Optical sensor and image forming device

Abstract

An optical sensor (3) radiates light toward a measurement target (TG) and detects reflected light from the measurement target (TG). The optical sensor (3) comprises: a substrate (30) having a mounting surface (3M); and an element group (3E) including a first light-emitting element (33), a second light-emitting element (35), a first light-receiving element (34), and a second light-receiving element (36) arrayed on the mounting surface (3M). The first light-receiving element (34) is disposed at a position where it is possible to receive specularly reflected light (L2) from a measurement target (TG) of first measurement light (L11) emitted from the first light-emitting element (33). The second light-receiving element (36) is disposed at a position where it is possible to receive diffusely reflected light (L3) from a measurement target (TG) of a second measurement light (L12) emitted from the second light-emitting element (35). A light-receiving region (RA) of the second light-receiving element (36) includes a wide portion (361) having a prescribed first width in an intersecting direction intersecting the array direction of the element group (3E), and a narrow portion (362) having a second width narrower than the first width.

Description

Optical sensor and image forming device

[0001] The present disclosure relates to an optical sensor including a light emitting element and a light receiving element, and an image forming apparatus.

[0002] An optical sensor is known that includes a light-emitting element that emits measurement light to be irradiated onto a measurement object and a light-receiving element that receives reflected light from the measurement light. The optical sensor is used, for example, to detect patch images formed on an intermediate transfer belt of a tandem image forming apparatus for measuring toner concentration and color shift. Patent Document 1 (JP-A-2005-102666) discloses an optical sensor that includes two pairs of a light-emitting element and a light-receiving element, one of which receives specularly reflected light and the other of which receives diffusely reflected light.

[0003] Japanese Patent Application Laid-Open No. 2020-42120

[0004] According to one aspect of the present disclosure, an optical sensor irradiates a measurement object with light and detects reflected light from the measurement object. The optical sensor includes a substrate having a mounting surface and an element group including a first light-emitting element, a second light-emitting element, a first light-receiving element, and a second light-receiving element arranged on the mounting surface. The first light-receiving element is positioned so as to receive specularly reflected light from the measurement object of the first measurement light emitted from the first light-emitting element. The second light-receiving element is positioned so as to receive diffusely reflected light from the measurement object of the second measurement light emitted from the second light-emitting element. The light-receiving region of the second light-receiving element includes a wide portion having a predetermined first width in a direction intersecting the arrangement direction of the element group and a narrow portion having a second width narrower than the first width.

[0005] FIG. 1 is a cross-sectional view schematically illustrating the internal structure of a color printer to which an optical sensor according to the present disclosure is applied. FIG. 2 is a perspective view illustrating an example of the arrangement of a density sensor, which is an example of an optical sensor. FIG. 3A is a schematic diagram illustrating the principle of detection of black toner. FIG. 3B is a schematic diagram illustrating the principle of detection of black toner. FIG. 4A is a schematic diagram illustrating the principle of detection of color toner. FIG. 4B is a schematic diagram illustrating the principle of detection of color toner. FIG. 5 is a cross-sectional view illustrating an optical sensor module according to an embodiment of the present disclosure. FIG. 6 is a graph illustrating the relationship between the distance to the object to be measured and the amount of light detected by the optical sensor module. FIG. 7 is an explanatory diagram illustrating the positional relationship between the light receiving area and the spot of measurement light when the distance to the object to be measured varies. FIG. 8 is a plan view illustrating a sensor substrate according to an example and a comparative example of the present disclosure. FIG. 9 is an explanatory diagram illustrating the positional relationship between the light receiving area of ​​a second light receiving element having a wide portion and a narrow portion and the spot of measurement light. FIG. 10 is a graph illustrating the relationship between the distance to the object to be measured and the amount of light detected by the optical sensor module for an example and a comparative example. FIG. 11A is a plan view showing an example of the formation of the light receiving region of the second light receiving element. FIG. 11B is a cross-sectional view taken along line XIB-XIB in FIG. 11A. FIG. 12A is a plan view showing another example of the formation of the light receiving region of the second light receiving element. FIG. 12B is a cross-sectional view taken along line XIIB-XIIB in FIG. 12A. FIG. 13A is a cross-sectional view of an optical sensor module including an aperture. FIG. 13B is a plan view showing another example of the formation of the light receiving region of the second light receiving element. FIG. 13C is a cross-sectional view taken along line XIIIC-XIIIC in FIG. 13B. FIG. 14A is a plan view showing a modified shape of the light receiving region of the second light receiving element. FIG. 14B is a plan view of a modified shape of the light receiving region of the second light receiving element. FIG. 14C is a plan view of a modified shape of the light receiving region of the second light receiving element. FIG. 14D is a plan view of a modified shape of the light receiving region of the second light receiving element. FIG. 14E is a plan view of a modified example of the shape of the light receiving region of the second light receiving element.

[0006] The optical sensor of the present disclosure will be described in detail below with reference to the drawings. The optical sensor of the present disclosure measures the physical properties of an object by irradiating the object with measurement light and receiving the reflected light. There are no particular limitations on the object to be measured, and the object can be a solid, semi-solid, liquid, powder, or the like. There are also no particular limitations on the physical properties to be measured, as long as they can be analyzed from the reflected light. For example, the optical sensor of the present disclosure is suitable for measuring the color and density of an object to be measured. In the embodiment described below, an optical sensor that is assembled in the form of a module into a color printer to detect the density of toner used in image formation is exemplified.

[0007] [Description of Color Printer] First, the configuration of a color printer to which the optical sensor of the present disclosure is applied will be described. FIG. 1 is a cross-sectional view that schematically shows the internal structure of a tandem color printer 1. The color printer 1 includes image forming units 2Y, 2C, 2M, and 2Bk, an optical scanning device 23, an intermediate transfer unit 28, and a fixing unit 29, all housed in a main body housing 10. A paper output tray 11 is provided on the top surface of the main body housing 10. A sheet output port 12 opens opposite the paper output tray 11. A manual paper feed tray 13 is provided on a side wall of the main body housing 10, and a paper feed cassette 14 that stores sheets for automatic paper feed, etc., is provided in the bottom of the main body housing 10.

[0008] Image forming units 2Y, 2C, 2M, and 2Bk are units that form toner images of yellow, cyan, magenta, and black, respectively, and are arranged in tandem at a predetermined interval horizontally. Each image forming unit 2Y, 2C, 2M, and 2Bk includes a photosensitive drum 21 having a circumferential surface that supports an electrostatic latent image and a toner image, a charger 22 that charges the circumferential surface of the photosensitive drum 21, a developer 24 that applies developer to the electrostatic latent image to form a toner image, yellow, cyan, magenta, and black toner containers 25Y, 25C, 25M, and 25Bk, respectively, that supply toner of each color to the developer 24, a primary transfer roller 26 that performs primary transfer of the toner image formed on the photosensitive drum 21, and a cleaning device 27 that removes residual toner from the circumferential surface of the photosensitive drum 21. An optical scanning device 23 scans the circumferential surface of the photosensitive drum 21 of each color as a scanned surface with a beam in the main scanning direction, forming an electrostatic latent image on the circumferential surface for forming a toner image.

[0009] The intermediate transfer unit 28 performs a primary transfer of the toner images formed on the photosensitive drums 21. The intermediate transfer unit 28 includes a transfer belt 281 that rotates while contacting the circumferential surface of each photosensitive drum 21, and a drive roller 282 and a driven roller 283 around which the transfer belt 281 is wound. The transfer belt 281 is a carrier that carries the toner, which is the object to be measured. The toner images on the photosensitive drums 21 of each color are primarily transferred onto the transfer belt 281, superimposed on the same location on the transfer belt 281. As a result, a full-color toner image is formed on the transfer belt 281. A secondary transfer roller 15 is disposed opposite the drive roller 282, sandwiching the transfer belt 281 to form a secondary transfer nip T. The full-color toner image on the transfer belt 281 is secondarily transferred onto a sheet at the secondary transfer nip T.

[0010] The fixing unit 29 includes a fixing roller 291 with a built-in heat source, and a pressure roller 292 that forms a fixing nip N together with the fixing roller 291. The fixing unit 29 applies heat and pressure to the sheet, onto which a toner image has been transferred in the secondary transfer nip T, in the fixing nip N, thereby performing a fixing process in which the toner is fused to the sheet. The sheet that has undergone the fixing process is discharged from the sheet discharge port 12 toward the paper discharge tray 11.

[0011] A density sensor 16 is disposed inside the main body housing 10. The density sensor 16 is an example of an optical sensor in the present disclosure. The density sensor 16 is disposed near the secondary transfer nip T, facing the outer peripheral surface of the transfer belt 281 on which the toner image is carried. The density sensor 16 optically detects the density of the toner image formed on the transfer belt 281 and converts it into an electrical signal. Specifically, the density sensor 16 irradiates the transfer belt 281 with measurement light and detects the toner density based on the detected light amount of the reflected light.

[0012] FIG. 2 is a perspective view showing an example of the arrangement of the density sensor 16. In FIG. 2, the density sensor 16 is illustrated as a first density sensor 16A and a second density sensor 16B spaced apart from each other in the main scanning direction. The first density sensor 16A is disposed at a first density detection position DP1 on the toner carrying surface 28T of the transfer belt 281, and the second density sensor 16B is disposed at a second density detection position DP2, facing each other. The two density sensors 16A and 16B optically detect toner detection patches dp carried on the toner carrying surface 28T. The toner detection patches dp include, for example, density detection patches for detecting the toner concentration of each color and position detection patches for detecting the printing position of each color. The transfer belt 281 rotates in the direction indicated by the white arrow in FIG. 2. The first density sensor 16A detects the toner concentration along a first inspection line DL1 extending from the first density detection position DP1 in the sub-scanning direction. The second density sensor 16B detects the toner density along a second inspection line DL2 that extends in the sub-scanning direction from the second density detection position DP2. Only one of the first density sensor 16A and the second density sensor 16B may be disposed opposite the transfer belt 281.

[0013] [Toner Detection Principle] Next, the principle of optically detecting toner on transfer belt 281 will be described with reference to FIGS. 3A to 4B. FIGS. 3A and 3B are schematic diagrams illustrating the detection principle for black toner BT, and FIGS. 4A and 4B are schematic diagrams illustrating the detection principle for color toner CT. A light-emitting element E1 and a light-receiving element E2 are arranged facing the toner carrying surface 28T of transfer belt 281. The light-emitting element E1 is, for example, an LED (Light Emitting Diode) capable of emitting light of a predetermined wavelength. The light-receiving element E2 is, for example, a PD (Photo Diode) that receives light, photoelectrically converts it, and outputs a current corresponding to the amount of light.

[0014] 3A shows the light emission and reception state when there is no black toner BT on the transfer belt 281. The toner carrying surface 28T is a smooth surface that generates specular reflection when irradiated with light. Measurement light L1 is emitted from the light-emitting element E1. The measurement light L1 is irradiated at a predetermined emission angle θ1 toward the density detection position DP on the toner carrying surface 28T. The measurement light L1 is reflected by the toner carrying surface 28T, generating specularly reflected light L2. The specularly reflected light L2 is incident on the light-receiving element E2. The light-receiving element E2 outputs a current AM1 corresponding to the amount of light received.

[0015] 3B shows the light emission and reception state when black toner BT is present on the transfer belt 281. A portion of the measurement light L1 irradiated toward the toner carrying surface 28T is absorbed by the black toner BT. In other words, in the area of ​​the toner carrying surface 28T where black toner BT is present, substantially no specularly reflected light L2 is generated. As a result, the amount of specularly reflected light L2 incident on the light receiving element E2 decreases. The light receiving element E2 outputs a current AM2 corresponding to the reduced amount of light. Naturally, the relationship AM1 > AM2 holds. Whether or not black toner BT is present is detected based on the fluctuation in the current output of the light emitting element E1 accompanying such a change in the amount of specularly reflected light L2 received.

[0016] 4A shows the light emission and reception state when no color toner CT is present on the transfer belt 281. Measurement light L1 is emitted from the light-emitting element E1. The measurement light L1 emission optical system is adjusted so that measurement light L1 is irradiated onto the concentration detection position DP at an emission angle θ2 that is larger than the emission angle θ1 in FIG. 3A. Measurement light L1 is reflected by the toner carrying surface 28T, generating specularly reflected light L2. Light-receiving element E2 is positioned at a position where specularly reflected light L2 does not enter. Therefore, the output of light-receiving element E2 is substantially zero.

[0017] 4B shows the light emission and reception state when color toner CT is present on the transfer belt 281. A portion of the measurement light L1 irradiated toward the toner carrying surface 28T is irradiated onto the color toner CT and diffusely reflected. In other words, not all of the measurement light L1 becomes specularly reflected light L2, but a portion becomes diffusely reflected light L3. A portion of the generated diffusely reflected light L3 is incident on the light receiving element E2. The light receiving element E2 outputs a current AM3 corresponding to the amount of diffusely reflected light L3 received. The color toner CT is detected based on the change in output of the light receiving element E2 from 0 to AM3. The optical sensor module described in the following embodiments applies the above-described detection principle.

[0018] [Configuration of Optical Sensor Module] Figure 5 is a cross-sectional view showing an optical sensor module SM equipped with an optical sensor according to an embodiment of the present disclosure. The optical sensor module SM corresponds to the density sensor 16 of the color printer 1 illustrated in Figure 1. The optical sensor module SM includes a sensor substrate 3, a lens unit 4, and a cover 5. The optical sensor module SM is disposed facing and spaced apart from the measurement target TG. In this embodiment, the measurement target TG is a toner patch printed on the toner carrying surface 28T of the transfer belt 281. The toner patch is formed using black toner BT or color toner CT.

[0019] The sensor substrate 3 corresponds to the optical sensor of the present disclosure and has the function of irradiating light toward the measurement object TG and detecting reflected light from the measurement object TG. The sensor substrate 3 includes a substrate 30 having a mounting surface 3M and an element group 3E arranged in a row on the mounting surface 3M. A circuit pattern for mounting the element group 3E is printed on the mounting surface 3M of the substrate 30. The sensor substrate 3 is arranged so that the mounting surface 3M faces the toner carrying surface 28T. A semiconductor substrate such as a silicon substrate may be used as the sensor substrate 3, and each element of the element group 3E may be directly formed on the semiconductor substrate.

[0020] The element group 3E includes a first light-emitting / light-receiving pair 31 for detecting black toner BT and a second light-emitting / light-receiving pair 32 for detecting color toner CT. The first light-emitting / light-receiving pair 31 consists of a first light-emitting element 33 and a first light-receiving element 34 arranged at a predetermined interval on the mounting surface 3M. The second light-emitting / light-receiving pair 32 consists of a second light-emitting element 35 and a second light-receiving element 36 arranged at a predetermined interval on the mounting surface 3M in a position different from the first light-emitting / light-receiving pair 31. The thickness of each element constituting the element group 3E is approximately 0.2 mm to 0.5 mm.

[0021] The first light-emitting element 33 and the second light-emitting element 35 are LEDs that emit light of a predetermined wavelength. The first light-receiving element 34 and the second light-receiving element 36 are PDs that output a current corresponding to the amount of light received. The elements of the element group 3E are arranged in a line in the main scanning direction shown in FIG. 2. Specifically, the elements of the element group 3E are arranged in a line on the mounting surface 3M in the order of the first light-emitting element 33, the first light-receiving element 34, the second light-receiving element 36, and the second light-emitting element 35. The elements of the element group 3E do not necessarily have to be arranged in a strict line; they may be arranged in a line with an offset that is equivalent to a line. Furthermore, the arrangement direction of the element group 3E may be the sub-scanning direction. Note that the order of the elements in the first light-emitting / light-receiving pair 31 may be reversed. That is, the element group 3E may be arranged in a line on the mounting surface 3M in the order of the first light-receiving element 34, the first light-emitting element 33, the second light-receiving element 36, and the second light-emitting element 35.

[0022] The lens unit 4 is disposed in front of the mounting surface 3M, i.e., between the sensor substrate 3 and the toner carrying surface 28T. The lens unit 4 includes a holder 40 and a lens that focuses light. The holder 40 is a thin, rectangular parallelepiped member that holds the lens. The lens includes a first lens 41, a second lens 42, a third lens 43, and a fourth lens 44. On the optical path of the first light-emitting / receiving pair 31, the first lens 41 is disposed in front of the first light-emitting element 33, and the second lens 42 is disposed behind the first light-receiving element 34. On the optical path of the second light-emitting / receiving pair 32, the third lens 43 is disposed in front of the second light-emitting element 35, and the fourth lens 44 is disposed behind the second light-receiving element 36.

[0023] The first lens unit 41 condenses the light emitted by the first light-emitting element 33 to generate a first measurement light L11 that is irradiated as a spot onto a predetermined concentration detection position on the toner carrying surface 28T. The second lens unit 42 condenses specularly reflected light L2 of the first measurement light L11 from the toner carrying surface 28T and causes the specularly reflected light L2 to be incident on the first light-receiving element 34. In other words, the first light-receiving element 34 is positioned so that it can receive the specularly reflected light L2 from the measurement target TG.

[0024] The third lens 43 focuses the light emitted by the second light-emitting element 35 to generate a second measurement light L12 that is spot-illuminated at the concentration detection position. The fourth lens 44 focuses the diffusely reflected light L3 of the second measurement light L12 from the toner carrying surface 28T and directs the light to the second light-receiving element 36. In other words, the second light-receiving element 36 is positioned so as to receive the optical image of the diffusely reflected light L3 from the measurement object TG that is generated by the fourth lens 44.

[0025] The cover 5 has a housing structure that protects the mounting surface 3M of the sensor board 3. The cover 5 includes a side plate 5A and a top plate 5B. The side plate 5A covers the sides of the element group 3E. The top plate 5B is spaced a predetermined distance from the mounting surface 3M and covers the front of the element group 3E. The lens unit 4 is attached to the top plate 5B. The top plate 5B holds a first light-shielding wall 51 and a second light-shielding wall 52 on its inner surface.

[0026] The first light-shielding wall 51 and the second light-shielding wall 52 are non-transparent members that do not allow light to pass through. The first light-shielding wall 51 is disposed in front of the mounting surface 3M, between the first light-emitting element 33 and the first light-receiving element 34. The first light-shielding wall 51 prevents light emitted from the first light-emitting element 33 from traveling directly toward the first light-receiving element 34 without passing through the toner carrying surface 28T. In other words, the first light-shielding wall 51 prevents light before being condensed by the first lens 41 from being received by the first light-receiving element 34. The second light-shielding wall 52 is disposed in front of the mounting surface 3M, between the second light-emitting element 35 and the second light-receiving element 36. The second light-shielding wall 52 prevents light emitted from the second light-emitting element 35 from traveling directly toward the second light-receiving element 36. In other words, the second light-shielding wall 52 prevents light before being condensed by the third lens 43 from being received by the second light-receiving element 36.

[0027] 5 , the optical sensor module SM is positioned so that measurement is performed at a measurement distance where the optical sensor module SM and the measurement target TG are separated by a predetermined reference detection distance ML. In this embodiment, the optical sensor module SM is attached to the main housing 10 so that the distance between the mounting surface 3M of the element group 3E on the sensor board 3 and the toner carrying surface 28T of the transfer belt 281 is the reference detection distance ML. Based on the detected light amounts of the first light receiving element 34 and the second light receiving element 36 when measurement is performed at the reference detection distance ML, the densities of the toners BT and CT printed on the toner carrying surface 28T are evaluated.

[0028] However, various factors can cause the measured distance between the optical sensor module SM and the measurement target TG to deviate from the reference detection distance ML. For example, fluctuations in the transfer belt 281 or installation errors in the optical sensor module SM can cause the measured distance to change. Alternatively, when different models of printers are equipped with the optical sensor module SM, the settable measurement distance may differ depending on the model.

[0029] When the measurement distance changes, the amount of light detected by the first light receiving element 34 and the second light receiving element 36 also changes. The color printer 1 cannot distinguish whether this fluctuation in the amount of detected light is due to a change in the density of the toner BT and CT, or to a change in the measurement distance. For this reason, even if the image formation conditions are corrected by calibration in response to fluctuations in the amount of detected light, there may be cases where an image with the appropriate density cannot be obtained.

[0030] 6 is a graph of a light intensity characteristic C1 showing the relationship between the distance to the measurement object TG and the detected light intensity of the second light receiving element 36 that receives the diffusely reflected light L3. In the graph of FIG. 6, the position of the measurement object TG when the measurement distance between the mounting surface 3M of the sensor substrate 3 and the measurement object TG is the reference detection distance ML is defined as the "reference position." The light intensity characteristic C1 shows the change in the detected light intensity of the second light receiving element 36 when the distance of the measurement object TG to the sensor substrate 3 becomes farther from the reference position and when the distance becomes closer to the reference position.

[0031] When the measurement distance becomes farther than the reference position, the optical path length from the second light-emitting element 35 to the second light-receiving element 36 via the measurement object TG becomes longer. Because the diffusely reflected light L3 is diffused, as the optical path length becomes longer, the amount of light detected by the second light-emitting element 35 tends to decrease. Conversely, when the measurement distance becomes closer to the reference position, the optical path length becomes shorter, and the amount of light detected by the second light-emitting element 35 tends to increase. Note that when the measurement distance becomes too close to the reference position, the optical path length becomes too short, causing the degree of imaging of the spot image of the diffusely reflected light L3 in the light-receiving area of ​​the second light-receiving element 36 to become weaker, and the amount of detected light tends to decrease.

[0032] As the measurement distance varies, the position of the measurement light incident on the second light-receiving element 36 varies, which may change the amount of light detected by the second light-receiving element 36. Figure 7 is an explanatory diagram illustrating the positional relationship between the light-receiving area RA of the second light-receiving element 36 and the spot image SP of the reflected light of the second measurement light L12 emitted by the second light-emitting element 35 when the measurement distance from the measurement object TG varies. Figure 7 illustrates the following states: when the transfer belt 281 carrying the measurement object TG is at the reference position, when it is at a far position farther away from the reference position, and when it is at a near position closer to the reference position relative to the sensor substrate 3. At each position, light-receiving areas 36R1, 36R2, and 36R3 corresponding to the light-receiving area RA of the second light-receiving element 36 and spot areas 35S1, 35S2, and 35S3 corresponding to the spot images SP1, SP2, and SP3 are shown.

[0033] When the transfer belt 281 is in the reference position, the light-receiving area 36R1 and the spot area 35S1 overlap each other. Therefore, the spot image SP1 is incident on the light-receiving area RA of the second light-receiving element 36 on the sensor board 3. Therefore, the second light-receiving element 36 can correctly detect the amount of diffusely reflected light L3.

[0034] In this embodiment, the emission angle θ21 of the second measurement light L12 is different from the incident angle θ22 of the diffusely reflected light L3 onto the second light receiving element 36 (θ21 > θ22). If θ21 = θ22, the positional relationship between the light receiving area RA and the spot image SP does not change even if the transfer belt 281 is displaced from the reference position to a far position or a near position. However, if θ21 ≠ θ22, the positional relationship does change. In this embodiment, since the relationship θ21 > θ22 holds, when a positional change occurs relative to the reference position, the positional shift of the spot area 35S is greater than that of the light receiving area 36R.

[0035] In the far position, the light-receiving area 36R2 is shifted by a first shift length d1 from the reference position. Meanwhile, the spot area 35S2 is shifted by a second shift length d2, which is longer than the first shift length d1, from the reference position. Therefore, as the movement of the transfer belt 281 toward the far position increases, the light-receiving area 36R2 and the spot area 35S2 no longer overlap. In other words, in the second light-receiving element 36, the spot image SP2 is formed at a position offset to the left of the light-receiving area RA, and the detected light intensity decreases. Similarly, in the near position, the light-receiving area 36R3 and the spot area 35S3 do not overlap, and the spot image SP3 is formed at a position offset to the right of the light-receiving area RA, and the detected light intensity decreases.

[0036] When the measurement distance fluctuates, the amount of light detected by the second light-receiving element 36 fluctuates to a non-negligible level due to the two factors mentioned above: (1) fluctuations in the amount of detected light caused by fluctuations in the optical path length, and (2) fluctuations in the relative positional relationship between the light-receiving area RA and the spot image SP. Therefore, when measuring the physical properties of the measurement target TG depending on the amount of detected light, the sensing performance of the optical sensor module SM deteriorates.

[0037] [Explanation of Sensor Substrate Embodiment] FIG. 8 is a plan view showing a sensor substrate 300 according to a comparative example and a sensor substrate 3 according to an example of the present disclosure. Here, the longitudinal direction of the sensor substrates 300 and 303 is the X direction, and the direction perpendicular to the X direction is the Y direction. For ease of explanation, one side of the X direction is designated +X, and the other side is designated −X. The sensor substrates 300 and 303 of the comparative example and example are the same in that two light-emitting / light-receiving pairs are mounted on the substrate 30. The sensor substrate 300 of the comparative example has a first light-emitting element 33, a first light-receiving element 34, a second light-receiving element 360, and a second light-emitting element 35 arranged in this order in the X direction. The light-receiving area RAA of the second light-receiving element 360 has a rectangular shape that is elongated in the X direction.

[0038] The sensor substrate 3 of the embodiment also has a first light-emitting element 33, a first light-receiving element 34, a second light-receiving element 36, and a second light-emitting element 35 arranged in this order in the X direction. The sensor substrate 3 differs from the comparative example in that the light-receiving area RA of the second light-receiving element 36 is not simply rectangular, but has a wide portion 361 and a narrow portion 362. The wide portion 361 has a predetermined first width in the intersecting direction that intersects with the arrangement direction of the element group, i.e., in the Y direction that is perpendicular to the X direction. The narrow portion 362 has a second width in the Y direction that is narrower than the first width. In other words, the light-receiving area RA of the second light-receiving element 36 is formed by a rectangular wide portion 361 and a narrow portion 362 that are connected in the X direction and have different Y-direction widths.

[0039] The X-direction width of the light-receiving area RA of the second light-receiving element 36 according to the example is set to be longer than the X-direction width of the light-receiving area RAA of the second light-receiving element 360 according to the comparative example. As shown in Fig. 7, as the measurement distance between the sensor substrate 3 and the measurement target TG varies, the incident position of the spot image SP on the light-receiving area RA shifts in the X direction. By increasing the X-direction width of the light-receiving area RA, it is possible to accommodate larger variations in the measurement distance.

[0040] The wide portion 361 of the second light receiving element 36 is disposed on the +X side of the light receiving area RA, closer to the second light emitting element 35. The narrow portion 362 is disposed on the -X side, farther from the second light emitting element 35 than the wide portion 361. The length of the narrow portion 362 in the X direction is longer than that of the wide portion 361. FIG. 8 shows, as an example, an example in which the width of the narrow portion 362 in the X direction is approximately twice that of the wide portion 361. Such a geometric feature of the light receiving area RA contributes to suppressing fluctuations in the amount of light detected by the second light receiving element 36, even when fluctuations in the measurement distance occur.

[0041] FIG. 9 is an explanatory diagram showing the positional relationship between the light-receiving area RA of the second light-receiving element 36, which has a wide portion 361 and a narrow portion 362, and the spot images SP1 to SP3 of the diffusely reflected light L3. The graph at the top of FIG. 9 is the same graph as the light intensity characteristic C1 shown in FIG. 6. FIG. 9 also shows the positional relationship between the measurement reference position and the light-receiving area RA. As previously described, the reference position is the position where the measurement object TG is at a predetermined reference detection distance ML relative to the sensor substrate 3, i.e., the position where the measurement object TG is located at the design measurement distance. The light-receiving area RA has a step portion 363 that forms the boundary between the wide portion 361 and the narrow portion 362. The reference position is set to be slightly further in the +X direction than the step portion 363 in the light-receiving area RA. In other words, the reference position is set to be near the step portion 363 of the light-receiving area RA, in the wide portion 361, which is the wide light-receiving area.

[0042] When the measurement target TG is at the reference position, the spot position of the spot image SP1 formed by the diffusely reflected light L3, which is the second measurement light L12 reflected from the measurement target TG, is located in the light-receiving area RA, straddling the wide portion 361 and the narrow portion 362. In other words, the reference detection distance ML is set so that the spot position of the spot image SP1 is located in a position straddling the wide portion 361 and the narrow portion 362.

[0043] When the measurement target TG is at a near position closer to the reference position, that is, when the measurement distance is shorter than the reference detection distance ML, the spot position of the spot image SP3 shifts in the -X direction from the reference position and is located on the narrow portion 362. Therefore, the spot image SP3 is irradiated onto the narrow portion 362. That is, the spot image SP3 is received by the narrow light-receiving region. On the other hand, when the measurement target TG is at a far position farther from the reference position, that is, when the measurement distance is longer than the reference detection distance ML, the spot position of the spot image SP2 shifts in the +X direction and is located on the wide portion 361. Therefore, the spot image SP2 is irradiated onto the wide portion 361. That is, the spot image SP2 is received by the wide light-receiving region.

[0044] At the reference position, the measurement optical path length is the design value. The center position of the spot is a small distance from the step portion 363 of the light-receiving area RA toward the +X side, which is the center position in the Y direction. Therefore, the spot image SP1, which has a diameter slightly larger than the Y-direction width of the wide portion 361, is irradiated onto the light-receiving area RA in a manner spanning the wide portion 361 and the narrow portion 362. In other words, the spot image SP1 does not overlap only the wide portion 361, but is intentionally set so that a portion of it extends beyond the step portion 363 and overlaps the narrow portion 362. In other words, the amount of detected light output by the second light-emitting element 35 at the reference position is intentionally suppressed. The spot center position of the spot image SP1 may be set at or near the step portion 363.

[0045] At the near position, the measurement optical path length is shorter than at the reference position, so the amount of light directed toward the second light-emitting element 35 tends to increase. For this reason, it is necessary to suppress the amount of light received by the second light-emitting element 35 at the near position. Furthermore, at the near position, the spot position shifts in the -X direction. In consideration of these points, the narrow portion 362 of the light-receiving area RA is disposed on the -X side of the reference position. At the narrow portion 362, the area where the spot image SP3 and the light-receiving area RA overlap is approximately half of the spot image SP3. Therefore, an increase in the amount of detected light output by the second light-emitting element 35 is suppressed.

[0046] At the far position, the measurement optical path length is longer, so the amount of light directed toward the second light-emitting element 35 tends to decrease. For this reason, it is necessary to increase the amount of light received by the second light-emitting element 35 at the far position. Furthermore, at the far position, the spot position shifts in the +X direction. In consideration of these points, the wide portion 361 of the light-receiving area RA is disposed on the +X side of the reference position. At the wide portion 361, the area where the spot image SP2 and the light-receiving area RA overlap is the majority of the spot image SP2. Therefore, a decrease in the amount of detected light output by the second light-emitting element 35 is suppressed.

[0047] 10 is a graph showing the relationship between the distance from the sensor substrate 3 to the measurement target TG and the detected light intensity for the example and the comparative example, and is a graph showing the light intensity characteristic C1 for the comparative example and the light intensity characteristic C2 for the example. In the case of the second light receiving element 360 having a simple rectangular shape as shown in the comparative example of FIG. 8, the light intensity characteristic C1 shows a large fluctuation in the detected light intensity relative to fluctuations in the measurement distance.

[0048] In contrast, the second light receiving element 36 of the embodiment having the narrow portion 362 on the near position side and the wide portion 361 on the far position side exhibits a light quantity characteristic C2 in which the fluctuation in the detected light quantity is small relative to fluctuations in the measurement distance. This is because when the spot position of the spot image SP shifts to the near position, the narrow portion 362 receives the spot image SP3, thereby suppressing an increase in the detected light quantity, and when the spot position shifts to the far position, the wide portion 361 receives the spot image SP2, thereby suppressing a decrease in the detected light quantity.

[0049] Furthermore, at the reference position, a portion of the spot image SP1 overlaps the narrow portion 362, suppressing the detected light amount of the second light-emitting element 35. Therefore, even if the spot position shifts from the reference position to the near position and the spot image SP1 overlaps predominantly with the narrow portion 362, the detected light amount does not decrease abruptly. Furthermore, as the spot position gradually shifts from the reference position to the far position, the degree to which the spot image SP1 overlaps with the wide portion 361 gradually increases, so the detected light amount also does not change abruptly. Therefore, even if the distance to the measurement target TG approaches or moves away from the reference position, a light amount characteristic C2 can be obtained that is less likely to cause fluctuations in the detected light amount.

[0050] By employing the second light-receiving element 36 of the embodiment, the amount of detected light can be equalized even when the measurement distance varies. FIG. 10 shows the effective measurement range EM, which is the range in which the distance from the sensor substrate 3 to the measurement target TG becomes longer or shorter than the reference detection distance ML within a predetermined tolerance. The second light-receiving element 36 of the embodiment, which has the light intensity characteristic C2, can suppress the variation in the amount of detected light within the effective measurement range EM to 10% or less. The variation in the amount of detected light refers to the variation in the amount of detected light measured within the effective measurement range EM relative to the amount of detected light at the reference position. Specifically, the variation in the amount of detected light can be expressed as the difference in the amount of detected light measured within the effective measurement range EM when the amount of detected light at the reference position is set to 100%. The variation in the amount of detected light is preferably 100% ± 20%, and more preferably 100% ± 10%.

[0051] [Example of Formation of Light Receiving Region] Next, an example of forming the light receiving region RA of the second light receiving element 36 having the wide portion 361 and the narrow portion 362 will be described. There are no particular limitations on the method for forming the light receiving region RA. For example, the light receiving region RA may be formed in the shape of the portion of the second light receiving element 36 that has the light receiving function, or the light receiving region RA may be formed by applying some kind of mask to the portion that has the light receiving function.

[0052] FIG. 11A is a plan view showing a second light-receiving element 36A having a light-receiving region RA according to a first formation example, and FIG. 11B is a cross-sectional view taken along line XIB-XIB in FIG. 11A. The first formation example is an example in which the light-receiving region RA is formed in the shape of the portion having the light-receiving function itself. The second light-receiving element 36A includes an n-type semiconductor substrate 364 and a p-type semiconductor layer 365. The semiconductor substrate 364 is, for example, an n-type silicon substrate. The p-type semiconductor layer 365 is disposed on the upper surface of the semiconductor substrate 364 and is a semiconductor layer doped with p-type impurities.

[0053] A pn junction is formed at the interface between the semiconductor substrate 364 and the p-type semiconductor layer 365. This pn junction is a photoelectric conversion region that performs photoelectric conversion when irradiated with light. In the first formation example, the wide portion 361 and the narrow portion 362 are formed according to the shape of the p-type semiconductor layer 365 itself, that is, according to the shape of the photoelectric conversion region itself. Specifically, the p-type impurity doped region is set to follow the shape of the light-receiving region RA having the wide portion 361 and the narrow portion 362. In the first formation example, the light-receiving region RA is defined by the shape of the photoelectric conversion region itself, which simplifies the process of forming the light-receiving region RA.

[0054] FIG. 12A is a plan view showing a second light-receiving element 36B having a light-receiving area RA according to a second formation example, and FIG. 12B is a cross-sectional view taken along line XIIB-XIIB in FIG. 12A. The second formation example is an example in which the light-receiving area RA is defined by an electrode shape. The second light-receiving element 36B includes an n-type semiconductor substrate 364 and a p-type semiconductor layer 365, similar to those in the first formation example, and an electrode 366. The electrode 366 extracts a current generated by photoelectric conversion at the pn junction.

[0055] In the second formation example, the electrode 366 serves as a mask for defining the light-receiving region RA. The electrode 366 is formed so as to straddle the upper surface of the semiconductor substrate 364 and the periphery of the p-type semiconductor layer 365. The p-type semiconductor layer 365 has a simple rectangular shape. Meanwhile, the shape of the electrode 366 is formed so that the p-type semiconductor layer 365 is exposed in a manner that includes a wide portion 361 and a narrow portion 362. In other words, the light-receiving region RA is defined by the shape of the electrode 366 superimposed on the photoelectric conversion region of the second light-receiving element 36B. According to the second formation example, various shapes of the light-receiving region RA can be formed by selecting the shape of the electrode 366.

[0056] 13A to 13C are diagrams illustrating a third example of the formation of the light-receiving region RA. The light-receiving region RA may be defined by the shape of an aperture that limits the area of ​​incidence of light relative to the photoelectric conversion region of the second light-receiving element 36. Fig. 13A is a cross-sectional view of an optical sensor module SM1 including an aperture 6, Fig. 13B is a plan view showing a second light-receiving element 36C including a light-receiving region RA according to the third example, and Fig. 13C is a cross-sectional view taken along line XIIIC-XIIIC in Fig. 13B.

[0057] The aperture 6 is disposed inside the cover 5 and in front of the sensor board 3. The aperture 6 has an emission opening that passes light emitted from the first light-emitting element 33 and the second light-emitting element 35, and an incidence opening that restricts light that enters the first light-receiving element 34 and the second light-receiving element 36. The shape of the incidence opening can define the range within which light can enter the photoelectric conversion region of the second light-receiving element 36.

[0058] Similar to the second formation example, the second light receiving element 36C has an n-type semiconductor substrate 364 and a p-type semiconductor layer 365 having a simple rectangular shape. An aperture 6 is located in front of the p-type semiconductor layer 365. The shape of the incident opening of the aperture 6 is formed so that the p-type semiconductor layer 365 is exposed in a manner having a wide portion 361 and a narrow portion 362. In other words, the light receiving area RA is defined by the shape of the aperture 6 located in front of the photoelectric conversion area of ​​the second light receiving element 36C. According to the third formation example, various shapes of the light receiving area RA can be formed by selecting the shape of the aperture 6.

[0059] [Various Shapes of Light-Receiving Region] In the above embodiment, an example was shown in which the light-receiving region RA of the second light-receiving element 36 has a rectangular wide portion 361 and a rectangular narrow portion 362 that is narrower in the Y direction than the wide portion 361 and longer in the X direction, and are arranged continuously in the X direction. This is just one example of the light-receiving region RA, and various modifications are possible as long as it includes the wide portion 361 and a portion that fulfills the role of the wide portion 361. Figures 14A to 14E are plan views showing modified shapes of the light-receiving region RA of the second light-receiving element 36.

[0060] 14A shows a second light receiving element 36D in which the X-direction widths of the wide portion 361 and the narrow portion 362 are approximately the same. The X-direction widths of the wide portion 361 and the narrow portion 362 may be set according to the allowable shift range of the spot image SP, i.e., the allowable fluctuation range of the measurement distance between the sensor substrate 3 and the measurement object TG.

[0061] 14B and 14C show examples in which the Y-direction width of the light-receiving region RA varies, including a portion where the Y-direction width gradually narrows from a wide portion 361 to a narrow portion 362. The second light-receiving element 36E in FIG. 14B has a tapered shape in which the Y-direction width of the narrow portion 362 gradually narrows with increasing distance from the wide portion 361. The wide portion 361 has a rectangular shape with a constant Y-direction width. The second light-receiving element 36F in FIG. 14C has a triangular light-receiving region 37 whose Y-direction width gradually narrows from the +X end to the -X end. In this case, the wide portion of the triangular light-receiving region 37 near the +X end functions as the wide portion 361, and the narrow portion near the -X end functions as the narrow portion 362.

[0062] 14D and 14E show examples in which the Y-direction width of the narrow portion 362 does not simply taper, but changes in multiple steps. The narrow portion 362 of the second light-receiving element 36G in FIG. 14D includes a first tapered portion 38A and a second tapered portion 38B. The first tapered portion 38A has a tapered shape in which the Y-direction width gradually narrows toward the -X side. The second tapered portion 38B has a tapered shape in which the Y-direction width gradually widens toward the -X side. The first tapered portion 38A and the second tapered portion 38B are connected at their narrowest portions. In other words, the narrow portion 362 of the second light-receiving element 36G has a shape in which the Y-direction width initially gradually narrows as it moves away from the wide portion 361 toward the -X side, and then gradually widens from the midpoint toward the -X end.

[0063] 14E includes a first portion 38C, a second portion 38D, and a third portion 38E. The first portion 38C is connected to the wide portion 361 and has a relatively wide Y-direction width. The second portion 38D is located near the -X end and has the same Y-direction width as the first portion 38C. The third portion 38E is located between the first portion 38C and the second portion 38D and has a relatively narrow Y-direction width. In other words, the narrow portion 362 of the second light receiving element 36H has a shape in which the Y-direction width narrows in the central region in the X direction.

[0064] The second light receiving elements 36G, 36H shown in Figures 14D and 14E can be said to have a shape that matches the light intensity characteristic C1 shown in Figure 6. The light intensity characteristic C1 has a mountain-shaped characteristic in which the detected light intensity increases as the distance from the reference position to the measurement object TG decreases, and then decreases. The second light receiving elements 36G, 36H have a narrow portion 362 whose Y-direction width narrows in the region where the detected light intensity increases as the sensor substrate 3 and the measurement object TG become closer. Therefore, the detected light intensity can be suppressed and leveled in the mountain region of the light intensity characteristic C1.

[0065] REFERENCE SIGNS LIST 1 color printer 16 density sensor (optical sensor) 3 sensor substrate (optical sensor) 3E element group 3M mounting surface 30 substrate 31 first light-emitting / receiving pair 32 second light-emitting / receiving pair 33 first light-emitting element 34 first light-receiving element 35 second light-emitting element 36 second light-receiving element 361 wide portion 362 narrow portion 364 semiconductor substrate 365 p-type semiconductor layer (photoelectric conversion region) 366 electrode 6 aperture L11 first measurement light L12 second measurement light L2 regular reflection light L3 diffuse reflection light TG measurement object RA light-receiving area X element arrangement direction Y intersection direction

Claims

1. An optical sensor that irradiates light toward a measurement object and detects reflected light from the measurement object, comprising: a substrate having a mounting surface; and an element group including a first light-emitting element, a second light-emitting element, a first light-receiving element, and a second light-receiving element arranged on the mounting surface, wherein the first light-receiving element is arranged at a position where it can receive specularly reflected light from the measurement object of the first measurement light emitted from the first light-emitting element; and the second light-receiving element is arranged at a position where it can receive diffusely reflected light from the measurement object of the second measurement light emitted from the second light-emitting element; and the light-receiving region of the second light-receiving element includes a wide portion having a predetermined first width in a direction intersecting the arrangement direction of the element group, and a narrow portion having a second width narrower than the first width.

2. An optical sensor as described in claim 1, wherein the group of elements is arranged in a row on the mounting surface in the order of a light emitting / receiving pair of the first light emitting element and the first light receiving element, the second light receiving element, and the second light emitting element, and the wide portion is arranged on the side closer to the second light emitting element in the light receiving region, and the narrow portion is arranged on the side farther from the second light emitting element than the wide portion.

3. An optical sensor according to claim 1 or 2, wherein the length of the narrow portion in the arrangement direction is longer than the length of the wide portion.

4. An optical sensor according to claim 1 or 2, wherein the light receiving region of the second light receiving element includes a portion whose width in the intersecting direction gradually narrows from the wide portion toward the narrow portion.

5. An optical sensor according to claim 1 or 2, wherein the narrow width portion includes a portion whose width in the intersecting direction changes in the arrangement direction.

6. An optical sensor according to any one of claims 1 to 5, wherein the light receiving region of the second light receiving element is defined by the shape of the photoelectric conversion region of the second light receiving element itself.

7. An optical sensor according to any one of claims 1 to 5, wherein the light receiving region of the second light receiving element is defined by the shape of an electrode superimposed on the photoelectric conversion region of the second light receiving element.

8. An optical sensor according to any one of claims 1 to 5, wherein the light receiving area of ​​the second light receiving element is defined by the shape of an aperture that limits the area of ​​incidence of light to the photoelectric conversion area of ​​the second light receiving element.

9. An image forming device comprising: an optical sensor according to any one of claims 1 to 8; and an image forming unit facing said optical sensor at a predetermined reference detection distance and comprising a carrier for carrying said object to be measured, wherein said reference detection distance is set so that the spot position of a spot image formed by the reflected light of said second measurement light from said object to be measured straddles said wide portion and said narrow portion.

10. An image forming apparatus according to claim 9, wherein when the distance between said optical sensor and said object to be measured is shorter than said reference detection distance, said spot position is located on said narrow portion.

11. An image forming apparatus according to claim 9, wherein when the distance between the optical sensor and the object to be measured is longer than the reference detection distance, the spot position is located on the wide portion.

12. An image forming apparatus as claimed in claim 9, wherein the variation in the amount of light detected by the second light receiving element is 10% or less within the effective measurement range in which the distance to the object to be measured becomes longer or shorter than the reference detection distance within a predetermined tolerance range.

Images