Image forming apparatus

Abstract

To avoid an increase in waiting time during image output while further stabilizing image formation quality.SOLUTION: The image forming apparatus includes an image carrier rotatable around a rotation shaft, a discharge electrode elongated in an axial direction of the rotation shaft and facing the image carrier, an image forming unit configured to form a toner image on the image carrier and transfer the toner image to a sheet, a cleaning device including a cleaning member configured to clean the discharge electrode, an environment sensor configured to detect temperature and humidity, and a control unit configured to execute a cleaning mode in which the cleaning member is moved to clean the discharge electrode when the number of toner images transferred to the sheet exceeds a predetermined threshold. The control unit determines, based on a detection result of the environment sensor, a threshold value for executing the cleaning mode and a movement range in which the cleaning member is reciprocated in the axial direction of the rotation shaft or is moved in one of the forward path and the backward path when the cleaning mode is executed.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus that forms an image by an electrophotographic method. [Background technology]

[0002] Some image forming apparatuses are equipped with a scorotron charger that generates corona discharge and is configured to charge the surface of an image carrier. This type of charger includes a perforated grid electrode and a long discharge electrode, which are arranged opposite the surface of the image carrier. The discharge electrode is composed of a discharge wire made of a metal such as tungsten and having a diameter of approximately 0.1 mm, or a stainless steel plate having a thickness of approximately 0.1 mm and multiple protrusions on its end, and is supplied with a high voltage (e.g., -3 kV or higher) from a power supply. When a high voltage is supplied from the power supply to the discharge electrode, an electric field concentrates on the surface of the discharge electrode, causing a dielectric breakdown in the surrounding air and generating a discharge.

[0003] Because this discharge phenomenon is used to charge the surface of the image carrier, suspended particles in the air are attracted to the discharge electrode, and discharge products are likely to be generated in the area where the discharge electrode is generating discharge. When discharge products are generated and adhere to a portion of the discharge electrode, discharge is less likely to occur at that adhesion point, preventing uniform charging of the surface of the image carrier, resulting in uneven charging. Uneven charging can affect processes such as exposure and development, resulting in uneven image density and potentially poor image quality. For this reason, image forming devices have been proposed that remove discharge products adhered to the discharge electrode by moving a cleaning member back and forth along the length of the discharge electrode from one end to the other while the cleaning member is in contact with the surface of the discharge electrode (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-227394 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-107431 Summary of the Invention [Problem to be solved by the invention]

[0005] While automating the cleaning of the discharge electrodes by periodically moving a cleaning member back and forth is expected to stabilize the quality of image formation, and because image quality problems caused by the adhesion of discharge products are effectively addressed by removing the discharge products in the early stages, it is desirable to shorten the cleaning intervals and increase the cleaning frequency. However, because one cleaning takes several tens of seconds, increasing the cleaning frequency could result in longer wait times for image output.

[0006] An object of the present disclosure is to provide an image forming apparatus that can further stabilize the quality of image formation by automatically cleaning the discharge electrodes, while avoiding long waiting times when outputting images. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present disclosure provides an image forming unit that includes an image carrier that can rotate around a rotation axis, a discharge electrode that extends in the axial direction of the rotation axis, is arranged opposite the image carrier, and is connected to a power source, an image forming unit that forms a toner image to be transferred to a sheet on the image carrier that has been charged by discharging the discharge electrode, and transfers the toner image to the sheet, a cleaning device that has a cleaning member that cleans the discharge electrode and moves the cleaning member in the axial direction of the rotation axis to clean the discharge electrode, an environmental sensor that detects temperature and humidity, and a control unit that is capable of executing a cleaning mode that controls the movement mechanism to move the cleaning member and clean the discharge electrode when the number of toner images to be transferred to the sheet exceeds a predetermined threshold, and is characterized in that the control unit determines, based on the detection result of the environmental sensor, a threshold for executing the cleaning mode and a movement range that determines whether the cleaning member should move back and forth in the axial direction of the rotation axis, or whether it should move in either a forward or backward direction when executing the cleaning mode.

[0008] Furthermore, in the image forming apparatus, it is preferable that the cleaning member is movable between a first position at one axial end of the rotating shaft, where the cleaning member does not interfere with the discharge operation of the discharge electrode, and a second position at the other axial end of the rotating shaft, where the cleaning member does not interfere with the discharge operation of the discharge electrode.

[0009] Furthermore, in the image forming apparatus, it is preferable that the control unit executes the cleaning mode in a first region where the amount of moisture in the air is low and which is defined by a predetermined temperature and humidity, at a threshold value that is lower than that in a second region which is a region other than the first region, and that the movement range of the cleaning member is one-way movement in either the forward or backward direction.

[0010] In the image forming apparatus, it is preferable that the control unit executes the cleaning mode while the image carrier is rotating and while no power is being supplied from a power source to the discharge electrode.

[0011] Furthermore, in the image forming apparatus, it is preferable that the image forming unit includes a developing device having a developing roller that supplies toner to the charged image carrier, and a developing power supply that supplies a developing bias of a predetermined voltage to the developing roller, and that the control unit supplies the developing bias from the developing power supply with a value different from that when a toner image is formed on the developing roller during execution of the cleaning mode.

[0012] Furthermore, in the image forming apparatus, it is preferable that the cleaning device further includes a position sensor arranged on one end side of the axial direction of the rotating shaft, a moving belt stretched over two rotating bodies arranged on one end side and the other end side of the axial direction of the rotating shaft and moving the cleaning member in the axial direction of the rotating shaft, and a drive mechanism for the rotating bodies, wherein the cleaning member has a first detection portion that is detected by the position sensor when it is in the first position, and the moving belt has a second detection portion that is detected by the position sensor when the cleaning member is in the second position.

[0013] In this case, it is further preferable that the position sensor is a transmission type sensor having an emitting unit and a light receiving unit that receives light from the emitting unit, and that the first detecting unit and the second detecting unit are configured to have different light transmittances. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to further stabilize the quality of image formation in an image forming apparatus while avoiding a long waiting time when outputting an image. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an explanatory diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment; [Figure 2] FIG. 2 is a perspective view showing a photosensitive unit provided in the image forming apparatus. [Figure 3] 3 is a cross-sectional view taken along the line AA in FIG. 2. [Figure 4] 3A and 3B are schematic explanatory views showing a cleaning roller provided in a cleaning device of a charging device and a cleaning state of a discharge electrode by the cleaning roller; [Figure 5] FIG. 2 is a perspective view showing a cleaning device for a charging device. [Figure 6] FIG. 6 is an enlarged perspective view of part B in FIG. 5. [Figure 7] FIG. 10 is an explanatory diagram showing a state in which the cleaning member is cleaning the discharge electrode. [Figure 8] FIG. 2 is a perspective view showing the arrangement position of a cleaning member. [Figure 9] FIG. 2 is a block diagram showing an outline of the electrical configuration of the image forming apparatus. [Figure 10] FIG. 10 is a diagram illustrating an example of the configuration of an environment table. [Figure 11] 10 is a flowchart showing a cleaning mode executed using an environment table. [Figure 12] FIG. 2 is an explanatory diagram illustrating a configuration example of a cleaning device and a position sensor provided in the image forming apparatus. [Figure 13] FIG. 10 is an explanatory diagram showing an example of movement of a position sensor. [Figure 14] FIG. 10 is an explanatory diagram showing an example of movement of a position sensor. DETAILED DESCRIPTION OF THE INVENTION

[0016] An image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

[0017] (Embodiment 1) 1 is an example of an image forming apparatus 1 according to an embodiment of the present disclosure, and is an explanatory diagram showing the overall configuration of the image forming apparatus 1. Note that components common to the first and second embodiments are denoted by common reference numerals, and duplicated explanations will be omitted.

[0018] The image forming apparatus 1 is a multifunction machine having a scanner function, a copy function, a printer function, a facsimile function, etc., and transmits an image of an original document read by an image reading device 18 to an external device, and also forms an image on a sheet in color or monochrome from the image of the original document read or an image received from an external device. The image forming apparatus 1 includes an image forming section 10 for forming an image on a sheet, which includes a photosensitive drum 11, a charging device 12, an optical scanning device 13, a developing device 14, a drum cleaning device 15, a transfer device 19, a fixing device 27, etc.

[0019] Image forming apparatus 1 handles image data corresponding to color images using black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). Image reading device 18 reads an original document or an original document transported from an automatic document feeder (ADF) to generate image data. Image forming apparatus 1 according to the exemplary embodiment is provided with four photosensitive drums 11, four charging devices 12, four developing devices 14, and four drum cleaning devices 15 for forming four types of toner images, each of which is unitized to correspond to the colors black, cyan, magenta, and yellow, and four process units Pa, Pb, Pc, and Pd are provided.

[0020] Photoconductor drum 11 is an image carrier that can rotate around a rotation axis and has a photosensitive layer on its surface that is insulating in the dark but becomes conductive in the area irradiated with light. Here, charging device 12 is a scorotron charger that charges the surface of photoconductor drum 11 to a predetermined potential. Optical scanning device 13 exposes the surface of each photoconductor drum 11, which has been charged to the predetermined potential, based on image data to form an electrostatic latent image.

[0021] The developing device 14 develops the electrostatic latent image formed on the surface of the photosensitive drum 11 with toner, forming a toner image on the surface of the photosensitive drum 11. The developing device 14 has a developing roller 141 that carries a developer containing toner on its surface and is supplied with a developing bias, which is a predetermined voltage, from a power source (not shown). Due to the potential difference between the developing bias supplied to the developing roller 141 and the electrostatic latent image, the toner on the developing roller 141 is supplied to the electrostatic latent image, forming a toner image. The toner image formed on each photosensitive drum 11 is intermediately transferred to an intermediate transfer belt 21 provided in a transfer device 19 (described later).

[0022] The drum cleaning device 15 removes and collects residual toner remaining on the surface of the photosensitive drum 11 after the toner image has been intermediately transferred to the intermediate transfer belt 21. Note that the process units Pa, Pb, Pc, and Pd of the present disclosure are composed of a photosensitive unit in which the photosensitive drum 11, the charging device 12, and the cleaning device 15 are combined into one unit, and a development unit made up of the developing device 14.

[0023] The transfer device 19 includes an intermediate transfer belt 21 and a (secondary) transfer unit 25. An intermediate transfer roller 16 is disposed above each photosensitive drum 11 with the intermediate transfer belt 21 interposed therebetween. The intermediate transfer belt 21 is stretched around a drive roller 22 and a tension roller 23 and rotates (circularly moves) in the direction of arrow C. The tension roller 23 applies a predetermined tension to the intermediate transfer belt 21. The intermediate transfer roller 16 brings the intermediate transfer belt 21 into contact with the corresponding photosensitive drum 11 to form an intermediate transfer nip area. The toner images of each color formed on the surface of each photosensitive drum 11 are sequentially transferred (primary transfer) onto the intermediate transfer belt 21 in the intermediate transfer nip area and overlapped. As a result, a color toner image is formed on the surface of the intermediate transfer belt 21.

[0024] Transfer roller 26 of transfer unit 25 is disposed opposite drive roller 22 so as to abut against intermediate transfer belt 21, forming a transfer nip area (secondary transfer position) between it and intermediate transfer belt 21. Transfer roller 26 sandwiches and transports a sheet transported through sheet transport path 31 in the transfer nip area. The toner image intermediately transferred onto the surface of intermediate transfer belt 21 in the transfer nip area is transferred to the sheet transported through sheet transport path 31, and the sheet is then transported to fixing device 27. Toner and the like remaining on intermediate transfer belt 21 are collected by belt cleaning device 24.

[0025] The fixing device 27 includes a fixing roller 28 and a pressure roller 29 that rotate while sandwiching the sheet. The fixing roller 28 has an internal heat source (not shown) that heats the surface to a predetermined temperature. When the sheet with the toner image transferred thereon is sandwiched between the fixing roller 28 and the pressure roller 29 and conveyed, the fixing device 27 heats and melts (softens) the toner image transferred onto the sheet, and fixes it to the sheet by applying pressure. The sheet with the fixed toner image is discharged to a sheet discharge section 37, which will be described later.

[0026] The sheet feeder 17 stores sheets to be used for image formation and is disposed below the optical scanning device 13. The sheet is picked up from the sheet feeder 17 by a pickup roller 33, transported through a sheet transport path 31, passes through a transfer nip area, a fixing device 27, and is transported to a sheet discharge section 37 via a discharge roller 36. The sheet transport path 31 is provided with a plurality of roller pairs, including a plurality of transport rollers 34 that promote sheet transport, a registration roller 35 that temporarily stops the sheet to align its leading edge and then starts transporting the sheet in accordance with the timing of the transfer of the toner image, and a discharge roller 36.

[0027] When an image is to be formed on the back side as well as the front side of the sheet, the sheet is conveyed in the reverse direction from the discharge roller 36 to the sheet reversal conveying path 32, the sheet is turned over, the sheet is guided again to the registration roller 35, an image is formed on the back side in the same manner as on the front side, and the sheet is conveyed to the sheet discharge section 37.

[0028] Although the image forming device 1 is shown as an example of a multifunction device configured as described above, the image forming device of the present disclosure is not limited to this and may be any device that performs various types of image formation, such as a printer device, a facsimile device, or a copier.

[0029] FIG. 2 is a perspective view showing a photosensitive unit 101 included in one process unit provided in the image forming section 10, and FIG. 3 is a cross-sectional view taken along the line AA in FIG.

[0030] 1 are detachably mounted on the image forming section 10. These four units have a common configuration except for the colors of the images they form, so the following description will be made without distinguishing between the individual process units and will focus on the detailed configuration of the photosensitive unit 101 provided in one process unit.

[0031] 2, the photosensitive unit 101 includes a photosensitive drum 11 and a charging device 12. The charging device 12 faces the surface of the photosensitive drum 11 and is disposed along the longitudinal direction of the photosensitive drum 11.

[0032] The charging device 12 extends along the axial direction X of the rotation shaft 111 of the photosensitive drum 11, and is disposed so as to face the photosensitive drum 11. As shown in FIG. 3, the charging device 12 includes a discharge electrode 121, a charging power supply 122 connected to the discharge electrode 121, a grid electrode 123, a grid power supply 124 connected to the grid electrode 123, a shield wall 125, an electrode holder 126, etc. The photosensitive unit 101 is configured so that the surface of the photosensitive drum 11 is uniformly charged to a predetermined potential by the discharge of the discharge electrode 121.

[0033] In the photosensitive unit 101, the electrode holder 126 is a case in which the discharge electrode 121 is fixed and housed, and is formed of, for example, resin so as to cover the side surface portion perpendicular to the longitudinal direction of the discharge electrode 121. The discharge electrode 121 fixed to the electrode holder 126 is made of stainless steel with a thickness of 0.1 mm, has an elongated shape extending along the axial direction X, and has a plurality of sawtooth-shaped tips 121a protruding toward the photosensitive drum 11 on the end surface portion on the photosensitive drum 11 side.

[0034] A charging power supply 122 is connected to the discharge electrode 121, and a predetermined DC voltage (high voltage), for example, −3.5 kV to −8 kV, is supplied from the charging power supply 122 to the discharge electrode 121 as a charging bias, thereby generating a discharge (corona discharge) from the multiple sawtooth tips 121a. (Note that the charging bias value is preferably a voltage of −4.0 kV to −5.5 kV, and the current value is 300 μA to 1000 μA.)

[0035] A stainless steel grid electrode 123, which is a 0.1 mm thick plate-like member with multiple fine slits across its entire surface, is provided between the sawtooth tip 121a and the photosensitive drum 11. A shield wall 125 is attached to the side of the electrode holder 126 opposite to the side on which the discharge electrode 121 is attached, and covers the discharge electrode 121 in a direction perpendicular to the axial direction X. The shield wall 125 is made of stainless steel and has a thickness of 0.5 mm, and is configured to extend to a position close to the end of the grid electrode 123.

[0036] A grid power supply 124 is connected to the grid electrode 123 and the shield wall 125. A grid bias (for example, −550 V), which is approximately the same voltage as the charged potential of the surface of the photosensitive drum 11, is supplied to the grid electrode 123 and the shield wall 125 from the grid power supply 124.

[0037] The difference between the grid bias supplied to the grid electrode 123 and the shield wall 125 and the charging bias supplied to the discharge electrode 121 causes a discharge from the discharge electrode 121 toward the grid electrode 123 and the shield wall 125. At this time, the discharge passing through the multiple slits formed in the grid electrode 123 charges the surface of the photosensitive drum 11. When the surface of the photosensitive drum 11 reaches the same value as the grid bias, any further charging is prevented by the grid electrode 123 recovering the discharge, so that the surface of the photosensitive drum 11 is uniformly charged to a predetermined potential. The discharge area of ​​the discharge electrode 121 is arranged to coincide with an area including the surface on which the toner image to be transferred onto the photosensitive drum 11 is formed, in the axial direction X of the rotation shaft 111 of the photosensitive drum 11.

[0038] As described above, the charging device 12 charges the surface of the photosensitive drum 11 to a predetermined potential by utilizing the discharge phenomenon that occurs in the discharge electrode 121, so if used over a long period of time, discharge products will adhere to the multiple sawtooth tips 121a, causing poor discharge properties and a decrease in charging uniformity. Therefore, the charging device 12 of the present disclosure is equipped with a cleaning device 40 that has a cleaning member 41 that cleans the sawtooth tips 121a and periodically moves the cleaning member 41 in the axial direction X to clean the discharge electrode 121 (tip 121a).

[0039] The cleaning device 40 will be described with reference to FIGS. 4 to 8. FIG. 4 is a schematic diagram illustrating a cleaning roller 42 included in a cleaning member 41 provided in the cleaning device 40, and the state in which the cleaning roller 42 cleans the tip portion 121a of the discharge electrode 121. FIG. 5 is a perspective view showing the cleaning device 40 of the charging device 12, illustrating a state in which the cleaning member 41 is positioned at one end side X1 of the axial direction X of the photosensitive drum 11. FIG. 6 is an enlarged perspective view of portion B in FIG. 5, FIG. 7 is an explanatory diagram illustrating a state in which the cleaning member 41 is cleaning the discharge electrode 121, and FIG. 8 is a perspective view illustrating a state in which the cleaning member 41 has reached a position at the end side X2 of the photosensitive drum 11 in the axial direction X.

[0040] 4 and 5, cleaning member 41 of cleaning device 40 includes cleaning roller 42, which has a rubber layer of a predetermined thickness (for example, 2 mm) provided around a resin rotating shaft, and holder 43 that rotatably supports cleaning roller 42. Cleaning member 41 is configured to move in axial direction X of rotating shaft 111 of photosensitive drum 11, and is configured so that the rubber layer of the predetermined thickness bites into tip portions 121a of multiple discharge electrodes 121 as it moves in axial direction X. Because the rubber layer is soft, even if tip portions 121a of discharge electrodes 121 bite into it, it does not deform tip portions 121a. Furthermore, when the tips 121a of the discharge electrodes 121 bite into the rubber layer, cracks are generated and cuts are formed. However, since the multiple tips 121a are arranged side by side in the axial direction X of the rotation shaft 111 of the photosensitive drum 11, the cuts are formed linearly on the surface (circumferential surface) of the rubber layer in a direction perpendicular to the direction of the resin rotation shaft. In other words, one cut formed during movement moves while rotating so as to envelop (both side surfaces of) the tips 121a of the multiple discharge electrodes 121, so that discharge products adhering to the tips 121a can be reliably removed. Furthermore, deformation of the tips 121a can be effectively prevented.

[0041] Tips 121a of the multiple discharge electrodes 121 are provided in a range in the axial direction X of the rotation shaft 111 of the photosensitive drum 11 that includes the toner image forming surface on which a toner image is formed on the photosensitive drum 11. In other words, the tips 121a of the discharge electrodes 121 are provided so as to uniformly charge the toner image forming surface. For this reason, the cleaning member 41 is provided so as to be located in an area where the tips 121a of the discharge electrodes 121 are not formed, that is, at position P in FIG. 5 (the end on one end side X1 in the axial direction X of the photosensitive drum 11), where no discharge occurs. By positioning the cleaning member 41 at this position, the toner image forming surface of the photosensitive drum 11 can be uniformly charged when a toner image is formed on the photosensitive drum 11.

[0042] 5, the cleaning device 40 has a helical member 44 provided with a drive gear 45 at its end and configured to engage with a holder 43 that axially supports the cleaning roller 42. The helical member 44 is a long, screw-shaped member provided with a helical groove, and is supported by the charging device 12 so as to be rotatable forward and backward parallel to the discharge electrode 121. When the photosensitive unit is attached to the image forming apparatus 1, the drive gear 45 engages with a gear connected to a drive source 46 (see FIG. 9) provided in the main body of the image forming apparatus 1, and is configured to rotate when the drive source 46 provided in the main body rotates. When the helical member 44 is rotated by the drive source 46, the holder 43 is configured to move in the axial direction X of the photosensitive drum 11.

[0043] As shown in Fig. 6, the holder 43 has a recess with an open top, and the cleaning roller 42 is attached to the inside of the recess. The tip 121a of the discharge electrode 121 is arranged so that it can enter the holder 43 of the cleaning member 41, which moves in the axial direction X. The bottom side of the holder 43 is engaged with the groove of the helical member 44, and as described above, the holder 43 is configured to move in the axial direction X of the photosensitive drum 11 as the helical member 44 rotates. When the cleaning member 41 moves in the axial direction X as the helical member 44 rotates, the sawtooth tip 121a of the discharge electrode 121 sinks into the cleaning roller 42, as shown in Fig. 4, and the tip 121a of the discharge electrode 121 is cleaned.

[0044] When the spiral member 44 rotates in the direction of the arrow R1 in Figure 6 (positive rotation R1), the holder 43 moves from a position P where no discharge occurs toward the direction X2, which is the axial direction X of the photosensitive drum 11, and begins cleaning the discharge electrode 121 (the tip 121a thereof).

[0045] 7 is a diagram showing a state in which the cleaning member 41 is moving in the X2 direction in the axial direction X, and as the drive source 46 continues to rotate, the cleaning member 41 reaches a second position Q, which is an end on the other end side X2 in the axial direction X and does not interfere with the discharge of the discharge electrode 121. This state is illustrated in FIG.

[0046] Here, the first position P is located on the front side of the image forming apparatus 1, and the second position Q is located on the rear side of the image forming apparatus 1. Note that the charging device 10 is provided with position sensors 47 and 48 on the front and rear sides to detect the position of the cleaning member 41. The position sensors 47 and 48 will be described later.

[0047] When not cleaning, the cleaning member 41 is disposed at the end side in the axial direction X (for example, the first position P in FIG. 5). At the first position P, the cleaning member 41 is stored outside the discharge region and can be detected by the position sensor 47. The cleaning member 41 moves from the first position P toward the other end side X2 toward the second position Q in accordance with the forward rotation R1 of the helical member 44, and finally reaches the second position Q as shown in FIG. 8. At the second position Q, the cleaning member 41 is stored outside the discharge region and can be detected by the position sensor 48. The position sensors 47 and 48 are provided at the one end side X1 and the other end side X2, respectively, and are transmission-type sensors including a light-emitting element 601 and a light-receiving element 602 that receives light from the light-emitting element 601, as shown in FIG. 6.

[0048] The cleaning member 41, which is positioned at the second position Q, moves in the direction of the one end side X1 from the second position Q toward the first position P in accordance with the reverse rotation R2 of the helical member 44. In this way, the cleaning member 41 is capable of reciprocating movement between the first position P and the second position Q. The cleaning member 41 is also capable of one-way movement, moving either on the outward path from the first position P to the second position Q or on the return path from the second position Q to the first position P.

[0049] FIG. 9 is a block diagram showing an outline of the electrical configuration of the image forming apparatus 1. The image forming apparatus 1 is equipped with a control unit 70. The control unit 70 has a memory unit 71, an image formation processing unit 72 that controls the image forming unit 10 to form a toner image and transfers and fixes the formed toner image onto a sheet, and a counter 73 that counts the cumulative number of images formed in the image forming process (the cumulative number of sheets onto which a toner image is transferred, i.e., the cumulative number of sheets onto which a toner image is transferred). The control unit 70 is also connected to an environmental sensor 50. The environmental sensor 50 is provided in the image forming apparatus 1 and detects the ambient temperature and humidity of the image forming unit 10 and outputs the detected values ​​to the control unit 70. The memory unit 71 stores a threshold value for determining whether to execute the cleaning mode and operating conditions that determine whether to move the cleaning member 41 only forward or backward along the axial direction X or whether to reciprocate the cleaning member 41 along the axial direction X when the cleaning mode is executed. The control unit 70 determines whether or not to clean the discharge electrode 121 based on the detection results of the environment sensor 50 and the counter 73 .

[0050] 10 is a diagram showing an environment table as an example of a determination table that defines thresholds for determining whether or not the control unit 70 should execute the cleaning mode. The determination table is stored in the storage unit 71 and defines multiple environment areas that combine temperature and humidity, the value of the cumulative number of formed images that is a threshold that serves as a criterion for determining whether or not to execute the cleaning mode for each of the multiple environment areas, and whether the cleaning member 41 should move only in one direction, either forward or backward, along the axial direction X, or whether the cleaning member 41 should move back and forth along the axial direction X.

[0051] As shown in Figure 10, the environment table defines four temperature ranges: less than 20°C, 20°C to less than 25°C, 25°C to less than 30°C, and 30°C or more; and four humidity ranges: less than 25%, 25% to less than 50%, 50% to less than 75%, and 75% or more, for a total of 16 environmental areas.

[0052] Each of the 16 environment areas defines the value of the cumulative number of formed images, which is a threshold for determining whether to execute the cleaning mode, and the conditions for moving the cleaning member 41. The 16 environment areas in the environment table shown in Fig. 10 are assigned the numbers 1 and 2, which represent the environment flags (1 or 2) that define the value of the cumulative number of formed images, which is the threshold, and the conditions for moving the cleaning member 41. Here, the area with environment flag 1 defines a threshold of, for example, 500 sheets, and the movement of the cleaning member 41 when the cleaning mode is executed as either a forward or backward movement, while the area with environment flag 2 defines a threshold of, for example, 1000 sheets (=standard value), and the movement of the cleaning member 41 when the cleaning mode is executed as a reciprocating movement (=standard condition).

[0053] In FIG. 10, the first region indicated by an environmental flag of 1 is an environment where discharge is likely to occur under low temperature and humidity conditions where the amount of moisture contained in the air is small.

[0054] There is a correlation between the humidity in the air and the amount of discharge products generated on the sawtooth discharge electrode 121; the lower the humidity and the lower the temperature, the greater the amount generated. Also, the higher the humidity or the higher the temperature, the less generated the amount tends to be. Therefore, in the low-temperature, low-humidity environment of the first region, discharge products are more likely to adhere to the discharge electrode 121.

[0055] Therefore, the image forming apparatus 1 according to this embodiment is configured to transition to execution of the cleaning mode at a low threshold value in order to increase the frequency of execution of the cleaning mode in the first region. Furthermore, when increasing the frequency of execution of the cleaning mode, in order to prevent the interruption of the image formation process from becoming too long, the cleaning member 41 is configured to move only one way rather than back and forth. More specifically, if the time required for cleaning by moving the cleaning member 41 back and forth is, for example, 20 seconds, cleaning by moving it one way can be completed in half that time, 10 seconds.

[0056] The required time can also be shortened by increasing the movement speed of the cleaning member 41, but because the cleaning roller 42 is configured to clean the tip 121a of the discharge electrode 121 by the elastic layer thereof coming into contact with the tip 121a, increasing the movement speed may cause deformation of the tip 121a due to the shock of contact with the cleaning roller 42. If the tip 121a is deformed, discharge from the tip 121a will stop, causing charging failure, and therefore there is a limit to how fast the movement speed can be increased.

[0057] FIG. 11 is a flowchart of the cleaning mode using the environment table.

[0058] As described above, an environment table is stored in advance in the memory unit 71 of the control unit 70. Based on the detection result input from the environment sensor 50, the control unit 70 refers to the environment table in the memory unit 71 and determines the threshold value and movement range for executing the cleaning mode.

[0059] More specifically, as shown in FIG. 11, when the control unit 70 starts the image forming process, the control unit 70 first causes the environment sensor 50 to detect the temperature and humidity (step S1).

[0060] The control unit 70 identifies the environmental flag corresponding to the detection result of the environmental sensor 50 from the environmental table and determines whether the area is the first area or the second area (step S2). If the area is the second area (No in step S2), it is determined that the environment is not low temperature and low humidity, and the amount of discharge products generated is not large, so it is appropriate to perform the normal cleaning mode. The threshold for performing the cleaning mode is determined to be a reference value (1,000 sheets) based on the environmental table (step S3).

[0061] Furthermore, when it is determined by referring to the environmental table that the printer is in the first region (Yes in step S2), the threshold for the cleaning mode is determined to be 1 / 2 of the reference value (for example, the cumulative number of images formed is 500) because the environment is low temperature and humidity, which means that the amount of discharge products generated is likely to be large (step S4).

[0062] Next, the image of the original document read by the image reading device 18 or the image received from the outside is processed to be image-formed on one sheet in color or monochrome, and the cumulative number of formed images is incremented by one (step S5). Then, it is determined whether the cumulative number of formed images has reached a threshold value (step S6). If the cumulative number of formed images has not reached the threshold value, it is determined whether to continue image formation (step S7).

[0063] When the cumulative number of formed images reaches the threshold value (Yes in step S6), it is determined whether the area is the first area (step S8), and if the area is the second area (No in step S8), the cleaning mode is executed under the conditions defined for the second area, and the cumulative number of formed images on counter 73 is reset (step S9). In this case, the normal cleaning mode is executed in which cleaning member 41 is reciprocated.

[0064] The control unit 70 executes the cleaning mode while the photosensitive drum 11 is rotating and power is not being supplied from the charging power supply 122 to the discharge electrode 121. If the rotation of the photosensitive drum 11 were to be stopped when the cleaning mode was executed, it would take time to stop the photosensitive drum 11 and then time to accelerate the rotation to rotate at a predetermined speed. Therefore, the cleaning mode is executed without stopping the rotation of the photosensitive drum 11, and processing is performed to shorten the time the image formation process is interrupted for cleaning.

[0065] Furthermore, during execution of the cleaning mode, the control unit 70 controls the development power supply to supply a development bias of a different value from that used when a toner image is formed on the development roller 141. In other words, during execution of the cleaning mode, the discharge electrode 121 is not discharged, and the surface of the photosensitive drum 11 is not charged to a predetermined potential (for example, minus 600 V). If the same development bias (for example, minus 425 V) as used when a toner image is formed is supplied to the development roller 141 in this state, there is a risk that toner will be supplied to the photosensitive drum 11 due to the potential difference. To prevent this, during execution of the cleaning mode, it is preferable to set the development bias to, for example, 0 V or approximately plus 50 V. This makes it possible to prevent toner from being supplied to the photosensitive drum 11 during execution of the cleaning mode.

[0066] After it is determined in step S6 that the cumulative number of formed images is equal to or greater than the threshold, if the determination as to whether or not the area is the first area determines that the area is the first area (Yes in step S8), a cleaning mode is executed in which the cleaning member 41 moves one way. Then, the cleaning member 41 moves from the first position P to the second position Q, or from the second position Q to the first position P, and the cumulative number of formed images on the counter 73 is reset (step S10).

[0067] When the cleaning mode ends, the cleaning member 41 stops at the second position Q or the first position P reached in the one-way movement.

[0068] In both the first and second regions, after the cleaning mode ends, the control unit 70 determines whether or not to continue the image formation process (step S7). Note that the position sensor 47 detects that the cleaning member 41 has returned to the first position P on one end side and stored outside the discharge region, and the position sensor 48 detects that the cleaning member 41 is located at the second position Q outside the discharge region. Note that if the position sensor 47 or the position sensor 48 does not detect the cleaning member 41 even after driving the drive source 46 for a predetermined time or longer, it can be said that some kind of abnormality has occurred, and the image formation process is interrupted and the occurrence of the abnormality is notified to the operator via a display device (not shown).

[0069] Discharge products are not generated uniformly on the discharge electrode 121, but are generated in large quantities in areas where discharge is likely to occur. When discharge products are generated, the amount of discharge in the area where the discharge products are generated gradually decreases, which may result in uneven discharge. When uneven discharge occurs, it causes a change in the surface potential of the photosensitive drum 11, resulting in variations in image density. Furthermore, since the magnitude of discharge unevenness caused by discharge products varies depending on environmental conditions even if the amount of discharge products remains the same, as described above, by changing the threshold for executing the cleaning mode and the movement range of the cleaning member based on the detection results of the environmental sensor 50, it is possible to clean the discharge electrode 121 at an appropriate timing and for an appropriate operating time.

[0070] In particular, in the case of the first region, an environment where density differences due to uneven discharge are likely to occur is used, and the cleaning mode is executed with a cumulative number of image formation sheets that is less than normal, for example, half the reference value. This allows for earlier removal of discharge products, which are generated in larger quantities than normal. In addition, by setting the range of movement to a one-way movement that allows cleaning to be completed in a short time, the time required for cleaning can be shortened, and the time during which the image formation process is interrupted can be reduced (the discharge products adhere weakly to the tip 121a of the discharge electrode 121, so they can be removed in a single cleaning operation). This makes it possible to avoid long waiting times when outputting images, even if the cleaning frequency is increased.

[0071] The mechanism for moving the cleaning member 41 provided in the cleaning device 40 is not limited to the screw-shaped helical member 44, and may be any member that supports the cleaning member 41 so that it can move.

[0072] (Embodiment 2) 12 to 14 are explanatory diagrams that schematically show examples of the configuration of the cleaning device 40 of the image forming apparatus 1 according to the second embodiment.

[0073] As shown in the first embodiment, when cleaning of the discharge electrode 121 is automated under the control of the control unit 70, it is more preferable that the cost required for the position sensor can be reduced if one position sensor can detect the cleaning member 41 at the first position P and at the second position Q. Therefore, in the image forming apparatus 1 according to the second embodiment, in addition to the execution of the cleaning mode by the control unit 70 described above, one position sensor 60 is moved in the axial direction X together with the cleaning member 41 of the cleaning device 40 to detect the cleaning member 41.

[0074] In this case, the cleaning device 40 includes a position sensor 60 for detecting the cleaning member 41 at either one end X1 or the other end X2 in the axial direction X. The position sensor 60 may be a transmission sensor having a light-emitting unit 601 and a light-receiving unit 602, similar to the position sensors 47 and 48 described in the first embodiment. In the illustrated embodiment, as shown in FIG. 12 , one position sensor 60 is provided at a first position P corresponding to the one end X1 in the axial direction X, and no position sensor is provided at a second position Q.

[0075] The cleaning member 41 is supported by a guide shaft 49 disposed parallel to the axial direction X and is connected to a moving belt 64 serving as a moving mechanism. The moving belt 64 is endless and includes rotating bodies 61 and 62 and a drive mechanism 63. The rotating bodies 61 and 62 are disposed at one end X1 and the other end X2 in the axial direction X, respectively. The moving belt 64 is stretched around these rotating bodies 61 and 62, and the drive mechanism 63 is connected to at least one of the rotating bodies 61 and 62. When the rotating body 61 is driven to rotate, the moving belt 64 rotates (moves in a circular motion) toward the one end X1 or the other end X2. This moves the cleaning member 41 in the axial direction X.

[0076] The cleaning member 41 has a first detector 411 that is detected by the position sensor 60 when the cleaning member 41 is at the first position P. For example, the first detector 411 is provided on the holder 43 of the cleaning member 41 that faces the position sensor 60. The moving belt 64 also has a second detector 641 that is detected by the position sensor 60 when the cleaning member 41 is at the second position Q. Both the first detector 411 and the second detector 641 are configured to act as optical path shields when disposed between the light-emitting unit 601 and the light-receiving unit 602 of the position sensor 60, respectively.

[0077] 12, when the cleaning member 41 is disposed at the first position P, the second detection unit 641 is at the second position Q, which is the end on the opposite side in the axial direction X. The first detection unit 411 provided on the cleaning member 41 is detected by the position sensor 60, and it is determined that the cleaning member 41 is at the first position P.

[0078] When the cleaning mode is executed, when the cleaning member 41 moves together with the movable belt 64 from the first position P to the second position Q, the second detection unit 641 moves in conjunction with this together with the movable belt 64 from the second position Q toward the first position P, as shown in FIG. 13. When the cleaning member 41 reaches the second position Q, the second detection unit 641 reaches the first position P, as shown in FIG. 14. The second detection unit 641 is detected by the position sensor 60.

[0079] The first detection unit 411 and the second detection unit 641 are preferably configured to have different light transmittances. The output value of the light amount by the position sensor 60 can be made different when detecting the first detection unit 411 and when detecting the second detection unit 641, making it possible to determine whether the position sensor 60 has detected the first detection unit 411 or the second detection unit 641. That is, for example, if the first detection unit 411 of the cleaning member 41 is detected at the first position P, and then the cleaning member 41 moves and a predetermined time elapses, and the position sensor 60 indicates a different output value of the light amount, it can be determined that the second detection unit 641 has been detected.

[0080] This makes it possible to reliably determine whether the cleaning member 41 is located at the first position P or the second position Q. Not only when the normal cleaning mode in which the cleaning member 41 moves back and forth is performed, but also when the cleaning mode in which the cleaning member 41 moves one way is performed, the position of the cleaning member 41 can be determined with one position sensor 60, making it possible to confirm that cleaning by the cleaning device 40 has been completed.

[0081] Furthermore, when image formation starts or when returning from an energy saving mode, etc., it is possible to determine whether the cleaning member 41 is located at the first position P or the second position Q by checking the output value of the light intensity detected by the position sensor 60. At this time, if the position sensor 60 determines that the cleaning member 41 is not located at either the first position P or the second position Q, the drive mechanism 63 is driven to move the moving belt 64 to a position where the position sensor 60 detects the first detection unit 411 or the second detection unit 641, thereby making it possible to position the cleaning member 41 at the first position P or the second position Q.

[0082] Therefore, in this embodiment, when the interval between executions of the cleaning mode in the image forming apparatus 1 is shortened and the cleaning frequency is increased, the cleaning time required for cleaning is shortened by limiting the range of movement of the cleaning member 41 to one-way movement, thereby shortening the time during which the image formation process is interrupted.In addition, it is possible to confirm the position of the cleaning member 41 within such a movement range with a single position sensor 60.While it used to take time to move the cleaning member 41 back and forth for one cleaning, by executing the one-way movement cleaning mode, it is possible to complete cleaning in half the time required for back and forth movement.This makes it possible to automate the cleaning of the discharge electrode 121 and further stabilize the image formation quality, while avoiding long wait times when outputting images.

[0083] In the above embodiment, the object to be cleaned by the cleaning device 40 is the sawtooth discharge electrode 121, but it may be another type of discharge electrode that discharges at high voltage. For example, the object to be cleaned may be a wire-type discharge electrode or another shape.

[0084] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the technical gist thereof, and all technical matters included in the technical ideas described in the claims are the subject of the present disclosure. The above-described embodiments are preferred examples, but various modifications can be realized from the disclosed contents, and such modifications are also included in the technical scope described in the claims. [Explanation of symbols]

[0085] 1. Image forming device 10 Image forming unit 101 Photoconductor unit 11 Photosensitive drum (image carrier) 111 Rotation axis 12 Charging device 121 Discharge electrode 122 Charged power supply (power supply) 13 Optical scanning device 14 Developing device 141 Developing roller 19 Transcription device 40 Cleaning equipment 41 Cleaning materials 411 First detection unit 42 Cleaning roller 43 Holder 44 Spiral member (moving mechanism) 50 Environmental Sensors 60 Position Sensor 601 Light-emitting part 602 Light receiving part 61, 62 Rotating body 63 Drive mechanism 64 Moving Belt 641 Second detection unit 70 Control Unit P 1st position Q 2nd position X-axis direction

Claims

1. an image carrier that is rotatable around a rotation axis; a discharge electrode extending in the axial direction of the rotary shaft, disposed so as to face the image carrier, and connected to a power source; an image forming unit that forms a toner image to be transferred onto a sheet on the image carrier that has been charged by discharging the discharge electrode, and transfers the toner image onto the sheet; a cleaning device having a cleaning member for cleaning the discharge electrode, the cleaning member being moved in the axial direction of the rotation shaft to clean the discharge electrode; an environmental sensor for detecting temperature and humidity; a control unit that is capable of executing a cleaning mode in which, when the number of the toner images transferred to the sheet exceeds a predetermined threshold, the cleaning member is moved by controlling the movement mechanism to clean the discharge electrode, The control unit determines, based on the detection results of the environmental sensor, a threshold value for executing the cleaning mode and a range of movement of the cleaning member when executing the cleaning mode, determining whether to move the cleaning member back and forth in the axial direction of the rotation shaft or to move the cleaning member in either a forward or backward direction.

2. 2. The image forming apparatus according to claim 1, an image forming apparatus characterized in that the cleaning member is movable between a first position at one end of the axial direction of the rotating shaft, where the cleaning member does not interfere with the discharge operation of the discharge electrode, and a second position at the other end of the axial direction of the rotating shaft, where the cleaning member does not interfere with the discharge operation of the discharge electrode.

3. 2. The image forming apparatus according to claim 1, The control unit executes the cleaning mode in a first region where the amount of moisture in the air is low and which is defined by a predetermined temperature and humidity, using a threshold value that is lower than that in a second region which is a region other than the first region, and is characterized by the image forming apparatus in which the movement range of the cleaning member is one-way movement in either the forward or return direction.

4. 2. The image forming apparatus according to claim 1, The image forming apparatus according to claim 1, wherein the control unit executes the cleaning mode while the image carrier is rotating and while no power is being supplied from a power source to the discharge electrode.

5. 4. The image forming apparatus according to claim 3, the image forming unit includes a developing device having a developing roller that supplies toner to the charged image carrier, and a developing power supply that supplies a developing bias, which is a predetermined voltage, to the developing roller; The image forming apparatus according to claim 1, wherein the control unit supplies, during execution of the cleaning mode, the developing bias from the developing power supply, which has a value different from that when a toner image is formed on the developing roller.

6. 3. The image forming apparatus according to claim 2, The cleaning device is a position sensor disposed on one end side of the rotary shaft in the axial direction; a moving belt that is stretched over two rotating bodies disposed on one end side and the other end side of the rotation shaft in the axial direction and moves the cleaning member in the axial direction of the rotation shaft; Further, a drive mechanism for the rotating body is provided, the cleaning member has a first detection portion that is detected by the position sensor when the cleaning member is in the first position; The image forming apparatus according to claim 1, wherein the moving belt has a second detection portion that is detected by the position sensor when the cleaning member is in the second position.

7. 7. The image forming apparatus according to claim 6, the position sensor is a transmission type sensor having a light emitting portion and a light receiving portion that receives light from the light emitting portion, The image forming apparatus is characterized in that the first detection unit and the second detection unit are configured to have different light transmittances.

Images