JP7809509B2 - Image forming device - Google Patents

Description

The present invention relates to electrophotographic image forming devices such as laser printers, copiers, and facsimiles.

Image forming devices using electrophotography are widely used. Furthermore, these image forming devices commonly use a process cartridge system in which the photosensitive drum and the process means that act on it are detachably attached to the main body of the image forming device as a single unit.

In recent years, cleanerless systems have been proposed with the aim of reducing the size of image forming apparatus main bodies and process cartridges (Patent Document 1). Cleanerless image forming apparatuses are not equipped with a dedicated cleaning device that removes and collects residual toner remaining on the surface of the photosensitive drum after the transfer process. In cleanerless image forming apparatuses, residual toner remaining on the surface of the photosensitive drum is removed from the surface of the photosensitive drum by a developing unit during the development process, collected, and reused (simultaneous cleaning during development).

However, in cleanerless image forming devices, a cleaning device for collecting residual toner after transfer is not located downstream of the transfer unit and upstream of the charging unit in the rotation direction of the photosensitive drum. As a result, areas on the photosensitive drum where paper dust adheres during the transfer process may become insufficiently charged during the charging process, which can result in poor image quality due to toner spots being missing during the development process.

In response, a configuration has been proposed in which a brush member (fixed brush) is positioned downstream of the transfer unit and upstream of the charging unit in the rotational direction of the photosensitive drum to collect paper dust that adheres to the surface of the photosensitive drum during the transfer process (Patent Document 2). The brush member accumulates not only paper dust, but also residual toner after transfer and toner on non-image areas of the photosensitive drum (fogging toner). If too much toner accumulates on the brush member, it cannot retain it all, causing the toner to slip through the brush member. This toner can then adhere to a charging member, which serves as a charging means, resulting in poor charging.

In response to this, a voltage can be applied to the brush member to make it easier for the toner to pass through. However, even when the brush member is made conductive and a voltage is applied to it in this way, the brush member is essentially always in contact with the photosensitive drum, so toner is captured and accumulates on the brush member. Therefore, in order to prevent excessive toner accumulation on the brush member, it is necessary, for example, to periodically expel toner from the brush member and clean the brush member.

Japanese Patent Application Laid-Open No. 2003-91181 Japanese Patent Application Laid-Open No. 2005-114754

Further improvements are needed with regard to brush members used to collect paper dust. For example, there is a need for a system that can clean the brush member by expelling both toner of normal polarity (the primary charging polarity of the toner during the development process) and non-normal polarity (opposite polarity to the normal polarity). Furthermore, for example, when the potential difference between the voltage applied to the brush member and the surface potential of the photosensitive drum is changed to clean the brush member, if a large amount of toner is expelled from the brush member in an instant, the toner may adhere to the charging member. For example, if toner adheres to a charging roller serving as a charging member, image defects may occur during the rotational cycle of the charging roller. Therefore, there is also a need to address issues caused by toner expelled from the brush member during the cleaning operation of the brush member.

The object of the present invention is to improve the cleaning performance of a brush member arranged in contact with a photosensitive drum.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image forming apparatus comprising: a rotatable photosensitive member; a charging member for charging the surface of the photosensitive member at a charging position; an exposure device for exposing the charged surface of the photosensitive member at an exposure position to form an electrostatic image on the surface of the photosensitive member; a developing device for supplying toner charged to a normal polarity to the electrostatic image on the surface of the photosensitive member at a development position to form a toner image on the surface of the photosensitive member; a transfer member for transferring the toner image on the surface of the photosensitive member to a transfer receiving member at a transfer position; a brush member that contacts the surface of the photosensitive member at a brush contact position downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member; a brush voltage application unit that applies a brush voltage to the brush member; and a control unit that controls the surface potential of the photosensitive member at the brush contact position, In an image forming apparatus in which the developing device recovers toner that accumulates on the surface of the photosensitive member, the control unit controls the surface potential of the photosensitive member at the brush contact position so that, when the contact position potential difference is the value obtained by subtracting the surface potential of the photosensitive member at the brush contact position from the value of the brush voltage, during a brush cleaning operation to clean the brush member, the control unit changes the contact position potential difference from a first potential difference to a second potential difference in a predetermined direction, either an increasing direction or a decreasing direction , and then changes the contact position potential difference from the second potential difference to a third potential difference in the predetermined direction, and the control unit controls the surface potential of the photosensitive member at the brush contact position so that the sign of the contact position potential difference is both positive and negative during the brush cleaning operation .

This invention improves the cleaning performance of the brush member placed in contact with the photosensitive member.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 4 is a timing chart for explaining the control of the first embodiment. FIG. 10 is a timing chart for explaining control of a modified example of the first embodiment. 5A and 5B are schematic diagrams for explaining the behavior of toner accumulated on a brush. 10A and 10B are schematic diagrams for explaining changes in the attitude of the brush. FIG. 10 is a timing chart for explaining the control of the second embodiment. FIG. 2 is a schematic block diagram for explaining a control mode of the image forming apparatus. FIG. 2 is a schematic block diagram illustrating a power supply configuration of the image forming apparatus. 10A and 10B are schematic diagrams for explaining another example of a method for controlling the surface potential of a photosensitive drum.

The image forming apparatus according to the present invention will be described in further detail below with reference to the drawings.

[Example 1]
1. Configuration and Operation of Image Forming Apparatus Fig. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a monochrome printer capable of forming a black monochrome image using an electrophotographic system (electrophotographic image forming process).

The image forming apparatus 100 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as an image carrier. In this embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member. This photosensitive drum 1 has a photosensitive layer on a grounded aluminum drum-shaped substrate, and is driven to rotate at a predetermined process speed in the direction of arrow R1 (clockwise) in the figure by a drive device (not shown). In this embodiment, the process speed corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1. Around the photosensitive drum 1, a charging roller 2, an exposure device 4, a developing device 3, a transfer roller 5, and a brush member 11, which will be described later, are provided.

The charging roller 2, a roller-type charging member (contact charging member) serving as charging means, contacts the photosensitive drum 1 with a predetermined pressure, forming a charging section. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 2. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging roller 2 by a charging power supply (high-voltage power supply) E1 (Figure 7), which serves as charging voltage application means (charging voltage application section).

In this embodiment, the exposure device 4 serving as the exposure means is a laser scanner device. The exposure device 4 outputs laser light corresponding to image information input from an external device such as a host computer, and scans and exposes the surface of the uniformly charged photosensitive drum 1. This exposure forms an electrostatic latent image (electrostatic image) corresponding to the image information on the surface of the photosensitive drum 1. Note that the exposure device 4 is not limited to a laser scanner device, and may, for example, be an LED array in which multiple LEDs are arranged along the rotational axis of the photosensitive drum 1.

The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed (visualized) by the developing device 3, which supplies toner as developer, to form a toner image (toner image, developer image) on the surface of the photosensitive drum 1. In this embodiment, a contact development method is used. The developing device 3 includes a developing roller 31 as a developer carrier (developing member), a toner supply roller 32 as developer supply means, a developer storage chamber 33 that stores toner, and a developing blade 34 as a regulating member that regulates the toner layer thickness on the developing roller 31. The toner supplied from the developer storage chamber 33 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity as it passes through the contact area between the developing roller 31 and the developing blade 34. In this embodiment, a one-component non-magnetic developer with an average particle size of 6 μm and a normal charging polarity (normal polarity) of negative is used as the developer. While this embodiment employs a single-component non-magnetic contact development method, other development methods, such as two-component non-magnetic contact/non-contact development, or magnetic development, may also be employed. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by toner delivered by the developing roller 31 at the development section, where the developing roller 31 faces (contacts) the photosensitive drum 1. During the development process, a predetermined development voltage (development bias) is applied to the developing roller 31 by a development power supply (high-voltage power supply) E2 ( FIG. 7 ), which serves as a development voltage application means (development voltage application section). In this embodiment, toner charged with the same polarity as the photosensitive drum 1 (negative polarity in this embodiment) adheres to the image area (image area) of the photosensitive drum 1 after charging, where the charge has decayed due to exposure (reverse development method).

Opposing the photosensitive drum 1 is a transfer roller 5, a roller-type transfer member serving as a transfer means. The transfer roller 5 is pressed against the photosensitive drum 1, forming a transfer section where the photosensitive drum 1 and the transfer roller 5 are in pressure contact. A transfer power supply (high-voltage power supply) E3 (Figure 7) serving as a transfer voltage application means (transfer voltage application section) is connected to the transfer roller 5, and a predetermined voltage is applied at a predetermined timing. The toner image formed on the surface of the photosensitive drum 1 is transferred to the surface of the recording material S, which is being conveyed between the photosensitive drum 1 and the transfer roller 5 at the transfer section. During the transfer process, the transfer power supply (high-voltage power supply) E3 (Figure 7) applies a predetermined transfer voltage (transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner, to the transfer roller 5. The transfer roller 5 preferably has an elastic layer formed from an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or NBR (nitrile butadiene rubber). In particular, a transfer roller 5 having a foamed elastic layer made of a foamed elastic material such as sponge rubber is suitable.

The recording material S is stored in a cassette 6. The recording material S stored in the cassette 6 is fed one sheet at a time from the cassette 6 by a feeding unit 7 and transported to a pair of registration rollers 8. The recording material S is then transported to the transfer unit by the pair of registration rollers 8 in time with the toner image formed on the surface of the photosensitive drum 1 reaching the transfer unit.

The recording material S with the transferred toner image is transported to a fuser 9, which serves as a fixing means. In this embodiment, the fuser 9 is a film heating type having a fuser film 91 and a pressure roller 92 that presses against the fuser film 91. A fuser heater and a thermistor for measuring the temperature of the fuser heater are disposed on the inner surface of the endless fuser film 91. The fuser 9 then heats and presses the recording material S carrying the unfixed toner image while transporting it using the fuser film 91 and pressure roller 92, thereby fixing (melting and adhering) the toner image to the surface of the recording material S. The recording material S with the fused toner image is then discharged (output) to the outside of the image forming apparatus main body 110 by a pair of discharge rollers 10 and loaded onto a tray 15 located at the top of the image forming apparatus main body 110.

In addition, any adhering matter, such as toner (residual toner) that remains on the surface of the photosensitive drum 1 without being transferred to the recording material S during the transfer process, is removed from the surface of the photosensitive drum 1 in the following process.

Transfer residual toner is primarily toner that is negatively charged, which is the normal polarity. However, transfer residual toner also contains a mixture of positively charged toner and toner that is negatively charged but does not have a sufficient charge. Transfer residual toner is recharged to negative polarity by discharge in the charging section. Transfer residual toner that has been recharged to negative polarity in the charging section reaches the development section as the photosensitive drum 1 rotates. Here, as described above, an electrostatic latent image is formed on the surface of the photosensitive drum 1 that has reached the development section. The behavior of transfer residual toner that has reached the development section will be explained separately for the image area (exposed area) and non-image area (non-exposed area) on the surface of the photosensitive drum 1.

Residual toner adhering to the non-image areas of the photosensitive drum 1 is transferred to the developing roller 31 in the developing section due to the potential difference between the potential of the non-image areas on the surface of the photosensitive drum 1 and the development voltage, and is then removed from the photosensitive drum 1 and collected in the developer storage chamber 33. The potential of the development voltage is set to a potential between the potential of the non-image areas on the surface of the photosensitive drum 1 and the potential of the image areas (exposed areas). The toner collected in the developer storage chamber 33 is used again for image formation.

Residual toner adhering to the image area (exposed area) on the surface of the photosensitive drum 1 does not transfer from the photosensitive drum 1 to the developing roller 31 in the development section. This residual toner, together with the toner supplied from the developing roller 31 to the photosensitive drum 1, forms a toner image, which is transferred to the recording material S in the transfer section and then removed from the photosensitive drum 1.

The structure and function of the brush member 11 as a paper dust removal means will be explained in detail later.

In this embodiment, the photosensitive drum 1, the charging roller 2 acting as the process means, the developing device 3, and the brush member 11 (described later) integrally constitute a process cartridge 14 that is detachable from the image forming apparatus main body 110.

Here, the position on the photosensitive drum 1 where charging is performed by the charging roller 2 in the direction of rotation of the photosensitive drum 1 is the charging position P1. In this embodiment, the charging roller 2 charges the surface of the photosensitive drum 1 by utilizing discharges generated in at least one of the minute gaps formed upstream and downstream of the contact point between the charging roller 2 and the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1. However, for simplicity, the position on the photosensitive drum 1 that contacts the charging roller 2, i.e., the position on the photosensitive drum 1 that forms the above-mentioned charging portion, can be considered to be the charging position P1. More precisely, the charging position P1 can be defined as the intermediate position between the most upstream and most downstream positions of the contact point between the charging roller 2 and the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1. Furthermore, the position on the photosensitive drum 1 where light is irradiated by the exposure device 4 in the direction of rotation of the photosensitive drum 1 is the exposure position P2. Furthermore, the position on the photosensitive drum 1 where toner is supplied from the developing roller 31 in the rotational direction of the photosensitive drum 1 (the position where the developing roller 31 contacts), i.e., the position on the photosensitive drum 1 where the above-mentioned developing portion is formed, is the development position P3. The position on the photosensitive drum 1 where toner is transferred to the recording material S on the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 (the position where the transfer roller 5 contacts), i.e., the position on the photosensitive drum 1 where the above-mentioned transfer portion is formed, is the transfer position P4. The position on the photosensitive drum 1 where paper dust is removed by the brush member 11 (described later) in the rotational direction of the photosensitive drum 1 (the position where the brush member 11 contacts), i.e., the position on the photosensitive drum 1 where the below-described brush contact portion is formed, is the brush contact position P5. The development position P3, transfer position P4, and brush contact position P5 can also be intermediate positions between the most upstream and most downstream positions in the rotational direction of the photosensitive drum 1.

7 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 50. The control unit 50 has a CPU 51 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage element) 52 such as a ROM or RAM as a storage means, an input/output unit (not shown) that controls the exchange of signals between the control unit 50 and elements connected to the control unit 50, and the like. The RAM stores the detection results of the sensors, the arithmetic results, and the like, and the ROM stores the control program, a pre-determined data table, and the like.

The control unit 50 is a control means capable of comprehensively controlling the operation of the image forming apparatus 100. Each unit of the image forming apparatus 100 is connected to the control unit 50. In this embodiment, the control unit 50 is connected to, for example, the charging power supply E1, the development power supply E2, the transfer power supply E3, the brush power supply E4 (described later), and the exposure device 4. In this embodiment, the transfer power supply E3 is configured to be able to apply positive and negative voltages to the transfer roller 5. The control unit 50 controls the operation (ON/OFF and output value) of the various power supplies (bias supply means), the operation (ON/OFF and exposure amount) of the exposure device 4, and the timing of these operations, thereby enabling the image forming operation and the brush cleaning operation (described later) to be performed.

The image forming apparatus 100 is capable of executing a print job (printing operation), which is a series of operations for forming an image on one or more recording materials S, initiated by a single start instruction. In this embodiment, the start instruction is input to the image forming apparatus 100 from an external device such as a personal computer. A print job generally includes an image formation process (printing process), a pre-rotation process, a paper spacing process when forming images on multiple recording materials S, and a post-rotation process. The image formation process is the period during which an electrostatic latent image is actually formed on the photosensitive drum 1, the electrostatic latent image is developed (a toner image is formed), the toner image is transferred, and the toner image is fixed; this period is referred to as the image formation period. More specifically, the timing of the image formation process differs depending on the positions where the electrostatic latent image is formed, the toner image is formed, the toner image is transferred, and the toner image is fixed. The pre-rotation process is the period during which preparatory operations are performed prior to the image formation process. The inter-sheet process (inter-image process) is the period between recording materials S when image formation is performed continuously on multiple recording materials S (during continuous image formation). The post-rotation process is the period during which a preparation operation (preparatory operation) is performed after the image formation process. The non-image formation period refers to periods other than image formation, including the pre-rotation process, inter-sheet process, post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state. Here, the timing during image formation corresponds to the period during which the image formation area on the photosensitive drum 1 passes through the positions where the electrostatic image is formed, the toner image is formed, the toner image is transferred, and the toner image is fixed. The timing during non-image formation corresponds to the period during which the non-image formation area on the photosensitive drum 1 passes through each of the above positions. The image formation area on the photosensitive drum 1 is the area where an image can be formed that is transferred to the recording material S and output from the image forming apparatus 100, and the non-image formation area is the area other than the image formation area.

Figure 8 is a schematic block diagram showing a power supply configuration different from that shown in Figure 7 that can be applied to the image forming apparatus 100 of this embodiment. Note that in Figure 8, elements having the same or corresponding functions or configurations as those shown in Figures 1 and 7 are assigned the same reference numerals as in Figures 1 and 7. Below, we will focus on the differences between the configuration in Figure 8 and the configuration in Figure 7. In the configuration in Figure 8, the development power supply E2 applies a development voltage to the development roller 31, and also applies a voltage to the development blade 34 and toner supply roller 32. In other words, the development roller 31, development blade 34, and toner supply roller 32 share a common power supply. For example, development voltage E2 applies a voltage of -380 V to the development roller 31, -580 V to the development blade, and -580 V to the toner supply roller. Power supply E1 (negative voltage source) applies a negative voltage to the transfer roller 5 and charging roller 2. In other words, the transfer roller 5 and charging roller 2 share a common power supply. The application of a negative voltage to the transfer roller 5 is performed, for example, to return toner or paper dust adhering to the transfer roller 5 to the photosensitive drum 1. Power source E3 (positive voltage source) also applies a positive transfer voltage to the transfer roller 5. A current detection circuit 801 is used to detect current during constant current control. A switch 802 switches ON/OFF the application of the negative voltage from power source E1 to the transfer roller 5. During normal image formation, the control unit 50 sets switch 802 to OFF, applying only the positive voltage from power source E3 to the transfer roller 5. FIG. 8 also shows a pre-exposure lamp, not shown in FIG. 1. A pre-exposure lamp may also be provided in this embodiment. The configuration of FIG. 8 simplifies the device configuration by sharing the same power source as described above. When the configuration of FIG. 8 is applied, the brush cleaning operation described below can be performed by controlling power sources E1, E3, and switch 802 with the control unit 50.

3. Brush Member Next, the structure and operation of the brush member 11 in this embodiment will be described.

As shown in FIG. 1, the image forming apparatus 100 of this embodiment has a brush member 11, which is a paper dust removal member (collection member) that serves as a paper dust removal means (paper dust removal mechanism). Paper dust is fibrous foreign matter derived from paper, and is generally pulp fibers, primarily composed of cellulose, that have peeled off from the paper, and may also contain fillers that have peeled off from the paper.

The brush member 11 is composed of pile yarns 11a, which are made of multiple bristles that rub against the surface of the photosensitive drum 1, and a base fabric 11b that supports the pile yarns 11a. The brush member 11 is positioned so that it contacts the photosensitive drum 1 downstream of the transfer position (transfer section) P4 and upstream of the charging position (charging section) P1 in the rotation direction (surface movement direction) of the photosensitive drum 1, forming a brush contact section (recovery section). The brush member 11 is supported by a support member (not shown) and positioned in a fixed position relative to the photosensitive drum 1, rubbing against the surface of the photosensitive drum 1 as the photosensitive drum 1 moves. As mentioned above, the position on the photosensitive drum 1 that forms the brush contact section in the rotation direction of the photosensitive drum 1 is the brush contact position P5.

The brush member 11 collects (recovers) paper dust and other adhering matter transferred from the recording material S onto the photosensitive drum 1 at the transfer position P4, reducing the amount of paper dust that moves toward the charging position P1 and development position P3 downstream of the brush contact position P5 in the rotational direction of the photosensitive drum 1.

In this embodiment, the pile yarns 11a of the brush member 11 are made of conductive nylon fibers, with nylon used as a binder and carbon mixed in as a conductive material. However, the material of the pile yarns 11a of the brush member 11 is not limited to this. Materials that use polyester or acrylic as a binder, for example, can also be used for the pile yarns 11a of the brush member 11, as long as they are conductive.

In this embodiment, the length of the brush member 11 in the direction generally parallel to the circumferential direction of the photosensitive drum 1 (hereinafter also referred to as the "short direction") is set to 5 mm. However, the length of the brush member 11 in the short direction is not limited to this. The length of the brush member 11 in the short direction may be changed as appropriate depending on, for example, the amount of paper dust, which changes depending on the lifespan of the image forming apparatus 100 or process cartridge 14 (which tends to increase as the lifespan increases).

In this embodiment, the pile length of the brush member 11 is set to 5 mm. However, the pile length of the brush member 11 is not limited to this. However, when using the brush member 11 to collect paper dust, it is necessary to ensure that the brush member 11 penetrates the photosensitive drum 1 by a certain amount or more. Therefore, if the pile length of the brush member 11 is short, the contact pressure with the photosensitive drum 1 will be strong, and there is a risk of damaging the surface of the photosensitive drum 1 due to friction. Therefore, it is desirable that the pile length of the brush member 11 be 4 mm or more. Although not limited to this, the pile length of the brush member 11 is typically 10 mm or less. The pile length of the brush member 11 is the distance to the tip of the pile yarn 11a exposed from the base fabric 11b when the brush member 11 is in a standalone state, i.e., when no external force is being applied to bend the pile yarn 11a.

In this embodiment, the length of the brush member 11 in the direction substantially parallel to the rotational axis of the photosensitive drum 1 (hereinafter also referred to as the "longitudinal direction") is set to 230 mm. However, the longitudinal length of the brush member 11 is not limited to this. The longitudinal length of the brush member 11 may be changed as appropriate depending on, for example, the maximum image formation width of the image forming device 100.

In this embodiment, the fineness of the brush member 11 is set to 2d (meaning 2g per 9000m of fiber). Note that "d" stands for denier. However, the fineness of the brush member 11 is not limited to this. However, if the fineness is high, each fiber will be stiff, and the contact pressure of the brush member 11 against the photosensitive drum 1 will be strong, which may damage the surface of the photosensitive drum 1 due to friction. For this reason, it is desirable that the fineness of the brush member 11 be 6d or less. Although not limited to this, the fineness of the brush member 11 is typically 1d or more.

In this embodiment, the density of the brush member 11 is set to 240 kF/ ^inch2 (kF/ ^inch2 is a unit of brush density, indicating the number of filaments per square inch). However, the density of the brush member 11 is not limited to this. However, when the brush member 11 is used for collecting paper dust, a low density increases the possibility that the paper dust will slip through. Therefore, it is desirable that the density be 120 kF/ ^inch2 or more. Although not limited to this, the density of the brush member 11 is typically set to 300 kF/ ^inch2 or less.

In this embodiment, the penetration depth of the brush member 11 is set to 1.5 mm. However, the penetration depth of the brush member 11 is not limited to this. However, when using the brush member to collect paper dust, if the penetration depth of the brush member 11 into the photosensitive drum 1 is small, the paper dust is more likely to slip through. Therefore, it is desirable that the penetration depth of the brush member 11 be 1 mm or more. Although not limited to this, the penetration depth of the brush member 11 is typically 3 mm or less. Note that when the pile length is L1 and the shortest distance from the base fabric 11b of the brush member 11 fixed to the support member to the photosensitive drum 1 is L2, the difference between L2 and L1 is the penetration depth of the brush member 11 into the photosensitive drum 1.

In this embodiment, a brush power supply (high-voltage power supply) E4 (Figure 7) serving as a brush voltage application means (brush voltage application unit) is connected to the brush member 11, and a predetermined voltage is applied at a predetermined timing. In this embodiment, a negative voltage is applied from the brush power supply E4 to the brush member 11 mainly to collect positive paper dust adhering to the negative surface of the photosensitive drum 1 at the transfer position P4. In this embodiment, the brush power supply E4 applies a voltage in the range of -500V to 0V to the brush member 11.

In this example, the electrical resistance of the brush member 11 was 1.0 x 10 ⁵ Ω when measured as follows: The brush member 11 was fixed to the aluminum cylinder with the tip of the pile yarn 11a inserted 1 mm in the pile length direction of the brush member 11. A voltage of 50 V was then applied to the brush member 11 while the aluminum cylinder was rotated at 50 mm/sec, and the electrical resistance of the brush member 11 was measured. However, the electrical resistance of the brush member 11 is not limited to this, and a brush member 11 with a relatively high resistance of approximately 1.0 x 10 ⁸ Ω or less may also be used.

4. Brush cleaning operation <Overview of brush cleaning operation>
Not only paper dust but also residual toner after transfer and toner (fogging toner) remaining on the non-image areas of the photosensitive drum 1 accumulate on the brush member 11. If too much toner accumulates on the brush member 11, the brush member 11 cannot hold all the toner, and the toner slips through the brush member 11 and adheres to the charging roller 2, which may cause poor charging.

In this embodiment, the image forming apparatus 100 is configured to be able to perform a brush cleaning operation (brush cleaning control) that expels toner from the brush member 11 at a predetermined timing when no image is being formed. This makes it possible to prevent excessive accumulation of toner on the brush member 11.

In this embodiment, the brush cleaning operation is performed during the post-rotation process, which is an example of a non-image-forming process. However, the brush cleaning operation can be performed during any non-image-forming process, and may be performed during the pre-rotation process, pre-multiple-rotation process, or between-sheet process. Furthermore, the brush cleaning operation is not limited to being performed during the post-rotation process each time a print job is executed. For example, the brush cleaning operation can be performed when any index value correlated with the amount of toner accumulated on the brush member 11 (amount of brush member 11 used), such as the number of images formed, the number of rotations or rotation time of the photosensitive drum 1, or the time voltage is applied to the brush member 11, exceeds a predetermined threshold.

<Control of this embodiment>
Next, the brush cleaning operation in this embodiment will be described. FIG. 2 is a timing chart showing the operation of each component when the brush cleaning operation is performed during the post-rotation operation of the image forming apparatus 100 in this embodiment, which is performed after an image forming operation (e.g., a single-sheet printing operation) and before the operation of the image forming apparatus 100 is stopped. The figure shows the time progression of the charging voltage applied to the charging roller 2 from the charging power supply E1, the brush voltage applied to the brush member 11 from the brush power supply E4, and the transfer voltage applied to the transfer roller 5 from the transfer power supply E3. The figure also shows the time progression of the surface potential of the photosensitive drum 1 after transfer, which is subjected to the transfer voltage, and the time progression of the difference between the brush voltage and the surface potential of the photosensitive drum 1 after transfer. The operation shown in FIG. 2 is controlled by the control unit 50 by sending control signals to each power supply.

The surface potential of the photosensitive drum 1 is also referred to simply as the "drum potential," and the surface potential of the photosensitive drum 1 after transfer is simply referred to as the "post-transfer drum potential." More specifically, the post-transfer drum potential is the surface potential of the photosensitive drum 1 when it passes through the contact position P5, i.e., the surface potential of the photosensitive drum 1 at the contact position P5. However, the post-transfer drum potential can be represented by the surface potential of the photosensitive drum 1 after it passes through the transfer position P4 and immediately before it reaches the brush contact position P5. Negatively charged toner is also referred to as "negative toner," and positively charged toner is also referred to as "positive toner." In this embodiment, the transfer voltage is controlled to a constant voltage. Constant voltage control of the transfer voltage adjusts the output voltage of the transfer power supply E4 so that it is approximately constant at a target voltage. The potential difference between the brush voltage and the post-transfer drum potential refers to the value (including the positive and negative signs) obtained by subtracting the post-transfer drum potential from the brush voltage, as will be described in detail later.

As shown in Figure 2, during image formation and brush cleaning operations, a charging voltage of -1300V is applied to the charging roller 2, and the drum potential is uniformly set to approximately -800V in the direction of the rotation axis of the photosensitive drum 1. Furthermore, during image formation and brush cleaning operations, a brush voltage of -400V, approximately halfway between the drum potential of -800V in the non-image area and the drum potential of 0 to -100V in the image area, is applied to the brush member 11. In this way, it is desirable to set the brush voltage so that image defects due to discharge between the brush member 11 and the photosensitive drum 1 do not occur (i.e., to a voltage whose absolute value is less than the discharge threshold between the brush member 11 and the photosensitive drum 1). Furthermore, by setting the brush voltage to a potential approximately halfway between the drum potential of the non-image area and the drum potential of the image area, the following effect can be achieved. In other words, by adjusting the drum potential, toner of both polarities, negative and positive toner, accumulated on the brush member 11 can be expelled from the brush member 11 to the photosensitive drum 1. Furthermore, setting the brush voltage in this manner also achieves the following effect. In other words, the brush voltage can be set to a potential relationship that allows negative toner (toner of normal polarity) contained in the residual toner to pass through the brush contact position P5 without adhering to the brush member 11, relative to the image area where the drum potential is approximately 0 to -100V. This makes it possible to prevent excessive accumulation of toner on the brush member 11.

During image formation, a transfer voltage of approximately +1000V is applied to the transfer roller 5. This transfer voltage during image formation can be changed based on, for example, the type of recording material S and the detection results of the electrical resistance of the transfer section. After transitioning to post-rotation operation (brush cleaning operation), a transfer voltage of -400V is applied to the transfer roller 5, a voltage range that does not reduce the absolute value of the drum potential due to discharge, relative to the drum potential of -800V in the non-image section. This widens the difference between the brush voltage and the post-transfer drum potential without reducing the absolute value of the post-transfer drum potential, and the magnitude of this potential difference expels the positive toner accumulated on the brush member 11 from the brush member 11 to the photosensitive drum 1. Thereafter, a transfer voltage of +1000V, equivalent to the transfer voltage during image formation, is applied to the transfer roller 5. This reduces the absolute value of the post-transfer drum potential to approximately 0 V, widening the difference between the brush voltage and the post-transfer drum potential in the opposite direction to the above-mentioned potential difference, and expelling negative toner that may have accumulated on the brush member 11 from the brush member 11 onto the photosensitive drum 1. The brush cleaning operation of Figure 2 can handle both toner of normal polarity (the main charging polarity of the toner during the development process) and non-normal polarity (polarity opposite to the normal polarity), improving the cleaning performance of the brush member 11, which is placed in contact with the photosensitive drum 1 to collect paper dust.

<Operation of this Example>
Next, the function of the brush cleaning operation in this embodiment will be further described. Increasing the absolute value of the potential difference between the brush voltage and the drum potential causes the brush member 11 to expel toner onto the photosensitive drum 1. As shown in FIG. 4A, if the drum potential is higher than the brush voltage with respect to the normal negative potential (i.e., if the potential difference between the brush voltage and the post-transfer drum potential is positive), positive toner is expelled from the brush member 11 onto the photosensitive drum 1. On the other hand, as shown in FIG. 4B, if the drum potential is lower than the brush voltage with respect to the normal negative potential (i.e., if the potential difference between the brush voltage and the post-transfer drum potential is negative), negative toner is expelled from the brush member 11 onto the photosensitive drum 1. Therefore, by changing the potential difference between the brush voltage and the drum potential to both positive and negative, both negative and positive toner can be expelled from the brush member 11 onto the photosensitive drum 1. In other words, the cleaning ability of the brush member 11 for collecting paper dust can be improved.

Furthermore, by creating a step in the surface potential of the photosensitive drum 1, rather than just creating a potential difference between the brush voltage and the drum potential, toner can be more efficiently expelled from the brush member 11 onto the photosensitive drum 1. This point will be explained using Figure 5.

Figure 5(a) is a schematic diagram showing the posture of the brush member 11 when the drum potential is set to -400V and the brush voltage is -400V during rotational driving of the photosensitive drum 1. Because the potential difference between the brush voltage and the photosensitive drum 1 is small, the electrostatic adsorption force is small. Therefore, although the bristles of the pile yarns 11a flow downstream in the rotational direction of the photosensitive drum 1 due to the dynamic friction force between the brush member 11 and the photosensitive drum 1, there is little change in the posture of the brush member 11 as a whole.

On the other hand, Figure 5(b) is a schematic diagram showing the posture of the brush member 11 when the drum potential is set to -200V while the brush voltage is -400V during rotational driving of the photosensitive drum 1. Because the electrostatic adsorption force is stronger than in the case of Figure 5(a), the tips of the pile yarns 11a and the photosensitive drum 1 are more closely attached to each other. As a result, the tips of the pile yarns 11a are pulled downstream in the direction of rotation of the photosensitive drum 1, and the entire brush member 11 assumes a posture in which it is pulled downstream in the direction of rotation of the photosensitive drum 1. When the posture of the entire brush member 11 changes, the following types of toner begin to move along with the brush member 11: toner that has not come into contact with the photosensitive drum 1, toner with a low charge that is difficult to move due to potential difference alone, and toner that is trapped by paper dust collected by the brush member 11 and is difficult to expel. When the toner particles come into contact with or approach the photosensitive drum 1, they are subjected to a force from the brush member 11 that causes them to be expelled onto the photosensitive drum 1, and the toner particles are expelled from the brush member 11 onto the photosensitive drum 1. In this way, by utilizing not only the potential difference but also the change in the posture of the brush member 11, the toner accumulated on the brush member 11 can be efficiently expelled onto the photosensitive drum 1.

Furthermore, as mentioned above, the relative potential difference, including the positive and negative signs, between the brush member and the drum potential is important for the posture change of the brush member 11. Therefore, here, the potential difference between the brush voltage and the drum potential refers to the relative potential difference, including the positive and negative signs, between the brush voltage and the drum potential.

Negative toner ejected from the brush member 11 onto the photosensitive drum 1 passes through the charging position P1. This is because the potential difference between the charging voltage (-1300V) and the drum potential (-800V) causes the electrostatic force toward the photosensitive drum 1 to be stronger than the force toward the charging roller 2. This negative toner is then collected into the developing device 3 due to the potential difference between the developing voltage (-400V) and the drum potential (-800V).

In addition, the positive toner ejected from the brush member 11 onto the photosensitive drum 1 is affected by the discharge at the charging position P1, and its charge polarity is reversed, turning it into negative toner, which is then collected in the developing device 3 in the same way as the negative toner described above.

However, further improvements can be made to the brush cleaning operation shown in Figure 2. Specifically, when a large amount of toner is expelled from the brush member 11, negative toner may not be able to pass through the charging position P1 due to the potential difference between the charging voltage and the drum potential alone. Furthermore, positive toner may not be able to be converted to negative toner due to the effects of discharge at the charging position P1. In either case, toner may adhere to the charging roller 2, contaminating the charging roller 2. A charging roller 2 with toner attached cannot uniformly charge the surface of the photosensitive drum 1 in the direction of its rotational axis, causing abnormal discharge and resulting in spot-like image defects (also referred to here as "white spots") on halftone images. It is desirable to address these issues. Below, we will explain a modification of this embodiment that addresses these issues.

<Control of Modification>
Next, the brush cleaning operation in the modified example will be described.

Figure 3 is a timing chart showing the operation of each part of a modified image forming apparatus 100 when a brush cleaning operation is performed during post-rotation operation after an image forming operation (e.g., a single-sheet printing operation) and before the operation of the image forming apparatus 100 is stopped. The process according to the timing chart in Figure 3 is carried out by the control unit 50 controlling the voltage output of each power supply. As with Figure 2, Figure 3 shows the time progression of the charging voltage, brush voltage, transfer voltage, post-transfer drum potential, and the potential difference between the brush voltage and the post-transfer drum potential. The operation shown in Figure 3 is controlled by the control unit 50 sending control signals to each power supply. Furthermore, in this modified example of the present embodiment, the transfer voltage is also controlled to a constant voltage.

In the modified example shown in Figure 3, the operations of each part from the start of rotation of the photosensitive drum 1 to the end of the image forming operation are the same as those shown in Figure 2.

In this modified example, after the transition to the post-rotation operation (brush cleaning operation), at T1, the transfer voltage applied to the surface of the photosensitive drum 1 positioned at transfer position P4 begins to be gradually changed. At T2, the surface of the photosensitive drum 1, to which the transfer voltage changed by one step from T1 has been applied, moves in the rotational direction of the photosensitive drum 1 and reaches brush contact position P5. The transfer voltage is then changed in stages from the transfer voltage of approximately +1000 V during image formation operation to -400 V. In other words, the potential difference between the brush voltage and the post-transfer drum potential is changed in stages from -400 V to +400 V. At T3, the transfer voltage begins to be changed in stages from -400 V in the positive polarity direction. At T4, the surface of the photosensitive drum 1, to which the transfer voltage changed by one step from T3 has been applied, moves in the rotational direction of the photosensitive drum 1 and reaches brush contact position P5. The transfer voltage is then changed in stages in 10 stages from -400 V to +1000 V. In other words, the potential difference between the brush voltage and the post-transfer drum potential is changed in 10 stages from +400 V to -400 V. Then, at T5, the surface of the photosensitive drum 1, to which the final transfer voltage of +1000 V has been applied in the brush cleaning operation in this modified example, moves in the direction of rotation of the photosensitive drum 1 and reaches brush contact position P5.

The amount of change in one step when the transfer voltage is changed in stages from the transfer voltage during image formation to -400V is approximately the same as the amount of change in one step when the transfer voltage is changed in 10 steps from -400V to +1000V (140V in the modified example). The number of steps when the transfer voltage is changed in stages from the transfer voltage during image formation to -400V varies depending on the transfer voltage during image formation.

<Effects of Modified Example>
Next, the action of the brush cleaning operation in the modified example will be described. Here, the action on the posture change of the brush member 11 when a potential step is formed on the photosensitive drum 1 will be described by comparing the brush cleaning operation in Fig. 2 (this embodiment) with the brush cleaning operation in Fig. 3 (modified example).

During the brush cleaning operation in Figure 2, a sudden change occurs in the drum potential, causing the attitude of the brush member 11 to suddenly change from the attitude shown in Figure 5(a) to the attitude shown in Figure 5(b), or from the attitude shown in Figure 5(b) to the attitude shown in Figure 5(a). As a result, a large amount of toner is instantly expelled from the brush member 11 onto the photosensitive drum 1.

On the other hand, in the brush cleaning operation of Figure 3, the drum potential is gradually changed, causing the posture of the brush member 11 to gradually change from the posture of Figure 5(a) to the posture of Figure 5(b), or from the posture of Figure 5(b) to the posture of Figure 5(a). In this way, the brush cleaning operation of Figure 3 prevents the posture of the brush member 11 from changing suddenly, so that toner is gradually expelled from the brush member 11 onto the photosensitive drum 1 each time a step in the drum potential passes through the brush abutment position P5.

The brush cleaning operation shown in Figure 3 can also handle toner of both regular polarity (the main charging polarity of the toner during the development process) and irregular polarity (opposite polarity to the regular polarity), improving the cleaning performance of the brush member 11, which is placed in contact with the photosensitive drum 1 to collect paper dust.

Here, "gradually changing the potential difference between the brush voltage and the post-transfer drum potential" refers to the following in more detail. For example, when the potential difference is changed abruptly as shown in FIG. 2, a change of 800 V occurs over approximately 100 ms. Gradual change of the potential difference simply means changing the potential difference sufficiently slower than the abrupt change described above, so as to sufficiently reduce the amount of toner instantaneously expelled from the brush member 11 to the photosensitive drum 1. For example, when changing the potential difference as shown in FIG. 3, a change of 800 V over approximately 500 ms to 3000 ms is sufficient. In other words, "gradually changing the potential difference between the brush voltage and the post-transfer drum potential" typically refers to changing the potential difference at a rate of change of approximately 0.2 V/ms to 2 V/ms. Furthermore, when changing the potential difference between the brush voltage and the post-transfer drum potential in stages, the change width for each stage can be set to achieve the rate of change described above. For example, when the potential difference is changed in stages as shown in FIG. 3, the change in each stage can be approximately 50 V to 100 V, with each change occurring over 50 ms to 100 ms. Concerns exist regarding the brush cleaning operation shown in FIG. 2, which may result in a large amount of toner being expelled from the brush member 11, and the brush cleaning operation shown in FIG. 3, which involves gradually changing the potential difference at the brush contact position P5, which may result in extended downtime. Therefore, appropriate conditions may be set taking into account the amount of toner expelled from the brush member 11. For example, the brush cleaning operation shown in FIG. 2 may be performed when the brush member 11 contains a small amount of toner, and the brush cleaning operation shown in FIG. 3 may be performed when the brush member 11 contains a large amount of toner. For example, the brush cleaning operation shown in FIG. 2 may be performed during intermittent printing on a single recording material S, while the brush cleaning operation shown in FIG. 3 may be performed during continuous printing on multiple recording materials S. Of course, the above conditions may also be controlled by predicting the amount of residual toner, etc.

5. Evaluation Tests Next, the results of evaluation tests conducted to confirm the effects of this embodiment and the modified examples will be described.

First, an evaluation test (also referred to here as "Evaluation Test 1") was conducted on the toner contamination of the charging roller 2. Evaluation Test 1 was conducted under the following conditions: In an environment with a temperature of 32.5°C and a relative humidity of 80% (high temperature and humidity environment), 10 full-black images were continuously printed on Xerox Vitality Multipurpose Printer Paper (product name, basis weight 75 g) manufactured by Xerox Corporation as the recording material S, and a post-rotation operation (brush cleaning operation) was performed. By continuously printing full-black images, more residual transfer toner was supplied to the brush member 11. Next, one halftone image with a density of 25% was printed. If many white spot-like images corresponding to the rotational cycle of the charging roller 2 appear in this halftone image, it is judged as "X (NG)", if only a few white spot-like images corresponding to the rotational cycle of the charging roller 2 appear, it is judged as "△ (minor, but may be problematic)", and if virtually no white spot-like images appear, it is judged as "◯ (OK)".

Following Evaluation Test 1, an evaluation test for brush cleanability (also referred to herein as "Evaluation Test 2") was also conducted. Evaluation Test 2 was conducted under the following conditions. As in Evaluation Test 1, 10 consecutive full-black images were printed. After printing 10 images, the operation of the image forming apparatus 100 was forcibly stopped before the post-rotation operation began. The amount of toner accumulated on the brush member 11 at that time was vacuumed with a toner vacuum cleaner, and the weight was measured to determine the "toner adhesion amount before cleaning." The brush member 11 was then cleaned once to remove essentially all of the toner from the brush member 11. Then, 10 consecutive full-black images were printed, and the post-rotation operation (brush cleaning operation) was performed. The amount of toner accumulated on the brush member 11 was vacuumed with a toner vacuum cleaner, and the weight was measured to determine the "toner adhesion amount after cleaning." The "toner adhesion amount after cleaning" was then subtracted from the "toner adhesion amount before cleaning," divided by the "toner adhesion amount before cleaning," and the result was multiplied by 100 to determine the cleanability value (%). The higher this cleaning performance value, the less toner remains on the brush member 11, the more toner is expelled from the brush member 11, and the better the cleaning is being performed.

The results of the above-mentioned evaluation tests 1 and 2 conducted on this embodiment (Figure 2) and the modified example (Figure 3) are shown in Table 1.

The results of Evaluation Test 1 in Table 1 show that with the brush cleaning operation in Figure 2, as described above, the potential difference on the photosensitive drum 1 was large, so a large amount of toner was instantly expelled from the brush member 11 onto the photosensitive drum 1, contaminating the charging roller 2 with toner and causing some white spots. In contrast, with the brush cleaning operation in Figure 3, as described above, toner was gradually expelled from the brush member 11 onto the photosensitive drum 1, so the charging roller 2 was not contaminated with toner and no white spots were produced.

Furthermore, the results of Evaluation Test 2 in Table 1 show that with the brush cleaning operation in Figure 2, although the instantaneous amount of toner expelled is large, the frequency of toner expelling is low, resulting in a relatively low cleaning performance value (29% in this case). On the other hand, with the brush cleaning operation in Figure 3, although the amount of toner expelled per potential step is smaller, the frequency of toner expelling is high, resulting in a high cleaning performance value (83% in this case).

In this way, the brush cleaning operation of this embodiment can accommodate both toner of regular polarity (the primary charging polarity of the toner during the development process) and irregular polarity (opposite polarity to the regular polarity), improving the cleaning performance of the brush member 11 for collecting paper dust. In particular, the brush cleaning operation of this modified embodiment gradually changes (stepwise in the modified embodiment) the potential difference between the brush voltage and the post-transfer drum potential. This reduces the amount of toner momentarily expelled from the brush member 11 to the photosensitive drum 1 during the brush cleaning operation, suppresses toner contamination of the charging roller 2, and reduces the occurrence of white spots.

In this embodiment and its modified examples, the brush voltage was kept constant at -400 V, and the potential difference between the brush voltage and the post-transfer drum potential was changed by controlling the transfer voltage. However, the present invention is not limited to this configuration, and the post-transfer drum potential may be changed by other means to change the potential difference between the brush voltage and the post-transfer drum potential. For example, the post-transfer drum potential may be controlled in the same way as in this embodiment and its modified examples by controlling the charging voltage, controlling exposure by the exposure device 3, or controlling exposure by a pre-exposure device 13 (Figure 9) positioned so as to expose the photosensitive drum 1 downstream of the transfer position and upstream of the brush contact position in the rotation direction of the photosensitive drum 1, or a combination of these.

In addition, in the modified example, the potential difference between the brush voltage and the post-transfer drum potential was changed in steps to gradually change the potential difference, but the potential difference may also be changed continuously. In this case, the potential difference may be changed substantially continuously in a linear manner, or substantially continuously in a curved manner. As mentioned above, having multiple potential steps is advantageous in terms of improving cleaning performance, but gradually changing the potential difference between the brush voltage and the post-transfer drum potential can have the effect of suppressing toner contamination of the charging roller 2. In this case, the desired cleaning performance can be achieved, for example, by increasing the number of times the potential difference between the brush voltage and the post-transfer drum potential is increased and decreased, as described below.

In addition, in the modified example, the voltage value of the transfer voltage applied was changed in stages using constant voltage control, but the transfer current that flows when the transfer voltage is applied may also be changed in stages using constant current control. Note that constant current control of the transfer voltage is control that adjusts the output voltage of the transfer power supply E4 so that the current flowing to the transfer unit (transfer member) is approximately constant at the target voltage. The same applies when the potential difference between the brush voltage and the post-transfer drum potential is changed sharply, as shown in Figure 2.

In addition, in the modified example, the potential difference between the brush voltage and the post-transfer drum potential is changed so that it gradually increases and then gradually decreases. However, the present invention is not limited to this embodiment, and the manner in which the potential difference is changed may be modified as appropriate. For example, the potential difference between the brush voltage and the post-transfer drum potential may be changed so that it gradually decreases and then gradually increases. The potential difference between the brush voltage and the post-transfer drum potential may also be changed so that it repeatedly increases and decreases, such as gradually increasing, then gradually decreasing, and then gradually increasing again. The number of times the potential difference between the brush voltage and the post-transfer drum potential is increased and decreased can be modified as appropriate depending on the desired cleaning performance, etc. The same applies to a case in which the potential difference between the brush voltage and the post-transfer drum potential is changed sharply, as shown in Figure 2.

The transfer voltage value (or transfer current value), which is changed in stages, may also be adjusted in response to durability and environmental changes, such as changes in capacitance due to wear on the surface of the photosensitive drum 1 caused by repeated use of the photosensitive drum 1, and changes in the electrical resistance of the transfer roller 5 due to repeated use of the transfer roller 5 or environmental temperature and humidity. The same applies when the potential difference between the brush voltage and the post-transfer drum potential is changed sharply, as shown in Figure 2. The same applies to adjusting each control item when changing the post-transfer drum potential by controlling the above-mentioned charging voltage, exposure by the exposure device 3, and exposure by the pre-exposure device 13.

In addition, while the present embodiment and modified examples have described the effects on the brush member 11 for collecting paper dust, the present invention is not limited to application to the brush member 11 for collecting paper dust. Examples include a brush member for charging transfer residual toner to a predetermined polarity during image formation operations, and a brush member for collecting at least a portion of transfer residual toner during image formation operations. Brush members for these applications may also need to be cleaned, for example, periodically by expelling toner from the brush member to prevent excessive toner accumulation on the brush member. Therefore, by applying the present invention to brush members for these applications, the same effects as those of the brush member 11 for collecting paper dust can be achieved. For example, not only for brush members for collecting paper dust, but also for other applications, large changes in the brush member's posture can cause the toner contained in the brush member to scatter. Therefore, by applying the brush cleaning operation of the modified example to brush members for other applications, the same effects as those of the brush member 11 for collecting paper dust can be achieved.

Thus, the image forming apparatus 100 according to the present invention comprises a rotatable photosensitive drum 1, a charging member 2 that charges the surface of the photosensitive drum 1 at a charging position P1, an exposure device 4 that exposes the charged surface of the photosensitive drum 1 at an exposure position P2 to form an electrostatic image on the surface of the photosensitive drum 1, a developing device 3 that supplies toner charged to the normal polarity to the electrostatic image on the surface of the photosensitive drum 1 at a development position P3 to form a toner image on the surface of the photosensitive drum 1, a transfer member 5 that transfers the toner image on the surface of the photosensitive drum 1 to a transfer recipient (recording material S) at a transfer position P4, a brush member 11 that contacts the surface of the photosensitive drum 1 at a brush contact position P5 downstream of the transfer position P4 and upstream of the charging position P1 in the rotational direction of the photosensitive drum 1, a brush voltage application unit E4 that applies a brush voltage to the brush member 11, and a control unit 50 that controls the surface potential of the photosensitive drum 1 at the brush contact position P5. After the transfer, the developing device 3 collects any toner remaining on the surface of the photosensitive drum 1. In the image forming apparatus 100 according to the present invention, the control unit 50 controls the surface potential of the photoconductor 1 at the brush contact position P5 so that, when the contact position potential difference is the brush voltage minus the surface potential of the photoconductor 1 at the brush contact position P5, the control unit 50 changes the contact position potential difference from the first potential difference to the second potential difference, and then changes the contact position potential difference from the second potential difference to the third potential difference. Note that the control unit 50 can perform this type of control when the non-image forming area on the photoconductor 1 passes through the brush contact position P5.

In particular, in this embodiment (Figure 2), the control unit 50 controls the surface potential of the photosensitive element 1 at the brush contact position P5 so that the contact position potential difference is changed in a predetermined direction, either increasing or decreasing, from the first potential difference to the second potential difference, and then changes the contact position potential difference in the direction opposite to the predetermined direction, from the second potential difference to the third potential difference. Furthermore, in this embodiment, the control unit 50 controls the surface potential of the photosensitive element 1 at the brush contact position P5 so that the sign of the contact position potential difference is both positive and negative.

In particular, in a modified example (Figure 3), the control unit 50 controls the surface potential of the photoconductor 1 at the brush contact position P5 so that the contact position potential difference is changed in a predetermined direction, either increasing or decreasing, from the first potential difference to the second potential difference, and then changes the contact position potential difference from the second potential difference to the third potential difference in the predetermined direction. In a modified example, the control unit 50 not only changes the contact position potential difference from the first potential difference to the second potential difference to the third potential difference in the predetermined direction, but also changes the contact position potential difference from the fourth potential difference to the fifth potential difference in the opposite direction, either increasing or decreasing, from the predetermined direction, and then changes the contact position potential difference from the fifth potential difference to the sixth potential difference in the opposite direction. In a modified example, the control unit 50 controls the surface potential of the photoconductor 1 at the brush contact position P5 so as to change the contact position potential difference in stages. However, the control unit 50 can also control the surface potential of the photosensitive element 1 at the brush contact position P5 so as to continuously change the contact position potential difference. In a modified example, the control unit 50 controls the surface potential of the photosensitive element 1 at the brush contact position P5 so that the sign of the contact position potential difference is both positive and negative.

The control unit 50 can control the surface potential of the photoconductor 1 at the brush contact position P5 by controlling at least one of the voltage applied to the charging member 2, the exposure of the photoconductor 1 by the exposure device 4, the voltage applied to the transfer member 5, and the exposure of the photoconductor 1 by the pre-exposure device 13, which is arranged to expose the surface of the photoconductor 1 downstream of the transfer position P4 and upstream of the brush contact position P5 in the rotation direction of the photoconductor 1. In this embodiment and its modified example, the image forming apparatus 100 includes a transfer voltage application unit E3 that applies a transfer voltage to the transfer member 5, and the control unit 50 controls the transfer voltage application unit E3 to control the surface potential of the photoconductor 1 at the brush contact position P5. In this embodiment and its modified example, the brush member 11 removes and collects paper dust from the surface of the photoconductor 1. In this embodiment and its modified example, the charging member 2 contacts the surface of the photoconductor 1 to charge the surface of the photoconductor 1.

As described above, this embodiment can improve the cleaning performance of the brush member 11 used to collect paper dust. Specifically, it can accommodate toner of both regular polarity (the primary charging polarity of the toner during the development process) and irregular polarity (opposite polarity to the regular polarity), improving the cleaning performance of the brush member 11 used to collect paper dust. Furthermore, this modified version of this embodiment can clean the brush member 11 without contaminating the charging roller 2 with toner, thereby achieving both the cleaning performance of the brush member 11 and the prevention of image defects caused by toner contamination of the charging roller 2.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are assigned the same reference numerals as those of the image forming apparatus of embodiment 1, and detailed descriptions thereof will be omitted.

1. Control of the Present Embodiment The brush cleaning operation of the present embodiment will now be described. FIG. 6 is a timing chart showing the operation of each component when the brush cleaning operation is performed during the post-rotation operation of the image forming apparatus 100 of the present embodiment, which is performed after an image forming operation (e.g., a single-sheet printing operation) and before the operation of the image forming apparatus 100 is stopped. Similar to FIGS. 2 and 3 , FIG. 6 shows the time transitions of the charging voltage, brush voltage, transfer voltage, post-transfer drum potential, and the potential difference between the brush voltage and the post-transfer drum potential. The operation shown in FIG. 6 is controlled by the control unit 50 by sending control signals to the respective power sources. Furthermore, similar to the first embodiment and the modified example of the first embodiment, the transfer voltage in this embodiment is controlled to a constant voltage.

The operations of each part in this embodiment, shown in Figure 6, from the start of rotation of the photosensitive drum 1 to the end of the image forming operation are the same as those shown in Figures 2 and 3.

In this embodiment, after transitioning to the post-rotation operation (brush cleaning operation), the post-transfer drum potential is first changed in stages so that it becomes equivalent to the brush voltage. The transfer voltage is then controlled so that it gradually changes in a direction that increases the negative potential difference between the brush voltage and the post-transfer drum potential. The post-transfer drum potential is then changed in a direction that increases the positive potential difference between the brush voltage and the post-transfer drum potential.

In a modified example of Example 1, with regard to the ejection of positive toner, which is the primary target of ejection in the brush cleaning operation, there is a period during which the potential difference between the brush voltage and the post-transfer drum potential is changed in a direction that reduces the absolute value of the potential difference. This is the period in Figure 3 during which the potential difference between the brush voltage and the post-transfer drum potential changes from +400V to 0V. In contrast, in this embodiment, with regard to the ejection of positive toner, which is the primary target of ejection in the brush cleaning operation, the potential difference between the brush voltage and the post-transfer drum potential changes in a direction that increases its absolute value. This is the period in Figure 6 during which the potential difference between the brush voltage and the post-transfer drum potential changes from 0V to +400V. Note that with regard to the ejection of negative toner, there is also a period during which the absolute value of the potential between the brush voltage and the post-transfer drum potential changes in a direction that increases. This is the period during which the potential difference between the brush voltage and the post-transfer drum potential changes from 0V to -400V.

2. Evaluation Tests Next, the results of evaluation tests conducted to confirm the effects of this embodiment will be described. The above-mentioned evaluation tests 1 and 2 were conducted. The results of evaluation tests 1 and 2 conducted for this embodiment are shown in Table 2 together with the results for the modified example of Example 1. The evaluation methods for evaluation tests 1 and 2 were the same as those described above, but when the speckled white dot images occurring during the rotation cycle of the charging roller 2 were more effectively suppressed, the result was judged as "Excellent (better)."

The results in Table 2 show that this example achieved better results in Evaluation Test 1 (toner contamination of the charging roller 2) than the modified example of Example 1. Furthermore, this example achieved results equivalent to those of the modified example of Example 1 in Evaluation Test 2 (cleaning ability).

These results demonstrate that this embodiment further suppresses toner contamination of the charging roller 2 during brush cleaning compared to the modified example of Example 1. This is believed to be because, for the following reasons, toner is expelled from the brush member 11 to the photosensitive drum 1 in smaller increments than the modified example of Example 1. In other words, for both negative and positive toners, this embodiment experiences a period in which the absolute values of the potential differences between the brush voltage and the post-transfer drum potential gradually increase from the post-transfer drum potential, which is approximately equal to the brush voltage. In particular, for the expulsion of positive toner, which is the primary target of expulsion during brush cleaning, this embodiment experiences a period in which the absolute value of the potential difference between the brush voltage and the post-transfer drum potential increases, but does not experience a period in which it decreases. Here, a larger absolute value of the potential difference between the brush voltage and the post-transfer drum potential is advantageous for expulsion, but it is preferable for the absolute value to change from a small value to a large value. In other words, when the absolute value of the potential difference is small, toner accumulated on the brush member 11 is preferentially selected and transferred to the photosensitive drum 1 in the order of toner particle size, toner charge, and adhesion to the brush member 11. By gradually increasing the absolute value of the potential difference from a small value, toner that is easily transferred from the brush member 11 to the photosensitive drum 1 can be gradually expelled in small amounts. Conversely, when the absolute value of the potential difference is gradually decreased from a large value, the amount of toner instantaneously expelled to the photosensitive drum 1 may increase when the absolute value of the potential difference is large. In the modified example of Example 1, this potential relationship exists during the period in which the potential difference between the brush voltage and the post-transfer drum potential in FIG. 3 changes from +400 V to 0 V. In contrast, in this embodiment, there is no period during which this potential relationship exists. Therefore, in this embodiment, the amount of toner instantaneously expelled can be further reduced than in the modified example of Example 1.

In contrast, in this embodiment, it is necessary to adjust the transfer voltage so that the post-transfer drum potential is approximately the same as the brush voltage. This is relatively easy if there is a means for measuring the drum potential within the image forming apparatus 100. However, if there is no means for measuring the drum potential, it is necessary to set the transfer voltage so that the post-transfer potential is equivalent to the brush voltage, taking into account fluctuations in the drum potential due to factors such as the ambient temperature and humidity, the electrical resistance of the transfer roller 5, and changes in the electrostatic capacitance of the photosensitive drum 1. In contrast, in the modified version of Example 1, it is not necessary to know the value of the transfer voltage that will make the brush voltage and post-transfer drum potential approximately the same. Therefore, it can be said that the control of the modified version of Example 1 is simpler than the control of this embodiment.

In this manner, in this embodiment, the control unit 50 controls the surface potential of the photosensitive element 1 at the brush contact position P5 so that the contact position potential difference is changed in a direction that increases the absolute value of the contact position potential difference during the period in which the sign of the contact position potential difference is opposite to the normal polarity of the toner.

As explained above, according to this embodiment, it is possible to further prevent the amount of toner expelled from the brush member 11 from increasing instantaneously compared to the modified example of Example 1, and to further reduce toner contamination of the charging roller 2 during the brush cleaning operation.

[others]
The present invention has been described above with reference to specific embodiments. The dimensions, materials, shapes, and relative positions of the components described in the above embodiments may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the above embodiments.

While the above-described embodiment illustrates a printer as an image forming apparatus, the present invention is not limited to such an embodiment. The present invention can also be applied to other image forming apparatuses, such as copiers and facsimile machines, or other image forming apparatuses, such as multifunction peripherals that combine the functions of these machines, and achieve the same effects as those described above. Furthermore, while the image forming apparatus in the above-described embodiment is a monochrome image forming apparatus, the present invention can also be applied to color image forming apparatuses, and achieve the same effects as those described above. The color image forming apparatus may be a tandem-type image forming apparatus equipped with multiple photoconductors. Tandem-type image forming apparatuses include those employing an intermediate transfer method in which a toner image, which has been primarily transferred from multiple photoconductors to an intermediate transfer medium, is secondarily transferred to a recording material, and those employing a direct transfer method in which a toner image is directly transferred from multiple photoconductors to a recording material carried by a recording material carrier. Even in image forming apparatuses that use an intermediate transfer medium (intermediate transfer belt) as a transfer medium, paper dust may adhere to the photoconductor via the intermediate transfer medium. Therefore, a paper dust removal member may be provided to remove paper dust from the photoconductor.

REFERENCE SIGNS LIST 1 Photosensitive drum 2 Charging roller 3 Developing device 4 Exposure device 5 Transfer roller 11 Brush member 50 Control unit

Claims (10)

a rotatable photoreceptor;
a charging member for charging the surface of the photoreceptor at a charging position;
an exposure device that exposes the charged surface of the photoreceptor at an exposure position to form an electrostatic image on the surface of the photoreceptor;
a developing device that supplies toner charged to a normal polarity to the electrostatic image on the surface of the photoconductor at a development position to form a toner image on the surface of the photoconductor;
a transfer member for transferring the toner image on the surface of the photosensitive member to a transfer receiving member at a transfer position;
a brush member that contacts the surface of the photosensitive member at a brush contact position that is downstream of the transfer position and upstream of the charging position in the rotation direction of the photosensitive member;
a brush voltage applying unit that applies a brush voltage to the brush member;
a control unit for controlling the surface potential of the photosensitive member at the brush contact position;
and
In an image forming apparatus, the toner remaining on the surface of the photosensitive member after the transfer is recovered by the developing device,
the control unit controls the surface potential of the photosensitive member at the brush contact position so that, when a contact position potential difference is a value obtained by subtracting a surface potential value of the photosensitive member at the brush contact position from a value of the brush voltage, the control unit changes the contact position potential difference from a first potential difference to a second potential difference in a predetermined direction, which is either an increasing direction or a decreasing direction, and then changes the contact position potential difference from the second potential difference to a third potential difference in the predetermined direction during a brush cleaning operation for cleaning the brush member ;
the control unit controls the surface potential of the photosensitive member at the brush contact position during the brush cleaning operation so that the sign of the contact position potential difference is both positive and negative.
An image forming apparatus characterized by: The image forming apparatus of claim 1, wherein the control unit controls the surface potential of the photosensitive element at the brush contact position so that, during the brush cleaning operation, in addition to changing the contact position potential difference in the predetermined direction from the first potential difference to the second potential difference via the second potential difference to the third potential difference, the contact position potential difference is changed in the opposite direction to the predetermined direction, either an increasing direction or a decreasing direction, from the fourth potential difference to the fifth potential difference, and then the contact position potential difference is changed in the opposite direction from the fifth potential difference to the sixth potential difference. 3. The image forming apparatus according to claim 1, wherein the control unit controls the surface potential of the photosensitive member at the brush contact position so as to change the contact position potential difference in stages during the brush cleaning operation . 3. The image forming apparatus according to claim 1, wherein the control unit controls the surface potential of the photosensitive member at the brush contact position so as to continuously change the contact position potential difference during the brush cleaning operation . The control unit controls at least one of the voltage applied to the charging member, the exposure of the photosensitive member by the exposure device, the voltage applied to the transfer member, and the exposure of the photosensitive member by a pre-exposure device arranged to expose the surface of the photosensitive member downstream of the transfer position and upstream of the brush contact position in the rotation direction of the photosensitive member, thereby controlling the surface potential of the photosensitive member at the brush contact position. a transfer voltage applying unit that applies a transfer voltage to the transfer member;
5. The image forming apparatus according to claim 1 , wherein the control unit controls the transfer voltage application unit to control the surface potential of the photosensitive member at the brush contact position. The image forming apparatus according to any one of claims 1 to 6 , characterized in that the control unit controls the surface potential of the photosensitive element at the brush contact position so as to change the contact position potential difference in a direction in which the absolute value of the contact position potential difference increases during a period in which the sign of the contact position potential difference is opposite to the normal polarity during the brush cleaning operation. 8. The image forming apparatus according to claim 1, wherein the brush member removes and collects paper dust from the surface of the photosensitive member. 9. The image forming apparatus according to claim 1, wherein the charging member contacts the surface of the photosensitive member to charge the surface of the photosensitive member. the brush member has brush bristles that come into contact with the surface of the photosensitive member,
10. The image forming apparatus according to claim 1, wherein the density of the brush bristles is 120 kF/inch ^<2> or more.