Image forming apparatus

Abstract

To provide a configuration that can remove toner from a recovery roller without increasing downtime.SOLUTION: A carrier recovery device 5a recovers a carrier attached to a photoconductor drum 1a. A voltage in which AC voltage is superimposed on DC voltage is applied to a recovery roller 52 of the carrier recovery device 5a. The carrier recovery device 5a has a conductor member 56 that is arranged to face the recovery roller 52 on the downstream side of a position where the recovery roller 52 is in the most proximity to the photoconductor drum 1a in terms of the direction of rotation of the recovery roller 52.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, or a multifunction machine having a plurality of these functions. [Background technology]

[0002] As an image forming apparatus, a configuration in which a toner image is formed using a two-component developer containing a non-magnetic toner and a magnetic carrier has been conventionally known. In this configuration, normally, in the developing process, an electrostatic latent image on a photosensitive drum is developed into a toner image by toner, but a certain percentage of the carrier may also adhere to the photosensitive drum (carrier adhesion). If carrier adhesion occurs, it will affect the output image, so for example, Patent Document 1 discloses a configuration equipped with a carrier recovery device that recovers the carrier that has adhered to the photosensitive drum.

[0003] The carrier recovery device described in Patent Document 1 includes a recovery roller and a magnet roller provided inside the recovery roller, and is further configured to apply a voltage in which an AC voltage is superimposed on a DC voltage to the recovery roller. As a result, the carrier on the photosensitive drum is recovered to the recovery roller by the magnetic force of the magnet roller and the electrostatic force due to the applied voltage. When the carrier is recovered by the carrier recovery device in this way, some toner may also be recovered by the recovery roller. For this reason, in the case of the configuration described in Patent Document 1, a toner removal mode is executed when no image is formed, and in the toner removal mode, the rotation speed of the photosensitive drum is reduced compared to when an image is formed, and an AC voltage is applied to the recovery roller to return the toner attached to the recovery roller to the photosensitive drum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-148920 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the rotation speed of the photosensitive drum is reduced in the toner removal mode as in the configuration described in Patent Document 1, the rotation speed of the photosensitive drum needs to be changed between image formation and toner removal mode. Therefore, the toner removal mode cannot be executed during image formation, and time must be secured for executing the toner removal mode separately from image formation. As a result, downtime, which is the time during which image formation cannot be performed, increases. On the other hand, when the toner removal mode is executed without reducing the rotation speed of the photosensitive drum, the execution time of the toner removal mode needs to be extended in order to sufficiently remove the toner adhering to the collection roller, resulting in increased downtime.

[0006] An object of the present invention is to provide a configuration that can remove toner from a collection roller without increasing downtime. [Means for solving the problem]

[0007] One aspect of the present invention includes an image carrier that rotates while carrying an electrostatic latent image on its surface; a developing device that develops the electrostatic latent image carried on the surface of the image carrier into a toner image in a developing section using a two-component developer containing a non-magnetic toner and a magnetic carrier; an intermediate transfer body that carries the toner image transferred from the image carrier and transfers it to a recording material; a transfer member that transfers the toner image from the image carrier to the intermediate transfer body in a transfer section; and a carrier recovery device that recovers the carrier attached to the image carrier downstream of the developing section and upstream of the transfer section in the rotation direction of the image carrier. The image forming apparatus is equipped with a carrier recovery device having a recovery roller that is arranged opposite the image carrier and rotates, and a magnetic field generating unit that is arranged non-rotatingly inside the recovery roller and uses magnetic force to attract the carrier to the surface of the recovery roller, a voltage application unit that can apply an AC voltage superimposed on a DC voltage to the recovery roller, and a control unit that controls the voltage application unit, wherein the carrier recovery device has a conductive member that is arranged opposite the recovery roller downstream of the position where the recovery roller is closest to the image carrier in terms of the rotation direction of the recovery roller. Effect of the Invention

[0008] According to the present invention, toner can be removed from the collection roller without increasing downtime. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a carrier recovery device according to the embodiment. [Diagram 3] FIG. 2 is a control block diagram of the image forming apparatus according to the embodiment. [Figure 4] 5 is a schematic diagram showing the relationship in the longitudinal direction between the magnet roller, the collection roller, and the conductive member according to the embodiment. FIG. [Diagram 5] FIG. 4 is a block diagram showing a configuration for applying voltage to a conductive member and a collection roller according to the embodiment. [Figure 6]4 is a timing chart showing voltage application timing for each component according to the embodiment. [Figure 7] 1A is a block diagram showing a configuration for applying voltage to a conductive member and a collection roller according to Modification 1; FIG. 1B is a circuit diagram of a rectifier substrate according to Modification 1; [Figure 8] 13A is a block diagram showing a configuration for applying voltage to a conductive member and a collection roller according to Modification 2; FIG. 13B is a circuit diagram of a rectifier board according to Modification 2; [Figure 9] FIG. 11 is a block diagram showing a configuration for applying voltage to a conductive member and a collection roller according to Modification 3. [Figure 10] FIG. 11 is a block diagram showing the relationship between a conductive member according to Modification 4 and a configuration for applying a voltage to a collection roller. [Figure 11] FIG. 13 is a block diagram showing the relationship between a conductive member according to Modification 5 and a configuration for applying a voltage to a collection roller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiment will be described with reference to Figures 1 to 11. First, a schematic configuration of an image forming apparatus 100 of the embodiment will be described with reference to Figure 1.

[0011] [Image forming device] The image forming apparatus 100 of this embodiment is a full-color image forming apparatus that employs an electrophotographic method, and includes four image forming units Pa, Pb, Pc, and Pd. The configuration of each image forming unit is substantially the same except for the different developing colors. Therefore, in the following, unless a distinction is particularly required, the image forming unit Pa will be described as a representative, and the other image forming units will be assigned the subscripts b, c, and d to indicate that they are part of that image forming unit, and detailed descriptions will be omitted.

[0012] The image forming section Pa includes a photosensitive drum 1a as an image carrier that carries an electrostatic latent image on its surface. The photosensitive drum 1a is an example of a photosensitive member for electrophotography, and is formed in a cylindrical shape. Such a photosensitive drum 1a rotates in the direction of the arrow (counterclockwise direction) in FIG. 1. Around the photosensitive drum 1a, a charger 2a as a charging section, a laser beam scanner 3a as a latent image forming section, a developing device 4a, a primary transfer roller 6a, a cleaning device 8a, a carrier recovery device 5a, and the like are arranged.

[0013] Next, the overall image formation sequence of the image forming apparatus 100 having the above configuration will be described. First, the surface of the photosensitive drum 1a is uniformly charged to a predetermined charging potential by the charger 2a. The photosensitive drum 1a charged by the charger 2a is then scanned and exposed by a laser beam modulated by an image signal by a laser beam scanner 3a, which is an example of an exposure device.

[0014] The laser beam scanner 3a is controlled based on input image data, and the image data for emitting the laser beam is input from an external terminal such as a document reader or a personal computer (PC). The surface potential of the photosensitive drum 1a charged by the charger 2a changes in the image area due to the laser beam of the laser beam scanner 3a, forming an electrostatic latent image on the photosensitive drum 1a.

[0015] The electrostatic latent image thus formed on the photosensitive drum 1a is reverse-developed by the developing device 4a with toner to become a visible image, i.e., a toner image. In this embodiment, the developing device 4a uses a two-component development method that uses a developer containing a non-magnetic toner and a magnetic carrier as a developer. That is, each of the developing devices 4a, 4b, 4c, and 4d contains a two-component developer containing a toner of each color. Specifically, the developing device 4a contains yellow (Y) toner, the developing device 4b contains magenta (M) toner, the developing device 4c contains cyan (C) toner, and the developing device 4d contains black (K) toner. Therefore, by performing the above-mentioned process for each image forming section Pa, Pb, Pc, and Pd, four toner images of yellow, magenta, cyan, and black are formed on the photosensitive drums 1a, 1b, 1c, and 1d, respectively.

[0016] Further, an intermediate transfer belt 60, which is an intermediate transfer body, is disposed below each of the image forming stations Pa, Pb, Pc, and Pd. The intermediate transfer belt 60 is suspended around rollers 61, 62, and 63, and is movable in the direction of the arrow. A secondary transfer roller 64 is disposed on the outer side of the intermediate transfer belt 24, which is suspended around the roller 63. The secondary transfer roller 64 is configured so that a recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0017] The toner images on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially primarily transferred to the intermediate transfer belt 60 at primary transfer sections T1a, T1b, T1c, and T1d as transfer sections by primary transfer rollers 6a, 6b, 6c, and 6d as primary transfer members. As a result, toner images of four colors, yellow, magenta, cyan, and black, are superimposed on the intermediate transfer belt 60 to form a full-color image. In addition, toner remaining on the photosensitive drum 1a without being transferred to the intermediate transfer belt 60 is collected by a cleaning device 8a.

[0018] This full-color image on the intermediate transfer belt 60 is secondarily transferred by the action of the secondary transfer roller 64 to a recording material fed from a feeding section (not shown) at a secondary transfer section T2 formed by the secondary transfer roller 64 and the intermediate transfer belt 60. Toner that is not transferred to the recording material and remains on the surface of the intermediate transfer belt 60 is collected by an intermediate transfer belt cleaning device 65. Meanwhile, the recording material to which the toner image has been transferred is sent to a fixing device 7, where the image is fixed, and then discharged outside the apparatus.

[0019] In this embodiment, the developer contained in the developing device 4a is a two-component developer in which a negatively charged non-magnetic toner and a magnetic carrier are mixed. The non-magnetic toner (hereinafter referred to as toner) is a resin such as polyester or styrene that contains colorants, wax components, etc., and is pulverized or polymerized to form a powder. The magnetic carrier (hereinafter referred to as carrier) is a core made of resin particles kneaded with ferrite particles or magnetic powder, and a resin coating is applied to the surface layer.

[0020] The developing process of the toner on the photosensitive drum 1a by the developing device 4a will be described. The developing device 4a has a developing sleeve 41 as a developer carrier. The developing sleeve 41 develops the electrostatic latent image on the photosensitive drum 1a with toner in a developing section D facing the photosensitive drum 1a to form a toner image. More specifically, the photosensitive drum 1a is uniformly charged to a charging potential by a DC voltage applied to the charger 2a or a voltage obtained by superimposing an AC voltage on a DC voltage. After that, the image portion is exposed to a laser beam from the laser beam scanner 3a, and the potential at the exposed position becomes the exposure potential, and an electrostatic latent image is formed on the photosensitive drum 1a. In this embodiment, the voltage applied to the charger 2a is a DC voltage of -500 [V] superimposed with an AC voltage that is a sine wave with a peak-to-peak voltage of 1200 [V] and a frequency of 2 [kHz]. As a result, the charging potential becomes -500 [V] and the exposure potential becomes -150 [V].

[0021] The developing device 4a conveys the developer to the developing section D by the developing sleeve 41. A DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve 41. In this embodiment, a voltage obtained by superimposing an AC voltage, which is a square wave having a duty ratio of 60%, a peak-to-peak voltage of 1400 [V], and a frequency of 12 [kHz], on a DC voltage of -350 [V] is applied to the developing sleeve 41. The negative polarity toner present in the developer is carried to the electrostatic latent image on the photosensitive drum 1a, which is at the exposure potential, by an electric field created by the charging potential and exposure potential of the developing sleeve 41 and the photosensitive drum 1a, and developed.

[0022] [Carrier recovery device] Next, the carrier recovery devices 5a, 5b, 5c, and 5d will be described with reference to FIG. 1 and FIG. 2. The carrier recovery devices 5a, 5b, 5c, and 5d have the same configuration, so the carrier recovery device 5a will be described below as a representative. As shown in FIG. 1, the carrier recovery device 5a recovers carriers attached to the photosensitive drum 1a downstream of the developing unit D (the area where the developing device 4a and the photosensitive drum 1a are close to each other) and upstream of the primary transfer unit T1a (the area where the primary transfer roller 6a and the photosensitive drum 1a are close to each other) in the rotation direction of the photosensitive drum 1a. As shown in FIG. 2, the carrier recovery device 5a includes a recovery roller 52 that is disposed facing the photosensitive drum 1a and rotates, a magnet roller 51 that is disposed inside the recovery roller 52 in a non-rotating manner and serves as a magnetic field generating unit that attracts the carriers to the surface of the recovery roller 52 by magnetic force, a recovery chamber 53, a conveying screw 54 that conveys the carriers collected in the recovery chamber 53, and a conductor member 56. These are placed in a collection container 55.

[0023] The magnet roller 51 has a plurality of magnetic poles (magnet pieces) 51a, 51b, and 51c (three in this embodiment). The magnetic pole 51a is disposed at a position facing the photosensitive drum 28Y via the collection roller 52. The magnetic pole 51a is a magnetic pole for attracting carriers attached to the outer peripheral surface of the photosensitive drum 1a, and for this reason, the magnetic pole 51a is disposed near the closest position P1 between the photosensitive drum 1a and the collection roller 52. The magnetic pole 51b is disposed downstream of the magnetic pole 51a in the rotation direction of the collection roller 52, and has a different polarity from the magnetic pole 51a. The magnetic pole 51c is disposed adjacent to the magnetic pole 51b downstream of the magnetic pole 51b in the rotation direction of the collection roller 52, and has the same polarity as the magnetic pole 51b.

[0024] 2, the magnetic field created by the magnetic pole 51a arranged around the photosensitive drum 1a causes the carrier adhering to the photosensitive drum 1a to be attracted to the surface of the recovery roller 52. The attracted carrier is transported with the rotation of the recovery roller 52 and is peeled off into a recovery chamber 53 by a repulsive magnetic field created by the magnetic poles 51b and 51c.

[0025] Note that, instead of the configuration of the repulsive magnetic field created by the magnetic poles 51b and 51c, or in addition to the configuration of the repulsive magnetic field created by the magnetic poles 51b and 51c, a blade may be disposed to face the collection roller 52 and peel off the carrier from the collection roller 52. For example, the blade may be disposed so as to face the collection roller 52 with a gap therebetween downstream of the position where the collection roller 52 faces the photosensitive drum 28Y in the rotation direction of the collection roller 52.

[0026] The transport screw 54, which serves as a carrier transport member, has a rotating shaft made of a non-magnetic metal and resin blades formed in a spiral shape around the rotating shaft. The transport screw 54 rotates to transport the carrier that has fallen from the collection roller 52 in the direction of its rotation axis. In this embodiment, the rotation axis of the transport screw 54 and the rotation axis of the collection roller 52 are substantially parallel to each other.

[0027] A voltage obtained by superimposing an AC voltage on a DC voltage is applied to the recovery roller 52 from a recovery high voltage board 130 (see FIG. 3 described below) serving as a voltage application unit. As shown in FIG. 3, the recovery high voltage board 130 is controlled by a control unit 101, and can apply an AC voltage superimposed on a DC voltage in accordance with the operation of the carrier recovery device 5a. The conductor member 56 will be described later.

[0028] [Control configuration] FIG. 3 is a block diagram showing a part of the control configuration of the image forming apparatus 100 in this embodiment. In this embodiment, the voltage applied to the chargers 2a to 2d is generated by the charging high voltage board 110 through the control unit 101. Moreover, the voltage applied to the developing sleeves 41 of the developing devices 4a to 4d is generated by the developing high voltage board 120 through the control unit 101. Furthermore, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the recovery roller 52 by the recovery high voltage board 130 through the control unit 101. The DC component of the voltage applied to the recovery roller 52 is a voltage having a difference of 100 [V] with respect to the charging potential of the photosensitive drums 1a to 1d in order to suppress the movement of the negative polarity toner developed on the electrostatic latent images on the photosensitive drums 1a to 1d to the recovery roller 52. In this embodiment, it is -600 [V]. In addition, the AC component of the voltage applied to the recovery roller 52 is intended to improve recovery of the carrier adhering to the photosensitive drums 1a to 1d, and in this embodiment, is a square wave with a duty ratio of 50%, a peak-to-peak voltage of 1500 [V], and a frequency of 5 [kHz]. The carrier recovery devices 5a to 5d recover the carrier adhering to the photosensitive drums 1a to 1d by the force of the magnetic field formed by the magnet roller 51 and the force of the electric field formed between the recovery roller 52 and the photosensitive drums 1a to 1d by the voltage applied to the recovery roller 52.

[0029] [Toner adhesion on the collection roller] Next, the adhesion of toner to the collection roller 52 will be described. As described above, a voltage is applied to the collection roller 52 to facilitate the collection of carrier on the surfaces of the photosensitive drums 1a to 1d at the closest position P1 between the photosensitive drums 1a to 1d and the collection roller 52. At this time, the collection roller 52 also collects so-called fog toner that has adhered to the surfaces of the photosensitive drums 1a to 1d. That is, the toner adheres to the collection roller 52.

[0030] The toner inside the developing device 1Y is negatively charged, but the toner adhering to the recovery roller 52 is mostly weakly charged toner with no charge, centered around 0 charge (i.e., toner with a charge of 0 or close to 0), or oppositely charged toner (i.e., toner charged to the positive polarity). Such toner adheres to the background of the image and becomes fog toner. Toner in a normal charged state adheres to the photosensitive drums 1a-1d by electrostatic force, but weakly charged toner and oppositely charged toner have a weak adhesion force to the photosensitive drums 1a-1d by electrostatic force. For this reason, the toner is easily transferred to the recovery roller 52 at the closest position P1 between the recovery roller 52 and the photosensitive drum 28Y.

[0031] Since the toner is a non-magnetic material, the toner transferred to the recovery roller 52 is not affected by the magnetic force generated by the magnetic poles of the magnet roller 51, and moves while remaining fixed to the surface of the recovery roller 52. However, when the toner reaches the peeling pole portions, namely magnetic poles 51b and 51c, it is rubbed by the carrier remaining in the peeling pole portions, accumulates together with the carrier, and is finally recovered in the recovery chamber 53.

[0032] However, if the amount of carrier on the recovery roller 52 is insufficient, the carrier remaining at the peeling pole portion will be insufficient, and the toner cannot be sufficiently recovered at the peeling pole portion. In this case, the toner will accumulate on the recovery roller 52. Then, when the gap between the photosensitive drum 28Y and the recovery roller 52 is filled with the toner on the recovery roller 52, the toner on the recovery roller 52 will adhere to the photosensitive drum 28Y again (so-called dripping occurs), and as a result, the toner will transfer to the output product and generate image noise. Therefore, in this embodiment, the toner adhering to the recovery roller 52 is collected by a conductive member 56 described below.

[0033] [Conductor material] Next, the conductive member 56 will be described. Note that, although the carrier recovery device 5a will be described below, the same applies to the carrier recovery devices 5b to 5d. As shown in FIG. 2, the conductive member 56 is disposed so as to face the recovery roller 52 downstream of the position (closest position P1) where the recovery roller 52 is closest to the photosensitive drum 1a in the rotation direction of the recovery roller 52. Also, as shown in FIG. 4 described later, the conductive member 56 is disposed so that both ends thereof are positioned outside both ends of the magnet roller 51 in the direction of the rotation axis of the recovery roller 52 (longitudinal direction, left-right direction in FIG. 4). A specific description will be given below.

[0034] As shown in FIG. 2, the carrier recovery device 5a has a recovery container 55. An opening 55a is formed at a position facing the photosensitive drum 1a in a part of the recovery container 55. A recovery roller 52 is disposed inside the recovery container 55, and the recovery roller 52 faces the photosensitive drum 1a through the opening 55a. The conductor member 56 is fixed at a position facing the recovery container 55 on the inner wall of the recovery container 55. The recovery container 55 also has a main body 55b having a recovery chamber 53 and an upper lid 55c covering the upper part of the main body 55b. In this embodiment, the conductor member 56 is disposed at a position facing the recovery roller 52 on the inner wall of the upper lid 55c. Therefore, the conductor member 56 is disposed upstream of the position where the recovery roller 52 faces the recovery chamber 53 with respect to the rotation direction of the recovery roller 52. Furthermore, in this embodiment, the conductor member 56 is disposed vertically above the rotation axis of the recovery roller 52.

[0035] The surface of the upper cover 55c facing the collection roller 52 has a curved shape that conforms to the surface of the collection roller 52. The conductive member 56 is fixed in a curved state so as to conform to the curved surface of the upper cover 55c. The conductive member 56 functions as a toner collecting section that mainly collects toner with a low charge amount that is collected by the collection roller 52 when it collects the carrier on the photosensitive drum 1a.

[0036] The conductor member 56 is a sheet-like member having a metal layer on the surface of a resin layer. In the present embodiment, the conductor member 56 is a member having a layered structure in which aluminum foil is vapor-deposited on a polyester film, and a sheet-like member having a width (length in the direction perpendicular to the longitudinal direction) of 4 mm is used. As such a conductor member 56, for example, Alpet (registered trademark) by Panac Corporation can be used.

[0037] The conductor member 56 extends approximately parallel to the longitudinal direction of the collection roller 52. FIG. 4 shows the relationship between the longitudinal lengths of the magnet roller 51, the collection roller 52, and the conductor member 56. The conductor member 56 has a length longer than the magnet roller 51 and shorter than the collection roller 52 in the longitudinal direction. That is, in terms of the longitudinal direction of the collection roller 52, both ends of the conductor member 56 are positioned outside both ends of the magnet roller 51, but inside both ends of the collection roller 52. For this reason, the region of the outer circumferential surface of the collection roller 52 where the carrier is attracted to the collection roller 52 by the magnetic force of the magnet roller 51 passes through a position facing the conductor member 56 as the collection roller 52 rotates.

[0038] 3, a DC voltage is applied to the conductor member 56 by a recovery high voltage board 130 serving as a voltage application unit. That is, the recovery high voltage board 130 outputs a predetermined voltage to each of the recovery roller 52 and the conductor member 56.

[0039] 5 is a schematic diagram showing a configuration for applying a voltage to the collection roller 52 and the conductor member 56. As described above, a DC voltage is applied to the conductor member 56. The DC voltage applied to the conductor member 56 is applied in the form of only a DC component from the same collection high voltage board 130 as the collection roller 52. That is, in this embodiment, a DC voltage of −600 [V] is applied to the conductor member 56.

[0040] In this manner, a DC component voltage is applied to the conductor member 56 and the collection roller 52 from the same collection high voltage board 130. Therefore, when the image forming operation is started, the conductor member 56 and the collection roller 52 have the same DC potential at the same timing. Therefore, an AC electric field is formed between the conductor member 56 and the collection roller 52 by the AC voltage applied to the collection roller 52. This electric field causes the low-charge toner on the collection roller 52 to be collected by the conductor member 56. That is, in the case of this embodiment, the conductor member 56 removes the toner from the collection roller 52 in parallel with the operation of the collection roller 52 to collect the carrier during image formation.

[0041] Fig. 6 shows a timing chart showing the timing of starting and ending voltage application when starting and ending an image forming operation. Fig. 6 describes image forming section Pa, but the same applies to other image forming sections Pb to Pd. The timing of starting (ON) voltage application is performed in the following order: AC voltage of charger 2a, DC voltage of charger 2a, DC voltage of developing sleeve 41 of developing device 4a, AC voltage of developing sleeve 41, DC voltage of collection roller 52, and AC voltage of collection roller 52. A DC voltage is also applied to conductor member 56 at the timing of application of the DC voltage of collection roller 52.

[0042] When the photosensitive drum 1a, which has been charged by the charger 2a, reaches a position facing the developing sleeve 41, a DC voltage of the developing sleeve 41 is raised. Furthermore, when the photosensitive drum 1a reaches a position facing the collection roller 52, a DC voltage of the collection roller 52 is raised. This is to prevent the toner or carrier on the developing sleeve 41 or the collection roller 52 from unintentionally adhering to the photosensitive drum 1a due to the timing of application of the voltage to the developing sleeve 41 or the collection roller 52 being too early or too late with respect to the region where the photosensitive drum 1a is charged and converges to the charging potential.

[0043] When the application of the voltage is ended (OFF), first, the AC voltage of the developing sleeve 41 and the collecting roller 52 is dropped. After that, the DC voltage is dropped in the order of the charger 2a, the developing sleeve 41, and the collecting roller 52. When the charging of the photosensitive drum 1a by the charger 2a is ended, the photosensitive drum 1a loses the charging potential, and the area converged to 0 [V] reaches a position facing the developing sleeve 41, the DC voltage of the developing sleeve 41 is dropped. Furthermore, when the area converged to 0 [V] reaches a position facing the collecting roller 52, the DC voltage of the collecting roller 52 is dropped. This is to prevent the toner or carrier on the developing sleeve 41 or the collecting roller 52 from unintentionally adhering to the photosensitive drum 1a due to the timing of the end of the voltage application of the developing sleeve 41 and the collecting roller 52 being too early or too late with respect to the area where the charging of the photosensitive drum 1a is ended, as in the case of the start-up operation. Finally, the AC voltage of the charging device 2a is dropped. In the case of this embodiment, the conductor member 56 extracts the same DC component of the collected high voltage board 130 as the collection roller 52 , so that the timing of starting and ending application is synchronized with the collection roller 52 .

[0044] In this manner, in this embodiment, the conductive member 56 is provided in the carrier recovery device 5a, and an electric field is formed between the recovery roller 52 and the conductive member 56, thereby making it possible to remove the toner accumulated on the recovery roller 52 during the image forming operation. Therefore, according to the configuration of this embodiment, the toner can be removed from the recovery roller 52 without increasing the downtime.

[0045] If the distance between the conductor member 56 and the collection roller 52 is too small, there is a risk of leakage, and if it is too large, the effect of the electric field is weakened and the toner collection effect is reduced. Therefore, the distance between the conductor member 56 and the collection roller 52 is preferably set to 0.2 mm or more and 3.0 mm or less at the closest position. In this embodiment, it is set to 0.5 mm.

[0046] In addition, in the longitudinal direction of the collection roller 52, the phenomenon of toner adhering to the collection roller 52 occurs particularly remarkably in the region where the magnet roller 51 is present. For this reason, it is preferable that the longitudinal length of the conductor member 56 is longer than that of the magnet roller 51, as shown in FIG.

[0047] As the image forming operation is repeated, collected toner accumulates on the conductor member 56. The accumulated toner may fall onto the photosensitive drum 1a or re-adhere to the photosensitive drum 1a via the recovery roller 52, which may cause image staining. For this reason, it is preferable to dispose the conductor member 56 vertically above the recovery roller 52. By disposing the conductor member 56 in this manner, even if toner continues to accumulate on the conductor member 56, it is possible to prevent image staining from occurring via the photosensitive drum 1a by rubbing against and adhering to the recovery roller 52.

[0048] Moreover, the conductor member 56 is preferably disposed downstream in the rotation direction of the recovery roller 52 from the position (closest position P1) where the recovery roller 52 faces the photosensitive drum 1a, and upstream from the position where the recovery roller 52 faces the recovery chamber 53. By disposing it in this manner, even if the toner accumulated on the conductor member 56 falls onto the recovery roller 52, it can be recovered in the recovery chamber 53 before being carried to the portion facing the photosensitive drum 1a.

[0049] [Regarding the voltage applied to the conductor member 56] In the developing device 4a, the toner charged by friction with the carrier is basically negative. However, the toner adhering to the collection roller 52 is mostly toner with a particularly low charge amount among the negative ones, or toner charged with the opposite polarity. For this reason, in this embodiment, the polarity of the DC voltage applied to the collection roller 52 is negative, and as described above, there is a potential difference with respect to the charging potential. In addition, the voltage applied to the conductor member 56 is the DC component of the voltage applied to the collection roller 52, so that the conductor member 56 and the collection roller 52 have the same potential, and the toner on the collection roller 52 is collected by an AC electric field. That is, in this embodiment, the DC voltage applied to the conductor member 56 is the same as the DC voltage applied to the collection roller 52. However, the same effect can be obtained even if the potential relationship between the collection roller 52 and the conductor member 56 is other than the above. Therefore, a modified example in which the configuration of the voltage applied to the collection roller 52 and the conductor member 56 is changed will be described.

[0050] [Variation 1] In the first modification, a voltage is applied to the conductor member 56 in the configuration shown in Fig. 7(a). That is, the AC voltage applied to the collection roller 52 is passed through the rectifier board 200, and the positive peak value is peak-held and applied to the conductor member 56. As described above, the voltage applied to the collection roller 52 is a voltage obtained by superimposing an AC voltage with a duty ratio of 50%, a peak-to-peak voltage of 1500 [V], and a frequency of 5 [kHz] on a DC voltage of -600 [V]. The voltage applied to the conductor member 56 in the first modification is +150 [V].

[0051] 7(b), the rectifier board 200 is composed of resistors 201 and 204, a diode 202, and a capacitor 203, and holds the positive peak value of the voltage applied to the collection roller 52 and outputs it to the conductor member 56. As described above, in the first modification, a DC voltage of −600 [V] is applied to the collection roller 52, and a DC voltage of +150 [V] is applied to the conductor member 56. As a result, the potential difference between the conductor member 56 and the collection roller 52 is +750 V. That is, in the first modification, the DC voltage applied to the conductor member 56 is a voltage with a magnitude such that the difference with respect to the DC voltage applied to the collection roller 52 is positive.

[0052] [Variation 2] In the second modification, a voltage is applied to the conductor member 56 in the configuration shown in Fig. 8(a). That is, the AC voltage applied to the collection roller 52 is passed through the rectifier board 210, and the negative peak value is peak-held and applied to the conductor member 56. The voltage applied to the conductor member 56 in the second modification is -1350 [V].

[0053] As shown in FIG. 8(b), the rectifier board 210 is composed of resistors 211 and 214, a diode 212, and a capacitor 213. The diode 212 is configured by swapping the anode and cathode of the diode 202 in the rectifier board 200 shown in FIG. 7(b). As a result, the negative peak value of the voltage applied to the collection roller 52 is peak-held and output to the conductor member 56. As described above, in the second modification, a DC voltage of −600 [V] is applied to the collection roller 52, and a DC voltage of −1350 [V] is applied to the conductor member 56. As a result, the potential difference of the conductor member 56 with respect to the collection roller 52 is −750 V. That is, in the second modification, the DC voltage applied to the conductor member 56 is a voltage with a magnitude such that the difference with respect to the DC voltage applied to the collection roller 52 is negative.

[0054] [Variation 3] In the third modification, the voltage applied to the conductor member 56 is a DC voltage applied from a toner collection high voltage board 140, which is different from the collection high voltage board 130 that applies a voltage to the collection roller 52, and the voltage is −300 [V], as shown in FIG. 9. That is, in the third modification, a toner collection high voltage board 140 is provided as a second voltage application section in addition to the collection high voltage board 130 as a first voltage application section. The toner collection high voltage board 140 has a DC power source. The collection high voltage board 130 applies a voltage to the collection roller 52, and the toner collection high voltage board 140 applies a DC voltage to the conductor member 56.

[0055] When the image forming operation is started, the toner collection high voltage board 140 generates a DC voltage at the same timing as the collection high voltage board 130, and applies the voltage to the conductor member 56. As described above, in the third modification, a DC voltage of -600 [V] is applied to the collection roller 52, and a DC voltage of -300 [V] is applied to the conductor member 56. As a result, the potential difference between the conductor member 56 and the collection roller 52 is +300 V. That is, in the third modification, the DC voltage applied to the conductor member 56 is a voltage such that the difference with respect to the DC voltage applied to the collection roller 52 is positive, as in the first modification.

[0056] [Variation 4] The fourth modification has a configuration shown in Fig. 10, in which the conductor member 56 is connected to the ground potential. That is, in the fourth modification, the conductor member 56 is grounded, and no voltage is applied to the conductor member 56 from the recovery high voltage board 130. As described above, in the fourth modification, a DC voltage of -600 [V] is applied to the recovery roller 52, and the potential of the conductor member 56 is 0 [V]. As a result, the potential difference of the conductor member 56 with respect to the recovery roller 52 is +600 V. That is, in the fourth modification, the DC voltage applied to the conductor member 56 is a voltage such that the difference with respect to the DC voltage applied to the recovery roller 52 is positive, as in the first modification.

[0057] [Variation 5] 11, in the fifth modification, the conductor member 56 is not connected to a high voltage board or ground potential, and the potential is not regulated, so that the conductor member 56 is in a so-called floating state. In the fifth modification, a DC voltage of −600 [V] is applied to the collection roller 52, but the potential of the conductor member 56 is unknown.

[0058] [experiment] In the configuration of the example of the first embodiment described above and the configurations of the modified examples 1 to 5 described above, the same amount of toner adheres to the collection roller 52 (toner weight per unit area is about 1.2 [mg / cm 2 The potential of the conductive member 56 in each configuration was set to about 100 mV, and the state of remaining toner on the recovery roller 52 after the recovery roller 52 was rotated 20 times was compared.

[0059] Table 1 shows the voltage applied to the conductive member 56, the potential difference between the conductive member 56 and the collection roller 52, the remaining toner ratio on the collection roller 52, and the complexity of the configuration for each configuration. The remaining toner ratio on the collection roller 52 was calculated from the weight of the toner on the collection roller 52 measured before and after the collection roller 52 had rotated 20 times. Regarding "complexity and cost of configuration," a configuration that was not complicated and could suppress an increase in cost was rated "good," a configuration that was even less complicated than "good" and could suppress an increase in cost was rated "excellent," a configuration that was slightly more complicated than "good" and had a smaller effect of suppressing an increase in cost was rated "slightly insufficient," and a configuration that was even more complicated than "slightly insufficient" and had a smaller effect of suppressing an increase in cost was rated "unsatisfactory." [Table 1]

[0060] Looking at the "proportion of remaining toner on the collection roller 52" in Table 1, good results are obtained in the configuration of the embodiment in which the potential difference between the conductive member 56 and the collection roller 52 is the same, and in the configurations of modified examples 1, 3, and 4 in which the conductive member 56 is more positive. This is thought to be due to the fact that although the toner adhering to the collection roller 52 has a low charge amount, the proportion of the toner that is negative is high.

[0061] On the other hand, in the configuration of Modification 2 in which the conductor member 56 is larger in the negative direction, the toner collection rate is slightly lower than the configurations of the embodiment, Modifications 1, 3, and 4. This is thought to be because Modification 2 is configured to make it easier to collect mainly positively charged toner, and the proportion of positively charged toner among the toner adhering to the collection roller 52 is slightly smaller.

[0062] Modification 5 has a very simple configuration because it does not require a connection from a high voltage board or a contact point with ground potential, but the effect of toner recovery is smaller than that of the other examples.

[0063] In the third modification, since it is necessary to add the toner collection high voltage board 140, there are concerns about high costs and an increase in the size of the device, but since it is independent of the recovery high voltage board 130, the voltage can be determined independently of the voltage applied to the recovery roller 52. Therefore, there is an advantage in that it is possible to easily change the potential difference between the recovery roller 52 and the conductor member 56 to an optimal value depending on the environment in which the image forming apparatus is used, and to easily change the timing of applying the voltage to the recovery roller 52 and the conductor member 56.

[0064] As described above, although the degree of effect varies depending on the potential relationship, any of the configurations can provide a certain degree of effect. Therefore, the conductor member 56 needs to be a conductor, not an insulator such as resin, so that it can have a uniform potential in the longitudinal direction, but the potential relationship between the conductor member 56 and the collection roller 52 may be other than the example shown above. If the potential difference with the collection roller 52 is between -1000 [V] and +1000 [V], there is no risk of leakage, and the effect of collecting toner on the collection roller 52 during image formation operation can be obtained. [Explanation of symbols]

[0065] 1a, 1b, 1c, 1d...Photosensitive drum (image carrier) 4a, 4b, 4c, 4d...developing device 5a, 5b, 5c, 5d Carrier recovery device 6a, 6b, 6c, 6d: Primary transfer roller (transfer member) 51 Magnet roller (magnetic field generating part) 52 Collection roller 53... Recovery Room 56 Conductor member 60···Intermediate transfer belt (intermediate transfer body) 100 Image forming apparatus 101...Control section 130: Recovery high voltage board (voltage application unit, first voltage application unit) 140: Toner collecting high voltage board 140 (second voltage application unit)

Claims

1. an image carrier that rotates and carries an electrostatic latent image on its surface; a developing device for developing the electrostatic latent image carried on the surface of the image carrier into a toner image by using a two-component developer containing a non-magnetic toner and a magnetic carrier in a developing section; an intermediate transfer member that carries the toner image transferred from the image carrier and transfers the toner image onto a recording material; a transfer member for transferring a toner image from the image carrier to the intermediate transfer member in a transfer section; a carrier recovery device that recovers carrier adhering to the image carrier downstream of the developing unit and upstream of the transfer unit in a rotation direction of the image carrier, the carrier recovery device having a recovery roller that is disposed facing the image carrier and rotates, and a magnetic field generating unit that is disposed inside the recovery roller in a non-rotating manner and that attracts the carrier to a surface of the recovery roller by a magnetic force; a voltage application unit capable of applying an AC voltage superimposed on a DC voltage to the collection roller; A control unit that controls the voltage application unit, An image forming apparatus characterized in that the carrier recovery device has a conductive member arranged to face the recovery roller downstream of the position where the recovery roller is closest to the image carrier in terms of the rotation direction of the recovery roller.

2. 2. The image forming apparatus according to claim 1, wherein the conductor member is disposed so that both ends thereof are positioned outside both ends of the magnetic field generating portion in the direction of the axis of rotation of the collection roller.

3. the carrier recovery device has a recovery chamber that recovers the carrier peeled off from the recovery roller, 2. The image forming apparatus according to claim 1, wherein the conductive member is disposed upstream of a position where the collection roller faces the collection chamber in a rotation direction of the collection roller.

4. 2. The image forming apparatus according to claim 1, wherein the voltage application section applies a DC voltage to the conductive member.

5. the voltage application unit is a first voltage application unit, 2. The image forming apparatus according to claim 1, further comprising a second voltage application section for applying a DC voltage to the conductive member.

6. the polarity of the DC voltage applied to the recovery roller is negative; 6. An image forming apparatus according to claim 4, wherein the DC voltage applied to the conductor member is the same as the DC voltage applied to the recovery roller, or is a voltage whose difference with respect to the DC voltage applied to the recovery roller is positive.

7. 2. The image forming apparatus according to claim 1, wherein the conductive member is grounded.

8. 2. The image forming apparatus according to claim 1, wherein the conductive member is disposed vertically above a rotation axis of the collection roller.

9. 2. The image forming apparatus according to claim 1, wherein the conductive member is a sheet-like member having a resin layer and a metal layer provided on the surface of the resin layer.

Images