JP2006091094A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which are devised to improve an image quality with high precision, and an image forming method. <P>SOLUTION: The image forming apparatus includes; a toner density detection part which detects a toner concentration in a developer storage part; a toner supply part which supplies toner into the developer storage part in the case the toner concentration detected by the toner concentration detection part is lower than a prescribed reference toner concentration; an average image density calculation part which calculates an average image density in a plurality of times of past image formation including this time image formation; a toner supply quantity integration part which integrates the quantity of tone supply to the developer storage part; and a toner discharging means which discharges toner in the developer storage part by sending out the toner from the developer storage part onto a photoreceptor at timing other than image formation timing when the average image density calculated by the average image density calculation part is lower than a prescribed reference image density and the quantity of toner supply integrated by the toner supply quantity integration part is lower than a prescribed reference quantity of toner supply. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention forms an image by forming a latent image on the surface of a photoreceptor, developing the latent image with toner to obtain a toner image, and finally transferring and fixing the toner image on a recording medium. The present invention relates to a method and an image forming apparatus.

  In recent years, image forming apparatuses such as printers, which are increasingly required to form images with high glossiness, achieve this by selecting a material that is highly adhesive and meltable as the main component of the toner. There is something.

  However, when such a highly viscous toner is used, it is difficult to peel off the toner image from the fixing member in the fixing step. Therefore, the releasability is improved by increasing the amount of the wax component in the toner.

  However, when the wax component easily precipitates on the toner surface due to an increase in the amount of the wax component, the image forming apparatus uses a so-called two-component developer by mixing the toner and the carrier. At the time of mixing, the external additive coated on the toner tends to be buried in the precipitation site of the wax component.

  As a result, in such an image forming apparatus, the longer the stirring time for mixing the toner and the carrier in the developer accommodating portion that accommodates the developer, the more the external additive is embedded in the wax precipitation surface. Progresses and the charging performance of the toner decreases.

  Thus, when toner is newly supplied into the developer accommodating portion in which the toner with reduced charging performance is accommodated, the charge distribution of the toner in the entire developer accommodating portion is doubled due to the difference in charging performance, In the image formation in such a state, the image quality may be deteriorated due to fogging on a non-image forming portion.

Therefore, by predicting the charging characteristics of the toner from the stirring time, etc., the potential difference between the developing bias potential of the developer carrying member such as a developing roll and the potential of the electrostatic latent image formed on the photosensitive member can be adjusted. A proposal has been made to improve image quality by adjusting the amount of toner supplied into the agent container (see Patent Document 1).
JP-A-7-295312

  However, the above proposal has a problem that accuracy is low.

  An object of the present invention is to provide an image forming apparatus and an image forming method that are devised to improve image quality with high accuracy.

In order to achieve the above object, an image forming apparatus of the present invention comprises:
In an image forming apparatus that forms a latent image on the surface of a photosensitive member, develops the latent image with toner, obtains a toner image, and finally forms an image by transferring and fixing the toner image on a recording medium.
A developer container that contains and stirs a developer composed of toner and carrier, and develops the latent image with toner of the developer;
A toner concentration detection unit for detecting the toner concentration in the developer containing unit;
A toner supply unit that supplies toner into the developer accommodating unit when the toner concentration detected by the toner concentration detection unit falls below a predetermined reference toner concentration;
An average image density calculation unit for calculating an average image density in a plurality of image formations including the current image formation and going back to the past;
A toner supply amount integration unit that integrates the toner supply amount to the developer storage unit in a plurality of image formations including the current image formation and going back to the past;
When the average image density calculated by the average image density calculation unit is lower than a predetermined reference image density and the toner supply amount integrated by the toner supply amount integration unit is lower than a predetermined reference toner supply amount, the developer And a toner discharge unit for discharging the toner in the storage unit by sending the toner from the developer storage unit onto the photosensitive member at a timing different from the image formation.

  In the image forming apparatus of the present invention, the average image density in a plurality of image formations including the current image formation is less than a predetermined reference image density, and the toner supply amount integrated by the toner supply amount integration unit is predetermined. When the toner supply amount falls below the reference toner supply amount, it is assumed that the charging performance of the toner stored in the developer container is deteriorated, and the toner is sent from the developer container to the photosensitive member at a timing different from that for image formation. As a result, it is discharged from the developer accommodating portion. As a result, in the image forming apparatus of the present invention, it is possible to suppress the coexistence of toners having extremely different charging performances in the developer accommodating portion as compared with the conventional case. Therefore, according to the image forming apparatus of the present invention, the image quality can be improved with high accuracy.

Here, the image forming apparatus of the present invention includes an agitation time measuring unit that measures the accumulated agitation time for the developer in the developer accommodating unit during a plurality of image formations including the current image formation and going back to the past. ,
And a reference changing means for raising the reference toner supply amount and the reference image density when the cumulative stirring time measured by the stirring time measuring unit exceeds a predetermined reference cumulative stirring time. Also good.

Further, the image forming apparatus according to the present invention calculates an average toner density that is an average of the toner densities detected by the toner density detecting unit during a plurality of image formations including the current image formation and going back to the past. A concentration calculator;
When the average toner density calculated by the average toner density calculating unit is lower than a predetermined reference toner density, a reference changing unit that increases the reference toner supply amount and the reference image density may be provided. .

  In this way, it is possible to further suppress the coexistence of toners having extremely different charging performances in the developer accommodating portion.

In order to achieve the above object, the image forming method of the present invention comprises:
A developer container configured to store and agitate a developer composed of toner and a carrier; a toner concentration detector configured to detect a toner concentration in the developer container; and a toner concentration detected by the toner concentration detector. An image forming apparatus having a toner supply unit that supplies toner into the developer accommodating portion when the toner concentration falls below a predetermined reference toner concentration, and is formed on the surface of the photoreceptor with the toner accommodated in the developer accommodating portion. The latent image is developed to obtain a toner image, and the toner image is finally transferred and fixed on a recording medium to form an image.
An average image density calculation process for calculating an average image density in a plurality of image formation dates back to the past including the current image formation,
A toner supply amount integration process for integrating the toner supply amount to the developer accommodating portion in a plurality of image formations including the current image formation and going back to the past;
If the image density calculated in the average image density calculation process is lower than a predetermined reference image density and the toner supply amount integrated in the toner supply amount integration process is lower than a predetermined reference toner supply amount, the developer storage is performed. And a toner discharge process for discharging the toner in the section by sending the toner from the developer storage section onto the photosensitive member at a timing different from that for image formation.

Here, the image forming method of the present invention includes an agitation time measurement process for measuring the accumulated agitation time for the developer in the developer accommodating portion during a plurality of image formations including the current image formation and going back to the past. ,
And a reference changing process for raising the reference toner supply amount and the reference image density when the cumulative stirring time measured in the stirring time measurement process exceeds a predetermined reference cumulative stirring time. Good.

In addition, the image forming method of the present invention calculates an average toner density that is an average of the toner densities detected by the toner density detecting unit during a plurality of image formations including the current image formation and going back to the past. Concentration calculation process;
When the average toner density calculated in the average toner density calculation process is lower than a predetermined reference toner density, a reference changing process for raising the reference toner supply amount and the reference image density may be included.

  According to the image formation using the image forming method of the present invention and the image forming apparatus of the present invention, the image quality can be improved with high accuracy.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram showing an embodiment of the image forming apparatus of the present invention suitable for carrying out an embodiment of the image forming method of the present invention.

  The printer 1 of this embodiment shown in FIG. 1 includes four image forming units 10Y, 10M, 10C, and 10K, and an image formation control unit 10 that controls image formation in the printer 1. The image forming units include photoreceptor rolls 11Y, 11M, 11C, and 11K, charging devices 12Y, 12M, 12C, and 12K, exposure devices 13Y, 13M, 13C, and 13K, developing devices 14Y, 14M, 14C, and 14K, and Primary transfer rolls 15Y, 15M, 15C, and 15K are provided. The printer 1 is capable of full-color printing, and the symbols Y, M, C, and K added to the end of each of the above components are yellow, magenta, cyan, and black images, respectively. It is a component for formation.

  The printer 1 also includes an intermediate transfer belt 30, a secondary transfer roll 32, a fixing device 33, and a tension roll 34 on which the intermediate transfer belt 30 is suspended.

  A basic image forming operation in the printer 1 will be described.

  First, toner image formation by the yellow image forming unit 10Y is started, and a predetermined charge is applied to the surface of the photoreceptor roll 11Y rotating in the direction of arrow A by the contact-type charging device 12Y. Next, the exposure device 13Y irradiates the surface of the photoreceptor roll 11Y with exposure light corresponding to a yellow image to form a latent image. The latent image is developed with yellow toner by the developing device 14Y to form a yellow toner image on the photoreceptor roll 11Y. The toner image is transferred to the intermediate transfer belt 30 by the primary transfer roll 15Y.

  The intermediate transfer belt 30 circulates in the direction of arrow B, and the yellow toner image transferred onto the intermediate transfer belt 30 reaches the primary transfer roll 15M of the next color image forming unit 10M in accordance with the timing. The magenta image forming unit 10M forms a toner image so that the next color magenta toner image reaches the primary transfer roll 15M. The magenta toner image formed in this way is transferred onto the yellow toner image on the intermediate transfer belt 30 while being superimposed on the primary transfer roll 15M.

  Subsequently, toner image formation by the cyan and black image forming units 10C and 10K is performed at the same timing as described above, and is sequentially superimposed on the yellow and magenta toner images of the intermediate transfer belt 30 in the primary transfer rolls 15C and 15K. Is transcribed.

  In this way, the multicolor toner image transferred onto the intermediate transfer belt 30 is secondarily transferred onto the paper 200 by the secondary transfer roll 32, and the multicolor toner image is conveyed along with the paper 200 in the direction of arrow C, and the fixing device. The image is fixed on the sheet 200 by being heated and pressed by the sheet 33.

  FIG. 2 is a schematic configuration diagram of the developing device shown in FIG. Since the functions of the four image forming units are substantially the same, the following description will be given taking the K color as a representative.

  The developing device 14K is provided with a developer containing portion 142K that contains toner and carrier coated with external additives, and a portion that is exposed from the developer containing portion 142K, and is rotatable in the direction of arrow D. The developing roller 141K, the toner density sensor 143K that detects the toner density in the developer container 142K, the toner cartridge 146K that stores the toner to be supplied to the developer container 142K, and the toner supplied from the toner cartridge 146K to the developer supply part 142K And a static mixer 145K built in the toner conveyance path 144K.

  The developer container 142K is provided with a partition member 1421K for partitioning the developer container and an agitator 1422K for stirring the toner and the carrier on one side partitioned by the partition member 1421K. The toner mixed with the carrier is agitated by the agitator 1422K that rotates in the direction beyond the partition plate 1421K and is sent to the developing roll 141K side. The toner agitated by the agitator 1422K together with the carrier is frictionally charged to a predetermined charge amount and is electrostatically attached to the carrier.

  The static mixer 145K rotates in response to an instruction from the image formation control unit 10 shown in FIG. 1, and feeds toner into the developer storage unit 142K.

  The toner concentration sensor 143K is provided near the bottom of the developer accommodating portion 142K, and detects the magnetic permeability for calculating the toner concentration of the developer composed of toner and carrier.

  Although not shown in the drawing, the developing roll 141K has a rotating hollow cylindrical developing sleeve, and a plurality of magnets arranged in the circumferential direction of the developing sleeve fixed independently of the developing sleeve inside the developing sleeve. The developer near the developing roll in the developer accommodating portion is adsorbed on the sleeve surface by a magnet disposed inside the developing sleeve. The toner of the developer adsorbed on the sleeve rotating in the direction of arrow D is electrostatically pulled toward the electrostatic latent image formed on the surface of the photoreceptor and used for developing the electrostatic latent image.

  FIG. 3 is an internal configuration diagram of the image formation control unit shown in FIG.

  An image formation control unit 10 shown in FIG. 3 is an image information analysis unit 101 that analyzes image information input from the outside for each of C color, M color, Y color, and K color, which is a basis of image formation, The information analysis unit 101 calculates the amount of discharged toner based on the image information analyzed for each color and the toner supply amount calculation unit 102 for integrating the amount of discharged toner, and the image information analysis unit 101 analyzes each color. An image density calculation unit 103 that calculates an image density based on image information and an average image density, and a toner concentration calculation unit 104 that calculates an average toner density based on toner density information detected by the toner concentration sensor 143K. And a counter 108 for accumulating the rotation time of the agitator 1422K.

  Also, the image formation control unit 10 shown in FIG. 3 stores a memory 105 that stores a reference cumulative stirring time, a reference image density, a reference toner concentration, a reference toner supply amount, and the like, which will be described in detail later. A determination unit 106 that determines whether or not the toner in the developer storage unit is discharged from the developer storage unit onto the photosensitive member at a timing different from the image formation based on the reference values and the like. And a data changing unit 107 that changes the reference value stored in the memory 105 based on the count value counted by the counter 108 and the average toner density calculated by the toner concentration calculating unit 104. Yes.

  FIG. 4 is a flowchart of a routine started up in the image control unit shown in FIG. 3 every time the power is turned on. This routine is started for each color.

  Hereinafter, the processing of FIG. 3 will be described in detail with reference to the flowchart shown in FIG.

  In step S1 shown in FIG. 4, the cumulative stirring time during the past 100 image formations including the current image formation has exceeded the reference cumulative stirring time stored in the memory 105 or the current image formation. It is determined whether or not the average toner density during 100 image formations in the past has fallen below the reference toner density stored in the memory 105. As described above, the accumulated stirring time is accumulated in the counter 108 shown in FIG.

  If it is determined in step S1 that none of them is applicable, the process proceeds to step S2 to specify ACL as the reference image density and THL as the reference toner supply amount. The reference image density ACL is lower than the reference image density ACH, and the reference toner supply amount THL is smaller than the reference toner supply amount THH.

  On the other hand, if it is determined in step S1 that one of them is satisfied, the process proceeds to step S3, where ACH is designated as the reference image density and THH is designated as the reference toner supply amount.

  In this printer 1, the toner is deteriorated because the cumulative stirring time exceeds the reference cumulative stirring time stored in the memory 105 or the average toner density is lower than the reference toner density stored in the memory 105. Since it is expected to progress further, the values of the reference image density and the reference cumulative stirring time can be switched so as to further promote the toner discharge from the developer accommodating portion.

  In step S4, calculation of the average image density (AC) and integration of the toner supply amount (NT) during the past 100 image formations including the current image formation are performed, and the image density calculation unit 103 and the toner supply amount integration are performed. The unit 102 is instructed. Thereafter, in step S5, it is determined whether or not the average image density (AC) exceeds the reference image density (ACL or ACH), and if it is determined that the average image density exceeds the reference image density, step S1. Returning to step S6, the process proceeds to step S6 if it is determined that it has not exceeded. In step S6, it is determined whether or not the calculated toner supply amount exceeds the reference toner supply amount. If it is determined that the toner supply amount is exceeded, the process returns to step S1. Instructing image creation at the timing between image formation. Thereafter, the process proceeds to step S8, the counter is reset, and then the process returns to step S1.

  Next, an example of the above-described printer 1 and a comparative example with respect to the example will be described. In Table 1 shown below, Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are shown.

  In these Examples and Comparative Examples, 1% by weight of negatively charged silica having a spherical shape and a particle diameter of 100 nm and 0.5% by weight of negatively charged titania having a rice shape and a length of 80 nm are externally added. Using a toner containing 9% by weight of a polypropylene wax having a melting point of 91 ° C., an image density of 160% (yellow (Y) 80%, magenta (M) 80% at high temperature and high humidity (28 ° C., 85% RH)) , Cyan (C) 0%, black (K) 0%), and the yellow, magenta, and cyan agitators are given a rotational driving force by a common motor. Yes. That is, in the image patterns (Y80%, M80%, C0%, K0%) of these examples and comparative examples, development of yellow and magenta is performed even though cyan (C) is not developed. Therefore, it will continue to be stirred. For this reason, for cyan (C), since toner is not discharged, toner in the cyan (C) developer storage unit accumulates stress. The toner concentration (TC) is detected by a magnetic permeability sensor provided in each developer accommodating portion. In addition, as an evaluation, charge distribution, fogging, and comprehensive determination are provided.

  Here, in the first and second embodiments, since the routine shown in FIG. 4 is started, the toner subjected to stress in the developer accommodating portion is released, so that the “charge distribution” is normal (◯). Yes, no “fog” (◯), and “determination” is good (OK).

  On the other hand, in Comparative Example 1, development for cyan (C) is not performed, but development for yellow and magenta is performed. Therefore, the toner in the cyan (C) developer storage unit accumulates stress, and charging is performed. The distribution forms a two-peak distribution on the normal high charge side and the positive side near zero charge. As a result, although the 'charge distribution' is doubled (Δ), it was barely acceptable (NG +) level in visual quality.

  In Comparative Example 2, similar to Comparative Example 1, the cyan (C) toner in the cyan (C) developer container is stressed, and the toner concentration is lower than that of Comparative Example 1, and friction (collision) with the carrier. Due to the large number of times the stress is applied, the stress is further increased, and the charge distribution is a defective (×) level in which a two-peak distribution is clearly formed on the normal high charge side and the positive electrode side near zero charge, and fogging becomes obvious (X), and the judgment by silent vision was bad (NG).

  As described above, in the printer 1 of the present embodiment, the average image density in 100 image formations including the current image formation and going back to the past is less than the predetermined reference image density and is integrated by the toner supply amount integration unit. When the supplied toner supply amount falls below a predetermined reference toner supply amount, the charging performance of the toner stored in the developer storage unit is regarded as deteriorated, and image formation is performed on the photoreceptor from the developer storage unit. It is discharged from the developer container by being sent out at a different timing. As a result, in the printer 1, it is possible to suppress the coexistence of toners having extremely different charging performances in the developer accommodating portion as compared with the conventional case. Therefore, according to the printer 1, the image quality can be improved with high accuracy.

In the embodiment described above, the cumulative stirring time exceeds the reference cumulative stirring time stored in the memory 105, or the average toner concentration falls below the reference toner concentration stored in the memory 105. The case where the reference is changed so as to further promote toner discharge from the developer storage unit has been described as an example. However, the reference may not be changed. Although the case where the image formation is performed 100 times is described as an example, the present invention is not limited to the image formation of 100 times as long as it is a plurality of times.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus of the present invention suitable for carrying out an embodiment of an image forming method of the present invention. It is a schematic block diagram of the developing device shown in FIG. FIG. 2 is an internal configuration diagram of an image formation control unit shown in FIG. 1. FIG. 4 is a flowchart of a routine activated in the image control unit shown in FIG. 3 every time power is turned on.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 10 Image formation control part 101 Image information analysis part 102 Toner supply amount calculating part 103 Image density calculating part 104 Toner density calculating part 105 Memory 106 Judgment part 107 Data changing part 108 Counter 14C, 14M, 14Y, 14K Developing device 141C, 141M, 141Y, 141K Developing rolls 142C, 142M, 142Y, 142K Developer container 1421C, 1421M, 1421Y, 1421K Partition members 1422C, 1422M, 1422Y, 1422K Agitator 143C, 143M, 143Y, 143K Toner density sensor 144C, 144M, 144M 144K Toner transport path 145C, 145M, 145Y, 145K Static mixer 146C, 146M, 146Y, 146K Toner cartridge

Claims (6)

In an image forming apparatus that forms a latent image on the surface of a photoreceptor, develops the latent image with toner to obtain a toner image, and finally forms the image by transferring and fixing the toner image on a recording medium.
A developer containing section for containing and stirring a developer composed of toner and carrier, and developing the latent image with toner of the developer;
A toner concentration detection unit for detecting a toner concentration in the developer containing unit;
A toner supply unit that supplies toner into the developer accommodating unit when the toner concentration detected by the toner concentration detection unit falls below a predetermined reference toner concentration;
An average image density calculation unit for calculating an average image density in a plurality of image formations including the current image formation and going back to the past;
A toner supply amount integrating unit that integrates the toner supply amount to the developer containing unit in a plurality of image formations including the current image formation and going back in the past;
When the average image density calculated by the average image density calculation unit is lower than a predetermined reference image density and the toner supply amount integrated by the toner supply amount integration unit is lower than a predetermined reference toner supply amount, the developer An image forming apparatus comprising: a toner discharging unit that discharges toner in a storage unit by sending the toner from the developer storage unit onto the photosensitive member at a timing different from image formation. An agitation time measurement unit for measuring the cumulative agitation time for the developer in the developer accommodating unit during a plurality of image formations including the current image formation and going back in the past;
And a reference changing means for raising the reference toner supply amount and the reference image density when the cumulative stirring time measured by the stirring time measuring unit exceeds a predetermined reference cumulative stirring time. The image forming apparatus according to claim 1. An average toner density calculation unit that calculates an average toner density that is an average of the toner density detected by the toner density detection unit during a plurality of image formations including the current image formation and going back in the past;
And a reference changing unit configured to increase the reference toner supply amount and the reference image density when the average toner concentration calculated by the average toner concentration calculation unit is lower than a predetermined reference toner concentration. Item 2. The image forming apparatus according to Item 1. A developer containing portion for containing and stirring a developer composed of toner and carrier, a toner concentration detecting portion for detecting a toner concentration in the developer containing portion, and a toner concentration detected by the toner concentration detecting portion; An image forming apparatus having a toner supply unit that supplies toner into the developer accommodating portion when the toner concentration falls below a predetermined reference toner density, and is formed on the surface of the photoreceptor with the toner accommodated in the developer accommodating portion. In the image forming method of forming an image by developing the latent image obtained to obtain a toner image, and finally transferring and fixing the toner image on a recording medium,
An average image density calculation process for calculating an average image density in a plurality of image formation dates back to the past including the current image formation,
A toner supply amount integration process for integrating the toner supply amount to the developer accommodating portion in a plurality of image formations including the current image formation and going back to the past;
When the image density calculated in the average image density calculation process is lower than a predetermined reference image density and the toner supply amount integrated in the toner supply amount integration process is lower than a predetermined reference toner supply amount, the developer is accommodated. An image forming method comprising: a toner discharging process for discharging toner in a unit by sending the toner from the developer storage unit onto the photosensitive member at a timing different from image formation. An agitation time measurement process for measuring a cumulative agitation time for the developer in the developer accommodating portion during a plurality of image formations including the current image formation and going back to the past;
And a reference changing process for raising the reference toner supply amount and the reference image density when the cumulative stirring time measured in the stirring time measurement process exceeds a predetermined reference cumulative stirring time. The image forming method according to claim 4. An average toner density calculation process for calculating an average toner density that is an average of the toner density detected by the toner density detection unit during a plurality of image formations including the current image formation and going back in the past;
2. A reference changing process for raising the reference toner supply amount and the reference image density when the average toner density calculated in the average toner density calculation process is lower than a predetermined reference toner density. 5. The image forming method according to 4.

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