JP2011197487A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which an image density adjusting unit forms a plurality of patterns for density adjustment on one recording paper to save on recording paper, and which eliminates the need to form a mark for identifying recording paper to save on toner.SOLUTION: The image density adjusting unit allows an image forming unit as an object of image density adjustment to sequentially form a plurality of predetermined toner patterns P1 to P4 for density adjustments while changing combinations of a charging bias and a developing bias, allows a transfer unit to transfer the patterns to different positions on the same surface of the recording paper S, and determines a combination of a charging bias and a developing bias for approximation to a target image density based upon image densities of the patterns read by an image reader.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine combining two or more of these.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these, the electrostatic latent image carrier is charged by a charging device under a charging bias, and an image is formed in the charged area. It generally includes one or more image forming portions that can be exposed to form an electrostatic latent image, and the electrostatic latent image can be developed with a developing device under a developing bias to form a toner image. is there.

  The toner image formed in the image forming unit is directly transferred to a recording paper, an overhead projector sheet or the like (hereinafter collectively referred to as “recording paper”), or is temporarily transferred to an intermediate transfer member once. The toner image secondarily transferred from the intermediate transfer member to the recording paper and transferred onto the recording paper as described above is usually fixed on the recording paper under heating and pressing by a fixing device.

  In such an image forming apparatus, image density adjustment may be performed in order to optimize the density of the toner image transferred and formed on the recording paper.

As an image forming apparatus capable of such image density adjustment,
The latent electrostatic image bearing member is charged with a charging device under a charging bias, image exposure is performed on the charging area to form an electrostatic latent image, and the electrostatic latent image is developed with a developing device under a developing bias. One or more image forming portions that can be developed to form a toner image;
A transfer device for transferring a toner image formed by the image forming unit to a recording paper;
A recording paper transport mechanism for transporting the recording paper to the transfer device;
An image reading device capable of reading the density of the image transferred and formed on the recording paper;
An image forming apparatus including an image density adjusting unit for performing image density adjustment on an image forming unit to be subjected to image density adjustment can be exemplified.

According to this type of image forming apparatus,
The image density adjustment unit
A density adjustment toner pattern is formed in an image forming portion to be adjusted for image density, the recording paper is transported to the transfer device by the recording paper transport mechanism, and the density adjustment toner pattern is transferred onto the recording paper by the transfer device. A toner pattern forming section to be
Based on the image density of the toner pattern for density adjustment transferred and formed on the recording paper, and the image density of the toner pattern read by the image reading device, the image is formed and transferred by the image forming unit to be subjected to image density adjustment. And a bias determining unit that determines a combination of a charging bias and a developing bias that directs the density of the toner image on the recording sheet transferred onto the recording sheet by the apparatus to the target image density.

  An image reading apparatus is already known, and can read an image mounted on a document, and reads the density of a toner pattern for density adjustment formed on a recording sheet using the image reading function. You can also.

  According to this image forming apparatus, on the basis of an instruction from the toner pattern forming unit of the image density adjusting unit, the image forming unit to be subjected to image density adjustment forms a plurality of density adjusting toner patterns while changing the combination of the charging bias and the developing bias. Then, the toner pattern for density adjustment can be transferred to the recording paper transported to the transfer device by the recording paper transport mechanism by the transfer device.

  For example, the user can set the recording paper on which the toner pattern for density adjustment is transferred and set the image reading apparatus to read the image density of the toner pattern.

  The bias combination determining unit of the image density adjusting unit is formed in the image forming unit to be adjusted by the image density based on the density of the density adjusting toner pattern read by the image reading device, and is transferred onto the recording paper by the transfer device. A combination of the charging bias and the developing bias is determined so that the density of the toner image on the recording paper is directed toward the target density.

  As described above, while adjusting the combination of the charging bias and the developing bias during sheet passing (during recording sheet conveyance), the density adjusting toner pattern is formed and transferred to the recording sheet, and the density adjusting toner transferred and formed on the recording sheet. An image forming apparatus that reads a pattern density with an image reading apparatus and determines a bias for forming an image on a recording sheet with a target image density based on the read density is described in, for example, Japanese Patent Application Laid-Open No. 2008-139588. Yes.

JP 2008-139588 A

  However, while changing the combination of the charging bias and the developing bias while passing paper (while transporting the recording paper), the density adjustment toner pattern is formed and transferred to the recording paper, and the density adjustment toner pattern transferred and formed on the recording paper is transferred. When the density is read by the image reading apparatus and the bias for forming an image on the recording paper with the target image density is determined based on the read density, the combination of the charging bias and the developing bias cannot be switched instantaneously. The switching takes a certain time.

  Therefore, after one toner pattern is formed and transferred onto the recording paper, the toner pattern transferred to the same recording paper by switching the bias is spaced from the preceding toner pattern in the paper passing direction. Transcribed.

  For example, with respect to the electrostatic latent image of the toner pattern, the electrostatic latent image is formed on the electrostatic latent image carrier with the exposure amount corresponding to the maximum image density, and the combination of the charging bias and the developing bias is changed. When four patterns of density adjustment toner patterns are formed on the recording paper, for example, to print all the patterns, for example, if A4 size recording paper is passed in the longitudinal direction, two A4 recording papers are required. It may become.

  As described above, although A4 recording paper has a sufficient area for placing all four patterns, it is necessary to consume one extra recording paper because of the time limitation of bias switching.

  As another problem, for example, when a toner pattern is printed on two sheets of A4 recording paper as described above, in order to know the number of images when scanning the toner pattern with an image reading device, 1 It is necessary to print the identification marks at different positions on the second and second sheets at the same time as the pattern, and the toner consumption increases accordingly.

  In addition, since the mark is preferably printed at the top of the recording paper where the positional accuracy is easy to be printed and printed at a high density so that the mark can be read reliably, for example, the size of the charging bias and the size of the developing bias The development bias is switched in the following order so as to keep the relationship of the above constant, and the bias setting in which the pattern density is increased may be switched to the bias setting in which the pattern density is decreased. The body is negatively charged, and the electrostatic latent image formed by exposure is reversely developed with negatively charged toner).

1st sheet: -400V (dark) → -200V (light)
Second sheet: -300V (dark) → -100V (light)

  However, when the pattern is printed from the dark side to the light side as described above, fog toner is generated at the time of switching the bias as shown in FIG. The generated fog toner streaks between patterns and is printed on recording paper.

  If a so-called two-component developer is used when carrier toner is not generated, carrier adhesion occurs. Therefore, as shown in FIG. 9, normally, the developing bias is switched with respect to the charging bias. Slightly delay time t1.

  As described above, in the conventional density adjustment toner pattern formation, the toner consumption is increased by the formation of the identification mark at the head of the recording paper or the generation of the fog toner.

Therefore, the present invention
The latent electrostatic image bearing member is charged with a charging device under a charging bias, image exposure is performed on the charging area to form an electrostatic latent image, and the electrostatic latent image is developed with a developing device under a developing bias. One or more image forming portions that can be developed to form a toner image;
A transfer device for transferring a toner image formed by the image forming unit to a recording paper;
A recording paper transport mechanism for transporting the recording paper to the transfer device;
An image reading device capable of reading the density of the image transferred and formed on the recording paper;
An image density adjustment unit for performing image density adjustment for an image forming unit to be image density adjusted,
The image density adjustment unit
A density adjustment toner pattern is formed in an image forming portion to be adjusted for image density, the recording paper is transported to the transfer device by the recording paper transport mechanism, and the density adjustment toner pattern is transferred onto the recording paper by the transfer device. A toner pattern forming section to be
Based on the image density of the toner pattern for density adjustment transferred and formed on the recording paper, and the image density of the toner pattern read by the image reading device, the image is formed and transferred by the image forming unit to be subjected to image density adjustment. An image forming apparatus including a bias determining unit that determines a combination of a charging bias and a developing bias that directs the density of the toner image on the recording sheet transferred onto the recording sheet by the apparatus to a target image density (hereinafter referred to as this type). The image forming apparatus may be referred to as an “image density adjustment type image forming apparatus”), and a plurality of density adjustment patterns can be formed on one sheet of recording paper, thereby saving the recording paper. In addition, it is not necessary to form marks for identifying recording paper as in the case of a plurality of recording papers on which a conventional density adjustment pattern is formed. And to provide an image forming apparatus which can suppress the over consumption.

In order to solve the above problems, the present invention provides the following image forming apparatus.
The latent electrostatic image bearing member is charged with a charging device under a charging bias, image exposure is performed on the charging area to form an electrostatic latent image, and the electrostatic latent image is developed with a developing device under a developing bias. One or more image forming portions that can be developed to form a toner image;
A transfer device for transferring a toner image formed by the image forming unit to a recording paper;
A recording paper transport mechanism for transporting the recording paper to the transfer device;
An image reading device capable of reading the density of the image transferred and formed on the recording paper;
An image density adjustment unit for performing image density adjustment for an image forming unit to be image density adjusted,
The image density adjustment unit
A density adjustment toner pattern is formed in an image forming portion to be adjusted for image density, the recording paper is transported to the transfer device by the recording paper transport mechanism, and the density adjustment toner pattern is transferred onto the recording paper by the transfer device. A toner pattern forming section to be
Based on the image density of the toner pattern for density adjustment transferred and formed on the recording paper, and the image density of the toner pattern read by the image reading device, the image is formed and transferred by the image forming unit to be subjected to image density adjustment. A bias determining unit that determines a combination of a charging bias and a developing bias that directs the density of a toner image on the recording paper transferred onto the recording paper by the apparatus to a target image density, and
The toner pattern forming unit of the image density adjusting unit sequentially forms a plurality of predetermined density adjusting toner patterns by changing a combination of the charging bias and the developing bias in the image forming unit to be adjusted. The recording paper transport mechanism transports the recording paper to the transfer device, and the transfer device transfers the density adjustment toner pattern to a different position on the same surface of the recording paper.

  According to the image forming apparatus of the present invention, the image forming unit subject to image density adjustment uses a combination of charging bias and developing bias based on an instruction from the toner pattern forming unit of the image density adjusting unit. It is possible to transfer the density adjusting toner pattern formed on the recording paper to the recording paper transported to the transfer device by the recording paper transport mechanism.

  At this time, the toner pattern forming unit of the image density adjusting unit sequentially forms a plurality of predetermined density adjusting toner patterns by changing the combination of the charging bias and the developing bias in the image forming unit targeted for image density adjustment. The recording paper transport mechanism transports the recording paper to the transfer device, and the transfer device transfers the density adjustment toner pattern to a different position on the same surface of the recording paper.

As described above, since the toner pattern for density adjustment can be printed on one sheet of recording paper, the recording paper can be saved as much.
Further, since the density adjustment toner pattern can be printed on one sheet of recording paper, it is not necessary to print the identification mark of the recording sheet which is necessary if the density adjustment toner pattern is printed on a plurality of recording sheets. Toner consumption can be suppressed.

  Then, for example, a user can set the recording paper on which the toner pattern for density adjustment is transferred and formed in the image reading apparatus as described above, and read the image density of the toner pattern.

  The bias combination determining unit of the image density adjusting unit is formed in the image forming unit to be adjusted by the image density based on the density of the density adjusting toner pattern read by the image reading device, and is transferred onto the recording paper by the transfer device. A combination of the charging bias and the developing bias is determined so that the density of the toner image on the recording paper is directed toward the target density.

  Furthermore, the bias determining unit of the image density adjusting unit sets the target combination of the charging bias and the developing bias that can obtain the target image density from the inclination of the image density change of each density adjusting toner pattern read by the image reading device. Adopted as a bias combination for obtaining image density.

Since the density adjustment toner pattern is printed on one sheet of recording paper, there is also an advantage that the scanning operation for causing the image reading apparatus to read the pattern density can be performed in such a short time.
Thus, an image having a target density can be formed under the combination of the charging bias and the developing bias determined as described above.

  In the image forming apparatus according to the present invention, the target image density can be set to the maximum image density as in the conventional image density adjustment. In this case, the toner pattern forming unit of the image density adjusting unit may cause the image exposure apparatus to expose the electrostatic pattern with an exposure amount corresponding to the maximum image density when forming the density adjusting toner pattern on the image forming unit to be adjusted. The latent image carrier may be exposed.

  Further, in the image forming apparatus according to the present invention, the toner pattern forming unit of the image density adjusting unit causes the same recording paper to pass through the transfer device a plurality of times by the recording paper transport mechanism to be on the same surface of the recording paper. The density adjusting toner pattern may be transferred at different positions.

  More specifically, the toner pattern forming unit of the image density adjusting unit, prior to the formation of the density adjusting toner pattern and the transfer to the recording paper, the recording paper passing speed (paper passing speed) in the transfer device, Based on the length of the recording paper in the transport direction, the length of the density adjustment toner pattern in the direction of transport of the recording paper, and the time required for changing the bias combination, the predetermined number of times passes through the transfer device once on the recording paper. If it is determined whether or not all of the plurality of density adjustment toner patterns can be transferred, and it is determined that all the toner patterns can be transferred through one transfer device, transfer of the recording paper to which the toner patterns are transferred The apparatus passes once, and when it is determined that the entire toner pattern cannot be transferred to one sheet of recording paper after passing the transfer apparatus once, the recording sheet is transferred by the recording sheet transport mechanism. Device passed several times at different positions on the same surface of the recording sheet may be caused to transfer the toner pattern.

The following cases can be given as typical examples of (but not limited to) transfer formation of the density adjusting toner pattern on the recording paper by the toner pattern forming section of the image density adjusting section.
First and second density adjustment toner patterns are sequentially formed in the image forming unit to be adjusted in image density by changing the combination of the charging bias and the developing bias, and the recording paper is transferred by the recording paper transport mechanism to the transfer device. And the transfer device transfers the first and second density adjustment toner patterns to different positions on the same surface of the recording paper at intervals in the conveyance direction of the recording paper. The third and fourth density adjustment toner patterns are sequentially formed in the image forming unit to be adjusted in image density by changing the combination of the charging bias and the developing bias, and the recording paper is again transferred by the recording paper transport mechanism. The third and fourth density adjusting toner patterns are conveyed to the transfer device and transferred onto the surface of the recording paper on which the first and second toner patterns are transferred. Third toner pattern is positioned between the first and second toner pattern is the fourth toner pattern is transferred so as to be located after the second toner pattern.

  In any case, when the toner pattern forming unit of the image density adjusting unit forms a plurality of density adjusting toner patterns and transfers them to the recording paper for one pass of the recording paper in the transfer device, the density In forming the toner pattern for adjustment, the toner pattern can be formed by changing the combination of the charging bias and the developing bias so that the density of the toner pattern becomes higher sequentially.

  By forming the density adjustment toner pattern in such a density sequence, if the pattern is formed from one having a high density to one having a low density, it may occur and adhere between the patterns by switching the combination of the charging bias and the developing bias. Generation of fog toner can be suppressed, and toner consumption can be suppressed accordingly.

  The recording paper transport mechanism includes a recording paper circulation transport mechanism capable of circulating the recording paper printed (printed) on one side in the transfer device to the transfer device again for reprinting on the same surface. it can. It may use a part or all of a transport mechanism that transports the recording paper so that printing can be performed on both sides of the recording paper.

  In any case, when such a recording paper circulation conveyance mechanism is adopted, the toner pattern forming unit of the image density adjusting unit transfers the density adjusting toner pattern by passing the recording paper through the transfer device a plurality of times. When the toner pattern is transferred, the recording paper can be circulated through the recording paper circulation conveyance mechanism.

Some image forming apparatuses change the paper passing speed (recording paper conveyance speed) in the image forming apparatus depending on the type of recording paper, the image forming mode, and the like.
Therefore, when a plurality of sheet passing speeds can be set, the toner pattern forming unit of the image density adjusting unit can perform the appropriate image density adjustment at each sheet passing speed for each sheet passing speed. You may determine the frequency | count of paper passing to a transfer apparatus. At that time, the size of the recording paper may be adopted as a factor that influences the number of paper passing times.

  As described above, according to the present invention, the image density adjustment type image forming apparatus can form a plurality of density adjustment patterns on one sheet of recording paper, and can save recording paper by that amount. To provide an image forming apparatus that does not require formation of a mark for identifying a recording sheet as in the case of a plurality of recording sheets on which a conventional density adjustment pattern is formed, and that can suppress toner consumption accordingly. it can.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus in FIG. 1. FIG. 6 is a diagram illustrating a state in which first and second density adjustment toner patterns are formed on a recording sheet while switching between a charging bias and a developing bias and transferred. FIG. 4 is a diagram illustrating a state in which third and fourth density adjustment toner patterns are further formed and transferred on the recording paper of FIG. 3 while switching between a charging bias and a developing bias. FIG. 2 is a diagram illustrating a recording sheet conveyance order when a recording sheet is passed through a transfer device a plurality of times by the image forming apparatus of FIG. 1 and a density adjustment toner pattern is transferred and formed on the same surface of the recording sheet. It is a figure which shows the outline of a structure of the other example of the image forming apparatus which concerns on this invention. FIG. 7 is a block diagram illustrating an outline of a control circuit of the image forming apparatus in FIG. 6. FIG. 10 is a diagram illustrating an example in which when a density adjustment pattern is formed, if a low density pattern is formed after a high density pattern, a toner fog portion is generated on the recording paper. FIG. 9 is a diagram illustrating the reason why toner fog occurs on recording paper as shown in FIG. 8.

Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows an example of the configuration of an image forming apparatus. An image forming apparatus 100 in FIG. 1 is a monochrome image forming apparatus, and is an image forming apparatus having functions of a copying machine, a facsimile machine, and a printer.

  The image forming apparatus 100 includes a photoreceptor 1 as an electrostatic latent image carrier. Around the photoreceptor 1, a charging device 2, an image exposure device 3, a developing device 4 and a transfer device 5 are arranged in this order. The photoreceptor 1, the charging device 2, the image exposure device 3, and the developing device 4 constitute one image forming unit.

  A timing roller pair 7 is disposed below the transfer device 5, and a recording paper supply unit 6 is disposed further below. A fixing device 8 is disposed above the transfer device 5, and a paper discharge roller pair 9 and a paper discharge tray T are disposed above the fixing device 8. An image reading device 10 is disposed above the paper discharge roller pair 9 and the tray T.

  A switching claw c1 in the recording paper conveyance direction is provided at a position facing the paper discharge roller pair 9. The claw c1 can take an ascending position indicated by a solid line in FIG. 1 or a descending position indicated by a thin line in FIG. 1 by the drive unit d1 (see FIG. 2). By causing the claw c1 to take the raised position, the recording paper S coming out of the fixing device 8 can be directed toward the paper discharge roller pair 9 and can be conveyed toward the tray T by the roller pair 9.

  The paper discharge roller pair 9 can be rotated forward and backward in accordance with an instruction from the controller Cont. During normal rotation, the recording paper S can be conveyed toward the tray T. With the trailing edge of the recording paper S transported onto the tray T passing through the switching claw c1, but not yet coming out of the paper discharge roller pair 9, the switching claw c1 is moved to the lowered position under the instruction of the control unit Cont. When the paper discharge roller pair 9 starts to reversely rotate in this state, the recording paper S is switched back and sent to the circulation conveyance path connected to the timing roller pair 7.

The recording paper fed into the circulation conveyance path is conveyed again to the tamming roller pair 7 by the conveyance rollers r1, r2, r3, and the like. As described above, the switching claw c1, the circulation conveyance path, the rollers r1 to r3, and the like constitute a recording sheet circulation conveyance mechanism CY.
An image can be formed on both sides of the same recording sheet by using the circulation conveyance mechanism CY.
Further, as will be described later with reference to FIG. 5, the same surface of the same recording paper can be again passed through the transfer device 5 toward the photosensitive member 1. Thereby, an image can be formed again on the same surface of the recording paper.

  The image reading apparatus 10 reads an original image and can use the read image data for image formation in an image forming unit including the photoreceptor 1 and the like, and is already known per se. Further, the image reading apparatus 10 can also read the density of a toner pattern for image density adjustment formed on the recording paper S as will be described later.

Each unit of the image forming apparatus 100 operates based on an instruction from the control unit Cont shown in FIG.
As shown in FIG. 2, an operation panel PA is also connected to the control unit Cont. Although not shown, the operation panel PA has a numeric keypad for setting the number of images to be formed, a recording paper specification key for specifying the size and conveyance direction of the recording paper for image formation, a key for specifying the image density adjustment mode, A display for displaying information is installed.

  According to the image forming apparatus 100, an image can be formed as follows under the instruction of the control unit Cont.

  When the photosensitive member driving motor M is started under the instruction of the control unit Cont, the photosensitive member 1 is rotated counterclockwise in FIG. 1, and the surface thereof is uniformly charged to a predetermined potential by the charging device 2. I'm damned. In this example, the photoreceptor 1 is a negatively chargeable photoreceptor, and is uniformly charged to a predetermined negative potential by the charging device 2. The charging device 2 may use a charging roller or the like. In this example, a scorotron charger is used, and a charging voltage is applied to the charger from a power supply (not shown), and the photosensitive member 1 is charged with a charging bias based thereon. The surface can be charged.

  Image exposure is performed on the charged area of the photoreceptor 1 from the image exposure device 3 to form an electrostatic latent image. The image exposure apparatus 3 uses a laser beam. Among the image data read by the image reading apparatus 10, the image data transmitted from an external computer (not shown), and the image data transmitted from the counterpart facsimile machine The electrostatic latent image can be formed by subjecting the photosensitive member 1 to image exposure based on any of the above.

  The electrostatic latent image thus formed is developed by the developing device 4 to form a toner image on the photoreceptor 1. The developing device 4 may use a so-called one-component developer mainly composed of toner, but in this example, a so-called two-component developer mainly composed of toner and carrier is used.

  The toner employed in the developing device 4 is negatively charged, and the electrostatic latent image on the photoreceptor 1 can be reversely developed by the developing roller 41 to which a negative developing bias is applied.

On the other hand, the recording paper S is pulled out from the recording paper supply unit 6 by the paper feed roller 61 at a predetermined timing under the instruction of the control unit Cont and conveyed to the timing roller pair 7. The recording sheet S is temporarily stopped there, and the toner image on the photoreceptor 1 is conveyed to the transfer area by the timing roller pair 7 at the timing when the toner image arrives at a transfer area of the transfer device 5.
The paper feed roller 61, the timing roller pair 7 and the like constitute a recording paper transport mechanism that transports the recording paper S to the transfer device 5 together with the recording paper circulation transport mechanism CY and the like.

  In this example, the transfer device 5 uses a transfer roller to which a transfer voltage is applied from a power supply (not shown).

Thus, the toner image on the photoreceptor 1 is transferred onto the recording paper S passing through the transfer device 5.
The recording sheet S to which the toner image has been transferred passes through the fixing device 8, where the toner image is fixed under heat and pressure, passes through the raised switching claw c 1, and is placed on the discharge tray T by the discharge roller pair 9. Can be discharged.

  Further, when the recording paper S passes through the switching claw c1, but the trailing edge of the recording paper has not yet passed through the paper discharge roller pair 9, the claw c1 is lowered and the roller pair 9 is reversed. The recording paper can be fed into the circulation conveyance path, and can be passed again through the transfer device 5 so that the other surface of the recording paper faces the photosensitive member 1, whereby images can be formed on both sides of the recording paper.

In the image forming apparatus 100, the image density of the toner image formed on the recording paper can be adjusted under the instruction of the image density adjusting unit A incorporated in the control unit Cont.
The image density adjusting unit A includes a toner pattern forming unit a1 and a bias determining unit a2. Here, some of the components of the control unit Cont also serve as the components of the image density adjusting unit A.

  The image density adjustment unit A performs image density adjustment based on preset timing or designation by an image density adjustment mode designation key on the operation panel PA.

  In the image density adjustment, the toner pattern forming unit a1 of the image density adjusting unit A instructs the image forming unit including the photoconductor 1, the charging device 2, the image exposure device 3, and the developing device 4 to place on the photoconductor 1. A toner pattern for density adjustment is formed, and the recording paper S is transported to a transfer area in the transfer device 5 by a recording paper transport mechanism including a paper feed roller 61 and a timing roller pair 7. The toner pattern is transferred, the toner pattern is fixed on the recording paper S by the fixing device 8, and the recording paper is discharged to the tray T.

  More specifically, the toner pattern forming unit a1 sequentially forms a plurality of predetermined density adjustment toner patterns while changing the combination of the charging bias by the charging device 2 and the developing bias by the developing device 4, and transports the recording paper. The recording paper S is conveyed to the transfer device 5 by the mechanism, and the transfer device 5 transfers the density adjustment toner pattern to a different position on the same surface of the recording paper S.

  The bias determining unit a2 of the image density adjusting unit A is the image density of the density adjusting toner pattern transferred and formed on the recording paper S, and the image density of the toner pattern read by the user by the image reading device 10 Based on the above, a combination of a charging bias and a developing bias that determines the density of the toner image on the recording paper formed by the image forming unit and transferred to the recording paper by the transfer device 5 to a predetermined target image density is determined. The charging bias and the developing bias are set for the charging device 2 and the developing device 4.

  Here, as in the case of the conventional image density adjustment, the target image density is set to the highest image density, and the toner pattern forming unit a1 causes the image exposure apparatus 3 to cope with the highest image density when forming the density adjustment toner pattern. The photosensitive member 1 is exposed with the exposure amount to be used.

  The pattern formation by the toner pattern forming unit a1 will be further described. Although not limited to this, in this example, the toe pattern forming unit a1 first changes the combination of the charging bias and the developing bias as follows. Then, the first toner pattern P1 and the second toner pattern P2 are sequentially formed, and as shown in FIG. 3, the A4 size recording paper S fed in the longitudinal direction is spaced apart in the transport direction. Transfer sequentially.

The patterns P1 and P2 are formed while maintaining the difference between the charging bias and the developing bias constant (200 V in this example) and changing the charging bias and the developing bias as follows.
First pattern P1: charging bias −300V development bias −100V
Second pattern P2: charging bias −500V development bias −300V

FIG. 5A shows the conveyance state of the recording paper S at this time.
Thereafter, as shown in FIGS. 5B to 5F, the recording sheet S is switched back twice using the circulation conveyance mechanism CY, and the surface on which the patterns P1 and P2 are formed is again the photosensitive member 1. So as to be directed to the transfer device 5.

On the other hand, in the image forming unit including the photosensitive member 1 and the like, after the formation and transfer of the patterns P1 and P2, the third toner pattern P3 is changed while changing the combination of the charging bias and the developing bias as follows. And the fourth toner pattern P4 are sequentially formed, and as shown in FIG. 4, the patterns P1 and P2 are transferred onto the same recording sheet S sent again to the transfer device 5 by the timing roller pair 7. Transfer is performed so that the third toner pattern P3 is positioned between the patterns P1 and P2 and the fourth toner pattern P4 is positioned after the second toner pattern P2. The difference between the charging bias and the developing bias is constant (200 V in this example).
Third pattern P3: charging bias −400V developing bias −200V
Fourth pattern P4: charging bias −600V developing bias −400V

  As described above, the toner pattern forming unit a1 forms a plurality (four in this example) of density adjustment toner patterns (P1, P2) and (P3, P4) while changing the charging bias and the developing bias. Then, the image is transferred to the same surface of the same recording sheet S at a different position, fixed by the fixing device 8 and discharged onto the tray T. FIG. 5H shows the recording paper conveyance state at this time.

  In these pattern formations, as shown in FIG. 9, the switching of the bias is slightly delayed from the switching of the charging bias to switch the developing bias to suppress the adhesion of the carrier to the recording paper. However, since the darker pattern P1 (P3) is formed next to the darker pattern P2 (P4), a fog toner band is formed between the patterns P1 and P2 or between the patterns P3 and P4. That is suppressed.

  The recording paper S on which the toner patterns P1 to P4 are thus formed is set in the image reading apparatus 10 by the user, the image density of each pattern is read, and the density information is input to the bias determination unit a2.

  The bias determination unit a2 determines a combination of the charging bias and the developing bias that can obtain the maximum image density from the gradient of the density change of the patterns P1 to P4 as the bias combination, and the charging bias of the charging device 2 and the developing device 4 The development bias is set according to each combination. Thereby, it is possible to form an image whose image density is adjusted.

  The toner pattern forming unit a1 of the image density adjusting unit A forms the density adjusting toner pattern on the image forming unit and transfers it onto the recording paper S by the transfer device 5 before passing the recording paper through the transfer device 5 (through the sheet speed). Change (switching) of the combination of the charging speed and the developing bias, the length in the conveyance direction of the recording paper S, the length of the density adjustment toner pattern in the conveyance direction (or the number of the patterns), and the number of the patterns. Based on the time required, it is determined whether or not all of the density adjustment toner pattern can be transferred on one sheet of recording paper through one transfer device, and all the toner patterns can be transferred through one transfer device. When the determination is made, the recording paper to which the toner pattern is transferred passes through the transfer device once. However, when it is determined that the entire toner pattern cannot be transferred to one sheet of recording paper after passing through the transfer device once, the same surface of the recording paper is passed through the transfer device by the recording paper transport mechanism several times. The toner pattern is transferred at different positions.

  In the transfer formation of the toner patterns P1 to P4 on the recording paper S, a circulation conveyance mechanism is used to transfer the entire recording pattern at intervals to different positions on the same surface of the recording paper S. Thus, a total of three passes including one empty transfer without pattern transfer is performed.

FIG. 6 schematically shows a configuration of another example of the image forming apparatus according to the present invention, and FIG. 7 is a block diagram showing an outline of a control circuit of the apparatus.
The image forming apparatus 200 is a monochrome image forming apparatus in which the recording paper circulation transport mechanism CY is omitted from the image forming apparatus 100 of FIG. 1, and the other points are substantially the same as the image forming apparatus 100. Parts, components, etc., that are the same as parts, components, etc. in apparatus 100 are given the same reference numerals as in apparatus 100.

  The image forming apparatus 200 includes a recording paper passing speed (paper passing speed) in the transfer device 5, a length in the conveyance direction of the recording paper S, and a length of the density adjustment toner pattern in the recording paper conveyance direction (or the number of the patterns). Based on the time required for changing (switching) the combination of the charging bias and the developing bias, it can be determined whether or not all of the density adjustment toner pattern can be transferred to a single sheet of recording paper through a single transfer device. When it is determined that all the toner patterns can be transferred through one transfer device, for example, four patterns as shown in FIG. It can be transferred and formed at different positions on the same surface.

  In other words, in the image forming apparatus 200, when the image density adjustment is performed, the number of density adjustment toner patterns required for the image density adjustment is applied to the recording paper after the recording paper passes through the transfer device 5 once. By selecting in advance the size of the recording paper used for image density adjustment, the length of the toner pattern in the recording paper conveyance direction, etc. The toner pattern for density adjustment can be transferred and formed.

  Further, the toner pattern forming unit a1 allows the user to set the same recording paper in the recording paper supply unit 6 a plurality of times, or when the user sets the same recording paper in a manual feed tray (not shown). For example, a plurality of patterns as shown in FIG. 4 can be transferred and formed on the sheet of recording paper by passing it through the transfer device 7 a plurality of times.

  In either case of the image forming apparatuses 100 and 200, if the sheet passing speed (recording sheet conveyance speed) in the image forming apparatus is changed depending on the type of recording sheet, the image forming mode, etc., toner The pattern forming unit a1 may be configured to determine the number of times of paper passing to the transfer device 5 for each paper passing speed so that appropriate image density adjustment can be performed at each paper passing speed. At that time, the size of the recording paper may be adopted as a factor that influences the number of paper passing times.

  Although the monochrome image forming apparatus has been described above, the present invention relates to an endless intermediate transfer belt that is rotationally driven, and a plurality of images that are sequentially arranged from the upstream side to the downstream side in the belt running direction along the intermediate transfer belt. Each of the image forming units includes an image carrier that is rotationally driven to face the intermediate transfer belt. The image carrier is charged by a charger, and image exposure is performed on the charged area. An electrostatic latent image can be formed, and the electrostatic latent image can be developed with a developing device using the assigned color toner to form a toner image. The toner image faces the image carrier with the intermediate transfer belt in between. A so-called tandem type color image forming apparatus capable of primary transfer on the intermediate transfer belt by a primary transfer member and secondary transfer of the primary transfer toner image onto a recording sheet by a secondary transfer device. Is also applicable.

In the present invention, the image carrier is charged by a charger, an electrostatic latent image is formed on the charged area by an exposure device, and the electrostatic latent image is moved to the electrostatic latent image developing area. A toner image is formed by developing with a developing device that holds the assigned color toner corresponding to the electrostatic latent image, and the toner image is primarily transferred to the intermediate transfer member, whereby the toner image is transferred onto the intermediate transfer member. A so-called cycle type in which a monochrome toner image or a multiple toner image composed of toner images of two or more colors is formed, and the toner image on the intermediate transfer member can be secondarily transferred and fixed on a recording medium by a secondary transfer device. It can also be applied to a color image forming apparatus.
This cycle type image forming apparatus can be understood to include a plurality of image forming units that share some of the components.
As described above, the present invention can be applied to various image forming apparatuses.

  The present invention provides an image density adjustment type image forming apparatus, which can form a plurality of density adjustment patterns on a single recording paper for image density adjustment, and can save recording paper accordingly. Can be used to do.

DESCRIPTION OF SYMBOLS S Recording medium 100, 200 Image forming apparatus 1 Photoconductor M Photoconductor drive motor 2 Charging apparatus 3 Image exposure apparatus 4 Developing apparatus 41 Developing roller 5 Transfer apparatus 6 Recording paper supply part 61 Paper feed roller 7 Timing roller pair 8 Fixing apparatus 9 Paper discharge roller pair 10 Image reading device T Paper discharge tray CY Recording paper circulation conveyance mechanism c1 Recording paper conveyance direction switching claw d1 Switching claw driving unit r1 to r3 Recording paper conveyance roller cont Control unit A Image density adjustment unit a1 Toner pattern formation unit a2 Bias determining unit PA Operation panel

Claims (8)

The latent electrostatic image bearing member is charged with a charging device under a charging bias, image exposure is performed on the charging area to form an electrostatic latent image, and the electrostatic latent image is developed with a developing device under a developing bias. One or more image forming portions that can be developed to form a toner image;
A transfer device for transferring a toner image formed by the image forming unit to a recording paper;
A recording paper transport mechanism for transporting the recording paper to the transfer device;
An image reading device capable of reading the density of the image transferred and formed on the recording paper;
An image density adjustment unit for performing image density adjustment for an image forming unit to be image density adjusted,
The image density adjustment unit
A density adjustment toner pattern is formed in an image forming portion to be adjusted for image density, the recording paper is transported to the transfer device by the recording paper transport mechanism, and the density adjustment toner pattern is transferred onto the recording paper by the transfer device. A toner pattern forming section to be
Based on the image density of the toner pattern for density adjustment transferred and formed on the recording paper, and the image density of the toner pattern read by the image reading device, the image is formed and transferred by the image forming unit to be subjected to image density adjustment. A bias determining unit that determines a combination of a charging bias and a developing bias that directs the density of a toner image on the recording paper transferred onto the recording paper by the apparatus to a target image density, and
The toner pattern forming unit of the image density adjusting unit sequentially forms a plurality of predetermined density adjusting toner patterns by changing a combination of the charging bias and the developing bias in the image forming unit to be adjusted. An image forming apparatus, wherein the recording paper transport mechanism transports the recording paper to the transfer device, and the transfer device transfers the density adjustment toner pattern to a different position on the same surface of the recording paper.   The target image density is the highest image density, and the toner pattern forming unit of the image density adjusting unit causes the image exposure apparatus to set the maximum image density when forming the density adjusting toner pattern in the image forming unit to be adjusted. The image forming apparatus according to claim 1, wherein the electrostatic latent image carrier is exposed with an exposure amount corresponding to a density.   The toner pattern forming unit of the image density adjusting unit allows the same recording paper to pass through the transfer device a plurality of times by the recording paper transport mechanism so as to change the position on the same surface of the recording paper, thereby adjusting the density adjusting toner pattern. The image forming apparatus according to claim 1, wherein the image is transferred.   The toner pattern forming unit of the image density adjusting unit prior to the formation of the density adjusting toner pattern and transfer to the recording paper, the recording paper passing speed in the transfer device, the length of the recording paper in the conveyance direction, and the density adjusting Based on the length of the toner pattern in the recording paper conveyance direction and the time required to change the bias combination, all of the plurality of predetermined density adjustment toner patterns that pass through the transfer device once on one recording paper. When it is determined whether or not all the toner patterns can be transferred in one transfer device, the transfer of the recording paper to which the toner pattern is transferred is set once and the transfer is performed once. When it is determined that the entire toner pattern cannot be transferred onto one sheet of recording paper after passing through the apparatus, the same recording sheet is passed through the transfer apparatus a plurality of times by the recording sheet transport mechanism and the same recording sheet is transferred. At different positions in the face image forming apparatus according to claim 1 or 2, wherein to transfer the toner pattern.   The toner pattern forming unit of the image density adjusting unit causes the image density adjusting target image forming unit to change the combination of the charging bias and the developing bias to sequentially form first and second density adjusting toner patterns, The recording paper is transported to the transfer device by the recording paper transport mechanism, and the first and second density adjustment toner patterns are transferred to different positions on the same surface of the recording paper by the transfer device in the transport direction of the recording paper. Further, the third and fourth density adjustment toner patterns are sequentially formed by changing the combination of the charging bias and the development bias in the same image density adjustment target image forming unit as described above, and transferring them at intervals. The recording paper transport mechanism transports the recording paper to the transfer device again, and the transfer device transfers the third and fourth density adjustment toner patterns to the recording paper. The third toner pattern is positioned between the first and second toner patterns on the surface on which the first and second toner patterns are transferred, and the fourth toner pattern is positioned after the second toner pattern. The image forming apparatus according to any one of claims 1 to 4, wherein the image is transferred.   The toner pattern forming unit of the image density adjusting unit forms a plurality of density adjusting toner patterns per transfer of the recording paper in the transfer device and transfers them to the recording paper. 6. The image formation according to claim 1, wherein the toner pattern is formed by changing the combination of the charging bias and the developing bias so that the density of the toner pattern becomes higher in order. apparatus.   The recording paper transport mechanism includes a recording paper circulation transport mechanism capable of circulating the recording paper printed on one side in the transfer device to the transfer device again for reprinting on the same surface, and the image The toner pattern forming section of the density adjusting section transfers the density adjusting toner pattern by passing the recording paper a plurality of times through the transfer device, and when the toner pattern is transferred, the recording paper is conveyed to the recording paper circulation conveyance mechanism. The image forming apparatus according to claim 1, wherein the image forming apparatus is circulated.   A plurality of sheet passing speeds can be set, and the toner pattern forming unit of the image density adjusting unit determines the number of sheet passing through the transfer device for each sheet passing speed. The image forming apparatus described.

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