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 • 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

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 • 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

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 >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.

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