JP2008225222A - Image forming apparatus and toner density control method - Google Patents

Abstract

Image formation capable of performing toner density control with little variation among a plurality of developing tanks even if variations in sensor output values with respect to the developer amount occur between a plurality of developing tanks in which toner density sensors are incorporated. An apparatus and a toner density control method are provided.
An image forming apparatus A including a developing device 2 having a developing tank 22 and a toner density sensor 23 sets in advance a reference sensor output value for a plurality of developer amounts, and a plurality of developer amounts. The measured sensor output value of the toner density sensor 23 with respect to the toner is measured, the measured sensor output value is compared with a preset reference sensor output value, and the sensor output value of the developing tank 22 with respect to the reference developing tank is compared. The sensor output value of the toner density sensor 23 is calculated so that the equivalent toner density value corresponding to the measured sensor output value approaches the equivalent toner density value corresponding to the reference sensor output value based on the calculated characteristic change. Correct.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus and a toner concentration control method thereof, and more particularly, to detect a developer tank containing a two-component developer containing toner and a carrier and a toner concentration of the two-component developer contained in the developer tank. The present invention relates to an electrophotographic image forming apparatus that includes a developing device having a toner density sensor and controls the toner density of the two-component developer based on the sensor output value of the toner density sensor, and a toner density control method thereof.

  In a conventional electrophotographic image forming apparatus, generally, the surface of an image carrier (for example, a photoconductor) is charged, and an image is exposed to the charged area to form an electrostatic latent image. The image is visualized (developed) as a toner image by a developing device, the toner image visualized is electrostatically transferred to a recording material such as recording paper, and then the toner transferred to the recording material The image is fixed to the recording material by a fixing device.

  In this type of image forming apparatus, when development is performed using a two-component developer containing toner and carrier, only the toner is carried on the toner and carrier in the developer contained in the developer tank of the developing apparatus. A method of attaching to the body and consuming it is generally adopted. For this reason, in the image forming apparatus, in order to maintain an appropriate toner concentration of the developer in the developing tank, toner concentration control is performed so that the toner is appropriately replenished to the developer.

  In such an image forming apparatus that performs toner density control, the developer toner density is usually detected directly or indirectly by a sensor, and the developer toner density control is performed based on the detected value. ing. A typical example of the sensor for detecting the toner concentration of the developer is a magnetic permeability toner concentration sensor for detecting the magnetic permeability of the developer.

  In general, the magnetic permeability toner concentration sensor detects the sensor output value related to the magnetic permeability of the developer in the vicinity of the sensor detection section as the toner concentration of the developer by using the inductance of the coil. .

  Such a toner density sensor is usually attached to a developing tank in a developing device, but at this time, the sensor sensitivity characteristic as a single unit is often only checked. For example, with a constant voltage applied to a single toner concentration sensor, the magnetic plate is brought close to the sensor detection unit, and the sensor output value is read to check whether an appropriate value is output. There are many.

  Therefore, when a toner concentration sensor is incorporated in the developing tank of an actual developing device and the toner density of the developer is detected in a state where the developer is contained in the developing tank, the sensor output value is originally output. The sensor output value to be different may be different. That is, the sensor output value when the toner density sensor is actually incorporated in the developing tank is higher or lower than the sensor output value that should be output originally, and as a result, is the target. It becomes higher or lower than the toner concentration.

On the other hand, in Patent Document 1 below, image formation is performed in which the difference between the individual sensor sensitivities of the toner density sensor is determined, and the sensor sensitivity is initially set so that the result is reflected in the toner density control by the toner density sensor. An apparatus is disclosed.
Japanese Patent Laid-Open No. 2000-56639

  However, in the image forming apparatus described in Patent Document 1, since the initial setting of the sensor sensitivity is performed so that the discrimination result of the difference between the individual sensor sensitivities is reflected in the toner density control, a certain pressure is applied to the sensor. It is effective when the toner concentration sensor detects the toner concentration in a developer state or a developer state having a constant fluidity, but between a plurality of developing tanks of the same type in which the toner concentration sensor is incorporated, Due to the difference in the assembly accuracy of the developing tank, the pressure and fluidity of the developer to the toner concentration sensor differ, and as a result, the sensor output value varies.

  As described above, in the image forming apparatus described in Patent Document 1, since the pressure and fluidity of the developer applied to the toner density sensor among the plurality of developing tanks are not taken into consideration, the sensor sensitivity can be increased to a certain extent. Even if the difference is determined and the sensor sensitivity is initially set satisfactorily, the state of toner replenishment (toner consumption) may differ among a plurality of developing tanks. For example, when the amount of developer changes with image formation, or when the bulk density of the developer changes according to the degree of deterioration of the developer, the pressure or fluidity of the developer on the toner density sensor is reduced. May be different. As a result, the sensor output value with respect to the developer amount varies among the plurality of developing tanks, thereby causing variations in toner density control.

  The present invention has been made in view of the above problems, and even if a variation in sensor output value with respect to the amount of developer occurs between a plurality of developing tanks in which a toner density sensor is incorporated, the variation between the plurality of developing tanks. An object of the present invention is to provide an image forming apparatus and a toner density control method capable of performing a low toner density control.

  According to the experiments of the present inventors, the following has been found. That is, in an image forming apparatus including a developing device that contains a two-component developer containing toner and a carrier, and a toner concentration sensor that detects a toner concentration of the two-component developer contained in the developing vessel. The characteristics of the sensor output value of the toner density sensor with respect to a plurality of different developer amounts differ among the plurality of developing tanks in which the toner density sensor is incorporated. For example, each time a predetermined amount of developer is added to the developing tank, the sensor output value of the toner density sensor is measured, and the toner density sensor is similarly applied in the state where all the developer amount of developer is finally put in the developing tank. Measure the output value. Then, it is possible to grasp the characteristic of the sensor output value of the toner density sensor due to the developer amount of the developing tank. FIG. 11 is a graph showing an example of the result of measuring the sensor output of the developer tanks of the two developing devices by adding a developer by a quarter of the total developer amount. .

  Therefore, the present inventor corrects the sensor output value of the toner density sensor so that the characteristic of the sensor output value of the developing tank approaches the characteristic of the sensor output value of the reference developing tank in the reference developing device. Thus, it has been found that toner density control with little variation can be performed even if variations in sensor output values occur.

The present invention is based on such knowledge, and provides the following image forming apparatus and toner density control method in order to solve the above-mentioned problems.
(1) Image forming apparatus A developing device including a developing tank for storing a two-component developer containing toner and a carrier, and a toner concentration sensor for detecting the toner concentration of the two-component developer stored in the developing tank, An image forming apparatus for controlling the toner density of the two-component developer based on a sensor output value of the toner density sensor, wherein the plurality of developers are different from each other in the two-component developer housed in a reference developing tank in the reference developing device. Setting means for presetting a reference sensor output value of the reference developing tank with respect to the amount; and a measurement sensor output value of the toner concentration sensor with respect to the plurality of developer amounts of the two-component developer accommodated in the developing tank. Each of the measurement means for measuring, the measurement sensor output value measured by the measurement means, and the reference sensor output value preset by the setting means are compared. A calculating means for calculating a characteristic change of the sensor output value of the developing tank with respect to the reference developing tank, and an equivalent toner density value corresponding to the measured sensor output value is calculated based on the characteristic change calculated by the calculating means. An image forming apparatus comprising: correction means for correcting a sensor output value of the toner density sensor so as to approach an equivalent toner density value corresponding to a reference sensor output value.
(2) Toner Concentration Control Method A developing device having a developing tank for storing a two-component developer containing toner and a carrier and a toner concentration sensor for detecting the toner concentration of the two-component developer stored in the developing tank is provided. A toner concentration control method for an image forming apparatus for controlling the toner concentration of the two-component developer based on a sensor output value of the toner concentration sensor, wherein the two-component developer contained in a reference developing tank in a reference developing device A reference sensor output value of the reference developer tank for a plurality of different developer amounts is set in advance, and the measurement sensor of the toner concentration sensor for the plurality of developer amounts of the two-component developer stored in the developer tank Each of the output values is measured, and the measured sensor output value thus measured is compared with the preset reference sensor output value. A characteristic change of the sensor output value of the developing tank is calculated, and based on the calculated characteristic change, an equivalent toner density value corresponding to the measurement sensor output value approaches an equivalent toner density value corresponding to the reference sensor output value. As described above, a toner density control method comprising correcting a sensor output value of the toner density sensor.

  The “equivalent toner density value” is the toner density of the developer after the control when it is assumed that the toner density of the developer is actually controlled based on the sensor output value detected by the toner density sensor. Corresponding value.

  According to the image forming apparatus and the toner density control method of the present invention, based on the characteristic change, an equivalent toner density value corresponding to the measurement sensor output value of the developing tank becomes the reference sensor output value of the reference developing tank. Since the sensor output value of the toner density sensor is corrected so as to approach the corresponding equivalent toner density value, regardless of the occurrence of variations in the sensor output value with respect to the developer amount among the plurality of developing tanks in which the toner density sensors are incorporated. Therefore, it is possible to perform toner density control with little variation among the plurality of developing tanks.

  Generally, in the two-component developer, the developer pressure and fluidity to the toner density sensor change with changes in the surrounding humidity, and the sensor output value also changes accordingly.

  From this point of view, the image forming apparatus according to the present invention includes a humidity sensor that detects a relative humidity around the developer accommodated in the developing tank, and the setting unit has a plurality of different relative humidity ranges within a predetermined range. A plurality of reference sensor output values corresponding respectively are preset, and the calculation means uses the measurement sensor output values measured by the measurement means and the humidity sensor among the plurality of relative humidity ranges. Comparing the reference sensor output value corresponding to the relative humidity range that matches the detected relative humidity to calculate a characteristic change of the sensor output value of the developing tank with respect to the reference developing tank, and the correction unit calculates the calculation Based on the characteristic change calculated by the means, an equivalent toner density value corresponding to the measurement sensor output value is detected by the humidity sensor in the plurality of relative humidity ranges. It is preferable to correct the sensor output value of the toner density sensor so as to approach the corresponding toner concentration value corresponding to the reference sensor output value corresponding to the matching relative humidity range relative humidity. This makes it possible to correct the sensor output value of the toner density sensor to an appropriate value regardless of the humidity change around the developer.

  In the image forming apparatus according to the present invention, as the characteristic change, for example, a change in a shift amount of the measurement sensor output value based on the reference sensor output value and a slope of the reference sensor output value with respect to the developer amount are used as a reference. A change in the inclination of the output value of the measurement sensor with respect to the amount of developer made can be mentioned.

  In this case, the toner concentration sensor is a magnetic permeability toner concentration sensor configured to be able to adjust an output operating point according to a change in an input control voltage value, and the calculation means corresponds to the reference sensor output value. A control voltage value for correction is calculated so as to obtain an output operating point corresponding to the shift amount of the equivalent toner density value corresponding to the measurement sensor output value based on the equivalent toner density value. Calculates the change rate of the inclination of the equivalent toner density value corresponding to the measured sensor output value with respect to the developer amount based on the inclination of the equivalent toner density value corresponding to the reference sensor output value, and serves as a reference for the toner density value A correction slope obtained by dividing a reference slope of the control voltage value by the change rate is calculated, and the correction means calculates the correction control voltage value calculated by the calculation means. The sensor output value of the toner density sensor is input to the toner density sensor and the correction slope calculated by the calculating means is set as the slope of the correction control voltage value of the toner density sensor with respect to the toner density value. It is preferable to correct. This makes it possible to correct the sensor output value of the toner density sensor with a simple configuration.

  The “toner density value” is the toner density of the developer recognized by the image forming apparatus based on the sensor output value detected by the toner density sensor.

  In the image forming apparatus according to the present invention, the sensor output value with respect to the developer amount is recognized by the image forming apparatus, for example, by dividing the developer into a plurality so as to correspond to the plurality of developer amounts. Each of the divided developer amounts is input to the developer tank to measure the sensor output value, and the sensor output value measured for each developer amount is instructed to the image forming apparatus together with the developer amount. ,It can be carried out.

  In the image forming apparatus according to the present invention, the measurement sensor output value of the toner density sensor for the plurality of developer amounts is preferably measured when the developer is put into the empty developing tank. By doing so, for example, the sensor output value of the toner density sensor can be corrected at the time of setting up the image forming apparatus or replacing the developer and / or the developing apparatus.

  In addition, from the viewpoint that the toner density control is actually performed in the vicinity of the total amount of the developer, in the image forming apparatus according to the present invention, the correction of the sensor output value of the toner density sensor is finally applied to the developing tank. It is preferable to carry out in the vicinity of the total amount of the predetermined developer that should be accommodated. By doing so, based on the characteristic change, the toner density value corresponding to the measurement sensor output value approaches the equivalent toner density value corresponding to the reference sensor output value in the vicinity of the total amount of the developer. The sensor output value of the density sensor can be corrected.

  In the image forming apparatus according to the aspect of the invention, it is preferable that the toner density sensor is disposed at the bottom of the developing tank in the direction of gravity. By doing so, the developer pressure to the toner concentration sensor is most easily applied, and thus it is possible to stably detect the toner concentration.

  In the image forming apparatus according to the present invention, it is preferable that a warning is issued when the characteristic change calculated by the calculating unit exceeds a predetermined range. In this configuration, it is possible to notify the user of the occurrence of a problem such as an extreme characteristic change of the measurement sensor output value with respect to the reference sensor output value.

  Further, in the image forming apparatus according to the present invention, the developing device includes a developer carrying member disposed in the developing tank, and a preliminary extending from the developing tank to one end side in the axial direction of the developer carrying body. A developing tank may be provided, and the developer and toner may be supplied to the preliminary developing tank. In this configuration, the developer is not supplied directly to the toner density sensor from the direction orthogonal to the axial direction of the developer carrier, but is uniformly supplied along the axial direction of the developer carrier. Therefore, the toner density can be detected by the toner density sensor without causing a sudden change in the toner density.

  As described above, according to the image forming apparatus and the toner density control method of the present invention, even if the sensor output value varies with respect to the developer amount among the plurality of developing tanks in which the toner density sensors are incorporated, Therefore, it is possible to perform toner density control with little variation between the developing tanks.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  FIG. 1 is a front view showing a schematic configuration of an image forming apparatus that implements a toner density control method according to the present invention.

  First, the overall configuration of the image forming apparatus A shown in FIG. 1 will be described. The image forming apparatus A shown in FIG. 1 includes an image forming unit 100 that forms a toner image on a sheet-like recording medium (hereinafter referred to as paper) P such as recording paper or an OHP film using toner.

  The image forming unit 100 includes an image carrier (here, a photoconductive drum) 3 (3a, 3b, 3c, 3d) and a charging device (here) for charging the surface of the photoconductor 3 (3a, 3b, 3c, 3d). A charging device) 5 (5a, 5b, 5c, 5d), an exposure device (here, an exposure unit) 1 for forming an electrostatic latent image on the photoreceptor 3 (3a, 3b, 3c, 3d), A developing device 2 (2a, 2b, 2c, 2d) for visualizing the electrostatic latent image with toner to form a toner image on the photoreceptor 3 (3a, 3b, 3c, 3d), and an intermediate transfer member ( Here, an intermediate transfer belt (7) and a primary transfer device (here, an intermediate transfer roller) 6 (here, an intermediate transfer roller) 6 for transferring the toner image on the photosensitive drum 3 (3a, 3b, 3c, 3d) onto the intermediate transfer belt 7 once. 6a, 6b, 6c, 6d) and the intermediate transfer roller 6 (6a, 6b) 6c, 6d) is a primary cleaning device (here, a cleaner unit) 4 (4a, 4b, 4c, 4d) that removes residual toner remaining on the surface of the photosensitive member 3 (3a, 3b, 3c, 3d) without being transferred. And a secondary transfer device (here, secondary transfer unit) 11 that transfers the toner image on the intermediate transfer belt 7 onto the paper P, and remains on the surface of the intermediate transfer belt 7 without being transferred by the secondary transfer unit 11. A secondary cleaning device (here, an intermediate transfer belt cleaning unit) 9 that removes residual toner, and a pair of fixing rollers that fix the toner image formed on the paper P by heating and melting and fixing the toner image on the paper P And a fixing mechanism 12 having 31 and 32.

  Further, the image forming apparatus A includes a document reading device (here, a scanner device) B, a paper feeding device 10, and a discharge unit 15, and image data corresponding to a document read by the document reading device B or externally. Multi-color and single-color images are formed on the paper P in accordance with the transmitted image data.

  More specifically, the image data handled in the image forming apparatus A corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y), or a single color ( For example, it corresponds to a monochrome image using black). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the charger 5 (5a, 5b, 5c, 5d), the cleaner unit 4 (4a, 4b, 4c, 4d) and four intermediate transfer rollers 6 (6a, 6b, 6c, 6d) are provided in order to form four types of images corresponding to the respective colors. The end codes a, b, c, and d correspond to black (K), cyan (C), magenta (M), and yellow (Y), respectively.

  That is, the image forming unit 100 includes a developing device 2a, a photosensitive drum 3a, a charger 5a, a cleaner unit 4a, and an intermediate transfer roller 6a, a black (K) image station, a developing device 2b, and a photosensitive drum 3b. A cyan (C) image station having a charger 5b, a cleaner unit 4b and an intermediate transfer roller 6b, and a magenta having a developing device 2c, a photosensitive drum 3c, a charger 5c, a cleaner unit 4c and an intermediate transfer roller 6c. An (M) image station and a yellow (Y) image station including a developing device 2d, a photosensitive drum 3d, a charger 5d, a cleaner unit 4d, and an intermediate transfer roller 6d are provided. Hereinafter, the last reference numerals of these members will be omitted.

  The image forming unit 100 is provided below the discharge unit 15 provided in the upper part of the image forming apparatus A.

  The charger 5 is a charging unit for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. As the charger 5, a contact type charger (for example, a roller type or a brush type) or a charger type charger as shown in FIG. 1 can be used.

  The exposure unit 1 has a function of forming an electrostatic latent image corresponding to image data on the surface by exposing the surface of the charged photosensitive drum 3 according to input image data. .

  As the exposure unit 1, a laser scanning unit (LSU) provided with a laser irradiation unit and a reflection mirror, or a writing device (for example, a writing head) in which light emitting elements such as EL and LED are arranged in an array can be used.

  The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners of each color (K, C, M, Y). The developing device 2 will be described in detail later.

  The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer. An intermediate transfer belt unit 8 is disposed above the photosensitive drum 3. The intermediate transfer belt unit 8 includes an intermediate transfer belt driving roller 81, intermediate transfer belt tension rollers 83 and 83, and an intermediate transfer belt driven in addition to the intermediate transfer belt 7, the intermediate transfer roller 6, and the intermediate transfer belt cleaning unit 9. A roller 82 is provided.

  The intermediate transfer belt drive roller 81, intermediate transfer belt tension rollers 83 and 83, intermediate transfer roller 6, intermediate transfer belt driven roller 82, and other rollers stretch and support the intermediate transfer belt 7. Can be moved in a predetermined direction (arrow D direction in the figure).

  The intermediate transfer roller 6 is rotatably supported on the side opposite to the photosensitive drum 3 with the intermediate transfer belt 7 interposed therebetween. The intermediate transfer roller 6 gives a transfer bias to the intermediate transfer belt 7 for the toner image on the photosensitive drum 3.

  The intermediate transfer belt 7 is provided so as to come into contact with the respective photosensitive drums 3, and the toner images of the respective colors formed on the photosensitive drums 3 are sequentially transferred onto the intermediate transfer belt 7. Thus, a color toner image (multicolor toner image) is formed on the intermediate transfer belt 7. Here, the intermediate transfer belt 7 is formed in an endless shape using a film having a thickness of about 100 μm to 150 μm.

  The toner image is transferred from the photosensitive drum 3 to the intermediate transfer belt 7 by the intermediate transfer roller 6 that is in contact with the back side of the intermediate transfer belt 7 (that is, the side opposite to the photosensitive drum 3 of the intermediate transfer belt 7). Done. The intermediate transfer roller 6 has a high-voltage transfer bias for transferring the toner image to the intermediate transfer belt 7, that is, a high-voltage transfer having a polarity (for example, a positive electrode) opposite to the toner charging polarity (for example, a negative electrode). A bias is applied. Here, the intermediate transfer roller 6 is based on a rotating shaft made of a metal having a diameter of 8 mm to 10 mm (for example, stainless steel), and the surface thereof is made of a conductive elastic material (for example, a material such as EPDM or urethane foam). ). The intermediate transfer roller 6 can apply a high voltage uniformly to the intermediate transfer belt 7 by the conductive elastic material. In this embodiment, a roller-shaped transfer electrode is used. However, the present invention is not limited to this, and a brush-shaped electrode can also be used.

  As described above, the toner image visualized with the toner of each color on the photosensitive drum 3 by the image data corresponding to the document read by the document reading device B or the image data received from the outside is an intermediate image. Laminated with the transfer belt 7. The toner images of the respective colors stacked in this manner are transferred to the sheet by the secondary transfer unit 11 disposed at the transfer portion where the sheet P and the intermediate transfer belt 7 face each other by the surface movement of the intermediate transfer belt 7 in the direction of arrow D. Transferred onto P.

  The intermediate transfer belt 7 and the transfer belt 11a of the secondary transfer unit 11 are pressed against each other to form a nip region. Also, the transfer belt 11a of the secondary transfer unit 11 has a voltage (that is, a negative polarity) opposite to the voltage for transferring the toner image of each color on the intermediate transfer belt 7 onto the paper P, that is, the toner charging polarity (for example, a negative electrode). For example, a positive electrode) voltage is applied. Further, in order to constantly obtain the nip region, either the roller of the secondary transfer unit 11 or the intermediate transfer belt drive roller 81 is made of a hard material such as a metal roller, and the other is a soft material such as an elastic roller. (For example, soft materials such as elastic rubber and foamable resin).

  By the way, the toner image of each color on the intermediate transfer belt 7 may not be completely transferred onto the paper P by the secondary transfer unit 11, and the toner may remain on the intermediate transfer belt 7. This residual toner causes toner color mixing in the next step.

  Therefore, the intermediate transfer belt cleaning unit 9 is configured to remove and collect the residual toner. For example, the intermediate transfer belt cleaning unit 9 includes a cleaning blade that contacts the intermediate transfer belt 7 as a cleaning member. The cleaning blade is supported on the back side of the intermediate transfer belt 7 at a position facing the intermediate transfer belt driven roller 82 (that is, the side opposite to the driven roller 82 of the intermediate transfer belt 7).

  The paper feed tray 10 is a tray for storing the paper P, and is provided below the image forming unit 100 of the image forming apparatus A. The discharge unit 15 is provided on the lower side of the document reading device B. In the present embodiment, the discharge unit 15 includes a discharge tray 15a. The paper discharge tray 15a is a tray for placing printed paper P face down.

  Further, the image forming apparatus A is provided with a substantially S-shaped main transport path S1 for sending the paper P in the paper feed tray 10 to the paper discharge tray 15a via the secondary transfer unit 11 and the fixing mechanism 12. It has been.

  Further, a pickup roller 16, a registration roller 14, and a fixing mechanism 12 are disposed along the main conveyance path S1 from the paper feed tray 10 to the paper discharge tray 15a.

  The pickup roller 16 is a pull-in roller that is provided at the end of the paper feed tray 10 and supplies the paper P from the paper feed tray 10 to the main transport path S1 one by one.

  The registration roller 14 temporarily stops the paper P conveyed from the paper feed tray 10 and aligns the leading ends of the paper P. The registration roller 14 has a function of conveying the paper P in a timely manner in synchronization with the toner image on the intermediate transfer belt 7.

  For example, the registration roller 14 conveys the paper P so that the image position of the toner image on the photosensitive drum 3 matches the image position on the paper P based on a detection signal from a pre-registration detection switch (not shown). It has become.

  The fixing mechanism 12 fixes a toner image formed on the paper P by heating and melting and fixing the toner image on the paper P, and includes a pair of fixing rollers 31 and 32. The pair of fixing rollers 31 and 32 can rotate with the paper P interposed therebetween, and at least one of them is a heating roller having a heat source 33. In the present embodiment, both of the pair of fixing rollers 31 and 32 are heating rollers.

  The pair of fixing rollers 31 and 32 are controlled so as to reach a predetermined fixing temperature by the control unit 200 described later based on a signal from the temperature detector 34. The pair of fixing rollers 31 and 32 has a function of thermally fixing the paper P to the paper P by fusing, mixing, and pressing the multicolor toner image transferred to the paper P by thermocompression bonding of the paper P. .

  Next, the developing device 2 will be described in detail. 2 is a schematic view showing the developing device 2 shown in FIG. 1, FIG. 2 (a) is a side view thereof, and FIG. 2 (b) is a plan view thereof. In FIG. 2A, symbol E indicates a two-component developer mainly composed of toner and carrier, and symbol E ′ indicates the upper surface of the developer E. An example of the carrier is a magnetic material such as ferrite.

  As shown in FIG. 2, the developing device 2 includes a developer carrier 21, a developing tank 22, and a magnetic permeability toner concentration sensor 23.

  The developer carrying member 21 carries the developer E, and is here a developing roller. The developer carrying member 21 is disposed in the developing tank 22 and carries the developer E on its surface and is driven to rotate. As a result, the developer carrying member 21 can transport the developer E carried on the surface to a developing region where the electrostatic latent image on the photosensitive drum 3 is developed.

  Specifically, the developer carrying member 21 has a cylindrical developing sleeve 21a that carries the developer E accommodated in the developing tank 22 on the outer peripheral surface and conveys it to the developing region, and the inside of the developing sleeve 21a. A magnet roll (not shown) is provided. The developing sleeve 21a is rotatable relative to the magnet roll and is driven to rotate in a predetermined rotational direction.

  The developing tank 22 contains the developer E. In the present embodiment, the developing tank 22 is provided with a first conveying member 22a and a second conveying member 22b. The 1st conveyance member 22a conveys the developer E in the developing tank 22 from the one side of an axial direction to the other side. The second conveying member 22b conveys the developer E in the developing tank 22 from the other side in the axial direction to one side.

  Specifically, here, the first conveying member 22a is a first conveying screw for conveying the developer E in the developing tank 22 from one side to the other side in the axial direction while supplying the developer E to the developer carrier 21. It is said that. Here, the second conveying member 22b is a second conveying screw for conveying the developer E in the developing tank 22 from the other side in the axial direction to one side while supplying the developer E to the first conveying member 22a. The first and second conveying screws 22a and 22b are provided with helical fins 22a 'and 22b' for conveying the developer E and mixing the toner and carrier, respectively.

  The magnetic permeability toner concentration sensor 23 utilizes a change in magnetic permeability of the developer E, and detects an output voltage value corresponding to the magnetic permeability of the developer E stored in the developing tank 22 as a toner concentration. . The toner density sensor 23 is disposed at a predetermined detection position in the developing tank 22.

  In the present embodiment, the toner concentration sensor 23 is disposed at the bottom of the developing tank 22 in the direction of gravity (see FIG. 2A). By doing so, the pressure of the developer E to the toner density sensor 23 is most easily applied, so that the toner density can be detected stably.

  Further, in the present embodiment, the developing device 2 includes a preliminary developing tank 24 that extends from the developing tank 22 toward one end in the axial direction of the developer carrier 21. The developing device 2 supplies the developer E and the toner to the preliminary developing tank 24.

  The image forming apparatus A further includes a toner replenishing device 30 that replenishes the developer E in the developing device 2 with toner. The toner replenishing device 30 is configured to replenish toner with respect to the developer E in the preliminary developing tank 24. Here, the toner replenishing device 30 is an intermediate hopper to which a toner bottle 31 can be attached.

  A toner replenishing device 30 is connected to the preliminary developing tank 24 of the developing device 2, and a toner bottle 31 is connected to the toner replenishing device 30. The toner bottle 31 supplies toner to the toner supply device 30. In addition, the preliminary developing tank 24 temporarily stores the developer E supplied from the outside when the later-described correction is performed when the developing tank 22 is empty, and the developer E is stored at one end of the developing tank 22. It can be supplied to the department. As a result, in the developing tank 22, the developer E can be uniformly supplied along the axial direction of the developer carrier 21 by the conveying members 22a and 22b, so that the toner density sensor does not cause a sudden change in toner density. 23 can detect the toner density.

  Further, the toner replenishing device 30 can replenish the preliminary developing tank 24 by an operation signal from the control unit 200. That is, the image forming apparatus A includes a control unit 200, and the control unit 200 performs toner density control based on the sensor output value of the toner density sensor 23 provided in the developing tank 22, so The toner is supplied to the developing tank 22 through the developing tank 24.

  FIG. 3 is a schematic block diagram of a control system mainly showing the control unit 200 of the image forming apparatus A shown in FIG.

  The control unit 200 shown in FIG. 3 includes a CPU (Central Processing Unit) (not shown) and a storage unit 201. The storage unit 201 stores various control programs and necessary functions, and includes a ROM (Read Only Memory) and a RAM (Random Access Memory).

  The control unit 200 is configured to perform image forming process control by reading various control programs from the storage unit 201 and executing the read control programs by the CPU.

  In the present embodiment, the toner concentration sensor 23 is configured so that the output operating point can be adjusted by changing the input control voltage value (Vc). The toner concentration sensor 23 is electrically connected to the control unit 200 so that the sensor output value (Vout) is transmitted to the control unit 200 and the control voltage value (Vc) is input from the control unit 200. Further, although not shown in FIG. 3, the toner replenishing device 30 is electrically connected to the control unit 200 so that an operation signal is received from the control unit 200.

  In the image forming apparatus A, the control unit 200 controls the toner density of the two-component developer E based on the sensor output value of the toner density sensor 23. In addition, when the image forming apparatus A controls the toner density of the developer E by the control unit 200, the characteristics of the sensor output value of the developing tank 22 are determined based on the characteristics of the reference developing tank in the reference developing apparatus serving as the reference of the developing apparatus 2. The sensor output value of the toner density sensor 23 is corrected so as to approximate the characteristics of the sensor output value.

In other words, the control program is for causing the control unit 200 to function as means including setting means, measurement means, calculation means, and correction means, which will be described later.
[1] Setting means [setting of reference sensor output value with respect to developer amount]
The setting means stores in the storage unit 201 in advance a reference sensor output value of the reference developer tank for a plurality of different developer amounts of the two-component developer accommodated in the reference developer tank in the reference developing device. It is like that.

  Table 1 below shows that the initial toner concentration of the two-component developer is 5 wt% (here, the weight ratio of the toner to the developer, hereinafter referred to as wt%), and the plurality of developer amounts are supplied to the developing tank. The developer amount is 25%, 50%, 75%, and 100% of the total amount of the predetermined developer to be finally stored, and the reference sensor output value (V) of the reference developer tank with respect to the developer amount and corresponding thereto 3 shows an example of the equivalent toner density value (wt%). The “equivalent toner density value” is a value corresponding to the toner density after control when it is assumed that the toner density of the developer is actually controlled based on the sensor output value detected by the toner density sensor 23. is there. Further, the equivalent toner density value with respect to the reference sensor output value can be obtained by using a predetermined conversion table or a predetermined conversion formula. The same applies to the equivalent toner density value for the measurement sensor output value in Table 2 to be described later. This conversion table or conversion formula is stored in advance in the storage unit 201 in the present embodiment.

［２］測定手段
［現像剤量に対する測定センサ出力値の測定］
前記測定手段は、現像槽２２に収容された２成分現像剤Ｅの前記複数の現像剤量に対するトナー濃度センサ２３の測定センサ出力値をそれぞれ測定するようになっている。

[2] Measuring means [Measurement of measurement sensor output value with respect to developer amount]
The measuring means measures the measurement sensor output value of the toner concentration sensor 23 with respect to the plurality of developer amounts of the two-component developer E accommodated in the developing tank 22.

  In this measurement, the developer E is divided (here, every 25%) so as to correspond to the plurality of developer amounts. Then, each divided developer amount (25% in this case) was added to the developing tank 22 with stirring through the preliminary developing tank 24, and the sensor output value was measured, and measured for each developer amount. The sensor output value is input together with the developer amount to an input unit (not shown) in the operation unit of the image forming apparatus A. Thereby, the sensor output value with respect to the developer amount can be recognized by the image forming apparatus A.

  Table 2 below shows the measurement sensor output value (V) of the developing tank 22 and the corresponding toner concentration value (wt%) corresponding to the developer amount of 25%, 50%, 75% and 100% of the total amount of the developer. An example is shown.

なお、図４は、表１に示す現像剤量に対する基準センサ出力値及び表２に示す現像剤量に対する測定センサ出力値をグラフにしたものである。また、図５は、表１に示す現像剤量に対する基準センサ出力値に対応する相当トナー濃度値及び表２に示す現像剤量に対する測定センサ出力値に対応する相当トナー濃度値をグラフにしたものである。

FIG. 4 is a graph showing the reference sensor output value with respect to the developer amount shown in Table 1 and the measurement sensor output value with respect to the developer amount shown in Table 2. FIG. 5 is a graph showing the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount shown in Table 1 and the equivalent toner density value corresponding to the measured sensor output value with respect to the developer amount shown in Table 2. It is.

In the present embodiment, the toner density control is controlled so that the target toner density of the two-component developer E is 5 wt%.
[3] Calculation means The calculation means compares the measurement sensor output value measured by the measurement means with the reference sensor output value preset by the setting means, and develops the reference developing tank. The characteristic change of the sensor output value of the tank 22 is calculated.

Specifically, in the present embodiment, the characteristic change is developed based on a change in the shift amount of the measurement sensor output value based on the reference sensor output value and an inclination of the reference sensor output value with respect to the developer amount. The change in the inclination of the output value of the measurement sensor with respect to the amount of the agent is assumed.
[Calculation of shift amount]
The calculating means calculates a shift amount of the equivalent toner density value corresponding to the measurement sensor output value based on the equivalent toner density value corresponding to the reference sensor output value.

  Here, the shift amount is calculated at the total amount of developer (100%). That is, the equivalent toner density value corresponding to the reference sensor output value is 5 wt% (see the shaded area in Table 1). Accordingly, the equivalent toner density value (5.2 wt) corresponding to the measurement sensor output value (2.4 V) based on the equivalent toner density value (5.0 wt%) corresponding to the reference sensor output value (2.5 V). %) (See the shaded area in Table 2) is 0.2 wt% (= 5.2 wt% -5.0 wt%).

  As described above, the toner density sensor 23 is configured so that the output operating point can be adjusted by changing the input control voltage value.

  Here, the output operation point of the magnetic permeability toner concentration sensor 23 to which the control voltage value can be input will be described.

  FIG. 6 is a graph showing the relationship between the control voltage value (Vc) for adjusting the output operating point of the toner density sensor 23 and the sensor output value (Vout) of the toner density sensor.

  As shown in FIG. 6, the magnetic permeability toner concentration sensor 23 can change the sensor output value (Vout) within a predetermined fluctuation range by the control voltage value (Vc).

  In the present embodiment, the predetermined fluctuation range of the sensor output value (Vout) of the toner concentration sensor 23 is 0V to 5V. Further, the predetermined adjustment range of the control voltage value (Vc) of the toner density sensor 23 is represented by 256 levels of indices 0 to 255.

  FIG. 7 is a graph showing the relationship between the toner density value of the developer and the output value (Vout) of the toner density sensor. The “toner density value” is the toner density of the developer E recognized by the control unit 200 of the image forming apparatus A based on the sensor output value (Vout) detected by the toner density sensor 23.

  As shown in FIG. 6, if the control voltage value (Vc) is changed, the sensor output value (Vout) can be changed accordingly. Further, as shown in FIG. 7, if the sensor output value (Vout) is changed, the toner density value and the corresponding toner density value can be changed accordingly. Therefore, if the control voltage value (Vc) is changed, the corresponding toner density value corresponding to the sensor output value (Vout) can be changed accordingly.

  Furthermore, if the ratio of the change amount of the control voltage value (Vc) to the change amount of the sensor output value (Vout) (the slope of the waveform in the straight line portion of FIG. 6) is changed, the change in the sensor output value (Vout) is accordingly changed. The ratio of the change amount of the toner density value to the amount (the slope of the waveform in the straight line portion in FIG. 7) can be changed. Therefore, if the ratio (slope) of the change amount of the control voltage value (Vc) to the change amount of the toner density value corresponding to the sensor output value (Vout) is changed, the change amount of the sensor output value (Vout) is changed accordingly. It is possible to change the ratio (slope) of the change amount of the equivalent toner density value corresponding to the toner density value.

As shown in FIG. 7, the magnetic permeability toner concentration sensor 23 changes its sensor output value with respect to the change in the toner density value of the developer E, and the center of the fluctuation range (here, 0V to 5V) of this sensor output value. Since the vicinity is the most stable, in this embodiment, the reference sensor output value of the reference developer tank is the center of the fluctuation range (here, 0 V to 5 V) at the target toner density value (here, 5 wt%). In addition to the position (2.5V here), the control voltage value is set to the center position (128 here) of the adjustment range (0 to 255 here).
[Calculation of control voltage value for correction]
The calculation means calculates a correction control voltage value so that an output operating point corresponding to the shift amount is obtained.

Here, since the shift amount is 0.2 wt%, the correction control voltage value (124) is calculated from the reference control voltage value (128) of the reference developing tank. The correction control voltage value for the shift amount can be calculated by using a predetermined conversion table or a predetermined conversion formula. This conversion table or conversion formula is stored in advance in the storage unit 201 in the present embodiment.
[Calculation of slope of equivalent toner density value with respect to developer amount]
Further, the calculating means calculates an inclination of the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount and an inclination of the equivalent toner density value corresponding to the measurement sensor output value with respect to the developer amount.

  Here, the slope of the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount is the ratio of the change amount of the equivalent toner density value corresponding to the reference sensor output value to the change amount of the developer amount in a predetermined section. Can be calculated. Similarly, the inclination of the equivalent toner density value corresponding to the measurement sensor output value with respect to the developer amount is the same as the inclination of the equivalent toner density value corresponding to the measurement sensor output value with respect to the change amount of the developer amount in the predetermined section. It can be calculated by the rate of change.

  Here, the calculation of the slope is also performed at the total amount of the developer (100%). Specifically, the predetermined section of the developer amount is 75% to 100% of the total amount of the developer. Therefore, the change amount of the developer amount in a predetermined section (75% to 100% of the total amount of the developer) is 25% (= 100% −75%), and the change amount of the developer amount in the predetermined section (25%). The ratio (slope) of the change amount 0.9 wt% (= 5.0 wt% -4.1 wt%) of the equivalent toner density value (4.1 wt% to 5.0 wt%) corresponding to the reference sensor output value is 0. 036 (= 0.9 wt% / 25%) (see Table 1).

Similarly, an equivalent toner density value (4.0 wt% to 5.2 wt%) corresponding to the measured sensor output value with respect to a change amount (25%) in a predetermined section of the developer amount (75% to 100% of the total amount of the developer). %) Of 1.2 wt% (= 5.2 wt% -4.0 wt%) (slope) is 0.048 (= 1.2 wt% / 25%) (see Table 2).
[Calculation of change rate of slope]
Further, the calculating means corresponds to the measurement sensor output value relative to the developer amount based on an inclination of an equivalent toner density value corresponding to the reference sensor output value relative to the developer amount (hereinafter referred to as a first inclination). The change rate of the slope of the toner density value (hereinafter referred to as the second slope) is calculated.

  That is, when the first slope is a and the second slope is b, the change ratio c can be calculated by the following (Equation 1).

c = b / a (Formula 1)
Here, since the first inclination a is 0.036 and the second inclination b is 0.048, the change ratio c is 4/3 (= 0.48 / 0.36).
[Calculation of reference slope]
Further, the calculating means calculates a reference slope of a control voltage value serving as a reference for the toner density value corresponding to the sensor output value of the density detection sensor. A reference control voltage value for the toner density value is set in advance. In the present embodiment, this reference control voltage value is stored in the storage unit 201 in advance.

  This inclination can be calculated by the ratio of the change amount of the reference control voltage value to the change amount of the toner density value in a predetermined section.

  Table 3 below shows reference control voltage values with respect to toner density values. Further, the solid line in FIG. 9 is a graph of the values shown in Table 3. The calculation of the reference control voltage value for the toner concentration value corresponding to the sensor output value can be obtained by using a predetermined conversion table or a predetermined conversion formula. This conversion table or conversion formula is stored in advance in the storage unit 201 in the present embodiment.

ここでは、表３に示すように、トナー濃度値の所定区間は４．５ｗｔ％〜５．０ｗｔ％とされている。従って、トナー濃度値の所定区間の変化量０．５ｗｔ％（＝５．０ｗｔ％−４．５ｗｔ％）に対する基準制御電圧値の変化量４（＝１３２−１２８）の割合（基準傾き）は８（＝４／０．５ｗｔ％）となる。
［補正用傾きの算出］
さらに、前記算出手段は、前記基準傾きを前記変化割合で割った補正用傾きを算出する。

Here, as shown in Table 3, the predetermined interval of the toner density value is 4.5 wt% to 5.0 wt%. Accordingly, the ratio (reference slope) of the change amount 4 (= 132−128) of the reference control voltage value to the change amount 0.5 wt% (= 5.0 wt% −4.5 wt%) of the toner density value in a predetermined section is 8. (= 4 / 0.5 wt%).
[Calculation of correction slope]
Further, the calculation means calculates a correction inclination obtained by dividing the reference inclination by the change rate.

Here, since the reference inclination is 8 and the change ratio c is 4/3, the correction inclination obtained by dividing the reference inclination (8) by the change ratio (4/3) is 6 (= 8 / (4/3)).
[4] Correction means The correction means changes the equivalent toner density value corresponding to the measurement sensor output value to the equivalent toner density value corresponding to the reference sensor output value based on the characteristic change calculated by the calculation means. The sensor output value of the toner density sensor 23 is corrected so as to approach.
[Correction by control voltage for correction]
Specifically, the correction means inputs the correction control voltage value calculated by the calculation means to the toner density sensor 23 and corrects the sensor output value of the toner density sensor 23.

  FIG. 8 shows a state where an equivalent toner density value corresponding to the measurement sensor output value is shifted by the correction control voltage value.

Here, the correction control voltage value (124) calculated by the calculation means is input to the toner density sensor 23. Then, although the waveform shown in FIG. 8 is obtained, the inclination of the equivalent toner density value with respect to the developer amount is considerably deviated as it is, so that the next correction inclination is corrected.
[Correction by tilt for correction]
In other words, the correction means uses the correction inclination calculated by the calculation means as the inclination of the correction control voltage value of the toner density sensor 23 with respect to the toner density value corresponding to the sensor output value. Correct the sensor output value.

  Table 4 below shows control voltage values after correction with respect to toner density values. Also, the chain line in FIG. 9 is a graph of the values shown in Table 4.

ここでは、トナー濃度値に対する補正後の制御電圧値の傾きは、補正用傾きである６となっている。即ち、表４に示すように、センサ出力値に対応するトナー濃度値の所定区間は４．５ｗｔ％〜５．０ｗｔ％とされているので、トナー濃度値の所定区間の変化量０．５ｗｔ％（＝５．０ｗｔ％−４．５ｗｔ％）に対する制御電圧値の変化量３（＝１２７−１２４）の割合（補正用傾き）は６（＝３／０．５ｗｔ％）となっている。

Here, the inclination of the corrected control voltage value with respect to the toner density value is 6 as a correction inclination. That is, as shown in Table 4, since the predetermined interval of the toner density value corresponding to the sensor output value is 4.5 wt% to 5.0 wt%, the amount of change in the predetermined interval of the toner density value is 0.5 wt%. The ratio (correction slope) of the change amount 3 (= 127-124) of the control voltage value with respect to (= 5.0 wt% −4.5 wt%) is 6 (= 3 / 0.5 wt%).

  By correcting in this way, as shown in FIG. 10, the equivalent toner density value corresponding to the measurement sensor output value of the developing tank 22 is brought close to the equivalent toner density value corresponding to the reference sensor output value of the reference developing tank. be able to. Thereafter, the toner density control is performed in such a corrected state.

  According to the image forming apparatus A according to the embodiment of the present invention, based on the characteristic change, an equivalent toner density value corresponding to the measurement sensor output value of the developing tank 22 corresponds to the reference sensor output value of the reference developing tank. The sensor output value of the toner density sensor 23 is corrected so as to approach the equivalent toner density value, that is, taking into account variations in the entire developing device including the assembly accuracy of the developing tank in addition to variations in sensitivity of the sensor alone. Therefore, between a plurality of developing tanks in which the toner density sensor 23 is incorporated, a change in the sensor output value with respect to the developer amount occurs due to a change in the developer amount accompanying image formation or a change in bulk density due to the deterioration of the developer E. Even if this occurs, it is possible to perform toner density control with little variation among the plurality of developing tanks.

  The toner density control is actually performed in the vicinity of the total amount of the developer. In this regard, in the present embodiment, the correction of the sensor output value of the toner density sensor 23 is performed at the total amount of the developer, so that the correction accuracy can be improved.

  In the image forming apparatus A according to the embodiment of the present invention, for example, the measurement sensor output value of the toner concentration sensor 23 for the plurality of developer amounts is measured when the developer E is put into the empty developing tank 22. It is preferable. In this way, the sensor output value of the toner density sensor 23 can be corrected when the image forming apparatus A is set up or when the developer E or the developing device 2 is replaced.

  Further, in the image forming apparatus A according to the embodiment of the present invention, when the characteristic change calculated by the calculating unit exceeds a predetermined range, an alarm is issued. By doing so, it is possible to notify the user of an extreme characteristic change in the measurement sensor output value with respect to the reference sensor output value or the occurrence of a sudden problem. As the alarm mode, an alarm device that displays a message on a display unit (not shown) of the operation unit provided in the image forming apparatus A, and the characteristic change exceeds a predetermined range. It is possible to exemplify an aspect including a determination unit that issues an alarm signal to the alarm device when it is determined whether or not the result of the determination is exceeded.

  Further, the image forming apparatus A according to the embodiment of the present invention may include a humidity sensor 25 that detects the relative humidity around the developer E accommodated in the developing tank 22 as shown in FIG. . The humidity sensor 25 is provided in the developing tank 22 in the illustrated example. Further, although not shown in FIG. 3, the humidity sensor 25 is electrically connected to the control unit 200 so that the sensor output value is transmitted to the control unit 200.

In this case, the control unit 200 of the image forming apparatus A can be configured as follows. Hereinafter, description of the same contents as above will be omitted.
[1] Setting means In other words, the setting means previously sets a plurality of reference sensor output values respectively corresponding to predetermined ranges of a plurality of different relative humidities in the storage unit 201.

  Table 5 below shows a predetermined range of a plurality of relative humidity (20% or more and less than 35%, with respect to the developer amount of 25%, 50%, 75%, 100% of the total amount of developer, with reference humidity being 60%. 35% or more and less than 50%, 50% or more and less than 60%, 60% or more and less than 75%, 75% or more and less than 90%, and 90% or more) corresponding toner corresponding to the reference sensor output value of the reference developing tank. An example of a density value is shown.

［２］測定手段
前記測定手段は、現像槽２２に収容された２成分現像剤Ｅの前記複数の現像剤量に対するトナー濃度センサ２３の測定センサ出力値をそれぞれ測定するようになっている。

[2] Measuring means The measuring means measures the measurement sensor output value of the toner concentration sensor 23 with respect to the plurality of developer amounts of the two-component developer E accommodated in the developing tank 22.

  Table 6 below shows relative humidity (20%, 35%, 50%) detected by the humidity sensor 25 with respect to the developer amount of 25%, 50%, 75%, 100% of the total amount of the developer into the developing tank 22. , 60%, 75%, 90%), an example of an equivalent toner density value corresponding to the measurement sensor output value of the developing tank 22 is shown.

［３］算出手段
［シフト量の算出］
前記算出手段は、前記複数の相対湿度範囲のうち湿度センサ２５にて検出された相対湿度（例えば７５％）に適合する相対湿度範囲（７５％以上９０未満）に対応する前記基準センサ出力値に対応する相当トナー濃度値を基準にした前記測定センサ出力値に対応する相当トナー濃度値のシフト量を算出する。

[3] Calculation means [calculation of shift amount]
The calculation means sets the reference sensor output value corresponding to a relative humidity range (75% or more and less than 90) that matches a relative humidity (for example, 75%) detected by the humidity sensor 25 among the plurality of relative humidity ranges. A shift amount of the equivalent toner density value corresponding to the measurement sensor output value based on the corresponding equivalent toner density value is calculated.

Here, since the shift amount is calculated at the total amount of the developer, when the humidity is 75%, the equivalent toner density value corresponding to the reference sensor output value is 4.8 wt% (Table 1). 5). Accordingly, the equivalent toner density value (5.0 wt%) corresponding to the measurement sensor output value based on the equivalent toner density value (4.8 wt%) corresponding to the reference sensor output value (see the shaded portion in Table 6). Is 0.2 wt% (= 5.0 wt% -4.8 wt%).
[Calculation of control voltage value for correction]
In addition, the calculating unit may be a relative humidity range that matches a relative humidity (for example, 75%) detected by the humidity sensor 25 among the plurality of relative humidity ranges so that an output operating point corresponding to the shift amount is obtained. A correction control voltage value corresponding to (75% or more and less than 90) is calculated.

  Table 7 below shows reference control voltage values respectively corresponding to the predetermined ranges of the plurality of relative humidity.

ここでは、表７に示すように、湿度７５％の場合、トナー濃度値５ｗｔ％に対する基準制御電圧は１２４となる。そして、前記シフト量が０．２ｗｔ％であるので、前記基準現像槽の基準制御電圧値（１２４）から補正用制御電圧値（１２０）を算出する。この補正用制御電圧値の算出も、前記と同様、換算テーブル又は換算式を用いることで求めることができる。
［現像剤量に対する相当トナー濃度値の傾きの算出］
また、前記算出手段は、現像剤量に対する前記基準センサ出力値に対応する相当トナー濃度値の傾き及び現像剤量に対する前記測定センサ出力値に対応する相当トナー濃度値の傾きを算出する。

Here, as shown in Table 7, when the humidity is 75%, the reference control voltage for the toner density value of 5 wt% is 124. Since the shift amount is 0.2 wt%, the correction control voltage value (120) is calculated from the reference control voltage value (124) of the reference developing tank. The calculation of the correction control voltage value can also be obtained by using a conversion table or a conversion formula, as described above.
[Calculation of slope of equivalent toner density value with respect to developer amount]
Further, the calculating means calculates an inclination of the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount and an inclination of the equivalent toner density value corresponding to the measurement sensor output value with respect to the developer amount.

  Here, since the slope is also calculated at the total amount of the developer, the predetermined section of the developer amount is 75% to 100% of the total amount of the developer. Accordingly, the amount of change in a predetermined section of developer amount (75% to 100% of the total amount of developer) is 25%. When the humidity is 75%, the reference sensor output value with respect to the amount of change in the predetermined section of developer amount is set. The ratio (first slope) of the change amount 0.9 wt% of the corresponding equivalent toner density value (3.9 wt% to 4.8 wt%) is 0.036 (see Table 5).

Similarly, when the humidity is 75%, an equivalent toner density value (3.8 wt% to 5 wt%) corresponding to the measured sensor output value with respect to a change amount in a predetermined section of the developer amount (75% to 100% of the total amount of the developer). (0.0 wt%) of the change amount 1.2 wt% (second slope) is 0.048 (see Table 6).
[Calculation of change rate of slope]
The calculating means calculates a change rate of the second inclination based on the first inclination.

That is, when the first inclination is a and the second inclination is b, the change ratio c is calculated by the above (Equation 1). Here, the inclination a is 0.036 and the inclination b is Since it is 0.048, the change ratio c is 4/3 (= 0.48 / 0.36).
[Calculation of reference slope]
The calculating means calculates a reference slope of the reference control voltage value with respect to the toner density value. Table 7 also shows the reference control voltage value with respect to the toner density value. The calculation of the reference control voltage value with respect to the toner density value can also be obtained by using a conversion table or a conversion formula, as described above.

Here, as shown in Table 7, the predetermined interval of the toner density value is 4.5 wt% to 5.0 wt%. Therefore, when the humidity is 75%, the change amount of the predetermined interval of the toner density value is 0.5 wt%. The ratio (reference slope) of the change amount 4 (= 128-124) of the reference control voltage value to% is 8 (see the hatched portion in Table 7).
[Calculation of correction slope]
Further, the calculation means calculates a correction inclination obtained by dividing the reference inclination by the change rate.

Here, since the reference inclination is 8 and the change rate c is 4/3, the correction inclination obtained by dividing the reference inclination by the change rate is 6.
[4] Correction means [correction by correction control voltage]
The correction means inputs the correction control voltage value calculated by the calculation means to the toner density sensor 23 and corrects the sensor output value of the toner density sensor 23.

Here, the correction control voltage value (120) calculated by the calculation means is input to the toner density sensor 23.
[Correction by tilt for correction]
Further, the correction means uses the correction slope (here, 6) calculated by the calculation means as the slope of the correction control voltage value of the toner density sensor 23 with respect to the toner density value. Correct the output value.

  Table 8 below shows control voltage values after correction with respect to toner density values.

ここでは、表８に示すように、トナー濃度値の所定区間は４．５ｗｔ％〜５．０ｗｔ％とされているので、湿度７５％の場合、トナー濃度値の所定区間の変化量０．５ｗｔ％に対する制御電圧値の変化量３（＝１２３−１２０）の割合（補正用傾き）は６となっている（表８の斜線部参照）。

Here, as shown in Table 8, the predetermined interval of the toner density value is 4.5 wt% to 5.0 wt%. Therefore, when the humidity is 75%, the change amount of the predetermined interval of the toner density value is 0.5 wt. The ratio (correction slope) of the change amount 3 (= 123−120) of the control voltage value with respect to% is 6 (see the hatched portion in Table 8).

  In the image forming apparatus A having such a configuration, the sensor output value of the toner density sensor 23 can be corrected to an appropriate value regardless of the humidity change around the developer E.

1 is a front view illustrating a schematic configuration of an image forming apparatus that performs a toner concentration control method according to the present invention. FIG. 2 is a schematic diagram illustrating the developing device illustrated in FIG. 1, in which FIG. 1A is a side view thereof, and FIG. FIG. 2 is a schematic block diagram of a control system mainly showing a control unit of the image forming apparatus shown in FIG. 1. The reference sensor output value with respect to the developer amount shown in Table 1 and the measurement sensor output value with respect to the developer amount shown in Table 2 are graphed. 3 is a graph showing the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount shown in Table 1 and the equivalent toner density value corresponding to the measurement sensor output value with respect to the developer amount shown in Table 2. FIG. 6 is a graph showing a relationship between a control voltage value (Vc) for adjusting an output operating point of a toner density sensor and a sensor output value (Vout) of the toner density sensor. 7 is a graph showing a relationship between a toner density of a developer and an output value (Vout) of a toner density sensor. 6 is a graph showing a state where an equivalent toner density value corresponding to a measurement sensor output value is shifted by a correction control voltage value. The values shown in Table 3 and Table 4 are graphed. 3 is a graph showing the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount and the corrected equivalent toner density value corresponding to the measured sensor output value with respect to the developer amount. It is a graph which shows an example of the result of having added the developer to the developing tank of two developing devices one by one of the total amount of developer, and measuring the sensor output.

Explanation of symbols

2 Developing device 21 Developer carrier 22 Developing tank 23 Toner density sensor 24 Preliminary developing tank 25 Humidity sensor 200 Control unit 201 Storage unit A Image forming apparatus E Developer

Claims (9)

A developing device having a developing tank for storing a two-component developer containing toner and a carrier, and a toner concentration sensor for detecting a toner concentration of the two-component developer stored in the developing tank, the sensor of the toner concentration sensor An image forming apparatus that controls the toner concentration of the two-component developer based on an output value,
Setting means for presetting a reference sensor output value of the reference developing tank for a plurality of different developer amounts of the two-component developer contained in the reference developing tank in the reference developing device;
Measuring means for respectively measuring measurement output values of the toner concentration sensor with respect to the plurality of developer amounts of the two-component developer contained in the developing tank;
By comparing the measured sensor output value measured by the measuring means with the reference sensor output value preset by the setting means, the characteristic change of the sensor output value of the developing tank relative to the reference developing tank is determined. A calculating means for calculating;
Based on the characteristic change calculated by the calculation means, the sensor output of the toner density sensor is adjusted so that the equivalent toner density value corresponding to the measurement sensor output value approaches the equivalent toner density value corresponding to the reference sensor output value. An image forming apparatus comprising: a correction unit that corrects the value. A humidity sensor for detecting the relative humidity around the developer contained in the developer tank;
The setting means is preset with a plurality of reference sensor output values respectively corresponding to a predetermined range of a plurality of different relative humidity,
The calculation means includes the reference sensor corresponding to a relative humidity range that matches the measurement sensor output value measured by the measurement means and the relative humidity detected by the humidity sensor among the plurality of relative humidity ranges. Compare the output value and calculate the characteristic change of the sensor output value of the developing tank relative to the reference developing tank,
The correction means is a relative humidity in which an equivalent toner density value corresponding to the measurement sensor output value is detected by the humidity sensor in the plurality of relative humidity ranges based on the characteristic change calculated by the calculation means. The image forming apparatus according to claim 1, wherein the sensor output value of the toner density sensor is corrected so as to approach an equivalent toner density value corresponding to the reference sensor output value corresponding to a relative humidity range that conforms to . The characteristic change is a change in the measurement sensor output value relative to the developer amount based on a change in the shift amount of the measurement sensor output value relative to the reference sensor output value and a slope of the reference sensor output value relative to the developer amount. Change in inclination,
The toner concentration sensor is a magnetic permeability toner concentration sensor configured to be able to adjust an output operating point according to a change in an input control voltage value.
The calculation means controls the correction so that an output operating point corresponding to the shift amount of the equivalent toner density value corresponding to the measurement sensor output value based on the equivalent toner density value corresponding to the reference sensor output value is obtained. A voltage value is calculated, and a change in the slope of the equivalent toner density value corresponding to the measured sensor output value with respect to the developer amount based on the slope of the equivalent toner density value corresponding to the reference sensor output value with respect to the developer amount is calculated. A ratio is calculated, and a correction slope is calculated by dividing the reference slope of the control voltage value serving as a reference for the toner density value by the change ratio,
The correction means inputs the correction control voltage value calculated by the calculation means to the toner density sensor, and uses the correction inclination calculated by the calculation means with respect to the toner density sensor. The image forming apparatus according to claim 1, wherein a sensor output value of the toner density sensor is corrected as an inclination of the correction control voltage value.   The measurement sensor output value of the toner density sensor for the plurality of developer amounts is measured when the developer is charged into the empty developing tank. Image forming apparatus.   5. The image formation according to claim 1, wherein the correction of the sensor output value of the toner density sensor is performed in the vicinity of a predetermined total amount of developer to be finally stored in the developing tank. apparatus.   The image forming apparatus according to claim 1, wherein the toner density sensor is disposed at a bottom portion in a gravity direction in the developing tank.   The image forming apparatus according to claim 1, wherein an alarm is issued when the characteristic change calculated by the calculating unit exceeds a predetermined range.   The developing device includes a developer carrying member disposed in the developing tank and a preliminary developing tank extending from the developing tank to one end side in the axial direction of the developer carrying body. The image forming apparatus according to claim 1, wherein a developer and toner are supplied to the image forming apparatus. A developing device having a developing tank for storing a two-component developer containing toner and a carrier, and a toner concentration sensor for detecting a toner concentration of the two-component developer stored in the developing tank, the sensor of the toner concentration sensor A toner concentration control method for an image forming apparatus for controlling the toner concentration of the two-component developer based on an output value,
The reference sensor output value of the reference developer tank is set in advance for a plurality of different developer amounts of the two-component developer housed in the reference developer tank in the reference developing device, and the two-component developer housed in the developer tank is set. A measurement sensor output value of the toner concentration sensor for each of the plurality of developer amounts of the agent is measured, and the measured sensor output value is compared with a preset reference sensor output value to determine the reference A characteristic change of the sensor output value of the developing tank with respect to the developing tank is calculated, and based on the calculated characteristic change, an equivalent toner density value corresponding to the measurement sensor output value corresponds to the reference toner output value A toner density control method, wherein the sensor output value of the toner density sensor is corrected so as to approach the density value.

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