JP2013109043A - Image stabilization method, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stabilization control of image density frequently in a short period without causing a decrease in image productivity and an increase in toner consumption.SOLUTION: An image stabilization method performed in a tandem-type color image forming apparatus 100 for forming a toner image on an intermediate transfer body 120 includes the steps of: detecting an amount of printing for every color; calculating an integrated value of the amount of printing for every color; forming fog of toner in one color that is predetermined and indicates the largest integrated value of the amount of printing on the intermediate transfer body at a predetermined timing; detecting the amount of the toner fog formed on the intermediate transfer body; and adjusting at least one of parameters that determines density of a toner image on the basis of the amount of the toner fog.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a facsimile machine, and a combination machine combining these, and more particularly to a color image forming apparatus capable of forming a color image using a plurality of color toners, and more particularly in a color image forming apparatus. It relates to stabilizing the toner image density.

  Although there are various types of color image forming apparatuses, the present invention particularly includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and each of the image forming units includes the above-described image forming unit. An electrostatic latent image corresponding to the assigned color is formed on the image carrier that is rotationally driven facing the intermediate transfer member, and the electrostatic latent image is developed using the assigned color toner to form a toner image. The image forming unit is capable of transferring an image to the intermediate transfer member, and the transfer toner image on the intermediate transfer member is related to a so-called tandem type image forming apparatus capable of transferring to a recording medium. Hereinafter, this type of image forming apparatus may be referred to as a “tandem type image forming apparatus”.

  In an electrophotographic image forming apparatus, the development of an electrostatic latent image is affected by variations in factors that affect the developability of the electrostatic latent image. Therefore, the image density is constant regardless of variations in factors that affect the developability. In general, image stabilization control for keeping the image at regular intervals is performed. Generally, image stabilization control is also performed in a tandem type image forming apparatus.

  In the image stabilization control, a toner pattern for image stabilization control is created, the toner pattern density is detected by the toner density detection means, and as a result, at least one of the parameters related to developability is determined by the target toner image density. A method of correcting in the obtained direction is common.

  Such image stabilization control has been performed for a long time, and is described in, for example, Japanese Patent Application Laid-Open No. 62-277779. In this publication, when performing image stabilization control in a tandem image forming apparatus, a patch pattern of each color toner for image adjustment is formed on an intermediate transfer member, and the toner adhesion amount of the patch pattern is measured by a toner adhesion amount sensor. A method for detecting and correcting a parameter related to the developability of each color (in the case of the same publication, the toner density in the developing device) in the direction in which the target toner image density or the like is obtained is described. Has been.

Japanese Patent Laid-Open No. 62-267777

  However, the developer is carried to the developing unit of the developing device that develops the electrostatic latent image formed on the image carrier, that is, the development area that develops the electrostatic latent image on the image carrier such as a photoreceptor. In a developing unit where a developing member such as a developing roller that is conveyed in opposition to the image carrier, the moisture content of the toner tends to be affected by the humidity of the environment in which the developing device is used.

  On the other hand, the toner container in the developing device is highly airtight, and the moisture content of the toner in the toner container is hardly affected by the use environment.

  Therefore, when the image forming apparatus is left in a high or low humidity environment (for example, when it is left in a state where printing (in other words, image formation) is not performed for a long time in an office that is not air-conditioned such as a holiday) ), The water content of the toner in the developing unit and the water content of the toner in the toner storage unit are greatly different.

  When printing (image formation) by the image forming apparatus is performed from such a state, the toner is consumed in the printing operation and the toner is supplied from the toner container, so that the moisture content of the toner in the developing unit changes. As a result, the developability of the electrostatic latent image changes, and the density of the formed toner image changes.

  This change depends on the moisture content of the toner and the print coverage in the developing unit, and image density adjustment may not be in time in the periodic image stabilization control cycle.

  If density confirmation is performed in a short cycle and parameters related to development are corrected, the image density can be stabilized more reliably. In image stabilization control repeated in such a short cycle, for example, color image formation In the case of an apparatus, a toner pattern for image stabilization control is created for each of a plurality of color toners, and the toner pattern density is detected by the toner density detecting means. As a result, there arises a disadvantage for the user, such as an increase in toner consumption due to formation of a toner pattern for image stabilization control.

  The present invention includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and each of the image forming units is in charge of an image carrier that is driven to rotate toward the intermediate transfer member. An image forming unit that forms an electrostatic latent image corresponding to a color, develops the electrostatic latent image with a color toner, forms a toner image, and transfers the toner image to the intermediate transfer member The toner image transferred on the intermediate transfer body is an image stabilization method for stabilizing the image density in an image forming apparatus that can transfer to a recording medium. Compared to repeating image stabilization control that moves the density toward the target image density, the image density is moved toward the target image density in a shorter cycle without causing a decrease in image productivity or an increase in toner consumption other than image formation. Image And to provide an image stabilizing method capable of performing reduction control.

  Further, the present invention includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and each image forming unit rotates and faces the intermediate transfer member. An image capable of forming an electrostatic latent image corresponding to the assigned color on the surface, developing the electrostatic latent image with the assigned color toner to form a toner image, and transferring the toner image to the intermediate transfer member An image forming apparatus that is a forming unit and is capable of transferring a transfer toner image on the intermediate transfer member to a recording medium. As described above, an image in which an image density is directed to a target image density in a short cycle in a conventional image forming apparatus Compared to the case where the stabilization control is repeated, it is possible to perform the image stabilization control in which the image density is directed to the target image density in a short cycle without causing a decrease in image productivity or an increase in toner consumption other than image formation. Possible image forming equipment It is an object of the present invention to provide a.

  According to the research of the present inventor, as shown by a solid line in FIG. 6, the toner having a high water content is not easily charged, and therefore the developing efficiency is not good and the density is secured because the force to move to the image carrier by the developing electric field is weak. Hard to do. In such a state, uncharged toner is likely to be generated and appear as fogging (fogging).

  Toner with a low water content is easily charged, but if the charge amount is too high, the force to move to the image carrier by the development electric field is strong, but the amount of toner that can be moved to the image carrier with the same development energy decreases. (In other words, the toner that can be moved to the image carrier when the exposed portion of the image carrier immediately reaches an electrically balanced state with a small amount of toner because the highly charged toner moves to the image carrier. Therefore, it is difficult to secure the concentration. Also, highly charged toner tends to carry uncharged toner to the image carrier and fog is likely to appear.

  Here, “fogging” or “toner fogging” refers to a state in which toner adheres in a scattered manner to a portion of an image carrier such as a photosensitive member where toner should not adhere, or an intermediate transfer member. In this state, the toner adheres like dots.

  The toner charge amount line indicated by a broken line in FIG. 6, together with the solid development efficiency (image density) line and the fog amount line, is likely to cause fogging if the toner charge amount is too low or too high, resulting in a decrease in image density. It is easy to do.

  According to the inventor's research, there is a correlation between the image density and the fog toner amount as described above, and in the image stabilization process, the fog toner amount can be obtained without creating a toner pattern for detecting the toner density. Thus, it is possible to grasp the developability of the toner.

  By checking the density not with the toner pattern but with the fog toner amount, even if the frequency of the image density stabilization processing is increased, the toner consumption amount does not increase to the extent that it should be regarded as a problem.

  Further, according to the inventor's research, even without checking the fog amount of all color toners, the toner consumption is large, the toner in the developing part is quickly replaced, and therefore the color toner whose density change is large, Image density adjustment can also be performed by determining the amount of fog toner for that color, and adjusting the density based on the result, and according to such a method, the image stabilization processing time can be shortened, thereby ensuring more certainty. Image stabilization processing can be performed frequently and finely while suppressing a decrease in image productivity.

  Since the image stabilization processing time can be shortened, toner fog is formed between the pages when forming images of multiple pages where the number of pages to be imaged is continuous on the intermediate transfer member, thereby ensuring more reliable image stabilization processing. Can be performed frequently and finely while suppressing the decrease in image productivity.

The toner of a color that consumes a lot of toner and the toner in the developing portion is replaced quickly, and therefore the density change is large, can be determined from the information of the image to be printed.

The present invention provides the following image stabilization method and image forming apparatus based on such knowledge.
(1) Image Stabilization Method An image carrier that includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and each image forming unit is rotationally driven toward the intermediate transfer member An electrostatic latent image corresponding to the assigned color is formed on the body, the electrostatic latent image is developed using the assigned color toner to form a toner image, and the toner image can be transferred to the intermediate transfer member An image forming unit, and an image stabilization method for stabilizing an image density in an image forming apparatus capable of transferring a transfer toner image on the intermediate transfer member to a recording medium,
A print amount detecting step for detecting a print amount for each color constituting the toner image when forming a target toner image on the intermediate transfer member using one or more of the image forming units;
A print amount integrated value integrating step for calculating an integrated value of the print amount for each color detected in the print amount detecting step;
The color indicating the largest print amount integrated value among the print amount integrated values for the respective colors obtained in the print amount integrated value integrating step, and a predetermined color toner on the intermediate transfer member. A fog is formed in the image forming section in charge of the color at a predetermined timing, and when the number of pages on which the image is to be formed on the intermediate transfer member is a plurality of continuous pages, the interval between the pages is adopted as the timing. Forming step;
A fog detection step for detecting the amount of toner fog formed on the intermediate transfer member;
An image density that adjusts at least one of the parameters that affect the density of the toner image based on the toner fog amount on the intermediate transfer member detected in the fog amount detection step so that the toner image density is directed toward the target density. An image stabilization method including adjustment steps.

(2) Image forming apparatus An image transfer body that includes an intermediate transfer body and a plurality of image forming sections sequentially arranged along the intermediate transfer body, and each of the image forming sections is driven to rotate toward the intermediate transfer body. An image capable of forming an electrostatic latent image corresponding to the assigned color on the surface, developing the electrostatic latent image with the assigned color toner to form a toner image, and transferring the toner image to the intermediate transfer member An image forming apparatus capable of transferring a transfer toner image on the intermediate transfer member to a recording medium,
A print amount detecting means for detecting a print amount for each color constituting the toner image when forming a target toner image on the intermediate transfer member using one or more of the image forming units;
A print amount integrated value integrating means for calculating an integrated value of the print amount for each color detected by the print amount detecting means;
On the intermediate transfer body, the toner of one color which is the color indicating the largest print amount integrated value among the print amount integrated values for each color obtained by the print amount integrated value integrating means and which is a predetermined color. A fog is formed in the image forming section in charge of the color at a predetermined timing, and when the number of pages on which the image is to be formed on the intermediate transfer member is a plurality of continuous pages, the interval between the pages is adopted as the timing. Forming means;
A fog amount detecting means for detecting the amount of toner fog formed on the intermediate transfer member;
An image density that adjusts at least one of the parameters that influence the density of the toner image based on the toner fog amount on the intermediate transfer member detected by the fog amount detection means so that the toner image density is directed toward the target density. An image forming apparatus including an adjusting unit.

  In these image stabilization methods and image forming apparatuses, “the color indicating the largest print amount integrated value among the print amount integrated values for each color obtained in the print amount integrated value integrating step (the print amount integrated value integrating means)” is used. The "predetermined color" in the description of "predetermined color" is the color when there is one color indicating the largest print amount integrated value, and the color indicating the largest print amount integrated value. Is a predetermined color among the plurality of colors. For example, in the case where yellow, magenta, cyan, and black image forming portions are arranged in this order in the intermediate transfer member surface movement direction, the yellow and cyan print amount integrated values are the same. If it is the largest, it is possible to exemplify a case where yellow having the highest arrangement order of image forming units is a “predetermined color”.

  According to the image stabilization method and the image forming apparatus according to the present invention, instead of detecting the density of all colors using the toner pattern and adjusting the density, the color toner that consumes a large amount of toner is selected from the image information to be printed. By reducing the number of colors and reducing the toner fog detection time for one time, the amount of fogging for that color can be detected, and the image density can be adjusted based on that information. The image density can be stabilized without causing a decrease in image productivity and an increase in toner consumption.

In both the image stabilization method according to the present invention and the image forming apparatus according to the present invention, each of the image forming units develops a toner image by developing an electrostatic latent image on the image carrier under a developing bias. A developing device for forming can be included.
In the fog forming step (fogging forming means), the color indicating the largest integrated value among the print amount integrated values for each color obtained in the print amount integrated value integrating step (the print amount integrated value integrating means); In addition, in forming the fog on the intermediate transfer member of one color toner having a predetermined color in the image forming unit in charge of the color, a developing bias is applied to the developing device in the image forming unit in charge of the color. The fog can be formed without applying a developing bias to the developing device in other image forming units.

  By forming fog in this manner, fog toner other than the color to be detected can be prevented from appearing on the intermediate transfer member, and the fog toner amount can be detected with such accuracy.

  According to the present invention, the image forming unit includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and the image forming units are rotated to face the intermediate transfer member. Image formation capable of forming an electrostatic latent image corresponding to the assigned color, developing the electrostatic latent image using the assigned color toner to form a toner image, and transferring the toner image to the intermediate transfer member An image stabilization method for stabilizing an image density in an image forming apparatus capable of transferring a transfer toner image on the intermediate transfer member to a recording medium, and the image density is targeted at a short cycle in a conventional image forming apparatus. Compared to repeating image stabilization control that moves toward image density, image stabilization that moves image density to the target image density in a short cycle without reducing image productivity or increasing toner consumption other than image formation Conversion system Image stabilization method capable of performing can be provided.

  In addition, according to the present invention, the image bearing unit includes an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and each of the image forming units rotates and faces the intermediate transfer member. An electrostatic latent image corresponding to the assigned color is formed on the body, the electrostatic latent image is developed using the assigned color toner to form a toner image, and the toner image can be transferred to the intermediate transfer member An image forming apparatus that is an image forming unit, and that can transfer a transfer toner image on the intermediate transfer member to a recording medium, and in the conventional image forming apparatus, image stabilization control that causes the image density to move toward a target image density in a short cycle Compared to the case of repeating the above, image stabilization control can be performed to make the image density move to the target image density in a short cycle without causing a decrease in image productivity or an increase in toner consumption other than image formation. Providing equipment It can be.

1 is a diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an apparatus control unit and related parts in the image forming apparatus of FIG. 1. It is a part of flowchart which shows the outline of operation | movement of the apparatus control part shown in FIG. It is the remainder of the flowchart which shows the outline | summary of operation | movement of the apparatus control part shown in FIG. It is a figure which shows the correction value table of the developing bias voltage used by image stabilization control. FIG. 5 is a diagram illustrating a relationship between a toner moisture content, fog generation, and development efficiency (image density), and a relationship between a toner charge amount, fog generation, and development efficiency (image density).

Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the configuration of an example 100 of an image forming apparatus. The image forming apparatus 100 is a tandem type full color printer.

  The printer 100 includes a printing unit 110, a print data development unit 160, an apparatus control unit 170, and a development bias power supply unit 180.

  The printing unit 110 includes an intermediate transfer belt 120. The intermediate transfer belt 120 is wound around a driving roller R1 that can be rotationally driven by a driving unit (not shown) and a counter roller R2 that faces the driving roller R1, and is rotated in the CCW direction in the drawing.

  A cleaning device CL for cleaning the secondary transfer residual toner and the like on the transfer belt 120 faces the opposing roller R2, and a secondary transfer roller 121 faces the drive roller R1.

  The secondary transfer roller 121 is pressed against a portion of the intermediate transfer belt 120 supported by the driving roller R1 by a pressing unit (not shown), forms a nip portion with the intermediate transfer belt 120, and rotates the intermediate transfer belt 120. It can be rotated by being driven, or following the movement of the recording sheet S fed into the nip portion, as will be described later, or driven by a drive unit (not shown). A secondary transfer bias can be applied to the secondary transfer roller 121 from a power supply (not shown).

  A fixing device 122 is disposed above the intermediate transfer belt 120 and the secondary transfer roller 121, a registration roller pair 130 is disposed below, and a recording sheet S such as recording paper is accommodated below the fixing roller pair 130. The recorded sheet storage cassette 140 is disposed.

  The fixing device 122 includes a fixing heating roller incorporating a heat source such as a halogen lamp heater and a pressure roller pressed against the fixing heating roller. The fixing device 122 may be other types.

  The recording sheets S stored in the recording sheet storage cassette 140 can be pulled out one by one by the supply roller device 141 and supplied to the registration roller pair 130.

  Between the rollers R1 and R2 around which the intermediate transfer belt 120 is wound, the yellow image forming unit 101Y and the magenta image forming unit 101M are moved along the transfer belt 120 from the roller R2 to the roller R1. , A cyan image forming unit 101C and a black image forming unit 101Bk are arranged in this order.

  Each of the image forming units 101Y, 101M, 101C, and 101Bk includes a drum-type photoreceptor 1 as an electrostatic latent image carrier, and a charger 2, a developing device 4, and a cleaning device 5 are provided around the photoreceptor. They are arranged in this order.

  An image exposure device 123 is disposed below these image forming units. The image exposure device 123 includes a yellow exposure unit 3Y that performs image exposure on the photoreceptor 1 in the yellow image forming unit 101Y to form a yellow image electrostatic latent image (yellow electrostatic latent image). The yellow exposure unit 3Y is arranged on the photosensitive member 1 based on yellow image information from the print data development unit 160 to which image information is provided from an external device 200 such as a personal computer or an image reading device. Yellow electrostatic latent image).

The image exposure apparatus 123 also includes a magenta exposure unit 3M for the unit 101M, a cyan exposure unit 3C for the unit 101C, and a black exposure unit 3Bk for the unit 101Bk.
Each exposure unit can perform image exposure on the photosensitive member 1 by blinking of a laser beam in accordance with image information provided from the print data development unit 160.

  A primary transfer roller 6 is disposed opposite to the photoreceptor 1 of each image forming unit with a belt 120 therebetween. The primary transfer roller 6 is pressed in the direction of the photoconductor 1 by a pressing unit (not shown), can contact the belt 120 and rotate, and can bring the belt 120 into contact with the photoconductor 1.

  A primary transfer bias for primary transfer of a toner image formed on the photoreceptor 1 to the belt 120 can be applied to the primary transfer roller 6 from a power supply (not shown).

  The photoconductor 1 in each image forming unit is a negatively chargeable photoconductor here, and can be driven to rotate clockwise in the drawing by a photoconductor drive motor (not shown).

  The charger 2 in each image forming unit is a scorotron charger in this example, and a charging voltage is applied from a power supply (not shown) at a predetermined timing. The charger 2 may be one using a charging roller.

  The developing device 4 in each image forming unit uses a so-called two-component developer mainly composed of a magnetic carrier and a nonmagnetic toner to generate an electrostatic latent image formed on the photoreceptor 1 from the developing bias power supply unit 180. Reversal development can be performed by the developing roller 41 to which a developing bias is applied. The developing device 4 may perform development using a so-called one-component developer containing toner as a main component.

  The developing bias power supply unit 180 can apply a bias Vdv_Y for forming a yellow toner image to the developing roller 41 of the image forming unit 101Y under the instruction of the control unit 170 described later. Similarly, a bias Vdv_M for forming a magenta toner image is formed on the developing roller 41 of the unit 101M, a bias Vdv_C for forming a cyan toner image is formed on the developing roller 41 of the unit 101C, and a black toner image is formed on the developing roller 41 of the unit 101Bk. Bias Vdv_Bk can be applied.

  Each of the image forming units, the exposure unit, and the primary transfer roller corresponding to each of the image forming units constitute an image forming unit that forms an assigned color toner image by an electrophotographic method and performs primary transfer onto the intermediate transfer belt 120.

The apparatus control unit 170 controls the operation of the entire printer, and each unit of the printer operates at a predetermined timing based on an instruction from the control unit 170.
The print data expansion unit 160 expands print information from the external device 200 into pixel data for printing, and includes a print amount calculation unit 161. The print amount calculation unit 161 calculates the print amount for each page printed.

The print amount calculation unit 161 prints each of the yellow image forming unit 101Y, the magenta image forming unit 101M, the cyan image forming unit 101C, and the black image forming unit 101Bk each time the print information from the external device 200 is developed into image data. The amounts Cov_Y, Cov_M, Cov_C, and Cov_Bk are calculated.
Here, the print amount is the number of dots that expose the photosensitive member 1 to form a toner image or a value that correlates with it.

  The apparatus control unit 170 receives information from the print data development unit 160 and controls the operation of the image forming apparatus 100 by controlling the printing unit 110 and the developing bias power supply unit 180.

According to this printer, an image can be formed using one or more of the 101Y, 101M, 101C, and 101Bk image forming units.
Taking a case where a full color image is formed using all of the image forming units as an example, first, a yellow toner image is formed in the yellow image forming unit 101Y, and this is primarily transferred to the transfer belt 120.

  That is, in the yellow image forming unit 101Y, the photosensitive member 1 is rotationally driven in the clockwise direction in the drawing, and the surface of the photosensitive member 1 is uniformly charged to a predetermined potential by the charger 2. From the exposure unit 3Y of the exposure device 123 to the charging area. The yellow image exposure is performed, and an electrostatic latent image for yellow is formed on the photoreceptor 1. This electrostatic latent image is developed by the developing roller 41 to which the developing bias Vdv_Y of the developing device 4 having yellow toner is applied, and becomes a visible yellow toner image. The yellow toner image is primarily transferred onto the transfer belt 120 by the primary transfer roller 6. At this time, a primary transfer bias is applied to the primary transfer roller 6 from a power supply (not shown).

Similarly, a magenta toner image is formed in the magenta image forming unit 101M and transferred to the transfer belt 120, a cyan toner image is formed in the cyan image forming unit 101C and transferred to the transfer belt 120, and the black toner in the black image forming unit Bk. An image is formed and transferred to the transfer belt 120.

Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 120 in an overlapping manner.
Thus, the multiple toner images formed on the transfer belt 120 move to the secondary transfer roller 121 by the rotation of the transfer belt 120.

  On the other hand, the recording sheet S is pulled out from the recording sheet storage cassette 140 by the supply roller device 141, supplied to the registration roller pair 130, and is on standby.

  In this way, the recording sheet S waiting at the registration roller pair 130 is supplied to the nip portion between the transfer belt 120 and the secondary transfer roller 121 in accordance with the multiple toner image sent by the intermediate transfer belt 120. . The multiple toner images are secondarily transferred onto the recording sheet S by a secondary transfer roller 121 to which a secondary transfer bias is applied from a power supply (not shown).

  Thereafter, the recording sheet S is passed through the fixing device 122 where the multiple toner images are fixed on the recording sheet S under heat and pressure. The recording sheet S is continuously discharged to the discharge tray 124 by the discharge roller pair DR.

  In the primary transfer of the toner image to the belt 120, residual toner or the like remaining on the photosensitive member 1 is cleaned by the cleaning device 5, and residual secondary toner or the like remaining on the belt 120 by the secondary transfer is cleaned by the cleaning device CL. It is cleaned with. Each of these cleaned and removed toners is sent to a waste container by a conveying means (not shown).

  In this printer 100, image stabilization control for keeping the density of the formed image constant is performed at a predetermined timing. The device control unit 170 will be further described in relation to the image stabilization control.

  As shown in FIG. 2, the control unit 170 includes a calculation unit 171, a print amount integration unit 172, a fog amount storage unit 173, a development bias storage unit 174, a toner replenishment amount integration unit 175, a voltage correction table 176, and a clock unit 177. It is out.

The print amount integrating unit 172 integrates the print amounts Cov_Y, Cov_M, Cov_C, and Cov_Bk of the respective colors received from the print amount calculating unit 161 of the print data developing unit 160 for each color, and print amount integrated values TTL_Cov_Y, TTL_Cov_M, and TTL_Cov_C of each color. TTL_Cov_Bk is obtained.
As will be described later, in determining the toner of the color forming the toner fog for the control of the toner image density stabilization, not only the printing amount for each color for the next one page is calculated, The print amount of each color calculated for the page is also adjusted (accumulated) for each color, and the toner of the color with the largest print amount integrated value is selected as described later, and fog is formed with the toner of that color.

  The fog amount storage unit 173 is a portion that stores fog amounts Fog_S_Y, Fog_S_M, Fog_S_C, and Fog_S_Bk of each color formed on the intermediate transfer belt 120 as described later.

  The development bias storage unit 174 is a part that stores development bias values Vdv_m_Y, Vdv_m_M, Vdv_m_C, and Vdv_m_Bk for each color used during printing.

  The voltage correction table 176 is a part including tables LUT_Y, LUT_M, LUT_C, and LUT_Bk for calculating voltage correction values for correcting the development bias value determined by the image stabilization control.

  The clock unit 177 continuously counts time and is used to calculate the elapsed time from a certain time point.

  The calculation unit 171 receives information from the print data development unit 160 and also detects fog amount information from the toner amount detection unit 150 that detects the amount of fog (fogging toner amount) formed on the intermediate transfer belt 120 as described later. In addition, environmental information from an environmental sensor 151 that detects ambient temperature and humidity is received, and the development bias power supply unit 173 and the like are controlled to stabilize the image density by using the print amount integration unit and the like.

  Here, the toner amount detection unit 150 irradiates light on the fog forming portion of the intermediate transfer belt 120 to obtain the fog amount based on the amount of reflected light, and is known as an optical device that detects toner concentration (image density) and the like. It uses a formula densitometer.

The control operation of image stabilization (image density stabilization) of the control unit 170 will be described with reference to the flowchart of FIG.
In step S101, the presence / absence of print information from the external apparatus 200 is confirmed. If print information is present, the process proceeds to the next step.

When printing information is received from the external device 200, the elapsed time from the previous printing operation is confirmed using the clock unit 177 in step S102.
If it is determined that the printing operation has not been performed for a predetermined long time (24 hours or more in this example) from the previous printing operation, the water content of the developer in the developing unit of the developing device 4 is placed in the printer 100. The image stabilization control is performed and the density is adjusted (S103).

  In addition, the fog amounts Fog_S_Y, Fog_S_M, Fog_S_C, and Fog_S_Bk of each color immediately after the image stabilization control are measured and stored in the fog amount storage unit 173 (S104), and the print amount integration unit 172 is initialized (S105).

  The received print information is developed into exposure data by the print data development unit 160 (S106). At this time, the print amount calculation unit 161 calculates the print amounts Cov_Y, Cov_M, Cov_C, and Cov_Bk for each color (S107), and the print amount integration unit 172 integrates the print amount integration values TTL_Cov_Y, TTL_Cov_M, TTL_Cov_C, and TTL_Cov_Bk for each color. Then, printing (image formation) is started (S109).

  When an image forming operation for one page is performed on the intermediate transfer belt 120, and it is determined in step S110 that the timing is outside the portion corresponding to the recording sheet ("paper" in FIG. 3), each color is determined in step S111. The print amount integrated values TTL_Cov_Y, TTL_Cov_M, TTL_Cov_C, and TTL_Cov_Bk are compared, the color with the largest print amount (the largest integrated value) is selected, and processing according to the result is performed (S200Y, S200M, S200C, or S200Bk) .

  Note that if there is one color with the largest amount of printing, that color is selected. If there are a plurality of colors with the largest amount of printing, here, the surface movement of the belt 120 is selected among the plurality of colors. The color of the unit with the highest order (early order) in the arrangement order of the image forming units in the direction is selected.

  In the following, the yellow print amount integrated value is the largest (the value of TTL_Cov_Y is the largest), and the process proceeds to step S200Y as an example with reference to the flowchart of FIG.

  In the state in which the developing bias is applied in the image forming units of all colors, the fog toners of the respective colors overlap on the intermediate transfer belt 120, and it is difficult to detect the fog amount of a specific color. In order to accurately detect a specific color (the fog toner amount of the selected color), it is desirable that fog toner other than the color whose fog amount is to be measured does not appear on the intermediate transfer belt 120.

  Therefore, in this example, as shown in FIG. 4, in order to confirm the amount of yellow fog toner in step S201Y, the yellow developing bias is turned on, the magenta developing bias is turned off, and the cyan developing bias is turned off with respect to the developing bias power supply unit 180. Instruct to turn off the black developing bias.

  As a result, toner other than yellow toner does not move to the photosensitive member 1, so the fog toner that appears on the intermediate transfer belt 120 is only yellow toner, and the yellow amount that appears on the intermediate transfer belt 120 by the toner amount detection unit 150. The amount of fog toner can be accurately detected.

  Similarly, in the case of toners of other colors, the development bias of the color for checking the fog toner amount is turned on, and the development bias of the other colors is turned off.

With the above setting, the toner fog amount on the intermediate transfer belt 120 is detected as Fog_Y by the toner amount detection unit 150. Based on the detected Fog_Y and the fog amount Fog_S_Y at the time of stabilization, a value Fog_d_Y in which the fog amount has changed is calculated by the following equation (S203).
(Fog_d_Y) = | (Fog_S_Y) − (Fog_Y) |

  In step S204Y, the value Fog_d_Y in which the amount of fog toner has changed is compared with a predetermined value Fog_TH_Y, and if the value Fog_d_Y in which the amount of fog toner has changed is equal to or smaller than the predetermined value Fog_TH_Y, it is determined that there has been no change in density. Then, without calculating the voltage correction value (S205Y), correcting (S206Y), and resetting the print amount integrated value TTL_Cov_Y (S207Y), the process proceeds to step S300.

If the value Fog_d_Y in which the fog toner amount has changed is larger than the predetermined value Fog_TH_Y, it is determined that there has been a change in density, and the LUT_Y of the voltage correction table 176 (LUT_Vdv_Y in FIG. ) To obtain a value for correcting the developing bias (S205Y), and correct the developing bias voltage (applied voltage) as follows (S206Y).
Applied voltage = stabilization determination value (Vdv_m_Y) + correction value In the table of FIG. 5, Fog_Val_1, Fog_Val_2, and Fog_Val_3 are values determined in advance by experiments or the like so as to achieve image density stabilization.

  Here, the applied voltage and the stabilization determination value are negative values, and the larger the absolute value, the higher the image density. The correction value is a value equal to or greater than 0, and the correction is performed so that the toner density decreases as the absolute value of the correction value increases.

  After the correction, the print amount integrated value TTL_Cov_Y is reset (S207Y), and the process proceeds to the next process (S300). Even when another process is selected in step S111, a process according to another color is performed.

  In step S300, it is determined whether or not there is a next page. If there is a next page, the process proceeds to step S106, and if there is no next page, the process ends.

  As described above, in the image density stabilization process in the printer 100, the density of all colors is not detected by using the toner pattern and density adjustment is performed. By selecting the toner and reducing the number of colors, the detection time for one toner fog is shortened, the fog amount of that color is detected, and the image density can be adjusted based on that information. By performing the process between recording sheets, the image density can be stabilized without causing a decrease in image productivity and an increase in toner consumption.

In the tandem type color image forming apparatus, the image density stabilization processing is performed frequently and finely without causing a decrease in image productivity that should be regarded as a problem and an increase in toner consumption for the stabilization processing. Available.

100 Printer (an example of an image forming apparatus)
110 Printing section 101Y Yellow image forming unit 101M Magenta image forming unit 101C Cyan image forming unit 101Bk Black image forming unit 120 Intermediate transfer belt 121 Secondary transfer roller 122 Fixing device 123 Image exposing device 3Y Yellow image exposing unit 3M Magenta image exposing unit 3C Cyan image exposure unit 3Bk Black image exposure unit 130 Registration roller 140 Recording sheet supply cassette 150 Toner amount detection unit 151 Environmental sensor 160 Print data development unit 161 Print amount calculation unit 170 Device control unit 171 Calculation unit 172 Print amount integration unit 173 Fog amount Storage unit 174 Development bias storage unit 175 Toner replenishment amount integration unit 178 Voltage correction table 180 Development bias power supply unit 200 External device

Claims (4)

An intermediate transfer member, and a plurality of image forming units sequentially arranged along the intermediate transfer member, each image forming unit corresponding to a color assigned to an image carrier rotated to face the intermediate transfer member An image forming unit capable of forming an electrostatic latent image, developing the electrostatic latent image with a color toner in charge to form a toner image, and transferring the toner image to the intermediate transfer member; An image stabilization method for stabilizing an image density in an image forming apparatus capable of transferring a transfer toner image on an intermediate transfer member to a recording medium,
A print amount detecting step for detecting a print amount for each color constituting the toner image when forming a target toner image on the intermediate transfer member using one or more of the image forming units;
A print amount integrated value integrating step for calculating an integrated value of the print amount for each color detected in the print amount detecting step;
The color indicating the largest print amount integrated value among the print amount integrated values for the respective colors obtained in the print amount integrated value integrating step, and a predetermined color toner on the intermediate transfer member. A fog is formed in the image forming section in charge of the color at a predetermined timing, and when the number of pages on which the image is to be formed on the intermediate transfer member is a plurality of continuous pages, the interval between the pages is adopted as the timing. Forming step;
A fog detection step for detecting the amount of toner fog formed on the intermediate transfer member;
An image density that adjusts at least one of the parameters that affect the density of the toner image based on the toner fog amount on the intermediate transfer member detected in the fog amount detection step so that the toner image density is directed toward the target density. An image stabilization method comprising an adjustment step.   Each of the image forming units includes a developing device for developing the electrostatic latent image on the image carrier under a developing bias to form a toner image. In the fog forming step, the print amount integration The color on the intermediate transfer body of the toner of one color which is the color indicating the largest print amount integrated value among the print amount integrated values for each color obtained in the value integrating step and which is a predetermined color. When forming the image forming unit in charge, the developing bias is applied to the developing device in the image forming unit in charge of the color, and the fog is formed without applying the developing bias to the developing device in the other image forming unit. The image stabilization method according to claim 1. An intermediate transfer member, and a plurality of image forming units sequentially arranged along the intermediate transfer member, each image forming unit corresponding to a color assigned to an image carrier rotated to face the intermediate transfer member An image forming unit capable of forming an electrostatic latent image, developing the electrostatic latent image with a color toner in charge to form a toner image, and transferring the toner image to the intermediate transfer member; An image forming apparatus capable of transferring a transfer toner image on an intermediate transfer member to a recording medium,
A print amount detecting means for detecting a print amount for each color constituting the toner image when forming a target toner image on the intermediate transfer member using one or more of the image forming units;
A print amount integrated value integrating means for calculating an integrated value of the print amount for each color detected by the print amount detecting means;
On the intermediate transfer body, the toner of one color which is the color indicating the largest print amount integrated value among the print amount integrated values for each color obtained by the print amount integrated value integrating means and which is a predetermined color. A fog is formed in the image forming section in charge of the color at a predetermined timing, and when the number of pages on which the image is to be formed on the intermediate transfer member is a plurality of continuous pages, the interval between the pages is adopted as the timing. Forming means;
A fog amount detecting means for detecting the amount of toner fog formed on the intermediate transfer member;
An image density that adjusts at least one of the parameters that influence the density of the toner image based on the toner fog amount on the intermediate transfer member detected by the fog amount detection means so that the toner image density is directed toward the target density. An image forming apparatus including an adjusting unit. Each of the image forming units includes a developing device for developing the electrostatic latent image on the image carrier with a developing bias to form a toner image, and the fog forming unit includes the print amount integrating unit The color representing the largest print amount integrated value among the print amount integrated values for each color obtained by the value integrating means, and the fog on the intermediate transfer member of one color toner which is a predetermined color is the color. When forming the image forming unit in charge, the developing bias is applied to the developing device in the image forming unit in charge of the color, and the fog is formed without applying the developing bias to the developing device in the other image forming unit. The image forming apparatus according to claim 3.