JP2015060101A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that eliminates unnecessary usage of toner during an image carrier refresh mode to remove discharge products on an image carrier, so as to suppress occurrence of abnormal images.SOLUTION: A ROM of control means 50 stores, as a data table, the relationship between conditions including temperature, humidity, and exposure time and the "appropriate adhesion amount of toner necessary for a photoreceptor refresh mode," which has been determined through experiments in advance. The control means 50 detects the adhesion amount of toner of a toner pattern formed on an intermediate transfer belt before executing the photoreceptor refresh mode, compares the detected amount with a target value extracted from the data table, and adjusts the difference and causes an optimal adhesion amount of toner to be adhered to a photoreceptor drum. Subsequently, the control means 50 executes the photoreceptor refresh mode.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, and a multifunction machine provided with at least one of them.

In this type of image forming apparatus, the surface of the photosensitive drum is uniformly charged by the charging device, and then an electrostatic latent image is formed on the photosensitive drum by the exposure device based on the image information. Is visualized as a toner image by a developing device.
The toner image is directly or indirectly transferred to a transfer material via an intermediate transfer member, and then the transfer material is passed through a fixing device to fix the toner image.
Residual toner and the like are removed from the surface of the photosensitive drum after the toner image is transferred by a cleaning device.

When a charging bias is applied by the charging device, ozone and nitrogen compound (NOx) are generated.
These discharge products are discharged out of the apparatus by an air flow for stabilizing the temperature around the photosensitive drum during image formation.
However, since the airflow stops after the image formation is completed, the discharge product remains around the photosensitive drum and adheres to the surface of the photosensitive drum.
When the discharge product adheres to the surface of the photosensitive drum, the charging characteristics of the photosensitive drum are greatly changed, and when a halftone image is formed, an abnormal image in which the portion is whitened is generated.
This phenomenon occurs especially after being left for a long time in a high temperature and high humidity environment.

In order to suppress the occurrence of such an abnormal image, it has been conventionally performed to execute a photoreceptor refresh mode for removing discharge products adhering to the surface of the photoreceptor drum before image formation.
The photoreceptor refresh mode is executed when the apparatus is left for a long time in an environment of high temperature and high humidity.
In the photoreceptor refresh mode, it is known that the toner is adhered to the surface of the photoreceptor drum and the discharge product is removed together with the toner by the cleaning device, as compared with the case where the toner is not adhered. .
This is presumably because the toner acts to scrape off the discharge products.

As another countermeasure for preventing the abnormal image, Patent Document 1 discloses that in a cleanerless system, a toner carrying region is formed on the surface of the photosensitive drum, and toner is not interposed between the photosensitive drum and the charging device during non-image formation. A configuration is disclosed in which the discharge product is prevented from adhering to the surface of the photosensitive drum by being interposed.
Patent Document 2 discloses a configuration in which a heater is provided to control the atmospheric temperature in the apparatus to suppress image blur and image flow under high humidity.

The toner used in the photoreceptor refresh mode is a non-contributing toner that does not contribute to actual image formation because it is used for the purpose of promoting the removal of discharge products.
For this reason, the amount to be used must be an appropriate amount necessary for refreshing the photosensitive drum. If the amount used is more than necessary, the toner is consumed wastefully, which is uneconomical, which increases the running cost. It can also contribute.
In Patent Document 1, the thickness of the toner layer (toner adhesion amount) that can suppress image blur is determined from the relationship with the discharge time, and the content is applicable to the appropriate amount of toner used in the photoreceptor refresh mode. Absent.
As in the invention described in Patent Document 2, in the method of providing a heater, an increase in cost due to the provision of the heater cannot be avoided, and the complexity of heater control at high temperatures and high humidity cannot be avoided.

  The present invention was devised in view of such a current situation, and is an image forming apparatus that eliminates waste of the amount of toner used in an image carrier refresh mode for removing discharge products and can suppress the occurrence of abnormal images. The purpose is to provide.

  To achieve the above object, the present invention provides an image carrier, charging means for charging the image carrier, and latent image formation for forming an electrostatic latent image on the charged image carrier based on image information. Means, a developing means for visualizing the electrostatic latent image as a toner image, and a cleaning means for cleaning the surface of the image carrier, and the toner image is finally transferred to a recording medium and fixed. The image forming apparatus includes an image carrier refresh mode in which toner is attached to the image carrier and the surface of the image carrier is cleaned by the cleaning unit during non-image formation. Control is performed to make the amount of toner attached to the image carrier constant at a target value that is necessary for refreshing the image carrier and is appropriate.

  According to the present invention, the amount of toner adhering to the image carrier in the image carrier refresh mode can always be an appropriate amount, the occurrence of abnormal images can be suppressed, and the uneconomical effect due to wasteful toner consumption can be reduced. Can be suppressed.

1 is a schematic diagram of a main part of a color copying machine as an image forming apparatus according to an embodiment of the present invention. It is a control block diagram. FIG. 6 is a diagram for explaining a problem that the surface potential of the photosensitive drum increases when the developing bias is increased.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, an outline of the configuration of a color copying machine as an image forming apparatus according to the present embodiment will be described with reference to FIG.
This color copying machine has a so-called tandem configuration in which four image forming units are arranged along a horizontal movement surface of an intermediate transfer belt 100 as an intermediate transfer member.

The most upstream image forming unit in the moving direction of the intermediate transfer belt 100 will be described.
Around the photosensitive drum 15a, a charger 10a as a charging unit, an exposure unit 11a as a latent image forming unit, a developing unit 12a as a developing unit, and a primary transfer unit 1 are sequentially arranged in the rotation direction. A next transfer roller 16a, a static eliminator 13a as a static elimination unit, and a drum cleaner 14a as a cleaning unit are arranged.
The primary transfer roller 16 a is disposed to face the photosensitive drum 15 a with the intermediate transfer belt 100 interposed therebetween, and is pressed against the intermediate transfer belt 100.
The drum cleaner 14a has a configuration in which, for example, the cleaning blade comes into contact with the surface of the photosensitive drum 15a so as to face the rotation direction of the photosensitive drum 15a.

Each image forming unit has the same configuration, and the other image forming units are distinguished from each other by adding alphabetic characters b, c, and d.
The developing device of each image forming unit stores toners of yellow, magenta, cyan, and black in an appropriate order.

The intermediate transfer belt 100 is rotatably supported mainly by support rollers 30 and 31 and is in contact with the photosensitive drums 15a to 15d.
The intermediate transfer belt 100 is rotationally driven using the support roller 30 as a driving roller, and moves endlessly in the direction of the arrow (clockwise direction).

Next, the image forming operation of the color copying machine will be described. Note that the alphabet for distinguishing the image forming units is omitted.
The photosensitive drum 15 is charged to a predetermined charging potential by the charger 10.
Thereafter, based on image information (image data) from a scanner (not shown) or a PC (personal computer), a laser beam is irradiated from the exposure device 11 to form an electrostatic latent image on the charged photosensitive drum 15. The
The electrostatic latent image is visualized as a toner image by the developing device 12.
The toner image formed on the photosensitive drum 15 is transferred onto the intermediate transfer belt 100.

In this case, the toner image is transferred onto the intermediate transfer belt 100 by applying a transfer bias with a current or voltage controlled by a constant current or a constant voltage to the primary transfer roller 16.
After the toner image is transferred onto the intermediate transfer belt 100, the photosensitive drum 15 has a process in which the residual charge is removed by the static eliminator 13, the toner remaining on the surface is removed by the drum cleaner 14, and the process returns to the charging step. Repeated.
The toner images on the respective photosensitive drums 15 are transferred onto the intermediate transfer belt 100 in a superimposed manner.

The toner image superimposed and transferred on the intermediate transfer belt 100 is transferred between a secondary transfer counter roller 103 that is one of the rollers that support the intermediate transfer belt 100 and a secondary transfer roller 102 as a secondary transfer unit. The secondary transfer portion is formed.
In accordance with this timing, the image is finally transferred onto a transfer material (hereinafter also referred to as “paper”) 104 as a recording medium conveyed by the registration rollers 22 and 23.
In the secondary transfer portion, a current is applied to the secondary transfer roller 102, and the transfer current flows into the secondary transfer counter roller 103, whereby the toner on the intermediate transfer belt 100 is transferred to the transfer material 104.
The transfer material 104 holding the toner image is passed through a fixing device as a fixing unit including the heating roller 21 and the pressure roller 20, and the toner is fixed to the transfer material.
After the fixing, the transfer material 104 is discharged to a discharge tray (not shown).

If the image forming apparatus is not used for a long time in an environment of high temperature and high humidity, discharge products such as ozone and nitrogen compounds generated from the charger 10 adhere to the surface of the photosensitive drum 15.
When the discharge product adheres, the charging characteristics of the photosensitive drum 15 are deteriorated. That is, when charging is performed by the charger 10 in order to form an image with the discharge product attached, charging unevenness occurs.
For this reason, when a halftone image or the like is printed out, an abnormal image appears white in the lateral direction of the paper.
In order to prevent this abnormal image, when left for a long time in an environment of high temperature and high humidity, a certain amount of toner is adhered to the photosensitive drum, so that ozone or Discharge products such as nitrogen compounds are removed with a drum cleaner 14.
This operation is referred to as an image carrier refresh mode (hereinafter referred to as “photoreceptor refresh mode”).

The photoreceptor refresh mode is executed by the control means 50 shown in FIG. The control means 50 is a microcomputer provided with a CPU, ROM, RAM, I / O interface and the like.
The image forming apparatus main body is provided with a temperature sensor 52 for detecting the temperature of the environment in which the apparatus is used and a humidity sensor 54 for detecting the humidity. These detection information is sent to the control means 50.
During normal image formation, image density adjustment (process control) is executed at a predetermined timing.

At the time of process control, a toner pattern is created, and the toner pattern transferred onto the intermediate transfer belt 100 is detected by a toner sensor 56 as toner adhesion amount detection means for detecting the toner adhesion amount.
The toner sensor 56 is a reflective optical sensor.
Although not clearly shown in FIG. 1, the toner sensor 56 is disposed in the vicinity of the support roller 30 so as to face the surface of the intermediate transfer belt 100.
The image density is adjusted based on the detection result of the toner sensor 56.

In the ROM of the control means 50, the relationship between the conditions such as temperature, humidity, and leaving time, and the corresponding “appropriate amount of toner necessary and appropriate for the photoreceptor refresh mode” is obtained in advance by experimentation and the like. Stored as a table.
“Toner adhesion amount necessary and appropriate for the photoreceptor refresh mode” is a target value of the toner adhesion amount used in the photoreceptor refresh mode.
When left for a long time in an environment of high temperature and high humidity, the charging characteristics of the photosensitive drum are deteriorated, so that the toner cannot be exposed by exposure in the same manner as in normal image formation.

The control unit 50 performs control for forming a toner pattern for the refresh mode on the photosensitive drum having a deteriorated charging characteristic before executing the photosensitive member refresh mode.
A toner sensor 56 detects the toner adhesion amount of the refresh mode toner pattern transferred onto the intermediate transfer belt 100.
The toner adhesion amount detected by the toner sensor 56 is compared with the toner adhesion amount (target value) corresponding to the current environmental conditions extracted from the reference table, and the difference is adjusted to determine the optimum toner adhesion amount. To adhere to the photosensitive drum.
The toner adhesion amount is adjusted by adjusting the developing bias by controlling the developing bias source 58.

When the adjustment amount for obtaining an appropriate toner adhesion amount is large, the development bias is set high as shown in FIG.
However, as a result, the potential of the surface of the photosensitive drum also increases, and a potential difference between the developing device and the photosensitive drum cannot be obtained, and the target toner adhesion amount may not be obtained.
In such a case, the control means 50 turns on the static eliminator 13 according to the value of the developing bias so as to lower the surface potential of the photosensitive drum.
That is, the potential of the surface of the photosensitive drum is always reduced to zero. As a result, a target potential difference can always be created between the developing device and the surface of the photosensitive drum, so that a target toner adhesion amount can be adhered to the photosensitive member.
In this way, the control unit 50 performs control to turn on / off the static eliminator 13 according to the value of the developing bias.

In the photoreceptor refresh mode, the discharge product is removed together with the toner by the drum cleaner 14 while rotating the photoreceptor drum 15 with the target toner adhesion amount adhered to the photoreceptor.
At this time, the toner on the photosensitive drum 15 is not transferred to the intermediate transfer belt 100.
The photoreceptor refresh mode is executed at a predetermined timing described later.
As a result, abnormal images can be prevented without wasting toner.

When the adjustment amount for obtaining an appropriate toner adhesion amount is small, the developing bias is set low.
However, when the lower limit of the value that can output the developing bias is below the potential difference between the developing device and the photosensitive drum, the target adhesion amount is not increased and the toner adhesion amount increases.
In such a case, the control means 50 controls the potential of the surface of the photosensitive drum to be raised in advance by applying a bias of the charger.
That is, the charging bias is adjusted according to the value of the developing bias.

In this way, even if the value of the developing bias is increased, the potential difference from the surface of the photosensitive drum can be reduced.
As a result, a target potential difference can always be created between the developing unit and the surface of the photosensitive drum (stabilization).
Thereby, a target toner adhesion amount can be adhered to the photosensitive drum, and an abnormal image can be prevented without wastefully consuming the toner.

The control means 50 monitors the leaving time after the image forming operation is ended by a timer (not shown), and when a predetermined condition (leaving time, temperature, humidity) is reached, that is, a predetermined timing at the time of non-imaging. To execute the photoreceptor refresh mode.
In the present exemplary embodiment, the toner adhesion amount detection unit is configured to use the toner sensor 56 that is generally used during process control of the image forming apparatus, but may be provided separately.

In this embodiment, the toner pattern for the refresh mode is detected by the toner sensor 56 on the intermediate transfer belt 100. However, the toner pattern for the refresh mode on the photosensitive drum is directly detected on the photosensitive drum. It is good also as a structure.
In this case, the toner sensor 56 is disposed opposite to the photosensitive drum 15 on the downstream side of the developing device 12a.
Since the toner adhesion amount to be actually controlled is the toner adhesion amount on the photosensitive drum, the direct detection configuration has higher accuracy.
In the above-described embodiment, the direct transfer type image forming apparatus is exemplified. However, the direct transfer type image forming apparatus that transfers the toner images on the respective photosensitive drums on the transported recording medium is similarly implemented. be able to.
In the above embodiment, a four-color type tandem configuration is exemplified, but the present invention can be similarly applied to a multi-color configuration of three colors or less and a monochrome machine.

DESCRIPTION OF SYMBOLS 10 Charger as charging means 11 Exposure device as latent image forming means 12 Developer as developing means 13 Charger as neutralizing means 14 Drum cleaner as cleaning means 15 Photosensitive drum as image carrier 56 Toner adhesion amount Toner sensor as detection means

JP 2002-31998 A JP 2001-75461 A

Claims (7)

An image carrier, a charging unit that charges the image carrier, a latent image forming unit that forms an electrostatic latent image on the charged image carrier based on image information, and the electrostatic latent image as a toner image In an image forming apparatus comprising: a developing unit that visualizes an image; and a cleaning unit that cleans a surface of the image carrier, and the toner image is finally transferred to a recording medium and fixed.
At the time of non-image formation, it has an image carrier refresh mode in which toner is attached to the image carrier and the surface of the image carrier is cleaned by the cleaning means,
An image forming apparatus characterized in that control is performed to make a toner adhesion amount that adheres to the image carrier in the image carrier refresh mode constant at a value that is necessary and appropriate for refreshing the image carrier. The image forming apparatus according to claim 1.
A toner adhesion amount detecting means for detecting the toner adhesion amount on the image carrier,
Prior to executing the image carrier refresh mode, a toner pattern is formed on the image carrier, and the toner adhesion amount of the toner pattern is detected by the toner adhesion amount detection means. An image forming apparatus characterized in that the value is a value. The image forming apparatus according to claim 1.
The toner image formed on the image carrier is transferred to an intermediate transfer member and then transferred to a recording medium.
A toner adhesion amount detecting means for detecting the toner adhesion amount on the intermediate transfer member;
Before executing the image carrier refresh mode, a toner pattern is formed on the image carrier, and the toner adhesion amount of the toner pattern on the intermediate transfer member is detected by the toner adhesion amount detection means. The image forming apparatus is characterized in that the target value is set based on the above. The image forming apparatus according to claim 3.
An image forming apparatus, wherein the toner adhesion amount detection means is a toner adhesion amount detection means used for image density adjustment in normal image formation. In the image forming apparatus according to any one of claims 2 to 4,
An image forming apparatus, wherein the target value is obtained by adjusting a developing bias. The image forming apparatus according to claim 5.
An image forming apparatus, comprising: a charge eliminating unit that removes electric charges of the image carrier, and turning the charge eliminating unit on and off according to a value of a developing bias. The image forming apparatus according to claim 5.
An image forming apparatus, wherein a charging bias by the charging unit is adjusted according to a value of a developing bias.

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