JP5054316B2 - Image forming apparatus - Google Patents

Description

The invention copier, a printer, relates to an image forming equipment of FAX or the like, an image forming apparatus having a charging device having a disposed the charging roller so as in particular contact the photoreceptor.

  Conventionally, corotron has been widely used as a device for charging a photoreceptor. Although corotron is effective as a means for uniformly charging the surface of the photoconductor, it is necessary to apply a high voltage to charge the photoconductor to a predetermined potential. Cause deterioration of rubber parts and photoreceptors. Furthermore, the electrode wire is soiled by dust in the air and fuser oil, and the resulting image is defective due to uneven charging. Therefore, a charging device has been proposed in which a charging roller is brought into contact with the photosensitive member and a bias voltage is applied to the charging roller in place of the corotron. FIG. 13 shows the configuration of a known image forming apparatus having such a charging device.

  The charging device includes a drum-shaped photosensitive member (hereinafter referred to as a photosensitive drum) 400 and a charging roller 401 in which rotation axes are arranged in parallel, and is pressed against the photosensitive drum 400 by a pressure spring (not shown). . The charging roller 401 includes a core portion 401a made of a conductive material such as iron or stainless steel, and an elastic body layer 401b made of ethylene propylene rubber containing carbon or the like provided around the core portion 401a. On the surface of 401b, a surface layer (not shown) made of an acrylic resin containing carbon powder is formed. The charging roller 401 is brought into contact with and pressed against the a-Si (amorphous-silicon) photoconductor drum 400 by a pressure spring (not shown), and rotates according to the rotation of the photoconductor drum 400 or a unique driving unit. To rotate. At this time, a voltage obtained by superimposing a DC voltage and an AC voltage on the core is applied from the power source, whereby the surface of the photosensitive drum 400 is charged to a predetermined potential.

  In addition to the charging device, the image forming apparatus has a configuration in which an exposure unit 402, a developing device 403, a transfer roller 409, a cleaning device 408, and the like are arranged around the photosensitive drum 400. The developing device 403 includes a developing container 404, and the developing container 404 stores magnetic toner. A stirring means (not shown) is disposed in the developing container 404, and a nonmagnetic rotating developing sleeve 406 including a fixed magnet roller 405 having a plurality of magnetic poles is disposed on the opening side of the photosensitive drum 400 of the developing container 404. Yes. A magnetic blade 407 is attached in the developing container 404, and a uniform toner layer is formed by the magnetic blade 407. Further, the toner is given a charged charge by friction with the rotary developing sleeve 406.

With such a configuration, the photosensitive drum 400 is uniformly charged by the charging device, an electrostatic latent image is formed based on the image data by the exposure unit 402, and the photosensitive drum 400 and the rotary developing sleeve 406 are disposed between the photosensitive drum 400 and the rotary developing sleeve 406. An alternating electric field is applied to develop the toner image on the electrostatic latent image formed on the photosensitive drum 400. Thereafter, the sheet is conveyed between the photosensitive drum 400 and the transfer roller 409 to transfer the toner image. On the other hand, after the transfer to the paper, the residual toner remaining on the photosensitive drum 400 is removed by the cleaning device 408.
JP 2004-279902 A

  However, the conventional charging device has the following problems. That is, the charged product due to the near discharge caused by the voltage application adheres to the surface of the photosensitive drum 400, whereby the surface friction coefficient increases and the surface state becomes unstable. As a result, the cleaning performance of the surface of the photosensitive drum 400 is deteriorated and the surface resistance is lowered, so that an image defect such as image blurring occurs.

The present invention has been made in view of the above circumstances, it stabilizes the surface condition of the photosensitive drum to obtain an image forming apparatus having a charging equipment which can prevent the image defects such as image flow occurs With the goal.

In order to achieve the above object, the first aspect of the present invention comprises a charging member that contacts a photosensitive member and charges it during a predetermined charging period.
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A print density measuring means for measuring an average print density in a predetermined period of a developer image obtained by developing an electrostatic latent image formed by exposure in a predetermined area on the photoconductor;
The control unit controls the magnitude of the AC voltage of the second charging voltage of the charging device according to the measured magnitude of the average print density ; and
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that controls the developing unit to perform a refresh operation for transporting the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period .
In addition, the second aspect of the present invention is a charging member that contacts a photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A print density measuring means for measuring an average print density in a predetermined period of a developer image obtained by developing an electrostatic latent image formed by exposure in a predetermined area on the photoconductor;
The control means controls the length of the weak charging period of the charging device according to the measured average print density, and a charging device ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that controls the developing unit to perform a refresh operation for transporting the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period .
Further, the third aspect of the present invention is a charging member that contacts a photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A printing number measuring means for measuring the number of printings on a recording medium in a predetermined period of a developer image obtained by developing an electrostatic latent image exposed and formed in a predetermined region on the photosensitive member;
The control unit controls the magnitude of the AC voltage of the second charging voltage of the charging device according to the measured magnitude of the number of printed sheets ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that controls the developing unit to perform a refresh operation for transporting the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period .
Further, the fourth aspect of the present invention is a charging body that contacts a photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A printing number measuring means for measuring the number of printings on a recording medium in a predetermined period of a developer image obtained by developing an electrostatic latent image exposed and formed in a predetermined region on the photosensitive member;
The control means controls the length of the weak charging period of the charging device according to the measured number of printed sheets ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that controls the developing unit to perform a refresh operation for transporting the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period .

According to a fifth aspect of the present invention, the weak charging period is a predetermined period before the start of the regular charging period, a predetermined period after the end of the regular charging period, or a plurality of regular charging periods. The image forming apparatus according to any one of the first to fourth aspects of the present invention, which is a predetermined period of time.

The sixth aspect of the present invention further comprises temperature measuring means for measuring the temperature in the vicinity of the photosensitive member,
The control unit controls the magnitude of the AC voltage of the second charging voltage in accordance with the temperature measured by the temperature measuring unit. It is.

The seventh aspect of the present invention further comprises temperature measuring means for measuring the temperature in the vicinity of the photoreceptor,
The control means is the image forming apparatus according to any one of the first to fourth aspects, wherein the length of the weak charging period is controlled according to the temperature measured by the temperature measurement means.

The eighth aspect of the present invention further includes humidity measuring means for measuring the humidity in the vicinity of the photoconductor,
The image forming apparatus according to any one of the first to fourth aspects, wherein the control unit controls the magnitude of the AC voltage of the second charging voltage according to the humidity measured by the humidity measuring unit. It is.

The ninth aspect of the present invention further includes humidity measuring means for measuring the humidity in the vicinity of the photosensitive member,
The control unit is the image forming apparatus according to any one of the first to fourth aspects, wherein the length of the weak charging period is controlled according to the humidity measured by the humidity measuring unit.

The tenth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects of the present invention, wherein the charging member is a charging roller and the photosensitive member is a photosensitive drum.

Also, the present invention eleventh, the control unit, when the average printing density measured falls below the reference density value, the said control of the refresh operation of the control and the developing unit of said voltage applying means This is the first or second image forming apparatus of the present invention.

The twelfth aspect of the present invention comprises a plurality of the developing means,
The printing density measuring unit measures the average printing density for each developing unit,
The control means is an image forming apparatus according to an eleventh aspect of the present invention, wherein the reference density value is set for each of the developing means.

A thirteenth aspect of the present invention is the image forming apparatus according to any one of the first to twelfth aspects, wherein the developer is a spherical toner.

  According to the present invention as described above, it is possible to stabilize the surface state of the photosensitive drum and prevent image defects such as image drift.

  Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

(Embodiment 1)
FIG. 1 shows a color image forming apparatus 600 according to Embodiment 1 of the present invention. An image forming mechanism is provided in the approximate center of the color image forming apparatus 600. The image forming mechanism includes a photosensitive drum 1, and a charging device 2, an LSU (laser scan unit) 3, a developing device 4, a transfer device 5, a cleaning blade 6, and rollers disposed around the photosensitive drum 1. 8. A static eliminator (not shown) and a scraping member are provided. A fixing device 7 is disposed downstream of the photosensitive drum 1 in the sheet conveyance direction. A carry-out device 150 having a plurality of paper discharge rollers 10 is arranged further downstream of the fixing device 7 in the paper conveyance direction. A paper feeding unit 20 is provided at the lower part of the image forming mechanism, and a plurality of paper feeding rollers 9 are disposed downstream of the paper feeding unit 20 in the paper feeding direction. The paper feed roller 9 that is closest to each other forms a carry-in device 100.

The charging device 2 is installed above the photosensitive drum 1 and is a device for uniformly charging the photosensitive drum 1, and includes a charging roller 201, a voltage applying unit 202, and a control unit 203. The charging roller 201 includes a core portion 201a made of a conductive metal such as iron, copper, stainless steel, and aluminum, and a conductive elastic member 201b formed of carbon-containing ethylene propylene rubber or polyurethane rubber impregnated with LiClO _4. Consists of.

  The voltage applying unit 202 is connected to the core portion 201a of the charging roller 201 so as to apply a bias voltage obtained by superimposing a DC voltage and an AC voltage as a charging voltage. The control unit 203 is a unit that controls the bias voltage of the voltage application unit 202.

  The photosensitive drum 1 has an electrostatic latent image formed on the surface. In this embodiment, an a-Si (amorphous silicon) photoconductor is used, and the structure thereof is a carrier injection blocking layer made of Si: H: B: O or the like on a conductive substrate, and a carrier made of Si: H or the like. An excitation / transport layer (photoconductive layer) and a surface protective layer made of SiC: H or the like are sequentially laminated (not shown). The LSU 3 is an apparatus for exposing and forming an electrostatic latent image on the photosensitive drum 1 based on the image data input from the image data input unit 60.

  The developing device 4 is a device that forms a toner image by supplying toner to the surface of the photosensitive drum 1 on which the electrostatic latent image is formed. Here, the developing device 4 includes a rotary rack 40 and a plurality of developing devices 4Y, 4M, 4C, and 4K. The rotary rack 40 rotates the plurality of developing devices 4Y, 4M, 4C, and 4K to the developing positions facing the photosensitive drum 1 in order while performing rotation by rotating around a rotating shaft 41 by a rotating means (not shown). It is. Among the plurality of developing devices, the yellow developing device 4Y, the magenta developing device 4M, the cyan developing device 4C, and the black developing device 4K are arranged and held in the circumferential direction of the rotation of the rotary rack 40 in the order of 4Y, 4M, 4C, and 4K. Adjacent developing devices are arranged at intervals of about 90 degrees in the circumferential direction.

  The transfer device 5 is a device for transferring the toner image on the photosensitive drum 1 to a transfer material such as paper, and includes an intermediate transfer belt 51, primary transfer rollers 52 and 53, a driving roller 55, and a secondary transfer counter roller 54. A secondary transfer roller 56 is provided. The intermediate transfer belt 51 is wound endlessly around the primary transfer rollers 52 and 53, the drive roller 55, and the secondary transfer counter roller 54, and is driven by the drive roller 55, and the toner image formed on the photosensitive drum 1. Plays the role of a transcript that is transferred and temporarily held. The secondary transfer roller 56 is disposed at a position facing the secondary transfer counter roller 54 on the outer peripheral surface of the intermediate transfer belt 51 and plays a role of transferring a toner image onto a transfer material.

  The cleaning blade 6 is a device for cleaning deposits such as toner remaining on the photosensitive drum 1. For example, urethane rubber having a hardness of 77 ° is brought into pressure contact with the photosensitive drum 1 at a linear pressure of 48 N / m. It has a configuration. The roller 8 is in contact with the surface of the photosensitive drum 1 and has a function of collecting and discharging toner and a buffer, and also has a function of polishing the surface of the photosensitive member with an abrasive in the adhered toner. Here, the roller 8 has a configuration in which, for example, a metal shaft is covered with foamed rubber having a hardness of 55 degrees, and is urged against the photosensitive drum 1 by a spring (not shown) at 1,000 gf (one side is 500 gf). . Further, the rotation direction of the roller 8 is the same direction (with direction) at the point of contact with the photosensitive drum 1, and the roller 8 can be rotated with a drum peripheral speed and a speed difference or driven by drum rotation.

  The fixing device 7 is a device for fixing the transferred toner image on a sheet.

  The power supply device 160 supplies power to the photosensitive drum 1, the charging device 2, the LSU 3, the developing device 4, the transfer device 5, the fixing device 7, the static eliminator, the carry-out device 150, the carry-in device 100, and the image input device 60. It is a means, and is connected to the above means and apparatus by a power supply line and a control signal line (not shown).

  Next, FIG. 2 shows details of the charging device 2. The core portion 201 a of the charging roller 201 is rotatably supported at both ends thereof by the folder 204 and is arranged substantially in parallel with the photosensitive drum 1. Each folder 204 is pressed and urged in the direction of the photosensitive drum 1 by a spring 205, whereby the charging roller 201 is pressed against the photosensitive drum 1.

  Next, FIG. 3 shows a control block of the image forming apparatus. The control unit 90 includes a control drive unit 91 corresponding to the control device 203 in FIG. 1 for controlling the charging voltage applied to the charging roller, and is configured by a microcomputer having a CPU, a RAM, a ROM, and the like. An image forming unit 85, a paper feeding unit 20, a paper discharge unit 30 (corresponding to the discharge device 150 in FIG. 1), an image data input unit 60, an input operation unit 70, an image data measurement unit 80, and the like. It is connected. Here, the image data input unit 60 is an interface means for receiving image data from a personal computer connected via a network or the like if it is a printer, FAX or the like, or an optical reading of a document if it is a copier. Realized as a scanner to perform. The image data received here is sent to the image forming unit 10 or the image data measuring unit 80 and the control unit 90.

  In the following description, it is assumed that the image data input unit 60 is an interface that receives input of image information from an external device such as a personal computer, and the color image forming apparatus 600 is a color printer.

  The input operation unit 70 has a key group and a display panel (not shown). The key group includes a numeric keypad and a start key. The image data measuring unit 80 measures the number of dots in the image of the image data received by the image data input unit 60 and obtains the printing rate. The control unit 90 controls operations such as image formation in the image forming unit 85, and controls the output of the high voltage substrate that controls the charging potential of the charging device 2.

  In the above configuration, the color image forming apparatus 600 corresponds to the image forming apparatus of the present invention, and the control unit 203, the control unit 90, and the control drive unit 91 correspond to the control unit of the present invention.

  The charging device 2 corresponds to the charging device of the present invention, the charging roller 201 corresponds to the charging body of the present invention, and the voltage applying unit 202 corresponds to the voltage applying unit of the present invention.

  LSU3 corresponds to the exposure means of the present invention. The photosensitive drum 1 corresponds to the photosensitive member of the present invention, and the developing device 4 corresponds to the developing unit of the present invention. The transfer device 5 corresponds to the transfer unit of the present invention, the fixing device 7 corresponds to the image fixing unit of the present invention, and the image data input unit 60 corresponds to the image information input unit of the present invention. The carry-in device 100 corresponds to the recording medium carry-in means of the present invention, and the carry-out device 150 corresponds to the recording medium carry-out means of the present invention. The power supply device 160 corresponds to the power supply unit of the present invention. The image data measuring unit 80 corresponds to the print density measuring means of the present invention.

That describes the operation of the color image forming apparatus 600 having the configuration described above.

  As described in the prior art, the color image forming apparatus 600 uniformly charges the photosensitive drum 1 by the charging device 2 and forms an electrostatic latent image based on the image data by the LSU 3 as the image forming operation. An alternating electric field is applied between the body drum 1 and the developing device 4 to develop a toner image on the electrostatic latent image formed on the photosensitive drum 1, and this is transferred to a transfer material by the transfer device 5. Like to do. In the case of the present embodiment, the above-described operation is performed four times for one transfer material. In the following description, a period required for the series of operations for one transfer material is referred to as an image forming period.

  At this time, the charging roller 201 of the charging device 2 is connected so that a bias voltage (Vdc + Vac) obtained by superimposing a direct current (Vdc) and an alternating current (Vac) is applied from the voltage applying unit 202 to the photosensitive roller 201. The charged product due to the near discharge due to the voltage application adheres to the surface of the photosensitive drum 1, and the surface friction μ of the photosensitive drum 1 is increased.

As a result of verifying the process in which the charged product adheres to the surface of the photosensitive drum 1, the inventor obtained the following results. That is, the amount of the charged product attached is related to the magnitude of the AC voltage superimposed on the charging voltage applied from the charging device 2, and the larger the AC voltage is, the more charged product is attached.

  On the other hand, in forming a uniform toner image, it is important to superimpose an AC voltage on a DC voltage when forming the electrostatic latent image in order to form a uniform electrostatic latent image. It is necessary to keep it safe.

  Therefore, the charging voltage of the charging device 2 is used to obtain an appropriate charging potential during the period of forming the electrostatic latent image in order to form a uniform electrostatic latent image during the image forming operation. The superposed voltage to which the AC voltage is applied is used, but during other periods, the AC voltage is applied with an AC voltage smaller than the appropriate charging potential or turned off to suppress the generation of charged products. did. That is, the operation time of the charging device 2 is set to a regular charging period using a voltage having a strength necessary for exposing and forming an electrostatic latent image on the photosensitive drum 1, and a charging period using a voltage sufficiently lower than this voltage. The weak charging period is set separately, and in the weak charging period, a DC voltage alone or a lower AC voltage than that applied during the image formation period is superimposed on the DC voltage as a bias voltage for charging. The superimposed voltage is applied to the photosensitive drum 1.

  Thereby, while maintaining the quality of the electrostatic latent image and the toner image, it is possible to reduce the generation and adhesion of the electrostatic product due to the near discharge, and to keep the surface quality of the photosensitive drum 1 high.

  In the weak charging period, it is desirable that only a DC voltage is applied from the viewpoint of suppressing the generation of the charged product, but it is desirable that the AC voltage is actually superimposed to some extent. If an AC voltage is not applied to some extent during the rise from the weak charging period to the regular charging period, a problem occurs in forming a uniform electrostatic latent image in the image forming period, or time is required. It is.

Hereinafter, along with the operating state of the color image forming apparatus 600, that describes the operation of the charging device of the present invention.

  As shown in FIG. 1, the image forming mechanism (photosensitive drum 1, charging device 2, LSU3, and the like) is turned on when the main power is turned on, that is, when the external power is supplied to the power supply device 160 and connected to the power supply device 160. When the developing device 4), the transfer device 5, the fixing device 7, the carry-out device 150, the carry-in device 100, and the image data input unit 60 become operable, the control device 203 of the charging device 2 (the control drive in FIG. 3). The control unit 90 controls the voltage application unit 202 to apply a bias voltage to the core 201a of the charging roller 201, and the control unit 90 forms an image while stopping the rotation of the rotary rack 40. The photosensitive drum 1 constituting the unit 10 is preliminarily rotated, and the entire surface of the photosensitive drum 1 is charged by the charging roller 201.

  Here, as described above, the bias voltage applied to the core portion 201a is obtained by superimposing a direct current voltage on the direct current voltage or an alternating current voltage lower than that applied when an electrostatic latent image is formed by exposure. Is not sufficient to form an electrostatic latent image for obtaining a uniform toner image, but a voltage sufficient to suppress the generation of a charged product in the vicinity of the surface of the photosensitive drum 1. It has become. Hereinafter, a charge generation in which a superimposed voltage applied to the core 201a during a normal charging period required for exposure formation of an electrostatic latent image is applied within a charging period other than the first charging voltage and the normal charging period. The description will be continued with the voltage that can suppress the generation of the object as the second charging voltage.

  The control unit 203 switches the bias voltage applied to the core portion 201a of the charging roller 201 from the second charging voltage to the first charging voltage when image data is input to the image data input unit 60 from the outside. The voltage applying means 202 is controlled.

  At the same time, the rotary rack 40 and the like are rotated so as to face the photosensitive drum 1 at a predetermined position, so that the LSU 3 can emit a laser beam modulated in accordance with the image data.

  Next, the image forming operation on the photosensitive drum 1, the transfer operation to the transfer material, and the fixing operation by the color image forming apparatus 600 are performed in the same manner as in the prior art. That is, during the image forming period, after the charging unit 2 charges the photosensitive drum 1 with the first charging voltage, the rotary rack 40 rotates around the rotation shaft 41 provided at the center thereof. . Then, the rotary rack 40 stops at the developing position where the developing device 4K corresponding to the first color, black, faces the photosensitive drum 1. In this state, exposure corresponding to black is performed by the LSU 3, and an electrostatic latent image corresponding to black is formed on the surface of the photosensitive drum 1. The electrostatic latent image is converted into a toner image by the developing device 4K, and the toner image formed on the surface of the photosensitive drum 1 is transferred onto the transfer belt 51 by a transfer bias applied to the primary transfer rollers 52 and 53. . When the formation of the black toner image on the transfer belt 51 is completed, the rotary rack 40 then rotates around the rotation shaft 41 provided at the center thereof, and the developing device 4M corresponding to cyan is brought to the developing position. Positioned. Such an operation is also performed for other colors, cyan, magenta, and yellow, and a full-color toner image is formed on the transfer belt 51.

  In the process of primary transfer of the toner image to the intermediate transfer belt 51, the secondary transfer roller 56 is separated from the transfer belt 51. On the other hand, when a full-color toner image is formed on the transfer belt 51, the secondary transfer roller 56 is brought into contact with the transfer belt 51. At that time, the transfer material as the recording medium of the present invention conveyed from the paper supply unit 20 to the transfer position by the paper supply unit 20 in accordance with the timing by the secondary transfer bias applied to the secondary transfer roller 56. The full color toner image formed on the transfer belt 51 is transferred. The image forming period by the image forming mechanism is completed here.

  Further, the full-color toner image transferred to the transfer material is fixed to the transfer material by heating and pressurizing by the fixing unit 7, and the transfer material passes through the carry-out device 150 (corresponding to the paper discharge unit 30 in FIG. 3) and then to the outside. It is carried out.

  The electric charge remaining on the photosensitive drum 1 is removed by a static eliminator, and the remaining developer on the surface is cleaned by a cleaning blade 6 and discarded in a waste toner container (not shown). The toner remaining on the transfer belt 51 is cleaned by bringing a cleaning device (not shown) of the transfer belt 51 into contact with the transfer belt 51 after the secondary transfer, and is discarded in a waste toner container (not shown). The cleaning device for the transfer belt 51 is separated from the transfer belt 51 after cleaning the entire circumference of the transfer belt 51.

  During monochrome image formation, the rotary rack 40 does not rotate, and development is performed with only the developing device 4K facing the photosensitive drum 1. Other operations for image formation are the same as those for color image formation.

  In the above operation, the series of operations from the electrostatic latent image to the toner image in the image forming unit 10 is black (by the developing device 4K), cyan (by the developing device 4C), magenta (by the developing device 4M), yellow (developing). The controller 203 controls the charging roller 201 at the time when the LSU 3 forms the electrostatic latent image corresponding to the yellow toner image in the final process. The voltage application unit 202 is controlled to switch the bias voltage applied to the core part 201a from the first charging voltage to the second charging voltage. At the same time, the rotary rack 40 is controlled so as to deviate from the rotation of the photosensitive drum 1, and the photosensitive drum 1 enters a preliminary rotation state. When the transfer material is carried out through the carry-out device 150 (corresponding to the paper discharge unit 30 in FIG. 3), the control device 203 performs control to stop the application of the second charging voltage, and the weak charging period. Exit.

  Thereby, the charging operation of the photosensitive drum 1 by the charging device 2 by the second charging voltage is started from the time when the exposure generation of the electrostatic latent image corresponding to the yellow toner image is completed on the surface of the photosensitive drum 1. Will be done. That is, the weak charging period starts immediately after the application of the bias voltage by the first charging voltage for the exposure formation of the electrostatic latent image on the photosensitive drum 1, which is a normal charging period, and the second charging is performed. The charging operation is performed by using the working voltage. This operation is the same when a monochrome image is formed.

  The above operation is performed when switching from the operation by the developing device 4K to the operation by the developing device 4C, when switching from the developing device 4C to the operation by the developing device 4M, and when switching from the developing device 4M to the operation by the developing device 4Y. May be performed in the same manner. That is, the second charging voltage may be applied during the switching operation of each developing device.

  In the operation of the color image forming apparatus 600 described above, during the weak charging period in which the charging device 2 applies the second charging voltage, (1) external power is supplied to the power supply device 106 and the image forming mechanism can operate. A period from when the image is input to when the image data is input to the image data input unit 60 from the outside, and (2) electrostatic latent image exposure formation corresponding to the toner image by the last developing device by the transfer device 5 Has been described as a period from when the transfer is completed to when the transfer material is carried out to the outside by the carry-out device 150. However, even when a plurality of transfer materials stored in the paper feeding unit 20 are continuously printed, the charging device 2 can be controlled to charge the photosensitive drum 1 with the second charging voltage.

  The operation in this case is performed as follows, for example. That is, the operation for printing the first transfer material is performed in the same manner as described above. However, when continuous printing is performed, the electrostatic latent image exposure formation corresponding to the toner image to be transferred to the first transfer material is performed. The period during which it is not necessary to form an electrostatic latent image on the photosensitive drum 1 after the completion of the process until the start of exposure formation of the electrostatic latent image corresponding to the toner image to be transferred to the next transfer material Is present, the photosensitive drum 1 performs preliminary rotation that the rotary rack 40 does not follow.

  The control unit 203 uses this period as a weak charging period, and controls the voltage applying unit 202 so that the second charging voltage is applied to the photosensitive drum 1. The application period of the second charging voltage is preferably one period or more of the rotation period of the photosensitive drum 1, but may be shorter than one period when performing high-speed printing or the like.

  Note that the application time of the second charging voltage is not limited to the case of the continuous printing, but also in the respective periods before and after the electrostatic latent image exposure formation of (1) and (2) above. It is desirable to take one rotation period or more of the rotation period, so that each surface of the photosensitive drum 1 can be kept in a stable state without unevenness.

  As described above, according to the present embodiment, in the color image forming apparatus 600, the charging device 2 performs exposure formation corresponding to this printing period in the period from the start to the end of image printing on the transfer material. The first charging voltage in which the AC voltage and the DC voltage of the predetermined voltage are superimposed is performed only during the period, and the AC voltage lower than the predetermined voltage is superimposed in the other period instead of the first charging voltage. By using the second charging voltage with the AC voltage turned off, the generation of charged products on the surface of the photosensitive drum 1 can be suppressed and the surface friction can be kept small.

  In the above description, the second charging voltage is the period before and after the exposure forming period corresponding to this printing period in the period from the start to the end of image printing on the transfer material. Although the description has been made assuming that the voltage is applied in both periods, it may be performed only before or after the exposure formation period, if necessary. In this case, for example, when the second charging voltage is applied only after the exposure forming period, the charging device 2 applies the first charging voltage from the time when the image forming apparatus 600 is turned on. If the second charging voltage is applied only before the exposure forming period, the first charging voltage is applied after the exposure forming period until the transfer material is unloaded through the unloading device 150. Will be applied.

(Embodiment 2)
In addition to the configuration of the charging device 2 of the first embodiment, the image forming apparatus according to the present embodiment has a certain amount or more of abrasive (supplied as a toner external additive) in the cleaning / polishing process of the photosensitive drum 1. In other words, the surface state of the photosensitive drum 1 is further maintained by suppressing the adhesion of the charged product within a certain level.

  Hereinafter, description will be given with reference to FIGS.

  Since the operation of each part before and after image formation is the same as that in the first embodiment, detailed description thereof is omitted.

  As described above, at the time of image formation, after the charging means 2 charges the photosensitive drum 1 with the first charging voltage, the rotary rack 40 has the rotating shaft 41 provided at the center thereof. Rotate to center. Then, the rotary rack 40 stops at the developing position where the developing device 4K corresponding to the first color, black, faces the photosensitive drum 1. In this state, exposure corresponding to black is performed by the LSU 3, and an electrostatic latent image corresponding to black is formed on the surface of the photosensitive drum 1. The electrostatic latent image is converted into a toner image by the developing device 4K, and the toner image formed on the surface of the photosensitive drum 1 is transferred onto the transfer belt 51 by a transfer bias applied to the primary transfer rollers 52 and 53. . When the formation of the black toner image on the transfer belt 51 is completed in this way, the rotary rack 40 then rotates around the rotation shaft 41 provided at the center thereof, and the developing device 4M corresponding to cyan. Is positioned at the development position.

  In the present embodiment, in parallel with the image forming operation described above, the image data measuring unit 80 measures the image data as a toner image as the number of dots, and measures the image print density an on the image. Print density a1, a2, a3,. . . , An average printing density is calculated and transferred to the control unit 90.

  When the average document density measured during this period falls below a predetermined reference density value 3 [%] with reference to a predetermined period set at the time of factory shipment or the like as a reference, the image forming operation is performed by the control means. 90 stops the image formation, stops the non-image forming state, that is, the operation for generating an electrostatic latent image based on the image data from the image data input unit 60 (LSU3 and other operations), and the developing device 4K. Control is performed so that each toner of ˜4Y is developed and consumed on the photosensitive drum 1 side. This toner consumption operation is referred to as a refresh operation. Although the case where image formation is immediately stopped has been described, when continuous printing is being performed, it may be performed after completion of continuous printing. Further, the calculation of the average print density and the comparison with the reference density value are performed for each of the developing devices 4K to 4Y, but may be an average of the developing devices.

  The toner adhered during the non-image formation of the photosensitive drum 1 by the refresh operation is scraped off by the cleaning blade 6 by the rotation of the photosensitive drum 1. At this time, the surface of the photosensitive drum 1 is polished by the abrasive contained in each of the developing devices 4K to 4Y as a toner additive. Further, the developing devices 4K to 4Y regularly discharge the toner to prevent the toner from being excessively charged, and to prevent image density reduction and fogging. At this time, since the DC bias voltage having the same polarity as the toner is applied to the transfer device 5, the toner does not adhere to the transfer belt 51.

  The refresh operation is performed for the following reason. That is, conventionally, when the image forming apparatus repeatedly performs image formation, particularly when the printing rate on the image is low, the amount of toner flying from the developing container 404 to the photosensitive drum 400 is small. The toner particles were not replaced so much that the toner was overcharged, resulting in a decrease in image density and fogging. In particular, in a device having a plurality of developing units such as a color machine, it is necessary to consider from the case of a high printing rate like a photograph or graphic image to the case of a low printing rate like a logo mark only, There are many variations from developer to developer.

  By performing the refresh operation, it is possible to eliminate such image defects such as a decrease in image density and fogging, and to prevent the charge distribution of the toner in the developing container from changing even after long-term use. it can.

  In the present embodiment, in parallel with the above refresh operation, the voltage charged by the charging device 2 to the photosensitive drum 1 by the control of the control unit 203 is replaced with the first charging voltage that is a conventional superimposed voltage. Thus, the second charging voltage of Embodiment 1 is used.

  Thereby, even when the photosensitive drum 1 is charged in the refresh operation, the generation of the charged product can be suppressed. Therefore, the effect of suppressing the charged product generation in the first embodiment and the generated charge generated by the refresh operation can be suppressed. Combined with the effect of removing the object, it is possible to maintain a good surface condition of the photosensitive drum 1 for a long period of time by exhibiting an even higher level of polishing power that does not increase the adhesion amount of the charged product but reduces it. it can.

  The a-Si photoconductor drum 1 is superior in abrasion resistance and the like because it has a higher surface hardness than a photoconductor drum using Se-based or OPC (Organic Photoconductor) -based material, but the surface is not scraped. Deposits, charged products and the like are likely to accumulate on the surface, and it is necessary to actively perform surface polishing using an abrasive. Therefore, the configurations of the first and second embodiments are particularly effective for the a-Si photosensitive drum.

  As in the first embodiment, it is desirable that the application time of the second charging voltage be one rotation period or more of the photosensitive drum. In particular, in the color image forming apparatus 600, when performing image formation by matching the phase of the photosensitive drum 1, the phase is also matched in the refresh operation, and only the same portion on the circumference on the photosensitive drum 1 is polished. Even when the phase is not matched, it is possible to prevent a defect from occurring in a portion remaining without being polished for each refresh process. It is also useful when the interval for performing the refresh process is wide.

  Furthermore, as the second charging voltage, it is particularly desirable to turn off the AC voltage. When a bias voltage that does not superimpose an AC voltage is used, there is a problem that it is difficult to keep the surface of the photosensitive drum 1 uniform in the toner image formed during the image formation period. However, in the refresh operation, the surface state of the toner image is changed. It is not necessary to consider. Thereby, the further effect of charge product removal can be expected.

  As described above, according to the present embodiment, when the average printing rate is calculated and then falls below a predetermined reference density value, the photosensitive drum 1 that is the electrostatic latent image carrier and the developing devices 4K to 4K. The development bias of the developing device 4 is controlled so that the refresh operation for consuming the toner is performed when the rotary rack 40 equipped with 4Y is in contact, and the generation of the charged product from the charging device 2 is suppressed. By charging the photosensitive drum 1 with the second charging voltage, it is possible to clean the surface of the photosensitive drum 1 while suppressing the generation of charged products on the photosensitive drum 1.

  Note that the reference density value is preferably set to a value lower than 3% in terms of average printing rate because toner charge-up easily occurs and the amount of residual toner increases. However, this is merely an example, and by setting several types of refresh modes and toner replenishment modes, the user can arbitrarily set the settings so as to respond to the situation (usage environment, etc.) of the image forming apparatus. Is also possible.

  The toner is particularly effective when it is a spherical toner. This is because when the residual toner on the photoconductor is a spherical toner, cleaning is particularly difficult, and it is important to stabilize the surface friction coefficient of the photoconductor drum 1. In many cases, this spherical toner is a toner prepared by a polymerization method. Although it is a polymerization toner that is advantageous in terms of image quality and cost, it is very difficult to clean. Since the polymerization toner is spherical, it does not get caught on its surface, and it is difficult to clean it by adhering it to a brush, a roller, or an internal mechanism of the image forming apparatus. Further, even with a blade system such as the cleaning blade 6, the toner hardly aggregates in the toner accumulation portion at the blade edge, and the blocking layer is not easily formed. (In the blade method, the toner external additive and the toner itself blocked by the cleaning blade 6 are compressed to form a stationary blocking layer. This blocking layer peels off the toner from the drum and enters the blade nip. It is important to stabilize this blocking layer.

(Embodiment 3)
The image forming apparatus according to the present embodiment preferably maintains the surface state of the photosensitive drum 1 by controlling the operation of the charging device 2 according to the first embodiment according to the temperature and humidity in the vicinity of the photosensitive member. It is for the purpose.

  FIG. 4 shows the configuration of the charging device according to Embodiment 3 of the present invention. 4, the same or corresponding parts as in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The temperature sensor 207 is a means for measuring the temperature of the surface of the photosensitive drum 1 and is realized by a sensor using a bimetal, a temperature-sensitive magnetic material, a semiconductor, or the like. The humidity sensor 208 is a means for measuring the humidity in the vicinity of the photosensitive drum 1 and is realized by a sensor using a polymer film, a ceramic sintered body, an electrolyte, or the like. The temperature sensor 207 corresponds to the temperature measuring means of the present invention, and the humidity sensor 208 corresponds to the humidity measuring means of the present invention.

  Hereinafter, description will be made with reference to FIGS. However, the part which overlaps with Embodiment 1, 2 is abbreviate | omitted.

  The temperature sensor 207 and the humidity sensor 208 measure the surface temperature of the photosensitive drum 1 and the humidity in the vicinity thereof during the operation of the image forming apparatus.

  As described in the first embodiment, the control unit 203 applies the second charging voltage to the photosensitive drum 1 during a charging period other than the normal charging period required for exposure formation of the electrostatic latent image. Control is performed to suppress the generation of charged products on the photosensitive drum 1. The second charging voltage is a voltage composed only of a DC voltage or a superimposed voltage formed by superimposing an AC voltage lower than that applied during the image formation period on the DC voltage. In the present embodiment, the control means 203 changes the magnitude of the AC voltage included in the second charging voltage in accordance with the temperature and humidity measured by the temperature sensor 207 and the humidity sensor 208.

  When the image forming apparatus is used continuously for a long period of time or placed under a high temperature condition, the photosensitive drum 1 also has higher heat than that during normal use. Since the internal resistance value of the photosensitive drum 1 made of a-Si decreases as the temperature rises, when the bias voltage having the same value as the normal charging is applied as the second charging voltage, the photosensitive drum 1 is normally used. An alternating current larger than that at the time flows, which is equivalent to the application of a higher bias voltage than that during normal use, and the effect of suppressing the generation of charged products is impaired.

  On the other hand, when the temperature measured by the temperature sensor 207 is higher than the temperature during normal use, the control unit 203 sets the superimposed AC voltage to a value lower than that during normal use in the second charging voltage. Control to be As a result, a superimposed voltage including an appropriately low AC voltage is applied to the photosensitive drum 1, and the effect of suppressing the generation of charged products can be suitably maintained.

  Further, when the humidity in the vicinity of the photosensitive drum 1 is high, the control unit 203 has the same effect as the temperature. Therefore, when the temperature measured by the humidity sensor 208 is higher than the temperature during normal use, the temperature is high. By performing the same control as in the high case, the effect of suppressing the generation of the charged product on the photosensitive drum 1 can be suitably maintained.

(Embodiment 4)
The image forming apparatus according to the present embodiment controls the operation of the charging device 2 according to the second embodiment in accordance with the temperature and humidity in the vicinity of the photoconductor, and the cleaning / polishing process of the photoconductor drum 1 is performed in accordance with this control. The purpose is to maintain the surface state of the photosensitive drum 1 more suitably by controlling.

  Since the configuration of this embodiment is the same as that of Embodiments 2 and 3, FIGS.

  In the second embodiment, the second charging voltage is applied during the refresh operation in which the charged product adhered to the charged drum 1 is polished and removed by the abrasive added to the toner. The generation of charged products was suppressed.

  Further, in this embodiment, the period for applying the second charging voltage is controlled according to the temperature or humidity obtained from the temperature sensor 207 and the humidity sensor 208 of the third embodiment.

As described in the third embodiment, when the temperature of the photosensitive drum 1 is high, the resistance value is low, so that a charged product is more easily generated than in normal use. Therefore, it is considered that more charged products are generated in the image forming operation immediately before the refresh operation than in normal use.

  Therefore, when the temperature measured by the temperature sensor 207 is higher than the temperature during normal use, the control unit 203 (control unit 90) sets the second charging voltage application period longer than that during normal use. Control to be As a result, the period of the refresh operation linked with the second charging voltage is extended with the extension of the application time of the second charging voltage, and the photosensitive drum 1 can be sufficiently polished. In addition, the generation of a charged product during the refresh operation can be suppressed by applying the second charging voltage.

  On the other hand, when the temperature measured by the temperature sensor 207 is lower than the temperature during normal use, the application period of the second charging voltage is controlled to be shorter than that during normal use. When the temperature of the photosensitive drum 1 is low, the resistance value is high, so that a charged product is less likely to be generated than during normal use. In the image forming operation immediately before the refresh operation, the charge is more charged than during normal use. This is because the amount of product produced is considered to be small.

  In this case, since the period of the refresh operation is also shortened with the application time of the second charging voltage, the time required for polishing the photosensitive drum 1 can be minimized, and the image forming operation can be quickly performed. it can.

  In the above case, the operation based on the temperature measurement by the temperature sensor 207 has been described. However, since the relationship between the upper and lower humidity and the characteristics of the photosensitive drum 1 is the same as the case of the temperature, the case based on the humidity measurement by the humidity sensor 208 is described. However, the same control is performed.

  Further, in the above description, the application time of the second charging voltage is controlled. However, as in the third embodiment, the second charging voltage AC is changed in accordance with the temperature and humidity. You may make it control the intensity | strength of a voltage component collectively.

(Embodiment 5)
The image forming apparatus according to the present embodiment controls the operation of the charging device 2 according to the average image print density measured during image formation and the number of printed developer images transferred to the transfer material. The purpose of this is to further maintain the surface state of the photosensitive drum 1 by controlling the cleaning / polishing process of the photosensitive drum 1.

  Since the configuration of the present embodiment is the same as that of the second embodiment, FIGS. However, the image data measurement unit 80 in FIG. 3 measures the average print density as in the second embodiment, and measures the number of prints on the transfer material by the transfer device 5 within a predetermined period. These measured or measured data are transferred to the control means 203 (control unit 90 in FIG. 3) of the charging device 2 and used as control parameters. The image data measuring unit 80 corresponds to a print density measuring unit and a printed sheet number measuring unit of the present invention.

  Hereinafter, description will be given with reference to FIGS. However, the part which overlaps with Embodiment 2 is abbreviate | omitted.

  In the second embodiment, the refresh operation is uniformly executed when the average print density is equal to or less than the reference density value (for example, 3 [%]). However, charging of the photosensitive drum 1 in the image forming apparatus is performed. The production state of the product changes according to the average print density. That is, when the average print density is smaller than the value close to the reference density value, the amount of charged products generated on the photosensitive drum 1 increases. This is because the toner consumption in the developing units 4K to 4Y is small, and it is difficult to obtain a polishing effect on the surface of the photosensitive drum 1 during the image forming period.

  Therefore, the control unit 203 (control unit 90) performs the second charging according to the actual measurement value of the average print density obtained from the image data measurement unit 80 (the magnitude of the difference between the actual measurement value and the reference density value). Control is performed so that the application period of the working voltage becomes longer. As a result, the period of the refresh operation linked with the second charging voltage is extended in accordance with the extension of the application time of the second charging voltage, and the photosensitive drum 1 can be sufficiently polished. it can. In addition, the generation of a charged product during the refresh operation can be suppressed by applying the second charging voltage.

  Further, the generation state of the charged product of the photosensitive drum 1 in the image forming apparatus is also affected by the number of prints on the transfer material by the transfer device 5. That is, the timing of the refresh operation is uniquely determined by the relationship between the average print density and the reference density value. However, if the number of printed sheets in the image forming period is large, the amount of toner consumed in the developing devices 4K to 4Y is correspondingly large. Therefore, the polishing effect on the surface of the photosensitive drum 1 can be obtained even during image formation. At the same time, since the effect of toner replacement is obtained, it is considered that the number of times and the number of times during which a refresh operation is performed in which a substantial effect is obtained vary depending on the number of printed sheets.

  In consideration of this case, the control unit 203 (control unit 90) controls the length of the application period of the second charging voltage according to the actual value of the number of printed sheets obtained from the image data measuring unit 80. Specifically, a predetermined number of printed sheets corresponding to a predetermined standard application time of the second charging voltage is set as a reference value, and is applied according to the difference between the actually measured value and the reference value. Control the length of time. When the actual measurement value is larger than the reference value, the amount of toner consumption is large. Therefore, the application period of the second charging voltage is controlled to be shorter than the reference value. In addition, since the consumption amount of toner is small when the value is smaller than the reference value, the second charging voltage application period is controlled to be longer than the reference value.

  As a result, the period of the refresh operation linked with the second charging voltage changes in accordance with the change in the application time of the second charging voltage, and the photosensitive drum 1 can be polished appropriately. . Further, the generation of the charged product during the refresh operation can also be suppressed by the application time of the second charging voltage.

  In the above description, the application time of the second charging voltage is controlled. However, as in the third embodiment, the second charging voltage is changed in accordance with the change in the average print density or the number of printed sheets. You may make it control the intensity | strength of the alternating voltage component of a voltage. At this time, the intensity may be changed with the application time, or only the intensity may be changed without changing the application time. As a result, the configuration in which the AC voltage control of the second charging voltage according to the third embodiment is performed according to a change in the average print density or the number of printed sheets, not the temperature and the humidity.

  In the first to fifth embodiments, the period during which the charging device 2 applies the second charging voltage corresponds to the weak charging period of the present invention, and the period during which the first charging voltage is applied. This corresponds to the regular charging period of the present invention. Further, the toner corresponds to the developer of the present invention, and the toner image corresponds to the developer image of the present invention.

  However, the weak charging period of the present invention is not limited to the period described in the above embodiment.

  That is, in the first embodiment, when the image forming mechanism becomes operable after the external power is supplied to the power supply device 160 of the image forming apparatus (1) and is turned on, the starting point is used. The period when the image data is input from the outside to the data input unit 60 and the exposure formation starts is the end point is an example of the weak charging period as the predetermined period before the start of the regular charging period of the present invention. However, the weak charging period (predetermined period before the start of the regular charging period) of the present invention is not limited to this. For example, the start point may be a period that is not the time of turning on the main power supply but the time of return from the power saving state (standby state). As an example of this return operation, in particular, in the case of a copying machine (including a multifunction device with a printer, a fax machine, etc.), various switches, interfaces, and the like that constitute the input operation unit 70 such as a known power button and a copy operation start button. Can be triggered by user input.

  In particular, when the image forming apparatus 600 is realized as a copying machine, the image data input unit 60 is realized as a scanner that optically reads a document and converts it into image data. In this case, as a starting point of a predetermined period, It can be set as the time when an original is set on the optical input surface of the scanner and the time when the scanner starts scanning the original. Further, when the scanner is configured to include an automatic document feeder, it may be at the time when the document is set on the automatic document feeder. In short, when the control unit 90 can detect that the scanner is ready for scanning (including a state where the document is set at a predetermined position for scanning), the detection time is arbitrarily set as the starting point. The state where the reading is completed and the LSU 3 can be formed by exposure can be set as the end point.

  Further, although the end point of the predetermined period has been described as the time point when the image data is input to the image data input unit 60, the end point may be earlier than this. In short, it is sufficient that a time interval is provided between the regular charging period and the weak charging period.

  For example, when the image data input unit 60 is a scanner, as an end point of a predetermined period, when the document is set on the optical input surface of the scanner, when the scanner starts scanning the document, the scanner starts the automatic document feeder. In the case of the configuration, it is possible to scan at the time when the document is set on the automatic document feeder (including the state where the document is set at a predetermined position of the scanner for scanning). When the control unit 90 can detect, the detection time may be arbitrarily set as the end point. Further, when the return from the standby state is taken as a viewpoint, the time when the warm-up of the transfer device 5 is completed may be set as the end point.

  Next, in the first embodiment, the transfer material is transferred to the outside by the carry-out device 150 from the time (2) when the electrostatic latent image corresponding to the toner image by the last developing device by the transfer device 5 is formed. The period until unloading is an example of the weak charging period as a predetermined period after the end of the regular charging period of the present invention. The period) is not limited to this. For example, the end point may be a period when the transfer material is completely sent from the developing device 5 to the fixing device 7 and when the transfer material is sent from the fixing device 7 to the carry-out device 5.

  Further, although the start point of the predetermined period has been described as the time point when the electrostatic latent image corresponding to the toner image is completed by the developing device, the start point may be later. For example, when the primary transfer of the toner image to the developing belt 51 is completed or the primary transfer of the toner image to the transfer material passes for a predetermined period, the toner image of the first transfer material on the surface of the photosensitive drum 1 is obtained. The point in time when it is no longer necessary to hold the corresponding electrostatic latent image may be the starting point. That is, a time interval may be provided between the regular charging period and the weak charging period.

  Further, in the first embodiment, when continuous printing is performed, the toner to be transferred to the next transfer material after the exposure and formation of the electrostatic latent image corresponding to the toner image to be transferred to the first transfer material is completed. The entire period during which no electrostatic latent image needs to be formed on the photosensitive drum 1 before the start of exposure formation of the electrostatic latent image corresponding to the image is between the plurality of regular charging periods of the present invention. This is an example of a predetermined period, and is an example between regular charging periods necessary for forming each electrostatic latent image when a plurality of the electrostatic latent images are continuously formed. The (predetermined period between a plurality of regular charging periods) is not limited to this.

  That is, in the above embodiment, in one operation for forming and transferring an image on each of a plurality of transfer materials, a weak charging period is assigned between exposure formation of each electrostatic latent image. As a predetermined period between a plurality of regular charging periods according to the present invention, when one operation for performing image formation and transfer on each of a plurality of transfer materials is performed a plurality of times, during the plurality of operations. A weak charging period may be assigned. For example, if the image forming apparatus is a color printer and a predetermined number of sheets are continuously printed, the apparatus is left for a while and then the continuous printing is resumed. You can do it. Note that a regular charging period may be continuously allocated during one continuous printing operation.

  Such a weak charging period is a charging period between regular charging periods necessary for forming each image group in the case of forming a plurality of image groups composed of a plurality of continuous electrostatic latent images of the present invention. It will be equivalent.

  When the image is continuously formed on the transfer material as described above, the second charging period is not to perform the charging operation continuously over the entire period. The second charging voltage may be applied only during a part of the period or periodically. At this time, as a method of providing the start point and the end point in the period, a time point that can be detected by the control means, such as return from the standby state, use state of the scanner, and the like is used as in the periods (1) and (2). Can be set arbitrarily.

  In the first to fifth embodiments described above, the image forming apparatus of the present invention has been described as a color printer. However, an information processing apparatus such as a FAX may be used. In short, as long as the image data input unit 60 is configured to receive image information as data as an electrical signal from the outside, the image forming apparatus of the present invention is configured to be incorporated in an apparatus for any application. Or may be implemented.

  In the first to fifth embodiments described above, the image forming apparatus is the color image forming apparatus 600 including the four color 4K to 4Y developing devices. However, the charging device and the image forming apparatus of the present invention are illustrated in FIG. The image forming apparatus may be realized as a monochrome image forming apparatus as shown in FIG. 13, and is not limited by the number of developers, colors, and the like.

  In the first to fifth embodiments, the charging roller 201 corresponds to the charging member of the present invention, and the photosensitive drum 1 corresponds to the photosensitive member of the present invention. The charging body is not limited to the configuration as long as it has a configuration capable of charging the charging body regardless of the roller shape, and may be used for, for example, a brush-shaped or belt-shaped charging means. Further, the photoreceptor of the present invention may have a belt shape without depending on the drum shape.

  The color image forming apparatus 600 according to the first to fifth embodiments as described above was created and operated, and compared with the conventional example.

The charging roller 201 constituting the charging device 2 is formed of a core portion made of a conductive metal such as iron, copper, stainless steel, and aluminum, and a polyurethane rubber impregnated with carbon-containing ethylene propylene rubber or LiClO ₄ . The surface of the conductive elastic member is provided with a surface layer having a resistivity of about 105 to 109 Ω · cm. The surface layer is not always necessary, but it is desirable to provide it in order to prevent deterioration and fatigue of the photoreceptor due to contact with the charging roll. Polyamide resin, polyethylene resin, polyurethane resin, acrylic resin containing conductive particles such as carbon and aluminum It is made of polyurethane impregnated with resin, LiClO ₄ or the like, and the thickness of the surface layer is preferably 1 to 50 μm. Further, in order to prevent pinhole leakage, a pressure resistant layer in which BaSO ₄ or the like is added to a cyano resin or byron resin may be provided between the conductive elastic member and the surface layer. It is good to set it as the range of -50 micrometers.

  In this embodiment, a force of 500 g is applied to both ends of the core portion 201a of the charging roller 201 by the springs 205, thereby being urged toward the photosensitive drum 1, and the charging roller 201 is moved to the photosensitive body. It was made to follow the rotation of the drum 1. The nip shape at this time is 0.5 mm at the center and 1.3 mm at both ends.

  The charging roller 201 has a diameter of 14 mm, and the core has a diameter of 8 mm at the center. The electrical resistance is 106-109Ω.

  The electrical resistance value is determined by applying a DC voltage of 100 V to the core portion 201a of the charging roller 201 in a state where the charging roller 201 is separated from the photosensitive drum 1, and bringing a measurement terminal into contact with a measurement location on the surface of the charging roller 201. It was obtained by measuring the current value at the time. This measurement terminal is made of a conductive metal.

  Further, spherical toner was used as the toner used in the developing devices 4K to 4Y, and it was manufactured by the following method. Polymerized into a mixed solution of 80 parts by weight of styrene, 20 parts by weight of 2-ethylhexyl methacrylate, 5 parts by weight of colorant, 3 parts of low molecular weight polypropylene, 2 parts of charge control agent (quaternary ammonium salt) and 1 part of divinylbenzene (crosslinking agent). Add 2 parts by weight of initiator 2,2-azobis (2,4-dimethylvaleronitrile), add it to 400 parts by weight of purified water, and further 5 parts by weight of calcium triphosphate and sodium dodecylbenzenesulfonate as a suspension stabilizer. 0.1 part by weight was added, and the mixture was stirred for 20 minutes at 7000 rpm and 14 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), and subjected to a polymerization reaction at 70 ° C. and 100 rpm for 10 hours in a nitrogen atmosphere. A 6.4 μm (spherical) toner was obtained.

  In this example, an average printing density (printing rate) A was calculated for every 200 transfer materials. Based on this printing rate, a refresh operation was performed after the output of the 200th sheet. In order to develop toner from the developing devices 4K to 4Y and consume the toner during a period when no image is formed on the photosensitive drum 1 (during non-image formation), the photosensitive drum 1 is not charged and is in accordance with the printing rate. A bias voltage as a first charging voltage was applied so that the toner amount consumed could be consumed. The conditions of the bias voltage as the first charging voltage are: DC voltage Vdc = 160 [V], AC voltage Vpp = 1500 [V], AC voltage frequency f = 2.5 [kHz], Duty = 30% ” As described later, the condition of the bias voltage as the second charging voltage is obtained by changing the value of the AC voltage Vpp to less than 1500 [V] among the above conditions. Note that a positive high-voltage bias is applied to the transfer device 5 in order to prevent toner from adhering to the transfer belt 51 when each of the bias voltages is applied. The linear velocity of the photosensitive drum 1 in this embodiment was set to 151 [mm / sec].

  FIG. 5 shows set values in the present embodiment. The result of the combination experiment for confirming each of these effects is shown in FIGS. In each figure, the toner consumption during the refresh operation at each printing rate, the bias application voltage value that is the charging voltage, and the replenishment start cumulative dot number are shown.

  The data obtained by experimenting under the above conditions were plotted with the image density ID (Macbeth density: 0.00 means white and 1.8 means black) on the vertical axis and the number of printed sheets on the horizontal axis.

  The graph of FIG. 6 shows the image density transition at each printing rate density. According to the graph of FIG. 5, when the printing rate falls below 3%, it can be confirmed that the image density after the printing durability evaluation is low. According to this embodiment, since toner is consumed during non-image formation based on the printing rate, it was confirmed that a good image density was maintained to some extent even after printing.

Example 1
FIG. 7 shows the relationship between the charging voltage for the refresh operation, which is the operation of the second embodiment, and the friction coefficient of the photosensitive drum 1, and the surface friction indicating the amount of the charged product adhering to the surface of the photosensitive drum 1. It is a figure which shows the graph which plotted the coefficient (micro) on the vertical axis | shaft and the number of printed sheets on the horizontal axis. The measurement was performed at a printing rate of 1% and a forced toner consumption equivalent to 1%.

  In addition, as a charging voltage at the time of refresh, a first charging voltage (AC voltage Vpp = 1500V) used at the time of image formation and a second AC voltage that is superposed is lowered (or turned OFF) in units of 200V. The case of using the charging voltage was plotted.

  As shown in the graph of FIG. 7, when the first charging voltage at the time of conventional image formation is used as the charging voltage at the refresh operation, the friction coefficient μ is increased when the number of printed sheets reaches about 10,000. About 0.69 is reached, and further printing becomes impossible. On the other hand, the first charging voltage is used by using the second charging voltage having a lower superimposed AC voltage value. In this case, a low friction coefficient could be maintained even when the number of printed sheets was over 10,000.

  With the above measured values, stable image forming and image forming operations were obtained when the friction coefficient μ was maintained at 0.55 or less. (Stable cleaning performance and no image flow image were observed.) Under other conditions, image formation becomes unstable and impractical.

(Example 2)
FIG. 8 shows the relationship between the forced toner consumption and the coefficient of friction of the photosensitive drum 1 as the refresh operation related to the operation of the second embodiment, and the amount of charged product adhering to the surface of the photosensitive drum 1. It is a figure which shows the graph which plotted the surface friction coefficient ((micro | micron | mu)) to show on the vertical axis | shaft, and set the number of printed sheets on the horizontal axis. In the operation shown in FIG. 8, as a comparative example of the second embodiment, the charging device 2 uses the first charging voltage (AC voltage Vpp = 1500 V).

As shown in the graph of FIG. 9, according to the printing rate Ri by the adjusting the forced consumption of toner, by increasing the toner forced consumption higher printing ratio is low, with an increase in the number of printed sheets, friction The increase in coefficient could be kept low. “No consumption” in the graph means that no refresh operation is performed.

  Next, FIG. 9 shows an example in which the charging device 2 uses the second charging voltage (AC voltage Vpp = 1100 V) under the same conditions as the comparative example of FIG. is there. It can be seen that an increase in the friction coefficient can be further suppressed as compared with the embodiment of FIG.

(Example 3)
FIG. 10 shows, as an example of the first embodiment, the relationship between the charging voltage and the friction coefficient of the photosensitive drum 1, and the surface friction coefficient (the surface friction coefficient indicating the amount of the charged product attached to the surface of the photosensitive drum 1). It is a figure which shows the graph which plotted (micro | micron | mu) on the vertical axis | shaft and the number of printed sheets on the horizontal axis. The forced consumption of toner was measured at 1%.

  As shown in the graph of FIG. 10, as the charging voltage, the first charging voltage (AC voltage Vpp = 1500V) used at the time of image formation and the AC voltage value to be superimposed are lowered by 400V, 800V, and 1500V, respectively. The case where the second charging voltage was used was plotted. The coefficient of friction is μ ≦ 0.6, preferably μ ≦ 0.55.

  According to FIG. 10, the surface friction coefficient (μ) of the photosensitive drum can be stabilized to 0.55 or less when the potential during non-image formation is 1100 V and consumption of 1% is performed. By lowering the non-image portion potential to 1100 V and forcing consumption equivalent to 1% by refreshing, it is possible to suppress a certain increase in the surface friction coefficient (μ). It was. Further, it is possible to suppress an increase in the surface friction coefficient (μ) by lowering the potential during non-image formation to 700V. Further, it is possible to further suppress the increase in the surface friction coefficient (μ) by setting the potential at the time of non-image formation to 0, that is, by not superimposing the AC voltage as the second charging voltage.

  As in the first and second embodiments, the friction coefficient increase when using the first charging voltage and the second charging voltage is more remarkable by combining with the refresh operation with the forced toner consumption 1%. Could be suppressed.

Example 4
FIG. 11 shows a second charging voltage (toner forced consumption refresh) according to the temperature and humidity in the vicinity of each of the four color photosensitive drums 1 as an example of the operation example of the third to fifth embodiments. The polishing time of the photosensitive drum 1 due to forced consumption of toner (corresponding to the application period of the second charging voltage) was changed according to the operation to change the voltage and the temperature and humidity. It is a table | surface which shows the performance in case as a grade of a surface friction coefficient (micro).

  As an example of environmental conditions, three conditions of temperature 10 ° C., relative humidity 20% RH, temperature 23 ° C., relative humidity 60% RH, and temperature 32 ° C., relative humidity 80% RH are prepared. Each time the condition increased, the second charging voltage was controlled to be smaller and the polishing time per time was made longer.

  The printing time of the first charging voltage during printing, that is, during image formation, was 2000 msec. This is the time to cover A4 size printing paper, and the speed is 151 mm / sec.

  Further, for each environment, the toner was forcibly consumed every 10 in terms of a printing rate of 5% and the number of printed sheets A4, and the photosensitive drum 1 was polished. The document printing rate is the same for each environment, and the forced toner consumption is the same. As a comparative example, an example is described in which toner is not forcibly consumed only when the polishing time is 500 msec. Note that the normal non-printing printing time without considering the environment is 500 msec in normal times. Therefore, in this embodiment, a case is shown in which this time is changed for each environment having different temperature and humidity conditions.

  In each environment, the surface friction coefficient (μ) of the photosensitive drum 1 was measured for every 200 printed sheets, and the value after stabilization was described. Therefore, the polishing time at which the surface friction coefficient (μ) having an appropriate value is given can be regarded as the optimum polishing time obtained in consideration of the environment such as the temperature and humidity of the photosensitive drum 1.

  In this embodiment, the first charging voltage (AC voltage Vpp) used at the time of image formation, that is, printing is also lowered (1800 V to 900 V) according to temperature and humidity. This is because the change in the resistance value of the photosensitive drum 1 due to changes in temperature and humidity in the vicinity of the photosensitive drum 1 affects the generation of an electrostatic latent image even during image formation.

  Taking the case of 500 msec in FIG. 11 as an example, regardless of whether toner is forcibly consumed or not, in each environment, the second charging voltage is lowered in consideration of the temperature at the time of non-printing. A surface friction coefficient (μ) better than that of the non-exposed one was obtained, and the effect of lowering the second charging voltage according to temperature and humidity was obtained. This tendency is maintained in other examples in which the polishing time is longer.

Next, from the case of low temperature and low humidity (temperature 10 ° C., relative humidity 20% RH) to high temperature and high humidity (temperature 32 ° C., relative humidity 80% RH), a single polishing time is taken longer. Otherwise, it can be seen that the surface friction coefficient (μ) cannot be reduced. In order to obtain the same performance as the surface friction coefficient (μ) with a single polishing time of 1000 msec in the case of (temperature 10 ° C., relative humidity 20% RH), (temperature 32 ° C., relative humidity 80% RH) In some cases, 3000 msec is necessary (in the blank area below this, an effective value could not be obtained as a measured value).
From this, it can be seen that in order to maintain a good surface friction coefficient (μ), it is desirable to take a longer polishing time according to temperature and humidity.

  In addition, as an environment in which an ideal surface friction coefficient (μ) 0.53 to 0.55 according to temperature and humidity can be obtained from FIG. 11, in the case of (temperature 10 ° C., relative humidity 20% RH) 2 charging voltage 1500 V, polishing time (application period) 2000, about 2500 msec (temperature 23 ° C., relative humidity 60% RH), second charging voltage 800 V, polishing time (application period) 2500, 300 msec. When the temperature is about 32 ° C. and the relative humidity is 80% RH, it is desirable that the second charging voltage is 600V and the polishing time (application period) is about 4500 and 5000 msec. Note that if the polishing time (application period) is longer than the above period, it is possible to lower the μ value, but it is not appropriate because it takes too long a refresh time.

  Next, FIG. 12 shows an example of an environment correction table when the charging device is operated in consideration of the external temperature and humidity.

  In the table of FIG. 12, the first charging voltage Vpp = 1100V and the second charging voltage Vpp−300V are defined as the reference. Therefore, in each condition, both the first and second charging voltages are increased or decreased according to changes in temperature and humidity.

  Based on the example shown in FIG. 11, the photosensitive drum 1 can be optimized quickly by setting the value of the second charging voltage and the polishing time (application period) more finely according to the external temperature and humidity. It was possible to maintain the surface friction coefficient (μ).

  As other operating conditions, as in the table of FIG. 11, toner forcible consumption is performed every 10 in terms of a printing rate of 5% and the number of printed sheets A4. When the printing rate was doubled, the polishing time (application period) of the second charging voltage could be reduced by 20%. On the contrary, when the printing rate is halved, the polishing time (application period) can be reduced by 50%.

Images forming apparatus that written to the present invention has a significant effect of solving the image defect such as image flow to stabilize the surface condition of the photosensitive drum, a copying machine, a printer, an image forming apparatus such as a FAX, etc. Useful.

1 is a diagram illustrating a configuration of an image forming apparatus according to first and second embodiments of the present invention. The figure which shows the structure of the charging device 2 of Embodiment 1, 2 of this invention. The figure which shows typically the control part of the image forming apparatus of this invention The figure which shows the structure of the charging device 2 of Embodiment 3 and 4 of this invention. Table showing set values in Examples 1 and 2 of the present invention The figure which shows the graph of (concentration stability) in order to demonstrate the Example of this invention The figure which shows the graph explaining Example 1 of this invention The figure which shows the graph explaining Example 2 of this invention The figure which shows the graph explaining Example 2 of this invention The figure which shows the graph explaining Example 3 of this invention The figure which shows the table | surface explaining Example 4 of this invention The figure which shows the table | surface explaining Example 4 of this invention The figure which shows the structure of the image forming apparatus containing the charging device by a prior art

Explanation of symbols

1 Photosensitive drum 2 Charging device 3 LSU (laser scan unit)
DESCRIPTION OF SYMBOLS 4 Developing apparatus 5 Transfer apparatus 6 Cleaning blade 7 Fixing apparatus 8 Roller 9 Paper feed roller 201 Charging roller 201a Core part 201b Conductive elastic member 202 Voltage application means 203 Control means

Claims (13)

A charging member that contacts the photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A print density measuring means for measuring an average print density in a predetermined period of a developer image obtained by developing an electrostatic latent image formed by exposure in a predetermined area on the photoconductor;
The control unit controls the magnitude of the AC voltage of the second charging voltage of the charging device according to the measured magnitude of the average print density ; and
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that performs control to cause the developing unit to perform a refresh operation for conveying the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period . A charging member that contacts the photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A print density measuring means for measuring an average print density in a predetermined period of a developer image obtained by developing an electrostatic latent image formed by exposure in a predetermined area on the photoconductor;
The control means controls the length of the weak charging period of the charging device according to the measured average print density, and a charging device ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that performs control to cause the developing unit to perform a refresh operation for conveying the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period . A charging member that contacts the photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A printing number measuring means for measuring the number of printings on a recording medium in a predetermined period of a developer image obtained by developing an electrostatic latent image exposed and formed in a predetermined region on the photosensitive member;
The control unit controls the magnitude of the AC voltage of the second charging voltage of the charging device according to the measured magnitude of the number of printed sheets ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that performs control to cause the developing unit to perform a refresh operation for conveying the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period . A charging member that contacts the photosensitive member and charges it during a predetermined charging period;
Voltage applying means for applying a charging voltage to the charged body;
Control means for controlling the operation of the voltage application means,
The control means includes
A normal charging period in which the voltage application means applies a DC voltage on which an AC voltage is superimposed as a first charging voltage, and the AC voltage is turned off to consist only of the DC voltage, or in the normal charging period. Each setting and controlling a weak charging period in which a second charging voltage formed by superimposing an AC voltage lower than the AC voltage on the DC voltage is applied;
The regular charging period is a period in which the charged body performs charging with a strength necessary for forming an electrostatic latent image on the photoreceptor,
The weak charging period is a period during which charging is weaker than the intensity necessary to form the electrostatic latent image,
A printing number measuring means for measuring the number of printings on a recording medium in a predetermined period of a developer image obtained by developing an electrostatic latent image exposed and formed in a predetermined region on the photosensitive member;
The control means controls the length of the weak charging period of the charging device according to the measured number of printed sheets ;
A photosensitive member charged by the charging member of the charging device;
Exposure means for exposing and forming an electrostatic latent image in a predetermined area on the photoreceptor;
Developing means for developing an electrostatic latent image on the photoreceptor;
Transfer means for transferring the developer image on the photoreceptor to the recording medium,
The control means of the charging device also controls the developing means,
An image forming apparatus that performs control to cause the developing unit to perform a refresh operation for conveying the developer on the developing unit side to the photosensitive member within a period corresponding to the weak charging period . The weak charging period is a predetermined period before the start of the regular charging period, a predetermined period after the end of the regular charging period, or a predetermined period between the plurality of regular charging periods. The image forming apparatus according to any one of? Further comprising a temperature measuring means for measuring the temperature in the vicinity of the photoreceptor,
The image forming apparatus according to claim 1, wherein the control unit controls the magnitude of the AC voltage of the second charging voltage in accordance with a temperature measured by the temperature measuring unit. . Further comprising a temperature measuring means for measuring the temperature in the vicinity of the photoreceptor,
The image forming apparatus according to claim 1, wherein the control unit controls the length of the weak charging period according to a temperature measured by the temperature measuring unit. Further comprising a humidity measuring means for measuring the humidity in the vicinity of the photoreceptor,
The image forming apparatus according to claim 1, wherein the control unit controls the magnitude of the AC voltage of the second charging voltage according to the humidity measured by the humidity measuring unit. . Further comprising a humidity measuring means for measuring the humidity in the vicinity of the photoreceptor,
The image forming apparatus according to claim 1, wherein the control unit controls the length of the weak charging period according to humidity measured by the humidity measuring unit. The image forming apparatus according to claim 1, wherein the charging member is a charging roller, and the photosensitive member is a photosensitive drum. 3. The control unit according to claim 1, wherein the control unit performs the control of the voltage application unit and the control of the refresh operation of the development unit when the measured average print density is lower than a reference density value. 4. Image forming apparatus. A plurality of the developing means;
The printing density measuring unit measures the average printing density for each developing unit,
The image forming apparatus according to claim 11 , wherein the control unit sets the reference density value for each of the developing units. The developer is a spherical toner, an image forming apparatus according to any one of claims 1 to 12.

Images