JP2006126698A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with which toner concentration can be correctly calculated by an optical system toner concentration detecting means even in case where spent occurs on the surface of carrier due to stress resulting from use of developer. <P>SOLUTION: The image forming apparatus develops an electrostatic latent image on each image carrier by using a corresponding developing device storing two-component developer composed of toner and carrier. In the image forming apparatus, using an optical sensor, a control section calculates toner concentration by measuring an amount of light reflected from developer in the developing device. The control section also separates only carrier from the developer by generating an electric field in the developing device. Using the the optical sensor, the control section then measures an amount of light reflected from the carrier separated. Using the amount of light reflected from the carrier, the value of the toner concentration calculated is corrected. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, and relates to an electrophotographic image forming apparatus, and more particularly, to an image forming apparatus that performs development using a two-component developer.

  In recent years, even in an electrophotographic image forming apparatus, a high-speed / high-quality image equivalent to offset printing has been required.

  In order to achieve high image quality, the toner needs to be uniformly charged in the development process. Further, in order to cope with the increase in speed, the toner needs to be quickly charged. In order to satisfy the performance required for these toners, it is advantageous to use a two-component developer composed of toner and carrier as a developer rather than a one-component developer composed of only toner. .

  On the other hand, the point when using a two-component developer is the control of the toner density.

  By controlling the toner density as desired, a target image density can be obtained. For this purpose, a means for detecting the toner density of the developer in the developing device is required.

  As the toner concentration detection means, a magnetic permeability type toner concentration sensor that measures the magnetic permeability of the developer and an optical toner concentration sensor that measures the amount of reflected light from the developer to obtain the toner concentration are widely known. .

  As a problem in the case of the magnetic permeability sensor, even if the toner concentration is constant, if the charge amount changes, the bulk density of the developer changes, and therefore the magnetic permeability of the developer changes. Therefore, it is determined that the toner density has also changed.

  Accordingly, an optical sensor is more suitable than a magnetic permeability sensor for a developer with large fluctuations in bulk density, and in particular, a color developer whose reflected light amount varies greatly depending on the toner concentration (generally with a low toner concentration). Suitable for small reflected light quantity, high toner density and large reflected light quantity).

As an optical toner density sensor, there is an example as shown in Patent Document 1 in the past. In the case of this conventional example, the toner concentration is obtained by measuring the amount of reflected light with respect to the developer carried on the developer carrying member dedicated to toner density measurement.
Japanese Patent Laid-Open No. 2004-29090

  Even with the optical toner concentration sensor disclosed in Patent Document 1, it is not always possible to detect the required satisfactory toner concentration.

  The problem with optical toner density sensors is that due to deterioration due to the use of the developer, even when compared with the same toner density, the amount of reflected light is larger than that of a new developer, and the toner density tends to be judged to be high. There is.

  The reason why the amount of reflected light from the developer is larger than that of a new developer due to deterioration due to the durability of the developer is that the developer is subjected to mechanical or thermal stress due to the use of the developer, and the carrier surface becomes fine powder. This is because a so-called spent phenomenon in which the toner is fixed occurs, and when a color developer is taken as an example, the color of the toner is slightly mixed with the original color of the carrier surface, resulting in a bright color.

  Therefore, erroneous detection is caused so as to determine that the toner density is high from the detection result that the amount of reflected light from the developer is large.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately calculating a toner density by an optical toner density detecting means even in a state in which a spent is generated on a carrier surface due to stress due to the use of a developer. is there.

The object is achieved by the inventions according to claims 1 to 5 below.
(Claim 1)
In an image forming apparatus that develops an electrostatic latent image on an image forming body using a developing device that contains a two-component developer composed of toner and a carrier,
The control unit uses an optical sensor to measure the amount of reflected light from the developer in the developing device to calculate the toner density, and forms an electric field in the developing device to separate only the carrier from the developer. An image forming apparatus characterized in that the amount of light reflected from the toner is measured by an optical sensor and the toner density calculation value is corrected using the amount of light reflected from the carrier.
(Claim 2)
A developer carrying body A for developing the toner on the image forming body, and a developer carrying body B for supplying the developer to the developer carrying body A;
Both developer carrier A and developer carrier B are composed of a rotatable non-magnetic cylindrical member and a magnet group disposed therein, and are installed so as to face each other.
When measuring the amount of reflected light from the developer, the developer carrier A and the developer carrier B are set to the same potential, and the developer carrier A has a magnet positioned at the closest facing portion between the two. The carrier B sets the phase of the magnet group so as to be an intermediate position between two magnets having different polarities from the magnet,
When measuring the amount of light reflected from the carrier, the phase of the magnet group is set so that an electric field is formed between the developer carrier A and the developer carrier B, and the magnets of the same polarity are opposed to each other at the closest facing portion between the two. Set,
The optical sensor measures the amount of reflected light from the developer or carrier carried on the developer carrier A.
The image forming apparatus according to claim 1.
(Claim 3)
A developer carrying body A for developing toner on the image forming body, and a developer carrying body B that peels off the developer from the developer carrying body A;
Both developer carrier A and developer carrier B are composed of a rotatable non-magnetic cylindrical member and a magnet group disposed therein, and are installed so as to face each other.
When measuring the amount of reflected light from the developer, the developer carrying body A and the developer carrying body B are set to the same potential, and the developer carrying body B has a magnet positioned at the closest facing portion between the two. The carrier A sets the phase of the magnet group so that it is in the middle position between the two magnets of opposite polarity and the polarity of the magnet,
When measuring the amount of light reflected from the carrier, the phase of the magnet group is set so that an electric field is formed between the developer carrier A and the developer carrier B, and the magnets of the same polarity are opposed to each other at the closest facing portion between the two. Set,
The optical sensor measures the amount of reflected light from the developer or carrier carried on the developer carrier B.
The image forming apparatus according to claim 1.
(Claim 4)
4. The image forming apparatus according to claim 1, wherein the amount of light reflected from the carrier is measured every predetermined developing device driving time.
(Claim 5)
The image forming apparatus according to claim 1, wherein the amount of light reflected from the carrier is measured every predetermined number of prints.

  According to the present invention described in claims 1 to 3, the measured developer toner is used to correct the change in the amount of reflected light due to the spent of the carrier in detecting the toner density by the optical toner density detecting means. The toner density is accurately calculated by separating the carrier alone from the developer and measuring the amount of reflected light and correcting the density detection value.

  According to the present invention, the toner density calculation value is corrected every predetermined developing device driving time or every predetermined number of prints, so that the toner is often used during the printing operation. At the time of density detection, an accurate toner density calculation value within an allowable range can be obtained simply by performing toner density detection by calculating using the correction value of the toner density calculation value previously performed. became.

  (1) Prior to the description of the image forming apparatus of the present invention, a method for correcting the toner density using the amount of light reflected from the carrier will be described.

  FIG. 1 shows the relationship between the toner concentration of the new developer and the developer after endurance (in this example, after 100,000 prints) and the amount of reflected light (in the case of a cyan developer). In any developer, the lower the toner density, the greater the influence of the carrier surface color (gray near black), so the amount of reflected light decreases, and the optical sensor output changes linearly with respect to the toner density. ing. At that time, the amount of reflected light increases with the same developer concentration in the durable developer in which the toner is spent on the carrier surface.

  On the other hand, in the region where the toner concentration is high, the influence of the carrier surface is small, so that it is difficult to be influenced by the change in the amount of reflected light due to spent. First, the amount of reflected light from the optical sensor is the same for the same toner density.

  Therefore, in the present invention, only the carrier is separated from the developer for every predetermined number of prints (for example, 3000 prints) of the image forming apparatus, and the reflected light amount from the carrier (output voltage V (C0)) and the reflected light amount from the developer (output). Voltage V (CX)) is measured with an optical sensor. In addition, a new developer is used in advance during the process adjustment to store a reflected light amount (output voltage V (D0)) having a toner concentration of 0% and a reflected light amount (output voltage V (D20)) having a toner concentration of 20%, and a control unit. A calibration curve (Curve D) is created.

  Relationship between toner density and optical sensor output voltage when a durable developer is used with a calibration curve (curve C) connecting the output voltage V (C0) from the carrier and the output voltage V (D20) at a toner density of 20%. The measured output voltage V (CA) from the developer is on the calibration curve (curve C).

  Conventionally, the toner concentration is obtained from a calibration curve (curve D) using the output voltage V (CA) measured from the developer. For this reason, the obtained toner density was recognized as a value higher than the actual value.

  In the present invention, the following calculation process is performed to correct the toner density calculation value, the change in reflected light amount due to spent is removed, and an accurate toner density calculation value V (DA) that does not cause a problem in use is obtained. Will be obtained.

V (DA) = V (CA) − {V (C0) −V (D0)} ×
[1- {V (CA) -V (C0)} / {V (D20) -V (C0)}]
(2) An image forming apparatus to which the present invention is applied will be described.

  FIG. 1 is an overall configuration diagram of an image forming apparatus that performs image exposure control according to the present invention.

  The image forming apparatus includes an image forming apparatus 100 and an image reading apparatus 200.

  The image forming apparatus 100 is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-shaped intermediate transfer member 6, a sheet feeding / conveying unit 20, and a fixing unit 70. It consists of.

  An image reading device 200 including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus 100.

  The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in the image processing unit 50, and once stored in the memory, exposure means (image writing) Means) 3Y, 3M, 3C, 3K.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 5Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 5M. An image forming unit 10C for forming a cyan (C) color image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 5C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 5K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit, and the photosensitive drums 1Y, 1M, and 1C. An electrostatic latent image is formed on 1K.

  4Y, 4M, 4C, and 4K are developing devices that include a two-component developer composed of a small particle size toner of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier, and development. A toner image of each color is formed on the photosensitive drums 1Y, 1M, 1C, and 1K.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  The toner images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) by the primary transfer units 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 to be combined. A colored image is formed.

  The transfer material P accommodated in the paper feeding cassette 21 of the paper feeding / conveying means 20 is fed by the paper feeding means 22, passes through the paper feeding rollers 23, 24, 25, 26, the registration rollers 27, etc., and is subjected to secondary transfer. It is conveyed to a means (transfer roller) 9 and a color image is transferred onto the transfer material P (secondary transfer).

  The transfer material P onto which the color image has been transferred is sandwiched between a fixing roller having a built-in heater in the fixing device 70 and a pressure roller in pressure contact with the fixing roller, and heat and pressure are applied to apply the transfer material P. The color toner image (or toner image) on P is fixed and fixed on the transfer material P, sandwiched between paper discharge rollers 27a and 28, and placed on a paper discharge tray 29 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer unit 9, the residual toner is removed by the cleaning unit 8 from the intermediate transfer body 6 from which the transfer material P is separated by curvature.

  When the transfer material P that has been subjected to the fixing process is reversely discharged, the transfer material P passes through a conveyance path on the right side of the branch plate 28A disposed between the fixing device 70 and the paper discharge roller 28, and the lower second transfer material P. After being transported to one transport path (1), it is transported in reverse, passes through the second transport path (2) on the left side of the branch plate 28 A, and is discharged out of the apparatus by the paper discharge roller 28.

  When copying on both surfaces of the transfer material P, after fixing the image formed on the first surface of the transfer material P, the transfer material P is transferred to the first conveyance path (1), and further to the fourth below the branch plate 28B. After being introduced into the conveyance path (4), the sheet is conveyed in the reverse direction, passed through the conveyance path on the right side of the branch plate 28B, conveyed to the third conveyance path (3), detoured upward, and conveyed by the paper feed roller 26. . On the transfer material P, images of the respective colors are formed on the second surface of the image forming means 10Y, 10M, 10C, and 10K, heated and fixed by the fixing device 70, and discharged to the outside by the paper discharge roller 28.

  In the description of the image forming apparatus 100, the color image formation has been described. However, the present invention includes a case of forming a monochrome image.

  (3) As shown in the first and second embodiments, the developing device 4 used in the image forming apparatus 100 of the present invention includes (A) a developer carrier 41A that develops an electrostatic latent image on the photosensitive drum 1, and And a developer carrier 42A for supplying developer to the developer carrier 41A, and the reflected light quantity of the developer or carrier attached to the developer carrier 41A can be measured by the optical sensor S4. (B) a developer carrier 41B that develops the electrostatic latent image on the photosensitive drum 1, and a developer carrier 42B that peels off the developer from the developer carrier 41B, and is developed by the optical sensor S4. In this configuration, the amount of reflected light from the developer or carrier that is attached to the agent carrier 42B can be measured.

  (A) The developing device of Example 1 will be described with reference to the block diagram shown in FIG.

  Opposite to the photosensitive drum 1, there is a developer carrier 41A composed of a magnet roll 411A having a plurality of magnets therein and a developing sleeve 412A that rotates the outer periphery of the magnet roll 411A in the direction of the arrow.

  In the vicinity of the developer carrier 41A, there is a developer carrier 42A that supplies the developer to the developer carrier 41A. The developer carrier 42A also includes a magnet roll 421A having a plurality of magnets therein, and a developing sleeve 422A that rotates the outer periphery of the magnet roll 421A in the direction indicated by the arrow.

  44A is an agitating member having a water wheel-like blade, which agitates the developer. The developer composed of the toner and the magnetic carrier is agitated and frictionally charged, and the toner is attached to the outer periphery of the carrier. The developing sleeve 422A is rotated and adhered to the peripheral surface of the developing sleeve 422A by a magnetic force, and moves with the rotation of the developing sleeve 422A.

  In the portion of the developing sleeve 422A that is closest to the developing sleeve 412A, the magnet roll 421A is in the middle position between the two magnets having the same magnetic pole, and the magnet roll 411A has a magnet having a different magnetic pole (FIG. 3 ( a)).

  Accordingly, the developer adhering to the developing sleeve 422A by the magnetic force moves to the developing sleeve 412A peripheral surface by the magnetic force difference at the opposite portion, and is conveyed to the developing region.

  While the developer is transported by the developing sleeve 412A, the layer thickness regulating member 43A limits the developer transport amount to a predetermined amount, and a developing bias in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 412A. In the development area, the toner adheres to the electrostatic latent image portion on the photosensitive drum 1 and development is performed.

  In the development process that forms part of the image formation, the optical density of the developer on the developing sleeve 412A is measured by the optical sensor S4 including a light emitting element and a light receiving element in a timely manner, and the toner density is detected and measured. When a correction described later is applied to the toner density output, and the corrected toner density output value falls below a specified value, the control unit performs control to perform toner replenishment.

  The image forming apparatus of the present invention has a toner density detection data correction mode in addition to the image forming mode described above, and detects the amount of reflected light from the carrier for the toner density detected by the optical sensor S4. The control system corrects the detected toner density.

  FIG. 4 is a block diagram showing an outline of the electric control system. Reference numeral 110 denotes a CPU that performs arithmetic control processing, and is connected to a RAM 111, a ROM 112, and a nonvolatile memory 113. The RAM 111 stores the print number integrated value or the development time integrated value, and is added to the integrated value as the number of prints or the development time increases.

  The ROM 112 stores an image formation mode program and a toner density detection data correction program. When the image is formed, the image formation mode program is called and the operation of an external device is controlled via the interface 120 to perform image formation. Do. When the print number integrated value reaches a predetermined integrated value by performing image formation, or when the development time integrated value reaches a predetermined integrated value, the CPU 110 calls a toner density detection data correction program and causes the interface 120 to Thus, the operation of the related members is controlled through the correction of the toner density detection data.

  Next, the toner density detection data correction operation will be described with reference to FIGS.

  The toner density detection data is corrected by first measuring the reflected light of the developer on the developing sleeve 412A by the optical sensor S4.

  The control unit 100 moves the magnet positions of the magnet roll 411A and the magnet roll 421A, and the magnet is positioned for the magnet roll 411A at the closest portion between the developer carrier 41A and the developer carrier 42A. The roll 421A is set so as to be at an intermediate position between two magnets having different magnetic polarities from the magnet positioned on the magnet roll 411A, and a bias voltage having the same potential is applied to the developing sleeve 412A and the developing sleeve 422A. Do. In this embodiment, the voltage is applied to -500 V to drive (see FIG. 3A).

  By performing such a driving operation, the developer adhered and conveyed to the circumferential surface of the developing sleeve 422A by the magnetic force moves to the circumferential surface of the developing sleeve 412A by the magnetic force difference at the facing portion where the developing sleeve 422A is closest to the developing sleeve 412A. The reflected light amount of the developer adhered on the peripheral surface of the developing sleeve 412A is measured as the output voltage V (CA) by the optical sensor S4.

  Next, the reflected light of the carrier on the peripheral surface of the developing sleeve 412A is measured by the optical sensor S4.

  The controller 100 moves the magnet position of the magnet roll 421A, sets the position so that the magnets of the same polarity face each other at the closest facing portion between the developer carrier 41A and the developer carrier 42A, and the developing sleeve A bias voltage having the same polarity as the toner (−500 V in this embodiment) is applied to 412A, the developing sleeve 422A is grounded, and an electric field is formed in the gap between the developing sleeve 412A and the developing sleeve 422A. Is driven (see FIG. 3B).

  By performing such a driving operation, only the carrier moves from the developing sleeve 422A to the developing sleeve 412A by an electric field between the developing sleeve 412A and the developing sleeve 422A.

  However, since a sufficient amount of carrier movement is not easy, the linear velocity of the developing sleeve 422A is changed to about 1.5 to 4 times the linear velocity of the developing sleeve 412A, or the above driving operation is changed to the developing sleeve 412A. The continuation state is performed while the motor rotates a plurality of times.

  In this way, the reflected light amount of the carrier adhering to the circumferential surface of the developing sleeve 412A is measured as the output voltage V (C0) by the optical sensor S4.

  The control unit 100 calculates the toner density from the output voltage V (CA) obtained by measuring the amount of reflected light from the developer and the output voltage V (C0) obtained by measuring the amount of reflected light from the carrier, using the arithmetic expression described above. Value correction is performed.

  The control unit 100 compares the corrected toner density calculated value with the specified toner density value recorded in the memory in advance, and when it is determined that the corrected toner density calculated value is lower than the specified toner density value. Then, toner supply by the toner supply means is performed.

  After the correction of the toner density detection data after the reflected light amount measurement is performed for only the carrier, the next predetermined print integrated value (for example, 2500 prints) or the next predetermined development time integrated value is reached. Regarding the toner density measurement during image formation performed in the meantime, the correction value of the toner density measurement value can be corrected by using the correction value obtained by the reflected light amount measurement of only the previous carrier as it is for the measured toner density output value. The necessity of toner replenishment is determined based on the corrected toner density measurement value.

  (B) The developing device of Example 2 will be described with reference to the block diagram shown in FIG.

  Opposing the photosensitive drum 1, there is a developer carrier 41B including a magnet roll 411B having a plurality of magnets therein and a developing sleeve 412B that rotates the outer periphery of the magnet roll 411B in the direction indicated by the arrow.

  In the vicinity of the developer carrier 41B, there is a developer carrier 42B that peels off the developer from the developer carrier 41B and conveys it. The developer carrier 42B also includes a magnet roll 421B having a plurality of magnets therein, and a developing sleeve 422B that rotates the outer periphery of the magnet roll 421B in the direction of the arrow.

  Reference numerals 442B and 443B are stirring members having water wheel-like blades, which stir the developer. The developer composed of the toner and the magnetic carrier is stirred and frictionally charged, and the toner is attached to the outer periphery of the carrier. At this time, it adheres to the peripheral surface of the rotating developing sleeve 412B by a magnetic force, and moves to the developing area close to the photosensitive drum 1 as the developing sleeve 412B rotates.

  In the portion of the developing sleeve 412B that is closest to the developing sleeve 422B, the magnet roll 411B is at an intermediate position between the two magnets having the same magnetic pole, and the magnet roll 421B has a magnet having a different magnetic pole (FIG. 5 ( a)).

  Therefore, the developer adhering to the developing sleeve 412B by the magnetic force moves to the peripheral surface of the developing sleeve 422B by the magnetic force difference at the opposite portion, and is conveyed to the developer reservoir.

  While the developer is transported by the developing sleeve 412B, the layer thickness regulating member 43B limits the developer transport amount to a predetermined amount, and a developing bias in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 412B. In the development area, the toner adheres to the electrostatic latent image portion on the photosensitive drum 1 and development is performed.

  In the development process that forms part of the image formation, the optical sensor S4 composed of a light emitting element and a light receiving element provided opposite to the developing sleeve 422B is appropriately timed on the developing sleeve 412B on the photosensitive drum 1. In a state where the developer that has passed through the image portion and has not been developed is moved and conveyed onto the developing sleeve 422B, the reflectance of the developer on the developing sleeve 422B is measured, and the toner density is detected and measured. When a correction described later is applied to the toner density output, and the corrected toner density output value falls below a specified value, the control unit performs control to perform toner replenishment.

  The image forming apparatus of the present invention has a toner density detection data correction mode in addition to the image forming mode described above, and detects the amount of reflected light from the carrier for the toner density detected by the optical sensor S4. The control system corrects the detected toner density.

  FIG. 6 is a block diagram showing an outline of the electric control system. Reference numeral 110 denotes a CPU that performs arithmetic control processing, and is connected to a RAM 111, a ROM 112, and a nonvolatile memory 113. The RAM 111 stores the print number integrated value or the development time integrated value, and is added to the integrated value as the number of prints or the development time increases.

  The ROM 112 stores an image formation mode program and a toner density detection data correction program. When the image is formed, the image formation mode program is called and the operation of an external device is controlled via the interface 120 to perform image formation. Do. When the print number integrated value reaches a predetermined integrated value by performing image formation, or when the development time integrated value reaches a predetermined integrated value, the CPU 110 calls a toner density detection data correction program and causes the interface 120 to Thus, the operation of the related members is controlled through the correction of the toner density detection data.

  Next, the toner density detection data correction operation will be described with reference to FIGS.

  The toner density detection data is corrected by first measuring the reflected light of the developer on the developing sleeve 422B by the optical sensor S4.

  The control unit 100 moves the magnet positions of the magnet roll 411B and the magnet roll 421B, and the magnet is positioned for the magnet roll 421B at the closest facing portion between the developer carrier 41B and the developer carrier 42B. The roll 411B is set to be at an intermediate position between two magnets having different magnetic polarities from the magnet located on the magnet roll 421B, and a bias voltage having the same potential is applied to the developing sleeve 412B and the developing sleeve 422B. Do. In this embodiment, voltage is applied to -500 V in both cases, and driving is performed in a state where a non-image area on the photosensitive drum 1 is developed, that is, a state where development is not substantially performed. At this time, the photosensitive member potential is set to −700 V (see FIG. 5A).

  By performing such a driving operation, the developer adhered and transported to the circumferential surface of the developing sleeve 412B by the magnetic force moves to the circumferential surface of the developing sleeve 422B by the magnetic force difference at the facing portion where the developing sleeve 412B is closest to the developing sleeve 422B. The reflected light amount of the developer adhered on the peripheral surface of the developing sleeve 422B is measured as the output voltage V (CA) by the optical sensor S4.

  Next, the reflected light of the carrier on the peripheral surface of the developing sleeve 422B is measured by the optical sensor S4.

  The control unit 100 moves the magnet position of the magnet roll 411B, sets the position so that the magnets of the same polarity face each other at the closest facing portion between the developer carrier 41B and the developer carrier 42B, and the developing sleeve A bias voltage having the same polarity as the toner (−500 V in this embodiment) is applied to 422B, the developing sleeve 412B is grounded, and an electric field is formed in the gap between the developing sleeve 422B and the developing sleeve 412B. Drive with. At this time, the photosensitive member is not charged (see FIG. 5B).

  By performing such a driving operation, only the carrier moves between the developing sleeve 422B and the developing sleeve 412B by an electric field from the developing sleeve 412B to the developing sleeve 422B.

  However, since a sufficient amount of carrier movement is not easy, the linear velocity of the developing sleeve 412B is changed to about 1.5 to 4 times the linear velocity of the developing sleeve 422B, or the above driving operation is changed to the developing sleeve 422B. The continuation state is performed while the motor rotates a plurality of times.

  In this way, the reflected light amount of the carrier adhering to the circumferential surface of the developing sleeve 422B is measured as the output voltage V (C0) by the optical sensor S4.

  The control unit 100 calculates the toner density from the output voltage V (CA) obtained by measuring the amount of reflected light from the developer and the output voltage V (C0) obtained by measuring the amount of reflected light from the carrier, using the arithmetic expression described above. Value correction is performed.

  The control unit 100 compares the corrected toner density calculated value with the specified toner density value recorded in the memory in advance, and when it is determined that the corrected toner density calculated value is lower than the specified toner density value. Then, toner supply by the toner supply means is performed.

  After the correction of the toner density detection data after the reflected light amount measurement is performed for only the carrier, the next predetermined print integrated value (for example, 2500 prints) or the next predetermined development time integrated value is reached. Regarding the toner density measurement during image formation performed in the meantime, the correction value of the toner density measurement value can be corrected by using the correction value obtained by the reflected light amount measurement of only the previous carrier as it is for the measured toner density output value. The necessity of toner replenishment is determined based on the corrected toner density measurement value.

  (C) As a comparative example, a conventional developing device that does not perform toner density correction by measuring the amount of reflected light from a carrier will be described with reference to the configuration diagram shown in FIG.

  In the developer carrying member 41C including the developing roller 412C that has a magnet roll 411C and rotates in the direction of the arrow, the developer that is agitated by the agitating member 44C, frictionally charged, and the toner is attached to the carrier is magnetically applied. Is attached to the circumferential surface of the developing sleeve 412C and conveyed to the developing region.

  In this comparative example, while the developer is transported by the developing sleeve 412C, the layer thickness regulating member 43C limits the developer transport amount to be a predetermined amount, and the developer on the developing sleeve 412C is the optical sensor S4. The toner density is detected by measuring the reflectance by the control unit, and when the measured toner density falls below a specified value, the control unit performs control to replenish the toner.

  (4) The present inventors performed a live-action test on Example 1, Example 2, and Comparative Example, and compared the stability of toner density transition.

(A) The common conditions are as follows.
Image forming device: A4 horizontal 80 sheets / minute machine (digital full color machine)
Process speed V: 400mm / sec
Photoconductor drum diameter: 80 mm
Photoreceptor charging voltage V0: -700V (variable: left is standard value)
Developer carrier potential Vdc: −500 V (variable: left is standard value)
Photoconductor solid exposure potential Vi: -50V
Development bias AC component Vac: 1 kVp-p rectangular wave 5 kHz
Latent image exposure means: Semiconductor laser (wavelength 780 nm)
Developer carrier diameter: 30 mm
Developer carrier-photoreceptor distance Ds: about 0.30 mm
Developer transport amount D on developer carrier: about 25 mg / cm ²
Developer carrier moving speed / process speed (= development θ): 2.0
Optical sensor configuration: light emitting element = infrared LED (central wavelength 880 nm)
Photodetector = Phototransistor
Incident angle 45 ° / light receiving angle 45 °
Toner: Polymerized toner carrier having a volume average particle diameter of 4.5 μm: Volume average particle diameter of 25 μm / magnetization strength of 60 emu / g
Set toner density: 6%
Measurement of reflected light amount of carrier only: Performed every 2500 prints (Example only)
(B) The test contents are as follows.
Printing pattern: Full color image printing mode with an average printing rate of 6% for each color: Continuous printing 100,000 printing environment: General environment (20 ° C, 50%)
Confirmation of toner density: The developer toner density in the developing device is measured every 5000 prints.

The toner concentration of the cyan developer was confirmed.
(Check whether the initial toner concentration is maintained at 6% or not. If within ± 1%, OK.)
(C) Test Results In Example 1 and Example 2, the toner density changed in the range of 6 ± 1% through 100,000 prints, and good performance was shown. FIG. 8 shows the state of toner density transition. The solid density of the output image was stable, and neither fogging nor toner scattering occurred. On the other hand, in the case of the comparative example, it was determined that the toner concentration was higher than the actual value due to the influence of spent, so the amount of toner replenishment was small, and the target of 6 ± 1%, which is the target of toner concentration in the second half of the test. The transition was lower than the range, and the decrease in image density became significant.

  Analysis of the developer after the completion of 100,000 printing revealed that spent was generated on the carrier surface in any of Example 1 / Example 2 / Comparative Example.

  From the above test results, when the image forming apparatuses according to the first and second embodiments of the present invention are used, even when the developer is stressed and a spent is generated on the surface of the carrier, the reflected light amount of only the carrier is measured by the optical sensor. Since the toner density of the developer is calculated by measuring the above, it has become clear that a stable transition of the toner density is exhibited and a good image can be obtained over a long period of time.

FIG. 6 is a relationship diagram of toner density versus reflected light amount of a new developer and a developer after durability. 1 is an overall configuration diagram of an image forming apparatus. 1 is a configuration diagram of a developing device according to Embodiment 1. FIG. 1 is a block diagram illustrating an outline of an electric control system according to a first embodiment. FIG. 6 is a configuration diagram of a developing device according to a second embodiment. FIG. 6 is a block diagram illustrating an outline of an electric control system according to a second embodiment. The block diagram of the image development apparatus of a comparative example. 6 is a graph showing a change in toner concentration between an example and a comparative example.

Explanation of symbols

1 Photosensitive drum 41A, (B) Developer carrier 411A, (B) Magnet roll 412A, (B) Development sleeve 42A, (B) Developer carrier 421A, (B) Magnet roll 422A, (B) Development sleeve 43A, (B) Layer thickness regulating member

Claims (5)

In an image forming apparatus that develops an electrostatic latent image on an image forming body using a developing device that contains a two-component developer composed of toner and a carrier,
The control unit uses an optical sensor to measure the amount of reflected light from the developer in the developing device to calculate the toner density, and forms an electric field in the developing device to separate only the carrier from the developer. An image forming apparatus characterized in that the amount of light reflected from the toner is measured by an optical sensor and the toner density calculation value is corrected using the amount of light reflected from the carrier. A developer carrying body A for developing the toner on the image forming body, and a developer carrying body B for supplying the developer to the developer carrying body A;
Both developer carrier A and developer carrier B are composed of a rotatable non-magnetic cylindrical member and a magnet group disposed therein, and are installed so as to face each other.
When measuring the amount of reflected light from the developer, the developer carrier A and the developer carrier B are set to the same potential, and the developer carrier A has a magnet positioned at the closest facing portion between the two. The carrier B sets the phase of the magnet group so as to be an intermediate position between two magnets having different polarities from the magnet,
When measuring the amount of light reflected from the carrier, the phase of the magnet group is set so that an electric field is formed between the developer carrier A and the developer carrier B, and the magnets of the same polarity are opposed to each other at the closest facing portion between the two. Set,
The optical sensor measures the amount of reflected light from the developer or carrier carried on the developer carrier A.
The image forming apparatus according to claim 1. A developer carrying body A for developing toner on the image forming body, and a developer carrying body B that peels off the developer from the developer carrying body A;
Both developer carrier A and developer carrier B are composed of a rotatable non-magnetic cylindrical member and a magnet group disposed therein, and are installed so as to face each other.
When measuring the amount of reflected light from the developer, the developer carrying body A and the developer carrying body B are set to the same potential, and the developer carrying body B has a magnet positioned at the closest facing portion between the two. The carrier A sets the phase of the magnet group so that it is in the middle position between the two magnets of opposite polarity and the polarity of the magnet,
When measuring the amount of light reflected from the carrier, the phase of the magnet group is set so that an electric field is formed between the developer carrier A and the developer carrier B, and the magnets of the same polarity are opposed to each other at the closest facing portion between the two. Set,
The optical sensor measures the amount of reflected light from the developer or carrier carried on the developer carrier B.
The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein the amount of light reflected from the carrier is measured every predetermined developing device driving time. The image forming apparatus according to claim 1, wherein the amount of light reflected from the carrier is measured every predetermined number of prints.

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