Image forming apparatus

Abstract

To provide an image forming apparatus capable of eliminating toner falling in a cleaner-less system using a recovery member and enhancing the stability of image quality with time.SOLUTION: The image forming apparatus includes an image carrier, a charging member, a collection member, a charging voltage applying unit, a developing unit, a developing voltage applying unit, a transfer unit, and a control unit, in which the collection process is an operation including a first collection process and a second collection process, and the control unit controls the charging voltage applying unit and the developing voltage applying unit such that an absolute value of a background potential in the second collection process is larger than an absolute value of a background potential in the first collection process.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [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 conventional configuration of the image forming apparatus described above, for example, it is known that toner adhering to the photosensitive member is cleaned by a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of image forming apparatuses, so-called cleanerless systems have been proposed, which do not include a cleaning means dedicated to cleaning the photosensitive member.

[0004] As an image forming apparatus employing a cleanerless system, a configuration is known in which a developing unit not only supplies toner but also collects toner remaining after transfer (see Patent Document 1).

[0005] Also known is an image forming apparatus that employs a cleanerless system using a contact charging roller (see Patent Document 2). Summary of the Invention [Problem to be solved by the invention]

[0006] The configuration disclosed in Patent Document 1 cannot fully recover the residual toner after transfer under harsh conditions such as durability and environmental conditions. In addition, there is a problem that the development bias cannot be reduced during image printing in terms of the amount of development, making it impossible to widen the background potential.

[0007] According to the configuration disclosed in Patent Document 2, when forming an image, the development bias and the applied voltage to the charging roller are set so that the density, gradation, etc. are optimal for the appropriate image, so there is a problem in that sufficient development recovery cannot be performed.

[0008] In other words, the conventional technology has an issue with regard to eliminating the so-called toner drop problem in image forming devices that employ a cleanerless system, where excessive toner is collected and held in the toner collection member, causing the toner to fall from the collection member onto components such as the photosensitive member.

[0009] SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can eliminate toner dropping in a cleaner-less system using a recovery member and improve the stability of image quality over time. [Means for solving the problem]

[0010] In order to solve the above problems, the image forming apparatus of the present invention comprises an image carrier, a charging member that charges the image carrier, a recovery member that is in contact with the charging member and is capable of holding toner, charging voltage application means that applies a voltage to the charging member, developing means that supplies toner to the image carrier and forms a toner image on the image carrier, developing voltage application means that applies a voltage to the developing means, transfer means that transfers the toner image to a transferee, and a control unit that controls a recovery process in which the developing means recovers transfer residual toner remaining on the image carrier after transfer, and the recovery process is performed by recovering normally charged toner from the transfer residual toner into the developing means during image printing. and further comprising a first recovery process for transferring reverse voltage toner, which is charged with a polarity opposite to that of normally charged toner, from the image carrier to the recovery member via the charging member, among the residual toner after transfer; and a second recovery process for transferring the reversely charged toner held on the recovery member from the recovery member to the image carrier via the charging member during non-image printing, and recovering the reversely charged toner from the image carrier to the developing means, wherein the control unit controls the charging voltage application means and the developing voltage application means so that the absolute value of the background potential in the second recovery process is greater than the absolute value of the background potential in the first recovery process. [Effects of the Invention]

[0011] According to the present invention, it is possible to eliminate toner dropping in a cleaner-less system using a recovery member, and to improve the stability of image quality over time. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an embodiment of an image forming apparatus of the present invention. [Figure 2] FIG. 2 is a block diagram illustrating an example of a hardware configuration of a control unit. [Figure 3] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 4]FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 5] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 6] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 7] 10 is a time chart for explaining a comparative example. [Figure 8] 4 is a time chart for explaining the first embodiment. [Figure 9] 10 is a time chart for explaining the second embodiment. [Figure 10] 6 is a graph illustrating the results of evaluation of toner falling over time in Examples 1 and 2. [Figure 11] 4 is a flowchart of a control process according to the present embodiment. [Figure 12] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 13] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 14] FIG. 10 is a schematic diagram illustrating another embodiment of the image forming apparatus of the present invention. [Figure 15] FIG. 2 is a schematic diagram illustrating an image forming unit. DETAILED DESCRIPTION OF THE INVENTION

[0013] The image forming apparatus and toner recovery method according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments, and can be modified, added, modified, deleted, or otherwise altered within the scope of what one skilled in the art can conceive. Any embodiment that achieves the functions and effects of the present invention is within the scope of the present invention.

[0014] Hereinafter, an embodiment of the image forming apparatus according to the present invention will be described, which is equipped with a system that does not use a dedicated cleaning device for cleaning the image carrier. Note that a system that does not use a dedicated cleaning device for cleaning the image carrier may be referred to as a "cleanerless system" below.

[0015] The image forming apparatus according to the present invention may be equipped with a means for cleaning the charging member and a means for cleaning the intermediate transfer belt, and even when these means are provided, it is still considered to be a cleanerless system. Furthermore, even when it is equipped with a means for temporarily collecting toner (residual toner after transfer) that serves as a developing member and temporarily remains on the image carrier, it is still considered to be a cleanerless system.

[0016] [Configuration of image forming device] 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. As shown in FIG. 1, a printer 100 as an example of an image forming apparatus according to the present embodiment includes at least a paper feed unit 4, a pair of registration rollers 6, a photosensitive drum 10 as an image carrier, a transfer roller 62, and a fixing device 12.

[0017] The device also includes a charging power supply 21 for supplying the bias voltage required for image formation, a developing power supply 22, a cleaning power supply 23, and a transfer power supply 24, and the magnitude of the output from these power supplies is controlled by a control unit 25.

[0018] 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 charging voltage applied to the charging roller 160 may be referred to as a charging bias voltage or the like.

[0019] The development power supply 22 is an example of a development voltage application means and applies a voltage to the development means. The development device 61 is an example of a development means and has, for example, a development roller 72 as a developer carrier. The development power supply 22 applies a voltage to the development roller 72. The development applied voltage applied to the development roller 72 may be referred to as a development bias voltage or the like.

[0020] The transfer power supply 24 is an example of a transfer voltage application means, and applies a voltage to the transfer roller 62 as a transfer means. 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.

[0021] The paper feed means 4 has a paper feed tray 14 in which paper sheets P serving as recording paper are 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 sheet at a time, starting from the top one. Recording paper is an example of a transfer medium, and may also be called a recording medium, recording material, medium, etc.

[0022] The recording paper 105 sent out by the paper feed roller 15 is stopped once by the pair of registration rollers 6, where any misalignment is corrected, and then the recording paper 105 is sent to the transfer area N3 by the pair of registration rollers 6 in synchronization with the rotation of the photosensitive drum 10. The timing in synchronization with the rotation of the photosensitive drum 10 refers to, for example, the 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 paper Pa in the transport direction.

[0023] Around the photosensitive drum 10, in the order of rotation indicated by the arrow R in FIG. 1, there are arranged a charging roller 160 as a 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. A collecting brush 161 is provided in contact with the charging roller 160. The collecting brush 161 is an example of a collecting member. The collecting brush 161 may also be called a brush roller, a cleaning brush, a cleaning member, or the like.

[0024] The charging roller 160 may be in contact with the photosensitive drum 10 or may not be in contact with the photosensitive drum 10. It is preferable that the charging roller 160 is provided so as to be in contact with the photosensitive drum 10. In this case, the discharge process (pre-charging discharge) can be stably performed.

[0025] 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.

[0026] When the photosensitive drum 10 begins to rotate, a charging bias voltage is applied to the charging roller 160 from the charging power supply 21, uniformly charging the photosensitive surface in the charging region N1. The position where the photosensitive drum 10 faces the charging roller 160 in the charging region N1 is referred to as the "charging position." Based on image information, exposure light Lb is irradiated onto the surface of the photosensitive drum 10 from the exposure unit 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 the development region N2 as the photosensitive drum 10 rotates, and at this time, a development bias voltage is applied from the development power supply 22 to the development roller 72 provided in the developing device 61. The position where the photosensitive drum 10 faces the development roller 72 in the development region N2 is referred to as the "developing position."

[0027] In development area N2, which serves as the development position, 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.

[0028] 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.

[0029] In the developing area N2, the residual toner moves onto the developing roller 72 and is collected into the developing device 61 in accordance with 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.

[0030] In the charging region N1, it is difficult to charge the 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.

[0031] A color sensor 65 is disposed downstream of the development area N2 and upstream of the transfer area N3 in the rotation direction (arrow R) of the photosensitive drum 10. The color sensor 65 is a sensor that detects color information of the toner adhering to the photosensitive drum 10.

[0032] A temperature and humidity sensor 66 is also provided as a mechanism for measuring the temperature and humidity inside the printer 100.

[0033] [Control configuration according to this embodiment] Fig. 2A is a block diagram for explaining the hardware configuration of the control unit 25 in this embodiment, and Fig. 2B is a block diagram showing an example of the hardware configuration of the control unit 25.

[0034] The control unit 25 includes, for example, a central processing unit (CPU) 10, which is a central element that performs arithmetic processing, and memories such as a random access memory (RAM) 111 and a read-only memory (ROM) 112, which are memory elements (storage units). The RAM 111 stores sensor detection results, calculation results, etc., and the ROM 112 stores control programs, pre-calculated data tables, etc. The control unit 25 controls, for example, a charging power supply 21, a developing power supply 22, a cleaning power supply 23, and a transfer power supply 24. The control unit 25 controls the ON / OFF and output value of each power supply. The control unit 25 controls the exposure unit 5. The control unit 25 controls a static elimination lamp 64 (static elimination unit), for example, to eliminate static electricity from the photosensitive drum 10 during pre-charging discharge.

[0035] The control unit 25 includes a CPU 110 , a RAM 111 , a ROM 112 , and a storage unit 113 , which are connected via a bus 117 .

[0036] The CPU 110 is a computing means and controls the overall operation of the printer 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 non-volatile 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, a solid state drive (SSD) or a hard disk drive (HDD).

[0038] [Printer 100 Operation] Next, the operation of printer 100 as an embodiment of a cleanerless image forming apparatus will be described with reference to Fig. 3. Fig. 3 is a simplified configuration diagram of printer 100 shown in Fig. 1, omitting control unit 25 and each power supply.

[0039] First, the charging roller 160 uniformly charges the photosensitive drum 10, which serves as an image carrier. The charging roller 160 according to this embodiment is disposed so as to contact the photosensitive drum 10, and applies, for example, a DC voltage to the photosensitive drum 10. Charging according to this embodiment is a contact DC charging method. The exposure unit 5 exposes the photosensitive drum 10 to exposure light L to form an electrostatic latent image on the photosensitive drum 10. The exposure unit 5 is not particularly limited, but an LED, for example, may be used.

[0040] 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 as appropriate, and the agitating roller 73 may or may not be in contact with the developing roller 72.

[0041] The transfer roller 62 transfers the toner image on the photosensitive drum 10 onto the recording paper 105 .

[0042] 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.

[0043] The above configuration is the basic configuration of the cleanerless printer 100. The printer 100 does not include a cleaning means such as a cleaning blade for cleaning the photosensitive drum 10 after the transfer process.

[0044] 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.

[0045] The printer 100 may also include a collection brush 161 (collection member) that collects toner on the charging roller 160.

[0046] Here, an example of the flow of toner in the example shown in FIG. 3 will be described. For the sake of explanation, the reference numerals of the toners 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.

[0047] 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.

[0048] [Embodiment of Toner Recovery Method] Next, an embodiment of a toner recovery method that can be performed in a configuration similar to that of printer 100 according to this embodiment will be described with reference to the drawings. Figures 4, 5, and 6 are diagrams that schematically show the steps of the toner recovery method according to this embodiment. Note that printer 100 is a cleanerless image forming apparatus, and the toner recovery method described below is an example of a method for recovering residual toner after transfer in printer 100.

[0049] Fig. 4 is a schematic diagram for explaining the state after the state illustrated in Fig. 3, and is a diagram that schematically shows the state during image printing. Here, "during image printing" 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. Fig. 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] The process of recovering the transfer residual toner explained with reference to FIG. 4 is a process that is performed during printing and is referred to as a "first recovery process."

[0058] Next, using Figures 5 and 6, we will explain the movement of toner when the device is shut down, which is an example of a period during non-image printing, and an example of toner recovery. As explained in Figure 4, the positive transfer 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. Note that the period during non-image printing may also be the interval (also called the paper gap) between successively fed sheets of paper P during continuous printing in which images are printed (printed) on sheets of paper P. It may also be a period during which the exposure unit 5 is not exposing the photosensitive drum 10.

[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, 5, and 6, 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 such toner may also be included in the transfer residual toner.

[0063] To move the toner as shown in the example of Fig. 5, for example, the potential of each component can be adjusted. For example, the potential of the collection brush 161 can be set to -150 V, the potential of the charging roller 160 to -350 V, the potential of the surface of the photosensitive drum 10 to -500 V, and the potential of the developing roller 72 to +250 V. While Fig. 5 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. 6. FIG. 6 is a continuation of FIG. 5. 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. 6, 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. 6 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] The process of recovering the transfer residual toner explained using FIGS. 5 and 6 is a recovery process that is performed during non-printing periods and is referred to as a "second recovery process."

[0070] [Timing chart of the toner recovery method according to the reference example] Next, an example of control in a toner recovery method as a reference example for the toner recovery method according to the present embodiment will be described using the timing chart of FIG. 7. In the timing chart of FIG. 7, the horizontal axis represents time, and each component is arranged vertically. Each component is indicated by its potential or ON / OFF. Each component is controlled by, for example, CPU 110.

[0071] Note that the displayed value for (c) the potential of the collection brush 161 is a relative value relative to the charging roller 160. Therefore, "-200V" for the collection brush 161 indicates that the potential is 200V lower than the potential of the charging roller 160.

[0072] 7, (a) exposure is ON between t1 and t2. That is, between t1 and t2, exposure of the photosensitive drum 10 is performed by the exposure means 5.

[0073] In this example, the period from t1 to t2, that is, the period when exposure is ON, is considered to be during printing. This "during printing" corresponds to the period during image printing described above. As will be explained below, in this example, the first recovery process shown in FIG. 2 is performed between t1 and t2. Note that in this embodiment, the period during printing (image printing) is not limited to t1 to t2, but may be t1 to t3, etc. In other words, the period during printing (image printing) may be not only the period during which exposure is ON, but also the period up to the time when the transfer step is performed. Therefore, the period during which the first recovery process is performed is not limited to t1 to t2, but may be t1 to t3, etc.

[0074] To explain again, the period during image printing (printing) includes, for example, the period during which exposure for image formation is performed, and also includes the period from the start of exposure for image formation until transfer is performed.

[0075] During the period from t1 to t2, the (c) collecting brush 161 applies a voltage that is 200 V lower than the (b) charging roller. During this period, the (b) charging roller is set to a potential of −1100 V, so the potential of the collecting brush 161 becomes −1300 V.

[0076] In this way, (b) the potential of the charging roller is set to -1100V, and (c) the potential of the collection brush 161 is set to -1300V, as shown in FIG. 4. As a result, of the transfer residual toner 203, the positively charged toner is collected by the charging roller 160 and then by the collection brush 161. This is shown as the toner indicated by the reference numerals 204 and 207 in FIG. 4, and is indicated by the arrows a and b in the figure. In this way, the first collection process can be performed. Note that the arrows a to c in FIG. 4 and the arrows a to f in FIG. 7 are not particularly related to each other.

[0077] Between t1 and t2, (d) the potential of the developing roller is set to -300V, and the transfer residual toner is collected by the developing roller 72. This is indicated by the arrow c in FIG. 4. That is, in this example, while an image is being printed, the first collection process is performed, and a process is also performed in which the normally charged toner on the photosensitive drum 10 is collected by the developing roller 72. This allows more transfer residual toner on the photosensitive drum 10 to be collected, making it possible to make the photosensitive drum 10 in an even cleaner state.

[0078] At t2, (a) exposure is turned off, and exposure for printing is completed. Between t2 and t3, the normally charged toner (which may also be referred to as print toner) on the photosensitive drum 10 is transferred to the recording paper 105. Note that t2 to t3 is the period (or distance) during which the exposed position reaches the transfer position.

[0079] Transfer ends at time t3, and transfer cleaning is performed from t3 to t4. Transfer cleaning involves cleaning the transfer roller 62. Note that in this embodiment, transfer cleaning is an optional step. By performing transfer cleaning, toner adhering to the transfer roller 62 can be removed, further reducing the occurrence of abnormal images. Also, at t3 in this example, (e) the potential of the transfer roller is switched from positive to negative. The value of the potential can be selected as appropriate.

[0080] t4 is the time when the transfer cleaning is completed. After the transfer cleaning is completed, the second collection process is performed. An example of the second collection process will be described below.

[0081] After the transfer cleaning is completed, the (f) discharge lamp 64 is turned off at time t6. By turning off the discharge lamp 64, the surface potential of the photosensitive drum 10 is not discharged, so the surface potential of the photosensitive drum 10 is maintained at -500V.

[0082] The period from t4 to t6 corresponds to the time (distance) required to move from the transfer position to the position of the charging roller 160.

[0083] At t6, the charge removal lamp 64 is turned off and at the same time, the potential of the (b) charging roller is set to -350 V. In this example, before the potential of the (b) charging roller is set to -350 V, the (c) collecting brush 161 is set to a higher potential than the (b) charging roller. In other words, at t5, the potential of the (c) collecting brush 161 is set to +200 V (relative value), and then at t6, the potential of the (b) charging roller is set to -350 V.

[0084] In this example, in the section from t5 (which may be t6) to t8 (which may be t9), the potential of the photosensitive drum 10 is set to -500V, the potential of the charging roller 160 is set to -350V, and the potential of the collection brush 161 is set to -150V. This potential relationship is the same as the example shown in FIG. 3A. As a result, as shown by arrows d and e in FIG. 5, the toner held on the collection brush 161 can be moved from the collection brush 161 to the charging roller 160, and further the toner can be moved from the charging roller 160 to the photosensitive drum 10.

[0085] The timing of t5, that is, the timing for changing the potential of (c) the collecting brush 161, can be selected as appropriate. In the figure, the period during which (c) the collecting brush 161 is set to +200V (relative value) is indicated by c1 to c2. The period from c1 to c2 is the same time (distance) as the period from t6 to t9.

[0086] The time it takes for the collection brush 161 to move from the contact point (also referred to as the brush nip) between the collection brush 161 and the charging roller 160 to the contact point (also referred to as the charging nip) between the charging roller 160 and the photosensitive drum 10 is defined as T1. It is preferable that the timing of t5, that is, the timing of changing the potential of the collection brush 161 (c), be executed earlier than the time t6 by T1. However, c1 may be t6, and c2 may be t9.

[0087] The period from t6 to t9, in other words the period from c1 to c2 (the period from t5 to t8), can be selected as appropriate. In this example, it is set to three revolutions of the charging roller 160. In other words, it is set to the time required for the charging roller to rotate three times. In this case, it is possible to increase the amount of toner 207 that moves from the collection brush 161 to the charging roller 160, and it is possible to keep the collection brush 161 clean. The period from c1 to c2 may be, for example, one revolution of the charging roller 160, but if it is one revolution, some toner may remain on the collection brush 161.

[0088] This will be explained again. In the second collection process, the period during which the toner is moved from the collection brush 161 to the charging roller 160 is preferably three or more rotations of the charging roller 160. This makes it possible to reduce the amount of toner remaining on the collection brush 161, and to make the collection brush 160 cleaner. There is no particular upper limit on the number of rotations of the charging roller 160 when the toner is moved from the collection brush 161 to the charging roller 160, and it may be determined taking into account the time available for the second collection process. This type of control is performed by, for example, the CPU 110.

[0089] Furthermore, in the second recovery process, the period during which the toner is moved from the charging roller 160 to the photosensitive drum 10 is preferably the period of one rotation (or approximately one rotation) of the photosensitive drum 10. In other words, the period from t6 to t9 is preferably the period of one rotation (or approximately one rotation) of the photosensitive drum 10.

[0090] When toner is moved from charging roller 160 to photosensitive drum 10, it is difficult for the toner to move from charging roller 160 in areas where toner is already present on photosensitive drum 10. In the process of moving toner from charging roller 160 to photosensitive drum 10, even if the number of rotations of photosensitive drum 10 is increased to two or more rotations, it is difficult to increase the amount of toner moved from charging roller 160. Therefore, by limiting the period for moving toner from charging roller 160 to one rotation of photosensitive drum 10, it is possible to prevent the second collection process from becoming too long.

[0091] Considering the above, in this embodiment, it is preferable that the time required for three revolutions of the charging roller 160 corresponds to the time required for one revolution of the photosensitive drum 10, and this is the case in this example. For example, the diameter of the photosensitive drum 10 is 30 mm, and the diameter of the charging roller 160 is 9.5 mm. By making the time required for three revolutions of the charging roller 160 and the time required for one revolution of the photosensitive drum 10 approximately equal, the above-mentioned control becomes easier to perform.

[0092] The peripheral speed of the photosensitive drum 10 and the peripheral speed of the charging roller 160 do not necessarily have to be the same. However, in this example, the peripheral speed of the photosensitive drum 10 and the peripheral speed of the charging roller 160 are set to be the same, so that the time required for the charging roller 160 to make three revolutions is likely to be the same as the time required for the photosensitive drum 10 to make one revolution.

[0093] However, the period from t6 to t9 may be shorter or longer than the time it takes for the photosensitive drum 10 to rotate once.

[0094] In this example, at time t7, the potential of the (d) developing roller is set to +250 V. As a result, the positively charged toner 209 on the photosensitive drum 10 passes the position of the developing roller 72 without being collected by the developing roller 72.

[0095] Between t6 and t9, the charge removal lamp 64 is turned on at the timing when the positive toner moves from the charging roller 160 to the photosensitive drum 10 for one rotation of the photosensitive drum 10. In other words, at the time t9, the charge removal lamp (f) is turned on. This causes the photosensitive drum 10 to be discharged.

[0096] (f) At the same time as the discharge lamp is turned on, that is, at time t9, (b) the charging roller is switched to -1100V to discharge the photosensitive drum 10. As a result, the positively charged toner 209 on the photosensitive drum 10 is reversed to negative. This may also be called "conversion to negative toner."

[0097] Next, at time t10 (d), the developing roller is set to -300 V. As a result, the negatively charged toner 209 on the photosensitive drum 10 is collected by the developing roller 72 due to the potential difference between the surface potential of the discharged and charged photosensitive drum 10 and the potential of the developing roller 72. Figure 6 shows that the positively charged toner 209 has been reversed to the negative charge, and that the reversed toner 209 is being collected by the developing roller 72 (arrow i).

[0098] The collection of toner onto the developing roller 72 ends when all of the positively charged toner on the photosensitive drum 10 has reversed to negative and has been collected onto the developing roller 72 .

[0099] As described above, the second recovery process in this example involves the steps of moving the toner from the recovery brush 161 to the charging roller 160 and then to the photosensitive drum 10, reversing the charge of the toner that has been transferred to the photosensitive drum 10, and transferring the toner on the photosensitive drum 10 to the developing roller 72.

[0100] In this example, the residual toner after transfer can be collected by the developing roller 72, and the toner on the charging roller 160 can be collected by the recovery brush 161. Furthermore, the toner recovered by the recovery brush 161 can be collected by moving it in the order of the charging roller 160, the photosensitive drum 10, and the developing roller 72.

[0101] In this example, the rotation speed of the collection brush 161 may be changed as appropriate. The rotation speed of the collection brush 161 in the second collection process is preferably faster than the rotation speed of the collection brush 161 in the first collection process. In other words, it is preferable to make the rotation speed of the collection brush 161 when transferring toner from the collection brush 161 to the charging roller 160 faster than the rotation speed of the collection brush 161 when transferring toner from the charging roller 160 to the collection brush 161.

[0102] If the rotation speed of the collection brush 161 is increased during printing (image printing), toner may be scattered, but if the rotation speed of the collection brush 161 is increased in the second collection process, it becomes easier to move toner from the collection brush 161. The same applies to the embodiments described later. The rotation speed of the collection brush 161 is controlled by the CPU 110, for example.

[0103] [Timing chart for the first embodiment of the toner recovery method] Next, an example of control in a first embodiment of the toner recovery method according to the present embodiment will be described using the timing chart of Fig. 8. The timing chart of Fig. 8 has some similar parts to the timing chart of Fig. 7 used as a reference example, so detailed explanations of these will be omitted and only the parts specific to the first embodiment will be described in detail.

[0104] In the first embodiment, the charging roller bias (b) at timing t9 is set to -1300 V, and the developing bias (d) at timing t10 ​​is set to -50 V. For biases other than these, the same operation as in the reference example (FIG. 7) already explained is performed. As a result, the background potential in the second recovery process is expanded, which can promote negative charging of the residual toner when it is recharged, reducing the return of positively charged toner to the charging roller and improving toner dropping.

[0105] Here, the background potential is the potential difference between the potential (surface potential) on the photosensitive drum 100 at a position downstream in the rotation direction of the photosensitive drum 100 from the charging position and upstream from the developing position, and the development bias of the developing roller 72. More specifically, it is the potential difference between the potential of the non-exposed portion of the photosensitive drum 100, that is, the portion not exposed by the exposure unit 5, and the development bias. The potential on the photosensitive drum 100 can be considered to be the same as the charging roller bias.

[0106] 8, in the first embodiment, the background potential in the first recovery process is |800V|, which is the difference between the charging roller bias (b) of −1100V and the developing roller bias (d) of −300V. The background potential in the second recovery process is |1250V|, which is the difference between the charging roller bias (b) of −1300V from timing t9 to t12 and the developing roller bias (d) of −50V from timing t10 ​​to t12. Therefore, in the first embodiment, the charging power supply 21 and the developing power supply 22 are controlled so that the absolute value of the background potential in the second recovery process is greater than the absolute value of the background potential in the first recovery process.

[0107] 8, in the first embodiment, the charging roller bias (b) from timing t9 to t12, which is the charging voltage applied to the charging roller 160 when the oppositely charged toner moved onto the photosensitive drum 10 in the second collection process passes the charging position, is −1300 V. On the other hand, the charging roller bias (b) from timing t1 to t2, which is the charging voltage applied to the charging roller 160 in the first collection process, is −1100 V. Therefore, the charging power supply 21 is controlled so that the absolute value of the charging voltage applied to the charging roller 160 when the oppositely charged toner moved onto the photosensitive drum 10 in the second collection process passes the charging position, is greater than the absolute value of the charging voltage applied to the charging roller 160 in the first collection process.

[0108] 8, in the first embodiment, the developing bias (d) at the timing t10 ​​to t12, which is the developing applied voltage applied to the developing roller when moving the oppositely charged toner to the developing roller in the second collection process, is -50 V. On the other hand, the developing bias (d) at the timing t1 to t2, which is the developing applied voltage applied to the developing roller in the first collection process, is -300 V. Therefore, the developing power supply 22 is controlled so that the absolute value of the developing applied voltage applied to the developing roller when moving the oppositely charged toner to the developing roller in the second collection process is lower than the absolute value of the developing applied voltage applied to the developing roller in the first collection process.

[0109] [Timing chart for the second embodiment of the toner recovery method] Next, an example of control in a second embodiment of the toner recovery method according to the present embodiment will be described using the timing chart of Fig. 9. The timing chart of Fig. 9 has some similar parts to the timing chart of Fig. 7 used as a reference example, so detailed explanations of these will be omitted and only the parts specific to the second embodiment will be described in detail.

[0110] In the second embodiment, the charging roller bias (b) at timing t9 is set to -1500V, and the developing bias (d) at timing t10 ​​is set to 0V. Other biases are assumed to operate in the same manner as in the reference example (FIG. 7) already described. In the second embodiment, the background potential is further increased compared to the first embodiment, improving toner dropout. Setting the developing bias (d) to 0V maximizes the recovery capacity between the photosensitive drum 10 and the developing roller 72, enabling the residual toner to be removed from the photosensitive drum 10 more efficiently.

[0111] 9, in the second embodiment, the background potential in the first recovery process is |800V|, which is the difference between the charging roller bias (b) of −1100V and the developing roller bias (d) of −300V. The background potential in the second recovery process is |1500V|, which is the difference between the charging roller bias (b) of −1500V from t9 to t12 and the developing roller bias (d) of 0V from t10 to t12. Therefore, in the second embodiment, as in the first embodiment, the charging power supply 21 and the developing power supply 22 are controlled so that the absolute value of the background potential in the second recovery process is greater than the absolute value of the background potential in the first recovery process.

[0112] [Toner drop evaluation results] <Evaluation 1: Relationship between the amount of toner on the collection member and the amount of toner that falls off> First, we investigated the relationship between the amount of toner retained in the collection brush 161 and toner dropping. Using the device shown in FIG. 1 and other figures, we performed the toner collection process (cleaning control) described in the first and second embodiments. For this evaluation, we used a non-magnetic, single-component pulverized toner with an average circularity of 0.953. After forming an image with a high coverage rate, we passed a recording sheet through the collection brush 161 without cleaning it, and measured the amount of toner in the collection brush 161. To measure the amount of toner, we sucked toner from the entire width and circumference of the collection brush 161, which has a predetermined width. We then weighed the sucked toner, and calculated the amount of toner per unit area in the brush from the circumference and width of the collection brush 161.

[0113] The photosensitive drum 10 was also checked for toner fall-off. The occurrence of toner fall-off was determined by visually checking whether or not abnormal images due to toner fall-off had occurred on the recording paper that was passed through after image formation. If no abnormal images due to toner fall-off had occurred on the recording paper, it was marked as ○, and if an abnormal image due to toner fall-off had occurred, it was marked as ×. This evaluation was repeated multiple times to check the relationship between the amount of toner per unit area in the recovery brush and the occurrence of toner fall-off. The results are shown in Table 1. The amount of toner in the brush refers to the amount of toner per unit area in the recovery brush.

[0114] [Table 1]

[0115] As shown in Table 1, the amount of toner per unit area of ​​the collection brush 161 is 9.0 mg / cm 2 Therefore, the amount of toner per unit area of ​​the collection brush 161 is 9.0 mg / cm. 2 It is preferable that:

[0116] The toner used in the evaluation was a non-magnetic component pulverized toner with a circularity of 0.953. The toner that can be used in this example can be selected as appropriate. Among these, a non-magnetic component pulverized toner with an average circularity of 0.959 or less is preferred. A non-magnetic single-component toner with an average circularity of 0.959 or less makes it easier to control the charge polarity of the toner, and pulverized toner can be used. Using pulverized toner can reduce the cost of toner used in image forming devices.

[0117] When the average circularity is 0.959 or less, the low average circularity results in low transfer efficiency, an increase in residual toner, and an increase in the amount of residual toner held by the collection brush 161. By implementing the control of the present invention, even when such toner is used, the collection brush 161 can be kept clean, and poor charging due to residual toner and abnormal images due to toner falling off can be suppressed.

[0118] The collection brush 161 used in the evaluation was a brush roller with conductive fibers. The fiber length was 1.5 mm, the fiber diameter was 6 denier, and the fiber resistance was 7.5 log Ω. These are average values. The fiber resistance of the collection brush 161 is preferably 8.0 log Ω or less. If it exceeds 8.0 log Ω, the voltage may not be applied sufficiently, making it difficult for the toner to move, and this may lead to poor charging or toner dropping.

[0119] <Evaluation 2: Evaluation of the amount of toner in the collection member over time> Next, long-term printing durability was evaluated for Example 1 and Example 2. The results are shown in Figure 10. In Evaluation 2, the same device configuration and toner were used as in Evaluation 1. In Evaluation 2, Example 1 and Example 2 were compared every 1,000 sheets printed at a print rate of 5% with one sheet intermittently. In Example 2, the second recovery process was repeated five times, as in Evaluation 2.

[0120] In Figure 10, the vertical axis represents the toner loss rank, and the horizontal axis represents the total number of printed sheets. The toner loss rank was evaluated by classifying the size and number of toner particles resulting from toner loss on a scale of 1 to 5 on the recording paper used for evaluation. However, as shown in the figure, ranks 1.5, 2.5, 3.5, and 4.5 were also available as evaluation results. Rank 5 was assigned to a printer with no toner loss at all. The ranks were categorized in increments of 1, but increments of 0.5 were added to allow for a more precise distinction between superiority and inferiority. Rank 4 indicates that there was a slight amount of toner loss, but this was at a level that would not cause any problems in actual use, and ranks 4 and above were considered acceptable.

[0121] Rank 5: No toner loss occurs on the image Rank 4: A small amount of toner is visible on the image, but this is not a problem for practical use. Rank 3: Toner loss was observed on the image, and it was at a level that was problematic for practical use (ranking was done on a scale of 1 to 3 based on the size of the black spots). Rank 2: Toner loss was observed on the image, and it was at a level that was problematic for practical use (ranking was done on a scale of 1 to 3 based on the size of the black spots). Rank 1: Toner loss was observed on the image, and it was at a level that was problematic for practical use (ranking was done on a scale of 1 to 3 based on the size of the black spots).

[0122] As shown in Figure 10, in the results of the toner drop evaluation, the comparative example (the aforementioned reference example) falls below rank 3 after printing 20,000 sheets, whereas Example 1 maintains rank 3 or higher even after printing more than 30,000 sheets. This is a level that is sufficiently usable for a printer 100 in the so-called low-speed range (20 to 50 sheets per minute), and is therefore considered acceptable. Furthermore, Example 2 did not experience any toner drop at all, maintaining rank 5.

[0123] In Example 1, the negative charge of the toner on the charging roller in the second recovery process was improved compared to the comparative example. However, the positive charge of the toner could not be completely suppressed. Nevertheless, it is believed that the degree of toner loss was improved compared to the comparative example.

[0124] In Example 2, the bias applied to the charging roller is further increased, increasing the efficiency of negative charge, and the negative charge of the positively charged toner progresses. Furthermore, by expanding the background potential, the efficiency of collecting residual toner from the developing roller is also improved. As a result, the amount of residual toner that enters the charging roller is reduced, which is thought to more reliably reduce the risk of toner falling off.

[0125] [Dot count control flow] Next, the flow of the dot count control process executed when the above process is performed in printer 100 will be explained using the flowchart in Figure 11. The following control process is executed by functions realized by cooperation between the hardware resources that make up control unit 25 and computer software that can be executed by control unit 25.

[0126] First, when a print request is made to the printer 100, the control unit 25 acquires print request information (S1101). The print request information includes information such as the number of prints and the image area ratio.

[0127] Next, the collection speed (V1) of the collection brush 163 is calculated in response to the print request (S1102). The collection speed is also the amount of post-transfer residual toner collected by the collection brush 163.

[0128] Next, information is acquired from the ID chip, which is an information storage element mounted on the process cartridge (which is the image forming unit 120 described below). The ID chip information or the memory stored in the main body to which the ID chip information is linked stores a print count counter (cumulative number of prints), a dot counter (image area), toner consumption, and the like. Therefore, the control unit 25 acquires this information from the memory (S1103). The print count counter and dot counter each successively acquire a log of the user's output history, which is useful for analysis by a service technician when a problem occurs. The toner consumption amount is calculated from information on the cumulative number of prints, image area, travel distance, and usage environment.

[0129] Based on the information acquired in step S1103, the collection speed (V2) of the collection brush 163 in the previous job (the job executed last time) is calculated (S1104).

[0130] Next, the control unit 25 determines whether the collection speed (V1) exceeds the first collection processing speed (S1105). If the collection speed (V1) does not exceed the first collection processing speed (S1105: NO), the printing process is started without changing the background potential (S1107). If the collection speed (V1) exceeds the first collection processing speed (S1105: YES), the background potential of the second collection process is changed (1106) according to the difference in collection processing speed (V1-V2), and the printing process is started (S1107).

[0131] In the control related to the above process, the amount of toner remaining in the collection brush 163 is predicted and calculated based on the print count counter, dot counter (image area), and toner consumption amount, and the background potential (charging bias, developing bias) in the second collection process is changed based on the calculation result. This can improve the efficiency of collection of residual toner after transfer. Note that in the above, the amount of toner remaining in the collection brush 163 is predicted and calculated based on all of the information on the print count counter, dot counter (image area), and toner consumption amount. However, the amount of toner remaining in the collection brush 163 may be predicted and calculated based on at least one of these pieces of information, and the background potential (charging bias, developing bias) in the second collection process may be changed. Furthermore, the frequency of the second collection process may be determined using this information.

[0132] It is desirable to be able to obtain the counter information in the ID chip and main memory not only at the time of printing, but also at the most recent history along with the time of acquisition, so that the rate at which ink accumulates on the collection brush can be accurately predicted based on the progress over time.

[0133] The amount of paper collected (collection speed) to the collection brush 163 can be predicted based on the number of printed sheets and the image area ratio, and the amount of change in background potential during the second collection process can be estimated from the difference between the collection speed of the previous job history and the predicted collection amount calculated from the number of printed sheets and the image area ratio at the time of the print request.

[0134] Since the consumption amount varies depending on the temperature and humidity difference, the above-described calculation of the consumption amount may be performed in the control process using temperature and humidity information acquired from the temperature and humidity sensor 66. Furthermore, control may be performed to change the background potential (charging bias, developing bias) in the second recovery process according to the temperature and humidity information acquired from the temperature and humidity sensor 66.

[0135] Furthermore, the amount of toner adhering to the photosensitive drum 10 after development can be calculated from color information of the toner on the photosensitive drum 10 detected by a color sensor 65 installed near the photosensitive drum 10. This makes it possible to predict the amount of residual toner after transfer and calculate the amount of residual toner collected by the collection brush 163, so that it is possible to perform control to change the background potential (charging bias, development bias) in the second collection process and the frequency of the second collection process.

[0136] [Details of image forming device] Next, a detailed example of the image forming apparatus of the present invention will be described with reference to another example. Another embodiment of the image forming apparatus of the present invention is shown in Fig. 12. The image forming apparatus 100A includes a photosensitive drum 10, a charging roller 20, an exposure device, a developing device 40, an intermediate transfer belt 50, and a static elimination lamp 70.

[0137] 12, the photosensitive drum 10 corresponds to the image carrier, the charging roller 20 corresponds to the charging member, the collection brush 161 corresponds to the collection member, and the developing device 40 corresponds to the developing means. Note that the control means and the power supply configuration are omitted from the illustration.

[0138] The intermediate transfer belt 50 is an endless belt stretched by three rollers 51 arranged inside and can move in the direction of the arrow in the figure. Some of the three rollers 51 also function as transfer bias rollers that can apply a transfer bias (primary transfer bias) to the intermediate transfer belt 50. A cleaning device 90 having a cleaning blade is arranged near the intermediate transfer belt 50. A transfer roller 80 that can apply a transfer bias (secondary transfer bias) to transfer the toner image to the transfer paper 95 is arranged facing the intermediate transfer belt 50. A corona charging device 58 for applying an electric charge to the toner image transferred to the intermediate transfer belt 50 is arranged around the intermediate transfer belt 50 between the contact point between the photosensitive drum 10 and the intermediate transfer belt 50 and the contact point between the intermediate transfer belt 50 and the transfer paper 95, relative to the rotation direction of the intermediate transfer belt 50.

[0139] The developing device 40 is composed of a developing belt 41 and a black developing unit 45K, a yellow developing unit 45Y, a magenta developing unit 45M, and a cyan developing unit 45C arranged around the developing belt 41. Each developing unit 45 includes a developer container 42, a developer supply roller 43, and a developing roller (developer carrier) 44. The developing belt 41 is an endless belt stretched over multiple belt rollers and can move in the direction of the arrow in the figure. A portion of the developing belt 41 contacts the photosensitive drum 10.

[0140] Even when the developing belt 41 is used, it is possible to collect the transfer residual toner on the photosensitive drum 10. As explained in the above example, the device configuration using the developing roller 72 is preferable.

[0141] Next, a method for forming an image using the image forming apparatus 100A will be described. First, the surface of the photosensitive drum 10 is uniformly charged using the charging roller 20, and then the photosensitive drum 10 is exposed to exposure light L using an exposure device to form an electrostatic latent image. Next, the electrostatic latent image formed on the photosensitive drum 10 is developed with toner supplied from the developing device 40 to form a toner image. Furthermore, the toner image formed on the photosensitive drum 10 is transferred (primary transfer) onto the intermediate transfer belt 50 by a transfer bias applied from the roller 51, and then transferred (secondary transfer) onto the transfer paper 95 by a transfer bias applied from the transfer roller 80. Meanwhile, the photosensitive drum 10, from which the toner image has been transferred onto the intermediate transfer belt 50, is neutralized by the neutralization lamp 70.

[0142] A second example of an image forming apparatus used in the present invention is shown in Figure 13. Image forming apparatus 100B has the same configuration as image forming apparatus 100A, except that it does not have developing belt 41 and has black developing unit 45K, yellow developing unit 45Y, magenta developing unit 45M, and cyan developing unit 45C arranged directly opposite each other around photosensitive drum 10.

[0143] In the image forming apparatus 100B of FIG. 13, the photosensitive drum 10 corresponds to the image carrier, the charging roller 20 corresponds to the charging member, the recovery brush 161 corresponds to the recovery member, and the developing units 45K, 45Y, 45M, and 45C each correspond to the developing means.

[0144] 14 shows a third example of an image forming apparatus used in the present invention. Image forming apparatus 100C is a tandem color image forming apparatus, and includes copying machine main body 150, paper feed table 200, scanner 300, and automatic document feeder (ADF) 400.

[0145] An intermediate transfer belt 50, provided in the center of the copying machine main body 150, is an endless belt stretched over three rollers 14, 15, and 16, and can move in the direction of the arrow in the figure. Near roller 15, a cleaning device 17 is disposed, which has a cleaning blade for removing toner remaining on the intermediate transfer belt 50 after the toner image has been transferred to the recording paper. Opposing the intermediate transfer belt 50 stretched over rollers 14 and 15 and moving along the conveyance direction, are image forming units for yellow, cyan, magenta, and black. 120Y, 120C, 120M and 120K are juxtaposed.

[0146] An exposure means 5 is disposed near the image forming unit 120. A secondary transfer belt 24 is disposed on the side of the intermediate transfer belt 50 opposite to the side where the image forming unit 120 is disposed. The secondary transfer belt 24 is an endless belt stretched over a pair of rollers 23, and the recording paper transported on the secondary transfer belt 24 and the intermediate transfer belt 50 can come into contact with each other between the rollers 16 and 23.

[0147] Also, near the secondary transfer belt 24 is disposed a fixing device 25 that includes a fixing belt 26, which is an endless belt stretched over a pair of rollers, and a pressure roller 27 that is positioned so as to be pressed against the fixing belt 26. Also, near the secondary transfer belt 24 and the fixing device 25 is disposed a sheet inverting device 28 for inverting the recording paper when forming images on both sides of the recording paper.

[0148] Next, a method for forming a full-color image using the image forming apparatus 100C will be described. First, a color original is placed on the platen 130 of the automatic document feeder (ADF) 400, or the automatic document feeder 400 is opened and the color original is placed on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed.

[0149] When the start switch is pressed, if an original is set on the automatic document feeder 400, the original is transported and moved onto the contact glass 32, and on the other hand, if the original is set on the contact glass 32, the scanner 300 is driven and the first traveling body 33 equipped with a light source and the second traveling body 34 equipped with a mirror start traveling. At this time, light irradiated from the first traveling body 33 is reflected from the surface of the original, reflected by the second traveling body 34, and then received by the reading sensor 36 via the imaging lens 35, thereby reading the original and obtaining image information of black, yellow, magenta, and cyan.

[0150] The image information for each color is transmitted to the image forming unit 120 for that color, and a toner image for that color is formed. The image forming unit 120 for each color can be configured, for example, as shown in Fig. 15. The image forming unit 120 for each color has an image forming means 18, and includes, for example, a photosensitive drum 10, a charging roller 160, a developing device 61, a transfer roller 62, and a discharging lamp 64.

[0151] In the image forming unit 120 of FIG. 15, the photosensitive drum 10 corresponds to the image carrier, the charging roller 160 corresponds to the charging member, the collecting brush 161 corresponds to the collecting member, and the developing device 61 corresponds to the developing means.

[0152] The charging roller 160 uniformly charges the photosensitive drum 10. The developing device 61 develops the electrostatic latent image with a developer of each color to form a toner image of each color. The transfer roller 62 transfers the toner image onto the intermediate transfer belt 50. In addition, an exposure device provided outside the image forming means 18 exposes the photosensitive drum 10 to exposure light L based on image information of each color to form an electrostatic latent image of each color.

[0153] The toner images of each color formed by the image forming units 120 of each color are transferred sequentially (primary transfer) onto the intermediate transfer belt 50, which is stretched and moves around rollers 14, 15, and 16, and are superimposed to form a composite toner image.

[0154] Meanwhile, in paper feed table 200, one of paper feed rollers 142 is selectively rotated to feed recording paper from one of paper feed cassettes 144 provided in multiple stages in paper bank 143, which is separated one sheet at a time by separation roller 145 and sent to paper feed path 146, then transported by transport roller 147 and guided to paper feed path 148 inside copying machine main body 150, where it is stopped by hitting registration roller 49. Alternatively, the paper feed roller is rotated to feed recording paper from manual feed tray 54, which is separated one sheet at a time by separation roller 52 and guided to manual feed path 53, where it is stopped by hitting registration roller 49. Note that registration roller 49 is generally grounded when used, but may be used with a bias applied to it in order to remove paper dust from the recording paper.

[0155] Next, the registration rollers 49 are rotated in synchronization with the composite toner image formed on the intermediate transfer belt 50, thereby feeding the recording paper between the intermediate transfer belt 50 and the secondary transfer belt 24, and the composite toner image is transferred (secondary transfer) onto the recording paper. Any toner remaining on the intermediate transfer belt 50 after the composite toner image has been transferred is removed by the cleaning device 17.

[0156] The recording paper onto which the composite toner image has been transferred is transported by secondary transfer belt 24, and then the composite toner image is fixed by fixing device 25. Next, the transport path of the recording paper is switched by switching claw 55, and the recording paper is discharged onto paper discharge tray 57 by discharge rollers 56. Alternatively, the transport path of the recording paper is switched by switching claw 55, the sheet is inverted by sheet inverting device 28, an image is formed on the back side in the same manner, and then the recording paper is discharged onto paper discharge tray 57 by discharge rollers 56.

[0157] For example, aspects of the present invention are as follows. <1> an image carrier; a charging member for charging the image bearing member; a collecting member that is in contact with the charging member and is capable of holding the toner; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier to form a toner image on the image carrier; a developing voltage applying means for applying a voltage to the developing means; a transfer means for transferring the toner image onto a transfer target; a control unit for controlling a recovery process in which the developing means recovers the transfer residual toner remaining on the image carrier after the transfer; An image forming apparatus having: The recovery process includes: a first recovery process in which, during image printing, the normally charged toner among the transfer residual toner is recovered by the developing means, and further, the reverse voltage toner, which is charged to a polarity opposite to that of the normally charged toner among the transfer residual toner, is moved from the image carrier to the recovery member via the charging member; a second recovery process in which, during non-image printing, the oppositely charged toner held on the recovery member is moved from the recovery member to the image carrier via the charging member, and the oppositely charged toner is recovered from the image carrier to the developing means, The control unit controlling the charging voltage application means and the developing voltage application means so that the absolute value of the background potential in the second recovery process is greater than the absolute value of the background potential in the first recovery process; The image forming apparatus is characterized by the above. <2> the background potential is a potential difference between a potential on the image carrier at a position downstream of a charging position of the image carrier facing the charging member in the rotation direction of the image carrier and upstream of a development position of the image carrier facing the developing means, and a development applied voltage applied to the developing means; The aforementioned <1> 2. The image forming apparatus according to claim 1, wherein: <3> the control unit controls the charging voltage application means so that the absolute value of the charging voltage applied to the charging member when the oppositely charged toner moved onto the image carrier passes through the charging position in the second recovery process is greater than the absolute value of the charging voltage applied to the charging member in the first recovery process. The aforementioned <2> 2. The image forming apparatus according to claim 1, wherein: <4> the control unit controls the developing voltage application unit so that the absolute value of the developing voltage applied to the developing unit when moving the oppositely charged toner to the developing unit in the second recovery process is lower than the absolute value of the developing voltage applied to the developing unit in the first recovery process. The aforementioned <1> and above <3> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <5> The control unit determining the frequency of the second collection process in accordance with at least one of the number of prints, the image area of ​​the image to be printed, and the amount of toner consumed; The aforementioned <1> and above <4> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <6> The control unit determining the value of the background potential in the second recovery process in accordance with at least one of the number of prints, the image area of ​​the image to be printed, and the amount of toner consumed; The aforementioned <1> and above <5> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <7> In the second recovery process, the difference between the surface potential of the image carrier and the surface potential of the developing carrier of the developing means is 500 V or more. The aforementioned <1> and above <6> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <8> a color sensor capable of detecting color information of toner adhering to the surface of the image carrier; The control unit changing the background potential of the second recovery process or the frequency of the second recovery process according to the color information detected by the color sensor; The aforementioned <1> and above <7> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <9> A temperature and humidity sensor is provided to measure temperature and humidity. The control unit changing the background potential in the second recovery process according to the temperature and humidity detected by the temperature and humidity sensor; The aforementioned <1> and above <8> 10. The image forming apparatus according to claim 9, wherein the first and second electrodes are arranged parallel to each other. <10> The amount of toner per unit area of ​​the recovery member is 9.0 mg / cm 2 Below is the The aforementioned <1> 2. The image forming apparatus according to claim 1, wherein: [Explanation of symbols]

[0158] 10: Photosensitive drum 61: Developing device 62: Transfer roller 65: Color sensor 66: Temperature and humidity sensor 72: Developing roller 100: Printer 160: Charging roller 161: Collection brush [Prior art documents] [Patent documents]

[0159] [Patent Document 1] Patent No. 6862117 [Patent Document 2] Japanese Patent Application Publication No. 2023-137933

Claims

1. an image carrier; a charging member for charging the image bearing member; a collecting member that is in contact with the charging member and is capable of holding the toner; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier to form a toner image on the image carrier; a developing voltage applying means for applying a voltage to the developing means; a transfer means for transferring the toner image onto a transfer target; a control unit for controlling a recovery process in which the developing means recovers the transfer residual toner remaining on the image carrier after the transfer; An image forming apparatus having: The recovery process includes: a first recovery process in which, during image printing, the normally charged toner among the transfer residual toner is recovered by the developing means, and further, the reverse voltage toner, which is charged to a polarity opposite to that of the normally charged toner among the transfer residual toner, is moved from the image carrier to the recovery member via the charging member; a second recovery process in which, during non-image printing, the oppositely charged toner held on the recovery member is moved from the recovery member to the image carrier via the charging member, and the oppositely charged toner is recovered from the image carrier to the developing means, The control unit controlling the charging voltage application means and the developing voltage application means so that the absolute value of the background potential in the second recovery process is greater than the absolute value of the background potential in the first recovery process; An image forming apparatus characterized by:

2. the background potential is a potential difference between a potential on the image carrier at a position downstream of a charging position of the image carrier facing the charging member in the rotation direction of the image carrier and upstream of a development position of the image carrier facing the developing means, and a development applied voltage applied to the developing means; The image forming apparatus according to claim 1 .

3. the control unit controls the charging voltage application means so that the absolute value of the charging voltage applied to the charging member when the oppositely charged toner moved onto the image carrier passes through the charging position in the second recovery process is greater than the absolute value of the charging voltage applied to the charging member in the first recovery process. The image forming apparatus according to claim 2 .

4. the control unit controls the developing voltage application unit so that the absolute value of the developing voltage applied to the developing unit when moving the oppositely charged toner to the developing unit in the second recovery process is lower than the absolute value of the developing voltage applied to the developing unit in the first recovery process. The image forming apparatus according to claim 1 .

5. The control unit determining the frequency of the second collection process in accordance with at least one of the number of prints, the image area of ​​the image to be printed, and the amount of toner consumed; The image forming apparatus according to claim 1 .

6. The control unit determining the value of the background potential in the second recovery process in accordance with at least one of the number of prints, the image area of ​​the image to be printed, and the amount of toner consumed; The image forming apparatus according to claim 1 .

7. In the second recovery process, the difference between the surface potential of the image carrier and the surface potential of the developing carrier of the developing means is 500 V or more. The image forming apparatus according to claim 1 .

8. a color sensor capable of detecting color information of toner adhering to the surface of the image carrier; The control unit changing the background potential of the second recovery process or the frequency of the second recovery process according to the color information detected by the color sensor; The image forming apparatus according to claim 1 .

9. A temperature and humidity sensor is provided to measure temperature and humidity. The control unit changing the background potential in the second recovery process according to the temperature and humidity detected by the temperature and humidity sensor; The image forming apparatus according to claim 1 .

10. The amount of toner per unit area of ​​the recovery member is 9.0 mg / cm ２ 2. The image forming apparatus according to claim 1, wherein:

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