Patent US3848974 - HEAD-UP DISPLAY APPARATUS

SHEET 8 OF 6 1 2

HEAD-UP DISPLAY APPARATUS The said finite distance may be in the range of 6 to

20 feet.

This invention relates to head-up display apparatus. Preferably the optical means includes a curved mirror, and, in such a case, the curved mirror may be a

Such apparatus is used, for example, to provide the 5 spherical mirror,

pilot of an aircraft with a display of information which The optical means may include a diverging lens dis

he can consult without having to divert his line-of-sight posed in an optical path between the display-producing

from the scene ahead of the aircraft. The head-up dis- means and the curved mirror.

play apparatus comprises generally a display-producing The optical means may include a planar mirror which

means (usually a cathode-ray tube) for producing the 10 is to be disposed in an optical path between the curved

display of information and a collimator which focuses mirror and the windscreen.

the display of information at infinity. In a common ar- The windscreen may be a laminated windscreen,

rangement, when the apparatus is fitted, for example, According to a further aspect of the present inven

in an aircraft, the collimator projects the display of in- tion there is provided a craft including a head-up dis

formation onto a flat, partially-transparent reflector 15 play apparatus as specified in any one of the preceding

which is disposed in the line-of-sight of the pilot. The six paragraphs.

reflector is inclined so that the display of information Two forms of head-up display apparatus in accor

projected onto the reflector appears in the line-of-sight dance with the present invention and including an as

of the pilot. Thus, the pilot sees the collimated display sembly for projecting onto a windscreen of an automo

of information against a background of the scene visi- 20 bile an indication of its speed will now be described, by

ble through the windscreen of the aircraft, and he may way of example, with reference to the accompanying

shift his attention from the display to the scene and drawings in which:

back without any need for refocussing of his eyes. The FIG. 1 is a diagrammatic view of one form of the

reflector must be flat to ensure that the collimation of head-up display apparatus;

the display of information is not disturbed. 25 FIG. 2 is a side view showing in more detail the as

Head-up display techniques may be advantageously sembly of FIG. 1;

employed in other situations. For example, the driver FIG. 3 shows one form of the display projected onto

of an automobile must always maintain adequate vigi- the automobile windscreen by the assembly of FIG. 2; lance over the road conditions ahead of the vehicle,

particularly in heavy traffic or bad weather. However, 30 FIG. 4 is a sectional side view of a part of the assem

in most modern cars the instruments, including the bly of FIG. 2;

speedometer, are mounted in a position which requires FIG. 5 is a diagrammatic view of an alternative form

the driver to divert his line-of-sight from the road ahead of the assembly;

and refocus his eyes before he can consult those instru- FIG. 6 is a part-sectional side view showing in more

ments. Since this can be very distracting and tedious, 35 detail the assembly of FIG. 5;

the driver may tend to rely on his own, probably very FIG. 7 is a plan view of a disc forming part of the asinaccurate, subjective judgement of the speed of the sembly of FIG. 6;

vehicle. This tendency to ignore the speedometer will FIG. 8 is a fragmentary sectional view on the line

most likely occur in complicated road conditions which VIII—VIII of FIG. 6; and

demand the driver's uninterrupted attention. However, 40 FIG. 9 is a part-sectional side view showing schemati

it is in such conditions that precise knowledge of the cally a method of mounting the assembly of FIG. 6 in

vehicle's speed is in fact vitally important. the automobile.

Although the head-up display apparatus described Referring to FIG. 1, the head-up display apparatus above is generally very acceptable for aviation use, it includes a conventional movement 10 of a speedomeis relatively expensive and is not therefore suitable for ter which is coupled to the automobile transmission by use in, for example, automobiles. Also, the extent to means of a flexible drive cable or a gear mechanism so which the person viewing the display may move his as to cause an output shaft of the movement 10 to be head while keeping the display in sight is limited by the displaced about its axis through an angle proportional dimensions of the partially-transparent reflector. If the to the speed of the automobile. The output shaft of the reflector were made large enough to avoid this prob- movement 10 carries a disc 11 having an arcuate lem, it would become unacceptably obtrusive and also speedometer scale formed around its periphery. The further increase the cost of the apparatus. speedometer scale is conventional in layout and, conAccording to one aspect of the present invention veniently, the disc 11 is of transparent material and is there is provided a head-up display apparatus for a 55 coated with opaque paint, the numerals of the speedcraft, including means for producing a display of infor- ometer scale being formed by appropriately shaped mation, and means for projecting the display of infor- gaps in the coating of opaque paint. A light source 12 mation, wherein the apparatus also includes a curved is provided to illuminate a predetermined arcuate windscreen for the craft on to which the display of in- length of the scale formed on the disc 11, and the anguformation is to be projected by the display-projecting 6Q lar position of the disc 11 on the output shaft of the means to appear in an observer's line-of-sight, and movement 10 is selected so that, at any particular anguwherein the optical characteristics of the display- lar position of the output shaft of the movement 10, the projecting means are selected in accordance with the speed indicated at the center of the illuminated length curvature of the windscreen so as to enable the display of the scale corresponds to the automobile speed. The of information projected on to the windscreen in the 6j illuminated speedometer display is projected onto a said line-of-sight to appear to the observer as emanat- curved windscreen 14 (which is preferably of the lamiing from a position which is a finite distance in front of nated type) by a spherical mirror 13. The light-rays rethe observer. fleeted by the mirror 13 pass through a glass window IS

in a dashboard coping 16 of the automobile. The mirror 13 is positioned so that the speedometer display is projected onto that portion of the windscreen 14 which is disposed in the normal, line-of-sight of the automobile driver. More particularly, the speedometer display is so positioned on the windscreen 14 that the center of the display will be aligned with the driver's line-of-sight when depressed through an angle d from the horizontal line-of-sight. In practice, this angle 0 is preferably between five and ten degrees of arc. The automobile driver thus views the projected display against the background of the scene visible through the windscreen 14.

In previously known head-up display apparatus the projected display of information in the obsever's lineof-sight has always been focussed at infinity. However, it has been found that this can be disadvantageous in an automobile. If, for example the display provided in the driver's line-of-sight is collimated, the display may distract the driver when the automobile is approaching the brow of a hill. This is particularly the case at night. Furthermore, since the windscreen 14 is curved, other problems can arise, such as splitting of the projected display into two separate images. Therefore, it is proposed to overcome these difficulties by arranging that the projected display appears to the driver as emanating from a position which is a finite distance in front of the driver, this distance being selected so that, on the one hand, the driver does not need significantly to refocus his eyes to view the display, and, on the other hand, is not unnecessarily distracted by it. In the apparatus of FIG. 1 this distance is arranged to be in the range of six to twenty feet in front of the driver. In addition, with such an arrangement, it has been found that spherical aberrations caused by the mirror 13 are to some extent cancelled out by the curvature of the windscreen 14. The windscreeen 14 thus forms an essential optical component of the head-up display apparatus.

Referring to FIG. 2, the speedometer movement 10 is housed within a compartment 17 the side walls of which have been removed to simplify the drawing. The disc 11 is carried by an output shaft 18 of the movement 10, the end of the output shaft 18 remote from the movement 10 being journalled in a wall 19 of the compartment 17. The light source 12 comprises two lamps 20 and 21, with the lamp 21 being disposed between the lamp 20 and the disc 11. The lamp 20 is of the screw-in type, whereas the lamp 21 is in the form of an elongate cylinder with an electrical contact at each end, the filament extending between the electrical contacts along the axis of the cylinder.

It is necessary to vary the level of illumination of the light source 12 in accordance with variations in the ambient light level. It has been found that this variation in the level of illumination of the light source 12 may be effected more effectively when the light source 12 comprises two lamps than would be the case if only one lamp were provided. It is arranged that normally only the lamp 20 is in use, as this provides a sufficiently bright display under most ambient light conditions, but when necessary the output of the lamp 20 is augmented by the lamp 21. The lamps 20 and 21 may both be relatively cheap, low power types, and both are operated in a manner that makes optimum use of their characteristics. Furthermore, if the lamp 20 should fail, its function can be taken over by the lamp 21, which thus pro

vides a standby facility and ensures continuity of the projected display.

The operation of the lamps 20 and 21 may be controlled automatically by a photo-electric cell positioned 5 in the automobile so as to sense the ambient light level.

The lamps 20 and 21 are mounted within a tubular housing 22 having circumferential fins 23 to assist dissipation of heat generated by the lamps 20 and 21. The 10 housing 22 has a reflector 24 for the lamp 20 of generally paraboloidal form which is shown in more detail in FIG. 4.

Referring to FIG. 4, the reflector 24 is formed on a face of a body 25 of aluminum and comprises a plural

15 ity of annular surface portions 26 centered on the longitudinal axis of the housing 22 and inclined relative to one another so that the shape of the reflector 24 approximates to a paraboloid. The lightrays reflected by the reflector 24 tend to be more nearly parallel to one

20 another than would be the case if the reflector 24 were in the form of a true paraboloid. This is because, in practice, the position of the filament in the lamp 20 varies considerably from lamp to lamp so that it is not possible accurately to position the filament at the focal

25 point of the reflector 24. It has been found that the reflector 24 is more capable than a true parabolic reflector of accommodating different positions of the lamp filament.

Referring again to FIG. 2, the output shaft 18 extends 3° through a mounting plate 27 disposed on the side of the disc 11 remote from the light source 12. The mounting plate 27 carries an apertured masking plate 28, disposed between the disc 11 and the mounting plate 27, which serves to limit the angular extent of the projected ■*5 display and also to provide a datum mark therein. The projected display is shown in FIG. 3 (in which the illuminated portions of the display are represented by the symbols), the datum mark being shown at 29. The angular extent of the projected display is arranged to be 40 sufficient to enable the driver readily to ascertain whether the speed of the automobile is above or below the value shown by the numeral nearer to the datum mark 29. The light rays passing through the aperture in the masking plate 28 continue through an aperture in the mounting plate 27 and then through a diverging lens 30 before being reflected by the mirror 13. The lens 30 is mounted in a housing 31 supported on the mounting plate 27 and the lens 30 and the mirror 13 are positioned relative to the disc 11 so that the illuminated portion of the disc 11 is disposed at a location which corresponds approximately to both the focal point of the lens 30 and the disc of least confusion of the mirror 13. It has been found that by providing the 55 lens 30, the size of the speedometer scale, for a given size of projected display, may be somewhat larger than would otherwise be the case, thereby simplifying considerably the manufacture of the disc 11. A further advantage is that the lens 30 increases the cut-off angle 60 of the projected display as seen by the automobile driver, thereby increasing the extent to which the driver may move his head without losing sight of the display.

The position from which the projected display ap65 pears to emanate may be adjusted by varying slightly the spacings between the disc 11, the lens 30 and the mirror 13. Optimum sacings may be provided between these components such that the apparent position of

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HEAD-UP DISPLAY APPARATUS