JP4896598B2 - Image forming apparatus - Google Patents

Description

  According to the present invention, a magnetic roller having a magnetic brush formed on a surface thereof is disposed opposite to the magnetic roller, and toner is supplied from the magnetic roller via the magnetic brush and is opposed to the photosensitive drum. A developing roller that supplies toner to the electrostatic latent image formed on the photosensitive drum to form a toner image, and a recovery roller that is disposed opposite the developing roller and collects the toner from the developing roller. And an image forming apparatus including the roller. In particular, the present invention relates to a copying machine, a printer, a facsimile machine, an Internet facsimile machine, which is an apparatus for forming an image on recording paper, and a multifunction machine having any one of these functions.

  In an image forming apparatus that forms an image on recording paper using electrophotographic technology, a two-component developer composed of a magnetic carrier and a nonmagnetic toner is used as a method for developing an electrostatic latent image on a photosensitive drum. There are a component development method and a one-component development method using a one-component developer containing only toner.

  Among these, in the two-component development method, there is a problem that the carrier adheres on the photosensitive drum to cause transfer failure, and a problem that this carrier further adheres to the transfer paper and causes a flaw on the fixing roller of the fixing device. Etc. On the other hand, the one-component developing system often has a problem that toner is charged by friction and image defects such as fog are likely to occur due to toner charging failure. A so-called hybrid development method has been proposed as a development method for solving these problems.

  In this hybrid development method, a two-component developer composed of a non-magnetic toner and a magnetic carrier is attached to the surface of the magnetic roller as a magnetic brush, and the magnetic brush is brought into contact with the surface of the developing roller, so that the non-developing material is non-coated on the developing roller. A toner layer consisting only of magnetic toner is formed, and the toner layer is further developed to fly onto an electrostatic latent image on the photosensitive drum. This method is advantageous in terms of suppressing deterioration in image quality because the development process is performed in a state where the developing roller and the photosensitive drum are not in contact with each other.

In this type of image forming apparatus, for example, density control is performed by, for example, detecting the toner density of a test pattern on an intermediate transfer body on which a toner image is transferred from a photosensitive drum, and using a magnetic brush to a developing roller based on the detected toner density This is done by controlling the transport bias for transporting the toner. (See Patent Document 1).
JP 2005-55841 A

  However, when an image with a low printing rate is repeatedly developed, a large amount of toner remains on the developing roller without being consumed by the developing process. ) May remain and accumulate. In such a case, there is a possibility that the image density of the portion corresponding to the portion where the highly charged toner is accumulated (= so-called ghost phenomenon occurs), and the image quality may be deteriorated.

  SUMMARY An advantage of some aspects of the invention is that it provides a hybrid development type image forming apparatus capable of suitably controlling an image density.

In order to achieve the above object, an image forming apparatus according to the present invention is provided with a magnetic roller having a magnetic brush formed on a surface thereof, a magnetic roller disposed opposite to the magnetic roller, and the toner from the magnetic roller via the magnetic brush. And a developing roller that is disposed to face the photosensitive drum and supplies toner to the electrostatic latent image formed on the photosensitive drum to form a toner image, and is arranged to face the developing roller. A collecting roller for collecting toner from the developing roller, wherein the first density detecting unit detects the density of the toner image formed on the photosensitive drum; and the first density detection Density determination means for determining whether or not the density detected by the means is an appropriate density, and potential control means for controlling the potential of the collection roller based on the determination result of the density determination means. That.

Alternatively, in order to achieve the above object, an image forming apparatus according to the present invention is provided with a magnetic roller having a magnetic brush formed on a surface thereof, and disposed opposite to the magnetic roller, from the magnetic roller via the magnetic brush. The toner is supplied, and is disposed opposite to the photosensitive drum, and is disposed opposite to the developing roller, the developing roller supplying toner to the electrostatic latent image formed on the photosensitive drum, An image forming apparatus comprising: a collecting roller that collects toner from a developing roller; and an intermediate transfer member to which a toner image formed on the photosensitive drum is transferred, wherein the density of the toner image transferred to the intermediate transfer member Based on the determination result of the second concentration detection unit for detecting the concentration, the concentration determination unit for determining whether or not the concentration detected by the second concentration detection unit is an appropriate concentration, and the determination result of the concentration determination unit And potential control means for controlling the potential of the collection roller, Ru comprising a.

In the above structure, an image forming apparatus according to claim 1 or claim 2, wherein the concentration determining means, said first concentration detection means or preset reference concentration detected by the second concentration detector A density ratio that is a ratio to the density may be calculated, and it may be determined whether or not the calculated density ratio is an appropriate density based on whether or not the calculated density ratio is within a preset range .

Further, in the above configuration, the apparatus further comprises threshold storage means for storing an upper limit value and a lower limit value of an appropriate range of the density ratio, and the density determination means reads the upper limit value and the lower limit value from the threshold storage means, and When the ratio is equal to or lower than the upper limit value and equal to or higher than the lower limit value, it may be determined that the concentration is appropriate .

In the above structure, receives an operation input from outside, based on the received operation input, be provided with a threshold setting means for setting at least one value of the stored upper and lower limit values in the threshold value storage unit Good.

In the above configuration, when the concentration determination unit determines that the concentration detected by the first concentration detection unit or the second concentration detection unit is not an appropriate concentration, the potential control unit performs the concentration ratio measurement. The potential of the collecting roller may be controlled based on the above .

Further, in the above configuration, the potential control unit has a higher capability of recovering toner from the developing roller as compared with a reference potential set in advance and when the recovery roller is set to the reference potential. A strong recovery potential that is a potential of the roller, and a weak recovery potential that is a potential of the recovery roller that has a low ability to recover toner from the developing roller, compared to a case where the recovery roller is set to the reference potential. The potential of the collecting roller may be controlled by switching the .

Further, in the above configuration, a potential storage unit that stores the reference potential, the strong recovery potential, and the weak recovery potential is provided, and the potential control unit reads the reference potential, the strong recovery potential, and the weak recovery potential from the potential storage unit. Then, the potential of the collecting roller may be controlled .

Further, in the above configuration, a potential setting that accepts an operation input from the outside and sets at least one value of a reference potential, a strong recovery potential, and a weak recovery potential stored in the potential storage means based on the received operation input. Means may be provided .

In the above configuration, the storage device further includes a potential storage unit that stores the potential of the collection roller in association with the density ratio, and the potential control unit includes the potential of the collection roller corresponding to the density ratio calculated by the density determination unit. The potential may be read from the potential storage unit, and the potential of the collecting roller may be controlled to the read potential .

According to the present invention , the density of the toner image formed on the photosensitive drum is detected, it is determined whether or not the detected density is an appropriate density, and the potential of the recovery roller is controlled based on the determination result. Therefore, the image density can be suitably controlled.

  That is, since the potential of the collecting roller is controlled based on the density of the toner image formed on the developing roller, an appropriate amount of toner collected on the developing roller is collected by the collecting roller. The decrease in image density due to the accumulation of charged toner is suppressed, and the image density can be suitably controlled.

Alternatively, according to the present invention , the density of the toner image formed on the intermediate transfer member is detected, it is determined whether or not the detected density is an appropriate density, and based on the determination result, the recovery roller Since the potential is controlled, the image density can be suitably controlled.

  In other words, since the potential of the collecting roller is controlled based on the density of the toner image formed on the intermediate transfer member, an appropriate amount of toner collected on the developing roller is collected by the collecting roller. Therefore, the decrease in the image density accompanying the accumulation of the charged toner is suppressed, and the image density can be suitably controlled.

In addition , a density ratio that is a ratio of the detected density to the reference density is calculated, and it is determined whether or not the calculated density ratio is an appropriate density based on whether or not the calculated density ratio is within a preset range. By doing so, it is possible to determine whether or not the concentration is accurately correct with a simple configuration.

Further, an upper limit value and the lower limit of the proper range of the stored concentration ratio is read, the concentration ratio is not more than the upper limit, and, as it is determined to be proper concentration is equal to or greater than the lower limit value Then, the upper limit value and lower limit value of the appropriate range of the density ratio can be easily set.

The operation input from the outside is accepted, based on the received operation input, when such at least one value of the upper limit value and the lower limit of the proper range of the concentration ratio is set, the proper range of the concentration ratio The upper limit value and the lower limit value can be set more easily.

In addition , when it is determined that the detected density is not an appropriate density, if the potential of the collection roller is controlled based on the density ratio, it is possible to secure a density with a desired accuracy.

  That is, when the detected density is determined not to be an appropriate density, the potential of the collection roller is controlled. Therefore, if the criteria for determining the appropriate density are set strictly, a highly accurate density can be secured. If the determination criterion is set gently, the frequency of controlling the potential of the collection roller is reduced, and the processing load can be reduced. Further, since the potential of the collecting roller is controlled based on the density ratio, the potential of the collecting roller can be controlled to an appropriate value.

Further , compared to a preset reference potential and a case where the collection roller is set to the reference potential, a strong collection potential that is a potential of the collection roller having a high ability to collect toner from the developing roller, and the collection roller is a reference compared to when it is set to a potential, and a weak recovery potential is the potential of the low recovery roller capable of collecting the toner from the developing roller, by switching the, when the potential of the collection roller is to be controlled, simpler With this configuration, the potential of the collecting roller can be controlled.

Further, the reference potential, is read out strong recovery potential and weak recovery potential, the potential of the collection roller is to be controlled, a reference potential, a strong recovery potential and weak recovery potential can be easily set.

Furthermore, accepted operation input from the outside, based on the received operation input, stored reference potential and at least one of the values of strength recovery potential and a weak recovery potential is to be set, the reference potential, strong recovery The potential and weak recovery potential can be set more easily.

Further, it is read potential of the collection roller corresponding to the concentration ratio, the potential of the read potential to the collection roller is to be controlled, is controlled to a proper value the potential of the collection roller with a simple structure be able to.

  Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. Here, the case where the image forming apparatus is a copying machine will be described. However, the image forming apparatus may be another image forming apparatus that forms an image on recording paper (for example, a facsimile, an Internet facsimile, a printer, a multifunction peripheral, etc.). Good. As shown in FIG. 1, the copier 100 includes an image generation unit 1, a control unit 2, a display unit 3, an operation unit 4, and a print processing unit 5.

  The image generation unit 1 reads an image formed on a document and generates document image information, and includes a reading unit 11 and an ADF 12. The reading unit 11 illuminates a document to be read and reads reflected light with a CCD (Charge Coupled Devices) or the like to generate document image information. An ADF (Automatic Document Feeder) 12 conveys a document to a document reading position of the reading unit 11.

  The control unit 2 controls the operation of the entire copying machine 100, and includes a CPU (Central Processing Unit) 21, a RAM (Random Access Memory) 22, and a ROM (Read Only Memory) (not shown). Yes.

  The display unit 3 includes an LCD (Liquid Crystal Display), an LED (Light Emitting Diode), and the like, and displays setting information, guidance information, message information, and the like so as to be visible to the user based on instructions from the control unit 2 (CPU 21). To do.

  The operation unit 4 receives an operation input from a user, generates operation input information corresponding to the received operation input, and outputs the operation input information to the control unit 2 (CPU 21). Here, an operation from the user is performed. Based on the input, an upper limit value and a lower limit value of an appropriate range of density ratio, which will be described later, and a reference potential, a strong recovery potential, and a weak recovery potential are received. The operation unit 4 includes, for example, various buttons such as a numeric keypad and a start button, and a touch panel formed integrally with the LCD disposed in the display unit 3.

  The print processing unit 5 forms an image on a recording sheet by an electrophotographic method (here, an image corresponding to the image information generated by the image generation unit 1), and includes a developing unit 6, a photosensitive unit 7 and the like. I have. The developing unit 6 forms a toner image by attaching toner to an electrostatic latent image corresponding to an original image formed on the surface of the photosensitive drum by a laser beam or the like. The photosensitive unit 7 includes a photosensitive drum made of amorphous silicon (a-Si) or the like. First, the surface of the photosensitive drum 71 is substantially uniformly charged by a charging roller, and then corresponds to a document image by the developing unit 6. Toner is attached to the electrostatic latent image to form a toner image, and the toner image is further transferred onto a recording sheet by a transfer roller. Here, the photosensitive drum 71 is rotationally driven at a peripheral speed of 180 mm / sec, and the surface potential of the photosensitive drum is set to 310V.

  FIG. 2 is a configuration diagram showing an example of the configuration of the developing unit 6 and the photosensitive unit 7. The developing unit 6 includes a magnetic roller 61, a developing roller 62, and a collection roller 63. The photosensitive unit 7 includes a photosensitive drum 71, an intermediate transfer belt 72, and a density sensor 73.

  The magnetic roller 61 is disposed so as to face the developing roller 62, and the magnetic brush 8 is formed on the surface, and the toner 81 is formed substantially uniformly on the surface of the developing roller 62 via the magnetic brush 8. is there. The magnetic roller 61 includes a sleeve formed of a non-magnetic metal material in a substantially cylindrical shape, and a plurality of fixed magnets for forming the magnetic brush 8 therein, and the sleeve rotates around the fixed magnet. It is configured to be possible.

  Here, the magnetic brush 8 is composed of a two-component developer including a toner 81 and a carrier 82. The volume average particle diameter of the toner 81 is approximately 7.5 μm here, and the volume average particle diameter of the carrier 82 is approximately 50 μm here. The magnetic roller 61 is provided with a blade 613 that regulates the height of the magnetic brush 8. Further, an AC bias power source 611 and a DC bias power source 612 are superimposed on the magnetic roller 61 and applied. Here, the AC bias power supply 611 is applied at 300 V (pp), the frequency is 2.7 kHz, and the duty ratio (Duty) is 27%, and the DC bias power supply 612 is applied at 400 V.

  The developing roller 62 is disposed to face the magnetic roller 61 and the photosensitive drum 71, and supplies the toner 81 supplied from the magnetic roller 61 onto the electrostatic latent image formed on the photosensitive drum 71 to form a toner image. Is. The surface of the developing roller 62 is formed of aluminum, stainless steel, conductive resin, or the like. An AC bias power source 621 and a DC bias power source 622 are superimposed on the developing roller 62 and applied. Here, the AC bias power source 621 is applied at 1.6 kV (pp), a frequency of 2.7 kHz, and a duty ratio of 27%, and the DC bias power source 612 is applied at 200 V. In addition, the developing roller 62 is disposed at a position where the distance from the magnetic roller 61 is 350 μm and the distance from the photosensitive drum 71 is 250 μm.

The collection roller 63 is disposed opposite to the developing roller 62 and collects the toner 81 from the developing roller 62. The surface of the collecting roller 63 suppresses leakage (= discharge) between the collecting roller 63 and the developing roller 62, and anodizing, in order to ensure the ability of the collecting roller 63 to collect the toner 81 from the developing roller 62. It is formed of a material having an electrical resistivity of 10 ⁷ Ωm to 10 ¹² Ωm such as a resin.

  A DC bias power source 631 is applied to the collection roller 63. The direct current bias power source 631 is configured to have a strong recovery potential (0 V in this case) that is a potential of the recovery roller 63 having a high capability of recovering the toner 81 from the developing roller 62 by a potential control unit 215 described later. Is set to one of a weak recovery potential (here, 50 V) that is a potential of the recovery roller 63 having a low ability to recover the power.

  As described above, since a DC bias of 200 V is applied to the developing roller 62, if the collecting roller 63 is set to 0 V, which is a strong collecting potential, the potential difference between the collecting roller 63 and the developing roller 62 is increased. Since the potential difference becomes larger compared to the case where the recovery roller 63 is set to 50 V, which is a weak recovery potential (in this case, the potential difference between the recovery roller 63 and the developing roller 62 is 150 V). The ability to collect the toner 81 from the developing roller 62 is improved.

  Further, a blade 633 is disposed on the collection roller 63 so as to be in sliding contact with the circumferential surface of the collection roller 63. The blade 633 peels off the toner 81 adhering to the surface of the collection roller 63, and can be collected by a collection mechanism including a collection screw (not shown). The collection mechanism mixes the toner 81 collected from the collection roller 63 with the carrier 82 and supplies it to the magnetic roller 61.

  The intermediate transfer belt 72 is for transferring a toner image formed on the photosensitive drum 71. Here, a toner image corresponding to a patch for density measurement is formed. The intermediate transfer belt 72 includes an endless belt stretched around a driving roller 721, and a toner image 722 corresponding to a density measurement patch is formed on the endless belt.

  A density sensor 73 (corresponding to a part of the second density detection means) 73 is a reflection type density sensor, and here, a toner image 722 corresponding to a density measurement patch formed on the intermediate transfer belt 72 is used. The concentration is measured. FIG. 3 is a configuration diagram showing an example of the configuration of the density sensor 73. The density sensor 73 includes a light emitting element 731, a first beam splitter 732, a first light receiving element 733, a second beam splitter 734, a second light receiving element 735, and a third light receiving element 736.

  The light (laser beam) emitted from the light emitting element 731 composed of an LED (Light Emitting Diode) or the like detects the direction of the toner image 722 and the light emission amount of the light emitting element 731 by the first beam splitter 732, and the amount of light is detected by the feedback circuit. It is divided into a first light receiving element (Photo Detector) 733 for keeping constant. Then, the light reflected by the toner image 722 is divided into two polarization components of the second light receiving element 735 and the third light receiving element 736 by the second beam splitter 734, and the light is reflected on the second light receiving element 735 and the third light receiving element 736. The density is detected by the ratio of the amount of incident light.

FIG. 4 is a graph showing an example of the relationship between the printing rate R of the toner image 722 and the output voltage VI of the density sensor 73. The horizontal axis represents the printing rate R of the toner image 722, and the vertical axis represents the output voltage VI of the density sensor 73. Here, the printing rate R is defined by the following equation (1).
(Print rate R) = (Number of dots to which toner is attached)
/ (Number of all dots) × 100 (1)

  That is, as shown in the graph G1, as the printing rate R increases, the output voltage VI of the density sensor 73 decreases almost monotonously. However, when the printing rate R is in the range of 50% or more or 20% or less, the change in the output voltage VI of the density sensor 73 accompanying the change in the printing rate R is small, so the toner image 722 corresponding to the density measurement patch. The printing rate R (corresponding to the reference density) is set in the range of 20% to 50%.

  FIG. 5 is a configuration diagram illustrating an example of a functional configuration of the control unit 2 (CPU 21 and RAM 22) illustrated in FIG. The CPU 21 functionally includes a potential setting unit 211, a threshold setting unit 212, a concentration detection unit 213, a concentration determination unit 214, and a potential control unit 215. The RAM 22 functionally includes a potential storage unit 221, and A threshold storage unit 222 is provided. Here, the CPU 21 reads out and executes a program stored in advance in a ROM or the like, whereby the potential setting unit 211, the threshold setting unit 212, the concentration detection unit 213, the concentration determination unit 214, the potential control unit 215, and the like. It functions as a functional unit, and causes the RAM 22 to function as functional units such as a potential storage unit 221 and a threshold storage unit 222.

  Further, among various data stored in the RAM 22 shown in FIG. 1 and a ROM (not shown), data that can be stored in a removable recording medium includes, for example, a hard disk drive, an optical disk drive, a flexible disk drive, a silicon disk drive, and a cassette medium. The recording medium may be readable by a driver such as a reader. In this case, the recording medium is, for example, a hard disk, an optical disk, a flexible disk, a CD, a DVD, a semiconductor memory, or the like.

  The potential storage unit 221 has a low recovery capability of recovering the toner 81 from the developing roller 62 compared to a preset reference potential VR0 (for example, 100 V) and the case where the recovery roller 63 is set to the reference potential VR0. The weak recovery potential VR1 (for example, 150V) that is the potential of the roller 63 and the recovery roller 63 having a higher ability to recover the toner 81 from the developing roller 62 compared to the case where the recovery roller 63 is set to the reference potential VR0. A strong recovery potential VR2 (for example, 50 V), which is a potential, is stored. The values of the reference potential VR0, the weak recovery potential VR1, and the strong recovery potential VR2 stored in the potential storage unit 221 are set by the potential setting unit 211 and read by the potential control unit 215.

  The threshold value storage unit 222 stores a density ratio upper limit value DH and a density ratio lower limit value DL for determining whether or not the density is appropriate. The upper limit value DH of the density ratio and the lower limit value DL of the density ratio stored in the threshold storage unit 222 are set by the threshold setting unit 212 and read by the density determination unit 214.

  The potential setting unit 211 (corresponding to a potential setting unit) receives an operation input from the user via the operation unit 4 illustrated in FIG. 1, and the reference stored in the potential storage unit 221 based on the received operation input. The values of the potential VR0, the weak recovery potential VR1, and the strong recovery potential VR2 are set.

  The threshold setting unit 212 (corresponding to the threshold setting unit) receives an operation input from the user via the operation unit 4 illustrated in FIG. 1, and the density stored in the threshold storage unit 222 based on the received operation input. The upper limit value DH of the ratio and the lower limit value DL of the density ratio are set.

  A density detector 213 (corresponding to a part of the second density detector) transfers the density (here, the toner image 722 corresponding to the density measurement patch transferred to the intermediate transfer belt 72 via the density sensor 73. , The printing rate R). That is, the density detector 213 receives the output voltage VI from the density sensor 7 and calculates the printing rate R corresponding to the output voltage VI using the graph shown in FIG.

The density determination unit 214 (corresponding to the density determination unit) determines whether or not the density detected by the density detection unit 213 is an appropriate density. More specifically, the density determination unit 214 first sets a density ratio D that is a ratio of the printing rate R detected by the density detection unit 213 to a preset reference printing rate R0 (corresponding to the reference density). The following equation (2) is used for calculation.
(Density ratio D) = (Print rate R) / (Standard print rate R0) × 100 (2)

  Then, the density determination unit 214 reads the upper limit value DH of the density ratio D and the lower limit value DL of the density ratio D stored in the threshold value storage unit 222. Further, the density determination unit 214 determines whether the density is an appropriate density based on whether the density ratio D obtained from the printing rate R detected by the density detection unit 213 is within the range between the upper limit value DH and the lower limit value DL. It is determined whether or not.

  That is, the density determination unit 214 determines that the density is an appropriate density when the density ratio D obtained from the printing rate R detected by the density detection unit 213 is equal to or lower than the upper limit value DH and equal to or higher than the lower limit value. When the density ratio D obtained from the printing rate R detected by the density detection unit 213 is greater than the upper limit value DH or less than the lower limit value, it is determined that the density is not an appropriate density.

  The potential control unit 215 (corresponding to the potential control unit) controls the potential of the collection roller 63 based on the density ratio when the determination unit 214 determines that the density is not an appropriate density.

  Specifically, the potential control unit 215 first reads the values of the reference potential VR0, weak recovery potential VR1, and strong recovery potential VR2 stored in the potential setting unit 211. The potential control unit 215 sets the potential of the recovery roller 63 to the weak recovery potential VR1 when the density ratio obtained from the printing rate R detected by the density detection unit 213 by the density determination unit 214 is less than the lower limit value DH. Set to. Further, the potential control unit 215 sets the potential of the recovery roller 63 to the strong recovery potential VR2 when the density ratio obtained from the printing rate R detected by the density detection unit 213 by the density determination unit 214 exceeds the upper limit value DH. Set to. Further, the potential control unit 215 determines that the recovery roller 63 has a density ratio obtained from the printing rate R detected by the density detection unit 213 by the density determination unit 214 when the density ratio is equal to or lower than the upper limit value DH and equal to or higher than the lower limit value. The potential is set to the reference potential VR0.

  FIG. 6 is a flowchart illustrating an example of the operation of the CPU 21. Here, in the potential storage unit 221 and the threshold storage unit 222, the values of the reference potential VR0, the weak recovery potential VR1, and the strong recovery potential VR2, the lower limit value DL, and the upper limit value DH are respectively stored in advance. Assume that it is stored. First, the density detector 213 detects the density (printing rate R) of the toner image 722 corresponding to the density measurement patch via the density sensor 73 (S101). Then, the density determination unit 214 calculates the density ratio D using the density detected in step S101 (S103). Next, the density determination unit 214 determines whether or not the density ratio D is less than the lower limit value DL (S105).

  If it is determined that the density ratio D is less than the lower limit value DL (YES in S105), the potential controller 215 sets the potential of the collection roller 63 to the weak recovery potential VR1 (S107), and the process is terminated. The When it is determined that the concentration ratio D is not less than the lower limit value DL (= more than the lower limit value DL) (NO in S105), the potential control unit 215 causes the concentration ratio D to exceed the upper limit value DH. Is determined (S109). When it is determined that the density ratio D exceeds the upper limit value DH (YES in S109), the potential control unit 215 sets the potential of the collection roller 63 to the strong recovery potential VR2 (S111), and the process is terminated. The

  When it is determined that the density ratio D is not greater than the upper limit value DH (= the density ratio D is equal to or lower than the upper limit value DH) (NO in S109), the potential control unit 215 causes the potential of the collection roller 63 to be the reference potential. VR0 is set (S113), and the process is terminated.

  In this way, the density of the toner image 722 formed on the intermediate transfer belt 72 is detected, and it is determined whether or not the detected density is an appropriate density. Based on the determination result, the density of the collecting roller 63 is determined. Since the potential is controlled, the image density can be suitably controlled.

  Further, a density ratio D, which is a ratio of the detected density to the reference density, is calculated, and whether or not the calculated density ratio D is an appropriate density based on whether or not it is within a preset range. Therefore, it is possible to accurately determine whether or not the density is appropriate with a simple configuration.

  Further, the upper limit value DH and the lower limit value DL of the appropriate range of the stored density ratio D are read, and when the density ratio D is equal to or lower than the upper limit value DH and equal to or higher than the lower limit value DL, the appropriate density is obtained. Since it is determined that there is, the upper limit value DH and the lower limit value DL of the appropriate range of the density ratio can be easily set.

  In addition, an operation input from the user is accepted via the operation unit 4, and the upper limit value DH and the lower limit value DL of the appropriate range of the density ratio D are set based on the accepted operation input. The upper limit value DH and the lower limit value DL of the appropriate range of the ratio D can be set more easily.

  Further, when it is determined that the detected density is not an appropriate density, the potential of the collection roller 63 is controlled based on the density ratio D, so that a density with a desired accuracy can be ensured.

  Furthermore, compared with the reference potential VR0 set in advance and the case where the recovery roller 63 is set to the reference potential VR0, the weak recovery potential VR1 which is the potential of the recovery roller 63 having a low ability to recover toner from the developing roller 62. By switching between the recovery roller 63 and the strong recovery potential VR2, which is the potential of the recovery roller 63 that has a higher ability to recover toner from the developing roller 62, compared to the case where the recovery roller 63 is set to the reference potential VR0, the recovery roller 63 Since the potential of 63 is controlled, the potential of the collection roller 63 can be controlled with a simple configuration.

  In addition, since the reference potential VR0, the weak recovery potential VR1 and the strong recovery potential VR2 are read and the potential of the recovery roller 63 is controlled, the reference potential VR0, the weak recovery potential VR1 and the strong recovery potential VR2 are easily set. can do.

  Further, an operation input from the user is accepted via the operation unit 4, and the stored reference potential VR0, weak recovery potential VR1 and strong recovery potential VR2 are set based on the received operation input. The potential VR0, the weak recovery potential VR1, and the strong recovery potential VR2 can be set more easily.

The present invention can also be applied to the following forms.
(A) Although the potential control unit 215 controls the DC bias power supply 631 by switching the reference potential VR0, the weak recovery potential VR1, and the strong recovery potential VR2 in the present embodiment, The DC bias power supply 631 may be controlled by other methods. For example, the potential controller 215 may control the DC bias power supply 631 according to the density ratio D.

More specifically, the potential controller 215 may control the potential of the DC bias power source 631 of the collection roller 63 using the following equation (3).
(Potential of DC bias power supply 631) = α × (concentration ratio D) + β (3)
Here, α and β are predetermined constants. In this case, the image density can be controlled more suitably.

  Further, in the above equation (3), the potential of the DC bias power supply 631 corresponding to each of the various density ratios D is calculated in advance and stored in a table or the like. The potential of the DC bias power supply 631 of the collection roller 63 may be controlled by reading and setting the potential of the corresponding DC bias power supply 631.

  (B) In this embodiment, the case where the potential control unit 215 controls the potential of the DC bias power supply 631 of the collection roller 63 has been described. However, the potential control unit 215 directly sets the potential of the collection roller 63 with respect to the developing roller 62. It is also possible to control automatically. In other words, instead of the DC bias power supply 631, a DC bias power supply may be provided between the developing roller 62 and the collection roller 63, and the potential control unit 215 may control this DC bias power supply.

  (C) In this embodiment, the case where the density detection unit 213 measures the density of the toner image 722 corresponding to the density measurement patch formed on the intermediate transfer belt 72 via the density sensor 73 has been described. The density detection unit 213 may measure the density of the toner image corresponding to the density measurement patch formed on the photosensitive drum 71. Alternatively, the density detection unit 213 may measure the density of the toner image corresponding to the density measurement patch formed on the intermediate transfer belt 72 and the photosensitive drum 71. In this case, it can be more accurately determined whether or not the concentration is within the appropriate range. Further, the density detection unit 213 may measure the density of the toner image corresponding to the density measurement patch formed on the recording paper.

FIG. 1 is a block diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. FIG. 3 is a configuration diagram illustrating an example of a configuration of a developing unit and a photosensitive unit. These are block diagrams which show an example of a structure of a density sensor. These are graphs showing an example of the relationship between the toner image printing rate R and the output voltage VI of the density sensor. These are block diagrams which show an example of a function structure of the control part (CPU, RAM) shown in FIG. These are the flowcharts which show an example of operation | movement of CPU.

Explanation of symbols

100 Copier 2 Control Unit 21 CPU
211 Potential setting unit (potential setting means)
212 Threshold setting unit (threshold setting means)
213 Concentration detection unit (part of concentration detection means)
214 Density determination unit (density determination means)
215 Potential control unit (potential control means)
22 RAM
221 Potential storage unit (potential storage means)
222 Threshold storage unit (threshold storage means)
6 Developing Unit 61 Magnetic Roller 62 Developing Roller 63 Recovery Roller 631 DC Bias Power Supply 7 Photosensitive Unit 71 Photosensitive Drum 72 Intermediate Transfer Belt (Intermediate Transfer Body)
73 Concentration sensor (part of concentration detection means)

Claims (10)

A magnetic roller having a magnetic brush formed on the surface;
An electrostatic latent image formed on the photosensitive drum is disposed opposite to the magnetic roller, supplied with toner from the magnetic roller via the magnetic brush, and disposed opposite to the photosensitive drum. A developing roller for supplying toner to form a toner image;
A collecting roller disposed opposite to the developing roller for collecting toner from the developing roller;
An image forming apparatus comprising:
First density detecting means for detecting the density of the toner image formed on the photosensitive drum;
A concentration determination unit that determines whether or not the concentration detected by the first concentration detection unit is an appropriate concentration;
A potential control means for controlling the potential of the collecting roller based on the determination result of the density determination means;
Equipped with a,
The potential control means includes
When the density determination means determines that the density detected by the first density detection means is greater than the appropriate density, the recovery is performed so that a potential difference between the developing roller and the recovery roller is increased. Control the potential of the roller,
When the density determination means determines that the density detected by the first density detection means is less than the appropriate density, the recovery is performed so that the potential difference between the developing roller and the recovery roller is reduced. An image forming apparatus for controlling a potential of a roller . A magnetic roller having a magnetic brush formed on the surface;
An electrostatic latent image formed on the photosensitive drum is disposed opposite to the magnetic roller, supplied with toner from the magnetic roller via the magnetic brush, and disposed opposite to the photosensitive drum. A developing roller for supplying toner to form a toner image;
A collecting roller disposed opposite to the developing roller for collecting toner from the developing roller;
An intermediate transfer member to which a toner image formed on the photosensitive drum is transferred;
An image forming apparatus comprising:
Second density detecting means for detecting the density of the toner image transferred to the intermediate transfer member;
Concentration determining means for determining whether or not the concentration detected by the second concentration detecting means is an appropriate concentration;
A potential control means for controlling the potential of the collecting roller based on the determination result of the density determination means;
Equipped with a,
The potential control means includes
When the density determination unit determines that the density detected by the second density detection unit is greater than the appropriate density, the collection is performed so that a potential difference between the developing roller and the collection roller becomes large. Control the potential of the roller,
When the density determination means determines that the density detected by the second density detection means is less than the appropriate density, the recovery is performed so that the potential difference between the developing roller and the recovery roller is reduced. An image forming apparatus for controlling a potential of a roller .   The density determination means calculates a density ratio that is a ratio of the density detected by the first density detection means or the second density detection means to a preset reference density, and the calculated density ratio is preset. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus determines whether the density is appropriate based on whether the density is within the range. Threshold storage means for storing an upper limit value and a lower limit value of the appropriate range of the density ratio,
The density determination means reads the upper limit value and the lower limit value from the threshold value storage means, and determines that the density is an appropriate density when the density ratio is equal to or lower than the upper limit value and equal to or higher than the lower limit value. The image forming apparatus according to claim 3.   5. The apparatus according to claim 4, further comprising a threshold value setting unit that receives an operation input from the outside and sets at least one of an upper limit value and a lower limit value stored in the threshold value storage unit based on the received operation input. The image forming apparatus described in 1.   The potential control means, when the concentration determination means determines that the concentration detected by the first concentration detection means or the second concentration detection means is not an appropriate concentration, based on the concentration ratio, 6. The image forming apparatus according to claim 3, wherein the potential of the collecting roller is controlled. The potential control means includes
A preset reference potential;
Compared to the case where the collection roller is set to the reference potential, a strong collection potential which is a potential of the collection roller having a high ability to collect toner from the developing roller;
Compared to the case where the collection roller is set to the reference potential, a weak collection potential which is a potential of the collection roller having a low ability to collect toner from the developing roller;
The image forming apparatus according to claim 1, wherein the potential of the collecting roller is controlled by switching between the two. Comprising a potential storage means for storing the reference potential, the strong recovery potential and the weak recovery potential;
The image forming apparatus according to claim 7, wherein the potential control unit reads the reference potential, the strong recovery potential, and the weak recovery potential from the potential storage unit, and controls the potential of the recovery roller.   And a potential setting unit configured to receive an operation input from the outside and set at least one value of a reference potential, a strong recovery potential, and a weak recovery potential stored in the potential storage unit based on the received operation input. The image forming apparatus according to claim 8. Electric potential storage means for storing the electric potential of the collecting roller in association with the density ratio;
The potential control unit reads the potential of the collection roller corresponding to the density ratio calculated by the density determination unit from the potential storage unit, and controls the potential of the collection roller to the read potential. The image forming apparatus according to claim 6.

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