JP2006293161A - Image forming apparatus and control program therefor - Google Patents

Abstract

An image forming apparatus capable of stably obtaining an image having smooth gradation or no fog according to an image to be output by controlling a developing potential according to an exposure gradation characteristic.
An image forming apparatus in which a charging station, an exposure station, a developing station, and a transfer station are arranged around an image carrier, and an image is formed by passing the surface of the image carrier through each of the stations. An image forming apparatus that selects an exposure gradation by an exposure station corresponding to a gradation of an image to be output; a bias voltage application unit that applies a bias voltage to the developing station; and a bias voltage application A bias voltage setting unit that sets a bias voltage of the image forming unit, and the bias voltage control unit sets the bias voltage so that a difference between the charging potential and the development potential becomes a predetermined voltage corresponding to the exposure gradation. An image forming apparatus.
[Selection] Figure 1

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 exposure gradation characteristics and a control program therefor.

  Image forming devices such as electrophotographic printers, copiers, and digital multifunction peripherals have a charging station, exposure station, developing station, transfer station, static eliminator, and cleaning around a cylindrical or endless belt-shaped photoreceptor. It has a configuration in which parts 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, charged toner is supplied from a developing station having a predetermined developing bias potential to the surface of the photoreceptor on which the electrostatic latent image is formed, and toner corresponding to the potential difference from the electrostatic latent image is attached by electrostatic force. A toner image is formed on the surface of the photoreceptor, and the toner is transferred to a transfer material to obtain a print output.

  The tone characteristics of the image depend on the discharge characteristics with respect to the exposure intensity of the photoconductor and the development amount (toner adhesion amount) characteristics with respect to the potential difference between the photoconductor potential and the development potential, and the output image is completely faithful to the original image. It is practically difficult to get. For this reason, improvements were examined from various viewpoints such as various conditions of the electrophotographic process, that is, setting of charging potential, development potential, toner miniaturization, developer material and shape, and development conditions, and practically acceptable characteristics were realized. is doing. Furthermore, in recent years, by digitizing and processing images, the degree of freedom of image processing has been increased, and improved image quality can be obtained by applying image filters, area gradation techniques, and other image processing techniques. It has become. However, not all image processing-specific characteristics can be compensated by image processing alone. Therefore, various methods are known for controlling the charging potential, the exposure intensity, and the developing potential so as to stabilize the image density against environmental changes and temporal changes (see, for example, Patent Document 1).

  Particularly in recent years, as colorization of image forming apparatuses progresses, stability of image quality tends to be emphasized. However, the parameters for evaluating the image quality are not only the gradation characteristics, but also the density, contrast, sharpness, uniformity of the solid part, fogging of the bright part, that is, toner adhesion to the brightest part of the image where the toner should not originally adhere. There are many factors such as the reproducibility of characters and line drawings. Some of these elements are contradictory to each other, for example, contrast and gradation, and it is technically difficult to achieve all of them. In addition, the number of types of transfer materials tends to increase with colorization. For example, smooth paper or glossy paper is often used to pursue high image quality as a color. Such kind of transfer material is different from plain paper in its surface properties and thickness.

Therefore, for images mainly consisting of characters and line drawings, a mode that gives an image with so-called γ characteristics with emphasis on line reproducibility, density and contrast, so-called text mode, is selected and selected. For an image where gradation is important, such as a mode in which an image with a moderate γ characteristic is obtained, a so-called photo mode is selected. There may also be an intermediate mode (graphic mode). Which is selected is often determined by the user's will on a user interface such as an operation panel or a dialog box for setting printing conditions.
Further, there is a type in which a mode is selected according to the paper type. For example, for a thick transfer material, there is a mode in which a sheet conveyance speed is reduced to secure a fixing time, a toner fixing property is improved, and a transfer voltage is increased to prevent transfer efficiency from being lowered.

  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. The reproducibility of characters and line drawings is related to the difference between the charging potential and the developing potential, that is, the cleaning voltage.

Conventionally, an apparatus that optimally controls the cleaning voltage is known. 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, there is known a method of controlling the charging potential or the developing potential so that the potential difference between the latent image potential and the developing bias 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. However, there is no disclosure that controls the cleaning voltage for a so-called tandem type image forming apparatus.
There is a demand for an image forming apparatus that can reproduce an image with little fog or a line without thinning in accordance with each mode.
Japanese Patent Laid-Open No. 9-101641

  In the text mode with γ characteristics, an image with high contrast is obtained, and image formation is performed under conditions that do not cause thinning of characters and line drawings. However, there is a limit to satisfy all the requirements for image quality only by switching image processing and exposure gradation characteristics. Therefore, the exposure gradation characteristics, the charging potential, the developing potential, etc. are appropriately set. In particular, it is preferable to appropriately control the cleaning voltage in order to realize an image quality without thinning of characters and line drawings.

  On the other hand, in the photo mode with a gentle γ characteristic, image formation is performed under such a condition that an image with reduced fog and tone gap can be obtained. However, since there is a limit to satisfy all the requirements for image quality by only switching image processing and exposure gradation characteristics, exposure gradation characteristics, charging potential, development potential, and the like are appropriately set. In particular, it is preferable to appropriately control the cleaning voltage in order to realize an image in which the fog, characters, and tone gap in the bright part are suppressed. In particular, with a transfer material having a smooth surface, the fog toner adhering to the photosensitive member is easily transferred to the transfer material and fog is likely to occur. Therefore, it is preferable to appropriately control the cleaning voltage.

  The present invention has been made in consideration of such circumstances, and by controlling the development potential according to the exposure gradation characteristics, an image formation in which an image having no line thinness or an image with less fog is stably obtained. A device is provided.

  The present invention is an image forming apparatus in which a charging station, an exposure station, a developing station, and a transfer station are arranged around an image carrier, and an image is formed by passing the surface of the image carrier through each of the stations. An image forming apparatus that selects an exposure gradation by an exposure station corresponding to a gradation of an image to be output; a bias voltage application unit that applies a bias voltage to the developing station; and a bias voltage application A bias voltage setting unit that sets a bias voltage of the image forming unit, and the bias voltage control unit sets the bias voltage so that a difference between the charging potential and the development potential becomes a predetermined voltage corresponding to the exposure gradation. An image forming apparatus is provided.

  In the image forming apparatus according to the present invention, the bias voltage control unit sets the bias voltage so that the difference between the charging potential and the developing potential becomes a predetermined voltage corresponding to the exposure gradation. A cleaning voltage can be selected. As a result, in the text mode mainly consisting of characters and line drawings, a small cleaning voltage is set so that an image with less thin characters and line drawings can be obtained. Therefore, it is possible to set a cleaning voltage that can realize a smooth gradation with little.

The image forming apparatus of the present invention is an image forming apparatus in which a charging station, an exposure station, a developing station, and a transfer 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 exposure gradation selection unit that selects an exposure gradation by an exposure station corresponding to a gradation of an image to be output, and a bias voltage application unit that applies a bias voltage to the development station. A bias voltage setting unit that sets a bias voltage of the bias voltage application unit, and the bias voltage control unit is configured so that a difference between the charging potential and the development potential becomes a predetermined voltage corresponding to the exposure gradation. Is set.
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 the case of the charging roller, the material is not particularly limited as long as the image carrier can be charged by applying a voltage. 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 development bias voltage. For example, a transfer roller is preferably used as the transfer station material. However, the transfer station material 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 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 image forming apparatus further includes an image mode selection unit that performs selection related to the gradation characteristics of the image, and the exposure gradation selection unit is configured to select an exposure gradation according to the selected image mode. May be.
The image forming apparatus further includes a paper type selection unit that selects an image forming condition according to the type of transfer material, and the bias voltage application unit determines that a difference between the charging potential and the development potential depends on the paper type. The voltage may be applied to the developing station so that the corrected voltage is obtained. In this way, the transfer voltage is set to an appropriate level for the transfer material type, especially the transfer material whose surface properties are significantly different from the normal transfer material, and image quality with little fogging for any transfer material. Can be obtained.

The transfer station drives a contact transfer unit that contacts the image carrier via a transfer material, and the speed of the contact portion of the contact transfer unit with respect to the image carrier is determined according to the exposure gradation. And a transfer drive control unit that sets the drive speed of the transfer drive unit so as to achieve the above-described speed. In this way, by setting the transfer peripheral speed ratio, which is the ratio of the relative speed of the contact part of the contact transfer part to the speed of the image carrier and the speed of the image carrier, according to the exposure gradation, In the text mode where the optimum transfer efficiency is set according to the tone and a cleaning voltage smaller than that in the photo mode is set, the transfer peripheral speed ratio is set so that the transfer efficiency is lower than that in the photo mode, thereby suppressing fogging. Can do.
Here, the transfer driving unit may be any unit that moves the surface of the contact transfer member at a predetermined speed, and the type and structure of the driving source are not particularly limited.

  From a different point of view, according to the present invention, a charging station, an exposure station, a developing station, and a contact transfer unit are arranged around the image carrier, and an image is formed by passing the surface of the image carrier through the stations. An exposure gradation that is executed by a computer to control the image forming apparatus configured as described above, wherein the image forming apparatus selects an exposure gradation by an exposure station corresponding to a gradation of an image to be output A selection unit and a bias voltage application unit that applies a bias voltage to the development station, and the computer applies a bias voltage that sets a difference between the charging potential and the development potential to a predetermined voltage according to the exposure gradation. Program for functioning as a bias voltage setting unit for setting the bias voltage application unit to be applied to the developing station To provide.

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, and is disposed in the developing device 2 so that toner is applied to the surface of the photosensitive member in accordance with the potential of each image area of the electrostatic latent 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. A transfer roller 6 that is a contact transfer member for transferring toner to the sheet 60 conveyed by the transfer, a transfer power source 63 that applies a transfer voltage to the transfer roller, and a photoconductor after transfer. A neutralizing lamp 59 for irradiating the surface with light to lower the electrical resistance of the photoreceptor and discharging the charge on the surface of the photoreceptor, and a cleaner for removing untransferred toner and the like remaining on the surface by a cleaning member in contact with the surface of the photoreceptor drum 3 Unit 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. It 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 a copier, the image formation start instruction 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 a humidity detection unit. The image formation 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.

  FIG. 1C shows control of the developing potential of the developing station with respect to the latent image potential in the text mode. The image formation control unit 81 holds a table storing cleaning voltage values corresponding to the selected exposure gradation. For example, -100 V is obtained as the value of the cleaning voltage Vcg1 for the exposure gradation G1 for the text mode. A large cleaning voltage is advantageous in terms of fog, but if it is too large, the line becomes thin and thin. Therefore, the setting value selected to achieve both of these factors is -100V. Since the charging potential Vdc is −600 V, the value of the developing bias voltage Vdg1 is set to −500 V so as to ensure the cleaning voltage Vcg1.

  FIG. 1D shows the characteristics of the latent image potential for each gradation in the photo mode. As shown in FIG. 1D, the gradation of the photo mode is gentler than the gradation of the text mode of FIG. 1B, and is set to a characteristic that emphasizes gradation rather than contrast. ing. FIG. 1E shows control of the developing potential of the developing station with respect to the latent image potential for the photo mode. The image formation control unit 81 obtains −150 V as the value of the cleaning voltage Vcg2 for the exposure gradation G2 for the photo mode. In the photo mode, it is important to reproduce the gradation of the bright area more smoothly than the thinning of characters and line drawings. The value is -150V. Then, the value of the developing bias voltage Vdg2 is set to −450 V so as to ensure the cleaning voltage Vcg2.

FIG. 2 is an explanatory diagram schematically showing an example of the relationship between the electrostatic latent image potential and the development potential in the electrophotographic process in the graphic mode having intermediate characteristics between the text mode and the photo mode. Also, cleaning voltage control for different transfer material types is shown. FIG. 2A shows the characteristics of the latent image potential for each gradation in the graphic mode. The gradation characteristics in the text mode in FIG. 1B or the gradation characteristics in the photo mode in FIG. Correspond. FIG. 2B shows control of the developing potential of the developing station with respect to the latent image potential for the graphic mode. FIG. 2B corresponds to the gradation characteristics of the text mode of FIG. 1C or the gradation characteristics of the photo mode of FIG. The image formation control unit 81 obtains −150 V as the value of the cleaning voltage Vcg3 for the exposure gradation G3 for the graphic mode. Then, the developing bias voltage Vdg3 is set to −450 V so as to ensure the cleaning voltage Vcg3.
The text mode, graphic mode, and photo mode are selected by the user's operation on the user interface such as an operation panel or a dialog box for setting printing conditions. However, image processing that determines the type of image is performed. The mode may be selected by the forming apparatus without depending on the user's operation.

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 W1 of the printing paper surface before printing, printing Assuming that the whiteness W2 of the surface of the non-toner image area of the word printing paper is R = W1-W2, 1.0 was used as an index for visual identification.
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.

  As described above, by setting the cleaning voltage in accordance with the image mode, it is possible to obtain an image with less thinness of characters and line drawings, or an image with less fog and smooth gradation in the bright part. Even when the charging potential changes due to density correction or the like, a cleaning voltage corresponding to the mode is set.

Further, FIG. 2C shows the characteristics of the latent image potential for each gradation in the graphic mode when the paper type is glossy paper, and FIG. 2D shows the graphic when the paper type is glossy paper. The control of the developing potential of the developing station with respect to the latent image potential for the mode is shown. The paper type setting is determined by a user operation on a user interface such as an operation panel or a dialog box for setting printing conditions. Alternatively, the image forming apparatus may execute a process for discriminating the type of the transferred transfer material using a sensor, and the mode may be selected without depending on a user operation.
Glossy paper is coated with a resin to give its surface gloss, and its surface properties are significantly different from normal paper. Compared to normal paper having a rough surface, the toner on the photoreceptor is more likely to adhere to the transfer material and fog is likely to occur. For this reason, the cleaning voltage is increased to reduce the fog on the photoconductor as compared with a normal transfer material, thereby suppressing the occurrence of fog in the print output.
2C and 2D show the characteristics when the glossy paper is passed in the graphic mode, the cleaning voltage is increased for the text mode and the photo mode as in the graphic mode. Make corrections.

<Moving speed and transferability of contact transfer member>
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, in the text mode, the transfer peripheral speed ratio is increased as compared with the photo mode, the transfer efficiency is increased, and the thinning of characters and line drawings is reduced.
Further, in the case of glossy paper, the transfer peripheral speed ratio is made smaller than that of a normal transfer material, and the transfer efficiency is lowered to reduce the fog on the transfer material.

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

表１に示すように、文字や線画のやせ細りを抑制するためにフォトモードやグラフィックモードのクリーニング電圧設定値の-150Ｖに比べてテキストモードのクリーニング電圧を50Ｖ小さい-100Ｖに設定している。一方、転写周速比は、フォトモードやグラフィックモードの1.0％の設定値よりも0.5％高い1.5％に設定し、転写効率を上げることによって文字や線画のやせ細りを抑制している。

As shown in Table 1, the text mode cleaning voltage is set to -100 V, which is 50 V smaller than the cleaning voltage setting value of -150 V in the photo mode and graphic mode, in order to suppress thinning of characters and line drawings. On the other hand, the transfer peripheral speed ratio is set to 1.5%, which is 0.5% higher than the set value of 1.0% in the photo mode and graphic mode, and the thinning of characters and line drawings is suppressed by increasing the transfer efficiency.

<Numerical example of correction according to the moving speed of the photoreceptor surface>
Table 2 shows a selection example of correction values when the cleaning voltage and the transfer peripheral speed ratio are corrected according to the moving speed of the photosensitive member surface.

表２に示すように、通常の転写材を想定したモノクロモードやカラーモードのクリーニング電圧設定値の-150Ｖに比べて光沢紙のクリーニング電圧を50Ｖ大きい-200Ｖに設定している。これによって、光沢紙がカブリにくくしている。一方、転写周速比は、モノクロモードやカラーモードの1.0％の設定値よりも0.25％低い0.75％に設定し、転写効率を下げることによって転写効率を下げ、光沢紙がカブリにくくしている。

As shown in Table 2, the glossy paper cleaning voltage is set to -200 V, which is 50 V larger than the cleaning voltage setting value of -150 V in the monochrome mode and color mode assuming a normal transfer material. This makes glossy paper difficult to fog. On the other hand, the transfer peripheral speed ratio is set to 0.75%, which is 0.25% lower than the set value of 1.0% in the monochrome mode and the color mode. By reducing the transfer efficiency, the transfer efficiency is lowered, and glossy paper is not easily fogged.

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 typically an example of the relationship between the electric potential of the electrostatic latent image of an electrophotographic process and the developing potential in the graphic mode having an intermediate characteristic between the text mode and the photo mode. 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 (5)

An image forming apparatus in which a charging station, an exposure station, a developing station, and a transfer station are arranged around an image carrier, and an image is formed by passing the surface of the image carrier through the stations.
An exposure gradation selection unit that selects an exposure gradation by an exposure station in accordance with the gradation of an image to be output;
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,
The image forming apparatus, wherein the bias voltage control unit sets a bias voltage so that a difference between a charging potential and a developing potential becomes a predetermined voltage corresponding to an exposure gradation. An image mode selection unit for performing selection related to the gradation characteristics of the image;
The image forming apparatus according to claim 1, wherein the exposure gradation selection unit selects an exposure gradation according to a selected image mode. A paper type selection unit for selecting an image forming condition according to the type of transfer material;
The image forming apparatus according to claim 1, wherein the bias voltage applying unit applies a voltage to the developing station so that a difference between the charging potential and the developing potential becomes a voltage corrected according to a sheet type. The transfer station is
A transfer drive unit that drives a contact transfer unit that contacts the image carrier via a transfer material;
The image forming apparatus according to claim 1, further comprising: a transfer driving control unit that sets a driving speed of the transfer driving unit so that a speed of the contact unit of the contact transfer unit with respect to the image carrier becomes a predetermined speed according to the exposure gradation. apparatus. A charging station, an exposure station, a developing station, and a contact transfer unit are arranged around the image carrier, and an image forming apparatus configured to form an image by passing the surface of the image carrier through the stations is controlled. A program to be executed by a computer,
The image forming apparatus includes an exposure gradation selection unit that selects an exposure gradation by an exposure station corresponding to a gradation of an image to be output, and a bias voltage application unit that applies a bias voltage to the development station,
The computer functions as 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 corresponding to the exposure gradation. Program to make.

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