JP2016133781A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can detect abnormality in an irradiation part that irradiates a photoreceptor with light on the downstream of a transfer position and the upstream of a charging position and notify a user of the abnormality.SOLUTION: An image forming apparatus 100 includes a control part 103 that detects, during a non-image formation period, a first current flowing in a charging member 12 with a detection part 106 when the surface of a photoreceptor 11 passed through an irradiation position X passes through a charging position Q when an irradiation part 112 is controlled to emit light at a first intensity of light, and detects a second current flowing in the charging member 12 with the detection part 106 when the surface of the photoreceptor 11 passed through the irradiation position X passes the charging position Q when the irradiation part 112 is controlled to emit light at a second intensity of light smaller than the first intensity of light or the irradiation part 112 is controlled not to emit light, and when a difference between the first current and the second current is smaller than a predetermined threshold, executes notification processing of notifying a user of abnormality.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus using an electrophotographic system.

  In an electrophotographic image forming apparatus, a rotatable electrophotographic photosensitive member (photosensitive member) which is generally a drum type is uniformly charged at a charging position and then exposed according to image information. As a result, an electrostatic image (electrostatic latent image) is formed on the photoreceptor. The electrostatic image formed on the photoconductor is developed with toner to form a toner image, and then transferred to the transfer target at the transfer position.

  In such an image forming apparatus, in order to erase the previous electrostatic image on the photosensitive member, a pre-exposure device as an irradiation unit is provided between the transfer position and the charging position in the rotation direction of the photosensitive member, and charging processing is performed. The surface of the previous photoconductor is uniformly exposed (Patent Document 1).

Japanese Patent Laid-Open No. 11-133825

  However, when an abnormality occurs in the pre-exposure device or the drive unit of the pre-exposure device, the exposure amount by the pre-exposure device may differ from the target exposure amount.

  For example, a case where the pre-exposure device does not emit light due to a failure of the pre-exposure device, or a case where the pre-exposure device always emits light due to an abnormality in the drive unit of the pre-exposure device is considered. In such a case, in the former case, an image defect called a ghost image in which an image density unevenness corresponding to the previously formed image occurs in an image to be formed later may occur due to the electrostatic image remaining on the photoreceptor. In the latter case, the life of the photoconductor may be reduced due to an increase in current flowing through the photoconductor due to the charging process.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of detecting an abnormality of an irradiating unit that irradiates light to a photoconductor downstream of a transfer position and upstream of a charging position and reporting the abnormality. It is.

  Another object of the present invention is to detect an abnormality in the irradiation unit that irradiates light to the photoconductor downstream from the transfer position and upstream from the charging position, and sets an operation setting at the time of image formation corresponding to the abnormality. It is an object of the present invention to provide an image forming apparatus that can be changed to the above.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable photosensitive member, a charging member that charges the photosensitive member at a charging position, a power source that applies a DC voltage to the charging member, and the charged photosensitive member by exposing the charged photosensitive member. An image exposure unit for forming an electrostatic image on the photoconductor, a developing unit for developing the electrostatic image on the photoconductor with toner to form a toner image, and a toner image on the photoconductor at the transfer position A transfer unit to be transferred to the body, an irradiation unit for irradiating the photosensitive member with light at an irradiation position downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member, and direct current from the power source to the charging member. A detection unit that detects a direct current that flows through the charging member when a voltage is applied; and the photosensitive that has passed through the irradiation position when the irradiation unit is controlled to emit light with a first light amount during non-image formation. The body surface passes through the charging position Sometimes, the first current flowing through the charging member is detected by the detection unit, and the irradiation unit is controlled to emit light with a second light amount smaller than the first light amount or not to emit light. When the surface of the photoconductor passing through the irradiation position passes through the charging position, a second current flowing through the charging member is detected by the detection unit, and the first current and the second current are detected. And a control unit that executes a notification process for notifying an abnormality when the difference is equal to or smaller than a predetermined threshold value.

  According to another aspect of the present invention, a rotatable photosensitive member, a charging member that charges the photosensitive member at a charging position, a power source that applies a DC voltage to the charging member, and the charged photosensitive member are exposed. An image exposure unit for forming an electrostatic image on the photoconductor, a developing unit for developing the electrostatic image on the photoconductor with toner to form a toner image, and a toner image on the photoconductor at a transfer position. A transfer unit to be transferred to the transfer body, an irradiation unit for irradiating light to the photoconductor at an irradiation position downstream from the transfer position and upstream from the charging position in the rotation direction of the photoconductor, and the power source to the charging member A detection unit that detects a direct current flowing through the charging member when a DC voltage is applied; and the non-image forming unit that has passed through the irradiation position when the irradiation unit is controlled to emit light with a first light amount. The surface of the photoreceptor passes through the charging position. The first current flowing through the charging member is detected by the detection unit, and the irradiation unit is caused to emit light with a second light amount smaller than the first light amount, or the irradiation unit is controlled not to emit light. When the surface of the photosensitive member that has passed through the irradiation position passes through the charging position, a second current flowing through the charging member is detected by the detection unit, and the first current and the second current are detected. An image forming apparatus is provided that includes a control unit that executes a change process for changing an operation setting at the time of image formation when the difference between the two is less than or equal to a predetermined threshold value.

  According to the present invention, it is possible to detect an abnormality in the irradiation unit that irradiates light to the photoconductor downstream from the transfer position and upstream from the charging position and to report the abnormality. In addition, according to the present invention, an abnormality in the irradiation unit that irradiates light to the photoconductor downstream from the transfer position and upstream from the charging position is detected, and the operation setting at the time of image formation is changed to an operation setting corresponding to the abnormality. It becomes possible to do.

1 is a schematic sectional view of an image forming apparatus. It is a typical sectional view of an image formation part. It is a schematic diagram which shows the structure of a pre-exposure apparatus. FIG. 2 is a block diagram illustrating a schematic control mode of a main part of the image forming apparatus. It is a graph which shows the relationship between a pre-exposure current and a charging current. It is a timing chart figure of pre-exposure amount control. It is a flowchart figure of pre-exposure amount control.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. First, the overall configuration and operation of the image forming apparatus 100 according to an embodiment of the present invention will be described. FIG. 1 is a schematic sectional view of an image forming apparatus 100 according to an embodiment of the present invention.

  The image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which first, second, third, and fourth image forming units PY, PM, PC, and PK are arranged along an intermediate transfer belt 31. .

  In the first image forming unit PY, a yellow toner image is formed on the photosensitive drum 11Y, and this toner image is primarily transferred to the intermediate transfer belt 31 at the primary transfer position TY. In the second image forming unit PM, a magenta toner image is formed on the photosensitive drum 11M, and this toner image is primarily transferred to the intermediate transfer belt 31 so as to overlap the yellow toner image at the primary transfer position TM. In the third image forming unit PC, a cyan toner image is formed on the photosensitive drum 11M, and this toner image is primary-transferred onto the intermediate transfer belt 31 so as to be superimposed on the yellow and magenta toner images at the primary transfer position TC. Is done. In the fourth image forming unit PK, a black toner image is formed on the photosensitive drum 11C, and this toner image is superimposed on the yellow, magenta, and cyan toner images at the primary transfer position TK. 31 is primarily transferred. The configuration and operation of each image forming unit PY, PM, PC, PK will be described later.

  The four-color toner images primarily transferred to the intermediate transfer belt 31 are secondarily transferred collectively to a recording material P such as a recording sheet or a plastic sheet at a secondary transfer position N. The recording material P is conveyed to the secondary transfer position N in timing with the toner image on the intermediate transfer belt 31. That is, the separating devices 23a and 23b separate the recording material P drawn from the recording material cassettes 21a and 21b by the pickup rollers 22a and 22b one by one and send them to the registration roller 25. Then, the registration roller 25 receives the recording material P in a stopped state and makes it wait, and sends the recording material P to the secondary transfer position N in synchronization with the toner image on the intermediate transfer belt 31. Further, the toner (secondary transfer residual toner) that is not transferred to the recording material P and remains on the intermediate transfer belt 31 is removed from the intermediate transfer belt 31 by the belt cleaning device 37 and collected. The belt cleaning device 37 slides the cleaning blade on the intermediate transfer belt 31 to remove the secondary transfer residual toner remaining on the surface of the intermediate transfer belt 31 after passing through the secondary transfer position N.

  The recording material P on which the four color toner images are secondarily transferred is heated and pressed by the fixing device 40, and the toner images are fixed (fixed) on the surface thereof. The fixing device 40 presses the pressure roller 41b against the fixing roller 41a provided with the heater 41c to form a heating nip. The recording material P is heated and pressurized in the process of being nipped and conveyed by the heating nip, the toner image is melted, and the full-color image is fixed on the surface. The recording material P is discharged outside the image forming apparatus 100 after the toner image is fixed.

  An intermediate transfer belt 31 formed of an endless belt, which is an example of a transfer target, is supported around a tension roller 33, a drive roller 36, and a counter roller 34. The intermediate transfer belt 31 rotates (circulates) in the direction of arrow R2 in the drawing at a peripheral speed of 300 mm / sec when a driving roller 36 connected to a pulse motor (not shown) is driven to rotate. A secondary transfer roller 38, which is an example of a secondary transfer unit, is disposed at a position facing the opposing roller 34 via the intermediate transfer belt 31. The secondary transfer roller 38 is pressed against the opposing roller 34 via the intermediate transfer belt 31 to form a secondary transfer position N where the intermediate transfer belt 31 and the secondary transfer roller 38 are in contact with each other. The secondary transfer roller 38 is applied with a positive DC voltage from a secondary transfer power supply (high voltage power supply) D2 (FIG. 4), which is an example of a secondary transfer voltage application unit. As a result, the toner image made of negative polarity toner carried on the intermediate transfer belt 31 is secondarily transferred to the recording material P passing through the secondary transfer position N.

  The image forming apparatus 100 includes a control unit 103 that comprehensively controls the operation of the image forming apparatus 100. The control unit 103 includes a control board and a motor drive board for controlling the operation of the mechanism in each unit of the image forming apparatus 100. The image forming apparatus 100 is provided with an environment sensor 105. The environmental sensor 105 is arranged so that the environmental temperature and humidity around the apparatus can be accurately measured without being affected by the fixing device 40 serving as a heat source in the apparatus main body 104 of the image apparatus 100. The control unit 103 performs various controls such as adjustment of operation conditions for image formation based on the output of the environment sensor 105.

2. Image Forming Process Next, the image forming process of the image forming apparatus 100 of this embodiment will be described. The image forming process of the image forming apparatus 100 includes the following pre-multi-rotation process, pre-rotation process, image forming process, and post-rotation process.

  In the pre-multi-rotation process, after the power switch (not shown) of the image forming apparatus 100 is turned on, the photosensitive drum 11 rotates and the image forming apparatus 100 is ready to start image formation (print ready state). Is the period. In the pre-multi-rotation process, operations such as an initial check of the image forming apparatus 100, toner remaining amount detection, density adjustment, and start-up of the fixing device 16 are performed.

  The pre-rotation process is a period in which the drive and output of each unit are turned on and stabilized in order to perform the image forming process after the image formation start instruction is input and before the image forming process is started.

  The image forming process is a period in which an electrostatic image is actually formed on the photoreceptor, and the electrostatic image is developed with toner to form a toner image.

  The post-rotation process is a period for turning off driving and output of each unit.

  The time of image formation refers to the period of the image forming process, and the time of non-image formation is a period other than the time of image formation, and includes the periods of the pre-multi-rotation process, the pre-rotation process, and the post-rotation process. In addition, a series of operations including the pre-rotation process, the image forming process, and the post-rotation process, in which an image is formed on one or a plurality of recording materials P and output from the image forming apparatus 100, which is started by one start instruction. Is also referred to as a “job”.

3. Image Forming Unit Next, the configuration and operation of the image forming unit P will be described. In this embodiment, the configuration and operation of the first, second, third, and fourth image forming units PY, PM, PC, and PK are such that the toner color used in the developing devices 14Y, 14M, 14C, and 14K is yellow. , Substantially different from magenta, cyan and black. Therefore, hereinafter, unless it is particularly necessary to distinguish between the elements, Y, M, C, and K at the end of the symbol indicating that the element is provided for any one of the image forming units is omitted, and the elements are generally summarized. explain. FIG. 2 is a schematic cross-sectional view of the image forming unit P of the present embodiment.

  The image forming unit P includes a photosensitive drum 11. The image forming unit P includes a charging roller 12, an exposure device 13, a developing device 14, a primary transfer roller 35, a pre-exposure device 112, and a cleaning device 15 arranged around the photosensitive drum 11.

  A rotatable drum type (cylindrical) photosensitive drum 11, which is an example of a photosensitive member, has a photosensitive layer having a negative polarity in charge polarity. The photosensitive drum 11 receives driving force from a driving motor (not shown) and rotates in the direction of arrow R1 in the drawing at a process speed of 300 mm / sec.

  The charging roller 12, which is an example of a charging member, is disposed in contact with the photosensitive drum 11 and is pressed toward the photosensitive drum 11. The charging roller 12 rotates following the rotation of the photosensitive drum 11. The charging roller 12 is applied with a DC voltage as a charging voltage (charging bias) from a charging power source (high voltage power source) D3 which is an example of a charging voltage applying unit. As a result, the surface of the photosensitive drum 11 is charged to a uniform negative potential. A charging position Q is a position where the charging roller 12 on the photosensitive drum 11 is charged in the rotation direction of the photosensitive drum 11. Note that in the rotation direction of the photosensitive drum 11, a minute gap between the photosensitive drum 11 and the charging roller 12 is formed on the upstream side and the downstream side of the contact portion between the photosensitive drum 11 and the charging roller 12. The charging roller 12 charges the surface of the photosensitive drum 11 by electric discharge generated at least one of the upstream and downstream gaps. However, here, for the sake of convenience, it may be assumed that the contact portion between the photosensitive drum 11 and the charging roller 12 is the charging position Q.

  An exposure device (laser scanner) 13, which is an example of an image exposure unit (image exposure unit), scans and exposes the surface of the charged photosensitive drum 11 according to image information, and electrostatic images (static images) are formed on the surface of the photosensitive drum 11. Electrostatic latent image) is formed. In other words, the exposure device 13 scans the laser beam, which is ON-OFF modulated based on the scanning line image data obtained by developing the separated color image corresponding to each image forming unit P, with the rotating mirror, thereby charging the photosensitive drum 11. The electrostatic image of the separation color image is written on the surface of the image. In the rotational direction of the photosensitive drum 11, the position exposed by the exposure device 13 on the photosensitive drum 11 is an exposure position U.

  The developing device 14 which is an example of a developing unit (developing unit) uses a two-component developer as a developer. The developing device 14 agitates and charges the two-component developer, carries the developer on the developing sleeve 14s that rotates in the counter direction with respect to the photosensitive drum 11 around the fixed magnetic pole 14j, and sensitizes with the two-component developer on the developing sleeve 14s. The surface of the drum 11 is rubbed. The developing sleeve 14s is applied with an oscillating voltage in which an AC voltage is superimposed on a negative DC voltage as a developing voltage (developing bias) from a developing power source (high voltage power source) D4 which is an example of a developing voltage applying unit. As a result, the negatively charged toner is transferred to the image portion of the electrostatic image on the photosensitive drum 11 having a positive polarity relative to the developing sleeve 14s, and the electrostatic image on the photosensitive drum 11 is developed. Is done. That is, the toner charged to the charged polarity (negative polarity in this embodiment) of the photosensitive member adheres to the exposed portion of the photosensitive member whose absolute value of potential has been lowered by being exposed after being uniformly charged. (Image part exposure, reversal development). The two-component developer is constituted by mixing a magnetic carrier having an average particle diameter of 50 μm, a nonmagnetic toner having an average particle diameter of 6 μm, and a predetermined external additive. In the rotation direction of the photosensitive drum 11, a position facing the developing sleeve 11 on the photosensitive drum 11 (a position where the two-component developer contacts) is a developing position W.

  A primary transfer roller 35, which is an example of a primary transfer unit (primary transfer unit), presses the intermediate transfer belt 31 toward the photosensitive drum 11, and sets a primary transfer position T at which the photosensitive drum 11 and the intermediate transfer belt 31 are in contact with each other. Form. The primary transfer roller 5 is applied with a positive DC voltage from a primary transfer power source (high voltage power source) D1 which is an example of a primary transfer voltage application unit. As a result, the toner image made of negative polarity toner carried on the photosensitive drum 11 is primarily transferred to the intermediate transfer belt 31 passing through the primary transfer position T. The primary transfer position T is a position where the primary transfer on the photosensitive drum 11 is performed in the rotation direction of the photosensitive drum 11.

  The cleaning device 15 which is an example of the photoconductor cleaning means (cleaning unit) employs a counter blade system. The cleaning device 15 includes a cleaning blade 110 that is held in the cleaning container 109 and is in contact with the surface of the photosensitive drum 11, and a screw 111 that conveys toner in the longitudinal direction in the cleaning container 109. Toner remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 31 (primary transfer residual toner) is removed from the photosensitive drum 11 by the cleaning device 15 and collected. The cleaning device 15 slides the cleaning blade 110 against the photosensitive drum 11 to remove the primary transfer residual toner remaining on the surface of the photosensitive drum 11 after passing through the primary transfer position T. The cleaning position Z is a position where the cleaning blade 110 contacts the photosensitive drum 11 in the rotation direction of the photosensitive drum 11.

  The pre-exposure device 112, which is an example of pre-exposure means (irradiation unit), exposes the surface of the photosensitive drum 11 at an irradiation position X downstream from the transfer position T and upstream from the charging position Q in the rotational direction of the photosensitive drum 11. Thus, at least part of the charge on the surface of the photosensitive drum 11 is removed. The pre-exposure device 112 will be described in more detail later.

  Here, in the image forming unit P, the photosensitive drum 11 and the charging roller 12, the developing device 14, and the cleaning device 15 as process means acting on the photosensitive drum 11 can be integrally attached to and detached from the apparatus main body 104. The process cartridge 101 is configured.

4). Pre-exposure device After an image having a high image density is formed, an image defect called a ghost image in which the density unevenness of the pattern of the previous dark image occurs in a portion having a low image density may occur. This phenomenon is also called a transfer memory. That is, the surface potential of the photosensitive drum 11 after the primary transfer changes according to the toner density at the primary transfer position T. Therefore, when the charging process is performed by the charging roller 12, the photosensitive drum 11 cannot be uniformly charged, and a ghost image is generated. In order to suppress such a ghost image, the image forming apparatus 100 according to the present embodiment performs exposure (also referred to as “pre-exposure”) of the photosensitive drum 11 before the charging process using the pre-exposure device 112.

  FIG. 3 is a schematic diagram showing the configuration of the pre-exposure device 112 in this embodiment. In this embodiment, the pre-exposure device 112 is arranged to irradiate the photosensitive drum 11 with light at an irradiation position X downstream of the transfer position T and upstream of the cleaning unit Z in the rotation direction of the photosensitive drum 11. ing.

  In the present embodiment, the pre-exposure device 112 includes an LED lamp 503 that is an example of a light source, and a light guide 501 that is an example of a light irradiation member (light guide unit). Then, light is emitted from the LED lamp 503 arranged at the end of the light guide 501 in the longitudinal direction (arrow C), reflected by the reflecting portion 502 formed on the light guide 501, and leaked from the side surface of the light guide 501. The surface of the photosensitive drum 11 is exposed (arrow D). The light guide 501 is disposed along the longitudinal direction (rotation axis) of the photosensitive drum 11 at a distance of 4 mm from the photosensitive drum 11 so as to irradiate the surface of the photosensitive drum 11 after the transfer process. ing. In this embodiment, the pre-exposure device 112 uniformly exposes the entire image forming area (area where a toner image can be formed) on the photosensitive drum 11. Thereby, the latent image ghost on the photosensitive drum 11 is removed.

  In this embodiment, the LED lamp 503 is attached to the apparatus main body 104. On the other hand, the light guide 501 is attached to the process cartridge 101. For this reason, the light guide 501 is replaced together with the photosensitive drum 11 or the like with the replacement of the process cartridge 101, but the LED lamp 503 is not replaced. The LED lamp 503 is disposed outside the side plate (not shown) of the apparatus main body 104 and outside the irradiation width (region) on the photosensitive drum 11 in the longitudinal direction. The LED lamp 503 makes output light incident on the end surface 506 of the light guide 501 from a direction parallel to the longitudinal direction of the light guide 501. Further, a light shielding measure (not shown) is provided around the LED lamp 503 so that the light from the LED lamp 503 does not unnecessarily expose the end of the photosensitive drum 11 in the longitudinal direction. For the light guide 501, a resin (acrylic, polycarbonate, polystyrene, or the like) with excellent translucency or glass is used.

  In this embodiment, one LED lamp 503 is provided at a position facing one end surface of the light guide 501 in the longitudinal direction. However, when the amount of light is insufficient, the number of light sources may be increased by, for example, providing two LED lamps 503 one by one at positions facing both end faces of the light guide 501 in the longitudinal direction.

  In this embodiment, the light guide 501 is provided on the process cartridge 101 side, but the light guide 501 is not provided on the process cartridge 101 but may be provided on the apparatus main body 104 side. In this case, since the light guide 501 is not provided, the cost of the process cartridge 101 can be reduced.

5. Control Mode FIG. 4 is a block diagram showing a schematic control mode of the main part of the image forming apparatus 100 in this embodiment.

  The control unit 103 determines the output conditions of the charging power source D3, the developing power source D4, the transfer power sources D1 and D2, and the exposure device 13 according to environmental conditions and durability conditions, and outputs them at a predetermined timing in image formation and adjustment operations.

  The output of the charging power source D3 is applied to the charging roller 12, and the DC current (charging current) flowing through the charging roller 12 at that time is also referred to as a DC current measuring circuit (hereinafter simply referred to as “ammeter”) as an example of a detection unit. ) 106, and the detection result is returned to the control unit 103.

  Further, when the control unit 103 sets the pre-exposure amount in the pre-exposure amount control circuit 208, the pre-exposure device 112 emits light with a predetermined light amount. The pre-exposure amount control circuit 208 can control the current (pre-exposure current) supplied to the pre-exposure device 112 in the range of 0 mA (minimum) to 20 mA (maximum) by PWM control. The pre-exposure current amount and the pre-exposure amount have a linear relationship, and the pre-exposure current and the pre-exposure duty (PWM duty) have a linear relationship. That is, the pre-exposure current is 0 mA when the pre-exposure duty is 0%, and the pre-exposure current is 20 mA when the pre-exposure duty is 100%.

  The memory 202 temporarily stores a charging current in pre-exposure amount control (pre-exposure duty control) described later. The memory 202 is an example of a storage unit.

  When an abnormality of the pre-exposure device 112 is detected in the pre-exposure amount control described later, the operation panel 203 displays a warning to notify the user of the abnormality. The operation panel 203 is an example of a notification unit. The determination of abnormality will be described in detail later.

6). Pre-exposure amount control (pre-exposure amount calculation control, abnormality detection control)
FIG. 5 is a graph showing a relationship between a direct current (charging current) flowing through the charging roller 12 when a charging voltage is applied and a pre-exposure current supplied to the pre-exposure device 112. As shown in FIG. 5, as the absolute value of the pre-exposure current is increased, the absolute value of the charging current is increased.

  The charging current changes due to a potential difference between the charging roller 12 and the surface of the photosensitive drum 11 facing the charging roller 12. For example, consider a case where the charging voltage is set to -1200V and the photosensitive drum 11 is uniformly charged to -600V. At this time, when the pre-exposure current is 0 mA, that is, when the pre-exposure device 112 does not emit light, the potential of the surface of the photosensitive drum 11 facing the charging roller 12 after the primary transfer is about −300V. Therefore, 300 V, which is the difference between -300 V and -600 V, is a potential difference between the charging roller 12 and the surface of the photosensitive drum 11 facing the charging roller 12, and the charging current flowing at this time is about 28 μA. On the other hand, when the pre-exposure current is 20 mA, the potential of the surface of the photosensitive drum 11 facing the charging roller 12 after the primary transfer is about 0V. Therefore, 600 V, which is the difference between 0 V and −600 V, is a potential difference between the charging roller 12 and the surface of the photosensitive drum 11 facing the charging roller 12, and the charging current flowing at this time is about 45 μA.

  Thus, when the pre-exposure current is 0 mA or sufficiently small, the potential of the photosensitive drum 11 remains after the primary transfer, so that the above-described ghost image is likely to occur. On the other hand, when the pre-exposure current is increased, the generation of a ghost image can be suppressed. However, as described above, the increase in the charging current leads to a shortened life of the photosensitive drum 11 due to dark decay. Therefore, it is desirable that the pre-exposure current is set to a predetermined value so that the charge is sufficiently removed from the photosensitive drum 11 and the charging current is not excessively increased.

  FIG. 6 is a timing chart of pre-exposure amount control executed in the pre-multi-rotation process in this embodiment. In this embodiment, in the pre-exposure amount control, pre-exposure amount calculation control (pre-exposure current calculation control) for calculating the pre-exposure current in the image forming process is performed. In the present embodiment, in the pre-exposure amount control, abnormality detection control for detecting abnormality of the pre-exposure device 112 is also performed.

  As shown in FIG. 6, after the power is turned on, the control unit 103 shifts to the front multi-rotation process of the image forming apparatus 100 and starts the rotation of the photosensitive drum 11. Thereafter, the control unit 103 starts application of a charging voltage (charging DC voltage), and starts application of a primary transfer voltage (primary transfer DC voltage) after a predetermined time. Thereafter, the control unit 103 uses the ammeter 106 to generate a charging current after the leading end in the moving direction of the region where the charging voltage and the primary transfer voltage are applied after the charging process of the photosensitive drum 11 has reached the charging position Q. Detect (arrow (1)). Thereafter, the control unit 103 sequentially changes the pre-exposure duty to 10%, 20%, and 100%. Then, while the region pre-exposed by each pre-exposure duty of the photosensitive drum 11 passes the charging position Q, the charging current is detected by the ammeter 106 (arrows (2), (3), (4) ).

  Then, the control unit 103 calculates the pre-exposure duty necessary for the image forming process from the charging current at the time of pre-exposure duty 0%, 10%, and 20% by a predetermined calculation. In other words, the target charging current in the image forming process is set in advance, and the pre-exposure duty for obtaining the target charging current is obtained from the relationship between each pre-exposure duty and the detected charging current. The process of determining the pre-exposure current (pre-exposure duty) in the above image forming process is called pre-exposure amount calculation control.

  Further, the control unit 103 calculates a difference between the charging current at the time of the pre-exposure duty 0% and the charging current at the time of the pre-exposure duty 100%. If this difference is 5 μA or less as a predetermined threshold (first threshold), it is determined that the pre-exposure device 112 (pre-exposure amount) is abnormal. Then, the control unit 103 displays a warning on the operation panel 203.

  Further, the controller 103 determines that the pre-exposure device 112 does not emit light if the absolute value of the charging current value at the time of the pre-exposure duty of 100% is 35 μA or less as another predetermined threshold (second threshold). to decide. Then, the control unit 103 reduces the image density in the subsequent image forming process until the state is improved, and makes a setting in which the ghost is unlikely to occur. On the other hand, if the absolute value of the charging current value when the pre-exposure duty is 100% is larger than 35 μA as the second threshold value, the control unit 103 determines that the pre-exposure device 112 is always emitting light. Then, until the state is improved, the control unit 103 sets the setting to prevent the life of the photosensitive drum from being lowered by lowering the charging current by lowering the output of the charging power source D3 in the subsequent image forming process. At this time, the settings such as the development voltage D4 and the transfer voltages D1 and D2 are also corrected according to the output of the charging voltage D3. The process of detecting an abnormality in the above-described pre-exposure apparatus, notifying the abnormality, and changing the operation setting of the image forming process is called abnormality detection control.

  As described above, in this embodiment, the pre-exposure device is based on the charging current when the pre-exposure device 112 does not emit light and the charging current when the maximum light amount is emitted in the pre-multi-rotation process before image formation. It is possible to detect the abnormality 112 and notify the user of the abnormality. In this embodiment, an abnormal state in which the pre-exposure device 112 does not emit light or always emits light can be determined. If it is determined that the pre-exposure device 112 is not emitting light, the setting is changed so as to reduce the image density by reducing the exposure amount of the exposure device 13 in the image forming process in order to suppress the generation of a ghost image. can do. If it is determined that the pre-exposure device 112 always emits light, it can be changed to a setting that reduces the charging current in the image forming process in order to suppress a decrease in the life of the photosensitive drum 1. . Thereby, even when an abnormality is detected in the pre-exposure device 112, the operation of the image forming apparatus 100 can be continued in the mode in which the setting is changed as described above (degeneration mode). That is, according to the present embodiment, even when the pre-exposure device 112 is in an abnormal state, the abnormal state is quickly warned and an image defect or damage to the image forming apparatus 100 is prevented until the abnormal state is repaired. Image formation can be continued with reduced settings.

  In this embodiment, the pre-exposure amount control is performed in the pre-multi-rotation process. This is because a plurality of adjustment controls and start-up controls are performed in the pre-multi-rotation process, and therefore the time of the pre-multi-rotation process hardly changes even if the pre-exposure amount control is performed. However, the present invention is not limited to this, and the pre-exposure amount control can be performed during non-image formation, such as a pre-rotation process. For example, the pre-exposure amount control may be performed in a pre-rotation process for each job, or may be performed in a single pre-rotation process for a plurality of jobs. Further, as in the present embodiment, by performing the pre-exposure amount calculation control and the abnormality detection control in the pre-exposure amount control in synchronization, when performing the pre-exposure amount calculation control that is a control necessary for the image forming process. The abnormality detection control can also be performed with almost no change in control time. Thereby, it is possible to suppress an increase in downtime (period in which an image cannot be output) due to abnormality detection control.

  FIG. 7 is a flowchart of the pre-exposure amount control (pre-exposure amount calculation control and abnormality detection control) described with reference to FIG. Table 1 shows an example of the charging current detected by the pre-exposure amount control and the determination result of the state of the pre-exposure device.

  After the power is turned on, the control unit 103 shifts to the pre-multi-rotation process of the image forming apparatus 100 and starts outputting the charging voltage, the developing voltage, and the transfer voltage (S101). Next, the control unit 103 detects the charging current I1 when the pre-exposure duty is 0% and stores it in the memory 202 (S102). Next, the control unit 103 sets the pre-exposure duty to 10% (S103). Thereafter, similarly, the control unit 103 detects the charging current I2 when the pre-exposure duty is 10%, stores it in the memory 202 (S104), and changes the pre-exposure duty to 20% (S105). Similarly, detection of the charging current I3 when the pre-exposure duty is 20%, storage in the memory 202 (S106), change of the pre-exposure duty to 100% (S107), charging current I4 when the pre-exposure duty is 100% Is detected and stored in the memory 202 (S108). Here, I1, I2, I3, and I4 are assumed to be absolute values of the charging current.

  Thereafter, the control unit 103 calculates a difference (I4-I1) between I4 and I1, and compares this difference with 5 μA as the first threshold (S109). If the difference is larger than 5 μA (YES in S109), the control unit 103 calculates the pre-exposure current (pre-exposure duty) in the image forming process from the values of I1, I2, and I3 (S110). Each high-voltage output is stopped at a predetermined timing in the multi-rotation process (S111). For example, in the cases of (1) and (2) in Table 1, I4-I1 is 20 μA and 15 μA, respectively, and is larger than 5 μA, so that the pre-exposure device 112 is determined to be normal.

  On the other hand, when the difference is 5 μA or less (NO in S109), the control unit 103 next compares the charging current I4 when the pre-exposure duty is 100% with 35 μA as the second threshold (S112). Then, if I4 is larger than 35 μA (YES in S112), the control unit 103 determines that there is a high possibility that the pre-exposure device 112 always emits light with a pre-exposure duty of 100% due to an abnormality in the drive circuit or the like. To do. Then, a correction value for correcting the high voltage output in the image forming process is calculated according to the value of I4 (S113). When the pre-exposure device 112 always emits light with a pre-exposure duty of 100%, the charging current is always high, so that the life of the photosensitive drum 11 is shortened. Therefore, when it is determined that the pre-exposure device 112 always emits light, the set value (absolute value) of the charging voltage is corrected to a lower side so that the charging current becomes a predetermined value. At this time, the set values of the development voltage and the transfer voltage are also corrected in accordance with the value of the charging voltage. For example, in the case of (3) in Table 1, since I4−I1 is 0 μA and I4 is 45 μA, it is determined that the pre-exposure device 112 always emits light.

  Note that a plurality of set values of the charging voltage to be changed at this time may be set so that they can be selected according to the detected I4. For example, a predetermined charging current (representative value) when the pre-exposure duty is 100%. Only one may be set in correspondence with. When setting a plurality of charging voltage setting values to be changed at this time, the charging voltage setting value (absolute value) to be changed can be set to be smaller as the detected I4 is larger.

  Further, when I4 is 35 μA or less (NO in S112), the control unit 103 determines that there is a high possibility that the pre-exposure device 112 is not emitting light due to a drive circuit abnormality, signal line disconnection, LED failure, or the like. To do. Then, since there is a possibility of generating a ghost image, a correction value for reducing the amount of toner of the toner image by reducing the exposure amount of the exposure device 13 in the image forming process (that is, reducing the image density) is calculated ( S115). For example, in the case of (4) in Table 1, since I4−I1 is 0 μA and I4 is 25 μA, it is determined that the pre-exposure device 112 is not emitting light.

  In this embodiment, since the toner image is formed by image portion exposure and reversal development, the toner amount of the toner image is reduced by reducing the exposure amount of the exposure device 13 that exposes the image portion of the electrostatic image. be able to. However, if the toner amount of the toner image (the amount of applied toner per unit area) can be reduced as compared with the case where the pre-exposure device 112 is normal, the method of changing the operation setting of the exposure device 13 is arbitrary and can be used. Possible methods can be used as appropriate. Further, the present invention is not limited to reducing the toner amount of the toner image at all gradation levels. If the ghost image can be suppressed, the toner amount of the toner image is smaller than when the pre-exposure device 112 is normal when compared with at least one gradation level, for example, by reducing the toner amount at the highest density level. For example.

  Further, after performing the processing of S113 or S115, the control unit 103 causes the operation panel 203 to display a warning for notifying the user that the pre-exposure device 112 is abnormal (S114). At this time, in response to the abnormality of the pre-exposure device 112, a display for notifying the user that the image forming process is performed in the low density mode may be performed.

  As described above, in this embodiment, the abnormality of the pre-exposure device 112 is detected in the sequence for detecting the charging current executed in the pre-multi-rotation process and calculating the pre-exposure amount in the image forming process. At this time, the pre-exposure device 112 always emits light based on the charging current when the pre-exposure device 112 does not emit light and the charging current when light is emitted with the maximum light amount (pre-exposure duty 100%). Alternatively, an abnormal state in which no light is emitted is determined. When it is determined that light emission is always performed, the high voltage set value is corrected. When it is determined that light emission is not performed, the exposure amount of the exposure device 13 is corrected, and the operation of the image forming apparatus 100 is continued. As a result, it is possible to continue image formation under a condition that suppresses a sudden decrease in the life of the photosensitive drum 1 due to an abnormality in the pre-exposure device 112 and the occurrence of a ghost image.

  In this embodiment, the process for notifying the abnormality of the pre-exposure device 112 and the process for changing the operation setting at the time of image formation are performed, but only one of them may be performed as desired. In this embodiment, as processing for changing the operation setting during image formation, processing for changing the exposure amount of the exposure apparatus 13 and processing for changing the charging voltage are performed. You may make it perform. Further, when any one of the process of changing the exposure amount of the exposure apparatus 13 and the process of changing the charging voltage is performed, the process and a process of notifying the abnormality of the pre-exposure apparatus 112 can be performed in combination. .

  Further, in this embodiment, in order to detect an abnormality in the pre-exposure device 112, a charging current when the pre-exposure device 112 is not caused to emit light and a charging current when the pre-exposure device 112 is caused to emit light with the maximum light amount are used. It was. However, the abnormality of the pre-exposure device 112 is detected using the charging current when the pre-exposure device 112 emits light with a sufficiently small light amount and the charging current when the pre-exposure device 112 emits light with a sufficiently large light amount. May be. That is, the pre-exposure device 112 is compared with the first threshold value by comparing the difference between the charging currents when the pre-exposure device 112 emits light with the first light amount and the second light amount smaller than the first light amount. If you know that is abnormal. This abnormality includes that the desired light amount of the pre-exposure device 112 cannot be obtained, or that the light is always emitted with a certain amount of light. In addition, by comparing the charging current when the pre-exposure device 112 emits light with the first light amount and the second threshold value, whether the abnormality is in a state where the desired light amount of the pre-exposure device 112 cannot be obtained. It is desirable to be able to determine whether or not the light is always emitted with a certain amount of light. Typically, the first light amount is larger than the light amount of the pre-exposure device 112 during image formation. Further, typically, the second light amount is smaller than the light amount of the pre-exposure device 112 at the time of image formation.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes the irradiation unit 112 that irradiates the photosensitive member 11 with light at the irradiation position X downstream of the transfer position T and upstream of the charging position Q in the rotation direction of the photosensitive member 11. . In addition, the image forming apparatus 100 includes a detection unit 106 that detects a DC current that flows through the charging member 12 when a DC voltage is applied to the charging member 12 from the power supply D3. In addition, the image forming apparatus 100 includes a control unit 103 that executes the following processing. That is, the controller 103 controls the charging member when the surface of the photoconductor 11 that has passed the irradiation position X passes the charging position Q when the irradiation unit 112 is controlled to emit light with the first light amount during non-image formation. 12 is detected by the detection unit 106. At the same time, the control unit 103 detects the second current flowing through the charging member 12 when the surface of the photoconductor 11 that has passed the irradiation position X passes the charging position Q when the irradiation unit 112 is controlled not to emit light. Detected by the unit 106. Here, instead of controlling the irradiation unit 112 not to emit light, the irradiation unit 112 may be controlled to emit light with a second light amount smaller than the first light amount. Then, when the difference between the first current and the second current is equal to or less than a predetermined threshold, the control unit 103 executes a notification process for notifying the abnormality of the irradiation unit 112 or an operation during image formation. A change process for changing the setting is executed, or the notification process and the change process are executed.

  Further, in this embodiment, the control unit 103 controls the image exposure unit at the time of image formation as the change process when the difference is equal to or less than the threshold value and the first current is equal to or less than another predetermined threshold value. The process of changing 13 operation settings is executed. In this case, the operation setting of the image exposure unit 13 at the time of image formation is changed so that the toner amount of the toner image is smaller than when the difference is larger than the threshold value. On the other hand, when the difference is equal to or smaller than the threshold value and the absolute value of the first current is larger than the another threshold value, the control unit 103 performs the change process from the power source D3 during image formation to the charging member 12. The process which changes the voltage applied to is performed. In this case, the absolute value of the voltage applied from the power source D3 to the charging member 12 at the time of image formation is made smaller than when the difference is larger than the threshold value. In this embodiment, the control unit 103 further controls the irradiation unit 112 to emit light with a plurality of different amounts of light during non-image formation, and forms an image based on the detection result of the detection unit 106 for each light amount. The determination process which determines the light quantity of the irradiation part 112 at the time is performed. And the control part 106 performs the process which acquires the said 1st, 2nd electric current synchronizing with the said determination process.

  As described above, according to the present embodiment, it is possible to detect an abnormality of the pre-exposure device 112 and notify the abnormality, or to change the operation setting at the time of image formation to an operation setting corresponding to the abnormality. Become.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  For example, in the above-described embodiment, in the pre-exposure amount control performed at the time of non-image formation, the control for calculating the pre-exposure amount at the time of image formation and the control for detecting abnormality of the irradiation unit are performed in synchronization. As a result, the above-described effects can be obtained. However, if desired, the control for calculating the pre-exposure amount at the time of image formation and the control for detecting abnormality of the irradiation unit may be performed at different timings.

  In the above-described embodiments, the case where the charging member is in contact with the photosensitive member has been described. However, a charging member such as a charging roller does not necessarily need to be in contact with the surface of the photosensitive member that is a member to be charged, and has a gap (gap) of, for example, several tens of μm if discharge is possible in the vicinity. And you may arrange | position close to non-contact. In this way, the charging member is arranged close to the photoconductor, and the photoconductor is discharged by discharge at a proximity portion thereof (corresponding to the gap upstream and downstream of the contact portion between the charging roller and the photoconductor in the above-described embodiment). The present invention can also be applied to a configuration in which charging is performed.

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Charging roller 103 Control part 106 DC current measuring circuit 112 Pre-exposure device

Claims (7)

A rotatable photoreceptor,
A charging member for charging the photosensitive member at a charging position;
A power source for applying a DC voltage to the charging member;
An image exposure unit that exposes the charged photoreceptor to form an electrostatic image on the photoreceptor;
A developing unit for developing the electrostatic image on the photosensitive member with toner to form a toner image;
A transfer unit that transfers the toner image on the photoconductor to a transfer target at a transfer position;
An irradiation unit configured to irradiate the photosensitive member with light at an irradiation position downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member;
A detection unit for detecting a direct current flowing in the charging member when a DC voltage is applied from the power source to the charging member;
A first current that flows through the charging member when the surface of the photosensitive member that has passed through the irradiation position passes through the charging position when the irradiation unit is controlled to emit light with a first light amount during non-image formation. Is detected by the detection unit, and the photosensitive unit that has passed through the irradiation position when the irradiation unit is controlled to emit light with a second light amount smaller than the first light amount or not to emit light. When the detector detects a second current flowing through the charging member when the surface of the body passes through the charging position, and the difference between the first current and the second current is equal to or less than a predetermined threshold value A control unit for performing a notification process for notifying abnormality,
An image forming apparatus comprising: A rotatable photoreceptor,
A charging member for charging the photosensitive member at a charging position;
A power source for applying a DC voltage to the charging member;
An image exposure unit that exposes the charged photoreceptor to form an electrostatic image on the photoreceptor;
A developing unit for developing the electrostatic image on the photosensitive member with toner to form a toner image;
A transfer unit that transfers the toner image on the photoconductor to a transfer target at a transfer position;
An irradiation unit configured to irradiate the photosensitive member with light at an irradiation position downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member;
A detection unit for detecting a direct current flowing in the charging member when a DC voltage is applied from the power source to the charging member;
A first current that flows through the charging member when the surface of the photosensitive member that has passed through the irradiation position passes through the charging position when the irradiation unit is controlled to emit light with a first light amount during non-image formation. Is detected by the detection unit, and the photosensitive unit that has passed through the irradiation position when the irradiation unit is controlled to emit light with a second light amount smaller than the first light amount or not to emit light. When the detector detects a second current flowing through the charging member when the surface of the body passes through the charging position, and the difference between the first current and the second current is equal to or less than a predetermined threshold value A control unit that executes change processing for changing operation settings during image formation;
An image forming apparatus comprising:   When the difference is less than or equal to the threshold and the first current is less than or equal to another predetermined threshold, the control unit sets the operation setting of the image exposure unit during image formation as the change process, The image forming apparatus according to claim 2, wherein a process for changing the toner amount of the toner image to be smaller than when the difference is larger than the threshold value is executed.   When the difference is equal to or less than the threshold and the absolute value of the first current is larger than another predetermined threshold, the control unit changes the power from the power supply during image formation to the charging member. The image forming apparatus according to claim 2, wherein a process of making the absolute value of the voltage to be applied smaller than when the difference is larger than the threshold value is executed.   The first light amount is larger than the light amount of the irradiation unit at the time of image formation, and the second light amount is smaller than the light amount of the irradiation unit at the time of image formation. The image forming apparatus according to one item.   The first light amount is the maximum light amount of the irradiating unit, and the second current is controlled so that the irradiating unit does not emit light, and the surface of the photosensitive member that has passed the irradiation position passes the charging position. 5. The image forming apparatus according to claim 1, wherein the current is a current that flows through the charging member detected by the detection unit when the image forming apparatus is operated. The control unit further controls the irradiation unit to emit light with a plurality of different amounts of light during non-image formation, and the surface of the photoconductor that has passed through the irradiation position when controlled to emit light with each amount of light. The detection unit detects a current flowing through the charging member when passing through the charging position, and executes a determination process for determining the light amount of the irradiation unit during image formation based on the detection result.
The image forming apparatus according to claim 1, wherein the control unit executes a process of detecting the first and second currents in synchronization with the determination process.

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