JP4403686B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that employs an electrophotographic system, and more particularly to an image forming apparatus that includes a charger that charges an image carrier.
[0002]
[Prior art]
In recent years, so-called full-color tandem machines have been proposed in image forming apparatuses such as printers, copiers, and facsimile machines for the purpose of forming color images at high speed and high image quality. As a typical tandem machine, four image forming units of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel with each other, and each of these image forming units. The toner images of yellow, magenta, cyan, and black that are sequentially formed in step 1 are temporarily transferred onto the intermediate transfer belt once in a multiple, and then transferred onto the transfer paper from the intermediate transfer belt. Examples include fixing a toner image formed on the transfer paper to form a full-color or black-and-white (monochrome) image.
[0003]
FIG. 15 is a diagram showing an example of such a tandem machine. The image forming apparatus shown in FIG. 15 includes four image forming units 300Y, 300M, 300C, and 300K that form toner images having different colors of yellow, magenta, cyan, and black, and these image forming units 300Y and 300M. , 300C, 300K are arranged in parallel at regular intervals along the horizontal direction. The image forming units 300Y, 300M, 300C, and 300K have substantially the same configuration except that the color of the toner image to be formed is different, and after the surface of the photosensitive drum 301 is uniformly charged by the charging device 302 The exposure device 303 exposes the surface of the photosensitive drum 301 to form an electrostatic latent image corresponding to the image information of each color. The electrostatic latent image formed on the surface of the photosensitive drum 301 is visualized by a developing device 304 of a corresponding color to become a toner image, and this toner image is transferred to an intermediate transfer belt by a charger 305 for primary transfer. Multiple images are sequentially transferred onto 306. The toner remaining on the surface of the photosensitive drum 301 is removed by the cleaning device 307 to prepare for the next image forming process.
[0004]
The intermediate transfer belt 306 is circulated and driven at a speed equal to the rotational speed of the photosensitive drum 301 by a plurality of rollers 308, 309, 310, 311, 312 including a driving roller. The yellow, magenta, cyan, and black toner images transferred in multiple onto the intermediate transfer belt 306 are intermediate at the secondary transfer position (the position of the roller 311) provided below the intermediate transfer belt 306. The secondary transfer roll 313 that is in contact with the surface of the transfer belt 306 is collectively transferred onto the transfer paper 314 that is fed at a predetermined timing to the secondary transfer position. Thereafter, the transfer sheet 314 is conveyed to a fixing device (not shown), and is subjected to fixing processing with heat and pressure by the fixing device, thereby forming a color or monochrome image.
[0005]
Here, as the charging device 302 for charging the surface of the photosensitive drum 301, a non-contact type discharging by a corona charging device has been widely used. However, in order to reduce the generation of ozone and reduce power consumption. In recent years, the contact type has attracted attention. In this contact type, for example, a charging member such as a charging roller or a charging brush is brought into contact with the photosensitive drum 301 which is a member to be charged, and a predetermined charging bias is applied so that the surface of the image carrier of the photosensitive drum 301 is fixed to a predetermined level. Charged to polarity and potential.
[0006]
At this time, if the contact-type charging member floats from the image carrier, the discharge cannot be performed, and the charge is not uniformized, resulting in image quality defects. For example, the contact-type charging member is added by a spring material or the like. A configuration is adopted in which the pressure is pressed against the image carrier. However, the portion that is always pressed, that is, the portion where the contact-type charging member contacts the image carrier is likely to be deformed. In particular, when a charging roll made of a rubber material is employed as the contact-type charging member, the rubber is distorted (deformed) and comes into close contact with the image carrier. In particular, when the image forming apparatus is left unattended for a long time, the contact-type charging member is forced to be deformed over a long period of time, and the deformed portion (distorted portion) is lifted from the image carrier. As a result, sufficient discharge cannot be performed. As a result, the discharge becomes non-uniform, causing charging failure, resulting in image quality defects.
[0007]
As a prior art using this contact-type charging member, in order to prevent instability of the initial potential of charging using a brush when the charging roller is permanently deformed, the charging operation takes about 1 minute when the process unit is new. Is executed as an initialization operation (see, for example, Patent Document 1). In addition, there is a technique including a mechanism for releasing the pressure of the charging roller in order to reduce the distortion of the charging roller (see, for example, Patent Document 2).
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-92752 (page 5-6, FIG. 5)
[Patent Document 2]
JP 2000-31002 A (page 10-11, FIG. 2)
[0009]
[Problems to be solved by the invention]
As described above, in order to avoid the distortion of the charging roller when the contact-type charging member is brought into contact with the image carrier such as the photosensitive drum 301 to be charged, the above-described Patent Document 1 describes the surface of the image carrier. On the other hand, since the charging is performed for a predetermined time before the image forming process, if this technique is applied in a state other than the initial operation, the charging time becomes long and the wear of the image carrier becomes severe. If a mechanism for releasing pressure (retract mechanism) is provided as in Patent Document 2 described above, the configuration becomes complicated and the cost increases.
[0010]
The present invention has been made to solve the technical problems as described above, and an object of the present invention is to reduce image quality defects due to compressive strain of a contact-type charging member.
Another object of the present invention is to use an image forming apparatus configured such that the charging member is pressed against the image carrier after the image carrier is stopped and left without performing image formation for a long time. However, it is possible to form an image with reduced image quality defects.
[0011]
[Means for Solving the Problems]
For this purpose, in the present invention, the contact portion of the contact-type charging member is released from the image carrier for a certain period of time in accordance with the previous stopped state or neglected state prior to execution of image formation. The image quality defect due to the contact distortion of the mold charging member is reduced. That is, an image forming apparatus to which the present invention is applied contacts an image carrier that carries an image at the time of image formation with the image carrier at a predetermined pressure, for example, following the rotation of the image carrier. A charging member configured to rotate the charging roller to charge the image carrier, and information related to a stop time of image formation using the image carrier, for example, including an image carrier and a charging member A non-volatile memory provided in the process cartridge, and a control circuit for controlling the rotation of the image carrier. The control circuit is in a stopped state before execution of image formation. And the image carrier is rotated for a predetermined time prior to the execution of image formation based on the grasped state. More specifically, this control circuit is characterized by grasping the temperature at which the apparatus main body is placed and determining the rotation condition of the image carrier based on the grasped temperature.
[0012]
From another point of view, the present invention is an image forming apparatus that performs an image forming process using a contact charger that contacts and charges the image carrier, An idle time information acquisition unit that acquires information on the idle time from the execution, and an idle time for calculating the idle rotation time for idly rotating the image carrier before performing the actual image forming process based on the acquired information on the idle time. Rotation time calculating means, rotating means for idly rotating the image carrier based on the calculated idling time, and image forming process executing means for executing actual image forming processing according to predetermined image forming conditions after idling. Including. Here, if the image forming conditions by the image forming processing execution means are conditions relating to the frequency of the AC voltage applied to the contact charger and / or the AC voltage control method, image defect reduction is further enhanced. It is preferable in that it can be performed.
[0013]
Furthermore, the present invention relates to a method for controlling an image forming apparatus that forms an image using a charger that is charged by being pressed with a predetermined pressing force and in contact with the image carrier. And a process of reducing the amount of distortion of the charger is executed based on the acquired information on the leaving state, and an actual image forming process is executed after this process is executed. The process of reducing the distortion amount of the charger is a process of changing the contact position of the charger with respect to the image carrier. More specifically, for example, the charger is driven by the image carrier with a roll member. If it rotates, it can comprise so that an image carrier may be rotated and the contact position of a roll member may be changed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram showing the overall configuration of an image forming apparatus to which this embodiment is applied, and shows a so-called tandem type digital color printer. An image forming apparatus shown in FIG. 1 includes an image processing system 10 that forms an image corresponding to gradation data of each color, a sheet conveyance system 40 that conveys recording paper (sheet), such as a personal computer or an image reader. An IPS (Image Processing System) 50, which is an image processing system that is connected to a device or the like and performs predetermined image processing on received image data, is provided.
[0015]
The image processing system 10 includes four image forming units 11Y and 11M of yellow (Y), magenta (M), cyan (C), and black (K), which are arranged in parallel at regular intervals in the horizontal direction. , 11C, 11K, a transfer unit 20 for transferring the toner images of the respective colors formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, 11K onto the intermediate transfer belt 21, and the image forming units 11Y, 11M, ROS (Raster Output Scanner) 30 which is an optical system unit for irradiating laser beams to 11C and 11K is provided. Further, the main body 1 is provided with a fixing device 29 for fixing the image on the recording paper (sheet) secondarily transferred by the transfer unit 20 to the recording paper using heat and pressure. Further, toner cartridges 19Y, 19M, 19C, and 19K are provided for supplying toner of each color to the image forming units 11Y, 11M, 11C, and 11K.
[0016]
The transfer unit 20 includes a drive roll 22 that drives an intermediate transfer belt 21 that is an intermediate transfer member, a tension roll 23 that applies a constant tension to the intermediate transfer belt 21, and a secondary transfer of the superimposed toner images of each color onto a recording sheet. For this purpose, a backup roll 24 and a cleaning device 25 for removing residual toner and the like existing on the intermediate transfer belt 21 are provided. The intermediate transfer belt 21 is wound around the drive roll 22, the tension roll 23, and the backup roll 24 with a constant tension, and is rotated by a dedicated drive motor (not shown) having excellent constant speed. The drive roll 22 is circulated at a predetermined speed in the direction of the arrow. As the intermediate transfer belt 21, for example, a belt whose resistance is adjusted with a belt material (rubber or resin) that does not cause charge-up is used. The cleaning device 25 includes a cleaning brush 25a and a cleaning blade 25b, and removes residual toner, paper dust, and the like from the surface of the intermediate transfer belt 21 after the toner image transfer process is completed, and performs the next image forming process. It is comprised so that it may prepare for.
[0017]
In addition to a semiconductor laser and a modulator (not shown), the ROS 30 includes a polygon mirror 31 that deflects and scans laser light (LB-Y, LB-M, LB-C, and LB-K) emitted from the semiconductor laser. In the example shown in FIG. 1, since the ROS 30 is provided below the image forming units 11Y, 11M, 11C, and 11K, there is a risk of contamination due to dropping of toner or the like. Therefore, the ROS 30 is provided with a rectangular parallelepiped frame 32 for sealing each component member, and a glass window 33 through which the laser light (LB-Y, LB-M, LB-C, LB-K) passes is provided. It is provided above the frame 32 so as to enhance the shielding effect together with the scanning exposure.
[0018]
The sheet conveying system 40 is loaded with a recording paper (sheet) on which an image is recorded and fed, a nudger roll 42 that picks up and feeds the recording paper from the paper feeding device 41, and is fed from the nudger roll 42. A feed roll 43 that separates and conveys the recording sheets that have been separated one by one and a conveyance path 44 that conveys the recording sheets separated one by one by the feed roll 43 toward the image transfer unit are provided. Also, a registration roll 45 that conveys the recording paper conveyed through the conveyance path 44 in time toward the secondary transfer position, and a backup roll 24 that is provided at the secondary transfer position and is in pressure contact with the recording paper. And a secondary transfer roll 46 for secondary transfer of the image. Further, a discharge roll 47 for discharging the recording paper on which the toner image is fixed by the fixing device 29 to the outside of the main body 1 and a discharge tray 48 for stacking the recording paper discharged by the discharge roll 47 are provided. In addition, a double-sided conveyance unit 49 is provided that enables double-sided recording by inverting the recording paper fixed by the fixing device 29.
[0019]
Next, the operation of the image forming apparatus shown in FIG. 1 will be described. A color material reflected light image of a document read by a document reading device (not shown) and color material image data formed by a personal computer (not shown) are, for example, R (red), G (green), and B (blue). Each 8-bit reflectance data is input to the IPS 50. In IPS 50, the input reflectance data is subjected to predetermined image processing such as various image editing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and moving editing. Is done. The image data that has been subjected to image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and is output to the ROS 30.
[0020]
In the ROS 30, laser light (LB-Y, LB-M, LB-C, LB-K) emitted from a semiconductor laser (not shown) is converted into f-θ in accordance with input color material gradation data. The light is emitted to the polygon mirror 31 through a lens (not shown). In the polygon mirror 31, the incident laser light is modulated in accordance with gradation data of each color, deflected and scanned, and image forming units 11Y, 11M, 11C, and 11K through an imaging lens and a plurality of mirrors (not shown). The photosensitive drum 12 is irradiated. On the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K, the charged surface is subjected to scanning exposure to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) in each of the image forming units 11Y, 11M, 11C, and 11K. Is done.
[0021]
The toner images formed on the photosensitive drums 12 of the image forming units 11Y, 11M, 11C, and 11K are multiplex-transferred onto an intermediate transfer belt 21 that is an intermediate transfer member. At this time, the black image forming unit 11 </ b> K that forms a black toner image is provided on the most downstream side in the moving direction of the intermediate transfer belt 21, and the black toner image is finally transferred to the intermediate transfer belt 21. Is done.
[0022]
On the other hand, in the sheet conveyance system 40, the nudger roll 42 rotates in accordance with the timing of image formation, and recording paper of a predetermined size is supplied from the paper feeding device 41. The recording sheets separated one by one by the feed roll 43 are conveyed to the registration roll 45 through the conveyance path 44 and are temporarily stopped. Thereafter, the registration roll 45 rotates in accordance with the movement timing of the intermediate transfer belt 21 on which the toner image is formed, and the recording paper is conveyed to the secondary transfer position formed by the backup roll 24 and the secondary transfer roll 46. . On the recording sheet conveyed from the lower side to the upper side at the secondary transfer position, the toner images in which the four colors are multiplexed are sequentially transferred in the sub-scanning direction using a pressing force and a predetermined electric field. The recording paper on which the toner images of the respective colors are transferred is subjected to a fixing process by heat and pressure by the fixing device 29 and then discharged by a discharge roll 47 to a discharge tray 48 provided on the upper portion of the main body 1. Instead of being discharged as it is to the discharge tray 48, the conveyance direction can be switched by a switching gate (not shown), and the recording sheet fixed by the fixing device 29 can be reversed by the duplex conveyance unit 49. After the reversed recording sheet is conveyed to the registration roll 45, an image can be formed on both sides of the recording sheet by forming an image on the other unprinted side by the same flow as described above. Become.
[0023]
Next, the image forming units 11Y, 11M, 11C, and 11K in the image process system 10 will be described in detail.
FIG. 2 is a diagram for explaining the configuration of the image forming units 11Y, 11M, 11C, and 11K. Here, the yellow (Y) image forming unit 11Y and the magenta (M) image forming unit 11M are shown. Has been. The other image forming units 11C and 11K are configured in substantially the same manner.
[0024]
The image forming units 11Y, 11M, 11C, and 11K include a photosensitive drum 12 as an image carrier that carries a toner image, a charger 13 that charges the photosensitive drum 12 using a charging roll 13a that is a charging member, and a charger. A developing device that develops an electrostatic latent image charged on the photosensitive drum 12 by the developing roller 14a by the laser beam (LB-Y, LB-M, LB-C, LB-K) from the ROS 30. 14. A primary transfer roll 15 provided on the intermediate transfer belt 21 so as to be opposed to the photosensitive drum 12 with the intermediate transfer belt 21 interposed therebetween. The toner image developed on the photosensitive drum 12 is transferred onto the intermediate transfer belt 21, and the photosensitive drum after transfer. 12 includes a cleaning device 16 that removes residual toner remaining on the surface 12.
[0025]
Next, the cartridge will be described.
FIG. 3 is a diagram for explaining the process cartridge in the present embodiment. In the present embodiment, the photosensitive drum 12, the charger 13, and the cleaning device 16 of each of the image forming units 11Y, 11M, 11C, and 11K are integrated for each color to form a process cartridge 60. Only the process cartridge 60 can be removed from the main body 1 of the image forming apparatus, and only the process cartridge 60 can be attached to the main body 1 so that the user can replace it. These process cartridges 60 can be used by being replaced between the image forming units 11Y, 11M, 11C, and 11K.
[0026]
FIG. 4 is a perspective view of the process cartridge as viewed from another direction. Each process cartridge 60 is provided with a nonvolatile memory 61. In the nonvolatile memory 61, for example, the process cartridge 60 is mounted in predetermined image forming units 11Y, 11M, 11C, and 11K such as the number of rotations of the photosensitive drum 12, the high voltage application time, and the number of prints. Each cartridge usage history information is stored. Since each process cartridge 60 is equipped with a non-volatile memory 61, even if the process cartridge 60 is used in different image forming units, its own use history information is stored in the process cartridge 60. You can save yourself. As a result, for example, the correct lifetime can be determined for each process cartridge 60.
[0027]
Next, the charger 13 will be described in detail.
FIG. 5 is a diagram illustrating a charger 13 to which the exemplary embodiment is applied. The charger 13 is in contact with the surface of the photosensitive drum 12 (see FIG. 1) and charges the surface of the photosensitive drum 12 to a predetermined potential, and a charging roll 13a as a contact type charging member, and the charging roll 13a. The housing 51 which accommodates. A metal shaft 13b is attached to both ends of the charging roll 13a. In the present embodiment, the charging roll 13a includes a base layer made of styrene butadiene rubber in which carbon is dispersed, and a surface layer made of polyurethane rubber in which an ionic conductor such as lithium perchlorate is dispersed. The housing 51 holds a bearing 53 and a cleaning brush 59 that are integrally provided at both ends in the longitudinal direction of the side wall that covers one side of the charging roll 13a and rotatably supports the shaft 13b of the charging roll 13a. In addition, a cleaner 54 that also serves as a bottom wall that covers the lower end surface of the charging roll 13a is provided. The cleaning brush 59 has a function of contacting the surface of the charging roll 13a and directly cleaning the charging roll 13a.
[0028]
Note that a bearing (not shown) that rotatably supports the shaft 13b of the charging roll 13a is attached to the bearing 53 so as to be movable in a direction in which it is in contact with and away from the photosensitive drum 12 (see FIG. 1). The bearing is urged in a direction approaching the photosensitive drum 12 by a coil spring 56 attached to the bearing portion 53, and a predetermined bias voltage is applied to the charging roll 13a via the coil spring 56. It has come to be. In the present embodiment, a drive mechanism that rotationally drives the charging roll 13a is not provided, and is configured to be driven to rotate as the photosensitive drum 12 that contacts the charging roll 13a rotates. The spring pressure by the coil spring 56 is about 500 gf on one side and about 1 kgf on both sides of the shaft 13 b, and the charging roll 13 a is pressed against the photosensitive drum 12 by the pressing force.
[0029]
Next, drive control in the image forming apparatus will be described.
FIG. 6 is a diagram for explaining drive control of the image forming apparatus to which the exemplary embodiment is applied. Based on the image signal subjected to the image processing by the IPS 50, the CPU (not shown) of the control circuit 100 executes the processing according to the program stored in the ROM (not shown). The control circuit 100 includes, as a drive system, a secondary transfer roll 46, a fixing device 29, a sheet conveying system 40, a main motor 101 that drives the developing device 14 (14K) in the black image forming unit 11K, and the like, and an intermediate portion of the transfer unit 20. An intermediate transfer member driving motor 102 for driving the transfer belt 21 and the like, and a photosensitive member for driving the photosensitive drum 12 (12Y, 12M, 12K) in the color image forming units 11Y, 11M, 11C except for the black image forming unit 11K. Development in the driving motor 103, the black photosensitive member driving motor 104 that drives the photosensitive drum 12 (12K) in the black image forming unit 11K, and the color image forming units 11Y, 11M, and 11C other than the black image forming unit 11K. The developing device drive motor 105 that drives the device 14 (14Y, 14M, 14C) is controlled. The control circuit 100 also controls a clutch 111 that is connected to the main motor 101 and switches the drive of the sheet conveying system 40, and a clutch 112 that is connected to the main motor 101 and switches the developing device 14 (14K) in the black image forming unit 11K. is doing. The control circuit 100 controls the operation of these various motors and clutches, thereby timing the respective portions in the image forming apparatus, and enables the image formation on the recording paper by the above-described operation.
[0030]
FIG. 7 is a diagram for explaining control of the image forming apparatus excluding drive control. The control circuit 100 controls a high voltage unit (HVPS) 120, and the high voltage unit 120 applies a charging bias to the charger 13 (13Y, 13M, 13C, 13K). . Here, description of the developing bias applied from the high voltage unit 120 to the developing device 14 is omitted. An environmental sensor 130 for detecting environmental conditions such as temperature and humidity of the image processing system 10 is provided in the main body 1 and in the vicinity of the image processing system 10. Furthermore, the control circuit 100 includes a clock 131 on its own or outside, and can grasp the current time.
[0031]
Furthermore, the control circuit 100 is connected to a non-volatile memory 61 (61Y, 61M, 61C, 61K) mounted on the process cartridge 60 constituting each of the image forming units 11Y, 11M, 11C, 11K. Further, it is connected to a main body memory 140 provided in the main body 1 of the image forming apparatus. In the nonvolatile memory 61 (61Y, 61M, 61C, 61K), information (history information and the like) related to past usage records in each process cartridge 60 is stored as described above. The main body memory 140 also includes information such as the number of prints of recording paper counted by a PV (Page Volume) counter and the number of rotations of the photosensitive drum 12 counted by a cycle counter, as well as the power supply of the main body 1 in the image forming apparatus. Stores information (usage information) related to use from when the power is turned on from OFF or when the power saving mode is restored. In the control circuit 100, the high-voltage unit 120 and the like are controlled based on each information obtained from the nonvolatile memory 61 (61Y, 61M, 61C, 61K) and the main body memory 140, and an instruction from the control circuit 100 is given. Based on this, the history information of the nonvolatile memory 61 (61Y, 61M, 61C, 61K) is updated. The history information stored in the nonvolatile memory 61 (61Y, 61M, 61C, 61K) includes not only the date of manufacture but also the time information when the image forming process was performed, and the time when this image process was performed. Environmental information such as temperature and humidity information can also be stored.
[0032]
The control circuit 100 controls the high voltage unit 120 and applies a charging bias to the charger 13 (13Y, 13M, 13C, 13K) by superimposing a DC voltage component and an AC voltage component including a vibration component (AC component). is doing. As the DC voltage, for example, −750 V is applied as constant voltage control. The AC voltage is a sine wave waveform, controlled at a process speed of 104 mm / sec (in full color mode), with a frequency f = 820 Hz, and an effective current value of 1.2 mA during constant current control. Is done. At this time, since the resistance value of the charger 13 (13Y, 13M, 13C, 13K) varies depending on the environment, the approximate voltage value is the peak-to-peak voltage Vpp = 1.8 kVpp in the normal environment (at room temperature), It becomes 2.2 kVpp at low temperature and low humidity (temperature 10 ° C., humidity 15%), and 1.6 kVpp at high temperature and high humidity (temperature 28 ° C., humidity 85%).
[0033]
Next, compression permanent distortion generated in the charging roll 13a in the present embodiment and countermeasures against horizontal stripes will be described.
FIGS. 8A and 8B are diagrams for explaining the state of the charging roll 13a before and after distortion. Here, for convenience of explanation in the distorted state, the positional relationship is different from that in FIG. 2, and the charging roll 13 a is pressed against the photosensitive drum 12 from above. As shown in FIG. 8A, the charging roll 13a is pressed against the photosensitive drum 12 with a predetermined pressing force. Therefore, the rubber is deformed in the pressed portion and is in close contact with the photosensitive drum 12. In particular, when the rubber material forming the charging roll 13a is forced to be deformed for a long time, distortion as shown in FIG. 8B occurs in the rubber material of the charging roll 13a.
[0034]
As shown in FIG. 8 (a), if the charging roll 13a is rotated again from a state where it has been left for a long time to be charged again, the discharge of the deformed (distorted) portion becomes non-uniform, and the recording paper is fed. A line on a horizontal streak extending in a direction (main scanning direction) perpendicular to the direction appears as a light and dark horizontal streak in the recording paper feed direction (sub-scanning direction). This horizontal stripe appears periodically in the sub-scanning direction in accordance with the circumferential pitch of the charging roll 13a. The larger the amount of distortion, the greater the amount of distortion in the horizontal streak-like defect that occurs, and the horizontal streak grade deteriorates. This relationship is shown in FIG. FIG. 9 is a diagram showing the relationship between the distortion amount and the horizontal stripes, where the horizontal axis indicates the distortion amount (μm), and the vertical axis indicates the level of horizontal stripes (Grade). As shown in FIG. 9, the distortion amount and the horizontal streak defect have a correlation as shown by a broken line, and it can be seen that the larger the distortion amount, the worse the horizontal stripe.
[0035]
Thus, as a result of intensive studies by the inventors on the occurrence phenomenon of such defects, it is found that the distortion amount depends on the leaving time and the leaving environment, that is, the defect occurrence phenomenon is influenced by the leaving time and the leaving environment. It came to.
FIG. 10 is a diagram showing the relationship between the leaving period and the horizontal stripe. Here, the horizontal axis indicates the standing period (days), and the vertical axis indicates the horizontal streak grade (Grade). The three conditions of low temperature (10 ° C), normal temperature (22 ° C), and high temperature (28 ° C) are shown. Below, an image was actually formed after a predetermined standing time, and the occurrence of horizontal streaks was observed. Note that the amount of distortion increases as the standing period increases, and the amount of distortion saturates when left for a certain period of time, and the amount of distortion depends on the environment in which it is left, and worsens as the temperature rises. The trend has been observed by the inventors. However, the description of the relationship between the leaving period and the distortion amount is omitted here. As shown in FIG. 10, it can be seen that the occurrence of horizontal streaks increases as the standing period increases, and increases as the temperature of the left atmosphere increases. In addition, it can be understood that the generation of horizontal streaks is hardly observed in a low temperature environment that is saturated in about 10 days.
[0036]
On the other hand, once the amount of distortion of the charging roll 13a is released, this time it will recover. Although it is difficult to completely restore it, streak-like defects can be restored to the point where they cannot be seen with the naked eye.
FIG. 11 is a diagram showing the relationship between the rotation time of the photosensitive drum 12 (charging roll 13a) and the horizontal stripe. The horizontal axis indicates the rotation time (minutes) of the photosensitive drum 12 (charging roll 13a), and the vertical axis indicates the horizontal stripe grade, which is 2 at normal temperature (22 ° C.) and high temperature (28 ° C.). Results for the conditions are shown. The longer the standing time and the larger the amount of distortion, the more recovery time is required. However, as shown in FIG. Becomes almost inconspicuous. When the process speed is 104 mm / sec, it is almost recovered by printing about 100 A4 size recording sheets.
[0037]
Therefore, in the present embodiment, when the main body 1 of the image forming apparatus starts (starts), first, from the non-volatile memory 61 (61Y, 61M, 61C, 61K) provided for each process cartridge 60, the previous photosensitive operation is performed. The body stop time (which may be the last operation time, etc.) is called. If the process cartridge 60 is new, the date and time of manufacture is called. Then, the stop time is calculated by comparing the information on the date and time of the call with the current time, and the idling time is determined in consideration of the environmental conditions at that time and the environmental conditions at the time of the stop. The For example, when it has been stopped for 10 days or more, or when it is determined that it has been stored at a high temperature such as 30 ° C. or more, it is determined that the amount of distortion has increased, and for example, the idle rotation for 5 minutes Is done. In this way, by performing the image forming process after idly rotating the photosensitive drum 12 based on the determined time, it is possible to reduce image quality defects such as horizontal stripes.
[0038]
FIG. 12 is a flowchart showing processing executed by the control circuit 100. Prior to the image forming process, the control circuit 100 first reads information on the previous stop time from the nonvolatile memory 61 (61Y, 61M, 61C, 61K) of each process cartridge 60 (step 201). Further, the temperature is measured from the environmental sensor 130 (step 202). Then, the stop time is calculated from the current time and the previous stop time read (step 203). Based on the results of these measurements and calculations, it is determined whether or not idling is necessary (step 204). For example, when the stop time is very short, or when the stop period is shorter than a predetermined period in a low temperature environment, it is determined whether or not to perform idling. If idling is not necessary, the process proceeds to step 207, and if idling is necessary, the process proceeds to step 205. In step 201, the information about the previous stop time is read from the non-volatile memory 61 of each process cartridge 60. For example, the information is read from the main body memory 140 provided in the main body 1 of the apparatus. It doesn't matter. However, it is necessary to read out information about a new cartridge from the nonvolatile memory 61 of each process cartridge 60 separately from the main body memory 140.
[0039]
In step 205, the idling time is calculated. For example, assuming that the stop time is T, the idling time is set to 0.3 minutes × T when 0 day <T <10 days, and the idling time is set to 3 minutes when T ≧ 10 days. The idling time is determined using the time.
[0040]
The idling time can also be determined according to the environment in which the apparatus is placed. FIG. 13 is a diagram for explaining the idling time with respect to the stop time. The horizontal axis indicates the stop time (days), and the vertical axis indicates the idling time (minutes). FIG. 13 shows that the idling time relative to the stop time varies depending on the temperature condition. For example, the temperature t is based on 17 ° C. ≦ t <22 ° C., and correction is applied depending on whether the temperature is higher or lower than this reference. In the example shown in FIG. 13, the vertical axis intercept is shifted downward when the temperature t is 12 ° C. ≦ t <17 ° C., and the vertical axis intercept is upward when the temperature t is 22 ° C. ≦ t <30 ° C. and 30 ° C ≦ t, respectively. I will shift. If the temperature is 12 ° C. or lower, idling is not performed.
[0041]
Furthermore, for example, when a high image quality mode (high resolution mode, image quality priority mode) is selected, horizontal stripes are more noticeable than in the normal mode, so the idle rotation time is further extended to make it less noticeable. You can also In addition, execution of frequency and constant voltage control, which will be described later, is also effective as a countermeasure for the high image quality mode.
[0042]
Based on the idling time calculated as described above, the photoconductor driving motor 103 and the black photoconductor driving motor 104 are operated to rotate the photoconductor drum 12, and the charging roll 13a is rotated to perform idling. Implement (step 206). Thereafter, normal image forming processing is executed (step 207). After the predetermined number of image forming processing is completed, the photosensitive member driving motor 103 and the black photosensitive member driving motor 104 are stopped, and the photosensitive drum 12 is stopped. (Step 208). At this time, the state at the time of the stop is grasped, the grasped various information is stored as history information in the nonvolatile memory 61 (61Y, 61M, 61C, 61K) (step 209), and the processing is ended. Thus, in this embodiment, by measuring the time from when the machine stops until it starts moving again, idling is performed according to the predicted distortion, and the occurrence of image quality defects is suppressed. .
[0043]
On the other hand, even when the distorted charging roll 13a is used, there is another method for suppressing the image quality defect by performing the process in addition to the idling rotation or in addition to the idling rotation.
FIGS. 14A and 14B are diagrams for explaining the suppression of horizontal stripes by other control methods. FIG. 14A shows the relationship between the frequency of the AC voltage and the occurrence of horizontal stripes. The horizontal axis shows the frequency of the AC voltage, and the vertical axis shows the level of the horizontal stripe. As a result of intensive studies by the inventor, when the charging roll 13a is distorted, if the frequency of the AC voltage is as low as 820 Hz, the occurrence of lateral streaks appears remarkably, but the frequency of the AC voltage is as high as 1500 Hz. In this case, the inventors found that the occurrence of horizontal stripes is suppressed. FIG. 14B shows the relationship between the type of bias applied to the charging roll 13a and the occurrence of horizontal stripes. The horizontal axis shows the difference between constant current control and low voltage control, and the vertical axis shows horizontal stripes. ) Level. Normally, the alternating current applied to the charging roll 13a is controlled by constant current. However, as apparent from FIG. 14B, when the charging roll 13a is distorted, constant voltage control is performed. It can be seen that the voltage fluctuation in the distortion portion is suppressed and the horizontal stripes are difficult to see.
[0044]
In response to this result, in addition to the above-described image forming condition by idling, it is possible to arbitrarily select an image forming condition such as increasing the frequency of the alternating voltage or adopting constant voltage control. Increasing the frequency of the AC voltage increases noise and shortens the life of the photosensitive drum 12, and if constant voltage control is continued for a long period of time, resistance fluctuations of the charging roll 13a and minute leaks (black dots) due to minute scratches. However, it is effective if it is used within a limited range. For example, when the distortion is large, the frequency is increased for about 10 to 100 sheets, or the constant voltage output is selected for about 10 to 100 sheets. As described above, this is particularly effective when, for example, a high image quality mode (high resolution mode, image quality priority mode) is selected.
[0045]
As described above in detail, according to the present embodiment, the time from when the machine stops until it starts to move again is measured, and the amount of distortion is predicted in consideration of other environmental conditions and the like. Yes. At this time, if the date and time when the motion stopped is stored in the memory, and the date and time when the motion is started again is subtracted, it can be understood how long the motion has stopped, and the amount of distortion can be predicted. In the case of a new manufacture, the date of manufacture is naturally the date and time when the nip of the charging roll 13a is started.
[0046]
In addition, although the magnitude of distortion changes depending on the environmental temperature, for example, the temperature at the time of stopping is also stored in the memory, the temperature when it starts moving again is measured, and if it is higher, it is left at a higher temperature. It is possible that the possibility is high. Usually, the machine temperature is expected to be high because it is often not operating in the machine. In the case of a new cartridge, it is difficult to predict the temperature, but in that case, it is stored at room temperature and the storage period becomes longer, so that it can be predicted that the distortion is also large. Moreover, if the resistance value of the charging roll 13a is measured (calculated by applying a specific voltage and measuring current), it can be predicted that the temperature is high.
[0047]
If the amount of distortion can be predicted to some extent, a countermeasure for performing idling is performed before image formation. It is preferable to carry out for about 1 to 5 minutes depending on the expected magnitude of distortion. Further, it is possible to further reduce image quality defects by increasing the frequency applied to the charging roll 13a or by further taking measures such as applying constant voltage control to the applied AC voltage.
[0048]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the image quality defect due to the compressive strain of the contact-type charging member.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied.
FIG. 2 is a diagram for explaining a configuration of an image forming unit.
FIG. 3 is a diagram for explaining a process cartridge according to the present embodiment.
FIG. 4 is a perspective view of a process cartridge as viewed from another direction.
FIG. 5 is a diagram for explaining a charger to which the exemplary embodiment is applied.
FIG. 6 is a diagram for describing drive control of an image forming apparatus to which the exemplary embodiment is applied.
FIG. 7 is a diagram for explaining control of the image forming apparatus excluding drive control.
FIGS. 8A and 8B are diagrams for explaining the state of the charging roll before and after distortion. FIG.
FIG. 9 is a diagram showing the relationship between the amount of distortion and horizontal stripes.
FIG. 10 is a diagram showing a relationship between a leaving period and a horizontal stripe.
FIG. 11 is a diagram illustrating a relationship between a rotation time of a photosensitive drum (charging roll) and a horizontal stripe.
FIG. 12 is a flowchart showing processing executed by a control circuit.
FIG. 13 is a diagram for explaining the idling time with respect to the stop time.
FIGS. 14A and 14B are diagrams for explaining the suppression of lateral stripes by other control methods. FIGS.
FIG. 15 is a diagram showing an example of a tandem machine as a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Main body, 10 ... Image process system, 11Y, 11M, 11C, 11K ... Image forming unit, 12 ... Photosensitive drum, 13 ... Charger, 13a ... Charging roll, 13b ... Shaft, 14 ... Developer, 14a ... Development Roll, 15 ... Primary transfer roll, 16 ... Cleaning device, 20 ... Transfer unit, 21 ... Intermediate transfer belt, 30 ... ROS, 40 ... Sheet conveying system, 50 ... IPS (Image Processing System), 51 ... Housing, 56 ... Coil Spring 60 ... Process cartridge 61 ... Non-volatile memory 100 ... Control circuit 120 ... High pressure unit 130 ... Environmental sensor 140 ... Body memory

Claims (7)

An image carrier for carrying an image during image formation;
A charging member that contacts the image carrier at a predetermined pressure, rotates following the rotation of the image carrier, and charges the image carrier;
A control circuit for controlling the rotation of the image carrier,
Prior to execution of image formation, the control circuit grasps the stop time until then, and based on the grasped stop time, the control circuit rotates the image carrier to reduce the amount of distortion of the charging member. If the normal mode is selected by the user's operation as the time , the first calculation rotation time is calculated, and the user's operation selects the high image quality mode in which the resolution in the image forming process is higher than the normal mode. If it is determined , a second calculated rotation time longer than the first calculated rotation time is calculated, and the image carrier is rotated during the calculated rotation time prior to execution of the image formation. An image forming apparatus.   The control circuit increases the frequency of the AC voltage applied to the contact member after rotating the image carrier during the calculated rotation time, and / or performs constant voltage control on the voltage applied to the contact member. The image forming apparatus according to claim 1, wherein the image forming process is controlled so as to execute the image forming process according to an image forming condition.   The image forming apparatus according to claim 2, wherein the control circuit controls to execute a predetermined number of image forming processes under the image forming conditions.   The image forming apparatus according to claim 1, wherein the control circuit grasps a temperature at which the apparatus main body is placed, and calculates the calculated rotation time based on the grasped temperature. An image forming apparatus that charges an image carrier in contact with the image carrier and executes an image forming process using a contact charger that rotates in accordance with the rotation of the image carrier.
A neglect time information acquisition means for acquiring information related to the neglect time since the last image formation processing;
Based on the information about the leaving time acquired by the leaving time information acquisition unit, the image carrier is idled before performing the actual image forming process, and the length of the empty space that reduces the distortion amount of the contact charger is reduced. When the normal mode is selected by the user's operation as the rotation time , the first idle rotation time is calculated, and the high image quality mode for increasing the resolution in the image forming process by the user's operation is higher than the normal mode. If you are selected, and the idling time calculation means for calculating the idling time long second than the first idling time,
An image forming apparatus comprising: a rotating unit that idles the image carrier based on the idling time calculated by the idling time calculating unit.   After idling by the rotating means, actual image formation is performed according to an image forming condition in which the frequency of the alternating voltage applied to the contact charger is increased and / or the voltage applied to the contact charger is controlled at a constant voltage. The image forming apparatus according to claim 5, further comprising an image forming process executing unit that executes the process.   The image forming apparatus according to claim 6, wherein the image forming process execution unit executes a predetermined number of image forming processes under the image forming conditions.

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