GB1588351A - Head-up displays - Google Patents

Head-up displays Download PDF

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Publication number
GB1588351A
GB1588351A GB2310177A GB2310177A GB1588351A GB 1588351 A GB1588351 A GB 1588351A GB 2310177 A GB2310177 A GB 2310177A GB 2310177 A GB2310177 A GB 2310177A GB 1588351 A GB1588351 A GB 1588351A
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United Kingdom
Prior art keywords
head
display head
display
observer
operational
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB2310177A
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Allard Way Holdings Ltd
Original Assignee
Elliott Brothers London Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Elliott Brothers London Ltd filed Critical Elliott Brothers London Ltd
Priority to GB2310177A priority Critical patent/GB1588351A/en
Priority to US05/909,831 priority patent/US4188090A/en
Priority to FR7816306A priority patent/FR2401436A1/en
Publication of GB1588351A publication Critical patent/GB1588351A/en
Expired legal-status Critical Current

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Classifications

    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B27/0149Head-up displays characterised by mechanical features
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B27/0101Head-up displays characterised by optical features
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B27/0101Head-up displays characterised by optical features
    • G02B2027/0123Head-up displays characterised by optical features comprising devices increasing the field of view
    • G02B2027/0125Field-of-view increase by wavefront division
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B27/0149Head-up displays characterised by mechanical features
    • G02B2027/0154Head-up displays characterised by mechanical features with movable elements
    • G02B2027/0156Head-up displays characterised by mechanical features with movable elements with optionally usable elements
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B27/0149Head-up displays characterised by mechanical features
    • G02B2027/0169Supporting or connecting means other than the external walls
    • GPHYSICS
    • G02OPTICS
    • G02BOPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/01Head-up displays
    • G02B2027/0192Supplementary details
    • G02B2027/0194Supplementary details with combiner of laminated type, for optical or mechanical aspects

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Instrument Panels (AREA)

Description

(54) IMPROVEMENTS IN OR RELATING TO HEAD-UP DISPLAYS (71) We, ELLIOTT BROTHERS (LON DON) LIMITED, of Marconi House, New Street, Chelmsford, Essex CM1 1UL, a Hnt- ish Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to display heads for aircraft head-up display systems.
A display head for an aircraft head-up display system (hereinafter referred to as a display head of the kind described") comprises an optical projector and an image combiner through which an observer, generally the pilot of the aircraft, can view a distant scene and from which collimated optical images develped by and projected from the optical projector are reflected to the observer. The optical images appear to the observer as virtual images "at infinity", and being, as it were, superimposed on the distant scene, such images can be viewed by the observer without demand for ocular accommodation.
The value of head-up display systems in military aircraft has been fully demonstrated.
More recently civil aircraft operators have evinced an interest in the introduction of head-up display systems in civil transport aircraft, recognizing that the introduction of the head-up display in such aircraft would create opportunities for pilot safe intervention in the control of aircraft during automatic landing Category 3 operations below normal Category 3A decision height, i.e. 50 feet, during automatic landings of the aircraft.
It is an object of the present invention to provide a display head of the kind described which is suitable for use in a civil transport aircraft.
According to the present invention, in a display head of the kind described the image combiner is supported from a light obstructive member which comprises a housing for the optical projection of the display head and which intrudes within the observer's field of view of the distant scene in use of the display head, but no intruding part of said member has a width greater than a prescribed interpupillary distance so that notwithstanding the intrusion of said member there is no obstruction by said member of the observer's view of the distant scene.
A display head in accordance with the invention will normally be arranged for monocular use by the observer.
The prescribed interpupillary distance will of course normally be the likely minimum distance between the pupils of observers using the display head.
Preferably the display head is displaceable between an operational position in which the display head is at a position intercepting the observer's line-of-sight to the distant scene and a stowed position at which the display head is at a position at which it does not intrude into the observer's field of view of the distant scene.
Preferably the display head is, in the operational position, dependent from a position above the observer's head.
In one particular embodiment the display head is rotatable about a single axis such that, in moving the display head from the operational position to the stowed position, the initial movement of the display head has a major component parallel to the observer's line-of-sight to the distant scene, and the terminal movement of the display head has a major component in a direction at right angles to said line of sight towards the stowed position.
In one such embodiment said single axis is an overhead transverse axis fixed in the aircraft; there is a releasable latch member operable to retain the display head in either the operational position or in the stowed position; the latch member is biassed by a spring; and the event of contact between the observer's head and the housing, the latch member moves, against the spring bias, so as to permit rotation of the dispaly unit, thereby reducing the risk of physical injury to the observer.
In an alternative embodiment said single axis is inclined with respect to the aircraft orthagonal axes at such an angle, and the display head is so shaped, that said terminal movement has a major component to the left or right of said line-of-sight.
In such an embodiment the display head is suitably connected to a member possessing compliance and the display head is pivotal about said single axis, through the overcentre position of the compliant member, between the operational and the stowed positions. The display head is movable through the overcentre position of the compliant member not only by manual pressure but also as a result of accidental contact with the observer's head.
Three embodiments of the invention are hereinafter described with reference to the accompanying drawings in which Figures 1, 2 3a and 3b relate to the first embodiment.
Figure 1 showing, to the scale indicated a geometrically and dimensionally true sectional elevation of a display unit, taken on the line I-I of Figure 2; Figure 2 shows to the same scale an elevation of the display unit as viewed in the direction of the arrow II in Figure 1; and Figures 3a and 3b illustrating the instantaneous and total fields of view of an observer using the unit and with one eye only positioned at the alert eye and normal eye positions, respectively; Figures 4 to 9 relate to the second embodiment Figure 4 showing to the scale indicated a frontal elevation of the display head; Figure 5 showing in plan, the underside of a mounting arrangement; Figure 6 showing a side view with the display head in the operational (full line) and stowed (chain dotted line) positions; Figure 7 showing a plan view with the display head in the operational and stowed posi tions; Figure 8 showing a detail of the assembly; and, Figure 9 showing a combiner; and Figures 10 to 14 relate to the third embodiment Figure 10 being a diagrammatic side elevation, to the scale shown, of the third embodiment; Figure 11 showing diagrammatically an elevation in the direction XI in Figure 1; Figure 12 showing diagrammatically a plan view in the direction XII in Figure 11; Figure 13 showing a section in direction XIII in Figure 10; and Figure 14 showing the instantaneous and total fields of view achievable with the unit of Figures 11 to 13.
In the first embodiment (Figures 1, 2, 3a and 3b) two flanges 1 lea and lib are dependent from an overhead frame member 13 adjacent to the aircraft windshield 15.
Extending between the flanges. gila, 11b, there is a pivot pin 17.
The display head 19 has a cylindrical boss 21. Between the end surfaces la and 21b of the boss 21 and the flanges, gila, lib, there are two toothed members 23a and 23b respectively. These are secured to the inner faces of the flanges Ila, lib.
The display head 19 has a tubular housing 25. At diametrically opposed lateral positions thereon there are secured two pivots 27a, 27b, on which are carried two latch members 29a, 29b, respectively.
The latch members 29a, 29b, have pivotal connections with a generally T-shaped spring-bias transmission member 31, the free end 33 of which extends into a pocket 35 of the display head and contacts a bias spring 37 therein.
As may be seen the toothed members, 23a, 23b, each have three notches 35a, 35b, 35c; and the latch members 29a, 29b, each have a pawl 30a, 30b, adapted to enter the notches 35a, 35b, 35c.
The bias transmission member 31 has a serrated step 38. Manual movement of the transmission member 31 against the bias of the spring 37 has the effect of disengaging the pawls 30a, 30b, from the notches in which they happen to be located so as to permit the display head to be rotated counter clockwise, as viewed in Figure 1, until under the bias of the spring 37, the pawls 30a, 30b enter the notches Sb. The unit is then in a stowed position away from the field of view of the observer, as indicated in Figure 1.
A collapsed position defined by notches 35c in members 23a, 23b which the unit may assume as a result of clockwise rotation, as viewed in Figure 1, of the head, as a result of contact between the observer's head and the head housing is further indicated in Figure 1.
The engagement between the pawls 30a, 30b and the notches 35a in members 23a, 23b, whilst serving to maintain the operational position, is nevertheless such that undue contact with the housing is sufficient to cause the pawls to ride out of the notches 35a against the bias of the spring 37. To further reduce the risk of injury to the observer the housing 25 has an impact absorbing part 36.
The major portion of the housing 25 is circular cylindrical but the end portion remote from the boss 21 has a substantially flat rear face 41 and a substantially flat forward face portion 43. The faces 41 and 43 are apertured to provide between them a generally rectangular passage 45 through which the observer can view the distant scene.
Located in the rectangular passage 45 there is a combiner element 47 which may take a variety of forms, but as shown in Figure 1 consists of a multi-film combiner element of the kind described in U.K. Patent Specification No. 1,538,545.
Briefly stated the multi-film combiner 47 comprises a Dluralitv of cemented together glass or other transparent refractive material elements at the interface of which there are three semi-reflective films 49. At one end surface 51 of the combiner element 47 there is a fully reflective coating. Optical data light images from an optical projector enter the element 47 via the other end surface 53, as further described below, for reflection to the observer at the films 49 and the coating on surface 51.
The films 49 are flat and parallel to one another and to the surface 51. The rearwards and forwards facing surfaces 52a, 52b of the combiner element are flat and parallel. The angle between the films 49 and the surface 52a is equal to the angle which the films 49 subtend with respect to the surface 53. It is a virtue of a multi-film combiner that because of the large field of view easily obtainable in pitch and in azimuth even relatively large movements of the observer's head with respect to the combiner do not prevent its effective use; the collimated projected optical data is still within the total field of view.
For a full understanding of the construction of such a combiner element reference should be made to the specification of the above-mentioned aDDlication.
In the optical projector an exit lens 55 is truncated, or cropped, so as to define a substantially rectangular exit aperture the major dimension of which is parallel to the direction of width of the combiner 47, i.e. in the direction perpendicular to the plane of Figure 1.
The exit lens 55 together with further lenses 59 and 61 and a prism 60 form a collimating optical subsystem in the projector whereby optical data presented at the screen 63 of a cathode ray tube 65 are projected collimated for reflection at the several reflective surfaces 49, 51 of the multicombiner 47 to the observer viewing the distant scene through the rectangular passage 45.
In order that the display head does not obstruct any part of the distant scene, the display head is constructed and designed so that no light obstructive part of the display head within the observer's field of view of the distant scene has a transverse dimension greater than the interpupillary distance of the observer's eyes. A suitable value for the maximum transverse dimension is 6.25 cms.
The display head is, it will be understood, used monocularly by either eye. There is no obstruction due to the presence of the display head because every point of the distant scene is visible to at least one eye and most of the scene will be visible to both eyes.
The fields of view of the projected optical data obtainable using the display head shown in Figures 1 and 2, are given in Figures 3a and 3b. It will be seen that even with the head at the normal eye position a substantial instantaneous field of view (16 x 30 ) is obtained.
A full azimuth total field of view (16 x 30 ) may be obtained by movement of the head 2.5 cms in each direction, as indicated by the dotted line.
With the head in the alert or operational eye position an instantaneous field of view 23 in azimuth and 27 in pitch is obtained; and the full 30 total field of view may be achieved by a mere 0.65 cm head movement in each direction as indicated by the dotted line, that is to say with substantially no head movement at all.
It will be appreciated that the alert or operational eye position is an eye position slightly nearer the display head than the normal eye position, the observer taking up the alert position when he requires a better view of the display than can be obtained at the more comfortable and relaxing normal position.
Whilst the combiner 47 is for preference a multi-film combiner it will be understood that a single film combiner could be used, such as is hereinafter described.
Referring now to Figures 4 to 9, the second embodiment comprises a display head 111 and a mounting arrangement 113 by which the display head is supported dependent from an overhead airframe member (not illustrated). The mounting arrangement 113 has a first part 115. Fixing means (not shown) secure the part 115 to the airframe member with the mounting face 117 of the part 115 in contact with the airframe member.
The mounting arrangement 113 includes a compliance device 121. The device 121 consists of a spring and damper unit 125 and a piston 127. The spring and damper unit 125 has a cylindrical housing within which is a zero rate spring (not visible) and a dashpot (not visible) in series therewith. The zero rate spring conveniently comprises a series of Belleville washer spring elements. Being a zero rate spring the force which it exerts is independent of its extension.
The display head 111 has a cylindrical housing 1 9 one end 131 of which is formed at an angle to the main body part of the housing.
Referring particularly to Figure 8, the part 115 of the mounting arrangement 113 has a stepped opening 133 which receives a ring element 135. Screws (not shown) hold the element 135 fast to the part 115. The element 135 has a lip 139; and the inner race 141 of a rolling bearing 143 is trapped between the lip 139 and the edge of a circular collar portion 145 of the part 115.
The end 131 of the housing 129 of the display head 111 has a projecting ear portion 146. The ear 146 is connected by a pivot 147 to the free end of the piston 127. The ear 146 is fixed to the outer race 149 of the bearing 143.
The pivot axis P-P of the bearing 143 and, hence, of the display head 111 is contained in the aircraft Y-Z plane makes an angle e of 51.5 with respect to the aircraft Z-axis (see Figure 4). The shape of the end 131 of the housing 129 of the display head 111 dictates that when the spring and damper unit 125 is at the angular position indicated by full lines in Figure 5, the display head 111 is at the operational position in which the longitudinal axis of the head is vertical, i.e. parallel to the Z-axis. When, by manual movement, or by accidental contact with the observer's head, the display head 111 is rotated about the axis P-P, the head moves first in a forwards direction and then sideways, i.e. first into and then in the plane of the paper in Figure 4, as indicated by the curves I, II and III in Figures 5, 6 and 7. The head 111 thus moves into a stowed position, indicated by chain dotted lines in Figures 6 and 7. During this movement the ring member 135 rotates through an angle Q) (see Figure 5) of 1300, the spring and damper unit 125 taking up the angular position indicated by the chain dotted line in Figure 5.
In passing to and from the operational and stowed positions, the compliance device 121 passes through its overcentre position.
As may be seen, the initial motion from the operational position has a large (though decreasing) component in a direction away from the observer and the final motion has a large and increasing component towards the stowed position.
In this embodiment the combiner 151 (see particularly Figure 9) comprises two glass elements 1 53a and 1 53b cemented together by an optical cement of matching refractive index. Exposed parallel faces 154a, 154b, through which the distant scene is observed, are ground and polished optically flat and parallel. The element 153b has a spherical surface 155 to which is cemented a lens 157 the surface 157a of which is made fully reflective. Adjacent to the surface 159 of the element 153a there is a field flattener lens 161.
At the interface between the elements 153a, 153b there is a thin optical film 163.
Light from the screen of a cathode ray tube (not shown) housed in the cylindrical housing 129 of the display head 111 with its screen contained in the focal plane of the surface 157a passes through the field lens 161, and the film 163, and is reflected at the surface 1 57a to produce a collimated image incident on the film 163, the lens 157 acting to compensate for aberrations which would otherwise be present in the image. The film 163 reflects the image to the observer using the display head, so that optical data produced on the cathode ray tube screen appears as a virtual image "at infinity" to the observer, superimposed on his view of the distant scene through the combiner.
Although a solid glass construction is used in the combiner 151, it would be entirely possible to employ an open optic at this point. The film 163 could be a film on a thin glass support and the lens 157 and full reflector 157a could be a separate spherical member.
Impact absorbing padding 165 is provided on appropriate surfaces of the head to reduce the possibility of injury to the observer.
As in the first described embodiment, the maximum width of the display head 111, i.e.
the horizontal dimension in Figure 4, is made less than the interpupillary distance of the observer's eyes.
Whilst in both the above embodiments the display head is fixed in azimuth in the opera tlonal position it may be desirable in other embodiments to enable the display head position to be changed in azimuth while operational, for example, to allow for crab angle of the aircraft due to cross wind during aircraft landing manoeuvres, or for helicopter use.
One such embodiment will now be described with reference to Figures 10 to 14.
Referring to Figures 10 to 13 the display head 211 has a generally tubular part 213 which houses a cathode ray tube 215. Secured to the free end surface 217 of the part 213 there is a combiner mounting 219. A combiner 221 supported by the mounting 219 has a spherical fully reflective surface 223 and is composed of two parts 22 1a, 22 1b cemented together with an optical cement of matching refractive index and having, at their interface, a partially light-transmissive, partially light-reflective coating 224 which is deposited on one of the two parts. It will thus be seen that the combiner is essentially of the same form as that used in the second embodiment described above.
Supported by the mounting 219 between the flat face 216 of the C.R.T. 215 and the combiner 221 there is a field flattener lens 225.
The tubular part 213 is supported between two dependent cheeks 223a, 223b of a cap part 227. It is pivotal in lane bearings 227a, 227b about a pitch axis Q-Q (see Figure 11.
For this purpose the cheeks 223a, 223b have two aligned openings, as 229. A pivot pin 231 is supported in the bearings 27a, 227b in the opening 229. The pin 231 extends through and is secured to the upper end of the tubular part 213 so that rotation of the tubular part 213 (and hence of the combiner 221) about the axis Q-Q causes rotation of the pin 231 within the bearings 227a, 227b of the cap part 227.
The cap part 227 has an upwardly projecting cylindrical boss 233. The latter portion 233 is secured to the inner races 235 of a double rolling bearing 237. The outer races 239 of the bearing 237 are secured to a toothed sector part 241. The latter part 241 has bosses (not shown) by means of which the part 241 and, hence, the entire unit 211 may be secured to an overhead member (not shown) of the crew station of the aircraft.
The overhead member is forward of the observers' seat position as indicated in Figure 10.
An arm member 243 secured to the cap part 227 has a sleeve portion 245. A plunger 247 extends through the sleeve 245 and is biased by a spring (not shown) within the sleeve 245 towards the circular rim of the toothed sector 241.
A powerful coil spring 249 surrounds the projecting end 251 of the pin 231. One end of the spnng 249 is fixed to the pin 231, being located in a hole near to its end. The other end of the spring 249 is secured to the arm 243 in like manner.
As may be seen, there are four notches 241a, b, c and d in the toothed sector 241.
Pivotally connected to the upper end of the tubular part 213 there is a catch member 253. The member 253 has an abutment portion 255 and is biased by a spring 257 in a counter-clockwise sense (Figure 10).
When the display head is not being used it may be put into a stowed position. In this position the head is not within the visual field of the user to the distant scene through the aircraft windshield W, but extends in a generally horizontal direction with its longitudinal axis directed in a generally forwards direction obliquely to the fore and aft axis of the aircraft from the mounting position of the head 211 of the overhead member.
The stowed position is best illustrated in Figure 12. From an operational position defined, as described more fully hereinafter, by positions X, Y and Z of the sector 241 the head 211 is rotated in azimuth in a clockwise sense (Figure 12). For this purpose the plunger 247 must first be withdrawn, and held withdrawn, from the relevant notch 241b, c or d until the angular position of the head 211 in azimuth with respect to the sector 241 is such that the plunger 247 is able to enter (under its bias) into the stowed position notch 241a.
Having reached the latter position, manual pressure on an energy absorbing member 259 is effective to free the catch member 255 from engagement with the cheek parts 223a of the cap 227. The head 211 then pivots under the bias of the spring 249 about axis Q-Q to the stowed position illustrated.
If the observer's head accidentally strikes the display head when in the operational position, the head similarly pivots to a collapsed position shown in Figure 10, thus reducing the likelihood of injury to the observer.
In the embodiment shown any one of three discrete azimuth operational positions X, Y or Z defined by notches 24 l b, c and d may be chosen. The head is, of course, a monocular device to be used in the same manner as that described in the above-described embodiments. The fields of view available to the observer at each of the azimuth positions X, Y and Z are depicted in Figure 14. The field of view is, of course, related to the alert eye position indicated in Figure 10. As will be clear the selection of the azimuth position X, Y or Z is performed by withdrawing the plunger 247 from another notch and rotating the head to the desired azimuth position.
The provision of three discrete azimuth positions is intended to allow for a range of aircraft drift angles due to cross-winds during a landing manoeuvre for example. Associated with the two outer azimuth positions X and Z, there may be provided a micro-switch 261a, 261b. When the position Y is selected the display symbols are central within the field of view position Y (Figure 14). If however position X or fl Is chosen the symbols may be outside of the field of view or at any rate at a distance off-centre of the viewing position rendering them unsatisfactory for use. The purpose of the micro-switches 26 la, 261b is to produce a deflection of the symbols presented at the face 216 of the cathode ray tube 215 so that the collimated images of those symbols are more nearly central within the field of view. More notches could of course be provided.
Ideally it would be desirable to servo the display so as to maintain the dynamic symbols of the display control within the field of view of the observer. Such an arrangement has the further virtue that being automatic, the user of the display would not have to manually adjust its position according to aircraft drift angle. It will of course be appreciated that the ideal cannot be accomplished without some degree of trade off. In particular, the provision of a servo arrangement would introduce added complexity and expense.
Finally, whilst in the embodiments described above the display head is displaceable in essentially a rotative manner between operational and stowed positions, other arrangements are possible. In particular the display head could be slidable between the stowed and operational positions. Moreover, the stowed position might be beneath the glare shield of the aircraft.
WHAT WE CLAIM IS: 1. A display head of the kind described wherein the image combiner is supported from a light obstructive member which comprises a housing for the optical projection of the display head and which intrudes within the observer's field of view of the distant scene in use of the display head, but no intruding part of said member has a width greater than a prescribed interpupillary distance so that notwithstanding the intrusion of said member there is no obstruction by said
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

**WARNING** start of CLMS field may overlap end of DESC **. has bosses (not shown) by means of which the part 241 and, hence, the entire unit 211 may be secured to an overhead member (not shown) of the crew station of the aircraft. The overhead member is forward of the observers' seat position as indicated in Figure 10. An arm member 243 secured to the cap part 227 has a sleeve portion 245. A plunger 247 extends through the sleeve 245 and is biased by a spring (not shown) within the sleeve 245 towards the circular rim of the toothed sector 241. A powerful coil spring 249 surrounds the projecting end 251 of the pin 231. One end of the spnng 249 is fixed to the pin 231, being located in a hole near to its end. The other end of the spring 249 is secured to the arm 243 in like manner. As may be seen, there are four notches 241a, b, c and d in the toothed sector 241. Pivotally connected to the upper end of the tubular part 213 there is a catch member 253. The member 253 has an abutment portion 255 and is biased by a spring 257 in a counter-clockwise sense (Figure 10). When the display head is not being used it may be put into a stowed position. In this position the head is not within the visual field of the user to the distant scene through the aircraft windshield W, but extends in a generally horizontal direction with its longitudinal axis directed in a generally forwards direction obliquely to the fore and aft axis of the aircraft from the mounting position of the head 211 of the overhead member. The stowed position is best illustrated in Figure 12. From an operational position defined, as described more fully hereinafter, by positions X, Y and Z of the sector 241 the head 211 is rotated in azimuth in a clockwise sense (Figure 12). For this purpose the plunger 247 must first be withdrawn, and held withdrawn, from the relevant notch 241b, c or d until the angular position of the head 211 in azimuth with respect to the sector 241 is such that the plunger 247 is able to enter (under its bias) into the stowed position notch 241a. Having reached the latter position, manual pressure on an energy absorbing member 259 is effective to free the catch member 255 from engagement with the cheek parts 223a of the cap 227. The head 211 then pivots under the bias of the spring 249 about axis Q-Q to the stowed position illustrated. If the observer's head accidentally strikes the display head when in the operational position, the head similarly pivots to a collapsed position shown in Figure 10, thus reducing the likelihood of injury to the observer. In the embodiment shown any one of three discrete azimuth operational positions X, Y or Z defined by notches 24 l b, c and d may be chosen. The head is, of course, a monocular device to be used in the same manner as that described in the above-described embodiments. The fields of view available to the observer at each of the azimuth positions X, Y and Z are depicted in Figure 14. The field of view is, of course, related to the alert eye position indicated in Figure 10. As will be clear the selection of the azimuth position X, Y or Z is performed by withdrawing the plunger 247 from another notch and rotating the head to the desired azimuth position. The provision of three discrete azimuth positions is intended to allow for a range of aircraft drift angles due to cross-winds during a landing manoeuvre for example. Associated with the two outer azimuth positions X and Z, there may be provided a micro-switch 261a, 261b. When the position Y is selected the display symbols are central within the field of view position Y (Figure 14). If however position X or fl Is chosen the symbols may be outside of the field of view or at any rate at a distance off-centre of the viewing position rendering them unsatisfactory for use. The purpose of the micro-switches 26 la, 261b is to produce a deflection of the symbols presented at the face 216 of the cathode ray tube 215 so that the collimated images of those symbols are more nearly central within the field of view. More notches could of course be provided. Ideally it would be desirable to servo the display so as to maintain the dynamic symbols of the display control within the field of view of the observer. Such an arrangement has the further virtue that being automatic, the user of the display would not have to manually adjust its position according to aircraft drift angle. It will of course be appreciated that the ideal cannot be accomplished without some degree of trade off. In particular, the provision of a servo arrangement would introduce added complexity and expense. Finally, whilst in the embodiments described above the display head is displaceable in essentially a rotative manner between operational and stowed positions, other arrangements are possible. In particular the display head could be slidable between the stowed and operational positions. Moreover, the stowed position might be beneath the glare shield of the aircraft. WHAT WE CLAIM IS:
1. A display head of the kind described wherein the image combiner is supported from a light obstructive member which comprises a housing for the optical projection of the display head and which intrudes within the observer's field of view of the distant scene in use of the display head, but no intruding part of said member has a width greater than a prescribed interpupillary distance so that notwithstanding the intrusion of said member there is no obstruction by said
member of the observer's view of the distant scene.
2. A display head according to Claim 1 wherein the display head is displaceable between an operational positon in which the display head is at a position intercepting the observer's line-of-sight to the distant scene and a stowed position at which the display head is at a position at which it does not intrude into the observer's field of view of the distant scene.
3. A display head according to Claim 2 wherein, in the operational position, the display head is dependent from a position above the observer's head.
4. A display head according to Claim 2 or Claim 3 wherein the display head is rotatable about a single axis such that in moving the display head from the operational position to the stowed position, the initial movement of the display head has a major component parallel to the observer's line-of-sight to the distant scene, and the terminal movement of the display head has a major component in a direction at right angles to said line-of-sight towards the stowed position.
5. A display head according to Claim 4 wherein said single axis is an overhead transverse axis fixed in the aircraft; there is a releasible latch member operable to retain the display head in either the operational position or in the stowed position; the latch member is biassed by a spring; and in the event of contact between the observer's head and the housing, the latch member moves, against the spring bias, so as to permit rotation of the display unit, thereby reducing the risk of physical injury to the observer.
6. A display head according to Claim 4 wherein said single axis is inclined with respect to the aircraft orthagonal axes at such an angle, and the display head is so shaped, that said terminal movement has a major component to the left or right of said line-ofsight.
7. A display head according to Claim 8 wherein said initial movement is in a direction away from the observer.
8. A display head according to Claim 6 or Claim 7 wherein the display head is connected to a member Dossessing compliance and the display head is pivotal about said single axis, through the overcentre position of the compliant member, between operational and the stowed positions.
9. A display head according to any one of Claims 1 to 3 wherein the display head is rotatable to allow the display head position to be changed in azimuth while the display head is operational.
10. A display head according to Claim 9 when dependent on Claim 2 wherein the display head is movable into the stowed position by rotation about a first axis, as for changing its azimuthal position, and further rotation about a second axis transverse to said first axis.
11. A display head according to Claim 10 wherein rotation about said second axis is possible when the display head is in an operational position, thereby reducing the risk of physical injury to the observer in the event of contact between the observer's head and the display head.
12. A display head according to any one of the preceding claims wherein the combiner is a multi-film combiner.
13. A display head according to any one of Claims 1 to 11 wherein the combiner comprises a partially light-reflective, partially light-transmissive film disposed between the face of an optical data source and a spherical reflecting surface; the data source is contained in the focal plane of the spherical reflector; and light from the data source is transmitted by the said film and reflected at the spherical reflector for reflection by the said film towards the observer's viewing position.
14. A display head according to Claim 13 wherein a field flattener is interposed adjacent the data source, in the path of light from the data source towards the partially reflective film and, by transmission therethrough, to the spherical reflector.
15. A display head substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 4 to 9 or Figures 10 to 14 of the accomDanving drawings.
GB2310177A 1977-06-01 1977-06-01 Head-up displays Expired GB1588351A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB2310177A GB1588351A (en) 1977-06-01 1977-06-01 Head-up displays
US05/909,831 US4188090A (en) 1977-06-01 1978-05-26 Retractable head-up displays
FR7816306A FR2401436A1 (en) 1977-06-01 1978-05-31 DISPLAY HEAD FOR AN AIRCRAFT PILOT COLLIMATOR

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2310177A GB1588351A (en) 1977-06-01 1977-06-01 Head-up displays

Publications (1)

Publication Number Publication Date
GB1588351A true GB1588351A (en) 1981-04-23

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Application Number Title Priority Date Filing Date
GB2310177A Expired GB1588351A (en) 1977-06-01 1977-06-01 Head-up displays

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GB (1) GB1588351A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4521074A (en) * 1982-01-22 1985-06-04 University Of Exeter Binocular presentation of visual information
GB2174213A (en) * 1985-04-17 1986-10-29 Gec Avionics Stowable head-up displays

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4521074A (en) * 1982-01-22 1985-06-04 University Of Exeter Binocular presentation of visual information
USRE32487E (en) * 1982-01-22 1987-09-01 University Of Exeter Binocular presentation of visual information
GB2174213A (en) * 1985-04-17 1986-10-29 Gec Avionics Stowable head-up displays

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Effective date: 19980525