JP5380126B2 - Toner adhesion amount detection method and color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus such as a color copying machine or a color printer, and more particularly to a toner adhesion amount detection method in a case where a toner adhesion amount of a reference image is detected and density correction is performed.

  In an image forming apparatus using an electrophotographic process, generally, toner is directly transferred onto a toner carrier to form a reference image, and the toner amount and position are detected to perform density correction and color misregistration correction. For example, in the case of a tandem full-color image forming apparatus, a cyan, magenta, yellow, and black image forming unit forms a reference image (patch image) for density correction for each color on the intermediate transfer belt, and the detection unit detects the image. Density and color misregistration correction is performed.

  As the detection means, generally, an optical detection means including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is used. For example, when measuring the toner adhesion amount on the transfer belt, measurement light is emitted from the light emitting element to the toner image. The measurement light is incident on the light receiving element as light reflected by the toner and light reflected by the belt surface.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amount of the light receiving element is reduced. On the other hand, when the adhesion amount of toner is small, conversely, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element. Therefore, the density of the reference image of each color is detected based on the output value of the received light signal based on the amount of received reflected light, and the charging potential, the developing bias characteristic value, the exposure amount of the exposure device, etc. are compared with a predetermined reference density. By adjusting, density correction is performed for each color.

  In order to perform density correction strictly using the reference image, it is necessary to measure the exact amount of toner adhering to the intermediate transfer belt. For example, in Patent Document 1, a reference image formed on a toner carrier is irradiated with measurement light, and the amount of regular reflection is detected to measure the amount of toner adhesion. In this case, if a toner carrier having a low surface glossiness is used, the sensor output becomes small regardless of the density of the reference image, making it difficult to accurately detect the density of the reference image. For this reason, in Patent Document 1, the glossiness of the surface of the toner carrying member is a predetermined value or more (50 to 98 or less at a measurement angle of 20 degrees).

  On the other hand, in Patent Document 2, the reference image is irradiated with measurement light, and the toner adhesion amount is measured by detecting the difference between the regular reflection light amount and the irregular reflection light amount. According to this method, compared with the method of Patent Document 1 that detects only the amount of specularly reflected light, the sensor output changes greatly according to the density of the reference image in both black toner and color toner, and therefore, particularly in a color image forming apparatus. In this case, it is possible to accurately detect the toner adhesion amount. Even in this case, in order to obtain a sufficient amount of regular reflection light, a material having a glossiness on the surface of the toner carrying member of a predetermined value or more is used as in Patent Document 1.

  By the way, in general, the surface state of the toner carrier changes depending on the usage period of the image forming apparatus and other components (for example, abrasive) other than the toner component contained in the toner. Therefore, the initial surface state cannot be maintained until the preset lifetime of the toner carrier is completed, and the light reception output of the light receiving element changes according to the change in the surface state. In this method, it is difficult to accurately measure the toner adhesion amount.

  Therefore, a method for accurately measuring the toner adhesion amount regardless of the change in the surface state of the toner carrier has been proposed. Patent Document 3 discloses a transfer in which the initial glossiness of the surface is 20 or less at a measurement angle of 60 degrees. An image forming apparatus using a belt (toner carrier) is disclosed. According to this method, by suppressing the initial glossiness of the belt surface to a low level, it is possible to accurately measure the toner adhesion amount by reducing the fluctuation range of the glossiness after durable use.

JP 2002-23433 A JP 2001-194443 A JP 2006-201587 A

  However, even when the toner carrier having a low initial glossiness disclosed in Patent Document 3 is used, it is difficult to accurately measure the toner adhesion amount when the glossiness change after durable use is large. . In addition, if the glossiness of the surface is extremely low, the output signal level of the reflected light from the reference image and the output signal level (background value) of the reflected light from the belt surface are close to each other, making it difficult to control the density. There was a problem of becoming.

  In view of the above problems, the present invention can execute a toner adhesion amount detection method capable of accurately measuring a toner adhesion amount regardless of a change in glossiness of the toner carrier, and can perform highly accurate image density control based on the toner adhesion amount. An object of the present invention is to provide a color image forming apparatus.

In order to achieve the above object, the present invention detects the toner adhesion amount of the reference image based on the received light output signals of the regular reflection light amount and the irregular reflection light amount from the color and black reference images, and the detected toner adhesion amount is obtained. In the density correction method of the color image forming apparatus for correcting the density of the color and black images by adjusting the development bias based on the above, the toner adhesion amount of the reference image based on only the light reception output signal of the irregularly reflected light amount for the color toner For black toner, a target value of the saturated toner adhesion amount for forming a single layer of toner is calculated from the extreme value of a curve obtained by approximating the difference between the light reception output signals of the regular reflection light amount and the irregular reflection light amount with a cubic function. is the density correction method and performing the adjustment of the development bias so that the target value amount impregnating toner adhesion is calculated

The present invention also provides an optical detection means capable of irradiating light on a color and black reference image formed on a toner carrier and measuring a regular reflection light quantity and an irregular reflection light quantity from the reference image; and the optical detection means A color image forming apparatus comprising: a control unit configured to detect a toner adhesion amount of the reference image based on a light reception output signal of the specular reflection light amount and the irregular reflection light amount measured by the control unit; For toner, the toner adhesion amount of the reference image is detected based on only the light reception output signal of the irregular reflection light amount, and the image density is controlled so that the toner adhesion amount becomes a target value. target value of the saturation toner adhesion amount of the difference of the cubic function approximated curve of the received light output signal is a single layer is formed toner adhesion amount of toner when an extreme value of the diffused reflection light amount and Controlling the image density Te is a color image forming apparatus according to claim.

According to the first configuration of the present invention, for the color toner, the toner adhesion amount is detected by using only the light reflection output signal of the irregular reflection light, and for the black toner, the difference between the light reception output signal of the regular reflection light amount and the irregular reflection light amount is calculated as a third order. By performing density correction using the toner adhesion amount calculated from the extreme value of the function approximated curve as the target value of the saturated toner adhesion amount, the toner adhesion amount of the reference image can be accurately detected regardless of the surface glossiness of the toner carrier. can do.

According to the second configuration of the present invention, for color toner, the toner adhesion amount is detected using only the diffused light reception / output signal, and the image density is controlled so that the toner adhesion amount becomes a target value. For black toner, the toner density is controlled by setting the toner adhesion amount when the curve obtained by approximating the difference between the light reception output signals of the regular reflection light amount and the irregular reflection light amount to a cubic function takes an extreme value, and using the toner adhesion amount as a target value of the saturated toner adhesion amount Since the toner adhesion amount of the reference image can be accurately detected regardless of the surface glossiness of the carrier, the image forming apparatus is capable of stable density control even at the end of the useful life of the toner carrier.

1 is a schematic diagram showing the overall configuration of a color image forming apparatus of the present invention. Side surface sectional view of the developing device used in the image forming apparatus of the present invention The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller 1 is a block diagram showing a control path of an image forming apparatus of the present invention. Schematic diagram of reference image for density correction 1 is a schematic diagram showing an example of a toner adhesion amount measuring device used in an image forming apparatus of the present invention. The graph which shows the relationship between the measured output value of the toner adhesion amount measuring apparatus and the toner adhesion amount when a cyan reference image is formed on an intermediate transfer belt having a surface glossiness of 18.5. A graph showing a relationship between a measured output value of a toner adhesion amount measuring apparatus and a toner adhesion amount when a magenta reference image is formed on an intermediate transfer belt having a surface glossiness of 18.5. The graph which shows the relationship between the measured output value of a toner adhesion amount measuring apparatus and a toner adhesion amount when a yellow reference image is formed on an intermediate transfer belt having a surface glossiness of 18.5. The graph which shows the relationship between the measured output value of a toner adhesion amount measuring apparatus and a toner adhesion amount when a black reference image is formed on an intermediate transfer belt having a surface glossiness of 18.5. The graph which shows the relationship between the measured output value of a toner adhesion amount measuring apparatus when a cyan reference image is formed on an intermediate transfer belt having a surface glossiness of 3.4 and the toner adhesion amount A graph showing a relationship between a measured output value of a toner adhesion amount measuring apparatus and a toner adhesion amount when a magenta reference image is formed on an intermediate transfer belt having a surface glossiness of 3.4. The graph which shows the relationship between the measured output value of the toner adhesion amount measuring apparatus and the toner adhesion amount when the yellow reference image is formed on the intermediate transfer belt having the surface glossiness of 3.4. The graph which shows the relationship between the measured output value of the toner adhesion amount measuring apparatus and the toner adhesion amount when a black reference image is formed on the intermediate transfer belt having a surface glossiness of 3.4 Graph that approximates the relationship between the measured output value of the black reference image and the toner adhesion amount by a cubic function Graph showing changes in toner adhesion when the toner adhesion measurement method is changed

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a color image forming apparatus of the present invention. In the main body of the image forming apparatus (color printer) 100, four image forming portions Pa, Pb, Pc and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is sequentially transferred (primary transfer) onto an intermediate transfer belt (toner carrier) 8 that moves adjacent to each image forming portion while rotating clockwise in FIG. 1 by a driving means (not shown). Then, the image is transferred (secondary transfer) onto the transfer paper P at a time by the secondary transfer roller 9, and further fixed on the transfer paper P by the fixing unit 7, and then discharged from the apparatus main body. ing. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. Further, a cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure device 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d includes a developing roller (developer carrying member) disposed opposite to the photosensitive drums 1a to 1d, and toners of cyan, magenta, yellow, and black are respectively supplied by a replenishing device (not shown). A predetermined amount is filled. The toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing devices 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure device 4. A toner image is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the primary transfer rollers 6a to 6d. Primary transferred onto. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a driven roller 10, a drive roller 11, and a tension roller 47, and the intermediate transfer belt 8 starts to rotate clockwise as the drive roller 11 is rotated by a drive motor (not shown). Then, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and at a nip portion (secondary transfer nip portion) with the intermediate transfer belt 8. The full color image is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13, and the toner image is fixed on the surface of the transfer paper P, so that a predetermined full color is obtained. An image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, the image is directly discharged onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is redistributed to the secondary transfer roller 9 in a state where the image surface is reversed by rotating the discharge roller pair 15 in the reverse direction to be distributed to the paper conveyance path 18 by the branching section 14. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  A toner adhesion amount measuring device 45 is disposed on the downstream side of the image forming unit Pd and the upstream side of the secondary transfer roller 9. The toner adhesion amount measuring device 45 irradiates the reference image formed on the intermediate transfer belt 8 in the image forming portions Pa to Pd with measurement light, and detects the amount of reflected light from the reference image. A detection result is transmitted to the control part 32 mentioned later as a light reception output signal. As the toner adhesion amount measuring device 45, generally, an optical sensor including a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is used. When measuring the density of the reference image, when the measurement light is sequentially irradiated from the light emitting element to each reference image on the intermediate transfer belt 8, the measurement light is received as light reflected by the toner and light reflected by the belt surface. Incident on the element. A specific configuration of the toner adhesion amount measuring device 45 will be described later.

  Since the toner adhesion amount measuring device 45 needs to strictly define the distance to the object to be measured, as shown in FIG. 1, it opposes the driving roller 11 having a small distance fluctuation to the surface of the intermediate transfer belt 8. The intermediate transfer belt 8 is positioned in the width direction according to the reference image formation position on the intermediate transfer belt 8.

  The toner adhesion amount measuring device 45 may be disposed at another position where the reference image on the intermediate transfer belt 8 can be detected. However, when the toner adhesion amount measuring device 45 is disposed downstream of the secondary transfer roller 9, for example, the image forming unit The time from when the reference image is formed by Pa to Pd to when the density detection is performed becomes longer, and the surface state of the reference image may change due to the reference image coming into contact with the secondary transfer roller 9. Therefore, as shown in FIG. 1, it is preferable to dispose on the downstream side of the image forming unit Pd and the upstream side of the contact position of the secondary transfer roller 9.

  FIG. 2 is a side sectional view showing a configuration of a developing device used in the image forming apparatus of the present invention. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and is supplied to the first and second via a developer passage (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  Note that a toner concentration sensor (not shown) is disposed in the developing container 20 so as to face the first stirring screw 21a, and the toner supply port 20d is supplied from the supply device according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 20 via

  The magnetic roller 22 includes a nonmagnetic rotating sleeve 22a and a fixed magnet roller body 22b having a plurality of magnetic poles (here, five poles) contained in the rotating sleeve. The developing roller 23 is composed of a non-magnetic developing sleeve, and the magnetic roller 22 and the developing roller 23 are opposed to each other at a facing position (opposing position) with a predetermined gap.

  Further, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC) applied to the developing roller 23 based on a control signal from the control unit 42 (see FIG. 4). ), Vslv (AC) and Vmag (DC) and Vmag (AC) applied to the magnetic roller 22 can be varied.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Then, a magnetic brush (not shown) is formed on the magnetic roller 22. After the layer thickness of the magnetic brush on the magnetic roller 22 is regulated by the ear cutting blade 25, the magnetic brush 22 is conveyed to the opposite portion between the magnetic roller 22 and the developing roller 23, and Vmag (DC) applied to the magnetic roller 22 and the developing roller 23. A toner thin layer is formed on the developing roller 23 by a potential difference (hereinafter referred to as ΔV between MSs) applied to the Vslv (DC) and a magnetic field between the fixed magnet roller body 22b.

  The thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference between the magnetic roller 22 and the developing roller 23, but can be controlled by the ΔV between MSs. When the ΔV between MSs is increased, the toner layer on the developing roller 23 becomes thicker, and when the ΔV between MSs is decreased, the toner layer becomes thinner. The range of ΔV between MSs during development is generally about 100V to 350V.

  FIG. 3 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. The magnetic roller 22 has a second composite waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a Vmag (AC) of a rectangular wave having a phase different from that of Vslv (AC). Applied from the bias circuit 31.

  Therefore, the voltage applied between the magnetic roller 22 and the developing roller 23 is a composite waveform Vmag−Vslv having Vpp (max) and Vpp (min) as shown in FIG. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a facing portion between the photosensitive drum 1 a and the developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  When an amorphous silicon (a-Si) photosensitive layer is used as the photosensitive layer of the photosensitive drum 1a, the surface post-exposure potential is very low, 20V or less. When it is made thinner, the saturation charging potential is lowered, and the withstand voltage leading to dielectric breakdown is also lowered. On the other hand, the surface charge density at the time of latent image formation becomes high and the development performance tends to be improved. This characteristic is particularly remarkable when the dielectric constant is as high as about 10 in the case of an a-Si photosensitive layer of 25 μm or less, preferably 20 μm or less. At this time, Vslv (DC) is set to 150 V or less, and Vslv (AC) is set to have a peak-to-peak value of 500 to 1500 V and a frequency of 1 to 5 kHz.

  On the other hand, when an organic photosensitive layer (OPC) is used as the photosensitive layer, the layer thickness of the photosensitive layer is set to 25 μm or more in order to reduce the residual charge after image formation to 100 V or less, and the addition amount of the charge generating material is increased. Is particularly important. In particular, OPC having a single-layer structure is advantageous because a charge generation material is added to the photosensitive layer, so that a sensitivity change due to a decrease in the thickness of the photosensitive layer is small. At this time, from the viewpoint of preventing a strong electric field from being applied to the toner, Vslv (DC) is set to 400 V or less, more preferably 300 V or less.

  The remaining toner that is not used for development is conveyed again to the opposite portion between the developing roller 23 and the magnetic roller 22 and collected by the magnetic brush on the magnetic roller 22. Then, the magnetic brush is peeled off from the magnetic roller 22 at the same polarity portion of the fixed magnet roller body 22b, and then formed again on the magnetic roller 22 as a two-component developer uniformly charged with an appropriate toner concentration. And conveyed to the ear cutting blade 25.

  Since the toner collection width on the developing roller 23 is equal to the width of the area where the magnetic brush is formed on the magnetic roller 22, the developing roller 23 is made shorter in the longitudinal direction than the area width of the magnetic brush. The upper toner uncollected area disappears. As a result, toner does not adhere to the developing roller 23 outside the magnetic brush region, and toner scattering from both ends of the developing roller 23 can be prevented.

  Further, by setting the rotation speed of the magnetic roller 22 to 1.0 to 2.0 times the rotation speed of the developing roller 23, the replacement of the toner thin layer on the developing roller 23 is promoted, and the residual toner on the developing roller 23 is increased. Can be recovered efficiently and a uniform toner layer can be re-formed. Further, in order to maintain a uniform image density, Vmag (DC) and Vslv (DC) are set to the same potential at a time other than the development timing, and ΔV between MSs is set to 0, so that the toner is not burdened. Residual toner on the developing roller 23 can be collected.

  FIG. 4 is a block diagram illustrating a control path of the image forming apparatus. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image input unit 40, an AD conversion unit 41, image forming units Pa to Pd, a control unit 42, a storage unit 43, an operation panel 44, a fixing unit 7, an intermediate transfer belt 8, a secondary transfer roller 9, And a toner adhesion amount measuring device 45 and the like.

  The toner adhesion amount measuring device 45 irradiates each reference image formed on the intermediate transfer belt 8 (see FIG. 1) with the measurement light in the image forming portions Pa to Pd, and detects the amount of reflected light from the reference image. The detection result is transmitted to the control unit 42 described later as a light reception output signal.

  When the image forming apparatus 100 is a copying machine, the image input unit 40 is a scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of reflected light from the document, and reflected light from the document. The image forming apparatus 100 is a printer as shown in FIG. 1, and includes a condensing lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. In some cases, the receiving unit receives image data transmitted from a personal computer or the like. The image signal input from the image input unit 40 is converted into a digital signal by the AD conversion unit 41 and then sent to the image memory 50 in the storage unit 43 described later.

  The storage unit 43 stores print image data input from the image input unit 40 and digitally converted by the AD conversion unit 41 in units of pages, and necessary data and image formation generated during the control of the image forming apparatus 100. A readable / writable RAM (Random Access Memory) 51 in which data and the like temporarily required for controlling the apparatus 100 are stored, and the image forming apparatus 100 such as a control program for the image forming apparatus 100 and numerical values necessary for the control. A read-only ROM (Read Only Memory) 52 that stores data that will not be changed during use is provided. The RAM 51 (or ROM 52) stores in advance the relationship between the measured output value of the toner adhesion amount measuring device 45 and the toner adhesion amount as toner adhesion amount data.

  The operation panel 44 displays the state of the image forming apparatus 100, the image forming status, and the number of copies, and as a touch panel, functions such as double-sided printing and black-and-white reversal, and various settings such as magnification setting and density setting, the number of printing copies When the image forming apparatus 100 has a FAX function, a numeric keypad for inputting the FAX number of the other party, a start button for instructing the user to start image formation, and when stopping image formation. A stop / clear button, a reset button used when setting various settings of the image forming apparatus 100 to a default state, and the like are provided, and the user operates the operation panel 44 to input an instruction, whereby the image forming apparatus 100 is set. Are set to execute various functions such as image formation.

  The control unit 42 is, for example, a central processing unit (CPU), and generally controls the image input unit 40, the image forming units Pa to Pd, the fixing unit 7 and the like according to a set program, and inputs from the image input unit 40. The converted image signal is converted into image data by scaling processing or gradation processing as necessary. The exposure device 4 irradiates laser light based on the processed image data, and forms latent images on the photosensitive drums 1a to 1d.

  Further, when a mode for appropriately setting the image density of each color (hereinafter referred to as a calibration mode) is input by the key operation on the operation panel 44, the control unit 42 is detected by the toner adhesion amount measuring device 45. A function for receiving the light reception output signal and calculating the toner adhesion amount based on the toner adhesion amount data stored in the storage unit 43, and determining the density of the reference image based on the calculated toner adhesion amount. By adjusting the developing bias of the developing devices 3a to 3d as compared with the reference density, the color density is corrected for each color. The calibration mode may be automatically set when the apparatus is turned on or when a predetermined number of image forming processes are completed.

An example of a density correction reference image is shown in FIG. When the calibration mode is set by the user, as shown in FIG. 5A, cyan (C), magenta (M), yellow (Y), and yellow (Y) are set at the left end in the traveling direction on the intermediate transfer belt 8. A rectangular reference image of each color of black (B) is formed in a line. The cyan (C) reference image formed by the photoconductive drum 1a is formed in order from the advancing direction with reference images C1 to C5 having five levels of density from the white solid image (C1) to the darkest image (C5). Is done.

  FIG. 5B shows an enlarged view of the portions C1 and C2 in FIG. As can be seen from the figure, the adjacent reference images C1 and C2 are each formed in a single color so that the density changes at the boundary. The reference images C3 to C5 are formed in the same manner, and the magenta (M) reference images M1 to M5, the yellow (Y) reference images Y1 to Y5, and the black (B) reference images B1 to B5 are also C1. To C5.

  In image formation by a tandem color image forming apparatus as shown in FIG. 1, toner images for reference image formation are formed on the photosensitive drums 1a to 1d by the above-described image forming process. The formed toner images are transferred to predetermined positions on the intermediate transfer belt 8 by the primary transfer rollers 6a to 6d, and reference images of cyan, magenta, yellow, and black are formed.

  FIG. 6 is a schematic diagram showing the configuration of the toner adhesion amount measuring apparatus. The toner adhesion amount measuring device 45 includes a light emitting element (for example, LED) 60 that projects measurement light onto the surface of the intermediate transfer belt 8 and first and second light receiving elements that receive reflected light reflected from the intermediate transfer belt 8. The polarizing filter 63 is disposed between the light emitting element 60 and the intermediate transfer belt 8, and the polarizing filter 63 transmits only P-polarized light. On the other hand, a polarization separation prism 64 is disposed between the second light receiving element 62 and the intermediate transfer belt 8, and this polarization separation prism 64 transmits P-polarized light to the first light receiving element 61. The S-polarized light is reflected and applied to the second light receiving element 62. The light emitting element 60 is disposed at an angle inclined by a predetermined amount with respect to the surface of the intermediate transfer belt 8.

  Assume that a sufficient amount (appropriate amount) of toner is transferred onto the intermediate transfer belt 8. When measurement light is projected from the light emitting element 60 onto the intermediate transfer belt 8, as shown in FIG. 6A, P-polarized light (hereinafter referred to as regular reflection light) P1 and S-polarized light (hereinafter referred to as irregular reflection light). The measurement light including S1 is cut by the polarization filter 63, and the light S1 is only projected onto the intermediate transfer belt 8 from the polarization filter 63 as light P1. The light P1 passes through the toner t, does not reach the surface of the intermediate transfer belt 8, and is all reflected by the surface of the toner t.

  The reflected light is separated into specularly reflected light P3 and irregularly reflected light S3 by the polarization separation prism 64, the light P3 is received by the first light receiving element 61, and the light S3 is received by the second light receiving element 62. The first and second light receiving elements 61 and 62 photoelectrically convert the received light and output first and second output signals. These first and second output signals are converted into A / D converters. Then, it is given to the control unit 42 (see FIG. 4).

  On the other hand, as shown in FIG. 6B, when measurement light including regular reflection light P1 and irregular reflection light S1 is projected onto the intermediate transfer belt 8 in a state where no toner image is formed on the intermediate transfer belt 8, polarization is caused. The light S1 is cut by the filter 63, and only the light P1 is projected onto the surface of the intermediate transfer belt 8, and includes regular reflection light and irregular reflection light corresponding to the surface shape (for example, surface roughness) of the intermediate transfer belt 8. It becomes reflected light. The reflected light is separated into regular reflected light P2 and irregularly reflected light S2 by the polarization separation prism 64, the light P2 is received by the first light receiving element 61, and the light S2 is received by the second light receiving element 62.

  The first and second light receiving elements 61 and 62 photoelectrically convert the received light (P2, S2) to output first and second output signals, and these first and second output signals are represented by A After being / D converted, it is given to the control unit 42. The control unit 42 sets the difference between the first and second output signals at this time as a reference value. As described above, after adjusting the output levels of the first and second light receiving elements 61 and 62 and setting the reference value, the toner adhesion amount on the intermediate transfer belt 8 shown in FIG. 6C is measured. Is done.

  In FIG. 6C, the measurement light including the P-polarized light P1 and the S-polarized light S1 is cut by the polarization filter 63 as in FIGS. 6A and 6B, and the light P1 Only the toner is projected. Now, assuming that the toner amount of the toner image formed on the intermediate transfer belt 8 is not sufficient, a part of the incident light P1 to the toner is reflected on the surface of the toner t, and the rest is transmitted through the toner t. The light transmitted through the toner t is reflected on the surface of the intermediate transfer belt 8.

  That is, the light P1 projected onto the surface of the intermediate transfer belt 8 is reflected as regular reflection light P2 and irregular reflection light S2. The regular reflection light P2 and the irregular reflection light S2 are separated by the polarization separation prism 64, the light P2 is received by the first light receiving element 61, and the light S2 is received by the second light receiving element 62. Similarly, the regular reflection light P3 and the irregular reflection light S3 reflected on the surface of the toner t are separated by the polarization separation prism 64, the light P3 is received by the first light receiving element 61, and the light S3 is received by the second light reception. Light is received by the element 62.

  As described above, the first and second light receiving elements 61 and 62 photoelectrically convert the received light and output the first and second output signals, and these first and second output signals are represented by A After being / D converted, it is given to the control unit 42. In the control unit 42, the difference between the first and second output signals is obtained as a measured output value, and the measured output value is corrected based on the above-described reference value to obtain a corrected output value. That is, if the correction output value when the toner is not attached is 1, the correction output value is obtained by (measurement output value / reference value).

  The storage unit 43 stores in advance the relationship between the measured output value and the toner adhesion amount as toner adhesion amount data, and determines the toner adhesion amount (image density) according to the corrected output value from the toner adhesion amount data. It will be output as a measurement result.

  Here, the difference in the output signal when no toner is attached is used as a reference value, the measured output value is corrected by (measured output value / reference value), and the toner adhesion amount is measured from the corrected output value. The correction output value calculation method is not limited to this. For example, the correction output value may be calculated by further multiplying the correction output value described above by a correction coefficient considering the contamination of the light receiving element.

  By the way, usually, the surface glossiness of the intermediate transfer belt 8 gradually decreases due to the usage period of the image forming apparatus and the adhesion of external additives contained in the toner. For this reason, the reference value fluctuates greatly at the beginning and end of the use period of the intermediate transfer belt 8, causing variations in the measured output value.

  7 to 14 show measured output values and toner adhesion amounts of the toner adhesion amount measuring device 45 when the toner adhesion amounts of the cyan, magenta, yellow and black reference images are measured in the image forming apparatus shown in FIG. 7 to 10 are graphs showing the relationship between the intermediate transfer belt 8 and the intermediate transfer belt 8 when the surface gloss (gloss) is 18.5 (high gloss). FIGS. The glossiness is 3.4 (low glossiness). In each graph, the first output signal (P wave) is indicated by a solid line, the second output signal (S wave) is indicated by a broken line, and the difference between the first and second output signals (PS wave) is indicated by a one-dot chain line. Show.

  As the conditions of the image forming apparatus, an a-Si photosensitive member was used as the photosensitive drums 1a to 1d, and the surface potential was charged to 250V. The drum-developing roller gap is 100 μm, the magnetic roller-developing roller gap is 320 μm, Vslv (DC) is 100 V, Vslv (AC) peak-to-peak value is 1.8 kV, Duty 45%, frequency 4.5 kHz. The peak-to-peak value of Vmag (AC) was 1.8 kV, Duty 70%, and frequency 4.5 kHz. As the developer, a two-component developer having a toner number average particle diameter of 6 μm, a carrier number average particle diameter of 35 μm, and a toner charge amount of 15 μC / g was used. Then, the output value of the toner adhesion amount measuring device 45 when the density (toner adhesion amount) of the reference image was changed by changing Vmag (DC) was measured.

  When comparing the relationship between the measured output value of the cyan reference image shown in FIGS. 7 and 11 and the toner adhesion amount, the measured output value of the P wave (solid line) and the PS wave (dashed line) with respect to the cyan toner adhesion amount. However, the measured output value of the S wave (broken line) is stable against the change in the toner adhesion amount regardless of the surface glossiness. From the comparison of FIGS. 8 and 12, and the comparison of FIGS. 9 and 13, it is understood that this tendency is the same for the magenta and yellow toners.

  Therefore, in the present invention, for cyan, magenta, and yellow color toners, the toner adhesion amount is measured using only the first output signal (output value of the irregularly reflected light S2) output from the first light receiving element 61. did. As a result, the amount of color toner adhered can be stably detected regardless of the change in the surface glossiness of the intermediate transfer belt 8.

  On the other hand, comparing the relationship between the measured output value of the black reference image shown in FIGS. 10 and 14 and the toner adhesion amount, the measured output value of the S wave (broken line) depends on the surface glossiness as in the case of the color toner. The toner adhesion amount is stable against changes. However, since the ratio of the change in the output value of the S wave with respect to the change in the toner adhesion amount is small in black toner, it is impossible to detect the accurate toner adhesion amount using only the first output signal (the output value of the irregularly reflected light S2). Have difficulty.

Therefore, for black toner, the toner adhesion amount is detected based on the difference (PS wave) between the first and second output signals. As can be seen from FIGS. 10 and 14, the measured output of the PS wave is detected. Since the value (one-dot chain line) is saturated in the vicinity of the target value of the toner adhesion amount of 0.5 to 0.6 mg / cm ² , there is a possibility that the detected value of the toner adhesion amount largely varies near the target value. Therefore, in the present invention, the measured output value of the PS wave is approximated by a cubic function using the least square method.

FIG. 15 is a graph obtained by approximating the relationship between the measured output value of the black reference image and the toner adhesion amount with a cubic function. In FIG. 15, the PS wave output value is set so that the y-axis is 0 when the toner adhesion amount (x-axis) is 0 and the y-axis is 1000 when the toner adhesion amount is near 0.5 mg / cm ^2. It is represented by a cubic polynomial (here, y = 2483.3x ³ -5743.5x ² + 4030.2x + 116.15). It can be seen that the curve represented by this polynomial has an extreme value in the vicinity of 0.5 to 0.6 mg / cm ² .

Here, the toner adhesion amount when the graph cubic function approximation in FIG. 15 is an extreme value will be described why coincides with the target value of the saturation toner adhesion amount. From the state where the reference image is not formed on the intermediate transfer belt 8 shown in FIG. 6B, an ideal reference image (a single layer of toner) is formed on the intermediate transfer belt 8 as shown in FIG. 6A. Until the formation, the regular reflection light P2 and the irregular reflection light S2 reflected on the surface of the intermediate transfer belt 8 in FIG. 6C decrease as the toner adhesion amount increases, and the regular reflection reflected on the surface of the toner t. The light P3 and the irregularly reflected light S3 increase.

  At this time, since the decrease rate of the regular reflection light P2 and the irregular reflection light S2 is larger than the increase rate of the regular reflection light P3 and the irregular reflection light S3, the measured output value of the PS wave decreases as shown in FIGS. To do. In the state of FIG. 6A, the regular reflection light P2 and the irregular reflection light S2 are 0, and only the regular reflection light P3 and the irregular reflection light S3 reflected on the surface of the toner t are detected. The measured output value is minimized.

When the toner further adheres from the state of FIG. 6A, the toner is irregularly stacked on the single layer of the toner, so that the regular reflection light P3 and the irregular reflection light S3 increase. At this time, since the increase rate of the regular reflection light P3 is slightly larger than the increase rate of the irregular reflection light S3, the measured output value of the PS wave slightly increases. That is, since the point of measurement output value of the P-S wave turns from decrease to increase appears as an extreme value in the graph of FIG. 15, the ideal reference image (a single layer of toner) is formed in the extreme It will be.

In the color toner, since the increasing rate of the irregularly reflected light S3 reflected on the surface of the toner t is larger than the decreasing rate of the irregularly reflected light S2, the measured output value of the S wave gradually increases from the state where the toner is not attached. (Dotted lines in FIGS. 7 to 9 and FIGS. 11 to 13). Further, the measured output value of the P wave decreases from the non-adhered state to the predetermined amount (about 0.3 mg / cm ² ) of toner when the surface glossiness of the intermediate transfer belt 8 is high, but thereafter Since the increase rate of the regular reflection light S3 is larger than the decrease rate of the regular reflection light S2, the measurement output value increases (solid line in FIGS. 7 to 9). On the other hand, when the surface glossiness of the intermediate transfer belt 8 is low, the toner gradually increases from the state where the toner is not adhered, as in the case of the S wave (solid lines in FIGS. 11 to 13). After a predetermined amount of toner of each color adheres, the measured output values of the P wave and the S wave increase at a substantially constant rate, and thus the measured output value of the PS wave does not have an extreme value.

Using the above-described principle, a reference image as shown in FIG. 5 is formed on the intermediate transfer belt 8, and for the color toner, the toner adhesion amount is detected using only the measured output value of the S wave. ΔV between MSs is set so that becomes the target value. Also, the black for toner is the target value of the toner adhesion amount of saturated amount of adhered toner is calculated from the extreme values of the graph cubic function approximating the measured output value of the P-S wave, MS amount saturation toner adhesion becomes the target value The interval ΔV is set. This makes it possible to accurately measure the adhesion amount of color and black toner over the entire belt usage period, so that the adhesion amount of color and black toner is set to a target value of 0.5 to 0.6 mg / cm ² . It can be set with high accuracy.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the case where a toner image is formed on the intermediate transfer belt 8 which is an example of the toner carrier and the toner adhesion amount on the intermediate transfer belt 8 is measured has been described. Not limited to this, in an image forming apparatus that sequentially transfers an image of each color onto a transfer sheet conveyed by a conveying belt, the present invention can be applied in the same manner when measuring the toner adhesion amount of a reference image formed on the conveying belt. It is. Alternatively, the present invention can be applied to the case where the density of the reference image is measured on the photosensitive drums 1a to 1d.

  In the above embodiment, as shown in FIG. 2, an image forming apparatus provided with developing devices 3a to 3d that holds only toner charged on the developing roller 23 by the magnetic brush on the magnetic roller 22 is taken as an example. Although the method for adjusting the density by varying the interval ΔV has been described, the present invention is not limited to this, and various methods using a magnetic one-component developer or a two-component developer composed of a toner component and a magnetic carrier are used. It can be applied to the developing device. For example, in the case of a developing device that does not use a magnetic roller, the density adjustment is performed by adjusting the surface potential of the photosensitive drum or the DC bias applied to the developing roller to vary the potential difference between the photosensitive drum and the developing roller. Alternatively, the exposure amount of the exposure apparatus when forming the electrostatic latent image may be adjusted.

  Further, here, as an example, a tandem color image forming apparatus having a plurality of image forming units has been described. However, the present invention is not limited to this, and a plurality of developing cartridges are provided at positions facing the photosensitive drum. Of course, the present invention can also be applied to a rotary type color image forming apparatus that develops an electrostatic latent image on a photosensitive drum by sequentially rotating and moving.

  Using the image forming apparatus that created the graphs of FIGS. 7 to 15, the toner adhesion amount measurement method was changed, and the variations in the toner adhesion amount when cyan, magenta, yellow, and black solid images were printed were compared. As a test method, from the start of printing up to 100,000 sheets, both color toner and black toner detect the amount of toner adhesion using the measured output value of PS wave, and after 100,000 sheets, the measured output value of S wave. Was used to detect the adhesion amount of the color toner, and the adhesion amount of the black toner was detected by approximating the measured output value of the PS wave to a cubic function. The results are shown in FIG.

As shown in FIG. 16, from the start of printing up to 100,000 sheets, cyan toner adhesion amount (indicated by a circle in the figure), magenta toner adhesion amount (indicated by a x in the figure), yellow toner adhesion amount (in the figure, Δ) in display), the toner adhesion amount of black (indicated by ● in the drawing) is remained in the range of 0.40~0.80mg / cm ^2, the variation of the order of 0.4 mg / cm ² was observed at the maximum. Change contrast, the toner adhesion amount of each color in the measurement method 100,000 sheets after changing the hovered in the range of 0.40~0.60mg / cm ^2, the variation of the coating weight and 0.2 mg / cm ² It was reduced to about 1/2 of the previous one.

The present invention irradiates light on the color and black reference images formed on the toner carrier, measures the regular reflection light quantity and irregular reflection light quantity from the reference image, and based on the received light output signals of the regular reflection light quantity and irregular reflection light quantity. It can be used in a color image forming apparatus that controls the image density by detecting the toner adhesion amount of the reference image. For color toner, the toner adhesion amount of the reference image is detected based only on the light reception output signal of the irregularly reflected light amount. For black toner, density correction is performed using the toner adhesion amount calculated from the extreme value of a curve obtained by approximating the difference between the light reception output signals of the regular reflection light amount and the irregular reflection light amount as a cubic function as a target value of the saturated toner adhesion amount.

  As a result, even when the surface glossiness of the toner carrier changes due to the passage of the use period or the external additive contained in the toner, the toner adhesion amount can be detected with high accuracy over the entire use period.

  In addition, since the image density is controlled based on the toner adhesion amount detected by using the above method, it is possible to always perform image formation capable of highly accurate density correction regardless of the usage period of the toner carrier and the change in the surface state. An apparatus can be provided.

Pa to Pd Image forming portion 1a to 1d Photosensitive drum 2a to 2d Charger 3a to 3d Developing device 4 Exposure device 6a to 6d Primary transfer roller 7 Fixing portion 8 Intermediate transfer belt (toner carrier)
DESCRIPTION OF SYMBOLS 9 Secondary transfer roller 10 Driven roller 11 Drive roller 22 Magnetic roller 23 Developing roller 42 Control part (control means)
43 Storage Unit 45 Toner Amount Measurement Device (Optical Detection Unit)
Reference Signs List 60 light emitting element 61 first light receiving element 62 second light receiving element 63 polarizing filter 64 polarization separating prism 100 image forming apparatus

Claims (2)

The toner adhesion amount of the reference image is detected based on the received light output signals of the regular reflection light amount and the irregular reflection light amount from the color and black reference images, and the color and color are adjusted by adjusting the developing bias based on the detected toner adhesion amount. In the density correction method of the color image forming apparatus for correcting the density of the black image,
For color toner, a toner adhesion amount of the reference image is detected based only on the light reception output signal of the irregular reflection light amount, and for black toner, a curve that approximates the difference between the regular reflection light amount and the light reception output signal of the irregular reflection light amount by a cubic function. A saturation toner adhesion amount target value for forming a single layer of toner is calculated from the extreme value, and the development bias is adjusted so that the saturation toner adhesion amount becomes the calculated target value. Correction method. Optical detection means capable of irradiating light on a color and black reference image formed on the toner carrier and measuring the amount of specular reflection and irregular reflection from the reference image;
Control means for controlling the image density by detecting the toner adhesion amount of the reference image based on the received light output signal of the regular reflection light quantity and the irregular reflection light quantity measured by the optical detection means;
In a color image forming apparatus comprising:
For the color toner, the toner density of the reference image is detected based on only the light reception output signal of the irregularly reflected light quantity, and the image density is controlled so that the toner adhesion quantity becomes a target value, and for the black toner, the regular reflected light quantity And controlling the image density using the toner adhesion amount when the curve obtained by approximating the difference between the received light output signal of the irregular reflection light quantity and the cubic function takes an extreme value as the target value of the saturated toner adhesion amount at which a single layer of toner is formed. A characteristic color image forming apparatus.

Images