Density detection method and image forming apparatus

Abstract

To provide a density detection method and an image forming apparatus with which it is possible to correct variations in sensitivity between two light receiving elements to perform more accurate density detection.SOLUTION: A density detection method includes: a step of obtaining a plurality of rays of regular reflected light on a non-image area on an image carrier in different light emission amounts; a step of obtaining a plurality of rays of diffused reflected light on a toner image in different light emission amounts; a third step of detecting reflected light on the toner image with the maximum density simultaneously by using a light receiving element for regular reflected light detection and a second light receiving element for diffused reflection detection; fourth to sixth steps of determining a correction conversion relationship and a sensitivity correction coefficient for outputs from the light receiving elements on the basis of results of the first to third steps; and a seventh step of obtaining a correction detection value for output from the first light receiving element and output from the second light receiving element for a toner image for a test, by using the correction conversion relationship and the sensitivity correction coefficient determined in the fourth to sixth step.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a toner patch density detection method and an image forming apparatus. [Background technology]

[0002] In an image forming apparatus, toner patch density detection is performed when an image quality adjustment process (process control) is performed. Patent Document 1 discloses a method for improving the accuracy of color toner patch density detection by measuring the amount of specularly reflected light and the amount of diffusely reflected light from a color toner patch and detecting the patch density from the difference between these light amounts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-194834 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the sensor for measuring the amount of reflected light from a toner patch requires two light-receiving elements: a light-receiving element (photodiode or phototransistor) for detecting the amount of specularly reflected light, and a light-receiving element for detecting the amount of diffusely reflected light. However, light-receiving elements vary in their light-receiving characteristics (output voltage relative to the amount of incident light), and the detected values ​​for the amount of specularly reflected light and the amount of diffusely reflected light contain errors due to variations in the sensitivity of each light-receiving element. For this reason, in a method for detecting patch density from the difference in the amount of specularly reflected light and the amount of diffusely reflected light, it is necessary to correct the variations in sensitivity of the two light-receiving elements to perform more accurate density detection.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a density detection method and an image forming apparatus that can correct the sensitivity variations between two light receiving elements and perform density detection with higher accuracy. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, a density detection method according to a first aspect of the present disclosure is a density detection method that irradiates a toner image formed on an image carrier with light using a light-emitting element, and detects the density of the toner image from an output of a first light-receiving element that detects specularly reflected light from the toner image and an output of a second light-receiving element that detects diffusely reflected light from the toner image, the density detection method including a first step of irradiating a non-image area on the image carrier with light from the light-emitting element multiple times with different light-emitting intensities and obtaining an output of the first light-receiving element in response to the reflected light at each light-emitting intensities, a second step of irradiating a toner image having a density equal to or higher than a predetermined density formed on the image carrier with light from the light-emitting element multiple times with different light-emitting intensities and obtaining an output of the second light-receiving element in response to the reflected light at each light-emitting intensities, and The method includes a third step of simultaneously obtaining the output of the light receiving element and the output of the second light receiving element; a fourth step of determining a correction conversion relationship for the amount of specularly reflected light based on the detection result of the first step; a fifth step of determining a correction conversion relationship for the amount of diffusely reflected light based on the detection result of the second step; a sixth step of determining a sensitivity correction coefficient for matching the sensitivities of the first light receiving element and the second light receiving element based on the detection result of the third step; and a seventh step of forming a test toner image on the image carrier and obtaining a corrected detection value for the output of the first light receiving element and the output of the second light receiving element for this test toner image using the correction conversion relationship for the amount of specularly reflected light determined in the fourth step, the correction conversion relationship for the amount of diffusely reflected light determined in the fifth step, and the sensitivity correction coefficient determined in the sixth step.

[0007] According to the above configuration, it is possible to correct variations in sensitivity between the first light receiving element and the second light receiving element, and to perform density detection with higher accuracy.

[0008] In the concentration detection method, the fourth step determines a correction conversion relationship for the amount of specularly reflected light by linear interpolation or polynomial interpolation from a plurality of combinations of the light emission amount of the light-emitting element and the output of the first light-receiving element obtained in the first step, the fifth step determines a correction conversion relationship for the amount of diffusely reflected light by linear interpolation or polynomial interpolation from a plurality of combinations of the light emission amount of the light-emitting element and the output of the second light-receiving element obtained in the second step, and the sixth step determines a ratio of the output value of the first light-receiving element and the output value of the second light-receiving element obtained in the third step as a sensitivity correction coefficient. It can be configured as follows.

[0009] In addition, in the concentration detection method, In the seventh step, an ideal specular reflection detection value VrI is calculated for the specular reflection detection value VR, which is the output of the first light receiving element for the test toner image, using the corrected conversion relationship for the amount of specular reflection light calculated in the fourth step, and an ideal diffuse reflection detection value VdI is calculated for the diffuse reflection detection value VD, which is the output of the second light receiving element for the test toner image, using the corrected conversion relationship for the amount of diffuse reflection light calculated in the fifth step, and further, the corrected detection value Vout is calculated using the sensitivity correction coefficient k calculated in the sixth step. Vout=VrI-k×VdI The desired configuration can be achieved as follows.

[0010] The concentration detection method may be configured such that the light emission amount of the light emitting element is made different between the first step and the second step.

[0011] According to the above configuration, specular reflection detection by the first light receiving element and diffuse reflection detection by the second light receiving element can be performed with the light emission intensity of the light emitting element appropriate for each element, which results in more accurate correction of variations in sensitivity of each light receiving element, enabling more accurate concentration detection.

[0012] The density detection method may be configured such that the detection of the light reflected from the toner image in the second and third steps is performed with the image carrier stopped.

[0013] According to the above configuration, since detection can be performed on a stationary toner image, it is possible to determine the correction conversion relationship without being affected by the unevenness of the toner image, thereby enabling accurate density detection.

[0014] In order to solve the above problem, the image forming apparatus of the second aspect of the present disclosure is an image forming apparatus that performs process control for image quality adjustment, and is capable of detecting the density of a toner image using the density detection method described above.By processing the first to sixth steps, the correction conversion relationship for the amount of specularly reflected light obtained in the fourth step, the correction conversion relationship for the amount of diffusely reflected light obtained in the fifth step, and the sensitivity correction coefficient obtained in the sixth step are stored in a memory unit, and during process control, the seventh step is executed using the correction conversion relationship and the sensitivity correction coefficient stored in the memory unit, and the density of a test toner image is detected. [Effects of the Invention]

[0015] The density detection method and image forming apparatus of the present disclosure have the advantage of being able to correct the sensitivity variations between the two light receiving elements and perform density detection with higher accuracy. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present disclosure. [Figure 2] FIG. 4 is a schematic diagram of a process unit for explaining a method for detecting the density of a toner patch. [Figure 3] FIG. 10 is a schematic diagram showing an image sensor when reading an intermediate transfer belt on which no toner patches are formed. [Figure 4]FIG. 2 is a schematic diagram showing an image sensor when reading color toner patches on an intermediate transfer belt. [Figure 5] 10 is a graph schematically showing the relationship between color toner patch density and image sensor output. [Figure 6] FIG. 2 is a block diagram of a control system in an image forming apparatus for implementing a density detection method according to the present disclosure. [Figure 7] 10 is a graph showing an example of the relationship between a light-emitting current value in a light-emitting element and a specular reflection detection value in a first light-receiving element. [Figure 8] 10 is a graph showing an example of the relationship between a light-emitting current value in a light-emitting element and a diffuse reflection detection value in a second light-receiving element. [Figure 9] FIG. 10 is an explanatory diagram of how to obtain a correction formula for calculating an ideal detection value from a specular reflection detection value. DETAILED DESCRIPTION OF THE INVENTION

[0017] [First embodiment] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus 10 according to an embodiment of the present disclosure.

[0018] As shown in FIG. 1, the image forming apparatus 10 is configured to include a main body 11, a document reading unit 12, a document transport device 13, and a paper feed device 14. The main body 11 has an internal image forming unit for forming (printing) an image on recording paper. The document reading unit 12 is disposed above the main body 11 and reads the document when copying the document. In automatic reading mode, the document transport device 13 sequentially transports documents placed on a document set tray toward the document placement table of the document reading unit 12. The paper feed device 14 has at least one paper feed cassette for stocking recording paper, and separates recording paper one sheet at a time from a selected paper feed cassette and transports it toward the main body 11. The main body 11 forms an image on the recording paper sent from the paper feed device 14.

[0019] Image data handled by image forming apparatus 10 corresponds to a color image using each of the colors black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (e.g., black). For this reason, image forming apparatus 10 has four process units Pa-Pd corresponding to black, cyan, magenta, and yellow as image forming sections. Each process unit Pa-Pd has a photosensitive drum 20a-20d (referred to as photosensitive drum 20 when no particular distinction is made) and forms a toner image corresponding to the image data using known electrophotographic technology.

[0020] The toner images formed on the photosensitive drums 20a to 20d of the process units Pa to Pd are sequentially transferred and superimposed on an intermediate transfer belt 15 (image carrier) of the intermediate transfer device 23. This forms a color toner image on the intermediate transfer belt 15. The color toner image on the intermediate transfer belt 15 is transferred onto a recording sheet by the transfer device 16, and the recording sheet is heated and pressed by the fixing unit 17 to fix the color toner image on the recording sheet.

[0021] In the image forming apparatus 10, image quality adjustment processing (process control) is performed at a predetermined timing so that the image quality of the formed image is maintained appropriately. During the process control, a toner patch is formed and the density of the toner patch is detected. FIG. 2 is a schematic diagram of a process unit for explaining a method of detecting the density of a toner patch. Note that the process unit shown in FIG. 2 is a schematic diagram of the black process unit Pa, but the configuration is compatible with any of the process units Pb to Pd.

[0022] Next, the image forming operation by the process unit Pa will be described with reference to FIG. 2. First, the surface of the photosensitive drum 20a, rotated by a drive source (not shown), is uniformly charged to, for example, −600 V by the charging device 21. An electrostatic latent image corresponding to image data is written onto the charged surface of the photosensitive drum 20a by exposure from the exposure device 24. The exposed surface of the photosensitive drum 20a exhibits insulating properties when not irradiated with light, but becomes conductive in areas irradiated with light. Therefore, the potential of the exposed surface area of ​​the photosensitive drum 20a drops to, for example, −80 V. This exposure results in an electrostatic latent image having a potential distribution corresponding to the image data being formed on the surface of the photosensitive drum 20a. The developing device 22 has a developing roller 22a carrying a developer containing toner on its surface. A developing power source 22b that outputs a predetermined voltage, a developing bias, is connected to the developing roller 22a. The difference in voltage between the value (voltage value) of the development bias supplied to the development roller 22a and the electrostatic latent image (surface potential of the exposed area) formed on the surface of the photosensitive drum 20a generates an electrostatic force, which supplies toner from the development roller 22a to the electrostatic latent image, forming a toner image on the surface of the photosensitive drum 20a. The toner image formed on the surface of the photosensitive drum 20a is transferred onto the intermediate transfer belt 15 by an intermediate transfer roller 23a provided in the intermediate transfer device 23. An image sensor 30 that reads the density of the toner image transferred onto the intermediate transfer belt 15 is provided in an area on the intermediate transfer belt 15 between a position facing the process unit Pa and a position facing the transfer device 16, and reads the density of the toner patch TP formed on the intermediate transfer belt 15 by the above operation during process control. Note that the image sensor 30 can be shared for the toner patches TP of each color formed by each of the process units Pa to Pd. After the toner image has been intermediately transferred, the surface of the photosensitive drum 20 is cleaned by a cleaning device and a static eliminator to remove any residual toner and eliminate any residual potential. Note that the exposure device, cleaning device, and static eliminator are not shown in Figure 2.

[0023] Fig. 3 is a schematic diagram showing the image sensor 30 when reading the intermediate transfer belt 15 on which no toner patches are formed. Fig. 4 is a schematic diagram showing the image sensor 30 when reading the color toner patches (toner images) on the intermediate transfer belt 15. In Figs. 3 and 4, the movement direction of the intermediate transfer belt 15 is perpendicular to the paper surface.

[0024] 3 and 4, the image sensor 30 includes one light-emitting element 31 and two light-receiving elements, namely, a first light-receiving element 32 and a second light-receiving element 33. The first light-receiving element 32 detects the amount of specularly reflected light (amount of specularly reflected light) emitted from the light-emitting element 31 and reflected by the intermediate transfer belt 15 or the toner patch. The second light-receiving element 33 detects the amount of diffusely reflected light (amount of diffusely reflected light) emitted from the light-emitting element 31 and reflected by the intermediate transfer belt 15 or the toner patch.

[0025] 3, when a toner patch has not been formed (transferred) on the intermediate transfer belt 15, most of the light (irradiated light) emitted from the light-emitting element 31 toward the intermediate transfer belt 15 is specularly reflected from the surface of the intermediate transfer belt 15 and detected by the first light-receiving element 32, but not detected by the second light-receiving element 33. This is because the surface of the intermediate transfer belt 15 is treated to have a mirror finish, and the irradiated light emitted from the light-emitting element 31 is totally reflected (specularly reflected) on the surface of the intermediate transfer belt 15. The amount of specularly reflected light detected by the first light-receiving element 32 decreases when a black toner patch is formed (transferred) on the surface of the intermediate transfer belt 15, as will be described in detail later.

[0026] FIG. 4 is a diagram showing the direction in which irradiated light is reflected by the surface of a color toner patch when the color toner patch is formed (transferred) on the intermediate transfer belt 15. As shown in FIG. 4, the irradiated light emitted from the light-emitting element 31 is reflected by the surface of the color toner patch not only in a specific direction but also in various directions (so-called diffuse reflection). As a result, a portion of the light reflected by the surface of the color toner patch is detected by the second light-receiving element 33. As described above, when there is no color toner patch on the intermediate transfer belt 15, the light emitted from the light-emitting element 31 is totally reflected by the surface of the intermediate transfer belt 15, and the second light-receiving element 33 does not detect the reflected light. The amount of diffuse reflected light detected by the second light-receiving element 33 increases as the density of the color toner patch increases.

[0027] The amount of light of the specular reflection component detected by the first light receiving element 33 in a state where color toner patches are formed on the intermediate transfer belt 15 will be described in detail later.

[0028] Fig. 5 is a graph showing a schematic relationship between each toner patch density and the detection value (sensor output) of the image sensor 30. In Fig. 5, line L1 shows the relationship between the color toner test patch density and the detection value (sensor output) of the first light receiving element 32, line L2 shows the relationship between the color toner test patch density and the detection value (sensor output) of the second light receiving element 33, and line L3 shows the relationship between the monochrome toner test patch density and the detection value (sensor output) of the first light receiving element 32.

[0029] As shown by line L3 in FIG. 5, the amount of specularly reflected light detected by the first light receiving element 32 in a monochrome toner test patch monotonically decreases as the density of the monochrome toner patch increases. This is because, as the density of the monochrome toner test patch increases, the amount of monochrome toner present on the intermediate transfer belt 15 increases, and the amount of light specularly reflected from the surface of the intermediate transfer belt 15 decreases. In other words, as the density of the monochrome toner patch increases (becomes darker), the surface area (for example, 1 cm²) of the monochrome toner patch decreases. 2This is because the coverage, which is the ratio of the area where monochrome toner is present to the total area of ​​the monochrome toner patch, increases. Here, a coverage of 0% refers to a state where no toner is present, and a coverage of 100% refers to a state where the entire surface of the monochrome toner patch is covered with toner, with no areas of the surface of the intermediate transfer belt 15 exposed through gaps between the toner particles. In particular, because the black pigment in monochrome toner has the property of absorbing light, an increase in coverage not only reduces the amount of specularly reflected light from the intermediate transfer belt 15, but also causes the light irradiated onto the area where monochrome toner is present to be absorbed by the black pigment, so when the density of the monochrome toner patch reaches a predetermined level or higher, the specularly reflected component detected by the first light receiving element 32 almost disappears.

[0030] On the other hand, the amount of diffuse reflection component light detected by the second light receiving element 33 for the color toner test patch monotonically increases as the density of the color toner patch increases, as shown by line L2 in FIG. 5 . This is because, as described above, as the density of the color toner test patch increases, the amount of color toner present on the intermediate transfer belt 15 increases, reducing the amount of light specularly reflected from the surface of the intermediate transfer belt 15 and increasing the amount of diffuse reflection component light reflected from the surface of the color toner. More specifically, color toner does not contain a light-absorbing pigment such as black, so it reflects light from its surface. However, since the surface of color toner, which is powder, has minute irregularities, the reflection direction, which is the direction of reflected light relative to the angle of incidence of incident light, becomes random. Therefore, the second light receiving element 33 is able to detect the reflected light reflected from the surface of the color toner patch. Furthermore, as the density of the color toner patch increases (becomes darker), the amount of color toner present on the surface of the intermediate transfer belt 15 increases, increasing the amount of diffuse reflection component light reflected from the surface of the color toner patch.

[0031] Next, we will explain the amount of specularly reflected light detected by the first light receiving element 32 for a color toner test patch. Line L3, which represents the output of the first light receiving element 32 for the monochrome toner test patch density, monotonically decreases as the toner patch density increases. However, line L1, which represents the output of the first light receiving element 32 for the color toner test patch density, does not monotonically decrease. This is because, as mentioned above, when the coverage of the color toner test patch—in other words, the density of the color toner test patch—exceeds the predetermined value A, the total reflected light component from the intermediate transfer belt 15 disappears and becomes zero. Meanwhile, as the density of the color toner patch increases, the diffused light component diffused on the surface of the color toner patch increases. Therefore, if the first light receiving element 32 and the second light receiving element 33 have the same sensitivity, line L1 and line L2 will have the same shape in areas where the test patch density is greater than the predetermined value A.

[0032] In other words, since the diffusely reflected light is diffused uniformly in all directions, the output value output by the first light receiving element 32 is equal to the output value of the second light receiving element 33 in the area where the density of the color toner test patch is equal to or greater than a predetermined value A.

[0033] As described above, by detecting the density of each toner patch based on the difference in output between the first light receiving element 32 and the second light receiving element 33, it is possible to detect density without the influence of diffused light. Note that for monochrome toner patches, diffuse reflected light does not increase even when the density of the toner patch increases, and density detection can be performed using only the output of the first light receiving element 32. However, there is no particular problem with detecting the density of monochrome toner patches based on the difference in output between the first light receiving element 32 and the second light receiving element 33, just as with color toner patches.

[0034] However, the graph in Figure 5 does not take into account variations in sensitivity between the two light-receiving elements, and in reality, there are variations in sensitivity between the two light-receiving elements due to product variations and other factors. Furthermore, while it is desirable for the relationship between the amount of incident light and the sensor output to be linear, for an actual light-receiving element, the graph showing the relationship between the amount of incident light and the sensor output will bend downward (see Figure 7). The sagging of this graph also tends to be smaller the higher the sensor sensitivity of the light-receiving element, and larger the lower the sensor sensitivity, and is affected by product variations.

[0035] In other words, when the density of the color toner patch is equal to or greater than a predetermined density A, the value of the specular reflected light component detected by the first light receiving element 32 is the diffuse reflected light only, and so the output of the first light receiving element 32 and the output of the second light receiving element 33 should be equal (see FIG. 5). However, in reality, even if the color toner patch has a density equal to or greater than the predetermined density A, the output of the first light receiving element 32 and the output of the second light receiving element 33 often do not equal each other due to a difference in sensitivity between the two light receiving elements. This difference can sometimes prevent accurate density detection.

[0036] The image forming apparatus 10 of the present disclosure can correct the sensitivity variations of the two light receiving elements (first light receiving element 32 and second light receiving element 33) in the image sensor 30 to detect the density of the toner patch with higher accuracy, and the density detection method is described below.

[0037] The density detection method in the image forming apparatus 10 includes first to seventh steps, which will be described below. FIG. 6 is a block diagram of a control system in the image forming apparatus 10 for implementing the density detection method described below. As shown in FIG. 6, the image forming apparatus 10 has a control unit 40 and a storage unit 41 for controlling the density detection of the present disclosure. The control unit 40 has a density calculation unit 401 that calculates density based on the output of the image sensor 30. The control unit 40 includes a processor such as a CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs calculation processing based on a computer program. The storage unit 41 is, for example, a memory that stores data and computer programs required for each process of the control unit 40.

[0038] (1st step) The first step is a step of obtaining a specular reflection detection value VR, which is the amount of light in the specular reflection direction detected by the first light receiving element 32. In this first step, light is irradiated from the light emitting element 31 multiple times at different light emission intensities onto a non-image area (area where no toner patch is formed) on the intermediate transfer belt 15, and the output (specular reflection detection value VR) of the first light receiving element 32 in response to the reflected light at each light emission intensities is obtained. The light emission control of the light emitting element 31 is performed by the control unit 40.

[0039] FIG. 7 is a graph showing an example of the relationship between the light-emitting current value, which is the value of the current supplied to the light-emitting element 31, and the detection value (specular reflection detection value VR) of the first light-receiving element 32 when there is no toner image on the intermediate transfer belt 15. FIG. 7 shows the output value of the first light-receiving element 32 when the light-emitting current value of the light-emitting element 31 is determined to produce a predetermined output, e.g., 2.6 V, and this is defined as the 100% light-emitting current value (reference current value). The graph also shows the output value of the first light-receiving element 32 when the light-emitting current value of the light-emitting element 31 is set to 80%, 60%, 40%, and 20% of the reference current value. For example, if the 100% reference current value is 9.80 mA, the 80% light-emitting current value can be calculated as 9.80 × 0.8 = 7.84 mA. The amount of light emitted by the light-emitting element 31 is proportional to the light-emitting current value.

[0040] 7, the specular reflection detection values ​​VR for light emission current values ​​of 20%, 40%, 60%, 80%, and 100% are designated Vreg1 to Vreg5, and these values ​​are obtained by performing detection multiple times (for example, five times) at each light emission current value and averaging the output values ​​obtained from the first light receiving element 32. The obtained Vreg1 to Vreg5 are stored in the memory unit 41 via the control unit 40. Note that the light emission current value used to measure the specular reflection detection value is not limited to the above example, and the specular reflection detection value may be measured any number of times and at any light emission current value.

[0041] (Second step) The second step is a step of obtaining a diffuse reflection detection value VD, which is the amount of light in the diffuse reflection direction detected by the second light receiving element 33. In this second step, the light emitting element 31 irradiates the color toner patch formed on the intermediate transfer belt 15 with light multiple times at different light emission intensities, and the output (diffuse reflection detection value VD) of the second light receiving element 33 in response to the reflected light at each light emission intensity is obtained. Note that the color toner patch formed in the second step preferably has a high patch density so as to increase the diffuse reflection detection value, and more preferably has a certain density of at least a predetermined density A (for example, density 1 measured on a commercially available X-rite printing densitometer). Therefore, the color toner patch used may not only be a single color toner, but also a patch in which two or more colors of color toner, such as magenta and yellow, are overlapped.

[0042] FIG. 8 is a graph showing an example of the relationship between the light-emitting current value, which is the value of the current supplied to the light-emitting element 31, and the detection value (diffuse reflection detection value VD) of the second light-receiving element 33 when a color toner image is formed on the intermediate transfer belt 15. FIG. 8 shows the output value of the second light-receiving element 33 when the light-emitting current value of the light-emitting element 31 is set to 100%, 80%, 60%, 40%, and 20% of the aforementioned reference value. In FIG. 8, the diffuse reflection detection values ​​VD for the light-emitting current values ​​of 20%, 40%, 60%, 80%, and 100% are designated Vdif1 to Vdif5. These values ​​are obtained by performing detection multiple times (e.g., five times) at each light-emitting current value and averaging the output values ​​of the second light-receiving element 33. The obtained Vdif1 to Vdif5 are stored in the memory unit 41 via the control unit 40.

[0043] (Third Step) The third step is a step of simultaneously obtaining the output of the first light receiving element 32 and the output of the second light receiving element 33 in response to the reflected light of a color toner patch having a predetermined density A or higher formed on the intermediate transfer belt 15. This third step can be performed simultaneously at the stage of the second step if the color toner patch formed in the second step has a density A or higher. For example, in the second step, when the light emitting current value of the light emitting element 31 is set to 100% to obtain the diffuse reflection detection value VD, detection can be performed by the first light receiving element 32 at the same time.

[0044] (Step 4) The fourth step is to determine a correction conversion relationship for the amount of specular reflection light based on the detection results of the first step. In the following explanation, this correction conversion relationship is determined as a correction formula, but it may also be determined as a conversion table. In Figure 7, the ideal straight line showing the relationship between the specular reflection detection value VR obtained in the first step and the ideal specular reflection detection value (VrI: ideal specular reflection detection value) for the light emission current value is shown by a dashed line. This ideal straight line connects the point where the light emission current value is 0% (specular reflection detection value 0 V) ​​and the point where the light emission current value is 100% (specular reflection detection value 2.60 V).

[0045] Table 1 shows an example of the relationship between the light emission current value and specular reflection detection value VR obtained in the first step and the corresponding ideal specular reflection detection value VrI. In the ideal line in Figure 7, the light emission current value and the ideal detection value are proportional to each other, so the ideal specular reflection detection value VrI in Table 1 can be calculated from the specular reflection detection value of 2.6 V at a light emission current value of 100%.

[0046] [Table 1] In the fourth step, a correction conversion relationship (correction formula) is determined for calculating the ideal specular reflection detection value VrI corresponding to the specular reflection detection value VR detected by the first light receiving element 32. This correction conversion relationship is obtained by calculating the ideal specular reflection detection value VrI from the specular reflection detection value VR by linear interpolation. Figure 9 is an explanatory diagram of how to determine the correction formula that shows this correction conversion relationship. Note that Figure 9 shows an example where the specular reflection detection value VR is equal to or greater than Vreg2 and less than Vreg3. A different correction method, such as polynomial interpolation, may also be used. The following describes an example using linear interpolation.

[0047] First, when the light emission current value corresponding to the specular reflection detection value VR is (L), the ideal specular reflection detection value VrI at a light emission current value of 100% exists on the ideal straight line in Figure 7, so VrI=Vreg5×L …(1) This becomes:

[0048] Here, if the light emitting current value (L) is calculated by linear interpolation between Vreg2 and Vreg3, it is as follows: L=0.4+0.2×(VR-Vreg2) / (Vreg3-Vreg2) …(2) This becomes:

[0049] The correction formula for calculating the ideal specular reflection detection value VrI corresponding to the specular reflection detection value VR is obtained by substituting formula (2) into formula (1): VrI=0.4×Vreg5+(0.4+0.2×(VR-Vreg2) /

[0050] (Vreg3-Vreg2)) …(3) This becomes:

[0051] Using the same concept as above, correction formulas are found for the entire range of specular reflection detection values ​​VR from 0 to Vreg5, resulting in the results shown in Table 2 below. The correction formulas found in Table 2 are pre-stored in memory unit 41, and these correction formulas are completed by substituting the specular reflection detection values ​​Vreg1 to Vreg5 measured in the first step.

[0052] [Table 2]

[0053] (5th step) The fifth step is to determine a correction formula for the amount of diffusely reflected light based on the detection results of the second step. In Figure 8, the ideal straight line showing the relationship between the diffuse reflection detection value VD obtained in the second step and the ideal diffuse reflection detection value (VdI: ideal diffuse reflection detection value) for the light-emitting current value is shown by a dashed line. This ideal line is a line connecting the point where the light-emitting current value is 0% (diffuse reflection detection value 0 V) ​​and the point where the light-emitting current value is 100% (diffuse reflection detection value 1.76 V).

[0054] Table 3 shows an example of the relationship between the light-emitting current value and diffuse reflection detection value VD obtained in the second step and the corresponding ideal diffuse reflection detection value VdI. In the ideal line in Figure 8, the light-emitting current value and the ideal detection value are proportional to each other, so the ideal diffuse reflection detection value VdI in Table 1 can be calculated from the diffuse reflection detection value of 1.76 V at a light-emitting current value of 100%.

[0055] [Table 3] In the fifth step, a correction conversion relationship is determined to calculate the ideal diffuse reflection detection value VdI corresponding to the diffuse reflection detection value VD detected by the second light receiving element 33. This correction conversion relationship is obtained by calculating the ideal diffuse reflection detection value VdI from the diffuse reflection detection value VD using linear interpolation. The correction calculation formula for the ideal diffuse reflection detection value VdI for diffuse reflected light can be determined using the same concept as for specular reflected light. A different correction method, such as polynomial interpolation, may also be used. Therefore, when the correction calculation formula is determined for the entire range of the diffuse reflection detection value VD from 0 to Vdif5, the results shown in Table 4 below are obtained. The correction calculation formulas in Table 4 are pre-stored in the memory unit 41, and these correction calculation formulas are completed by substituting the diffuse reflection detection values ​​Vdif1 to Vdif5 measured in the second step.

[0056] [Table 4]

[0057] (Step 6) The sixth step is a step of calculating a sensitivity correction coefficient k for matching the sensitivity of the two light receiving elements based on the detection results of the third step. As described above, when the color toner patch has a density equal to or higher than the predetermined density A, the specular reflection light is zero and only diffuse reflection light is generated. Therefore, if there is no sensitivity difference between the first light receiving element 32 and the second light receiving element 33, the detection values ​​of the two light receiving elements will be equal. Therefore, in the sixth step, the ratio of the output value of the first light receiving element 32 and the output value of the second light receiving element 33, which are simultaneously detected in the third step (for example, the ratio of the output value of the first light receiving element 32 to the output value of the second light receiving element 33), is calculated as the sensitivity correction coefficient k.

[0058] In this embodiment, the detection in the third step is performed with the light-emitting current value of the light-emitting element 31 set to 100%. If the specular reflection detection value VR of the color toner patch with the light-emitting current value of the light-emitting element 31 set to 100% is Vreg5', the sensitivity correction coefficient k is k = Vreg5' / Vdif5...(4) For example, if Vdif5 is 1.76 V and Vreg5′ is 1.00 V as shown in Table 3, the sensitivity correction coefficient k is 1.00 / 1.76=0.568. The calculated sensitivity correction coefficient k is stored in the storage unit 41.

[0059] The above processes (Step 1) to (Step 6) are basically performed before the image forming apparatus 10 is shipped. That is, the image forming apparatus 10 is shipped with the correction formula and the sensitivity correction coefficient k stored in the storage unit 41. Furthermore, the image forming apparatus 10 may perform the processes (Step 1) to (Step 6) again at a predetermined timing (for example, after a predetermined number of process controls have been executed) or in response to an operation by a service technician, etc., to update the correction formula and the sensitivity correction coefficient k after shipping. By updating the correction formula and the sensitivity correction coefficient k, even if a change occurs in the characteristics of the light-emitting element 31, the first light-receiving element 32, or the second light-receiving element 33 of the image sensor 30 due to aging or the like, it is possible to respond to such characteristic changes.

[0060] (7th step) The seventh step is a step in which the density of the toner patch is actually detected during process control. In the seventh step, the correction formula obtained in the fourth and fifth steps and the sensitivity correction coefficient k obtained in the sixth step are used to obtain corrected detection values ​​of the color toner patches formed on the intermediate transfer belt 15, and the density of the color toner patch can be detected based on these corrected detection values. Note that in the seventh step (i.e., during process control), multiple color toner patches (test toner images) with different densities are formed on the intermediate transfer belt 15, and density detection is performed on these multiple color toner patches.

[0061] In the seventh step, in order to detect the diffuse reflection component of the color test patch detected by the first light receiving element 32, the diffuse reflection detection value by the second light receiving element 33 is subtracted from the specular reflection detection value (which includes diffuse reflection) by the first light receiving element 32.

[0062] At this time, for the specular reflection detection value, an ideal specular reflection detection value VrI is calculated based on the correction formula obtained in the fourth step for the actual specular reflection detection value VR by the first light receiving element 32. Also, for the diffuse reflection detection value, an ideal diffuse reflection detection value VdI is calculated based on the correction formula obtained in the fifth step for the actual diffuse reflection detection value VD by the second light receiving element 33. Then, the corrected detection value Vout for the amount of pure specular reflection light from the color test patch is further calculated using a sensitivity correction coefficient k, as follows: Vout = VrI-k × VdI…(5) It can be calculated using the formula:

[0063] Here, an example of calculating the corrected detection value Vout when the specular reflection detection values ​​Vreg1 to Vreg5 and the diffuse reflection detection values ​​Vdif1 to Vdif5 are the values ​​shown in Tables 1 and 3 and the sensitivity correction coefficient k is 0.568 is shown below. In this example, it is assumed that the specular reflection detection value VR by the first light receiving element 32 is 0.53v and the diffuse reflection detection value VD by the second light receiving element 33 is 0.81v for a test patch of the same color (e.g., magenta).

[0064] In this case, the specular reflection detection value 0.53v is equal to or greater than Vreg1 and less than Vreg2, and from the correction formula in Table 2, the ideal specular reflection detection value VrI is VrI=0.2×2.60+0.2×2.60× (0.53-0.27) / (0.76-0.27) =0.80 That is, the specular reflection detection value VR of 0.53V is corrected to the ideal detection value VrI of 0.80V.

[0065] In addition, the diffuse reflection detection value 0.81v is greater than or equal to Vdif2 and less than Vdif3, and according to the correction formula in Table 4, the ideal diffuse reflection detection value VdI is: VdI=0.4×1.76+0.2×1.76× (0.81-0.45) / (0.83-0.45) =1.04 That is, the diffuse reflection detection value VD of 0.81V is corrected to the ideal diffuse reflection detection value VdI of 1.04V.

[0066] Then, the final corrected detection value Vout is calculated from equation (5): Vout=0.80-0.568×1.04 =0.21 and the corrected detection value Vout is calculated as 0.21v. From the above, the corrected detection value Vout can be calculated from the detection value of the image sensor 30 by the above-mentioned correction, and the image forming apparatus 10 calculates the density of the color toner patch (in other words, the amount of toner adhesion per unit area (g / cm 2 ) can be detected with high accuracy. The color toner patch density is calculated from the corrected detection value Vout by a density calculation unit 401 in the control unit 40. A known method can be used as the calculation method in the density calculation unit 401.

[0067] As described above, the concentration detection method of the present disclosure makes it possible to perform more accurate concentration detection by correcting variations in sensitivity between the first light receiving element 32 and the second light receiving element 33. Furthermore, this concentration detection method does not require the selection of the two light receiving elements to be used, such as by combining elements with similar sensitivities, which has the advantage of simplifying the manufacturing procedure and reducing parts costs.

[0068] Second Embodiment In the first embodiment, the light-emitting current value of the light-emitting element 31 in the first step and the light-emitting current value of the light-emitting element 31 in the second step are the same (100% light-emitting current value is 9.80 mA). However, the light-emitting current value of the light-emitting element 31 (i.e., the light emission amount of the light-emitting element 31) may be different between the first step and the second step.

[0069] For example, if the output range of the light receiving elements used as the first light receiving element 32 and the second light receiving element 33 is 0 to 3.3 V, the light emitting current value may be set so that the 100% light emitting current value is as close as possible to the light receiving element output value of 3.3 V. Table 5 shows an example of the relationship between the light emitting current value and specular reflection detection value obtained in the first step and the corresponding ideal detection value. Table 6 shows an example of the relationship between the light emitting current value and diffuse reflection detection value obtained in the second step and the corresponding ideal detection value.

[0070] [Table 5]

[0071] [Table 6] In the method of this embodiment, the light-emitting current value used to obtain the specular reflection detection value VR and the light-emitting current value used to obtain the diffuse reflection detection value VD are set to different current values. This allows the specular reflection detection value VR and the diffuse reflection detection value VD to be detected using the light-emitting element 31's light-emitting intensity appropriate for each. Specifically, detection can be performed using almost the entire output range of each of the first light-receiving element 32 and the second light-receiving element 33, thereby improving the accuracy of the correction formulas obtained in the fourth and fifth steps. In other words, variations in the sensitivity of each light-receiving element can be detected more accurately, resulting in more accurate concentration detection.

[0072] Third Embodiment In the second and third steps described above, when detecting reflected light from the color toner patch, the intermediate transfer belt 15 may be stopped with the color toner patch moved to the detection position of the image sensor 30.

[0073] In this case, the image sensor 30 can perform detection on the stopped color toner patch, so that the correction formula can be determined without being affected by the unevenness of the color toner patch, and the density can be detected accurately.

[0074] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be determined based on the claims.

[0075] For example, in each of the above embodiments, the color toner patch to be detected by the image sensor 30 is formed on the intermediate transfer belt 15 as an image carrier, but the image carrier of the color toner patch to be detected may also be the photosensitive drum 20. [Explanation of symbols]

[0076] 10 Image forming device 15 Intermediate transfer belt (image carrier) 20 Photosensitive drum 30 Image Sensor 31 Light-emitting element 32 first light receiving element 33 Second light receiving element 40 Control Unit 41 Storage section 401 Concentration calculation section Pa~Pd process unit

Claims

1. A density detection method comprising: irradiating a toner image formed on an image carrier with light by a light-emitting element; and detecting the density of the toner image from an output of a first light-receiving element that detects specularly reflected light from the toner image and an output of a second light-receiving element that detects diffusely reflected light from the toner image, a first step of irradiating a non-image area on the image carrier with light from the light-emitting element multiple times with different light emission intensities, and obtaining an output of the first light-receiving element in response to reflected light at each light emission intensity; a second step of irradiating a toner image having a density equal to or higher than a predetermined density formed on the image carrier with light from the light emitting element a plurality of times with different light emission intensities, and obtaining an output of the second light receiving element in response to reflected light at each light emission intensity; a third step of simultaneously obtaining an output from the first light receiving element and an output from the second light receiving element in response to reflected light from a toner image having a predetermined density or higher formed on the image carrier; a fourth step of determining a correction conversion relationship for the amount of specularly reflected light based on the detection result of the first step; a fifth step of determining a correction conversion relationship for the amount of diffusely reflected light based on the detection result of the second step; a sixth step of calculating a sensitivity correction coefficient for adjusting the sensitivities of the first light receiving element and the second light receiving element based on the detection result of the third step; a seventh step of forming a test toner image on the image carrier, and obtaining a corrected detection value for the output of the first light receiving element and the output of the second light receiving element for the test toner image using the correction conversion relationship for the amount of specular reflected light obtained in the fourth step, the correction conversion relationship for the amount of diffuse reflected light obtained in the fifth step, and the sensitivity correction coefficient obtained in the sixth step.

2. 2. The concentration detection method according to claim 1, the fourth step is to determine a correction conversion relationship for the amount of specular reflection light by linear interpolation or polynomial interpolation from a plurality of combinations of the light emission amount of the light-emitting element and the output of the first light-receiving element obtained in the first step; the fifth step is to determine a correction conversion relationship for the amount of diffusely reflected light by linear interpolation or polynomial interpolation from a plurality of combinations of the light emission amount of the light-emitting element and the output of the second light-receiving element obtained in the second step; The sixth step of the concentration detection method comprises determining a ratio between the output value of the first light receiving element and the output value of the second light receiving element obtained in the third step as a sensitivity correction coefficient.

3. 3. The concentration detection method according to claim 2, In the seventh step, an ideal specular reflection detection value VrI is obtained for the specular reflection detection value VR, which is the output of the first light receiving element for the test toner image, using the corrected conversion relationship related to the amount of specular reflection light obtained in the fourth step, and an ideal diffuse reflection detection value VdI is obtained for the diffuse reflection detection value VD, which is the output of the second light receiving element for the test toner image, using the corrected conversion relationship related to the amount of diffuse reflection light obtained in the fifth step, and further, a corrected detection value Vout is calculated using the sensitivity correction coefficient k obtained in the sixth step. Vout=VrI-k×VdI A concentration detection method characterized by determining the concentration as follows.

4. 2. The concentration detection method according to claim 1, A concentration detection method, characterized in that the light emitting element emits light in an amount different from that emitted in the first step and the second step.

5. 2. The concentration detection method according to claim 1, The density detecting method is characterized in that the detection of the light reflected from the toner image in the second and third steps is carried out with the image carrier stopped.

6. An image forming apparatus that performs process control for image quality adjustment, The density of a toner image can be detected by using the density detection method according to any one of claims 1 to 5, By performing the processes of the first step to the sixth step, the correction conversion relationship regarding the amount of specularly reflected light obtained in the fourth step, the correction conversion relationship regarding the amount of diffusely reflected light obtained in the fifth step, and the sensitivity correction coefficient obtained in the sixth step are stored in a storage unit; an image forming apparatus, characterized in that, during process control, the seventh step is executed using the correction conversion relationship and sensitivity correction coefficient stored in the storage unit, and the density of a test toner image is detected.

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