JP2015045828A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that image quality after the exchange of a toner cartridge is deteriorated due to a print history before the toner cartridge exchange.SOLUTION: An image forming apparatus includes: an image forming unit 10; a toner cartridge 20; a toner residual amount detection part 11; a print duty measurement part; and a bias determination or the like. The print duty measurement part measures a print duty since the predetermined value of a toner residual amount in the image forming unit 10 is detected by the toner residual amount detection part 11 until the toner cartridge 20 is exchanged. The bias determination part changes a bias difference between a development bias DB after the exchange of the toner cartridge 20 and a supply bias in accordance with the measured print duty. Thus, it is possible to improve paper space covering after the exchange of the toner cartridge.

Description

  The present invention relates to an image forming apparatus using an electrophotographic process such as a printer or a facsimile machine (hereinafter referred to as “FAX”).

  Conventionally, for example, in the image forming apparatus described in Patent Document 1, a developing bias voltage (hereinafter referred to as “bias voltage”) applied to a developing member for developing a developer image according to the remaining amount of developer in the image forming unit. "Is simply referred to as" bias ") and the supply bias applied to the developer supply member for the developing member is simultaneously set high or low. As a result, the developer charge amount and the image density in the image forming unit are uniformly adjusted to maintain the image quality.

JP 2002-258676 A

  However, in the conventional image forming apparatus, the image quality after replacing the developer cartridge may be deteriorated depending on the printing history before replacing the developer cartridge for supplying the developer.

  An image forming apparatus according to the present invention includes an image carrier that carries an electrostatic latent image, and a developer that is attached to the electrostatic latent image to develop the electrostatic latent image, and the developer on the image carrier. An image forming unit having a developing member that generates an image and a supply member that supplies the developer to the developing member is provided.

  Furthermore, the image forming apparatus of the present invention includes a developer cartridge that contains the developer and is replaceably attached to the image forming unit, and replenishes the stored developer to the image forming unit; A developing member power source for applying a developing bias to the developing member, a supplying member power source for applying a supplying bias to the supplying member, a developer remaining amount detecting unit for detecting a developer remaining amount in the image forming unit, A printing density measuring unit that measures printing density; and a bias determining unit that determines a first voltage difference between the developing bias and the supply bias based on the measured printing density.

  Then, the bias determination unit determines whether the developer cartridge is in accordance with the measured print density from when the detected remaining amount of developer reaches a predetermined value until the developer cartridge is replaced. The first voltage difference after replacement is changed.

  According to the image forming apparatus of the present invention, the developer cartridge is replaced in accordance with the printing density from when the remaining amount of developer in the image forming unit decreases to a predetermined value until the developer cartridge is replaced. The voltage difference between the later developing bias and the supply bias is changed. Thereby, it is possible to improve the fogging on the paper after the developer cartridge is replaced.

FIG. 1 is an enlarged sectional view showing the vicinity of one image forming unit 10 in FIG. FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a schematic block diagram illustrating a circuit configuration of a control system in the image forming apparatus 1 according to the first embodiment. FIG. 4 is a graph showing the transition of the color difference Δ of the paper cover in Example 1 and the comparative example. FIG. 5 is a diagram showing an outline of bias setting in the first embodiment. FIG. 6 is a diagram illustrating the relationship between the print duty, the compensation amount, and the toner layer potential in the first embodiment. FIG. 7 is a diagram illustrating the relationship between the printing duty, the correction bias, and the toner layer potential in the first embodiment. FIG. 8 is a flowchart illustrating bias control after toner cartridge replacement from toner LOW according to the first exemplary embodiment. FIG. 9 is a schematic block diagram showing a circuit configuration of a control system in the image forming apparatus 1A according to the second embodiment of the present invention. FIG. 10 is a diagram showing the transition of the color difference Δ of the paper cover in Example 2 and the comparative example. FIG. 11 is a diagram illustrating the relationship between the printing duty and the compensation amount according to the second embodiment. FIG. 12 is a diagram illustrating the relationship between the print duty, the correction bias, and the toner layer potential in the second embodiment. FIG. 13 is a flowchart illustrating bias control after toner cartridge replacement from toner LOW according to the second exemplary embodiment.

  Modes for carrying out the present invention will become apparent from the following description of the preferred embodiments when read in light of the accompanying drawings. However, the drawings are only for explanation and do not limit the scope of the present invention.

(Configuration of Example 1)
FIG. 2 is a schematic configuration diagram illustrating the image forming apparatus according to the first embodiment of the present invention.

  The image forming apparatus 1 is, for example, a tandem color electrophotographic printer. The image forming apparatus 1 is an image forming unit 10 (for example, a black image forming unit 10K, a yellow image forming unit 10Y, a magenta image) that is a developing device for four colors in the conveying direction of an arrow of a printing paper 2 as a printing medium. A forming unit 10M and a cyan image generating unit 10C) are disposed. At the top of each image forming unit 10, toner cartridges 20 (for example, black toner cartridge 20K, yellow toner cartridge 20Y, magenta toner cartridge 20M, and cyan toner cartridge 20C) as developer cartridges for four colors are respectively provided. It is attached detachably. In the vicinity of each image forming unit 10, a light emitting diode (hereinafter referred to as "LED") head 22 (for example, a black LED head 22K, a yellow LED head 22Y) as an exposure device corresponding to the image forming unit 10 for four colors. , A magenta LED head 22M and a cyan LED head 22C) are provided.

  Below the image forming unit 10 for four colors, a transfer belt 30 for transporting the printing paper 2 in the transport direction indicated by the arrow is disposed. The transfer belt 30 is stretched by a drive roller 31 disposed on the downstream side in the transport direction of the printing paper 2 and a driven roller 32 disposed on the upstream side in the transport direction so as to face the drive roller 31. Thus, the printing paper 2 is conveyed in the conveyance direction indicated by the arrow. Inside the transfer belt 30, a transfer roller 33 (for example, a black transfer roller 33K, a yellow transfer roller 33Y, a magenta transfer roller 33M, and a cyan transfer roller 33C) as a transfer member of each color is opposed to the image forming unit 10 of each color. ) Are arranged respectively. Each transfer roller 33 holds the printing paper 2 and the transfer belt 30 together with each image forming unit 10, and transfers a toner image as a developer image formed in each image forming unit 10 to the printing paper 2. It is.

  A fixing device 34 is disposed on the downstream side of the driving roller 31. The fixing device 34 is a device that heats and pressurizes the toner image transferred to the printing paper 2 and fixes the toner image, for example, a heating roller 34a for heating the printing paper 2 and the printing paper 2 to the heating roller 34a. And a pressure roller 34b that is in pressure contact. The printing paper 2 fixed by the fixing device 34 is discharged in the direction of the arrow.

FIG. 1 is an enlarged cross-sectional view showing the vicinity of one image forming unit 10 in FIG.
Each color image forming unit 10 (= 10K, 10Y, 10M, 10C), toner cartridge 20 (= 20K, 20Y, 20M, 20C), and LED head 22 (= 22K, 22Y, 22M, 22C) have the same structure. Therefore, the structure near one image forming unit 10 will be described below.

  A toner cartridge 20 filled with toner 21 as a developer is replaceably mounted on the upper portion of the image forming unit 10 (that is, detachable). A toner discharge port 20 a is formed in the lower part of the toner cartridge 20. By attaching the toner cartridge 20 to the image forming unit 10, the toner 21 is supplied from the toner discharge port 20 a into the image forming unit 10. The toner 21 is, for example, a non-magnetic one-component toner having an average particle diameter of 6 μm and silica or the like as an external additive.

  In the image forming unit 10, a toner remaining amount detection unit 11 that detects the remaining amount of toner as the remaining amount of developer in the image forming unit 10 is provided below the toner discharge port 20 a in the toner cartridge 20. The toner remaining amount detection unit 11 is made of, for example, a metal rod having a diameter of about 2 mm, and is driven to rotate at a constant speed in the counterclockwise direction indicated by an arrow. A supply roller 12 as a supply member for supplying the toner 21 is provided below the toner remaining amount detection unit 11. The supply roller 12 receives the toner 21 discharged from the toner discharge port 20a and supplies it to the developing roller 13 as a developing member. The supply roller 12 is formed of, for example, a foamed elastic body such as silicone rubber or urethane rubber, and a plurality of cells including recesses are formed on the outer peripheral surface. The developing roller 13 is in contact with the outer peripheral surface of the supply roller 12.

  A developing blade 14 as a regulating member and a photosensitive drum 15 as an image carrier are disposed in contact with the outer peripheral surface of the developing roller 13. The developing roller 13 supplies the toner 21 supplied from the supply roller 12 to the photosensitive drum 15 and develops the electrostatic latent image on the photosensitive drum 15 to generate a toner image. The developing roller 13 includes, for example, a metal shaft and a semiconductive material having a suitable elasticity such as a semiconductive urethane rubber material provided on the surface of the metal shaft.

  The developing blade 14 in contact with the developing roller 13 regulates the toner layer as a developer layer on the developing roller 13 to a certain thickness. The developing blade 14 is, for example, a stainless steel thin plate having a thickness of 0.08 mm and a length in the longitudinal direction substantially matching the width of the semiconductive material of the developing roller 13, and one end in the longitudinal direction is fixed to the frame. A bent portion is formed at the tip of the other end, and the surface slightly ahead from the apex of the bent portion is disposed so as to contact the outer peripheral surface of the developing roller 13.

  The photosensitive drum 15 in contact with the developing roller 13 carries an electrostatic latent image formed by light rays emitted from the LED head 22. The LED head 22 is configured by combining, for example, an LED array and a SELFOC (registered trademark) lens array. The photosensitive drum 15 includes, for example, a conductive support and a photoconductive layer provided on the surface of the conductive support. For example, an aluminum metal pipe is used as the conductive support. The photoconductive layer is formed of, for example, an organic photoreceptor in which a charge generation layer and a charge transport layer are sequentially stacked.

  A charging roller 16 as a charging member and a cleaning member 17 are disposed in contact with the photosensitive drum 15. The charging roller 16 charges the photoconductor drum 15 and includes, for example, a metal shaft and a semiconductive rubber layer provided on the surface of the metal shaft. The cleaning member 17 removes residual toner after transfer on the photosensitive drum 15.

  FIG. 3 is a schematic block diagram illustrating a circuit configuration of a control system in the image forming apparatus 1 of FIGS. 1 and 2 according to the first embodiment.

  The image forming apparatus 1 includes a control unit 41 that performs program control of the entire image forming apparatus in accordance with a print command including image data from a host device 25 such as a personal computer. The control unit 41 is configured by, for example, a central processing unit (CPU). The control unit 41 includes a storage unit 42, a print duty measurement unit 43 that measures a print duty (Duty) as a print density, a high voltage power supply control unit 44, a toner remaining amount detection unit 11, and four-color LEDs. The head 22 (= 22K, 22Y, 22M, 22C) is connected. The high voltage power supply controller 44 includes a developing roller power supply 45 that applies a developing bias (for example, −200 V) to the developing roller 13, and a supply roller power supply 46 that applies a supply bias (for example, −300 V) to the supply roller 12. , To control.

  The image forming apparatus 1 further includes a charging roller power supply 47 for applying a charging bias (for example, −1000 V) to the charging roller 16 and a blade bias (for example, −300 V) as a regulating bias for the developing blade 14. A developing blade power source 48 and a transfer roller power source 49 for applying a transfer bias to each color transfer roller 33 (= 33K, 33Y, 33M, 33C) are provided.

  The control unit 41 includes a bias determination unit 41a. The bias determination unit 41a calculates the first voltage difference between the development bias and the supply bias (for example, the difference between the absolute values of the development bias and the supply bias) based on the print duty as the print density measured by the print duty measurement unit 43. Determine the applied bias to compensate. The storage unit 42 has a voltage correction table 42a, stores the print duty measurement result, and is configured by a readable / writable memory (RAM) or the like.

  The print duty measured by the print duty measuring unit 43 is a ratio of the toner consumption amount used per printing sheet, that is, the ratio of the number of printed printing sheets 2 and the used toner consumption amount. When the amount of toner consumed in one sheet of printing paper is small, low duty printing is performed. Here, the number of printed sheets may be the number of rotations of the photosensitive drum 15 or the like, and the toner consumption may be replaced with a consumption dot count.

The print duty is expressed by the following equation, for example.
Print duty = [Cm (i) / (Cd × C0)] × 100
However,
Cm (i): dots actually used for printing when the photosensitive drum 15 rotates Cd
(Ie, the number of dots exposed).
C0: The number of dots per rotation of the photosensitive drum, that is, not only the presence or absence of exposure,
Dots that are possible per revolution of the light drum (potentially dots are printed)
Yes, the number of dots used for a solid image.
Cd × C0: Possible when the photosensitive drum 15 rotates Cd (potentially dots are printed)
Effective number of dots.

  The bias determination unit 41a is measured from the time when the toner remaining amount in the image forming unit 10 detected by the toner remaining amount detecting unit 11 decreases to a predetermined value until the toner cartridge 20 is replaced. It has a function of changing a first voltage difference that is a difference between the developing bias and the supply bias after the replacement of the toner cartridge 20 in accordance with the printing duty.

  The predetermined value of the remaining amount of toner is set as follows, for example. Initially, the toner 21 is supplied from the toner cartridge 20 into the image forming unit 10. However, the toner 21 is gradually consumed and the toner 21 in the toner cartridge 20 is exhausted. Then, the amount of toner in the image forming unit 10 decreases, and eventually the toner becomes empty (EMPTY). On the premise of such a process, the remaining toner amount in the image forming unit 10 when the filling rate of the toner amount in the image forming unit 10 is 100% (however, the remaining toner amount in the toner cartridge 20 is zero). Is a predetermined value (for example, 50%), the toner 21 is low, and it is determined that the toner is low (LOW).

  The print duty measuring unit 43 is configured to wait until the toner cartridge 20 is replaced after the toner remaining amount detecting unit 11 detects the toner LOW of the toner remaining amount (that is, the toner remaining amount in the image forming unit 10 is 50%). Measure the printing duty between. Then, the bias determination unit 41a has a function of changing the first voltage difference after replacement of the toner cartridge 20 according to the measured print duty.

  The replacement of the toner cartridge 20 is performed, for example, in the following cases (a) and (b).

  (A) When the remaining amount of toner in the toner cartridge 20 becomes zero, the toner cartridge 20 is replaced with a new toner cartridge filled with new toner.

  (B) When replacing the toner cartridge, it is possible to replace not only a new toner cartridge but also a used toner cartridge in which toner remains in the toner cartridge. That is, it is possible to replace the toner cartridge with usable toner remaining. For example, when the life / replacement time of the image forming unit 10 comes before all the toner in the toner cartridge is used up, it is replaced with a new image forming unit. In this case, the toner cartridge can be reused.

(Operation of Example 1)
Regarding the image forming apparatus 1 of the first embodiment, (1) the overall operation of the image forming apparatus 1 of FIGS. 1 to 3, (2) the problem of fogging on paper, and (3) bias control will be described.

(1) Overall Operation of Image Forming Apparatus 1 in FIGS. 1 to 3 In the image forming process of image forming apparatus 1, charging roller 16 in image forming unit 10 in FIG. Is applied with a charging bias (for example, −1000 V), and the surface of the photosensitive drum 15 is uniformly and uniformly charged. When the photosensitive drum 15 rotates and the charged surface reaches a position facing the LED head 22, the image data from the host device 25 is patterned into an image signal via the control unit 41, and the LED head. A light beam corresponding to the image signal is emitted by the light source 22. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 15.

  Subsequently, when the photosensitive drum 15 rotates and the surface on which the electrostatic latent image is formed reaches a position facing the developing roller 13, the toner 21 is supplied from the developing roller 13. A developing bias (for example, −200 V) is applied to the developing roller 13 from the developing roller power supply 45, and a potential difference is provided between the developing roller 13 and the photosensitive drum 15. Therefore, the toner 21 on the developing roller 13 adheres to the surface of the photosensitive drum 15 due to the Coulomb force or the frictional force, and a toner image is formed.

  A supply bias (for example, −300 V) is applied to the supply roller 12 from a power supply 46 for supply roller, and the toner 21 is charged by being rotationally driven with a constant peripheral speed ratio with the developing roller 13. Further, by providing a potential difference between the supply roller 12 and the developing roller 13, the toner 21 in the image forming unit 10 is supplied from the supply roller 12 to the developing roller 13.

  The developing blade 14 is in contact with the developing roller 13 and makes the thickness of the toner layer on the developing roller 13 uniform. A blade bias (for example, −300 V) is applied to the developing blade 14 from a power supply 48 for the developing blade. Therefore, the toner on the developing roller 13 is charged by friction between the developing roller 13 and the developing blade 14 and charge injection.

  In the first exemplary embodiment, the toner 21 has an average charge amount of about −25 μC / g, and is normally negatively charged during the image forming process. Correspondingly, a negative bias is applied to the supply roller 12, the developing roller 13, the charging roller 16, and the developing blade 14.

  Next, in the image forming apparatus 1 in FIG. 2, the printing paper 2 is conveyed by the transfer belt 30 below the four-color image forming units 10 (= 10K, 10Y, 10M, and 10C). When the printing paper 2 passes through the four-color transfer rollers 33 (= 33K, 33Y, 33M, and 33C), a transfer bias is applied to each transfer roller 33 from the transfer roller power supply 49, and The toner image on the surface is transferred to the printing paper 2. Subsequently, the printing paper 2 is conveyed to the fixing device 34, and is sandwiched from both sides by the rotating heating roller 34a and the pressure roller 34b, and is pressed while being heated. The toner constituting the toner image is melted by the heat of the heating roller 34a, and the melted toner is pressurized and penetrates between the fibers of the printing paper 2 to fix the toner image. Thereafter, the printing paper 2 is discharged out of the image forming apparatus 1. The toner remaining on the photosensitive drum 15 after the transfer process is scraped off and collected by the cleaning member 17.

(2) The problem of fogging on paper In recent years, the speed of image forming apparatuses has progressed, and the toner tends to deteriorate due to increased friction between element members such as a developing roller and a supply roller in the image forming unit. Yes. In particular, when the amount of toner remaining in the image forming unit is small and printing with a low print duty is continued, the frequency of friction between specific toners increases, so the toner deteriorates significantly. Toner deterioration refers to deterioration in charging ability or change in toner configuration due to external friction, and external additives such as silica that are externally added to increase the toner charge amount on the toner surface. This is caused by peeling and embedding of toner, toner aggregation, wax exudation, and the like.

FIG. 4 is a graph showing the transition of the color difference Δ of the paper fog in Example 1 and the comparative example.
In FIG. 4, the horizontal axis represents the number of printed sheets (unit k (= 1000)), the vertical axis represents the color difference ΔE of the paper cover, and the color difference ΔE of the paper cover when low duty printing with a print duty of 0.5% continues. Transition (change) is shown. The thick broken line 60 is the characteristic of the first embodiment, and the thin broken line 61 is the characteristic of the comparative example with respect to the first embodiment. A thick horizontal straight line 62 is an allowable level of the color difference Δ, and broken vertical lines 63 and 64 are toner cartridge replacement locations. Y is the difference between the development bias DB and the blade bias BB (that is, the second voltage difference).

  Here, the fogging on the paper is a printing defect that generally occurs when the positively charged toner 21 or the like adheres to the high negatively charged portion of the photosensitive drum 15. A fog that adheres to a background portion (that is, a non-image portion) of an image due to a toner having a low charge amount or a toner charged to a reverse polarity with respect to a normally charged dust is called fogging. A toner having a low charge amount that causes this fogging or a toner charged to a reverse polarity is called a fogging toner.

The measurement conditions and measurement method for the paper surface fog are as follows, for example.
As printing paper 2 used for printing, Oki Electric excellent gloss paper (weighing 128 g / m ² ) is used. The printing pattern performs blank paper printing without forming an electrostatic latent image. The measuring instrument for measuring the color difference ΔE of the fog on the paper is an American X-Rite product (spectral densitometer 500 series), and is set with a light source D50 and a viewing angle of 2 °, based on excellent gloss paper before printing. The color difference ΔE before and after is measured.

That is, the usage environment of the image forming apparatus 1 is an N / N environment (temperature 23 ° C./humidity 55%). Excellent gloss paper (128 g / m ² ) was used as the printing paper 2 used for printing. The X-Rite (500 series) is used as a measuring instrument for measuring the color difference ΔE of the paper surface fog. The light source D50, the viewing angle is 2 °, and the color difference ΔE before and after printing is measured with reference to excellent gloss paper before printing. did. In addition, the toner cartridge 20 is exchanged 63 and 64 for 15k (= 15000) and 25k (= 25000) printed sheets.

  FIG. 4 shows that in the image forming apparatus of the comparative example (61), the value of the color difference ΔE of the fog after the toner cartridge replacement 63, 64 is increased. Here, the smaller the value of the color difference ΔE, the smaller the fog on the paper surface, that is, the better the quality, and the acceptable level (spec.) 62 is ΔE ≦ 2.0. Therefore, it can be seen that the fogging on the paper surface deteriorates after the replacement of the toner cartridges 63 and 64, and the permissible level 62 is reached after the replacement of the toner cartridge 64 with the number of printed sheets 25k (= 25000). It can also be seen that the color difference ΔE is restored to the level before the toner cartridge replacement 63, 64 according to the number of printed sheets after the toner cartridge replacement 63, 64.

  The cause of the deterioration of the color difference ΔE after the replacement of the toner cartridge is a process in which low-duty printing continues and the deteriorated toner with deteriorated charging performance is mixed with the new (fresh) toner of the new cartridge. Repeats friction. This is because, at this time, charge movement occurs and reversely charged toner that causes fogging is generated, or the toner charge amount is relatively reduced. In the image forming unit 10 after the toner cartridge replacement 63 and 64, the amount of deteriorated toner decreases every time printing is performed, and at the same time, the toner is frictionally charged, and the toner charge amount gradually increases, so the fog level gradually increases. Go to recover.

  In the comparative example (61) of FIG. 4, the transition of the color difference ΔE of the fog is shown. FIG. 5 shows the bias setting at this time.

FIG. 5 is a diagram illustrating an outline of bias setting in the first embodiment.
In FIG. 5, the vertical axis indicates the setting values of the developing bias DB applied to the developing roller 13 and the supply bias SB applied to the supply roller 12, and the horizontal axis indicates the number of printed sheets. Z is a specified value for the number of printed sheets.

The initial development bias DB ₀ is set to −200V, and the initial supply bias SB ₀ is set to −300V. The development bias DB is a parameter for determining a density value, and since the density is difficult to obtain at the initial stage of the image forming unit 10 and the density increases according to the number of printed sheets, generally, the initial development bias DB ₀ is set high. The development bias DB is set low according to the number of printed sheets.

  In practice, the value of the development bias DB may change due to control such as density correction, but the tendency that the development bias DB changes to a lower value according to the number of printed sheets does not change. X (= DB−SB) is a difference between applied biases of the developing roller 13 and the supply roller 12 (that is, a first voltage difference). As described above, the supply roller is higher than the development bias DB of the developing roller 13. 12 supply bias SB is set high on the minus side. Therefore, the value of the applied bias difference X (= DB−SB) is a positive value. The applied bias difference X (= DB−SB) is a parameter for controlling the thickness of the toner layer on the developing roller 13, and in the comparative example (61), DB−SB = X is set. Further, since the blade bias BB applied to the developing blade 14 is set higher than the developing bias DB applied to the developing roller 13 to the minus side, the developing bias DB and the blade bias BB as the second voltage difference are set. As the value of the difference Y (= DB−BB), a positive value is obtained. In Example 1 (60), DB-BB = Y = 100, which is always set to a constant value.

  As shown in FIG. 5, in Example 1 (60), DB-SB after toner cartridge replacement 64 is set to X + α (compensation amount α ≧ 0). As shown in the results of FIG. 4, in Example 1 (60), DB-SB after toner cartridge replacement 63 and 64 is set to X + α, and the color difference ΔE of the paper fog under the same conditions as in Comparative Example (61). The color difference ΔE after toner cartridge replacement 63 and 64 improved by 0.3 to 0.5. This is because the applied bias difference X (= DB−SB) is corrected so as to be larger than the comparative example (61) by the correction amount α, thereby increasing the potential difference between the developing roller 13 and the supply roller 12. It is considered that the reversely charged toner that is the cause of the fog becomes difficult to move to the developing roller 13.

here,
α = α ₀ −α ₀ × Number of printed sheets after toner replacement / Z (Z is the number of printed sheets whose compensation amount α is canceled)
However, α ≧ 0, α ₀ ≧ 0
It is defined as

  FIG. 6 is a diagram illustrating the relationship between the print duty, the correction amount, and the toner layer potential in the first embodiment. Furthermore, FIG. 7 is a diagram illustrating the relationship between the printing duty, the correction bias, and the toner layer potential in the first embodiment.

In FIG. 7, the horizontal axis represents the print duty (%), and the vertical axis represents the correction bias = α ₀ (V) and the toner layer potential (V). A curve 65 is DB-SB difference correction amount immediately after the toner cartridge replacement = α ₀ (V), and a curve 66 is the toner layer potential (V) on the developing roller 13 immediately after the toner cartridge replacement.

These FIG. 6 and FIG. 7 show the DB-SB difference correction amount immediately after the toner cartridge replacement = α ₀ , the toner layer potential on the developing roller 13 immediately after the toner cartridge replacement in the comparative example (61), and the toner LOW. The relationship of the average print duty until the toner cartridge replacement is shown. The relational expressions shown in FIGS. 6 and 7 are stored in the voltage correction table 42a in the storage unit 42 in FIG.

Here, the lower the average print duty, to increase the compensation amount alpha _0, as the average print duty is high, and decrease the compensation amount alpha _0.

As described above, the toner 21 is likely to be deteriorated during the period from the toner LOW when the remaining amount of toner decreases to the replacement of the toner cartridge. The degree of toner deterioration during this period is determined by the printing duty. Adding new toner to the deteriorated toner generated by printing with a low printing duty deteriorates the fog level. Therefore, the lower the printing duty, the more the correction amount α ₀ was increased. Further, the toner layer potential on the developing roller 13 immediately after the replacement of the toner cartridge becomes lower as the duty printing is performed before the replacement of the toner cartridge. From this, it can be seen that the lower the average print duty before the toner cartridge replacement is, the lower the charge amount and the more reversely charged toner.

The reason for optimizing the correction amount α ₀ when the printing duty is 0% to 60 V is that if the value is further increased, the toner layer potential on the developing roller 13 becomes too high, the stain margin is eliminated, and the stain becomes easy. Because. Also, the high duty areas of the printing duty is 50% or more, since the toner 21 is not substantially degraded, and the compensation amount alpha ₀ is zero.

(3) Bias Control FIG. 8 is a flowchart illustrating the bias control after the toner cartridge replacement from the toner LOW according to the first exemplary embodiment.

The operation of bias control performed in the control system of FIG. 3 will be described with reference to FIG.
When the bias control process is started by the control unit 41, in step S1, the remaining toner amount detecting unit 11 detects the remaining toner amount in the image forming unit 10, and the remaining toner amount is set to toner LOW (for example, image formation). When the remaining amount of toner in the unit 10 is not 50%) (No), the detection of the remaining amount of toner is repeated, and when the remaining amount of toner is toner LOW (Yes), the process proceeds to step S2. In step S2, the print duty measuring unit 43 measures the print duty, the average value of the print duty is stored in the storage unit 42 under the control of the control unit 41, and the process proceeds to step S3. In step S <b> 3, the toner remaining amount detection unit 11 determines whether or not the toner cartridge 20 has been replaced. If the replacement has not been performed (No), the processing is repeated and the toner cartridge 20 is replaced. If yes (Yes), the process proceeds to step S4.

In step S4, the bias determination unit 41a of the control unit 41 reads the average print duty stored in the storage unit 42 in step S2, and compares it with the voltage correction table 42a in which the relational expressions shown in FIGS. 6 and 7 are stored. Then, the correction amount α ₀ of the difference X (= DB−SB) between the development bias DB and the supply bias SB corresponding to the average printing duty is determined, and the process proceeds to step S5. In step S5, the bias determining unit 41a in the control unit 41, a DB-SB difference compensation amount alpha ₀ determined in step S4, determines the DB-SB setpoint X + alpha at the time of printing, the process proceeds to step S6.

  In step S6, the control unit 41 controls the image forming operation based on the bias setting value X + α determined in step S5, and proceeds to step S7. In step S7, the control unit 41 determines whether or not the number of printed sheets after replacement of the toner cartridge has reached a specified value Z (for example, 1000 sheets). If the specified value Z has not been reached (No), step S7 is performed. Returning to S5, if the specified value Z has been reached (Yes), the process proceeds to step S8. In step S8, the bias determination unit 41a in the control unit 41 returns the DB-SB setting value at the time of printing to X. The control unit 41 controls the image forming operation based on the DB-SB set value X and ends the process.

(Modification of Example 1)
The correction values α and α ₀ of the applied bias in the sheet fog and the specified value Z of the number of printed sheets are examples, and can be arbitrarily determined according to the characteristics of the image forming apparatus 1.

(Effect of Example 1)
In the conventional image forming apparatus, depending on the printing history before the toner cartridge replacement, there is a problem that the toner charge amount changes after the toner cartridge replacement and the fogging on paper becomes worse.

  Therefore, in the first embodiment, in order to improve the paper fog after the toner cartridge replacement, the print duty measurement unit 43 measures the print duty from the toner LOW to the toner cartridge replacement, and after the toner cartridge replacement, The bias determining unit 41a changes only the difference X between the development bias DB and the supply bias SB based on the measured printing duty (that is, compensates with the compensation amount α).

  According to the first embodiment, by adopting such a configuration, when low-duty printing continues before the toner cartridge replacement, the deteriorated toner formed in the image forming unit 10 is added after the toner cartridge replacement. As a result, it is possible to improve the fogging on the paper, which is worsened by mixing with the new toner and reducing the toner charge amount.

(Configuration of Example 2)
In the image forming apparatus 1A according to the second embodiment of the present invention, the overall configuration and the configuration of the image forming unit are the same as those in FIGS. 2 and 1 of the first embodiment, and only the configuration of the control system is shown in FIG. 3 and different.

  FIG. 9 is a schematic block diagram showing a circuit configuration of a control system in the image forming apparatus 1A according to the second embodiment of the present invention. Elements common to the elements in FIG. It is attached.

  In the control system of the image forming apparatus 1A according to the second embodiment, a high voltage power supply control unit 44A having a function different from that of the high voltage power supply control unit 44 in the image forming apparatus 1 according to the first embodiment is provided. The high-voltage power supply control unit 44A controls the developing roller power supply 45 and the supply roller power supply 46 as in the first embodiment, and also has a function of controlling the developing blade power supply 48A. The other charging roller power supply 47 and transfer roller power supply 49 are fixed power supplies that are not controlled by the high voltage power supply controller 44A, as in the first embodiment. Other configurations are the same as those of the first embodiment.

(Operation of Example 2)
Regarding the image forming apparatus 1A of the second embodiment, (1) the overall operation of the image forming apparatus 1A, (2) the problem of paper fogging, and (3) bias control will be described.

(1) Overall Operation of Image Forming Apparatus 1A The overall operation of image forming apparatus 1A according to the second embodiment is substantially the same as the overall operation of image forming apparatus 1 according to the first embodiment.

(2) Problem of paper fog FIG. 10 is a diagram showing the transition of the color difference Δ of the paper fog in Example 2 and the comparative example. Elements common to the elements in FIG. Is attached.

  In FIG. 10, substantially the same as FIG. 4 of the first embodiment, the horizontal axis represents the number of printed sheets (unit k (= 1000)), the vertical axis represents the color difference ΔE of the paper cover, and low duty printing with a printing duty of 0.5%. The transition (change) of the color difference ΔE of the paper fog when the is continued is shown. The thick broken line 67 is the characteristic of the second embodiment, and the thin broken line 61 is the characteristic of the comparative example with respect to the second embodiment. A thick horizontal line 62 is an allowable level of the color difference ΔE, and broken vertical lines 63 and 64 are toner cartridge replacement points. Y is the difference between the development bias DB and the blade bias BB (that is, the second voltage difference).

  The definition of the paper fog is the same as that in the first embodiment. Further, the measurement conditions and measurement method for the paper surface fog are the same as those in the first embodiment.

  From FIG. 10, it can be seen that in the image forming apparatus of the comparative example (61), the value of the fog color difference ΔE after the toner cartridge replacement 63, 64 is increased. Here, the smaller the value of the color difference ΔE, the smaller the fog on the paper surface, that is, the better the quality, and the acceptable level (spec.) 62 is ΔE ≦ 2.0. Therefore, it can be seen that the fogging on the paper surface deteriorates after the replacement of the toner cartridges 63 and 64, and the permissible level 62 is reached after the replacement of the toner cartridge 64 with the number of printed sheets 25k (= 25000). It can also be seen that the color difference ΔE is restored to the level before the toner cartridge replacement 63, 64 according to the number of printed sheets after the toner cartridge replacement 63, 64.

  As in the first embodiment, the reason why the color difference ΔE deteriorates after replacement of the toner cartridge is a process in which the low-duty printing continues and the new (fresh) toner of the new cartridge is mixed with the deteriorated deteriorated toner whose charging performance is reduced. This is because the deteriorated toner and the new toner are repeatedly rubbed, and at this time, the movement of the charge occurs, and the reversely charged toner that causes the fogging is generated or the toner charge amount is relatively decreased. . In the image forming unit 10 after the toner cartridge replacement 63 and 64, the amount of deteriorated toner decreases every time printing is performed, and at the same time, the toner is frictionally charged, and the toner charge amount gradually increases, so the fog level gradually increases. Go to recover.

  In the comparative example (61) of FIG. 10, the transition of the fog color difference ΔE is shown. The voltage setting of the DB-SB difference between the developing bias DB and the supply bias SB at this time is the same as in the first embodiment. As shown in FIG.

In Example 1,
α = α ₀ −α ₀ × Number of printed sheets after toner replacement / Z (Z is the number of printed sheets whose compensation amount α is canceled)
However, α ≧ 0, α ₀ ≧ 0
It is defined as On the other hand, in the second embodiment, in addition to the definition of the compensation amount α, the compensation amount β is defined as follows.
β = β ₀ −β ₀ × Number of printed sheets after toner replacement / Z (Z is the number of printed sheets whose compensation amount β is canceled)
However, β ≧ 0, β ₀ ≧ 0

Here, the correction amount β is determined by the blade bias BB applied to the developing blade 14 and the developing bias DB applied to the developing roller 13 after the toner cartridge replacement 63, 64 and before printing the prescribed value Z sheets, (That is, the second voltage difference) Y = DB−BB. The correction amount β ₀ is a difference Y = DB−BB between the blade bias BB applied to the developing blade 14 immediately after the toner cartridge replacement 63 and 64 and the developing bias DB applied to the developing roller 13. If DB-BB = Y in the bias setting of the comparative example (61), DB-BB = Y + β after replacement of the toner cartridge is obtained.

  As described above, the absolute value of the blade bias BB applied to the developing blade 14 is set higher than the developing bias DB applied to the developing roller 13. Further, the larger the absolute value difference DB−BB between the blade bias BB applied to the developing blade 14 and the developing bias DB applied to the developing roller 13, the larger the difference from the developing blade 14 to the toner layer on the developing roller 13. The charge easily moves and the toner layer potential increases.

  FIG. 11 is a diagram illustrating the relationship between the printing duty and the compensation amount in the second embodiment, and corresponds to FIG. 6 in the first embodiment. Further, FIG. 12 is a diagram illustrating the relationship between the printing duty, the correction bias, and the toner layer potential in the second embodiment, and corresponds to FIG. 7 in the first embodiment.

In FIG. 12, the horizontal axis represents the print duty (%), and the vertical axis represents the correction amounts β ₀ and α ₀ (V) and the toner layer potential (V). Curve 65 is DB-SB difference correction amount immediately after toner cartridge replacement = α ₀ (V), curve 66 is the toner layer potential (V) on developing roller 13 immediately after toner cartridge replacement, and curve 67 is toner cartridge replacement. Immediately following blade bias BB correction amount = β ₀ (V).

11 and 12 show that the DB-SB difference correction amount immediately after replacement of the toner cartridge = α ₀ , the correction amount of the blade bias BB after replacement of the toner cartridge = β ₀ , and the toner cartridge in the comparative example (61). The relationship between the toner layer potential on the developing roller 13 immediately after replacement and the average print duty from toner LOW to toner cartridge replacement is shown. The relational expressions shown in FIGS. 11 and 12 are stored in the voltage correction table 42a in the storage unit 42 in FIG. Here, the correction amounts α ₀ and β ₀ are increased as the average printing duty is lower, and the correction amounts α ₀ and β ₀ are decreased as the average printing duty is higher.

As described above, the toner 21 is likely to be deteriorated during the period from the toner LOW when the remaining amount of toner decreases to the replacement of the toner cartridge. The degree of toner deterioration during this period is determined by the print duty, and the fog level is deteriorated by adding new toner to the deteriorated toner generated by printing with a low print duty. α ₀ and β ₀ are increased. Further, the toner layer potential on the developing roller 13 immediately after the replacement of the toner cartridge becomes lower as the duty printing is performed before the replacement of the toner cartridge. From this, it can be seen that the lower the average print duty before the toner cartridge replacement is, the lower the charge amount and the more reversely charged toner.

The reason for optimizing the correction amount α ₀ to 40 V and the correction amount β ₀ to 30 V when the printing duty is 0% is that if the value is increased further, the toner layer potential on the developing roller 13 becomes too high, This is because the dirt margin disappears and the dirt becomes easy. Further, in the high duty region where the print duty is 50% or more, the toner 21 is hardly deteriorated, so the correction amounts α ₀ and β ₀ are set to zero. This is also because when the toner cartridge is replaced after the high duty printing is continued, if the correction amounts α ₀ and β ₀ are increased, the toner layer potential on the developing roller 13 becomes too high and image smearing occurs. It is. Therefore, the correction amounts α ₀ and β ₀ when the print duty is a high duty of 50% or more are optimized to ± 0V.

  In Embodiment 2, as described above, the color difference ΔE as shown in FIG. 10 is changed by correcting the values of the applied bias difference DB-SB and the applied bias difference DB-BB after the toner cartridge replacement. . As shown in the results of FIG. 10, in Example 2, the result that the value of the color difference ΔE was constant before and after the replacement of the toner cartridge was obtained, thereby preventing the deterioration of the fog due to the replacement of the toner cartridge.

  This is because the potential difference between the developing roller 13 and the supply roller 12 becomes large, and it becomes difficult for the reversely charged toner that causes fog to move to the developing roller 13, and the toner on the developing roller 13 from the developing blade 14. This is because the toner layer potential on the developing roller 13 is increased as a result of the charge injection.

(3) Bias Control FIG. 13 is a flowchart showing bias control after toner cartridge replacement from the toner LOW in the second embodiment. Elements common to those in FIG. Has been.

  In the flowchart of FIG. 13, instead of steps S4, S5, and S8 in FIG. 8 of the first embodiment, steps S14, S15, and S18 having different processing contents are provided.

The bias control operation performed in the control system of FIG. 9 will be described with reference to FIG.
When the bias control process is started by the control unit 41, the remaining toner amount detection unit 11 detects the remaining toner amount in the image forming unit 10 in step S1 as in the first embodiment, and the remaining toner amount is determined. If the toner is not LOW (for example, the remaining amount of toner in the image forming unit 10 is 50%) (No), the detection of the remaining amount of toner is repeated. If the remaining amount of toner is toner LOW (Yes), the process proceeds to step S2. move on. In step S2, as in the first embodiment, the print duty measuring unit 43 measures the print duty, and the average value of the print duty is stored in the storage unit 42 under the control of the control unit 41, and the process proceeds to step S3. In step S3, as in the first exemplary embodiment, the toner remaining amount detection unit 11 determines whether or not the toner cartridge 20 has been replaced. If the replacement has not been performed (No), the processing is repeated. If the toner cartridge 20 has been replaced (Yes), the process proceeds to step S14.

In step S14, unlike the first embodiment, the bias determination unit 41a of the control unit 41 reads the average print duty stored in the storage unit 42 in step S2, and stores the relational expressions shown in FIGS. The correction amount α ₀ of the difference X (= DB−SB) between the development bias DB and the supply bias SB corresponding to the average print duty and the difference Y between the development bias DB and the blade bias BB, compared to the voltage correction table 42a. (= DB−BB) is determined as a correction amount β _0, and the process proceeds to step S15. In step S15, unlike the first embodiment, the bias determination unit 41a in the control unit 41 performs printing from the DB-SB difference correction amount α ₀ and the DB-BB difference correction amount β ₀ determined in step S14. DB-SB set value X + α and DB-BB set value Y + β are determined, and the process proceeds to step S6.

  In step S6, the control unit 41 controls the image forming operation based on the bias setting values X + α and Y + β determined in step S15, and proceeds to step S7. In step S7, as in the first embodiment, the control unit 41 determines whether or not the number of printed sheets after the toner cartridge replacement has reached a specified value Z (for example, 1000 sheets), and has not reached the specified value Z. In the case (No), the process returns to step S15, and in the case where the specified value Z has been reached (Yes), the process proceeds to step S18. In step S18, unlike the first embodiment, the bias determination unit 41a in the control unit 41 returns the DB-SB setting value at the time of printing to X and the DB-BB setting value to Y. The control unit 41 controls the image forming operation based on the DB-SB setting value X and the DB-BB setting value Y, and ends the processing.

(Modification of Example 2)
The correction values α, α ₀ , β, β ₀ of the applied bias in the paper surface fog and the value of the specified value Z of the number of printed sheets are examples, and can be arbitrarily determined according to the characteristics of the image forming apparatus 1A.

(Effect of Example 2)
According to the second embodiment, the print duty measurement unit 43 measures the print duty from the toner LOW to the toner cartridge replacement, and after the toner cartridge replacement, the bias determination unit 41a based on the measured print duty. The difference X between the development bias DB and the supply bias SB and the difference Y between the development bias DB and the blade bias BB are changed (that is, compensated by the compensation amounts α and β). As a result, it is possible to prevent deterioration of the paper fog after the replacement of the toner cartridge and to keep the color difference ΔE of the paper fog constant.

(Other variations of Examples 1 and 2)
The present invention is not limited to the first and second embodiments, and various other forms of use and modifications are possible. For example, the following forms (a) and (b) are used as the usage form and the modified examples.

  (A) The overall structure of the image forming apparatuses 1 and 1A, the configuration of the control system, or the configurations of the image forming unit 10 and the toner cartridge 20 may be changed to configurations other than those illustrated.

  (B) The image forming apparatuses 1 and 1A of the present invention are not limited to the color electrophotographic printer described in the first and second embodiments, and can be applied to a digital multifunction peripheral (MFP), a FAX, a copying apparatus, and the like.

DESCRIPTION OF SYMBOLS 1,1A Image forming apparatus 2 Printing paper 10, 10K, 10Y, 10M, 10C Image forming unit 11 Toner remaining amount detection part 12 Supply roller 13 Developing roller 14 Developing blade 15 Photosensitive drum 16 Charging roller 20, 20K, 20Y, 20M , 20C toner cartridge 21 toner 22, 22K, 22Y, 22M, 22C LED head 33 transfer roller 34 fixing device 41 control unit 41a bias determination unit 42 storage unit 43 print duty measurement unit 44, 44A high voltage power supply control unit 45 power supply for developing roller 46 Power supply for supply roller 48, 48A Power supply for developing blade

Claims (15)

An image carrier that carries an electrostatic latent image; a developing member that develops the electrostatic latent image by causing a developer to adhere to the electrostatic latent image to generate a developer image on the image carrier; An image forming unit having a supply member that supplies the developer to the developing member;
A developer cartridge in which the developer is accommodated and removably attached to the image forming unit, and the accommodated developer is supplied to the image forming unit;
A developing member power source for applying a developing bias voltage to the developing member;
A power supply for a supply member for applying a supply bias voltage to the supply member;
A developer remaining amount detecting unit for detecting the remaining amount of developer in the image forming unit;
A print density measuring unit for measuring the print density;
A bias determining unit that determines a first voltage difference between the developing bias voltage and the supply bias voltage according to the measured printing density;
With
The bias determination unit
The first voltage difference after replacement of the developer cartridge according to the measured printing density after the detected remaining amount of developer reaches a predetermined value and before the developer cartridge is replaced. An image forming apparatus characterized by changing the above. The printing density measuring unit measures the printing density from when the developer remaining amount detecting unit detects the predetermined value of the developer remaining amount until the developer cartridge is replaced,
The image forming apparatus according to claim 1, wherein the bias determination unit changes the first voltage difference after replacement of the developer cartridge according to the measured print density. The image forming apparatus according to claim 1 or 2, further comprising:
An image forming apparatus comprising: a storage unit that stores a measurement result of the print density. The first voltage difference is
The image forming apparatus according to claim 1, wherein the image forming apparatus is an absolute value difference between the developing bias voltage and the supply bias voltage.   The image forming apparatus according to claim 1, wherein when the printing density is low, the first voltage difference is increased.   6. The bias determination unit cancels the changed first voltage difference after a predetermined number of print media have been printed after replacement of the developer cartridge. 6. The image forming apparatus described in 1. The image forming apparatus according to claim 1, further comprising:
A regulating member that regulates the developer layer on the developing member;
A power supply for a regulating member that applies a regulating bias voltage to the regulating member;
With
The bias determination unit
In accordance with the measured printing density from when the detected remaining developer amount reaches the predetermined value until the developer cartridge is replaced, the first after the replacement of the developer cartridge. An image forming apparatus, wherein a voltage difference and a second voltage difference between the developing bias voltage and the regulating bias voltage are changed. The printing density measuring unit measures the printing density from when the developer remaining amount detecting unit detects the predetermined value of the developer remaining amount until the developer cartridge is replaced,
The image according to claim 7, wherein the bias determination unit changes the first voltage difference and the second voltage difference after replacement of the developer cartridge according to the measured print density. Forming equipment. The image forming apparatus according to claim 7 or 8, further comprising:
An image forming apparatus comprising: a storage unit that stores a measurement result of the print density. The first voltage difference is a difference in absolute value between the development bias voltage and the supply bias voltage;
The second voltage difference is a difference in absolute value between the development bias voltage and the regulation bias voltage.
The image forming apparatus according to claim 7, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 7, wherein when the printing density is low, the first voltage difference and the second voltage difference are increased.   The bias determining unit cancels the changed first voltage difference and second voltage difference after the developer cartridge is replaced and after a predetermined number of print media have been printed. 12. The image forming apparatus according to any one of 11 above.   The replacement of the developer cartridge may be performed by replacing the developer cartridge with a new developer cartridge filled with a new developer, or replacing the developer cartridge with a usable developer remaining. The image forming apparatus according to any one of 1 to 12.   The image forming apparatus according to claim 1, wherein the print density is a ratio of a consumption amount of the developer used for one print medium. The image carrier is a photosensitive drum,
The developing member is a developing roller;
The supply member is a supply roller;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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