Image projection device using a microprism array

Abstract

This invention provides an image projection device using a microprism array that can improve visibility by ensuring the sharpness of the projected image while suppressing the number of prism cells. [Solution] In a road surface projection device 1 using a microprism array, when a continuous projection image is formed by a first illumination range LS1 generated on the projection surface S by the projection light beam of a single first prism cell 111 constituting the microprism array 10, and a second illumination range LS2 generated on the projection surface S by the projection light beam of another single second prism cell 112 and adjacent to the first illumination range LS1, the illuminance centers LC1 and LC2 of the first and second illumination ranges LS1 and LS2 are located at a distance D of half width h or less, which is half the peak illuminance in the illuminance distribution of the illumination ranges of each single prism cell 111 and 112.

Description

Technical Field

[0001] The present invention relates to an image projection device using a micro prism array.

Background Art

[0002] Conventionally, a technique has been proposed in which an image projection device is installed on a vehicle, a building, or an outdoor pillar, etc., and a projected image such as a figure or a character is displayed on a road surface to transmit information to a driver or a pedestrian (see, for example, Patent Documents 1 to 3, etc.).

[0003] On the other hand, as an alternative to an image projection device composed of a lens and a light source, in recent years, the realization of an image projection device using an optical element called a micro prism array has been expected. A micro prism array is an optical element in which fine prisms are arranged in a two-dimensional array, and it is possible to project a projected image of a desired pattern by projecting light from a light source unit (see, for example, Non-Patent Documents 1, 2, etc.).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

[0006] However, in the conventional image projection device using a microprism array described above, there is no optical conjugate relationship between the projection pattern and the projected image. The light generated from the light source is merely bent by the prism cells in the microprism array toward the respective positions that make up the projected image. As the projected image moves away from the microprism array, the projection range expands or diffuses, increasing the blurring of the projected image. Consequently, the visibility and decorative properties of the projected image are not sufficient, and improvements are desired.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide an image projection device using a microprism array that can improve visibility by ensuring the sharpness of the projected image while suppressing the number of prism cells. [Means for solving the problem]

[0008] The present invention relates to an image projection device using a microprism array, comprising one or more light sources and a microprism array in which a plurality of irregularly shaped prism cells, each constituting a discontinuous microprism, are arranged in a two-dimensional array corresponding to a target projection pattern, wherein when a continuous projection image is formed with a first illumination range generated on the projection surface by a projection luminous beam from a single first prism cell constituting the microprism array and a second illumination range adjacent to the first illumination range, the illuminance centers of the first and second illumination ranges are located at a distance of half width at half maximum, which is half the peak illuminance in the illuminance distribution of the illumination range of each of the single prism cells.

[0009] With this configuration, the illuminance centers of adjacent first and second illumination ranges are located at a distance of less than half the half-width (FWHM), which is half the peak illuminance in the illuminance distribution of each prism cell's illumination range. As a result, the ranges of less than half the peak illuminance in the first and second illumination ranges overlap, allowing for the formation of a clear, continuous projected image. Therefore, it is possible to provide an image projection device using a microprism array that can improve visibility by ensuring the sharpness of the projected image while suppressing the number of prism cells.

[0010] Furthermore, when a continuous projection image is formed in the first and second irradiation ranges, the illuminance centers of the first and second irradiation ranges are located at a distance of less than or equal to the half-width and at least half the half-width from each other.

[0011] With this configuration, the illuminance centers of the first and second illumination ranges are located at a distance of less than or equal to half the width at half maximum and more than or equal to half the width at half maximum, so a continuous and clear projected image can be efficiently formed with a small number of prism cells.

[0012] Furthermore, when a discrete projection image is formed in the first and second irradiation ranges, the illuminance centers of the first and second irradiation ranges are located at a distance of at least twice the half-width, which is half the peak illuminance in the illuminance distribution of the irradiation range of a single prism cell.

[0013] With this configuration, the illuminance centers of adjacent first and second illumination ranges are located at a distance of more than twice the half-width (FWHM), which is half the peak illuminance in the illuminance distribution of each prism cell's illumination range. As a result, the ranges with predetermined illuminances in the first and second illumination ranges are sufficiently separated from each other, allowing for the clear formation of discrete projected images. Therefore, it is possible to provide an image projection device using a microprism array that can improve visibility by ensuring the sharpness of the projected image while suppressing the number of prism cells.

[0014] Furthermore, the system has two or more ray paths from the prism cells for the same irradiation surface position formed by the irradiated light beam from the prism cells.

[0015] With this configuration, a projected image is formed by the light beams from two or more prism cells onto the same illuminated surface position, thereby increasing contrast and ensuring good visibility of the projected image even in environments with high background illumination.

[0016] Furthermore, the prism cell has a square cross-section with dimensions of 0.5 mm × 0.5 mm or less, perpendicular to the optical axis.

[0017] This configuration allows for the projection of a clear and highly visible image despite its compact size.

[0018] The aforementioned image projection device is a road surface projection device for projecting an image onto the road surface.

[0019] This configuration allows for the clear projection of various types of information regarding pedestrians and oncoming vehicles onto the road surface as projected images using a simple setup with a microprism array. [Brief explanation of the drawing]

[0020] [Figure 1]It is an overall configuration diagram schematically showing a road surface projection device using a micro prism array according to an embodiment of the present invention. [Figure 2] It is a perspective view showing an example of a micro prism array. [Figure 3] It is a plan view showing the whole of the micro prism array. [Figure 4] It is a plan view showing a part of the micro prism array enlarged. [Figure 5] It is an explanatory diagram schematically showing a state where a target projection pattern is formed on the micro prism array. [Figure 6] It is an arrangement diagram showing the positional relationship and size of a light source, a prism cell, and a projected image in the road surface projection device according to the embodiment. [Figure 7] It is a radiation characteristic diagram of the LED used as the light source in this embodiment. [Figure 8] It is a diagram showing the illuminance distribution formed by the light beam passing through one prism cell decomposed into 11×11 pixels. [Figure 9] It is a perspective view schematically showing a first prism cell and a second prism cell. [Figure 10] It is a diagram schematically showing the relationship between the first prism cell and the second prism cell and the first irradiation range and the second irradiation range. [Figure 11] It is a diagram showing an example of a projected image including continuous lines and discrete lines. [Figure 12] It is a graph showing an example of the illuminance distribution when drawing a continuous projected image. [Figure 13] It is a graph showing an example of the illuminance distribution when drawing a discrete projected image. [Figure 14] It is a diagram showing the simulation of the projected image according to Example 1 in which two adjacent irradiation ranges are shifted by three pixels in the upper part, and the illuminance distribution graph thereof in the lower part. [Figure 15] It is a diagram showing the simulation of the projected image according to Example 2 in which two adjacent irradiation ranges are shifted by four pixels in the upper part, and the illuminance distribution graph thereof in the lower part. [Figure 16]The upper panel shows a simulation of the projection image for Comparative Example 1, in which two adjacent illumination areas are shifted by 5 pixels, and the lower panel shows the illuminance distribution graph. [Figure 17] The upper panel shows a simulation of the projection image for Comparative Example 2, in which two adjacent illumination areas are shifted by 6 pixels, and the lower panel shows the illuminance distribution graph. [Figure 18] The upper panel shows a simulation of the projection image for Comparative Example 3, in which two adjacent illumination areas are shifted by 6 pixels, and the lower panel shows the illuminance distribution graph. [Figure 19] The upper panel shows a simulation of the projection image for Comparative Example 4, in which two adjacent illumination areas are shifted by 7 pixels, and the lower panel shows the illuminance distribution graph. [Figure 20] The upper panel shows a simulation of the projection image according to Example 3, in which two adjacent illumination areas are shifted by 8 pixels, and the lower panel shows the illuminance distribution graph. [Figure 21] The upper panel shows a simulation of the projection image according to Example 4, in which two adjacent illumination areas are shifted by 9 pixels, and the lower panel shows the illuminance distribution graph. [Figure 22] This figure shows the projection source image of the target projection pattern according to Example 5. [Figure 23] Figure 22 shows a simulation of the projection image of the original projection image. [Figure 24] This is a schematic diagram illustrating how a beam of light from one prism cell illuminates each pixel of a projected image. [Figure 25] This is a schematic diagram illustrating how light beams from two prism cells illuminate one pixel of a projected image. [Figure 26] This is a schematic diagram illustrating how light beams from four prism cells illuminate one pixel of a projected image. [Figure 27] This is a schematic diagram illustrating how light beams from nine prism cells illuminate one pixel of a projected image. [Figure 28] This graph shows the relationship between background illumination and contrast. [Figure 29]This figure compares and shows projected images at various contrast levels. [Figure 30] This is a table showing a guideline for brightness relative to illuminance. [Figure 31] Figure (1 / 2) shows a comparison of the projected images with 1, 4, and 9 cells per pixel at different background illumination levels. [Figure 32] Figure (2 / 2) shows a comparison of the projected images with 1, 4, and 9 cells per pixel at different background illumination levels. [Figure 33] In the modified example, the illuminance distribution formed by the light beam transmitted through a single prism cell is shown, decomposed into 11x11 pixels. The left side shows a planar representation, and the right side shows a three-dimensional representation. [Modes for carrying out the invention]

[0021] Hereinafter, various embodiments of the road surface projection device that embody the image projection device using the microprism array of the present invention will be described with reference to the drawings.

[0022] <First Embodiment> First, a road surface projection device 1 (hereinafter simply referred to as "road surface projection device 1") using a microprism array according to an embodiment of the present invention will be described with reference to Figures 1 to 13. Figure 1 is a schematic overall configuration diagram of the road surface projection device 1. Figure 2 is a perspective view showing an example of a microprism array 10. Figure 3 is a plan view showing the entire microprism array 10. Figure 4 is a plan view showing an enlarged part of the microprism array 10. Figure 5 is a schematic explanatory diagram showing how a target projection pattern P is formed on the microprism array 10. Figure 6 is an arrangement diagram showing the positional relationship between the light source 20, the prism cell 11, and the projected image in the road surface projection device 1. Figure 7 is a radiation characteristic diagram of the LED used as the light source 20. Figure 8 is a diagram showing the illuminance distribution formed by the light beam transmitted through one prism cell 11, decomposed into 11 × 11 pixels. Figure 9 is a schematic perspective view showing the first prism cell 111 and the second prism cell 112. Figure 10 schematically shows the relationship between the first prism cell 111 and the second prism cell 112 and the first illumination range LS1 and the second illumination range LS2. Figure 11 shows an example of a projected image containing continuous and discrete lines. Figure 12 is a graph showing an example of the illuminance distribution when a continuous projected image is drawn. Figure 13 is a graph showing an example of the illuminance distribution when a discrete projected image is drawn.

[0023] The road surface projection device 1 is a device for projecting a projection image based on a target projection pattern P onto a road surface S, and comprises a microprism array 10 and a light source 20.

[0024] The microprism array 10 is formed by arranging multiple microprisms in a two-dimensional pattern corresponding to the target projection pattern P. More specifically, the microprism array 10 is made of a transparent resin material and is an optical component formed by arranging multiple irregularly shaped prism cells 11, each constituting a discontinuous microprism, in a two-dimensional array, as shown in Figure 2. Specifically, PMMA (polymethyl methacrylate), PC (polycarbonate), etc., can be suitably used as the resin material constituting the microprism array 10. In this specification, "each discontinuous prism" means that the boundary between adjacent prisms is discontinuous. In the following description, the term "individual prism" is also used to refer to individual prism cells 11.

[0025] The microprism array 10 is formed by arranging multiple prism cells (b x c) in a two-dimensional array, each prism cell 11 being a square in plan view with side length a, as shown in Figures 3 and 4, so that the entire microprism array 10, consisting of b x c cells, is rectangular (including square) with one side a x b = B and the other side a x c = C. Each prism cell 11 can be set to any size depending on the application; for example, it may be a tiny prism with a side length a of less than 1.0 mm, or it may be a prism with a length a of several mm or more. Each prism cell 11 preferably has a square cross-section perpendicular to the optical axis LA with a size of 0.5 mm x 0.5 mm or less. In this specification, when each prism cell 11 consists of tiny prisms, it is referred to as a microprism array. Furthermore, each prism cell 11 is not limited to a square in plan view with the same length for both vertical and horizontal sides, but may also be rectangular in plan view with different lengths for the vertical and horizontal sides.

[0026] The micro prism array 10 is designed to project a target projection pattern P, such as a predetermined figure or character, onto a projection surface S by a plurality of prism cells 11 that are discontinuous prisms. The thickness of the prism, the inclination angle and orientation of the exit surface, etc. have irregular concave and convex shapes that are different for each prism cell 11. In this embodiment, as shown in FIG. 5, the target projection pattern P is a figure of the character "stop", and is a figure that includes a continuous image pattern (for example, a vertical bar region or a horizontal bar region) and a discrete image pattern (for example, a region where two vertical bars cross in the X direction). Further, the character "stop" serves as a sign that requests a vehicle or the like to stop temporarily when its projected image is projected onto the road surface.

[0027] Also, in the above-described micro prism array 10, since the size of each individual prism is as small as 0.5 mm square as described above, and the number of individual prisms is also several hundred to several thousand, it is very difficult to generate its shape by cutting or polishing in mass production. In order to provide a low-cost micro prism array 10, it is desirable to produce its material by injection molding or hot stamping using a thermoplastic resin. Further, in order to ensure optical transparency, the material constituting the micro prism array 10 is desirably a thermoplastic resin made of polymethyl methacrylate, polycarbonate, polystyrene, cyclic olefin polymer, or a copolymer thereof. With a manufacturing method such as injection molding using these materials, not only the micro prism array 10 but also the engagement shape with the mating parts to which it is attached can be shaped simultaneously, and the number of parts of the road surface projection device 1 can be minimized.

[0028] The microprism array 10 is manufactured by a manufacturing method that includes, for example, a mold design step of designing a mold model having an inverted shape of a molded product model of the microprism array 10 based on a pre-designed molded product model of the microprism array 10; a mold processing step of manufacturing a mold having an uneven structure by machining the mold base material based on the mold model designed in the mold design step; and a molding step of molding the molding material into the microprism array 10 using a mold apparatus having the mold. This manufacturing method has the effect of efficiently mass-producing high-quality microprism arrays 10 because, in the mold processing step, an irregular uneven structure is formed by machining the mold base material to manufacture the mold, and in the molding step, the molding material is molded into the microprism array 10 using a mold apparatus equipped with the mold.

[0029] The light source 20 is composed of light-emitting elements. The light-emitting elements constituting the light source 20 are arranged facing the incident surface 10a of the microprism array 10. Preferably, the light-emitting elements are arranged such that the normal to the center in the XY direction on the incident surface 10a of the microprism array 10 passes through the center in the XY direction of the light-emitting elements. The light-emitting elements are composed of, for example, LEDs (light-emitting diodes).

[0030] Next, the size and arrangement of each part of the road surface projection device 1 will be described with reference to Figure 6. Figure 6 is a schematic diagram showing the positional relationship on the optical axis between the prism cell 11, which is a prism as a piece of prism constituting the microprism array 10 of this embodiment, the light source 20, and the projection surface. In this embodiment, the size of the prism cell 11 in the microprism array 10 is 0.5 mm square, and the chip size of the LED as the light source 20 is 0.6 mm square. The light source 20 is positioned 50 mm away from the incident surface of the microprism array 10, and the projection surface S is positioned 2000 mm away from the exit surface of the microprism array 10. The projected image on the projection surface S has a geometrically optical theoretical size of 20 mm square and a measured size of 80 mm square.

[0031] In this embodiment, in geometric optical ray tracing, the light rays emitted from the light source 20 pass through the opening formed by the optical surface of the prism (a square of 0.5 mm square in the figure) and irradiate a square range of 20 mm square that is similar to the individual prism opening on the projection surface. In reality, since the light source 20 is not a strict point source but a surface light source of 0.6 mm square corresponding to an LED chip, and due to shape errors around the opening, etc., the irradiation range generated on the projection surface is about 80 mm square in experimental measurements, and the half-value width is about 50 mm. If the size of the individual prism is made larger than 0.5 mm, only projection images with an interval of 100 mm or more can be projected and visually recognized, and fine display on the road surface projection cannot be achieved.

[0032] As shown in FIG. 6, the ratio of the shortest side d (the length of one side in the case of a square) of the cross-section in the plane perpendicular to the optical axis of the individual prism to the distance L from the cross-section to the light source position determines the pixel size of the projection image. Considering the balance between the illuminance and sharpness of the projection image, for the road surface projection device 1, it is desirable that 30 < L / d < 170. This is because when trying to increase the illuminance of the projection pixels by increasing the light beam capture from the LED light source, L / d should be decreased, while when seeking the fineness of the projection image, L / d should be increased. This is a desirable condition for implementing appropriate projection as the road surface projection device 1 while achieving both illuminance and image fineness. If the lower limit is exceeded, the blurring of the projection image becomes severe, and if the upper limit is exceeded, the light beam capture decreases and the brightness of the projection image cannot be ensured.

[0033] The LED as the light source 20 has the radiation characteristics shown in FIG. 7. Specifically, the total luminous flux of the LED is 170 lumens, and the relative light intensity has a half-value width at an angle of ±66 degrees.

[0034] In the road surface projection device 1 having the arrangement shown in FIG. 6, the measured illuminance distribution formed by the light beam irradiated from one prism cell 11 is shown in FIG. 8. FIG. 8 shows the measured illuminance distribution decomposed into pixels of 11x11. When the illuminance at the center of the light beam is set to 1.0, it is shown that the relative value of the illuminance decreases as 0.9, 0.6, 0.3,... as the distance from the center increases.

[0035] In the road surface projection device 1, when drawing and projecting line segments with the microprism array 10, the drawn image is decomposed into a point cloud using a pre-set square grid, and the shape of the prism cells 11 of the microprism array 10 is determined so that light from a light source illuminates each of the decomposed points. The overall shape of the microprism array 10 is then determined by superimposing these shapes. The projected illumination pattern is drawn by superimposing the illumination patterns shown in Figure 8. The line segments (curve segments) of the original image of the drawn image are decomposed into discrete point clouds, but if the spacing between these points is made large, that is, if the pitch of the square grid is made large, the peripheral parts (dark areas) of the illumination distribution become more prominent, resulting in a dotted line drawing rather than a straight line drawing.

[0036] In this embodiment, in view of the image formation process using the microprism array 10, the half-width of the projected illuminance by the prism cell 11 as a single prism is used as a reference to obtain a projected image that sufficiently reflects the original image. In other words, the road surface projection device 1 according to this embodiment is a road surface projection device that uses a microprism array 10 such that the angle of each individual prism is determined so that adjacent point cloud elements after image development are arranged within the range of the half-width, and the overlap of the point cloud becomes a continuous illuminance distribution. Similarly, when drawing discrete line segments or surfaces in the original image of the drawn image, it is a road surface projection device in which it is possible to visually confirm that the illuminance distribution formed by the point cloud is clearly separated.

[0037] <Principles of formation of continuous and discrete projection images> Next, the formation principles of continuous projection images and discrete projection images will be described while referring to FIGS. 9 to 13. In the following description, in the micro prism array 10 of the road surface projection device 1, it is assumed that a projection image is formed by a single first prism cell 111 and another single second prism cell 112 as shown in FIG. 9. Note that in FIG. 9, an example where the first prism cell 111 and the second prism cell 112 are adjacent to each other is shown, but it is not limited thereto. As shown in FIG. 10, the first prism cell 111 forms a first irradiation range LS1 having an illuminance center LC1 on the projection surface S, and the second prism cell 112 forms a second irradiation range LS2 having an illuminance center LC2 on the projection surface S. It is assumed that the illuminance center LC1 of the first irradiation range LS1 and the illuminance center LC2 of the second irradiation range LS2 are separated by a distance D.

[0038] First, in the road surface projection device 1, the principle of forming a continuous projection image by a single first prism cell 111 and another single second prism cell 112 that form part of the micro prism array 10 will be described. Here, the "continuous projection image" means a linear or curved projection image that is continuous along the A direction in FIG. 11. In the projection image corresponding to the character "stop" which is the target projection pattern P shown in FIG. 5, the projection images of line segments such as vertical bars and horizontal bars correspond to the "continuous projection image".

[0039] In the present embodiment, when a continuous projection image is formed by the first irradiation range LS1 generated on the projection surface S by the projection light beam of a single first prism cell 111 constituting the micro prism array 10 and the second irradiation range LS2 generated on the projection surface S by the projection light beam of another single second prism cell 112 and adjacent to the first irradiation range LS1, as shown in FIG. 12, the illuminance centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS two are located at a distance D (D ≦ h) that is less than or equal to the half-value width h, which is half of the peak illuminance in the illuminance distribution of the irradiation range of each single prism cell 111 and 112. Note that FIG. 12 shows the case where the distance D between the illuminance centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS2 is equal to the half-value width h (D = h).

[0040] That is, since the illumination centers LC1 and LC2 of adjacent first and second irradiation ranges LS1 and LS2 are located at a distance of not more than the half-value width h, which is half of the peak illumination in the illumination distribution of the irradiation range of each prism cell 111 and 112, the ranges below half of the peak illumination in the first and second irradiation ranges LS1 and LS2 overlap with each other, and a continuous projected image can be clearly formed. When the first prism cell 111 and the second prism cell 112 are used in the road surface projection device 1, the inclination angle of the prism top surface and the like are set when designing and processing the micro prism array 10 so that the distance D between the illumination centers LC1 and LC2 is not more than the half-value width h.

[0041] Next, in the road surface projection device 1, the principle of forming a discrete projected image by a single first prism cell 111 forming part of the micro prism array 10 and another single second prism cell 112 will be described. Here, the "discrete projected image" means a projected image of discrete line segments or points existing in the B direction in FIG. 11. In the projected image of the character "stop" which is the target projection pattern P shown in FIG. 5, the projected image of the line segment or point when two vertical bars are horizontally crossed corresponds to the "discrete projected image".

[0042] In the present embodiment, when forming a discrete projected image with a first irradiation range LS1 generated on the projection surface S by the projection light beam of a single first prism cell 111 constituting the micro prism array 10 and a second irradiation range LS2 generated on the projection surface S by the projection light beam of another single second prism cell 112 and adjacent to the first irradiation range LS1, as shown in FIG. 13, the illumination centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS2 are located at a distance D (D ≧ h×2) of not less than twice the half-value width h, which is half of the peak illumination in the illumination distribution of the irradiation range of each single prism cell 111 and 112. In FIG. 13, the case where the distance D between the illumination centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS2 is equal to twice the half-value width h (D = h×2) is shown.

[0043] In other words, the illuminance centers LC1 and LC2 of the adjacent first and second illumination ranges LS1 and LS2 are located at a distance of more than twice the half-width h, which is half the peak illuminance in the illuminance distribution of the illumination range of each prism cell 111 and 112. As a result, the areas with predetermined illuminances in the first and second illumination ranges LS1 and LS2 are sufficiently separated from each other, and a discrete projection image can be clearly formed. The inclination angle of the prism top surface of the first prism cell 111 and the second prism cell 112 are set when the microprism array 10 is designed and manufactured so that the distance D between the illuminance centers LC1 and LC2 is more than twice the half-width h when used in the road surface projection device 1.

[0044] <Description of Examples and Comparative Examples Regarding Continuous Projection Image Formation> Next, Examples 1 and 2 and Comparative Examples 1 and 2 concerning the formation of a continuous projection image will be described with reference to Figures 14 to 17. Figure 14 shows the simulation results of the projection image according to Example 1, in which the first irradiation range LS1 from the first prism cell 111 and the second irradiation range LS2 from the second prism cell 112 are shifted by 3 pixels. In Example 1, as shown in the lower part of Figure 14, the centers of the first and second irradiation ranges LS1 and LS2 are located close to each other at a distance of half-width h × 0.75, which is half the peak illuminance in the illuminance distribution of the irradiation range of a single prism cell 111, and so on, so that a portion of the irradiation ranges overlap. In Example 1, as shown in the upper part of Figure 14, the illuminance distributions are integrated to form a single continuous projection image.

[0045] Figure 15 shows the simulation results of the projection image according to Example 2, in which the first irradiation range LS1 and the second irradiation range LS2 are shifted by 4 pixels. In Example 2, as shown in the lower part of Figure 15, the centers of the first and second irradiation ranges LS1 and LS2 are located close together at a distance of half-maximum × 1.0, so a portion of the irradiation ranges overlap. In Example 2, as shown in the upper part of Figure 15, the illuminance distribution is integrated to form a single continuous projection image.

[0046] Figure 16 shows the simulation results of the projection image for Comparative Example 1, in which the first irradiation range LS1 and the second irradiation range LS2 are shifted by 5 pixels. In Comparative Example 1, as shown in the lower part of Figure 16, the centers of the first and second irradiation ranges LS1 and LS2 are located at a distance of 1.25 times the half-maximum range. In Comparative Example 1, as shown in the upper part of Figure 16, the projection image is indistinctly constricted in the left and right centers, and is unsuitable as a continuous projection image.

[0047] Figure 17 shows the simulation results of the projection image for Comparative Example 2, in which the first irradiation range LS1 and the second irradiation range LS2 are shifted by 6 pixels. In Comparative Example 1, as shown in the lower part of Figure 17, the centers of the first and second irradiation ranges LS1 and LS2 are located at a distance of 1.5 times the half-maximum range. In Comparative Example 2, as shown in the upper part of Figure 17, the projection image is indistinctly constricted in the left and right centers and is unsuitable as a continuous projection image.

[0048] <Description of Examples and Comparative Examples Regarding Discrete Projection Image Formation> Next, Examples 3 and 4 and Comparative Examples 3 and 4 concerning discrete projection image formation will be described with reference to Figures 18 to 21. Figure 18 shows the simulation results of the projection image for Comparative Example 3, in which the first irradiation range LS1 from the first prism cell 111 and the second irradiation range LS2 from the second prism cell 112 are shifted by 6 pixels. In Comparative Example 3, as shown in the lower part of Figure 18, the centers of the first and second irradiation ranges LS1 and LS2 are located at a distance of half-maximum × 1.5 from each other. In Comparative Example 17, as shown in the upper part of Figure 18, the tails of the illuminance distribution overlap and are not visible as two completely separate projection images, so it is unsuitable as a discrete projection image.

[0049] Figure 19 shows the simulation results of the projection image for Comparative Example 4, in which the first illumination range LS1 and the second illumination range LS2 are shifted by 7 pixels. In Comparative Example 4, as shown in the lower part of Figure 19, the centers of the first and second illumination ranges LS1 and LS2 are located at a distance of 1.75 times the half-maximum range. In Comparative Example 4, as shown in the upper part of Figure 19, the tails of the illuminance distribution overlap and are not visible as two completely separate projection images, making it unsuitable as a discrete projection image.

[0050] Figure 20 shows the simulation results of the projection image according to Example 3, in which the first illumination range LS1 and the second illumination range LS2 are shifted by 8 pixels. In Example 3, as shown in the lower part of Figure 20, the centers of the first and second illumination ranges LS1 and LS2 are located at a distance of half-maximum × 2.0. In Example 3, as shown in the upper part of Figure 20, a discrete projection image is formed in which the two illuminance distributions are completely separated.

[0051] Figure 21 shows the simulation results of the projection image according to Example 4, in which the first illumination range LS1 and the second illumination range LS2 are shifted by 9 pixels. In Example 4, as shown in the lower part of Figure 21, the centers of the first and second illumination ranges LS1 and LS2 are located at a distance of 2.25 times the half-maximum range. In Example 4, as shown in the upper part of Figure 21, a discrete projection image is formed in which the two illuminance distributions are completely separated.

[0052] <Example 5> Next, Example 5, in which a figure including continuous and discrete parts is projected using the road surface projection device 1 according to this embodiment, will be described with reference to Figures 22 and 23. Figure 22 is a diagram showing the target projection pattern of Example 5. Figure 23 is the projected image of Example 5 projected based on the target projection pattern of Figure 22. As shown in Figure 23, in Example 5, a projected image including continuous and discrete parts is clearly realized.

[0053] <Summary of the First Embodiment> As is clear from the detailed description above, the road surface projection device 1 using a microprism array according to the first embodiment comprises one or more light sources 20 and a microprism array 10 which is formed by arranging a plurality of irregularly shaped prism cells 11, etc., each constituting a discontinuous microprism, in a two-dimensional array corresponding to a target projection pattern. When a continuous projection image is formed by a first illumination range LS1 generated on the projection surface S by the projection light beam from a single first prism cell 111 constituting the microprism array 10 and a second illumination range LS2 generated on the projection surface S by the projection light beam from another single second prism cell 112 and adjacent to the first illumination range LS1, the illuminance centers LC1 and LC2 of the first and second illumination ranges LS1 and LS2 are located at a distance D of half-width h or less, which is half the peak illuminance in the illuminance distribution of the illumination range of each single prism cell 111, 112.

[0054] With this configuration, the illuminance centers LC1 and LC2 of adjacent first and second illumination ranges LS1 and LS2 are located at a distance D of half-width h or less, which is half the peak illuminance in the illuminance distribution of the illumination ranges of each prism cell 111 and 112. As a result, the ranges of half or less of the peak illuminance in the first and second illumination ranges LS1 and LS2 overlap, allowing for the formation of a clear, continuous projected image. Therefore, it is possible to provide a road surface projection device 1 using a microprism array that can improve visibility by ensuring the sharpness of the projected image while suppressing the number of prism cells.

[0055] Furthermore, when a continuous projection image is formed in the first irradiation range LS1 and the second irradiation range LS2, the illuminance centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS2 are located at a distance of less than or equal to the half-width h and at least half the half-width h.

[0056] This configuration allows for the efficient formation of a continuous and sharp projection image with a small number of prism cells. Specifically, while a large number of prism cells are required to form a continuous projection image of the desired length when the distance between the illuminance centers LC1 and LC2 is extremely close, by positioning them at a distance of less than or equal to the full width at half maximum (FWHM) and more than half the FWHM, a continuous projection image of the desired length can be formed with a small number of prism cells.

[0057] Furthermore, when discrete projection images are formed in the first irradiation range LS1 and the second irradiation range LS2, the illuminance centers LC1 and LC2 of the first and second irradiation ranges LS1 and LS2 are located at a distance D (D ≥ h × 2) that is more than twice the half-width h.

[0058] With this configuration, the illuminance centers LC1 and LC2 of the adjacent first and second illumination ranges LS1 and LS2 are located at a distance D of more than twice the half-width h, which is half the peak illuminance in the illuminance distribution of the illumination ranges of each prism cell 111 and 112. As a result, the areas with illuminance above a certain level in the first and second illumination ranges LS1 and LS2 are sufficiently separated from each other, and a clear discrete projection image can be formed.

[0059] Furthermore, the prism cell 11 has a square cross-section with dimensions of 0.5 mm × 0.5 mm or less, perpendicular to the optical axis.

[0060] This configuration allows for the projection of a clear and highly visible image despite its compact size.

[0061] The road surface projection device 1 according to this embodiment is a projection device for projecting a projected image onto a road surface.

[0062] With this configuration, various types of information regarding pedestrians and oncoming vehicles can be clearly projected onto the road surface as projected images using a simple configuration with a microprism array 10.

[0063] <Second Embodiment> In the first embodiment described above, as shown in Figure 24, an example was shown in which a light beam from one prism cell 11 is irradiated onto one pixel of the projected image. In contrast, the second embodiment is characterized in that a light beam from multiple prism cells 11 is irradiated onto one pixel of the projected image. The configuration of the second embodiment will be described below with reference to Figures 25 to 27. Figure 25 shows an example in which a light beam from two prism cells 11 is irradiated onto one pixel of the projected image. Figure 25 shows an example in which a light beam from four prism cells 11 is irradiated onto one pixel of the projected image. Figure 26 shows an example in which a light beam from nine prism cells 11 is irradiated onto one pixel of the projected image. According to this embodiment, high contrast can be achieved even when the background illumination is high, and the visibility of the projected image can be ensured.

[0064] Next, the effects of the second embodiment will be explained in detail. First, the relationship between background illuminance and contrast will be explained with reference to Figure 28. Figure 28 is a graph showing the relationship between background illuminance and contrast when the number of prism cells 11 per pixel of the projected image (hereinafter referred to as the number of cells) is changed to 1, 2, 4, and 9. The graph shows that for each number of cells, the higher the background illuminance, the lower the contrast. It also shows that the larger the number of cells, the better the contrast at the same background illuminance.

[0065] Next, the relationship between the visibility of the projected image and contrast will be explained with reference to Figure 29. As shown in Figure 29, good visibility can be obtained at contrasts of 100%, 80%, 60%, 40%, 30%, and 20%. At a contrast of 15%, the minimum necessary visibility is ensured. On the other hand, at contrasts of 10% and 5%, the necessary visibility is not ensured. From the above, it can be seen that a contrast of 15% or more is necessary to ensure the visibility of the projected image (i.e., a lower limit of 15%), and 20% or more is preferable.

[0066] Furthermore, the relationship between illuminance and brightness guidelines will be explained with reference to the table in Figure 30. The source of the table shown in Figure 30 is the Koyomi Handbook 2006-2008 (published by the Osaka Science Museum), http: / / photon.sci-museum.kita.osaka.jp / publish / text / koyomi / 66.html. The road surface projection device 1 according to this embodiment is mainly intended for use under streetlights (50-100 lux), and it is preferable that it can be used at the brightness of sunrise and sunset (300 lux), and more preferably at the brightness of sunlight one hour before sunset on a clear day (1000 lux). In summary, based on the results shown in Figures 28 to 30 described above, the road surface projection device 1 is required to be able to secure a contrast of 15% or more, preferably 20% or more, at a background illuminance of 100 lux or less, preferably 1,000 lux or less.

[0067] Next, we will explain the simulation results of the projected image and its contrast at various background illuminances for the cases of 1 cell per pixel of the projected image (hereinafter referred to as M1), 4 cells (hereinafter referred to as M4), and 9 cells (hereinafter referred to as M9), with reference to Figures 31 and 32. Figures 31 and 32 are simulation results showing how visibility changes with background illuminance when the ratio of the number of prism cells in the microprism array 10 to the number of pixels (point resolution) of the projected image is changed. The simulation conditions are as follows: the total luminous flux of the LED light source 20 is 170 lumens, the half-width of the radiation angle is 60 degrees, the distance from the light source 20 to the microprism array 10 is 50 mm, and the cell pitch of the microprism array 10 (XY dimension perpendicular to the optical axis Z of the individual prism) is 0.5 mm. The illuminance of the projection surface generated by the individual prisms was simulated using the measured illuminance in Figure 8 to determine the illuminance of the overall image.

[0068] At a background illumination of 0 (lx), the contrast of all M1 to M9 is 100, resulting in a clear projected image. At a background illumination of 35000 (lx), the contrast of all M1 to M9 is 0, and the projected image is almost invisible.

[0069] At a background illumination of 3 (lx), the contrasts of M1, M4, and M9 are 76, 93, and 97, respectively. Sufficient contrast is achieved for all three, resulting in a clear projected image.

[0070] At a background illumination of 50 lux, the contrasts of M1, M4, and M9 are 16, 44, and 64, respectively. M1 achieves the necessary contrast, producing a visible projected image. M4 and M9 achieve sufficient contrast, resulting in clear projected images.

[0071] At a background illumination of 150 lux, the contrasts of M1, M4, and M9 are 6, 21, and 37, respectively. M1 lacks sufficient contrast, making the projected image difficult to see. On the other hand, M4 and M9 achieve sufficient contrast, resulting in a clear projected image.

[0072] At a background illumination of 200 lux, the contrast values ​​for M1, M4, and M9 are 5, 16, and 30, respectively. M1 lacks sufficient contrast, making the projected image difficult to see. M4 achieves the necessary contrast, resulting in a visible projected image. On the other hand, M9 achieves sufficient contrast, resulting in a clear projected image.

[0073] At a background illumination of 250 lux, the contrasts of M1, M4, and M9 are 4, 13, and 26, respectively. M1 and M4 lack sufficient contrast, making the projected image difficult to see. On the other hand, M9 achieves sufficient contrast, resulting in a clear projected image.

[0074] At a background illumination of 370 lux, the contrasts of M1, M4, and M9 are 3, 10, and 19, respectively. M1 and M4 lack sufficient contrast, making the projected image difficult to see. On the other hand, M9 achieves sufficient contrast, resulting in a clear projected image.

[0075] At a background illumination of 600 lux, the contrasts of M1, M4, and M9 are 2, 6, and 13, respectively. The contrast is insufficient for all three, making the projected image difficult to see.

[0076] At a background illumination of 2000 (lx), the contrasts of M1, M4, and M9 are 0, 2, and 4, respectively. The contrast is insufficient for all three, making the projected image difficult to see.

[0077] Furthermore, referring again to the graph in Figure 28, we can see that when there is one cell per pixel of the projected image, the background illuminance (horizontal axis) corresponding to a contrast of 15% (vertical axis 0.15) is 150 (lx), indicating that visibility can be ensured "under a streetlamp". Also, when there are two cells, the background illuminance (horizontal axis) corresponding to a contrast of 15% (vertical axis 0.15) is 250 (lx), indicating that visibility can be ensured in a "nighttime arcade", which is brighter than "under a streetlamp". Also, when there are four cells, the background illuminance (horizontal axis) corresponding to a contrast of 15% (vertical axis 0.15) is 500 (lx), indicating that visibility can be ensured in a "sunrise / sunset" or "fluorescent-lit office", which are brighter than a "nighttime arcade". Furthermore, with 9 cells, the background illuminance (horizontal axis) corresponding to a contrast of 15% (vertical axis 0.15) is 1200 (lx), indicating that visibility can be ensured in brighter conditions than "sunrise and sunset" and "fluorescent-lit office," such as "sunlight one hour before sunset on a clear day," "inside a pachinko parlor," and "department store sales floor."

[0078] <Summary of the second embodiment> As is clear from the above detailed description, the road surface projection device 1 using a microprism array according to the second embodiment has two or more light beam paths from prism cells 11 for the same irradiation surface position formed by the irradiation light beam from the prism cells 11.

[0079] This configuration ensures good visibility of the projected image by increasing contrast even in environments with high background illumination.

[0080] In other words, the simulation results described above show that when the background illumination is bright, the projected image of the microprism array 10 becomes obscured by the background, making it impossible to see the projected image under a bright background. To solve this, it is necessary to increase the amount of light absorbed by the microprism array 10. On the other hand, to maintain the clarity of the projected image, increasing the cell pitch of the individual prisms (prism cells 11) that make up the microprism array 10 to increase the amount of light absorbed would be counterproductive. Therefore, it becomes necessary to illuminate each pixel of the projected image with light beams from multiple individual prisms.

[0081] In this embodiment, the effects of background illuminance and the number of cells in the microprism array 10 were determined through actual measurements and simulations, and it was found that in order to ensure versatility as a road surface projection device (visibility even in bright places), illumination from individual prisms of at least twice (preferably four times or more) the number of projection pixels is necessary. To ensure visibility of the projected image even when the background illuminance is bright, increasing the total luminous flux of the light source 20 could be considered as a means, but this would require increasing the current supplied to the light source, resulting in increased power consumption of the device and the need for additional heat countermeasures, which is undesirable for low cost and miniaturization. This embodiment makes it possible to realize a road surface projection device using a microprism array that can maintain visibility of the projected image even under a bright background without increasing the luminous flux emitted from the light source 20 or the supplied current.

[0082] <Variation> The present invention is not limited to the embodiments and modifications described above, and various modifications can be made without departing from the spirit of the invention. For example, in each of the above embodiments, the peak illuminance of the illuminance distribution in the irradiation range of a single prism cell 11 was described using a distribution that is symmetrical in all directions, but even if this is asymmetrical, the conditions related to pixel separation and joining of the projected image remain the same. Here, Figure 33 is a diagram showing the illuminance distribution formed by the light beam transmitted through one prism cell in a modified example, decomposed into 11 × 11 pixels, with a planar representation on the left and a three-dimensional representation on the right. As shown in the modified example in Figure 33, the same effects of the present invention can be obtained even with an asymmetrical illuminance distribution.

[0083] Furthermore, while the above embodiments show examples of applying the image projection device using the microprism array according to the present invention to a road surface projection device, the invention is not limited to this. For example, it can also be applied to a wall projection device for projecting guidance images onto the exterior walls of buildings, the walls of rooms or corridors, or the walls of fences. [Industrial applicability]

[0084] The image projection device using the microprism array according to the present invention is envisioned to be incorporated into the turn signals of automobiles to create a variety of images on the road surface to alert pedestrians, or to be used as an effective guide light by creating a variety of images on pathway guidance lights inside buildings. [Explanation of symbols]

[0085] 1. Road surface projection device (image projection device using a microprism array) 10 Microprism Arrays 11 Prism Cells 111 First Prism Cell 112 Second Prism Cell 20 light source P Target projection pattern S projection surface LS1 First Irradiation Range LS2 Second irradiation range LC1,LC2 Illuminance center h Half-width D distance

Claims

1. An image projection device comprising one or more light sources and a microprism array in which multiple irregularly shaped prism cells, each constituting a discontinuous microprism, are arranged in a two-dimensional array corresponding to a target projection pattern, An image projection device using a microprism array, wherein when a continuous projected image is formed by a first illumination range generated on the projection surface by a projection luminous beam from a single first prism cell constituting the microprism array, and a second illumination range generated on the projection surface by a projection luminous beam from another single second prism cell and adjacent to the first illumination range, the illuminance centers of the first and second illumination ranges are located at a distance of half width at half maximum, which is half the peak illuminance in the illuminance distribution of the illumination range of each of the single prism cells.

2. An image projection apparatus using a microprism array according to claim 1, wherein, when a continuous projection image is formed in the first irradiation range and the second irradiation range, the illuminance centers of the first and second irradiation ranges are located at a distance of less than or equal to the half-width and at least half the half-width from each other.

3. An image projection apparatus using a microprism array according to claim 1, wherein, when a discrete projection image is formed in the first irradiation range and the second irradiation range, the illuminance centers of the first and second irradiation ranges are located at a distance of at least twice the half-width between them.

4. An image projection device comprising one or more light sources and a microprism array in which multiple irregularly shaped prism cells, each constituting a discontinuous microprism, are arranged in a two-dimensional array corresponding to a target projection pattern, An image projection device using a microprism array, wherein when a discrete projection image is formed by a first illumination range generated on the projection surface by a projection luminous beam from a single first prism cell constituting the prism array, and a second illumination range generated on the projection surface by a projection luminous beam from another single second prism cell and adjacent to the first illumination range, the illuminance centers of the first and second illumination ranges are located at a distance of at least twice the half-width, which is half the peak illuminance in the illuminance distribution of the illumination range of the single prism cell.

5. An image projection device using a microprism array according to any one of claims 1 to 4, wherein the array has two or more light paths from the prism cells to the same irradiation surface position formed by the irradiation beam from the prism cells.

6. The image projection apparatus using a microprism array according to any one of claims 1 to 4, wherein the prism cell has a square cross-section of 0.5 mm × 0.5 mm or less perpendicular to the optical axis.

7. The image projection device is a road surface projection device for projecting an image onto a road surface, an image projection device using a microprism array according to any one of claims 1 to 4.

Images