JPH11174869A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always form an image of high quality even in the case the resistance value of an intermediate transfer body is changed with a lapse of time and the fluctuation of the resistance value occurs due to the variation at the time of manufacturing the device by installing a voltage impressing means for respectively impressing primary and secondary transfer voltages suitable to the resistance value detected by a resistance detecting means on primary and secondary transfer means. SOLUTION: Current values detected by a current detection circuit 25 are read and stored by a main controller 24 in synchronism with the counted values of a counter, then, the values are averaged so as to obtain a mean current value, then, the resistance value of the intermediate transfer body 9 is calculated based on the mean current value and a prescribed voltage. And, the primary transfer voltage selected based on the calculated mean resistance value of the intermediate transfer body 9 is impressed on a bias roller 3 by a primary transfer high voltage power supply 16. And also, the selected secondary transfer voltage is impressed on a transfer roller 13 by a secondary transfer high voltage power supply 17, in the case of secondary-transferring the toner image on the intermediate transfer body onto a transfer paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image carrier on which a toner image is formed on the surface, an intermediate transfer body on which the toner image is primarily transferred, and a toner on the surface of the image carrier upon application of a primary transfer voltage. Primary transfer means for primary transferring the image to the surface of the intermediate transfer member, and secondary transfer means for applying a secondary transfer voltage and secondary transferring the toner image primarily transferred to the surface of the intermediate transfer member to a recording medium The present invention relates to an image forming apparatus provided.

[0002]

2. Description of the Related Art An image forming apparatus of the above-mentioned type configured as a copying machine, a printer, a facsimile or a multifunction machine having at least two functions of the above-described devices is capable of transferring a toner image formed on an image carrier surface to an intermediate transfer body surface. The toner image is secondarily transferred to a recording medium, so that a single-color toner image is formed on the surface of the intermediate transfer member, and the second transfer is performed on the recording medium to obtain a single-color image or to perform intermediate transfer. It is possible to form an image of two or more colors on a recording medium by superimposing and primary transferring a plurality of color toner images on the body surface and then performing secondary transfer of the toner images collectively on a recording medium.

[0003] The resistance value of the intermediate transfer member used in such an image forming apparatus varies with time, or varies slightly depending on the individual intermediate transfer member due to variations during manufacture. When a uniform primary transfer voltage and secondary transfer voltage are applied to the primary transfer means and the secondary transfer means, respectively, to such an intermediate transfer body, the recording is performed by the resistance value of the intermediate transfer body. The image quality of the toner image finally secondary-transferred to the medium may fluctuate, and the image quality may be degraded.

[0004]

SUMMARY OF THE INVENTION The present invention has been made based on the above-described novel recognition, and an object of the present invention is to change the resistance value of an intermediate transfer member over time, An object of the present invention is to provide an image forming apparatus of the type described at the beginning, which can always form a high-quality image even when it fluctuates due to variations in time.

[0005]

In order to achieve the above object, the present invention provides an image forming apparatus of the type described at the beginning, wherein a resistance detecting means for detecting a resistance value of the intermediate transfer member, An image forming apparatus comprising: voltage applying means for applying a primary transfer voltage and a secondary transfer voltage suitable for the resistance value detected by the above to the primary transfer means and the secondary transfer means, respectively. Item 1).

[0006] At this time, the resistance detecting means is configured to detect a current value flowing through the intermediate transfer member between the primary transfer device to which a predetermined voltage is applied in contact with the intermediate transfer member and a ground member in contact with the intermediate transfer member. And a calculating means for calculating a resistance value of the intermediate transfer member from a current value detected by the current detecting means, wherein the voltage applying means is suitable for a calculation result by the calculating means. It is advantageous to have a high voltage power supply for primary transfer and a high voltage power supply for secondary transfer for applying a primary transfer voltage and a secondary transfer voltage to the primary transfer means and the secondary transfer means, respectively.

Further, in the image forming apparatus according to the first or second aspect, it is advantageous that the resistance detecting means is configured to detect an average resistance value of the entire circumference of the intermediate transfer body. Item 3).

Further, in the image forming apparatus according to any one of claims 1 to 3, n is an integer of 2 or more,
When S is the length in the circumferential direction of the intermediate transfer member, the resistance detection unit detects an average resistance value of each intermediate transfer member portion for each S / n of the intermediate transfer member, and the voltage application unit includes:
When a toner image is primarily transferred to each intermediate transfer member, a primary transfer voltage suitable for the average resistance value of each intermediate transfer member is applied to the primary transfer means, and a primary transfer voltage is applied to each intermediate transfer member. When each of the transferred toner images is secondarily transferred to each recording medium, a secondary transfer voltage suitable for the average resistance value of each intermediate transfer member is applied to the secondary transfer means. Is advantageous (claim 4).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic explanatory view showing an example of an image forming apparatus according to the present invention.
It is configured to be able to form a single-color image, an image of two or more colors, and a full-color image. Here, the configuration of the image forming apparatus of the present embodiment will be clarified while first explaining the operation when forming a full-color image.

In FIG. 1, a latent image carrier constituted as a drum-shaped photosensitive member 1 is rotatably supported on a machine frame (not shown) of an image forming apparatus main body, and the photosensitive member 1 performs an image forming operation. Sometimes it is driven to rotate counterclockwise. At this time, the surface of the photoreceptor is uniformly charged by the charging device 2 to a predetermined polarity, in the example of FIG. The charged surface is irradiated with light-modulated laser light L emitted from an exposure device including the writing optical unit 14, thereby forming a first electrostatic latent image on the photoconductor. in this way,
The charging device 2 and the exposure device constitute a latent image forming means for forming an electrostatic latent image on the surface of the image carrier made of the photoreceptor 1.

When the electrostatic latent image passes through the developing device 4,
The black toner image is visualized as a black toner image by the negative polarity black toner carried on the developing roller 19BK of the black developing device 4BK. At this time, a negative bias voltage is applied to the developing roller 19BK. The developing device 4 shown here is configured as a rotary developing device, and has a cyan developing device 4C, a magenta developing device 4M, and a yellow developing device 4Y in addition to the black developing device 4BK. Each developing unit is a photoconductor 1
And the developing device performs the above-described developing operation.

On the other hand, a bias roller 3, an earth roller 8, which will be described later, and other rollers 5, 6, 7 including a driving roller.
An intermediate transfer member 9 composed of a flexible endless belt wound around the photosensitive member is opposed to the surface of the photoreceptor, and the intermediate transfer member 9 is rotated between the bias roller 3 and the ground roller 8 while being rotated in the direction of the arrow. Abuts on the surface of the photoreceptor 1, and at the contact portion, moves at the same linear velocity as the linear velocity of the photoreceptor surface in the same direction as the direction of movement of the photoreceptor surface. The intermediate transfer member 9 is made of a medium resistor.

A high-voltage power supply 16 shown in FIG. 2 applies to the bias roller 3 a DC voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor surface, that is, a positive polarity in the illustrated example. I have. For this reason, when the above-described black toner image formed on the photosensitive member reaches the contact portion between the photosensitive member 1 and the intermediate transfer member 9, the black toner image on the photosensitive member 1 is stuck on the surface of the intermediate transfer member 9. It is transferred electrically.

Here, the voltage applied to the bias roller 3 as described above is referred to as a primary transfer voltage, and the transfer of the toner image on the photoreceptor 1 to the intermediate transfer member 9 by the action thereof is referred to as a primary transfer. At the same time, the power supply 16 shown in FIG. 2 is referred to as a high voltage power supply for primary transfer.

After the primary transfer of the toner image as described above, the transfer residual toner adheres to the surface of the photosensitive member.
When the toner passes through the cleaning device 10 shown in FIG. 1, the cleaning member 11 removes the toner from the surface of the photoreceptor.
2 irradiates light to lower its surface potential to a reference value.

Next, exactly as described above,
A second electrostatic latent image is formed on the photoreceptor, and the latent image is formed by the cyan toner carried on the developing roller 19C of the cyan latent imager 4C facing the photoreceptor 1 by the rotation of the developing device 4. It is visualized as an image. This toner image is also primarily transferred onto the surface of the intermediate transfer member 9 in a superimposed state from the top of the previously transferred black toner image by the action of the primary transfer voltage applied to the bias roller 3. The surface of the photoreceptor after the transfer of the toner image is
The cleaning operation is performed by zero, and the static elimination lamp 12 receives the static elimination action, which is no different from the previous operation.

Further, just as described above, the third and fourth electrostatic latent images sequentially formed on the photoreceptor 1 are:
Magenta developing device 4M and yellow developing device 4Y of developing device 4
Are sequentially visualized as a magenta toner image and a yellow toner image by the magenta toner and the yellow toner carried by each of the developing rollers 19M and 19Y.
The toner image is sequentially primary-transferred onto the surface of the intermediate transfer member in a state of being superimposed on the previously transferred toner image. In this manner, four color toner images are formed on the surface of the intermediate transfer member in a superimposed state.

As described above, in order to visualize the electrostatic latent image formed on the image carrier composed of the photosensitive member 1 as a toner image, the developing device 4 contains a plurality of developers containing different colors of developer. The intermediate transfer member 9 has a developing device, and primary transfer is performed by superimposing toner images of different colors formed on the surface of the image carrier.

On the other hand, the roller 6 around which the intermediate transfer member 9 is wound
The transfer roller 13 is disposed opposite to the intermediate transfer member 9 so that the toner image primarily transferred to the intermediate transfer member 9 is not disturbed. Away from the surface.

On the other hand, a transfer paper P, which is an example of a recording medium, is fed from a paper feeder (not shown).
Are transferred to the transfer roller 1 at a timing matching with the toner image on the intermediate transfer member 9 by the rotation of the registration roller pair 15.
It is fed between the roller 3 and the roller 6 facing the roller 3 as shown by an arrow A. When or immediately before the leading end of the transfer paper P reaches between the transfer roller 13 and the opposing roller 6, the transfer roller 13 occupies the position shown by the solid line in FIG. 1 and the transfer roller 13 is wound around the roller 6. It comes into contact with the intermediate transfer member 9. At this time, the leading end of the superimposed toner image on the intermediate transfer member 9 reaches the transfer roller 13 and the transfer roller 1
3, a high-voltage power supply 17 shown in FIG. 2 applies a DC voltage having a polarity opposite to the charging polarity of the toner on the intermediate transfer member 9, that is, a positive polarity in the example of FIG. The combined toner images are collectively transferred onto the transfer paper P. The transfer at this time is called a secondary transfer, and the voltage applied to the transfer roller 13 at this time is called a secondary transfer voltage, and the high voltage power supply 17 shown in FIG. 2 is called a high voltage power supply for secondary transfer. I will.

The transfer paper P on which the toner image has been transferred is carried and carried on a conveyor belt 18, and when passing through a fixing device 20, the toner image on the transfer paper P is transferred to the transfer paper P by the action of heat and pressure. Settled on the surface. Next, the transfer paper P is discharged out of the apparatus as a final copy paper.

After transfer of the toner image onto the transfer paper P, the transfer residual toner adhering to the surface of the intermediate transfer member is removed from the surface of the intermediate transfer member by the cleaning member 22 of the cleaning device 21. The cleaning member 22 is separated from the surface of the intermediate transfer body 9 when the toner image on the intermediate transfer body 9 before being transferred passes through the cleaning member 22. When the transfer of the toner image onto the transfer paper P is completed, the transfer roller 13 retreats to the position shown by the chain line in FIG. 1 and prepares for the next secondary transfer operation.

The above is the multi-color image forming mode for obtaining a full-color image of four colors. However, in the case of the multi-color image forming mode for obtaining a three-color superposed toner image or a two-color superposed toner image, the designated The above-described operation is performed for the selected color and the number of colors.

In the case of the single-color image forming mode, a toner image is formed on the photoreceptor only by the developing device of the designated color.
The toner image is primarily transferred to the intermediate transfer member 9 and secondarily transferred to transfer paper. At this time, the cleaning device 21
Cleaning member 22 may be kept in contact with the surface of the intermediate transfer member.

As described above, the image forming apparatus of the present embodiment has an image carrier formed as the photoreceptor 1 on the surface of which a toner image is formed, and an intermediate transfer member 9 on which the toner image is primarily transferred.
A primary transfer means configured as a bias roller 3 to which a primary transfer voltage is applied to primarily transfer the toner image on the surface of the image carrier to the surface of the intermediate transfer member, and a secondary transfer voltage is applied to the surface of the intermediate transfer member. Roller 13 for secondary-transferring the toner image primary-transferred onto a recording medium made of transfer paper P
And a secondary transfer unit configured as:

By the way, with this type of image forming apparatus, toner images of two or more colors are sequentially formed on the surface of the photosensitive member 1 as described above, and the toner images are sequentially superimposed on the surface of the intermediate transfer member 9. In the case of primary transfer, it is necessary to correctly superpose each toner image on the surface of the intermediate transfer member. Therefore,
The timing at which a toner image starts to be formed on the photoconductor 1 and the rotation timing of the intermediate transfer member 9 must be matched. Therefore, in the illustrated image forming apparatus, FIG.
A reference position mark M is formed on the surface of the intermediate transfer member 9 as shown in FIG. 3, and a mark detecting means comprising a mark sensor 23 for detecting the mark M as shown in FIGS. Is provided. The detection of the reference position mark M is performed in the above-described multi-color image forming mode, and is not performed in the single-color image forming mode. FIG. 4 shows an example of the sequence at this time.

In FIG. 4, a cycle of an image forming operation in this image forming apparatus is started by a start signal. When a document image is read by an image reading unit not shown in FIG. 1 and the document image is copied, a start signal is generated by pressing a start button of an operation unit (not shown). When an image is formed based on image information from an external device such as a personal computer, a word processor or a facsimile, a print request from these external devices becomes a start signal.

When a start signal is received, it is determined by a command whether data to be transferred to the writing optical unit 14 is one color or two or more colors (S1 in FIG. 4). In the case of one color, since there is no need to detect the reference position mark M, transfer of image data is started from the above-described image reading unit or the external device. In accordance with the data, the writing optical unit 14 irradiates the laser beam L onto the photoreceptor 1 as described above, thereby forming an electrostatic latent image, which is visualized by toner of a predetermined color. I do. That is, the process of writing to the photoconductor 1 is executed (S2 in FIG. 4). This toner image is primarily transferred onto the intermediate transfer body 9, and a transfer sheet P is fed from the pair of registration rollers 15 in accordance with the leading end of the transferred toner image (S <b> 3 in FIG. 4). The toner image is secondarily transferred onto the paper P, and this transfer paper passes through a fixing device and is discharged outside the apparatus.

The toner image transferred onto the intermediate transfer member 9 is 2
When the number of colors is equal to or more than the respective colors, each toner image must be secondarily transferred without being shifted onto the intermediate transfer member 9. Therefore, before the writing process on the photosensitive member 1 is started, the mark position is determined by the mark sensor 23. The mark M is detected (FIG. 4S
4), a write process is executed based on this detection signal (S5 in FIG. 4). That is, when the two color toner images are to be transferred onto the intermediate transfer member 9 in a superimposed manner, the intermediate transfer member 9
Is rotated twice, and at the first rotation, the reference position mark M
Is detected by the mark sensor 23, transfer of image data from the image reading unit or the external device is started based on this. Thereby, the laser beam is irradiated on the photoconductor 1 by the writing optical unit 14 as described above,
The electrostatic latent image thus formed is visualized by the developing device 4 as a toner image of a predetermined color. Also, during the second rotation of the intermediate transfer body 9, the mark sensor 23
, The reference position mark M is detected, and a writing process is executed in the same manner as described above with reference to the reference position mark M, and a toner image of another color is formed on the photoreceptor 1, and this is primarily transferred onto the intermediate transfer body 9. Is done. At this time, as described above, the toner images of the respective colors are sequentially formed on the photoreceptor 1 based on the detection of the reference position mark M, so that the toner images of the respective colors are superimposed on the intermediate transfer member 9 without displacement. The primary transfer is performed.

Similarly, when the toner image primarily transferred to the intermediate transfer member 9 is three or four colors, the intermediate transfer member 9 is rotated three or four times, and the reference position mark M is detected by the mark sensor at each rotation. As described above, the writing process is executed by using this as a reference, so that a multicolor toner image without color shift is primarily transferred onto the intermediate transfer body 9.

When the toner images of all colors are primary-transferred to the intermediate transfer member 9, feeding of the transfer paper P is started in accordance with the leading end of the toner image (S6 and S7 in FIG. 4). As described above, the color toner images are collectively secondary-transferred.

As described above, the illustrated image forming apparatus includes:
When the toner images of different colors are primarily transferred to the intermediate transfer member 9, the timing at which the toner images of the respective colors are started to be formed on the image carrier made of the photoreceptor 1 so that the respective toner images do not shift. A reference position mark M for control is formed on the intermediate transfer body 9 and a mark detecting means configured as a mark sensor 23 for detecting the mark is provided. An image forming start signal generating means for starting to form an electrostatic latent image is provided. In the illustrated example, the main controller 24 shown in FIG.
Constitutes an image formation start signal generating means.

In the example described above, one sheet of toner image is formed on the intermediate transfer member 9, and a plurality of toner images are successively formed on the surface of the intermediate transfer member 9 in the circumferential direction. It can also be configured to do so. In this case, the length of the intermediate transfer member 9 in the circumferential direction is set to at least twice the length of the maximum size toner image, whereby a plurality of toner images are continuously formed on the intermediate transfer member 9. Then, the respective toner images are secondarily transferred to separate transfer papers. Or, the intermediate transfer member 9
Is set to be at least twice the length of a reference size toner image (for example, A4 horizontal size), and the transfer paper size detection device (not shown) detects the size of the transfer paper. Thus, it is determined whether or not a plurality of toner images can be formed continuously in the circumferential direction of the intermediate transfer member 9. If this is possible, two or more toner images can be continuously formed in the circumferential direction on the intermediate transfer member 9. The toner images are secondarily transferred to separate transfer papers. With this configuration, the image forming speed can be increased.

By the way, as described above, the resistance value of the above-mentioned intermediate transfer member 9 changes with time, and may slightly vary from one intermediate transfer member to another due to variations in the manufacturing process. Therefore, when the toner image on the photosensitive member 1 is primarily transferred to the intermediate transfer member 9 or the toner image is secondarily transferred to the transfer paper P, the transfer voltage of the constant value is always applied to the bias roller 3 and the transfer roller 13 respectively. Is applied, the image quality of the image formed on the transfer paper P may be deteriorated.

Further, the reference position mark M is provided on the intermediate transfer member 9 as described above, and this is detected.
When the primary transfer of the toner image is started from the above-mentioned fixed image formation start position, the resistance values of the intermediate transfer body 9 on the upstream and downstream sides of the start position change. Further, when a plurality of toner images are sequentially formed on the intermediate transfer member 9 sequentially, an intermediate transfer member portion on which odd-numbered toner images are formed and an intermediate transfer member on which even-numbered toner images are formed. There is a possibility that a difference occurs in the resistance value of the body part. In such a case, if a constant transfer voltage is always applied to each of the bias roller 3 and the transfer roller 13, the image on the completed transfer paper may have uneven density and different colors, and the image quality may be degraded. There is.

Therefore, in the image forming apparatus of this embodiment,
Before the primary transfer of the toner image on the photoreceptor 1 to the intermediate transfer member 9, the resistance value of the intermediate transfer member 9 is detected by the resistance detecting means, and the primary transfer suitable for the detected resistance value is detected by the voltage applying means. A voltage and a secondary transfer voltage are applied to the bias roller 3 and the transfer roller 13, respectively, to transfer the toner images, so that high transfer efficiency can be obtained regardless of the resistance value of the intermediate transfer body 9 and transfer. The image quality of the applied toner image is enhanced.

Specific examples of the resistance detecting means and the voltage applying means are as follows.

As shown in FIGS. 1 and 2, the intermediate transfer member 9
On the rear surface of the intermediate transfer member 9, an earth member composed of the above-described earth roller 8 and the bias roller 3 are arranged at a predetermined interval in the moving direction of the intermediate transfer member 9. In contact. Before the reference position mark M is detected by the mark sensor 23 in order to detect the timing of forming an electrostatic latent image on the photoreceptor 1 as described above, the photoreceptor 1 and the intermediate transfer member 9 are moved in the direction of the arrow in FIG. The main control unit 24 shown in FIG. 2 controls the primary transfer high-voltage power supply 16 based on the time when the mark sensor 23 detects the reference position mark M, A voltage V is applied to the bias roller 3. For example, at the same time when the reference position mark M is detected by the mark sensor 23, the application of the predetermined voltage V to the bias roller 3 starts. Then, a current flows from the bias roller 3 to the earth roller 8 through the intermediate transfer member 9, and the current value I of the current is detected by the current detection circuit 25 shown in FIGS.
Detected by the current detecting means. At this time,
The transfer roller 13 is kept away from the intermediate transfer body 9. The current detection circuit 25 is interposed between the ground roller 8 and the main controller 24.

On the other hand, the counter of the main control unit 24 starts counting at the same time as the start of application of the predetermined voltage V to the bias roller 3, and counts the count value N that the intermediate transfer member 9 makes one rotation from the start. At this time, the counter is initialized and the application of the voltage V to the bias roller 3 is stopped. In this way, while the intermediate transfer body 9 rotates by one rotation, the main control device 24 reads, stores and stores the current value detected by the current detection circuit 25 in synchronization with the count value of the counter. This is averaged to obtain an average current value I, and a resistance value of the intermediate transfer body 9 is calculated from the average current value I and the predetermined voltage V (R = V / I). Then, based on the calculated average resistance value R of the intermediate transfer body 9, optimal primary and secondary transfer voltages corresponding to the resistance values, that is, voltage values at which the image quality of the transferred toner image is the best, are set in the control table. Choose from In this way, when the toner image on the photoconductor 1 is primarily transferred to the intermediate transfer member 9, the selected primary transfer voltage is applied to the bias roller 3 by the high voltage power supply 16 for primary transfer, and the primary transfer voltage is applied to the intermediate transfer member 9. When the toner image is secondarily transferred onto the transfer paper P, the selected secondary transfer voltage is applied to the transfer roller 13 by the secondary transfer high-voltage power supply 17.

As described above, even when the resistance value of the intermediate transfer member 9 changes with time or the resistance value of each intermediate transfer member 9 is different due to a variation in manufacturing, the optimum conditions are maintained. The primary transfer of the toner image on the photoreceptor 1 onto the intermediate transfer member 9 and the secondary transfer of the toner image on the transfer paper P can always provide a high quality image.

The above-described detection of the resistance value of the intermediate transfer member may be performed every time image formation is started. However, after the image formation is performed several times, the resistance value of the intermediate transfer member is detected. ,
Corresponding primary and secondary transfer voltages may be applied to the bias roller 3 and the transfer roller 13, respectively.

As described above, the image forming apparatus of this embodiment includes a resistance detecting means for detecting the resistance value of the intermediate transfer member 9, a primary transfer voltage suitable for the resistance value detected by the resistance detecting means, and a secondary transfer voltage. It has a bias roller 3 that is an example of a primary transfer unit and a voltage application unit that applies a transfer voltage to a transfer roller 13 that is an example of a secondary transfer unit.

Moreover, in the image forming apparatus of this embodiment,
The above-described resistance detecting means includes a primary transfer means including a bias roller 3 to which a predetermined voltage V is applied in contact with the intermediate transfer member 9 and a ground roller 8 which is an example of a ground member contacting the intermediate transfer member 9. Current detection means configured as a current detection circuit 25 for detecting a current value flowing in the intermediate transfer member between the two, and a calculation means for calculating the resistance value of the intermediate transfer member 9 from the current value detected by the current detection means. With
The voltage applying means converts the primary transfer voltage and the secondary transfer voltage suitable for the calculation result by the calculation means to the bias roller 3.
And a high-voltage power supply for primary transfer 16 and a high-voltage power supply 17 for secondary transfer to be applied to the primary transfer means and the secondary transfer means, respectively. In the illustrated example, the main control device 24 constitutes the above-described calculation means.
In this manner, the resistance detecting means and the voltage applying means can be easily constituted.

Further, the resistance detecting means of this embodiment is configured to detect the average resistance value of the entire circumference of the intermediate transfer member 9, whereby the resistance value of the intermediate transfer member 9 can be correctly grasped, and an appropriate value can be obtained. By applying the primary transfer voltage and the secondary transfer voltage to the bias roller 3 and the transfer roller 13, respectively, a high quality image can be obtained.

As described above, when a plurality of toner images are continuously formed on the intermediate transfer member 9 in the circumferential direction, each toner image is primarily transferred to each portion of the intermediate transfer member. When the toner image is primarily transferred from the photoreceptor 1 to the intermediate transfer member portion by detecting the resistance values thereof,
When a primary transfer voltage suitable for the resistance value of the intermediate transfer member is applied to the bias roller 3 and each toner image transferred to each intermediate transfer member is secondarily transferred to the transfer sheet P, It is preferable to apply a secondary transfer voltage suitable for the resistance value of the intermediate transfer member to the transfer roller 13.

For example, when two toner images are formed on the surface of the intermediate transfer body 9 along the circumferential direction thereof, a predetermined position of the reference position mark M is detected by the bias roller 3 with reference to the time when the mark sensor 23 detects the reference position mark M. , And from this point on, the first intermediate transfer member portion detected by the current detection circuit 25 until the count value of the counter reaches half the circumference of the intermediate transfer member 9, that is, N / 2. determining a first average value I ₁ of the current flowing. Similarly, the average value I ₂ second current value flowing through the second intermediate transfer member portion the count value detected by the current detection circuit 25 from N / 2 to a N. Then, the respective average values I ₁ , I
The respective average resistance values of the first and second intermediate transfer members are calculated from the values of ₂ and the voltage V, and the optimum primary and secondary transfer voltage values for these are selected from the control table.
When the toner image is primarily transferred from the photoconductor 1 to the first intermediate transfer member, the selected primary transfer voltage is applied to the bias roller 3 by the primary transfer high-voltage power supply 16. Similarly, when the toner image is primarily transferred from the photoconductor 1 to the second intermediate transfer member, a primary transfer voltage suitable for the resistance value of the intermediate transfer member is applied to the bias roller 3 by the primary transfer high-voltage power supply 16. I do. Similarly, when the respective toner images primary-transferred to the first and second intermediate transfer member portions are secondarily transferred to the transfer paper P, the secondary transfer voltage optimal for the resistance value of each intermediate transfer member portion is also obtained. Is applied to the transfer roller 13. The same applies to the case where three or more toner images are successively formed successively at predetermined intervals in the circumferential direction of the intermediate transfer member.

Generally, n is an integer of 2 or more,
When S is the length of the intermediate transfer member 9 in the circumferential direction, the above-described resistance detecting means detects the average resistance value of each intermediate transfer member portion for each S / n of the intermediate transfer member 9 and applies the above-described voltage application. The bias roller 3 is an example of a primary transfer unit when a toner image is primarily transferred to each intermediate transfer member.
A primary transfer voltage suitable for the average resistance value of each intermediate transfer member is applied, and each toner image primarily transferred to each intermediate transfer member is secondarily transferred to each recording medium made of transfer paper P. Then, a secondary transfer voltage suitable for the average resistance value of each intermediate transfer member is applied to a transfer roller 13 which is an example of a secondary transfer unit.

With this configuration, when a plurality of toner images are sequentially formed on the intermediate transfer member 9 at predetermined intervals in the circumferential direction, and when these are secondarily transferred to separate transfer papers P, the odd-numbered toner It is possible to prevent a problem that the image quality of the image differs from that of the even-numbered toner image.

The present invention can be applied to various image forming apparatuses other than the illustrated type, and is widely applied to, for example, an image forming apparatus using an image carrier formed of a belt and an image forming apparatus using an intermediate transfer body formed of a drum. Applicable.

[0051]

According to the image forming apparatus of the present invention, even when the resistance value of the intermediate transfer member changes with time or differs for each intermediate transfer member or for each image forming device, High quality images can be obtained.

According to the image forming apparatus of the second aspect,
The resistance detecting means and the voltage applying means can be configured at low cost and easily.

According to the image forming apparatus of the third aspect,
The resistance value of the intermediate transfer member can be correctly detected.

According to the image forming apparatus of the fourth aspect,
Even when a plurality of toner images are sequentially formed on the surface of the intermediate transfer member in the circumferential direction, the primary transfer voltage and the secondary transfer voltage corresponding to the resistance value of the intermediate transfer member on which each toner image is formed are respectively primary-transferred. And high-quality images can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram illustrating an example of an image forming apparatus.

FIG. 2 is a block diagram of the image forming apparatus shown in FIG.

FIG. 3 is a perspective view showing a reference position mark formed on an intermediate transfer member and a mark sensor for detecting the reference position mark.

FIG. 4 is a flowchart illustrating a basic operation of the image forming apparatus illustrated in FIG. 1;

FIG. 5 is a diagram illustrating an example of a current detection circuit.

[Explanation of symbols]

 9 Intermediate transfer member 16 High voltage power supply for primary transfer 17 High voltage power supply for secondary transfer

Claims (4)

[Claims] 1. An image carrier on which a toner image is formed, an intermediate transfer member on which the toner image is primarily transferred, and a toner image on the surface of the image carrier, which is applied with a primary transfer voltage, is transferred to the surface of the intermediate transfer member. An image forming apparatus comprising: a primary transfer unit for performing primary transfer to a secondary transfer voltage; and a secondary transfer unit for applying a secondary transfer voltage to secondary transfer a toner image primarily transferred on the surface of the intermediate transfer body to a recording medium. A resistance detecting means for detecting a resistance value of the intermediate transfer body; and applying a primary transfer voltage and a secondary transfer voltage suitable for the resistance value detected by the resistance detecting means to the primary transfer means and the secondary transfer means, respectively. An image forming apparatus comprising: 2. The method according to claim 1, wherein the resistance detecting unit detects a current value flowing through an intermediate transfer member between the primary transfer unit to which a predetermined voltage is applied in contact with the intermediate transfer member and a ground member in contact with the intermediate transfer member. Current detecting means for detecting, and a calculating means for calculating a resistance value of the intermediate transfer member from a current value detected by the current detecting means, wherein the voltage applying means is a primary means suitable for a calculation result by the calculating means. 2. The image forming apparatus according to claim 1, further comprising a high voltage power supply for primary transfer and a high voltage power supply for secondary transfer for applying a transfer voltage and a secondary transfer voltage to the primary transfer unit and the secondary transfer unit, respectively. 3. The image forming apparatus according to claim 1, wherein the resistance detection unit detects an average resistance value of the entire circumference of the intermediate transfer body. 4. When n is an integer of 2 or more and S is the length of the intermediate transfer member in the circumferential direction, the resistance detecting means determines the average resistance of each intermediate transfer member portion of each S / n of the intermediate transfer member. The voltage application means detects the primary transfer voltage suitable for the average resistance value of each intermediate transfer member when the toner image is primarily transferred to each intermediate transfer member. When each toner image primarily transferred to each intermediate transfer member portion is secondarily transferred to each recording medium, a secondary transfer voltage suitable for the average resistance value of each intermediate transfer member portion is applied. The image forming apparatus according to claim 1, wherein the image is applied to a next transfer unit.