Helmet-Mounted Displays: - USAARL - The - U.S. Army

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Optical Designs 71 Figure 3.4. Comparisons between refractive and catadioptric HMDs with and without prism combiners. distortions and aberrations increase rapidly (Buchroeder, 1987). An example of a modest off-axis catadioptric design with a plano combiner is shown in Figure 3.5 (Droessler and Rotier, 1989; Rotier, 1989). This catadioptric design achieves a 50º x 60º FOV with a 10-exit pupil and 30mm eye relief (measured from plano combiner intercept to apex of eye along primary line of sight). However, note the optical complexity with 11 refractive elements and 3 reflective surfaces with very complex coatings for both eyepiece reflective surfaces to maximize see-through and display transmissions. The modest trapezoidal distortion of 7.5% (Figure 3.6) will be aligned with the power combiner. Another promising HMD is the Monolithic Afocal Relay Combiner (MONARC), which is an off-axis, rotationally symmetrical lens system with modest FOV potential, but excellent see-through approach (Figure 3.7). However, for any of the offaxis binocular systems, the distortions will have to be corrected to achieve point for point image alignment throughout the FOV. The primary advantage of the off-axis reflective HMD design is that it provides the highest potential percent luminance transfer from the display with the most see-through vision and increased eye clearances for a given FOV. The primary disadvantages are very complex optical designs, shape distortions, and low structural integrity and stability of the reflective surface. Figure 3.8 shows the conceptual drawings (top and side view) of an off-axis HMD using the visor as the eyepiece. Note the locations of the aerial images, which are shown for the left eye. The location of the relay optics will be either on top of the helmet, or below, where both locations have undesirable characteristics such as a high center of mass, or produce lower obstructions to unaided vision. Also, note that the head seems to get in the way with the optics or relay image. Again, there have been prototypes and a few HUDs, but no production off-axis reflective HMDs. Where there are no provisions for electronic distortion correction, as found with NVGs, the off-axis designs become unacceptable from the keystone or trapezoidal type distortions. Pupil and nonpupil forming A nonpupil forming virtual display uses a simple eyepiece to collimate or focus a real image source. An example is NVG where eyepieces focus the 18-mm phosphor screens to produce a 40º FOV. The display size,
72 William E. McLean eyepiece focal length, eye clearance, exit p u p i l diameter, and f/# define the F O V relationships similar to viewing through a knot hole (Figure 3.1a). A method to increase the apparent size of a display u p t o approximately 2x Figure 3.5. Ray trace of 50º x 60º t ilted cat o c u l a r (Droessler and Rotier,1989).
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Helmet-Mounted Displays: Design Iss
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The views, opinions, and/or finding
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vi Contents 4. Visual Coupling Clar
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viii Contents References ..........
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x Ben T. Mozo, Research Physicist U
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xii Foreword began its phenomenal e
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xiv Preface Acknowledgments The aut
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Introductory Overview 1 Clarence E.
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Introductory Overview 5 Figure 1.2.
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Introductory Overview 7 The trend f
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Introductory Overview 9
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Introductory Overview 11 aviator to
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Introductory Overview 13 1970's. Ta
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Introductory Overview 15 Image sour
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Introductory Overview 17
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Table 1.3. HMD performance figures-
Page 36 and 37: Introductory Overview 21 direct vie
Page 38 and 39: Introductory Overview 23 Figure 1.9
Page 40 and 41: Introductory Overview 25 Figure 1.1
Page 42 and 43: Introductory Overview 27 Ercoline,
Page 44 and 45: Introductory Overview 29 II, Procee
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Page 49 and 50: 34 Clarence E. Rash, Melissa H. Led
Page 55 and 56: 40 Liquid crystal Clarence E. Rash,
Page 70 and 71: Optical Designs 3 William E. McLean
Page 72 and 73: Optical Designs 57 and plotted in l
Page 74 and 75: Optical Designs 59 phosphors, (b) u
Page 76 and 77: Optical Designs 61 optics. Examples
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Page 80 and 81: prism combiner. Optical Designs 65
Page 82 and 83: Figure 3.2. (continued) Optical Des
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Page 88 and 89: Optical Designs 73 Figure 3.6. Opti
Page 90 and 91: Optical Designs 75 Figure 3.8. Refl
Page 92 and 93: Optical Designs 77 Figure 3.9. Ray
Page 94 and 95: Optical Designs 79 incidence and re
Page 96 and 97: 80 Clarence E. Rash hinted at befor
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Page 100 and 101: 84 Clarence E. Rash the performance
Page 102 and 103: 86 Clarence E. Rash Figure 4.3. Hig
Page 104 and 105: 88 Clarence E. Rash imagery in HMDs
Page 106 and 107: 90 Clarence E. Rash as with ANVIS.
Page 108 and 109: 92 Clarence E. Rash performance, on
Page 110 and 111: 94 Clarence E. Rash effects on visu
Page 112 and 113: 96 Clarence E. Rash concerning roll
Page 114 and 115: 98 Aeromedical Research Laboratory.
Page 116: DESIGN ISSUES PART TWO
Page 119 and 120: 102 Clarence E. Rash and William E.
Page 121 and 122: 104 Contrast Clarence E. Rash and W
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120 Clarence E. Rash and William E.
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168 Number of SOG = � log (C r) /
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Visual Performance 6 William E. McL
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Visual Performance 171 observer is
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seen. Visual Performance 173 Figure
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Visual Performance 175 perception.
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Visual Performance 177 with monovis
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Visual Performance 179 individuals
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Visual Performance 181 0 to -5.25 d
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Visual Performance 183 Report No. 9
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Biodynamics 7 B. Joseph McEntire He
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Biodynamics 187 behavior of this de
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Figure 7.2. Head anatomical coordin
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Biodynamics 191
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Biodynamics 193 al., 1972), and man
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Biodynamics 195 Figure 7.5. Vertica
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Biodynamics 197 disability and fata
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Biodynamics 199 been fabricated int
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Biodynamics 201 Ty pic al acc ele r
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Biodynamics 203 exceed the mechanic
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Biodynamics 205 complexity and comp
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Type Reference helmet Foam in place
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Biodynamics 209 the fitting problem
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Biodynamics 211 adjustment buckle,
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Biodynamics 213 down. The helmet ma
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Biodynamics 215 Desert Shield/Deser
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Biodynamics 217 Donelson, S. M., an
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219 Fort Rucker, AL: U.S. Army Aero
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220 Ben T. Mozo Figure 8.1. Noise l
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222 Ben T. Mozo available in the ne
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224 Ben T. Mozo Protectors”(ANSI,
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226 Ben T. Mozo language. Tests of
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228 Ben T. Mozo Figure 8.6. Speech
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230 Ben T. Mozo the communications
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232 Ben T. Mozo Item Mass (grams) C
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Ribera, J. E., and Mozo, B. T. Unda
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236 Joseph R. Licina operational us
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238 Joseph R. Licina Standard MIL-S
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240 Joseph R. Licina On electro-opt
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242 Joseph R. Licina For HMDs with
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244 Joseph R. Licina 1994b) that wi
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246 Joseph R. Licina Table 9.2. Hea
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248 Joseph R. Licina provided a 93.
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250 Joseph R. Licina and buckles, a
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252 Joseph R. Licina authorized to
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254 Joseph R. Licina a nuclear flas
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256 Joseph R. Licina requirements:
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HMD PERFORMANCE ASSESSMENT PART THR
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262 Clarence E. Rash, John C. Mora,
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Glossary 11
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270 making stereoposis possible. Bi
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272 John C. Mora and M elissa H. Le
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NOTES ON CONTRIBUTORS Melissa H. Le
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Notes on Contributors 281 Research
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284 Index Breakaway force (see Fran
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286 Index movement, 55, 80, 84, 90,
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288 Index 198, 204, 205, 208, 210,
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290 Index Microphone, 15, 186, 224,
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292 Index Speech intelligibility (S
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Helmet-Mounted Displays: - USAARL - The - U.S. Army

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