Droplet sensor

Abstract

The present invention provides a low-cost droplet sensor capable of suppressing the entry of external light into a photodetector. The droplet sensor comprises: an optical cover, which is a portion of a rotating ellipsoid and has an elliptical surface; a light source disposed at or near a first focus of the elliptical surface; and a photodetector disposed at or near a second focus of the elliptical surface. The elliptical surface serves as an effective detection area, and light output from the light source is reflected toward the photodetector. The amount of reflected light changes as droplets adhere to the elliptical surface. A curved surface with a greater curvature than the elliptical surface is connected to a tangent line outside the effective detection area of ​​the optical cover.

Description

Technical Field

[0001] The present invention relates to a liquid drop sensor for sensing liquid drops such as raindrops and water droplets. Background Art

[0002] A device is known that detects raindrops by utilizing changes in reflectivity when raindrops land on a raindrop detection area of ​​a transparent plate (see, for example, Patent Documents 1 and 2). In this device, light emitted from a light-emitting element is reflected by the surface of the transparent plate and received by a light-receiving unit. When a raindrop lands on the raindrop detection area, the reflectivity changes at the interface of the transparent plate, and the amount of received light changes, thereby detecting the presence of a raindrop.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 6094354

[0006] Patent Document 2: Japanese Patent No. 6167799 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, the optical elements used in the devices described in Patent Documents 1 and 2 have a problem of being difficult to manufacture due to their complex shapes.

[0009] Therefore, the applicant has proposed a new droplet sensor with a simple structure and easy manufacturing (Japanese Patent Application No. 2017-254956). This droplet sensor comprises, for example: an optical cover having a shape obtained by cutting a rotational ellipsoid at a plane including the major axis; a light source disposed at a first focal position of the rotational ellipsoid; and a light detector disposed at a second focal position of the rotational ellipsoid.

[0010] This droplet sensor is not only simple in structure and easy to manufacture, but also, by adjusting the eccentricity of the rotating ellipsoid, the area where the two conditions of total reflection are satisfied at the interface with gas (such as air) and not total reflection are satisfied at the interface with liquid (such as water) (hereinafter referred to as the effective detection area) is maximized, thereby realizing a highly sensitive droplet sensor with a larger detection area.

[0011] When using a droplet sensor or the like outdoors, there is a risk that external light, such as sunlight, may enter the optical cover from outside the effective detection area and enter the photodetector. This intrusion of external light can cause noise, making it difficult to use as a droplet sensor if the required dynamic range cannot be maintained. Therefore, the present applicant has proposed forming a coating film composed of a light-absorbing or light-reflecting film on the surface of the optical cover in areas outside the effective detection area.

[0012] The formation of such a coating film is effective as a countermeasure against noise caused by external light, but requires an additional manufacturing step for forming the coating film, resulting in increased costs.

[0013] An object of the present invention is to provide a liquid drop sensor that does not use the above-mentioned coating film, is low-cost, and can suppress the entry of external light into a photodetector.

[0014] Solutions to Problems

[0015] In order to solve the above-mentioned problems, a droplet sensor is provided, which is characterized in that it comprises: an optical cover, which is a part of a rotating ellipsoid and has an elliptical surface; a light source, which is arranged at or near the first focus of the above-mentioned elliptical surface; and a light detector, which is arranged at or near the second focus of the above-mentioned elliptical surface, wherein the above-mentioned elliptical surface is an effective detection area, and the light output from the above-mentioned light source is reflected toward the above-mentioned light detector, and the amount of reflected light changes due to the attachment of droplets to the above-mentioned elliptical surface. On the outside of the above-mentioned effective detection area of ​​the above-mentioned optical cover, a tangent is connected to a curved surface with a curvature larger than that of the above-mentioned elliptical surface.

[0016] The effects of the invention are as follows.

[0017] According to the present invention, a liquid drop sensor capable of suppressing external light from entering a photodetector is realized at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a side view of the rain sensor according to the first embodiment.

[0019] Figure 2 It is a perspective view of the rain sensor according to the first embodiment.

[0020] Figure 3 is a cross-sectional view of the rain sensor.

[0021] Figure 4 This is a perspective view of the optical cover viewed from the bottom side.

[0022] Figure 5 1 is a diagram showing the optical path of light output from a light emitting element and incident on a light receiving element.

[0023] Figure 6 This is a diagram showing an example of a change in the optical path caused by raindrops adhering to the effective detection area.

[0024] Figure 7 It is a diagram for explaining the effects of the rain sensor according to the first embodiment.

[0025] Figure 8This is a simulation diagram showing the optical path when a virtual light source is arranged at the second focal point.

[0026] Figure 9 It is a cross-sectional view showing the structure of a rain sensor according to a second embodiment.

[0027] Figure 10 This is an enlarged view of the second space in the second embodiment.

[0028] Figure 11 This is a simulation diagram showing the optical path when a hypothetical light source is arranged at the second focal point.

[0029] Figure 12 It is a cross-sectional view showing the structure of a rain sensor according to a third embodiment.

[0030] Figure 13 This is an enlarged view of the second space in the third embodiment.

[0031] Figure 14 It is a perspective view showing the second space in the third embodiment.

[0032] Figure 15 This is a simulation diagram showing the optical path when a virtual light source is arranged at the second focal point.

[0033] Figure 16 This is a simulation diagram of the optical path when a hypothetical light source is arranged at the second focus, as viewed from a direction parallel to the long axis.

[0034] Figure 17 It is a cross-sectional view showing the structure of a rain sensor according to a fourth embodiment.

[0035] Figure 18 This is an enlarged view of the second space 6b in the fourth embodiment.

[0036] Figure 19 It is a perspective view showing the second space in the fourth embodiment.

[0037] Figure 20 This is a simulation diagram showing the optical path when a virtual light source is arranged at the second focal point.

[0038] Figure 21 It is a diagram for explaining setting conditions of the first plane, the second plane, and the third plane included in the second space.

[0039] Figure 22 It is a diagram for explaining the setting conditions of the inclination angle of the first plane.

[0040] In the picture:

[0041] 2—optical cover, 2a—ellipsoidal surface, 2b, 2c—spherical surface, 2d—convex edge, 2e—bottom surface, 2f—ellipsoidal surface, 3—light-emitting element, 4—light-receiving element, 5a, 5b—dividing line, 6a—first space, 6b—second space, 10, 10b, 10c—rain sensor, 60—spherical surface, 61—plane, 70—spherical surface, 71—first plane, 72—second plane, 80—spherical surface, 81—first plane, 82—second plane, 83—third plane. DETAILED DESCRIPTION

[0042] In embodiments of the present invention, the difference in refractive index between gas and liquid causes a change in reflectivity at the interface with the optical cover, and this change in reflectivity is used to optically detect the presence of liquid droplets. In addition to raindrops, the droplet sensor can also be used to detect droplets such as condensation, water droplets, and ink. The following embodiments describe examples of using the droplet sensor in a rain sensor.

[0043] <First embodiment>

[0044] Figure 1 It is a side view of the rain sensor 10 according to the first embodiment. Figure 2 This is a perspective view of a rain sensor 10 according to the first embodiment. The rain sensor 10 detects the adhesion of raindrops. Based on the detection results of raindrops, the amount of rain per unit time and / or per unit area can be measured, for example.

[0045] The rain sensor 10 includes an optical cover 2, a light-emitting element 3, and a light-receiving element 4. The optical cover 2 has an ellipsoidal surface 2a, spherical surfaces 2b and 2c, and a flange 2d. The light-emitting element 3 is positioned at or near the first focus F1 of the ellipsoidal surface 2a. The light-receiving element 4 is positioned at or near the second focus F2 of the ellipsoidal surface 2a. Here, the light-emitting element 3 is an example of a light source, and the light-receiving element 4 is an example of a photodetector.

[0046] The optical cover 2 is a solid cover made of a material transparent to the wavelength of the output light of the light emitting element 3. The optical cover 2 may be made of transparent ceramics, glass, high-refractive-index plastic, or the like in addition to resins such as polycarbonate and acrylic.

[0047] The ellipsoidal surface 2a corresponds to the effective detection area D described below. The spherical surfaces 2b and 2c are connected to the ellipsoidal surface 2a on the outside of the long axis direction so that the inclined portion is smoothly continuous with the ellipsoidal surface 2a. Specifically, the ellipsoidal surface 2a and the spherical surface 2b are connected so that the tangent lines coincide with the boundary line 5a between the two (tangent connection) (see Figure 3 ) Similarly, the ellipsoidal surface 2a and the spherical surface 2c are connected so that the tangent lines coincide with each other at the boundary line 5b (tangent connection).

[0048] The elliptical surface 2a is formed by having a major axis ( Figure 1 The spherical surface 2b is a portion of the surface of a sphere with a point on the major axis La as the center C1. Similarly, the spherical surface 2c is a portion of the surface of a sphere with a point on the major axis La as the center C2.

[0049] The optical cover 2 has a three-dimensional shape obtained by rotating the top view shape having the elliptical surface 2a and the spherical surfaces 2b and 2c about the major axis La. The portion other than the flange portion 2d of the optical cover 2 has a three-dimensional shape obtained by cutting the above-mentioned rotating body at a plane horizontal to the XY plane including the major axis La. Figure 1 and Figure 2 In the figure, for the sake of convenience, the height direction of the optical cover 2 is referred to as the Z direction.

[0050] The flange portion 2d is a portion extending from the lower portion of the optical cover 2 in the XY plane direction, and its top view shape is, for example, circular. In addition, the top view shape of the flange portion 2d is not limited thereto, and may also be other shapes such as an ellipse or a square. The flange portion 2d has a constant thickness W in the Z direction. The thickness W of the flange portion 2d is, for example, approximately 25% of the height H of the optical cover 2. The flange portion 2d functions as a mounting portion for fixing the optical cover 2 to the main body side, etc. The thickness W of the flange portion 2d may be less than 25% of the height H of the optical cover 2 if it can ensure strength against stress applied to the fixation, for example, when the mounting portion is screwed to fix the optical cover, it will not be damaged by the tightening of the screws.

[0051] The light-emitting element 3 is, for example, a light-emitting diode that emits near-infrared light. The light-receiving element 4 is, for example, a quantum well-type light-receiving element sensitive to light in the near-infrared region. The light-emitting element 3 outputs light toward the ellipsoidal surface 2a of the optical cover 2. The light-receiving element 4 receives light emitted by the light-emitting element 3 and reflected by the ellipsoidal surface 2a of the optical cover 2. The light-emitting element 3 and the light-receiving element 4 are mounted on a substrate (not shown).

[0052] Figure 1 In the figure, the effective detection area D, indicated by dotted shading, is the area where light output from the light-emitting element 3 is totally reflected when the optical cover 2 is surrounded by air, and corresponds to the ellipsoidal surface 2a. The shape of this effective detection area D is determined so that the total reflection condition is not met only when raindrops are attached. In other words, the effective detection area D satisfies the total reflection condition at the interface with gas but not at the interface with liquid. The effective detection area D that achieves this condition depends on the refractive index of the optical cover 2 and the eccentricity of the ellipsoidal surface 2a.

[0053] When the curved surface portion of the optical cover 2 is formed by a single ellipse and is formed using a resin with a refractive index of 1.57 (such as polycarbonate), the range of the incident angle θm of the detectable area capable of detecting the attachment of raindrops to the optical cover 2 is approximately 39.6°<θm<57.9°, but in this embodiment, the range of the incident angle θi satisfying 44.3°<θi<51.4° is used as the effective detection area D. Figure 1 In the figure, the range satisfying the above-mentioned incident angle θi is defined as the ellipsoidal surface 2a, and the spherical surfaces 2b and 2c are connected to the outer tangent line thereof.

[0054] The eccentricity is determined by the ratio of the distance from the center of the ellipsoidal surface 2a to the focal point to the major axis radius. When the refractive index of the optical cover 2 is 1.57, the area functioning as the detectable region is maximized when the eccentricity is 0.781. The shape of the detectable region is described in detail in a prior application filed by the present applicant (Japanese Patent Application No. 2017-254956).

[0055] As described above, the flange 2d functions as a mounting portion for mounting the optical cover 2 on a main body, a substrate, or the like. Light reflected from an area below approximately 25% of the height H of the optical cover 2 is hardly detected by the light receiving element 4, and thus the area below approximately 25% of the height H is used as the flange 2d, which serves as the mounting portion. This is because, when the light receiving element 4 is arranged with the light receiving surface facing upward, the detection sensitivity for light from above is high, while the detection sensitivity for light from the lateral direction (XY direction) is low. By using this low-sensitivity area as the flange, the rain sensor, which assumes raindrops falling from above, has little loss of detection area for raindrops deposited from above, and has no effect on the presence or absence of raindrops or the amount of raindrops collected. This allows the flange 2d, which serves as the mounting portion, to be formed with little reduction in detection sensitivity.

[0056] Figure 3 1 is a cross-sectional view of the rain sensor 10 taken along an XZ plane including the long axis La. Figure 4 It is a perspective view of the optical cover 2 viewed from the bottom surface 2e side.

[0057] like Figure 3 and Figure 4 As shown, a first space 6a and a second space 6b are formed within the optical cover 2. The first space 6a is a hemispherical space centered on the first focal point F1 where the light-emitting element 3 is located. Its interface with the optical cover 2 is a transmissive mirror surface (a smooth, non-concave surface through which light passes without scattering). The second space 6b is a hemispherical space centered on the second focal point F2 where the light-receiving element 4 is located. Its interface with the optical cover 2 is a transmissive mirror surface or a transmissive scattering surface (a surface with concave and convex surfaces such as a sanded surface through which light scatters).

[0058] In the present embodiment, the radii of the first space 6 a and the second space 6 b are substantially the same as the thickness W of the flange portion 2 d .

[0059] Thus, because the surface of first space 6a is spherical, light output from light-emitting element 3 is allowed to enter the interior of optical cover 2 without being refracted. Similarly, because the surface of second space 6b is spherical, light reflected from ellipsoidal surface 2a (effective detection area D) is allowed to enter second space 6b without being refracted. This makes it possible to realize a rain sensor that utilizes the fundamental property of a rotating ellipsoid: light output from one focus of the ellipse converges at the other focus.

[0060] Figure 5 1 is a diagram showing the optical path of light output from the light emitting element 3 and incident on the light receiving element 4 . Figure 6 1 and 2 are diagrams showing an example of a change in the optical path caused by raindrops adhering to the effective detection area D.

[0061] like Figure 5 As shown in FIG. 1 , when raindrops are not attached to the effective detection area D, all the light output from the light emitting element 3 and incident on the effective detection area D is totally reflected and guided to the light receiving element 4. On the other hand, Figure 6 As shown, if raindrops land on the effective detection area D, the reflectivity changes in the portion where the raindrops land because the total reflection condition is not met at the interface of the effective detection area D, allowing the incident light from the light-emitting element 3 to pass through. This reduces the amount of light received by the light-receiving element 4. By monitoring the change in the amount of light received by the light-receiving element 4, the presence and amount of raindrops can be detected.

[0062] Figure 7 It is a diagram for explaining the effects of the rain sensor 10 according to the first embodiment. Figure 7 In (A), as a comparative example, a case where the area outside the effective detection area D of the optical cover is an elliptical surface is shown. Figure 7 The ellipsoidal surface 2f outside the effective detection area D shown in (A) is part of the surface of the same rotating ellipsoid as the ellipsoidal surface 2a constituting the effective detection area D. Because the ellipsoidal surface 2f outside the effective detection area D includes an area that does not satisfy the total reflection condition, there is an optical path for external light such as sunlight to enter the optical cover from the ellipsoidal surface 2f and reach the light receiving element 4.

[0063] Figure 7 (B) shows the case where the area outside the effective detection area D of the optical cover is a spherical surface. Figure 7 As shown in (B), in this embodiment, the curvature of the spherical surface 2c outside the effective detection area D is greater than the curvature of the elliptical surface 2f, so that Figure 7Compared to the comparative example shown in FIG. 1 (A), the optical path of external light entering the optical cover 2 from the spherical surface 2 c deviates toward the inside of the optical cover 2 , thereby suppressing the external light from entering the light receiving element 4 .

[0064] Figure 8 This figure shows the results of a simulation to determine the optical path of a hypothetical light source (hereinafter referred to as the hypothetical light source) placed at the second focal point F2, in order to confirm the intrusion path of external light. Based on the principle of light reversibility, if light emitted from the hypothetical light source placed at the position of the light-receiving element 4 leaks outward, this means that there is an optical path for light traveling in the opposite direction from the outside to enter the light-receiving element 4. Conversely, if no light leaks outward (for example, if all light ultimately enters the lower side of the optical cover), this means that there is no optical path for light from above the optical cover to enter the light-receiving element 4. Here, the refractive index of the optical cover is set to 1.57, and the surrounding area of ​​the optical cover is set to air (refractive index 1.0). It can be confirmed that the light output from the hypothetical light source is totally reflected at the interface between the optical cover and air, and does not leak upward to the outside of the optical cover. Therefore, external light does not enter the light-receiving element 4 placed at the second focal point F2.

[0065] Figure 8 In (A), as a comparative example, the case where the area outside the effective detection area D of the optical cover is an elliptical surface is shown. Figure 8 As shown in (A), there are multiple optical paths on the elliptical surface 2f outside the effective detection area D, where light output from the imaginary light source leaks upward outside the optical cover. In other words, there are extensive areas on the elliptical surface 2f that guide external light to the second focal point F2.

[0066] Figure 8 (B) shows the case where the area outside the effective detection area D of the optical cover 2 is a spherical surface. Figure 8 As shown in (B), in this embodiment, the light output from the imaginary light source and incident on the spherical surface 2c is almost totally reflected, and there is no light path that leaks to the outside (upward) of the optical cover 2 except near the area A. In other words, there is almost no area on the spherical surface 2c that guides external light to the second focus F2. However, near the connection portion of the spherical surface 2c with the flange portion 2d, there is a slight area where the light output from the imaginary light source leaks to the outside of the optical cover ( Figure 8 External light may enter from this region A toward the second focal point F2, but the region A can be reduced by changing the thickness W of the flange portion 2d, the radius of the space 6b, etc., which will be specifically described in detail in the second embodiment and subsequent embodiments.

[0067] As described above, the rain sensor 10 of this embodiment includes an optical cover 2 in which the outer sides of the ellipsoidal surface 2a, which serves as the effective detection area D, in the direction of the major axis are formed into spherical surfaces 2b and 2c, thereby suppressing the entry of external light into the light receiving element 4. Furthermore, the rain sensor 10 of this embodiment does not require a light-shielding coating film to be formed on the optical cover 2 to limit the incident light in order to suppress the entry of external light into the light receiving element 4. Furthermore, the rain sensor 10 of this embodiment does not require additional manufacturing steps, thereby enabling low-cost manufacturing. The optical cover 2 can be manufactured, for example, by resin injection molding using a metal mold.

[0068] Furthermore, by connecting the ellipsoidal surface 2 a and the spherical surfaces 2 b and 2 c with tangent lines, the property of water droplets adhering to the surface of the optical cover 2 naturally flowing down along the surface is maintained.

[0069] In the first embodiment described above, the external light is Figure 8 In order to prevent the possibility of external light entering the area A of (B) toward the second focus F2, various embodiments for preventing external light from also entering the area A will be described below.

[0070] <Second embodiment>

[0071] Figure 9 2 is a cross-sectional view showing the structure of a rain sensor 10a according to the second embodiment. The rain sensor 10a according to the present embodiment has the same structure as the rain sensor 10 according to the first embodiment, except for the structure of the second space 6b where the light receiving element 4 is arranged.

[0072] Figure 10 This is an enlarged view of the second space 6b of this embodiment. Figure 10 As shown, in this embodiment, a hemisphere is obtained by cutting a sphere centered at the second focus F2 at the XY plane including the second focus F2, and the second space 6b has a shape obtained by cutting the hemisphere at the YZ plane. Therefore, a spherical surface 60 and a plane 61 are formed between the second space 6b and the optical cover 2. The plane 61 is located outside the second focus F2 ( Figure 11 That is, the second focus F2 is located in the second space 6b.

[0073] And, as Figure 9 As shown, in this embodiment, the radius of the spherical surface 60 as the size of the second space 6b is set to a smaller value than the second space 6b of the first embodiment and smaller than the thickness W of the flange portion 2d.

[0074] Spherical surface 60 reflects light emitted from light-emitting element 3 using ellipsoidal surface 2a and then guides the light to second focal point F2, thus acting as a transmissive mirror or transmissive scattering surface, similar to the first embodiment. Plane 61 functions to prevent light entering from the outside and heading toward second focal point F2 from reaching light-receiving element 4 by total reflection or refraction. By reducing the radii of plane 61 and spherical surface 60, area A, described in the first embodiment, is eliminated.

[0075] Figure 11 This figure shows the results of solving the light path when a hypothetical light source is placed at the second focal point F2 through simulation in order to confirm the intrusion path of external light. In this embodiment, the light path output from the hypothetical light source is changed to the convex edge portion 2d on the right side of the area A, and is changed in the direction that satisfies the total reflection condition within the convex edge portion 2d, so that the area A disappears. Figure 11 As shown in FIG, light output from a virtual light source disposed at the second focal point F2 and incident on the plane 61 is refracted at the plane 61 and directed toward the flange portion 2d. Figure 10 As shown, the lower end point K1 of the plane 61 is located to the right of the focus F2. That is, in the first embodiment, it can be confirmed that the light from the imaginary light source toward the area A of the spherical surface 2c (refer to Figure 8 (B)) in Figure 10 The light is refracted at the plane 61 and directed toward the convex edge 2d located outside the spherical surface 2c. The light path within the convex edge 2d is changed in a direction that satisfies the total reflection condition, thereby preventing the external light from reaching the light receiving element 4. Furthermore, in order to guide all the light refracted at the plane 61 to the outside of the spherical surface 2c, the size of the second space 6b (the radius of the spherical surface 60) and the position of the plane 61 need to be appropriately set.

[0076] On the other hand, light output from the imaginary light source disposed at the second focal point F2 and incident on the spherical surface 60 passes through the spherical surface 60 and is then totally reflected by the ellipsoidal surface 2a (effective detection area D) or the spherical surface 2c.

[0077] Thus, in this embodiment, for external light incident from area A of the spherical surface 2c and heading toward the second focus F2, the plane 61 functioning as an optical path changing portion changes the optical path to prevent the external light from incident on the light receiving element 4 located at the second focus F2.

[0078] <Third embodiment>

[0079] Figure 12 1 is a cross-sectional view showing the structure of a rain sensor 10b according to a third embodiment. The rain sensor 10b according to this embodiment has the same structure as the rain sensor 10 according to the first embodiment, except for the structure of the second space 6b where the light receiving element 4 is arranged.

[0080] Figure 13 This is an enlarged view of the second space 6b in this embodiment. Figure 14 : is a perspective view showing the second space 6b of this embodiment. Figure 13 and Figure 14 As shown, in this embodiment, a hemispherical body is obtained by cutting a sphere centered at the second focus F2 at an XY plane including the second focus F2 , and the second space 6 b has a shape obtained by forming a wedge-shaped cutout in the hemispherical body.

[0081] Therefore, a spherical surface 70, a first plane 71, and a second plane 72 are formed between the second space 6b and the optical cover 2. The first plane 71 and the second plane 72 are each perpendicular to the XZ plane. The intersection of the first plane 71 and the second plane 72 is parallel to the Y direction. The second focus F2 is located within the second space 6b.

[0082] In this embodiment, similarly to the first embodiment, the radius of the spherical surface 70 , which is the size of the second space 6 b , is set to be the same as the thickness W of the flange portion 2 d .

[0083] Spherical surface 70 reflects light emitted from light-emitting element 3 using ellipsoidal surface 2a and then guides the light to second focal point F2, thus acting as a transmissive mirror or transmissive scattering surface, similar to the first embodiment. First plane 71 and second plane 72 function to prevent light entering from the outside and heading toward second focal point F2 from reaching light-receiving element 4 by total reflection or refraction. First plane 71 and second plane 72 also function to eliminate region A described in the first embodiment.

[0084] Figure 15 This figure shows the result of solving the light path when a hypothetical light source is arranged at the second focus F2 by simulation in order to confirm the intrusion path of external light. In this embodiment, the light path output from the hypothetical light source is changed to the left side of the area A (towards the ellipsoidal surface 2a), so that the area A disappears. Figure 15 As shown in FIG, light output from a hypothetical light source disposed at the second focal point F2 and incident on the first plane 71 is refracted at the first plane 71 and directed toward the spherical surface 2c. Figure 13 As shown, the intersection K2 of the extended plane 72 and the major axis La is arranged to the left of the focus F2. In other words, it can be confirmed that in the first embodiment, the light from the imaginary light source toward the area A of the spherical surface 2c (refer to Figure 8(B)) is refracted at first plane 71, thereby changing the optical path so that it enters the ellipsoidal surface 2a and spherical surface 2c in the area inward of area A of spherical surface 2c at an angle that satisfies the total reflection condition (that is, the optical path that prevents external light from reaching light receiving element 4). In addition, a portion of the light refracted at first plane 71 is directed toward second plane 72 and is totally reflected by second plane 72. The light reflected by second plane 72 is directed toward the area inward of area A of spherical surface 2c.

[0085] Thus, in this embodiment, for external light incident from region A of the spherical surface 2c and directed toward the second focal point F2, the first plane 71 and the second plane 72, functioning as optical path changing portions, change the optical path, thereby preventing the external light from entering the light receiving element 4 located at the second focal point F2. Furthermore, the space 6a can be appropriately modified based on conditions such as the refractive index and eccentricity of the ellipse, the radii of the first space 6a and the second space 6b, and the height of the flange 2d, so that the light shielding performance is most effectively achieved.

[0086] Figure 16 This is a simulation diagram of the light path when an imaginary light source is arranged at the second focus F2 as viewed from a direction parallel to the long axis La. Figure 16 As shown, the optical path is not limited to the optical path parallel to the XZ plane, and there is no optical path that is not parallel to the XZ plane and the light leaks upward from the spherical surface 2c, so it can be confirmed that there is no optical path for external light to enter the light receiving element 4 arranged at the second focus F2.

[0087] <Fourth embodiment>

[0088] Figure 17 This is a cross-sectional view showing the structure of a rain sensor 10c according to a fourth embodiment. Rain sensor 10c according to this embodiment has the same structure as rain sensor 10 according to the first embodiment, except for the structure of second space 6b where light receiving element 4 is located. Based on the features and effectiveness of the above-described embodiments, this embodiment is easier to form and has higher feasibility.

[0089] Figure 18 This is an enlarged view of the second space 6b in this embodiment. Figure 19 6b is a perspective view showing the second space 6b of this embodiment. In this embodiment, the optical path of the light output from the imaginary light source is changed to the left side (toward the elliptical surface 2a) of the region A, so that the region A disappears. Figure 18 and Figure 19 As shown, in this embodiment, a hemispherical body is obtained by cutting a sphere centered at the second focus F2 at an XY plane including the second focus F2, and the second space 6b has a shape obtained by forming a wedge-shaped cutout with a flat tip in the hemispherical body.

[0090] Therefore, a spherical surface 80, a first plane 81, a second plane 82, and a third plane 83 are formed between the second space 6b and the optical cover 2. The first plane 81, the second plane 82, and the third plane 83 are each orthogonal to the XZ plane. The third plane 83 is, for example, parallel to the XY plane. The third plane 83 intersects with the first plane 81, and their intersection is parallel to the Y direction. The third plane 83 intersects with the second plane 82, and their intersection is parallel to the Y direction. The second focus F2 is located within the second space 6b.

[0091] In the present embodiment, the radius of the spherical surface 80 , which is the size of the second space 6 b , is the same as the thickness W of the flange portion 2 d .

[0092] The spherical surface 80 reflects light emitted from the light-emitting element 3 using the ellipsoidal surface 2a and then guides the light to the second focal point F2. Similar to the first embodiment, it functions as a transmissive mirror or transmissive scattering surface. Similar to the first plane 71 and second plane 72 of the third embodiment, the first plane 81, the second plane 82, and the third plane 83 function to prevent light from reaching the light-receiving element by totally reflecting or refracting light directed toward the second focal point F2 from the external light. The first plane 81, the second plane 82, and the third plane function to eliminate the area A described in the first embodiment.

[0093] Figure 20 : is a diagram showing the result of solving the light path when a hypothetical light source is arranged at the second focus F2 by simulation in order to confirm the intrusion path of external light. Figure 20 As shown, the light output from the imaginary light source disposed at the second focal point F2 and incident on the first plane 81 is refracted at the first plane 81 and directed toward the spherical surface 2c. Similarly, the light output from the imaginary light source disposed at the second focal point F2 and incident on the third plane 83 is slightly refracted at the third plane 83 and directed toward the spherical surface 2c. Figure 18 As shown, the intersection K3 of the extended plane 81 and La is located to the left of the focus F2. That is, it can be confirmed that in the first embodiment, the light from the imaginary light source toward the area A of the spherical surface 2c (see Figure 8 (B)) is refracted at the first plane 81 or the third plane 83, thereby changing the light path so that it is incident on the area inside the spherical surface 2c than the area A at an angle that satisfies the total reflection condition, thereby avoiding the external light from reaching the light receiving element 4.

[0094] Thus, in this embodiment, for external light incident from region A of the spherical surface 2c and directed toward the second focal point F2, the first plane 81, the second plane 82, and the third plane 83, functioning as optical path changing portions, change the optical path, thereby preventing the external light from entering the light-receiving element 4 located at the second focal point F2. Furthermore, the radius of the spherical surface 80, the inclination angles of the first plane 81, the second plane 82, and the third plane 83, and the like can be appropriately varied based on conditions such as the refractive index and eccentricity of the ellipse, the radii of the first space 6a and the second space 6b, and the height of the flange portion 2d, so that the light-shielding performance is most effectively achieved.

[0095] Next, setting conditions of the first plane 81 , the second plane 82 , and the third plane 83 will be described. Figure 21 It is a diagram for explaining setting conditions of the first plane 81 , the second plane 82 , and the third plane 83 included in the second space 6 b .

[0096] like Figure 21 As shown, in the XZ plane, the intersection point of the spherical surface 2c and the flange portion 2d is defined as P1, and the straight line connecting the intersection point P1 and the second focus F2 is defined as L1. The first plane 81 is a plane perpendicular to the XZ plane including the straight line connecting the point P2 and the point P3 on the spherical surface 80.

[0097] Furthermore, the distance from point P2 to the second focal point F2 is smaller than the radius of the spherical surface 80. Furthermore, point P3 is located closer to the flange portion 2d than line L1. That is, the angle α formed between line L2 connecting point P3 and the second focal point F2 and the major axis La is smaller than the angle β formed between line L1 and the major axis La.

[0098] The third plane 83 is parallel to the XY plane including point P2. The second plane 82 is set so that the intersection point P4 where the imaginary extension line L3 extending toward the long axis La intersects with the long axis La is located further inward than the second focus F2 (on the opposite side of the flange portion 2d).

[0099] And, as Figure 22 As shown, the angle γ formed by the first plane 81 and the XY plane needs to be at least a value greater than 0.

[0100] <Other embodiments>

[0101] In the above embodiment, the outer side of the ellipsoidal surface 2a, which serves as the effective detection area D of the optical cover, is connected to the spherical surfaces 2b and 2c by tangent lines. However, it may also be connected to a curved surface having a shape other than a spherical surface by tangent lines. The curved surface may be a portion of the surface of a body of rotation centered about the major axis La of the ellipsoidal surface 2a, and may have a greater curvature than the ellipsoidal surface 2a.

[0102] Furthermore, when the optical path changing portion shown in the second to fourth embodiments is formed in the second space 6b where the light receiving element 4 is arranged, the area outside the effective detection area D of the optical cover may be formed as an elliptical surface ( Figure 7 Elliptical surface 2f shown in (A). Elliptical surface 2a and elliptical surface 2f are part of the surface of the same spherical ellipsoid. In this case, by changing the optical path of external light by the optical path changing portion based on conditions such as the refractive index, eccentricity, and the height of the convex edge portion 2d, it is possible not only to suppress the entry of external light into the light receiving element 4 but also to prevent the entry of external light.

[0103] Furthermore, in the above-mentioned embodiments, the light-emitting surface of the light-emitting element 3 and the light-receiving surface of the light-receiving element 4 are set to exist at the first focus F1 and the second focus F2, respectively, and the light path is simplified. However, in fact, the light-emitting surface of the light-emitting element 3 and the light-receiving surface of the light-receiving element 4 that perform their functions have limited sizes, so it is preferred to form the light path changing portion taking into account the actual sizes of the light-emitting surface and the light-receiving surface so as to obtain the required light-shielding performance.

[0104] In the droplet sensor of the present invention, the light-emitting element 3 and the light-receiving element 4 are respectively arranged at the first focus F1 and the second focus F2 or near them, but are preferably arranged according to the shape, size, and outgoing light profile of the light-emitting part of the light-emitting element 3, and the shape and size of the light-receiving part of the light-receiving element 4.

[0105] Furthermore, the device can also be used in rain sensors and condensation sensors. Rain sensors can be installed on roadside trees or streetlights to measure local rainfall distribution and obtain weather information, or they can be used to control vehicle wipers. Condensation sensors can be used in office automation equipment such as copiers and servers. Furthermore, rain sensors can be integrated into environmental sensors and used in combination with other sensors (such as temperature sensors and wind direction and volume sensors).

Claims

1. A droplet sensor, characterized in that: have: an optical housing comprising an ellipsoidal surface that is a portion of a rotating ellipsoid; a light source disposed at or near the first focus of the elliptical surface; as well as a light detector disposed at or near the second focus of the elliptical surface; The elliptical surface is an effective detection area, and the light output from the light source is reflected toward the light detector. The amount of reflected light changes due to the adhesion of the droplets to the elliptical surface. The optical cover further includes a curved surface having a curvature greater than that of the elliptical surface, and a tangent line of the curved surface is connected to the outside of the effective detection area of ​​the optical cover.

2. The droplet sensor according to claim 1, characterized in that The curved surface is a portion of the surface of a sphere centered at a point on the major axis of the ellipsoid.

3. The droplet sensor according to claim 2, characterized in that The optical cover has a shape obtained by cutting the rotational ellipsoid and the sphere along a plane including the major axis.

4. The droplet sensor according to claim 3, characterized in that The optical cover includes a first space having a hemispherical surface centered at the first focal point and a second space having a hemispherical surface centered at the second focal point.

5. The droplet sensor according to claim 4, characterized in that The second space includes an optical path changing portion at an interface with the optical cover, the optical path changing portion changing an optical path of external light incident from outside the optical cover to the hemispherical surface and directed toward the second focal point.

6. The droplet sensor according to claim 5, characterized in that The optical path changing portion is composed of at least one plane that refracts or reflects the external light.

7. The liquid drop sensor according to claim 5, characterized in that The optical path changing portion includes a first plane and a second plane for refracting or reflecting the external light, and the first plane and the second plane intersect with each other.

8. The liquid drop sensor according to claim 5, characterized in that The optical path changing portion includes a first plane, a second plane, and a third plane for refracting or reflecting the external light, and the first plane and the second plane intersect with the third plane respectively.

9. The liquid drop sensor according to any one of claims 3 to 8, characterized in that: The optical cover is formed with a flange portion extending outward from a lower portion including the major axis.

10. A droplet sensor, characterized in that: have: an optical housing comprising an ellipsoidal surface that is a portion of a rotating ellipsoid; a light source disposed at or near the first focus of the elliptical surface; as well as a light detector disposed at or near the second focus of the elliptical surface; The elliptical surface is an effective detection area, and the light output from the light source is reflected toward the light detector. The amount of reflected light changes due to the adhesion of the droplets to the elliptical surface. The optical cover includes a first space having a hemispherical surface centered at the first focal point and a second space having a hemispherical surface centered at the second focal point. The second space includes an optical path changing portion at an interface with the optical cover, the optical path changing portion changing an optical path of external light incident from outside the optical cover to the hemispherical surface and directed toward the second focal point.

11. The liquid drop sensor according to claim 10, characterized in that: The optical path changing portion is composed of at least one plane that refracts or reflects the external light.

12. The liquid drop sensor according to claim 10, characterized in that The optical path changing portion includes a first plane and a second plane for refracting or reflecting the external light, and the first plane and the second plane intersect with each other.

13. The liquid drop sensor according to claim 10, characterized in that The optical path changing portion includes a first plane, a second plane, and a third plane for refracting or reflecting the external light, and the first plane and the second plane intersect with the third plane respectively.

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