JP2007148176A - Toner density controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a toner density controller of an image forming apparatus that suppresses margins of a Q/M rise and solid carrier sticking even when low-area images are successively printed. <P>SOLUTION: The image forming apparatus is equipped with a developing device which performs development by using a two-component developer, a toner supply device, a reference pattern imaging means of imaging a reference pattern on a photoreceptor, a reference density pattern detecting means of detecting the density of the reference pattern imaged on the photoreceptor, an image area calculating means of calculating the image of a print image, a toner density detecting device which detects the toner density of a developer in the developing device, and a toner density controller which has an upper-limit value and/or a lower-limit value as the toner density controller performing toner density control over the developer, and the toner density controller determines the upper-limit value and/or lower-limit value of the toner density controller based upon an integral value the image area of the printed image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to a toner density control apparatus used in an image forming apparatus using a two-component developer composed of a magnetic carrier and toner.

Conventionally, in an image forming apparatus such as an electrophotographic copying apparatus, a two-component developing apparatus that performs development using a two-component developer composed of a magnetic carrier and toner, and a one-component developing apparatus that performs development using only toner. It has been known.
The two-component developing device usually includes a developing sleeve that is a cylindrical developer carrying member that includes a magnet roller including a magnet body having a plurality of magnetic poles therein and is rotatably supported. While carrying the magnetic carrier with the toner attached to the surface of the developing sleeve, it is transported to a developing area that is a portion facing the image carrier and developed with a magnetic brush made of a two-component developer. . In the two-component developing device, since charging is performed by stirring and mixing the magnetic carrier and the toner, the chargeability of the toner is stabilized, and a relatively stable good image can be obtained. However, there is a drawback that the mixing ratio of the toner and the magnetic carrier fluctuates because the toner concentration fluctuates due to carrier deterioration or the consumption of toner in the developer. In order to suppress the fluctuation of the mixing ratio of the toner and the magnetic carrier, it is necessary to provide a toner concentration control device and replenish the toner as necessary to suppress the fluctuation.
On the other hand, the one-component developing device carries out development by transporting the toner carried on the surface of the developer carrying member to the development area. Unlike the two-component developing device, it does not have the disadvantage of having a carrier deterioration or toner concentration control device, but has the disadvantage that the charging property is difficult to stabilize.

  When a two-component developing device is used, the triboelectric charge amount of the developer varies depending on the environment, running conditions, mechanical conditions, and sensor variations. If this change in charge amount is controlled using an optical sensor so that the amount of pattern adhesion is constant, the toner concentration will fluctuate instead of the charge amount becoming substantially constant. In particular, if the toner density rises above a certain value due to low-temperature humidity and fluctuations in the charge amount of the carrier, there is a limit to the coverage of the carrier. Toner is generated, causing toner scattering, background dirt, and the like. On the contrary, when the charge amount of the developer is lowered, if the pattern adhesion amount is controlled to be constant, there is a problem that the toner density is lowered and the image density is insufficient and carrier adhesion occurs in a solid image.

In order to prevent this problem, a method is generally used in which a limiter is provided in the reference value of the output value of the toner density sensor so that the output value falls within a certain value (or above) (for example, Patent Document 1). 2).
However, it is possible to suppress the increase (decrease) in toner density over time and the environment to some extent by these methods, but in addition to these variations, there are variations in sensitivity of the toner concentration sensor itself and variations in sensor mounting. The toner density limiter cannot be applied to this value.
For example, in Patent Document 2, the upper limit value VrefH and the lower limit value VrefL of the reference value Vref are determined in accordance with the output value Vti of the toner density sensor when the initial agent is loaded. However, in this method, since the control voltage Vcnt is fixed, when the toner density of the initial agent is set to the toner density upper limit value or the toner density lower limit value, the sensor on the toner density upper limit side or the toner density lower limit side, respectively. When the sensitivity is low, that is, the region L (FIG. 11) where the sensor sensitivity is not good with respect to the change in the toner density is used, and the accuracy is reduced with respect to various variations. Even if the above-mentioned variation can be reduced, when the limiter is applied with the toner density, the image density may differ depending on the charge level of the developer at that time.

Some developers have extremely different charge levels depending on the image area (toner consumption per unit number). This is because, in a low image, since the toner consumption is small, it becomes a mode for scraping the carrier coating layer, so that the area of poor charging on the surface of the coating layer is scraped, and a surface with high charging capability inside the coating layer appears. There is a cause. On the other hand, since the toner consumption is high in high images, the charge sites on the carrier surface are reduced by the accumulation of external additives in the coat layer faster than the carrier coat layer is scraped, and the charging ability of the carrier is reduced. There is a cause.
When such a developer is controlled at a constant image density, the toner density increases in a low image area. Therefore, when the toner density limiter is applied at a fixed value, the image density becomes extremely low. If this state continues, the developer's charge increases, the developer's fluidity deteriorates, a toner density error detection occurs, and a phenomenon in which the toner density is lowered may occur.

In the two-component developing device, the toner particles tend to be reduced in size in response to the recent demand for higher image quality, and the magnetic carrier tends to be reduced accordingly.
However, the smaller the particle size of the magnetic carrier, the smaller the magnetization and the easier the carrier adheres to the image carrier. There are two types of carrier adhesion, carrier adhesion to the edge portion due to counter charge (hereinafter referred to as “edge portion carrier adhesion”) and carrier adhesion to the high density image portion due to electrostatic induction ( Hereinafter, it is referred to as “solid carrier adhesion”).
In color copiers, the carrier resistance is lowered in order to improve the solid uniformity, but the solid carrier adhesion is caused by the electrostatic charge induced in the carrier when the development potential of the solid image portion is too large. The carrier adheres to the surface. Further, when the resistance of the carrier is increased, electrostatic induction can be reduced and thus the solid part carrier adhesion can be prevented. However, this is in a direction contrary to the above-described countermeasure for preventing the edge part carrier adhesion.
In addition, the prevention of solid carrier adhesion can be reduced to some extent by selecting the development potential and background potential, that is, adjusting the set electric field, but these adjustment characteristics also have an effect on image density and background contamination. Since it is large, it cannot often be determined only by carrier adhesion.

  Furthermore, along with the recent demand for miniaturization of machines, there is a tendency to reduce the drum diameter of the photosensitive drum as the image carrier and the sleeve diameter of the development sleeve as the developer carrier. As the drum diameter and the sleeve diameter are reduced, the magnetic binding force on the carrier of the magnetic brush tip downstream of the development region (exit side) is reduced, and thus carrier adhesion is likely to occur.

Here, the occurrence of solid carrier adhesion has the following tendency.
・ The larger the development potential, the more likely it is.
-It is more likely to occur as the toner concentration is lower.
・ It occurs as the background potential increases.
・ The lower the carrier resistance, the more likely it is.
-The lower the carrier saturation magnetization, the more likely it is.
-The smaller the magnetic force of the development main pole and P2 pole (the pole immediately downstream of the main pole), the more likely it is.
-The smaller the combined magnetic force between the development main pole and the P2 pole, the more likely it is.
・ Even if the main magnetic flux density is the same as that of the P2 pole, it tends to occur if the distance between the two poles is long.

Since solid carrier adhesion is very deteriorated when the toner concentration is low, solid carrier adhesion becomes severe in a developer whose charge is reduced when printing a high image area. Further, when the carrier coat layer can be scraped with a low image area, the resistance is lowered and becomes more severe.
In order to prevent this, conventionally, an apparatus has been proposed in which a toner density lower limiter is provided so that the toner density does not decrease below a certain value (see, for example, Patent Document 3).
However, in the method of Patent Document 3, since the toner density lower limiter is a fixed value, the low image area is followed by the low carrier resistance, and then the high image area is followed by the toner density is lowered. The limiter is applied at the same toner density as when the toner density is lowered while the image area continues and the carrier resistance remains high. Therefore, if the limiter is set to increase the toner density (TC) which gives a margin for solid carrier adhesion, when the high image continues, the limiter is applied at a higher TC, and the toner charge amount Q / M is reduced. Problems such as scattering occur.

JP 2003-57939 A Japanese Patent No. 3451470 JP 2001-154427 A

  With the above-described conventional technology, even with a small particle size carrier, solid carrier adhesion can be suppressed within a certain allowable range. However, when a fixed toner concentration upper limiter is used when a low image area continues. When the toner charge amount Q / M increased and the low image area continued, there was a problem that the solid carrier adhesion margin decreased when the fixed toner concentration lower limiter was used, exceeding the allowable limit.

  The present invention has been made in view of the above problems, and provides a toner concentration control device for an image forming apparatus that suppresses the Q / M increase and the solid carrier adhesion margin even when a low-area image is continuously printed. This is the issue.

As means for achieving the above object, the present invention has the following features.
The toner density control device of the present invention includes an image carrier, a charging device that charges the image carrier, an exposure device that exposes the charged image carrier to form an electrostatic latent image, and a two-component developer. A toner density control device for use in an image forming apparatus comprising a developing device for developing an electrostatic latent image and a toner replenishing device for replenishing toner to the developing device, wherein a reference pattern is formed on the image carrier. A reference pattern image forming means for image formation, a reference density pattern detection means for detecting the density of the reference pattern formed on the image carrier, an image area calculation means for calculating the image area of the print image, In a toner concentration detection device that detects the toner concentration of a developer and a toner concentration control device that has an upper limit value and / or a lower limit value that controls the toner concentration of the developer, the toner concentration control device includes: Based on the integrated value of the image area, and determines the upper limit value and / or the lower limit of the toner density control apparatus.
Further, the toner density control device of the present invention is characterized in that, based on the integrated value of the print image, when the low image area continues, the lower limit value of the toner density of the toner density control device is increased.
The toner density control device according to the present invention is characterized in that, based on the integrated value of the print image, when the low image area continues, the upper limit value of the toner density of the toner density control device is increased.
The toner density control device of the present invention is characterized in that a limit value is provided for the total amount of change of the upper limit value and / or the lower limit value of the toner density control of the toner density control device.

According to the toner density control apparatus of the present invention, the upper limit value and / or the lower limit value of the toner density control apparatus is determined based on the integrated value of the image area of the print image. Even for carriers where film scraping progresses or Q / M increases, it is possible to prevent solid carrier adhesion and Q / M from rising excessively by performing optimal toner concentration control.
Further, according to the toner density control device of the present invention, when the low image area continues based on the integrated value of the print image, the lower limit value of the toner density of the toner density control device is increased. Even when the image area continues to be scraped, and then the toner density is lowered by taking a high image area, it is possible to prevent sticking of the solid carrier by not reducing the toner density too much. .
Further, according to the toner density control device of the present invention, when the low image area continues based on the integrated value of the print image, the upper limit value of the toner density of the toner density control device is increased. When the image area continues, the toner density upper limiter is increased, so that it is possible to reduce the phenomenon that the Q / M increases excessively due to the limiter.
Further, according to the toner concentration control apparatus of the present invention, since the total amount of the change amount of the upper limit value and / or lower limit value of the toner density of the toner density control device is set, a limit value is provided. Even after that, the correction could be kept to the optimum value.

  The best mode for carrying out the present invention will be described below with reference to the drawings. However, these are merely embodiments and do not limit the scope of the claims of the present invention.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to the present embodiment. The image forming apparatus 100 includes a photoreceptor unit 1 including a charging device and a cleaning device, an exposure device 104, a developing unit 2 as a developing device, a transfer device 105, a fixing device 106, and a paper feeding / conveying device.
FIG. 2 is an enlarged view of the transfer device of the image forming apparatus according to the present embodiment. The transfer device 105 is configured such that an endless transfer belt 105a is stretched over a support roller and pressed against the support roller via the transfer belt 105a. The reference density pattern sensor (P sensor) 121 detects the density of the reference pattern formed on the transfer belt 105a.
In the image forming apparatus 100 configured as described above, the surface of the rotating photoreceptor 5 is uniformly charged by the charging device, and then irradiated with the laser beam of the exposure device 104 based on the image information, An electrostatic latent image is formed on the photoreceptor 5. A toner image is formed by attaching toner charged by an electrostatic latent image formed on the photoconductor 5 to form a visible image. On the other hand, the transfer paper P is fed from a paper feed tray 109 by a paper feed / conveyance device, and then conveyed to a transfer portion where the photoconductor 5 and the transfer device 105 face each other. Then, the toner image formed on the photoconductor 5 is transferred to the transfer paper P by applying a charge having a polarity opposite to that of the toner image on the photoconductor 5 to the transfer paper P by the transfer device 105. Next, the transfer paper P is separated from the photoconductor 5, sent to the fixing device 106, and an image is obtained by fixing the toner to the transfer paper P. Thereafter, the paper is discharged by a paper discharge roller 111 to a paper discharge tray outside the image forming apparatus 100.

FIG. 3 is an enlarged view of the photosensitive unit and the developing unit of the image forming apparatus according to the present embodiment. A charging device 4, a cleaning device 3, a developing unit 2 as a developing device, and the like are sequentially disposed around a photoconductor 5 as an image carrier.
The photoconductor unit 1 has a configuration common to each color by storing the charging / cleaning process in one unit. The photosensitive member 5 is charged by the charging roller 4A. The charging cleaning roller 4B attached to the upper part of the charging roller 4A cleans the charging roller 4A. Untransferred toner on the photoreceptor 5 is collected by the cleaning blade 3C and the cleaning brush 3A, and sent to the waste toner conveying coil 3B side. The waste toner is transported from the waste toner transport coil 3B to the waste toner discharge port and collected by a waste toner bottle (not shown).
The development unit 2 has a common configuration for each color when it is new. When the toner of each color is replenished from the toner cartridge 6 separately provided in the main body of the image forming apparatus 100 after being installed in the image forming apparatus 100, the developing unit 2 is independent. Unit. The developing unit 2 after the toner is replenished becomes incompatible and cannot be replaced between the colors. Each photoconductor unit 1 and each developing unit 2 are configured such that they can be replaced as needed by releasing their stoppers when necessary.
The toner density of the developing unit 2 is confirmed by the toner density sensor 2C and the reference density pattern sensor (P sensor) 121 shown in FIG. The toner concentration sensor 2C is an inductance sensor, and detects the toner concentration from the ratio of the toner and the carrier by measuring the magnetic permeability of the developer mixed with the toner and the carrier. When the toner density is equal to or lower than a predetermined value, toner is supplied to the developing unit 2 from the toner cartridge 6.

FIG. 4 is a schematic configuration diagram of the developing device of the image forming apparatus according to the present embodiment. This developing device is provided as a developing unit 2 on the side of the photoreceptor 5 and serves as a developer carrying member that carries a two-component developer (hereinafter referred to as “developer”) containing toner and a magnetic carrier on the surface. The non-magnetic developing roller 2D is provided. The developing roller 2D is attached so as to be partially exposed from an opening formed on the photosensitive member side of the developing casing, and is rotated by a driving device (not shown). In addition, a magnet roller (not shown) composed of a fixed magnet group as a magnetic field generating means is fixedly arranged inside the developing roller 2D. Further, the developing device includes a doctor blade 2E as a developer regulating member made of a rigid body that regulates the amount of developer carried on the developing sleeve of the developing roller 2D. A developer accommodating portion for accommodating the developer is formed on the upstream side of the rotation direction of the developing roller 2D with respect to the doctor blade 2E, and a conveying screw (left) 2A for agitating and mixing the developer in the developer accommodating portion, conveying A screw (right) 2B is provided. Further, a toner replenishing port disposed above the developer accommodating portion, a toner cartridge 6 filled with toner to be replenished to the developer accommodating portion, and a toner flow device for connecting the toner replenishing port and the toner cartridge 6 are provided. Is provided.
In the developing device having the above-described configuration, the developer in the developer container is agitated by rotating the transport screw (left) 2A and the transport screw (right) 2B, and the toner and the magnetic carrier are triboelectrically charged in opposite polarities. Is done. The developer is supplied to the peripheral surface of the developing sleeve of the developing roller 2D that is rotationally driven, and the supplied developer is carried on the peripheral surface of the developing sleeve, and is conveyed in the rotation direction by the rotation of the developing sleeve. Next, the amount of the conveyed developer is regulated by the doctor blade 2E, and the regulated developer is conveyed to a development area where the photoconductor 5 and the developing roller 2D face each other. In this developing region, the toner in the developer is electrostatically transferred to the electrostatic latent image on the surface of the photoconductor 5, and the electrostatic latent image is visualized as a toner image.

Next, an example of toner density control will be described with reference to FIGS.
FIG. 5 is a diagram showing the configuration of the toner concentration control device.
In image forming apparatuses such as copiers and printers, in order to maintain the image density, an image is formed so that the amount of adhesion is optimized by creating a toner test pattern outside the printing area and detecting the amount of pattern adhesion. It is necessary to control the conditions. In particular, in a full color machine, it is necessary to detect a high density portion to a low density portion in order to maintain density gradation and color reproducibility.
Further, when detecting from a high density part to a low density part, it is necessary to create a plurality of toner image patterns in order to obtain gradation. As a method of creating a plurality of toner image patterns, an image is formed by varying the developing bias and exposure energy in the rotation direction on the image carrier, and when the toner image pattern reaches the position of the density sensor, the density is sequentially detected. Go. Such a method is general. In this case, since the detection time becomes long, frequent detection cannot be performed, and the detection is performed at a predetermined time or at a predetermined print number interval.

FIG. 6 is a flowchart of an embodiment regarding the calculation of the image area / toner supply amount. This will be described below with reference to steps S1 to S14.
(S1) Print start: When a copy button is pressed or print data is transmitted from the PC, print job is started.
(S2) When printing job is started, the polygon motor is turned on. When the polygon motor is in a steady state, the photosensitive member driving motor, the developing roller driving motor, and the transfer belt driving motor are turned on, and a charging bias, a developing bias, and a transfer bias are applied.
(S3) FGATE ON: Sub-scanning gate signal FGATE is turned ON when exposure standby is set.
(S4) Reading the density sensor output: The T sensor that reads the output of the toner density sensor (hereinafter referred to as “T sensor”) is disposed in the developing conveying screw section, and outputs a value proportional to the magnetic permeability in the vicinity. The As shown in FIG. 11, the magnetic permeability is a value that is inversely proportional to the toner / carrier mixture ratio.
(S5) FGATE OFF: When the first image portion exposure is completed, FGATE is turned OFF.
(S6) Completion of pixel number reading: The LD control unit counts the number of exposed pixels.
(S7) Pixel density determination: The resolution of 600 × 600 dpi or 1200 × 1200 dpi is determined.
(S8) Image area is calculated: Image area = number of pixels / pixel density (in the case of 600 dpi, 600 ² ÷ 2.54 ² )
(S9) Calculating the integration of the image area: n (A4 from the print number counter / number of sheets converted to the area per sheet) = 0 p (integration of the image area) from 0 is calculated.
(S10) m is calculated: m = p / n
(S11) Calculation of toner replenishment amount: Toner replenishment amount = T sensor proportional coefficient × (T sensor output value Vti−T sensor target value Vref) + image area proportional coefficient × image area where Vref is, for example, the development bias The developing ability (γ) is calculated from the reflection density of the toner image that has been changed to create a gradation, and the value is multiplied by a certain coefficient.
Basically, toner is supplied or not supplied until Vti-Vref becomes 0.
By providing upper and lower limit values for Vref according to the potential (VrefH, VrefL), it is possible to control the toner density within a range corresponding to these values.
(S12) m · Toner replenishment amount is stored in the nonvolatile memory.
(S13) Print job end determination: If the print job ends, the motors stop operation starts. If the job is not completed, S3 to S12 are repeated for the next print.
(S14) Motor stop: When the above is completed, the charging bias, the developing bias, and the transfer bias are turned off, and the polygon motor, the photosensitive member driving motor, the developing roller driving motor, and the transfer belt driving motor are turned off.

FIG. 7 is a flowchart of an embodiment for determining the toner density lower limit value. Hereinafter, steps S15 to S23 will be described.
(S15) Print job start (S16) The number counter n is counted up for each print. In this embodiment, the number counter is calculated in terms of A4. (Example: n = n + 2 for A3 • 1 and n = n + 3 for A4 • 3)
Although not shown, n = 0 when the developing device is replaced.
(S17) If n is less than 1000 sheets (corresponding to A4), the print job end determination is made as it is.
(S18) If n is 1000 or less, it is determined whether m (average image area ratio = p / n) calculated in FIG. 6 is 1% or less. If m ≧ 1%, the print job end determination is made.
(S19) VrefL (toner density lower limit) is set to VrefL = 5 V when the developing device is replaced (not shown). Since VrefL becomes smaller every time it is corrected, there is no point in providing a lower toner density limit if it is made unlimited, so in this embodiment, if it is smaller than 4V, no further correction is performed.
(S20) If it is greater than 4V, VrefL is further reduced by -0.2V.
(S21) When the VrefL correction is performed, the number counter n = 0.
(S22) When VrefL correction is performed, the image area ratio integration counter m = 0 is set.
(S23) When the print job is finished, the VrefL correction is also finished.

FIG. 8 is a flowchart of an embodiment for determining the toner density upper limit value. Hereinafter, steps S24 to S32 will be described.
(S24) Print job start (S25) The print counter n is counted up for each print. In this embodiment, the number counter is calculated in terms of A4. (Example: n = n + 2 for A3 • 1 and n = n + 3 for A4 • 3)
Although not shown, n = 0 when the developing device is replaced.
(S26) When n is less than 1000 sheets (corresponding to A4), the print job end determination is made as it is.
(S27) If n is 1000 or less, it is determined whether m (average image area ratio = p / n) calculated in FIG. 6 is 1% or less. If m ≧ 1%, the print job end determination is made.
(S28) VrefH (toner density upper limit value) is set to VrefH = 3V when the developing device is replaced (not shown). Since VrefH becomes smaller every time it is corrected, there is no point in setting an upper limit of toner density if it is made unlimited, so in this embodiment, when it is smaller than 2V, no further correction is performed.
(S29) If it is greater than 2V, VrefH is further reduced by -0.2V.
(S30) When the VrefH correction is performed, the number counter n = 0.
(S31) When VrefH correction is performed, the image area ratio integration counter m = 0 is set.
(S32) When the print job is finished, the VrefH correction is also finished.

FIG. 9 is a flowchart of an embodiment regarding execution of toner replenishment. Hereinafter, steps S201 to S210 will be described.
(S201) Start print job: Printing is started when the copy button is pressed or print data is transmitted from the PC.
(S202) Motor activation: When printing is started, the polygon motor is turned on. When the polygon motor is in a steady state, the photosensitive member driving motor, the developing roller driving motor, and the transfer belt driving motor are turned on, and a charging bias, a developing bias, and a transfer bias are applied.
(S203) FGATE ON: When the exposure standby is set, the sub-scanning gate signal (FGATE) is turned ON.
(S204) Toner replenishment amount is read (S205) The toner replenishment motor ON time is calculated: toner replenishment motor ON time sec = toner replenishment amount mg / replenishment capacity mg / sec per unit time
(S206) The toner supply motor is turned on (S207) The toner supply motor has been turned on (S208) The toner supply motor is turned off: The toner supply motor is turned on for the time calculated in S205. The replenished toner is supplied into the developing conveyance path and conveyed onto the magnet roller while being mixed with the carrier.
(S209) Print job end determination: If printing is ended, the motors stop operation is started. If printing is not completed, S203 to S208 are repeated for the next print.
(S210) Motor stop: The charging bias, developing bias, and transfer bias are turned off, and the polygon motor, photosensitive member driving motor, developing roller driving motor, and transfer belt driving motor are turned off.

FIG. 10 is a flowchart of an embodiment regarding toner density control. Hereinafter, the steps S301 to S311 will be described.
(S301) Motor start-up: Density control is performed when the power is turned on or after printing a predetermined number of sheets. When density control is executed, the polygon motor is turned on. When the polygon motor is in a steady state, the photosensitive member driving motor, the developing roller driving motor, and the transfer belt driving motor are turned on, and a charging bias, a developing bias, and a transfer bias are applied.
(S302) Toner replenishment amount is read (S303) Image area is read (S304) The development motor is turned on (S305) Toner image density detection pattern creation start: A density detection toner image pattern is created. As an example of creating the density detection pattern, five patterns of 15 mm in the main scanning and 10 mm in the sub-scanning are created at intervals of 5 mm.
(S306) Judgment whether the toner image density detection pattern has reached the position of the photo sensor (S307) Reading the photo sensor output When the created toner image pattern reaches the position of the sensor, the toner image density is detected. The toner image density has the property that the surface roughness (regular reflectance) of the transfer belt and the surface roughness (regular reflectance) of the toner image are different and correlate with the density of the toner image, and the surface roughness (regular reflectance). The toner image density is estimated using the fact that the toner has a property of changing.
(S308) Determination of image portion image forming condition: When the toner image density is estimated, the image forming condition is determined so that the toner image density becomes appropriate.
As an example, when creating a toner image density pattern, gradation is created by varying the development bias, and a relational expression between the development bias and the toner image density is obtained. From this relational expression, a developing bias that obtains the target density is calculated and set as an image forming condition. In addition, in order to keep the density of the halftone part and the highlight part appropriately, the gradation is created by changing the exposure condition and the exposure condition is determined so that the target density of the halftone part and the highlight part can be obtained. . Alternatively, control such as controlling the toner density target level may be used in order to keep the developing ability (γ) appropriate.
(S309) Motor stop: When the above is completed, the charging bias, the developing bias, and the transfer bias are turned off, and the polygon motor, the photosensitive member driving motor, the developing roller driving motor, and the transfer belt driving motor are turned off.

1 is a diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. FIG. 2 is an enlarged view of a transfer device of the image forming apparatus according to the present embodiment. FIG. 2 is an enlarged view showing a photosensitive unit and a developing unit of the image forming apparatus according to the present embodiment. 1 is a schematic configuration diagram of a developing device of an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating a configuration of a toner density control device. 6 is a flowchart of an embodiment for calculating an image area and a toner replenishment amount. 6 is a flowchart of an embodiment for determining a toner density lower limit value. 7 is a flowchart of an embodiment for determining a toner density upper limit value. 10 is a flowchart of an embodiment regarding toner replenishment execution. 6 is a flowchart of an embodiment regarding toner density control. 6 is a graph showing characteristics of a conventional toner density sensor.

Explanation of symbols

1 Photosensitive unit 2 Developing unit 2A Conveying screw (left)
2B Conveying screw (right)
2C Toner density sensor (T sensor)
2D Developing roller 2E Doctor blade 3 Cleaning device 3A Cleaning brush 3B Waste toner transfer coil 3C Cleaning blade 4 Charging device 4A Charging roller 4B Charging cleaning roller 5 Photoconductor 6 Toner cartridge 100 Image forming device 103 Manual feed tray 104 Exposure Device 105 Transfer device 105a Transfer belt 105b Belt drive roller 106 Fixing device 107 Duplex unit 108 Reversing unit 109 Paper feed tray 109a Separation paper feed portion 109b Registration roller pair 111 Paper discharge roller pair 118 Waste toner container 121 Reference density pattern sensor (P Sensor)
122 Cleaning blade 123 Cleaning bias roller 124 Waste toner collection coil 125 Bias brush (each color)
126 Conveyance backup roller (each color)
127 Slide rail 128 Paper adsorption roller P Transfer paper

Claims (4)

An image carrier, a charging device for charging the image carrier, an exposure device for exposing the charged image carrier to form an electrostatic latent image, and developing the electrostatic latent image using a two-component developer A toner concentration control device used in an image forming apparatus comprising a developing device and a toner replenishing device for replenishing toner to the developing device,
Reference pattern image forming means for forming a reference pattern on the image carrier, reference density pattern detection means for detecting the density of the reference pattern formed on the image carrier, and an image for calculating the image area of the print image In an area calculating means, a toner concentration detecting device for detecting the toner concentration of the developer in the developing device, and a toner concentration control device having an upper limit value and / or a lower limit value for controlling the toner concentration of the developer,
The toner density control apparatus determines an upper limit value and / or a lower limit value of the toner density control apparatus based on an integrated value of an image area of a printed image. 2. The toner density control device according to claim 1, wherein the toner density control device increases a lower limit value of the toner density of the toner density control device when a low image area continues based on an integrated value of the print image. Toner density control device. 2. The toner density control device according to claim 1, wherein the toner density control device increases the upper limit value of the toner density of the toner density control device when a low image area continues based on an integrated value of the print image. Toner density control device. 4. The toner density control device according to claim 1, wherein a limit value is provided for a total amount of change of the upper limit value and / or the lower limit value of the toner density control of the toner density control device. The toner density control device described.

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