Note: Descriptions are shown in the official language in which they were submitted.
2052137
TWO-PAGE AUTOMOTIVE VIRTUAL IMAGE DISPLAY
BACKGROUND OF THE INVENTION
The disclosed invention is directed generally to
virtual image displays, and is more particularly directed
to a virtual image display for vehicle instrumentation
which provides a plurality of different displays in the
same location.
Vehicle instrumentation commonly includes primary
instrumentation which is located in front of the operator,
for example, in a traditional instrument cluster posi-
tioned in front of the steering wheel. Secondary instru-
ments, including, for example, radio control statusindicators, environment control status indicators, trip
computer controls and indicators, maintenance annuncia-
tors, and message indicators, are commonly located in a
center-mounted panel. With advances in display tech-
nology, the displays of the secondary instruments arebeing implemented with vacuum fluorescent displays (VFDs)
or cathode ray tubes (CRTs).
A consideration with the separation of primary and
secondary instruments, however, includes the required head
and eye motion for reading the secondary instruments,
producing at least a nuisance if not a potential hazard.
-2- 20~2437
1 SUMMARY OF THE INVENTION
It would therefore be an advantage to provide a
vehicle instrumentation display that provides for display
of primary and secondary instrumentation at the same
position ahead of the vehicle operator.
Another advantage would be to provide a vehicle
instrumentation display that permits the selective display
of different types of information at the same position
ahead of the driver.
The foregoing and other advantages are provided by
the invention in a virtual image display for vehicles that
includes a first image source for providing first imaging
illumination, second image source for providing second
imaging illumination, a combiner responsive to the first
and second imaging illumination for providing combiner
imaging illumination, a negative power aspheric off-axis
mirror responsive to the combiner imaging illumination for
providing diverging reflected imaging illumination, and a
positive power aspheric off-axis mirror responsive to the
diverging imaging illumination for providing converging
reflected imaging illumination that produces a virtual
image of the image sources observable by the vehicle
operator. By way of example, the first and second image
2S s~urces can be selectively illuminated so as to display
only one image source at any given time, or they can be
selectively illuminated so that the first image source
provides certain components of the virtual image while the
second image source provides other components of the
virtual image.
2052437
- 2a -
Other aspects of this invention are as follows:
A virtual image display for a vehicle, compris-
ing:
a first image source for providing first
imaging illumination;
a second image source for providing second
imaging illumination;
a combiner responsive to said first and second
imaging illumination for providing combiner imaging
illumination;
negative power aspheric off-axis optical means
responsive to said combiner imaging illumination for
providing diverging imaging illumination; and
positive power aspheric off-axis optical means
responsive to said diverging imaging illumination
for providing converging imaging illumination that
produces a virtual image of said first image source
and ~aid -~econd image source observable by the
operator of the vehicle;
said aspheric optical means being off-axis
whereby the image source and the virtual imaqe do
not lie on the optical axe~ of the aspheric elements
and being aspherically deformed to reduce distor-
t$ons including distortions produced by their
off-axis configurations.
The vlrtual image display for a vehicle,
comprlsings
a first image aource for providing first
imaging illumination~
a second image source for providing second
imaging $11umination;
20524~7
-2b-
a combiner for combining said first and second
imaging illumination for providing combiner imaging
illumlnation~
a negative power a~pheric off-axis mirror
respon~ive to sald combiner imaging illumination for
providlng diverging lmaging illumination; and
positive power aspheric mirror responsive to
said diverging imaging illumination for provLding
convorging imaging lllumination that produces a
virtual image of said first and second image sources
ob~erva~le by the operator of the vehicleS
said a~pheric mirrors being off-axis whereby
the image source and the virtual image do not lie on
the optical axe~ of the aspheric elements and being
1~ aspherically deformed to reduce distortions
including distortions produced by their off-axis
configurations.
2~ BRIEF DESCRIPTION OF THE DRAWING
The advantages and features of the disclosed inven-
tion will readily be appreciated by persons skilled in the
2052~37
1 art from the following detailed description when read in
conjunction with the drawing wherein:
FIG. 1 is an elevational sectional view schematic-
ally illustrating the disclosed two-page virtual image
display.
FIG. 2 is a schematic illustration of a display
produced by one of the image sources of the display of
FIG. 1.
FIG. 3 is a schematic illustration of a display
produced by the other image source of the display of FIG.
1.
FIG. 4 is an elevational view of a single lens
display system that is helpful in understanding the
virtual image display of FIG. 1.
FIG. 5 is an elevational view of a dual lens display
system that is an unfolded version of the virtual image
display of FIG. 1 and is helpful in understanding the
virtual image display of FIG. 1.
FIGS. 6A and 6B are side and front views of an
illustrative example of the negative power mirror of the
virtual image display of FIG. 1.
FIGS. 7A and 7B are side and front views of an
illustrative example of the positive power mirror of the
virtual image display of FIG. 1.
FIG. 8 is a schematic view illustrating an off-axis
lens system that is helpful in understanding the off-axis
configuration of the virtual image display of the inven-
tion.
FIG. 9 is a schematic view of an on-axis lens system
that utilizes an off-axis portion of a lens that is
helpful in understanding known off-axis systems that
utilize off-axis portions of optical elements.
20~2~37
1 DETAILED DESCRIPTION OF T~E DISCLOSURE
In the following detailed description and in the
several figures of the drawing, like elements are iden-
tified with like reference numerals.
Referring now to FIG. 1, shown therein is a virtualimage display system for a vehicle in accordance with the
invention. The virtual image display can be located, for
example, above the vehicle steering column and ahead of
the steering wheel, for example, generally in the region
traditionally occupied by an instrument panel.
The display system includes a first image source 11
and a planar combiner 13 for reflecting at least a portion
of the imaging illumination from the first image source
11. A second image source 12 provides second imaging
illumination to the planar combiner 13 which transmits at
least a portion of the second imaging illumination. The
reflected first imaging illumination and the transmitted
second imaging illumination are directed to an off-axis
convex negative power mirror 15 which provides for diverg-
ing reflected illumination. The mirror 15 is charac-
terized as having negative power since it would produce
image reduction if viewed directly, and is further charac-
terized as providing for diverging reflection since
parallel rays incident thereon would diverge upon reflec-
tion.
The illumination from the negative power mirror 15
is incident upon an off-axis concave positive power mirror
17 which provides for converging reflected illumination.
The mirror 17 is characterized as having positive power
since it provides for image magnification, and is further
characterized as providing for converging reflection since
parallel rays incident thereon would converge upon reflec-
tion.
20~2~27
s
1 The illumination reflected by the positive power
mirror 17 passes through a curved protective window 19 to
the observer. The curved protective window 19 is more
particularly, as viewed from outside the display system, a
concave portion of an elliptically shaped cylinder that is
configured so that the reflections therefrom that can be
seen by the observer will be limited to reflections of a
darkened light trap located above the protective window.
By way of illustrative example, the first image
source 11 comprises (a) a group of electromechanical
gauges for indicating speed, engine RPMs, oil temperature,
oil pressure, and fuel level, for example; and (b) annun-
ciator lights for turn-signals, high beam, and emergency
engine indications, for example. FIG. 2 sets forth a
schematic illustration of an example of the display that
can be produced by the first image source.
By way of further illustrative example, the second
image source comprises a large alpha-numeric display, such
as a VFD or a liquid crystal display (LCD), for example,
for providing alphanumeric information such as messages,
maintenance instructions, and environmental status and
settings. FIG. 3 sets forth a schematic illustration of
an example of the display that can be produced by the
second image source.
The combiner 13 comprises a half-silvered mirror or
a dielectric dichroic mirror, for example. By way of
particular example, the dichroic mirror is configured to
reflect illumination in the yellow/orange/red region of
the spectrum and to transmit illumination in the
blue/green region. The electromechanical gauges of the
first image source would be illuminated with appropriately
filtered incandescent bulbs, and the annunciator lights
would be configured to produce the appropriate light for
reflection by the dichroic mirror. The VFD is self
6 20~2~37
1 luminous and its output would be in the appropriate
spectrum range for transmission by the dichroic mirror.
In operation, the first and second image sources can
be displayed independently to provide a two-page display
wherein the source to be displayed would illuminated while
the other source would not be illuminated. Also, portions
of each display can be selectively illuminated so as to
produce a virtual image that comprises the illuminated
portions from each image source. For example, the speed-
ometer in the first image source can be the only firstimage source component illuminated, and selected portions
of the second image source are illuminated to produce
virtual image components around the speedometer virtual
image.
The negative and positive power mirrors 15 and 17
have aspheric, non-rotationally symmetrical reflecting
surfaces, and can comprise, for example, injection molded
or cast molded plastic substrates having requisite
aspheric surfaces which are coated with a metallic reflec-
tive coating.
The aspheric elements 15, 17 have respective optical
axes OAl, OA2 which are the optical axes defined by the
base radii of the respective reflecting surfaces prior to
being aspherically deformed. The optical axes pass
through the optical axis points Pl, P2 which are utilized
as the origins of the re$pective coordinate syste~s
utilized to define the aspheric deformation of the respec-
tive surfaces. In other words, the optical axis points
P1, P2 and the axes passing therethrough remain fixed
while the surrounding areas are aspherically deformed.
For the reflecting surface of the negative mirror
15, the optical axis OA1 bisects the incidence and reflec-
tion portions of a central axis CA which is defined by the
ray that joins the image source center with the image
center and passes through the optical axis points P1, P2.
2052~7
1 For the reflecting surface of the positive mirror 17, the
optical axis OA2 also bisects the incidence and reflection
portions of the central axis CA.
Relative to the optical axes OA1, OA2, the aspheric
elements are off-axis since the central axis CA is not
colinear with the optical axes, and the image source and
image do not lie on the optical axes of the aspheric
elements including any reflective folds thereof.
The central axis CA further defines an optical path
travelled by the imaging illumination from the image
source to the eyes of the vehicle operator, and as dis-
cussed further herein such optical path has a distance
that is greater than the effective viewing distance of the
virtual image (i.e., the distance at which the operator's
eyes focus in order to view the virtual image).
It is noted that although prior systems have used
mirrors comprising off-axis portions of spherical or
aspherical sections of a conic (e.g., paraboloid), such
systems place the image source on the optical axis of the
conic sections used to define the mirrors. This is done
to maintain some rotational symmetry for ease of fabrica-
tion. However, this limits the performance of such
optical systems by constraining the de~ree of asphericity
that one can apply to the mirror surfaces. The optical
system described in this invention does away with this
restriction by placing the image source off-axis, thereby
decoupling the optical axis of the aspheric surface from
the image source. The aspheric mirrors of the invention
are not rotationally symmetric, taking any shape that
improves the overall visual performance. This added
degree of design freedom allows this invention to exceed
the performance of previous designs.
The negative mirror 15 is the smaller mirror and is
positioned relative to the larger positive mirror 17
pursuant to relatively simple optical formulae (e.g., as
8 20~2~37
1 in a Cassegrain telescope) to achieve a reasonable magni~
fication range for a magnified virtual image without
necessitating a change in the sizes of the image source
11, 12 or the virtual image range (i.e., the effect ve
distance at which the viewer's eyes focus to see the
virtual image). In accordance with the invention, the
virtual image range is in the range of about 4 to 12 feet,
which is greater than the typical distance between the
driver's eyes and direct view instrumentation in an
instrument panel.
The use of a negative mirror and a positive mirror
provides for appropriate magnification, virtual image
range, field of view, and optical performance (i.e.,
reduction of distortion and disparity), while maintaining
an optical system length (i.e., the distance between the
image source and the mirror optically closest to the
nominal eye position) that is more compact than a single,
positive mirror system having comparable parameters. In
other words, for a given magnification, virtual image
range, field of view, and optical performance, the dis-
closed dual mirror system would have a shorter system
length than a comparable single positive mirror system and
therefore a smaller optical package.
The compactness of the dua~ mirror system results
from the reverse telephoto arrangement of the negative and
positive mirrors, which provides for an increased working
focal length without a significant increase in the system
length. The working focal length is the distance from the
image source to the "first principle plane" which, as is
well known, is located at the position at which a single
lens or mirror would be located to produce a single lens
or mirror optical system having substantially the same
parameters. The first principle plane for the dual mirror
system is located between the nominal eye position and the
mirror optically closest thereto, while the first
9 20~2437
1 principle plane for a single positive mirror system is
located at the mirror. In other words, the first princi-
ple plane for the dual mirror system is not constrained to
be at the physical location of one of the optical ele-
ments.
The factors that allow the dual mirror system to
achieve a more compact system length can be better under-
stood by a comparison of the single and dual lens systems
respectively depicted in FIGS. 4 and 5, which essentially
are unfolded versions of a single lens system and a dual
mirror system, and are easier to understand. The perti-
nent optical parameters are as follows:
Range (R): The distance from the nominal eye
position to the virtual image.
Eye Relief (L): The distance from the nominal eye
position to the first lens surface.
Eye Box (Y): The diameter of the space about the
nominal eye position where the virtual image can be
viewed without any vignetting.
Field of View (FOV): The angular substance of the
virtual image as viewed from the nominal eye posi-
tion.
System Length (Z): The distance between the lens
closest to the eye and the image source.
Back Focus (B): The distance from the image source
to the lens nearest the image source.
Working Focal Length (F): The distance from the
image source to the first principle plane of the
optical system.
Working Diameter (D): The diameter of the first
principle plane.
Working F-Number (F/#): The ratio of the working
focal length and the working diameter (i.e., F/D).
2052~37
1 Image Source Size (H): The height (in the vertical
plane) of the image source.
Virtual Image Size (H'): The height (in the verti-
cal plane) of the virtual image.
The optical performance of the respective single and
dual lens systems (i.e., the reduction of distortion and
disparity) is directly related to the working F/#. In
particular, performance deteriorates as the working F/# is
decreased. Therefore, for a given performance specifica-
tion, the working F/# is generally fixed. Also, it may be
desirable to make the system length Z as short as practic-
able to minimize the optical package.
For a single lens system as shown in FIG. 4, the
working focal length F, the back focus B, and the system
length Z are equal. The working diameter D is simply the
diameter of the lens. For a given range R, eye relief L,
eye box size Y, and and field of view FOV, the working
diameter D can be expressed as follows:
D = 2 L tan(FOV/2) + Y (1 - L/R) (Equation 1)
or
D = 2 L tan(FOV/2) + Y, for R ->~ (Equation 2)
The required image source size H can be determined
by understanding that the ratio of the virtual image size
H' and the image source size H is equal to the ratio of
the image distance (lens to image) to the image source
distance (len-q to image source):
H = (2 R tan(FOV/2) F)/(R-L) (Equation 3)
or
11 2052~7
1 H = 2 F tan(FOV/2), for R -~ (Equation 4)
Thus, for specific FOV, range, eye box, and eye
relief requirements, the working diameter is defined by
Equation 1. Since the working F/# is minimized and fixed
for a specific performance requirement, the working focal
length is also fixed (since F = DF/#), and the image
source size is then defined by Equation 1.
A single lens system provides adequate performance
if the image sources can be arbitrarily sized to match the
image source size requirements discussed above. Such
sizing can be achieved if the image sources comprise
liquid crystal displays (LCDs) or VFDs wherein the size of
the graphics can be readily changed to be sufficiently
small. However, electromechanical gauges cannot be mini-
aturized smaller than a certain size, for example, about
one inch in diameter. Given the size constraint for an
analog image source, the foregoing equations will need to
be applied in reverse starting with a given image source
size.
If the analog gauge is larger than the proposed
image source size dictated by the equations, then both the
working focal length and the FOV will have to increase for
a constant working F/#. If the FOV must remain constant,
then the working diameter will also be constant, and the
only way to use a larger image source size will be to
increase the F/~. This will also increase the working
focal length (even greater than in the case where the FOV
can be increased). Given that an analog gauge image
source cannot be made as small as an LCD or VFD source,
the net result is that the system length must be increased
for a single lens system if an analog gauge is used as the
image source. A longer system means a longer box and an
overall increase in the optical package size.
2052~37
12
1 Consider now the dual lens system of FIG. 5 which is
the unfolded version of the disclosed dual mirror system,
and functions as a reverse telephoto arrangement that
provides for an increased working focal length without an
increase in the system length. For simplicity, the range
is set to infinity as above relative to the single lens
system. The focal length of the two lenses are fl and f2,
with fl being a positive focal length and f2 a negative
focal length. The distance between the two lenses is x.
Therefore, the working focal length of this system is:
F = (fl)(f2)/(fl+f2-x) (Equation 5)
As can be seen in FIG. 5, the focal length actually
exceeds the system length. By varying fl and f2, the
focal length is substantially independent of the back
focus and the system length. The distance L1 from the
nominal eye position to the first principle plane is:
L1 = L + x + B - F (Equation 6)
And the working diameter is:
D = 2 L1 tan(FOV/2) + Y (Equation 7)
Solving for the image source size H with the range R
at infinity, Equation 7 reduces to the following:
H = 2 F tan(FOV/2) (Equation 8)
which is the same as Equation 4.
If the image source size is changed while keeping
the working F/# and the field of view FOV constant, the
working focal length is set by Equation 8; the working
diameter D is set by the working F/#; and L1 is set by
13 20~24:37
1 Equation 7. Equation 6 can then be solved for the quan-
tity (x + B) which is the system length.
As an example of the difference between the single
and dual-lens systems, the optical parameters for the
single and dual-lens systems will be calculated for the
following system specification:
R , ~
L = 24"
Y = 2.5"
FOV = 3
-
For reasonable performance, the working F/# should not be
less than 2Ø
Using Equation 2 for a single lens system, the
working diameter must be 3.757 inches which requires a
focal length of 7.514 inches (from F/# - F/D), which is
also the system length since for a single lens system the
system length is equal to the working focal length. From
Equation 4 the image source size must be 0. 394 inch.
Consider now the use of an analog gauge package that
is one inch in size for the image source. From Equation 4
and keeping the FOV at 3, the focal length must increase
to 19.094 inches. This is a 150% increase in the system
length. The working diameter will remain at 3.757 inches
leaving u~ with an F/# of 5.082.
If the system length of 19.094 inches cannot be
tolerated, the FOV can be changed to reduce the focal
length. By substituting (D) (F/#) for the focal length F
in Equation 2, and by substituting the expression for D
from Equation 2, the image source can be related to the
working F/~ and the FOV:
H = (2 F/# tan (FOV/2) ) t~ L tan (FOV/2) +Y] (Equation 9)
20~2437
14
1 Solving for the FOV in the above quadratic equation
(and keeping the working F/# fixed at 2.0 for our exam-
ple), provides a value of 5.803. Substituting that value
in Equation 4 results in a working focal length of 9.865
inches and a working diameter of 4.933 inches. Though the
system length has been reduced to 9.865 inches (still
greater than the original 7.514 inches for a smaller image
source size of 0.394 inch), the working diameter has
increased from 3.757 inches to 4.933 inches (31% larger).
Thus, even with the new FOV, the overall size of the
system has increased
The dual lens approach will now be analyzed for an
imaqe source size of one inch. From Equation 8, the
working focal length is 19.094 inches for a 3~ FOV.
Setting the distance between the two lenses, x, to be 3
inches and setting the system length to be 7.514 inches
(the shortest possible single lens design for the spec-
ified eye relief L, eyebox Y, and field of view FOV), the
back focus will be 4.514 inches. From Equation 6, Ll is
then equal to 12.42 inches. The focal lengths of each
lens can vary relative to one another, but one solution
from Equation 5 is that fl is 7.568 inches and f2 is
-7.568 inches. Since the size of fl is the same as the
working diameter of the single lens system of 3.757, the
F/~ of fl is 2.014.
From the foregoing comparison, it should be appreci-
ated that for a specified image source size along with the
optical specification of range, FOV, etc., the dual lens
system provided for a system length that is comparable to
a single lens system having a smaller image source size.
It is also pointed out that since the working F/#'s of the
individual lenses in the dual lens system are not too
fast, the optical performance will be better than the
single lens approach since there are two lenses to opti-
mize.
2052~37
1 As to the implementation of the disclosed dual
mirror virtual display system, the foregoing analysis of
the dual lens system could be utilized to arrive at a
first-order design, which would be followed by utilizing
an optical design computer program with the spherical
mirror versions of the first-order design. With the
computer program, the nominal spherical surfaces are
deformed to meet the desired criteria of minimizing
distortions when viewed in the eyebox. Since the eyebox
and virtual image are off-axis with respect to the indi-
vidual axes of the two mirrors, the equation of the
aspheric surfaces can be adjusted independently from the
axis joining the eye and the virtual image. This provides
for greater latitude in the design process and will better
correct the optical aberrations and distortions. Such
distortions can cause vertical disparity and magnification
variations that are objectionable in the final design,
Referring now to FIGS. 4A, 4B, 5A, 5B, the following
sets forth illustrative examples of the aspheric reflect-
ing surfaces of the negative and positive mirrors for adual mirror virtual image display in accordance as in this
invention, wherein the surfaces have aspherically deformed
to reduce distortions. The dimensions of the mirrors
sh~wn in these figures is in inches.
The aspheric surface of the illustrative example of
the negative mirror satisfies the following surface
equation relative to the coordinate system shown in FIGS.
4A and 4B:
Z (X,Y) = S (X,Y) +i lCiFi (
where Ci and F(X,Y)i are as follows:
20~2437
16
Cl F(X,y)i
1-0.152819 x 10 1 x2_y2
2-0.228226 x 10 2 y(X2+y2
3-0.384185 x 10 2 y(3X2 y2
4-0.279668 x 10 3 X4-Y4
5-0.652462 x 10 6 Y(X2+Y2)2
and S(X,Y) is:
S(X,y) = R+(R2_x2_y2)1/2
and R = -11.8231.
The following table sets forth data for sample
points (in inches) along the aspheric surface of the
negative mirror:
NEGATIVE MIRROR SURFACE SAMPLE POINTS
X y z
+1 0 -0.057928
0 +1 -0.025~44
0 -1 -0.028365
+1 +1 -0.097131
+1 -1 -0.072639
The aspheric surface of the positive mirror utilized
with the foregoing described negative mirror satisfies the
following surface equation relative to the coordinate
system shown in FIGS. SA and 5B:
Z (X,Y) = S (X~Y) +i~lCiFi (
where Ci and F(X,Y) are as follows:
17 20~2~7
1 i _ F(X,Y)
1-0.617592 x 10 2 X2_y2
2-0.593066 x 10 3 y(x2+
3-0.560451 x 10 3 y(3x2 y2
4-0.206953 x 10 4 X4-Y4
5-0.181196 x 10 4 Y(X2+Y')2
and S(X,Y) is:
S(X,y) _ R - (R2_X2_y2)1/2
and R = -14.1672.
The following table sets forth data for sample
points (in inches) along the aspheric surface of the
positive mirror:
POSITIVE MIRROR SURFACE SAMPLE POINTS
X Y Z
+1 0 -0.041533
0 +1 -0.029191
0 -1 -0.029089
+1 +1 -0.073142
+1 -1 -0.068383
The foregoing mirror surfaces can be utilized in a
display system having the following parameters:
Range R: 80 inches
Eye Relief L: 24 inches
Back Focus B: 5.7 inches
System Length Z: 9 inches
. Image Source Size: 1.25 by 5 inches
Virtual Image Size: 4 x 16 at 80 inch range
18 2052~37
1 It should be appreciated that the optical axes OA1,
OA2 of the aspheric elements described above are along the
respective Z axes of the respective coordinate systems
utilized to define the aspheric deformation of the respec-
tive surfaces, that the central axis CA of the display
system that includes the aspheric elements passes through
the origins of such coordinate systems, and that such
origins correspond to the optical axis points Pl, P2.
Referring now to FIG. 8, shown therein is a simple
off-axis lens system illustrating the use of "off-axis" in
conjunction with the invention. The central axis CA that
joins the center of the object and the center of the image
is not coincident with the optical axis OA of the lens,
and thus the central axis is "off-axis" as are the object
and image. In the invention, the off-axis configuration
is initially set up relative to the optical axis of a
spherical element which is then distorted as described
above to achieve the appropriate aspheric surface.
Referring now to FIG. 9, shown therein is a simple
lens system illustrating known on-axis systems that
utilize a portion of an optical element that is positioned
off-axis relative to the optical axis of the optical
element, where such optical axis is defined by the base
radius of the optical element. While an off-axis portion
of an optical element is used, the central axis that joins
the center of the object and the center of the image is
coincident with the optical axis OA and thus "on-axis," as
are the object and image (i.e., the object and image lie
on the optical axis).
From the foregoing, it should be appreciated that as
a result of the configuration of the optical elements for
use with electromechanical analog gauqes, the second image
source comprising an alphanumeric display can be larger
than those utilized with a single mirror system, which
permits more detail in the graphics. It should also be
20S2~37
19
1 appreciated that different types of image sources can be
utilized, including for example segmented graphical
displays, and that both image sources can be of the same
type; i.e., both can be electromechanical, alpha-numeric,
or segmented graphical displays, for example.
The foregoing has been a disclosure of a compact
virtual image display system which can advantageously
display different vehicle instrumentation information at
different times at the same location, which reduces the
amount of dashboard space required for instrumentation and
further enhances the ease of viewing the instrumentation.
Further, the use of magnification permits the use of
smaller alphanumeric image sources which are less expen-
sive than the larger direct view versions.
Although the foregoing has been a description and
illustration of specific embodiments of the invention,
various modifications and changes thereto can be made by
persons skilled in the art without departing from the
scope and spirit of the invention as defined by the
following claims.
