Optical sensor and image forming device

Abstract

To prevent a reduction in detection accuracy that may be caused by reflected light from a surface to be irradiated in an optical sensor, such as a toner sensor.SOLUTION: A circuit board is mounted with a light emitting device and a light receiving unit. A housing has a first opening and a second opening. The first opening is provided in a first light guide path arranged between the light emitting device and a surface to be irradiated and is arranged such that light output from the light emitting device is directed to the surface to be irradiated. The second opening is provided in a second light guide path arranged between the surface to be irradiated and the light receiving unit. The first opening is an emission port of a through hole provided to penetrate the housing. The shape of the through hole is a shape in which diffraction light having an order of diffraction of +1 or more and diffraction light having an order of diffraction of -1 or more generated on the surface to be irradiated are not incident on the light receiving unit.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to an optical sensor and an image forming apparatus. [Background technology]

[0002] An image forming apparatus forms a toner image on a photosensitive drum, transfers the toner image from the photosensitive drum to an intermediate transfer body, and further transfers the toner image from the intermediate transfer body to a sheet. In particular, an optical sensor is used to check the transfer position and color reproducibility of the toner image (Patent Document 1). Such an optical sensor is called a toner sensor. Toner remaining on the intermediate transfer body is cleaned by a cleaning blade. In order to improve the durability of this cleaning blade, an uneven shape such as grooves may be formed on the surface of the intermediate transfer body (Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-221902 [Patent Document 2] JP 2013-044878 A Summary of the Invention [Problem to be solved by the invention]

[0004] A toner sensor receives specularly reflected light from the surface (base) of an intermediate transfer body to detect the intermediate transfer body, and receives diffusely reflected light from the toner to detect the toner. However, when grooves or the like are formed on the surface of the intermediate transfer body, the specularly reflected light from the base decreases and the diffusely reflected light from the base increases. In particular, when diffracted light generated by the grooves functioning as a diffraction grating is incident on a light receiving element that receives specularly reflected light, it becomes difficult to accurately detect the specularly reflected light from the base. Therefore, an object of the present invention is to suppress a decrease in detection accuracy that may occur due to reflected light from an irradiated surface in an optical sensor such as a toner sensor. [Means for solving the problem]

[0005] The present invention relates to, for example, A belt with a moving surface; A light emitting element that irradiates light toward a surface of the belt that is set relative to the measurement object; A first light receiving unit that receives specularly reflected light from a surface of the measurement object; A second light receiving unit that receives diffusely reflected light from a surface of the object to be measured; a circuit board on which the light emitting element and the first light receiving unit are mounted; a housing having a first opening and a second opening and provided to surround the light emitting element and the first light receiving unit; the first opening is provided in a first light guide path disposed between the light emitting element and the surface of the belt, and is disposed so that light output from the light emitting element is directed toward the surface of the belt; the second opening is provided in a second light guide path disposed between the surface of the belt and the first light receiving unit, the light-emitting element and the first light-receiving unit are provided at positions where they overlap in a first direction in which the surface of the belt moves, and the light-emitting element and the second light-receiving unit are provided at positions where they do not overlap in the first direction; The first light receiving unit and the second light receiving unit are provided so as to overlap each other in a direction perpendicular to the first direction. 、 The first opening provided in the housing is an emission port of a through hole provided to penetrate the housing, and the shape of the through hole is such that light output from the light emitting element and reflected by a wall surface of the through hole does not enter the first light receiving unit through the surface of the belt. The present invention provides an optical sensor characterized by the above. Effect of the Invention

[0006] According to the present invention, it is possible to suppress a decrease in detection accuracy in an optical sensor that may occur due to reflected light from an illuminated surface. [Brief description of the drawings]

[0007] [Figure 1] FIG. [Diagram 2] FIG. 4 is a diagram for explaining a test pattern. [Diagram 3] FIG. [Figure 4] FIG. 4 is a diagram illustrating grooves in an intermediate transfer belt. [Diagram 5] FIG. 4 is a diagram illustrating grooves in an intermediate transfer belt. [Figure 6] A graph explaining BRDF. [Figure 7] 1 is a graph illustrating the relationship between the grating spacing, the reflection angle, the incidence angle, and the diffraction order. [Figure 8] 1A and 1B are diagrams illustrating an optical sensor. [Figure 9] FIG. 2 is a diagram illustrating an optical path of an optical sensor. [Figure 10] 1A and 1B are diagrams for explaining diffracted light of various orders; [Figure 11] 1A and 1B are diagrams for explaining diffracted light of various orders; [Figure 12] FIG. 2 is a diagram illustrating the diffraction angles of various orders. [Figure 13] 11A to 11C are diagrams illustrating diffracted light of various orders in a comparative example. [Figure 14] 6A and 6B are diagrams for explaining detection results of a test pattern. [Figure 15] 5A and 5B are diagrams for explaining differences in distribution of reflected light intensity. [Figure 16] 5A and 5B are diagrams for explaining the output of an optical sensor and the amount of toner. [Figure 17] 5 is a diagram for explaining the relationship between groove depth and output of an optical sensor. [Figure 18] 13A and 13B are diagrams illustrating an effect produced by reducing the light-emitting area of ​​a light-emitting element. [Figure 19] 11A to 11C are diagrams for explaining an optical sensor according to a third embodiment. [Figure 20] FIG. 11 is a diagram for explaining an optical path of an optical sensor according to a third embodiment. [Figure 21] FIG. 11 is a diagram for explaining the optical path of diffracted light of the first irradiation light in the third embodiment. [Figure 22] FIG. 11 is a diagram for explaining the optical path of diffracted light of the second irradiation light in the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a plurality of features, not all of these features are essential to the invention, and the plurality of features may be combined in any manner. Furthermore, in the accompanying drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0009] <Example 1> 1. Overall configuration of image forming device As shown in Fig. 1, image forming apparatus 100 is an electrophotographic color laser printer. It is equipped with process cartridges 7Y, 7M, 7C, and 7K that are detachably attached to the main body of image forming apparatus 100. The four process cartridges 7Y, 7M, 7C, and 7K have the same structure, but each form an image using toner of a different color, such as yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, the symbols YMCK will be omitted except when each color is individually described.

[0010] The process cartridge 7 has a photosensitive drum 1 which is an image carrier, a charging roller 2 which is a charger, and a developing roller 24 which is a developer. The charging roller 2 uniformly charges the surface of the photosensitive drum 1 using a charging voltage. The exposure device 3 forms an electrostatic latent image by irradiating the surface of the photosensitive drum 1 with light according to an image signal. The developing roller 24 develops the electrostatic latent image with toner using a developing voltage to form a toner image.

[0011] The intermediate transfer unit includes an intermediate transfer belt 12a, a driving roller 12b that drives the intermediate transfer belt 12a, and a driven roller 12d that rotates following the intermediate transfer belt 12a. The intermediate transfer belt 12a is an endless belt type intermediate transfer body, but a drum-shaped intermediate transfer body may also be used. The primary transfer roller 26 is disposed inside the intermediate transfer belt 12a so as to face the photosensitive drum 1. The primary transfer roller 26 transfers the toner image formed on the photosensitive drum 1 onto the intermediate transfer belt 12a using a primary transfer voltage. The multi-color toner image formed by multiple transfer of four color toner images onto the intermediate transfer belt 12a is conveyed to the secondary transfer roller 16 as the intermediate transfer belt 12a rotates.

[0012] The paper feed roller 9 feeds the sheet S from a paper feed cassette 11 that stores the sheet S to a conveying path. The conveying roller pair 10 conveys the fed sheet S to a registration roller pair 17. The registration roller pair 17 conveys the sheet S conveyed from the feeding device to a secondary transfer roller 16. The secondary transfer roller 16 transfers the toner image on the intermediate transfer belt 12a to the conveyed sheet S. The fixing device 14 fixes the toner image on the surface of the sheet S. The paper discharge roller pair 20 discharges the sheet S with the fixed toner image.

[0013] The cleaning blade 22a is a cleaning member that cleans the toner remaining on the intermediate transfer belt 12a. The optical sensor 31 is an optical sensor that detects a test image formed on the intermediate transfer belt 12a. The test image may include a pattern for adjusting the formation position of each of the YMCK toner images, and a pattern for adjusting the density (tone) and color of the toner image.

[0014] 2. Calibration of image forming device Calibration performed by forming a test pattern on the intermediate transfer belt 12a includes registration control and density control. Registration control refers to adjusting the image formation position, which reduces color misregistration. Density control refers to controlling the density of the toner image, which improves color reproducibility.

[0015] As shown in FIG. 2, the image forming apparatus 100 performs calibration during a period when the image forming apparatus 100 is not forming an image input by a user. The image forming apparatus 100 forms a test pattern 30 on the intermediate transfer belt 12a, and optically detects the test pattern 30 with an optical sensor 31. In this example, two optical sensors 31 are arranged to face the driving roller 12b of the intermediate transfer belt 12a. The two optical sensors 31 are arranged at different positions in the width direction of the intermediate transfer belt 12a. The direction parallel to this width direction may be defined as the y direction. The rotation axis of the driving roller 12b is also parallel to the y direction. The movement direction of the intermediate transfer belt 12a may be defined as the x direction. The direction perpendicular to both the x direction and the y direction may be defined as the z direction. Three or more optical sensors 31 may be arranged.

[0016] The test pattern 30 has a toner pattern 30a for registration control and a toner pattern 30b for density control. The toner pattern 30a is formed at an angle to the transport direction. This is because it is convenient for detecting the amount of color shift and the amount of magnification shift. The toner pattern 30b is formed for each color of YMCK, and has multiple density patterns from 0% to 100%.

[0017] 3. Registration Control 3, the controller 29 is a control circuit that performs overall control of the image forming apparatus 100, and may include, for example, a storage device and a CPU (Central Processing Unit). The controller 29 has a registration control unit 29a that performs registration control, and a density control unit 29b that performs density control of the toner image.

[0018] The registration control unit 29a controls the exposure device 3 so that the scanning speed of the exposure device 3 becomes a predetermined target value and the amount of exposure light becomes a predetermined target value. Furthermore, the registration control unit 29a adjusts the exposure start timing of the exposure device 3 based on the detection result of the test pattern 30 by the optical sensor 31. This adjusts the image formation positions of YMCK and corrects color misregistration. Note that the adjustment of the image formation position includes adjustment of the position of the toner image in the main scanning direction, the position in the sub-scanning direction, and the width (magnification) of the toner image in the main scanning direction.

[0019] The registration control unit 29a controls the image forming apparatus 100 to form i rows of test patterns 30 for detecting color shift for each color on the intermediate transfer belt 12a, where i is an integer equal to or greater than 2. The registration control unit 29a detects the test patterns 30 using i optical sensors 31 to obtain the amount of color shift. The amount of color shift includes the relative amount of color shift in the main scanning direction between each color, the relative amount of color shift in the sub-scanning direction, the magnification in the main scanning direction, and the relative inclination. Based on the detection result, the registration control unit 29a corrects the write timing (exposure start timing) of the image for each color so that the relative amount of color shift for each color is reduced.

[0020] 4. Toner image density control The density of a toner image may vary depending on the temperature and humidity conditions of the environment in which the image forming apparatus 100 is installed and the degree of use of the image forming stations for each color. To correct this variation, the density control unit 29b controls the image forming apparatus 100 to form a test pattern 30 for density detection on the intermediate transfer belt 12a. The density control unit 29b detects the density of the test pattern 30 with an optical sensor 31, and controls the density factor based on the detection result so as to obtain the desired density characteristics.

[0021] Specifically, the density control unit 29b controls the high-voltage power supply 29c to set density factors such as the charging voltage, the developing voltage, and the amount of exposure light to specific values, and starts forming the test pattern 30. Image data for forming the test pattern 30 may be generated by the host computer 27 or by the controller 29. The density control unit 29b stores the adjustment results of the density factors in a memory or the like, and uses the adjustment results when forming an image input by a user on the sheet S.

[0022] 5. Intermediate Transfer Belt Structure As shown in Fig. 4(A), the intermediate transfer belt 12a may have a plurality of grooves 83 formed therein for reducing friction with the cleaning blade 22a made of urethane rubber or the like. Fig. 4(B) is a cross-sectional view of the intermediate transfer belt 12a cut parallel to the zy plane.

[0023] As shown in Fig. 4(A), the fine grooves 83 are formed substantially parallel to the x direction. As shown in Fig. 4(B), the intermediate transfer belt 12a has a base layer 81 and a surface layer 82 formed on the base layer 81. The base layer 81 is the thickest layer among the multiple layers constituting the intermediate transfer belt 12a. The surface layer 82 constitutes the surface (outer peripheral surface) of the intermediate transfer belt 12a and carries the toner transferred from the photosensitive drum 1.

[0024] The base layer 81 may be, for example, a layer of about 70 μm in thickness, in which carbon black is dispersed and mixed as an electrical resistance adjusting agent in polyethylene naphthalate resin. The polyethylene naphthalate resin is merely one example of the material for the base layer 81, and any thermoplastic resin may be used. Materials such as polyimide, polyester, polycarbonate, polyarylate, acrylonitrile-butadiene-styrene copolymer (ABS), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVdF), and mixed resins of these may be used. As the electrical resistance adjusting agent (conductive agent), for example, an ionic conductive agent may be used in addition to an electronic conductive agent.

[0025] The surface layer 82 may be a layer having a thickness of about 3 μm, in which an electrical resistance adjusting agent (e.g., zinc oxide) is dispersed and mixed into an acrylic resin. A resin material (curable resin) may be adopted as the material for the surface layer 82 from the viewpoint of strength such as abrasion resistance and crack resistance. Among the curable resins, for example, an acrylic resin obtained by curing an acrylic copolymer containing unsaturated double bonds may be adopted. As the electrical resistance adjusting agent (conductive agent), for example, an ionic conductive agent may be adopted in addition to an electronic conductive agent.

[0026] In general, the combination of urethane rubber and acrylic resin has a large friction resistance due to sliding. Therefore, the cleaning blade 22a is likely to turn over, and the cleaning blade 22a is likely to wear due to repeated use. In order to reduce friction, the surface of the intermediate transfer belt 12a may be subjected to fine unevenness processing. For example, the average interval d of the multiple grooves 83 in the y direction may be 2 μm or more and 10 μm or less. The grooves 83 may be called groove shapes or groove portions. The grooves 83 are provided in substantially the entire area of ​​the outer circumferential surface of the intermediate transfer belt 12a. In the y direction, the multiple grooves 83 are formed in substantially the entire area of ​​the contact area where the cleaning blade 22a and the intermediate transfer belt 12a contact each other. The grooves 83 may not be provided in the area of ​​the surface layer 82 of the intermediate transfer belt 12a where the cleaning blade 22a does not contact.

[0027] Generally, techniques for forming fine irregularities include polishing, cutting, and imprinting. Any processing technique that can obtain the desired distance d can be used. From the viewpoint of processing cost and productivity, imprinting may be used, taking advantage of the photocuring properties of the acrylic resin that is the base material of the surface layer 82.

[0028] The width (groove width) w of the groove 83 is the width of the opening in the y direction, which is approximately perpendicular to the longitudinal axis direction of the groove 83. The groove width w is the distance of the section where the thickness of the surface layer 82 is relatively thin. The thickness of the surface layer 82 is the thickest at the outermost surface 84. The groove width w is, for example, 1.2 μm. The groove width w may be less than the average particle size of the toner. More specifically, the groove width w may be less than half the average particle size of the toner. By making the groove width w smaller than the average particle size of the toner, the toner is less likely to enter the groove 83, and the toner is more reliably cleaned by the cleaning blade 22a. In order to suppress the collapse of the convex portion of the mold used to form the groove 83, the groove width w may be, for example, 0.5 μm or more. More specifically, the groove width w may be 0.5 μm or more and 6 μm or less. Furthermore, the groove width w may be 1 μm or more and 2 μm or less.

[0029] The depth (groove depth) l of the groove 83 is defined as the depth from the opening (outermost surface 84) of the groove 83 to the bottom of the groove 83 in the thickness direction of the intermediate transfer belt 12a. The groove depth l is, for example, 0.45 μm at the beginning of use (when new) of the intermediate transfer belt 12a. For example, the groove depth l may be 0.2 μm or more and less than the thickness of the surface layer 82 at the beginning of use of the intermediate transfer belt 12a. If the groove depth l is too small, the groove 83 is likely to disappear or cleaning failures may occur due to scraping of the surface layer 82. If the groove depth l is less than the thickness of the surface layer 82, the groove 83 does not reach the base layer 81 and exists only in the surface layer 82. Here, the thickness of the surface layer 82 may be designed to be 1 μm or more and 5 μm or less from the viewpoint of reducing a decrease in durability due to being too thin and cracking of the surface layer due to being too thick. More typically, the thickness of the surface layer 82 is set to be equal to or greater than the thickness at which the grooves 83 do not reach the base layer 81, and equal to or less than 3 μm. To make the friction coefficient equal to or less than 0.6, the interval d is designed to be equal to or less than 5 μm. From the viewpoint of manufacturing precision of the grooves 83, the interval d is required to be equal to or greater than 2 μm.

[0030] The interval d between the grooves 83 is defined as the distance from one end (e.g., left end) of the opening of the j-th groove 83 in the y direction to one end (e.g., left end) of the opening of the j+1-th groove 83 in the y direction. j is an integer of 1 or more. A plurality of grooves 83 are formed at an equal pitch (approximately the same interval d) of 3.7 μm in almost the entire area in the y direction. The interval d may be defined based on the right end of the opening, or may be defined as the interval between the bottoms of two adjacent grooves 83. If the interval d is too small, it may be difficult to form a uniform uneven shape. Also, if the interval d is too large, it may be difficult to suppress wear of the cleaning blade 22a. Therefore, the interval d may be designed to be 2 μm or more and 10 μm or less, or more specifically, 3 μm or more and 6 μm or less.

[0031] In FIG. 4A, the groove 83 is formed substantially parallel to the y direction. Furthermore, the groove 83 is formed continuously and substantially linearly around one circumference in the circumferential direction (rotation direction) of the intermediate transfer belt 12a. However, the extending direction of the groove 83 may be parallel to the direction intersecting with the y direction. As shown in FIG. 5A, the extending direction of the groove 83 may have an angle with respect to the conveying direction of the intermediate transfer belt 12a. This angle θ may be, for example, 45 degrees or less, and more specifically, 10 degrees or less. Typically, θ may be set to approximately zero. The groove 83 having the angle θ may be formed by using a mold having a convex portion formed obliquely with respect to the rotation direction of a cylinder forming the mold. The groove 83 may be formed by holding the mold having a convex portion formed substantially parallel to the rotation direction of the cylinder forming the mold obliquely with respect to the x direction.

[0032] 6. Diffraction Phenomenon Figure 5(B) shows the diffraction phenomenon caused by a reflection type diffraction grating. In general, the equation showing the diffraction angle from a reflection type diffraction grating is expressed by the following Equation 1.

[0033] d[sin(θi)+sin(θm)]=mλ...Equation 1 d is the spacing of the diffraction grating. λ is the wavelength of the light. θi is the angle of incidence of the light with respect to the normal direction of the diffraction grating. θm is the angle of reflection (diffraction angle). m is the diffraction order (m = positive or negative integers of ±0, ±1, ±2, ...). When m = 0 (i.e., in the case of specular reflection), θi = θm = 0. Therefore, for specular reflected light, the grating spacing d and the light wavelength λ do not affect the diffraction angle. For other orders, the reflected lights constructively interact at a diffraction angle θm where the optical path difference of each reflected light is an integer multiple of the wavelength, depending on the spacing d and the light wavelength λ. Expanding equation 1 for the diffraction angle θm gives the following equation 2.

[0034] sinθm=mλ / d-sinθi...Equation 2 If the angle of incidence with respect to the normal to the irradiated surface is defined as negative, the following tendency exists. However, m may also be defined as m>0.

[0035] ●The larger the absolute value of the incident angle θi, the larger the right side of equation 2 becomes, and the larger the diffraction angle θm becomes.

[0036] ●The larger the light wavelength λ, the larger the right side of equation 2 becomes and the larger the diffraction angle θm becomes.

[0037] ●The smaller the grating spacing d, the larger the right hand side of equation 2 becomes, and the larger the diffraction angle θm becomes.

[0038] In the intermediate transfer belt 12a, the average interval d of the grooves 83 formed on the surface corresponds to the interval d of the grating.

[0039] 7. Scattering characteristics of intermediate transfer belt FIG. 6 is a graph showing the angular distribution characteristic of scattered light (hereinafter, abbreviated as "BRDF" by taking the initial letters of bidirectional reflectance distribution function). The vertical axis shows the relative reflected light intensity of scattered light. The horizontal axis shows the reflection angle. The solid line shows the BRDF obtained by irradiating the surface of the intermediate transfer belt 12a, on which a plurality of grooves 83 (uneven shape) with a spacing d of 3.7 μm are formed, with light of λ=622 nm at an incident angle of -20°. The BRDF was measured using a small and simple scattering measurement device Mini-Diff V1 by Cybernet Corporation. In FIG. 6, an intermediate transfer belt 12a (hereinafter, abbreviated as "coated belt") that is not subjected to fine uneven processing on the surface and is merely coated with acrylic resin is used as a comparative example. The dashed line shows the BRDF of the comparative example.

[0040] As can be seen from Figure 6, the BRDF of the coated belt has a broad diffuse reflection component relative to the peak of the specular reflection light. In contrast, the BRDF of the intermediate transfer belt 12a, which has been subjected to fine unevenness, has a diffraction phenomenon in which the amount of zero-order specular reflection light decreases and the amount of reflected light increases at periodic angles. The intensity of the diffracted light decreases as the order m increases.

[0041] The BRDF of the intermediate transfer belt 12a having a concave-convex shape has diffuse reflection components around each order of diffracted light. Therefore, the diffuse reflection components of the BRDF of the intermediate transfer belt 12a having a concave-convex shape are significantly stronger than the diffuse reflection components of the BRDF of the coated belt.

[0042] Figures 7(A) and 7(B) show the relationship between the diffraction order and the reflection angle calculated using Equation 1. In Figure 7(A), the light wavelength λ is 850 nm, the spacing d is 3.7 μm, and the incidence angles are 0°, -20°, and -40°. In Figure 7(B), the light wavelength λ is 850 nm, the spacing d is 20 μm, and the incidence angles are 0°, -20°, and -40°.

[0043] Here, it is assumed that the range indicated by the dashed line is set as the light receiving range of the specular reflected light in the optical sensor 31. At d=3.7 μm, the diffracted light with an incident angle of 0° and a diffraction order of +1, and the diffracted light with an incident angle of -40° and a diffraction order of -1 enter the light receiving range of the specular reflected light with an incident angle of -20°. On the other hand, at d=20 μm, the diffracted light with an incident angle of -20° and the diffracted light with an incident angle of +1 and -1 enter the light receiving range of the specular reflected light with an incident angle of -20°. However, the diffracted light caused by the light rays with different incident angles does not enter the light receiving range.

[0044] If the distance d is smaller than 20 μm, diffracted light caused by light rays with different angles of incidence may enter the light receiving area. However, if the diffraction order of the diffracted light becomes large, the light intensity of the diffracted light becomes low, so it is unlikely to affect the reception of the specularly reflected light.

[0045] From the above, when the interval d between the grooves 83 is small, diffracted light at different angles of incidence is likely to enter the light receiving range of the specularly reflected light from the surface (base) of the intermediate transfer belt 12a. However, diffracted light at different angles of incidence does not enter the light receiving range of the diffusely reflected light from the toner image. This is because the grooves 83 are hidden by the toner and the diffraction phenomenon does not occur. In this way, with a measurement object where an error is likely to occur only in one of the detection results of the specularly reflected light from the base and the detection result from the toner pattern 30, the detection accuracy of the optical sensor 31 may decrease.

[0046] The actual light receiving range of the optical sensor 31 may not be wider than the light receiving range shown in Figures 7(A) and 7(B). However, as shown in Figure 6, the diffuse reflection components occurring around the diffracted light of each order in the BRDF of the intermediate transfer belt 12a having the uneven shape have a spread. Furthermore, these diffuse reflection components are significantly stronger than the diffuse reflection components of the BRDF of the coated belt. Therefore, light other than the diffracted light with the peak intensity among the diffracted lights for different incident angles affects the detection result.

[0047] 8. Toner sensor configuration FIG. 8(A) is a schematic perspective view of the optical sensor 31. FIG. 8(B) is an exploded perspective view showing the components of the optical sensor 31. While x, y, and z are directions based on the image forming apparatus 100, x1, y1, and z1 are directions based on the optical sensor 31. The x1 direction is the short-side direction of the optical sensor 31. The x and x1 directions do not have to be parallel to each other, but are assumed to be parallel to each other here. The y1 direction is the long-side direction of the optical sensor 31. The y and y1 directions are parallel to each other here. The z1 direction is the height direction of the optical sensor 31 (the normal direction of the circuit board 34). The z and z1 directions do not have to be parallel to each other, but are assumed to be parallel to each other here.

[0048] FIG. 9 shows a cross-sectional view of the optical path with the x1 direction as the line of sight. That is, the cross-section passing through the rotation axis of the driving roller 12b and the center of the LED 35 is shown. The optical sensor 31 is disposed so as to face the substantially cylindrical surface formed by the intermediate transfer belt 12a being wound around the driving roller 12b. As shown in FIG. 8(A) and FIG. 8(B), the optical sensor 31 has a cover member 32, a housing 33, and a circuit board 34. The LED 35, which is a light-emitting element, the first light-receiving unit 36, and the second light-receiving unit 37 are mounted on the circuit board 34. In addition, the straight line connecting the center of the mounting position of the LED 35, the center of the mounting position of the first light-receiving unit 36, and the center of the mounting position of the second light-receiving unit 37 is substantially parallel to the rotation axis of the driving roller 12b.

[0049] As shown in FIG. 8B, the LED 35 has a light emitting chip 35a surrounded by a light transmitting member 35b. The light transmitting member 35b is a member having light transparency (e.g., resin or glass). Light emitted from the light emitting chip 35a is scattered at the boundary surface of the light transmitting member 35b, and as a result, the light is emitted from almost the entire surface of the light transmitting member 35b. Here, the three-dimensional shape of the light emitting chip 35a and the three-dimensional shape of the light transmitting member 35b are each illustrated as a rectangular parallelepiped. The three-dimensional shape of the light transmitting member 35b may be a semi-dome shape. A part of the light emitted from the LED 35 is reflected by the surface of the intermediate transfer belt 12a to become diffusely reflected light, which is detected by the first light receiving unit 36. A part of the light emitted from the LED 35 is reflected by the surface of the intermediate transfer belt 12a to become specularly reflected light, which is detected by the second light receiving unit 37. That is, the first light receiving unit 36 ​​has a plurality of light receiving elements that receive the diffusely reflected light. The second light receiving unit 37 has a plurality of light receiving elements that receive the specularly reflected light. These multiple light receiving elements are arranged parallel to the short side direction (x1 direction) of the circuit board 34. The number of light receiving elements in each unit is, for example, 16. By configuring the first light receiving unit 36 ​​and the second light receiving unit 37 with multiple light receiving elements in this way, even if there is a deviation within the tolerance range in the positional relationship between the cylindrical surface of the drive roller 12b and the optical sensor 31, the reflected light can be sufficiently detected.

[0050] As shown in FIG. 8B, a first opening 40, a second opening 41, and a third opening 42 are provided on the upper surface of the housing 33. The first opening 40 forms a part of a light guide path through which light from the LED 35 toward the intermediate transfer belt 12a passes. The second opening 41 forms a part of a light guide path through which reflected light from the intermediate transfer belt 12a toward the first light receiving unit 36 ​​and the second light receiving unit 37 passes. The third opening 42 forms a part of a light guide path through which light from the LED 35 toward the intermediate transfer belt 12a passes. The housing 33 may be provided with a light shielding wall 38. The light shielding wall 38 prevents the light from the LED 35 from directly entering the first light receiving unit 36 ​​and the second light receiving unit 37.

[0051] A first lens unit 43, a second lens unit 44, and a third lens unit 45 may be provided on the back side of the cover member 32 (the side where the housing 33 is arranged). The first lens unit 43 functions so that the light passing through the first opening 40 forms a desired spot on the irradiated surface. The second lens unit 44 functions so that the diffusely reflected light from the intermediate transfer belt 12a forms an image on the first light receiving unit 36, and the regular reflected light from the intermediate transfer belt 12a forms an image on the second light receiving unit 37. The third lens unit 45 functions so that the light passing through the third opening 42 forms a desired spot on the irradiated surface. The first lens unit 43, the second lens unit 44, and the third lens unit 45 may be provided individually or integrally.

[0052] 9. Optical path for detecting diffusely reflected light In FIG. 9, the y direction and the y1 direction are parallel to the width direction of the intermediate transfer belt 12a. Therefore, the extension direction of the groove 83 is parallel to the direction from the back to the front of the paper. As shown in FIG. 9, the light output from the LED 35 passes through the first opening 40 and enters the first lens portion 43. The light that enters the first lens portion 43 passes through the flat portion 32a, which is a part of the upper surface of the cover member 32, and enters the surface of the intermediate transfer belt 12a. This incident light is expressed as a first irradiation light 46. As shown in FIG. 9, the first irradiated region 47 is an irradiated region of the first irradiation light 46 for detecting diffuse reflection light.

[0053] The housing 33 is made of black resin. This reduces stray light. The cover member 32 is made of transparent resin (translucent resin). The refractive index of the cover member 32 is different from the refractive index of the space in front of and behind the cover member 32. Therefore, the first irradiation light 46 is refracted by the surface of the first lens portion 43 and the flat portion 32a and is irradiated to the first irradiated region 47. The material of the cover member 32 is set to polystyrene with a refractive index of 1.59, for example. The lens radius of the first lens portion 43 is designed so that the light emitting chip 35a is located at the focal point of the first lens portion 43. Therefore, the first irradiation light 46 incident on the first lens portion 43 becomes approximately parallel light and is irradiated to the intermediate transfer belt 12a.

[0054] As shown in FIG. 9, the first opening 40 and the first lens portion 43 are disposed at a position shifted to the right (in the +y1 direction) of a perpendicular line from the LED 35 to the rotation axis of the drive roller 12b. The perpendicular line is parallel to the normal line of the circuit board 34. The first irradiation light 46 is also a light ray that travels in a direction inclined to the right of this perpendicular line. As shown in FIG. 9, an irradiation angle θD1 is defined here. The irradiation angle θD1 of the first irradiation light 46 is, for example, -25°. Here, the irradiation angle is defined as - and the reflection angle as +, but + and - are omitted when the magnitude of the angle is of interest.

[0055] 9, a first light receiving area 48, which is an area in which the first light receiving unit 36 ​​can receive reflected light, is an area from point 48a to point 48b. Point 48a is a point obtained by extending a line connecting the left corner 36a of the first light receiving unit 36 ​​to the upper right corner 41b of the second opening 41 along the light guide path. Point 48b is a point obtained by extending a line connecting the right corner 36b of the first light receiving unit 36 ​​to the lower left corner 41c of the second opening 41 along the light guide path.

[0056] 9 and other figures, the first irradiated area 47 is smaller than the first light-receiving area 48. Therefore, the range that the first light-receiving unit 36 ​​can detect is actually the first irradiated area 47. In other words, the first light-receiving unit 36 ​​for detecting diffusely reflected light detects the diffusely reflected light from the first irradiated area 47.

[0057] 10. Optical path for detecting specularly reflected light As shown in FIG. 9, the housing 33 is provided with a third opening 42 for irradiating the intermediate transfer belt 12a with light. The cover member 32 is provided with a third lens portion 45 for irradiating the intermediate transfer belt 12a with light, separate from the first lens portion 43. The light output from the LED 35 passes through the third opening 42 and enters the third lens portion 45. The light that enters the third lens portion 45 passes through a flat portion 32a provided on the upper surface of the cover member 32 and enters the surface of the intermediate transfer belt 12a. This incident light is referred to as a second irradiation light 49. The second irradiated region 50 is an area where the second irradiation light 49 is irradiated to detect the specular reflection light. The lens radius of the third lens portion 45 is designed so that the light emitting chip 35a is located at the focus of the third lens portion 45. Therefore, the second irradiation light 49 that enters the third lens portion 45 becomes substantially parallel light and is irradiated onto the intermediate transfer belt 12a.

[0058] As shown in Fig. 9, the third opening 42 and the third lens portion 45 are disposed at a position shifted to the left (-y direction) with respect to the perpendicular line to the LED 35. In Fig. 9, the second irradiation light 49 is a light beam inclined to the left with respect to the perpendicular line. Here, the irradiation angle of the second irradiation light 49 is defined as θS1. The irradiation angle θS1 of the second irradiation light 49 is, for example, -19.1°.

[0059] 9, the second light receiving area 51, which is the range in which the second light receiving unit 37 can receive light, is the range from point 51a to point 51b. Point 51a is an extension of a line connecting the left corner 37a of the second light receiving unit 37 to the lower right corner 41d of the second opening 41. Point 51b is an extension of a line connecting the right corner 37b of the second light receiving unit 37 to the upper left corner 41a of the second opening 41.

[0060] 9, the dimensions of the second irradiated region 50 are smaller than the dimensions of the second light receiving region 51. As a result, the substantial range in which the second light receiving unit 37 can detect light is the second irradiated region 50. In other words, the second light receiving unit 37 detects the specularly reflected light from the second irradiated region 50.

[0061] 11. Diffraction light caused by light irradiated by the toner sensor Fig. 10 shows the optical path of the diffracted light of the first irradiation light 46 as viewed from the downstream side in the transport direction of the intermediate transfer belt 12a. Fig. 11 shows the optical path of the diffracted light of the second irradiation light 49 as viewed from the downstream side in the transport direction of the intermediate transfer belt 12a. The interval d between the grooves 83 of the intermediate transfer belt 12a is 3.7 μm, and the wavelength λ of the LED 35 is 850 nm. The distance between the intermediate transfer belt 12a and the circuit board 34 of the optical sensor 31 is 11.5 mm. The distance between the intermediate transfer belt 12a and the flat portion 32a of the cover member 32 is 5.5 mm.

[0062] The diffraction angle of the diffracted light caused by the second irradiation beam 49 shown in Fig. 11 can be calculated by replacing the irradiation angle θi in Equation 2 with θS1 (θS1 = -19.1°). When the diffraction angle is calculated when m = -1, 0, +1, the diffraction angle shown in Fig. 12(B) is obtained.

[0063] As can be seen from the diffracted light beams shown in FIG. 11, in the optical sensor 31, when the range that the second light receiving unit 37 can detect is limited to the second irradiated region 50, the high-intensity low-order (±1st order) diffracted light is less likely to enter the second light receiving unit 37. As shown in FIG. 9 and FIG. 11, the third opening 42 is a light exit port of a through hole (light guide path) that penetrates the housing 33. Furthermore, the shape of this through hole is approximately a truncated cone or a tapered shape. As an example, the inclination of the through hole is 30° with respect to the horizontal plane (plane parallel to the surface of the circuit board 34). Moreover, the depth of the through hole is, for example, 0.2 mm. Such thinning of the light guide path makes it possible to limit the angle of incidence of the second irradiation light 49 in the second irradiated region 50. In other words, although the parallel light from the LED 35 enters as the second irradiation light 49, the wall reflection light generated by reflection on the wall surface of the third opening 42 is less likely to occur. When the wall reflected light is less likely to occur, the second irradiated area 50 (spot radius) is less likely to expand.

[0064] The diffracted light caused by the first irradiation light 46 detected by the first light receiving unit 36 ​​is calculated by replacing the irradiation angle θi in Equation 2 with θD1 (θD1=-25°). As shown in Figs. 10 and 12(A), the orders of the diffracted light that are about to enter near the first light receiving unit 36 ​​are -6th, -5th, and -4th orders. In particular, -5th order diffracted light may be incident on the first light receiving unit 36. The amount of diffusely reflected light is small compared to specularly reflected light, and the amount of higher order diffracted light is small. Therefore, the optical sensor 31 of this embodiment is not easily affected by these factors. 12. Comparison of detection performance of optical sensors 13 shows an example of an optical sensor 31' of a comparative example. The structure of the optical sensor 31' is the same as that of the optical sensor 31, except for the shape of the housing 33. Therefore, a description of the points common to both will be omitted.

[0065] In the optical sensor 31', the shape of the first opening 40 and the shape of the third opening 42 provided in the housing 33 are different from those in the optical sensor 31. Specifically, the first opening 40 is a cylindrical through hole perpendicular to the circuit board 34. The third opening 42 is also a cylindrical through hole perpendicular to the circuit board 34. The hatched wall 52 is the inner side surface of the through hole. The wall surface reflected light 53 generated by the wall 52 is incident on the intermediate transfer belt 12a. Due to the presence of the wall surface reflected light 53, the area of ​​the second irradiated area 50' in the comparative example is larger than the second irradiated area 50 in the embodiment. If the intermediate transfer belt 12a does not have a fine uneven surface, diffracted light is not generated, so the expansion of the irradiated area does not affect the second light receiving unit 37. Therefore, the diffuse reflection component only increases slightly. In the case of the intermediate transfer belt 12a having a fine unevenness treatment, the wall reflected light 53 is diffracted by the intermediate transfer belt 12a, generating +1-order diffracted light with a strong light intensity. Furthermore, this low-order diffracted light is incident on the second light receiving unit 37. Therefore, the optical sensor 31' of the comparative example cannot correctly measure the toner amount or the position of the toner image, as compared to the embodiment. On the other hand, the optical sensor 31 of the embodiment can correctly measure the toner amount or the position of the toner image.

[0066] 13. Effects of Example 1 (Effect on registration control) FIG. 14(A) shows the detection result of the pattern 30a in the embodiment. FIG. 14(B) shows the detection result of the pattern 30a in the comparative example. The horizontal axis indicates time. The vertical axis indicates the output of each sensor. The pattern 30a is a 2 mm wide toner image tilted at 45° with respect to the width direction (y direction) of the intermediate transfer belt 12a. The pattern 30a was formed with 100% image density for each color of Y, M, C, and K. When the output is less than the threshold, the controller 29 determines that the leading edge of the pattern 30a has been detected. Furthermore, when the output is equal to or greater than the threshold, the controller 29 determines that the trailing edge of the pattern 30a has been detected. The controller 29 recognizes the midpoint (indicated by a circle in the figure) between the timing at which the leading edge is detected and the timing at which the trailing edge is detected as the pattern position of each color. The reference color when calculating the color shift amount is K. The controller 29 calculates the relative color shift amount between the reference color and the other colors Y, M, and C. In the optical sensor 31 of the embodiment, the detected waveform of the pattern 30a is symmetrical, whereas the detected waveform of the optical sensor 31' of the comparative example is asymmetrical.

[0067] Fig. 15(A) shows the state when one pattern 30a passes through the optical sensors 31, 31'. Fig. 15(B) shows the reflected light intensity distribution in the width direction (y direction) for the second irradiated region 50 of the embodiment. Fig. 15(C) shows the reflected light intensity distribution in the width direction (y direction) for the second irradiated region 50' of the comparative example.

[0068] As shown in Fig. 15(B), the reflected light intensity distribution of the embodiment is symmetrical. As shown in Fig. 15(C), the reflected light intensity distribution of the comparative example is asymmetrical. Furthermore, in the comparative example, there is also a step in the reflected light intensity distribution. In the comparative example, the left-right difference and step in the reflected light intensity distribution affect the detection of the leading and trailing ends of the pattern 30a.

[0069] In this way, the optical sensor 31' of the comparative example is affected by the waveform distortion, and therefore the detection accuracy of the position of the pattern 30a is reduced. On the other hand, the optical sensor 31 of the embodiment has improved detection accuracy of the position of the pattern 30a.

[0070] (Effect on concentration control) FIG. 16(A) shows the detection results of pattern 30b by optical sensors 31, 31'. The detection results include the detection results of specularly reflected light by second light receiving unit 37 and the detection results of diffusely reflected light by first light receiving unit 36. The horizontal axis indicates image density. The vertical axis indicates sensor output value. The image densities of pattern 30b are 0%, 20%, 40%, 60%, 80%, and 100%. There is no difference in the detection results of diffusely reflected light between optical sensors 31 and 31'.

[0071] The optical sensor 31' of the comparative example receives diffracted light generated in a place other than the irradiated area 50 for detecting the regular reflection light. Therefore, when the optical sensor 31' receives the reflected light from the intermediate transfer belt 12a, the sensor output value of the optical sensor 31' becomes high. On the other hand, when detecting the patterns 30b with image densities of 20%, 40%, 60%, 80%, and 100%, the toner hides the grooves 83. Therefore, both of the optical sensors 31 and 31' are less susceptible to the influence of diffracted light. According to FIG. 16(A), the sensor output value of the pattern 30b with an image density of 100% is larger than the sensor output value of the pattern 30b with an image density of 80%. The reason for this is that as the amount of toner hiding the intermediate transfer belt 12a increases, the intensity of the diffuse reflection light generated on the toner surface increases. The controller 29 may subtract the output value of the first light receiving unit 36 ​​of the optical sensor 31 from the output value of the second light receiving unit 37. This makes it possible to reduce the component of diffusely reflected light that enters the second light receiving unit 37.

[0072] Fig. 16(B) shows the toner amount calculated from the detection results of pattern 30b by optical sensors 31 and 31'. The horizontal axis shows image density. The vertical axis shows toner amount. As Fig. 16(B) shows, there is a difference in the detection results of the toner amount in the low density range between the embodiment and the comparative example.

[0073] Even in the optical sensor 31' of the comparative example, if the amount of diffracted light incident on the second light receiving unit 37 is constant, the controller 29 will be able to correct the toner amount using the conversion table. However, the unevenness on the surface of the intermediate transfer belt 12a changes depending on the usage time of the intermediate transfer belt 12a. This is because the depth of the grooves 83 changes when the surface layer of the intermediate transfer belt 12a is worn by the cleaning blade 22a or paper. If the convex parts of the intermediate transfer belt 12a are smooth and the shape of the grooves 83 (concave parts) is close to a rectangle, the multiple grooves 83 can function as a laminar diffraction grating. The diffraction efficiency of the laminar diffraction grating changes depending on the depth of the grooves 83 and the duty ratio (groove width relative to the groove period). When the convex parts on the surface of the intermediate transfer belt 12a are worn, the grooves 83 become shallower and the diffracted light decreases.

[0074] FIG. 17 shows the relationship between the depth of groove 83 and the sensor output value. The horizontal axis indicates the depth of groove 83. The vertical axis indicates the sensor output value. As groove 83 becomes shallower, the amount of specularly reflected light increases and the amount of diffusely reflected light decreases. If the depth of groove 83 could be measured accurately, it might be possible to estimate the amount of diffracted light mixed in. However, it is difficult to measure the depth of groove 83 accurately. Therefore, it would be difficult to detect the amount of toner taking the amount of diffracted light mixed in into account.

[0075] According to this embodiment, the angle of incidence of the irradiated light output from the light source and incident on the irradiated area is limited by the shape of the housing 33. In particular, light reflected by the side wall (wall 52) of the through hole extending from the third opening 42 of the irradiated light toward the light source is unlikely to enter the second light receiving unit 37. This allows the optical sensor 31 to accurately detect the measurement object even if the surface of the measurement object has a fine uneven shape. For example, it becomes possible to accurately detect the position and density of a toner image formed on an intermediate transfer body or image carrier having a plurality of grooves.

[0076] In the first embodiment, the angle of incidence of the irradiation light is limited by the shape of the housing, but a housing shape that makes the light receiving area 51 smaller than the irradiated area 50 may be adopted. In the first embodiment, the second irradiation light 49 and the first irradiation light 46 are parallel lights for convenience of explanation. However, the second irradiation light 49 and the first irradiation light 46 may be convergent lights.

[0077] The second opening 41 is used both as an opening for detecting diffusely reflected light and an opening for detecting specularly reflected light. However, the opening for detecting diffusely reflected light and the opening for detecting specularly reflected light may be provided independently in the housing 33.

[0078] The second lens unit 44 is used as a lens for detecting diffusely reflected light from the intermediate transfer belt 12a and as a lens for detecting regularly reflected light. However, these may be independent lenses. In addition, although the first lens unit 43 and the third lens unit 45 are independent, they may be realized by an integrated lens.

[0079] In the first embodiment, the first light receiving unit 36 ​​and the second light receiving unit 37 are described as each having a plurality of light receiving elements. However, when the first light receiving unit 36 ​​and the second light receiving unit 37 can each detect light sufficiently, each may be realized by a single light receiving element.

[0080] <Example 2> In the first embodiment, the incident angle of the irradiated light is limited by the shape of the housing 33, thereby maintaining the area of ​​the irradiated area 50 at an appropriate area or less. There are other methods for limiting the area of ​​the irradiated area 50 to an appropriate area or less. For example, by further limiting the light emission range of the light source, the intensity distribution of the irradiated light in the width direction of the intermediate transfer belt 12a becomes symmetrical and sharp. The only difference between the first embodiment and the second embodiment is the configuration of the LED 35.

[0081] 9, the LED 35 has a light emitting chip 35a and a light transmitting member 35b surrounding the light emitting chip 35a. The light output from the light emitting chip 35a is scattered at the boundary surface of the light transmitting member 35b, so that the light is emitted from the entire surface of the light transmitting member 35b. In the second embodiment, the areas of the light emitting chip 35a and the light transmitting member 35b (particularly the dimension in the y direction) are smaller than those in the first embodiment. As a result, the incident angle of the second irradiation light 49 is limited, and the second irradiated region 50 is also smaller.

[0082] Fig. 18(A) shows the light quantity distribution in the second irradiated region 50 for the LED 35 of Example 2. Fig. 18(B) shows the light quantity distribution in the second irradiated region 50 for the LED 35 of Example 1. Fig. 18(C) shows the chip width of the LED 35 and the width of the light transmitting member 35b. Here, a visible light LED of the same type as the LED 35 was used, and light was irradiated onto the surface of the intermediate transfer belt 12a. The light quantity distribution (image intensity) was obtained by photographing the image with a digital camera.

[0083] 18(A) and 18(B), the overall width of the second irradiated region 50 in Example 2 is narrower than the overall width of the second irradiated region 50 in Example 1. In addition, the width at the center of the second irradiated region 50 in Example 2 is also narrower than the width at the center of the second irradiated region 50 in Example 1. The ratio of the skirt intensity to the maximum intensity in Example 2 is lower than the ratio of the skirt intensity to the maximum intensity in Example 1.

[0084] Therefore, the LED 35 of the second embodiment is advantageous in that it limits the incident angle of the light emitted from the light source and reduces the amount of light in the peripheral part relative to the center of the light emitted. That is, the risk of receiving diffracted light is further reduced in the second embodiment than in the first embodiment. The second light receiving unit 37 of the second embodiment can accurately detect the regular reflection component, so that the detection accuracy of the optical sensor 31 of the second embodiment is improved.

[0085] In this way, by reducing the chip width of the LED 35 and the width of the light transmitting member 35b, the incident angle of the irradiated light is limited and the light intensity distribution becomes sharper, which makes it possible to accurately detect the position and amount of toner on the image carrier having a fine uneven shape.

[0086] <Example 3> 14. Toner sensor configuration Next, the third embodiment will be described in detail with reference to Figs. 19 to 22. Fig. 19(A) is a schematic perspective view showing the optical sensor 31 after assembly is completed. Fig. 19(B) is a schematic perspective view (exploded view) showing the optical sensor 31 before assembly. In the third embodiment, x1, y1, and z1 also indicate directions (axes) based on the optical sensor 31. That is, the x1 direction is the short side direction of the optical sensor 31. The y1 direction is the long side direction of the optical sensor 31. The z1 direction is the height direction of the optical sensor 31 (the normal direction of the circuit board 34).

[0087] 20(A) to 20(D) are diagrams showing the optical path of the optical sensor 31 and its arrangement. In particular, FIG. 20(A) is a schematic cross-sectional view (left side cross-sectional view) of the optical sensor 31 when viewed from the negative side to the positive side of the y1 axis. FIG. 20(B) is a plan view (top view) of the optical sensor 31 when viewed from the positive side to the negative side of the z1 axis. Similarly, FIG. 20(C) is a schematic cross-sectional view (right side cross-sectional view) of the optical sensor 31 when viewed from the positive direction to the negative direction of the y1 axis. FIG. 20(D) is a schematic cross-sectional view (front cross-sectional view) of the optical sensor 31 when viewed from the positive direction to the negative direction of the x1 axis.

[0088] A major difference between the third embodiment and the first and second embodiments is that an L-shaped arrangement is adopted. Here, the L-shaped arrangement means that the LED 35 and the second light receiving unit 37 are arranged on a line substantially parallel to the x1 direction, while the first light receiving unit 36 ​​and the second light receiving unit 37 are arranged on a line substantially parallel to the y1 direction, as shown in FIG. 20(B). Therefore, in the x1 direction, the position of the rotation axis of the driving roller 12b and the position of the LED 35 are shifted. In the x1 direction, the second light receiving unit 37 is arranged on the opposite side of the LED 35 across the rotation axis of the driving roller 12b (or the line projected onto the circuit board 34).

[0089] 19(B), a first opening 40, a second opening 41, a third opening 42, and a fourth opening 54 are provided in the upper part of the housing 33. A first lens portion 43, a second lens portion 44, a third lens portion 45, and a fourth lens portion 55 are provided in the cover member 32 attached to the top of the housing 33.

[0090] As shown in Figures 20(B) and 20(C), the first irradiation light 46 travels from the LED 35 toward the intermediate transfer belt 12a. The first opening 40 and the first lens portion 43 form a part of a light guide path through which the first irradiation light 46 passes. As shown in Figures 20(A) and 20(B), the second irradiation light 49 travels from the LED 35 toward the intermediate transfer belt 12a. The third opening 42 and the third lens portion 45 form a part of a light guide path through which the second irradiation light 49 passes.

[0091] As shown in Figure 20(C) and other figures, the second opening 41 and the second lens portion 44 form part of a light guide path through which reflected light passes from the first light receiving area 48 on the intermediate transfer belt 12a toward the first light receiving unit 36.

[0092] As shown in Figure 20(A) and other figures, the fourth opening 54 and the fourth lens portion 55 form part of another light guide path through which reflected light passes from the second light receiving area 51 of the intermediate transfer belt 12a toward the second light receiving unit 37.

[0093] 20(A) and 20(C), the housing 33 is provided with a light-shielding wall 38. This prevents the light from the LED 35 from directly entering the first light-receiving unit 36 ​​and the second light-receiving unit 37.

[0094] 15. Optical path for detecting diffusely reflected light As shown in FIG. 20C, the first irradiated region 47 is located at a position deviated from the point 56. Here, the point 56 is a point on a cylindrical surface formed by the intermediate transfer belt 12a being wound around the drive roller 12b, and is a part of a line segment in which the distance between the intermediate transfer belt 12a and the optical sensor 31 is the shortest in the z1 direction. The first opening 40 and the first lens unit 43 are arranged so that the first irradiated region 47 is located at a position deviated from the point 56. In other words, the size, optical characteristics, and position of the first opening 40 and the first lens unit 43 are designed so that the first irradiation light 46 irradiates a position deviated from the point 56. In FIG. 20C, the irradiation angle θ D2x = 14° is defined. Irradiation angle θ D2x is the x1-direction component of the angle formed by the first irradiation light 46 and a straight line connecting the rotation axis of the driving roller 12b and the center of the first irradiated area 47. This straight line may be understood as a normal line of the first irradiated area 47 that passes through the center of the first irradiated area 47.

[0095] The first light receiving region 48 is a detection region of the first light receiving unit 36. The first light receiving region 48 is larger than the first irradiated region 47. The first light receiving region 48 is disposed so as to encompass the entire area of ​​the first irradiated region 47.

[0096] 20D, as the first irradiation light 46 approaches the intermediate transfer belt 12a, it moves away from the second irradiation light 49. In other words, the y1-direction component of the irradiation angle of the first irradiation light 46 does not match the y1-direction component of the irradiation angle of the second irradiation light 49. Here, the irradiation angle θ D2y =39° is defined.

[0097] The second opening 41 and the second lens portion 44 are arranged so that the first light receiving region 48 encompasses the entire area of ​​the first irradiated region 47. In other words, the position and size of the first light receiving region 48 depend on the position and size of the second opening 41, as well as the position, size, and optical characteristics (e.g., focal length) of the second lens portion 44.

[0098] 20(D), the light entrance surface of first lens portion 43 is configured to be a convex spherical surface. Similarly, the light exit surface of second lens portion 44 is also configured to be a convex spherical surface. In this manner, first lens portion 43 and second lens portion 44 each have a curved surface that is convex in the -z1 direction.

[0099] In the third embodiment, the first lens portion 43 is designed so that the focal length of the first lens portion 43 is slightly greater than the distance between the first lens portion 43 and the LED 35. Therefore, the first irradiation light 46 becomes weakly divergent light by passing through the first lens portion 43. For example, the radius of the spherical surface of the first lens portion 43 is designed to be R2.5 mm. In order to make the area of ​​the first light receiving region 48 greater than the area of ​​the first irradiated region 47, the second lens portion 44 is designed so that the focal length of the second lens portion 44 is greater than the distance between the second lens portion 44 and the first light receiving unit 36. For example, the radius of the spherical surface of the second lens portion 44 is designed to be R4.0 mm.

[0100] By designing the optical characteristics and arrangement of each lens in this way, the first light receiving unit 36 ​​can stably detect the diffusely reflected light from the toner. For example, there may be cases where the mounting positions of the LED 35 and the first light receiving unit 36 ​​are misaligned, or where there is a tolerance in size or position regarding the opening or lens portion. In such cases, the optical sensor 31 of the third embodiment can detect the diffusely reflected light with high accuracy.

[0101] In the third embodiment, the radius of the first lens portion 43 is designed so that the first irradiation light 46 becomes weakly divergent light, but this is merely an example. The focal length of the first lens portion 43 may be designed to be equal to the distance from the LED 35, and the first irradiation light 46 may be designed to become parallel light. Alternatively, the radius of the first lens portion 43 may be designed to be smaller than R2.5 mm so that the first irradiation light 46 becomes convergent light.

[0102] 16. Optical path for detecting specularly reflected light 20A, the third opening 42 and the third lens unit 45 are disposed so that the approximate center of the second irradiated region 50 coincides with point 57. Here, point 57 is a point on a cylindrical surface formed by the intermediate transfer belt 12a being wound around the drive roller 12b, and is a part of a line segment where the distance between the intermediate transfer belt 12a and the optical sensor 31 is the shortest in the z1 direction. S2x = 15° is defined. Irradiation angle θ S2x is the x1-direction component of the angle formed by the second irradiation light 49 and the normal line of the second irradiated area 50 that passes through the point 57. In FIG. 20(A), this normal line may be understood as a straight line that passes through the rotation axis of the driving roller 12b and the point 57.

[0103] As shown in FIG. 19(B), the third lens portion 45 is a convex cylindrical lens having a radius in the y1z1 plane and a central axis extending in the x1 direction. For example, the radius of the third lens portion 45 is set to R3 mm. The third opening 42 is also rectangular so that the second irradiated area 50 is approximately rectangular (rectangle in the third embodiment). For example, the size of the third opening 42 is designed to be 0.5 mm×0.7 mm (length in the x1 direction×length in the y1 direction).

[0104] 20(A), 20(B), and 20(D), the second light receiving region 51 is a region detectable by the second light receiving unit 37. The approximate center of the second light receiving region 51 coincides with point 57. The area and position of the second irradiated region 50 are designed so that the second irradiated region 50 encompasses the entire area of ​​the second irradiated region 50. The position and size of the fourth opening 54 and the position, size, and optical characteristics (e.g., focal length) of the fourth lens portion 55 are designed so that such conditions are satisfied.

[0105] As shown in FIG. 19(B), the fourth lens portion 55 is also a cylinder lens. The radius of this cylinder lens also exists in the y1z1 plane (strictly speaking, a plane parallel to the y1z1 plane). For example, the radius of the fourth lens portion 55 is designed to be R2.3 mm. The central axis of the cylinder lens extends parallel to the x1 direction. The fourth opening 54 is also rectangular. For example, the fourth opening 54 is designed to be 1.2 mm x 1.5 mm (length in the x1 direction x length in the y1 direction).

[0106] 20D, the third opening 42 and the third lens portion 45 are arranged so that the second irradiation light 49 apparently travels along the normal direction of the circuit board 34 and is incident on the surface of the intermediate transfer belt 12a. S2y = 0°. In other words, the second irradiation light 49 does not travel in the y1 direction. As shown in Fig. 20(A), the traveling direction of the second irradiation light 49 is actually tilted relative to the normal direction of the circuit board 34. In other words, the second irradiation light 49 is parallel to the x1z1 plane but tilted relative to the y1z1 plane.

[0107] The position and size of the second light receiving region 51 are designed so that the second light receiving region 51 also encompasses the entire second irradiated region 50. In other words, the fourth opening 54 and the fourth lens portion 55 are designed so that the second light receiving unit 37 can detect an area wider than the second irradiated region 50.

[0108] The third lens portion 45 is designed so that the focal length of the third lens portion 45 is slightly greater than the distance between the third lens portion 45 and the LED 35. Therefore, the second irradiation light 49 becomes weakly divergent light by passing through the third lens portion 45. The radius of the fourth lens portion 55 is designed so that the focal length of the fourth lens portion 55 is equal to the distance between the fourth lens portion 55 and the second light receiving unit 37.

[0109] There may be a deviation in the mounting positions of the LED 35 and the second light receiving unit 37, or a tolerance in the size or position of the opening or the lens portion. However, in the third embodiment, the second light receiving area 51 is larger than the second irradiated area 50, so that the second light receiving unit 37 can stably detect the second irradiated area 50.

[0110] 17. Optical path of diffracted light of first irradiation light The following describes in detail the diffracted light from the intermediate transfer belt 12a caused by the first irradiation light 46. Figures 21(A) and 21(B) show the optical path of the diffracted light caused by the first irradiation light 46. In particular, Figure 21(A) is a schematic cross-sectional view of the optical sensor 31 when viewed from the positive side to the negative side of the x1 axis. Figure 21(B) is a schematic cross-sectional view of the optical sensor 31 when viewed from the positive side to the negative side of the y1 axis.

[0111] As described with reference to FIG. 4A, the grooves formed in the intermediate transfer belt 12a are formed along the circumference of the cylindrical surface. In other words, a plurality of grooves are arranged parallel to the x1z1 plane or the rotation direction of the intermediate transfer belt 12a. As shown in FIG. 21A, a plurality of diffracted lights of different orders travel toward different positions in the y1 direction. In FIG. 21A, the first irradiation light 46 is inclined to the right, and the irradiation angle is θ D2y= 39°. Therefore, the reflected light generated by the intermediate transfer belt 12a also travels with an inclination to the right (the reflection angle of the zeroth-order diffracted light (specular reflection light) is -39°). As a result, the zeroth-order diffracted light of the first irradiation light 46 travels in a direction away from the second lens unit 44 and the second opening 41, which are part of the light guide path for receiving light. Focusing on the mth-order diffracted light (m = -1, +1, -2, -3), the mth-order diffracted light also travels with an inclination to the right. In other words, the mth-order diffracted light travels in a direction away from the second lens unit 44 and the second opening 41. Therefore, in the configuration of the third embodiment, theoretically, the low-order diffracted light of at least m = -3 or less of the first irradiation light 46 is not detected by the first light receiving unit 36.

[0112] 21B, the first irradiation light 46 is incident on the intermediate transfer belt 12a having a substantially cylindrical shape at a point 58 deviated to the left from a point 56 at an angle θ D2x =15°. Therefore, the zeroth-order diffracted light travels tilted to the left (reflection angle of -15°). That is, also in FIG. 21(B), the zeroth-order diffracted light of the first irradiation light 46 travels in a direction away from the second lens portion 44 and the second opening 41. The mth-order diffracted light (m=-1, +1, -2, -3) shown in FIG. 21(A) also travels in a direction away from the second lens portion 44 and the second opening 41. Therefore, in theory, the low-order diffracted light is not detected by the first light receiving unit 36.

[0113] The first light receiving unit 36 ​​is an element that detects diffusely reflected light from the surface of the toner, which is a test patch on the intermediate transfer belt 12a. In order to realize a highly accurate optical sensor 31, the amount of diffracted light from the intermediate transfer belt 12a that enters the first light receiving unit 36 ​​should be reduced as much as possible. As described above, the diffracted light from the first irradiation light 46 in the third embodiment is less likely to enter the first light receiving unit 36, so that the diffusely reflected light from the toner surface can be detected with high accuracy.

[0114] The specular reflection light and the diffracted light originating from the first irradiation light 46 travel in a direction away from the second light receiving unit 37 as shown in FIG. 21(B). Therefore, these lights are less likely to enter the second light receiving unit 37. The second light receiving unit 37 is a light receiving unit that detects the specular reflection light irradiated to the second light receiving region 51. Therefore, the reflection light and the diffracted light originating from the first irradiation light 46 should not be detected by the second light receiving unit 37. According to the third embodiment, the reflection light and the diffracted light originating from the first irradiation light 46 are less likely to be detected by the second light receiving unit 37.

[0115] 18. Optical Path of Diffracted Light of Second Irradiation Light Hereinafter, the diffracted light from the intermediate transfer belt 12a generated by the second irradiation light 49 will be described in detail. FIGS. 22(A) and 22(B) show the optical paths of the diffracted light generated by the second irradiation light 49. In particular, FIG. 22(A) is a schematic cross-sectional view of the optical sensor 31 when viewed from the minus side to the plus side of the y1 axis. FIG. 22(B) is a schematic cross-sectional view of the optical sensor 31 when viewed from the plus side to the minus side of the x1 axis.

[0116] As described with reference to FIG. 4(A), the grooves formed in the intermediate transfer belt 12a are substantially parallel to the circumference of the cylindrical surface in FIG. 22(A) (the rotation direction of the intermediate transfer belt 12a). That is, in the y1 direction shown in FIG. 22(B), a plurality of grooves are arranged. Therefore, a plurality of diffracted lights traveling toward different positions in the y1 direction are generated. As described above, in FIG. 22(A), the second irradiation light 49 is incident on the intermediate transfer belt 12a at an irradiation angle of θ S2x = 15° centered on the point 57. Therefore, all diffracted lights from the 0th order to the ±2nd order are reflected at an angle of -15°. As shown in FIG. 22(B), the second irradiation light 49 appears to be incident on the intermediate transfer belt 12a along the normal direction of the intermediate transfer belt 12a. Therefore, the ±1st order diffracted light and the ±2nd order diffracted light travel in a seemingly symmetric manner, respectively. That is, the +n-th order diffracted light and the -n-th order diffracted light form a pair.

[0117] In the third embodiment, only the zeroth-order diffracted light is incident on the fourth opening 54. Therefore, the second light receiving unit 37 does not detect the ±1st-order or higher diffracted light.

[0118] The diffracted light originating from the second irradiation light 49 does not enter the first light receiving unit 36. This is because the housing 33 is configured to block part of the -1st order diffracted light and the -2nd order diffracted light of the second irradiation light 49. The first light receiving unit 36 ​​is not disposed on the extension of the diffracted light that is not blocked here. Therefore, the first light receiving unit 36 ​​does not erroneously detect the diffracted light originating from the second irradiation light 49.

[0119] Next, the reason why only the zeroth-order diffracted light is incident on the fourth opening 54 in the third embodiment will be described in more detail. The second irradiation light 49 is irradiated onto the surface of the intermediate transfer belt 12a through the third lens unit 45, which is a cylindrical lens. Therefore, as shown in FIG. 20B, the spot shape of the second irradiation light 49 is wide in the x1 direction and narrow in the y1 direction. As described above, the radius of the third lens unit 45 is set to R3 mm so that the second irradiation light 49 becomes a slightly divergent light compared to a parallel light. Furthermore, the length of the third opening 42 in the y1 direction is set to 0.7 mm, which is a very small value. Therefore, the irradiation range of the second irradiation light 49 becomes a very small range in the y1 direction, and the irradiation angle of the second irradiation light 49 becomes a relatively uniform irradiation angle. In other words, the angular distribution of the irradiation angle of the second irradiation light 49 becomes narrow.

[0120] On the other hand, the radius of fourth lens portion 55 is set to a small value (R2.3 mm). Therefore, the zeroth order diffracted light passing through the center of the circle of fourth lens portion 55 enters fourth aperture 54. The ±1st order and ±2nd order diffracted light passing through a position away from the center of the circle of fourth lens portion 55 travel in a direction away from fourth aperture 54. Therefore, theoretically, only the zeroth order diffracted light is incident on second light receiving unit 37.

[0121] In the third embodiment, the radius of the third lens portion 45 is set to R3 mm. The radius of the fourth lens portion 55 is set to R2.3 mm, for example. When the radius of the third lens portion 45 and the radius of the fourth lens portion 55 are each set to R2.3 mm, the second irradiation light 49 and the reflected light become completely parallel light, and the above-mentioned effect can be obtained in this case as well. The above-mentioned effect can be obtained even when the radius of the third lens portion 45 is set to R2.3 mm and the radius of the fourth lens portion 55 is set to R3 mm.

[0122] 19. Technical Concept of Example 3 First, the irradiation area of ​​the irradiation light is small and the distribution of the irradiation angle is relatively narrow. Ideally, the irradiation light is parallel light.

[0123] The second point is that a light receiving area that provides a sufficient amount of received light is ensured even if tolerances and variations in mounting occur during the mass production process of the optical sensor 31. However, the area of ​​the light receiving area may be ensured to be the minimum necessary. Furthermore, the lens may be designed so that the irradiated light becomes weakly divergent light by passing through the lens.

[0124] As shown in FIG. 22B, the second irradiation light 49 is irradiated onto the intermediate transfer belt 12a so as to be parallel to the normal direction of the intermediate transfer belt 12a. The longitudinal direction of the circuit board 34 on which the LED 35, the first light receiving unit 36, and the second light receiving unit 37 are mounted is also disposed substantially parallel to the y1 direction. The second light receiving unit 37 may be disposed so that the optical axis of the specularly reflected light (zeroth-order diffracted light) passes through the center of the second light receiving unit 37, the shape of the spot of the specularly reflected light is symmetrical with respect to the center, and the amount of light in the spot is uniform. As a result, even if mounting variations or tolerances occur, the performance of the optical sensor 31 is sufficiently ensured.

[0125] As shown in FIG. 22B, the second irradiation light 49 travels along the direction approximately normal to the circuit board 34 so that a plurality of diffracted lights generated by the diffraction of the second irradiation light 49 on the surface of the intermediate transfer belt 12a travel toward different positions in the y1 direction. That is, the second irradiation light 49 travels parallel to the x1z1 plane. However, even if the LED 35 is arranged on the circuit board 34 shifted to either the positive side or the negative side of the y1 axis, the above effect can be obtained. More specifically, even if the incident angle of the second irradiation light 49 is inclined by about 5° from the normal to the irradiated surface, the above effect can be obtained. Note that, when the second irradiation light 49 is inclined by about 5° with respect to the normal to the irradiated surface, the parallelism of the LED 35 and the second light receiving unit 37 with respect to the x1 direction in FIG. 20B is lost. In the third embodiment, the LED 35 and the second light receiving unit 37 are inclined by about 29° with respect to the x1 direction. However, an inclination of about 30° will not hinder the above effect.

[0126] As described above, the second irradiation light 49 is assumed to have a small variation in irradiation angle and is ideally a parallel light, but this is only an example. The distribution of the irradiation angle may be as wide as about 5°. In the third embodiment, the received light is assumed to be a weakly divergent light and is ideally a parallel light. However, this is only an example. The distribution of the reflection angle may vary by about 5°.

[0127] Here, in Example 3, the position and refractive index of first lens portion 43 are designed so that the focal length of first lens portion 43 is slightly longer than the distance between first lens portion 43 and LED 35. In other words, the radius of first lens portion 43 is set so that the focal point of first lens portion 43 approximately coincides with the position of the light emitting element. Therefore, the light emitted from first lens portion 43 becomes weakly divergent light.

[0128] In the third embodiment, the irradiation angle θ S2x Although a case where the irradiation angle is 15° is introduced, this is only one example. S2x The irradiation angle θ may be 20° or 40°. In either case, the above-mentioned effect can be obtained. As shown in FIG. 20(A), S2xmay be understood as the angle between the z1 axis and the second irradiation light 49 in the x1z1 plane. S2x In order to increase θ, the distance between the LED 35 and the point 57 on the intermediate transfer belt 12a in the x1 direction should be increased. Similarly, the distance between the point 57 and the second light receiving unit 37 in the x1 direction should be increased. As a result, the size of the optical sensor 31 in the x1 direction must be increased, but the above effect can be obtained. S2x As long as the optical system is designed so that the reflected light from the illuminated surface is incident on the second light receiving unit 37 in accordance with the above, the above effect can be obtained.

[0129] In the third embodiment, the first light receiving unit 36 ​​and the second light receiving unit 37 are arranged on a straight line substantially parallel to the y1 direction, but this is merely an example. The first light receiving unit 36 ​​and the second light receiving unit 37 may be arranged on an inclined straight line that is not parallel to the y1 direction. That is, the first light receiving unit 36 ​​may be arranged so that the target light caused by the first irradiation light 46 enters the first light receiving unit 36, but the non-target light (diffracted light) does not enter the first light receiving unit 36. Similarly, the second light receiving unit 37 may be arranged so that the target light caused by the second irradiation light 49 enters the second light receiving unit 37, but the non-target light (diffracted light) does not enter the second light receiving unit 37. That is, it is not essential that the first light receiving unit 36 ​​and the second light receiving unit 37 are arranged on a straight line substantially parallel to the y1 direction. If the first light receiving unit 36 ​​and the second light receiving unit 37 are not arranged on a straight line substantially parallel to the y1 direction, the size of the optical sensor 31 in the x1 direction simply increases. In order to realize a small optical sensor 31, it would be advantageous to arrange the first light receiving unit 36 ​​and the second light receiving unit 37 on a straight line substantially parallel to the y1 direction.

[0130] <Technical ideas derived from examples> <Point 1> The LED 35 is an example of a light-emitting element that irradiates light onto an irradiated surface set for the object to be measured. The second light-receiving unit 37 is an example of a light-receiving unit (first light-receiving unit) that receives specularly reflected light from the surface of the object to be measured. The circuit board 34 is an example of a circuit board on which the light-emitting element and the light-receiving unit are mounted. The housing 33 is an example of a housing having a first opening (e.g., third opening 42) and a second opening (e.g., second opening 41) and provided to surround the light-emitting element and the light-receiving unit. As shown in FIG. 9 and other figures, the first opening is provided in a first light guide path that is provided between the light-emitting element and the irradiated surface (e.g., irradiated area 50), and is arranged so that the light output from the light-emitting element is directed toward the irradiated surface. The second opening is provided in a second light guide path that is provided between the irradiated surface and the light-receiving unit. As shown in FIG. 9 and other figures, the first opening provided in the housing 33 is an exit port of a through hole that is provided to penetrate the housing 33. The shape of the through hole is such that the +1st order or higher diffracted light and the -1st order or higher diffracted light generated on the irradiated surface do not enter the light receiving unit. For example, as shown in FIG. 7(A), an opening is required that prevents diffracted light caused by other light incident on the irradiated surface at an incident angle (e.g., 0°, -40°) different from the incident angle (e.g., -20°) of light incident on the irradiated surface from the light source from the light source from the light source. Such other light may occur on a wall surface without a through hole. On the other hand, as shown in FIG. 11, the +1st order diffracted light and the -1st order diffracted light generated by the diffraction of the second irradiation light 49 in the irradiated area 50 do not enter the light receiving unit. This is also a benefit of the shape of the through hole (light guide path provided in the housing 33). Therefore, by devising the shape of the through hole, the deterioration of detection accuracy that may occur due to reflected light from the irradiated surface in an optical sensor such as a toner sensor is suppressed.

[0131] <Point 2> The shape of the through hole may be such that the light output from the light emitting element and reflected by the wall surface of the through hole does not enter the light receiving unit through the irradiated surface, thereby suppressing a decrease in detection accuracy in an optical sensor such as a toner sensor that may be caused by the reflected light from the irradiated surface.

[0132] <Point 3-8> As shown in FIG. 9 and the like, the size of the light exit of the through hole may be smaller than the size of the light entrance of the through hole. This makes it difficult for the reflected light that may occur on the inner wall of the through hole to enter the light receiving unit. As shown in FIG. 9 and the like, the three-dimensional shape of the through hole may have a cross-sectional area that gradually decreases from the light exit toward the light entrance. This cross-sectional area is a cross-sectional area parallel to the mounting surface of the circuit board 34. The three-dimensional shape of the through hole may be tapered. The three-dimensional shape of the through hole may be a truncated cone. The angle that the inclined surface of the tapered shape makes with the circuit board may be 30 degrees. The depth of the through hole, which is the distance from the light exit to the light entrance of the through hole, may be 0.2 mm. These conditions will make it difficult for the reflected light that may occur on the inner wall of the through hole to enter the light receiving unit.

[0133] <Point 9> The object to be measured may be a rotating body, or a toner image carried on the rotating body, in which case the optical sensor is effective as a toner sensor.

[0134] <Points 10 and 11> The rotating body may be an endless belt stretched between a cylindrical driving roller and a driven roller. In order to reduce wear of the endless belt, a plurality of grooves 83 may be formed on the surface of the endless belt. In this case, diffracted light may be generated. In other words, even in the case where such a measurement object is adopted, the optical sensor 31 of the embodiment will be able to detect the measurement object with high accuracy.

[0135] <Point 12> Equation 2 may be satisfied between the incident angle θi with respect to the irradiated surface, the wavelength λ of the light output from the light emitting element, and the diffraction angle θm of the m-th order diffracted light generated by the light being diffracted by a plurality of grooves arranged at intervals d. Even in such a case, the optical sensor 31 of the embodiment will be able to detect the measurement object with high accuracy. In particular, this embodiment will be extremely effective when the wavelength λ of the light is less than 20 μm (particularly, 400 nm or more and 1000 nm or less) and the interval d is 2 μm or more and 10 μm or less.

[0136] <Point 13> The light-emitting element may have an LED chip 35a and a light-transmitting member 35. As shown in Fig. 18(C), the width of the LED chip 35a in the longitudinal direction (y direction) of the circuit board 34 may be 0.37 mm or less and 0.23 mm or more. The width of the light-transmitting member 35b in the longitudinal direction of the circuit board 34 may be 3.0 mm or less and 1.5 mm or more. In particular, the narrower these widths are, the smaller the size of the irradiated area 50 becomes, so that unnecessary diffracted light is less likely to enter the light-receiving unit.

[0137] <Point 14> The first light receiving unit 36 ​​is an example of a second light receiving unit that receives diffusely reflected light incident from the irradiated surface. As described in relation to Fig. 16(B), the controller 29 may function as a correction unit that corrects the output of the first light receiving unit, which is a light receiving unit that receives specularly reflected light, with the output of the second light receiving unit. This allows the toner amount to be calculated with high accuracy.

[0138] <Points 15, 29> The photosensitive drum 1, intermediate transfer belt 12a, secondary transfer roller 16, etc. form an image forming section that forms a toner image on sheet S via a rotating body. An optical sensor 31 detects specularly reflected light from the surface of the rotating body and diffusely reflected light from the toner image carried on the surface of the rotating body. A controller 29 functions as an adjustment section that adjusts the formation position of the toner image or the density of the toner image based on the detection result of the optical sensor 31. This makes it possible to accurately correct color shifts, and toner image density and color.

[0139] <Point 16> The y1 direction described in the third embodiment is an example of a direction (first direction) in which a plurality of grooves are arranged on the irradiated surface. The direction in which a plurality of grooves extend on the irradiated surface may be expressed as a second direction (e.g., x1 direction). The depth direction of the grooves may be expressed as a third direction (e.g., z1 direction). As shown in FIG. 20(D), the light (e.g., second irradiation light 49) output from the light-emitting element (e.g., LED 35) is irradiated from a direction substantially normal to the irradiated surface (e.g., second irradiated region 50). In other words, the y1 direction and the traveling direction of the second irradiation light 49 are perpendicular to each other.

[0140] <Point 17> As shown in FIG. 20(D), the light output from the light emitting element may be substantially parallel light that does not diverge at least in the first direction (y1 direction) in which the plurality of grooves are aligned on the illuminated surface.

[0141] <Point 18> 20(A) and 20(B), the light emitting element and the light receiving unit are arranged in different positions on a line parallel to the second direction (e.g., the x1 direction) on the circuit board 34. As shown in FIG. 20(A), the light output from the light emitting element is angled at a predetermined angle (90 degrees-θ S2x In other words, the light output from the light emitting element is tilted at a predetermined angle θ S2x It is just tilted.

[0142] <Points 19 and 20> As shown in Fig. 20(D) and the like, a first lens (e.g., third lens section 45) may be disposed in the first light guide path, and a second lens (e.g., fourth lens section 55) may be disposed in the second light guide path. At least one of the first lens and the second lens may have a curved surface (cylindrical side surface) protruding in the third direction. At least one of the first lens and the second lens may be a cylindrical lens having a flat surface facing the irradiated surface.

[0143] <Point 21> The radius (curvature or refractive index) and the mounting position of the first lens may be set so that the focal point of the first lens approximately coincides with the position of the light emitting element (first condition). The radius (curvature or refractive index) and the mounting position of the second lens may be set so that the focal point of the second lens approximately coincides with the position of the first light receiving unit (second condition). One or both of the first condition and the second condition may be satisfied.

[0144] <Point of View 22> As shown in FIG. 20(B) and the like, the optical sensor may have a third opening, a fourth opening, and the third and fourth light guide paths provided at positions different from the first and second light guide paths. The third opening (e.g., first opening 40) may be provided in the third light guide path arranged between the light emitting element and the irradiated surface. The fourth opening (e.g., second opening 41) may be provided in the fourth light guide path arranged between the irradiated surface and the second light receiving unit (e.g., first light receiving unit 36). The first light receiving unit (e.g., second light receiving unit 37) is arranged so that regular reflection light, diffracted light, and diffuse reflection light from the first irradiated region 47 originating from the light (first irradiation light 46) emitted from the first light guide path are not incident. The second light receiving unit (first light receiving unit 36) is arranged so that regular reflection light and diffracted light from the second irradiated region 50 originating from the light (second irradiation light 49) emitted from the third light guide path are not incident.

[0145] <Point of View 23> As shown in FIG. 20(D) and other figures, the second light receiving unit (first light receiving unit 36) may be disposed at a position where the specularly reflected light, diffracted light, and diffusely reflected light from the second irradiated region 50 are not incident.

[0146] <Point of View 24> The angle that the first irradiation light (e.g., second irradiation light 49) output from the first light guide path toward the irradiated surface makes with respect to the first direction is different from the angle that the second irradiation light (first irradiation light 46) output from the third light guide path toward the irradiated surface makes with respect to the first direction. The angle that the first irradiation light makes with respect to the second direction is different from the angle that the second irradiation light makes with respect to the second direction. These will be apparent from Figures 20(A), 20(C) and 20(D).

[0147] <Point of View 25> As shown in Figure 20(B), the surface irradiated by the first irradiation light (e.g., second irradiated area 50) and the surface irradiated by the second irradiation light (e.g., first irradiated area 47) do not overlap in both the first direction and the second direction.

[0148] <Point of View 26> As shown in FIG. 20(D) and other figures, the second irradiation light (eg, first irradiation light 46) travels away from the first irradiated region (eg, second irradiated region 50) at least in the first direction.

[0149] <Point of View 27> As shown in Figures 21(A) and 21(B), the irradiation angle of the second irradiation light (e.g., first irradiation light 46) with respect to the irradiated surface is an irradiation angle such that, in the first direction, the specularly reflected light and diffracted light originating from the second irradiation light move away from the fourth opening.

[0150] <Point of View 28> 19(B), a third lens (e.g., first lens portion 43) may be disposed in the third light guide path, and a fourth lens (e.g., second lens portion 44) may be disposed in the fourth light guide path.

[0151] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0152] 31: optical sensor, 32: housing, 34: circuit board, 35: LED, 36: first light receiving unit, 40: first opening, 41: second opening

Claims

1. A belt with a moving surface; A light emitting element that irradiates light toward a surface of the belt that is set relative to the measurement object; A first light receiving unit that receives specularly reflected light from a surface of the measurement object; A second light receiving unit that receives diffusely reflected light from a surface of the object to be measured; a circuit board on which the light emitting element and the first light receiving unit are mounted; a housing having a first opening and a second opening and provided to surround the light emitting element and the first light receiving unit; the first opening is provided in a first light guide path disposed between the light emitting element and the surface of the belt, and is disposed so that light output from the light emitting element is directed toward the surface of the belt; the second opening is provided in a second light guide path disposed between the surface of the belt and the first light receiving unit, the light-emitting element and the first light-receiving unit are provided at positions where they overlap in a first direction in which the surface of the belt moves, and the light-emitting element and the second light-receiving unit are provided at positions where they do not overlap in the first direction; The first light receiving unit and the second light receiving unit are provided so as to overlap each other in a direction perpendicular to the first direction; An optical sensor characterized in that the first opening provided in the housing is an exit port of a through hole provided to penetrate the housing, and the shape of the through hole is such that light output from the light-emitting element and reflected on the wall surface of the through hole does not enter the first light-receiving unit through the surface of the belt.

2. 2. The optical sensor according to claim 1, wherein the size of the exit opening of the through-hole is smaller than the size of the entrance opening of the through-hole.

3. 3. The optical sensor according to claim 2, wherein the three-dimensional shape of the through hole has a cross-sectional area that gradually decreases from the exit port to the entrance port, the cross-sectional area being a cross-sectional area parallel to a mounting surface of the circuit board.

4. The optical sensor according to claim 3 , wherein the through hole has a three-dimensional shape that is tapered.

5. The optical sensor according to claim 4 , wherein the three-dimensional shape of the through hole is a truncated cone shape.

6. 6. The optical sensor according to claim 4, wherein the inclined surface of the tapered shape forms an angle of 30 degrees with the circuit board.

7. 7. The optical sensor according to claim 2, wherein a depth of the through hole, which is a distance from the exit opening to the entrance opening of the through hole, is 0.2 mm.

8. 8. The optical sensor according to claim 1, wherein the measurement object is the belt and a toner image carried on the surface of the belt.

9. 9. The optical sensor according to claim 8, wherein the belt is an endless belt stretched around a cylindrical driving roller and a cylindrical driven roller.

10. 10. The optical sensor according to claim 1, wherein a plurality of grooves are formed on the surface of the belt.

11. The optical sensor according to claim 10, characterized in that the multiple grooves are formed on the surface of the belt so that sin θm = mλ / d - sin θi holds between the incident angle θi with respect to the surface of the belt, the wavelength λ of the light output from the light-emitting element, and the diffraction angle θm of m-th order diffracted light generated when the light is diffracted by the multiple grooves arranged at an interval d.

12. The light emitting element has an LED chip and a light transmitting member, The width of the LED chip in the longitudinal direction of the circuit board is 0.37 mm or less and 0.23 mm or more; 12. The optical sensor according to claim 1, wherein the width of the light transmitting member in the longitudinal direction of the circuit board is 3.0 mm or less and 1.5 mm or more.

13. a correcting means for correcting an output of the first light receiving unit with an output of the second light receiving unit; 12. The optical sensor according to claim 10 or 11, further comprising:

14. an image forming unit that forms a toner image on a sheet via a rotating body; 4. The optical sensor according to claim 1, wherein the optical sensor detects the specularly reflected light and the diffusely reflected light from a surface of the belt; an adjustment unit that adjusts a forming position of the toner image or a density of the toner image based on a detection result of the optical sensor; An image forming apparatus comprising:

15. The plurality of grooves are arranged on the surface of the belt in a second direction perpendicular to the first direction, and the traveling direction of the light output from the light emitting element is perpendicular to the second direction.

14. The optical sensor according to claim 13.

16. The light output from the light emitting element is substantially parallel light that does not diverge at least in the second direction.

16. The optical sensor of claim 15.

17. The light output from the light emitting element is inclined at a predetermined angle with respect to a third direction perpendicular to both the first direction and the second direction.

17. The optical sensor according to claim 15 or 16.

18. a first lens is disposed in the first light guide path; a second lens is disposed in the second light guide path; At least one of the first lens and the second lens has a curved surface protruding at least in the third direction.

20. The optical sensor of claim 17.

19. At least one of the first lens and the second lens is a cylindrical lens having a flat surface facing the surface of the belt.

20. The optical sensor of claim 18.

20. The radius of the first lens is set so that the focal point of the first lens is approximately aligned with the position of the light emitting element, or the radius of the second lens is set so that the focal point of the second lens is approximately aligned with the position of the first light receiving unit, or both of these are satisfied.

20. The optical sensor according to claim 18 or 19.

21. The housing further has a third opening and a fourth opening. the third opening is provided in a third light guide path disposed between the light emitting element and the surface of the belt, the fourth opening is provided in a fourth light guide path disposed between the surface of the belt and the second light receiving unit, The first light receiving unit is arranged so as to prevent specular reflection light, diffracted light, and diffuse reflection light from a first irradiated area originating from the light emitted from the first light guide path toward the surface of the belt from entering the first light receiving unit, and the second light receiving unit is arranged so as to prevent specular reflection light and diffracted light from a second irradiated area originating from the light emitted from the third light guide path toward the surface of the belt from entering the second light receiving unit.

21. The optical sensor according to claim 15, wherein the optical sensor is a casing.

22. the second light receiving unit is disposed so as not to receive specularly reflected light, diffracted light, and diffusely reflected light from the second irradiated region; 22. The optical sensor of claim 21.

23. an angle formed by a first illumination light outputted from the first light guide path toward the surface of the belt with respect to the first direction is different from an angle formed by a second illumination light outputted from the third light guide path toward the surface of the belt with respect to the first direction, 23. The optical sensor according to claim 21, wherein an angle that the first irradiation light makes with respect to the first direction is different from an angle that the second irradiation light makes with respect to the first direction.

24. a surface of the belt of the first irradiation light and a surface of the belt of the second irradiation light do not overlap in both the first direction and the second direction; 24. The optical sensor of claim 23.

25. The second irradiation light travels in the second direction away from the first irradiated area.

25. The optical sensor according to claim 23 or 24.

26. an irradiation angle of the second irradiation light with respect to the surface of the belt in the second direction such that the specular reflected light and the diffracted light originating from the second irradiation light are away from the fourth opening; 26. The optical sensor according to any one of claims 23 to 25.

27. a third lens is disposed in the third light guide path, and a fourth lens is disposed in the fourth light guide path; 27. The optical sensor according to any one of claims 21 to 26.

28. an image forming unit that forms a toner image on a sheet via a rotating body; 28. The optical sensor according to claim 15, further comprising: an optical sensor that detects the specularly reflected light and the diffusely reflected light; an adjustment unit that adjusts a forming position of the toner image or a density of the toner image based on a detection result of the optical sensor; An image forming apparatus comprising:

29. An optical sensor described in any one of claims 1 to 13 and 15 to 27, characterized in that the first light receiving unit and the second light receiving unit are arranged at a position where they do not overlap with each other in the first direction.

30. An optical sensor described in any one of claims 1 to 13 and 15 to 27 and 29, characterized in that the first light receiving unit is arranged at a position where the first light receiving unit and the light emitting element do not overlap each other in a second direction perpendicular to the first direction.

31. An optical sensor described in any one of claims 1 to 13, 15 to 27, and 29 to 30, characterized in that the second light receiving unit is arranged at a position where the second light receiving unit and the light emitting element do not overlap each other in a second direction perpendicular to the first direction.

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