JP2019219541A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that effectively prevents rear-end accumulation.SOLUTION: Developing devices 3a to 3d attach a toner to electrostatic latent images on photoreceptor drums 1a to 1d by using a two-component developer. A controller 33, when a predetermined condition is established, decreases a target value of a toner ratio in the two-component developer in the developing devices 3a to 3d to prevent rear-end accumulation. A screen processing unit 41, when the predetermined condition is established, reduces the number of screen lines in screen processing to prevent rear-end accumulation.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus such as a printer, the same image forming is performed due to a change in temperature and humidity in the apparatus, abrasion due to durability of a photosensitive drum, a change in toner chargeability in a leaving environment, and deterioration of other parts. Even when an image is formed under the conditions, the amount of toner adhering to the photosensitive drum changes, the toner density in the toner image may not be constant, and the image quality may not be stable. Therefore, calibration is performed to adjust the image density.

  The parameters for adjusting the image density by calibration in the touch-down development method include (a) the potential difference between the photoconductor and the sleeve roller (development bias), and (b) the potential difference between the mag roller and the sleeve roller (conveyance). Bias) and (c) the amount of exposure. The developing bias and the transport bias are parameters for adjusting the solid density, and the exposure amount is a parameter for adjusting the half density (halftone density). By appropriately setting the developing bias and the conveying bias, an appropriate toner layer thickness is secured on the sleeve roller, and the toner on the sleeve roller flies onto the drum by setting the developing bias. A concentration is achieved.

  In one image forming apparatus, a magnetic brush is formed on a developing sleeve with a two-component developer, and toner is attached to the electrostatic latent image on the photosensitive drum with the magnetic brush. The amplitude of the AC component of the developing bias is adjusted based on the difference between the measured density value and the measured density value at the edge of the image, thereby suppressing edge enhancement at the edge in the sub-scanning direction. reference).

JP-A-5-66654

  At the rear end of the solid image, the above-described edge enhancement occurs due to the edge effect. In particular, when an amorphous silicon photosensitive drum is used, the amorphous silicon photosensitive drum has a high relative dielectric constant and can hold a large amount of toner. The density of the solid image is controlled by forming a thin toner layer on the developing roller at a saturation density of less than or equal to and adhering all the formed toner layer to the photoreceptor. Then, since the developing roller rotates at a higher speed than the photosensitive drum, a large amount of toner adheres to the rear end portion of the solid image, and the rear end accumulation becomes conspicuous. However, in the method of adjusting the amplitude of the AC component of the developing bias as in the above-described image forming apparatus, it is difficult to sufficiently suppress the rear end accumulation when a photosensitive drum having such a high relative dielectric constant is used. It is.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus that effectively suppresses rear end accumulation.

  An image forming apparatus according to the present invention includes: a photosensitive drum; and a developing device that uses a two-component developer to attach toner to an electrostatic latent image on the photosensitive drum. A controller configured to reduce a target value of a toner ratio of the two-component developer in the developing device in order to suppress the end accumulation.

  An image forming apparatus according to the present invention includes a photosensitive drum, a developing device that attaches toner to an electrostatic latent image on the photosensitive drum using a two-component developer, and a developing device that prints an image to be printed by the printing device. A screen processing unit that performs screen processing. Then, when a predetermined condition is satisfied, the screen processing unit reduces the screen ruling of the screen processing in order to suppress rear end accumulation.

  According to the present invention, it is possible to obtain an image forming apparatus that effectively suppresses rear end accumulation.

  The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a sectional view showing an example of the developing device 3a in FIG. FIG. 3 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram for explaining the relationship between the screen ruling and the number of trailing pixels. FIG. 5 is a flowchart illustrating the operation of the image forming apparatus illustrated in FIGS. 1 and 3.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copier, and a multifunction peripheral.

  The image forming apparatus of this embodiment has a tandem type color developing device. This color developing device has photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are photoconductors of four colors of cyan, magenta, yellow and black. For example, the photosensitive drums 1a to 1d are made of amorphous silicon, and this developing device performs development by a touch-down developing method. Further, the developing rollers in the developing devices 3a to 3d rotate at a higher speed than the photosensitive drums 1a to 1d (at a speed of about 1.6 to 1.8 times). For this reason, the rear end accumulation is likely to occur.

  The exposing devices 2a to 2d are devices that irradiate the photosensitive drums 1a to 1d with laser light while scanning them to form electrostatic latent images. The laser light is scanned in a direction (main scanning direction) perpendicular to the rotation direction (sub-scanning direction) of the photosensitive drums 1a to 1d. Each of the exposure devices 2a to 2d has a laser diode which is a light source of laser light, and a laser scanning unit including an optical element (a lens, a mirror, a polygon mirror, etc.) for guiding the laser light to the photosensitive drums 1a to 1d.

  Further, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged around the photosensitive drums 1a to 1d. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the charge remover removes the charges on the photosensitive drums 1a to 1d after the primary transfer.

  The developing devices 3a to 3d attach toner to the electrostatic latent images on the photosensitive drums 1a to 1d using a two-component developer. Specifically, the developing devices 3a to 3d have toner containers filled with toners of four colors of cyan, magenta, yellow and black, and transfer the toners to the electrostatic latent images on the photosensitive drums 1a to 1d. To form a toner image. The toner forms a two-component developer together with the carrier, and further includes an external additive such as titanium oxide.

  Magenta is developed by the photosensitive drum 1a, the exposure device 2a and the developing device 3a, and cyan is developed by the photosensitive drum 1b, the exposure device 2b and the developing device 3b, and the photosensitive drum 1c and the exposure device 2c are developed. The developing unit 3c develops yellow, and the photosensitive drum 1d, the exposing unit 2d, and the developing unit 3d develop black.

  The intermediate transfer belt 4 is an annular image carrier (intermediate transfer member) that comes into contact with the photoconductor drums 1a to 1d and primarily transfers the toner images on the photoconductor drums 1a to 1d. The intermediate transfer belt 4 is stretched around a driving roller 5 and circulates in a direction from a contact position with the photosensitive drum 1d to a contact position with the photosensitive drum 1a by a driving force from the driving roller 5.

  The transfer roller 6 makes the conveyed paper contact the intermediate transfer belt 4 and secondary-transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, contacts the cleaning brush with the intermediate transfer belt 4, and removes the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 irradiates the intermediate transfer belt 4 with a light beam and detects reflected light from the surface of the intermediate transfer belt 4 or a toner pattern on the surface. For example, when adjusting the toner density, the sensor 8 irradiates a predetermined area of the intermediate transfer belt 4 with a light beam, detects reflected light of the light beam, and outputs an electric signal corresponding to the light amount.

  FIG. 2 is a sectional view showing an example of the developing device 3a in FIG. Although FIG. 2 illustrates the developing device 3a, the developing devices 3b to 3d have the same configuration, and the same toner concentration sensor 15 as the toner ratio sensor 15 is provided for the developing devices 3b to 3d. Are provided respectively.

  As shown in FIG. 2, the developing device 3a includes a housing 11, a stirring screw 12, a magnetic roller 13, and a developing roller 14.

  A toner container (not shown) is connected to the developing device 3a, and toner is supplied from the toner container into the housing 11 through a supply port by a toner supply mechanism (not shown). In the housing 11, the two-component developer containing the non-magnetic toner and the magnetic carrier is stirred by the stirring screw 12.

  The magnetic roller 13 holds the two-component developer on its surface in a brush shape. The toner in the two-component developer is transferred to the developing roller 14 according to a transport bias that is a voltage between the magnetic roller 13 and the developing roller 14.

  The developing roller 14 holds the toner transferred from the magnetic roller 13 on its surface as a thin toner layer. That is, the developing roller 14 holds the toner to be attached to the electrostatic latent image on the photosensitive drum 1a. The toner layer formed on the surface of the developing roller 14 is a voltage between the developing roller 14 and the photosensitive drum 1a. The developing bias shifts to the photosensitive drum 1a. The photoconductor drum 1a is an image carrier on whose surface an electrostatic latent image is formed by the exposure device 2a. The toner transferred from the developing roller 14 adheres to the electrostatic latent image on the photosensitive drum 1a.

  As shown in FIG. 2, the toner ratio sensor 15 is provided on the bottom surface of the developing device 3a, and a toner ratio of the two-component developer at a predetermined measurement position in the housing 11 of the developing device 3a (that is, the toner and the carrier). (T / C ratio). Specifically, the toner ratio sensor 15 detects the relative magnetic permeability of the two-component developer corresponding to the toner ratio.

  FIG. 3 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 3, the image forming apparatus includes a communication device 21, an arithmetic processing device 22, and a printing device 23.

  The communication device 21 is a device that can be connected to a host device via a network or a peripheral device interface and performs data communication using a predetermined communication protocol.

  The arithmetic processing unit 22 includes an ASIC (Application Specific Integrated Circuit) and / or a computer, and implements various processing units using hardware and / or software. The computer includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, loads a program from a storage device (not shown), the ROM, or the like to the RAM, and executes the program by the CPU. Thus, various processing units are realized by software.

  The printing device 23 is an internal device that prints an original image with a mechanical configuration as shown in FIGS.

  In this embodiment, the arithmetic processing unit 22 operates as a processing unit such as an operating system (not shown), a communication processing unit 31, a rendering unit 32, a controller 33, and an image processing unit 34.

  The communication processing unit 31 is a processing unit that controls the communication device 21 to execute data communication with a host device or the like. For example, the communication processing unit 31 receives document data as a print request from the host device.

  Further, the rendering unit 32 receives a print request based on a user operation on the operation panel or a print request supplied from the host device, and executes a print job according to the request. For example, when document data in a predetermined data format such as PDL (Page Description Language) and PDF (Portable Document Format) is received from the host device as a print request, the rendering unit 32 converts the bitmap image data from the document data. Generate This bitmap image data is, for example, 8-bit RGB data. When the original data of the bitmap data is received from the host device, the rendering unit 32 uses the original data as it is as the image data.

  The controller 33 is a processing unit that monitors and controls an internal device such as the printing device 23. The controller 33 controls a drive source (not shown) for driving the above-described rollers, a bias application circuit for applying a developing bias and a primary transfer bias, and the exposure devices 2a to 2d to develop, transfer, and fix the toner image. , And a processing circuit for executing paper feeding, printing, and paper discharging. The developing bias is applied between the photosensitive drums 1a to 1d and the developing devices 3a to 3d, respectively, and the primary transfer bias is applied between the photosensitive drums 1a to 1d and the intermediate transfer belt 4, respectively.

  The controller 33 controls the toner from the toner container to the developing devices 3a to 3d based on the sensor output signal of the toner wide area sensor 15 so that the toner ratio of the two-component developer in the developing devices 3a to 3d becomes the target value. Control the supply. Then, the controller 33 lowers the target value of the toner ratio of the two-component developer in the developing devices 3a to 3d in order to suppress the rear end accumulation when a predetermined condition in which the rear end accumulation easily occurs is satisfied. .

  Specifically, the controller 33 controls the toner ratio of the two-component developer in the developing devices 3a to 3d to suppress the trailing edge accumulation when the toner consumption at the predetermined number of prints is equal to or more than the predetermined value. Lower the target value.

  That is, when the toner consumption is large, the charge amount of the toner in the developing devices 3a to 3d decreases, and the toner density increases, so that the amount of the trailing edge accumulation increases. Therefore, by lowering the target value of the toner ratio, the charge amount of the toner in the developing devices 3a to 3d is increased.

  Alternatively, when the toner consumption at the predetermined number of prints is equal to or more than the predetermined value and the driving time of the developing devices 3a to 3d is equal to or more than the predetermined value per one sheet at the predetermined number of prints, the controller 33 sets In order to suppress this, the target value of the toner ratio of the two-component developer in the developing devices 3a to 3d is reduced.

  The toner consumption is specified by an existing method based on the image data. Further, as the toner consumption, a printing rate corresponding to the toner consumption may be specified based on the image data.

  Further, the image processing unit 34 performs predetermined image processing such as color conversion (for example, color conversion from RGB data to CMYK data), gamma correction, and screen processing on the image data, and print data (for example, color data). (Print image data binarized for each plane). The image processing unit 34 includes a screen processing unit 41.

  The screen processing unit 41 performs screen processing of an image to be printed by the printing device 23. The screen processing unit 41 reduces the screen ruling of the screen processing in order to suppress the rear end pool when a predetermined condition in which the rear end pool is likely to occur is satisfied.

  Specifically, the screen processing unit 41 reduces the screen ruling of the screen processing in order to suppress the trailing edge accumulation when the toner consumption at the predetermined print number is equal to or more than the predetermined value.

  Alternatively, the screen processing unit 41 determines that the toner consumption amount at the predetermined number of prints is equal to or more than a predetermined value, and that the driving time of the developing devices 3a to 3d per predetermined number of prints is equal to or more than the predetermined value. In order to suppress the trailing edge accumulation, the screen ruling of the screen processing is reduced.

  FIG. 4 is a diagram illustrating the relationship between the screen ruling and the number of trailing pixels. As shown in FIG. 4, even if the screen expresses the same density, as the number of screen lines increases, the number of lines increases, and the total number of trailing pixels in the sub-scanning direction in all lines also increases.

  Further, in this embodiment, the screen processing unit 41 determines the screen ruling of the screen processing when the toner consumption amount in the predetermined period is equal to or more than the predetermined value, and when the image to be printed is a character document image. If the image to be printed is not a character document image without lowering, the screen ruling of the screen processing is reduced in order to suppress trailing edge accumulation.

  Next, the operation of the image forming apparatus will be described. FIG. 5 is a flowchart illustrating the operation of the image forming apparatus illustrated in FIGS. 1 and 3.

  The controller 33 controls the printing device 23 to execute continuous printing of a plurality of pages. At the start of printing, the controller 33 sets a counter for the number of prints n to zero. After the start of printing (step S1), the controller 33 sets the default toner ratio target value in the developing devices 3a to 3d and sets the default screen ruling in the screen processing unit 41 (step S2). The print ratio of each print page and the drive time of the developing devices 3a to 3d (development drive time) are derived, and the number of prints n is counted each time one print is completed (step S3). It is determined whether or not it is equal to or greater than THa (step S4).

  If the number n of prints is equal to or greater than the threshold value THa, the controller 33 calculates an average printing ratio X and a development drive time t per one of the n prints (steps S5 and S6). Thereafter, the controller 33 resets the counter for the number of prints n to zero (step S7). The average printing ratio X for n prints corresponds to the toner consumption for n prints.

  Then, the controller 33 determines whether or not the above-described average printing ratio X is equal to or greater than the threshold value THb, and whether or not the development drive time t per sheet is equal to or greater than the threshold value THc (step S8).

  If the average printing rate X is not equal to or greater than the threshold value THb, or if the developing drive time t per sheet is not equal to or greater than the threshold value THc, the controller 33 returns to step S3 and continues printing.

  On the other hand, when the average printing rate X is equal to or greater than the threshold value THb and the development drive time t per sheet is equal to or greater than the threshold value THc, the controller 33 sets the target toner ratio value in the developing devices 3a to 3d. The value is reduced by a predetermined value or a predetermined ratio (step S9).

  That is, the developing devices 3 a to 3 d supply the toner from the toner container into the housing 11 so that the toner ratio detected by the toner ratio sensor 15 becomes the toner ratio target value. Therefore, when the toner ratio target value is reduced, the toner ratio in the housings 11 of the developing devices 3a to 3d is reduced.

  Further, in this case, the screen processing unit 41 determines whether or not the image to be printed is a character document image and the character reproducibility priority setting is turned on (step S10).

  Note that the user turns on only one of the character reproducibility priority setting and the image density uniformity priority setting. Whether or not the image to be printed is a character document image is specified based on user settings or automatically based on the result of character recognition processing on the image to be printed.

  When the image to be printed is not a character document image or the character reproducibility priority setting is turned off, the screen processing unit 41 reduces the screen ruling of the screen processing by a predetermined value or a predetermined ratio. (Step S11).

  On the other hand, if the image to be printed is a character document image and the character reproducibility priority setting is on, the screen processing unit 41 does not change the screen ruling.

  Then, the controller 33 determines whether or not the printing has been completed (step S12). If the printing has not been completed, the process returns to step S3 to continue the printing.

  As described above, according to the above-described embodiment, the developing devices 3a to 3d use the two-component developer to attach toner to the electrostatic latent images on the photosensitive drums 1a to 1d. When the predetermined condition is satisfied, the controller 33 lowers the target value of the toner ratio of the two-component developer in the developing devices 3a to 3d in order to suppress the rear end accumulation. Further, when the predetermined condition is satisfied, the screen processing unit 41 reduces the screen ruling of the screen processing in order to suppress the rear end pooling.

  Thus, for example, in various configurations such as a configuration in which the photosensitive drums 1a to 1d having a high relative permittivity are used and a touch-down development method is adopted, the rear end accumulation is effectively suppressed.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included in the scope of the claims.

  For example, in the above embodiment, the measurement of the development drive time t per sheet is omitted, and in step S8, without determining whether the development drive time t per sheet is equal to or longer than the threshold value THc. Alternatively, it may be determined whether or not the above-described average printing ratio X is equal to or greater than the threshold value THb.

  In the above embodiment, only one of the reduction of the toner ratio target and the reduction of the screen ruling may be performed in order to suppress the rear end accumulation.

  Further, in the above embodiment, even if the count value of the number of prints n becomes equal to or greater than the threshold value THa, the print ratio X for the latest n prints is not reset for each print without resetting the number of prints n. Alternatively, the development drive time t may be calculated, and the processing after step S8 may be performed.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

1a-1d Photoreceptor drum 3a-3d Developing device 23 Printing device 33 Controller 41 Screen processing unit

Claims (8)

A photosensitive drum,
A developing device for attaching toner to the electrostatic latent image on the photosensitive drum using a two-component developer;
A controller configured to reduce a target value of a toner ratio of the two-component developer in the developing device in order to suppress rear end accumulation when a predetermined condition is satisfied;
An image forming apparatus comprising:   The controller reduces a target value of the toner ratio of the two-component developer in the developing device in order to suppress trailing edge accumulation when a toner consumption amount at a predetermined number of prints is equal to or more than a predetermined value. The image forming apparatus according to claim 1, wherein:   When the toner consumption amount at the predetermined number of prints is equal to or more than a predetermined value, and the driving time of the developing device per one sheet at the predetermined number of prints is equal to or more than a predetermined value, the controller sets the rear end accumulation. 2. The image forming apparatus according to claim 1, wherein a target value of a toner ratio of the two-component developer in the developing device is reduced in order to suppress the image formation. The printing apparatus further includes a screen processing unit that performs screen processing of an image to be printed by the printing apparatus,
The screen processing unit, when a predetermined condition is satisfied, in order to suppress rear end pooling, to reduce the screen ruling of the screen processing,
The image forming apparatus according to claim 1, wherein: A photosensitive drum,
A developing device for attaching toner to the electrostatic latent image on the photosensitive drum using a two-component developer;
A screen processing unit that performs screen processing of an image to be printed by the printing apparatus,
The screen processing unit, when a predetermined condition is satisfied, in order to suppress rear end pooling, to reduce the screen ruling of the screen processing,
An image forming apparatus comprising:   5. The screen processing unit according to claim 4, wherein, when the toner consumption at a predetermined number of prints is equal to or more than a predetermined value, the number of screen lines of the screen processing is reduced in order to suppress the trailing edge accumulation. An image forming apparatus according to claim 5.   The screen processing unit, when the toner consumption at the predetermined number of prints is equal to or more than a predetermined value and the driving time of the developing device per one sheet at the predetermined number of prints is equal to or more than a predetermined value, The image forming apparatus according to claim 4, wherein the number of screen lines in the screen processing is reduced to suppress edge accumulation.   The screen processing unit reduces the number of screen lines in the screen processing when the toner consumption at the predetermined number of prints is equal to or more than the predetermined value, and (a) when the image to be printed is a text document image. 7. The image forming apparatus according to claim 6, wherein (b) when the image to be printed is not a character document image, the screen ruling of the screen processing is reduced to suppress trailing edge accumulation.

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