JP3921466B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus such as a digital color copying machine, and more particularly to a so-called tandem type color image forming apparatus.

  In recent years, as the performance of color image forming apparatuses such as digital color copiers has improved, it has become possible to copy banknotes more faithfully, increasing the risk of counterfeiting. Therefore, in an ordinary digital color copying machine, when a specific image (an image that should not be faithfully copied such as banknotes) is included in the image of the document read by the scanner, the image forming operation is stopped or the faithful Copying can be prohibited (see, for example, Patent Documents 1 to 3).

  The color image forming apparatus includes a plurality of (for example, four) photosensitive drums, and each color toner (for example, cyan (C), magenta (M), yellow (Y), and yellow) is provided on the surface of each photosensitive drum. There is a type (so-called tandem type) that can form a toner image by attaching black (BK), and sequentially superimpose these toner images on paper (so-called tandem type). reference).

  A transport belt for transporting paper is disposed at a position facing the plurality of photoconductive drums, and a transfer corresponding to each photoconductive drum is placed on the opposite side of each photoconductive drum across the transport belt. The device is arranged. When the paper is being transported by the transport belt, a voltage having a polarity opposite to that of the toner is applied to each transfer device, so that the toner adhering to the surface of the corresponding photosensitive drum is transferred to the transfer device side. Is electrostatically attracted to the toner image, and the toner image is transferred to the paper.

In a tandem type digital color copying machine, an image forming operation is usually started before reading of a document image is completed by a scanner. That is, the scanning for reading the document in the scanner and the image forming operation based on the image data continuously input along with the scanning are performed in parallel, so that copying can be performed at a higher speed. It has become.
Japanese Patent Publication No. 6-50901 Japanese Patent No. 2873220 JP 2001-309166 A JP 2001-94762 A

  In the tandem type digital color copying machine, as described above, since the image forming operation is started before the reading of the original image is finished, the image forming operation is stopped when the specific image is read by the scanner, or the faithful operation is performed. Even if copying is prohibited, image formation is performed immediately before the completion of reading the specific image, and a part of the specific image may be formed (output) on the paper.

  The present invention has been made under such background, and an object thereof is to provide a tandem type color image forming apparatus capable of preventing the output of a specific image.

The invention described in claim 1 for achieving the above object is a color image forming apparatus (1) capable of forming an image by sequentially superimposing a plurality of color toners based on image data on a sheet. A plurality of photosensitive drums (3M, 3C, 3Y, 3BK) respectively corresponding to the plurality of color toners, arranged at a predetermined interval from each other, and rotated in a predetermined direction at the time of image formation. A developing device (5M, 5C, 5Y, 5BK) for forming a toner image based on image data by adhering a corresponding color toner to the surface of each of the plurality of photosensitive drums; A plurality of transfer devices (6M, 6C, 6Y, 6BK) disposed to face the photosensitive drums, respectively, between the plurality of transfer devices and the plurality of photosensitive drums. When the paper is being transported, the toner's potential (negative potential) and reverse polarity (positive potential) voltage are applied respectively, thereby electrostatically removing the toner adhering to the surface of the corresponding photosensitive drum. A plurality of transfer devices for drawing onto the paper and transferring them onto the paper, specific image data detection means (101, S3) for detecting whether or not the specific image data is included in the image data, and the specific image data detection Voltage that applies a voltage having the same polarity (negative potential) as that of toner to at least one transfer device (6Y) among the plurality of transfer devices when it is detected that the image data includes specific image data. and control means (101, S4), the plurality of transfer device by said voltage control means (101, S4) (6M, 6C, 6Y, 6BK) at least one transfer device of the 6Y), when a voltage having the same polarity as that of the toner is applied, speed control means (101, S5) that changes the relative speed between the rotational speed of the photosensitive drum (3Y) corresponding to the transfer device and the paper transport speed. ), And the plurality of color toners include yellow toner, and the voltage control means (101, S4) includes a photosensitive drum (3Y) to which the yellow toner is attached. ) Is applied to the transfer device (6Y) corresponding to the toner, and the speed control means (101, S5) rotates the photosensitive drum (3Y) corresponding to the yellow toner. The color image forming apparatus is characterized in that the relative speed between the speed and the paper transport speed is changed .

The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
According to this configuration, when the specific image data detection unit detects that the specific image data is included in the image data, the voltage control unit applies the voltage having the same polarity as the toner to the sheet. The transferred toner can be electrostatically separated from the paper and adhered to the surface of the photosensitive drum corresponding to the transfer device.

Therefore, if a voltage having the same polarity as the toner is applied to the transfer device corresponding to the photosensitive drum on the downstream side in the paper conveyance direction, the toner image of the specific image is transferred to the paper by the action of the photosensitive drum and the transfer device on the upstream side in the paper conveyance direction. Even when the toner image has already been transferred, the toner image of the specific image can be electrostatically separated from the paper, so that the output of the specific image can be prevented.
Also, by applying a voltage of the same polarity as the toner to the transfer device, the toner image of a specific image can be electrostatically separated from the paper without providing new components, preventing an increase in manufacturing costs. it can.

If the voltage control means (101, S4) applies a voltage having the same polarity as the toner to the transfer device on the downstream side in the paper conveyance direction, the toner image of the specific image already transferred to the paper is conveyed. Since it can isolate | separate in the direction downstream, the output of a specific image can be prevented more effectively .

When the specific image data detecting unit detects that the specific image data is included in the image data, the surface of the photosensitive drum can be brought into sliding contact with the paper, so that it has already been transferred to the paper. The toner image of the specific image can be separated so as to be scraped off. Therefore, the output of the specific image can be prevented more effectively.
The speed control means (101, S5) is a photosensitive drum corresponding to the transfer device (6Y) to which a voltage having the same polarity as the toner is applied by the voltage control means (101, S4) with respect to the sheet conveyance speed. It is preferable to increase the relative rotational speed of (3Y). In this case, compared to a configuration in which the relative rotation speed of the photosensitive drum is reduced with respect to the paper conveyance speed, the toner on the paper can be more favorably adhered to the surface of the photosensitive drum. It is possible to prevent toner from accumulating in the sliding contact portion between the toner and the photoconductor.

The speed control means (101, S5) increases the rotation speed of the photosensitive drum (3Y) corresponding to the transfer device (6Y) to which the voltage having the same polarity as the toner is applied by the voltage control means (101, S4). It may be one that reduces the sheet conveyance speed.
The relative speed between the rotational speed of the photosensitive drum corresponding to the yellow toner and the paper transport speed, which has a relatively small influence on the image due to scratches generated on the surface of the photosensitive drum, is changed. The effect of scratches on the surface of the photoconductive drum on the image can be further reduced by the sliding contact.
According to a second aspect of the present invention, the speed control means (101, S5) is a transfer device in which a voltage having the same polarity as the toner is applied to the paper transport speed by the voltage control means (101, S4). a color image forming apparatus according to claim 1, wherein (1), characterized in that the 6Y) is intended to increase the speed of the relative rotational speed of about 2-fold less of the corresponding photosensitive drums (3Y).

According to this configuration, it is possible to suitably set a balance between the efficiency at which the toner transferred onto the paper is separated so as to be scraped off and the degree of damage on the surface of the photosensitive drum that is in sliding contact with the paper. Accordingly, it is possible to reduce the influence on the image of scratches generated on the surface of the photosensitive drum by slidingly contacting the paper .

According to a third aspect of the present invention, the surface of the photosensitive drum (3Y) whose relative rotational speed with respect to the paper transport speed is changed by the speed control means (101, S5) is formed of a material containing amorphous silicon. The color image forming apparatus (1) according to claim 1 or 2 , wherein the color image forming apparatus (1) is a color image forming apparatus (1).

  According to this configuration, the surface of the photosensitive drum that is in sliding contact with the paper is formed of a material containing amorphous silicon having a relatively high hardness, so that scratches generated on the surface of the photosensitive drum can be suppressed. Therefore, it is possible to further reduce the influence on the image of scratches generated on the surface of the photosensitive drum by slidingly contacting the paper.

Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a schematic sectional view showing an internal configuration of a digital color copying machine 1 according to an embodiment of the present invention.
Referring to FIG. 1, this digital color copying machine 1 has color image data (red (R), green (G), and blue (B) density value data) of a document read by a scanner (not shown). The image forming unit 2 can form a full-color image by sequentially superimposing cyan (C), magenta (M), yellow (Y), and black (BK) toners on a sheet. Type digital color copier.

  The image forming unit 2 includes four substantially cylindrical photosensitive drums corresponding to the respective color toners (photosensitive drum 3M corresponding to magenta, photosensitive drum 3C corresponding to cyan, photosensitive drum 3Y corresponding to yellow, and black). Are arranged at regular intervals in the left-right direction in this order. The distance between the axes of the adjacent photosensitive drums 3M to 3BK is about 90 mm, and therefore the distance between the axes of the leftmost photosensitive drum 3M and the rightmost photosensitive drum 3BK is about 270 mm. The surfaces of these four photosensitive drums 3M to 3BK are covered with a photoconductive thin film formed of a material containing amorphous silicon (a-Si).

  Around each of the photosensitive drums 3M to 3BK, LSUs (laser scanning units) 4M, 4C, 4Y, 4BK, developing devices 5M, 5C, 5Y, 5BK, transfer devices 6M, 6C, 6Y, 6BK, and cleaning devices 7M, 7C, 7Y, 7BK, etc. are arranged in association with each other. At the time of image formation, the photosensitive drums 3M to 3BK are rotated counterclockwise in FIG. 1, and the surfaces of the photosensitive drums 3M to 3BK are uniformly charged to a positive potential by a main charger (not shown). Thereafter, light based on image data is irradiated on the surfaces of the photosensitive drums 3M to 3BK by the LSUs 4M to 4BK, so that so-called electrostatic latent images are formed on the surfaces of the photosensitive drums 3M to 3BK. Each of the developing devices 5M to 5BK contains toner of each color charged to a negative potential, and the surface of each of the photosensitive drums 3M to 3BK on which the electrostatic latent image is formed is formed by the developing devices 5M to 5BK. Corresponding color toner is electrostatically attached to form a toner image.

The paper to be used is a paper of Japanese Industrial Standard (JIS) A row No. 3 (so-called A3) size or A row No. 4 (so-called A4) size, etc., with the short side extending in the left-right direction. Housed in a cassette 8. A3 size paper is 297 mm (short side) × 420 mm (long side), and A4 size paper is 210 mm (short side) × 297 mm (long side).
At the time of image formation, the paper accommodated in the paper cassette 8 is sent to the paper transport path 10 along the short side direction (laterally) by the paper feed roller 9, and then passes through this paper transport path 10. The sheet is conveyed to the forming unit 2 side, and is temporarily stopped when the leading end reaches the registration roller 11.

  A conveyance belt 12 that is wound around a pair of belt rollers 121 with a predetermined tension is disposed downstream of the registration rollers 11 in the sheet conveyance direction. The conveyor belt 12 extends straight in the left-right direction from the lower left side of the leftmost photosensitive drum 3M to the lower right side of the rightmost photosensitive drum 3BK, and the upper surface of the upper portion thereof has four upper surfaces of the photosensitive drums 3M to 3BK. Abut. At the time of image formation, the pair of belt rollers 121 are rotated in the clockwise direction in FIG. 1, whereby the conveyance belt 12 is rotated in the clockwise direction, and the sheet fed from the registration rollers 11 at a predetermined timing is conveyed to the conveyance belt 12. To the downstream side (right side).

  Below the photosensitive drums 3M to 3BK, transfer devices 6M to 6BK are arranged with the upper portion of the conveyor belt 12 interposed therebetween. In the process in which the paper is transported between the transport belt 12 and each of the photosensitive drums 3M to 3BK, the transfer device 6M to 6BK has a voltage having a polarity (negative potential) opposite to that of the toner (negative potential). By applying each, the toner adhering to the surface of the corresponding photosensitive drums 3M to 3BK is electrostatically attracted to the transfer devices 6M to 6BK and transferred to the paper. The toner remaining on the surfaces of the photosensitive drums 3M to 3BK after the toner image transfer is collected by cleaning devices 7M to 7BK provided corresponding to the photosensitive drums 3M to 3BK.

  The sheet on which the toner image has been transferred is guided to the fixing device 13 by the conveying belt 12 and subjected to a predetermined fixing process, and then discharged onto a discharge tray 14 arranged outside the apparatus. The fixing device 13 includes a heat roller 131 that is heated to a predetermined fixing temperature, and a pressure roller 132 that is pressed against the heat roller 131 with a predetermined fixing pressure. As the paper passes between the heat roller 131 and the pressure roller 132, the toner particles transferred to the paper are heated and pressurized to be melted and fixed on the paper.

FIG. 2 is a block diagram showing an electrical configuration of the digital color copying machine 1.
Referring to FIG. 2, the operation of this digital color copying machine 1 is controlled by a control unit 100 including a microcomputer. The control unit 100 includes a CPU 101 that controls the digital color copying machine 1 and a memory 102 for storing image data of a document read by the scanner 15.

  The scanner 15 includes a light source 151 for irradiating light toward the document, and a CCD image sensor 152 that receives reflected light from the document and outputs an analog signal. The CCD image sensor 152 is configured by arranging a plurality of CCD elements in a line, and the electric main scanning in the arrangement direction of these CCD elements and the originals of the light source 151 and the CCD image sensor 152 are performed. Reading of an original image is achieved by sub-scanning by relative movement. The analog signal output from the CCD image sensor 152 is A / D converted into multi-value (for example, 0 to 255) digital data (color image data), subjected to predetermined image processing, and stored in the memory 102. Is done.

  In addition to the LSUs 4M to 4BK, the transfer devices 6M to 6BK, the fixing device 13 and the scanner 15, the control unit 100 includes various rollers (such as a paper feed roller 9, a registration roller 11, and a belt roller 121) for conveying paper. Roller driving mechanism 16 for rotating the photosensitive drums, drum motors 31M, 31C, 31Y, 31BK for rotating the photosensitive drums 3M-3BK, and developing motors 51M, 51C, 51Y, for driving the developing devices 5M-5BK, 51BK etc. are connected.

  In the digital color copying machine 1 according to this embodiment, the image forming operation is started before the scanner 15 finishes reading the original image. That is, the scanning for reading the document in the scanner 15 and the image forming operation in the image forming unit 2 based on the image data continuously stored in the memory 102 along with this scanning are performed in parallel. Copying can be performed at a higher speed.

  One of the features of the digital color copying machine 1 is that a specific image (such as banknotes) is faithfully copied on the original image based on the original image data read by the scanner 15 and continuously stored in the memory 102. It is determined whether or not a specific image is included, and when a specific image is included, a process (specific image removal process) for removing the specific image that has already been transferred to the paper is performed. It is in the point that can be done.

FIG. 3 is a flowchart showing the flow of control of the CPU 101 during image formation. FIG. 4 is a timing chart showing the operation contents of the digital color copying machine 1 when copying a document image not including a specific image. FIG. 4 shows a case where image formation is performed based on an A3 size document.
3 and 4, when an operation unit (not shown) provided in digital color copying machine 1 is operated and an image forming operation is started, first, drum motors 31M to 31BK and developing motor 51M are operated. -51BK, after the fixing device 13 and the conveyance belt 12 are started to be driven (timing T1), the paper feeding roller 9 is driven to rotate for a predetermined time (timing T2 to T3), and is stored in the paper cassette 8. The leading edge of the sheet that has reached the registration roller 11.

  Thereafter, when the registration roller 11 is driven to rotate (timing T4), the conveyance of the sheet toward the image forming unit 2 is started, and a predetermined voltage having a positive potential is applied to each of the transfer devices 6M to 6BK after a predetermined time has elapsed. (Timing T5). Thereafter, reading of the document by the scanner 15 is started (step S1, timing T6), and image data of the document continuously read by the scanning of the scanner 15 is stored in the memory 102 and continuously stored in the memory 102. Based on the image data to be processed, the image forming operation in the image forming unit 2 is performed in parallel (step S2).

During reading of the document image (timing T6 to T7), the CPU 101 performs pattern matching between the specific image data stored in advance in the control unit 100 and the image data continuously stored in the memory 102, thereby performing the document matching. It is monitored whether or not the specific image is included in the image (step S3).
At the time of image formation, in parallel with the reading of the original by the scanner 15, light based on the image data is sequentially irradiated from the LSUs 4M to 4BK to the surfaces of the corresponding photosensitive drums 3M to 3BK, thereby each photosensitive drum 3M. After the electrostatic latent images are formed on the surfaces of 3BK, toner images are formed on the surfaces of the photosensitive drums 3M-3BK by the functions of the developing devices 5M-5BK. The toner images formed on the surfaces of the photosensitive drums 3M to 3BK are sequentially transferred by the functions of the transfer devices 6M to 6BK in a process in which the paper passes between the photosensitive drums 3M to 3BK and the conveying belt 12. Overlaid on paper. Therefore, the toner images formed on the surfaces of the photosensitive drums 3M to 3BK are transferred onto the paper during periods (periods PM, PC, PY, PBK) that are shifted from each other by a predetermined time.

In this manner, the specific image data is not detected from the image data continuously stored in the memory 102 in the process in which the toner images formed on the surfaces of the photosensitive drums 3M to 3BK are transferred to the paper ( When the reading of the original by the scanner 15 is completed (YES in step S6), the specific image removal process is not performed.
Thereafter, when all of the toner images formed on the photosensitive drums 3M to 3BK are transferred to the paper, the driving voltages for the transfer devices 6M to 6BK are sequentially turned off (timing T8, T9, T10, T12), and the process ( For example, between the timing T10 and the timing T12, the trailing edge of the sheet passes the registration roller 11, and the rotation of the registration roller 11 is stopped (timing T11).

  In the digital color copying machine 1 according to this embodiment, toner is adhered from the photosensitive drums 3M to 3BK onto the conveyance belt 12 when the sheet is not conveyed, and the density of the toner adhered on the conveyance belt 12 is increased. Based on the above, processing for correcting an error between the original image and the output image (error correction processing) can be performed. Therefore, when the error correction process is performed, the toner adheres on the conveyance belt 12. In addition, toner may be scattered from the photosensitive drums 3M to 3BK and the developing devices 5M to 5BK during image formation, and the toner may adhere to the conveyance belt 12. In this embodiment, when the specific image removal process is not performed, a process (belt cleaning process) for removing the toner adhering to the conveyance belt 12 can be performed.

  That is, when the specific image data is not detected from the image data continuously stored in the memory 102 and the specific image removal process is not performed (YES in step S6, NO in step S7). ), A predetermined voltage having a reverse polarity (negative potential) is applied to the transfer device 6Y corresponding to the yellow toner until a predetermined period (timing T13 to T14) elapses after the image forming operation ends (YES in step S10). At the same time (step S8), the rotational speed of the photosensitive drum 3Y corresponding to the yellow toner is increased to about twice the speed (step S9).

  As described above, when the specific image removal process is not performed, the transfer device 6Y corresponding to the yellow toner is supplied with a reverse polarity (negative potential) voltage, that is, a voltage having the same polarity as the potential (negative potential) of the toner. If applied, even if the toner adheres on the conveyor belt 12, the toner adhered on the conveyor belt 12 can be electrostatically separated from the conveyor belt 12, so that the toner adheres on the conveyor belt 12. The removed toner can be removed well.

Further, the rotational speed of the photosensitive drum 3Y corresponding to yellow toner is increased to about twice, so that the surface of the photosensitive drum 3Y can be slidably contacted with the transport belt 12. Therefore, since the toner adhering to the conveyance belt 12 can be separated so as to be scraped off, the toner adhering to the conveyance belt 12 can be removed better.
FIG. 5 is a timing chart showing the operation content of the digital color copying machine 1 when copying a document image including a specific image, and shows a case where the specific image is included on the leading end side of an A3 size document. . Even when the original image including the specific image is copied, the original image not including the specific image described with reference to FIG. 4 is copied for the operations (timing U1 to U6) from the start of the image forming operation to the start of reading the original. Since this is the same as the operation in the case (timing T1 to T6), description thereof is omitted.

  Referring to FIGS. 3 and 5, when reading of the document is started (timing U6), CPU 102 stores the specific image data in the image data continuously stored in memory 102, as in FIG. Whether or not it is included is monitored (step S3). When specific image data is detected from the image data continuously stored in the memory 102 in the process in which the toner images formed on the surfaces of the photosensitive drums 3M to 3BK are transferred to the paper (YES in step S3) ), The CPU 101 starts the specific image removal process (steps S4 and S5) immediately at that time (timing U7). That is, the drive voltages for the transfer devices 6M, 6C, and 6BK corresponding to the magenta, cyan, and black toners are turned off, and a predetermined voltage with a reverse polarity (negative potential) is applied to the transfer device 6Y that corresponds to the yellow toner. (Step S4). At this time, the rotational speed of the photosensitive drum 3Y corresponding to the yellow toner is increased to about twice the speed (step S5).

  As described above, when specific image data is detected from the image data continuously stored in the memory 102, the transfer device 6Y corresponding to the yellow toner has a reverse polarity (negative potential) voltage, that is, the potential of the toner ( If a voltage having the same polarity as the negative potential is applied, the toner image of the specific image has already been transferred to the sheet by the functions of the transfer apparatuses 6M and 6C and the photosensitive drums 3M and 3C on the upstream side of the transfer apparatus 6Y. Even when the transfer is performed, the toner image of the specific image can be electrostatically separated from the sheet when the sheet passes between the transfer device 6Y and the photosensitive drum 3Y. Output can be prevented.

In addition, the toner image of the specific image can be electrostatically separated from the paper without providing new parts by simply applying a voltage having the same polarity as the toner to the transfer device 6Y, which increases the manufacturing cost. Can be prevented.
In particular, as shown in FIG. 5, when a specific image is detected before the start of the period PY during which yellow toner is transferred to a sheet, the photosensitive drum 3Y and transfer device corresponding to the yellow toner are transferred. Since a voltage having a reverse polarity can be applied to the transfer device 6Y before the paper passes between 6Y, the transfer devices 6M and 6C and the photosensitive drums 3M and 3C on the upstream side in the paper transport direction from the transfer device 6Y. The toner image that has already been transferred to the paper can be completely separated from the paper by the action. Accordingly, since it is impossible to recognize in which part of the document the specific image was included from the output paper, the output of the specific image can be prevented more effectively.

Further, the rotational speed of the photosensitive drum 3Y corresponding to the yellow toner is increased to about twice, so that the surface of the photosensitive drum 3Y can be brought into sliding contact with the paper. Therefore, since the toner image of the specific image that has already been transferred to the paper can be separated so as to be scraped off, the output of the specific image can be more effectively prevented.
Thereafter, the reading of the original by the scanner 15 is finished (timing U8), and the rotation of the registration roller 11 is stopped after the trailing edge of the sheet passes the registration roller 11 (timing U9). Then, after a predetermined time has elapsed, the drive voltage for the transfer device 6Y corresponding to yellow toner is turned off, and at the same time, the rotational speed of the photosensitive drum 3Y corresponding to yellow toner is returned to the original speed, and the conveyor belt 12 is restored. Is stopped (timing U10). Further, after a predetermined time elapses, driving of the drum motors 31M to 31BK, the developing motors 51M to 51BK, and the fixing device 13 is stopped, and the image forming operation ends.

As described above, when the specific image data is detected from the image data continuously stored in the memory 102 and the specific image removal process is performed (YES in step S7), after the image forming operation is completed (timing U11). In addition, the belt cleaning process (steps S8 and S9) is not performed.
FIG. 6 is a timing chart showing the operation contents of the digital color copying machine 1 when copying a document image including a specific image, showing a case where the specific image is included on the rear end side of the A3 size document. Yes. Even when the specific image is included on the trailing edge side of the document, the operation from the start of the image forming operation to the start of reading the document (timing V1 to V6) and the operation from the end of reading the document to the end of the image forming operation ( Timings V8 to V11) are the same as the operations (timing U1 to U6 and U8 to U11) described in FIG.

  As shown in FIG. 6, when the specific image is included on the trailing edge side of the document, the sheet has already been detected when the specific image data is detected from the image data continuously stored in the memory 102 (timing V7). Transfer of yellow toner to the toner (period PY) is started. Therefore, even if the specific image removal process is started immediately at this time, the toner image already transferred to the sheet cannot be completely separated from the sheet as in the case of FIG. However, even in this case, when the yellow toner is transferred to the first half of the sheet (the first half of the period PY), the specific image data is detected and the specific image removal process is performed. The toner image of the specific image that has already been transferred to the rear end side of the sheet by the action of the body drums 3M and 3C is reliably separated from the sheet when the sheet passes between the transfer device 6Y and the photosensitive drum 3Y. can do.

As mentioned above, although embodiment of this invention and its effect were demonstrated concretely, in this embodiment, there exist the following effects other than the effect mentioned above.
That is, if the configuration is such that the rotational speed of the photosensitive drum 3Y corresponding to yellow toner is increased to about twice as high during the specific image removal process or the belt cleaning process as in the above embodiment, Alternatively, it is possible to suitably set a balance between the efficiency at which the toner transferred to the transport belt 12 is separated so as to be scraped off and the degree of scratches on the surface of the photosensitive drum 3Y that is in sliding contact with the paper or the transport belt 12. . Therefore, it is possible to reduce the influence on the image of scratches generated on the surface of the photosensitive drum 3Y by slidingly contacting the paper or the conveyance belt 12.

  However, the rotational speed of the photoconductive drum 3Y is not limited to a configuration that increases the speed to about twice, and may be increased to a speed that is less than twice or increased to a speed that is twice or more. It may be a thing. Further, the configuration is not limited to the configuration in which the rotation speed of the photosensitive drum 3Y is increased with respect to the paper or the conveyance belt 12, but the configuration in which the rotation speed of the conveyance belt 12 is decreased with respect to the photosensitive drum 3Y is also possible. Good.

  In this embodiment, the rotational speed of the photosensitive drum 3Y corresponding to yellow toner that has a relatively small influence on the image due to scratches generated on the surface of the photosensitive drum during the specific image removal process or the belt cleaning process. Therefore, the effect of scratches on the surface of the photosensitive drum 3Y by sliding on the paper or the conveyance belt 12 can be further reduced.

  Furthermore, in this embodiment, the surface of the photosensitive drum 3Y that is in sliding contact with the paper or the conveyor belt 12 during the specific image removal process or the belt cleaning process is formed of a material containing relatively high hardness amorphous silicon, thereby providing a photosensitive body. Scratches generated on the surface of the drum 3Y can be suppressed. Therefore, it is possible to further reduce the influence on the image of scratches generated on the surface of the photosensitive drum 3Y by slidingly contacting the paper or the conveyance belt 12.

The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims.
For example, a transfer device to which a voltage having the same polarity as that of the toner is applied during the specific image removal process and a photosensitive drum having a rotational speed increased by a factor of about 2 include a transfer device 6Y corresponding to yellow toner, and For example, the transfer device 6BK and the photosensitive drum 3BK corresponding to black toner may be used, or all the transfer devices 6M to 6BK and the photosensitive drums 3M to 3BK may be used. .

  During the specific image removal process, a voltage having the same polarity as that of the toner is applied to the transfer device 6BK corresponding to the black toner, and the rotational speed of the photosensitive drum 3BK corresponding to the black toner is increased by about twice. In the case of the configuration, the distance between the axes of the photosensitive drum 3BK and the leftmost photosensitive drum 3M is 270 mm, which is shorter than the short side (210 mm) of the A4 size paper. At the time of reading, at the end of reading the document, the sheet still does not reach between the photosensitive drum 3BK corresponding to the black toner and the transfer device 6BK. Therefore, the toner image that has already been transferred to the paper can be completely separated from the paper, regardless of which part of the original image contains the specific image.

In the above-described embodiment, the configuration in which the surfaces of all the photosensitive drums 3M to 3BK are formed of a material containing amorphous silicon has been described. For example, the photosensitive drum 3Y corresponding to yellow toner (rotation speed is Only the surface of the photosensitive drum to be increased may be formed of a material containing amorphous silicon.
The photoconductive drums 3M, 3C, 3Y, and 3BK provided in the image forming unit 2 are not limited to the configuration arranged in the left-right direction in this order, and may be arranged in another order.

Further, the type of toner that is sequentially superimposed on the paper during image formation may be three colors or less, or five or more colors, instead of the four colors magenta, cyan, yellow, and black. In this case, the number of photosensitive drums is not limited to four, but may be three or less, or may be five or more.
In the above embodiment, the digital color copying machine 1 has been described as an embodiment of the present invention. However, the present invention is not limited to the digital color copying machine but can be applied to other image forming apparatuses such as a digital color printer. It is. In this case, it may be configured to detect whether or not the specific image data is included in the image data input to the digital color copying machine from a personal computer or the like.

1 is a schematic cross-sectional view showing an internal configuration of a digital color copying machine according to an embodiment of the present invention. 1 is a block diagram showing an electrical configuration of a digital color copying machine. 4 is a flowchart illustrating a flow of control of a CPU during image formation. 6 is a timing chart showing the operation content of a digital color copying machine when copying a document image not including a specific image. 5 is a timing chart showing the operation content of the digital color copying machine when copying a document image including a specific image, and showing a case where the specific image is included on the leading end side of an A3 size document. 6 is a timing chart showing the operation content of the digital color copying machine when copying a document image including a specific image, and shows a case where the specific image is included on the rear end side of an A3 size document.

Explanation of symbols

1 Digital Color Copier 3M, 3C, 3Y, 3BK Photosensitive Drum 5M, 5C, 5Y, 5BK Developing device 6M, 6C, 6Y, 6BK Transfer device 101 CPU

Claims (3)

A color image forming apparatus capable of forming an image by sequentially superimposing toners of a plurality of colors based on image data on a sheet,
A plurality of photosensitive drums respectively corresponding to the plurality of colors of toner, the photosensitive drums being spaced apart from each other and rotated in a predetermined direction during image formation; and the plurality of photosensitive drums A developing device for forming toner images based on image data by attaching toners of corresponding colors to the surface of
A plurality of transfer devices arranged to face the plurality of photosensitive drums, respectively, and the toner has when a sheet is conveyed between the plurality of transfer devices and the plurality of photosensitive drums. A plurality of transfer devices for electrostatically attracting and adhering toner adhering to the surface of the corresponding photosensitive drum to a sheet by applying a voltage having a polarity opposite to that of the potential;
Specific image data detection means for detecting whether or not the specific image data is included in the image data;
Voltage control means for applying a voltage having the same polarity as the toner to at least one of the plurality of transfer devices when the specific image data detection means detects that the specific image data is included in the image data and,
When a voltage having the same polarity as the toner is applied to at least one transfer device among the plurality of transfer devices by the voltage control means, the rotation speed of the photosensitive drum corresponding to the transfer device and the paper transport speed Speed control means for changing the relative speed, and
The multi-color toner includes a yellow toner,
The voltage control means applies a voltage having the same polarity as the toner to the transfer device corresponding to the photosensitive drum to which the yellow toner is attached,
The color image forming apparatus , wherein the speed control means changes a relative speed between a rotational speed of a photosensitive drum corresponding to yellow toner and a paper transport speed . The speed control means increases the relative rotational speed of the photosensitive drum corresponding to the transfer device to which a voltage having the same polarity as the toner is applied by the voltage control means to a speed within about twice the paper transport speed. The color image forming apparatus according to claim 1, wherein 3. The color image formation according to claim 1, wherein the surface of the photosensitive drum, the relative rotation speed of which is changed by the speed control unit with respect to the sheet conveyance speed, is formed of a material containing amorphous silicon. apparatus.

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