JP3449122B2 - Image forming device - 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 a copying machine, a facsimile, a printer, etc., and more specifically, a visible image formed on an image carrier is primarily transferred onto an intermediate transfer body,
The present invention relates to an intermediate transfer type image forming apparatus that secondarily transfers a primary transfer image on the intermediate transfer body to a transfer material.

[0002]

2. Description of the Related Art In recent years, an electrophotographic image forming apparatus capable of copying and printing a full color image has been put into practical use. As a method of transferring a full color image to a transfer material in this type of image forming apparatus, (A) Transfer drum system: Each image of yellow (Y), magenta (M), cyan (C), and black (BK) formed for each color on an image bearing member such as a photosensitive drum is transferred onto a transfer drum. (B) Intermediate transfer method: Y, M, C, and BK images formed on the image carrier such as a photoconductor drum for each color are sequentially superimposed and transferred to a transfer material fixed to It can be roughly classified into a system in which the images are sequentially superposed and transferred onto the intermediate transfer member in the primary transfer region, and the full-color toner image on the intermediate transfer member is collectively transferred onto the transfer material in the secondary transfer region. Of these, since it has a paper-free property that it can be transferred to thick paper and the like, and it is possible to copy the entire surface without being unable to form an image on the clamp / holding part at the tip unlike the transfer drum system, the above (b) The intermediate transfer method of is advantageous.

[0003]

[Problems to be Solved by the Invention]

[Problem 1] For example, in the above-mentioned intermediate transfer method (b), when an intermediate transfer belt is used as an intermediate transfer member, an abnormal image called "half-tone white blank" may occur. This phenomenon is likely to occur when an image of a halftone portion such as an orange chart is copied, and it periodically occurs in the advancing direction of the image as density unevenness that becomes white in a horizontal band. The generation place is not on the photoconductor drum but on the intermediate transfer belt after the transfer. The main cause is
There is uneven resistance within the circumference of the intermediate transfer belt. That is,
In belt transfer, transfer is performed by the transfer electric field generated in the transfer nip portion, and the transfer electric field is determined by the potential difference between the transfer bias in the transfer nip portion and the photoconductor potential. For this reason, if there is uneven resistance in the intermediate transfer belt, transfer is performed with a normal transfer electric field at a high resistance value, but the transfer electric field becomes excessive at a low resistance value. The toner is reversely transferred to the photosensitive drum. The area corresponding to the location where the toner has fallen out is an image with a blank white band in the halftone portion. It was found that this phenomenon occurs more remarkably when the photoconductor potential Vd related to the transfer electric field becomes higher.

[Problem 2] Moreover, in a low humidity environment,
Abnormal images called "stickiness" and "crown nail marks" are more likely to occur during paper transfer. Solid toner means the toner on the solid portion is scattered on the non-toner surface. This is a state in which streaky toner with a high toner density is mixed in, and it looks just like a bird's footprint.These phenomena cause the resistance value of the transfer paper to increase in a low humidity environment, and It is caused by the difference between the charge on the surface and the charge on the back side.
In a low-humidity environment, the charge amount on the back surface side is larger than the charge amount on the toner surface side of the transfer paper that has passed through the paper transfer nip portion.Therefore, the toner on the transfer paper is not transferred along the electric field generated by this difference. It is caused by the phenomenon that the toner particles fly to the toner surface and the electric field thereof causes discharge.

The present invention has been made in view of the above problems, and a first object of the present invention is to provide an image forming apparatus capable of reducing the white band loss in the halftone portion.

[0006] The second object is to reduce the scratches on the halftone white belt, stickiness and crows that occur in a low humidity environment.

[0007]

In order to achieve the above-mentioned first object, the invention of claim 1 primary-transfers a visible image formed on an image bearing member to an intermediate transfer member, and transfers the intermediate transfer member. In an intermediate transfer type image forming apparatus that secondarily transfers a primary transfer image on a body to a transfer material, it is predetermined that no electric discharge will occur between the intermediate transfer body portion and the image carrier after the primary transfer. And a control means for controlling the transfer bias voltage based on the relationship between the potential of the image carrier and the transfer bias potential applied to the intermediate transfer member, and the potential information of the image carrier. To do.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a potential sensor for detecting the potential of the image carrier is provided, and the potential information is obtained from the potential sensor. Is.

In order to achieve the second object, the invention of claim 3 is the image forming apparatus of claim 1 or 2.
The transfer bias voltage applied to the intermediate transfer member is corrected according to environmental conditions.

According to a fourth aspect of the invention, in the image forming apparatus according to the first, second or third aspect, a switching means for switching between execution and non-execution of control by the control means of the first aspect is provided. .

According to the first aspect of the present invention, a predetermined potential of the image carrier and the intermediate transfer member are set so that no discharge occurs between the intermediate transfer member portion and the image carrier after the primary transfer. Relationship with the transfer bias potential applied to
Based on the potential information of the image carrier, the transfer bias voltage is controlled to a voltage at which discharge does not occur between the intermediate transfer member portion after the primary transfer and the image carrier. That is, when the present inventors examined the relationship between the image carrier potential and the transfer bias voltage applied to the intermediate transfer member,
It was revealed that the discharge did not occur when the transfer bias voltage was within a specific range with respect to the potential of the image carrier, and the discharge occurred outside the range. Therefore, the discharge can be suppressed by setting the transfer bias voltage so that the transfer bias voltage falls within the specific range.

According to the second aspect of the invention, the potential information is obtained from a potential sensor that detects the potential of the image carrier.
Therefore, accurate potential information can be obtained.

In the third aspect of the invention, the transfer bias voltage is corrected according to the environmental conditions. Specifically, in a low-humidity environment where sticky marks and crows' nail marks are likely to occur, the upper limit of the transfer bias voltage is increased to reduce the difference in charge amount between the visible image side and the back surface side of the transfer material. Reduce. This suppresses the discharge caused by the difference in charge amount between the visible image side and the back surface side of the transfer material. If the transfer bias potential is set too high in such a low humidity environment,
After the primary transfer, discharge easily occurs between the intermediate transfer member and the image carrier. Therefore, the correction of the transfer bias voltage is performed only within the range where the discharge does not occur.

In the invention of claim 4, the switching means can switch the control execution / non-execution by the control means of claim 1.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. The present invention relates to an image forming apparatus having a carrier that carries toner, transfer paper, or toner and transfer paper, and conveys the unsupported material to the next step. Specifically, the carrier bears a toner image visualized in a developing process, and is rotatably driven to the next process such as a transfer process to convey the toner image,
An intermediate transfer member that carries the toner image transferred from the image carrier and conveys the toner image by being rotationally driven until the step of transferring it to a transfer target such as transfer paper, or transfer carrying the transfer paper or the toner image. It is a conveyor belt that carries the carrier by carrying the paper etc. and rotating it until the next process such as the transfer process or fixing process. It is common to other carriers that carry and carry the carrier electrostatically. Is the technical idea of.

FIG. 1 is a schematic configuration diagram of a copying machine 100 according to the present embodiment, and FIG. 2 is an enlarged view around a photosensitive drum and an intermediate belt. The configuration and operation of the copying machine 100 will be described below with reference to FIGS. 1 and 2. A color image reading apparatus (hereinafter, referred to as a color scanner) 1 forms an image of an original 3 on a color sensor 7 via an illumination lamp 4, mirror groups 5a to 5c, and a lens 6, and outputs color image information of the original. For example, each color separation light of blue (Blue, hereinafter B), green (Green, hereinafter G), red (Red, hereinafter R) is read and converted into an electrical image signal. In this example, the color sensor 7 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three colors. Then, based on the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk) and cyan. (Cyan,
Color image data of magenta (hereinafter, referred to as M) and yellow (hereinafter, referred to as Y) are obtained. This is a color image recording device (hereinafter,
2) Bk, C, M, Y
Is visualized as a final color copy. The operation method of the color scanner 1 for obtaining the Bk, C, M, and Y image data is as follows when the scanner start signal in timing with the operation of the color printer 2 is received.
At, the illumination / mirror optical system scans the document in the direction of the left arrow to obtain image data of one color for each scanning. Then, each time, the image is sequentially visualized by the color printer 2, and these are superposed to form a four-color full-color image.

Next, the outline of the color printer 2 will be described. The writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 9. The unit 8 includes a laser light source 8a, a light emission drive control unit (not shown), a polygon mirror 8b, a rotation motor 8c, an f / θ lens 8d, and a reflection mirror 8e.
Etc.

The photoconductor drum 9 rotates counterclockwise as shown by the arrow, and around the photoconductor drum 9, as shown in FIG. 2, a photoconductor cleaning unit (including a pre-cleaning charge eliminator) 10,
Charge eliminating lamp 11, charger 12, potential sensor 13, Bk developing device 14, C developing device 15, M developing device 16, Y developing device 1
7, an optical sensor 18 for detecting a development density pattern, an intermediate transfer belt 19 and the like are arranged.

Each developing device has a developing sleeve (14a, 15a, 16a, 17a) which rotates by bringing a brush of the developer into contact with the surface of the photosensitive drum 9 to develop the electrostatic latent image,
It is composed of a developing paddle (14b, 15b, 16b, 17b) that rotates to draw up and agitate the developer, and a toner concentration sensor (14c, 15c, 16c, 17c) of the developer. In the standby state, the agent on the developing sleeves is in the state of cutting off (development inoperative) state in all of the four developing devices. Next, an outline of the copying operation will be described by taking an example in which the developing operation order (color image forming order) is Bk, C, M, and Y (however, the image forming order is not limited to this).

When the copying operation is started, the color scanner 1 starts reading Bk image data at a predetermined timing, and optical writing by a laser beam and latent image formation start based on the image data (hereinafter, referred to as Bk image data). The electrostatic latent image by Bk is referred to as Bk latent image, and C, M, and Y are referred to as C latent image, M latent image, and Y latent image, respectively). This B
Before the latent image front end reaches the developing position of the Bk developing device 14 so that development can be performed from the front end of the k latent image, the developing sleeve 1
4a is started to rotate, the spike of the agent is set, and the Bk latent image is changed to Bk.
Develop with toner. After that, the developing operation of the Bk latent image area is continued, and when the trailing edge of the latent image passes the Bk developing position, the agent on the Bk developing sleeve 14a is quickly cut off to make the developing inoperative state. This is completed at least before the leading edge of the C latent image by the next C image data arrives. In addition, the cutting of the ears is performed by switching the rotation direction of the BK developing sleeve 14a to the opposite direction to that during the developing operation.

The Bk toner image formed on the photosensitive drum 9 is transferred to the surface of the intermediate transfer belt 19 which is driven at the same speed as the photosensitive drum 9 (hereinafter, the toner from the photosensitive drum to the intermediate transfer belt is transferred). Image transfer is called belt transfer).
The belt transfer is performed by applying a predetermined bias voltage to the transfer bias roller 20a while the photosensitive drum 9 and the intermediate transfer belt 19 are in contact with each other. In addition, on the intermediate transfer belt 19, Bk sequentially formed on the photosensitive drum 9,
C, M, Y toner images are sequentially aligned on the same plane,
A belt transfer image of four colors is formed, and then bulk transfer is performed on the transfer paper. This intermediate transfer belt unit will be described later.

On the side of the photoconductor drum 9, the process B is followed by the process C. However, the C image data reading by the color scanner 1 is started at a predetermined timing, and the laser light is written by the image data to form the C latent image. I do. The C developing device 15 starts rotating the C developing sleeve 15a after the trailing edge of the previous Bk latent image has passed to the developing position and before the leading edge of the C latent image reaches the developing position so that the agent ears Stand up and develop the C latent image with C toner. After that, the development of the C latent image area is continued, and when the trailing edge of the latent image passes,
As in the case of the k developing device, the developer on the C developing sleeve 15a is cut off to make the developing inoperative state. This is also completed before the leading edge of the next M latent image arrives. Note that the image data reading, latent image forming, and developing operations of the M and Y steps are the same as those of the above-described Bk and C steps, and therefore description thereof will be omitted.

Next, the intermediate transfer belt unit will be described. The intermediate transfer belt 19 is stretched around a drive roller 21, a transfer bias roller 20a, an earth roller 20b, and a group of driven rollers, and is drive-controlled by a drive motor (not shown). Belt cleaning unit 2
Reference numeral 2 includes a brush roller 22a, a rubber blade 22b, and a belt contact / separation mechanism 22c.
While the second, third, and fourth colors are transferred on the belt after the Bk image of the color is transferred on the belt, they are separated from the belt surface by the contact / separation mechanism 22c. Then, the intermediate transfer belt 1
The images of the four colors are accurately aligned on the sheet 9 and the images of the respective colors are transferred one after another to form a superimposed image of the four colors on the intermediate transfer belt 19.

The paper transfer unit 23 is composed of a paper transfer bias roller 23a, a roller cleaning blade 23b, and a belt contact / separation mechanism 23c. The bias roller 23a is normally separated from the surface of the belt 19, but when the superimposing images of four colors formed on the surface of the intermediate transfer belt 19 are collectively transferred to the transfer paper, the contact / separation mechanism 23c is timed. Is pressed, and a predetermined bias voltage is applied to the roller 23a to transfer it to the paper. As shown in FIG. 1, the transfer paper 24 is fed by the paper feed roller 25 and the registration roller 26 at the timing when the leading end of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position. To be done.

As a method of driving the intermediate transfer belt 19, the following three methods are conceivable as an operation method after the belt transfer of the Bk toner image of the first color is completed up to the end. One of these methods, or In terms of copy speed, the intermediate transfer belt 19 is driven by efficiently combining a plurality of methods according to the copy size.

(1) Constant speed forward movement method Even after the Bk toner image is transferred onto the belt, the forward movement is continued at a constant speed. Then, when the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position of the contact portion with the photosensitive drum 9 again, the front end portion of the next C toner image on the photosensitive drum 9 side is just that position. The image is formed so as to come to the position. As a result, the C image is accurately aligned with the Bk image and is transferred onto the intermediate transfer belt 19 in a superimposed manner. After that, the same operation is performed to proceed to the M and Y image process, and a belt transfer image of four colors is obtained. Following the belt transfer process for the 4th Y toner image,
While moving forward, the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is collectively transferred onto the transfer paper 24 as described above.

(2) Skip Forwarding Method After the belt transfer of the Bk toner image is completed, the intermediate transfer belt 19 is separated from the surface of the photosensitive drum 9, and the intermediate transfer belt 19 is skipped in the forward direction at a high speed to move a predetermined amount. Return to the forward speed. In addition, after that, the photoconductor drum 9 again
The intermediate transfer belt 19 is brought into contact with. When the front end position of the Bk image on the surface of the intermediate transfer belt 19 reaches the belt transfer position again, the photosensitive drum 9 side takes a timing so that the front end portion of the next C toner image comes to that position. Has been formed. As a result, the C image is accurately aligned with the Bk image and transferred onto the belt in a superimposed manner. After that, the same operation is performed to proceed to the M and Y image process, and a belt transfer image of four colors is obtained. Subsequent to the transfer process of the Y-color toner image belt for the fourth color, the four-color superimposed toner images on the surface of the intermediate transfer belt 19 are collectively transferred onto the transfer paper 24 at the same forward speed.

(3) Reciprocating (quick return) system After the belt transfer of the Bk toner image is completed, the intermediate transfer belt 19 is separated from the surface of the photosensitive drum 9, and
At the same time as stopping the forward movement, it makes a high speed return in the opposite direction. In this return, the front end position of the Bk image on the surface of the intermediate transfer belt 19 passes through the position corresponding to the belt transfer in the opposite direction, and after moving by a preset distance, it is stopped and put in a standby state. Next, when the front end portion of the C toner image on the photoconductor drum 9 side reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is restarted in the forward direction. Further, the intermediate transfer belt 19 is brought into contact with the surface of the photosensitive drum 9 again. Also in this case, the C image is transferred under the condition that it is accurately overlapped with the Bk image on the surface of the intermediate transfer belt 19. After that, the same operation is performed to proceed to the Y and M image processes, and a belt transfer image of four colors is obtained. Following the belt transfer process for the 4th Y toner image,
It does not return but moves forward at the same speed, and the four-color superposed toner images on the surface of the intermediate transfer belt 19 are collectively transferred onto the transfer paper 24.

The transfer paper 24 on which the four-color superposed toner images have been collectively transferred from the surface of the intermediate transfer belt 19 is conveyed to the fixing device 28 by the paper conveying unit 27 and is applied to the fixing roller 28a controlled to a predetermined temperature. The toner image is melted and fixed by the pressure roller 28b and carried out to the copy tray 29 to obtain a full color copy.

The photosensitive drum 9 after the belt transfer is
As shown in FIG. 2, the surface is cleaned by the photoconductor cleaning unit 10 (pre-cleaning static eliminator 10a, brush roller 10b, rubber blade 10c), and the static elimination lamp 11 uniformly neutralizes the surface. The surface of the intermediate transfer belt 19 after the toner image is transferred onto the transfer paper is cleaned by pressing the cleaning unit 22 again by the contact / separation mechanism 22c.

At the time of repeat copy, the color scanner 1
And the image formation on the photosensitive drum 9
(4th color) After the image process, 2 at a predetermined timing
Proceed to the Bk (first color) image step for the first sheet. Further, in the intermediate transfer belt 19, the second Bk toner image is formed in the area where the surface is cleaned by the cleaning unit 22, following the batch transfer process of the first four-color superimposed image onto the transfer paper. Allow the belt to be transferred. After that, the same operation as the first sheet is performed.

The paper feed cassettes 30, 31, 3 shown in FIG.
Transfer sheets 2 and 33 of various sizes are stored, and the registration rollers 2 are arranged at a timing from a cassette in which size sheets designated by an operation panel (not shown) are stored.
Paper is fed and conveyed in six directions. Reference numeral 34 is a manual paper feed tray for OHP paper or thick paper.

The above is the description of the copy mode for obtaining four full colors, but in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. It will be. In the case of the single-color copy mode, until the predetermined number of sheets are finished, only the developing device of that color is in a developing operation (agent standing) state, and the intermediate transfer belt 19 contacts the surface of the photosensitive drum 9. Then, the copying operation is performed in a state where the belt cleaner 22 is driven at a constant speed in the forward direction and the belt cleaner 22 is still in contact with the intermediate transfer belt 19.

[Embodiment 1] Next, an embodiment of the copying machine configured as described above will be described in which the occurrence of white banding in the halftone portion during belt transfer is reduced. FIG. 3 is a block diagram showing the configuration of the control system in the first embodiment, and shows the configuration around the photosensitive drum / intermediate belt. The control system of this embodiment includes a potential sensor 13 as a photoconductor potential detection unit, a belt transfer power source 35, and a belt transfer electric field control unit 36. The potential sensor 13 detects potential information (photoconductor potential) on the surface of the photoconductor drum 9 and outputs it to the belt transfer electric field control means 36. The belt transfer power supply 35 applies a predetermined transfer bias voltage to the transfer bias roller 20a. The belt transfer electric field control means 36 controls the belt transfer power source 35 as follows based on the photoconductor potential detected by the potential sensor 13.

FIG. 4 is a characteristic diagram showing the range in which an abnormal image occurs, with the photoconductor potential (Vd) on the vertical axis and the transfer nip portion potential (Vb) on the horizontal axis. In this characteristic diagram,
A shows an area in which half-tone white banding is generated, and B shows an area in which solid nails and crow's nail marks described later occur. Further, C (hatched area) indicates an area where no abnormal image occurs. Further, the transfer nip portion potential (Vb) is represented by numerical values (V / BIT) in two upper and lower stages. Of these, the upper part shows the effective potential (V) of the transfer bias in the transfer nip portion, and the lower part shows the set value (BIT) by the operation key. In the following description, in order to distinguish two numerical values, for example, "2000V / 2100BI
The transfer nip potential and the transfer bias voltage are both represented by (Vb).

The belt transfer electric field control means 36 controls such that the relationship between the photoconductor potential and the transfer nip portion potential is always within the area C in FIG. That is, the belt transfer electric field control means 36 sets the transfer bias voltage so that the transfer nip portion potential corresponds to the photosensitive drum potential detected by the potential sensor 13 in the area C in FIG. Then, the transfer bias voltage in the belt transfer power supply 35 is controlled.

According to the copying machine configured as described above,
The transfer bias voltage with respect to the photoconductor potential is controlled so as to fall within the area C in FIG. In this C region, it is possible to suppress a partial excess of the transfer electric field due to the uneven resistance of the intermediate transfer belt 19, so that it is possible to reduce the white band missing in the halftone portion caused by the uneven resistance of the intermediate transfer belt 19. .

[Embodiment 2] Next, in the configuration of Embodiment 1 described above, white band loss in the halftone portion is reduced, and nail marks of sticky dust and crows generated in a low humidity environment are also reduced. Will be described.

FIG. 5 is a block diagram showing the construction of the transfer nip portion and the construction of its control system in the second embodiment. The control system of this embodiment is provided with temperature / humidity detecting means 48 for detecting temperature / humidity as an environmental condition. The other structure is the same as that of FIG. 3, and the same portions are denoted by the same reference numerals. As described above, the resistance value of the transfer paper becomes high in a low humidity environment, so a difference occurs between the charge amount on the toner surface of the transfer paper and the charge amount on the back surface side, and sticky marks and crow's nail marks are transferred to the paper. Sometimes it is more likely to occur. Therefore, in this embodiment, the temperature / humidity detecting means 48 detects the temperature and the humidity and feeds it back to the belt transfer electric field control means 36, and the detected temperature / humidity data is detected by the belt transfer electric field control means 36 in the absolute humidity D (g / g / It is converted into m3) and the transfer bias voltage is corrected using this absolute humidity to apply an appropriate transfer bias voltage according to the environmental conditions.

Although the temperature / humidity detecting means 48 is installed in the vicinity of the paper feeding cassette, there is no heat source or air blowing mechanism nearby,
It may be installed in another place as long as the environmental conditions are relatively stable.

FIG. 6 is a characteristic diagram showing the relationship between the absolute humidity D of the environmental conditions and the upper limit value of the transfer bias. The vertical axis represents the transfer bias voltage Vb (kV) and the horizontal axis represents the absolute humidity D (g / m3. )
Is shown. The absolute temperature D is in three areas A (D <4.
3), B (4.3 <D <11.3), C (11.3 <D)
The upper limit of the transfer bias voltage is determined according to which region the absolute temperature D as an environmental condition falls into. Here, the absolute humidity D is 4.
When it is 3 or less, the transfer bias voltage Vb is controlled to 2000 V, when the absolute humidity D is in the range of 4.3 to 11.3, it is 1600 V, and when the absolute humidity D is 11.3 or more, it is controlled to 1200 V.

As described above, by controlling the upper limit of the transfer bias voltage to increase as the environmental conditions become lower, the difference in charge amount between the toner surface side and the back surface side of the transfer paper is reduced. Eliminates and reduces the scratches of sticky dust and crows caused by the difference in charge amount.

However, as described above, merely increasing the transfer bias voltage causes a problem that the occurrence of white band missing in the halftone portion becomes remarkable. Therefore, in this embodiment, a characteristic diagram (graph information) showing the relationship between the photoconductor potential (Vd) and the transfer bias voltage (Vb) is set for each of the regions, and the transfer bias voltage is set based on this graph information. The value of (Vb) is corrected.

Belt transfer electric field control means 3 of this embodiment
In FIG. 6, a characteristic diagram (graph information) showing the relationship between the photoconductor potential and the transfer bias voltage is set for each absolute humidity. The belt transfer electric field control means 36 corrects the transfer bias voltage with respect to the photoconductor potential based on the graph information corresponding to the absolute humidity converted from the temperature and humidity data. Here, the absolute humidity D of the environmental conditions is D <
At 4.3, the transfer bias voltage (Vb) with respect to the photoconductor potential (Vd) is: 1) When Vd ≦ 530, Vb = 2000 (V) /
2100 (BIT) 2) 530 <Vd <660, Vb = ((−) 5.3) × ‖Vd‖ + (4908) where (−) 5.3 and 4908 are coefficients for correction. 3) When 660 ≦ Vd, Vb = 1200 (V) /
It is controlled to be 1410 (BIT). Further, when the absolute humidity D of the environmental conditions is 4.3 <D <11.3, the transfer bias voltage (Vb) with respect to the photoconductor potential (Vd) is 1) When Vd ≦ 530, Vb = 1600 (V) /
1740 (BIT) 2) When 530 <Vd <660, Vb = ((−) 2.54) × ‖Vd‖ + (3086) However, (−) 2.54 and 3086 are coefficients for correction. 3) When 660 ≦ Vd, Vb = 1200 (V) /
It is controlled to be 1410 (BIT). Furthermore, when the absolute humidity D of the environmental conditions is 11.3 <D, the transfer bias voltage (Vb) is Vb = 1200 (V) / 1410 regardless of the value of the photoconductor potential (Vd).
(BIT) is controlled.

FIG. 7 is a characteristic diagram showing the relationship between the photoconductor potential (Vd) and the transfer bias voltage (Vb) in the region A of FIG. 6, and FIG. 8 is the photoconductor potential (V of the region B in FIG. 6).
d) and a transfer bias voltage (Vb). FIG. 9 is a characteristic diagram showing a relationship between the transfer bias voltage (Vb) and the transfer bias voltage (Vb).
It is a characteristic view which shows the relationship between d) and transfer bias voltage (Vb). As is clear from FIGS. 7 to 9, as the absolute humidity D of the environmental conditions decreases (C → A), the correction range of the transfer bias voltage (Vb) increases and the absolute humidity D increases (A → C). ), The correction width becomes smaller. In a low humidity environment, not only sticky scratches and crows' nail marks are likely to occur, but also white band missing in the halftone portion becomes prominent, so the transfer bias voltage (Vb) depends on the photoconductor potential (Vd). This is because the bias value is appropriately adjusted so that such an abnormal image does not occur.

When the temperature / humidity detecting means 48 fails to accurately detect the environmental conditions, an abnormal transfer bias voltage that does not match the actual environmental conditions may be set. In order to prevent this, the control for setting the upper limit value of the transfer bias according to the absolute humidity (see FIG. 6).
It is also possible to configure so as to select "control" or "not control". According to this
It is possible to prevent runaway of the system due to a failure of the temperature / humidity detecting means 38. Further, when used in a place where the environmental conditions do not change extremely, by not performing the above control, the processing load of the control system can be reduced.

According to the copying machine configured as described above,
Since the graph information showing the relationship between the photoconductor potential and the transfer bias voltage is set according to the environmental conditions and the value of the transfer bias voltage is corrected according to this graph information, halftone that occurs in a low humidity environment Not only can you reduce the white spots on the part, but you can also reduce the scratches of sticky spots and crows.

[0048]

According to the first to fourth aspects of the invention, the relationship between the predetermined potential of the image carrier and the transfer bias potential applied to the intermediate transfer member, and the potential of the image carrier. Based on the information, the transfer bias voltage is controlled so as not to generate a discharge between the intermediate transfer member portion and the image carrier after the primary transfer, so that partial transfer due to uneven resistance of the intermediate transfer member is performed. It is possible to suppress the occurrence of the discharge due to the excessive electric field being amplified by the potential of the image carrier, and reduce the white band loss in the halftone portion due to the discharge.

In particular, according to the third aspect of the invention, by correcting the transfer bias voltage according to the environmental conditions, the discharge caused by the difference in the charge amount between the visible image side and the back surface side of the transfer material is generated. Since it can be suppressed, it is possible to reduce the scratches of sticky dust and crows that occur in a low-humidity environment.

Further, according to the invention of claim 4, since the control means of the control means of claim 1 can be switched by the switching means, for example, the potential sensor of claim 2 or the control means of claim 3 can be used. If an abnormal transfer bias voltage is set due to a sensor failure for detecting environmental conditions, etc., switch to non-execution above to prevent system runaway due to such failure. You can Further, when used in a place where the environmental conditions do not change extremely, by not performing the above control, the processing load of the control system can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a copying machine according to an embodiment.

FIG. 2 is an enlarged view around a photosensitive drum and an intermediate belt.

FIG. 3 is a block diagram showing the configuration of a control system in the first embodiment.

FIG. 4 is a characteristic diagram showing a range in which an abnormal image occurs.

FIG. 5 is a block diagram showing a configuration of a transfer nip portion and a configuration of a control system thereof in the second embodiment.

FIG. 6 is a characteristic diagram showing a relationship between an absolute humidity D of environmental conditions and an upper limit value of a transfer bias.

FIG. 7 is a characteristic diagram showing a relationship between a photoconductor potential (Vd) and a transfer bias voltage (Vb) in a region A of FIG.

8 is a characteristic diagram showing a relationship between a photosensitive member potential (Vd) and a transfer bias voltage (Vb) in a region B of FIG.

9 is a characteristic diagram showing a relationship between a photosensitive member potential (Vd) and a transfer bias voltage (Vb) in a region C of FIG.

[Explanation of symbols]

9 Photosensitive drum 13 Potential sensor 19 Intermediate transfer belt 20a transfer bias roller 24 Transfer paper 35 Belt transfer power supply 36 Belt transfer electric field control means 37 Transfer Nip Potential Detection Unit 48 Temperature / humidity detection means

Continuation of the front page (56) Reference JP-A-5-80664 (JP, A) JP-A-6-161294 (JP, A) JP-A-5-150670 (JP, A) JP-A-8-54789 (JP , A) JP 8-190286 (JP, A) JP 4-1790 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/00 303

Claims (4)

(57) [Claims] 1. An intermediate transfer type image forming apparatus for primary-transferring a visible image formed on an image carrier to an intermediate transfer body and secondarily transferring a primary transfer image on the intermediate transfer body to a transfer material. A relationship between a predetermined potential of the image carrier and a transfer bias potential applied to the intermediate transfer member, in which no discharge occurs between the intermediate transfer member portion and the image carrier after the primary transfer, An image forming apparatus comprising: a control unit that controls the transfer bias voltage based on potential information of the image carrier. 2. The image forming apparatus according to claim 1, further comprising a potential sensor for detecting a potential of the image carrier, wherein the potential information is obtained from the potential sensor. 3. The image forming apparatus according to claim 1, wherein:
An image forming apparatus, characterized in that a transfer bias voltage applied to the intermediate transfer member is corrected according to environmental conditions. 4. The image forming apparatus according to claim 1, 2 or 3, further comprising switching means for switching between control execution and non-execution by the control means according to claim 1.