Image forming apparatus

Abstract

When performing calibration in two stages, if the reference image is formed at the same location on the intermediate transfer belt, the present invention provides an image forming apparatus that can perform the second adjustment with high accuracy. [Solution] The image forming apparatus comprises an image carrier, a charging device, an exposure device, a developing device, an intermediate transfer belt, a cleaning brush, an image density sensor, and a control unit. The control unit performs calibration including: a first adjustment step of adjusting the image forming conditions based on the detection result of a first reference image formed on the intermediate transfer belt; a first surface measurement step of detecting the formation region of the first reference image with the image density sensor after the execution of the first adjustment step; and a second adjustment step of changing the image forming conditions based on the detection result of a second reference image formed in the formation region of the first reference image after the execution of the first surface measurement step. If the output value of the image density sensor in the first surface measurement step is less than or equal to a threshold, the second adjustment step is executed.

Description

Technical Field

[0001] The present invention relates to an intermediate transfer type image forming apparatus that removes residual toner on the surface of an intermediate transfer belt using a cleaning brush.

Background Art

[0002] Conventionally, there is known an intermediate transfer type image forming apparatus including an endless intermediate transfer belt that rotates in a predetermined direction and a plurality of image forming units provided along the intermediate transfer belt. After sequentially overlapping toner images of respective colors on the intermediate transfer belt by each image forming unit and performing primary transfer, secondary transfer is performed onto a recording medium.

[0003] In an intermediate transfer type image forming apparatus, when the intermediate transfer belt has an elastic layer, a cleaning brush that mechanically and electrically collects residual toner on the surface of the intermediate transfer belt, a recovery roller that recovers toner from the cleaning brush, a scraper that scrapes off toner from the surface of the recovery roller, and a transport spiral that transports the toner scraped off from the surface of the recovery roller to a waste toner collection container are provided in a housing and used as a cleaning device.

[0004] On the other hand, in an intermediate transfer type image forming apparatus, a calibration operation is performed to adjust image density and color shift by detecting the density of a reference image (patch image) transferred onto the intermediate transfer belt. At this time, if there are scratches or dirt on the intermediate transfer belt, it is impossible to accurately adjust image density and color shift in the calibration operation.

[0005] Therefore, methods have been proposed to prevent false detection of the reference image due to scratches or dirt on the intermediate transfer belt. Patent Document 1 discloses an image forming apparatus that includes a detection sensor for detecting a correction pattern, a means for operating the detection means without writing the correction pattern to determine whether or not there is a false detection output due to scratches or dirt on the transfer belt, a means for selecting and switching to a threshold that eliminates the false detection if one occurs, and a means for controlling the timing of operating the above means.

[0006] Patent Document 2 discloses an image forming apparatus that includes an optical reflection characteristic detection means for detecting the optical reflection characteristics of a test toner image formed on an image carrier, and a means for determining whether there is a defect on the image carrier, and if there is a defect on the image carrier, changes the position in which the test toner image is formed on the image carrier. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-98795 [Patent Document 2] Japanese Patent Publication No. 2006-17987 [Overview of the project] [Problems that the invention aims to solve]

[0008] Scratches and dirt on the intermediate transfer belt can be caused by deterioration of the belt itself, as well as deterioration of the cleaning system. In particular, in cleaning systems that use cleaning brushes as described above, a decrease in cleaning performance occurs due to the flattening of the brush bristles.

[0009] The method described in Patent Document 1 detects scratches and dirt on the transfer belt, determines the timing for replacing the transfer belt, and displays a message. While it can determine the condition of the transfer belt itself, it cannot determine the condition of the cleaning system as well. The method described in Patent Document 2 can determine whether dirt has occurred on the transfer belt due to cleaning, but it assumes localized dirt and cannot determine whether the dirt is constant. Furthermore, it could not determine the condition of the cleaning system.

[0010] In view of the above problems, the present invention aims to provide an image forming apparatus that can perform the second stage of calibration with high accuracy when a reference image is formed at the same location on the intermediate transfer belt during a two-stage calibration. [Means for solving the problem]

[0011] To achieve the above objective, the first configuration of the present invention is an image forming apparatus comprising an image carrier, a charging device, an exposure device, a developing device, an intermediate transfer belt, a cleaning brush, an image density sensor, and a control unit. A photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image with reduced charge. The developing device has a developer carrier that carries a developer containing toner, and develops the electrostatic latent image formed on the image carrier into a toner image. The intermediate transfer belt is endless and rotates in contact with the image carrier, thereby primary transferring the toner image formed on the image carrier. The cleaning brush removes toner remaining on the intermediate transfer belt. The image density sensor detects the density of the toner image primary transferred onto the intermediate transfer belt. The control unit performs calibration to correct the image density based on the density of a reference image detected by the image density sensor. Calibration includes: a first adjustment step of detecting the density of a first reference image formed on an intermediate transfer belt and adjusting the image formation conditions based on the detection result; a first surface measurement step of detecting the formation region of the first reference image using an image density sensor after the intermediate transfer belt has completed one or more rotations following the execution of the first surface measurement step; and a second adjustment step of detecting the density of a second reference image formed in the formation region of the first reference image after the intermediate transfer belt has completed one rotation following the execution of the first surface measurement step and changing the image formation conditions to be different from those of the first adjustment step based on the detection result. The control unit determines that the surface condition of the intermediate transfer belt is normal and executes the second adjustment step if the amplitude of the output waveform of the image density sensor in the first surface measurement step is below a threshold. [Effects of the Invention]

[0012] According to the first configuration of the present invention, the second adjustment step is executed only if the surface condition of the intermediate transfer belt is determined to be normal by the first surface measurement step. This allows the second adjustment step to be executed with high accuracy. [Brief explanation of the drawing]

[0013] [Figure 1]Schematic diagram showing the internal configuration of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 2] Side cross-sectional view showing the configuration around the intermediate transfer unit 30 mounted on the image forming apparatus 100. [Figure 3] Figure 2: Enlarged view of the area around the image forming section Pa. [Figure 4] Block diagram showing an example of the control path of the image forming apparatus 100. [Figure 5] A schematic diagram showing an example of calibration in the image forming apparatus 100. [Figure 6] A schematic diagram showing another example of calibration in the image forming apparatus 100. [Figure 7] A flowchart showing an example of calibration control performed in the image forming apparatus 100. [Figure 8] Graph showing scalp measurement results when cleaning brush 23 is performing normally. [Figure 9] Graph showing scalp measurement results when the performance of cleaning brush 23 deteriorates. [Figure 10] The graph shows the scalp measurement results when the intermediate transfer belt 8 is rotated one more time from the state shown in Figure 9. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing the configuration of an image forming apparatus 100 according to one embodiment of the present invention. Here, a so-called tandem color printer is shown as the image forming apparatus 100.

[0015] Inside the main body of the image forming apparatus 100, four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the conveyance direction (the right side in FIG. 1). In these image forming units Pa to Pd, photosensitive drums 1a, 1b, 1c, and 1d that carry images of different four colors (cyan, magenta, yellow, and black) are respectively arranged, and cyan, magenta, yellow, and black images are sequentially formed through the processes of charging, exposure, development, and transfer. Further, an intermediate transfer belt 8 that rotates in the counterclockwise direction in FIG. 1 is provided adjacent to the photosensitive drums 1a to 1d.

[0016] Next, the image forming units Pa to Pd will be described. Around the photosensitive drums 1a to 1d, charging devices 2a to 2d, developing devices 3a to 3d, and cleaning devices 7a to 7d are arranged along the drum rotation direction (the clockwise direction in FIG. 1), and primary transfer rollers 6a to 6d are arranged sandwiching the intermediate transfer belt 8. Also, on the upstream side in the rotation direction of the intermediate transfer belt 8 with respect to the photosensitive drum 1a, a belt cleaning unit 19 that faces a tension roller 10 sandwiching the intermediate transfer belt 8 is arranged.

[0017] Next, the image forming procedure in the image forming apparatus 100 will be described. When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and an electrostatic latent image corresponding to the image data is formed on each of the photosensitive drums 1a to 1d. The developing devices 3a to 3d are filled with a two-component developer (hereinafter also simply referred to as a developer) containing toners of cyan, magenta, yellow, and black colors by toner containers 4a to 4d in a predetermined amount. The developing devices 3a to 3d have developing rollers 31 (refer to FIG. 3) that carry the developer. Toner in the developer is supplied to the photosensitive drums 1a to 1d by the developing rollers 31 and electrostatically adheres. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0018] Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photoreceptor drums 1a to 1d, and the cyan, magenta, yellow, and black toner images on the photoreceptor drums 1a to 1d are primary transferred onto the intermediate transfer belt 8. After the primary transfer, any toner remaining on the surface of the photoreceptor drums 1a to 1d is removed by the cleaning devices 7a to 7d.

[0019] The transfer paper P onto which the toner image is transferred is housed in a paper cassette 16 located at the bottom of the image forming apparatus 100, or placed on a manual feed tray 16b located on the side of the image forming apparatus 100. The transfer paper P in the paper cassette 16a or on the manual feed tray 16b is fed into the paper transport path 17 by the paper feed roller 12a. The transfer paper P is transported by the registration roller pair 12b at a predetermined timing to the secondary transfer roller 9 located adjacent to the intermediate transfer belt 8 and to the nip portion of the intermediate transfer belt 8 (secondary transfer nip portion N, see Figure 2) of the intermediate transfer belt 8. The transfer paper P onto which the toner image has been secondary transferred is transported to the fuser unit 13. Toner and other residues remaining on the surface of the intermediate transfer belt 8 are removed by the belt cleaning unit 19.

[0020] The transfer paper P, transported to the fixing unit 13, is heated and pressurized by the fixing roller pair 13a, fixing the toner image to the surface of the transfer paper P and forming a predetermined full-color image. The transfer paper P, on which the full-color image has been formed, is then discharged from the paper transport path 17 to the discharge tray 20 via the discharge roller pair 15 (or after being diverted to the inversion transport path 18 by the branching unit 14 and images are formed on both sides).

[0021] An image density sensor 50 is positioned opposite the drive roller 11, with the intermediate transfer belt 8 in between. Generally, an optical sensor is used as the image density sensor 50, which includes a light-emitting element such as an LED and a light-receiving element such as a photodiode. When measuring the amount of toner deposited on the intermediate transfer belt 8, measurement light is shone from the light-emitting element onto each patch image (reference image) formed on the intermediate transfer belt 8, and the measurement light is incident on the light-receiving element as light reflected by the toner and light reflected by the belt surface.

[0022] The light reflected from the toner and belt surface includes specular and diffuse reflection. This specular and diffuse reflection is separated by a polarization separation prism and then incident on separate photodetectors. Each photodetector converts the received specular and diffuse reflections into photoelectric signals and outputs them to the control unit 90 (see Figure 4).

[0023] Then, the image density (toner amount) and image position of the patch image are detected from the characteristic changes of the output signals of specular and diffuse reflected light. By comparing these with predetermined reference density and reference position, the characteristic value of the development voltage, the exposure start position and timing of the exposure device 5, etc., image density correction and color shift correction (calibration) are performed for each color.

[0024] Figure 2 is a side cross-sectional view showing the configuration around the intermediate transfer unit 30 mounted on the image forming apparatus 100. Figure 3 is an enlarged view of the area around the image forming section Pa in Figure 2. The intermediate transfer unit 30 includes an intermediate transfer belt 8 stretched between an upstream tension roller 10 and a downstream drive roller 11, primary transfer rollers 6a to 6d that contact the photoreceptor drums 1a to 1d via the intermediate transfer belt 8, backup rollers 21a and 21b, a belt cleaning unit 19, a pre-brush 41, and a roller contact / separation mechanism 32. A belt drive motor 40 is connected to the drive roller 11 via a gear train (not shown).

[0025] The intermediate transfer belt 8 is an elastic rubber belt in which an elastic layer is laminated on the surface of a base material layer. By providing an elastic layer, it is possible to prevent the phenomenon of image gaps caused by stress concentration during secondary transfer. As the material of the base material layer, for example, polyimide resin or PVDF (polyvinylidene fluoride) can be used, which is made by mixing conductive materials such as ionic conductive materials or conductive carbon to impart conductivity. As the material of the elastic layer, for example, hydrin rubber, chloroprene rubber, or polyurethane rubber can be used. Furthermore, a coating layer may be provided to protect the elastic layer. As the material of the coating layer, acrylic, silicone, fluororesin, etc. can be used.

[0026] The belt cleaning unit 19 includes a cleaning brush 23, a recovery roller 25, a scraper 27, and a transport spiral 29 within its housing. The cleaning brush 23 is positioned opposite the tension roller 10 via the intermediate transfer belt 8. The cleaning brush 23 rotates in a counter-clockwise direction (counterclockwise in Figure 2) relative to the direction of movement of the intermediate transfer belt 8, thereby scraping off foreign matter such as toner, carrier, and paper dust remaining on the intermediate transfer belt 8. The brush portion of the cleaning brush 23 that contacts the recovery roller 25 is made of conductive fibers with an electrical resistance of approximately 1 to 900 MΩ.

[0027] The recovery roller 25 rotates in the opposite direction to the cleaning brush 23 (clockwise in Figure 2) while in contact with the surface of the cleaning brush 23, thereby recovering toner and other materials adhering to the cleaning brush 23. The recovery roller 25 is connected to a belt cleaning voltage power supply 55, and a cleaning voltage, which is a DC voltage with the opposite polarity to the normal charge polarity of the toner (hereinafter referred to as "opposite polarity to toner"), is applied when the intermediate transfer belt 8 is being cleaned.

[0028] Specifically, since the toner used in this embodiment is positively charged, a negative polarity cleaning voltage is applied. Also, the tension roller 10 is grounded. As a result, the toner scraped off the intermediate transfer belt 8 is electrically and mechanically collected on the brush portion of the cleaning brush 23 and then electrically moved to the collection roller 25. The transport spiral 29 transports the toner scraped off the collection roller 25 by the scraper 27 to a waste toner collection container (not shown) outside the housing.

[0029] The pre-brush 41 is positioned upstream of the belt cleaning unit 19 in the direction of movement of the intermediate transfer belt 8. A pre-brush voltage power supply 56 is connected to the pre-brush 41, and a pre-brush voltage (pre-cleaning voltage), which is a DC voltage with the same polarity as the charge polarity of the toner (hereinafter referred to as "same polarity as the toner"), is applied to the pre-brush 41 to equalize the charge amount of residual toner on the intermediate transfer belt 8. Since the toner used in this embodiment is positively charged, a positive polarity pre-brush voltage is applied. This allows the cleaning brush 23 to easily remove residual toner on the intermediate transfer belt 8.

[0030] The pre-brush 41 is preferably formed from a material with a lower charge series than the elastic layer of the intermediate transfer belt 8. A charge series is a system in which, when two materials are rubbed together to charge, materials that tend to become positively (+) charged are placed higher, and materials that tend to become negatively (-) charged are placed lower. The charge polarity of a material changes depending on the material it is rubbing against; when a material higher and a material lower in the charge series are rubbed together, the higher material becomes positively charged and the lower material becomes negatively charged. In this embodiment, the pre-brush 41 becomes charged with the opposite polarity (negative polarity) of the toner due to friction with the intermediate transfer belt 8. Examples of materials for such a pre-brush 41 include polyester and acrylic.

[0031] The roller contact / separation mechanism 32 can be switched between a color mode in which the four primary transfer rollers 6a to 6d are pressed against the photoreceptor drums 1a to 1d via the intermediate transfer belt 8, a monochrome mode in which only the primary transfer roller 6d is pressed against the photoreceptor drum 1d via the intermediate transfer belt 8, and a primary transfer separation state in which all four primary transfer rollers 6a to 6d are separated from the intermediate transfer belt 8.

[0032] Figure 4 is a block diagram showing an example of a control path used in the image forming apparatus 100. Since various controls are performed on different parts of the image forming apparatus 100 during its operation, the overall control path of the image forming apparatus 100 is complex. Therefore, this section will focus on explaining the parts of the control path that are necessary for implementing the present invention.

[0033] The control unit 90 includes at least a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 as a read-only memory, a RAM (Random Access Memory) 93 as a read-write memory, a temporary memory 94 for temporarily storing image data, etc., a counter 95, and multiple (in this case, two) I / F (interfaces) 96 for transmitting control signals to each device in the image forming apparatus 100 and receiving input signals from the operation unit 70. Furthermore, the control unit 90 can be placed anywhere inside the main body of the image forming apparatus 100.

[0034] ROM 92 stores control programs for the image forming apparatus 100, necessary control values, and other data that should not be changed during use of the image forming apparatus 100. RAM 93 stores necessary data generated during the control of the image forming apparatus 100, as well as data temporarily required for the control of the image forming apparatus 100. For example, it stores the relationship between the output value of the image density sensor 50 and the image forming conditions in the first and second adjustment steps when performing calibration as described later, and the threshold value of the fluctuation range of the output value of the image density sensor 50 in the surface measurement step. Counter 95 accumulates and counts the number of printed sheets.

[0035] Furthermore, the control unit 90 transmits control signals from the CPU 91 to each part and device of the image forming apparatus 100 via the I / F 96. In addition, signals indicating their status and input signals are transmitted from each part and device to the CPU 91 via the I / F 96. Examples of parts and devices controlled by the control unit 90 include the image forming units Pa to Pd, the exposure apparatus 5, the primary transfer rollers 6a to 6d, the secondary transfer roller 9, the image density sensor 50, the voltage control circuit 51, and the operation unit 70.

[0036] The voltage control circuit 51 is connected to the charging voltage power supply 52, the developing voltage power supply 53, the transfer voltage power supply 54, the belt cleaning voltage power supply 55, and the pre-brush voltage power supply 56, and operates each of these power supplies by output signals from the control unit 90. Specifically, the control signal from the voltage control circuit 51 causes the charging voltage power supply 52 to apply a predetermined charging voltage to the charging rollers 21 in the charging devices 2a to 2d. The developing voltage power supply 53 applies a predetermined developing voltage to the developing rollers 31 in the developing devices 3a to 3d. The transfer voltage power supply 54 applies predetermined primary transfer voltages and secondary transfer voltages to the primary transfer rollers 6a to 6d and the drive roller 11, respectively. The belt cleaning voltage power supply 55 applies a predetermined cleaning voltage to the recovery roller 25 of the belt cleaning unit 19. The pre-brush voltage power supply 56 applies a predetermined pre-brush voltage to the pre-brush 41. In this example, a secondary transfer voltage of the same polarity as the toner is applied to the drive roller 11 facing the secondary transfer roller 9. However, a secondary transfer voltage of the opposite polarity to the toner may also be applied to the secondary transfer roller 9.

[0037] The control unit 70 is equipped with a liquid crystal display 71 and LEDs 72 that indicate various statuses. The user can stop image formation by operating the stop / clear button on the control unit 70, and reset the various settings of the image forming apparatus 100 to their default state by operating the reset button. The liquid crystal display 71 is designed to show the status of the image forming apparatus 100, as well as the image formation status and the number of copies to be printed. Various settings of the image forming apparatus 100 are made from the printer driver on a personal computer.

[0038] Figure 5 is a schematic diagram showing an example of calibration in the image forming apparatus 100. As shown in Figure 5, a reference image C1 (first reference image) for correcting the development voltage is formed on the first rotation of the intermediate transfer belt 8. The reference image C1 consists of a solid cyan image. The image density sensor 50 detects the image density of the reference image C1, and corrects the development voltage applied to the development roller 31 of the cyan development apparatus 3a based on the detection result. Next, a reference image C1' (first reference image) after correcting the development voltage is formed, and the image density sensor 50 detects the image density of the reference image C1' to determine whether the image density (toner development amount) is at the target value (first adjustment step).

[0039] No reference image is formed during the second rotation of the intermediate transfer belt 8; only cleaning of reference images C1 and C1' is performed by the belt cleaning unit 19.

[0040] During the third rotation of the intermediate transfer belt 8, the image density sensor 50 detects the surface condition of the intermediate transfer belt 8 in the region where reference images C1 and C1' were formed (surface measurement), and the belt cleaning unit 19 determines whether or not reference images C1 and C1' have been recovered (first surface measurement step).

[0041] In the fourth rotation of the intermediate transfer belt 8, a reference image C2 (second reference image) for correcting the gradation input value (exposure setting value) (gamma correction) is formed. The reference image C2 consists of patch images with multiple density levels, from the lightest image to the darkest image. Adjacent patch images are each formed in a single color such that the density changes at the boundary.

[0042] The image density sensor 50 detects the image density of the reference image C2, and corrects the gradation input value (exposure setting value) based on the detection result. Specifically, the amount of toner attached to each patch image (toner density) is detected by the image density sensor 50 and compared with a predetermined target density, and the average value of the density difference between each toner density and the target density is calculated. The parameter value used for gradation correction is determined according to the average value of the obtained density difference, and gradation correction is performed for each density. Next, a reference image C2' (second reference image) after the gradation input value has been corrected is formed, and the image density of the reference image C2' is detected by the image density sensor 50 to determine whether the image density of each patch image is at the target value or not (second adjustment step).

[0043] In development voltage correction, to determine the maximum toner development amount, solid images with a large amount of toner are formed on the intermediate transfer belt 8 as reference images C1 and C1'. Therefore, in the brush cleaning method using the cleaning brush 23, it is not easy to collect the reference images C1 and C1' in a single step after image density measurement.

[0044] Therefore, in the example shown in Figure 5, the intermediate transfer belt 8 is rotated twice after the development voltage correction is performed, and the reference images C1 and C1' are collected in two separate steps. This ensures that even under conditions where the collection performance of the cleaning brush 23 is reduced, the reference images C1 and C1' do not affect the surface measurement before gamma correction is performed.

[0045] In the example shown in Figure 5, the correction of the tone input value was performed after the development voltage correction. However, as shown in Figure 6, after the development voltage correction, reference images C3 and C3' (second reference image) may be formed and light intensity correction may be performed to determine the light intensity (laser power) of the laser light of the exposure apparatus 5. After the light intensity correction, reference images C2 and C2' may be formed and the correction of the tone input value may be performed. In the example in Figure 6, after the development voltage correction, the intermediate transfer belt 8 may be rotated twice, and the surface measurement (first surface measurement step) may be performed before the light intensity correction and gamma correction.

[0046] The above explains the calibration for cyan, but the process is exactly the same for magenta, yellow, and black. Specifically, base images M1, M1', Y1, Y1', K1, and K1' are formed to correct the development voltage. Base images M2, M2', Y2, Y2', K2, and K2' are formed to correct the gamma. Furthermore, base images M3, M3', Y3, Y3', K3, and K3' are formed to correct the light intensity.

[0047] Incidentally, if the cleaning performance of the cleaning brush 23 is lower than expected, even if the intermediate transfer belt 8 is rotated twice to collect the reference images C1, C1'~K1, K1' in two separate passes, a small amount of toner may remain on the intermediate transfer belt 8, potentially affecting the skin surface measurement. If no threshold is set for the skin surface measurement, the detection of the skin surface will include noise due to the remaining toner, which may prevent proper gamma correction or light intensity correction after the skin surface measurement.

[0048] Furthermore, while setting a threshold for surface measurement allows for accurate measurement of the surface condition of the intermediate transfer belt 8, calibration cannot be performed if the surface condition of the intermediate transfer belt 8 is not normal. For example, if scratches or irregularities occur on the surface of the intermediate transfer belt 8, calibration may be stopped as an abnormality is detected. However, if the cleaning performance of the cleaning brush 23 deteriorates and toner remains, a problem occurs where calibration is not performed even though the surface condition of the intermediate transfer belt 8 is normal.

[0049] Therefore, in this embodiment, if an abnormality is detected during scalp measurement, the calibration procedure is changed. Specifically, if the amplitude of the output waveform of the image density sensor 50 during scalp measurement is greater than or equal to a threshold, the intermediate transfer belt 8 is rotated one more time and the scalp measurement is performed again (second scalp measurement step). This allows residual toner generated due to a decrease in the cleaning performance of the cleaning brush 23 to be recovered, and normal scalp detection can be performed.

[0050] Furthermore, if the intermediate transfer belt 8 is rotated one more time and surface measurements are taken, and abnormalities are detected as before, it can be determined that scratches, irregularities, or other damage have occurred on the surface of the intermediate transfer belt 8. This allows for an accurate prediction of when the intermediate transfer belt 8 needs to be replaced.

[0051] Figure 7 is a flowchart showing an example of calibration control performed in the image forming apparatus 100. The calibration procedure will be explained following the steps in Figure 7, referring to Figures 1 to 6 and Figures 8 to 10 described later as needed. In Figure 7, as shown in Figure 5, a calibration is described in which development voltage correction and gamma correction are performed sequentially.

[0052] First, the control unit 90 determines whether or not it is time to perform calibration (step S1). The timing for performing calibration is determined, for example, by whether or not the cumulative number of printed pages since the last calibration has reached a predetermined number.

[0053] If it is time to perform calibration (Yes in step S1), first, the first adjustment process is performed (step S2). Specifically, reference images C1 to K1 (see Figure 5) are formed on the intermediate transfer belt 8, and density detection is performed by the image density sensor 50. Then, the development voltage is corrected based on the detection result, and reference images C1' to K1' are formed with the corrected development voltage. Furthermore, the density of reference images C1' to K1' is detected by the image density sensor 50 to determine whether the image density is at the target value.

[0054] Next, the intermediate transfer belt 8 is rotated twice to collect the reference images C1-K1 and C1'-K1' with the cleaning brush 23, and then the first surface measurement process is performed (step S3). The control unit 90 determines whether or not the amplitude of the output waveform is below a threshold (step S4).

[0055] Figure 8 is a graph showing the results of skin surface measurement when the cleaning brush 23 is performing normally. When the cleaning brush 23 is performing normally, the reference images C1~K1 and C1'~K1' can be completely recovered by rotating the intermediate transfer belt 8 twice. Therefore, it can be confirmed that the output waveform of the image density sensor 50 is not distorted.

[0056] Figure 9 is a graph showing the results of surface measurement when the performance of the cleaning brush 23 deteriorates. When the performance of the cleaning brush 23 deteriorates, the reference images C1~K1 and C1'~K1' cannot be completely recovered even after the intermediate transfer belt 8 is rotated twice. As a result, a peak occurs in the output waveform of the image density sensor 50 due to the influence of residual toner.

[0057] As shown in Figure 9, if a peak occurs due to the influence of residual toner and the amplitude of the output waveform exceeds the threshold (No in step S4), the control unit 90 drives the intermediate transfer belt 8 for one more rotation (step S5). Then, the second surface measurement process is performed (step S6) to determine whether or not the amplitude of the output waveform is below the threshold (step S7).

[0058] Figure 10 is a graph showing the results of the scalp measurement when the intermediate transfer belt 8 is rotated one more time from the state shown in Figure 9. When the intermediate transfer belt 8 is rotated one more time, it can be confirmed that the output waveform is not distorted, similar to Figure 8.

[0059] As shown in Figure 10, if the amplitude of the output waveform is below a threshold (Yes in step S7), the surface condition of the intermediate transfer belt 8 is determined to be normal, and the second adjustment process is executed (step S8). Specifically, reference images C2 to K2 (see Figure 5) are formed on the intermediate transfer belt 8, and density detection is performed by the image density sensor 50. Then, parameter values ​​to be used for gradation correction are determined based on the detection results, and reference images C2' to K2' are formed after correcting the gradation input values. Furthermore, the density of the reference images C2' to K2' is detected by the image density sensor 50 to determine whether the image density is at the target value. The control unit 90 also notifies the user of a decrease in the cleaning performance of the cleaning brush 23 (step S9). Specifically, a message prompting the user to replace the cleaning brush 23 is displayed on the liquid crystal display unit 71 (see Figure 4).

[0060] If the amplitude of the output waveform exceeds a threshold in step S7 (No in step S7), that is, if the surface condition of the intermediate transfer belt 8 does not return to normal even after rotating the intermediate transfer belt 8 one more time, the control unit 90 determines that scratches or irregularities have occurred on the surface of the intermediate transfer belt 8 and cancels the calibration (step S10). The control unit 90 also notifies the system of the abnormality of the intermediate transfer belt 8 (step S11). Specifically, it displays a message on the liquid crystal display unit 71 (see Figure 4) prompting the system to replace the intermediate transfer belt 8.

[0061] On the other hand, if the amplitude of the output waveform is below the threshold in step S4 (Yes in step S4), the second adjustment process is performed without rotating the intermediate transfer belt 8 one more time (step S12).

[0062] According to the control example shown in Figure 7, based on the surface measurement results during calibration, it is possible to detect a decrease in the performance of the cleaning brush 23 or an abnormality in the intermediate transfer belt 8. If the performance of the cleaning brush 23 has decreased, the intermediate transfer belt 8 can be rotated one more time to collect the remaining toner, thereby preventing the calibration from being performed. In addition, if any abnormalities such as scratches or unevenness occur in the intermediate transfer belt 8, the user can be notified promptly.

[0063] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiments, a tandem-type color printer as shown in Figure 1 was used as an example of the image forming apparatus 100, but it is not limited to color printers and can be applied to various image forming apparatuses using an intermediate transfer method equipped with a cleaning brush, such as color copiers and color multifunction printers. [Industrial applicability]

[0064] The present invention can be used in a cleaning device that removes residual toner from the surface of an intermediate transfer belt using a cleaning brush. By using the present invention, when calibration is performed in two stages and a reference image is formed at the same location on the intermediate transfer belt, an image forming device can be provided that can perform the second stage of calibration with high accuracy. [Explanation of Symbols]

[0065] Pa~Pd Image Forming Unit 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Exposure apparatus 8. Intermediate transfer belt 9. Secondary transfer roller 19 Belt Cleaning Unit 23 Cleaning brush 25 Recovery Roller 27 Scraper 29 Conveyor spiral 30 Intermediate Transfer Unit 31. Developing roller (developer carrier) 50 Image density sensor 100 Image forming apparatus Y1, Y1' Reference image (First reference image) Y2, Y2' Reference image (Second reference image) Y3, Y3' Reference image (Second reference image)

Claims

1. An image carrier having a photosensitive layer formed on its surface, A charging device for charging the surface of the image carrier, An exposure apparatus that forms an electrostatic latent image with reduced charge by exposing the surface of the image carrier that has been charged by the charging apparatus, A developing apparatus having a developer carrier that carries a developer containing toner, and developing the electrostatic latent image formed on the image carrier into a toner image, An endless intermediate transfer belt rotates in contact with the image carrier, thereby transferring the toner image formed on the image carrier as a primary transfer. A cleaning brush for removing toner remaining on the intermediate transfer belt, An image density sensor for detecting the density of the toner image that has been primary transferred onto the intermediate transfer belt, A control unit that performs calibration to correct the image density based on the density of a reference image detected by the image density sensor, In an image forming apparatus equipped with, The aforementioned calibration is A first adjustment step involves detecting the density of a first reference image formed on the intermediate transfer belt and adjusting the image formation conditions based on the detection result. After the execution of the first adjustment step, when the intermediate transfer belt has completed one or more rotations, the first surface measurement step involves detecting the formation region of the first reference image using the image density sensor. After the execution of the first scalp measurement step, when the intermediate transfer belt has completed one rotation, the density of the second reference image formed in the formation region of the first reference image is detected, and the image formation conditions are changed from those of the first adjustment step based on the detection result in a second adjustment step. Includes, The image forming apparatus is characterized in that, when the amplitude of the output waveform of the image density sensor in the first surface measurement step is below a threshold, the control unit determines that the surface condition of the intermediate transfer belt is normal and executes the second adjustment step.

2. If the amplitude of the output waveform of the image density sensor in the first scalp measurement step exceeds the threshold, the control unit executes a second scalp measurement step in which the intermediate transfer belt is rotated one more time and the formation region of the first reference image is detected by the image density sensor. The image forming apparatus according to claim 1, characterized in that the second adjustment step is performed when the amplitude of the output waveform of the image density sensor in the second scalp measurement step is less than or equal to the threshold.

3. The image forming apparatus is equipped with a notification unit capable of notifying the status of each part of the image forming apparatus, including the cleaning brush. The image forming apparatus according to claim 2, characterized in that the control unit notifies of a decrease in the performance of the cleaning brush using the notification unit when the amplitude of the output waveform of the image density sensor in the second scalp measurement step is less than or equal to the threshold.

4. The image forming apparatus according to claim 2, characterized in that the control unit cancels the calibration without executing the second adjustment step if the amplitude of the output waveform of the image density sensor in the second scalp measurement step exceeds the threshold.

5. The image forming apparatus is equipped with a notification unit capable of notifying the status of each part of the image forming apparatus, including the intermediate transfer belt. The image forming apparatus according to claim 4, characterized in that the control unit, when the amplitude of the output waveform of the image density sensor in the second scalp measurement step exceeds the threshold, uses the notification unit to provide a notification prompting the replacement of the intermediate transfer belt.

6. The first adjustment step involves detecting the density of the solid image formed as the first reference image on the intermediate transfer belt and adjusting the development voltage applied to the developer carrier based on the detection result. The image forming apparatus according to claim 1, characterized in that the first surface measurement step is performed when the intermediate transfer belt has completed two rotations after the first adjustment step has been performed.

7. The image forming apparatus according to claim 1, characterized in that the second adjustment step involves detecting the density of the second reference image formed on the intermediate transfer belt and adjusting at least one of the light intensity and gradation input value of the exposure apparatus based on the detection result.

Images