JP3347505B2 - 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 using an electrophotographic process such as a printer or a copying machine, and more particularly to an image forming apparatus having an intermediate transfer member.

[0002] The electrophotographic photosensitive member in the image forming apparatus is a roller-shaped member (drum-shaped member), a belt-shaped member, or the like. The intermediate transfer member is a roller-shaped member (drum-shaped member), a belt-shaped member, or the like. It is. Further, the recording medium is a transfer paper, a recording paper, a printing paper, a card, a letter, a postcard, and the like, and the material is not limited to paper.

[0003]

2. Description of the Related Art Conventionally, this type of image forming apparatus has a configuration as shown in FIG. That is, a photosensitive drum 51 serving as an image carrier is provided substantially at the center thereof, and a primary charger 57, a yellow developing device (hereinafter abbreviated as a Y developing device) 53, and a magenta developing device (hereinafter abbreviated as a yellow developing device) are provided around the photosensitive drum 51 along the rotation direction. M developing device) 54, cyan developing device (hereinafter abbreviated as C developing device) 5
5, a black developing device (hereinafter abbreviated as Bk developing device) 56, an intermediate transfer drum 50 as an intermediate transfer member, and a photosensitive drum cleaner 60.

Around the intermediate transfer member 50, there are provided an intermediate transfer member cleaner 60 and a transfer roller 61, which can be moved toward and away from the intermediate transfer member 50, respectively. Further, the image forming apparatus separates the recording medium 64 from the intermediate transfer body 50 by registering a registration roller 63 that feeds a recording medium 64 such as a transfer paper in time with a nip portion between the intermediate transfer body 50 and the transfer roller 61. A corona charger 58 for removing electricity and a fixing device 62 are provided.

The operation of the image forming apparatus having the above configuration will be described below. The photosensitive drum 51 is charged by the charging roller 57. Next, a latent image is formed on the photosensitive drum 51 by the laser scanning unit 52 based on the image data output from the controller (not shown). The latent image is developed by the Y developing device 53, and a yellow toner image is formed on the photosensitive drum 51. The yellow toner image is primarily transferred from the photosensitive drum 51 to the intermediate transfer member 50 by a bias applied to the intermediate transfer member 50 by a high-voltage power supply (not shown). At this time, the toner remaining on the photosensitive drum 51 without being transferred to the intermediate transfer body 50 is cleaned by the photosensitive drum cleaner 60. Hereinafter, similarly to the above, the M developing device 54,
The toner images formed by the C developing unit 55 and the Bk developing unit 56 are transferred onto the intermediate transfer body 50 in a superimposed manner.

In this way, a full-color image is formed on the intermediate transfer body 50 by four rotations. The recording medium 64 fed from a paper feeding unit (not shown) is timed by a registration roller 63 so as to be synchronized with the toner image on the intermediate transfer body 50 at the fifth rotation.
To the nip. At this time, the transfer roller 61 comes into contact with the intermediate transfer body 50 immediately before the recording medium 64 comes to the nip portion. Then, the toner image is transferred to the recording medium 64, and an AC bias is applied to the corona charger 58, whereby the recording medium 64 is separated from the intermediate transfer body 50. Next, the fixing device 62 fixes the toner image on the recording medium 64 as a permanent image. The toner remaining on the intermediate transfer member 50 is cleaned by bringing the intermediate transfer member cleaner 59 into contact.

The printing operation for the next page and thereafter is performed after the toner image is secondarily transferred to the recording medium.

[0008]

However, in the conventional example, when a full-size image is formed on the intermediate transfer member 50, the intermediate transfer member 50 must be rotated five times for one image formation. .

When a full-size image is to be formed by four rotations, the intermediate transfer member 5 is moved from the photosensitive drum 51 to the intermediate transfer member 5.
When the primary transfer to 0 and the secondary transfer from the intermediate transfer body 50 to the recording medium 64 overlap with a part of the image when the fourth color is black, the intermediate transfer body 50 is set to the ground potential. In addition, a potential having the same polarity as the charged polarity of the toner must be applied to the photosensitive drum 51.

In this case, an adverse effect due to a change in the primary transfer bias sometimes occurs in the secondary transfer.

The peripheral length of the intermediate transfer member 50 is, for example, A3
When two images of A4 landscape size are formed by one rotation of the intermediate transfer body, the remaining amount of the recording medium in the sheet cassette is either zero or one or more. In the case where the remaining amount of the recording medium is one at the time of forming the two images, after transferring the one sheet, the remaining one toner image must be cleaned. did not become. For this reason, the burden on the intermediate transfer member cleaner is large, and the inside of the machine may be stained.

Accordingly, a first object of the present invention is to provide an image forming apparatus capable of preventing an adverse effect on an image due to simultaneous primary transfer and secondary transfer.

A second object of the present invention is to start the secondary transfer from the intermediate transfer member to the recording medium during the fourth rotation of the intermediate transfer member while applying the primary transfer bias from the photosensitive member to the intermediate transfer member. An object of the present invention is to provide an image forming apparatus which does not adversely affect an image.

[0014] A third object of the present invention is to provide an image processing apparatus in which the primary transfer of the first color of the (n + 1) th printing is started during the secondary transfer of the nth printing when performing continuous printing. An object of the present invention is to provide an image forming apparatus which does not adversely affect the image forming apparatus.

[0015] A fourth object of the present invention is to form a second toner image on the intermediate transfer member when only one recording medium is present at the time of forming images for two recording media on the intermediate transfer member. An object of the present invention is to provide an image forming apparatus that can be removed.

[0016]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier on which an electrostatic latent image is formed; developing means for developing the electrostatic latent image with one of a plurality of color toners to form a toner image on the image carrier; and An image forming apparatus comprising: an intermediate transfer member that forms a color toner image by sequentially transferring the toner images of each color by contact rotation; and a transfer unit that transfers the color toner image formed on the intermediate transfer member to a recording medium. In the apparatus, before the transfer of the color toner image formed on the intermediate transfer body to the recording medium is started, the transfer of the toner image formed on the image carrier to the intermediate transfer body is performed. Applying a predetermined potential to the intermediate transfer body and stopping the application of the predetermined potential after the transfer of the toner image to the intermediate transfer body is completed, and applying the predetermined potential to the color toner image formed on the intermediate transfer body. Start transfer to recording media After that, even when the transfer of the toner image formed on the image carrier to the intermediate transfer member is completed, the application of the predetermined potential is performed until the transfer of the color toner image to the recording medium is completed. Is an image forming apparatus characterized by continuing without stopping.

[0017]

[0018]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 Embodiment 1 of an image forming apparatus according to the present invention will be described with reference to FIG. In FIG. 1, the image forming apparatus has a photosensitive drum 2 serving as an image carrier at substantially the center, a laser scanning unit 12 above the photosensitive drum 2, and a charging roller 7 serving as a primary charger, a developing unit 16 and an intermediate unit. A transfer body 1 and a photosensitive drum cleaner 10 are provided. A transfer roller 1 is provided around the intermediate transfer member 1 so as to be able to contact and separate from the intermediate transfer member 1.
1, a corona charger 8, an intermediate transfer member cleaner 9 that can be brought into contact with and separated from the intermediate transfer member 1, and a fixing device 15.

The developing unit 16 includes the yellow developing unit 3
(Hereinafter abbreviated as Y developing device), magenta developing device 4 (hereinafter abbreviated as M developing device), cyan developing device 5 (hereinafter abbreviated as C developing device), and black developing device 6 (hereinafter abbreviated as Bk developing device). Each developing unit is rotatable and can sequentially contact the photosensitive drum 2.

The peripheral length of the intermediate transfer member 1 is set so that an image of A3 size can be formed, for example, and (A3 size portrait) + (developer switching time) × (process speed) has a predetermined margin. Have been.

Next, the printing operation of one A3 size full color sheet or intermittent printing in the image forming apparatus of this embodiment will be described with reference to FIGS.

The photosensitive drum 2 is negatively and uniformly charged by the charging roller 7. Then, a latent image is formed on the photosensitive drum 2 by the laser beam of the laser scanning unit 12 based on data transmitted from an image data generation unit (not shown). This latent image is developed by the Y developing device 3 with a negatively charged yellow toner to form a toner image.

The yellow toner image thus formed on the photosensitive drum 2 is applied to the intermediate transfer member 1 at a portion where the photosensitive drum 2 rotates in the direction of the arrow shown in FIG. The primary transfer is performed by the applied positive bias (approximately +100 to 2000 V with respect to the ground potential).

At this time, the primary transfer bias is started to be applied to the intermediate transfer member 1 immediately before the intermediate transfer member 1 reaches the position shown in FIG. 2A, and immediately after the intermediate transfer member 1 reaches the position shown in FIG. The application of the primary transfer bias ends. The timing at this time is like the Y primary transfer bias shown in the sequence chart of FIG.

The toner remaining on the photosensitive drum 2 without being transferred onto the intermediate transfer member 1 is cleaned by a cleaner 10.

Next, at the timing when the magenta toner image is transferred to the same position as the yellow toner image, a magenta toner image is formed and transferred in the same manner as in the case of yellow. The output timing of the primary transfer bias of magenta at this time is as shown in the sequence chart of FIG.

Next, at the timing when the cyan toner image is transferred to the same position as the two color toner images, a cyan toner image is formed and transferred in the same manner as described above. The output timing of the primary transfer bias for cyan at this time is as shown in the sequence chart of FIG.

After the yellow, magenta, and cyan toner images are formed on the intermediate transfer member 1, the black toner image is transferred at the fourth rotation, and the full-color image of four colors is transferred to the recording medium 14. The procedure is described below.

As shown in FIG. 2A, the intermediate transfer member 1
A latent image is formed and toner is developed such that a black toner image is primarily transferred at a nip portion between the top of the three color toner images and the photosensitive drum 2.

Then, as shown in FIG. 2C, a secondary transfer bias is applied to the transfer roller 11 immediately before the leading ends of the four full-color images reach the nip portion with the transfer roller 11. The value of the secondary transfer bias at this time is suitably about 1 to 5 kV with respect to the intermediate transfer body potential (the intermediate transfer body potential (100 to 2000 V) + (1
５5 kV).

When the transfer to the recording medium 14 is started and the trailing edge of the image passes the blade position of the intermediate transfer member cleaner 9, the cleaner 9 contacts the intermediate transfer member 1 and the cleaning of the intermediate transfer member starts. Is done.

Then, as shown in FIG. 2D, the applied bias for the primary transfer to the intermediate transfer body 1 is continued even after the primary transfer at the rear end of the image is completed.

Further, as shown in FIG. 2E, immediately after the secondary transfer of the full-color toner image on the intermediate transfer member 1 to the recording medium, the application of both the primary transfer bias and the secondary transfer bias is completed.

The above-described bias application sequence is as shown in the sequence chart of FIG. When the rear end portion of the toner image on the intermediate transfer body 1 has passed the position of the cleaner 9, the cleaner 9 is separated, and the rotation of the intermediate transfer body 1 ends. The recording medium 14 on which the secondary transfer has been performed is de-electrified and separated by applying an AC bias to the corona charger 8 and fixed by the fixing unit 15 to obtain a full-color print output.

In FIG. 2, the portion from the rear end of the image outside the image area on the intermediate transfer member to the front end of the image is for switching the developing unit 16 during multicolor printing. Long)> (Developer switching time) × (Process speed).

In the above description, the operation of four-color printing has been described. However, in the case of a single-color printing operation, formation of a latent image of the final color (black in the above description), development,
Only the sequence of the secondary transfer and the secondary transfer is performed.

Next, the sequence of full-color continuous printing of A3 size of the image forming apparatus will be described with reference to the sequence chart of FIG.

In the printing of the first sheet, the primary transfer of Y, M and C is the same as in the case of the printing of the single sheet of A3. At the fourth rotation, as shown in FIG.
A latent image is formed such that a black toner image is primarily transferred at a nip portion between the tip of the toner image for the color and the photosensitive drum 2;
The development of the toner is performed.

Next, as shown in FIG. 2C, the transfer roller 11 is brought into contact with the intermediate transfer member 1 immediately before the leading ends of the four color toner images come to the nip portion with the transfer roller 11, and the registration is performed. The recording medium 14 is conveyed by the roller 13 in synchronization with the toner image on the intermediate transfer body 1, and a secondary transfer bias is applied to the transfer roller 11 immediately before the toner image contacts the recording medium 14.

Next, after the image starts to be secondarily transferred to the recording medium 14, when the rear end of the image passes the blade position of the cleaner 9, the cleaner 9 is brought into contact with the intermediate transfer member 1, and
Cleaning starts. The primary transfer bias to the intermediate transfer member 1 is maintained during the secondary transfer to the recording medium.
As shown in (f), the latent image formation and development of the second yellow image are performed so that the second yellow toner image is transferred at a position where the leading end of the image contacts the photosensitive drum.

As shown in FIG. 2E, when the first toner image has been transferred onto the recording medium, the application of the secondary transfer bias ends, and the transfer roller 11 is separated. When the trailing edge of the toner image has passed the blade of the cleaner 9, the cleaner 9 is separated. As shown in FIG. 2B, when the yellow toner image is transferred to the intermediate transfer member 1, the application of the primary transfer bias ends.

Thereafter, the toner image formation after magenta is performed in the same manner as the printing of the first sheet. The above sequence is as shown in the sequence chart of FIG.

Next, an operation for printing one sheet of A4 horizontal size or intermittently in the apparatus of this embodiment will be described with reference to FIGS. 1, 5 and 6. FIG.

The photosensitive drum 2 is negatively and uniformly charged by the charging roller 7. Then, a latent image is formed on the photosensitive drum 2 by the laser beam of the laser scanning unit 12 based on data transmitted from an image data generation unit (not shown). This latent image is developed by the Y developing device 3 with a negatively charged yellow toner to be a toner image.

The yellow toner image thus formed on the photosensitive drum 2 is transferred to the intermediate transfer member 1 at a portion where the photosensitive drum 2 rotates in the direction of the arrow shown in FIG. The primary transfer is performed by the applied positive bias (about +100 to 2000 V with respect to the ground potential).
At this time, the application of the primary transfer bias to the intermediate transfer body is started just before the position of FIG. 5A, and the A shown in FIG.
Immediately after reaching the rear end position of the four horizontal images, the bias application ends. The timing at this time is like the Y primary transfer bias shown in the sequence chart of FIG. The toner remaining on the photosensitive drum 2 without being transferred onto the intermediate transfer body 1 is cleaned by the cleaner 10.

Next, at the timing when the magenta toner image is transferred to the same position as the yellow toner image, a magenta toner image is formed and transferred in the same manner as in the case of yellow. The output timing of the primary transfer bias of magenta at this time is as shown in the sequence chart of FIG.

Next, at the timing when the cyan toner image is transferred to the same position as the two color toner images, a cyan toner image is formed and transferred in the same manner as described above. The output timing of the primary transfer bias for cyan at this time is as shown in the sequence chart of FIG.

After the yellow, magenta, and cyan toner images are formed on the intermediate transfer body 1, the black toner image is transferred at the fourth rotation, and the full-color image of four colors is transferred to the recording medium 14. The procedure is described below.

First, as shown in FIG. 5A, the leading ends of the three color toner images on the intermediate transfer member 1 are latently transferred so that the black toner image is primarily transferred at the nip portion with the photosensitive drum. Image formation and toner development are performed. And FIG.
Immediately after the image reaches the rear end position of the A4 horizontal image as shown in (b), the bias application ends.

Thereafter, as shown in FIG.
The transfer roller 11 is brought into contact with the intermediate transfer body 1 immediately before the leading end of the full-color image reaches the nip portion of the transfer roller 11. Then, the recording medium 14 is conveyed by the registration rollers 13 in synchronization with the image on the intermediate transfer body 1, and the recording medium 14
A positive secondary transfer bias is applied to the transfer roller 11 immediately before the toner image contacts the transfer roller 11. The value of the secondary transfer bias at this time is 1 to 5 k with respect to the potential of the intermediate transfer member (ground).
V is suitable.

Note that the cleaner 9 is brought into contact with the intermediate transfer member 9 and the cleaning of the intermediate transfer member is started before the transfer starts and before the leading end of the image reaches the blade position of the cleaner 9. Then, as shown in FIG.
Immediately after the secondary transfer of the full-color toner image to the recording medium is completed, the application of the secondary transfer bias ends. The above bias application sequence is as shown in FIG.
When the rear end portion of the toner image on the intermediate transfer body 1 has passed the position of the cleaner 9, the cleaner 9 is separated, and the rotation of the intermediate transfer body 1 ends.

The recording medium on which the secondary transfer has been performed is a corona charger 8.
Is applied with an AC bias, the charge is separated therefrom, and the image is fixed by the fixing device 15 to obtain a full-color print output.

Next, the sequence of full-color continuous printing of A4 landscape size will be described. In the first printing, the primary transfer of yellow, magenta, and cyan is the same as in the case of the above-described single printing of A4, so that the description is omitted, and only the fourth and subsequent rotations of the first printing in the continuous printing will be described below. , FIGS. 1, 5 and 7. FIG.

As shown in FIG. 5A, at the fourth rotation, the leading end of the toner image of three colors on the intermediate transfer body 1 is primarily transferred at the nip portion between the photosensitive drum 2 and the black toner image. The latent image formation and toner development are performed as described above. FIG.
A primary transfer bias is applied from the state shown in FIG. 5A to the state shown in FIG. 5B, and toner images of four colors are formed on the intermediate transfer member 1.

Next, as shown in FIG.
Immediately before the leading end of the color toner image reaches the nip portion with the transfer roller 11, the transfer roller 11 is brought into contact with the intermediate transfer body 1, and the registration medium 13 causes the recording medium 14 to synchronize with the toner image on the intermediate transfer body 1. The recording medium 14 is conveyed, and a primary transfer bias and a secondary transfer bias are applied immediately before the toner image comes into contact with the recording medium 14. The bias value at this time is the same as in the case of A3 printing.

The transfer to the recording medium is started, and before the leading edge of the image reaches the blade position of the cleaner 9, the cleaner 9 is moved.
Is brought into contact with the intermediate transfer member 1 and cleaning of the intermediate transfer member 1 is started.

Next, as shown in FIG. 5D, the leading end of the second yellow toner image on the intermediate transfer body 1 is nip with the photosensitive drum 2 and the yellow toner image is primarily transferred. As a result, the latent image is formed and the toner is developed, and the primary transfer of the second yellow sheet is started at the position shown in FIG.

Next, as shown in FIG. 5E, the secondary transfer bias is applied immediately after the secondary transfer of the first full-color toner image on the intermediate transfer member 1 to the recording medium 14 is completed. finish. Thereafter, printing of the second and subsequent sheets is performed in the same manner as in the case of the first sheet.

Embodiment 2 Next, Embodiment 2 of the image forming apparatus according to the present invention will be described.
This will be described with reference to FIGS. In FIG. 8, the same members as those shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 8, the image forming apparatus has a photosensitive drum 2 as an image carrier substantially at the center, a laser scanning unit 12 above the photosensitive drum 2, a charging roller 7 as a primary charger around the photosensitive drum 2, and a developing unit. 16, an intermediate transfer member 1, and a photosensitive drum cleaner 10. Further, a transfer roller 1 that can be brought into contact with and separated from the intermediate transfer body 1 is provided around the intermediate transfer body 1.
1, a corona charger 8, an intermediate transfer member cleaner 9 that can be brought into contact with and separated from the intermediate transfer member 1, and a fixing device 15.

The developing unit 16 comprises a Y developing unit 3, an M developing unit 4, a C developing unit 5, and a Bk developing unit 6.
Each of the developing devices is rotatable and can sequentially contact the photosensitive drum 2.

The circumference of the intermediate transfer body 1 is set so that an image of A3 size can be formed, for example, and (A3 size portrait) + (developer switching time) × (process speed) has a predetermined margin. Have been.

Next, the printing operation of one A3-size full-color or intermittent printing in the image forming apparatus of this embodiment will be described with reference to FIGS.

The photosensitive drum 2 is negatively and uniformly charged by the charging roller 7. Then, a latent image is formed on the photosensitive drum 2 by the laser beam of the laser scanning unit 12 based on data transmitted from an image data generation unit (not shown). This latent image is developed by the Y developing device 3 with a negatively charged yellow toner to be a toner image.

The yellow toner image formed on the photosensitive drum 2 in this manner is applied to the intermediate transfer member 1 at a portion where the photosensitive drum 2 rotates in the direction of the arrow shown in FIG. The primary transfer is performed by the applied positive bias (approximately +100 to 2000 V with respect to the ground potential). At this time, the primary transfer bias is started to be applied to the intermediate transfer body 1 immediately before the intermediate transfer body 1 reaches the position shown in FIG. 9A, and the primary transfer bias is applied immediately after the intermediate transfer body 1 reaches the position shown in FIG. 9B. The application of the bias ends. The timing at this time is like the Y primary transfer bias shown in the sequence chart of FIG.

The toner remaining on the photosensitive drum 2 without being transferred onto the intermediate transfer member 1 is cleaned by the cleaner 10.

Next, at the timing when the magenta toner image is transferred to the same position as the yellow toner image, a magenta toner image is formed and transferred in the same manner as in the case of yellow. The output timing of the primary transfer bias of magenta at this time is as shown in the sequence chart of FIG.

Next, at the timing when the cyan toner image is transferred to the same position as the two color toner images, a cyan toner image is formed and transferred in the same manner as described above. The output timing of the primary transfer bias for cyan at this time is as shown in the sequence chart of FIG.

After the yellow, magenta, and cyan toner images are formed on the intermediate transfer body 1, the black toner image is transferred at the fourth rotation, and the full-color images of four colors are transferred to the transfer medium 14. The procedure is described below.

As shown in FIG. 9A, the intermediate transfer body 1
A latent image is formed and toner is developed such that a black toner image is primarily transferred at a nip portion between the top of the three color toner images and the photosensitive drum 2.

Then, as shown in FIG. 9C, the transfer roller 11 is brought into contact with the intermediate transfer member 1 immediately before the front ends of the four full-color images come to the nip portion of the transfer roller 11. Then, the recording medium 14 is conveyed by the registration rollers 13 in synchronization with the image on the intermediate transfer body 1, and the recording medium 14
A positive secondary transfer bias is applied to the transfer roller 11 immediately before the toner image contacts the transfer roller 11. The value of the secondary transfer bias at this time is preferably about 1 to 5 kV with respect to the intermediate transfer body potential (the intermediate transfer body potential (100
２０００2000 V) + (1-5 kV).

When the transfer to the recording medium 14 is started and the leading end of the image passes the blade position of the intermediate transfer member cleaner 9, the cleaner 9 contacts the intermediate transfer member 9 and the cleaning of the intermediate transfer member is started. You.

As shown in FIG. 9D, the applied bias for the primary transfer to the intermediate transfer member 1 is continued even after the primary transfer at the rear end of the image is completed.

Further, as shown in FIG. 9E, immediately after the secondary transfer of the full-color toner image on the intermediate transfer member 1 to the recording medium, the application of both the primary transfer bias and the secondary transfer bias ends.

The above bias application sequence is shown in FIG.
As shown in the sequence chart of FIG.

When the rear end portion of the toner image on the intermediate transfer member 1 passes the position of the cleaner 9, the cleaner 9 is separated, and the rotation of the intermediate transfer member 1 is completed. The recording medium on which the secondary transfer has been performed is discharged and separated by applying an AC bias to the corona charger 8 and is fixed by the fixing device 15 to obtain a full-color print output.

In FIG. 9, the portion from the rear end of the image outside the image area on the intermediate transfer member to the front end of the image is for switching the developing unit 16 during multicolor printing. Long)> (Developer switching time) × (Process speed).

In the above description, the operation of four-color printing has been described. However, in the case of a single-color printing operation, formation of a latent image of the final color (black in the above description), development,
Only the sequence of the secondary transfer and the secondary transfer is performed.

Next, the sequence of the full-color continuous printing of A3 size of the image forming apparatus will be described.

In the printing of the first sheet, the primary transfer of Y, M and C is the same as in the case of the printing of one sheet of A3. At the fourth rotation, as shown in FIG.
A latent image is formed such that a black toner image is primarily transferred at a nip portion between the tip of the toner image for the color and the photosensitive drum 2;
The development of the toner is performed.

Next, as shown in FIG. 9C, the transfer roller 11 is brought into contact with the intermediate transfer body 1 immediately before the leading ends of the four color toner images come to the nip portion with the transfer roller 11, and The recording medium 14 is conveyed by the roller 13 in synchronization with the toner image on the intermediate transfer body 1, and a secondary transfer bias is applied to the transfer roller 11 immediately before the toner image contacts the recording medium.

Next, after the image has begun to be secondarily transferred to the recording medium, when the trailing edge of the image has passed the blade position of the cleaner 9, the cleaner 9 is brought into contact with the intermediate transfer member 1 and cleaning is started. The primary transfer bias to the intermediate transfer body 1 is maintained during the secondary transfer to the recording medium, and FIG.
The latent image formation and development of the second yellow image are performed such that the second yellow toner image is transferred at the position where the image leading edge position contacts the photosensitive drum as shown by.

As shown in FIG. 9E, when the transfer of the first toner image onto the recording medium is completed, the application of the secondary transfer bias ends, and the transfer roller 11 is separated. When the trailing edge of the toner image has passed the blade of the cleaner 9, the cleaner 9 is separated. As shown in FIG. 9B, when the yellow toner image is transferred to the intermediate transfer member 1, the application of the primary transfer bias ends.

Thereafter, the toner image formation after magenta is performed in the same manner as the printing of the first sheet. The above sequence is as shown in the sequence chart of FIG.

Next, the printing operation of A4 horizontal size of the apparatus of this embodiment will be described with reference to FIGS. 8, 12 and 13. FIG.

The photosensitive drum 2 is negatively and uniformly charged by the charging roller 7. Then, a latent image is formed on the photosensitive drum 2 by the laser beam of the laser scanning unit 12 based on data transmitted from an image data generation unit (not shown). The latent image is developed by the Y developing device 3 with yellow toner charged negatively.

The yellow toner image formed on the photosensitive drum 2 in this manner is transferred to the intermediate transfer body 1 at a portion where the photosensitive drum 2 rotates in the direction of the arrow shown in FIG. The primary transfer is performed by the applied positive bias (about +100 to 2000 V with respect to the ground potential).
At this time, just before the position in FIG.
The application of the next transfer bias is started, and the bias application ends immediately after reaching the rear end position of the image on the A4 side shown in FIG.

The toner remaining on the photosensitive drum 2 without being transferred onto the intermediate transfer body 1 is cleaned by the cleaner 10.

Next, at the timing when the magenta toner image is transferred to the same position as the yellow toner image, a magenta toner image is formed and transferred in the same manner as in the case of yellow.

Next, at the timing when the cyan toner image is transferred to the same position as the two color toner images, the cyan toner image is formed and transferred in the same manner as described above.

After the yellow, magenta, and cyan toner images are formed on the intermediate transfer member 1, the black toner image is transferred at the fourth rotation, and the four full-color images are transferred to the recording medium 14. The procedure is described below.

At the fourth rotation, as shown in FIG. 12A, a black toner image is primarily transferred at the nip portion between the photosensitive drum 2 and the leading end of the toner image for three colors on the intermediate transfer member 1. The latent image formation and toner development are performed as described above. FIG.
A primary transfer bias is applied from the state shown in FIG. 3A, and four color toner images are formed on the intermediate transfer member 1.

Thereafter, as shown in FIG.
Immediately before the leading ends of the four color toner images reach the nip portion with the transfer roller 11, the transfer roller 11 is brought into contact with the intermediate transfer body 1, and
The recording medium 14 is conveyed by the registration roller 13 in synchronization with the toner image on the intermediate transfer body 1, and a secondary transfer bias is applied immediately before the toner image contacts the recording medium 14. The value of the secondary transfer bias at this time is preferably about 1 to 5 kV with respect to the intermediate transfer body potential (intermediate transfer body potential (100 to 2000 V) + (1 to 5 K with respect to the ground potential).
v)).

The application of the primary transfer bias is continued even after passing the primary transfer position of the image as shown in FIG. Transfer to the recording medium is started, and the leading edge of the image is
Before the blade 9 comes to the position, the cleaner 9 starts cleaning the intermediate transfer member.

Then, as shown in FIG. 12E, the primary transfer bias and the secondary transfer bias are applied immediately after the secondary transfer of the first full-color toner image on the intermediate transfer member 1 to the recording medium is completed. Both ends the application. Thereafter, printing of the second and subsequent sheets is performed in the same manner as in the case of the first sheet. The above sequence is shown in FIG.

Third Embodiment Next, a third embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In FIG. 14,
The same members as those shown in FIG. 1 are denoted by the same reference numerals.

In FIG. 14, the image forming apparatus has a photosensitive drum 2 as an image carrier substantially at the center, a laser scanning unit 12 above the photosensitive drum 2, a charging roller 7 as a primary charger around the photosensitive drum 2, and a developing unit. 16, an intermediate transfer member 1, and a photosensitive drum cleaner 10. Further, a transfer roller 1 that can be brought into contact with and separated from the intermediate transfer body 1 is provided around the intermediate transfer body 1.
1, a corona charger 8, an intermediate transfer member cleaner 9 that can be brought into contact with and separated from the intermediate transfer member 1, and a fixing device 15.

The developing unit 16 comprises a Y developing unit 3, an M developing unit 4, a C developing unit 5, and a Bk developing unit 6.
Each of the developing devices is rotatable and can sequentially contact the photosensitive drum 2.

A paper feed cassette 22 serving as a recording medium loading means for storing the recording medium 14 is provided with a paper feed roller 2 for feeding the recording medium 14 from the paper feed cassette 22 one by one.
1 and a remaining paper detection sensor 23 which is a detecting means for detecting the remaining amount of the recording medium 14 in the cassette 22.
A sheet feed registration roller 1 for feeding a recording medium 14 at a nip portion between the intermediate transfer body 1 and the transfer roller 11 at a proper timing.
3 and can be conveyed to the nip. Further, the paper feed roller 21 is capable of conveying the recording medium 14 through the conveyance guide 20 to the paper feed registration roller 13 before the secondary transfer.

The peripheral length of the intermediate transfer member 1 is set such that two A4 size or A3 size images can be formed.
This is a setting in which a predetermined margin is provided for (vertical length of three sizes) + (developer switching time) × (process speed) + (interval between two sheets of A4 horizontal size).

A case where there are three recording media in a sheet cassette in continuous printing in which two A4-size toner images are formed on an intermediate transfer member in the apparatus of this embodiment will be described below with reference to FIGS. I do. Note that A3 size printing and the like are the same as those in the first embodiment.

The photosensitive drum 2 is negatively and uniformly charged by the charging roller 7. Then, the image data is transmitted from an image data generation unit (not shown). A latent image is formed on the photosensitive drum 2 by the laser beam of the laser scanning unit 12 according to the data. The latent image is developed by the Y developing device 3 with yellow toner charged negatively.

The yellow toner image thus formed on the photosensitive drum 2 is applied to the intermediate transfer member 1 at a portion where the photosensitive drum 2 rotates in the direction of the arrow shown in FIG. The primary transfer is performed by the applied positive bias (approximately +100 to 2000 V with respect to the ground potential).
At this time, immediately before the state shown in FIG. 15A, the primary transfer bias is started to be applied to the intermediate transfer member, the first toner image is primarily transferred, and the second toner image is transferred from the position shown in FIG. Is primarily transferred.

Next, immediately after reaching the position shown in FIG. 15C, the application of the primary transfer bias is completed. The timing at this time is as shown in the sequence chart of FIG.

The toner remaining on the photosensitive drum 2 without being primarily transferred onto the intermediate transfer member 1 is cleaned by the cleaner 10 by the cleaner 10.

In parallel with the formation of the toner image by the apparatus, before the intermediate transfer member 1 is brought to the position shown in FIG. 15C, the recording medium is fed by the paper feed roller 21 as shown in FIG. 14 is transported to the position of the registration roller 13.

Next, at the timing when the magenta toner image is transferred to the same position as that of the yellow toner image, a magenta toner image is formed and transferred in the same manner as in the case of yellow. The output timing of the primary transfer bias of magenta at this time is as shown in the sequence chart of FIG.

Next, at the timing when the cyan toner image is transferred to the same position as the two color toner images, the cyan toner image is formed and transferred in the same manner as described above. The output timing of the primary transfer bias for cyan at this time is as shown in the sequence chart of FIG.

After the yellow, magenta, and cyan toner images are formed on the intermediate transfer member 1, the black toner image is transferred at the fourth rotation, and the four full-color images are transferred to the recording medium. The procedure is described below.

First, as shown in FIG. 15A, the leading ends of the three color toner images on the intermediate transfer body 1 are latently transferred so that the black toner image is primarily transferred at the nip portion with the photosensitive drum. Image formation and toner development are performed.

Next, as shown in FIG. 15D, the transfer roller 11 abuts on the intermediate transfer body 1 immediately before the leading edge of the first full color image of the four colors reaches the nip portion with the transfer roller 11. Is done.

Then, the recording medium 14 which has been conveyed in advance to the position of the registration roller 13 is conveyed in synchronization with the toner image on the intermediate transfer body 1 and has a positive secondary transfer bias immediately before the toner image comes into contact with the recording medium. Is applied to the transfer roller 11. The value of the secondary transfer bias at this time is suitably about 1 to 5 kV with respect to the intermediate transfer body potential (the intermediate transfer body potential (100 to 2000 V) + (1
５5 kV)).

Note that the recording medium 14 is
Then, when the sheet is conveyed to the secondary transfer nip, the second recording medium is conveyed by the feed roller 21. When the transfer to the recording medium is started and the trailing edge of the second toner image passes the blade position of the cleaner 9,
The cleaner 9 is brought into contact with the intermediate transfer body 1 and cleaning of the intermediate transfer body is started.

Next, as shown in FIG.
When the secondary transfer of the sheet is started, the conveyance of the third recording medium to the registration roller 13 is started.

The third recording medium is conveyed to the registration roller 13 until the state shown in FIG. As a result, the apparatus control unit (not shown) executes a sequence when there is no recording medium by the remaining paper amount detection sensor 23. This is shown below. The first 2
In the course of the next transfer, as shown in FIG. 16 and FIG.
The primary transfer of the sheet is started.

The control unit (not shown) performs the primary transfer of the first color of yellow on the third and fourth sheets in the same manner as the first and second sheets (see FIG. 16). In the case of magenta, cyan, and black for the second and subsequent colors, the third toner image is set in the same manner as described above.
Next transfer is performed at a portion where the fourth toner image is on the photosensitive drum 2 and is in contact with the intermediate transfer member 1 (FIG. 15).
By applying a negative bias (−1 to −3 kV) to the intermediate transfer member 1 (from (b) to 15 (c)), the magenta, cyan, and black toner images on the photosensitive drum are transferred to the intermediate transfer member. 1 and the yellow toner image is returned to the photosensitive drum 2 and the toner is cleaned by the cleaner 10.

When the formation of the fourth toner image of the fourth color is completed (FIG. 15B), the negative reverse transfer bias applied to the intermediate transfer member is as shown in FIGS. 15F to 15G. The voltage continues to be applied during the secondary transfer to the third recording medium shown in the figure, and the application ends when the application of the secondary transfer bias to the recording medium ends.

The secondary transfer bias applied at the position shown in FIG. 15F is obtained by adding an intermediate transfer member potential (-1 to -3 kV) to 1 to 5 kV. The above sequence is as shown in the sequence chart of FIG.

The control unit (not shown) transmits a predetermined signal to the image forming unit (not shown) that the fourth image could not be formed. Is supplied, the image from the fourth sheet is output.

[0122]

As is apparent from the above description, the image forming apparatus according to the present invention has a structure in which the color toner image formed on the intermediate transfer member is transferred onto the image carrier before the transfer to the recording medium is started. A predetermined potential is applied to the intermediate transfer body during transfer of the toner image to be formed on the intermediate transfer body, and after the transfer of the toner image to the intermediate transfer body, the application of the predetermined potential is stopped to form the toner image on the intermediate transfer body. After the transfer of the color toner image to the recording medium is started, the transfer of the color toner image to the recording medium is completed even if the transfer of the toner image formed on the image carrier to the intermediate transfer body is completed. Until the application of the predetermined potential is continued without stopping, the adverse effect on the image due to the simultaneous execution of the primary transfer and the secondary transfer can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram for explaining one A3 size full-color or intermittent printing operation of the image forming apparatus of FIG. 1;

FIG. 3 is a sequence chart relating to the printing operation shown in FIG. 2;

FIG. 4 is a sequence chart illustrating an A3-size full-color continuous printing operation of the image forming apparatus of FIG. 1;

FIG. 5 is an explanatory diagram for explaining one sheet or intermittent printing operation of A4 horizontal size of the image forming apparatus of FIG. 1;

FIG. 6 is a sequence chart related to the printing operation shown in FIG.

FIG. 7 is a sequence chart for explaining full-color continuous printing operation of A4 horizontal size of the image forming apparatus of FIG. 1;

FIG. 8 is a schematic configuration diagram showing a second embodiment of the image forming apparatus according to the present invention.

9 is an explanatory diagram for explaining one A3 size full color or intermittent printing operation of the image forming apparatus of FIG. 8;

FIG. 10 is a sequence chart relating to the printing operation shown in FIG. 9;

11 is a sequence chart for explaining an A3-size full-color continuous printing operation of the image forming apparatus of FIG. 8;

12 is an explanatory diagram for explaining one sheet or intermittent printing operation of A4 horizontal size of the image forming apparatus of FIG. 8;

13 is a sequence chart related to the printing operation shown in FIG.

FIG. 14 is a schematic configuration diagram showing a third embodiment of the image forming apparatus according to the present invention.

FIG. 15 is an explanatory diagram for describing a continuous printing operation of the image forming apparatus of FIG. 1 in which two A4-size toner images are formed on an intermediate transfer member.

FIG. 16 is a sequence chart related to the printing operation of FIG.

FIG. 17 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intermediate transfer body 2 Photosensitive drum (image carrier) 11 Transfer roller (transfer means) 14 Recording medium 16 Developing means 20 Conveyance guide (conveyance means) 22 Paper feed cassette (recording medium stacking means) 23 Paper remaining sensor (detection means) )

Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114 G03G 21/14

Claims (1)

(57) [Claims] An image carrier on which an electrostatic latent image is formed; developing means for developing the electrostatic latent image with one of a plurality of color toners to form a toner image on the image carrier; An intermediate transfer member that rotates in contact with the image carrier and sequentially transfers the toner images of each color to form a color toner image; and a transfer unit that transfers the color toner image formed on the intermediate transfer member to a recording medium Before the transfer of the color toner image formed on the intermediate transfer member to the recording medium is started, the intermediate transfer of the toner image formed on the image carrier is performed. Applying a predetermined potential to the intermediate transfer body during transfer to the body, and stopping the application of the predetermined potential after the transfer of the toner image to the intermediate transfer body is completed. The recording medium for a color toner image After the transfer to the recording medium is started, the transfer of the color toner image to the recording medium is completed even after the transfer of the toner image formed on the image carrier to the intermediate transfer body is completed. An image forming apparatus, wherein application of the predetermined potential is continued without stopping.