JP4985493B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Image forming apparatuses such as printers, copiers, and facsimiles include color image forming apparatuses that can form color (plural color) images in addition to single color (mainly black) images.

As this color image forming apparatus, a plurality of image forming apparatuses for forming a developer image (so-called toner image) composed of a developer of a predetermined color on an image carrier such as a photosensitive drum is used and arranged in series. Then, the developer images of the respective colors formed by the respective image forming devices are transferred to a paper transporting body or an intermediate transfer body that rotates so as to sequentially pass in a state of being in contact with the image holding body of each image forming device ( the transfer to) that the paper conveyed by the paper carrier in the case of using the sheet conveying member, there is of the type (tandem type) forming a monochromatic image or color images.

  In such a tandem type, in a color image forming apparatus in which a sheet conveying body is brought into contact with an image holding body by a pressing member, when image formation is performed using a part of the plurality of image holding bodies. In the transfer position corresponding to the image carrier that does not perform image formation, the pressing member does not contact the paper carrier with the image carrier, and the transfer charging bias is not applied to the transfer device. One is known (Patent Document 1).

JP-A-10-186773

  Even if a single-color image forming operation and a multi-color image forming operation are performed while being mixed and switched at various ratios, a plurality of image forming devices (particularly, a developer image is formed at the time of forming a single-color image). It is an object of the present invention to provide an image forming apparatus capable of stably charging each image carrier in an image forming apparatus).

  The image forming apparatus according to the present invention (A1) includes an image holding member that rotates while having an image holding surface, a charging device that charges the image holding surface of the image holding member by applying a charging voltage, and the image holding member. A developing device that develops the electrostatic latent image formed on the charged image holding surface with a developer of a predetermined color to form a developer image, and a transfer that transfers the developer image by applying a transfer voltage. A plurality of image forming apparatuses, and a sheet conveying body or an intermediate sheet that sequentially passes in contact with an image holding surface of the image holding body at a transfer position where transfer by the transfer apparatus of each image forming apparatus is performed. When performing an operation of forming a single color image composed of a transfer body and one color developer image formed by one of the plurality of image forming devices, and by the plurality of image forming devices Forms multi-color images that are formed by combining the developer images of each color to be formed Measuring means for individually measuring and accumulating the amount of rotation of the image carrier when performing the operation, and for charging to be applied to the charging device of the imaging device that does not form a developer image when forming the monochrome image. For the voltage, from the initial set value, a first correction value determined based on a cumulative value of the rotation amount of the image holding body at the time of forming the monochromatic image measured by the measurement unit and the measurement unit measured by the measurement unit And control means for changing to a value obtained from the second correction value determined based on the accumulated value of the rotation amount of the image carrier when forming a multi-color image.

  The image forming apparatus of the invention (A2) is the image forming apparatus of the invention A1, wherein the first correction value of the image carrier in the image forming apparatus does not form a developer image when forming a monochrome image. A value obtained from a cumulative value of the rotation amount and a correction coefficient set in accordance with a variation amount of the charging potential of the image holding member at the time of forming the monochrome image, and the second correction value is a multi-color image. Is set according to the cumulative value of the rotation amount of the image carrier in the image forming apparatus that does not form the developer image at the time of forming the image, and the amount of change in the charging potential of the image carrier at the time of forming the multi-color image. It is assumed that the value is obtained from the correction coefficient.

  The image forming apparatus of the invention (A3) is the image forming apparatus of the invention A1 or A2, wherein the rotation amount of the image carrier is obtained from the rotation speed or the rotation time.

  The image forming apparatus according to the present invention (A4) is a replacement part for detachably mounting at least the image carrier in each of the image forming apparatuses to the apparatus main body in the image forming apparatus according to any one of the inventions A1 to A3. And storage means for individually storing and holding the accumulated value of each rotation amount of the image holding body at the time of single-color image formation and multi-color image formation measured by the measurement means in each replacement part And the control means reads and uses the accumulated value of each rotation amount stored in the storage means.

The image forming apparatus of the present invention (A5) is configured as a replacement part for detachably mounting at least the image carrier in each image forming apparatus to the apparatus main body in the image forming apparatus of the above-described invention A4. The amount of rotation of each replacement part for each image carrier is individually measured and accumulated by the measurement unit, and stored in the control unit when each replacement part is replaced with a new replacement part. The accumulated value of the rotation amount of the image carrier in the exchanged replacement part is returned to zero.

  The image forming apparatus according to the invention (A6) is the image forming apparatus according to any one of the inventions A1 to A5, wherein the control means does not form a developer image when forming the monochrome image. A transfer voltage is not applied to the transfer device, or a low voltage lower than the transfer voltage is applied.

  The image forming apparatus according to the present invention (A7) is the image forming apparatus according to any one of the above inventions A1 to A6, wherein the control means forms the developer image when forming the monochromatic image. With respect to the charging voltage applied to the charging device, from the initial setting value, the accumulated value of the rotation amount of the image holding body at the time of forming the monochromatic image measured by the measuring unit and the image holding at the time of forming the multi-color image It is changed to a value obtained by subtracting the correction value determined based on the total value of the accumulated values of body rotation.

  According to the image forming apparatus of the invention A1, even when the single-color image forming operation and the multi-color image forming operation are switched at various ratios as compared with the case of not having the configuration of the present invention, It is possible to stably charge each image carrier in a plurality of image forming apparatuses.

  In the image forming apparatus according to the invention A2, the image holding members in the plurality of image forming apparatuses can be charged with high accuracy and stability as compared with the case where the image forming apparatus does not have the configuration.

  In the image forming apparatus of the invention A3, charging of each image carrier in a plurality of image forming apparatuses can be performed with high accuracy and stability compared to the case where the image forming apparatus does not have the configuration.

  In the image forming apparatus according to the invention A4, the image holding members in the plurality of image forming apparatuses can be stably charged even when the image forming apparatus is replaced as compared with the case of not having the configuration. Can do.

  In the image forming apparatus according to the invention A5, as compared with the case where the image forming apparatus is not provided, the image holding members in the plurality of image forming apparatuses are reliably and stably charged even after the image forming apparatus is replaced. Can do.

  In the image forming apparatus according to Invention A6, the charged surface potential of the image holding surface of the image holding member is lowered by applying a transfer voltage having a polarity opposite to the surface potential, as compared with the case where the image forming apparatus does not have the configuration. Thus, surface deterioration of the image holding surface due to current flowing into the image holding body during subsequent charging is suppressed, and charging of each image holding body in a plurality of image forming apparatuses can be performed more stably.

  In the image forming apparatus according to the invention A7, it is possible to easily and stably charge each image carrier in all of the plurality of image forming apparatuses as compared with the case where the image forming apparatus does not have the configuration.

  FIG. 1 is an explanatory view showing a main part of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus 1 is configured as a color printer, for example, and is a dry printer based on input image information using an electrophotographic method, an electrostatic recording method, or the like inside a housing (not shown). A plurality of image forming apparatuses 10 for forming toner images developed with toner (colored fine powder) as a developer, and a sheet 9 on which the toner images formed by the respective image forming apparatuses 10 are transferred. A paper conveying device 20 and a fixing device 30 for fixing the toner image by passing the paper 9 after the toner image is transferred by being conveyed by the paper conveying device 20 are mainly installed. A one-dot chain line with an arrow in the figure indicates a main conveyance path of the paper 9.

  The image forming device 10 has four image forming devices (10Y, 10M, 10C, 10K), and the image forming apparatuses 10 are arranged in series. The image forming devices (10Y, 10M, 10C, and 10K) have a substantially common configuration as described below.

  Each image forming apparatus 10 basically includes a photosensitive drum 12 that rotates in the direction of an arrow (in this example, the clockwise direction shown in the drawing). Such a device is mainly arranged. The main devices are a charging device 13 for charging the surface (image holding surface) of the photosensitive drum 12 to a predetermined potential, and irradiating the charged surface of the photosensitive drum 12 with light based on image information (signal). Then, an exposure device 14 as a latent image forming device for forming an electrostatic latent image (for each color) having a potential difference, and toner of each color (Y, M, C, K) are transferred and attached to the latent image. The developing device 15 (Y, M, C, K) that performs development for developing the image and the toner image is transferred to the paper 9 conveyed by the paper conveying device 20 (the paper conveying belt 21). The transfer device 16, the neutralization device 17 that neutralizes the image holding surface of the photosensitive drum 12 after the transfer, and the adhering matter such as toner remaining on the surface of the photosensitive drum 12 are scraped off with a blade or the like. This is a drum cleaning device 18.

  The photosensitive drum 12 is obtained by forming an image holding surface having a photoconductive layer (photosensitive layer) made of an organic photosensitive material on a cylindrical base material to be grounded. The charging device 13 includes a charging roll that rotates in contact with the image holding surface of the photosensitive drum 12 and is applied with a charging voltage. The exposure device 14 includes an LED array, a laser scanning device, and the like. Such an exposure device 14 does not illustrate image information input from a device such as a document reading device, a storage medium reading device, or a personal computer (PC) that is installed in or connected to the image forming apparatus 1. Necessary processing is performed by the image processing apparatus, and an image signal for each color component obtained after the processing is input. Note that one exposure device 14 may be arranged independently for each image forming device 10.

  The developing device 15 holds the developer (toner) accommodated in the developer accommodating portion while rotating and conveys the developer (toner) to a developing area facing the photosensitive drum 12, and a developing roll 15a to which a developing voltage is applied. have. The static eliminator 17 has, for example, a configuration in which light emitted from an LED or the like installed in the internal space of the photosensitive drum 12 is refracted and irradiated to the image holding surface of the photosensitive drum 12 by an optical element such as a resin lens. in use.

  The charging device 12 (the charging roll), the developing device 15 (the developing roll 15a), and the transfer device 16 (the transfer roll) in each image forming apparatus 10 have their respective power supplies as shown in FIG. A charging voltage, a developing voltage, and a transfer voltage are supplied and applied from the devices 12b, 15b, and 16b, respectively, at predetermined times. In this example, a DC voltage is applied as the charging voltage and the transfer voltage, and a voltage obtained by superimposing the DC voltage on the AC voltage is applied as the developing voltage. In addition, the photosensitive drum 12 and the developing roller 15a of the developing device are rotated in a predetermined direction by the power of a rotation driving device (not shown) in principle when an image is formed.

  The sheet conveying device 20 passes between the photosensitive drum 12 and the transfer device 16 (transfer position) of each image forming device 10 in a state of being in contact with the image holding surface of each of the photosensitive drums 12 (this direction) In the example, a sheet conveying belt 21 rotating in the counterclockwise direction shown in the drawing), a plurality of support rolls 22 and 23 for supporting the sheet conveying belt 21 in a desired state and rotatably supporting the sheet conveying belt 21 are not shown. A suction roll 25 that electrostatically attracts the paper 9 supplied one by one from the paper feeder to the outer peripheral surface of the paper transport belt 21, and unnecessary toner, paper dust, etc. adhering to the outer peripheral surface of the paper transport belt 21 The belt cleaning device 26 mainly removes deposits.

  As the paper transport belt 21, for example, a material formed in a form of an endless belt having a predetermined thickness using a material in which a resistance adjusting agent such as carbon is dispersed in a synthetic resin such as polyimide resin or polyamide resin is used. Is done. The support roll 23 is a drive roll that rotates by receiving the power of a rotary drive device (not shown), and rotates the paper transport belt 21 in the above direction. A sheet suction voltage is applied to the suction roll 25 at a time when the sheet 9 is sucked from the power supply device 25b (FIG. 3 and the like).

  The fixing device 30 is of a type in which the toner image transferred to the paper 9 in the image forming device 10 is fixed by heating and pressing. As the fixing device 30, for example, a heating rotator that is rotationally driven in a predetermined direction and heated by a heating unit so that the surface temperature is maintained at a predetermined temperature in a dedicated housing, and the heating A roll-type or belt-type pressurizing rotary body that is driven and rotated in contact with a predetermined pressure so as to substantially follow the axial direction of the rotary body is used. Fixing by the fixing device 30 is performed by introducing and passing the paper 9 on which the toner image is transferred to a contact portion where the heating rotator and the pressure rotator contact each other.

  FIG. 2 shows a control apparatus that mainly controls the operation of the image forming apparatus 10 in the image forming apparatus 1.

  The control device 5 is mainly composed of a logical operation processing device, storage means, control means and the like. The control device 5 includes a photosensitive drum control unit 51 that controls the operation of a rotation driving device that rotates the photosensitive drum 12 in each image forming device 10 (Y, M, C, and K), and a charging device 13 for charging. A charging control unit 52 that controls the operation of the power supply device that applies the voltage, an exposure control unit 53 that controls the operation of the exposure device 14, a development control unit 54 that controls the operation of the developing device 15, and a transfer voltage to the transfer device 16. A charge control unit 55 that controls the operation of the power supply device to be applied, a charge removal control unit 56 that controls the operation of the charge removal device 17, and the like are connected. The development control unit 54 controls the operation of a rotation drive device that rotates the development roll 15a, and the bias control unit controls the operation of a power supply device that applies a development voltage (development bias) to the development roll 15a. 54b.

  The control device 5 is also connected to an operation display unit, an input / output unit, detection means such as various sensors, and the like (not shown), and inputs and outputs necessary information (including display). The control operation by the control device 5 is executed in accordance with various control programs and data stored in the storage means while incorporating various necessary input information. Incidentally, the control device 5 controls each operation (rotation operation, heating operation, etc.) of the sheet conveyance control unit and the fixing device 30 that controls each operation (rotation operation, paper adsorption operation, etc.) of the paper conveyance device 20. A fixing control unit or the like may be connected.

  An image forming operation (hereinafter also referred to as “printing operation”) by the image forming apparatus 1 is performed as follows.

  First, the image forming apparatus 1 forms a color printing mode for forming a full color image composed of toner images of the four colors (Y, M, C, K) as a multi-color image and a black image as a single color image. The printing operation is executed separately from the monochrome (black only) printing mode. Selection between the color printing mode and the monochrome printing mode is performed by selecting instruction information included in input image information or information specified by a user on a display screen of a printer driver displayed on a PC connected to the image forming apparatus 1. Etc.

  First, a basic printing operation when a full-color image is formed on one side of the paper 9 in the color printing mode will be described.

  When the control device 5 receives a print operation start command in the color print mode, the control device 5 performs a control operation to form the photosensitive drums of the image forming devices 10 (Y, M, C, K) as shown in FIG. 12 and the developing roll 15a and the paper conveying belt 21 of the paper conveying device 20 start to rotate, and the charging device 13, the developing device 15 and the transfer device 16 of each image forming device 10 (Y, M, C, K) are powered on. Predetermined charging voltage, developing voltage, and transfer voltage start to be applied from the devices 12b, 15b, and 16b, respectively. At this time, the photosensitive drum 12 and the paper transport belt 21 rotate at substantially the same peripheral speed.

  As a result, each charging device 13 in the image forming device 10 charges the image holding surface of each photosensitive drum 12 to a predetermined polarity and potential. Subsequently, the exposure device 14 performs exposure based on the image signal on the charged image holding surface of the photosensitive drum 12 to form an electrostatic latent image having a predetermined potential difference. Thereafter, each developing device 15 develops each electrostatic latent image formed on the photoconductive drum 12 with toner charged to a predetermined polarity (for example, reverse development), and visualizes it as a toner image. As a result, in all of the four image forming apparatuses 10 (Y, M, C, K), toner images of the respective colors (Y, M, C, K) are formed exclusively on the respective photosensitive drums 12.

  On the other hand, in accordance with the image forming operation timing of the toner image, a sheet 9 having a desired size, type, and the like is conveyed and supplied from a sheet feeding device (not shown) to the sheet conveying device 20, and the rotating sheet conveying belt. 21 is attracted to the outer peripheral surface of 21 by the electrostatic action of the suction roll 25. After that, when the sheet 9 is conveyed by the sheet conveying belt 21 and passes the transfer position of each image forming device 10 (Y, M, C, K), the image forming device 10 on the photosensitive drum 12 is used. The toner image is transferred in such a state that the toner image is superposed on the sheet 9 side in order under the electrostatic action of the transfer device 16. During this transfer, a transfer voltage having a polarity opposite to the polarity of the charging potential of the image holding surface of the photosensitive drum 12 (in this example, the same as the charging polarity of the toner) is applied to the transfer device 16. The surface of the photosensitive drum 12 after the transfer is completed is discharged by the discharging device 17 and cleaned by the cleaning device 18.

  Subsequently, the sheet 9 on which the toner image has been transferred is peeled off from the sheet conveying belt 21 and then conveyed to the fixing device 30 and introduced. In the fixing device 30, the toner of the toner image is melted and applied to the paper 9 by heating and pressurizing the paper 9 on which the toner image has been transferred through the contact portion between the heating rotary body and the pressurizing rotary body. Let it settle. The paper 9 after the fixing is completed is transported and accommodated in a paper discharge unit (not shown) discharged from the fixing device 30 when only image formation on one side is performed.

  Through the above series of operations, a full-color image composed of four color toner images of Y, M, C, and K is formed on one side of the paper 9, and basic color printing on one sheet is completed. When there is an instruction for continuous color printing for a plurality of sheets, the above-described series of operations is similarly repeated for the number of sheets instructed.

  Next, a basic printing operation when a black image is formed on one side of the paper 9 in the monochrome printing mode will be described.

  When the control device 5 receives a print operation start command in the monochrome print mode, the image forming device 10K that forms a black (K) toner image by the control operation of the control device 5 as shown in FIG. As in the printing mode, the photosensitive drum 12 and the developing roll 15a start to rotate, and predetermined charging voltage, developing voltage, and transfer voltage are applied to the charging device 13, the developing device 15, and the transfer device 16, respectively. It begins to be applied.

  On the other hand, in the image forming device 10 (Y, M, C) that does not form toner images of Y, M, and C colors, the photosensitive drum 12 is rotated and the charging device 13 is rotated as shown in FIG. The charging voltage (for the monochrome printing mode) is applied and the developing voltage is applied to the developing roll 15a of the developing device 15, and the other components are not operated. That is, neither exposure by the exposure device 14 in the image forming device 10 (Y, M, C), rotation of the developing roller 15a of the developing device 15, nor application of a transfer voltage to the transfer device 16 is performed. Device 17 does not work. A symbol 16 d in FIG. 4 conceptually indicates a switch (function) for cutting off the supply of the transfer voltage to the charging device 16 of each power supply device 16 b, and actually includes a function included in the transfer control unit 55. It corresponds to.

  Thereby, in the black (K) image forming device 10K, black is formed by charging the photosensitive drum 12 by the charging device 13 as described above, forming an electrostatic latent image for black by the exposure device 14, and developing by the developing device 15. The toner image is formed and the black toner image is transferred by the transfer device 16.

  At this time, the toner image of each color of Y, M, and C is not formed in the image forming device 10 (Y, M, C). Further, in this image forming apparatus 10 (Y, M, C), since each photosensitive drum 12 rotates idly, the image holding surface of each photosensitive drum 12 comes into contact with the rotating paper transport belt 21 with a speed difference. There is nothing. Further, since the image holding surface of each photoconductive drum 12 is charged and the developing voltage is applied to the developing roll 15a of each developing device, the developing device 15 is applied to the holding surface of each photoconductive drum 12. The toner does not move and adhere. In addition, since a transfer voltage is not applied to each transfer device 16, the image holding surface of the photosensitive drum 12 when the paper transport belt 21 passes through the transfer position of the image forming device 10 (Y, M, C). There is no electrical factor that lowers the potential due to the application of a transfer voltage having the opposite polarity to the surface potential.

  Next, the sheet 9 conveyed by the sheet conveying belt 21 and passing the transfer position of each image forming device 10 (Y, M, C, K) is transferred to the transfer position of the image forming device 10 (Y, M, C). The toner image is not transferred, and the black toner image on the photosensitive drum 12 is transferred by the electrostatic action of the transfer device 16 at the transfer position of the black image forming device 10K. The sheet 9 on which the black toner image has been transferred is conveyed to the fixing device 30 and subjected to a fixing process, and then discharged to the discharge unit.

  Through the series of operations described above, a monochrome image composed of one black toner image is formed on one side of the sheet 9, and basic monochrome printing on one sheet is completed. In addition, when there is an instruction for continuous monochrome printing for a plurality of sheets, the above-described series of operations is similarly repeated for the instructed number of sheets.

  Here, FIG. 9 shows the charging devices 13 (Y, M, C, K) of the four image forming devices 10 (Y, M, C, K) when monochrome printing is repeatedly performed. The results of measuring the amount of rotation (rotation speed or rotation time) of each photosensitive drum 12 and the charging potential (surface potential of the image holding surface) of each photosensitive drum 12 when the same charging voltage is applied are schematically shown. It is shown.

  All the charging potentials on the respective photosensitive drums 12 tend to gradually increase (become higher) as the rotation amount of the photosensitive drum 12 increases (increases). As described above, this is because the image holding surface (surface layer) of the photosensitive drum 12 is worn due to contact (sliding) with the cleaning device 18 or contact with the paper transport belt 21 or charged by the charging device 13. This is considered to be due to the fact that toner or the like adheres to a member (charging roll or the like) and the charging performance deteriorates. What should be noted here is that the degree of increase (increase) in the charging potential in the three-color image forming device 10 (Y, M, C) of Y, M, and C is the same as that in the black image forming device 10K. This is a point in which the charging potential tends to decrease gradually as the rotation amount of the photosensitive drum 12 increases rather than the degree of increase of the charging potential.

  FIG. 10 shows the results of measuring the wear rate of the image bearing surface (film) of each photosensitive drum 12 of the image forming device 10 (Y, M, C, K) during color printing and monochrome printing. is there. FIG. 4A shows the result of color printing, and FIG. 4B shows the result of monochrome printing.

  The measurement was carried out after a predetermined sample image was formed continuously for the number of rotations of the photosensitive drum 12 to be 300,000 rotations in each printing state with the new photosensitive drum 12 mounted. The film thickness of the surface layer of each photosensitive drum 12 after each printing was measured at the end of printing for 100000 rotations of the photosensitive drum by an eddy current type film thickness measuring device. At the time of monochrome printing, as described above, both the application of the transfer voltage and the neutralization operation of the neutralization device 18 are turned off. The wear ratio was indicated by a value obtained by subtracting the measured film thickness after wear from the initial film thickness and dividing the value by the number of revolutions of the photosensitive drum. At the time of color printing, the photosensitive drums 12 (Y, M, C, K) of the four colors have almost the same film wear rate. Also, during monochrome printing, the film wear rate of the black photosensitive drum 12K is almost the same as that during color printing, whereas the Y, M, C color photosensitive drums 12 (Y, M, C) are similar. The film wear ratio was lower (about 30%) than in the case of color printing.

  From the above, the rate of film abrasion of the photosensitive drum 12 varies depending on the ratio of color printing and monochrome printing, and this also contributes to the fact that the charged potential of the photosensitive drum 12 varies. Guessed.

  Therefore, in the image forming apparatus 1, the charging voltage applied to the charging device 13 in the four image forming devices (Y, M, C, K) is controlled as described below.

  First, as shown in FIG. 2, when the monochrome printing mode is selected and an operation for forming a single color image is executed, and when the color printing mode is selected and an operation for forming a color image is executed, predetermined operations are performed. There is provided an accumulation counter 6 for the number of rotations of the photosensitive drum that individually measures and accumulates the number of rotations of the photosensitive drum 12 in the image forming apparatus 10. In this example, the photoconductor drum 12 to be counted is a photoconductor drum in the black image forming device 10K.

  The cumulative count 6 measures the rotation time of the motor that rotates and drives the photosensitive drum 12 to be counted, and divides the information obtained by dividing the time required for the photosensitive drum 12 to make one revolution into monochrome printing. It is configured to be accumulated and stored separately in the time of color printing and stored in predetermined storage means (which may be dedicated or may be storage means of the control device 5 or the charging control unit 52). As the cumulative count value (information), the cumulative rotation speed Ek for monochrome printing and the cumulative rotation speed Ec for color printing are obtained. The cumulative counter 6 is connected to the control device 5 so that the count information can be transmitted to the control device 5 side.

Then, in the charge control unit 52 of the control unit 5, the image forming apparatus 10 that does not form a toner image on the formation of single-color image in the monochrome printing mode (Y, M, C) charging device 13 (Y, M, C) to The applied charging voltage (Vhc) is corrected as follows.

  That is, with respect to the charging voltage (Vhc), the first correction value determined from the initial set value (Vhc0) based on the cumulative rotational speed (Ek) of the photosensitive drum 12 during monochrome printing measured by the cumulative counter 6. (ΔV1) is changed to a value (= Vhc0− (ΔV1 + ΔV2) = Vhc ′) obtained by subtracting the second correction value (ΔV2) determined based on the accumulated rotational speed (Ec) of the photosensitive drum 12 during color printing. To do. The initial set value (Vhc0) is stored in advance in the storage means of the charging control unit 52, for example.

  At this time, the first correction value (ΔV1) is equal to the cumulative number of rotations Ek of the photosensitive drum 12 during monochrome printing, and the photoreceptor in the Y, M, and C image forming apparatus 10 that does not form a toner image during monochrome printing. A value (= Ek × α) obtained by multiplying a correction coefficient α set according to the amount of change in the charging potential of the drum 12 is used. The second correction value (ΔV2) is the cumulative rotation speed Ec of the photosensitive drum 12 at the time of color printing, and the charged potential of the photosensitive drum 12 in the Y, M, C color image forming device 10 at the time of color printing. A value (= Ec × β) obtained by multiplying the correction coefficient β set according to the fluctuation amount is used.

  Further, the correction coefficients α and β are derived as follows. A fixed amount of monochrome printing operation and color printing operation are separately performed in the state where the same charging voltage is applied to the photosensitive drum 12 of the image forming device 10 (Y, M, C) in the image forming apparatus 1, and each printing is performed. The difference (variation amount) between the initial charging potential and the final charging potential of the photosensitive drum when the operation was performed was measured with a surface potential measuring device, and the variation amount of the charging potential was divided by the number of rotations of the photosensitive drum. It is calculated as a value. A certain amount of printing operation can be specified by, for example, the number of rotations of the photosensitive drum 12. As a specific example, when the fluctuation amount of the charging potential is 20 V when the photosensitive drum is rotated 10,000 times and monochrome printing or color printing is performed, the correction coefficient at that time is generally 20/10000 = 0. .0002 (V / number of revolutions).

  On the other hand, since the black image forming device 10K forms a toner image in both monochrome printing and color printing, the charging voltage (Vhk) applied to the charging device 13K of the image forming device 10K is as follows. It is corrected as follows.

  That is, from the initial setting value (Vhk0) of the charging voltage (Vhk), the cumulative rotation speed (Ek) of the photosensitive drum 12 at the time of monochrome printing measured by the cumulative counter 6 and the photosensitive drum 12 at the time of color printing. The value is changed to a value (= Vhk0− (ΔV3) = Vhk ′) obtained by subtracting the third correction value (ΔV3) determined based on the accumulated rotational speed (Ec). In this case, the third correction value (ΔV3) is set to the total value (Ek + Ec) of the cumulative rotational speed Ek of the photosensitive drum 12 during monochrome printing and the cumulative rotational speed Ec of the photosensitive drum 12 during color printing. The value obtained by multiplying the coefficient β (= (Ek + Ec) × β).

  The control of the charging voltage is set to be executed at a part or all of the timings such as when the image forming apparatus 1 is turned on, at the start of the printing operation, at the end of the printing operation, and the like.

  The charging voltage is controlled as follows.

  First, control of the charging voltage (Vhc) applied to the charging device 13 of the Y, M, C color image forming device 10 (Y, M, C) will be described. First, when it is time to execute the charging voltage control, the controller 5 and the charging control unit 52, as shown in FIG. 5, accumulate the rotational speed (Ek) of the photosensitive drum 12 during past monochrome printing. ) And the past rotational speed (Ec) of the photosensitive drum 12 at the time of color printing are read from the storage means related to the cumulative counter 6 (step 10: S10).

Subsequently, the first correction value (ΔV1) relating to monochrome printing and the second correction value (ΔV2) relating to color printing correspond to the accumulated rotational speeds Ek and Ec and the fluctuation amount of the charging potential during monochrome printing. Using the correction coefficient α that is set and the correction coefficient β that is set in accordance with the amount of change in the charging potential during color printing, they are respectively calculated by the following equations (S11 to S12).
ΔV1 = Ek × α, ΔV2 = Ec × β

Thereafter, the correction value (Vhc ′) of the charging voltage (Vhc) is calculated by the following equation using the initial setting value (Vhk0), the first correction value (ΔV1), and the second correction value (ΔV2). Calculated (S13).
Vhc ′ = Vhc0− (ΔV1 + ΔV2)

  Finally, the charging voltage (Vhc) is replaced with the correction value (Vhc ′) and changed (S14). Thereby, in monochrome printing and color printing executed thereafter, the correction value (Vhc ′) is applied as the charging voltage to the charging device 13 of the image forming device 10 (Y, M, C).

  On the other hand, control of the charging voltage (Vhk) applied to the charging device 13 of the K-color image forming device 10K will be described.

  Also in this case, as in the case of the control of the charging voltage (Vhc), when it is time to execute the control of the charging voltage, in the control device 5 and the charging control unit 52, as shown in FIG. The cumulative rotational speed (Ek) of the photosensitive drum 12 at the time of past monochrome printing and the cumulative rotational speed (Ec) of the photosensitive drum 12 at the time of past color printing are respectively read from the storage means related to the cumulative counter 6 (S20). ). Actually, this step is executed as a common operation with the control operation of the charging voltage (Vhc).

Subsequently, a common third correction value (ΔV3) for monochrome printing and color printing is set according to the accumulated rotational speeds Ek and Ec and the variation amount of the charging potential during color printing. Are respectively calculated by the following formulas (S21).
ΔV3 = (Ek + Ec) × β

Thereafter, a correction value (Vhk ′) of the charging voltage (Vhk) is calculated by the following equation using the initial setting value (Vhk0) and the third correction value (ΔV3) (S22).
Vhk ′ = Vhk0− (ΔV3)

  Finally, the charging voltage (Vhk) is replaced with the correction value (Vhk ′) and changed (S24). As a result, in monochrome printing and color printing performed thereafter, the correction value (Vhk ′) is applied as the charging voltage to the charging device 13 of the image forming device 10K.

  For example, the correction coefficients α and β are “α = 0.00006 (V / rotation speed), β = 0.0002 (V / rotation speed)”, and the cumulative rotation speed Ek for monochrome printing and the cumulative rotation for color printing. When the number Ec is “Ek = 100000, Ec = 50000”, the charging voltages (Vhc, Vhk) are changed as follows.

  Regarding the charging voltage (Vhc) applied to the Y, M, C color charging device 13, ΔV1 = Ek × α = 100000 × 0.00006 = 6 (V), ΔV2 = Ec × β = 50000 × 0.0002 = 10 (V), so that a value obtained by subtracting the first correction value ΔV1 and the second correction value ΔV2 from the initial setting value (Vhc0) (= Vhc0− (ΔV1 + ΔV2) = Vhc0-16) is the correction value ( Vhc ′).

  On the other hand, with respect to the charging voltage (Vhk) applied to the K-color charging device 13, ΔV3 = (Ek + Ec) × β = (100000 + 50000) × 0.0002 = 30 (V), so the initial setting value (Vhk0 ) Minus the third correction value ΔV3 (= Vhk0−ΔV3 = Vhc0−30) is the correction value (Vhk ′).

  In this specific example, with respect to the correction coefficients α and β, the K-color photosensitive drum 12 and the (Y, M, C) -color photosensitive drum 12 are rotated 10,000 times with −900 V being applied as the charging voltage. Thus, monochrome printing and color printing were performed individually, and the fluctuation amount of each charging potential at this time was derived based on the above-described calculation formula from the results of 6 V for monochrome printing and 20 V for color printing (α = 6). / 100,000, β = 20/50000).

  FIG. 7 shows the charging voltage (Vhc) and charging potential for the Y, M, and C colors when the charging voltage is controlled as described above when monochrome printing and color printing are performed together. Each transition state is schematically shown. In other words, the transition state of the charging voltage (Vhc) is applied when each printing is started assuming that the above control is performed each time monochrome printing and color printing are finished. The charging voltage to be corrected and the charging voltage to be corrected when the printing is completed are connected by a straight line. As shown in FIG. 7, the correction amount (degree of change) when monochrome printing is performed is relatively less than the correction amount when color printing is performed. As described above, in this charging voltage control, the charging voltage for the Y, M, and C colors (Vhc) is substantially equivalent to the operation amount during monochrome printing (the accumulated rotational speed of the photosensitive drum). And the amount of movement during color printing (same as above).

[Modification]
In the above embodiment, as shown in FIGS. 1 and 8, the process cartridge in which the photosensitive drum 12, the charging device 13, the developing device 15, the charge eliminating device 17, and the cleaning device 18 in each image forming device 10 are integrated. 7 (Y, M, C, K), and the process cartridge 7 can be configured as a replacement part that is detachably attached to the main body (not shown) of the image forming apparatus 1.

  In this case, the accumulated rotational speeds (Ek, Ec) of the photosensitive drum 12 at the time of monochrome printing and color printing measured by the cumulative counter 6 are assigned to the process cartridges 7 (Y, M, C, K). A cartridge memory 72 (RAM that can be stored and held: random access memory) 72 that is stored and held individually is attached. On the other hand, on the main body side of the image forming apparatus 1, a cartridge memory read / write device 75 connected to the cartridge memory 72 and the process cartridge is provided in the process cartridge mounting portion. As shown in FIG. 2, the read / write device 75 is connected to the control device 5 so as to be able to transmit / receive required information including the accumulated rotational speed.

  And when comprised in this way, in addition to each cumulative rotation speed (Ek, Ec) measured with the accumulation counter 6 being written in the recording means of the control apparatus 5 or the charge control part 52, each process It is also written and stored in the cartridge memory 72 of the cartridge 7 (Y, M, C, K). Further, in controlling the charging voltage described above, the control device 5 and the charging control unit 52 read out and use the accumulated rotational speeds (Ek, Ec) stored in the cartridge memory 72.

  Accordingly, for example, the cumulative counter 6 is individually installed for each of the Y, M, C, and K photoconductor drums 12, and the cumulative rotation speed of each photoconductor drum 12 (Y, M, C, K) is set. If each of the process cartridges 7 (Y, M, C, K) is stored in the cartridge memory 72 and stored in the cartridge memory 72, a part of each of the process cartridges 7 (Y, M, C, K) becomes a new cartridge or a used used cartridge. Even if the cartridge is replaced, the accumulated rotational speed is managed for each cartridge 7, so that the replaced process cartridge 7 has a different (unique) cumulative rotational speed from the other non-replaced cartridges 7. The charging voltage can be controlled based on the above.

In the case of the above configuration, when each process cartridge 7 (Y, M, C, K) is replaced with a new cartridge 7, it is stored in the storage device of the control device 5 or the charging control unit 52. the cumulative number of rotations of the photosensitive drum 12 in the process cartridge 7 which is remove in exchange to return to zero.

  As a result, the accumulated rotational speed of the photosensitive drum 12 of the replaced process cartridge 7 is correctly recognized, and the subsequent charging voltage control is executed. Incidentally, identification at the time of replacement of the old and new process cartridges 7 can be performed, for example, by storing identification information unique to the cartridge memory 72 and collating the difference between the identification information at the time of replacement. The process cartridge 7 only needs to have at least the photosensitive drum 12 mounted thereon, and other components to be mounted can be arbitrarily selected.

  Further, in the above embodiment, the first correction value (ΔV1) and the second correction value (ΔV2) are obtained by calculating from the respective correction rotational speeds Ek, Ec and the corresponding correction coefficients α, β. The first correction value (ΔV10) and the second correction value (ΔV20) for each of the predetermined cumulative rotational speeds Ek and Ec are set in advance, and the first correction is performed when the cumulative rotational speeds Ek and Ec are reached. It is also possible to configure so that the value (ΔV10) and the second correction value (ΔV20) are collated and adopted.

  Further, in the above-described embodiment, the accumulated rotational speed of the photosensitive drum 12 at the time of monochrome printing and color printing is measured, but the rotational time of the photosensitive drum 12 at that time may be accumulated and measured. Good.

  In the above-described embodiment, the transfer voltage is not applied to the Y, M, and C color transfer devices 16 during monochrome printing. Instead, a low voltage lower than the transfer voltage is used. May be applied. At this time, the low voltage means that the potential of the image holding surface of the photosensitive drum 12 when a normal transfer voltage is applied is lowered, and the photosensitive drum 12 in a state where the surface potential is lowered is charged by the charging device 13. Any voltage can be used as long as the voltage can be maintained in a state in which the surface potential of the image holding surface is sufficiently lower than the current flowing into the charging device 13 from the image holding surface. The value is about 05 to 0.5 times. Further, for example, when there is little risk of film abrasion on the image holding surface of the photosensitive drum 12 due to contact with the paper conveyance belt 21, it is also normal for the Y, M, C color transfer device 16 for monochrome printing. The transfer voltage may be applied.

  In addition, for the image forming apparatus 1, an intermediate transfer body in the form of a belt or the like that temporarily holds and conveys the toner image formed by the image forming apparatus and finally transfers the toner image to a sheet or the like. It is also possible to apply an image forming apparatus of a type using Further, the image forming apparatus 1 may be of a type that does not use the static eliminating device 17. Furthermore, it is sufficient that at least two imaging devices 10 are provided.

1 is an explanatory diagram illustrating a main part of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of a main control system in the image forming apparatus of FIG. 1. It is explanatory drawing which shows the main operation states at the time of color printing. It is explanatory drawing which shows the main operation states at the time of monochrome printing. It is a flowchart which shows control operation | movement of the charging voltage of Y, M, and C color. It is a flowchart which shows the control operation of the charging voltage of K color. It is explanatory drawing which shows typically the transition state by control of the charging voltage of Y, M, and C color. It is explanatory drawing which shows the structure of a process cartridge. The graph which showed typically the result of having measured the relationship between the rotation speed of each photoconductive drum when a fixed charging voltage is applied, and the charge potential of the photoconductive drum of each color (Y, M, C, K) It is. It is a graph which shows the result of having measured the abrasion rate of the photosensitive drum for each color (Y, M, C, K) at the time of color printing and monochrome printing, respectively.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 5 ... Control apparatus (a part of control means), 6 ... Accumulation counter (measurement means) of photosensitive drum rotation speed, 7 ... Process cartridge (replacement part), 10 ... Imaging device, 12 ... Photosensitive drum (image holder), 13... Charging device, 15... Developing device, 16.

Claims (5)

An image holding body having an image holding surface and rotating, a charging device for applying a charging voltage to charge the image holding surface of the image holding body, and a charged image holding surface of the image holding body. A plurality of image forming apparatuses comprising: a developing device that develops an electrostatic latent image with a developer of a predetermined color to form a developer image; and a transfer device that applies a transfer voltage to transfer the developer image; ,
A sheet transport body or an intermediate transfer body that sequentially passes in contact with the image holding surface of the image holding body at a transfer position where transfer by the transfer device of each image forming apparatus is performed;
When performing an operation of forming a single color image composed of one color developer image formed by one of the plurality of image forming devices, and each color formed by the plurality of image forming devices Measuring means for individually measuring and accumulating the amount of rotation of the image carrier when performing an operation of forming a multi-color image configured by combining the developer images.
The image holding at the time of monochromatic image formation measured by the measuring means from the initial setting value for the charging voltage applied to the charging device of the image forming apparatus that does not form a developer image when the monochromatic image is formed. A first correction value determined based on a cumulative value of the rotation amount of the body, and a second correction value determined based on a cumulative value of the rotation amount of the image carrier when the multi-color image is formed, measured by the measuring unit. And a control means for changing to a value obtained from
The first correction value is a cumulative value of the rotation amount of the image carrier in the image forming apparatus that does not form a developer image when a monochrome image is formed, and a charging potential of the image carrier when the monochrome image is formed. It is a value obtained from the correction coefficient set according to the fluctuation amount,
The second correction value is a cumulative value of the amount of rotation of the image carrier in the image forming apparatus that does not form the developer image when a multi-color image is formed, and a value of the image carrier when the multi-color image is formed. value der obtained from the correction coefficient set according to the amount of variation of charged potential is,
In addition, the control unit is configured to measure the monochromatic color measured by the measuring unit from an initial setting value for a charging voltage applied to the charging device of the image forming device that forms a developer image when forming the monochromatic image. The sum of the accumulated value of the rotation amount of the image carrier during image formation and the accumulated value of the rotation amount of the image carrier during the formation of the multi-color image is multiplied by the correction coefficient in the second correction value. An image forming apparatus comprising: changing to a value obtained by subtracting the third correction value .   The image forming apparatus according to claim 1, wherein the rotation amount of the image carrier is obtained from a rotation number or a rotation time. It is configured as a replacement part that is detachably mounted on the apparatus main body at least the image carrier in each image forming device,
In addition, each of the replacement parts is provided with a storage unit that individually stores and holds a cumulative value of each rotation amount of the image holding body at the time of monochromatic image formation and multi-color image formation measured by the measurement unit, The image forming apparatus according to claim 1, wherein the control unit reads and uses a cumulative value of each rotation amount stored in the storage unit. At least the image carrier in each image forming device is configured as a replacement part that is detachably attached to the apparatus main body, and the rotation amount of each replacement part for each image carrier is individually measured by the measuring unit. Cumulative,
Further, when each of the replacement parts is replaced with a new replacement part, the accumulated value of the rotation amount of the image carrier in the replaced replacement part stored in the control unit is returned to zero. The image forming apparatus described.   The control means does not apply a transfer voltage or applies a low voltage lower than the transfer voltage to the transfer device of the image forming apparatus that does not form a developer image when forming the monochrome image. 5. The image forming apparatus according to any one of 4 above.

Images