Virtual image display device, virtual image display method, and program

Abstract

This virtual image display device comprises: a liquid crystal panel that has a display surface for displaying a display image; a backlight that faces the back surface of the liquid crystal panel on the opposite side from the display surface and has an emission surface that irradiates the back surface with light for each of a plurality of illumination segments; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that controls local dimming on the backlight. The liquid crystal panel has a region in which the distance between the back surface and the emission surface of the backlight is large. When the temperature detected by the temperature detection unit is equal to or higher than a prescribed temperature, the control unit moves the display image to a region where the distance increases, and selectively lights up the illumination segment corresponding to the display image.

Description

Virtual image display device, virtual image display method, and program

[0001] The present disclosure relates to a virtual image display device, a virtual image display method, and a program that can be implemented as a head-up display (HUD) device.

[0002] A prior art virtual image display device is described in, for example, Japanese Patent Application Laid-Open No. 2003-222999.

[0003] Patent No. 6299523

[0004] The virtual image display device according to the present disclosure is a virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, and includes: a liquid crystal panel having a display surface that displays the display image; a backlight that faces the back surface of the liquid crystal panel opposite the display surface and has an exit surface that irradiates light onto the back surface; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that divides the backlight into a plurality of lighting segments, performs local dimming control, and turns on the lighting segments that correspond to the display image, wherein the liquid crystal panel has regions where the distance between the back surface and the exit surface of the backlight varies, and when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, the control unit moves the display image to a region where the distance between the back surface of the liquid crystal panel and the exit surface of the backlight is increased, and selectively turns on the lighting segments that correspond to the display image.

[0005] The virtual image display method according to the present disclosure is a virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, the virtual image display device including: a liquid crystal panel having a display surface that displays the display image; a backlight facing the back surface of the liquid crystal panel opposite the display surface and having an exit surface that irradiates light onto the back surface; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that divides the backlight into a plurality of lighting segments, performs local dimming control, and turns on the lighting segments that correspond to the display image, the liquid crystal panel having regions where the distance between the back surface and the exit surface of the backlight varies. The virtual image display device includes the steps of: preparing a virtual image display device; determining, by the control unit, whether the temperature detected by the temperature detection unit is equal to or greater than a predetermined temperature; and, when the detected temperature is equal to or greater than the predetermined temperature, moving the display image to a region where the distance between the back surface of the liquid crystal panel and the exit surface of the backlight is increased, and selectively turning on the lighting segments that correspond to the display image.

[0006] The program according to the present disclosure is a virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, the program including: a liquid crystal panel having a display surface that displays the display image; a backlight facing the back surface of the liquid crystal panel opposite the display surface and having an exit surface that irradiates light onto the back surface; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that divides the backlight into a plurality of lighting segments, performs local dimming control, and turns on the lighting segments corresponding to the display image, the liquid crystal panel having regions where the distance between the back surface and the exit surface of the backlight varies. The program is for displaying a virtual image using a virtual image display device, and causes a computer to function as a control unit that executes the steps of: determining whether the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature; and, when the detected temperature is equal to or higher than the predetermined temperature, moving the display image to a region where the distance between the back surface of the liquid crystal panel and the exit surface of the backlight is increased, and selectively turning on the lighting segments corresponding to the display image using the backlight.

[0007] The objectives, features, and advantages of the present disclosure will become clearer from the following detailed description and drawings.

[0023] FIG. 1 is a cross-sectional view of a main portion of a virtual image display device 1 according to an embodiment of the present disclosure.

[0024] FIG. 2 is a diagram showing a display image and an external scene displayed by a liquid crystal panel.

[0025] FIG. 3 is a diagram showing a state in which the display image has been moved to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased.

[0026] FIG. 4 is a cross-sectional view schematically showing a liquid crystal panel and a backlight.

[0027] FIG. 5 is a graph showing the relationship between the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight and the temperature reached by the liquid crystal panel.

[0028] FIG. 6 is a diagram for explaining the relationship between the position of a display image according to the angle of the liquid crystal panel and the distance between the liquid crystal panel and the backlight.

[0029] FIG. 7 is a diagram showing a display area on the display surface of the liquid crystal panel.

[0030] FIG. 8 is a diagram showing the emission surface of the backlight.

[0031] FIG. 9 is a flowchart showing an embodiment of a virtual image display method.

[0032] FIG. 10 is a diagram showing the position of a display image corresponding to tilt angles of 90° to 76° when the distance d0 is 43 mm.

[0033] FIG. 11 is a diagram showing the position of a display image corresponding to tilt angles of 75° to 60° when the distance d0 is 43 mm.

[0034] FIG. 12 is a diagram showing the position of a display image corresponding to tilt angles of 59° to 45° when the distance d0 is 43 mm. FIG. 10 is a diagram showing the positions of a display image corresponding to tilt angles of 90° to 76° when the distance d0 is 45 mm. FIG. 11 is a diagram showing the positions of a display image corresponding to tilt angles of 75° to 60° when the distance d0 is 45 mm. FIG. 12 is a diagram showing the positions of a display image corresponding to tilt angles of 59° to 45° when the distance d0 is 45 mm. FIG. 13 is a diagram showing the positions of a display image corresponding to tilt angles of 90° to 76° when the distance d0 is 47 mm. FIG. 14 is a diagram showing the positions of a display image corresponding to tilt angles of 75° to 60° when the distance d0 is 47 mm. FIG. 15 is a diagram showing the positions of a display image corresponding to tilt angles of 59° to 45° when the distance d0 is 47 mm.

[0008] The conventional technology includes a liquid crystal panel that displays a display image, a backlight that is arranged on the back of the liquid crystal panel and illuminates the liquid crystal panel in areas, a temperature detection unit that detects the temperature of the liquid crystal panel, and a control unit that controls the liquid crystal panel to make the display image smaller when the temperature of the temperature detection unit is equal to or higher than a predetermined temperature, and controls the backlight to control the area to be illuminated corresponding to the display image.

[0009] In the conventional technology of Patent Document 1, when sunlight enters the device from outside, the ambient temperature of the liquid crystal panel rises. Furthermore, when light is irradiated from a backlight, the temperature of the liquid crystal panel rises due to the non-transmitted light that does not pass through the liquid crystal panel, heating the liquid crystal within the liquid crystal panel. When the temperature of the liquid crystal reaches a phase transition temperature, for example, if the liquid crystal is a nematic liquid crystal, the liquid crystal undergoes a phase transition from the nematic phase to the isotropic phase. When the liquid crystal undergoes a phase transition, both the orientation and alignment become disordered, resulting in display defects. Therefore, there is a need for a virtual image display device, a virtual image display method, and a program that can suppress the phase transition caused by heating of the liquid crystal in the liquid crystal panel and thereby suppress display defects.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The drawings used in the following description are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0011] FIG. 1 is a cross-sectional view of a main portion of a virtual image display device 1 according to an embodiment of the present disclosure. The following description will be given assuming that an embodiment of a virtual image display method according to the present disclosure is implemented by the virtual image display device 1 according to the present embodiment. The virtual image display device 1 according to the present embodiment operates as the virtual image display device 1 by executing a program according to the present disclosure. The virtual image display device 1 according to the present embodiment includes a display unit 2, a reflecting member 3, and a control unit 4. The virtual image display device 1 allows a user 5 to view a virtual image M3 superimposed on an external view through a windshield WS. The virtual image display device 1 is also referred to as a head-up display (HUD). In the following description, the head-up display may be abbreviated as HUD. The virtual image display device 1 may be mounted on a mobile object such as a vehicle, a ship, or an aircraft. When the virtual image display device 1 is mounted on a mobile object, the user 5 may be the driver, operator, or passenger of the mobile object.

[0012] The display unit 2 displays an image to be projected into the field of view of the user 5. The display unit 2 may be configured as a transmissive display device. The transmissive display device may be, for example, a liquid crystal device such as an LCD (Liquid Crystal Display) including a backlight (BL) 6 and a liquid crystal panel 7. The backlight 6 and the liquid crystal panel 7 are arranged in this order from the side farthest from the user 5 along the optical path of image light of the image displayed to the user 5.

[0013] The backlight 6 may be a direct-type backlight for a HUD. The direct-type backlight for a HUD uses a fluoride red phosphor (K ２ SiF ６ : Mn ４＋ The backlight 6 includes a plurality of light-emitting diodes (LEDs) 61 having a KSF (Korean Surface Diffusion) and an exit surface 6a capable of emitting light emitted from the plurality of light-emitting diodes 61. The backlight 6 may include a base 62 and a diffuser 63. The base 62 may have a main surface 62a facing the liquid crystal panel 7, and the plurality of light-emitting diodes 61 may be arranged two-dimensionally (in a matrix) on the main surface 62a. The diffuser 63 may be located in front of the base 62 (on the left side in FIG. 1 ) and cover the plurality of light-emitting diodes 61. The diffuser 63 diffuses the light emitted from the plurality of light-emitting diodes 61, thereby allowing the backlight 6 to irradiate the liquid crystal panel 7 with light with improved uniformity. The exit surface 6a may be the surface of the diffuser 63 facing the liquid crystal panel 7 and may be parallel to the main surface 62a of the base 62.

[0014] Each of the plurality of light-emitting diodes 61 includes at least one light source unit. The light source unit may be, for example, a point light source. The LEDs include mini LEDs and micro LEDs.

[0015] The liquid crystal panel 7 has a display surface 7a. The display surface 7a is a surface that emits image light based on an image display signal, and can emit image light toward the reflector 3 using light emitted from the emission surface 6a of the backlight 6. The liquid crystal panel 7 may be configured to include a pair of opposing substrates formed of a transparent material such as glass or resin, transparent electrodes formed on each of the opposing surfaces of the pair of substrates and made of ITO (indium tin oxide) or the like, alignment films covering each transparent electrode, a sealant that bonds the pair of substrates, liquid crystal sealed in a space approximately 10 to 30 μm thick between the pair of substrates, and a pair of polarizing plates arranged to sandwich the substrates from the outside. If the liquid crystal is a nematic liquid crystal, when a drive voltage is applied between the two transparent electrodes, the liquid crystal molecules rotate, and the molecular axes are tilted relative to the electrode surfaces and no longer perpendicular. Therefore, the transmitted light becomes elliptically polarized light due to the birefringence effect, and a portion of the light passes through the polarizing plate, allowing a high-contrast display image to be formed at a low voltage and current value without causing dynamic scattering.

[0016] The liquid crystal panel 7 may be, for example, any of a TN (Twisted Nematic) type, a VA (Vertical Alignment) type, an STN (Super-Twisted Nematic) type, or a passive drive type. The polarizers may be arranged in either a crossed Nicol configuration or a parallel Nicol configuration, in which the transmission axes are arranged perpendicular or parallel to each other, depending on the type of the liquid crystal panel 7 and the negative / positive display.

[0017] In local dimming control, the control unit 4 typically individually controls a plurality of light-emitting diodes 61 arranged as light-emitting elements on the light source surface of the backlight 6 in accordance with the displayed image. This makes it possible to increase the contrast ratio between the image and non-image areas by making the light-emitting diodes 61 relatively bright in relatively bright areas of the display surface 7a (e.g., image areas) and relatively dark in relatively dark areas of the display surface 7a (e.g., non-image areas). Furthermore, local dimming control can prevent the postcard phenomenon, in which the light source surface of the backlight 6 is faintly reflected as a virtual background image (also known as a postcard image), from occurring.

[0018] The liquid crystal panel 7 may be a known liquid crystal panel. Examples of known liquid crystal panels include in-plane switching (IPS) panels, fringe field switching (FFS) panels, vertical alignment (VA) panels, and electrically controlled birefringence (ECB) panels. The liquid crystal panel 7 may include a plurality of liquid crystal display elements (pixels each having a liquid crystal layer), the pair of substrates described above arranged to sandwich the plurality of liquid crystal display elements, and a color filter CF. Each substrate may be a glass substrate, or may be a light-transmitting plastic substrate, ceramic substrate, or the like.

[0019] The control unit 4 controls the backlight 6. The control unit 4 switches each of the plurality of light-emitting diodes 61 between an emitting state and a non-emitting state. The control unit 4 may control the light emission brightness of the light-emitting diodes 61 that are in the emitting state based on image data of an image to be displayed on the display surface 7 a. The control unit 4 may control the light emission brightness of the light-emitting diodes 61 that are in the emitting state based on the background brightness in the field of view of the user 5.

[0020] The control unit 4 may control not only the backlight 6 but also each component of the virtual image display device 1. The control unit 4 is configured as, for example, a processor. The control unit 4 may include one or more processors. The processor may include a general-purpose processor that loads a specific program to execute a specific function, and a dedicated processor specialized for a specific process. The dedicated processor may include an application-specific integrated circuit (ASIC). The processor may include a programmable logic device (PLD). The PLD may include a field-programmable gate array (FPGA). The control unit 4 may be either a system-on-a-chip (SoC) or a system-in-a-package (SiP) in which one or more processors work together. The control unit 4 may include a memory unit 9, and the memory unit 9 may store various information or programs for operating each component of the virtual image display device 1. In this embodiment, the storage unit 9 stores reference tables shown in FIGS. 8A to 8I, which are described below, in which the distance d between the center of the rear surface 7b and the center of the exit surface 6a and the tilt angle θ are used as variables to set the amount of movement of the displayed image. The storage unit 9 may be configured, for example, with a semiconductor memory. The storage unit 9 may function as a work memory for the control unit 4.

[0021] The program is a virtual image display device 1 that displays a virtual image by irradiating a reflecting member 3 with image light of a display image, and includes a liquid crystal panel 7 having a display surface 7a that displays the display image, a backlight 6 that faces a back surface 7b on the opposite side of the liquid crystal panel 7 from the display surface 7a and has an emission surface 6a that irradiates the back surface 7b with light, a temperature detection unit 8 that detects a temperature Ts of the liquid crystal panel 7, and a control unit 4 that divides the backlight 6 into a plurality of lighting segments Seg, performs local dimming control, and turns on the lighting segments Seg that correspond to the display image. The liquid crystal panel 7 has a back surface 7b and an emission surface 6a that emits light. A program for displaying a virtual image by a virtual image display device (1) having regions where the distance d between the backlight and the light exit surface (6a) of the light (6) varies, and causes the computer to function as a control unit (4) that executes the steps of determining whether the temperature Ts detected by the temperature detection unit (8) is equal to or higher than a predetermined temperature (Tm), and, when the detected temperature (Ts) is equal to or higher than the predetermined temperature (Tm), moving the displayed image to a region where the distance d between the back surface (7b) of the liquid crystal panel (7) and the light exit surface (6a) of the backlight (6) is increased, and selectively lighting up the lighting segment (Seg) corresponding to the displayed image by the backlight (6).

[0022] The reflecting member 3 is located in the optical path of image light emitted from the display unit 2 and reaching the eyes of the user 5. The reflecting member 3 projects the image light emitted from the display unit 2 onto the eyes of the user 5, forming a virtual image M3 in the eyes of the user 5. The reflecting member 3 may enlarge or reduce the image displayed on the display unit 2 and form the image in the eyes of the user 5. The reflecting member 3 includes a first reflecting member 3a and a second reflecting member 3b. The first reflecting member 3a reflects the image light from the display surface 7a toward the second reflecting member 3b. The second reflecting member 3b reflects the image light reflected by the first reflecting member 3a toward the eyes of the user 5. The number of members constituting the reflecting member 3 is not limited to two, and may be three or more, or may be four or more. The reflecting member 3 may include a reflecting member including a convex or concave mirror. The reflecting member 3 may include a reflecting member including a free-form surface mirror. The reflecting member 3 may include a refractive member including a convex lens or a concave lens. The convex lens includes a biconvex lens, a plano-convex lens, and a convex meniscus lens. The concave lens includes a biconcave lens, a plano-concave lens, and a concave meniscus lens. Each reflecting member is not limited to a reflecting mirror member or a refractive member, but may include various other optical members such as a hologram element.

[0023] 2A is a diagram showing a display image and an external scene displayed by a liquid crystal panel, and FIG. 2B is a diagram showing a state in which the display image has been moved to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased. The virtual image display device 1 of this embodiment allows a user 5 to view the display image M2 superimposed on the external scene M1 as a virtual image by irradiating the reflecting member 3 with image light of the display image M2. The virtual image display device 1 includes a liquid crystal panel 7, a backlight 6, a temperature detection unit 8 that detects temperature, and a control unit 4. When the temperature Ts detected by the temperature detection unit 8 is equal to or higher than a predetermined temperature Tm, the control unit 4 moves the display image M2 to a region where the distance d between the rear surface 7b of the liquid crystal panel 7 and the emission surface 6a of the backlight 6 is increased, i.e., in direction A, and performs local dimming control of the backlight 6 so that the illumination segments Seg corresponding to the display image M2 are selectively illuminated.

[0024] The liquid crystal of the liquid crystal panel 7 is a thermotropic liquid crystal, and has a nematic-isotropic phase transition temperature (TＮＩ ) has. T ＮＩ If the temperature reaches or exceeds this value, an image cannot be displayed. The temperature detection unit 8 may be realized by, for example, a thermistor. The thermistor may be configured to detect the temperature of the central portion of the liquid crystal panel 7, where the temperature is highest, and output the detected value as an analog signal. The thermistor may be configured to detect the temperature of the portion of the liquid crystal panel 7, where the distance d between the back surface 7b of the liquid crystal panel 7 and the emission surface 6a of the backlight 6 is the smallest, and output the detected value as an analog signal.

[0025] The aforementioned thermistors are available in various shapes and have the advantages of being inexpensive, highly sensitive to temperature, and having a wide operating temperature range. The thermistor may be attached, for example, to the widthwise center of a flexible printed circuit (FPC) connected to the liquid crystal panel 7, near the connection portion with the liquid crystal panel 7, or to the center of the upper edge of the emission surface 6 a of the backlight 6. As other embodiments of the temperature detection unit 8, a radiation thermometer, a thermocouple, an infrared radiator, or the like may be used instead of a thermistor.

[0026] FIG. 3 is a cross-sectional view schematically illustrating a liquid crystal panel and a backlight. The liquid crystal panel 7 is disposed with its rear surface 7b tilted at a predetermined angle θ on the plane of FIG. 3 including the center line L1 of the backlight 6. The rear surface 7b of the liquid crystal panel 7 and the light-emitting surface 6a of the backlight 6 are parallel to the center line L1 and have a distance d between them. The center line L1 of the backlight 6 corresponds to a normal line at the center C of the light-emitting surface 6a. The distance d is defined as d0 between the center C of the light-emitting surface 6a and the center C of the rear surface 7b, d1 between the upper edge of the rear surface 7b and the upper edge of the light-emitting surface 6a, and d2 between the lower edge of the rear surface 7b and the lower edge of the light-emitting surface 6a. The backlight 6 has a plurality of illumination segments Seg arranged in a matrix, each equipped with a light-emitting diode 61. The distance d1 is narrow due to the tilt of the plurality of liquid crystal panels 7 at the angle θ, and is 35 mm. Furthermore, there is a distance d0 between the center C of the rear surface 7b of the liquid crystal panel 7 and the center C of the emission surface 6a of the backlight 6. This distance d0 is 45 mm. Furthermore, there is a distance d2 between the lower edge of the rear surface 7b of the liquid crystal panel 7 and the lower edge of the emission surface 6a of the backlight 6. This distance d2 is 55 mm. Therefore, the rear surface 7b of the liquid crystal panel 7 is spaced apart from the emission surface 6a of the backlight 6 from the upper edge toward the lower edge, and the distance d increases in the order of d1, d0, and d2. Note that the distances d1, d0, and d2 are collectively referred to as distance d. Furthermore, the distance d may decrease in the order of d1, d0, and d2, as long as it is inclined relative to the emission surface of the backlight 6. FIG. 3 illustrates a case where the rear surface 7b of the liquid crystal panel 7 is inclined at a predetermined angle θ on the plane of FIG. 3 including the center line L1 of the backlight 6, but this is not limited thereto. For example, the rear surface 7b of the liquid crystal panel 7 may have a curved portion.

[0027] 4 is a graph showing the relationship between the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight and the temperature reached by the liquid crystal panel. When the backlight 6 is driven, light emitted from the light-emitting diodes 61 is irradiated onto the liquid crystal panel 7, and the light that does not pass through the liquid crystal panel 7 is converted into heat within the liquid crystal panel 7, heating the liquid crystal within the liquid crystal panel 7. The nematic-isotropic phase transition temperature (hereinafter referred to as the "phase transition temperature") of this liquid crystal is, for example, 120°C. In this embodiment, the phase transition refers to a change from a nematic phase, in which the liquid crystal molecules are randomly positioned but the axial directions of the rod-shaped molecules are aligned, to an isotropic phase, when the liquid crystal is, for example, a nematic liquid crystal.

[0028] In this embodiment, the predetermined temperature set in the control unit 4 is set to 120° C., which is an example of the phase transition temperature. In other embodiments of the present disclosure, the predetermined temperature is not limited to the phase transition temperature, and may be, for example, a temperature that is 5 to 20° C. lower than the phase transition temperature (120° C. in this embodiment).

[0029] Liquid crystals with a phase transition temperature of 120°C can be made by mixing several types of liquid crystal molecules and adjusting them to have the desired optical and electrical properties, and by mixing several types of liquid crystal molecules so that the phase transition temperature is also 120°C, so that the liquid crystal has the desired optical and electrical properties overall and a phase transition temperature of 120°C.

[0030] The temperature detection unit 8 detects the temperature of the central portion C of the back surface 7b of the liquid crystal panel 7. At an ambient temperature of 85°C, the liquid crystal phase transition temperature is exceeded near the central portion C of the image displayed on the liquid crystal panel 7, but the temperature does not exceed the liquid crystal phase transition temperature in the lower region, so no display defects occur. If the tilt angle θ is set so that the displayed image is positioned within this region, no display defects due to the liquid crystal phase transition will occur up to an ambient temperature of 85°C.

[0031] Fig. 5 is a diagram illustrating the relationship between the position of the displayed image according to the angle of the liquid crystal panel and the distance between the liquid crystal panel and the backlight, Fig. 6 is a diagram showing the display area of ​​the display surface of the liquid crystal panel, and Fig. 7 is a diagram showing the emission surface of the backlight. The emission surface 6a of the backlight 6 is divided into a plurality of illumination segments Seg arranged in a matrix.

[0032] 8 is a flowchart showing an embodiment of a virtual image display method. In the virtual image display method according to the present disclosure, in a preparation step s1, a virtual image display device 1 for displaying a virtual image is prepared, the virtual image display device 1 including a liquid crystal panel 7 having a display surface 7a for displaying a display image, a backlight 6 facing a rear surface 7b opposite the display surface 7a of the liquid crystal panel 7 and having an emission surface 6a for irradiating the rear surface 7b with light, a temperature detection unit 8 for detecting the temperature of the liquid crystal panel 7, and a control unit 4 that divides the backlight 6 into multiple lighting segments Seg, performs local dimming control, and turns on the lighting segments Seg corresponding to the display image. The liquid crystal panel 7 has regions with different distances d between the rear surface 7b and the emission surface 6a of the backlight 6. Next, in step s2, the control unit 4 executes a step of determining whether the temperature Ts detected by the temperature detection unit 8 is equal to or higher than a predetermined temperature Tm. If the temperature Ts is lower than the predetermined temperature Tm, the process returns to step s2. If the temperature Ts is equal to or higher than the predetermined temperature Tm, the process proceeds to step s3. In step s3, the control unit 4 moves the display image to an area where the distance d between the back surface 7b of the liquid crystal panel 7 and the exit surface 6a of the backlight 6 is increased, and selectively lights up the lighting segment Seg corresponding to the display image.

[0033] 9A to 9F are diagrams showing the contents of the lookup table, in which Fig. 9A shows the positions of the display image corresponding to tilt angles of 90° to 76° when the distance d0 is 43 mm, Fig. 9B shows the positions of the display image corresponding to tilt angles of 75° to 60° when the distance d0 is 43 mm, and Fig. 9C shows the positions of the display image corresponding to tilt angles of 59° to 45° when the distance d0 is 43 mm. 9D shows the position of the display image corresponding to tilt angles of 90° to 76° when the distance d0 is 45 mm, FIG. 9E shows the position of the display image corresponding to tilt angles of 75° to 60° when the distance d0 is 45 mm, FIG. 9F shows the position of the display image corresponding to tilt angles of 59° to 45° when the distance d0 is 45 mm, FIG. 9G shows the position of the display image corresponding to tilt angles of 90° to 76° when the distance d0 is 47 mm, FIG. 9H shows the position of the display image corresponding to tilt angles of 75° to 60° when the distance d0 is 47 mm, and FIG. 9I shows the position of the display image corresponding to tilt angles of 59° to 45° when the distance d0 is 47 mm. In FIGS. 9A to 9I, the horizontal axis is the angle θ, and the vertical axis is the position where the center C is the center of the display area and the direction toward the upper edge is positive and the direction toward the lower edge is negative, with the center C being 0. The gray area indicates the range of display image positions that can be selected by the control unit 4 to extract the amount of movement required to keep the liquid crystal of the liquid crystal panel 7 below the phase transition temperature.

[0034] The liquid crystal panel 7 used to create the look-up table is a 4.1-inch transmissive liquid crystal panel, and the dimension H of the display surface 7a in the main scanning direction is 92 mm, and the dimension V in the sub-scanning direction is 46 mm.

[0035] 4, if the distance d is equal to or greater than about 45 mm, display defects due to phase transition of the liquid crystal in the liquid crystal panel 7 do not occur, and therefore, by moving the display image M2 to the gray colored region (d45 mm) in the lookup tables shown in Figures 9A to 9I, display defects due to liquid crystal phase transition can be avoided. The extent to which the display image is moved (the amount of movement) depends on the distance d between the liquid crystal panel 7 and the backlight 6; the smaller the distance d (for example, 43 mm), the greater the amount of movement of the display image M2, and the greater the distance d (for example, 47 mm), the smaller the amount of movement of the display image M2.

[0036] For example, when the tilt angle θ of the liquid crystal panel 7 is 55°, the amount of movement of the display image at a position of +15 mm is 19 mm or more when the distance d is set to 43 mm, whereas it is 12 mm or more when the distance d is 47 mm. In other words, the control unit 4 is configured to select the amount of movement of the display image M2 to a value greater than the amount of movement corresponding to the phase transition temperature of the liquid crystal.

[0037] 9A to 9I are stored in the storage unit 9, and the control unit 4 refers to the reference tables stored in the storage unit 9 to determine the amount of movement of the display image, thereby suppressing the occurrence of liquid crystal phase transition. When the control unit 4 reads the display position of the display image from the image signal to be displayed, it refers to the reference table in the storage unit 9 and operates to move the display image in direction A, increasing the distance d from the display position written in the image signal, and display the image. Therefore, in the backlight 6, the light-emitting diodes 61 of the illumination segment Seg corresponding to the display position after movement are illuminated, and as a result, the liquid crystal does not rise to a temperature that would cause a liquid crystal phase transition, thereby suppressing the occurrence of display defects.

[0038] According to the virtual image display device 1 of the present disclosure, when image light of a display image M2 is irradiated onto the reflecting member 3, the display image is displayed as a virtual image via the reflecting member 3. Light is irradiated from the emission surface 6a of the backlight 6 onto the rear surface 7b of the liquid crystal panel 7 in which liquid crystal is sealed. The backlight 6 is locally dimmed by the control unit 4, so that an illumination segment Seg corresponding to the display image is selected, and light is irradiated from the selected illumination segment Seg onto the liquid crystal panel 7. The temperature of the liquid crystal panel 7 is detected by the temperature detection unit 8. When the temperature Ts detected by the temperature detection unit 8 is equal to or higher than a predetermined temperature Tm, the control unit 4 moves the display image to a region where the distance d between the rear surface 7b of the liquid crystal panel 7 and the emission surface 6a of the backlight 6 increases, i.e., in direction A. As a result, the selected illumination segment Seg of the backlight 6 that is locally dimmed is moved to a region where the distance d between the rear surface 7b of the liquid crystal panel 7 and the emission surface 6a of the backlight 6 increases, corresponding to the display image M2. As a result, the rise in ambient temperature caused by the backlight 6 and the amount of light irradiated onto the liquid crystal panel 7 are suppressed, thereby reducing the amount of heat applied to the liquid crystal panel 7, suppressing the phase transition of the liquid crystal in the liquid crystal panel 7, and preventing display defects from occurring.

[0039] The reason why the temperature of the liquid crystal can be kept below the phase transition temperature by moving the display image to the region where the distance d is large (the lower edge side on the display surface) will be described below.

[0040] Light energy that does not pass through the liquid crystal panel 7 is converted into heat energy, heating the liquid crystal. However, because the light transmittance of the liquid crystal panel 7 is uniform across the screen, light of the same brightness is converted into heat energy uniformly across the screen when irradiated. Furthermore, because brightness is proportional to distance, the brightness decreases as the distance d increases. Therefore, by moving to an area where the distance d is greater (toward the lower edge on the display surface), the temperature of the liquid crystal can be kept below the phase transition temperature.

[0041] The liquid crystal is not limited to nematic liquid crystal, but may be cholesteric liquid crystal or smectic liquid crystal. Both cholesteric liquid crystal and smectic liquid crystal have in common the fact that they are long, rod-shaped molecules and have an electric dipole moment, and the temperature rise caused by the backlight 6 can suppress the liquid crystal phase transition and prevent display defects.

[0042] In the embodiment of the present disclosure, the control unit 4 moves the display image to a region where the distance d between the rear surface 7b of the liquid crystal panel 7 and the emission surface 6a of the backlight 6 increases, but this is not limiting. For example, at least one of the liquid crystal panel 7 and the backlight 6 may be moved in a direction where the distance d between a portion of the rear surface 7b of the liquid crystal panel 7 and a portion of the emission surface 6a of the backlight 6 increases, or the tilt angle θ of the liquid crystal panel 7 may be changed in a direction where the distance d between a portion of the rear surface 7b of the liquid crystal panel 7 and a portion of the emission surface 6a of the backlight 6 increases.

[0043] According to the virtual image display device, virtual image display method, and program disclosed herein, when image light of a display image is irradiated onto a reflective member, it is displayed as a virtual image. Light is irradiated onto the rear surface of a liquid crystal panel from the emission surface of a backlight. The backlight is locally dimmed by a control unit, so that an illumination segment corresponding to the display image is selected, and light from the selected illumination segment is irradiated onto the liquid crystal panel. The temperature of the liquid crystal panel is detected by a temperature detection unit. When the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, the control unit moves the display image in a direction increasing the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight. As a result, the selected illumination segment of the locally dimmed backlight is moved to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight increases, corresponding to the display image. As a result, the increase in ambient temperature caused by the backlight and the amount of light irradiated onto the liquid crystal panel are suppressed, thereby reducing the amount of heating of the liquid crystal panel, suppressing phase transition of the liquid crystal in the liquid crystal panel, and avoiding display defects.

[0044] The present disclosure can implement the following configurations (1) to (9).

[0045] (1) A virtual image display device that displays a virtual image by irradiating a reflective member with image light of a display image, the virtual image display device including: a liquid crystal panel having a display surface that displays the display image; a backlight that faces at an angle the rear surface of the liquid crystal panel opposite the display surface and has an emission surface that irradiates light onto the rear surface; and a control unit that divides the backlight into a plurality of lighting segments, performs local dimming control, and turns on the lighting segments that correspond to the display image; wherein the liquid crystal panel has regions where the distance between the rear surface and the emission surface of the backlight varies; and when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, the control unit moves the display image to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased, and selectively turns on the lighting segments that correspond to the display image.

[0046] (2) The virtual image display device according to the above configuration (1), wherein the liquid crystal panel is inclined with respect to the light exit surface of the backlight.

[0047] (3) The virtual image display device according to the above configuration (1) or (2), wherein the control unit includes a memory unit that stores a reference table in which the amount of movement of the display image is set using the distance between the back surface and the exit surface and the inclination angle as variables.

[0048] (4) The virtual image display device according to the above configuration (3), wherein the control unit refers to the reference table and selects a movement amount that exceeds a movement amount corresponding to a phase transition temperature of the liquid crystal.

[0049] (5) The virtual image display device according to any one of the above configurations (1) to (4), wherein the temperature detection unit detects the temperature of the center of the back surface of the liquid crystal panel.

[0050] (6) A virtual image display device described in any one of the above configurations (1) to (4), wherein the temperature detection unit detects the temperature of the part of the liquid crystal panel where the distance between the back surface and the backlight output surface is the smallest.

[0051] (7) The virtual image display device according to any one of the above configurations (1) to (6), wherein the control unit further reduces the display image.

[0052] (8) A virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, the virtual image display device including: a liquid crystal panel having a display surface that displays the display image; a backlight facing the back surface opposite the display surface of the liquid crystal panel and having an emission surface that irradiates light onto the back surface; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that divides the backlight into a plurality of lighting segments, performs local dimming control on the backlight, and turns on the lighting segments corresponding to the display image, the liquid crystal panel having regions where the distance between the back surface and the emission surface of the backlight varies; a virtual image display method comprising the steps of: preparing a virtual image display device; determining, by the control unit, whether the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature; and, when the detected temperature is equal to or higher than the predetermined temperature, moving the display image to a region where the distance between the back surface of the liquid crystal panel and the emission surface of the backlight is increased, and selectively turning on the lighting segments corresponding to the display image, by the control unit.

[0053] (9) A program for displaying a virtual image using the virtual image display device described in the above configuration (1), which causes a computer to function as a control unit that executes the steps of: determining whether the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature; and, when the detected temperature is equal to or higher than the predetermined temperature, moving the display image to an area where the distance between the back surface of the liquid crystal panel and the exit surface of the backlight is increased; and selectively lighting up the lighting segments corresponding to the display image using the backlight.

[0054] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible within the scope of the gist of the present disclosure. It goes without saying that all or part of the components constituting each of the above-described embodiments can be combined as appropriate within the scope of not contradicting each other.

[0055] REFERENCE SIGNS LIST 1 Virtual image display device 2 Display unit 3 Reflecting member 3a First reflecting member 3b Second reflecting member 4 Control unit 5 User 6 Backlight 6a Emission surface 61 Light-emitting diode 7 Liquid crystal panel 7a Display surface 7b Rear surface 8 Temperature detection unit 9 Memory unit 61 Light-emitting diode 62 Base 62a Main surface 63 Diffuser d, d0, d1, d2 Distance L1 Center line M1 Outside view M2 Display image M3 Virtual image θ Tilt angle

Claims

1. A virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, comprising: a liquid crystal panel having a display surface for displaying the display image; a backlight facing the rear surface of the liquid crystal panel opposite the display surface and having an emission surface for irradiating light onto the rear surface; a temperature detection unit that detects the temperature of the liquid crystal panel; and a control unit that divides the backlight into a plurality of lighting segments and performs local dimming control to light up the lighting segments corresponding to the display image, wherein the liquid crystal panel has areas where the distance between the rear surface and the emission surface of the backlight varies, and when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, the control unit moves the display image to an area where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased, and selectively lights up the lighting segments corresponding to the display image.

2. The virtual image display device according to claim 1, wherein the liquid crystal panel is inclined with respect to the emission surface of the backlight.

3. A virtual image display device as described in claim 1 or 2, wherein the control unit includes a memory unit that stores a reference table in which the amount of movement of the display image is set using the distance between the back surface and the exit surface and the inclination angle as variables.

4. The virtual image display device according to claim 3, wherein the control unit refers to the reference table and selects an amount of movement that exceeds an amount of movement that corresponds to a phase transition temperature of the liquid crystal.

5. The virtual image display device according to any one of claims 1 to 4, wherein the temperature detection section detects the temperature of the center of the rear surface of the liquid crystal panel.

6. A virtual image display device according to any one of claims 1 to 4, wherein the temperature detection unit detects the temperature of a portion of the liquid crystal panel where the distance between the rear surface and the backlight emission surface is the smallest.

7. The virtual image display device according to any one of claims 1 to 6, wherein the control unit further reduces the displayed image.

8. A virtual image display device that displays a virtual image by irradiating a reflective member with image light of a display image, the virtual image display device including a liquid crystal panel having a display surface for displaying the display image, a backlight facing a rear surface opposite the display surface of the liquid crystal panel and having an emission surface for irradiating light to the rear surface, a temperature detection unit that detects the temperature of the liquid crystal panel, and a control unit that divides the backlight into a plurality of lighting segments and performs local dimming control to light up the lighting segments corresponding to the display image, the liquid crystal panel having areas where the distance between the rear surface and the emission surface of the backlight varies, the virtual image display device comprising: a step of determining by the control unit whether the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature; and a step of moving the display image to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased and selectively lighting up the lighting segments corresponding to the display image, when the detected temperature is equal to or higher than the predetermined temperature, by the control unit.

9. A virtual image display device that displays a virtual image by irradiating image light of a display image onto a reflective member, the virtual image display device including a liquid crystal panel having a display surface for displaying the display image, a backlight facing the rear surface of the liquid crystal panel opposite the display surface and having an emission surface for irradiating light onto the rear surface, a temperature detection unit that detects the temperature of the liquid crystal panel, and a control unit that divides the backlight into a plurality of lighting segments and performs local dimming control to light up the lighting segments corresponding to the display image, the liquid crystal panel having areas where the distance between the rear surface and the emission surface of the backlight varies. A program for displaying a virtual image by a virtual image display device, the program causing a computer to function as a control unit that executes a step of determining whether the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature, and a step of moving the display image to a region where the distance between the rear surface of the liquid crystal panel and the emission surface of the backlight is increased when the detected temperature is equal to or higher than the predetermined temperature, and a step of causing the backlight to selectively light up the lighting segments corresponding to the display image.

Images