JP5452509B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using a photosensitive drum, and more particularly to a method for removing moisture on the surface of a photosensitive drum.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a facsimile, a powder developer (hereinafter referred to as toner) is mainly used, and an electrostatic image formed on an image carrier such as a photosensitive drum. In general, the latent image is visualized with toner in the developing device, and the toner image is transferred onto a recording medium, and then a fixing process is performed. In such an image forming apparatus, as a device for charging the surface of the photoreceptor, for example, a corona discharge device that discharges when a high voltage is applied using a thin wire or the like as an electrode, and a conductive material around a conductive core material. A contact-type charging device that applies a voltage in a state where a charging member typified by a charging roller provided with a conductive rubber, a high-resistance coating layer, or the like is in contact with the surface of a photoreceptor has been widely used.

  The corona discharge device requires a high voltage, and discharge products such as ozone, NOx and SOx generated by the discharge from the wire adhere to the shield and grid surface of the charging device. On the other hand, the contact-type charging device has an advantage that it can operate at a low voltage and generates less ozone.

  However, in the contact charging method, since the charging process on the surface of the photoreceptor is performed by discharge near the surface, the photosensitive layer is liable to cause local dielectric breakdown (leakage) called a pinhole. This pinhole appears as a color point or color streak on the image, which is a big problem in image quality. In particular, in a high-temperature and high-humidity environment or in a dew-condensed environment, leakage is likely to occur due to the influence of moisture on the photosensitive layer or the charging roller when the image forming apparatus is turned on or returned from the sleep (power saving) mode. In an intermediate transfer type image forming apparatus, leakage may occur due to the water on the intermediate transfer belt flowing around the photosensitive member.

  Further, even if no leak occurs in the photoconductor, the discharge product on the surface of the photoconductor drum absorbs moisture, and an image flow occurs due to a decrease in the surface resistance of the photoconductor drum. Therefore, it is necessary to remove moisture from the photosensitive drum and its peripheral members in a high humidity environment.

  Therefore, Patent Document 1 discloses an image in which moisture and discharge products on the surface of the photosensitive drum are removed by discharging the deteriorated toner in the developing device onto the photosensitive drum and removing it while rubbing with a rubbing member. A forming apparatus is disclosed. Further, even when the toner concentration in the developer discharged on the photosensitive drum is lower than a predetermined value and there is not an amount of abrasive necessary and sufficient to remove the discharge products on the photosensitive drum, It is described that it is possible to sufficiently remove discharge products and prevent image flow by making the rotational speed of the photosensitive drum faster than that at the time of image formation.

JP 2007-286404 A

  However, although the discharge product on the photosensitive drum can be removed by the method disclosed in Patent Document 1, in particular, in the case of the contact charging method, the charging roller is turned on when the image forming apparatus is turned on or returned from the power saving mode (sleep state). In addition, there is a problem that moisture on the intermediate transfer belt cannot be removed effectively.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of sufficiently removing moisture from a photosensitive drum and peripheral members before starting a printing operation in a high-temperature and high-humidity environment or a condensation environment.

  In order to achieve the above object, the present invention provides an image bearing member having a photosensitive layer formed on the surface thereof, and applying a charging bias including a direct current bias to the surface of the image bearing member in a contact or non-contact state. A charging member for charging the surface of the carrier, a developing device for forming a toner image corresponding to the electrostatic latent image by attaching toner to the electrostatic latent image formed on the surface of the image carrier, and the image carrier A cleaning blade that is pressed against the surface with a predetermined pressure and removes residual toner on the surface of the image carrier, and rotates the image carrier during non-image formation, and the image carrier surface is rotated by the cleaning blade. A first moisture removing step for removing moisture from the toner, and the toner in the developing device is transported to the image carrier, and the toner on the surface of the image carrier is adsorbed to the transported toner and removed together with the toner. A moisture removal mode in which a second moisture removal step and a third moisture removal step of removing moisture on the surface of the charging member and the image carrier by applying a DC bias to the charging member in this order can be executed. Image forming apparatus.

  According to the present invention, in the image forming apparatus configured as described above, the rotational speed of the image carrier during execution of the moisture removal mode is faster than the rotational speed of the image carrier during image formation.

  In the image forming apparatus having the above-described configuration, the DC bias applied to the charging member at the time of executing the third moisture removing step is ½ or less of the DC bias applied to the charging member at the time of image formation. It is characterized by being.

  According to the present invention, in the image forming apparatus configured as described above, the DC bias applied to the charging member at the time of executing the third moisture removing step is increased stepwise.

  According to the present invention, in the image forming apparatus having the above-described configuration, the image forming apparatus includes a plurality of the image carriers and an intermediate transfer member on which the toner images formed on the image carriers are sequentially stacked. A bias is applied to the intermediate transfer member during the execution of the process.

  According to the present invention, in the image forming apparatus having the above-described configuration, a temperature detecting unit that detects temperatures inside and outside the image forming apparatus, a humidity detecting unit that detects humidity outside the image forming apparatus, and the temperature detecting unit and the humidity detecting unit. Control means for determining whether or not to execute the moisture removal mode according to the temperature and humidity detected by the means.

  According to the first configuration of the present invention, large droplets on the surface of the image carrier are removed by the cleaning blade in the first moisture removal step, and minute water droplets on the surface of the image carrier are removed together with the toner in the second moisture removal step. In the third moisture removing step, a very small amount of moisture on the surface of the image carrier is completely removed. Therefore, the moisture on the surface of the image carrier can be removed stepwise and completely in a short time, and image defects such as leakage, color points, color streaks, and image flow can be effectively prevented over a long period of time. Can be prevented.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, the rotational speed of the image carrier during execution of the moisture removal mode is higher than the rotational speed of the image carrier during image formation. By doing so, the execution time of the moisture removal mode can be shortened.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the DC bias applied to the charging member at the time of executing the third moisture removing step is changed to the charging member at the time of image formation. By making the DC bias to be 1/2 or less of the DC bias applied to, the moisture in the image carrier and the charging member can be effectively removed while preventing the occurrence of leakage in the third moisture removal step.

  According to the fourth configuration of the present invention, in the image forming apparatus having the third configuration, the DC bias applied to the charging member at the time of executing the third moisture removing step is increased stepwise to increase the third level. The occurrence of leakage in the moisture removal process can be prevented more reliably.

  According to the fifth configuration of the invention, in the image forming apparatus having any one of the first to fourth configurations, the plurality of image carriers and the toner images formed on the respective image carriers are sequentially provided. The intermediate transfer member is laminated, and a bias is applied to the intermediate transfer member at the time of performing the third moisture removing step, thereby simultaneously removing the moisture on the surface of the intermediate transfer member together with the water on the image carrier and the charging member. Can do.

  According to the sixth configuration of the present invention, in the image forming apparatus having any one of the first to fifth configurations, the temperature detecting means for detecting the temperature inside and outside the image forming apparatus, and the outside of the image forming apparatus. And a control means for determining whether to execute the moisture removal mode in accordance with the temperature and humidity detected by the temperature detection means and the humidity detection means. The moisture removal mode is automatically executed by detecting a high humidity environment or a dew condensation environment. Therefore, it is not necessary for the user himself to set the moisture removal mode, and it is possible to avoid mode setting mistakes, forgetting to set, or unnecessary execution of the moisture removal mode.

1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus of the present invention. Partial enlarged view of the periphery of the image forming portion Pa in FIG. 1 is a block diagram showing a control path of an image forming apparatus of the present invention. 7 is a flowchart illustrating an example of control of a water removal mode in the image forming apparatus of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus of the present invention. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c and 1d for carrying visible images (toner images) of the respective colors. Here, an organic photosensitive layer is provided on the outer peripheral surface of the aluminum drum. An OPC photoreceptor on which (OPC) is formed is used. Further, an intermediate transfer belt 8 that rotates clockwise in FIG. 1 by a driving means (not shown) is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. As the photosensitive drums 1a to 1d, for example, an image forming process for the photosensitive drums 1a to 1d is performed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. Around and below the photosensitive drums 1a to 1d having organic photosensitive layers (OPC) rotatably disposed, charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d, and respective photosensitive drums Remaining on the photosensitive drums 1a to 1d, the exposure unit 4 that exposes image information to the photosensitive drums 1a to 1d, the developing devices 3a, 3b, 3c, and 3d that form toner images on the photosensitive drums 1a to 1d. Cleaning devices 5a to 5d for removing the developer (toner) are provided.

  When an image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d includes a developing roller disposed so as to face the photosensitive drums 1a to 1d, and is filled with a predetermined amount of a two-component developer containing toner of each color of yellow, cyan, magenta, and black. This toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing devices 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure unit 4. A toner image is formed.

  Then, the primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and yellow, cyan, magenta, and yellow on the photosensitive drums 1a to 1d are applied. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched around a plurality of suspension rollers including a driven roller 10 and a drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). Is started, the transfer paper P is transported from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the nip portion (secondary transfer nip portion) with the intermediate transfer belt 8 is transferred. ), The full color image is secondarily transferred onto the transfer paper P. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13, and the toner image is fixed on the surface of the transfer paper P, so that a predetermined full color is obtained. An image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once protruded from the discharge roller 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the registration roller pair 12b with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. , And discharged to the discharge tray 17.

  FIG. 2 is an enlarged view of the vicinity of the image forming portion Pa in FIG. Since the image forming units Pb to Pd have basically the same configuration, description thereof is omitted. Around the photosensitive drum 1a, a charging device 2a, a developing device 3a, a cleaning device 5a, and a charge eliminating lamp 20 are disposed along the drum rotation direction (counterclockwise in FIG. 2), and the intermediate transfer belt 8 is interposed therebetween. The primary transfer roller 6a is arranged.

  The charging device 2 a includes a charging roller 21 that contacts the photosensitive drum 1 a and applies a charging bias (DC voltage) to the drum surface, and a charging cleaning roller 23 for cleaning the charging roller 21. In the present invention, in order to reduce the amount of ozone generated and to reduce the cost of the charging bias power source 42 (see FIG. 3), a charging bias consisting only of a DC voltage is applied to the charging roller 21. A bias applying method in which an AC bias is superimposed on the bias may be used.

  The developing device 3a is a two-component developing type having two agitating and conveying screws 25, a magnetic roller 27, and a developing roller 29, and a toner thin film is applied to the developing roller 29 using a magnetic brush standing on the surface of the magnetic roller 27. A layer is formed, and a developing bias having the same polarity (positive) as the toner is applied to the developing roller 29 to cause the toner to fly on the drum surface.

  The cleaning device 5 a has a cleaning blade 31 and a recovery screw 33.

  A cleaning blade 31 is fixed in contact with the photosensitive drum 1a on the photosensitive drum 1a surface downstream of the contact surface with the intermediate transfer belt 8 in the rotation direction. As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive member at the contact point. The material, hardness, dimensions, the amount of biting into the photosensitive drum 1a, the pressure contact force, and the like of the cleaning blade 31 are appropriately set according to the specifications of the photosensitive drum 1a. Residual toner removed from the surface of the photosensitive drum 1 a by the cleaning blade 31 is discharged to the outside of the cleaning device 5 a as the recovery screw 33 rotates.

  A neutralizing lamp 20 is disposed between the cleaning device 5a and the charging device 2a. The neutralization lamp 20 removes residual charges on the surface of the drum by irradiating the surface of the photosensitive drum 1a with light.

  When the image forming apparatus of the present invention is not transferred to a recording medium, for example, when the image forming apparatus is started up from a power-off state or a sleep (power saving) mode to a printing start state, the photosensitive drum 1a is used by the cleaning blade 31. Step of removing moisture from the surface of 1d (first moisture removing step), and the toner on the developing roller 29 in the developing devices 3a to 3d is conveyed to the photosensitive drums 1a to 1d side, and the photosensitive drums 1a to 1d side The surface of the photosensitive drums 1a to 1d is adsorbed by the toner conveyed to the surface, and the surface of the photosensitive drums 1a to 1d is removed together with the toner (second moisture removing step), and a voltage is applied to the charging roller 21. Thus, it is configured to be able to execute a moisture removal mode in which the process of removing moisture on the surfaces of the charging roller 21 and the photosensitive drums 1a to 1d (third moisture removal process) is sequentially performed. Hereinafter, each step in the moisture removal mode will be described in detail.

(First moisture removal step)
In the first moisture removal step, the surface of the photosensitive drums 1a to 1d is physically scraped by the cleaning blade 31 pressed against the photosensitive drums 1a to 1d. Effective when condensation is present. This first moisture removal step is performed continuously for at least the time for which the photosensitive drums 1a to 1d make one round.

(Second moisture removal step)
In the second moisture removal step, the toner in the developing devices 3a to 3d is supplied from the developing roller 29 to the photosensitive drum 1 side, and moisture and contaminants on the surfaces of the photosensitive drums 1a to 1d are adsorbed to the toner, and then cleaned. The blade 31 is used for removal. The supply of toner in the second moisture removing step is continuously performed for at least the time for which the photosensitive drums 1a to 1d make one round.

  In the second moisture removal step, the toner layer supplied onto the photosensitive drums 1a to 1d becomes a thin layer by limiting the toner supply amount per unit area (hereinafter simply referred to as toner supply amount). All of the supplied toner can be used for removing moisture from the surface of the photoreceptor, so that the efficiency of removing moisture can be improved and the amount of toner supply can be minimized.

  Normally, the toner is supplied to the photosensitive drums 1 a to 1 d during image formation by exposing the entire surface of the photosensitive drums 1 a to 1 d uniformly charged by the charging device 2 with the exposure unit 4, This is performed by a normal image forming process in which a developing bias having the same polarity (positive) as that of the toner is applied to cause the toner to fly on the drum surface. However, it is dangerous to apply a normal bias value (at the time of image formation) to sufficiently charge the photosensitive drums 1a to 1d before the moisture on the surfaces of the photosensitive drums 1a to 1d is sufficiently removed. The method is undesirable. In this method, the amount of toner supplied per unit area increases, and it is difficult to make the toner layer thin.

  Therefore, a method is used in which charging is not performed by the charging device 2 and toner is supplied to the drum surface by applying a developing bias to the developing roller 29 in a state where the surface potential of the photosensitive drums 1a to 1d is near 0V (ground). Is preferred. At this time, the developing bias applied to the developing roller 29 is set to a value (approximately 30 to 50 V) slightly higher than the bias value at which the toner starts to fly toward the drum surface.

(Third moisture removal step)
In the third moisture removing step, the surface of the photosensitive drums 1a to 1d is charged by rotating the photosensitive drum 1 while applying a DC bias to the charging roller 21 of the charging device 2 (charging aging). The water on the surface of 1d is removed by evaporation, and the water adhering to the surface of the charging roller 21 is also removed.

  The DC bias applied to the charging roller 21 is applied with a bias value less than half of the charging bias applied during image formation. For example, when the DC bias value applied at the time of image formation is 1.4 kV, the DC bias value applied in the third moisture removing step is about 700V.

  Further, even if the DC bias value is less than half that at the time of image formation, if a target bias value is applied at a time, dielectric breakdown may occur when moisture remains on the surfaces of the photosensitive drums 1a to 1d. There is. Therefore, after confirming that the current value when a predetermined DC bias (for example, 400 V) lower than the target value is applied is equal to or less than a certain current value, the DC bias is raised to the next level (for example, 550 V), and the DC voltage is increased. It is preferable to perform feedback control in which the bias value is increased stepwise up to a target value (for example, 700 V).

  Further, by applying a bias to the intermediate transfer belt 8 from the primary transfer rollers 6a to 6d during the execution of the third moisture removing step, discharge occurs between the photosensitive drums 1a to 1d and the intermediate transfer belt 8. In addition, moisture on the surface of the intermediate transfer belt 8 can also be removed.

  If the third moisture removing step is executed before the first and second minute removing steps, a large amount of moisture remains on the photosensitive drum 1, so that the photosensitive layers of the photosensitive drums 1a to 1d are insulated. It will cause destruction. By executing the first to third moisture removal steps in this order, large water droplets on the surfaces of the photosensitive drums 1a to 1d are first removed by the cleaning blade 9 in the first moisture removal step. Next, in the second moisture removal step, minute water droplets on the surfaces of the photosensitive drums 1a to 1d are removed together with the toner. Finally, in the third moisture removing step, a very small amount of moisture on the surfaces of the photosensitive drums 1a to 1d is completely removed.

  That is, an effective moisture removal system that can remove moisture on the surfaces of the photosensitive drums 1a to 1d in a short time stepwise and completely, and effectively prevent the occurrence of leakage and image flow over a long period of time. It becomes. The execution time of each step is appropriately set according to the configuration of the photosensitive layer to be used, the usage environment of the apparatus, the elapsed time from the start of use of the photosensitive drums a to 1d, and the like.

  Further, by increasing the rotational speed of the photosensitive drums 1a to 1d when the moisture removal mode is executed, the moisture removal area per unit time by the cleaning blade 31 is widened in the first moisture removal step. In the second moisture removal step, the toner adhesion area per unit time is increased. Further, in the third moisture removing step, the charging area per unit time by the charging roller 21 is widened. Accordingly, it is possible to shorten the time required to remove the moisture on the surfaces of the photosensitive drums 1a to 1d, that is, the execution time of the moisture removal mode.

  Next, the control path of the image forming apparatus of the present invention will be described. FIG. 3 is a block diagram for explaining an embodiment of the control means used in the image forming apparatus of the present invention. Note that since various controls of each part of the apparatus are performed when the image forming apparatus 100 is used, the control unit 90 itself of the image forming apparatus 100 is complicated. Therefore, here, a portion of the control means 90 that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a readable / writable storage unit, A plurality of I / Fs (interfaces) for transmitting a control signal to each device in the image forming apparatus 100 and receiving an input signal from the operation unit 50. ) 96 at least. Further, the control means 90 can be arranged at any location inside the apparatus main body 1.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. The ROM 92 (or RAM 93) also includes an environment correction table (described later) that stores the internal temperature and external humidity and the necessity of executing the moisture removal mode in association with each other. The counter 95 counts the number of printed sheets. For example, the RAM 93 may store the number of printed sheets without providing the counter 95 separately.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. For example, the image forming units Pa to Pd, the exposure unit 4, the primary transfer rollers 6 a to 6 d, the fixing unit 7, the secondary transfer roller 9, and the image input unit may be used as the respective units and devices controlled by the control unit 90 in this embodiment. 40, a bias control circuit 41, an operation unit 50, and the like. In addition, the control content of the water | moisture-content removal mode in this embodiment is mentioned later.

  The image input unit 40 is a receiving unit that receives image data transmitted from a personal computer or the like to the color printer 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, and the transfer bias power source 44, and operates each of these power sources in accordance with an output signal from the control unit 90. In accordance with a control signal from the control circuit 41, the charging bias power source 42 is applied to the charging roller 21 in the charging devices 2a to 2d, and the developing bias power source 43 is applied to the magnetic roller 27 and the developing roller 29 in the developing devices 3a to 3d. A predetermined bias 44 is applied to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively.

  The operation unit 50 is provided with a liquid crystal display unit 51 and an LED 52 indicating various states, and displays the state of the printer 100 and displays the image forming status and the number of copies to be printed. Various settings of the printer 100 are performed from a printer driver of a personal computer.

  In addition, the operation unit 50 includes a start button for instructing the user to start image formation, a stop / clear button used when the image formation is stopped, and various settings of the image forming apparatus 100 in a default state. A reset button or the like is provided for use.

  The in-machine temperature sensor 97a detects the temperature inside the apparatus, particularly the temperature of the surface or the periphery of the photosensitive drums 1a to 1d, and is disposed in the vicinity of the image forming portions Pa to Pd. The external temperature sensor 97b detects the temperature outside the apparatus, and the external humidity sensor 98 detects the humidity outside the apparatus. The outside temperature sensor 97b and the outside humidity sensor 98 are installed in the vicinity of an air intake duct (not shown) on the side of the paper cassette 16 in FIG. It can also be installed in other locations where it can be detected accurately.

  The in-machine temperature sensor 97a and the out-of-machine temperature sensor 97b always detect the temperature inside and outside the apparatus every predetermined time. The external humidity sensor 98 always detects the humidity outside the apparatus every predetermined time. The in-machine humidity is calculated from the in-machine temperature, assuming that the absolute moisture content (determined by temperature) inside and outside the machine is the same. When an image output is instructed from the operation unit 50 to the CPU 91, the internal / external temperature detected by the internal temperature sensor 97a, the external temperature sensor 97b, and the external humidity detected by the external humidity sensor 98 are I / O. It is sent to the CPU 91 via F96, and the necessity of executing the moisture removal mode is selected by the environmental correction table using the temperature inside and outside the apparatus and the humidity outside the apparatus, and outputted to the CPU 91.

  Accordingly, whether or not to execute the moisture removal mode can be determined based on the detection results of the in-machine temperature sensor 97a, the out-of-machine temperature sensor 97b, and the out-of-machine humidity sensor 98. Moisture removal mode is executed under the conditions where the temperature difference is large and the humidity outside the machine is more than a certain level and condensation is likely to occur. Execution can be suppressed. In addition, the humidity inside the machine increases even under high-temperature and high-humidity conditions where the temperature and humidity outside the machine are both high, but the moisture removal mode is executed to prevent leakage of the drum surface and image flow. Occurrence can be prevented. Although it is preferable to control the moisture removal mode using the detected temperature and humidity immediately before execution as much as possible, the control may be performed using the temperature and humidity detected at other timings. It is also possible to detect the temperature and humidity a predetermined number of times and use the average value of the detected values.

  In addition, when the moisture removal mode is executed, an optimal execution time is set according to the surrounding environment, and the moisture removal mode is continued for a minimum time necessary for removing moisture on the surfaces of the photoconductive drums 1a to 1d. The formation efficiency can be maximized. Tables 1 and 2 show examples of the environment correction table used in the present invention.

  Table 1 is a table for selecting whether or not to execute the moisture removal mode under high temperature and high humidity conditions. In Table 1, the external temperature T is assigned to each row of the environmental correction table from 20 ° C. to 45 ° C. at 5 ° C. intervals, and the external humidity H is assigned to each column from 8% to 88% at 8% intervals. ing. Since the in-machine humidity is calculated from the out-of-machine temperature T, the out-of-machine humidity H, and the in-machine temperature detected by the in-machine temperature sensor 97a and the usage environment of the apparatus is predicted, the detected out-of-machine temperature T and the detected outside humidity H The flag at the position where the row and column corresponding to intersect is selected. The flag is assigned either 0 (no execution required) or 1 (execution required) at the position where the row and the column intersect. For example, when the in-machine temperature exceeds 20 ° C., there is no risk of condensation, but in a high-temperature and high-humidity environment where the outside temperature T exceeds 30 ° C. and the outside humidity H exceeds 80%, the surface of the photosensitive drum It is necessary to remove water. Accordingly, the flag 1 is set at the position where the row of 80 <H ≦ 88 and the column of 30 <T intersect, and the moisture removal mode is executed. On the other hand, when the outside humidity H is 80% or less, the execution of the moisture removal mode is not necessary, so the flag is set to 0.

  Table 2 is a table for selecting whether or not to execute the moisture removal mode under conditions where condensation easily occurs. In Table 2, a temperature difference t between the outside temperature T and the inside temperature when the outside temperature is higher than the inside temperature is assigned to each row of the environment correction table at intervals of 2 ° C. from 0 ° C. to 16 ° C. Is assigned at 8% intervals from 8% to 88%. When the in-machine temperature is 20 ° C. or less, if the temperature difference t between the out-of-machine temperature T and the in-machine temperature exceeds 4 ° C. and the outside humidity H exceeds 64%, condensation may occur. Therefore, it is necessary to remove moisture from the surface of the photosensitive drum. Accordingly, the flag 1 is set at the position where the row of 4 <t and the column of 64 <H intersect, and the moisture removal mode is executed.

  Moreover, not only the necessity of execution of the moisture removal mode but also the execution time of each process in the optimum moisture removal mode according to the outside temperature T and the outside humidity H or the temperature difference t and the outside humidity H is set. By doing so, the duration time of the moisture removal mode is minimized, so that the waiting time of the user can be shortened and the image forming efficiency can be kept high. The illustration of the environment correction table in which the execution time of the moisture removal mode is set is omitted.

  Next, the operation of the image forming apparatus of this embodiment will be described. FIG. 4 is a flowchart showing an image output operation of the image forming apparatus of the present invention. The control of the water removal mode when the image forming apparatus is turned on will be described in accordance with the steps of FIG. 4 with reference to FIGS.

  When the image forming apparatus 100 is turned on (step S1), first, the in-machine temperature, the outside temperature, and the outside humidity data detected by the in-machine temperature sensor 97a, the outside temperature sensor 97b, and the outside humidity sensor 98 are detected. Is transmitted to the CPU 91 (step S2). On the other hand, a control signal is transmitted from the CPU 91 to the fixing unit 7 and the temperature of the fixing roller starts to increase at the same time.

  Next, it is determined whether or not to execute the moisture removal mode based on the transmitted temperature and humidity data (step S3). This determination is made based on whether the flag is 0 or 1 based on the environment correction table (see Tables 1 and 2). When the moisture removal mode is executed, the first moisture removal process is executed (step S5) for a predetermined time while rotating the photosensitive drums 1a to 1d at a higher speed (for example, double speed) than during printing (step S4). After the elapse of time, the second moisture removal step is executed (step S6), and after the predetermined time has passed, the third moisture removal step is executed (step S7). The execution time of the first to third moisture removal steps is measured by a timer-95.

  After the first to third moisture removal steps are completed, the photosensitive drums 1a to 1d are stopped (step S8), and the moisture removal mode is terminated. Thereafter, it is determined whether or not the fixing unit 7 has been heated to a predetermined temperature (step S9). If the temperature has been increased, the process proceeds to a sleep (power saving) mode (step S10). If the flag is 0 in step S3, that is, if the moisture removal mode is not executed, the process shifts to the sleep mode after waiting for the fixing temperature to rise (step S9) (step S10).

  By performing the above control, moisture on the surfaces of the photosensitive drums 1a to 1d and the surface of the charging roller 21 is completely removed in a short time when the image forming apparatus 100 is turned on in a high-temperature and high-humidity environment and a dew-condensed environment. It is possible to effectively prevent the occurrence of color points and color streaks, image flow, and the like due to leakage of the photosensitive layer surface. Although the moisture removal mode control at power-on has been described with reference to FIG. 4, stable image output can be performed immediately after returning from the sleep mode by performing the same control when returning from the sleep mode.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the example in which the OPC photoconductor is used as the photoconductor drums 1a to 1d has been described. However, the case where the amorphous silicon photoconductor is used is described in the same manner. In the above embodiment, the moisture removal mode is controlled using the environmental correction table corresponding to the in-machine temperature and the outside humidity. However, the in-machine humidity for detecting the humidity inside the apparatus instead of the outside humidity sensor 98 is used. It is also possible to provide a sensor and control the moisture removal mode using an environment correction table corresponding to the in-machine temperature and the in-machine humidity.

  Further, the present invention is not limited to the color printer as shown in FIG. 1, but includes a photosensitive drum such as a tandem or rotary type color copier and printer, a monochrome copier, a digital multi-function peripheral, and a facsimile. Of course, the present invention can be applied to various image forming apparatuses. Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  The relationship between the peripheral speed of the photosensitive drum in the moisture removal mode executed in the image forming apparatus of the present invention, the execution time, and the moisture removal effect was evaluated. As an evaluation method, a tandem type color printer (FS-C5300DN modified machine manufactured by Kyocera Mita Co., Ltd.) as shown in FIG. 1 is used, and the photosensitive drums 1a to 1d are subjected to high humidity conditions (35 ° C., 80%). The time required for the first to third moisture removal steps required for moisture removal and the total duration of the moisture removal mode when the moisture removal mode was executed while changing the peripheral speed were compared.

  Further, the occurrence of leakage and defective images was investigated when the total duration of the moisture removal mode was fixed at 90 seconds and the peripheral speed of the photosensitive drums 1a to 1d was changed. The occurrence of leakage was detected by the value of the current flowing between the photosensitive drum and the charging roller. The case where no leakage occurred was marked with ◯, and the case where leakage occurred was marked with ×. Occurrence of image defects is the occurrence of color points and color streaks when the test image is actually printed, the image flow is visually observed, ◯ is a level where there is no practical problem, △ is the level at which image defects are slightly anxious, The level at which image defects occurred remarkably was marked with x. The results are shown in Tables 3 and 4.

  As is apparent from Table 3, the time required for the first to third moisture removal steps is shortened as the peripheral speed of the photosensitive drum is 1.5 times and twice as fast as that during printing. The duration was also reduced from 126 seconds to 100 times at 1.5 times speed and to 87 seconds at 2 times speed.

  As is apparent from Table 4, when the total duration of the moisture removal mode is fixed at 90 seconds, when the photosensitive drum is rotated at the peripheral speed during printing, either the high temperature / high humidity environment or the condensation environment is used. Also, leaks and image defects occurred. On the other hand, when the peripheral speed of the photosensitive drum is 1.2 times that at the time of printing, an image defect occurs in both a high temperature and high humidity environment and a condensation environment, but no leakage occurs. When it was tripled, only a slight image defect occurred in the condensation environment. Furthermore, when the printing was performed 1.5 times or 2 times, neither leakage nor image defect occurred.

  From this result, when performing the moisture removal mode of the present invention in which the first to third moisture removal steps are executed in this order, the peripheral speed of the photosensitive drum is made faster than that at the time of printing, so that the total execution time of the moisture removal mode is increased. It was confirmed that can be greatly shortened. This is considered to be because the processing area (moisture removal area) on the surface of the photosensitive drum per unit time in each process is widened.

  The present invention can be used to remove moisture on the surface of a photosensitive drum in an image forming apparatus using a photosensitive drum as an image carrier, and includes a first moisture removal step of removing moisture from the surface of an image carrier with a cleaning blade. The toner in the developing device is transported to the image carrier side, the moisture on the surface of the image carrier is adsorbed to the transported toner and removed together with the toner, and charging is performed by applying a DC bias to the charging member. It is possible to execute a moisture removal mode in which the third moisture removal step of removing moisture on the surface of the member and the image carrier is performed in this order.

  By utilizing the present invention, moisture on the surface of the image carrier can be removed stepwise and completely in a short time, and image defects such as occurrence of leaks, color points, color streaks, and image flow over a long period of time. It is possible to provide an image forming apparatus capable of effectively preventing the above.

1a to 1d Photosensitive drum (image carrier)
2a to 2d charging device 3a to 3d developing device 5a to 5d cleaning device 4 exposure unit 21 charging roller (charging member)
29 Developing roller 31 Cleaning blade 90 Control unit (control means)
97a In-machine temperature sensor (temperature detection means)
97b External temperature sensor (temperature detection means)
98 External humidity sensor (humidity detection means)
100 Image forming apparatus

Claims (6)

An image carrier having a photosensitive layer formed on the surface;
A charging member that charges the surface of the image carrier by applying a charging bias including a direct current bias in a contact or non-contact state to the surface of the image carrier;
A developing device that forms a toner image corresponding to the electrostatic latent image by attaching toner to the electrostatic latent image formed on the surface of the image carrier;
A cleaning blade that is pressed against the surface of the image carrier at a predetermined pressure and removes residual toner on the surface of the image carrier.
A first moisture removing step of rotating the image carrier during non-image formation and removing moisture from the surface of the image carrier by the cleaning blade, and a time for the image carrier to rotate the toner in the developing device once. above the conveyed to image bearing member, and a second moisture removing step of removing with moisture is adsorbed toner of the image bearing member surface to the transported toner, the charging member and by applying a DC bias to said charging member An image forming apparatus characterized in that a water removal mode in which a third water removal step of removing water on the surface of the image carrier is performed in this order is executable.   The image forming apparatus according to claim 1, wherein a rotation speed of the image carrier during execution of the moisture removal mode is faster than a rotation speed of the image carrier during image formation.   2. The DC bias applied to the charging member during execution of the third moisture removing step is ½ or less of the DC bias applied to the charging member during image formation. The image forming apparatus according to 2.   The image forming apparatus according to claim 3, wherein a DC bias applied to the charging member at the time of executing the third moisture removing step is increased stepwise.   A plurality of image carriers and an intermediate transfer member on which toner images formed on the respective image carriers are sequentially laminated, and a bias is applied to the intermediate transfer member when the third moisture removing step is executed. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Temperature detection means for detecting the temperature inside and outside the image forming apparatus;
Humidity detecting means for detecting humidity outside the image forming apparatus;
Control means for determining whether to execute the moisture removal mode according to the temperature and humidity detected by the temperature detection means and the humidity detection means;
The image forming apparatus according to claim 1, further comprising:

Images