JP2010091804A - Development method and device for image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development method and device for preventing excessive image density and fogging, reduction in image density, and occurrence of image density irregularity in a touchdown development method. <P>SOLUTION: The relationship between the toner charge amount which is varied by varying the environmental temperature and humidity and the potential difference ΔV for making constant the toner layer thickness on the development roller 11 is previously stored in a table form as the relationship among the temperature and humidity and the potential difference ΔV. In setting the density of a pattern for toner layer thickness detection detected during calibration as a target density, the corrected value of the target density corrected by the variation in γ value is stored in a table form, the potential difference ΔV and the target density corrected value are read at the environmental temperature and humidity, direct-current toner thin layer forming bias and direct-current development bias are controlled by using them, and a constant toner amount is formed on the development roller 11 so that density that corresponds to the varying γ value is obtained. <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. A developer is used to form a thin layer of only the charged toner uniformly on the developing roller, and the electrostatic latent image formed on the photosensitive drum is developed by flying the toner from the developing roller to form an image. The present invention relates to a developing method and apparatus in an image forming apparatus.

  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, since the toner is charged by the charge roller and the layer thickness on the developing roller is regulated by the elastic regulating blade, it is difficult to stably maintain the toner charge amount. May adhere to the charge roller and decrease the charging ability, or toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects. Since it is required, 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 development method called a touch-down development method or 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 the photoreceptor on which the electrostatic latent image is formed. This is a method of developing as a toner image.

  In this touch-down development method, it is important to always keep the toner layer amount on the development row 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 application disclosed in Patent Document 1 a solid pattern using a toner layer formed while the developing roller is rotating twice and a halftone pattern using a toner layer formed during the next rotation. The toner layer thickness detection pattern is visualized, the toner density of the toner layer thickness detection pattern is detected by the density sensor, and the toner layer on the developing roller is controlled to a predetermined layer thickness by the detected toner density Thus, a developing method has been proposed in which the toner layer thickness on the developing roller is always stabilized over a long period of time without making the developing device complicated, thereby maintaining a stable image without density change.

JP 2005-55841 A

  However, in the developing method disclosed in Patent Document 1, a toner thin layer forming bias for conveying toner from the magnetic roller to the developing roller is used so that the density of the half pattern on the photosensitive drum or the transfer body is always constant. Although it is controlled, the toner layer thickness on the developing roller, that is, the toner layer amount is not controlled. Further, since the solid pattern density on the photosensitive drum or on the transfer body to which the toner image on the photosensitive drum is transferred is not controlled, there is a problem that the solid image density is not stable.

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. 13, the horizontal axis represents the DC toner thin 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 In normal temperature and normal humidity (N / N) environment, ◆ indicates the toner amount at the position corresponding to the left side of the developing device (DLP left side), ■ indicates the toner amount at the position corresponding to the right side of the developing device (DLP right side), and the broken line indicates low temperature and low humidity In the (L / L) environment, a toner layer is formed on the developing roller where ◆ is a toner amount at a position corresponding to the left side of the developing device (DLP left side), and ■ is a toner amount at a position corresponding to the right side of the developing device (DLP right side). Therefore, the potential difference ΔV (Vmag−Vslv) between the DC toner thin 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. In this case, the direct current toner thin layer forming bias voltage (Vmag) applied to the magnetic roller is changed.

  As can be seen from the graph of FIG. 13, since the toner charge amount usually increases 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 DC toner thin layer formation bias voltage 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 is around 470 V, the normal temperature / normal humidity is reached. The difference from the (N / N) environment is small.

  In the image forming apparatus, as described in Patent Document 1, in order to make the image density constant, the toner layer thickness including a half density pattern for image density adjustment on the photosensitive drum prior to image formation. Calibration is performed to form a detection pattern, read the density of the toner layer thickness detection pattern or the toner layer thickness detection pattern transferred onto the transfer body with a density sensor, and control the density to be constant. Yes. However, when the toner charge amount changes with temperature and humidity, as shown in the graph of FIG. 14, the development γ curve showing the relationship between the printing rate and density in the formed image changes.

  In the graph of FIG. 14, the horizontal axis represents the printing rate (unit:%) for black solids designated at the time of image formation, the vertical axis represents the density (ID) of the formed image, and the DC toner thin layer formation bias voltage Vmag is 430V, DC developing bias voltage Vslv is 180V, the potential difference ΔV (Vmag−Vslv) between the DC toner thin layer forming bias voltage and the DC developing bias voltage Vslv is ΔV = 250V. In the case of (H / H) environment, the solid line plotting ■ indicates the printing rate in the normal temperature / humidity (N / N) environment, and the broken line plotting ▲ indicates the printing rate in the low temperature / low humidity (L / L) environment. It is the graph which plotted how each density | concentration (ID) changed when it changed, ie, how the development gamma curve changed.

  As can be seen from the graph of FIG. 14, the amount of charge increases in a low temperature / low humidity (L / L) environment, so that even if the bias for forming the toner thin layer for moving the toner from the magnetic roller to the developing roller is increased, -Compared to the normal humidity (N / N) environment, the toner is less likely to move and the amount of toner is reduced, so that the solid density is decreased. Conversely, the charge amount is high in a high temperature / high humidity (H / H) environment The amount of movement to the photoconductive drum increases and the solid density increases or unevenness occurs.

  Therefore, the toner charge amount changes due to environmental changes, and the development γ curve changes. Therefore, when calibration is performed using a toner layer thickness detection pattern consisting of a half density pattern for toner density adjustment, low temperature and low humidity ( In the L / L) environment, compared to the normal temperature and normal humidity (N / N) environment, the reduction amount of the half image density is smaller than the reduction amount of the solid image density, and conversely, the high temperature and high humidity (H / H) environment. In contrast to the low temperature and low humidity (L / L) environment, the half image density is low although the solid image density is high. Therefore, when trying to optimize the half image density in a low temperature / low humidity (L / L) environment, the solid image density is insufficient. Conversely, in a high temperature / high humidity (H / H) environment, try to optimize the half image density. Then, the solid image density becomes excessive.

  This is a problem related to the ability of the density sensor used for calibration. For example, a general reflection type density sensor used in Patent Document 1 has a reading accuracy of how accurately the density can be read by half. The density area has sufficient accuracy, but the solid density area does not have sufficient accuracy. The target in normal calibration is to control the solid image density to be constant, and since the reflection density sensor does not have sufficient accuracy in the solid density area, it reads half image density instead. At present, the solid image density is indirectly controlled by controlling the half image density.

  However, as described above, when the development γ curve changes in each environment due to the change in the toner charge amount on the developing roller, the relationship between the half image density and the solid image density is not constant, causing a problem of a change in the solid image density. That is why.

  Therefore, in the present invention, even if the toner charge amount changes due to environmental conditions or the like in the touch-down development method, control is performed so that the toner amount on the developing roller is always an appropriate amount, and excessive image density, fog, and image density are controlled. An image forming apparatus that prevents the occurrence of lowering and unevenness in image density, and the solid image density does not become excessive or insufficient even when the development γ curve changes due to the change in the toner charge amount of the developer. 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.
Toner and carrier formed on a magnetic roller having a developing roller facing a photosensitive drum for forming an electrostatic latent image by an electrophotographic method, and a magnetic roller having a magnet inside facing the developing roller A toner layer is formed on the developing roller by a potential difference ΔV between a DC toner thin layer forming bias voltage applied to the magnetic roller and a DC developing bias voltage applied to the developing roller from a magnetic brush of a two-component developer comprising: In the developing method in the image forming apparatus for developing the toner by flying toner onto the electrostatic latent image on the photosensitive drum with the developing bias,
The relationship between the toner charge amount changed by changing the environmental temperature and humidity in advance and the potential difference ΔV that makes the toner layer thickness on the developing roller constant is tabulated as the relationship between temperature, humidity, and potential difference ΔV. The voltage difference ΔV of the table corresponding to the temperature and humidity at the time of image formation is read, and the toner layer on the developing roller is controlled by controlling the toner thin layer forming bias and the developing bias to be the read potential difference ΔV. Forming the electrostatic latent image and developing the electrostatic latent image.

And the developing device for carrying out this developing method is:
A developing roller that faces a photosensitive drum on which an electrostatic latent image is formed by an electrophotographic method, and develops the toner by flying toner onto the electrostatic latent image by an applied developing bias; The magnetic brush of the two-component developer composed of toner and carrier is held by a magnet disposed on the magnet, and only the toner of the magnetic brush is applied with a potential difference ΔV between the DC component of the toner thin layer forming bias and the DC component of the developing bias. In a developing device in an image forming apparatus having a magnetic roller moved to a developing roller,
The temperature / humidity sensor detects the relationship between a temperature / humidity sensor that detects environmental temperature and humidity, and the potential difference ΔV that keeps the toner layer thickness on the developing roller constant and the toner charge amount that varies with the environmental temperature and humidity. A storage device storing data tabulated as a relationship between temperature and humidity and the potential difference ΔV, and a temperature and humidity signal detected by the temperature and humidity sensor, and reading a corresponding potential difference ΔV stored in the storage device A development control device for controlling the direct current difference between the toner thin layer forming bias and the developing bias to be the read potential difference ΔV to form a toner layer on the developing roller and developing the electrostatic latent image It is characterized by comprising.

  As described above, the relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the potential difference ΔV that keeps the toner layer thickness on the developing roller constant is stored as the relationship between the environmental temperature and humidity, and the potential difference ΔV. By reading the potential difference ΔV corresponding to the environmental temperature and humidity at the time of formation, and controlling the toner thin layer formation bias and development bias, the toner layer thickness on the development roller can be kept constant at any humidity and temperature. The toner amount on the developing roller is always an appropriate amount, and excessive image density, fogging, reduction in image density, and occurrence of uneven image density can be prevented.

And
The image forming apparatus forms a toner layer thickness detection pattern composed of a half density pattern for image density adjustment, measures the density, and controls the toner thin layer forming bias and the developing bias based on the measurement result to form A calibration mode in which the target image density is the target density,
The relationship between the toner charge amount and the γ value of the formed image (a value indicating the relationship between the printing rate and the density in the formed image) that changes by changing the environmental temperature and humidity in advance is changed corresponding to the changed γ value. The target density correction value that is the correction amount of the target density to be checked is checked, the target density correction value is stored in a table corresponding to the temperature and humidity,
When forming the toner layer thickness detection pattern, the target density correction value of the table corresponding to temperature and humidity is read, and the target density is corrected with the target density correction value to form an image.
An apparatus for carrying out this image forming method is
The image forming apparatus forms a toner layer thickness detection pattern composed of a half density pattern for image density adjustment, measures the density, and controls the toner thin layer forming bias and the developing bias based on the measurement result to form A calibration mode in which the target image density is the target density,
A toner density sensor that reads the density of the toner layer thickness detection pattern, and a temperature and humidity sensor that measures environmental temperature and humidity;
The storage device changes the environmental temperature and humidity examined in advance, and changes the relationship between the toner charge amount that changes and the γ value of the formed image (a value indicating the relationship between the printing rate and the density in the formed image) and the change. The relationship with the target density correction value for correcting the target density corresponding to the γ value is stored as a table in which the target density correction value is arranged corresponding to the temperature and humidity,
The development control device receives signals from the temperature / humidity sensor and the toner concentration sensor, reads out a target density correction value corresponding to the temperature and humidity detected by the temperature / humidity sensor from the storage device, and corrects the target density. The control is performed so that the density of the toner layer thickness detection pattern detected by the toner density sensor is set to the corrected target density.

  In this way, even if the toner charge amount changes due to environmental conditions or the like and the development γ curve changes, the solid image density does not become excessive or insufficient, and as described above, Thus, the toner amount is always an appropriate amount, and it is possible to prevent excessive image density, fogging, image density reduction, and image density unevenness.

  Further, the correction of the image density to the target density is performed by correcting the DC toner thin layer forming bias voltage. Therefore, the development control device controls the DC toner thin layer forming bias voltage to control the target density. Since the correction is performed, the target density can be easily set and corrected.

  As described above, in the developing method and apparatus in the image forming apparatus according to the present invention, the toner layer thickness on the developing roller is always constant even when environmental changes such as temperature and humidity occur. And the occurrence of image density unevenness can be prevented. Similarly, even if the toner charge amount changes due to environmental changes such as temperature and humidity, and the development γ curve changes, the solid image density does not become excessive or insufficient, and the toner amount on the developing roller is always constant. Combined with the appropriate amount, the development method and apparatus in the image forming apparatus can always provide a high-quality image by preventing the decrease in image density and the occurrence of image density unevenness.

  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.

  FIG. 1 is a schematic configuration diagram of a touch-down developing device for carrying out a developing method in an image forming apparatus according to the present invention, and FIG. 2 is a schematic view of an embodiment of an image forming apparatus for performing a developing method according to the present invention. .

  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.

FIG. 1 is a schematic configuration diagram of a touch-down developing device for carrying out the developing method in the image forming apparatus according to the present invention. The photosensitive drum 10 (K, Y, C, M) and the developing roller 11 shown in FIG. (K, Y, C, M), magnetic roller 15 (K, Y, C, M), bias power source indicated by 13, 14, 19, 20 and control circuits 22, 23, etc. It is. 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 toner thin layer forming bias applied from a DC toner thin layer forming bias power source (DC2) 19 and an AC toner thin layer forming bias power source (AC2) 20 is formed by forming a magnetic brush 18 of a two-component developer comprising a carrier 17. Thus, a magnetic roller for forming a toner layer 12 on the developing roller 11, 21 is a magnetic roller 1
5 is a cutting blade for keeping the height of the magnetic brush 18 above 5 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 thin layer forming bias power source for the magnetic roller 15. (DC2) 19, a magnetic roller bias power supply controller for controlling AC toner thin layer forming bias power supply (AC2) 20, and 24 for giving a voltage instruction to the developing roller bias power supply controller 22 and magnetic roller bias power supply controller 23. A development control device 25 for controlling the development device stores data such as the temperature detected by the temperature / humidity sensor 26, the development bias to the development roller 11 corresponding to the humidity, and the toner thin layer formation bias to the magnetic roller 15. The storage device 27 has a toner layer thickness at the time of calibration for adjusting the density of the formed image. A toner density sensor for measuring the concentration of knowledge pattern.

  In the storage device 25, the charge amount of the toner 16 changes due to changes in temperature and humidity in the image forming device 20, and the thickness of the toner layer 12 on the developing roller 12, that is, the toner amount changes, and the image density changes. Data for preventing this is stored. Further, in the image forming apparatus, in order to adjust the density of an image to be formed, a toner layer thickness detection pattern for image density adjustment is formed prior to image formation as described above, and the density is measured to obtain a target density. Calibration for adjusting the development bias and the toner thin layer formation bias is performed so that the toner charge amount changes as the temperature and humidity in the image forming apparatus 20 change, and the print rate and density in the formed image are changed. The γ value indicating the above relationship changes, and on the contrary, a phenomenon in which the solid image density becomes excessive or insufficient due to calibration may occur. For this reason, data for correcting the target density for preventing such a situation is also stored.

  Although details of these data will be described later, in brief, the toner layer 12 on the developing roller 11 includes a voltage of a DC toner thin layer forming bias power source (DC2) 19 applied to the magnetic roller 15, and a developing roller. The toner 16 is formed by moving only the toner 16 from the magnetic brush 18 formed on the magnetic roller 15 to the developing roller 11 due to the potential difference ΔV of the voltage of the DC developing bias power supply (DC1) 13 applied to the developing roller 11. However, at that time, the amount of movement decreases when the charge amount of the toner 16 increases in a low temperature and low humidity state, and the amount of movement increases when the charge amount decreases in a high temperature and high humidity state. Further, the γ value indicating the relationship between the printing rate and the density in the formed image is such that when the charge amount of the toner 16 is increased in a low temperature and low humidity state, the half image density is high and the solid image density is low. When the charge amount of the toner 16 decreases in a wet state, the half image density decreases and the solid image density increases.

  Therefore, first, the data for making the thickness of the toner layer 12 on the developing roller 12, that is, the toner amount constant, includes the toner charge amount that varies depending on the environmental temperature and humidity, and the toner of the toner layer 12 on the developing roller 11. FIG. 5 is a table showing the relationship between the potential difference ΔV in which the amount is always constant and the relationship between the temperature and humidity detected by the temperature / humidity sensor 26 and the corresponding potential difference ΔV. The data for preventing the phenomenon that the solid image density becomes excessive or insufficient due to the calibration is based on the relationship between the toner charge amount that changes with the environmental temperature and humidity and the γ value described above. 5 is a table in which temperature and humidity are associated with density correction values of target density necessary for correcting a changed γ value.

  The data stored in the storage device 25 has been described above. Returning to FIG. 1 again, the elements constituting the developing device will be described. The outermost surface of the developing roller 11 has uniform conductive aluminum, SUS, conductive resin coating, and the like. In order to prevent leakage, it is preferable to increase the resistance value by applying an alumite treatment of about 20 μm and a resin coat, for example. 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. Generally, the spread of the particle size distribution of the toner is measured by a Coulter counter, and the spread of the particle size distribution is determined by the volume distribution average particle size and number. Expressed as a ratio of the distribution average particle size. 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 hybrid type developing apparatus configured as described above, the two-component composed of the toner 16 and the carrier 17 corresponding to the respective colors such as yellow, cyan, magenta, and black. The developer is supplied from the developer container to each developing device 34, and the magnetic brush 10 is formed on the magnetic roller 15 shown in FIG. 1, and the toner 16 is charged by stirring. Then, the magnetic brush 10 on the magnetic roller 15 is layer-regulated by the regulating blade 9, and between the DC toner thin 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. 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 the recording paper. The toner image is transferred, 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.

  Next, the developing method of Example 1 of the present invention will be described with reference to the graph of FIG. 6, the graph of FIG. 7, the graph of FIG. 8, the graph of FIG. 9, and the graph of FIG. These graphs show that the toner amount on the developing roller is based on the potential difference ΔV between the DC developing bias Vslv supplied to the developing roller 11 and the DC toner thin layer forming bias Vmag supplied to the magnetic roller 15 in the graph of FIG. FIG. 7 is a graph showing how the transition occurs. When the potential difference ΔV is constant and the DC toner thin layer forming bias Vmag is changed, and the charge amount of the toner 16 changes depending on the environmental temperature and humidity, FIG. 8 is a graph showing how the toner charge amount of the toner changes, FIG. 8 is a graph showing how the toner amount on the developing roller changes depending on the charge amount of the toner 16, and FIG. A graph showing how the amount of toner on the photosensitive drum 10 changes according to the charge amount of the toner 16, and the graph of FIG. 10 shows the charge amount of the toner 16. 6 is a graph showing how the development efficiency on the photosensitive drum 10 changes.

6, 8, 9, and 10, the horizontal axis represents the DC developing bias Vslv supplied from the DC developing bias power supply (DC1) 13 to the developing roller 11, and the horizontal axis in the graph of FIG. The vertical axis is the graph of FIG. 6, the graph of FIG. 8 is the toner amount on the developing roller 11 (unit: mg / cm ² ), and the graph of FIG. 7 is the toner charge amount (unit: μC / g). 9 is the amount of toner (unit: mg / cm ² ) on the photosensitive drum 10, and the graph of FIG. 10 is how much toner 16 on the developing roller 11 has jumped to the photosensitive drum 10, that is, photosensitive. A toner layer formed on the developing roller 11 is obtained by multiplying the ratio of the solid toner amount on the body drum 10 and the toner amount on the developing roller 11 by the ratio of the peripheral speed of the developing roller 11 and the peripheral speed of the photosensitive drum 10. 1 A: amount of toner and the developing efficiency represented by the ratio of the amount of toner used for developing an electrostatic latent image on the photosensitive drum 10 (in%).

  The image forming apparatus used in this investigation is an image forming apparatus using a touch-down developing method manufactured by Kyocera Mita. The photosensitive drum 10 used has an outer diameter of 30 mm and a peripheral speed of 169.0 mm / sec. The outer diameter is 16 mm and the peripheral speed is 270.4 mm / sec. The magnetic roller 15 has an outer diameter of 16 mm and the peripheral speed is 421.8 mm / sec. Further, the blade gap between the magnetic roller 15 and the ear cutting blade 21 is 0.27 to 0.32 mm, the M / S gap between the magnetic roller 15 and the developing roller 11 is 0.29 mm, and the developing roller 11 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 11 to the peripheral speed of the photosensitive drum 10 is about 1.6, and the developer is an average particle of black (K). A two-component developer composed of a toner having a reduced particle diameter of 6.8 μm and a carrier was used.

  First, in the graph of FIG. 6 shown as “toner amount on the developing roller”, the difference ΔV between the DC developing bias Vslv (DC) for the developing roller and the magnetic roller DC toner thin layer forming bias Vmag (DC) is 400 V (◆). ), 320V (■), 240V (▲). From the graph of FIG. 6, the toner amount of the toner layer 12 formed on the developing roller 11 is at least in the range of about 20 V to 180 V of the DC developing bias Vslv (DC), and the voltage of the DC developing bias power source (DC) 13. It corresponds to the potential difference ΔV between Vslv and the voltage Vmag of the magnetic roller DC toner thin layer forming bias power supply (DC) 19, and it can be seen that the larger the value of this potential difference ΔV, the larger the amount becomes.

  In the graph of FIG. 7, the horizontal axis represents the DC toner thin layer forming bias voltage (unit: V) to the magnetic roller, and the vertical axis represents the toner charge amount (unit: μC / g) on the developing roller. 6 is a graph in which the toner charge amount is plotted. The solid line ◆ indicates the toner charge amount on the left side of the developing device (DLP left side) in a normal temperature and normal humidity (N / N) environment, the ■ indicates the toner charge amount on the right side of the developing device (DLP right side), and the broken line ◆ indicates low temperature and low humidity (L / L) The toner charge amount on the left side of the developing device (left side of DLP) in the environment, ■ is the toner charge amount on the right side of the developing device (on the right side of DLP), 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 (DLP left side) toner charge amount, ■ is the toner charge amount on the right side of the developing device (DLP right side), ΔV is 220V in high temperature / high humidity (H / H) environment, normal temperature / normal humidity (N / N) environment In the low-temperature and low-humidity (L / L) environment, the voltage is controlled to be a constant value of 280 V, but the DC toner thin layer forming bias voltage applied to the magnetic roller 15 is changed. Plotting.

  As can be seen from the graph of FIG. 7, the toner charge amount on the developing roller in the high temperature / high humidity (H / H) environment indicated by the alternate long and short dash line is much smaller than that in the normal temperature / normal humidity (N / N) environment. Increased in low temperature and low humidity (L / L) environments.

  The graph of FIG. 8 shown as “toner amount on the developing roller” is a graph showing how the toner amount on the developing roller 12 changes depending on the charge amount of the toner 16, and environmental factors such as temperature and humidity. Therefore, when the toner charge amount in the developer changes, the toner amount on the developing roller 11 changes accordingly. In the graph of FIG. 8, ♦ is a toner amount with a toner charge amount Q / M of 9.4 μC / g, ■ is a toner amount of 16.2 μC / g, and ▲ is a toner amount of 26.8 μC / g, In this case, the potential difference ΔV is changed so that the DC developing bias for the developing roller becomes constant at 200 V with the change of the DC toner thin layer forming bias. When the toner charge amount increases, the toner amount on the developing roller 16 decreases. I can see that 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 layer amount on the developing roller 11 decreases.

  In the graph of FIG. 9 in which the amount of toner on the photosensitive drum 10 changes depending on the charge amount of each toner 16, the ◆ is the toner charge amount Q / M 9.4 μC as in the graph of FIG. The amount of toner in the case of / g, the amount of toner in the case where ■ is also 16.2 μC / g, the amount of toner in the case where ▲ is also 26.8 μC / g, and Vslv is changed under the condition that the potential difference ΔV is constant at 200V. It is plotted how the amount of toner on the photosensitive drum 10 changes when it is set.

  As can be seen from the graph of FIG. 9, 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. 10 in which the development efficiency on the photosensitive drum 10 is changed according to the charge amount of the toner 16, where ◆ is the toner charge amount Q / M is 9.4 μC. The development efficiency in the case of / g, the development efficiency in the case of ■ is 16.2 μC / g, and the development efficiency in the case of ▲ is 26.8 μC / g. When the change is made, the manner in which the toner flying efficiency onto the photosensitive drum 10 changes is plotted.

  As can be seen from the graph of FIG. 10, the line plotting the highest ▲ of toner charge amount Q / M of 26.8 μC / g shows a rapid increase in development efficiency 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. 9, 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 16 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. In the graph of FIG. As can be seen, by making the potential difference ΔV between the DC toner thin 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. Can be 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.

This state is shown in the graph of FIG. The graph of FIG. 11 corresponds to each environment of high temperature / high humidity (H / H), normal temperature / normal humidity (N / N), low temperature / low humidity (L / L), and direct current toner to the magnetic roller. 6 is a graph showing that the amount of toner on the photosensitive drum 10 can be made almost constant by selecting the thin layer forming bias voltage Vmag. In the graph of FIG. 11, the horizontal axis represents the DC toner thin layer forming bias voltage Vmag (unit: V) to the magnetic roller, and the vertical axis represents the amount of toner (unit: mg / cm ² ) on the photosensitive drum 10. The solid line indicates the toner amount when the developing device is on the left side (DLP left side) in the normal temperature and normal humidity (N / N) environment, the solid line indicates the toner amount when the developing device is on the right side (DLP right side), and the broken line indicates the low temperature and low humidity (L / L) In the environment, ◆ is the toner amount when the developing device is on the left side (DLP left side), ■ is the toner amount when the developing device is on the right side (DLP right side), and the alternate long and short dash line is in a high temperature / high humidity (H / H) environment Is the toner amount when the developing device is on the left side (DLP left side), and ■ is the toner amount when the developing device is on the right side (DLP right side). In each environment, the DC toner thin layer forming bias voltage Vmag to the magnetic roller is changed to change the sensitivity. Body drum 1 It is a plot of the change in the amount of toner above.

The horizontal line drawn at a position of about 0.55 mg / cm ² is the optimum toner amount on the photosensitive drum 10, and as can be seen from the graph of FIG. 11, a high temperature / high humidity (H / H) environment (H / H) environment ( In the alternate long and short dash line), the DC toner thin layer formation bias voltage Vmag is about 330 V, in the normal temperature / normal humidity (N / N) environment (solid line), about 410 V, and in the low temperature / low humidity (L / L) environment (dashed line). Is about 470 V, the amount of toner on the photosensitive drum 10 can be made substantially the same. Note that the value of the DC toner thin layer forming bias voltage Vmag to the magnetic roller varies depending on the charge amount of the toner 16.

  Therefore, in the present invention, the relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the thickness of the toner layer 12 on the developing roller 11, that is, the potential difference ΔV that makes the toner amount constant, is The relationship between temperature, humidity and potential difference ΔV is summarized as shown in the table of FIG. 3 and stored in the storage device 25 of FIG. This table in FIG. 3 takes a temperature range of 2 ° C. to 4 ° C. in the horizontal direction and a humidity range of 10% in the vertical direction, and arranges a potential difference ΔV corresponding to the intersection of temperature and humidity. In a low-temperature / low-humidity (L / L) environment where the temperature is 15 degrees or less and the humidity is 35% or less, the potential difference ΔV is reduced to 280 V, and then the potential difference ΔV is reduced every time the temperature and humidity rise, and the temperature is high at 37 ° C. and 76% humidity.・ In a high humidity (H / H) environment, the potential difference ΔV is as low as 220V.

  At the time of image formation, the development control device 24 receives temperature and humidity measurement data detected by the temperature / humidity sensor 26 installed in the image forming apparatus 30, and the toner amount on the developing roller 11 is constant. Is read from the storage device 25 and instructed to the developing roller bias power supply control device 22 and the magnetic roller bias power supply control device 23, and the direct current developing bias power supply (DC1) 13 and the direct current toner thin layer forming bias power supply (DC2). 19, the toner layer thickness on the developing roller 11 is controlled to be constant so that the potential difference ΔV becomes the read value.

The graph of FIG. 12 shows the result of controlling the potential difference ΔV in this way. In the graph of FIG. 12, the horizontal axis indicates the DC toner thin layer forming bias Vmag, the vertical axis indicates the amount of toner on the developing roller 11 (unit: mg / cm ² ), and the solid line indicates 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. 12, 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. By developing as a value, the toner amount on the developing roller 11 can be kept constant at approximately 0.60 g / cm ² . That is, by doing this, the toner layer thickness on the developing roller 11 can be kept constant even if the toner charge amount changes depending on the temperature and humidity in the image forming apparatus. In addition, it is possible to prevent image density reduction and image density unevenness.

  The above is the developing method according to the first embodiment of the present invention. Next, the second embodiment of the present invention which copes with the case where the toner charge amount changes due to the environmental condition and the development γ curve changes as described above. A developing method will be described. The table used in this case is the table of FIG.

  In the table of FIG. 4, the calibration described above is performed in the calibration mode, and the density of the toner layer thickness detection pattern obtained by the calibration is different from the predetermined target density, and the change in temperature and humidity As described above, when the toner charge amount changes and the development γ curve changes, the density of the toner layer thickness detection pattern is controlled to the predetermined target density as it is, as described above, at low temperature and low humidity (L / L). Optimizing the half-image density in an environment results in insufficient solid image density. Conversely, optimizing the half-image density in a high-temperature / high-humidity (H / H) environment solves the problem of excessive solid image density. It is a table.

  That is, the target density of the toner layer thickness detection pattern is, for example, the density reading value of the toner density sensor, and magenta (M) = 530, cyan (M) = 530, yellow (M) = 530, and black (M) = 530. Suppose there is. Then, as described above, if the density of the toner layer thickness detection pattern is set to this value in the low temperature / low humidity (L / L) environment, the solid image density is insufficient, and conversely in the high temperature / high humidity (H / H) environment. If the density of the toner layer thickness detection pattern is set to this value, the solid image density becomes excessive. Therefore, in the table of FIG. 4, the printing rate is higher in the low temperature / low humidity (L / L) environment than in the normal temperature / normal humidity (N / N) environment based on the development γ curve shown in FIG. Since the density becomes lower, the density of the toner layer thickness detection pattern is controlled to be higher than the target density. Compared to a normal temperature / normal humidity (N / N) environment in a high temperature / high humidity (H / H) environment, Since the density is low when the printing rate is low and the density is high when the printing rate is high, a value is provided for controlling the density of the toner layer thickness detection pattern to be lower than the target density.

  The table shown in FIG. 4 is similar to the table shown in FIG. 3 described above, and takes a temperature range of 2 ° C. to 4 ° C. in the horizontal direction and a humidity range of 10% in the vertical direction, and corresponds to the intersection of temperature and humidity. Correction value for target density, that is, correction value for magenta (M) = 530, cyan (M) = 530, yellow (M) = 530, black (M) = 530, for example, the density reading value of the toner density sensor described above. Is remembered. Therefore, in a low-temperature / low-humidity (L / L) environment where the temperature is 15 degrees or less and the humidity is 35% or less, +50 is arranged as a correction value. As described above, in a high temperature / high humidity (H / H) environment with a humidity of 76% or more, a correction value of −240 is arranged.

  Therefore, in the second embodiment of the present invention, when performing the calibration with the calibration mode described above, the development control device 24 shown in FIG. 1 first detects the temperature / humidity detected by the temperature / humidity sensor 26. Based on the above, the target density correction value is read out from the table shown in FIG. 4 stored in the storage device 25 to correct the target density. Then, the corrected target density is compared with the density of the toner layer thickness detection pattern detected by the toner density sensor 27 so that the density of the toner layer thickness detection pattern becomes the corrected target density. The power supply control device 22 and the magnetic roller bias power supply control device 23 are instructed so that image formation is performed.

  There are various calibration methods for this calibration. For example, when a calibration instruction is issued from a control circuit of the entire image forming apparatus (not shown), for example, a half of a printing rate of 37.5% is formed on the photosensitive drum 10. A toner layer thickness detection pattern composed of a density pattern is formed, and the density of the toner layer thickness detection pattern transferred onto the transfer body is detected by a toner density sensor 27 (see FIG. 1), and development control is performed. The comparison is made with the target density corrected by the above-described method by the apparatus 24, and the developing roller bias and magnetic roller bias are controlled accordingly. Since detailed examples of the calibration and the reflective density sensor used at the time of calibration are described in Patent Document 1 described above, description thereof will be omitted.

  Further, the correction of the density of the toner layer thickness detection pattern to the corrected target density can be easily performed by correcting the DC toner thin layer forming bias voltage Vmag, as apparent from the graph of FIG. It can be carried out.

  FIG. 5 shows the developing method of Example 1 in which the toner charge amount that changes with temperature and humidity is tabulated as the relationship between the temperature and humidity and the potential difference ΔV, and the relationship between the changed toner charge amount and the γ value of the formed image. Is a flowchart of the developing method of Example 2 in which the correction amount of the target density to be changed corresponding to the changed γ value, that is, the target density correction value is tabulated.

  When the process starts in step S10, a batch for calibration is printed in step S11. For example, as shown in step S11, the patch is printed with a DC toner thin layer forming bias Vmag19 of 450V, a DC developing bias Vslv13 of 200V, and a pattern 2 of DC toner thin layer forming bias Vmag19 of 400V. The pattern 3 is drawn with the DC developing bias Vslv13 set at 150V, the DC toner thin layer forming bias Vmag19 set at 350V, and the DC developing bias Vslv13 set at 100V.

  When the image is drawn, the development control device 24 confirms the signal from the temperature / humidity sensor 26 in step S12 to detect the environmental temperature and humidity. Based on the detection result, the development control device 24 shown in FIG. 4 in step S13. The target density correction value corresponding to the current temperature / humidity is read from the storage device 25 in which the table is stored. Then, the target density is corrected with the target density correction value read in step S14, and an instruction is given to the developing roller bias power supply control device 22 and the magnetic roller bias power supply control device 23.

  In the next step S15, the density of the calibration patch drawing data drawn in step S11 is read by the toner density sensor 27, and the DC toner thin layer forming bias voltage Vmag for obtaining the target density corrected in step S14 is determined. In the next step S16, the optimum potential difference ΔV for the current temperature and humidity is read from the table stored in the storage device 25 shown in FIG. 3 based on the temperature and humidity detection results, and determined in step S16. The DC developing bias Vslv is determined from the DC toner thin layer forming bias Vmag and the potential difference ΔV in step S17, the image is formed with the DC toner thin layer forming bias Vmag and the DC developing bias Vslv determined in step S18, and the process is completed. .

  In this way, even if the toner charge amount changes due to environmental conditions and the development γ curve changes, the solid image density does not become excessive or insufficient, and as described above, the developing roller 11 The upper toner amount is always an appropriate amount, and it is possible to prevent excessive image density, fogging, a decrease in image density, and occurrence of uneven image density.

  According to the present invention, there is no excessive image density or fogging at any environmental temperature and humidity, no decrease in image density, no occurrence of image density unevenness, no excessive or insufficient solid image density, and high quality over a long period of time. It is possible to provide an image forming apparatus capable of forming a stable image.

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. The relationship between the toner charge amount that changes depending on the environmental temperature and humidity and the thickness of the toner layer 12 on the developing roller 11, that is, the potential difference ΔV that makes the toner amount constant, corresponds to the environmental temperature and humidity. It is the table which arranged ΔV. In the example of the table of the second embodiment of the present invention, a correction value for correcting the target density corresponding to the environmental temperature and humidity is arranged in order to correspond to the γ value that changes depending on the toner charge amount that changes depending on the environmental temperature and humidity. is there. It is a flowchart of the developing method in the image forming apparatus according to the present invention. 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 thin layer forming bias Vmag (DC) supplied to the magnetic roller 15. It is the graph which investigated whether to do. This graph shows how the toner charge amount on the developing roller changes when the charge amount of the toner 16 is changed by the environmental temperature and humidity by changing the DC toner thin layer forming bias Vmag with a constant potential difference ΔV. is there. 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 represents the DC toner thin layer forming bias voltage (Vmag, unit: V) to the magnetic roller, and the vertical axis represents the amount of toner (unit: mg / cm ² ) on the photosensitive drum. 6 is a graph plotting the amount of toner on a photosensitive drum when the charge amount changes. The horizontal axis is the DC toner thin layer forming bias Vmag, and 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 is substantially constant by the potential difference ΔV corresponding to each environment. It is the graph which showed that it becomes. The horizontal axis represents the DC toner thin 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 the amount changes. A graph in which the printing rate (unit:%) for black solids is plotted on the horizontal axis, and the density (ID) of the formed image is plotted on the vertical axis, and the γ curve that changes as the toner charge amount changes with temperature and humidity is plotted. It is.

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 Storage Device 26 Temperature / Humidity Sensor 27 Toner Concentration Sensor

Claims (6)

Toner and carrier formed on a magnetic roller having a developing roller facing a photosensitive drum for forming an electrostatic latent image by an electrophotographic method, and a magnetic roller having a magnet inside facing the developing roller A toner layer is formed on the developing roller by a potential difference ΔV between a DC toner thin layer forming bias voltage applied to the magnetic roller and a DC developing bias voltage applied to the developing roller from a magnetic brush of a two-component developer comprising: In the developing method in the image forming apparatus for developing the toner by flying toner onto the electrostatic latent image on the photosensitive drum with the developing bias,
The relationship between the toner charge amount changed by changing the environmental temperature and humidity in advance and the potential difference ΔV that makes the toner layer thickness on the developing roller constant is tabulated as the relationship between temperature, humidity, and potential difference ΔV. The voltage difference ΔV of the table corresponding to the temperature and humidity at the time of image formation is read, and the toner layer on the developing roller is controlled by controlling the toner thin layer forming bias and the developing bias to be the read potential difference ΔV. A developing method in an image forming apparatus, comprising: forming and developing the electrostatic latent image. The image forming apparatus forms a toner layer thickness detection pattern composed of a half density pattern for image density adjustment, measures the density, and controls the toner thin layer forming bias and the developing bias based on the measurement result to form A calibration mode in which the target image density is the target density,
The relationship between the toner charge amount and the γ value of the formed image (a value indicating the relationship between the printing rate and the density in the formed image) that changes by changing the environmental temperature and humidity in advance is changed corresponding to the changed γ value. The target density correction value that is the correction amount of the target density to be checked is checked, the target density correction value is stored in a table corresponding to the temperature and humidity,
When the toner layer thickness detection pattern is formed, the target density correction value of the table corresponding to temperature and humidity is read, and the target density is corrected with the target density correction value to form an image. A developing method in the image forming apparatus according to claim 1.   The developing method for an image forming apparatus according to claim 2, wherein the correction of the image density to the target density is performed by correcting the DC toner thin layer forming bias voltage. A developing roller that faces a photosensitive drum on which an electrostatic latent image is formed by an electrophotographic method, and develops the toner by flying toner onto the electrostatic latent image by an applied developing bias; The magnetic brush of the two-component developer composed of toner and carrier is held by a magnet disposed on the magnet, and only the toner of the magnetic brush is applied with a potential difference ΔV between the DC component of the toner thin layer forming bias and the DC component of the developing bias. In a developing device in an image forming apparatus having a magnetic roller moved to a developing roller,
The temperature / humidity sensor detects the relationship between a temperature / humidity sensor that detects environmental temperature and humidity, and the potential difference ΔV that keeps the toner layer thickness on the developing roller constant and the toner charge amount that varies with the environmental temperature and humidity. A storage device storing data tabulated as a relationship between temperature and humidity and the potential difference ΔV, and a temperature and humidity signal detected by the temperature and humidity sensor, and reading a corresponding potential difference ΔV stored in the storage device A development control device for controlling the direct current difference between the toner thin layer forming bias and the developing bias to be the read potential difference ΔV to form a toner layer on the developing roller and developing the electrostatic latent image And a developing device in the image forming apparatus. The image forming apparatus forms a toner layer thickness detection pattern composed of a half density pattern for image density adjustment, measures the density, and controls the toner thin layer forming bias and the developing bias based on the measurement result to form A calibration mode in which the target image density is the target density,
A toner density sensor that reads the density of the toner layer thickness detection pattern, and a temperature and humidity sensor that measures environmental temperature and humidity;
The storage device changes the environmental temperature and humidity examined in advance, and changes the relationship between the toner charge amount that changes and the γ value of the formed image (a value indicating the relationship between the printing rate and the density in the formed image) and the change. The relationship with the target density correction value for correcting the target density corresponding to the γ value is stored as a table in which the target density correction value is arranged corresponding to the temperature and humidity,
The development control device receives signals from the temperature / humidity sensor and the toner concentration sensor, reads out a target density correction value corresponding to the temperature and humidity detected by the temperature / humidity sensor from the storage device, and corrects the target density. 5. A developing device in an image forming apparatus according to claim 4, wherein control is performed so that the density of the toner layer thickness detection pattern detected by the toner density sensor is set to the corrected target density. .   6. The developing device in an image forming apparatus according to claim 5, wherein the developing control device is configured to correct the target density by controlling the DC toner thin layer forming bias voltage.

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