Image forming apparatus

Abstract

To reduce the frictional force of a cleaning nip part in control of image density of an image forming apparatus.SOLUTION: A CPU performs control to allow execution of a patch measurement step (S919-S925) of causing an optical sensor to irradiate a patch with light from a light-emitting device and detect reflected light, and a background measurement step (S916-S918) of causing the optical sensor to irradiate a surface of an intermediate transfer belt with light from a light source and detect reflected light, and when the background measurement step is executed, the CPU forms a patch for gain adjustment for supplying toner to a nip part in a second area that is an area of the intermediate transfer belt different from a first area (S916).SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and more particularly to, for example, a color image forming apparatus.

Background Art

[0002] Conventionally, an intermediate transfer body system has been known as an electrophotographic color image forming apparatus such as a copying machine or a laser printer. In a color image forming apparatus of the intermediate transfer body system, a toner image formed on a photosensitive drum is primarily transferred onto an intermediate transfer body and then secondarily transferred onto a transfer material. At this time, since toner that could not be completely transferred onto the transfer material remains on the intermediate transfer body as residual toner, it is necessary to clean the residual toner. As cleaning means, a plate-shaped cleaning member (cleaning blade) formed of an elastic material such as rubber is often used. Then, the edge of the cleaning blade is brought into contact with the intermediate transfer body to scrape off and remove the residual toner. This cleaning blade method has a simple configuration and low cost, and excellent residual toner removal performance, and has been widely put into practical use.

[0003] On the other hand, in a color image forming apparatus of the intermediate transfer body system, as it is used, nitrogen oxides, toner resin, etc. adhere to the surface of the intermediate transfer body, increasing the friction coefficient of the surface of the intermediate transfer body. As a result, the frictional force of the cleaning nip portion, which is the contact portion between the edge portion of the cleaning blade and the intermediate transfer body, also increases. When this frictional force increases, a stick-slip motion of the cleaning blade occurs, causing cleaning failures, abnormal noises (blade rattling), and abnormal vibrations (shivering). If this state continues, there is a risk of image defects due to, for example, damage to the edge portion of the cleaning blade or the surface of the intermediate transfer body. To solve such problems, for example, Patent Document 1 proposes a method of periodically supplying a toner image as a lubricant to the cleaning nip portion.

[0004] Furthermore, the market constantly demands higher image quality from color image forming machines. Generally, changes in the environment or prolonged use can cause fluctuations in various parts of the machine, resulting in variations in the density and gradation characteristics of the resulting images. Such fluctuations disrupt the color balance of the output image and significantly degrade image quality (also known as image resolution). Therefore, in order to obtain high-quality images, it is necessary to equip color image forming machines with adjustment mechanisms to maintain a constant density and gradation characteristics.

[0005] Therefore, the following method is used to obtain stable density and gradation characteristics in the image forming apparatus. First, a test toner image called a patch is formed on an intermediate transfer medium using toners of each color provided by the color image forming apparatus under predetermined image forming conditions. The amount of toner applied to the formed patch (toner weight per unit area) is detected by an optical sensor or the like to obtain density-related information (density, chromaticity, etc.). Then, image density control is performed by applying feedback to the image forming conditions based on the relationship between the image forming conditions when the patch was formed and the density-related information of the obtained patch. This ensures that an image with stable density and gradation characteristics is obtained. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-282010 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in conventional image density control, preparatory operations such as measuring the circumference and surface condition of the intermediate transfer body, which is the image carrier, are required before patch formation. As a result, the intermediate transfer body circulates more frequently than during normal image formation when no toner image is being formed. In particular, if this image density control is performed in conditions where the frictional force of the cleaning nip is high, such as in a high-temperature, high-humidity environment, the cleaning blade is more likely to exhibit stick-slip motion.

[0008] This invention was made under these circumstances and aims to reduce the frictional force of the cleaning nip portion in the image density control of an image forming apparatus. [Means for solving the problem]

[0009] To solve the above-mentioned problems, the present invention has the following configuration. (1) an endlessly shaped image carrier; forming means for forming a toner image on the image carrier; a light source for irradiating the surface of the image carrier and the toner image formed on the image carrier with light; a first detection means for detecting reflected light reflected by the image carrier or the toner image formed on the image carrier by irradiating the image carrier or the toner image formed on the image carrier with light from the light source; a removal means for contacting the image carrier to form a nip portion and removing toner from the image carrier at the nip portion; and a first toner image formed in a first region detectable by the first detection means on the image carrier. An image forming apparatus comprising: control means for controlling image forming conditions when forming an image on a transfer material based on the result of detecting the reflected light, wherein the control means controls to enable the execution of: a first measurement in which the first detection means irradiates the first toner image with light from the light source and detects the reflected light; and a second measurement in which the first detection means irradiates the surface of the image carrier with light from the light source and detects the reflected light; and when the second measurement is performed, the control means controls to form a second toner image for supplying toner to the nip portion in a second region which is a region of the image carrier different from the first region. [Effects of the Invention]

[0010] According to the present invention, the frictional force of the cleaning nip portion can be reduced in the image density control of an image forming apparatus. [Brief explanation of the drawing]

[0011] [Figure 1]Vertical cross-sectional view showing the schematic configuration of the image forming apparatuses of Examples 1 and 2 [Figure 2] Enlarged schematic view of the intermediate transfer belt and the imprint processing die of Examples 1 and 2 [Figure 3] Schematic configuration diagram of the optical sensor of Examples 1 and 2 [Figure 4] Graph showing the spectral reflectance of the toner of Examples 1 and 2 [Figure 5] Diagram showing the state of the reflected light when the irradiation light of the optical sensor of Examples 1 and 2 is irradiated [Figure 6] Diagram showing the state of the reflected light from the black toner to the optical sensor of Examples 1 and 2 [Figure 7] Enlarged schematic view of the imprint overlapping portion of the intermediate transfer belt of Examples 1 and 2 [Figure 8] Graph showing the state of the specular reflection output near the imprint overlapping portion of Examples 1 and 2 [Figure 9] Flowchart showing the image density control process of Example 1 [Figure 10] Diagram showing the relationship of various timings of the image density control process of Example 1 [Figure 11] Diagram showing the relationship of the shift amount of the sampling data of Example 1 [Figure 12] Diagram showing the gain adjustment patch and the lubricating toner image of Example 1 [Figure 13] Diagram showing the configuration of the patch in the patch measurement of Example l [Figure 14] Diagram showing the relationship between the patch and the measurement spot of Example 1 [Figure 15] Diagram showing another configuration of the control unit and the lubricating toner image of Example 2

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings by way of examples.

Examples

[0013] Hereinafter, the image forming apparatus according to Example 1 will be described in detail with reference to FIGS. 1 to 14. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this example are not intended to limit the scope of the present invention only to these, unless specifically described.

[0014] [Image Forming Apparatus] FIG. 1 shows an example of an image forming apparatus that forms a color image on a transfer material in Example 1, and also shows the vertical direction. The image forming apparatus 100 shown in FIG. 1 is an intermediate transfer type tandem full-color image forming apparatus 100 using an intermediate transfer member as an image carrier, and FIG. 1 is a longitudinal sectional view showing its schematic configuration. The image forming apparatus 100 shown in FIG. 1 has four image forming units as forming means, that is, image forming units SY, SM, SC, and SBk that form toner images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk), arranged in order from upstream to downstream. Here, upstream and downstream refer to upstream and downstream in the moving direction (also referred to as the rotation direction or the pivoting direction) of the intermediate transfer belt 14 described later. Above the image forming units SY, SM, SC, and SBk, an intermediate transfer belt 14, which is an intermediate transfer member stretched over rollers 13, 19, and 30, is disposed. The configuration of the intermediate transfer belt 14 will be described later. Hereinafter, except when describing members used for forming an image of a specific color, the subscripts Y, M, C, and Bk of the reference numerals are omitted.

[0015] Each image forming unit S includes an integrated process cartridge composed of a drum unit 10 and a developing unit 8. Among these, the drum unit 10 includes a photosensitive drum 1, which is a photoreceptor having an OPC (organic photoconductor) photosensitive layer, a cleaning blade 9 made of elastic rubber, and a charging roller 2. The developing unit 8 includes a developing roller 5 as developing means, a non-magnetic one-component toner 3 charged negatively, a toner coating roller 6, and a toner coating blade 7.

[0016] Below each image forming section SY, SM, SC, SBk, there is an exposure apparatus 11 consisting of a scanner unit that scans laser light using a multifaceted mirror. The exposure apparatus 11 irradiates the photosensitive drums 1Y, 1M, 1C, 1Bk with modulated scanning beams 12Y, 12M, 12C, 12Bk based on the image data to form an electrostatic latent image. In Embodiment 1, the image data is represented by 8-bit data for each color, i.e., 256 levels from 00H to FFH (H means hexadecimal representation). Image data FFH represents the image with the highest image density (hereinafter referred to as a solid image), and as the image data decreases, the image density decreases, with 00H being a non-image (hereinafter referred to as a solid white image).

[0017] Inside the intermediate transfer belt 14 are primary transfer rollers 4Y, 4M, 4C, and 4Bk, which press the intermediate transfer belt 14 against the photosensitive drums 1Y, 1M, 1C, and 1Bk from above. A constant current controlled positive voltage is applied to these primary transfer rollers 4 from a power supply (not shown), and the toner image formed on the photosensitive drum 1 (on the photoreceptor) is transferred to the intermediate transfer belt 14 (on the image carrier) (hereinafter referred to as primary transfer). The secondary transfer rollers 20 transfer the toner image formed on the intermediate transfer belt 14 to the transfer material P (hereinafter referred to as secondary transfer). A constant current controlled positive voltage is applied to the secondary transfer rollers 20 from a power supply (not shown).

[0018] Of the three rollers 13, 19, and 30 that support the intermediate transfer belt 14, roller 13 is both a drive roller and a secondary transfer opposing roller, driving and conveying the intermediate transfer belt 14 in the direction of arrow R14, and forming a secondary transfer nip portion with the secondary transfer roller 20 via the transfer material P. Roller 30 is an auxiliary roller, maintaining a predetermined angle between the transfer material P near the secondary transfer nip portion and the surface of the intermediate transfer belt 14, thereby suppressing abnormal discharge between the transfer material P and the toner image on the intermediate transfer belt 14. Roller 19 is a tension roller, stretching the intermediate transfer belt 14 at a predetermined tension.

[0019] A cleaning blade 22, which is a removal means, is positioned opposite the roller 19, with the intermediate transfer belt 14 in between. The cleaning blade 22 contacts the intermediate transfer belt 14 to form a nip, and removes toner from the intermediate transfer belt 14 at the nip. The cleaning blade 22 consists of a urethane rubber plate blade as an elastic blade for cleaning toner that remains on the intermediate transfer belt 14 without being transferred to the transfer material P during secondary transfer (hereinafter referred to as residual toner). Since the cleaning blade 22 is positioned relative to the roller 19, a predetermined angle and amount of penetration are maintained even with respect to the movement of the roller 19. In Example 1, the longitudinal width for image formation is, for example, 214 mm, so the longitudinal width of the cleaning blade 22 is set to 220 mm. Here, longitudinal width refers to the length in the longitudinal direction, and the longitudinal direction refers to the direction of the rotation axis of the roller 19. The fixing device 21 consists of a fixing roller 21a and a pressure roller 21b, and melts and fixes the unfixed toner image formed on the transfer material P.

[0020] [Control Unit] The image forming apparatus 100 has a control unit 29, and the detailed configuration of the control unit 29 is shown on the left side of Figure 1. The control unit 29 of the image forming apparatus 100 has a CPU 24, RAM 25, ROM 26, non-volatile RAM 27, pattern generation unit 28, and timer 40. The CPU 24 is connected to the exposure device 11, as well as the RAM 25, ROM 26, non-volatile RAM 27, pattern generation unit 28, etc. ROM 26 is a read-only memory, and programs and various data for the CPU 24 to control the image forming apparatus 100 are written to it. RAM 25 is a read-write memory, and data from ROM 26 is extracted from it, and data for image density control is stored there. The pattern generation unit 28 generates image data for patches for image density control, which will be described later. Non-volatile RAM 27 is a read-write memory whose contents are retained even when the power to the image forming apparatus 100 is cut off. The timer 40 is used by the CPU 24 to perform various timing controls of the image forming apparatus 100.

[0021] [Image Formation Process] When the image formation operation begins, the photosensitive drum 1 and the intermediate transfer belt 14, etc., start rotating in the direction of the arrow at a predetermined process speed (160 mm / s in this case). The photosensitive drum 1 is uniformly charged by the charging roller 2 to which a predetermined charging voltage is applied. Subsequently, an electrostatic latent image based on the image signal is formed by the scanning beam 12 from the exposure device 11. At this time, the electrostatic latent images of each color are formed at predetermined timings for each color so that the four colors will later be superimposed on the intermediate transfer belt 14 to form a full-color image. As the exposed photosensitive drum 1 rotates further, the electrostatic latent images on the photosensitive drum 1 are visualized (developed) by the developing roller 5 to which a developing voltage is applied. Then, toner images of Y, M, C, and Bk are formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk, respectively. As the toner image on the photosensitive drum 1Y rotates further, the yellow toner image is transferred onto the intermediate transfer belt 14 by the primary transfer roller 4Y to which a transfer voltage is applied. Then, in sync with the movement of the intermediate transfer belt 14, the toner images of M, C, and Bk are sequentially transferred onto the intermediate transfer belt 14 by the application of transfer voltages by the primary transfer rollers 4M, 4C, and 4Bk, and four-color toner images are formed on the intermediate transfer belt 14.

[0022] The transfer material P loaded in the paper feed cassette 15 is fed by the crescent-shaped paper feed roller 16, separated into individual sheets by the separation roller 17, and transported to the registration (hereinafter referred to as resist) roller 18, where it is temporarily stopped. The temporarily stopped transfer material P is transported (supplied) to the secondary transfer nip section by the resist roller 18 in synchronization with the timing when the four-color toner images formed on the intermediate transfer belt 14 reach the secondary transfer nip section. Then, the full-color toner image on the intermediate transfer belt 14 is transferred onto the transfer material P by the application of voltage between the secondary transfer roller 20 and the secondary transfer opposing roller 13. The transfer material P with the transferred toner image is separated from the intermediate transfer belt 14 and sent to the fixing device 21. There, the toner image is melted and fixed to the surface of the transfer material P by heating and pressurizing by the fixing roller 21a and the pressure roller 21b, and the fixed transfer material P is discharged onto the discharge tray 31.

[0023] In the primary transfer, any remaining toner on the photosensitive drum 1 that was not transferred to the intermediate transfer belt 14 is removed by the cleaning blade 9. In the secondary transfer, any remaining toner on the intermediate transfer belt 14 that was not transferred to the transfer material P is removed at the cleaning nip portion 32 (nip portion), which is the contact point between the edge of the cleaning blade 22 and the intermediate transfer belt 14, and is collected in the waste toner container 33. The optical sensor 23 will be described later.

[0024] [Intermediate transfer belt configuration] Figure 2(a) is an enlarged schematic view of the intermediate transfer belt 14 as seen from the cross-sectional direction. The intermediate transfer belt 14 is endless in shape and consists of a base layer 141 and a surface layer 142. In Example 1, the surface layer 142 is in contact with the cleaning blade 22, and the base layer 141 is in contact with the rollers 13, 19, and 30. The base layer 141 is made of a polyethylene naphthalate resin substrate in which carbon is dispersed as a conductive agent, and the volume resistivity is, for example, 1 × 10⁻⁶ 10 The material is adjusted to be Ω·cm. The thickness of the base layer 141 is 70 μm, and its color is, for example, black. In Example 1, polyethylene naphthalate resin was used as the base material and carbon as the conductive agent, but the configuration is not limited to this.

[0025] The surface layer 142 consists of an acrylic resin substrate with zinc oxide, for example, dispersed as an electrical resistance modifier. The layer thickness is approximately 3 μm. From the viewpoint of strength, including abrasion resistance and crack resistance, the surface layer 142 is preferably made of a resin material (curable resin) among curable materials, and in particular, an acrylic resin obtained by curing an unsaturated double bond-containing acrylic copolymer is preferred. Since acrylic resin is transparent, the intermediate transfer belt will be black.

[0026] To improve the wear resistance of the cleaning blade 22 surface during long-term use, a fine uneven surface 142a is applied to the surface of the intermediate transfer belt 14, specifically the surface layer 142. In Figure 2(a), only some of the uneven surfaces are labeled with reference numerals. Polishing, cutting, and imprinting are generally known methods for processing the fine uneven surface 142a, but in the configuration of Example 1, imprinting was adopted from the viewpoint of processing cost, productivity, and shape accuracy.

[0027] In the imprint process, the intermediate transfer belt 14 is first pressed into a core made of carbon tool steel. Figure 2(b) is an enlarged schematic diagram of the imprint die G for forming a fine uneven shape 142a on the surface of the intermediate transfer belt 14. The imprint die G (hereinafter referred to as die G) is formed by cutting parallel to the circumferential direction of the cylinder at equal intervals of p = 7.0 μm, with a tip width v = 2.0 μm and a height h = 2.0 μm. In Figure 2(b), only one of the protrusions is labeled G1 for clarity. The die G is heated by a heater (not shown) to a temperature of 130°C, which is 5 to 15°C higher than the glass transition temperature of polyethylene naphthalate, the base material of the base layer 141. With the intermediate transfer belt 14 in contact with the mold G, the core is rotated once at a peripheral speed of 264 mm / s to drive the mold G into rotation, and then the mold G is separated to obtain the intermediate transfer belt 14 with an imprinted surface. As a result, the intermediate transfer belt 14 of Example 1 is black, and the convex parts of its surface are mirror-finished.

[0028] Observation of the surface shape of the intermediate transfer belt 14 after imprint processing using a Keyence VK-X250 laser microscope revealed the formation of concave grooves with a spacing of approximately w = 7.5 μm and a depth of d = 1.0 μm. These fine irregularities 142a reduce the frictional force between the intermediate transfer belt 14 and the cleaning blade 22, thereby suppressing wear of the cleaning blade 22 over a long period of time.

[0029] [Optical sensor] As shown in Figure 1, an optical sensor 23 is positioned downstream of the image forming unit SBk, facing the roller 30 via an intermediate transfer belt 14. The optical sensor 23 functions as a first detection means that detects reflected light reflected by the intermediate transfer belt 14 or the toner image formed on the intermediate transfer belt 14 by irradiating the intermediate transfer belt 14 or the toner image formed on the intermediate transfer belt 14 with light from a light source. This allows for the detection of the amount of toner applied. Here, the amount of toner applied is the weight of toner per unit area. The optical sensor 23 is positioned approximately in the center of the longitudinal direction (rotation axis direction) of the roller 30 and is connected to the CPU 24. Note that there is a correlation between the amount of toner applied and density-related information (density and chromaticity), so these terms may be used interchangeably from now on.

[0030] As shown in Figure 3, the optical sensor 23 consists of a light-emitting element 231 such as an LED, light-receiving elements 232 and 233 such as a photodiode and CdS, a holder 234, and a circuit section 235. The light-emitting element 231 is a light source that irradiates light onto the surface of the intermediate transfer belt 14 and the toner image formed on the intermediate transfer belt 14. The CPU 24 controls the light emission intensity of the light-emitting element 231 by controlling the drive circuit 236. The first light-receiving element 232 outputs a current corresponding to the amount of light received to the IV conversion section 237. The second light-receiving element 233 outputs a current corresponding to the amount of light received to the IV conversion section 238. The IV conversion section 237 converts the input current into a voltage and outputs it to the gain adjustment amplifier section 239. The IV conversion section 238 converts the input current into a voltage and outputs it to the gain adjustment amplifier section 240. The first amplifier section, the gain adjustment amplifier section 239, amplifies the input voltage by a predetermined gain (first gain) and outputs the analog signal 241 to the A / D (analog-to-digital conversion) port of the CPU 24. The second amplifier section, the gain adjustment amplifier section 240, amplifies the input voltage by a predetermined gain (second gain) and outputs the analog signal 242 to the A / D (analog-to-digital conversion) port of the CPU 24. The gains in the gain adjustment amplifier sections 239 and 240 are adjusted and set by the CPU 24.

[0031] The light-receiving element 232 is positioned to detect so-called specular reflected light, which is reflected from the surface of the intermediate transfer belt 14 at the same angle as the irradiated light. On the other hand, the light-receiving element 233 is positioned to detect diffusely reflected light from the intermediate transfer belt 14. In this configuration, the optical sensor 23 irradiates light from the light-emitting element 231 onto a patch T formed on the intermediate transfer belt 14. The optical sensor 23 outputs signals according to the amount of light received, with the reflected light received by the patch T being treated as a specular reflection output by the light-receiving element 232 and as a diffuse reflection output by the light-receiving element 233. Specifically, the optical sensor 23 outputs signal 241 as a specular reflection output to the CPU 24 and signal 242 as a diffuse reflection output to the CPU 24. Hereafter, the signal 241 output to the CPU 24 will also be referred to as the specular reflection output, and the signal 242 as the diffuse reflection output.

[0032] The spectral reflectance of each toner in Example 1 is shown in Figure 4. Figure 4 is a graph showing wavelength (nm) on the horizontal axis and reflectance (%) on the vertical axis. In Figure 4, the wide-pitch dashed line shows the case where patch T is yellow (Y), the solid line shows the case where patch T is magenta (M), the narrow-pitch dashed line shows the case where patch T is cyan (C), and the dashed-dot line shows the case where patch T is black (Bk). Spectral reflectance shows the change in reflectance when light is shone on an object while changing the wavelength. The region indicated by the arrow in Figure 4 (760nm to 1000nm) is the near-infrared region, and the reflectance in the near-infrared region is almost the same regardless of the color for color toners, showing a high reflectance (over 80%). Furthermore, the reflectance in this region shows the same change in response to the change in the amount of toner applied, regardless of the color Y, M, or C. Therefore, an LED emitting near-infrared light around 850nm was used as the light-emitting element 231 of the optical sensor 23 in Example 1. In the case of black (Bk), the spectral reflectance is low, less than 10%, which indicates that light in the near-infrared region is absorbed by the black patch T.

[0033] Next, the characteristics of the reflected light detected when the patch T is detected by the optical sensor 23 will be described in detail. As shown in Figure 5(a), the light irradiated onto the intermediate transfer belt 14 is reflected by the surface of the intermediate transfer belt 14 and detected by the photodetectors 232 and 233. However, since the intermediate transfer belt 14 in Example 1 is black and the convex parts of its surface are mirrored, most of the near-infrared light irradiated onto the intermediate transfer belt 14 becomes specularly reflected light, and most of it is detected by the photodetector 232, with almost no detection by the photodetector 233. Here, the amount of specularly reflected light is represented by the number of arrows. On the other hand, as shown in Figure 5(b), when a patch of black toner (hereinafter referred to as black toner) tn1 is formed on the intermediate transfer belt 14, the amount of specularly reflected light from the intermediate transfer belt 14 decreases. This is because, as can be seen from the spectral reflectance in Figure 4, the black toner tn1 absorbs the near-infrared irradiated light and also hides the surface of the intermediate transfer belt 14, which is the base material, with the patch itself.

[0034] The relationship between the amount of toner applied to the patch and the amount of specularly reflected light at this time is a one-to-one relationship, as shown in Figure 5(c). Figure 5(c) shows the amount of toner applied on the horizontal axis and the amount of specularly reflected light on the vertical axis. Figure 5(c) shows that the amount of specularly reflected light decreases as the amount of toner applied increases. It also shows that the amount of specularly reflected light decreases rapidly until the amount of toner applied reaches a predetermined amount, and then the rate of decrease in specularly reflected light becomes more gradual even if the amount of toner applied increases thereafter. If this relationship is established in advance, the amount of toner applied to the patch can be determined from the amount of specularly reflected light. In other words, the CPU 24 can determine the amount of toner applied to the patch based on the detection result of the optical sensor 23.

[0035] On the other hand, when near-infrared light is shone onto patches of colored toners such as Y, M, and C (hereinafter referred to as colored toners), they reflect the shone light, unlike black toners, as can be seen from the spectral reflectance in Figure 4. Most of this reflection is diffuse reflection. As a result, as shown in Figure 6(a), the specularly reflected light detected by the light-receiving element 232 is the sum of "light specularly reflected by the substrate," which decreases with increasing toner coverage, and "light diffusely reflected by the toner," which increases with increasing toner coverage. In Figure 6(a), tn2 represents the colored toner. The group of arrows radiating from the colored toner tn2 also represents diffusely reflected light.

[0036] Therefore, the relationship between the amount of toner applied and the amount of specularly reflected light is as shown in Figure 6(b). In Figure 6(b), the horizontal axis shows the amount of toner applied, and the vertical axis shows the amount of reflected light. In Figure 6(b), the thick solid line shows the light detected by the optical sensor 23, the thin solid line shows the specular reflection component detected by the light-receiving element 232, and the dashed line shows the diffuse reflection component detected by the light-receiving element 233. As shown in Figure 6(b), the sum of the thin solid line, which is the characteristic of specular reflection, and the dashed line, which is the characteristic of diffuse reflection, is a negative characteristic, i.e., a thick solid line. A negative characteristic is a characteristic in which the amount of reflected light decreases as the amount of toner applied increases, but the amount of specularly reflected light begins to increase again once the amount of toner applied increases beyond a certain point. This indicates that there is not a one-to-one relationship between the amount of toner applied and the amount of specularly reflected light necessary to detect the amount of toner applied. In other words, even if the same amount of reflected light is detected, multiple amounts of toner applied corresponding to that amount of reflected light can be obtained. Therefore, it is necessary to remove the diffuse reflection component from the specular reflected light detected by the light-receiving element 232 when a patch is detected, and extract only the specular reflection component. In Example 1, the diffuse reflection component contained in the specular reflected light detected by the light-receiving element 232 is calculated from the diffuse reflected light detected by the light-receiving element 233. Then, by subtracting the diffuse reflection component calculated from the specular reflected light detected by the light-receiving element 232, only the original specular reflection component is extracted. As a result, a one-to-one relationship is obtained between the amount of toner applied and the amount of specular reflected light, as shown by the specular reflection component (thin solid line) in Figure 6(b).

[0037] [Optical properties in the imprinted overlap area] Figure 7 shows a schematic diagram of a magnified portion of the surface of the intermediate transfer belt 14. Figure 7 also shows the circumferential direction (direction of movement) H (which is also the R14 direction in Figure 1) of the intermediate transfer belt 14, and the direction I perpendicular to the circumferential direction H. Direction I is also the rotation axis direction of rollers 13, 19, and 30 (the longitudinal direction mentioned above). The imprinted intermediate transfer belt 14 has periodic convex portions 143 and concave portions 144 in the direction I perpendicular to the circumferential direction H. Imprint processing starts in the H direction from the starting position 145 (hereinafter referred to as the starting position) and continues until the ending position 146 (hereinafter referred to as the ending position). Since the ending position 146 of the imprint processing is located approximately 5 to 10 mm beyond the starting position 145, an imprint overlap portion (hereinafter referred to as the IO portion) 147, which will be described later as an optically singular region, is formed. Furthermore, in the circumferential direction H of the intermediate transfer belt 14, the region where the imprint processing does not overlap, i.e., the region excluding the IO section 147, is called the imprint non-overlapping section 148.

[0038] In the IO section 147, the recess 144 is highly likely to be misaligned in the I direction. This is due to the intermediate transfer belt 14 moving in the I direction during the imprinting process. When this misalignment occurs, the proportion of the protrusion 143 to the entire surface decreases in the IO section 147 compared to the imprint non-overlapping section 148. Here, "entire surface" means the imprint non-overlapping section 148 in the circumferential direction H, and the entire length of the intermediate transfer belt 14 in direction I. Also, since the IO section 147 is imprinted twice, the depth of the recess 144 becomes greater. For these reasons, the amount of reflected light in the specular reflection direction when light is irradiated into the IO section 147 decreases compared to the imprint non-overlapping section 148. In other words, the intermediate transfer belt 14 has areas in the direction of movement where the detection result by the optical sensor 23 is optically different from other areas excluding those areas.

[0039] Figure 8(a) shows the specular reflection output for approximately one full rotation of the intermediate transfer belt 14. In Figure 8(a), the horizontal axis shows the position [mm] in the circumferential direction H of the intermediate transfer belt 14, and the vertical axis shows the specular reflection output as a voltage value [V]. The horizontal axis also shows the IO section 147 and the imprint non-overlapping section 148. The specular reflection output fluctuates depending on the position of the intermediate transfer belt 14, and decreases significantly, especially near the IO section 147. Figure 8(b) is a magnified view of the specular reflection output near the IO section 147 (500mm~600mm). The horizontal and vertical axes of the graph in Figure 8(b) are the same as in Figure 8(a). The specular reflection output voltage is roughly 2.5V around the entire circumference of the intermediate transfer belt 14, but drops to about 1.3V at this dip (IO section 147). Thus, the IO section 147 is an optically singular region with different optical characteristics from the imprint non-overlapping section 148.

[0040] For the optical sensor 23 to have good detection accuracy, it is desirable that the difference between the output when there is no toner and the specular reflection output when there is toner is large, that is, that the dynamic range is wide. Therefore, if the specular reflection output drops, such as near the IO section 147, the dynamic range narrows, making it more susceptible to noise and leading to a decrease in the accuracy of detecting the amount of toner applied. Consequently, in order to accurately detect the amount of toner applied to a patch, the patch formation position must avoid the IO section 147.

[0041] [Image density control process] The image density control process in Example 1 consists of the following steps. 1. I / O detection process (optical singularity detection process) (4th measurement) 2. Belt circumference measurement process (perimeter measurement process) (3rd measurement) 3. Substrate measurement process (second measurement) 4. Patch measurement process (test toner image measurement process) (first measurement) Here, the belt circumference refers to the length of the intermediate transfer belt 14 in the circumferential direction H (length of one rotation), and the substrate refers to the surface (surface layer 142) of the intermediate transfer belt 14. In Example 1, the CPU 24 controls the execution of a patch measurement step, which is the first measurement, and a substrate measurement step, which is the second measurement. When the substrate measurement step is executed, the CPU 24 controls the formation of a second toner image (gain adjustment patch T1, described later) in order to supply toner to the nip portion in the second region, which is a region of the intermediate transfer belt 14 different from the first region, described later. The patch measurement step is a step in which the optical sensor 23 irradiates the first toner image (patch T2, described later) with light from a light source and detects the reflected light. The substrate measurement step is a step in which the optical sensor 23 irradiates the surface of the intermediate transfer belt 14 with light from a light source and detects the reflected light.

[0042] The image density control process will be explained below using the flowchart in Figure 9 and the diagram in Figure 10 that shows the relationship between various timings. In Figure 10, (i) shows the case where the belt circumference is the lower limit of the range that can be tolerated in the design, and (ii) shows the case where the belt circumference is the so-called nominal dimension (nominal value, ideal value, nominal value). Figure 10(iii) shows the case where the belt circumference is the upper limit, and the horizontal axis shows the timing (a certain time). The timing corresponds to the position on the circulating intermediate transfer belt 14, and the horizontal axis in Figure 10 can also be said to be the position on the intermediate transfer belt 14. In Figure 10, the downward sloping hatching indicates the IO section 147, and the mesh hatching indicates the margin. Furthermore, Figure 10 also shows each of the processes 1 to 4 described above.

[0043] (IO detection process) As described above, in order to accurately detect the amount of toner applied to the patch, the patch formation position must avoid the IO unit 147, so the position of the IO unit 147 is detected first. First, the CPU 24 detects an appropriate timing such as power-on of the image forming apparatus 100 or elapsed time since power-on, number of printed pages (number of images formed), environmental changes, and instructions from the host computer or user. Based on this, the CPU 24 starts the image density control process from step (hereinafter referred to as S) 902 onwards.

[0044] In S902, the CPU 24 starts the initial operation of the image forming apparatus 100, such as rotating the photosensitive drum 1 and the intermediate transfer belt 14 at a predetermined process speed (e.g., 160 mm / s) and charging the photosensitive drum 1. In S903, the CPU 24 controls the drive circuit 236 to cause the light-emitting element 231 of the optical sensor 23 to emit light at a predetermined amount. In S904, the CPU 24 starts sampling the specular reflection output. As the optical sensor 23 starts emitting light in S903, the analog signal 241 of the specular reflection output of the optical sensor 23 is converted into 10-bit digital data by the A / D converter in the CPU 24 and sampled at predetermined intervals, for example, at 0.1 mm intervals. Hereinafter, the 0.1 mm interval will also be called a 0.1 mm step. As described above, the optical sensor 23 can detect specular reflection and diffuse reflection. However, since specular reflection reflects changes in the surface state of the intermediate transfer belt 14 more sensitively, the specular reflection output is used for detection in the IO unit 147. At this time, the gain Gr0 of the specular reflection output set in the gain adjustment amplifier section 239 is set to about half of the maximum output to ensure that the output does not saturate. Specifically, since the optical sensor 23 in Example 1 has a maximum output of 5V, the CPU 24 is set to approximately 2.5V.

[0045] In S905, the CPU 24 monitors the change in specular reflection output while sampling, continuously updating the maximum value Vrmax of the specular reflection output, and successively overwriting and saving the maximum value Vrmax in RAM 25 each time it is updated. In S906, the CPU 24 detects the timing t1 when the specular reflection output falls below the threshold Vt and the timing t2 when it exceeds the threshold Vt, as shown in Figure 8(b). The CPU 24 stores the detected timing t1 as the start timing Ts of the IO unit 147 and timing t2 as the end timing Te of the IO unit 147 in RAM 25. Meanwhile, the updating of the maximum value Vrmax continues. Since the circumference of the intermediate transfer belt 14 is not determined at this point, the maximum value for one circumference of the belt can be determined by updating the maximum value Vrmax for 805 mm, taking into account the nominal value of 800 mm and the maximum circumference variation of ±5 mm due to the belt circumference tolerance. In S907, CPU24 updates the maximum value Vrmax by 805mm, then stops sampling the specular reflection output and waits until IO unit 147 reaches the detection position again. The start timing Ts obtained in S906 is used as the basis for subsequent processes.

[0046] In S908, CPU24 calculates the gain Gr for specular reflection output. Once the start timing Ts is determined, CPU24 uses the maximum value Vrmax of the specular reflection output when the gain Gr is 0, stored in RAM25, to adjust the gain for specular reflection output. Specifically, using Vrtgt (=3277dec), which is a 10-bit data of a target adjustment of 4V with a margin relative to the maximum output of optical sensor 23 of 5V, and 4096dec, which is a 10-bit data of 5V, Gr = Vrtgt / Vrmax × Gr0 Then, the gain Gr for the specular reflection output used for subsequent measurements is calculated and stored in RAM25.

[0047] (Belt circumference measurement process) To measure the belt circumference, the CPU 24 restarts sampling of the specular reflection output from 10 mm (margin) before the nominal circumference of 800 mm of the intermediate transfer belt 14 from the start timing Ts. Here, since the process speed is 160 mm / s, the time it takes for 790 mm to move from the start timing Ts is 4.94 seconds (≈ 790 mm / 160 mm / s). Therefore, in S909, the CPU 24 checks the timer 40 to determine whether 4.94 seconds have elapsed from the start timing Ts. If it determines that the time has not elapsed, it returns to processing S909; if it determines that the time has elapsed, it proceeds to processing S910. In S910, the CPU 24 changes the specular reflection output gain of the optical sensor 23 from G0 to Gr and starts sampling of the specular reflection output. The data obtained here is called specular reflection output data U1(i) (i≧0, positive integer). i represents the sampling position on the intermediate transfer belt 14 and is also called a point. Furthermore, the timing at which sampling of the specular reflection output data U1(i) begins, with the specular reflection output gain set to G0, is defined as timing Ts1 (see Figure 10).

[0048] As shown in Figure 10, the maximum width of the IO unit 147 is set to 10 mm and the sampling width of the specular reflection output data U1(i) is set to 25 mm so that data from the IO unit 147 can be sampled even at the upper limit of the belt circumference in (iii). As described above, sampling is performed in 0.1 mm steps, so 251 data points are obtained as specular reflection output data U1(i), with i ranging from 0 to 250. In S911, the CPU 24 stores the specular reflection output data U1(0) to U1(250) in the RAM 25 and stops sampling. In S912, the CPU 24 determines whether the intermediate transfer belt 14 has completed another rotation, that is, whether 4.94 seconds have elapsed since timing Ts1, by referring to the timer 40. In S912, if the CPU 24 determines that 4.94 seconds have not elapsed since timing Ts1, it returns to processing S912; if it determines that 4.94 seconds have elapsed, it proceeds to processing S913. Timing Ts2 is defined as the timing 4.94 seconds after timing Ts1 (see Figure 10).

[0049] At S913, the CPU 24 resumes sampling of the specular reflection output from timing Ts2 and stores the sampled data Ur(i) in RAM 25. At S914, the CPU 24 sets the gain of the gain adjustment amplifier section 240 of the optical sensor 23 (called the diffuse reflection output gain) to its initial value Gs0 and also starts sampling the diffuse reflection output data Us(i).

[0050] In S915, CPU24 samples 40 mm of the sampled specular reflection output data Ur(i) to calculate the circumference L of the intermediate transfer belt 14. 401 data points are obtained as specular reflection output data Ur(i), with i ranging from 0 to 400. For the calculation, specular reflection output data U1(0) to U1(250) and specular reflection output data Ur(0) to Ur(400), stored in RAM25, are used. Specular reflection output data U1(i) is the sampled data around the IO section 147 during the circumference measurement process, and specular reflection output data Ur(i) is the sampled data around the IO section 147 in the next rotation. Specular reflection output data U1(i) and Ur(i) are measured values ​​of specular reflection light reflected from the surface of the intermediate transfer belt 14, reflecting the surface condition of the intermediate transfer belt 14. Therefore, the amount of deviation in the sampled data is calculated using the following method. X is the deviation amount, which will be described later.

[0051] In Example 1, we use I(X) defined by the following formula.

number

[0052] First, CPU24 calculates the cumulative value I(0) when X=0 and stores the result in RAM25. Next, CPU24 increments the value of X by one and similarly calculates the cumulative value I(1) when X=1 and stores it in RAM25. This process is repeated until X becomes 150. In other words, CPU24 calculates up to I(150). When calculating I(150), when i=250, specular reflection output data U1(250) and specular reflection output data Ur(400 (=250+150)) are used.

[0053] Next, the CPU 24 calculates the value of X when I(X) is minimized. Since the surface state of the intermediate transfer belt 14 is not uniform, the measured values ​​detected from the same point are extremely similar, and there is no periodicity in the pattern of change of the measured values. Therefore, the amount of shift X when I(X) is minimized becomes the amount of shift of the specular reflection output data U1(i) and specular reflection output data Ur(i) relative to the same sampling position. Thus, by shifting Ur(i) by the amount of shift X, it can be obtained as the data for the same sampling position of the specular reflection output data U1(i).

[0054] This is shown in Figure 11. In Figure 11, the horizontal axis shows the position (or point), and the vertical axis shows the specular reflection output data. Figure 11 also shows the starting position for sampling the specular reflection output data U1(i) and the specular reflection output data Ur(i). Figure 11 plots the specular reflection output data U1(i) and specular reflection output data Ur(i) in a certain point interval. Here, it is shown that when the shift amount X = 59, the sampled data of the specular reflection output data U1(i) and the specular reflection output data Ur(i+X) coincide and I(X) is minimized.

[0055] Since the specular reflection output data Ur(0) is sampled starting 4.94 seconds (790.4 mm) after timing Ts1, the circumference L [mm] of the intermediate transfer belt 14 in Example 1 is L = 790.4 + X × 0.1 This allows for the calculation. In Example 1, sampling is performed in 0.1 mm steps. The CPU 24 stores the calculated circumference L in the RAM 25.

[0056] (Substrate measurement process) The substrate measurement process is a process of measuring the state of the surface (substrate) of the intermediate transfer belt 14 before forming patches on the intermediate transfer belt 14. When the substrate measurement process starts, the CPU 24 forms a gain adjustment toner image before measuring the state of the intermediate transfer belt 14. Specifically, in S916, the CPU 24 first forms a gain adjustment toner image (hereinafter referred to as gain adjustment patch T1) in order to adjust the gain of the diffuse reflection output of the optical sensor 23. At a predetermined timing, the CPU 24 generates reference signals (Y-Top, M-Top, C-Top) for each color for image formation of the gain adjustment patch T1 so that the gain adjustment patch T1 is formed behind the direction of travel of the IO unit 147. Note that a black Bk patch, which does not have diffuse reflection output, does not need to be adjusted and is therefore not formed. Then, the CPU 24 sends the image data of the gain adjustment patch T1 of each color, generated from the pattern generation unit 28 based on the reference signals of each color, to the exposure device 11. In order to accurately detect diffuse reflection output, it is necessary to set the optimal gain setting that widens the dynamic range. Therefore, the image data of the gain adjustment patch T1 is set to FFH (solid image), which maximizes the amount of diffusely reflected light. Then, the CPU 24 uses the scanning beams 12Y, 12M, and 12C to form a latent image of the gain adjustment patch T1 on the photosensitive drums 1Y, 1M, and 1C, respectively.

[0057] (Gain adjustment patch for adjusting the gain of diffuse reflection output) The gain adjustment patch T1 also serves as a lubricating toner image for the cleaning blade 22. Figure 12 shows the gain adjustment patch T1 formed on the intermediate transfer belt 14 in S916, and also shows the IO section 147 and the circumferential direction H. As shown in Figure 12, the width in the main scanning direction is the image-forming width Wg, and the width in the sub-scanning direction is 7 mm. Here, the width in the main scanning direction refers to the length in the main scanning direction, which is the direction perpendicular to the circumferential direction H and is the rotation axis direction of rollers 13, 19, and 30. The sub-scanning direction refers to the direction perpendicular to the main scanning direction and corresponds to the circumferential direction H. The formation position of the gain adjustment patch T1 at this time is set to two turns of the nominal length (800 mm) of the intermediate transfer belt 14 from the timing Te, and is set to be 10 mm behind the IO section 147, taking tolerances into account. In Figure 10, the "starting point of the gain adjustment patch" is shown by a dashed line. As a result, as shown in Figure 10(iii), the gain adjustment patch T1 is not formed on the IO section 147 even at the upper limit of the belt circumference. Here, the gain adjustment patch T1, which is the second toner image, includes portions T1a (within the dashed frame) as a gain adjustment patch detected by the optical sensor 23, and portions T1a and T1b as lubricating toner images. Portion T1b is a portion not detected by the optical sensor 23 and functions as a lubricating toner image. Portion T1a, which is the third toner image, is formed in a first region on the intermediate transfer belt 14 that is detectable by the optical sensor 23, and is a toner image for adjusting the second gain. The gain adjustment patch T1 includes portions T1a and T2a. Portion T1b is formed in a second region, which is a different region of the intermediate transfer belt 14 from the first region.

[0058] In S917, CPU24 updates the maximum value Vsmax. CPU24 monitors changes in diffuse reflection output data Us(i) while continuing to sample specular reflection output data Ur(i) and Us(i) which started from the belt circumference measurement process. Then, CPU24 continues to update the maximum value Vsmax of the diffuse reflection output, and each time it is updated, it overwrites and saves the maximum value Vsmax in RAM25.

[0059] In S918, the CPU 24 calculates the gain Gs. When the CPU 24 determines that the gain adjustment patch T1 has passed the detection position of the optical sensor 23, it stops sampling because it will no longer use the specular reflection output data Us(i). The CPU 24 also uses the maximum value Vsmax of the diffuse reflection output when the gain is Gs0, which is stored in RAM 25, to adjust the gain for the diffuse reflection output. Specifically, it uses Vstgt (=3277dec), which is a 10-bit data of a target adjustment of 4V with a margin relative to the maximum output of the optical sensor 23 of 5V, and 4096dec, which is a 10-bit data of 5V. Gs = Vstgt / Vsmax × Gs0 Then, the gain Gs for the diffuse reflection output for subsequent measurements is calculated and stored in RAM25. The sampling of specular reflection output data Ur(i) and its storage in RAM25 continues until partway through the next patch measurement process. After the gain adjustment patch T1 passes the detection position of the optical sensor 23, it reaches the cleaning nip section 32 as a lubricant.

[0060] (Patch measurement process) In step S919, the CPU 24 performs the formation of patches of each color during the patch measurement process. Based on timing Ts2, the CPU 24 generates reference signals (Y-Top, M-Top, C-Top, Bk-Top) for each color for patch image formation at predetermined timings that take into account the determined circumference L of the intermediate transfer belt 14. The CPU 24 then sends the image data of each color patch generated from the pattern generation unit 28 based on the reference signals of each color to the exposure apparatus 11. Then, on the photosensitive drums 1Y, 1M, 1C, and 1Bk, latent images of, for example, 17 patch groups are formed in the direction of rotation using predetermined image data. Each color patch consists of a solid black area of ​​FFH and image data of 8H, 10H, 20H, 30H, 40H, 50H, 60H, 70H, 80H, 90H, A0H, B0H, C0H, D0H, E0H, and F0H, as shown in Figure 13(a). These will be referred to as PY1-PY17, PM1-PM17, PC1-PC17, and PBk1-PBk17, respectively, for each color. One patch is, for example, a square with sides of 10mm.

[0061] The latent images of these patches are developed by the developing units 8Y, 8M, 8C, and 8Bk at predetermined developing voltages and formed on the photosensitive drums 1Y, 1M, 1C, and 1Bk, respectively. Patches PY1 to PY17, PM1 to PM17, PC1 to PC17, and PBk1 to PBk17 are transferred onto the intermediate transfer belt 14 by applying a predetermined primary transfer voltage between the photosensitive drums 1Y, 1M, 1C, and 1Bk and the primary transfer rollers 4Y, 4M, 4C, and 4Bk. The transfer position of the patches at this time is set so as not to overlap with the position where the gain adjustment patch T1 was formed in the previous rotation (see Figure 12), for example, starting 5 mm behind the formation position of the gain adjustment patch T1. On the intermediate transfer belt 14, a patch T2 as shown in Figure 13(b) is formed at a location corresponding to the measurement position of the optical sensor 23. Note that there is a gap of one patch width (1 mm) between each group of colored patches. The CPU 24 controls the image formation conditions when forming an image on the transfer material P based on the detection of reflected light reflected by patch T2, which is a first toner image formed at a position (first region) detectable by the optical sensor 23 on the intermediate transfer belt 14.

[0062] In the substrate measurement process, when the lubricating toner image (parts T1a, T1b) including the gain adjustment patch T1 (part T1a) reaches the cleaning nip section 32, the frictional force between the cleaning blade 22 and the intermediate transfer belt 14 decreases sharply. As a result, the intermediate transfer belt 14 may slip. Therefore, the IO section 147 may reach the detection position of the optical sensor 23 earlier than it should, so sampling in the patch measurement process is started 10 mm earlier than the timing at which the IO section 147 would normally reach. In S920, the CPU 24 starts sampling at timing Ts3, which is calculated from timing Ts2 by (L(mm)-10(mm)) / 160(mm / s) (see Figure 10). The data obtained from the sampling started in S920 is defined as specular reflection output data Pr(i) and diffuse reflection output data Ps(i). The CPU 24 stores the specular reflection output data Pr(i) and the diffuse reflection output data Ps(i), which are set to gain Gs, from the optical sensor 23 into the RAM 25. At the same time, the specular reflection output data Ur(i) is also being measured.

[0063] At S921, CPU24 measures specular reflection output data Ur(i) in the section from timing Ts2 to the circumference L plus a margin of 40mm, and then terminates sampling of specular reflection output data Ur(i). This section, starting from timing Ts2, is also shown in Figure 10 as "Ur(i) sampling (L+40)mm" with a white double arrow. At S922, CPU24 measures specular reflection output data Pr(i) and diffuse reflection output data Ps(i) in the section from timing Ts3 to the circumference L of the intermediate transfer belt 14 plus a margin of 50mm, and then terminates sampling. This section, starting from timing Ts3, is also shown in Figure 10 as "Pr(i), Ps(i) sampling (L+50)mm" with a white double arrow.

[0064] In S923, CPU24 cleans the toner images of patch T2, namely PY1-PY17, PM1-PM17, PC1-PC17, and PBk1-PBk17, which have been measured, using cleaning blade22.

[0065] At S924, since all samplings have been completed, the CPU 24 corrects the background data. Using the specular reflection output data Ur(0) to Ur(400) near the first IO unit 147 during background measurement and the specular reflection output data Ur(n) to Ur(n + 500) near the IO unit 147 during the next rotation of the intermediate transfer belt 14, the slip amount during background measurement is calculated using the following formula. J(X) is the same formula as I(X) that obtained the shift amount X above. n is the point advanced (L - 10) mm from the timing Ts2, and the calculation range of the shift amount X is X = 0, 1, 2, …, 100.

Equation

[0066] Therefore, when X when J(X) is minimized is in the range of 0 < X < 100 (when slip occurs), the background data is corrected. It is expected that slip will occur at the timing when the gain adjustment patch T1 detected by the optical sensor 23 reaches the cleaning nip portion 32. Therefore, in Example 1, the section where slip is expected to occur (hereinafter referred to as the expected slip section) is set to S to S + 200 based on the timing Ts2. S and the slip occurrence range (200) were set from mechanical dimensions and margins. Since the slip amount is (100 - X)[0.1 mm], when slip occurs, the 201 data obtained from the sampling in the section from S to S + 200 originally will be reduced to (101 + X) data. In order to accurately calculate the toner loading amount of the patch, it is necessary to align the measurement position of the background on the intermediate transfer belt 14 and the measurement position of the patch. Therefore, the reduced sampling data is interpolated by the following method.

[0067] (Interpolation of data reduced due to slip occurrence) For example, if the slip amount is 3 mm (X=70), the data that would normally be sampled 201 times is reduced to 171 times. Here, Table 1 is a table that explains the interpolation method. [Table 1] The first row of Table 1 shows the points (0-200) corresponding to the sampling interval on the intermediate transfer belt 14 when no slip occurs. The second row of Table 1 shows the points from the first row after processing (1) described later. The third row of Table 1 shows the specular reflection output data Ur(S) corresponding to the points in the second row after processing (2) described later. The fourth row of Table 1 shows the specular reflection output data Uc(S) corresponding to the points in the second row after processing (3) described later.

[0068] First, as shown in (1) of Table 1, the interval S to S+170, where the sampling data has decreased, is evenly distributed among the 201 points in the original interval S to S+200. That is, 0.85 (=170 ÷ 200) × j (where j is a non-negative integer) is added to S. Specifically, point 0 corresponds to S, point 1 to S+0.85, point 2 to S+1.7, ..., point 20 to S+17, ..., point 200 to S+170, and so on. At this time, some points in the S to S+170 interval will have decimal values. If the subscript of the specular reflection output data Ur(i), which is the background data, is also changed from the interval S to S+170 to the interval S to S+200, it will look like (2).

[0069] Of the points in (2), for example, point 20 is S+17, so we can use the data for point 17. However, of the points in (2) that are decimals have not been sampled, so we will calculate this data using the sampled data. For example, the specular reflection output data Ur(S+0.85) can be obtained by interpolating using the data for the interval containing S+0.85, Ur(S) and Ur(S+1), as shown in the equation below.

number

[0070] Similarly, we find Ur(S+1.7) to Ur(S+170) and substitute them into the corresponding Uc(i) as shown in (3). Here, Uc(i) is the specular reflection output data after interpolation as shown in Equation 3, and i is S to S+200. Specifically, Uc(S)=Ur(S), Uc(S+1)=Ur(S+0.85), ..., Uc(S+199)=Ur(S+169.15), Uc(S+200)=Ur(170).

[0071] As a result, the corrected background data Ur'(i) is obtained using the shift amount X, Ur'(i) = Ur(i) i = 0, ..., S-1 Ur'(i)=Uc(i) i=S,...,(S+200) Ur'(i)=Ur(i-(100-X)) i = (S + 201), ..., 10 × L + 400 Therefore, even if slippage occurs, the underlying data will be corrected to the data as if no slippage had occurred.

[0072] The sampling of specular reflection output data Pr(i) and diffuse reflection output data Ps(i) starts from a point (L-10) mm ahead of the specular reflection output data Ur(0). Therefore, if there is no slip, the data measured at the same position as Ur(0) on the intermediate transfer belt 14 will be specular reflection output data Pr(100) and diffuse reflection output data Ps(100). If slip is taken into consideration, the specular reflection output data becomes Pr(X) and specular reflection output data Ps(X). Thus, corrected specular reflection output data Pr'(i) = Pr(i+X) and corrected diffuse reflection output data Ps'(i) = Ps(i+X) are defined. In addition, specular reflection output data Pr'(i) and diffuse reflection output data Ps'(i) are defined by shifting them by X, respectively. This allows the measurement positions on the intermediate transfer belt 14 of the corrected substrate data Ur'(i), the corrected specular reflection output data Pr'(i), and the diffuse reflection output data Ps'(i) to be aligned. In this case, i = 0, ..., 10 × L + 500 - X.

[0073] Let's return to the explanation of the flowchart in Figure 9. At S925, the CPU 24 extracts the measurement values ​​corresponding to each patch and the measurement values ​​corresponding to the background of that patch from each measurement data, and determines the density as density-related information for the patch. When the FFH toner patch formed on the intermediate transfer belt 14 reaches the detection position of the optical sensor 23, the amount of specular reflected light changes as shown in Figure 14(a), regardless of the toner color. In Figure 14, the horizontal axis shows time and the vertical axis shows the amount of specular reflected light. The optical sensor 23 is adjusted so that the amount of specular reflected light when there is no patch on the surface of the intermediate transfer belt 14 (hereinafter referred to as the background level) is at most about Vrtgt (=3277 dec). In this state, when the FFH patch comes to the detection position of the optical sensor 23a, the amount of specular reflected light decreases to about 1 / 4 of Vrtgt. At this time, if point 121, where the specular reflected light amount becomes half of Vrtgt, is taken as the leading edge of the patch, and point 122 is taken as the trailing edge of the patch, the length of the patch calculated from the time between points 121 and 122 closely matches the actual length of the patch. Therefore, in Example 1, the point at which the specular reflected light amount becomes Vrtgt / 2 from the substrate level is taken as the leading edge of the patch. As explained in Figure 8, a similar decrease in specular reflected light amount occurs in the IO section 147 as well.

[0074] Patches PY1, PM1, PC1, and PBk1 in Figure 13(b) are solid images of the FFH image data, and these serve as reference patches for extracting patch data. First, the CPU 24 sets i=1 and checks if the specular reflection output data Pr(i) of the specular reflection light stored in RAM 25 is less than or equal to Vrtgt / 2 (=1638dec). If Pr(i)>Vrtgt / 2, i is incremented by 1 and the next specular reflection output data Pr(i) is checked. The specular reflection output data Pr(i) always includes the measurement data of the IO unit 147 before the patch measurement data. Therefore, when Pr(i) ≤ Vrtgt / 2 is first obtained, the CPU 24 determines that it is the measurement data of the IO unit 147 and ignores it. Then, when the specular reflection output data Pr(i) exceeds Vrtgt / 2 once and then becomes Pr(i) ≤ Vrtgt / 2 again, i (=m) is determined to be the tip of the patch.

[0075] Figure 14(b) shows the relationship between patch PY1 and the measurement area (hereinafter referred to as the measurement spot) RY(x) of the optical sensor 23. As shown in Figure 14(b), when the measurement spot RY(m) is determined to be the tip of patch PY1, it is not completely inside patch PY1. The measurement value at this time does not reflect the concentration of patch PY1. The concentration of patch PY1 is reflected only when the measurement spot RY(x) is completely inside patch PY1. In Example 1, the central 6 mm area, 2 mm inside patch PY1 from both the tip and the rear end, where the measurement spot RY(x) is sufficiently inside patch PY1, is considered the area that reflects the concentration of patch PY1. Therefore, for the first patch PY1, the data from points m+20 to m+79 are valid data. In other words, the specular reflection output data Pr(m+20)~Pr(m+79) and diffuse reflection output data Ps(m+20)~Ps(m+79) measured by the measurement spots RY(m+20)~RY(m+79) represent the data that reflects the concentration of the first patch PY1.

[0076] Therefore, using the concentration correlation data s(i), the specular reflection output data Pr(i) obtained in S920, the specular reflection output data Ps(i), and the Ur(i) data obtained up to S921, for example, s(i)=(Pr(i)-α×Ps(i)) / Ur(i) D(i)=f(s(i)) The concentration data D(i) for each measurement point is obtained using the following formula. α is a predetermined coefficient, and f(x) is a means of converting the concentration correlation data s(i) to the concentration data D(i) using a formula or table. The concentration correlation data s(i) may be calculated using a method other than this formula or table. D(i) may be an index other than the concentration data, such as the chromaticity difference ΔE in the CIE color system.

[0077] After calculating these concentration data D(i) in the region of point i from (m+20) to (m+79), the concentration DY1 of the first patch PY1 can be obtained, for example, by averaging.

[0078] The concentrations DY2 to DY17 of the remaining patches PY2 to PY17 of Y are calculated by averaging the respective concentration data as follows. PY2:D(m+120)~D(m+179) PY3:D(m+220)~D(m+279) ~ PY16:D(m+1520)~D(m+1579) PY17:D(m+1620)~D(m+1679)

[0079] When the Y patch ends and i > m + 1679, the leading edges of the C, M, and Bk reference patches are detected by the optical sensor 23 in the same manner. The densities DY1~DY17, DM1~DM17, DC1~DC17, and DBk1~DBk17 for each patch are then calculated and stored in the RAM 25.

[0080] Returning to the explanation of the flowchart in Figure 9, at S926, the CPU 24 calculates the density of the patch for each color image data, and then, based on the calculated density, provides feedback to the image formation conditions to achieve the predetermined density and gradation characteristics, thereby ending the image density control process.

[0081] [Appropriate timing of toner image formation for lubrication] In the image density control process, the lubricating toner image (hereinafter referred to as the lubricating toner image) is as described above. 1. I / O detection process 2. Belt circumference measurement process 3. Substrate Measurement Process 4. Patch measurement process Regardless of which of the processes the lubricating toner image is formed in, the effect of providing lubrication to the cleaning nip portion 32 can be obtained. In this embodiment, it is particularly preferable to form the lubricating toner image in step 3, the substrate measurement process. The reason for this is explained below.

[0082] In the IO section detection process, the position of the IO section 147 cannot be determined, making it impossible to know where on the intermediate transfer belt 14 the lubricating toner image will be formed. Therefore, if the positional relationship is such that the IO section 147 reaches the detection position of the optical sensor 23 when the lubricating toner image reaches the cleaning nip section 32, the amount of signal drop at the IO section 147 may decrease due to slippage. This can lead to misdetection of the position of the IO section 147 or misdetection of its width, potentially causing the subsequent patch formation position to overlap with the IO section 147. In the IO section detection process, the gain is set to half of the maximum output that does not saturate in order to reduce the downtime required for gain adjustment of the specular reflection output, which also makes misdetection in the event of slippage more likely. To avoid this, the IO section detection process must be performed after the lubricating toner image has passed the cleaning nip section 32, which results in extra rotation of the intermediate transfer belt 14.

[0083] During the belt circumference adjustment process, if the lubricating toner image reaches the cleaning nip section 32, the intermediate transfer belt 14 may slip, potentially leading to a false detection of a shorter belt circumference. This false detection of belt circumference can cause a mismatch between the formation position of the base material and the patch in the subsequent patch density calculation, potentially leading to a decrease in the accuracy of density calculation.

[0084] If the lubricating toner image is formed during the patch measurement process, it will be formed at the very end of the image density control process. Since we want to send the lubricating toner image to the cleaning nip section 32 as early as possible, we want to make the formation timing as early as possible compared to the patch measurement process. Based on the above considerations, even if slippage of the intermediate transfer belt 14 occurs, forming the lubricating toner image during the substrate measurement process, which allows for correction, is the optimal timing for image formation.

[0085] Furthermore, the lubrication toner image can be formed at a location other than 10 mm behind the IO section 147 as in Example 1, by adjusting the patch formation position during the patch measurement process. However, in the case of an image forming apparatus 100 with a configuration like that of Example 1, the timing at which the lubrication toner image reaches the cleaning nip section 32 must be earlier than the timing at which the patch exposure begins during the patch measurement process. This is because slippage of the intermediate transfer belt 14 may affect the rotation of the photosensitive drum 1, potentially distorting the latent image or toner image of the patch. In addition, the gain adjustment patch T1 is formed in a region on the intermediate transfer belt 14 where the longitudinal width of the lubrication toner image when it reaches the cleaning nip section 32 corresponds to the length of the cleaning blade 22 in a direction perpendicular to the direction of movement of the intermediate transfer belt 14. To obtain effective lubrication, it is desirable that the longitudinal width of the gain adjustment patch T1, which functions as a lubrication toner image, when it reaches the cleaning nip section 32 is, for example, 70% or more of the longitudinal width of the cleaning nip section 32.

[0086] As described above, in Example 1, the frictional force of the cleaning nip portion of the intermediate transfer body can be reduced by forming a lubricating toner image during the image density control process. Furthermore, by forming the lubricating toner image during the substrate measurement process, the frictional force of the cleaning nip portion can be effectively reduced without causing unnecessary downtime or a decrease in the accuracy of patch density calculation. In addition, by including a gain adjustment patch in the lubricating toner image, the amount of toner consumed can be minimized.

[0087] As described above, according to Example 1, the frictional force of the cleaning nip portion can be reduced in the image density control of the image forming apparatus. [Examples]

[0088] The image forming apparatus 100 according to Example 2 will be described below. Components with the same configuration and operation as in Example 1 will be given the same numbers and their descriptions will be omitted. In Example 1, a toner image was always formed as a lubricant during image density control, but in Example 2, the frictional force in the cleaning nip section is predicted and the lubricating toner image is changed accordingly. Here, the lubricating toner image refers to part T1b of the gain adjustment patch T1 explained in Figure 12, and part T1a is used to adjust the gain Gs of the gain adjustment amplifier section 240. The frictional force is predicted using environmental (absolute humidity) data of the environment in which the image forming apparatus 100 is placed and the time it has been left unattended until image density control is performed.

[0089] As shown in Figure 15(a), the image forming apparatus 100 of Embodiment 2 is equipped with an environmental sensor 41, which is a second detection means for detecting the state of the environment in which the image forming apparatus 100 is installed. Here, the state of the environment is temperature and / or humidity, moisture content (absolute moisture content), etc. Temperature and / or humidity may be detected as relative values ​​or absolute values, and in Embodiment 2, the environmental sensor 41 detects absolute humidity, for example. The environmental sensor 41 is positioned so as not to be affected by heat-generating devices such as the fixing device 21 or the power supply device (not shown). The CPU 24 measures the time the image forming apparatus 100 has been left unattended using a timer 40, which is a measurement means. Based on the detection result from the environmental sensor 41 and / or the elapsed time, the CPU 24 changes the shape of the gain adjustment patch T1, in other words, the shape of the lubricating toner image. Here, the shape of the lubricating toner image includes at least one of the following: the color (Y, M, C), the number of colors, the amount of toner applied (density), and the shape of the toner image to be formed.

[0090] Table 2 shows the relationship between absolute humidity (g / kg(DA)) and the frictional force predicted from the storage time. The first column of Table 2 shows the absolute humidity value (<6 (g / kg(DA)), 8, etc.), and the subsequent columns show the storage time (<1 (hour), 3, etc.). For each storage time, the frictional force (A~E) for each absolute humidity in the first column is shown. Here, the frictional force is highest at A and lowest at D. In other words, the frictional force decreases from A to B, C, etc. When focusing on a given storage time, the frictional force increases as the absolute humidity increases. Also, when focusing on a given absolute humidity, the frictional force increases as the storage time increases. [Table 2]

[0091] Depending on this frictional force, At frictional force A, three colors of solid lubricating toner are required. With frictional force B, one color of solid lubricating toner is required. At frictional force C, three colors of lubricating toner are required for the 40H image data. At frictional force D, one color of lubricating toner image data with a 40H rating is required. With frictional force E, no lubricating toner image is required. This is how it is set. In other words, the CPU 24 increases the density of the lubricating toner image (gain adjustment patch T1) and / or increases the number of colors used in the lubricating toner image as the frictional force increases. For example, if the image forming apparatus 100 is left for 5 hours in an environment with an absolute humidity of 14 g / kg (DA), the frictional force is predicted to be "B" from Table 2, and it is determined that one solid lubricating toner image is needed. Also, for example, if the absolute humidity is 20 g / kg (DA) and the time left is 9 hours or more, the frictional force is predicted to be A, so three solid lubricating toner images will be formed.

[0092] If the friction force is predicted to be E, the lubricating toner image is deemed unnecessary, which means that the portion T1b, which serves as the lubricating toner image, is deemed unnecessary. Furthermore, if the friction force is predicted to be E and it is not necessary to calculate the gain Gs for diffuse reflection output, the portion T1a, which serves as the gain adjustment patch, may also be deemed unnecessary. In addition, when predicting the friction force, the prediction may be based solely on the detection results of the environmental sensor 41, or solely on the elapsed time.

[0093] By changing the lubricating toner image according to the friction force prediction table in Table 2, it is possible to supply the minimum necessary amount of lubricating toner image under various environmental conditions and storage situations. Thus, in Example 2, the CPU 24 changes the shape of the lubricating toner image (T1b) according to at least one of the absolute moisture content and the elapsed time since the previous image formation.

[0094] Furthermore, the image forming apparatus according to the present invention is not limited to the embodiments described above, and can be modified in various ways within the scope of its essence. 1) Although only specular reflection was measured as the base for the patch, diffuse reflection may also be measured and used for density calculation. 2) The number of patches does not have to be 17 for each color, and the image data, arrangement, and color order can be chosen arbitrarily. 3) Although the patch was formed in the center, it may also be formed at either the left or right edge, and the mounting position of the optical sensor may be changed accordingly. 4) The patch formation positions may be placed at both ends, and the number of optical sensors may be increased to two accordingly, distributing the patches to be formed to the left and right. 5) In addition to reducing the amount of toner applied by image data, the lubricating toner image may also be divided by color as shown in Figure 15(b). Here, Figure 15(b) shows the gain adjustment patch T3, and is the same as Figure 12 except for the gain adjustment patch T3. The gain adjustment patch T3 includes a portion T3a as a gain adjustment patch detected by the optical sensor 23, and portions T3a and T3b as lubricating toner images. Portion T3b includes a yellow patch divided into two parts and a cyan batch divided into two parts. In this way, the lubricating toner image may be divided by color. 6) Multiple optical sensors may be arranged longitudinally opposite the auxiliary roller, and the patch formation positions may be made multiple accordingly. 7) In addition to in-line color image forming apparatuses, the present invention can also be applied to conventional color image forming apparatuses (e.g., rotary type) that are equipped with multiple developing devices for a single photosensitive drum, which are well known in the past. 8) In addition to the intermediate transfer method, this method can also be applied to image forming apparatuses that form an image by directly transferring a toner image onto a transfer material supported on a transfer material carrier, and which form an image density control patch on the transfer material carrier.

[0095] As described above, according to Example 2, the frictional force of the cleaning nip portion can be reduced in the image density control of the image forming apparatus. [Explanation of symbols]

[0096] 14 Intermediate transfer belt 22 Cleaning Blades 23 Optical Sensors 24 CPU 231 Light-emitting element S Image forming section

Claims

1. An endless image carrier; forming means for forming a toner image on the image carrier; a light source that irradiates light onto a surface of the image carrier and the toner image formed on the image carrier; a first detection means for detecting reflected light reflected by the image carrier or the toner image formed on the image carrier by irradiating the light from the light source onto the image carrier or the toner image formed on the image carrier, the first detection means including a first light receiving section for receiving regular reflected light from the image carrier or the toner image on the image carrier, and a second light receiving section for receiving diffuse reflected light from the image carrier or the toner image on the image carrier; a removing unit that comes into contact with the image carrier to form a nip portion and removes toner from the image carrier at the nip portion; a control means for controlling an image forming condition when forming an image on a transfer material based on a result of detecting the reflected light reflected by a first toner image formed in a first area on the image carrier that can be detected by the first detection means; An image forming apparatus comprising: The control means (i) controlling the first detection means to be able to execute a first measurement in which the first detection means irradiates the first toner image with light from the light source and detects the reflected light, and a second measurement including a measurement step in which the first detection means irradiates a surface of the image carrier with light from the light source and detects the reflected light to measure a state of the image carrier; (ii) when the second measurement is performed, a second toner image is formed in a second area of ​​the image carrier different from the first area to supply toner to the nip portion; (iii) when the second measurement is started, controlling so as to form the second toner image before the measurement step; the second toner image is formed at a position detectable by the first detection means, and contains toner for detecting the diffusely reflected light by the second light receiving portion.

2. 2. The image forming apparatus according to claim 1, wherein the second area is different from the first area in a direction perpendicular to the moving direction of the image carrier.

3. 2. The image forming apparatus according to claim 1, wherein in the first measurement, the first detection means detects the reflected light in order to measure the density of the first toner image.

4. 2. The image forming apparatus according to claim 1, wherein the control means controls the second measurement to be performed before the first measurement.

5. The first detection means includes a first amplifier section that amplifies a voltage corresponding to the amount of specularly reflected light received by the first light receiving section by a set first gain and outputs the voltage, and a second amplifier section that amplifies a voltage corresponding to the amount of diffusely reflected light received by the second light receiving section by a set second gain and outputs the voltage, 5. The image forming apparatus according to claim 1, wherein the second toner image includes a third toner image for adjusting the second gain.

6. 6. The image forming apparatus according to claim 5, wherein the control means forms the second toner image in an area on the image carrier corresponding to a length of the removing means in a direction perpendicular to a moving direction of the image carrier.

7. 7. The image forming apparatus according to claim 6, wherein the control means forms the second toner image in an area on the image carrier corresponding to 70% or more of the length of the removing means.

8. A second detection unit that detects the state of the environment in which the image forming apparatus is installed; A measuring means for measuring an elapsed time from the end of image formation; Equipped with 8. The image forming apparatus according to claim 7, wherein the control unit changes the state of the second toner image based on the detection result by the second detection unit and / or the elapsed time.

9. The second detection means detects absolute humidity, 9. The image forming apparatus according to claim 8, wherein the frictional force acting between the image carrier and the removing means increases as the absolute humidity increases and as the elapsed time increases.

10. 10. The image forming apparatus according to claim 9, wherein the control unit increases a density of the second toner image and / or increases a number of colors used in the second toner image as the frictional force increases.

11. the forming unit includes a photoconductor on which an electrostatic latent image is formed, and a developing unit that develops the electrostatic latent image with toner to form a toner image; 11. The image forming apparatus according to claim 10, wherein the image carrier is an intermediate transfer member onto which the toner image formed on the photoconductor is transferred.

12. 12. The image forming apparatus according to claim 11, wherein the control unit performs a third measurement to measure a length of one circumference in the moving direction of the image carrier before performing the second measurement.

13. the image carrier has a region in a partial region in the moving direction in which a detection result by the first detection unit is optically different from other regions excluding the partial region, 13. The image forming apparatus according to claim 12, wherein the control unit performs a fourth measurement for identifying the position of the partial area before performing the third measurement.

14. the forming unit includes a photoconductor on which an electrostatic latent image is formed, and a developing unit that develops the electrostatic latent image with toner to form a toner image; 11. The image forming apparatus according to claim 10, wherein the image carrier is a transfer material carrier that carries a transfer material onto which the toner image formed on the photoconductor is transferred.

15. 15. The image forming apparatus according to claim 14, wherein the control unit performs a third measurement to measure a length of one circumference in the moving direction of the image carrier before performing the second measurement.

16. the image carrier has a region in a partial region in the moving direction in which a detection result by the first detection unit is optically different from other regions excluding the partial region, 16. The image forming apparatus according to claim 15, wherein the control unit performs a fourth measurement for identifying the position of the partial area before performing the third measurement.

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