Aerial projection device

Abstract

Provided is an aerial projection device that can display an image in midair by using an image display means having a simple structure. This aerial projection device 10 is configured from: a holographic projector unit 10a that emits diffracted light which is illuminated collimated light diffracted on the basis of interference information regarding a hologram of a cube which is a prescribed image; and a projection unit 10b that comprises a stereoscopic screen 28 onto which the diffracted light is illuminated such that the cube is projected thereon, a second half-silvered mirror 30 which is disposed at an angle relative to the diffracted light illuminated onto the stereoscopic screen 28 at a location illuminated by transmitted-diffused light of the diffracted light that has been transmitted through and diffused by the screen, and a retroreflective sheet 32 which is illuminated by light transmitted through the second half-silvered mirror 30, wherein a real image 34 of the cube is formed in midair by reflected light, which is obtained by the light transmitted through the second half-silvered mirror 30, of the transmitted-diffused light, being reflected by the retroreflective sheet 32, emitted in the opposite direction along the original incidence path, and reflected by the second half-silvered mirror 30.

Description

[Technical Field]

[0001] The present invention relates to an aerial projection device. [Background technology]

[0002] There is a demand for an aerial projection device that can project an image of an elevator button in the air, thereby making elevator buttons contactless for the purpose of preventing the spread of infectious diseases, or an aerial projection device that can project a predetermined image in the air for educational purposes, games, etc. As an example of such an aerial projection device, Patent Document 1 listed below describes an aerial image forming device that can project an image displayed on a display device into the air. In this aerial image forming device, light output from the display device is reflected by a beam splitter toward a retroreflective sheet, and the light retroreflected by this retroreflective sheet passes through the beam splitter to form an image in the air. Patent Document 2 listed below also describes a spatial display device that can project an image displayed on an image display unit into the air. In this spatial display device, light output from the image display unit is reflected by a selective reflective film toward a retroreflective material, retroreflected by the retroreflective material, and passes through the selective reflective film to form an image in the air. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-207574 [Patent Document 2] JP 2018-92000 A Summary of the Invention [Problem to be solved by the invention]

[0004] The aerial image forming devices and spatial display devices described in the aforementioned Patent Documents 1 and 2 can display images displayed on a display device or image display unit in the air. However, as described in Patent Document 2, the display device or image display unit is required to emit image light having three-dimensional position information, resulting in a complex structure. For example, the image display unit in Patent Document 2 has a microlens array arranged on the display surface of a display panel such as a liquid crystal display panel. Aerial image forming devices and spatial display devices using image display means with such a complex structure are complex overall.

[0005] SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aerial projection device that can display an image in the air using image display means with a simple structure. [Means for solving the problem]

[0006] The aerial projection device of the present invention, which has been made to achieve the above-mentioned object, comprises a holographic projector unit that emits diffracted light obtained by diffracting irradiated parallel light based on interference information of a hologram of a predetermined image; a screen onto which the diffracted light is irradiated and the predetermined image is projected; a half mirror that is installed at an angle to the diffracted light irradiated onto the screen at a position where the transmitted diffused light of the diffracted light that has passed through the screen and diffused is irradiated; and a projection unit that comprises a retroreflection element onto which the transmitted light or reflected light of the half mirror is irradiated, wherein the transmitted light or reflected light of the transmitted diffused light from the half mirror is retroreflected by the retroreflection element and emitted in the opposite direction along the original incident path, and a real image of the predetermined image is formed in the air on one side of the half mirror by the reflected light reflected by the half mirror or the transmitted light that has passed through the half mirror.

[0007] By positioning the screen in a position forward or backward from the predetermined position where the real image is projected based on the interference information of the hologram so that the real image appears blurred, the range of expression of the aerial projection device can be expanded.

[0008] The retroreflective element is tilted so that the virtual image corresponding to the real image visible on the other side of the half mirror moves out of the field of view due to specular reflection from the retroreflective element, allowing the real image to be clearly visible.

[0009] Diffracted light diffracted based on the interference information of each hologram of at least two predetermined images is emitted from the holographic projector unit, and the diffracted light based on the interference information of one of the predetermined images is irradiated onto the screen and formed in the air via the half mirror and the retroreflective element, along with a real image of one of the predetermined images.In addition, diffracted light based on the interference information of the other of the predetermined images passes through the half mirror without being irradiated onto the screen and is irradiated onto the retroreflective light emission surface of the retroreflective element, thereby projecting the other of the predetermined images.At the same time, a virtual image of the other of the predetermined images can be seen in the air on the side opposite the reflective surface of the half mirror due to the reflected light of the retroreflective light emitted from the retroreflective light emission surface reflected by the half mirror, allowing the real image and virtual image to be recognized simultaneously.

[0010] By positioning the screen and / or the retroreflective element in a position forward or rearward of the predetermined position where the real image and / or the virtual image are projected based on the interference information of the hologram so that the real image and / or the virtual image appear blurred, one or both of the real image and the virtual image can be made to appear blurred, further expanding the range of expression of the aerial projection device.

[0011] When the screen is a stereoscopic screen, a stereoscopic image can be formed in the air.

[0012] The screen is made of Japanese paper or nonwoven fabric, so that a screen such as a three-dimensional screen can be easily formed.

[0013] At least two pairs of combinations of the half mirror and the screen are provided, and the two pairs of combinations are arranged in series at a predetermined interval so that the real image is formed in the air on the same side of each of the half mirrors, thereby making it possible to form a complex real image in the air.

[0014] The screen onto which a projected image corresponding to one of the real images is projected from the holographic projector unit is arranged to be movable in a direction toward or away from the half mirror so that at least one of the real images formed in the air on the same side of each of the half mirrors moves toward or away from the half mirror.By moving the screen in a direction toward or away from the half mirror, the real images can be moved toward or away from each other or one real image can be made to move behind the other real image.

[0015] Preferably, the hologram is a computer-generated hologram, and a spatial light modulator is provided that modulates the parallel light into diffracted light based on interference information of the computer-generated hologram, which makes it possible to easily create a desired hologram.

[0016] The computer-generated hologram is an amplitude hologram, and the amplitude hologram is expressed by the following formula (1):

number

[0017] The computer-generated hologram is a phase hologram, and the phase hologram is expressed by the following formula (2):

number

[0018] The aerial projection device of the present invention can have a simple structure in which the image display means is composed of a hologram on which interference information of a predetermined image is recorded, and a screen that has both translucency and diffusivity and onto which the predetermined image is projected by irradiating diffracted light based on the interference information of this hologram, and the structure of the device as a whole can also be simple. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram illustrating an aerial projection device to which the present invention is applied. [Figure 2] 10 is a schematic diagram illustrating another aerial projection device to which the present invention is applied. FIG. [Figure 3] 10 is a schematic diagram illustrating another aerial projection device to which the present invention is applied. FIG. [Figure 4] 10 is an explanatory diagram illustrating the state of a real image when the position of the screen is moved in another aerial projection device to which the present invention is applied. FIG. [Figure 5] 10 is an explanatory diagram illustrating the movement of a virtual image that is visually recognized in correspondence with a real image when the retroreflective element is tilted in another aerial projection device to which the present invention is applied. FIG. [Figure 6] 10 is a schematic diagram illustrating another aerial projection device to which the present invention is applied, in which a real image and a virtual image can be simultaneously viewed. FIG. [Figure 7] 1 is a schematic diagram illustrating the state of a real image and a virtual image when a retroreflective sheet is moved in an aerial projection device to which the present invention is applied, in which a real image and a virtual image can be simultaneously viewed. [Figure 8] 1 is a schematic diagram illustrating an aerial projection device to which the present invention is applied, in which a real image and a virtual image can be simultaneously viewed, in which a retroreflective sheet is divided and arranged when a flat screen is used. FIG. [Figure 9] 1 is a schematic diagram illustrating an aerial projection device to which the present invention is applied, in which a real image and a virtual image can be simultaneously viewed using a three-dimensional screen, in which a retroreflective sheet is divided and arranged. [Figure 10] 1 is a schematic diagram illustrating a device for measuring the visible light transmittance and diffusivity of a material used in a screen. [Figure 11] 1 is a schematic diagram illustrating an aerial projection device that allows multiple virtual images to be simultaneously viewed in the air. [Figure 12] FIG. 12 is a perspective view illustrating the installation state of a retroreflective sheet used in the aerial projection device shown in FIG. [Figure 13] 12 is a schematic diagram illustrating how a virtual image appears when a light-blocking object is placed on the other side of the second half mirror that constitutes the aerial projection device shown in FIG. 11. FIG. [Figure 14] 12 is a schematic diagram illustrating the movement of a virtual image when one of two retroreflective sheets used in the aerial projection device shown in FIG. 11 is moved in the vertical direction. [Figure 15] 12 is a schematic diagram illustrating the movement of a virtual image when the optical path from one half mirror 30 of the two retroreflective sheets used in the aerial projection device shown in FIG. 11 is lengthened. FIG. [Figure 16] 12 is a schematic diagram illustrating the movement of a virtual image when the aerial projection device shown in FIG. 11 uses one retroreflective sheet and the retroreflective sheet is movable. FIG. [Figure 17] 12 is a schematic diagram illustrating how a virtual image appears when two retroreflective sheets used in the aerial projection device shown in FIG. 11 are arranged side by side in the left and right directions of a rectangular half mirror. FIG. [Figure 18] Fig. 18(a) is a schematic diagram illustrating a guide device that guides a three-dimensional screen to the projection position of the holographic projector unit of an aerial projection device. Fig. 18(b) is a perspective view showing the projection state when the three-dimensional screen is positioned at the projection position of the holographic projector unit, and Fig. 18(c) is a perspective view showing the projection state when the three-dimensional screen is deviated from the projection position of the holographic projector unit. [Figure 19] Figure 19(a) is a front view showing the projection state when a flat screen is positioned at the projection position of the holographic projector unit, and Figure 19(b) is a front view showing the projection state when the flat screen is off the projection position (focal position) of the holographic projector unit. [Figure 20] 19 is a schematic diagram illustrating an example in which the guide device shown in FIG. 18 is used in a personal authentication device. [Figure 21] 19 is a schematic diagram illustrating an example in which the guide device shown in FIG. 18 is used in another personal authentication device. [Figure 22] FIG. 1 is a conceptual diagram for explaining the principle of creating a computer-generated hologram. [Figure 23] 3 is a schematic diagram illustrating the configuration of a CGH calculation unit that calculates an amplitude hologram. FIG. [Figure 24] 10 is a pseudocode for calculating an amplitude hologram. [Figure 25] 1 is a flowchart for calculating an amplitude hologram. [Figure 26] 3 is a schematic diagram illustrating the configuration of a CGH calculation unit that calculates a phase hologram. FIG. [Figure 27] 1 is a pseudocode for calculating a phase hologram. [Figure 28] 1 is a flowchart for calculating a phase hologram. [Figure 29] FIG. 29(a) is another pseudo-code for calculating an amplitude hologram, and FIG. 29(b) is another pseudo-code for calculating a phase hologram. [Figure 30] FIG. 4 is a schematic diagram illustrating an arrangement of three projection units 10b of the aerial projection device shown in FIG. 3. [Figure 31] 31 is a schematic diagram illustrating the direction in which a real image moves when the frame 26 of the projection unit 10b-2, out of the two projection units 10b-1 and 10b-2 shown in FIG. 30, is moved in the up-down direction. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in detail below, but the scope of the present invention is not limited thereto.

[0021] FIG. 1(a) shows an aerial projection device to which the present invention is applied. The aerial projection device 10 shown in FIG. 1(a) is composed of a holographic projector unit 10a and a projection unit 10b. The holographic projector unit 10a is composed of a personal computer (PC) 12 connected to a tablet-type terminal device 11, a reflective spatial light modulator (SLM) 14, a first half mirror 22, and a parallel light emitting unit 15. The parallel light emitting unit 15 is composed of a laser light emitting unit 16, an objective lens 18, and a plano-convex lens 20. In the holographic projector unit 10a, a computer-generated hologram (CGH) of a cube as a predetermined image input from the tablet-type terminal device 11 is calculated by a CGH calculation unit 17 of the PC 12 and displayed on the SLM 14. The interference fringes displayed on the SLM 14 are interference information holograms that project the cube at a predetermined position. Parallel light is irradiated onto the display surface of the SLM 14 on which such interference fringes are displayed. This parallel light is laser light emitted from laser light emitting unit 16 of parallel light emitting unit 15, which is first focused by objective lens 18 and then spreads, becomes parallel light by plano-convex lens 20, and is reflected toward the display surface of SLM 14 by first half mirror 22. The parallel light irradiated onto the display surface of SLM 14 becomes diffracted light based on the hologram interference information displayed on the display surface, emerges from the display surface of SLM 14, passes through first half mirror 22, and is emitted to projection unit 10b.

[0022] Projection unit 10b is composed of mirror 24, horizontally placed frame 26, three-dimensional screen 28 supported by support base 27 placed on the frame portion of frame 26, second half mirror 30 tilted at 45° with respect to frame 26 (tilt angle 45°), and retroreflective sheet 32 ​​as a retroreflective element arranged to face frame 26. Diffracted light incident on projection unit 10b from holographic projector unit 10a is reflected by mirror 24 placed at a tilt angle of 45°, passes through the hollow portion of frame 26, and illuminates three-dimensional screen 28. Three-dimensional screen 28 is formed in a shape similar to a cube as the predetermined image for which the computer-generated hologram is calculated, and is supported by support base 27 at a predetermined position that was the premise for calculating the computer-generated hologram.

[0023] As shown in FIG. 1(b), the three-dimensional screen 28 is made of a frame 28b and Japanese paper 28c (Tengu paper: weight 18 g / m 2 ) is attached to the stereoscopic screen 28. The Japanese paper 28c has a transmittance of 55% or more at the optical axis of the irradiated visible light (green laser light with a wavelength of 532 nm). As shown in FIG. 1(a), the diffusivity of the transmitted light from the irradiated visible light that has passed through the Japanese paper 28c at an angle of -10° to +10° relative to the optical axis of the visible light (green laser light with a wavelength of 532 nm) is 15% or more at the height between the top of the stereoscopic screen 28 and the midpoint of the second half mirror 30. The Japanese paper 28c forms three faces of a cube, which is supported by a support base 27 so that the three faces with the Japanese paper 28c facing the frame 26, as shown in FIG. 1(a). When diffracted light is irradiated onto the stereoscopic screen 28, a hologram-like projection image 28a of the cube is projected. The Japanese paper 28c forming the three surfaces of the stereoscopic screen 28 is a transparent diffuser that transmits and diffuses at least a portion of the irradiated diffracted light, so that, as shown in Figure 1(a), for example, light that has transmitted through each of the projection points 29a, 29a of the cubic projection image 28a is diffused and becomes transmitted diffused light. This transmitted diffused light passes through the second half mirror 30 and is incident on the retroreflective sheet 32.

[0024] As shown in FIG. 1(c), the retroreflective sheet 32 ​​has a transparent resin layer 33c formed on one side of the reflective sheet 33a, in which numerous glass beads 33b are arranged. As shown in FIG. 1(c), the retroreflective sheet 32 ​​retroreflects light by emitting outgoing light in the opposite direction to the incident light, along the path of the incident light. The diffused light incident on the retroreflective sheet 32 ​​is reflected by the second half mirror 30, as shown in FIG. 1(a), and forms a three-dimensional real image 34 of a cube in the air on one side of the second half mirror 30. Projection points 29a and 29b of the cube image 28a projected onto the stereoscopic screen 28 correspond to image points 34a and 34b of the real image 34. The real image 34 shown in FIG. 1(a) is a shape viewed from the side, and an enlarged view of the real image 34 viewed from the front is shown in FIG. 1(d). Points 34a and 34b shown in Figure 1(d) correspond to the image points 34a and 34b of real image 34 shown in Figure 1(a). While real image 34 shown in Figure 1 is a cube, changing its shape can be easily achieved by inputting the other shape from tablet terminal device 11 to PC 12, which then calculates a computer-generated hologram of the other shape, thereby easily displaying interference fringes of the other shape on SLM 14. The same applies to adding a pattern to a shape. While retroreflective sheet 32 ​​shown in Figure 1(c) uses a large number of glass beads 33b, it may also be a retroreflective sheet using a large number of prisms.

[0025] The projection unit 10b of the aerial projection device 10 shown in Fig. 1 is arranged parallel to the frame 26 on which the retroreflective sheet 32 ​​is arranged horizontally, but the retroreflective sheet 32 ​​may also be arranged perpendicular to the frame 26 as shown in Fig. 2. In this case, the real image 34 is also formed at approximately the same position in the air as the projection unit 10b shown in Fig. 1. However, in this case, when the real image 34 is viewed from the front, the image reflected by the retroreflective sheet 32 ​​may come into view.

[0026] While a three-dimensional screen 28 is used in Figures 1 and 2, a flat screen 36 (hereinafter simply referred to as screen 36) can also be created by attaching the peripheral edge of a sheet of Japanese paper to the frame of frame 26, as shown in Figure 3. Projected image 36a projected onto such a single screen 36 is a two-dimensional image (triangle) as shown in Figure 3(b), and real image 38 formed in the air is also a two-dimensional image. Figure 3(c) shows the shape of real image 38 (triangle) formed in the air as viewed from the front. Figure 3(c) shows image points 38a and 38b of real image 38, which correspond to projection points 37a and 37b of projected image 36a shown in Figures 3(a) and 3(b).

[0027] In the aerial projection device 10 shown in Figures 1 to 3, the interference fringes displayed on the SLM 14 of the holographic projector unit 10a are computer-generated holograms (CGHs) calculated by the CGH calculation unit 17 of the PC 12 so that a predetermined image is clearly projected onto the installed three-dimensional screen 28 or screen 36, in other words, so that the image is in focus on the three-dimensional screen 28 or screen 36. If the frame 26 on which the screen 36 in Figure 3(a) is mounted is moved to a position 26' on the second half mirror 30 side as shown in Figure 4(a), i.e., behind the CGH focal position, without changing the focal position of the CGH, the projected image 36a' (two-dimensional image (triangle)) projected onto the screen 36 becomes blurred as shown in Figure 4(b), and the resulting real image 38' also becomes blurred as shown in Figure 4(c). Moreover, this real image 38' is formed at a position closer to the second half mirror 30 as shown in Figure 4(a). In this way, simply by moving the position of the screen 36, the aerial image can be made blurred, thereby expanding the range of aerial image representation. For example, by gradually moving the screen 36 away from the second half mirror 30, the aerial image can be made to change from a blurred shape located far away to a clear shape located close by, making it possible to represent an object moving from far to close. In FIG. 4, the position of the screen 36 is moved behind the focal position of the CGH. However, if the screen 36 is moved forward (toward the mirror 24) from the focal position of the CGH, the real image 38' will also be blurred. However, in this case, the distance between the real image 38' and the second half mirror 30 will be wider than the distance between the real image 38 and the second half mirror 30. Note that while FIG. 4 shows an example of the screen 36, the same effect can be achieved with the 3D screen 28 by moving its position.

[0028] In the retroreflective sheeting 32 shown in Figures 1 to 4, a portion of the irradiated diffracted light is specularly reflected, and a virtual image 39 corresponding to the real image 38 is visible on the other side of the second half mirror 30, as shown in Figure 5(a). This virtual image 39 does not cause any problems when the real image 38 is clear, but if the real image 38 becomes slightly unclear, the virtual image 39 may become an eyesore. In such a case, by tilting the retroreflective sheeting 32 as shown in Figure 5(b), the virtual image 39 can be moved out of the field of view without changing the position of the real image 38, allowing the real image 38 to be reliably viewed. The retroreflective sheeting 32 shown by the solid line in Figure 5(b) is tilted so that the real image 38 side (the front side from the viewer) is lower, in which case the virtual image 39' moves downward. On the other hand, the retroreflective sheet 32' shown by the dotted line in Figure 5(b) is tilted so that the real image 38 side is higher, in which case the virtual image 39" moves upward. Figure 5 shows the case where the retroreflective sheet 32 ​​is tilted forward and backward, but if the retroreflective sheet 32 ​​is tilted left and right, the virtual image 39 can also move left and right and be outside the field of view.

[0029] 1 to 5 have been described with respect to an aerial projection device that forms a real image in the air, but since the CGH calculation unit 17 of the PC 12 that constitutes the holographic projector unit 10a can simultaneously display the interference information of each hologram for a plurality of predetermined images on the SLM 14, diffracted light diffracted based on the interference information of each hologram for at least two predetermined images can be simultaneously emitted from the holographic projector unit 10a. Therefore, as shown in FIG. 6(a), a portion of the diffracted light based on the interference information of one of the predetermined images is irradiated onto a screen 36 placed on a frame 26 to project a projected image 36a, and the transmitted and diffused light that passes through the screen 36 passes through a second half mirror 30 and a retroreflective sheet 32 ​​as a retroreflective element to form a real image 38 of one of the predetermined images that is formed in the air, and can be viewed. At the same time, diffracted light based on the interference information of the other side of the predetermined image is transmitted through the second half mirror 30 and projected onto the retroreflected light exit surface of the retroreflective sheet 32 ​​without being projected onto the screen 36, thereby projecting the other side of the predetermined image 40. The retroreflected light from each of the projection points 40a and 40b of the projected image 40 on the retroreflected light exit surface is reflected by the second half mirror 30, allowing a virtual image 42 of the other side of the predetermined image to be viewed in the air on the side opposite the reflective surface of the second half mirror 30. Points 42a and 42b shown in FIG. 6 correspond to the projection points 40a and 40b of the projected image 40. Thus, with the aerial projection device 10 shown in FIG. 6(a), a real image 38 and a virtual image 42 can be simultaneously viewed, as shown in FIG. 6(b). In the aerial projection device 10 shown in FIG. 6, the focal position of one CGH of the predetermined image is the screen 36, and the focal position of the other CGH of the predetermined image is the retroreflection sheet 32.

[0030] In the aerial projection device 10 shown in FIG. 6, by moving only the screen 36 forward or backward from the focal position of the CGH as shown in FIG. 4 without changing the focal position of the CGH, the virtual image 42 can be maintained clear and only the real image 38 can be blurred. Furthermore, by moving the retroreflective sheet 32 ​​to a position 32' behind the focal position of the CGH as shown in FIG. 7(a), the projected image 40' projected onto the retroreflective sheet 32 ​​becomes blurred, resulting in a blurred virtual image 42' as shown in FIG. 7(b). Because the gap between the retroreflective sheet 32 ​​and the second half mirror 30 widens when moved to position 32', the virtual image 42' is positioned farther from the second half mirror 30 than the virtual image 42, as shown in FIG. 7(a). Since the position of the screen 36 does not change, the real image 38 remains clear and is formed at the same position. The points 42a' and 42b' shown in FIG. 7(a) correspond to the projected points 40a' and 40b' of the retroreflective sheet 32 ​​that has moved to the position 32'.

[0031] As shown in Figure 8, by dividing the sheet into a retroreflective sheet 32a for real images and a retroreflective sheet 32b for virtual images, only the retroreflective sheet 32b can be moved, and only the virtual image 42 can be blurred and its position can be moved. Also, if you want to blur only the real image 38, this can be achieved by moving the position of the screen 36. While Figure 8 shows an example of a screen 36, even when a 3D screen 28 is used, by dividing the sheet into a retroreflective sheet 32a for real images and a retroreflective sheet 32b for virtual images as shown in Figure 9, only the retroreflective sheet 32b can be moved, and only the virtual image 42 can be blurred and its position can be moved.

[0032] In the above explanation, the stereoscopic screen 28 or screen 36, or the retroreflective sheet 32 ​​is moved without changing the focal position of the CGH, and the real image 34 (stereoscopic screen 28) or real image 38 (screen 36) and / or virtual image 42 is blurred and its position is also moved, but by changing the focal position of the CGH, it is possible to blur the real image 38 and / or virtual image 42 without changing their positions, without moving the screen 36 or stereoscopic screen 28, or the retroreflective sheet 32. Because the CGH is calculated by the CGH calculation unit 17 of the PC 12, the focal position of the CGH can be changed quickly.

[0033] The Japanese paper 28c used in the three-dimensional screen 28 or screen 36 of the aerial projection device 10 shown in Figures 1 to 9 has a transmittance of 55% or more at the optical axis of the irradiated visible light (green laser light with a wavelength of 532 nm). It also has a diffusion rate of 15% or more across the entire range of angles from -10° to +10° relative to the optical axis of the visible light at the height between the top of the three-dimensional screen 28 and the midpoint of the second half mirror 30, as shown in Figure 1. Measurement of such visible light transmittance was performed using a measuring device shown in Figure 10. The measuring device shown in Figure 10 includes a light source 50 that emits visible light such as laser light, an objective lens 52, a plano-convex lens 54, a plate-like body 56 with a hole 58 of a predetermined diameter in its center, and a light-receiving surface 62 of an actinometer (laser power meter). The plate-like body 56 is erected at a distance L from the light source 50 so that the center line of the hole 58 coincides with the optical axis 51 of the laser light from the light source 50. The light receiving surface 62 of the actinometer is disposed at a position where the distance M from the plate-like body 56 is equal to the height from the screen to the midpoint of the second half mirror 30, so that the hole 58 and the light receiving surface 62 of the actinometer face each other. When the screen is a 3D screen 28 as shown in FIG. 1, this distance M is the height between the top edge of the 3D screen 28 and the midpoint of the second half mirror 30 (the height indicated as M in FIG. 1). Furthermore, the light receiving surface 62 of the actinometer is disposed so as to be rotatable about the center line of the hole 58 as shown in FIG. 10. The radius of rotation of the light receiving surface 62 is the distance M. In the measurement device shown in FIG. 10, light emitted from the light source 50 is first focused by the objective lens 52, then spreads, is converted into parallel light by the plano-convex lens 54, and irradiates the hole 58 in the plate-like body 56. The amount of light transmitted through the hole 58 is received and measured by the light receiving surface 62 of the actinometer. This measurement was performed by first bringing the light receiving surface 62 of the actinometer into contact with the plate-shaped body 56 so as to block the hole 58 (M = 0 cm in FIG. 10). The amount of light transmitted at this time was defined as T0. Next, the measurement object 60 was attached so as to block the hole 58, and the amount of light received that transmitted through the hole 58 and the screen material, measured with the actinometer with the light receiving surface 62 positioned opposite the hole 58 (M = 0 cm), was defined as T. The transmittance was defined as (T / T0) × 100. Furthermore, the distance between the light receiving surface 62 of the actinometer and the screen material attached to the hole 58 is always kept at 15 cm (rotation radius of the light receiving surface 62: 15 cm), and the light receiving surface 62 of the actinometer is rotated by a predetermined angle ±θ with respect to the optical axis 51 to measure the amount of received light at position 62'. This amount of received light is the amount of diffusion (T') that has passed through the measurement object 60 and diffused in the angle ±θ direction. The diffusion rate is the ratio (T' / T1) to the amount of received light (T1) measured at an angle of 0° × 100.

[0034] From the results of measurements using the measuring device shown in FIG. 10, a screen with a transmittance of at least 47% along the optical axis of irradiated visible light is particularly preferred, as it allows a real image formed in the air to be clearly visible even in a bright room. Screens with a transmittance of less than 47% tend to make it significantly harder to see a real image formed in the air in a bright room, but the real image is visible in a dark room. Examples of screen materials with a visible light transmittance of 47% or more include woven fabrics, nonwoven fabrics, Japanese paper, and diffusion plates made of resins such as acrylic (FANTAREX DREAM D-710M and FANTAREX DREAM D-709M (both trade names) manufactured by Nitto Jushi Kogyo Co., Ltd., and DF-LFV3-100 (trade name) manufactured by CCS Inc.). The transmittance is preferably 55 to 65%. Even with a screen with a transmittance of over 65%, such as a transparent screen made of transparent film, a real image is formed in the air, but a virtual image caused by the retroreflection of the retroreflective material is also visible, making the real image difficult to see. However, as mentioned above, by tilting the retroreflective element, the virtual image can be moved left and right or forward and backward to remove it from the field of view so that only the real image is in the field of view. In some cases, the virtual image can also be eliminated by covering the periphery of the mirror 24 with a light-shielding mask to block excess diffracted light that passes through the second half mirror 30 and illuminates the retroreflective sheet 32 ​​without being irradiated onto the screen.

[0035] At a height M from the top of the three-dimensional screen 28 shown in FIG. 1 to the midpoint of the second half mirror 30, a three-dimensional screen having a diffusion rate of at least 15% across the entire range of angles from -10° to +10° relative to the optical axis of the irradiated visible light can be suitably used. A screen with such a diffusion rate can form a clear real image in the air even in a bright room. A screen with a diffusion rate of less than 15% in some ranges within the range of -10° to +10°, particularly at -10° and / or +10°, tends to make it difficult to see the real image formed in the air in a bright room. A screen with a diffusion rate of 78% or more within this range of -10° to +10° can clearly view the real image formed in the air even if its transmittance is 65% or more. From these measurement results, it is found that Japanese paper or nonwoven fabric is preferable for the screens shown in Figs. 1 to 9, and in particular, a paper with a basis weight of 11 to 24 g / m 2 Specifically, thin paper (machine-made Japanese paper: basis weight 15 g / m) can be used as a screen. 2 ), Hidaka Co., Ltd.'s Tengu paste paper (weight 18g / m 2 ), Usumino 3 momme (weight 20.42g / m 2 ) can be mentioned.

[0036] In the aerial projection devices described above, a real image is formed in the air, but it is also possible to have only a virtual image visible in the air, as shown in Fig. 11. The aerial projection device shown in Fig. 11 includes a holographic projector unit 10a in which parallel light is irradiated onto a hologram created so that each of a plurality of predetermined images is projected at a different predetermined position, and diffracted light diffracted based on interference information of the hologram is emitted, a second half mirror 30 that is installed at an angle with respect to the irradiated diffracted light and through which the diffracted light is irradiated and transmitted, and a plurality of retroreflective sheets 32a, 32b as retroreflective elements arranged without overlapping each other, which are positioned a predetermined distance from one side of the second half mirror 30 and are positioned at predetermined positions where the diffracted light that has transmitted through the second half mirror 30 is irradiated and projected images corresponding to each of the predetermined images are projected. and a projection unit 10b consisting of the retroreflective sheets 32a and 32b, the retroreflective light emission surfaces of which are arranged facing one side of the half mirror 30 so that the retroreflective light of the projected image emitted from the retroreflective light emission surfaces is reflected by the second half mirror 30 and can be seen as a virtual image in the air on the other side of the second half mirror 30, and at least one of the retroreflective sheets 32a and 32b is arranged to be movably positioned at the projection position of the corresponding predetermined image, or all of the retroreflective sheets 32a and 32b or each of the remaining retroreflective sheets excluding the movably positioned retroreflective sheet is arranged at the projection position of the corresponding predetermined image.

[0037] The holographic projector unit 10a shown in Figure 11 is composed of a personal computer (PC) 12 connected to a tablet terminal device 11, a reflective spatial light modulator (SLM) 14, a first half mirror 22, and a parallel light emitting unit 15. The parallel light emitting unit 15 is composed of a laser light emitting unit 16, an objective lens 18, and a plano-convex lens 20. In the holographic projector unit 10a, a computer-generated hologram (CGH) of a predetermined image, such as a character or figure, input from the tablet terminal device 11 is calculated by a CGH calculation unit 17 of the PC 12 and displayed on the SLM 14. The interference fringes displayed on the SLM 14 are interference information created so that the predetermined image is focused at a predetermined position. Parallel light is irradiated onto the display surface of the SLM 14 on which such interference fringes are displayed. This parallel light is laser light emitted from laser light emitting unit 16 of parallel light emitting unit 15, which is first focused by objective lens 18 and then spreads, becomes parallel light by plano-convex lens 20, and is reflected toward the display surface of SLM 14 by first half mirror 22. The parallel light irradiated onto the display surface of SLM 14 becomes diffracted light based on the interference information of the hologram displayed on the display surface, emerges from the display surface of SLM 14, passes through first half mirror 22, and is emitted to projection unit 10b.

[0038] The projection unit 10b is composed of a mirror 24 tilted at a 45° angle, a second half mirror 30 also installed at a 45° angle, and retroreflective sheets 32a and 32b as retroreflective elements arranged on one side (inclined surface side) of the second half mirror 30. The retroreflective sheet 32a is arranged on the lower end side of the inclined surface of the second half mirror 30, and the retroreflective sheet 32b is arranged on the upper end side of the inclined surface of the second half mirror 30. The retroreflective sheets 32a and 32b are arranged without overlapping each other, and both retroreflected light exit surfaces face the one side of the second half mirror 30, which is also the projection surface of the predetermined image for which the CGH is calculated by the CGH calculation unit 17 of the PC 12. The diffracted light incident on the projection unit 10b from the holographic projector unit 10a is reflected by the mirror 24, passes through the second half mirror 30, and illuminates the retroreflected light exit surfaces of the retroreflecting sheets 32a and 32b. A projected image a is projected onto the retroreflected light exit surface of the retroreflecting sheet 32a illuminated by the diffracted light. From the retroreflected light exit surface of the retroreflecting sheet 32a onto which the projected image a is projected, retroreflected light is emitted in the opposite direction to the incident light of the projected image a. This retroreflected light is reflected off one side of the second half mirror 30 and enters the human eye, and a virtual image a corresponding to the projected image a can be seen in the air on the other side of the second half mirror 30. The depth from the other surface of the second half mirror 30 to the virtual image a (indicated by Fa' in FIG. 11) is equal to the height from one surface of the second half mirror 30 to the retroreflective sheet 32a (indicated by Fa in FIG. 11). Furthermore, a projected image b is projected onto the retroreflected light exit surface of the retroreflective sheet 32b irradiated with diffracted light. From the retroreflected light exit surface of the retroreflective sheet 32b onto which projected image b is projected, retroreflected light is emitted in the opposite direction to the incident light of the projected image b. This retroreflected light is reflected by one surface of the second half mirror 30 and enters the human eye, and a virtual image b corresponding to projected image b can be seen on the other surface of the second half mirror 30, further back than virtual image a. The depth from the other side of the second half mirror 30 to the virtual image b (shown as Fb' in FIG. 11) is also equal to the height from one side of the second half mirror 30 to the retroreflective sheet 32b (shown as Fb in FIG. 11).In this way, when viewed from one side of the second half mirror 30, the retroreflective sheets 32a, 32b are each arranged as retroreflective elements at projection positions corresponding to each of the specified images so that all of the virtual images corresponding to the multiple specified images can be seen simultaneously, and therefore clear virtual images a, b for the multiple specified images can be seen simultaneously.

[0039] Furthermore, the height Fa from one side of the second half mirror 30 to the projection surface of the retroreflective sheet 32a is longer than the height Fb from one side of the second half mirror 30 to the retroreflective sheet 32b, but the reason why virtual image b can be seen further back than virtual image a is because the retroreflective sheet 32a is disposed on the lower end side of the inclined surface of the second half mirror 30. In this way, the heights Fa and Fb from one side of the second half mirror 30 corresponding to virtual image a and virtual image b to the retroreflective sheets 32a and 32b as retroreflective elements are adjusted so that virtual image a and virtual image b appear in different positions from the other side of the second half mirror 30, and therefore clear virtual images of multiple predetermined images can be seen in different positions at the same time.

[0040] 12 shows a state in which the letter "A" is projected as projected image a onto the projection surface (hereinafter simply referred to as the projection surface) that is the retroreflected light exit surface of the retroreflecting sheet 32a from the holographic projector unit 10a (see FIG. 11), and the letter "B" is projected as projected image b onto the projection surface (hereinafter simply referred to as the projection surface) that is the retroreflected light exit surface of the retroreflecting sheet 32b. The letter "A" projected onto the retroreflecting sheet 32a is visible as virtual image a on the other side of the second half mirror 30, and the letter "B" projected onto the projection surface of the retroreflecting sheet 32b is visible as virtual image b on the other side of the second half mirror 30, behind the letter "A" in virtual image a. In this way, with one holographic projector unit 10a, clear virtual images of the letters "A" and "B" at different distances can be simultaneously viewed from one side of the second half mirror 30 to the other side of the second half mirror 30.

[0041] Here, when mirrors were placed in place of the retroreflective sheets 32a and 32b in Figure 11, virtual images a and b were not visible. This is presumably due to the difference in reflection between the mirror and the retroreflective sheet. Furthermore, when white or black paper was placed in place of the retroreflective sheets 32a and 32b, virtual images a and b were visible but were significantly unclear. This is presumably due to the fact that the reflectivity of white or black paper in the retroreflective direction is lower than that of the retroreflective sheet.

[0042] 11, even if a light-shielding plate 31 is inserted between the virtual images a and b shown in FIG. 11 as shown in FIG. 13, the virtual image b can be viewed through the light-shielding plate 31. Furthermore, as shown in FIG. 14, by moving the retroreflective sheet 32b in the direction of arrow f (toward the second half mirror 30) to position 32b', the position at which the virtual image b can be viewed can be moved in the direction of arrow f' (toward the second half mirror 30), to position b' in front of the virtual image a. However, when moving the retroreflective sheet 32b, a computer-generated hologram (CGH) in which the projected image b is projected at position 32b' shown in FIG. 14 must be calculated by the CGH calculation unit 17 of the PC 12 and displayed on the SLM 14.

[0043] 11 to 14, the position at which virtual images a and b can be seen corresponds to the distance (optical path length) between the retroreflective sheets 32a and 32b and the second half mirror 30, and the longer the distance (optical path length) between the retroreflective sheet and the second half mirror 30, the further back the virtual image can be seen from the second half mirror 30. When it is desired to increase the distance (optical path length) between the retroreflective sheet and the second half mirror 30 and there are physical constraints such as the size of the room, a mirror 35 may be installed between the retroreflective sheet 32a and the second half mirror 30 as shown in FIG. 15 to bend the optical path between the retroreflective sheet 32a and the second half mirror 30 and increase the optical path length.

[0044] Although the projection unit 10b shown in FIGS. 11 to 15 has two retroreflective sheets, only one movable retroreflective sheet 32a may be used as in the projection unit 10b shown in FIG. 16. Diffracted light is emitted from the holographic projector unit 10a so as to project projected images a and b at predetermined positions on one side (inclined surface) of the second half mirror 30. Therefore, at the position of the retroreflective sheet 32a shown in FIG. 16, projected image a is projected and virtual image a can be seen on the other side of the second half mirror 30. When the retroreflective sheet 32a, which is at the projection position of projected image a, is moved to projection position 32a' where projected image b is projected, virtual image a disappears, but projected image b is projected onto the retroreflective sheet 32a and virtual image b can be seen on the other side of the second half mirror 30. Virtual image b can be seen further back than virtual image a. By moving the movably provided retroreflective sheet 32a to the position where the projected image b is projected, the virtual image b can be visually recognized as having a different perspective from the virtual image a.

[0045] In the projection unit 10b of Figures 11 to 16, the retroreflective sheets 32a and 32b are arranged in series on the upper and lower ends of the second half mirror 30 as shown in Figure 12, but the positions of the virtual images a and b are also affected by the tilt of the second half mirror 30. To avoid such an effect due to the tilt of the second half mirror 30, it is preferable to arrange the retroreflective sheets 32a and 32b in parallel on the left and right sides of the rectangular second half mirror 30 as shown in Figure 17(a). By arranging the retroreflective sheets 32a and 32b in this way, it is possible to predict that the virtual images a and b will be visible at positions corresponding to the distance (optical path length) of each of the retroreflective sheets 32a and 32b from the second half mirror 30, as shown in Figure 17(b).

[0046] In the aerial projection device 10 described above, diffracted light is emitted from the holographic projector unit 10a so that a predetermined image is projected at the projection position (focal position) of the CGH. Accurately knowing the focal position of this CGH is necessary to obtain a clear real or virtual image, or a real or virtual image with a desired blurred shape. The focal position of the CGH can be accurately determined by a guide device that guides a projection target to a predetermined spatial position. This guide device includes a hologram on which an interference pattern is formed, adjusted so that an image of a predetermined shape having a narrow gap pattern is formed at the predetermined spatial position, and a parallel light emitting means that emits parallel light toward the hologram so that, when the projection target is guided to the predetermined spatial position, the diffracted light irradiated onto the hologram is diffracted based on the interference pattern, and the pattern formed on the projection target coincides with the pattern of the image. The guiding method using this guide device uses a holographic projector whose imaging position is adjusted so that an image of a predetermined shape having a narrow gap pattern is projected at a predetermined spatial position, and when an image is projected from the holographic projector onto a projection object placed near this spatial position, the projection object is guided to a spatial position where the pattern of the image reflected on the projection object matches the pattern of the image.

[0047] This guide device and guide method will be described in detail with reference to FIG. 18 . The guide device 70 shown in FIG. 18 comprises a holographic projector unit 10a and a three-dimensional screen 28 as a projection target mounted on a mounting base 75 so as to be slidable in the direction of arrow F. The holographic projector unit 10a comprises a personal computer (PC) 12 connected to a tablet terminal device 11, a reflective spatial light modulator (SLM) 14, a half mirror 22, and a parallel light emitter 15. The parallel light emitter 15 comprises a laser light emitter 16, an objective lens 18, and a plano-convex lens 20. In the holographic projector unit 10a, a computer-generated hologram (CGH) of a cube having a pattern of narrow gaps is calculated by a CGH calculation unit 17 of the PC 12 as a predetermined image input from the tablet terminal device 11, and the CGH is displayed on the SLM 14. The interference fringes of the hologram displayed on the SLM 14 are interference information calculated so that the projection position (focal position) of the cube as the predetermined image is projected at a predetermined spatial position. Parallel light is irradiated onto the display surface of SLM 14, on which these interference fringes are displayed. This parallel light is laser light emitted from laser light emitting unit 16 of parallel light emitting unit 15, which is first focused by objective lens 18 and then spreads, becomes parallel light by plano-convex lens 20, and is then reflected toward the display surface of SLM 14 by half mirror 22. The parallel light irradiated onto the display surface of SLM 14 is diffracted based on the interference information of the hologram displayed on the display surface, emerges from the display surface of SLM 14, passes through half mirror 22, and is emitted onto 3D screen 28.

[0048] The three-dimensional screen 28 has a cubic shape as shown in FIG. 18(a), and is formed by attaching a white sheet to a frame. Three-dimensional screen 28 is supported via support rods 73 on support base 74, which is placed on mounting base 75 so as to be able to slide in the direction of arrow F. Three-dimensional screen 28 is also rotatable horizontally as indicated by arrow F′ and vertically as indicated by arrow F″. Three-dimensional screen 28 on support base 74 shown in FIG. 18( a) is adjusted so that two of its side faces serve as projection surfaces onto which diffracted light emitted from holographic projector unit 10a is irradiated and images of the corresponding two faces of a cube are projected. An image of a cube with a pattern of narrow gaps is projected from holographic projector unit 10a, located to the left of three-dimensional screen 28, which is slidably placed on mounting base 75. This image is input from tablet terminal device 11. When the pattern of the input image matches the pattern projected onto three-dimensional screen 28, it is clear that three-dimensional screen 28 is positioned at the projection position (focal position) of holographic projector unit 10a.

[0049] The pattern of this narrow gap is preferably a pattern consisting of a plurality of thin lines and dots spaced at a predetermined interval, for example, a dotted line pattern 76 as shown in Figure 18(b) in which a plurality of thin, straight dotted lines are formed with narrow gaps and projected over the entire projection surface of the three-dimensional screen 28 located at the projection position (focal position) of the holographic projector unit 10a (where the corners of the three-dimensional screen 28 shown in Figures 18(a) and 18(b) are A, B, B', A', C', and C, the surface is surrounded by sides AB, BB', B'-A', A'-C', C'-C, and CA). As shown in Figure 18(a), when the three-dimensional screen 28 is placed on a mounting base 75 with its side AA' closest to the holographic projector unit 10a, the diffracted light from the holographic projector unit 10a is irradiated onto the white sheet projection surface of the three-dimensional screen 28, forming a dotted pattern 76. When the projection surface of the three-dimensional screen 28 is viewed from the direction of the diffracted light, as shown in Figure 18(b), if the thin, straight dotted lines that make up the dotted pattern 76 are clearly distinguishable across the entire projection surface of the three-dimensional screen 28, it can be determined that the three-dimensional screen 28 is located at the projection position (focal position) of the holographic projector unit 10a. On the other hand, when the three-dimensional screen 28 is located farther away from the projection position (focal position) of the holographic projector unit 10a, a slanted line pattern 77 different from the dotted pattern 76 in Figure 18(b) can be seen when the projection surface of the three-dimensional screen 28 is viewed from the direction of the diffracted light, as shown in Figure 18(c). Furthermore, even when the three-dimensional screen 28 is positioned closer to the holographic projector unit 10a than the projection position (focal position) of the holographic projector unit 10a, when the projection surface of the three-dimensional screen 28 is viewed from the projection direction of the diffracted light, a slanted line pattern 77 different from the dotted line pattern 76 in Fig. 18(b) can be seen, as shown in Fig. 18(c). In this way, the dotted line pattern 76 projected onto the projection surface of the three-dimensional screen 28 makes it easy to determine whether the three-dimensional screen 28 is positioned at the projection position (focal position), and the three-dimensional screen 28 can be slid to guide it to the projection position (focal position).

[0050] Furthermore, when projecting a predetermined image onto a flat screen 36 as shown in FIG. 3 or onto retroreflective sheets 32a and 32b as shown in FIG. 11, it is preferable to use a pattern of narrow gaps, such as a dotted line pattern 78 formed by multiple thin dotted lines spaced apart by narrow gaps, as shown in FIG. 19(a). When the thin, straight dotted lines that make up the dotted line pattern 78 are clearly visible across the entire projection surface of the screen 36 or retroreflective sheet 32 ​​as shown in FIG. 19(a), it is clear that the screen 36 or retroreflective sheet 32 ​​is positioned at the projection position (focal position) of the holographic projector unit 10a. On the other hand, when a slanted line pattern 79 different from the dotted line pattern 78 in FIG. 19(a) is visible as shown in FIG. 19(b), it is clear that the screen 36 or retroreflective sheet 32 ​​is positioned away from the projection position (focal position) of the holographic projector unit 10a. Therefore, by moving the screen 36 or retroreflective sheet 32 ​​to a position where the dotted line pattern 78 shown in FIG. 19(a) is formed, it can be accurately set at the projection position (focus position) of the holographic projector unit 10a.

[0051] The guide device 70 shown in FIG. 18 can be used in a personal authentication device, for example, a personal authentication device using the iris of a human eye, as shown in FIG. 20. The device shown in FIG. 20 is used to determine the position of a subject in an iris-based personal authentication device. In the position determination device shown in FIG. 20, an image having a narrow gap pattern is projected onto the subject's forehead from a holographic projector unit 10a. The image projected onto the subject's forehead is captured by a camera 80 and displayed on a display device 82 so that the subject can view it. When the image projected onto the subject's forehead matches the pattern of the image input from the tablet terminal device 11, the subject's eyes are within the depth range of the iris imaging camera (not shown). This image having a narrow gap pattern may be a narrow gap pattern, for example, a dotted line pattern 78 formed by multiple thin dotted lines spaced apart, as shown in FIG. 19(a). When the pattern projected onto the subject's forehead, photographed by camera 80, and displayed on display device 82 is dotted line pattern 78 as shown in FIG. 19(a), the subject's eyes are within the depth range of the iris photographing camera (not shown) of the personal authentication device, and the subject's iris can be photographed by the iris photographing camera. On the other hand, when the pattern displayed on display device 82 is slanted line pattern 79 as shown in FIG. 19(b), the subject's iris is not located within the depth range of the face iris photographing camera, and the subject moves their face to a position where the pattern displayed on display device 82 becomes dotted line pattern 78 as shown in FIG. 19(a). Note that when dotted line pattern 78 is projected onto the subject's forehead from holographic projector unit 10a as shown in FIG. 20, if there is a risk that diffracted light from SLM 14 may enter the subject's eyes, SLM 14 may be illuminated with light from a light-emitting diode (LED) or infrared light that is invisible to humans but can be recognized by camera 80.

[0052] Furthermore, the guide device 70 shown in FIG. 18 can be used in a personal authentication device using hand veins, as shown in FIG. 21. The device shown in FIG. 21 is used to determine the position of a subject's hand in a personal authentication device using veins. In the position determination device shown in FIG. 21, when the subject holds out their hand over a vein imaging camera 84, an image having a pattern of narrow gaps is projected onto the arm from a holographic projector unit 10a. The image projected onto the subject's arm can be viewed directly by the subject, and when the image matches the pattern of the image input from the tablet terminal device 11, the subject's hand is within the depth range of the vein imaging camera 84. This image having a pattern of narrow gaps may be a pattern of narrow gaps, such as a dotted line pattern 78 formed by multiple thin lines with narrow gaps, as shown in FIG. 19(a). When the pattern projected onto the subject's arm becomes a slanted line pattern 79 as shown in Figure 19(b) and does not match the dotted line pattern 78, the subject's hand is not located within the depth range of the vein imaging camera 84, and the subject moves their hand and arm up or down to a position where the pattern displayed on their arm becomes the dotted line pattern 78 as shown in Figure 19(a). Note that in the device shown in Figure 21, SLM 14 may be irradiated with laser light to prevent diffracted light from SLM 14 from entering the subject's eyes and to make the pattern projected onto the arm clearer.

[0053] In the aerial projection device 10 described above, a computer-generated hologram (CGH) of a predetermined image input from the tablet terminal device 11 to the PC 12 is calculated by the CGH calculation unit 17 and output to the SLM 14. The computer-generated hologram (CGH) calculated by the CGH calculation unit 17 will now be described. A computer-generated hologram (hereinafter simply referred to as CGH) of a three-dimensional object composed of N object points shown in FIG. 22 is generated by calculating the light intensity of each point (x h ,y h ,0) comp (x h ,y h ,0) is expressed by the following formula (3)

number

[0054] Incidentally, there are two types of SLMs: one that displays an amplitude hologram and one that displays a phase hologram. Here, as shown in Figure 22, the position coordinates of the nth point light source on a three-dimensional object are expressed as P(x n ,y n ,z n ) and its brightness is A n , the size of one pixel is Δ x ×Δ y , the coordinates of the pixel in the CGH located at the i-th and j-th positions in the x and y directions are (x h ,y h )=(iΔ x ,jΔ y ), then each point (x h ,y h ,0) amp (x h ,y h ,0) is expressed by the following formula (4)

number

[0055] Also, each point (x h ,y h Phase I in (0) phase (x h ,y h ,0) is expressed by the following formula (5)

number

number

[0056] An amplitude hologram can be calculated based on the above formula (4), and a phase hologram can be calculated based on the above formula (6), and these can be used to calculate CGHs of three-dimensional still images. However, in the case of three-dimensional video, a further improvement in the calculation speed is required compared to the calculation of CGH using the above formula (4) or (6). Therefore, in order to improve the calculation speed of CGH, the light intensity (I amp (x h ,y h , 0)) into the following formula (7):

number

number

[0057] In order to calculate the amplitude hologram based on the above formula (7) in the CGH calculation unit 17 of the PC 12 of the aerial projection device 10, as shown in FIG. 23, the CGH calculation unit 17 includes a position coordinate data storage unit 17a that stores data on the position coordinates of the point light source of the three-dimensional image input from the tablet terminal device 11, a CGH x-direction trigonometric function table 17b that stores values ​​obtained by calculating sinX and cosX in the x-direction of the CGH based on the position coordinate data of the position coordinate data storage unit 17a, a CGH y-direction trigonometric function table 17c that stores values ​​obtained by calculating sinY and cosY in the y-direction of the CGH based on the position coordinate data of the position coordinate data storage unit 17a, and a calculation unit 17c for calculating the light intensity (I amp (x h ,y h , 0)) and the amplitude hologram calculation unit 17d calculates the light intensity (I amp (x h ,y h, 0)) and outputs it to the SLM 14.

[0058] The pseudocode for calculating an amplitude hologram in the CGH calculation unit 17 shown in Fig. 23 is shown in Fig. 24, and its flowchart is shown in Fig. 25. The pseudocode shown in Fig. 24 assumes that the CGH resolution is W × H, and the flowchart shown in Fig. 25 is for a 3D video, but it can also be applied to a 3D still image. 24 and 25, trigonometric function table 17b is created before trigonometric function table 17c, but trigonometric function table 17b may be created before trigonometric function table 17c, or trigonometric function tables 17b and 17c may be created in parallel. Furthermore, the creation of trigonometric function tables 17b and 17c, the calculation of the amplitude hologram by amplitude hologram calculation unit 17d, and the output of the amplitude hologram by amplitude hologram data storage unit 17e to SLM 14 may be processed in parallel. Furthermore, if trigonometric function tables 17b and 17c are created in advance for each frame of a 3D video and can be used to create and display an amplitude hologram on SLM 14, the point light source loop may be the innermost loop in the flowchart shown in FIG.

[0059] In order to calculate a phase hologram based on the above formula (8) in the CGH calculation unit 17 of the PC 12, as shown in FIG. 26, the CGH calculation unit 17 includes a position coordinate data storage unit 17a that stores position coordinate data of a point light source of a three-dimensional image input from the tablet terminal device 11, a trigonometric function table 17b of the x direction of the CGH that stores values ​​obtained by calculating sinX and cosX in the x direction of the CGH based on the position coordinate data of the position coordinate data storage unit 17a, and a trigonometric function table 17b of the y direction of the CGH that stores values ​​obtained by calculating sinX and cosX in the y direction of the CGH based on the position coordinate data of the position coordinate data storage unit 17a. a trigonometric function table 17c for the y direction of the CGH that stores calculated values ​​of sinY and cosY of the above; an imaginary part / real part calculation unit 17f that calculates an imaginary part Im{Icomp} and a real part Re{Icomp} using the trigonometric function values ​​stored in the trigonometric function tables 17b and 17c; an imaginary part / real part storage unit 17g that stores the imaginary part Im{Icomp} and real part Re{Icomp} calculated by the imaginary part / real part calculation unit 17f; and a phase (I phase (x h ,y h , 0)) and the phase hologram calculation unit 17h calculates the phase (I phase (x h ,y h , 0)) and outputs it to the SLM 14.

[0060] The pseudocode for calculating a phase hologram in the CGH calculation unit 17 shown in Fig. 26 is shown in Fig. 27, and its flowchart is shown in Fig. 28. The pseudocode shown in Fig. 27 assumes that the CGH resolution is W × H, and the flowchart shown in Fig. 28 is for a 3D video, but it can also be applied to a 3D still image. 27 and 28, trigonometric function table 17b is created before trigonometric function table 17c is created, but trigonometric function table 17b may be created before trigonometric function table 17c, or trigonometric function tables 17b and 17c may be created in parallel. Also, the creation of trigonometric function tables 17b and 17c, the calculation of imaginary part Im{Icomp} and real part Re{Icomp} in imaginary part / real part calculation unit 17f, and the calculation of phase hologram phase (I phase (x h ,y h , 0)) and the output of the phase hologram by the phase hologram data storage unit 17i to the SLM 14 may be processed in parallel. Furthermore, if trigonometric function tables 17b and 17c are created in advance for each frame of the three-dimensional video and can be used to create and display a phase hologram to be displayed on the SLM 14, the point light source loop may be the innermost loop in the flowchart shown in Figure 28.

[0061] A CGH calculation unit 17 that calculates and processes an amplitude hologram based on the above formula (7) or a phase hologram based on the above formula (8) can be provided within a CPU (Central Processing Unit) and / or a GPU (Graphics Processing Unit). Both CPUs and GPUs have multiple cores, but to achieve real-time playback of 3D video, at least 30 CGHs must be calculated and played back per second. However, CPUs have significantly fewer cores than GPUs, and their processing speed is slower. While they can be used to process 3D still images, they are not suitable for 3D video processing. On the other hand, GPUs have many cores and can be used not only to process 3D still images but also to process 3D video.

[0062] The explanation so far has been about the case where there is one projection unit 10b, but multiple projection units may be installed. Figure 30 shows an example where three projection units 10b, as shown in Figure 3, are installed. In Figure 30(a), projection units 10b-1, 10b-2, and 10b-3 are arranged in series so that real images are formed on the same side of second half mirror 30. A flat screen 36 is placed on each frame 26, and diffracted light 1, diffracted light 2, and diffracted light 3 of holograms with different shapes are irradiated onto each screen 36 from holographic projector unit 10a (not shown) shown in Figure 1(a). On the screen 36 illuminated by diffracted light 1, a circular image 36a-1 shown in FIG. 30(b) is projected. On the screen 36 illuminated by diffracted light 2, a circular image 36a-2 with a smaller diameter than the circular image 36a-1 is projected, as shown in FIG. 30(b). On the screen 36 illuminated by diffracted light 3, a circular image 36a-3 with a smaller diameter than the circular images 36a-1 and 36a-2 is projected, as shown in FIG. 30(b). The circular images 36a-1, 36a-2, and 36a-3 projected onto each screen 36 are formed as real images 38-1, 38-2, and 38-3 in the space on one side of each second half mirror 30. When viewed from the real image 38-1 side, these real images 38-1, 38-2, and 38-3 appear as concentric circles, as shown in FIG. 30(c). By arranging multiple projection units 10b in this manner, complex real images can be formed in the air. Diffracted light 1, diffracted light 2, and diffracted light 3 shown in Fig. 30 may be emitted from the same holographic projector unit or from different holographic projector units. Although Fig. 30 uses a flat screen 36, a three-dimensional screen 28, as shown in Fig. 1, can be used to view a complex real image formed in the air from multiple angles. Although Fig. 30 uses three retroreflective sheets 32, a single retroreflective sheet 32 ​​large enough to cover the three second half mirrors 30 may be used.

[0063] The frames 26 on which the screens of the three projection units 10b-1, 10b-2, and 10b-3 shown in Fig. 30 are mounted are all the same height, but as shown in Fig. 31, moving one frame 26 up and down also moves the screen 36 up and down, and the real image formed in the air moves left and right, approaching and separating from the real images of the other units. In Fig. 31, the two projection units 10b-1 and 10b-2 shown in Fig. 30 are arranged in series so that real images 38-1 and 38-2 are formed in the air on the same side of the second half mirror 30. A flat screen 36 is mounted on each frame 26, and diffracted light 1 and diffracted light 2 of holograms with different shapes are irradiated onto each screen 36 from the holographic projector unit 10a (not shown) shown in Fig. 1(a), so that real images 38-1 and 38-2 are formed on one side of each second half mirror 30. Here, when the frame 26 of the projection unit 10b-2 is raised to an upper position 26-1 and the projection position (focal position) of the holographic projector unit is aligned with the screen 36-1 that has moved to position 26-1, the formed real image 38-2' moves to the right (in the direction of arrow f-1) of the real image 38-2 and becomes farther away from the real image 38-1 of the projection unit 10b-1. On the other hand, when the frame 26 of the projection unit 10b-2 is lowered to the lower position 26-2 and the projection position (focal position) of the holographic projector unit is aligned with the screen 36-2 that has moved to the position 26-2, the formed real image 38-2" moves to the left (in the direction of the arrow f-2) of the real image 38-2 and approaches the real image 38-1 of the projection unit 10b-1. In this way, by moving the frame 26 on which the screens 36 of the multiple projection units 10b are placed in the vertical direction, the real images 38 of the projection units 10b that have moved in the horizontal direction can approach and separate from each other. A variety of movements can be imparted to the real image. In Fig. 31, only the frame 26 of the projection unit 10b-2 is moved up and down, but by also moving the frame 26 of the projection unit 10b-1 up and down, the real image 38-1 of the projection unit 10b-1 also moves left and right, making it possible to overlap the real image 38-2 of the projection unit 10b-2 or to move the real image 38-1 behind the real image 38-2. In Fig. 31, two retroreflective sheets 32 are used, but a single retroreflective sheet 32 ​​large enough to cover the two second half mirrors 30 may be used.Although the flat screen 36 has been described with reference to FIG. 31, the stereoscopic screen 28 can also impart various movements to the real image.

[0064] In the above explanation, a reflective SLM 14 was used, but a transmissive SLM may also be used. Although a predetermined image was input from tablet terminal device 11 to PC 12, the predetermined image may also be input directly to PC 12. Furthermore, although a computer-generated hologram calculated by PC 12 was displayed on SLM 14, interference fringes of the hologram may also be printed on film. Furthermore, although laser light was irradiated onto SLM 14, light from a light-emitting diode (LED) may also be irradiated. [Example]

[0065] Examples of the present invention will be described in detail below, but the scope of the present invention is not limited to these examples.

[0066] Example 1 Measure the visible light transmittance and diffusion rate of the screen material. (Measuring equipment) The measurement device shown in Figure 10 was used. Light source 50: Emits green laser light (wavelength 532 nm) Hole diameter of hole 58: 2.5cm Light meter: Laser power meter (LP1 manufactured by Sanwa Electric Instruments Co., Ltd.) Distance L: 1m Distance M: When measuring transmittance: 0 cm When measuring diffusion rate: 15 cm

[0067] (Screen materials) The screen materials used for the measurements are shown in Table 1. All of the screen materials shown in Table 1 were white.

[0068] [Table 1]

[0069] (Transmittance measurement) The transmittance of visible light irradiated on the optical axis of each of the screen materials listed in Table 1 was measured. As described above, the measurement was performed by irradiating the hole 58 with parallel green laser light (wavelength 532 nm) emitted from the light source 50 shown in FIG. 10 , and measuring the amount of light received T0 when the hole 58 was not blocked by the screen material using a laser power meter installed at a position where the light-receiving surface 62 abutted against the hole 58 (M = 0 cm). Next, a screen material was attached to block the hole 58, and the amount of light received T of the light transmitted through the hole 58 and the screen material was measured using a laser power meter installed at a position where the light-receiving surface 62 faced the hole 58 (M = 0 cm). The transmittance was calculated as (T / T0) × 100. The transmittance of each of the screen materials listed in Table 1 is shown in Table 2 below.

[0070] (Measurement of diffusivity) The amount of received light was measured by rotating the light-receiving surface 62 of the laser power meter shown in FIG. 10 at an angle of +10° to -10° relative to the optical axis 51. The distance between the light-receiving surface 62 of the laser power meter and the screen material attached to the hole 58 was always kept at 15 cm (rotation radius of the light-receiving surface 62: 15 cm). The amount of received light measured when the light-receiving surface 62 was rotated at an angle of ±θ relative to the optical axis 51 is the amount of diffused light (T') that passed through the screen material and diffused at an angle of ±θ relative to the optical axis 51. The diffusivity at a position at an angle of ±θ relative to the optical axis 51 is expressed as the ratio (T' / T1) of the amount of received light (T1) measured at an angle of 0° (M = 15 cm). The diffusivities of each of the screen materials listed in Table 1 are shown in Table 2 below.

[0071] [Table 2]

[0072] Example 2 The three-dimensional screen 28 shown in Figure 1(b) was fabricated using the screen materials listed in Table 1, and the characters "Kochi" and a pattern were painted on it. This three-dimensional screen 28 was placed in a bright room (527 lux (lx)) using the aerial projection device 10 shown in Figure 1(a). Visual observation was performed to determine whether a real cubic image 34 could be seen in the air from the front. The retroreflective sheet 32 ​​used was the RF-Ax aerial display reflector manufactured by Nippon Carbide Industries Co., Ltd. The distance from the SLM 14 to the three-dimensional screen 28 was 3 m, and the distance M from the top edge of the three-dimensional screen 28 to the midpoint of the second half mirror 30 was 15 cm. Green laser light (wavelength 532 nm) was emitted from the parallel light emitting unit 15. Furthermore, in a dark room (0.03 lux (lx)) with the room lights turned off and the windows covered with blackout curtains, the images were observed with the naked eye in the same manner as in the bright room. The results are shown in Table 3 below. In Table 3, real image 34 is marked as "clearly visible" (++), "distinguishable" (+), and "unclear" (±). The illuminance of the room was measured using an illuminance meter (T-10A (product name)) manufactured by Konica Minolta Japan, Inc.

[0073] [Table 3]

[0074] As is clear from Tables 2 and 3, screen materials Nos. 5, 9, and 11 have transmittances of less than 47% on the optical axis, making the real image 34 "barely visible" (±) in the air in a bright room. This is because the amount of light transmitted through the 3D screen 28 is reduced. In contrast, screen materials Nos. 1 to 4, 6 to 8, 10, and 12 to 15 had transmittance of 47% or more on the optical axis, and a real image 34 could be seen in the air even in a bright room. This was because the amount of light transmitted through the 3D screen 28 was greater than that of screen materials Nos. 5, 9, and 11. In particular, screen materials Nos. 10, 13, and 15 (tissue paper, Tengu paper (18 g / m 2), and Usuminoshi 3 momme (thickness: 3 momme). The light transmission rate at the optical axis of the three-dimensional screen 28 was 55-65%, and the diffusion rate across the entire range of -10° to +10° from the optical axis was 15% or more, so the letters and patterns of "Kochi" in the real image 34 were clearly visible even in a bright room. This is because, when the transmittance and diffusion rate of the three-dimensional screen 28 are both high, the virtual image (corresponding to virtual image 39 shown in FIG. 5(a)) generated by the specular reflection of the diffused light irradiated on the retroreflective sheeting 32 becomes difficult to see, while the real image 34 becomes easy to see. It is presumed that when the diffusion rate of the three-dimensional screen 28 is high, the diffused light diffused over a wide range from the projection point 29a of the three-dimensional screen 28 shown in FIG. 1(a) is retroreflected by the retroreflective sheeting 32 and concentrated from a wide range to the image point 34a, making it easy to see. On the other hand, the specular reflection of the retroreflective sheeting 32 is spread, making the virtual image difficult to see. In contrast, in Nos. 1 to 4, 6 to 8, and 14, a virtual image (corresponding to virtual image 39 shown in Figure 5(a)) was also seen superimposed on the real image 34, but by tilting the retroreflective sheet 32 ​​as shown in Figure 5(b), the virtual image could be moved out of the field of view. In this way, in a bright room (527 lux (lx)), the real image 34 was rated as "distinguishable" (+) or "hard to see" (±) for the 3D screens 28 Nos. 2, 5, 6, 9, 11, and 12, but in a dark room (0.03 lux (lx)), the real image 34 was rated as "clearly visible" (++) for all of them.

[0075] Example 3 In Example 2, the screen materials No. 5 (plain cotton lawn), No. 9 (machine paper (machine-made paper)), and No. 11 (Tengu paper: basis weight 34 g / cm) were used, which were judged to be "hard to see" (±) in a bright room (527 lux (lx)). 2)) and the screen materials of the diffusers Nos. 16 to 22 in Table 1 were used to create flat screens, and the word "Kochi" was written on the screen to create screen 36 shown in Figure 3(a). Using this screen 36, a real image 38 of the characters "Kochi" projected in the air using the aerial projection device shown in Figure 3(a) was observed with the naked eye in a bright room (527 lux (lx)) to determine whether it was visible from the front. As a result, as shown in Table 4 below, the real image 38 of the characters "Kochi" was "clearly visible" (++) on all screens.

[0076] [Table 4]

[0077] Example 4 The CGH calculation unit 17 of the PC 12 shown in Figure 1 was installed in a CPU or GPU, and the CGH creation speed due to differences in the calculation formula for the CGH of the amplitude hologram was measured by changing the number of object points. The results are shown in Table 5 below. Amplitude hologram calculation formula The above formula (4) [Pseudocode: Figure 29(a)] The above formula (7) [Pseudocode: Figure 24] CGH calculation section 17 CPU: Intel Corporation Core™ i7-8700K GPU: NVIDIA Corporation GeForce RTX™ 3080

[0078] [Table 5] As is clear from Table 5, the speed of CGH creation using Equation (7) is faster than that using Equation (4), and the speed of CGH creation using a GPU is significantly faster than that using a CPU. This shows that amplitude holograms using Equation (7) on a GPU can be applied to 3D video. Here, when calculating Equation (4) on a CPU, the computational load of the cos function becomes large. Therefore, to speed up the calculation, we sampled one period from 0 to 2π into 256 equal parts, and used a cos table in which the range of the sampled cos function, -1 to +1, is an 8-bit integer value between -127 and 127. In addition, we used the Intel C++ compiler classic Version 2021.2.0 (options: -O3 -xCORE-AVX2 -qopenmp) as the compiler, and set the number of OpenMP threads to 12.

[0079] Example 5 The CGH calculation unit 17 of the PC 12 shown in Figure 1 was installed in a CPU or GPU, and the CGH creation speed due to differences in the calculation formula for the CGH of a phase hologram was measured by changing the number of object points. The results are shown in Table 6 below. Phase hologram calculation formula The above formula (6) [Pseudocode: Figure 29(b)] The above formula (8) [Pseudocode: Figure 27] CGH calculation section 17 CPU: Intel Corporation Core™ i7-8700K GPU: NVIDIA Corporation GeForce RTX™ 3080

[0080] [Table 6] As is clear from Table 6, the CGH creation speed using Equation (8) is faster than Equation (6), and the CGH creation speed using a GPU is significantly faster than that using a CPU. This shows that phase holograms using Equation (8) on a GPU can be applied to 3D video. Here, when calculating Equation (6) on a CPU, the calculation load of the cos and sin functions becomes large. Therefore, to speed up the calculation, we sampled one period from 0 to 2π into 256 equal parts, and used a cos and sin table in which the range of the sampled cos and sin functions, -1 to +1, is an 8-bit integer value from -127 to 127. In addition, we used the Intel C++ compiler classic Version 2021.2.0 (options: -O3 -xCORE-AVX2 -qopenmp) as the compiler, and set the number of OpenMP threads to 12. [Industrial Applicability]

[0081] The aerial projection device according to the present invention can be used as an aerial projection device capable of projecting images of elevator buttons, etc., in the air, or as an aerial projection device capable of projecting predetermined images in the air for educational purposes, games, etc. [Explanation of symbols]

[0082] 10: aerial projection device, 10a: holographic projector unit, 10b, 10b-1, 10b-2, 10b-3: projection unit, 11: tablet-type terminal device, 12: personal computer, 14: spatial light modulator (SLM), 15: parallel light emitting unit, 16: laser light emitting unit, 17: CGH calculation unit, 17a: position coordinate data storage unit, 17b, 17c: trigonometric function table, 17d: amplitude hologram calculation unit, 17e: amplitude hologram data storage unit, 17f: imaginary part / real part calculation unit, 17g: imaginary part / real part storage unit, 17h: phase hologram calculation unit, 17i: phase hologram data data memory unit, 18, 52: objective lens, 20, 54: plano-convex lens, 22: first half mirror, 24, 35: mirror, 26: frame, 26', 26-1, 26-2: position of frame 26, 27, 74: support base, 28: 3D screen, 28a: projection image of cube, 28b: frame, 28c: Japanese paper, 29a, 29b, 37a, 37b, 37a', 37b', 40a, 40b, 40a', 40b': projection point, 30: second half mirror, 31: light shielding plate, 32, 32a, 32b: retroreflective sheet, 32': position of retroreflective sheet 32, 32b': position of retroreflective sheet 32b, 32a': projection position, 33a: reflective sheet, 33b: glass beads, 33c: transparent resin layer, 34, 38, 38', 38-1, 38-2, 38-3, 38-2', 38-2": real image, 34a, 34b, 38a, 38b, 38a', 38b': image point, 36, 36-1, 36-2: screen, 36a, 36a', 36a-1, 36a-2, 36a-3, 40, 40': projected image, 39, 39', 39" 42, 42': virtual image, 39a, 39a': corresponding point of image point 38a, 39b, 39b': corresponding point of image point 38b, 42a, 42b, 42a', 42b': projection Corresponding points of points 40a, 40b, 40a', 40b', 50: light source, 51: optical axis, 56: plate-like body, 58: hole, 60: measurement object, 62: light receiving surface, 62': position, 70: guide device, 73: support rod, 75: mounting base, 76, 78: dotted line pattern, 77, 79: inclined line pattern, 80: camera, 82: display device, 84: vein imaging camera, A, B, C, A', B', C': corners of the 3D screen 28, F: sliding direction of the support base 74, F-1, F-2: movement direction of the frame body 26, F': rotation direction of the 3D screen 28 on the horizontal plane, Fa, Fb: height, Fa', Fb': depth, L,M: distance, F″: rotation direction on the vertical plane of the stereoscopic screen 28, f: movement direction of the retroreflective sheet 32b, f-1, f-2: movement direction of the real image 38-2, f′: movement direction of the virtual image b, b′: movement position of the virtual image b, θ: angle, W: number of horizontal pixels of the CGH, H: number of vertical pixels of the CGH, x, h : x-coordinate of pixel on hologram, y h : y-position coordinate of pixel on hologram, Δ x : pixel size in x direction, Δ y : y-direction pixel size, P(x n, y n, z n ): The position coordinates of the nth object point P of a three-dimensional object

Claims

1. The present invention is configured with a holographic projector unit that emits diffracted light obtained by diffracting irradiated parallel light based on interference information of a hologram of a predetermined image, a screen onto which the diffracted light is irradiated and the predetermined image is projected, a half mirror that is installed at an angle with respect to the diffracted light irradiated onto the screen at a position onto which transmitted and diffused light of the diffracted light that has passed through the screen and diffused is irradiated, and a projection unit that includes a retroreflection element onto which the transmitted light or reflected light of the half mirror is irradiated, An aerial projection device characterized in that the transmitted or reflected light of the half mirror of the transmitted diffused light is retroreflected by the retroreflection element and emitted in the opposite direction along the original incident path, and a real image of the specified image is formed in the air on one side of the half mirror by the reflected light reflected by the half mirror or the transmitted light that passes through the half mirror.

2. 2. The aerial projection device according to claim 1, wherein the screen is positioned in front of or behind a predetermined position where the real image is projected based on interference information of the hologram so that the real image appears blurred.

3. 2. The aerial projection device according to claim 1, wherein the retroreflective element is tilted so that a virtual image corresponding to the real image visible on the other side of the half mirror moves out of the field of view due to specular reflection from the retroreflective element.

4. Diffracted light diffracted based on interference information of each hologram of at least two predetermined images is emitted from the holographic projector unit, The diffracted light based on the interference information of one of the predetermined images is irradiated onto the screen and passes through the half mirror and the retroreflection element to form a real image of one of the predetermined images in the air, The aerial projection device described in claim 1, characterized in that diffracted light based on the interference information of the other of the specified images passes through the half mirror without being irradiated onto the screen and is irradiated onto the retroreflected light emission surface of the retroreflecting element, thereby projecting the other of the specified images, and the retroreflected light emitted from the retroreflected light emission surface is reflected by the half mirror, making it possible to see a virtual image of the other of the specified images in the air on the side opposite the reflective surface of the half mirror.

5. The aerial projection device according to claim 4, characterized in that the screen and / or the retroreflective element are positioned in front of or behind a predetermined position where the real image and / or the virtual image are projected based on the interference information of the hologram so that the real image and / or the virtual image appear blurred.

6. 2. The aerial projection device according to claim 1, wherein the screen is a stereoscopic screen.

7. 7. The aerial projection device according to claim 1, wherein the screen is made of Japanese paper or nonwoven fabric.

8. 2. The aerial projection device according to claim 1, wherein at least two pairs of combinations of the half mirror and the screen are provided, and the two pairs of combinations are installed in series at a predetermined interval so that the real image is formed in the air on the same side of each of the half mirrors.

9. The aerial projection device according to claim 8, wherein the screen onto which a projected image corresponding to one of the real images is projected from the holographic projector unit is movable in a direction toward or away from the half mirror so that at least one of the real images moves toward or away from the half mirror.

10. 2. The aerial projection device according to claim 1, wherein the hologram is a computer-generated hologram, and a spatial light modulator is provided that modulates the parallel light into diffracted light based on interference information of the computer-generated hologram.

11. The computer-generated hologram is an amplitude hologram, and the amplitude hologram is expressed by the following formula (1): [Equation 1] 11. The aerial projection device according to claim 10, wherein the aerial projection device is calculated based on the following formula:

12. The computer-generated hologram is a phase hologram, and the phase hologram is expressed by the following formula (2): [Equation 2] 11. The aerial projection device according to claim 10, wherein the aerial projection device is calculated based on the following formula:

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