Projection device

Abstract

A projection device according to one embodiment of the present disclosure includes: a light source unit; a retroreflective plate for reflecting light incident from the light source unit at a predetermined offset angle with respect to the incident direction; a rotation drive unit for rotating the retroreflective plate; and a first reflection mirror for reflecting light emitted from the retroreflective plate in a predetermined direction.

Description

Projection device

[0001] The present disclosure relates to a projection device used, for example, as a head-up display.

[0002] For example, Patent Document 1 discloses an information display device that relaxes the restrictions on the installation location by using a reflector having a plurality of unit regions two-dimensionally arranged on the main surface.

[0003] International Publication No. 2018 / 061444

[0004] By the way, a projection device for displaying driving support information to a vehicle driver is required to display a virtual image with a wide viewing angle.

[0005] It is desirable to provide a projection device capable of displaying a virtual image with a wide viewing angle.

[0006] The projection device according to an embodiment of the present disclosure includes a light source unit, a retroreflector that reflects light incident from the light source unit by giving a predetermined offset angle with respect to the incident direction, a rotation drive unit that rotates the retroreflector, and a first reflection mirror that reflects the light emitted from the retroreflector in a predetermined direction.

[0007] In the projection device according to an embodiment of the present disclosure, by providing a rotation drive unit that rotates a retroreflector that reflects the light emitted from the light source unit by giving a predetermined offset angle with respect to the incident direction, the light is made to be emitted in a desired direction. Thereby, for example, a virtual image with a wide angle of view is drawn without using a huge mirror optical system.

[0008] Figure 1 is a schematic diagram showing an example of the configuration of a projection device according to one embodiment of the present disclosure. Figure 2 is a functional block diagram showing the configuration of the projection device shown in Figure 1. Figure 4 is a schematic plan view of the special retroreflector shown in Figure 1. Figure 4 is a diagram illustrating the retroreflective elements constituting the special retroreflector shown in Figure 3. Figure 5 is a schematic cross-sectional view showing an example of the configuration of the special retroreflector corresponding to the I-I' line shown in Figure 3. Figure 6 is a diagram illustrating the configuration of the retroreflective elements at each position of the special retroreflector shown in Figure 1. Figure 7 is a top view showing the position of the retroiris of the special retroreflector shown in Figure 1. Figure 8 is a top view showing the movement of the retroiris due to the rotation of the special retroreflector shown in Figure 1. Figure 9 is a flowchart illustrating the operation of the projection device shown in Figure 1. Figure 10 is a front view showing an example of the direction of movement of the eyebox due to the rotation of the eyebox and the special retroreflector when the projection device shown in Figure 1 is mounted on a vehicle. Figure 11A is a diagram showing the incidence of light rays emitted from the display device shown in Figure 10 onto the eyebox. Figure 11B is a diagram illustrating the movement of the eyebox due to the rotation of the special retroreflective plate. Figure 12 is a front view illustrating another example of the direction of movement of the eyebox due to the rotation of the eyebox and the special retroreflective plate when the projection device shown in Figure 1 is mounted on a vehicle. Figure 13 is a diagram illustrating the movement of the eyebox due to the rotation of the special retroreflective plate. Figure 14 is a schematic diagram illustrating an example of the configuration of a projection device with an added pupil tracking device. Figure 15 is a plan view (A), a cross-sectional view (B), and a schematic diagram (C) illustrating the mode of rotation, illustrating an example of the configuration of the special retroreflective plate according to Modification 1 of this disclosure. Figure 16 is a plan view (A), a cross-sectional view (B), and a schematic diagram (C) illustrating the mode of rotation, illustrating another example of the configuration of the special retroreflective plate according to Modification 1 of this disclosure. Figure 17 is a plan view (A), a cross-sectional view (B), and a schematic diagram (C) illustrating the mode of rotation, illustrating another example of the configuration of the special retroreflective plate according to Modification 1 of this disclosure. Figure 18 is a schematic diagram illustrating an example of the configuration of a projection device according to Modification 2 of this disclosure. Figure 19 is a perspective view showing the configuration of the anisotropic prism sheet shown in Figure 10. Figure 20 is a schematic cross-sectional view showing an example of the configuration of the anisotropic prism sheet shown in Figure 19. Figure 21 is a schematic diagram showing an example of the configuration of a display device according to Modification 3 of this disclosure. Figure 22 is a perspective view showing an example of the configuration of a pupil replicating device.Figure 23 illustrates the principle of pupil replication in the X-axis direction. Figure 24 illustrates the compensation relationship between diffraction and wavelength dispersion. Figure 25 illustrates the principle of pupil replication in the Y-axis direction. Figure 26 is a schematic diagram showing another example of the configuration of the pupil replication device. Figure 27 is a diagram showing the behavior of light incident on the pupil replication device shown in Figure 26.

[0009] The embodiments described below will be explained in detail with reference to the drawings. The following description is one specific example of the disclosure, and the disclosure is not limited to the following embodiments. Furthermore, the disclosure is not limited to the arrangement, dimensions, dimensional ratios, etc., of each component shown in each figure. The order of explanation is as follows: 1. Embodiment (Example of a projection device having a special retroreflective plate and a rotational drive unit for rotating it) 2. Modifications 2-1. Modification 1 (Another example of the configuration of the retroreflective plate) 2-2. Modification 2 (Another example of the configuration of the projection device) 2-3. Modification 3 (Another example of the configuration of the display device)

[0010] <1. Embodiments> Figure 1 shows an example of the configuration of a projection device (projection device 1) according to one embodiment of the present disclosure. The projection device 1 is used in a head-up display (HUD) system that displays speed, navigation, etc., to the driver in the front seat of a vehicle, and displays a virtual image including driving support information and warning information using light reflection from the windshield.

[0011] [Configuration of the projection device] The projection device 1 comprises a display device 10, a special retroreflector 20, a reflective mirror 30, a rotation drive unit 40, and a detection camera 51. The special retroreflector 20 reflects light incident from the display device 10 with a predetermined offset angle relative to the incident direction. The rotation drive unit 40 rotates the special retroreflector 20 by a predetermined angle, for example, in the in-plane direction.

[0012] Here, the display device 10 corresponds to a specific example of the "light source unit" in one embodiment of the present disclosure. The special retroreflective plate 20 corresponds to a specific example of the "retroreflective plate" in one embodiment of the present disclosure. The reflective mirror 30 corresponds to a specific example of the "first reflective mirror" in one embodiment of the present disclosure. The rotary drive unit 40 corresponds to a specific example of the "rotary drive unit" in one embodiment of the present disclosure.

[0013] Figure 2 is a functional block diagram showing the configuration of the projection device 1.

[0014] The display device 10 projects a virtual image in front of the observer 100. The display device 10 is connected to an external image supply device, such as a PC (not shown) or various image players, via an I / F (interface), and projects a virtual image based on the image signal input to this interface.

[0015] The display device 10 includes, for example, a light source device 11, a control unit 12, a light source drive unit 13, a light modulation device 14, an image processing unit 15, a frame memory 16, a panel drive unit 17, a projection optical system drive unit 18, and a projection optical system 19.

[0016] The light source device 11, although not shown in the diagram, includes a light source driver for driving the light sources and a current value setting unit for setting the current values ​​when driving the light sources. The light source driver generates a current with the current value set by the current value setting unit, synchronized with the signal input from the light source drive unit 13, based on the power supply from a power supply circuit (not shown). The generated current is supplied to each light source.

[0017] The control unit 12 controls the rotation drive unit 40 based on the position information of the observer 100's eyes detected by the light source drive unit 13, image processing unit 15, panel drive unit 17, projection optical system drive unit 18, and detection camera 51.

[0018] The light source drive unit 13 outputs signals to control the light emission timing of the light source located in the light source device 11. This light source drive unit 13 includes, for example, a PWM setting unit, a PWM signal generation unit, and a limiter (not shown), and controls the light source driver of the light source device 11 based on the control of the control unit 12, and controls the light source using PWM to turn the light source on and off, or adjust the brightness.

[0019] The optical modulator 14 generates image light by modulating the light (illumination light) output from the light source 11 based on the image signal. The optical modulator 14 is composed of, for example, three light bulbs corresponding to each of the RGB colors described later. Examples of the optical modulator 14 include a liquid crystal display panel that modulates blue light (B) (panel (B)), a liquid crystal display panel that modulates red light (R) (panel (R)), and a liquid crystal display panel that modulates green light (G) (panel (G)). The RGB color lights modulated by the optical modulator 14 are combined by a cross dichroic prism or the like (not shown) and guided to the projection optical system 19.

[0020] The image processing unit 15 acquires an image signal input from an external source and performs functions such as determining the image size, resolution, and whether it is a still image or a moving image. If it is a moving image, it also determines the attributes of the image data, such as the frame rate. Furthermore, if the resolution of the acquired image signal differs from the display resolution of the optical modulator 14, it performs a resolution conversion process. The image processing unit 15 then expands the image after each of these processes into the frame memory 16 frame by frame, and outputs the image of each frame expanded in the frame memory 16 as a display signal to the panel drive unit 17.

[0021] The panel drive unit 17 drives the optical modulator 14. The drive of this panel drive unit 17 changes the light transmittance at each pixel arranged in the optical modulator 14, thereby forming an image.

[0022] The projection optical system drive unit 18 includes a motor that drives the lenses arranged in the projection optical system 19. This projection optical system drive unit 18 drives the projection optical system 19 according to the control of the control unit 12, and performs operations such as zoom adjustment, focus adjustment, and aperture adjustment.

[0023] The projection optical system 19 includes a group of lenses and the like for imaging the light modulated by the light modulation device 14.

[0024] In addition to the three-panel system using the three liquid crystal display panels described above, the display device 10 may also be configured as a single-panel time-division projector using one liquid crystal display panel as the optical modulation device 14.

[0025] Figure 3 schematically shows the planar configuration of the special retroreflective plate 20.

[0026] First, let's explain a typical retroreflector. A typical retroreflector has a mechanism that returns reflected light directly to the optical axis of the incident light. A retroreflector consists of multiple retroreflective elements arranged periodically in a two-dimensional array. A retroreflective element is generally made up of, for example, three plane mirrors arranged perpendicular to each other with their reflective surfaces facing inward, like the vertices of a cube, forming a triangular pyramidal recess. When viewed from directly above, a retroreflector with such retroreflective elements arranged in a two-dimensional array has equilateral triangles arranged in the densest possible order, as shown in Figure 3, for example. Light that reaches any of the reflective surfaces is reflected by the three corner deflectors and returns in the direction from which it was incident (retroreflection).

[0027] The special retroreflector 20 of this embodiment, like the general retroreflector described above, consists of multiple retroreflector elements 21, each having three reflective surfaces, arranged periodically in a two-dimensional array. However, the special retroreflector 20 differs from a general retroreflector in that one of the three surfaces constituting the retroreflector element 21 is a tilted surface that is inclined by an angle θ from a state where the angle it makes with the other adjacent surfaces is a right angle (90°). Specifically, for example, as shown in Figure 4, when the three mutually orthogonal surfaces are designated as surface A S1, surface B S2, and surface C S3, the retroreflector element 21 consists of three surfaces: the mutually orthogonal surfaces A S1 and B S2, and, for example, surface C' S3' which is inclined by an angle θ inward into a triangular pyramidal recess from surface C S3. The angle at which surface C' S3' is raised determines the offset angle of the emitted light relative to the incident light.

[0028] Note that angle θ may be greater than or less than 0°. In other words, face C' S3' may be inclined outward from the concave part of the triangular pyramidal shape.

[0029] Figure 5 schematically shows an example of the cross-sectional configuration of the special retroreflector 20 corresponding to the line I-I' shown in Figure 3. The special retroreflector 20 has a pair of opposing surfaces 20S1 and 20S2, and on the surface 20S1 side, the multiple triangular pyramidal recesses of the multiple retroreflective elements 21 that constitute the special retroreflector 20 are arranged in the closest possible proximity. As described above, one of the three surfaces (surface A S1, surface B S2, and surface C' S3') that constitute the retroreflective element 21 (surface C' S3') is a tilt surface that is inclined by an angle θ from a state where the angle it makes with the other adjacent surfaces is a right angle (90°). The tilt surfaces (surface C' S3') of the multiple retroreflective elements 21 are adjacent to each other in the YZ plane, for example, in the Z-axis direction which is the direction of travel of the vehicle, as shown in Figures 3 and 5.

[0030] Figure 6 illustrates the configuration of the retroreflective elements 21 at each position (pos1 to pos9) within the plane of the special retroreflective plate 20. The rotation angle (rotation angle) of the retroreflective elements 21 placed at each of pos1 to pos9 within the plane of the special retroreflective plate 20 can be determined depending on each position, for example, as shown in Table 1. Here, "determined" means the conditions that must be met for the eye box to be offset and reflect around the observer's eyes 100. The values ​​shown in Table 1 represent the amount of change from the direction of extension of one side by the C' plane S3' of the retroreflective element 21 at pos5, with the direction of extension of one side by the C' plane S3' constituting the bottom surface of the triangular pyramidal retroreflective element 21 placed at pos5 being the reference (0).

[0031]

[0032] Furthermore, the angle of the C' plane S3' of the retroreflective element 21 at each position (pos1 to pos9) within the plane of the special retroreflective plate 20 can also be determined depending on each position, as shown in Table 2, for example. The values ​​shown in Table 2 represent the amount of change from the C' plane S3' of the retroreflective element 21 at pos5, with the angle of the C' plane S3' of the retroreflective element 21 at pos5 being the reference (0).

[0033]

[0034] The rotation angles of each of the multiple retroreflective elements 21 arranged within the plane of the special retroreflective plate 20, and the angles between the mutually orthogonal A-planes S1 and B-planes S2 and the tilt plane (C'-plane S3'), are configured to change continuously from the left end to the right end of the special retroreflective plate 20. In this way, in a special retroreflective plate 20 where the angles between the A-planes S1 and B-planes S2 and the tilt plane (C'-plane S3') are optimized according to their positions within the plane, for example, the angle between a light ray incident at position pos1 and the tilt plane and the angle between a light ray incident at position pos9 and the tilt plane become the same, and the light is focused to a single point.

[0035] The reflective mirror 30, for example, reflects light emitted from the special retroreflector 20 in a predetermined direction. In this case, the reflective mirror 30 reflects the light emitted from the special retroreflector 20 towards the area around the observer 100's eyes by partial reflection. The reflective mirror 30 can also be used, for example, as a mirror to reflect light emitted from the display device 10 back to the special retroreflector 20.

[0036] The rotational drive unit 40 rotates the special retroreflective plate 20 by a predetermined angle in the in-plane direction. The rotational drive unit 40 includes a rotary motor 41 and a shaft 42 that connects the special retroreflective plate 20 and the rotary motor 41.

[0037] The detection camera 51 is for detecting the position of the observer's eyes 100.

[0038] In the projection device 1, light emitted from the display device 10 positioned above the observer 100 is directed toward a special retroreflector 20 positioned below the observer 100. Light from each image height is incident upon the special retroreflector 20 before it converges as an image, and after repeated specular reflection at each retroreflector element 21, it is given a predetermined offset angle and reflected as divergent light in a direction different from the direction of incidence. The divergent light emitted from the special retroreflector 20 is partially reflected by the reflection mirror 30 and incident around the observer 100's eyes. As a result, a wide-field-of-view (wide FOV) distant virtual image is displayed in front of the observer 100.

[0039] [Eyebox tracking behavior]

[0040] As mentioned above, typical retroreflectors work by returning reflected light directly to the optical axis of the incident light. The retroreflective elements that make up such retroreflectors are, for example, made by combining three plane mirrors at right angles to each other with their reflective surfaces facing inward, like the vertices of a cube. Therefore, even if the elements themselves are tilted or rotated, the reflected light rays are not altered. In other words, the pupil shift effect cannot be obtained.

[0041] In contrast, as described above, among the three surfaces of each of the plurality of retroreflective elements 21 constituting the special retroreflective plate 20 of the present embodiment, one surface is a tilt surface inclined by θ degrees from a state where the angle formed with the other adjacent surface is a right angle (90°). Therefore, by rotating or changing the position in the height direction of the element, the catadioptric pupil can be shifted in a uniaxial direction. The "catadioptric pupil" is defined as an optically conjugate positional relationship. Here, the light rays of each angular field radiated from the emission position of the light source reach the retroreflective element, and after retroreflection while maintaining the angle (or having a constant offset angle), the point that converges to a single point in space is defined as the catadioptric pupil as the point conjugate to the light source position.

[0042] In a head-up display, the point that converges to a single point in space (or the surface enlarged by a light guide plate or the like) is referred to as an eyebox, and the point in space where the entire angular field of this virtual image can be visually recognized may be defined as the catadioptric pupil.

[0043] FIG. 7 is a top view showing the position of the catadioptric pupil of the special retroreflective plate 20. FIG. 8 is a top view showing the movement of the catadioptric pupil due to the rotation of the special retroreflective plate 20. That is, by rotating the special retroreflective plate 20 in which the plurality of retroreflective elements 21 are periodically and repeatedly arranged in a two-dimensional array, for example, as shown in FIG. 8, in the YZ plane direction by θ, the catadioptric pupil position can be shifted in the direction of both eyes of the observer 100 (Y-axis direction).

[0044] FIG. 9 is a flowchart for explaining the driving of the projection device 1.

[0045] First, the detection camera 51 detects the position of the eyes of the observer 100 (step S101). After detecting the position of the eyes of the observer 100, the detection camera 51 outputs the position information to the control unit 12 (step S102).

[0046] Next, the control unit 12 calculates the rotation amount of the special retroreflective plate 20 based on the eye position information of the observer 100 input from the detection camera 51 (step S103). The rotation amount of the special retroreflective plate 20 is calculated, for example, as follows. First, the coordinate system of the detection camera 51 is compared with the coordinate system of the only point (eye box) where the entire virtual image can be visually recognized, and a target point for making the eye box follow the position of the observer 100's eyes is calculated. Next, the rotation amount of the special retroreflective plate 20 is calculated from the target point of the position information.

[0047] Subsequently, the control unit 12 generates a rotation signal corresponding to the calculated rotation amount and outputs it to the rotation drive unit 40 (step S104).

[0048] The rotation drive unit 40 drives the rotation motor 41 based on the input rotation signal to rotate the shaft 42, and rotates the special retroreflective plate 20 by a predetermined angle (step S105).

[0049] As described above, the eye box moves to the position of the observer 100's eyes detected by the detection camera 51 (step S106).

[0050] [Mounting Example on a Vehicle] When the projection device 1 is mounted on a vehicle, for example, the display device 10 is installed on the ceiling inside the vehicle, the special retroreflective plate 20 is arranged on the dashboard 32, and the windshield 31 also serves as a reflecting mirror 30. The detection camera 51 is arranged around the driver's seat (for example, in front of the driver (observer 100)) (see, for example, FIG. 14).

[0051] FIG. 10 shows an example of the movement direction of the eye box due to the rotation of the eye box and the special retroreflective plate 20 when the projection device 1 is mounted on a vehicle. The display device 10A has light sources 110R and 110L for the right eye and the left eye, and is arranged, for example, above the head of the observer 100. In the display device 10A having two light sources 110R and 110L for the right eye and the left eye, eye boxes ER and EL for the right eye and the left eye are formed respectively. The eye boxes ER and EL for the right eye and the left eye are shifted in the substantially Y direction as shown by the double-headed arrows in FIG. 10 by rotating the special retroreflective plate 20 arranged on the dashboard 32 in the in-plane direction.

[0052] Figure 11A shows the incidence of light rays emitted from the light sources 110A and 110B of the display device 10A onto the eye boxes ER and EL. Figure 11B shows the movement of the eye boxes due to the rotation of the special retroreflector 20. For example, if the observer 100 moves to the right from Figure 11A to Figure 11B, the special retroreflector 20 is rotated counterclockwise from the perspective of the observer 100, causing the light rays emitted from the light sources 110A and 110B to be reflected to the right. As a result, the eye boxes ER and EL shift to follow the observer 100's eyes as they move to the right.

[0053] Furthermore, the right and left eye eye boxes ER and EL, respectively, formed by independent light sources for the right and left eyes, have a vertically elongated shape, as shown in Figure 10, etc. Therefore, the movement of the observer 100 in the axial direction (X-axis direction) is covered by these optical eye boxes.

[0054] Figure 12 shows another example of the direction of movement of the eyebox due to the rotation of the eyebox and the special retroreflective plate 20 when the projection device 1 is mounted on a vehicle. The display device 10B has one light source 110 and is positioned, for example, above the head of the observer 100. In the display device 10A consisting of one light source 110, one eyebox E is formed. This one eyebox E is shifted approximately in the Y-axis direction, as shown by the double arrows in Figure 12, by rotating the special retroreflective plate 20, which is positioned on the dashboard 32, in the in-plane direction.

[0055] Figure 13 illustrates the movement of the eyebox due to the rotation of the special retroreflector 20 in response to the light rays emitted from the display device 10 shown in Figure 12. For example, if the observer 100 moves to the right, rotating the special retroreflector 20 counterclockwise from the observer 100's perspective causes the light rays emitted from the light source 110 to reflect to the right, as shown in Figure 13. As a result, the eyebox E shifts to follow the eyes of the observer 100 as they move to the right.

[0056] Furthermore, the eye box E formed by a single light source has a horizontally elongated shape that spans both eyes of the observer 100, as shown in Figure 12, etc. Therefore, movement of the observer 100 in the axial direction (X-axis direction) can be covered by combining it with a separate pupil tracking device.

[0057] Figure 14 shows an example configuration of a projection device 1A equipped with an eye-tracking device having a mirror device 52 and a rotary motor 53. The mirror device 52 reflects light emitted from the display device 10B in a predetermined direction and corresponds to a specific example of the "second reflective mirror" as one embodiment of the present disclosure. The rotary motor 53 shifts the mirror device 52 in the direction of vehicle travel (Z-axis direction) and corresponds to a specific example of the "first drive unit" as one embodiment of the present disclosure.

[0058] In the projection device 1A, the position (height) information of the observer 100's eyes is grasped by the detection camera 51, and after calculating the amount to shift the eye box in the X-axis direction, the eye box is made to track according to the pupil tracking output. For example, as shown in Figure 14, when the mirror device 52 is moved back and forth in the direction of vehicle travel (Z-axis direction), the incident position of the light emitted from the display device 10B onto the special retroreflector 20 and the incident position of the light emitted from the special retroreflector 20 (reflected light) onto the windshield 31 are shifted accordingly in the direction of vehicle travel (Z-axis direction). In other words, the eye box comes to track the direction of the observer 100's body axis (X-axis direction), and the eye box can be substantially enlarged.

[0059] Furthermore, the tracking of the eyebox in the direction of the observer 100's body axis (X-axis direction) can also be achieved, for example, by moving the position of the special retroreflective plate 20 in the direction of the observer 100's body axis (X-axis direction).

[0060] [Function and Effects] In the projection device 1 of this embodiment, a rotation drive unit 40 is provided to rotate a special retroreflector 20 that reflects light emitted from the display device 10 with a predetermined offset angle relative to the incident direction, thereby directing the light in a desired direction. This allows for the projection of a wide-angle virtual image without, for example, using a large mirror optical system. This will be explained below.

[0061] In recent years, development has been progressing on HUD (Head-Up Display) systems that display speed, navigation, and other information to the driver in the front seats of a vehicle, and use light reflection on the windshield to display virtual images including driving support information and warning information.

[0062] Generally, due to the size limitations of display devices, existing HUDs are limited to displaying information only in an area with a viewing angle of about 10 degrees (the central area in front). On the other hand, in the world of computer graphics (CG), there are many examples of warning information and augmented reality (AR) information being superimposed and displayed across the entire windshield. However, in reality, no device exists that can actually achieve this, and none are installed in actual vehicles.

[0063] For example, when a display device is placed in the dashboard area, there is a method that uses the Pepper's Ghost technique to make a virtual image appear to float over a wide area. However, in this method, the virtual image is only visible for the distance between the display device and the windshield, so it is not possible to display virtual images at a distance. Therefore, conventional technology has not been able to display virtual images at a wide FOV and at a distance, and there has been no way to realize the ideal world of computer graphics.

[0064] In contrast, in this embodiment, the light emitted from the display device 10 is directed in a desired direction using a special retroreflector 20 that reflects the light with a predetermined offset angle relative to the incident direction. Light from each image height is incident on the special retroreflector 20 before it forms an image as convergent light, and is reflected as divergent light in a direction different from the incident direction. The divergent light emitted from the special retroreflector 20 is partially reflected by the reflection mirror 30 and incident on the area around the observer 100's eyes. As a result, a virtual image with a wide field of view is drawn in front of the observer 100.

[0065] As a result, it is possible to provide a projection device 1 capable of displaying a virtual image with a wide field of view (FOV).

[0066] Furthermore, the projection device 1 of this embodiment is equipped with a rotation drive unit 40 that rotates the special retroreflective plate 20 by a predetermined angle in the in-plane direction. This makes it possible to shift the light rays returning to the area around the observer's eyes 100 to a desired position without moving the display device 10. In other words, it becomes possible to realize a HUD that can move the eye box to a desired position in a compact volume.

[0067] Next, modifications 1 to 3 of the present disclosure will be described. In the following, components similar to those in the above embodiments will be denoted by the same reference numerals, and their descriptions will be omitted as appropriate.

[0068] <2. Modified Examples> (2-1. Modified Example 1) Figure 15 shows an example of the configuration of a special retroreflective plate (special retroreflective plate 20A) according to Modified Example 1 of the present disclosure. Figure 15(A) schematically shows the planar configuration of the special retroreflective plate 20A. Figure 15(B) schematically shows the cross-sectional configuration of the special retroreflective plate 20A. Figure 15(C) schematically shows the rotational modes of each structural part constituting each region of the special retroreflective plate 20A.

[0069] In the above embodiment, an example was shown in which the entire special retroreflective plate 20 is rotated, but the invention is not limited to this. In this modified example, the special retroreflective plate 20A is divided into five regions X1 to X5 in a strip-like shape, and each region is rotated independently.

[0070] The special retroreflective plate 20A consists of five structural parts 20-1 to 20-5, each divided into regions X1 to X5. The structural parts 20-1 to 20-5 are arranged in two layers: a first layer 22 and a second layer 23. Specifically, the three structural parts 20-1, 20-3, and 20-5 that constitute regions X1, X3, and X5 are arranged in the first layer 22, and the two structural parts 20-2 and 20-4 that constitute regions X2 and X4 are arranged in the second layer 23. Each of the structural parts 20-1 to 20-5 is configured to partially overlap with an adjacent structural part. A rotational drive unit 40 is provided for each of the five structural parts 20-1 to 20-5.

[0071] Figure 16 shows another example of the configuration of the special retroreflective plate according to Modification 1 of the present disclosure (special retroreflective plate 20B). Figure 16(A) schematically shows the planar configuration of the special retroreflective plate 20B. Figure 16(B) schematically shows the cross-sectional configuration of the special retroreflective plate 20B. Figure 16(C) schematically shows the rotational modes of each structural part constituting each region of the special retroreflective plate 20B.

[0072] The special retroreflective plate 20 may be divided in a grid pattern within its surface into, for example, 15 regions X1 to X15, as shown in the special retroreflective plate 20B in Figure 16. The special retroreflective plate 20B consists of 15 structural parts 20-1 to 20-15, each separated for regions X1 to X15. The structural parts 20-1 to 20-15 have a substantially rectangular shape and are arranged in four layers: a first layer 22, a second layer 23, a third layer 24, and a fourth layer 25. Specifically, the six structural parts 20-1, 20-3, 20-5, 20-11, 20-13, and 20-15 that constitute regions X1, X3, X5, X11, X13, and X15 are arranged on the first layer 22, the four structural parts 20-2, 20-4, 20-12, and 20-14 that constitute regions X2, X4, X12, and X14 are arranged on the second layer 23, the three structural parts 20-6, 20-8, and 20-10 that constitute regions X6, X8, and X10 are arranged on the third layer 24, and the two structural parts 20-7 and 20-9 that constitute regions X7 and X9 are arranged on the fourth layer 25. Each of the structural parts 20-1 to 20-15 is configured to partially overlap with the adjacent structural part. Each of the structural parts 20-1 to 20-15 is provided with a rotary drive unit 40.

[0073] Figure 17 shows another example of the configuration of the special retroreflective plate according to Modification 1 of the present disclosure (special retroreflective plate 20C). Figure 17(A) schematically shows the planar configuration of the special retroreflective plate 20C. Figure 17(B) schematically shows the cross-sectional configuration of the special retroreflective plate 20C. Figure 17(C) schematically shows the rotational modes of each structural part constituting each region of the special retroreflective plate 20C.

[0074] The special retroreflective plate 20 may be divided in a honeycomb shape within its surface into, for example, 17 regions X1 to X17, as shown in the special retroreflective plate 20C in Figure 16. The special retroreflective plate 20C consists of 17 structural parts 20-1 to 20-17, each separated for regions X1 to X17. The structural parts 20-1 to 20-17 have a substantially honeycomb shape and are arranged in three layers: a first layer 22, a second layer 23, and a third layer 24. Specifically, the five structural parts 20-6, 20-7, 20-13, 20-14, and 20-15 that constitute regions X6, X7, X13, X14, and X15 are arranged in the first layer 22. The five structural parts 20-3, 20-4, 20-5, 20-11, and 20-12 that constitute regions X3, X4, X5, X11, and X12 are arranged on the second layer 23. The seven structural parts 20-1, 20-2, 20-8, 20-9, 20-10, 20-16, and 20-17 that constitute regions X1, X2, X8, X9, X10, X16, and X17 are arranged on the third layer 24. Each of the structural parts 20-1 to 20-17 is configured to partially overlap with the adjacent structural part. Each of the structural parts 20-1 to 20-17 is provided with a rotary drive unit 40.

[0075] In this way, by dividing the special retroreflective plate 20 into multiple regions and rotating each region, the area required to rotate the special retroreflective plate 20 can be reduced. Furthermore, by dividing the special retroreflective plate 20 into multiple regions and rotating each region, the load on the rotary motor 41 that constitutes the rotation drive unit 40 for rotating the special retroreflective plate 20 can be reduced. Therefore, it becomes possible to realize a HUD that can move the eye box to a desired position in a more compact volume.

[0076] Furthermore, the special retroreflective plates 20A, 20B, and 20C of this modified example can have a degree of freedom in their rotation angle for each region. For example, the special retroreflective plates 20A, 20B, and 20C can adjust the angle of light for each field of view according to the rotation angle for each region, so that the return position of the reflected and bent light rays can be adjusted according to the curvature of the windshield 31. In other words, although the curvature of the windshield differs depending on the vehicle model, by determining the rotation angle of each structural part for each region while taking into account the curvature shape of the windshield, it becomes possible to realize a HUD that can accommodate multiple vehicle models.

[0077] (2-2. Modification 2) Figure 18 shows an example configuration of a projection device (projection device 2) according to Modification 2 of the present disclosure. Similar to the above embodiment, projection device 2 is used in a head-up display (HUD) system that displays speed, navigation, etc., to the driver in the front seat of a vehicle, and displays a virtual image including driving support information and warning information using light reflection from the windshield.

[0078] [Configuration of the projection device] The projection device 2 comprises a display device 10, a reflective mirror 30, a rotation drive unit 40, a detection camera 51 (not shown), a special retroreflective group 60, and a polarizing plate 64. The special retroreflective group 60 includes an anisotropic prism sheet 61, a λ / 4 wave plate 62, and a retroreflective plate 63.

[0079] The display device 10 projects a virtual image in front of the observer 100 and has the same configuration as in the above embodiment.

[0080] The reflective mirror 30, for example, reflects light L emitted from the display device 10 in a predetermined direction. Here, the reflective mirror 30 reflects the light L emitted from the display device 10 toward the special retroreflection group 60, and also reflects the light emitted from the special retroreflection group 60 (returned light) toward the area around the observer 100's eyes by partial reflection.

[0081] The rotational drive unit 40 rotates the special retroreflective group 60 by a predetermined angle in the in-plane direction. The rotational drive unit 40 includes a rotary motor 41 and a shaft 42 that connects the special retroreflective group 60 and the rotary motor 41.

[0082] The special retroreflection group 60 reflects light L incident via the reflective mirror 30 with an angle offset in a predetermined direction, and corresponds to one specific example of a "retroreflector" as one embodiment of the present disclosure. The special retroreflection group 60 is composed of, for example, an anisotropic prism sheet 61, a λ / 4 wave plate 62, and a retroreflector 63.

[0083] The anisotropic prism sheet 61 is an optical component having refractive index anisotropy. Figure 19 is a perspective view showing an example of the configuration of the anisotropic prism sheet 61. Figure 20 schematically shows an example of the cross-sectional configuration of the anisotropic prism sheet 61. As shown in Figure 19, the anisotropic prism sheet 61 consists of multiple prisms having ridges extending in the X-axis direction, arranged in parallel in the Y-axis direction.

[0084] As described above, the anisotropic prism sheet 61 has refractive index anisotropy. Specifically, when the refractive index in the direction of the prism's edge (X-axis direction) is nx, the refractive index in the parallel direction of the multiple prisms (Y-axis direction) is ny, and the refractive index in the thickness direction of the prism (Z-axis direction) is nz, the refractive index nx is the largest, and the refractive indexes ny and nz are approximately equal (nx > ny ≈ nz).

[0085] Preferably, the refractive index nx and refractive index ny (or refractive index nz) have a refractive index difference Δn of 0.1 or more (Δn = nx - ny ≥ 0.1). Furthermore, preferably, the refractive index nx and refractive index ny (or refractive index nz) have a refractive index difference Δn of 0.2 or more (Δn = nx - ny ≥ 0.2). The refractive index difference Δn between refractive index nx and refractive index ny (or refractive index nz) determines the offset amount of the emission angle of light L emitted from the special retroreflection group 60 with respect to the incidence angle of light L incident on the special retroreflection group 60, as described later. A larger refractive index difference Δn has the advantage of allowing for a larger offset amount. On the other hand, increasing the refractive index difference Δn presents challenges such as difficult manufacturing processes and difficulty in material selection.

[0086] The pitch (W) of the multiple prisms constituting the anisotropic prism sheet 61 is preferably, for example, 10 μm or more and 200 μm or less. This is because if the prism pitch (W) is too small, light will diffract. Also, if the prism pitch (W) is too large, there is a concern that it will be difficult to manufacture.

[0087] The anisotropic prism sheet 61 can be formed, for example, using a crystalline resin material that exhibits refractive index anisotropy upon stretching. Examples of such resin materials include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and aramid.

[0088] The λ / 4 wave plate 62 is a polarizing optical element that corrects the polarization state of the light passing through it, and is designed to generate a phase difference of λ / 4 wavelength with respect to the passing light. The axis of the λ / 4 wave plate 62 is in the XY plane and is tilted at 45° from the X-axis direction. Here, the λ / 4 wave plate 62 is selected in the polarizer 64, and a phase difference of λ / 4 wavelength is applied to the S-polarized light L that has passed through the anisotropic prism sheet 61, causing it to be emitted as right-handed circularly polarized light.

[0089] The retroreflector 63 is a general retroreflector as described in the above embodiment, and has a mechanism that returns the reflected light directly to the optical axis of the incident light. The retroreflector 63 has multiple retroreflecting elements arranged periodically in a two-dimensional array. The light ray (right-handed circularly polarized) incident on each retroreflecting element undergoes sequential specular reflection on a reflective surface consisting of three surfaces arranged at right angles to each other, and as a result, ultimately returns in the direction of incidence as left-handed circularly polarized light.

[0090] The retroreflector 63 preferably has a transparent resin layer provided on a base material on which a reflective surface including three faces is formed. This is because the light L incident on the retroreflector 63 is refracted by the resin layer, allowing for more efficient retroreflection compared to the case where there is no resin layer and no refraction occurs. The resin layer preferably has a high refractive index and high transparency. Examples of materials that can be used for the resin layer include acrylic resin, polycarbonate resin, and epoxy resin.

[0091] In actual retroreflective panels, when circularly polarized light is reflected once, most of it becomes reverse-polarized light, with a small amount of light remaining in its original circular polarization state. However, this technology works without problems even in such cases.

[0092] The polarizing plate 64 includes a polarizer having a polarization axis in a predetermined direction and rectifies the polarization of light L emitted from the display device 10. The polarizing plate 64 polarizes or selectively transmits light L emitted from the display device 10 in a predetermined direction. Specifically, the polarizing plate 64 has a transmission axis perpendicular to the plane of the paper (YZ plane) in Figure 18 (in the X-axis direction), and selectively transmits the S-polarized component of the light L emitted from the display device 10, which includes both S-polarized and P-polarized components.

[0093] Furthermore, if polarized light L is emitted directly from the display device 10, the polarizing plate 64 can be omitted.

[0094] The behavior of the light L emitted from the display device 10 will be explained with reference to Figure 18.

[0095] First, let's explain the forward path. Light L emitted from the display device 10 passes through the polarizing plate 64, becoming linearly polarized (S-polarized), and is incident on the anisotropic prism sheet 61 constituting the special retroreflection group 60 via the reflective mirror 30. The S-polarized light L incident on the anisotropic prism sheet 61 has its refractive index nx in the direction of the edge of the anisotropic prism sheet 61 as its effective refractive index, and is emitted from the anisotropic prism sheet 61 with a refraction angle corresponding to the refractive index nx and the angle of the prism, while maintaining its polarization. The S-polarized light L emitted from the anisotropic prism sheet 61 is incident on the λ / 4 wave plate 62, and is emitted as right-handed circularly polarized light. This completes the forward path.

[0096] Next, when right-handed circularly polarized light L is incident on the retroreflector 63, as shown in Figure 7, for example, it is reflected once each by the three surfaces 331S1, 331S2, and 331S3 of the unit element 331, for a total of three times, and is emitted as left-handed circularly polarized light. This is because, in ideal reflection, circularly polarized light becomes reversed circularly polarized light after one reflection, and when this is repeated three times, left-handed circularly polarized light is emitted in response to right-handed circularly polarized light.

[0097] Next, let's explain the return journey. The left-handed circularly polarized light L emitted from the retroreflector 63 is incident on the λ / 4 wave plate 62 and is emitted as linearly polarized light (P-polarized light) parallel to the plane of the paper. When the P-polarized light L emitted from the λ / 4 wave plate 62 is incident on the anisotropic prism sheet 61, the refractive index ny in the parallel direction of the multiple prisms and the refractive index nz in the thickness direction of the prism become the effective refractive index, and the light is emitted from the anisotropic prism sheet 61 with a refraction angle corresponding to the refractive index ny and refractive index nz and the angle of incidence, and with the polarization maintained. Here, since the refractive index ny and refractive index nz are small compared to the refractive index nx, the degree of refraction of the light L incident on the anisotropic prism sheet 61 is smaller on the return journey compared to the outward journey. As a result, the angle of the light L emitted from the special retroreflector group 60 (return light) is offset with the angle of the light L (incident light) incident on the special retroreflector group 60. The P-polarized light L emitted from the anisotropic prism sheet 61 passes through the reflective mirror 30 and enters the eye of the observer 100.

[0098] Thus, in the projection device 2 of this modified example, a special retroreflective group 60 is used, which includes an anisotropic prism sheet 61, a λ / 4 wave plate 62, and a retroreflective plate 63. Even with this configuration, the projection device 2 of this modified example can obtain the same effects as the projection device 1 of the above embodiment.

[0099] (2-3. Modification 3) Figure 21 schematically shows an example of the configuration of a display device (display device 10C) according to Modification 3 of the present disclosure. The projection device 1 of the above embodiment and the projection device 2 of Modification 2 can be further enlarged by using a display device 10C equipped with a pupil replicating device, which will be described later.

[0100] The display device 10C uses, for example, a reflective liquid crystal (LCOS) or Digital Lighting Processing (DLP) intensity modulation panel 14A to emit illumination light (light L) with image information superimposed on it. The display device 10C includes, for example, an intensity modulation panel 14A, a PBS 141, a projection lens 192 consisting of multiple lenses with pupils at the exit port, and a pupil replicating device (for example, a pupil replicating device 70).

[0101] Figure 22 shows an example of the configuration of a pupil replicating device (pupil replicating device 70). The pupil replicating device 70 includes, for example, a light guide plate 71 extending in the X-axis direction and a transmittance adjustment prism 74 positioned on the HOE 73B and extending in the Y-axis direction.

[0102] The light guide plate 71 is a so-called holographic light guide plate, for example, having a light-reflecting film 72 on one of a pair of opposing surfaces and holographic optical elements (HOEs) 73A and 73B on the other surface, and is positioned at the pupil position X of the projection lens 192. HOE 73A is for propagating incident light into the light guide plate 71 and is positioned at the pupil position X. HOE 73B is for extracting light from the light guide plate 71 and is positioned at one or more locations after propagation. As a result, multiple pupils Xa, Xb, and Xc are duplicated in the X-axis direction.

[0103] Figure 23 illustrates the principle of pupil replication in the X-axis direction by the light guide plate 71. Figure 24 illustrates the compensation relationship between diffraction and wavelength dispersion. The wavelength dispersion of light L incident on the light guide plate 71 is compensated for by the in and out HOEs 73A and 73B.

[0104] Figure 25 illustrates the principle of pupil duplication in the Y-axis direction using a transmittance adjustment prism 74. The transmittance adjustment prism 74 consists of multiple prisms with adjusted transmittance arranged in a single axis direction. For example, seven prisms 741, 742, 743, 744, 745, 746, and 747 are arranged in a single axis direction. In the transmittance adjustment prism, the transmittance of the n prisms arranged in a single axis direction is adjusted in stages. By setting the reflectance of the first prism to (N-1) / N and the reflectance of the second and subsequent prisms to 1 / (N-n+1), the amount of light emitted from each surface becomes equal. For example, when the amount of light incident on the transmittance adjustment prism is P and the number of prisms is N, the amount of light emitted from the nth prism surface is expressed by the following formula (1).

[0105]

[0106] By setting these values ​​appropriately, the amount of light emitted from each prism 741, 742, 743, 744, 745, 746, and 747 can be made uniform. This allows for the viewing of an image with consistent intensity at any point within the eye box.

[0107] Figure 26 schematically shows the planar and cross-sectional configurations of a pupil replicating device 80 as another example of the configuration of a pupil replicating device. The pupil replicating device 80 is a light guide plate having a pair of opposing surfaces 81S1 and 81S2. The light guide plate 81 has, for example, a total reflection region 82 in which a plurality of prisms 821, each having a reflective surface inclined in a predetermined direction (for example, a reflective surface inclined at approximately 45° with respect to the body axis direction (X-axis direction) of the observer 100), are arranged in the X-axis direction, and an emission region 83 in which a plurality of prisms 831 extending in the X-axis direction are arranged in the Y-axis direction. An incident portion 84 is provided on the surface 81S2 of the light guide plate 81 opposite to the surface 81S1 which is the light emission surface.

[0108] The pupil duplication device 80 is positioned at the pupil position of the projection lens 192. Light L incident on the incident section 84 from the projection lens 192 propagates through the total reflection region 82 and is reflected in the Y-axis direction by each prism 821 arranged in the X-axis direction. The light L reflected by each prism 821 is then reflected in the Z-axis direction by each prism 831 arranged in the Y-axis direction and emitted from the surface 81S1, for example, as shown in Figure 27. For example, in a light guide plate 81 where 10 prisms 821 are arranged in the X-axis direction and 5 prisms 831 are arranged in the Y-axis direction, as shown in Figure 26, one incident light ray is expanded (duplicated) into 10 light rays in the total reflection region 82, and further expanded (duplicated) into 50 light rays in the emission region 83 before being emitted. In other words, 50 pupils are duplicated in the X-axis and Y-axis directions.

[0109] Thus, by using the display device 10C of this modified example, which is equipped with a pupil replicating device 70 and a pupil replicating device 80, the projection devices 1 and 2 described above can further expand the eye box in the direction of the observer 100's body axis (X axis direction) and binocular direction (Y axis direction).

[0110] Although embodiments and modifications 1 to 3 have been described above, this disclosure is not limited to the above embodiments, and various modifications are possible. For example, the arrangement and number of optical system components illustrated in the above embodiments are merely examples, and it is not necessary to include all components, and other components may also be included.

[0111] Furthermore, while the above embodiments show an example of shifting the eye box towards the observer 100's eyes by rotating the special retroreflective plate 20 in the in-plane direction, the invention is not limited to this. For example, by moving the special retroreflective plate 20 up and down in an upright direction perpendicular to the in-plane direction, the eye box can be shifted in the direction of the observer 100's body axis.

[0112] Furthermore, the effects described herein are merely examples and are not limited to those described; other effects may also occur.

[0113] The present technology can also take the following configurations. According to the present technology with the following configurations, a rotation drive unit is provided to rotate a retroreflector that reflects light with a predetermined offset angle with respect to the incident direction, so that the light emitted from the light source is emitted in a desired direction. For example, a wide-angle virtual image can be drawn without using a large mirror optical system. Therefore, it is possible to provide a projection device that can display a wide-field-of-view virtual image. (1) A projection device comprising: a light source; a retroreflector that reflects light incident from the light source with a predetermined offset angle with respect to the incident direction; a rotation drive unit that rotates the retroreflector; and a first reflective mirror that reflects the light emitted from the retroreflector in a predetermined direction. (2) The projection device according to (1), wherein the rotation drive unit rotates the retroreflector in the in-plane direction. (3) The projection device according to (1) or (2), wherein the retroreflector has a plurality of regions in the in-plane direction, and the rotation drive unit rotates the retroreflector independently in the in-plane direction for each region. (4) The projection apparatus according to (3), wherein the retroreflector consists of a plurality of structural parts that each constitute the plurality of regions. (5) The projection apparatus according to (4), wherein a rotary motor is provided in each of the plurality of structural parts. (6) The projection apparatus according to (4) or (5), wherein each of the plurality of structural parts is arranged in a plurality of layers such that a portion of them overlaps with each other in the thickness direction perpendicular to the in-plane direction. (7) The projection apparatus according to any one of (4) to (6), wherein each of the plurality of structural parts has a substantially rectangular shape. (8) The projection apparatus according to any one of (4) to (6), wherein each of the plurality of structural parts has a substantially honeycomb shape. (9) The projection apparatus according to any one of (1) to (8), wherein the retroreflector includes a plurality of retroreflector elements arranged in an array in the in-plane direction, the plurality of retroreflector elements consist of one adjacent face and a plurality of other faces, the plurality of other faces are in contact with each other at an angle of 90°, and the one face and the plurality of other faces are in contact with each other at an angle greater than or less than 90°.(10) The projection device according to any one of (1) to (9), wherein the retroreflector includes a plurality of retroreflectors arranged in an array in the in-plane direction, and each of the plurality of retroreflectors has a triangular pyramidal shape consisting of three faces. (11) The projection device according to any one of (1) to (10), further comprising a first polarizing optical element, a second polarizing optical element, and an anisotropic prism sheet having refractive index anisotropy between the light source and the retroreflector, wherein the first polarizing optical element is positioned downstream of the light source, the second polarizing optical element is positioned between the anisotropic prism sheet and the retroreflector, and the rotation drive unit rotates the anisotropic prism sheet, the second polarizing optical element, and the retroreflector in the in-plane direction. (12) The projection apparatus according to any one of (1) to (11), further comprising a pupil-tracking device between the light source and the retroreflective plate, wherein the direction of the human body axis is the X-axis direction and the direction of both eyes is the Y-axis direction, and the viewing area is shifted in the X-axis direction or the Y-axis direction according to the position of the human pupil. (13) The projection apparatus according to (12), wherein the pupil-tracking device comprises a second reflective mirror that reflects the light emitted from the light source in a predetermined direction and a first drive unit that shifts the second reflective mirror in the Z-axis direction. (14) The projection apparatus according to any one of (1) to (13), further comprising a pupil-replicating device between the light source and the retroreflective plate, wherein the direction of the human body axis is the X-axis direction and the direction of both eyes is the Y-axis direction, and the pupil is replicated in at least one of the Y-axis direction and the X-axis direction. (15) The projection apparatus according to (14), wherein the pupil replicating device has a holographic optical element on one surface and a light guide plate extending in one of the Y-axis direction and the X-axis direction. (16) The projection apparatus according to (15), wherein the pupil replicating device further has a transmittance adjustment prism disposed on the one surface side of the light guide plate and extending in the other of the Y-axis direction and the X-axis direction. (17) The projection apparatus according to any one of (1) to (16), further having a detection camera for detecting the position of a human pupil.

[0114] This application claims priority based on Japanese Patent Application No. 2024-163644, filed with the Japan Patent Office on September 20, 2024, and all contents of that application are incorporated herein by reference.

[0115] Those skilled in the art will understand that various modifications, combinations, subcombinations, and changes can be conceived depending on design requirements and other factors, and that these fall within the scope of the attached claims and their equivalents.

Claims

1. A projection device comprising: a light source unit; a retroreflector that reflects light incident from the light source unit with a predetermined offset angle relative to the incident direction; a rotation drive unit that rotates the retroreflector; and a first reflective mirror that reflects light emitted from the retroreflector in a predetermined direction.

2. The projection apparatus according to claim 1, wherein the rotational drive unit rotates the retroreflective plate in the in-plane direction.

3. The projection apparatus according to claim 1, wherein the retroreflector has a plurality of regions in the in-plane direction, and the rotation drive unit rotates the retroreflector independently in the in-plane direction for each region.

4. The projection apparatus according to claim 3, wherein the retroreflective plate comprises a plurality of structural parts that each constitute the plurality of regions.

5. The projection apparatus according to claim 4, wherein each of the plurality of structural parts is provided with the rotational drive unit.

6. The projection apparatus according to claim 4, wherein the plurality of structural parts are arranged in a plurality of layers such that a portion of each overlaps with the others in a thickness direction perpendicular to the in-plane direction.

7. The projection apparatus according to claim 4, wherein each of the plurality of structural parts has a substantially rectangular shape.

8. The projection apparatus according to claim 4, wherein each of the plurality of structural parts has a substantially honeycomb shape.

9. The projection apparatus according to claim 1, wherein the retroreflector includes a plurality of retroreflector elements arranged in an array in the in-plane direction, the plurality of retroreflector elements consist of one adjacent face and a plurality of other faces, the plurality of other faces are in contact with each other at an angle of 90°, and the one face and the plurality of other faces are in contact with each other at an angle greater than or less than 90°.

10. The projection device according to claim 1, wherein the retroreflective plate includes a plurality of retroreflective elements arranged in an array in the in-plane direction, and each of the plurality of retroreflective elements has a triangular pyramidal shape consisting of three faces.

11. The projection apparatus according to claim 1, further comprising a first polarizing optical element, a second polarizing optical element, and an anisotropic prism sheet having refractive index anisotropy between the light source unit and the retroreflector, wherein the first polarizing optical element is positioned downstream of the light source unit, the second polarizing optical element is positioned between the anisotropic prism sheet and the retroreflector, and the rotation drive unit rotates the anisotropic prism sheet, the second polarizing optical element, and the retroreflector in the in-plane direction.

12. The projection apparatus according to claim 1, further comprising a pupil-tracking device between the light source and the retroreflective plate, wherein the X-axis direction of the human body is defined as the X-axis direction and the Y-axis direction of both eyes is defined as the Y-axis direction, and the visual field is shifted in the X-axis direction or the Y-axis direction according to the position of the human pupil.

13. The projection apparatus according to claim 12, wherein the pupil tracking device comprises a second reflective mirror that reflects the light emitted from the light source in a predetermined direction, and a first drive unit that shifts the second reflective mirror in the Z-axis direction.

14. The projection apparatus according to claim 1, wherein the axis of the human body is the X-axis direction and the direction of both eyes is the Y-axis direction, and a pupil replication device for replicating pupils in at least one of the Y-axis direction and the X-axis direction is further provided between the light source unit and the retroreflective plate.

15. The projection device according to claim 14, wherein the pupil replication device has a holographic optical element on one surface and a light guide plate extending in one of the Y-axis direction and the X-axis direction.

16. The projection apparatus according to claim 15, further comprising a transmittance adjustment prism disposed on one side of the light guide plate and extending in the other direction of the Y-axis and the X-axis, as the pupil replication apparatus.

17. The projection device according to claim 1, further comprising a detection camera for detecting the position of a human pupil.

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