JP2014215333A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly correct toner concentration with high responsiveness even after a long time or in different printing conditions, to maintain the toner concentration at a target value.SOLUTION: An image forming apparatus configured to apply a color material by means of a developing apparatus to an electrostatic latent image formed on an image carrier, to be visualized, and transfers, fixes and outputs the visualized image to a recording medium includes: means for counting pixels of the image; means for accumulating the amount of color material to be supplied for each pixel and the number of pixels; magnetic permeability detection means which detects magnetic permeability of developer in the developing apparatus; and means for estimating concentration of the color material on the basis of the magnetic permeability of the developer detected by the magnetic permeability detection means. According to moving distance and moving time of the developing apparatus, a conversion formula of the magnetic permeability and the color material concentration is corrected, and a difference between target color material concentration and the current color material concentration is fed back to the amount of color material to be supplied per pixel, for control.

Description

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

  2. Description of the Related Art Conventionally, image forming apparatuses such as so-called electrophotographic copying machines, printers, and multifunction machines have been widely used mainly in offices. An electrophotographic image forming apparatus uniformly charges a photosensitive member (image carrier) with a charging device, exposes it with an exposure device based on image data, and forms an electrostatic latent image on the photosensitive member. The electrostatic latent image is developed with toner as a color material to be visualized. Then, the toner image is transferred onto a recording medium such as transfer paper through an intermediate transfer member or directly, and fixed on the recording medium by heating or the like.

  With regard to development, there are generally two systems, one-component development and two-component development. One-component development does not require a carrier for charging the toner, and is a method for charging the toner by friction of a roller, a brush or the like, and has an advantage that it can be mounted at low cost although the durability of the unit is inferior. In the two-component development, the toner is charged by mixing the toner and the carrier in the developing device. This is more expensive than one-component development, but has the advantages of high durability and high image quality.

In the two-component development, however, there is a problem of stable control of toner density.
Since the two-component development is performed by mixing the toner and the carrier, if the toner density in the developing device is not appropriate, various problems such as density fluctuations, toner scattering, and background contamination may be caused.

Conventionally, in order to maintain the toner density appropriately, there is a technique for forming an image patch on an intermediate transfer belt and correcting the toner replenishment amount by reading the image density.
As another example, a sensor is arranged in the developing device, and the toner concentration (Tc) of the developer is determined by detecting the magnetic permeability (Vt) of the developer (mixed toner and carrier) by the sensor. Estimation is done. Thus, the magnetic permeability corresponding to the target toner concentration is set as the target magnetic permeability Vtref, and toner is supplied so that Vt approaches Vtref (for example, Patent Document 1). That is, as shown in FIG. 8, the toner supply amount is controlled to increase when the estimated (calculated) toner density (Tc) is below the target value Tcref, and the toner supply amount is controlled to decrease when the toner concentration (Tcref) exceeds the target value Tcref. is there. The toner discharge amount may be controlled instead of the toner replenishment amount.

  As a method of bringing Vt detected by a sensor close to the target value Vtref, the number of dots of an image is counted to estimate consumed toner, and the amount of consumed toner is replenished (for example, Patent Document 2).

  In addition, the two-component development has another problem of carrier deterioration. This is a phenomenon in which, in the process of stirring the developer in the developing device, the charging ability is lowered due to peeling of the carrier surface or adhesion of a toner additive to the surface. Since the developer is stirred and circulated with the toner by a screw or the like in the developing device, the number of printed sheets increases, and the developer gradually deteriorates as the stirring time is extended.

  There is a problem of toner scattering as a problem that becomes healthy due to carrier deterioration. This is because the toner charge amount is reduced, so that the toner is likely to be scattered, and the inside and outside of the image forming apparatus are soiled, or the toner falls in the image and causes a defective image. In addition, when toner having a charging failure is applied to a latent image, it may appear as background stains in the image.

  In a situation where the carrier has deteriorated, the fluidity of the developer and the bulk density at the magnetic permeability detector change, and the correspondence between the magnetic permeability measured in the developing device and the toner concentration collapses, so that the toner concentration can be accurately estimated. It may not be possible. In addition, even if toner is replenished by the above-described pixel count, the toner consumed for toner scattering and dirt increases, and the balance between replenishment and consumption is lost.

  The present invention solves the above-mentioned problems in the conventional image forming apparatus using two-component development, and corrects the toner density with high responsiveness even under time and different printing conditions, and keeps the toner density at a target value. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to solve the above problems, the present invention visualizes an electrostatic latent image formed on an image carrier by applying a coloring material from a developing device and transferring the visualized image to a recording medium for output. In the image forming apparatus, the means for counting the pixels of the image, the means for accumulating the color material replenishment amount per pixel and the number of pixels, the magnetic permeability detecting means for detecting the magnetic permeability of the developer in the developing device, Means for estimating the color material concentration based on the magnetic permeability of the developer detected by the magnetic permeability detection means, and conversion of the magnetic permeability and the color material concentration according to the travel distance or travel time of the developing device. The equation is corrected, and the difference between the target color material density and the current color material density is fed back to the color material supply amount per pixel and controlled.

  According to the image forming apparatus of the present invention, it is possible to perform toner replenishment in accordance with the toner consumption amount that varies depending on the charge amount of the toner and the image area, while reducing the detection error of the toner density due to carrier deterioration. For this reason, the toner density can be well corrected with high responsiveness even with time or different printing conditions, and the toner density can be maintained at a target value.

1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus according to the present invention. 6 is a graph showing changes in development travel distance and toner charge amount. It is a figure which shows an example of the characteristic change of the magnetic permeability and toner density by a developing travel distance. It is a flowchart which shows the example of the flow of a rough process of image data. FIG. 4 is a schematic diagram illustrating a difference between digital data and a printed toner image. FIG. 6 is a schematic diagram for explaining a phenomenon in which density increases around a toner pixel. It is a graph which shows the relationship between the number of pixels and image density. It is a figure for demonstrating the control of the conventional toner replenishment amount.

  As an embodiment of the present invention, toners of four colors of black (K), cyan (C), magenta (M), and yellow (Y) are used as color materials, which are common for electrophotographic image forming apparatuses. A two-component development type image forming apparatus will be described as an example. The number of colors and the color order are not limited to those shown in the figure. Further, the present invention can be applied not only to the intermediate transfer system but also to a direct transfer system.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. The color printer 100 shown in this figure is a color printer that can form a full-color image by adopting a tandem method, and has four image forming units 10 (K, C, M, Y) at almost the center of the apparatus main body. It is arranged. The image forming units 10 (K, C, M, Y) are arranged side by side along the upper running side of the intermediate transfer belt 11. The intermediate transfer belt 11 wound around the support rollers 12 and 13 is driven to run counterclockwise in the figure. A cleaning unit 14 for cleaning the intermediate transfer belt 11 is disposed between the right support roller 12 and the yellow image forming unit 10Y.

  Each image forming unit 10 has the same configuration except for the color of the toner to be handled, and includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging unit 2, a developing device 3, a cleaning unit 4, and the like are disposed. Further, a transfer as a primary transfer unit is provided inside the intermediate transfer belt 11 so as to face each photosensitive drum 1. A roller 5 is provided. In addition, in order to avoid the complexity of the figure, the reference numerals of the devices constituting the imaging unit 10 are shown only for the black imaging unit 10K, and the reference numerals are omitted for the imaging units of other colors.

  The developing device 3 contains a two-component developer composed of toner and carrier. Although not shown, there is a sub hopper at the upper part of the developing device 3 and a toner bottle at the upper part. When the bottle rotates, the toner is replenished into a hopper located between the toner bottle and the developing device. Then, the toner is replenished into the developing device. The replenished toner is supplied to the developing sleeve while being agitated and charged with the carrier by the screw shaft in the developing device to form a magnetic spike. A photosensitive drum 1 is disposed at a position facing the developing sleeve.

  An optical writing device 20 is provided above the four image forming units 10. The optical writing device 20 has a polygon mirror, a group of mirrors, etc., and irradiates the surface of the photosensitive drum 1 of each color image forming unit with light-modulated laser light. A configuration in which writing means is provided for each image forming unit is also possible.

  A paper feed unit 30 is provided at the lower part of the apparatus, and a paper feed tray 31 on which the paper P is stacked is provided. A paper feed roller 32 for feeding paper is attached to the paper feed tray 31 and a separation pad (not shown) is arranged. The paper fed by the paper feed roller 32 is conveyed to the registration roller 34 via the conveyance roller 33. Above the registration roller 34, a transfer roller 35 as a secondary transfer unit is provided to face the support roller 12 to form a secondary transfer portion.

  A fixing device 40 is provided above the secondary transfer unit. The fixing device 40 of the present example has a fixing roller and a pressure roller, and fixes the sheet on which the unfixed toner image is transferred at the secondary transfer unit by heating and pressing. A paper discharge roller 41 is provided above the fixing device 40 and discharges the fixed paper onto a paper discharge tray 42 formed on the upper surface of the device.

An image forming operation in the color printer 100 configured as described above will be briefly described.
The photosensitive drum 1 of the image forming unit 10 is rotated in the clockwise direction in the drawing by a driving unit (not shown), and the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity by the charging unit 2. The charged photoconductor surface is irradiated with laser light from the optical writing device 20, thereby forming an electrostatic latent image on the photoconductor drum 1 surface. At this time, the image information exposed on each photosensitive drum 1 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. Each color toner is applied from the developing device 3 to the electrostatic latent image formed in this way, and visualized as a toner image.

  Further, the intermediate transfer belt 11 is driven to run counterclockwise in the figure, and the respective color toner images are sequentially transferred from the photosensitive drum 1 to the intermediate transfer belt 11 by the action of the primary transfer roller 5 in each image forming unit 10. In this way, the intermediate transfer belt 11 carries a full-color toner image on the surface thereof.

  Note that any one of the image forming units 10 can be used to form a single-color image or a two-color or three-color image. In the case of monochrome printing, image formation is performed using the black unit 10K on the left side of the drawing among the four image forming units.

  The residual toner adhering to the surface of the photosensitive drum after the toner image is transferred is removed from the surface of the photosensitive drum by the cleaning unit 4, and then the surface potential is initialized by the action of the static eliminator. Prepare for the next image formation.

  On the other hand, the paper is fed from the paper feed tray 31 and is sent toward the secondary transfer position by the registration roller pair 34 in timing with the toner image carried on the intermediate transfer belt 11. The toner image on the surface of the intermediate transfer belt is collectively transferred onto the sheet by the action of the transfer bias applied to the secondary transfer roller 35. When the sheet on which the toner image has been transferred passes through the fixing device 40, the toner image is fused and fixed to the sheet by heat and pressure. The fixed sheet is discharged by a discharge roller 41 to a discharge tray 42 formed on the upper surface of the apparatus main body.

  In forming an image, the photosensitive drum 1 is charged to a desired potential Vd by the charging roller 2. In this embodiment, exposure is performed on a pixel position on the photosensitive member where image formation is desired. In the exposed portion, the charged potential drops to the post-exposure potential Vl, and toner adheres to this portion from the developing sleeve, forming a latent image on the surface of the photoreceptor. When the potential of the developing sleeve is Vb with respect to this latent image, toner having a charge amount sufficient to fill | Vb−Vl | (referred to as developing potential) is supplied.

  When the toner density in the developing device fluctuates, the density that can be developed changes with the same development potential. For this reason, in this embodiment, for each predetermined number of printed sheets, a predetermined reference image (image patch) is formed on the intermediate transfer belt 11, the density is read by the sensor, and the developing bias Vb (and so on) is obtained so as to obtain the target density. Vd, V1) are adjusted.

  In the present embodiment, the toner adhesion amount detection sensor 15 as a density sensor is located downstream of the black image forming unit 10K that is located on the most downstream side (the transport direction of the intermediate transfer belt 11) of the tandem image forming unit. It is arranged. As the toner adhesion amount detection sensor, an appropriate configuration can be used, but in this embodiment, an optical sensor (photo sensor) is used.

  However, if the toner density fluctuates at a period earlier than the correction execution interval, the correction may not catch up. Although it is possible to reduce this by reducing the correction interval, it is necessary to form an image patch, so it is necessary to secure an adjustment time, and the amount of toner consumption increases due to the formation of the adjustment patch. There is. In addition, when the toner density fluctuates greatly, problems other than the density such as a case where the adjustment cannot be made within the control range of the developing bias or a toner scattering (mainly at a high density) may occur.

  For this reason, a sensor (not shown) for magnetic permeability detection is installed in the container of the developing device 3, thereby detecting the magnetic permeability Vt of the developer (mixed toner and carrier) to thereby adjust the toner concentration. Tc is estimated. Then, the magnetic permeability Vtref capable of obtaining a target toner concentration is compared with the current magnetic permeability Vt, and toner replenishment control is performed so as to fill the difference.

  This may be a control that simply replenishes if it is insufficient, and does not replenish if it is sufficient, but the amount of toner consumed varies depending on the image to be printed. Is estimated (calculated).

  To estimate the toner consumption based on this image data, count the pixels in the image, increase the amount of toner supply when there are many latent image forming pixels, and supply toner when the number of latent image forming pixels is small. The amount is reduced. Specifically, a toner replenishment amount per pixel is determined, and the toner consumption is estimated by multiplying this by the total number of pixels, and toner is replenished accordingly.

  By the way, it is known that the carrier in the developing device deteriorates as the number of printed sheets increases. This is because the carrier and toner are agitated in the developing device, so that the surface layer of the carrier is peeled off or the additive of the toner adheres to the surface of the carrier and the chargeability of the carrier is lowered. As the carrier deteriorates, the charging ability of the toner decreases, and the image density may fluctuate, causing problems such as toner scattering and background contamination.

  In a conventional apparatus, when toner scattering or scumming is caused, toner that does not contribute to image formation is output from the developing device. Therefore, even if the toner replenishment amount obtained from the pixel count is replenished, the toner density does not follow. There is a case. In addition, the fluidity of the developer may change due to carrier deterioration, and the correspondence between Vt and Tc may change due to the change in the bulk density of the developer in the vicinity where the magnetic permeability is detected.

  Therefore, in the present invention, the rate of change of Vt and Tc is corrected based on the development travel distance (for example, the number of images to be formed) or the development travel time (for example, the developing device drive time), and the comparison between Vt and Vtref (or The toner consumption is corrected from the corresponding Tc and Tcref), and the toner density in the developing device is appropriately maintained with good responsiveness. That is, according to the development travel distance or the development travel time, the conversion formula between the magnetic permeability and the color material density (toner density) is corrected, and the difference between the target color material density and the current color material density is a color per pixel to be described later. This feeds back to the amount of material supply.

  In order to maintain the toner density appropriately, it is necessary to appropriately detect the toner density in the developing device. When the carrier deteriorates, the toner charge amount decreases. FIG. 2 shows changes in development travel distance and toner charge amount.

  If the carrier deterioration progresses, the characteristics of the magnetic permeability Vt and the toner concentration Tc also change, and this is corrected. Since carrier deterioration basically depends on the travel distance of the developing device, the relationship between the development travel distance (which may be managed by time, such as the developing device drive time) and Vt-Tc is experimentally determined. It is only necessary to investigate, prepare this correction formula by a mathematical formula or a reference table, and correct it appropriately. FIG. 3 shows an example of a change in characteristics of the magnetic permeability Vt and the toner concentration Tc depending on the development travel distance. “K” in the three straight lines descending to the right indicates “1000 sheets”. In addition, the case of FIG. 3 is a case where a characteristic moves in parallel. Since the characteristics depend on the developer, the structure of the developing device, and the characteristics of the sensor, the change characteristics are not limited to this.

Further, even if the relationship between the magnetic permeability Vt and the toner concentration Tc is corrected, the toner concentration will still fluctuate if the replenishment is not properly performed for the toner consumption.
In particular, when the charge amount of the toner is decreased due to the deterioration of the carrier, toner scattering and background contamination may occur, and the toner consumption may increase. In this embodiment, toner supply corresponding to the toner consumption is performed by estimating the toner consumption from the image data.

  First, an example of a rough processing flow of image data will be described with reference to the flowchart of FIG. In the embodiment, processing of image data, estimation of toner consumption, correction of toner replenishment amount, control of toner replenishment operation, and the like described below are performed (controlled) by a control unit (not shown) of the image forming apparatus.

In general, image data is input as RGB 8-bit data.
The input RGB data of 8 bits (256 gradations of each color) is first subjected to color management processing and converted to CMYK 8-bit data, which is a color plate that can be handled by the image forming apparatus, where color matching processing is performed ( Thereafter, the gradation may be adjusted by γ correction).

  Then, the 8-bit data of each color of CMYK is replaced with dot data of each pixel (whether or not a dot is to be formed in the case of 1 bit) that can be actually formed by the image forming apparatus by halftone processing, and the data corresponding to this exposure data. Then, latent images are formed on the photoconductors of the respective colors (scanning light from the writing device is irradiated to the portions where the dots are turned on to form latent images), and toner is applied as a color material to form an image. Is printed.

  As a dot count method, there is a method of first performing the data after halftone processing. In this case, if the output is 1 bit, it is converted to ON / OFF data, so the total number of ON data is counted and the toner consumed in the image is estimated by multiplying the toner replenishment amount per pixel. it can. The unit for counting may be a predetermined number of printed sheets, or a unit of jobs, pages, or pages.

  As another method, a method of processing multi-value data is possible. In this case, the toner replenishment amount is weighted with respect to data having gradation, for example, 8-bit data of each color of CMYK before halftone processing.

  This is because the image density and the number of pixels to be developed are not necessarily in a linear relationship. This is because an electric field wraparound phenomenon known as an edge effect occurs, and a difference occurs in the amount of toner to be developed depending on how pixels are filled.

The former is due to the characteristic between the reflection density and the number of pixels due to the dot gain of the latent image and the optical dot gain.
As shown in FIG. 5, this is due to the difference between digital pixels (digital data) and the printed toner image. Although a digital image has square pixels, a toner image that is actually printed does not have a square shape, so that the coverage ratio on paper is higher than that of digital pixels. Further, a light amount drop called optical dot gain occurs around the toner fixed on the paper surface. This is a phenomenon in which a part of the light incident and reflected around the toner pixel is absorbed by the toner pixel, and the amount of reflected light decreases and the density increases even in the vicinity of the portion where the toner is actually placed (see FIG. 6).

  For these reasons, as shown in FIG. 7, the number of pixels and the density (brightness is almost the same) do not necessarily have a linear relationship, and in the low gradation with many gaps on the paper, the paper is efficiently filled with the number of pixels. Therefore, the density (or lightness) can be changed linearly, but when the paper surface is filled, the change in the density (or lightness) with respect to the number of pixels in which overlap occurs between pixels becomes dull.

  For this reason, when designing density (or lightness) characteristics, input / output gradation characteristics, that is, pixel increase / decrease characteristics are adjusted in advance by halftone processing and γ correction. For this reason, for example, when gradation design is performed with a density linear characteristic, the gradation value and the number of generated pixels generally do not have a linear relationship.

  In the latter case, the developing toner amount fluctuates in the first place. This is a phenomenon in which when there are many blanks around the latent image pixels, the electric field of the latent image portion goes around the blank portions, and the toner is not developed well at the edge portions of the latent image pixels. For this reason, there may be a difference in the amount of toner consumed when printing a solid image with the same total number of pixels and when printing an image with a blank surrounding like a halftone.

  As described above, since the number of dots generated and the consumed toner amount differ depending on the gradation value, the toner amount consumed for each gradation is experimentally obtained, and the toner for each gradation is calculated using a calculation formula or a reference table. It is preferable to multiply consumption. In this way, the toner consumption can be estimated with higher accuracy.

Next, correction of the toner replenishment amount will be described.
This is determined by looking at the transition of the difference between Vtref and Vt.
For example, the basic replenishment amount per pixel is a, and the magnetic permeability that varies thereby is Va. If the difference from the target Vt is ΔVt (= Vtref−Vt), it is necessary to change the replenishment amount per pixel to (ΔVt / Va) × a in order to fill this difference.

  The estimation of the toner consumption amount may be defined for each predetermined number of printed sheets, or may be defined for each job, for each page, or divided into smaller areas. The finer the correction cycle is, the faster the correction cycle becomes.

As will be described later, since the relationship between Vt and Tc varies depending on conditions, it is preferable to manage the toner density by replacing Vt with Tc.
For example, when the characteristics of Vt−Tc are different between condition 1 and condition 2, it is necessary to correct Vtref one by one. If it is managed by Tc, the target value does not need to be changed.

  In the explanation of this article, there is a part where the comparison of Vt and Vtref is made for convenience of explanation. However, the comparison may be made with Vt as it is, or with the Tc estimated from Vt. Also good.

  The determination of ΔVt (or ΔTc) is determined by looking at the transition of Vt (or Tc), and this is corrected by looking at the moving average value (the difference between the target color material density and the color material density is the moving average). It is preferable to compare with the value taken. The magnetic permeability tends to cause an error depending on the bulk density of the developer around the sensor. In addition, there is a time lag between the actual toner replenishment and the agitation and sensor detection so that the toner is already replenished but may not be reflected in the detection result at the detection site.

  Conventionally, there is a method of performing correction by fixing the replenishment amount per pixel and adding another correction replenishment amount (PID) that varies according to ΔVt to the replenishment amount per pixel. However, in this case, since the replenishment amount data per pixel is fixed, the replenishment amount is not corrected immediately even if the image area to be printed changes, and the follow-up of the replenishment amount starts only when ΔVt increases. In contrast, since the present invention always corrects the correction amount per pixel, there is a merit that it is excellent in the followability of toner density fluctuation particularly when the fluctuation of the image area is large.

  As described above, the relationship between Vt and Tc fluctuates with a change in charging ability, but this may occur even when the image forming apparatus is started up. When the agitation in the developing device is stopped at the end of printing, the toner charge amount in the developing device decreases with time. For this reason, when the image forming apparatus is restarted after a certain amount of time has elapsed, the charging ability of the toner is lowered, and it is detected that Tc is lower than the actual toner density, and the toner is replenished excessively. There is a case. Therefore, this can be reduced by implementing at least one of the following (1) and (2).

  (1) If the development has been stopped for a predetermined time or longer, the toner replenishment amount per pixel is not changed for a certain period from the restart, and the toner is based on the Tc before the development stops and the toner density per pixel. Replenish.

(2) The prediction formula of Tc from Vt at the time of restart is corrected according to the elapsed time from the stop of development, and the supply operation is performed while updating the toner supply amount per pixel using the correction formula.
Next, a description will be given of a case where there are two or more types of printing modes.

  An image forming apparatus may have two or more types of printing modes. For example, it has a standard mode and a low-speed mode with higher resolution. This speed difference is mainly divided into the case where the writing device is exposed to the exposure speed and the case where the fixing time such as the recording paper type needs to be changed. It is necessary to reduce the scanning speed of exposure or increase the number of scans. For this reason, it is necessary to change the rotation speed of the development accordingly.

  In this case, since the developer agitation speed in the developing device is different, the friction condition between the carrier and the toner is changed, the charge amount is changed, and the bulk density of the developer at the sensor position is changed. This is because a difference occurs in the detection output.

For this reason, the relationship between Vt and Tc may be corrected between linear velocities.
Therefore, it is preferable to adjust the Tc and the toner replenishment amount by switching the Vt-Tc characteristic according to the linear velocity. Since it is the toner density to be finally managed, it is preferable to manage the target value with Tc estimated from Vt because the target value does not have to be changed even if the linear velocity is switched.

  The printer of the present embodiment has a standard mode (standard speed mode) and a low-speed mode with higher resolution than that. By switching the Vt-Tc characteristic according to the linear speed (printing speed) as described above, Tc and toner replenishment amount are adjusted. In other words, in an image forming apparatus having two or more types of printing speeds, by correcting the characteristic difference between the color material density and the magnetic permeability between the linear velocities, or by using a relational expression between the magnetic permeability and the color material density for each linear velocity. The color material density is estimated and the color material supply amount is corrected.

  It is also preferable to set a toner replenishment amount per pixel for each linear velocity. This is because the image forming conditions such as the resolution are different between the print modes, so the amount of toner to be developed, the background contamination, and the amount of scattered toner are different (in the first place, the area per pixel is different if the resolution is different in the first place) The toner consumption per pixel is also different). Therefore, in this embodiment, the color material supply amount (toner supply amount) setting can be individually set for each print mode.

  Next, in a configuration using a plurality of color toners (color materials) or a configuration including a plurality of image forming units (sometimes referred to as an image forming station), toner supply amount per image, characteristics of Vt and Tc Is preferably set for each color material or each image forming unit. This is because different types of toner may be used depending on the color, or even the same type of toner may have different charging and flow characteristics depending on the color.

Further, since variations in detection of sensors for measuring Vt also occur on the image forming unit side, it is preferable to individually set the toner replenishment amount and the characteristic condition of Vt-Tc.
In this embodiment, at least one of the color material replenishment amount, the estimation of the color material density from the magnetic permeability, and the estimation of the color material density from the magnetic permeability with respect to the development travel distance (or time) is used as the color material type or the image forming unit. Set for each.

  Next, correction of condition settings according to the environment will be described. The environment means an ambient environment where the device is used such as temperature and humidity. When the temperature and humidity of the environment around the apparatus changes, the state of the developer also changes, and the amount of charge also changes (for example, it is easy to be charged at low temperature / low humidity, and is difficult to be charged at high temperature / high humidity).

  Further, since the developer is a powder, it is easy to disperse at a low temperature / low humidity and is easy to aggregate at a high temperature / high humidity. For this reason, the characteristics of the magnetic permeability Vt and Tc change, and the consumption characteristics of the toner such as the scattering of toner and the background stains also change.

Therefore, it is preferable to correct the toner supply amount and the condition setting of Vt−Tc according to the temperature and humidity environment.
In the present embodiment, at least one of the color material replenishment amount and the color material density estimation from the magnetic permeability is provided for each ambient environment.

  Specifically, a sensor (not shown) for detecting temperature and humidity is attached to the image forming apparatus, and a desired parameter may be reflected according to the reading value of the temperature and humidity sensor. For example, a Vt-Tc characteristic for each environment set in a predetermined stage is prepared as a parameter and reflected according to the sensor output value.

  Incidentally, some image forming apparatuses can exchange an image forming unit including a developing device. There is also an image forming apparatus having a mechanism for supplying / discharging the developer and keeping the developer fresh. In the apparatus having such a configuration, when the developing device or the developer is replaced, the characteristics of the magnetic permeability Vt and the toner concentration Tc according to the development travel distance (or time) and the toner replenishment amount characteristics per pixel are replaced. It is used after being calibrated (calibrated) under the developed conditions.

  For example, when the developing unit is replaced with a new one, the carrier is usually not deteriorated, and the initial developer is sealed at a predetermined toner concentration. For this reason, by setting a developing unit in the image forming apparatus main body and operating the developing apparatus, the setting of the Vt-Tc characteristic and the replenishment amount per pixel are also reset (since the initial toner density is known, the Vt-Tc Adjust the reference point.Return the replenishment amount per pixel to the initial condition without carrier deterioration).

  If a memory is mounted on the development unit for these pieces of information, the state of the unit can be recorded and the optimum conditions can be reflected in the unit. For example, even when the developing unit being used is attached to another image forming apparatus, if the Vt-Tc characteristic of this developing unit, the toner replenishment amount per pixel, etc. are recorded, information is exchanged at the replacement image forming apparatus. Reading, reflecting settings, and updating can be performed.

  In the printer of this embodiment, the image forming unit 10 including the developing device 3 is provided as a process cartridge so as to be replaceable. Further, the developing device 3 has means for supplying / discharging the developer, and has a mechanism for keeping the developer fresh. When the developing device 3 or the developer is replaced, at least one of the estimation of the color material density from the magnetic permeability according to the development travel distance (or time) or the color material replenishment amount is the replaced developing device or developer. Is calibrated according to

  Further, a memory is mounted in the developing device 3 and at least one piece of information on the estimation of the color material density from the magnetic permeability according to the development travel distance (or time) and the color material supply amount is stored in the memory. That is, the Vt-Tc characteristic, the toner replenishment amount per pixel, and the like are recorded in the memory.

  As described above, according to the image forming apparatus of the present invention, while reducing the detection error of the toner density due to the deterioration of the carrier, the toner matched with the toner consumption amount that varies depending on the toner charge amount and the image area. Since replenishment can be performed, the toner density can be well corrected with high responsiveness over time and different printing conditions, and the toner density can be maintained at a target value.

  In addition, the pixel of the image is composed of multiple gradations, and the color material replenishment amount is calculated for each pixel weighted with the color material replenishment amount for each gradation. By calculating the color material replenishment amount, and the color material replenishment amount per pixel changes the replenishment amount for each gradation of each pixel, the toner replenishment amount can be set according to the latent image characteristics of the image. It becomes possible.

  It also has means for detecting the elapsed time since the previous development drive. (1) When development has been stopped for a predetermined time or longer, the toner replenishment amount per pixel is changed for a certain period from the restart. First, toner replenishment is performed based on Tc before development stops and the toner density per pixel. (2) The prediction formula of Tc from Vt at the time of restart is corrected according to the elapsed time from the stop of development, and the supply operation is performed while updating the toner supply amount per pixel using the correction formula. By performing at least one of the above, it is possible to perform appropriate toner replenishment even when development is left / redriven.

  In addition, when correcting the color material replenishment amount, the difference between the target color material density and the color material density is compared with a value obtained by taking a moving average, thereby performing the replenishment operation while suppressing the influence of detection variation. It becomes possible.

  Further, in a configuration having two or more types of printing speeds, the color material density and permeability characteristic difference between the linear speeds is corrected, or the color material by using a relational expression between the magnetic speed and the color material density for each linear speed. By estimating the density and correcting the color material replenishment amount, it is possible to perform a replenishment operation in accordance with the print mode (printing speed).

Further, since the color material replenishment amount setting can be individually set for each print mode, a replenishment operation in accordance with the print mode can be performed.
Further, at least one of the color material replenishment amount, the estimation (calculation) of the color material density from the magnetic permeability, and the estimation (calculation) of the color material density from the magnetic permeability with respect to the development travel distance (or time) is the color material type or the production. By setting for each image unit, it is possible to perform an optimal replenishment operation for the color material type or the image forming unit.

In addition, since at least one of the color material replenishment amount and the color material density estimation from the magnetic permeability is set for each ambient environment, it is possible to perform a replenishment operation in accordance with the use environment.
Further, when the developing device or the developer is replaced, at least one of the estimation (calculation) of the color material density from the magnetic permeability according to the development travel distance (or time) or the color material replenishment amount is the replaced developing device or By calibrating according to the developer, it is possible to carry out the optimum replenishment operation by taking over the setting even when the developer or the developing device is replaced.

  Further, the developing device is equipped with a recording unit, and at least one piece of information on the color material density estimation (calculation) from the magnetic permeability according to the development travel distance (or time) and the color material supply amount is stored in the recording unit. At the same time, by reading out the information stored in the storage means installed in the developing device and correcting the color material replenishment amount and performing the replenishment processing, the settings are inherited even when the developer and the developing device are replaced, and the optimum A replenishment operation can be performed.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. The number of colors and the color order used in the image forming apparatus are not limited to the illustrated form. Further, the present invention can be applied not only to the intermediate transfer system but also to a direct transfer system. As the configuration of the image forming unit, an appropriate configuration can be adopted. The configuration of the detection means for detecting the toner density is arbitrary, and is not limited to detecting the toner density on the photosensitive member or the intermediate transfer belt, but detects the image density on the paper (the density of the image output on the paper). It may be configured.

  In addition to the tandem type, a configuration in which a plurality of developing devices are arranged around a single photosensitive member, or a configuration using a revolver type developing device is also possible. The present invention can also be applied to a full color machine using three color toners, a multicolor machine using two color toners, or a monochrome apparatus. Of course, the image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile machine, or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging means 3 Developing device 4 Photoconductor cleaning means 5 Primary transfer roller 10 Image forming unit 11 Intermediate transfer belt 15 Toner adhesion amount detection sensor (density sensor)
20 Optical writing device 100 Color printer

JP-A-2-34877 JP 2008-76895 A

Claims (10)

In an image forming apparatus for visualizing an electrostatic latent image formed on an image carrier by applying a coloring material from a developing device, and transferring and fixing the visualized image on a recording medium,
Means for counting the pixels of the image, means for integrating the color material replenishment amount per pixel and the number of pixels, magnetic permeability detecting means for detecting the magnetic permeability of the developer in the developing device, and magnetic permeability detecting means Means for estimating the colorant concentration based on the detected magnetic permeability of the developer,
While correcting the conversion formula between the magnetic permeability and the color material density according to the travel distance or travel time of the developing device, the difference between the target color material density and the current color material density is used as the color material replenishment amount per pixel. An image forming apparatus controlled by feedback.   The pixel is composed of multiple gradations, and the color material replenishment amount is calculated for each pixel weighted with the color material replenishment amount for each gradation, and the calculated color material replenishment amount for each pixel is integrated by the number of pixels. The color material replenishment amount in a predetermined section is calculated, and the color material replenishment amount per pixel changes the replenishment amount for each gradation of each pixel. The image forming apparatus described. 3. The image forming apparatus according to claim 1, further comprising: means for detecting an elapsed time since the previous driving of the developing device, and performing at least one of the following (1) and (2).
(1) When the elapsed time exceeds a certain value, the pixel replenishment amount is not changed for a certain period from the restart of development driving.
(2) According to the elapsed time, the estimation of the color material density from the magnetic permeability at the time of resuming development driving is corrected.   4. When the color material supply amount is corrected, the difference between the target color material density and the current color material density is compared with a value obtained by taking a moving average. The image forming apparatus described in the item.   It is possible to perform printing operations at two or more printing speeds, and corrects the characteristic difference between the color material concentration and the magnetic permeability between the printing speeds, or the relationship between the individual magnetic permeability and the color material concentration for each printing speed. 5. The image forming apparatus according to claim 1, wherein the color material density is estimated by using the color material, and the color material supply amount is corrected.   6. The image forming apparatus according to claim 1, wherein the color material replenishment amount can be individually set for each printing mode. A plurality of color materials can be used or a plurality of image forming units are provided.
At least one of the color material replenishment amount, the estimation of the color material density based on the magnetic permeability, and the estimation of the color material density from the magnetic permeability with respect to the travel distance or the travel time of the developing device is a color material type or each production. The image forming apparatus according to claim 1, wherein the image forming apparatus is set for each image unit. Having environmental condition detection means for detecting environmental conditions;
8. At least one of the color material replenishment amount or the color material density estimation from the magnetic permeability is set according to the environmental condition detected by the environmental condition detection means. The image forming apparatus described in the item. The developing device can be replaced, or the developer in the developing device can be replaced,
When the developing device or the developer in the developing device is replaced, at least one of the estimation of the color material density from the magnetic permeability according to the travel distance or travel time of the developing device or the color material supply amount is replaced. 9. The image forming apparatus according to claim 1, wherein calibration is performed according to the developed developing device or developer. The developing device includes a storage unit, and the storage unit stores at least one piece of information on the color material density estimation from the magnetic permeability according to the travel distance or travel time of the developing device or the color material replenishment amount. As well as storing
The information stored in the storage unit mounted on the developing device is read to perform correction of the color material supply amount and supply processing of the color material. The image forming apparatus described.

Images