Image display device and head-up display system

Abstract

This image display device comprises: a display unit that emits beams of light for forming an image visually recognizable by an observer as a virtual image; a light guide body that guides the beams of light to a light-transmitting member; a control unit that controls the image displayed by the display unit; and a sensor that detects a physical quantity used in order to obtain the wavelength of the beams of light. When beams of light enter an incidence surface of the light guide body, the traveling direction of the light changes inside the light guide body, and the light is emitted from an emission surface so as to be copied in the horizontal direction and vertical direction of the virtual image visually recognized by the observer, thereby expanding the field of view region. The control unit controls the position and shape of the image displayed by the display unit, on the basis of the physical quantity detected by the sensor.

Description

[Technical Field]

[0001] The present disclosure relates to an image display device and a head-up display system including the image display device and displaying a virtual image. [Background technology]

[0002] Conventionally, a head-up display system includes an image display device that displays an image. The head-up display system is a vehicle information projection system that uses the image display device to display augmented reality (AR). The head-up display device projects light representing a virtual image onto the windshield of the vehicle, for example, allowing the driver to view the virtual image together with the real view outside the vehicle.

[0003] As a device for displaying a virtual image, Patent Document 1 describes an optical element having a waveguide (light guide) for expanding an exit pupil in two directions. The optical element can expand the exit pupil by utilizing a diffractive optical element. Furthermore, Document 2 describes a head-mounted display that performs augmented reality (AR) display using a volume hologram diffraction grating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,429,645 [Patent Document 2] International Publication No. 2018 / 198587 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the wavelength of the light emitted from the image display device changes, distortion occurs in the displayed virtual image.

[0006] An object of the present disclosure is to provide an image display device and a head-up display system that reduce distortion of a virtual image. [Means for solving the problem]

[0007] The image display device of the present disclosure includes a display unit that emits a light beam that forms an image that is viewed by an observer as a virtual image, a light guide that guides the light beam to a light-transmitting member, a control unit that controls the image displayed by the display unit, and a sensor that detects a physical quantity used to obtain the wavelength of the light beam. The light guide has an incident surface onto which the light beam from the display unit is incident and an exit surface from which the light beam exits the light guide. The light beam that enters the incident surface of the light guide is redirected within the light guide and exits from the exit surface so as to replicate the virtual image viewed by the observer in the horizontal and vertical directions, thereby expanding the field of view. The control unit controls the position and shape of the image displayed by the display unit based on the physical quantity detected by the sensor.

[0008] In addition, the head-up display system of the present disclosure includes the above-mentioned image display device and a translucent member that reflects the light beam emitted from the light guide, and displays a virtual image superimposed on the actual scene that can be seen through the translucent member. [Effects of the Invention]

[0009] According to the image display device and head-up display system of the present disclosure, distortion of a virtual image can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of a light guide body. [Figure 2] An explanatory diagram showing the direction of incident light and emitted light to a light guide of a head-mounted display. [Figure 3] FIG. 1 is an explanatory diagram showing the directions of incident light and emitted light to a light guide of a head-up display; [Figure 4A] FIG. 1 is an explanatory diagram showing the optical path of a light beam emitted from a display unit. [Figure 4B] FIG. 10 is an explanatory diagram showing an example of an image displayed on a display unit; [Figure 4C] An explanatory diagram showing an example of a virtual image seen by an observer. [Figure 5A]FIG. 10 is an explanatory diagram showing the optical path of a light beam when the wavelength of the light beam emitted from the display unit changes. [Figure 5B] An explanatory diagram showing an example of a virtual image distorted by a change in the wavelength of a light beam. [Figure 6] 1 is a YZ plane cross-sectional view of a vehicle equipped with a head-up display system according to an embodiment. [Figure 7] FIG. 1 is an explanatory diagram showing the optical path of a light beam emitted from a display unit. [Figure 8A] FIG. 1 is a perspective view showing the configuration of a light guide body. [Figure 8B] FIG. 1 is a perspective view of a light guide showing the optical path of a light beam emitted from a display unit and incident on a sensor; [Figure 9A] Graph showing an example of sensor characteristics [Figure 9B] Graph showing an example of sensor characteristics [Figure 9C] An explanatory diagram showing the change in the amount of incident light depending on the position of the sensor [Figure 9D] Graph showing an example of sensor characteristics [Figure 10] Flowchart showing the flow of image correction processing [Figure 11] FIG. 10 is an explanatory diagram illustrating a change in the optical path of a light beam emitted from a display unit due to image correction. [Figure 12] FIG. 10 is an explanatory diagram illustrating a change in the optical path of a light beam emitted from a display unit due to image correction. [Figure 13] FIG. 10 is an explanatory diagram illustrating a change in an image displayed on a display unit due to image correction. [Figure 14] FIG. 10 is an explanatory diagram showing an example in which dots are displayed as virtual images. [Figure 15] A table showing the angles at which each dot appears as a virtual image when exposed to a beam of light of a certain wavelength. [Figure 16] A table showing the angles at which each dot appears as a virtual image when the wavelength of the light beam is increased [Figure 17] A table showing the angular difference of each dot as a virtual image due to changes in the wavelength of the light beam. [Figure 18A] FIG. 1 is a diagram showing the configuration of a photodetector according to a first modification of the first embodiment; [Figure 18B]FIG. 1 is a diagram showing the configuration of a photodetector according to a first modification of the first embodiment; [Figure 18C] FIG. 1 is a diagram showing the configuration of a photodetector according to a first modification of the first embodiment; [Figure 19A] FIG. 10 is a diagram showing the configuration of a photodetector according to a second modification of the first embodiment; [Figure 19B] FIG. 10 is a diagram showing the configuration of a photodetector according to a second modification of the first embodiment; [Figure 19C] FIG. 10 is a diagram showing the configuration of a photodetector according to a second modification of the first embodiment; [Figure 20A] FIG. 10 is a diagram showing the configuration of a photodetector according to a third modification of the first embodiment; [Figure 20B] FIG. 10 is a diagram showing the configuration of a photodetector according to a third modification of the first embodiment; [Figure 21] FIG. 10 is a diagram showing the configuration of a photodetector according to Modification 4 of Embodiment 1. [Figure 22] FIG. 10 is a diagram showing the configuration of an image display device according to a second embodiment. [Figure 23] Graph showing the relationship between semiconductor laser temperature and wavelength [Figure 24] 10 is a flowchart showing the flow of image correction processing in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Summary of the Disclosure) An overview of the present disclosure will first be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the configuration of a light guide 13. A so-called pupil widening type light guide 13 is used in an image display device 2 used in a head-mounted display (hereinafter referred to as HMD) or the like. The pupil widening type light guide 13 includes a coupling region 21 that receives image light from a display unit 11 and changes the direction of travel of the light, a first widening region 23 that widens in a first direction, and a second widening region 25 that widens in a second direction. The first direction and the second direction may intersect with each other, for example, they may be perpendicular to each other.

[0012] The coupling region 21, the first expansion region 23, and the second expansion region 25 each have a diffraction power for diffracting image light, and an embossed hologram or a volume hologram is formed therein. The embossed hologram is, for example, a diffraction grating. The volume hologram is, for example, an interference pattern formed by a dielectric film. The coupling region 21 changes the traveling direction of the image light incident from the outside so that it heads toward the first expansion region 23 by using the diffraction power.

[0013] The first expansion region 23 has, for example, a diffraction grating element disposed therein, and replicates the incident image light by splitting the incident image light into image light traveling in a first direction using diffraction power and image light traveling to the second expansion region 25. For example, in FIG. 1 , the first expansion region 23 has diffraction grating elements disposed at four points 23p aligned in the direction in which the image light travels after repeated total reflection. The diffraction grating element splits the image light at each point 23p, and causes the split image light to travel to the second expansion region 25. As a result, the incident light beam is expanded by being replicated into four light beams of image light in the first direction.

[0014] The second expansion region 25 includes, for example, a diffraction grating element, which splits the incident image light into image light traveling in the second direction using diffraction power and image light emitted from the second expansion region 25 to the outside, thereby duplicating the image light. For example, in FIG. 1 , three points 25p are arranged in each row in the direction in which the image light travels through repeated total reflection in the second expansion region 25, for a total of four rows, with a diffraction grating element arranged at each of the twelve points 25p. The image light is split at each point 25p, and the split image light is emitted to the outside. As a result, the incident image light beams in the four rows are each duplicated into three image light beams in the second direction, thereby expanding the field of view. In this way, the light guide 13 can duplicate twelve image light beams from a single incident image light beam, thereby expanding the field of view by duplicating the light beams in both the first and second directions. The observer can visually recognize each of the twelve beams of image light as a virtual image, and the visual recognition area in which the observer can visually recognize the image light can be widened.

[0015] Next, the difference between a pupil widening type HMD and a head-up display (hereinafter referred to as HUD) will be explained with reference to Figures 2 and 3. Figure 2 is an explanatory diagram showing incident light and outgoing light of an HMD. Figure 3 is an explanatory diagram showing incident light and outgoing light of an HUD.

[0016] 2, the light guide 13 in the HMD faces substantially directly toward the viewing area Ac in which the observer can view a virtual image. Image light incident perpendicularly from the display unit 11 is split within the light guide 13, and the split image light is emitted perpendicularly from the exit surface 27 of the light guide 13 toward the viewing area Ac.

[0017] 3, in the case of a HUD, the image light emitted from the light guide 13 is reflected by, for example, the windshield 5 and made incident on the viewing area Ac, so that the divided image light is emitted obliquely from the emission surface 27 of the light guide 13. When the image light is reflected by the non-flat windshield 5 and shown to the observer D, it has been newly discovered that if the wavelength of the image light emitted from the display unit 11 changes, distortion occurs in the virtual image.

[0018] A change in the temperature of the light source 11b of the display unit 11 causes a drift in the wavelength of the image light emitted from the display unit 11. The diffraction pitch d at which the light beam constituting the image light is diffracted, the incident angle α, the diffraction angle β, and the wavelength λ of the light beam satisfy the following relational expression: d(sinα-sinβ)=mλ Therefore, the wavelength of the image light emitted from the light source 11b is monitored, and the display position of the image on the display unit 11 is corrected.

[0019] As such, HUDs differ from HMDs in that the diffraction pitch is not constant because the image light emitted from the light guide 13 is reflected by the windshield 5 and enters the viewing area Ac, and therefore distortion of the virtual image due to changes in the wavelength of the image light is more noticeable in HUDs.

[0020] 4A, when a light beam L1 having a designed wavelength is incident on the light guide 13, the traveling direction of the light beam is bent in the coupling region 21 toward the first extended region 23. The light beam is repeatedly duplicated in the first extended region 23, and the traveling direction of the duplicated light beam is bent toward the second extended region 25. The light beam is repeatedly duplicated in the second extended region 25, and is emitted from the light guide 13 as a light beam L2 that displays a virtual image.

[0021] Since light beam L2 emitted from light guide 13 is distorted when reflected by windshield 5, the image displayed on display unit 11 can be deformed in advance in the opposite direction to the distortion, allowing the viewer to view an image without distortion. For example, when a deformed rectangular image 12 is displayed in display area 11a of display unit 11 as shown in Fig. 4B, it is replicated by light guide 13, and image 12 is distorted by windshield 5, allowing the viewer to view a rectangular virtual image Iva as designed, as shown in Fig. 4C.

[0022] However, as the temperature of the light source 11b of the display unit 11 increases, the wavelength of the light beam L1 emitted from the display unit 11 changes. If a narrow-band light source such as a laser element is used as the light source 11b, the wavelength increases as the temperature increases. As a result, as shown in FIG. 5A , the light beam diffracted by the coupling region 21 may be diffracted at a larger angle than the designed angle, traveling outside the first extended region 23 and increasing the amount of light that is not diffracted to the second extended region 25. Furthermore, the light beam diffracted at a larger angle than the designed angle by the coupling region 21 may also be diffracted at a larger angle by the first extended region 23 and then by the second extended region 25, resulting in greater image distortion.

[0023] As a result, the rectangular virtual image Iva shown in Fig. 4C before the temperature of the display unit 11 rises becomes a distorted virtual image Ivb as shown in Fig. 5B after the temperature rises, and the viewer sees this distorted virtual image Ivb. Hereinafter, an image display device 2 will be described that reduces the distortion of the virtual image even when the temperature of the display unit 11 rises.

[0024] (Embodiment 1) Hereinafter, the first embodiment will be described with reference to Figures 6 to 8B. Note that components having the same functions as those described above are denoted by the same reference numerals. Also, the inclination angle of the windshield in the figures is shown for ease of understanding and may vary depending on the figure.

[0025] [1-1.Configuration] [1-1-1. Overall configuration of image display device and head-up display system] A specific embodiment of a head-up display system 1 (hereinafter referred to as HUD system 1) according to the present disclosure will be described. FIG. 6 is a diagram showing a cross section of a vehicle 3 equipped with a HUD system 1 according to the present disclosure. FIG. 7 is an explanatory diagram showing the optical path of a light beam emitted from a display unit. In the embodiment, the HUD system 1 equipped in a vehicle 3 will be described as an example.

[0026] The directions related to the HUD system 1 will be described below based on the X-axis, Y-axis, and Z-axis shown in FIG. 6. The Z-axis direction is the direction in which the observer views the virtual image Iv from the visibility area Ac in which the observer can view the virtual image Iv. The X-axis direction is the horizontal direction perpendicular to the Z-axis. The Y-axis direction is the direction perpendicular to the XZ plane formed by the X-axis and Z-axis. Therefore, the X-axis direction corresponds to the horizontal direction of the vehicle 3, the Y-axis direction corresponds to the approximately vertical direction of the vehicle 3, and the Z-axis direction corresponds to the approximately forward direction of the vehicle 3.

[0027] As shown in FIG. 6, an image display device 2 is disposed inside a dashboard (not shown) below a windshield 5 of a vehicle 3. An observer D sitting in the driver's seat of the vehicle 3 recognizes the image projected from the HUD system 1 as a virtual image Iv. In this way, the HUD system 1 displays the virtual image Iv superimposed on the real scene visible through the windshield 5. Since multiple replicated images are projected into the visibility area Ac, the observer D can view the virtual image Iv within the visibility area Ac even if the position of his or her eyes is shifted in the Y-axis and X-axis directions. The observer D is a passenger in a moving body such as the vehicle 3, for example, the driver or a passenger sitting in the passenger seat.

[0028] The image display device 2 includes a display unit 11, a light guide 13, a control unit 15, a storage device 17, and a sensor 19. The display unit 11 emits a light beam that forms an image that is visually recognized by the observer as a virtual image Iv. The light guide 13 divides and copies the light beam L1 emitted from the display unit 11, and guides the copied light beam L2 to the windshield 5. The light beam L2 reflected by the windshield 5 is displayed as a virtual image Iv superimposed on the actual scene that is visible through the windshield 5.

[0029] The display unit 11 displays an image under the control of an external control unit 15. The display unit 11 having the light source 11b may be, for example, a backlit liquid crystal display (LCD), an organic light-emitting diode (OLED) display, or a plasma display. A laser element may also be used as the light source 11b. The display unit 11 may generate an image using a screen that diffuses or reflects light, a projector, or a scanning laser. The display unit 11 can display image content including various information such as road navigation guidance, the distance to the vehicle ahead, the remaining battery charge, and the current vehicle speed. In this way, the display unit 11 emits a light beam L1 including image content that is visually recognized by the observer D as a virtual image Iv.

[0030] The control unit 15 can be realized by a circuit configured with semiconductor elements and the like. The control unit 15 can be configured with, for example, a microcomputer, a CPU, an MPU, a GPU, a DSP, an FPGA, or an ASIC. The control unit 15 realizes predetermined functions by reading data and programs stored in a built-in storage device 17 and performing various arithmetic processing. The control unit 15 also includes the storage device 17. The control unit 15 corrects the position and shape of the image displayed on the display unit 11 according to the detection value of the sensor 19.

[0031] The storage device 17 is a storage medium that stores programs and data necessary to realize the functions of the control unit 15. The storage device 17 can be realized, for example, by a hard disk drive (HDD), an SSD, a RAM, a DRAM, a ferroelectric memory, a flash memory, a magnetic disk, or a combination of these. The storage device 17 stores an image representing the virtual image Iv and shape data for displaying the image on the display unit 11. The storage device 17 also stores a first lookup table that associates wavelengths with display positions and image shapes. The storage device 17 also stores a second lookup table that associates the amount of light detected by the sensor 19 with the wavelength of light. The control unit 15 determines the shape of the image to be displayed on the display unit 11 based on the detection value of the sensor 19. The control unit 15 reads the determined display image and shape data from the storage device 17 and outputs them to the display unit 11.

[0032] The sensor 19 receives a light beam emitted from the light guide 13 that is not visible to the observer D. For example, the sensor 19 receives a light beam that is emitted from the display unit 11 and propagates along an optical path that branches off from the optical path to the visible area AD of the observer D. The sensor 19 detects a physical quantity used to obtain the wavelength of the light beam L1. The sensor 19 is, for example, a photodetector that detects the wavelength and amount of light received and transmits the detected value to the control unit 15. The sensor 19 is, for example, arranged on a straight line connecting the display unit 11 and the combined area 21.

[0033] [1-1-2. Light guide] The configuration of the light guide 13 will be described with reference to FIGS. 4A and 8A. FIG. 8A is a perspective view showing the configuration of the light guide 13. The light guide 13 has a first main surface 13a, a second main surface 13b, and a side surface 13c. The first main surface 13a and the second main surface 13b are opposite each other. The light guide 13 has an incident surface 20, a coupling region 21, a first extended region 23, a second extended region 25, and an exit surface 27. The incident surface 20 is included in the second main surface 13b, and the exit surface 27 is included in the first main surface 13a. If the coupling region 21, the first extended region 23, and the second extended region 25 are diffraction gratings, they are included in the second main surface 13b. If the coupling region 21, the first extended region 23, and the second extended region 25 are volume holograms, they are disposed between the first main surface 13a and the second main surface 13b.

[0034] Exit surface 27 faces second expansion region 25. First main surface 13a faces windshield 5. In this embodiment, incident surface 20 is included in coupling region 21, but it may also be a surface facing coupling region 21 and included in first main surface 13a. Exit surface 27 may also be included in second expansion region 25.

[0035] The coupling region 21, the first extension region 23, and the second extension region 25 each have a different diffraction power, and each has a diffraction grating or a volume hologram formed therein. The coupling region 21, the first extension region 23, and the second extension region 25 each have a different diffraction angle of image light. The light guide 13 is configured to totally reflect the incident light beam inside. The light guide 13 is formed, for example, of a glass or resin plate with a mirror-finished surface. The light guide 13 is not limited to a flat shape, but may also have a curved shape. In this way, the light guide 13 includes a diffraction grating or a volume hologram that diffracts light in a portion thereof. When the coupling region 21, the first extension region 23, and the second extension region 25 include a volume hologram, they become three-dimensional regions.

[0036] The coupling region 21 is a region where the light beam L1 emitted from the display unit 11 enters through the incident surface 20 and changes the traveling direction of the light beam L1. The coupling region 21 has diffractive power and changes the propagation direction of the incident light beam L1 toward the first extended region 23. In this embodiment, coupling refers to a state in which the light beam L1 propagates within the light guide 13 under total reflection conditions. As shown in FIG. 8B , the light beam L1a that is transmitted through the coupling region 21 without being diffracted travels straight and enters the sensor 19 that is arranged on an extension from the display unit 11 to the coupling region 21.

[0037] As shown in FIGS. 4A and 8A, the first expansion region 23 expands the light beam L1 in a first direction and outputs it toward the second expansion region 25 in a second direction intersecting the first direction. The length of the first expansion region 23 expanding the light beam L1 in the first direction is greater than the length of the second direction. The light guide 13 is disposed so that the first direction is the horizontal direction (the direction of the X-axis). The light beam L1 diffracted and propagated in the coupling region 21 propagates in the first direction while repeatedly undergoing total reflection at the first principal surface 13a and the second principal surface 13b. The light beam L1 is then replicated by the diffraction grating of the first expansion region 23 formed on the second principal surface 13b and output to the second expansion region 25.

[0038] The second extension region 25 expands the light beam L1 in, for example, a second direction perpendicular to the first direction, and emits the expanded light beam L2 from the exit surface 27. Note that the light guide 13 is disposed such that the second direction is the negative direction of the Z axis. The light beam L1 propagating from the first extension region 23 propagates in the second direction while repeatedly being totally reflected by the first principal surface 13a and the second principal surface 13b. The light beam L1 is then duplicated by the diffraction grating of the second extension region 25 formed on the second principal surface 13b and emitted to the outside of the light guide 13 via the exit surface 27.

[0039] Therefore, from the viewpoint of observer D, the light guide 13 expands the light beam L1, which has entered the incident surface 20 and changed its direction of travel, in the horizontal direction (the direction of the X axis) of the virtual image Iv viewed by observer D, and then further expands it in the vertical direction (the direction of the Y axis) of the virtual image Iv, and emits the light beam L2 from the exit surface 27.

[0040] [1-1-3. Order of pupil dilation] In the light guide 13 arranged as described above, the order of pupil dilation in the first embodiment will be described with reference to FIGS. 4A and 8A.

[0041] The light beam L1 of the image light incident on the light guide 13 changes its propagation direction to the first expansion region 23, which expands the pupil in the horizontal direction (negative direction of the X axis) as a first direction, by the diffractive element formed in the coupling region 21. Therefore, after being obliquely incident on the coupling region 21, the light beam L1 is affected by the wave vector k1 shown in FIG. 4A and then propagates in the direction of the first expansion region 23.

[0042] Light beam L1 propagating toward the first extended region 23 extending in the first direction is split by the diffraction element formed in the first extended region 23 while repeatedly undergoing total reflection into light beam L1 propagating in the first direction and light beam L1 that is duplicated and changes its propagation direction toward the second extended region 25. At this time, the duplicated light beam L1 is affected by the wave vector k2 shown in FIG. 9B and propagates toward the second extended region 25.

[0043] The light beam L1, whose propagation direction has been changed to the second extended region 25 extending along the negative direction of the Z axis as the second direction, is split by the diffraction element formed in the second extended region 25 into the light beam L1 propagating in the second direction and the light beam L2 that is duplicated and emitted from the second extended region 25 to the outside of the light guide 13 via the exit surface 27. At this time, the duplicated light beam L2 is affected by the wave vector k3 shown in FIG. 4A and propagates in the direction of the exit surface 27.

[0044] [1-1-4. Detection of changes in wavelength of light] The sensor 19 directly or indirectly detects a change in the wavelength of the light beam L1. The sensor 19 includes, for example, a filter having a transmittance that varies depending on the wavelength, as shown in FIG. 9A. The characteristics of this filter are known in advance, and the transmittance changes within the wavelength change range AL of the light source 11b. Therefore, while the same image is displayed on the display unit 11, a change in the wavelength of the light beam L1 can be detected by detecting a change in the amount of light detected by the sensor 19. For example, in the filter shown in FIG. 9A, the longer the wavelength, the greater the amount of light that passes through the filter, and the greater the amount of light detected by the sensor 19.

[0045] 9B, by measuring the relationship between the change in wavelength of the light beam L1 and the diffraction efficiency in advance, the wavelength of the light beam L1 can be estimated from the amount of light that is not diffracted. For example, the amount of light that is not diffracted in the coupling region 21 is incident on the sensor 19, and the wavelength of the light beam L1 can be detected from the amount of light detected by the sensor 19.

[0046] 9C, for example, when the sensor 19 is disposed on an extension of the coupling region 21 to the first extended region 23, the diffraction angle of the coupling region 21 and the first extended region 23 changes depending on the wavelength of the light beam L1. Therefore, when the same image is displayed on the display unit 11, the amount of light incident on the sensor 19 changes depending on the wavelength of the light beam L1. For example, at the position of the sensor 19 in FIG. 9C, the light beam L1b with a long wavelength has a large diffraction angle, and therefore a large amount of light is incident on the sensor 19. On the other hand, the light beam L1c with a short wavelength has a small diffraction angle, and therefore a small amount of light is incident on the sensor 19. As shown in FIG. 9D, by measuring the relationship between the change in wavelength of the light beam L1 and the amount of light incident on the sensor 19, the wavelength of the light beam L1 can be detected from the amount of light detected by the sensor 19.

[0047] By using these wavelength detection methods, the wavelength of the light beam L1 can be detected from the amount of light detected by the sensor 19. These wavelength detection methods may be used alone or in combination.

[0048] Next, the flow of image correction processing of the image display device 2 will be described with reference to Fig. 10 to Fig. 13. Fig. 10 is a flowchart showing the flow of image correction processing. Figs. 11 and 12 are explanatory diagrams explaining changes in the optical path of a light beam emitted from the display unit due to image correction. Fig. 13 is an explanatory diagram explaining changes in the image displayed on the display unit due to image correction.

[0049] In step S1, when the control unit 15 causes an image to be displayed on the display unit 11, it acquires the amount of light detected by the sensor 19 and acquires the wavelength of the light beam L1 emitted from the display unit 11 by referring to a second lookup table stored in the memory device 17 in which the amount of light is associated with the wavelength.

[0050] Next, in step S2, control unit 15 refers to a first lookup table stored in storage device 17, which associates the wavelength of light beam L1 with the display position and shape of an image displayed on display unit 11. Next, in step S3, control unit 15 controls the image to be displayed on display unit 11 based on the reference result of the first lookup table. For example, as shown in Fig. 13, control unit 15 corrects the shape and position of image 12 displayed on display unit 11 based on the first lookup table so as to reduce image distortion caused by the light beam emitted from light guide 13, and displays image 12a with the corrected position and shape on display unit 11.

[0051] For example, when the wavelength of light beam L1 emitted from display unit 11 increases due to a rise in temperature of display unit 11, the display position of the image is corrected downward compared to before the temperature increase, as shown in Figures 11 and 12. If display unit 11 is, for example, a liquid crystal display device, in response to the increase in temperature and the increase in the wavelength of light beam L1, control unit 15 shifts the position of light beam L1 emitted from display area 11a of display unit 11 downward, and convex lens 11d arranged opposite display area 11a causes light beam L1 to enter combining area 21 with the same entrance pupil before and after the correction. Convex lens 11d may be arranged inside or outside display unit 11.

[0052] As a result, the light beam L1 incident on the light guide 13 is diffracted in the coupling region 21, the first expansion region 23, and the second expansion region 25, respectively, and can exit the light guide 13 at the exit angle before the temperature rise, allowing the observer D to see a virtual image Iv with reduced distortion.

[0053] The virtual image Iv in the first embodiment will be described with reference to FIGS.

[0054] The coordinates of each of the five dots Dt1 to Dt5 in FIG. 14, expressed as an angle, are shown in FIG. 15. Each of the dots Dt1 to Dt5 is displayed by a light beam L1 with a wavelength of 520 nm emitted from the display unit 11. The angular coordinates of dot D1 located at the center of the screen are Dt1 (0.00, 0.00), dot D2 located at the bottom left of the screen are Dt2 (-5.00, -2.00), and dot D3 located at the top left of the screen are Dt3 (-5.00, +2.00). The angular coordinates of dot D4 located at the bottom right of the screen are Dt4 (+5.00, -2.00), and dot D5 located at the top right of the screen are Dt5 (+5.00, +2.00).

[0055] When the wavelength of the light beam L1 emitted from the display unit 11 is increased to 530 nm, the coordinates of dots Dt1 to Dt5 as the virtual image Iv seen by the viewer D are shown in Fig. 16. Fig. 17 shows the difference in angle when the wavelength is increased from 520 nm to 530 nm.

[0056] 16 shows that the position of the virtual image Iv seen by the observer D changes when the wavelength of the light beam L1 emitted from the display unit 11 changes. When the wavelength is changed to a longer wavelength, the virtual image shifts downward as a whole, and since the amount of movement of the positions of the dots Dt2 to Dt5 at the four corners is not uniform, it can be seen that distortion occurs in the virtual image.

[0057] 17, there is an angular difference of approximately 0.09 degrees horizontally and approximately 0.04 degrees vertically at the center of the screen, and a maximum angular difference of approximately 0.1 degrees occurs at the periphery of the screen. These angular differences are easily noticeable by an observer with normal eyesight.

[0058] Therefore, by using the image display device 2 of embodiment 1 to control the position and shape of the image displayed on the display unit 11 in accordance with changes in the wavelength of the light beam L1 emitted from the display unit 11, it is possible to display the dots Dt1 to Dt5 shown in Fig. 14 even if the wavelength changes from 520 nm to 530 nm. In this way, the image display device 2 of embodiment 1 can reduce movement and distortion of the virtual image.

[0059] Next, a first modification of the first embodiment will be described with reference to Figures 18A and 18B. In the first embodiment, the sensor 19 is arranged on an extension from the display unit 11 to the combined region 21, but this is not limited to this. In the first modification, the sensor 19 is arranged on an extension in the first direction of the first expansion region 23.

[0060] The side surface 13c of the light guide 13 is on an extension of the first extended region 23 in the first direction. If the side surface 13c is roughened, the light beam L1 incident on the side surface 13c is scattered and exits the light guide 13. The sensor 19 of the first modification receives the light beam L1 that is not diffracted by the first extended region 23 and exits from the side surface 13c of the light guide 13 after repeated total reflection. This allows the image display device 2 of the first modification to have the same function as that of the first embodiment. Alternatively, as shown in FIG. 18C , the sensor 19 may be attached to the side surface 13c of the light guide 13 that is on an extension of the first extended region 23 in the first direction. In this case, the light beam L1 can be incident on the sensor 19 even if the side surface 13c is not roughened.

[0061] Next, a second modification of the first embodiment will be described with reference to Figures 19A and 19B. In the first embodiment, the sensor 19 is arranged on an extension from the display unit 11 to the combined region 21, but this is not limited to this. In the second modification, the sensor 19 is arranged on an extension in the second direction of the second expansion region 25.

[0062] The side surface 13d of the light guide 13 is on an extension of the second extended region 25 in the second direction. If the side surface 13d is roughened, the light beam L1 incident on the side surface 13d is scattered and emitted to the outside of the light guide 13. The sensor 19 of the second modification receives the light beam L1 that is not diffracted by the second extended region 25 but is repeatedly totally reflected and emitted from the side surface 13d of the light guide 13. This allows the image display device 2 of the second modification to have the same function as that of the first embodiment. Furthermore, as shown in FIG. 19C , the sensor 19 may be closely attached to the side surface 13d of the light guide 13 that is on an extension of the second extended region 25 in the second direction.

[0063] 20A and 20B, a third modification of the first embodiment will be described. In the third modification, the sensor 19 detects the light beam L1 diffracted from the first expansion region 23 and propagating to the outside of the second expansion region 25.

[0064] On both sides of the second expansion region 25 in the first direction, off-axis light beam L1 that does not enter the second expansion region 25 propagates in the second direction. The light guide 13 has a diffractive section 26. For example, in FIG. 20A , the diffractive section 26 diffracts the light beam L1 that propagates along the coupling region 21 side of the second expansion region 25 within the light guide 13 downward. As shown in FIG. 20B , a sensor 19 is disposed below the light guide 13, and the light beam L1 diffracted by the diffractive section 26 enters the sensor 19. This allows the wavelength of the light beam L1 to be detected.

[0065] Next, a fourth modification of the first embodiment will be described with reference to Fig. 21. In the fourth modification, the image display device 2 may include a sensor 19A that directly detects wavelength instead of the sensor 19 that detects the amount of light.

[0066] The sensor 19A includes an entrance slit 31, a collimator lens 33, a transmission grating 35, a focus lens 37, and an image sensor 39. The transmission grating 35 separates the incident light, and the image sensor 39 detects the amount of light for each wavelength of the separated light.

[0067] Since the sensor 19A directly detects the wavelength of the light beam L1 emitted from the display unit 11, image correction according to the wavelength can be performed with high precision.

[0068] [1-2. Effects, etc.] The image display device 2 of the present disclosure includes a display unit 11 that emits a light beam L1 that forms an image viewed by an observer D as a virtual image Iv, and a light guide 13 that guides the light beam L1 to a windshield 5. The image display device 2 further includes a control unit 15 that controls the image displayed by the display unit 11, and a sensor 19 that detects a physical quantity used to obtain the wavelength of the light beam L1. The light guide 13 has an incident surface 20 onto which the light beam L1 from the display unit 11 is incident, and an exit surface 27 from which the light beam L1 exits the light guide 13. The light beam L1 that enters the incident surface 20 of the light guide 13 changes its traveling direction within the light guide 13 and exits from the exit surface 27 so as to expand the field of view by replicating the virtual image Iv viewed by the observer D in the horizontal and vertical directions. The control unit 15 controls the position and shape of the image displayed by the display unit 11 based on the physical quantity detected by the sensor 19.

[0069] Even if the wavelength of the light beam L1 emitted from the display unit 11 changes, the sensor 19 detects the physical quantity used to obtain the wavelength of the light beam L1, and based on the detected physical quantity, the control unit 15 controls the position and shape of the image displayed on the display unit 11. As a result, even if the traveling direction within the light guide 13 changes due to a change in the wavelength of the light beam L1, a virtual image with reduced distortion can be displayed by controlling the position and shape of the image displayed on the display unit 11.

[0070] The sensor 19 is an optical sensor that receives a portion of the light beam L1 that is not visible to the observer and detects the physical quantity of the light, thereby obtaining the physical quantity for obtaining the wavelength of the light beam while maintaining the brightness of the virtual image.

[0071] The sensor 19 may detect the wavelength of the received light. Since the sensor 19 directly detects the wavelength of the light, it is possible to improve the accuracy of wavelength detection.

[0072] The sensor 19 may detect the amount of light received, and the control unit 15 determines the wavelength of light of the light beam L1 based on the amount of light detected by the sensor 19. Because a light amount sensor is used as the sensor 19, the space required for placing the sensor 19 can be reduced, leading to cost reductions.

[0073] Furthermore, by projecting the light emitted from the HUD system 1 onto the windshield 5 of the vehicle 3, a virtual image Iv suitable for the observer D aboard the vehicle 3 can be displayed.

[0074] (Embodiment 2) 22 and 23, a second embodiment will be described below. In the first embodiment, the wavelength of the light beam L1 is detected from a physical quantity related to light using a sensor 19 that detects light, but in the second embodiment, the wavelength of the light beam L1 is detected from the temperature of the display unit 11B using a sensor 19B that detects temperature. Apart from this and other points that will be described below, the second embodiment is identical to the first embodiment in terms of configuration.

[0075] The sensor 19B used in the display device 2B of the second embodiment is a temperature sensor instead of a light-detecting sensor, and detects the temperature of the display unit 11B or the temperature of the light source 11b. The sensor 19B may be disposed inside the display unit 11B or on the outer surface of the display unit 11B. A third lookup table is stored in the storage device 17, in which the relationship between the temperature detected by the sensor 19B and the wavelength of the light beam L1 emitted from the display unit 11B is previously associated.

[0076] Based on the temperature detected by sensor 19B, control unit 15 determines the wavelength of light beam L1 emitted from display unit 11B by referring to a third lookup table stored in storage device 17. Sensor 19B can detect the wavelength of light beam L1 with higher accuracy by measuring the temperature at a position as close as possible to the light-emitting point of light source 11b.

[0077] Based on the determined wavelength, the control unit 15 controls the position and shape of the image displayed on the display unit 11B, as in the first embodiment. This makes it possible to display a virtual image Iv with reduced distortion even if the traveling direction of the light beam L1 within the light guide 13 changes due to a change in the wavelength of the light beam L1.

[0078] Next, a description will be given of a modified example of the above-mentioned embodiment 2. By combining embodiment 2 with modification 2 of embodiment 1, the modified example of embodiment 2 can correct both changes in the wavelength of the light beam L1 and changes in the diffraction angle due to temperature changes in the coupling region 21, the first extended region 23, and the second extended region 25.

[0079] As the temperatures of the coupling region 21, the first extension region 23, and the second extension region 25 increase, the pitch of the diffraction grating widens, and the diffraction angle of the light beam decreases. The resulting change in the diffraction angle is detected by sensor 19, and the change in the wavelength of the light beam L1 is detected by sensor 19B. A correction parameter for the change in the wavelength of the light beam L1 is prepared based on the detection value of sensor 19B, and a correction parameter for the change in the diffraction angle is prepared based on the detection value of sensor 19. A fourth lookup table that associates these two parameters with the display position and shape of the corresponding image is stored in the storage device 17 in advance. The control unit 15 controls the position and shape of the image displayed on the display unit 11B based on the detection values ​​of sensors 19 and 19B and the third and fourth lookup tables, thereby enabling more accurate correction of the distortion of the virtual image.

[0080] (Embodiment 3) Hereinafter, a third embodiment will be described with reference to Fig. 24. In the third embodiment, the control unit 15 is configured to control the display image according to the display mode of the display unit 11. In this respect and other points described below, the configuration of the third embodiment is the same as that of the first embodiment.

[0081] The display mode is set according to the type of image to be displayed on the display unit 11. For example, there are about five display modes set according to the ratio of the amount of light emitted by red, blue, and green. Also, a fifth lookup table is stored in advance in the storage device 17, which associates the detection value of the sensor 19 with the wavelength of the light beam L1 according to each display mode.

[0082] In step S11, control unit 15 acquires information about the display mode of the image being displayed from display unit 11. In step S12, control unit 15 acquires a detection value from sensor 19. In step S13, control unit 15 refers to a fifth lookup table corresponding to the acquired display mode, and determines the wavelength of light beam L1 from the acquired detection value of sensor 19.

[0083] Next, steps S2 and S3 are carried out in the same manner as in the first embodiment, and the position and shape of the image displayed on the display unit 11 are controlled, thereby reducing distortion of the virtual image.

[0084] (Other embodiments) As described above, the above embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which appropriate modifications, substitutions, additions, omissions, etc. are made. Therefore, other embodiments will be described below as examples.

[0085] In the above embodiment, the configuration uses sensor 19, sensor 19A or sensor 19B, but it is also possible to combine multiple sensors 19, sensors 19A or sensors 19B and have control unit 15 determine the wavelength of light beam L1 based on the detection values ​​of each.

[0086] In the above embodiment, the split and replicated light beam L2 is reflected by the windshield 5 to allow the observer D to view the virtual image Iv, but this is not limiting. A combiner may be used instead of the windshield 5, and the split and replicated light beam L2 may be reflected by the combiner to allow the observer D to view the virtual image Iv.

[0087] In the above embodiment, the first direction in which the light beam L1 is expanded in the first expansion region 23 and the second direction in which the light beam L1 is expanded in the second expansion region 25 are perpendicular to each other, but this is not limited to this. The first expansion region 23 expands the light beam L1 in the first direction as long as the component expanding horizontally is larger than the component expanding in the direction along the Z axis, and the second expansion region 25 expands the light beam L1 in the second direction as long as the component expanding in the direction along the Z axis is larger than the component expanding in the horizontal direction.

[0088] In the above embodiment, the light guide 13 expands the light beam L1 incident on the incident surface 20 in the horizontal direction of the virtual image Iv and then in the vertical direction, but this is not limited to this. The light guide 13 may expand the light beam L1, which has been incident on the incident surface 20 and has its traveling direction changed, in the vertical direction (Y-axis direction) of the virtual image Iv viewed by the observer D from the viewpoint of the observer D, and then further expand it in the horizontal direction (X-axis direction) of the virtual image Iv to emit the light beam L2 from the exit surface 27.

[0089] In the above embodiment, the HUD system 1 is described as being applied to a vehicle 3 such as an automobile. However, the object to which the HUD system 1 is applied is not limited to the vehicle 3. The object to which the HUD system 1 is applied may be, for example, a train, a motorcycle, a ship, or an airplane, or may be an amusement machine that does not involve movement. In the case of an amusement machine, the light beam from the display unit 11 is reflected by a transparent curved plate that serves as a translucent member that reflects the light beam emitted from the display unit 11 instead of the windshield 5. Furthermore, the actual scene that the user can view through the transparent curved plate may be an image displayed by another image display device. In other words, a virtual image generated by the HUD system 1 may be superimposed on an image displayed by another image display device. In this manner, any of the windshield 5, a combiner, and a transparent curved plate may be used as the translucent member in the present disclosure.

[0090] (Outline of the embodiment) (1) The image display device of the present disclosure includes a display unit that emits a light beam that forms an image that is viewed by an observer as a virtual image, a light guide that guides the light beam to a light-transmitting member, a control unit that controls the image displayed by the display unit, and a sensor that detects a physical quantity used to obtain the wavelength of the light beam. The light guide has an incident surface onto which the light beam from the display unit is incident and an exit surface from which the light beam exits the light guide. The light beam that enters the incident surface of the light guide is redirected within the light guide and exits from the exit surface so as to replicate the virtual image viewed by the observer in the horizontal and vertical directions, thereby expanding the field of view. The control unit controls the position and shape of the image displayed by the display unit based on the physical quantity detected by the sensor.

[0091] As a result, even if the wavelength of the light beam emitted from the display unit changes, the sensor detects the physical quantity used to obtain the wavelength of the light beam, and the control unit controls the position and shape of the image displayed by the display unit based on the detected physical quantity.As a result, even if the traveling direction within the light guide changes due to a change in the wavelength of the light beam, it is possible to display a virtual image with reduced distortion by controlling the position and shape of the image displayed on the display unit.

[0092] (2) In the image display device of (1), the sensor is a photodetector that detects the physical quantity of light.

[0093] (3) In the image display device of (2), the sensor detects the wavelength of the received light.

[0094] (4) In the image display device of (3), the sensor is an image sensor having a diffraction grating.

[0095] (5) In the image display device of (2), the sensor detects the amount of light received, and the control unit determines the wavelength of the light beam based on the amount of light detected by the sensor.

[0096] (6) In the image display device of (5), the sensor has a filter whose transmittance changes depending on the wavelength.

[0097] (7) In the image display device of any one of (1) to (6), the light guide has a region that guides a part of the light flux to the emission surface and a region that guides a part of the light flux to the sensor.

[0098] (8) In the image display device of (1), the sensor is a temperature detector and detects the temperature of the display unit as a physical quantity, and the control unit determines the wavelength of the light beam based on the temperature of the display unit.

[0099] (9) In any one of the image display devices (1) to (8), the light guide has a coupling region that changes the direction of travel of a light beam incident on the incident surface, a first expansion region that replicates the light beam whose direction has been changed in the coupling region in a first direction within the light guide, and a second expansion region that replicates the light beam replicated in the first expansion region in a second direction intersecting the first direction within the light guide, and the coupling region, the first expansion region, and the second expansion region each have different diffraction powers and diffraction angles, and the light beam replicated in the second expansion region is emitted from the exit surface.

[0100] (10) In the image display device of (9), at least one of the combined region, the first extended region, and the second extended region includes a volume hologram.

[0101] (11) In the image display device of (9), the coupling region, the first extension region, and the second extension region are regions having diffractive structures, and the magnitudes of the wave vectors of the respective diffractive structures are different.

[0102] (12) In the image display device of (1) to (11), the control unit controls the position and shape of the image so as to reduce distortion of the image caused by the light beam emitted from the light guide.

[0103] (13) The head-up display system of the present disclosure comprises any one of the image display devices (1) to (12) and a light-transmitting member that reflects the light beam emitted from the light guide, and displays the virtual image superimposed on the real scene visible through the light-transmitting member.

[0104] (14) In the head-up display of (13), the light-transmitting member is a windshield of a moving object. [Industrial Applicability]

[0105] The present disclosure is applicable to an image display device used in a head-up display system. [Explanation of symbols]

[0106] 1 Head-up display system 2 Image display device 3 vehicles 3a center line 5 Windshield 11 Display section 11a Display area 11b Light source 13 Light guide 13a First main surface 13b Second principal surface 13c side 15 Control Unit 17 Storage device 18 Temperature Sensor 19 Sensors 20 Entrance plane 21 Combined area 23 First Expansion Area 23a points 25 Second Expansion Area 25a points 26 Diffraction section 27 Exit surface 31 Entrance slit 33 Collimating Lens 35 Transmission grating 37 Focus Lens 39 Image Sensor Ac Visibility Zone D. Observer IV Virtual Image k1, k2, k3 wave vectors L1, L2 luminous flux

Claims

1. a display unit that emits a light beam that forms an image that is visually recognized by an observer as a virtual image; a light guide having a diffractive structure and an optical path that guides the light beam to a light-transmitting member while changing the traveling direction of the light beam by the diffractive structure; a control unit that controls the image displayed by the display unit; a sensor that is out of the optical path and receives a portion of the light beam that has passed through the light guide, and detects a physical quantity of light used to obtain the wavelength of the light beam; the light guide has an incident surface onto which the light flux from the display unit is incident and an exit surface from which the light flux exits the light guide, The light beam incident on the incident surface of the light guide is changed in its traveling direction by the diffractive structure within the light guide, and is emitted from the exit surface so as to expand the field of view by replicating the virtual image visually recognized by the observer in the horizontal and vertical directions, the control unit controls the position and shape of the image displayed by the display unit based on the physical quantity detected by the sensor. Image display device.

2. the sensor is disposed at a position where the light beam deviates from the optical path without being changed in its traveling direction by the diffractive structure, and passes through the light guide. The image display device according to claim 1 .

3. the sensor detects the wavelength of the received light as the physical quantity; The image display device according to claim 2 .

4. the sensor is an image sensor having a diffraction grating, which separates incident light, measures the amount of light for each wavelength of the separated light, and detects the wavelength of the light; 4. The image display device according to claim 3.

5. the sensor detects the amount of received light as the physical quantity; the control unit determines the wavelength of the light of the light beam based on the amount of light detected by the sensor, based on a relationship between the wavelength of the light beam, the diffraction angle, and the position of the sensor. The image display device according to claim 2 .

6. the sensor has a filter whose transmittance changes depending on the wavelength, and detects the amount of light received through the filter; the control unit determines the wavelength of the light of the light beam based on the amount of light detected by the sensor, based on a relationship between the wavelength of the light beam and the transmittance. The image display device according to claim 2 .

7. The control unit detects the wavelength of the light of the light beam based on the amount of light detected by the sensor, based on the relationship between the change in wavelength of the light beam and diffraction efficiency. The image display device according to claim 2 .

8. Further comprising a temperature detector for detecting the temperature of the display unit, the control unit determines a position and a shape of the image to be displayed by the display unit based on the physical quantity and the temperature of the display unit. The image display device according to claim 2 .

9. the light guide includes a coupling region that changes the traveling direction of the light beam incident on the incident surface, a first extension region that replicates the light beam whose traveling direction has been changed in the coupling region in a first direction within the light guide, and a second extension region that replicates the light beam replicated in the first extension region in a second direction intersecting the first direction within the light guide, the coupling region, the first extension region, and the second extension region have the diffractive structures, and each of the diffractive structures has a different diffractive power and a different diffractive angle; The light beam replicated in the second expansion region is emitted from the exit surface.

9. The image display device according to claim 1.

10. At least one of the coupling region, the first expansion region, and the second expansion region includes a volume hologram. The image display device according to claim 9 .

11. the coupling region, the first extension region, and the second extension region have different wave vector magnitudes of the diffraction structures, The image display device according to claim 9 .

12. the control unit controls the position and shape of the image so as to reduce distortion of the image caused by the light beam emitted from the light guide.

12. The image display device according to claim 1.

13. An image display device according to any one of claims 1 to 12; the light-transmitting member that reflects the light beam emitted from the light guide, The virtual image is displayed superimposed on a real scene visible through the light-transmitting member, The light-transmitting member has a non-planar shape, and reflects the light beam emitted from the light guide body to be incident on the viewing area, so that the diffraction pitch of the diffraction structure is not constant. Head-up display system.

14. The light-transmitting member is a windshield of a moving object.

14. The head-up display system of claim 13.

Images