JP2016122042A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which performs density correction accurately by generating a proper toner patch even when a surface of an image carrier is changed with time and a base reflection light amount becomes uneven.SOLUTION: A printer 100 comprises an intermediate transfer belt 2, a drive roller 26 thereof, an image formation part 10 forming a toner image or the like on the intermediate transfer belt 2, a density detection sensor 80 detecting the density of the toner image or the like, transfer parts (2a-d) transferring the toner image to a recording material, a light amount detection part (80) detecting a base reflection light amount of a toner patch formation region of the intermediate transfer belt 2, a light amount correction part (S810) correcting the detected base reflection light amount by using an evaluation value changed with time in accordance with rubbing between the intermediate transfer belt 2 and the recording material, a correction part (S812) correcting the image density on the basis of the corrected base reflection light amount and density detection value of the toner patch, and a CPU 201a changing a region for forming the toner patch along the width direction when the evaluation value exceeds a prescribed threshold.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus that transfers a toner image formed on an image carrier to a recording material.

  Conventionally, in an image forming apparatus such as a copying machine or a printer employing an electrophotographic system, image density correction has been performed as follows. That is, a toner image (toner patch) for density correction is formed on an image carrier such as a photosensitive drum or an intermediate transfer member, the density of the toner patch is detected by an optical sensor, and the target is determined based on the difference between the detection result and the ideal output. Correction data such as exposure intensity and applied voltage for obtaining density are created. Then, an image having a target density is formed by correcting the corresponding image forming conditions based on the created correction data.

  In such density correction processing, it is necessary to grasp in advance the amount of light reflected from the ground, which is the image carrier itself, at a position on the image carrier where the toner patch is formed. This is because the detection output when determining the density of the toner patch includes the amount of light reflected from the background.

  In addition, since the image bearing member such as the photosensitive drum or the intermediate transfer member has gloss, most of the irradiated light is reflected and read by the optical sensor. In particular, since an image with a low density is formed by reducing the amount of toner, a low-density toner patch has a higher degree of exposure of the background than a high-density toner patch. For this reason, in order to accurately calculate the density of the low density toner patch, it is necessary to sufficiently consider the amount of light reflected from the background.

  Therefore, based on the positional relationship between the home position and the toner patch per rotation of the image carrier obtained by rotating the image carrier provided with the home position mark and detecting it with an optical sensor, the reflected light amount of the background is determined. A technique for specifying is proposed (see Patent Document 1). In Patent Document 1, the toner density is corrected using the specified background reflected light amount and the reflected light amount correction value corresponding to the toner area ratio of the toner image.

JP 2005-345740 A

  However, in the image forming apparatus, when the image formed by the image forming unit is transferred to the recording material, the image carrier and the recording material rub against each other, so that the surface of the image carrier is scraped over time. . Then, the reflectance of light on the surface of the image carrier is reduced due to surface scraping, whereby the amount of base reflected light on the image carrier decreases with time.

  Further, the degree of rubbing between the image carrier and the recording material varies depending on the toner density of the formed toner image. Therefore, when the toner density is not uniform on the recording surface as in a normal document or image, the degree of friction between the image carrier and the recording material varies depending on the location. If the degree of rubbing is not uniform, the amount of decrease in the amount of reflected base light also varies from place to place. If a toner patch for density correction is formed on the surface of the image carrier where the amount of change in the amount of reflected base light is not uniform, the error increases as the number of image formations increases, so that appropriate density correction is realized. I can't.

  In order to perform density correction processing that takes into account the temporal change in the amount of reflected light from the background, it is effective to re-examine the background profile immediately before the density correction processing. However, if a background profile for one rotation of the image carrier is acquired for each density correction process, the adjustment time increases and the productivity of the image forming apparatus itself decreases. Therefore, the acquisition of the base profile is usually performed at intervals of, for example, 1000 image formations so that the influence on productivity is as small as possible. On the other hand, there is a problem that the amount of background reflected light of the image carrier changes when the background profile is acquired and when the toner patch density is detected, and the density correction accuracy decreases. Further, as described above, when a low density toner patch is formed, the influence of the reflected light amount of the background becomes large. Therefore, if the density correction is performed by the low density patch at a place where the change of the reflected light amount of the background is large, the density is increased. Correction accuracy further decreases.

  The present invention provides an image forming apparatus capable of generating an appropriate toner patch and performing density correction with high accuracy even when the surface of the image carrier changes with time and the amount of reflected light from the background becomes non-uniform. There is to do.

  In order to solve the above problems, an image forming apparatus according to claim 1, an image carrier, driving means for rotating the image carrier, a toner image and a density correction toner patch on the image carrier. Image forming means to be formed, density detecting means for detecting the density of the toner image and the toner patch, transfer means for transferring the toner image to a recording material, and an area where the toner patch is formed on the image carrier A light amount detecting means for detecting a ground reflected light amount of the image carrier in a predetermined region unit in a circumferential direction with respect to a plurality of width direction regions divided by a constant width in a direction parallel to the rotation axis, and the detected ground reflected light amount Is corrected using an evaluation value of the surface state of the image carrier that changes over time according to the rubbing between the image carrier and the recording material, the corrected ground reflected light amount, Correction means for correcting the density of the toner image based on the detected density value of the toner patch, and a region where the toner patch is formed along the width direction of the image carrier when the evaluation value exceeds a predetermined threshold value And control means for controlling the density correction processing of the toner image by forming the toner patch in the changed area.

  According to the present invention, when the evaluation value of the surface state of the image carrier that changes over time exceeds a predetermined threshold value, the region for forming the toner patch is changed along the width direction of the image carrier, and the change is made. Control is performed so that a toner patch is formed in the region and the density correction processing of the toner image is executed. As a result, even when the surface of the image carrier changes with time and the amount of ground reflected light becomes non-uniform, it is possible to generate an appropriate toner patch and perform density correction with high accuracy.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a partially enlarged view of an intermediate transfer unit in FIG. 1. FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus in FIG. 1. 2 is a flowchart illustrating a procedure of density correction processing executed by the image forming apparatus 100 in FIG. 1. FIG. 4 is a diagram illustrating a configuration of an intermediate transfer belt drive unit and a belt-delay position detection unit. It is a figure which shows a response | compatibility with the output of the belt edge sensor 62, and a belt side position. It is a figure for demonstrating reading of an initial background profile. It is a timing chart at the time of acquiring a ground profile. 6 is a diagram illustrating a correspondence between a toner area in a predetermined region and an evaluation value of a scraping amount S. FIG. FIG. 6 is a diagram for explaining an evaluation procedure for a scraping amount of an intermediate transfer belt. It is a figure which shows the positional relationship of the belt and density | concentration detection sensor before and behind the change of a belt position. FIG. 2 is a perspective view illustrating an intermediate transfer unit in the image forming apparatus of FIG. 1. It is a figure for demonstrating the position moving means attached | subjected to the density | concentration detection sensor. It is a figure which shows the modification of FIG.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment. In FIG. 1, an image forming apparatus 100 is a tandem intermediate transfer type full color printer in which four image forming stations are arranged along an intermediate transfer belt.

  An image forming apparatus (hereinafter, referred to as “printer”) 100 includes an apparatus main body 50, an image forming unit 10 provided at a substantially central portion of the apparatus main body 50, and an intermediate transfer unit provided at an upper portion of the image forming unit 10. 20 and a paper feeding unit 30 provided in the lower part of the image forming unit 10.

  The image forming unit 10 exposes four image forming stations 10a, 10b, 10c, and 10d that form toner images corresponding to the colors yellow, magenta, cyan, and black, and an exposure device 6 that exposes the photosensitive drum of each image forming station. It has. Each of the image forming stations 10a, 10b, 10c, and 10d is an exchange unit (process cartridge) including the photosensitive drums 1a, 1b, 1c, and 1d, and has the same configuration.

  Each of the photosensitive drums 1a to 1d is made of an aluminum cylinder, and a photosensitive layer having a negative charge polarity is formed on the outer peripheral surface thereof. The photosensitive drums 1a to 1d are rotated at a predetermined process speed by a driving force of a driving motor (not shown). The photosensitive drums 1a to 1d are charged to a uniform negative potential by charging rollers (not shown) incorporated in the image forming stations 10a to 10d, respectively.

  The exposure device 6 scans the scanning line image data obtained by developing the separation color image of each color with a rotating mirror, and thereby forms electrostatic latent images on the surfaces of the photosensitive drums 1a to 1d. To do. The electrostatic latent images formed on the photosensitive drums 1a to 1d are developed into toner images by developing devices (not shown) incorporated in the image forming stations 10a to 10d, respectively.

  The intermediate transfer unit 20 is an exchange unit that is detachably formed with respect to the apparatus main body 50. The intermediate transfer unit 20 includes an intermediate transfer belt 2, a driving roller 26, a tension roller 27, a secondary transfer stretching roller 25, and primary transfer stretching rollers 28 and 29 that stretch the intermediate transfer belt 2 in a reversible manner. It is configured. The intermediate transfer belt 2 is composed of an endless belt member that does not expand and contract, and is driven to rotate in the direction of the arrow R2 in the drawing by the drive roller 26. Primary transfer rollers 2a, 2b, 2c, and 2d are disposed at positions facing the photosensitive drums 1a, 1b, 1c, and 1d of the respective image forming stations with the intermediate transfer belt 2 interposed therebetween.

  The primary transfer rollers 2a to 2d are urged by a spring member to press the intermediate transfer belt 2, and between the photosensitive drums 1a to 1d and the intermediate transfer belt 2, primary transfer portions Ta, Tb, Tc, Td. Form. An intermediate transfer belt in which negative four-color toner images formed on the photosensitive drums 1a to 1d pass through the primary transfer portions Ta to Td by applying a positive DC voltage to the primary transfer rollers 2a to 2d. The color image is formed by being transferred so as to be superimposed on 2.

  In the intermediate transfer belt 2, a density detection sensor 80 for detecting the amount of reflected light on the surface of the intermediate transfer belt 2 or the density of the toner image on the intermediate transfer belt 2, and a reference position mark in the circumferential direction of the intermediate transfer belt 2 are detected. A home position sensor 90 is provided.

  A secondary transfer roller 22 is disposed at a position facing the secondary transfer stretching roller 25 with the intermediate transfer belt 2 interposed therebetween, and a nip portion where the intermediate transfer belt 2 and the secondary transfer roller 22 are in contact with each other is a secondary transfer roller. Part T2. The secondary transfer stretching roller 25 is assembled on the intermediate transfer unit 20 side, while the secondary transfer roller 22 is assembled on the main body 50 side of the image forming apparatus 100.

  Below the image forming unit 10, a paper feeding unit 30 including the recording material cassette 4 is provided. A separation roller 8 is disposed on the upper end of the recording material cassette 4. A conveyance path 35 for a recording material (hereinafter referred to as “sheet”) is provided from the separation roller 8 to the fixing unit 5 and the paper discharge roller 11 which will be described later through the secondary transfer portion T2. A registration roller 9 is disposed on the upstream side of the secondary transfer portion T <b> 2 of the transport path 35. The separation roller 8 separates the sheets P pulled out from the recording material cassette 4 one by one, and sends them to the registration roller 9 through the conveyance path 35. The registration roller 9 receives and waits for the sheet P in the stopped state, and sends the sheet P to the secondary transfer portion T2 in time with the toner image transferred to the intermediate transfer belt 2.

  In the secondary transfer portion T2, a toner image is transferred between the secondary transfer tension roller 25 connected to the ground potential by applying a positive DC voltage to the secondary transfer roller 22 from a power supply (not shown). An electric field is formed. The color image formed on the intermediate transfer belt 2 is transferred to the sheet P by a transfer electric field. The sheet P on which the color image has been transferred is conveyed to the fixing unit 5.

  The fixing device 5 includes a fixing roller 5a including a fixing heater and a pressure roller 5b, and forms a heating nip portion by pressing the fixing roller 5a and the pressure roller 5b. The sheet P on which the color image has been transferred is heated and pressed in the heating nip, whereby the color image is melted and fixed on the sheet P. The sheet P on which the color image is fixed is discharged to the paper discharge tray 7 by the paper discharge roller 11.

  FIG. 2 is a partially enlarged view of the intermediate transfer unit 20 in FIG. The intermediate transfer belt 2 stretched by the secondary transfer stretching roller 25 or the like is provided with one reflecting material 95 indicating a reference origin (home position, hereinafter referred to as “HP”). A home position sensor (HP sensor) 90 is disposed so as to face the intermediate transfer belt 2. The HP sensor 90 determines the reference position (HP) in the conveyance direction of the intermediate transfer belt 2 by detecting the reflective material 95. Usually, the reflective material 95 is provided on the back surface (inside) of the intermediate transfer belt 2 so as not to hinder image formation, and the HP sensor 90 is also disposed at a position facing the back surface (inside) of the intermediate transfer belt 2. Yes.

  On the other hand, the density detection sensor 80 is provided so as to face the image forming surface of the intermediate transfer belt 2. The density detection sensor 80 includes a light source and a light receiving unit (both not shown) as a light emitting unit, and the light receiving unit receives reflected light emitted from the light source and applied to the toner image 98 on the intermediate transfer belt 2 and reflected. Thus, a density detection output corresponding to the amount of reflected light is generated. The density of a toner patch to be described later can also be detected by forming it on the surface of the intermediate transfer belt 2 within the detection range of the density detection sensor 80. That is, the density detection sensor 80 performs intermediate transfer in units of a predetermined area in the circumferential direction for a plurality of width direction areas divided by a constant width in a direction parallel to the rotation axis including the area where the toner patch is formed on the intermediate transfer belt 2. The background reflected light amount of the belt 2 is detected.

  The intermediate transfer unit 20 includes a shift position control mechanism that controls the shift position of the intermediate transfer belt 2 in the width direction. Details of the shift position control mechanism will be described later.

  FIG. 3 is a block diagram showing a control configuration of the image forming apparatus of FIG.

  In FIG. 3, the printer 100 includes a control unit 200 that incorporates a CPU 201a. The control unit 200 controls the entire printer 100 in an integrated manner. That is, the control unit 200 plays a role of driving each load in the printer 100, collecting and analyzing information of sensors, image control, and exchanging data with the operation unit 202 which is a user interface.

  An operation unit 202 is connected to the control unit 200. The operation unit 202 includes input means (not shown) such as a keyboard for inputting information such as a copy magnification and a density setting value set by the user. Further, the operation unit 202 includes display means for indicating to the user the status of the printer 100, for example, the number of images formed, information on whether or not images are being formed, occurrence of a jam, occurrence location, and the like. The operation unit 202 exchanges input / output data with the CPU 201a of the control unit 200.

  The control unit 200 includes a RAM 201b and a ROM 201c in addition to the CPU 201a in order to perform the above-described roles. The CPU 201a is connected to the RAM 201b and the ROM 201c, and executes various sequences based on a predetermined image forming sequence in accordance with a program stored in the ROM 201c. Further, when executing various sequences, the CPU 201a stores rewritable data that needs to be temporarily or permanently stored in the RAM 201b.

  The RAM 201b is configured such that all or part of the data in the storage area is not lost even when the printer 100 is turned off by an auxiliary power source such as a backup battery (not shown). The RAM 201b stores, for example, a high voltage set value for a high voltage control unit 205 described later, image formation command information from the operation unit 202, various data, and the like. The ROM 201c stores various programs executed by the CPU 201a.

  The control unit 200 includes a sensor IF 209, and the belt home position sensor 90, the belt edge sensor 62, and other sensors 214 are connected to the CPU 201a via the sensor IF 209. The belt home position sensor 90 detects the HP of the intermediate transfer belt 2. The belt edge sensor 62 detects a shift position in the width direction of the intermediate transfer belt 2. Examples of the other sensor 214 include a photo interrupter and a micro switch for detecting the state of recording paper and the apparatus.

  The control unit 200 also includes a motor control unit 207. The belt drive motor 70, the belt steering motor 223, and other motors 212 are connected to the CPU 201a via the motor control unit 207. The belt drive motor 70 rotates the drive roller 26 that drives the intermediate transfer belt 2. The belt steering motor 223 controls the position of the intermediate transfer belt 2 in the width direction by moving the drive roller 26 up and down (see FIG. 12 described later). Examples of the other motor 212 include a drive motor that drives various rollers, a photosensitive drum, and the like.

  The control unit 200 also includes a DC load control unit 208, and the clutch / solenoids (CL, SL) 213 are connected to the CPU 201a via the DC load control unit 208. The CPU 201a controls the clutch / solenoids 213 via the DC load control unit 208 while detecting the input from the other sensors 214 via the sensor IF 209, thereby smoothly proceeding with the image forming operation.

  The control unit 200 also includes an A / D converter 203, and the density detection sensor 80 and the thermistor 204 are connected to the CPU 201a via the A / D converter 203. The density detection sensor 80 is an analog sensor whose output value changes according to the amount of light read. The output voltage as the output value of the density detection sensor 80 is converted into, for example, 8-bit digital data by the A / D converter 203 based on the reference voltage, and then input to the CPU 201a. The thermistor 204 reads the temperature of the fixing heater 211. The output of the thermistor 204 is an analog voltage corresponding to the temperature, and is input to the CPU 201a via the A / D converter 203.

  The control unit 200 also includes a high voltage control unit 205, and the high voltage unit 206 is connected to the CPU 201a via the high voltage control unit 205. The high voltage unit 206 is controlled by the high voltage control unit 205 and applies an appropriate high voltage to a primary charger, a transfer charger, a developing roller in the developing device, and the like that electrostatically charge the photosensitive drum and the charging roller.

  The control unit 200 also includes an AC driver 210, and the fixing heater 211 is connected to the CPU 201a via the AC driver 210. The AC driver 210 drives an AC power load including the fixing heater 211 in accordance with an instruction from the CPU 201a.

  The control unit 200 also includes an image control unit 220, and the image forming unit 10 is connected to the CPU 201 a via the image control unit 220. The image control unit 220 processes print image data input from a document line reading device or a network line such as Ethernet (registered trademark) via the external IF 222, and sends it to the image forming unit 10 including an LED head and a laser scanner. The processed image data is sent out.

  Hereinafter, the density correction processing executed in the image forming apparatus of FIG. 1 will be described. This density correction processing is executed by the CPU 201a of the control unit 200 in the printer 100 according to a density correction processing program stored in the ROM 201c.

  FIG. 4 is a flowchart showing the procedure of density correction processing executed by the printer 100 of FIG. When this density correction processing is applied to an actual image forming apparatus, it is formed so that toner patches formed for density correction do not overlap with images formed on the intermediate transfer belt 2 based on at least the image data. Executed. This is for more correct density correction.

  In FIG. 4, when the density correction process is started, the CPU 201a first confirms that the density detection sensor 80 faces the center position (4) of the intermediate transfer belt 2 near the belt (step S801). ). The density detection sensor 80 is disposed to face the center position (4) of the intermediate transfer belt 2 near the belt, so that the density detection sensor 80 outputs the background output of the center position (4) and the formed toner patch. Can be detected properly.

  Hereinafter, the position near the belt will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a diagram illustrating a configuration of an intermediate transfer belt driving unit and a belt-shift position detecting unit. In FIG. 5, the belt drive motor 70 of the intermediate transfer belt 2 is arranged at one end of the second frame 40 so as to be offset. The belt drive motor 70 transmits a driving force to the drive roller 26 via the gear 75 and the gear 74, and rotationally drives the intermediate transfer belt 2 at a desired speed.

  A belt edge sensor 62 serving as a belt shift position detection sensor includes a sensor flag 62c that is pivotally supported by a rotation shaft 62b, and a plurality of photosensors 62d to 62d that are arranged along a rotation locus at one end of the sensor flag 62c. 62h. The belt edge sensor 62 includes a detection roller 62a formed at the other end in the vicinity of the rotation shaft 62b of the sensor flag 62c.

  The detection roller 62a is in contact with the belt edge of the intermediate transfer belt 2, and the photosensors 62d to 62h detect the position of the sensor flag 62c that rotates on the opposite side of the detection roller 62a with the rotation shaft 62b interposed therebetween. The position near the belt is detected. That is, by detecting the position of the sensor flag 62c, the position of the detection roller 62a is specified, and based on the position of the detection roller 62a, the edge position of the transfer belt 2 that is in contact with the detection roller 62a is detected as the position near the belt. Is done.

  In the belt edge sensor 62, the photosensors 62d, 62e, 62f, 62g, and 62h are arranged along the rotation locus portion of the sensor flag 62c as described above. Accordingly, the position of the intermediate transfer belt 2 near the belt can be detected from the combination of the output states of these five photosensors. The number of sensors is not limited to five.

  FIG. 6 is a diagram showing the correspondence between the output of the belt edge sensor 62 and the position near the belt.

  In FIG. 6, the relative position of the density detection sensor 80 corresponding to the belt shift amount is displayed. The density detection sensor 80 detects the density of the toner patch on the intermediate transfer belt 2.

  In FIG. 6, the position near the belt is defined corresponding to the detection states of the photo sensors 62 d to 62 h of the belt edge sensor 62. For example, when all of the photo sensors 62d to 62h detect the sensor flag 62c, the position near the belt is determined as the center position. An appropriate position of the density detection sensor for detecting the density of the toner patch formed on the intermediate transfer belt 2 at the center position is, for example, “4”. If only the photo sensor 62d detects the sensor flag 62c and the other photo sensors cannot detect the sensor flag 62c, the belt shift position is determined as “front shift 4”, and the density corresponding to the front shift 4 is determined. The appropriate position of the detection sensor is “8”. Conversely, if only the photosensor 62h detects the sensor flag 62c and the other photosensors fail to detect the sensor flag 62c, the position near the belt is determined as the backside 4, and the density detection corresponding to the backside 4 is detected. The appropriate position of the sensor is “0”.

  When all the photosensors 62d to 62h cannot detect the sensor flag 62c, it is determined that the abnormal state is the front error or the back error. In the case of a front-side error or a back-side error, since the deviation of the belt-side position is too large, it is determined as an uncontrollable range, and the other nine points (density detection sensor positions: 0 to 8) are determined as a controllable range. The

  Returning to FIG. 4, after confirming the position of the density detection sensor 80 (step S801), the CPU 201a acquires the background profile B (n) along the conveyance direction of the intermediate transfer belt 2 and stores it in the RAM 201b (step S802). ).

  The belt length of the intermediate transfer belt 2 is, for example, 893 mm, and the background profile is sequentially acquired from B (0) to B (892) by dividing the belt by 1 mm along the belt conveyance direction.

  FIG. 7 is a diagram for explaining reading of the initial base profile.

  In FIG. 7, with respect to the width direction region divided into a plurality of predetermined regions along the width direction of the intermediate transfer belt 2, the HP marks are used as a reference along the circumferential direction of the intermediate transfer belt 2 at predetermined intervals, for example, 1 mm intervals. The divided predetermined areas are shown. Then, a background profile is acquired for each predetermined area. Each divided region in the width direction is divided at an interval corresponding to the position near the belt in FIG. 6, and a toner patch is formed in one of the width direction regions facing the density detection sensor position. The width direction region where the toner patch is formed may be within the image forming region applied to image formation since the background profile change is evaluated as described later.

  FIG. 8 is a timing chart when acquiring the base profile, and FIG. 8A shows the output of the HP sensor 90 that detects the home position as the reference position. Accordingly, in FIG. 8A, the time interval between the output change points corresponds to one rotation of the intermediate transfer belt 2.

  In FIG. 8, when acquiring the background profile, the CPU 201a first rotates the intermediate transfer belt 2 one or more times in a state where the toner image is not transferred in order to acquire the reference background profile. Then, the output of the density detection sensor 80 for one round is acquired with reference to the position of the HP mark detected by the HP sensor. Next, the CPU 201 stores the acquired output of the density detection sensor 80 as a background profile B (n), for example, in the RAM 201b (FIG. 8B).

  After acquiring the background profile in this manner, in the conventional technique, the measurement result of the patch density is corrected using the acquired background profile (FIGS. 8C and 8D).

  That is, density detection is performed when a toner patch having a predetermined density is formed at a predetermined position on the intermediate transfer belt 2, the intermediate transfer belt 2 on which the toner patch is formed is rotated, and the reflected light of the toner patch is detected by the density detection sensor. The output of the sensor is obtained (FIG. 8 (c)). Then, the toner patch density is calculated based on the difference between the obtained output and the profile stored in the RAM 201b (FIG. 8D), and the correction coefficient is calculated based on the calculated density value and the density reference value of the reference patch. And the density correction processing was executed using the correction coefficient.

  However, the present inventor has found that the surface of the image carrier is scraped over time due to the rubbing between the image carrier and the sheet, and the degree of shaving varies depending on the toner area of the image transferred to the sheet. I found. That is, it has been found that the amount of scraping of the intermediate transfer belt 2 becomes more prominent as the formed toner area (= toner amount) increases, and the sensor output obtained from the base profile changes due to fluctuations in the degree of scraping.

  In order to realize more accurate density correction, the inventor needs to correct the background profile according to the degree of abrasion on the surface of the image carrier, and the degree of abrasion exceeds a predetermined threshold. In this case, it was found that the toner patch formation position needs to be changed.

  In other words, in the present embodiment, the background profile of the intermediate transfer belt 2 as an image carrier is used to transfer the toner image formed on the intermediate transfer belt 2 that affects the surface scraping amount of the intermediate transfer belt 2 and transferred to the sheet P. Correction is made according to the toner area.

  Returning to FIG. 4, after obtaining the base profile B (n) and storing it in the storage unit (step S802), the CPU 201a starts a normal image forming operation (step S803). At this time, it corresponds to the scraping amount S (m, n) of the intermediate transfer belt 2 according to the toner area of the image data formed in the region (m, n) which is a predetermined region on the intermediate transfer belt 2 at the same time as the image formation. Obtain an evaluation value. For example, when the toner area ratio in a predetermined area is 0 to 9%, the evaluation value is 0 point, and when the toner area ratio is 10 to 19%, the evaluation value is 1 point. Correspondingly, an evaluation value of 0 to 10 is assigned (step S804).

  FIG. 9 is a diagram illustrating a correspondence between the toner area of the predetermined region and the evaluation value of the scraping amount S (m, n). In FIG. 9, the evaluation value S (m, n) when the toner area is 0 to 9% is “0”, and the abrasion amount S (m, n) when the toner area is 100%. The evaluation value is “10”. Further, a portion between the scraping amount S (m, n) evaluation values 0 to 10 is divided at equal intervals with a toner area interval of 10%, and the scraping amount evaluation values 1 to 9 are respectively assigned. M in the scraping amount S (m, n) represents a position in the width direction of the intermediate transfer belt 2, and is a coordinate disposed at an interval corresponding to the belt-delay position in FIG. On the other hand, n represents the position of the intermediate transfer belt 2 in the transport direction, and is set by dividing one turn of the intermediate transfer belt 2 into, for example, 0 to 892, similarly to the coordinates storing the background profile.

  When the intermediate transfer belt 2 makes one round, as shown in FIG. 10A, an evaluation value of the scraping amount S (m, n) for one round is obtained. FIG. 10 is a diagram for explaining a procedure for evaluating the amount of scraping of the intermediate transfer belt. FIG. 10A illustrates the amount of scraping S (for each predetermined region along the circumferential direction of the intermediate transfer belt 2. The evaluation value of m and n) is shown.

  Returning to FIG. 4, after obtaining the evaluation value of the scraping amount (step S804), the CPU 201a, based on the obtained evaluation value, average value AveS (1) of the evaluation values for one belt round for each predetermined region in the belt width direction. m) is obtained (step S805). FIG. 10B is a diagram showing an average evaluation value AveS (m) obtained by averaging the evaluation values of the shaving amounts S (m, n) obtained for each predetermined region in the region unit in the width direction. In FIG. 10B, an average evaluation value AveS (m) obtained by averaging the evaluation values of the scraping amount S (m, n) obtained for each predetermined region along the conveyance direction of the intermediate transfer belt 2 in the region unit in the width direction. ). That is, AveS (m) can be a value that evaluates the degree of scraping for one round of the belt for each region unit in the width direction.

  Next, the CPU 201a calculates HAveS (m) by adding the calculated average evaluation value AveS (m) for one rotation of the belt to the integration register (step S806). FIG. 10C is a diagram showing an integrated evaluation value HAveS (m) obtained by integrating the average evaluation value AveS (m).

The CPU 201a repeats the operations in steps S803 to S806 during the image forming operation, and then determines whether or not the cumulative image forming number has reached 100, for example (step S807). As a result of the determination in step S807, when the cumulative number of formed images has reached 100 (“YES” in step S807), the CPU 201a advances the process to step S808.
That is, the CPU 201a determines whether or not the integrated evaluation value HAveS (m = density detection sensor position) in the width direction region corresponding to the density detection sensor position as the amount of change in the surface of the intermediate transfer belt 2 has reached a predetermined threshold value. (Step S808).

  As a result of the determination in step S808, if HAveS (m) is equal to or smaller than the predetermined threshold (“NO” in step S808), the CPU 201a advances the process to step S809. That is, the CPU 201a determines that the integrated evaluation value is a density correction possible level, forms a toner patch with a predetermined density in the width direction region opposed to the density detection sensor 80, and controls the density detection sensor 80 to obtain the toner patch density. The output value L (n) is read (step S809).

  Next, the CPU 201a corrects the background profile B (n) stored in the RAM 201b with the integrated evaluation value HAveS (sensor position) of the sensor position, for example, as in the following formula (1), and corrects the background profile B (n). 'Is obtained (step S810).

B (n) ′ = B (n) × α × HAveS (sensor position) (1)
α is a shaving weighting coefficient obtained by experiments or the like. The CPU 201a functions as a light amount correction unit that corrects the light amount B (n) as the background profile.

  Next, the CPU 201a calculates the corrected patch density L (n) ′ from the patch density L (n) read in step S809 and the corrected background profile B (n) ′ obtained in step S810 as shown in the following equation (2). Is obtained (step S811).

L (n) ′ = B (n) ′ − L (n) (2)
Next, the CPU 201a determines density patch density information based on the obtained correction patch density L (n) ′, and executes a density correction operation for appropriately correcting image forming conditions such as laser intensity and high-pressure control value, for example. (Step S812), and this process is terminated. In other words, the CPU 201a uses the background reflected light amount (B (n) ′) to correct the toner patch density detection value (L (n)) and corrects the toner patch density (L (n) ′) after correction. The image forming unit 10 is controlled so as to be obtained as a detection result of the sensor.

  On the other hand, if the result of determination in step S808 is that HAveS exceeds a predetermined threshold (“YES” in step S808), the CPU 201a forms a toner patch at the current sensor corresponding position and performs density correction processing. It is estimated that the amount of shaving of the transfer belt is excessive. Then, the CPU 201a obtains a position m ′ (≠ 4) where the integrated evaluation value HAveS (m) is minimum in a belt shift controllable range, that is, a position corresponding to the density detection sensor positions 0 to 8 in FIG. Step S813).

  Next, the CPU 201a drives the steering motor 223 to move the belt position so that the density detection sensor 80 faces the belt position m ', for example, m = 6 (step S814).

  FIG. 11 is a diagram illustrating a positional relationship between the belt and the density detection sensor before and after the change of the belt position. In FIG. 11, for example, as shown in FIG. 11A, when the density detection sensor 80 is directly facing the position of m = 4 before the position change, the integrated evaluation value HAveS (m = 4) at this position is the threshold value. It is assumed that it exceeded. In this case, the CPU 201a changes the position of the belt so that the area of m = 6 where the integrated evaluation value HAveS is the smallest among m = 0 to 8 which is the controllable range of the position of the belt faces the density detection sensor 80. To do.

  FIG. 12 is a perspective view showing the intermediate transfer unit 20 in the image forming apparatus 100 of FIG.

  In FIG. 12, both ends of the drive roller 26 that drives the intermediate transfer belt 2 are rotatably supported by the second frame 40. One end of the drive roller 26 can be raised and lowered in the direction of arrow H in FIG. 12 by a belt steering motor 223 (not shown). When one end of the driving roller 26 is raised or lowered, the driving roller 26 is tilted upward or downward with respect to the horizontal position, and accordingly, the intermediate transfer belt 2 approaches one end of the roller 26. Therefore, the region in the width direction facing the density detection sensor 80 is changed.

  After changing the position near the belt in this way, the CPU 201a executes the same density correction processing as in steps S809 to S812 described above (steps 809 to S812). If the cumulative number of images formed has not reached 100 as a result of the determination in step S807 (“NO” in step S807), the CPU 201a returns the process to step S803.

  According to the present embodiment, when the integrated evaluation value indicating the scraping amount of the surface of the intermediate transfer belt 2 exceeds a predetermined threshold value, the position where the density detection sensor 80 faces directly, that is, the position where the toner patch is formed is changed. To perform density correction processing. As a result, even when the surface of the intermediate transfer belt 2 in the region where the density detection sensor 80 is directly facing is greatly scraped and the fluctuation of the amount of reflected light on the background is excessive, an appropriate toner patch is formed to perform appropriate density correction. Can be realized. At this time, the toner patch is formed in an area where the integrated evaluation value after the area change is smaller than the integrated evaluation value before the area change, so that the influence of the reflected light amount is reduced even if the toner patch density is somewhat low. Correct correction is possible.

  Further, according to the present embodiment, the density correction process is executed as follows. In other words, the background profile B (n) of the toner patch formation region on the intermediate transfer belt 2 is corrected according to the surface scraping amount as a change with time of the intermediate transfer belt 2 to obtain a corrected background profile B (n) ′ (step S810). . Then, a correction patch density L (n) ′ is obtained using the obtained correction base profile B (n) ′ (step S811), and for example, the laser intensity is corrected so that the correction patch density is obtained as a detection result. Correct the image density. As a result, even when the surface of the intermediate transfer belt 2 is scraped over time due to rubbing against the recording paper P and the background profile as the background reflected light amount fluctuates, it is possible to realize appropriate density correction.

  In this embodiment, the integrated evaluation value HAveS (m) corresponding to the scraping amount of the surface of the intermediate transfer belt 2 is set to 0 at the density detection sensor position in FIG. 6 which is a belt shift control range at least with respect to the belt width direction. It is preferable to obtain it corresponding to ~ 8. Also, if the capacity of the temporary storage area RAM 201b permits, a scraping amount S register can be prepared corresponding to an area of m> 8 or more. The maximum value of m is the belt width / division interval. On the other hand, the maximum value of n is one circumference in the belt conveyance direction / division interval. Since the evaluation value corresponding to the scraping amount S depends on the material of the recording paper used, the evaluation value can be determined for each type of recording paper.

  In the present embodiment, the change in the width direction region of the intermediate transfer belt 2 facing the density detection sensor 80 is performed by moving the intermediate transfer belt 2 using the steering motor 223 which is a belt shift control means. However, it can also be realized by moving the density detection sensor 80 facing the intermediate transfer belt 2 without moving the intermediate transfer belt 2.

  FIG. 13 is a diagram for explaining the position moving means attached to the density detection sensor.

  In FIG. 13, a density detection sensor 80 is locked on a screw gear 1202 that is drivingly connected to a movable motor 1201. In such a configuration, the density detection sensor 80 can be moved in the width direction of the intermediate transfer belt 2 via the screw gear 1202 by rotating the movable motor 1201 forward and backward.

  Further, in the present embodiment, a case has been described in which one density detection sensor 80 is used and its position is changed. However, it is also possible to arrange a plurality of density detection sensors so as to face the intermediate transfer belt 2 and appropriately select and apply a sensor directly facing a region where the integrated evaluation value HAveS (m) is small.

  FIG. 14 is a diagram showing a modification of FIG. In FIG. 14, a plurality of density detection sensors 1301 a to 1301 h are provided facing the intermediate transfer belt 2. In such a configuration, it is possible to appropriately select and apply a sensor that directly faces a region where the integrated evaluation value HAveS (m) is smaller. In the case of FIGS. 13 and 14, the toner patch is located in the width direction region that can be read by the density detection sensor on the intermediate transfer belt 2 facing the selected density detection sensor position or the position where the density detection sensor is moved. It is necessary to control the image control unit 220 to be formed.

  In the present embodiment, the threshold value in step S808 can be defined as a difference from the initial state where there is no shaving. Further, as shown in FIG. 10 (d), it can be defined as a difference (ΔHYS) from the average value of the integrated evaluation value HAveS (m) as a whole.

  In the present embodiment, the change over time of the surface state of the intermediate transfer belt 2 is scraping of the surface due to the intermediate transfer belt 2 rubbing against the sheet P in accordance with the image forming process.

  In the present embodiment, the density detection sensor 80 also functions as a light amount detection sensor for measuring the background reflected light amount of the intermediate transfer belt 2, but a light amount measurement sensor for measuring the background reflected light amount of the intermediate transfer belt 2 is used. It can also be provided separately from the density detection sensor 80. In that case, it is appropriate that the newly provided sensor is arranged so as to measure the extreme end of the belt 2 where no image is formed, and the output of the new sensor is used as the base profile.

1a, 1b, 1c, 1d Photosensitive drum 2 Intermediate transfer belt 10 Image forming units 10a to 10d Image forming station 26 Belt driving roller 62 Belt edge sensor 80 Density detection sensor 90 Home position sensor 100 Image forming apparatus (printer)
200 Control unit 201a CPU
201b RAM
201c ROM
223 Belt steering motor 1201 Movable motors 1301a to 1301h Concentration detection sensor

Claims (14)

An image carrier;
Drive means for rotating the image carrier;
Image forming means for forming a toner image and a toner patch for density correction on the image carrier;
Density detecting means for detecting the density of the toner image and the toner patch;
Transfer means for transferring the toner image to a recording material;
For a plurality of width direction areas divided by a constant width in a direction parallel to a rotation axis including an area where the toner patch is formed on the image carrier, the amount of background reflected light of the image carrier is determined in a predetermined area unit in the circumferential direction. A light amount detecting means for detecting;
A light amount correcting means for correcting the detected background reflected light amount by using an evaluation value of a surface state of the image carrier that changes with time according to the rubbing between the image carrier and the recording material;
Correction means for correcting the density of the toner image based on the corrected background reflected light amount and the density detection value of the toner patch;
When the evaluation value exceeds a predetermined threshold, the toner patch forming area is changed along the width direction of the image carrier, and the toner patch is formed in the changed area to correct the density of the toner image. Control means for controlling the processing to be executed;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit changes an area where the toner patch is formed into an area where the evaluation value after the area change is smaller than the evaluation value before the area change. apparatus. An evaluation means for obtaining the evaluation value for each predetermined area;
An integration means for obtaining an integrated evaluation value obtained by averaging the average evaluation value obtained by averaging one round of the image carrier for each region in the width direction with respect to the obtained evaluation value; Prepared,
3. The image according to claim 1, wherein when the integrated evaluation value in the area where the toner patch is formed exceeds a predetermined threshold, the control unit changes the area where the toner patch is formed. Forming equipment.   When the evaluation value in the area where the toner patch is formed is equal to or less than a predetermined threshold, the control unit controls the correction process to be executed without changing the area where the toner patch is formed. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   5. The evaluation value according to claim 1, wherein the evaluation value is determined according to a toner area ratio in image data formed in the predetermined area of the image carrier, and increases as the toner area ratio increases. The image forming apparatus according to claim 1. A shift position control means for controlling a shift position along the width direction of the image carrier, further comprising:
2. The shift position control unit changes a region in the width direction of the image carrier facing the density detection unit by moving the image carrier along the width direction. 6. The image forming apparatus according to any one of items 1 to 5. A moving means for moving the density detecting means along the width direction of the image carrier;
6. The moving unit according to claim 1, wherein the moving unit changes the region in the width direction of the image carrier facing the density detecting unit by moving the density detecting unit. The image forming apparatus described.   The said moving means moves the said density | concentration detection means so that the said density | concentration detection means may oppose the area | region where the said evaluation value after area | region change becomes smaller than the said evaluation value before area | region change. 8. The image forming apparatus according to 7. The density detecting means is disposed at least at two locations along the width direction of the image carrier,
The control means controls one of the plurality of density detection means so as to change a widthwise region of the image carrier that the density detection means faces. The image forming apparatus according to claim 1.   The control unit performs control so that a density detection unit facing a region where the evaluation value after the region change is smaller than the evaluation value before the region change is selected from the plurality of density detection units. The image forming apparatus according to claim 9.   The region where the toner patch is formed is a region along the circumferential direction of the image carrier obtained by dividing the surface of the image carrier into a plurality along the width direction, and is formed by the image forming means on the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is located in an image forming area where an image is formed.   The predetermined region in the circumferential direction is a divided region obtained by dividing one region of the image carrier at predetermined intervals along the width direction of the image carrier along the conveyance direction of the image carrier. The image forming apparatus according to claim 11.   The image forming apparatus according to claim 1, wherein the density detection unit also has a function as the light amount detection unit.   The image forming apparatus according to claim 1, wherein the evaluation value is an evaluation value corresponding to a degree of surface abrasion of the image carrier.