CA1121591A - Flight simulator visual display apparatus - Google Patents

Abstract

Abstract The invention provides line scanning and frame scanning apparatus for the projection of images, particularly for head-coupled area-of-interest visual display apparatus for ground-based flight simulators. The line scan apparatus is cockpit-mounted and comprises a modulated laser beam which is scanned over a line of fibre optic guides forming a ribbon by which the line image is transmitted to a helmet-mounted frame scanner. Sensing means detects head/helmet movement to permit voluntary scanning of a wide angle of simulated view from the craft. The invention permits of light-weight helmet-mounted equipment for this purpose.

P.2096/1

Description

Description This invention relates to visual display apparatus, particularly for ground-based flight simulators and particularly for providing a display cover-ing a wide-angle field of view. The invention may be used in apparatus capable of providing either pseudo-collimated or stereoscopic viewing for a pilot.
The apparatus is of the head-coupled area-of-interest type, wherein an image is projected upon a screen and is appropriately changed both according to the simulated craft position and angular orientation and according to view-er's instantaneous line to view and is simultaneously moved on the screen tooccupy the viewer's field of view.
Apparatus of this type was described in British patent specification Number 1,489,758. Such apparatus provided an area-of-interest display for a viewer which was pseudo-collimated, that is, the same image was projected for left and right eyes, so as to appear at infinity.
The present invention is used in an improved form of such apparatus in which line scanning apparatus is cockpit-mounted, line image transmission is by fibre optic light guide ribbon and solely the frame scanning apparatus is mounted upon a helmet worn by the viewer.
Accordingly, the invention provides for apparatus .~3 ~

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providing a raster scanned image upon a screen by deflecting a light spot of modulated intensity to form a scanned line and deflecting successive scanned lines to form the raster scanned image, line scanning, frame scanning and intermediate flexible light guide means comprising a fibre optic light guide having groups of fibres thereof fanned at the input and output ends of the light guide into concave arcuate shape, the fibres corresponding to individual image spot elements being arranged in the same relative sequence at both input and output ends, movable mirror means positioned to reflect an incident modu-lated light beam over the arcuate configuration of fibres at the input end of the light guide, thereby to scan one line of the raster scanned image, movable mirror means positioned at the output end of the light guide for frame scanning successive lines of the raster scanned image and lens means positioned between the output end of the light guide and the frame scanning mirror for focussing the output ends of the fibres onto the said screen.

~'i 1121~i Short Description of Drawln~s In order that the invention may readily,be carried into practice, one embodiment will now be described in detail, by way of example, with reference to the accompanying drawings, in which:-Fig. 1 is a diagrammatic perspective view showing apilot seated in relation to a part-spherical screen for pseudo-collimated viewing of a head-coupled area-of-interest visual display;
Fig. 2 is a diagrammatic view of laser source, laser beam modulator, line scanning, fibre optic light guide ribbon and frame scanning apparatus which uses the present invention in the line scanning, light guide and frame scanning apparatus;
Fig. 3 is a side view of the frame scanner of Fig. 2; and Fig. 4 is a detail view showing an alternative line scanner to that of Fig. 2.

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Description of the Example The apparatus of Figure 1 will be described first in order ~o illus-trate the form of apparatus in which the present invention may be employed.
Figure 1 shows in diagrammatic form apparatus for generating and displaying a pseudo-collimated area-of-interest view. A pilot 10 wearing a helmet 12 is seated within a partspherical shell having a retro-reflective interior surface partially represented in Figure 1 by the concave retro-reflective screen 14. The pilot's line of vision, for right and left eyes and for distant viewing, intersects the screen at points 16 and 18, respective-ly. The field of view for each eye is centred on the respective one of thesetwo points. The views displayed are identical for right eye and left eye but are displaced laterally by the distance between the points 16 and 18 so that the pilot 12 sees a pseudo-collimated view, that is to say, the displayed view appears to be at infinity and not at the distance of the screen 14. The combined left eye and right eye views will be referred to as the displayed scene.
The displayed scene depends, in this example, upon the simulated position of an aircraft during an exercise flight, the attitude of the air-craft, the pilot's seating position in the aircraft and the pilot's instant-aneous line of view as determined by the instantaneous oricntation oE thepilot's head and helmet. The position oE points 1~ and 18 on the screen 14 and hence the position of the displayed vicws on ~' .. , ~

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the screen depends only on the pilot's head and helmet orientation.
The image required is generated by an image generator 20 of the computer-generated image type and which includes a frame buffer store 20'. The pilo-t's head orientation is sensed by a head orientation sensor 22, which is fixedly mounted within the simulated aircraft cockpit in a mounting 24.
The displayed view is projected onto the screen 14, centred in the appropriate locations as two raster-scanned images, the line scan apparatus being cockpit-mounted and the frame scan apparatus being mounted on the helmet 12. Line scan may be either across the screen 14 or up or down. In the present example, line scan is such that the projected scan line upon the screen and the line between the pilot's two eyes lie in the same plane. The frame scan is orthogonal -thereto. Thus, when the pilot's head is erect, line scan is horizontal and frame scan vertical.
Referring still to Fig. 1, a laser source 30 provides an output laser beam 31 which is directed through R full colour modulator 3~ to provide a modulated laser beam 3l'. The modulated beam 31' is directed -through beam-splitter and reflector elements 32, 33 to provide two beams 34 and 36 of equal intensity. The modulator 38 is con-trolled from the image generator 20 according to the view to be projected. Both modulated beams 34 and 36 pass to a double line scanner 42 fixedly mounted in the simulated aircraf-t cockpit. The two P.2096 ~2~9 scanners, described in detail later herein, provide two respective scanned beams 44 and 46 whi.ch are respectively scanned over the input ends 48 and 50 of two fibre optic light guide ribbons 52 and 54.
The two fibre optic light guides provide a flexible linkage between the fixed line scanner 42 and the movable helmet 12. The emergent scanned light beams from the respective ends 56 and 58 of the light guides 52 and 54 are focussed by spherical lenses 62 and 64 onto the screen 14 and directed onto a plane mirror 60. The right eye beams are reflected by the mirror 60 along divergent paths to form a scan line, the centre of which is shown at 66.
Similarly, the left eye beams are ref`lected by the mirror 60 along divergent paths to form a scan line, the centre of which is shown at 68. The cen-tre line of -the respective right eye and left eye views is thereby formed on the screen 14, each line having its respective mid point at 16 and 18 and being viewed by the pilot 10 in the respec-tive line of view 70 and 72.
The mirror 60 is long in reLat:i.on to i.ts width arld i.s carried in bearings at its end which are mount~d on the helmet 12. These bearings are provided by mo-tors 74 and 76 at the two ends which move the mirror 60 to provide the required frame scan.
The mirror 60 may be a single plane mirror whi.ch i.s either oscillated or rotated by the motors 74, 76 on its axis P.2096 . ' ` ' ' ~lSg~

parallel to the plane in which the line scan is projected or the mirror 60 may be a multi-faceted polygon mirror rod of, for example, octagonal cross-section which is continuously rotated by the motors 74, 76. In the present example, the mirror 60 is a single plane mirror and is rotationally oscillated for frame scan.
As the pilot's head moves, so does the displayed view move over the screen, so as to be in the pilot's new line of view and the view itself is changed according to the simulated real world view in the direction of the line of view.
To this end, the visual system receives data from -the host flight computer on lines 80 and 81. Position da-ta de:fining the simulated aircraft position throughout a simulated flight exercise is supplied to the image generator 20 on line 80. Attitude data, defining -the simulated aircraft instantaneous attitude, is supplied on line 81 to a vector summing unit ~2 together with head orientation da-ta, defining the pilot's actual instantaneous line of view, on line 84.
The summed output is supplied to the image generator 20 on li.ne 86. A throughput delay error signal obtained by subtracting the head attitude lnpu-t to the image generator one throughput delay period ago from the current head attitude position, is supplied to the throughput delay error control ~mit 100 on line 119.
The duplicated in1age, respective:Ly for the right eye and P.2096 . .
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left eye views, in accordance with the inputted data, and allowing for the known seating position of the pilot in the simulated aircraft type, are supplied to the respective modula-tors 38 and 40 on lines 88 and 90.
It will be appreciated that the change of the displayed image with simulated aircraft position is relatively slow.
However, the change of the displayed image with head orientation is complete and relatively very rapid. The image generator is unable to cornpute an entirely new image immediately a new line of view is established due to the throughput delay of the image generator computer. To overcome this limitation the residual old displayed view is derotated to its former screen position until the computed new displayed view is available.
The required image dero-tation can be effected by controlling the relationship between the video signal and the line scan and frame scan posi-tions. This con-trol can be produced in a number of ways.
The line scanner is typically a continously rotating polygon mirror which sweep,s the input laser beam or beams through an arc to produce a line scan, as in the example o~
~ig. 2. Three al-ternatives are available:
(i) If the video signal is produced at a constant rate then the line scan drive may be phase modulated to maintain the correct line in space to produce an image with the correct spatial orientation. If -the line projec-tion system P.2096 .

' 5~l g is capable of -transmitting only the displayed field of view, then the image size will only be that part which is common to both the computed and projected images. If the fibre optic ribbon and the projection system is capable of projecting more than the required field of view in the line scan direction then the field of view obtained may be held constant.
(ii) The video signal may be produced at a constant rate and the line scanner rotated at a constant rate. The required angular shift may then be introduced with a supplementary mirror. Line scanning apparatus, alternative to that of Fig. 2 and including such a supplementary mirror is described later herein with reference to Fig. 4.
(iii) The polygon mirror may be run at a constant angular velocity and the video signal timing adjusted by altering the time at which the video signal is read out of the frame store 20' of -the image generator 20. This ensures that the video signal corresponding to a point in space is produced at the predetermined time that the scanner points the light beam at that part of the screen representing the required point in space.
Of -these three methods desoribed above, method (i) involves the phase modulation of a mechanical system rotating at high speed and has the disadvantages associated with -the inertia and response times of such a system. Me-thod (ii) overcomes some of these problems by using a supplementary P.2096 ~ -:
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mirror. This mirror does not rotate at high speed but nevertheless has inertia inherent in any mechanical system and so it will have some response time. Method (iii) requires only the ability to read out a memory at controlled times.
Since a memory is not a mechanical system, it has no inertia and can be read out in a discontinuous manner if required.
Accordingly, method (iii) is the preferred method for line scan synchronisation in the present invention.
The frame scanner of Fig. 1 does not offer the same options as does the line scanner due to the difficulties of implementation. The alternative methods corresponding to those described for the line scanner are as follows:
(i) If the video signal is produced at a constant rate then the frame scan drive may be controlled to give the required poin-ting direction. In this case the frame scanner will be a position servomechanism driven by a sawtooth waveform in which the starting point of the ramp may vary in a controlled manner and the slope of the ramp may vary in a controlled manner in order to give a constan-t angular sweep in free space when the pro~ector mount ls belng sub~ected to angular shifts.
(ii) The use of a supplementary mirror is imprac-tical in the frame scanner of Fig. 1.
(iii) If the frame sc:anner is driven with a sawtoo-th of constant period, start point and slope, then -the read out times from the frame store 20' may be adjusted to produce P.2096 1~21S~

the video signal when the scanner is a-t the required orientation in free space.
Of these three methods, method (i) requires adjustments to the period and rate of a mechanical system which, due to its construction, has a very low inertia. Hence, the settling time following such a disturbance may be acceptable. It can preserve the instantaneous field of view constant through the throughpu-t delay period. Method (ii) is impractical due to the physical constraints of the projection lens and frame scanner assembly of Fig. 1. Method (iii) involves adjustment to a system without iner-tia or the requirements o~ continuity. ~owe~er method (iii) reduces the virtual field of view during -the throughput delay period.
Continuing wlth the description of the apparatus of Fig. 1, a synchronising pulse generator 106 supplies pulses on line 108 to the -throughpu-t delay error control unit 100.
Line scan control signals are supplied to the line scanners of unit 42 from unit 92 by way of line 94. Frame scan control signals are supplied -to the frame scan motors 7~, 76 from un:it 96 by way of a Llexib:le line 9~. Vidco synchronisation timing pulses are fed -to the frame buffer 20' of the C.G.I. image generator 20, from -the unit 100 on line l10. Con-trol of the relative timings between the line scan control 92, the frame scan control 96 and the C.G.I.
image generator frame buffer 20' is effected by -the throughput delay error compensation circuit 100 by way of lines 102, 104 and 110, respectively.

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I-t will be noted that the projection middle lines 66 and 68 do not coincide with the lines of view 70 and 72 for the reason that projection is effected from above the pilot's eyes. Projected onto any horizontal plane, the respective lines are coincident but, projected onto any vertical plane, the respective lines diverge away from the screen. The angle of divergence is small but is nevertheless great enough, compared with the apex angle of the half-brilliance cone of reflection of a retro-reflective screen material, to result in a viewed scene of much reduced brilliance. It is preferred therefore to use a screen of modified retro-reflective material for which the axis of the half-brilliance cone of reflec-tion is depressed downwardly by the angle between the projection lines 66, 68 and the line of view lines 70, 72.

P.2096 lS~l Laser Source, Laser Beam Modulator, Line Scanner~ Fibre Optic Li~ht Guide Ribbon and Frame Scanner Onelaser source and laser beam modulator and the line scanner, fibre optic light guide ribbon and frame scanner apparatus of the present invention will be described together with reference to Fig. 2 and Fig. 3.
Fig. 3 shows the laser beam source 30 which provides the output laser beam 31 directed through the full colour modulator 38. Both -the laser beam source 30 and the modulator 38 are of known form. The full-colour modulated beam output is shown at 31' in this figure, in which inter~ediate beam-splitters are not showrl. The line scanner is shown generally at 42.
The line scanner comprises a synchronously-driven polygonal section mirror drum 144 which rotates continuously in the direction shown by the arrow 145 to sweep the beam 31' over the scan path 44. One pass occurs for the ~ovement of each mirror facet of the mirror drum 144 past the beam 31'.
A fibre op-tic light guide, formed into a flat ribbon 52 over most of its length, has indivi(lual groups of flbres forrned into an arc at the input end ~l~ of` the light guide. The width of the line scan 44 exactly covers the arc at 48, so that the modulated beam 31' is scanned along the arc at 4~ for each line of the image.
At the output end 56 of the fibre optic light guide 52, P.2096 llZlS~

the individual groups of fibres are similarly formed into an arc the fibre groups occurring in the same sequence at the two ends 48 and 56, so that the scanned image line at the input end 48 is exactly reproduced at -the ou-tput end 56.
The emergent rays from the output end 56 of the light guide 52 are focussed by the spherical lens 62 onto the face of the frame scanning mirror 60. As shown in Fig. 1,the mirror 60 is mounted on the pilot's helmet 12 in bearings provided by reciprocating motors 74 and 76.
With the mirror 60 stationary, the emergent rays are reflected from the mirror 60, as shown instantaneously at 66, to form a single line of the image. As the mirror 60 is moved, successive lines of the image are projected to form the entire scanned image.
Fig. 3 shows, in side view, the output end 56 of the light guide 52, the spherical lens 62, the mirror 60 and the reflected beam 66 as described above with reference to ~ig. 2.
A second line scanner, comprising a second mirror drum, produces a second line scan over the input end 50 o~ the second ~ibre optic l.ight guide 54, as is shown in ~ig. 1. The output end 58 of this second light guide 54 provides emergent rays which are focussed by a second spherical lens 64 onto the same reciprocating mirror 60. The two helmet mounted optical systems, with the common frame scan mirror 60 J

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together provide the right eye image and left eye image of the pilot's displayed view. As already explained, the identical right eye and left eye images provide the pseudo collimated display for the pllot. The line scanner, fibre optic light guide ribbon and output lens are duplicated, with a common frame scanner, in order to provide, in the duplication of the fibre optic light guides, for possible fracture of one or more fibres associated with any specific spot in the raster lines.
For stereoscopic viewing, different left-eye and right-eye images comprising a stereoscopic pair of images would be transmitted by the -two light guides.
Fig. 4 shows line scanning apparatus alternative to that of Fig. 2 and including a supplementary mirror 202. The mirror 202 is pivotable on an axis 203 which is parallel to the spin axis 204 of the polygon mirror line scanner 144.
To effect image derotation for head movement in the direction of line scan by the method (ii) described earlier, the mirror 202 is rotationally positioned about i-ts axis 203 by a motor 205 in a controlled manne~r so that the swep~ arc 4L~
is positione~ at the reql1lred part of the arc 48 at the input end of the ~`ibre optic light guide 52. The motor 205 is controlled from the throughput delay error control unit 100 by a signal on line 102.

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Claims (7)

Claims

1. For apparatus providing a raster scanned image upon a screen by deflecting a light spot of modulated intensity to form a scanned line and deflecting successive scanned lines to form the raster scanned image, line scanning,frame scanning and intermediate flexible light guide means comprising a fibre optic light guide having groups of fibres thereof fanned at the input and output ends of the light guide into concave arcuate shape the fibres corresponding to individual image spot elements being arranged in the same relative sequence at both input and output ends, movable mirror means positioned to reflect an incident modulated light beam over the arcuate configuration of fibres at the input end of the light guide, thereby to scan one line of the raster scanned image, movable mirror means positioned at the output end of the light guide for frame scanning successive lines of the raster scanned image and lens means positioned between the output end of the light guide and the frame scanning mirror for focussing the output ends of the fibres onto the said screen.

2. Apparatus as claimed in Claim 1, for a ground-based flight simulator, in which the line scanning means is cockpit-mounted, the frame scanning means is mounted on a pilot's helmet and the intermediate flexible light guide provides a flexible light-transmitting means between the static line scanning means and the relatively movable frame scanning means.

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3. Apparatus as claimed in Claim 1 or Claim 2, in which the line scanning means is a rotating polygon mirror arranged to scan a modulated light beam directly over the concave arctuate shaped input fibres of the fibre optic light guide.

4. Apparatus as claimed in Claim 1 or Claim 2, in which the line scanning means is a rotating polygon mirror arranged to scan a modulated light beam over the concave arctuate shaped input fibres of the fibre optic light guide by way of an intermediate mirror which is movable to select that portion of the arc formed by the light guide input fibres which is scanned by the polygon mirror.

5. Apparatus as claimed in Claim 2, in which the frame scanning means is a plane mirror pivotably mounted on the pilot's helmet, driven by motor means for frame scanning movement and lens means are provided between the output end of the fibre optic light guide and the frame scanning mirror for focussing output light from the light guide onto the said screen by way of the frame scanning mirror.

6. Apparatus as claimed in Claim 5, in which the frame scanning mirror simultaneously performs frame scanning of a right-eye image and a left-eye image for the pilot.

7. Apparatus as claimed in Claim 6, having the output ends of a pair of fibre optic light guides together with associated lens means respectively for said right-eye and left-eye images, mounted at spaced-apart positions on the pilot's helmet above pilot right-eye and left-eye locations relatively to said helment.