTIMATED SUBTOTAL
O2 mask MBU-12/P
TOTAL
1593
2088
273
1866
3.51
4.60
0.60
4.11
Misc Subassemblies
Visor
Optics assy
(includes backlight,IF board)
wt (g)
96.3
130.2
wt (lb)
0.21
0.29
mm
41
54
in
1.63
2.14
estimated Center of Gravity from
Tragion Center1
forward (z)
above (y)
1
wt (g)
741.9
741.7
Uses measured weights, does NOT include Head wt./CG
CG from pupil center
y (in)
z (in)
2.46
-1.33
-3.50
1.44
1.59
-0.92
Conclusions
• 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
Conclusions
• 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.
Conclusions
• 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