JPH082735A - Image forming device - Google Patents

Abstract

PURPOSE:To decrease a number of clutch means, as small as possible, set up in an image forming device main unit. CONSTITUTION:Paired conveying rollers 14, 16, 18, 20 for a relay, set up in the halfway of conveying paths 13', 15, 17, 19 between each paired separating roller 6, 8, 10, 12 and paired register roller 21, are driven in such a manner that the rollers 14, 16 are driven by a drive mechanism 28 and the rollers 18, 20 are driven by a drive mechanism 29. The drive mechanisms 28, 29 comprise an electromagnetic clutch 31 set up in a roller shaft end of drive rollers 16A, 20A, gear 28 mounted on a roller shaft of the drive rollers 16A, 20A and a timing belt 40 wound to a gear 39 mounted on a roller shaft of drive rollers 14A, 18A. Drive power of a main motor is transmitted to the electromagnetic clutch 31, and when this clutch is turned on, two sets of the conveying rollers 14, 16 or 18, 20 are simultaneously driven.

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 and a facsimile.

[0002]

2. Description of the Related Art FIG. 4 shows the overall structure of a conventional image forming apparatus (copier).

Here, the flow of the sheet material in the image forming apparatus main body 100 will be described.

In this image forming apparatus, two sheet feeding cassettes (front loading cassettes) 101 and 102 which store sheet materials of different sizes are installed in the image forming apparatus main body 100. For example, B5 size sheet material S1 is stored in the upper paper feed cassette 101, and A4 size sheet material S2 is stored in the lower paper feed cassette 102. .

When the B5 size sheet material S1 is selected, the uppermost sheet material S1 in the paper feed cassette 101 is fed by the paper feed roller 103, and the separation roller pair 10 is fed.
The registration roller pair 109 is separated one by one by 4
Sent to.

When the A4 size sheet material S2 is selected, the uppermost sheet material S2 in the paper feed cassette 102 is fed by the paper feed roller 105, and the separation roller pair 10 is fed.
The registration roller pair 109 is separated one by one by 6
Sent to.

In the case of this image forming apparatus, the paper feed cassette 10
Since the B5 size sheet material S1 fed from 1 reaches the registration roller pair 109, the conveyance distance is long.
A relay transport roller pair 107 is installed in the middle of the transport path (downstream of the separation roller pair 104).

Further, since the A4 size sheet material S2 fed from the paper feed cassette 102 reaches the registration roller pair 109 for a long transportation distance, it is relayed in the middle of the transportation path (downstream of the separation roller pair 106). A conveyance roller pair 108 is installed. The sheet material S2 of A4 size is also relayed by the pair of transport rollers 107.

When a B5 size sheet material S1 is fed from the paper feed cassette 101, the pair of conveyance rollers 107 for relaying the conveyance of the B5 size sheet material S1 corrects the skewed state of the sheet material S1. The sheet material S1 is rotated and sent to the registration roller pair 109.

When an A4 size sheet material S2 is fed from the paper feed cassette 102, a pair of conveying rollers 108 for relaying the conveyance of the A4 size sheet material S2 corrects the skewed state of the sheet material S2. Then, the sheet material S2 is rotated and sent to the registration roller pair 109.

The conveying roller pairs 107 and 108 are rotationally driven by the driving force transmitted from the same driving source (for example, a main motor or the like). In this case, each of the conveying roller pairs 107 and 108 is individually provided with unillustrated clutch means (electromagnetic clutch, spring clutch, etc.) (1) and (2) for turning on and off the driving force from the driving source. There is.

When a sheet material detection sensor (photo sensor) 110 installed immediately upstream of the conveying roller pair 107 detects the leading edge of the B5 size sheet material S1 fed from the paper feed cassette 101, a predetermined time elapses. Then, the clutch means (1) is turned on and the conveying roller pair 107 is rotated. Between the detection of the leading edge of the sheet material S1 and the lapse of a predetermined time, the leading edge of the sheet material S1 abuts on the nip of the transport roller pair 107 in which rotation is stopped, and a predetermined loop is formed, whereby the skew of the sheet material S1 is formed. The line condition is corrected.

When the sheet material detection sensor 111 installed immediately upstream of the conveying roller pair 108 detects the leading edge of the A4 size sheet material S2 fed from the paper feed cassette 102, the clutch means ( When 1) and (2) are turned on, the conveying roller pair 107 and 108 are rotated. Between the detection of the leading end of the sheet material S2 and the elapse of a predetermined time, the leading end of the sheet material S2 is in a rotation stop state.
The skewed state of the sheet material S2 is corrected by hitting the nip of 08 and forming a predetermined loop.

The sheet material S (S) fed from the paper feed cassette 101 or 102 to reach the registration roller pair 109.
1 or S2) is the registration roller pair 109 whose rotation is stopped.
A predetermined loop is formed by hitting the nip of No. 1 to correct the skewed state immediately before image formation.

After that, the sheet material S is moved between the photosensitive drum 112 and the transfer roller 113 by a pair of registration rollers 109 which start rotating in synchronization with the toner image on the photosensitive drum 112 which is rotating clockwise. The toner image on the photosensitive drum 112 is transferred to the sheet surface by the transfer roller 113.

While the registration roller pair 109 is conveying the sheet material S, in order to reduce the driving load of the registration roller pair 109 and stabilize the conveyance of the sheet material S,
The conveying roller pairs 107 and 108 continue to rotate until the trailing edge of the sheet material S leaves the nip.

Then, the sheet material S after the transfer of the toner image at the transfer portion is sent to the fixing device (fixing roller pair) 115 by the conveying belt 114, and the fixing device 115 fixes the toner image.

The sheet material S after the fixing process of the toner image is completed.
In the case of single-sided copying, the paper is discharged onto the paper discharge tray 117 outside the apparatus by the paper discharge roller pair 116. In the case of double-sided copying or multiplex copying, the sheets are temporarily stacked on the intermediate tray 119 through the re-feeding path 118.

The sheet materials S stacked on the intermediate tray 119 are sequentially fed out from the uppermost sheet material by the re-feeding roller 120, separated one by one by the separation roller pair 121, and sent to the registration roller pair 109. .

At this time, since the sheet material S re-fed from the intermediate tray 119 reaches the registration roller pair 109 by a long transportation distance, the sheet material S is conveyed by the transportation roller pair 122, 108, 107 in the middle of the transportation path. The transport of S is relayed.

The transport roller pair 122 includes the transport roller pair 1
The driving force is transmitted from the same driving source as 07 and 108. The conveying roller pair 122 is provided with clutch means (3) (not shown) for turning on and off the driving force from the driving source.

When the sheet material detection sensor 123 installed immediately upstream of the conveying roller pair 122 detects the leading edge of the sheet material S fed from the intermediate tray 119, after a predetermined time elapses, the clutch means (1), ( 2) and (3) are turned on, and the conveying roller pairs 107, 108, 122 rotate. Between the detection of the leading edge of the sheet material S and the elapse of a predetermined time, the leading edge of the sheet material S is not rotating and the pair of conveying rollers 12
The skewed state of the sheet material S is corrected by hitting the nip 2 and forming a predetermined loop.

In this image forming apparatus, the electrostatic latent image of the document placed on the document table 124 is rotated clockwise by the latent image forming means 125 including an optical system on the photosensitive drum 112. Are sequentially formed. Then, the electrostatic latent image formed on the photosensitive drum 112 is visualized (toner image) by the developing device 126.

[0024]

However, like the image forming apparatus of the above-mentioned conventional example, the pair of transfer rollers for relay 107,
When the method of individually controlling the driving of 108 and 122 via the clutch means (1), (2), and (3) provided respectively, the number of relay roller pairs is equal to the number of relay roller pairs. Since the clutch means is required, particularly in the case of an image forming apparatus using a large number of conveying roller pairs, it has been a bottleneck in promoting downsizing of the image forming apparatus main body and cost reduction. Since the clutch means for turning on and off the drive of the relay conveyance roller pair needs to sufficiently satisfy the conveyance torque and have good responsiveness, the clutch means becomes large and expensive.

The clutch means (1), (2),
In the case where the electromagnetic clutch is used in (3), if the electric wiring process (routing) is not carefully done, a bundle break or the like may occur, and for this reason, an image forming apparatus using a large number of electromagnetic clutches. However, there is a problem in that reliability is impaired because the frequency of occurrence of bundle breakage and the like naturally increases.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming apparatus in which the number of clutch means installed in the main body of the image forming apparatus can be reduced as much as possible. And

[0027]

The present invention provides a drive source (3
0) is the same and is related to an image forming apparatus provided with a plurality of sheet material conveying means (14, 16) which are simultaneously driven to rotate.

In the present invention, in order to achieve the above object, the driving force of the driving source (30) is passed through one clutch means (31) to the sheet material conveying means (14, 1).
It is characterized in that it is transmitted to 6).

[0029]

According to the image forming apparatus of the present invention having the above-mentioned structure, by turning on and off one clutch means (31), a plurality of sheet material conveying means (14, 1) are simultaneously operated.
The drive of 6) can be controlled.

Therefore, the number of clutch means installed in the main body of the image forming apparatus is reduced as much as possible as compared with the case where the drive of each sheet material conveying means is individually controlled through the clutch means provided for each. can do.

The reference numerals in parentheses refer to the drawings and do not limit the structure of the present invention.

[0032]

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

FIG. 1 shows the structure of the main part of the image forming apparatus (copying machine) of the present invention.

In this image forming apparatus, four sheet feeding cassettes (front loading cassettes) 1 to 4 containing sheet materials of different sizes are installed in the image forming apparatus main body (not shown). For example, a sheet material S1 of B5 size is stored in the sheet feeding cassette 1 installed in the uppermost stage (first stage), and an A4 size sheet is stored in the sheet feeding cassette 2 installed in the second stage. Sheet material S2 of B4 size is stored in the sheet feeding cassette 3 installed in the third stage,
A3 size sheet material S4 is stored in the paper feed cassette 4 installed in the fourth stage.

When the B5 size sheet material S1 is selected, the uppermost sheet material S1 in the paper feed cassette 1 is fed by the paper feed roller 5 and is separated by the separation roller pair 6 to 1
The sheets are separated one by one and sent to the registration roller pair 21.

When the A4 size sheet material S2 is selected, the uppermost sheet material S2 in the paper feed cassette 2 is fed by the paper feed roller 7 and is separated by the separation roller pair 8 to 1
The sheets are separated one by one and sent to the registration roller pair 21.

When the B4 size sheet material S3 is selected, the uppermost sheet material S3 in the paper feed cassette 3 is fed by the paper feed roller 9 and separated one by one by the separation roller pair 10 to form the registration roller pair. Sent to 21.

When the A3 size sheet material S4 is selected, the uppermost sheet material S4 in the sheet feeding cassette 4 is fed out by the sheet feeding roller 11 and separated one by one by the separating roller pair 12 to form the registration roller pair. Sent to 21.

In the case of the present image forming apparatus, since the B5 size sheet material S1 fed from the sheet feeding cassette 1 reaches the registration roller pair 21 by a long transportation distance, it is relayed in the middle of the transportation path 13. A pair of conveying rollers (sheet material conveying means) 14 is installed.

A4 fed from the paper feed cassette 2
Since the conveyance distance until the size sheet material S2 reaches the registration roller pair 21 is long, the conveyance roller pair (sheet material conveyance means) 16 for relay is installed in the middle of the conveyance path 15. A4 size sheet material S2 has a pair of transport rollers 14
Also relayed by.

Further, B4 fed from the paper feed cassette 3
Since the conveying distance until the sheet material S3 of the size reaches the registration roller pair 21 is long, a conveying roller pair (sheet material conveying means) 18 for relay is installed in the middle of the conveying path 17. B4 size sheet material S3 is a pair of transport rollers
It is also relayed by 6,14.

A3 fed from the paper feed cassette 4
Since the conveyance distance until the size sheet material S4 reaches the registration roller pair 21 is long, a conveyance roller pair (sheet material conveyance means) 20 for relay is installed in the middle of the conveyance path 19. A3 size sheet material S4 is a pair of transport rollers
It is also relayed by 8, 16, and 14.

When a B5 size sheet material S1 is fed from the paper feed cassette 1, this B5 size sheet material S1
The conveyance roller pair 14 that relays the conveyance of the sheet is corrected after the skewed state of the sheet material S1 and then rotated to feed the sheet material S1 to the registration roller pair 21.

Further, when the A4 size sheet material S2 is fed from the paper feed cassette 2, the conveyance roller pair 16 which relays the conveyance of the A4 size sheet material S2 corrects the skewed state of the sheet material S2. After that, the sheet material S2 is rotated and sent to the registration roller pair 21.

When a B4 size sheet material S3 is fed from the paper feed cassette 3, the pair of transport rollers 18 for relaying the transportation of the B4 size sheet material S3 corrects the skewed state of the sheet material S3. After that, the sheet material S3 is rotated to feed the sheet material S3 to the registration roller pair 21.

When the sheet material S4 of A3 size is fed from the paper feed cassette 4, the pair of conveying rollers 20 for relaying the conveyance of the sheet material S4 of A3 size corrects the skewed state of the sheet material S4. After that, the sheet material S4 is rotated and sent to the registration roller pair 21.

Sheet material detecting sensors (photosensors) 22 to 26 for detecting the leading edge of the sheet material S are installed immediately upstream of the conveying roller pairs 14, 16, 18, 20 and the registration roller pair 21, respectively. There is. The sheet material detection sensors 22 to 26 are shielded by the detection lever 27 and output a detection signal when the detection lever 27 rotatable about the support shaft 27A rotates counterclockwise due to the collision of the tip of the sheet material.

The conveying roller pairs 14, 16, 18, 20 are rotationally driven by the driving force transmitted from a main motor (not shown) in the main body of the image forming apparatus. Here, the two transport roller pairs 14, 16 on the downstream side are integrally driven by the drive mechanism 28, and the two transport roller pairs 18, 18 on the upstream side are driven.
20 is integrally driven by a drive mechanism 29.
The drive mechanisms 28 and 29 have the same structure.

In FIG. 2, two pairs of conveying rollers 14 and 16 are shown.
Drive mechanism 28 for integrally driving (or 18, 20)
(Or 29) shows the detailed configuration.

At the shaft end of the drive roller 16A (or 20A) of the conveying roller pair 16 (or 20), the main motor 30
An electromagnetic clutch (clutch means) 31 for turning on / off the driving force from the vehicle is installed.

A final gear 33 of a power transmission mechanism for transmitting the driving force of the main motor 30 meshes with a clutch gear 32 of the electromagnetic clutch 31, and a motor shaft gear 34 mounted on the output shaft 30 of the main motor 30 engages with the final gear 33. Is engaged with the first gear 35 of the transmission mechanism.

On the roller shaft 36 of the driving roller 16A (or 20A) of the conveying roller pair 16 (or 20) and on the driving roller 14A (or 18) of the conveying roller pair 14 (or 18).
Gears 38 and 39 are mounted on the roller shaft 37 of A), and a timing belt (power transmission means) 40 is wound around the gears 38 and 39. The gear 39
Are mounted on the roller shaft 37 via a one-way rotation clutch 41.

When the main motor 30 rotates in a predetermined direction, its driving force is transmitted via the final gear 33 to the clutch gear 3.
2. When the electromagnetic clutch 31 is in the off state, the clutch gear 32 is rotating in the free state.

When the electromagnetic clutch 31 is turned on in this state, the rotation of the clutch gear 32 causes the driving roller 16A (or 20A) of the conveying roller pair 16 (or 20) and the driving roller 14A (of the conveying roller pair 14 (or 18)). Or 18
A) and each one. As a result, the drive rollers 16A (or 20A) and 14A (or 18A) are rotationally driven in the sheet material conveying direction (counterclockwise), and the driven rollers 16B (or 20B) and 14B (or 18B) are driven to rotate. .

Turning on / off the electromagnetic clutch 31 controls the overall operation of the image forming apparatus by a CPU (control means) 4
Controlled by two.

When the B5 size sheet material S1 is fed from the paper feeding cassette 1, the pair of conveying rollers 14 is stopped rotating. That is, the electromagnetic clutch 31 of the drive mechanism 28 is C
It is turned off by the PU 42.

When the sheet material detection sensor 22 detects the leading edge of the sheet material S1, the CPU 42 turns on the electromagnetic clutch 31 after a predetermined time to drive the pair of conveying rollers 14 and 16. Between the detection of the leading edge of the sheet material S1 and the lapse of a predetermined time, the leading edge of the sheet material S1 hits the nip of the pair of transport rollers 14 whose rotation is stopped, and a predetermined loop is formed, whereby the skew of the sheet material S1 The line condition is corrected.

When the A4 size sheet material S2 is fed from the paper feed cassette 2, the pair of feed rollers 16 is stopped rotating. That is, the electromagnetic clutch 31 of the drive mechanism 28 is C
It is turned off by the PU 42.

When the sheet material detection sensor 23 detects the leading edge of the sheet material S2, the CPU 42 turns on the electromagnetic clutch 31 after a predetermined time to drive the conveying roller pairs 16 and 14. Between the detection of the leading edge of the sheet material S2 and the elapse of a predetermined time, the leading edge of the sheet material S2 hits the nip of the pair of transport rollers 16 whose rotation is stopped, and a predetermined loop is formed so that the sheet material S2 is inclined. The line condition is corrected.

FIG. 3 shows a state in which the sheet material S2 of A4 size is continuously fed from the paper feed cassette 2.

The sheet material S2-2 fed later is in a state in which the leading edge of the sheet material S2-2 abuts on the nip of the conveying roller pair 16 whose rotation is stopped and the loop 43 for correcting skew is formed.

On the other hand, the sheet material S2-1 previously fed
Has been sent to the transfer portion between the photosensitive drum 44 and the transfer roller pair 45 by the registration roller pair 21 that has already started to rotate.

At this time, the rear portion of the sheet material S2-1 is often sandwiched by the nip of the conveying roller pair 14 which is integrally stopped with the conveying roller pair 16, but the conveying roller pair 14 has a nip. The drive roller 14A is a one-way rotation clutch 41.
Is released and is in a free state, so that the sheet material S2-1 is carried by the registration roller pair 21. Therefore, even if the rear portion of the sheet material S2-1 is sandwiched by the nip of the transport roller pair 14, the driving load of the registration roller pair 21 increases and the transport stability of the sheet material S2-1 is impaired. There is no.

The electromagnetic clutch 31 of the drive mechanism 29 in the CPU 42 when the B4 size sheet material S3 is fed from the paper feed cassette 3 and when the A3 size sheet material S4 is fed from the paper feed cassette 4. The on / off control is performed in the same manner as the on / off control of the electromagnetic clutch 31 of the drive mechanism 28.

However, the electromagnetic clutch 31 of the drive mechanism 29
When turning on, the electromagnetic clutch 31 of the drive mechanism 28 is simultaneously
Also turn on.

Further, when the B4 size sheet material S3 is continuously fed from the paper feeding cassette 3,
When the sheet material S4 of A3 size is continuously fed from the sheet material, the rear portion of the previously fed sheet material S3-1, S4-1 (not shown) is sandwiched by the nip of the transport roller pair 16. , The registration roller pair 21 is the sheet material S3-1, S
Simultaneously with the start of the conveyance of 4-1, the electromagnetic clutch 31 of the drive mechanism 28 is turned on, and the conveying roller pairs 14 and 16 are rotationally driven until the trailing edge of the sheet material passes through the nip of the conveying roller pair 16.

In this embodiment, the driving force transmitted from the main motor 30 is turned on / off by the electromagnetic clutch 31.
Although it is turned off, it may be turned on / off by a spring clutch or the like.

Further, in the present embodiment, the rotation of the clutch gear 32 is transmitted to the drive roller pair 14A of the transport roller pair 14 by the timing belt 40, but it may be transmitted by a gear train or the like.

Further, in this embodiment, the clutch means (electromagnetic clutch 31) is used as the conveying roller pair 16 (or 20).
Although it is arranged on the side, it may be arranged on the side of the conveying roller pair 14 (or 18), or may be arranged between the pair of conveying rollers 16 (or 20) and the pair of conveying rollers 14 (or 18) to provide a timing belt or The driving force may be transmitted to each pair of conveying rollers by a gear train or the like.

Further, in the present embodiment, the sheet materials S1 and S reaching the conveying roller pairs 14, 16, 18 and 20.
2, S3 and S4 are formed with loops to correct the skewed state, but when skew does not occur so much, the skew is corrected by the conveying roller pairs 14, 16, 18, 20. You don't have to.

In this embodiment, the driving roller 14A (or 18A) of the pair of conveying rollers 14 (or 18) is provided with the one-way rotation clutch 41 so that the pair of conveying rollers 14 (or 18).
(Or 18) drive roller 14A (or 1 while drive is stopped)
8A) is set to rotate freely, but it is not necessary to provide the one-way rotation clutch 41 unless the driving load of the registration roller pair 21 increases or the conveyance stability of the sheet material is impaired. .

The present invention is not limited to the sheet material conveying means installed in the conveying path between the sheet feeding section and the transfer section, and for example, re-feeding for double-sided image formation or multiple image formation. It can be similarly applied to the sheet material conveying means installed in a path or the like.

[0073]

As described above, in the image forming apparatus of the present invention, it is possible to control the driving of a plurality of sheet material conveying means by one clutch means, so that the driving of each sheet material conveying means is performed respectively. It is possible to reduce the number of clutch means installed in the image forming apparatus main body as much as possible as compared with the case of individually controlling via the clutch means provided in.

Therefore, the size of the image forming apparatus main body can be reduced and the cost can be reduced by the amount of the clutch means.

Further, by reducing the number of clutch means, the frequency of wire bundle breakage and the like when an electromagnetic clutch is used is reduced, and the reliability of the image forming apparatus is also improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing a configuration of a main part of an image forming apparatus (copier) according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the configuration of a drive mechanism that simultaneously drives a plurality of conveyance roller pairs in the image forming apparatus.

FIG. 3 is a vertical cross-sectional side view for explaining the state of each sheet material and the operation of a pair of conveyance rollers when the sheet material is continuously fed from the second-stage paper feed cassette.

FIG. 4 is a vertical cross-sectional side view showing the overall configuration of a conventional image forming apparatus (copying machine).

[Explanation of symbols]

1-4 Paper feed cassettes 14, 16, 18, 20 Conveying roller pairs (sheet material conveying means) 22-25 Sheet material detection sensor (sheet material detection means) 30 Main motor (drive source) 31 Electromagnetic clutch (clutch means) 40 Timing belt (power transmission means) 41 One-way rotation clutch 42 CPU (control means)

Claims (9)

[Claims] 1. An image forming apparatus comprising a plurality of sheet material conveying means which are driven by the same driving source and are driven to rotate at the same time, wherein the driving force of the driving source is passed through one clutch means for each sheet material. An image forming apparatus, characterized in that the image is transmitted to a conveying means. 2. The driving force of the drive source is transmitted to one of the plurality of sheet material conveying means via the clutch means, and further transmitted to another sheet material conveying means via a power transmission means. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 1, wherein the driving force of the driving source is transmitted from the clutch means to each of the sheet material conveying means via each power transmission means. 4. Each of the sheet material conveying means is arranged on the lower side and a downstream side conveying roller for conveying the sheet material fed from a sheet feeding cassette installed on the upper side of the image forming apparatus main body. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is an upstream conveying roller that conveys the sheet material fed from the sheet feeding cassette. 5. The driving force of the drive source is transmitted to the upstream-side transport roller via the clutch means, and the driving force transmitted to the upstream-side transport roller is transferred to the upstream-side transport roller via the power transmission means. The image forming apparatus according to claim 4, wherein the image forming apparatus is transmitted to the conveying roller. 6. The image forming apparatus according to claim 5, wherein the conveying roller on the downstream side is provided with a one-way rotation clutch for transmitting the driving force transmitted by the power transmission means to the roller shaft. apparatus. 7. A first sheet material detecting means for detecting a sheet material at an upstream portion of the downstream side conveying roller, and a second sheet material detecting means for detecting a sheet material at an upstream portion of the upstream side conveying roller. Means, and a control means for turning on the clutch means after a lapse of a predetermined time after the first sheet material detecting means or the second sheet material detecting means detects the leading edge of the sheet material. The image forming apparatus according to claim 4 or 5. 8. The electromagnetic clutch or the spring clutch is used as the clutch means.
Alternatively, the image forming apparatus according to item 5. 9. The image forming apparatus according to claim 1, wherein the power transmission means includes a timing belt or a gear train.