JP2010122398A - Developing method and apparatus for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing method and an apparatus for an image forming apparatus, by which a toner layer is always formed in a fixed layer thickness on a developing roller and a ghost performance is stabilized even when there is a variation in toner charged amount or a variation in MS gap due to an environmental condition or the like in a touch down developing method. <P>SOLUTION: In the image forming apparatus, the formation of the toner layer on the developing roller and the developing of an electrostatic latent image are carried out by executing: a layer thickness calibration for determining a potential difference ΔV between the DC developing bias voltage and the DC bias voltage for forming toner layer so that a target image density is obtained by varying the DC bias voltage for forming toner layer while fixing the DC developing bias voltage and measuring the image density by forming a detection pattern for toner layer thickness that is composed of a half density pattern for adjusting the image density; and a bias calibration for determining the DC bias voltage for forming toner layer by varying the DC bias voltage for forming toner layer and the DC developing bias voltage while maintaining the potential difference ΔV and forming the detection pattern for toner layer thickness and making the image density to be the target image density. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing method and an apparatus in an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using an electrophotographic method, and more particularly, a two component for charging a nonmagnetic toner using a magnetic carrier. An image forming apparatus that uses a developer, forms only a thin layer of charged toner uniformly on the developing roller, and then develops the electrostatic latent image formed on the photosensitive drum by flying the toner from the developing roller. The developing method and apparatus in FIG.

  Development methods using dry toner in image forming apparatuses such as copiers, printers, facsimiles, and composite machines using electrophotography are two-component development methods that use only toner, and toner and carrier. A two-component development system using a component developer is known.

  Of these, the two-component development system is suitable for extending the life because a stable charge amount can be obtained over a long period of time by friction between the toner and the carrier. However, in the two-component development method, since the magnetic brush formed by the carrier and the toner is brought into contact with an electrostatic latent image carrier (hereinafter referred to as a photosensitive drum) for development, the electrostatic latent image is faithfully developed. However, there is a problem of print smearing (fogging) on the non-latent image area and a carrier adhesion problem where the carrier is used for development together with the toner or developed to the non-latent image area. In addition, the toner image formed on the photosensitive member is disturbed.

  On the other hand, the one-component development method that does not contact the photoconductor does not disturb the formed toner image, and can produce a sharp image with an edge and is advantageous for fogging, and is suitable for high image quality. Yes. However, in this method, the toner is charged by the charge roller, and the layer thickness on the developing roller is regulated by the elastic regulating blade, so that it is difficult to stably maintain the charge amount of the toner. May adhere to the charge roller and reduce the charging ability, or toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects, and color toners require transparency. It must be a non-magnetic toner.

  Therefore, in a full-color image forming apparatus, a non-magnetic toner is used to develop a one-component development method with the aim of improving the image quality of the development region, and a two-component development method is adopted for the charging region in consideration of extending the service life. A so-called touch-down development method or a development method called a hybrid development method that takes advantage of the respective advantages of these two development methods has attracted attention. In particular, in a full-color image forming apparatus in which high image quality and long life are important, the characteristics of this development method are sufficiently exhibited.

  This touch-down development method uses a two-component developer containing toner and carrier to secure a stable charge amount and forms a magnetic brush on the surface of the developer carrying member (hereinafter referred to as a magnetic roller). After only a toner is transferred from a magnetic brush to the surface of a toner carrier (hereinafter referred to as a developing roller) to form a thin layer of toner, the toner is allowed to fly to the surface of a photosensitive drum on which an electrostatic latent image is formed. The toner image is developed as a toner image.

  On the other hand, in recent years, color image forming apparatuses are also required to be reduced in price and increased in definition with personalization, and a reduction in toner particle diameter is being studied. However, the reduction in toner particle size results in improved image quality (high resolution images), but the toner density from the developing roller to the photosensitive drum (development) is weak. Is difficult to occur, causing problems such as generation of ghost images and toner adhesion to the surface of the developing roller due to selective development.

  That is, toner movement from the toner layer formed on the developing roller to the photoconductive drum is performed from toner that has a relatively low charge amount per unit volume and is relatively easy to fly. Low particle size toner with low chargeability and high charge amount is difficult to be used for development and selective development occurs. When continuous printing (printing durability) is performed, fine toner adheres to the developing roller and is not easily consumed. The problem is that fine powder toner having a low density increases in the developing device and the image quality deteriorates.

  Further, when an image is formed by forming a thick toner layer on the developing roller, when the toner layer is formed on the developing roller with the magnetic brush formed on the magnetic roller, it is sufficient to rotate the developing roller only once. No layer is formed, and a difference occurs between the toner consumption area and the non-consumption area. Therefore, a potential difference occurs between the toner remaining on the developing roller and the newly supplied toner, and a so-called afterimage (ghost) is generated in which a part of the previous developed image remains as a history when the next image is developed. There is also a problem.

  For example, Patent Document 1 discloses a first image exposure unit, a first development unit, a second image exposure unit, a development roller, and a supply roller (magnetic roller) that supplies toner to the development roller. And a second developing unit having a potential difference applying unit that applies a potential difference that causes toner to adhere only to the developing roller. In order to obtain a two-color image without color mixture, A potential detecting means for detecting the image surface potential after the development by the first developing means is provided between the first developing means and the second developing means, and the developing roller by the potential difference applying means is supplied according to the detected surface potential. A two-color image forming apparatus having a potential control means for controlling the potential between rollers is disclosed.

Patent Document 2 also relates to a two-color or multi-color image forming apparatus. In the first and second inventions, a bias in which a DC voltage of +340 V is superimposed on an AC voltage of 2000 Hz and 1300 V _PP is applied to the developing roller. A voltage is applied, a DC voltage of +260 V is applied between the developing roller and the supply roller, a bias is set so that the potential of the supply roller is always 260 V higher than the potential of the developing roller, and the toner on the developing roller is peeled off In the multi-color mode, the multi-color developed image formed on the image carrier is transferred to the transfer material at once by dropping the peeling roller to the ground and allowing the toner to be peeled off by the potential difference with the developing roller. In particular, there is disclosed an image forming apparatus that has good color reproducibility and is free from problems such as blurring of characters and lines and can obtain high-quality images. To have.

  Further, in the third invention of Patent Document 2, toner development comprising a latent image forming device that forms toner patches using several different types of development bias and a patch detection device that measures the toner amount of the developed toner patches. A device for measuring the amount, a device for detecting the amount of moving charge flowing in the image carrier, and a bias power supply device capable of varying the electric field applied to the developer carrying member, and the detected toner development amount and the image carrier It is shown that an optimum developing bias condition for optimizing the DC component of the developing bias with respect to the developer carrying member is set in accordance with the toner charge amount obtained from the moving charge amount.

  In Patent Document 3 filed by the applicant of the present application, a DC bias is applied to the magnetic roll side, and a bias in which AC is superimposed on the DC is applied to the developing roll side, respectively, and the DC bias power source is an independent power source. At the end of development, with the AC bias applied to the developing roll side, the one DC bias is changed to collect the toner on the developing roll, so that development ghost and selective development can be performed without complicating the developing device. A developing roller toner recovery method in a developing device used in a high-speed and inexpensive small tandem type image forming apparatus that prevents generation and supplies reliably charged toner to a developing roll to obtain stable image quality for a long period of time. Proposed.

  Similarly, in Patent Document 4, the applicant of the present application will perform the toner layer peeling on the developing roller and the toner layer re-formation at the non-development interval between the latent image images corresponding to the recording papers. When the supply roller applied voltage to be applied is changed according to the toner layer re-formation state of the developing roller, and the toner layer on the developing roller is peeled off and re-formed between papers during continuous printing, the re-formation time As much as possible, high-speed printing is possible, and the density of the toner layer on the developing roller is constantly stabilized over a long period by detecting the image density at the time of re-formation, so that a stable image with no change in image density can be maintained. A developing device in the image forming apparatus is proposed.

JP-A-4-58267 JP-A-6-27778 JP 2003-287959 A JP 2005-55839 A

  However, the image forming apparatus disclosed in Patent Document 1 has a potential control unit that controls the potential between the developing roller and the supply roller by the potential difference applying unit according to the surface potential detected by providing the potential detecting unit. However, a specific method for controlling the toner amount on the developing roller and a specific method for preventing selective development and ghost are not described.

  In the first and second aspects of the image forming apparatus disclosed in Patent Document 2, the bias is set so that the potential of the supply roller is 260 V higher than the potential of the developing roller, and the toner on the developing roller is stripped off. The roller is grounded so that the toner on the developing roller can be removed. In the third aspect of the invention, the toner developing amount measuring device, the detecting device for the amount of moving charge flowing in the image carrier, and the developer carrying member And a bias power supply device that can vary the electric field applied to the toner, and optimize the DC component of the developing bias with respect to the developer carrying member in accordance with the toner charge amount obtained from the toner development amount and the image carrier moving charge amount. However, this is a complicated configuration in which a peeling roller, a toner developing amount measuring device, a detecting device for the amount of moving charge flowing in the image carrier, and the like are provided, which causes a problem in cost.

  The toner recovery method for the developing roll in the developing device disclosed in Patent Document 3 is that a bias voltage is applied to the magnetic roll and the developing roll by an independent DC bias power source, and one of the DC biases is changed at the end of development to change the toner on the developing roll. However, since the thickness of the toner layer on the developing roll is not taken into consideration, when a thick toner layer is formed, a sufficient toner layer can be obtained only by rotating the developing roll once. It is inevitable that ghosts will not be formed.

  Further, the developing device in the image forming apparatus disclosed in Patent Document 4 uses a supply roller applied voltage as a toner layer of the developing roller when stripping the toner layer on the developing roller and re-forming the toner layer at a non-development interval between papers. Although it changes according to the re-formation state, the re-formation time is reduced as much as possible to enable high-speed printing, but a specific method for preventing a ghost that occurs when a thick toner layer is formed on the developing roller is shown. Do not mean.

The temperature and humidity in the image forming apparatus are influenced by the environment when the power is turned on, and the internal temperature increases and the humidity decreases with time from heat from the fixing device and the motor. In that case, the charge amount of the toner changes depending on the environment where the image forming apparatus is placed and particularly the temperature and humidity in the housing, and accordingly, as shown in the graph of FIG. The amount changes. In the graph of FIG. 16, the horizontal axis represents the DC toner layer forming bias voltage (Vmag, unit: V) to the magnetic roller, the vertical axis represents the toner amount (unit: mg / cm ² ) on the developing roller, and the solid line represents room temperature. -In the normal humidity (N / N) environment, ◆ is the amount of toner at the position corresponding to the left side of the developing device (DLP left side), ■ is the amount of toner at the position corresponding to the right side of the developing device (DLP right side), and the broken line is low temperature / low humidity ( L / L) In the environment, ◆ indicates the toner amount at a position corresponding to the left side of the developing device (DLP left side), and ■ indicates the toner amount at a position corresponding to the right side of the developing device (DLP right side). The potential difference ΔV (Vmag−Vslv) between the DC toner layer forming bias voltage applied to the magnetic roller and the DC developing bias voltage (Vslv, unit: V) applied to the developing roller is constant at 250V. This is a case where the direct current toner layer forming bias voltage (Vmag) applied to the magnetic roller is changed under the above control.

  As can be seen from the graph of FIG. 16, since the toner charge amount is usually high in a low temperature / low humidity (L / L) environment, the toner amount on the developing roller is in a normal temperature / normal humidity (N / N) environment. In comparison, it decreases when the DC toner layer forming bias voltage (Vmag) to the magnetic roller is low. However, as the DC toner layer forming bias voltage is increased, the amount of toner on the developing roller in a normal temperature / normal humidity (N / N) environment decreases. When the DC toner layer forming bias voltage is around 470 V, the normal temperature / normal humidity (N / N) The difference from the environment is small.

  In addition, the toner layer thickness on the developing roller changes not only due to the change in the toner charge amount but also due to variations in the MS gap, which is the distance between the developing roller and the magnetic roller.

  Therefore, in the present invention, an image forming apparatus that has a simple configuration and always forms a toner layer having a constant layer thickness on the developing roller even if there is a variation in toner charge amount, a variation in MS gap, etc., and ghost performance is stable. It is a problem to provide a developing method and apparatus.

In order to solve the above problems, the developing method in the image forming apparatus according to the present invention is as follows.
A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller containing a magnet and enclosing a toner layer forming bias in which alternating current is superimposed on direct current, and alternating current is superimposed on direct current from the magnetic brush. In the developing method in the image forming apparatus, after the toner layer is formed on the developing roller to which the developing bias is applied, the toner is ejected to the electrostatic latent image formed on the photosensitive member by the electrophotographic method.
The DC developing bias voltage at the developing bias is fixed and the DC toner layer forming bias voltage at the toner layer forming bias is changed to form a toner layer thickness detection pattern consisting of a half density pattern for image density adjustment, thereby adjusting the image density. A layer thickness calibration is performed to determine a potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage so that the measurement result becomes a target image density, and to set the toner layer thickness on the developing roller to the target toner layer thickness. And
While maintaining the potential difference ΔV determined by the layer thickness calibration, the DC toner layer formation bias voltage and the DC development bias voltage are changed, the toner layer thickness detection pattern is formed, and the image density is measured. Determining a DC development bias voltage with the measurement result as a target image density, and performing a bias calibration with a toner amount flying from the developing roller to the photoconductor as a target toner amount;
The electrostatic latent image is developed by forming a toner layer on the developing roller with the DC toner layer forming bias voltage and the DC developing bias voltage determined by the layer thickness calibration and the bias calibration. It is characterized by that.

And the developing device for carrying out this developing method is:
A toner layer forming bias that includes a magnet and superimposing alternating current on a direct current is applied, a magnetic roller that holds a magnetic brush of a two-component developer composed of toner and a carrier, and a developing bias that is superimposed on direct current is applied. In a developing device in an image forming apparatus, a toner layer is formed by the magnetic brush, and a developing roller that causes the toner layer to fly and develop an electrostatic latent image formed on a photoreceptor by an electrophotographic method. ,
The image forming apparatus measures the image density of a toner layer thickness detection pattern formed on the photoconductor or formed of a half-density pattern for image density adjustment formed on the photoconductor and transferred to the transfer body. A toner density sensor;
The DC developing bias voltage at the developing bias is fixed and the DC toner layer forming bias voltage at the toner layer forming bias is changed to form a toner layer thickness detection pattern comprising a half density pattern for image density adjustment, thereby forming the toner density The image density is measured by a sensor, the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage with the measured image density as the target image density is determined, and the toner layer thickness on the developing roller is determined. Layer thickness calibration mode to target toner layer thickness,
The potential difference ΔV determined in the layer thickness calibration mode is maintained, the DC toner layer forming bias voltage and the DC developing bias voltage are changed, and the formed toner layer thickness detection pattern density is applied to the toner density sensor. A DC calibration bias voltage having a target image density as a target image density is determined, a bias calibration mode in which a toner amount flying from the developing roller to the photosensitive member is a target toner amount, and the DC toner is A toner layer on the developing roller is formed using the layer forming bias voltage and the DC developing bias voltage determined in the layer thickness calibration mode and the bias calibration mode, and the electrostatic latent image is developed. And a development control device.

  Thus, by first performing the layer thickness calibration, the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage that realizes the most preferable layer thickness on the developing roller can be determined. It is impossible to eliminate the variation in the toner layer thickness caused by the variation in the toner charge amount due to the ambient temperature and humidity and the variation in the MS gap. However, the potential difference ΔV determined by the layer thickness calibration is maintained, bias calibration is performed to measure the toner layer thickness detection pattern density, and the DC toner layer formation is performed so that the measurement result becomes the target image density. By determining the bias voltage and the DC development bias voltage, it is possible to eliminate the variation in the toner layer thickness caused by the variation in the toner charge amount, the MS gap, and the like. It is possible to provide a developing method and apparatus in an image forming apparatus in which constant development and ghosting are prevented from occurring.

  The DC developing bias voltage to be fixed in the layer thickness calibration is selected as a voltage that causes all of the toner on the developing roller to fly to the photoconductor, and therefore the DC developing bias voltage to be fixed in the layer thickness calibration mode. Is stored as a voltage for causing all the toner on the developing roller to fly to the photoconductor, and the development control device is configured to store the DC developing bias voltage to be fixed in the layer thickness calibration mode. The direct current developing bias voltage is fixed to the read voltage, and the direct current toner layer forming bias voltage is changed to determine the potential difference ΔV.

  As described above, the toner charge amount varies depending on the environmental temperature and humidity, thereby changing the ratio of the toner layer thickness on the developing roller and the amount of toner flying to the photosensitive drum with respect to the variation amount of the DC developing bias voltage. Therefore, by setting the DC development bias voltage to be fixed in the layer thickness calibration in this way to a voltage that causes all the toner on the developing roller to fly to the photoconductor, all the toner on the developing roller flies to the photoconductor. Since the thickness of the toner layer on the developing roller is accurately known, the potential difference ΔV between the DC developing bias voltage having the image density as the target image density and the DC toner layer forming bias voltage can be accurately determined.

  As described above, according to the present invention, the toner layer thickness on the developing roller is determined by the layer thickness calibration, and further, the toner layer thickness variation caused by the variation in the toner charge amount or the variation in the MS gap is detected by the bias calibration. Therefore, the ghost performance can be stabilized and the developing method and apparatus in the image forming apparatus capable of forming a high-quality image over a long period of time can be obtained.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Absent.

  First, the outline of the present invention will be briefly described. In the present invention, a two-component developer comprising a toner and a carrier is placed on a magnetic roller containing a magnet and applied with a toner layer forming bias in which an alternating current is superimposed on a direct current. After forming a magnetic brush and forming a toner layer on a developing roller to which a developing bias in which alternating current is superimposed on direct current is applied from the magnetic brush, an electrostatic latent image formed on a photosensitive member by electrophotography is formed. The present invention is applied to a touch-down developing device that develops toner by flying.

  Conventionally, in an image forming apparatus, prior to image formation, a calibration is performed to form a toner layer thickness detection pattern composed of a half density pattern for image density adjustment, measure the image density, and control to always obtain the same image density. In the present invention, first, the DC developing bias voltage is fixed to a voltage that causes all toner on the developing roller to fly to the photosensitive member, and the DC toner layer forming bias voltage is changed to change the image density adjusting half voltage. A layer thickness for determining a potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage so that a toner layer thickness detection pattern comprising a density pattern is formed and the image density is measured and the measurement result is a target image density. Perform calibration.

  Then, while maintaining the potential difference ΔV determined by this layer thickness calibration, the DC toner layer formation bias voltage and the DC development bias voltage are changed, the toner layer thickness detection pattern is formed again, and the image density is measured. A DC development bias voltage with the measurement result as a target image density is determined, and bias calibration is performed with the DC toner layer forming bias voltage as a voltage corresponding to the difference between the determined DC development bias and the potential difference ΔV.

  That is, as described above, the charge amount of the toner changes depending on the environmental temperature and humidity, thereby changing the ratio of the toner layer flying to the photosensitive drum with respect to the toner layer thickness on the developing roller and the change amount of the DC developing bias voltage. To do. Therefore, in the present invention, the DC developing bias voltage to be fixed in the layer thickness calibration is stored in a storage device so that the voltage for causing all the toner on the developing roller to fly to the photoreceptor can be selected as described above. Keep it.

  In addition, even if the layer thickness calibration is performed in consideration of the charge amount of the toner that changes depending on the environmental temperature and humidity in this way, the DC developing bias voltage at the time of the layer thickness calibration is the developing roller as described above. Since it is a voltage that causes all of the toner above to fly to the photoreceptor, it is not necessarily a voltage necessary for developing an electrostatic latent image on the photoreceptor drum. Further, as described above, the toner layer thickness on the developing roller also changes due to variations in the MS gap between the developing roller and the magnetic roller. The ghost described above also increases or decreases with the DC toner layer forming bias voltage.

  Therefore, in the present invention, the DC developing bias voltage is selected so that the color difference ΔE between the half portion and the ghost history portion in the toner layer thickness detection pattern is not more than a predetermined value while maintaining the potential difference ΔV determined by the layer thickness calibration. Execute bias calibration.

  As described above, the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage that realizes the most preferable layer thickness on the developing roller is determined by the layer thickness calibration, and then the toner charge amount variation and the MS gap variation are determined. The bias calibration is performed so that the color difference ΔE between the half portion and the ghost history portion in the toner layer thickness detection pattern is equal to or less than a predetermined value in the toner layer thickness detection pattern. Development method in an image forming apparatus in which variation in toner layer thickness due to variations such as MS gap can be eliminated, toner layer thickness on the developing roller is always constant, and selective development and ghosting are prevented. It can be a device.

  The above is the outline of the present invention. Next, referring to FIG. 1 and FIG. 2, the configuration of the touch-down developing device (FIG. 1) for carrying out the developing method in the image forming apparatus according to the present invention and the present invention are obtained. A schematic diagram (FIG. 2) of an embodiment of an image forming apparatus that performs the developing method will be described.

  In the image forming apparatus 30 shown in FIG. 2, an endless belt 31 is arranged so that the recording paper from the paper feed cassette 32 can be conveyed toward the fixing device 33, and the endless belt 31 that conveys the recording paper is arranged. On the upper side of the figure, a black developing device 34K, a yellow developing device 34Y, a cyan developing device 34C, and a magenta developing device 34M are arranged. These developing devices 34 (K, Y, C, M) are developed in close proximity to the magnetic roller 15 (K, Y, C, M) and the magnetic roller 15 (K, Y, C, M), respectively. A roller 11 (K, Y, C, M) is disposed, and the photosensitive drum 10 (K, Y, C, M) faces the developing roller 11, and further around the photosensitive drum 10, A charger 35 (K, Y, C, M) and an exposure device 36 (K, Y, C, M) are arranged.

  1 shows the photosensitive drum 10 (K, Y, C, M), the developing roller 11 (K, Y, C, M), and the magnetic rollers 15 (K, Y, C, M) and 13 shown in FIG. , 14, 19, 20 and the configuration of the control circuits 22, 23 and the like. In the figure, reference numeral 10 denotes a photosensitive drum, and an amorphous silicon (a-Si) photosensitive member, an organic photosensitive member (OPC), or the like is used as a material. An electrostatic latent image 11 is formed on the photosensitive drum 10 by an electrophotographic method with a developing bias applied from a DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14. A developing roller 15 for developing the toner 16 by flying the toner 16 is formed in a cylindrical shape with a nonmagnetic metal material, and has a rotatable sleeve in which a plurality of fixed magnets are disposed. A magnetic brush 18 of a two-component developer composed of a carrier 17 is formed, and a toner layer forming bias applied from a DC toner layer forming bias power source (DC2) 19 and an AC toner layer forming bias power source (AC2) 20; A magnetic roller for forming the toner layer 12 on the developing roller 11 due to a potential difference ΔV between the developing bias and the DC toner layer forming bias, 21 is a magnetic roller The height of the magnetic brush 18 on 5 is a doctor blade for keeping constant.

  Reference numeral 22 denotes a developing roller bias power source controller for controlling the voltages of the DC developing bias power source (DC1) 13 and the AC developing bias power source (AC1) 14 of the developing roller 11, and 23 denotes a DC toner layer forming bias power source (for the magnetic roller 15). DC2) 19, a magnetic roller bias power supply controller for controlling AC toner layer forming bias power supply (AC2) 20, and 24 a developing roller bias power supply controller 22 and a magnetic roller bias power supply controller 23 by giving a voltage instruction to the developing device. Development control device for controlling The development control device 24 according to the present invention controls the development roller bias power supply control device 22 and the magnetic roller bias power supply control device 23 as described above, so that the toner layer thickness on the development roller 11 is a predetermined thickness. A routine for executing a calibration mode and a bias calibration mode for determining a DC developing bias and a DC toner layer forming bias so that no ghost occurs.

  Reference numeral 25 denotes a storage device that stores information that causes all toner on the developing roller to fly to the photosensitive member during the above-described layer thickness calibration and bias calibration.

  The elements constituting the developing device will be described. The outermost surface of the developing roller 11 is composed of a sleeve made of uniform conductive aluminum, SUS, conductive resin coating, etc., and an alumite treatment of about 20 μm, for example, to prevent leakage. It is preferable to increase the resistance value by coating the surface with a resin. A DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14 are connected to the shaft portion, and the direct current and alternating current are connected between the rotating developing roller 11, the photosensitive drum 10, and the magnetic roller 15. The developing bias voltage superimposed with the above is applied. The AC component supplied by the AC developing bias power source (AC1) 14 is constituted by, for example, a rectangular wave having a duty ratio of 73% or less.

For the toner 16, for example, a toner having a small particle diameter on the order of 6 μm of about 6.8 μm with 10 ¹³ to 10 ¹⁴ Ω is used for high definition of the formed image. In order to avoid selective development, it is important to define the particle size distribution. Generally, the spread of the particle size distribution of the toner is measured by a Coulter counter, and the ratio of the volume distribution average particle size to the number distribution average particle size is determined by the ratio. It is expressed with. When the distribution is wide, toner having a relatively small particle size is accumulated on the developing roller 11 during continuous printing, and developability is lowered.

As the carrier 17, a magnetite carrier, Mn-based ferrite, Mn—Mg-based ferrite, or the like can be used, and it can also be used after being surface-treated within a range that does not increase an appropriate resistance value. In the present invention, as an example, a ferrite carrier having a volume resistivity of 10 ⁸ Ωcm ³ and a saturation magnetization of 40 emu / g and an average particle size of 35 μm was used. When the average particle size exceeds 50 μm, the stress of the carrier increases and the toner blending ratio with respect to the carrier cannot be increased, and the amount of toner supplied to the developing roller 11 decreases.

  The mixing ratio of the toner 16 and the carrier 17 is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier 17 and the toner 16. If the mixing ratio of the toner 16 is less than 5% by weight, the charge amount of the toner 16 becomes high and a sufficient image density cannot be obtained, and if it exceeds 20% by weight, a sufficient charge amount cannot be obtained this time. The toner 16 scatters from the developing device and contaminates the inside of the image forming apparatus, or toner fog occurs on the image.

  Returning to FIG. 2 again, in the tandem type image forming apparatus having the touch-down type developing apparatus configured as described above, a toner 2 and a carrier 17 corresponding to respective colors such as yellow, cyan, magenta, and black are provided. The component developer is supplied from the developer container to each developing device 34, and the magnetic brush 18 is formed on the magnetic roller 15 shown in FIG. 1, and the toner 16 is charged by stirring. The magnetic brush 18 on the magnetic roller 15 is layer-regulated by the regulating blade 9, and is between the DC toner layer forming bias Vmag (19) applied to the magnetic roller 15 and the DC developing bias Vslv (13) applied to the developing roller 11. The toner layer 12 including only the toner 16 is formed on the developing roller 11 by the potential difference ΔV and the AC biases 14 and 20.

  When a print start signal is received from a control circuit (not shown), first, the photosensitive drum 10 composed of a positively charged organic photosensitive member (positive OPC) is charged to, for example, 420 V by the charger 35 shown in FIG. For example, by exposure by the exposure device 36 using an LED having a wavelength of 770 nm, the post-exposure potential of the photosensitive drum 10 becomes about 100 V and a latent image is formed. The latent image is developed with the toner 16 that has jumped from the toner layer 12 on the developing roller 11 to the photosensitive drum 10 by the DC developing bias 13 and the AC bias 14 applied to the developing roller 11 to form a toner image. Is done. Then, when the recording paper is fed from the paper feed cassette 32 and sent by the belt 54 and reaches the photosensitive drum 10, a transfer bias is applied by the transfer device 37 (K, Y, C, M) to record the recording paper. The toner image is transferred to the toner image, fixed by the fixing device 33, and discharged. The toner 16 that has not been used for the development on the developing roller 11 is peeled off by the magnetic brush 18 formed on the magnetic roller 15 and the above-described bias voltage, and a new toner layer 12 is formed and the next toner layer 12 is formed. Prepared for development.

  The above is the outline and operation of the image forming apparatus embodying the present invention. As a method for controlling the image density in the above-described calibration, conventionally, the voltage between the image portion and the non-image portion on the photosensitive drum 10 is conventionally used. In order to keep the relationship constant, the DC toner layer forming bias voltage (Vmag) applied to the magnetic roller 15 is changed while the DC developing bias voltage (Vslv) is kept constant (the potential difference between the DC toner layer forming bias voltage and the DC developing bias voltage). ΔV = Vmag−Vslv is changed), and the toner density on the developing roller 11 is changed to control the image density. However, in this method, when the toner layer thickness is increased, a so-called ghost image in which the history of the solid image appears in the half image portion appears remarkably in the image pattern in which the solid image is included in the half image.

  FIG. 3 shows the amount of toner layer on the developing roller 11 and the static on the photosensitive drum 10 in order to consider under what conditions the above-described selective development and ghost images occur and how to prevent them. The relationship between the amount of toner necessary for developing the electrostatic latent image and the bias applied to the developing roller 11 and the magnetic roller 15, and the toner 12 on the developing roller 11 for developing the electrostatic latent image on the photosensitive drum 10. FIG. 4 to FIG. 6 are graphs showing the results of the table in FIG. 3. FIG. 4 to FIG. 6 are graphs summarizing the results of experiments and investigations on the development efficiency indicating how much is used.

In the table of FIG. 3, “ΔVmag−slv” in the left column represents the DC toner layer forming bias voltage Vmag supplied from the DC bias power supply DC19 for the magnetic roller to the magnetic roller 15 and the DC development supplied to the developing roller 11. A voltage difference (ΔV) from the DC developing bias voltage Vslv supplied to the developing roller 11 from the bias power supply DC13, “toner amount on Slv” is a toner amount on the developing roller 11 (unit: mg / cm ² ), “Drum top” “Toner amount” is the toner amount on the photosensitive drum 10 (unit: mg / cm ² ), and “Drum / (Slv × S / D ratio)” is developed to “Drum toner amount” and “Slv toner amount”. The toner amount of the toner layer 12 formed on the developing roller 11 and the photosensitive member by the ratio of the value obtained by multiplying the peripheral speed (S) of the roller 11 by the peripheral speed (D) of the photosensitive drum 10. The development efficiency expressed as a ratio to the amount of toner used for developing the electrostatic latent image on the drum 10 is expressed in%. Here, S / D was about 1.6.

  “Ghost ΔE” prints a ghost chart having a solid image portion on a half image background with a 25% half portion, and indicates the color difference (ΔE) between the half portion and the ghost history portion in the ghost image appearing in the half image portion. Represents. “Solid ID” is the image density (unit: ID) of the solid part, and “Half 25% ID” is the image density (unit: ID) of the 25% half part. In the table of FIG. 3, the data is arranged in descending order of the DC developing bias voltage Vslv for each potential difference ΔV between the DC toner layer forming bias voltage Vmag and the DC developing bias voltage Vslv.

  Then, based on the values shown in the table of FIG. 3, the values shown in FIGS. 4 to 6 are plotted so as to meet the purpose of the investigation. In these graphs, the horizontal axis indicates the DC developing bias voltage Vslv. The vertical axis is a value corresponding to each graph. When the potential difference ΔV between the DC toner layer forming bias voltage Vmag and the DC developing bias voltage Vslv is 240V, 320V, and 400V, the DC developing bias voltage Vslv is It is the graph which showed how the value of the vertical axis changes when it changes.

  The image forming apparatus used in this investigation is a modified experimental machine using a touch-down developing method manufactured by Kyocera Mita. The photosensitive drum 10 used has an outer diameter of 30 mm, a peripheral speed of 168.2 mm / sec, and a developing roller. 20 has an outer diameter of 16 mm and a peripheral speed of 269.1 mm / sec, and the magnetic roller 21 has an outer diameter of 16 mm and a peripheral speed of 419.8 mm / sec. Further, the blade gap between the magnetic roller 21 and the ear cutting blade 24 is 0.27 to 0.32 mm, the M / S gap between the magnetic roller 21 and the developing roller 20 is 0.29 mm, the developing roller 20 and the photosensitive drum 10 are The D / S gap is 0.15 mm, the ratio (S / D) of the peripheral speed of the developing roller 20 to the peripheral speed of the photosensitive drum 10 is about 1.6, and the developer is an average particle of black (BK). A two-component developer composed of a toner having a diameter of 6.8 μm and a carrier was used.

Before explaining the graphs of FIGS. 4 to 6, the results of experiments on the optimum toner amount for developing the electrostatic latent image formed on the photosensitive drum 10 will be described. The amount of solid toner per transfer was changed in various ways and transferred to paper, which was measured with a color difference meter to determine the amount of toner that reproduces the color most vividly. At this time, when the toner amount is small, the reproduced color is light, and as the toner amount increases, the vividness increases. However, when the amount exceeds a certain amount, the color becomes black with no glossiness. As a result, it was found that the toner amount of about 0.55 (mg / cm ² ) on the photosensitive drum 10 is optimum for the toner having the average particle diameter of 6.8 μm.

First, in the graph shown as “developing roller toner thin layer amount” in FIG. 4, the horizontal axis is the DC developing bias voltage Vslv as described above, and the vertical axis is shown as “toner amount on Slv” in the table of FIG. Taking the toner amount (unit: mg / cm ² ) of the toner layer on the developing roller 20, the potential difference ΔV between the DC toner layer forming bias voltage Vmag and the DC developing bias voltage Vslv is set to 400V (◆), 320V (▲), 240V. (■). From the graph of FIG. 4, the toner amount of the toner layer formed on the developing roller 20 (slv) is at least in the range of 20 V to 180 V of the DC developing bias voltage Vslv, regardless of the value of the DC developing bias voltage Vslv. It can be seen that the value increases as the value of the potential difference ΔV increases.

Next, the graph shown as “solid toner amount on the drum” in FIG. 5 shows the toner amount (unit: mg / cm) on the photosensitive drum 10 indicated as “toner amount on Drum” in the table of FIG. 3 on the vertical axis. ² ). From this graph, it can be seen that the amount of solid toner on the photosensitive drum 10 increases as the potential difference ΔV between the DC developing bias voltage Vslv and the DC toner layer forming bias voltage Vmag and the DC developing bias voltage Vslv increase. Show.

  The graph shown as “Development efficiency (Drum toner amount / Slv toner amount × S / D ratio)” in FIG. 6 is shown as “Drum / (Slv × S / D ratio)” in the table of FIG. 3 on the vertical axis. Further, the ratio of the peripheral speed (S) of the developing roller 20 and the peripheral speed (D) of the photosensitive drum 10 to the toner amount on the photosensitive drum 10 (Drum) and the toner amount on the developing roller 20 (Slv) ( 1.6) is a graph showing the development efficiency (%) of how much the toner on the developing roller 20 has been transferred to the photosensitive drum 10 by a ratio to the value obtained by multiplying by 1.6). As shown in the graph of FIG. 6, the development efficiency is such that the potential difference ΔV between the DC toner layer forming bias voltage Vmag and the DC developing bias voltage Vslv is any of 400V (◆), 320V (▲), and 240V (■). In this case, the voltage rises in proportion to the voltage Vslv. However, when the ΔV is the lowest, 240V, the rate of increase is the largest, and the maximum development efficiency is such that the ΔV is the same when the DC development bias voltage Vslv is about 180V. The case of the lowest 240V is the largest.

Therefore, from the graphs of FIG. 4, FIG. 5 and FIG.
(1). The toner layer thickness on the developing roller 11 depends on ΔV. (2). The amount of solid toner on the photosensitive drum 10 depends on the DC developing bias voltage Vslv. (3). The development efficiency is almost linearly proportional to Vslv, and the smaller ΔV, the higher the Vslv, the higher the efficiency (4). The optimum amount of solid toner on the photosensitive drum 10 is about 0.55 (mg / c) as described above.
m ² ), from FIG. 5, in the case of ΔV240V, Vslv is about 110V, 32
In the case of 0V, it may be set to about 55V, and in order to obtain the optimum amount of solid toner on the photosensitive drum 10 and high development efficiency, it is better that Vslv is higher.
It can be seen that V240V is preferable. Further, reducing the potential difference ΔV between the DC developing bias Vslv and the DC toner layer forming bias Vmag indicates that the toner layer amount on the developing roller 11 is reduced from the graph of FIG.

  The table shown in FIG. 7 shows that the solid image density (unit: ID) is 25% when the distance (M / S gap) between the magnetic roller 15 and the developing roller 11 is changed and the DC toner layer forming bias Vmag is changed. The result of investigating how the halftone image density (unit: ID) changes, and the correlation between the changed DC toner layer forming bias Vmag and the “ghost property ΔE” 8 to 10 are graphs showing the results of the table of FIG.

  In the table of FIG. 7, Vmag in the left column is a DC toner layer forming bias, “BK (MS0.28)” is black toner, and the interval (M / S gap) between the magnetic roller 15 and the developing roller 11 is 0. When .28 mm, “BK (MS 0.35)” uses the same black toner, and when the M / S gap is set to 0.35 mm, “ghosting ΔE” is a half that is 25% half as described above. A ghost chart (a half density pattern for image density adjustment) provided with a solid image portion is printed on the image background, and represents a color difference (ΔE) between the half portion and the ghost history portion in a ghost image appearing in the half image portion. “Solid ID” is the image density (unit: ID) of the solid part, and “Half 25% ID” is the image density (unit: ID) of the 25% half part. 7 is similar to the table shown in FIG. 3 described above, the data is arranged in the descending order of the DC toner layer forming bias voltage Vmag, and the potential difference ΔV between the DC developing bias Vslv and the DC toner layer forming bias Vmag. Was investigated as fixed at 200V.

  Based on the values shown in the table of FIG. 7, the values plotted to meet the purpose of the investigation are shown in FIGS. 8 to 10. In these graphs, the horizontal axis represents the DC toner layer forming bias voltage. 8 and FIG. 9 are ID (image density), and FIG. 10 is ghost property ΔE. In each graph, ♦ indicates a case where the M / S gap is 0.28 mm, and ▲ indicates a case where the M / S gap is 0.35 mm. In addition, the line drawn to 2.0 of the ghost property ΔE in FIG. 10 is a line indicating the upper limit of the ghost property, and the ghost property is preferably less than this.

  First, from the graphs of FIGS. 8 and 9, even if the M / S gap is changed, neither the solid ID nor the 25% ID has a large effect, and the change is almost the same due to the change in the DC toner layer forming bias voltage Vmag. You can see that However, in the graph of the correlation between Vmag and ΔE in FIG. 10, the ghost property ΔE when the M / S gap is narrowed to 0.28 mm is at least less than the allowable value of 2.0 in the range of Vmag from 300 V to 500 V, It can be seen that the ghost property is better when the M / S gap is made smaller. However, when Vmag is about 420 V or less, the ghost property ΔE is less than 2.0 even when the M / S gap is 0.35 mm.

Therefore, from the graphs of FIG. 8, FIG. 9, and FIG.
(5). A narrower M / S gap is advantageous (6). It can be seen that the ghost property ΔE is less than 2.0 when Vmag is about 420 V or less.

Therefore, from the above-described table of FIG. 3 and the graphs of FIGS. 4 to 6 and the tables of FIG. 7 and the graphs of FIGS. It turns out that it is effective to do like (a)-(d).
(A). Narrow the M / S gap as long as no leaks occur (b). DC toner layer forming bias Vmag is set to about 420 V or less as much as possible (c). Reduce the potential difference ΔV between Vmag and Vslv as much as possible (d). However, it is necessary to select Vslv so that the amount of solid toner on the photosensitive drum 10 is optimal.

  On the other hand, as described with reference to the graph of FIG. 16, the temperature and humidity in the image forming apparatus are influenced by the environment when the power is turned on, and the internal temperature rises due to heat from the fixing device and the motor as time passes and the humidity increases. It will decline. In this case, the charge amount of the toner varies depending on the environment in which the image forming apparatus is placed and particularly the temperature and humidity in the housing. The graph of FIG. 16 is a graph plotting how the toner amount on the developing roller changes with the environmental temperature / humidity, but the graph of FIG. 11 shows the environmental temperature / humidity on the developing roller 11. 6 is a graph showing how the charge amount of the toner is affected.

  In the graph of FIG. 11, the horizontal axis is the DC toner layer forming bias voltage (unit: V) to the magnetic roller 15, the vertical axis is the toner charge amount (unit: μC / g) on the developing roller 11, and the solid line ◆ Is the toner charge amount on the left side (DLP left side) of the developing device in a normal temperature and normal humidity (N / N) environment, ■ is the toner charge amount on the right side of the developing device (DLP right side), and ◆ on the broken line is low temperature and low humidity (L / L) The toner charge amount on the left side of the developing device (DLP left side) in the environment, ■ is the toner charge amount on the right side of the developing device (DLP right side), and ◆ on the alternate long and short dash line is the left side of the developing device in the high temperature / high humidity (H / H) environment (left side of DLP) ) Is the toner charge amount, and ■ is the toner charge amount on the right side of the developing device (DLP right side). ΔV is 220V in high temperature and high humidity (H / H) environment, 250V in normal temperature and normal humidity (N / N) environment, and 280V in low temperature and low humidity (L / L) environment. The DC toner layer forming bias voltage to be applied to the magnetic roller 15 is changed by controlling the voltage so as to be the adjusted voltage.

  As can be seen from the graph of FIG. 11, in the high temperature / high humidity (H / H) environment indicated by the alternate long and short dash line, the toner charge amount on the developing roller 11 is much higher than that in the normal temperature / normal humidity (N / N) environment. It is decreasing and increasing in a low temperature and low humidity (L / L) environment.

Further, the graph of FIG. 12 shown as “toner amount on the developing roller 11” is a graph in which it is examined how the toner amount on the developing roller 11 changes depending on the charge amount of the toner 16 shown in FIG. In other words, when the toner charge amount in the developer changes due to environmental factors such as temperature and humidity, the toner amount on the developing roller 11 changes accordingly. In the graph of FIG. 12, the horizontal axis represents the DC developing bias voltage (Vslv, unit: V) to the developing roller 11, the vertical axis represents the toner amount (unit: mg / cm ² ) on the developing roller 11, and ◆ represents the toner The charge amount Q / M is a toner amount of 9.4 μC / g, the solid square is also a toner amount of 16.2 μC / g, and the solid triangle is a toner amount of 26.8 μC / g. In each case, the DC developing bias Vslv for the developing roller 11 is changed while the potential difference ΔV is kept constant at 200 V in accordance with the change in the DC toner layer forming bias, but the toner charging is performed regardless of the value of Vslv. It can be seen that the toner amount on the developing roller 11 decreases as the amount increases. In particular, when the toner charge amount increases in a low temperature / low humidity (L / L) environment, the toner layer forming ability of the magnetic roller 15 decreases and the toner amount on the developing roller 11 decreases.

FIG. 13 is a graph showing how the amount of toner on the photosensitive drum 10 changes according to the charge amount of the toner 16 that varies with the environmental temperature and humidity. In the graph of FIG. 13, the horizontal axis represents the DC developing bias voltage (Vslv, unit: V) to the developing roller 11, and the vertical axis represents the amount of toner (unit: mg / cm ² ) on the photosensitive drum 10. Is the toner amount when the toner charge amount is Q / M 9.4 μC / g, ■ is the toner amount when the same is 16.2 μC / g, and ▲ is the toner amount when the same is 26.8 μC / g. The graph plots how the amount of toner on the photosensitive drum 10 changes when Vslv is changed under a constant condition of 200V.

  As can be seen from the graph of FIG. 13, when the toner charge amount Q / M of ▲ is as high as 26.8 μC / g, even if the value of the DC developing bias voltage Vslv to the developing roller 11 is increased, the flying to the photosensitive drum 10 is performed. The amount of toner decreases, and the toner increase rate on the photosensitive drum 10 is very small at 180 V or higher. As a result, although not shown in the figure, a decrease in image density and uneven image density occurred. This is because the absolute amount of toner 16 on the developing roller 11 is insufficient.

  This is shown in the graph of FIG. 14 in which the development efficiency on the photosensitive drum 10 is changed according to the charge amount of the toner 16, and the horizontal axis indicates the DC development bias voltage to the development roller 11. (Vslv, unit: V), the vertical axis represents the development efficiency (unit:%) on the photosensitive drum 10, ♦ is the development efficiency when the toner charge amount Q / M is 9.4 μC / g, and ■ is When the DC development bias Vslv is changed under the condition that the developing efficiency is 16.2 μC / g and the potential difference ΔV is 200 V at the developing efficiency when ▲ is 26.8 μC / g, respectively, it is transferred onto the photosensitive drum 10. This plots how the toner flight efficiency changes.

  As can be seen from the graph of FIG. 14, the line plotted with the highest ▲ of the toner charge amount Q / M of 26.8 μC / g shows that the development efficiency rapidly increases to about 180 V of the DC development bias voltage Vslv. After that, although the rate of increase has slowed, it has continued to increase and finally increased to nearly 100%. That is, the toner having the highest toner charge amount of 26.8 μC / g has very good development efficiency, but as shown in the graph of FIG. 13, the toner on the photosensitive drum 10 is increased even if the DC development bias voltage Vslv is increased. The amount does not increase, image density is lowered, and image density unevenness occurs. This is because the absolute amount of the toner 12 on the developing roller 11 is insufficient, and when the toner layer amount on the developing roller 11 is thin as described above, a decrease in image density and uneven image density appear. is there.

  As the toner charge amount changes with temperature and humidity in this way, the toner amount on the developing roller 11 and the toner amount on the photosensitive drum 10 decrease or increase, but in the graph of FIG. As can be seen, by making the potential difference ΔV between the DC toner layer forming bias voltage 19 applied to the magnetic roller 15 and the DC developing bias voltage 13 applied to the developing roller 11 constant, the amount of toner on the developing roller 11 is reduced. It can be made substantially constant. Therefore, the toner amount on the developing roller 11 can be used in a high temperature / high humidity (H / H) environment, a normal temperature / normal humidity (N / N) environment, and a low temperature / low humidity (L / L) environment. If the required amount of conditions is obtained, the toner amount on the developing roller 11 can always be controlled to an appropriate amount even if the toner charge amount changes due to environmental conditions or the like, and the image density is excessive or fogged, and the image density is lowered. And image density unevenness can be prevented.

That is, as understood from the graphs of FIGS. 4 to 6 and FIGS. 8 to 10,
(A). Narrow the M / S gap as long as no leaks occur (b). DC toner layer forming bias Vmag is set to about 420 V or less as much as possible (c). Reduce the potential difference ΔV between Vmag and Vslv as much as possible (d). However, it is necessary to select Vslv so that the amount of solid toner on the photoconductive drum 10 is optimal, but as can be seen from the graph of FIG. 11, the charge amount of the toner on the developing roller 11 varies with the environmental temperature and humidity, and accordingly. As shown in FIG. 13, the amount of toner on the photosensitive drum 10 changes.

  Therefore, at the time of the above-described layer thickness calibration, the scan voltage (Vslv) is set to a voltage that causes all of the toner on the developing roller 12 to fly to the photosensitive drum 10 in any environment, for example, 300 V, and the DC developing bias voltage and the DC It is considered effective to determine the potential difference ΔV of the toner layer forming bias voltage. When the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage is determined in this way, the DC toner layer forming bias voltage and the DC developing bias are maintained while maintaining the potential difference ΔV determined by the layer thickness calibration. In order to change the voltage and to select Vslv as described in (d) above so that the amount of solid toner on the photosensitive drum 10 is optimal, a toner layer thickness detection pattern is formed again to measure the image density. Perform bias calibration. The DC toner layer forming bias voltage is a voltage that makes the color difference (ΔE) between the half portion and the ghost history portion of the toner layer thickness detection pattern shown in FIG. 10 equal to or less than a predetermined value (2.0 or less in this example). With care, the DC developing bias voltage (Vslv) at which the toner amount on the photosensitive drum 10 becomes a predetermined toner amount may be selected with reference to the graph shown in FIG.

  In this way, the toner layer 12 on the developing roller 11 is formed with the DC toner layer forming bias voltage and the DC developing bias voltage determined by the layer thickness calibration and the bias calibration, and the electrostatic latent image on the photosensitive drum 10 is formed. Can eliminate selective development, ghosting, etc. caused by variations in toner charge amount or toner layer thickness caused by variations in MS gap, etc., and high-quality image formation can be achieved over a long period of time. A developing method and apparatus in an image forming apparatus can be obtained.

  Returning to FIG. 2 again, in order to carry out the above, in the present invention, first, a voltage for causing all the toner on the developing roller 12 to fly to the photosensitive drum 10 is applied to the storage device 25 shown in FIG. Remember me. As described above, when the layer thickness calibration mode is performed, the development control device 24 reads the DC development bias voltage that causes all the toner on the development roller 12 stored in the storage device 25 to fly to the photosensitive drum 10, The developing roller bias power supply control device 22 is instructed to set the DC developing bias voltage applied to the developing roller 11 to the read voltage. Next, the magnetic roller bias power supply controller 23 is instructed to change the DC toner layer forming bias voltage, form a toner layer thickness detection pattern, and read it by the toner density sensor 27. The read result is the target image density. Judge whether there is. If it is not the target image density, the above-described routine of changing the DC toner layer forming bias voltage, forming the toner layer thickness detection pattern, and measuring the image density is performed until the target image density is reached. A potential difference ΔV from the DC toner layer forming bias voltage is determined.

  When the potential difference ΔV that sets the toner layer on the developing roller 11 to a predetermined thickness is determined in this way, the development control device 24 then maintains the potential difference ΔV while further maintaining the value of the DC toner layer forming bias voltage Vmag. Is directed to the magnetic roller bias power supply control device 23 and the developing roller bias power supply control device 22 while taking care that the color difference ΔE is, for example, 2.0 or less, and the DC toner layer forming bias voltage and the DC developing bias voltage are instructed. To change. As in the layer thickness calibration mode, a toner layer thickness detection pattern is formed and read by the toner density sensor 27, and it is determined whether or not the read result is the target image density. Here, when the target image density is not reached, the above-described DC toner layer forming bias voltage and DC developing bias voltage are further changed while maintaining the potential difference ΔV to form the toner layer thickness detection pattern and measure the image density. The DC developing bias voltage and the DC toner layer forming bias voltage are determined.

  When the DC toner layer forming bias voltage and the DC developing bias voltage are thus determined in the layer thickness calibration mode and the bias calibration mode, the developing control device 24 controls the developing roller bias power supply so that these voltages are set. The apparatus 22 and the magnetic roller bias power supply controller 23 are instructed to form the toner layer 12 on the developing roller 11 with the respective voltages, and the electrostatic latent image on the photosensitive drum 10 is developed.

The graph of FIG. 15 shows the result of controlling the potential difference ΔV in this way. In the graph of FIG. 15, the horizontal axis represents the DC toner thin layer forming bias Vmag, the vertical axis represents the amount of toner on the developing roller 11 (unit: mg / cm ² ), and the solid line represents the normal temperature / normal humidity (N / N) environment. Is the toner amount on the left side of the developing device (DLP left side), ■ is the toner amount on the right side of the developing device (DLP right side), and the broken line is the toner on the left side of the developing device (DLP left side) in a low temperature / low humidity (L / L) environment , Is the amount of toner on the right side of the developing device (DLP right side), the dashed line is the amount of toner on the left side of the developing device (DLP left side) in a high temperature / high humidity (H / H) environment, and ■ is the right side of the developing device (DLP right side) ), The potential difference ΔV is 220V for a high temperature / high humidity (H / H) environment, 250V for a normal temperature / normal humidity (N / N) environment, and a low temperature / low humidity (L / L) environment. Is 280V.

As apparent from the graph of FIG. 15, the potential difference ΔV corresponds to each of the high temperature / high humidity (H / H) environment, the normal temperature / normal humidity (N / N) environment, and the low temperature / low humidity (L / L) environment. Thus, the toner amount on the developing roller 11 can be kept constant at approximately 0.60 g / cm ² . That is, by doing so, the toner layer thickness on the developing roller 11 can always be constant even if the toner charge amount changes depending on the temperature and humidity in the image forming apparatus. The potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage that realizes the layer thickness of the toner is determined, and the toner layer thickness variation caused by the variation in the toner charge amount, the MS gap variation, etc. is eliminated. Development in the image forming apparatus in which the color difference ΔE between the half portion and the ghost history portion in the layer thickness detection pattern is set to a predetermined value or less so that the toner layer thickness on the developing roller is always constant and the ghost is not caused. It can be a method and apparatus.

  According to the present invention, there is provided an image forming apparatus capable of forming a high-quality image over a long period of time without causing a ghost at any environmental temperature and humidity and without causing a decrease in image density or image density unevenness. be able to.

1 is a schematic configuration diagram of a touch-down developing device for performing a developing method in an image forming apparatus according to the present invention. 1 is a schematic diagram of an embodiment of an image forming apparatus that performs a developing method according to the present invention. In order to consider under what conditions selective development and ghost images occur and how to prevent them, it is necessary to develop the toner layer amount on the developing roller 11 and the electrostatic latent image on the photosensitive drum 10. Development representing the relationship between the amount of toner and the bias applied to the developing roller 11 and the magnetic roller 15 and how much toner on the developing roller 11 is used for developing the electrostatic latent image on the photosensitive drum 10 It is the table | surface which summarized the result of having experimented and investigated efficiency. How the toner amount on the developing roller changes due to the potential difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller 11 and the DC toner layer forming bias Vmag (DC) supplied to the magnetic roller 15. It is the graph which investigated. How the toner amount on the photosensitive drum 10 is changed by the potential difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller 11 and the DC toner layer forming bias Vmag (DC) supplied to the magnetic roller 15. It is the graph which investigated whether it changed. What is the development efficiency on the photosensitive drum 10 by the potential difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller 11 and the DC toner layer forming bias Vmag (DC) supplied to the magnetic roller 15. It is the graph which investigated whether it changed to. When the gap (M / S gap) between the magnetic roller 15 and the developing roller 11 is changed and the DC toner layer forming bias Vmag is changed, the solid image density (unit: ID) and the image density of 25% halftone (unit: ID) Is a table summarizing the results of examining the correlation between the DC toner layer forming bias Vmag and the “ghost property ΔE”. 6 is a graph plotting the results of examining how the solid ID changes when the distance (M / S gap) between the magnetic roller 15 and the developing roller 11 is changed and the DC toner layer forming bias Vmag is changed. . A graph plotting the results of examining how the 25% half ID changes when the distance (M / S gap) between the magnetic roller 15 and the developing roller 11 is changed and the DC toner layer forming bias Vmag is changed. It is. The results of examining how the “ghost property ΔE” changes when the distance (M / S gap) between the magnetic roller 15 and the developing roller 11 is changed and the DC toner layer forming bias Vmag is changed are plotted. It is a graph. FIG. 7 is a graph showing how the toner charge amount on the developing roller changes when the DC toner layer forming bias Vmag is changed while the potential difference ΔV is constant and the charge amount of the toner 16 is changed by the environmental temperature and humidity. . 6 is a graph showing how the toner amount on the developing roller changes according to the charge amount of the toner. 6 is a graph showing how the amount of toner on the photosensitive drum 10 changes depending on the charge amount of the toner 16; 6 is a graph showing how the development efficiency on the photosensitive drum 10 changes depending on the charge amount of the toner 16. The horizontal axis is the DC toner layer forming bias Vmag, the vertical axis is the toner amount on the developing roller 11 (unit: mg / cm ² ), and the toner amount on the developing roller 11 becomes substantially constant by the potential difference ΔV corresponding to each environment. It is the graph which showed that. The horizontal axis represents the DC toner layer forming bias voltage (Vmag, unit: V) to the magnetic roller, and the vertical axis represents the toner amount (unit: mg / cm ² ) on the developing roller. 6 is a graph plotting the amount of toner on the developing roller that has changed as a result of the change.

Explanation of symbols

10 Photosensitive drum 11 Developing roller 12 Toner layer 13 DC developing bias power supply (DC1)
14 AC development bias power supply (AC1)
15 Magnetic roller 16 Non-magnetic toner 17 Carrier 18 Magnetic brush 19 DC toner layer forming bias power source (DC2)
20 AC toner layer forming bias power supply (AC2)
21 Bone Cutting Blade 22 Developing Roller Bias Power Supply Control Device 23 Magnetic Roller Bias Power Supply Control Device 24 Development Control Device 25 Storage Device 26 Temperature / Humidity Sensor 27 Toner Concentration Sensor

Claims (4)

A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller containing a magnet and enclosing a toner layer forming bias in which alternating current is superimposed on direct current, and alternating current is superimposed on direct current from the magnetic brush. In the developing method in the image forming apparatus, after the toner layer is formed on the developing roller to which the developing bias is applied, the toner is ejected to the electrostatic latent image formed on the photosensitive member by the electrophotographic method.
The DC developing bias voltage at the developing bias is fixed and the DC toner layer forming bias voltage at the toner layer forming bias is changed to form a toner layer thickness detection pattern consisting of a half density pattern for image density adjustment, thereby adjusting the image density. A layer thickness calibration is performed to determine a potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage so that the measurement result becomes a target image density, and to set the toner layer thickness on the developing roller to the target toner layer thickness. And
While maintaining the potential difference ΔV determined by the layer thickness calibration, the DC toner layer formation bias voltage and the DC development bias voltage are changed, the toner layer thickness detection pattern is formed, and the image density is measured. Determining a DC development bias voltage with the measurement result as a target image density, and performing a bias calibration with a toner amount flying from the developing roller to the photoconductor as a target toner amount;
The electrostatic latent image is developed by forming a toner layer on the developing roller with the DC toner layer forming bias voltage and the DC developing bias voltage determined by the layer thickness calibration and the bias calibration. A developing method in an image forming apparatus.   2. The developing method in an image forming apparatus according to claim 1, wherein a DC developing bias voltage to be fixed in the layer thickness calibration is selected as a voltage that causes all of the toner on the developing roller to fly to the photosensitive member. A toner layer forming bias that includes a magnet and superimposing alternating current on a direct current is applied, a magnetic roller that holds a magnetic brush of a two-component developer composed of toner and a carrier, and a developing bias that is superimposed on direct current is applied. In a developing device in an image forming apparatus, a toner layer is formed by the magnetic brush, and a developing roller that causes the toner layer to fly and develop an electrostatic latent image formed on a photoreceptor by an electrophotographic method. ,
The image forming apparatus measures the image density of a toner layer thickness detection pattern formed on the photoconductor or formed of a half-density pattern for image density adjustment formed on the photoconductor and transferred to the transfer body. A toner density sensor;
The DC developing bias voltage at the developing bias is fixed and the DC toner layer forming bias voltage at the toner layer forming bias is changed to form a toner layer thickness detection pattern comprising a half density pattern for image density adjustment, thereby forming the toner density The image density is measured by a sensor, the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage with the measured image density as the target image density is determined, and the toner layer thickness on the developing roller is determined. Layer thickness calibration mode to target toner layer thickness,
The potential difference ΔV determined in the layer thickness calibration mode is maintained, the DC toner layer forming bias voltage and the DC developing bias voltage are changed, and the formed toner layer thickness detection pattern density is applied to the toner density sensor. A DC calibration bias voltage having a target image density as a target image density is determined, a bias calibration mode in which a toner amount flying from the developing roller to the photosensitive member is a target toner amount, and the DC toner is A toner layer on the developing roller is formed using the layer forming bias voltage and the DC developing bias voltage determined in the layer thickness calibration mode and the bias calibration mode, and the electrostatic latent image is developed. And a developing control device for developing the image forming apparatus.   A DC storage bias voltage that is fixed in the layer thickness calibration mode; and a storage device that stores all the toner on the developing roller as a voltage that causes the toner to fly to the photoconductor, and the development control device includes the layer thickness calibration In the mode, the fixed DC developing bias voltage is read from the storage device, the DC developing bias voltage is fixed to the read voltage, the DC toner layer forming bias voltage is changed, and the potential difference ΔV is determined. A developing device in the image forming apparatus according to claim 3.

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