JP2010128352A - Development method and device in image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development method and device in an image forming apparatus using a touchdown development system, controlling the toner quantity on a developing roller to be normally within a proper amount, preventing decrease of image density or image density unevenness, and obtaining high-quality image for a long period of time even if the toner charging quantity changes according to environmental conditions. <P>SOLUTION: A DC development bias voltage is changed with maintaining constant the potential difference ΔV between the DC development bias voltage and a toner layer forming DC bias voltage. Calibration is performed using as a target image density a toner layer thickness detecting pattern density consisting of an image density adjusting half density pattern formed on a photoreceptor, or formed on the photoreceptor and transferred to a transfer body. The toner layer is formed on the developing roller by the DC development bias voltage and the potential difference ΔV at that time if the target image density is obtained and by the DC development bias voltage and the potential difference ΔV when obtaining the target image density after re-performing the calibration by changing the potential difference ΔV if the target density is notobtained. <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.

  In this touch-down development method, it is important to always keep the toner layer amount on the developing roller constant in order to maintain stable image quality over a long period of time. That is, if the amount of toner layer on the developing roller cannot be kept constant, the amount of toner flying to the photoconductor with the same developing bias differs, and an image with a constant density cannot be obtained.

  For this reason, the applicant of the present invention includes an image density detection unit that detects an image density of a toner image formed from a document having a predetermined image density pattern in Patent Document 1, and the image density is a target image density based on the detection result of the image density. An electrophotographic image forming apparatus has been proposed in which the DC voltage applied to the magnetic roll (magnetic roller) and the developing roll (developing roller) is controlled so that the image density is maintained at a constant target value over a long period of time.

JP 2007-121940 A

  However, in the developing method of the image forming apparatus disclosed in Patent Document 1, the DC voltage applied to the magnetic roller and the developing roller is controlled so that the image density becomes the target image density. For example, as shown in FIG. Thus, when the charge amount of the toner changes depending on the environmental temperature and humidity, the desired image density cannot be obtained even if the DC voltage applied to the magnetic roller and the developing roller is simply controlled so that the image density becomes the target image density. There is a case.

  That is, 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 with time. In that case, the charge amount of the toner varies depending on the environment where the image forming apparatus is placed and particularly the temperature and humidity in the housing, and as shown in the graph of FIG. Also changes.

The horizontal axis in the graph of FIG. 9 is the DC toner thin layer forming bias voltage (Vmag, unit: V) applied to the magnetic roller, and the vertical axis is the toner amount (unit: mg / cm ² ) on the developing roller, which is a solid line. Indicates the amount of toner at the position corresponding to the left side of the developing device (DLP left side), ■ indicates the amount of toner at the position corresponding to the right side of the developing device (DLP right side), and the broken line indicates the low temperature / normal humidity (N / N) environment. In a low-humidity (L / L) environment, a toner layer is formed on the developing roller with ◆ where the toner amount is at the position corresponding to the left side of the developing device (DLP left side), and ■ is the toner amount at the position corresponding to the right side of the developing device (DLP right side). Therefore, a potential difference ΔV (Vmag−Vslv) between a DC toner thin layer forming bias voltage Vmag applied to the magnetic roller and a DC developing bias voltage (Vslv, unit: V) applied to the developing roller is 25 This is a case where the DC toner thin layer forming bias voltage (Vmag) applied to the magnetic roller is changed by controlling to be constant at 0V.

  As can be seen from the graph of FIG. 9, 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 thin layer forming bias voltage (Vmag) to the magnetic roller is low. However, as the direct current toner thin layer formation bias voltage Vmag is increased, the amount of toner on the developing roller in a normal temperature / normal humidity (N / N) environment decreases, and when the direct current toner thin layer formation bias voltage Vmag is around 470V, The difference from the normal humidity (N / N) environment is small.

  In this way, particularly in a low humidity environment, when the toner charge amount increases, the toner thin layer forming ability of the magnetic roller decreases, the toner thin layer amount decreases, and the absolute amount of toner becomes insufficient. In such a state, even if the value of the DC developing bias Vslv is increased and the flying efficiency of the toner from the developing roller to the photosensitive drum (jumping developing efficiency) is increased to near 100%, the amount of toner flying on the photosensitive drum Does not rise sufficiently and reaches a peak, resulting in a decrease in image density and uneven image density.

  Therefore, in the present invention, in a developing device using the touch-down development method, even if the toner charge amount changes due to environmental conditions or the like, the toner amount on the developing roller is controlled so as to be always an appropriate amount to reduce the image density. It is an object to provide a developing method and apparatus in an image forming apparatus that can prevent occurrence of image density unevenness and provide a high-quality image over a long period of time.

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 is changed while maintaining a constant potential difference ΔV between the DC developing bias voltage in the developing bias and the DC toner layer forming bias voltage in the toner layer forming bias, or formed on the photoconductor. Perform calibration using the pattern density for toner layer thickness detection consisting of the half density pattern for image density adjustment formed above and transferred to the transfer body as the target image density, and the DC development bias voltage can be changed in the calibration When the target image density is obtained within the range, the DC development bias voltage at that time and the potential difference ΔV. When the target image density is not obtained, the DC development bias voltage and the DC toner layer forming bias voltage The potential difference ΔV is changed, the calibration is performed again, and the target image darkness is changed. Forms a toner layer on the developing roller by the direct current developing bias voltage and the potential difference ΔV obtained, characterized in that to perform the development of the electrostatic latent image.

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. A developing roller in which a toner layer is formed by the magnetic brush and the toner is developed by causing the toner to fly from the toner layer to an electrostatic latent image formed on a photoreceptor by an electrophotographic method. In
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. While maintaining a constant potential difference ΔV between the toner density sensor and the DC developing bias voltage at the developing bias and the DC toner layer forming bias voltage at the toner layer forming bias, the DC developing bias voltage is changed to change the image density adjusting half. A toner layer thickness detection pattern consisting of a density pattern is formed, an image density is measured by the toner density sensor, and a calibration mode is performed in which the image density of the measurement result is a target image density. The target image density is obtained within the changeable range of the DC developing bias voltage. The DC developing bias voltage and the DC toner layer forming bias are obtained in a state where the target image density is not obtained with the DC developing bias voltage and the potential difference ΔV with the toner layer thickness detection pattern as the target image density. The calibration mode is re-executed by changing the potential difference ΔV with respect to the voltage, and a toner layer on the developing roller is formed with the DC development bias voltage at which the target image density is obtained and the potential difference ΔV to form the static voltage. And a development control device for developing the electrostatic latent image.

  As will be described later, when the potential difference ΔV is constant, the toner amount on the developing roller is substantially constant. However, as described above, when the toner charge amount changes depending on the environmental temperature and humidity, the toner amount on the developing roller also changes, resulting in image density reduction and image density unevenness. Therefore, if the target image density cannot be obtained even if the DC development bias voltage is changed within the changeable range and the calibration is performed while the potential difference ΔV is kept constant, the toner charge amount depends on the environmental temperature and humidity. Since there is a possibility that it has changed, by further changing the potential difference ΔV and performing calibration again, the toner amount on the developing roller can be made constant corresponding to the changed toner charge amount. When the target image density is obtained, if development is performed with the DC developing bias voltage at that time and the potential difference ΔV, image density reduction and image density unevenness do not occur corresponding to the changed toner charge amount, and the target density is obtained. The developing method can obtain an image having an image density.

  If the target image density is not obtained and the image density of the toner layer thickness detection pattern is thin at the upper limit of the changeable range of the DC development bias voltage, the potential difference ΔV is increased by a predetermined voltage, and the DC development is performed. When the image density of the toner layer thickness detection pattern is high at the lower limit of the changeable range of the bias voltage, the potential difference ΔV is lowered by a predetermined voltage and the recalibration is performed, so that the target image density cannot be obtained. In this state, the development control device raises the potential difference ΔV by a predetermined voltage when the image density of the toner layer thickness detection pattern is thin at the upper limit of the changeable range of the DC development bias voltage, and changes the DC development bias voltage. When the image density of the toner layer thickness detection pattern is high at the lower limit of the possible range, the potential difference ΔV is lowered by a predetermined voltage, Changing the position difference ΔV be configured to implement the calibration mode. As a result, even if the toner charge amount changes due to environmental conditions or the like, the potential difference ΔV is changed in response to the low or high image density thus obtained. Thus, it is possible to provide a developing method and apparatus in an image forming apparatus that can control the toner amount to be always an appropriate amount and can provide a high-quality image over a long period of time.

  As described above, the developing method and apparatus in the image forming apparatus according to the present invention allows the toner layer thickness on the developing roller to be always constant even when the toner charge amount changes due to environmental changes such as temperature and humidity. It is possible to provide a developing method and an apparatus in an image forming apparatus that can prevent a decrease and occurrence of uneven image density and can provide a high-quality image over a long period of time.

  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. Has been done. In the present invention, this calibration is performed by first changing the DC developing bias voltage while maintaining the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage constant to form a toner layer thickness detection pattern. The image density is measured, and the measurement result is set to the target image density.

  As a result of the calibration, when the target image density is obtained within the changeable range of the DC developing bias voltage, the DC developing bias voltage at which the target image density is obtained and the DC toner layer forming voltage determined by the potential difference ΔV are developed. The toner is applied to the roller and the magnetic roller, and a toner layer is formed on the developing roller to develop the electrostatic latent image on the photosensitive drum.

  On the other hand, if the target image density is not obtained within the changeable range of the DC development bias voltage as a result of calibration, the potential difference ΔV between the DC development bias voltage and the DC toner layer forming bias voltage is changed, and the calibration is performed again. Thus, a potential difference ΔV at which a target image density can be obtained is searched, a DC toner layer forming voltage determined by the DC developing bias voltage and the potential difference ΔV is applied to the developing roller and the magnetic roller, and a toner layer is formed on the developing roller to be photosensitive. The electrostatic latent image on the body drum is developed.

  In this case, the potential difference ΔV between the DC developing bias voltage and the DC toner layer forming bias voltage is increased by a predetermined voltage of about 20 V, for example, when the image density is low at the upper limit of the changeable range of the DC developing bias voltage. Similarly, when the image density is high at the lower limit of the changeable range of the bias voltage, the potential difference ΔV is lowered by a predetermined voltage of about 20V, for example. Then, a toner layer thickness detection pattern is formed by calibration using the changed potential difference ΔV, and the above-described change in potential difference ΔV is performed until the image density is measured and a potential difference ΔV at which the measurement result becomes the target image density is obtained. When the target image density is obtained, development is performed with the DC developing bias voltage and the DC toner layer forming bias voltage at that time. Note that the voltage 20V to be raised and lowered is an example, and it is obvious that the voltage is not limited to this value.

  This makes it possible to control the amount of toner on the developing roller to be always an appropriate amount even if the toner charge amount changes due to environmental conditions, etc., even though it is a very simple method. It is possible to provide a developing method and apparatus in an image forming apparatus that can provide a high-quality image.

  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. The developing roller 11 is formed with a toner layer 12 and is electrostatically formed on the photosensitive drum 10 by an electrophotographic method by a developing bias applied from a DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14. Development is performed by flying toner 16 onto the latent image. The magnetic roller 15 is formed of a nonmagnetic metal material in a cylindrical shape, has a rotatable sleeve in which a plurality of fixed magnets are disposed, and is a magnetic component of a two-component developer composed of a nonmagnetic toner 16 and a carrier 17. The brush 18 is formed, and the toner layer 12 is formed on the developing roller 11 by the toner layer forming bias applied from the DC toner layer forming bias power source (DC2) 19 and the AC toner layer forming bias power source (AC2) 20. The ear cutting blade 21 keeps the height of the magnetic brush 18 on the magnetic roller 15 constant.

  The developing roller bias power supply control device 22 controls the voltages of the DC developing bias power supply (DC1) 13 and the AC developing bias power supply (AC1) 14 of the developing roller 11. The magnetic roller bias power source controller 23 controls the DC toner layer forming bias power source (DC 2) 19 and the AC toner layer forming bias power source (AC 2) 20 of the magnetic roller 15. The development control device 24 gives a voltage instruction to the development roller bias power supply control device 22 and the magnetic roller bias power supply control device 23 to control the development device. The development control device 24 according to the present invention controls the developing roller bias power source control device 22 and the magnetic roller bias power source control device 23 as described above, and performs calibration so that the toner layer thickness on the developing roller 11 is a predetermined thickness. Has a routine to implement the mode.

  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 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 developability, it is important to define the particle size distribution. In general, 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. It is expressed with it. 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. If the average particle size exceeds 50 μm, the carrier stress increases and the toner density 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.

That is, as shown in the graph of FIG. 4 with “toner amount on the developing roller”, the toner amount of the toner layer formed on the developing roller is at least in the range of 20V to 180V of the DC developing bias Vslv. It corresponds to the potential difference ΔV between the developing bias voltage Vslv and the direct current toner thin layer formation bias voltage Vmag, and increases as the value of the potential difference ΔV increases. In FIG. 4, the horizontal axis is the DC developing bias Vslv (unit: V), the vertical axis is the toner amount (unit: mg / cm ² ) on the developing roller (SLV), and the line plotted with ◆ is the DC developing for developing roller When the potential difference ΔV between the bias voltage Vslv and the DC toner thin layer forming bias voltage Vmag for the magnetic roller is 400V, the line plotted with ■ is the same when 320V, and the line plotted with ▲ is the same when 240V.

However, as described above, when the charge amount of the toner changes with the environmental temperature and humidity, even if the potential difference ΔV between the DC developing bias voltage Vslv and the DC toner thin layer forming bias voltage Vmag is kept constant, the graph of FIG. As described above, the amount of toner on the developing roller changes. In the graph of FIG. 5, as in the case of FIG. 4, the horizontal axis represents the DC developing bias Vslv (unit: V), and the vertical axis represents the toner amount (unit: mg / cm ² ) on the developing roller (SLV). The line plotted with ♦ is when the toner charge amount Q / M is 9.4 μC / g, the line plotted with ■ is also 16.2 μC / g, the line plotted with ▲ is also 26.8 μC / g This is the case. The potential difference ΔV between the DC developing bias voltage Vslv and the DC toner thin layer forming bias voltage Vmag is constant at 200 V. However, as the toner charge amount increases, the toner amount on the developing roller decreases, particularly at low temperature and low humidity (L / L) When the toner charge amount increases in the environment, the toner layer forming ability of the magnetic roller 15 decreases, and the toner layer amount on the developing roller decreases.

When the toner charge amount changes as described above, the toner amount on the photosensitive drum also changes as shown in the graph of FIG. In the graph of FIG. 6, as in FIG. 5, the horizontal axis represents the DC developing bias Vslv (unit: V), the vertical axis represents the amount of toner on the photosensitive drum (unit: mg / cm ² ), and ◆ The plotted line is for ♦ when the toner charge amount Q / M is 9.4 μC / g, the line plotted for ■ is also 16.2 μC / g, the line plotted with ▲ is also 26.8 μC / g In this case, Vslv is changed under the condition that the potential difference ΔV is constant at 200V.

  As can be seen from the graph of FIG. 6, when the toner charge amount Q / M of ▲ is as high as 26.8 μC / g, the flying toner to the photosensitive drum 10 even if the value of the DC developing bias voltage Vslv to the developing roller is increased. The amount of toner decreases, and at 180 V or higher, the toner increase rate on the photosensitive drum 10 is very small. 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 is insufficient.

  This is shown in the graph of FIG. 7 in which the development efficiency on the photosensitive drum 10 is changed depending on the charge amount of the toner. The black dot indicates the toner charge amount Q / M is 9.4 μC / The development efficiency in the case of g, the development efficiency in the case where ■ is 16.2 μC / g, and the development efficiency in the case where ▲ is 26.8 μC / g, and the DC development bias Vslv is changed under the condition that the potential difference ΔV is constant at 200V. A plot of the change in the efficiency of toner flying onto the photosensitive drum is shown.

  As can be seen from the graph of FIG. 7, the line plotting the mark ▲ where the toner charge amount Q / M is the highest, 26.8 μC / g, shows that the development efficiency increases rapidly 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. However, as seen in the graph of FIG. 6, 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 toner 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. .

  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 thin layer forming bias voltage Vmag applied to the magnetic roller 15 and the DC developing bias voltage Vslv applied to the developing roller 11 constant, the amount of toner on the developing roller 11 is reduced. Can be constant.

  Therefore, in the present invention, the toner amount of the toner layer formed on the developing roller 10 described in the graph of “toner amount on the developing roller” in FIG. 4 is changed to the DC developing bias voltage Vslv and the DC toner thin layer forming bias voltage Vmag. In the graph shown as “toner amount on the drum” in FIG. 8 when the charge amount of the toner changes by utilizing the fact that the constant amount increases as the value of the potential difference ΔV increases. As shown, the amount of toner on the developing roller 10 is kept constant by changing the potential difference ΔV.

In the graph of FIG. 8, the horizontal axis is the DC developing bias Vslv (unit: V), the vertical axis is the toner amount (unit: mg / cm ² ) on the photosensitive drum 10, and the line plotted with ◆ is for the developing roller When the potential difference ΔV between the DC developing bias voltage Vslv and the DC toner thin layer forming bias voltage Vmag for the magnetic roller is 200V, the line plotted with ■ is the same when 220V, and the line plotted with ▲ is the same when 240V.

  As can be seen from the graph of FIG. 8, the toner amount on the photosensitive drum 10 is increased by increasing the potential difference ΔV to 200 V, 220 V, and 240 V, and the rate of increase increases as the potential difference ΔV increases. It is linear in proportion to the bias voltage Vslv. When ΔV is small, the rate of increase after the DC development bias voltage Vslv is lower. That is, as described with reference to FIGS. 5 and 6, when the toner charge amount increases and the toner amount on the developing roller 11 and the toner amount flying onto the photosensitive drum 10 decrease, as shown in FIG. By increasing the potential difference ΔV, it is possible to compensate for the decrease in the amount of toner flying on the photosensitive drum 10.

  Therefore, in the present invention, as described in the outline of the present invention, first, the potential difference ΔV between the DC developing bias voltage Vslv at the developing bias and the DC toner layer forming bias voltage Vmag at the toner layer forming bias is kept constant. On the other hand, the DC developing bias voltage Vslv is changed to form an image density adjusting half density pattern formed on the photosensitive drum 10 or transferred to a transfer body (not shown) formed on the photosensitive drum 10. When calibration is performed using the toner layer thickness detection pattern density as the target image density, and the target image density is obtained within the changeable range of the DC developing bias voltage Vslv as a result of the calibration, the target image density is obtained. DC toner layer forming voltage determined by the developed DC developing bias voltage Vslv and the potential difference ΔV A pressure Vmag is applied to the developing roller 11 and the magnetic roller 15 to form a toner layer 12 on the developing roller 11 to develop the electrostatic latent image on the photosensitive drum 10.

  However, when the target image density is not obtained within the changeable range of the DC developing bias voltage Vslv by this calibration, the potential difference ΔV between the DC developing bias voltage Vslv and the DC toner layer forming bias voltage Vmag is changed to perform calibration. The potential difference ΔV at which the target image density can be obtained by searching again is searched, the DC developing bias voltage Vslv and the DC toner layer forming voltage Vmag determined by the potential difference ΔV are applied to the developing roller 11 and the magnetic roller 15, and the developing roller 11 A toner layer is formed thereon to develop the electrostatic latent image on the photosensitive drum 10.

  In this case, the potential difference ΔV between the DC developing bias voltage Vslv and the DC toner layer forming bias voltage Vmag is the upper limit of the changeable range of the DC developing bias voltage Vslv. If the image density is low, the potential difference ΔV is, for example, about 20V as described above. When the image density is high at the lower limit of the changeable range of the DC developing bias voltage Vslv, the potential difference ΔV is lowered by a predetermined voltage of about 20V, for example. Then, a toner layer thickness detection pattern is formed by calibration using the changed potential difference ΔV, and the above-described change in potential difference ΔV is performed until the image density is measured and a potential difference ΔV at which the measurement result becomes the target image density is obtained. When the target image density is obtained, development is performed with the DC developing bias voltage Vslv and the DC toner layer forming bias voltage Vmag at that time.

  This makes it possible to control the amount of toner on the developing roller 11 to be always an appropriate amount even if the toner charge amount changes due to environmental conditions or the like, although it is a very simple method. It is possible to provide a developing method and apparatus in an image forming apparatus that can provide a high-quality image over a wide range.

  FIG. 3 is a flowchart of the developing method according to the present invention, which is carried out based on such a concept. The developing method in the image forming apparatus of the present invention will be described below with reference to the flowchart shown in FIG. 3 and FIG.

  When the process starts in step S30, the development control device 24 in FIG. 1 instructs the development roller bias power supply control device 22 and the magnetic roller bias power supply control device 23 in step S32, and the DC development bias voltage Vslv at the current development bias is set. The DC developing bias voltage Vslv is changed while maintaining the potential difference ΔV with respect to the DC toner layer forming bias voltage Vmag in the toner layer forming bias, and is formed on the photosensitive drum 10 or on the photosensitive drum 10. Calibration is performed in which the toner density sensor 25 reads the toner layer thickness detection pattern formed of the half density pattern for image density adjustment, which is formed and transferred to a transfer body (not shown).

  In the next step S34, the development control device 24 determines whether or not the target image density is obtained within the changeable range of the DC development bias voltage Vslv as a result of the calibration, and if it is obtained, the process proceeds to step S44. The developing roller bias power supply controller 22, the magnetic roller bias so as to apply to the developing roller 11 and the magnetic roller 15 the DC developing bias voltage Vslv at which the target image density is obtained and the DC toner layer forming voltage Vmag determined by the potential difference ΔV. The power controller 23 is instructed to form the toner layer 12 on the developing roller 11 and develop the electrostatic latent image on the photosensitive drum 10 in step S46, and the process ends in step S48.

  On the other hand, if it is determined in step S34 that the target image density has not been obtained, the development control device 24 next determines in step S36 whether or not the image density is low. If the image density is low, the process proceeds to step S38. Proceed to step S40. When the process proceeds to step S38, the development control device 24 increases the potential difference ΔV between the DC development bias voltage Vslv at the current development bias and the DC toner layer formation bias voltage Vmag at the toner layer formation bias by, for example, 20V. When the process proceeds to step S40, the developing roller bias power supply control device 22 and the magnetic roller bias power supply control device 23 are instructed to reduce the potential difference ΔV by, for example, 20V, and the calibration is restarted in the same manner as described above at step S42. carry out.

  After that, the process returns to step S34, and the development control device 24 determines whether or not the target image density is obtained within the changeable range of the DC development bias voltage Vslv as a result of the recalibration. In step S44, the developing roller bias power supply control is performed so that the DC developing bias voltage Vslv at which the target image density is obtained and the DC toner layer forming voltage Vmag determined by the potential difference ΔV are applied to the developing roller 11 and the magnetic roller 15. 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 and develop the electrostatic latent image on the photosensitive drum 10. If the target image density cannot be obtained even by this recalibration, the above processing is repeated until the target image density is obtained.

  In this way, as described several times, the amount of toner on the developing roller 11 is always maintained even if the toner charge amount changes due to environmental conditions or the like, despite the very simple method. It is possible to provide a developing method and apparatus in an image forming apparatus that can be controlled to an appropriate amount and can provide a high-quality image over a long period of time.

  According to the present invention, it is possible to control the amount of toner on the developing roller 11 to be always an appropriate amount at any environmental temperature and humidity, and to provide a developing method in an image forming apparatus capable of providing a high-quality image over a long period of time. An apparatus can be provided.

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. It is a flowchart of the image development method which becomes this invention. When the DC developing bias Vslv is changed by changing the potential difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller and the DC toner layer forming bias Vmag (DC) supplied to the magnetic roller to be constant. 6 is a graph showing how the amount of toner on the developing roller changes. 6 is a graph showing how the toner amount on the developing roller changes when the DC developing bias Vslv is changed according to the toner charge amount. 6 is a graph showing how the toner amount on the photosensitive drum changes when the DC developing bias Vslv is changed according to the toner charge amount. 6 is a graph showing how the ratio (jumping efficiency) of the amount of toner flying onto the photosensitive drum changes when the DC developing bias Vslv is changed according to the toner charge amount. When the DC developing bias Vslv is changed by changing the potential difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller and the DC toner layer forming bias Vmag (DC) supplied to the magnetic roller to be constant. 6 is a graph showing how the amount of toner on the photosensitive drum changes. 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 thin layer forming bias power source (DC2)
20 AC toner thin 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 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 is changed while maintaining a constant potential difference ΔV between the DC developing bias voltage in the developing bias and the DC toner layer forming bias voltage in the toner layer forming bias, or formed on the photoconductor. Perform calibration using the pattern density for toner layer thickness detection consisting of the half density pattern for image density adjustment formed above and transferred to the transfer body as the target image density, and the DC development bias voltage can be changed in the calibration When the target image density is obtained within the range, the DC development bias voltage at that time and the potential difference ΔV. When the target image density is not obtained, the DC development bias voltage and the DC toner layer forming bias voltage The potential difference ΔV is changed, the calibration is performed again, and the target image darkness is changed. Developing method in an image forming apparatus wherein the toner layer on the developing roller is formed to perform the development of the electrostatic latent image by the electric potential difference ΔV between the direct current developing bias voltage obtained is.   When the target image density is not obtained, the potential difference ΔV is increased by a predetermined voltage when the image density of the toner layer thickness detection pattern is thin at the upper limit of the changeable range of the DC development bias voltage, and the DC development bias voltage is increased. 2. The image formation according to claim 1, wherein when the image density of the toner layer thickness detection pattern is high at a lower limit of the changeable range, the potential difference ΔV is lowered by a predetermined voltage and the recalibration is performed. Development method in the apparatus. 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. A developing roller in which a toner layer is formed by the magnetic brush and the toner is developed by causing the toner to fly from the toner layer to an electrostatic latent image formed on a photoreceptor by an electrophotographic method. In
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. While maintaining a constant potential difference ΔV between the toner density sensor and the DC developing bias voltage at the developing bias and the DC toner layer forming bias voltage at the toner layer forming bias, the DC developing bias voltage is changed to change the image density adjusting half. A toner layer thickness detection pattern consisting of a density pattern is formed, an image density is measured by the toner density sensor, and a calibration mode is performed in which the image density of the measurement result is a target image density. The target image density is obtained within the changeable range of the DC developing bias voltage. The DC developing bias voltage and the DC toner layer forming bias are obtained in a state where the target image density is not obtained with the DC developing bias voltage and the potential difference ΔV with the toner layer thickness detection pattern as the target image density. The calibration mode is re-executed by changing the potential difference ΔV with respect to the voltage, and a toner layer on the developing roller is formed with the DC development bias voltage at which the target image density is obtained and the potential difference ΔV to form the static voltage. A developing control device for developing an electrostatic latent image; and a developing device in the image forming apparatus.   In a state where the target image density is not obtained, the development control device increases the potential difference ΔV by a predetermined voltage when the image density of the toner layer thickness detection pattern is low at the upper limit of the changeable range of the DC development bias voltage. When the image density of the toner layer thickness detection pattern is high at the lower limit of the changeable range of the DC developing bias voltage, the potential difference ΔV is lowered by a predetermined voltage, and the calibration mode is performed by changing the potential difference ΔV. 4. The developing device in the image forming apparatus according to claim 3, wherein the developing device is configured.

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