JP2023090198A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that detects scumming on a transfer target member and improves the situation.SOLUTION: An image forming apparatus comprises: an image carrier that carries a latent image; a developing device that develops the latent image on the image carrier into a toner image; a transfer device (transfer unit 30) that transfers the toner image to a transfer target member; a detection device (detection unit 60) that detects image density and a color of the transfer target member (recording material P); and a memory that holds a preset permissible level of scumming for the image density and the color. When a background part is defined as an area where a color is not constantly present on image data, and an electrification area of the image carrier is developed and transferred to the transfer target member, and a background reference part as an area on the transfer target member not directly or indirectly in contact with the image carrier, the image forming apparatus changes an imaging condition when a difference in the image density and the color between the background part and the background reference part exceeds the permissible level.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art In an electrophotographic image forming apparatus, an image is formed by developing a latent image on an image carrier, transferring a toner image onto a recording material, and fixing the toner image. At this time, the oppositely charged toner generated by charge exchange between toner particles is developed not in the exposed area where the latent image is carried, but in the white area where the latent image does not exist, resulting in recording called "scumming" or "fogging". The entire surface of the white part on the material is stained (hereinafter referred to as "background stain"). Up to now, for suppression of scumming, it has been considered to change the conditions up to the development process. For example, in Patent Document 1, scumming on the surface of an image carrier is monitored, and if the scumming exceeds a certain standard, the toner replenishment control is changed to improve the scumming.
However, the scumming on the recording material as the transfer receiving member is not detected, and the scumming on the photoreceptor is also transferred to the recording material with good transferability. Even so, there is a problem that scumming on the recording material may reach an unacceptable level.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of detecting and improving scumming on a transfer receiving member.

In order to solve the above-described problems, the image forming apparatus of the present invention includes:
an image carrier that carries a latent image;
a developing device that visualizes the latent image on the image carrier into a toner image;
a transfer device for transferring the toner image onto a transfer receiving member;
a detection device for detecting image density and color of the transferred member;
a memory for holding a preset permissible level of scumming for the image density and color;
with
The background portion is always an area where no color exists in the image data and the charged area of the image carrier is developed and transferred to the transfer receiving member;
Assuming that the background reference portion is an area on the transfer-receiving member that is not in direct or indirect contact with the image bearing member,
The image forming conditions are changed when the difference in image density and color between the background portion and the background reference portion exceeds the allowable level.

According to the present invention, it is possible to provide an image forming apparatus capable of detecting and improving scumming on a transfer receiving member.

1 is a schematic diagram illustrating a main part of a configuration example of an image forming apparatus according to an embodiment of the present invention; FIG. It is a schematic diagram explaining the detection means which detects a scumming of a comparative example, (A) shows an example in the case of low smoothness paper, (B) shows an example in the case of high smoothness paper. 7 is a graph for explaining an example of thresholds of allowable levels for different types of recording materials in a comparative example; FIG. 2 is a schematic diagram illustrating a detection unit for detecting scumming according to the present embodiment, in which (A) shows an example of low smoothness paper and (B) shows an example of high smoothness paper. 7 is a graph illustrating an example of thresholds of allowable levels for different types of printing materials in the embodiment; 3A and 3B are diagrams for explaining a transfer unit and a detection unit according to the first embodiment; FIG. 4A and 4B are diagrams for explaining an image forming unit according to the first embodiment; FIG. FIG. 10 is a table for explaining control for reducing scumming, where (A) shows the case of adjusting charging potential, and (B) shows the case of adjusting lubricant application amount. 4 is a diagram illustrating an example of adjusting the charging potential of an image carrier in the first embodiment; FIG. FIG. 5 is a diagram for explaining an example of adjusting the lubricant application amount in the first embodiment; 7A and 7B are diagrams for explaining a transfer unit and a detection unit according to the second embodiment; FIG. FIG. 10 is a diagram illustrating an example of adjusting a secondary transfer current in the second embodiment; FIG. 11 is a diagram for explaining the scumming level of the background portion on the recording material C when printing is performed on the recording material C in the third embodiment; 8A and 8B are diagrams for explaining detection results of image density and color of a solid portion in an image on a recording material C when printing is performed on the recording material C; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. In addition, in each drawing for explaining the embodiments of the present invention, constituent elements such as members and constituent parts having the same function or shape are denoted by the same reference numerals as much as possible, and will be described once. We omit the explanation.

First, a configuration example of an image forming apparatus according to an embodiment of the present invention will be described.
FIG. 1 is a schematic diagram for explaining a main part of a configuration example of an image forming apparatus according to an embodiment of the present invention, and shows a configuration example of an electrophotographic laser printer as an example. In FIG. 1, an image forming apparatus 100 includes four toner image forming units (process cartridges) 6Y for forming toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K); Equipped with 6M, 6C and 6K.

Below the toner image forming sections 6Y, 6M, 6C, and 6K in the drawing, an intermediate transfer unit 15 is provided for endlessly moving an intermediate transfer belt 8 as an intermediate transfer member while being stretched.
The intermediate transfer unit 15 includes an intermediate transfer belt 8, four primary transfer bias rollers 9Y, 9M, 9C, and 9K, a cleaning device 10, and the like.
The intermediate transfer belt 8 is endlessly moved clockwise in the figure.
The primary transfer bias rollers 9Y, 9M, 9C, and 9K sandwich the intermediate transfer belt 8, which is moved endlessly, between the photosensitive members 1Y, 1M, 1C, and 1K as image bearing members to form primary transfer nips. are doing. The primary transfer bias rollers 9Y, 9M, 9C, and 9K are of a type that applies a transfer bias having a polarity opposite to that of the toner (for example, positive) to the back surface of the intermediate transfer belt 8 (inner peripheral surface of the loop). All the rollers except the primary transfer bias rollers 9Y, 9M, 9C and 9K are electrically grounded.

The four toner image forming units 6Y, 6M, 6C, and 6K use Y toner, M toner, C toner, and K toner of different colors as image forming substances, but otherwise have the same configuration. The toner image forming section 6Y for forming a Y toner image will be described as an example. The toner image forming section 6Y includes a drum-shaped photoreceptor 1Y, a drum cleaning device 2Y, a neutralizing device (not shown), a charging device 4Y, a developing device 5Y, and the like.
The charging device 4Y uniformly charges the surface of the photoreceptor 1Y which is rotated counterclockwise in the drawing by a driving means (not shown). The surface of the uniformly charged photoreceptor 1Y is exposed and scanned by a laser beam from an exposure device 7Y serving as latent image forming means based on image information sent from a document reading device (not shown) or an external personal computer (PC). to form a Y electrostatic latent image.

This Y electrostatic latent image is developed into a Y toner image by a developing device 5Y using Y toner. Then, it is intermediately transferred onto the intermediate transfer belt 8 .
The drum cleaning device 2Y removes toner remaining on the surface of the photoreceptor 1Y after the intermediate transfer process. Also, the static eliminator eliminates residual charges on the photoreceptor 1Y after cleaning. By this static elimination, the surface of the photoreceptor 1Y is initialized to prepare for the next image formation.

M toner images, C toner images, and K toner images are similarly formed on the photoreceptors 1M, 1C, and 1K in the other toner image forming portions 6M, 6C, and 6K. As the intermediate transfer belt 8 moves endlessly, it passes through the primary transfer nips for Y, M, C, and K successively, and transfers the Y toner image and the M toner image on the photoreceptors 1Y, 1M, 1C, and 1K. An image, a C toner image, and a K toner image are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8 .

The secondary transfer backup roller 12 of the intermediate transfer unit 15 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The four-color toner image formed on the intermediate transfer belt 8 is conveyed between the intermediate transfer belt 8 and the secondary transfer roller 19 which move in the forward direction at the secondary transfer nip. transcribed to Transfer residual toner that has not been transferred onto the recording material P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. It is cleaned by cleaning device 10 .
The four-color toner image transferred to the surface of the recording material P sent out from the secondary transfer nip is fixed by heat and pressure when passing between the rollers of the fixing device 20 .

In FIG. 1, between the most downstream toner image forming portion 6K and the secondary transfer nip portion, a toner adhesion amount detection sensor (for example, a reflective optical sensor) 40 is disposed facing the intermediate transfer belt 8. It is
A toner adhesion amount detection sensor 40 detects toner adhering to the intermediate transfer belt 8 .
In FIG. 1, after the fixing device 20, an image density detection sensor (for example, a diffuse reflection type optical sensor) 50 is arranged so as to face the image fixed on the recording material P. As shown in FIG.
The image density detection sensor 50 detects image density (or image density and color) fixed on the recording material P. FIG.

The control unit 70 is configured by storage means such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), for example. The CPU of the control unit 70, for example, reads various programs stored in a ROM or the like, develops them in a RAM, and executes various processes such as image forming processing and processing for reducing scumming according to the developed programs.

The image forming apparatus 100 also includes a storage unit (not shown), an operation display unit, and the like. The storage unit is composed of, for example, an HDD (Hard Disk Drive), a semiconductor non-volatile memory, or the like.
The storage unit stores various programs such as a system program and a processing program executed by the control unit 70, and data necessary for executing these programs.
The operation display unit includes a display screen, a display unit for displaying various information on the screen, and an operation unit used for inputting various instructions by the user.

Although the supply and discharge of the recording material P are omitted in FIG. 1, the recording material P is supplied to the secondary transfer nip from a recording material storage section (not shown). Further, the recording material P on which the toner image is fixed by the fixing device 20 is discharged from a discharge section (not shown).
Further, in the following description, the four toner image forming units 6Y, 6M, 6C, 6K and their constituent elements will be denoted by Y, M, C, and K when there is no need to distinguish colors. , such as "toner image forming section 6" and "primary transfer bias roller 9".

Next, processing for detecting scumming will be described with reference to a comparative example.
FIG. 2 is a schematic diagram illustrating a detection means for detecting scumming in a comparative example.
FIG. 3 is a graph illustrating an example of thresholds of allowable levels for different types of recording materials in a comparative example.
FIG. 4 is a schematic diagram for explaining detection means for detecting scumming according to the present embodiment.
FIG. 5 is a graph for explaining an example of thresholds of allowable levels for different types of printing materials in this embodiment.
2 and 4, (A) shows an example of using low-smooth paper as the recording material P, and (B) shows an example of using high-smooth paper as the recording material P. As shown in FIG. 2 and 4 schematically show objects to be detected by the detection means and the arrangement of the detection means.

The image forming apparatus 100c of the comparative example monitors scumming on the photosensitive member before the toner image is transferred by the toner adhesion amount detection sensor 40c. In the configuration example of FIG. 1, when the toner adhesion amount detection sensor 40 monitors scumming on the intermediate transfer member, the situation is similar to the case of monitoring scumming on the photosensitive member.
In this method, even if the scumming on the photosensitive member is the same, the image density of the scumming on the recording material finally transferred to the recording material may differ because the transferability differs depending on the recording material P used. know. As shown in FIG. 3, the permissible level of scumming differs between paper with a rough surface (low-smooth paper) with a low transfer rate and paper with a smooth surface (high-smooth paper) with a high transfer rate. For this reason, in the method of monitoring scumming on the photoreceptor of the comparative example, for example, when the threshold is set based on the reflection density on the photoreceptor when the scumming level of low-smooth paper is at the permissible level, high On smooth paper, scumming of unacceptable image density occurs.

To solve this problem, the image forming apparatus 100 of the present embodiment provides the image density detection sensor 50 at a position where the toner image on the photoreceptor 1 can be detected after being transferred onto the recording material P, and the toner image on the recording material P is directly detected. Monitor fouling and reduce scumming if acceptable levels are exceeded. This stabilizes the scumming quality when the recording material P is changed. As shown in FIG. 5, for each recording material P, a scumming tolerance level is set as a threshold. In this way, regardless of the type of recording material P, determination is made based on whether the scumming permissible level is exceeded for each recording material P, so the image density of scumming can always be kept below a certain level.

The state of scumming on the recording material P can be grasped by detecting the margin area of the recording material P during printing, for example. Alternatively, when the recording material P is changed or at a specific timing, an image of the background portion is output and the image density of the recording material P is detected.
Note that even if the recording material P is white paper, the image density varies depending on the type. It is preferable to store the difference (ΔID) from the image density of the background portion of the printed image to determine the scumming state. This is because the scumming image density is a small value, and the scumming state can be more accurately determined by using the difference. The same applies to colored paper.
The difference (ΔID) between the image density of the background portion of the printed image and the image density of the reference background portion is preferably within 0.05, for example. When the difference exceeds 0.05, scumming is likely to be confirmed on the image.

In the following description, the “texture portion” and the “texture reference portion” of the transferred member are distinguished as follows.
The "background portion" is defined as an area where no color exists in the image data and where the charged area of the image carrier (photoreceptor) is developed and transferred to the transfer receiving member. In contrast to the image transfer area where the toner image is transferred on the transfer receiving member, the background portion can also be said to be a non-image transfer area where the toner image is not transferred.
The "ground reference portion" is defined as a region of the transfer-receiving member that is not in direct or indirect contact with the image carrier. It can be said that the background reference portion is outside the range of the area where the image carrier transfers to the transfer receiving member.
Here, the member to be transferred is a member on which the toner image is transferred, and is a recording material P, for example.

As the image density detection sensor 50, in addition to a reflective optical sensor, a contact image sensor (CIS) or a reduction optical system sensor can be used. Since these colors can be distinguished, it is possible to distinguish colors with a lot of scumming and change the control for each color. They can also be used as line sensors. When detecting the background image density, it is possible to detect a fixed position from the margin, etc., but if a line sensor is used, the background part can be grasped from the image information, and the background image density can be detected even within the image area. can be measured.

Also, when the recording material P is switched, scumming exceeding the permissible level may occur. For example, there is a case where low smooth paper is switched to high smooth paper when scumming is near an allowable level during printing on low smooth paper. Regarding this point, the image forming apparatus 100 holds a scumming coefficient for each recording material P, and when the recording material P is switched, the scumming control factor parameter is set using the stored coefficient. By changing the setting, it is possible to reduce the scumming immediately after switching to the allowable level or less.
Further, although the productivity is lowered, it is effective to improve by executing an adjustment mode for changing the control factor parameter while monitoring the scumming on the recording material P when the recording material P is switched.

Methods for reducing scumming when it exceeds the permissible level include the following methods.
1. Toner replacement in the developing device2. 2. Background potential increase, which is the difference between the developing bias and the photoreceptor charging potential. 4. Toner density reduction of developer. 4. Decrease in the amount of lubricant applied to the photoreceptor; Decrease in charging applied voltage Vpp (Voltage peak to peak) (when the charging method is AC)
The above 1, 2 and 3 are methods for improving scumming due to deteriorated toner, and 4 and 5 are methods for improving scumming due to deteriorated lubricant.

If it is determined that the scumming exceeds the permissible level, the image forming conditions are changed to improve the scumming. Change the range conditions.
The quality of the image forming area (exposed area) where image data exists on the photoreceptor largely depends on the process up to development, which is upstream of the image forming process. For example, if the amount of toner required to obtain the target image density is not developed on the photoreceptor 1 by the development process, it is difficult to achieve the target image density under subsequent process conditions. When the toner density is lowered to improve the scumming, the density of the image forming area is lowered unless other conditions are changed. To compensate for this, it is necessary to adjust, for example, the developing bias. The steps leading up to development include charging, exposure, and development in a broad flow, and also include steps incidental to these steps.

The toner existing in the non-image forming area (white area) where no image data exists on the photoreceptor is determined as scumming on the printed image when it is transferred onto the recording material P. FIG. Therefore, in the embodiment according to the present invention, the scumming is improved by changing the conditions up to the transfer process onto the recording material P even after the development process. In order to change the adhesion state of the toner, which is much smaller than the image forming area, such as scumming, it is possible to change the conditions of the process which has little influence on the image forming area. Furthermore, since the effect on the image formation area is small, it is not necessary to adjust the quality of the image formation area by adjusting other conditions. The processes after the development process include a primary transfer process and a secondary transfer process, and the photoreceptor cleaning process is also included in the processes after the development.

As an example of change in the range after the development process, there is a change in the transfer current (5. Decrease in the charging applied voltage Vpp described above). The transfer current is a condition for moving the toner image on the photosensitive member onto the intermediate transfer member or the toner image on the intermediate transfer member onto the recording material. In the case of a small amount of toner such as scumming, the scumming state can be changed by a small change that does not change the transfer state of the toner in the image portion.

Another example of modification is to change the amount of lubricant applied to the photoreceptor (4. Decrease the amount of lubricant applied to the photoreceptor described above). The lubricant is applied to the photoreceptor to prevent the cleaning blade from curling up when cleaning residual toner on the photoreceptor after the transfer of the toner image. However, the lubricant that remains after cleaning deteriorates during charging in the next image formation, thereby exacerbating scumming. The degree of scumming is related to the amount of lubricant applied. Therefore, when it is detected that the scumming is unacceptable, the deterioration of the scumming can be suppressed by reducing the lubricant application amount. Since the lubricant application amount is not a condition that directly determines the formation state of the toner image on the image portion, it is less likely to affect the image portion and is suitable as a change condition.

Processing for improving background stains by the image forming apparatus according to the embodiment of the present invention will be described below. Although the basic configuration example of the image forming apparatus 100 is the same as that of FIG. 1, each embodiment will be described using the following image forming section, transfer section, or detection section.

An image forming unit as a developing device has an image carrier that carries a latent image, and visualizes the latent image on the image carrier into a toner image. As an example, the image forming units are the toner image forming units 6Y, 6M, 6C, and 6K shown in FIG. 1, but each embodiment will be described without distinguishing between colors.
A transfer unit as a transfer device transfers the toner image onto a transfer receiving member. As an example, the transfer section is assumed to be the intermediate transfer unit 15 shown in FIG. means having the same function as ). In addition, each configuration of the transfer section shall be appropriately changed in each embodiment.

The detection unit as a detection device is a sensor for detecting scumming of the transferred member, and for example, the image density detection sensor 50 shown in FIG. 1 may be used. In addition, the arrangement position of the detection unit is not limited to the arrangement example of FIG. 1, and can be arranged at a preferable position in each embodiment.
The detection unit detects the image density and color of the transfer receiving member.

Embodiment 1.
In Embodiment 1, one aspect of improving scumming by adjusting the amount of lubricant applied to the photoreceptor and the charging potential of the image bearing member will be described.

2. Description of the Related Art In an electrophotographic image forming apparatus using AC charging, a lubricant is applied to the surface of an image carrier in order to suppress deposits on the image carrier and ensure toner cleaning performance. However, it has been found that background contamination varies depending on the magnitude of the AC electric field (charging potential) at the charging portion. Further investigation revealed the possibility that the lubricating agent was changed in quality by the AC electric field, and the toner adhered to the developing section, resulting in scumming.

The scumming due to this cause can be suppressed by reducing the AC electric field of the charging portion and reducing the amount of lubricant applied on the image carrier.
However, if the AC electric field of the charging portion is reduced, the charging of the image bearing member becomes unstable, and abnormal images such as white spots appear on the image. Also, if the amount of lubricant to be applied is extremely small, the cleaning blade will turn over due to an increase in the friction coefficient of the surface.
Thus, there is a trade-off between reducing the AC electric field of the charging portion and reducing the amount of lubricant applied.
Therefore, the image forming apparatus of the present embodiment makes it possible to suppress scumming within an acceptable range by adjusting the amount of lubricant applied and the AC electric field of the charging section to appropriate adjustment values during printing.

FIG. 6 is a diagram for explaining the transfer section and the detection section of the first embodiment.
The transfer section 30 has at least an intermediate transfer belt 8 , a secondary transfer backup roller 12 , and a secondary transfer section 31 as means having the same function as the secondary transfer roller 19 .
The secondary transfer portion 31 has a surface (hereinafter referred to as a “conveyance surface”) on which the recording material P onto which the toner image of the intermediate transfer belt 8 is transferred is placed, and functions as a conveying means for conveying the recording material P.
The detection unit 60 is arranged downstream of the fixing device 20 .

The scumming is transferred to the recording material P by the transfer unit 30, but the transfer unit 30 and the recording material P are separated from each other so that the toner image is not transferred. Image density and color (density and color of background reference portion) can be detected. The control unit 70 of the image forming apparatus 100 sets the permissible levels of the image density and color (also referred to as the “permissible level of background contamination”) using the detected density and color detection values of the background reference portion of the recording material P. can do. The acceptable level of scumming shall be recorded in memory. Any memory can be used as long as it can be referenced by the control unit 70. For example, in addition to the storage unit described above, a memory detachable from the image forming apparatus 100, or a RAM temporarily stores information acquired through communication means. It may be the case that
Also, the recording material P as the transfer receiving member is assumed to be a plurality of types of recording materials (eg, low smoothness paper and high smoothness paper). It is assumed that the control unit 70 records the permissible levels of the density and color of the background contamination and the detection values of the density and color of the background reference portion for each type of recording material.

Further, in the present embodiment, the recording material P is not continuous paper but has an arbitrary size, and the layout of the recording material P is laid out so that the space between two recording materials P (inter-paper portion) can also be detected. As a result, the detection unit 60 detects scumming on the conveying surface on which the recording material P is placed on the secondary transfer unit 31, and makes it possible to detect scumming regardless of the recording material P as well.
As described above, the detection unit 60 is provided so as to be able to detect the image density and color of the conveying surface on which the recording material P is placed and conveyed as the transfer receiving member. , the recording material P and the conveying surface of the secondary transfer portion 31 can be targeted as transfer receiving members for which image density and color are detected. This makes it easy to detect the difference between the image data and the printed matter, which can be detected as the image density difference of each color.

At this time, the texture portion and the texture reference portion on the conveying surface are the same as those of the recording material P as described above.
It is assumed that the density and color of the background reference portion of the conveying surface are held in a memory that can be referred to by the control section 70 .

7A and 7B are diagrams for explaining an image forming unit according to the first embodiment. FIG. 7 shows the intermediate transfer belt 8 in addition to the image forming unit 80, and the arrow indicates the conveying direction of the intermediate transfer belt 8. As shown in FIG.
The image forming section 80 has an image carrier 81 , a charging section 82 , an exposure section 83 , a developing section 84 , a lubricant application section 85 and a potential detection section 86 .
A charging unit 82 as a charging device is applied with an AC electric field to charge the image carrier 81 .
The exposure unit 83 exposes the image carrier 81 with laser light to form an electrostatic latent image.
The developer station 84 develops the charged and exposed image. The developing unit 84 visualizes the latent image on the image carrier 81, for example, with a developer carrying member carrying a developer composed of non-magnetic toner and magnetic carrier.

A lubricant application unit 85 as an application device applies a lubricant to the image carrier 81 . The image forming unit 80 can adjust the amount of lubricant applied by adjusting the number of rotations (motor torque) of a lubricant applying member 85 between the lubricant and the image carrier 81 .
A potential detection unit 86 as a measuring device detects the surface potential of the image carrier 81 and measures the charge potential of the image carrier 81 (hereinafter also referred to as “image carrier charge potential” as appropriate).

Next, control for reducing scumming will be described with reference to FIG.
FIG. 8 is a table for explaining control for reducing scumming, in which (A) shows the case of adjusting the charging potential, and (B) shows the case of adjusting the lubricant application amount.
It is assumed that the allowable level of electrification potential and the allowable level of lubricant application amount are set in advance and recorded in a memory that can be referred to by control unit 70 .

In FIG. 8A, the image forming condition for improving the scumming is the applied charging voltage (Vpp) applied to the charging section 82, and the charging applied voltage (Vpp) is lowered to reduce the charging potential of the surface of the image carrier 81. deterioration of the lubricant is suppressed by lowering the Further, when the charging potential is out of the allowable range, the image forming apparatus performs control to increase the charging potential regardless of whether the scumming is within the allowable range.
The control unit 70 controls the charging unit 82 as shown in FIG. 8A based on the permissible level of scumming and the permissible level of charging potential.
The charging application voltage (Vpp) applied to the charging section 82 is adjusted to bring the charging potential on the surface of the image carrier 81 within the allowable range.
The charging section 82 raises or lowers the image carrier charging potential in the range of 2.0 to 3.0 kV, for example.

In FIG. 8B, the image forming condition for improving scumming is the lubricant application amount, and by decreasing the lubricant application amount, the amount of deteriorated lubricant causing scumming is reduced. Further, when the lubricant application amount is out of the allowable range, the image forming apparatus performs control to increase the lubricant application amount regardless of whether the scumming is within the allowable range.
The control unit 70 controls the lubricant application unit 85 as shown in FIG. 8(B) based on the permissible level of scumming and the permissible level of the lubricant application amount.
The lubricant application unit 85 adjusts the amount of lubricant applied so that the amount of lubricant applied is within the allowable range.
The lubricant application unit 85 adjusts the amount of lubricant application by, for example, increasing or decreasing the motor torque in the range of 0.20 to 0.40 mg/km. The motor torque is the amount of lubricant consumed with respect to the motor traveling distance.

Next, scumming when the above-described control is performed and transition of characteristics that are trade-offs of each control will be described.
FIG. 9 is a diagram for explaining an example of adjusting the charging potential of the image carrier in the first embodiment.
FIG. 10 is a diagram for explaining an example of adjusting the lubricant application amount in the first embodiment.

In the three graphs shown in FIG. 9, as values that change with the number of printed recording materials P (horizontal axis), the background contamination level is shown in the upper row, the charge potential of the image carrier is shown in the middle row, and the charging applied voltage (lower row) is shown. Vpp) [V]. In the three graphs, the values of the numbers N11, N12, and N13 of the recording material P are connected by dashed lines.
The background contamination level is a value (texture portion - background reference part, hereinafter referred to as "ID" as appropriate). The allowable level of scumming is assumed to be 0.01 in ID, for example.
Assume that the allowable level of the image carrier charging potential is -30V, for example.
The charging applied voltage (Vpp) is the voltage [V] applied to the image carrier 81 by the charging section 82 .

FIG. 9 shows an example in which the charging applied voltage (Vpp) is adjusted as follows in accordance with the scumming level based on the number of printed sheets of the recording material P and changes in the charge potential of the image carrier.
In the printing of the number N11 of the recording material P, the scumming exceeds the permissible level (ID: 0.01), so Vpp is lowered.
When printing the number of sheets N12, the charge potential of the image carrier fell below the allowable level (target -30 V), so Vpp is increased.
In the printing of the number of sheets N13, the scumming exceeds the permissible level (ID: 0.01), so Vpp is lowered.

As shown in FIG. 9, when the charging potential of the image carrier falls below the allowable level, the applied charging voltage is increased. be provided.

In the three graphs shown in FIG. 10, as values that change with the number of printed recording materials P (horizontal axis), the background contamination level is shown in the upper row, the image carrier driving motor torque [N·m] is shown in the middle row, and so on. The number of revolutions [rpm] of the lubricant applying roller is shown in the lower part. In the three graphs, the values of the numbers N21, N22, and N23 of the recording material P are connected by dashed lines.
The background dirt level is a value obtained by subtracting the detection value of the reference portion from the detection value of the background portion, and is the same as in FIG.
The image carrier drive motor torque is the value of the drive motor torque of the lubricant application unit 85 that applies the lubricant to the image carrier 81 . For example, the lower limit of the allowable level of the image carrier driving motor torque is set to 0.35 N·m.
The rotation speed of the lubricant application roller is the rotation speed of the roller with which the lubricant application unit 85 applies the lubricant to the image carrier 81 .
Here, the image carrier drive motor torque is the load of the drive means for driving the lubricant application unit 85, and the lubricant application amount is increased/decreased by increasing/decreasing the rotation speed of the lubricant application roller.

FIG. 10 shows an example in which the number of revolutions of the lubricant application roller is adjusted as follows according to the scumming level based on the number of printed sheets of the recording material P and the change in the torque of the image carrier driving motor.
In the printing of the number of sheets N21, the scumming exceeded the permissible level (ID: 0.01), so the number of revolutions of the lubricant application roller was decreased to reduce the lubricant application amount.
When the number of sheets N22 was printed, the motor torque for driving the image carrier fell below the lower limit of the allowable level (0.35 N·m).
In the printing of the number of sheets N23, the scumming exceeded the permissible level (ID: 0.01), so the number of revolutions of the lubricant application roller was decreased to reduce the lubricant application amount.

As shown in FIG. 10, when the image carrier driving motor torque falls below the allowable level, the number of revolutions of the lubricant application roller is increased to increase the lubricant application amount. A lower limit is established based on the load of

As described above, according to the present embodiment, when the scumming exceeds the allowable level, the scumming can be stabilized by adjusting the charging potential or the lubricant application amount.
In this way, even if the lubricant applied to the image bearing member is degraded by the AC electric field of the charging section and becomes conspicuous in the image as background stains in the developing section, the degradation of the lubricant is suppressed. As a result, scumming that cannot be suppressed by changing the conditions up to the development process can be improved.

Embodiment 2.
In this embodiment, one aspect of changing the image forming conditions by changing the secondary transfer current will be described.
FIG. 11 is a diagram illustrating a transfer section and a detection section according to the second embodiment.
A transfer unit 90 as a transfer device has at least an intermediate transfer belt 8, a secondary transfer backup roller 12, a secondary transfer roller 19, a secondary transfer first power source 91, and a secondary transfer second power source 92. .
Assume that the image density detection sensor 50 as a detection unit is arranged downstream of the fixing device 20 as shown in FIG.
For example, the image forming unit 80 of the first embodiment may be used as the image forming unit.

A secondary transfer first power supply 91 applies a voltage to the secondary transfer backup roller 12 to flow a secondary transfer current.
A secondary transfer second power supply 92 applies a voltage to the secondary transfer roller 19 to flow a secondary transfer current.
The secondary transfer backup roller 12 and the secondary transfer roller 19 are charged secondary transfer charging devices through which the secondary transfer current flows. The secondary transfer charging device may be either the secondary transfer backup roller 12 or the secondary transfer roller 19 .
The secondary transfer first power supply 91 and the secondary transfer second power supply 92 are secondary transfer power supply devices that apply voltage to the secondary transfer charging device to charge it. The secondary transfer power supply may be either the secondary transfer first power supply 91 or the secondary transfer second power supply 92 .

The control unit 70 controls the voltage applied by the secondary transfer first power supply 91 or the secondary transfer second power supply 92 based on the permissible level of scumming, and the secondary transfer backup roller 12 and the secondary transfer roller 19 are controlled. Adjust the value of the secondary transfer current applied to the In this embodiment, for example, the control unit 70 presets the permissible level of scumming and stores it in a memory that can be referred to. A case where the control unit 70 performs control using, for example, a reference value of 1 as the permissible level of scumming will be described. As recording material P, recording material A and recording material B are used.

FIG. 12 is a diagram illustrating an example of adjusting the secondary transfer current in the second embodiment. In FIG. 12, the scumming level of the background portion on the recording material when 5 pages printed on the recording material A and 5 pages printed on the recording material B whose surface smoothness is higher than that of the recording material A are repeatedly printed is Indicated by a black circle. As in the first embodiment, the contamination level of the recording material A or the recording material B is a value obtained by subtracting the detection value of the background reference portion from the detection value of the background portion.

A reference value of 1 is set to the upper limit at which scumming is permissible.
In the image printed on the recording material A, the scumming level of the background portion is below the reference value 1. However, when the recording material is changed to B, the scumming level of the background portion exceeds the reference value 1.

Therefore, the control unit 70 changes the image forming condition from the image forming condition a to the image forming condition b. The change from the image forming condition a to the image forming condition b here is, for example, a change to lower the secondary transfer current. When this change is reflected, the scumming level of the background portion falls below the reference value 1. Then, when the recording material is changed from A to B next time, by changing in advance to the image forming condition b from the first page after the change, an image whose scumming does not exceed the allowable range can be obtained.

For changing the secondary transfer current value, it is preferable to decrease the current value by 10 μA, for example. If the scumming level does not fall below the reference value 1 even after being lowered by 10 μA, the secondary transfer current value may be further lowered by 10 μA and repeated until the value falls below the reference value 1.
Also, the amount of change in the secondary transfer current is not a constant value, but can be set based on the excess amount of the scumming level with respect to the reference value 1. FIG.

The controller 70 controls the secondary transfer first power supply 91 and/or the secondary transfer second power supply 92 in order to change the secondary transfer current value, for example, according to the scumming level. Under the control of the controller 70 , the secondary transfer first power supply 91 adjusts the secondary transfer current flowing through the secondary transfer backup roller 12 , and the secondary transfer second power supply 92 flows through the secondary transfer roller 19 . Adjust the secondary transfer current. In this control, the secondary transfer current set value is changed, and the output is changed accordingly. Note that the secondary transfer current has an allowable range from the viewpoint of transferability, and is changed within the allowable range.

According to this embodiment, when the scumming exceeds the allowable level, the scumming can be stabilized by adjusting the secondary transfer current value.

Embodiment 3.
In this embodiment, a mode of changing the image forming conditions using a plurality of reference values will be described.
In this embodiment, for example, the configuration examples of the above embodiments can be used.
For example, the control unit 70 presets a plurality of permissible levels of scumming and stores them in a memory that can be referred to. A case where the control unit 70 performs control using, for example, three types of reference value 1, reference value 2, and reference value 3 as the permissible level of scumming will be described.
Also, the recording material C is used as an example of the recording material P, and the contamination level of the recording material C is the value obtained by subtracting the detection value of the reference portion from the detection value of the background portion, as in the first embodiment.

FIG. 13 is a diagram for explaining the scumming level of the background portion on the recording material C when printing on the recording material C in the third embodiment.
A reference value of 1 is set to the upper limit at which scumming is permissible. The reference value 2 is set to be slightly less than the unacceptable amount of scumming, and when the scumming level of the background portion exceeds this value, it indicates that the scumming margin is low. A reference value of 3 indicates that there is a sufficient margin for scumming when the value falls below this value.
If the amount of printing increases during printing under the image forming condition c, the scumming gradually worsens, and the scumming level of the background portion of the image gradually rises and exceeds the reference value 2 .

If this state continues for a certain period of time, the control unit 70 determines that the scumming may become unacceptable, and controls to change the image forming condition to d. The change from the image forming condition c to the image forming condition d is, for example, a change to reduce the lubricant application amount. After the change, the scumming was improved, and after a while, the standard value fell below 3. When this state continues for a certain period of time, the control unit 70 determines that the scumming margin is sufficient, and performs control to restore the image forming condition c before the change. It should be noted that the fixed period is preferably set in advance and held in a memory or the like.
By detecting the image density of the background portion of the printed image in this manner, an image in which background stains can be tolerated at any time can be obtained.

The lubricant application amount is changed in the same manner as in the first embodiment, and the number of revolutions of the lubricant application roller is changed by increasing or decreasing the motor torque. Increasing the number of revolutions of the lubricant application roller increases the amount of lubricant applied, and conversely, decreasing the number of rotations decreases the amount of application. The amount of change can be freely reduced within the allowable range of the motor torque, but it is preferable to adjust according to the amount exceeding the reference value 2.
Note that, as shown in FIG. 14, even if the amount of lubricant applied is changed, the density of the image portion does not change significantly. 14A and 14B are diagrams for explaining detection results of image density and color of a solid portion in an image on the recording material C when printing is performed.

Other embodiments.
In each of the above-described embodiments, when a toner image is visualized using a plurality of toners of different colors in the developing section 84, the detecting section 60 separates the color of the background reference portion of the transferred member and forms an image. It is desirable to be able to detect the image density and color of the transferred member for each color. At this time, it is assumed that the permissible level of scumming is held in a memory that can be referred to by the control unit 70 for each color to be imaged.
In this way, background stains for each image forming color can be detected and improved.

Further, in each of the above embodiments, the image forming conditions can be changed without stopping the image forming process. By doing so, the image forming apparatus 100 can be efficiently operated.

It should be noted that the present invention is not limited to the embodiments shown above. Within the scope of the present invention, each element of the above embodiments can be changed, added, or converted into contents that can be easily conceived by those skilled in the art. Further, the above embodiments can be combined as appropriate.

1Y, 1M, 1C, 1K photoconductors 6Y, 6M, 6C, 6K toner image forming unit (process cartridge)
8 intermediate transfer belts 9Y, 9M, 9C, 9K primary transfer bias roller 10 cleaning device 12 secondary transfer backup roller 15 intermediate transfer unit 19 secondary transfer rollers 30, 90 transfer section 31 secondary transfer section 60 detection section 80 image forming section 81 Image carrier 82 Charging unit 83 Exposure unit 84 Development unit 85 Lubricant application unit 86 Potential detection unit 91 Secondary transfer first power supply 92 Secondary transfer second power supply

Japanese Patent No. 4348951

Claims (10)

an image carrier that carries a latent image;
a developing device that visualizes the latent image on the image carrier into a toner image;
a transfer device for transferring the toner image onto a transfer receiving member;
a detection device for detecting image density and color of the transferred member;
a memory for holding a preset permissible level of scumming for the image density and color;
with
The background portion is always an area where no color exists in the image data and the charged area of the image carrier is developed and transferred to the transfer receiving member;
Assuming that the background reference portion is an area on the transfer-receiving member that is not in direct or indirect contact with the image bearing member,
An image forming apparatus for changing image forming conditions when the difference in image density and color between the background portion and the background reference portion exceeds the allowable level. The transfer-receiving member is a plurality of types of recording materials,
2. The image forming apparatus according to claim 1, wherein the memory stores the permissible level and the density and color of the background reference portion for each type of the recording material. The detection device is provided so as to be capable of detecting image density and color of a conveying surface on which the recording material is placed and conveyed as the transfer receiving member,
3. The image forming apparatus according to claim 2, wherein the memory holds the density and color of the background reference portion of the conveying surface. The developing device visualizes the toner image using a plurality of toners of different colors,
The detection device decomposes the color of the background reference portion and detects the image density and color of the transferred member for each color to be imaged,
4. The image forming apparatus according to claim 1, wherein the memory stores the permissible level of the scumming for each color of the image to be formed. further comprising a charging device for charging the surface of the image carrier,
5. The image forming condition according to any one of claims 1 to 4, wherein the image forming condition to be changed is a charging applied voltage applied by the charging device to the surface of the image carrier, and the charging applied voltage is lowered. Image forming device. further comprising a measuring device for measuring the surface potential of the image carrier,
6. The image forming apparatus according to claim 5, wherein the charging applied voltage has a lower limit based on a change in the surface potential. further comprising an applicator for applying a lubricant onto the image carrier;
7. The image forming apparatus according to claim 1, wherein the image forming condition to be changed is a lubricant application amount, and the lubricant application amount is reduced. 8. The image forming apparatus according to claim 7, wherein a lower limit of the lubricant application amount is set based on a load of driving means for driving the application device. The transfer device has a secondary transfer charging device through which a secondary transfer current flows,
further comprising a secondary transfer power supply device for applying a voltage to the secondary transfer charging device to charge it,
9. The image according to any one of claims 1 to 8, wherein the image forming condition to be changed is the voltage applied by the secondary transfer power supply device to the secondary transfer charging device, and the voltage is lowered. forming device. 10. The image forming apparatus according to claim 1, wherein the image forming conditions are changed without stopping image forming processing.

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