JP3346091B2 - Toner image transfer device and transfer voltage control method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser printer for transferring an unfixed toner image held on a belt-shaped image carrier onto a recording medium such as paper. The present invention relates to a toner image transfer device.

[0002]

2. Description of the Related Art An image forming apparatus having a belt-shaped image carrier is disclosed in JP-A-6-289737 (FE93).
[00135] The ones listed are known. In particular,
As shown in FIG. 5, a latent image carrier 100 such as a photosensitive drum
Developing units 103 corresponding to each color of black (Bk), yellow (Y), magenta (M), and cyan (C)
To 106 are formed, an unfixed toner image T of each color is formed for each rotation of the latent image carrier 100, and these unfixed toner images T are formed on the intermediate transfer member 101 which rotates synchronously with the latent image carrier 100. The unfixed toner image T thus superimposed is secondarily transferred from the intermediate transfer body 101 to the recording medium 102 again to form a desired image on the recording medium 102.

In this apparatus, the transfer of the unfixed toner image T from the intermediate transfer body 101 to the recording medium 102 is performed by a semi-conductive bias roll 108 disposed on the back side of the recording medium 102 at the transfer position. When a transfer voltage having a polarity opposite to that of the toner is applied to the roll 108, the unfixed toner image is transferred from the intermediate transfer body 101 to the recording medium 102.

On the other hand, at a position facing the bias roll 108 with the intermediate transfer member 101 interposed therebetween, a backup roll 109 serving as a counter electrode of the roll 108 is provided. The backup roll 109 is formed by covering a grounded conductive roll with a semiconductive or insulating thin layer, or formed by covering an insulating roll with a grounded semiconductive thin layer. But this is the recording medium 1
When the type and size of the print medium 02 change, an excessive current is prevented from flowing from the bias roll 108 to the backup roll 109, and the intermediate transfer body 101 and the recording medium 10 are prevented from flowing.
The purpose of this is to form a stable transfer electric field between the transfer roller 2 and the transfer roller 2 and prevent transfer failure of the unfixed toner image.

[0005]

However, in the secondary transfer of such an image forming apparatus, the resistance values of the bias roll and the backup roll are liable to fluctuate greatly due to environmental fluctuations and deterioration over time. Such a variation has a magnitude of about two digits, depending on the structure and material of the roll.
Therefore, if a constant transfer voltage is always applied to the bias roll, the voltage drop amount in the bias roll and the backup roll fluctuates, so that a stable transfer electric field is always formed between the recording medium and the intermediate transfer body. Therefore, there is a problem that the transfer failure of the toner image easily occurs.

FIG. 6 is a graph showing the range of the optimum transfer voltage according to the change in the resistance value of the bias roll and the backup roll. The area between the upper and lower two solid lines or broken lines is the optimum transfer voltage for each bias roll resistance. Range. The lower limit of the optimum transfer voltage is the minimum transfer voltage required for the toner to move toward the recording medium overcoming the adhesive force with the intermediate transfer member, and the upper limit is the Paschen discharge between the intermediate transfer member and the recording medium. Is the highest transfer voltage that causes image quality defects and a decrease in transfer efficiency due to overcharging of the toner. That is, it can be understood from this graph that when the resistance values of the bias roll and the backup roll change, the optimum transfer voltage also changes.

On the other hand, Japanese Patent Application Laid-Open No. 2-212872 discloses a toner image transfer device in consideration of such a change in the resistance value of a bias roll. In this device,
Before the start of the image forming cycle, a current value flowing from the bias roll to the intermediate transfer body is measured, and a voltage applied to the bias roll is controlled based on the measured value so that a predetermined current always flows to the secondary transfer system. I have to. That is,
If the voltage applied to the bias roll is constant, the value of the current flowing from the bias roll to the intermediate transfer member should be inversely proportional to the resistance of the entire secondary transfer system. It can be said that the transfer electric field is stabilized after grasping.

However, the resistance values of the bias roll and the backup roll fluctuate individually. For example, when the resistance value of the backup roll becomes extremely small, the fluctuation of the resistance value of the bias roll becomes the fluctuation of the transfer electric field. Therefore, in order to ensure the stabilization of the transfer electric field, it is necessary to separately grasp the resistance values of the bias roll and the backup roll. In this regard,
The image forming apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. H2-212872 grasps only the resistance value of the entire secondary transfer system including the bias roll and the backup roll, and cannot completely stabilize the transfer voltage. Has problems.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a method for transferring a toner image held on a belt-shaped image carrier to a recording medium due to environmental fluctuation and aging. It is an object of the present invention to provide a toner image transfer apparatus capable of always forming a stable transfer electric field and preventing a transfer failure of a toner image irrespective of practical use, and a transfer voltage control method using the apparatus.

[0010]

To achieve the above object, a toner image transfer device of the present invention is a toner image transfer device for transferring a toner image held on a belt-shaped image carrier to a recording medium. A bias roll that appropriately contacts the image carrier to transfer the toner image to a recording medium; a backup roll that supports the image carrier from the back side at a position facing the bias roll; A ground member that contacts the bias roll separated from the bias roller; current detection means for detecting a current flowing through the bias roll when the bias roll and the image carrier are in contact with each other; Calculating means for determining a voltage to be applied to the bias roll based on the value; and applying a transfer voltage to the bias roll according to a calculation result of the calculating means. It is characterized in being composed of a pressure control means.

In the transfer voltage control method using the toner image transfer device, a measuring voltage is applied to the bias roll while the bias roll is in contact with the image carrier, and a current flowing through the bias roll is controlled. Detecting,
A step of applying a voltage to the bias roll while the bias roll is in contact with the ground member, detecting a current flowing through the bias roll, and transferring the toner image based on the two current values detected in the preceding two steps And a step of determining a transfer voltage to be used.

[0012]

According to such technical means, when the bias roll and the intermediate transfer member are in contact with each other, current flows from the bias roll to the backup roll, while the bias roll and the intermediate transfer member are separated from each other. Current flows from the bias roll to the ground member, and the current detecting means detects the current flowing to the bias roll in each case. Thereby, the calculating means can grasp the resistance value of each of the bias roll and the backup roll from the detected value, so that the voltage control means applies the optimum voltage corresponding to these resistance values to the bias roll. Can be applied.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a toner image transfer apparatus according to the present invention and a transfer voltage control method using the same. FIG. 1 shows a schematic configuration of a color electrophotographic copying machine to which the present invention is applied. Reference numeral 1 denotes a photosensitive drum (latent image carrier), and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum by a well-known electrophotographic process (not shown) with rotation in the direction of arrow A. Is done. That is, after the photosensitive drum 1 is charged to a predetermined dark potential by the charger 1a, exposure is performed according to an image signal by a light beam Bm emitted from a laser beam scanner (not shown). Black (Bk) around the photosensitive drum 1
Developing devices 5 to 8 corresponding to the respective colors of yellow (Y), magenta (M) and cyan (C) are provided, and any one of the developing devices is used for developing the electrostatic latent image formed on the photosensitive drum 1. To form a toner image T. Therefore, if the electrostatic latent image written on the photosensitive drum 1 corresponds to the yellow image information, this electrostatic latent image is developed by the developing device 6 containing yellow (Y) toner, and A yellow toner image is formed on the body drum 1.

Reference numeral 2 denotes a belt-shaped intermediate transfer member arranged so as to be in contact with the surface of the photosensitive drum 1, and is stretched around a plurality of rolls and rotates in the direction of arrow B.
The unfixed toner image T formed on the photosensitive drum 1 is
The image is transferred from the photosensitive drum 1 to the surface of the intermediate transfer member 2 at a primary transfer position where the photosensitive drum 1 contacts the intermediate transfer member 2. At this primary transfer position, a corona discharger 9 is provided on the back side of the intermediate transfer body 2, and by applying a voltage having a polarity opposite to the charging polarity of the toner to the corona discharger 9, 1 is electrostatically attracted to the intermediate transfer body 2.

When a single-color image is formed, the unfixed toner image T primarily transferred to the intermediate transfer body 2 is secondarily transferred to the recording medium 3 immediately. When the toner image is formed, the formation of the toner image on the photosensitive drum 1 and the primary transfer process of the toner image are repeated for the number of colors. For example, when a full-color image is formed by superimposing four color toner images, an unfixed toner image T of black, yellow, magenta, and cyan is formed on the photosensitive drum 1 for each rotation, and these unfixed toner images are formed. The image T is sequentially primary-transferred onto the intermediate transfer body 2. On the other hand, the intermediate transfer body 2 rotates at the same cycle as the photosensitive drum 1 while holding the black unfixed toner image T that has been primarily transferred first, and the intermediate transfer body 2 has yellow, The magenta and cyan unfixed toner images T are transferred to be superimposed on the black unfixed toner image T.

The unfixed toner image T primarily transferred to the intermediate transfer body 2 in this manner is conveyed to a secondary transfer position facing the conveyance path of the recording medium 3 as the intermediate transfer body 2 rotates. You. At the secondary transfer position, the semiconductive bias roll 10 is in contact with the intermediate transfer member 2 and the feed roller 11
Thus, the recording medium 3 carried out of the tray 12 at a predetermined timing is sandwiched between the bias roll 10 and the intermediate transfer body 2. On the back side of the intermediate transfer member at the secondary transfer position, a backup roll 4 serving as an opposite electrode of the bias roll 10 is disposed, and a voltage having a polarity opposite to the charging polarity of the toner is applied to the bias roll 10. Then, the unfixed toner image T carried on the intermediate transfer body 2 is electrostatically transferred to the recording medium 3 at the secondary transfer position.

Then, the recording medium 3 to which the unfixed toner image has been transferred is peeled off from the intermediate transfer body by a peeling claw 13,
The sheet is sent to a fixing device (not shown) by the conveyor belt 14 and a fixing process of an unfixed toner image is performed. On the other hand, the residual toner is removed by the cleaner 15 from the intermediate transfer body 2 on which the secondary transfer of the unfixed toner image has been completed.

In such a configuration, the bias roll 10, the peeling claw 13, and the cleaner 15 are connected to the intermediate transfer member 2.
When a color image is formed, these members are separated from the intermediate transfer member 2 until the final unfixed toner image is primarily transferred to the intermediate transfer member 2. I have.

FIG. 2 is a view showing the details of the backup roll 4 and the bias roll 10 which come into contact with the intermediate transfer member 2 at the secondary transfer position. The intermediate transfer member 2 is formed by adding an appropriate amount of an antistatic agent such as carbon black to a resin such as acryl, vinyl chloride, polyester, or polycarbonate, or various rubbers. The resistivity is adjusted to 10 ⁹ Ω · cm.

The backup roll 4 is formed by covering an insulating roll 23 with a semiconductive thin film 24 having a thickness of 10 μm to 200 μm and a volume resistivity of 10 ⁴ Ω · cm or more. The resistivity is 10 ⁸ Ω / □
(□: unit area). Also,
The conductive film 2 is disposed on the thin film 24 at a distance of 20 to 30 mm in the circumferential direction from the contact position with the intermediate transfer body 2.
5 is in contact with the thin film 2 at this position.
4 is grounded. Note that, instead of the conductive roll 25, a conductive brush or a conductive film may be contacted.

On the other hand, the bias roll 10 has conductive rubber dispersed in a rubber roll of silicon rubber or the like, and its volume resistivity is adjusted to 10 ⁸ Ω · cm, and the toner image is transferred from the intermediate transfer body 2 to the recording medium 3. When the image is transferred, a transfer voltage is applied by the voltage control unit 31.

According to the above configuration, when a predetermined voltage is applied to the bias roll 10 in a state where the recording medium 3 is fed between the bias roll 10 and the intermediate transfer body 2 which are in contact with each other, While a weak current flows from the bias roll 10 to the backup roll 4,
A transfer electric field having a predetermined intensity is formed between the recording medium 3 and the two intermediate transfer members, and the toner image is transferred from the intermediate transfer member 2 to the recording medium 3.

At this time, the magnitude of the value of the current flowing between the bias roll 10 and the backup roll 4 depends on the magnitude of the resistance value of the rolls 4 and 10. , 10 fluctuate due to use environment such as temperature and humidity or deterioration over time, and it is difficult to stably form a transfer electric field having a predetermined strength. Therefore, in this embodiment, the resistance values of the bias roll 10 and the backup roll 4 are measured prior to the start of the image forming operation, and the transfer voltage applied to the bias roll during the image forming operation is changed based on the measurement result. Constant current is always applied to the bias roll 10 and the backup roll 4
So that it flows between them.

More specifically, a current detector 32 is provided in series with the voltage controller 31, and a current i ₀ flowing through the bias roll 10 in the current detector 32 when a predetermined voltage is applied to the bias roll 10 on a test basis. And the calculation unit 33 calculates the resistance values of the bias roll 10 and the backup roll 4 based on the measured value.

As described above, the bias roll 1
Numeral 0 is disposed so as to be able to abut or separate from the intermediate transfer member as appropriate, but a grounded earth roll 30 is disposed at the separated position (the position indicated by the one-dot chain line in FIG. 2) and set to the position. Bias roll 10 and ground roll 30
And abut. Thus, when the bias roll 10 is separated from the intermediate transfer member 2, a current i ₁ flows from the bias roll 10 via the ground roll 30 by applying a voltage to the bias roll 10, so that the bias roll 10 Only the resistance value can be measured.

FIG. 3 is a flowchart showing a control program for determining the transfer voltage. Such a control program is executed, for example, when the power of the copier is turned on or between copy jobs before and after. However, if executed too frequently, the copy job of the user is hindered. It is preferable to execute it only when it is not present.

When the control program starts, first, the voltage control unit 31 applies a measurement voltage to the bias roll 10 in a state where the bias roll 10 is in contact with the intermediate transfer body 2 (the position indicated by the solid line in FIG. 2). (ST1) At this time, the current i ₀ flowing through the bias roll 10 by the current detection unit 32 is set.
Is detected (ST2). Then, the calculation unit 33 calculates the sum R ₀ of the resistance values of the bias roll 10 and the backup roll 4 based on the detection signal of the current detection unit 32 (S
T3). Next, in a state where the bias roll 10 is separated from the intermediate transfer body 2 (a position indicated by a broken line in FIG. 2), that is, in a state where the bias roll 10 is in contact with the earth roll 30, the voltage control unit 31 applies the measurement voltage to the bias roll. 10 (ST4), and the current detector detects the current i _BTR flowing through the bias roll 10 in the same manner as in ST2 (ST5).
Then, the calculation unit 33 calculates the resistance value R _{BTR of} only the bias roll 10 based on the detection signal of the current detection unit 32 (ST6).

Thereafter, the calculation unit 33 calculates the resistance value R _BUR of the backup roll 4 from the total resistance value R ₀ determined in ST 3 and the resistance value R _BTR of the bias roll 10 determined in ST 6 (ST 7). An optimum transfer voltage is determined based on the calculation result in ST7, and is set in the voltage control unit 31 (ST8). As a result, the transfer voltage control program ends, and the secondary transfer of the toner image in the subsequent copy job is performed using the transfer voltage newly set in the voltage control unit 31.

Therefore, in the color copying machine of this embodiment, even if the resistance values of the semiconductive bias roll 10 and the backup roll 4 fluctuate greatly due to a change in the use environment and deterioration over time, the resistance value is not changed. Is applied to the bias roll 10, and a stable transfer electric field can be formed between the intermediate transfer member and the recording medium.

In this embodiment, the resistance value is calculated for each of the bias roll 10 and the backup roll 4, and the optimum transfer voltage to be applied to the bias roll 10 is determined based on these results. It is possible to accurately form a transfer voltage required for forming an electric field.

As shown in FIG. 4, the backup roll 4 of the present embodiment has a structure in which the surface of a grounded conductive roll 21 is covered with a semiconductive or insulating thin film 22. good. As the conductive roll 21, a rubber roller or a metal roll in which conductive carbon is dispersed can be used. On the other hand, as the thin film 22, an appropriate amount of an antistatic agent such as carbon black is dispersed in acryl to obtain a volume resistance. Those with adjusted rates can be used. The other configuration in FIG. 4 is the same as that of the embodiment shown in FIG. 2, so the same reference numerals are given in the drawing and the description thereof will be omitted. Even in this case, if the resistance values of the bias roll 10 and the backup roll 4 are measured as described above, and the transfer voltage applied to the bias roll is controlled based on the measurement result, a stable transfer electric field can be obtained. Can be obtained.

[0032]

As described above, according to the toner image transfer apparatus and the transfer voltage control method using the same according to the present invention, the bias roll and the backup roll are affected by fluctuations in the use environment such as temperature and humidity and deterioration over time. Even if the resistance value fluctuates, it is possible to accurately grasp the fluctuation of these resistance values and apply the optimum transfer voltage to the bias roll, so that a stable transfer electric field is always formed. It is possible to prevent transfer failure of the toner image.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a color electrophotographic copying machine to which the present invention is applied.

FIG. 2 is a schematic diagram illustrating a toner image transfer device of a color electrophotographic copying machine according to an embodiment.

FIG. 3 is a flowchart showing a transfer voltage control program.

FIG. 4 is a schematic diagram illustrating a modified example of the toner image transfer device according to the embodiment.

FIG. 5 is a schematic view showing a conventional image forming apparatus.

FIG. 6 is a graph showing a change in an optimum transfer voltage according to a change in a resistance value of a bias roll and a backup roll.

[Explanation of symbols]

2 ... intermediate transfer member (image carrier), 3 ... recording medium, 4 ... backup roll, 10 ... bias roll, 30 ... earth roll

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01

Claims (2)

(57) [Claims] 1. A toner image transfer device for transferring a toner image held on a belt-shaped image carrier to a recording medium, the bias being configured to appropriately contact the image carrier and transfer the toner image to a recording medium. A roll, a backup roll supporting the image carrier from the back side at a position facing the bias roll, a ground member abutting on the bias roll separated from the image carrier, and a bias roll and the image carrier. Current detecting means for detecting a current flowing through the bias roll at each of contact and separation, calculating means for determining a voltage to be applied to the bias roll based on a detection value of the current detecting means, and calculating means And a voltage control means for applying a transfer voltage to the bias roll in accordance with the result of the calculation. 2. A transfer voltage control method using the toner image transfer device according to claim 1, wherein a voltage for measurement is applied to the bias roll while the bias roll is in contact with an image carrier. Detecting a current flowing through the bias roll, applying a voltage to the bias roll in a state where the bias roll is in contact with the ground member, and detecting a current flowing through the bias roll; Determining a transfer voltage used for transferring the toner image based on the two current values.