Image forming apparatus

Abstract

This improves the efficiency of removing toner from the recovery roller while minimizing downtime. [Solution] An image forming apparatus comprising: an image carrier; a developer carrier; a transfer member; a rotatable sleeve positioned downstream of the development position and upstream of the transfer position, facing the image carrier; and a non-rotating magnet positioned inside the sleeve; a carrier recovery device for recovering carriers on the image carrier; a voltage application unit for applying a voltage including an AC voltage to the sleeve; and a control unit for applying a first bias to the sleeve when performing an image forming operation, and for controlling the voltage application unit to apply a second bias different from the first bias to the sleeve in a predetermined mode when not forming an image; wherein the carrier recovery device is provided with a charge application member for applying an electric charge to the toner on the sleeve upstream of the position where the sleeve is closest to the image carrier with respect to the rotation direction of the sleeve.

Description

Technical Field

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

Background Art

[0002] As an image forming apparatus, a configuration in which a toner image is formed using a two-component developer including a non-magnetic toner and a magnetic carrier has been conventionally known. In this configuration, usually, in the developing process, the electrostatic latent image on the photosensitive drum is developed into a toner image by the toner, but the carrier may also adhere to the photosensitive drum at a certain ratio (carrier adhesion). When carrier adhesion occurs, it affects the output image. For example, Patent Document 1 discloses a configuration provided with a carrier recovery device that recovers the carrier adhering 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 further, a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the recovery roller. Thereby, the carrier on the photosensitive drum is recovered by the recovery roller by the magnetic force of the magnet roller and the electrostatic force by the applied voltage. When recovering the carrier with such a carrier recovery device, some toner may also be recovered by the recovery roller. Therefore, in the case of the configuration described in Patent Document 1, the toner removal mode is executed during non-image formation, and in the toner removal mode, the rotation speed of the photosensitive drum is lowered compared to that during image formation. At the same time, an AC voltage is applied to the recovery roller to return the toner adhering to the recovery roller to the photosensitive drum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] As described in Patent Document 1, when the rotation speed of the photoreceptor drum is reduced in toner removal mode, the rotation speed of the photoreceptor drum must be changed between image formation and toner removal mode. Therefore, toner removal mode cannot be performed during image formation, and time must be allocated separately to perform toner removal mode. As a result, downtime, which is the time when image formation cannot be performed, increases. On the other hand, when toner removal mode is performed without reducing the rotation speed of the photoreceptor drum, the execution time of toner removal mode must be extended in order to sufficiently remove the toner adhering to the recovery roller, which also increases downtime.

[0006] This invention has been made in view of the above-mentioned problems. The object of this invention is to provide an image forming apparatus that can improve the efficiency of removing toner from the recovery roller while suppressing downtime. [Means for solving the problem]

[0007] To achieve the above objective, an image forming apparatus according to one aspect of the present invention has the following configuration. That is, an image forming apparatus capable of performing an image forming operation, comprising: a rotatable image carrier on which an electrostatic latent image is formed; a developing container containing a developer including toner and a carrier; a developer carrier carrying the developer to develop the electrostatic latent image formed on the image carrier into a toner image; a transfer member onto which the toner image carried on the image carrier is transferred; a rotatable sleeve positioned opposite the image carrier downstream of the developing position where the electrostatic latent image formed on the image carrier is developed, and upstream of the transfer position where the toner image carried on the image carrier is transferred to the transfer member, with respect to the rotation direction of the image carrier; and the sleeve The carrier recovery device comprises a magnet positioned non-rotating inside a sleeve, a carrier recovery device for recovering carriers on the image carrier, a voltage application unit for applying a voltage including an AC voltage to the sleeve, and a control unit for applying a first bias to the sleeve when performing an image forming operation and for controlling the voltage application unit to apply a second bias different from the first bias to the sleeve in a predetermined mode when not forming an image, wherein the carrier recovery device is provided with a charge application member for applying an electric charge to the toner on the sleeve upstream of the position where the sleeve is closest to the image carrier with respect to the rotational direction of the sleeve.

[0008] Furthermore, in order to achieve the above objective, an image forming apparatus according to another aspect of the present invention has the following configuration. That is, an image forming apparatus capable of performing an image forming operation, comprising: a rotatable image carrier on which an electrostatic latent image is formed; a developing container containing a developer including toner and a carrier; a developer carrier carrying the developer for developing the electrostatic latent image formed on the image carrier into a toner image; a transfer member onto which the toner image carried on the image carrier is transferred; a rotatable sleeve positioned opposite the image carrier downstream of the developing position where the electrostatic latent image formed on the image carrier is developed, and upstream of the transfer position where the toner image carried on the image carrier is transferred to the transfer member, with respect to the rotational direction of the image carrier; and The device is characterized by comprising: a carrier recovery device having a magnet non-rotatingly positioned inside the sleeve for recovering carriers on the image carrier; a voltage application unit for applying a voltage including an AC voltage to the sleeve; a control unit for applying a first bias to the sleeve when performing an image forming operation and for controlling the voltage application unit to apply a second bias different from the first bias to the sleeve in a predetermined mode when not forming an image; and a charge application member positioned downstream of the development position and upstream of the position where the image carrier is closest to the sleeve with respect to the rotation direction of the image carrier for applying an electric charge to the toner on the image carrier. [Effects of the Invention]

[0009] According to the present invention, it is possible to improve the efficiency of removing toner from the recovery roller while suppressing downtime. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing the configuration of the image forming apparatus according to this embodiment. [Figure 2] This is a cross-sectional view showing the configuration of the carrier recovery device (Example 1). [Figure 3] This diagram illustrates the behavior of toner between the carrier recovery device and the photoreceptor drum. [Figure 4]This figure shows a comparison of the charge levels of toner inside the developing unit and the charge levels of toner attached to the recovery roller. [Figure 5] This is a cross-sectional view showing the configuration of the charge-applying member (Example 1). [Figure 6] This is a plan view showing the configuration of the grid electrode (Example 1). [Figure 7] This is a block diagram showing the control configuration of an image forming apparatus (Example 1). [Figure 8] This is a cross-sectional view showing the configuration of a carrier recovery device (modified example 1-1). [Figure 9] This is a cross-sectional view showing the configuration of a carrier recovery device (modified example 1-2). [Figure 10] This is a cross-sectional view showing the configuration of a carrier recovery device (modified example 1-3). [Figure 11] This is a cross-sectional view showing the configuration of the carrier recovery device (Example 2). [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention as defined in the claims, and not all combinations of features described in these embodiments are necessarily essential to the solutions of the present invention. The present invention can be implemented in various applications, such as photocopiers, printers, facsimile machines, and combinations having multiple functions thereof.

[0012] <First Embodiment> [Image forming apparatus] First, the general configuration of the image forming apparatus 100 of this embodiment will be explained using Figure 1.

[0013] The image forming apparatus 100 of the present embodiment is a full-color image forming apparatus 100 that employs an electrophotographic method and includes four image forming units Pa, Pb, Pc, and Pd. Note that the configurations of the respective image forming units are substantially the same except for the different developing colors. For this reason, hereinafter, when there is no particular need for distinction, the image forming unit Pa will be described as a representative, and for the other image forming units, subscripts b, c, and d indicating the configurations of those image forming units will be attached to the reference numerals, and detailed descriptions will be omitted.

[0014] The image forming unit 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 arrow R1 (counterclockwise) in FIG. 1. Around the photosensitive drum 1a, a charger 2a as a charging unit, a laser beam scanner 3a as a latent image forming unit, a developing device 4a, a primary transfer roller 6a, a cleaning device 8a, a carrier recovery device 5a, and the like are arranged.

[0015] Next, the overall image forming 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 subjected to scanning exposure by laser light modulated by an image signal by a laser beam scanner 3a, which is an example of an exposure device.

[0016] The laser beam scanner 3a is controlled based on the input image data, and the image data for emitting the laser light is input from an external terminal such as a document reading device or a personal computer (PC). Due to the laser light of the laser beam scanner 3a, the surface potential of the photosensitive drum 1a charged by the charger 2a changes in the image area, and an electrostatic latent image is formed on the photosensitive drum 1a.

[0017] The electrostatic latent image formed on the photoreceptor drum 1a is inverted and developed by the developing device 4a using toner to form 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 non-magnetic toner and a magnetic carrier as the developer. Each developing device 4a, 4b, 4c, and 4d has a developing container that holds a two-component developer containing toner of each color. Specifically, developing device 4a holds yellow (Y) toner, developing device 4b holds magenta (M) toner, developing device 4c holds cyan (C) toner, and developing device 4d holds black (K) toner. Therefore, by performing the above process for each image forming unit Pa, Pb, Pc, and Pd, toner images of four colors, yellow, magenta, cyan, and black, are formed on the photoreceptor drums 1a, 1b, 1c, and 1d, respectively.

[0018] Furthermore, an intermediate transfer belt 60, which is an intermediate transfer body, is positioned below each image forming section Pa, Pb, Pc, and Pd. The intermediate transfer belt 60 is suspended from rollers 61, 62, and 63 and is movable in the direction of arrow R2. A secondary transfer roller 64 is positioned outside the intermediate transfer belt 60 that is stretched over roller 63. The secondary transfer roller 64 is configured so that recording material can pass between it and the intermediate transfer belt 60. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0019] The toner images on each photoreceptor drum 1a, 1b, 1c, and 1d are sequentially transferred to the intermediate transfer belt 60 by primary transfer rollers 6a, 6b, 6c, and 6d, which act as primary transfer members, at the primary transfer sections T1a, T1b, T1c, and T1d, which act as transfer sections. As a result, the toner images of four colors—yellow, magenta, cyan, and black—are superimposed on the intermediate transfer belt 60 to form a full-color image. Any toner remaining on the photoreceptor drum 1a that is not transferred to the intermediate transfer belt 60 is collected by the cleaning device 8a.

[0020] The full-color image on the intermediate transfer belt 60 is transferred to the recording material fed from a feeding unit (not shown) in a secondary transfer section T2 formed by the secondary transfer roller 64 and the intermediate transfer belt 60, by the action of the secondary transfer roller 64. Toner remaining on the surface of the intermediate transfer belt 60 that is not transferred to the recording material is collected by the intermediate transfer belt cleaning device 65. Meanwhile, the recording material on which the toner image has been transferred is sent to the fuser 7, where the image is fixed and then discharged outside the machine.

[0021] 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 made by pulverizing or polymerization a resin such as polyester or styrene, which contains colorants, wax components, etc., and is made into a powder. The magnetic carrier (hereinafter referred to as carrier) is made by coating the surface of a core made of resin particles mixed with ferrite particles or magnetic powder with resin.

[0022] The process of developing toner onto the photoreceptor drum 1a by the developing device 4a will now be described. The developing device 4a has a developing sleeve 41 as a developer carrier. In the developing section D (developing position) facing the photoreceptor drum 1a, the developing sleeve 41 develops the electrostatic latent image on the photoreceptor drum 1a with toner to form a toner image. More specifically, the photoreceptor drum 1a is uniformly charged to a charging potential by a DC voltage applied to the charger 2a, or a voltage obtained by superimposing a DC voltage and an AC voltage. Subsequently, the image section is exposed by the laser light of the laser beam scanner 3a, and the potential at the exposed position becomes the exposure potential, forming an electrostatic latent image on the photoreceptor drum 1a. In this embodiment, the voltage applied to the charger 2a is a bias obtained by superimposing an AC voltage which is a sine wave with a peak-to-peak voltage of 1200 V and a frequency of 2 kHz onto a DC voltage of -500 V. As a result, the charging potential becomes -500[V] and the exposure potential becomes -150[V]. The movement speed of the photoreceptor drum 1a is set to 400 mm / s.

[0023] The developing device 4a transports the developer to the developing unit D by the developing sleeve 41. At this time, the moving speed of the developing sleeve 41 is set to 600 mm / s. 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 with a peak-to-peak voltage of 1400 V and a frequency of 10 kHz, on a DC voltage of -350 V is applied to the developing sleeve 41. The electric field created by the charging potential and exposure potential of the developing sleeve 41 and the photoreceptor drum 1a carries the negative polarity toner present in the developer to the electrostatic latent image on the photoreceptor drum 1a, which is at the exposure potential, and develops it.

[0024] [Carrier retrieval device] Next, the carrier recovery devices 5a, 5b, 5c, and 5d in Embodiment 1 of this embodiment will be described with reference to Figure 1 and with reference to Figure 2. Since the configurations of the carrier recovery devices 5a, 5b, 5c, and 5d are the same, the carrier recovery device 5a will be described as a representative example below.

[0025] As shown in Figure 1, the carrier recovery device 5a recovers carriers (carriers on the image carrier) attached to the photoreceptor drum 1a downstream of the developing unit D and upstream of the primary transfer unit T1a with respect to the rotation direction (R1 direction) of the photoreceptor drum 1a. The developing unit D is the area where the developing device 4a and the photoreceptor drum 1a are in close proximity. The primary transfer unit T1a is the area where the primary transfer roller 6a and the photoreceptor drum 1a are in close proximity.

[0026] As shown in Figure 2, the carrier recovery device 5a includes a recovery roller 52 (sleeve) that is positioned opposite the photoreceptor drum 1a and rotates. Also, as shown in Figure 2, the carrier recovery device 5a includes a magnet roller 51 (magnet) that is positioned non-rotating inside the recovery roller 52 and acts as a magnetic field generating unit that attracts the carrier to the surface of the recovery roller 52 by magnetic force. Furthermore, as shown in Figure 2, the carrier recovery device 5a includes a recovery chamber 53, a transport screw 54 for transporting the carrier collected in the recovery chamber 53, and a charge-applying member 50 for applying an electric charge to the toner on the recovery roller 52 (toner on the sleeve). These are all arranged inside the recovery container 56.

[0027] The magnetic roller 51 has multiple (three in this embodiment) magnetic poles (magnetic pieces) 51a, 51b, and 51c. Magnetic pole 51a is positioned opposite the photoreceptor drum 1a via the recovery roller 52. Magnetic pole 51a is for attracting carriers attached to the outer surface of the photoreceptor drum 1a, and for this purpose, magnetic pole 51a is positioned near the closest proximity position P1 between the photoreceptor drum 1a and the recovery roller 52. Magnetic pole 51b is positioned downstream of magnetic pole 51a with respect to the rotation direction of the recovery roller 52 and is of the opposite pole to magnetic pole 51a. Magnetic pole 51c is positioned downstream of magnetic pole 51b with respect to the rotation direction of the recovery roller 52 and adjacent to magnetic pole 51b, and is of the same pole as magnetic pole 51b.

[0028] The recovery roller 52 is positioned opposite the photoreceptor drum 1a, downstream of the developing unit D (developing position) and upstream of the primary transfer unit T1a (transfer position) with respect to the rotation direction of the photoreceptor drum 1a. The recovery roller 52 rotates in the direction of arrow R3 in Figure 2, and the magnetic field created by the magnetic poles 51a positioned around the photoreceptor drum 1a attracts carriers attached to the photoreceptor drum 1a to the surface of the recovery roller 52. The attracted carriers are transported as the recovery roller 52 rotates and are stripped into the recovery chamber 53 by the repulsive magnetic field created by the magnetic poles 51b and 51c.

[0029] The conveying screw 54, which serves as a carrier conveying member, has a rotating shaft made of non-magnetic metal and resin blades formed spirally around the rotating shaft. The conveying screw 54 rotates to convey the carrier that has fallen from the recovery roller 52 in the direction of the rotation axis. In this embodiment, the rotation axis direction of the conveying screw 54 and the rotation axis direction of the recovery roller 52 are approximately parallel.

[0030] Furthermore, the recovery roller 52 receives a superimposed voltage of DC voltage and AC voltage from the recovery high-voltage substrate 130 (see Figure 7, described later), which acts as a voltage application unit. As shown in Figure 7, described later, this recovery high-voltage substrate 130 is controlled by the control unit 101 and can apply a superimposed DC voltage and AC voltage in accordance with the operation of the carrier recovery device 5a.

[0031] The carrier recovery device 5a recovers carriers attached to the photoreceptor drum 1a by the force produced by the magnetic field formed by the magnet roller 51 and the electric field formed between the recovery roller 52 and the photoreceptor drum 1 by the voltage applied to the recovery roller 52.

[0032] As will be explained in detail in Figures 5 and 6, in Example 1 of this embodiment, a corona charger 500 is used as the charge-applying member 50.

[0033] [Toner buildup on the recovery roller] Next, Figures 3 and 4 will be used to explain the adhesion of toner to the recovery roller 52. Figure 3 is a diagram illustrating the behavior of toner between the carrier recovery device 5 and the photoreceptor drum 1a. Figure 4 is a diagram comparing the charge amount of toner in the developing device 4 with the charge amount of toner attached to the recovery roller 52.

[0034] As shown in Figure 3, a voltage is applied to the recovery roller 52 to facilitate the recovery of carriers from the surfaces of the photoreceptor drums 1a to 1d at the closest proximity position P1 between the photoreceptor drums 1a to 1d and the recovery roller 52.

[0035] At this time, the recovery roller 52 also recovers the so-called "fouled toner" that has adhered to the surface of the photoreceptor drums 1a to 1d. In other words, toner adheres to the recovery roller 52.

[0036] As shown in Figure 4, the toner in the developing device 4 (normally charged toner) is negatively charged. On the other hand, the toner adhering to the recovery roller 52 is mostly weakly charged toner with a charge of 0 (i.e., toner with a charge of 0 or close to 0), or reversely charged toner (i.e., positively charged toner). Such toner adheres to the background of the image, becoming a fouling toner. Normally charged toner adheres to the photoreceptor drums 1a to 1d by electrostatic force, but weakly charged toner and reversely charged toner have weaker electrostatic adhesion to the photoreceptor drums 1a to 1d. For this reason, weakly charged toner and reversely charged toner are easily transferred to the recovery roller 52 at the closest proximity position P1 between the recovery roller 52 and the photoreceptor drum 1a.

[0037] Since 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. On the other hand, when the toner transferred to the recovery roller 52 reaches the peeling poles, the magnetic poles 51b and 51c, it is rubbed by the carriers accumulated in the peeling poles and accumulates together with the carriers, and is finally collected in the recovery chamber 53.

[0038] However, if the amount of carrier on the recovery roller 52 is insufficient, there will be insufficient carrier remaining at the peeling electrode, and the toner cannot be adequately recovered at the peeling electrode. In this case, toner will accumulate on the recovery roller 52. When the gap between the photoreceptor drum 1a and the recovery roller 52 is filled with toner on the recovery roller 52, the toner on the recovery roller 52 will adhere to the photoreceptor drum 1a again (so-called toner dripping occurs), and as a result, it will transfer to the output and cause image noise.

[0039] [Charging the toner adhering to the recovery roller] The inventors' studies revealed that ejecting the aforementioned weakly charged toner and reverse-charged toner from the recovery roller 52 to the photoreceptor drum 1a via the toner ejection sequence takes extra time. This is because weakly charged toner and reverse-charged toner have poorer electric field tracking ability compared to toner in a normal charged state, and therefore cannot move quickly even if an electric field is formed between the recovery roller 52 and the photoreceptor drum 1a. In this embodiment, the electric field tracking ability is improved and the time required for the toner ejection sequence is reduced by applying a charge to the weakly charged toner and reverse-charged toner adhering to the recovery roller 52 using the charge-applying member 50. The details are described below.

[0040] (Example 1) [Charge-generating member] Next, the charge-applying member 50 in Example 1 of this embodiment will be described using Figures 5 and 6. Figure 5 is a cross-sectional view showing the configuration of the charge-applying member 50 in Example 1.

[0041] The charge-applying member 50 in Example 1 is a scorotron-type corona charger 500 (corona discharge device) as shown in Figure 5. As shown in Figure 2, the corona charger 500 is positioned so as to face the recovery roller 52 upstream of the position where the recovery roller 52 is closest to the photoreceptor drum 1a (nearest contact position P1) with respect to the rotation direction of the recovery roller 52 (R3 direction).

[0042] The corona charger 500 includes a discharge wire (wire electrode, discharge wire) 550, a grid electrode (control electrode, grid) 551, and a shield electrode (housing, shield) 552. The discharge wire 550 is a linear member made of a conductive material and is arranged approximately parallel to the rotation axis direction of the recovery roller 52. The discharge wire 550 is a tungsten wire with a diameter of 60 μm. The grid electrode 551 is a member made of a conductive material and is a substantially flat base material with multiple openings (through holes) formed therein. The base material of the grid electrode 551 is arranged approximately parallel to the rotation axis direction of the recovery roller 52. The grid electrode 551 is positioned between the discharge wire 550 and the recovery roller 52. The shield electrode 552 (552a, 552b) is a box-shaped member made of a conductive material that surrounds the discharge wire 550 and has an open surface facing the recovery roller 52.

[0043] Figure 6 is a plan view of a portion of the grid electrode 551 in Example 1, as seen from the recovery roller 52 side. In Figure 6, arrow X indicates the short direction of the grid electrode 551, and arrow Y indicates the long direction of the grid electrode 551.

[0044] The grid electrode 551 is constructed by etching a plate-shaped substrate made of SUS (stainless steel) and forming multiple openings (through holes) 5511 in a mesh-like pattern. The width of the grid electrode 551 in the short direction (L1) is 10 mm, and the width in the long direction (L2) is 340 mm. The thickness of the substrate of the grid electrode 551 is 100 μm.

[0045] The mesh portion 5512 of the grid electrode 551 has a shape in which a plurality of openings 5511 inclined with respect to the longitudinal direction of the grid electrode 551 are arranged substantially parallel to the longitudinal direction of the grid electrode 551. The mesh portion 5512 has a shape in which a plurality of mesh wire portions 5513 inclined with respect to the longitudinal direction of the grid electrode 551 are arranged substantially parallel to the longitudinal direction of the grid electrode 551, and openings 5511 are formed between each mesh wire portion 5513. The pitch (spacing) (L3) in the width direction of the mesh wire portions 5513 is 0.3 mm. The width (L4) of the mesh wire portions 5513 is 0.07 mm. The angle (A0) of the mesh wire portions 5513 with respect to the longitudinal direction of the grid electrode 551 is 45 degrees.

[0046] [Control Configuration] Figure 7 is a block diagram showing a part of the control configuration of the image forming apparatus 100 in Embodiment 1 of this embodiment. In this embodiment, the voltage applied to the chargers 2a to 2d is generated by the high-voltage charging substrate 110 via the control unit 101. The voltage applied to the developing sleeves 41 of the developing apparatus 4a to 4d is generated by the high-voltage developing substrate 120 via the control unit 101. Furthermore, a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the recovery roller 52 by the high-voltage recovery substrate 130 via the control unit 101. The DC component of the voltage applied to the recovery roller 52 is a voltage with a difference of 100[V] from the charging potential of the photoreceptor drums 1a to 1d, in order to suppress the movement of negative polarity toner developed on the electrostatic latent image on the photoreceptor drums 1a to 1d to the recovery roller 52. In this embodiment, it is -600[V]. The AC component of the voltage applied to the recovery roller 52 is for improving the recovery of carriers attached to the photoreceptor drums 1a to 1d. In this embodiment, the AC component of the voltage applied to the recovery roller 52 is a square wave with a duty cycle of 50%, a peak-to-peak voltage of 1500 [V], and a frequency of 5 [kHz]. The carrier recovery devices 5a to 5d recover carriers attached to the photoreceptor 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 photoreceptor drums 1a to 1d by the voltage applied to the recovery roller 52.

[0047] In Example 1, as shown in Figure 7, the discharge wire 550 is connected to a DC power supply, the discharge high-voltage substrate 140. The grid electrode 551 is also connected to a DC power supply, the grid high-voltage substrate 150. In Example 1, the voltage applied by the discharge high-voltage substrate 140 to the discharge wire 550 is controlled by a constant current. The voltage applied by the grid high-voltage substrate 150 to the grid electrode 551 is controlled by a constant voltage. The grid electrode 551 and the shield electrodes 552 (552a, 552b) are electrically connected so that they are at the same potential. In Example 1, the voltage applied to the discharge wire 550 is variable so that the current flowing through the discharge wire 550 is in the range of -400 to -1200 μA. The voltage applied to the grid electrode 551 is also variable in the range of -0 to -1200 V.

[0048] The material and shape of the discharge wire 550, the shape of the mesh portion 5512 of the grid electrode 551, the material of the substrate, and whether or not there is a coating on the substrate surface are not limited to the configuration described in Example 1. They may be changed to other shapes as appropriate depending on the configuration and operating conditions of the image forming apparatus 100.

[0049] [Toner removal operation on the recovery roller] In this embodiment, in order to improve the efficiency of removing toner from the recovery roller 52, a toner removal mode (second mode) can be executed during non-image formation times, separate from the image formation operation (first mode). In the toner removal mode, toner on the recovery roller 52 is removed by moving the toner from the recovery roller 52 to the photoreceptor drum 1a using an electric field. Here, the operating conditions (set values) of the recovery roller 52 and the photoreceptor drum 1a in the toner removal mode are shown in Table 1. As shown in Table 1, the bias applied to the recovery roller 52 in the toner removal mode is different from the bias applied to the recovery roller 52 during the image formation operation.

[0050] [Table 1]

[0051] In toner removal mode, the peripheral speed of the photoreceptor drum 1a is driven at 400 mm / s, the same as during image formation. In toner removal mode, a voltage consisting of a superimposed DC voltage and AC voltage is applied to the recovery roller 52. The DC voltage is -700V, and the AC voltage Vpp is set higher than during image formation, at 1.6kV. In toner removal mode, the frequency of the AC component of the voltage applied to the recovery roller 52 is set to 1000Hz to achieve high toner removal efficiency.

[0052] Furthermore, in toner removal mode, the surface potential of the photoreceptor drum 1a is controlled to -500V, and the voltage applied to the grid electrode 551 is set to -900V. In addition, to set the execution time of toner removal mode to 3 seconds, the voltage applied to the recovery roller 52 and the grid electrode 551 is set to 3 seconds.

[0053] The toner removal mode is executed when it is expected that a considerable amount of toner has adhered to the surface of the recovery roller 52. The amount of toner adhering to the surface of the recovery roller 52 is estimated, for example, from information regarding the temperature and humidity around the image forming apparatus 100. The amount of fouled toner on the photoreceptor drum 1a changes depending on the temperature and humidity of the environment in which the image forming apparatus 100 is placed. Depending on the amount of fouled toner on the photoreceptor drum 1a, it is expected that toner will adhere to the surface of the recovery roller 52. Therefore, if the amount of toner adhering falls below a predetermined threshold, the image forming operation (printing operation) is performed on a predetermined number of recording materials, and then the image forming operation is interrupted and the toner removal mode is executed.

[0054] In the toner removal mode of this embodiment, the peripheral speed of the photoreceptor drum 1a is driven at the same speed as during image formation, but the voltage applied to the recovery roller 52 is different from that during image formation. In this embodiment, although it is necessary to allocate time separately from the image formation time to execute the toner removal mode, the focus is on suppressing downtime by improving the toner removal efficiency of the recovery roller 52.

[0055] Table 2 shows the relationship between the amount of toner charge predicted from relative humidity and the amount of toner on the surface of the recovery roller 52 observed after performing printing operations for the number of printed pages. The number of printed pages refers to the cumulative image area converted to the number of A4 sheets. The "Amount of Toner Contamination on Recovery Roller" column in Table 2 shows the results of evaluating the amount of toner adhering to the recovery roller 52 in three stages, "◎", "〇", and "×", by visual inspection or measurement of the amount of toner adhering. "◎" indicates no toner adhering at all, "〇" indicates that toner adhering is observed visually but no toner buildup is confirmed, and "×" indicates that toner has been built up on the surface of the recovery roller 52 visually.

[0056] [Table 2]

[0057] As shown in Table 2, when the toner charge is -30 μC / g or higher, no toner is observed to adhere to the recovery roller 52 regardless of the number of printed pages, indicating that the charge is sufficient. On the other hand, when the toner charge falls below -25 μC / g, toner will begin to adhere to the recovery roller 52 as printing continues. When the toner charge is -25 μC / g, toner will begin to accumulate on the surface of the recovery roller 52 after continuing to print 50,000 pages or more. After printing 10,000 pages, toner will begin to adhere to the surface of the recovery roller 52, but it will not accumulate. Therefore, when the toner charge is -25 μC / g or lower, the amount of toner on the recovery roller 52 can be kept below the target value by executing the toner removal mode every 10,000 pages of printing.

[0058] In Example 1, the corona charger 500, which serves as the charge-applying member 50, is provided opposite the recovery roller 52, whereas in the conventional example, such a charge-applying member 50 is not provided.

[0059] On the other hand, the conditions other than the presence or absence of the charge-applying member 50 (operating conditions of the recovery roller 52 and photoreceptor drum 1a in toner removal mode) are the same in the conventional example and Example 1. Specifically, in both the conventional example and Example 1, in toner removal mode, the surface potential of the photoreceptor drum 1a is controlled to be -500V, and the voltage applied to the grid electrode 551 is -900V. Also, in both the conventional example and Example 1, the execution time of the toner removal mode is set to 3 seconds, so the voltage application time between the recovery roller 52 and the grid electrode 551 is set to 3 seconds.

[0060] In Example 1, a corona charger 500, which serves as the charge-applying member 50, is provided opposite the recovery roller 52, whereas in the conventional example, such a charge-applying member 50 is not provided. On the other hand, in Example 1 and the conventional example, conditions other than the presence or absence of the charge-applying member 50 (operating conditions of the recovery roller 52 and photoreceptor drum 1a in toner removal mode) are the same.

[0061] Table 3 shows a comparison of the results between the conventional example and Example 1.

[0062] [Table 3]

[0063] In both the conventional example and Example 1, toner buildup on the recovery roller 52 did not occur.

[0064] On the other hand, in conventional examples, it takes extra time to discharge weakly charged toner or reversely charged toner attached to the recovery roller 52 from the recovery roller 52 to the photoreceptor drum 1a through the toner discharge sequence. In contrast, in Example 1, by applying a charge to the weakly charged toner or reversely charged toner attached to the recovery roller 52 using the corona charger 500, the electric field tracking ability is improved, allowing the toner to move quickly when an electric field is formed between the recovery roller 52 and the photoreceptor drum 1a. In this way, in Example 1, by applying a charge to the uncharged toner on the recovery roller 52, the time required for the toner discharge sequence can be significantly reduced compared to conventional examples.

[0065] As described above, the image forming apparatus 100 of Example 1 is equipped with a carrier recovery device 5a that recovers carriers from the surface of the photoreceptor drum 1a by the action of electric and magnetic fields. In addition, in Example 1, in the toner removal mode for removing toner adhering to the recovery roller 52, a corona charger 500 is used as a charge-applying member 50 to apply a charge to the adhering toner. This promotes the movement of toner from the recovery roller 52 to the photoreceptor drum 1a, and enables efficient removal of toner on the recovery roller 52.

[0066] (Extreme variation 1-1) Figure 8 shows the carrier recovery device 5a' in Modification 1-1. In Example 1, the charge-applying member 50 was a corona charger 500, whereas in Modification 1-1, the charge-applying member 50 is a charging needle 553. The charging needle 553, which is a characteristic of Modification 1-1 as the charge-applying member 50, will be explained using Figure 8.

[0067] As shown in Figure 8, the charging needle 553 is positioned so as to face the recovery roller 52 upstream of the position where the recovery roller 52 is closest to the photoreceptor drum 1a (nearest contact position P1) with respect to the rotational direction of the recovery roller 52 (R3 direction).

[0068] The charging needle 553 is made from a thin sheet of SUS304 stainless steel with a thickness of 0.1 mm, processed into a sawtooth shape, with a pitch of 1 mm between adjacent sawtooths. The charging needle 553 is positioned non-contact with the recovery roller 52, and is installed so that the tips of the sawtooths face the recovery roller 52. The charging needle 553 is attached to the recovery container 56. A high-voltage power supply (not shown) is connected to the charging needle 553 to apply a variable toner charging bias to the charging needle 553, allowing the toner charging bias to be applied to the charging needle 553 at a predetermined timing. This high-voltage power supply is controlled by the control unit 101 shown in Figure 7 to apply the toner charging bias to the charging needle 553. The polarity of the toner charging bias is set to negative polarity.

[0069] The charged needle 553 generates corona discharge when a toner charging bias is applied, and the charged particles associated with the corona discharge irradiate the surface of the recovery roller 52, charging the uncharged toner. The toner charging bias is variable from -2kV to -3.5kV, and in this case, a DC voltage of -3kV is applied.

[0070] As described above, the image forming apparatus 100 of Modified Example 1-1 is equipped with a carrier recovery device 5a' that recovers carriers from the surface of the photoreceptor drum 1a by the action of electric and magnetic fields. Furthermore, in Modified Example 1-1, in the toner removal mode for removing toner adhering to the recovery roller 52, a charged needle 553 as a charge-applying member 50 is used to apply a charge to the adhering toner. This promotes the movement of toner from the recovery roller 52 to the photoreceptor drum 1a, and enables efficient removal of toner on the recovery roller 52.

[0071] (Variations 1-2) Figure 9 shows the carrier recovery device 5a'' in Modification 1-2. In Example 1, the charge-applying member 50 was a corona charger 500, whereas in Modification 1-2, the charge-applying member 50 is an electrostatic brush member 554. The electrostatic brush member 554, which is a characteristic of Modification 1-2 as the charge-applying member 50, will be explained with reference to Figure 9.

[0072] As shown in Figure 9, the electrostatic brush member 554 is positioned so as to contact the recovery roller 52 upstream of the position where the recovery roller 52 is closest to the photoreceptor drum 1a (nearest contact position P1) with respect to the rotational direction (R3 direction) of the recovery roller 52.

[0073] The electrostatic brush component 554 is made by dispersing resistance modifiers such as carbon or metal powder in fibers such as rayon, acrylic, or polyester to adjust the resistance value. Furthermore, the electrostatic brush component 554 has a fiber thickness of 30 denier or less and a bristle density of 7750 to 77500 fibers / cm². 2 (50,000 to 500,000 lines / inch) 2 ) or higher is preferable. In modified examples 1-2, the brush fiber thickness is 6 denier (denier: weight per unit length), and the bristle density is 15,500 bristles / cm². 2 (100,000 units / inch) 2 ), length from fixed end to free end of fiber 5mm, brush resistance value 5×10 4 A material with a density of Ω·cm was used. The electrostatic brush member 554 is fixed to the collection container 56, and the free end of the fiber is in contact with the collection roller 52.

[0074] A high-voltage power supply (not shown) is connected to the electrostatic brush member 554 to apply a negative polarity DC voltage. This high-voltage power supply is controlled by the control unit 101 shown in Figure 7 to apply a negative polarity DC voltage to the electrostatic brush member 554. Specifically, a DC voltage of -1000V is applied to the electrostatic brush member 554. The uncharged toner on the recovery roller 52 is charged by contact charging with the electrostatic brush, and further by charge injection due to the conductivity of the brush. Note that the electrostatic brush member 554 is not limited to the brush shape shown in Figure 9, but may also use a rotatable fur brush or the like.

[0075] As described above, the image forming apparatus 100 in the modified example 1-2 is equipped with a carrier recovery device 5a'' that recovers carriers from the surface of the photoreceptor drum 1a by the action of electric and magnetic fields. Furthermore, in the modified example 1-2, in the toner removal mode for removing toner adhering to the recovery roller 52, an electrostatic brush member 554 as a charge-applying member 50 is used to apply a charge to the adhering toner. This promotes the movement of toner from the recovery roller 52 to the photoreceptor drum 1a, and enables efficient removal of toner on the recovery roller 52.

[0076] (Variations 1-3) Figure 10 shows the carrier recovery device 5a'''' in Modification 1-3. In Example 1, the charge-applying member 50 was a corona charger 500, whereas in Modification 1-3, the charge-applying member 50 is an elastic blade 555. The elastic blade 555 as the charge-applying member 50, which is a feature of Modification 1-3, will be explained using Figure 10.

[0077] As shown in Figure 10, the elastic blade 555 is positioned so as to contact the recovery roller 52 upstream of the position where the recovery roller 52 is closest to the photoreceptor drum 1a (nearest contact position P1) with respect to the rotational direction of the recovery roller 52 (R3 direction).

[0078] The elastic blade 555 is fixed in the recovery chamber 53 and contacts the recovery roller 52 at its tip, imparting an electric charge to the toner on the recovery roller 52. The tip position of the elastic blade 555 is set to penetrate the recovery roller 52, and upon contact with the recovery roller 52, it deforms, generating a pressing force through its repulsive force. The elastic blade 555 is a plate-shaped elastic member, and to provide elasticity (springiness), a thin metal plate, specifically stainless steel, is used. However, in addition to stainless steel, phosphor bronze, aluminum alloy, etc., may also be used, or it may be made from a high-hardness resin. Furthermore, the elastic blade 555 is positioned so as to face the counter-direction with respect to the rotation direction of the recovery roller 52.

[0079] A high-voltage power supply (not shown) is connected to the elastic blade 555 to apply a negative polarity DC voltage. This high-voltage power supply is controlled by the control unit 101 shown in Figure 7 to apply a negative polarity DC voltage to the elastic blade 555. Specifically, a DC voltage of -1000V is applied to the elastic blade 555. The uncharged toner on the recovery roller 52 is charged by contact charging with the elastic blade 555, and further by charge injection from the elastic blade 555.

[0080] As described above, the image forming apparatus 100 in modified example 1-3 is equipped with a carrier recovery device 5a'''' that recovers carriers from the surface of the photoreceptor drum 1a by the action of electric and magnetic fields. Furthermore, in modified example 1-2, in the toner removal mode for removing toner adhering to the recovery roller 52, an elastic blade 55 as a charge-applying member 50 is used to apply a charge to the adhering toner. This promotes the movement of toner from the recovery roller 52 to the photoreceptor drum 1a, and enables efficient removal of toner on the recovery roller 52.

[0081] <Second Embodiment> The configuration of the image forming apparatus 100 in the second embodiment is the same as that of the first embodiment described above, so a detailed explanation will be omitted.

[0082] In the first embodiment, an example was described in which, in the carrier recovery device 5a, a charge-applying member 50 is provided upstream of the closest proximity position P1 between the photoreceptor drum 1a and the recovery roller 52 with respect to the rotational direction of the recovery roller 52, for applying an electric charge to the toner on the recovery roller 52. In this first embodiment, an electric charge is applied to the toner on the recovery roller 52 to promote the movement of toner from the recovery roller 52 to the photoreceptor drum 1a.

[0083] In contrast, the second embodiment focuses on reducing downtime by applying an electric charge to the toner on the photoreceptor drum 1a to suppress toner adhesion to the recovery roller 52, thereby shortening the time required to execute the toner removal mode. The details are described below.

[0084] (Example 2) The carrier recovery device 5a''''´ according to Embodiment 2 of this embodiment will be described with reference to Figure 11. As shown in Figure 11, the carrier recovery device 5a''''´ of Embodiment 2 is not provided with a charge-applying member 50 for applying charge to the toner on the recovery roller 52. On the other hand, in this embodiment, a corona charger 5500 as a post-charger 55 is positioned opposite the photoreceptor drum 1a downstream of the developing unit D and upstream of the closest proximity position P1 between the photoreceptor drum 1a and the recovery roller 52 with respect to the rotation direction of the photoreceptor drum 1a.

[0085] The corona charger 5500 includes a discharge wire (wire electrode, discharge wire) 5501, a grid electrode (control electrode, grid) 5510, and a shield electrode (housing, shield) 5521.

[0086] The discharge wire 5501 is a linear member made of a conductive material, positioned approximately parallel to the rotation axis of the photoreceptor drum 1a. The discharge wire 5501 is a tungsten wire with a diameter of 60 μm. The grid electrode 5510 is a member made of a substantially flat base material made of a conductive material, with multiple openings (through holes) formed therein. The base material of the grid electrode 5510 is positioned approximately parallel to the rotation axis of the photoreceptor drum 1a. The grid electrode 5510 is positioned between the discharge wire 5501 and the photoreceptor drum 1a.

[0087] In this embodiment, the voltage applied by the discharge high-voltage substrate 140 to the discharge wire 5501 is controlled by a constant current. The voltage applied by the grid high-voltage substrate 150 to the grid electrode 5510 is controlled by a constant voltage. Furthermore, the grid electrode 5510 and the shield electrode 5521 are electrically connected to the same potential. In the second embodiment, the voltage applied to the discharge wire 5501 is variable so that the current flowing through the discharge wire 5501 is in the range of -400 to -1200 μA. Also in this embodiment, the voltage applied to the grid electrode 551 is variable in the range of -0 to -1200 V.

[0088] Table 4 shows the relationship between the amount of toner charge predicted from relative humidity and the amount of toner on the surface of the recovery roller 52 observed after performing printing operations for the number of printed pages. The number of printed pages refers to the cumulative image area converted to the number of A4 sheets. The "Amount of Toner Contamination on Recovery Roller" column in Table 4 shows the results of evaluating the amount of toner adhering to the recovery roller 52 in three stages, "◎", "〇", and "×", by visual inspection or measurement of the amount of toner adhering. "◎" indicates no toner adhering at all, "〇" indicates that toner adhering is observed visually but no toner buildup is confirmed, and "×" indicates that toner has been built up on the surface of the recovery roller 52 visually.

[0089] [Table 4]

[0090] As shown in Table 4, when the toner charge is -30 μC / g or higher, no toner is observed to adhere to the recovery roller 52 regardless of the number of printed pages, indicating that the charge is sufficient. On the other hand, when the toner charge falls below -25 μC / g, no toner buildup is observed on the recovery roller 52 due to continued printing. This is because the weakly charged toner on the photoreceptor drum 1a gains charge due to the charge imparted by the post-charger 55, increasing its adhesion to the photoreceptor drum 1a and reducing its movement to the recovery roller 52.

[0091] Table 5 shows the results for the conventional example, Example 1 and Example 2 (with carrier recovery device), and the results for the post-charger with and without the carrier recovery device.

[0092] [Table 5]

[0093] Image defects due to carrier adhesion were evaluated on a three-point scale: ◎, ○, and ×. ◎ means there is 1 or fewer image defects due to carrier adhesion per 10 sheets of A4 paper. ○ means there are 3 or fewer image defects due to carrier adhesion per 10 sheets of A4 paper. × means there are 30 or fewer image defects due to carrier adhesion per 10 sheets of A4 paper.

[0094] The reason why the image defects due to carrier adhesion worsened in the second embodiment (Example 2) compared to the first embodiment (Example 1) is that the corona charger 5500 also imparted charge to the carriers, slightly increasing the adhesion force with the drum. However, when the carrier recovery device 5a'''''' is removed while the corona charger 5500 is still in place (i.e., with post-charger + without carrier recovery device), the image defects due to carrier adhesion become ×. Therefore, it can be seen that the carrier recovery device 5a'''''' (conventional example) also has the effect of recovering carriers.

[0095] Regarding the amount of toner deposited on the recovery roller 52, there was no difference in any of the conventional example, Example 1, and Example 2, indicating good results.

[0096] Toner ejection time was evaluated on a three-point scale: ◎, ○, and ×. ◎ meant an ejection time of 0 seconds, ○ meant an ejection time of 3 seconds or less, and × meant an ejection time of 30 seconds or more.

[0097] In Example 2, toner adhesion to the recovery roller 52 is suppressed by the charge application by the post-charger 55, so toner ejection time is not required, resulting in a ◎. On the other hand, in Example 1, the ejection time can be suppressed by applying a charge to the uncharged toner adhering to the recovery roller 52 by the charge application member 50, resulting in a ○.

[0098] In the second embodiment, an example was described in which a corona charger 5500 is used as the post-charger 55, but the invention is not limited to this. Instead of the corona charger 5500, a comb-shaped electrode (modified example 2-1), an electrostatic fur brush (modified example 2-2), or an elastic blade (modified example 2-3) may be used.

[0099] Furthermore, the first embodiment (Example 1) and the second embodiment (Example 2) may be combined as appropriate. By combining the first embodiment (Example 1) and the second embodiment (Example 2), a configuration is achieved in which a voltage is applied to the corona charger 55 facing the photoreceptor drum 1a, and a voltage is also applied to the charge-applying member 50 facing the recovery roller 52. This configuration allows for the combined effect of applying a charge to the toner on the photoreceptor drum 1a to suppress toner adhesion to the recovery roller 52, and applying a charge to the toner on the recovery roller 52 to promote the movement of toner from the recovery roller 52 to the photoreceptor drum 1a.

[0100] Furthermore, in an example combining the first embodiment (Example 1) and the second embodiment (Example 2), the operation of the charge-applying member 50 and the operation of the post-charger 55 may be switched as appropriate according to the user's request. Specifically, for users who prioritize preventing image defects due to carrier adhesion, the application of voltage to the post-charger 55 facing the photoreceptor drum 1a can be stopped, and voltage can be applied to the charge-applying member 50 facing the recovery roller 52. On the other hand, for users who prioritize productivity, the application of voltage to the charge-applying member 50 facing the recovery roller 52 can be stopped, and voltage can be applied to the post-charger 55 facing the photoreceptor drum 1a.

[0101] <Other Embodiments> The present invention is not limited to the embodiments described above, and various modifications (including organic combinations of each embodiment) are possible based on the spirit of the invention, and these are not excluded from the scope of the invention.

[0102] In the above embodiment, an example was described in which the toner removal mode is executed at a time when it is expected that a considerable amount of toner has adhered to the surface of the recovery roller 52. However, a modified version may be provided that allows the mode to be executed at any time instructed by the user or service technician.

[0103] Furthermore, the image forming apparatus 100 is not limited to an MFP, but may also be a copier, printer, or facsimile machine. Also, although the developing apparatus in each of the embodiments described above has been configured to have two developing rollers, it may also have a configuration with one developing roller. [Explanation of Symbols]

[0104] 1a, 1b, 1c, 1d Photoreceptor drum (image carrier) 4a, 4b, 4c, 4d developing device 5a, 5b, 5c, 5d Carrier recovery device 51 Magnetic Roller (Magnet) 52 Recovery Roller (Sleeve) 50 Charge-applying member 60 Intermediate transfer belt (transfer member) 101 Control Unit 140 High-voltage discharge substrate 150 grid high-voltage substrate 500 Corona Charger 550 Discharge Wire 551 Grid electrode 552 Shielded electrode (housing, shield)

Claims

1. An image forming apparatus capable of performing image forming operations, A rotatable image carrier on which an electrostatic latent image is formed, A developing apparatus comprising: a developing container for containing a developer containing toner and a carrier; and a developer carrier for carrying the developer in order to develop the electrostatic latent image formed on the image carrier into a toner image; A transfer member onto which the toner image supported on the image carrier is transferred, A carrier recovery device for recovering carriers on the image carrier comprises: a rotatable sleeve positioned opposite the image carrier downstream of the development position where the electrostatic latent image formed on the image carrier is developed, and upstream of the transfer position where the toner image carried on the image carrier is transferred to the transfer member, with respect to the rotation direction of the image carrier; and a non-rotating magnet positioned inside the sleeve. A voltage application unit that applies a voltage including an AC voltage to the sleeve, A control unit controls the voltage application unit to apply a first bias to the sleeve when performing an image forming operation, and to apply a second bias different from the first bias to the sleeve in a predetermined mode when not forming an image. Equipped with, The carrier recovery device is provided with a charge-applying member that applies an electric charge to the toner on the sleeve upstream of the position where the sleeve is closest to the image carrier in the rotational direction of the sleeve. An image forming apparatus characterized by the following:

2. The charge-applying member is a corona charger, The corona charger is positioned upstream of the position where the sleeve is closest to the image carrier, with respect to the rotational direction of the sleeve. The image forming apparatus according to feature 1.

3. The charge-applying member is a comb-shaped electrode, The comb-shaped electrode is positioned upstream of the position where the sleeve is closest to the image carrier, with respect to the rotational direction of the sleeve. The image forming apparatus according to feature 1.

4. The charge-applying member is an electrostatic fur brush, The electrostatic fur brush is positioned so as to be in contact with the image carrier upstream of the position where the sleeve is closest to the image carrier with respect to the rotational direction of the sleeve. The image forming apparatus according to feature 1.

5. The charge-applying member is an elastic blade, The elastic blade is positioned so as to be in contact with the image carrier upstream of the position where the sleeve is closest to the image carrier with respect to the rotational direction of the sleeve. The image forming apparatus according to feature 1.

6. The system further comprises a second charge-applying member positioned downstream of the development position and upstream of the position where the image carrier is closest to the sleeve, with respect to the rotational direction of the image carrier, for applying an electric charge to the toner on the image carrier. The image forming apparatus according to feature 1.

7. An image forming apparatus capable of performing image forming operations, A rotatable image carrier on which an electrostatic latent image is formed, A developing apparatus comprising: a developing container for containing a developer containing toner and a carrier; and a developer carrier for carrying the developer in order to develop the electrostatic latent image formed on the image carrier into a toner image; A transfer member onto which the toner image supported on the image carrier is transferred, A carrier recovery device for recovering carriers on the image carrier comprises: a rotatable sleeve positioned opposite the image carrier downstream of the development position where the electrostatic latent image formed on the image carrier is developed, and upstream of the transfer position where the toner image carried on the image carrier is transferred to the transfer member, with respect to the rotation direction of the image carrier; and a non-rotating magnet positioned inside the sleeve. A voltage application unit that applies a voltage including an AC voltage to the sleeve, A control unit controls the voltage application unit to apply a first bias to the sleeve when performing an image forming operation, and to apply a second bias different from the first bias to the sleeve in a predetermined mode when not forming an image. A charge-applying member is positioned downstream of the development position and upstream of the position where the image carrier is closest to the sleeve, with respect to the rotational direction of the image carrier, and applies an electric charge to the toner on the image carrier. An image forming apparatus characterized by comprising the following:

8. The charge-applying member is a corona charger, The corona charger is positioned downstream of the development position and upstream of the position where the image carrier is closest to the sleeve, with respect to the rotational direction of the image carrier. The image forming apparatus according to feature 7.

Images