Droplet sensor

Abstract

The present invention provides a droplet sensor capable of achieving uniform detection sensitivity. The droplet sensor comprises an optical cover, which is a portion of a rotating ellipsoid and has an ellipsoidal surface; a light source disposed at or near a first focal point of the ellipsoidal surface; and a photodetector disposed at or near a second focal point of the ellipsoidal surface. The ellipsoidal surface includes an effective detection area that reflects light output from the light source toward the photodetector, with the amount of reflected light varying due to the adhesion of droplets to the ellipsoidal surface. The optical cover includes a space having a spherical surface centered at the second focal point, and a transmissive scattering surface is formed on the spherical surface in an area where light from the effective detection area enters.

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 along a plane including its 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] Droplet detection sensitivity is expressed as the ratio of the amount of light received by the photodetector when the droplet is attached to the effective detection area to when it is not. Therefore, droplet detection sensitivity depends on the irradiance distribution of light irradiated from the light source to the effective detection area.

[0012] The irradiance on the effective detection area mainly depends on the "radiation profile of the emitted light caused by the light source", "the distance from the light source to each area within the effective detection area", and "the incident angle from the light source to each area within the effective detection area".

[0013] Since the light emission profile of a light emitting element generally has angle dependence, the irradiance varies depending on the emission angle, thereby forming a "radiation profile of the emitted light from the light source."

[0014] Since light enters radially from the light source, the irradiance on the surface perpendicular to the light decreases in inverse proportion to the square of the distance from the light source, thus forming the "distance from the light source to each area within the effective detection area."

[0015] If the incident angle of light on the illuminated surface is set to θ in advance, the irradiance on the illuminated surface decreases according to cosθ as the incident angle increases, thereby forming the "incident angle from the light source to each area in the effective detection area."

[0016] In the aforementioned optical cover, the effective detection area is an elliptical surface. The distance from the light source varies depending on the area within the effective detection area. Consequently, even if the radiation profile of the light source is the same, the irradiance across the effective detection area is not uniform, and detection sensitivity generally becomes non-uniform. Specifically, given the same radiation profile, areas closer to the light source within the effective detection area have higher irradiance, resulting in higher detection sensitivity. On the other hand, due to eccentricity, areas farther from the light source within the effective detection area have lower irradiance, resulting in lower detection sensitivity.

[0017] An object of the present invention is to provide a liquid drop sensor capable of making detection sensitivity uniform or controllable.

[0018] Solutions to Problems

[0019] In order to solve the above-mentioned problems, the present droplet sensor 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 includes an effective detection area, which reflects the light output from the above-mentioned light source toward the above-mentioned light detector, and the amount of reflected light changes due to the attachment of the droplets to the above-mentioned elliptical surface, and a space having a spherical surface centered on the above-mentioned second focus is formed in the above-mentioned optical cover, and a transmission scattering surface is formed on the above-mentioned spherical surface and in the area for the light from the above-mentioned effective detection area to be incident.

[0020] The effects of the invention are as follows.

[0021] According to the present invention, a liquid drop sensor capable of making detection sensitivity uniform is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a side view of the rain sensor according to the first embodiment.

[0023] Figure 2 It is a perspective view of the rain sensor according to the first embodiment.

[0024] Figure 3 is a cross-sectional view of the rain sensor.

[0025] Figure 4 This is a perspective view of the optical cover viewed from the bottom side.

[0026] 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.

[0027] 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.

[0028] Figure 7 This is a simulation diagram of the light path when the radiation profiles of the light-emitting elements are made the same.

[0029] Figure 8 It will Figure 7 The simulation results shown are graphs showing the irradiance distribution of the light components received by the light-receiving element in the effective detection area.

[0030] Figure 9 It is a perspective view showing the interface between the second space and the optical cover.

[0031] Figure 10 3 is a diagram showing the relationship between the transmission scattering surface and the effective detection area.

[0032] Figure 11 1 is a diagram showing an example of the intensity distribution of reflected light after passing through each region of the transmission scattering surface.

[0033] Figure 12 Is to have Figure 11 The diagram shows simulation results of the irradiance distribution of the light components received by the light-receiving element in the effective detection area when the transmission scattering surface of the intensity distribution shown is applied to the boundary surface of the second space.

[0034] Figure 13 This is a simulation diagram of the light path when the radiation profile of the light-emitting element has extremely strong directivity.

[0035] Figure 14 It will Figure 13The simulation results shown are graphs showing the irradiance distribution of the light components received by the light-receiving element in the effective detection area.

[0036] Figure 15 It is a perspective view showing the interface between the second space and the optical cover according to a modified example.

[0037] Figure 16 3 is a diagram showing the positional relationship of the light receiving element with respect to the second focal point in a modified example.

[0038] Figure 17 1 is a diagram showing an example of the intensity distribution of the transmission scattered light after passing through the transmission scattering surface.

[0039] Figure 18 This figure shows the simulation results of the irradiance distribution of the light components received by the light-receiving element in the effective detection area, taking into account the effects of the transmission scattering surface and the light-receiving element.

[0040] In the picture:

[0041] 2—optical cover, 2a—elliptical surface, 2b—convex edge, 2c—bottom surface, 3—light-emitting element (light source), 4—light-receiving element (light detector), 5a—first space, 5b—second space, 6—interface (spherical surface), 7—transmission scattering surface, 7a—first area, 7b—second area, 7c—third area, 8—transmission scattering surface, 8a—upper end, 8b—lower end, 10—rain sensor. 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 elliptical surface 2a and a flange 2b. The light-emitting element 3 is positioned at or near the first focus F1 of the elliptical surface 2a. The light-receiving element 4 is positioned at or near the second focus F2 of the elliptical surface 2a. 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 forming a part of a rotating ellipsoid and is formed of a material that is transparent to the wavelength of the output light of the light emitting element 3. Figure 1 In the example, a rotational ellipsoid is obtained by rotating an ellipse having a major axis in the X direction and a minor axis in the Y direction around the major axis La, and the optical cover 2 has a shape obtained by cutting the rotational ellipsoid at a plane horizontal to the XY plane including the major axis La. Figure 1 In the figure, for the sake of convenience, the height direction of the optical cover 2 is referred to as the Z direction.

[0047] The optical cover 2 may be formed of transparent ceramics, glass, high-refractive-index plastic, or the like, in addition to resins such as polycarbonate and acrylic.

[0048] The flange portion 2b 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 or elliptical. In addition, the top view shape of the flange portion 2b is not limited thereto, and may also be square or other shapes. The flange portion 2b has a constant thickness W in the Z direction. The thickness W of the flange portion 2b is, for example, approximately 25% of the height H of the optical cover 2. The flange portion 2b functions as a mounting portion for fixing the optical cover 2 to the main body side, etc. The thickness W of the flange portion 2b 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 due to the tightening of the screws.

[0049] 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).

[0050] Figure 1In the figure, the dotted shadowed area D is the effective detection area, which is included in the ellipsoidal surface 2a. The effective detection area D is the area on the ellipsoidal surface 2a that totally reflects the light output from the light-emitting element 3 when the optical cover 2 is surrounded by air. The shape of the 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 area of ​​the effective detection area D that meets this condition depends on the refractive index of the optical cover 2 and the eccentricity of the ellipsoidal surface 2a.

[0051] When a resin with a refractive index of 1.57 (such as polycarbonate) is used to form the optical cover 2, the range of the incident angle θm of the detectable area that can detect the attachment of raindrops is approximately 39.6°<θm<57.9°, but in this embodiment, the eccentricity is set to 0.781, and the range of the incident angle θi satisfying 44.3°<θi<51.4° is used as the effective detection area D.

[0052] The reason why 39.6<θ<44.3 is not used as the effective detection area is that due to deformation caused by molding errors of the optical cover 2, thermal expansion and other factors, and wavelength differences of optical elements, it may become an area where raindrop detection using total reflection conditions may not be possible.

[0053] Because the area outside the effective detection area D (θi < 44.3°) includes the detectable area, the light-receiving element 4 also detects reflected light from the detectable area outside the effective detection area D. Consequently, the reflected light from the effective detection area D is mixed with the reflected light from the detectable area outside the effective detection area D, and the light-receiving element 4 receives this light, which affects the raindrop detection results in the effective detection area D. Therefore, by applying a light-shielding coating outside the effective detection area D, the reflected light from the detectable area outside the effective detection area D is maintained at a constant intensity, enabling accurate detection of water droplets deposited in the effective detection area D. Furthermore, the light-shielding coating prevents the intrusion of external light noise from outside the detectable area.

[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 the prior application filed by the present applicant (Japanese Patent Application No. 2017-254956).

[0055] As described above, the flange 2b functions as a mounting portion for mounting the optical cover 2 on the main body side, 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, so the area below approximately 25% of the height H is used as the flange 2b serving 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 area with low sensitivity as the flange, the detection area that contributes to information on raindrop adhesion is hardly lost as a rain sensor assuming that raindrops are falling from above, and the presence or absence of raindrops or the amount of raindrop adhesion is not affected. Therefore, the flange 2b serving as the mounting portion can be formed with little reduction in detection sensitivity.

[0056] Figure 3 This 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 2c side.

[0057] like Figure 3 and Figure 4 As shown, a first space 5a and a second space 5b are formed within the optical cover 2. The first space 5a is a hemispherical space centered on the first focal point F1 where the light-emitting element 3 is located. Its interface (spherical surface) with the optical cover 2 is a transmissive mirror surface (a smooth, non-concave surface through which light passes without scattering). The second space 5b is a hemispherical space centered on the second focal point F2 where the light-receiving element 4 is located. Its interface (spherical surface) with the optical cover 2 comprises a transmissive scattering surface (a surface with concave and convex surfaces such as a sanded surface through which light scatters) and a transmissive mirror surface. The interface between the second space 5b and the optical cover 2 is described in detail below.

[0058] In the present embodiment, the radii of the first space 5 a and the second space 5 b are substantially the same as the thickness W of the flange portion 2 b .

[0059] In this way, because the first space 5a has a spherical surface, the light output from the light-emitting element 3 is allowed to enter the interior of the optical cover 2 without being refracted. Similarly, because the second space 5b has a spherical surface, the light reflected by the ellipsoidal surface 2a is allowed to enter the second space 5b without being refracted. (If the second space 5b is a transmission scattering surface, the light entering the second space 5b is scattered, but the light at the center of its intensity distribution enters the second space 5b without being refracted.) This realizes 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 51 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. Figure 6 As shown, if raindrops land on effective detection area D, the reflectivity changes in the portion where the raindrops land because the interface with effective detection area D does not meet the conditions for total reflection. This causes nearly all of the incident light from light-emitting element 3 to be transmitted. Consequently, the amount of light received by light-receiving element 4 decreases. By monitoring changes in the amount of light received by light-receiving element 4 using a monitoring circuit that monitors the output of light-receiving element 4, the presence and amount of raindrops can be detected.

[0062] Figure 7 This is a simulation diagram of the optical path when the radiation profiles of the light emitting elements 3 are made uniform (isotropic). Figure 7 , a case where the radiation profile of the light emitting element 3 is uniformly outputted is represented by rays of light at equal angles, and the optical path until the light is received by the light receiving element 4 is represented.

[0063] Figure 8 It will Figure 7 The simulation results shown are expressed as a graph of the irradiance of the effective detection area D. Figure 8 (A) is the side view, Figure 8 (B) is a top view. Figure 8 In the figure, irradiance is represented by shades, with areas closer to white indicating higher irradiance. Furthermore, in the case of air surrounding the image, light emitted from light-emitting element 3 is reflected by effective detection area D and received by light-receiving element 4. This irradiance distribution is represented solely by the received light components. Furthermore, the irradiance shades appear patchy, but this depends on conditions such as the number of light rays set during the simulation. By simulating conditions closer to actual usage environments, such as increasing the number of light rays, the patchiness is reduced and the shading becomes smoother.

[0064] like Figure 7 As shown in FIG, when the radiation profile of the light emitting element 3 is set to be the same (i.e., the angular dependence of the radiation from the light emitting element 3 is small), when observed in the XZ plane, the light density in the effective detection area D is larger the closer it is to the light emitting element 3 (closer to the first focus F1). This corresponds to the fact that the radiation illuminance is inversely proportional to the square of the distance, as shown in FIG. Figure 8 As shown, the closer to the light emitting element 3 (the closer to the first focus F1), the greater the irradiance.

[0065] As mentioned above, irradiance also varies depending on the angle at which light enters the detection surface, but the influence of distance is dominant. More specifically, the detection surface of the droplet sensor assumed in this embodiment has a spherical shape, resulting in a 2.8-fold difference in the distance from the light source to the effective detection area between areas closer to the light source and areas farther away. Consequently, the irradiance in the plane perpendicular to the light beam differs by a factor of 7.8. Meanwhile, the angle of incidence from the light source to the effective detection surface reaches its maximum at 51.4° on the minor axis and decreases as it approaches the major axis vertices on either side, reaching a minimum angle of 44.3° at the ends of the effective detection area. This influence results in a 1.15-fold difference in irradiance.

[0066] And, according to Figure 8 As can be seen, the irradiance in the effective detection area D decreases as it is compared in a plane perpendicular to the La axis, with the area closer to the flange 2b (the farther from the long axis La in the Y direction). This is because the light-receiving surface of the light-receiving element 4 is flush with the XY plane and faces the +Z direction.

[0067] In this embodiment, the light-receiving surface is oriented in the +Z direction because, since raindrops fall from above (vertically) relative to the effective detection area D and deposit more, and less from the sides, the purpose is to prioritize information on changes in the surface caused by raindrops depositing from above (vertically) over information obtained from raindrops depositing from the sides. Furthermore, if uniform sensitivity within a plane perpendicular to the long axis is desired, the light-receiving surface of the light-receiving element 4 can be arranged, for example, toward the -X direction.

[0068] Next, the interface between the second space 5 b and the optical cover 2 will be described.

[0069] Figure 9 2 is a perspective view showing the interface 6 between the second space 5b and the optical cover 2. Figure 9 As shown, a transmissive scattering surface 7 is formed on the spherical interface 6 to scatter the incident light. In this embodiment, the area of ​​the interface 6 other than the transmissive scattering surface 7 is a transmissive mirror surface, but it may also be a transmissive scattering surface. Alternatively, other surface treatments may be applied.

[0070] The transmissive scattering surface 7 is a so-called roughened surface with a fine concavo-convex structure. Multiple regions with different surface roughness are formed on the transmissive scattering surface 7. In this embodiment, the transmissive scattering surface 7 is composed of a first region 7a, a second region 7b, and a third region 7c.

[0071] The first region 7a, the second region 7b, and the third region 7c are each a rotationally symmetric region with the major axis La as the rotation axis. The surface roughness is greatest in the first region 7a and smallest in the third region 7c.

[0072] Figure 10 : is a diagram showing the relationship between the transmission scattering surface 7 and the effective detection area D. Figure 10 As shown, in this embodiment, first region 7a of transmission scattering surface 7 corresponds to first detection region D1, second region 7b corresponds to second detection region D2, and third region 7c corresponds to third detection region D3. First detection region D1, second detection region D2, and third detection region D3 are each rotationally symmetric about the long axis La.

[0073] Regarding the distance from the light emitting element 3, the first detection area D1 is the closest and the third detection area D3 is the farthest. Therefore, the irradiance decreases in the order of the first detection area D1, the second detection area D2, and the third detection area D3 (see Figure 8 ).

[0074] The first region 7a is an area into which light emitted from the light-emitting element 3 and reflected by the first detection region D1 enters. The second region 7b is an area into which light emitted from the light-emitting element 3 and reflected by the second detection region D2 enters. The third region 7c is an area into which light emitted from the light-emitting element 3 and reflected by the third detection region D3 enters.

[0075] Light incident from the effective detection area D onto the transmission scattering surface 7 is scattered by the transmission scattering surface 7 during transmission. As a result, the emission angle (scattering angle) is dispersed according to the surface roughness, and the central intensity decreases. The greater the surface roughness of the transmission scattering surface 7, the greater the decrease in the central intensity of the transmission scattered light.

[0076] Figure 11 This figure shows an example of the intensity distribution of reflected light after passing through each region of the transmission scattering surface 7. For scattered light on a sanded surface, the scattering angle depends on the surface roughness, but in most cases its profile shows properties close to a Gaussian distribution (normal distribution), so it is assumed here that the scattered light follows a Gaussian distribution.

[0077] Figure 11 In the figure, S1, S2, and S3 correspond to the first region 7a, the second region 7b, and the third region 7c, respectively, and show the relative values ​​of the intensity distribution (radiance) when the same amount of light is scattered into each region. The surface roughness of the first region 7a, the second region 7b, and the third region 7c is set so that the standard deviation σ of the scattering angle is, for example, 15°, 12°, and 10°, respectively. Therefore, the effect of reducing the central intensity of the transmitted scattered light is greatest in the first region 7a, and least in the third region 7c.

[0078] With the above configuration, the light from the first detection area D1, which has the highest irradiance, has its central intensity significantly reduced within the first area 7a and is incident on the light receiving element 4. On the other hand, the light from the third detection area D3, which has the lowest irradiance, has its central intensity reduced within the third area 7c and is incident on the light receiving element 4, but the reduction in central intensity is smaller than that of the light from the first detection area D1.

[0079] Thus, for light from the effective detection area D, the decrease in central intensity due to transmission through the transmissive scattering surface 7 is greater for light from the detection area with greater irradiance. Consequently, the difference in irradiance on the detection surface of the light-receiving element 4 is offset by the light-receiving element 4 after passing through the transmissive scattering surface 7, thereby reducing the regional dependence of the amount of light received by the light-receiving element 4. Consequently, the droplet detection sensitivity becomes uniform across the detection surface along the long axis (e.g., the detection surface located on the XZ plane including the long axis La).

[0080] Figure 12 is shown in the Figure 11 The diagram shows simulation results of the irradiance of the light component received by the light receiving element 4 on the detection surface when the transmission scattering surface of the intensity distribution shown is applied to the boundary surface of the second space. Figure 12 (A) is the side view, Figure 12 (B) is a top view. Figure 12 and Figure 8 It can be seen that the detection sensitivity of the droplet along the long axis direction is made uniform by the effect of the transmission scattering surface 7.

[0081] Furthermore, in the above embodiment, the transmission scattering surface 7 is divided into three regions having different surface roughnesses. However, the number of divisions is not limited to three, and the number of divisions and the size of each region can be changed as appropriate.

[0082] In this embodiment, assuming raindrops falling vertically (from above), sensitivity uniformity is described along the long-axis vertex, which is believed to efficiently collect raindrop deposition information. However, by also varying the surface roughness in the ±Y directions, sensitivity can also be uniformed or controlled along the short-axis side (±Y directions). However, in this case, it should be noted that since the light-receiving surface of the light-receiving element 4 is arranged along the +Z direction, the light-receiving efficiency of light incident on the light-receiving surface at an angle close to 90 degrees is extremely low, making uniformity difficult to achieve by adjusting the scattering surface. For detection surfaces with an angle of incidence close to 90 degrees, which are unlikely to be conducive to collecting raindrop deposition information, it is possible to pre-deflect the detection surface from the target by applying a light-shielding coating or increasing the height of the ridge, which can also serve as a fixing point for the cover.

[0083] Furthermore, as described above, by installing light-emitting elements 3 having the same radiation profile (i.e., the radiated light from the light-emitting element 3 has less angular dependence), even if the intensity center deviates from the angle in the up, down, left, and right directions relative to the major axis La, the change in the radiation profile of the light-emitting element 3 incident on the effective detection area D caused by the angular deviation is small, thereby being able to suppress detection errors.

[0084] Modifications

[0085] Next, modifications of the above-described embodiment will be described.

[0086] Figure 13 This is a simulation diagram of the light path when the radiation profile of the light emitting element 3 has extremely strong directivity. Specifically, Figure 13 In the embodiment, the radiation angle of the light emitting element 3 is reduced so that the output direction of the light from the light emitting element 3 is parallel to the long axis La as shown by the arrow A and is directed toward the second focus F2. Figure 13 , the optical path of light output from the light-emitting element 3 and received by the light-receiving element 4 is shown. When the radiation profile of the light-emitting element 3 has extremely strong directivity, the light density in the effective detection area D increases as it approaches the light-emitting element 3 (towards the second focal point F2) when viewed in the XZ plane.

[0087] Figure 14 It will Figure 13 The simulation results shown are expressed as a graph of the irradiance of the effective detection area D. Figure 13 (A) is the side view, Figure 13 (B) is a top view. Figure 12 In the figure, the irradiance is represented by shades, with areas closer to white indicating higher irradiance. Furthermore, this irradiance is the irradiance on the effective detection area D, which is the target of light output from the light-emitting element 3, reflected by the effective detection area D, and received by the light-receiving element 4.

[0088] like Figure 13 As shown in FIG, when the radiation profile of the light emitting element 3 has a very strong directivity, the center intensity of the light emitting element 3 is extremely large, so that the light density in the effective detection area D becomes larger along the long axis La in the detection area farther from the light emitting element 3. In this case, as Figure 14 As shown, along the long axis La, the irradiance of the detection area farther from the light emitting element 3 is greater than that of the detection area closer to the light emitting element 3 .

[0089] Figure 15 1 is a perspective view showing the interface 6 between the second space 5b and the optical cover 2 of this modification. Figure 15As shown, in this modified example, a transmissive scattering surface 8 is formed on the interface 6 to scatter the incident light. In addition, the area of ​​the interface 6 other than the transmissive scattering surface 8 is a transmissive mirror surface, but it can also be a transmissive scattering surface. Alternatively, other surface treatments can be applied.

[0090] As shown in the above embodiment, by providing the transmission scattering surface 8 with a plurality of transmission scattering surfaces having different surface roughnesses, it is possible to achieve uniformity in detection sensitivity. However, in this modification, as shown in FIG. Figure 15 As shown in FIG. 1 , the surface roughness of the transmission scattering surface 8 is set to be the same. The transmission scattering surface 8 is a region into which the light output from the light emitting element 3 and reflected by the effective detection area D enters. The intensity distribution of the transmission scattered light transmitted from the transmission scattering surface 8 is, for example, Figure 11 Intensity distribution S3 is shown.

[0091] Figure 16 FIG. 4 is a diagram showing the positional relationship of the light receiving element 4 relative to the second focus F2 in this modification. Figure 16 As shown in FIG. 1 , the position of the light receiving element 4 is displaced from the second focal point F2 in the −X direction along the major axis La. Figure 16 In the equation, Δ represents the displacement.

[0092] As shown in the above embodiment, when the light receiving element 4 is arranged at the second focal point F2, the light receiving element 4 receives light with a scattering angle of 0° in the transmitted scattered light after passing through the transmitted scattering surface 8 as the center, but by displacing the light receiving element 4 from the second focal point F2, light with a scattering angle other than 0° is received as the center.

[0093] Furthermore, when the light receiving element 4 is displaced from the second focal point F2, the scattering angle of the transmission scattered light received by the light receiving element 4 varies depending on the position where the reflected light from the effective detection area D passes through the transmission scattering surface 8. Figure 16 As shown, when the light receiving element 4 is displaced from the second focal point F2, light having a scattering angle θa of the transmission scattered light transmitted through the upper end portion 8a of the transmission scattering surface 8 is selectively received by the light receiving element 4, and light having a scattering angle θb of the transmission scattered light transmitted through the lower end portion 8b of the transmission scattering surface 8 is selectively received by the light receiving element 4. Here, θa>θb.

[0094] Figure 17 1 is a diagram showing an example of the intensity distribution of the transmission scattered light after passing through the transmission scattering surface 8 . Figure 17 In FIG, the solid line is the intensity of light incident from the upper end 8a, and the double-dashed line is the intensity of light incident from the lower end 8b. Figure 17As shown, since θa>θb, the intensity of light near the scattering angle θa is smaller than the intensity of light near the scattering angle θb. Therefore, the larger the scattering angle, that is, the closer the transmission area in the transmission scattering surface 8 is to the upper end 8a, the smaller the intensity of light received by the light receiving element 4.

[0095] As described above, in this modification, the irradiance is greater in the effective detection area D farther from the light-emitting element 3. Therefore, in this modification, light from the area with greater irradiance is transmitted through the area of ​​the transmission-scattering surface 8 closer to the upper end 8a, reducing the intensity of light received by the light-emitting element 3. This cancels out the difference in irradiance across the effective detection area D, resulting in a more uniform droplet detection sensitivity.

[0096] Figure 18 This is a diagram showing simulation results of irradiance taking into account the effects of the transmission scattering surface 8 and the light receiving element 4 . Figure 18 (A) is the side view, Figure 18 (B) is a top view. Figure 18 and Figure 14 It can be seen that the detection sensitivity of the droplets is made uniform by the effects of the transmission scattering surface 8 and the light receiving element 4.

[0097] also, Figure 16 In the embodiment of the present invention, the light receiving element 4 is displaced in the -X direction relative to the second focal point F2, but it can also be displaced in the +X direction. Furthermore, in the case where the irradiance on the left side of the detection surface is greater than that on the right side, as is the case with this modification, the sensitivity can be made uniform by displacing the light receiving element 4 in the ±Z directions.

[0098] 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 in the vicinity thereof, but it is necessary to consider 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 to adjust to the optimal position, and it is preferred that they are respectively arranged so that the sensitivity characteristics on the effective detection area D become as uniform as possible or can be controlled.

[0099] Furthermore, the droplet sensor of the present invention can be applied to rain sensors, condensation sensors, and other applications. 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 cover that is a portion of a rotating ellipsoid and has an elliptical surface; 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 includes an effective detection area that reflects light output from the light source toward the light detector, and the amount of reflected light changes due to the adhesion of the droplet to the elliptical surface. A space having a spherical surface centered at the second focal point is formed in the optical cover. A transmission scattering surface is formed on the spherical surface in an area where light from the effective detection area is incident. The transmission scattering surface has multiple areas with different surface roughness. The plurality of regions are rotationally symmetric regions with the major axis of the elliptical surface as the rotation axis. In the plurality of regions, the surface roughness increases as light from a region with a higher irradiance enters the effective detection region.

2. The droplet sensor according to claim 1, characterized in that The photodetector is disposed at a position displaced from the second focus along the major axis or the minor axis of the ellipsoid.

3. The droplet sensor according to claim 1 or 2, characterized in that: The area of ​​the spherical surface other than the transmission scattering surface is a transmission mirror surface.

4. The droplet sensor according to claim 1 or 2, characterized in that: The optical cover has a shape obtained by cutting the rotational ellipsoid along a plane including the major axis.

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

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