JP2009251171A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of setting a constant voltage for transferring a toner image of an image by quickly finishing the setting of a potential in an solid white part. <P>SOLUTION: A control part 110 sets a developing contrast Vcont using a controlling toner image, in a rotation process executed before forming the image, and sets the constant voltage Vtr4 using a solid white image part (bright part potential VL). Transfer voltage control applied to a primary transfer roller 15 is switched to constant current control, when setting the developing contrast Vcont, and the transfer voltage control is switched to constant voltage control, when setting the constant voltage Vtr4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for transferring a control toner image formed on an image carrier to an intermediate transfer member for use in image density control, and more specifically, a transfer voltage for transferring a control toner image to an intermediate transfer member. Regarding control.

  An image forming apparatus for transferring a control toner image formed on an image carrier to an intermediate transfer body and using it for image density control has been put into practical use.

  An image forming apparatus that controls the voltage applied to the transfer unit momentarily so that the transfer current becomes a constant current when the toner image formed on the image carrier is transferred to the intermediate transfer member has been put into practical use.

  In an image forming apparatus that transfers a toner image of an image from an image carrier to an intermediate transfer member by applying a constant voltage to a transfer member, when an image forming job is received, the potential of the white portion (solid white portion) of the electrostatic image And a developing bias (DC voltage Vdc) are set.

  After that, let the white background part where the potential is set appropriately pass through the transfer part, find the `` relation between the voltage applied to the transfer part and the flowing current '', and set a constant voltage corresponding to the predetermined current value Actual image formation is started.

  Here, the reason for setting the constant voltage using the white background is that the toner is transferred to the intermediate transfer member and is wasted, or the toner that has not been transferred to the recording material transferred to the intermediate transfer member is used in the image forming apparatus. This is because the aircraft is contaminated.

  Patent Document 1 discloses a control in which a constant voltage applied to a transfer member is increased stepwise prior to image formation, and a constant voltage at the time when a desired transfer current is measured is used as a constant voltage during image formation. Indicated.

  Patent Document 2 discloses an image forming apparatus that detects the density of a control toner image transferred from an image carrier to an intermediate transfer member by arranging an optical sensor facing the intermediate transfer member.

  Patent Document 3 discloses an image forming apparatus that appropriately sets the potential of the white background portion of the electrostatic image by forming the control toner image by changing the potential of the white background portion of the electrostatic image in a plurality of stages.

Japanese Patent Laid-Open No. 5-6112 JP 2003-241470 A JP 2006-78889 A

  When the potential of the white background portion is changed in order to adjust the image density, the transfer current when the control toner image passes through the transfer portion to which a constant voltage is applied and is transferred to the intermediate transfer member is changed. While the toner application amount of the control toner image formed on the image carrier changes with the potential of the white background portion, the transfer efficiency of the control toner image transferred from the image carrier to the intermediate transfer member also changes.

  For this reason, the control toner image transferred to the intermediate transfer member may not reflect the density of the control toner image formed on the image carrier, and the potential of the white portion of the electrostatic image may not be set appropriately. There is.

  Therefore, the control for setting a constant voltage for transferring the control toner image is performed by passing the transfer portion each time the potential of the white background portion is changed, obtaining the relationship between the voltage applied to the transfer portion and the flowing current. was suggested.

  However, in this case, an unneeded “constant voltage for just transferring the control toner image” is set for transferring the toner image of the image, and it takes time to set the potential of the white background image formation. Will start late.

  An object of the present invention is to provide an image forming apparatus capable of setting a constant voltage for transferring a toner image of an image after quickly setting a potential of a white background portion.

  The image forming apparatus of the present invention includes an image carrier, a charging device that charges the image carrier to a uniform potential, an exposure device that forms an electrostatic image by exposing the charged image carrier, and A developing device that electrically transfers toner to an electrostatic image and develops the toner image, and the toner image is transferred from the image carrier to the intermediate transfer member by pressing against the image carrier via the intermediate transfer member. And a transfer member that forms a transfer portion. Further, a constant voltage and a constant current controlled voltage can be output, and a power source that applies a voltage to the transfer portion, and a control that is formed in a predetermined size on the image carrier and transferred to the intermediate transfer member And a control unit that adjusts the potential of the white portion of the electrostatic image by controlling at least one of the conditions of the charging device and the exposure device using the toner image. Further, when transferring a toner image of an image, the power supply outputs the constant voltage, while when transferring the control toner image, the power supply outputs a voltage under constant current control.

  In the image forming apparatus of the present invention, an image bearing member charged to a uniform potential is exposed to form an electrostatic image (a developing portion to be developed and a white background portion not to be developed). Then, the toner image of the image formed by electrically transferring the toner to the electrostatic image developing portion is transferred to a transfer portion to which a constant voltage and a constant current controlled voltage are output by a power source capable of outputting a constant voltage. Transferred to an intermediate transfer member.

  The density of the control toner image is detected on the intermediate transfer member or the recording material, and the density detection result is reflected in the white background potential as the toner image forming condition.

  The toner image for control formed in a predetermined size is transferred from the image carrier to the intermediate transfer member with the same transfer efficiency even if the potential of the white background is different in the transfer portion to which a constant current controlled voltage is applied. The This is because even if the control toner image is formed under the condition that the potential of the white background portion is different, the voltage under constant current control is automatically adjusted so that a constant current density is formed within a predetermined size.

  This eliminates the need to adjust the constant voltage applied to the transfer area in accordance with the difference in potential of the white background, so that the potential of the white background can be adjusted in a shorter time than when adjusting only by constant voltage control. it can. The setting of the constant voltage for transferring the toner image of the image can be started by quickly setting the potential of the white background portion.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the control toner image is transferred to the intermediate transfer member by constant current control when the solid toner potential, which is the potential of the white background, is changed to form the control toner image, the configuration of the embodiment In another embodiment, a part or all of the above may be replaced by the alternative configuration.

  Therefore, not only a method for detecting the density of the control toner image carried on the intermediate transfer member but also an image forming apparatus for detecting the density after the control toner image is transferred to a recording material and fixed.

  In addition to an image forming apparatus that transfers a single-color toner image to an intermediate transfer member, the image forming apparatus can superimpose a plurality of color toner images on an intermediate transfer member. As a full-color image forming apparatus, not only a one-drum type in which one photosensitive drum provided with a plurality of color developing devices is attached to an intermediate transfer member, but also a plurality of photosensitive drums having different development colors along the intermediate transfer member. It can also be implemented in an arrayed tandem type.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter of the control using the image forming apparatus and the control toner image disclosed in Patent Documents 1 to 3, the illustration is omitted and redundant description is omitted.

  Further, in the description, the reference symbols indicated in parentheses in the configuration names used in the claims are examples for helping understanding of the invention, and the configuration is limited to corresponding members in the embodiment. Not intended to do.

<First Embodiment>
FIG. 1 is an explanatory diagram of a configuration of the image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 100 is a monochrome image forming apparatus in which a single photosensitive drum 1 is attached to the intermediate transfer belt 9 so as to be compatible with high-speed recording and various types of recording materials.

  Around the photosensitive drum 1 as an image carrier, a charging device 2, an exposure device 3, a surface potential sensor 22, a developing device 4, a primary transfer roller 15, and a cleaning device 19 are arranged.

  The photosensitive drum 1 has an OPC (organic optical semiconductor) photosensitive layer formed on the outer peripheral surface of an aluminum cylinder, is rotatably supported, and rotates in the direction of arrow R1.

  The charging device 2 applies a negative DC voltage from the power source D3 to generate corona discharge, and irradiates the discharge particles to charge the surface of the photosensitive drum 1 to a uniform positive potential.

  The exposure device 3 scans a scanning beam image data obtained by developing the image data with a laser beam that is ON-OFF modulated by a rotating mirror (not shown), and writes an electrostatic image on the surface of the charged photosensitive drum 1.

  A drum heater (not shown) keeps the temperature in the vicinity of the surface of the photosensitive drum 1 constant, adjusts the absolute moisture content in the atmosphere, avoids condensation, and enables stable electrostatic image formation.

  The surface potential sensor 22 detects the surface potential (dark portion potential VD) of the photosensitive drum 1 charged by the charging device 2 and feeds it back to the operating condition of the charging device 2. Further, the surface potential (bright part potential VL) which has been lowered by exposure after charging is detected.

  The developing device 4 charges a two-component developer including a magnetic carrier and a non-magnetic toner, and supports the photosensitive drum 1 on a developing sleeve 41 that rotates in the counter direction around the fixed magnetic pole 42 and rubs the photosensitive drum 1. Thus, the electrostatic image is developed.

  The power source D4 applies a developing voltage obtained by superimposing an AC voltage to a positive DC voltage to the developing sleeve 41, and attaches toner to the solid white portion (dark portion potential VD) of the photosensitive drum 1, thereby normalizing the electrostatic image. develop.

  The primary transfer roller 15 sandwiches the intermediate transfer belt 9 between the photosensitive drum 1 and forms a primary transfer portion T 1 between the photosensitive drum 1 and the intermediate transfer belt 9.

  The power source D <b> 1 can switch and output a constant voltage set by the control unit 110 and a voltage that is constant current controlled by a constant current set by the control unit 110.

  The power source D1 applies a positive constant voltage to the primary transfer roller 15 to transfer the toner image of the image carried on the photosensitive drum 1 to the intermediate transfer belt 9 passing through the primary transfer portion T1.

  The cleaning device 19 slides the cleaning blade against the photosensitive drum 1 to remove the transfer residual toner that has passed through the primary transfer portion T <b> 1 while being carried on the photosensitive drum 1.

  The intermediate transfer belt 9 is supported across the drive roller 12, the backup roller 13, the tension roller 14, the support rollers 10 and 11, and the primary transfer roller 15, and rotates in the direction of arrow R2.

The intermediate transfer belt 9 is formed of a material in which an appropriate amount of carbon black is contained as an antistatic agent in a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acrylic, or vinyl chloride, or various rubbers. The intermediate transfer belt 9 has a volume resistivity of 1 × 10 ⁸ to 1 × 10 ¹³ [Ω · cm] and a thickness of 70 to 100 μm.

  The secondary transfer roller 16 is pressed against the backup roller 13 via the intermediate transfer belt 9 to form a secondary transfer portion T <b> 2 between the intermediate transfer belt 9 and the secondary transfer roller 16.

  The power source D2 applies a positive constant voltage to the secondary transfer roller 16 to transfer the toner image carried on the intermediate transfer belt 9 to the recording material 20 fed to the secondary transfer portion T2 and sandwiched and conveyed. Secondary transfer. The recording material 20 is temporarily stopped by the registration roller 17 and then sent to the secondary transfer portion T2 at a timing that matches the toner image on the intermediate transfer belt 9.

  The fixing device 8 heats and presses the recording material 20 to which the toner image is transferred and delivered from the secondary transfer portion T <b> 2 to fix the toner image on the surface of the recording material 20.

  The cleaning device 21 rubs the cleaning blade against the intermediate transfer belt 9 to remove residual toner that has passed through the secondary transfer portion T2 while being carried on the intermediate transfer belt 9.

  The secondary transfer roller 16 and the cleaning device 21 are disposed so as to be able to contact and separate from the intermediate transfer belt 9. When a plurality of color images are formed, the secondary transfer roller 16 and the cleaning device 21 are separated from the intermediate transfer belt 9 until the toner image before the final color passes through the secondary transfer portion T2 and the cleaning device 21. Is done.

  The optical sensor 23 irradiates the control toner image (patch image) primarily transferred to the intermediate transfer belt 9 with detection light (infrared light) to detect regular reflection light.

  The optical sensor 23 is preferably arranged around the photosensitive drum 1 and can directly detect the control toner image formed on the photosensitive drum 1. This is because, when the control toner image is primarily transferred to the intermediate transfer belt 9, a part of the toner is lost, and the fluctuation in transfer efficiency becomes a density detection error.

  However, around the photosensitive drum 1, the charging device 2, the exposure device 3, the developing device 4, and the like are arranged without gaps, and a space for installing a relatively large optical sensor 23 cannot be secured. For this reason, it is appropriate in terms of space to install an optical sensor 23 in the vicinity of the intermediate transfer belt 9 to detect the density of the control toner image on the intermediate transfer belt 9.

<Regular development>
FIG. 2 is an explanatory diagram of regular development, and FIG. 3 is an explanatory diagram of control for setting the potential of a solid white portion in regular development.

  As shown in FIG. 2 with reference to FIG. 1, the charging device 2 charges the surface of the photosensitive drum 1 to a dark portion potential VD = + 450 V, which is a potential of a developing portion (solid black potential) in an electrostatic image.

  The exposure device 3 exposes a region where the toner image is not developed, and eliminates the charge to a bright portion potential VL = + 100 V which is a solid white portion potential (solid white potential).

  A developing voltage in which an AC voltage is superimposed on a DC voltage Vdc = + 250 V is applied to the developing sleeve 41 of the developing device 4 from a power source D4.

  The solid white portion contrast Vback (= Vdc−VL) is a potential difference between the development potential Vdc and the bright portion potential VL, and the adhesion of the positively charged magnetic carrier to the photosensitive drum 1 or the bright portion potential VD of the toner. This is a potential difference for preventing adhesion to the region. The solid white portion contrast Vback is secured at a constant value regardless of the absolute water content in the air and the color of the toner.

  The negatively charged toner of the developing device 4 has an amount corresponding to the charge amount per unit mass (Q / M) and the development contrast Vcont (= VD−Vdc) of the developing portion (dark portion potential VD) of the photosensitive drum 1. ).

  Therefore, in order to keep toner density at a predetermined density by adhering toner to the photosensitive drum 1, it is necessary to adjust the development contrast Vcont according to the charge amount (Q / M) per unit mass of the toner. The charge amount (Q / M) per unit mass of the toner decreases when the absolute moisture content in the air increases in a high humidity environment, and increases when the absolute moisture content in the air decreases in a low humidity environment. Therefore, it is necessary to reduce the development contrast Vcont in a high humidity environment where the charge amount (Q / M) is small, and to increase the development contrast Vcont in a low humidity environment where the charge amount (Q / M) is high.

  In view of this, the image forming apparatus 100 forms a control toner image by changing the development contrast Vcont in a plurality of stages and performs primary transfer onto the intermediate transfer belt 9. Then, the control toner image carried on the intermediate transfer belt 9 is detected by an optical sensor, and the amount of applied toner at a plurality of stages of development contrast Vcont is measured. Then, a development contrast Vcont corresponding to an appropriate amount of applied toner is set.

  As shown in FIG. 3 with reference to FIG. 1, the dark portion potential VL, which is a charging potential, is fixed and the exposure amount of the exposure apparatus 3 is adjusted to change the development contrast Vcont, and the dark portion potential VL is gradually increased to VL1. , VL2 and VL3. Then, the DC voltage Vdc1 applied to the developing sleeve 41 is shifted to Vdc2 and Vdc3 by the variations ΔV and ΔV ′ of VL changed in three stages. That is, the solid white portion contrast Vback = Vdc−VL is fixed, and the development contrast Vcont = VD−Vdc is changed.

  At this time, the amount of toner on the control toner image developed on the photosensitive drum 1 changes in three stages due to the fluctuation of the development contrast Vcont.

  Therefore, the exposure amount of the exposure device 3 and the DC voltage Vdc are set so that the control toner image at each stage is detected by the optical sensor 23 and the development contrast Vcont at which the control toner image has the optimum density is obtained. adjust.

<Transfer member, power supply>
FIG. 4 is a perspective view of the primary transfer roller.

As shown in FIG. 4, the primary transfer roller 15 has an elastic layer 15b on the outer peripheral surface of a conductive core 15a, and a conductive filler is dispersed in the elastic layer 15b so that the resistance value is 1 × 10 ⁶ to. It is adjusted to about 1 × 10 ¹⁰ (Ω). An ion conductive primary transfer roller 15 containing an ion conductive material is used for the elastic layer 15b. For example, a surfactant dispersed in the elastic layer 15b may be used.

  However, as the primary transfer roller, a material such as urethane itself having conductivity, or an EPDM roller or urethane roller in which a conductive filler such as carbon or metal oxide is dispersed can be used.

  The primary transfer roller 15 is employed in the primary transfer portion T1, and the toner image on the photosensitive drum 1 is electrostatically applied to the intermediate transfer belt 9 by appropriately applying a charge having a polarity opposite to the toner charging polarity to the primary transfer roller 15. Primary transfer. The contact transfer method using the primary transfer roller 15 can achieve low output and cost reduction of the power supply.

  When the transfer voltage applied to the primary transfer roller 15 is controlled at a constant current, the transfer efficiency changes according to the amount of toner present in the longitudinal direction of the photosensitive drum 1 of the primary transfer portion T1. This is because the impedance of the primary transfer portion T1 is different between a solid black in which a toner image is present in the entire longitudinal direction of the photosensitive drum 1 and a thin line image having a small area in which the toner is present in the entire longitudinal direction.

  Therefore, if the constant current is matched with the impedance at the time of solid black, in the thin line image, the current flows into the solid white portion, and the current necessary for the image portion cannot be secured. On the other hand, when a constant current is applied to the thin line image, the transfer current is too strong in the solid black image, and a transfer image defect occurs.

  For this reason, the power source D1 controls the transfer voltage applied to the primary transfer roller 15 disposed at a position facing the photosensitive drum 1 and in contact with the inner surface of the intermediate transfer belt 9 at a constant voltage.

  However, when a constant voltage is applied to the primary transfer roller 15, if the potential difference between the bright portion potential VL, which is a solid white potential, and the constant voltage Vtr applied to the primary transfer roller 15 is large, a transfer current easily flows, and this potential difference If it is small, the transfer current is difficult to flow. Accordingly, there is a possibility that the transfer current changes due to a difference in the bright portion potential VL which is a solid white potential and becomes inappropriate.

  Even if the potential difference between the bright portion potential VL and the constant voltage Vtr applied to the primary transfer roller 15 is the same, the transfer current easily flows if the resistance of the primary transfer roller 15 is low, and the transfer current hardly flows if the resistance is high. Since the resistance of the primary transfer roller 15 varies according to the temperature and humidity in the machine and the energization time like the toner, when a constant voltage is applied to the primary transfer roller 15, an appropriate charge is applied to the primary transfer portion T1. There are cases where transfer cannot be performed and a transfer defect is induced.

  Therefore, in the image forming apparatus 100, after setting the bright portion potential VL, the transfer current flowing from the primary transfer roller 15 is appropriately controlled to appropriately primary-transfer the toner image of the developed image. The reason why the transfer adjustment process is performed at the VL potential is that when the photosensitive drum 1 is set to the VD potential and the transfer adjustment process is performed, a toner image is formed at a portion facing the developing device 4 with respect to the VD potential. This is because the toner is wasted.

  In order to prevent occurrence of primary transfer failure due to resistance fluctuation of the primary transfer roller 15, a current flowing through the primary transfer portion T <b> 1 when a predetermined number of measurement constant voltages are applied to the primary transfer roller 15. Measure. Then, according to the measurement result using the measurement constant voltage, the constant voltage applied to the primary transfer roller 15 when the toner image of the image is transferred is appropriately controlled.

<Example 1>
FIG. 5 is a flowchart of the control of the first embodiment, FIG. 6 is a time chart of the control of the first embodiment, and FIG. 7 is an explanatory diagram of calculation when setting a constant voltage used for primary transfer.

  The control of the first embodiment uses (1) the development contrast Vcont using the control toner image and (2) the solid white image portion (bright portion potential VL) in the pre-rotation step executed before image formation. The set constant voltage Vtr4 is executed.

  Then, (1) when the development contrast Vcont is set, the primary transfer voltage control is switched to constant current control, and (2) when the constant voltage Vtr4 is set, the primary transfer voltage control is switched to constant voltage control.

  As shown in FIG. 5 with reference to FIG. 1, when receiving the image forming job, the control unit 110 starts pre-rotation (S11) and sets an initial setting value (S12). The light portion potential VL0 of the photosensitive drum 1, the DC voltage Vdc0 applied to the developing sleeve 41, and the constant voltage Vtr0 used for primary transfer are set, and the voltage applied to the primary transfer roller 15 is controlled at a constant voltage.

  The control unit 110 switches the power source D1 to constant current control (S13). Thereby, the power supply D1 changes the voltage applied to the primary transfer roller 15 every moment so that the transfer current determined according to the amount of absolute moisture in the atmosphere flows.

  The constant current Itc set in the power supply D1 has a current value that matches the impedance of the primary transfer portion T1 when the control toner image passes through the primary transfer portion T1. The impedance of the primary transfer portion T1 varies depending on the image ratio of the toner image. Therefore, if the control toner image used when adjusting the development contrast Vcont, that is, the control toner image when the primary transfer portion T1 is controlled with a constant current, is fixed to a specific pattern, the change in impedance is taken into consideration. There is no need to do.

  If the transfer voltage is fixed to the constant current Itc as constant current control as described above, the control toner image can be transferred with an appropriate current Itc even if the bright portion potential VL changes to VL1, VL2, and VL3. .

  The control unit 110 changes the exposure intensity of the exposure apparatus 3 to change the bright part potential VL0 to the specified value VL1 as shown in FIG. 6, and the DC voltage Vdc applied to the developing sleeve 41 is (VL1-VL0) only. Set to increased Vdc1.

  Then, exposure is stopped in an area corresponding to the control toner image to form an electrostatic image having a solid black potential (dark portion potential (VD0) (S14). As a result, a toner image having a development contrast Vcont = VD0-Vdc1 is formed. Formed on the photosensitive drum 1 and primarily transferred to the intermediate transfer belt 9 by constant current control.

  The controller 110 detects the reflected light of the control toner image with the development contrast Vcont = VD0−Vdc1 by the optical sensor 23, and measures the density (S15).

  The control unit 110 changes the exposure intensity of the exposure apparatus 3 to change the bright portion potential VL1 to the specified value VL2 as shown in FIG. 6, and the DC voltage Vdc applied to the developing sleeve 41 is (VL2-VL1) only. Set to increased Vdc2.

  Then, exposure is stopped in an area corresponding to the control toner image to form an electrostatic image with a solid black potential (dark portion potential (VD0) (S16). As a result, a toner image with a development contrast Vcont = VD0-Vdc2 is formed. Formed on the photosensitive drum 1 and primarily transferred to the intermediate transfer belt 9 by constant current control.

  The controller 110 detects the reflected light of the control toner image with the development contrast Vcont = VD0−Vdc2 by the optical sensor 23, and measures the density (S17).

  The control unit 110 changes the exposure intensity of the exposure apparatus 3 to change the bright part potential VL2 to the specified value VL3 as shown in FIG. 6, and the DC voltage Vdc applied to the developing sleeve 41 is (VL3-VL2) only. Set to increased Vdc3.

  Then, exposure is stopped in an area corresponding to the control toner image to form an electrostatic image having a solid black potential (dark portion potential (VD0)) (S18). As a result, a toner image having a development contrast Vcont = VD0-Vdc3 is formed. Formed on the photosensitive drum 1 and primarily transferred to the intermediate transfer belt 9 by constant current control.

  The controller 110 detects the reflected light of the control toner image with the development contrast Vcont = VD0−Vdc3 by the optical sensor 23, and measures the density (S19).

  As shown in FIG. 6, even if the bright part potential changes to VL1, VL2, and VL3, the DC voltage is made to follow Vdc1, Vdc2, and Vdc3, so that the solid white part contrast Vback is always constant. Therefore, when the bright portion potential changes to VL1, VL2, and VL3, the development contrast Vcont becomes VD0-Vdc1 when VL1, VD0-Vdc2 when VL2, and VD0-Vdc3 when VL3.

  The control unit 110 calculates the bright portion potential VL4 at which the control toner image having an appropriate density is formed from the density measurement result of the control toner image having the three-stage development contrast Vcont. Then, as shown in FIG. 6, the exposure intensity of the exposure apparatus 3 is changed so that the output of the surface potential sensor 22 becomes the bright portion potential VL4 (S20).

  The control unit 110 switches the power source D1 to constant voltage control (S21).

  The controller 110 sets a constant voltage Vtr1 to the power source D1 as shown in FIG. Then, with the entire surface of the photosensitive drum 1 exposed to the bright portion potential VL4, a constant voltage Vtr1 is applied from the power source D1 to the primary transfer roller 15, and the transfer current Itr1 is measured by the current detection circuit A1 (S22). ). Thus, the transfer current Itr1 due to the potential difference between the constant voltage Vtr1 and the bright portion potential VL4 is measured.

  The controller 110 sets a constant voltage Vtr2 to the power source D1 as shown in FIG. Then, with the entire surface of the photosensitive drum 1 exposed to the bright portion potential VL4, a constant voltage Vtr2 is applied from the power source D1 to the primary transfer roller 15, and the transfer current Itr2 is measured by the current detection circuit A1 (S23). ). As a result, the transfer current Itr2 due to the potential difference between the constant voltage Vtr2 and the bright portion potential VL4 is measured.

  The controller 110 sets a constant voltage Vtr3 to the power supply D1 as shown in FIG. Then, with the entire surface of the photosensitive drum 1 exposed to the bright portion potential VL4, a constant voltage Vtr3 is applied from the power source D1 to the primary transfer roller 15, and the transfer current Itr3 is measured by the current detection circuit A1 (S24). ). As a result, the transfer current Itr3 due to the potential difference between the constant voltage Vtr3 and the bright portion potential VL4 is measured.

  The application of the constant voltages Vtr1, Vtr2, and Vtr3 is continued while the primary transfer roller 15 makes one revolution, and the output of the current detection circuit A1 is output at a timing obtained by dividing the time that the primary transfer roller 15 makes one revolution into ten. Capture 10 times. An average of 10 current values flowing into the transfer portion T1 is obtained to obtain transfer currents Itr1, Itr2, and Itr3.

  As shown in FIG. 7, the control unit 110 calculates a constant voltage Vtr4 at which a specified appropriate current Iyt is obtained using three constant voltage-transfer current data of Vtr1-Itr1, Vtr2-Itr2, and Vtr3-Itr3. To set the power supply D1. Three constant voltage-transfer current data are interpolated to determine a constant voltage Vtr4 as a transfer partial voltage at the time of image formation so that the current at the time of primary transfer becomes an appropriate current Iyt (S25). At the time of image formation, a constant voltage Vyt obtained by adding a toner image sharing voltage determined according to the image to the transfer partial voltage is applied to the primary transfer roller 15.

  What is important at this time is that a constant voltage Vtr4 corresponding to the appropriate current Iyt is included in Vtr1, Vtr2, and Vtr3 used for adjustment. That is, it is important to determine the constant voltage Vtr4 in a region where the current / voltage relationship in the primary transfer portion T1 is obtained by interpolation of three plots of Vtr1, Vtr2, and Vtr3. This is because in the extrapolation region, the current / voltage relationship in that region is unknown.

  Therefore, since the constant voltages Vtr1, Vtr2, and Vtr3 at the time of adjustment are difficult to predict an appropriate constant voltage Vtr4 due to the resistance fluctuation of the primary transfer portion T1, a potential difference of 500 to 1000 V is added so as not to be out of the interpolation range. ing. For example, Vtr1 = 1500V, Vtr2 = 2000V, and Vtr3 = 2500V (potential difference 500V in this case) are determined to determine the constant voltage Vtr4.

  When this adjustment is completed, the development contrast Vcont adjustment and the primary transfer constant voltage adjustment are completed, and preparations for obtaining an appropriate toner application amount and an appropriate primary transfer voltage are completed, and an image forming operation is started.

  The controller 110 ends the pre-rotation and starts image formation (S26), and repeats image formation until the image formation is completed (NO in S27) (S26). When image formation is completed (YES in S27), post-rotation is executed (S28), and the image forming apparatus 100 is stopped.

  In the control of the first embodiment, the development contrast Vcont is adjusted by changing the bright portion potential VL which is a solid white potential. Then, the transfer bias is switched to constant current control at the time of adjusting the development contrast Vcont so that the transfer current does not change even if the bright part potential VL, which is a solid white potential, changes. As a result, the control for setting the optimum constant voltage for each solid white potential becomes unnecessary, and accurate adjustment can be performed in a shorter time.

  Further, when adjusting the development contrast Vcont, the control toner image of a predetermined size is formed and adjusted at least in the longitudinal direction of the photosensitive drum 1, thereby eliminating the disadvantages of the constant transfer control of the primary transfer portion T1. it can.

<Example 2>
FIG. 8 is an explanatory diagram of the configuration of the image forming apparatus of the second embodiment, FIG. 9 is a time chart of the control of the second embodiment, and FIG. 10 is a calculation of setting a constant voltage used for primary transfer in the control of the second embodiment. It is explanatory drawing.

  In the control of Example 1, the primary transfer portion T1 was controlled with a constant current during the development contrast Vcont adjustment, and the primary transfer portion T1 was controlled with a constant voltage during the subsequent constant voltage adjustment.

  In the control of the second embodiment, three voltages required for setting the constant voltage by detecting the three-stage transfer voltage applied to the primary transfer portion T1 in the process in which the primary transfer portion T1 is controlled by the constant current. -Obtain current data. The three-stage transfer voltage detected in the process of obtaining an appropriate development contrast Vcont is fed back to a constant voltage at the time of image formation.

  As shown in FIG. 8, a voltage detection circuit V1 for detecting a transfer voltage applied to the primary transfer roller 15 is attached to the power supply D1. Since the other configuration is the same as in FIG. 1, the same reference symbols as those in FIG.

  As shown in FIG. 9 with reference to FIG. 8, the control unit 110 switches the power supply D1 to constant current control in the region of time t1 / t2 / t3, and executes the development contrast Vcont adjustment in the same manner as in the first embodiment. To do. The control unit 110 controls the exposure device 3 to switch the bright portion potential VD to VL1, VL2, and VL3 to form a control toner image, primarily transfers it to the intermediate transfer belt 9, and measures the density with the optical sensor 23. .

  The control unit 110 measures, by the voltage detection circuit V1, the voltage output from the power source D1 at the constant current Itr when the bright portion potentials VL1, VL2, and VL3 of the photosensitive drum 1 pass through the primary transfer portion T1. The voltages Vtr1, Vtr2, and Vtr3 applied to the primary transfer portion T1 corresponding to the bright portion potentials VL1, VL2, and VL3, which are solid white potentials, are measured. Vtr1 = 800V, Vtr2 = 1200V, and Vtr3 = 1600V.

  Then, the control unit 110 ends the development contrast Vcont adjustment by calculating and setting the bright portion potential VL4 so that the density of the toner image is appropriate from the density measurement results of the three levels of control toner images.

  As shown in FIG. 10, the control unit 110 interpolates three data of VL1-Vtr1, VL2-Vtr2, and VL3-Vtr3 to calculate a constant voltage Vtr4 and sets it to the power supply D1. The detection voltage (1400 V in the drawing) corresponding to the bright portion potential VL4, which is the solid white potential determined by the development contrast Vcont adjustment from the relationship between the solid white potential and the detection voltage, is changed from the constant current control to the constant voltage control. Applied to the primary transfer portion T1. The constant voltage Vtr4 = 1400V at which the constant current Itr is obtained at the bright portion potential VL4 used for the primary transfer of the toner image of the image.

  According to the control of the second embodiment, the development contrast Vcont adjustment and the constant voltage Vtr4 adjustment are performed at the same time, so that the process of applying the stepped constant voltage described in the first embodiment to the primary transfer roller 15 can be omitted. For this reason, after adjusting the development contrast Vcont (determining VL4), the processing performed after the power source D1 is switched from the constant current control to the constant voltage control is omitted, and the adjustment time before image formation is further shortened compared to the control of the first embodiment. it can.

  In the image forming apparatus 100, at the time of adjusting the development contrast Vcont, adjustment is performed with a control toner image (color patch) of a predetermined size at least in the longitudinal direction of the photosensitive drum 1 so that the transfer control can be a constant current control. Then, in the step of adjusting the developing conditions of the developing device 4 in the pre-rotation, the power source D1 is set to constant current control, and the subsequent image forming step is set to constant voltage control. Thereby, the adjustment of the optimum constant voltage for each solid white potential can be omitted while eliminating the disadvantages of the constant current control, and the accurate adjustment can be performed in a shorter time.

<Comparative example>
FIG. 11 is a time chart of the control of the comparative example, and FIG. 12 is an explanatory diagram of calculation when setting a constant voltage used for primary transfer in the control of the comparative example.

  In the control of Comparative Example 1, the development contrast Vcont is adjusted by constant voltage control using the image forming apparatus 100 shown in FIG. Based on the measurement result of the relationship between the voltage applied to the primary transfer roller 15 and the flowing current, a constant voltage used for primary transfer of the control toner image is appropriately set.

  As shown in FIG. 11 with reference to FIG. 1, in the control of Comparative Example 1, a VL potential is set so that an appropriate development contrast Vcont is obtained in the environment. Thereafter, with the photosensitive drum 1 charged to the VL potential, voltages 800V, 1200V, and 1600V under constant voltage control are applied to the primary transfer roller 15, and the current value at that time is detected by the current detection circuit A1. FIG. 12 shows the relationship between the voltage applied to the primary transfer roller 15 at this time and the current flowing through the primary transfer portion T1.

  Next, when the optimum current flowing to the primary transfer portion T1 is 35 μA, the relationship between the voltage and current flowing to the primary transfer portion T1 shown in FIG. Constant voltage control. The above transfer adjustment process is performed during the pre-rotation process immediately before the image forming process.

  By performing such an adjustment process, even if the resistance of the primary transfer roller 15 fluctuates, the toner and the reverse polarity charge can be appropriately applied from the primary transfer roller 15 to the intermediate transfer belt 9 during the primary transfer. When a constant voltage is applied to the primary transfer roller 15 to cause a current having a polarity opposite to that of the toner to flow, the value of the flowing current is determined by the potential difference between the bright portion potential VL, which is a solid white potential, and the potential Vtr of the primary transfer roller 15. Therefore, if the current flowing from the primary transfer roller 15 can be properly controlled, the developed toner image is properly primary-transferred.

  However, an operation of changing the VL potential occurs when adjusting the development contrast Vcont in normal development. At this time, since the relationship between the constant voltage Vtr and the bright portion potential VL that is a solid white potential changes, the amount of current flowing through the primary transfer portion T1 changes.

  Further, since the development contrast Vcont adjustment is controlled based on the density detected on the intermediate transfer belt 1 using the optical sensor 23, the constant voltage is set to an appropriate value with respect to several stages of fluctuations in the VL potential. Need to control.

  As shown in FIG. 11 with reference to FIG. 1, it is first assumed that the photosensitive drum potential VL0 and the constant voltage Vtr0 were before the time zone t1 in the figure. From this state, the solid white potential is changed in several steps in order to optimize the development contrast Vcont. That is, the solid white potential is changed in three steps from VL1 to VL3.

  The solid white potential is changed from VL0 to VL1 in the time zone t1. By changing from the bright part potential VL0, which is a solid white potential, to VL1, the relationship between VL and Vtr changes. That is, the constant voltage applied to the primary transfer roller 15 must be optimized.

  Further, since the potential difference between VL and Vdc (solid white portion contrast Vback) is fixed, the development bias is also changed from Vdc0 to Vdc1 by the change from the bright portion potential VL0, which is a solid white potential, to VL1.

  As for the transfer voltage used for transferring the toner image of the image, a constant voltage is determined as Vtr1 / Vtr2 / Vtr3 and Vtr4 from which a proper current can be obtained from the detected current when the transfer voltage is changed.

  Next, in order to form a control toner image in a state where the solid white potential is VL1, the developing sleeve 41 potential Vdc1, and the transfer voltage is Vtr4, the exposure is turned off to obtain the VD potential and the solid black potential is determined by the Vdc1 to VD potential difference. Create a toner image.

  The solid black control toner image is transferred to the intermediate transfer belt 9 with an appropriate transfer voltage, and the density is detected by the optical sensor 23. However, since the control toner image is not always at an appropriate density, the exposure apparatus 3 similarly changes the solid white potential to VL2, which is the next VL potential.

  Since the solid white potential is changed to VL2 and the solid white potential is changed in the time zone t2, the transfer voltage is optimized as in the time zone t1. The transfer voltage is determined to be Vtr5 from which a proper current is obtained at the bright portion potential VLL2 which is a solid white potential from the detection current when the transfer voltage is varied with Vtr1 / Vtr2 / Vtr3.

  As described above, the above adjustment is continued several times until the control toner image having the optimum density is detected by the optical sensor 23.

  In adjusting the transfer voltage, it is desirable to take a time equal to or longer than one turn of the primary transfer roller 15 at each potential Vtr1 / Vtr2 / Vtr3. The reason is to minimize the influence of the resistance unevenness of the primary transfer roller 15 on the current detection result.

  With the above adjustment, the solid white potential is determined to be VL4, the final transfer voltage adjustment is performed, the proper development contrast Vcont adjustment and transfer voltage adjustment are completed, and the apparatus moves to an image forming operation.

  As described above, in the control of the comparative example, in order to perform appropriate development contrast Vcont control, it is necessary to change the solid white potential by several steps, and the transfer voltage is adjusted for each solid white potential. For this reason, it takes a lot of adjustment time, which is a great disadvantage in an image forming apparatus that requires high productivity. In recent years, since the time until the start of copying has kept the user waiting until an output image is obtained, an output that is as fast as 1 second is required.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of regular development. It is explanatory drawing of the control which sets the electric potential of the solid white part in regular development. It is a perspective view of a primary transfer roller. 3 is a flowchart of control according to the first embodiment. 3 is a time chart of control in Embodiment 1. It is explanatory drawing of the calculation at the time of setting the constant voltage used for primary transfer. FIG. 6 is an explanatory diagram of a configuration of an image forming apparatus according to a second embodiment. 6 is a time chart of control in Embodiment 2. FIG. 10 is an explanatory diagram of calculation when setting a constant voltage used for primary transfer in the control of Example 2; It is a time chart of control of a comparative example. It is explanatory drawing of the calculation at the time of setting the constant voltage used for primary transfer in control of a comparative example.

Explanation of symbols

1 Image carrier (photosensitive drum)
2 Charging device 3 Exposure device 4 Developing device 9 Intermediate transfer member (intermediate transfer belt)
15 Transfer member (primary transfer roller)
22 Surface potential sensor 23 Optical sensor 41 Developing sleeve 42 Fixed magnetic pole 100 Image forming apparatus 110 Control means (control unit)
D1 power supply T1 transfer section (primary transfer section)

Claims (5)

An image carrier;
A charging device for charging the image carrier to a uniform potential;
An exposure apparatus that exposes the charged image carrier to form an electrostatic image;
A developing device for developing the toner image by electrically transferring toner to the electrostatic image;
An image forming apparatus comprising: a transfer member that presses against the image carrier via an intermediate transfer member to form a transfer portion that transfers a toner image from the image carrier to the intermediate transfer member;
A power source capable of outputting a constant voltage and a constant current controlled voltage, and applying a voltage to the transfer portion;
A control toner image formed to a predetermined size on the image carrier and transferred to the intermediate transfer member is used to control at least one of the conditions of the charging device and the exposure device, and a white background of the electrostatic image Control means for adjusting the potential of the part,
When transferring a toner image, the power supply outputs the constant voltage, and when transferring the control toner image, the power supply outputs a voltage controlled by the constant current. Image forming apparatus. Upon receiving the image forming job, the control unit sets the potential of the white background portion based on the density detection result of the control toner image formed by changing the potential of the white background portion in a plurality of stages.
A constant voltage for measurement is output from the power source, a current when a white background portion of the electrostatic image passes through the transfer portion is measured, and the constant voltage corresponding to a predetermined current value is set. The image forming apparatus according to claim 1. When receiving the image forming job, the control unit sets the potential of the white background based on the density detection result of the control toner image formed by varying the potential of the white background in a plurality of stages.
2. The constant voltage corresponding to a predetermined current value is set by measuring the constant current controlled voltage in a process in which the potential of the white background portion passes through the transfer portion in a plurality of stages. The image forming apparatus described. An optical sensor for irradiating the control toner image with detection light to detect reflected light is disposed to face the intermediate transfer member,
4. The image forming apparatus according to claim 2, wherein the control unit detects a density of the control toner image based on an output of the optical sensor. The potential of the white background portion is formed by exposing the image bearing member uniformly charged by the charging device to the exposure device,
The image forming apparatus according to claim 4, wherein the control unit changes the exposure intensity of the exposure apparatus in a plurality of stages to vary the potential of the white background portion in a plurality of stages.

Images