JP2019135553A - Image forming apparatus - Google Patents

Abstract

To reduce consumption of toner while suppressing deterioration of toner, with a configuration that can execute a forcible consumption mode to causing a developing device to forcibly consume toner.SOLUTION: When executing a forcible consumption mode, the image forming apparatus discharges a toner in the amount equivalent to a value obtained by multiplying a discharge execution threshold A by a coefficient less than 1 (0.5) (S32). After executing the forcible consumption mode, the image forming apparatus resets a toner deterioration integrated value X to a value obtained by subtracting the value obtained by multiplying the discharge execution threshold A by the above-mentioned coefficient from the toner deterioration integrated value X at that time (X-(A×0.5)). This reduces the amount of toner consumed in the forcible consumption mode, and subsequent formation of images with high image ratio and execution of the forcible consumption mode at an appropriate timing suppress deterioration of toner.SELECTED DRAWING: Figure 12

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine having a plurality of these functions, and more particularly to a configuration having a forced consumption mode for forcibly consuming a developer.

  In general, in an image forming apparatus such as an electrophotographic system, when the ratio of image formation with a low image ratio (printing rate) is large, the ratio of toner that moves from the developing sleeve to the photosensitive drum in the developing apparatus decreases. In such a state, if the developing device continues to be driven for a long time, the toner is deteriorated in the developing device, and image defects such as toner scattering and fogging are likely to occur. For this reason, conventionally, the developing device has been forced to consume toner.

  For example, when the value indicating the amount of toner used for each image formation is smaller than a set threshold value, the difference is calculated, and when the integrated value obtained by integrating the calculated difference reaches a predetermined value, An invention for executing forced consumption has been proposed (Patent Document 1).

JP 2006-23327 A

  By the way, for example, when an image with a large amount of toner consumption (high image ratio) is formed immediately after executing the forced consumption of toner, the previous forced toner consumption operation (forced consumption mode) may not be executed. In some cases, this image formation may eliminate toner deterioration. In such a case, the toner consumption amount due to the forcible toner consumption operation immediately before becomes excessive with respect to the toner consumption amount necessary for eliminating the toner deterioration.

  In view of such circumstances, an object of the present invention is to make it possible to suppress toner consumption while suppressing toner deterioration with a configuration capable of executing a forced consumption mode.

  The present invention provides an image carrier, a developing device that develops the electrostatic latent image formed on the image carrier with toner, a replenishing unit that replenishes the developing device with toner according to the amount of developer consumed, Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device, wherein the control means includes a consumption value corresponding to the amount of toner consumed for each predetermined unit of image formation, and A difference calculating means for calculating a difference from a reference value set for a predetermined unit; an integrating means for integrating the differences to obtain an integrated value; and when the integrated value is greater than a predetermined threshold, Execution means for executing a forced consumption mode, wherein the execution means executes the forced consumption mode so that a toner amount corresponding to a value obtained by multiplying the predetermined threshold by a coefficient less than 1 is consumed. The accumulating means When a mode is executed, a value obtained by subtracting a value obtained by multiplying the predetermined threshold by the coefficient from the integrated value at that time is set as a reset value, and after execution of the forced consumption mode, the reset value is set to the reset value. In the image forming apparatus, the difference is integrated.

  The present invention also provides an image carrier, a developing device that develops the electrostatic latent image formed on the image carrier with toner, and a replenishing unit that replenishes the developing device with toner according to the amount of developer consumed. And a control unit capable of executing a forced consumption mode for forcibly consuming toner in the developing device, wherein the control unit continuously forms images corresponding to an image ratio equal to or less than a predetermined ratio. In the case where the average image ratio is the same condition, the forced consumption mode is executed so that the interval until the forced consumption mode is executed is shorter than the first time from the timing when the predetermined condition is satisfied. The image forming apparatus is characterized in that the operation is controlled.

  The present invention also provides an image carrier, a developing device that develops the electrostatic latent image formed on the image carrier with toner, and a replenishing unit that replenishes the developing device with toner according to the amount of developer consumed. And a control unit capable of executing a forced consumption mode for forcibly consuming toner in the developing device, wherein the control unit has information regarding a toner consumption amount consumed per unit driving time of the developing device. In the case where images corresponding to less than a predetermined value are continuously formed, the interval until the forced consumption mode is executed when the information is under the same condition is greater than the first time from the timing when the predetermined condition is satisfied, In the image forming apparatus, the operation in the forced consumption mode is controlled so that the time after that is shorter.

  According to the present invention, in a configuration capable of executing the forced consumption mode, it is possible to suppress toner consumption while suppressing toner deterioration.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram of an image forming station according to a first embodiment. FIG. 1 is a block diagram showing a system configuration of an image forming apparatus according to a first embodiment. 1 is a schematic cross-sectional view of a developing device according to a first embodiment. FIG. FIG. 3 is a control block diagram of a temperature sensor provided in the developing device according to the first embodiment. The figure which shows the experimental result which measured the toner deterioration threshold value video count Vt of each color. 6 is a flowchart for determining whether to execute a forced consumption mode according to the first embodiment. The flowchart which shows operation | movement of the forced consumption mode which concerns on a comparative example. The figure which shows each parameter in the case of black low duty, and the case of high duty. The schematic diagram which shows the relationship of each parameter at the time of forming the image of black low duty continuously in a comparative example. The flowchart which shows operation | movement of the forced consumption mode which concerns on 1st Embodiment. FIG. 4 is a schematic diagram illustrating a relationship between parameters when black low-duty images are continuously formed in the first embodiment. The flowchart which shows operation | movement of the forced consumption mode which concerns on the 2nd Embodiment of this invention. FIG. 10 is a diagram illustrating a relationship between an average printing rate and a forced consumption coefficient of the image forming apparatus according to the second embodiment. 10 is a flowchart for determining whether to execute a forced consumption mode according to the third embodiment of the present invention.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. First, a schematic configuration of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIGS.

[Image forming apparatus]
As shown in FIG. 1, the image forming apparatus 100 according to the present embodiment includes four image forming stations Y, M, C, and K each including a photosensitive drum 101 (101Y, 101M, 101C, and 101K) as image carriers. Have. An intermediate transfer device 120 is arranged above each image forming station. The intermediate transfer device 120 is configured such that an intermediate transfer belt 121 as an intermediate transfer member is stretched around rollers 122, 123, and 124 and travels in the direction of an arrow.

  Around the photosensitive drum 101, a primary charging device 102 (102Y, 102M, 102C, 102K), a developing device 104 (104Y, 104M, 104C, 104K), a cleaner 109 (109Y, 109M, 109C, 109K), and the like are arranged. ing. The configuration around the photosensitive drum and the image forming operation will be described with reference to FIGS. Since the configuration around the photosensitive drum is the same for each color, when there is no particular need to distinguish between them, a subscript indicating the configuration of the image forming station for each color will be omitted.

  The photosensitive drum 101 is driven to rotate in the arrow direction. The surface of the photosensitive drum 101 is uniformly charged by a charging roller type primary charging device 102 which is contact charging. An electrostatic latent image is formed on the surface of the charged photosensitive drum 101 by being exposed by a laser light emitting element 103 as an exposure device. The electrostatic latent image formed in this way is visualized with toner by the developing device 104, and a toner image is formed on the photosensitive drum 101. In each image forming station, toner images of yellow (Y), magenta (M), cyan (C), and black (K) are formed.

  The toner image formed at each image forming station is transferred and superimposed on the intermediate transfer belt 121 made of polyimide resin by the primary transfer bias by the primary transfer roller 105 (105Y, 105M, 105C, 105K). The four color toner images formed on the intermediate transfer belt 121 are recorded on a recording material (for example, a sheet material such as paper or an OHP sheet) by a secondary transfer roller 125 serving as a secondary transfer unit disposed opposite to the roller 124. Transferred to P. The toner remaining on the intermediate transfer belt 121 without being transferred to the recording material P is removed by the intermediate transfer belt cleaner 114b. The recording material P onto which the toner image has been transferred is pressed / heated by a fixing device 130 having fixing rollers 131 and 132 to fix the toner image. Further, the primary transfer residual toner remaining on the photosensitive drum 101 after the primary transfer is removed by the cleaner 109 to prepare for the next image formation.

  Next, the system configuration of the image processing unit in the image forming apparatus 100 of the present embodiment will be described with reference to FIG. In FIG. 3, reference numeral 200 denotes an external input interface (external input I / F). Color image data is input as RGB image data from an external device (not shown) such as a document scanner or a computer (information processing device) as needed via the external input interface 200. A LOG conversion unit 201 converts luminance data of RGB image data input based on a lookup table (LUT) including data stored in the ROM 210 into CMY density data (CMY image data). To do. A masking / UCR unit 202 extracts black (Bk) component data from the CMY image data, and performs a matrix operation on the CMKY image data in order to correct the color turbidity of the recording color material. Reference numeral 203 denotes a look-up table unit (LUT unit), and each color of CMYK image data input using a gamma look-up table (γ look-up table) in order to match the image data with the ideal gradation characteristics of the printer unit. Density correction is performed every time. The γ lookup table is created based on the data developed on the RAM 211, and the contents of the table are set by the CPU 206. A pulse width modulation unit 204 outputs a pulse signal having a pulse width corresponding to the level of image data (image signal) input from the LUT unit 203. Based on this pulse signal, the laser driver 205 drives the laser light emitting element 103 and irradiates the photosensitive drum 101 to form an electrostatic latent image.

  The video signal count unit 207 integrates the level (0 to 255 level) for each pixel of the image data (in this embodiment, 600 dpi) input to the LUT unit 203 for one image. This integrated image data value is called a video count value. This video count value becomes the maximum value 1023 when all the output images are at 255 level. When there is a limitation on the circuit configuration, the video count value is obtained by similarly calculating the image signal from the laser driver 205 using the laser signal count unit 208 instead of the video signal count unit 207. Is possible.

[Developer]
Next, the developing device 104 of this embodiment will be described in detail with reference to FIGS. The developing device 104 includes a developing container 20 in which a two-component developer containing toner and a carrier as a developer is accommodated. Further, the developing container 20 includes a developing sleeve 24 as a developer carrying means and a panning member 25 that regulates the ears of the developer carried on the developing sleeve 24.

  The inside of the developing container 20 is divided into a developing chamber 21a and a stirring chamber 21b in the horizontal direction by a partition wall 23 extending in a direction perpendicular to the paper surface of FIG. 4, and the developer is developed in the developing chamber 21a. And it is accommodated in the stirring chamber 21b. In the developing chamber 21a and the agitating chamber 21b, first and second conveying screws 22a and 22b, which are conveying members as developer agitating / conveying means, are arranged, respectively. As shown in FIG. 5, the first conveying screw 22a is disposed substantially parallel to the bottom of the developing chamber 21a along the axial direction of the developing sleeve 24, and rotates to remove the developer in the developing chamber 21a. It is transported in one direction along the axial direction. The second conveying screw 22b is disposed at the bottom of the stirring chamber 21b substantially in parallel with the first conveying screw 22a, and conveys the developer in the stirring chamber 21b in the direction opposite to the first conveying screw 22a. To do.

  As described above, the developer is transported by the rotation of the first and second transport screws 22a and 22b so that the developer passes through the openings (that is, the communication portions) 26 and 27 (see FIG. 5) at both ends of the partition wall 23. And the agitating chamber 21b. In the present embodiment, the developing chamber 21a and the agitating chamber 21b are arranged on the left and right in the horizontal direction. However, in the developing device in which the developing chamber 21a and the agitating chamber 21b are arranged above and below, or in other forms of developing devices, The present invention is applicable.

  There is an opening at a position corresponding to the developing area A facing the photosensitive drum 101 of the developing container 20, and the developing sleeve 24 is rotatably disposed in this opening so as to be partially exposed in the photosensitive drum direction. . In the present embodiment, the diameter of the developing sleeve 24 is 20 mm, the diameter of the photosensitive drum 101 is 30 mm, and the closest region between the developing sleeve 24 and the photosensitive drum 1 is a distance of about 300 μm. With this configuration, the developer transported to the development area A is set so that development can be performed in a state where the developer is in contact with the photosensitive drum 101. The developing sleeve 24 is made of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 24m, which is a magnetic field means, is installed in a non-rotating state inside the developing sleeve 24.

  With the above configuration, the developing sleeve 24 rotates in the direction indicated by the arrow (counterclockwise) during development, and carries a two-component developer whose layer thickness is regulated by the cutting of the magnetic brush by the cutting unit 25. The developing sleeve 24 conveys the developer whose layer thickness is regulated to the developing area A facing the photosensitive drum 101, and supplies the developer to the electrostatic latent image formed on the photosensitive drum 101 to develop the latent image. To do. At this time, in order to improve the developing efficiency, that is, the application rate of toner to the latent image, a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 24 from a power source. In this embodiment, a DC voltage of −500 V, a peak-to-peak voltage Vpp of 1800 V, and an AC voltage having a frequency f of 12 kHz are used. However, the DC voltage value and the AC voltage waveform are not limited to this.

  In general, in the two-component magnetic brush development method, when an AC voltage is applied, the development efficiency increases and the image becomes high-quality, but conversely, fogging easily occurs. For this reason, fogging is prevented by providing a potential difference between the DC voltage applied to the developing sleeve 24 and the charged potential of the photosensitive drum 1 (that is, the white background potential).

  The ear cutting member (regulating blade) 25 is composed of a non-magnetic member formed of plate-like aluminum or the like extending along the longitudinal axis of the developing sleeve 24. Further, the ear cutting member 25 is disposed upstream of the photosensitive drum 101 in the developing sleeve rotation direction. Then, both the toner of the developer and the carrier pass between the tip of the spike cutting member 25 and the developing sleeve 24 and are sent to the developing area A.

By adjusting the gap between the ear cutting member 25 and the surface of the developing sleeve 24, the amount of the developer magnetic brush carried on the developing sleeve 24 is regulated and the amount of developer conveyed to the developing area is reduced. Adjusted. In the present embodiment, the amount of developer coat per unit area on the developing sleeve 24 is regulated to 30 mg / cm ² by the ear cutting member 25. Further, the gap between the ear cutting member 25 and the developing sleeve 24 is set to 200 to 1000 μm, preferably 300 to 700 μm. In this embodiment, it is set to 500 μm.

  In the developing area A, both the developing sleeve 24 of the developing device 104 moves in the forward direction and the moving direction of the photosensitive drum 101, and the peripheral speed ratio is 1.80 times the photosensitive drum. The peripheral speed ratio is set between 0 and 3.0 times, and preferably any number as long as it is set between 0.5 and 2.0 times. The larger the moving speed ratio, the higher the development efficiency. However, if the movement speed ratio is too large, problems such as toner scattering and developer deterioration occur. Therefore, the moving speed ratio is preferably set within the above range.

  Further, a temperature sensor 104T as a developer temperature detecting means is disposed in the opening (that is, the communicating portion) 26 in the developing container 20. As for the location of the temperature sensor 104T in the developing container 20, a position where the sensor surface is buried in the developer is desirable in order to improve detection accuracy.

  Here, the temperature sensor 104T will be described in detail with reference to FIG. In the present embodiment, a temperature / humidity sensor SHT1X series manufactured by SENSIONION is used as the temperature sensor 104T. The configuration includes a capacitive polymer sensing element 1001 as a humidity detection device and a band gap temperature sensor 1002 as a temperature detection device. These are all CMOS devices that are coupled to a 14-bit A / D converter 1003 and have a serial output through a digital interface 1004.

  A band gap temperature sensor, which is a temperature detection device, calculates a temperature from a resistance value by using a thermistor whose resistance value linearly changes with respect to the temperature. A sensing element 1001 that is a humidity detecting device is a capacitor in which a polymer is inserted as a dielectric. Such a sensing element 1001 uses the fact that the capacitance of the capacitor changes linearly with respect to the humidity as a result of the amount of moisture adsorbed on the polymer depending on the humidity, thereby converting the capacitance into humidity. It is detected by doing. The temperature sensor 104T used in the present embodiment can detect both temperature and humidity. However, since only the temperature detection result is actually used, a sensor that can detect only other temperatures is sufficient.

[Developer supply]
Next, a developer replenishing method in this embodiment will be described with reference to FIGS. A toner replenishing device 30 serving as a replenishing unit that replenishes toner to the developing device 104 according to the consumption amount of the developer is disposed above the developing device 104. The toner replenishing device 30 includes a hopper 31 that houses a replenishing two-component developer (usually toner / replenishing developer = 100% to 80%) in which toner and a carrier are mixed. The hopper 31 includes a screw-like supply member, that is, a supply screw 32 at a lower portion, and one end of the supply screw 32 extends to the position of a developer supply port 30 </ b> A provided at the rear end portion of the developing device 104.

  The toner consumed by the image formation is replenished into the developing container 20 from the hopper 31 through the developer replenishing port 30A by the rotational force of the replenishing screw 32 and the gravity of the developer. The amount of replenishment developer replenished from the hopper 31 to the developing device 104 in this way is roughly determined by the number of rotations of the replenishment screw 32. The number of rotations is determined by the CPU 206 (FIG. 3) as a control unit based on a video count value of image data, a detection result of a toner density detection unit (not shown) installed in the developing container 20, and the like.

  Here, the two-component developer composed of the toner and the carrier contained in the developing container 20 will be described in detail. The toner includes colored resin particles containing a binder resin, a colorant, and other additives as necessary, and colored particles to which an external additive such as colloidal silica fine powder is externally added. Yes. The toner is a negatively chargeable polyester resin, and the volume average particle size is preferably 4 μm or more and 10 μm or less. More preferably, it is 8 μm or less. Further, in recent toners, a toner having a low melting point or a toner having a low glass transition point Tg (for example, Tg ≦ 70 ° C.) is often used in order to improve the fixability. Further, in some cases, the toner contains a wax in order to improve the separability after fixing. The developer of this embodiment is a pulverized toner containing a wax.

As the carrier, for example, surface-oxidized or non-oxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals and their alloys, or oxide ferrite can be preferably used. The method for producing the particles is not particularly limited. The carrier has a weight average particle diameter of 20 to 60 μm, preferably 30 to 50 μm, and a resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. In this example, a 10 ⁸ Ωcm one was used.

  For the toner used in this embodiment, the volume average particle diameter was measured by the following apparatus and method. As a measuring device, an SD-2000 sheath flow electric resistance type particle size distribution measuring device (manufactured by Sysmex Corporation) was used. The measuring method is as follows. That is, 0.1 ml of surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of 1% NaCl aqueous electrolytic solution prepared using primary sodium chloride, and 0.5 to 50 mg of a measurement sample is added. Add. The electrolytic aqueous solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic dispersion device. Then, by using the SD-2000 sheath flow electrical resistance type particle size distribution measuring apparatus, the particle size distribution of 2 to 40 μm particles is measured using a 100 μm aperture as the aperture to obtain a volume average distribution. The volume average particle diameter is obtained from the volume average distribution thus obtained.

  In addition, a sandwich type cell having a measurement electrode area of 4 cm and a distance between electrodes of 0.4 cm was used for the resistivity of the carrier used in this embodiment. Measurement was performed by applying an applied voltage E (V / cm) between the two electrodes to one electrode under a pressure of 1 kg and obtaining the carrier resistivity from the current flowing in the circuit.

[Forced consumption mode]
Next, the forced consumption mode of this embodiment will be described with reference to FIGS. First, in the image forming apparatus 100, when image formation with a low image formation ratio (printing rate) (low duty image) continues, the image formation is interrupted or at the time of post-rotation accompanying the end of the image formation job. A forced consumption mode that forcibly consumes toner can be executed. That is, when low-duty images are continuous, the proportion of toner that moves from the developing container 20 to the photosensitive drum 101 decreases. For this reason, the toner in the developing container 20 is subjected to agitation by the first and second conveying screws 22a and 22b and rubbing when passing through the ear cutting member 25 for a long time. As a result, the above-described external additive of the toner is peeled off or embedded in the toner surface, so that the fluidity and charging performance of the toner are lowered and the image quality is deteriorated. Therefore, in general, image formation is interrupted (with a downtime) or, during post-rotation, the deteriorated toner in the developing device 104 is developed in the non-image area of the photosensitive drum 101 and is forcibly discharged (consumed). ) Execute forced consumption mode.

[Toner deterioration threshold setting]
First, setting of a toner deterioration threshold that is a reference value set for a predetermined unit of image formation used for executing the forced consumption mode will be described. The predetermined unit for image formation is a unit set for image formation, such as one A4 size recording material. The predetermined unit is not limited to the size and the number of sheets, and may be, for example, a size such as A3 or B5. It is set as appropriate according to the situation. In the present embodiment, one A4 size recording material is set as a predetermined unit.

  As described above, when the ratio of toner transfer to the photosensitive drum is small and toner replenishment to the developing container 20 is small (when the printing rate is low), toner deterioration proceeds. In this embodiment, “toner deterioration threshold video count Vt” is set as a value (reference value) indicating how low the printing rate causes image quality deterioration due to toner deterioration.

  The toner deterioration threshold video count Vt can be calculated by an experiment as described below. For example, in this embodiment, a continuous image formation is performed on one side of A4 size paper by varying the printing rate of each color (from 0% to 5%), and the change in image quality before and after the continuous image formation is examined. It was. The results of this experiment are shown in the table of FIG. In FIG. 7, “◯” indicates that the image quality has not deteriorated, and “X” indicates that one or more of the image quality deteriorations such as fogging, toner scattering, and graininess reduction has occurred. Show.

  Accordingly, in this embodiment from FIG. 7, image deterioration due to toner deterioration occurs when the printing ratios for each color are lower than Y = 1%, M = 2%, C = 1%, and K = 2%, respectively. In this embodiment, the video count of a full-color image (image with a printing rate of 100%) on one side of A4 size paper for a certain color is 512. In this embodiment, this video count corresponds to a consumption value corresponding to the amount of toner consumed for each predetermined unit of image formation. As described above, the toner deterioration threshold video count in this embodiment is Vt (Y) = 5, Vt (M) = 10, Vt (C) = 5, and Vt (K) = 10. In the calculation of the toner deterioration threshold video count, the decimal part is rounded off. Further, since the toner deterioration threshold varies depending on the material of the developer (toner and carrier) and the like, it may be appropriately calculated and set.

[Determining whether to execute forced consumption mode]
Next, determination of whether or not the forced consumption mode can be executed will be described with reference to FIG. As a premise, the concept of forced consumption mode for each color is the same. Therefore, there are cases where descriptions about colors are omitted in the following flowcharts, etc., but in this case, common control is performed for each color. In this embodiment, as an easy-to-understand example, an image in which the printing rate per sheet is Y = 5%, M = 5%, C = 5%, and K = 1% for each color of YMCK (hereinafter referred to as “black low”). Consider a case in which a continuous image is formed on an A4 size sheet of “Duty Image Chart”).

  First, when image formation starts, the video signal count unit 207 shown in FIG. 3 calculates video counts V (Y), V (M), V (C), and V (K) for each color. That is, the above-mentioned consumption value is calculated (S1). In the present embodiment, the video count of an entire solid image (image with a printing rate of 100%) on one side of A4 size paper for a certain color is 512. Then, the video count of the “black low duty image chart” is V (Y) = 26, V (M) = 26, V (C) = 26, and V (K) = 5. Here, in the calculation of the video count, the decimal part is rounded off.

  Next, the toner deterioration threshold video count Vt is calculated from the toner deterioration threshold video count Vt table shown in FIG. 7 stored in the RAM 211 of FIG. 3 (S2). That is, a reference value set for a predetermined unit is calculated. From FIG. 7, the Y and C toner deterioration threshold video count Vt is 5, and the M and K toner deterioration threshold video count Vt is 10. This toner deterioration threshold video count Vt represents a threshold at which image quality can be maintained. When an image having a printing rate / video count smaller than Vt is output, the toner deterioration proceeds.

  Subsequently, the difference Vt−V between the video count V and the toner deterioration threshold video count Vt described above is calculated (S3). That is, the CPU 206, which is also a difference calculating means, calculates the difference (Vt−V) by subtracting the video count V (consumption value) from the toner deterioration threshold video count Vt (reference value). This difference becomes deterioration information determined based on the consumption value and the reference value. Further, the CPU 206, which is also an integration means, adds (integrates) Vt-V to the toner deterioration integrated value X, which is an integrated value, regardless of whether the value of Vt-V is positive or negative (S4). Here, the toner deterioration integrated value X is an index representing the current toner deterioration state, and is an integrated value of the video count value calculated by Vt−V. Therefore, when the developing device is used from an unused state (when the developer is new (for example, immediately after replacement of the developing device), the toner deterioration integrated value X is 0. Further, the difference (Vt−V) Corresponds to “value relating to the amount of toner consumed for each predetermined unit of image formation” in the claims.

  The above S4 will be described in detail. For example, when the printing rate is low, the value of V becomes small and the value of Vt−V becomes a positive value. By adding the positive value of Vt−V calculated above to the toner deterioration integrated value X, it represents a state in which the toner deterioration is progressing. On the other hand, for example, when the printing rate is high, the value of V becomes large, and the value of Vt−V becomes a negative value. By adding the negative value of Vt−V calculated above to the toner deterioration integrated value X, it represents a state where the toner deterioration is recovered. That is, it represents a state in which the toner is consumed at a high printing rate and newly replenished by the replenishment control, and the deteriorated state of the toner is recovered.

  Next, the CPU 206, which is also a control means, determines whether the latest toner deterioration integrated value X calculated in S4 is positive or negative (S5). If the toner deterioration integrated value X is a negative value, the toner deterioration integrated value X is reset to 0 (S6). That is, in this case, the toner deterioration is reset by toner consumption and supply with a high printing rate. Therefore, the toner deterioration integrated value X is reset to 0, and then image formation is executed (return to S1).

  On the other hand, when the toner deterioration integrated value X is a positive value, the CPU 206 determines a discharge execution threshold A that is a predetermined threshold with respect to the toner deterioration integrated value X calculated and updated for each image formation by the above-described steps. (A−X) is calculated (S7). Here, the discharge execution threshold A is a predetermined threshold that can be arbitrarily set. The smaller the discharge execution threshold A, the more the forced consumption mode (toner discharge operation) is executed for continuous image formation with the same printing rate. Increases frequency. The discharge execution threshold A is set to 512 in the present embodiment. If the discharge execution threshold A is set too large, it takes a long time for the toner deterioration to proceed until the forced consumption mode is executed. Therefore, it is desirable that the entire surface of one side of the A4-A3 size paper (print rate of 100%) be printed. The video count value of the image) is good. Further, for example, the toner discharge execution threshold A tends to be set larger as the volume of the developer that can be held in the developing container 20 is larger.

  Next, the CPU 206, which is also an execution unit, determines whether the difference (A−X) between the toner deterioration integrated value X calculated in S7 and the discharge execution threshold A is positive or negative (S8). If the difference (A−X) is positive or 0, that is, if the toner deterioration integrated value X (integrated value) is equal to or less than the discharge execution threshold A (below a predetermined threshold), the forced consumption mode is not executed. (S9). That is, in this case, the toner deterioration is not progressing so much that the forced consumption mode must be executed immediately. Therefore, the image formation is continuously executed without executing the forced consumption mode. At this time, the toner deterioration integrated value X is continued as it is. That is, the subsequent difference (Vt−V) is added to the toner deterioration integrated value X at that time.

  On the other hand, when the difference (A−X) is negative, that is, when the toner deterioration integrated value X (integrated value) is larger than the discharge execution threshold A (predetermined threshold), the forced consumption mode is executed (S10). . That is, in this case, since the toner deterioration is sufficiently advanced, it is necessary to execute the forced consumption mode immediately. For this reason, image formation is interrupted and the forced consumption mode is executed. After executing the forced consumption mode, image formation is restarted.

[Comparative example]
Here, the operation in the forced consumption mode in the comparative example of the present invention will be described with reference to FIG. If the difference (A−X) is a negative value in S10 of FIG. 8 described above, the image formation is interrupted and the forced consumption mode is executed. First, a primary transfer bias (that is, a transfer bias having the same polarity as that of the toner image on the photosensitive drum 101) having a polarity opposite to that during normal image formation is applied to the primary transfer roller 105 (FIGS. 1 and 2) (S21). Next, a toner amount corresponding to a video count equivalent to the discharge execution threshold A is discharged to the photosensitive drum 101 (S22). In this comparative example, the discharge execution threshold A is set to 512 (corresponding to the video count of an A4 single-sided full-surface printing rate of 100% image), and an operation of discharging an A4 single-sided full-face image to the photosensitive drum is executed. Further, the latent image on the photosensitive drum for discharging the toner is preferably a solid image on the entire surface in the longitudinal direction (rotational axis direction) of the photosensitive drum 101 in order to minimize downtime due to the discharge.

  Next, since the primary transfer bias has the same polarity as the toner, the toner discharged onto the photosensitive drum 101 is not transferred to the intermediate transfer belt and is collected by the cleaner 109 (S23). Here, the toner deterioration integrated value X is reset to 0 (S24). Finally, the primary transfer bias is returned to the polarity bias at the time of normal image formation (S25), the forced consumption mode is terminated, and the normal image formation operation is restored.

  In the forced consumption mode of the comparative example described above, the case where 104 “black low duty image charts” are formed intermittently and then one “black high duty image chart” is newly formed. Think concretely. One-sheet intermittent means that one image is formed in one job, and in one-sheet intermittent, pre-rotation, single-image formation, and post-rotation operations are performed. Further, as described above, the “black low duty image chart” is a chart in which an image having a printing rate of Y = 5%, M = 5%, C = 5%, and K = 1% is formed on one side of A4. The “black high duty image chart” is a chart in which an image having a printing rate of Y = 5%, M = 5%, C = 5%, and K = 100% is formed on one side of A4.

  First, when the “black low-duty image chart” and the “black high-duty image chart” are each formed on the A4 single-sided image, how the toner deterioration integrated value X in the forced consumption mode is added and integrated in each color. This is shown in FIG. As shown in FIG. 10, in the image formation of the “black low duty image chart”, Y (yellow), M (magenta), and C (cyan) are sufficiently high, and the toner deterioration integrated value X is reached. The addition of becomes a negative value. On the other hand, for K (black), since the printing rate is low, the addition to the toner deterioration integrated value X is a positive value +5. Accordingly, when the “black low-duty image chart” is printed, the toner deterioration of K (black) proceeds gradually.

  Further, in the image formation of the “black high duty image chart”, since the printing rate is sufficiently high for Y (yellow), M (magenta), and C (cyan), addition to the toner deterioration integrated value X is negative. Value. On the other hand, for K (black), since the printing rate is very high, the addition to the toner deterioration integrated value X becomes a large negative value -502. Therefore, when the “black high duty image chart” is printed, the K (black) toner deterioration is rapidly recovered.

  Here, as described above, 104 “black low duty image charts” are formed intermittently on one sheet, and then one new “black high duty image chart” is formed (A4 one-sided 105 in total) Transition of sheet image formation) will be described. For Y (yellow), M (magenta), and C (cyan), as shown in FIG. 10, the addition to the toner deterioration integrated value X is always a negative value. Therefore, as shown in S5 and S6 of FIG. 8, the toner deterioration integrated value X is always reset to 0. Therefore, hereinafter, the transition of K (black) will be described with reference to FIG.

  As described above, while the “black low duty image chart” is printed, the toner deterioration integrated value X is integrated by +5. Therefore, as shown in FIG. 11, the toner deterioration integrated value X increases monotonically as 5, 10, 15,... 515 from the first sheet to the 103rd sheet. Further, the difference (A−X) between the toner discharge execution threshold A (= 512) and the toner deterioration integrated value X monotonously decreases to 507, 502, 497. Finally, at the 103rd sheet, (A−X) = − 3 and becomes a negative value.

  At this time, the forced consumption mode is executed according to the flowcharts of FIGS. 8 and 9, and the forced toner consumption corresponding to A = 512 is executed (S22 in FIG. 9). In this comparative example, image formation is performed intermittently on one sheet, and therefore the forced consumption mode is executed during post-rotation in the 103rd image formation job. When image formation is performed continuously rather than intermittently, the image formation is interrupted after the 103rd image formation is completed, and the forced consumption mode is executed. When the forced consumption mode is executed, the toner deterioration integrated value X is reset to 0 (S24 in FIG. 9). Next, when the 104th “black low duty image chart” is printed, the toner deterioration integrated value X = 5 and (A−X) = 507. Finally, when the 105th “black high-duty image chart” is printed, −502 is added to the toner deterioration integrated value X as described in FIG. 10, and the new toner deterioration integrated value X becomes −497. , 0 (S6 in FIG. 8).

  From the above, for K (black), the total toner consumption amount when 105 sheets are passed when the forced consumption mode of the comparative example is operated is estimated. Then, the respective video counts are “black low duty image chart” 104 sheets = 5 × 104 = 520, “black high duty image chart” 1 sheet = 512 × 1 = 512, toner forced consumption once = 512 It becomes. As a result, in the operation of the comparative example, toner corresponding to the video count 1544 is consumed in total.

[Operation in forced consumption mode of this embodiment]
Next, the operation in the forced consumption mode of this embodiment will be described with reference to FIG. In the case of this embodiment as well, whether or not the forced consumption mode can be executed is determined according to the flow of FIG. If the difference (A−X) is a negative value in S10 of FIG. 8 described above, the image formation is interrupted and the forced consumption mode is executed. First, a primary transfer bias (that is, a transfer bias having the same polarity as that of the toner image on the photosensitive drum 101) having a polarity opposite to that during normal image formation is applied to the primary transfer roller 105 (FIGS. 1 and 2) (S31). Next, a toner amount corresponding to a value (video count) obtained by multiplying the discharge execution threshold A by a coefficient less than 1 (0.5, that is, 50% in this embodiment) is discharged to the photosensitive drum 101 (S32). . In other words, a part of the toner amount corresponding to the toner deterioration integrated value X is consumed. In the present embodiment, the discharge execution threshold A is set to 512 (corresponding to the video count of an A4 single-sided full-surface coverage 100% image). For this reason, an operation of discharging a solid image having a length of 50% to the photosensitive drum 101 in the sub-scanning direction (the rotating direction of the photosensitive drum 101) on one side of A4, that is, a toner amount corresponding to A × 0.5 is consumed. Run the forced consumption mode as follows.

  Next, since the primary transfer bias has the same polarity as the toner, the toner discharged onto the photosensitive drum 101 is not transferred to the intermediate transfer belt and is collected by the cleaner 109 (S33). Here, the toner deterioration integrated value X is reset to a value of X− (A × 0.5) (S34). That is, the CPU 206 resets the integrated value (toner deterioration integrated value X) to a predetermined positive value smaller than a predetermined threshold (discharge execution threshold A) in accordance with the execution of the forced consumption mode. Furthermore, when the forced consumption mode is executed, a reset value (X) is obtained by subtracting a value obtained by multiplying the discharge execution threshold A by the coefficient (0.5) from the toner deterioration integrated value X at that time. − (A × 0.5)). Finally, the primary transfer bias is returned to the polarity bias at the time of normal image formation (S35), the forced consumption mode is terminated, and the normal image formation operation is restored. After returning (after execution of the forced consumption mode), the difference (Vt−V) is added to the reset value (X− (A × 0.5)) according to the flow of FIG. 8 (S4 in FIG. 8). .

  As described above, in the forced consumption mode operation of the present embodiment, the toner deterioration integrated value X is not reset to 0 by executing the forced consumption mode once. That is, in the comparative example described above, the toner corresponding to the A4 single-sided solid image is refreshed by executing the forced consumption mode, and the toner deterioration integrated value X is also reset to zero. However, in the present embodiment, the toner corresponding to 50% of the A4 single-sided solid is refreshed by executing the forced consumption mode, and the toner deterioration integrated value X is reset only by about 50%. That is, the forced consumption mode is executed so as to leave a predetermined level of toner deterioration while maintaining the image quality without completely resetting the toner deterioration state.

[Specific example of operation in forced consumption mode of this embodiment]
In the forced consumption mode of the present embodiment as described above, similarly to the comparative example, 104 “black low duty image charts” are formed intermittently and then one “black high duty image chart” is newly formed. The transition when an image is formed will be described. Note that how the toner deterioration integrated value X is added and integrated in each color when the A4 single-sided image is formed on each of the “black low duty image chart” and the “black high duty image chart”. It is the same as the table of FIG. For Y (yellow), M (magenta), and C (cyan), addition to the toner deterioration integrated value X is always a negative value, as shown in FIG. Therefore, as shown in S5 and S6 of FIG. 8, the toner deterioration integrated value X is always reset to 0. Therefore, hereinafter, the transition of K (black) will be described with reference to FIG.

  As described with reference to FIG. 10, while the “black low duty image chart” is printed, the toner deterioration integrated value X is integrated by +5. Therefore, as shown in FIG. 13, the toner deterioration integrated value X increases monotonically as 5, 10, 15... 515 from the first sheet to the 103rd sheet. Further, the difference (A−X) between the toner discharge execution threshold A (= 512) and the toner deterioration integrated value X monotonously decreases to 507, 502, 497. Finally, at the 103rd sheet, (A−X) = − 3 and becomes a negative value.

  At this time, the forced consumption mode is executed according to the flowcharts of FIGS. 8 and 12, and the forced toner consumption corresponding to A × 0.5 = 256 is executed (S32 in FIG. 12). In this embodiment as well, image formation is performed intermittently for one sheet, so the forced consumption mode is executed at the time of post-rotation in the 103rd image formation job. When image formation is performed continuously rather than intermittently, the image formation is interrupted after the 103rd image formation is completed, and the forced consumption mode is executed. When the forced consumption mode is executed, the toner deterioration integrated value X is reset to X− (A × 0.5) = 515−256 = 259 (S34 in FIG. 12). Next, when the 104th “black low-duty image chart” is printed, the toner deterioration integrated value X = 264 and (A−X) = 248. Finally, when the 105th “black high duty image chart” is printed, as described with reference to FIG. 10, −502 is added to the toner deterioration integrated value X, and the new toner deterioration integrated value X becomes −238. , 0 (S6 in FIG. 8).

  From the above, for K (black), the total toner consumption amount when 105 sheets are passed when the forced consumption mode of this embodiment is operated is estimated. Then, the respective video counts are “black low duty image chart” 104 sheets = 5 × 104 = 520, “black high duty image chart” 1 sheet = 512 × 1 = 512, toner forced consumption once = 256 It becomes. As a result, in the operation of the present embodiment, toner corresponding to the video count 1288 is consumed in total.

[Comparison between this embodiment and comparative example]
As described above, in the comparative example, when 104 black low duty image charts are formed intermittently and then one black high duty image chart is formed, a total of 1544 video counts are formed. A considerable amount of toner is consumed. On the other hand, in the case of the present embodiment, toner corresponding to a total of 1288 video counts is consumed as described above. Therefore, in the case of this embodiment, it is possible to suppress the toner consumption amount of about 16.6% compared to the comparative example.

  As for the image quality, in this embodiment, the maximum value of the toner deterioration integrated value X is 515, and the same level as that of the comparative example can be maintained. Furthermore, as the downtime, the number of times of control in the forced consumption mode is one in both the comparative example and this embodiment, but in the control of this embodiment, the length of the toner discharge image in the sub-scanning direction is approximately 50%. One control time can be shortened. Therefore, the effect of reducing the downtime of about 1 second also occurs.

  Note that the toner consumption reduction effect varies depending on the print job configuration (number of sheets, intermittent number of sheets, paper size, image duty, single-sided / double-sided, etc.), and the downtime reduction effect depends on the print job configuration and image forming apparatus. It depends on the process speed. The set number is the number of images formed in one image forming job. Therefore, in the above, a specific example in which the effect of the present invention is easily understood is described. In this embodiment, the control configuration in which toner is forcibly consumed by 50% (coefficient) of the toner discharge execution threshold A has been described. However, the effect of the present invention is not limited to 50%. However, in order to exhibit the effect of the present invention more suitably, it is desirable that the coefficient is set in the range of 0.3 to 0.7, that is, 30 to 70%.

  Here, in FIG. 13 described above, the example in which the “black high duty image chart” is printed on the 105th sheet is described, but a case where images having the same image ratio are continuously formed (printed) will be considered. More specifically, consider a case where images corresponding to an image ratio equal to or less than a predetermined ratio are continuously formed. Here, the predetermined ratio or less is set depending on the model of the image forming apparatus such as a printing rate of 10% or less, 5% or less, 2% or less, 1% or less. In this case, if the average image ratio is the same, for example, when “black low duty image chart” is continuously printed, the forced consumption mode is executed after the 103rd sheet as in FIG. At this time, in this embodiment, the toner deterioration integrated value X is reset to X− (A × 0.5). Therefore, if the “black low duty image chart” is continuously printed subsequently, the forced consumption mode is executed at an earlier timing than when the toner deterioration integrated value X is zero.

  That is, the number of image formations from the time when the forced consumption mode is executed to the next execution of the forced consumption mode, rather than the number of image formations at which the forced consumption mode is executed the first time from the timing when the toner deterioration integrated value X is 0. The forced consumption mode is executed so as to reduce the amount. In other words, the interval until the forced consumption mode is executed is shorter than the first time from the timing when the predetermined condition is satisfied (the timing when the toner deterioration integrated value X is 0). However, the amount of toner consumed in the forced consumption mode is an amount corresponding to A × 0.5, and the amount of toner consumed in one forced consumption mode is the amount corresponding to A as in the comparative example. Is less than when consuming. For this reason, when images having the same image ratio are continuously formed in the present embodiment and the comparative example, the consumed toner amount is substantially the same.

  From the above, in the case of the present embodiment, the conditions for executing the forced consumption mode are different between the first and subsequent times from the timing when the predetermined condition is satisfied. Here, the predetermined condition is that the toner deterioration integrated value X is set to a predetermined reset condition when the developing device is used from an unused state or when an image with a high image ratio is formed as in S6 of FIG. This is a case where the toner deterioration integrated value X is reset when the above is satisfied. In the present embodiment, the predetermined reset condition is that the toner deterioration integrated value X becomes a negative value in S5 of FIG. 8, and in this case, the toner deterioration integrated value X is reset to 0 in S6. Further, when the use of the developing device is started from an unused state, the toner deterioration integrated value X is 0 as described above. For this reason, in this embodiment, the timing at which the predetermined condition is satisfied is the timing at which the toner deterioration integrated value X is zero.

  In the case of this embodiment, when the toner deterioration integrated value X is larger than the discharge execution threshold A (predetermined threshold), the forced consumption mode is executed, and the toner deterioration integrated value X is set from the unused state. It is different from the value when starting to use. That is, the toner deterioration integrated value X when the developing device is used from an unused state is 0, whereas the toner deterioration integrated value X when the forced consumption mode is executed is X− (A × 0. 5).

  Thus, in the case of the present embodiment, in the forced consumption mode, the toner amount corresponding to the value (A × 0.5) obtained by multiplying the discharge execution threshold A by a coefficient (0.5) less than 1 is consumed. I have to. In other words, when the forced consumption mode is executed, the toner discharge is executed by an amount corresponding to a part of the toner deterioration index (discharge execution threshold A). For this reason, the toner consumption in the forced consumption mode can be suppressed. Further, even if the toner consumption amount in the forced consumption mode is small as described above, if an image with a high image ratio is formed thereafter, the toner deterioration is eliminated as described above with reference to FIG. That is, in the present embodiment, the amount of toner consumed in the forced consumption mode is suppressed in consideration of the case where an image with a high image ratio is formed after the forced consumption mode is executed. Therefore, if an image with a high image ratio is formed thereafter and toner deterioration is eliminated, it is possible to suppress image defects due to toner deterioration even if the amount of toner consumed in the forced consumption mode is small. At the same time, since the amount of toner consumed in the forced consumption mode is small, the overall toner consumption can be suppressed.

  Further, the reset value of the toner deterioration integrated value X is a value obtained by subtracting a value (X− (A × 0.5)) obtained by multiplying the discharge execution threshold A by a coefficient (0.5) from the toner deterioration integrated value X. Yes. In other words, only a part of the toner deterioration index is recovered in accordance with the toner discharging operation. For this reason, even if an image with a high image ratio is not formed thereafter, the forced consumption mode is executed at an appropriate timing so that the toner deterioration does not affect the image. For example, the forced consumption mode is executed at an earlier stage than when the reset value of the toner deterioration integrated value X is set to zero. Even in the forced consumption mode at this time, the toner consumption amount is similarly suppressed. Therefore, the toner consumption amount can be made equal to that when the reset value of the toner deterioration integrated value X is set to zero. As a result, in the case of the present embodiment, it is possible to suppress the toner consumption while appropriately eliminating the toner deterioration.

<Second Embodiment>
Next, a second embodiment of the present invention will be described with reference to FIGS. In the first embodiment described above, the control for discharging the toner amount corresponding to 50% of A in the forced consumption mode is described by setting the coefficient to be multiplied to the toner discharge execution threshold A to 0.5 (50%). . In contrast, in the present embodiment, the coefficient Z is changed according to the average image ratio (average printing rate). Since other configurations and operations are the same as those in the first embodiment described above, overlapping descriptions and illustrations are omitted or simplified, and the following description will focus on parts that are different from the first embodiment.

  First, the important point of the present invention is that the toner amount in the forced consumption mode is suppressed, and the high duty image chart (image having a high image ratio) that may come in the future is effectively used to suppress the toner deterioration. That is. Therefore, for example, if there is a high possibility of a high duty image, the total toner consumption is more likely to be suppressed by forcibly consuming a smaller amount of toner with respect to the toner discharge execution threshold A. For this reason, in this embodiment, the operation flow in the forced consumption mode is changed according to the average video count (a value corresponding to the average image ratio) of a predetermined number of image formation sheets (the past 1000 sheets in this embodiment). ing.

  The operation flow in the forced consumption mode of this embodiment will be described with reference to FIG. In the case of this embodiment as well, in the same way as in the first embodiment, if the difference (A−X) is a negative value in step S10 shown in FIG. 8, image formation is interrupted and the flowchart of FIG. To execute the forced consumption mode. First, a primary transfer bias (that is, a transfer bias having the same polarity as the toner image on the photosensitive drum 101) having a polarity opposite to that during normal image formation is applied to the primary transfer roller 105 (FIGS. 1 and 2) (S41).

  Next, as a new flow step, a forced consumption coefficient Z, which is a coefficient less than 1, is determined according to the average video count of the past 1000 sheets (S42). The compulsory consumption coefficient Z is a value determined according to the average video count of the past 1000 sheets calculated from the table of FIG. 15 and stored in the RAM 211 (FIG. 3) which is a video count storage unit. That is, the CPU 206 (FIG. 3), which is also an image ratio calculation means, reads the video count of a predetermined number of image formation sheets (1000 sheets) stored in the RAM 211. Then, an average video count corresponding to an average image ratio which is an image ratio per predetermined unit (per A4 sheet) to a predetermined number of image formation sheets (1000 sheets) is calculated. Then, the CPU 206 refers to the table of FIG. 15 stored in the RAM 211 and determines the forced consumption coefficient Z corresponding to the calculated average video count. For example, when the average print rate (average image ratio) of the past 1000 sheets is 20%, the average video count is 102, and the forced consumption coefficient Z = 30%.

  Next, a toner amount corresponding to a video count of A × Z is discharged to the photosensitive drum 101 with respect to the discharge execution threshold A (S43). In the present embodiment, the discharge execution threshold A is set to 512 (corresponding to the video count of an A4 single-sided full-surface coverage 100% image). For this reason, for example, when the average video count of the past 1000 pictures is 102, Z = 0.3 (30%). Therefore, the forced consumption mode is executed so that a solid image having a length of 30% in the sub-scanning direction on one side of A4 is discharged to the photosensitive drum 101, that is, a toner amount corresponding to A × 0.3 is consumed.

  When the average printing rate is high in this way, there is a high possibility that an image with a high printing rate will come in the future. For this reason, even if the toner deterioration reaches a threshold value in a low duty image, the amount of toner refresh in the forced consumption mode can be suppressed, and an image with a high print rate coming in the future can be expected and refreshed naturally. . For this reason, in the present embodiment, the CPU 206 increases the forced consumption coefficient Z when the average image ratio is the first ratio and when the second ratio is smaller than the first ratio. . That is, when the average video count corresponding to the average image ratio is large (the first ratio), there is a high possibility that an image with a high printing rate will come in the future. Therefore, the forced consumption coefficient Z is reduced. As a result, the amount of toner consumed in the forced consumption mode can be reduced. On the other hand, if the average video count is smaller (than the first ratio) (second ratio), it is unlikely that an image with a high printing rate will come in the future, so toner deterioration is eliminated by this high printing rate image. It is also unlikely to be done. For this reason, the forced consumption coefficient Z is increased so as to eliminate toner deterioration as much as possible in the forced consumption mode.

  Next, since the primary transfer bias has the same polarity as the toner, the toner discharged onto the photosensitive drum 101 is not transferred to the intermediate transfer belt, but is collected by the cleaner 109 (S44). Here, the toner deterioration integrated value X is reset to a value of X− (A × Z) (S45). That is, when the forced consumption mode is executed, the CPU 206 subtracts a value obtained by subtracting a value obtained by multiplying the discharge execution threshold value A from the above-described coefficient Z from the toner deterioration integrated value X at that time by the reset value (X− (A × Z)). Finally, the primary transfer bias is returned to the polarity bias at the time of normal image formation (S46), the forced consumption mode is terminated, and the normal image formation operation is restored. After returning (after executing the forced consumption mode), the difference (Vt−V) is added to the reset value (X− (A × Z)) according to the flow of FIG. 8 (S4 in FIG. 8).

  As described above, in the present embodiment, when the probability of a high printing rate is high from the average video count value of the past 1000 sheets as compared with the control of the first embodiment, the toner consumption amount in the forced consumption mode By reducing this, the total toner consumption is reduced.

  A specific effect of this embodiment will be considered with reference to FIG. 13 of the first embodiment, for example. Here, a case is considered where the average video count of the past 1000 images is 102 at the time of the 103rd image in FIG. For example, this corresponds to the case where the image before the first sheet in FIG. 13 has a high printing rate. Further, the process is the same as that of the first embodiment until the negative value (A−X) = − 3 at the 103rd sheet.

  At this time, the forced consumption mode is executed according to the flowcharts of FIGS. 8 and 14, and the forced toner consumption corresponding to A × 0.3 = 154 is executed according to the calculation table of the forced consumption coefficient Z of FIG. S43 in FIG. Then, the toner deterioration integrated value X is reset to X− (A × 0.3) = 515−154 = 361 (S45 in FIG. 14). Next, when the 104th “black low-duty image chart” is printed, the toner deterioration integrated value X = 366 and (A−X) = 146. Finally, when the 105th “black high duty image chart” is printed, −502 is added to the toner deterioration integrated value X as described in FIG. 10, and the new toner deterioration integrated value X becomes −136. , 0 (S6 in FIG. 8).

  From the above, for K (black), the total toner consumption amount when 105 sheets are passed when the forced consumption mode of this embodiment is operated is estimated. Then, for each video count, “black low duty image chart” 104 sheets = 5 × 104 = 520, “black high duty image chart” 1 sheet = 512 × 1 = 512, toner forced consumption once = 154 It becomes. As a result, in the operation of this embodiment, toner corresponding to the video count 1186 is consumed in total.

  Here, in the first embodiment, the toner consumption corresponds to a total of 1288 video counts, and in this embodiment, the toner consumption corresponds to a total of 1186 video counts. For this reason, the present embodiment can further suppress the toner consumption amount of about 7.9% compared to the first embodiment.

  As for the image quality, in this embodiment, the maximum value of the toner deterioration integrated value X is also 515, and the same level as that of the comparative example and the first embodiment can be maintained. Further, as the downtime, the number of times of control in the forced consumption mode is one in the comparative example, the first embodiment, and the present embodiment. However, in this embodiment, since the length of the toner discharge image in the sub-scanning direction is approximately 30%, the control time for one time can be further shortened, and the downtime can be reduced by approximately 1.4 seconds compared with the comparative example. Also occurs.

<Third Embodiment>
A third embodiment of the present invention will be described with reference to FIG. In the first and second embodiments described above, as shown in FIG. 8, the toner deterioration threshold video count Vt as a reference value is fixed, Vt−V is calculated, and this is integrated, The execution of forced consumption mode was determined. On the other hand, in this embodiment, the driving time of the developing device for each sheet of image formation is calculated, and the reference value is changed according to this driving time. That is, in this embodiment, the reference value is a value obtained by multiplying the toner deterioration threshold video count Vt as a fixed value by the variable St corresponding to the driving time. Since other configurations and operations are the same as those in the first embodiment or the second embodiment described above, overlapping explanations and illustrations are omitted or simplified, and hereinafter, different parts from the first embodiment will be mainly described. Explained.

  First, when the present inventors examine the mechanism of toner deterioration in more detail, it depends on the driving time of the developing device (the driving time of the developing sleeve 24 and the driving time of the first and second conveying screws 22a and 22b). Turned out to be. Therefore, in this embodiment, the forced consumption mode is executed according to the driving time of the developing sleeve 24 and the video count.

  Here, the value of the toner deterioration threshold video count Vt shown in FIG. 7 described above is obtained by experimentally examining a threshold value at which an image defect occurs in the continuous image formation of 1000 sheets, and the total development at this time The sleeve driving time was about 2000 seconds. Therefore, for example, with respect to Y (yellow), the occurrence of image defects can be suppressed if the toner is deteriorated due to the developing sleeve driving time of 2 seconds and the replacement by toner replenishment with a printing rate of 1% = video count 5 occurs. It means that. In the case of continuous image formation, since there is no control of the pre-rotation and post-rotation in the formation of one image other than the first and last of the job, the image forming apparatus according to this embodiment develops one image. The sleeve driving time (reference time Su) is 2 seconds. However, the reference time Su, which is the developing sleeve driving time per continuous image formation, is a value determined according to the performance of the image forming apparatus, and differs depending on the model.

  The determination as to whether or not the forced consumption mode according to this embodiment can be executed under such preconditions will be described. As in FIG. 3, the concept of the forced consumption mode for each color is the same as a premise. Therefore, there are cases where descriptions about colors are omitted in the following flowcharts, etc., but in this case, common control is performed for each color. As an easy-to-understand example in this embodiment, an image (black low duty image chart) in which the printing rate per sheet is Y = 5%, M = 5%, C = 5%, and K = 1% for each color of YMCK. ) Is considered to be intermittently formed on one A4 size sheet.

  First, when image formation starts, the video signal count unit 207 calculates video counts V (Y), V (M), V (C), and V (K) for each color as described above with reference to FIG. Further, the developing sleeve driving time St (second) is calculated by the CPU 206 (FIG. 3) which is also the driving time calculating means (S51). In the present embodiment, the video count of an entire solid image (image with a printing rate of 100%) on one side of A4 size paper for a certain color is 512. Then, the video count of the “black low duty image chart” is V (Y) = 26, V (M) = 26, V (C) = 26, and V (K) = 5. Here, in the calculation of the video count, the decimal part is rounded off.

  The developing sleeve drive time St is 2 seconds as described above in the case of one sheet other than the first and last in the case of continuous image formation. In the case of one of these, post-rotation time is added to this. In addition, when control other than the forced consumption mode is entered midway and image formation is interrupted, when the developing sleeve is driven, the time may be added to image formation at that time. In this embodiment, since image formation is performed intermittently for one sheet, the developing sleeve driving time is about 2.5 seconds (St = 2.5 seconds) per sheet. This St corresponds to the unit driving time of the developing device (developing sleeve 24).

  Next, the toner deterioration threshold video count Vt is calculated from the toner deterioration threshold video count Vt table (see FIG. 7) obtained in the above-described experiment or the like (S52). From FIG. 7, the Y and C toner deterioration threshold video count Vt is 5, and the M and K toner deterioration threshold video count Vt is 10. The toner deterioration threshold video count Vt is appropriately set according to the reference time Su. That is, as described above, the reference time Su is determined depending on the model. If the reference time is long, the deterioration degree of the toner per image forming sheet also changes. For this reason, it is preferable to set Vt according to Su. In the present embodiment, Vt is set as described above because the model is for Su of 2 seconds.

  Subsequently, Vt · St−V · Su is calculated from the video count V and the toner deterioration threshold video count Vt, the developing sleeve drive time St and the reference time Su (S53). In the present embodiment, since St is 2.5 seconds and Su is 2 seconds, Vt · 2.5−V · 2. That is, the CPU 206 subtracts V · 2 (consumption value) from Vt · St (reference value) to calculate a difference (Vt · St−V · Su). Further, Vt, St-V, and Su are added to the toner deterioration integrated value X regardless of whether the values of Vt, St-V, and Su are positive or negative (S54).

  The above S54 will be described in detail. For example, when the printing rate is low, the value of V becomes small and the value of Vt · St−V · Su becomes a positive value. Also, for example, when the developing sleeve drive time St becomes longer due to operations such as pre-rotation and post-rotation in continuous image formation, the value of Vt · St−V · Su can be a positive value. By adding the positive value of Vt · St−V · Su calculated above to the toner deterioration integrated value X, a state where the toner deterioration is progressing is represented. On the other hand, for example, when the printing rate is high, the value of V becomes large, and the values of Vt, St-V, and Su become negative values. By adding the negative value of Vt · St−V · Su calculated above to the toner deterioration integrated value X, the toner deterioration is recovered. Here, Vt / Su-V / St is obtained by dividing (Vt.St-V.Su) by (Su.Su). At this time, Vt / Su is a fixed value, and V / St is information on the amount of toner consumed per unit driving time of the developing device. If this information V / St is less than a predetermined value, that is, less than Vt / Su, Vt / Su−V / St becomes a positive value, indicating that deterioration is in progress. The deterioration information determined based on the information V / St and the predetermined value Vt / Su corresponds to Vt · St−V · Su.

  Next, the CPU 206 determines whether the latest toner deterioration integrated value X calculated in S54 is positive or negative (S55). If the toner deterioration integrated value X is a negative value, the toner deterioration integrated value X is reset to 0 (S56). That is, in this case, the toner deterioration is reset by toner consumption and supply with a high printing rate. Therefore, the toner deterioration integrated value X is reset to 0, and then image formation is executed (return to S1).

  On the other hand, when the toner deterioration integrated value X is a positive value, the CPU 206 calculates a difference (A) from the discharge execution threshold A with respect to the toner deterioration integrated value X calculated / updated for each image formation by the above-described steps. -X) is calculated (S57). S58 to S60 are the same as S8 to 10 in FIG. As the operation flow in the forced consumption mode in S60, the forced consumption mode is executed as in the first embodiment (FIG. 12) or the second embodiment (FIG. 14). Accordingly, it is possible to provide an image forming apparatus that prevents toner deterioration and maintains good image quality while minimizing toner consumption in the forced consumption mode.

  In the present embodiment, the toner deterioration integrated value X is determined in consideration of the developing sleeve driving time St. That is, the reference value for obtaining the toner deterioration integrated value X is Vt · St, so that the developing sleeve driving time St is reflected in the toner deterioration integrated value X. In order to reflect St in the reference value, the video count V is multiplied by the reference time Su. As a result, the toner deterioration integrated value X that matches the toner deterioration can be calculated, and toner deterioration can be prevented more appropriately.

  In this embodiment, consider a case where images corresponding to a toner consumption amount consumed per unit driving time of the developing device are continuously formed (printed) corresponding to a predetermined value or less. More specifically, consider the case where the information V / St is less than Vt / Su. In this case, if the average image ratio is the same condition (the information is the same condition), for example, when the “black low duty image chart” is continuously printed, forcibly consumed after the 103rd sheet as in FIG. Run the mode. At this time, in this embodiment, the toner deterioration integrated value X is reset to X− (A × 0.5 or Z). Therefore, if the “black low duty image chart” is continuously printed subsequently, the forced consumption mode is executed at an earlier timing than when the toner deterioration integrated value X is zero.

  That is, the number of image formations from the time when the forced consumption mode is executed to the next execution of the forced consumption mode, rather than the number of image formations at which the forced consumption mode is executed the first time from the timing when the toner deterioration integrated value X is 0. The forced consumption mode is executed so as to reduce the amount. In other words, the interval until the forced consumption mode is executed is shorter than the first time from the timing when the predetermined condition is satisfied (the timing when the toner deterioration integrated value X is 0). However, the amount of toner consumed in the forced consumption mode is an amount corresponding to A × 0.5 or Z, and the amount of toner consumed in one forced consumption mode is A as in the comparative example described above. Compared to the case where the amount corresponding to is consumed. For this reason, when images having the same image ratio are continuously formed in the present embodiment and the comparative example, the consumed toner amount is substantially the same.

  In the description of each embodiment described above, the video count is used as the consumption value corresponding to the amount of toner consumed for each predetermined unit of image formation and the reference value set for the predetermined unit. The present invention is not limited to this. That is, it is only necessary to know the amount of toner consumed with image formation.

  101 (101Y, 101M, 101C, 101K) ... photosensitive drum (image carrier) / 104 (104Y, 104M, 104C, 104K) ... developing device / 24 ... developing sleeve / 30 ... toner replenishment Device (replenishment means) / 206... CPU (control means, difference calculation means, integration means, execution means, image ratio calculation means, drive time calculation means)

Claims (16)

An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device,
The control means includes
Difference calculating means for calculating a difference between a consumption value corresponding to the amount of toner consumed for each predetermined unit of image formation and a reference value set for the predetermined unit;
Integrating means for integrating the difference to obtain an integrated value;
Execution means for executing the forced consumption mode when the integrated value is greater than a predetermined threshold;
The execution means executes the forced consumption mode so as to consume a toner amount corresponding to a value obtained by multiplying the predetermined threshold by a coefficient less than 1.
When the forced consumption mode is executed, the integration means sets a value obtained by subtracting a value obtained by multiplying the predetermined threshold by the coefficient from the integrated value at that time, and executes the forced consumption mode. After that, the difference is added to the reset value.
An image forming apparatus. The integrating means integrates the difference from 0 when the developing device is used from an unused state;
The image forming apparatus according to claim 1, wherein: The difference calculating means calculates the difference by subtracting the consumption value from the reference value,
The control means resets the integrated value of the integrating means to 0 if the value obtained by integrating the difference by the integrating means is a negative value.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When the integrated value is less than or equal to the predetermined threshold, the control means does not cause the execution means to execute the forced consumption mode, and causes the integrating means to add the subsequent difference to the integrated value at that time. Let
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Image ratio calculating means for calculating an average image ratio that is an image ratio per predetermined unit with respect to a predetermined number of image formations;
The execution means increases the coefficient in the case of the second ratio smaller than the first ratio than in the case where the average image ratio is the first ratio.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Drive time calculating means for calculating the drive time of the developing device for each sheet of image formation;
The control means changes the reference value according to the driving time.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When the control unit continuously forms images having the same image ratio, the compulsory consumption mode is executed more than the number of image formations in which the compulsory consumption mode is executed for the first time from the timing when the integration value of the integration unit is 0. Executing the forced consumption mode so that the number of images formed after the consumption mode is executed and then the forced consumption mode is executed is reduced;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device,
In the case where images corresponding to an image ratio equal to or less than a predetermined ratio are continuously formed and the average image ratio is the same condition, the control means sets the interval until the forced consumption mode is executed as a predetermined condition. The operation of the forced consumption mode is controlled so that the time after that is shorter than the first time from the timing of satisfying
An image forming apparatus. An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device,
The control means may be configured such that when the information on the toner consumption consumed per unit driving time of the developing device continuously forms images corresponding to less than a predetermined value, the information is the same condition. In this case, the interval until the forced consumption mode is executed controls the operation of the forced consumption mode so that the interval after the timing when the predetermined condition is satisfied is shorter than the first time.
An image forming apparatus. The predetermined condition is a case where use of the developing device is started from an unused state.
The image forming apparatus according to claim 8, wherein the image forming apparatus is an image forming apparatus. The control unit includes an integration unit that integrates a value related to the amount of toner consumed for each predetermined unit of image formation, and the value integrated by the integration unit is predetermined when an image having a high image ratio is formed. When the reset condition is satisfied, the accumulated value is reset,
The predetermined condition is a case where the integrated value is reset.
The image forming apparatus according to claim 8, wherein the image forming apparatus is an image forming apparatus. The control means executes the forced consumption mode when the value accumulated by the accumulation means is larger than a predetermined threshold;
The image forming apparatus according to claim 11, wherein: The control means executes the forced consumption mode when the images having the same image ratio are continuously formed, more than the number of image formations in which the forced consumption mode is executed for the first time from the timing when the predetermined condition is satisfied. The forced consumption mode is executed so that the number of images formed until the forced consumption mode is executed next is reduced.
The image forming apparatus according to claim 8, wherein the image forming apparatus is an image forming apparatus. An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device,
The control unit includes an integration unit that integrates a value related to the amount of toner consumed for each predetermined unit of image formation, and the forced consumption when the value integrated by the integration unit is greater than a predetermined threshold value. Executing the mode, and resetting the accumulated value to a predetermined positive value smaller than the predetermined threshold according to the execution of the forced consumption mode,
An image forming apparatus. An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
An integrated value of deterioration information determined based on a consumption value corresponding to the amount of toner consumed for each predetermined unit of image formation and a reference value set for the predetermined unit is greater than a predetermined threshold value. Control means capable of executing a forced consumption mode for forcibly consuming toner in the developing device when
The control means consumes a part of the toner amount corresponding to the integrated value in the forced consumption mode.
An image forming apparatus. An image carrier;
A developing device for developing the electrostatic latent image formed on the image carrier with toner;
Replenishing means for replenishing toner to the developing device according to the amount of developer consumed;
When the integrated value of deterioration information determined based on information related to toner consumption consumed per unit driving time of the developing device and a predetermined value is larger than a predetermined threshold, the developing device is compulsory. Control means capable of executing a forced consumption mode for consuming toner.
The control means consumes a part of the toner amount corresponding to the integrated value in the forced consumption mode.
An image forming apparatus.

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