Image projection device using a microprism array

Abstract

This invention provides an image projection device using a microprism array that can form a highly visible projected image with excellent uniformity of illumination even when the projection surface is illuminated at an oblique angle. [Solution] The ground-type directional indicator light 1, which is an image projection device using a microprism array, comprises at least one light source 20 and a microprism array 10 in which a plurality of irregularly shaped prism cells 11, each constituting a discontinuous microprism, are arranged in a two-dimensional array corresponding to a target projection pattern P. The image projection device forms a projected image PI consisting of a plurality of drawing pixels Q on the projection surface S by projecting light emitted from the light source 20 obliquely onto the projection surface S through each prism cell 11. The number of prism cells 11 assigned to each drawing pixel Q of the projected image PI is set based on the distance of each drawing pixel Q from the light source 20 and the angle of incident light.

Description

[Technical Field]

[0001] The present invention relates to an image projection device using a microprism array, and more particularly to an image projection device that forms a projected image by oblique projection onto a projection surface. [Background technology]

[0002] Conventionally, technologies have been proposed that involve installing image projection devices on vehicles, buildings, or outdoor pillars, etc., to project images of shapes, characters, etc., onto the ground surface in order to transmit information to drivers and pedestrians (see, for example, Patent Documents 1 to 3).

[0003] On the other hand, as an alternative to image projection devices consisting of a lens and a light source, the realization of an image projection device using an optical element called a microprism array has been anticipated 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 emitting light from a light source (see, for example, Non-Patent Documents 1 and 2). In the above-mentioned conventional image projection device using a microprism array, a projection image is drawn on a projection surface arranged parallel to the incident surface of a single microprism array. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-218254 [Patent Document 2] Japanese Patent Publication No. 2008-7079 [Patent Document 3] Japanese Patent Publication No. 2017-159904 [Non-patent literature]

[0005] [Non-Patent Document 1] "Collection of Research Results (FY2022), p. 18, Influence of Microprism Array Molding Errors on Projected Images," 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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when the image projection device using the conventional microprism array described above is applied to applications such as automotive lighting, where an image is projected diagonally onto the ground from a certain height, uneven illumination occurs due to the distance between the microprism array and the pixel position in the projected image, as well as the angle of incidence to the ground, raising concerns about reduced visibility of the projected image.

[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 form a highly visible projected image with excellent uniformity of illumination even when the projection surface is illuminated at an oblique angle. [Means for solving the problem]

[0008] The present invention relates to an image projection device using a microprism array, comprising at least one light source 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 light emitted from the light source is projected obliquely onto the projection surface through each of the prism cells to form a projected image consisting of a plurality of drawing pixels on the projection surface, and the number of prism cells assigned to each of the drawing pixels of the projected image is set based on the distance of each drawing pixel from the light source and the angle of incident light.

[0009] With this configuration, each pixel of the projected image is assigned a number of prism cells based on the distance from the light source and the angle of incident light. Therefore, even with a projected image formed by an obliquely irradiated microprism array, it is possible to obtain a projected image with excellent uniformity of illumination that suppresses differences in illumination within the projected image, resulting in the effect of forming a highly visible projected image.

[0010] Furthermore, when L0 is the straight-line distance between the reference pixel, which is the closest drawing pixel to the light source in the projected image, and the light source, L is the straight-line distance between any drawing pixel in the projected image and the light source, θ0 is the average value of the incident angle formed by the light rays from one or more prism cells incident on the reference pixel and the normal to the projection surface, θ is the average value of the incident angle formed by the light rays from one or more prism cells incident on any drawing pixel and the normal to the projection surface, and n0 is the number of prism cells in the microprism array assigned to the reference pixel, the number of prism cells n assigned to each drawing pixel is expressed by the following formula. n=n0×ceil{κ×(L 2 / L0 2 (x cosθ0 / cosθ) (κ is a positive coefficient)

[0011] With this configuration, the number of prism cells n assigned to each drawing pixel is set using the number of prism cells n0 assigned to the reference pixel in the microprism array, based on the inverse square law of illuminance, which represents the relationship between illuminance and distance from the light source, and the cosine law of the angle of incidence, which represents the relationship between illuminance and the angle of incident light. Therefore, it is possible to reliably obtain a projected image with excellent illuminance uniformity that suppresses illuminance differences within the projected image.

[0012] Furthermore, the aforementioned κ is 0.8 or greater. This configuration makes it possible to more reliably improve the uniformity of illumination in the projected image.

[0013] Furthermore, the aforementioned κ is between 2 and 5. This configuration makes it possible to further improve the uniformity of illumination in the projected image while suppressing an increase in the size of the device.

[0014] Further, n0 is an integer of 2 or more. According to this configuration, by allocating two or more prism cells to the reference pixel, the illuminance can be increased over the entire projection image, and good visibility can be ensured.

[0015] Also, θ and θ0 satisfy the relationship of θ < 2×θ0. According to this configuration, the decrease in illuminance due to the cosine law of the incident angle can be suppressed, and a projection image excellent in illuminance uniformity with a suppressed illuminance difference within the projection image can be surely obtained.

[0016] Further, the image projection device is a ground-drawing type direction indicator that draws a direction-indicating image on the ground surface as the projection surface. According to this configuration, with a simple configuration using a micro prism array, a projection image of a direction-indicating image excellent in illuminance uniformity with a suppressed illuminance difference can be projected even in the case of oblique irradiation onto the ground surface.

Brief Description of the Drawings

[0017] [Figure 1] It is an overall configuration diagram schematically showing a ground-drawing type direction indicator 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 micro prism array. [Figure 4] It is a plan view showing a part of the micro prism array in an enlarged manner. [Figure 5] It is an explanatory view schematically showing a micro prism array in which a direction-indicating figure as a target projection pattern is formed. [Figure 6] It is an explanatory view schematically showing the state of projection by the ground-drawing type direction indicator according to the embodiment in a plan view. [Figure 7] It is an explanatory view schematically showing the state of projection by the ground-drawing type direction indicator according to the embodiment in a side view. [Figure 8]This is an explanatory diagram schematically showing the measurement conditions for the decrease in illuminance due to the distance from the light source and the angle of incidence to the projection surface in the examples and modified examples. [Figure 9] This figure shows the measured illuminance distribution as a function of distance from the light source, in grayscale. [Figure 10] This table shows the measurement results (numerical data) of the illuminance distribution as a function of distance from the light source. [Figure 11] This map shows the number of prism cells assigned to each pixel in the projected image, calculated based on the table in Figure 10. [Figure 12] This figure shows the original image of the projection used in the illuminance simulation of the example. [Figure 13] This is an illuminance simulation diagram related to Comparative Example 1, in which the number of prism cells assigned to each drawing pixel was set to the same number, and the projection image simulation was performed. [Figure 14] This is an illuminance simulation diagram related to Example 1, in which the number of prism cells assigned to each drawing pixel was set based on the map in Figure 11, and the projection image was simulated. [Figure 15] This is an illuminance simulation diagram relating to Examples 2 to 15. [Modes for carrying out the invention]

[0018] Hereinafter, an embodiment of a ground-based directional indicator light that embodies the image projection device using the microprism array of the present invention will be described with reference to the drawings.

[0019] <Configuration of the embodiment> First, the configuration of the ground-projection type directional indicator light 1 (hereinafter simply referred to as "ground-projection type directional indicator light 1") using a microprism array according to an embodiment of the present invention will be described with reference to Figures 1 to 7. Figure 1 is a schematic overall configuration diagram showing the ground-projection type directional indicator light 1. Figure 2 is a perspective view showing an example of the 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 the microprism array 10 on which a directional indicator figure as a target projection pattern P has been formed. Figure 6 is a schematic explanatory diagram showing the projection state by the ground-projection type directional indicator light 1 in a plan view, and Figure 7 is a schematic explanatory diagram showing the same in a side view.

[0020] The ground-projection type directional indicator light 1 is a device for projecting a projected image PI based on a target projection pattern P, which is a directional indicator figure, onto a ground surface S, and comprises a microprism array 10 and a light source 20.

[0021] 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.

[0022] 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.

[0023] The microprism array 10 is designed to project a target projection pattern P, 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 output surfaces. In this embodiment, as shown in Figure 5, the target projection pattern P is a figure representing an arrow as a directional indicator.

[0024] 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, and the number of parts of the ground-type direction indicator light 1 can be minimized.

[0025] 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.

[0026] 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).

[0027] <Assignment of prism cells to each drawing pixel in the projected image> Next, the principle of projection onto the ground surface by the ground-projection type directional indicator light 1 will be explained with reference to Figures 6 and 7. The ground-projection type directional indicator light 1 projects light emitted from the light source 20 obliquely onto the ground surface S, which serves as the projection surface, through the microprism array 10, thereby forming a projected image PI consisting of multiple drawing pixels Q on the ground surface. In this specification, "drawing pixel" refers to the smallest unit that constitutes the drawing of the projected image PI, and the projected image PI is formed by arranging multiple drawing pixels Q in a predetermined pattern in a two-dimensional manner.

[0028] The number of prism cells 11 assigned to each drawing pixel Q in the projected image PI is predetermined based on the distance between the light source 20 and the drawing pixel Q in the projected image PI on the projection surface S, and the angle of incidence of the light rays projected from the prism cells 11 onto the projection surface S at the drawing pixel Q, so as to minimize the difference in illuminance between each drawing pixel Q in the projected image PI. In other words, this embodiment utilizes the fact that the amount of light beam absorbed by a drawing pixel Q varies depending on the number of prism cells 11 assigned to that drawing pixel Q, and aims to equalize the illuminance of each drawing pixel Q by individually adjusting the illuminance of each drawing pixel Q by assigning one or more predetermined numbers of prism cells 11 to each drawing pixel Q.

[0029] Specifically, when L0 is the straight-line distance between the light source 20 and the reference pixel Q0, which is the closest drawing pixel on the projection surface S to the light source 20, L is the straight-line distance between any drawing pixel Q on the projection surface S and the light source 20, θ0 is the average value of the angle of incidence formed by the light rays from one or more prism cells 11 incident on the reference pixel Q0 and the normal NL of the projection surface S, θ is the average value of the angle of incidence formed by the light rays from one or more prism cells 11 incident on any drawing pixel Q and the normal NL of the projection surface S, and n0 is the number of prism cells 11 in the microprism array 10 assigned to the reference pixel Q0, the number of prism cells 11 assigned to each drawing pixel Q in the projected image PI is expressed by the following equation 1. n=n0×ceil{κ×(L2 / L0 2 (x cosθ0 / cosθ) (κ is a positive coefficient) ... (Equation 1)

[0030] In equation 1 above, "ceil{}" represents the ceiling function, and for a number x, ceil{x} represents the smallest integer greater than or equal to x (the same applies hereafter). A detailed explanation of the derivation of equation 1 will be given later.

[0031] <Simulation and mapping of illuminance reduction due to oblique illumination> Next, the results of the simulation and mapping regarding the decrease in illuminance due to oblique illumination to the ground will be explained with reference to Figures 8 to 11. Figure 8 is a schematic diagram illustrating the measurement conditions for the decrease in illuminance due to the distance from the light source 20 and the angle of incidence to the projection surface S in each embodiment and modification described later. Figure 9 is a grayscale diagram showing the measurement results of the illuminance distribution with respect to the distance from the light source 20. Figure 10 is a table showing the measurement results (numerical data) of the illuminance distribution with respect to the distance from the light source 20. The table in Figure 10 represents the numerical value of illuminance with respect to the distance on the ground from the light source 20, with the horizontal axis of the table showing the distance on the ground in the direction in which the optical axis extends from the light source 20, and the vertical axis of the table showing the distance on the ground in the direction perpendicular to the optical axis, both in millimeters. Figure 11 is a map showing the results of calculating the number of prism cells 11 assigned to each drawing pixel Q in the projected image PI based on Equation 1, with the vertical and horizontal axes of the table being the same as in Figure 10.

[0032] In this simulation, as shown in Figure 8, it is assumed that the light source 20 is set at a height H = 1000 mm from the ground and is installed at an angle toward the ground, which serves as the projection plane S. The optical axis of the light source 20 is at a distance L from the light source 20 on the ground. CENT It is assumed that it will be positioned at a location of 2000mm. The drawing pattern assumed in the design is from a position L0 = 1000mm above the ground from the light source 20. MAX It is assumed that a projection image PI of a symmetrical directional indicator shape with a width of 800 mm (400 mm to the left and right of the center in the width direction) will be projected over a distance range of up to 3000 mm.

[0033] According to Figures 9 and 10, the illuminance decreases as the position on the projection surface S moves away from the light source 20 (microprism array 10), and the furthest distance from the projection surface S is L. MAX It has been shown that at the center line of L0 = 3000 mm, the illuminance drops to less than 10% of that at the position L0 = 1000 mm on the projection center axis. From this result, it can be seen that when the number of prism cells corresponding to each drawing pixel Q in the projected image PI is uniform within the microprism array 10, illuminance unevenness occurs as shown in Figure 9.

[0034] In this simulation, under the conditions shown in Figure 8, the relative illumination on the projection plane S was normalized to 1 when the relative illumination at the position L0 = 1000 mm on the projection center axis was set to 1. Focusing on the distance square law in illuminance calculation, i.e., the illuminance of a diffuse light source is inversely proportional to the square of the distance, and the cosine law, i.e., proportional to the cosine of the angle of incidence of the incident light beam, the relative illumination was mapped as shown in Figure 11 based on Equation 1 above.

[0035] <Example 1, Comparative Example 1> Next, the illuminance simulations for Example 1 and Comparative Example 1 will be described with reference to Figures 12 to 14. Figure 12 is a diagram showing the original image of the projected image PI used in the illuminance simulation. Figure 13 is a simulation diagram showing the results of Comparative Example 1, in which the number of prism cells 11 assigned to each drawing pixel Q was set to the same number and the projection image PI was simulated. Figure 14 is a simulation diagram showing the results of Example 1, in which the number of prism cells 11 assigned to each drawing pixel Q was set based on the map in Figure 11 and the projection image PI was simulated.

[0036] In Comparative Example 1, the same number of prism cells 11 was assigned to each drawing pixel Q in the white portion of the original drawing shown in FIG. 12 over the entire micro prism array 10. In Comparative Example 1, assuming that the radiation characteristics of the light source 20 are uniform for simplicity and applying the relative illuminance calculation results in FIGS. 9 and 10, the illuminance distribution shown in FIG. 13 was obtained. As can be seen from FIG. 13, since the irradiation points on the far side from the light source 20 are considerably dark, it can be said that it is difficult to obtain a projection image PI with sufficient visibility as a ground drawing type direction indicator.

[0037] Example 1 is intended to eliminate the occurrence of illuminance unevenness seen in Comparative Example 1. More specifically, in Example 1, the result shown in FIG. 14 was obtained by applying the allocation of the number of prism cells in FIG. 11, which was obtained by rounding up the reciprocal of the illuminance distribution shown in FIG. 10 to an integer, to each prism cell 11 in the micro prism array 10. Example 1 aims to equalize the illuminance by allocating a large number of prism cells 11 to projections to drawing positions far from the light source 20. FIG. 14 shows the result of illuminance calculation when the prism cells 11 with the allocation numbers determined in FIG. 11 are arranged for each drawing pixel Q. In Example 1, the illuminance unevenness within the projection image PI is significantly reduced compared to Comparative Example 1. In Example 1, the illuminance difference between the far side and the near side with respect to the light source 20 within the projection image PI is particularly small, and a preferable projection illumination for drawing the projection image PI as a ground drawing type direction indicator can be realized.

[0038] The illuminance calculation in Example 1 follows the inverse square law of distance and the cosine law. The relationship between the number n0 of prism cells 11 in the micro prism array 10 assigned to the reference pixel Q0, which is the drawing pixel closest to the light source 20 in the light source 20 and the projection image PI, and the number n of prism cells assigned to an arbitrary drawing pixel Q in the projection image PI is expressed by the following formula 2. n / n0 ∝ L 2 / L0 2 × cosθ0 / cosθ ···(Formula 2)

[0039] Here, L0 is the straight-line distance between the light source 20 and the reference pixel Q0, which is the closest drawing pixel on the projection surface S to the light source 20; L is the straight-line distance between any drawing pixel Q on the projection surface S and the light source 20; θ0 is the average incident angle formed by the light rays from one or more prism cells 11 incident on the reference pixel Q0 and the normal NL of the projection surface S; and θ is the average incident angle formed by the light rays from one or more prism cells 11 incident on any drawing pixel Q and the normal NL of the projection surface S.

[0040] Expressing Equation 2 as an equation for n, the number of prism cells n assigned to each drawing pixel Q is obtained by rounding up the decimal part of the calculated value in parentheses on the right side of Equation 3 below to an integer. n = n0 × ceil(L 2 / L0 2 ×cosθ0 / cosθ) (Formula 3) As a result, a projection image PI with uniform illuminance, as shown in Figure 14, is obtained.

[0041] <Examples 2-15> In the design of actual microprism arrays, due to constraints on the total number of prism cells and the size of the device, it is sometimes not possible to construct the microprism array 10 using values ​​directly obtained from Equation 3. On the other hand, a significant deviation from Equation 3 affects the illuminance, so a favorable range for ground-type directional indicator lights was found using Examples 2 to 15. Examples 2 to 15 will be described below with reference to Figure 15. Figure 15 is an illuminance simulation diagram related to Examples 2 to 15.

[0042] Examples 2 to 15 are illuminance simulations when a microprism array is designed with the number of prism cells n obtained by Equation 4 below, which is obtained by multiplying the coefficient κ in the right-hand side of Equation 3. n=n0×ceil{κ×(L 2 / L0 2 ×cosθ0 / cosθ)} (Formula 4)

[0043] Here, Examples 2 to 15 shown in Figure 15 are illuminance simulation results with coefficient κ values ​​set to κ=0.4, κ=0.5, κ=0.6, κ=0.7, κ=0.8, κ=0.9, κ=1.0, κ=2.0, κ=3.0, κ=4.0, κ=5.0, κ=6.0, κ=8.0, and κ=10.0, respectively.

[0044] As shown in Figure 15, in Examples 2 to 15, where κ = 0.4 or higher, the uniformity of illuminance is improved compared to Comparative Example 1. Furthermore, comparing Examples 2 to 15 with each other, it can be seen that the higher the value of the coefficient κ, the better the uniformity of illuminance. In particular, Examples 6 to 15 showed that if the coefficient κ is 0.8 or higher, the uniformity of illuminance is at a level that is practically acceptable.

[0045] On the other hand, as can be seen from Figure 15, the larger the coefficient κ, the better the illuminance uniformity. However, if the coefficient κ is made too large, the number of prism cells 11 in the microprism array 10 must be increased significantly, leading to increased design and manufacturing costs. Furthermore, it is assumed that the size of the microprism array 10 will increase, and the overall size of the device will also increase. Therefore, in order to suppress the enlargement of the device, it is preferable to set the upper limit of the coefficient κ value to around 5. In addition, to further improve the illuminance uniformity, it is more preferable for the coefficient κ to be 2 or higher, as shown in the results in Figure 15.

[0046] Furthermore, the number n0 of prism cells 11 assigned to the reference pixel Q0 closest to the light source 20 is preferable to be two or more, as this serves as the basis for raising the overall illuminance. As the total number of prism cells 11 in the microprism array 10 increases, the amount of light beam taken in from the light source 20 increases, thus raising the overall illuminance.

[0047] Furthermore, considering the effect of illuminance uniformity according to the present invention, it is preferable that θ < 2 × θ0, in light of the incidence angle and illuminance reduction due to the cosine law. This is because as θ increases, the illuminance reduction due to the cosine law becomes more pronounced, reducing the effect of the present invention and making it impossible to obtain a projection image PI with excellent illuminance uniformity.

[0048] <Summary> As is clear from the above detailed description, the ground-display type direction indicator light 1 according to this embodiment comprises at least one light source 20 and a microprism array 10 which is made up of a plurality of irregularly shaped prism cells 11, each constituting a discontinuous microprism, arranged in a two-dimensional array corresponding to a target projection pattern P. The image projection device using the microprism array forms a projected image PI consisting of a plurality of drawing pixels Q on the projection surface S by projecting light emitted from the light source 20 obliquely onto the projection surface S through each prism cell 11. The number of prism cells 11 assigned to each drawing pixel Q of the projected image PI is set based on the distance of each drawing pixel Q from the light source 20 and the angle of incident light.

[0049] With this configuration, each drawing pixel Q of the projected image PI is assigned a number of prism cells 11 based on the distance from the light source 20 and the angle of incident light (angle of incidence). Therefore, even with a projected image PI formed by an obliquely irradiated microprism array 10, it is possible to obtain a projected image PI with excellent uniformity of illumination that suppresses differences in illumination within the projected image PI, resulting in the effect of forming a highly visible projected image PI.

[0050] Furthermore, when L0 is the straight-line distance between the reference pixel Q0, which is the closest drawing pixel to the light source 20 in the projected image PI, and the light source 20, L is the straight-line distance between any drawing pixel Q in the projected image PI and the light source 20, θ0 is the average value of the incident angle formed by the light rays from one or more prism cells 11 incident on the reference pixel Q0 and the normal NL of the projection plane S, θ is the average value of the incident angle formed by the light rays from one or more prism cells 11 incident on any drawing pixel Q and the normal NL of the projection plane S, and n0 is the number of prism cells 11 in the microprism array assigned to the reference pixel Q0, then the number of prism cells 11 assigned to each drawing pixel Q, n, is expressed by the following formula. n=n0×ceil{κ×(L 2 / L0 2 (x cosθ0 / cosθ) (κ is a positive coefficient)

[0051] With this configuration, the number of prism cells 11 assigned to each drawing pixel Q is set using the number of prism cells 11 in the microprism array assigned to the reference pixel Q0, based on the inverse square law of illuminance, which represents the relationship between illuminance and distance from the light source 20, and the cosine law of the angle of incidence, which represents the relationship between illuminance and the angle of incident light. Therefore, a projected image PI with excellent illuminance uniformity that suppresses illuminance differences within the projected image PI can be reliably obtained.

[0052] Furthermore, the coefficient κ is 0.8 or greater. This configuration makes it possible to more reliably improve the uniformity of illumination in the projected image PI.

[0053] Furthermore, the coefficient κ is between 2 and 5. This configuration allows for a more reliable improvement in the uniformity of illumination in the projected image PI while suppressing an increase in the size of the device.

[0054] Furthermore, the number n0 of prism cells 11 in the microprism array 10 assigned to the reference pixel Q0 is an integer of 2 or more. With this configuration, by assigning 2 or more prism cells 11 to the reference pixel Q0, the illumination can be increased across the entire projected image PI, ensuring good visibility.

[0055] Furthermore, the average incident angle θ formed by the light rays from one or more prism cells 11 incident on any drawing pixel Q and the normal NL of the projection surface S, and the average incident angle θ0 formed by the light rays from one or more prism cells 11 incident on a reference pixel Q0 and the normal NL of the projection surface S, satisfy the relationship θ < 2 × θ0. With this configuration, the decrease in illuminance due to the cosine law of the incident angle is kept within a certain range, and a projection image PI with excellent illuminance uniformity and small illuminance differences within the projection image PI can be reliably obtained.

[0056] Furthermore, the ground-based direction indicator light 1 is an image projection device for drawing a direction indicator image on the ground surface S. With this configuration, a simple setup using a microprism array 10 allows for the projection of a direction indicator image PI with excellent uniformity of illumination and reduced illumination differences, even when illuminating the ground surface at an oblique angle.

[0057] <Variation> 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. For example, the above embodiment shows an example in which an image projection device using the microprism array 10 according to the present invention is applied to a ground-type directional indicator light, but it is not limited to this, and can also be applied to a wall projection device for projecting guidance images as projected images onto the exterior walls of buildings, the walls of rooms or corridors, the walls of fences, etc. [Industrial applicability]

[0058] 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 ground 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]

[0059] 1. Ground-based projecting direction indicator light (image projection device using a microprism array) 10 Microprism Arrays 11 Prism Cells 20 light source P Target projection pattern Q Any pixel Q0 reference pixel S projection surface PI projection image

Claims

1. An image projection apparatus comprising at least one light source 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 light emitted from the light source is projected obliquely onto the projection surface through each of the prism cells, thereby forming a projected image consisting of a plurality of drawing pixels on the projection surface, An image projection device using a microprism array, wherein the number of prism cells assigned to each drawing pixel of the projected image is set based on the distance of each drawing pixel from the light source and the angle of incident light.

2. L is the straight-line distance between the reference pixel, which is the closest drawing pixel to the light source in the projected image, and the light source. ０ L is the straight-line distance between any drawing pixel in the projected image and the light source, and θ is the average value of the incident angle formed by the light rays from one or more prism cells incident on the reference pixel and the normal to the projection surface. ０ θ is the average value of the incident angle formed by the light rays from one or more prism cells incident on the arbitrary drawing pixel and the normal to the projection surface, and n is the number of prism cells in the microprism array assigned to the reference pixel. ０ When that is the case, The image projection apparatus using a microprism array according to claim 1, wherein the number n of prism cells assigned to each drawing pixel in the projected image is expressed by the following formula. n = n ０ ×ceil{κ×(L ２ / L ０ ２ ×cosθ ０ (where κ is a positive coefficient)

3. The image projection apparatus using a microprism array according to claim 2, wherein the κ is 0.8 or greater.

4. The image projection apparatus using a microprism array according to claim 3, wherein κ is 2 or more and 5 or less.

5. said n ０ The image projection apparatus using the micro prism array according to any one of claims 2 to 4, wherein n is an integer of 2 or more.

6. The θ and the θ ０ θ < 2 × θ ０ An image projection device using a microprism array according to any one of claims 2 to 4, satisfying the relationship.

7. The image projection device is a ground-drawing type directional indicator light that draws a directional indicator image on the ground surface which serves as the projection surface, an image projection device using a microprism array according to any one of claims 1 to 4.

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