JP2006337604A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a printing speed by substantially shortening an interval between sheet printings. <P>SOLUTION: Two-component developer constituted of a magnetic carrier and a magnetic toner is used for the image forming apparatus, and in the case of developing an electrostatic latent image formed on a photoreceptor drum, The number of rounds the developing roller to be rotated is calculated as a rotation round quantity, and a thin toner layer forming control is stopped before finishing the developing operation as long as a developing roller driving time required to rotate the developing roller by the round amount from a first position where the developing roller comes closest to the photoreceptor drum up to a second position where the thin toner layer is formed on the developing roller by a magnetic brush, based on the rotational round quantity and the rotating speed of the developing roller, and a toner scraping control of scraping the toner on the developing roller is started. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic process, and in particular, a developing roller using a two-component developer composed of a magnetic carrier and a non-magnetic toner. The present invention relates to an image forming apparatus having a developing device that holds a non-magnetic toner thereon to develop an electrostatic latent image.

  As a developing method in the image forming apparatus, a two-component developer that charges a non-magnetic toner using a magnetic carrier is used, and the electrostatic latent image is developed by holding only the charged non-magnetic toner on the developing roller. The so-called hybrid development system is known. In this hybrid development system, a magnetic brush of a two-component developer composed of a magnetic carrier and a non-magnetic toner is held on a magnetic roller, and this magnetic brush is used on the development roller. Then, a toner thin layer is formed and the electrostatic latent image is developed by flying the toner from the toner thin layer to the photosensitive drum side by an alternating electric field. The toner remaining on the developing roller is collected (stripped) by the magnetic brush.

  By the way, in the hybrid developing system, the toner on the developing roller is stripped between the sheets (between sheets), and then the toner thin layer is formed. That is, after the development is completed, the toner is peeled off and the toner thin layer is formed, and then the development is started.

  For example, when peeling off the toner, the development of the image is stopped, the magnitude of the differential bias applied between the developing roller and the magnetic roller 46 is changed, and the toner on the developing roller is peeled off. A device in which the developing roller is cleaned is known (see Patent Document 1).

  Furthermore, a DC bias is applied to the magnetic roller side, a bias in which an AC is superimposed on the DC is applied to the developing roller side, and the DC bias power source is an independent power source. In some cases, the toner on the developing roller is refreshed (replaced with collection) by changing the ratio (see Patent Document 2). Here, the toner on the developing roller is collected between the paper and at the end of printing. It has been broken.

Japanese Unexamined Patent Publication No. 7-72733 JP 2003-345134 A

  By the way, in both Patent Documents 1 and 2, the toner thin layer is continuously formed on the developing roller until the electrostatic latent image on the photosensitive drum is completed. Has started. In other words, when printing on one sheet is completed, the toner on the developing roller is stripped off, a thin toner layer is formed on the developing roller, and development is started, so that printing is performed on the next sheet. ing. In other words, the toner is stripped and the toner thin layer is formed between the sheets.

  As described above, the toner thin layer is continuously formed on the developing roller until the electrostatic latent image on the photosensitive drum is completed, and when the development is completed, the toner on the developing roller starts to be peeled off. Therefore, the paper interval time is the sum of the time required for toner removal and the time required for the formation of the toner thin layer, and the toner removal time is the time required for the developing roller to make one round. There is a problem that it cannot be ignored, that is, the time between sheets becomes long, and as a result, the printing process of the image forming apparatus is lowered.

  Therefore, an object of the present invention is to provide an image forming apparatus capable of substantially shortening the sheet interval time and improving the printing processing speed.

In order to solve the above-described problems, the present invention is directed to an image bearing member on which an electrostatic latent image is formed, a developing roller that develops the electrostatic latent image with a thin toner layer into a toner image, a carrier, and toner. An image forming apparatus comprising: a magnetic roller formed of a two-component developer comprising a toner thin layer on the developing roller; and a magnetic roller that strips off the toner on the developing roller with the magnetic brush. In the device
Control means for performing toner thin layer formation control for forming the toner thin layer and stripping control for stripping off the toner;
The control means is characterized in that the toner thin layer formation control is stopped and the stripping control is started before the development is completed.

  In the present invention, the control means obtains the number of rotations of the developing roller required for developing the electrostatic latent image on the image carrier, and develops based on the number of rotations and the rotation speed of the developing roller. When the image forming process is completed, the rotation amount from the first position where the developing roller and the image carrier are closest to each other to the second position where the thin toner layer is formed on the developing roller by the magnetic brush. Before the developing roller driving time required for the developing roller to rotate, the toner thin layer formation control is stopped and the peeling control is started.

  In the present invention, for example, the developing roller driving time is a time required for the developing roller to make a half turn, and the developing roller is rotated by one turn in the peeling control.

  As described above, in the present invention, since the toner thin layer formation control is stopped and the peeling control is started before the development is completed, the peeling start time is earlier than the development end time, and the development is started. The time between sheets defined by the time from the end to the formation of the toner layer is substantially shortened, and the print processing speed can be improved.

  In the present invention, the number of rotations of the developing roller required for developing the electrostatic latent image on the image carrier is obtained, and when the development is completed based on the number of rotations and the rotation speed of the developing roller, Toner before the developing roller driving time required for the developing roller to rotate by the rotation circumference from the first position where the carrier is closest to the second position where the toner thin layer is formed on the developing roller by the magnetic brush. Since the thin layer formation control is stopped and the stripping control is started, it is not necessary to form a toner thin layer that does not contribute to development, and as a result, the printing time of the image forming apparatus can be reduced by shortening the paper interval time. There is an effect that it can be improved.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a diagram showing an example of an image forming apparatus according to the present invention. In the illustrated image forming apparatus 10, a full color image is displayed according to color information of document image data sent from an external computer (not shown in FIG. 1). Select either output or monochrome image output. The image forming apparatus 10 includes an intermediate transfer belt 11. The intermediate transfer belt 11 is stretched around a driving roller 12, a driven roller 13, and an auxiliary roller (tension roller) 14, and a solid line arrow is driven by the driving roller 12. Is driven to rotate in the direction indicated by.

  Four image forming units 15M, 15C, 15Y, and 15B are sequentially arranged along the intermediate transfer belt 11 from the upstream side in the conveyance direction of the intermediate transfer belt 11, and in the illustrated example, the upstream side in the rotation direction of the intermediate transfer belt 11 is arranged. The magenta (M) image forming unit 15M, the cyan (C) image forming unit 15C, the yellow (Y) image forming unit 15Y, and the black (BK) image forming unit 15B are arranged along the intermediate transfer belt 11 in this order. Are arranged.

  Each of the image forming units 15M, 15C, 15Y, and 15B includes photosensitive drums (image bearing members) 16a to 16d, and a charger, an LED print head unit, and a developing unit are provided around the photosensitive drums 16a to 16d, respectively. Devices 16e to 16h, a drum cleaning device, and the like are arranged. Further, primary transfer rollers 17a to 17d are arranged facing the photosensitive drums 16a to 16d with the intermediate transfer belt 11 interposed therebetween. Further, a secondary transfer roller 18 is disposed opposite to the auxiliary roller 14 with the intermediate transfer belt 11 interposed therebetween.

  When image formation is performed in the color mode, the photosensitive drums 16a to 16d are in contact with the intermediate transfer belt 11, and M to BK toner images are formed on the photosensitive drums 16a to 16d, respectively. By the primary transfer bias voltage applied to the primary transfer rollers 17a to 17d, the M to BK toner images are sequentially transferred onto the intermediate transfer belt 11 to form a color toner image on the intermediate transfer belt 11.

  The sheet is conveyed from the sheet feeding cassette 19 to the secondary transfer position, and the color toner image on the intermediate transfer belt 11 is transferred to the sheet by the secondary transfer bias voltage applied to the secondary transfer roller 18. Thereafter, the sheet is conveyed to the fixing device 20 where the color toner image is fixed and discharged to a discharge unit (discharge tray) 21.

  When image formation is performed in the monochrome mode, the transfer belt unit including the intermediate transfer belt 11 is rotated around the axis of the drive roller 12 so that the photosensitive drums 16 a to 16 c are separated from the transfer belt 11. Thus, only the photosensitive drum 16d is in contact with the primary transfer roller 17d with the intermediate transfer belt 11 interposed therebetween. Then, a primary transfer bias voltage is applied to the primary transfer roller 17d, and the black toner image is transferred onto the paper as described above, and then discharged through the fixing device 20.

  Referring to FIG. 2, developing devices 16e to 16h have the same configuration. Here, focusing on developing device 16e, developing device 16e shown in the drawing has a magnetic carrier and a non-magnetic toner. A two-component developer is used. The developing device 16e includes a magnetic roller 33 and a developing roller 34, and the developing roller 34 faces the photosensitive drum 16a.

  The magnetic roller 33 is a rotatable sleeve body formed of a non-magnetic metal material in a cylindrical shape and having a plurality of fixed magnets disposed therein. The magnetic roller 33 is placed on the magnetic roller 33 by a spike cutting blade (layer thickness regulating blade) 39. The height of the magnetic brush 37 formed in this way is kept constant, and a thin toner layer 38 is formed on the developing roller 34 by the magnetic brush 37. A direct current (DC) bias Vdc 1 and an alternating current (AC) bias are applied to the magnetic roller 33 by the power supply 40. Further, a direct current (DC) bias Vdc 2 and an AC bias are applied to the developing roller 34 by the power source 41.

  Here, as described above with reference to FIG. 3, an electrostatic latent image is formed on the photosensitive drum 16a in accordance with the print data, but the controller (not shown) starts development. When the AC bias is applied to the developing roller 34, for example, the DC bias Vdc2 = 100V is applied, and in the state where the AC bias is applied to the magnetic roller 33, the DC bias Vdc1 = 400V is applied. A thin toner layer is formed on 34.

  Then, the electrostatic latent image on the photosensitive drum 16a is developed with a thin toner layer on the developing roller 34 to obtain a toner image. In this way, toner images are formed on the photosensitive drums 16a to 16d, respectively, sequentially transferred to the intermediate transfer belt 11, and then the color toner image on the intermediate transfer belt 11 is transferred to the sheet.

  When development is completed in the developing device 16e, that is, when the controller determines that development is completed based on the amount of print data, the controller performs stripping control for collecting the toner thin layer on the developing roller 34 on the magnetic roller 33. In the stripping control, the controller changes the DC bias Vdc1 = 0V and rotates the developing roller 34 once with the DC bias Vdc2 = 100V. As a result, the toner on the developing roller 34 is peeled off by the magnetic brush 37 and collected on the magnetic roller 33 side.

  When the developing roller 34 is rotated once, that is, when the toner removal is completed, the DC bias Vdc1 = 400 V is set, and the magnetic brush 37 on the magnetic roller 33 forms a thin toner layer on the developing roller 34 for development. Start.

  As shown in FIG. 3, when the development for one sheet is completed, the toner is removed and the toner thin layer is formed, and then the development for the next sheet is started. That is, the toner is peeled off and the toner thin layer is formed during the paper interval.

  During development, a thin toner layer is continuously formed on the developing roller 34. As shown in FIG. 2, the position A where the developing roller 34 faces (closest to) the photosensitive drum 16a. The (first position) and the position B where the developing roller 34 faces the magnetic roller 33 (that is, the position where the toner is supplied by the magnetic brush: the second position) are about 180 degrees (that is, a half circumference of the developing roller 34). When the development is completed, the toner thin layer formed between the position B and the position A in the rotation direction of the developing roller 34 is not used for the development, and the peeling control is performed. Is collected by the magnetic roller 33.

  For example, the diameter of the developing roller 34 is 16.8 mm, the diameter of the magnetic roller 33 is 16.0 mm, the diameter of the photosensitive drum 16 a is 30.0 mm, and the rotation speed ratio between the developing roller 34 and the magnetic roller 33 is the magnetic roller 33. Is about 1.5 times the number of rotations of the developing roller 20. The gap between the ear cutting blade 39 and the magnetic roller 33 is about 0.3 to 1.5 mm, and the gap between the magnetic roller 33 and the developing roller 34 is about 0.3 to 1.5 mm. The thin layer of toner on the developing roller 34 is set to a thickness of 10 to 100 μm, preferably 30 to 70 μm. This thickness is a value corresponding to about 5 to 10 layers of toner when the average particle size of the toner is 7 μm.

  The gap between the developing roller 34 and the photosensitive drum 16a is 150 to 400 μm, preferably 200 to 300 μm. If it is smaller than 150 μm, it causes fogging. If it is larger than 400 μm, it becomes difficult to cause the toner to fly to the photosensitive drum 16 a, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development. Here, the gap between the ear cutting blade 39 and the magnetic roller 33 is 0.55 mm, the gap between the magnetic roller 33 and the developing roller 34 is 0.40 mm, and the thin toner layer on the developing roll is about 60 μm. To be maintained.

  As described above, the magnetic brush 37 is formed on the magnetic roller 33, the layer thickness is regulated by the ear cutting blade 39, and for example, +400 V by the DC bias power source applied to the magnetic roller 33 and applied to the developing roller 3420. A thin toner layer is formed on the developing roller 34 by a potential difference of +100 V, for example, by the DC bias power supply 30a.

At the time of image formation, the photosensitive drum 16a is charged to, for example, 400V, and then, after exposure, the post-exposure potential of the photosensitive drum 16a becomes about 70V to form an electrostatic latent image. This electrostatic latent image is a rectangular wave of +100 V by a DC bias power source applied to the developing roller 34, V _p-p 1.6 kV by an AC bias power source superimposed during development, a frequency of 3.0 kHz, and a duty ratio of 30%. As a result, the toner is developed with the toner flying from the thin toner layer on the developing roller 34 to the photosensitive drum 16a to form a toner image. In order to prevent toner scattering, an AC bias is applied immediately before development.

  The magnetic brush 37 comes into contact with the toner layer on the developing roller 34 and the toner remaining on the developing roller is collected by the brush effect or the like due to the peripheral speed difference between the two rollers. For example, the rotation speed of the magnetic roller 33 is set to 1.0 to 2.0 times the rotation speed of the developing roller 34, and the toner on the developing roller 34 is collected and the developing is set to an appropriate toner density. By supplying the agent to the developing roller 34, a uniform toner layer can be formed. Also, in order to prevent afterimages, during image formation after development, the bias voltage to the magnetic roller 33 is set such that the DC voltage of the DC bias power source is + 100V and the AC duty ratio supplied by the AC bias power source is 50%. Is set to 0 V, and the toner on the developing roller 34 is returned to the magnetic roller 33.

  By the way, the paper interval time is the sum of the time required for toner removal and the time required for forming the toner thin layer, and the toner removal time is the time required for the developing roller to make a round. As a result, it becomes impossible (that is, the time between sheets becomes longer), and as a result, the printing process of the image forming apparatus is lowered.

  In order to deal with such problems, stripping control was performed here as follows. 2, 4, and 5, the controller (control unit) monitors the amount of print data to be printed on one sheet, and the controller is given the rotation speed of the developing roller 34. The controller knows the developing time for one sheet (that is, the time required to develop the electrostatic latent image on the photosensitive drum 16a: developing roller driving time) according to the print data amount (step S1). Based on the developing roller driving time and the rotation speed of the developing roller 34, the number of rotations of the developing roller 34 when printing on one sheet is determined (step S2).

  If the developing roller 34 is rotated N times (N is a number of 1 or more) before the development is completed, the controller rotates the developing roller 34 (N-1 / 2) (step S3), and then starts stripping control. Then, with the DC bias Vdc2 = 100 V, the DC bias Vdc1 is changed to 0 V (step S4), and the developing roller 34 is rotated once (step S5). As a result, the toner on the developing roller 34 is peeled off by the magnetic brush 37 and collected on the magnetic roller 33 side.

  When the developing roller 34 makes one rotation (one turn), that is, when the toner removal is completed (step S6), the DC bias Vdc1 = 400V is set (step S7), and the magnetic brush 37 on the magnetic roller 33 causes the developing roller 34 to move on the developing roller 34. Then, a toner thin layer is formed and development is started (step S8).

  In this way, the stripping control is started before the development is completed, that is, without forming a toner thin layer that does not contribute to the development. Therefore, as shown in FIG. It becomes earlier than the end point of development, and the paper interval time is the time from the end of development to the toner layer formation, and the paper interval time is shorter than that in FIG. 3, substantially improving the printing process of the image forming apparatus. be able to.

  In the above-described example, the image forming apparatus including the intermediate transfer member such as the intermediate transfer belt has been described. However, the image forming units 15M, 15C, 15Y, and 15B are arranged along the conveyance belt that conveys the sheet. The present invention can also be applied to an image forming apparatus in which each color toner image is directly transferred onto a sheet.

  Since the toner thin layer formation control is stopped and the peeling control is started before the development is completed, the peeling start time is earlier than the development completion time, and the time from the development completion to the toner layer formation is determined. As a result of shortening the specified inter-sheet time, it can be applied to increase the printing processing speed of the image forming apparatus.

It is sectional drawing which shows the image forming apparatus by Example 1 of this invention. It is a figure for demonstrating operation | movement of the developing device shown in FIG. 6 is a timing chart for explaining a comparative example for facilitating understanding of toner thin layer formation and stripping control performed by the developing device according to the present invention. 6 is a timing chart for explaining toner thin layer formation and stripping control performed by the developing device according to the present invention; 6 is a flowchart for explaining toner thin layer formation and stripping control performed by the developing device according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 14 Auxiliary roller (tension roller)
15M, 15C, 15Y, 15B Image forming units 16a to 16d Photosensitive drums 16e to 16h Developing devices 17a to 17d Primary transfer roller 18 Secondary transfer roller 19 Paper feed cassette 20 Fixing device 21 Discharge unit (paper discharge tray)
33 Magnetic roller 34 Developing roller 37 Magnetic brush 38 Thin toner layer 39 Regulating blade 40, 41 Power supply

Claims (3)

It is formed of a two-component developer composed of a developing roller comprising a carrier and toner, and a developing roller that faces the image carrier on which the electrostatic latent image is formed and develops the electrostatic latent image with a thin toner layer to form a toner image. In an image forming apparatus comprising a developing device that forms a toner thin layer on the developing roller with a magnetic brush and a magnetic roller that strips off the toner on the developing roller with the magnetic brush.
Control means for performing toner thin layer formation control for forming the toner thin layer and stripping control for stripping off the toner;
The image forming apparatus according to claim 1, wherein the control unit stops the toner thin layer formation control and starts the stripping control before the development is completed. The control means obtains the number of rotations of the developing roller required for developing the electrostatic latent image on the image carrier,
When development is completed based on the number of rotations and the rotation speed of the developing roller, the toner thin film is applied to the developing roller by the magnetic brush from the first position where the developing roller and the image carrier are closest to each other. The toner thin layer formation control is stopped and the peeling control is started before the developing roller driving time required for the developing roller to rotate by the rotation circumference to the second position where the layer is formed. The image forming apparatus according to claim 1.   3. The developing roller driving time according to claim 2, wherein the developing roller driving time is a time required for the developing roller to make a half turn, and the developing roller is rotated by one turn in the peeling control. Image forming apparatus.

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