JP4923726B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a multifunction machine of these.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged with a predetermined potential by a charging device, and this is used as image information. An electrostatic latent image is formed by exposure with controlled light. Then, the electrostatic latent image is developed by a developing device to form a toner image, and the toner image is further transferred and fixed on the recording paper, thereby forming a toner image on the recording paper.

  In general, a photosensitive drum used in such an image forming apparatus has a so-called “time-dependent change in which charging characteristics (a relationship between a voltage applied to the charging device and a surface potential of the photosensitive drum) change as an image forming cycle is repeated. "Is likely to occur. That is, the photosensitive layer (for example, the charge transport layer CTL) of the photosensitive drum is scraped or the charging device is contaminated, and the charging condition in the charging device is maintained at a predetermined setting while the charging condition on the photosensitive drum is maintained. If charging continues, a phenomenon occurs in which the charged potential of the photosensitive drum gradually increases (or decreases). Therefore, if the charging conditions in the charging device and the developing conditions in the developing device are kept at predetermined settings, sufficient potential contrast (simply referred to as potential contrast) cannot be obtained, and so-called fogging (background stain) occurs. In addition, the image quality is deteriorated such that desired image density and gradation cannot be obtained.

  Therefore, in order to cope with such a problem, the following techniques exist conventionally. For example, a plurality of charging potential values are set on the photosensitive member, and a developing bias value corresponding to the charging potential value is set on the developing device, and the developing bias value is set in accordance with fluctuations in the charging potential of the photosensitive member. There exists a technique for determining the amount of correction (see, for example, Patent Document 1). In addition, there is a technique of measuring the total number of rotations or the total number of copies of the image forming apparatus and changing process conditions such as charging conditions and development conditions in accordance with the measured values (see, for example, Patent Document 2).

  By the way, in the image forming apparatus using the above-described electrophotographic method, a color image forming method called “tandem method” is often used as a method for forming a color image. In the tandem image forming apparatus, Y (yellow), M (magenta), C (cyan), and K (black) toner images are formed on different photosensitive drums, and are formed on the respective photosensitive drums. Each color toner image is sequentially transferred directly to the recording paper, or indirectly transferred to the recording paper via an intermediate transfer member, thereby forming a full color image in which the respective color toner images are superimposed.

  Such a tandem image forming apparatus has a configuration in which various process means such as a charging device and a developing device are individually arranged on each of the photosensitive drums that form the respective color toner images. As one form of such a configuration, the image forming unit (process cartridge) in which the photosensitive drum and one or a plurality of process units are integrated is used. For example, it corresponds to the life of the photosensitive drum and the consumption of the developer. In addition, an apparatus of a system that simplifies maintenance by exchanging the entire process cartridge is also widespread.

  In such a tandem image forming apparatus, in order to ensure a predetermined potential contrast corresponding to the change in charging characteristics of the photosensitive drum as described above, charging conditions in the charging apparatus and developing conditions in the developing apparatus are set. It is necessary to set each photosensitive drum separately. Therefore, conventionally, the charging device and the developing device arranged on each photoconductive drum are provided with individual power supplies, respectively, and respond to changes in the state of the photoconductive drum and the charging device (that is, changes with time). Charging conditions and development conditions have been set.

JP-A-3-148675 (page 3-4) Japanese Patent No. 3032650 (page 4-6)

However, if a separate power source is provided for the charging device and the developing device provided for each photosensitive drum in order to cope with the change in charging characteristics of the photosensitive drum with time, the manufacturing cost of the image forming apparatus is reduced. There is a certain limit to this. In addition, since it is necessary to secure a space for arranging the power supply, there is a restriction on downsizing of the apparatus.
For this reason, in a tandem type image forming apparatus in which a plurality of photosensitive drums are used, for example, the power source arranged for each of the plurality of photosensitive drums is changed to several power sources smaller than the number of one or a plurality of photosensitive drums. In addition to the common use, it is required to realize a configuration capable of maintaining a sufficient potential contrast even when the charging characteristics of the respective photosensitive drums change with time.

  Therefore, the present invention has been made to solve the technical problems as described above, and the object of the present invention is to be arranged in an image forming apparatus having a common power source connected to the process means. It is to always ensure a sufficient potential contrast in each of the plurality of photosensitive drums.

  For this purpose, the image forming apparatus of the present invention includes a plurality of image carriers, each charging member disposed on each of the plurality of image carriers and charging the surface of the image carrier, and a plurality of image carriers. Each developing member that is arranged on each of the bodies and that develops the electrostatic latent image formed on the image holding member, and one charging voltage supply means that is commonly connected to a plurality of charging members in each charging member A plurality of developing voltage supply means individually connected to each developing member; a charging voltage supplied from the charging voltage supplying means to the plurality of charging members; and a developing voltage supplied from the developing voltage supply means to each developing member; And a control unit that calculates a charging voltage correction value corresponding to a change with time of each of the plurality of image carriers, and supplies the charging voltage from the charging voltage supply unit based on the calculated charging voltage correction value. The charging voltage is determined and the charging voltage is supplied. It is characterized by determining the development voltage corresponding to the charging potential of each formed in a plurality of image carriers in Rukoto.

  Here, the control unit determines that the charging voltage and the developing voltage determined by the charging voltage supply means are present when the absolute value of the developing voltage is smaller than the first predetermined value among the determined developing voltages. A process of correcting the charging voltage and the development voltage by subtracting the second predetermined value from the development voltage determined in the supply means may be further performed. In particular, the control unit can set the difference between the minimum absolute value of the set developing voltage and the first predetermined value as the second predetermined value.

  The control unit also calculates a correction voltage calculation unit for calculating a charging voltage correction value, calculates an average value of the charging voltage correction value for each of the charging members, and supplies the calculated average value of the charging voltage correction value to the charging voltage. A charging voltage setting unit determined as a charging voltage supplied from the means, and a charging potential estimation unit that estimates a charging potential formed on each of the plurality of image carriers by supplying a charging voltage determined by the charging voltage setting unit And a developing voltage setting unit that determines a developing voltage supplied from the developing voltage supply means with reference to the charging potential of each of the image carriers estimated by the charging potential estimating unit. it can. In particular, the correction voltage calculation unit calculates a charging voltage correction value corresponding to any one or more of an integrated rotation speed, an integrated rotation time, and an integrated image forming cycle for each of the image carriers. Can do. Furthermore, the image processing apparatus further includes a memory that stores any one or more of an accumulated rotation speed, an accumulated rotation time, and an accumulated image forming cycle for each of the image holding bodies, and the correction voltage calculation unit stores the image holding body from the memory. Any one or more of the accumulated rotation speed, the accumulated rotation time, and the accumulated image forming cycle may be acquired.

  Further, the image holding member, the charging member, the developing member, and the memory that stores any one or more of the accumulated rotation speed, the accumulated rotation time, and the accumulated image forming cycle of the image holding member are integrally configured. It can also be a feature.

  Further, the present invention is regarded as an image forming method. In the image forming method of the present invention, each of a plurality of image carriers is charged by a charging member disposed on each of the image carriers, and is formed on the image carrier. An image forming method in which an electrostatic latent image is developed by a developing member disposed on each of the image carriers, and a charging voltage correction value is calculated corresponding to a change with time of each of the plurality of image carriers, A step of determining charging voltages to be supplied to a plurality of the charging members from one charging voltage supply means based on the calculated charging voltage correction value, and a plurality of image carriers by supplying the charging voltages from the charging voltage supply means And a step of determining a developing voltage to be supplied to each developing member in accordance with a charging potential formed on each of the above.

  Here, an average value of the charging voltage correction values for each of the calculated charging members is calculated, and the calculated average value of the charging voltage correction values is determined as a charging voltage supplied from the charging voltage supply means. be able to. Further, when there is a predetermined developing voltage whose absolute value is smaller than the first predetermined value, the charging voltage determined by the charging voltage supplying means and the developing voltage supplying means are determined. The method may further include a step of correcting the charging voltage and the developing voltage by subtracting the second predetermined value from the developed voltage. Further, by supplying a charging voltage set to the charging voltage supply means, a charging potential formed on each of the plurality of image holding members is estimated, and a developing voltage is determined based on each estimated charging potential. Can be a feature.

  According to the present invention, in an image forming apparatus having a common power source connected to the process means, it is possible to always ensure a sufficient potential contrast in each of the plurality of arranged photosensitive drums.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus 1 shown in FIG. 1 is a so-called tandem type in which four image forming units (process cartridges) 10Y, 10M, 10C, and 10K are arranged in parallel in the vertical direction (substantially vertical direction) with a predetermined interval. It is configured. The process cartridges 10Y, 10M, 10C, and 10K are provided on a photosensitive drum 11 as an image carrier, a charging roll 12 as an example of a charging member that uniformly charges the surface of the photosensitive drum 11 at a predetermined potential, and a developing roll. A two-component developing system as an example of a developing member that develops an electrostatic latent image formed on the photosensitive drum 11 using a developer composed of held toner (negative charging characteristics) and carrier (magnetic particles). A developing unit 13 and a drum cleaner 14 for cleaning the surface of the photosensitive drum 11 after transfer are integrally formed.

Here, the process cartridges 10Y, 10M, 10C, and 10K are configured in substantially the same manner except for the toner stored in the developing device 13. Each of the process cartridges 10Y, 10M, 10C, and 10K forms yellow (Y), magenta (M), cyan (C), and black (K) toner images.
The process cartridges 10Y, 10M, 10C, and 10K are configured to be detachable from the main body of the image forming apparatus 1. For example, when the toner in the developing device 13 is consumed, the process cartridges 10Y, 10Y, It is configured to be exchangeable every 10M, 10C, 10K.

  In the image forming apparatus 1 of the present embodiment, as an exposure system, a laser exposure apparatus 20 that exposes the photosensitive drums 11 disposed in the process cartridges 10Y, 10M, 10C, and 10K, and the photosensitive drum 11 after transfer. A static elimination lamp 21 for neutralizing the static electricity is provided.

  Further, in the image forming apparatus 1 of the present embodiment, the conveyance belt 30 that conveys the paper P that is a recording material (recording paper) so as to contact the photosensitive drums 11 of the process cartridges 10Y, 10M, 10C, and 10K. Is arranged. The conveyor belt 30 is formed of a film-like endless belt that can electrostatically attract the paper P. Then, a paper conveyance path M1 is formed which is stretched between the driving roll 32 and the idle roll 33 and is circulated and is conveyed from the lower side to the upper side in the substantially vertical direction. ing.

Transfer rolls 31 are arranged at positions inside the conveyor belt 30 and facing the respective photosensitive drums 11. The transfer roll 31 forms a transfer electric field between the transfer drum 31 and the photosensitive drum 11 so that each color formed by the process cartridges 10Y, 10M, 10C, and 10K on the paper P held and transported by the transport belt 30. The toner images are sequentially transferred.
In addition, an adsorption roll 34 that charges the conveyance belt 30 is disposed at the most upstream portion of the conveyance belt 30 on the photosensitive drum 11 side. Since the surface of the transport belt 30 is charged to a predetermined potential by the suction roll 34, the paper P can be stably electrostatically attracted.
On the other hand, on the downstream side of the conveyance belt 30 along the sheet conveyance path M1, a fixing device 40 that performs fixing processing by heat and pressure on an unfixed toner image on the sheet P is disposed.

The image forming apparatus 1 according to the present embodiment includes a charging voltage supply unit that applies a predetermined charging bias voltage to the charging rolls 12 of the process cartridges 10Y, 10M, 10C, and 10K as a power source (voltage supply unit). A charging power source 61 as an example, a developing power source 62 as an example of a developing voltage supply means for applying a predetermined developing bias voltage to the developing device 13 of each process cartridge 10Y, 10M, 10C, 10K, a predetermined transfer to each transfer roll 31 A transfer power supply 63 for applying a voltage is provided. The charging power supply 61, the developing power supply 62, and the transfer power supply 63 are subjected to output control such as output voltage values and output timing by the control unit 60. Although detailed description is omitted, the control unit 60 also controls the operation of the entire image forming apparatus 1.
The charging power source 61 and the developing power source 62 of the present embodiment are configured to output a negative DC voltage while varying it. However, either one or both of the charging power supply 61 and the developing power supply 62 may be configured to output a voltage obtained by superimposing an AC voltage having a predetermined value on a negative variable DC voltage.
Further, the transfer power supply 63 of the present embodiment is configured to output a positive DC voltage.

Further, in the image forming apparatus 1 according to the present embodiment, as a paper transport system, the paper cassette 50 containing the paper P and the paper P accumulated in the paper cassette 50 are taken out at a predetermined timing on the paper feeding side. A pick-up roll 51 to be transported, a transport roll 52 to transport the paper P fed out by the pick-up roll 51, and a registration roll 53 to send the paper to the transport belt 30 in accordance with the image forming operation are provided.
Further, on the paper discharge side, a paper discharge roll 54 that conveys the paper P fixed by the fixing device 40, and in the case of single-sided printing, the paper P is directed toward a paper discharge unit 70 provided in the upper part of the apparatus main body. In the case of double-sided printing, the paper P on which one side is fixed by the fixing device 40 is directed to the double-sided conveyance path M2 by reversing from the rotation direction toward the paper discharge unit 70 at a predetermined timing. A reversing roll 55 that is fed out is disposed. In addition, a conveyance roll 56 is disposed along the double-side conveyance path M2 in the double-side conveyance path M2.

  In the image forming apparatus 1 of the present embodiment, under the operation control by the control unit 60, the laser exposure apparatus 20 generates a laser beam modulated based on the image information, and each process cartridge 10Y, 10M, An electrostatic latent image is formed on the photosensitive drum 11 of 10C and 10K. For example, in the yellow (Y) process cartridge 10Y, the surface of the photosensitive drum 11 uniformly charged at a predetermined potential by the charging roll 12 is scanned and exposed with the laser beam generated by the laser exposure device 20, and the photosensitive member is detected. An electrostatic latent image is formed on the drum 11. The formed electrostatic latent image is developed by the developing device 13, and a Y toner image is formed on the photosensitive drum 11. Similarly, M, C, and K color toner images are formed in the process cartridges 10M, 10C, and 10K, respectively.

When the formation of each color toner image is started in each of the process cartridges 10Y, 10M, 10C, and 10K, the paper P taken out from the paper cassette 50 is transferred to the conveyor belt 30 by the registration roll 53 in accordance with the toner image formation timing. Supplied. The paper P is transported through the paper transport path M1 while being electrostatically attracted onto the transport belt 30 that circulates and moves in the direction of the arrow in FIG. Then, the respective color toner images are sequentially transferred onto the paper P in a superimposed manner by the transfer electric field formed by the transfer roll 31.
The sheet P on which the toner image has been electrostatically transferred is peeled from the transport belt 30 downstream of the process cartridge 10K and transported to the fixing device 40. When the paper P is conveyed to the fixing device 40, the unfixed toner image on the paper P is fixed to the paper P by receiving a fixing process using heat and pressure. The paper P on which the fixed image is formed is placed on a paper discharge unit 70 provided in a discharge unit of the image forming apparatus 1. On the other hand, during double-sided printing, the same transfer process is performed again via the double-sided conveyance path M2, and then placed on the paper discharge unit 70.

Subsequently, the connection between the charging power source 61 and the charging rolls 12 of the process cartridges 10Y, 10M, 10C, and 10K and the developing power source 62 and the process cartridges 10Y, 10M, 10C, and 10K in the image forming apparatus 1 of the present embodiment. The connection with the developing device 13 will be described. FIG. 2 is a wiring diagram for explaining the connection between the charging power source 61 and each charging roll 12 and the connection between the developing power source 62 and each developing device 13.
As shown in FIG. 2, a first charging power supply (charging voltage supply means) 611 provided in the charging power supply 61 is connected to the charging roll 12K of the process cartridge 10K. A second charging power supply (charging voltage supply means) 612 provided in the charging power supply 61 is connected to the charging rolls 12Y, 12M, 12C of the process cartridges 10Y, 10M, 10C. That is, the power supply for applying the charging bias voltage to the charging rolls 12Y, 12M, and 12C is shared by the single second charging power supply 612, and the charging bias voltage of the same value is applied to the charging rolls 12Y, 12M, and 12C. It is configured to be. As described above, in the image forming apparatus 1 according to the present embodiment, the number of power sources can be reduced by sharing the power source for applying the charging bias voltage to the charging rolls 12Y, 12M, and 12C of the process cartridges 10Y, 10M, and 10C. Thus, the image forming apparatus 1 can be reduced in size and cost.

  Further, a first developing power source (developing voltage supply means) 621 provided in the developing power source 62 is connected to the developing device (developing roll) 13K of the process cartridge 10K. A second developing power source (developing voltage supply means) 622 provided in the developing power source 62 is connected to the developing device (developing roll) 13C of the process cartridge 10C. A third developing power source (developing voltage supply means) 623 provided in the developing power source 62 is connected to the developing device (developing roll) 13M of the process cartridge 10M. A developing device (developing roll) 13Y of the process cartridge 10Y is connected to a fourth developing power source (developing voltage supply means) 624 provided in the developing power source 62. In other words, each developing device (developing roll) 13 is connected to an independent developing power source 62, and a developing bias voltage corresponding to each developing device is applied.

Subsequently, a control method for setting the charging bias voltage in the second charging power source 612 performed by the control unit 60, and a second developing power source 622, a third developing power source 623, and a fourth developing power source corresponding thereto. A control method for setting the developing bias voltage at 624 will be described.
Here, first, the surface potential (VH: photosensitive member charging potential) of the photosensitive drum 11 charged by the charging roll 12 and the potential (VL) of the region where the charged photosensitive drum 11 is exposed by the laser exposure device 20. The relationship between the exposure portion potential) and the developing bias voltage (VD: developing voltage) applied to the developing device (developing roll) 13 will be described. FIG. 3 is a diagram showing the relationship among the photosensitive member charging potential (VH), the exposure portion potential (VL), and the developing bias voltage (VD). The image forming apparatus 1 according to the present embodiment employs a reversal development method in which charging of the photosensitive drum 11 by the charging roll 12 is performed with a negative charge and development at the developing device 13 is performed with a negatively charged toner. Used. Therefore, the region of the exposed portion potential in FIG. 3 is an image portion, and the region of the photosensitive member charging potential is a white portion (background).

The development contrast potential (V2), which is the difference between the exposure portion potential (VL) and the development bias voltage (VD) shown in FIG. 3, is a factor for setting the image density and gradation of the image portion. That is, when the development contrast potential (V2) is small, sufficient image density and gradation cannot be obtained. Therefore, the development contrast potential (V2) needs to be secured at a predetermined value or more.
Also, the white background contrast potential (V1), which is the difference between the development bias voltage (VD) and the photosensitive member charging potential (VH) shown in FIG. 3, is a so-called “fogging” (background stain) amount in the white background. It becomes a factor to decide. That is, when the white background portion contrast potential (V1) exceeds a predetermined value, the reversely charged toner (that is, positively charged toner) adheres to the white background portion and becomes fogged or similarly reversely charged. Carriers adhere and cause image contamination, internal contamination, and the like. On the other hand, when the white background portion contrast potential (V1) becomes smaller than a predetermined value, normally charged toner (that is, negatively charged toner) cannot be removed from the white background portion, resulting in fogging. Therefore, it is necessary to set the white background portion contrast potential (V1) within a predetermined range.

Next, a so-called “time-dependent change” in which the charging characteristics (the relationship between the charging bias voltage applied to the charging roll 12 and the photosensitive member charging potential (VH)) generated in the photosensitive drum 11 as the image forming cycle accumulates changes. State. The time-dependent change in the charging characteristics of the photosensitive drum 11 is caused by the removal of the photosensitive layer (for example, the charge transport layer CTL) of the photosensitive drum 11 or the contamination of the charging roll 12, and the like. Phenomenon in which the photosensitive drum charging potential (VH) of the photosensitive drum 11 gradually increases (or decreases) when the charging of the photosensitive drum 11 is continued while the charging bias voltage applied to is maintained at a predetermined value. It is.
FIG. 4 shows the integrated value of the number of rotations of the photosensitive drum 11 (that is, the integrated value of the image forming cycle) and the photosensitive drum when the charging bias voltage (Vdc: charging voltage) applied to the charging roll 12 is maintained at a predetermined value. It is the figure which showed the relationship with body charging potential (VH). As shown in FIG. 4, even if the charging bias voltage (Vdc) is maintained at a predetermined value, as the accumulated value of the rotational speed of the photosensitive drum 11 increases, the charging characteristics of the photosensitive drum 11 change with time. The photosensitive member charging potential (VH) gradually increases. FIG. 4 shows the case where the photosensitive member charging potential (VH) increases. However, the material, layer thickness, and charging of the photosensitive layer (charge generation layer CGL, charge transport layer CTL, etc.) constituting the photosensitive drum 11 are shown. Depending on the material of the roll 12 and the like, the photosensitive member charging potential (VH) may gradually decrease.

In order to cope with the change over time in the charging characteristics of the photosensitive drum 11 in which the photosensitive member charging potential (VH) increases (or decreases) as the image forming cycle as shown in FIG. A method of controlling the output voltage at the charging power supply 61 is effective so that the charging bias voltage (Vdc) is gradually decreased (or increased) as the integrated value of the drum rotation speed increases.
FIG. 5 shows a charging bias voltage that keeps the photosensitive member charging potential (VH) substantially constant even when image forming cycles are repeated for the photosensitive drum 11 showing the change over time of the charging characteristics shown in FIG. It is the figure which showed (Vdc). As shown in FIG. 5, by correcting the charging bias voltage (Vdc) to gradually decrease as the integrated value of the photosensitive drum rotation speed (image forming cycle) increases, the photosensitive member charging potential (VH) is corrected. ) Can be maintained substantially constant.

Incidentally, as described above, in the image forming apparatus 1 of the present embodiment, the same second charging power source 612 is used as a power source for applying a charging bias voltage to the charging rolls 12Y, 12M, 12C of the process cartridges 10Y, 10M, 10C. Is used. Therefore, the charging bias voltage having the same value is applied to the charging rolls 12Y, 12M, and 12C.
However, the toner consumption of each process cartridge 10Y, 10M, 10C is usually different. Therefore, the process cartridges 10Y, 10M, and 10C are almost always replaced at different timings. As a result, a situation occurs in which the process cartridges 10 </ b> Y, 10 </ b> M, and 10 </ b> C having different integrated values of the rotational speed of the photosensitive drum 11 (integrated values of the image forming cycle) are installed in the image forming apparatus 1. Therefore, as shown in FIG. 5, the charging bias voltage (charging voltage correction value) corrected in accordance with the integrated value of the rotational speed of the photosensitive drum is originally different for each process cartridge 10Y, 10M, 10C. Should be set to a value.
Therefore, in the control unit 60 of the present embodiment, the charging bias voltage corresponding to the integrated value of the photosensitive drum rotation speed in the second charging power source 612 is set as follows.

That is, in the image forming apparatus 1 of the present embodiment, the integrated value of the photosensitive drum rotation speed is stored for each of the process cartridges 10Y, 10M, and 10C. The integrated value of the photosensitive drum rotation speed for each of the process cartridges 10Y, 10M, and 10C, and the charging value for maintaining the integrated value of the photosensitive drum rotation speed and the photosensitive member charging potential (VH) shown in FIG. Based on the relationship with the bias voltage, a charging voltage correction value (Vdcm) for maintaining the photosensitive member charging potential (VH) substantially constant for each of the process cartridges 10Y, 10M, and 10C is obtained. Then, the calculated charging voltage correction values (Vdcm) in the respective process cartridges 10Y, 10M, and 10C are averaged, and the average value of the calculated charging voltage correction values (Vdcm) (average charging bias voltage: VDC) is calculated. Is set as an output value (charging voltage) from the second charging power source 612.
Further, in the image forming apparatus 1 according to the present embodiment, when the average charging bias voltage (VDC) is applied from the second charging power source 612, it is formed on the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C. The photosensitive member charging potential (VH) is estimated from the relationship shown in FIG. In each of the process cartridges 10Y, 10M, and 10C, the difference between the estimated photosensitive member charging potential (VH) and the developing bias voltage (VD) applied to the developing devices 13Y, 13M, and 13C is substantially the same. The developing bias voltage (VD) output from the second developing power source 622, the third developing power source 623, and the fourth developing power source 624 is determined.

In the following, the setting process of the charging bias voltage for the second charging power source 612 performed by the control unit 60 of the present embodiment and the corresponding processing for the second developing power source 622, the third developing power source 623, and the fourth developing power source 624 are performed. A developing bias voltage setting process will be described.
Here, FIG. 6 is a block diagram illustrating a functional configuration of the control unit 60 in the image forming apparatus 1 of the present embodiment. First, in the control unit 60 shown in FIG. 6, the function of writing the integrated value of the rotational speed of the photosensitive drum 11 to the storage memories CRMC, CRMM, and CRMY installed in the process cartridges 10Y, 10M, and 10C, and each storage The function of reading the integrated value of the rotational speed of the photosensitive drum 11 from the memories CRMC, CRMM, CRMY will be described.

As shown in FIG. 6, the control unit 60 of the present embodiment includes a photosensitive drum rotational speed measuring unit 601 that measures the rotational speed of the photosensitive drum 11, and sets the rotational speed of the photosensitive drum to each process cartridge 10Y, 10M, A data writing unit 602 for writing to the storage memories CRMY, CRMM, and CRMC installed in 10C, and a data reading unit 603 for reading the accumulated value of the rotational speed of the photosensitive drum 11 written to each of the storage memories CRMY, CRMM, and CRMC. I have.
The photosensitive drum rotation speed measurement unit 601 acquires rotation speed data (or drive motor drive time data) from, for example, a drive motor (not shown) of the image forming apparatus 1, and acquires the acquired rotation speed data (drive) of the drive motor. The rotational speed of the photosensitive drum 11 is measured based on time data. Then, data relating to the rotational speed of the photosensitive drum 11 is generated. Data relating to the rotational speed of the photosensitive drum 11 generated by the photosensitive drum rotational speed measurement unit 601 is stored in the storage memories CRMY, CRMM, and CRMC installed in the process cartridges 10Y, 10M, and 10C from the data writing unit 602. Each written. In that case, on the storage memory CRMY, CRMM, CRMC side installed in each process cartridge 10Y, 10M, 10C, the photosensitive drum rotation speed obtained from the data writing unit 602 of the control unit 60 is integrated, and the photosensitive drum The accumulated value of the rotational speed is stored.
On the other hand, the data reading unit 603 reads the integrated value of the rotational speed of the photosensitive drum stored in each storage memory CRMY, CRMM, CRMC, and outputs it to the charging bias voltage calculation unit 604 described later.

  In the image forming apparatus 1 of the present embodiment, the configuration in which the storage memories CRMY, CRMM, and CRMC are installed in the process cartridges 10Y, 10M, and 10C has been described. However, the image forming apparatus 1 of the present embodiment is not limited to such a configuration. For example, a configuration in which a storage memory that stores the integrated value of the rotation speed of the photosensitive drum 11 is arranged in the control unit 60 may be used. That is, a storage member such as an IC chip that stores process cartridge identification information is installed in each of the process cartridges 10Y, 10M, and 10C. The control unit 60 acquires identification information from the storage member, and allocates a storage area for each acquired identification information to the storage memory. Then, it is also possible to store the integrated value of the rotational speed of the photosensitive drum 11 corresponding to each identification information in the storage area allocated for each identification information. In that case, since it is not necessary to install the storage memories CRMY, CRMM, and CRMC in the process cartridges 10Y, 10M, and 10C, the process cartridges 10Y, 10M, and 10C can be manufactured at low cost. In addition, the identification information of each process cartridge 10Y, 10M, and 10C can be described by, for example, a bar code or the like, and an optical reading method can be used.

Subsequently, in the control unit 60 shown in FIG. 6, the charging bias voltage applied from the second charging power source 612 based on the rotation number integrated value of the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C (that is, the above-described charging bias voltage). A process for setting the average charging bias voltage (VDC) will be described. The setting process of the charging bias voltage (VDC) applied from the second charging power source 612 is performed by the charging bias voltage calculation unit 604 provided in the control unit 60.
FIG. 7 is a flowchart showing an example of a procedure for setting the charging bias voltage (VDC) performed by the charging bias voltage calculation unit 604 of the control unit 60. As shown in FIG. 7, first, the charging bias voltage calculation unit 604 acquires the rotational speed integrated value of the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C from the data reading unit 603 (S101).

Next, the charging bias voltage calculation unit 604 obtains the accumulated rotational speed value of the photosensitive drum 11 of each of the process cartridges 10Y, 10M, and 10C, and the accumulated rotational speed value of the photosensitive drum 11 and the photosensitive body shown in FIG. Using the relationship with the charging bias voltage (Vdc) that maintains the charging potential (VH) substantially constant, the rotational speed integrated value of the photosensitive drum 11 (the horizontal axis in FIG. 5) for each of the process cartridges 10Y, 10M, and 10C. ) To obtain a charging voltage correction value (Vdcm) (S102). Accordingly, the charging bias voltage calculation unit 604 here functions as a correction voltage calculation unit.
FIG. 8 is a diagram showing the relationship between the rotation speed integrated value (horizontal axis) of the photosensitive drum 11 of the process cartridges 10Y, 10M, and 10C and the charging voltage correction value (Vdcm) as an example. In the case shown in FIG. 8, the charging voltage correction value in the accumulated rotation number value of the process cartridge 10C is Vdcm3, the charging voltage correction value in the accumulated rotation number value of the process cartridge 10M is Vdcm2, and the charging in the accumulated rotation number value of the process cartridge 10Y. The voltage correction value is Vdcm1.

Further, the charging bias voltage calculation unit 604 performs an operation of averaging the charging voltage correction values Vdcm1, Vdcm2, and Vdcm3 for the process cartridges 10Y, 10M, and 10C obtained in step 102, and calculates the average value of the charging voltage correction values. Calculate (S103). Then, the average value of the calculated charging voltage correction values Vdcm1, Vdcm2, and Vdcm3 is set as a charging bias voltage (VDC) applied from the second charging power source 612 (S104). Therefore, the charging bias voltage calculation unit 604 here functions as a charging voltage setting unit.
In this way, by setting the average value of the charging voltage correction values Vdcm1, Vdcm2, and Vdcm3 as the charging bias voltage (VDC) applied from the second charging power supply 612, a new process cartridge that has just been replaced can be obtained. Even when process cartridges having almost the same lifetime are used together, it is possible to suppress the occurrence of a large difference in the photosensitive member charging potential (VH). Therefore, it is possible to suppress the development bias voltage (VD) described below from having significantly different values.

  Subsequently, in the control unit 60 shown in FIG. 6, the rotational speed integrated value of the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C and the charging bias voltage (VDC) set by the charging bias voltage calculation unit 604. Based on the above, processing for setting the developing bias voltage (VD) output from the second developing power source 622, the third developing power source 623, and the fourth developing power source 624 will be described. The development bias voltage calculation unit 605 provided in the control unit 60 performs setting processing of the development bias voltage (VD) output from the second development power source 622, the third development power source 623, and the fourth development power source 624.

  As described above, the charging bias voltage calculation unit 604 sets the average value of the charging voltage correction values Vdcm1, Vdcm2, and Vdcm3 as the charging bias voltage (VDC) applied from the second charging power source 612. Thus, for example, referring to FIG. 8, in the process cartridge 10C, a charging bias voltage (VDC) closer to the 0 potential side by | Vdcm1-VDC | than the charging voltage correction value Vdcm1 is applied. On the other hand, in the process cartridges 10M and 10Y, a charging bias voltage (VDC) having a higher potential is applied to the minus side by | VDC−Vdcm2 | and | VDC−Vdcm3 | than the charging voltage correction values Vdcm2 and Vdcm3, respectively. . Therefore, the charging potential VH of the photosensitive drum 11 of each of the process cartridges 10Y, 10M, and 10C is a different potential.

  Therefore, in the development bias voltage calculation unit 605 of the present embodiment, the rotation number integrated value of the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C and the charging bias voltage (set by the charging bias voltage calculation unit 604). VDC), and a conversion table in which the relationship between the rotation speed integrated value, the charging bias voltage (VDC), and the charging potential (VH) of the photosensitive drum 11 is stored in advance, and each process cartridge 10Y, 10M, 10C. The charging potential (VH) of the photosensitive drum 11 at is estimated. Then, the developing bias voltage (VD) is determined so that the difference between the developing bias voltage (VD) and the estimated charged potential (VH ′) of the photosensitive drum 11 becomes a predetermined white background contrast potential (V1). . Here, as the white background portion contrast potential (V1), V1M is set as a white background portion contrast potential that can suppress the occurrence of fogging or carrier adhesion to the white background portion (background).

  FIG. 9 is a flowchart showing an example of a processing procedure for setting the developing bias voltage (VD) performed by the developing bias voltage calculation unit 605 of the control unit 60. As shown in FIG. 9, first, the developing bias voltage calculation unit 605 acquires the rotation speed integrated value of the photosensitive drums 11 of the process cartridges 10Y, 10M, and 10C from the data reading unit 603 (S201). Further, the charging bias voltage (VDC) set by the charging bias voltage calculation unit 604 is acquired from the charging bias voltage calculation unit 604 (S202).

  Next, the developing bias voltage calculation unit 605 obtains the rotational speed integrated value acquired in step 201, the charging bias voltage (VDC) acquired in step 202, the rotational speed integrated value, the charging bias voltage (VDC), and the photosensitive. The estimated value (VH ′) of the charging potential of the photosensitive drum 11 in each of the process cartridges 10Y, 10M, and 10C is used using a conversion table in which the relationship with the charging potential (VH) of the photosensitive drum 11 is stored in advance. Obtain (S203). Accordingly, the developing bias voltage calculation unit 605 here functions as a charging potential estimation unit.

Then, the developing bias voltage calculation unit 605 adds the white background portion contrast potential V1M to the estimated charging potential (VH ′) of the photosensitive drum 11 obtained in step 203 (S204). That is, the calculation of the following equation (1) is performed to calculate a temporary development bias voltage (VD ′) for each of the process cartridges 10Y, 10M, and 10C.
VD ′ = VH + V1M (1)

  Subsequently, the development bias voltage calculation unit 605 determines whether or not the absolute value of the temporary development bias voltage (VD ′) calculated in step 204 is smaller than a predetermined value (first predetermined value). Judgment is made (S205). That is, as described above, the development contrast potential (V2), which is the difference between the exposure portion potential (VL) and the development bias voltage (VD), is a factor that sets the image density and gradation of the image portion. If the contrast potential (V2) is small, sufficient image density and gradation cannot be obtained. Therefore, since it is necessary to secure a sufficient development contrast potential (V2), the absolute value of the temporary development bias voltage (VD ′) is set to a predetermined value (here, a sufficient image) in any of the process cartridges 10Y, 10M, and 10C. It is determined whether or not there is a voltage smaller than (set V2M as a development contrast potential for obtaining density and gradation).

If it is determined in step 205 that the absolute value of the temporary development bias voltage (VD ′) in any one of the process cartridges 10Y, 10M, and 10C is smaller than the development contrast potential V2M, the development bias voltage The calculation unit 605 calculates a difference (second predetermined value) between the development contrast potential V2M and the absolute value of the provisional development bias voltage (VD ′) determined to be small in the process cartridges 10Y, 10M, and 10C. A process of subtracting (subtracting) from the development bias voltage (VD ') is performed (S206). That is, the calculation of the following equation (2) is performed to correct the developing bias voltage (VD).
VD = VD ′ − (V2M− | VD ′ |) (2)
The development bias voltages (VD) thus obtained are set as the development bias voltages (VD) output from the second development power source 622, the third development power source 623, and the fourth development power source 624 (S207).

Similarly, with respect to the charging bias voltage (VDC) applied from the second charging power source 612 set at step 104 in FIG. 7, the developing bias voltage calculation unit 605 is also small at the developing contrast potential V2M at step 205. A process of subtracting (subtracting) the difference from the absolute value of the provisional development bias voltage (VD ′) determined to be subtracted from the charging bias voltage (VDC) is performed (S208). That is, the following equation (3) is calculated to correct the charging bias voltage (VDC).
VDC = VDC− (V2M− | VD ′ |) (3)

On the other hand, if it is determined in step 205 that the absolute values of all the temporary development bias voltages (VD ′) are equal to or higher than the development contrast potential V2M, the temporary development bias obtained by the calculation of equation (1). The voltage (VD ′) is set as the developing bias voltage (VD) output from the second developing power source 622, the third developing power source 623, and the fourth developing power source 624, respectively (S209). Therefore, the developing bias voltage calculation unit 605 here functions as a developing voltage setting unit.
In this case, the development bias voltage calculation unit 605 does not change the charging bias voltage (VDC).
In this way, by setting the development bias voltage (VD) and the charging bias voltage (VDC), the reversely charged toner (that is, the positively charged toner) adheres to the white background portion and becomes fogged. Similarly, it is possible to prevent the reversely charged carrier from adhering and causing image contamination, in-machine contamination, and the like. In addition, it is possible to prevent the normally charged toner (that is, negatively charged toner) from being attached to the white background and causing fogging. Furthermore, sufficient image density and gradation can be obtained.

  In the image forming apparatus 1 of the present embodiment, one second charging power source 612 is commonly connected to the charging rolls 12Y, 12M, and 12C of the process cartridges 10Y, 10M, and 10C, and the charging rolls 12Y, 12M, and 12C are connected. The charging bias voltage having the same value is applied to the head. The present invention is not limited to such a configuration, and can be applied to any configuration as long as a common charging power source is connected to the plurality of charging rolls 12. For example, one charging power source is commonly connected to the charging rolls 12Y and 12M of the process cartridges 10Y and 10M, and the other charging power source is commonly connected to the charging rolls 12C and 12K of the process cartridges 10C and 10K. The same can be applied to the case.

As described above, in the image forming apparatus 1 of the present embodiment, the integrated value of the photosensitive drum rotation speed is stored for each of the process cartridges 10Y, 10M, and 10C. The integrated value of the photosensitive drum rotation speed for each of the process cartridges 10Y, 10M, and 10C, and the charging value for maintaining the integrated value of the photosensitive drum rotation speed and the photosensitive member charging potential (VH) shown in FIG. Based on the relationship with the bias voltage, a charging voltage correction value (Vdcm) for maintaining the photosensitive member charging potential (VH) substantially constant for each of the process cartridges 10Y, 10M, and 10C in accordance with the change with time of the photosensitive drum 11. Ask for. Then, the calculated charging voltage correction values (Vdcm) in the respective process cartridges 10Y, 10M, and 10C are averaged, and the average value (average charging bias voltage: VDC) of the calculated charging voltage correction values is calculated as a second value. It is set as an output value (charging voltage) from the charging power source 612.
Further, when the average charging bias voltage (VDC) is applied from the second charging power source 612, the photosensitive member charging potential (VH) formed on the photosensitive drum 11 of each process cartridge 10Y, 10M, 10C is estimated. In each of the process cartridges 10Y, 10M, and 10C, the difference between the estimated charged potential value (VH ′) and the developing bias voltage applied to the developing devices 13Y, 13M, and 13C is substantially the same. The developing bias voltage (VD) output from the second developing power source 622, the third developing power source 623, and the fourth developing power source 624 is determined.

As a result, in the image forming apparatus 1 of the present embodiment, the power supply for applying the charging bias voltage to the charging rolls 12Y, 12M, and 12C of the process cartridges 10Y, 10M, and 10C can be shared. The number of can be reduced. For this reason, it is easy to realize downsizing and cost reduction of the image forming apparatus 1.
Also with such a configuration, a high-quality image can be provided. That is, it prevents the reversely charged toner (ie, positively charged toner) from adhering to the white background and causing fogging, and similarly the reversely charged carrier from adhering to causing image stains and machine contamination. it can. In addition, it is possible to prevent the normally charged toner (that is, negatively charged toner) from being attached to the white background and causing fogging. Furthermore, sufficient image density and gradation can be obtained.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the present invention is applied. It is a wiring diagram explaining the connection between the charging power source and each charging roll, and the connection between the developing power source and each developing device. FIG. 6 is a diagram illustrating a relationship among a photosensitive member charging potential (VH), an exposed portion potential (VL), and a developing bias voltage (VD). FIG. 6 is a diagram showing a relationship between an integrated value of the number of rotations of a photosensitive drum and a photosensitive member charging potential (VH) when a charging bias voltage applied to a charging roll is maintained at a predetermined value. FIG. 6 is a diagram showing a charging bias voltage that maintains a photosensitive member charging potential (VH) substantially constant. It is the block diagram which showed the function structure of the control part. It is the flowchart which showed an example of the procedure of the process which sets a charging bias voltage (Vdc). FIG. 6 is a diagram showing a relationship between a rotation speed integrated value of a photosensitive drum and a corrected charging bias voltage. It is the flowchart which showed an example of the procedure of the process which sets a developing bias voltage (VD).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10Y, 10M, 10C, 10K ... Image forming unit (process cartridge), 11 (11Y, 11M, 11C, 11K) ... Photosensitive drum, 12 (12Y, 12M, 12C, 12K) ... Charging roll , 13 (13Y, 13M, 13C, 13K) ... developer, 14 (14Y, 14M, 14C, 14K) ... drum cleaner, 20 ... laser exposure device, 21 (21Y, 21M, 21C, 21K) ... static elimination lamp, 31 ... Transfer roll, 60 ... Control unit, 61 ... Charging power source, 62 ... Developing power source, 63 ... Transfer power source, 601 ... Photoconductor drum rotation speed measuring unit, 602 ... Data writing unit, 603 ... Data reading unit, 604 ... Charging Bias voltage calculation unit, 605... Development bias voltage calculation unit, 611... First charging power source, 612 .. second charging power source, 621... First developing power source, 622. ... third developing power, 624 ... fourth developing power

Claims (8)

A plurality of image carriers;
Each charging member disposed on each of the plurality of image carriers and charging the surface of the image carrier;
Each developing member disposed on each of the plurality of image carriers and developing an electrostatic latent image formed on the image carrier;
One charging voltage supply means commonly connected to a plurality of charging members in each of the charging members;
A plurality of developing voltage supply means individually connected to each of the developing members;
A control unit that controls a charging voltage supplied from the charging voltage supply means to the plurality of charging members and a developing voltage supplied from the developing voltage supply means to each of the developing members;
When the charging unit supplies the charging voltage to each of the plurality of charging members from the one charging voltage supply unit , the control unit is configured to control each of the charging members corresponding to a change with time of each of the plurality of image carriers. Calculating a charging voltage correction value, calculating an average value of the charging voltage correction value for each of the calculated charging members, and determining the calculated average value of the charging voltage correction value as the charging voltage; When supplying the developing voltage from each of the plurality of developing voltage supply means to each of the developing members, a charging potential formed on each of the plurality of image carriers is estimated by supplying the charging voltage. An image forming apparatus , wherein the developing voltage is determined so that a difference from the charged potential is substantially the same in each of the developing members with respect to each of the estimated charged potentials . Wherein, the first predetermined value is a potential predetermined development contrast potential is obtained is set in advance, than the absolute value of the first predetermined value of the developing voltage in the developing voltage defined If there is a small one , the difference between the minimum absolute value of the determined development voltage and the first predetermined value is set as a second predetermined value, which is determined by the charging voltage supply means. by subtracting the second predetermined value from the the developing voltage defined on the charging voltage and the developing voltage supply means, further characterized by performing a process of correcting the said charging voltage and the developing voltage The image forming apparatus according to claim 1. The controller is
A correction voltage calculation unit for calculating the charging voltage correction value;
A charging voltage setting unit that calculates an average value of the charging voltage correction value for each of the charging members, and determines the calculated average value of the charging voltage correction value as the charging voltage supplied from the charging voltage supply unit;
A charging potential estimation unit that estimates a charging potential formed on each of the plurality of image carriers by supplying the charging voltage determined by the charging voltage setting unit;
The developing voltage supply means supplies the development voltage supply means so that a difference from the estimated charging potential is substantially constant with reference to the charging potential of each of the image carriers estimated by the charging potential estimation unit. The image forming apparatus according to claim 1, further comprising a development voltage setting unit that determines a development voltage. The correction voltage calculation unit calculates the charging voltage correction value corresponding to any one or more of an integrated rotation speed, an integrated rotation time, and an integrated image forming cycle for each of the image carriers. The image forming apparatus according to claim 3 . A memory for storing any one or more of an accumulated rotation speed, an accumulated rotation time, and an accumulated image forming cycle for each of the image carriers;
5. The image forming apparatus according to claim 4, wherein the correction voltage calculation unit acquires one or more of an accumulated rotation speed, an accumulated rotation time, and an accumulated image forming cycle of the image holding body from the memory. .   The image carrier, the charging member, the developing member, and a memory that stores any one or more of an accumulated rotation speed, an accumulated rotation time, and an accumulated image forming cycle of the image carrier are integrally configured. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. Each of the plurality of image holding bodies is charged by a charging member that is disposed on each of the plurality of image holding bodies and is supplied with a charging voltage from a single charging voltage supply unit that is connected in common to each of the plurality of image holding bodies. An electrostatic latent image formed on each of the plurality of image holding bodies by a developing member which is disposed on each of the bodies and is supplied with a development voltage from each of a plurality of development voltage supply means connected individually. An image forming method for developing ,
When supplying a charging voltage from the one charging voltage supply means to each of the plurality of charging members, a charging voltage correction value for each of the charging members corresponding to a change with time of each of the plurality of image carriers is calculated. Calculating the average value of the charging voltage correction value for each of the calculated charging members, and determining the calculated average value of the charging voltage correction value as the charging voltage ;
When supplying the developing voltage from each of the plurality of developing voltage supply means to each of the developing members, the charging voltage is supplied to the plurality of charging members to form each of the plurality of image carriers. Including a step of estimating a charging potential and determining the developing voltage so that a difference from the charging potential is substantially the same for each of the developing members with respect to each of the estimated charging potentials. Image forming method. The first predetermined value is a potential predetermined development contrast potential is obtained is set in advance, the absolute value of the developing voltage in the developing voltage defined exists smaller than the first predetermined value In this case, a difference between the minimum absolute value of the determined developing voltage and the first predetermined value is set as a second predetermined value, and the charging voltage determined by the charging voltage supply means and the by from the developing voltage defined as the developing voltage supply means for subtracting the second predetermined value, according to claim 7, further comprising the step of correcting the said charging voltage and the developing voltage Image forming method.

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