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

1
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

2
Introduction

• Purpose
• Performance evaluation of a prototype binocular,
  WFOV, off-visor HMD
• Armys 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

3
Introduction

• Purpose
• Test key performance attributes
• FOV
• Resolution
• Test key ergonomic attributes
• Eye box
• Binocular alignment/stability
• Head borne weight/CG

4
Introduction

• Test Methods
• NVESD Near Eye Display Test Station employed for
  all tests except system weight and CG
• Weight/CG
• CG determined by analysis

5
WFOV HMD Goals

• Risk mitigation effort
• Binocularoff-visor
• Stability/alignment
• Profile
• 4.1 lbBinocular
• Stability/alignment
• Eye reliefFOV
• Profile/CG
• Platform demo of emerging technology
• LCD vs. CRT

6
System Evaluation
Display unit
Helmet unit

• Description
• Display unit (DU)
• Binocular optical support structure (BOSS)
• Relay optics assemblies
• Visor/combiner
• Helmet unit (HU)
• Electronics Unit (EU)

7
System Evaluation

• Description- Display unit

BOSS
Visor/combiner
Relay optic assembly(right)
8
System Evaluation

• Description- Helmet unit

LCD cables
Retention/retraction
Interface PCB
Helmet shell
Suspension fit latches
Main cable
9
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.

10
System Evaluation

• Performance test results
• FOV

11
System Evaluation

• Performance test results
• FOV
• Inscribed rectangular areas

12
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.

13
System Evaluation

• Performance test results Resolution
• Methods

Raw data
Distortion correction applied
14
System Evaluation

• Performance test results Resolution

Right channel
Left channel
15
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

16
System Evaluation

• Performance test results Eye box

Units in mm Luminance DC contrast Nyquist
contrast
17
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.

18
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

19
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

20
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

21
System Evaluation

• Performance test results Alignment/Stablity

22
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.

23
System Evaluation

• Performance test results Weight/CG

24
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

25
Conclusions

• WFOV promising performance attributes
• FOV gt40 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.

26
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