Image forming apparatus and method for recovering transfer residual toner

Abstract

To provide an image forming apparatus that can reduce the time required for control of a movement of toner from an electrifying member, extend the life of an image carrier, and remove a static eliminating device to reduce cost.SOLUTION: An image forming apparatus performs a first recovery operation to apply a DC bias to an electrifying member to move a reversely-electrified toner, of a transfer residual toner, to the electrifying member, and a second recovery operation to recover the transfer residual toner with developing means in a non-image printing period after image printing. The second recovery operation performs (a)-(c). (a) Stopping application of voltage to a transfer member and reducing the voltage applied to the electrifying member to move the reversely-electrified toner from the electrifying member to an image carrier. (b) Applying a voltage having the same polarity as the voltage applied to the transfer member during image printing to reduce the absolute value of the surface potential of the image carrier. Increasing the voltage applied to the electrifying member to generate pre-electrification discharge, thereby electrifying the reversely-electrified toner on the image carrier to have a normal polarity. (c) Recovering a normally-electrified toner.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] Patent Document 1 discloses a toner recycling type image forming apparatus that does not have a cleaning device. Patent Document 1 discloses an image forming apparatus that has a roller that faces a photosensitive member and a sleeve that is wrapped around the roller, and considers the shape of the sleeve as well as the mechanism for moving the roller and sleeve together. Patent Document 1 claims that filming can be removed from the image carrier. Patent Document 1 also discloses control of toner movement from a charging brush included in a charging device that charges the photosensitive member.

[0006] In the cleanerless image forming apparatus disclosed in Patent Document 2, external additives have been studied. According to Patent Document 2, it is possible to suppress the occurrence of abnormal images for a long period of time. Patent Document 2 also discloses a control method for moving toner from a charging member to a photosensitive member using, for example, a static eliminator that eliminates static electricity from the photosensitive member. Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, an AC bias is applied to a charging member during printing to charge the surface of a photoconductor. As a result, both normally charged toner (charged to the normal polarity) and reversely charged toner (charged to the opposite polarity) adhere to the charging member. Therefore, when transferring the toner adhered to the charging member to the photoconductor, separate processes are required to transfer both the normally charged toner and the reversely charged toner to the photoconductor, resulting in a problem of an increased number of processes. This increases the time required for control and the travel distance of the photoconductor. A longer travel distance of the photoconductor can lead to problems such as abrasion of the photoconductor surface, shortening the photoconductor's lifespan.

[0008] In Patent Document 2, the control of transferring toner adhering to a charging member to a photoconductor requires fewer steps than in Patent Document 1, and the time required for control is expected to be shorter. Meanwhile, due to demands for further device miniaturization, there is a need to reduce the number of static eliminators that eliminate static electricity from the surface of the photoconductor. Static eliminators are used for purposes such as adjusting the potential of the surface of the photoconductor to transfer toner from the charging member to the photoconductor, or adjusting the charge of toner transferred from the charging member to the photoconductor. Eliminating static eliminators in cleanerless image forming devices is expected to further reduce the size of the device, reduce the number of components, and lower costs.

[0009] Therefore, the present invention aims to provide an image forming apparatus that can shorten the control for moving toner from a charging member, thereby preventing the life of the image carrier from being shortened, and can reduce the number of discharge devices that discharge the surface of the image carrier, thereby reducing costs. [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 contacts the image bearing member and charges the image bearing member; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member facing the image carrier and transferring the toner image onto a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit that controls a first recovery operation in which a DC bias is applied to the charging member during image printing, and reversely charged toner that is charged to a polarity opposite to a normal charge among transfer residual toner remaining on the image carrier after transfer is moved to the charging member, and a second recovery operation in which, during non-image printing, the transfer residual toner that has moved to the charging member is moved from the charging member to the image carrier and then to the developing means, The control unit performs the following steps (a) to (c) in the second collecting operation: It is characterized by: (a) The application of voltage to the transfer member is stopped, or the transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the same polarity as that applied to the transfer member during image printing, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means. [Effects of the Invention]

[0011] According to the present invention, it is possible to shorten the control for moving toner from the charging member, thereby preventing the shortening of the life of the image carrier, and it is possible to reduce the number of discharge devices that discharge the surface of the image carrier, thereby providing an image forming apparatus that can reduce costs. [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] 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 embodiment of the image forming apparatus of the present invention. [Figure 4] FIG. 1 is a schematic diagram for explaining a first embodiment. [Figure 5A] FIG. 2 is another schematic diagram for explaining the first embodiment. [Figure 5B] FIG. 2 is another schematic diagram for explaining the first embodiment. [Figure 6] FIG. 10 is a schematic diagram for explaining a second embodiment. [Figure 7A] FIG. 10 is another schematic diagram for explaining the second embodiment. [Figure 7B] FIG. 10 is another schematic diagram for explaining the second embodiment. [Figure 8] 10 is a timing chart for explaining the third embodiment. [Figure 9] 10 is a timing chart for explaining the fourth embodiment. [Figure 10] 10 is a timing chart for explaining an example of the fifth embodiment. [Figure 11] 10 is a timing chart for explaining another example of the fifth embodiment. [Figure 12] FIG. 10 is a schematic diagram for explaining Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] (First embodiment) The image forming apparatus of this embodiment includes: an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member facing the image carrier and transferring the toner image onto a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit that controls a first recovery operation in which a DC bias is applied to the charging member during image printing, and reversely charged toner that is charged to a polarity opposite to a normal charge among transfer residual toner remaining on the image carrier after transfer is moved to the charging member, and a second recovery operation in which, during non-image printing, the transfer residual toner that has moved to the charging member is moved from the charging member to the image carrier and then to the developing means, The control unit performs the following steps (a) to (c) in the second collecting operation: It is characterized by: (a) The application of voltage to the transfer member is stopped, or the transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the same polarity as that applied to the transfer member during image printing, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means.

[0015] 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.

[0016] The method for recovering residual toner after transfer according to this embodiment includes the steps of: an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member that faces the image carrier and transfers the toner image onto a transfer target, the method comprising: a first recovery step of applying a DC bias to the charging member during image printing, thereby transferring toner particles charged to a polarity opposite to a normal charge among the residual toner particles remaining on the image carrier after transfer to the charging member; a second recovery step of recovering the transfer residual toner that has been transferred to the charging member during non-image printing, from the charging member to the image carrier and then to the developing means, The second recovery step is characterized by carrying out the following steps (a) to (c): (a) The application of voltage to the transfer member is stopped, or a voltage of the opposite polarity to the voltage applied to the transfer member during image printing is applied to the transfer member, and the absolute value of the voltage applied to the charging member is made smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) A voltage of the same polarity as that applied to the transfer member during image printing is applied to the transfer member, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the absolute value of the voltage applied to the charging member is made larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means.

[0017] In this embodiment, the period during which transfer is taking place is referred to as "image printing," and "image printing" may include not only the period during which transfer is taking place but also the period during which exposure and development are taking place. Furthermore, the period during which image printing is not taking place is referred to as "non-image printing." The period during which image printing is taking place may be referred to as "image formation," and the period during which non-image printing is taking place may be referred to as "non-image formation." In this embodiment, during image printing, a direct current bias (also referred to as a DC bias) is applied to the charging member to move the reversely charged toner, which is charged to the polarity opposite to the normal charge, among the transfer residual toner, to the charging member.

[0018] In Patent Document 1, an alternating current bias (also referred to as an AC bias) is applied to a charging member to print an image. As a result, both positive and negative toners adhere to the charging member. To move both types of toner from the charging member to the image carrier, a separate process for moving each type of toner is required. As a result, in Patent Document 1, not only is the time required for control longer, but the travel distance of the photoconductor is also longer. If the travel distance of the photoconductor is longer, the surface of the photoconductor may be worn away, shortening the life of the photoconductor.

[0019] On the other hand, in this embodiment, only the oppositely charged toner is transferred to the charging member by the DC bias applied to the charging member during image printing. Therefore, when cleaning the charging member, only the oppositely charged toner needs to be transferred from the charging member to the image carrier. This shortens the control time required to transfer the toner from the charging member, thereby preventing the image carrier from shortening in life. Furthermore, preventing the image carrier from shortening in life can reduce running costs, resulting in reduced costs.

[0020] In this embodiment, during non-image printing after image printing, the transfer residual toner is transferred from the charging member to the image carrier and then to the developing unit, and the transfer residual toner is collected by the developing unit, thereby constituting a cleanerless system. In this embodiment, the transfer residual toner is collected by the developing unit as described above in (a) to (c), which makes it possible to eliminate the need for a static eliminator that eliminates static electricity from the surface of the image carrier. When collecting the transfer residual toner by the developing unit in a cleanerless system, a static eliminator may be used to eliminate static electricity from the surface of the image carrier, and the potential of the surface of the photoconductor may be adjusted to transfer the toner from the charging member to the photoconductor, or the charge of the toner transferred from the charging member to the photoconductor may be adjusted. In this embodiment, the potential of the surface of the photoconductor is adjusted by controlling the voltage applied to the transfer member, which makes it possible to eliminate the static eliminator, thereby reducing the number of components, further miniaturizing the device, and reducing costs.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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. 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.

[0025] The paper feed means 4 includes a paper feed tray 14 in which sheets of paper 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 object, and may also be called a recording medium, recording material, medium, etc.

[0026] The recording paper 105 sent out by the paper feed roller 15 is stopped temporarily by the pair of registration rollers 6, and after any misalignment has been corrected, it is sent to the transfer location N3 by the pair of registration 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 paper Pa in the transport direction.

[0027] 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.

[0028] The charging roller 160 is a contact charging type that comes into contact with the photosensitive drum 10. In this case, pre-charging discharge is easily and stably performed. Note that the charging member that charges the photosensitive drum 10 is not limited to the charging roller 160, and a charging brush roller or the like may also be used.

[0029] 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.

[0030] 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. Based on image information, the exposure means 5 irradiates the surface of the photosensitive drum 10 with exposure light Lb, 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 development device 61.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 2(A) 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 that performs arithmetic processing, and memories such as ROM and RAM, which are storage elements (storage units). The RAM stores the detection results of the sensors and the results of calculations, while the ROM stores control programs and pre-determined 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.

[0036] FIG. 2B is a block diagram showing an example of the hardware configuration of the control unit 25.

[0037] 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.

[0038] 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.

[0039] 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).

[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 a direct current voltage (DC voltage) to the photosensitive drum 10. Charging in this example is performed using a contact DC charging method.

[0044] The exposure device 121 exposes the photosensitive drum 10 to exposure light L, and forms an electrostatic latent image on the photosensitive drum 10. The exposure device 121 is not particularly limited, but may be, for example, an LED.

[0045] The developing roller 72 is an example of a developer carrier included 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. An example of the application means is a developing power source 22 controlled by the control unit 25. 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 .

[0046] 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.

[0047] 3, for example, −300 V is applied to the developing roller 72, and −1200 V is applied to the charging roller 160. For example, the surface of the photosensitive drum 10 is neutralized by the transfer roller 62 to about −100 V, and is charged by the charging roller 160 to about −500 V.

[0048] 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.

[0049] 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.

[0050] Toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. 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, as described below.

[0051] Example 1 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.

[0052] FIG. 4 is a schematic diagram for explaining the state after FIG. 3, and is a diagram for schematically explaining an example of processing during printing (also referred to as during image formation or during image printing). In this example, during image printing is the period when transfer is being performed. During non-image printing is the period other than during image printing, such as between sheets when performing continuous printing, when starting up the image forming apparatus to prepare for printing, or when shutting down the image forming apparatus after printing is completed. This is the period when image printing is not being performed. Furthermore, printing is not limited to characters, but also includes forming images such as symbols, pictures, and patterns.

[0053] 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.

[0054] The position where the photosensitive drum 10 and the transfer roller 62 face each other is also referred to as the transfer position. When transferring an image onto the recording paper 105 passing through the transfer position, a voltage of, for example, +1000 V is applied to the transfer roller 62, and the toner image is transferred to the recording paper 105. If a voltage of +1000 V is still applied to the transfer roller 62 after the recording paper 105 has passed, the surface of the photosensitive drum 10 is discharged. For example, if the surface of the photosensitive drum 10 is approximately -500 V, when the transfer roller 62 discharges the printed area of ​​the photosensitive drum 10, the printed area is discharged to -50 V, and the blank area is discharged to -100 V. When the surface of the photosensitive drum 10 is discharged in this manner, the potential difference between the charging roller 160 and the photosensitive drum 10 increases, and a discharge (also referred to as a pre-charge discharge) occurs between the charging roller 160 and the photosensitive drum 10 in both the printed area and the blank area before the charging position. By the pre-charging discharge, for example, the photosensitive drum 10 is charged to −500 V. The discharge is illustrated schematically in FIG.

[0055] Due to the discharge before charging, the transfer residual toner 203 is negatively charged (reference numeral 206 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 small amount of transfer residual toner 203 that remains 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.

[0056] The arrow a in the figure schematically shows the transfer residual toner 203 on the photosensitive drum 10 adhering to the charging roller 160. The transfer residual toner 203 on the photosensitive drum 10 adhering to the charging roller 160 may also be referred to as moving or collecting.

[0057] In this embodiment, during image printing, a DC bias is applied to the charging roller 160 (charging member), and a first recovery operation is performed in which reversely charged toner (e.g., positive toner) that is charged with a polarity opposite to the normal charge (e.g., negative) among the residual toner remaining on the image carrier after transfer is moved to the charging roller 160. The first recovery step can be performed by the first recovery operation. As shown in the figure, in this example, only positive toner is recovered by the charging roller 160.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Although there are no particular limitations on the method for recovering toner with the developing roller 72 as described above, one example is to adjust the potential of each component. One example is to set the surface of the photosensitive drum 10 after neutralization (after passing the transfer position) to -50V to -100V, the charging roller 160 to -1100V, the recovery brush 161 to -1300V, the surface of the photosensitive drum 10 after charging to -500V, and the developing roller 72 to -300V. While FIG. 4 illustrates the potentials as an example, the present invention is not limited to this.

[0062] Next, we will explain the movement of toner when the device is shut down and an example of toner recovery using Figures 5A and 5B. Here, the device shut down refers to a part of the non-image printing period, during which a predetermined operation is performed after printing (image formation operation) is completed.

[0063] In this embodiment, during non-image printing, a second collection operation is performed in which the transfer residual toner that has moved to the charging roller 160 is moved from the charging roller 160 to the photosensitive drum 10 and then to the developing roller 72. The second collection step can be performed by the second collection operation. In addition, the above-mentioned steps (a) to (c) are performed in the second collection operation.

[0064] 4, the positive residual toner 203 (as well as the toner 206) that did not become negative during discharge before charging adheres to the charging roller 160 and is collected by the collection brush 161. Since this collection is repeated during printing, positively charged toner 207 accumulates on the collection brush 161.

[0065] When shutting down the device, 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 arrow d in the figure. The movement of toner from the collection brush 161 to the charging roller 160 may also be referred to as "spitting out the toner."

[0066] 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 arrow e in the figure. This moved toner is indicated as toner 209 in the figure. The movement of toner from the charging roller 160 to the photosensitive drum 10 may also be referred to as expelling the toner.

[0067] 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.

[0068] 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.

[0069] Although there is no particular limitation on how to move toner as shown in the example of Fig. 5A, one example is to adjust the potential of each component. For example, the potential of the collection brush 161 may 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.

[0070] In the example shown in FIG. 5A, the transfer roller 62 is labeled "OFF or negative potential." This represents a portion of the control of (a) above (the first half of (a) above). That is, the transfer power supply 24 (transfer voltage application means) is controlled to stop (OFF) the application of voltage to the transfer roller 62, or to apply to the transfer roller 62 a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing. Transfer to the transfer recipient is completed by stopping the application of voltage to the transfer roller 62 or applying to the transfer roller 62 a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing. The completion of transfer to the transfer recipient can also be considered the completion of image printing. Note that in this example, as shown in FIG. 4, a positive voltage (e.g., +1000 V) is applied to the transfer roller 62 during image printing, and therefore a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing becomes a negative potential.

[0071] 5A, applying −350 V to the charge roller 160 represents a part of the control of (a) above (the latter half of (a) above). In other words, the charging power source 21 (charging voltage application means) is controlled so that the absolute value of the voltage applied to the charge roller 160 after image printing is completed is smaller than the absolute value of the voltage applied to the charge roller 160 during image printing. As shown in FIG. 4, for example, −1100 V is applied to the charge roller 160 during image printing, and as shown in FIG. 5A, a voltage with an absolute value lower than −1100 V, for example, −350 V, is applied to the charge roller 160. In this way, as shown in the figure, reversely charged toner (positive toner in this example) charged to the polarity opposite to the normal polarity is moved from the charge roller 160 to the photosensitive drum 10.

[0072] Next, the recovery of toner from the photosensitive drum 10 when the device is shut down will be described with reference to Figure 5B. Figure 5B is a continuation of Figure 5A.

[0073] As shown in the figure, +550 V is applied to transfer roller 62 at a predetermined timing. This causes a discharge due to the potential difference between the potential of transfer roller 62 and the surface potential of photosensitive drum 10 (for example, -500 V), and photosensitive drum 10 is neutralized. As photosensitive drum 10 is neutralized, the potential difference between charging roller 160 and photosensitive drum 10 increases, causing discharge between charging roller 160 and photosensitive drum 10. The discharge is shown schematically in the figure.

[0074] 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).

[0075] 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.

[0076] Although there is no particular limitation on the method for moving toner as shown in the example of Fig. 5B, one example is a method of adjusting the potential of each component. For example, the potential of transfer roller 62 may be set to +550V, the potential of recovery brush 161 to -1300V, the potential of charging roller 160 to -1100V, the potential of the surface of photosensitive drum 10 after passing the transfer position to -50V, the potential of the surface of photosensitive drum 10 after passing the charging position to -500V, and the potential of developing roller 72 to -300V. Fig. 5B illustrates the potentials as an example, but the present invention is not limited to this.

[0077] In the example shown in FIG. 5B, applying +550 V to the transfer roller 62 represents part of the control (the first half of (b)). That is, the transfer power supply 24 (transfer voltage application means) is controlled to apply a voltage of the same polarity to the transfer roller 62 during image printing, thereby making the absolute value of the surface potential of the photosensitive drum 10 smaller than the absolute value of the surface potential before the photosensitive drum 10 passes the position facing the transfer roller 62. In the example shown in FIG. 4, the voltage applied to the transfer roller 62 during image printing is, for example, +1000 V, and therefore, in the example shown in FIG. 5B, a positive voltage of the same polarity is applied to the transfer roller 62. Furthermore, a voltage of, for example, +550 V, which is smaller in absolute value than +1000 V, is applied to the transfer roller 62. This allows the photosensitive drum 10 to be neutralized. As shown in the figure, before passing through the position opposite the transfer roller 62 (which may also be referred to as the transfer position), the surface potential of the photosensitive drum 10 is, for example, -500 V, and after passing through the transfer position, the surface potential of the photosensitive drum 10 becomes, for example, -50 V, and the photosensitive drum 10 is de-electrified.

[0078] Note that the control of the application of voltage to the transfer roller 62 in (a) above also includes stopping the application of voltage to the transfer roller 62.

[0079] The timing for applying +550V to transfer roller 62 can be selected as appropriate. For example, the potential of transfer roller 62 is switched to +500V immediately before the toner expelled from charging roller 160 passes over transfer roller 62. The surface potential of photosensitive drum 10 is, for example, -50V, so that the positive toner remains attracted to photosensitive drum 10 and the toner is prevented from moving to transfer roller 62. For example, in FIG. 8 described below, +550V is applied to transfer roller 62 after charging roller 160 has rotated three times since the transfer bias was turned off (t3 to t6).

[0080] In the example shown in FIG. 5B , applying a voltage of −1100 V to the charge roller 160 represents part of the control of (b) (the latter half of (b)). That is, by controlling the charging power source 21 (charging voltage application means) so that the absolute value of the voltage applied to the charge roller 160 is greater than that in (a), a discharge is generated between the charge roller 160 and the photosensitive drum 10. In the example shown in FIG. 5A , a voltage of −350 V is applied to the charge roller 160, and in the example shown in FIG. 5B , a voltage with an absolute value greater than −350 V, for example, −1100 V, is applied to the charge roller 160. This allows a discharge (pre-charge discharge) to occur between the charge roller 160 and the photosensitive drum 10. By generating the pre-charge discharge in this manner, the oppositely charged toner (positive toner in this example, reference numeral 209) that has been moved to the photosensitive drum 10 by (a) can be charged to the normal polarity (negative in this example).

[0081] It is preferable to start the control of the latter half of (b) after starting the control of the former half of (b). In the example of the timing chart shown in Fig. 8 described later, the control of the former half of (b) starts at t6, and then the control of the latter half of (b) starts at t7. This is because the charging position is located downstream of the transfer position in the rotation direction of the photosensitive drum 10.

[0082] 5B, the negatively charged toner 209 is collected by the developing roller 72, which represents the control (c) described above. In other words, the normally charged toner (negative toner in this example) charged to the normal polarity by the control (b) described above is moved to the developing roller 72.

[0083] In this manner, in this embodiment, during non-image printing after image printing, the control of moving the transfer residual toner from the charging roller 160 to the photosensitive drum 10 and developing roller 72 in this order is performed as described above in (a) to (c). As described above, in this embodiment, it is possible to neutralize the surface of the photosensitive drum 10 without using a neutralization device that neutralizes the surface of the photosensitive drum 10.

[0084] The potential of each component is adjusted by, for example, the control unit 25. The control unit 25 controls, for example, the charging power supply 21, the developing power supply 22, the cleaning power supply 23, and the transfer power supply 24, and adjusts the potential of the photosensitive drum 10, the transfer roller 62, the developing roller 72, the charging roller 160, the collection brush 161, and the like. The control unit 25 may also be referred to as a controller, and includes a CPU, etc. Note that while the control unit 25 is illustrated in FIG. 1, it is omitted from FIG. 3 and other figures.

[0085] The voltage applied to each member (at least the collection brush 161 (collection member)) to move the transfer residual toner is not limited to a DC voltage, but may be a voltage in which an AC voltage is superimposed on a DC voltage. When such a superimposed voltage is used, the effect of vibrating the transfer residual toner and making it easier to move is obtained. When the collection brush 161 expels the transfer residual toner, it is preferable that a voltage in which an AC voltage is superimposed on a DC voltage is applied. In this case, the transfer residual toner is more easily moved from the collection brush 161.

[0086] In this embodiment, during image printing, a direct current voltage (DC bias) is used as the voltage applied to the charging roller 160. On the other hand, during non-image printing, an alternating current voltage (AC bias) may be used as the voltage applied to the charging roller 160. For example, when transferring toner from a charging brush roller serving as a charging member to a photosensitive member, applying a voltage in which an AC voltage is superimposed on a DC voltage to the charging brush roller has the effect of vibrating the transfer residual toner and making it easier to move.

[0087] The image forming apparatus of this embodiment can employ the cleanerless system described above. The cleanerless system described above controls the charging characteristics of the toner and moves and collects the toner using an electric field in each process. This prevents toner contamination of the charging roller 160 and the collection brush 161.

[0088] Example 2 Next, a second embodiment of the method for recovering residual toner in a cleanerless image forming apparatus will be described with reference to Figures 6, 7A, and 7B. Descriptions of matters similar to those in the first embodiment may be omitted.

[0089] In the second embodiment, a charging brush roller 162 is used as the charging member, and the charging brush roller 162 can serve both to charge the photosensitive drum 10 and to collect the residual toner after transfer. The charging brush roller 162 can be, for example, one in which a fiber brush is wrapped around a roller substrate, or one in which fibers are implanted in a roller substrate. Therefore, according to the second embodiment, a cleanerless system can be realized at even lower cost. The method of collecting the residual toner in the second embodiment can be the same as the method of expelling the toner from the charging roller 160 in the first embodiment.

[0090] FIG. 6 is a schematic diagram for explaining the state after FIG. 3, and is a diagram for explaining a schematic example of processing during printing (also referred to as during image formation or during image printing).

[0091] When transferring an image onto recording paper 105 passing through the transfer nip, a voltage of +1000 V, for example, is applied to transfer roller 62, transferring the toner image onto recording paper 105. If a voltage of +1000 V is still applied to transfer roller 62 after recording paper 105 has passed, the surface of photoconductor drum 10 is discharged. For example, if the surface of photoconductor drum 10 is approximately −500 V, when discharged by transfer roller 62, the printed area of ​​photoconductor drum 10 is discharged to −50 V and the blank area is discharged to −100 V. When the surface of photoconductor drum 10 is discharged in this manner, the potential difference between charging brush roller 162 and photoconductor drum 10 increases, and a discharge (pre-charge discharge) occurs between charging brush roller 162 and photoconductor drum 10 in both the printed area and the blank area before the charging position. Due to the pre-charge discharge, photoconductor drum 10 is charged to, for example, −500 V. FIG. 6 shows a schematic diagram of the discharge.

[0092] Due to the discharge before charging, the transfer residual toner 203 is negatively charged. Due to the discharge before charging, some of the transfer residual toner 203 is negatively charged, while some remains slightly positively charged. The small amount of transfer residual toner 203 that remains positively charged adheres to the charging brush roller 162 at (or near) the point where the charging brush roller 162 and the photosensitive drum 10 come into contact. The toner that has adhered to the charging brush roller 162 is shown as toner 204.

[0093] The arrow a in the figure schematically shows that the transfer residual toner 203 on the photosensitive drum 10 adheres to the charging brush roller 162 .

[0094] In this example, a charging brush roller 162 is used as the charging member, and the charging brush roller 162 can accumulate residual toner within the brush. If the charging roller is charged with residual toner adhering to its surface, charging may not be performed well. Even if residual toner has accumulated, the charging brush roller 162 can be charged until the residual toner can no longer be accumulated within the brush.

[0095] Of the transfer residual toner 203 on the photosensitive drum 10, negatively charged toner does not adhere to the charging brush roller 162 and remains on the photosensitive drum 10. This toner is illustrated as toner 206. Note that both toner 203 and toner 206 are transfer residual toner.

[0096] 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 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.

[0097] Although there are no particular limitations on the method for recovering toner with the developing roller 72 as described above, one example is to adjust the potential of each component. One example is to set the surface of the photosensitive drum 10 after neutralization (after passing the transfer position) to -50V to -100V, the charging brush roller 162 to -1100V, the surface of the photosensitive drum 10 after charging to -500V, and the developing roller 72 to -300V. While FIG. 6 illustrates the potentials as an example, the present invention is not limited to this.

[0098] Next, we will explain the movement of toner when the device is shut down and an example of toner recovery using Figures 7A and 7B. Here, the device shut down refers to a part of the non-image printing period, during which a predetermined operation is performed after printing (image formation operation) is completed.

[0099] 6, the positive residual toner 203 (as well as toner 206) that did not become negative during the discharge before charging adheres to the charging brush roller 162 and is collected inside the charging brush roller. Since this collection is repeated during printing, positively charged toner 207 accumulates on the charging brush roller.

[0100] When the device is shut down, the toner 205 accumulated on the charging brush roller 162 moves to the photosensitive drum 10 due to the potential difference between the charging brush roller 162 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.

[0101] 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.

[0102] Although there is no particular limitation on how to move toner as shown in the example of Fig. 7A, one example is to adjust the potential of each component. For example, the potential of charging brush roller 162 may be set to -350V, the potential of the surface of photosensitive drum 10 may be set to -500V, and the potential of developing roller 72 may be set to +250V. While Fig. 7A illustrates the potentials as an example, the present invention is not limited to this.

[0103] Next, the recovery of toner from the photosensitive drum 10 when the device is shut down will be described with reference to Figure 7B. Figure 7B is a continuation of Figure 7A.

[0104] As shown in the figure, +550 V is applied to transfer roller 62 at a predetermined timing. This causes a discharge due to the potential difference between the potential of transfer roller 62 and the surface potential of photosensitive drum 10 (for example, -500 V), and photosensitive drum 10 is neutralized. As photosensitive drum 10 is neutralized, the potential difference between charging roller 160 and photosensitive drum 10 increases, causing discharge between charging roller 160 and photosensitive drum 10. The discharge is shown schematically in the figure.

[0105] The timing for applying +550V to transfer roller 62 can be selected as appropriate. For example, the potential of transfer roller 62 is switched to +500V immediately before the toner expelled from charging roller 160 passes over transfer roller 62. The surface potential of photosensitive drum 10 is, for example, -50V, so that the positive toner remains attracted to photosensitive drum 10 and the toner is prevented from moving to transfer roller 62. For example, in FIG. 8 described below, +550V is applied to transfer roller 62 after charging roller 160 has rotated three times since the transfer bias was turned off (t3 to t6).

[0106] The above-described discharge negatively charges the toner 209. Note that, as in Figure 6, the toner 209 that is not negatively charged and remains positively charged adheres to and accumulates on the charging brush roller 162.

[0107] The toner 209, which has been negatively charged by the above-described discharge, does not move to the charging brush roller 162 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 drawing). The toner collected by the developing roller 72 is shown as toner 208 in the drawing.

[0108] Although there is no particular limitation on the method for moving toner as shown in the example of Fig. 7B, one example is a method for adjusting the potential of each component. For example, the potential of the transfer roller may be set to +550V, the potential of the charging brush roller 162 to -1100V, the potential of the surface of the photosensitive drum 10 after static elimination to -50V, the potential of the surface of the photosensitive drum 10 to 500V, and the potential of the developing roller 72 to -300V. While Fig. 7B illustrates the potentials as an example, the present invention is not limited to this.

[0109] The voltage applied to each component to move the residual toner is not limited to a DC voltage, but may be a voltage obtained by superimposing an AC voltage on a DC voltage. Such a superimposed voltage has the effect of vibrating the residual toner and making it easier to move. It is preferable that a voltage obtained by superimposing an AC voltage on a DC voltage be applied to the charging brush roller at least in the second collection process. In this case, the residual toner is more easily moved from the charging brush roller.

[0110] The image forming apparatus of this embodiment can employ the cleanerless system described above. The cleanerless system described above controls the charging characteristics of the toner and uses an electric field to move and collect the toner in each process. This prevents toner contamination of the charging brush roller 162.

[0111] In this second embodiment, the above steps (a) to (c) are also carried out. In the example shown in FIG. 7A, the transfer roller 62 is labeled "OFF or negative potential." This represents a portion of the control of (a) above (the first half of (a) above). That is, the transfer power supply 24 is controlled to stop (OFF) the application of voltage to the transfer roller 62 or to apply to the transfer roller 62 a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing. Transfer to the transfer receiver is completed by stopping the application of voltage to the transfer roller 62 or applying to the transfer roller 62 a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing. The completion of transfer to the transfer receiver can also be considered the completion of image printing. Note that in this example, as shown in FIG. 6, a positive voltage (e.g., +1000 V) is applied to the transfer roller 62 during image printing, and therefore a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing becomes a negative potential.

[0112] 7A, applying −350 V to charging brush roller 162 represents a part of the control of (a) above (the latter half of (a) above). In other words, charging power supply 21 is controlled so that the absolute value of the voltage applied to charging brush roller 162 after image printing is completed is smaller than the absolute value of the voltage applied to charging brush roller 162 during image printing. As shown in FIG. 6, for example, −1100 V is applied to charging brush roller 162 during image printing, and as shown in FIG. 7A, a voltage with an absolute value lower than −1100 V, for example, −350 V, is applied to charging brush roller 162. In this way, as shown in the figure, reversely charged toner (positive toner in this example) charged to the polarity opposite to the normal polarity is moved from charging brush roller 162 to photosensitive drum 10.

[0113] In the example shown in FIG. 7B, applying +550 V to the transfer roller 62 represents part of the control (b) (the first half of the control (b)). In other words, the transfer power supply 24 is controlled to apply a voltage of the same polarity to the transfer roller 62 during image printing, thereby making the absolute value of the surface potential of the photosensitive drum 10 smaller than the absolute value of the surface potential before the photosensitive drum 10 passes the position facing the transfer roller 62. In the example shown in FIG. 6, the voltage applied to the transfer roller 62 during image printing is, for example, +1000 V, so in the example shown in FIG. 7B, a positive voltage of the same polarity is applied to the transfer roller 62. Furthermore, a voltage of, for example, +550 V, which is smaller in absolute value than +1000 V, is applied to the transfer roller 62. In this manner, the photosensitive drum 10 can be neutralized. As shown in the figure, before passing through the position opposite the transfer roller 62 (which may also be referred to as the transfer position), the surface potential of the photosensitive drum 10 is, for example, -500 V, and after passing through the transfer position, the surface potential of the photosensitive drum 10 becomes, for example, -50 V, and the photosensitive drum 10 is de-electrified.

[0114] In the example shown in FIG. 7B, applying a voltage of −1100 V to the charging brush roller 162 represents part of the control of (b) (the latter half of (b)). That is, by controlling the charging power supply 21 so that the absolute value of the voltage applied to the charging brush roller 162 is greater than that in (a), a discharge is generated between the charging brush roller 162 and the photosensitive drum 10. In the example shown in FIG. 7A, a voltage of −350 V is applied to the charging brush roller 162, and in the example shown in FIG. 7B, a voltage with an absolute value greater than −350 V, for example, −1100 V, is applied to the charging brush roller 162. This allows a discharge (pre-charge discharge) to occur between the charging brush roller 162 and the photosensitive drum 10. By generating a pre-charge discharge in this manner, the oppositely charged toner (positive toner in this example, reference numeral 209) that has been moved to the photosensitive drum 10 by (a) can be charged to the normal polarity (negative in this example).

[0115] 7B, the negatively charged toner 209 is collected by the developing roller 72, which represents (c) above. In other words, the normally charged toner (negative toner in this example) charged to the normal polarity by (b) above is moved to the developing roller 72.

[0116] In this manner, in this embodiment, during non-image printing after image printing, the control of moving the transfer residual toner from the charging brush roller 162 to the photosensitive drum 10 and developing roller 72 in this order is performed as described above in (a) to (c). As described above, in this second embodiment as well, it is possible to neutralize the surface of the photosensitive drum 10 without using a neutralization device that neutralizes the surface of the photosensitive drum 10.

[0117] Example 3 Next, an example of control in this embodiment will be described using the timing chart of Figure 8. The description of this embodiment 3 can be applied to the above-mentioned embodiments 1 and 2. Although not limited thereto, the voltage applied to the charging roller in embodiment 1 and the voltage applied to the charging brush roller in embodiment 2 can be controlled in the same way. In the following description, charging roller 160 will be used as an example.

[0118] 8, the horizontal axis represents time, and each component is arranged vertically. The potential value or ON / OFF of each component is shown. The control of each component is performed by, for example, the control unit 25.

[0119] In the figure, "charge" refers to, for example, the voltage applied to the charging roller 160. "develop" refers to, for example, the voltage applied to the developing roller 72. "transfer" refers to, for example, the voltage applied to the transfer roller 62.

[0120] In the drawing, exposure is turned on between t1 and t2. That is, between t1 and t2, exposure of the photosensitive drum 10 is performed by the exposure device 121. The operation of turning on exposure is also described in FIG.

[0121] In this embodiment, the period during which transfer is being performed is referred to as image printing, and image printing may include not only the period during which transfer is being performed but also the period during which exposure and development are being performed. Also, in this embodiment, the period during which image printing is not being performed is referred to as non-image printing. In this example, the period from t1 to t3 is referred to as image printing. Image printing may also be referred to as printing, image formation, etc. In this example, the period after t3 is referred to as non-image printing.

[0122] From t1 to t3, during image printing, a DC bias of -1100V is applied to the charge roller 160, and the potential of the development roller 72 is set to -300V, so that the normally charged toner (e.g., negative toner) among the transfer residual toner is collected by the development roller 72, and the oppositely charged toner (e.g., positive toner) is moved to the charge roller 160. The movement of the oppositely charged toner to the charge roller 160 is also represented in FIG. 4 as toner designated by reference numeral 204, and is indicated by arrow a in the figure. Furthermore, the collection of the normally charged toner by the development roller 72 is indicated by arrow c in FIG. 4. By having the normally charged toner on the photosensitive drum 10 collected by the development roller 72 during image printing, the transfer residual toner on the photosensitive drum 10 can be collected and the photosensitive drum 10 can be kept clean.

[0123] At t2, the exposure is turned off, and the exposure for printing is completed. From t1 to t3, the normally charged toner (which may also be called print toner) on the photosensitive drum 10 is transferred onto, for example, the recording paper 105. Note that t2 to t3 can also be said to be the period (or distance) during which the exposed position reaches the transfer position.

[0124] At t3, transfer is turned off and the application of voltage to the transfer roller 62 is stopped. The point at which the application of voltage to the transfer roller 62 is stopped marks the end of image printing. In this example, t3 is the point at which the control in the first half of (a) above is performed. This corresponds to the OFF state shown for the transfer roller 62 in FIG. 5A.

[0125] In the control of the first half of (a) above, a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing may be applied to the transfer roller 62. The value of the voltage applied to the transfer roller 62 at this time is not particularly limited and can be selected appropriately. Even when a voltage of the opposite polarity to the voltage applied to the transfer roller 62 during image printing is applied to the transfer roller 62, it can be said that the image printing has ended.

[0126] After transfer is completed at time t3, the toner can be collected by the developing roller 72 between t3 and t4. If any residual toner remains, the residual toner from transfer to charging can be negatively charged and collected by the developing roller 72. Furthermore, by turning off the voltage to the transfer roller 62 at time t3, the surface potential of one revolution of the photosensitive drum 10 is maintained at -500V at time t4. For example, as shown in FIG. 5A, the surface potential of the photosensitive drum 10 is illustrated as -500V.

[0127] From t4 to t7, the potential of the charging roller is set to -350 V. This corresponds to the control in the latter half of (a) above. In other words, the absolute value of the voltage applied to the charging roller 160 after image printing is completed is set to be smaller than the absolute value of the voltage applied to the charging roller 160 during image printing. As shown in FIG. 8, the voltage of -350 V applied to the charging roller 160 from t4 to t7 is smaller in absolute value than the voltage of -1100 V applied to the charging roller 160 from t1 to t3.

[0128] As described above, the surface potential of the photosensitive drum is maintained at −500 V, and therefore this potential relationship is the same as the example shown in Fig. 5A. As a result, the toner held on the charging roller 160 can be moved to the photosensitive drum 10, as indicated by the arrow e in Fig. 5A.

[0129] The period from t4 to t7 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 204 that moves from the charging roller to the photosensitive drum, and the charging roller can be kept clean. For example, it may be set to one revolution of the charging roller 160, but if it is set to one revolution, toner may remain on the charging brush roller. In Figure 8, D2 represents three revolutions of the charging roller 160.

[0130] The period from t3 to t6 can be selected as appropriate, and in this example, it is set to three revolutions of the charging roller 160. In other words, the period for performing the control of the first half of (a) above is set to three revolutions of the charging roller 160. Although not particularly limited, in this example, three revolutions of the charging roller 160 and one revolution of the photosensitive drum 10 are set to the same or approximately the same.

[0131] In the control of the first half of (a) above, the period during which application of voltage to transfer roller 62 is stopped (or the period during which a voltage of the opposite polarity to that applied to transfer roller 62 during image printing is applied to transfer roller 62) preferably corresponds to one rotation (or approximately one rotation) of photosensitive drum 10. In other words, the period from t3 to t6 preferably corresponds to one rotation (or approximately one rotation) of photosensitive drum 10. When transferring toner from charging roller 160 to photosensitive drum 10, toner is difficult to transfer from charging roller 160 in areas where toner is already present on photosensitive drum 10. In the process of transferring 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 transferred from charging roller 160. Therefore, the period for transferring the toner from the charging roller 160 to the photosensitive drum 10 is the period for one rotation of the photosensitive drum 10, so that the photosensitive drum 10 can be prevented from running too far.

[0132] 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 24 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.

[0133] It should be noted that the peripheral speed of the photosensitive drum 10 does not necessarily have to be the same as that of the charging roller 160. In this example, the peripheral speed of the charging roller 160 is set to 1.25 times the peripheral speed of the photosensitive drum 10, 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.

[0134] However, the period from t3 to t6 and the period from t4 to t7 may be shorter or longer than the time required for one rotation of the photosensitive drum 10. This should be determined based on a balance with the wear life of the photosensitive drum in terms of travel distance. It is preferable that the period from t3 to t6 and the period from t4 to t7 are the same.

[0135] In this example, the potential of the developing roller is set to +250 V at time t5. 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. The period from t4 to t5 can also be said to be the period from the charging position to the developing position.

[0136] At t6, +550 V is applied to the transfer roller 62. This corresponds to the control in the first half of (b) above. That is, after the control of the voltage application to the transfer roller 62 in (a) above (transfer OFF from t3 to t6 in this example), a voltage of the same polarity (positive in this example) as the voltage (+1000 V) applied to the transfer roller 62 during image printing is applied to the transfer roller 62. In this example, +550 V is applied to the transfer roller 62. This makes the absolute value of the surface potential of the photosensitive drum 10 smaller than the absolute value of the surface potential before passing the position facing the transfer roller 62. In the example shown in FIG. 5B, the surface potential of the photosensitive drum 10 before passing the transfer position is -500 V, and the absolute value of the surface potential of the photosensitive drum 10 after passing the transfer position is -50 V. In this way, the photosensitive drum 10 is neutralized by applying, for example, +550 V to the transfer roller 62.

[0137] The absolute value of the voltage applied to the transfer roller 62 at t6 can be selected as appropriate, and as in this example, it is preferable that the voltage be lower (for example, +500 V) than the voltage applied during image printing (for example, +1000 V). When such a voltage is applied to the transfer roller 62, excessive neutralization of the photosensitive drum 10 can be prevented, and neutralization can be performed satisfactorily. This provision is restated below. When the control unit applies a voltage of the same polarity to the transfer member as that applied to the transfer member during image printing in (b), it is preferable that the control unit applies a voltage to the transfer member that is lower than the voltage applied during image printing.

[0138] Furthermore, as in this example, the absolute value of the voltage applied to the transfer roller 62 at t6 is preferably 750 V or less. When such a voltage is applied to the transfer roller 62, excessive neutralization of the photosensitive drum 10 can be prevented, and neutralization can be performed satisfactorily. This provision is restated below. When applying a voltage of the same polarity to the transfer member during image printing in (b), the control unit preferably sets the absolute value of the voltage applied to the transfer member to 750 V or less.

[0139] A supplementary explanation will be given regarding the voltage applied to the transfer roller 62 at t6. During image printing, the transfer roller 62 applies a transfer voltage via a transfer receiving material (e.g., a recording medium or an intermediate transfer material). However, when discharging during non-image printing, the transfer roller 62 directly contacts the toner or the photosensitive drum 10 without using a transfer receiving material. Therefore, when discharging during non-image printing, a transfer bias is not required; a bias lower than that during image printing is sufficient. If the same bias as during image printing is used when discharging during non-image printing, the photosensitive drum 10 may be overcharged, causing the surface potential of the photosensitive drum 10 to become positive after passing the transfer position. This may result in a smaller absolute value of the surface potential of the photosensitive drum 10 during the next image printing, resulting in a higher density. Therefore, as described above, by setting the voltage applied to the transfer roller 62 during discharging to a voltage lower than the voltage applied during image printing or an absolute value of 750 V or less, it is possible to prevent excessive discharging of the photosensitive drum 10 and suppress a higher density during the next image printing.

[0140] At t7, -1100V is applied to the charging roller 160 (this may also be referred to as "switching"). This corresponds to the latter half of the control described in (b). That is, after controlling the application of voltage to the charging roller 160 in the control described in (a), the absolute value of the voltage applied to the charging roller 160 is increased compared to that in the control described in (a). In the control described in (a), -350V is applied to the charging roller 160 from t4 to t7, and in the control described in (b), -1100V, which has an absolute value greater than -350V, is applied at t7. This causes a discharge (pre-charge discharge) between the charging roller 160 and the photosensitive drum 10, and charges the oppositely charged toner on the photosensitive drum 10 to the normal polarity. In this example, the positively charged toner 209 on the photosensitive drum 10 is reversed to a negative polarity. This may also be referred to as "converting to negative toner."

[0141] It is preferable to start the control of the latter half of (b) after starting the control of the former half of (b). In consideration of the positional relationship between the transfer position and the charging position, in the example of the timing chart shown in Figure 8, the control of the former half of (b) starts at t6, and then the control of the latter half of (b) starts at t7.

[0142] Next, at time t8, 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. FIG. 5B shows that the positively charged toner 209 has been reversed to a negative charge, and that the reversed toner 209 is being collected by the developing roller 72 (arrow i).

[0143] This corresponds to the control (c) described above. In other words, the normally charged toner charged to the normal polarity by the control (b) described above is collected by the developing means. The period for which the control (c) described above is performed is not particularly limited, but may be set to, for example, one rotation of the photosensitive drum 10. By rotating the photosensitive drum 10 once, the toner can be collected by the developing means and the photosensitive drum 10 can be prevented from running too far. In this example, the period for which the control (c) described above is performed is from t8 to t10.

[0144] The collection of toner onto the developing roller 72 ends, for example, when all of the positively charged toner on the photosensitive drum 10 has reversed to negative and been collected onto the developing roller 72 .

[0145] The period from t7 to t9 corresponds to, for example, one rotation of the photosensitive drum 10. D1 represents one rotation of the photosensitive drum 10. At t10, preparations are made for charging and developing for printing the next image. The period from t9 to t10 corresponds to, for example, the period from the charging position to the developing position.

[0146] The timing of performing (a) to (c) can be selected appropriately. For example, it can be performed between image printing and the next image printing. When (a) to (c) are performed between image printing and the next image printing, they can be performed every time, or at predetermined intervals. When they are performed every time between image printing and the next image printing, the charging member can be kept clean, and contamination of the charging member can be further reduced. When they are performed at predetermined intervals between image printing and the next image printing, the charging member can be kept clean and the time required for overall control can be shortened. Furthermore, when (a) to (c) are performed between image printing and the next image printing, they can be performed multiple times.

[0147] Based on the above, an example of the timing for carrying out (a) to (c) above will be described below. The control unit performs the steps (a) to (c) between printing an image and the next printing an image, and the control unit performs the steps (a) to (c) at predetermined intervals between printing an image and the next printing an image, thereby keeping the charging member in a cleaner state and further reducing contamination of the charging member.

[0148] Example 4 Next, another example of control in this embodiment will be described. The description of this embodiment 4 can be applied to the above-mentioned embodiment 1 and embodiment 2. The description of the same matters as those in the above-mentioned embodiments will be omitted.

[0149] This fourth embodiment is an example of a case where a transfer cleaning operation is performed. For example, in the example shown in FIG. 8, the transfer cleaning operation may be performed after the control of applying a voltage to the transfer roller 62 in (b) above is performed. The transfer cleaning operation may be performed when, for example, negative toner adheres to the transfer roller 62, and there is a possibility that the back of the paper will be soiled or a transfer failure will occur due to contamination of the transfer roller 62 when the next image is printed. By performing the transfer cleaning operation, the toner adhered to the transfer roller 62 can be moved to the image carrier and collected by the developing means, and it is possible to prevent the back of the paper from being soiled or a transfer failure due to contamination of the transfer roller 62 when the next image is printed.

[0150] This Example 4 will be described. In this embodiment, the control unit 25 further performs the following (d) and (e): The controls for performing the following (d) and (e) correspond to the transfer cleaning operation. (d) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, thereby moving the normally charged toner that has adhered to the transfer member and is charged to the normal polarity to the image carrier. (e) The normally charged toner transferred to the image carrier by (d) is transferred to the developing means.

[0151] This fourth embodiment will be described with reference to Fig. 9. Fig. 9 is an example of a timing chart of this embodiment. Explanation of matters similar to those in the third embodiment will be omitted.

[0152] The transfer cleaning operation in this embodiment occurs from t9 to t10. At t9, for example, -1100 V is applied to the transfer roller 62. Since the voltage applied to the transfer roller 62 during image printing is positive, a negative voltage of the opposite polarity is applied. The absolute value of the voltage is not particularly limited and can be determined appropriately depending on the level of contamination.

[0153] From t9 to t10, the minus toner moves from the transfer roller 62 to the photosensitive drum 10, and the toner that moves to the developing roller 72 as the photosensitive drum 10 rotates is collected by the developing roller 72. The period from t9 to t10 corresponds to the controls (d) and (e) described above.

[0154] It can also be said that t9 is the timing when the transfer roller 62 has neutralized the photosensitive drum 10 for one rotation of the photosensitive drum 10. In other words, the period from t6 to t9 corresponds to one rotation of the photosensitive drum 10, and is represented by D1 in the figure. It can also be said that t9 is the time after the control of the application of voltage (application of +550 V) to the transfer roller 62 in (b) above has been performed.

[0155] The period for performing the transfer cleaning operation in this embodiment, i.e., the period from t9 to t10, can be selected as appropriate. For example, in this example, it is set to two revolutions of the transfer roller 62, and in the figure, two revolutions of the transfer roller 62 are represented by D3. The period for performing the transfer cleaning operation can be determined as appropriate depending on the level of contamination.

[0156] The timing of performing (d) and (e) can be selected appropriately. For example, they can be performed between image printing and the next image printing. When (d) and (e) are performed between image printing and the next image printing, they can be performed every time, or at predetermined intervals. When they are performed every time between image printing and the next image printing, the transfer member can be kept clean, and contamination of the transfer member can be further reduced. When they are performed at predetermined intervals between image printing and the next image printing, the transfer member can be kept clean and the time required for overall control can be shortened. Furthermore, when (d) and (e) are performed between image printing and the next image printing, they can be performed multiple times.

[0157] Based on the above, an example of the timing for carrying out (d) and (e) above will be described below. The control unit performs steps (d) and (e) between printing an image and the next printing an image, and the next printing an image is performed after steps (d) and (e) are completed, and performs steps (d) and (e) at predetermined intervals between printing an image and the next printing an image. By doing so, the charging member can be kept in a cleaner state, and contamination of the charging member can be further reduced.

[0158] Example 5 Next, another example of control in this embodiment will be described. The description of this embodiment 5 can be applied to the above-mentioned embodiment 1 and embodiment 2. The description of the same matters as those in the above-mentioned embodiments will be omitted.

[0159] This fifth embodiment is an example of a case where a cleaning operation (also referred to as a cleaning mode) of the charging member is performed. For example, if the operation of moving the oppositely charged toner from the charging roller 160 to the photosensitive drum 10 by the above (a) is insufficient, the cleaning operation of the charging member may be performed. The cleaning operation of the charging member is performed, for example, at the end of the image printing operation, before preparation for the next image printing.

[0160] This fifth embodiment will be described with reference to Fig. 10. Fig. 10 is an example of a timing chart of this embodiment. Explanations of matters similar to those of the above embodiments will be omitted. The cleaning operation of the charging member is started from t1, which can be, for example, the timing of t10 in Fig. 8, and is carried out during non-image printing. Between t1 and t2, there is a state where the surface potential of the photosensitive drum 10 is zero, so +250 V is applied to the developing roller 72 to prevent the negative toner from moving from the developing roller 72 to the photosensitive drum 10. The period from t1 to t2 corresponds to the period from the charging position to the developing position.

[0161] From t1 to t4, −1100 V is applied to the charging roller 160. Furthermore, t1 to t4 corresponds to one rotation (D1) of the photosensitive drum 10. In this way, when −1100 V is applied to the charging roller 160 for one rotation of the photosensitive drum 10 from t1 to t4, the surface potential of the photosensitive drum 10 becomes, for example, −500 V. Therefore, the relationship between the charging roller 160 from t4 to t10 in FIG. 10 is the same as that between t3 and t9 in FIG. 8, and toner moves from the charging roller 160 to the photosensitive drum 10, and is then collected by the developing roller 72.

[0162] 10, in this fifth embodiment, the control (operation) performed from t4 to t10 is repeated. As a result, toner is expelled from the charging roller 160 multiple times, and the state of the charging roller 160 becomes even cleaner. After the repetition, t11 and thereafter are the same as, for example, t10 and thereafter in FIG. 8. In this way, the charging roller 160 can be kept even cleaner, and poor charging and abnormal images caused by dirt on the charging roller 160 can be suppressed.

[0163] In this example, the period from t4 to t7 is set to three revolutions of the charging roller 160 (D2 in the figure). In this case, the charging roller 160 can be cleaned and the operation time can be prevented from becoming too long. On the other hand, in order to increase the amount of dust discharged from the charging member and improve cleaning performance, the period from t4 to t7 may be set to more than three revolutions of the charging roller 160. Furthermore, the number of times t4 to t10 are repeated can be selected appropriately, and may be increased to improve cleaning performance.

[0164] The cleaning operation (cleaning mode) of the charging member is preferably performed at predetermined intervals to prevent the accumulation of residual toner stains on the charging member. The predetermined interval is preferably determined using a factor that correlates with an increase in stains, such as the cumulative print dot count or cumulative travel distance. The cleaning mode may also be initiated by a user.

[0165] 11 is another example of a timing chart of this embodiment. Explanation of matters similar to those in the above embodiment will be omitted. Figure 11 shows an example in which a transfer cleaning operation is further performed in the example shown in Figure 10. In the figure, from t11 to t12, the transfer cleaning operation described in Example 4 above is performed. In this example, since the transfer cleaning operation is performed in addition to the cleaning operation of the charging member, the device can be kept even cleaner.

[0166] Example 6 Next, another example of control in this embodiment will be described. The description of this embodiment 5 can be applied to the above-mentioned embodiment 1 and embodiment 2, etc. Explanation of matters similar to those in the above-mentioned embodiments will be omitted.

[0167] In this sixth embodiment, the transfer roller 62 is separated from the photosensitive drum 10 while the control (a) is being performed. This prevents the oppositely charged toner (e.g., positive toner) from adhering to the transfer roller 62 when the oppositely charged toner passes through the transfer position. Furthermore, after the control (a), the transfer roller 62 is brought into contact with the photosensitive drum 10 when the control (b) is performed. This prevents the control of the separation of the transfer roller 62 from affecting the de-electrification of the photosensitive drum 10.

[0168] This example will be described again. The image forming apparatus of this embodiment has a contact / separation mechanism that brings the transfer member into contact with and separates it from the image carrier, and the contact / separation mechanism is controlled by the control unit, and the control unit separates the transfer member from the image carrier from the start of control (a) until it performs control (b), and brings the transfer member into contact with the image carrier when performing control (b).

[0169] Regarding the contact and separation of the transfer roller 62 with the photosensitive drum 10, for example, in the section from t3 to t6 in FIG. 8, the transfer roller 62 is separated from the photosensitive drum 10. In this case, the transfer roller 62 is brought into contact with the photosensitive drum 10 at t6.

[0170] A contact / separation mechanism controlled by the control unit is used to move the transfer roller 62 toward and away from the photosensitive drum 10. The contact / separation mechanism is not particularly limited and can be selected appropriately.

[0171] 12 is a schematic diagram for explaining the present embodiment 6. In the drawing, a contact / separation mechanism 164 is shown, and the contact / separation mechanism 164 is controlled by the control unit 25 to contact and separate the transfer roller 62 with respect to the photosensitive member 10. The contact / separation mechanism 164 may be configured, for example, by a cam that contacts the shaft portion of the transfer roller 62 and a cam drive motor that rotates the cam. The control unit 25 controls the cam drive motor to rotate the cam, thereby displacing the transfer roller 62 between a position in contact with the photosensitive drum 10 and a position separated from the photosensitive drum 10. The contact / separation mechanism 164 may be a mechanism that moves the transfer roller 62 using a solenoid, other than a cam mechanism.

[0172] (Second 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 voltage of the charging roller (charging member) is controlled based on the absolute humidity determined from the temperature and humidity. That is, in this embodiment, the control unit controls the voltage to be applied to the charging member based on the absolute humidity inside or outside the image forming apparatus, and such control is performed during image printing and / or non-image printing.

[0173] The control can be performed, for example, as follows: A memory (storage unit) is used for image formation, and multiple settings for the voltage applied to the charging roller are stored in advance. The voltage applied to the charging roller is selected from the various settings according to the absolute humidity, and the settings are changed accordingly.

[0174] The absolute humidity is calculated based on the output of a sensor that detects the temperature and humidity inside or outside the image forming apparatus. The calculated absolute humidity is compared with a threshold value pre-stored in the memory of the image forming apparatus. If the absolute humidity is below the threshold, the applied voltage is switched to a value lower than the applied voltage value selected when the threshold is not exceeded.

[0175] For example, when the absolute humidity is low, the toner becomes more easily charged, so the voltage applied to the charging roller during image formation is set high to ensure density, and when recovered by the developing means, the voltage applied to the charging roller during pre-charge discharge is lowered to prevent the transfer residual toner from becoming highly charged. According to this embodiment, when pre-charge discharge is performed, the transfer residual toner can be stably charged to an appropriate amount without being affected by changes in absolute humidity.

[0176] For example, aspects of the present invention are as follows. <1> an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member facing the image carrier and transferring the toner image onto a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit that controls a first recovery operation in which a DC bias is applied to the charging member during image printing, and reversely charged toner that is charged to a polarity opposite to a normal charge among transfer residual toner remaining on the image carrier after transfer is moved to the charging member, and a second recovery operation in which, during non-image printing, the transfer residual toner that has moved to the charging member is moved from the charging member to the image carrier and then to the developing means, The control unit performs the following steps (a) to (c) in the second collecting operation: An image forming apparatus characterized by: (a) The application of voltage to the transfer member is stopped, or the transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the same polarity as that applied to the transfer member during image printing, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means. <2> When applying a voltage of the same polarity as that applied to the transfer member during image printing in (b), the control unit applies a voltage lower than that applied during image printing to the transfer member. Characterized by <1> 2. The image forming apparatus according to claim 1 . <3> The control unit, when applying a voltage of the same polarity as that applied to the transfer member during image printing in (b), to the transfer member, sets the absolute value of the voltage applied to the transfer member to 750 V or less. Characterized by <1> or <2> 2. The image forming apparatus according to claim 1 . <4> a contact / separation mechanism for contacting and separating the transfer member with respect to the image carrier; the contact / separation mechanism is controlled by the control unit, The control unit separates the transfer member from the image carrier from when the control of (a) is started until the control of (b) is performed, and brings the transfer member into contact with the image carrier when the control of (b) is performed. Characterized by <1> from <3> 10. The image forming apparatus according to claim 9, wherein <5> The control unit performs the steps (a) to (c) between image printing and the next image printing, and performs the next image printing after the steps (a) to (c) are completed, and performs the steps (a) to (c) at predetermined intervals during the period between image printing and the next image printing. Characterized by <1> from <4> 10. The image forming apparatus according to claim 9, wherein <6> The control unit further performs the following (d) and (e): Characterized by <1> from <5> 10. The image forming apparatus according to claim 9, wherein (d) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, thereby moving the normally charged toner that has adhered to the transfer member and is charged to the normal polarity to the image carrier. (e) The normally charged toner transferred to the image carrier by (d) is transferred to the developing means. <7> The control unit performs the steps (d) and (e) between image printing and the next image printing, and the next image printing is performed after the steps (d) and (e) are completed, and performs the steps (d) and (e) at predetermined intervals during the period between image printing and the next image printing. Characterized by <6> 2. The image forming apparatus according to claim 1 . <8> The control unit controls the voltage applied to the charging member based on the absolute humidity inside or outside the image forming apparatus. Characterized by <1> from <7> 10. The image forming apparatus according to claim 9, wherein <9> an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member that faces the image carrier and transfers the toner image onto a transfer target, the method comprising: a first recovery step of applying a DC bias to the charging member during image printing, thereby transferring toner particles charged to a polarity opposite to a normal charge among the residual toner particles remaining on the image carrier after transfer to the charging member; a second recovery step of recovering the transfer residual toner that has been transferred to the charging member during non-image printing, from the charging member to the image carrier and then to the developing means, The method for recovering residual toner after transfer, characterized in that the second recovery step comprises the following steps (a) to (c): (a) The application of voltage to the transfer member is stopped, or a voltage of the opposite polarity to the voltage applied to the transfer member during image printing is applied to the transfer member, and the absolute value of the voltage applied to the charging member is made smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) A voltage of the same polarity as that applied to the transfer member during image printing is applied to the transfer member, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the absolute value of the voltage applied to the charging member is made larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means. [Explanation of symbols]

[0177] 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 162 Charging brush roller 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]

[0178] [Patent Document 1] Japanese Patent Application Publication No. 10-213968 [Patent Document 2] Japanese Patent Application Publication No. 2023-137933

Claims

1. an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a charging voltage applying means for applying a voltage to the charging member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member facing the image carrier and transferring the toner image onto a transfer target; a transfer voltage applying means for applying a voltage to the transfer member; a control unit that controls a first recovery operation in which a DC bias is applied to the charging member during image printing, and reversely charged toner that is charged to a polarity opposite to a normal charge among transfer residual toner remaining on the image carrier after transfer is moved to the charging member, and a second recovery operation in which, during non-image printing, the transfer residual toner that has moved to the charging member is moved from the charging member to the image carrier and then to the developing means, The control unit performs the following steps (a) to (c) in the second collection operation: An image forming apparatus characterized by: (a) The application of voltage to the transfer member is stopped, or the transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member smaller than the absolute value of the voltage applied to the charging member during image printing, thereby moving the oppositely charged toner, which has been charged to a polarity opposite to the normal polarity, from the charging member to the image carrier. (b) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the same polarity as that applied to the transfer member during image printing, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the charging voltage application means is controlled so as to make the absolute value of the voltage applied to the charging member larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means.

2. When applying a voltage of the same polarity as that applied to the transfer member during image printing in (b), the control unit applies a voltage lower than that applied during image printing to the transfer member.

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

3. The control unit, when applying a voltage of the same polarity as that applied to the transfer member during image printing in (b), to the transfer member, sets the absolute value of the voltage applied to the transfer member to 750 V or less.

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

4. a contact / separation mechanism for contacting and separating the transfer member with respect to the image carrier; the contact / separation mechanism is controlled by the control unit, The control unit separates the transfer member from the image carrier from when the control of (a) is started until the control of (b) is performed, and brings the transfer member into contact with the image carrier when the control of (b) is performed.

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

5. The control unit performs the steps (a) to (c) between image printing and the next image printing, and the next image printing is performed after the steps (a) to (c) are completed, and performs the steps (a) to (c) at predetermined intervals during the period between image printing and the next image printing.

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

6. The control unit further performs the following (d) and (e):

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium. (d) The transfer voltage application means is controlled so as to apply to the transfer member a voltage of the opposite polarity to the voltage applied to the transfer member during image printing, thereby moving the normally charged toner that has adhered to the transfer member and is charged to the normal polarity to the image carrier. (e) The normally charged toner transferred to the image carrier by (d) is transferred to the developing means.

7. The control unit performs the steps (d) and (e) between image printing and the next image printing, and the next image printing is performed after the steps (d) and (e) are completed, and performs the steps (d) and (e) at predetermined intervals during the period between image printing and the next image printing.

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

8. The control unit controls the voltage applied to the charging member based on the 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.

9. an image carrier; a charging member that contacts the image bearing member and charges the image bearing member; a developing means for supplying toner to the image carrier and forming a toner image on the image carrier; a transfer member that faces the image carrier and transfers the toner image onto a transfer target, the method comprising: a first recovery step of applying a DC bias to the charging member during image printing, thereby transferring toner particles, which are charged to a polarity opposite to the normal charge, among the residual toner particles remaining on the image carrier after transfer, to the charging member; a second recovery step of recovering the transfer residual toner that has been transferred to the charging member during non-image printing, from the charging member to the image carrier and then to the developing means, The method for recovering residual toner after transfer, wherein the second recovery step comprises the following steps (a) to (c): (a) By stopping the application of voltage to the transfer member, or by applying a voltage of the opposite polarity to the voltage applied to the transfer member during image printing to the transfer member, and by making the absolute value of the voltage applied to the charging member smaller than the absolute value of the voltage applied to the charging member during image printing, the reversely charged toner, which has been charged to a polarity opposite to the normal polarity, is moved from the charging member to the image carrier. (b) A voltage of the same polarity as that applied to the transfer member during image printing is applied to the transfer member, and the absolute value of the surface potential of the image carrier is made smaller than the absolute value of the surface potential before passing through a position facing the transfer member, and the absolute value of the voltage applied to the charging member is made larger than that in (a), thereby causing discharge between the charging member and the image carrier, and charging the oppositely charged toner that has moved onto the image carrier by (a) to the normal polarity. (c) The normally charged toner charged to the normal polarity by (b) is moved to the developing means.

Images