JP2008157975A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of appropriately determining a transfer voltage. <P>SOLUTION: A voltage that a desired current flows through a transfer roller is detected, and then a transfer voltage is determined from the detected voltage value and a development voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to control of a transfer voltage applied to a transfer member when a toner image on an image carrier is transferred to an intermediate transfer member or the like.

  As shown in Patent Document 1, an electrophotographic image forming apparatus irradiates a charged photosensitive drum with laser light to form a yellow electrostatic image of the first color. The electrostatic image is developed by a yellow developing device to which a developing voltage is applied, and a yellow toner image is formed. Subsequently, a primary transfer voltage is applied to the primary transfer roller, and the yellow toner image on the photosensitive drum is primarily transferred to the intermediate transfer member. Subsequently, in the same manner, magenta, cyan, and black toner images are primarily transferred to the intermediate transfer member.

  The four-color toner images primarily transferred to the intermediate transfer member are further secondarily transferred to a recording material by a secondary transfer roller. The recording material on which the four-color toner images are secondarily transferred is conveyed to a fixing device, and the toner images are fixed.

  By the way, in the image forming apparatus, a desired current is supplied during the primary transfer regardless of the area ratio of the image portion (region where the toner image is formed) and the non-image portion (region where the toner image is not formed). The transfer voltage is controlled at a constant voltage so as to flow through However, the resistance of the primary transfer roller changes due to long-term use or the like, and the transfer voltage for flowing a desired current changes.

Therefore, a voltage Vp necessary for a desired current to flow through the transfer roller is obtained, and the transfer voltage is determined by adding this voltage to the image portion potential.
JP2002-244369 JP 2006-126320 A

  However, in order to make the fog in the non-image area inconspicuous, if the potential difference between the non-image area potential of the electrostatic image and the development voltage (hereinafter referred to as Vback potential) is set to be different for each color, the image area of the photosensitive drum The desired current did not flow, resulting in transfer failure.

Here, FIG. 9A shows the non-image area potential (Vd), the image area potential (Vl), and the development voltage (Vl) of the yellow electrostatic latent image. Similarly, FIG. 9B shows the non-image portion potential (Vd), the image portion potential (Vl), and the development voltage (Vl) of the magenta electrostatic latent image.
As shown in FIGS. 9A and 9B, when the Vback potential is different, the potential difference Vg between the non-image potential (Vd) of the electrostatic image and the image portion potential (Vl) is different.

  Further, since the yellow toner image and the magenta toner image are transferred by the same transfer roller, the voltage Vp necessary for a desired current to flow through the transfer roller is the same.

  Accordingly, when the transfer voltage is determined by adding the voltage Vp to the non-image portion potential, the potential difference Vf between the image portion potential and the transfer voltage is different between yellow and magenta. However, since the yellow toner and the magenta toner have substantially the same charge amount, the potential difference Vf between the transfer voltage and the image portion potential should be the same for good transfer.

  In this way, when the Vback potential is different, the transfer voltage is not set appropriately, and a desired current does not flow to the image portion, resulting in a transfer failure.

The present invention has been made in view of the above problems, and its purpose is as follows.
By providing an image forming apparatus capable of appropriately determining a transfer voltage in an image forming apparatus that detects a voltage necessary for a desired current to flow through a transfer roller and determines a transfer voltage from the detection result. is there.

An image carrier for carrying an electrostatic image;
A developing unit to which a developing voltage is applied and which develops the electrostatic image to form a toner image;
An image forming apparatus comprising: a transfer member that applies a transfer voltage to transfer the toner image to a transfer medium; and a detection unit that detects a voltage applied to the transfer member in order to flow a predetermined current to the transfer member. In
An image forming apparatus, comprising: a transfer voltage determination unit that determines the transfer voltage based on a detection result of the detection unit and the development voltage.

  According to the present invention, since a voltage necessary for a predetermined current to flow through the transfer member is detected and the transfer voltage is determined based on the detection result and the development voltage, the transfer voltage can be appropriately determined. it can.

<Overall configuration of image forming apparatus>
FIG. 1 is an overall explanatory diagram of an image forming apparatus according to an embodiment of the present invention. First, the overall configuration of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus 100 forms toner images of a plurality of colors on a photosensitive drum (image carrier) 1, superimposes the toner images on an intermediate transfer belt 11 and performs primary transfer, and the toner images of the plurality of colors are collectively recorded. Secondary transfer to P to form a full color image.

  The photosensitive drum 1, which is an image carrier, rotates in the direction of the arrow a1 in the drawing to form a toner image. Around the photosensitive drum 1, a charging roller (charging unit) 2, an exposure device 3, a rotary developing device holding unit 4, a primary transfer unit T 1, and a photosensitive drum cleaner 12 are provided. In the rotary developing device holder 4 that rotates in the a2 direction, four developing devices (developing means) 4y, 4m, 4c, and 4k filled with toners of different colors are arranged.

That is, 4y is filled with yellow toner, 4m is magenta toner, 4c is filled with cyan toner, and 4k is filled with black toner. The charge amount per unit amount of toner of each color is substantially equal. Below the photosensitive drum 1, an intermediate transfer belt 11 to which a toner image formed on the photosensitive drum 1 is primarily transferred is provided. An intermediate transfer belt (transfer medium, intermediate transfer member) 1 is supported by a plurality of rollers. The toner image on the intermediate transfer belt 11 is secondarily transferred collectively to the recording material P at the secondary transfer portion T2, and the recording material on which the toner image is secondarily transferred is conveyed to the fixing device 9. It should be noted that the density of the toner of this embodiment is adjusted so that an optical density of 1.5 is obtained when the toner is fixed on the recording material P by the fixing device 9 in a toner amount state of 0.5 mg / cm ² . The optical density is a value measured with a spectrodensitometer 504 manufactured by X-Rite.

  First, a negative charging voltage is applied to the charging roller 2, and the outer peripheral surface of the photosensitive drum 2 is uniformly charged to a negative polarity. The photosensitive drum 1 is obtained by providing a photosensitive layer on an aluminum cylinder having a diameter of 84 mm. Subsequently, based on the yellow image signal of the first color, the exposure device 3 exposes the outer peripheral surface of the photosensitive drum 1 to form an electrostatic latent image (electrostatic image). By the rotation of the rotary developing device holding unit 4, the developing device 4 y loaded with the yellow toner charged to the negative polarity moves to a position facing the photosensitive drum 1. In the developing device 4y, a toner conveying mechanism (not shown) supplies yellow toner to a developing sleeve (not shown). The yellow toner supplied to the developing sleeve is applied in a thin layer to the developing sleeve by a regulating blade (not shown) pressed against the outer periphery of the developing sleeve. When a negative developing voltage is applied to the developing device 4y from the developing power source 41, an electric field is formed in the gap (300 μA) between the developing sleeve and the photosensitive drum 1. The electrostatic latent image is developed by the yellow toner that moves by receiving the electrostatic force received from the electric field, and a yellow toner image is formed. When the yellow toner image reaches the primary transfer portion T1 by the rotation of the photosensitive drum 1, it is applied to the intermediate transfer belt 11 by the primary transfer roller (transfer member) 5 to which a positive transfer voltage is applied from the primary transfer power source 51. Primary transfer is performed.

The primary transfer roller 5 was provided with a foam rubber layer based on EPDM subjected to a foam treatment on a steel core having a diameter of 8 mm, and the diameter was 16 mm. The resistance value of the primary transfer roller 5 of this embodiment is 10 ^6.5 Ω (100 v applied) in an environment of 23 ° C./50% RH, but is 10 ^5.0 Ω to 10 ^7.0 Ω. You can also

The intermediate transfer belt 11 is adjusted to a resistance adjuster of 10 ^9.5 Ω · cm in a polyimide resin having a thickness of 85 μm. The intermediate transfer belt 11 is supported by a primary transfer downstream roller 6, a counter roller 81, a driven roller 82, a drive roller 83, and a secondary transfer inner roller 71. By the rotation of the driving roller 83, the intermediate transfer belt 11 rotates in the arrow a3 direction at a speed of 130 mm / s. The primary transfer downstream roller 6 is a SUS roller having a diameter of 6 mm. Since the primary transfer downstream roller 6 is in contact with the back surface of the intermediate transfer belt 11 to which a charge is applied by applying a primary transfer voltage to the primary transfer roller 5, it is electrically grounded to prevent charge-up. ing.

  The photosensitive drum 1 to which the yellow toner image is primarily transferred is removed by the photosensitive drum cleaner 12 without being primarily transferred.

  Subsequently, a magenta toner image of the second color is formed on the photosensitive drum 11. The photosensitive drum 1 from which the toner has been removed by the photosensitive drum cleaner 12 is again negatively charged by the charging roller 2. The exposure device 3 exposes the outer peripheral surface of the photosensitive drum 1 based on the magenta image signal to form an electrostatic latent image. By the rotation of the rotary developing device holding unit 4, the developing device 4 m loaded with magenta toner charged to negative polarity moves to a position facing the photosensitive drum 1. When a negative development voltage is applied to the developing device 4m, the electrostatic latent image is developed and a magenta toner image is formed. When the magenta toner image reaches the primary transfer portion T1, it is primarily transferred to the intermediate transfer belt 11 that holds the yellow toner image by the primary transfer roller 5 to which a positive transfer voltage is applied.

  Similarly, the cyan toner of the third color and the black toner image of the four colors are primarily transferred to the intermediate transfer 11.

  The four-color toner images primarily transferred to the intermediate transfer belt 11 are collectively transferred to the recording material P at the secondary transfer portion T2 where the secondary transfer inner roller 71 and the secondary transfer outer roller sandwich the intermediate transfer belt 11. Second transfer is performed. The secondary transfer inner roller 71 is electrically grounded, and when the toner image on the intermediate transfer belt 11 is secondarily transferred, the secondary transfer outer roller 72 receives positive secondary transfer from the secondary transfer power source 73. A voltage is applied.

The secondary transfer outer roller 72 is provided with a foamed rubber layer based on a fired NBR on a steel core metal having a diameter of 12 mm, and further provided with an NBR layer on the outer side thereof to have a diameter of 24 mm. . In the secondary transfer outer roller 72, an ion conductive substance is dispersed as a resistance adjusting agent, and the resistance value is adjusted to 10 ^7.5 Ω (2 Kv applied). As the secondary transfer outer roller 72, a roller in the range of 10 ^7.0 Ω to 10 ^7.8 Ω can be used.

  The recording material P onto which the toner image has been secondarily transferred from the intermediate transfer belt 11 is conveyed to the fixing device 9 and fixed by heating and pressing to obtain a permanent image.

  Further, the intermediate transfer belt cleaner 10 that has been separated from the intermediate transfer belt 11 during the primary transfer comes into contact with the intermediate transfer belt 11 prior to the start of the secondary transfer. The toner remaining on the intermediate transfer belt 11 without being secondarily transferred to the recording material P is removed by the intermediate transfer belt cleaner 10.

<Control of charging voltage and development voltage>
The sensitivity of the photosensitive drum 1 to light changes due to long-term use of the photosensitive drum 1.
Regardless of this change, the charging voltage and the development voltage are controlled so that the toner amount of the solid toner image formed on the photosensitive drum 1 does not deviate significantly from 0.5 mg / cm ² . That is, the toner voltage per unit area of the toner image formed on the photosensitive drum 1 is adjusted by controlling the charging voltage and the developing voltage.

  In this embodiment, the Vback potential is set to be different for each toner color in consideration of the difference in the fogging of each color toner. When the temperature and humidity were 23 ° C./50% RH, the yellow Vback potential was 190 v, magenta and cyan were 200 v, and black was 210 v.

  In order to reduce the fog, the Vback potential may be increased. However, when the potential at which the charger 2 charges the photosensitive drum 1 increases, the potential of the image portion becomes unstable. Further, in the case of using a so-called two-component development method using a developer in which toner and carrier are mixed, the carrier adheres to the photosensitive drum 1 when the Vback potential is increased. Therefore, it is preferable to reduce the Vback potential for a color where fog is not noticeable.

  In the image forming apparatus according to this embodiment, the charging voltage applied to the charger 2 and the developing potential applied to the developing device 4ymck are adjusted for each color in consideration of the difference in the Vback potential of each color. A method for adjusting the charging voltage and the developing voltage will be described with reference to the flowchart of FIG. Since the adjustment method of the charging voltage and the developing voltage for each color is the same, a description will be given by taking a yellow toner image as an example. The following control is performed by the voltage controller (voltage control means) 201 in FIG.

  The temperature and humidity in the apparatus main body are measured by the temperature / humidity sensor 14 (S101).

  Subsequently, the Vback potential corresponding to the temperature and humidity is read from the table recorded in the memory 202 in FIG. 1 (S102). Now, since the temperature and humidity is 23 ° C./50% RH, the yellow Vback potential is set to 190v.

  Next, the reflected light amount R1 of the intermediate transfer belt 11 is measured by the optical sensor 13 (S103).

  A toner patch is formed on the photosensitive drum 1 by using [-360v] as a charging voltage [-550v] and [-360v] obtained by adding [+ 190v] of Vback to the charging voltage [-550v], and primary transfer to the intermediate transfer belt 11 (S104). Note that a value corresponding to the temperature and humidity is stored in the memory 202 as the transfer voltage when the toner patch is primarily transferred, and the transfer voltage corresponding to the temperature and humidity is applied. Then, the reflected light amount R2 of the toner patch primarily transferred to the intermediate transfer belt 11 is detected (S105). Next, [(reflected light amount R2 of toner patch) / (reflected light amount R1 of intermediate transfer belt 11)] (hereinafter, this value is referred to as a light amount ratio) is calculated (S106). Here, the smaller the reflected light amount R2 of the toner patch, the larger the toner amount of the toner of the toner patch. Therefore, the smaller the light quantity ratio, the larger the toner amount of the toner patch.

  It is determined whether or not the light amount ratio is larger than a predetermined value (S107). If it is determined in S107 that the light quantity ratio is larger than the predetermined value, the absolute values of the developing voltage and the charging voltage are increased while maintaining the Vback potential [+ 190v]. (S108). At this time, in this embodiment, the charging voltage and the absolute value of the charging voltage are increased by 10 v. Therefore, the charging voltage is [−560 v] and the development voltage is [−370 v]. By increasing the absolute value of the developing voltage, the electric field between the developing sleeve and the photosensitive drum 1 increases, and the amount of toner on the photosensitive drum 1 increases.

  Then, the process returns to S104, and a toner patch is formed again on the photosensitive drum 11 with the changed development voltage and charging voltage, and transferred to the intermediate transfer belt 11. On the intermediate transfer belt 11, the reflected light amount of this patch is detected again.

  Conversely, if it is determined in S107 that the light quantity ratio is not larger than the predetermined value, it is determined whether or not the light quantity ratio is smaller than the predetermined value (S109).

  If it is determined in S109 that the light amount ratio is smaller than the predetermined value, the absolute values of the developing voltage and the charging voltage are reduced while maintaining the Vback potential (S110). At this time, in this embodiment, the charging voltage and the absolute value of the charging voltage are reduced by 10 v. Therefore, in this embodiment, the charging voltage is [−540v] and the developing voltage is [−350v]. Then, the process returns to S104, and a toner patch is formed again on the photosensitive drum 11 with the changed development voltage and charging voltage, and transferred to the intermediate transfer belt 11. On the intermediate transfer belt 11, the reflected light amount of this patch is detected again.

If it is determined in S109 that the light amount ratio is not smaller than the predetermined value, the developing voltage and charging voltage at this time are set as the developing voltage and charging voltage when an image is actually formed. (S111)
By the above method, the charging voltage for forming the yellow toner image in this embodiment is determined as [-540v], and the developing voltage is determined as [-350v].

  Subsequently, the charging voltage and developing voltage for forming the magenta toner image are determined according to the flow of FIG. When the temperature and humidity is 23 ° C./50% RH, the Vback potential of magenta is set to 200v. In step S104, a toner patch is formed on the photosensitive drum 1 by using [-350v] as a charging voltage [-550v] and [-350v] obtained by adding [+ 200v] of Vback to the charging voltage [-550v]. Perform primary transfer.

  In this embodiment, the charging voltage of magenta was determined to be [−580v] and the developing voltage was determined to be [−380v]. Further, cyan and black charging voltages and developing voltages are also determined according to the flow of FIG.

  In this embodiment, the toner patch is a toner image having the highest density that can be formed by the apparatus, and is a square of 20 mm × 20 mm. One toner patch is detected at 16 points at 1 mm intervals. The average value of the 16 points of detection results is used as the reflected light amount of the toner patch. FIG. 3 shows the configuration of the optical sensor 13 of the present embodiment. The optical sensor 13 is a specular reflection type sensor that detects reflected light. The LED light source 101 that is inclined at an angle φ with respect to the detection position on the surface of the intermediate transfer belt 11 that is stretched around the driving roller 83, and a photo as a light receiving element that is also inclined at an angle φ. And the transistor 102. The reflected light emitted from the LED light source 101 to the toner patch is detected as a light amount by the phototransistor 102, so that the optical density of the toner patch can be estimated.

<Determination of transfer voltage>
Once the charging voltage and developing voltage for each color are determined, the transfer voltage is then determined.
When applying the transfer voltage by constant voltage control, control for setting an optimum transfer voltage is performed. The resistance of the transfer roller 3 changes due to durability deterioration or the like.
Therefore, a target voltage value Vb for allowing a desired current (target current value Ia) to flow through the transfer roller 3 is detected.

  Further, the Vback potential is different for each color, and as a result, the potential difference between the image portion potential of the electrostatic latent image and the non-image portion potential is different for each color. Accordingly, in the conventional method in which the voltage value obtained by adding the target voltage Vb to the non-image portion potential of each color is the transfer voltage at the time of image formation, the potential difference between the image portion potential and the transfer voltage differs for each color. However, the potential difference between the image portion potential and the transfer voltage necessary for proper transfer is substantially the same for each color. Accordingly, it is difficult to appropriately determine the transfer voltage by the conventional method in which the target voltage Vb is applied to the non-image portion potential.

  Therefore, since the potential difference between the development voltage and the image portion potential does not differ greatly for each color, the potential difference between the target voltage Vb and the development voltage is added to the development voltage for each color to determine the transfer voltage at the time of image formation.

FIG. 4 shows a flow of the transfer voltage determination process of this embodiment.
First, the photosensitive drum 1 is charged with a reference charging voltage (−500 v) (S201). Next, the current I1 flowing through the transfer roller 3 when the test voltage V1 (+100 v) is applied to the transfer roller 3 and the current I2 when the test voltage V2 (+400 v) is applied are detected (S202). In this example, I1 = 4 μA and I2 = 16 μA. The currents I1 and I2 are detected by an ammeter (current detection means) 52. The temperature / humidity is detected, and the target current value Ib corresponding to the current temperature / humidity is read from the memory 202 in which the target current value Ib corresponding to the temperature / humidity is recorded (S203). Assuming that the current temperature and humidity is 25 ° C./50% RH, the target current value is 10 μA in this embodiment. From the current-voltage relationship obtained in S202 (FIG. 5), [+ 250v] is detected as the target voltage Vb applied to the transfer roller 3 because 10 μA, which is the target current value Ia, flows through the transfer roller 3. (S204). The target voltage Vb is detected by a target voltage detector (detection means) 203. Note that V1, V2, I1, and I2 obtained in S202 are linearly complemented to obtain a current-voltage relationship.

Here, in an environment of 25 ° C./50% RH, when a charging voltage is a reference charging voltage [−500] and a developing voltage is a reference developing voltage [−310 v], a good yellow toner image is formed on the photosensitive drum 1. It has been confirmed that it is formed. Further, when the optimum transfer voltage at this time is Vk, it is known that 10 μA flows when Vk is applied to the transfer roller 3 in a state where the photosensitive drum 1 is charged with the charging voltage [−500 V]. At this time, 10 μA is set as the target current value b. When the temperature and humidity are the same, the amount of charge per unit amount of toner does not vary greatly. Therefore, in the environment of 25 ° C./50% RH, even if the charging voltage and the developing voltage are different from the above values, the potential difference between the image portion potential and the developing potential does not vary greatly. (See Figure 7)
A transfer voltage determiner (transfer voltage determining means) 204 determines a transfer voltage from the target voltage Vb. The following flow is performed by the transfer voltage determiner (transfer voltage determining means) 204.

  Next, a transfer contrast voltage Vc, which is a voltage difference between the reference development voltage [−310 v] and the voltage Vb [+250 v], is determined as 250 v − (− 310 v) = 560 v (S205). Then, the transfer contrast voltage Vc is recorded in the memory 202 (S206).

The transfer contrast voltage Vc is added to the development voltage [-350v] of the yellow toner image obtained by detecting the patch image, and -350v + 560v = + 210v, and [+ 210v] is determined as the transfer voltage of the yellow toner image (S207). (See Figure 7)
Subsequently, the transfer voltage of the magenta toner image is determined.

  FIG. 8 shows a flow for determining the transfer voltage of the magenta toner image.

  Since there is no significant difference between the charge amounts of the yellow toner and the magenta toner, it is considered that the potential difference between the image portion potential and the transfer voltage for good transfer is substantially equal between yellow and magenta. Further, the potential difference between the magenta image portion potential and the developing voltage is considered to be substantially equal to the potential difference between the yellow image portion potential and the developing voltage.

  Therefore, in this embodiment, first, the transfer contrast potential Vc obtained at the time of determining the yellow transfer voltage is read from the memory 202 (S301). The magenta transfer voltage is determined by applying the development voltage [-380v] of the magenta toner image obtained by detecting the patch image (S202). That is, −380v + 560v = + 180v, and the magenta transfer voltage is determined to be + 180v.

  Similarly, the transfer contrast voltage Vc obtained when determining the yellow transfer voltage is applied to the cyan and black development voltages to determine the cyan and black transfer voltages.

By the way, in the above transfer voltage determination process,
The transfer voltage is determined by “{(target voltage Vb) − (reference development voltage)} + (development voltage)”. That is, the transfer voltage is determined by adding to the target voltage Vb a correction value (development voltage-reference development voltage) that is changed with the change of the development voltage.

  In the present embodiment, the control of the charging voltage and the developing voltage and the control of the transfer voltage are performed when the apparatus main body is turned on, but can be performed every predetermined number of prints (for example, 500 sheets). In addition, when controlling the charging voltage, the developing voltage, and the transfer voltage for each predetermined number of prints, the transfer voltage for primary transfer of the patch toner image is determined using the result of the previous control. You can also.

  In the embodiment, the embodiment has a configuration in which the Vback potential differs depending on the color of the toner. However, the present invention can also be applied to an image forming apparatus that changes the Vback potential even for toner of the same color by long-term use of the developing device. .

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. The figure which shows the flow of the adjustment method of a charging voltage and a developing voltage. The figure which shows the structure of an optical sensor. The figure which shows the flow of the control method of the transfer voltage of yellow. The figure which shows the relationship between test voltage V1, V2 and electric current I1, I2. The figure which shows the flow of the control method of the magenta transfer voltage. The figure for demonstrating embodiment in detail. The figure for demonstrating embodiment in detail. The figure for demonstrating the subject which this invention tends to solve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 4 Developer 5 Primary transfer roller 11 Intermediate transfer belt 201 Voltage controller 203 Transfer voltage determiner

Claims (3)

An image carrier for carrying an electrostatic image;
Charging means for charging the image carrier to form the electrostatic image;
A developing unit to which a developing voltage is applied and which develops the electrostatic image to form a toner image;
An image forming apparatus comprising: a transfer member that applies a transfer voltage to transfer the toner image to a transfer medium; and a detection unit that detects a voltage applied to the transfer member in order to flow a predetermined current to the transfer member. In
An image forming apparatus, comprising: a transfer voltage determination unit that determines the transfer voltage based on a detection result of the detection unit and the development voltage.   The image forming apparatus according to claim 1, wherein a toner image of a plurality of colors is formed on the image carrier.   3. The image forming apparatus according to claim 1, wherein the transfer medium is an intermediate transfer body on which a toner image is primarily transferred from the image carrier, and further, the toner image is secondarily transferred to a recording material. .

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