JP2009031412A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus further improves responsiveness thereof than before, in printing conditions including a color image and a monochrome image, suppresses deterioration in a photoreceptor and consumption of color toner, etc., and improves economic efficiency. <P>SOLUTION: In the image forming apparatus, when the printing frequency R of the color image with respect to a prescribed reference print sheets of printed images Qs is a prescribed value A or more, a standby mode is set to a color mode in which color photoreceptor drums 1a to 1c come into contact with an intermediate transfer belt 8 and when the color printing frequency R is less than the prescribed value A, the standby mode is set to a monochrome mode in which the color photoreceptor drums 1a to 1c are separated from the intermediate transfer belt 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic method, and more particularly to control of a printing mode in a tandem type color image forming apparatus.

  In a color image forming apparatus using an electrophotographic method, usually, four image forming units are arranged in the main body of the image forming apparatus corresponding to images of four different colors (cyan, magenta, yellow and black). Yes. Cyan, magenta, yellow, and black toner images are sequentially formed on each photoconductor provided in these image forming units by respective charging, exposure, and development processes, and an intermediate transfer belt or a conveyance belt is used as each photoconductor. The toner images formed on the surface of the photoreceptor are sequentially transferred.

  Each toner image is primarily transferred onto the intermediate transfer belt and then secondarily transferred onto the transported paper, or directly transferred onto the transported paper on the transport belt, and then made into a permanent image by a fixing process. The

  As described above, in a color image forming apparatus using electrophotography, normally, in a color mode in which a color image is transferred, a toner image is transferred by transfer from all photoconductors, and in a monochrome mode in which a monochrome image is transferred. Then, a black image is transferred only from a photoconductor carrying black toner (hereinafter referred to as “black photoconductor”).

  Therefore, when the color mode and the monochrome mode are selectively executed, in the monochrome mode, a cyan, magenta, and yellow color image forming photoconductor (hereinafter referred to as “color photoconductor”) is not used for transfer. Nevertheless, if the roller contacts with the intermediate transfer belt and rotates, the three color photoconductors are likely to deteriorate.

  In order to avoid such a problem, for example, a transfer roller for transferring a color toner image is disposed in the color transfer unit, and the transfer roller presses the intermediate transfer belt in the color mode by moving the unit. In this case, a technique is used in which the color photosensitive member is brought into contact (pressing three colors), and in the monochrome mode, the pressing is released and separated from the color photosensitive member (three colors are released).

  However, in recent years, there has been a demand for continuous image formation (printing) in a state where monochrome images and color images are mixed in random order in order to improve work efficiency. Under these circumstances, if the mechanical operation such as the three-color press or the three-color release is frequently performed according to the image to be printed, the operation is stopped during the operation, which may lead to an increase in standby time. The increase in the standby time has a great influence on the response of the image forming apparatus such as the first print time and the decrease in the printing speed from the print setting to the end of printing, and there is a possibility that the productivity of the printed image may be reduced. .

Therefore, a technique has been proposed for preventing deterioration of the photosensitive member by canceling the three colors and improving the response of the image forming apparatus. For example, in Patent Document 1, it is determined whether an image to be printed next is a single color (monochrome) or a color, and as a result of the determination, it is determined that the image is monochrome. Only when the accumulated result satisfies a predetermined condition, the standby mode when the printing operation is not performed is switched from the color mode to the monochrome mode. On the other hand, as a result of the determination, the image to be printed next is color. If it is determined that the standby mode is switched to the color mode, a technique is disclosed.
JP-A-11-167238

  However, in the technique of Patent Document 1, the monochrome mode is set only when a certain number of monochrome images are continuously printed, and if the next image is a color image, the color mode is uniformly set. For this reason, for example, when color printing is sporadically inserted in the middle despite the large number of monochrome printing as a whole, the color mode may be set as the standby mode. In such a case, it is necessary to cancel three colors for each monochrome printing, which may affect the response of the image forming apparatus.

  If monochrome printing is performed using only the black photoconductor without canceling the three colors while the standby mode is set to the color mode, as described above, deterioration of the color photoconductor that is not involved in image formation is sufficiently avoided. There is a risk that it cannot be done. On the other hand, it is also possible to perform monochrome printing by mixing three color toners without canceling the three colors. However, in such monochrome printing, color toner consumption may be unnecessarily increased.

  Therefore, in order to sufficiently cope with a state in which a color image and a monochrome image are mixed, it is necessary to appropriately switch the standby mode to the color mode or the monochrome mode according to the print image.

  In view of the above problems, the present invention makes it possible to further improve the response of an image forming apparatus under printing conditions in which a color image and a monochrome image are mixed, as well as deterioration of a photoreceptor and color toner. An object of the present invention is to provide an image forming apparatus that is excellent in economy, such as suppressing the consumption of toner.

  The present invention provides a plurality of image forming units including a photoreceptor and a developing device, an endless intermediate transfer belt on which toner images developed on the photoreceptor are sequentially laminated, and toner developed on the photoreceptor. An image forming apparatus comprising: a transfer unit that stacks an image on the intermediate transfer belt; and a secondary transfer unit that transfers a toner image stacked on the intermediate transfer belt onto a recording medium at a time. The body includes a black photoreceptor on which a black toner image is formed and one or more color photoreceptors on which a toner image of a color other than black is formed, and the intermediate transfer belt serves as the black photoreceptor and the color photoreceptor. A switching unit that can be selectively set to a color mode in contact with a body and a monochrome mode in which the intermediate transfer belt is separated from the color photoreceptor, and whether the print image is a color image or a monochrome image. Having a function of detecting whether or not, based on the detection result, the number of color images to be printed included in a predetermined reference print number is calculated as a color print frequency, and when the color print frequency is equal to or greater than a predetermined value, Control for setting the standby mode in which the printing operation is not performed by the switching unit to a color mode and setting the standby mode to a monochrome mode by the switching unit when the color printing frequency is less than a predetermined value. And a control means for performing the operation.

  The present invention also provides a plurality of image forming units including a photoconductor and a developing device, an endless conveyance belt that conveys the recording medium to the image forming unit, and a toner image developed on the photoconductor as a recording medium. In the image forming apparatus provided with a transfer unit that transfers the toner image onto the conveying belt or the transfer belt, the photosensitive member forms a black photosensitive member on which a black toner image is formed and a toner image of a color other than black. A color mode comprising one or more color photoconductors, and selectively setting a color mode in which the conveyance belt contacts the black photoconductor and the color photoconductor and a monochrome mode in which the conveyance belt is separated from the color photoconductor. And a switching unit capable of detecting whether the print image is a color image or a monochrome image. The number of characters is calculated as a color printing frequency. When the color printing frequency is equal to or higher than a predetermined value, the switching unit sets a standby mode in which the printing operation is not performed to a color mode, and the color printing frequency is predetermined. Control means for performing control to set the standby mode to the monochrome mode by the switching means when the value is less than the value is provided.

  Further, the present invention is characterized in that, at the end of a series of printing operations, the control means calculates the color printing frequency from the end to a time point that is back by the reference print number.

  In the invention, it is preferable that the control means calculates the color printing frequency when the number of printed sheets from the previous execution of the control has reached the reference number of printed sheets at the end of a series of printing operations. It is said.

  According to the first and second configurations of the present invention, if the color image printing frequency included in the predetermined reference number of prints is equal to or higher than a predetermined value, it is determined that the color printing operation frequency during the printing operation is high. If the standby mode is set to the color mode and the color image printing frequency is less than the predetermined value, it is determined that the monochrome printing operation frequency is high, and the standby mode is set to the monochrome mode. Even when monochrome images are mixed, the switching frequency between the color mode and the monochrome mode can be reduced, and the waiting time can be shortened.

  In addition, since the waiting time does not increase even if the cancellation of three colors is performed, monochrome printing with unnecessary contact between the color photoconductor and the intermediate transfer belt or the conveyance belt in the pressed state of three colors or a color photoconductor is used. The need to perform monochrome printing can also be avoided. Accordingly, it is possible to further improve the response of the image forming apparatus even under printing conditions in which a color image and a monochrome image are mixed, and to suppress deterioration of the photosensitive member, and to achieve color toner. It is also excellent in economic efficiency, for example, by suppressing consumption.

  According to the third configuration of the present invention, in the image forming apparatus having the above first or second configuration, at the end of a series of printing operations, the color from the end to the point back by the reference number of prints. By calculating the printing frequency, it is possible to calculate and determine the color printing frequency and set the standby mode every time the printing operation ends. As a result, it is possible to cope with minute changes in the color printing frequency, and it is possible to set the standby mode more flexibly and more appropriately in accordance with the use status or use environment of the apparatus. .

  According to the fourth configuration of the present invention, in the image forming apparatus having the first or second configuration, at the end of a series of printing operations, the number of printed sheets from the immediately preceding control execution becomes the reference number of printed sheets. By arriving, it is possible to calculate and determine the color printing frequency for each predetermined number of sheets, and set the standby mode by calculating the color printing frequency. As a result, it is possible to respond to changes in color printing frequency more regularly, and it is possible to set the standby mode more flexibly and more appropriately according to the usage status and usage environment of the device. It becomes.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus according to the first embodiment of the present invention. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image is formed sequentially.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The toner images thus transferred are sequentially transferred (primary transfer) onto an intermediate transfer belt 8 that moves adjacent to each image forming unit while rotating clockwise in FIG. 1 by a driving means (not shown). The image is transferred onto the paper P at a time (secondary transfer) by the next transfer roller 9 and further fixed on the paper P by the fixing unit 7 and then discharged from the apparatus main body.

  Then, an image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG. Details of the configuration around the image forming portions Pa to Pd and the intermediate transfer belt 8 will be described later.

  The paper P onto which the toner image is transferred is housed in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a belt in which the flange portions are overlapped and joined to each other to form an endless shape, or a belt without a seam (seamless) is used. Further, a cleaning blade 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing units 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing units 3a to 3d includes a developing roller (developer carrying member) arranged to face the photosensitive drums 1a to 1d, and toners of cyan, magenta, yellow, and black colors are supplied by a replenishing device (not shown). A predetermined amount is filled. This toner is supplied onto the photosensitive drums 1a to 1d by the developing rollers of the developing units 3a to 3d, and electrostatically adheres to the electrostatic latent image formed by exposure from the exposure unit 4. A toner image is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred onto the intermediate transfer belt 8 by the transfer rollers 6a to 6d. The primary transfer. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched over a driven roller 10, a drive roller 11, and a tension roller 20, and the intermediate transfer belt 8 starts to rotate clockwise as the drive roller 11 is rotated by a drive motor (not shown). Then, the sheet P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the sheet P is conveyed at a nip portion (secondary transfer nip portion) with the intermediate transfer belt 8. A full color image is secondarily transferred onto P. The paper P on which the toner image is transferred is conveyed to the fixing unit 7.

  The sheet P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13 to fix the toner image on the surface of the sheet P, and a predetermined full-color image is formed. It is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when forming images on both sides of the paper P, a part of the paper P that has passed through the fixing unit 7 is once projected from the discharge roller 15 to the outside of the apparatus. Thereafter, the paper P is distributed to the paper transport path 18 by the branching section 14 by rotating the discharge roller 15 in the reverse direction, and is transported again to the secondary transfer roller 9 with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image, It is discharged to the discharge tray 17.

  As described above, in the color image forming apparatus using the electrophotographic method, the photosensitive drums 1a to 1d carrying the toners of cyan, magenta, yellow, and black and the intermediate transfer belt 8 come into contact with each other. The toner images formed on the surfaces of the photosensitive drums 1a to 1d are sequentially transferred.

  2 and 3 are side cross-sectional views showing configurations around the image forming unit and the intermediate transfer belt of the tandem type color image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a color mode, and FIG. A configuration in monochrome mode is shown. Portions common to FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  Along the inner peripheral surface of the intermediate transfer belt 8, a driven roller 10 is further upstream of the cyan photosensitive drum 1a on the most upstream side, and a driving roller 11 is further downstream of the black photosensitive drum 1d on the most downstream side. A tension roller 20 is disposed on the upstream side of the driven roller 10 and on the downstream side of the driving roller 11, and a first support roller 21 (switching means) is black between the cyan photosensitive drum 1 a and the driven roller 10. A second support roller 22 is disposed between the photosensitive drum 1d and the yellow photosensitive drum 1c.

  The transfer roller 6d for transferring the black toner image and the transfer rollers 6a to 6c for transferring the color toner image have the black photosensitive drum 1d and the color photosensitive drums 1a to 1c with the intermediate transfer belt 8 interposed therebetween. 2 and 3 are biased downward by a biasing member (not shown) such as a spring so as to come into contact with 1c. The first support roller 21 is connected to a drive motor (not shown) via a gear, and receives the drive by the drive motor to contact the intermediate transfer belt 8 with the color photoreceptors 1a to 1c. And it can move to the up-down direction shown in FIG.2 and FIG.3 so that it may space apart.

  As shown in FIG. 2, when the first support roller 21 moves downward, the intermediate transfer belt 8 is pressed by the first support roller 21 and moves downward together with the color transfer rollers 6a to 6c. Then, they are in contact with the color photosensitive drums 1a to 1c (three color pressing). Thereby, the color mode can be set.

  In such a color mode, the intermediate transfer belt 8 is stretched by a driving roller 11, a driven roller 10, a tension roller 20, and a first support roller 21, and is cyan photoreceptor drum 1a, magenta photoreceptor drum 1b, and yellow photoreceptor. The drum 1c and the black photosensitive drum 1d are sequentially contacted and rotated clockwise while receiving primary transfer by the transfer rollers 6a to 6d.

  On the other hand, as shown in FIG. 3, when the first support roller 21 moves upward, the intermediate transfer belt 8 is released from being pressed by the first support roller 21, and attached to the color transfer rollers 6a to 6c. Against the forces, they move upward while pushing them up and move away from the color photosensitive drums 1a to 1c (release of three colors). Thereby, the monochrome mode can be set.

  In such a monochrome mode, the intermediate transfer belt 8 is stretched by the driving roller 11, the driven roller 10, and the tension roller 20, is driven by the driving roller 11, contacts only with the black photosensitive drum 1d, and is transferred by the transfer roller 6d. It rotates clockwise while receiving the primary transfer.

  As described above, in this embodiment, the first support roller 21 is switched to the color mode or the monochrome mode by moving the intermediate transfer belt 8 in the direction in which the intermediate transfer belt 8 contacts and separates from the color photosensitive drums 1a to 1c. However, such mode switching is not particularly limited to the present embodiment.

  For example, a backup roller is provided between the black photosensitive drum 1d and the yellow photosensitive drum 1c, and the backup roller and the color transfer rollers 6a to 6c are provided in the color transfer unit, and the color transfer unit. Is supported by the eccentric cam, and the eccentric cam is rotated to bring the intermediate transfer belt 8 into contact with the color photosensitive drums 1a to 1c (pressing the three colors) and separating (releasing the three colors). You can also switch the setting to monochrome mode.

  FIG. 4 is a block diagram illustrating a control path of the tandem color image forming apparatus according to the first embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 includes an image forming unit Pa to Pd, an image input unit 30, an AD conversion unit 31, a control unit 32, a storage unit 33, an operation panel 34, a fixing unit 7, an intermediate transfer belt 8, a first support roller 21, and the like. It is the structure containing.

  The image input unit 30 is a receiving unit that receives image data transmitted from a personal computer or the like when the image forming apparatus 100 is a color printer as shown in FIG. 1, and the image forming apparatus 100 is a color copying machine. A scanning optical system equipped with a scanner lamp that illuminates the original during copying, a mirror that changes the optical path of the reflected light from the original, a condensing lens that focuses the reflected light from the original, and forms an image The image reading unit includes a CCD or the like that converts the image light thus converted into an electrical signal. The image signal input from the image input unit 30 is converted into a digital signal by the AD conversion unit 31 and then sent to the image memory 40 in the storage unit 33.

  The storage unit 33 includes an image memory 40, a RAM 41, and a ROM 42. The image memory 40 stores an image signal input from the image input unit 30 and digitally converted by the AD conversion unit 31, and is stored in the control unit 32. Send it out. The RAM 41 and the ROM 42 store a processing program, processing content, and the like of the control unit 32.

  In the RAM 41 (or ROM 42), as will be described later, the number Q of prints, the determination result of whether each print image is a color image or a monochrome image, a predetermined reference print number Qs, the number of color image prints (color print number) Qc, a predetermined value A that is a threshold value of the color printing frequency R, a parameter that associates the color printing frequency R with switching of the standby mode in which the printing operation is not performed, and the like are stored. The storage unit 33 stores a standby mode set at the end of the printing operation (or at the time of shipment or reset).

  The operation panel 34 includes an operation unit composed of a plurality of operation keys, and a display unit (none of which is shown) that displays setting conditions, the state of the apparatus, and the like, and the user sets printing conditions and the like. In addition, for example, when the image forming apparatus 100 has a facsimile function, it is also used for various settings such as registering a facsimile transmission destination in the storage unit 33 and reading or rewriting the registered transmission destination.

  The control unit 32 is, for example, a central processing unit (CPU), and from the image input unit 30, the image forming units Pa to Pd, the fixing unit 7, the driving roller 11, and the paper cassette 16 (see FIG. 1) according to a set program. In addition to generally controlling the conveyance of the paper P, the image signal input from the image input unit 30 is converted into image data by scaling processing or gradation processing as necessary, and is exposed to the exposure unit 4. Send a signal. The exposure unit 4 receives the exposure signal, irradiates laser light based on the converted image data, and forms latent images on the photosensitive drums 1a to 1d.

  In addition, the control unit 32 has a function of counting the number Q of printed images, a function of receiving an image signal and detecting whether the printed image is a color image or a monochrome image, a function of coefficienting the number Qc of color prints, A function of calculating a reference print number Qs serving as a determination reference among the print number Q, a function of calculating a color print number Qc included in the reference print number Qs, and a ratio of the color print number Qc included in the reference print number Qs, A function of calculating the color printing frequency R (Qc / Qs). Further, the control unit 32 may have a function of determining whether or not the number of printed sheets Q has reached the reference number of printed sheets Qs.

  Further, the control unit 32 determines whether to set the standby mode to the color mode or the monochrome mode based on the predetermined value A that is the threshold value of the color printing frequency R stored in the storage unit 33. Based on the determination result, after the printing operation is completed, the first support roller 21 is moved to switch the standby mode, the standby mode at the end of the previous printing operation is read from the storage unit 33, and the standby mode at the start of the printing operation is set. It has the function to do.

  Next, control (standby mode setting control) for setting a standby mode in the image forming apparatus according to the first embodiment will be described. FIG. 5 is a flowchart illustrating a first control procedure in standby mode setting control of the image forming apparatus according to the first embodiment. The execution procedure of this control example will be described according to the steps in FIG. 5 with reference to FIGS.

  First, when the power is turned on, the control unit 32 reads out the standby mode set at the end of the previous printing operation (or at the time of shipment or reset) from the storage unit 33 and switches to the color mode or the monochrome mode. Is set. After the printing conditions such as the number of prints and the printing magnification are manually set by the user through the operation panel 34 or the input operation from the personal computer, the paper size is set manually by the input operation or automatically set by the document reading operation (step S1). Then, printing is started when the start button is turned on (step S2).

  When printing is started, the printing operation proceeds while the printing mode is switched to the color mode or the monochrome mode by the control unit 32 according to the image to be printed. At this time, the control unit 32 counts the number of prints Q (step 3), and for each print image, detects whether the print image is a color image or a monochrome image (step S4). Qc is counted (step S5).

  Next, whether or not the printing process for the number of prints set in step S1 has been completed is determined by the control unit 32 (step S6). If printing is in progress, the process returns to step S3 and the same process is performed (step S6). S3 to S6). If the printing process for the predetermined number of sheets set in step S1 has been completed, the control unit 32 causes the control unit 32 to print the number of color prints included in the reference number of prints Qs from the end of the printing operation to the time point that goes back to the reference number of prints Qs. Qc is calculated as a color printing frequency R (Qc / Qs) (step S7).

  Further, the control unit 32 determines whether or not the color printing frequency R is equal to or greater than a predetermined value A (R ≧ A) (step S8). If R ≧ A, the control unit 32 prints a color image. The standby mode is set to the color mode, and the three-color press is performed (step S9). On the other hand, when the color printing frequency R is smaller than A (R <A), it is determined that there is a high tendency to print a monochrome image, the standby mode is set to the monochrome mode, and the three colors are canceled (step S10).

  As described above, after the standby mode is set to one of the above modes, the series of printing processes is terminated ((1)). When the next series of printing operations is performed, the process returns to step S1 and the above control is executed.

  By setting the standby mode at the end of the printing operation according to the color printing frequency R in the above procedure, for example, for a user who frequently uses color printing, the standby mode can be set to the color mode. For users who frequently use monochrome printing, the standby mode can be set to monochrome mode. Therefore, even if monochrome printing is inserted when the standby mode is color mode, the standby mode is Even if color printing is inserted in the monochrome mode, the frequency of mode switching can be reduced because the frequency of printing of these inserted print images is low.

  In addition, by reducing the frequency of mode switching, the number of mechanical operations such as three-color pressing and three-color releasing accompanying mode switching can be reduced, and the standby time can be shortened. Further, by shortening the waiting time, it is not necessary to perform monochrome printing in a state where three colors are pressed. It is also possible to avoid performing monochrome printing by using it.

  Therefore, even in printing conditions in which color images and monochrome images are mixed, the delay in the first print time and the decrease in the printing speed from the print setting to the end of printing are avoided, and the response of the image forming apparatus is improved. It is possible to improve the productivity of printed images. In addition, it is excellent in economic efficiency such as suppressing deterioration of the photoreceptor and suppressing consumption of color toner.

  In this control example, the color printing frequency R is calculated and determined after the printing operation is finished, but such a control step can be designed as appropriate according to the use state of the apparatus, the use environment, and the like. For example, it may be assumed that the number of printed sheets Q does not reach a predetermined reference number of printed sheets Qc immediately after shipment of the apparatus or after resetting. In such a case, whether the number of printed sheets Q has reached the reference number of printed sheets Qc (Q ≧ Qs) between the operation of determining the end of the printing operation (step S6) and the operation of calculating the color printing frequency R (step S7). If Q ≧ Qs, the process proceeds to the color printing frequency R calculation operation (step S7), and if Q <Qs, the process is terminated with the standby mode set at the start of the printing operation. It can also be done.

  In this control example, the color printing frequency R is determined and the standby mode is set every time the printing operation is finished. However, the standby mode setting control is not limited to this embodiment, It can be designed as appropriate according to the type of medium, the usage status of the apparatus, the usage environment, and the like.

  FIG. 6 is a flowchart illustrating a second control procedure in standby mode setting control of the image forming apparatus according to the first embodiment. In this control example, the process up to step S6 is exactly the same as the first control procedure, and thus the description thereof is omitted. In this control, the color printing frequency R is calculated when the number Q of prints since the last execution of the control has reached the reference number Qs. Then, after it is determined in step S6 that the printing operation is completed, the number Q of printed sheets from the previous execution of the control reaches the reference number of printed sheets Qs between the start of printing and the end of printing (steps S3 to S6). It is determined whether or not (step S7).

  If the reference print number Qs has been reached (Q ≧ Qs), at the end of the printing operation, the control unit 32 determines that the color print number Qc included in the reference print number Qs is a color print, as in the first control procedure. Calculated as the frequency R (Qc / Qs) (step S8). Next, the controller 32 determines whether or not the color printing frequency R is R ≧ A (step S9). If R ≧ A, the standby mode is set to the color mode (step S10), and printing is performed. The process is terminated ((1)). If the printing frequency R is less than the predetermined value A (R <A) in step S9, the standby mode is set to the monochrome mode (step S11), and the printing process is terminated ((1)). Then, when the next series of printing operations is performed, the process returns to step S1 as in the first control procedure.

  On the other hand, if the reference print number Qs has not been reached in step S7 (Q <Qs), the process returns to step S1 while the standby mode at the start of the print operation is set, and waits for the next series of print operations. Others are the same as those in the first control procedure, and thus description thereof is omitted. In the present control example, the immediately preceding control execution time can be, for example, at the start of the first printing operation when the control has not yet been executed, such as at the time of shipment or resetting.

  FIG. 7 is a schematic view showing a tandem color image forming apparatus according to the second embodiment of the present invention. FIGS. 8 and 9 are images of the tandem color image forming apparatus according to the second embodiment of the present invention. FIGS. 8A and 8B are side cross-sectional views showing the configuration around the forming unit and the conveyor belt, FIG. 8 shows the configuration in the color mode, and FIG. 9 shows the configuration in the monochrome mode. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted.

  In the first embodiment, an intermediate transfer system in which a full color image formed by sequentially laminating toner images of respective colors on the intermediate transfer belt 8 which is an example of a toner carrier is transferred onto the paper P at a time. Although the tandem type color image forming apparatus has been described, in this embodiment, as shown in FIG. 7, a direct transfer type tandem that sequentially transfers the toner images of each color onto the paper P carried and transported on the transport belt 50. The configuration is exactly the same as that of the first embodiment, except that a type color image forming apparatus is used and LED heads 4a to 4d for individually exposing the photosensitive drums 1a to 1d are provided instead of the exposure unit 4. Therefore, explanation is omitted.

  In the present embodiment, the conveying belt 50 is disposed so as to contact the upper portions of the photosensitive drums 1a to 1d. However, when the color mode is set, as shown in FIG. When moving to the upper direction in the figure and setting the monochrome mode, as shown in FIG. 9, the first support roller 21 is moved in the lower direction in the figure to set the mode exactly as in the first embodiment. Can be switched. Since the configuration of other parts and the standby mode setting control are the same as those in the first embodiment, the description thereof is omitted.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the configuration shown in the above control procedure is merely an example, the number of reference print sheets Qs serving as a reference for calculating the color print frequency R, the calculation method such as the calculation timing of the reference print sheet Qs, the color print frequency R, and the like. The predetermined value A, which is a threshold value, can be appropriately set according to the type of recording medium to be printed, toner component, apparatus configuration, and the like.

  Further, in each of the above embodiments, the black photosensitive drum 1d is the most downstream side, but the black photosensitive drum 1d may be the most upstream side. For example, the photosensitive drums can be arranged in the order of the black photosensitive drum 1d, the yellow photosensitive drum 1c, the magenta photosensitive drum 1b, and the cyan photosensitive drum 1a from the upstream side.

  As Example 1 of the present invention, as shown in FIG. 5, using the first control procedure in the first embodiment of the present invention, the standard print number Qs is 500 sheets, and the predetermined value A which is the threshold value of the color print frequency R is 0. The printing operation with 5 is shown. FIG. 10 is a diagram showing a control result when the printing operation is performed using the first control procedure in the first embodiment of the present invention (Example 1 of the present invention).

  First, the number of prints is set to 500 on the operation panel 34 (see FIG. 4), and continuous printing is performed in a state where color images and monochrome images are mixed as shown in FIG. The number of color prints Qs was calculated from 500 print images printed up to the end, and the color print frequency R was calculated. As a result, since Qc = 300 (sheets) and R = 0.6 (≧ 0.5), the standby mode was set to the color mode, and the printing process was terminated.

  Next, the number of prints was set to 100 using the operation panel 34 (see FIG. 4), and monochrome images were continuously printed (a total of 500 to 600). The number Qs of color prints and the color print frequency R were calculated from the print results of 500 sheets (from 101 sheets to 600 sheets in total) printed by the end of the series of printing operations. As a result, since Qc = 200 (sheets) and R = 0.4 (<0.5), the standby mode was set to the monochrome mode, and the printing process was terminated.

  Next, as a second example of the present invention, as shown in FIG. 6, the second control procedure in the first embodiment of the present invention is used, the reference print number Qs is 500, and a predetermined value A which is a threshold value for the color print frequency R. Shows the printing operation when. FIG. 11 is a diagram showing a control result when the printing operation is performed using the second control procedure in the first embodiment of the present invention (Example 2 of the present invention).

  First, the number of prints is set to 500 on the operation panel 34 (see FIG. 4), and continuous printing is performed in a state where color images and monochrome images are mixed as shown in FIG. From the printed images (from 1 to 500 sheets in total) from the start time to the time when 500 sheets were reached, the number of color prints Qs was calculated, and the color print frequency R was calculated. As a result, since Qc = 300 (sheets) and R = 0.6 (≧ 0.5), the standby mode was set to the color mode, and the printing process was terminated.

  Next, the number of prints is set again to 500 on the operation panel 34 (see FIG. 4), and as shown in FIG. 11, continuous printing is performed in a state where color images and monochrome images different from the above are mixed, and the total From the printed images (from 501 sheets to 1000 sheets in total) from the time of reaching 501 sheets (the previous control execution time), the number of color printed sheets Qc and the color printing frequency R were calculated as described above. As a result, since Qc = 200 (sheets) and R = 0.4 (<0.5), the standby mode was set to the monochrome mode, and the printing process was terminated.

  As shown in Invention Example 1 and Invention Example 2, the standby mode is selectively set to the color mode or the monochrome mode according to the color printing frequency R by using the standby mode setting control according to the present invention. It was shown that it can be done.

  The present invention relates to an endless intermediate transfer belt or recording that is stretched over a plurality of rollers, in which a plurality of image forming units including a photoreceptor and a developing device, and a toner image developed on the photoreceptor are sequentially stacked. In the image forming apparatus, comprising: a conveying belt that conveys the medium; and a unit that transfers the toner image developed on the photosensitive member onto the intermediate transfer belt or the conveying belt. The photosensitive member is a black toner image. And a one or more color photosensitive members on which a toner image of a color other than black is formed, and the intermediate transfer belt or the conveyance belt is in contact with the black photosensitive member and the color photosensitive member. Switching means that can be selectively set between a color mode and a monochrome mode in which the intermediate transfer belt or the conveyance belt is separated from the color photosensitive member, and a print image -It has a function to detect whether it is an image or a monochrome image, and based on the detection result, the number of color images included in a predetermined reference number of prints is calculated as a color print frequency, and the color print When the frequency is not less than a predetermined value, the switching unit sets the standby mode in which the printing operation is not performed to the color mode, and when the color printing frequency is less than the predetermined value, the switching unit sets the standby mode. And a control means for performing control to set the monochrome mode.

  As a result, even when a color image and a monochrome image are mixed, the switching frequency between the color mode and the monochrome mode can be reduced, so that the standby time can be shortened, and the color in a state where three colors are pressed is displayed. It is also possible to avoid monochrome printing with unnecessary contact between the photosensitive member and the intermediate transfer belt, or monochrome printing using a color photosensitive member. Therefore, even under printing conditions in which a color image and a monochrome image are mixed, it is possible to further improve the response of the image forming apparatus, suppress the deterioration of the photoreceptor, and suppress the consumption of color toner. Also excellent in economic efficiency.

  At the end of a series of printing operations, the color printing frequency is calculated and determined every time the printing operation is completed by calculating the color printing frequency from the end of the printing operation to the time point that is back by the reference number of prints. Can be set. Accordingly, it is possible to cope more with fine changes in the color printing frequency, and it is possible to set the standby mode more flexibly and appropriately in accordance with the use state of the apparatus and the use environment.

  Also, at the end of a series of printing operations, when the number of printed sheets from the previous execution of control has reached the reference number of printed sheets, the color printing frequency is calculated and determined for each predetermined number of sheets by calculating the color printing frequency. The standby mode can be set. As a result, it is possible to respond to changes in color printing frequency more regularly, and it is possible to set the standby mode more flexibly and more appropriately according to the usage status and usage environment of the device. It becomes.

FIG. 1 is a schematic diagram illustrating an overall configuration of an intermediate transfer type tandem color image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a side cross-sectional view showing the configuration of the periphery of the image forming unit and the intermediate transfer belt in the color mode of the image forming apparatus according to the first embodiment. FIG. 2 is a side cross-sectional view illustrating the configuration of the periphery of the image forming unit and the intermediate transfer belt in the monochrome mode of the image forming apparatus according to the first embodiment. FIG. 3 is a block diagram illustrating a control path of the image forming apparatus according to the first embodiment. These are flowcharts showing a first control procedure in standby mode setting control of the image forming apparatus according to the first embodiment. These are flowcharts showing a second control procedure in standby mode setting control of the image forming apparatus according to the first embodiment. These are the schematic diagrams which show the whole structure of the tandem type color image forming apparatus of the direct transfer system which concerns on 2nd Embodiment of this invention. These are side surface sectional drawings which show the structure of the image formation part and conveyance belt periphery in color mode of the image forming apparatus which concerns on 2nd Embodiment. These are side surface sectional drawings which show the structure of the image forming part and conveyance belt periphery in monochrome mode of the image forming apparatus which concerns on 2nd Embodiment. These are figures which show the control result when printing operation is performed using the 1st control procedure in 1st Embodiment of this invention (invention example 1). These are figures which show the control result when performing printing operation using the 2nd control procedure in 1st Embodiment of this invention (invention example 2).

Explanation of symbols

Pa to Pd Image forming unit 1a to 1d Photosensitive drum 2a to 2d Charger 3a to 3d Developing unit (developing device)
4 Exposure unit 4a-4d LED head 6a-6d Transfer roller (transfer means)
7 Fixing Section 8 Intermediate Transfer Belt 9 Secondary Transfer Roller (Secondary Transfer Unit)
10 driven roller 11 drive roller 20 tension roller 21 first support roller (switching means)
22 2nd support roller 32 Control part (control means)
50 Conveying belt 100 Image forming apparatus

Claims (4)

A plurality of image forming units including a photoconductor and a developing device; an endless intermediate transfer belt on which the toner images developed on the photoconductor are sequentially stacked; and a toner image developed on the photoconductor In an image forming apparatus comprising: a transfer unit that is stacked on a transfer belt; and a secondary transfer unit that transfers a toner image stacked on the intermediate transfer belt onto a recording medium at a time.
The photoconductor includes a black photoconductor on which a black toner image is formed and one or more color photoconductors on which a toner image of a color other than black is formed,
A switching unit capable of selectively setting a color mode in which the intermediate transfer belt is in contact with the black photoreceptor and a color photoreceptor and a monochrome mode in which the intermediate transfer belt is separated from the color photoreceptor;
It has a function to detect whether the printed image is a color image or a monochrome image,
Based on the result of the detection, the number of printed color images included in a predetermined reference number of printed sheets is calculated as the color printing frequency,
When the color printing frequency is equal to or higher than a predetermined value, the switching unit sets the standby mode in which the printing operation is not performed to the color mode,
Control means for performing control to set the standby mode to monochrome mode by the switching means when the color printing frequency is less than a predetermined value;
An image forming apparatus comprising: A plurality of image forming units including a photosensitive member and a developing device, an endless conveying belt that conveys a recording medium to the image forming unit, and a toner image developed on the photosensitive member on a recording medium or the conveying belt An image forming apparatus comprising:
The photoconductor includes a black photoconductor on which a black toner image is formed and one or more color photoconductors on which a toner image of a color other than black is formed,
A switching unit capable of selectively setting a color mode in which the conveyor belt contacts the black photoreceptor and the color photoreceptor, and a monochrome mode in which the conveyor belt is separated from the color photoreceptor;
It has a function to detect whether the printed image is a color image or a monochrome image,
Based on the result of the detection, the number of printed color images included in a predetermined reference number of printed sheets is calculated as the color printing frequency,
When the color printing frequency is equal to or higher than a predetermined value, the switching unit sets the standby mode in which the printing operation is not performed to the color mode,
Control means for performing control to set the standby mode to monochrome mode by the switching means when the color printing frequency is less than a predetermined value;
An image forming apparatus comprising:   3. The image formation according to claim 1, wherein the control unit calculates the color printing frequency from the end of the series of printing operations to a point back by the reference number of prints. 4. apparatus.   2. The color printing frequency according to claim 1, wherein the control means calculates the color printing frequency when the number of printed sheets from the previous execution of control reaches the reference number of printed sheets at the end of a series of printing operations. Or the image forming apparatus according to 2;

Images