Image projection device using a microprism array

Abstract

This invention provides an image projection device using a microprism array that can improve the clarity of projected images without increasing the overall size of the device. [Solution] The image projection device 1 comprises a microprism array 10, which is made up of multiple irregularly shaped prism cells 11, each constituting a discontinuous microprism, arranged in a two-dimensional array corresponding to a target projection pattern TP, and a light source unit 20 which projects light toward the microprism array 10 by positioning a light-emitting surface (pinhole opening 23a) having a finite area in a plane perpendicular to the optical axis LA opposite the incident surface of the microprism array 10. When the individual piece size of each prism cell 11 is represented by the cell pitch P, which is the arrangement pitch of the prism cells 11, the light source unit 20 is set so that the maximum diameter L of the pinhole opening 23a in the direction perpendicular to the optical axis LA is greater than twice and less than eight times the cell pitch P.

Description

[Technical Field]

[0001] The present invention relates to an image projection apparatus using a microprism array, and particularly to an image projection apparatus capable of drawing high-definition projection images. [Background Art]

[0002] Conventionally, a technique for transmitting information to drivers or pedestrians by installing an image projection apparatus on a vehicle, a building, an outdoor pillar, or the like and displaying a projection image such as a figure or characters on the ground surface has been proposed (see, for example, Patent Documents 1 to 3).

[0003] On the other hand, as an alternative to image projection apparatuses composed of a lens and a light source, realization of an image projection apparatus using an optical element called a microprism array has been expected in recent years. A microprism array is an optical element in which fine prisms are arranged in a two-dimensional array, and can project a projection image of a desired pattern by projecting light from a light source unit (see, for example, Non-Patent Documents 1, 2 and 3). [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-218254 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-7079 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-159904 [Non-Patent Documents]

[0005] [Non-Patent Document 1] "Collection of Research Result Cases (Implemented in FY2022), Page 18, Influence of Molding Error of Microprism Array on Projection Image", Shizuoka Prefectural Industrial Technology Research Institute, April 2023 [Non-Patent Document 2] "Shizuoka Prefectural Industrial Technology Research Institute Research Report No. 16, November 2023, pp. 121-122, Evaluation of Projection Performance of a Graphic Projection Device Using a Microprism Array," Shizuoka Prefectural Industrial Technology Research Institute, ISSN 1883-2350, CODEN:SKGKBP [Non-Patent Document 3] "Shizuoka Prefectural Industrial Technology Research Institute Research Report No. 15, October 2022, pp. 128-129, Design of a Microprism Array for Projecting Figures," Shizuoka Prefectural Industrial Technology Research Institute, ISSN 1883-2350, CODEN:SKGKBP [Overview of the project] [Problems that the invention aims to solve]

[0006] However, Non-Patent Document 3 suggests increasing the number of cells in the microprism array or increasing the distance between the light source and the microprism array in order to sharpen the projected image. However, there is a concern that increasing the number of cells in the microprism array within a limited size would either require miniaturizing the size of the microprism cells, or conversely, keeping the cell pitch the same as the existing size would lead to an increase in the overall size of the microprism array, resulting in a device size that is unsuitable for mounting in vehicles or embedding in walls.

[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 the clarity of the projected image without increasing the overall size of the device. [Means for solving the problem]

[0008] The present invention provides an image projection device using a microprism array, comprising: 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; and at least one light source unit that projects light toward the microprism array, with a light-emitting surface having a finite area in a plane perpendicular to the optical axis, positioned opposite the incident surface of the microprism array, wherein when the individual piece size of each prism cell is represented by the cell pitch, which is the arrangement pitch of the prism cells, the light source unit is set such that the maximum diameter of the light-emitting surface in the direction perpendicular to the optical axis is greater than twice and less than eight times the cell pitch.

[0009] In this configuration, when the light source emits light from its projection surface toward the microprism array, a projection image of the target projection pattern is projected onto a projection surface located on the opposite side of the light source, across the microprism array. Since the maximum diameter of the light source's projection surface in the direction perpendicular to the optical axis is set to be more than twice but less than eight times the cell pitch of the microprism array, a high-definition projection image can be projected onto the projection surface. Therefore, this provides an image projection device using a microprism array that can improve the clarity of the projection image without increasing the overall size of the device.

[0010] Furthermore, the light source unit is configured to include a light source element and a light shielding plate having a pinhole opening that is positioned between the light source element and the microprism array in the optical axis direction and functions as the light-emitting surface, wherein the maximum diameter of the pinhole opening of the light shielding plate is set to be more than twice the cell pitch and less than eight times the cell pitch.

[0011] In this configuration, light emitted from the light source element is projected from a pinhole opening in the light-shielding plate, which serves as a light-projecting surface, toward the microprism array. Since the maximum diameter of the pinhole opening in the light-shielding plate is set to be more than twice the cell pitch but less than eight times, a light-projecting surface for drawing high-definition projected images can be realized with a simple structure, regardless of the size of the light source element.

[0012] Furthermore, the light source unit further includes a focusing optical system between the light source element and the light shielding plate in the optical axis direction, which focuses the light incident from the light source element toward the pinhole opening.

[0013] With this configuration, the light emitted from the light source element is focused toward the pinhole opening by a focusing optical system provided between the light source element and the light-shielding plate in the optical axis direction, increasing the amount of light and thus increasing the brightness. This makes it possible to achieve both high resolution and brightness of the projected image without increasing the size of the device.

[0014] Furthermore, the light-gathering optical system includes a light-gathering lens that focuses the light incident from the light source element toward the pinhole opening.

[0015] With this configuration, the light emitted from the light source element is focused towards the pinhole opening by a focusing lens, increasing the amount of light captured. This allows for the realization of a focusing optical system with a simple configuration, achieving both sharpness and brightness in the projected image.

[0016] Furthermore, the focusing optical system includes a reflective focusing optical system that reflects the light incident from the light source element and focuses it toward the pinhole opening.

[0017] With this configuration, light emitted from the light source element is reflected by the reflective focusing optical system and focused towards the pinhole aperture, increasing the amount of light captured. This allows for the realization of a focusing optical system with a simple configuration, achieving both sharpness and brightness in the projected image. [Effects of the Invention]

[0018] The image projection device using a microprism array according to the present invention makes it possible to obtain an image projection device using a microprism array that can produce high-resolution images without increasing the size of the device. [Brief explanation of the drawing]

[0019] [Figure 1] Fig. 1 is an overall configuration diagram schematically showing an image projection apparatus using the microprism array according to the first embodiment of the present invention in perspective view. [Figure 2] Fig. 2 is an overall configuration diagram schematically showing an image projection apparatus using the microprism array according to the first embodiment in side view. [Figure 3] Fig. 3 is a configuration diagram schematically showing the light source unit in the first embodiment in side view. [Figure 4] Fig. 4 is a perspective view showing an example of the microprism array. [Figure 5] Fig. 5 is a plan view showing the entire microprism array. [Figure 6] Fig. 6 is an enlarged plan view showing a part of the microprism array. [Figure 7] Fig. 7 is an explanatory diagram schematically showing a microprism array on which a direction indication graphic as a target projection pattern is formed. [Figure 8] Fig. 8 is a conceptual diagram of ray tracing for individual microprism pieces. [Figure 9] Fig. 9 is a first explanatory diagram schematically showing, in side view, the arrangement of a light projection surface and the microprism array and the spread of a projected image for explaining the operation when the light projection surface size is large. [Figure 10] Fig. 10 is a second explanatory diagram schematically showing, in side view, the arrangement of a light projection surface and the microprism array and the spread of a projected image for explaining the operation when the light projection surface size is reduced. [Figure 11] Fig. 11 is a graph showing the illuminance profiles of a projected image on a projection surface that depend on different light projection surface sizes (different opening sizes of a light shielding plate). [Figure 12] Fig. 12 is a graph showing the results obtained from actually captured images of the projected image illuminance profiles on a projection surface and their half-width characteristics that depend on different light projection surface sizes. [Figure 13] Fig. 13 is a diagram showing an example of obtaining brightness from an actually captured projection image. [Figure 14] Fig. 14 is an explanatory diagram showing the illuminance characteristics, half-width, and 30-70% rising width in one cross-section of a projected image. [Figure 15] This diagram shows the brightness rise characteristics of projected images due to differences in the size of the light-emitting surface. [Figure 16] This figure shows a graph illustrating the illuminance profile of the projected image on the projection surface for different projection surface sizes, and compares it with actual images for each projection surface size (aperture size). [Figure 17] This figure shows a graph illustrating the relationship between the light-emitting surface size (aperture size of the light-shielding plate) and the peak illuminance of a V-shaped prism, alongside actual images of each light-emitting surface size (aperture size). [Figure 18] This is a schematic overall diagram showing an image projection device using a microprism array according to the second embodiment. [Figure 19] This is a schematic diagram showing a side view of the light source unit in the second embodiment. [Figure 20] This is a schematic overall diagram showing an image projection device using a microprism array according to the third embodiment. [Figure 21] This is a schematic diagram showing a side view of the light source unit in the third embodiment. [Figure 22] This is a schematic diagram showing a side view of the light source unit in a first modified example of the first embodiment. [Figure 23] This is a schematic diagram showing a side view of the light source unit in a second modified example of the first embodiment. [Figure 24] This is a schematic diagram showing a side view of the light source unit in a modified example of the third embodiment. [Figure 25] This is a perspective view showing the appearance of a kaleidoscope used in a modified example of the third embodiment. [Modes for carrying out the invention]

[0020] Hereinafter, various embodiments of the high-precision drawing image projection device that embodies the image projection device using the microprism array of the present invention will be described with reference to the drawings.

[0021] <Configuration of the first embodiment> First, the configuration of the image projection device 1 (hereinafter simply referred to as "image projection device 1") using a microprism array according to the first embodiment of the present invention will be described with reference to Figures 1 to 8. Figure 1 is a schematic overall configuration diagram showing the image projection device 1 in an oblique view, and Figure 2 is a schematic overall configuration diagram showing the same in a side view. Figure 3 is a schematic configuration diagram showing the light source unit 20 in a side view. Figure 4 is an oblique view showing an example of the microprism array 10, Figure 5 is a plan view showing the whole, and Figure 6 is a plan view showing a part enlarged. Figure 7 is an explanatory diagram schematically showing the microprism array 10 on which a directional indicator figure as a target projection pattern TP is formed. Figure 8 is a conceptual diagram of ray tracing of individual microprism pieces. Note that the schematic diagrams in Figures 1 to 3 and Figure 8 depict the microprism array 10 relatively large for ease of viewing, and do not accurately represent its size relationship with the light source element 21 and the pinhole opening 23a of the light shielding plate 23, which will be described later (the same applies to Figures 9, 10, and 18 to 24, which will be described later).

[0022] The image projection device 1 is a device for projecting a projection image PI based on a target projection pattern TP onto a projection surface S, and as shown in Figures 1 to 3, it comprises a microprism array 10 and a light source unit 20 having a light source element 21 and a light shielding plate 23.

[0023] The microprism array 10 is formed by arranging multiple microprisms in a two-dimensional pattern corresponding to the target projection pattern TP. 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 4. 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.

[0024] 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 4 and 5, 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 of vertical and horizontal sides, but may also be a rectangular in plan view with different lengths of vertical and horizontal sides. In this embodiment, since each prism cell 11 is square in plan view, the cell pitch P, which is the distance between the centerlines of adjacent prism cells 11, is equal to the length a of one side of each prism cell 11. For this reason, in the following description, the length a of one side of each prism cell 11 will also be referred to as the cell pitch P.

[0025] The microprism array 10 is designed to project a target projection pattern TP, such as a predetermined figure or character, onto a projection surface S using multiple prism cells 11, which are discontinuous prisms. Each prism cell 11 has an irregular uneven shape with different prism thicknesses, inclination angles and orientations of the emission surfaces. In this embodiment, as shown in Figure 6, the target projection pattern TP is a V-shape that serves as a directional indicator.

[0026] Furthermore, in the microprism array 10 described above, the individual prism size is small, as described above, at 0.5 mm square, and the number of individual prisms is several hundred to several thousand. Therefore, it is extremely difficult to mass-produce its shape by cutting or polishing. To provide a low-cost microprism array 10, it is preferable to produce it using injection molding or hot stamping with thermoplastic resin. Moreover, in order to ensure optical transparency, it is preferable that the material constituting the microprism array 10 is a thermoplastic resin consisting of polymethyl methacrylate, polycarbonate, polystyrene, cyclic olefin polymer, or copolymers thereof. With manufacturing methods such as injection molding using these materials, not only the microprism array 10 but also the engagement shape with the mating part to which it is attached can be formed simultaneously, thus minimizing the number of parts in the image projection device 1.

[0027] 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.

[0028] The light source element 21 constituting the light source unit 20 is composed of a light-emitting element. The light-emitting element constituting the light source element 21 is arranged toward the incident surface 10a of the microprism array 10. Preferably, the light-emitting element is 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 element. The light-emitting element is composed of, for example, an LED (light-emitting diode).

[0029] The light-shielding plate 23 is a plate-shaped member positioned between the microprism array 10 and the light source element 21, and is provided with a pinhole opening 23a having a finite area in a plane perpendicular to the optical axis LA. Light emitted from the light source element 21 toward the microprism array 10 is transmitted only through the pinhole opening 23a and blocked by other parts of the light-shielding plate 23. The end face of the pinhole opening 23a facing the microprism array 10 functions as the light-projecting surface toward the microprism array 10.

[0030] <Basic form and effect of the present invention> Next, the basic form and effects of the present invention will be described with reference to Figures 9 to 17. Figure 9 is a first explanatory diagram schematically showing the arrangement of the light-emitting surface and the microprism array 10 and the spread of the projected image in a side view to explain the operation when the light-emitting surface size is large, and Figure 10 is a second explanatory diagram schematically showing the arrangement of the light-emitting surface and the microprism array 10 and the spread of the projected image in a side view to explain the operation when the light-emitting surface size is small. Figure 11 is a graph showing the illuminance profile of the projected image on the projection surface S for different light-emitting surface sizes (aperture size of the light-shielding plate 23). Figure 12 is a graph showing the results of obtaining the illuminance profile of the projected image on the projection surface S for different light-emitting surface sizes and their half-width characteristics from actual images. Figure 13 is a diagram showing an example of determining brightness from a projected actual image. Figure 14 is an explanatory diagram of the illuminance characteristics, half-width, and 30-70% rise width in one cross-section of the projected image. Figure 15 is a diagram of the brightness rise characteristics of the projected image for different light-emitting surface sizes. Figure 16 is a graph showing the illuminance profile of the projected image on the projection surface S for different projection surface sizes, compared with actual images for each projection surface size (aperture size). Figure 17 is a graph showing the relationship between the projection surface size (aperture size of the light-shielding plate 23) and the V-shaped prism peak illuminance, compared with actual images for each projection surface size (aperture size).

[0031] Note that in the graph shown in Figure 11, the vertical axis unit is a mix of "lx," which represents the measured brightness, and "digit," which represents the pixel signal intensity of the actual image. However, the actual image uses an 8-bit signal from 0 to 255 to represent brightness, and the shape of the graph still represents the illuminance profile. Similarly, the horizontal axis contains both "mm" and "pixel" notations. The latter represents the position on the actual image, and when converted to the image size, it has the same meaning as "mm," and the characteristic profile shown in the graph is equivalent.

[0032] Figure 11 is a histogram of the number of rays reaching the projection surface per unit area, based on the geometric ray tracing results when the light source's projection surface is of a finite size rather than a point light source, based on the arrangements in Figures 1, 3, and 8. The graph shows the projection surface size L and the illuminance full width at half maximum of the image on the projection surface. Here, the projection surface size L is defined by the maximum diameter of the projection surface (pinhole opening 23a) in the direction perpendicular to the optical axis LA. The maximum diameter of the projection surface is the length of the diameter of the circumscribed circle in the cross-section perpendicular to the optical axis LA at the exit end of the pinhole opening 23a. Therefore, for example, if the pinhole opening 23a as the projection surface is circular, the maximum diameter of the projection surface corresponds to the diameter of the circle forming the cross-section of the pinhole opening 23a. Also, if the pinhole opening 23a is square, the maximum diameter of the projection surface corresponds to the length of the diagonal of the square forming the cross-section of the pinhole opening 23a. Illuminance half-width refers to the range in the illuminance distribution of an illuminance spot where the illuminance is more than half of the peak illuminance.

[0033] The graph in Figure 11 indicates that the illuminance spot on the projection surface S created by each individual prism cell 11 changes depending on the projection surface size L of the light source unit (light source unit 20), and that the degree of change is greater than the change due to the size (cell pitch P) of the prism cell 11. In other words, the size of the projection image formed by each individual prism cell 11 changes depending on the projection surface size from which the light of an LED, commonly used as a light source element, is projected toward the microprism array 10. By using a light source unit 20 with a small projection surface size L, the projection image of each individual prism cell 11 can be made smaller. This results in a finer overall projection image, making it possible to add even finer detail within the limited projection image range.

[0034] Figure 16 shows the changes in the projected image when the light-emitting surface size L is changed, using actual images. Specifically, Figure 16 shows actual images of the projected image when the light-emitting surface size L is changed to 2.6 mm, 2.0 mm, 1.8 mm, 1.5 mm, 1.0 mm, 0.7 mm, 0.5 mm, and 0.3 mm. The microprism array 10 in this embodiment is designed to draw a pictogram of the "<" mark, and the cell pitch P representing the size of the prism cell 11 is 0.3 mm × 0.3 mm, the light source distance from the light-emitting surface to the microprism array 10 is 50 mm, and the projection distance is 2000 mm. In the actual images, when the light-emitting surface size L of the light source unit 20 is 2.6 mm, the boundary between the light and dark areas of the drawn image is blurred, and the projected image appears to have a flare overall. This is because the projected image per cell, as shown in Figure 9, is spread more due to the area light source than when a point light source is assumed.

[0035] Figure 10 shows a schematic diagram of the case when the light projection surface size is reduced in Figure 11. It can be seen that by reducing the light projection surface, it becomes closer to an ideal point light source, and the light rays from the periphery of the light projection surface are illuminated without spreading. Figure 16 shows the results of verifying this with an actual device, and it can be seen that a projected image with a smaller light projection surface size, which is closer to a point light source, has thinner lines and a clearer image with sharper contrast. In other words, reducing the light projection surface size L is effective when trying to obtain a fine-grained image. Looking at Figures 11 and 12 in more detail, it has been shown that the line width (spot size) of the image, which is used as a surrogate value for fineness, and the light projection surface size are almost proportional when the ratio L / P of the maximum diameter L of the light projection surface to the cell pitch P is 2 or more, and that a light source unit 20 with a light projection surface size that matches the required image can be selected. In the following explanation, the maximum diameter L of the light projection surface will also be referred to as the light projection surface size L.

[0036] Referring to Figure 11, as mentioned earlier, in the region where L / P≦2, more specifically, in the case of cell pitch P=0.3mm, the projection surface size L on the horizontal axis is 0.6mm or less (L / P≦2=0.6 / 0.3), and in the case of P=0.7mm, the projection surface size L on the horizontal axis is 1.4mm or less (L / P≦2=1.4 / 0.7), the proportional relationship between the projection surface size L and the spot size begins to break down, and the spot no longer decreases in response to changes in the projection surface size L. Therefore, it can be seen that even if the projection surface size L is reduced to less than twice P, the contribution of the microprism array 10 to the clarity of the projected image becomes small.

[0037] On the other hand, Figure 15 shows how the reciprocal of the rise width from black to white in the projected image changes with respect to the projection surface size L, as determined from the actual image. Here, a conceptual diagram for evaluating the brightness of the actual image is shown in Figure 13. Figure 14 is a plot of the brightness of each pixel in the image along the analysis line in Figure 13. The width occupied by more than half the height of this brightness profile is called the "full width at half maximum," and the width rising from 30% to 70% height is called the "30-70% rise width."

[0038] Figure 15 plots how the reciprocal of the 30-70% rise width changes with the projection surface size L. The numbers on the vertical axis represent resolution and spatial frequency, which are common values ​​for photographic lenses, and indicate the trend of how fine an image can be projected by the microprism array 10. Figure 15 is plotted for a case where the cell pitch P is 0.3 mm, and the change becomes smaller when the projection surface size L on the horizontal axis exceeds 2.5 mm. This trend indicates that when the projection surface size L exceeds 2.5 mm, the blurring of the projected image increases, and even if the projection surface size L is changed, the projected image remains significantly blurred.

[0039] That is, it can be seen that in the region where L / P≧8 (≈2.5 / 0.3), the brightness of the entire projected image increases, while sharp definition begins to break down. Further, as shown in FIG. 11, as the light projection surface size L increases, the dependency on the cell pitch P weakens, so the condition of L / P at which the breakdown of sharp definition starts can be considered to be approximately the same when the cell pitch P is 0.7 mm as when it is 0.3 mm. Therefore, it can be said that when attempting to obtain a clear projected image with the microprism array 10, L / P<8 is required. From these simulations and actual measurement results, a clear and bright projected image can be obtained if 2<L / P<8 is satisfied (in other words, if the maximum diameter L of the light projection surface is set to more than 2 times and less than 8 times the cell pitch P).

[0040] When the projected image of the microprism array 10 is used for simple outdoor display, brightness is often prioritized over the fineness of the projected image, so it is desirable to increase L / P. FIG. 17 is a plot of the maximum illuminance in an actual captured image, with the light projection surface size L taken on the horizontal axis for the case where the cell pitch P is 0.3 mm. Further, FIG. 17 shows actual captured projected images when the light projection surface size L is changed to 2.6 mm, 2.0 mm, 1.8 mm, 1.5 mm, 1.0 mm, 0.7 mm, 0.5 mm, and 0.3 mm. As can be seen from FIG. 17, the illuminance value starts to rise when L<1.5, that is, when L / P exceeds 5, and it can be seen that the change in maximum illuminance is larger than the change in the sharpness of the projected image. From this, in cases where brightness is prioritized over the fineness of the projected image, it is a desirable condition to select the cell pitch P and the light projection surface size L that satisfy 5<L / P<8 (in other words, the maximum diameter L of the light projection surface is more than 5 times and less than 8 times the cell pitch P).

[0041] On the other hand, for common LEDs used as light source elements, the size of the light-emitting surface is limited, and in reality, high-luminance LEDs having a fine light-emitting surface that meets the above conditions are not commercially available. In the present embodiment, in consideration of the case where no LED satisfying the above conditions exists, the present invention contemplates reducing the light projection surface size L for projecting light toward the microprism array 10 by using a pinhole opening 23a provided in a light shielding plate 23 as shown in FIG. 1 and FIG. 3. By using this means, even a small L / P ratio can be achieved, and fine drawing can be realized without reducing the size of individual prism cells of the microprism array 10 even when fine drawing is required. Even in the structure using this pinhole opening 23a, by setting the maximum diameter L of the pinhole opening 23a in the direction perpendicular to the optical axis LA to satisfy 2 < L / P < 8 in relation to the cell pitch P, a clear and bright projected image by the microprism array 10 can be obtained. Further, similarly, in cases where priority is given to brightness over the fineness of the projected image, it is a desirable condition to select the cell pitch P and the light projection surface size L that satisfy 5 < L / P < 8.

[0042] The pinhole opening 23a that defines the light projection surface size L or the light emitting element shape is generally rectangular or circular, but the present embodiment is not limited thereto, and may be polygonal or any opening shape. In this case, it is desirable that the shape of the prism cells 11 constituting the microprism array 10 is similar to the shape of the light projection surface (the cross-sectional shape of the pinhole opening 23a). Accordingly, for example, when the configuration of the microprism array 10 is an integration of square lattice shapes, it is desirable that the shape of the light projection surface is also square. Similarly, if the configuration of the microprism array is a so-called honeycomb shape (integration of regular hexagons), it is desirable that the shape of the light projection surface is a regular hexagon. As a result, the projected image in the direction along each side of the square approximates the projection of the light projection surface shape, so an effect contributing to improvement in sharpness can be obtained. Of course, when the light projection surface shape is defined by the light shielding plate 23 having the pinhole opening 23a, a basic effect can be obtained by adopting a circular opening in view of ease of processing. Also in this case, if L that satisfies 2<L / P<8 defined in the above description satisfies the maximum diameter of the opening (the diameter for a circle, and the diagonal length for a rectangle), the effect of improving the sharpness of the projected image can be obtained.

[0043] <Summary of First Embodiment> An image projection apparatus 1 using the microprism array according to the present embodiment includes: a microprism array 10 formed by two-dimensionally arranging a plurality of irregularly shaped prism cells 11 each constituting a discontinuous microprism corresponding to a target projection pattern TP; and a light source unit 20 as a light source section that arranges a light projection surface (pinhole opening 23a) having a finite area in a plane perpendicular to the optical axis LA to face the incident surface of the microprism array 10 and projects light toward the microprism array 10, wherein when the individual size of each prism cell 11 is represented by the cell pitch P which is the arrangement pitch of the prism cells 11, the light source unit 20 is set such that the maximum diameter L of the light projection surface (pinhole opening 23a) in the direction perpendicular to the optical axis LA is more than 2 times and less than 8 times the cell pitch P.

[0044] In this configuration, when the light source unit 20 projects light from the pinhole opening 23a, which serves as the light-emitting surface, toward the microprism array 10, the projected image PI of the target projection pattern TP is projected onto the projection surface S located on the opposite side of the light source unit 20, across the microprism array 10. The light-emitting surface (pinhole opening 23a) of the light source unit 20 is set so that its maximum diameter L in the direction perpendicular to the optical axis LA is more than twice but less than eight times the cell pitch P of the microprism array 10. Therefore, this provides an image projection device using a microprism array that can improve the clarity of the projected image without increasing the overall size of the device.

[0045] Furthermore, the light source unit 20 is configured to include a light source element 21 and a light shielding plate 23 having a pinhole opening 23a that is positioned between the light source element 21 and the microprism array 10 in the optical axis LA direction and functions as a light-emitting surface, wherein the maximum diameter of the pinhole opening 23a of the light shielding plate 23 is set to be more than twice the cell pitch P and less than eight times.

[0046] In this configuration, light emitted from the light source element 21 is projected toward the microprism array 10 through a pinhole opening 23a, which serves as a light-projecting surface, provided in the light-shielding plate 23. Since the maximum diameter L of the pinhole opening 23a of the light-shielding plate 23 is set to be more than twice the cell pitch P but less than eight times, a light-projecting surface for drawing a high-definition projected image PI can be realized with a simple structure, regardless of the size of the light source element 21.

[0047] The image projection device 1 using a microprism array according to this embodiment has the effect of enabling high-resolution drawing without increasing the size of the device.

[0048] <Configuration of the second embodiment> The second embodiment was devised to resolve the conflict between detail and brightness described above. In other words, in the pinhole opening 23a of the first embodiment, depending on conditions such as arrangement, it is conceivable that only a portion of the light beam emitted from the light source element 21 may reach the microprism array 10. In this embodiment, the divergent light beam emitted from the light source element 21 is focused by a focusing lens 25, and this focusing point is set as the projection position of the microprism array 10, thereby effectively utilizing the light beam that would not have reached the microprism array 10 if the focusing lens 25 were not present. Figure 18 is a schematic overall configuration diagram showing the image projection device 1 using a microprism array according to the second embodiment. Figure 19 is a schematic configuration diagram showing the light source unit 20 in the second embodiment in a side view.

[0049] The light beam emitted by the light source element 21 is focused through the focusing lens 25 to the conjugate point of the light source element 21. By positioning this conjugate point at the pinhole opening 23a of the light shielding plate 23, and using this pinhole opening 23a as the light projection surface of the microprism array 10, a small yet bright light source unit can be realized, enabling both detail and brightness in the depicted image.

[0050] <Summary of the second embodiment> In the image projection apparatus 1 according to this embodiment, the light source unit 20 further includes a condensing lens 25 as a condensing optical system that focuses the light incident from the light source element 21 toward the pinhole opening 23a between the light source element 21 and the light shielding plate 23 in the optical axis LA direction.

[0051] With this configuration, the light emitted from the light source element 21 is focused toward the pinhole opening 23a by a focusing lens 25 provided between the light source element 21 and the light shielding plate 23 in the optical axis LA direction. This increases the amount of light taken in and increases the brightness, thus achieving a balance between the detail and brightness of the projected image PI without increasing the size of the device.

[0052] Furthermore, the light-gathering optical system is configured to include a light-gathering lens 25 that focuses the light incident from the light source element 21 toward the pinhole opening 23a.

[0053] With this configuration, the light emitted from the light source element 21 is focused by the condensing lens 25 towards the pinhole aperture 23a, increasing the amount of light captured. This allows for the realization of a condensing optical system with a simple configuration, achieving both fineness and brightness in the projected image PI.

[0054] In this embodiment, as in the first embodiment, the effect of enabling high-resolution drawing without increasing the size of the device is achieved.

[0055] <Configuration of the third embodiment> The third embodiment replaces the focusing lens 25 of the second embodiment with a rod integrator 27. Figure 20 is a schematic overall diagram showing the image projection device 1 using a microprism array according to the third embodiment. Figure 21 is a schematic side view diagram showing the light source unit 20 in the third embodiment.

[0056] In the present embodiment, the light beam incident on the rod integrator 27 is repeatedly reflected inside, and when it reaches the exit side end, it becomes a fine light source with a uniformized luminance distribution within the exit side end. By using this exit side end as a light projection surface that projects light onto the microprism array 10, a light source that is small yet bright and has uniform brightness can be obtained, and as in the second embodiment, both the fineness and brightness of a drawn image can be achieved. This rod integrator 27 has a truncated pyramid structure, allows a light source beam to enter from the bottom surface of the truncated pyramid, repeats internal reflection on the slope of the truncated pyramid, and emits light from the exit side end. The truncated pyramid is at least a truncated triangular pyramid or more, and a truncated quadrangular pyramid similar to the microprism array arrangement is preferably effective from the viewpoint of light beam utilization efficiency. Although FIGS. 20 and 21 show an example in which a light shielding plate 23 is provided separately from the rod integrator 27, the light shielding plate 23 can be omitted if the maximum diameter L of the exit side end of the rod integrator 27 can be made to satisfy the condition of 2<L / P<8. In this case, the rod integrator 27 serves as both the condensing optical system and the light shielding plate.

[0057] <Summary of the Third Embodiment>

[0058] In the image projection apparatus 1 according to the present embodiment, the condensing optical system includes a rod integrator 27 serving as a reflective condensing optical system that condenses light incident from a light source element 21 toward a pinhole opening 23a while reflecting the light.

[0059] According to this configuration, the light emitted from the light source element 21 is condensed toward the pinhole opening 23a by the rod integrator 27, increasing the amount of light taken in. Therefore, a condensing optical system can be realized with a simple configuration, and both the fineness and brightness of the projected image PI can be achieved.

[0060] Also in the present embodiment, similarly to the first and second embodiments, there is an effect that high-definition drawing can be performed without increasing the size of the apparatus.

[0061] <Modification> The present invention is not limited to the embodiments or modifications described above, and various modifications can be made without departing from the spirit of the invention.

[0062] For example, the shape of the pinhole opening 23a of the light-shielding plate 23 is not limited to those of the embodiments described above. Figure 22 is a schematic diagram showing a side view of the light source unit 20 in a first modified example of the first embodiment, and Figure 23 is a diagram showing a second modified example. Both modified examples have an opening cross-sectional structure to improve the efficiency of light utilization from the light source element 21. That is, in the first modified example shown in Figure 22, a conical dome 23b is formed on the side of the pinhole opening 23a of the light-shielding plate 23 that faces the light source element 21. In the second modified example shown in Figure 23, a hemispherical dome 23c is formed on the side of the pinhole opening 23a of the light-shielding plate 23 that faces the light source element 21. In these modified examples, the light rays reflected in the space between the light-shielding plate 23 having the pinhole opening 23a and the LED mounting substrate as the light source element 21 exit from the pinhole opening 23a, which is expected to contribute to the illumination of the microprism array and suppress the decrease in illuminance of the projected image. Furthermore, by mirror-finishing the inside of the light source side of this pinhole opening 23a, an even greater improvement in light utilization efficiency can be achieved, contributing to the illuminance of the projected image.

[0063] On the other hand, to achieve brighter and sharper image quality, it is desirable to set the pinhole and light source size so that L / P < 5, and it is desirable to compensate for the resulting decrease in illuminance with the structure of the second and third embodiments. Furthermore, since reducing the prism cell size can also be expected to improve sharpness, it is desirable to use this in conjunction with the selection of the light source size. From the viewpoint of experimental results and the durability of the mold processing tools, it is desirable that the cell pitch P corresponding to the microprism individual piece size at this time be 0.2 mm or more and 0.5 mm or less. If it is lower than this, tool wear in mold processing of the microprism array becomes at a level that cannot be ignored, the surface roughness of the prism cells in the microprism array does not become uniform, and phenomena such as increased scattering or decreased transmittance are observed in some prism cells, and if it exceeds the upper limit, it leads to a decrease in the sharpness of the projected image.

[0064] In the third embodiment, the rod integrator, as a reflective focusing optical system, utilizes reflection on its inner surface. However, by replacing this reflective surface with a mirror, a similar effect can be obtained by creating a kaleidoscope 29 (kaleidoscope structure) as shown in Figure 25, as in the modified example of the third embodiment shown in Figure 24, and this is also effective as a light source unit for a microprism array. In both the rod integrator and the mirror-based design, it is desirable to give the frustum body height at least three times the maximum diameter (diagonal dimension in the case of a square) of the top surface of the frustum body (light emission surface) for uniform projection illumination of the microprism array.

[0065] (Note) Each of the embodiments described above can also be expressed as follows:

[0066] In other words, the image projection device 1 using a microprism array according to the first embodiment has a light source unit 20 as one or more light sources and a microprism array 10 which is an aggregate of fine prisms in which fine prisms are accumulated on a plane perpendicular to the optical axis LA emitted from the light source unit 20. The image projection device uses the microprism array 10 to project light from the light source unit 20 at a refraction angle predetermined for each prism in the microprism array 10, thereby drawing specific shapes such as figures and characters on a plane facing directly or obliquely to the light source unit 20 across the microprism array 10. The image projection device is characterized in that the projection surface size L of the light source unit 20 that irradiates the microprism array 10 with light is more than twice but less than eight times the cell pitch P which is the size of the individual prisms constituting the microprism array 10.

[0067] Furthermore, the image projection device 1 using a microprism array according to the first embodiment has one or more light source units 20 and a microprism array 10 which is an aggregate of fine prisms in which fine prisms are accumulated on a plane perpendicular to the optical axis LA emitted from the light source unit 20. The image projection device uses the microprism array 10 to project light from the light source unit 20 at the refraction angle predetermined for each prism in the microprism array 10, thereby drawing specific shapes such as figures and characters on a plane facing directly or obliquely to the light source unit 20 across the microprism array 10. The image projection device has a light shielding plate 23 between the light source element 21 and the microprism array 10, with a maximum diameter of pinhole openings 23a that are more than twice and less than eight times the cell pitch P which is the size of the individual prisms constituting the microprism array 10, and the light shielding plate 23 is provided at the design light source position of the microprism array 10.

[0068] The image projection device 1 using a microprism array according to the second embodiment comprises a light source unit 20 as a light source section, which includes a light source element 21 having a finite area and emitting light in a specific direction, a condensing lens 25 as a condensing optical system consisting of one or more lenses that concentrate the light emitted from the light source element 21, and a light shielding plate 23 having a pinhole opening 23a that allows some or all of the light from the light source element 21 focused by the condensing lens 25 to pass through, and a microprism array 10 which is an aggregate of fine prisms in which fine prisms are accumulated on a plane perpendicular to the optical axis LA emitted from the light source, characterized in that the maximum diameter L of the pinhole opening 23a in the light shielding plate 23 is greater than twice and less than eight times the cell pitch P of the fine prisms.

[0069] The image projection device 1 using a microprism array according to the third embodiment comprises a light source element 21 having a finite area and emitting light in a specific direction, a rod integrator 27 as a tunnel-shaped focusing optical system composed of at least three mirrors that reflect the light emitted from the light source element 21, and a microprism array 10 which is an aggregate of fine prisms in which fine prisms are accumulated on a plane perpendicular to the optical axis LA emitted from the light source element 21, characterized in that the maximum diameter L of the output-side aperture of the rod integrator 27 is more than twice but less than eight times the dimension of the cell pitch P corresponding to the size of the individual prisms constituting the microprism array 10.

[0070] From the embodiments described above, the means of the present invention described below can be extracted.

[0071] 1. An image projection device having one or more light sources and a microprism array which is a collection of microprisms arranged on a plane perpendicular to the optical axis emitted from the light sources, wherein the microprism array projects specific shapes such as figures or characters onto a plane directly facing or obliquely facing the light source, with respect to the refraction angle predetermined for each prism in the microprism array, across the microprism array. An image projection device using a microprism array, wherein the size of the light-emitting surface of the light source that irradiates the microprism array with light is set to be more than twice but less than eight times the cell pitch, which is the size of the individual prisms constituting the microprism array.

[0072] 2. An image projection device having one or more light sources and a microprism array which is a collection of microprisms arranged on a plane perpendicular to the optical axis emitted from the light sources, wherein the microprism array projects specific shapes such as figures or characters onto a plane directly facing or obliquely facing the light sources, with respect to the refraction angle predetermined for each prism in the microprism array, across the microprism array. An image projection device using a microprism array, wherein a light-shielding plate is provided between the light source element and the microprism array, having a maximum diameter of more than twice but less than eight times the cell pitch, with respect to the cell pitch which is the size of the individual prisms constituting the microprism array, and the light-shielding plate is provided at the design light source position of the microprism array.

[0073] 3. An image projection device using the microprism array described in 1. or 2., comprising a light source element having a finite area and emitting light in a specific direction, a focusing optical system consisting of one or more lenses for focusing the light emitted from the light source element, a light shielding plate having a pinhole opening that allows some or all of the light from the light source element focused by the focusing optical system to pass through, and a microprism array which is a collection of fine prisms formed by accumulating fine prisms on a plane perpendicular to the optical axis emitted from the light source, wherein the maximum aperture dimension of the light shielding plate is more than twice but less than eight times the dimension of the fine prism.

[0074] 4. An image projection device using a microprism array as described in 1. or 2., comprising a light source element having a finite area and emitting light in a specific direction, a tunnel-shaped focusing optical system composed of at least three mirrors that reflect the light emitted from the light source element, and a microprism array which is an aggregate of fine prisms formed by accumulating fine prisms on a plane perpendicular to the optical axis emitted from the light source element, wherein the maximum diameter of the output-side aperture of the focusing optical system is more than twice but less than eight times the size of the individual prisms constituting the microprism array. [Industrial applicability]

[0075] The image projection device using a microprism array according to the present invention can be used for automotive communication lighting, road surface direction indicators, as well as evacuation guidance lights, destination indicator lights, and proximity warning lights inside buildings. [Explanation of Symbols]

[0076] 1. Image projection device using a microprism array 10 Microprism Arrays 11 Prism Cells 20 Light source unit (light source section) 21 Light source elements 23 Light-blocking version 23a Pinhole opening (light-emitting surface) 23b Conical dome 23c Hemispherical dome 25. Focusing lens (focusing optical system) 27. Rod Integrator (Reflective Focusing Optical System) 29. Kaleidoscope (Reflective and Focusing Optical System) LA Optical Axis TP Target Projection Pattern S projection surface PI projection image P prism cell individual piece size (cell pitch) L Maximum diameter of the light-emitting surface (light-emitting surface size)

Claims

1. An image projection device comprising: a microprism array comprising a plurality of irregularly shaped prism cells, each constituting a discontinuous microprism, arranged in a two-dimensional array corresponding to a target projection pattern; and at least one light source unit that projects light toward the microprism array, with a light-emitting surface having a finite area in a plane perpendicular to the optical axis, positioned opposite the incident surface of the microprism array; When the individual size of each prism cell is represented by the cell pitch, which is the arrangement pitch of the prism cells, the light source is an image projection device using a microprism array in which the maximum diameter of the light projection surface in a direction perpendicular to the optical axis is set to be more than twice and less than eight times the cell pitch.

2. The light source unit comprises a light source element and a light shielding plate having a pinhole opening that is positioned between the light source element and the microprism array in the optical axis direction and functions as the light projection surface. The image projection apparatus using a microprism array according to claim 1, wherein the light-shielding plate has a maximum diameter of the pinhole opening set to be more than twice the cell pitch but less than eight times the cell pitch.

3. The image projection apparatus using a microprism array according to claim 2, wherein the light source unit further comprises a focusing optical system between the light source element and the light shielding plate in the optical axis direction, which focuses the light incident from the light source element toward the pinhole opening.

4. The image projection apparatus using a microprism array according to claim 3, wherein the focusing optical system comprises a focusing lens that focuses light incident from the light source element toward the pinhole opening.

5. The image projection apparatus using a microprism array according to claim 3, wherein the focusing optical system comprises a reflective focusing optical system that reflects light incident from the light source element and focuses it toward the pinhole opening.

Images