Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/01—Head-up displays
  • G02B27/0101—Head-up displays characterised by optical features
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/01—Head-up displays
  • G02B27/0101—Head-up displays characterised by optical features
  • G02B2027/0118—Head-up displays characterised by optical features comprising devices for improving the contrast of the display / brillance control visibility
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/01—Head-up displays
  • G02B27/0101—Head-up displays characterised by optical features
  • G02B2027/014—Head-up displays characterised by optical features comprising information/image processing systems
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells

Definitions

• the present invention relates to a head-up display.
• It relates more particularly to a head-up display configured to produce a visible image both when the driver wears polarizing glasses (typically polarizing sunglasses) than when he does not.
• polarizing glasses typically polarizing sunglasses
• an image generating unit emits a light beam, which is partially returned to the eyes of the driver, for example by means of a partial reflection on the windshield of the vehicle.
• the image to be displayed is thus superimposed visually on the environment facing the vehicle.
• an optimum brightness of the visualized image is generally obtained for a polarization of the light beam perpendicular to the plane of incidence containing the average direction of the light beam incident on the windshield and the average direction of this light beam after reflection by the windshield.
• the reflection coefficient of the windshield is significantly higher for this polarization than for a polarization parallel to the plane of incidence.
• polarizing glasses for example sunglasses
• polarizing glasses for example sunglasses
• the present invention provides a head-up display comprising:
• an image generation unit emitting a light beam intended to be projected, at the output of the display, towards a partially transparent blade
• liquid crystal cell disposed in the path of said light beam, configured so that said light beam emerges from said cell by presenting:
• the display being configured so that the polarization of said light beam at the output of the display depends directly on the polarization of said light beam at the output of the liquid crystal cell.
• the display comprises a control unit adapted to generate said control signal, autonomously, in the form of a succession of alternations between said first value and said second value.
• Switching from one to the other of the first and second polarizations makes it possible to alternately favor a visualization with polarizing glasses, and a visualization without polarizing glasses.
• the light beam repeatedly switches between this first and second polarization.
• a user in practice a driver of the vehicle is able to visualize the image produced by the display, whether or not it wears polarizing glasses, and without being obliged for that to indicate to the display whether or not he wears such glasses.
• the image generation unit being configured to successively generate several representative frames each of an image
• the control unit is configured so that the control signal switches from one to the other of said first and second values; during a time interval separating two of said generations of successive frames;
• control unit is configured so that the generated control signal is periodic, with a period of less than 0.1 seconds;
• control unit is configured so that said period is furthermore less than 0.05 seconds
• the liquid crystal cell is configured, in response to a switchover of the control signal from one to the other of the first and second values, to switch the polarization state of the light beam coming out of said cell; one to the other of the first and second polarizations, in a response time less than half of said period;
• control unit is configured so that the control signal that it generates is a periodic signal in crenellations having a duty ratio of between 10% and 90%;
• control unit is configured so that the control signal has, during said period, successively said first value, then said second value, then a third value equal to or less than the opposite of said first value, then said second value;
• said first polarization is linear
• said second polarization is linear
• said second polarization is orthogonal to said first polarization
• the display comprises means for projecting said light beam towards a partially transparent blade
• one of the first and second polarizations is parallel to the plane of incidence containing the average direction of said incident light beam on said plate and the mean direction of this same light beam after reflection by said blade.
• FIG. 1 shows schematically, seen from the side, a display implementing the teachings of the invention
• FIG. 2 shows schematically the evolution of a control signal of a liquid crystal cell of the display
• FIG. 3 shows schematically, for a variant of the display of Figure 1, the evolution of this control signal.
• Figure 1 shows schematically the main elements of a display head 1 high, equipping a vehicle, for example a motor vehicle, a train, a boat (such as a barge), a tram or a bus.
• a vehicle for example a motor vehicle, a train, a boat (such as a barge), a tram or a bus.
• the display 1 comprises an image generation unit 10, which here comprises a liquid crystal display (LCD) and a backlight system of this screen.
• the LCD screen generates an image to display.
• the light beam F which emerges from the liquid crystal screen is intended to be projected, at the output of the display, towards a partially transparent blade located in front of the eyes 3 of a user of the display (this user being in general the driver of the vehicle).
• a projection optical system here directs the light beam from the image generation unit to the partially transparent blade.
• This blade here the windshield 2 of the vehicle, partially reflects the light beam F to the eyes 3 of the user.
• the image to be displayed is thus superimposed visually on the environment facing the vehicle.
• the projection optical system comprises projection means, made here by folding mirror 13 arranged to reflect the light beam F from the image generation unit 10 to the windshield 2.
• the folding mirror can be plane , spherical, or have a shape adapted to compensate for geometric aberrations introduced by reflection on the windshield.
• the projection optical system could comprise, in addition to the above-mentioned folding mirror, one or more other mirrors or optical components disposed in the path of the light beam between the unit. image generation and windshield.
• the image generation unit could be oriented so as to direct the light beam that it emits directly to the windshield, the folding mirror then being omitted.
• the display 1 here comprises a housing, in which are housed the image generation unit 10 and the projection optical system.
• This housing has an exit opening, through which the light beam F leaves the display 1, in the direction of the blade 2.
• the display 1 also comprises a liquid crystal cell 11, arranged in the path of the light beam F, downstream of the image generation unit 10.
• the liquid crystal cell 1 1 has input and output faces which, preferably, are sufficiently wide to be traversed by the light beam F without the diaphragm.
• the liquid crystal cell 1 1 is disposed here against an output face of the image generation unit 10, or at least in the vicinity of this output face.
• the liquid crystal cell at the opening of the display housing mentioned above.
• the liquid crystal cell then closes this exit opening in the manner of a protective window, and prevents dust or foreign bodies from entering the display housing.
• an additional optical component protection window
• the liquid crystal cell in order not to diaphragm the light beam, the liquid crystal cell must have wider input and output faces when it is arranged at the exit opening of the display than when it is arranged just after the image generation unit (and is therefore more expensive).
• the transverse extension of the light beam at the output of the display is generally greater than its transverse extension immediately after the image generation unit.
• the liquid crystal cell could be disposed in the path of the light beam at any position between the image generating unit and the outlet opening mentioned above.
• the display 1 is devoid, downstream of the liquid crystal cell 1 1, of optical components capable of modifying the polarization of the light beam F. The polarization of this light beam is then identical, at the output of the crystal cell liquid 1 1, and output of the display. Otherwise formulated, the liquid crystal cell 1 1 imposes the polarization of the light beam at the output of the display.
• the display 1 being configured so that the polarization of the light beam F at the output of the display 1 directly depends on the polarization of this light beam F at the output of the liquid crystal cell 1 January.
• the display is devoid, downstream of the liquid crystal cell 1 1, a polarizing filter that transmits only a given polarization.
• the liquid crystal cell 1 1 is configured so that the light beam F has, at the output of this cell:
• the first polarization P1 is that which maximizes the luminous intensity of this light beam after reflection by the windshield 2.
• the first polarization is that which maximizes the light intensity of the light beam F reaching the eyes 3 of the user.
• the first polarization P1 is linear and perpendicular to the plane of incidence containing the mean direction of the light beam incident on the windshield and the mean direction of the same light beam after reflection on the windshield (such a polarization is called polarization S in the field of optics).
• This plane of incidence corresponds, in Figure 1, to the plane of this figure (plane of the sheet).
• the second polarization P2 is, among the different polarizations that can present the light beam F, that which maximizes the light intensity of the light beam reaching the eyes 3 of the user when it wears polarizing glasses (generally polarizing sunglasses).
• the second polarization P2 is linear and parallel to the aforementioned plane of incidence (a such polarization is called polarization P in the field of optics).
• the first and second polarizations could, in order to maximize the light intensity reaching the user's eyes, present orientations different from those mentioned above. and / or be slightly elliptical instead of linear.
• the display 1 is configured so that the light beam F has, before passing through the liquid crystal cell 1 1, said first polarization.
• the liquid crystal screen is oriented so that the light beam F has, at the output of the image generation unit 10, said first polarization (more precisely, its angular position, around a axis perpendicular to the screen, is chosen for this purpose).
• the image generation unit could be made by means of an at least partially translucent diffusing screen, and a scanning system of a rear face of this screen diffusing by a laser beam, rather than 'by means of the LCD screen.
• a polarizing film can be arranged between the image generation unit and the liquid crystal cell. polarizing film being oriented so that the light beam has said first polarization after passing through the polarizing film.
• the liquid crystal cell 11 is essentially transparent: its transmittance is, in practice, greater than about 80%. It comprises two electrodes parallel to its input and output faces. It also comprises, contained between these two electrodes, a solution of molecules in the form of rods. These molecules are organized in the form of a cholesteric liquid crystal (more precisely in the form of a nematic liquid crystal in torsion), as long as the electrical voltage applied between these electrodes is zero, or at least lower than a given threshold. .
• the control signal of the cell corresponds to the voltage applied between these two electrodes.
• the aforementioned molecules are aligned substantially perpendicular to the electrodes.
• the polarization of the light beam F is not changed at the crossing of the liquid crystal cell January 1.
• the light beam F then has, at the output of the liquid crystal cell, the first polarization P1.
• the crossing of the cell induces a rotation of the polarization of the light beam.
• a predetermined angle of rotation fixed at the manufacture of the cell, equal here to 90 degrees.
• the light beam F then has, at the output of the liquid crystal cell, the second polarization P2.
• the display 1 comprises a control unit 12 adapted to generate the control signal s, autonomously, in the form of a succession of alternations between the first value V1 and the second value V2.
• control signal s passes successively from the first value to the second value, is held at the second value for a predetermined duration, then goes from the second value to the first value, remains at the first value for one ( other) predetermined time and so on.
• the user of the display in practice the driver of the vehicle, is able to visualize the image produced by the display, whether it is wearing polarizing or non-polarizing sunglasses, and without to be obliged to indicate to the display whether or not he wears such glasses.
• This result is particularly interesting because it would be burdensome for the user to always indicate whether or not he wears such glasses.
• the control unit 12 generates the control signal s autonomously in the sense that, when the display 1 is electrically powered, the control unit 12 generates the control signal s, in the form mentioned above, without the intervention of the user of the display.
• the control unit 12 is realized in practice by means of an electronic circuit such as a generator of crenellated signals, or sinusoidal signals, or else pseudo-random signals.
• the light intensity, just upstream of the eyes 3 of the user varies when the control signal s switches from one to the other of the first and second values V1 and V2. Also, if the value of the control signal is maintained for a long time at the first value, then at the second value, and so on, the user perceives a variation of brightness of the displayed image, in the manner of a flashing .
• control unit 12 is configured so that the control signal s it generates is periodic, of period T less than 0.1 seconds.
• the user then perceives, thanks to the retinal persistence effect, an image of constant brightness, or at least substantially constant, which is more comfortable and visually resting than a flashing image.
• control unit is even configured so that the period T of the control signal is less than 0.05 seconds, to further reduce any variations in apparent brightness of the image that could perceive the user.
• the period T of the control signal is thus less than the average retentive persistence time (which is equal to about 0.05 seconds) makes it possible, during the period T, to maintain the brightness of the image perceived by the user at a substantially constant level.
• control signal generated by the control unit is shown diagrammatically in FIG. 2, as a function of time t, for the embodiment considered here.
• control unit 12 is configured here to generate the control signal s in the form of a periodic signal in slots having, during the period T:
• the corresponding duty cycle equal to the first duration T1 divided by the period T, is between 10% and 90%. This duty cycle is more particularly equal here at 50%.
• the liquid crystal cell 11 is configured to: in response to a switch of the control signal s from one to the other of the first and second values V1 and V2, to switch the polarization state of the light beam F leaving said cell, from one to the other of the first and second polarizations P1 and P2 in a response time tp less than half the period T of the control signal .
• the response time tp of the liquid crystal cell 1 1 is short enough to allow, during the period T, to switch from the first polarization to the second polarization, and then from the second polarization to the first polarization ( or the opposite).
• the response time tp of the cell is less than 25 milliseconds.
• the liquid crystal cell has a response time of less than 10 milliseconds, or even less than 4 milliseconds, in order to obtain, during each period, clear tilts between the first and second polarizations (the light beam then having polarizations intermediate between them only for a short time compared to the period T).
• the response time tp of the cell is defined more precisely as the time required, after a switch of the control signal s from the first value V1 to the second value V2, to change from a normalized transmittance value of 10% to a standardized transmittance value of 90%.
• This normalized transmittance corresponds to the normalized transmittance of a system comprising the liquid crystal cell followed by a polarizing film passing only the second polarization.
• the value 100% corresponds to the maximum transmittance of this system.
• This system is mentioned here to define precisely the response time tp, but it will of course be noted that in the display 1 described here, the liquid crystal cell 11 is not followed by such a polarizing film.
• liquid crystal cells exhibiting such response times are commercially available.
• the switchover between the first value V1 and the second value V2 is performed during a time interval separating two successive generations of frames by the image generation unit 10.
• the image generated by the image generation unit is decomposed into successively formed frames, at a given projection frequency.
• a frame corresponds to a refresh of all the pixels of the screen. Between two successive frames, during a reduced time interval, no pixel refresh takes place.
• This allows, from the point of view of the liquid crystal cell, to have a longer duration to switch from the first to the second polarization, which allows to use a liquid crystal cell slower, and therefore less expensive .
• control unit is configured to generate the control signal s of the liquid crystal cell in the form of a succession of alternations between:
• the control signal s presents this sequence of four successive values periodically, the corresponding period being twice the time period T mentioned previously.
• the switching between two of said values can be performed in the interval separating the projections of two successive frames.
• the control signal s has the third value V3
• the polarization of the light beam F after the liquid crystal cell corresponds to the first polarization P1 (c ' that is, in this case, to a polarization S, optimizing the visibility of the image in the absence of polarizing glasses).
• the third value V3 as well as the first value V1 makes it possible to obtain, for the light beam F, the first polarization P1.
• the first and second polarizations P1 and P2 are respectively perpendicular (polarization P1) and parallel (polarization P2) to the plane of incidence, which contains the direction average of the light beam incident on the windshield as well as the average direction of this same light beam after reflection on the windshield.
• the first polarization is parallel to this plane of incidence, to maximize the light intensity reaching the user's eyes when wearing polarizing sunglasses,
• the second polarization is then perpendicular to the plane of incidence to maximize the light intensity reaching his eyes in the absence of such glasses.

Landscapes

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

Applications Claiming Priority (2)

Publications (1)

Family

ID=59031123

Family Applications (1)

Country Status (3)

Citations (3)

Family Cites Families (5)

• 2017
  • 2017-03-17 FR FR1752209A patent/FR3064080B1/fr active Active
• 2018
  • 2018-03-16 WO PCT/EP2018/056763 patent/WO2018167314A1/fr not_active Ceased
  • 2018-03-16 EP EP18712190.0A patent/EP3596540A1/de active Pending

Patent Citations (3)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events