JP2007079071A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having an intermediate transfer body, and first and second electrode members for imparting charge to an image conveying body such as a recording material carrier, and capable of applying appropriate voltage to the electrode members considering the mutual influence between the first and the second electrode members. <P>SOLUTION: In the image forming apparatus equipped with a voltage decision means 10 deciding voltage applied to the first electrode member 54 on the basis of the result of detection by a first detection means 121 and voltage applied to the second electrode member 55a on the basis of the result of detection by a second detection means 111a, the voltage decision means 10 is constituted to decide the voltage applied to the second electrode member 55a by applying monitor voltage or monitor current while the second electrode member 55a is positioned in the area of the image conveying body 51 to which charge is imparted by the application of the decided voltage to the first electrode member 54. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system, an electrostatic recording system, or the like. More specifically, the present invention has a plurality of bias application positions in the surface movement direction of an image carrier such as an intermediate transfer member or a recording material carrier, and bias values applied at the plurality of bias application positions are image forming steps. The present invention relates to an image forming apparatus determined in advance.

  Conventionally, for example, in an electrophotographic image forming apparatus, an electrostatic image (latent image) formed on an electrophotographic photosensitive member (photosensitive member) is developed with toner to form a toner image. Thereafter, the toner image formed on the photoconductor is finally transferred to a recording material (recording paper, OHP sheet, etc.), fixed, and then output to the outside of the image forming apparatus. As a system for transferring a toner image on a photoconductor to a recording material, there is a direct transfer system for directly transferring a toner image formed on a photoconductor to a recording material. Further, there is an intermediate transfer system in which a toner image formed on a photosensitive member is once transferred onto an intermediate transfer member, and then the toner image on the intermediate transfer member is transferred onto a recording material. In the process until the toner image is transferred onto the recording material, a transfer bias is applied to the back surface of the recording material and the back surface of the intermediate transfer member. Thereby, the toner is moved electrostatically. As a transfer member, a corona charger, a roller charger (transfer roller), a brush charger (transfer brush), a blade charger (transfer blade), or the like is known.

  The corona charger has a problem of ozone generated during charging or static elimination and a problem of requiring large electric power. Therefore, recently, a contact-type charger (transfer) that applies a bias by bringing a conductive transfer member that generates a small amount of ozone and can be charged with a small amount of power into contact with the back surface of a recording material or an intermediate transfer member. Rollers, transfer brushes, transfer blades, etc.) are often used.

  In recent years, the types of recording materials have become abundant. In addition, the required thickness and electrical resistance of recording materials are becoming wider. For this reason, there are many cases in which an intermediate transfer system that can cope with the type of recording material is employed.

  In order to prevent the amount of charge supplied to the toner image from becoming constant due to a difference in image ratio, recording material width, etc., the transfer bias is more suitable for constant voltage control than constant current control.

  Further, the electrical resistance of the intermediate transfer member and the transfer roller, the film thickness of the surface layer of the photosensitive member, or the like may change with changes in the atmospheric environment such as temperature and humidity, or with durability. Therefore, it is desirable to change the transfer voltage applied to the transfer member in accordance with these changes.

  Therefore, voltage determination control is performed to determine a control value (voltage value) of constant voltage control before image formation so that a desired transfer voltage is obtained during image formation.

  For example, Patent Document 1 discloses ATVC control (Active Transfer Voltage Control) as a voltage determination method. That is, a desired constant current voltage is applied from the transfer roller to the photoconductor during the non-image forming process of the image forming apparatus, and the voltage value at that time is held. Thereby, the electric resistance of the transfer roller is detected, and a constant voltage corresponding to the electric resistance value is applied to the transfer roller as a transfer voltage during transfer in the image forming process.

Patent Document 2 discloses PTVC control (Programmable Transfer Voltage Control) as another voltage determination method. The ATVC control detects the electric resistance of the transfer roller by constant current control, whereas the PTVC control detects the electric resistance of the transfer roller only by constant voltage control. Therefore, in the PTVC control, the circuit is simplified and the detection accuracy is improved. More specifically, in PTVC control, a constant voltage is applied when detecting the electrical resistance of the transfer roller, and the output current value flowing through the photosensitive member at this time is detected. And the voltage value which can flow a desired setting current value is determined by changing a voltage value from the difference of this electric current value and a setting electric current value.
JP-A-2-123385 JP-A-5-181373

  However, the following problems arise when a plurality of electrode members to which a voltage is applied are provided in contact with the image carrier (intermediate transfer member).

  For example, an image forming apparatus using an intermediate transfer member as an image carrier, that is, a primary transfer material that transfers a toner image from an image carrier to an image carrier in a primary transfer unit, and a toner image from the image carrier to a recording material Consider an image forming apparatus having a secondary transfer member for transferring the image at the secondary transfer portion. In this case, it is assumed that bias control is performed on both the primary transfer member and the secondary transfer member using ATVC control or PTVC control.

  The charge supplied from the secondary transfer member onto the image carrier may remain on the intermediate transfer member even at the primary transfer portion. If the voltage applied to the primary transfer member is controlled in this state, an appropriate charge may not be supplied from the primary transfer member.

  In addition, the charge supplied on the image carrier in the primary transfer unit may remain on the image carrier in the secondary transfer unit. Therefore, the charge supplied at the primary transfer unit may affect the secondary transfer unit.

  In addition, electrostatic cleaning means for electrostatically removing secondary transfer residual toner remaining on the image carrier has been proposed. According to such electrostatic cleaning means, the life of the intermediate transfer member can be extended, and cleaning performance independent of the surface state of the intermediate transfer member can be exhibited. This electrostatic cleaning means is disposed between the secondary transfer portion and the primary transfer portion. In this case, the mutual influence of the electrostatic cleaning means, the primary transfer member, and the secondary transfer member cannot be ignored.

  Further, in the case where a plurality of primary transfer parts are provided and a plurality of primary transfer members are provided, the mutual influence cannot be ignored between the plurality of primary transfer members.

  Under such conditions, when ATVC control or PTVC control is performed on the two electrode members, the history of the charged state of the image carrier by the upstream electrode member in the moving direction of the image carrier is changed to the downstream electrode member. This may affect the control of the voltage applied to. Therefore, there are cases where appropriate bias control cannot be performed.

  In the above description, the conventional problems have been described particularly with respect to the intermediate transfer type image forming apparatus. However, the same problem may occur in a so-called direct transfer type image forming apparatus in which an image carrier conveys a recording material onto which an image has been transferred.

  Accordingly, an object of the present invention is to provide an image forming apparatus having first and second electrode members for applying an electric charge to an image transfer body such as an intermediate transfer member and a recording material carrier, and the first and second electrode members are connected to each other. It is an object of the present invention to provide an image forming apparatus capable of applying an appropriate voltage to an electrode member in consideration of the influence.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention is directed to an image carrier that carries a toner image, first and second electrode members that apply a charge to the image carrier, and a monitor voltage or a monitor current applied to the first electrode member. A first detection means for detecting a voltage-current relationship when applied; a second detection means for detecting a voltage-current relationship when a monitor voltage or a monitor current is applied to the second electrode member; A voltage determination for determining a voltage to be applied to the first electrode member based on a detection result of the first detection means and a voltage to be applied to the second electrode member based on a detection result of the second detection means. An image forming apparatus comprising: a voltage determining unit configured to apply a voltage determined by the first electrode member to the region of the image carrier to which a charge is applied. In the state where the electrode member of By applying a terpolymer voltage or monitor current, which is an image forming apparatus and determines the voltage applied to the second electrode member.

  According to the present invention, in an image forming apparatus having first and second electrode members for applying an electric charge to an image carrier such as an intermediate transfer member or a recording material carrier, the voltage applied to the first and second electrode members Control can be performed in consideration of the mutual influence of the first and second electrode members. Therefore, an appropriate voltage can be applied to the first and second electrodes.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Entire configuration of image forming apparatus]
FIG. 1 shows a schematic sectional configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a laser beam printer that can form a full color image on a recording material (recording paper, OHP sheet, cloth, or the like) using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (stations) Sa for forming yellow, magenta, cyan, and black images as image forming units that form toner images. , Sb, Sc, Sd.

  In this embodiment, the configuration of each image forming unit Sa, Sb, Sc, Sd is the same except for the color of the toner to be used. Accordingly, in the following, when there is no particular need to distinguish, subscripts a, b, c, and d attached to the reference numerals to indicate that they are elements provided for any color will be omitted, and a general description will be given. To do.

  The image forming unit S is provided with a cylindrical photosensitive member, that is, a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 as a charging unit and a laser beam scanner 3 as an exposure unit are arranged. Further, around the photosensitive drum 1, a developing device 4 as a developing means and a cleaning device 6 as a cleaning means are arranged. Further, an intermediate transfer unit 5 is disposed so as to face the photosensitive drums 1a to 1d of the image forming portions Sa to Sd.

  The intermediate transfer unit 5 has an intermediate transfer belt (image carrier) 51 as an intermediate transfer member. The intermediate transfer belt 51 is wound around a driving roller 52, a driven roller 53, and a secondary transfer inner roller (inner roller) 54 as a plurality of support members. When the driving force is transmitted to the driving roller 52, the intermediate transfer belt 51 rotates (rotates) in the direction of the arrow R2 in the drawing. On the inner peripheral surface side of the intermediate transfer belt 51, primary transfer rollers (electrode members) 55 as primary transfer units are disposed at positions facing the photosensitive drums 1a to 1d of the image forming units Sa to Sd. Has been. Each primary transfer roller 55a to 55d presses the intermediate transfer belt 51 toward the photosensitive drums 1a to 1d, so that the primary transfer portion (primary transfer nip) N1a where the intermediate transfer belt 51 contacts the photosensitive drum 1; N1b, N1c, and N1d are formed.

  Here, a toner image is formed on the intermediate transfer belt 51 by the first image forming unit Sa and the primary transfer roller 55a that opposes the first image forming unit Sa via the intermediate transfer belt 51. A first toner image forming unit is configured. Similarly, second, third, and fourth toner images are formed by the second, third, and fourth image forming units Sb, Sc, and Sd and the primary transfer rollers 55b, 55c, and 55d, respectively. The part is composed.

  A secondary transfer outer roller (outer roller) 56 is disposed at a position facing the inner roller 54 with the intermediate transfer belt 51 interposed therebetween. The intermediate transfer belt 51 is sandwiched between an inner roller 54 and an outer roller 56 constituting a secondary transfer unit. That is, the inner roller (electrode member) 54 contacts the inner periphery of the intermediate transfer belt 51, and the outer roller 56 contacts the outer periphery of the intermediate transfer belt 51. As a result, a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 51 and the outer roller 56 are in contact is formed.

  The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in a direction (counterclockwise direction) indicated by an arrow R1 in the drawing. The peripheral surface of the photosensitive drum 1 is charged (primarily charged) to a predetermined polarity and potential by a charging roller 2 that is a contact charging member.

  The laser beam scanner 3 outputs laser light that is on / off modulated in accordance with image information input from an external device such as an image scanner or a computer. The laser beam scanner 3 scans and exposes the charged surface on the photosensitive drum 1 with the laser beam. An electrostatic image (latent image) corresponding to target image information is formed on the photosensitive drum 1 by scanning exposure by the laser beam scanner 3.

  The electrostatic image formed on the photosensitive drum 1 is visualized as a toner image by the developing device 4. In this embodiment, the developing device 4 contains a two-component developer including non-magnetic resin toner particles (toner) and magnetic carrier particles (carrier) as developers. The developing device 4 has a developing sleeve 41 as a developer carrying member disposed to face the photosensitive drum 1. Then, by supplying toner from the developer carried on the developing sleeve 41 to the photosensitive drum 1, the electrostatic image on the photosensitive drum 1 is developed.

  The toner image formed on the photosensitive drum 1 is electrostatically transferred (primary transfer) onto the intermediate transfer belt 51 by the transfer roller 55 in the primary transfer portion N1. At this time, an appropriate primary transfer bias is output from the primary transfer bias power source 110 as the primary transfer bias output means and applied to the primary transfer roller 55 as the bias applying member. For example, + 900v is used as the primary transfer bias. Further, when a primary transfer bias is applied to the primary transfer roller 55, the primary transfer roller 55 imparts an electric charge to the intermediate transfer belt 51. That is, the bias output from the primary transfer vice power supply 110 is applied to the intermediate transfer belt 51 at the primary transfer portion N1 via the primary transfer roller 55 as a bias applying member. In the present embodiment, the primary transfer bias power source 110 outputs a primary transfer bias with constant voltage control during the primary transfer process. In this embodiment, a bias having a polarity opposite to the normal charging polarity of the negative polarity toner is applied to the primary transfer roller 55 during image formation. Control of the primary transfer bias applied at this time will be described later.

  The primary transfer residual toner remaining on the photosensitive drum 1 after the primary transfer process is scraped off and collected by the cleaning device 6. As a result, the surface of the photosensitive drum 1 is cleaned and repeatedly used for image formation.

  For example, when a full-color image is formed, the above-described operation is sequentially performed in the first to fourth image forming units Sa to Sd. As a result, the toner images of the respective colors are transferred onto the intermediate transfer belt 51 in the primary transfer portions N1a to N1d.

  On the other hand, the recording material P is conveyed from the recording material supply unit 8 to the secondary transfer unit N2 in synchronization with the toner image on the intermediate transfer belt 51. The recording material P is sent out from a cassette 81 in which the recording material P is stored by a supply roller 82 and is transported to a registration roller pair 84 by a transport roller 83. Then, the recording material P is supplied to the secondary transfer portion N2 in timing with the toner image on the intermediate transfer belt 51.

  The toner image on the intermediate transfer belt 51 is electrostatically transferred to the recording material P by the electric field between the inner roller 54 and the outer roller 56 in the secondary transfer portion N2. Here, by applying a bias to either the inner roller 54 or the outer roller 56, an electric field can be formed between these rollers. In this embodiment, an appropriate secondary transfer bias is output from the secondary transfer bias power source 120 as the secondary transfer bias output means during the secondary transfer process, and applied to the inner roller 54 as the bias applying member. For example, −2.3 Kv is used as the secondary transfer bias. That is, the bias output from the secondary transfer bias power source 120 is applied to the intermediate transfer belt 51 at the secondary transfer portion N2 via the inner roller 54 as a bias applying member. Further, when a secondary transfer bias is applied to the inner roller 54, the inner roller 54 imparts a charge to the intermediate transfer belt 51. In this embodiment, a secondary transfer bias controlled by constant voltage is output from the secondary transfer bias power source 120 during the secondary transfer process. In the present embodiment, at the time of image formation, a bias having the same polarity as the normal charging polarity of the negative polarity toner is applied to the inner roller 54. Control of the secondary transfer bias applied at this time will be described later.

  The recording material P on which the toner image has been transferred in the secondary transfer portion N2 is then transported and introduced into the fixing device 7 through a transport path. The fixing device 7 heats and pressurizes the recording material P with a fixing roller 72 including a heating unit 71 and a driving roller 73 to fix the toner image on the recording material P. Thereafter, the recording material P is discharged out of the image forming apparatus main body.

  In this embodiment, the surface of the intermediate transfer belt 51 after the secondary transfer process is completed and the recording material P is separated is subjected to cleaning of secondary transfer residual toner, paper dust, and the like by the cleaning device 57. Thereby, the intermediate transfer belt 51 is repeatedly subjected to an image forming process.

  In addition, the image forming apparatus 100 can form an image of a desired color such as a black single color image using only the desired image forming unit. In this case, only the desired image forming unit performs the same image forming process as described above, and forms only a desired color toner image on the intermediate transfer belt 51. Then, the toner image is transferred to the recording material P and fixed.

In this embodiment, as the intermediate transfer belt 51, a semiconductive polyimide resin having a relative dielectric constant ε = 3 to 5 and a volume resistivity ρv = 10 ⁶ to 10 ¹¹ Ω · m was used.

As the primary transfer roller 55, it is possible to use a semiconductive one having a resistance value of 10 ² to 10 ⁸ Ω when 2000V is applied. In this embodiment, as the primary transfer roller 55, an ion conductive sponge roller formed by blending nitrile rubber and an ethylene-epichlorohydrin copolymer and having an outer diameter of φ16 mm and a core metal diameter of φ8 mm was used. The resistance value of the primary transfer roller 55 was about 10 ⁶ to 10 ⁸ Ω (applied voltage 2 kV) at a temperature of 23 ° C. and a humidity of 50%.

  The resistance value of the primary transfer roller 55 was measured by a resistance measuring device shown in FIG. That is, the primary transfer roller 55 is pressed with a contact pressure of 9.8 N on a core metal at both ends on an aluminum drum (measurement body) 1A having an outer diameter of 30 mm that is rotationally driven. Rotate the follower. Then, 2.0 kV is applied from the bias application power source 500 between the metal core and the ground. At this time, the current flowing through the aluminum drum 1A is measured by an ammeter 600. In the above measurement, the current value when the primary transfer roller 55 was rotated once or more was sampled, and the resistance value was calculated from the average value of the sampled values. Here, assuming that the maximum value and the minimum value of the sampling current value are IMAX and IMIN, the primary transfer roller 55 satisfying IMAX / IMIN ≦ 1.5 is used in this embodiment. That is, the primary transfer roller 55 having a resistance unevenness (circumferential unevenness) of 1.5 or less in the rotation direction was used.

As the inner roller 54, a semiconductive roller having an outer diameter of 20 mm and a core metal diameter of 16 mm, in which conductive carbon is dispersed in EPDM rubber, was used. The resistance value of the inner roller 54 was about 10 ¹ to 10 ⁵ Ω (applied voltage 10 V) at a temperature of 23 ° C. and a humidity of 50% by the same measuring method as described above.

As the outer roller 56, an ion conductive sponge roller formed by blending nitrile rubber and ethylene-epichlorohydrin copolymer and having an outer diameter of 24 mm and a core metal diameter of 12 mm was used. The resistance value of the outer roller 56 was about 10 ⁶ to 10 ⁸ Ω (applied voltage 2 kV) at a temperature of 23 ° C. and a humidity of 50% by the same measuring method as described above.

[Transfer bias control]
Next, the control for determining the primary transfer bias applied to the primary transfer rollers 55a to 55d and the control for determining the secondary transfer bias applied to the inner roller 54 will be described with reference to FIGS. To do.

  In this embodiment, the distance A from the primary transfer portion (fourth primary transfer portion) N1d of the fourth image forming portion Sd to the secondary transfer portion N2 is 430 mm.

  Here, the primary transfer portion N1d is the primary transfer portion N1 that finally passes through until the intermediate transfer belt 51 that has passed the secondary transfer portion N2 reaches the secondary transfer portion N2 again. .

  The distance B from the secondary transfer portion N2 to the primary transfer portion (first primary transfer portion) N1a of the first image forming portion Sa is 170 mm. The distance C between the primary transfer portions N1 of the adjacent image forming portions S is 100 mm. The process speed corresponding to the surface moving speed of the photosensitive drum 1 and the intermediate transfer belt 51 is 200 mm / s.

Effect between the fourth primary transfer portion N1d and the secondary transfer portion N2:
First, in this embodiment, the amount of current applied at the primary transfer portion N1 is 20 μA, and the longitudinal width of the primary transfer roller 55 (primary transfer portion N1) (in the direction orthogonal to the surface movement direction of the intermediate transfer belt 51). (Width) is 350 mm. Therefore, the charge density Q0 / S given by the primary transfer portion N1 is
Q0 = 20 × 10 ⁻⁶ /0.2/0.35=2.9×10 ⁻⁴ (C / m ² )
It becomes. The charge density given by the primary transfer portion N1 is the same in the first to fourth primary transfer portions N1a to N1d.

Here, the dielectric constant ε of the intermediate transfer belt 51 is 5 and the volume resistivity ρv is 1 × 10 ¹⁰ Ω · m. At this time, the residual charge amount Q1 (C / m ² ) in the secondary transfer portion N2 of the charge density Q0 (C / m ² ) given by the fourth primary transfer portion N1d is:
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv))
= 2.9 × 10 ⁻⁴ × exp (− (430/200) / (8.854 × 10 ⁻¹² × 5 × 1 × 10 ¹⁰ ))
= 2.2 × 10 ⁻⁶ (C / m ² )
It becomes. That is, in this embodiment, the residual charge amount Q1 (C / m ² ) in the secondary transfer portion N2 of the charge density Q0 (C / m ² ) given by the fourth primary transfer portion N1d is 1/100. It becomes the following.

In this embodiment, the amount of current applied from the inner roller 54 at the secondary transfer portion N2 is 40 μA, and the longitudinal width of the inner roller 54 (secondary transfer portion N2) (perpendicular to the surface movement direction of the intermediate transfer belt 51). Width in the direction to be) is 350 mm. Therefore, the charge density Q2 / S given by the secondary transfer portion N2 is
Q2 = 40 × 10 ⁻⁶ /0.2/0.35=5.7×10 ⁻⁴ (C / m ² )
It becomes.

  Here, the accuracy of determining the high-voltage output causes an error of about 10% in consideration of an error with respect to the setting value of the applied bias at the time of bias determination control, a current detection error, an error of an interface between the control boards, and the like. Therefore, the remaining charge of 10% or less of the supplied charge amount may be ignored.

That is, the influence of the remaining charge on the upstream side of the supply charge on the downstream side has the following relationship. A distance between two bias application positions with respect to the image carrier 51 along the surface movement direction of the image carrier 51 is defined as A (mm). That is, the first and second electrode members are in contact with the image carrier 51 in the first contact area and the second contact area, respectively. At this time, the distance between the center position of the first contact area and the center position of the second contact area in the moving direction of the image carrier 51 is A (mm). The relative dielectric constant of the image carrier 51 is ε, the volume resistivity of the image carrier 51 is ρv (Ω · m), and the dielectric constant of vacuum is ε0. Further, the surface moving speed (process speed) of the image carrier 51 is set to V (mm / s). Further, the charge density supplied to the image carrier at the bias application position upstream of the surface movement direction of the image carrier 51 out of the two bias application positions is Q0 (C / m ² ). That is, the charge density of the charge applied to the image carrier 51 by the first electrode member is Q0 (C / m ² ). Further, the charge density supplied to the image carrier 51 at the bias application position downstream of the image carrier 51 in the surface movement direction among the two bias application positions is Q2 (C / m ² ). That is, the charge density of the charge applied to the image carrier 51 by the second electrode member is Q2 (C / m ² ). At this time, if the remaining charge amount Q1 of Q0 at the bias application position downstream of the image carrier 51 in the surface movement direction of the two bias application positions has the relationship of the following equation 1, the remaining supply charge on the upstream side The charge affects the downstream supply charge. That is, when the remaining charge amount Q1 of Q0 at the center position of the second contact region has the relationship of the following formula 1, the remaining charge of the upstream supply charge affects the downstream supply charge.
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv))> 1/10 × Q2 (Formula 1)

When the residual charge amount Q1 has the relationship of the following formula 2, the residual charge of the upstream supply charge does not affect the downstream supply charge.
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv)) ≦ 1/10 × Q2 (Formula 2)

In this embodiment, as described above, the residual charge amount Q1 in the secondary transfer portion N2 of the charge amount Q0 (C / m ² ) given by the fourth primary transfer portion N1d is 2.2 × 10 ⁻⁶ (C / M ² ) The charge amount Q2 given by the secondary transfer portion N2 is 5.7 × 10 ⁻⁴ (C / m ² ).

Thus, in this embodiment, the residual charge amount Q1 (C / m ² ) in the secondary transfer portion N2 having the charge density Q0 (C / m ² ) given by the fourth primary transfer portion N1d is secondary. The charge density Q2 (C / m ² ) supplied at the transfer portion N2 is 1/10 or less. That is, the relationship of the above formula 2 is satisfied.

  Accordingly, it can be said that the influence of the electric charge given by the fourth primary transfer portion N1d on the secondary transfer portion N2 may be ignored.

Effect between the secondary transfer portion N2 and the first primary transfer portion N1a:
Next, assuming that the charge density given by the secondary transfer portion N2 is Q0 (C / m ² ), as described above,
Q0 = 40 × 10 ⁻⁶ /0.2/0.35=5.7×10 ⁻⁴ (C / m ² )
It is.

When the remaining charge amount in the first primary transfer portion N1a of the charge density (C / m ² ) given by the secondary transfer portion N2 is calculated in the same manner as above, Q1 (C / m ² )
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv))
= 5.7 × ⁻⁴ × exp (− (170/200) / (8.854 × 10 ⁻¹² × 5 × 1 × 10 ¹⁰ ))
= 8.4 × 10 ⁻⁵ (C / m ² )
It becomes.

If the charge density given by the first primary transfer portion N1a is Q2 (C / m ² ), as described above,
Q2 = 20 × 10 ⁻⁶ /0.2/0.35=2.9×10 ⁻⁴ (C / m ² )
It is.

Thus, in this embodiment, the residual charge amount (C / m ² ) in the first primary transfer portion N1a having the charge density Q0 (C / m ² ) given by the secondary transfer portion N2 is the first More than 1/10 of the charge density Q2 (C / m ² ) supplied by the primary transfer portion N1a. That is, the relationship of the above formula 1 is satisfied.

  Accordingly, the electric charge given by the secondary transfer portion N2 affects the first primary transfer portion N1a.

  Here, the primary transfer portion N1a is the primary transfer portion N1 through which the intermediate transfer belt 51 that has passed through the secondary transfer portion N2 first passes.

・ Effects between the primary transfer parts N1:
Next, the distance between adjacent primary transfer portions N1 is 100 mm. Of the adjacent primary transfer portions N1, the charge density given by the primary transfer portion N1 (for example, the first primary transfer portion N1a) on the upstream side in the surface movement direction of the intermediate transfer belt 51 is Q0 (C / m ² ). Then, as mentioned above,
Q0 = 20 × 10 ⁻⁶ /0.2/0.35=2.9×10 ⁻⁴ (C / m ² )
It is.

The remaining charge amount in the downstream primary transfer portion N1 of the charge density (C / m ² ) given by the upstream primary transfer portion N1 among the adjacent primary transfer portions N1 is defined as Q1 (C / m ² ). As a calculation similar to the above,
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv))
= 2.9 × 10 ⁻⁴ × exp (− (100/200) / (8.854 × 10 ⁻¹² × 5 × 1 × 10 ¹⁰ ))
= 9.2 × 10 ⁻⁵
It becomes.

Since the charge density (C / m ² ) given by each primary transfer portion N1 is the same, the downstream primary transfer portion N1 (for example, the second primary transfer portion, for example) among the adjacent primary transfer portions N1. If the charge density given by N1b) is Q2 (C / m ² ),
Q2 = 20 × 10 ⁻⁶ /0.2/0.35=2.9×10 ⁻⁴ (C / m ² )
It is.

As described above, in this embodiment, the charge density Q0 (C / m ² ) given by the adjacent upstream primary transfer portion N1 has a remaining charge amount (C / C) in the adjacent downstream primary transfer portion N1. m ² ) is larger than 1/10 of the charge density Q2 (C / m ² ) supplied by the primary transfer portion N1 on the downstream side. That is, the relationship of the above formula 1 is satisfied.

  Therefore, the electric charge given by the adjacent upstream primary transfer portion N1 affects the adjacent downstream primary transfer portion N1.

  Accordingly, one of the objects of the present invention is to perform an appropriate bias determination in consideration of the influence between the bias application positions when performing the bias determination control at a plurality of bias application positions for supplying charges to the image carrier. is there.

・ Bias determination control:
Therefore, in this embodiment, as described below, bias determination control is performed at each bias application position.

  The image forming apparatus 100 includes a first bias applying member (first electrode member) that supplies charges to the intermediate transfer belt 51 at a first bias application position, and an intermediate transfer belt 51 at a second bias application position. And a second bias applying member (second electrode member) for supplying electric charges. Here, it is assumed that the second bias application position is located downstream of the first bias application position in the surface movement direction of the intermediate transfer belt 51. The image forming apparatus 100 includes a first bias output unit that outputs a bias to the first bias applying member, and a second bias output unit that outputs a bias to the second bias applying member. And having.

  Then, the first bias output from the first bias output means to the first bias applying member except when the toner image area received by the intermediate transfer belt 51 passes through the first bias applying position. A first bias determination step for determining a value is performed. In the first bias determination step, the first detection bias is output from the first bias output means to the first bias application member, so that the first bias output member outputs the first bias when the toner image region passes the first bias application position. The first bias value output by one bias output means is determined.

  The second bias determining step for determining the second bias value to be output from the second bias output means to the second bias applying member is performed as follows. That is, the second bias determination step is performed at a time other than when the toner image region passes through the second bias application position. In the second bias determination step, an area on the image carrier that has passed through the first bias application position when the first bias application output means outputs the first bias value determined as described above. Is performed when passing through the second bias application position. In the second bias determination step, the second detection bias is output from the second bias output means to the second bias applying member, so that the toner image region passes through the second bias applying position. The second bias value output by the second bias output means is determined at the time.

  In the present embodiment, typically, the first and second bias application positions correspond to the secondary transfer portion N2 and the first primary transfer portion N1a, respectively. The first bias applying member corresponds to the inner roller 54, and the second bias applying means corresponds to the primary transfer roller 55a. In this case, the first and second bias output means are the secondary transfer bias power source 120 and the primary transfer bias power source (first primary transfer bias power source) 110a of the first image forming unit Sa, respectively. In the present embodiment, the first and second bias application positions also correspond to the upstream primary transfer portion N1 and the downstream primary transfer portion N1 of the adjacent primary transfer portions N1, respectively. In this case, the first and second bias output units respectively include the primary transfer bias power supply 110 of the upstream image forming unit S and the primary transfer bias of the downstream image forming unit S among the adjacent image forming units S. Power supply 110. This will be described in more detail below.

  FIG. 4 shows a control mode of the first primary transfer bias power source 110 a and the secondary transfer bias power source 120. In this embodiment, the first primary transfer bias power source 110a and the secondary transfer bias power source 120 can output constant voltage controlled bias to the first primary transfer roller 55a and the inner roller 54, respectively. it can. The first primary transfer bias power supply 110a and the secondary transfer bias power supply 120 have detection units (detection means) 111a and 121 that detect output current values during constant voltage control, respectively. Here, the detection units 121 and 111a correspond to a first detection unit and a second detection unit, respectively. The first primary transfer bias power supply 110 a and the secondary transfer bias power supply 120 are controlled by a CPU (control means, voltage determination means) 10. In this embodiment, the CPU 10 includes a first primary transfer bias power source 110 a and a secondary transfer bias power source 120, and performs overall control of the operation of the image forming apparatus 100. In the first to fourth image forming units Sa to Sd, the configuration of the primary transfer bias power source 110 that outputs a bias to the primary transfer roller 55 and the control mode thereof are the same.

  The CPU 10 determines a control value (voltage value) of a constant voltage-controlled bias output from the first primary transfer bias power supply 110a and the secondary transfer bias power supply 120 during image formation at a predetermined timing other than during image formation. A bias determination step is performed. Predetermined timings other than image formation (non-image formation) are continuous during a preparatory operation before the image forming operation (pre-rotation), during a preparatory operation after the image formation operation (post-rotation), or continuously to a plurality of recording materials. Thus, the timing corresponding to the interval between the recording materials when the image is formed (paper interval) or the like.

  First, in this embodiment, the bias determination control (first bias determination step) of the secondary transfer portion N2 is performed, and the control value (voltage) of the secondary transfer bias under constant voltage control applied to the inner roller 54 at the time of image formation. Value).

  For example, the CPU 10 rotates the intermediate transfer belt 51 at times other than the time of the pre-rotation image formation. When the rotation of the intermediate transfer belt 51 becomes stable, the output voltage of the secondary transfer bias power source 120 as a detection bias is switched in multiple stages. In other words, a plurality of different voltages (monitor voltages) are sequentially applied from the secondary transfer bias power source 120 to the inner roller 54. And the electric current with respect to each voltage is detected by the detection part 121.

  In this embodiment, as shown in FIG. 5, the voltage is switched in three stages (first voltage V1, second voltage V2, and third voltage V3). In this embodiment, the monitor voltages applied to the inner roller 54 are V1 = 3.0 Kv, V2 = 2.5 Kv, and V3 = 2.0 Kv. Then, the CPU 10 derives a voltage-current characteristic (VI characteristic) that is a relationship between the applied voltage and the current value detected by the current detection unit. In addition, linear interpolation was performed except for the measurement points. In this embodiment, V3 <V2 <V1, but this is not restrictive.

  The first voltage V1 is applied for one turn of the inner roller 54, the current value at that time is detected by the current detecting means 121, and the averaged value is set to I1. Similarly, a current value I2 for the second voltage V2 and a current value I3 for the third voltage V3 are obtained. FIG. 6 shows the VI characteristic at this time. This VI characteristic is temporarily stored in a storage means (RAM or the like) built in or connected to the CPU 10.

Here, the transfer current required in the secondary transfer portion N2 is predetermined for each type of recording material P. This transfer current value is associated with the type of the recording material P and stored in a storage means (RAM or the like) built in or connected to the CPU 10. In this embodiment, as an example of the transfer current value, 60 μA was used when using paper having a basis weight of 80 g / m ² . The CPU 10 can obtain the reference voltage Vb, which is applied to the inner roller 54 and necessary for flowing the transfer current, from the VI characteristic shown in FIG.

For example, let Ib be the transfer current required to transfer the toner image on the intermediate transfer belt 51 to a certain recording material P. For example, when Ib <I2 as shown in FIG.
Vb = (V3-V2) (Ib-I2) / (I3-I2) + V2
From this, the voltage Vb can be obtained.

When Ib ≧ I2, the following formula:
Vb = (V2-V1) (Ib-I1) / (I2-I1) + V1
From this, the voltage Vb can be obtained.

  As described above, the control value of the secondary transfer bias that is constant current controlled during image formation, that is, the secondary transfer voltage is determined. The secondary transfer bias power source 120 continues to apply the determined secondary transfer voltage to the inner roller 54 in preparation for bias determination control in the next first primary transfer portion N1a.

  After the head of the area on the intermediate transfer belt 51 charged by the determined secondary transfer voltage passes through the first primary transfer portion N1a, the first primary transfer roller 55a is controlled at a constant voltage during image formation. The bias determination control (second bias determination step) for determining the control value (voltage value) of the bias to be applied is started. The surface potential of the photosensitive drum 1a of the first image forming unit Sa is controlled in advance by the charging roller 2a to the same potential as that at the time of image formation before entering the bias determination control.

  In this way, the voltage determining means (CPU) 10 is in a state in which the second electrode member is located in the region of the intermediate transfer belt 51 to which the charge is applied by applying the determined voltage to the first electrode member. Apply the monitor voltage (or monitor current: described later). Then, the voltage applied to the second electrode member is determined.

  The basic control method for the primary transfer portion N1a is the same as the control method for the secondary transfer portion, and a detailed description thereof will be omitted. That is, the voltage necessary for obtaining the VI characteristic by applying the monitor voltage and supplying the transfer current (35 μA in this embodiment) required in the first primary transfer portion N1a determined in advance. The value is determined from its VI characteristic. As monitor voltages, V1 = 0.5 Kv, V2 = 1.0 Kv, and V3 = 1.5 Kv were used.

  The first primary transfer bias power supply 110a applies the determined primary transfer voltage to the first primary transfer roller 55a in preparation for bias determination control in the next second primary transfer portion N1b. to continue.

  As the charging history of the intermediate transfer belt 51, the top of the area on the intermediate transfer belt 51 where the application of the determined primary transfer voltage to the first primary transfer roller 55a is started is the second primary transfer portion N1b. Is passed, the bias determination control in the second primary transfer portion N1b is started. Thereby, a control value (voltage value) of the bias applied to the second primary transfer roller 55b by the constant voltage control at the time of image formation is determined. Also at this time, the VI characteristic is obtained by applying the monitor voltage to the primary transfer roller 55. Then, a voltage at which a desired transfer current flows is obtained from the obtained VI characteristic and applied at the time of transfer. Here, the primary transfer portion N1a and the primary transfer portion N1b are adjacent to each other.

  Thereafter, similarly, bias determination control is performed in the third and fourth primary transfer portions N1c and N1d. Until the bias determination control in the fourth primary transfer portion N1d is completed, the voltage determined as described above is applied to each member of the inner roller 54 and the first to third primary transfer rollers 55a to 55c. Continue to be applied. When all the voltages are determined, the image forming operation is started.

  By performing the bias determination control as described above, it is possible to determine an optimum voltage value in consideration of the influence between a plurality of bias application positions that supply charges to the intermediate transfer belt 51.

  Instead of the monitor voltage, a bias (monitor current) through which a plurality of different current amounts flow is applied, and the voltage required to flow the current is measured. From this measurement result, the VI characteristic can also be obtained. Here, as an example of the monitor current, the current applied to the primary transfer roller 55 can be I1 = 10 μA, I2 = 15 μA, and I3 = 30 μA. The current applied to the inner roller 54 can be I1 = 10 μA, I2 = 30 μA, and I3 = 50 μA.

  That is, the bias determination control described in this embodiment is a representative example, and the present invention is not limited to this. In the bias determination step, a detection bias subjected to constant current control or constant voltage control is output from the bias output means. Then, the output voltage value or output current value of the bias output means at that time is detected, and information related to the impedance at the bias application position is obtained. Based on the result, it is only necessary to be able to determine the constant voltage controlled or constant current controlled bias value output by the bias output means during image formation. That is, the image forming apparatus preferably outputs the output voltage value of the first bias output unit when the first bias output unit outputs the first detection bias controlled by constant current control or constant voltage control. First detection means for detecting the output current value is included. In addition, the image forming apparatus preferably outputs the output voltage value of the second bias output unit when the second bias output unit outputs the second detection bias controlled by constant current control or constant voltage control. Second detection means for detecting the output current value is included. In the first bias determination step, the first bias value is determined based on the detection result of the first detection means. In the second bias determination step, the second bias value is determined based on the detection result of the second detection means. Preferably, the first and second bias output means output the first and second bias values controlled by constant voltage, respectively.

  As described above, according to the present exemplary embodiment, when performing bias determination control at a plurality of bias application positions that supply charges to the intermediate transfer belt 51, the influence between the bias application positions is minimized, and appropriate bias determination is performed. Can do.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Therefore, elements having the same or equivalent functions as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals and detailed description thereof is omitted, and characteristic points of the present embodiment will be described below.

  FIG. 7 shows a schematic cross-sectional configuration of the image forming apparatus 200 of the present embodiment. In this embodiment, an electrostatic cleaning unit is used as a unit for removing toner on the intermediate transfer belt 51 on the downstream side of the secondary transfer unit N2 (upstream side of the first primary transfer unit N1a). Different from 1.

  In the present embodiment, the electrostatic cleaning device 9 as an electrostatic cleaning unit includes a conductive fur brush 91 as an electrostatic cleaning member (removal member), a bias roller 92 formed of a metal roller, and a scraping member. And a rubber blade 93. A cleaning bias is applied to the bias roller 92 from a cleaning bias power source 130 as a cleaning bias output unit. The conductive fur brush 91 rotates in contact with the intermediate transfer belt 51 at the cleaning unit N3.

  Then, the secondary transfer residual toner remaining on the intermediate transfer belt 51 is electrostatically collected through the conductive fur brush 91. The toner is scraped off from the bias roller 92 by a rubber blade 93 and is stored in a collection container (not shown). That is, the bias output from the cleaning bias power supply 130 is applied to the intermediate transfer belt 51 at the cleaning unit N3 via the bias roller 92 and the conductive fur brush 91 functioning as a bias applying member.

  In this embodiment, the cleaning bias power supply 130 has substantially the same configuration as the primary transfer bias power supply 110 and the secondary transfer bias power supply 120, and a cleaning bias controlled at a constant voltage is applied during electrostatic cleaning. Apply to the bias roller 92. In this embodiment, during electrostatic cleaning, a bias having a polarity opposite to the normal charging polarity of the negative polarity toner is applied to the bias roller 92.

  Referring to FIG. 8, the conductive fur brush 91 is disposed 70 mm (distance D) downstream of the secondary transfer portion N2 and 100 mm (distance E) upstream of the first primary transfer portion N1a. The current value required for cleaning is 20 μA. For this reason, as is clear from the description of the first embodiment, the cleaning unit N3 is not only influenced by the voltage applied at the secondary transfer unit N2, but also the voltage applied at the electrostatic cleaning N3 is The first primary transfer portion N1a on the downstream side is affected. That is, there is the relationship of Equation 1 described in the first embodiment between the secondary transfer portion N2 and the cleaning portion N3 and between the cleaning portion N3 and the first primary transfer portion N1a.

  Therefore, in this embodiment, as in the first embodiment, bias determination control is performed so as to take into account the influence between the bias application positions. That is, in the present embodiment, typically, the first and second bias application positions correspond to the secondary transfer portion N2 and the cleaning portion N3, respectively. At this time, the first and second bias applying members (first and second electrode members) correspond to the inner roller 54 and the conductive fur brush 91. In this case, the first and second bias output means are the secondary transfer bias power source 120 and the cleaning bias power source 130, respectively. In this embodiment, the first and second bias application positions also correspond to the cleaning unit N3 and the first primary transfer unit N1a, respectively. In this case, the first and second bias output means are the cleaning bias power supply 130 and the first primary transfer bias power supply 110a, respectively. Further, in this embodiment, the first and second bias application positions are the primary transfer portion N1 on the upstream side and the primary transfer portion on the downstream side among the adjacent primary transfer portions N1 as in the first embodiment. It also corresponds to the part N1. This will be described in more detail below.

  In this embodiment, as shown in FIG. 9, first, bias determination control is performed at the secondary transfer portion N2, and the determined voltage is applied at the secondary transfer portion N1. Next, bias determination control is performed in the cleaning unit N3 located immediately downstream thereof. The bias determination control in the cleaning unit N3 is started after the region on the intermediate transfer belt 51 that has started to apply the voltage determined by the bias determination control in the secondary transfer unit N2 passes through the cleaning unit N3. When the voltage is determined, the voltage determined in the cleaning unit N3 is continuously applied in preparation for the bias determination control in the next first primary transfer unit N1a. In the bias determination control in the first primary transfer portion N1a, the region on the intermediate transfer belt 51 that has started applying the voltage determined by the bias determination control in the cleaning portion N3 passes through the first primary transfer portion N1a. Will be started after. The subsequent control is the same as in the first embodiment.

  The bias determination control in the primary transfer portion N1 and the secondary transfer portion N2 is the same as that in the first embodiment. The bias determination control in the cleaning unit N3 is the same as that in the primary transfer unit N1 and the secondary transfer unit N2. That is, V1 = 1.0 Kv, V2 = 1.25 Kv, and V3 = 1.5 Kv can be used as monitor voltages. As monitor voltages, I1 = 15.0 μA, I2 = 17.5 μA, and I3 = 20.0 μA can be used.

  In the case of the electrostatic cleaning method, it is more effective to use two electrostatic cleaning members having different polarities of the applied bias. For example, as shown in FIG. 10, in the configuration having the first and second electrostatic cleaning devices 9A and 9B having the same configuration as described above, the distance between the bias application positions is further shortened, and it is easy to influence each other. . Therefore, in such a configuration, the sequence of this embodiment is more effective.

  As described above, according to the present exemplary embodiment, as in the first exemplary embodiment, when performing bias determination control at a plurality of bias application positions that supply charges to the intermediate transfer belt 51, the influence between the bias application positions is minimized, Appropriate bias determination can be made.

Example 3
Next, still another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first and second embodiments. Therefore, elements having the same or equivalent functions as those of the image forming apparatuses of the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. Characteristic points of the present embodiment will be described below.

  FIG. 11 shows a schematic cross-sectional configuration of the image forming apparatus 300 of the present embodiment. In this embodiment, as described in the second embodiment, the first and second electrostatic cleaning devices 9A and 9B are provided for the intermediate transfer belt 51. Further, in this embodiment, a roller cleaning device 58 serving as electrostatic cleaning means is also provided for the outer roller 56.

  The roller cleaning device 58 has the same configuration as the first and second electrostatic cleaning devices 9A and 9B. However, the bias applied from the roller cleaning bias power source 59 as the bias output means in the roller cleaning device 58 is controlled at a constant current. The constant current value in this example is 16 μA. The applied bias of the roller cleaning device 58 may affect the secondary transfer portion N2.

  As described above, even a member that does not perform the bias determination control itself may have a bias applied to the member, and the bias may affect the bias determination control. In this case, the bias application to the member is started before the bias determination control at a plurality of bias application positions is started. The application of the bias is continued until the final bias determination control of the bias determination control at the plurality of bias application positions with respect to the intermediate transfer belt 51 is completed. It is desirable that the bias applied to the member is the same as the bias applied during image formation.

  In other words, in the present exemplary embodiment, the image forming apparatus 300 includes a third bias applying member that supplies charges to the intermediate transfer belt 51 in addition to the first and second bias applying members that perform bias determination control. Further, a third bias output means for outputting a bias to the third bias applying member is provided. In this case, the third bias output means starts outputting the bias to the third bias applying member before the first bias determining step among the bias determining steps performed at the plurality of bias applying positions is started. Then, the output of the bias is continued until the last bias determination step is completed.

  For example, as such a situation, there is a case where the second bias is applied to one of two opposing members via the intermediate transfer belt 51 related to the bias determination control as in this embodiment. Further, there is a case where the member is in contact with the intermediate transfer belt 51 and the residual charge on the intermediate transfer belt 51 due to the bias applied to the member affects the bias determination control. In other words, in this embodiment, the third bias applying member charges the intermediate transfer belt 51 at a position facing the bias applying member at the bias applying position where the bias determination step is performed via the intermediate transfer belt 51. To supply. In particular, when the third bias output unit outputs a constant current controlled bias to the third bias applying member, the effect of the present embodiment becomes more remarkable.

  As described above, according to this embodiment, it is possible to obtain the same effects as those of the above-described embodiments.

  As described above, the present invention has been described based on specific examples, but the present invention is not limited to the above-described embodiments. For example, in each of the above-described embodiments, the image forming apparatus is described as using the intermediate transfer method. However, the present invention can also be applied to a direct transfer image forming apparatus, and can achieve the same effects as described above. .

  FIG. 12 shows a schematic cross-sectional configuration of an example of an image forming apparatus employing a direct transfer method. In the image forming apparatus 400 of FIG. 12, elements having the same or equivalent functions and configurations as those of the image forming apparatuses of the above embodiments are denoted by the same reference numerals. That is, the direct transfer type image forming apparatus 400 includes a transfer unit 405 instead of the intermediate transfer unit 5 in the image forming apparatuses of the above-described embodiments. The transfer unit 405 includes, for example, a belt-shaped recording material carrier that moves endlessly, that is, a conveyance belt 451 as an image conveyance body. Transfer rollers 55a to 55d as transfer means are provided on the inner peripheral surface side of the conveyor belt 451 so as to face the photosensitive drums 1a to 1d. At the position of the transfer roller 55a, the transport belt 451 comes into contact with the photosensitive drum 1, and the transfer portion N is formed. The transfer portion N is a plurality of bias application positions for applying a bias to the conveyance belt N. The toner images formed on the photosensitive drums 1a to 1d of the image forming units Sa to Sd are sequentially transferred in a superimposed manner onto the recording material P carried and conveyed on the conveyance belt 451 in each transfer unit N. The

  In such a direct transfer type image forming apparatus 400 as well, when performing bias determination control at a plurality of bias application positions, the present invention can be suitably applied to suppress the influence between the bias positions. it can. In this case, typically, the first and second bias application positions correspond to the upstream transfer portion N and the downstream transfer portion N of the adjacent transfer portions N, respectively. At this time, the first and second bias applying members are the upstream transfer roller 55 and the downstream transfer roller 55, respectively. In this case, the first and second bias output means are the transfer bias power source 110 of the upstream image forming unit S and the transfer bias power source 110 of the downstream image forming unit S of the adjacent image forming units S, respectively. . Further, when an electrostatic cleaning unit is used as a cleaning unit for the conveyor belt 451, the influence between the cleaning unit and another bias applying unit is suppressed as described in the second embodiment. May be.

1 is a schematic cross-sectional configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a schematic diagram for demonstrating the measuring method of the resistance value of a roller. FIG. 2 is an explanatory diagram for explaining a distance between bias application positions in the image forming apparatus of FIG. 1. FIG. 5 is a schematic control block diagram according to one embodiment of bias determination control according to the present invention. It is a sequence chart figure concerning one example of bias determination control according to the present invention. It is a graph for demonstrating the bias determination method. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of an image forming apparatus according to the present invention. FIG. 8 is an explanatory diagram for explaining a distance between bias application positions in the image forming apparatus of FIG. 7. It is a sequence chart figure concerning other examples of bias determination control according to the present invention. FIG. 6 is a schematic cross-sectional configuration diagram of another embodiment of an image forming apparatus according to the present invention. FIG. 6 is a schematic cross-sectional configuration diagram of still another embodiment of the image forming apparatus according to the present invention. It is a schematic sectional block diagram of the other example of the image forming apparatus which can apply this invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
5 Intermediate transfer unit 51 Intermediate transfer belt (image carrier)
54 Secondary transfer inner roller (bias applying member, electrode member)
55 Primary transfer roller (bias application member, electrode member)
91 Conductive fur brush (bias application member, electrode member)
110 Primary transfer bias power supply (bias output means)
120 Secondary transfer bias power supply (bias output means)
130 Cleaning bias power supply (bias output means)
S Image forming unit (image forming means)

Claims (7)

An image carrier for conveying a toner image;
First and second electrode members for applying charge to the image carrier;
First detection means for detecting a voltage-current relationship when a monitor voltage or a monitor current is applied to the first electrode member;
Second detection means for detecting a voltage-current relationship when a monitor voltage or a monitor current is applied to the second electrode member;
Voltage determination means for determining a voltage to be applied to the first electrode member based on a detection result of the first detection means, and a voltage to be applied to the second electrode member based on a detection result of the second detection means. An image forming apparatus comprising:
The voltage determining means is configured to apply the monitor voltage or the voltage in a state where the second electrode member is positioned in the region of the image carrier to which an electric charge is applied by applying the determined voltage to the first electrode member. An image forming apparatus, wherein a voltage applied to the second electrode member is determined by applying a monitor current.   An image carrier on which a toner image is formed, wherein the image carrier is an intermediate transfer body on which a toner image formed on the image carrier is electrostatically transferred, and the first electrode member is A secondary transfer member that electrostatically transfers the toner image on the intermediate transfer member onto a recording material, and the second electrode member is configured to transfer the toner image on the image carrier onto the intermediate transfer member. The image forming apparatus according to claim 1, wherein the image forming apparatus is a primary transfer member that transfers electrostatically.   A plurality of toner image forming portions each including an image carrier that carries a toner image and a primary transfer member that electrostatically transfers the toner image to the image carrier; and the toner on the image carrier 2. The image according to claim 1, further comprising a secondary transfer member that electrostatically transfers an image to a recording material, wherein the first and second electrode members are the primary transfer member. Forming equipment.   An image carrier on which a toner image is formed, a primary transfer member that electrostatically transfers the toner image to the image carrier, and an electrostatic transfer of the toner image on the image carrier to a recording material A secondary transfer member that removes toner on the image carrier electrostatically, the first electrode member is the secondary transfer member, and the second electrode member is the The image forming apparatus according to claim 1, wherein the image forming apparatus is a removing member.   An image carrier on which a toner image is formed, a primary transfer member that electrostatically transfers the toner image to the image carrier, and the toner image on the image carrier to the recording material. A secondary transfer member that removes toner on the image carrier electrostatically, the first electrode member is the removal member, and the second electrode member is the primary member. The image forming apparatus according to claim 1, wherein the image forming apparatus is a transfer member.   A plurality of image forming portions each including an image carrier on which a toner image is formed and a transfer member that transfers the toner image to a recording material carried on the image carrier; and the first and second electrodes The image forming apparatus according to claim 1, wherein the member is the transfer member. The first and second electrode members are in contact with the image carrier at a first contact region and a second contact region, respectively, and a center position of the first contact region in the moving direction of the image carrier, The distance from the center position of the second contact area is A (mm), the relative dielectric constant of the image carrier is ε, the volume resistivity of the image carrier is ρv (Ω · m), and the dielectric constant of vacuum Ε0, the moving speed of the image carrier is V (mm / s), the charge density of the charge applied to the image carrier by the first electrode member is Q0 (C / m ² ), and the second electrode member is When the charge density of the charge applied to the image carrier is Q2 (C / m ² ), the residual charge amount Q1 of Q0 at the center position of the second contact region is expressed by the following equation:
Q1 = Q0 × exp (− (A / V) / (ε0 × ε × ρv))> 1/10 × Q2
The image forming apparatus according to claim 1, wherein the image forming apparatus has the following relationship.

Images