Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent a failure in image formation at low cost without increasing new components.SOLUTION: An image forming apparatus 1 comprises: a photoreceptor drum 20 that can be rotated by a driving source 24 in a rotation direction R1; a cleaning blade 30 that removes an attachment attached to the photoreceptor drum 20; a charging roller 41 that is in contact with the photoreceptor drum 20 on the downstream side of the cleaning blade 30 in the rotation direction R1 of the photoreceptor drum 20 and charges the photoreceptor drum 20 with electricity; an exposure device 50 that exposes the photoreceptor drum 20 charged with electricity to form an electrostatic latent image; a developing device 10 that develops the electrostatic latent image with toner; an image sensor 21 that is arranged at a position facing the photoreceptor drum 20 across a sheet conveyance path 204 for conveying a sheet P and detects the quantity of reflected light from the photoreceptor drum 20 and the sheet P; and an abnormality determination unit 120 that determines whether an image forming operation can be continued on the basis of a first detection value and a second detection value detected by the image sensor 21.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus that forms an image on paper using toner. [Background technology]

[0002] In an electrophotographic image forming apparatus, the surface of a photosensitive drum (image carrier) is charged by a charging roller or the like of a charging device, an electrostatic latent image is formed on the surface of the photosensitive drum by an exposure device, the electrostatic latent image is visualized as a toner image by a developing device by supplying toner, and the toner image is transferred from the photosensitive drum to a sheet of paper. Since toner remaining on the surface of the photosensitive drum after the toner image is transferred can cause image formation defects during the next transfer, it is scraped off by, for example, contacting a cleaning blade against the photosensitive drum.

[0003] However, due to reasons such as a malfunction of the cleaning blade, toner removal from the surface of the photosensitive drum may be insufficient, resulting in problems such as poor image formation. In such cases, the operation of the image forming apparatus must be stopped to perform maintenance. In such cases, the occurrence of poor image formation can be prevented by detecting the condition of the surface of the photosensitive drum with a sensor.

[0004] However, image formation defects can also be caused by factors other than insufficient removal of toner from the surface of the photosensitive drum. For example, image formation defects can also occur when there is a problem with the contact between the photosensitive drum and the charging roller.

[0005] By detecting the occurrence of the cause of such image formation defects, it is possible to suppress the image formation defects. For example, Patent Document 1 discloses an image forming apparatus equipped with a contact state determination device having a photosensitive drum, a charging roller capable of charging the photosensitive drum, and a controller that detects the state of current flowing between the photosensitive drum and the charging roller while the photosensitive drum and the charging roller are displaced relative to each other, and determines the contact state between the photosensitive drum and the charging roller. With this image forming apparatus, it is possible to suppress the image formation defects by setting the image formation conditions based on the determination result of the contact state determination device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-84736 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the image forming apparatus disclosed in Patent Document 1 requires a current detection unit to detect the state of the current flowing between the photosensitive drum and the charging roller, which increases costs. Furthermore, as mentioned above, if a sensor is installed to detect the surface condition of the photosensitive drum, a malfunction may occur in the sensor, making it impossible to correctly detect the cause of image formation defects.

[0008] The present disclosure has been made in consideration of the above circumstances, and its purpose is to provide an image forming apparatus that can prevent image formation defects at low cost without adding new parts. [Means for solving the problem]

[0009] An image forming apparatus according to one aspect of the present disclosure includes an image carrier that can be rotated in a predetermined direction by a drive source, a cleaning blade that contacts the image carrier and removes material adhering to the image carrier, a charging roller that contacts the image carrier downstream of the cleaning blade in the rotation direction of the image carrier and charges the image carrier to a predetermined potential, an exposure device that exposes the image carrier charged by the charging roller to light to form an electrostatic latent image, a developing device that visualizes the electrostatic latent image with toner and forms a toner image on the image carrier, and a developing device that develops the electrostatic latent image on the image carrier. The image forming apparatus is characterized by comprising: a paper transport path for transporting the paper to a position where the toner image formed on the paper is transferred to the paper; an image sensor arranged opposite the image carrier across the paper transport path and having a light source for irradiating light toward the image carrier, and detecting the amount of light reflected from the image carrier and the paper; and an abnormality determination unit for determining whether or not to continue the image forming operation based on a first detection value which is the value of the amount of light reflected from the image carrier detected by the image sensor and a second detection value which is the value of the amount of light reflected from the paper detected by the image sensor.

[0010] This makes it possible to reliably determine whether the problem is that the image carrier is soiled with toner, etc., or that the image carrier is not soiled but the image sensor is soiled with toner, etc., and to appropriately select whether to continue or stop the image forming operation.Furthermore, image formation defects can be prevented at low cost without adding new parts.

[0011] In the image forming apparatus described above, the second detection value may be a value of the amount of light reflected from a margin at the leading or trailing end of the sheet in the transport direction.

[0012] This allows for more accurate abnormality determination, and even when images are formed on both sides of a sheet of paper (double-sided printing), accurate abnormality determination can be performed.

[0013] Furthermore, in the image forming apparatus described above, the charging roller may be disposed adjacent to the cleaning blade downstream in the rotation direction of the image carrier, one end of the cleaning blade contacts the image carrier, and the cleaning blade is held by a holding member over a predetermined length from the other end toward the one end, and a first length L1, which is the length from the end of the holding member on the one end side to the one end of the cleaning blade, may be longer than a second length L2, which is the length from the end of the holding member to the contact position of the charging roller with the image carrier.

[0014] As a result, when the cleaning blade reverses and turns over, the tip of the cleaning blade comes into contact with the charging roller and separates from the surface of the photosensitive drum 20, allowing the abnormality to be detected quickly.

[0015] The image forming apparatus may further include a charging power supply that supplies a voltage or current in which an AC current is superimposed on a DC current to the charging roller.

[0016] This allows the image carrier to be charged more uniformly than when a DC voltage or current is supplied to the charging roller.

[0017] In addition, the above-mentioned image forming apparatus may further include a memory unit in which a reflected light threshold value is pre-stored, and the abnormality determination unit may determine whether or not to continue the image forming operation by comparing at least one of the first detection value and the second detection value with the reflected light threshold value.

[0018] This allows for more accurate determination of an abnormality, and allows for a more appropriate decision as to whether to continue or stop the image forming operation. Note that it is preferable that the reflection threshold value is set to a value smaller than the second detection value when no abnormality is present.

[0019] In addition, the above-mentioned image forming apparatus may further include a display unit, and the abnormality determination unit may determine that there is no abnormality if the first detection value is equal to or greater than the reflected light threshold value, and continue the image forming operation; if the first detection value is smaller than the reflected light threshold value and the second detection value is smaller than the first detection value, determine that an abnormality has occurred in the image sensor, and the display unit may display a message indicating that dirt has occurred in the image sensor; the image forming operation may continue; if the first detection value is smaller than the reflected light threshold value and the second detection value is equal to or greater than the first detection value, determine that there is an abnormality, and stop the image forming operation.

[0020] This allows for a more accurate determination of abnormality, and allows for a more appropriate decision to be made as to whether to continue or stop the image forming operation.

[0021] In addition, the above-mentioned image forming apparatus may further include a light emission amount adjustment unit that adjusts the light emission amount of the light source, and a memory unit in which a calibration value is pre-stored, and the light emission amount adjustment unit may adjust the light emission amount of the light source using the light emission amount adjustment unit so that the amount of reflected light in an area of ​​the image carrier that has not been exposed by the exposure device becomes the calibration value every time a predetermined number of image formations are performed.

[0022] This allows for a preferable adjustment of the light amount, a more accurate determination of abnormalities, and a more appropriate selection of whether to continue or stop the image forming operation. [Effects of the Invention]

[0023] According to the present disclosure, it is possible to provide an image forming apparatus that can prevent image formation defects at low cost without adding new parts. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present disclosure. [Figure 2]1 is a schematic cross-sectional view showing a developing device and its peripheral configuration according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is an enlarged schematic cross-sectional view of FIG. 2 showing the peripheral configuration of the photosensitive drum. [Figure 4] 1 is a block diagram illustrating a functional configuration of an image forming apparatus according to an embodiment of the present disclosure. [Figure 5A] 5A and 5B are diagrams illustrating detection positions of an image sensor on a photosensitive drum according to an embodiment of the present disclosure. [Figure 5B] 10A and 10B are diagrams illustrating detection positions of an image sensor on a sheet according to an embodiment of the present disclosure. [Figure 6] 1 is a graph showing the reflectance of general paper. [Figure 7] 10 is a flowchart illustrating an example of a flow of an abnormality determination process in an image forming apparatus according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0025] An image forming apparatus 1 according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0026] (Image forming device) 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present disclosure. In this embodiment, the image forming apparatus 1 will be described taking as an example a monochrome multifunction peripheral that forms a single-color image (monochrome image) on a recording medium, namely, paper P. Note that the image forming apparatus 1 is not limited to this, and can also be applied to various image forming apparatuses including a color printer, a color multifunction peripheral, a monochrome printer, etc.

[0027] When the image forming apparatus 1 is viewed from the front, in the front-to-back direction X, the front side (near side) of the image forming apparatus 1 is referred to as the front direction X1, and the back side (rear side) of the image forming apparatus 1 is referred to as the back direction X2, in the left-to-right direction Y, the left side is referred to as the left direction Y1, the right side is referred to as the right direction Y2, and in the up-down direction Z, the upper side is referred to as the up direction Z1, and the lower side is referred to as the down direction Z2, as will be described below.

[0028] The image forming apparatus 1 is roughly equipped with a document transport unit 201, an image reading unit 202, an image forming unit 203, a paper transport path 204, and a paper feeding unit 205. The image forming apparatus 1 employs a two-component development method that uses a two-component developer containing toner and a magnetic carrier as the developer.

[0029] When at least one document is set on the document tray 211, the document transport unit 201 pulls out the document one by one from the document tray 211 and transports it, and guides the document onto a first platen glass 223 of the image reading unit 202 and makes it pass through.

[0030] The image reading unit 202 is provided with an optical unit including a first scanning unit 221 and a second scanning unit 222 below a first platen glass 223. When a document passes over the first platen glass 223, the surface of the document is exposed to light by the light source of the first scanning unit 221, and the mirrors of the first scanning unit 221 and the second scanning unit 222 guide the light reflected from the document surface to an imaging lens 224, which then forms an image of the document surface on a CCD (Charge Coupled Device) 225. The CCD 225 repeatedly reads the image of the document surface in the main scanning direction and outputs image data indicating the image of the document surface.

[0031] When an original is placed on the second platen glass 226 on the top surface of the image reading unit 202, the first scanning unit 221 and the second scanning unit 222 are moved in the sub-scanning direction while maintaining a predetermined speed relationship with each other, and the first scanning unit 221 exposes the surface of the original on the second platen glass 226, and the first scanning unit 221 and the second scanning unit 222 further reflect the reflected light from the original surface and direct it to the imaging lens 224, which then forms an image of the original surface on the CCD 225.

[0032] The output image data undergoes various image processing by a control circuit and is then output to an image forming unit 203. The image forming unit 203 is provided, in approximately the center thereof, with a photosensitive drum 20 as an image carrier that is rotated by a drive source 24. Around the photosensitive drum 20, there are arranged a developing device 10 as a developing means, a cleaning blade 30, a charging device 40, an exposure device 50 as an exposure means, a transfer device 60, and the like.

[0033] The photoreceptor drum 20 has an insulating substrate that becomes conductive in areas irradiated with light, and is rotated by a drive source 24. The photoreceptor drum 20 is provided with a drum-shaped substrate and a photoconductive layer formed as a thin film on the surface of the substrate. For example, the substrate can be made of a metal such as aluminum. The photoconductive layer can be made of, for example, an organic photoconductor (OPC) or amorphous silicon (a-Si).

[0034] The charging device 40 includes a charging roller 41 that receives a voltage or current from a first power source to uniformly charge the surface of the photosensitive drum 20. A charging bias power source 42 (see FIG. 4) supplies a voltage or current consisting of AC superimposed on DC to the charging roller 41. This allows the photosensitive drum 20 to be more uniformly charged than when a DC voltage or current is supplied to the charging roller 41. However, this increases the number of discharges, which increases the coefficient of friction between the cleaning blade 30 and the charging roller 41, making the cleaning blade 30 more susceptible to reversal and peeling. However, as described below, the image forming apparatus 1 according to this embodiment allows for easy detection of defects in the cleaning blade 30. The exposure device 50 forms an electrostatic latent image by exposing the uniformly charged surface of the photosensitive drum 20 to light while modulating the intensity of a light beam according to image data. A laser, LED, or the like can be used as the exposure device 50.

[0035] The developing device 10 receives a voltage supply from a second power supply and supplies a developer (toner) to the electrostatic latent image on the photosensitive drum 20, thereby forming a toner image on the surface of the photosensitive drum 20. A toner cartridge 18 for replenishing toner is connected to the developing device 10. Details of the developing device 10 will be described later.

[0036] The transfer device 60 includes a transfer roller 61, and transfers the toner image on the photosensitive drum 20 onto the paper P while sandwiching and transporting the paper P between the transfer roller 61 and the photosensitive drum 20. In addition to the transfer roller 61, the transfer device 60 may include, for example, a transfer belt, a charging brush, or a corona charger.

[0037] The cleaning blade 30 comes into contact with the surface of the photosensitive drum 20 after the toner image has been transferred to the paper P, and scrapes off toner and other adhering matter adhering to the surface of the photosensitive drum 20. A flexible blade material is used for the cleaning blade 30, and the cleaning blade comes into contact with the photosensitive drum 20 in an elastically bent state.

[0038] A fixing device 80 is disposed above the photosensitive drum 20. The fixing device 80 sandwiches the paper P between a fixing roller 81 equipped with an internal heat source and a pressure roller 82, and fixes the image by heat and pressure. After fixing, the paper P is transported by a transport roller, and is discharged by a paper discharge roller 241 of the paper transport path 204 to a paper discharge tray 244 provided in the internal paper discharge space between the image reading unit 202 and the image forming unit 203.

[0039] When forming images on both sides of the paper P, the paper P is reversed and transported in the opposite direction by the paper discharge roller 241, then transported to the reverse transport path 243, where it is turned over and transported again to the image forming unit 203, where the toner image is transferred and fixed on the back side.

[0040] The paper feed unit 205 includes a paper feed cassette 251, and separates and supplies paper P one sheet at a time from a tray in the paper feed cassette 251. The paper P is temporarily stopped by a registration roller 242, which is one of the conveying rollers provided in the paper conveying path 204 and is provided before the photosensitive drum 20 and the transfer device 60, and is then supplied between the photosensitive drum 20 and the transfer device 60 in accordance with the timing of transfer, where the toner image on the photosensitive drum 20 is transferred.

[0041] Fig. 2 is a schematic cross-sectional view showing the developing device 10 and its peripheral configuration according to an embodiment of the present disclosure. Fig. 3 is a schematic cross-sectional view enlarging Fig. 2 and showing the peripheral configuration of the photosensitive drum 20. Note that the drawings are schematic, omitting hatching indicating cross sections, to make each component easier to see.

[0042] The developing device 10 has a developing roller 15, and supplies non-magnetic toner contained in a two-component developer onto the surface of the photosensitive drum 20 by a developing electric field formed between the photosensitive drum 20 and the developing device 10 when a voltage or current is supplied to the developing roller 15 from a developing bias power supply 19 (see FIG. 4). The developing device 10 is disposed elongated in the front-rear direction X and has a developer tank (container) 14 that contains a two-component developer containing toner and a magnetic carrier. The developer tank 14 has an opening located opposite the photosensitive drum 20. The photosensitive drum 20 is disposed facing this opening. A toner supply port 16 extends from the top of the developing tank 14.

[0043] Inside developer tank 14, first agitation transport member 11 and second agitation transport member 12 are provided as agitation transport members that rotate within developer tank 14 to agitate and transport developer containing toner. Each of first agitation transport member 11 (and second agitation transport member 12) has a spiral blade (not shown) attached to the outer periphery of its rotation shaft, and the rotation of first agitation transport member 11 (and second agitation transport member 12) allows the developer containing toner to be agitated and transported. Furthermore, inside developing device 10, first agitation transport member 11 and second agitation transport member 12 are arranged parallel to each other, and their rotation allows the developer to be circulated within developer tank 14 while being agitated. This agitation generates friction between the toner and magnetic carrier contained in the developer, which charges the non-magnetic toner.

[0044] During the image forming operation, developer is supplied to photosensitive drum 20. The toner constituting the developer is attracted to photosensitive drum 20, thereby developing the electrostatic latent image on the surface of photosensitive drum 20 and forming a toner image. As the toner image is formed, the toner concentration in developer tank 14 gradually decreases. Therefore, toner is replenished to developer tank 14. Specifically, developer tank 14 is provided with a toner concentration sensor (not shown) that detects the toner concentration, and when a decrease in the toner concentration is detected, toner is replenished to developer tank 14.

[0045] The developing roller 15 is a magnetic roller that functions as a developer carrier, and is disposed in a position facing the photosensitive drum 20. As the developing roller 15 rotates, the developer in the developer tank 14 is carried on its surface, and the toner contained in the carried developer is transported to the surface of the photosensitive drum 20.

[0046] 2, a transport paddle 13 serving as a transport member is disposed between the developing roller 15 and the second agitation transport member 12. The transport paddle 13 is provided to transport the developer to the developing roller 15 and to collect the developer from the developing roller 15.

[0047] The rotation direction R2 of the developing roller 15 is set to be the same as the rotation direction R1 of the photosensitive drum 20 at the position facing the photosensitive drum 20. In the development region where the photosensitive drum 20 and the developing roller 15 face each other, the electrostatic latent image formed on the surface of the photosensitive drum 20 is developed with toner.

[0048] The toner image developed on the photosensitive drum 20 is transferred onto paper P by transfer device 60. An image sensor 21 (described later) is provided upstream of transfer roller 61 in rotation direction R3 as a detection unit that detects the density of the toner image formed on photosensitive drum 20 from the amount of reflected light. Specifically, image sensor 21 irradiates photosensitive drum 20 with light and receives the light reflected by photosensitive drum 20 to detect the amount of reflected light. Image sensor 21 is disposed opposite the surface of photosensitive drum 20 across paper transport path 204.

[0049] The surface of the photosensitive drum 20 is neutralized by a static eliminator 70, which is disposed upstream of the cleaning blade 30 in the rotation direction R1 of the photosensitive drum 20 during image formation. The toner adhering to the surface of the photosensitive drum 20 is scraped off by the cleaning blade 30 after the electrostatic adhesion between the photosensitive drum 20 and the toner is weakened by light irradiation from the static eliminator 70. The charging roller 41 of the charging device 40 is disposed downstream of the cleaning blade 30 in the rotation direction R1 of the photosensitive drum 20, and is disposed adjacent to and in the vicinity of the cleaning blade 30.

[0050] (cleaning blade) 3, the cleaning blade 30 is in contact with the surface of the photosensitive drum 20 at its tip end 301. The cleaning blade 30 is held by a support member 31 at its base end 302, which is opposite the tip end 301. The base end 302 of the cleaning blade 30 is in contact with (fixed to) the support member 31 over a predetermined length S. That is, the length from the base end 302 of the cleaning blade 30 to the end 303 of the support member 31 corresponds to the length S. Here, the length S of the cleaning blade 30 according to the present disclosure is 5 mm, but it may be longer.

[0051] The cleaning blade 30 is provided such that the length from the end 303 of the holding member 31 to the tip 301 of the cleaning blade 30 has a first length L1. The length from the end 303 of the holding member 31 to the contact position C1 between the charging roller 41 and the photosensitive drum 20 is provided as a second length L2. In this case, the first length L1 is longer than the second length L2 (L1>L2). Here, the first length L1 in the present disclosure is 12 mm and the second length L2 is 10 mm, but this is just an example, and the relationship L1>L2 may be satisfied.

[0052] (Abnormality judgment section) 4 is a block diagram showing the functional configuration of the image forming apparatus 1. An image forming unit 203, a storage unit 110, an abnormality determination unit 120, a display unit 90, a light emission amount adjustment unit 91, an image sensor 21, and the like are connected to a control unit 100 serving as a control means. The control unit 100 is a functional unit that controls the image forming apparatus 1, and realizes various functions of the image forming apparatus 1 by reading and executing various programs and data stored in the storage unit 110. The control unit 100 is configured by, for example, a CPU (Central Processing Unit) and the like.

[0053] Details of the image forming unit 203 have been described with reference to Figure 1, and only the functional units necessary to explain the functional configuration of the image forming apparatus 1 according to this embodiment are described here.

[0054] The storage unit 110 can be configured, for example, from a semiconductor memory such as an EEPROM or a DRAM, or a magnetic disk such as an HDD. Various data, programs, etc. are stored in the storage unit 110. The storage unit 110 also stores the detection value of the amount of reflected light by the image sensor 21 (described later), a reflected light threshold value used for determination in the abnormality determination unit 120, a calibration value used for adjusting the amount of light from the light source 22, etc.

[0055] The display unit 90 is, for example, a touch panel display, and not only displays images related to operations, but also allows the user to operate the image forming apparatus 1 by touching the display unit 90. The display unit 90 can also display information to notify the user. Specifically, as will be described later, the display unit 90 can display information to notify the user that the image sensor 21 is dirty and needs to be cleaned, or to notify the user that the image forming operation has been stopped due to an abnormality.

[0056] Image sensor 21 is used when executing image quality adjustment processing (process control, hereinafter simply referred to as procon) for adjusting image density and gradation, and is equipped with a light source 22 and a reflected light detection unit 23 to detect the density of the toner image. Light source 22 irradiates the surface of photosensitive drum 20 with a predetermined spot diameter (e.g., 1 mm). Reflected light detection unit 23 receives light reflected from photosensitive drum 20 and outputs a value corresponding to the amount of light received. In other words, image sensor 21 detects the amount of light reflected from the toner image formed on the surface of photosensitive drum 20 using reflected light detection unit 23.

[0057] Furthermore, as will be described in more detail later, the image sensor 21 detects the amount of reflected light from the photosensitive drum 20 and the paper P in order to determine whether or not the image forming operation should be stopped when the surface of the photosensitive drum 20 is contaminated with toner or the like and the density of the toner image cannot be accurately detected by the abnormality determination unit 120, or whether or not to issue an alert to inform the user that the image sensor 21 is contaminated with toner or the like even though the surface of the photosensitive drum 20 is not contaminated, and that the image sensor 21 should be cleaned.

[0058] Since the amount of reflected light received by reflected light detection unit 23 correlates with the amount of toner attached on photoconductor drum 20, the correlation between the amount of toner attached and the current or voltage value of the electrical signal output according to the amount of reflected light is acquired in advance as a correlation equation or table data, so that the amount of toner attached on the surface of photoconductor drum 20, the density of the toner image, and the amount of reflected light can be detected. In other words, by comparing the current or voltage value output according to the amount of reflected light detected by reflected light amount detection unit 23 with the table data, the density of the toner image on the surface of photoconductor drum 20 and the degree of contamination on the surface of photoconductor drum 20 can be detected. In addition, contamination on the leading or trailing end portions of paper P in the transport direction F (see FIG. 5B) can also be detected.

[0059] The light emission amount adjuster 91 adjusts the amount of light emitted from the light source 22. For example, when there is no reverse curling of the cleaning blade 30, the light emission amount of the light source 22 is adjusted so that the amount of reflected light (detected by the image sensor 21) in the non-exposed area on the photosensitive drum 20 that is not exposed by the exposure device 50 becomes equal to a calibration value (reference value) pre-stored in the memory unit 110. This adjustment of the light emission amount may be performed every time images are formed on a predetermined number of sheets of paper P (e.g., 1,000 sheets). Alternatively, the light emission amount may be adjusted when a predetermined environmental change occurs or whenever the cumulative time of the image forming operation reaches a predetermined time. By adjusting the light emission amount in this manner, the light emission amount of the light source 22 can be maintained at a more appropriate value.

[0060] In the image forming apparatus 1, process control (hereinafter referred to as process control) is performed to control the image forming operation. Process control is classified into inter-sheet process control (inter-sheet process control) which is performed during continuous image forming operation, in which exposure based on image data to be printed by the exposure device 50 is not performed, i.e., a non-exposure operation area where no image is formed, utilizing the space between successive sheets of paper P (surface area), and normal process control (normal process control) which is performed before the image forming operation or while the continuous image forming operation is temporarily interrupted.

[0061] A normal process control is performed at a predetermined timing (when the power is turned on, when the environment changes, when consumables are replaced, etc.) or every predetermined number of sheets (for example, 300 to 500 sheets), generating test patches of different densities, detecting those densities, and feeding them back into the image formation conditions, etc., so that the target gradation can be achieved. An inter-sheet process control is performed every predetermined number of sheets (for example, 50 sheets) during continuous image formation operation, generating only test patches of a certain density between sheets, detecting those densities, calculating the amount of relative change based on the immediately preceding result, and feeding it back into the image formation conditions, etc.

[0062] During image forming operation, the non-exposed portion of the surface of the photosensitive drum 20 is an area where a toner image is not formed. In the image forming apparatus 1 according to this embodiment, the image sensor 21 can detect the optical reflection density (amount of reflected light) on the photosensitive drum 20 by utilizing the gap between sheets when the exposure device 50 is not performing an exposure operation during the image forming operation, or alternatively, by detecting the optical reflection density (amount of reflected light) on the photosensitive drum 20 before or after the image forming operation when the exposure device 50 is not performing an exposure operation. The image sensor 21 can also detect the amount of reflected light at the leading edge PS (see FIG. 5) of the transported paper P in the transport direction F.

[0063] The abnormality determination unit 120 determines whether an abnormality has occurred based on the detection results of the image sensor 21 on the surface area of ​​the photosensitive drum 20 and the leading edge portion PS of the paper P, while the control unit 100 controls the drive source 24 to rotate the photosensitive drum 20 and controls the first power source and the second power source to supply voltage or current to the charging roller 41 and the developing device 10, respectively. A specific method for determining an abnormality will be described below.

[0064] (Regarding abnormality detection) Fig. 5A is a diagram illustrating a detection position 21a of the image sensor 21 on the photosensitive drum 20 according to an embodiment of the present disclosure. Fig. 5B is a diagram illustrating a detection position 21b of the image sensor 21 on the paper P according to an embodiment of the present disclosure.

[0065] 5A shows a state when light from light source 22 of image sensor 21 is irradiated onto photosensitive drum 20 at the start of an image forming operation or between sheets of paper P being conveyed sequentially (between sheets). In this state, light from light source 22 of image sensor 21 is incident on photosensitive drum 20 at detection position 21a and reflected, and the reflected light is received by reflected light detection unit 23 of image sensor 21. As a result, reflected light detection unit 23 of image sensor 21 detects a first detection value, which is the amount of light reflected from photosensitive drum 20 at detection position 21a.

[0066] 5B shows a state in which a sheet of paper P is conveyed between the photosensitive drum 20 and the image sensor 21 after the first detection value is detected in the state shown in FIG. 5A. At this time, light irradiated from the light source 22 of the image sensor 21 toward the photosensitive drum 20 is incident on the sheet of paper P at the detection position 21b and reflected, and the reflected light is received by the reflected light detection unit 23 of the image sensor 21. As a result, a second detection value, which is the amount of light reflected from the sheet of paper P at the detection position 21b, is detected by the reflected light detection unit 23 of the image sensor 21. The detection position 21b where the amount of reflected light from the sheet of paper P is detected is the leading edge portion PS of the sheet of paper P in the conveyance direction F. Specifically, the leading edge portion PS is a blank area where no image is printed (no image is formed) even when images are formed on both sides of the sheet of paper P (double-sided printing). As a result, the amount of reflected light detected at the detection position 21b is the amount of light reflected from the sheet of paper P in its original state, where no image is formed (no toner is attached).

[0067] The abnormality determination unit 120 performs an abnormality determination based on a first detection value, which is the amount of reflected light when the image sensor 21 irradiates light onto the gap between sheets of paper P (photosensitive drum 20), and a second detection value, which is the amount of reflected light when the image sensor 21 irradiates light onto the leading edge portion PS of the paper P, and determines the operation of the image forming device 1 based on the determination result.

[0068] 5A, before image forming apparatus 1 starts image forming operation or between sheets of paper P, image sensor 21 detects the amount of reflected light to detect a first detection value, which is the amount of reflected light from photosensitive drum 20, and memory unit 110 stores this first detection value. Then, abnormality determination unit 120 compares the first detection value with a reflected light threshold value pre-stored in memory unit 110. If the first detection value is equal to or greater than the predetermined reflected light threshold value, it is determined that there is no abnormality because the amount of contamination, such as toner, adhering to detection position 21a on photosensitive drum 20 is below the standard. In this case, image forming operation continues.

[0069] However, when the abnormality determination unit 120 compares the reflected light threshold value with the first detection value and finds that the first detection value is smaller than the reflected light threshold value, it determines that the amount of toner or other contaminants adhering to the detection position 21a on the photosensitive drum 20 is greater than the standard, and that there is a high possibility that there is a problem with image formation.

[0070] However, in this case, the photosensitive drum 20 is not contaminated with toner or other contaminants, but the image sensor 21 is contaminated with toner or other contaminants, so only a portion of the light emitted from the light source 22 reaches the detection position 21a. Furthermore, the reflected light from the detection position 21a is blocked by the toner or other contaminants on the image sensor 21, resulting in the first detection value being smaller than the reflected light threshold. Even when the image sensor 21 is contaminated in this way, the photosensitive drum 20 may not be contaminated, and image formation may proceed without any problems. If the image sensor 21 is contaminated but the photosensitive drum 20 is not, the problem is not serious enough to stop the image formation operation; the user can simply clean the image sensor 21 after the image formation operation is completed, and this is considered a minor problem. On the other hand, if the photosensitive drum 20 is contaminated and a problem occurs, continuing the image formation operation as is would cause a problem, so the image formation operation must be stopped and professional maintenance performed.

[0071] In other words, when the abnormality determination unit 120 compares the reflected light threshold value with the first detection value and finds that the first detection value is smaller than the reflected light threshold value, it cannot determine whether the photosensitive drum 20 is dirty or whether the photosensitive drum 20 is not dirty but the image sensor 21 is dirty. On the other hand, if the photosensitive drum 20 is dirty, specialized maintenance is required regardless of whether the image sensor 21 is dirty, and therefore the image formation operation is stopped. On the other hand, if the photosensitive drum 20 is not dirty but the image sensor 21 is dirty, it is necessary to display a message on the display unit 90 urging the user to clean the image sensor 21. Note that dirt may adhere to the image sensor 21 due to, for example, toner scattered or falling from the developing device 10 or the transfer device 60.

[0072] Therefore, in the image forming apparatus 1 according to the embodiment of the present disclosure, to determine whether the photosensitive drum 20 is dirty or whether the photosensitive drum 20 is clean but the image sensor 21 is dirty, as shown in FIG. 5B , when the leading edge portion PS of the sheet P conveyed in the conveyance direction F reaches the detection position 21b, the light source 22 emits light and detects a second detection value, which is the amount of light reflected from the leading edge portion PS at the detection position 21b. The detected second detection value is stored in the memory unit 110. The abnormality determination unit 120 then compares the previously detected first detection value and the second detection value stored in the memory unit 110. If the second detection value is equal to or greater than the first detection value, it is determined that the amount of dirt adhering to the detection position 21a on the photosensitive drum 20 exceeds the standard, and an abnormality has occurred. Then, when image formation on the sheet P used to detect the second detection value is completed, the image forming operation is stopped, and image formation on the sheet P scheduled for subsequent image formation is not performed. Additionally, the display unit 90 may also display a message informing the user that an abnormality has occurred and that maintenance is required.

[0073] On the other hand, when the abnormality determination unit 120 compares the first detection value with the second detection value and determines that the second detection value is smaller than the first detection value, it determines that the photosensitive drum 20 is not dirty but that the image sensor 21 is dirty. Then, the image forming operation continues without being stopped, and the display unit 90 displays a message urging the user to clean the image sensor 21.

[0074] As described above, the image forming apparatus 1 according to this embodiment can detect whether the dirt on the photosensitive drum 20 exceeds the standard and requires maintenance, or whether the dirt on the photosensitive drum 20 is below the standard but it is better to remove the dirt on the image sensor 21. Furthermore, there is no need to add new components, and the image sensor 21 provided in the image forming apparatus 1 for image quality adjustment processing can be used to determine abnormalities, so there is no increase in costs. Furthermore, abnormalities can be determined through simple operations.

[0075] Note that the measurement of the second detection value was performed with the leading edge portion PS of the paper P in the transport direction F as the detection position 21b, but even when images are formed on both sides of the paper P (double-sided printing), the amount of reflected light detected by the image sensor 21 in a blank area where no printing (no image formed), that is, an area where no toner is attached, can be used as the detection position 21b and used as the second detection value. Therefore, for example, the trailing edge portion of the paper P in the transport direction F can be used as the detection position to detect the second detection value.

[0076] Here, the reflected light threshold may be set to a value smaller than the detection value (second detection value) of the amount of reflected light from the paper P by the image sensor 21 when there is no contamination. For example, the reflected light threshold may be set to the amount of reflected light by the image sensor 21 when the amount of toner adhesion is half the amount of toner adhesion at a solid image density on the photosensitive drum 20 of the present disclosure. In this case, the reflected light threshold is a value corresponding to a reflectance of, for example, about 30%, where the reflectance when the normal image sensor 21 detects the amount of reflected light from a normal photosensitive drum 20 with no contamination such as toner on its surface is set to 100%. Note that in the image forming apparatus 1 according to the embodiment of the present disclosure, the reflected light detection unit 23 of the image sensor 21 is set to output a smaller output value relative to a calibration value (reference value) as the amount of received light decreases. Therefore, the reflected light threshold is set to be lower than the calibration value (reference value).

[0077] Figure 6 is a graph showing the reflectance of common paper, with values ​​obtained by actual measurements. The horizontal axis in Figure 6 shows a number of commonly available paper types, with the reflectance of each of 29 types of paper, No. 1 to No. 29. Figure 6 shows that the reflectance of most of the paper types No. 1 to No. 29 is between 40 and 65%, and the reflectances of paper types No. 1, 7, and 9, which have reflectances below this range, are 38.4%, 38.4%, and 37.5%, respectively. As can be seen from this, it is sufficient to set the reflected light threshold value to a value corresponding to a reflectance of about 30%, as described above.

[0078] 3, the cleaning blade 30 of the image forming unit 203 is provided with a first length L1 that is longer than the second length L2. Therefore, if the cleaning blade 30 reverses and turns over, the tip 301 of the cleaning blade 30 comes into contact with the charging roller 41 and separates from the surface of the photosensitive drum 20.

[0079] When the charging roller 41 separates from the photosensitive drum 20, the surface of the photosensitive drum 20 cannot be charged to a predetermined potential, and the surface potential of the photosensitive drum 20 drops to nearly 0 V. At this time, because a voltage or current is supplied to the developing roller 15 from the developing bias power supply 19, the potential difference between the surface of the photosensitive drum 20 and the developing roller 15 causes toner to be forcibly supplied onto the photosensitive drum 20, resulting in an unintended development (so-called fogging). In other words, by configuring the positional relationship between the cleaning blade 30 and the charging roller 41 as described above, it becomes possible to determine that the cleaning blade 30 has been turned over when the image sensor 21 detects a toner image in a non-image area where a toner image is not supposed to be formed. Similarly, an abnormality can be detected when the charging bias power supply 42 is malfunctioning even if the cleaning blade 30 is not turned over. Such abnormality determination may also be performed by the abnormality determination unit 120.

[0080] (Example of abnormality determination execution process) 7 is a flowchart showing an example of the flow of an abnormality determination process in the image forming apparatus 1 according to an embodiment of the present disclosure. The determination of the presence or absence of an abnormality by the abnormality determination unit 120 will be described with reference to this flowchart.

[0081] 7, when an image formation instruction is output and image forming unit 203 starts an image forming operation, image sensor 21 detects the amount of reflected light (first detection value) from photosensitive drum 20 in a state where no paper P is present between image sensor 21 and photosensitive drum 20. In other words, the image sensor 21 detects the case where no paper P is present at detection position 21a (step S1).

[0082] The abnormality determination unit 120 compares the first detection value with the reflected light threshold value and determines whether the first detection value is equal to or greater than the reflected light threshold value (step S2). If the first detection value is equal to or greater than the reflected light threshold value (YES in step S2), it checks whether an image formation instruction continues (step S3). If an image formation instruction continues (YES in step S3), the process returns to step S1 again; if an image formation instruction continues (NO in step S3), the process ends.

[0083] Furthermore, if the first detection value is not greater than or equal to the reflected light threshold (if the first detection value is smaller than the reflected light threshold) (NO in step S2), the amount of reflected light (second detection value) is detected when the leading edge portion PS of the paper P in the conveying direction F reaches the detection position 21b of the image sensor 21 (step S4).

[0084] The abnormality determination unit 120 compares the second detection value with the first detection value and determines whether the second detection value is equal to or greater than the first detection value (step S5). If the second detection value is equal to or greater than the first detection value (YES in step S5), when image formation on the sheet P for which the second detection value was detected is completed, the image formation operation is stopped (step S7) and the process is terminated, even if an image formation instruction has been continuously output.

[0085] If the second detection value is not equal to or greater than the first detection value (if the second detection value is smaller than the first detection value) (NO in step S5), the display unit 90 displays a message urging the user to clean the image sensor 21 (step S6) and checks whether there is a continuing image formation instruction (step S3). If there is a continuing image formation instruction (YES in step S3), the process returns to step S1 again, and if there is no continuing image formation instruction (NO in step S3), the process ends.

[0086] As described above, the image forming apparatus 1 can detect whether the photosensitive drum 20 is dirty or not, and whether the photosensitive drum 20 is clean but the image sensor 21 is dirty or not, without providing a separate dedicated sensor. This makes it possible to determine whether to stop the image forming operation or not depending on the degree of the problem when a malfunction occurs, and to select and perform an appropriate operation.

[0087] In addition, it is possible to detect the occurrence of reverse curling of the cleaning blade 30, and it is possible to prevent erroneous detection of the occurrence of reverse curling of the cleaning blade 30, and further it is possible to prevent image forming operations from being continued in a state in which reverse curling of the cleaning blade 30 has occurred.

[0088] Note that the image forming device 1 is an example of a multifunction device that can form a multicolor or monochrome image on a recording medium according to image data transmitted from the outside or image data read from a document using a scanner, etc. However, the image forming device of the present disclosure is not limited to this, and for example, the image carrier is not limited to a photosensitive drum 20.

[0089] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the technical gist thereof, and all technical matters included in the technical ideas described in the claims are the subject of the present disclosure. The above-described embodiments are preferred examples, but various modifications can be realized from the disclosed contents, and such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0090] 1. Image forming device 10 Developing device 11 First agitation and conveyance member 12 Second agitation and conveyance member 13 Transport paddle 14 Developer tank 15 Developing roller 18 Toner cartridges 19 Developing bias power supply 20 Photosensitive drum (image carrier) 21 Image Sensor 21a Detection position 21b Detection position 22 Light source 23 Reflected light detection unit 24 Power Source 30 Cleaning Blade 31 Retaining member 40 Charging device 41 Charging roller 42 Charging bias power supply 50 Exposure equipment 60 Transcription device 61 Transfer roller 70 Static eliminator 80 Fixing device 90 Display section 91 Light intensity adjustment section 110 Storage section 120 Abnormality determination section 201 Document transport unit 202 Image reading unit 203 Image forming unit 204 Paper transport path 205 Paper feed section 211 Document tray 223 First platen glass 221 First Scanning Unit 222 Second Scanning Unit 224 Imaging Lens 225 CCD F Conveying direction P Paper PS tip part 226 Second platen glass R1 Rotation direction R2 Rotation direction R3 Rotation direction

Claims

1. an image carrier that can be rotated in a predetermined direction by a drive source; a cleaning blade that contacts the image carrier and removes deposits that have adhered to the image carrier; a charging roller that is in contact with the image carrier downstream of the cleaning blade in the rotation direction of the image carrier and charges the image carrier to a predetermined potential; an exposure device that exposes the image carrier charged by the charging roller to light to form an electrostatic latent image; a developing device that develops the electrostatic latent image with toner to form a toner image on the image carrier; a paper transport path for transporting the paper to a position where the toner image formed on the image carrier is transferred onto the paper; an image sensor that is disposed at a position facing the image carrier across the paper transport path, has a light source that irradiates light toward the image carrier, and detects the amount of light reflected from the image carrier and the paper; an abnormality determination unit that determines whether or not to continue image forming operations based on a first detection value, which is the value of the amount of light reflected from the image carrier detected by the image sensor, and a second detection value, which is the value of the amount of light reflected from the paper detected by the image sensor.

2. 2. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the second detection value is a value of the amount of reflected light from a margin portion at the leading or trailing end of the paper in the transport direction.

3. 2. The image forming apparatus according to claim 1, the charging roller is disposed downstream of the cleaning blade in the rotation direction of the image carrier so as to be adjacent to the cleaning blade, the cleaning blade has one end contacting the image carrier and is held by a holding member over a predetermined length from the other end toward the one end, an image forming apparatus characterized in that a first length L1, which is the length from the end of the holding member on the one end side to the one end of the cleaning blade, is longer than a second length L2, which is the length from the end of the holding member to the contact position of the charging roller with the image carrier.

4. 4. The image forming apparatus according to claim 3, The image forming apparatus further comprises a charging power source that supplies a voltage or current in which an AC current is superimposed on a DC current to the charging roller.

5. 2. The image forming apparatus according to claim 1, Further comprising a storage unit in which a reflected light threshold value is stored in advance, The image forming apparatus, characterized in that the abnormality determination unit determines whether or not to continue the image forming operation by comparing at least one of the first detection value and the second detection value with the reflected light threshold value.

6. 6. The image forming apparatus according to claim 5, Further comprising a display unit, The abnormality determination unit If the first detection value is equal to or greater than the reflected light threshold value, it is determined that there is no abnormality, and the image forming operation is continued. If the first detection value is smaller than the reflected light threshold value and the second detection value is smaller than the first detection value, it is determined that an abnormality has occurred in the image sensor, and the display unit displays a message informing the user that dirt has occurred in the image sensor, and the image forming operation is continued. an image forming apparatus characterized in that, when the first detection value is smaller than the reflected light threshold value and the second detection value is equal to or greater than the first detection value, an abnormality is determined and the image forming operation is stopped.

7. 2. The image forming apparatus according to claim 1, a light emission amount adjusting unit that adjusts the light emission amount of the light source; a storage unit in which calibration values ​​are stored in advance, The image forming apparatus is characterized in that the light emission amount adjustment unit adjusts the light emission amount of the light source by the light emission amount adjustment unit so that the reflected light amount of an area of ​​the image carrier that has not been exposed by the exposure device becomes the calibration value every time a predetermined number of image formations are performed.

Images