JP2000267542A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image while keeping away from an image inhibition area set on a photoreceptor with inexpensive constitution. SOLUTION: Based on relative position information concerning a photoreceptor belt 15 and an intermediate transfer belt 16, a controller 26 selects a specified intermediate transfer body reference mark being image forming start timing that a toner image is not formed in the image inhibition area set on the belt 15 out of four intermediate transfer body reference marks c1, c2, c3 and c4 formed on the belt 16, and adjusts an image forming start position. Thus, the image is formed while keeping away from the image inhibition area set on the belt 15 with the inexpensive constitution.

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 printer, a facsimile, etc., which forms an image using an electrophotographic system, and more particularly to an intermediate transfer member for temporarily transferring a toner image formed on a photosensitive member. The present invention relates to an image forming apparatus which performs primary image transfer on the intermediate transfer member, and secondarily transfers a toner image transferred to the intermediate transfer member onto a transfer material to form an image.

[0002]

2. Description of the Related Art FIG. 5 is a schematic view showing an electrophotographic full-color image forming apparatus provided with a belt-shaped photosensitive member (hereinafter referred to as a photosensitive belt) as an image carrier and an intermediate transfer belt as an intermediate transfer member. FIG.

This image forming apparatus includes a photosensitive belt 15 stretched between a driving roller 9a and driven rollers 9b and 9c, and is rotated (moved) in the direction of arrow A by the driving of the driving roller 9a.

As shown in FIG. 6, the photosensitive belt 15 has a joint a in a direction intersecting the circumferential direction (rotation direction).
The area before and after the seam a is an image prohibited area T. Therefore, the area other than the image prohibition area T is an image formable area, and the image formation area is determined by the size of a transfer material such as paper on which an image is formed.

As shown in FIG. 6, a photoconductor reference mark detection sensor 20 is provided on one side of the photoconductor belt 15 so as to sandwich the photoconductor belt 15 in a non-contact manner. The photoconductor reference mark detection sensor 20 optically detects a photoconductor reference mark b indicating a reference position of the photoconductor belt 15 provided near the rotation direction upstream side of the photoconductor belt 15 at the seam a. The image prohibition region T including the joint a can be detected.

[0006] Around the photosensitive belt 15, a photosensitive belt 1 is provided.
A charging device 19 for uniformly charging the photosensitive drum 5, an exposure device 18 for imagewise exposing the photosensitive belt 15 with a laser beam, and developing devices 11, 12, 13, containing toners of black, yellow, magenta, and cyan, respectively. And an intermediate transfer belt 16 as an intermediate transfer member.

The intermediate transfer belt 16 includes a driving roller 10a
And the driven rollers 10b and 10c, and is rotated (moved) in the direction of arrow B by the rotational driving of the driving roller 10a. The intermediate transfer belt 16 has an endless belt shape and has no joint.

As shown in FIG. 7, on one side of the intermediate transfer belt 16, an intermediate transfer belt 16 is provided on the intermediate transfer belt 16 so as to sandwich the intermediate transfer belt 16 in a non-contact manner. An intermediate transfer body reference mark detection sensor 22 for detecting the body reference mark c is provided. The intermediate transfer member reference mark detection sensor 22 can detect the reference position of the intermediate transfer belt 16 by optically detecting the intermediate transfer member reference mark c.

A primary transfer roller 21 is provided on the back side of the intermediate transfer belt 16 in the primary transfer portion N1 where the photosensitive belt 15 and the intermediate transfer belt 16 abut. Further, a secondary transfer roller 23 is provided at a secondary transfer portion N2 for secondary-transferring the toner image primary-transferred onto the intermediate transfer belt 16 to a transfer material P so that the secondary transfer roller 23 can freely contact and separate from the intermediate transfer belt 16. Have been. The secondary transfer roller 23 is separated from the intermediate transfer belt 16 while the full-color toner image is transferred onto the intermediate transfer belt 16, and is used when transferring the full-color toner image on the intermediate transfer belt 16 to the transfer material P. 16
Abut.

Next, an image forming operation of the image forming apparatus will be described.

The photosensitive belt 15 is driven to rotate in the direction of arrow A, and the surface thereof is uniformly charged by a charger 19. Thereafter, image exposure is performed in accordance with image information input by an exposure device 18 to form an electrostatic latent image. I do.

Then, the first color black developing device 11
Is brought into contact with the photosensitive belt 15 so that toner is adhered to the electrostatic latent image on the photosensitive belt 15 and developed as a black toner image. At this time, the other developing units 12, 13, and 14 are separated from the photosensitive belt 15.

The black toner image is transferred to the photosensitive belt 1
Intermediate transfer belt 1 which rotates in the direction of arrow B while contacting the belt 6
In the primary transfer nip portion T1, primary transfer is performed by the primary transfer roller 21 to which a transfer bias is applied.

Thereafter, the developing units 12, 13, and 14 are similarly operated.
The yellow toner image of the second color, the magenta toner image of the third color, and the cyan toner image of the fourth color sequentially formed and carried on the photosensitive belt 15 by the
A full-color toner image is formed by superimposing and transferring the image on the image.

A transfer material P such as paper is fed one by one by a feed roller 25 in accordance with the formation of the full-color toner image on the intermediate transfer belt 16, and the registration roller 24 feeds the transfer material P on the intermediate transfer belt 16. The transfer material P is transported to the secondary transfer portion N2 in accordance with the leading end of the full-color toner image, and the full-color toner image is collectively secondarily transferred onto the transfer material P by the secondary transfer roller 23 to which a transfer bias is applied. You.

The transfer material P to which the full-color toner image has been transferred is conveyed between the fixing roller 17a and the pressure roller 17b of the fixing device 17, heated and pressed, and the full-color toner image is fixed on the surface and discharged. Is done.

Incidentally, the cycle of one rotation of the photosensitive belt 15 and the intermediate transfer belt 16 (the cycle of the photosensitive belt 15;
Although T1 and the cycle of the intermediate transfer belt 16; T2) are set to be equal, strictly speaking, there are strict tolerances and variations in the mechanical dimensions, and furthermore, the aging of the photosensitive belt 15, the intermediate transfer belt 16, the drive rollers 9a and 10a, and the like. As a result, T1 ≧ T2
Or, T1 ≦ T2.

The photosensitive belt 15 and the intermediate transfer belt 1
The sixth drive rollers 9a and 10a have a clutch mechanism (not shown), and have a configuration in which the drive to the photosensitive belt 15 and the intermediate transfer belt 16 can be turned ON / OFF.

Next, the relative positional relationship between the photosensitive belt 15 and the intermediate transfer belt 16 during the above-described image forming operation will be described.

As shown in FIGS. 8A and 8B, the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 is
The intermediate transfer member reference mark detection sensor 22 is formed after a predetermined time t0 elapses after the intermediate transfer member reference mark c on the intermediate transfer belt 16 is detected. The predetermined time t0 needs to have a constant value in order to accurately superpose the toner images of the respective colors on the intermediate transfer belt 16. 8A and 8B show a state at the time of continuous image formation. When T1 = T2, the photoconductor reference mark detection sensor 20 detects the photoconductor reference mark b on the photoconductor belt 15. After a lapse of a predetermined time t1, the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 is transferred to the intermediate transfer belt 1.
6 is transferred as a formed image (toner image) G2.

After a lapse of a predetermined time t0 from the detection of the intermediate transfer member reference mark c, the electrostatic latent image G1 formed on the photosensitive belt 15 is formed in a range avoiding the image prohibition region T including the joint a. There must be. When an image is formed in a range including the image prohibition region T, image deterioration due to the seam a occurs.

On the photosensitive belt 15, as shown in FIG. 8B, if it is assumed that a time t1 has elapsed after the photosensitive member reference mark detection sensor 20 detects the photosensitive member reference mark b,
The image formation start timing needs to satisfy tx1 <t1 <tx2. In other words, when t1 <tx1, the leading end of the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 enters the image inhibition area T, and when t1> tx2, the formation on the photosensitive belt 15 is performed. Since the rear end of the image (electrostatic latent image, toner image) G1 enters the image prohibition region T, there is a possibility of image deterioration. At this time, tx2 is determined by the size of the transfer material P on which an image is formed in the transport direction.

The intermediate transfer member reference mark detecting sensor 2
Assuming that the detection time of the intermediate transfer member reference mark c by t2 is tc and the detection time of the photosensitive member reference mark b by the photosensitive member reference mark detection sensor 20 is tb, t1 = tc + t0−tb.
Therefore, the time relationship between the photosensitive belt 15 and the intermediate transfer belt 16 must be set as in the following equation (1).

Tx1 <tc + t0−tb <tx2 (1) However, although the periods of the photosensitive belt 15 and the intermediate transfer belt 16 are substantially equal, the period of the photosensitive belt 15 is one cycle because of the period difference as described above. Is T1, and one cycle of the intermediate transfer belt 16 is T2, the relationship of T1 ≧ T2 or T1 ≦ T2 occurs.

Here, after N cycles of t1, t1 = t1 + N. (T2-T1) (2), and when T1 ≧ T2, t1 becomes small. It approaches the prohibited area T. On the other hand, when T1 ≦ T2, t1 increases, and the rear end of the image approaches the image prohibition region T.

Therefore, conventionally, when the image forming operation is repeated and the formed image approaches the image prohibition region, the drive of either the photosensitive belt 15 or the intermediate transfer belt 16 is interrupted for a predetermined time by the above-mentioned clutch mechanism. The image forming start position is adjusted so that the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 does not interfere with the image prohibition region T.

[0027]

As described above, in the prior art, when the image forming operation (electrostatic latent image, toner image) G1 approaches the image prohibition region T by repeating the image forming operation, the above-described clutch mechanism is used. Accordingly, it is necessary to temporarily stop the image forming operation by interrupting the drive of either the photosensitive belt 15 or the intermediate transfer belt 16 for a predetermined time.

At this time, since the image forming start position is adjusted, a mechanism for separating and contacting the photosensitive belt 15 and the intermediate transfer belt 16 in the primary transfer portion N1 is required, which increases the cost. Further, the photosensitive belt 15 and the intermediate transfer belt 16
When a mechanism for separating and contacting is not provided, the surface of the photosensitive belt 15 and the surface of the intermediate transfer belt 16 are deteriorated due to friction at the time of adjusting the image forming start position, and the life is shortened.

Therefore, according to the present invention, when the image formed on the photoconductor approaches the image prohibition area, the image formation start position is adjusted with an inexpensive configuration so that the image formed on the photoconductor does not enter the image prohibition area. It is an object of the present invention to provide an image forming apparatus having the above configuration.

[0030]

In order to achieve the above object, the present invention is directed to a rotatable image carrier on which a toner image is formed and a toner image formed on a primary transfer portion abutting on the image carrier. And a rotatable intermediate transfer member for performing a secondary transfer of the primary-transferred toner image to a transfer material at a secondary transfer portion. An image prohibition area set along a direction intersecting the direction, an image carrier reference mark provided on the image carrier and indicating a reference position of the image carrier, and a uniform interval in a circumferential direction on the intermediate transfer body. A plurality of intermediate transfer member reference marks indicating reference positions of the intermediate transfer member, an image carrier reference mark detecting means for detecting the image carrier reference mark and detecting a reference position of the image carrier; Detecting the intermediate transfer member reference mark to determine the reference position of the intermediate transfer member. An intermediate transfer member reference mark detecting means, a reference position information of the image carrier detected by the image carrier reference mark detecting means, and a reference position information of the intermediate transfer member detected by the intermediate transfer member reference mark detecting means. And control means for detecting a relative position between the image carrier and the intermediate transfer body based on the input information, wherein the control means detects the relative positions of the image carrier and the intermediate transfer body. Based on the relative position information, from the plurality of intermediate transfer body reference marks, a predetermined intermediate transfer body reference mark that is an image formation start timing at which the toner image is not formed in the image prohibited area is selected to form an image. It is characterized in that the start position is adjusted.

Further, the control means controls the next toner image formed on the image carrier at the time of continuous image formation based on the detected relative position information between the image carrier and the intermediate transfer member. If you determine that it will interfere with the prohibited area,
The present invention is characterized in that the toner image formed in the image forming area on the image carrier is changed to a predetermined intermediate transfer body reference mark which is an image forming start timing that does not interfere with the image prohibition area.

Further, the control means selects the intermediate transfer member reference mark during an initial rotation of the image bearing member when power is turned on.

Further, the control means selects the intermediate transfer member reference mark during a pre-rotation of the image carrier before an image forming operation.

Further, the control means selects the intermediate transfer member reference mark when the image carrier is rotated after the image forming operation.

Further, the invention is characterized in that the length of one circumference of the image carrier is substantially equal to the length of one circumference of the intermediate transfer body.

Further, the image carrier is a belt-shaped photosensitive member having a seam in a direction intersecting with the rotation direction, and the vicinity of the seam is the image prohibited area.

Further, the intermediate transfer member is an endless belt-shaped intermediate transfer belt.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 shows an image forming apparatus according to Embodiment 1 of the present invention (this image forming apparatus is an electrophotographic full-color image forming apparatus having a photosensitive belt and an intermediate transfer belt). FIG. 6 is a schematic configuration diagram showing the same members as those of the conventional image forming apparatus shown in FIG. Also in the image forming apparatus of the present embodiment, image formation is performed in the same manner as in the above-described conventional image forming apparatus. In the present embodiment, the description of the image forming operation is omitted.

In the present image forming apparatus, a photosensitive belt 15 is provided in a non-image area on one end side of the photosensitive belt 15 having the joint a.
Photoconductor reference mark b for detecting the reference position of
A plurality of (four in the present embodiment) for detecting the reference position of the intermediate transfer belt 16 is provided in a non-image area on one end side of the seamless endless belt-like intermediate transfer belt 16. , The intermediate transfer member reference marks c1, c2, c3,
c4 is formed uniformly in the circumferential direction (rotation direction). That is, the intermediate transfer belt 16 is formed so that the intermediate transfer belt reference marks c1, c2, c3, and c4 are circumferentially divided into four in the circumferential direction. The cycle T1 of the photosensitive belt 15 and the cycle T2 of the intermediate transfer belt 16 are substantially the same.

Detection information of the photoconductor reference mark b on the photosensitive belt 15 detected by the photoconductor reference mark detection sensor 20 and the intermediate transfer body reference mark on the intermediate transfer belt 16 detected by the intermediate transfer body reference mark detection sensor 22 The detection information of c1, c2, c3, and c4 is transmitted to the control device (CP
U) 26, and the control device (CPU) 26 detects the relative position between the photosensitive belt 15 and the intermediate transfer belt 16 based on the input detection information. Further, based on the detected relative position information between the photosensitive belt 15 and the intermediate transfer belt 16, the control device (CPU) 26 forms an image on the photosensitive belt 15 avoiding the image prohibition region T including the seam a. (Details will be described later).

Next, the relative positional relationship between the photosensitive belt 15 and the intermediate transfer belt 16 during continuous image formation in this embodiment will be described.

As shown in FIGS. 2A and 2B, the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 is
The intermediate transfer member reference mark detection sensor 22 detects four intermediate transfer member reference marks c1, c2, and c on the intermediate transfer belt 16.
3, is formed after a predetermined time t0 elapses after detecting c1 which is one of c4. The predetermined time t0 needs to have a constant value in order to accurately superpose the toner images of the respective colors on the intermediate transfer belt 16. 2A and 2B show a state at the time of continuous image formation, and when T1 = T2, the photoconductor reference mark detection sensor 20 detects the photoconductor reference mark b on the photoconductor 15 and After a lapse of a predetermined time t1, the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 is transferred onto the intermediate transfer belt 16 as a formed image (toner image) G2.

After a lapse of a predetermined time t0 from the detection of the intermediate transfer member reference mark c1, the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 avoids the image prohibited area T including the seam a. Must be formed in range. When an image is formed in a range including the image prohibition region T, image deterioration due to the seam a occurs.

After the photoconductor reference mark detection sensor 20 detects the photoconductor reference mark b on the photoconductor belt 15, t 1
Assuming that the time has elapsed, the image formation start timing needs to satisfy tx1 <t1 <tx2. That is, when t1 <tx1, the leading end of the formed image (electrostatic latent image, toner image) G1 enters the image prohibition region T, and t1> t
In the case of x2, the image rear end of the formed image (electrostatic latent image, toner image) G1 enters the image prohibition region T, so that the possibility of image deterioration occurs. At this time, tx2 is the transfer material P on which an image is to be formed.
In the transport direction.

The intermediate transfer member reference mark detecting sensor 2
2, the detection time of the intermediate transfer member reference mark c1 is tc
1. Assuming that the detection time of the photoconductor reference mark b by the photoconductor reference mark detection sensor 20 is tb, t1 is t1
= Tc1 + t0−tb, the time relationship between the photosensitive belt 15 and the intermediate transfer belt 16 must be set as in the following equation (3).

Tx1 <tc1 + t0−tb <tx2 (3) However, although the periods of the photosensitive belt 15 and the intermediate transfer belt 16 are substantially equal (T1 ≒ T2), there is a period difference as described above. Assuming that one cycle of the belt 15 is T1 and one cycle of the intermediate transfer belt 16 is T2, a relationship of T1 ≧ T2 or T1 ≦ T2 occurs.

Here, after N cycles of t1, t1 = t1 + N ・ (T2-T1) (4), and when T1 ≧ T2, t1 becomes small. Latent image, toner image)
The image tip of G1 approaches the image prohibition region T. On the other hand, T1
In the case of ≦ T2, t1 increases, and the trailing edge of the formed image (electrostatic latent image, toner image) G1 approaches the image prohibition region T.

Hereinafter, in the present embodiment, when T1 ≧ T2, that is, when the image tip of the formed image (electrostatic latent image, toner image) G1 approaches the image inhibition area T by repeating the image forming operation, A control operation for forming an image while avoiding the image prohibition region T at the tip will be described.

As shown in FIGS. 3A and 3B, the leading end of the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 approaches the image prohibition region T, and t1 ≦ tx1. In this case, if the image is continuously formed as it is, the leading end of the formed image (electrostatic latent image, toner image) G1 interferes with the image prohibition region T, and the image is deteriorated.

The controller 26 forms the image based on the detection information of the photoconductor reference mark b from the photoconductor reference mark detection sensor 20 and the detection information of the intermediate transfer body reference mark c1 from the intermediate transfer body reference mark detection sensor 22. (Electrostatic latent image, toner image) When it is determined that the leading edge of the image of G1 is approaching the image prohibition region T, the intermediate transfer member reference mark selected from the intermediate transfer member reference mark detection sensor 22 in place of the intermediate transfer member reference mark c1. The detection information of the mark c2 is input.

Thus, the control device 26 controls the image forming operation on the intermediate transfer belt 16 by delaying the image forming start timing on the photosensitive belt 15 by the time ts (changing from t1 to t1 '). Therefore, t1 'is t1' = tx1 + ts.

Further, since the image prohibition region T is set with a margin as described above, no problem occurs in the image quality at the leading end of the image immediately after t1 ≦ tx1 is detected.

Here, the circumferential length of the intermediate transfer belt 16 is L,
In the transfer material P on which the image forming apparatus can form an image, M is the length of the maximum size in the transport direction, K is the length of the image prohibited area T on the photosensitive belt 15 in the transport direction, and the intermediate transfer member reference of the intermediate transfer belt 16 Assuming that the number of marks is n, the configuration of the image forming apparatus needs to satisfy the following expression (5).

(L−K) / n · (n−1)> M (5) If this condition is not satisfied, an image is formed on the photosensitive belt 15 on the transfer material P having the maximum size in the transport direction. When the start timing is changed to t1 ', the formed image (the electrostatic latent image,
The rear end of the image of the toner image G1 enters the image prohibition region T.

However, since the peripheral speeds of the photosensitive belt 15 and the intermediate transfer belt 16 may have a difference in speed, in practice, it is better to take a little margin with respect to the condition of the above equation (5). Although it is preferable, if the margin is too large, the photosensitive belt 15 and the intermediate transfer belt 16 become long and the cost becomes high. Therefore, it is necessary to set an appropriate length while satisfying the above conditions.

As described above, in the present embodiment, when the image tip of the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 approaches the image prohibition region T during continuous image formation, The intermediate transfer member reference mark, which is the image formation start timing at which the formed image (electrostatic latent image, toner image) G1 does not enter the image prohibition region T, is changed from the intermediate transfer member reference mark c1 to c2 to change the image formation start position. By performing the adjustment, the image forming start position can be easily adjusted with an inexpensive configuration without interrupting the drive of either the photosensitive belt 15 or the intermediate transfer belt 16 for a predetermined time by the clutch mechanism as in the related art. .

Since there is no deterioration due to friction between the photosensitive belt 15 and the intermediate transfer belt 16 at the time of adjusting the image forming start position, the photosensitive belt 15 and the intermediate transfer belt 1 are not deteriorated.
6 can be extended.

As described above, the image forming start timing is adjusted by changing the intermediate transfer member reference mark, which is the image formation start timing, from the intermediate transfer member reference mark c1 to c2, and then repeating the image forming operation. When the image tip of the formed image (electrostatic latent image, toner image) G1 approaches the image prohibition region T, the next c3 is selected from the intermediate transfer member reference mark c2, and further, c3 to c4 is selected.
At the time of continuous image formation, it is possible to prevent the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 from interfering with the image prohibition region T, and to form a good image.

<Second Embodiment> In the first embodiment, T1 ≧
Although the case of T2 has been described, in the present embodiment, when T1 ≦ T2, that is, by repeating the image forming operation, the trailing end of the formed image (electrostatic latent image, toner image) G1 becomes the image prohibition region T A control operation for causing the image rear end of the formed image (electrostatic latent image, toner image) G1 to avoid the image prohibition region T and perform image formation in the case of approaching will be described. Note that, also in the present embodiment, the image forming apparatus of the first embodiment shown in FIG. 1 is used, and redundant description will be omitted.

As shown in FIGS. 4A and 4B, the trailing end of the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 approaches the image prohibition region T, and t1 ≧ tx2. In such a case, if the image is continuously formed as it is, the rear end of the formed image (electrostatic latent image, toner image) G1 interferes with the image prohibition region T, and the image is deteriorated.

The controller 26 forms the image based on the detection information of the photoconductor reference mark b from the photoconductor reference mark detection sensor 20 and the detection information of the intermediate transfer body reference mark c1 from the intermediate transfer body reference mark detection sensor 22. (Electrostatic latent image, toner image) When it is determined that the rear end of the image of G1 is approaching the image prohibition region T, the intermediate transfer member selected from the intermediate transfer member reference mark detection sensor 22 in place of the intermediate transfer member reference mark c1. The detection information of the reference mark c4 is input.

Thus, the control device 26 controls the image forming operation to be performed by delaying the image forming start timing on the photosensitive belt 15 with respect to the intermediate transfer belt 16 by the time ts (change from t1 to t1 '). Therefore, t1 'is t1' = tx1 + ts.

Further, as described above, since the image prohibition region T is set with a margin, no problem occurs in the image quality at the rear end of the image immediately after t1 ≧ tx2 is detected.

Also, in the present embodiment, it is necessary to satisfy the above expression (5). If the above expression (5) is not satisfied, the transfer material P having the maximum size in the transport direction is
When the image formation start timing on the photosensitive belt 15 is changed to t1 ', the leading end of the formed image (electrostatic latent image, toner image) G1 enters the image prohibited area T.

However, since the peripheral speed of the photosensitive belt 15 and the intermediate transfer belt 16 may have a speed difference, it is actually better to take a little margin with respect to the condition of the above equation (5). Although it is preferable, if the margin is too large, the photosensitive belt 15 and the intermediate transfer belt 16 become long and the cost becomes high. Therefore, it is necessary to set an appropriate length while satisfying the above conditions.

As described above, also in the present embodiment, when a continuous image is formed, the rear end of the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 approaches the image prohibited area T. Changes the intermediate transfer member reference mark, which is the image formation start timing at which the formed image (electrostatic latent image, toner image) G1 does not enter the image prohibition region T, from the intermediate transfer member reference mark c1 to c4, and starts image formation. By adjusting the position, the photosensitive belt 15 can be moved by the clutch mechanism as in the prior art.
Alternatively, it is possible to easily adjust the image formation start position with an inexpensive configuration without interrupting the driving of either of the intermediate transfer belts 16 for a predetermined time.

Since there is no deterioration due to friction between the photosensitive belt 15 and the intermediate transfer belt 16 at the time of adjusting the image forming start position, the photosensitive belt 15 and the intermediate transfer belt 16 are not deteriorated.
Life can be extended.

As described above, the image forming start position is adjusted by changing the intermediate transfer member reference mark, which is the image formation start timing, from the intermediate transfer member reference mark c1 to c4, and the image forming operation is further repeated. When the trailing end of the formed image (electrostatic latent image, toner image) G1 approaches the image prohibition region T, the next c3 is selected from the intermediate transfer member reference mark c4, and further, the c2 is selected from c3.
At the time of continuous image formation, it is possible to prevent the formed image (electrostatic latent image, toner image) G1 on the photosensitive belt 15 from interfering with the image prohibition region T, and to form a good image.

<Embodiment 3> Embodiment 1 described above,
In 2, the control operation of the image forming start position of the present invention at the time of continuous image formation has been described.
The control operation of the present invention will be described. Note that, also in the present embodiment, the image forming apparatus of the first embodiment shown in FIG. 1 is used, and redundant description will be omitted.

(1) When the power is turned on When the image forming apparatus is turned on, when the photosensitive belt 15 is initially rotated, the control device 26 determines from the detection results of the photoconductor reference mark detection sensor 20 and the intermediate transfer body reference mark detection sensor 22. Since the time (= tc−tb) from the detection of the photoconductor reference mark b to the detection of each of the intermediate transfer body reference marks c1, c2, c3, and c4 is detected, the intermediate time that satisfies the following expression (6) is obtained. Select the transfer body reference mark.

Tx1 <tc + t0−tb <tx2 (6) When there are a plurality of intermediate transfer body reference marks that satisfy the condition of the expression (6), they are selected under the following conditions.

When T1 ≧ T2, (T1: photosensitive belt 1
5, one cycle of T2, one cycle of the intermediate transfer belt 16), and the time from detection of the photoconductor reference mark b to detection of each of the intermediate transfer body reference marks c1, c2, c3, c4 (= tc).
The image forming start position is adjusted by selecting the intermediate transfer member reference mark having the largest -tb).

When T1 ≦ T2, (T1: photosensitive belt 1
5, one cycle of T2, one cycle of the intermediate transfer belt 16), and the time from detection of the photoconductor reference mark b to detection of each of the intermediate transfer body reference marks c1, c2, c3, c4 (= tc).
-Tb) selects the smallest reference mark of the intermediate transfer member and adjusts the image formation start position.

(2) At the time of pre-rotation At the time of pre-rotation before the image forming operation, the control device 26 controls the intermediate transfer member reference marks c1, c2, c3, and c4 selected from the detection of the photosensitive member reference mark b up to that point. The time until detection (= tc−tb) is detected, and the equation (6)
Is selected.

When the above expression (6) is satisfied, the image forming operation is started as it is. When the above expression (6) is not satisfied, there are a plurality of intermediate transfer member reference marks which satisfy the above expression (6). In this case, select according to the following conditions.

When T1 ≧ T2, (T1: photosensitive belt 1
5, one cycle of T5, one cycle of the intermediate transfer belt), and the time from detection of the photoconductor reference mark b to detection of each of the intermediate transfer body reference marks c1, c2, c3, and c4 (= tc−t).
b) The intermediate transfer member reference mark having the largest value is selected, and the image formation start position is adjusted.

When T1 ≦ T2, (T1: photosensitive belt 1
5, one cycle of T2, one cycle of the intermediate transfer belt 16), and the time from detection of the photoconductor reference mark b to detection of each of the intermediate transfer body reference marks c1, c2, c3, c4 (= tc).
-Tb) selects the smallest reference mark of the intermediate transfer member and adjusts the image formation start position.

(3) Post-rotation At the time of post-rotation, the same control operation as at the time of pre-rotation described above can be performed.

As described above, even in cases other than the continuous image formation (the initial rotation, the pre-rotation, and the post-rotation of the photosensitive belt 15 when the power is turned on), the image formation start timing at which the toner image is not formed in the image prohibited area By adjusting the image forming position by selecting a predetermined intermediate transfer member reference mark as described above, the drive of either the photosensitive belt 15 or the intermediate transfer belt 16 is not interrupted for a predetermined time by the clutch mechanism as in the related art. Adjustment of the image forming start position can be easily performed at low cost.

In each of the above-described embodiments, the four intermediate transfer member reference marks c 1 and c
Although 2, c3 and c4 are formed at equal intervals, the present invention can be similarly applied to a case where the number of intermediate transfer member reference marks is other than four.

[0082]

As described above, according to the present invention,
By selecting a predetermined intermediate transfer member reference mark that is an image formation start timing at which no toner image is formed in the image prohibition area from among the plurality of intermediate transfer member reference marks, and adjusting the image formation start position, as in the related art. In addition, the adjustment of the image forming start position can be easily performed with an inexpensive configuration without interrupting the drive of either the photosensitive member or the intermediate transfer member by the clutch mechanism for a predetermined time.

Since there is no deterioration due to friction between the photosensitive member and the intermediate transfer member at the time of adjusting the image forming start position,
The life of the photosensitive member and the intermediate transfer member can be extended.

[Brief description of the drawings]

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

FIGS. 2A and 2B are diagrams illustrating a relative positional relationship between a photosensitive belt and an intermediate transfer belt according to the first embodiment.

FIGS. 3A and 3B show an image in which the image tip of a formed image (electrostatic latent image, toner image) G1 on the photosensitive belt according to the first embodiment avoids an image prohibited area T on the photosensitive belt. The figure which showed the control operation | movement which performs formation.

FIGS. 4 (a) and 4 (b) show a state in which an image rear end of a formed image (electrostatic latent image, toner image) G1 on the photosensitive belt according to the second embodiment avoids an image prohibited area T on the photosensitive belt. FIG. 4 is a diagram illustrating a control operation for performing image formation.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus in a conventional example.

FIG. 6 is a diagram illustrating an image prohibition area and a photoconductor reference mark on a photoconductor belt of the image forming apparatus.

FIG. 7 is a diagram illustrating an intermediate transfer member reference mark on an intermediate transfer belt of the image forming apparatus.

FIGS. 8A and 8B are diagrams showing a relative positional relationship between a photosensitive belt and an intermediate transfer belt in a conventional example.

[Explanation of symbols]

11, 12, 13, 14 Developing device 15 Photosensitive belt (image carrier) 16 Intermediate transfer belt (intermediate transfer member) 17 Fixing device 18 Exposure device 19 Charging device 20 Photoconductor reference mark detection sensor (Image carrier reference mark detecting means) 22) Intermediate transfer body reference mark detection sensor (intermediate transfer body reference mark detection means) 26 Controller (control means) a seam b Photoconductor reference mark (image carrier reference mark) c1, c2, c3, c4 Intermediate transfer body reference mark

Claims (8)

[Claims] A first transfer unit that contacts a rotatable image carrier on which a toner image is formed, and a primary transfer unit that contacts the image carrier; An image forming apparatus including a rotatable intermediate transfer body that performs secondary transfer to a transfer material in a secondary transfer unit, wherein an image prohibition area set along a direction that intersects a rotation direction of the image carrier; An image carrier reference mark provided on the image carrier and indicating a reference position of the image carrier; and an intermediate transfer indicating a plurality of reference positions of the intermediate transfer member provided at equal intervals in a circumferential direction on the intermediate transfer member. Body reference mark; image carrier reference mark detecting means for detecting the image carrier reference mark to detect a reference position of the image carrier; and detecting the intermediate transfer body reference mark to detect the reference of the intermediate transfer body. An intermediate transfer body reference mark detecting means for detecting a position, and the image The reference position information of the image carrier detected by the carrier reference mark detecting means and the reference position information of the intermediate transfer body detected by the intermediate transfer body reference mark detecting means are input, and based on these input information, A controller configured to detect a relative position between the image carrier and the intermediate transfer member, wherein the controller controls the plurality of intermediate transfer members based on detected relative position information between the image carrier and the intermediate transfer member. An image forming start position that is adjusted by selecting a predetermined intermediate transfer body reference mark that is an image forming start timing at which the toner image is not formed in the image prohibited area from among the reference marks. apparatus. 2. The image forming apparatus according to claim 1, wherein the control unit is configured to detect the next toner image formed on the image carrier during continuous image formation based on the detected relative position information between the image carrier and the intermediate transfer body. If it is determined that the toner image interferes with the prohibited area, the toner image formed on the image forming area on the image carrier is changed to the predetermined intermediate transfer body reference mark that is an image forming start timing that does not interfere with the image prohibited area. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 1, wherein the control unit selects the intermediate transfer member reference mark during an initial rotation of the image carrier when power is turned on. 4. The image forming apparatus according to claim 1, wherein the control unit selects the intermediate transfer member reference mark during a pre-rotation of the image carrier before an image forming operation. 5. The image forming apparatus according to claim 1, wherein the control unit selects the intermediate transfer member reference mark when the image carrier is rotated after the image forming operation. 6. The image forming apparatus according to claim 1, wherein a length of one circumference of the image carrier is substantially equal to a length of one circumference of the intermediate transfer body. 7. The image bearing member is a belt-shaped photosensitive member having a seam in a direction intersecting a rotation direction, and the vicinity of the seam is the image prohibited area. 7. The image forming apparatus according to 5 or 6. 8. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an endless belt-shaped intermediate transfer belt.