Virtual image display device and mobile object

Abstract

This virtual image display device includes: a transmissive display panel having an active area; a backlight having emission units that emit light in corresponding illumination regions of the active area; an optical system that forms an image of image light from the active area as a virtual image; and a control unit. The active area has an image display region and an image non-display region, and the control unit turns on an emission unit corresponding to an illumination region including the image display region. The control unit controls the backlight so that (a+b) / a is equal to or less than a predetermined value, where a represents a first luminance that is the background luminance of a virtual-image background region corresponding to an emission unit in a turned-off state, and b represents a second luminance that is the luminance of the image non-display region included in an illumination region illuminated by an emission unit in a turned-on state.

Description

Virtual image display device and mobile object

[0001] The present disclosure relates to a virtual image display device and a moving object.

[0002] 2. Description of the Related Art A head-up display such as that described in Patent Document 1 is known.

[0003] Patent No. 6299523

[0004] The virtual image display device of the present disclosure includes: a transmissive display panel having an active area for displaying an image; a backlight that irradiates light onto the active area, the backlight having irradiation units that irradiate light corresponding to each of a plurality of irradiation areas that divide the active area; an optical system that forms a virtual image from the image light emitted from the active area; and a control unit, wherein the active area has an image display area where an image is displayed and a non-image display area where an image is not displayed; and the control unit turns on the irradiation units among the plurality of irradiation units that correspond to the irradiation area including the image display area, and controls the backlight so that (a + b) / a is equal to or less than a predetermined value, where a background luminance of a background area of ​​the virtual image that corresponds to the irradiation units in the non-lit state is a first luminance a and a luminance of the non-image display area included in the irradiation area irradiated by the irradiation units in the lit state is a second luminance b.

[0005] A moving body according to the present disclosure includes the above-described virtual image display device.

[0006] Objects, features, and advantages of the present disclosure will become clearer from the following detailed description and drawings. Fig. 1 is a cross-sectional view of a main part showing a virtual image display device according to an embodiment of the present disclosure. Fig. 2 is a cross-sectional view of a main part showing an example of a moving body equipped with the virtual image display device of Fig. 1. Fig. 3 is a front view showing an example of an image displayed on an active area. Fig. 4 is a front view showing an example of a virtual image viewed by a user. Fig. 5 is a partially enlarged front view showing an enlarged view of part A of Fig. 4. Fig. 6 is a diagram illustrating calculation of background contrast. Fig. 7 is a cross-sectional view of a main part showing a backlight. Fig. 8 is a cross-sectional view of a main part showing a virtual image display device according to another embodiment of the present disclosure. Fig. 9 is a front view showing an example of a virtual image viewed by a user of the virtual image display device of Fig. 8.

[0007] Various head-up displays have been proposed that are mounted on a moving object such as a vehicle and allow the driver of the moving object to view a virtual image superimposed on the view ahead. A head-up display includes, for example, a liquid crystal display device including a liquid crystal display panel and a backlight, and an optical system that projects image light emitted from the liquid crystal display device as a virtual image into the user's field of view. For example, the head-up display described in Patent Document 1 has a backlight with multiple lighting segments arranged to divide the light source surface, and is configured to perform local dimming control to light only the lighting segments directly below the area where the liquid crystal display panel displays an image.

[0008] With conventional head-up displays, when local dimming control is performed, the outline of the virtual image seen by the user becomes blurred, making it difficult to see the outline of the virtual image, which can result in the user having difficulty seeing the virtual image.

[0009] 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.

[0010] Fig. 1 is a cross-sectional view of a main part of a virtual image display device according to an embodiment of the present disclosure, and Fig. 2 is a cross-sectional view of a main part of an example of a moving body equipped with the virtual image display device of Fig. 1. Fig. 3 is a front view showing an example of an image displayed in an active area, Fig. 4 is a front view showing an example of a virtual image viewed by a user, Fig. 5 is a partially enlarged front view showing an enlarged view of part A of Fig. 4, Fig. 6 is a diagram for explaining calculation of background contrast, and Fig. 7 is a cross-sectional view of a main part showing a backlight. Fig. 8 is a cross-sectional view of a main part of a virtual image display device according to another embodiment of the present disclosure, and Fig. 9 is a front view showing an example of a virtual image viewed by a user of the virtual image display device of Fig. 8.

[0011] As shown in Fig. 1 , the virtual image display device 1 of this embodiment includes a transmissive display panel 2, a backlight 3, an optical system 4, and a control unit 5. The virtual image display device 1 is also called a head-up display (HUD). As shown in Fig. 2 , the virtual image display device 1 may be mounted on a vehicle 20, which is a mobile object. The virtual image display device 1 may also be mounted on a mobile object such as a ship or an aircraft. The virtual image display device 1 allows a user (e.g., a driver or passenger of the mobile object) 7 to view a virtual image Q that overlaps with a foreground (also referred to as an external view).

[0012] The display panel 2 has an active area 21 that displays an image. The active area 21 is also referred to as an effective portion of the display surface. The display surface may include the effective portion and a non-effective portion (also referred to as a non-display portion or black portion) around the effective portion, or the entire display surface may be the effective portion. The active area 21 includes a plurality of subpixels arranged in a grid pattern along a first direction and a second direction intersecting the first direction. The first direction may be the horizontal direction. The second direction may be the vertical direction. Each subpixel corresponds to one of red, green, and blue, and a group of three subpixels, red, green, and blue, may constitute one pixel. One pixel is also referred to as one picture element.

[0013] The display panel 2 may be a liquid crystal display panel. The liquid crystal display panel may be a known liquid crystal display panel. Examples of known liquid crystal display panels include in-plane switching (IPS) panels, fringe field switching (FFS) panels, vertical alignment (VA) panels, and electrically controlled birefringence (ECB) panels.

[0014] The backlight 3 is located on the rear side (the side opposite to the display surface) of the display panel 2. The backlight 3 has a light source surface 3 a, and irradiates light from the light source surface 3 a onto the display panel 2. The irradiated display panel 2 emits image light L of the image displayed on the active area 21.

[0015] The backlight 3 includes a plurality of illumination units 31. Each of the plurality of illumination units 31 includes at least one light source 32 (see FIG. 7 ) (also referred to as a light-emitting element 32). The light source 32 may be a self-luminous element such as a light-emitting diode (LED) element, an organic light-emitting diode (OLED) element, or a semiconductor laser (LD) element. The LED element may be a mini-LED element or a micro-LED element.

[0016] The backlight 3 may be a direct type backlight. The backlight 3 is made of a fluoride red phosphor (K2SiF6:Mn 4+ In this case, the KSF type backlight 3 can prevent a decrease in the color purity of the virtual image. 4+ This is because KSF (Korean Fluorescent Phosphor) is a type of line-emitting phosphor that has a wide color gamut and a narrow wavelength spectrum width of the three primary colors RGB (high sharpness of the wavelength spectrum).

[0017] The display panel 2 may be configured to be inclined with respect to the backlight 3. In this case, the virtual image Q is displayed so that the lower side is closer to the user 7 and the upper side is farther from the user 7. This allows the user 7 to view the virtual image Q with a sense of perspective and three-dimensionality. The angle of inclination may be, for example, between 10° and 45°, but is not limited to this range.

[0018] The multiple irradiation units 31 illuminate multiple irradiation regions 33 formed by partitioning the active area 21. One irradiation unit 31 corresponds to one irradiation region 33. That is, in a plan view (top view) viewed from the display surface side, one irradiation unit 31 may be located directly below one irradiation region 33. One irradiation unit 31 includes at least one light-emitting element 32. Below, a case where one light-emitting element 32 is included in one irradiation unit 31 will be described. Each irradiation region 33 may include, for example, several tens to several hundreds of pixels. The multiple irradiation regions 33 may be regions obtained by partitioning the active area 21 in a matrix. The multiple irradiation regions 33 may be configured not to overlap each other, or adjacent irradiation regions 33 may be configured to partially overlap each other.

[0019] The optical system 4 is located in the optical path of the image light L emitted from the active area 21. The optical system 4 projects the image light L emitted from the active area 21 as a virtual image Q into the field of view of the user 7. The optical system 4 may control the optical path length and traveling direction of the image light L so that the image viewed by the user 7 is enlarged or reduced. The optical system 4 may control the traveling direction of the image light L so that the shape of the image viewed by the user 7 is deformed based on a predetermined matrix pattern.

[0020] The optical system 4 may include mirrors 4a and 4b, which are reflective members. The number of mirrors 4a and 4b constituting the optical system 4 is not limited to two, and may be one, or three or more. The mirrors 4a and 4b may be concave mirrors, convex mirrors, flat mirrors, etc. If the mirrors 4a and 4b are concave or convex mirrors, the shape of the mirrors 4a and 4b may include at least a portion of a spherical, aspherical, or free-form surface. The optical system 4 is not limited to mirrors 4a and 4b, but may also include lenses. The lenses may be concave lenses, convex lenses, etc. Convex lenses include biconvex lenses, plano-convex lenses, and convex meniscus lenses. Concave lenses include biconcave lenses, plano-concave lenses, and concave meniscus lenses. The lens shape may include at least a portion of a spherical, aspherical, or free-form surface. The optical system 4 is not limited to mirrors 4a and 4b and lenses, but may also include various other optical components, such as hologram elements. When the virtual image display device 1 is mounted on a vehicle 20 that has a windshield, the windshield of the vehicle 20 may constitute a part of the optical system 4 .

[0021] The mirrors 4a and 4b may be free-form reflecting mirrors. A free-form reflecting mirror can suppress aberration of its reflected light and reduce distortion of the virtual image Q. The free-form reflecting mirror may be an XY polynomial surface (also called an SPS XYP surface) defined by the following formulas (1) and (2). The XY polynomial surface is expanded into polynomials of up to the tenth degree that are added to the reference conic surface. Therefore, in formulas (1) and (2), the sum of m and n is 10 or less. In formula (1), z is the sag of the surface parallel to the z-axis (also called the optical axis), c is the vertex curvature, and r is the radial distance (i.e., r ２ = x ２ +y ２ ), k is the conic constant, and Cj is the monomial x ｍ y ｎ is the coefficient of

[0022] As shown in FIG. 1 , the optical system 4 includes a mirror 4a, which is a first concave reflecting member that faces the display panel 2 at an angle, and a mirror 4b, which is a second concave reflecting member that faces the mirror 4a at an angle. The mirror 4b may have a transflective concave surface. The mirrors 4a and 4b suppress diffusion of the image light L and converge it toward the user 7, thereby preventing a decrease in brightness and resolution of the virtual image Q generated by the image light L. The concave surfaces of the mirrors 4a and 4b may be spherical, elliptical, hyperbolic, free-form, or the like. Furthermore, since the windshield of a moving body such as an automobile (e.g., vehicle 20) has a transflective concave surface, with the surface facing the user 7 being concave, the mirror 4b may be the windshield.

[0023] The curvature of mirror 4b may be smaller than that of mirror 4a. The curvature may be the curvature of the concave surface, or if the concave surface is aspherical, the curvature may be the average curvature of the entire concave surface. Mirror 4a may have a relatively large curvature to converge the image light L of the liquid crystal display panel, which is divergent and has an angle of view. Mirror 4b, which forms a defocused virtual image formed by reflected light (divergent light) of the image light L, may have a relatively small curvature. Therefore, mirror 4b may be a plane mirror. The curvature of mirror 4a may be more than 1 time and up to about 3 times the curvature of mirror 4b, but is not limited to this range.

[0024] The curvature may be defined as follows: When the mirror 4a is a concave mirror, in a cross section along the optical axis of the image light L incident on the mirror 4a, the length of a line segment (line segment LS) that passes through the center of the reflecting surface of the mirror 4a and connects both ends is defined as 2×H, and the maximum length (also referred to as the maximum depth) of the direction along the optical axis between a point on the reflecting surface and the line segment LS is defined as D. ＭＡＸ When D ＭＡＸ / H. ＭＡＸ When / H changes depending on how the cross section is taken, D when the position of the cross section is changed ＭＡＸ The maximum value of / H may be used as the curvature.

[0025] The control unit 5 may be connected to each component of the virtual image display device 1. The control unit 5 may be configured to control each component. Components controlled by the control unit 5 include the display panel 2, the backlight 3, and the optical system 4. The control unit 5 may be configured as, for example, a processor. The control unit 5 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 an FPGA (field-programmable gate array). The control unit 5 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 5 may include a memory unit that stores various information or programs for operating each component of the virtual image display device 1. The storage unit may be configured, for example, by a semiconductor memory, etc. The storage unit may function as a work memory for the control unit 5.

[0026] The control unit 5 performs local dimming control of the backlight 3. The local dimming control performed by the control unit 5 will be described below. As shown in FIG. 3 , the active area 21 has an image display region P where an image is displayed and an image non-display region N where no image is displayed. The image display region P and the image non-display region N may move, rotate, or expand or contract over time. The image display region P and the image non-display region N may disappear or appear over time.

[0027] The control unit 5 can individually control the lighting and non-lighting states of the multiple illumination units 31. As shown in FIGS. 3 and 4 , the control unit 5 turns on the illumination units 31 (also referred to as display-corresponding illumination units 31a) corresponding to the illumination areas 33 (also referred to as display-corresponding illumination areas 33a) that include the image display area P. The control unit 5 also turns on the illumination units 31 (also referred to as display-non-corresponding illumination units 31b) corresponding to the illumination areas 33 (also referred to as display-non-corresponding illumination areas 33b) that do not include the image display area P. In other words, the control unit 5 turns on the light sources 32 in the display-corresponding illumination units 31a and turns off the light sources 32 in the display-non-corresponding illumination units 31b. This makes it possible to make the image display area P brighter than the image non-display area N and the image non-display area N darker than the image display area P, thereby increasing the contrast ratio of the image displayed in the active area 21 and, as a result, increasing the contrast ratio of the virtual image Q viewed by the user 7. Furthermore, by controlling the backlight 3 by local dimming, it is possible to suppress the occurrence of the postcard phenomenon in which the light source surface 3a of the backlight 3 is faintly reflected as a background image of the virtual image Q. Furthermore, by turning off some of the multiple irradiation units 31, it is possible to reduce the power consumption of the backlight 3.

[0028] The control unit 5 may turn on only the display-corresponding irradiation unit 31a corresponding to the display-corresponding irradiation area 33a including the image display area P. In this case, it is possible to further reduce the power consumption of the backlight 3. The control unit 5 may also turn off the light source 32 in the display-non-corresponding irradiation unit 31b in the non-image display area N that covers the range where the postcard phenomenon occurs.

[0029] 4, the virtual image displayable region R of the virtual image display device 1 is composed of a virtual image region V and a background region B. The virtual image displayable region R is a region corresponding to the entire active area 21, i.e., a region representing the maximum size of the virtual image Q that can be projected into the visual field of the user 7. The virtual image region V is a region corresponding to the image display region P of the active area 21, i.e., a region where the image display region P is projected into the visual field of the user 7. The background region B is a region corresponding to the image non-display region N of the active area 21, and is a region other than the virtual image region V in the virtual image displayable region R.

[0030] As described above, local dimming control of the backlight 3 can increase the contrast ratio between the virtual image region V and the background region B. However, as shown in FIGS. 3 to 5 , the display-corresponding illumination region 33a may include an image display region P and a non-image display region N. In this case, in the display-corresponding illumination region 33a, light emitted from the light source 32 of the display-corresponding illumination unit 31a passes through the non-image display region N included in the display-corresponding illumination region 33a with low light transmittance. As a result, the non-image display region N included in the display-corresponding illumination region 33a is not completely black, and the purity of the black is reduced compared to the display-non-corresponding illumination region 33b where the light source 32 is not lit. Furthermore, the light emitted from the light source 32 of the display-corresponding illumination unit 31a has a component that migrates from the image display region P to the non-image display region N in the display-corresponding illumination region 33a. As a result, as shown in FIG. 5 , a phenomenon (hereinafter also referred to as a halo phenomenon) in which the background region B surrounding the virtual image region V becomes brighter may occur. When the halo phenomenon occurs, the outline of the virtual image area V viewed by the user 7 becomes blurred, making it difficult for the user 7 to view the outline of the virtual image area V, and making it difficult for the user 7 to view the virtual image area V. The halo phenomenon is likely to occur when the background luminance in the field of view of the user 7 is low, and also when the emission luminance of the illuminating unit 31 in the lit state is high.

[0031] The control unit 5 controls the backlight 3 so that the background contrast c is equal to or less than a predetermined value (hereinafter also referred to as a predetermined value t) in order to suppress the occurrence of the halo phenomenon. The background contrast c is determined by adjusting the background luminance in the visual field of the user 7 to a first luminance a (cd / m ２), and the luminance in the visual field of the user 7 of the image non-display area N included in the display-corresponding illumination area 33a illuminated by the illumination unit 31 in the lit state is defined as a second luminance b (cd / m ２ ), c is expressed as c = (a + b) / a. The second luminance b corresponds to the luminance when the user 7 views the image non-display area N included in the display-corresponding illumination area 33a illuminated by the illumination unit 31, and does not include the contribution of the first luminance a. The control unit 5 can calculate the second luminance b based on, for example, the light emission luminance (light emission luminance distribution) of the illumination unit 31, the light transmittance of the active area 21, etc.

[0032] For example, the display panel 2 may be a liquid crystal display panel, and the light transmittance of the active area 21 may be set by electrically controlling the liquid crystals provided in the liquid crystal display panel. That is, the transmittance of light passing through the pixel can be set by controlling the voltage applied to the pixel electrodes provided in the pixels of the liquid crystal display panel to change the orientation of the liquid crystal molecules. For example, when no voltage is applied to the liquid crystal, the rod-shaped liquid crystal molecules are oriented along the display surface, resulting in minimum light transmittance. When a voltage (approximately 3 V to approximately 5 V) is applied to the liquid crystal, the rod-shaped liquid crystal molecules are oriented perpendicular to the display surface, improving light transmittance. The maximum light transmittance of the liquid crystal display panel is approximately 5% to approximately 10%, and the minimum light transmittance is approximately 0.005% to approximately 0.1%. Therefore, slight light leakage occurs in the image-non-display area N included in the display-corresponding illumination area 33a.

[0033] When the background contrast c is greater than a predetermined value t, the portion of the background region B adjacent to the virtual image region V becomes brighter, resulting in bright and dark portions in the background region B and the occurrence of a halo. By setting the background contrast c to the predetermined value t or less, the occurrence of the halo can be suppressed, making it easier for the user 7 to view the virtual image region V.

[0034] Table 1 shows the results of simulation experiments confirming the occurrence of the halo phenomenon under various environments. The simulation experiments were conducted using a simulator in which an optical system 4 projects image light from a display panel 2 onto a transparent substrate made of a glass substrate simulating an automobile windshield, generating a virtual image Q. Furthermore, to enable adjustment of the illuminance of the environment surrounding the simulator, a lighting device with adjustable illuminance and an openable blackout curtain that blocks ambient light and the light from the lighting device may be provided around the simulator. The illuminance of the environment surrounding the simulator may also be set in natural conditions without using a lighting device or a blackout curtain. Table 1 shows the case where the illuminance of the environment surrounding the simulator is set in natural conditions.

[0035] "Environment" in Table 1 indicates a time period. "Night" may be, for example, a time period from 6 PM to 3 AM. "Evening" may be, for example, a time period from 3 PM to 6 PM. "Day" may be, for example, a time period from 9 AM to 3 PM. "First luminance a" is a typical background luminance (cd / m) under each environment. 2 , cd: candela). The "brightness of the virtual image area" is the brightness of the virtual image area V, and is set so that the user 7 can see the virtual image area V under each environment (cd / m 2 The "second luminance b" indicates the luminance (cd / m) of the image non-display area N included in the display-corresponding illumination area 33a illuminated by the illumination unit 31 within the visual field of the user 7. 2 ). Table 1 shows the second luminance b calculated based on the light emission luminance distribution of the irradiation unit 31, the light transmittance of the active area 21, the distance between the backlight 3 and the display panel 2, etc. The background contrast c shows a value calculated using the formula c = (a + b) / a. "Halo phenomenon" shows the result of visually checking whether or not the halo phenomenon occurs in the image of the virtual image displayable region R generated by a simulation experiment (see Figures 4 and 5).

[0036]

[0037] As can be seen from Table 1, the occurrence of the halo phenomenon can be suppressed by setting the background contrast c to a predetermined value t or less. As a result, the user 7 can easily view the virtual image region V. The control unit 5 can set the background contrast c to a predetermined value t or less by controlling the brightness of the virtual image region V. The control unit 5 can control the brightness of the virtual image region V by controlling the light emission brightness of the illuminating unit 31 in the lit state. The predetermined value t may be set to 4 or less, or may be set to 3.5 or less.

[0038] The control unit 5 may control the light emission brightness of the illuminating unit 31 in the lit state based on a table indicating the correspondence between time periods such as "night," "evening," and "daytime" and the brightness of the virtual image region V. In this case, the occurrence of a halo phenomenon can be suppressed and the visibility of the virtual image region V can be improved while reducing the processing burden on the control unit 5. When the virtual image display device 1 is mounted on a vehicle 20, the control unit 5 may control the light emission brightness of the illuminating unit 31 in the lit state based on a table indicating the correspondence between time periods (night, evening, daytime, etc.), weather around the vehicle 20 (sunny, cloudy, rainy, snowy, etc.), road surface conditions (dry, wet, snow-covered, etc.), and the brightness of the virtual image region V. In this case, the occurrence of a halo phenomenon can be further suppressed and the visibility of the virtual image region V can be further improved while reducing the processing burden on the control unit 5. The control unit 5 may include an external communication device. In this case, the control unit 5 may acquire information regarding the weather around the vehicle 20, the road surface conditions, etc. from a network via the external communication device. The virtual image display device 1 may include an imaging device that captures images of the area in front of the vehicle 20. In this case, the control unit 5 may acquire images from the imaging device and perform image analysis of the acquired images to determine the weather around the vehicle 20, the condition of the road surface, etc.

[0039] The control unit 5 may execute control when the first luminance a becomes equal to or less than a predetermined luminance. The background contrast c = (a + b) / a tends to increase as the first luminance a decreases. In other words, the halo phenomenon becomes more easily visible. Therefore, the predetermined luminance is set to 100 (cd / m 2 ) and 10 (cd / m 2 ) and 1 (cd / m 2 ), but is not limited to these values.

[0040] As shown in FIG. 2 , the virtual image display device 1 may include a luminance meter 6 that measures the background luminance of the user 7's field of view. The luminance meter 6 may be a surface luminance meter arranged so that its light-receiving surface faces forward in the user 7's field of view (the direction of the user 7's line of sight). While FIG. 1 shows an example in which the luminance meter 6 is located on the ceiling of the vehicle cabin, the luminance meter 6 may be located anywhere inside or outside the vehicle 20. The luminance meter 6 may be located inside or on the dashboard. The control unit 5 may acquire the background luminance of the user 7's field of view from the luminance meter 6 and use the acquired background luminance as a first luminance a used to calculate the background contrast c. The control unit 5 and the luminance meter 6 are connected via wired or wireless communication. When the virtual image display device 1 is installed in the vehicle 20, the control unit 5 and the luminance meter 6 may be connected via a network within the vehicle 20, such as a control area network (CAN).

[0041] The virtual image display device 1 may not include the luminance meter 6. The control unit 5 may acquire the background luminance in the field of view of the user 7 from an external luminance meter, and may use the acquired background luminance as the first luminance a used to calculate the background contrast c. The external luminance meter may be a luminance sensor provided in the vehicle 20. The control unit 5 may acquire the background luminance from the luminance sensor via an ECU (Electronic Control Unit) of the vehicle 20.

[0042] Next, a more detailed description will be given of the configuration of the backlight 3. The backlight 3 includes a plurality of light sources 32, a substrate 34, and a reflector 35, as shown in FIG.

[0043] The substrate 34 may be made of, for example, a glass material, a ceramic material, a resin material, a metal material, a semiconductor material, or the like. The substrate 34 has a first surface 34a, and the plurality of light sources 32 are arranged on the first surface 34a. The plurality of light sources 32 may be arranged in a matrix at a predetermined pitch S. Electrode pads to which the light sources 32 are connected, wiring conductors for driving the light sources 32, and the like are located on the first surface 34a.

[0044] The reflector 35 is located on the first surface 34a. When viewed from a direction perpendicular to the first surface 34a, the reflector 35 may have a lattice shape. At least one light source 32 is located in each region of the first surface 34a partitioned by the reflector 35. The side surface 35a of the reflector 35 facing the light source 32 may be light reflective. The side surface 35a of the reflector 35 may be made of a metal material such as aluminum (Al) or silver (Ag). The reflector 35 can suppress diffusion of light emitted from the light source 32 in the planar direction of the first surface 34a.

[0045] 7 , the virtual image display device 1 may include a first lens member 8, a second lens member 9, and a diffuser plate 10. The first lens member 8, the second lens member 9, and the diffuser plate 10 may be located between the backlight 3 and the display panel 2. The first lens member 8 may constitute a part of the backlight 3. The light source surface 3 a of the backlight 3 may be the surface of the first lens member 8 facing the display panel 2.

[0046] The first lens member 8 condenses the light emitted from each irradiation unit 31. The first lens member 8 may be a microlens array in which a plurality of microlenses are arranged two-dimensionally. Each microlens may be, for example, a biconvex lens, a plano-convex lens, a convex meniscus lens, or the like. The first lens member 8 may be a compound lens combining two cylindrical lenses, or may be a prism sheet.

[0047] The second lens member 9 anisotropically diffuses light that has passed through the first lens member 8. The second lens member 9 has a diffusion power in a first direction (horizontal direction) that is different from that in a second direction (vertical direction), and anisotropically diffuses and emits incident light. The diffusion power in the first direction and the diffusion power in the second direction may be set according to the dimensions of the illumination area 33 in the first direction and the second direction. When light collected by the first lens member 8 enters the second lens member 9, the second lens member 9 can diffuse the incident light at a diffusion angle (also referred to as a light distribution angle) as designed.

[0048] The second lens member 9 may be a lens member having a large number of microlenses regularly arranged on the surface of a plate-like or sheet-like member made of transparent resin. The second lens member 9 may also be a microlens array having a plurality of microlenses arranged two-dimensionally. Each microlens may be, for example, a biconcave lens, a plano-concave lens, a concave meniscus lens, or the like.

[0049] Diffusion plate 10 diffuses the light emitted from second lens member 9. Diffusion plate 10 may be composed of, for example, a substrate made of transparent resin, glass, or the like, and light-diffusing particles made of silicone resin, polystyrene resin, silica, calcium carbonate, or the like dispersed in the substrate.

[0050] The virtual image display device 1 includes the first lens member 8, the second lens member 9, and the diffuser 10, so that each of the multiple irradiators 31 can uniformly irradiate the corresponding irradiation area 33. As a result, the effectiveness of local dimming control can be improved, and the effectiveness of background contrast control (control for keeping the background contrast c equal to or less than a predetermined value t) can be improved. As a result, the user 7 can view a highly visible virtual image Q.

[0051] As shown in FIG. 3 , the image displayed in the active area 21 may include a partial image P1 consisting only of graphics and a partial image P2 consisting of text. The control unit 5 may perform background contrast control only on the illumination unit 31 that illuminates the partial image P2, and not on the illumination unit 31 that illuminates the partial image P1. In this case, the visibility of the virtual image of the partial image P2 can be improved while reducing the processing burden on the control unit 5. In other words, the information indicated by the partial image P2 can be conveyed to the user 7 while reducing the processing burden on the control unit 5. The partial image consisting only of graphics may be, for example, an arrow indicating the turning direction of the vehicle 20, an icon indicating an obstacle (pedestrian, other vehicle, etc.) located ahead of the vehicle 20, an icon indicating a road sign, etc. The partial image consisting of text may be, for example, an image indicating the speed of the vehicle 20, engine speed, remaining fuel level, etc.

[0052] Furthermore, when there are partial images P1 and P2 with different sizes (for example, display area), the control unit 5 performs background contrast control only on the irradiation unit 31 that irradiates the relatively small-sized partial image P2, and does not need to perform background contrast control on the irradiation unit 31 that irradiates the relatively large-sized partial image P1. In this case, the background contrast control is performed only on the irradiation unit 31 that irradiates the relatively small-sized partial image P2, which is more likely to be difficult to see due to the halo phenomenon, making it possible to improve the visibility of the virtual image of the partial image P2 while reducing the processing load on the control unit 5.

[0053] Furthermore, when there are partial images P1 and P2 with different display periods (e.g., periods in seconds or minutes), the control unit 5 performs background contrast control only on the irradiation unit 31 that irradiates the partial image P2 with the relatively long display period, and does not have to perform background contrast control on the irradiation unit 31 that irradiates the partial image P1 with the relatively short display period. In this case, the background contrast control is performed only on the irradiation unit 31 that irradiates the partial image P2 with the relatively long display period, which is difficult to see for a long period due to the halo phenomenon. This makes it possible to improve the visibility of the virtual image of the partial image P2 while reducing the processing load on the control unit 5.

[0054] Furthermore, when there are partial images P1 and P2 with different display brightnesses, the control unit 5 performs background contrast control only on the irradiation unit 31 that irradiates the partial image P2 with a relatively high brightness, and does not have to perform background contrast control on the irradiation unit 31 that irradiates the partial image P1 with a relatively low brightness. In this case, the background contrast control is performed only on the irradiation unit 31 that irradiates the partial image P2 with a relatively high brightness, which is likely to be more difficult to see due to the halo phenomenon, and therefore it is possible to improve the visibility of the virtual image of the partial image P2 while reducing the processing load on the control unit 5.

[0055] Furthermore, the control unit 5 may control the value of c = (a + b) / a to increase when the speed of the moving object is increasing (when accelerating), and may control the value of c = (a + b) / a to decrease when the speed of the moving object is decreasing (when decelerating). For example, when accelerating, the second luminance b may be increased so that the value of c = (a + b) / a increases as the speed increases, and may be increased within a range of 1 to 4. In this case, even if the speed of the moving object increases, the second luminance b increases, making the virtual image Q more visible. Furthermore, for example, when decelerating, the second luminance b may be decreased as the speed decreases, making the value of c = (a + b) / a smaller, and may be decreased within a range of 1 to 4. In this case, because the speed of the moving object decreases, the visibility of the virtual image Q is less likely to deteriorate even if the second luminance b is decreased.

[0056] The virtual image display device 1 may include an optical element that separates the image light L emitted from the active area 21 into left-eye image light that enters the left eye of the user 7 and right-eye image light that enters the right eye. In this case, it is possible to allow the user 7 to view a three-dimensional virtual image Q. The optical element may be a parallax barrier or a lenticular lens. The parallax barrier may be a liquid crystal shutter. The optical element may be located after the display panel 2 in the traveling direction of light emitted from the backlight 3, or may be located between the backlight 3 and the display panel 2.

[0057] As shown in Fig. 8, the virtual image display device 1 may have a configuration in which the active area 21 is inclined with respect to the light source surface 3a of the backlight 3. In this case, as shown in Fig. 9, the user 7 can view a virtual image Q with excellent visibility and a sense of depth. The inclination angle θ of the active area 21 with respect to the light source surface 3a may be approximately 10° to 45°.

[0058] According to the present disclosure, it is possible to allow a user to view a virtual image with excellent visibility.

[0059] 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.

[0060] Vehicles in the present disclosure may include, for example, automobiles, industrial vehicles, rail vehicles, utility vehicles, and fixed-wing aircraft that travel on runways. Automobiles may include, for example, passenger cars, trucks, buses, motorcycles, and trolleybuses. Industrial vehicles may include, for example, agricultural and construction industrial vehicles. Industrial vehicles may include, for example, forklifts and golf carts. Agricultural industrial vehicles may include, for example, tractors, cultivators, transplanters, binders, combines, and lawn mowers. Construction industrial vehicles may include, for example, bulldozers, scrapers, excavators, cranes, dump trucks, and road rollers. Vehicles may include human-powered vehicles. Vehicle classifications are not limited to the above examples. For example, automobiles may include industrial vehicles that can travel on roads. The same vehicle may be included in multiple classifications. Marine vessels in the present disclosure may include, for example, marine jets, boats, and tankers. Aircraft in the present disclosure may include, for example, fixed-wing aircraft and rotary-wing aircraft.

[0061] The present disclosure can be implemented in the following configurations (1) to (16).

[0062] (1) A virtual image display device including: a transmissive display panel having an active area for displaying an image; a backlight that irradiates light onto the active area, the backlight having irradiation units that irradiate light corresponding to each of a plurality of irradiation areas formed by partitioning the active area; an optical system that focuses the image light emitted from the active area as a virtual image; and a control unit, wherein the active area has an image display area where an image is displayed and a non-image display area where an image is not displayed, and the control unit turns on the irradiation units among the plurality of irradiation units that correspond to the irradiation area including the image display area, and controls the backlight so that (a + b) / a is equal to or less than a predetermined value, where a background luminance of a background area of ​​the virtual image corresponding to the irradiation units in the non-lighting state is a first luminance a and a luminance of the non-image display area included in the irradiation area irradiated by the irradiation units in the lit state is a second luminance b.

[0063] (2) The virtual image display device according to (1), wherein the predetermined value is 4 or less.

[0064] (3) The virtual image display device according to (1) or (2) above, further comprising a luminance meter that measures the background luminance, wherein the control unit acquires the background luminance from the luminance meter and defines the acquired background luminance as the first luminance a.

[0065] (4) The virtual image display device according to (3), wherein the control unit controls the backlight when the first luminance a becomes equal to or lower than a predetermined luminance.

[0066] (5) The predetermined luminance is 100 cd / m 2 (cd: candela) The virtual image display device according to (4) above.

[0067] (6) A virtual image display device described in any one of (1) to (5) above, wherein the control unit calculates the second luminance b based on the light emission luminance of the irradiation unit in a lit state and the light transmittance of the active area.

[0068] (7) The virtual image display device according to (6), wherein the display panel is a liquid crystal display panel, and the light transmittance of the active area is set by electrically controlling a liquid crystal provided in the liquid crystal display panel.

[0069] (8) The virtual image display device according to any one of (1) to (7) above, wherein the backlight includes a plurality of light-emitting elements having a fluoride red phosphor.

[0070] (9) The virtual image display device according to any one of (1) to (8), wherein the display panel is inclined with respect to the backlight.

[0071] (10) The virtual image display device according to any one of (1) to (9) above, wherein the optical system includes a reflecting member.

[0072] (11) The virtual image display device described in (10) above, wherein the optical system comprises a first concave reflecting member that faces the display panel at an angle, and a second concave reflecting member that faces the first reflecting member at an angle, and the second concave reflecting member has a transmissive-reflective concave surface.

[0073] (12) The virtual image display device according to (11), wherein the curvature of the concave surface of the second concave reflecting member is smaller than the curvature of the concave surface of the first concave reflecting member.

[0074] (13) A moving body including the virtual image display device according to any one of (1) to (12) above.

[0075] (14) The moving body according to (13), wherein the optical system includes a windshield, and the virtual image is generated by projecting the image light onto the windshield.

[0076] (15) A moving body as described in (13) or (14) above, comprising a luminance meter for measuring the background luminance, the luminance meter having a light receiving surface facing forward in the user's field of view, and the control unit acquiring the background luminance from the luminance meter and setting the acquired background luminance as the first luminance a.

[0077] (16) A moving body described in any of (13) to (15) above, wherein the control unit controls the value of (a+b) / a to increase when the speed of the moving body is increasing, and controls the value of (a+b) / a to decrease when the speed of the moving body is decreasing.

[0078] REFERENCE SIGNS LIST 1 Virtual image display device 2 Display panel 21 Active area (display surface) 3 Backlight 31 Irradiation section 31a Display-corresponding irradiation section 31b Display-non-corresponding irradiation section 32 Light source (light-emitting element) 33 Irradiation area 33a Display-corresponding irradiation area 33b Display-non-corresponding irradiation area 34 Substrate 34a First surface 35 Reflector 35a Side surface 4 Optical system 4a, 4b Mirror 5 Control section 6 Luminance meter 7 User 8 First lens member 9 Second lens member 10 Diffuser 20 Vehicle R Virtual image displayable area V Virtual image area B Background area L Image light P Image display area N Image non-display area Q Virtual image

Claims

1. A virtual image display device comprising: a transmissive display panel having an active area for displaying an image; a backlight which irradiates light onto the active area, the backlight having an irradiation unit which irradiates light corresponding to each of a plurality of irradiation areas formed by partitioning the active area; an optical system which forms a virtual image from the image light emitted from the active area; and a control unit, wherein the active area has an image display area where an image is displayed and a non-image display area where an image is not displayed, and the control unit turns on the irradiation units among the plurality of irradiation units which correspond to the irradiation area including the image display area, and controls the backlight so that (a+b) / a is equal to or less than a predetermined value, where a background luminance of a background area of ​​the virtual image corresponding to the irradiation units in a non-lighted state is a first luminance a and a luminance of the non-image display area included in the irradiation area irradiated by the irradiation units in a lit state is a second luminance b.

2. The virtual image display device according to claim 1, wherein the predetermined value is 4 or less.

3. A virtual image display device as described in claim 1 or 2, further comprising a luminance meter that measures the background luminance, wherein the control unit acquires the background luminance from the luminance meter and sets the acquired background luminance as the first luminance a.

4. The virtual image display device according to claim 3, wherein the control unit executes control of the backlight when the first luminance a becomes equal to or lower than a predetermined luminance.

5. The predetermined luminance is 100 cd / m 2 5. The virtual image display device according to claim 4, wherein the luminance is in the range of 1000 to 10000 cd (candela).

6. A virtual image display device according to any one of claims 1 to 5, wherein the control unit calculates the second luminance b based on the emission luminance of the irradiation unit in a turned-on state and the light transmittance of the active area.

7. The virtual image display device according to claim 6, wherein the display panel is a liquid crystal display panel, and the light transmittance of the active area is set by electrically controlling liquid crystal provided in the liquid crystal display panel.

8. The virtual image display device according to any one of claims 1 to 7, wherein the backlight comprises a plurality of light-emitting elements having a fluoride red phosphor.

9. The virtual image display device according to any one of claims 1 to 8, wherein the display panel is inclined with respect to the backlight.

10. The virtual image display device according to any one of claims 1 to 9, wherein the optical system includes a reflecting member.

11. The virtual image display device described in claim 10, wherein the optical system comprises a first concave reflecting member facing the display panel at an angle, and a second concave reflecting member facing the first reflecting member at an angle, and the second concave reflecting member has a transmissive-reflective concave surface.

12. The virtual image display device according to claim 11, wherein the degree of curvature of the concave surface of the second concave reflecting member is smaller than the degree of curvature of the concave surface of the first concave reflecting member.

13. A moving object including a virtual image display device according to any one of claims 1 to 12.

14. The moving body according to claim 13, wherein the optical system includes a windshield, and the virtual image is generated by projecting the image light onto the windshield.

15. A moving body as described in claim 13 or 14, comprising a luminance meter for measuring the background luminance, the luminance meter having a light receiving surface facing forward in the user's field of vision, and the control unit acquiring the background luminance from the luminance meter, and setting the acquired background luminance as the first luminance a.

16. A moving body according to any one of claims 13 to 15, wherein the control unit controls the value of (a+b) / a to be larger when the speed of the moving body is increasing, and controls the value of (a+b) / a to be smaller when the speed of the moving body is decreasing.

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