JP2006235103A - Image forming apparatus and its control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which controls a developing station and a transfer part so that a stable image may be obtained by restraining the occurrence of fogging against environmental change. <P>SOLUTION: The image forming apparatus is equipped with: an operating environment detection part for detecting humidity in the operating environment; a bias voltage applying part for applying bias voltage to the developing station; a bias voltage setting part for setting the bias voltage of the bias voltage applying part; a transfer driving part for driving a contact transfer part abutting on an image carrier through transfer material; and a transfer driving control part for setting the driving speed of the transfer driving part. A bias voltage control part sets the bias voltage so that a difference between charge potential and development potential may be predetermined voltage in accordance with the humidity, and the transfer driving control part sets the driving speed so that the speed of the abutting part of the contact transfer part on the image carrier may be predetermined speed in accordance with the humidity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a control program therefor, and more particularly to an image forming apparatus that controls an electrophotographic process according to the degree of humidity and a control program therefor.

  Image forming devices such as electrophotographic printers, copiers, and digital multifunction peripherals have a charging station, exposure station, development station, transfer unit, static elimination unit, and cleaning around a cylindrical or endless belt-shaped photosensitive member. It has a configuration in which stations and the like are appropriately arranged. In the electrophotographic process, a photoconductor whose surface is uniformly charged by a charging station is exposed with an exposure intensity corresponding to the distribution of light and shade of the image, and a two-dimensional potential distribution on the surface, that is, an electrostatic latent image. Create an image. Then, by applying a predetermined bias voltage to the surface of the photoreceptor on which the electrostatic latent image is formed, charged toner is supplied from a developing station that is at a developing potential with respect to the ground potential, The toner corresponding to the potential difference is attached by electrostatic force to form a toner image on the surface of the photoreceptor, and the toner is transferred to a transfer material to obtain a print output.

  The density of the dark portion of the image, that is, the toner adhesion amount depends on the difference between the latent image potential in the dark portion and the development potential, the toner charge amount, and the like. Here, the latent image potential in the dark portion depends on the charging potential and the exposure intensity. On the other hand, the amount of fog in the bright portion of the image depends on the difference between the latent image potential in the bright portion and the development potential, the toner charge amount, and the like. Here, the latent image potential of the bright portion depends on the charging potential.

Conventionally, various methods for controlling a charging potential, an exposure intensity, and a developing potential so as to stabilize an image density against an environmental change or a change with time are known (for example, see Patent Document 1). However, there is no known device that controls the difference between the latent image potential in the bright portion and the development potential with respect to environmental changes and changes with time, and optimally controls the amount of fogging. For example, with respect to a multicolor image forming apparatus that sequentially forms and superimposes toner images of respective colors on a single photoconductor and then transfers them collectively, the image quality is stabilized against environmental changes and changes over time. For this purpose, a technique is known in which the charging potential or the bias voltage is controlled so that the potential difference between the latent image potential and the development potential becomes a predetermined value (see, for example, Patent Document 2). However, the control is specific to the image forming apparatus of the above-mentioned type, and after a toner image is individually formed on a single-color image forming apparatus or a photoconductor provided for each color, it is sequentially transferred to a transfer material. Application to a so-called tandem type image forming apparatus is not disclosed.
JP 2001-183876 A Japanese Patent Laid-Open No. 9-101641

It is known that fogging tends to occur when the operating environment, particularly humidity, is low. The toner adhering to the white background portion of the image, which is referred to as “fogging”, is caused by the charged toner adhering to the photoconductor by the mirror image force. The toner adhesion of the fog is caused by the mirror image force of the charged toner, and the toner adhesion and the adhesion mechanism of the image portion where the toner adheres are controlled by the Coulomb force acting on the electrostatic latent image charge. In order to reduce fogging, the development potential is set higher than that of the white background. As a result, the mirror image force is canceled by the Coulomb force acting on the charged toner so that the toner does not go to the photosensitive member.
However, when the humidity is low, the charge amount of the toner increases, so that the image power becomes stronger and the fog tends to increase than when the humidity is high.

  The present invention has been made in consideration of such circumstances, and by controlling the developing station and the transfer section so as to obtain a stable image by suppressing the occurrence of fog against environmental changes, a more stable image can be obtained. Is provided.

  The present invention is an image forming apparatus in which a charging station, an exposure station, a developing station, a contact transfer unit, and a cleaning station are arranged around an image carrier, and an image is formed by passing the surface of the image carrier through each station. The image forming apparatus includes an operating environment detecting unit for detecting humidity of the operating environment, a bias voltage applying unit that applies a bias voltage to the developing station, and a bias that sets a bias voltage of the bias voltage applying unit. A voltage setting unit; a transfer driving unit that drives a contact transfer unit that contacts the image carrier via a transfer material; and a transfer driving control unit that sets a driving speed of the transfer driving unit. The bias voltage is set so that the difference between the charging potential and the development potential becomes a predetermined voltage corresponding to the humidity. To provide an image forming apparatus, characterized in that the speed of the contact portion of the contact transfer section for carrier sets the driving speed to a predetermined speed corresponding to the humidity.

  In the image forming apparatus of the present invention, the bias voltage control unit sets a bias voltage so that a difference between the charging potential and the development potential becomes a predetermined voltage corresponding to humidity, and the transfer drive control unit Since the driving speed is set so that the speed of the contact portion of the contact transfer portion with respect to the body becomes a predetermined speed corresponding to the humidity, it is possible to set the bias voltage corresponding to the humidity and the driving speed of the contact transfer portion. Accordingly, the difference between the charging potential and the development potential according to the humidity, that is, the cleaning voltage can be set, and the smooth gradation of the image or the bright part without fogging can be stably realized against the fluctuation of the humidity. Can do.

  In the image forming apparatus according to the present invention, a charging station, an exposure station, a developing station, a contact transfer unit, and a cleaning station are arranged around the image carrier, and an image is formed by the surface of the image carrier passing through each station. An image forming apparatus, wherein the image forming apparatus detects an operating environment humidity, a bias voltage applying unit that applies a bias voltage to the developing station, and a bias voltage of the bias voltage applying unit A bias voltage setting unit for setting the bias, a transfer driving unit for driving a contact transfer unit that contacts the image carrier via a transfer material, and a transfer driving control unit for setting a driving speed of the transfer driving unit, The voltage controller sets a bias voltage so that a difference between the charging potential and the developing potential becomes a predetermined voltage corresponding to the humidity, and the transfer Dynamic control unit, and sets the driving speed to a predetermined speed that the speed of the contact portion of the contact transfer section according to the humidity on the image bearing member.

Here, the image carrier may be a so-called cylindrical photosensitive drum, but is not limited thereto, and may be an endless belt-shaped photosensitive sheet. Alternatively, it may be a photoreceptor sheet that is not endless. The charging station may be a charging roller that contacts the image carrier, but is not limited thereto, and may be a charger that utilizes air discharge.
In addition, the material of the charging roller is not particularly limited as long as it can apply a voltage to charge the image carrier. The exposure station may be, for example, one that scans the surface of the image carrier by scanning a laser beam, but is not limited to this, for example, one that uses a light emitting element such as an LED array or a liquid crystal shutter. It may be a thing.

  The development station may be two-component development, but is not limited thereto, and may be one-component development. The method is not limited as long as development is performed by applying a bias voltage. The operating environment detection unit may detect absolute humidity, but is not limited thereto, and may detect relative humidity. Further, since temperature and humidity tend to be related to each other and are likely to become high humidity at a high temperature, the correction of fog due to a change in humidity may be performed by detecting the temperature. Since temperature detection is easier and cheaper than humidity detection, temperature detection can be substituted when high accuracy is not required. For example, a transfer roller is preferably used as the contact charging station material, but is not particularly limited to a roller, and may be, for example, a belt-shaped transfer member. The material is not particularly limited as long as the toner image can be transferred onto the transfer material by applying a transfer voltage. The transfer drive unit is not particularly limited as long as the surface of the contact transfer unit is moved at a predetermined speed, and the type and structure of the drive source are not particularly limited.

  The image forming apparatus may be a single color image forming apparatus, but is a multicolor image forming apparatus that forms toner images on a plurality of image carriers corresponding to the respective colors and sequentially transfers them onto a transfer material. It may be. Alternatively, a single toner image is formed on a single image carrier, transferred to an intermediate transfer member, and this is sequentially repeated for each color, superimposed on the intermediate transfer member, and then transferred to a transfer material at a time. It may be a thing.

  The bias voltage control unit is configured to set a bias voltage that provides a cleaning voltage according to the detected humidity level, and the transfer drive control unit is configured to set a driving speed according to the detected humidity level. May be. In this way, the cleaning voltage and the drive speed of the contact transfer unit can be set at a humidity level corresponding to the required humidity detection accuracy, so correction can be performed without overloading the setting process. Can be realized.

  Furthermore, the bias voltage application unit may set the bias voltage so that the difference between the charging potential and the developing potential is smaller as the humidity is higher. In this way, when the humidity is high, fog is reduced too much and a burden is placed on the cleaner blade used in the cleaning station, etc., thereby reducing the cleaning voltage and reducing the burden on the cleaning station by generating appropriate fog. Can be made.

  Further, the transfer drive control unit may set the relative speed of the contact transfer unit with respect to the image carrier to be lower as the humidity is higher. In this way, if the cleaning voltage is reduced when the humidity is high and appropriate fog is generated, the drive speed is set so that the transfer efficiency is lowered, and the fog toner is transferred to the transfer material. Therefore, it is possible to reduce the burden on the cleaning station and suppress fogging on the transfer material.

  The exposure station may be configured to switch the intensity of exposure according to the degree of humidity. In this way, the exposure intensity is switched according to the setting of the cleaning voltage and transfer efficiency according to the humidity. Therefore, the exposure intensity is corrected and the potential of the dark image area regardless of the setting of the cleaning voltage and transfer efficiency. Can be kept constant. Here, the control of the intensity of exposure may be performed by duty control by time-division driving, but is not limited to this, for example, it controls instantaneous power by controlling drive current or the like. In addition, a driving method in which both are combined may be used.

  Furthermore, the exposure station may reduce the intensity of exposure as the humidity increases. In this way, when the humidity is high and the cleaning voltage is set low, correction can be performed so as to keep the potential of the dark image portion constant.

  From a different point of view, a charging station, an exposure station, a developing station, a contact transfer unit, and a cleaning station are arranged around the image carrier, and an image is formed by the surface of the image carrier passing through each station. A program to be executed by a computer to control a configured image forming apparatus, wherein the image forming apparatus applies a bias voltage to an operating environment detection unit for detecting humidity of an operating environment and the developing station. A bias voltage applying unit and a transfer driving unit that drives a contact transfer unit that contacts the image carrier via a transfer material, and the computer determines a difference between the charging potential and the developing potential according to humidity. A bias voltage is set so that the bias voltage application unit applies the bias voltage to the developing station. Providing a pressure setting unit, a program to function as a transfer drive control unit for setting the driving speed such that a predetermined speed that the speed of the contact portion in accordance with the humidity of the contact transfer section to the image bearing member.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings.
<First Aspect of Image Forming Apparatus>
One aspect of the image forming apparatus according to the present invention will be described. FIG. 3 is an explanatory diagram showing the configuration of the image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 forms multicolor and single color images on a predetermined sheet (recording paper) in accordance with image data transmitted from the outside. As shown in FIG. 3, exposure units 1a, 1b, 1c, 1d, developing devices 2a, 2b, 2c, 2d, photosensitive drums 3a, 3b, 3c, 3d, chargers 5a, 5b, 5c, 5d, The cleaner unit 4a, 4b, 4c, 4d, transfer conveyance belt unit 8, fixing unit 12, paper conveyance path S, paper feed tray 10, paper discharge trays 15, 33, and the like.

  Note that image data handled in the image forming apparatus corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the exposure units 1a, 1b, 1c, 1d, the developing devices 2a, 2b, 2c, 2d, the photosensitive drums 3a, 3b, 3c, 3d, the chargers 5a, 5b, 5c, 5d, and the cleaner units 4a, 4b, 4c. , 4d are provided to form four types of latent images corresponding to each color, and the letter a at the end of each code corresponds to black, b corresponds to cyan, c corresponds to magenta, and d corresponds to yellow. There are four image stations.

  Hereinafter, black (K) will be described as a representative. The photosensitive drum 3a is disposed (attached) at substantially the center of the image forming apparatus. The charger 5a is a charging means for uniformly charging the surface of the photosensitive drum to a predetermined potential. In addition to a contact-type roller-type or brush-type charger, a charger-type charger as shown in FIG. Is used. As the exposure unit 1a, for example, an EL or LED writing head in which light emitting elements are arranged in an array, a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror is used. The charged photosensitive drum 3a is exposed according to the input image data, thereby forming an electrostatic latent image corresponding to the image data on the surface. The developing device 2a visualizes the electrostatic latent image formed on the photosensitive drum with toner. The cleaner unit 4a removes and collects toner remaining on the surface of the photosensitive drum after development and image transfer. The above configuration is the same for yellow, cyan, and magenta.

  The transfer conveyance belt unit 8 disposed below the photosensitive drums 3a to 3d includes a transfer belt 7, a transfer belt driving roller 71, a transfer belt tension roller 73, transfer belt driven rollers 72 and 74, transfer rollers 6a and 6b, 6c and 6d, and a transfer belt cleaning unit 9.

  The transfer belt driving roller 71, the transfer belt tension roller 73, the transfer roller 6, the transfer belt driven rollers 72, 74, and the like stretch the transfer belt 7 and rotate the transfer belt 7 in the direction of arrow B.

  The transfer rollers 6a, 6b, 6c, and 6d are rotatably supported by transfer roller mounting portions 76 of the housing 75 of the transfer belt unit 8, respectively, and transfer the toner images on the photosensitive drums 3a, 3b, 3c, and 3d. A transfer bias is applied to transfer onto a sheet (recording paper) that is sucked and conveyed on the belt 7.

  The transfer belt 7 is provided so as to come into contact with the respective photosensitive drums 3a, 3b, 3c, and 3d, and the toner images of the respective colors formed on the photosensitive drums 3a, 3b, 3c, and 3d are formed into sheets ( The recording sheet has a function of forming a color toner image (multicolor toner image) by sequentially superimposing and transferring the recording sheet). This transfer belt is formed endlessly using a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drums 3a, 3b, 3c, and 3d to the sheet (recording paper) is performed by transfer rollers 6a, 6b, 6c, and 6d that are in contact with the back side of the transfer belt 7. To the transfer rollers 6a, 6b, 6c, and 6d, a high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (-)) is applied to transfer the toner image. The transfer rollers 6a, 6b, 6c and 6d are based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm, and the surface thereof is a roller covered with a conductive elastic material (for example, EPDM, urethane foam or the like). is there. With this conductive elastic material, a high voltage can be uniformly applied to the recording paper (sheet). In this embodiment, the transfer rollers 6a, 6b, 6c, and 6d are used as the transfer electrodes. However, a brush or the like is also used.

  Further, the toner adhering to the transfer belt 7 due to contact with the photosensitive drums 3a, 3b, 3c, and 3d causes the back surface of the recording paper to become dirty, so that it is removed and collected by the transfer belt cleaning unit 9. Is set. The transfer belt cleaning unit 9 includes a cleaning blade as a cleaning member that contacts the transfer belt 7, for example, and the transfer belt 7 that contacts the cleaning blade is supported by a transfer belt driven roller 74 from the back side.

  The paper feed tray 10 is a tray for storing sheets (recording paper) used for image formation, and is provided below the image forming unit of the image forming apparatus 100. A paper discharge tray 15 provided on the upper part of the image forming apparatus 100 is a tray for placing printed sheets face down, and is provided on a side portion of the image forming apparatus. The paper tray 33 is a tray on which an image-formed sheet is placed face up.

  Further, the image forming apparatus 100 is provided with an S-shaped sheet conveyance path S for sending the sheet in the sheet feeding tray 10 to the sheet discharge tray 15 via the transfer conveyance unit 8 and the fixing unit 12. ing. Further, in the vicinity of the sheet conveyance path S from the sheet feed tray 10 to the sheet discharge tray 15 and the sheet discharge tray 33, a pickup roller 16, a registration roller 14, a fixing unit 12, a conveyance direction switching guide 34, and a conveyance for conveying a sheet. A roller 25 and the like are arranged.

The conveyance roller 25 is a small roller for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 25 are provided along the sheet conveyance path S. The pickup roller 16 is a drawing roller that is provided at the end of the paper feed tray 10 and supplies sheets from the paper feed tray 10 to the paper transport path S one by one.
The conveyance direction switching guide 34 is rotatably provided on the side cover 35, and separates the sheet from the middle of the conveyance path S by discharging from the state indicated by the solid line to the state indicated by the broken line and discharges the sheet to the paper discharge tray 33. It can be done. In the state indicated by the solid line, the sheet passes through the conveyance unit S ′ (part of the sheet conveyance path S) formed between the fixing unit 12, the side cover 35, and the conveyance switching guide 34, and the upper discharge tray 15. To be discharged.

  Further, the registration roller 14 temporarily holds the sheet being conveyed on the sheet conveyance path S. The sheet has a function of transporting the sheet with good timing in accordance with the rotation of the photosensitive drum 3 so that the toner image on the photosensitive drum 3 can be satisfactorily transferred onto the sheet.

  That is, the registration roller 14 conveys the sheet so that the leading edge of the toner image on each photosensitive drum 3 is aligned with the leading edge of the image forming range on the sheet based on a detection signal output from a pre-registration detection switch (not shown). Is set to

The fixing unit 12 includes a heat roller 31, a pressure roller 32, and the like, and the heat roller 31 and the pressure roller 32 rotate with the sheet interposed therebetween.
The heat roller 31 is set to a predetermined fixing temperature by the control unit based on a signal from a temperature detector (not shown), and is transferred to the sheet by thermocompression bonding the sheet together with the pressure roller 33. The resulting multicolor toner image is melted, mixed, and pressed to thermally fix the sheet.

  The sheet on which the multicolor toner image has been fixed is transported to the reverse paper discharge path of the paper transport path S by the transport rollers 25, and is discharged in a reversed state (with the multicolor toner image facing downward). The paper is discharged onto the paper tray 15.

<Second Aspect of Image Forming Apparatus>
FIG. 4 is an explanatory diagram schematically showing each part of the electrophotographic process arranged around the photosensitive drum 3 in a monochrome image forming apparatus having a different form from the image forming apparatus 100 of FIG. Unlike the image forming apparatus of FIG. 3, a laser light emitting element 42 is used for exposure of the photosensitive member. In FIG. 4, the frame surrounded by the chain line is the laser scanning unit 1 constituting the laser optical system. As shown in FIG. 4, the laser beam emitted from the semiconductor laser 42 passes through a collimator lens and a cylindrical lens (not shown) for making the beam parallel light, and is reflected on the reflecting mirror constituting the polyhedron of the rotating polygon mirror 44. Then, after the scanning beam is formed, the surface of the photosensitive member is irradiated through the fΘ lens 45 and the cylindrical mirror 55. Then, a laser beam scanned in the direction parallel to the rotation axis of the photosensitive member, that is, the main scanning direction is irradiated on the surface of the photosensitive drum 3 that is rotationally driven by a photosensitive member driving motor (not shown).

  Around the photosensitive drum 3 as an image bearing member, a charging roller 5 as a charging station for charging the surface of the photosensitive member, a charging power supply 61 for applying a charging voltage to the charging roller 5, and a laser optical system are passed. An exposure station that irradiates the surface of the photosensitive member with a laser beam to form an electrostatic latent image corresponding to the image. A developing station composed of a developing roller 2A to which the toner is applied, a developing bias power supply 62 as a bias voltage applying unit for supplying a bias voltage to the developing roller, and the same speed as the photosensitive drum 3 by synchronizing the feeding timing to the electrostatic latent image. The transfer roller 6 which is a contact transfer unit for transferring toner to the sheet 60 conveyed by the transfer, a transfer power supply 63 for applying a transfer voltage to the transfer roller, and the photoreceptor surface after transfer A neutralizing lamp 59 that lowers the electrical resistance of the photosensitive member by irradiating light to discharge the electric charge on the surface of the photosensitive member, and a cleaner unit that removes untransferred toner remaining on the surface by a cleaning member that contacts the surface of the photosensitive drum 3 4 is arranged.

  Further, the sheet 60 on which the toner from the surface of the photosensitive member is transferred by the transfer unit is heated by a fixing unit (not shown), the toner on the sheet is melted, and after the toner is fixed to the sheet 60, the sheet 60 is discharged out of the apparatus. .

<Configuration of process control means>
Next, in the electrophotographic image forming apparatus shown in FIG. 4, the functional configuration of each part for controlling each part of the electrophotographic process arranged around the photosensitive drum 3 will be described. However, the image forming apparatus of FIG. 3 also has a control block for each of the photosensitive drums 3a, 3b, 3c, and 3d, and only the elements used for the charging station and the exposure station are different. Application of the present invention to the forming apparatus will be apparent to those skilled in the art. FIG. 5 is a block diagram showing a functional block configuration relating to control of each part of the electrophotographic process. As shown in FIG. 5, the image formation start instruction unit 80 is a block that sends an image formation instruction to the image formation control unit 81. For example, in the case of copier, the image formation start instructing unit 80 may be a program that detects that the user has pressed a copy start key provided on the operation panel. The program may be executed by a control CPU of the operation unit. Alternatively, it may be a program that receives print data from the host and starts printing the print data. The program may be executed by a control CPU. Upon receiving an image formation instruction from the image formation start instructing unit 80, the image formation control unit 81 receives each block related to image formation, for example, an image data processing unit 83, a polygon mirror drive circuit 85, a photoreceptor drive motor control unit 37, The charging power supply 61, the developing bias power supply 62, the transfer power supply 63, the charge removal lamp 59, the transfer roller drive motor control unit 37, and the like are controlled to execute an electrophotographic process related to image formation. The charging power supply 61, the developing bias power supply 62, the transfer power supply 63, and the charge removal lamp 59 correspond to FIG. Further, the image formation control unit 81 detects the degree of humidity by the humidity sensor 64 which is an operating environment detection unit. The image forming control unit 81 may be realized by a control CPU executing a program for controlling the image forming apparatus.

  The image data generation unit 82 is a block that generates image data to be printed by processing the image data read by the scanner in the case of copying. In the case of a printer, this is a block that develops print data received from the host and generates image data to be printed. The image data processing unit 83 is a block that processes the image data generated by the image data generation unit 82 and outputs it as a signal for causing the laser light emitting element 42 to emit light. The image data processing unit 83 includes a function as an exposure gradation selection unit that determines the intensity at which the laser light emitting element 42 emits light corresponding to the gradation of the image according to conditions such as the image mode. The laser drive circuit 84 drives the laser light emitting element 42 in accordance with the on / off of digital representation and the light emission intensity information from the image data processing unit 83. In laser drive, the drive current, that is, the laser power may be continuously changed according to the emission intensity, but the time-sharing drive is performed to perform duty control according to the emission intensity to control the temporal average laser power. Alternatively, a driving method in which both are combined may be used. The polygon mirror drive circuit 85 starts / stops the polygon mirror drive motor 46. The photoconductor drive motor control unit 37 controls the start / stop and rotation speed of the photoconductor drive motor 56.

  Further, the image formation control unit 81 controls the charging power supply 61, the developing bias power supply 62, and the transfer power supply 63 to turn on / off at predetermined timings respectively. A voltage having a magnitude determined by correction or correction for humidity is output.

  Further, the image formation control unit 81 turns on / off the static elimination lamp 59 at a predetermined timing, and the transfer roller drive motor control unit 38 controls the start / stop and the rotation speed of the transfer roller drive motor 13.

<Process control characteristics>
FIG. 1 is an explanatory view schematically showing an example of the relationship between the electrostatic latent image potential and the development potential in the electrophotographic process according to this embodiment. FIG. 1A shows that the charging potential Vdc on the surface of the photosensitive drum by the charging roller 5 is −600 V with respect to 0 V, that is, the ground potential. Here, the charging potential is a voltage substantially equal to the output voltage of the charging power source.

  FIG. 1B shows the characteristics of the latent image potential with respect to each gradation after scanning the surface of the photoconductor whose surface is charged uniformly at −600 V with a laser beam and performing exposure according to the density of the image. Show. When the area gradation technique is used, it is the average of the secondary distribution of the latent image potential. The horizontal arrow indicates the correspondence between the latent image potential and the brightness of the image. The brightest white part of the image is not exposed at all. Accordingly, the latent image potential of the white background portion is equal to the charging potential and is −600V. On the other hand, since the dark part of the image is exposed most intensely, the potential drops to near the ground potential and is -50V. The gradation characteristic between the bright part and the dark part, so-called γ characteristic, consists of a finite gradation in order to handle the density as digital data. The image data processing unit 83 can change the image quality setting such as text mode and photo mode and change with time. Then, the exposure intensity for each gradation is determined in accordance with corrections to changes in environmental conditions.

  The image formation control unit 81 holds a table that gives the value of the cleaning voltage corresponding to the detected humidity level. For example, when the degree of humidity detected by the humidity sensor 64 is h1, −150 V is obtained as the value of the cleaning voltage Vch1 with respect to h1. Since the charging potential Vdc is −600 V, the value of the bias voltage Vdh1 is set to −450 V so as to ensure the cleaning voltage Vch1. At this time, the potential difference Vkh1 between the developing potential and the latent image potential in the dark part is 400V. The voltage Vkh1 is related to the strength of electrostatic force at which the toner of the developing station adheres to the dark portion, that is, the density of the toner image.

  In FIGS. 1A and 1B, the humidity is h1. On the other hand, FIG. 1C shows the control of the developing potential when the humidity level detected by the humidity sensor 64 is h2. Here, h2 has a higher humidity than h1. FIG. 1D shows the latent image potential for each gradation after exposure when the humidity level is h2. To prevent the toner charge amount from decreasing due to high humidity, which increases the toner adhesion amount in the dark area, and to maintain a constant toner adhesion amount, the exposure intensity is reduced. ing. For this reason, the potential of the latent image in the dark part is lower than that in the case where the humidity is h1, and becomes -80V.

  FIG. 1E shows the control of the developing potential when the humidity level is h2. The image formation control unit 81 obtains -100V as the value of the cleaning voltage corresponding to the detected humidity level. Since the charging potential Vdc is −600 V, the value of the bias voltage Vdh2 is set to −500 V so as to ensure the cleaning voltage Vch2. As mentioned above, fogging is difficult to occur when the humidity is high, so if the cleaning voltage is too high, the amount of toner on the white background is reduced, which results in an increase in the load on the cleaning blade used in the cleaner unit, resulting in blade wear. This is in order to prevent the occurrence of a harmful effect that the blade becomes fast or the blade is reversed. Although the developing potential is lower than that in FIG. 1C, the potential difference Vkh2 between the developing potential and the dark portion latent image potential is 420V, which is larger by 20V than Vkh1, since the latent image potential in the dark portion is also reduced by correcting the exposure intensity. become. However, since the transfer efficiency is lowered by correcting the transfer peripheral speed ratio of the transfer portion as will be described later, the density of the output image is kept substantially constant.

FIG. 7 is a graph showing an example of the relationship between the cleaning voltage and fog in the image forming apparatus of FIG. The horizontal axis in FIG. 7 is the cleaning voltage, which is the difference between the charging potential and the development potential, and the vertical axis is ΔR as an evaluation index of fog, which is the whiteness R1 of the printing surface of the transfer material before printing. (%) And the difference between the whiteness R2 (%) of the printed surface after printing and ΔR = R1-R2 (%). Considering the visual gradation discrimination ability, the value of the fogging ΔR is 2.0 or less. Desirably, and more desirably 1.0 or less.
In the characteristics shown in FIG. 7, in order to make ΔR 1.0 or less, it is sufficient to ensure 150 V or more as the cleaning voltage.

FIG. 2 is an explanatory diagram showing a state in which the charging potential is set to −650 V, which is 50 V lower than that in FIG. 1. The charging potential is corrected, for example, as a result of image density correction for the deterioration of the photoreceptor. Since the absolute value of the charging potential Vdc 'is larger than -600 V in the case of FIG. 1, it is necessary to increase the exposure intensity in accordance with the change in the charging potential if the latent image potential in the dark part is to be kept around -50 V. (See FIGS. 2A and 2B). Then, in order to secure -150V as the cleaning voltage Vch1, the development potential Vdh1 'is set to -500V (see FIG. 1C). As a result, the absolute value of the charging potential is larger than that in FIG. 1C, so that the potential difference Vkh1 ′ between the developing potential and the latent image potential in the dark portion is 450V lower than Vkh1, and becomes 450V. Vkh1 is increased to compensate for the decline.
When the degree of humidity is h2, the latent image potential in the dark part is set to −80 V by correcting the exposure intensity to be lower than that in FIG. 2B (FIG. 2D). Further, in order to secure −100 V as Vch2, the developing potential Vdh2 ′ is set to −550 V (see FIG. 2E).

As described above, by setting the cleaning voltage in accordance with the degree of humidity, it is possible to always obtain a stable image without fog. Even when the charging potential changes due to density correction or the like, a cleaning voltage corresponding to the degree of humidity is set.
Further, as described above, not only the exposure intensity, that is, the emission intensity of the laser light emitting element 42 is corrected according to the change in the charging potential, but also the exposure intensity is corrected according to the setting of the cleaning voltage according to the degree of humidity. Then, correction is performed so that the toner adhesion amount in the dark portion, that is, the image density is kept constant.

<Moving speed and transferability of contact transfer part>
FIG. 6 is a graph showing an example of transfer efficiency characteristics with respect to the transfer peripheral speed ratio in the image forming apparatus of FIG. Here, the transfer peripheral speed ratio is a ratio of the relative speed of the surface of the transfer roller 6 to the moving speed of the surface of the photosensitive drum 3 and the moving speed of the surface of the photosensitive drum 3. The state where the value of the transfer peripheral speed ratio is 0% is a state where the moving speed of the surface of the photosensitive drum 3 is equal to the moving speed of the surface of the transfer roller 6. 6, the transfer efficiency η when the moving speed of the surface of the photosensitive drum 3 is equal to the moving speed of the surface of the transfer roller 6 is about 87.5%, and the difference between the relative speeds is larger than this. The higher transfer efficiency is obtained. However, when the transfer peripheral speed ratio is 2.0% or more, the transfer efficiency reaches a peak, and even if the transfer peripheral speed ratio is increased, the transfer efficiency does not increase.

The change in image density due to the transfer peripheral speed ratio is considered to occur for the following reason. When the toner adhering to the surface of the photosensitive drum 3 is transferred to the transfer material, if there is a difference in the relative speed between the transfer material and the photosensitive drum, a physical action such as scrubbing off the toner works. It becomes easy to transfer to a transfer material.
However, if the transfer peripheral speed ratio is increased too much, the toner will not be sufficiently transferred inside the image line, and a so-called hollow-out phenomenon will occur in which the toner is transferred only to the edge portion. An appropriate transfer peripheral speed ratio is selected from the balance.

  In this embodiment, when the degree of humidity is h2, in order to reduce the burden on the cleaning unit, the cleaning voltage is reduced to easily cause fogging. However, if fog toner attached to the surface of the photosensitive drum 3 is transferred to the transfer material, the burden on the cleaning unit cannot be reduced. In addition, it is not preferable that fog is increased in the output image. Therefore, when the humidity level is h2, the transfer peripheral speed ratio is reduced as compared with the case of h1, the transfer efficiency is lowered, and fog toner easily remains on the surface of the photosensitive drum 3. When the transfer efficiency decreases, the density of the transferred image also decreases. However, by appropriately setting the degree of correction of the exposure intensity described above, the density of the transferred toner image, that is, the print density is changed with respect to the change in humidity. Control to stabilize.

<Numerical example of correction according to humidity>
As described above, Table 1 shows an example of selection of correction values when the cleaning voltage, laser power, and transfer peripheral speed ratio are corrected according to humidity.

  As shown in Table 1, the entire humidity range is divided into seven areas, and the area to which the detection result of the humidity sensor 64 belongs is set as the humidity area of the detection result. On the other hand, correction values for the cleaning voltage, laser power, and transfer peripheral speed ratio are determined in advance and stored as a correction value data table. The image formation control unit 81 refers to the data table and obtains each correction value for the detected humidity area. Then, the cleaning voltage, the laser power, and the transfer peripheral speed ratio are determined based on the obtained correction value. For example, the humidity detection may be performed at a constant sampling period set sufficiently short with respect to the temporal change of the humidity area. Alternatively, when the density correction for the environmental change is performed, the designer may determine appropriately such as performing the correction simultaneously with the correction.

It is explanatory drawing which shows typically an example of the relationship between the electric potential of the electrostatic latent image of the electrophotographic process in this Embodiment of this invention, and development potential. It is explanatory drawing which shows a mode when a charging potential is set to -650V low 50V with respect to FIG. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. FIG. 4 is an explanatory view schematically showing each part of an electrophotographic process arranged around a photosensitive drum in a monochrome image forming apparatus having a different form from FIG. 3. FIG. 5 is a block diagram showing a functional block configuration related to control of each part of the electrophotographic process shown in FIG. 4. 5 is a graph showing an example of transfer efficiency characteristics with respect to a transfer peripheral speed ratio in the image forming apparatus of FIG. 5 is a graph showing an example of a relationship between a cleaning voltage and fog in the image forming apparatus of FIG.

Explanation of symbols

1 laser scanning unit 1a, 1b, 1c, 1d exposure unit 2A developing roller 2, 2a, 2b, 2c, 2d developing unit 3, 3a, 3b, 3c, 3d photosensitive drum 4, 4a, 4b, 4c, 4d cleaner unit DESCRIPTION OF SYMBOLS 5 Charging roller 5a, 5b, 5c, 5d Charger 6, 6a, 6b, 6c, 6d Transfer roller 7 Transfer belt 8 Transfer conveyance belt unit 9 Transfer belt cleaning unit 10 Paper feed tray 12 Fixing unit 13 Transfer roller drive motor 14 Resist Roller 15 Paper discharge tray 16 Pickup roller 25 Transport roller 31 Heat roller 32 Pressure roller 33 Paper discharge tray 34 Transport direction switching guide 35 Side cover 36 Encoder 37 Photoconductor drive motor controller 38 Transfer roller drive motor controller 42 Semiconductor laser, Laser light emitting device 44 Polygon mirror 45 fΘ lens 46 Polygon mirror drive motor 55 Cylindrical mirror 56 Photoconductor drive motor 59 Static elimination lamp 60 Sheet 61 Charging power supply 62 Development bias power supply 63 Transfer power supply 64 Humidity sensor 71 Transfer belt drive roller 73 Transfer belt tension rollers 72, 74 Transfer belt driven roller 80 Image formation start instruction section 81 Image formation control section 82 Image data generation section 83 Image data processing section 84 Laser drive circuit 85 Polygon mirror drive circuit 100 Image forming apparatus S Paper transport path

Claims (7)

An image forming apparatus in which a charging station, an exposure station, a developing station, a contact transfer unit, and a cleaning station are arranged around an image carrier, and an image is formed by passing the surface of the image carrier through each station.
The image forming apparatus is an operating environment detection unit for detecting the humidity of the operating environment;
A bias voltage application unit for applying a bias voltage to the developing station;
A bias voltage setting unit for setting a bias voltage of the bias voltage application unit;
A transfer drive unit that drives a contact transfer unit that contacts the image carrier via a transfer material;
A transfer drive control unit for setting the drive speed of the transfer drive unit,
The bias voltage control unit sets the bias voltage so that the difference between the charging potential and the development potential becomes a predetermined voltage according to humidity,
The image forming apparatus, wherein the transfer driving control unit sets a driving speed so that a speed of a contact portion of the contact transfer unit with respect to the image carrier is a predetermined speed corresponding to humidity. The bias voltage control unit sets a bias voltage that gives a cleaning voltage according to the detected humidity level,
The image forming apparatus according to claim 1, wherein the transfer drive control unit sets a drive speed according to the detected humidity level.   The image forming apparatus according to claim 1, wherein the bias voltage application unit sets the bias voltage so that the difference between the charging potential and the developing potential is reduced as the humidity is higher.   The image forming apparatus according to claim 1, wherein the transfer drive control unit sets the relative speed of the contact transfer unit with respect to the image carrier to be lower as the humidity is higher.   The image forming apparatus according to claim 1, wherein the exposure station switches exposure intensity according to humidity.   6. The image forming apparatus according to claim 5, wherein the exposure station reduces the exposure intensity as the humidity increases. An image forming apparatus configured such that a charging station, an exposure station, a developing station, a contact transfer unit, and a cleaning station are arranged around the image carrier, and an image is formed by passing the surface of the image carrier through each station. A program to be executed by a computer to control
The image forming apparatus detects an operating environment humidity, an operating environment detecting unit, a bias voltage applying unit that applies a bias voltage to the developing station, and a contact transfer unit that contacts the image carrier via a transfer material A transfer driving unit for driving
The computer,
A bias voltage setting unit that sets the bias voltage application unit to apply the bias voltage to the development station so that the difference between the charging potential and the development potential is a predetermined voltage according to humidity;
A program that functions as a transfer drive control unit that sets a drive speed such that the speed of the contact portion of the contact transfer unit with respect to the image carrier is a predetermined speed corresponding to humidity.

Images