Image forming apparatus

Abstract

To provide an image forming apparatus that detects ozone blurring locally occurring along a main scanning direction and removes a discharge product causing the blurring.SOLUTION: An image forming apparatus forms a test image of a dot half pattern on a recording sheet (S601), reads the test image from the recording sheet (S602), and checks shading abnormality for every main scan line (S604). When detecting shading abnormality (S605: YES), the image forming apparatus refers to a main scan line one cycle before at a circumferential pitch of a photoreceptor drum corresponding to the main scan line (S607), if shading abnormality is at the same position in the main scanning direction (S608: YES), determines that the shading abnormality is linear blurring caused by a discharge product attached to the surface of a photoreceptor (S609), and cleans the peripheral surface of the photoreceptor.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus, and more particularly to a technique for efficiently eliminating local image noise generated by the adhesion of discharge products to the surface of a photoreceptor.

Background Art

[0002] An electrophotographic image forming apparatus forms an electrostatic latent image by exposing a uniformly charged photoreceptor surface, develops the electrostatic latent image into a toner image, and executes an electrophotographic process of transferring the toner image onto a transfer material such as a recording sheet. Among these processes, in the charging process of charging the photoreceptor surface, discharge products such as ozone and nitrogen oxides are generated by the ionization of air.

[0003] The discharge products generated by the charging device diffuse and adhere to various parts inside the image forming apparatus. In particular, since the photoreceptor is located relatively close to the charging device and faces the charging device, the discharge products are likely to adhere. When the discharge products adhering to the photoreceptor surface absorb moisture, their electrical resistance decreases and their conductivity increases. Through such discharge products, the charged charges at the unexposed portions of the photoreceptor surface flow to the exposed portions of the photoreceptor surface, and when the unexposed portions are discharged, image noise occurs (ozone fogging).

[0004] If the discharge products adhering to the photoreceptor surface are removed, ozone fogging is eliminated. In an electrophotographic image forming apparatus, after the transfer process of the toner image, the residual transfer toner remaining on the photoreceptor surface is scraped off and removed by a cleaning member such as a cleaning blade. Therefore, during the execution of the image forming process, the discharge products are scraped off from the photoreceptor surface together with the residual transfer toner and discarded.

[0005] On the other hand, when time elapses without executing the image forming process, such as at night, the discharge products tend to accumulate on the photoreceptor surface. In particular, in the region of the photoreceptor surface facing the charging device, the adhesion of the discharge products becomes remarkable, and thus the ozone fogging also becomes significant.

[0006] When the deterioration of image quality due to ozone fog occurs under the user, the imaging unit has to be replaced because the image quality has to be quickly restored. Then, the life of the imaging unit is significantly shortened in the sense that the photosensitive member that should have been usable without the attachment of discharge products becomes unusable. In addition, in order to perform the replacement work of the imaging unit, the period (downtime) during which the user cannot use the image forming apparatus becomes long, and the convenience of the user is reduced.

[0007] For such ozone fog, for example, a technique has been proposed in which a recovery mode is provided to remove discharge products from the surface of the photosensitive member by using a cleaning member or the like. In addition, a cleaning member having a high frictional force with the surface of the photosensitive member has been proposed in order to surely remove the discharge products. In this way, even when the image forming process is not being executed, the discharge products can be removed, so that ozone fog can be suppressed.

[0008] However, it is troublesome for the user to activate the recovery mode for a user who has visually recognized ozone fog in the printed matter. In addition, if the recovery mode is applied regularly every morning or the like regardless of the presence or absence of ozone fog, the life of the photosensitive member is unnecessarily shortened, such as the photosensitive member being worn due to rubbing with the cleaning member. In particular, when a cleaning member having a high frictional force with the surface of the photosensitive member is used, the wear of the photosensitive member is accelerated, so that the life of the imaging unit is significantly shortened.

[0009] For this reason, a technique for removing discharge products that can suppress the wear of the photosensitive member without causing trouble to the user has been demanded. That is, a form in which the occurrence of ozone fog is accurately detected and the recovery mode is applied only when ozone fog occurs is desirable.

[0010] For example, since discharge products become conductive by humidification, there is a known technique of detecting the temperature and humidity around the photoreceptor and applying a recovery mode when the temperature and humidity at which ozone fogging is likely to occur are reached. However, in this conventional technique, even if there is no discharge product attached to the surface of the photoreceptor, the recovery mode is applied simply because the temperature and humidity around the photoreceptor reach a predetermined level, so wear of the photoreceptor cannot necessarily be sufficiently suppressed.

[0011] Also, there is a known technique of detecting the drive torque for rotating the photoreceptor drum and the surface potential of the photoreceptor, and when these vary beyond a predetermined fluctuation range, determining that a discharge product is attached and applying a recovery mode.

[0012] However, it is difficult to accurately detect the adhesion state of the discharge product from the drive torque and surface potential of the photoreceptor drum. For this reason, if it is erroneously detected that a discharge product is attached when it is not, and the recovery mode is applied, wear of the photoreceptor cannot be sufficiently suppressed. Conversely, if it is erroneously detected that a discharge product is not attached when it is, the recovery mode is not applied, so ozone fogging cannot be sufficiently suppressed.

[0013] Furthermore, there has been proposed a conventional technique of forming a detection pattern for detecting ozone fogging, detecting the density of the formed detection pattern on the photoreceptor or the intermediate transfer body, and applying a recovery mode when the detected density fluctuates beyond a threshold value (see, for example, Patent Documents 1 to 3). According to these conventional techniques, it is expected that false detection of ozone fogging can be reduced because the presence or absence of ozone fogging is directly detected from the density variation of the detection pattern.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

[0015] As described above, it is known that discharge products are likely to accumulate particularly in a region of the photoreceptor surface facing the charging device during a period in which the photoreceptor drum stops rotating for a long time. The region facing the charging device is only a part in the circumferential direction (sub-scanning direction) while covering the entire width in the rotational axis direction (main scanning direction) of the photoreceptor drum on the photoreceptor surface.

[0016] Focusing on this point, in the above prior art, there is one that detects the adhesion position of discharge products in the sub-scanning direction by forming a detection pattern of discharge products only in a part in the main scanning direction (Patent Documents 1 and 2).

[0017] There is also one that forms a detection pattern on the image carrier at predetermined intervals in the sub-scanning direction and detects the presence or absence of image noise due to discharge products from its density waveform (Patent Document 3).

[0018] However, in recent years, the application range of electrophotographic image forming apparatuses has been continuously expanding, and even high-definition printed materials for commercial use are trying to fall within that category. In image forming apparatuses for commercial use, even higher reliability and durability are required.

[0019] In order to form a high-definition image, it is required to eliminate ozone fog by detecting and removing even discharge products locally attached in the main scanning direction without omission.

[0020] Also, in order to achieve high reliability and durability, it is necessary to suppress wear of the photoreceptor so that the recovery mode is not unnecessarily applied due to false detection of discharge products.

[0021] In response to such a request, when discharge products are locally attached only to a part between one end and the other end in the main scanning direction on the outer peripheral surface of the photoreceptor drum, in the above prior art, there is a risk that the detection pattern of the discharge products formed only on a part in the main scanning direction may deviate from the attachment position of the discharge products in the main scanning direction and cannot be detected.

[0022] Further, even if a detection pattern is formed over the entire width in the main scanning direction, if the discharge products are attached only to a part in the main scanning direction, the total value of the time when a difference is detected between the density measurement signal and the reference value becomes short, and there is also a risk that the discharge products cannot be detected.

[0023] If the discharge generation unit cannot detect, the recovery mode cannot be applied to remove the discharge products from the surface of the photoreceptor, so that high-definition image quality cannot be achieved.

[0024] Therefore, if the recovery mode is applied regardless of the presence or absence of the discharge products, the wear of the photoreceptor is promoted, and the requirements regarding high reliability and durability cannot be met.

[0025] The present disclosure has been made in view of the above problems, and an object thereof is to provide an image forming apparatus that detects ozone fog locally generated in the main scanning direction and removes the discharge products that cause the ozone fog.

Means for Solving the Problems

[0026] To achieve the above object, an image forming apparatus according to an aspect of the present disclosure includes a toner image forming unit that forms a toner image on the outer peripheral surface of a photoreceptor rotator and transfers the formed toner image to a transfer body, a detection unit that detects density abnormalities in the toner image on the photoreceptor rotator or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photoreceptor rotator, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects density abnormalities at the same position in the main scanning direction for each circumference of the photoreceptor rotator in the sub-scanning direction. Well, the density abnormality is a local density abnormality in the main scanning direction It is characterized by this.

[0028] Further, the toner image forming unit may form a toner image in a dot half pattern, and the detection unit may detect density abnormality of the toner image in the dot half pattern.

[0030] An image forming apparatus according to another aspect of the present disclosure forms a toner image on an outer peripheral surface of a photosensitive rotating body, and transfers the formed toner image to a transfer body. The apparatus includes a toner image forming unit, a detection unit that detects a density abnormality in the toner image on the photosensitive rotating body or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects a density abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction. The detection unit detects a density abnormality in the toner image carried on the recording sheet, and the The toner image carried on the recording sheet is the toner image fixed on the recording sheet. is characterized by 。

[0031] Further, the cleaning unit may clean the entire circumference of the photosensitive rotating body.

[0032] An image forming apparatus according to still another aspect of the present disclosure forms a toner image having a predetermined line width on an outer peripheral surface of a photosensitive rotating body, and transfers the formed toner image to a transfer body. The apparatus includes a toner image forming unit, a detection unit that detects a line width abnormality in the toner image on the photosensitive rotating body or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction. The detection unit detects a line width abnormality in the toner image carried on the recording sheet, and the To stabilize the quality of the toner image, an image stabilization processing unit for forming a toner image is provided in the toner image forming unit. and The detection unit detects density abnormality at the timing when the image stabilization processing unit executes the process of stabilizing the quality. is characterized by 。

[0033] Further, the detection unit may detect density abnormality in the toner image formed by the toner image forming unit by the image stabilization processing unit.

[0034] Further, the detection unit may detect density abnormality in the toner image formed after a predetermined time or more has elapsed since the toner image forming unit formed the previous toner image.

[0035] Further, a durability state specifying unit for specifying the durability state of the photosensitive rotating body and a prohibiting unit for prohibiting the detection unit from detecting density abnormality when the durability state is equal to or lower than a threshold value may be provided.

[0036] Further, the cleaning unit may supply toner onto the outer peripheral surface of the photosensitive rotating body and perform the cleaning by scraping off the toner.

[0037] Further, after cleaning by the cleaning unit, the toner image forming unit further forms the toner image, the detection unit detects density abnormality in the further formed toner image, and when the detection unit detects density abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction in the further formed toner image, it may be provided with a notification unit that notifies to that effect.

[0038] Also, the Furthermore image forming apparatus according to another aspect forms a toner image having a predetermined line width on the outer peripheral surface of a photosensitive rotating body, and transfers the formed toner image to a transfer body, and includes a toner image forming unit, a detection unit that detects line width abnormality in the toner image on the photosensitive rotating body or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction. Well, the line width abnormality is a local line width abnormality in the main scanning direction It is characterized by that.

[0040] Also, the toner image having the predetermined line width may be a line pattern provided at regular intervals in the sub-scanning direction.

[0042] An image forming apparatus according to still another aspect of the present disclosure forms a toner image having a predetermined line width on an outer peripheral surface of a photosensitive rotating body, and transfers the formed toner image to a transfer body. The apparatus includes a toner image forming unit, a detection unit that detects a line width abnormality in the toner image on the photosensitive rotating body or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction. The detection unit detects a line width abnormality in the toner image carried on the recording sheet, and the The toner image carried on the recording sheet is the toner image fixed on the recording sheet. is characterized by .

[0043] Also, the cleaning unit may clean the entire circumference of the photosensitive rotating body.

[0044] An image forming apparatus according to still another aspect of the present disclosure includes a toner image forming unit that forms a toner image having a predetermined line width on an outer peripheral surface of a photosensitive rotating body and transfers the formed toner image to a transfer body, a detection unit that detects an abnormality in the line width of the toner image on the photosensitive rotating body or the transfer body, a cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body, and a control unit that causes the cleaning unit to perform cleaning when the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction, and To stabilize the quality of the toner image, an image stabilization processing unit that forms a toner image in the toner image forming unit and is provided, and the detection unit detects line width abnormality at the timing when the image stabilization processing unit executes the process of stabilizing the quality. is characterized by .

[0045] Also, the detection unit may detect line width abnormality in the toner image formed by the toner image forming unit by the image stabilization processing unit.

[0046] Further, the detection unit may detect an abnormal line width in the toner image formed after a predetermined time or more has elapsed since the toner image forming unit formed the previous toner image.

[0047] Further, it may include a durability state specifying unit that specifies the durability state of the photosensitive rotating body, and a prohibiting unit that prohibits the detection unit from detecting an abnormal line width when the durability state is equal to or less than a threshold value.

[0048] Further, the cleaning unit may perform the cleaning by supplying toner onto the outer peripheral surface of the photosensitive rotating body and scraping off the toner.

[0049] Further, after the cleaning by the cleaning unit, the toner image forming unit further forms the toner image on the toner image forming unit, the detection unit detects an abnormal line width in the further formed toner image, and when the detection unit detects an abnormal line width at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction in the further formed toner image, it may include a notification unit that notifies to that effect.

Advantages of the Invention

[0050] In this way, paying attention to the feature that the adhesion location of the discharge product appears at the same position in the main scanning direction for each rotation cycle of the photosensitive rotating body on the toner image, detecting ozone fogging (linear fogging) that locally occurs in the main scanning direction, and removing the discharge product that caused it, it is possible to achieve high-definition image quality and suppress wear of the photosensitive rotating body associated with the removal.

Brief Description of the Drawings

[0051]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0052] Hereinafter, embodiments of the image forming apparatus according to the present disclosure will be described with reference to the drawings. [1] Configuration of the Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.

[0053] The image forming apparatus 1 according to the present embodiment is a so-called tandem type color multifunction peripheral (MFP), and as shown in FIG. 1, includes an image forming unit 100, a paper feeding unit 110, an image reading unit 120, and an operation panel 130. The image reading unit 120 reads an image from a document and generates image data.

[0054] The image forming unit 100 forms an image using the image data generated by the image reading unit 120 or the image data received via a communication network such as a LAN (Local Area Network) or the Internet. In this case, an image is formed on the recording sheet supplied by the paper feeding unit 110, and then the recording sheet on which the image is formed is discharged onto the paper discharge tray 102.

[0055] The image forming unit 100 includes a control unit 101. The control unit 101 monitors and controls the operations and states of the image forming unit 100, the paper feeding unit 110, the image reading unit 120, and the operation panel 130. [2] Configuration of the Image Forming Unit 100 Next, the configuration of the image forming unit 100 will be described.

[0056] As shown in FIG. 2, the image forming unit 100 includes image forming units 200Y, 200M, 200C, and 200K that form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Hereinafter, when describing the common features of the image forming units 200Y, 200M, 200C, and 200K, the characters YMCK representing the toner colors will be omitted from the reference numerals.

[0057] The image forming unit 200 has a configuration in which a charging device 202, an exposure device 203, a developing device 204, a primary transfer roller 205, and a cleaning device 206 are sequentially arranged along the outer peripheral surface of a photosensitive drum 201 as a photosensitive rotating body. (2-1) Photosensitive Drum 201 The photosensitive drum 201 has a photosensitive layer formed along the outer peripheral surface in a cylindrical shape, and the outer peripheral surface of the photosensitive layer is covered with a protective layer. The photosensitive drum 201 is rotationally driven in the direction of arrow A by a photosensitive drum drive motor 411 (shown in FIG. 4).

[0058] The photosensitive layer of the photosensitive drum 201 is made of a resin containing an organic photoconductor, for example, an organic photosensitive layer formed on the outer peripheral surface of a drum-shaped metal substrate. As the resin constituting the photosensitive layer, for example, polycarbonate resin, silicone resin, polystyrene resin, acrylic resin, methacrylic resin, epoxy resin, polyurethane resin, vinyl chloride resin, melamine resin, etc. can be used. (2-2) Charging device 202 The charging device 202 uniformly charges the outer peripheral surface of the photosensitive drum 201. At this time, the charging device 202 generates discharge products such as ozone and nitrogen oxides (NOx: Nitrogen Oxides). The generated discharge products diffuse and adhere to the inside of the image forming apparatus 1, particularly, the outer peripheral surface of the photosensitive drum 201. Further, when the rotation of the photosensitive drum 201 is stopped for a long time after forming an image, discharge products tend to accumulate in the region of the outer peripheral surface of the photosensitive drum that faces the charging device 202.

[0059] In the present embodiment, the case where a scorotron charging device is used as the charging device 202 will be described as an example, but it goes without saying that the present disclosure is not limited to this, and a corotron charging device may be used, or a charging roller may be used. The charging device 202 causes discharge to occur in the electrode portion by applying a DC bias or an AC bias in which an AC voltage is superimposed on a DC voltage, and uniformly charges the outer peripheral surface of the photosensitive drum 201 to a predetermined charging potential. When a charging roller is used as the charging device 202, discharge occurs on the roller surface to charge the outer peripheral surface of the photosensitive drum 201. (2-3) Exposure device 203 The exposure device 203 irradiates the outer peripheral surface of the photosensitive drum 201 with laser light modulated according to the image signal received from the control unit 101. In the exposed area of the outer peripheral surface of the photosensitive drum 201 where the laser light is irradiated, the photosensitive body becomes conductive and the charged charges on the outer peripheral surface are lost. In the non-exposed area where the laser light is not irradiated, the charged charges on the outer peripheral surface are maintained. In this way, an electrostatic latent image is formed. (2-4) Developing device 204 The developing device 204 develops an electrostatic latent image by supplying toner onto the outer peripheral surface of the photoreceptor drum 201 to form a toner image. In this specification, the case of using the reversal development method in which toner charged to the same polarity as the charging potential in the non-exposed area of the photoreceptor drum 201 is supplied to attach toner to the exposed area will be described as an example. However, it goes without saying that a positive development method in which toner charged to the opposite polarity to the charging potential in the non-exposed area is supplied to attach toner to the non-exposed area may also be used.

[0060] As shown in FIG. 3, for example, the developing device 204 includes a developing sleeve 311 disposed to face the photoreceptor drum 201 via a developing area. A developing bias, which is, for example, a DC developing bias having the same polarity as the charging polarity by the charging device 202 or a developing bias in which a DC voltage having the same polarity as the charging polarity by the charging device 202 is superimposed on an AC voltage, is applied to the developing sleeve 311. By this developing bias, reversal development in which toner is adsorbed to the exposed area on the outer peripheral surface of the photoreceptor drum 201 is performed.

[0061] The developing device 204 develops an electrostatic latent image using a two-component developer containing toner and a carrier.

[0062] The toner is not particularly limited, and known toners generally used can be used. Known toners generally used are, for example, those obtained by incorporating a colorant, and if necessary, a charge control agent, a release agent, etc. into a binder resin and treating with an external additive.

[0063] As the external additive, fine particle metal oxides such as silica and titania are used, and those having a particle size ranging from a small particle size of about 30 nm to a relatively large particle size of about 100 nm can be used. The toner particle size is not limited to this, but is preferably about 3 to 15 μm.

[0064] The carrier is a component for charging the toner. The carrier is not particularly limited, and known carriers generally used can be used. Known carriers generally used are, for example, binder type carriers, coat type carriers, etc. The carrier particle size is preferably 15 to 100 μm, although not limited thereto. (2-5) Primary transfer roller 205 The primary transfer roller 205 is pressed against the photosensitive drum 201 with the intermediate transfer belt 211 interposed therebetween. The primary transfer roller 205 applies a primary transfer bias voltage between itself and the photosensitive drum 201, thereby electrostatically transferring the toner image carried on the outer peripheral surface of the photosensitive drum 201 onto the outer peripheral surface of the intermediate transfer belt 211 (primary transfer). The primary transfer bias voltage is usually of the opposite polarity to the toner. (2-6) Cleaning device 206 The cleaning device 206 discharges the charges remaining on the outer peripheral surface of the photosensitive drum 201 after primary transfer, and scrapes off and discards the toner remaining on the outer peripheral surface. As shown in FIG. 3, the cleaning device 206 includes a cleaning blade 301, a lubricant application mechanism 302, and an eraser 303. The cleaning blade 301 scrapes off and discards the toner remaining on the outer peripheral surface of the photosensitive drum 201 (blade cleaning method). (2-6-1) Cleaning blade 301 The cleaning blade 301 is a flat elastic member. As physical properties of the cleaning blade, the resilience modulus and hardness are important. The resilience is preferably 10 to 80%, more preferably 30 to 70% at a temperature of 25°C. Also, the JIS A hardness is preferably 20 to 90°, particularly preferably 60 to 80°.

[0065] When the JIS A hardness is less than 20°, the cleaning blade is too soft and blade curling is likely to occur. On the other hand, when the JIS A hardness is greater than 90°, it becomes difficult to follow even slight irregularities or foreign matters on the photosensitive member, and poor cleaning of toner particles is likely to occur. (2-6-2) Lubricant application mechanism 302 The lubricant application mechanism 302 includes a lubricant 304, a brush 305, and a leveling blade 306. The lubricant 304 is applied to suppress wear on the outer peripheral surface of the photoreceptor drum 201 by reducing friction between the outer peripheral surface of the photoreceptor drum 201 and the cleaning blade 301.

[0066] While rotating in the same direction as the photoreceptor drum 201, the brush 305 scrapes off the lubricant 304 and applies the lubricant 304 to the outer peripheral surface of the photoreceptor drum 201. Needless to say, the application member that applies the lubricant 304 to the outer peripheral surface of the photoreceptor drum 201 is not limited to the brush 305, and for example, an application member other than the brush 305 such as a sponge may be used.

[0067] The lubricant 304 is a solid lubricant formed in a bar shape and is pressed against the brush 305 using a spring (not shown). In this embodiment, the case where zinc stearate is used as the lubricant 304 will be described as an example. Needless to say, the lubricant 304 is not limited to zinc stearate, and fatty acid metal salts, silicone oil, fluororesin, etc. can be used.

[0068] These lubricants may be used alone or in combination of two or more. Among the above lubricants, fatty acid metal salts are particularly preferred. As the fatty acid, a linear hydrocarbon is preferred. For example, myristic acid, palmitic acid, stearic acid, oleic acid, etc. are preferred, and stearic acid is even more preferred.

[0069] As the metal, lithium, magnesium, calcium, strontium, zinc, cadmium, aluminum, cerium, titanium, iron, etc. can be used. Among these, zinc stearate, magnesium stearate, aluminum stearate, iron stearate, etc. are preferred, and particularly, zinc stearate is most preferred.

[0070] In FIG. 3, an example is illustrated where the lubricant application mechanism 302 is disposed on the downstream side of the cleaning blade 301 in the rotation direction of the photoreceptor drum 201. However, it goes without saying that the present disclosure is not limited thereto, and the lubricant application mechanism 302 may be disposed on the upstream side of the cleaning blade 301. Further, the effects of the present disclosure can be obtained even if the lubricant application mechanism 302 is omitted from the image forming unit 200.

[0071] The leveling blade 306 levels the lubricant so that the thickness of the lubricant applied on the outer peripheral surface of the photoreceptor drum 201 becomes uniform. As the leveling blade, it is preferable to use an elastic member in the same manner as the cleaning blade 301. (2-6-3) Eraser 303 The eraser 303 exposes the outer peripheral surface of the photoreceptor drum 201 to make the entire surface conductive and discharges the charges remaining on the outer peripheral surface. As the eraser 303, a light source such as an LED (Light Emitting Diode) can be used. After the photoreceptor drum 201 is discharged by the eraser 303, it can be charged again by the charging device 202 and form the next electrostatic latent image.

[0072] The image forming units 200Y, 200M, 200C, and 200K perform primary transfer of toner images in synchronization so that the toner images of YMCK colors overlap on the outer peripheral surface of the intermediate transfer belt 211. Thereby, a color toner image is formed.

[0073] The intermediate transfer belt 211 is an endless belt, is wound around the secondary transfer roller pair 212 and the rollers 213, 214, and runs in a circulating manner in the direction of arrow B. As a result, the toner image carried on the outer peripheral surface of the intermediate transfer belt 211 is conveyed to the secondary transfer nip of the secondary transfer roller pair 212.

[0074] The secondary transfer roller pair 212 consists of a pair of rollers to which a secondary transfer bias voltage is applied. By pressing against each other with the intermediate transfer belt 211 sandwiched therebetween, the pair of rollers forms a secondary transfer nip. The recording sheet S is conveyed from the paper feeding unit 110 in the direction of arrow C in synchronization with the conveyance of the toner image carried on the outer peripheral surface of the intermediate transfer belt 211 to the secondary transfer nip.

[0075] Thereby, the toner image is electrostatically transferred (secondary transfer) from the outer peripheral surface of the intermediate transfer belt 211 onto the image forming surface of the recording sheet S. The fixing device 215 heats and melts the toner image carried on the recording sheet S and crimps it to the image forming surface of the recording sheet S (thermal fixing).

[0076] The scanner device 216 reads the image formed on the image forming surface of the recording sheet S to generate image data and transmits it to the control unit 101. As the scanner device 216, for example, a line type CCD (Charge Coupled Device) image sensor that reads the recording sheet S conveyed from the fixing device 215 to the paper discharge tray 102 can be used. Also, not limited to the CCD, a line scanner such as a contact image sensor (CIS) can also be used.

[0077] The recording sheet S on which the reading of the image on the image forming surface has been completed is discharged onto the paper discharge tray 102. When forming a plurality of images, the recording sheets S are sequentially stacked on the paper discharge tray 102. [3] Ozone blur (linear blur) locally occurring in the main scanning direction Ozone blur is a phenomenon that occurs when discharge products such as ozone and nitrogen oxides (NOx: Nitrogen Oxides) generated in the charging process adhere to the outer peripheral surface of the photoreceptor drum 201 and further absorb moisture to lower the resistance.

[0078] When ozone fogging occurs, the charged charges on the outer peripheral surface of the photoreceptor drum 201 diffuse from the non-exposed area to the exposed area via the discharge products with reduced resistance, resulting in density anomalies and image noise that makes the image appear blurred. For example, in a dot halftone pattern, as illustrated in FIG. 7(b), image noise appears as if the dots are connected, and in a line image, as illustrated in FIG. 9(b), image noise appears as if the lines are stretched.

[0079] When the image forming process is executed, discharge products are generated from the charging device 202. After the image forming process is executed, if the next image forming process or the like is not executed and a long period of time elapses with the rotation of the photoreceptor drum 201 stopped, a specific region in the circumferential direction of the outer peripheral surface of the photoreceptor drum 201 continues to face the charging device 202, so the discharge products continue to adhere and accumulate.

[0080] Therefore, ozone fogging becomes particularly prominent. Such ozone fogging appears at the rotation period (circumferential pitch) of the photoreceptor drum 201. Further, since the charging device 202 faces the outer peripheral surface of the photoreceptor drum 201 over the entire width in the axial direction of the photoreceptor drum 201, ozone fogging appears over the entire width in the main scanning direction on the image.

[0081] When the cleaning blade 301 removes residual toner from the outer peripheral surface of the photoreceptor drum 201, it cleans the outer peripheral surface of the photoreceptor drum 201 over the entire width in the axial direction of the photoreceptor drum 201. Therefore, in the prior art, the discharge products adhering over the entire width in the axial direction (main scanning direction) of the photoreceptor drum 201 are also removed using the cleaning blade 301.

[0082] However, in recent years, in order to achieve the high-definition image quality for commercial use required in the printing industry, the inventors investigated and found that in addition to the ozone fogging that appears over the entire width in the main scanning direction known in the prior art, there is also ozone fogging that occurs locally in the main scanning direction. Such ozone fogging was discovered only when high-definition printing for commercial use was required.

[0083] When observing the ozone fog that occurs locally in the main scanning direction in detail, it can be seen that there are fine linear density irregularities in the circumferential direction of the photoreceptor drum 201. Therefore, hereinafter, this ozone fog will be referred to as "linear fog".

[0084] It is considered that the linear fog is generated when the photoreceptor drum 201 is rotationally driven and discharge products enter the fine damaged areas on the outer peripheral surface of the photoreceptor drum 201 by rubbing against members such as the cleaning blade 301 and the brush 305, and absorb moisture to reduce the resistance.

[0085] It is speculated that the discharge products that have entered the fine damaged areas on the outer peripheral surface of the photoreceptor drum 201 are not sufficiently affected by the scraping force of the cleaning blade 301. If a cleaning blade 301 made of a normal material is used, it will take a long time to remove them. However, if a cleaning blade 301 with a high frictional force is used, the wear of the photoreceptor drum 201 may be accelerated, and the service life may be shortened.

[0086] Therefore, in this embodiment, when the linear fog is detected, only the outer peripheral surface of the photoreceptor drum 201 is intensively cleaned to realize high-definition image quality while suppressing the wear of the photoreceptor drum 201. [4] Configuration of the control unit 101 Next, the configuration of the control unit 101 will be described.

[0087] As shown in FIG. 4, the control unit 101 is configured such that a CPU (Central Processing Unit) 401, a ROM (Read Only Memory) 402, a RAM (Random Access Memory) 403, etc. are connected so as to be able to communicate with each other by an internal bus 406.

[0088] When the CPU 401 is reset, such as when the image forming apparatus 1 is powered on, it reads a boot program from the ROM 402 to start up, uses the RAM 403 as a working storage area, and reads and executes an OS (Operating System) and a control program from the HDD (Hard Disk Drive) 404.

[0089] The NIC (Network Interface Card) 405 executes processes for communicating with an external device such as a personal computer via a communication network such as a LAN (Local Area Network) or the Internet. As a result, an image forming job can be received from the external device.

[0090] The control unit 101 rotationally drives the photosensitive drum 201 by controlling the photosensitive drum drive motor 411. The control unit 101 further controls the charging device 202, the exposure device 203, the developing device 204, the primary transfer roller 205, the cleaning device 206, the secondary transfer roller pair 207, the fixing device 215, the paper feeding unit 110, and the image reading unit 120 to execute image forming processing.

[0091] When detecting linear blurring, in addition to the above, the scanner device 216 is further controlled to read an image formed on the recording sheet S on the conveyance path of the recording sheet S from the fixing device 215 to the paper discharge tray 102. [5] Operation of the control unit 101 Next, the operation of the control unit 101 will be described.

[0092] As shown in FIG. 5, when the control unit 101 receives an image forming job (S501: YES), it checks whether the cumulative number of images formed for each of the image forming units 200Y, 200M, 200C, and 200K is equal to or greater than a threshold value.

[0093] As a result of the confirmation, if there is no image forming unit 200 in which the cumulative number of printed images has reached or exceeded the threshold (S502: NO), the image forming job is executed as it is (S510). For each of the YMCK colors, the number of images formed in the image forming job is added to the cumulative number of printed images to update the cumulative number of printed images (S511), and then the process proceeds to step S501 to wait for the next image forming job.

[0094] If there is one or more image forming units 200 in which the cumulative number of printed images has reached or exceeded the threshold, for the image forming unit(s) 200 in which the cumulative number of printed images has reached or exceeded the threshold, a linear blur detection process is executed (S503). Details of the linear blur detection process will be described later.

[0095] Note that the linear blur detection process is executed only for the image forming unit(s) 200 in which the cumulative number of printed images has reached or exceeded the threshold because linear blur is likely to become apparent after durability when the number of fine damaged areas on the outer peripheral surface of the photosensitive drum 201 increases. Relatively, in the initial stage of durability, no damaged areas have occurred on the outer peripheral surface of the photosensitive drum 201, and there is a high possibility that no linear blur will occur, so it is not necessary to execute the linear blur detection process deliberately.

[0096] Also, as will be described later, since a test image is formed in the linear blur detection process, if the linear blur detection process is not executed for the image forming unit 200 with a small cumulative number of printed images, the toner of that color can be consumed unnecessarily.

[0097] However, needless to say, from the perspective of only the purpose of detecting linear blur, the linear blur detection process may be executed for all the image forming units 200 regardless of the number of cumulative printed images.

[0098] As a result of executing the linear blur detection process, if linear blur is detected, as a recovery mode, the outer peripheral surface of the photosensitive drum 201 is cleaned (S505). In this cleaning, the photosensitive drum 201 is rotated a predetermined number of times, and the outer peripheral surface is rubbed against the cleaning blade 301 to scrape off the discharge products adhering to the outer peripheral surface.

[0099] In the recovery mode, the photosensitive drum 201 may be rotated while supplying toner from the developing device 204. By doing so, since the toner can be made to act as an abrasive when the cleaning blade 301 is brought into sliding contact with the outer peripheral surface of the photosensitive drum 201, the discharge products adhering to the outer peripheral surface can be effectively removed.

[0100] The number of rotations of the photosensitive drum 201 is desirably the number sufficient to remove the discharge products that have entered the damaged portions on the outer peripheral surface. However, since the photosensitive drum 201 wears more as the number of rotations increases, an appropriate number of rotations should be determined by experiments or the like.

[0101] After cleaning, the linear blur detection process is executed again (S506). The linear blur detection process in step S506 may be executed only for the image forming unit 200 in which linear blur was detected in the linear blur detection process in step S503.

[0102] As a result of executing the linear blur detection process in step S506, if linear blur is detected again for the image forming unit 200 in which linear blur was detected in the linear blur detection process in step S503 (S507: YES), the control unit 101 displays a warning message on the operation panel 130 (S508).

[0103] Even if the outer peripheral surface of the photosensitive drum 201 is cleaned, the linear blur cannot be eliminated, and high-definition printing for commercial use cannot be performed. Therefore, it is necessary to replace the photosensitive drum 201 or the image forming unit 200 including the photosensitive drum 201.

[0104] For the same reason, the image forming job is canceled (S509) and the process is terminated. Since linear blur occurs even when the image forming job is executed, a high-definition image cannot be formed.

[0105] If no linear blur is detected in the linear blur detection process of step S503, an image forming job is executed (S510). After adding the number of images of each of the YMCK colors formed in the image forming job to the cumulative number of image formations corresponding to the color (S511), the process proceeds to step S501 to wait for the next image forming job.

[0106] Also, even if linear blur is detected in the linear blur detection process of step S503, if it is confirmed that the discharge products have been removed from the outer peripheral surface of the photoreceptor drum 201 by the cleaning in step S505 and the linear blur has been eliminated (S507: NO), the image forming job is executed in the same manner (S510). After updating the cumulative number of image formations (S511), the process proceeds to step S501 to wait for the next image forming job.

[0107] In this way, only when linear blur is detected, cleaning is performed to remove the discharge products that caused the linear blur from the outer peripheral surface of the photoreceptor drum 201. Therefore, it is possible to suppress unnecessary wear of the photoreceptor drum 201 compared to the case where the cleaning is performed regardless of the presence or absence of linear blur. Thus, the service life of the photoreceptor drum 201 can be extended. [6] Linear blur detection process Next, the linear blur detection process executed in steps S503 and S506 will be described.

[0108] The linear blur detection process is a process for detecting linear blur. Linear blur has the following characteristics. That is, (a) It is image noise caused by discharge products that have entered damaged areas on the outer peripheral surface of the photoreceptor drum 201. Since it is difficult for the frictional force by the cleaning blade 301 to act, it takes more time to disappear compared to normal ozone blur. (b) For the same reason, it repeatedly occurs at a specific position in the main scanning direction at the circumferential pitch of the photoreceptor drum, while (c) There is no specific tendency regarding which position in the main scanning direction the specific position is. (d) Since the damaged areas caused by the outer peripheral surface of the photoreceptor drum 201 rubbing against the cleaning blade 301 or the like are linear in the circumferential direction of the photoreceptor drum 201, they become linear in the sub-scanning direction. Therefore, by focusing on the above characteristics, linear blur can be detected.

[0109] In the linear blur detection process, as shown in FIG. 6, the control unit 101 first forms a test image (S601).

[0110] In the present embodiment, an image of a dot half pattern is formed as the test image. As illustrated in FIG. 7(a), the dot half pattern 700 is an image that expresses intermediate gradations by a dot pattern. In the present embodiment, taking the case of using the reversal development method as an example, dots 701 are drawn by toner adhering to the areas where the charged charges on the outer peripheral surface of the photoreceptor drum 201 are lost due to exposure, and the unexposed areas become white areas where toner does not adhere.

[0111] When a dot half pattern is formed using the photoreceptor drum 201 whose outer peripheral surface is damaged by rubbing against the cleaning blade 301 or the like and discharge products have entered the damaged areas, as illustrated in FIG. 7(b), a linear blur 711 with the sub-scanning direction as the longitudinal direction occurs at the position corresponding to the damaged areas in the dot half pattern 710.

[0112] In the present embodiment, the discharge products that have entered the damaged areas on the outer peripheral surface of the photoreceptor drum 201 and contain moisture and have a reduced electrical resistance conduct the non-exposed area and the exposed area in the vicinity of the discharge products on the outer peripheral surface of the photoreceptor drum 201, reducing the charged charges in the non-exposed area. As a result, the charged charges are lost at the damaged areas and their vicinity, and toner adheres during development, so that the linear blur 711 occurs.

[0113] In order to detect this linear blur 711, in order to also confirm the periodicity in the circumferential direction (sub-scanning direction) of the photoreceptor drum 201, the dot half pattern 710 needs to be at least two cycles in size at the circumferential pitch of the photoreceptor drum 201 in the sub-scanning direction. Also, it is necessary to continuously measure the density in the main scanning direction. In this embodiment, this is made possible by scanning the image after it is fixed on the paper with a CCD (or CID).

[0114] Also, the smaller the size of the dots 701 in the dot half pattern 710 and the narrower the interval between the dots 701 in accordance with the size of the dots 701, the more finely the linear blur 711 can be detected, which is effective in ensuring high-definition image quality.

[0115] The toner image of the dot half pattern formed on the outer peripheral surface of the photoreceptor drum 201 is transferred and fixed to the recording sheet S in the same manner as during normal image formation. When executing the linear blur detection process, the control unit 101 reads the image formed on the recording sheet S line by line with the scanner device 216 (S602). By this reading, image data of the read test image (hereinafter simply referred to as the "test image") is generated.

[0116] The control unit 101 executes loop processing from step S603 to step S610 for each main scanning line of the test image. That is, for each pixel of the main scanning line, a difference value (density profile) obtained by subtracting the pixel value of the original test image from the pixel value of the read test image is obtained, and this difference value is compared with the threshold Th, and whether there is a portion exceeding the threshold Th is used to confirm density abnormality (S604).

[0117] FIG. 7(c) is a graph illustrating the density abnormality (difference value) in the main scanning line (D-D line) that crosses the linear blur 711 among the dot half patterns 710 having the linear blur 711. In this graph, a density abnormality appears at the position corresponding to the linear blur 711. The density abnormality has occurred because the area that was white in the original test image has become non-white due to the linear blur 711.

[0118] When the control unit 101 detects a density abnormality from the comparison between the difference value and the threshold value (S605: YES), it checks whether there is a first cycle main scanning line of the current main scanning line at the circumferential pitch of the photosensitive drum 201 in the test image. At the initial stage of the loop process, there is no main scanning line one cycle before the current main scanning line.

[0119] When there is a main scanning line one cycle before (S606: YES), the control unit 101 refers to the first cycle main scanning line at the circumferential pitch of the photosensitive drum 201 in the test image (S607), and checks whether a density abnormality is also detected at the same position as the density abnormality of the current main scanning line for the main scanning line one cycle before.

[0120] When a density abnormality is detected at the same position as the density abnormality of the current main scanning line for the main scanning line one cycle before (S608: YES), it is determined that there is a linear blur (S609). Regarding the position of the density abnormality in the main scanning direction, considering the possibility of positional deviation due to the skew of the recording sheet S, etc., it is desirable to determine that the positions of the density abnormalities are the same if they are at positions close within a certain error range.

[0121] Also, an upper limit value of the distance (e.g., the number of pixels) in which the portions where the difference value exceeds the threshold Th are continuous in the main scanning direction is set, and when the distance exceeds the upper limit value, in other words, when it is not a local density abnormality in the main scanning direction, it may be determined that there is no linear blur.

[0122] However, even if it is not linear blur, there is a possibility that discharge products adhere to the corresponding location on the outer peripheral surface of the photoreceptor drum 201, causing ozone blur. Therefore, it is effective to apply the recovery mode to eliminate such ozone blur.

[0123] In the profile image of density abnormality illustrated in FIG. 8(a), density abnormalities 801, 802, 803, and 804 appear periodically at the same position in the main scanning direction with a circumferential pitch L of the photoreceptor drum 201. Also, in the profile of the density abnormality on the E-E line passing through the corresponding position in the sub-scanning direction, as shown in FIG. 8(b), corresponding to the density abnormalities 801, 802, and 803, it can be confirmed that the portions where the density abnormality (difference value) exceeds the threshold Th appear periodically in the sub-scanning direction with the circumferential pitch L of the photoreceptor drum 201.

[0124] Therefore, it can be determined that linear blur is occurring from the density abnormalities 801, 802, 803, and 804. On the other hand, since neither of the density abnormalities 811 and 812 appears periodically in the sub-scanning direction, they do not contribute to the determination of the presence or absence of linear blur.

[0125] If no density abnormality is detected for the current main scanning line (S605: NO), if there is no main scanning line one cycle before (S606: NO), if no density abnormality is detected for the main scanning line one cycle before (S608: NO), and if the positions of the density abnormality detected for the current main scanning line and the density abnormality detected for the main scanning line one cycle before are different (S609: NO), the process for the next main scanning line is performed while maintaining the determination of the presence or absence of linear blur.

[0126] After that, when the loop process is completed, the routine returns to the upper routine. Note that when it is determined that there is linear blur, the loop process may be terminated and the routine may return to the upper routine. This is because in the upper routine, if even one linear blur is detected, the outer peripheral surface of the photoreceptor drum 201 is cleaned regardless of the number of detected linear blurs (S505).

[0127] In this way, it is possible to accurately detect linear blurring caused by discharge products entering damaged areas on the outer peripheral surface of the photoreceptor drum 201. [7] Modification example As described above, the present disclosure has been described based on the embodiments. However, it goes without saying that the present disclosure is not limited to the above-described embodiments, and the following modification examples can be implemented. (7-1) In the above embodiment, the case where the test image is a dot half pattern has been described as an example. Needless to say, the present disclosure is not limited to this, and a test image other than the dot half pattern may be used.

[0128] For example, a thin line pattern may be used as the test image. In this case, in the thin line pattern 900 shown in FIG. 9(a), thin lines 901 extending in the main scanning direction are repeatedly drawn at equal intervals in the sub-scanning direction.

[0129] When linear blurring 911 occurs in the thin line pattern 900, since the linear blurring is caused by discharge products entering damaged areas extending in the sub-scanning direction (circumferential direction of the photoreceptor drum 201), as illustrated in FIG. 9(b), the line width of the thin line becomes wider at the location where the linear blurring occurs.

[0130] Therefore, in the linear blurring detection process for detecting linear blurring using the thin line pattern, by sequentially referring to the sub-scanning lines of the test image read by the scanner device 216, as illustrated in FIG. 9(c), in the density profile, at the location where the line width of the thin line 901 is originally w1, whether the locations where it becomes w2, w3, w4, w5, which are larger than a predetermined threshold Th, periodically repeat at the circumferential pitch L of the photoreceptor drum 201 can be used to determine the presence or absence of linear blurring 911.

[0131] If the thin line pattern 900 is used as the test image, the merit that the amount of toner used to form the test image can be small can be obtained.

[0132] When using the thin line pattern 900 as the test image, if the period (the sum of the line width and the interval) of the thin lines 901 in the sub-scanning direction is not an integer fraction of the circumferential pitch L of the photoreceptor drum 201, the position where the thin lines 901 pass through the linear blur in the sub-scanning direction is not constant, so it may be impossible to detect the periodicity of the linear blur.

[0133] On the other hand, if the period of the thin lines 901 in the sub-scanning direction is set to an integer fraction of the circumferential pitch L of the photoreceptor drum 201, the detection accuracy of the linear blur can be improved in the sense that the positional relationship between the linear blur and the thin lines 901 can be kept constant.

[0134] Also, when using the thin line pattern 900, linear blurs with a length in the sub-scanning direction shorter than the period of the thin lines 901 may not be detected. Therefore, when it is desired to achieve high-definition image quality, it is desirable to use a thin line pattern 900 in which the period of the thin lines 901 is smaller than the length of the linear blur that can be tolerated in the sub-scanning direction.

[0135] In addition, in FIG. 9(a), the thin line pattern 900 in which the thin lines 901 extend in the main scanning direction is shown. However, if the extending direction of the thin lines 901 is a direction other than the sub-scanning direction, in the sub-scanning direction, it is possible to determine the presence or absence of the linear blur based on whether the portions where the line width of the thin lines 901 is large appear periodically at the circumferential pitch L of the photoreceptor drum 201.

[0136] Note that even when using the thin line pattern 900 as the test image, similar to the case of using the dot half pattern as the test image, an upper limit value of the distance (for example, the number of pixels) where the portions where the line width of the thin lines 901 is large are continuous in the main scanning direction is set. When the distance exceeds the upper limit value, it may be determined that it is not a linear blur.

[0137] Also, in this case as well, since there is a possibility that ozone blur other than the linear blur occurs, it is effective to apply the recovery mode to eliminate the ozone blur.

[0138] In this way, even when the thin line pattern 900 is used as the test image, linear blur can be detected. As long as the image is formed by an electrostatic latent image in which the exposed area and the non-exposed amount appear alternately at a period shorter than the length of the linear blur to be detected in the sub-scanning direction, test images other than the dot half pattern 700 and the thin line pattern 900 can also be used for detecting linear blur. (7-2) In the above embodiment, the case where the test image fixed on the recording sheet S is read by the scanner device 216 to detect linear blur has been described as an example.

[0139] As in the above embodiment, if it is on the conveyance path of the recording sheet S from the fixing device 215 to the paper discharge tray 102, since there is room in the space, it is easy to arrange the scanner device 216. Further, when detecting linear blur, the scanner device 216 is also excellent in that it is difficult to be contaminated.

[0140] However, it goes without saying that the present disclosure is not limited to this, and the following may be done instead.

[0141] For example, linear blur may be detected on the outer peripheral surface of the photoreceptor drum 201. In this way, since it is not necessary to transfer or fix the test image to the recording sheet S, the power consumption and member wear for transfer and fixing can be suppressed, and the recording sheet S can be saved.

[0142] Also, linear blur may be detected from the test image carried on the intermediate transfer belt 211. The detection of linear blur may be performed on the circumferential travel path of the intermediate transfer belt 211 from the image forming unit 200 (in FIG. 2, the image forming unit 200K) located at the most downstream in the circumferential travel direction of the intermediate transfer belt 211 to the secondary transfer roller pair 212.

[0143] Also, when detecting linear blurring on the downstream side of the secondary transfer roller pair 212, it is desirable to stop applying the secondary transfer bias voltage to the secondary transfer roller pair 212, apply a bias voltage with a polarity opposite to that of the secondary transfer bias voltage, or separate the secondary transfer roller pair 212.

[0144] By doing so, it is possible to prevent the test image from being disturbed on the intermediate transfer belt 211 due to the influence of the secondary transfer bias applied to the secondary transfer roller pair 212, so that linear blurring can be detected accurately.

[0145] Also, as described above, when detecting linear blurring on the outer peripheral surface of the photosensitive drum 201, it is necessary to arrange a detection device individually for each photosensitive drum 201. On the other hand, when detecting linear blurring from the test image carried on the intermediate transfer belt 211, linear blurring can be detected using a common detection device regardless of which photosensitive drum 201 the test image is formed on.

[0146] In this way, since fewer detection devices for detecting linear blurring are required, the cost and size of the image forming apparatus 1 can be reduced.

[0147] Note that the region for forming the test image does not have to be the entire width in the main scanning direction of the photosensitive drum 201 or the intermediate transfer belt 211, and high-definition image quality can be ensured as long as it covers the entire effective image area. Also, even if it does not cover the entire effective image area, if a test image with a certain width is formed, linear blurring can be detected with high accuracy. (7-3) In the above embodiment, the case where the recovery mode is applied when linear blurring is detected has been described as an example. Needless to say, the present disclosure is not limited to this. In addition, when image noise other than linear blurring is detected, an image noise elimination sequence for eliminating the image noise may be applied.

[0148] In addition, when image noise other than linear blur is detected together with linear blur, if the image noise detected other than linear blur can be eliminated by applying a recovery mode for linear blur, only the recovery mode is applied, and an image noise elimination sequence for eliminating the image noise detected other than linear blur may be omitted. By doing so, it is possible to suppress the consumption of the photosensitive drum 201 and other members as compared with the case where both the recovery mode for linear blur and other image noise elimination sequences are applied. (7-4) In the above embodiment, the case where it is confirmed whether or not the density abnormality exceeds the threshold in the difference image between the original test image (dot half pattern) and the test image read by the scanner device 216 has been described as an example. Also, in the above modification, the case where it is confirmed whether or not the line width is larger than the threshold in order to determine the presence or absence of linear blur in the test image of the thin line pattern 900 has been described as an example. Needless to say, the present disclosure is not limited to this, and instead, the following may be done.

[0149] For example, it may be determined based on whether or not there is a place where the variation in density abnormality or line width is equal to or greater than the threshold with respect to the average value of the density abnormality or line width in the region where it is determined that no linear blur has occurred.

[0150] Here, in order to determine whether or not it is a region where no linear blur has occurred, a histogram of density abnormality or line width may be used. Since linear blur does not occur in most regions of the test image, the region with the overwhelmingly high frequency of density abnormality or line width in the histogram of density abnormality or line width is the region where no linear blur has occurred.

[0151] Therefore, by obtaining the average value of the density abnormality or line width with a high frequency in the histogram, it is possible to obtain the average value of the density abnormality or line width in the region where it is determined that no linear blur has occurred.

[0152] In addition to the shading abnormalities and line widths with overwhelmingly high frequencies in the histogram, if there are shading abnormalities and line widths with relatively high frequencies, shading abnormalities and line widths that can distinguish between these shading abnormalities and line widths can be set as thresholds, and candidates for linear blur can be detected from the test image using the thresholds. Among the candidates for linear blur, those that periodically appear at the circumferential pitch L of the photoreceptor drum 201 in the sub-scanning direction are the desired linear blur. (7-5) In the above embodiment, the case where linear blur is detected (Fig. 5, S504: YES), after applying the recovery mode (S505), and when linear blur is detected again (S507: YES), a warning message is displayed (S508), and the image formation job is canceled (S509) was taken as an example for explanation. Needless to say, the present disclosure is not limited to this, and the following may be done instead.

[0153] For example, the cycle of detecting linear blur and applying the recovery mode may be repeated two or more times. That is, in each recovery mode, the number of rotations of the photoreceptor drum 201 for removing discharge products may be reduced, and the outer peripheral surface of the photoreceptor drum 201 may be cleaned while checking the elimination status of linear blur.

[0154] In this way, when linear blur that can be eliminated even with a small number of rotations of the photoreceptor drum 201 occurs, it is possible to prevent the promotion of wear of the photoreceptor by unnecessarily rotating the photoreceptor drum 201 even though the linear blur has been eliminated.

[0155] Conversely, even if the number of rotations of the photoreceptor drum 201 can be increased to eliminate linear blur, it is possible to prevent the convenience of the user of the image forming apparatus 1 from being reduced by displaying a warning message or canceling the image formation job.

[0156] Thus, if the linear blur is not eliminated even after repeating the cycle of applying the recovery mode a predetermined number of times, it may be determined that there is a damaged area on the photoreceptor that cannot be recovered, and a warning message may be displayed or the image forming job may be canceled. (7-6) In the above embodiment, the case where the linear blur detection process (S506) is further executed after executing the recovery mode of the linear blur (FIG. 5, S505) has been described as an example. Needless to say, the present disclosure is not limited to this, and the following may be done instead.

[0157] For example, if applying the recovery mode can surely remove the discharge products and eliminate the linear blur because the number of rotations of the photoreceptor drum 201 in the recovery mode is very large, etc., after executing the recovery mode, the image forming job may be executed as usual without performing the linear blur detection process again.

[0158] In this way, even though the linear blur is surely eliminated, it is possible to avoid unnecessarily executing the linear blur detection process, increasing the FCOT (First Copy Out Time), and reducing the user convenience. (7-7) In the above embodiment, the case where the outer peripheral surface of the photoreceptor drum 201 is cleaned using the cleaning blade 301 has been described as an example. Needless to say, the present disclosure is not limited to this, and instead of the cleaning blade 301, for example, a cleaning member other than the cleaning blade 301, such as a brush, may be used. In this case, the magnetic brush formed by the developing device 204 can also be used as the cleaning member.

[0159] When a rotating body such as a rotating brush is used as the cleaning member, when applying the recovery mode, the rotating body may be rotated under conditions different from those when executing the image forming job. For example, if the rotation speed is increased compared to when executing the image forming job, the frictional force on the outer peripheral surface of the photoreceptor drum 201 can be increased, so that the discharge products can be removed more surely.

[0160] Also, if only the rotating body that rubs the outer peripheral surface of the photoreceptor drum 201 where linear blur is detected is rotated or its rotation speed is increased, the photoreceptor drum 201 where no linear blur is detected will not be rubbed much, so wear on the outer peripheral surface of the photoreceptor drum 201 can be suppressed. Therefore, the service life of the photoreceptor drum 201 and the image forming unit 200 including the photoreceptor drum 201 can be extended. (7-8) In the above embodiment, the case where the presence or absence of linear blur is confirmed prior to the execution of an image forming job if the cumulative number of image formations is equal to or greater than a threshold value has been described as an example. Needless to say, the present disclosure is not limited to this, and instead of this, or in addition to this, the following may be done.

[0161] For example, the presence or absence of linear blur may be confirmed only when the time elapsed since the completion of the previous image forming process is equal to or greater than a predetermined threshold value. As described above, when the image forming process is completed, the rotation of the photoreceptor drum 201 stops, and a specific region on the outer peripheral surface of the photoreceptor drum 201 continues to face the charging device 202. Therefore, discharge products generated from the charging device 202 are intensively accumulated in the region, and if there is a damaged portion due to rubbing in the region, linear noise is likely to occur.

[0162] On the other hand, when the image forming process is repeated, when the transfer residual toner remaining on the outer peripheral surface of the photoreceptor drum 201 after primary transfer is scraped off by the cleaning blade 301, the discharge products are also scraped off, so the linear noise is likely to be eliminated.

[0163] Focusing on this point, if the detection process for linear blur is not executed when the time elapsed since the completion of the previous image forming process is less than a predetermined threshold value, it is possible to suppress forming a test image unnecessarily, consuming toner wastefully, and wearing the outer peripheral surface of the photoreceptor drum 201 to clean the toner, even though the probability of detecting linear blur is low. In the above embodiment, the case where the number of rotations of the photosensitive drum 201 is one or more when the recovery mode is applied has been described as an example. Needless to say, the present disclosure is not limited to this, and instead, the number of rotations of the photosensitive drum 201 may be less than one rotation.

[0164] For example, when detecting linear blur on the outer peripheral surface of the photosensitive drum 201, the adhesion position of the discharge product on the outer peripheral surface of the photosensitive drum 201 can be specified. Therefore, the photosensitive drum 201 may be rotated within a range where the adhesion position passes through the rubbing position of the cleaning blade 301 to clean the outer peripheral surface.

[0165] Needless to say, except when the adhesion position is directly below the cleaning blade 301, before rotating the photosensitive drum 201 once, the adhesion position passes through the rubbing position of the cleaning blade 301, so the discharge product adhering to the adhesion position can be rubbed and cleaned with the cleaning blade 301.

[0166] In this way, the distance that the cleaning blade 301 rubs against the outer peripheral surface of the photosensitive drum 201 to clean the discharge product can be minimized, so that the wear of the photosensitive drum 201 can be suppressed.

[0167] Also, as described in the above modification example, after applying the recovery mode, the detection process of linear blur is performed again, and if the recovery mode is applied until linear blur is no longer detected, the number of times the recovery mode is applied can be minimized. In this sense as well, the wear of the photosensitive drum 201 can be suppressed. (7-10) In the above embodiment, the case where linear blur is detected when the cumulative number of printed images is equal to or greater than a threshold value has been described as an example. Needless to say, the present disclosure is not limited to this. Instead of the cumulative number of printed images, conditions other than the cumulative number of printed images, such as the running distance of the photoreceptor drum 201 or the cumulative number of rotations, may be determined to determine whether to execute the linear blur detection process. Even in this case, by applying the present disclosure, the same effects as those of the above embodiment can be obtained. (7-11) In the above embodiment, the case where the linear blur detection process is executed at the timing when an image formation job is received has been described as an example. Needless to say, the present disclosure is not limited to this. Instead of this, or in addition to this, the following may be done.

[0168] For example, the linear blur detection process may be executed in conjunction with so-called image stabilization processing. Image stabilization processing is a process of updating the operation parameters of the image forming apparatus 1 in order to keep the image quality constant by adjusting the image density, adjusting the positional accuracy of the front and back sides when forming images on both sides of the recording sheet S, or performing other adjustments. The image stabilization processing is executed when the image forming apparatus 1 is started up, before it is stopped, or when no image formation job is being executed.

[0169] In the image stabilization processing, a test image is formed to detect the current operating state. Therefore, if the test image formed for the image stabilization processing is also used for detecting linear blur, the costs such as toner and processing time for forming the test image can be reduced.

[0170] Also, if the linear blur detection process is performed only during the image stabilization processing and not when an image formation job is received, the FCOT when executing the image formation job can be shortened. Therefore, the convenience for the user can be improved. In the above embodiment, the case where a dot half pattern is formed as a test image has been described as an example. Needless to say, the present disclosure is not limited to this, and the following may be done instead.

[0171] For example, by executing an image forming job, the image formed on the recording sheet S may be read by the scanner device 216 as a test image to detect linear blurring. When linear blurring is detected, after applying the recovery mode to remove discharge products, the image is formed again. Further, when linear blurring is not detected, the next image of the image forming job may be formed as it is, or the next image forming job may be executed.

[0172] In this way, since it is not necessary to form a test image separately from the image related to the image forming job, the recording sheet S and toner can be saved. Further, when linear blurring is not detected in the image, even if discharge products are attached to the outer peripheral surface of the photosensitive drum 210, an image with high-definition image quality is formed, so there is no problem in terms of image quality.

[0173] When the attachment location of the discharge products does not straddle the exposed area and the non-exposed area, linear blurring due to the movement of the charged charge does not occur. Therefore, even if discharge products are attached to the outer peripheral surface of the photosensitive drum 201, linear blurring does not occur depending on the image to be formed.

[0174] Further, the recovery mode is applied only when an image is formed in which linear blurring occurs and is detected, and when an image is formed in which linear blurring does not occur and thus is not detected, the recovery mode is not applied even if discharge products are attached. Therefore, compared with the case where a dedicated test image is used to accurately detect linear blurring and the recovery mode is applied every time linear blurring is detected, wear of the photosensitive drum 201 can also be suppressed. In the above embodiment, the case where the image forming apparatus 1 is a tandem type color multifunction printer has been described as an example. Needless to say, the present disclosure is not limited to this, and it may be a color multifunction printer of a type other than the tandem type, or a monochrome multifunction printer.

[0175] Further, the image forming apparatus 1 may be a single function machine such as a printer device, a copying device having a scanner function for reading an image from a document, or a facsimile device having a facsimile communication function, and the same effect can be obtained by applying the present disclosure.

Industrial Applicability

[0176] The image forming apparatus according to the present disclosure is useful as an apparatus that can efficiently eliminate linear blur, which is local image noise generated by the adhesion of discharge products to the surface of the photoreceptor.

Explanation of Signs

[0177] 1………………………………………Image forming apparatus 100…………………………………Image forming unit 101…………………………………Control unit 130…………………………………Operation panel 200…………………………………Image forming unit 201…………………………………Photoreceptor drum 202…………………………………Charging device 205…………………………………Primary transfer roller 211…………………………………Intermediate transfer belt 212…………………………………Secondary transfer roller pair 215…………………………………Fixing device 216…………………………………Scanner device 301…………………………………Cleaning blade 700, 710………………………Dot half pattern 701…………………………………Dot 711, 801 - 804, 911…Linear blur 900…………………………………Fine line pattern 901…………………………………Fine line

Claims

1. A toner image forming unit that forms a toner image on the outer peripheral surface of a photoreceptor and transfers the formed toner image to a transfer body; A detection unit that detects density irregularities in the toner image on the photoreceptor or the transfer body; A cleaning unit that cleans the outer peripheral surface of the photoreceptor; A control unit that causes the cleaning unit to perform cleaning when the detection unit detects density irregularities at the same position in the main scanning direction for each circumference of the photoreceptor in the sub-scanning direction, and The density irregularity is a local density irregularity in the main scanning direction An image forming apparatus characterized by this.

2. A toner image forming unit that forms a toner image on the outer peripheral surface of a photoreceptor and transfers the formed toner image to a transfer body; A detection unit that detects density irregularities in the toner image on the photoreceptor or the transfer body; A cleaning unit that cleans the outer peripheral surface of the photoreceptor; A control unit that causes the cleaning unit to perform cleaning when the detection unit detects density irregularities at the same position in the main scanning direction for each circumference of the photoreceptor in the sub-scanning direction, and The detection unit detects density irregularities in the toner image carried on the recording sheet, The toner image carried on the recording sheet is a toner image fixed on the recording sheet An image forming apparatus characterized by this.

3. A toner image forming unit that forms a toner image on the outer peripheral surface of a photoreceptor and transfers the formed toner image to a transfer body; A detection unit that detects density irregularities in the toner image on the photoreceptor or the transfer body; A cleaning unit that cleans the outer peripheral surface of the photoreceptor; A control unit that causes the cleaning unit to perform cleaning when the detection unit detects density irregularities at the same position in the main scanning direction for each circumference of the photoreceptor in the sub-scanning direction, and An image stabilization processing unit that causes the toner image forming unit to form a toner image in order to stabilize the quality of the toner image, and The detection unit detects density irregularities at the timing when the image stabilization processing unit executes processing to stabilize the quality An image forming apparatus characterized by this.

4. The detection unit detects density irregularities in the toner image formed by the toner image forming unit caused by the image stabilization processing unit The image forming apparatus according to claim 3, characterized by this.

5. The toner image forming unit forms a toner image in a dot half pattern, The detection unit detects density irregularities in the toner image in the dot half pattern The image forming apparatus according to any one of claims 1 to 4, characterized in that...

6. The cleaning unit cleans the entire circumference of the photosensitive rotating body The image forming apparatus according to any one of claims 1 to 5, characterized in that...

7. The detection unit detects density anomalies in the toner image formed after a predetermined period or more has elapsed since the toner image forming unit formed the previous toner image The image forming apparatus according to any one of claims 1 to 6, characterized in that...

8. A durability state specifying unit that specifies the durability state of the photosensitive rotating body; A prohibiting unit that prohibits the detection unit from detecting density anomalies when the durability state is equal to or lower than a threshold value. The image forming apparatus according to any one of claims 1 to 7, characterized in that...

9. The cleaning unit supplies toner onto the outer peripheral surface of the photosensitive rotating body and performs the cleaning by scraping off the toner The image forming apparatus according to any one of claims 1 to 8, characterized in that...

10. After the cleaning by the cleaning unit, the toner image forming unit further forms the toner image, The detection unit detects density anomalies in the further formed toner image, When the detection unit detects density anomalies at the same positions in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction in the further formed toner image, it includes a notification unit that notifies to that effect. The image forming apparatus according to any one of claims 1 to 9, characterized in that...

11. A toner image forming unit that forms a toner image with a predetermined line width on the outer peripheral surface of the photosensitive rotating body and transfers the formed toner image to a transfer target; A detection unit that detects line width anomalies in the toner image on the photosensitive rotating body or the transfer target; A cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body; A control unit that causes the cleaning unit to perform cleaning when the detection unit detects a line width anomaly at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction, The line width anomaly is a local line width anomaly in the main scanning direction The image forming apparatus, characterized in that...

12. A toner image forming unit that forms a toner image with a predetermined line width on the outer peripheral surface of the photosensitive rotating body and transfers the formed toner image to a transfer target; A detection unit that detects line width anomalies in the toner image on the photosensitive rotating body or the transfer target; A cleaning unit that cleans the outer peripheral surface of the photosensitive rotating body; When the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotator in the sub-scanning direction, a control unit that causes the cleaning unit to perform cleaning; The detection unit detects a line width abnormality in the toner image carried on the recording sheet; The toner image carried on the recording sheet is a toner image fixed to the recording sheet. An image forming apparatus characterized by the above.

13. A toner image forming unit that forms a toner image with a predetermined line width on the outer peripheral surface of the photosensitive rotator and transfers the formed toner image to a transfer target; A detection unit that detects a line width abnormality in the toner image on the photosensitive rotator or the transfer target; A cleaning unit that cleans the outer peripheral surface of the photosensitive rotator; When the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotator in the sub-scanning direction, a control unit that causes the cleaning unit to perform cleaning; An image stabilization processing unit that causes the toner image forming unit to form a toner image in order to stabilize the quality of the toner image; The detection unit detects a line width abnormality at the timing when the image stabilization processing unit executes a process for stabilizing the quality. An image forming apparatus characterized by the above.

14. The detection unit detects a line width abnormality in the toner image formed by the toner image forming unit by the image stabilization processing unit. The image forming apparatus according to claim 13, characterized by the above.

15. The toner image with the predetermined line width is a line pattern provided with a constant interval in the sub-scanning direction. The image forming apparatus according to any one of claims 11 to 14, characterized by the above.

16. The cleaning unit cleans the entire circumference of the photosensitive rotator. The image forming apparatus according to any one of claims 11 to 15, characterized by the above.

17. The detection unit detects a line width abnormality in the toner image formed after a predetermined time or more has elapsed since the toner image forming unit formed the previous toner image. The image forming apparatus according to any one of claims 11 to 16, characterized by the above.

18. A durability state specifying unit that specifies the durability state of the photosensitive rotator; A prohibiting unit that prohibits detection of a line width abnormality by the detection unit when the durability state is equal to or less than a threshold value. The image forming apparatus according to any one of claims 11 to 17, characterized by the above.

19. The cleaning unit supplies toner to the outer peripheral surface of the photosensitive rotator and performs the cleaning by scraping off the toner. The image forming apparatus according to any one of claims 11 to 18, characterized in that...

20. After being cleaned by the cleaning unit, the toner image forming unit further forms the toner image. The detection unit detects a line width abnormality in the further formed toner image. When the detection unit detects a line width abnormality at the same position in the main scanning direction for each circumference of the photosensitive rotating body in the sub-scanning direction in the further formed toner image, the apparatus includes a notification unit that notifies to that effect. The image forming apparatus according to any one of claims 11 to 19, characterized in that...

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