JP6068270B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that performs an image forming process for transferring a toner image formed on an image carrier to a recording medium based on image data.

  In the image forming apparatus, the peripheral surface of the photoconductor is charged to a predetermined potential by a charger, and after forming an electrostatic latent image based on image data, toner is supplied to form a toner image on the photoconductor. However, there are some which transfer a toner image to a recording medium. In such an image forming apparatus, variation in charging potential in the toner image carried on the photosensitive member may occur depending on the environment such as humidity and leaving time. At locations where the charging potential is low, the toner tends to scatter and fall from the photoreceptor. For this reason, toner may adhere to the discharge electrode of the charger and the discharge electrode may be contaminated.

  In addition, in an intermediate transfer type image forming apparatus in which toner images formed on a plurality of photoconductors are primary transferred sequentially so as to be superimposed on an intermediate transfer member, and then secondarily transferred from the intermediate transfer member to a recording medium. In the toner image, the charged potential of the portion superimposed on the plurality of layers becomes higher than the charged potential of the portion of one layer, and therefore, the charged potential varies easily in the toner image carried on the intermediate transfer member. For this reason, in such an image forming apparatus, in order to improve the secondary transfer performance by making the potential of the toner in the toner image carried on the intermediate transfer member uniform, it is between the primary transfer position and the secondary transfer position. Although it is preferable to include a pre-transfer charger, toner may be scattered and dropped from the intermediate transfer member to the pre-transfer charger, and the discharge electrode of the pre-transfer charger may be contaminated.

  When the discharge electrode is contaminated, the image quality of the image formed on the recording medium is degraded.

  Therefore, an image forming apparatus that includes a pre-transfer charger and controls the cleaning timing by a cleaning unit based on image density information detected from image data is known (for example, see Patent Document 1).

JP 2008-256893 A

  However, the amount of toner adhering to the discharge electrode of the charging unit, such as a charger or a pre-transfer charger, is not determined only by the image density, but also a photosensitive member or a toner carrying the toner before dropping to the discharge electrode. It is also affected by the charging potential of the toner on the image carrier such as a transfer member. If the degree of contamination of the discharge electrode cannot be detected accurately, the cleaning frequency of the discharge electrode cannot be adjusted appropriately. If the frequency of cleaning the discharge electrode is too low, the image quality is degraded, and if the frequency of cleaning the discharge electrode is too high, there is a waste of performing a cleaning operation even though it is not necessary to clean the discharge electrode.

  An object of the present invention is to provide an image forming apparatus capable of optimizing the frequency of cleaning the discharge electrodes by detecting the degree of contamination of the discharge electrodes due to toner adhesion with high accuracy.

  The image forming apparatus of the present invention performs an image forming process for transferring a toner image formed on an image carrier to a recording medium based on image data. The image forming apparatus includes a charging unit, a cleaning unit, an image density detection unit, a toner amount detection unit, an adjustment unit, and a control unit. The charging unit has a discharge electrode. The cleaning unit cleans the discharge electrode. The image density detection unit acquires image density information based on the image data. The toner amount detection unit detects the amount of toner per unit area attached to the image carrier. The adjustment unit adjusts the image forming condition based on the toner amount detected by the toner amount detection unit. The control unit controls the cleaning frequency by the cleaning unit based on the image density information detected by the image density detection unit and the image forming conditions adjusted by the adjustment unit.

  In this configuration, the state of the toner on the image carrier is determined based on the amount of toner per unit area attached to the image carrier, and the image forming conditions are adjusted based on the determination result. Therefore, it is possible to determine the toner state on the image carrier based on the image forming conditions adjusted by the adjustment unit, and thereby to determine the toner adhesion amount to the discharge electrode of the charging unit. Further, the toner is more likely to fall from the image carrier to the discharge electrode of the charging unit when the image density is high than when the image density is low. Therefore, by determining based on both the image density information and the image forming conditions adjusted by the adjustment unit, it is possible to detect the contamination degree of the discharge electrode due to toner adhesion with high accuracy.

  In the above configuration, the control unit acquires the image density level value based on the image density information, and is configured to increase the cleaning frequency when the integrated value of the image density level value is equal to or greater than a preset threshold value. be able to.

  In this configuration, it is considered that when the image forming process is repeated, the image density level value increases and the degree of contamination of the discharge electrode increases. For this reason, when the integrated value of the image density level values is equal to or greater than the threshold value, the cleaning frequency is increased, so that deterioration in image quality and waste of the cleaning operation can be suppressed.

  Further, the image forming condition is a developing bias voltage value, and the control unit can be configured to increase the cleaning frequency when the developing bias voltage value adjusted by the adjusting unit is equal to or less than a preset threshold value. .

  In this configuration, when the charge amount of the toner for developing the toner image is reduced due to moisture or discharge due to leaving, the toner tends to fly during development, and the amount of adhesion to the image carrier increases and the image density increases. Therefore, it is necessary to suppress excessive flying of the toner. For this reason, when the adjustment by the adjustment unit is executed, the developing bias voltage value is adjusted so that the absolute value becomes smaller. In such a case, the amount of charge of the toner carried on the image carrier is relatively low, and scattering and dropping are likely to occur. For this reason, contamination of the discharge electrode of the charging unit with toner is likely to occur. Therefore, when the development bias voltage value after adjustment by the adjustment unit is equal to or less than the threshold value, it is possible to suppress deterioration in image quality by increasing the cleaning frequency.

  Further, the adjustment unit can be configured to adjust the image forming condition based on the toner amount of a predetermined reference toner image formed on the image carrier prior to the image forming process.

  In this configuration, the image forming condition can be adjusted more accurately by performing adjustment based on a predetermined reference toner image. Further, by performing the adjustment by the adjustment unit prior to the image forming process, a high-quality image can be formed from the first image forming process.

  An image forming apparatus that primarily transfers a toner image formed on a photoconductor on the basis of image data to an intermediate transfer member, and secondarily transfers the toner image from the intermediate transfer member to a recording medium. It can be configured to be a pre-transfer charger arranged between the next transfer position.

  In this configuration, when a toner image is superimposed on a plurality of layers on the intermediate transfer member, a variation in charging potential tends to occur in the toner image due to a difference in the thickness of the superimposed layers. It is made uniform by. However, since the charged potential of the toner conveyed to the position opposite to the pre-transfer charger varies, the toner is likely to fall on the pre-transfer charger. Therefore, by controlling the cleaning frequency based on the image density information and the image forming conditions adjusted by the adjustment unit as described above, the cleaning frequency is optimized, and deterioration in image quality and waste of the cleaning operation can be suppressed.

  According to this invention, the cleaning frequency of the discharge electrode can be optimized by detecting the degree of contamination of the discharge electrode due to toner adhesion with high accuracy.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 3 is a schematic diagram of a pre-transfer charger provided in the image forming apparatus. 1 is a block diagram showing a schematic electrical configuration of an image forming apparatus. It is a flowchart which shows the process sequence of a control part.

  As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment of the present invention includes an apparatus main body 110 and an automatic document feeder (ADF) 120. The image forming apparatus 100 forms a multicolor or single color image on a sheet based on image data generated from a document or image data input from the outside. The paper is an example of a recording medium. Examples of the recording medium include photographic paper and OHP film in addition to paper.

  The ADF 120 is disposed on the apparatus main body 110.

  The apparatus main body 110 includes an image reading unit 130, an image forming unit 140, and a paper feeding unit 150.

  The image reading unit 130 is arranged on the upper part of the apparatus main body 110, reads an image of a fixedly arranged document in the fixed document reading mode, generates image data, and is transported one by one by the ADF 120 in the transported document reading mode. The image of the original is read to generate image data.

  The image forming unit 140 includes an optical scanning device 3, four image forming stations 30A, 30B, 30C, and 30D, an intermediate transfer unit 40, a secondary transfer unit 50, and a fixing device 70, and an electrophotographic image on a sheet. A forming process is performed.

  The intermediate transfer unit 40 includes an intermediate transfer belt 41, a driving roller 42, a driven roller 43, a tension roller 44, an intermediate transfer belt cleaning device 45, a pre-transfer charger 46, and a counter roller 47. The intermediate transfer belt 41 is an intermediate transfer member, and is stretched by a drive roller 42, a driven roller 43, and a tension roller 44 to form a loop-shaped movement path.

  The image forming unit 140 supplies toner images (developer images) of black and four hues of cyan, magenta, and yellow, which are three subtractive primary colors obtained by color separation of a color image, to an image forming station. Form in 30A-30D. The image forming stations 30 </ b> A to 30 </ b> D are arranged in a line along the moving path of the intermediate transfer belt 41. The image forming stations 30B to 30D are configured substantially in the same manner as the image forming station 30A.

  The black image forming station 30A includes a photosensitive drum 1A, a charger 2A, a developing unit 4A, a primary transfer roller 5A, and a cleaning unit 6A.

  The photosensitive drum 1A is rotated in a predetermined direction by receiving a driving force. The charger 2A charges the peripheral surface of the photosensitive drum 1A to a predetermined potential.

  The optical scanning device 3 rotates the circumference of each of the photosensitive drums 1A, 1B, 1C, and 1D of the image forming stations 30A to 30D with each of laser beams modulated by image data of black, cyan, magenta, and yellow hues. Expose the surface. Electrostatic latent images based on image data of black, cyan, magenta, and yellow hues are formed on the peripheral surfaces of the photosensitive drums 1A to 1D, respectively.

  The developing unit 4A supplies black toner (developer) that is the hue of the image forming station 30A to the peripheral surface of the photosensitive drum 1A, and visualizes the electrostatic latent image into a toner image. Similarly, the developing units 4B, 4C, and 4D of the image forming stations 30B to 30D supply toners of the respective hues to the peripheral surfaces of the photosensitive drums 1B to 1D.

  The outer peripheral surface of the intermediate transfer belt 41 sequentially faces the peripheral surfaces of the photosensitive drums 1A to 1D. A primary transfer roller 5A is disposed at a position facing the photosensitive drum 1A with the intermediate transfer belt 41 interposed therebetween. Each of the positions where the intermediate transfer belt 41 and the photosensitive drums 1A to 1D face each other is a primary transfer position.

  To the primary transfer roller 5A, a primary transfer bias having a toner charging polarity (for example, minus) and a reverse polarity (for example, plus) is applied by constant voltage control. The same applies to the image forming stations 30B to 30D. As a result, the toner images of the respective hues formed on the peripheral surfaces of the photosensitive drums 1 </ b> A to 1 </ b> D are primarily transferred onto the outer peripheral surface of the intermediate transfer belt 41 while being sequentially superimposed. A toner image is formed.

  However, when image data of only a part of the hues of black, cyan, magenta, and yellow is input, only a part corresponding to the hue of the input image data among the four photosensitive drums 1A to 1D. Then, an electrostatic latent image and a toner image are formed, and only a partial toner image is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 41.

  The cleaning unit 6A collects toner remaining on the peripheral surface of the photosensitive drum 1A after development and primary transfer.

  The toner image primarily transferred to the outer peripheral surface of the intermediate transfer belt 41 at each primary transfer position is rotated by the intermediate transfer belt 41 and the secondary transfer roller 51 provided in the intermediate transfer belt 41 and the secondary transfer unit 50. Are conveyed toward the secondary transfer position which is the opposite position.

  The pre-transfer charger 46 and the counter roller 47 are positions along the lower movement path of the loop-shaped movement path of the intermediate transfer belt 41, and are four primary transfer positions in the movement direction of the intermediate transfer belt 41. Among these, it is disposed between the primary transfer position on the most downstream side and the secondary transfer position. In the first embodiment, the pre-transfer charger 46 corresponds to the charging unit of the present invention.

  The pre-transfer charger 46 is disposed on the outer peripheral surface side or lower side of the intermediate transfer belt 41, the counter roller 47 is disposed on the inner peripheral surface side or upper side, and the pre-transfer charger 46 and the counter roller 47 are connected to the intermediate transfer belt 41. It faces each other across the.

  The pre-transfer charger 46 applies a charge having the same polarity as the toner charging polarity (for example, minus) to the toner of the toner image carried on the intermediate transfer belt 41 prior to the secondary transfer. As a result, even when the toner carried on the intermediate transfer belt 41 has a variation in charging potential in the toner image, the variation in charging potential is made uniform, and the secondary transfer performance is improved.

  The paper feed unit 150 includes a paper feed cassette 151, a manual feed tray 152, and a paper transport path 61. Sheets are selectively supplied to the sheet conveyance path 61 one by one from either the sheet feeding cassette 151 or the manual feed tray 152.

  The sheet conveyance path 61 is formed so as to reach the sheet discharge tray 62 from each of the sheet feed cassette 151 and the manual feed tray 152 via the secondary transfer position and the fixing device 70.

  The secondary transfer roller 51 is in pressure contact with the drive roller 42 with a predetermined nip pressure across the intermediate transfer belt 41.

  When the sheet fed from the sheet feeding unit 150 passes through the secondary transfer position, the secondary transfer bias is applied to the secondary transfer roller 51 with the toner charging polarity (for example, minus) and the opposite polarity (for example, plus). Is applied by constant voltage control, whereby the toner image carried on the outer peripheral surface of the intermediate transfer belt 41 is secondarily transferred to the paper.

  The toner remaining on the intermediate transfer belt 41 after the toner image is transferred to the paper is collected by the intermediate transfer belt cleaning device 45.

  The sheet on which the toner image is transferred is guided to the fixing device 70. The fixing device 70 includes a heating roller 71 and a pressure roller 72, and heats and presses the paper passing between the heating roller 71 and the pressure roller 72 to fix the toner image on the paper. The sheet on which the toner image is fixed is discharged onto the discharge tray 62 with the surface on which the toner image is fixed facing down.

  As shown in FIG. 2, the pre-transfer charger 46 includes a housing 81, a corona wire 82, a cleaning member 83, a home position detection sensor 84, an encoder 85, a motor 86, a worm gear 87, and a drive side shaft joint 88. Yes. The cleaning member 83, the home position detection sensor 84, the encoder 85, the motor 86, the worm gear 87, and the drive side shaft coupling 88 constitute a cleaning unit that cleans the corona wire 82. The corona wire 52 is an example of a discharge electrode. Other examples of the discharge electrode include a long electrode such as a needle electrode or a creeping electrode.

  The casing 81 has a rectangular parallelepiped shape having an open surface 811 on the upper surface. The casing 81 is arranged so that the longitudinal direction thereof coincides with the width direction of the intermediate transfer belt 41 and the open surface 811 faces the outer peripheral surface of the intermediate transfer belt 41. The corona wire 82 is stretched in the longitudinal direction in the housing 81. The corona wire 82 is a discharge wire in which a tungsten wire is plated with gold. A direct current power source is connected to the corona wire 82, and a voltage of 3.5 to 8 kV is applied.

  The cleaning member 83 includes a conveying screw 831, a cleaning pad 832, and a passive side shaft joint 833. The transport screw 831 is rotatably supported by the housing 81.

  The transport screw 831 is a rod having a spiral groove and is disposed in parallel to the corona wire 82. The cleaning pad 832 is configured to be movable in the longitudinal direction of the transport screw 831 in a state where rotation about the transport screw 831 is restricted. The cleaning pad 832 has a protrusion that meshes with the groove of the transport screw 831, and moves in the longitudinal direction of the transport screw 831 as the transport screw 831 rotates. The cleaning pad 832 cleans the surface of the corona wire 82 when moving.

  The passive side shaft coupling 533 is attached to one end portion of the conveying screw 531. The drive side shaft joint 88 is connected to the passive side shaft joint 533. The motor 86 can rotate in both forward and reverse directions.

  The worm gear 87 includes a worm 871 and a worm wheel 872. The worm 871 decelerates the rotational force supplied from the motor 86 and transmits it to the worm wheel 872. The worm wheel 872 changes the direction of the rotation shaft by 90 degrees and transmits the rotational force to the drive side shaft coupling 88.

  In the vicinity of both ends of the corona wire 82, a home position P1 and a return position P2 are set. The home position detection sensor 84 is disposed at the home position P1, and detects that the cleaning pad 832 is located at the home position P1. The encoder 85 is a linear coder and measures the moving distance of the cleaning pad 832 from the home position P1.

  The cleaning pad 832 is located at the home position P1 during non-cleaning, and reciprocates a predetermined number of times between the home position P1 and the return position P2 during cleaning.

  As illustrated in FIG. 3, the image forming apparatus 100 further includes a control unit 10, an operation unit 11, an image density detection unit 12, a toner amount detection sensor 13, and an adjustment unit 14.

  The operation unit 11 includes a display unit and an input operation unit, and receives input operations such as various settings relating to image formation processing and an instruction to start image formation processing.

  The image density detection unit 12 acquires image density information based on the image data and outputs it to the control unit 10.

  The toner amount detection sensor 13 detects the toner amount per unit area of a predetermined patch image formed on the intermediate transfer belt 41 and outputs it to the control unit 10. In the first embodiment, a reflection type optical sensor is used as the toner amount detection sensor 13. As an example, a patch image is formed between print jobs. The patch image is a reference toner image. In the first embodiment, the intermediate transfer belt 41 is an image carrier.

  In order to always obtain a constant image quality, the adjusting unit 14 is provided with a charger for each of the image forming stations 30A to 30D so as to correspond to the environment in which the image forming apparatus 10 is installed, the material change with time, and the like. A so-called process control is performed to adjust various image forming conditions such as a charging potential by 2A, a charging potential by the pre-transfer charger 46, an exposure amount by the optical scanning device 3, and a developing bias voltage value in the developing units 4A to 4D.

  The adjustment unit 14 adjusts the development bias voltage values in the development units 4A to 4D based on the toner amount detected by the toner amount detection sensor 13 during the process control.

  When the charge amount of the toner in the developing units 4A to 4D is reduced due to discharge due to moisture, leaving, etc., the toner tends to fly during development, and the amount of adhesion to the photosensitive drums 1A to 1D increases and the image density. Therefore, the image density on the intermediate transfer belt 41 is also increased. For this reason, it is necessary to suppress excessive flying of the toner. Therefore, in this case, when the process control by the adjustment unit 14 is executed, the development bias voltage value is adjusted so that the absolute value becomes smaller. For example, when the reference value is −500V, the reference value is changed to −200V. In such a case, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively low, and the toner is likely to be scattered and dropped. For this reason, the pre-transfer charger 46 is easily contaminated.

  On the other hand, when the charge amount of the toner in the developing units 4A to 4D is high, the toner is difficult to fly during development, and the amount of adhesion to the photosensitive drums 1A to 1D is reduced and the image density is lowered. The image density at is also low. For this reason, it is necessary to promote the flying property of the toner. Therefore, in this case, when the process control by the adjustment unit 14 is executed, the development bias voltage value is adjusted so that the absolute value becomes large. For example, when the reference value is −500V, it is changed to −700V. In such a case, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively high, and scattering and dropping are unlikely to occur. For this reason, the pre-transfer charger 46 is less contaminated.

  The control unit 10 comprehensively controls each device of the image forming apparatus 100.

  As shown in FIG. 4, when image data is input (S1), the control unit 10 acquires image density information based on the image data (S2). The control unit 10 acquires an image density level value based on the image density information. As an example, the image density level value is calculated by weighting each density of a character portion, a fine line portion, and a solid image portion.

  The control unit 10 stores an image density level value for each image forming process, and the integrated value A1 of the image density level value is equal to or greater than a preset reference value (threshold value) A0 of the image density level value. It is determined whether or not (S3).

  When the control unit 10 determines that the integrated value A1 is equal to or greater than the reference value A0, the adjusted development bias voltage value V1 obtained by executing the process control is set to a reference value (threshold value) set in advance for the development bias voltage value. ) It is further determined whether it is V0 or less (S4). The development bias voltage value V1 and the reference value V0 are absolute values.

  When the control unit 10 determines that the integrated value A1 of the image density level values is equal to or greater than the reference value A0 and the development bias voltage value V1 is equal to or less than the reference value V0, the control unit 10 sets the cleaning frequency of the pre-transfer charger 46 to a predetermined high value. The level is set (S5).

  When the pre-transfer charger 46 is cleaned, the control rod 10 returns the integrated value A1 of the image density level value to the initial value 0.

  As an example, the cleaning frequency is represented by the number of image forming processes performed between the previous cleaning execution time and the next cleaning execution time. In the first embodiment, when the frequency of cleaning is changed from low to medium, or from medium to high, in the increasing direction, and when the number of image forming processes after the change is exceeded at the time of change, Cleaning is performed immediately.

  When the image density is high, toner scattering and dropping from the intermediate transfer belt 41 to the pre-transfer charger 46 are likely to occur. Further, when the development bias voltage value V1 after adjustment due to execution of the process control is small, as described above, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively low, and the toner is scattered and dropped. This is likely to occur, and the corona wire 82 of the pre-transfer charger 46 is likely to be contaminated. Therefore, a reduction in image quality can be suppressed by increasing the cleaning frequency.

  When the control unit 10 determines that the integrated value A1 of the image density level values is equal to or greater than the reference value A0 and the development bias voltage value V1 exceeds the reference value V0, the control unit 10 sets the cleaning frequency of the pre-transfer charger 46 to a predetermined value. Is set to the middle level (S6).

  When the image density is high, toner scattering and dropping from the intermediate transfer belt 41 to the pre-transfer charger 46 are likely to occur. On the other hand, when the development bias voltage value V1 after adjustment due to execution of process control is high, as described above, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively high, and the toner is scattered and dropped. Hard to occur. Therefore, the cleaning frequency is optimized by setting the cleaning frequency to a medium level.

  When determining in S3 that the integrated value A1 of the image density level values is less than the reference value A0, the control unit 10 further determines whether or not the developing bias voltage value V1 is equal to or less than the reference value V0 (S7).

  When determining that the integrated value A1 of the image density level values is less than the reference value A0 and the development bias voltage value V1 is less than or equal to the reference value V0, the control unit 10 sets the cleaning frequency of the pre-transfer charger 46 to a predetermined value. The level is set (S6).

  When the image density is low, toner scattering and dropping from the intermediate transfer belt 41 to the pre-transfer charger 46 are unlikely to occur. On the other hand, when the development bias voltage value V1 after adjustment due to the execution of the process control is small, as described above, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively low, and the toner is scattered and dropped. Likely to happen. Therefore, the cleaning frequency is optimized by setting the cleaning frequency to a medium level.

  When the control unit 10 determines that the integrated value A1 of the image density level values is less than the reference value A0 and the development bias voltage value V1 exceeds the reference value V0, the control unit 10 sets the cleaning frequency of the pre-transfer charger 46 to a predetermined value. Is set to a low level (S8).

  When the image density is low, toner scattering and dropping from the intermediate transfer belt 41 to the pre-transfer charger 46 are unlikely to occur. Further, when the development bias voltage value V1 after adjustment due to execution of the process control is high, the charge amount of the toner carried on the intermediate transfer belt 41 is relatively high as described above, and the toner is scattered and dropped. It is hard to generate and the corona wire 82 of the pre-transfer charger 46 is less contaminated. Therefore, by setting the cleaning frequency to a low level, it is possible to suppress waste of performing the cleaning operation even though it is not necessary to clean the corona wire 82.

  As described above, according to the image forming apparatus 10, by determining based on both the image density information and the development bias voltage value V <b> 1 after adjustment by the adjustment unit 14, the degree of contamination of the corona wire 82 due to toner adhesion is increased. It can be detected with accuracy. Therefore, the cleaning frequency of the corona wire 82 can be optimized, and deterioration in image quality and waste of the cleaning operation can be suppressed.

  In particular, in the intermediate transfer type image forming apparatus 10, when a toner image is superimposed on a plurality of layers on the intermediate transfer member 41, the charged potential varies in the toner image due to the difference in the thickness of the superimposed layers. This variation is easily made uniform by the pre-transfer charger 46. However, since the charged potential of the toner conveyed to the position opposite to the pre-transfer charger 46 varies, the toner tends to fall on the pre-transfer charger 46. Therefore, as described above, the cleaning frequency is controlled by controlling the cleaning frequency based on the image density information and the development bias voltage value V1 adjusted by the adjusting unit, thereby suppressing the deterioration of the image quality and the waste of the cleaning operation. Can do.

  In addition, the development bias voltage value can be adjusted more accurately by adjusting the development bias voltage value based on a predetermined patch image. Further, by performing the adjustment by the adjustment unit 14 prior to the image forming process, a high-quality image can be formed from the first image forming process.

  It is also possible to set at least one of the reference value A0 and the reference value V0 and set the cleaning frequency to four or more levels.

  In the first embodiment described above, the configuration for adjusting the cleaning frequency of the pre-transfer charger 46 based on the patch image formed on the intermediate transfer belt 41 has been described. The cleaning unit is configured to clean the chargers 2A of the stations 30A to 30D, and the cleaning frequency of the chargers 2A of the image forming stations 30A to 30D is controlled based on the patch images formed on the photosensitive drums 1A to 1D. It can also be configured to. In this case, the photosensitive drums 1A to 1D correspond to the image carrier of the present invention.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1A to 1D Photosensitive drum 2A Charger 10 Control unit 12 Image density detection unit 13 Toner amount detection sensor (toner amount detection unit)
14 Adjustment unit 41 Intermediate transfer belt (image carrier)
46 Pre-transfer charger (charger)
83 Cleaning member 84 Home position detection sensor 85 Encoder 86 Motor 87 Worm gear 88 Drive side shaft coupling

Claims (4)

An image forming apparatus that primarily transfers a toner image formed on a photoconductor based on image data to an intermediate transfer body and secondary transfer from the intermediate transfer body to a recording medium,
A charging unit having a discharge electrode;
A cleaning unit for cleaning the discharge electrode;
An image density detector for acquiring image density information based on the image data;
A toner amount detection unit for detecting a toner amount per unit area attached to the image carrier;
An adjustment unit that adjusts image forming conditions based on the toner amount detected by the toner amount detection unit;
A control unit that controls the frequency of cleaning by the cleaning unit based on the image density information detected by the image density detection unit and the image forming conditions adjusted by the adjustment unit;
The image forming apparatus , wherein the charging unit is a pre-transfer charger disposed between a primary transfer position and a secondary transfer position .   The said control part acquires an image density level value based on image density information, and when the integrated value of an image density level value becomes more than the preset threshold value, the said cleaning frequency is raised. Image forming apparatus. The image forming condition is a developing bias voltage value,
The image forming apparatus according to claim 1, wherein the control unit increases the cleaning frequency when a developing bias voltage value after adjustment by the adjustment unit is equal to or less than a preset threshold value.   4. The image forming apparatus according to claim 1, wherein the adjustment unit adjusts an image forming condition based on a toner amount of a predetermined reference toner image formed on the image carrier prior to an image forming process. 5. .

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