Note: Descriptions are shown in the official language in which they were submitted.
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
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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.
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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
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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
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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
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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
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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
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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
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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.
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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,
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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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