Image projection device

Abstract

To provide a video projection device that is high in luminance and reduces speckle noise by a simple device configuration.SOLUTION: A video projection device comprises at least: a video emission unit that emits a video an observer is caused to visually recognize by scanning laser light of visible light two-dimensionally; a transmission type screen that projects the video by transmission and scattering of the incident laser light; a projection lens that projects the video projected on the transmission type screen to eyeballs of a user; and a multiplexing optical element that multiplexes light transmitting the projection lens and light of an external world to project to the eyeball, in which the video emission unit includes an incidence angle adjustment mechanism that can adjust an incidence angle of the laser light that is incident upon the transmission type screen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a video projection device using a laser beam. In particular, it relates to a glasses-type display device.

Background Art

[0002] Conventionally, as glasses-type video projection devices called HMD (Head Moundted Display) and smart glasses, there have been proposed many methods such as the LCOS method using a reflective liquid crystal panel, which is the same method as a projector, the DLP method using a DMD device, the OLED method using an organic EL panel for the purpose of miniaturization and power saving, the method using a micro LED display, and the laser scanning method using a laser light source.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional display elements using liquid crystal or organic EL have low brightness, and there are problems with the visibility of images in bright places.

[0005] In order to achieve high definition and high brightness, a micro LED display requires advanced manufacturing technology. While a laser light source is small, power-saving, and has the characteristics of high brightness, since it is coherent light, when projecting an image onto a screen, scattered light from the screen interferes, forming a random interference pattern called speckle noise, resulting in a problem of image quality degradation.

[0006] Even when using a laser light source, in a retinal projection method that projects an image directly onto the retina of a user without using a screen, speckle noise does not occur. However, in this method, it is necessary to incident the laser light into the pupil so as to achieve Maxwell view. Since the average pupil diameter of a human is about 4 mm, there is a problem that the image cannot be viewed at all due to a deviation of several millimeters of the light beam. Thus, a mechanism for scanning the laser light following the movement of the eyeball is separately required.

[0007] In view of the above problems, an object of the present invention is to provide an image projection device with a simple device configuration, high brightness, and reduced speckle noise.

Means for Solving the Problems

[0008] The image projection device according to the present invention includes at least an image emitting unit that emits an image to be visually recognized by an observer by two-dimensionally scanning a laser beam of visible light, a transmissive screen that projects the image by transmitting and scattering the incident laser beam, a projection lens that projects the image projected on the transmissive screen onto the eyeball of a user, and a multiplexing optical element that multiplexes the light transmitted through the projection lens and the light from the outside and projects it onto the eyeball. The image projection unit includes an incident angle adjustment mechanism that can adjust the incident angle of the laser light incident on the transmissive screen. The incident angle adjustment mechanism has a mechanism that can select either that the non-diffused laser light, which is the non-diffused component of the laser light transmitted through the transmissive screen and travels straight without being diffused by scattering during transmission, is incident on the eyeball or not incident on the eyeball It is characterized by this.

[0010] It is characterized in that the non-diffused laser light and the image projected on the transmissive screen can be visually recognized simultaneously.

[0011] The transmissive screen has a plurality of transmissive scattering layers that transmit and scatter laser light, and is configured by stacking the transmissive scattering layers having different haze values.

[0012] The transmissive screen has the transmissive scattering layer on a surface on the observer side with respect to the optical axis from the image emitting unit to the observer, and each layer constituting the transmissive scattering layer is arranged such that the haze value decreases in the direction of the optical axis toward the observer.

Effects of the Invention

[0013] According to the present invention, it is possible to reduce speckle noise, which is a problem when using a laser light source, and to prevent visual field loss due to the movement of the user's eyeball, which is a problem of the retinal projection method. By separating the diffused component and the non-diffused component due to the scattering of the laser light, it is possible to adjust the brightness and the presence or absence of flicker of the image without changing the output of the laser light.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] FIG. 1 is a schematic configuration diagram of a video projection device 1 according to an embodiment of the present invention. The video projection device 1 shown in FIG. 1 includes a video emission unit 11, a transmissive screen 13, an incident angle adjustment mechanism 14, a projection lens 15, and a multiplexing optical element 16. FIG. 1 shows the display with the observer's eyeball 17. The configuration of FIG. 1 illustrates the case where the non-diffusing laser light, which is the non-diffusing component of the laser light 12 emitted from the video emission unit 11 and travels straight without being diffused by scattering during transmission, does not enter the eyeball 17. By adopting the arrangement shown in FIG. 1, it is possible to suppress the flicker of the video when projecting the video. Further, since the non-diffusing laser light does not directly enter the eyeball, it is possible to prevent the retina of the observer from being damaged by an excessive laser output exceeding the rated value caused by applying an overcurrent to the laser oscillator.

[0017] FIG. 2 is a schematic configuration diagram when the position of the video emission unit 11 is changed by the incident angle adjustment mechanism 14 from the configuration of FIG. 1 so that the non-diffusing laser light enters the eyeball 17. By adopting the arrangement shown in FIG. 2, it is possible to increase the luminance of the video when used in a bright place or the like.

[0018] In FIG. 2, the position of the video emission unit 11 is changed by the incident angle adjustment mechanism 14 from the configuration of FIG. 1 so that the non-diffusing laser light of the laser light 12 can enter the eyeball 17. As another embodiment, as shown in FIG. 3, without changing the position of the video emission unit 11 from FIG. 1, by separately installing a reflecting mirror 18, the non-diffusing laser light of the laser light 12 can be configured to enter the eyeball 17. Thus, in FIGS. 2 and 3, it is also possible to simultaneously view the video by the non-diffusing laser light and the video by the scattered light projected onto the transmissive screen. As a result, even when the non-diffusing laser light is not guided into the pupil due to the movement of the eyeball and, as a result, the video by the non-diffusing laser light is not visible, it is possible to easily view the video generated by the transmissive screen. In FIG. 3, by making the non-diffusing laser light enter the eyeball 17 so as to be Maxwell view, a focus-free video can be viewed.

[0019] The image projection unit 11 includes a laser oscillator, a collimating lens for collimating the laser beam 12, and an image projection mechanism that projects a two-dimensional image by irradiating the laser beam 12. As the laser oscillator, a visible laser diode can be used. When projecting an image in full color, it is desirable to use three or four laser diodes of red, green, blue, or including yellow. When using a plurality of laser diodes, a wavelength multiplexer for multiplexing into a single laser beam is provided in front of the collimating lens. As the image projection mechanism, an MEMS mirror or a DMD can be used. By configuring the image projection mechanism to include an imaging lens, a higher-resolution image can be projected onto the transmissive screen 13. Also, as the laser oscillator, a surface-emitting laser diode can be used, and in that case, a DMD is desirable for the image projection mechanism. The laser oscillator can be configured to keep the intensity of the laser beam constant by incorporating a photodiode. Further, when excessive laser output or when the MEMS mirror stops, a safety mechanism for stopping the emission of the laser beam can be provided to ensure safety for the observer's eyes.

[0020] The laser beam 12 is a light beam of the laser beam emitted from the image projection unit 11 and traveling straight, and here it is assumed not to include a light beam diffused by scattering. In FIG. 1, the laser beam 12 is shown as a line for convenience, but it has a certain thickness for projecting an image, and the light beam in the projection area of the image projection device 1 among the laser beams emitted from the image projection unit 11 is included in the laser beam 12.

[0021] The transmissive screen 13 is a screen member that transmits and scatters visible light. A part of the incident light is diffused by scattering, and the rest travels straight without being diffused by transmission. The diffused light that is scattered by the transmissive screen 13 and transmitted through the emission surface, which is the surface opposite to the incident surface, is defined as diffused transmitted light. The optical characteristics of the transmissive screen 13 are represented by the transmittance and the haze value, which is the ratio of the diffused transmitted light to the total luminous flux transmitted light. The total luminous flux transmitted light represents all the transmitted light that has passed through the emission surface regardless of the presence or absence of scattering. In order to reduce speckle noise, the transmissive screen 13 preferably has a multilayer structure as shown in FIG. 4, and has a multilayer transmissive scattering layer that transmits and scatters the laser light on the surface on the observer side with respect to the optical axis from the video projection unit 11 to the observer's eyeball 17. It is desirable that the haze values of the respective layers constituting the transmissive scattering layer are arranged so as to decrease in the direction toward the observer along the optical axis. By configuring the transmissive screen 13 as described above, the interference of the scattered light can be averaged, and the speckle noise can be reduced. In FIG. 4, the upward direction of the paper surface is the observer direction of the optical axis, and the haze value of each layer of the three-layer transmissive scattering layer decreases as it goes upward. Therefore, in FIG. 4, the haze value of the uppermost layer is the smallest, and the haze value of the lowermost layer is the largest. In FIG. 4, as an example of the configuration, a three-layer structure is shown, but the number of layers is not limited. The transmissive scattering layer has a structure in which minute scatterers that scatter visible light are dispersed on the surface or inside of a transparent body that transmits visible light, and the magnitude of the haze value can be adjusted by changing the size and concentration of the minute scatterers. The above concentration depends on the closest distance between the minute scatterers. When the closest distance is short, the value of the concentration is large, and conversely, when the closest distance is long, the value of the concentration is small. The minute scatterers may generate either Mie scattering or Rayleigh scattering. However, in the particle size range of the Mie scattering region, the forward scattering intensity increases, and the speckle noise increases as the particle size increases. Therefore, the average particle size is preferably 1 μm or less, and more preferably 0.6 μm or less. It is desirable that the standard deviation of the particle size is small.When the transmissive screen 13 has a multilayer structure, if the thickness of the screen exceeds the depth of focus of the imaging lens encapsulated in the image projection unit 11, it will cause a deterioration in image quality. Therefore, it is desirable that the thickness be below the depth of focus. The transmissive screen 13 can be used in combination with a transparent liquid crystal image display device. In this case, a different image from the image drawn by the laser light can be projected simultaneously.

[0022] The incident angle adjustment mechanism 14 has a holding mechanism for holding the image projection unit 11 and an angle adjustment mechanism for adjusting the installation angle of the image projection unit 11 with respect to either a horizontal plane or a vertical plane as a reference plane. By changing the installation angle, the incident angle of the laser light 12 incident on the transmissive screen 13 can be adjusted. The installation angle is the tilt angle with respect to the reference plane and can be either the tilt angle within the vertical plane or the tilt angle within the horizontal plane. As shown in FIG. 1, by adjusting the installation angle so that the laser light 12 after passing through the transmissive screen 13 does not enter the multiplexing element 16, it is possible to prevent the laser light 12 from entering the eyeball 17. Thereby, the flicker of the image when projecting the image can be suppressed.

[0023] When it is desired to increase the luminance of the image when used in a bright place or the like, the installation angle can be adjusted so that the laser light 12 enters the multiplexing element 16 as shown in FIGS. 2 and 3 and also enters the pupil of the eyeball 17. It is desirable that the installation angle can be switched according to the user's application. As shown in FIG. 1, when the laser light 12 does not enter the eyeball 17, it is desirable to provide a mechanism for blocking the laser light 12 after passing through the transmissive screen 13 so that it does not leak to the outside.

[0024] The projection lens 15 refracts the diffused transmitted light of the transmissive screen 13 and guides it to the eyeball 17 through the multiplexing optical element 16. When the video projection unit 11 has a plurality of wavelengths in the visible light region, it is desirable to use a lens that corrects chromatic aberration for the projection lens 15. The simplest method is to use an achromatic compound lens corresponding to visible light. The focal length of the projection lens 15 is preferably determined according to the distance between the projection lens 15 and the transmissive screen 13. The most convenient method for the projection lens 15 is to use a convex lens, but a flat diffractive optical element can also be used because of its thinness.

[0025] The multiplexing optical element 16 has a reflective material that reflects a part of the visible light incident on a transmissive material that transmits visible light, reflects a part of the scattered light generated by the transmissive screen 13 toward the eyeball 17, and is arranged so that the user can visually recognize the video. For example, a half mirror can be used for the multiplexing optical element 16, or a lens for glasses with a reflective coating applied to a part thereof can be used. The transmittance of the transmissive material can be selected according to the illuminance of the environment in which it is used. When used in a dark place such as indoors, it is desirable that the transmittance is high. When used in a bright place such as outdoors, it is desirable that the transmittance is low within a range where the transmitted light can be sufficiently visually recognized. The reflectance of the reflective material is preferably selected according to the illuminance of the usage environment. As the reflective material, for example, a metal film such as aluminum, silver, or gold, or a multilayer dielectric film can be used, or a diffraction grating can be formed as the reflective material. Also, in order to project the video in an enlarged manner, a concave lens can be used in combination with the multiplexing optical element 16, or the surface of the multiplexing optical element 16 can be made concave. For miniaturization, the multiplexing optical element 16 can be integrated with a light guide plate.

[0026] Regarding the light guiding from the projection lens 15 to the multiplexing optical element 16, in addition to the free-space optical transmission through the air, a method of transmission using an optical fiber or other waveguides can be used.

[0027] The eyeball 17 is the user's eyeball. Light that constitutes the image incident through the pupil is projected onto the retina by the lens, enabling the user to recognize the image. When the user is nearsighted, a contact lens or spectacle lens for correcting nearsightedness can be used in combination.

Example

[0028] The following shows a configuration example of the image projection device 1 and an example of an AR display. The image emitting unit 11 uses RGB three-color laser diodes in the laser oscillator, uses an optical waveguide type combiner to combine the three laser beams emitted from the laser oscillator into one, uses a collimating lens to collimate the laser beam, combines and uses a MEMS mirror and an imaging lens in the image projection mechanism. The transmissive screen 13 uses a transmissive screen (DiaLumier manufactured by Nichika Chemical Co., Ltd.), the projection lens 15 uses a visible light achromatic plano-convex lens, and the combining optical element 16 uses a half mirror with a reflectivity of 10% and a transmittance of 90%. By connecting the drive circuits of the laser diode and the MEMS mirror and the PC with an HDMI (registered trademark) cable, the screen image of the PC is projected. The configured image projection device 1 was attached to the spectacle frame and actually worn by the observer. First, as a result of arranging the image emitting unit 11 to have the configuration shown in FIG. 1, the screen image was projected in a form superimposed on the actual scenery. Also, as a result of changing the position of the image emitting unit 11 to have the arrangement shown in FIG. 2, the brightness of the screen image increased.

Example

[0029] As the transmission scattering layer of the transmissive screen 13, three transmissive screens (DiaLumi NDL-100, NDL-270, NDL-1000 manufactured by Nichika Chemical Co., Ltd.) with different optical characteristics shown in Table 1 were used. The three screens were overlapped under different conditions to evaluate the speckle noise. Table 1 shows the transmittance and haze values of the three transmissive screens used. In the evaluation, a camera was installed on the observer side shown in Fig. 4, and the screen was photographed under the condition that an image was projected from the image projection unit 11 installed on the opposite side. The projected image is a still image in which the entire screen is filled with a single color of green. As a method for calculating the speckle noise, the quotient obtained by dividing the average value of the normalized luminance, which normalizes the luminance of the image photographed by the camera from 0 to 1, by the standard deviation was used as the value of the speckle noise. In comparing the speckle noise, Table 2 shows the results of the relative speckle noise, which is the relative value under each lamination condition when the measured value of the speckle noise under the condition of using one screen 3 is set to 1. A to C of the layer configuration shown in Table 2 are the same as those in Fig. 4, and the A layer is on the observer side. As shown in Table 2, in the condition of Configuration 3 in which the transmission scattering layer is arranged so that the haze value decreases in the direction toward the observer, the speckle noise is the smallest, and it is reduced by 43% compared with Configuration 1.

[0030]

Table 1

[0031]

Table 2

Explanation of Signs

[0032] 1 Image projection device 11 Image projection unit 12 Laser light 13 Transmissive screen 14 Incident angle adjustment mechanism 15 Projection lens 16 Wave combining optical element 17 Eyeball 18 Concave mirror a Transmission scattering layer (upper) b Through the scattering layer (middle) c Through the scattering layer (lower)

Claims

1. A video projection device comprising at least: a video projection unit that projects a video visible to an observer by two-dimensionally scanning a laser beam of visible light; a transmissive screen that projects the video by transmitting and scattering the incident laser beam; a projection lens that projects the video projected on the transmissive screen onto the user's eyeball; and a multiplexing optical element that multiplexes the light transmitted through the projection lens and the light from the outside world and projects it onto the eyeball. The video projection unit is provided with an incident angle adjustment mechanism that enables adjustment of the incident angle of the laser beam incident on the transmissive screen. The incident angle adjustment mechanism has a mechanism that enables selection of whether the non-diffused laser beam, which is the non-diffused component of the laser beam that travels straight without being diffused by scattering during transmission among the laser beams transmitted through the transmissive screen, enters or does not enter the eyeball.

2. The video projection device according to Claim 1, characterized in that the non-diffused laser beam and the video projected on the transmissive screen can be visually recognized simultaneously.

3. The video projection device according to Claim 1 or 2, characterized in that the transmissive screen has a plurality of transmissive scattering layers that transmit and scatter the laser beam, and is configured by stacking the transmissive scattering layers having different haze values.

4. The video projection device according to Claim 3, characterized in that the transmissive screen has the transmissive scattering layer on the surface on the observer side with respect to the optical axis from the video projection unit to the observer, and each layer constituting the transmissive scattering layer is arranged such that the haze value decreases in the direction of the optical axis toward the observer.

Images