Image forming apparatus and method for recovering transfer residual toner

Abstract

To provide an image forming apparatus that can satisfactorily recover a transfer residual toner with developing means.SOLUTION: An image forming apparatus has an image carrier, an electrifying member, developing means, transfer means, transfer voltage application means, and a control unit, and recovers, with the developing means, a transfer residual toner remaining on the image carrier after transfer. The control unit controls the transfer voltage application means so that a transfer current in a non-transfer period has the same polarity as that and a current value with a different absolute value from that of the transfer current in a transfer period, or the transfer current in the non-transfer period becomes zero, and so as to, in recovering the transfer residual toner with the developing means, adjust the amount of charge of the transfer residual toner, after passing through an electrification position in the direction of rotation of the image carrier and before passing through a developing position, to be -30 μC / g or more and -25 μC / g or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus and a method for recovering transfer residual toner. [Background technology]

[0002] In an electrophotographic image forming apparatus, a photosensitive member (image carrier) is charged by a charging member such as a charging roller, toner is supplied to the photosensitive member by a developing means, and the toner on the photosensitive member is transferred to a recording medium or an intermediate transfer member.

[0003] In the prior art, for example, toner adhering to a photosensitive member is removed by a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of the device, a so-called cleanerless system has been proposed, which does not include a cleaning means dedicated to cleaning the photosensitive member.

[0004] In a known cleaner-less image forming apparatus, residual toner remaining on the photosensitive drum after transfer is collected by a developing unit. In such a cleaner-less image forming apparatus, residual toner is collected by the developing unit and reused, thereby reducing waste toner. This simplifies user maintenance and eliminates the need for a waste toner container, thereby reducing waste.

[0005] For example, the following methods are known for cleanerless image forming apparatuses. One method is to recover residual toner by increasing the voltage (charging bias) applied to the charging member to widen the range of the background potential (the potential difference between the potential of the charging member and the potential of the photosensitive member). Another method is to use the potential difference between the charging bias and the surface potential of the photosensitive member to expel toner adhering to the charging member onto the photosensitive member and recover it with a developing means.

[0006] However, if the recovery by the developing means is insufficient, the residual toner that was not recovered by the developing means will remain on the photosensitive drum and will be transferred onto the paper when it is sent to the transfer position again, appearing as a residual transfer ghost. This type of problem is also called retransfer. For example, the following proposals have been made to address this problem.

[0007] Patent Document 1 discloses an image forming apparatus in which toner remaining on a photosensitive member after transfer is collected into a developing means in a developing unit. In Patent Document 1, the amount of exposure by a pre-transfer exposure means is changed so that the potential difference between the non-image portion and the image portion of the electrostatic image on the photosensitive member when passing through the transfer unit satisfies a predetermined relationship. According to Patent Document 1, it is possible to effectively collect the residual toner after transfer in the developing unit and to effectively transfer the toner image to a recording material in the transfer unit.

[0008] Patent Document 2 discloses a tandem-type color image forming apparatus or the like equipped with multiple contact-charging, cleanerless image forming units. In Patent Document 2, the timing of the discharge of transfer residual developer from the image carriers of the multiple image forming units to the recording material carrier or intermediate transfer body is controlled to prevent the discharged developer from overlapping on the recording material carrier or intermediate transfer body. This makes it possible to prevent re-transfer caused by a large amount of developer discharged at once being sent to the transfer unit of the downstream image forming unit. Summary of the Invention [Problem to be solved by the invention]

[0009] However, in conventional technologies, there is a need to improve the recovery of transfer residual toner by the developing unit. For example, if the charging ability of the toner is reduced due to usage conditions, the charge amount of the transfer residual toner before passing through the charging member may be small, and as a result, the charge amount of the transfer residual toner after passing through the charging member may not be fully increased. In addition, even if the voltage applied to the transfer member is set high in terms of transfer efficiency or the margin for abnormal images, the charge amount of the transfer residual toner after passing through the charging member may not be fully increased. If the charge amount of the transfer residual toner after passing through the charging member is not fully increased, even if the background potential is set high, the recovery ability of the developing unit decreases, and re-transfer may occur.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can effectively collect residual toner after transfer by a developing unit. [Means for solving the problem]

[0011] In order to solve the above problems, the image forming apparatus of the present invention comprises: a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; an image forming apparatus in which residual toner remaining on the image carrier after the transfer is collected by the developing means, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control unit controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period becomes zero, and controls the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be -30 μC / g or more and -25 μC / g or less. It is characterized by: [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an image forming apparatus that can effectively collect residual toner after transfer by the developing means. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram illustrating an embodiment of an image forming apparatus of the present invention. [Figure 2] 1A and 1B are block diagrams illustrating an example of the hardware configuration of a control unit. [Figure 3] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 4] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 5A] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 5B] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 6A] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 6B] FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 7] 10A and 10B are diagrams illustrating an example of transfer current, charge amount after passing through a charging station, and occurrence of re-transfer. [Figure 8] 1 is an image chart used for evaluation of the experiment. [Figure 9] 1 is an example of a timing chart. [Figure 10] 10 is an example of the evaluation results of retransfer. [Figure 11] 10 is another example of a timing chart. [Figure 12] FIG. 10 is a diagram illustrating an example of a table according to the second embodiment. [Figure 13] FIG. 10 is a schematic diagram for explaining a third embodiment. [Figure 14] FIG. 10 is a schematic diagram for explaining a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] The image forming apparatus and the method for recovering residual toner according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and other modifications, additions, corrections, deletions, and other changes can be made within the scope of what a person skilled in the art can conceive. Any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0015] (First embodiment) The image forming apparatus of this embodiment includes: a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; an image forming apparatus in which residual toner remaining on the image carrier after the transfer is collected by the developing means, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control unit controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period becomes zero, and controls the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be -30 μC / g or more and -25 μC / g or less. It is characterized by:

[0016] The image forming apparatus may be called an electrophotographic apparatus, a printing apparatus, a printer, etc. The image forming apparatus of the present invention may be a cleanerless image forming apparatus. The cleanerless system may be called a cleanerless system, a cleanerless imaging system, etc.

[0017] The method for recovering residual toner after transfer according to this embodiment includes the steps of: a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; and a method for recovering transfer residual toner, the method being performed by an image forming apparatus having the image forming apparatus and causing the developing unit to recover transfer residual toner remaining on the image carrier after transfer, the method comprising: a control step, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control step controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period is zero, and adjusts the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be −30 μC / g or more and −25 μC / g or less. It is characterized by:

[0018] Next, a cleanerless image forming apparatus used in the present invention will be described with reference to the drawings. In the following description, a charging roller is used as an example of a charging member. The developing means has, for example, a developing roller, and the following description will be made using the developing roller. A photosensitive body or a photosensitive drum is used as an example of an image carrier. Although paper or recording paper is used as an example of a transfer medium, other intermediate transfer bodies (e.g., intermediate transfer belts) can also be used as the transfer medium.

[0019] 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. As shown in the figure, a printer as an example of an image forming apparatus according to the present embodiment includes a paper feed unit 4, a pair of registration rollers 6, a photosensitive drum 10 as an image carrier, a transfer roller 62, a fixing device 12, etc.

[0020] The image forming apparatus also includes a charging power supply 21 for supplying a bias voltage required for image formation, a developing power supply 22, a cleaning power supply 23, a transfer power supply 24, and the like, and the outputs of these power supplies are controlled by a control unit 25.

[0021] The charging power supply 21 is an example of a charging voltage application means, and applies a voltage to the charging roller 160. The charging roller 160 is an example of a charging member. The voltage applied to the charging roller 160 may be referred to as a charging bias voltage or the like. The developing power supply 22 is an example of a developing voltage application means, and applies a voltage to the developing means. The developing device 61 is an example of a developing means, and has, for example, a developing roller 72. The developing roller 72 is an example of a developing member. Although the developing power supply 22 is described as applying a voltage to the developing means, the developing power supply 22 may also apply a voltage to the developing roller 72. The voltage applied to the developing roller 72 may be referred to as a developing bias voltage or the like. The transfer power supply 24 is an example of a transfer voltage application means, and applies a voltage to the transfer roller 62. The transfer roller 62 is an example of a transfer member, and a voltage is applied to the transfer roller 62 to perform transfer. The voltage applied to the transfer roller 62 may be referred to as a transfer bias voltage or the like.

[0022] The paper feed means 4 includes a paper feed tray 14 in which recording paper 105 as recording paper is stored in a stacked state, and a paper feed roller 15 that separates and feeds the recording paper 105 stored in the paper feed tray 14 one by one, starting from the top one. Recording paper is an example of a transfer object, and may also be called a recording medium, recording material, medium, etc.

[0023] The recording paper 105 sent out by the paper feed roller 15 is stopped once by the pair of resist rollers 6, and any misalignment is corrected.Then, the recording paper 105 is sent to the transfer area N3 (which may also be called the transfer position) by the pair of resist rollers 6 at a timing synchronized with the rotation of the photosensitive drum 10, that is, at a timing when the leading edge of the toner image formed on the photosensitive drum 10 coincides with a predetermined position of the leading edge of the recording paper 105 in the transport direction.

[0024] Around the photosensitive drum 10, in the rotational direction indicated by the arrow, there are arranged a charging roller 160 as charging means, a developing device 61 equipped with a developing roller 72, and a transfer roller 62. Of these, the charging roller 160 and the developing roller 72 are provided in contact with the photosensitive drum 10. In addition, a collecting brush 161 (which may also be called a brush roller, cleaning brush, cleaning member, etc.) is provided in contact with the charging roller 160. The collecting brush 161 is an example of collecting means.

[0025] The charging roller 160 may or may not be in contact with the photosensitive drum 10. The charging roller 160 is preferably provided so as to be in contact with the photosensitive drum 10. In this case, the discharge process (pre-charging discharge) can be stably and easily performed.

[0026] Between the charging roller 160 and the developing device 61, the exposure means 5 irradiates the surface of the photosensitive drum 10 with exposure light Lb, causing it to be scanned.

[0027] When the photosensitive drum 10 begins to rotate, a charging bias voltage is applied to the charging roller 160 from the charging power source 21, uniformly charging the photosensitive surface in a charging region N1 (which may also be referred to as a transfer position). Based on image information, exposure light Lb is irradiated onto the surface of the photosensitive drum 10 from the exposure means 5, and an electrostatic latent image is formed by discharging the portion of the photosensitive surface corresponding to the image to be created. This electrostatic latent image moves to a development region N2 (which may also be referred to as a development position) as the photosensitive drum 10 rotates, and at this time a development bias voltage is applied from the development power source 22 to the development roller 72 provided in the development device 61.

[0028] In development area N2, the negatively charged toner held on the development roller is supplied from development roller 72 to photosensitive drum 10 in accordance with the potential difference between the potential of the exposed area and the development bias voltage, forming a toner image on photosensitive drum 10. The toner image formed on photosensitive drum 10 moves to transfer area N3 at a predetermined timing. At this time, a transfer bias voltage is applied to transfer roller 62 from transfer power supply 24, and the toner image is transferred onto recording paper 105 that has entered transfer area N3.

[0029] The transfer bias voltage (also referred to as transfer bias) is determined by the control unit 25. The control unit 25 adjusts the transfer bias voltage using information from, for example, a sensor, a timer, a driving unit, and the like.

[0030] The recording paper 105 bearing the toner image is transported toward the fixing device 12, where it is fixed, and then discharged and stacked on a paper output tray. Residual toner that was not transferred to the recording paper 105 in the transfer area N3 and remains on the photosensitive drum 10 reaches the charging area N1 as the photosensitive drum 10 rotates. In the charging area N1, the residual toner is charged to a negative polarity by a minute discharge of the charging bias voltage applied to the charging roller 160, and is returned to the development area N2.

[0031] In the developing area N2, the transfer residual toner moves onto the developing roller 72 and is collected into the developing device 61 according to the potential difference between the potential of the non-exposed portion, ie, the portion not exposed by the exposure means 5, and the developing bias voltage.

[0032] In the charging region N1, it is difficult to charge the transfer residual toner completely to a negative polarity, and positive toner ends up adhering to the charging roller 160. For this reason, it is preferable to use a recovery brush 161 to scrape off dirt from the charging roller 160. A cleaning bias voltage is applied to the recovery brush 161 from the cleaning power supply 23, and the positive toner adhering to the charging roller 160 is cleaned by the potential difference and mechanical scraping. By using the recovery brush 161, the charging roller 160 can be made even cleaner.

[0033] FIG. 2A is a block diagram illustrating the hardware configuration of the control unit 25 in this embodiment. The control unit 25 includes, for example, a CPU, which is a central element for performing calculations, and memories such as ROM and RAM, which are memory elements (storage units). The RAM stores sensor detection results and calculation results, and the ROM stores control programs and pre-calculated data tables. The control unit 25 controls, for example, the charging power supply 21, the developing power supply 22, the cleaning power supply 23, the transfer power supply 24, and the exposure unit 5. The control unit 25 controls the ON / OFF and output value of each power supply output. The control unit 25 controls the static elimination lamp 64 (static elimination unit), for example, to eliminate static electricity from the photosensitive drum 10 during pre-charging discharge.

[0034] FIG. 2B is a block diagram showing an example of the hardware configuration of the control unit 25.

[0035] The control unit 25 includes a CPU (Central Processing Unit) 110, a RAM (Random Access Memory) 111, a ROM (Read Only Memory) 112, and a storage unit 113, which are connected via a bus 117.

[0036] The CPU 110 is a computing unit that controls the overall operation of the image forming apparatus 100. The RAM 111 is a volatile storage medium that allows high-speed reading and writing of information. When the CPU 110 processes information, the RAM 111 is used as a working area for the CPU 110. The ROM 112 is a read-only nonvolatile storage medium that stores programs such as firmware.

[0037] The storage unit 113 is a non-volatile storage medium that can read and write information, and stores an OS (Operating System), various control programs, application programs, etc. The storage unit 113 is, for example, an SSD (Solid State Drive) or an HDD (Hard Disk Drive).

[0038] Furthermore, a timer 114, a sensor 115, and a drive unit 116 are connected to the CPU 110 and the like via a bus 117. The timer 114 is hardware that counts various times, such as the drive time for driving the drive unit, etc. However, the timer 114 is not limited to this, and may be software. The sensor 115 is, for example, a temperature and humidity sensor, and is used to determine the absolute humidity inside or outside the image forming apparatus. The driving unit 116 is, for example, a driving source for driving the developing member, and may be, for example, a motor, a clutch, or the like.

[0039] Using the CPU 110, timer 114, sensor 115, drive unit 116, etc., the control unit 25 can determine the absolute humidity inside or outside the image forming apparatus, the integrated development drive amount obtained by integrating the drive amount of the development member from the start to the end of drive of the development member, and the integrated number of transfers obtained by integrating the number of transfers. The integrated development drive amount may also be referred to as the travel distance, etc. The integrated number of transfers may also be referred to as the number of sheets of paper passed, etc., and can be counted by the control unit 25. These values ​​determined by the control unit 25 are used, for example, to adjust the transfer bias.

[0040] In the image forming apparatus of this embodiment, residual toner remaining on the image carrier is collected by a developing unit. The image forming apparatus of this embodiment is configured without using a cleaning unit (e.g., a cleaning blade) for cleaning the image carrier (also called an electrostatic latent image carrier, photosensitive member, etc.). This has the advantage of allowing for a more compact apparatus.

[0041] Hereinafter, a system that does not use a cleaning device for cleaning the image carrier may also be referred to as a cleanerless system. However, a system that includes a device for cleaning the charging member or a device for cleaning the intermediate transfer belt may also be included in the cleanerless system. Furthermore, a system that includes a device for temporarily collecting residual toner remaining on the image carrier is also included in the cleanerless system.

[0042] The basic configuration and operation of a cleanerless image forming apparatus will be explained with reference to FIG. 3 is a diagram illustrating an example of a process for forming an image. As the charging member, for example, a charging roller can be used, and the following description will be given taking the charging roller as an example.

[0043] First, the charging roller 160 uniformly charges the photosensitive drum 10, which serves as an image carrier. The charging roller 160 in this example is disposed so as to contact the photosensitive drum 10, and applies, for example, a DC voltage to the photosensitive drum 10. Charging in this example is performed using a contact DC charging method. The exposure device 121 exposes the photosensitive drum 10 to exposure light L to form an electrostatic latent image on the photosensitive drum 10. The exposure device 121 is not particularly limited, but an LED, for example, is used.

[0044] The developing roller 72 is an example of a developer carrier provided in the developing device 61. A developing bias is applied to the developing roller 72 by an application means, and the developing roller 72 supplies the toner 200 to the photosensitive drum 10. As a result, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10. The developing device 61 may have, for example, an agitating roller 73, which agitates the toner within the developing device 61. The rotation direction of the agitating roller 73 can be selected appropriately, and the agitating roller 73 may or may not be in contact with the developing roller 72. The transfer roller 62 transfers the toner image on the photosensitive drum 10 onto the recording paper 105 . The static elimination lamp 64 eliminates the potential of the photosensitive drum 10. For example, static elimination is performed by irradiating the photosensitive drum with static elimination light QL.

[0045] The above-described configuration is the basic configuration of a cleanerless image forming apparatus, which does not include a cleaning device such as a cleaning brush for cleaning the photosensitive drum 10 after the transfer process.

[0046] 3, for example, −300 V is applied to the developing roller 72, and −1100 V is applied to the charging roller 160. For example, when the photosensitive drum 10 is neutralized, the surface potential becomes approximately −50 V, and when the photosensitive drum 10 is charged, the surface potential becomes approximately −500 V. The image forming apparatus of this embodiment may be provided with a collection brush 161 (collection means) that collects toner on the charging roller 160. In the example shown in Fig. 3, the collection brush 161 is not provided, and is therefore indicated by a dashed line in the drawing.

[0047] Here, an example of the flow of toner will be described in the example shown in Fig. 3. For the sake of explanation, the reference symbols of toner in the figure are changed depending on the position and state of the toner. The developing roller 72 carries toner 200, and the toner 200 carried by the developing roller 72 is supplied to the photosensitive drum 10. The toner supplied to the photosensitive drum 10 forms a toner image (visible image) in accordance with the electrostatic latent image (toner 201). The toner 201 on the photosensitive drum 10 is transferred to the recording paper 105. The toner 202 transferred to the recording paper 105 is fixed to the recording paper 105 in a later process.

[0048] Toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. After the charge removal process, the transfer residual toner 203 adheres to the charging roller 160 at (or near) the contact point between the photosensitive drum 10 and the charging roller 160. Among the transfer residual toner 203, there is also toner 206 that does not adhere to the charging roller 160, and this toner 206 remains on the photosensitive drum 10. This toner 206 is collected by the developing roller 72.

[0049] Next, an example of a method for collecting residual toner after transfer in a cleaner-less image forming apparatus will be described with reference to FIGS. 4, 5A, and 5B. Figure 4 is a schematic diagram for explaining the state after Figure 3, and is a diagram that schematically shows the state during printing. "During printing" here means the state in which the device is operating, and includes not only the process of transferring toner to recording paper, but also the process of preparing to transfer toner to recording paper (exposure and development). Figure 4 is a diagram that explains the process that is performed between transfer to the previous recording paper and transfer to the next recording paper.

[0050] As explained in FIG. 3, toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. In FIG. 4, transfer residual toner 203 is shown remaining on the photosensitive drum 10 downstream of the transfer roller 62. After transfer to the previous recording paper 105, the surface of the photosensitive drum 10 is neutralized by the neutralization lamp 64. This increases the potential difference between the charging roller 160 and the photosensitive drum 10, causing discharge between the charging roller 160 and the photosensitive drum 10 before charging. The discharge is shown schematically in the figure.

[0051] Due to the discharge before charging, the transfer residual toner 203 is negatively charged (not shown in FIG. 4). Due to the discharge before charging, some of the transfer residual toner 203 is negatively charged, while some remains slightly positively charged. The transfer residual toner 203 that remains slightly positively charged adheres to the charging roller 160 at (or near) the point where the charging roller 160 and the photosensitive drum 10 come into contact. The toner that adheres to the charging roller 160 is shown as toner 204.

[0052] The arrow a in the figure schematically illustrates the transfer residual toner 203 on the photosensitive drum 10 adhering to the charging roller 160. The adhesion of the transfer residual toner 203 on the photosensitive drum 10 to the charging roller 160 may also be referred to as movement or the like.

[0053] The image forming apparatus of this example has a collection brush 161 that collects toner adhering to the charging roller 160. Positive toner 204 adhering to the charging roller 160 is collected by the collection brush 161. Arrow b in the figure schematically illustrates the toner 204 on the charging roller 160 being collected by the collection brush 161. The collection of toner 204 on the charging roller 160 by the collection brush 161 may also be referred to as movement, etc. A collection bias is applied to the collection brush 161. The value of the collection bias is not particularly limited and can be selected as appropriate.

[0054] Of the transfer residual toner 203 on the photosensitive drum 10, negatively charged toner does not adhere to the charging roller 160 and remains on the photosensitive drum 10. This toner is illustrated as toner 206. Note that both the toner 203 and the toner 206 are transfer residual toner.

[0055] Toner 206 remaining on the photosensitive drum 10 is collected by the developing roller 72. The toner collected by the developing roller 72 is illustrated as toner 208. The act of being collected by the developing roller 72 may also be referred to as "moving." The toner 206 passing between the photosensitive drum 10 and the developing roller 72 moves toward the developing roller 72 due to the potential difference between the photosensitive drum 10 and the developing roller 72. The arrow c in the figure schematically illustrates the toner 206 on the photosensitive drum 10 being collected by the developing roller 72.

[0056] To recover the toner with the developing roller 72 as described above, for example, the potential of each component can be adjusted. One example is to set the surface of the photosensitive drum 10 after neutralization to -50 V, the charging roller 160 to -1100 V, the recovery brush 161 to -1300 V, the surface of the photosensitive drum 10 after charging to -500 V, and the developing roller 72 to -300 V. While the potentials are shown in FIG. 4 as an example, they are not limited to this.

[0057] In the image forming apparatus of the present invention, it is preferable to have the collection brush 161, but the collection brush 161 is not essential. If the image forming apparatus does not have a collection means (for example, the collection brush 161) for collecting toner present on the charging roller 160, it is preferable to adjust the potential so as to reduce the amount of toner that moves to the charging roller 160.

[0058] Next, an example of the movement of toner when the device is shut down and toner recovery will be described with reference to Figures 5A and 5B. As explained in Figure 4, the positive residual toner 203 (as well as toner 206) that did not become negative during discharge before charging adheres to the charging roller 160 and is recovered by the recovery brush 161. Since this recovery is repeated during printing, positively charged toner 207 accumulates on the recovery brush 161.

[0059] When the device is shut down, the potential difference between the collection brush 161 and the charging roller 160 is adjusted to move a small amount of positively charged toner 207 toward the charging roller 160. This is indicated by the arrow d in the figure.

[0060] The toner 205 that has moved to the charging roller 160 moves to the photosensitive drum 10 due to the potential difference between the charging roller 160 and the photosensitive drum 10. This is indicated by the arrow e in the figure. This moved toner is indicated as toner 209 in the figure. Note that when the device is shut down, the photosensitive drum 10 is not neutralized by the neutralization lamp 64, and the potential difference between the charging roller 160 and the photosensitive drum 10 is adjusted taking this into consideration.

[0061] The positively charged toner 209 on the photosensitive drum 10 is not collected by the developing roller 72, but passes through the developing roller 72. The toner 209 then passes through the transfer roller 62. In this way, when the device is shut down, the positively charged toner 209 remains on the photosensitive drum 10.

[0062] 4, 5A, and 5B, toner particles 203, 206, and 209 are shown on the photosensitive drum 10. All of these are considered to be transfer residual toner. Toner particle 209 is transfer residual toner particle 203 that has been collected by collection brush 161 and then moved back onto the photosensitive drum 10, and this toner may also be included in the transfer residual toner.

[0063] To move the toner as shown in the example of Fig. 5A, for example, the potential of each component can be adjusted. For example, the potential of the collection brush 161 can be set to -150V, the potential of the charging roller 160 to -350V, the potential of the surface of the photosensitive drum 10 to 500V, and the potential of the developing roller 72 to +250V. While Fig. 5A illustrates the potentials as an example, the present invention is not limited to this.

[0064] Next, the recovery of toner from the photosensitive drum 10 during device shutdown will be described with reference to FIG. 5B. FIG. 5B is a continuation of FIG. 5A. As shown, the photosensitive drum 10 is neutralized by the neutralization lamp 64 at a predetermined timing. By performing neutralization, the potential difference between the charging roller 160 and the photosensitive drum 10 increases, causing discharge between the charging roller 160 and the photosensitive drum 10. The figure shows the discharge diagrammatically. Note that the neutralization shown is not for image formation, but for toner recovery.

[0065] Due to the above-described discharge, the toner 209 becomes negatively charged. As in Fig. 4, the toner 209 that is not negatively charged and remains positively charged adheres to the charging roller 160 and is collected by the collection brush 161 (arrows g and h in the figure).

[0066] The toner 209, which has been negatively charged by the above-described discharge, does not move to the charging roller 160 but remains on the photosensitive drum 10. The negatively charged toner 209 is then collected by the developing roller 72 to which a developing bias is applied (arrow i in the figure). The toner collected by the developing roller 72 is shown as toner 208 in the figure.

[0067] To move the toner as shown in the example of Fig. 5B, for example, the potential of each component can be adjusted. For example, the potential of the collection brush 161 can be set to -1300V, the potential of the charging roller 160 can be set to -1100V, the surface of the photosensitive drum 10 after static elimination can be set to -50V, the potential of the surface of the photosensitive drum 10 can be set to 500V, and the potential of the developing roller 72 can be set to -300V. While Fig. 5B illustrates the potentials as an example, the present invention is not limited to this.

[0068] The static elimination lamp 64 is an example of a static eliminator. The static eliminator may also be called static eliminator.

[0069] 6A and 6B are other schematic diagrams illustrating the image forming apparatus of this embodiment. Descriptions of matters similar to those in the above example will be omitted. 6A is a schematic diagram for explaining an example of charging, exposure, development, and transfer. As shown in the figure, charging roller 160 charges photosensitive drum 10. Photosensitive drum 10 is exposed to exposure light L. Development roller 72 supplies toner to photosensitive drum 10. Transfer roller 62 performs transfer onto recording paper 105.

[0070] FIG. 6B is a schematic diagram for explaining an example of collection of transfer residual toner by the developing unit. Discharge (pre-charge discharge) is generated between the charging roller 160 and the photosensitive drum 10, and the transfer residual toner is charged to a negative polarity (normal polarity). The negatively charged transfer residual toner is collected by the developing roller 72 due to the background potential (potential difference between VB and VD). In other words, the collection of transfer residual toner by the developing means is achieved by the background potential causing the normally charged toner to move from the photosensitive drum 10 to the developing roller 72. In the cleanerless system, after the normal image formation process, the normal charge polarity of the transfer residual toner is utilized to collect it by the developing means due to the background potential. It should be noted that VB is the voltage applied to the developing roller 72 (also referred to as the developing bias or the developing bias voltage), and VD is the surface potential of the photosensitive drum 10 after passing through the charging roller 160.

[0071] Next, the characteristic features of this embodiment will be further described. The inventors focused on the relationship between the photosensitive drum 10 and the transfer roller 62 and conducted extensive research into the voltage (transfer bias) applied to the transfer roller 62 and the transfer current flowing through the transfer roller 62. During the research, they also focused on the transfer period when the transfer member transfers the toner image to the transfer recipient, and the non-transfer period when the transfer member does not transfer the toner image to the transfer recipient. They also focused on the behavior of the residual toner during the transfer period, the relationship between the transfer roller 62 and the photosensitive drum 10 during the non-transfer period, pre-charge discharge, the behavior of the residual toner, etc.

[0072] It has been discovered that during the transfer period, residual toner can be minimized by adjusting the voltage applied to the transfer roller 62 and setting an appropriate transfer current. In this regard, control may be performed to set an appropriate transfer current based on, for example, the usage situation, and a detailed example of using the usage situation will be described later.

[0073] Furthermore, during the non-transfer period, there is no transfer object between the transfer roller 62 and the photosensitive drum 10, so the voltage applied to the transfer roller 62 affects the surface potential of the photosensitive drum 10. The surface potential of the photosensitive drum 10 after passing the transfer position affects the discharge between the photosensitive drum 10 and the charging roller 160 and the charge amount of the residual toner after passing the charging position. Retransfer can be suppressed by adjusting the transfer current during the non-transfer period to prevent a decrease in the normal charge of the toner. For example, if the transfer current during the non-transfer period is lower than that during the transfer period, it is expected that retransfer can be further suppressed.

[0074] One possible method is to increase the potential difference between the surface potential of the photosensitive drum and the voltage applied to the developing roller to ensure sufficient background potential when the developing roller collects the toner. However, if the toner's charging ability is reduced due to usage conditions such as a high humidity environment or long-term use, the amount of charge on the transfer residual toner before it passes through the charging member may be small, and as a result, the amount of charge on the transfer residual toner after it passes through the charging member may not be sufficient. If the amount of charge on the transfer residual toner after it passes through the charging member is not sufficient, even if the background potential is set high, the collection ability by the developing unit may be reduced, resulting in re-transfer.

[0075] Another possible method is to switch between the transfer current flowing through the transfer member during the transfer period and the transfer current flowing through the transfer member during the non-transfer period. The transfer current can be determined, for example, by the amount of toner expelled from the charging member, but because the optimal transfer current differs depending on the usage conditions, there is a possibility that re-transfer may occur if the transfer current is determined solely by the amount of toner expelled.

[0076] The inventors have further investigated and found that the recovery ability by the developing means varies depending on the charge amount of the transfer residual toner that has passed through the charging position where the image carrier is charged by the charging member. Therefore, in this embodiment, the transfer voltage application means is controlled to switch between the transfer current during the transfer period and the transfer current during the non-transfer period, and the charge amount of the transfer residual toner after passing through the charging position is set to a target value.

[0077] This allows the developing unit to efficiently collect the residual toner after transfer, thereby suppressing re-transfer. In a preferred embodiment of the present invention, control is performed in accordance with the usage conditions, thereby further improving the collection of the residual toner after transfer by the developing unit.

[0078] In this embodiment, the position where the image carrier and the charging member face each other is referred to as the charging position, the position where the image carrier and the developing member face each other is referred to as the developing position, the current flowing through the transfer member is referred to as the transfer current, the period during which the transfer member transfers the toner image to the transferee is referred to as the transfer period, and the period during which the transfer member does not transfer the toner image to the transferee is referred to as the non-transfer period. Furthermore, unless otherwise specified, "after passing through the charging position" refers to the period after the image carrier has passed through the charging position in the rotational direction and before passing through the developing position.

[0079] The features of this embodiment will be further described with reference to FIG. 7. FIG. 7 shows experimental results illustrating an example of the relationship between transfer current and the amount of charge on the toner after passing through the charging device. In the figure, the horizontal axis represents the transfer current (μA), and the vertical axis represents the amount of charge on the toner after passing through the charging device (μC / g). The experiment shown in FIG. 7 was conducted in an environment of 23°C and 50% humidity.

[0080] The charge amount (or charge quantity) of the toner after passing through the charging device is measured using a suction-type toner charge amount measuring device. The photosensitive drum 10 is stopped, and the toner on the photosensitive drum 10 is sucked from the nozzle by a pump, and the charge amount of the toner collected in a Faraday cage equipped with a filter inside the nozzle is measured.

[0081] The transfer current is determined by measuring the current that flows between the transfer power supply 24 and the transfer roller 62 when a transfer bias voltage is applied. Since the transfer current and the transfer bias are correlated, the control unit controls the voltage (transfer bias) applied to the transfer member to be lowered when the transfer current is to be lowered.

[0082] As shown in the figure, when the transfer current changes, the amount of charge on the toner after passing through the charging device changes, so by adjusting the transfer current, the amount of charge on the toner after passing through the charging device can be adjusted.

[0083] Next, the charging bias voltage Vc and the developing bias voltage Vb were set to predetermined values, and printing was performed while varying the transfer current, and retransfer was evaluated.

[0084] Figure 8 shows an example of an image chart used for evaluating retransfer. Reference numeral 300 denotes a solid patch, and reference numeral 301 denotes a frame placed for evaluating transfer residual ghosts. In this image chart, two 48 mm x 10 mm solid patches 300 are arranged near the center. Below the solid patches 300, two frames 301 for evaluating retransfer are arranged side by side at positions spaced apart by the length of one circumference of the photosensitive drum.

[0085] In Figure 7, the area where the toner charge amount after passing through the charging device is less than -30 μC / g (upper part of the page) is called Region 1. The area where the toner charge amount after passing through the charging device is less than -25 μC / g and greater than -30 μC / g (center of the page) is called Region 2. The area where the toner charge amount after passing through the charging device is greater than -25 μC / g (lower part of the page) is called Region 3.

[0086] In the experimental results shown in Figure 7, retransfer occurred in regions 1 and 3. In the area 1, the absolute value of the charge amount of the transfer residual toner after passing through the charging device was greater than 30 μC / g, and the electrostatic adhesion force was too strong, causing re-transfer. In region 3, the absolute value of the charge amount of the transfer residual toner after passing through the charging device is smaller than 25 μC / g, and the normal charge amount of the transfer residual toner is small, so the transfer residual toner is less likely to move to the developing means due to the background potential. This is why re-transfer occurs.

[0087] On the other hand, in region 2, where the absolute value of the toner charge amount after passing through the charging device is 25 μC / g to 30 μC / g, no retransfer occurred. In region 2, the electrostatic adhesion force between the transfer residual toner and the photosensitive drum 10 can be prevented from becoming too high, and the toner movement to the developing means due to the background potential can be prevented from becoming difficult. When the absolute value of the toner charge amount after passing through the charging device is 25 μC / g to 30 μC / g, it can be said that the normal charge polarity of the transfer residual toner can be maintained.

[0088] In this embodiment, to set the toner charge amount after passing through the charging circuit to -30 μC / g to -25 μC / g, the transfer current during the non-transfer period is switched while maintaining the positive and negative polarities of the transfer current during the transfer period and the non-transfer period, or the transfer current during the non-transfer period is switched to zero. That is, the control unit in this embodiment controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but a current value with a different absolute value, or so that the transfer current during the non-transfer period is zero. By controlling the transfer current during the non-transfer period and the transfer period to have the same polarity but different absolute current values, the toner charge amount before and after transfer can be adjusted and abnormal charging due to reverse polarity current can be prevented, making it easier for the toner charge amount after passing through the charger to be -30 μC / g to -25 μC / g. Also, by controlling the transfer current during the non-transfer period to be zero, it is possible to prevent a decrease in toner charge before and after transfer, making it easier for the toner charge amount after passing through the charger to be -30 μC / g to -25 μC / g.

[0089] When the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but a different absolute value, the magnitude relationship can be selected appropriately taking into account the purpose, regardless of which is larger. It is preferable to make the absolute value of the transfer current during the transfer period smaller than the absolute value of the transfer current during the non-transfer period. In other words, it is preferable that the control unit controls the transfer voltage application means so that the absolute value of the transfer current during the transfer period is smaller than the absolute value of the transfer current during the non-transfer period.

[0090] By reducing the absolute value of the transfer current during the transfer period, it is possible to further suppress retransfer. For example, in some cases, the transfer current during image formation is set low to prevent the occurrence of abnormal images such as image dust. In such cases, by increasing the absolute value of the transfer current during the non-transfer period, it is possible to optimize the toner charge amount after passing through the charging device. Furthermore, by reducing the absolute value of the transfer current during the transfer period, it becomes easier to maintain the normal charge polarity of the residual toner after passing through the charging device.

[0091] When performing such control, the value of the transfer current can be selected appropriately. For example, considering Figure 7, to achieve region 2, the transfer current during the non-transfer period is preferably approximately 10 to 16 μA. In this case, to avoid the occurrence of abnormal images such as image dust, the transfer current during the transfer period is preferably less than 10 μA. The lower limit of the transfer current in the region where an image is formed on the transfer medium or photosensitive drum (also referred to as the image area) is the lower limit of the output of the transfer power supply, so the lower limit of the transfer current during the transfer period is, for example, 5 μA. For these reasons, when the transfer current during the non-transfer period is approximately 10 to 16 μA, the transfer current during the transfer period is selected to be, for example, less than 10 μA, or, for example, 5 μA or more.

[0092] On the other hand, the absolute value of the transfer current during the non-transfer period may be smaller than the absolute value of the transfer current during the transfer period. For example, if the transfer current during the non-transfer period is set to 10 to 16 μA, the transfer current during the transfer period may be set to 26 μA, taking into account the possibility of abnormal images in the image area. When the transfer current during the transfer period is set to 26 μA, the charge amount of the transfer residual toner after passing through the charger is approximately −20 μC / g, as shown in FIG. 7b. In this embodiment, the charge amount of the transfer residual toner after passing through the charger during the non-transfer period only needs to be −30 to −25 μC / g, so the charge amount of the transfer residual toner after passing through the charger during the transfer period may deviate from −30 to −25 μC / g. A transfer current of 26 μA during the transfer period is also included in this embodiment, and setting the transfer current during the transfer period to 26 μA can avoid abnormal images such as toner lumps and white areas on the image, resulting in an acceptable retransfer image.

[0093] Considering Figure 7, the transfer current during the non-transfer period is preferably 10 μA or more and 16 μA or less to fall within region 2. In other words, the control unit preferably controls the transfer voltage application means so that the transfer current during the non-transfer period is 10 μA or more and 16 μA or less. By setting the transfer current within this range, it becomes easier to keep the charge amount of the residual toner after passing through the charging device within an optimal range, making it easier to prevent re-transfer.

[0094] In Figure 7, the range in which the transfer current during the non-transfer period is between 10 μA and 16 μA is indicated by "a." By keeping the transfer current during the non-transfer period within the range of "a," it becomes easier to keep the charge amount of the residual toner after passing through the charging device to between -30 and -25 μC / g.

[0095] Next, an example of a timing chart in this embodiment will be described. Fig. 9 is a timing chart of this example. In this example, recording paper will be used as an example of the transfer target.

[0096] First, at t1, (a) preparation for exposure begins, then at t3, (b) photoconductor drive begins and (f) application of development bias begins, and at t4, (d) application of charging bias and (e) charging brush bias begins. Photoconductor drive begins at t3 and is fully turned on at t6. t6 can also be said to be the point at which the start-up of photoconductor drive, charging, and development has finished.

[0097] At t6, when the photosensitive drum drive is turned on, (g) non-transfer is turned on and a transfer current is passed during the non-transfer period. As a control at this time, the control unit controls the transfer voltage application means so that a transfer current passes through the transfer roller 62 during the non-transfer period, and turns on the non-transfer transfer bias. In (g) of the figure, the ON state of the non-transfer transfer bias is indicated as "non-transfer ON," and the ON state of the transfer bias for transfer is indicated as "transfer ON."

[0098] When the recording paper is transported from the paper feed section and reaches the position of the registration roller pair 6, a sensor (registration sensor) near the registration roller pair 6 detects that the paper has reached just before the transfer position. At t8, (c) the registration sensor detection is turned ON.

[0099] When the leading edge of the recording paper enters the transfer position, at t9 the transfer current during the (g) non-transfer period is switched to the transfer current during the transfer period. This control is indicated by (g) Transfer ON in the diagram. This switching occurs after the (c) registration sensor detection turns ON (t8) and after the transfer switching time expressed by the following formula has elapsed. The linear velocity is the transport speed of the recording paper. Transfer switching time = distance from registration sensor position to transfer position / linear speed

[0100] In the figure, the transfer switching time is indicated by x. As shown in the figure, the period from t8 to t9 is represented by x. At t8, the leading edge of the recording paper is detected by the registration sensor, and at t9, the leading edge of the recording paper reaches the transfer position.

[0101] The transfer of the toner image to the recording paper begins at t9 and ends at t12. At t10, the detection of the (c) registration sensor is turned OFF. This means that the trailing edge of the recording paper has passed the registration sensor position. Therefore, the distance (time) from t10 to t12 is the transfer switching time (x in the diagram).

[0102] At t12, transfer ends, and the transfer current during the (g) transfer period is switched to the transfer current during the non-transfer period. The timing for switching the transfer current at t12 can be determined by the registration sensor detection, the distance from the registration sensor position to the transfer position, and the linear speed, just as with the formula for t9 above. In other words, at t10, the current is switched after the transfer switching time from when the registration sensor detection (c) turns OFF.

[0103] If there is no registration sensor, the ON / OFF state of the registration drive (driving the pair of registration rollers 6) can be used instead. The transfer current can be switched based on the ON / OFF state of the registration drive.

[0104] Similarly, transfer to the next recording paper is performed from t13 to t16, and then from t17 to t19 to the next recording paper. In other words, the next transfer period is from t13 to t16, and the next next transfer period is from t17 to t19. Similarly, the next non-transfer period is from t12 to t13, and the next next non-transfer period is from t16 to t17.

[0105] As shown in the timing chart of this example, the control unit controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a different absolute value. This control ensures that the charge amount of the residual toner after passing through the charging position is between -30 μC / g and -25 μC / g. In the timing chart of this example, the period from t12 to t13 is when the charge amount of the residual toner after passing through the charging position is between -30 μC / g and -25 μC / g. By keeping the charge amount of the residual toner after passing through the charging position within the above range during this period, the recovery of the residual toner by the developing means is improved. The same applies to t16 and t17.

[0106] In this example, the timing chart shows that the absolute value of the transfer current during the non-transfer period is smaller than the absolute value of the transfer current during the transfer period, but the present invention is not limited to this. The transfer voltage application means may be controlled so that the absolute value of the transfer current during the transfer period is smaller than the absolute value of the transfer current during the non-transfer period, and each has its own advantages.

[0107] Furthermore, while the timing chart in this example illustrates a case where the absolute value of the transfer current during the non-transfer period is not zero, the present invention is not limited to this. The transfer voltage application means may be controlled so that the transfer current during the non-transfer period is zero. In this case, the charge amount of the residual toner after passing through the charging device can also be kept within the above range. When the transfer voltage application means is controlled so that the transfer current during the non-transfer period is zero, the difference is that it is easier to maintain the charge of the toner charged by the developing device compared to when the transfer current is not zero. Whether or not to set the transfer current during the non-transfer period to zero can be determined taking into account the usage situation, purpose, etc.

[0108] As shown in the figure, the period from t3 to t7 corresponds to the print preparation (image formation startup) period, the period from t7 to t18 corresponds to the period from the start of paper feed to printing, and the period from t18 onwards corresponds to the print preparation (image formation shutdown) period. During the period from t7 to t18, (f) the developing roller bias is set to, for example, -200 V. During this period, toner is supplied from the developing roller 72 to the photosensitive drum 10, and residual toner after transfer is collected from the photosensitive drum 10 to the developing roller 72.

[0109] Next, an example of control of the charging member during the transfer period and the non-transfer period will be described. 1, the inventors evaluated re-transfer by changing the applied voltage Vc (charging bias) of the charging roller 160 and the applied voltage Vb (developing bias) of the developing roller 72. The image chart in FIG. 8 was used to evaluate re-transfer.

[0110] FIG. 10 shows the evaluation results. The horizontal axis is the charging bias Vc [V], and the vertical axis is the developing bias Vb [V]. In the evaluation, the transfer current was kept constant, and the charging bias and developing bias were changed. An evaluation chart was created by changing Vc and Vb, and the results were evaluated on a scale of 1 to 5. Rank 5 means a good result and is considered a pass. The evaluation criteria for ranks 1 to 5 are shown in the figure.

[0111] This example shows the results when evaluation was performed using development unit A. A development unit is an example of a development means. M / A means the amount of toner per unit area on the development roller, where M means the amount of toner (mg) and A means Area.

[0112] As shown in the figure, when Vb is the same, the larger the absolute value of Vc, the better the retransfer rank. In other words, the rank improves as you move to the left on the page. In other words, setting a higher absolute value for Vc improves the retransfer rank.

[0113] Although it is difficult to generalize because it depends on the usage environment and conditions, in this example, for example, when the development bias Vb is -200 V, it is preferable to set the absolute value of the charging bias Vc in the non-image area to -1100 V or higher, which can further suppress retransfer. However, if the absolute value of the charging bias Vc is set too high, the residual toner may be discharged due to the potential difference between the charging roller and the photosensitive drum and become excessively negatively charged. In this case, the electrostatic attraction force between the residual toner and the photosensitive drum becomes strong, making it difficult for the residual toner to move from the photosensitive drum, and the residual toner on the photosensitive drum may be retransferred without being collected by the developing means.

[0114] For these reasons, it is preferable that the increase in the charging bias Vc be within approximately 100 V. The blank spaces in the figure represent results in which the discharge is slightly inferior and the retransfer rank is slightly inferior to the pass level. The increase in this case refers to the range from the value at which the absolute value of the charging bias Vc is minimum when the retransfer rank is pass level 5 to the value at which the absolute value increases by 100 V.

[0115] Furthermore, it is preferable that the control unit controls the charging voltage application unit so that a voltage smaller in absolute value than the voltage applied to the charging member during the non-transfer period is applied to the charging member during a part of the transfer period. By controlling in this manner, a more optimal post-charging charge can be obtained, and the effect of suppressing re-transfer can be improved.

[0116] Fig. 11 is a timing chart for explaining an example of such control. t0 to t20 are shown in the same way as in Fig. 9, and t21 and t22 in Fig. 11 are additionally shown.

[0117] In this example, before the leading edge of the recording paper reaches the transfer position, the charging bias is switched to a charging bias (e.g., |-1100V|) that is smaller in absolute value than the charging bias (e.g., -1200V) applied during the non-transfer period. This switching of the charging bias is performed at t21, t12, and t16, and is performed after the charge switching time expressed by the following formula has elapsed since the (c) registration sensor detection turned ON (t8). The linear velocity is the transport speed of the recording paper. Charge switching time = (distance from registration sensor position to transfer position - distance from charging position to transfer position) / linear speed

[0118] In the figure, the charge switching time is indicated by y. As shown in the figure, the period from t8 to t21 is represented by y. At t8, the leading edge of the recording paper is detected by the registration sensor, and the charging bias is switched at t21 before the leading edge of the recording paper reaches the transfer position.

[0119] Also, before the trailing edge of the recording paper passes the transfer position, the charging bias is switched to the bias (for example, -1200 V) that is applied during the non-transfer period. That is, at t11, the charging bias is switched to -1200 V. Although the value of the charging bias is not shown from t11 to t12 in the figure, it is set to -1200 V from t11 to t12. The same is true from t15 to t16.

[0120] In this example, during a portion of the transfer period, a voltage (e.g., |-1100V|) having an absolute value smaller than the absolute value of the voltage (e.g., |-1200V|) applied to the transfer member during the non-transfer period is applied to the charging member. By doing so, a more optimal post-charging charge can be achieved, and the effect of suppressing re-transfer can be improved.

[0121] (Second embodiment) Next, an example of adjusting the transfer current will be described. Explanation of the same matters as those in the above embodiment will be omitted.

[0122] In the present invention, the transfer voltage application means is controlled to adjust the transfer current so that the charge amount of the transfer residual toner after passing through the charging device is between -30 μC / g and -25 μC / g. The range of the transfer current in which the charge amount of the transfer residual toner after passing through the charging device is between -30 μC / g and -25 μC / g may vary depending on the usage conditions, etc. Therefore, in this embodiment, the transfer current is appropriately adjusted depending on the usage conditions, etc. This makes it easier for the charge amount of the transfer residual toner after passing through the charging device to fall within the above range, further suppressing retransfer.

[0123] Examples of usage conditions include the cumulative development drive amount, the number of sheets passed (cumulative number of transfers), and the temperature and humidity environment. By adjusting the transfer current using one or more of these, retransfer can be further suppressed.

[0124] An example in which the integrated development drive amount is used will be described. The control unit preferably calculates an integrated development drive amount by integrating the drive amounts of the developing member, and adjusts the transfer current in the transfer period and / or the transfer current in the non-transfer period based on the integrated development drive amount. Since the charge of the toner changes over time even for the same transfer current, the transfer current is adjusted using the amount of development member used, which allows the charge amount of the transfer residual toner after passing through the charging device to be accurately kept within the above range even over time.

[0125] The integrated development drive amount is the integrated amount of drive (e.g., rotation) of the development member. The integrated development drive amount is obtained, for example, by counting the time during which the drive unit 116 is driven to rotate the development roller 72 using the timer 114. The integrated development drive amount may also be referred to as a travel distance, and is measured in units of mm, for example. The integrated development drive amount is obtained, for example, by calculating the distance from the time from development drive ON to development drive OFF, and adding this to the drive amount recorded in the control unit.

[0126] An example of a formula for calculating the integrated development drive amount is shown below: The linear speed in the formula is, for example, the rotational speed of the development roller 72. The unit of the linear speed is, for example, mm / sec. Accumulated development drive amount [mm] = Σ {(time from development drive ON to development drive OFF) × (linear speed)}

[0127] When the cumulative development drive amount is large, more foreign matter adheres to the development roller 72, increasing the resistance of the development roller 72. This increases the development bias Vb (V=IR) even if the voltage applied to the development roller 72 is the same before and after aging. Therefore, as the cumulative development drive amount increases over time, the background potential (|Vd-Vb|) decreases. Therefore, when the cumulative development drive amount is large, the control unit controls the transfer current to increase the surface potential Vd of the photosensitive drum 10 in order to suppress a decrease in the background potential, thereby reducing the amount of static electricity removed from the photosensitive drum 10 by the transfer roller 62. In other words, when the cumulative development drive amount is large, the control unit controls the transfer bias, for example, to decrease.

[0128] The following provides a supplementary explanation regarding the adjustment of the transfer current during the transfer period and / or the transfer current during the non-transfer period. When the control unit adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period, it may adjust both transfer currents, or it may adjust only one of the transfer currents. For example, both transfer currents are adjusted when an environmental change occurs or the transfer member deteriorates. In this case, the same adjustment is performed for the transfer period and the non-transfer period. For example, if the transfer current during the transfer period is increased, the transfer current during the non-transfer period is also increased. Furthermore, for example, if retransfer images and other abnormal images are to be avoided or the tolerance ratio for these images is to be changed, only one of the transfer currents is adjusted.

[0129] During the transfer period, the toner image is transferred to the transfer medium, so it is preferable to determine the transfer current in consideration of preventing retransfer and taking into account the basic image quality. During the non-transfer period, the toner image is not transferred to the transfer medium, so there is no need to consider image quality, and it is preferable to determine the transfer current so that re-transfer does not occur. The supplementary explanation given here also applies to the number of transfers and absolute humidity described below.

[0130] An example in which the number of sheets passed (cumulative number of transfers) is used will be described. It is preferable that the control unit adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period based on the total number of transfers obtained by accumulating the number of times transfers have been performed. As the number of transfers (cumulative number of transfers) increases with use over time, more foreign matter adheres to the transfer roller 62, causing the resistance of the transfer roller 62 to increase. Therefore, the control unit adjusts the transfer current, for example, to lower it (V=IR), in order to keep the transfer voltage constant. This allows the charge amount of the residual toner after passing through the charging device to be accurately kept within the above range even with long-term use. Because the transfer current and transfer bias are correlated, the control unit adjusts the transfer current to lower it as the cumulative number of transfers increases.

[0131] An example of a formula for calculating the cumulative number of transfers is shown below. Total number of transfers = Σ (number of transfers performed)

[0132] The cumulative number of transfers can be counted by the control unit 25. Transfer may be performed onto a recording medium such as paper, or onto an intermediate transfer body such as an intermediate transfer belt. The number of transfers refers to the number of transfers performed onto a transfer-receiving body. The cumulative number of transfers may be calculated for each transfer or for each job. If the transfer current is adjusted for each transfer, the cumulative number of transfers can be calculated for each transfer, and if the transfer current is adjusted for each job, the cumulative number of transfers can be calculated for each job. When calculating the cumulative number of transfers for each job, the above formula can be considered as follows: Total number of transfers = Σ (number of transfers performed in that job)

[0133] An example of using a temperature and humidity environment will be described. The control unit preferably adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period based on the temperature and absolute humidity inside or outside the image forming apparatus. Since the charge of the toner changes depending on the temperature and humidity environment even for the same transfer current, by adjusting the transfer current based on the temperature and humidity environment, the charge amount of the transfer residual toner after passing through the charging device can be accurately kept within the above range without being affected by changes in the temperature and humidity environment.

[0134] It is preferable to adjust the transfer current using two or more of the integrated development drive amount, the integrated number of transfers, the temperature, and the absolute humidity (temperature and humidity environment). An example of this case will be described below. The control unit preferably adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period based on two or more of the integrated development drive amount obtained by integrating the drive amount of the developing member, the integrated number of transfers obtained by integrating the number of transfers, and the temperature and absolute humidity inside or outside the image forming apparatus. In this case, the charge amount of the transfer residual toner after passing through the charging device can be accurately set within the above range. Note that temperature and absolute humidity are considered to be one condition of the temperature and humidity environment, and are preferably treated in the same way as the integrated development drive amount and the integrated number of transfers.

[0135] The control unit can calculate the temperature and absolute humidity inside or outside the image forming apparatus using, for example, sensor 115. The temperature and humidity may be obtained using separate sensors. The temperature and absolute humidity may also be referred to as the temperature and humidity environment.

[0136] The transfer current may be determined using a correction value. For example, when adjusting the transfer current using multiple values ​​from the cumulative development drive amount, cumulative transfer count, temperature, and absolute humidity, the control unit may determine the transfer current using one of these values ​​and adjust the transfer current using the remaining values. The transfer current determined using one of these values ​​is also referred to as the transfer current value, and the value used to correct the transfer current is also referred to as the transfer current correction value. The transfer current correction value may be expressed as, for example, a percentage. When performing such adjustments, the charge amount of the transfer residual toner after passing through the charging device can be accurately adjusted to the above range.

[0137] In particular, it is more preferable to adjust the transfer current using the cumulative number of transfers and the temperature and humidity environment. An example of using the cumulative number of transfers and absolute humidity will be described below. The control unit adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period, which are selected based on the temperature and absolute humidity inside or outside the image forming device, based on a current correction value selected based on the cumulative number of transfers, which is the cumulative number of times transfers have been performed. By adjusting in this way, the charge amount of the transfer residual toner after passing through the charging device can be set within the above range with good precision. An example of this case will be described later with reference to FIG.

[0138] It is preferable that the control unit sets a higher transfer current value as the temperature and absolute humidity increase, and sets a higher transfer current correction value as the cumulative number of transfers increases. By adjusting in this way, the charge amount of the transfer residual toner after passing through the charging device can be set within the above range with good precision. An example of this case will be described later with reference to FIG.

[0139] The transfer current value and transfer current correction value may be stored in advance as a table in a memory unit or the like, and the transfer current may be adjusted by referring to the table using the cumulative development drive amount, cumulative number of transfers, and temperature and humidity environment obtained by measurement.

[0140] FIG. 12 shows an example of a table used to determine the transfer current. This table is prepared in advance and stored in an arbitrary memory unit. (1) is the transfer current when the temperature and humidity environment (temperature and absolute humidity) is divided into three ranges, and (2) is the transfer current correction value [%] when the cumulative number of transfers is divided into three ranges. The cumulative number of transfers can be measured in units of, for example, times or sheets. There are no restrictions on how the ranges are divided.

[0141] For example, as in this example, the temperature and humidity environment is divided into three sections, and it is determined which section the temperature and absolute humidity measured by a sensor or the like fall into, and the transfer current for the corresponding section is set. For example, when the temperature is low and the absolute humidity is less than a, the transfer current is set to A [μA]. The same applies to room temperature and high temperature. The ranges of low temperature, room temperature, and high temperature in this example can be selected as appropriate. Also, while (1) in the figure shows the temperature and humidity environment, this is not limited to this, and the accumulated number of transfers or the accumulated development drive amount can also be used.

[0142] (2) in the figure is the transfer current correction value. For example, if the cumulative number of transfers is less than d, D [%] is used as the transfer current correction value. The transfer current correction value is applied to the transfer current determined in (1) in the figure, for example. For example, if the temperature is low, the absolute humidity is less than a, and the cumulative number of transfers is less than d, the selected transfer current value is A [μA] and the selected transfer current correction value is D [%]. In this case, the transfer current is adjusted to A [μA] × D [%]. Alternatively, for example, if the temperature is normal, the absolute humidity is between a and b, and the cumulative number of transfers exceeds e, the selected transfer current value is B [μA] and the selected transfer current correction value is F [%]. In this case, the transfer current is adjusted to B [μA] x F [%].

[0143] Furthermore, it is preferable that A, B, and C in (1) in the figure be set to increasing values ​​in that order. For example, it is preferable to adjust the transfer current to be larger as the temperature increases, and to adjust the transfer current to be larger as the absolute humidity increases. Furthermore, it is also possible to adjust the transfer current to be larger as the cumulative number of transfers increases, or to adjust the transfer current to be larger as the cumulative development drive amount increases.

[0144] Also, it is preferable to set D, E, and F in (2) of the figure to higher values ​​in that order. For example, it is preferable to adjust the transfer current correction value to be larger as the cumulative number of transfers increases. For example, D=100%, E=105%, and F=110%.

[0145] In this way, by using a predetermined table, the transfer current can be adjusted according to usage over time and the temperature and humidity environment, and the amount of charge on the residual toner after transfer can be optimized, thereby further suppressing retransfer.

[0146] Although the transfer period and non-transfer period are not shown in Fig. 12, tables such as those shown in Fig. 12 are defined for each of the transfer period and non-transfer period. The table for the transfer period and the table for the non-transfer period may be the same or different.

[0147] (Third embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. This embodiment uses a peeling roller. In this embodiment, the peeling roller reduces the adhesion of toner that has strongly adhered (fixed) to the photosensitive member. This allows the developing unit to effectively collect the residual toner after transfer. In addition, this embodiment can suppress filming on the photosensitive member.

[0148] 13 is a schematic diagram illustrating an example of an image forming apparatus of this embodiment, and is a diagram similar to FIG. 1. In this example, the peeling roller 165 is disposed in contact with the photosensitive drum 10. In this example, the peeling roller 165 is disposed downstream of the transfer roller 62 and upstream of the charging roller 160 in the rotation direction of the photosensitive drum 10. The peeling roller 165 is made of, for example, a silicone resin sponge.

[0149] In the present invention, it is possible to configure the device without using the static elimination lamp 64 (static elimination means), and this example is an example in which a static elimination lamp is not used.

[0150] In this example, for example, the difference in peripheral speed between the peeling roller 165 and the photosensitive drum 10 can peel the transfer residual toner from the photosensitive drum 10. The peeling roller 165 rubs against the surface of the photosensitive drum 10, thereby peeling the transfer residual toner from the surface of the photosensitive drum 10. Furthermore, a negative voltage is applied to the peeling roller 165 in this example. It is preferable that a voltage (negative) smaller than the absolute value of the voltage applied to the charging roller 160 is applied to the peeling roller 165 when the charge amount of the transfer residual toner after passing through the charging device is set to -30 μC / g or more and -25 μC / g or less.

[0151] By applying a voltage to the peeling roller 165 in this manner, the transfer residual toner peeled off by the peeling roller 165 is charged by the peeling roller 165 and re-adheres to the surface of the photosensitive drum 10. Then, the transfer residual toner, which has been negatively charged by the pre-charge discharge by the charging roller 160, is collected by the developing roller 72. The transfer residual toner is peeled off from the photosensitive drum 10 by the peeling roller 165 and re-adheres to the photosensitive drum 10 with weak adhesive force, making it easier for the developing roller 72 to collect the transfer residual toner. This makes it possible to suppress filming on the photosensitive drum 10.

[0152] In this way, in this example, the adhesion of toner that has strongly adhered (fixed) to the photosensitive drum 10 is reduced by the peeling roller 165. In this example, the peeling roller 165 can reduce the adhesion between the transfer residual toner and the surface of the photosensitive drum 10, making it easier to collect the transfer residual toner with the developing roller 72.

[0153] This embodiment will be described again. In this embodiment, a peeling roller is provided downstream of the position where the transfer member performs transfer in the rotation direction of the image carrier, and upstream of the charging position, and the peeling roller rotates in contact with the image carrier, peeling off the residual toner adhering to the surface of the image carrier by the difference in peripheral speed with the image carrier. By arranging the peeling roller in this manner, the adhesive force of the residual toner before pre-charge discharge can be reduced, and the residual toner can be easily peeled off by utilizing the difference in peripheral speed.

[0154] In this embodiment, it is preferable that a voltage smaller in absolute value than the voltage applied to the charging member is applied to the peeling roller. In this case, the adhesive force of the transfer residual toner that has re-adhered to the photosensitive drum 10 can be reduced.

[0155] (Fourth embodiment) Next, another embodiment of the present invention will be described, and a description of the same matters as those in the above embodiment will be omitted. In this embodiment, the charging member is of a non-contact charging type, and a temporary cleaning roller is provided on the photosensitive drum. The cleanerless system uses a developing roller to collect toner, and even if a temporary cleaning roller is used in addition to the development roller, it is still considered a cleanerless system.

[0156] Fig. 14 is a schematic diagram for explaining an example of an image forming apparatus according to this embodiment, and is a diagram similar to Fig. 1. In this example, a scorotron charger is used as the charging member. This charging member is shown as charger 163 in the figure. As shown in the figure, charger 163 is of a non-contact charging type.

[0157] Furthermore, a temporary cleaning roller 166 is provided downstream of the transfer roller 62 and upstream of the charger 163 in the rotation direction of the photosensitive drum 10. The temporary cleaning roller 166 is, for example, a brush roller.

[0158] A voltage, for example, a negative voltage, is applied to the temporary cleaning roller 166 by the cleaning power supply 23. In this case, the positively polarized transfer residual toner is temporarily stored on the temporary cleaning roller 166. "Stored" here means that the positively polarized transfer residual toner moves toward the temporary cleaning roller 166 and is held by the temporary cleaning roller 166. The transfer residual toner temporarily stored on the temporary cleaning roller 166 is toner charged with a polarity opposite to the normal charge. The normal charge is, for example, a negative polarity, and the toner charged with a polarity opposite to the normal charge is, for example, the positively polarized transfer residual toner as described above.

[0159] On the other hand, the negatively charged residual toner passes through the cleaning roller 166 temporarily, is injected with a negative charge by pre-charging discharge from the charging roller 160 , and is then collected by the developing roller 72 .

[0160] In this example, when a job is completed, a positive voltage is applied to the temporary cleaning roller 166. As a result, the potential difference between the temporary cleaning roller 166 and the photosensitive drum 10 causes the positively charged residual toner stored on the temporary cleaning roller 166 to move to the photosensitive drum 10. This movement is also called expulsion. The transferred residual toner is injected with a negative charge by pre-charge discharge using the charger 163, and is then collected by the developing roller 72. This allows the temporary cleaning roller 166 to be kept clean.

[0161] Furthermore, in this example, the temporary cleaning roller 166 is disposed upstream of the charger 163 in the rotation direction of the photosensitive drum 10. Therefore, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is immediately injected with a negative charge by the charger 163. In other words, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is injected with a negative charge by pre-charge discharge immediately after movement, so the distance that the photosensitive drum 10 must rotate before the negative charge is injected into the transfer residual toner by pre-charge discharge can be shortened.

[0162] In this example, the distance that the photosensitive drum 10 must rotate before negative charge is injected into the residual toner by pre-charge discharge can be made shorter than in the above embodiment (the embodiment using the collection brush 161). This makes it possible to slow down deterioration of the photosensitive drum 10 and extend the life of the photosensitive drum 10.

[0163] In the case of the configuration using the collection brush 161, the transfer residual toner held on the collection brush 161 moves from the collection brush 161 to the charging roller 160, passes the positions of the development roller 72 and the transfer roller 62, and then undergoes pre-charge discharge. Therefore, in this embodiment, the distance over which the photosensitive drum 10 rotates until the accumulated transfer residual toner undergoes pre-charge discharge can be shortened compared to the configuration using the collection brush 161. In the description here, the transfer residual toner temporarily accumulated on the cleaning roller 166 or the transfer residual toner accumulated on the collection brush 161 is referred to as accumulated transfer residual toner.

[0164] This embodiment will be described again. The charging member in this embodiment is a non-contact charging member that does not come into contact with the image carrier, and is located downstream of the position where the transfer means performs transfer in the rotation direction of the image carrier, and has a temporary collection means upstream of the charging position, and the temporary collection means temporarily collects transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier (for example, positive). The temporary collecting means is, for example, a temporary cleaning roller 166. By using a non-contact charging member, it is possible to prevent transfer residual toner from moving to the charging member and causing charging failure. By using the temporary collection means arranged as described above, it is possible to temporarily store transfer residual toner on the image carrier. Furthermore, when a non-contact charging member and temporary collection means are used, a collection means (e.g., collection brush 161) is not required, and the number of parts can be reduced.

[0165] In addition, the image forming apparatus of this embodiment has a cleaning voltage application means (e.g., cleaning power supply 23) that applies voltage to the temporary collection means, and the control unit controls the cleaning voltage application means at the end of image formation to move the transfer residual toner collected by the temporary collection means to the image carrier. By doing so, the transfer residual toner collected in the temporary collection means and discharged onto the image carrier can be subjected to pre-charge discharge immediately after being discharged, thereby reducing the distance the image carrier must rotate. This can extend the life of the image carrier. Furthermore, by moving the transfer residual toner collected in the temporary collection means back onto the image carrier, the temporary collection means can be kept clean over time.

[0166] For example, aspects of the present invention are as follows. <1> a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; an image forming apparatus in which residual toner remaining on the image carrier after the transfer is collected by the developing means, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control unit controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period becomes zero, and controls the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be -30 μC / g or more and -25 μC / g or less. An image forming apparatus characterized by: <2> The control unit calculates an integrated development drive amount by integrating drive amounts of the developing member, and adjusts the transfer current in a transfer period and / or the transfer current in a non-transfer period based on the integrated development drive amount. Characterized by <1> 2. The image forming apparatus according to claim 1 . <3> The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period based on an integrated number of transfers obtained by integrating the number of times the transfers have been performed. Characterized by <1> or <2> 2. The image forming apparatus according to claim 1 . <4> The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period based on the temperature and absolute humidity inside or outside the image forming apparatus. Characterized by <1> from <3> 10. The image forming apparatus according to claim 9, wherein <5> The control unit adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period based on two or more selected from an integrated development drive amount obtained by integrating the drive amount of the developing member, an integrated number of transfers obtained by integrating the number of times the transfers have been performed, and the temperature and absolute humidity inside or outside the image forming apparatus. Characterized by <1> from <4> 10. The image forming apparatus according to claim 9, wherein <6> The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period, which are selected based on the temperature and absolute humidity inside or outside the image forming apparatus, based on a current correction value selected based on an integrated number of transfers obtained by accumulating the number of times the transfers have been performed. Characterized by <1> from <5> 10. The image forming apparatus according to claim 9, wherein <7> The control unit sets the transfer current value higher as the temperature and absolute humidity increase, and sets the transfer current correction value higher as the cumulative number of transfers increases. Characterized by <6> 2. The image forming apparatus according to claim 1 . <8> The control unit controls the transfer voltage application unit so that the absolute value of the transfer current during a transfer period is smaller than the absolute value of the transfer current during a non-transfer period. Characterized by <1> from <7> 10. The image forming apparatus according to claim 9, wherein <9> The control unit controls the charging voltage application unit to apply a voltage to the charging member during a part of a transfer period that is smaller in absolute value than the voltage applied to the charging member during a non-transfer period. Characterized by <1> from <8> 10. The image forming apparatus according to claim 9, wherein <10> The control unit controls the transfer voltage application unit so that the transfer current during a non-transfer period is 10 μA or more and 16 μA or less. Characterized by <1> from <9> 10. The image forming apparatus according to claim 9, wherein <11> The charging member is provided so as to be in contact with the image bearing member. Characterized by <1> from <10> 10. The image forming apparatus according to claim 9, wherein <12> a peeling roller located downstream of a position where the transfer member performs transfer in the rotation direction of the image carrier and upstream of the charging position; The peeling roller rotates in contact with the image carrier, and peels off the transfer residual toner adhering to the surface of the image carrier by the difference in peripheral speed between the peeling roller and the image carrier. Characterized by <1> from <11> 10. The image forming apparatus according to claim 9, wherein <13> A voltage smaller in absolute value than the voltage applied to the charging member is applied to the peeling roller. Characterized by <12> 2. The image forming apparatus according to claim 1 . <14> the charging member is a non-contact charging member that does not come into contact with the image bearing member, a temporary collection means located downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The temporary collecting means temporarily collects the transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier. Characterized by <1> from <13> 10. The image forming apparatus according to claim 9, wherein <15> a cleaning voltage applying means for applying a voltage to the temporary collecting means; The control unit controls the cleaning voltage application unit to move the transfer residual toner collected by the temporary collection unit to the image carrier at the end of image formation. Characterized by <14> 2. The image forming apparatus according to claim 1 . <16> a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; and a method for recovering transfer residual toner, the method being performed by an image forming apparatus having the image forming apparatus and causing the developing unit to recover transfer residual toner remaining on the image carrier after transfer, the method comprising: a control step, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control step controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period is zero, and adjusts the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be −30 μC / g or more and −25 μC / g or less. A method for recovering residual toner after transfer. [Explanation of symbols]

[0167] 10 Electrostatic latent image carrier (photosensitive drum) 28 Fixing device 61 Developing device 62 Transfer roller 64 Static elimination lamp 72 Developing roller 73 Agitating roller 105 Recording paper 121 Exposure equipment 160 charging roller 161 Collection Brush 165 Peeling roller 166 Temporary cleaning roller 172 Photoconductor unit 180 Transfer belt 181 Conveyor roller 182 Cleaning roller 183 Recovery Roller 184 Cleaning Blade 185 Belt cleaning mechanism 186 Waste toner container [Prior art documents] [Patent documents]

[0168] [Patent Document 1] Patent No. 6410559 [Patent Document 2] Patent No. 3780136

Claims

1. a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; an image forming apparatus in which residual toner remaining on the image carrier after the transfer is collected by the developing means, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control unit controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period becomes zero, and controls the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be −30 μC / g or more and −25 μC / g or less. An image forming apparatus characterized by:

2. The control unit calculates an integrated development drive amount by integrating drive amounts of the developing member, and adjusts the transfer current in a transfer period and / or a non-transfer period based on the integrated development drive amount.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period based on an integrated number of transfers obtained by integrating the number of times the transfers have been performed.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period based on the temperature and absolute humidity inside or outside the image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The control unit adjusts the transfer current during the transfer period and / or the transfer current during the non-transfer period based on two or more selected from an integrated development drive amount obtained by integrating the drive amount of the developing member, an integrated number of transfers obtained by integrating the number of times the transfers have been performed, and the temperature and absolute humidity inside or outside the image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The control unit adjusts the transfer current during a transfer period and / or the transfer current during a non-transfer period, which are selected based on the temperature and absolute humidity inside or outside the image forming apparatus, based on a current correction value selected based on an integrated number of transfers obtained by accumulating the number of times the transfers have been performed.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. The control unit sets the transfer current value higher as the temperature and absolute humidity increase, and sets the transfer current correction value higher as the cumulative number of transfers increases.

7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. The control unit controls the transfer voltage application unit so that the absolute value of the transfer current during a transfer period is smaller than the absolute value of the transfer current during a non-transfer period.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. The control unit controls the charging voltage application unit to apply a voltage to the charging member during a part of a transfer period that is smaller in absolute value than the voltage applied to the charging member during a non-transfer period.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

10. The control unit controls the transfer voltage application unit so that the transfer current during a non-transfer period is 10 μA or more and 16 μA or less.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

11. The charging member is provided so as to be in contact with the image bearing member.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

12. a peeling roller located downstream of a position where the transfer member performs transfer in the rotation direction of the image carrier and upstream of the charging position; The peeling roller rotates in contact with the image carrier, and peels off the transfer residual toner adhering to the surface of the image carrier by the difference in peripheral speed between the peeling roller and the image carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

13. A voltage smaller in absolute value than the voltage applied to the charging member is applied to the peeling roller.

13. The image forming apparatus according to claim 12.

14. the charging member is a non-contact charging member that does not come into contact with the image bearing member, a temporary collection means located downstream of a position where the transfer means performs transfer in the rotation direction of the image carrier and upstream of the charging position; The temporary collecting means temporarily collects the transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

15. a cleaning voltage applying means for applying a voltage to the temporary collecting means; The control unit controls the cleaning voltage application unit to move the transfer residual toner collected by the temporary collection unit to the image carrier at the end of image formation.

15. The image forming apparatus according to claim 14.

16. a rotatable image carrier; a charging member for charging the image bearing member; a developing unit that includes a developing member that supplies toner to the image carrier and forms a toner image on the image carrier; a transfer member for transferring the toner image to a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit; and a method for recovering transfer residual toner, the method being performed by an image forming apparatus having the image forming apparatus and causing the developing unit to recover transfer residual toner remaining on the image carrier after transfer, the method comprising: a control step, a position where the image carrier and the charging member face each other is defined as a charging position; a position where the image carrier and the developing member face each other is defined as a developing position; The current flowing through the transfer member is defined as a transfer current, a transfer period is a period during which the transfer member transfers the toner image to the transfer-receiving member; a non-transfer period is a period during which the transfer member does not transfer the toner image to the transfer-receiving member; The control step controls the transfer voltage application means so that the transfer current during the non-transfer period has the same polarity as the transfer current during the transfer period but has a current value with a different absolute value, or so that the transfer current during the non-transfer period is zero, and adjusts the charge amount of the transfer residual toner after passing the charging position and before passing the developing position in the rotation direction of the image carrier to be −30 μC / g or more and −25 μC / g or less. A method for recovering residual toner after transfer.

Images