JP2017191210A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress ghost caused by transfer memory with a simple configuration.SOLUTION: An image forming apparatus 100 comprises: a detection part 23 that detects a DC current flowing in a charging member 2 by the charging member 2 being applied with a charging voltage by a charging power supply D3 in an image forming part P on the downstream side; and an adjustment part 110 that adjusts a transfer voltage in the image forming parts P on the downstream side during an image forming operation on the basis of a result of detection performed by the detection part 23 while an image forming part P on the upstream side forms a predetermined test toner image on a transfer body 10 and a transfer voltage is applied in the image forming part P on the downstream side, when an area of a photoreceptor 1 in contact with the test toner image passes through a charging part a in a transfer part T1.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrophotographic image forming apparatus.

  Conventionally, in an electrophotographic image forming apparatus, a potential difference due to residual charges is generated at a position where a toner image is formed on a photosensitive member, and the effect of the potential difference appears as an image density difference particularly in an image such as a halftone. There is a phenomenon called " As the types of ghosts, there are a positive ghost in which the position corresponding to the previously formed image in the image formed this time is darker than the surroundings, and a negative ghost that is thinner than the surroundings.

  In addition, for example, in the tandem type image forming apparatus for transferring a toner image so as to sequentially overlap a plurality of photosensitive members on an intermediate transfer member, the following types of ghosts are available. In other words, there is a phenomenon called “transfer memory” in which a potential difference is generated on the photosensitive member at the downstream transfer portion due to the toner transferred to the intermediate transfer member at the upstream transfer portion. Cause. A ghost caused by a transfer memory is also referred to as a “multi-order color ghost” because a multi-order toner image in which a plurality of color toners are superimposed on a plurality of upstream transfer sections easily generates a potential difference on a downstream photoconductor. .

  The transfer memory, which is a potential difference on the photoconductor that causes multi-color ghosts, depends on the amount of applied toner of the toner image transferred to the intermediate transfer body at the upstream transfer section, and the more it tends to deteriorate, the more it becomes. is there. For example, when an image forming unit for forming yellow, magenta, cyan, and black toner images is provided, the cyan image after the red solid image is formed on the intermediate transfer member in the upstream image forming unit. The density difference is particularly noticeable in the halftone part.

  Here, the following methods are known as methods for removing the potential difference on the photoconductor that causes ghosts. First, a method is known in which neutralization is performed by irradiating light on the surface of a photoreceptor that has passed through a transfer portion (Patent Document 1). Further, there is known a method of removing an afterimage by applying a voltage having the same polarity as the charging potential of the photosensitive member by an electrode disposed in contact with the photosensitive member that has passed through the transfer portion (Patent Document 2). . Further, a method is known in which at least one of a surface potential difference or a toner adhesion amount difference of a photoconductor is measured to detect the presence / absence of a ghost in a halftone image, and an image forming condition is corrected based on the detection result. (Patent Document 3).

Japanese Patent No. 3331219 JP-A-5-173460 JP 2008-122440 A

  However, in the method of Patent Document 1, there is a concern that light irradiation on the photoconductor is repeated, thereby promoting photodegradation of the photoconductor and shortening the life of the photoconductor.

  Further, in the method of Patent Document 2, since an electrode in contact with the photoconductor is used, there is a possibility that toner that could not be cleaned on the photoconductor adheres to the electrode portion, and potential unevenness of the photoconductor may occur.

  Further, the method of Patent Document 3 requires space and cost for providing a potential sensor for detecting a surface potential difference or a photosensor for detecting the amount of toner adhesion around the photoreceptor.

  Accordingly, an object of the present invention is to provide an image forming apparatus that can suppress a ghost caused by a transfer memory with a simple configuration.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention includes a rotatable photosensitive member, a charging member that charges the photosensitive member with a charging unit, a charging power source that applies a charging voltage for charging to the charging member, and the charging member. An exposure unit that exposes the charged photoreceptor to form an electrostatic image; a developing unit that supplies toner to the electrostatic image formed on the photoreceptor to form a toner image; A movable transfer body to which a toner image is transferred from the body, a transfer power source for applying a transfer voltage for the transfer to the transfer section, and a toner image carried on the transfer body and conveyed to the transfer section Toner image forming means for forming the toner image on the transfer body, and transferring the toner image from the photoconductor to the transfer body so as to be superimposed on the toner image formed on the transfer body by the toner image forming means. Image forming operation to form images In the executable image forming apparatus, a detection unit that detects a direct current flowing through the charging member when the charging voltage is applied to the charging member by the charging power source, and a predetermined image is applied to the transfer body by the toner image forming unit. Based on the detection result of the detection unit when the region of the photoconductor that is in contact with the test toner image in the transfer unit in the state where the transfer voltage is applied passes through the charging unit. And an adjusting unit that adjusts the transfer voltage during the image forming operation.

  According to another aspect of the present invention, a rotatable photosensitive member, a charging member that charges the photosensitive member with a charging unit, a charging power source that applies a charging voltage for charging to the charging member, and the charging member An exposure unit that exposes the photosensitive member charged by the toner to form an electrostatic image; a developing unit that supplies toner to the electrostatic image formed on the photosensitive member to form a toner image; A movable transfer member to which a toner image is transferred from a photosensitive member, a transfer power source for applying a transfer voltage for the transfer to the transfer unit, and a toner carried on the transfer member and conveyed to the transfer unit Toner image forming means for forming an image on the transfer body, and transferring the toner image from the photoconductor to the transfer body so as to be superimposed on the toner image formed on the transfer body by the toner image forming means. Image formation to form an image In the image forming apparatus capable of performing the operation, a detection unit that detects a direct current flowing through the charging member when the charging voltage is applied to the charging member by the charging power source, and the transfer body by the toner image forming unit. A detection result of the detection unit when a region of the photoconductor that is in contact with the test toner image in the transfer unit passes through the charging unit in a state where a predetermined test toner image is formed on the transfer unit and the transfer voltage is applied. And a detection result of the detection unit when a region of the photoconductor that is not in contact with the test toner image in the transfer unit in the state where the transfer voltage is applied passes through the charging unit. And an adjusting unit that adjusts the toner amount of the toner image formed on the transfer body by the toner image forming unit during the image forming operation. .

  According to the present invention, it is possible to suppress a ghost caused by a transfer memory with a simple configuration.

1 is a schematic sectional view of an image forming apparatus. It is a schematic sectional drawing of an image formation part. It is an explanatory diagram of the surface potential of the photoconductor after passing through the transfer portion. 3 is a block diagram illustrating a control mode of a main part of the image forming apparatus. FIG. FIG. 6 is a flowchart of primary transfer bias adjustment control. It is a graph showing the correlation between the surface potential of the photoconductor after passing through the transfer portion and the ghost level. It is a graph showing the correlation between the charging current and the surface potential of the photoreceptor after passing through the transfer portion. It is explanatory drawing of the other example of the surface potential of the photoreceptor after passing a transfer part. It is a block diagram which shows the schematic control aspect of the other example of an image forming apparatus. FIG. 6 is a flowchart of toner applied amount adjustment control. FIG. 6 is a graph showing a correlation between a difference in surface potential of a photoreceptor between a toner part and a non-toner part after passing through a transfer part and a ghost level. FIG. 6 is a graph showing a correlation between a difference in charging current between a toner portion and a non-toner portion and a difference in surface potential of a photoreceptor after passing through a transfer portion between the toner portion and a non-toner portion.

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

[Example 1]
1. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units PY, PM, PC, and PK as a plurality of image forming units (stations). The first, second, third, and fourth image forming units PY, PM, PC, and PK are arranged in a straight line in this order along the rotation direction of the intermediate transfer member 10 to be described later. (Y), magenta (M), cyan (C), and black (K) images are formed.

  It should be noted that elements having similar functions and configurations provided corresponding to the respective image forming units PY, PM, PC, and PK are elements for any color unless particularly distinguished. The elements Y, M, C, and K at the end of the reference numerals are omitted, and the elements will be described collectively. In addition, elements for each color may be distinguished by adding Y, M, C, K to the beginning of the word.

  FIG. 2 is a schematic diagram showing one image forming unit P in detail as a representative. The image forming unit P includes a rotatable drum type (cylindrical) electrophotographic photosensitive member (photosensitive drum) 1. In each image forming unit P, the following devices are sequentially arranged around the photoreceptor 1. First, a charging roller 2 that is a roller-type charging member as a charging unit is disposed. Next, an exposure device (laser scanner) 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-type primary transfer member as a primary transfer unit is disposed. Next, a cleaning device 6 as a cleaning means is arranged.

  The photosensitive member 1 as a member to be charged is an organic photosensitive member in which an organic photosensitive layer 1b and a surface protective layer 1c are sequentially laminated on a conductive support 1a. The surface protective layer contains fluororesin fine particles. The photoreceptor 1 of this embodiment uses aluminum having a thickness of 1 mm as a conductive support, and an outer diameter of 30 mm is formed by laminating a photosensitive layer and a surface protective layer thereon. In addition, the photosensitive member 1 is driven to rotate at a predetermined peripheral speed in the direction of the arrow R1 in the drawing with a driving force of a motor (not shown) serving as a driving unit around the rotation axis.

A charging roller 2 that is a charging rotator is disposed in contact with the photoreceptor 1. The charging roller 2 has a structure in which a conductive metal core 21 serving as a shaft portion is used as a base, and an elastic layer 22 is provided thereon. The conductive metal core 21 can be made of a metal material such as iron, copper, stainless steel, and aluminum. In this embodiment, aluminum is used. In addition, as long as electroconductivity is not lost, this electroconductive core metal 21 may be plated for rust prevention and scratch resistance. The elastic layer 22 is subjected to a polishing process so as to have a so-called crown shape so that the central portion in the longitudinal direction is thick and the both end portions in the longitudinal direction are thin in consideration of bending when the photosensitive member 1 is pressed. ing. This is because both ends in the longitudinal direction of the charging roller 2 are structured to receive a predetermined pressure toward the photosensitive member 1 by the pressure mechanism. In other words, the contact pressure of the charging roller 2 at the central portion in the longitudinal direction with respect to the photosensitive member 1 tends to be smaller than that at both end portions. Further, the elastic layer 22 has an electric resistance so that the volume low efficiency is less than 10 ¹⁰ Ωcm by dispersing carbon black as a conductive agent in rubber (EPDM (ethylene-propylene-diene rubber)) as an elastic material. Regulated and conductive. In addition, as a conductive agent, you may use electronic conductive things, such as a graphite and a conductive metal oxide, and ion conductive systems, such as an alkali metal salt. As the elastic material, natural rubber, SBR, silicone rubber, urethane rubber, epichlorohydrin rubber, synthetic rubber such as IR, BR, NBR and CR, polyamide resin, polyurethane resin, and silicone resin may be used. The charging roller 2 of the present embodiment uses a conductive core bar 21 having a diameter of 8 mm, and the volume resistivity is adjusted to 1 × 10 ⁶ Ωcm by adding a conductive agent to the elastic layer 22. The outer diameter is 14 mm. Further, the charging roller 2 of the present embodiment is pressed toward the photosensitive member 1 so as to have a predetermined contact pressure. The charging roller 2 is driven to rotate as the photosensitive member 1 rotates. The charging roller 2 may be driven using a motor or a gear.

  A charging power source (high voltage power source) D3 as a charging bias applying means is connected to the core metal 21 of the charging roller 2. In this embodiment, an ammeter (current detection circuit) is provided between the charging power source D3 and the charging roller 2 as a detecting unit that detects a current flowing through the charging roller 2 when the charging power source D3 applies a voltage to the charging roller 2. ) 23 is connected. In the present embodiment, during the charging process, the charging power source D3 applies an oscillating voltage obtained by superimposing a DC voltage and an AC voltage to the charging roller 2 as a charging bias (charging voltage). In this embodiment, the charging bias is an oscillating voltage in which a DC voltage of −600 V and an AC voltage having a peak-to-peak voltage of 1700 V are superimposed. In the present embodiment, the ammeter 23 can detect a DC current component (hereinafter also simply referred to as “charging current”) in a time-resolved manner (that is, can detect a DC current component with respect to the time axis). Is. Here, it is desirable that the time resolution is at least 5 msec, particularly 1 msec or less.

  Further, the image forming apparatus 100 includes an intermediate transfer body (intermediate transfer belt) 10 formed of an endless belt so as to face the photoconductors 1 of all the image forming portions P. The intermediate transfer member 10 is an example of a movable transfer member to which a toner image is transferred from the photoreceptor 1. The intermediate transfer member 10 is stretched around a driving roller 11, a tension roller 12, and a secondary transfer counter roller 13 as a plurality of stretching rollers (support rollers). In this embodiment, the intermediate transfer member 10 is formed of a polyimide resin, and the electrical resistance is adjusted by containing an appropriate amount of an antistatic agent such as carbon black. The intermediate transfer body 10 is circulated and rotated (rotated) at a predetermined peripheral speed in the direction of arrow R2 in the figure when driving is transmitted to the drive roller 11.

  The primary transfer rollers 5Y, 5M, 5C, and 5K described above are arranged on the inner peripheral surface side of the intermediate transfer body 10 so as to correspond to the photoreceptors 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is urged (pressed) toward the photoconductor 1 through the intermediate transfer body 10. As a result, the primary transfer roller 5 sandwiches the intermediate transfer member 10 with the photosensitive member 1, and a primary transfer portion (primary transfer nip) that is a contact portion between the photosensitive member 1 and the intermediate transfer member 10. ) T1 is formed. A primary transfer power source D1 as a primary transfer bias applying unit is connected to the primary transfer roller 5. During the primary transfer process, the primary transfer power source D1 applies a DC voltage having a polarity opposite to the charging polarity (normal charging polarity) of the toner during development as a primary transfer bias (primary transfer voltage). Apply to. In this embodiment, a constant voltage method is employed in which the primary transfer bias is controlled at a constant voltage during the primary transfer.

  Further, on the outer peripheral surface side of the intermediate transfer body 10, a secondary transfer roller 14 that is a roller-type secondary transfer member as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 13. The secondary transfer roller 14 is urged (pressed) toward the secondary transfer counter roller 13 via the intermediate transfer body 10. As a result, the secondary transfer roller 14 sandwiches the intermediate transfer body 10 between the secondary transfer counter roller 13 and a secondary transfer section that is a contact portion between the intermediate transfer body 10 and the secondary transfer roller 14. (Secondary transfer nip) T2 is formed. A secondary transfer power source D2 as a secondary transfer bias applying unit is connected to the secondary transfer roller 14. During the secondary transfer process, the secondary transfer power source D2 applies a DC voltage having a polarity opposite to the normal charging polarity of the toner to the secondary transfer roller 14 as a secondary transfer bias (secondary transfer voltage).

  In addition, an intermediate transfer member cleaning device 19 as an intermediate transfer member cleaning unit is disposed at a position facing the tension roller 12 on the outer peripheral surface side of the intermediate transfer member 10.

  Further, the image forming apparatus 100 is provided with a feeding / conveying device that supplies the recording material S such as recording paper to the secondary transfer portion T2, a fixing device 15 that fixes the toner image on the recording material S, and the like.

  At the time of image formation, the surface of the rotating photosensitive member 1 is charged substantially uniformly to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 to which a charging bias is applied. A position charged by the charging roller 2 on the photosensitive member 1 in the rotation direction of the photosensitive member 1 is a charging portion (charging position) a. In the rotational direction of the photoconductor 1, a minute gap between the photoconductor 1 and the charging roller 2 is formed on the upstream side and the downstream side of the contact portion between the photoconductor 1 and the charging roller 2. The charging roller 2 charges the surface of the photosensitive member 1 by a discharge generated at least one of the upstream and downstream gaps. However, for the sake of convenience, the contact portion between the photosensitive member 1 and the charging roller 2 may be assumed to be the charging portion a for the sake of convenience.

  The charged surface of the photoconductor 1 is image-exposed (scanned exposure) with a laser beam L based on image information irradiated by the exposure device 3, and an electrostatic latent image (electrostatic image) is formed on the photoconductor 1. . The electrostatic latent image formed on the photoconductor 1 is developed (visualized) as a toner image with toner as a developer by the developing device 4, and a toner image is formed on the photoconductor 1. The developing device 4 includes a developing roller 41 as a developer carrying member that carries toner and conveys the toner to a portion facing the photoreceptor 1. During the development process, an oscillating voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing roller 41 as a developing bias (developing voltage) from a developing power supply D4 as a developing bias applying unit. In this embodiment, a toner image is formed by image portion exposure and reversal development. In other words, the toner charged to the same polarity as the charged polarity of the photosensitive member 1 adheres to the exposed portion on the photosensitive member 1 where the absolute value of the potential has decreased by being exposed after being charged substantially uniformly.

  The toner image formed on the photosensitive member 1 is transferred (primary transfer) onto the intermediate transfer member 10 by the primary transfer roller 5 to which a primary transfer bias is applied in the primary transfer portion T1. In the rotation direction of the photosensitive member 1, the photosensitive member 1 and the intermediate transfer member 10 are in contact with each other, and the position at which the toner image is transferred from the photosensitive member 1 to the intermediate transfer member 10 is a primary transfer portion (primary transfer position) T1. is there. For example, when a full color image is formed, toner images of each color of yellow, magenta, cyan, and black formed on each photosensitive member 1 are transferred to the intermediate transfer member 10 so as to be superimposed on each primary transfer portion T1. The toner image formed on the intermediate transfer member 10 is transferred (secondary transfer) onto the recording material S by the secondary transfer roller 14 to which a secondary transfer bias is applied in the secondary transfer portion T2. The recording material S is sent out from the cassette 18 which is a storage unit, is conveyed by the conveyance roller pair 17, and is synchronized with the toner image on the intermediate transfer member 10 by the registration roller pair 16, and is conveyed to the secondary transfer unit T2. It will be.

  The recording material S to which the toner image has been transferred is heated and pressurized in the fixing device 15. As a result, the toner image is fixed (melted and fixed) to the recording material S. Thereafter, the recording material S is discharged out of the apparatus.

  Further, the toner (primary transfer residual toner) remaining on the photoreceptor 1 after the primary transfer process is removed from the photoreceptor 1 by the cleaning device 6 and collected. The cleaning device 6 scrapes off the primary transfer residual toner from the surface of the photosensitive member 1 rotated by the cleaning blade 61 and stores it in the collected toner container 62. Further, the toner (secondary transfer residual toner) remaining on the intermediate transfer body 10 after the secondary transfer step is removed from the intermediate transfer body 10 by the intermediate transfer body cleaning device 19 and collected. Thus, a series of image forming processes is completed.

  In this embodiment, each image forming unit P constitutes a toner image forming unit that forms a toner image on the intermediate transfer member 10. In this embodiment, the image forming apparatus 100 performs the intermediate transfer from the photoreceptor 1 of the downstream image forming unit P so as to be superimposed on the toner image formed on the intermediate transfer member 10 by the upstream image forming unit P. An image forming operation for transferring the toner image to the body 10 to form an image can be executed.

2. Next, the transfer memory will be described. Here, the fact that each of the plurality of image forming portions P is disposed relatively upstream or downstream in the rotation direction (movement direction) of the intermediate transfer member 10 is simply “upstream”. , Sometimes called “downstream”.

  A toner image is formed on the photosensitive member 1 by electrically attaching a predetermined amount of toner based on the potential of the electrostatic latent image formed by image exposure. The toner image is electrically transferred to the intermediate transfer body 10 by the action of a transfer current supplied by a transfer voltage applied to the primary transfer portion T1. At this time, an electrostatic latent image remains even after the transfer process, thereby causing a potential difference on the photosensitive member 1 and generating a ghost. Here, even when the electrostatic latent image is not formed by one image forming unit P, the toner image formed by the image forming unit P upstream of the one image forming unit P is the one image forming unit. When passing through the primary transfer portion T1 of P, a potential difference can be generated on the photoreceptor 1 of the one image forming portion P. This is a portion where toner is present when the toner image formed by the upstream image forming portion P passes through the primary transfer portion T1 of the downstream image forming portion P (hereinafter also referred to as “toner portion”). This phenomenon occurs because there is a difference in the current flowing from the primary transfer roller 5 to the photoreceptor 1 of the downstream image forming unit P between the toner-free portion (hereinafter also referred to as “non-toner portion”). . As described above, this phenomenon is called “transfer memory” and causes multi-color ghosts.

  FIG. 3 shows the surface potential of the photoreceptor 1 of the downstream image forming unit P after the toner image from the upstream image forming unit P has passed through the primary transfer unit T1 of the downstream image forming unit P. This is a schematic representation. The surface potential of the photosensitive member 1 represented by a diagram in FIG. 3 is a positive potential on the upper side and a negative potential on the lower side.

  Generally, in the normal use of the image forming apparatus 100, the current flowing from the primary transfer roller 5 to the photosensitive member 1 is designed so that no ghost is generated by the transfer memory. However, for example, when the electrical resistance of the primary transfer roller 5 increases more than expected, the current flowing from the primary transfer roller 5 to the surface of the photoreceptor 1 may be insufficient. Therefore, the surface potential of the photoreceptor 1 after passing through the primary transfer portion T1 and before passing through the charging portion a (hereinafter also simply referred to as “after passing through the transfer portion”) and the voltage applied to the charging roller 2 And the potential difference (hereinafter also simply referred to as “contrast”) cannot be maintained. As a result, the potential difference on the photosensitive member 1 generated between the toner portion and the non-toner portion cannot be eliminated, and a transfer memory may be formed, which may cause a ghost.

  Here, the following experiment was conducted. The red solid image formed by the YM image forming portions PY and PM is sent to the primary transfer portion T1 of the C image forming portion PC that only performs the charging process of the photosensitive member 1 and does not form the electrostatic latent image. Then, the surface potential of the region (toner portion, red solid image portion) in contact with the red solid image at the primary transfer portion T1 on the photoreceptor 1 of the C image forming portion PC after passing through the transfer portion is measured by a surface potentiometer. . Next, the surface potential after passing through the transfer portion of the non-toner portion in the photoreceptor 1 of the C image forming portion PC when image formation is not performed in the YM image forming portions PY and PM is measured. The red solid image was formed over the entire image forming area (area where a toner image can be formed) in the longitudinal direction (rotation axis direction) of the photoreceptor 1. In this embodiment, the test toner image for detecting the charging current is a solid image formed over the entire image forming area in the longitudinal direction of the photoreceptor 1 unless otherwise specified. The surface potential meter is provided downstream of the primary transfer portion T1 and upstream of the charging portion a in the rotation direction of the photosensitive member 1 for the experiment. It does not mean that control using a surface electrometer is performed.

  For example, when the photosensitive member 1 of the C image forming unit PC is charged almost uniformly to -600 V by the charging roller 2, the surface potential after passing through the transfer portion of the red solid image portion on the photosensitive member 1 is -200 V, and the non-toner portion The surface potential after passing through the transfer portion was −150V. Thus, it can be seen that due to the images formed by the upstream YM image forming portions PY and PM, a potential difference causing a ghost occurs in the downstream C image forming portion PC. At this time, the total current in the longitudinal direction of the photosensitive member 1 flowing from the primary transfer roller 5 to the photosensitive member 1 in the C image forming unit PC (herein, simply referred to as “transfer current”) is about 25 μA. In this case, no ghost occurred on the next image even when the potential difference occurred. This is presumably because a sufficient contrast is maintained between the surface potential of the photosensitive member 1 after passing through the transfer portion and the voltage applied to the charging roller 2 (FIG. 3B).

  A similar experiment was performed by adjusting the transfer current flowing from the primary transfer roller 5 to the photoreceptor 1 in the C image forming unit PC to about 15 μA. In this case, the surface potential after passing through the transfer portion of the red solid image portion on the photoreceptor 1 of the C image forming portion PC was −400 V, and the surface potential after passing through the transfer portion of the non-toner portion was −350 V. The images sent from the upstream YM image forming portions PY and PM to the primary transfer portion T1 of the C image forming portion PC are the same as in the above-described experiment. The difference in surface potential after passing through the transfer portion is the same 50V. However, a ghost occurred in the next image. This is presumably because sufficient contrast is not maintained between the surface potential of the photosensitive member 1 after passing through the transfer portion and the voltage applied to the charging roller 2 (FIG. 3A).

  Next, the relationship between the charging current (charging DC current) and the ghost will be described. When the region of the photoreceptor 1 that is substantially uniformly charged to the charging potential Vd by the charging roller 2 passes through the primary transfer portion T1, it receives a discharge from the primary transfer roller 5 and becomes the surface potential Vt after passing through the transfer portion. . In the above-described experiment, Vt1 = −200 V when the transfer current is 25 μA, and Vt2 = −400 V when the transfer current is 15 μA. With this potential maintained, the contrast ΔV when the photoreceptor 1 is again charged almost uniformly to the charging potential Vd by the charging roller 2 is ΔV = | Vd−Vt |.

The value of the charging current Idc is expressed by the following formula 1. In the following formula 1, ΔV [V] (in the above-described experiment, ΔV = | Vd−Vti |, i = 1, 2) is the contrast during the charging process. In the following formula 1, L [m] is the length in the longitudinal direction of the photoreceptor (represented by the length of the contact portion between the photoreceptor 1 and the charging roller 2 in the longitudinal direction of the photoreceptor 1), v [m / s] is the peripheral speed of the photoconductor 1, d [m] is the film thickness of the photoconductor 1, ε is the relative dielectric constant, and ε0 is the vacuum dielectric constant.
Idc = ε × ε0 × L × v × ΔV / d (Formula 1)

Here, the length L and the peripheral speed v in the longitudinal direction of the photosensitive member 1 are predetermined values, and the film thickness d of the photosensitive member 1 can be calculated almost accurately from, for example, charging time and traveling time. From the above equation 1, the relationship between the charging current Idc (1) when the transfer current is 25 μA and the charging current Idc (2) when the transfer current is 15 μA in the above experiment is
Idc (1) = 2 × Idc (2)
It can be expressed as.

  As described above, when the transfer current changes, the fluctuation of the surface potential after passing the transfer portion of the red solid image portion on the photoreceptor 1 can be predicted by detecting the charging current. There is a proportional relationship between the charging current Idc and the contrast ΔV. Therefore, a decrease in the charging current Idc means that the contrast ΔV has decreased. Further, since the charging potential Vd of the photosensitive member 1 is constant, the decrease in the contrast ΔV means that the absolute value of the surface potential Vti after passing through the transfer portion is increased. When the absolute value of the surface potential Vti after passing through the transfer portion exceeds a certain potential, the minimum required contrast ΔV cannot be maintained, and a ghost is generated by the transfer memory (see FIG. 3A). In this embodiment, the constant potential at which this ghost is generated is set as the ghost generation threshold Vg.

  In this embodiment, the surface potential Vti of the photosensitive member 1 after passing through the transfer portion is controlled by feeding back the detection result of the charging current to the primary transfer bias applied to the primary transfer roller 5. Thereby, it becomes possible to suppress the ghost by maintaining the necessary contrast ΔV.

3. In the present embodiment, a test toner image is formed in the upstream image forming portion P, and the region (toner portion) of the photoreceptor 1 in the downstream image forming portion P that is in contact with the toner image is formed in this embodiment. The charging current when passing through the charging part a is detected. When the charging current determined by the contrast between the surface potential of the photosensitive member 1 after passing through the transfer portion and the potential of the charging roller 2 is small, the potential convergence during the charging process is reduced, and the toner portion and the non-toner portion that cause ghosting. The surface potential difference between and cannot be leveled, and ghosts may occur. Therefore, in this embodiment, in that case, the absolute value of the primary transfer bias of the downstream image forming portion P is adjusted to be increased, the transfer current is increased, and the absolute value of the surface potential after passing through the transfer portion is increased. Try to reduce the value. Thereby, it is possible to suppress the occurrence of a ghost caused by the transfer memory in the downstream image forming portion P during the subsequent image forming operation.

  In this embodiment, when the region (toner portion) of the photoreceptor 1 that has contacted the test toner image is charged in the primary transfer portion T1 (when the toner portion passes through the charging portion a). Using the charging current detected by the ammeter 23, the surface potential after passing through the transfer portion is obtained based on the relational expression described above. Then, when the absolute value of the surface potential after passing through the transfer portion exceeds the absolute value of the ghost generation threshold value Vg, the absolute value of the primary transfer bias is adjusted to be increased. However, the present invention is not limited to this. If the charging current detected by the ammeter 23 becomes smaller than a predetermined threshold value when the toner portion is charged, the absolute value of the primary transfer bias is not limited. What is necessary is just to adjust so that a value may be enlarged.

  Further, the primary transfer bias may be changed according to the environment or the use state of transfer means such as the intermediate transfer member 10 and the primary transfer roller 5 (information on the usage amount from the initial use). When the transfer current changes as described above, the charging current changes. Therefore, the threshold value can be set (single or plural) according to the setting of the primary transfer bias in the detection operation of forming the test toner image and detecting the charging current. Further, as can be seen from the above relational expression, when the charging potential of the photosensitive member 1 changes, the charging current changes. Therefore, the threshold value can be set (single or plural) according to the setting of the charging potential in the detection operation of forming the test toner image and detecting the charging current.

  Further, the degree of increasing the absolute value of the primary transfer bias can be set as appropriate so that the ghost caused by the transfer memory can be sufficiently suppressed. Further, in this embodiment, in order to suppress a ghost caused by the transfer memory, which is likely to occur when the electrical resistance of the primary transfer roller 5 rises beyond an allowable value, for example, the absolute value of the primary transfer bias is set with the threshold as a boundary. Change the value from a relatively small value before adjustment to a relatively large value. However, the present invention is not limited to this, and a plurality of threshold values are provided in stages, and each time the detected absolute value of the surface potential becomes larger than each threshold value (or every time the detected current value becomes smaller than each threshold value). B) The absolute value of the primary transfer bias may be increased stepwise. Further, the absolute value of the desired primary transfer bias with respect to the absolute value (or current value) of the surface potential is examined in advance and stored as a table or the like, and 1 according to the detected absolute value (or current value) of the surface potential. The absolute value of the next transfer bias may be continuously changed.

4). Control Mode FIG. 4 is a block diagram showing a schematic control mode of the main part of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 is provided with a control unit 110 as a control unit that comprehensively controls each unit of the image forming apparatus 100. The control unit 110 includes a CPU 111 that is a central element that performs arithmetic processing, a ROM 112 that is a storage element (memory) as a storage unit, a RAM 113, and the like. The RAM 113 stores sensor detection results, calculation results, and the like, and the ROM 112 stores control programs, data tables obtained in advance, and the like. In relation to the present embodiment, the control unit 110 is connected to an ammeter (current detection circuit) 23, a primary transfer bias control circuit (drive circuit) 120, and the like. Then, the control unit 110 controls the primary transfer bias control circuit 120 to adjust the absolute value of the primary transfer bias based on the detection result of the charging current by the ammeter 23 (primary transfer bias adjustment control). I do. The primary transfer bias control circuit 120 performs constant voltage control on the primary transfer bias applied to the primary transfer roller 5 from the primary transfer power source D1 in the primary transfer process with the target voltage set by the control of the control unit 110. . In this embodiment, the control unit 110 has a function of a calculation unit (ghost detection unit using a transfer memory) that calculates the surface potential of the photosensitive member 1 after passing through the transfer unit, and performs primary transfer bias adjustment control. An adjustment unit is executed to adjust the primary transfer bias.

  Here, the image forming apparatus 100 performs a “job” that is a series of image output operations for forming and outputting an image on a single or a plurality of recording materials S, which is started by one start instruction. In general, a job includes an image forming process (printing process), a pre-rotating process, a paper-to-paper process when images are formed on a plurality of recording materials S, and a post-rotating process. The image forming process is a period for forming an electrostatic latent image, forming a toner image, and transferring a toner image of an image that is actually formed and output on the recording material S. Say. The pre-rotation process is a period for performing a preparatory operation before the image forming process from when the start instruction is input until the actual image formation is started. The inter-sheet process is a period corresponding to the interval between the recording material S and the recording material S when performing continuous image formation in which images are continuously formed on a plurality of recording materials S. The post-rotation process is a period during which an organizing operation (preparation operation) after the image forming process is performed. The non-image forming period is a period other than the image forming time, and is a preparatory operation at the time of turning on the power of the image forming apparatus 100 or returning from the sleep state. This is included during the previous multi-rotation process.

  In this embodiment, the primary transfer bias adjustment control is performed in the post-rotation process and the inter-sheet process of the job every time the number of images formed as information regarding the usage amount of the primary transfer roller 5 exceeds a predetermined threshold. However, the present invention is not limited to this, and the primary transfer bias adjustment control can be performed at any timing during non-image formation.

5. Primary Transfer Bias Adjustment Control Next, primary transfer bias adjustment control (ghost detection operation) in this embodiment will be described. FIG. 5 is a flowchart showing a procedure of primary transfer bias adjustment control in the present embodiment. Here, as an example, a procedure of primary transfer bias adjustment control in the C image forming unit PC will be described.

  For example, when the post-rotation process at the end of the job is started (S101), the CPU 111 determines whether or not 100 sheets (for example, A4 size converted value) or more images have been formed from the previous primary transfer bias adjustment control. (S102).

  If it is determined in S102 that the number is 100 or more, the CPU 111 starts an operation of forming a test toner image and detecting a charging current (S103). Here, a red solid image is formed on the intermediate transfer body 10 as a test toner image by the YM image forming portions PY and PM, and this red solid image is sent to the primary transfer portion T1 of the C image forming portion PC. Then, in the C image forming unit PC, when the primary transfer unit T1 on the photosensitive member 1 is charged with a region (toner unit) in contact with the red solid image (when the toner unit passes through the charging unit a). ) Is detected by the ammeter 23.

  Next, the CPU 111 calculates the surface potential Vti after passing through the transfer portion based on the charging current Idc (n) detected by the ammeter 23 and stores it in the RAM 113 (S104).

  Next, the CPU 111 compares the calculated absolute value of the surface potential Vti after passing through the transfer portion with the absolute value of the ghost occurrence threshold Vg stored in advance in the ROM 112 (S105). If | Vti |> | Vg | is determined, feedback is instructed to the primary transfer bias control circuit 120 (S106). Specifically, in this embodiment, the setting of the primary transfer bias in the primary transfer bias control circuit 120 is changed so that the absolute value of the primary transfer bias is larger than that before adjustment. Thereafter, when the predetermined post-rotation process is completed, the job is terminated (S107).

  On the other hand, if it is determined in S102 that the number is less than 100, the CPU 111 does not perform the test toner image formation operation or the charging current detection operation, and ends the job when the predetermined post-rotation process operation is completed (S107). . If it is determined in step S105 that | Vti | ≦ | Vg |, the CPU 111 ends the job when the predetermined post-rotation operation is completed without adjusting the primary transfer bias (S107).

  When the primary transfer bias adjustment control is performed in the inter-sheet process, the image forming operation of the job is continuously performed after the primary transfer bias is adjusted (or after it is decided not to adjust).

  The case where a red solid image is formed as a test toner image and the primary transfer bias in the C image forming unit PC is adjusted has been described above as an example. In the image forming apparatus 100 of the present embodiment, the ghost due to the transfer memory is likely to occur in the K image forming unit PK as well as in the C image forming unit PC. Therefore, in this embodiment, the primary transfer bias adjustment control is performed for the K image forming unit PC in the same manner as the pre-exposure amount adjustment control of the C image forming unit PC. At this time, in this embodiment, as with the C image forming unit PC, a red solid image (even if formed for the pre-exposure amount adjustment control of the C image forming unit PC) is newly formed as a test toner image. May be used). However, the present invention is not limited to this, and a green solid image or a blue solid image may be used as the test toner image. Further, since the increase in the absolute value of the surface potential after passing through the transfer portion of the photosensitive member 1 is slight compared to the secondary color image, ghosts are unlikely to occur, but a single color image such as yellow, magenta, or cyan is used for the test toner image. May be used to detect the charging current in the same manner as described above in the image forming portion P on the downstream side. That is, the primary transfer bias adjustment control of this embodiment is provided corresponding to the photoreceptor 1 downstream of the most upstream photoreceptor 1 in the rotation direction of the intermediate transfer body 10 among the plurality of photoreceptors 1. The present invention can be applied to the adjustment of the primary transfer bias applied to the primary transfer roller 5.

  In addition, when a solid (particularly multi-color solid) image is formed by the upstream image forming unit P, a ghost due to the transfer memory is likely to occur in the downstream image forming unit P. As the toner image, a solid image (a toner image having the highest density level) is preferable. However, the toner loading amount of the test toner image may be a predetermined amount or more that may cause a ghost by the transfer memory, and may be a halftone image if desired.

6). Effect FIG. 6 is a graph showing the correlation between the surface potential of the toner portion (red solid image portion) after passing through the transfer portion and the ghost level in the photoreceptor 1 of the C image forming portion PC. FIG. 7 is a graph showing the correlation between the charging current detected by the ammeter 23 and the surface potential of the photoreceptor 1 after passing through the transfer portion.

  From the relationship shown in FIGS. 6 and 7 derived from the experiment, the surface potential Vti of the photoreceptor 1 after passing through the transfer portion exceeds the ghost occurrence threshold Vg because the charging current becomes smaller than a certain threshold, and the transfer memory It can be seen that ghosts are more likely to occur. In contrast, in this embodiment, the level of ghost generation by the transfer memory is predicted by detecting the charging current and fed back to the primary transfer bias applied to the primary transfer roller 5. Specifically, when the charging current becomes smaller than a predetermined threshold (the absolute value of the surface potential after passing through the transfer portion based on the charging current may exceed the predetermined threshold), the absolute value of the primary transfer bias Adjust to increase the value. As a result, it is possible to suppress the occurrence of ghosts due to the transfer memory.

  As described above, according to the present embodiment, the deterioration of the photoconductor 1 can be achieved with a simple configuration advantageous in terms of space and cost without providing a detection means such as a surface electrometer in the vicinity of the photoconductor 1. It is possible to suppress the ghost caused by the transfer memory.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, in the present embodiment, elements having the same or corresponding functions or configurations as those of the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted.

In Example 1, a test toner image is formed in the upstream image forming portion P, and the charging current when the toner portion of the photoreceptor 1 passes through the charging portion a is detected in the downstream image forming portion P. The primary transfer bias of the downstream image forming portion P was adjusted based on the absolute value of the current. On the other hand, in this embodiment, the current amount of the toner portion and the non-toner portion is detected, and based on the difference between them, the toner amount of the toner image of the upstream image forming portion P (specifically, the maximum loading amount). The amount [mg / cm ² ]). This will be described in more detail below.

1. Transfer Memory As described in the first embodiment, even in the image forming portion P that does not form an electrostatic latent image, transfer is performed between a portion where toner is present and a portion where toner is not formed by the toner image formed in the upstream image forming portion P. A difference in current may occur, and a ghost due to the transfer memory may occur. At this time, the degree of occurrence of the ghost by the transfer memory may vary depending on the toner loading amount of the toner image formed in the upstream image forming portion P passing through the primary transfer portion T1 of the downstream image forming portion P. . Specifically, when an amount of toner larger than expected due to some reason such as deterioration of the photoreceptor 1 passes through the downstream primary transfer portion T1, the toner portion and the non-toner portion in the downstream image forming portion P. And the difference in the amount of current flowing from the primary transfer roller 5 to the photosensitive member 1 increases. For this reason, the difference in surface potential between the toner part and the non-toner part of the photosensitive member 1 after passing through the transfer part becomes excessive, and the potential difference generated between the toner part and the non-toner part during the charging process cannot be eliminated. May cause.

  FIG. 8 shows the surface potential of the photoreceptor 1 of the downstream image forming portion P after the toner image from the upstream image forming portion P passes through the primary transfer portion T1 of the downstream image forming portion P. This is a schematic representation. The surface potential of the photosensitive member 1 represented by a diagram in FIG.

  Here, in the same manner as in Example 1, the following experiment was performed to measure the surface potential after passing through the transfer portion of the photoreceptor 1 using a surface potential meter. The primary transfer portion T1 of the C image forming portion PC in which the red solid image formed by the YM image forming portions PY and PM under normal use conditions is only subjected to the charging process of the photoreceptor 1 and the electrostatic latent image is not formed. Send to. Then, in the photoreceptor 1 of the C image forming unit PC, the region that has contacted the red solid image (toner portion, red solid image portion) in the primary transfer portion T1 and the region that has not contacted (non-toner portion) pass through the transfer portion. The subsequent surface potential is measured with a surface potentiometer.

  For example, when the photosensitive member 1 of the C image forming unit PC is charged almost uniformly to -600 V by the charging roller 2, the surface potential after passing through the transfer portion of the red solid image portion on the photosensitive member 1 is -200 V, and the non-toner portion The surface potential after passing through the transfer portion was −150V. Thus, it can be seen that due to the images formed by the upstream YM image forming portions PY and PM, a potential difference causing a ghost occurs in the downstream C image forming portion PC. At this time, the transfer current flowing from the primary transfer roller 5 to the photoreceptor 1 in the C image forming unit PC is about 25 μA. In this case, no ghost occurred on the next image even when the potential difference occurred. This is considered to be because the potential difference between the toner portion and the non-toner portion after passing through the transfer portion is sufficiently small, and the potential difference can be sufficiently eliminated by passing through the charging roller 2 (FIG. 8B).

  In a similar experiment, the toner application of the red solid image formed by the upstream YM image forming units PY and PM while the transfer current flowing from the primary transfer roller 5 to the photosensitive member 1 is maintained at 25 μA in the C image forming unit PC. The amount was increased to 1.2 times the normal amount. In this case, the surface potential after passing through the transfer portion of the red solid image portion on the photoreceptor 1 of the C image forming portion PC was −300 V, and the surface potential after passing through the transfer portion of the non-toner portion was −150 V. Since the transfer current flowing from the primary transfer roller 5 to the photosensitive member 1 in the C image forming unit PC is the same as the above-described experiment (normal amount of toner on the solid image), the surface potential of the non-toner portion after passing through the transfer portion Maintains the same −150 V as in the above experiment. However, a ghost occurred in the next image. This is presumably because the step of the surface potential of the photoreceptor 1 after passing through the transfer portion between the toner portion and the non-toner portion becomes large, and this cannot be solved by the charging process with the charging roller 2.

Next, the relationship between the difference in charging current (charging DC current) and the ghost will be described. When the region of the photoreceptor 1 that is substantially uniformly charged to the charging potential Vd by the charging roller 2 passes through the primary transfer portion T1, it receives a discharge from the primary transfer roller 5 and becomes the surface potential Vt after passing through the transfer portion. . In the above experiment, when the transfer current is 25 μA, the non-toner portion Vt3 = −150V, the normal toner amount Vt4 = −200, and the normal toner amount Vt5 = −300V which is 1.2 times the normal toner amount. is there. With this potential maintained, the contrast ΔV when the photoreceptor 1 is again charged almost uniformly to the charging potential Vd by the charging roller 2 is ΔV = | Vd−Vt |. The contrast ΔV in the above experiment is
ΔV1 = | Vd−Vt3 | (non-toner portion)
ΔV2 = | Vd−Vt4 | (a toner portion having a normal toner amount)
ΔV3 = | Vd−Vt5 | (toner portion having a toner amount 1.2 times the normal amount)
It becomes.

Therefore, the difference ΔVc1 in contrast between the toner portion and the non-toner portion with the normal toner loading amount, and the contrast difference ΔVc2 between the toner portion and the non-toner portion with the toner loading amount 1.2 times the normal toner amount are respectively It can be expressed as
ΔVc1 = | ΔV1−ΔV2 |
ΔVc2 = | ΔV1−ΔV3 |

Further, based on the relationship of Formula 1 described in the first embodiment, the charging current difference Idc (3) between the toner portion of the normal toner loading amount and the non-toner portion and the toner loading of 1.2 times the normal toner loading amount. The relationship between the charging current difference Idc (4) between the toner portion and the non-toner portion is expressed as follows.
1.2 Idc (3) = Idc (4)

  As described above, when the amount of applied toner of the toner image formed in the upstream image forming unit P changes, the fluctuation of the surface potential of the photoreceptor 1 after passing through the transfer unit of the downstream image forming unit P is determined. It is possible to predict by detecting the charging current. There is a proportional relationship between the difference in charging current between the toner portion and the non-toner portion and the difference ΔVc in contrast ΔV between the toner portion and the non-toner portion. Therefore, an increase in the charging current difference means that the difference ΔVc in contrast ΔV has increased. When the difference ΔVc of the contrast ΔV exceeds a certain potential difference ΔVcg, the photosensitive member 1 cannot be uniformly charged by the charging roller 2 and a ghost is generated by the transfer memory (FIG. 8A). In this embodiment, the constant potential difference ΔVcg at which this ghost occurs is set as the ghost generation threshold.

  In this embodiment, the detection result of the charging current in the downstream image forming unit P is fed back to the toner application amount of the toner image formed in the upstream image forming unit P, thereby the downstream image forming unit P. The difference ΔVc of the contrast ΔV is controlled. Accordingly, it is possible to suppress the ghost by maintaining the difference ΔVc between the acceptable toner part and non-toner part contrast ΔV.

2. In this embodiment, a test toner image is formed in the upstream image forming portion P, and the region (toner portion) of the photoreceptor 1 of the downstream image forming portion P that is in contact with the toner image The charging current when the non-contact area (non-toner part) passes through the charging part a is detected. When the difference in charging current between the toner portion and the non-toner portion is large, the difference in surface potential between the toner portion and the non-toner portion of the photoreceptor 1 after passing through the transfer portion is also large, and the potential difference is charged in the charging step. Sometimes it cannot be leveled and ghosts may occur. Therefore, in this embodiment, in this case, the amount of applied toner of the toner image formed in the upstream image forming unit P is adjusted to be small, and the photosensitive member after passing through the transfer unit in the downstream image forming unit P. The difference in surface potential between the toner portion 1 and the non-toner portion is reduced. Specifically, the exposure amount (the amount of light per unit time irradiated on the surface (per unit area) of the photoreceptor) when the electrostatic latent image is formed by the exposure device 3 of the upstream image forming unit P is reduced. Thus, the maximum loading amount [mg / cm ² ] is adjusted to be small. Thereby, in the subsequent image formation, it is possible to suppress the occurrence of ghost due to the transfer memory in the downstream image forming portion P.

  In this embodiment, when the difference ΔVc of the contrast ΔV in the downstream image forming unit P exceeds the ghost occurrence threshold value ΔVcg, the toner application amount of the toner image formed in the upstream image forming unit P is reduced. However, the present invention is not limited to this. When the difference in the detected charging current between the toner portion and the non-toner portion in the downstream image forming portion P becomes larger than a predetermined threshold value, the upstream image forming portion P forms the image. What is necessary is just to adjust so that the toner loading of a toner image may be made small.

  Further, as described in the first embodiment, the threshold value is set according to the setting of the primary transfer bias in the detection operation for forming the test toner image and detecting the charging current, or the setting of the charging potential (single or even). More than one).

  Further, the ghost caused by the transfer memory in the downstream image forming unit P can be sufficiently suppressed by reducing the amount of applied toner (exposure amount by the exposure device 3) of the toner image formed in the upstream image forming unit P. It can set suitably as follows. In this embodiment, the applied toner amount is changed from a relatively large value before adjustment to a relatively small value with the above threshold as a boundary. However, the present invention is not limited to this, and as described in the first exemplary embodiment, a plurality of threshold values may be provided in stages, and the applied toner amount may be reduced in stages. Further, as described in the first exemplary embodiment, the applied toner amount may be continuously changed.

3. Control Mode FIG. 9 is a block diagram showing a schematic control mode of the main part of the image forming apparatus 100 of the present embodiment. The control mode of the present embodiment is the same as that of the first embodiment shown in FIG. 4, but the control unit 110 controls the exposure condition control circuit 130 based on the charging current detection result by the ammeter 23 to control the toner. The difference is that control for adjusting the applied amount (toner applied amount adjustment control) is performed. The exposure condition control circuit 130 controls the exposure amount by the exposure device 3 during the exposure process (electrostatic latent image forming process). In the present embodiment, the control unit 110 has a function of a calculation unit (ghost detection unit using a transfer memory) that calculates a surface potential of the photosensitive member 1 after passing through the transfer unit, and executes toner application amount adjustment control. Thus, an adjustment unit for adjusting the amount of applied toner is configured.

  In this embodiment, toner application amount adjustment control is performed in the post-rotation process and the inter-sheet process of the job every time the number of images formed as information regarding the usage amount of the primary transfer roller 5 exceeds a predetermined threshold. However, the present invention is not limited to this, and the applied toner amount adjustment control can be performed at an arbitrary timing during non-image formation.

4). Next, toner applied amount adjustment control (ghost detection operation) in the present embodiment will be described. FIG. 10 is a flowchart showing the procedure of toner applied amount adjustment control in this embodiment. Here, as an example, a procedure for detecting the charging current in the C image forming unit PC and adjusting the toner applied amount (maximum applied amount of the secondary color) of the toner image formed in the YM image forming units PY and PM will be described. To do.

  For example, when the post-rotation process at the end of the job is started (S201), the CPU 111 determines whether 100 sheets (for example, A4 size conversion value) or more of images have been formed from the previous toner amount adjustment control. (S202).

  If it is determined in S202 that there are 100 or more sheets, the CPU 111 starts an operation of forming a test toner image and detecting the charging current (S203). Here, a red solid image is formed on the intermediate transfer body 10 as a test toner image by the YM image forming portions PY and PM, and this red solid image is sent to the primary transfer portion T1 of the C image forming portion PC. Then, in the C image forming unit PC, the region where the primary transfer unit T1 on the photoreceptor 1 is in contact with the red solid image (toner portion) and the region where it is not in contact (non-toner portion) are respectively charged. The charging current Idc (n) at the time of being detected is detected by the ammeter 23.

  Next, the CPU 111 calculates the difference ΔVc of the contrast ΔV between the toner portion and the non-toner portion after passing through the transfer portion based on the charging current Idc (n) detected by the ammeter 23 and stores it in the RAM 113 ( S204).

  Next, the CPU 111 compares the calculated difference ΔVc of the contrast ΔV with the ghost occurrence threshold value ΔVcg previously stored in the ROM 112 (S205). If it is determined that ΔVc> ΔVcg, feedback is instructed to the exposure condition control circuit 130 (S206). Specifically, in this embodiment, exposure of the YM image forming units PY and PM is performed so that the toner applied amount (maximum applied amount) of the toner image formed by the YM image forming units PY and PM is smaller than that before adjustment. The exposure amount setting corresponding to the maximum density in the condition control circuit 130 is changed. At this time, as the exposure amount setting corresponding to the highest density is changed, the exposure amount settings corresponding to other gradations may be corrected. Thereafter, when the operation of the predetermined post-rotation process is completed, the job is terminated (S207).

  On the other hand, if it is determined in S202 that the number is less than 100, the CPU 111 does not perform the test toner image formation operation or the charging current detection operation, and ends the job when the predetermined post-rotation process operation is completed (S207). . If it is determined in step S205 that ΔVc ≦ ΔVcg, the CPU 111 ends the job when the predetermined post-rotation process operation ends without adjusting the toner application amount (S207).

  In the case where the toner application amount adjustment control is performed in the inter-sheet process, the image forming operation of the job is continuously performed after the toner application amount is adjusted (or it is determined not to adjust).

  In the above, a case where a solid red image is formed as a test toner image, the charging current is detected by the C image forming unit PC, and the amount of applied toner of the toner image formed by the YM image forming units PY and PM is adjusted is described as an example. did. However, the present invention is not limited to this. Instead of or in addition to this, the charging current of the toner image formed by the YM image forming units PY and PM is adjusted by detecting the charging current by the K image forming unit PK. be able to. In addition, a solid solid image can be formed as a test toner image, the charging current can be detected by the K image forming unit PK, and the toner loading amount of the toner image formed by the YC image forming units PY and PC can be adjusted. Further, a blue solid image can be formed, the charging current can be detected by the K image forming unit PK, and the toner loading amount of the toner image formed by the MC image forming units PM and PC can be adjusted. Further, as in the case of the first embodiment, a single color image such as yellow, magenta, and cyan is formed as a test toner image, and an upstream side where a charging current is detected by the downstream image forming unit P to form a test toner image. The amount of applied toner of the toner image formed by the image forming unit P may be adjusted. That is, the toner application amount adjustment control according to the present exemplary embodiment performs toner application of a toner image formed on the upstream side photoreceptor 1 in the rotation direction of the intermediate transfer body 10 among the plurality of photoreceptors 1. Applicable for quantity adjustment.

5. Effect FIG. 11 is a graph showing the correlation between the difference ΔVc of the contrast ΔV between the toner portion (red solid image portion) after passing through the transfer portion and the non-toner portion of the photoreceptor 1 of the C image forming portion PC, and the ghost level. FIG. FIG. 12 shows the difference between the charging current detected by the ammeter 23 between the toner portion and the non-toner portion, and the contrast ΔV between the toner portion (red solid image portion) after passing through the transfer portion and the non-toner portion. It is a graph which shows a correlation with difference (DELTA) Vc.

  From the relationship shown in FIGS. 11 and 12 derived by experiments, the following can be understood. That is, when the difference between the charging currents exceeds a certain threshold, the difference ΔVc between the toner portion and the non-toner portion after passing through the transfer portion exceeds the ghost image generation threshold ΔVcg, and the ghost caused by the transfer memory is generated. It tends to occur. On the other hand, in this embodiment, the occurrence level of ghost by the transfer memory is predicted by detecting the charging current in the downstream image forming unit P, and the toner loading of the toner image formed in the upstream image forming unit P is detected. Feedback to quantity. Specifically, when the difference in charging current is greater than a predetermined threshold (the difference in surface potential (contrast difference) between the toner part and the non-toner part after passing through the transfer part based on the difference in charging current) ) To adjust the toner amount of the toner image to be small. As a result, it is possible to suppress the occurrence of a ghost due to the transfer memory in the downstream image forming unit P.

[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, the case where the charging member is in contact with the photosensitive member has been described. However, the present invention is not limited to this. Ghost problems such as multi-order color ghosts due to the transfer memory are common problems regardless of charging methods such as non-contact and proximity. Therefore, the charging member such as the charging roller does not necessarily need to be in contact with the surface of the photoconductor as the 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.

  In the above-described embodiment, the AC charging method using the oscillating voltage obtained by superimposing the DC voltage and the AC voltage as the charging bias is adopted. However, the present invention is not limited to this. Ghost problems such as multi-color ghosts due to transfer memory tend to be more prominent in the DC charging method using a charging bias consisting of only a DC voltage, which has a lower potential convergence of the photoconductor than the AC charging method. . Therefore, a higher effect is exhibited by applying the present invention.

  In the above-described embodiments, the tandem type image forming apparatus has been described as an example. However, the present invention can also be applied to so-called one-drum type image forming. In the one-drum type image forming apparatus, a plurality of developing devices are provided for one photoconductor, and the electrostatic latent images of the respective color components sequentially formed on the photoconductor are used by switching the developing device. Develop sequentially. Each time a toner image of each color is formed on the photoconductor, the toner image is primarily transferred so as to sequentially overlap the photoconductor to the intermediate transfer body in the primary transfer portion. The intermediate transfer member carries the transferred toner image and repeatedly passes through the primary transfer portion. Then, the finally formed multiple toner image is secondarily transferred to the recording material at the secondary transfer portion. In such an image forming apparatus as well, in the primary transfer process for the second and subsequent colors, ghost problems such as multi-color ghosts due to the transfer memory may occur, as in the image forming apparatus of the above-described embodiment. Therefore, the present invention can also be applied to such an image forming apparatus, and the same effects as those of the above-described embodiments can be obtained. That is, the test toner image transferred from the photosensitive member to the transfer member at the transfer unit is conveyed again to the transfer unit, and the charging current when the region of the photosensitive member that has come into contact with the test toner image is charged is detected. This makes it possible to adjust the transfer bias when transferring a toner image of a color other than at least the first color formed to the transfer body when forming an image with a plurality of colors of toner. In addition, the test toner image transferred from the photosensitive member to the transfer member in the transfer unit is conveyed again to the transfer unit, and the regions of the photosensitive member that are not in contact with the regions of the photosensitive member that are in contact with the test toner image are charged. Detects the charging current when Accordingly, it is possible to adjust the amount of applied toner of a toner image of a color other than at least the last color formed when an image is formed with a plurality of colors of toner.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging roller 3 Exposure apparatus 5 Primary transfer roller 10 Intermediate transfer belt 23 Ammeter

Claims (10)

A rotatable photoreceptor,
A charging member for charging the photoreceptor with a charging unit;
A charging power source for applying a charging voltage for charging to the charging member;
Exposure means for exposing the photoreceptor charged by the charging member to form an electrostatic image;
Developing means for supplying toner to the electrostatic image formed on the photoreceptor to form a toner image;
A transferable transfer body on which a toner image is transferred from the photoconductor in a transfer section;
A transfer power supply for applying a transfer voltage for the transfer to the transfer portion;
Toner image forming means for forming on the transfer body a toner image carried on the transfer body and conveyed to the transfer section;
An image capable of executing an image forming operation for forming an image by transferring the toner image from the photosensitive member to the transfer member so as to be superimposed on the toner image formed on the transfer member by the toner image forming unit In the forming device,
A detection unit that detects a direct current flowing through the charging member by applying the charging voltage to the charging member from the charging power source;
A predetermined test toner image is formed on the transfer body by the toner image forming means, and a region of the photoconductor that is in contact with the test toner image in the transfer section while the transfer voltage is applied passes through the charging section. An adjustment unit that adjusts the transfer voltage in the image forming operation based on a detection result of the detection unit when
An image forming apparatus comprising: The toner image forming unit has another photoconductor disposed upstream of the photoconductor in the moving direction of the transfer body,
The image forming apparatus according to claim 1, wherein the test toner image is formed on the other photoconductor, transferred from the other photoconductor to the transfer body, and conveyed to the transfer unit. . The toner image forming unit includes the photoconductor,
2. The image formation according to claim 1, wherein the test toner image is formed on the photoconductor, transferred from the photoconductor to the transfer body at the transfer unit, and conveyed again to the transfer unit. apparatus.   The adjustment unit adjusts the absolute value of the transfer voltage to be larger than before the adjustment when the current detected by the detection unit is smaller than a predetermined threshold. The image forming apparatus according to claim 1. A rotatable photoreceptor,
A charging member for charging the photoreceptor with a charging unit;
A charging power source for applying a charging voltage for charging to the charging member;
Exposure means for exposing the photoreceptor charged by the charging member to form an electrostatic image;
Developing means for supplying toner to the electrostatic image formed on the photoreceptor to form a toner image;
A transferable transfer body on which a toner image is transferred from the photoconductor in a transfer section;
A transfer power supply for applying a transfer voltage for the transfer to the transfer portion;
Toner image forming means for forming on the transfer body a toner image carried on the transfer body and conveyed to the transfer section;
An image capable of executing an image forming operation for forming an image by transferring the toner image from the photosensitive member to the transfer member so as to be superimposed on the toner image formed on the transfer member by the toner image forming unit In the forming device,
A detection unit that detects a direct current flowing through the charging member by applying the charging voltage to the charging member from the charging power source;
A predetermined test toner image is formed on the transfer body by the toner image forming means, and a region of the photoconductor that is in contact with the test toner image in the transfer section while the transfer voltage is applied passes through the charging section. The detection unit when the detection unit detects the detection result when the transfer unit is in contact with the test toner image in the transfer unit when the transfer voltage is applied. An adjustment unit that adjusts the toner amount of the toner image formed on the transfer body by the toner image forming unit in the image forming operation based on the difference between
An image forming apparatus comprising: The toner image forming means includes another photosensitive member disposed upstream of the photosensitive member in the moving direction of the transfer member, another charging member for charging the other photosensitive member, and the other charging member. Another exposure unit that exposes the other charged photoreceptor to form an electrostatic image, and another development that forms a toner image by supplying toner to the electrostatic image formed on the other photoreceptor Means,
The test toner image is formed on the other photoconductor, transferred from the other photoconductor to the transfer body, and conveyed to the transfer unit,
The image forming apparatus according to claim 5, wherein the adjustment unit adjusts the toner amount by adjusting an exposure condition of the another photoconductor by the other exposure unit. The toner image forming unit includes the photoconductor,
The test toner image is formed on the photoconductor, transferred from the photoconductor to the transfer body at the transfer unit, and conveyed again to the transfer unit,
The image forming apparatus according to claim 5, wherein the adjustment unit adjusts the toner amount by adjusting an exposure condition of the photosensitive member by the exposure unit.   8. The image formation according to claim 5, wherein when the difference is larger than a predetermined threshold, the adjustment unit adjusts the toner amount to be smaller than that before the adjustment. apparatus.   The image forming apparatus according to claim 1, wherein the test toner image is a toner image having a highest density level.   The image forming apparatus according to claim 1, wherein the charging power source applies only a DC voltage to the charging member.

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