DE19806310A1 - Head-up display for aircraft pilots - Google Patents

Abstract

The display forms a luminous image (4,5,7) which is polarized (8) to reduce the parasitic image. The luminous image is passed to a reflecting screen (6) and reflected on to a collimator (2) which transmits the light along the same path towards the eye (1) as the visual scene.

Description

The invention relates to an overhead sighting device and has an overhead sighting device with simple and economical architecture that is relevant to the user offers good comfort.

The invention relates in particular to the sighting devices, the main collimator element is a spherical semi-reflection containing tile.

An overhead sighting device enables the display of Information in front of a user, this information collations and the direct Landscape views can be overlaid when the view is from is good enough.

The overhead sighting devices usually contain a cathode beam tube, on the screen of which a symbolic image is displayed.

The representation of symbol information by a Overhead sighting device provides assistance with the aircraft control and navigation.  

The sighting devices affected by the invention have a simple architecture. So that they have the symbol information can collimate, they contain a head element with a spherical semi-reflective plate chen is formed, which is arranged in front of the user's head with its concave inner surface facing the user. This spherical plate ensures on the one hand by means of Light transmission gives a direct view of the front of the user located landscape and on the other hand by means of light reflection on its inner surface a steering of the symbol information the user's eyes with infinite focus.

A semi-reflective flat plate that lies between the Eyes of the user and the spherical plate creates an image of the cathode ray tube in which the Center of the screen near the focal point of the spherical Platelet.

The screen of the cathode ray tube is in front of the flat one Plate, so that this is the image generated on the screen for spherical plate steers. In general, the axis of the Tube and the optical axis of the spherical plate other vertical. The normal of the flat tile lies on the bisector of these two axes.

The symbol image generated on the screen of the cathode ray tube is reflected on the flat plate, this reflec the image through the spherical plate essentially is aligned in parallel.

The collimation by the spherical plate is only approxi mativ and can verbes by a secondary collimator element be formed by a simple correction lens which is arranged in front of the screen of the cathode ray tube.

The overhead sighting devices have such a simple one and relatively cheap optical architecture. she  have meanwhile for low positions of the eye and for direction of observation directed towards the lower edge of the visual field a major disadvantage. Under these conditions of use the user receives a second symbol image, which is slightly shifted in relation to the main symbol image and whose intensity is the observation of the main symbol image and the Impaired observation of the landscape.

This obstructive parasitic image is caused by the reflection of the Icon image from the screen of the cathode ray tube, which on the rear surface of the semi-reflective flat plate done, caused.

This rear surface of the flat plate becomes an anti subjected to reflex processing to increase parasitic reflection to reduce.

The anti-reflective edits that are relatively easy to get out of are only for a limited angle of incidence range of light rays to be processed very effectively.

Because of the geometry of the overhead sighting device under consideration show the reason for the obstructive parasitic image bil the light rays have a large angle of incidence of 40 ° by an angle of incidence of 45 ° with respect to the normal of the flat tiles.

This makes it easy, for example, to do anti-reflective processing perform that for an angle of incidence of the light rays 45 ° has a reflection coefficient reduced to 0.05% points, but points out the same editing for an idea angle of 65 ° has a reflection coefficient of 3%, the is too high to perceive an obstructive parasitic Avoid image by the user.

Such anti-reflective processing therefore does not allow sufficient reduction in total parasitic reflection, so  that a parasitic image continues to exist during this processing is there.

This parasitic reflection could be better reduced by an uneven anti-reflection processing at the level of the plane Platelet, so that there is a minimal reflection coefficient ent corresponding angle of incidence gradually from 25 ° to the Top of the flat plate at 65 ° on the underside elevated.

However, such processing would reduce the overall cost of this Highly increase overhead sighting devices.

It is about the parasitic picture that comes with a simple Anti-reflective processing continues to reduce.

The invention has for its object a To create overhead sighting device with which an essential Redu adornment of the parasitic image at low cost and without Impairment of the passage of the landscape and the Icon image is obtained.

This object is achieved by a Overhead sighting device having the features specified in claim 1 owns. The dependent claims are on expedient execution tion of the invention directed.

In practice, the reflection medium is a parasitic Introduces a semi-reflective flat plate, which in an angle of 45 ° to the axis of the cathode ray tube is tiert, while the collimating agent is a spherical Spie gel is. The latter is conveniently semi-reflective to in addition to viewing a parallel image to allow a direct view of the landscape. The Polarisa a linear polarizer that is direct in front of the screen of the cathode ray tube and parallel to the surface of the screen is arranged.  

The principle is that the polarizer blocks the light in of the direction that is supposed to polarize the reflection the front surface of the semi-reflective flat plate favored.

Opposite an overhead sighting device of the prior art Technique, the user of the invention observes a reduction of the parasitic image without changing the transmission of the landscape is higher than the reduction of the symbol bil that is.

The disability caused by the parasitic image is therefore for the Less users of the invention. In addition, the invention the advantage of being an inexpensive improvement on a existing visor allows.

This embodiment of the invention can be done by adding a Quarter-wave plate can be improved between the flat plate and the spherical plate inserted is. This quarter-wave plate then has the advantage that the user increases the luminance of the Sym bole obtained in connection with the power of the polarizer Reduction of the proportion of the parasitic image without interference solution of the passage of the landscape can observe.

The cost increase due to the quarter wave plate remains reasonable in relation to the comfort gained.

To verify the luminance of the symbols seen by the user can also improve the luminance of the source be caused by interference on the screen of the cathode ray tube Is attached filter that the luminous flux around the normal of the Concentrated. This interference filter can be found in existing Use or lack of a quarter-wave plate be det.

Other features and advantages of the invention will be better ver of course more useful when reading the following description  Embodiments referring to the attached drawing; it demonstrate:

Fig. 1 is a view of an overhead sighting device according to the invention;

Fig. 2 is a view for explaining the trajectories of light rays len, which are reflected from the two surfaces of the flat plate; and

Fig. 3 is a view of an embodiment of the invention, which contains a quarter-wave plate.

In the drawing, the same reference numerals designate the same che or equivalent elements.

The overhead sighting device shown in FIG. 1 is a sighting device with a simple architecture, which mainly contains a cathode ray tube 4 , a spherical semi-reflecting plate 2 and a flat semi-reflecting plate 6 ent.

The user's eye 1 observes the concave surface of this plate 2 through the semi-reflecting plate 6 .

The cathode ray tube 4 and the spherical semi-reflective plate 2 are arranged in such a way that the two straight lines, which correspond to the optical axis D of the spherical plate 2 or the normal in the center of the screen 5 of the cathode ray tube 4 , lie in the same plane, which is the plane P of Fig. 1, and form a right angle with each other. Their intersection is given by point 3 . The point 3 is located between the spherical plate 2 and the eye 1 .

For reasons of space requirement, the cathode ray tube is generally arranged above the optical axis D at the level of the ceiling of the cockpit of the aircraft, its screen 5 being directed to point 3 .

The light rays emitted by the screen 5 are directed with the aid of the flat semi-reflecting plate 6 to the spherical plate 2 , which is located near the point 3 . The normal of this flat plate 6 , which runs through the point 3 , is a straight line in the plane P, which forms an angle close to 45 ° with the normal of the screen 5 of the tube.

The semi-reflecting surface of the plate 6 forms its front surface, which is turned towards the spherical plate 2 . The plate 6 lets the images from the spherical plate pass through to the eye.

The rear surface becomes a mostly uniform anti-reflection processing subjected to the reflection of light rays, that come from the cathode ray tube and not from the front have been reflected by this rear surface as far as possible to avoid.

A field compensation lens 7 is located in the path of the light rays between the screen 5 and the flat plate 6 and corrects the main errors of the collimator function of the spherical plate 2 .

The eye 1 of the user receives the light coming from the landscape and the spherical plate 2 and the flat plate 6 crossing light beams, this reception being superimposed by a parallel symbol image which is displayed on the screen 5 . The overhead sighting device of Fig. 1 also includes a linear polarizer 8, the rised the light emitted from the screen 5 of the cathode ray tube 4 pola light.

The linear polarizer 8 is arranged in front of the screen 5 , expediently between the screen 5 and the correction lens 7 . The linear polarizer 8 is formed from an essentially flat material, this plane being parallel to the plane of the screen 5 .

The polarizer receives the light rays from the screen 5 . The light is directed at the output of the polarizer. It is polarized in a straight line, the polarizer 8 being oriented in such a way that for a light beam of the plane P output by the screen 5 , the direction of oscillation, which is the direction of the electric field of the light wave, at the output of the polarizer 8 to the plane P. , ie perpendicular to the normal of the flat plate 6 .

This polarization filter 8 does not interfere with the perception of the landscape by the user because it does not change the intensity of the landscape image transmitted from the sighting device to the user, but it has the disadvantage of the intensity of the light source of the symbols which the user is shown will reduce.

Despite this reduction in luminance of the useful image, it is observed that with a sighting device such as that shown in FIG. 1, the parasitic image is less of a hindrance than with a sighting device of the prior art which does not have the polarizer 8 ; the luminance of the parasitic image is namely reduced in a larger ratio than the luminance of the useful image.

The strength of the parasitic image in relation to the symbol image is evaluated by the degree of parasitic image, which is called Relationship between the value of the perceived by the user Luminance of the parasitic symbol image and the value of the User-defined luminance of the symbol image defined is.

The degree of the parasitic image is lower for the sighting device according to FIG. 1 equipped with the polarizer 8 than for a sighting device which is not equipped with it.

FIG. 2 shows in more detail the light rays which result in the useful image and the parasitic image generated by the rear surface of the flat plate 6 .

A light beam 11 emanating from the screen 5 strikes the semi-reflecting surface 9 of the plate 6 , where it is divided into a reflected beam 12 and a beam 13 transmitted through the plate 6 .

The reflected beam is in turn largely reflected on the spherical plate 6 and then transmitted in succession through the front surface 9 and through the rear surface 10 of the flat plate 6 to the user's eye 1 .

The transmitted beam 13 strikes the surface 10 of the flat plate 6 , where it is partly reflected in the form of the beam 14 in the flat plate 6 and is transmitted through the surface 9 as a beam 15 which leaves the flat plate 6 .

The beam 15 is subjected to the same transformations up to the user's eye as the beam 12 reflected directly onto the surface 9 .

The reflected beam 12 and the beam 15 generally mean on the spherical plate 2 at different points and thus give the eye 1 cause for two offset images that represent the perceived symbol image and the parasitic image.

The beam 15 is called a parasitic beam.

The reflection on the surface 10 of the plate 6 , which has just been described, is insufficiently reduced by the antireflection treatment of this surface 10 : certain rays of the parasitic beam type 15 have too strong a light intensity and generate the obstructive parasitic image of the sights of the stand of the technique.

On the other hand, the vibration present in each light radiation can be broken down into two mutually orthogonal components, in particular into a vibration parallel to the plane P, which contains the normals of the plate 6 and the screen 5 , and into a vibration perpendicular to this plane P.

These have two components for the non-polarized light same intensity.

Each light beam of the overhead sighting device of Fig. 1 can be decomposed in this manner, generally have the two components of unequal intensities.

In particular, the decomposition into rays of the reflected beam type 12 and into rays of the parasitic beam type 15 is observed.

Therefore, the luminance of the symbols, which is perceived by the user's eye 1 and comes from rays of the reflected beam 12 type, is partly due to the light whose oscillation is perpendicular to the plane P and which is called perpendicularly polarized light, and other part caused by the light, the vibration of which is parallel to the plane P and is called parallel polarized light.

The luminance of the parasitic image is also one Proportion from the light polarized perpendicular to the plane P and to a complementary part from the parallel to plane P pola standardized light.

The polarizer provided in the invention endeavors to give the light the direction of polarization, which facilitates reflection on the front surface 9 of the plate 6 and to the same extent reduces the proportion of light transmitted into the plate 6 .

For example, the composition of light reflected from the semi-reflecting plate for non-polarized incident light could be examined for angles of incidence that correspond to the lower part of the plate (most inclined angle of incidence):
Typically, 87% of the light reflected from the front surface is polarized perpendicular to the plane P; however, as for the light reflected from the rear surface, which represents parasitic light, the polarization in the other direction, that is, in the direction parallel to the plane P, is 87%.

In the polarizer 8 , the luminance of the parasitic image is therefore mainly due to the light polarized parallel to the plane P, while the luminance of the symbols is mainly caused by the light polarized perpendicular to the plane P.

The appropriately oriented polarizer 8 arranged at the level of the screen 5 eliminates the source of the light component polarized parallel to the plane P, which is the cause of the major part of the parasitic image.

It can be an example of the improvement created for you typical application.

It is assumed that the front surface 9 of the plate 6 has a reflection coefficient of 40% (light transmission 0.6) for light polarized perpendicular to the plane P and a reflection coefficient of 10% (light transmission 0.9) for parallel polarized light.

In addition, it is believed that the flat plate has been subjected to anti-reflection processing on the surface 10 with a reflection coefficient of 3%.

Then a degree of parasitic image of 2.7% is obtained, which represents a reduction by two thirds of the degree of parasitic image of 8.6% which is obtained in the absence of the polarizer 8 .

The presence of the polarizer 8 provides a permeability for symbols of 3.5%, which is a good quarter reduction in relation to the value of 4.8% obtained for the transmission of the symbols in the absence of the polarizer 8 , represents. This reduction is unfortunate, but is largely offset by the significant reduction in disability due to the parasitic image.

The processing of the parasitic image by the polarizer 8 , the cost of which is low, is well adapted to the conditions of use of the overhead sighting device in which the user is not disturbed by a reduction in the brightness of the symbols. The overhead sighting device according to FIG. 1 is therefore well suited if the landscape does not shine too strongly.

For those cases where this reduction is unacceptable, it is also suggested that a quarter-wave plate 16 enhances the luminance of the symbols. The principle is explained with reference to FIG. 3.

The quarter-wave plate 16 is inserted between the spherical plate 2 and the flat plate 6 . Its double refraction axis is located on the bisector of the directions of the polarization parallel or perpendicular to the plane of incidence P of the flat plate 6 .

In this embodiment of the invention, a degree of parasitic image is observed that is equivalent to that obtained with the embodiment of FIG. 1 which does not contain a quarter wavelength plate. The parasitic rays 15 namely namely the reflected rays 12 , which originate from light polarized by the polarizer 8 , have the same polarization, both types of rays being subjected to the same transformation in their double passage through the quarter-wave plate, so that the ratio of Luminance of the parasitic image to that of the symbols in the invention with and without quarter-wave plates is maintained.

However, an improvement in the transmission of the symbols is observed in the embodiment of the invention containing the quarter-wave plate 16 .

The light emitted by the screen 5 is polarized linearly and perpendicularly to the plane P in order to favor the reflection through the surface 9 of the flat plate 6 and thereby limit the passage of the light into the plate 6 .

The polarized light is reflected by the flat plate 6 .

This reflected light of the reflected beam type 12 maintains its linear polarization perpendicular to the plane P until the first passage through the plate 16 , where it is transformed into circularly polarized light.

After reflection on the spherical plate 2 , the direction of rotation of the circular polarization is reversed. After the second passage through the plate 16 , the light is linearly polarized again, but the polarization is parallel to the plane P.

The presence of the plate 16 converts the vertically polarized light into parallel polarized light. Furthermore, the flat plate 6 on its surface 9 has a transmission coefficient for parallel polarized light with a value of 0.9 (in the example of the plate 6 considered above), which is better than the value of 0.6 of its transmission coefficient for perpendicularly polarized light is.

The change in the polarization of the light of the symbols before it passes through the surface 9 of the plate 6 thus favors the transmission of the symbols to the eye 1 .

In this way, with the embodiment according to FIG. 3, a passage coefficient of 5.2% for the symbols from the screen 5 to the eye 1 is obtained, which is not only higher than that which is obtained from the invention without a plate 16 , but is also higher than the value of 4.8%, which is obtained for the passage of the symbols through the sighting device according to FIG. 1, from which the polarizer 8 is removed, although in the invention the polarizer 8 from the source half the light energy of the screen 5 suppressed. In addition, the plate 16 practically does not attenuate the light passing through it because it has a good transmission coefficient.

In order not to hinder the user by parasitic reflections, the plate 16 must also be subjected to an anti-reflection treatment on each of its surfaces; this is carried out at a low cost with good effectiveness because the impact angle dynamics of the light rays on the plate 16 are in a range of 20 ° for which the antireflective conditions are effective.

In the embodiment according to FIG. 3, the addition of the quarter-wave plate 16 requires a change in the field compensation lens 7 in order to also compensate for the aberrations caused by the plate 16 .

The variant of the invention that uses a quarter wavelength plate Chen contains, therefore proves to be more expensive, it enables however, better use of the over equipped with it Head sighting device when the landscape is very bright tet.

In comparison to the embodiment according to FIG. 1, this variant has the same reduction in the disability due to the parasitic image of the plate 6 , but with better transmission of the symbol image. This improvement in the passage is particularly useful for the sighting devices examined, whose very simple architecture severely disadvantages the passage of the symbol images.

However, a new parasitic image remains due to the plate 16 , which can be evaluated by the degree of the parasitic image, which is equal to the quotient of the symbol luminance which is parasitically reflected by this plate 16 and the symbol luminance after the passage through this plate 16 , a reflection on the spherical plate 2 and an opposite passage through the plate 16 .

The parasitic image caused by the plate 16 then has a degree which is equal to the ratio of the reflection coefficient of the plate 16 and the plate 2 .

The plate 16 has a low residual reflection coefficient with a value of, for example, 0.5%. Furthermore, a neutral, semi-reflective spherical plate has a reflection coefficient between 20 and 30%, so that the degree of parasitic image through the plate 16 is equal to the quotient of 0.5% and 25%, which corresponds to a value of 2%. A new parasitic image with this value remains tolerable for the user who, with a prior art sighting device, such as the sighting device according to FIG. 1, from which the polarizer 8 has been removed, a parasitic image due to the plate 6 of the order of magnitude Endure 10% in the lower part of the observation field.

The quarter-wave plate therefore adds a new one of its own parasitic image, but its strength is limited.

On the other hand, the semi-reflective plate 2 of a sighting device with simple architecture, which forms the subject of the invention, can be of the holographic type. If this plate 2 , which is also called combiner, contains a hologram to perform the function of reflecting the symbol images, its reflection coefficient has special properties. Such a plate has a reflection coefficient which is practically zero in the entire spectrum, with the exception of the wavelength which corresponds to the emission of phosphorus from the screen 5 , at which the reflection coefficient is close to one. For example, if this coefficient is 90%, the degree of parasitic image on a wafer 16 is equal to the quotient of 0.5% and 90% as described above and remains approximately half a percent.

The quarter-wave plate design is particularly useful for a simple architecture sighting device that includes a holographic semi-reflective plate. The reduction in the parasitic image of the plate 6 is effective and the improvement obtained is not deteriorated by a new obstructive parasitic image.

A further perfection of the invention is before to insert an interference filter into the screen of the cathode ray tube put, this filter's job being from the tube emitted light energy around the axis of this tube wear.

Since the sighting devices of the prior art with simple architecture let through the symbol images only to a small extent, they generally contain a screen 5 of a cathode ray tube, which is formed from very bright and very monochrome phosphor. With such a screen, the light radiation of which has a narrow band, the arrangement of an interference filter enables a gain of approximately 30% of the luminance of this screen.

In this embodiment of the invention, the tube screen an interference filter and one in front of this filtered screen Contains polarizer, a degree of parasitic image will be observed respects who is equivalent to the degrees that with the first Aus leadership and can be obtained with the second version.  

In addition, a transmission coefficient for the symbols is obtained which is equal to 4.5% and thus higher than that of the first embodiment and is very close to that of the prior art sighting devices which do not contain an absorbing polarizer 8 .

This version reduces the parasitic image and deteriorates The passage of the symbols is very little. The so Equipped sighting device points for all uses Conditions of the prior art sighting device for give the user better comfort.

The interference filter can be used both in the embodiment according to FIG. 1 and in that according to FIG. 3.

In this latter case, the degree of the parasitic image comparable to those described in the three Aus guides have been received. The transmission coefficient for that However, the image of the symbols then has a value of 6.8% is higher than that described in each of the others Executions is obtained.

It is noted that this coefficient is also significant is better than that of 4.8% with a sighting device obtained with simple architecture of the prior art becomes.

Claims (13)

1. overhead sighting device with a cathode ray tube (4), on the screen (5) a light image is displayed, means (6) in the reflection of the image into a reflected image and a means (2) for collimating the reflected image, by a means ( 8 ) for polarizing the light emitted from the luminous image to reduce the parasitic image caused by the reflection means ( 6 ). 2. Device according to claim 1, characterized in that the polarization means ( 8 ) orien oriented to the light received by it to promote the reflection of this oriented light on the reflection means ( 6 ). 3. Device according to claim 2, characterized in that the reflection means ( 6 ) is a semi-reflective flat plate. 4. Device according to claim 3, characterized in that the polarizing means ( 8 ) polarizes the light in a straight line and oriented in a direction in which the oscillation of the polarized light is oriented in a direction perpendicular to the normal of this flat plate ( 6 ). 5. Device according to one of claims 3 or 4, characterized in that the polarization means ( 8 ) between the screen ( 5 ) and the reflection means ( 6 ) is arranged. 6. Device according to claim 5, characterized by a correction lens ( 7 ) which complements the collimation means ( 2 ). 7. Device according to claim 6, characterized in that the polarization means ( 8 ) between the screen ( 5 ) and the correction turlens ( 7 ) is arranged. 8. Device according to one of claims 3 to 7, characterized in that the collimation means ( 2 ) is a semi-reflective platelet which ensures collimation by reflection. 9. Device according to claim 8, characterized in that the collimation means ( 2 ) is a spherical semi-reflecting plate. 10. The device according to claim 9, characterized in that the normal of the semi-reflecting flat plate ( 6 ) on the bisector of the optical axis of the spherical plate ( 2 ) and the normal of the screen ( 5 ) of the cathode ray tube ( 4 ). 11. The device according to claim 8, characterized by a four tel Wavelength plate ( 16 ) between the collimator ( 2 ) and the flat plate ( 6 ), which is oriented in such a way that the light on the outlet side of the quarter wavelength plate ( 16 ) and the semi-reflective plate ( 2 ) containing unit is linearly polarized and is oriented vertically to orientate the light on the inlet side of this unit. 12. The device according to claim 11, characterized in that the semi-reflective plate ( 2 ) is of the holographic type. 13. Device according to claim 5 and one of claims 8 to 12, characterized in that the screen ( 5 ) is a cathode ray tube screen having an interference filter.