JP2007171540A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress image defects such as electrostatic offset and toner scattering irrespective of the amount of charges of a transfer material after a transfer process. <P>SOLUTION: An image forming apparatus includes an image carrier 1d, a transfer means 56d for transferring a toner image to a transfer material P, a transfer bias output means G1d for outputting a bias to a transfer means Td, a fixing means 9 for fixing the toner image onto a transfer material P below a transfer part in the movement direction of the transfer material P, and a fixing bias output means G3 for outputting a bias to the fixing means 9. The image forming apparatus includes a grounded detection member 110 disposed adjacently to the movement path of the transfer material P below the transfer part and above the fixing part in the movement direction of the transfer material P and a detection means 140 for detecting a current flowing between the detection member 110 and the earth and is so configured that the current is detected by the detection means 140 to control the output bias of the fixing bias output means G3 when the transfer material P passes a position adjacent to the detection member 110 before entering the fixing part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that forms an image by transferring a toner image formed by using an electrophotographic method or an electrostatic recording method onto a transfer material and then fixing it.

  Conventionally, for example, in an electrophotographic image forming apparatus, an electrostatic image formed on an electrophotographic photosensitive member, which is generally a drum type as an image carrier, is developed as a toner image with toner, and this toner image is finally formed. In other words, it is electrostatically transferred to a transfer material such as recording paper. Thereafter, the toner image on the transfer material is typically fixed on the transfer material by heating and pressing.

  In such an image forming apparatus, for example, when image formation is performed in a low humidity environment, a transfer material for transferring toner may be overcharged.

  For example, an image forming apparatus that employs a reversal development method and uses negatively chargeable toner as an example will be described below. In this case, the transfer material is transferred from the photosensitive drum in the transfer step of transferring the toner onto the transfer material. The negative charge is discharged. Then, the toner carrying surface of the transfer material is negatively overcharged. Since the negative charge and the toner have the same polarity, they cause repulsion and may cause image defects such as electrostatic offset and toner scattering in the fixing process. The electrostatic offset is a phenomenon in which the toner holding force of the transfer material is weakened, and the toner is electrostatically transferred to the fixing member without being fixed to the transfer material. As a result, the toner adhered to the fixing member may be fixed to the transfer material after one rotation of the fixing member. The toner scattering is a phenomenon in which the toner on the transfer material is disturbed due to a reduction in the binding force of the toner to the transfer material.

  In addition, as an electrophotographic color image forming apparatus, a direct transfer system that forms a multicolor image by transferring toner formed on a plurality of photosensitive drums onto a transfer material conveyed by a transfer belt. There is an image forming apparatus. In such a direct transfer type multicolor image forming apparatus, the transfer material is easily charged to a larger potential because the transfer process is performed a plurality of times (usually four times) on the transfer material. Therefore, image defects such as electrostatic offset and toner scattering as described above are likely to deteriorate.

As a means for suppressing the electrostatic offset and toner scattering as described above, there is a method in which the transfer material after the transfer process is neutralized by corona discharge (see Patent Document 1). Alternatively, there is a method of forming an electric field that restrains a toner image on a transfer material by applying a bias to a fixing member constituting the fixing process, specifically, a heating member and / or a pressure member (see Patent Document 2). ). In addition, there is a method of changing the bias applied to the fixing member according to the current flowing between the fixing member or between the fixing members or between the fixing member and an electrode arranged to be in contact with the transfer material (patent) Reference 3).
JP 2004-4334 A Japanese Patent Laid-Open No. 3-217885 JP 2000-221819 A

  Since the charge amount of the transfer material varies depending on the use conditions of the image forming apparatus and the type and state of the transfer material, when discharging the transfer material or applying a bias to the fixing member, the discharge or bias becomes excessive. It's not enough. For this reason, the desired effect of suppressing image defects may not be obtained. In extreme cases, on the contrary, toner scattering may be induced.

  That is, in the case of the method for removing the charge from the transfer material, it is effective to remove the charge from the transfer material by performing a positive corona discharge on the toner carrying surface of the transfer material when the transfer material is negatively overcharged. . However, if the positive corona discharge is excessive, a negative charge is induced on the back surface of the transfer material. For this reason, the binding force of the toner to the transfer material is reduced, and the toner may be scattered. In addition, when the positive corona discharge is insufficient, the transfer material is poorly discharged, and the above-described electrostatic offset and toner scattering may occur.

  In the method of applying a bias to the fixing member, when applying a bias to the heating member that contacts the toner carrying surface of the transfer material, a negative bias is applied to restrain the toner image on the transfer material. In this case, if this negative bias is excessive, the toner has the same polarity as the toner. Therefore, before the transfer material enters the fixing nip formed by the heating member and the pressure member, the toner moves backward on the transfer material. May be scattered. Further, when a bias is applied to the pressure member in contact with the toner non-carrying surface of the transfer material, a positive bias is applied in order to increase the holding force of the toner image on the transfer material. In this case, if this plus bias is excessive, a negative charge may be induced on the transfer material toner carrying surface and the toner may be scattered. On the other hand, when the bias applied to the fixing member is insufficient, the electric field for restraining and holding the toner on the transfer material becomes small, and the above-described electrostatic offset and toner scattering may occur.

  Here, according to the technique disclosed in Patent Document 3, the bias applied to the fixing member is changed based on the current actually flowing through the fixing nip. As a result, it is possible to apply a bias to the fixing member in accordance with variations in manufacturing of the fixing member, changes in the resistance value of the transfer material depending on the paper type, and changes in the resistance value of the fixing member and the transfer material due to the environment.

  However, with the technique described in Patent Document 3, the bias cannot be adjusted until the transfer material enters the fixing nip. Therefore, for example, when the bias applied to the fixing member is excessive, it is not possible to prevent toner from splashing backward on the transfer material before the transfer material enters the fixing nip.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of effectively suppressing image defects such as electrostatic offset and toner scattering regardless of the charge amount of the transfer material after the transfer process.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention provides an image carrier that carries a toner image, transfer means for transferring a toner image from the image carrier to a transfer material in a transfer unit, and a bias for the transfer. A transfer bias output means for outputting to the transfer means; a fixing means for fixing a toner image on the transfer material at a fixing portion downstream of the transfer portion in the moving direction of the transfer material; and a bias output to the fixing means. An image forming apparatus including a fixing bias output unit, and a grounded detection member disposed adjacent to the transfer material movement path on the downstream side of the transfer unit and on the upstream side of the fixing unit in the transfer material movement direction. Detecting means for detecting a current flowing between the detection member and the ground, and when the transfer material before entering the fixing portion passes through a position adjacent to the detection member, The current detected by serial detection means, based on the detection result, an image forming apparatus and controls the bias output by the fixing bias output unit.

  According to the second aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit, and a bias for the transfer to the transfer unit And a transfer bias output means for outputting, a fixing means for fixing a toner image on the transfer material at a fixing portion downstream of the transfer portion in the transfer material moving direction, and a downstream of the transfer portion in the transfer material moving direction. An image forming apparatus comprising: a charge eliminating unit that removes charges on a transfer material in a charge eliminating unit upstream of the fixing unit and a charge eliminating bias output unit that outputs a bias to the charge eliminating unit. A detecting member disposed downstream of the transfer unit and upstream of the fixing unit in the moving direction and adjacent to a transfer material moving path; Detecting means for detecting a current flowing through the fixing portion, and when the transfer material before entering the fixing portion passes through a position adjacent to the detecting member, the detecting means detects the current and detects the current. On the basis of the result, there is provided an image forming apparatus characterized in that the bias output by the static elimination bias output means is controlled.

  According to the third aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit, and a bias for the transfer to the transfer unit. A transfer bias output means for outputting the toner image, a fixing means for fixing the toner image on the transfer material at a fixing portion downstream of the transfer portion in the moving direction of the transfer material, and a fixing bias for outputting a bias to the fixing device. An image forming apparatus having an output unit, and having a grounded detection member arranged adjacent to the transfer material movement path downstream of the transfer unit and upstream of the fixing unit in the transfer material movement direction. When the transfer material before entering the fixing portion passes through a position adjacent to the detection member, the value of the current flowing between the detection member and the ground is the first value and the second value. Time and , The image forming apparatus is provided, wherein a value of the bias to be outputted by the fixing bias output unit is different.

  According to the fourth aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit, and a bias for the transfer to the transfer unit And a transfer bias output means for outputting, a fixing means for fixing a toner image on the transfer material at a fixing portion downstream of the transfer portion in the transfer material moving direction, and a downstream of the transfer portion in the transfer material moving direction. In the image forming apparatus, the image forming apparatus includes: a charge eliminating unit that removes the charge of the transfer material at a charge eliminating unit upstream of the fixing unit; and a charge eliminating bias output unit that outputs a bias to the charge eliminating unit. A detection member that is disposed adjacent to the transfer material movement path downstream of the transfer unit and upstream of the fixing unit in the direction and is grounded, and before entering the fixing unit. The static elimination bias output means when the value of the current flowing between the detection member and the ground when the transfer material passes through a position adjacent to the detection member is a first value and a second value. The image forming apparatus is characterized in that the output bias value is different.

  According to the present invention, image defects such as electrostatic offset and toner scattering can be effectively suppressed regardless of the charge amount of the transfer material after the transfer process.

  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 cross section of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment can form a full-color image corresponding to an image information signal on a transfer material (recording medium) P such as a recording sheet or an OHP sheet using an electrophotographic method. It is a full color laser beam printer. The image forming apparatus 100 according to the present embodiment employs a tandem method, a reversal development method, a direct transfer method, a heating / pressure fixing method, and the like well known to those skilled in the art.

  The image forming apparatus 100 includes four image forming units, that is, first to fourth stations Sa, Sb, Sc, and Sd. Each station Sa, Sb, Sc, Sd is for forming an image of each color of yellow, magenta, cyan, and black, respectively. In the present embodiment, the configurations and operations of the stations Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, when there is no particular need to distinguish, subscripts a, b, c, and d given to the reference numerals are omitted to indicate that they are elements provided for any color, and a general description will be given. To do.

  The station S includes a cylindrical electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier that carries a toner image. Around the photosensitive drum 1, an image forming unit is configured by arranging a charging unit 2, an exposure unit 3, a developing unit 4, a transfer unit 56, a cleaning unit 6 and the like in order according to the rotation direction.

  A charging roller 2 as a charging unit uniformly charges the surface of the photosensitive drum 1. A laser scanner 3 as an exposure unit irradiates a laser beam based on image information, and forms an electrostatic image (latent image) on the photosensitive drum 1. The developing device 4 as developing means attaches toner to the electrostatic image on the photosensitive drum 1 and visualizes it as a toner image. A transfer roller 56 as a transfer unit provided in the transfer unit 5 transfers the toner image on the photosensitive drum 1 onto the transfer material P. The transfer unit 5 is further provided with a transfer belt 51 that moves endlessly as a transfer material carrier. A cleaner 6 as a cleaning unit collects toner remaining on the surface of the photosensitive drum 1 after the transfer process.

  Here, in this embodiment, the photosensitive drum 1 and the charging means 2, the developing means 4 and the cleaning means 6 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge to form a process cartridge 7. is doing. The laser scanner 3 and process cartridge 7 of each station S and the transfer unit 5 constitute an image forming unit.

  The image forming apparatus 100 also includes a feeding unit 8 for supplying the transfer material P to the image forming unit. The transfer material P fed from the feeding unit 8 is a transfer unit (transfer nip) T formed by the transfer belt 51 of the transfer unit 5 in contact with the photosensitive drum 1 and the transfer belt 1 at each station S. It is conveyed to.

  For example, at the time of full color image formation, each color toner image is sequentially transferred to the transfer material P on the transfer belt 51 in each transfer portion T. The transfer material P on which the color toner images are formed by sequentially transferring the color toner images is then conveyed to a fixing device 9 as a fixing unit. The unfixed toner image on the transfer material P is fixed on the transfer material P by the fixing device 9. Thereafter, the transfer material P is discharged to the discharge portion 19 by the discharge roller 18 pair.

  In the case of double-sided printing, the transfer material P on which the toner image is fixed by the fixing device 9 is conveyed to the double-sided conveyance path 15 by the reverse rotation of the discharge roller 18 before being discharged by the discharge roller pair 18. The The transfer material P conveyed to the double-sided conveyance path 15 passes through the oblique feeding roller 16 on the front surface of the apparatus main body and is conveyed vertically downward to the U-turn roller 17. Thereafter, the sheet is conveyed to the image forming unit by the U-turn roller 17 and the registration roller 84.

  Next, the configuration of each part of the image forming apparatus 100 will be described in more detail.

  The feeding unit 8 includes a feeding cassette 81, a multi feeding tray 82 that is a multi feeding device, a multi feeding unit 83, and a registration roller 84. The feeding cassette 81 stores a plurality of transfer materials P and is loaded on the inner bottom of the apparatus main body. When an image is formed on the transfer material P from the feeding cassette 81, the transfer material P is separated and conveyed one by one by the cassette pickup roller 85, and is conveyed to the image forming unit by the cassette conveyance roller 86 and the registration roller 84.

  The multi-feed tray 82 is usually stored in front of the apparatus main body. The multi-feed tray 82 is rotated and opened from the apparatus main body during use, and for example, a plurality of transfer materials P are set. When forming an image from the multi-feed tray 82, the transfer material P is separated and conveyed one by one by the multi-pickup roller 87, and conveyed to the image forming unit by the multi-conveying roller 88 and the registration roller 84.

  Separation and conveyance of the transfer material P in the feeding cassette 81 and the multi-feeding unit 83 are performed via a gear drive train by a feeding motor in the feeding unit.

  The photosensitive drum 1 as an image carrier is configured by applying an organic photoconductive layer (OPC) to the outer peripheral surface of an aluminum cylinder. The photosensitive drum 1 is rotatably supported at both ends by flanges, and is driven to rotate in the direction of the arrow (counterclockwise) in FIG. 1 by transmitting a driving force from one drive to the other end. Is done.

  The charging roller 2 as a charging unit is a conductive member (conductive roller) formed in a roller shape. The charging roller 2 is in contact with the surface of the photosensitive drum 1 and is applied with a charging bias voltage output from a charging bias power source (not shown) as a charging bias output unit. Thereby, the charging roller 2 uniformly charges the surface of the photosensitive drum 1.

  The laser scanner 3 as an exposure unit includes a polygon mirror, a laser diode, and the like. The polygon mirror is irradiated with image light corresponding to the image signal from the laser diode. The polygon mirror scans and exposes the photosensitive drum 1 with this image light.

  The developing device 4 as a developing unit includes a toner storage unit that stores toner, a developing roller as a developer carrier, and the like. In this embodiment, negatively chargeable toner is used. The developing roller is disposed adjacent to the surface of the photosensitive drum 1 and is driven to rotate by a driving unit. In the developing process, a developing bias voltage output from a developing bias power source (not shown) as a developing bias output means is applied to the developing roller.

  Further, inside the transfer belt 51 provided in the transfer unit 5, transfer rollers 56 a, 56 b, 56 c, and 56 d that are in contact with the transfer belt 51 so as to face the four photosensitive drums 1 a, 1 b, 1 c, and 1 d, respectively. Is provided. Each transfer roller 56 is connected to a transfer bias power source G1 (FIG. 2) as transfer bias output means. During the transfer process, the transfer bias output from the transfer bias power supply G 1 is applied to the transfer roller 56. In this embodiment, a positive charge having a polarity opposite to the normal charging polarity of the toner is applied from the transfer roller 56 to the transfer material P via the transfer belt 51. By this electric field, the negative toner image on the photosensitive drum 1 is transferred to the transfer material P in contact with the photosensitive drum 1.

  The transfer material P is conveyed from the feeding unit 8 to the image forming unit by a transfer belt 51 as a transfer material carrier provided in the transfer unit 5. The transfer belt 51 serving as a transfer material carrier constituting the transfer material P conveying means is stretched around four rollers, that is, a driving roller 52 and driven rollers 53, 54, and 55, and is rotatably supported. The transfer belt 51 is disposed to face all the photosensitive drums 1. The transfer material P is conveyed on the transfer belt 51 to the transfer portion (transfer position) T by the rotational driving force transmitted to the drive roller 52. In the transfer portion T, the toner image on the photosensitive drum 1 is transferred to the transfer material P on the transfer belt 51.

As a material for forming the transfer belt 51, a dielectric resin such as a polyethylene terephthalate resin (PET resin), a polyvinylidene fluoride resin, a polyurethane resin, or a polyimide resin can be preferably used. The volume resistivity of the transfer belt 51 is 1 × 10 ⁹ so that no electrical interference occurs between the transfer portions (for example, between the transfer rollers 56a and 56b of the first and second stations Sa and Sb). It is preferable that it is Ω · cm or more and 1 × 10 ¹⁸ Ω · cm or less.

  In addition, the transfer material 51 is sandwiched together with the transfer belt 51 at the most upstream position of the transfer belt 51 in the moving direction of the recording material P, that is, at a position upstream of the transfer portion Ta of the first station Sa. An adsorption roller 58 that adsorbs the material P to the transfer belt 51 is provided. In this embodiment, a suction bias power source (not shown) as a suction bias output unit is connected to the suction roller 58. When the transfer material P is conveyed, the suction bias voltage output from the suction bias power source is applied to the suction roller 58 to form an electric field with the grounded driven roller 55 facing the suction roller 58. As a result, dielectric polarization is generated between the transfer belt 51 and the transfer material P, and an electrostatic attracting force is generated between them.

  A fixing device 9 as a fixing unit applies heat and pressure to the image formed on the transfer material P and fixes the image. The fixing device 9 includes, as a fixing member, a fixing belt (heating member) 91 in which a heating unit 92 is disposed inside, and a pressure roller (pressure member) 93. In this embodiment, the fixing belt 91 contacts the toner carrying surface of the transfer material P. Further, the pressure roller 93 comes into contact with the toner non-carrying surface of the transfer material. The toner carrying surface and the toner non-carrying surface mean a surface on which unfixed toner is placed after the transfer process to the transfer material P and a surface on the opposite side.

  The fixing belt 91 is a cylindrical belt member having an electromagnetic induction heat generating layer. The fixing belt 91 is guided by a belt guide member 92 having a built-in magnetic field generating means including an exciting coil and a T-shaped magnetic core as a heating means. The pressure roller 93 is formed of an elastic roller and is pressed against the belt guide member 92 with a predetermined pressing force with the fixing belt 91 interposed therebetween. As a result, a fixing portion (fixing nip) N having a predetermined width is formed between the fixing belt 91 and the pressure roller 93.

  The pressure roller 93 is rotationally driven by the driving means, and the cylindrical fixing belt 91 is rotated accordingly, and power is supplied from the excitation circuit to the excitation coil of the fixing guide 92, thereby generating electromagnetic induction heat of the fixing belt 91. .

  In a state where the fixing unit N rises to a predetermined temperature and is temperature-controlled, the transfer material P carrying the unfixed toner image conveyed from the image forming unit is introduced into the fixing unit N. At this time, the toner carrying surface (image surface) on the transfer material P faces the fixing belt 91 side, and the opposite surface of the transfer material P faces the pressure roller 93 side. In the fixing unit N, the toner carrying surface is in close contact with the outer surface of the fixing belt 91, and the transfer material P is nipped and conveyed together with the fixing belt 91. In this process, the unfixed toner image on the transfer material P is heated by the fixing belt 91 and fixed on the transfer material P.

[Configuration between transfer unit and fixing unit]
FIG. 2 is an enlarged view of the configuration from the end of the transfer process to the transfer material P in the transfer portion Td of the fourth station Sd to the fixing portion N in the image forming apparatus 100 of the present embodiment. The transfer portion Td of the fourth station Sd is the transfer portion that is the most downstream in the moving direction of the transfer material P, and the transfer process of the toner image onto the transfer material P is completed at this transfer portion Td.

  The transfer material P that has finished the transfer process in the fourth station Sd is conveyed while being adsorbed to the transfer belt 51, and is separated from the transfer belt 51 at the position of the drive roller 52. In this embodiment, the transfer material P is separated (curvature separation) from the transfer belt 51 using the curvature of the driving roller 52. Thereafter, the transfer material P is guided to the conveyance guide 110 and the fixing entrance guide 120 and introduced into the fixing unit N.

  In the image forming apparatus 100 of the present embodiment, a corona static eliminator 130 as a static eliminator is provided between the conveyance guide 110 and the fixing entrance guide 120 on the downstream side of the transfer portion Td of the fourth station Sd. . The corona neutralizer 130 is disposed toward the toner carrying surface of the transfer material P. That is, the corona neutralizer 130 removes the charge on the transfer material P in the neutralization portion Q downstream of the transfer portion Td and upstream of the fixing portion N in the moving direction of the transfer material P.

  In this embodiment, the corona static eliminator 130 neutralizes the transfer material P, which is negatively overcharged in the transfer process, by positive corona discharge. The corona static eliminator 130 includes a static elimination needle 131 and a shield 132. The static elimination needle 131 is connected to a static elimination bias power source G2 as a static elimination bias output means. Then, corona discharge is performed from the static elimination needle 131 to the shield 132 connected to the ground. In other words, in the present embodiment, a bias having a polarity opposite to the normal charging polarity of the toner is output from the neutralization bias power source G2 to the neutralization needle 131 disposed so as to face the toner carrying surface of the transfer material P. The

  Further, in the image forming apparatus 100 of the present embodiment, an electrically grounded detection member is disposed adjacent to the transfer path of the transfer material P between the transfer portion Td and the fixing portion N of the fourth station Sd. Has been. That is, the detection member is disposed adjacent to the movement path of the transfer material P on the downstream side of the transfer portion Td and the upstream side of the fixing portion N in the movement direction of the transfer material P, and is grounded. In particular, in this embodiment, the detection member is disposed adjacent to the transfer path of the transfer material P on the downstream side of the transfer portion Td and on the upstream side of the charge removal portion Q in the transfer direction of the transfer material P.

  The detection member may be a member that directly or indirectly contacts the transfer material P, or a member that is non-contact. Here, the detection member disposed in contact with the transfer material P or in contact with the member in contact with the transfer material P is referred to as a contact-type detection member. On the other hand, as will be described in detail in Example 3 to be described later, the detection member disposed in a non-contact manner with respect to the transfer material P and the member in contact with the transfer material P is referred to as a non-contact detection member.

  Examples of the contact type detection member include a tension roller (a driving roller 53 in this embodiment) of the transfer belt 51, a conveyance guide 110, a fixing entrance guide 120, and the like disposed at a position after the final transfer process. Can be used. Of course, a special detection member may be provided separately. The contact type detection member is disposed on the toner non-carrying surface side of the transfer material P.

  As the non-contact type detection member, an electrode 160 (FIG. 6) described in Embodiment 3 can be provided. In principle, a non-contact type detection member can be provided on the toner carrying surface side of the transfer material P. However, since there is a possibility that the electrode may be soiled by the toner, it is preferable to provide the transfer material P on the toner non-carrying surface side.

  In this embodiment, the conveyance guide 110 that can contact the transfer material P also functions as a detection member.

  Further, an ammeter 140 is interposed between the detection member 110 and the ground as detection means for detecting a current flowing between the detection member 110 and the ground. The ammeter 140 is connected with a controller 150 as a control means. The ammeter 140 outputs a signal corresponding to the measured current value to the controller 150. The ammeter 140 measures the current I1 that flows from the detection member 110 to the ground when the transfer material P passes through the position of the detection member 110, and outputs it to the controller 150. That is, when the transfer material P before entering the fixing portion N passes through a position adjacent to the detection member 110, the ammeter 140 detects the current I1 flowing between the detection member 110 and the ground. In particular, in the present embodiment, the current I1 flowing between the detection member 110 and the ground is detected by the ammeter 140 when the transfer material P before entering the static elimination portion Q passes through the position adjacent to the detection member 110. Is done.

  Then, the controller 150 controls the bias value output from the static elimination bias power supply G2 based on the detection result of the current I1, and controls the current value supplied to the corona static eliminator 130.

  That is, a leakage current from a member connected to the ground when the transfer material P passes between the transfer portion Td and the fixing portion N that is the most downstream in the moving direction of the transfer material P is detected. Then, the charge amount of the transfer material P is estimated from the detection result, and the charge of the transfer material P is removed based on the current value. As a result, an effect of static elimination with no excess or deficiency with respect to the charge amount of the transfer material P can be obtained, and the occurrence of electrostatic offset and toner scattering can be suppressed.

  Here, the surface potential of the transfer material P will be described. For example, for a paper having a thickness of about 100 μm, a potential difference equivalent to 1000 to 3000 V is typically formed between the toner carrying surface and the toner non-carrying surface of the transfer material P. The value of this potential difference is based on the results obtained from the experiments described below. Of course, the potential difference between the front and back surfaces of the transfer material does not always match the value in this range. However, it is certain that the charge amount of the transfer material P varies depending on conditions such as the use conditions of the image forming apparatus and the type / state of the transfer material.

  The potential difference between the front and back surfaces of the transfer material P can be measured, for example, as follows. After the toner image is transferred from the image forming apparatus with the fixing device removed, the transfer material P in which the toner image is not fixed is gripped by an insulating member and taken out. Then, as shown in FIG. 7, the transfer material P is left on a grounded ground plate. At this time, the surface potential of the transfer material P is measured from the surface opposite to the ground plate side of the transfer material P with a surface potential meter. The reason why the transfer material P is left on the ground plate is to eliminate the influence of the charge on the non-measurement surface of the transfer material P.

  Table 1 shows the measurement result of the charging potential of the transfer material P between the driving roller 52 and the fixing portion N when the recording paper is passed as the transfer material P to the image forming apparatus 100 of this embodiment, and the image The evaluation results are shown. As the transfer material P, a recording sheet commercially available from a registered trademark office planner (Canon sales) was used. The evaluation environment (temperature / humidity) is 15 ° C./10% RH.

  Usually, the transfer material P tends to dry more after being left in the environment than immediately after opening the wrapping paper. Further, the transfer material P left in the environment dries more when printed on both sides than when printed on one side. As shown in Table 1, as the transfer material P is dried, the charging potential of the transfer material P increases. Further, the absolute value of the potential difference between the toner carrying surface and the toner non-carrying surface of the transfer material P also increases as the transfer material P is dried, and the negative potential becomes dominant as a whole of the transfer material P. For this reason, it is considered that the level of electrostatic offset deteriorates.

  As can be seen from Table 1, as the transfer material P is dried, the charging potential of the transfer material P increases. Therefore, the potential difference between this potential and the ground, that is, the current I1 flowing from the transfer material P to the ground is detected. Thus, the charge amount of the transfer material P can be estimated.

  Next, a mechanism for estimating the charge amount of the transfer material P by measuring the current I1 will be described. FIG. 3 is a schematic diagram for explaining this mechanism, in which the transfer material P and the detection member 110 are replaced with an electric resistance / capacitor model.

  When the detection member 110 is in contact with the transfer material P as in this embodiment (FIG. 3A), the positive charge on the toner non-carrying surface of the transfer material P flows to the ground via the resistance component of the detection member 110. . The ammeter 140 detects this current value I1.

  Alternatively, when the driving roller 52 that contacts the surface opposite to the transfer material carrying surface of the transfer belt 51 is used as the detection member (FIG. 3B), the toner non-carrying surface of the transfer material P is used. The positive charge flows to the ground through the resistance component of the detection member 52 across the transfer belt 51. The ammeter 140 detects this current value I1.

Here, the volume resistivity of the contact-type detection member is desirably 1 × 10 ⁷ Ωcm or more and 1 × 10 ¹⁴ Ωcm or less. If it is less than 1 × 10 ⁷ Ωcm, the positive charge on the toner non-carrying surface of the transfer material P is largely lost, which may disturb the toner image. On the other hand, if it exceeds 1 × 10 ¹⁴ Ωcm, the current I1 flowing from the detection member to the ground becomes very small, and the detection accuracy of the current I1 may be deteriorated. In this embodiment, the volume resistivity of the conveyance guide 110 serving as a detection member is set to 5.2 × 10 ¹⁰ Ωcm.

  The shape of the detection member is not particularly limited, but is preferably a flat plate provided parallel to the transfer material P. Even if a needle-shaped / saw-shaped detection member is used, it is possible to detect the current I1 as described above. However, the sharply shaped portion is discharged due to charge concentration, so that the toner image on the transfer material P is discharged. It is possible to generate a trace.

  In the present embodiment, the controller 150 controls the value of the current supplied to the static elimination needle 131 from the static elimination bias power supply G2 based on the detection result of the current I1 using the detection member 110. As a control method, for example, a table as shown in Table 2 may be stored in the storage unit in the controller 150, and the current value I2 for energizing the corona static eliminator 130 may be set for each detection current I1.

  That is, in this embodiment, when the transfer material P before entering the fixing portion N passes through a position adjacent to the detection member 110, the value of the current I1 flowing between the detection member 110 and the ground is the first value. The value of the bias output by the static elimination bias power supply G2 differs between the time of the second and the second value. When the value of the current I1 is a second value larger than the first value, the bias value output from the static elimination bias power supply G2 is greater than that when the value of the current I2 is the first value. Is also big.

  As described above, in this embodiment, the charge amount of the transfer material P is predicted by detecting the current I1 flowing from the detection member 110 to the ground, and the discharge amount of the corona static eliminator 130 is controlled based on the prediction. For this reason, the potential of the transfer material P can be maintained in an optimum range.

  That is, as described above, when the discharge amount of the corona static eliminator 130 is larger than the charge amount of the transfer material P, a negative charge is induced on the toner non-carrying surface of the transfer material P. For this reason, the binding force of the toner to the transfer material P is reduced, and the toner may be scattered. On the other hand, when the discharge amount of the corona static eliminator 130 is smaller than the charge amount of the transfer material P, the charge removal effect of the transfer material P is reduced, and electrostatic offset and toner scattering may occur.

  On the other hand, according to the present embodiment, the discharge amount of the corona static eliminator 130 can be selected within an optimum range. In this embodiment, the current flowing between the detection member 110 and the ground is detected by the ammeter 140 when the transfer material P before entering the fixing portion N passes through a position adjacent to the detection member 110. The For this reason, at least when the transfer material P is introduced into the fixing portion N, the transfer material P can be in a state of being neutralized with the optimized discharge amount of the corona neutralizer 130. Therefore, it is possible to effectively prevent the electrostatic offset from being generated at the fixing unit N at the fixing unit N due to the insufficient discharge amount of the corona charger 130. Further, since the discharge amount of the corona charger 130 becomes excessive, the binding force of the toner to the transfer material P is reduced, and the occurrence of toner scattering at the fixing portion N can be effectively suppressed.

  In the present embodiment, particularly, when the transfer material P before entering the static eliminating portion Q passes through a position adjacent to the detection member 110, the current flowing between the detection member 110 and the ground is detected by the ammeter 140. Detected. For this reason, when the transfer material P is introduced into the static elimination portion Q, the discharge amount of the corona static eliminator 130 can already be optimized. Therefore, the transfer material P can be reliably discharged from the front end in the moving direction of the transfer material P with the optimized discharge amount. For this reason, electrostatic offset and toner scattering in the fixing unit N can be more reliably suppressed, and toner scattering that may occur in the static eliminating unit Q due to an excessive discharge amount of the corona neutralizer 130 is also prevented. It can be effectively suppressed.

  Table 3 shows the results of image evaluation using the transfer material P under the conditions shown in Table 1 in the image forming apparatus 100 of this example. Moreover, as Comparative Example 1, the image evaluation result when the current I2 to the corona static eliminator 130 is kept constant at 30 μA is also shown.

  As shown in Table 3, in the image forming apparatus 100 according to the present embodiment, the current supplied to the corona static eliminator 130 changes according to the state of the transfer material P. Therefore, an image defect occurs regardless of the state of the transfer material P. It never occurred.

  On the other hand, in the image forming apparatus of Comparative Example 1, the discharge amount of the corona static eliminator 130 is excessive with respect to the charge amount of the transfer material P. A splatter occurred. Further, since the discharge amount of the corona static eliminator 130 is insufficient with respect to the charge amount of the transfer material P, an electrostatic offset occurs in the transfer material P for environmentally left-over paper and double-sided printing.

  As described above, according to this embodiment, the current flowing from the conveyance guide 110 serving as a detection member provided between the transfer portion Td and the fixing portion N that is the most downstream in the moving direction of the transfer material P is detected. To do. Based on the detection result, the amount of current flowing to the corona static eliminator 130 is controlled. As a result, regardless of the environment in which the image forming apparatus 100 is used and the type / state of the transfer material P, it is possible to perform the optimal charge removal on the transfer material P. Therefore, according to this embodiment, it is possible to effectively suppress the occurrence of image defects such as electrostatic offset and toner scattering regardless of the charge amount of the transfer material P.

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 and configurations as those 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.

  In this embodiment, an example in which a bias is applied to a heating member or a pressure member of the fixing device 9 without using a corona static eliminator will be described.

  The corona neutralizer performs neutralization by corona discharge from the toner carrying surface side of the transfer material P. However, since the corona neutralizer is located on the toner carrying surface side, the neutralizer is soiled by the toner, and the discharge amount may decrease.

  Therefore, in this embodiment, the transfer material P is not neutralized after the transfer process, and a bias is applied to the fixing member to form an electric field that restrains the toner image on the transfer material P in the vicinity of the fixing portion N. This suppresses the occurrence of image defects such as electrostatic offset and toner scattering.

  That is, a leakage current from a member connected to the ground when the transfer material P passes between the transfer portion Td and the fixing portion N that is the most downstream in the moving direction of the transfer material P is detected. Then, the charge amount of the transfer material P is estimated from the detection result, and a bias is applied to the fixing member based on the current value. As a result, an effect of applying a bias to the fixing member which is not excessive or insufficient with respect to the charge amount of the transfer material P can be obtained, and the occurrence of electrostatic offset and toner scattering can be suppressed.

  The polarity of the bias applied to the fixing member is set as follows. When a negatively chargeable toner is used, a negative bias is applied to a heating member, that is, a fixing member that contacts the toner carrying surface of the transfer material P. On the other hand, a positive bias is applied to a pressure member, that is, a fixing member that contacts the toner non-carrying surface of the transfer material P.

  There is no difference in the effect in each bias application method, and it may be selected according to the characteristics of the apparatus. It is also possible to apply a bias to both the heating member and the pressure member at the same time.

  In the present embodiment, the fixing device 9 employs an electromagnetic induction heat generation method, and has a configuration in which it is difficult to apply a bias to the fixing belt 91. Therefore, a positive bias is applied to the pressure roller 93. That is, in this embodiment, the pressure roller 93 is connected to a fixing bias power source G3 as a fixing bias output means, and the fixing bias having a polarity opposite to the normal charging polarity of the toner is applied to the pressure roller by the fixing bias power source G3. 93 is output.

  When a bias is applied to one of the members that sandwich the transfer material P at the fixing portion N, the member to which no bias is applied is grounded to the ground in order to form an electric field.

  In this embodiment, similarly to the first embodiment, a grounded detection member is provided adjacent to the transfer path of the transfer material P between the transfer section Td and the fixing section N of the fourth station Sd. . That is, in this embodiment, the detection member is disposed adjacent to the movement path of the transfer material P on the downstream side of the transfer portion Td and the upstream side of the fixing portion N in the movement direction of the transfer material P, and is grounded. In the present embodiment, as in the first embodiment, the conveyance guide 110 is used as the detection member.

  Further, in this embodiment, as in the first embodiment, the ammeter 140 measures the current I1 flowing from the detection member 110 to the ground when the transfer material P passes through the position of the detection member 110, and the measurement result. Is output to the controller 150. Then, the controller 150 controls the bias value output from the fixing bias power supply G3 based on the detection result. The current detection method using the detection member 110 is the same as that in the first embodiment.

  Here, when a bias is applied to the heating member, the applied bias has the same polarity as the toner. For this reason, if the bias is excessive, the toner may scatter backward on the transfer material P before the transfer material P enters the fixing portion N formed by the heating member and the pressure member.

  Further, when a bias is applied to the pressure member, a bias having a polarity opposite to that of the toner is applied in order to increase the holding force of the toner image on the transfer material P. Therefore, if this bias is excessive, a negative charge may be induced on the toner carrying surface of the transfer material P, and the toner may be scattered.

  On the other hand, when the bias applied to the fixing member is insufficient, the electric field that restrains the toner on the transfer material P becomes small, and electrostatic offset and toner scattering may occur.

  On the other hand, according to the present embodiment, by detecting the current I1 flowing from the detection member 110 to the ground, the charge amount of the transfer material P is predicted, and based on this, the value of the bias applied to the fixing member is determined. Control. Thereby, an electric field in accordance with the potential amount of the transfer material P can be formed in the vicinity of the fixing portion N.

  In this embodiment, when the transfer material P before entering the fixing portion N passes through a position adjacent to the detection member 110, the controller 150 causes the ammeter 140 to connect the detection member 110 and the ground. Detect the flowing current. For this reason, when the transfer material P is introduced into the fixing portion N, a bias having an optimized value can already be applied to the pressure roller 93. Accordingly, it is possible to effectively prevent the electrostatic offset from being generated in the fixing unit N due to the insufficient bias applied to the pressure roller 93. Further, since the bias applied to the pressure roller 93 becomes excessive, the occurrence of toner scattering at the fixing portion N can be effectively suppressed.

  As a control method, for example, a table as shown in Table 4 may be stored in the storage unit in the controller 150, and the bias value V1 applied to the fixing member may be set for each detection current I1. Here, a table for setting a bias to be applied to the pressure roller 93 is shown.

  That is, in this embodiment, when the transfer material P before entering the fixing portion N passes through a position adjacent to the detection member 110, the value of the current I1 flowing between the detection member 110 and the ground is the first value. The value of the bias output from the fixing bias power supply G3 differs depending on whether the second value or the second value. When the value of the current I1 is a second value larger than the first value, the bias value output from the fixing bias power supply G3 is greater than that when the value of the current I1 is the first value. Is also big.

  Table 5 shows the results of image evaluation using the transfer member P under the conditions shown in Table 1 in the image forming apparatus 100 of the present embodiment. Further, as Comparative Example 2, the image evaluation result when the bias applied to the pressure roller 93 is constant at 500 V is also shown.

  As shown in Table 5, in the image forming apparatus 100 of the present embodiment, the bias value applied to the pressure roller 93 changes according to the state of the transfer material P. There were no failures.

  On the other hand, in the image forming apparatus of Comparative Example 2, the bias value applied to the pressure roller 93 is excessive with respect to the charge amount of the transfer material P. Spattering occurred. Further, since the bias value applied to the pressure roller 93 is insufficient with respect to the charge amount of the transfer material P, an electrostatic offset is generated in the transfer material P for environmentally untreated paper and double-sided printing.

  As described above, according to the present embodiment, the current flowing from the detection member 110 provided between the most downstream transfer portion Td and the fixing portion N in the moving direction of the transfer material P to the ground is detected. Based on the detection result, the bias application amount to the fixing member (the pressure roller 93 in this embodiment) is controlled. Thereby, regardless of the use environment of the image forming apparatus 100 and the type / state of the transfer material P, the binding force of the toner to the transfer material P in the fixing unit N can be optimized.

Example 3
Next, still 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 and configurations as those 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.

  In the present embodiment, as the non-contact type detection member, an electrode 160 provided so as to be in direct contact with the transfer material P is used. That is, the electrode 160 is disposed adjacent to the moving path of the transfer material P on the downstream side of the transfer portion Td and the upstream side of the fixing portion N in the moving direction of the transfer material P, and is grounded. The electrode 160 can be disposed downstream of the transfer portion Td and upstream of the charge removal portion Q in the moving direction of the transfer material P.

  In the first embodiment, the detection member is the conveyance guide 110 that contacts the transfer material P. However, when the transfer material P is in contact with the detection member, the following problems can be considered. (1) The contact between the transfer material P and the detection member is affected by the type, thickness, and leaving condition of the transfer material P under the environment, and is not stably performed every time, and current detection becomes unstable. (2) It is easily affected by the resistance variation of the detection member. (3) Unstable contact between the detection member and the transfer material P, resistance unevenness in the member of the detection member, or the like causes charge unevenness in the transfer material P, causing an image defect in an unfixed toner image.

  In the present embodiment, since the detection member is installed in a non-contact manner with respect to the transfer material P, the problems (1) to (3) can be prevented.

  Here, a mechanism for estimating the charge amount of the transfer material P using a non-contact type detection member will be described. FIG. 6 is a schematic diagram for explaining this mechanism, in which the transfer material P, the electrode 160 as a detection member, and the air layer formed between them are replaced with an electric resistance / capacitor model.

  When the electrode 160 is not in contact with the transfer material P, the positive charge on the toner non-carrying surface of the transfer material P flows to the ground through the resistance component of the electrode 160 with the air layer serving as a capacitor component interposed therebetween. The ammeter 140 detects this current value I1.

  The non-contact type detection member may be arranged so as to face the inner peripheral surface of the transfer belt 51. That is, the non-contact type detection member can be disposed so as to face the member in contact with the transfer material P in a non-contact manner.

The volume low efficiency of the non-contact type detection member is desirably 1 × 10 ⁷ Ωcm or less. This is because, unlike the contact-type detection members described in the first and second embodiments, the air layer has an electrical resistance. If it exceeds 1 × 10 ⁷ Ωcm, the current flowing from the detection member to the ground becomes minute and the current detection accuracy is deteriorated. Further, the volume resistivity is preferably as small as possible, and there is no need to provide a lower limit. In this embodiment, the electrode 160 as the detection member is a flat plate made of aluminum, and is installed at a location 10 mm away from the toner non-carrying surface of the transfer material P.

  Table 6 shows the occurrence frequency of toner scattering when 100 sheets of the transfer material P under the following conditions are continuously fed in the image forming apparatus 100 of the present embodiment under the environment of 25 ° C./60% RH. Results are shown. In addition, the results when the same evaluation is performed in the image forming apparatus 100 of the first embodiment are also described. As the transfer material P, a recording paper marketed by a registered trademark office planner (Canon sales) was used.

  As shown in Table 6, in the image forming apparatus 100 of the present embodiment, no image defect occurred regardless of the state of the transfer material P. On the other hand, in the image forming apparatus 100 according to the first embodiment, toner scattering may occur in the transfer material P left in the environment.

  As described above, according to the present embodiment, the detection member is the non-contact electrode 160 with respect to the transfer material P. This suppresses problems that may occur when using a contact-type detection member, and detects the current flowing between the detection member and the ground to more effectively suppress electrostatic offset and toner scattering. can do.

  As described in the second embodiment, when a bias is applied to the fixing member, it is naturally possible to use a non-contact type detection member.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to the aspect of each said Example. For example, in each of the above embodiments, the image forming apparatus has been described as an image forming apparatus employing a tandem method / direct transfer method. In such an image forming apparatus, since the transfer material is easily overcharged as described above, the present invention works extremely effectively. However, the present invention is not limited to this.

  For example, the present invention can be applied to an intermediate transfer type image forming apparatus. The intermediate transfer type image forming apparatus secondarily transfers a single-color or multi-color toner image primarily transferred from a single or a plurality of image carriers to an intermediate transfer body (such as an intermediate transfer belt) onto a transfer material, This toner image is fixed on the transfer material. FIG. 8 shows a schematic cross-sectional configuration of an example of such an intermediate transfer type image forming apparatus. In the image forming apparatus 200 of FIG. 8, elements having the same functions or configurations as those of the image forming apparatus 100 of FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  An image forming apparatus 200 illustrated in FIG. 8 includes an intermediate transfer belt 201 that moves endlessly as an intermediate transfer member. The toner images formed on the photosensitive drums 1a to 1d of the stations Sa to Sd are primary-transferred sequentially to the intermediate transfer belt 201 by the primary transfer roller 201 as the primary transfer unit in the primary transfer portions T1a to T1d. . Next, the toner image on the intermediate transfer belt 201 is secondarily transferred collectively to the transfer material P by the secondary transfer roller 203 as a secondary transfer unit in the secondary transfer portion T2. At this time, the secondary transfer bias output from the secondary transfer bias power source 204 as the secondary transfer bias output means is applied to the secondary transfer roller 203. Thereafter, the transfer material P is conveyed to the fixing device 9 where the toner image is fixed on the transfer material P.

  In the case of such an intermediate transfer type image forming apparatus 200, the present invention can be applied to the configuration between the secondary transfer portion T2 and the fixing portion N. In the example shown in FIG. 8, in the configuration in which the fixing bias is applied from the fixing bias power source G3 to the pressure roller of the fixing device 9 as in the second embodiment, the conveyance guide 110 also functions as a detection member.

  The present invention is equally applicable to a single color image forming apparatus having only one transfer portion. Furthermore, a plurality of developing units are provided for a single image carrier, and toner images sequentially formed on the image carrier are transferred directly to a transfer material on the transfer material carrier or temporarily to an intermediate transfer member. There is an image forming apparatus that later transfers to a transfer material and then fixes the toner image. The present invention can be equally applied to such an image forming apparatus. When the toner image is transferred directly from the image carrier onto the transfer material, the present invention can be applied to the configuration between the transfer portion of the toner image from the image carrier to the transfer material and the fixing portion. Further, when the toner image is transferred to the transfer material via the intermediate transfer member, the present invention can be applied to the configuration between the secondary transfer portion and the fixing portion as described above.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a schematic cross-sectional configuration diagram of a transfer material conveyance path from a transfer unit to a fixing unit in an embodiment of the present invention. It is a model figure of an example of the conduction | electrical_connection path | route from a detection member to earth | ground. FIG. 6 is a schematic cross-sectional configuration diagram of a transfer material conveyance path from a transfer portion to a fixing portion in another embodiment of the present invention. FIG. 10 is a schematic cross-sectional configuration diagram of a transfer material conveyance path from a transfer portion to a fixing portion in still another embodiment of the present invention. It is a model figure of the other example of the conduction | electrical_connection path from a detection member to earth | ground. It is a schematic diagram for demonstrating the measuring method of the charge amount of a transfer material. 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 Transfer unit 9 Fixing device (fixing means)
51 Transfer Belt 52 Drive Roller 56 Transfer Roller (Transfer Unit)
91 Fixing belt (fixing member, heating member)
93 Pressure roller (fixing member, pressure member)
110 Transport guide (detection member)
120 Fixing entrance guide 130 Corona static eliminator (static elimination means)
G1 Transfer bias power supply (transfer bias output means)
G2 static elimination bias power supply (static elimination bias output means)
G3 Fixing bias power supply (fixing bias output means)
N fixing part T transfer part

Claims (17)

An image carrier that carries a toner image; a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit; and a transfer bias output unit that outputs a bias for the transfer to the transfer unit. An image forming apparatus comprising: a fixing unit that fixes a toner image on the transfer material at a fixing unit downstream of the transfer unit in the moving direction of the transfer material; and a fixing bias output unit that outputs a bias to the fixing unit. In
A detection member disposed adjacent to the transfer material movement path on the downstream side of the transfer unit and the upstream side of the fixing unit in the transfer material movement direction, and a current flowing between the detection member and the ground. Detecting means for detecting the current when the transfer material before entering the fixing section passes through a position adjacent to the detecting member, and detecting the current based on the detection result. An image forming apparatus that controls a bias output by the fixing bias output means. An image carrier that carries a toner image; a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit; and a transfer bias output unit that outputs a bias for the transfer to the transfer unit. A fixing means for fixing the toner image on the transfer material in a fixing unit downstream of the transfer unit in the transfer material moving direction; and a downstream side of the transfer unit and an upstream side of the fixing unit in the transfer material moving direction. In an image forming apparatus comprising: a charge eliminating unit that removes a charge on a transfer material in a charge eliminating unit; and a charge eliminating bias output unit that outputs a bias to the charge eliminating unit.
A detection member disposed adjacent to the transfer material movement path on the downstream side of the transfer unit and the upstream side of the fixing unit in the transfer material movement direction, and a current flowing between the detection member and the ground. Detecting means for detecting the current when the transfer material before entering the fixing section passes through a position adjacent to the detecting member, and detecting the current based on the detection result. An image forming apparatus that controls a bias output by the static elimination bias output means.   The detection member is disposed adjacent to the transfer material movement path on the downstream side of the transfer unit and the upstream side of the charge removal unit in the transfer material movement direction, and before the current enters the charge removal unit. The image forming apparatus according to claim 2, wherein when the transfer material passes through a position adjacent to the detection unit, the detection unit detects the transfer material. An image carrier that carries a toner image; a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit; and a transfer bias output unit that outputs a bias for the transfer to the transfer unit. An image forming apparatus comprising: a fixing unit that fixes a toner image on the transfer material at a fixing unit downstream of the transfer unit in the moving direction of the transfer material; and a fixing bias output unit that outputs a bias to the fixing unit. In
A transfer material having a grounded detection member disposed adjacent to the transfer material movement path on the downstream side of the transfer portion and the upstream side of the fixing portion in the moving direction of the transfer material and before entering the fixing portion Is output by the fixing bias output means when the value of the current flowing between the detection member and the ground when it passes the position adjacent to the detection member is the first value and the second value. Image forming apparatus having different bias values.   When the current value is the second value larger than the first value, the bias value output by the fixing bias output means is greater than when the current value is the first value. The image forming apparatus according to claim 4, wherein An image carrier that carries a toner image; a transfer unit that transfers a toner image from the image carrier to a transfer material in a transfer unit; and a transfer bias output unit that outputs a bias for the transfer to the transfer unit. A fixing means for fixing the toner image on the transfer material in a fixing unit downstream of the transfer unit in the transfer material moving direction; and a downstream side of the transfer unit and an upstream side of the fixing unit in the transfer material moving direction. In an image forming apparatus, comprising: a charge eliminating unit that removes a charge of a transfer material in a charge eliminating unit; and a charge eliminating bias output unit that outputs a bias to the charge eliminating unit.
A transfer material having a grounded detection member disposed adjacent to the transfer material movement path on the downstream side of the transfer portion and the upstream side of the fixing portion in the moving direction of the transfer material and before entering the fixing portion Is output by the static elimination bias output means when the value of the current flowing between the detection member and the ground when passing through the position adjacent to the detection member is the first value and the second value. Image forming apparatus having different bias values.   When the current value is the second value larger than the first value, the bias value output by the static elimination bias output means is greater than when the current value is the first value. The image forming apparatus according to claim 6, wherein   The detection member is arranged adjacent to the transfer path of the transfer material on the downstream side of the transfer unit and on the upstream side of the charge removal unit in the transfer material movement direction, and the first value and the second value. 8 is a value of a current flowing between the detection member and the ground when the transfer material before entering the charge removal unit passes through a position adjacent to the detection unit. The image forming apparatus described in 1.   The image forming apparatus according to claim 1, wherein the detection member is disposed in contact with a transfer material or in contact with a member in contact with the transfer material.   The image forming apparatus according to claim 9, wherein the detection member is in contact with a surface opposite to a transfer material carrying surface of a transfer material carrying body that carries and conveys the transfer material.   The image forming apparatus according to claim 10, wherein the detection member is a roller on which the belt-shaped transfer material carrier that supports and conveys the transfer material is stretched.   The image forming apparatus according to claim 9, wherein the detection member is a guide that guides a transfer material from the transfer unit toward the fixing unit. The image forming apparatus according to claim 9, wherein a volume resistivity of the detection member is 1 × 10 ⁷ Ωcm or more and 1 × 10 ¹⁴ Ωcm or less.   The image forming apparatus according to claim 1, wherein the detection member is disposed in a non-contact manner with respect to the transfer material and a member that contacts the transfer material.   The image forming apparatus according to claim 14, wherein the detection member is disposed at a position directly facing the transfer material. The image forming apparatus according to claim 14, wherein the detection member has a volume resistivity of 1 × 10 ⁷ Ωcm or less.   A plurality of the image carrier and the transfer means are provided along the movement direction of the transfer material, and a plurality of the transfer portions are formed along the movement direction of the transfer material. 17. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed downstream of the most downstream transfer portion in the moving direction of the transfer material.

Images