JPH09146434A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image of high quality regardless of the rigidity of a sheet for transferring an image from an intermediate transfer body without enlarging a device or delaying the operation. SOLUTION: The image of a toner 9 is formed on the surface of a photoreceptor drum 1 by developing equipments 2B, 2Y, 2M, 2C, and this is transferred to an intermediate transfer belt 7 by a primary transfer corotron 8. Further, the image is transferred to a sheet 11 by a secondary transfer roll 10, and the image is then fixed on the sheet 1 by a fixing equipment 15 while carrying the sheet 1. The carrying directional length L1 from the transfer position of the image to the sheet 11 by the secondary transfer means to the fixing equipment 15 is set smaller than the carrying directional length L0 of the sheet 11. A control means 22 changes the carrying speed V1 of the sheet 11 by the fixing equipment 15 according to the material or thickness of the sheet 11, and changes the moving speed V2 of the intermediate transfer belt 7 so as to be conformed to the carrying speed V1 . The changing timing of the speed V2 is the time while the length L12 of the image on the intermediate transfer belt 7 corresponds to the length L0 .

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 or a facsimile, and more specifically to an image formed on an image bearing member such as a photoconductor drum or the like, such as an intermediate transfer belt or the like. The present invention relates to an image forming apparatus that first-transfers an image to an intermediate transfer member, secondarily transfers an image from the intermediate transfer member to a sheet, and then fixes the image.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, a visible image is formed by toner on a surface of an image bearing member such as a photosensitive drum, and the visible image is transferred to a sheet such as paper, A visible image is fixed on the sheet by heat or pressure. In recent years, as described in JP-B-49-209 and JP-A-62-206567, an image formed on an image carrier is primarily transferred to an intermediate transfer member such as an intermediate transfer belt. Further, an image forming apparatus is also realized in which the image is fixed after the image is secondarily transferred from the intermediate transfer member to the sheet.

FIG. 1 shows an example of an apparatus using an intermediate transfer member. In this apparatus, first, four developing devices (image forming means) 2B, 2Y, 2 are provided on the surface of the photosensitive drum (image carrier) 1.
A toner image is formed by M and 2C. Developer 2B, 2Y, 2M, 2C
Can supply black (Bk), yellow (Y), magenta (M), and cyan (C) toners, respectively.
The photoconductor drum 1 is rotatable at a peripheral speed V ₃ in a direction indicated by an arrow. Further, an intermediate transfer belt (intermediate transfer member) 7 wound around rolls 3, 4, 5, 6 is arranged so as to be adjacent to the photosensitive drum 1, and this intermediate transfer belt 7 is By driving the roll, the peripheral speed V
It is possible to drive in the direction indicated by the arrow at ₂ . A primary transfer corotron (primary transfer means) 8 to which a bias voltage is applied is arranged inside the intermediate transfer belt 7, and an electric field generated by the primary transfer corotron 8 causes a toner image on the photosensitive drum 1 to be formed. The primary transfer is performed on the intermediate transfer belt 7. In this device, a toner image is formed on the surface of the photosensitive drum 1 from each of the developing devices 2B, 2Y, 2M, and 2C for each rotation of the photosensitive drum 1, and the toner image is immediately formed. The image is primarily transferred onto the intermediate transfer belt 7. Then, by repeating this operation, the toner images are stacked on the intermediate transfer belt 7 one by one and a color toner image is formed. In the figure, reference numeral 9 indicates toner.

Toner 9 formed on the intermediate transfer belt 7
Image is conveyed to the backup roll 6 by the intermediate transfer belt 7. Near the backup roll 6,
Secondary transfer roll (secondary transfer means, bias transfer roll)
10 is arranged and is pressed toward the backup roll 6. Between the intermediate transfer belt 7 supported by the backup roll 6 and the secondary transfer roll 10, a sheet 11 such as a copy sheet or an OHP sheet, which is an image forming object, is supplied.
Further, a bias voltage is applied to the secondary transfer roll 10, so that the toner 9 on the intermediate transfer belt 7 is secondarily transferred to the sheet 11. The secondary transfer roll 10 is generally rotatable, and is driven to rotate as the intermediate transfer belt 7 runs.

A large number of sheets 11 are accommodated in a paper feed tray (not shown), and are fed by various rolls to the nip between the intermediate transfer belt 7 and the secondary transfer roll 10, which is the secondary transfer position. It is like this. Note that reference numerals 12 and 13 indicate registration rolls, and the registration rolls 12 and 13 are the sheet 1
The sheet 11 is fed to the secondary transfer position at a timing suitable for transferring the toner 9 while adjusting the direction of 1. The sheet 11 onto which the image of the toner 9 has been transferred at the secondary transfer position is conveyed by the conveyor belt 14, and the fixing device (fixing means) 15
Be passed through. The fixing device 15 includes a heating roll 16 having a built-in heat source and a pressure roll 17 pressed against the heating roll 16. The sheet 11 is passed through a nip between the rolls 16 and 17 to heat and press it. To be done. In this way, the toner 9 on the sheet 11 is fixed on the sheet 11. The heating roll 16 is rotated at the peripheral speed V ₁ , and the sheet 11 is also conveyed at the speed V ₁ . In general, the pressure roll 17 is rotatable and is driven to rotate as the heating roll 16 rotates. Reference numeral 18 denotes a peeling claw that forcibly peels off the sheet 11 when attached to the intermediate transfer belt 7.

The secondary transfer roll 10 and the peeling claw 18 are
When a color image is formed, these members can be moved toward and away from the intermediate transfer belt 7, and until the image of the toner 9 of the final color is primarily transferred onto the intermediate transfer belt 7, these members are It is separated from the intermediate transfer belt 7. As a result, the image of the toner 9 that has been primarily transferred onto the intermediate transfer belt 7 is prevented from being disturbed.

Such an image forming apparatus obtains a color image by stacking the image of the toner 9 on the intermediate transfer belt 7 instead of the sheet 11 and then secondarily transfers the color image to the sheet 11 collectively. Therefore, there is an advantage that a color image is formed without being influenced by conveyance characteristic factors such as thickness, material, and surface characteristics that differ depending on the type of sheet. Further, the intermediate transfer belt 7 has an advantage that the traveling locus can be designed and changed according to the shape of the apparatus, and the space in the apparatus can be effectively utilized.

[0008]

By the way, the copying paper, which is usually used for image formation as the sheet 11, has a thickness of about 0.05 to 0.1 mm and is not so high in rigidity. Accordingly, the peripheral velocity V ₁ of the heating roll 16, and a peripheral velocity V ₂ of the intermediate transfer belt 7 that substantially coincide, as shown, the distal end side of the sheet 11 is nipped between the rolls 16 and 17, Even when the trailing edge side is sandwiched by the nip at the secondary transfer position, the sheet 11 is pulled between the fixing device 15 and the intermediate transfer belt 7, and conversely, the sheet 11 is excessively sagged. Absent.

On the other hand, for example, when an OHP sheet or a thick paper such as a postcard is used as the sheet 11 and an image is formed on the sheet 11, the fixing device 15 is provided in order to sufficiently develop and permeate the toner. Therefore, it is necessary to apply a large amount of heat to the sheet 11. This point must be particularly taken into consideration when forming a color image. For this reason, conventionally, for OHP sheets and thick paper, the driving means of the heating roll 16 is controlled to reduce the peripheral speed V ₁ .

However, in this case, since the peripheral velocity V ₁ of the heating roll 16 becomes lower than the traveling velocity V ₂ of the intermediate transfer belt 7, the nip between the rolls 16 and 17 and the nip at the secondary transfer position are In the meantime, the sheet 11 may sag, and the toner 9 thereon may be rubbed by other parts and disturbed. Then, due to this, a defect occurs in the formed image. Further, an excessive transport load due to the slackened sheet 11 may be applied to the fixing device 15 to cause the sheet 11 to be jammed, which may delay the image forming work. Further, the sheet 11 whose front end conveyance speed is suppressed gives a force that impedes the running of the intermediate transfer belt 7, and the speed of the intermediate transfer belt 7 may suddenly decrease. In this case, at the rear end portion of the sheet 11 where the image is secondarily transferred from the intermediate transfer belt 7, there may be a problem that the image of the toner 9 that is secondarily transferred is disturbed.

The length L ₁ between the nip between the rolls 16 and 17 and the nip at the secondary transfer position is determined by the sheet 11 to be used.
Although such a problem can be solved by making the length L ₀ larger than the length L ₀ in the transport direction, this is not practical because it causes an increase in the size of the apparatus and a longer image forming operation. In the figure, L ₀ indicated by the solid line is the length (296 mm) in the longitudinal direction of the A4 size sheet 11, and L indicated by the imaginary line.
₀ is the length in the longitudinal direction of the A3 size sheet 11 (42
0 mm). Usually, OHP sheets that are commercially available are up to A4 size. Therefore, when using an OHP sheet and ordinary copy paper, it is desirable that good image transfer can be performed up to A4 size regardless of both materials. On the other hand, thick paper is commercially available up to a considerably large size, and in an ordinary image forming apparatus, it is possible to convey a sheet 11 of maximum A3 size along its longitudinal direction to form an image. It is desirable that an image can be similarly formed on a cardboard of a size.

The present invention has been made in consideration of the above problems, and does not cause an increase in the size of the device and a delay in the operation,
An object of the present invention is to provide an image forming apparatus that forms a high-quality image regardless of the rigidity of a sheet that transfers an image from an intermediate transfer body.

[0013]

In order to solve the above-mentioned problems, in the image forming apparatus according to the first aspect of the present invention, a movable image carrier and an image is formed on the surface of the image carrier. Image forming means, movable intermediate transfer body, primary transfer means for transferring the image on the image carrier to the intermediate transfer body, and secondary transfer means for transferring the image on the intermediate transfer body to a sheet. Fixing means for fixing the image on the sheet while conveying the sheet having the image transferred to the surface by the secondary transfer means, and a conveyance direction length from the secondary transfer position to the fixing means. is L ₁ is, in small image forming apparatus than the length L ₀ of the sheet conveyance direction, a first speed control means for changing the conveyance speed V ₁ of the said sheet by said fixing means, of said intermediate transfer member the moving speed V _2, the fixing The conveyance speed V ₁ of the said sheet by stage, is characterized in that it comprises a second speed control means for changing to match approximately. In this configuration, when an image is formed on a sheet having a large heat capacity such as an OHP sheet or a thick paper, the fixing unit applies a large amount of heat to the sheet, and therefore the first speed control unit causes the fixing unit to remove the sheet. The transport speed V ₁ is decreased, and the moving speed V ₂ of the intermediate transfer member is reduced by the second speed control means.
Can be changed to approximately match the speed V ₁ . By making the speeds V ₁ and V ₂ substantially equal to each other, it is possible to prevent the sheet from excessively sagging between the fixing unit and the secondary transfer position. Therefore, it is possible to prevent the image on the sheet from being rubbed and disturbed by other parts due to the large slack of the sheet, and to prevent the sheet from being jammed due to an excessive conveyance load applied to the fixing unit by the sheet. It Further, it is also possible to prevent the intermediate transfer member from being given a force that hinders the conveyance via the sheet. Therefore, it is possible to form a high-quality image regardless of the rigidity of the sheet on which the image is transferred from the intermediate transfer member, without causing a delay in the operation. As described above, considering that the fixing unit gives a large amount of heat to the sheet when forming an image on a sheet having a large heat capacity such as an OHP sheet or a thick paper, the first The speed control means may change the transport speed V _{1 of the} sheet by the fixing means according to at least one of the material and the thickness of the sheet.

Further, in the above construction, as described in claim 3, the image on the image carrier is transferred from the primary transfer position where the image is transferred to the intermediate transfer body to the moving direction of the intermediate transfer body. The length L ₂ to the secondary transfer position is made larger than the length L _{0 of the} sheet in the transport direction, and the moving direction length L _i2 of the image transferred to the intermediate transfer member is the sheet in the transport direction. The second speed control means changes the moving speed V ₂ of the intermediate transfer member so as to be substantially equal to the conveyance speed V _{1 of the} sheet by the fixing means while the length L ₀ is L ₀ minutes. You may do it. In this case, the moving speed V ₂ of the intermediate transfer body is changed after the image of the length L ₀ of the sheet in the transport direction is transferred from the image carrier to the intermediate transfer body. Therefore, the image during the primary transfer from the image carrier to the intermediate transfer member is not affected by the speed change at all, and the transfer gap at the primary transfer,
Image defects due to uneven transfer are prevented. Further, since the moving speed V ₂ of the intermediate transfer member is changed when the secondary transfer of the image from the intermediate transfer member to the sheet is also not performed, the transfer skip and the transfer at the secondary transfer due to the speed change are performed. Image defects due to unevenness are completely prevented

Alternatively, as described in claim 4, from the primary transfer position where the image on the image carrier is transferred to the intermediate transfer member to the secondary transfer position along the moving direction of the intermediate transfer member. L ₂ and the length L ₁ in the transport direction from the secondary transfer position to the fixing unit are greater than the length L _{0 of the} sheet in the transport direction, and the transfer is performed on the intermediate transfer body. The sum of the moving direction length L _i2 of the formed image and the conveying direction length L _i1 of the image transferred from the intermediate transfer member to the sheet is the length L _{0 of the} sheet in the conveying direction.
The second speed control means may change the moving speed V ₂ of the intermediate transfer member to substantially match the sheet conveyance speed V ₁ of the fixing means during the period of time. Good. In this case, the length L of the sheet in the conveyance direction
_{After the 0-} minute image is transferred from the image bearing member to the intermediate transfer member, and while the image is secondarily transferred from the intermediate transfer member to the sheet, the intermediate transfer is performed in accordance with the conveyance speed V ₁ of the fixing unit. The moving speed V _{2 of the} body is changed. Therefore, the speed change does not affect the image on the way of the primary transfer from the image carrier to the intermediate transfer member, as in the above case. Here, the moving speed V ₂ of the intermediate transfer member during the secondary transfer is
Since there is a possibility that the image that has been secondarily transferred will not be transferred because there is a change, by slowly changing the speeds V ₁ and V ₂ by the first control means and the second speed control means, It is possible to sufficiently suppress the transfer omission and the like. The main effect in this case is that even when the length L ₂ from the primary transfer position to the secondary transfer position is smaller than the length L ₀ of the sheet in the transport direction, image defects such as transfer omission of the image at the time of transfer. Is to be suppressed as much as possible.

When the speed V ₂ of the intermediate transfer member is changed during the secondary transfer of the image, the secondary transfer means sets the constant voltage to a constant voltage. A controlled bias transfer roll is preferred. As described later, this is because the constant voltage controlled bias transfer roll does not depend on the speed fluctuation and the stability of image transfer is higher than that of the transfer corotron or the constant current controlled bias transfer roll. This is because it is possible to suppress image defects during secondary transfer.

Further, in addition to the structure described in claim 1, as described in claim 6, the moving speed V _{3 of the} image carrier is
To the sheet conveying speed V ₁ by the fixing means,
A primary transfer position at which an image on the image carrier is transferred from the image forming position on the image carrier by the image forming unit to the intermediate transfer member Up to the length L ₃ along the moving direction of the image carrier and the length L ₂ from the primary transfer position to the secondary transfer position along the moving direction of the intermediate transfer member Direction length L _{0 of the} sheet, the moving direction length L _i3 of the image formed on the image carrier, and the moving direction of the image transferred from the image carrier to the intermediate transfer member. While the sum of the length L _i2 and the length L _{0 of the} sheet in the transport direction is equal to the length L ₀ , the second speed control unit controls the moving speed V ₂ of the intermediate transfer member by the fixing unit. the conveyance speed V ₁ of the sheet, and at the same time changed to match almost The third movement speed V ₃ of the speed control means said image bearing member, the conveyance speed V ₁ of the said sheet by the fixing means, it is possible to be changed to match approximately. In this case, an image corresponding to the length L ₀ of the sheet in the transport direction is formed on the image carrier, and further, the image is primarily transferred from the image carrier to the intermediate transfer member, and the image is transported by the fixing unit. in accordance with the velocity V _1, the moving speed V ₃ of the moving speed V ₂ and the image bearing member of the intermediate transfer member is changed. Therefore, the speed change has no effect on the image during the secondary transfer from the intermediate transfer member to the sheet. Then, not only the moving speed V ₂ of the intermediate transfer member but also the moving speed V ₃ of the image carrier is changed, so that defects such as transfer omission of the image during the primary transfer due to the speed change are suppressed. . Here, since the speeds V ₂ and V ₃ are changed at the time of the primary transfer, there is a possibility that the image that has been primary-transferred may be skipped.
The velocity V ₂ by the second control means and the third control means,
By changing V ₃ slowly, it is possible to sufficiently suppress the omission of transfer. The main effect in this case is that even when the length L ₂ from the primary transfer position to the secondary transfer position is smaller than the length L ₀ of the sheet in the transport direction, image defects such as transfer omission of the image at the time of transfer. Is to be suppressed as much as possible.

Alternatively, as described in claim 7, a third speed control for changing the moving speed V ₃ of the image carrier so as to substantially match with the conveying speed V _{1 of the} sheet by the fixing means. And a means for moving the image carrier from an image forming position on the image carrier by the image forming means to a primary transfer position where an image on the image carrier is transferred to the intermediate transfer member. A length L ₃ , a length L ₂ from the primary transfer position to the secondary transfer position along the moving direction of the intermediate transfer member, and a transport direction length L from the secondary transfer position to the fixing unit. The sum of ₁ and the length L _{0 of the} sheet in the transport direction is made larger than the length L _{i 3} in the moving direction of the image formed on the image carrier, and the intermediate transfer member from the image carrier. a moving direction length L _i2 of transferred image, the The sum of the transport direction length L _i1 of image transferred to the sheet from between transfer member, while a _0-minute length L of the sheet in the conveying direction, said second speed control means, said intermediate The transfer member moving speed V ₂ is changed so as to substantially match the sheet conveying speed V ₁ by the fixing means, and at the same time, the third speed controlling means changes the moving speed V ₃ of the image bearing member. The sheet conveying speed V ₁ by the fixing unit may be changed so as to substantially match. In this case, an image corresponding to the length L ₀ of the sheet in the transport direction is formed on the image carrier, and the image is being primarily transferred from the image carrier to the intermediate transfer member, In addition, while a part of the image is being secondarily transferred from the intermediate transfer body to the sheet, the moving speed V ₂ of the intermediate transfer body and the moving speed V of the image carrier are matched with the conveying speed V ₁ by the fixing means. ₃ is changed. In this way, even when the length L ₂ from the primary transfer position to the secondary transfer position is considerably smaller than the sheet length L _{0 in} the transport direction, image defects such as omission of image transfer during transfer are possible. It can be suppressed as much as possible.

As in the structure of claim 6 or 7,
When the image is primarily transferred, the speed V ₂ of the intermediate transfer member
In the case of changing the speed V ₃ of the image carrier, it is preferable that the primary transfer means is a bias transfer roll whose constant voltage is controlled.
This is because the constant voltage controlled bias transfer roll is more independent of speed fluctuations than the transfer corotron and the constant current controlled bias transfer roll, and the stability of image transfer is high, and This is because image defects can be suppressed.

As mentioned above, the commercially available OH is usually used.
The P sheet is up to A4 size, and the length of the A4 size sheet in the longitudinal direction is 296 mm. Therefore,
As described in claim 9, when the length L _{0 of the} sheet in the transport direction in the above configuration is set to about 296 mm, normally,
The above effect can be achieved with respect to an OHP sheet. On the other hand, cardboard is commercially available in a considerably large size, and in an ordinary image forming apparatus, it is possible to convey a maximum A3 size sheet along its longitudinal direction to form an image. It is desirable that an image can be similarly formed on the thick paper. The length of the A3 size sheet in the longitudinal direction is 420 mm. Therefore, as described in claim 10, if the length L _{0 of the} sheet in the transport direction in the above configuration is about 420 mm, the above effect can be achieved for thick paper. Note that, in the same image forming apparatus, the length L ₀ of the sheet in the conveying direction is set to about 420 mm.
And the length L of the sheet in the transport direction at the same time.
It is also possible to set ₀ to about 296 mm and make the configurations of claims 3, 4 and 6 compatible. Further, in the same image forming apparatus, the length L ₀ of the sheet in the carrying direction is set to about 420 mm to form the configuration as in claim 4 or 6, and at the same time, the length L ₀ of the sheet in the carrying direction is set to about 296.
It is also possible to make the configuration compatible with the configuration as claimed in claim 3 by setting to mm.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the figure, parts corresponding to the respective parts in FIG. (1) First Embodiment A. First Embodiment Configuration of Embodiment First, FIG. 2 is a schematic side view showing an image forming apparatus according to a first embodiment of the present invention. In the present embodiment, the intermediate transfer belt 7 is made of a material in which an appropriate amount of an antistatic agent such as carbon black is contained in acrylic resin, and has a thickness of 0.07.
It is formed in a band shape of 5 mm and is formed by fusing both ends thereof. Its volume resistivity is 10 ¹⁰ Ω
cm.

The peripheral length of the intermediate transfer belt 7 is 520 mm. This is to form an image of the color toner 9 on an A3 size sheet 11 (having a length L ₀ in the transport direction of 420 mm, which is shown by an imaginary line in FIG. 2) on the surface of the intermediate transfer belt 7. This is so that
The peripheral length of the intermediate transfer belt 7 is 100 mm longer than the length of the A3 size sheet 11 because
This is because it is not preferable to transfer the image of the toner 9 in the vicinity of the seam of fusion bonding because of the surface roughness and the thickness, so that the vicinity of this seam is used as an inter-image area (non-image area). The length L ₂ from the primary transfer position where the image of the toner 9 on the photosensitive drum 1 is transferred to the intermediate transfer belt 7 to the secondary transfer position along the moving direction of the intermediate transfer belt 7 is 350 mm. Has been done. This length L ₂ is
It is larger than the length L ₀ (296 mm, shown by a solid line in FIG. 2) of the sheet 11 in the transport direction when the longitudinal direction of the A4 size sheet 11 is the transport direction.

The photosensitive drum 1 and the roll 3 are rotated by one motor 20 via a gear transmission mechanism (not shown). The roll 3 is a drive roll that gives a driving force to the intermediate transfer belt 7. The peripheral speeds V ₂ and V ₃ of the photoconductor drum 1 and the intermediate transfer belt 7 are made equal by adjusting the gear ratio of the gear transmission mechanism.

The heating roll 16 of the fixing device 15 is driven by another motor 21 and rotated at a peripheral speed V ₁ . As a result, the conveyance speed of the sheet 11 by the fixing device 15 is also set to V ₁ . These motors 20, 2
The rotation speed of No. 1 is made controllable by the control means (first control means, second control means, third control means) 22, so that the speeds V ₁ , V ₂ , V ₃ can be controlled. ing. In this embodiment, the speeds V ₁ , V ₂ and V ₃ when forming an image on ordinary copy paper are set to 160 mm / sec. The velocities V ₁ , V ₂ , and V ₃ are decelerated from 160 mm / sec to 60 mm / sec in 0.2 sec.

B. Operation of the Embodiment Now, the outline of the image forming procedure in the present embodiment is as described above. However, in the present embodiment, the case where the OHP sheet is used as the sheet 11 and the normal copy paper is used as the sheet 11
It is characterized in that the speed control is different when used as. Therefore, in the present embodiment, the user sets and inputs whether the sheet 11 to be used is a normal copy sheet or an OHP sheet, or the sheet 11 is used.
Is automatically determined at any position until it reaches the secondary transfer roll 10. When the user makes a setting input, the input signal is taken into the control means 22. Further, in the case of automatically determining, for example, a detecting means for detecting the flexibility, electric resistance, etc. of the sheet is provided, and the detection signal of this detecting means is input to the control means 22 so that the control means 22 can operate normally. It is advisable to judge whether it is a copy sheet or an OHP sheet.

B-1. In the case of normal copy paper If the sheet 11 is normal copy paper, the fixing device 15
The conveyance speed V ₁ of the sheet 11, the movement speed V ₂ of the intermediate transfer belt 7, and the movement speed V ₃ of the photosensitive drum 1 by
The initial set speed of 160 mm / sec is kept constant, and the operation of each part is performed. Therefore, the sheet 11 is transferred with the image of the toner 9 from the intermediate transfer belt 7 at the secondary transfer position, receives the driving force of the intermediate transfer belt 7, and has a speed V ₂ (1
60 mm / sec), and the heating roll 16 as it is
It is sandwiched between the pressure roller 17 and the pressure roll 17, and the speed V ₁ (16
It is transported at 0 mm / sec). This is because in the case of ordinary copy paper, sufficient color development and penetration of the toner 9 can be performed without applying a large amount of heat to the fixing device 15.

B-2. On the other hand, in the case of an OHP sheet On the other hand, if the sheet 11 is an OHP sheet, a large amount of heat must be applied by the fixing device 15 in order to provide sufficient color development and penetration of the toner 9. Therefore, in the fixing device 15, the transport speed V ₁ of the sheet 11 is reduced. The control operation therefor will be described below. First, the speeds V ₂ and V _{3 of} the photosensitive drum 1 and the intermediate transfer belt 7 are 160 mm / se.
Driven by c, in this state, development from the developing devices 2B, 2Y, 2M, 2C to the photosensitive drum 1 and primary transfer of the image from the photosensitive drum 1 to the intermediate transfer belt 7 are performed. Then, as shown in the figure, the photosensitive drum 1 and the intermediate transfer belt 7 are kept at a constant velocity V ₂ , V ₃ of 160 mm / sec until the leading edge of the image of the toner 9 reaches 40 mm before the secondary transfer position.
Driven by The length L ₂ from the primary transfer position to the secondary transfer position along the moving direction of the intermediate transfer belt 7 is 350.
Since this is mm, the moving direction length L _i2 of the image of the toner 9 transferred to the intermediate transfer belt 7 at this point is already 296 mm, which is the length of the A4 size sheet 11 in the longitudinal direction. Since a commercially available OHP sheet which is normally commercially available has a maximum size of A4, the length L _i2 of the image at this point is the length L ₀ of the sheet 11 in the transport direction.
It has become a minute.

From this point, deceleration of the photosensitive drum 1 and the intermediate transfer belt 7 is started, and the velocity V ₂ ,
Both V ₃ are decelerated from 160 mm / sec to 60 mm / sec. During this time, the traveling distance of the intermediate transfer belt 7 is 20 m.
It is about m, and the leading edge of the image of the toner 9 has not yet reached the primary transfer position. Then, the speeds V ₂ and V ₃ are 60
After being set to mm / sec, the sheet 11 is supplied to the primary transfer position by the registration rolls 12 and 13 at the timing when the image of the toner 9 reaches the primary transfer position, and the secondary transfer is started. And sheet 11
Reaches the fixing device 15 while being transferred by the intermediate transfer belt 7 at a speed of 60 mm / sec while receiving the secondary transfer of the toner 9 from the intermediate transfer belt 7. In the fixing device 15, the peripheral velocity V ₁ of the heating roll 16 is 60 mm / se before any time until the leading edge of the sheet 11 arrives.
set to c. As a result, even if the leading edge of the sheet 11 is sandwiched between the heating roll 16 and the pressure roll 17, the sheet 11 is conveyed without adversely affecting the intermediate transfer belt 7.

As described above, in this embodiment, when the OHP sheet is used as the sheet 11, the intermediate transfer belt 7 is used.
While the length L _i2 of the image of the toner 9 transferred onto the sheet in the moving direction is equal to the length L ₀ of the sheet 11 in the conveying direction, the control unit 2
2 determines the moving speed V ₂ of the intermediate transfer belt 7 to the fixing device 15
The conveyance speed V ₁ of the sheet 11 is changed so as to substantially match. Therefore, when the sheet 11 passes through the secondary transfer position, the velocities V ₁ and V ₂ have already coincided, so that the sheet 11 is transferred between the fixing device 15 and the secondary transfer position.
Is prevented from sagging excessively, the image on the sheet 11 is rubbed and disturbed by other parts due to the large slack of the sheet 11, and the sheet 11 causes an excessive conveyance load. It is possible to prevent the sheet 11 from being jammed due to the load. Further, it is also possible to prevent the fixing device 15 from applying a force to the intermediate transfer belt 7 via the sheet 11 to obstruct the conveyance. The speed V ₃ of the photosensitive drum 1 is also changed in accordance with the speed V ₂ as a result of the configuration of the drive system, but this causes the driving force between the photosensitive drum 1 and the intermediate transfer belt 7 to change. The speed of the intermediate transfer belt 7 is surely controlled without giving and receiving.

Further, the image being transferred from the photoconductor drum 1 to the intermediate transfer belt 7 is not affected by the speed change at all, and the defects of the image due to the transfer omission and the transfer unevenness during the primary transfer are prevented. Furthermore, since the moving speed V ₂ of the intermediate transfer belt 7 is changed when the secondary transfer of the image from the intermediate transfer belt 7 to the sheet 11 is not performed, the transfer at the time of the secondary transfer due to the speed change. Image defects due to bleeding and uneven transfer are completely prevented. In this way, it is possible to form a high-quality image regardless of whether the sheet 11 is an OHP sheet or a normal copy sheet. Further, as in the conventional case, since the length L ₁ in the transport direction from the secondary transfer position to the fixing device 15 is smaller than the length L ₀ of the sheet 11 in the transport direction, the apparatus may be upsized and the operation may be delayed. Absent.

C. Modification Example In the first embodiment, the speed control is different depending on whether the sheet 11 is an OHP sheet or a normal copy sheet. However, if the sheet is up to A4 size, even if it is a thick sheet, It is also possible to perform speed control similar to that of the above-mentioned OHP sheet. In this case, as the means for detecting the flexibility of the sheet, any means for detecting the thickness of the sheet will suffice. In addition, although the apparatus becomes larger, the length of the intermediate transfer belt 7 is made longer so that the length L ₂ from the primary transfer position to the secondary transfer means along the moving direction of the intermediate transfer belt 7 is slightly longer than 420 mm. Thus, the length L ₀ of the sheet 11 in the transport direction is 4 as in the case of transporting along the longitudinal direction of the A3 size sheet 11.
Even if it is 20 mm (shown in phantom in FIG. 2), the sheet 1
The speed control can be changed according to the material or thickness of 1, that is, the heat capacity. In this case, the moving direction length L of the image of the toner 9 transferred to the intermediate transfer belt 7
_{While i2} is 420 mm, the speed V of the intermediate transfer belt 7
₂ and the peripheral velocity V ₃ of the photosensitive drum 1 may be reduced.

(2) Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. The present invention has a configuration similar to that of the first embodiment, but the arrangement of the intermediate transfer belt 7 is different. In this case, the length L ₂ from the primary transfer position where the image on the photosensitive drum 1 is transferred to the intermediate transfer belt 7 to the secondary transfer position along the moving direction of the intermediate transfer belt 7 is 25.
It is set to 0 mm. The length L ₂ is the length of the sheet 11 when the longitudinal direction of the A4 size sheet 11 is set as the conveyance direction.
Is smaller than the length L ₀ (296 mm, indicated by the solid line in FIG. 3) in the transport direction. However, the length L ₁ from the secondary transfer position to the fixing device 15 is set to 100 mm, and the total 350 mm of L ₁ and L ₂ exceeds 296 mm.

In this embodiment, as in the first embodiment, the speed of ordinary copy paper is not changed and the OHP is not changed.
When a sheet is used, the speed V ₂ of the intermediate transfer belt 7
And the speed V ₁ of the photosensitive drum 1 is reduced from 160 mm / sec to 60 mm / se. The deceleration start timing is, as shown in the figure, the moving direction length L _i2 of the image transferred to the intermediate transfer belt 7 and the conveyance direction length L _{i1 of} the image transferred from the intermediate transfer belt 7 to the sheet 11. And the sum of
This is during the length L ₀ of the sheet 11 in the transport direction. Specifically, the front end of the sheet 11 moves the secondary transfer position by 60 mm.
When passing, that is, from the intermediate transfer belt 7 to the sheet 11
This is the time when an image of 60 mm (L _i1 ) has been transferred. Here, when forming an image with the longitudinal direction of the A4 size sheet 11 as the conveyance direction, the moving direction length L _i2 of the image remaining on the intermediate transfer belt 7 is 236 mm obtained by subtracting 60 mm from 296 mm. Since the length L ₂ from the primary transfer position to the secondary transfer position is 250 mm,
At this point, the photosensitive drum 1 has already been transferred to the intermediate transfer belt 7
The primary transfer of the image to is completed.

Therefore, the image being transferred from the photosensitive drum 1 to the intermediate transfer belt 7 is not affected by the speed change. In the present embodiment, since the moving speed V ₂ of the intermediate transfer belt 7 is changed at the time of the secondary transfer, there is a possibility that the image being secondary-transferred may be skipped, but the speed V ₁ , By changing V ₂ slowly over 0.2 sec and by controlling the secondary transfer roll 10 at a constant voltage as described later, it is possible to suppress the transfer omission and the like. As described above, in the present embodiment, even when the length L ₂ from the primary transfer position to the secondary transfer position is smaller than the length L ₀ of the sheet 11 in the transport direction, transfer of an image at the time of transfer or the like may occur. Image defects can be suppressed as much as possible.

In this embodiment, the intermediate transfer belt 7
The secondary transfer of the image of the toner 9 from the sheet to the sheet 11 is performed by the secondary transfer roll 10. On the other hand, with the same configuration, the secondary transfer roll 10 is replaced with a corotron,
When the secondary transfer of the image was actually performed, the transferability was changed by changing the speed of the intermediate transfer belt 7 during the secondary transfer, and a good image quality was not obtained. The same was true when the secondary transfer roll 10 was controlled with a constant current. However, when the secondary transfer roll 10 was subjected to constant voltage control, there was no change in transferability and good image quality was obtained.

FIG. 8 is a graph showing the relationship between the speed V ₂ of the intermediate transfer belt 7 at the time of secondary transfer and the voltage applied to the secondary transfer roll 10 necessary for transfer to the sheet 11. As shown in the figure, the voltage required for transfer was 1400 V regardless of the change in speed V ₂ . It is considered that this is because, in the case of constant voltage control, the charge density applied from the secondary transfer roll 10 to the sheet 11 is made constant without depending on the speed of the sheet 11.

On the other hand, when the transfer corotron and the secondary transfer roll 10 are controlled with a constant current, the charge density applied to the sheet 11 is inversely proportional to the speed of the sheet 11, so that the quality of the transferred image deteriorates. It is thought to invite. Therefore, in these cases, depending on the change of the speed V ₂ ,
It is also necessary to control the transfer current, which can solve the problem of transferability deterioration, but it is considered that the control system becomes complicated.

Also in the second embodiment, if the sheet is up to A4 size, the above-mentioned OHP is also applied to thick paper.
It is also possible to perform speed control similar to that of the seat.

(3) Third Embodiment FIG. 4 shows a third embodiment of the present invention. In this embodiment,
Although the same control as that of the second embodiment is performed, the speed control of the A3 size sheet 11 can be changed according to the heat capacity. The present invention has the same configuration as that of the first embodiment shown in FIG. The length L ₂ from the primary transfer position where the image on the photosensitive drum 1 is transferred to the intermediate transfer belt 7 to the secondary transfer position along the moving direction of the intermediate transfer belt 7 is set to 350 mm, and the secondary transfer is performed. From position to fixing device 15
The length L _{1 up to} is set to 120 mm. As a result, the total of L ₁ and L ₂ is set to 470 mm. this is,
The length L ₀ in the transport direction of the sheet 11 when the longitudinal direction of the A3 size sheet 11 is the transport direction (420 mm, which is shown by a virtual line in FIG. 4) is made larger. However, the length L ₂ from the primary transfer position to the secondary transfer position is smaller than L ₀ .

[0040] Also in this embodiment, for the normal copying paper, change of speed is not performed, when using cardboard, velocity V ₁ of the intermediate transfer belt speed 7 V ₂ and the photosensitive drum 1
Is reduced from 160 mm / sec to 60 mm / se. The deceleration start timing is, as shown in the figure, the moving direction length L _i2 of the image transferred to the intermediate transfer belt 7 and the conveyance direction length L _{i1 of} the image transferred from the intermediate transfer belt 7 to the sheet 11. Is the total length L of the sheet 11 in the transport direction.
_While it is ₀ minutes. Specifically, after the front end of the sheet 11 has passed the secondary transfer position by 80 mm and the front end of the toner 9 has been secondarily transferred. At this time, the primary transfer of the trailing edge of the image is completed.

Therefore, the same effect as the second embodiment of FIG. 3 can be obtained. In this case as well, it is preferable that the secondary transfer roll 10 be subjected to constant voltage control, as described above. In the present embodiment, control is performed to change the speed for thick paper, but if there is an A3 size OHP sheet, similar control can be performed for this. In the present embodiment, when an image is formed on a thick paper or OHP sheet smaller than A3 size, the front end of the sheet 11 passes through the secondary transfer position and the front end of the toner 9 is doubled as in the A3 size. It is conceivable to reduce the speeds V ₂ and V ₃ after the next transfer. Alternatively, just as in the first embodiment of FIG. 2, while all the images of the toner 9 are on the intermediate transfer belt 7, the speeds V ₂ and V ₃ may be increased.
It is also possible to slow down.

(4) Fourth Embodiment FIG. 5 shows a fourth embodiment of the present invention. In the present embodiment, the primary transfer of the image from the photosensitive drum 1 to the intermediate transfer belt 7 is performed by the primary transfer roll (primary transfer means, bias transfer roll) 28, not by the primary transfer corotron 8. The primary transfer roll 28 is under constant voltage control. In the intermediate transfer belt 7, the length L ₂ from the primary transfer position where the image on the photosensitive drum 1 is transferred to the intermediate transfer belt 7 to the secondary transfer position along the moving direction of the intermediate transfer belt 7 is 350 mm. Is A3
It is smaller than the length L ₀ (420 mm, which is shown by an imaginary line in FIG. 5) in the transport direction of the sheet 11 when the longitudinal direction of the size sheet 11 is the transport direction. However, the cyan developing device 2 located most downstream around the photosensitive drum 1
The length L ₃ along the moving direction of the photoconductor drum 1 from C to the primary transfer position is 100 mm, and the total length L ₂ and L ₃ of 450 mm exceeds the length L ₀ .

[0043] Also in this embodiment, for the normal copying paper, change of speed is not performed, when using cardboard, velocity V ₁ of the intermediate transfer belt speed 7 V ₂ and the photosensitive drum 1
Is reduced from 160 mm / sec to 60 mm / se. The deceleration start timing is, as shown in the figure, the length L _i3 in the moving direction of the image of the final color (cyan) formed on the photosensitive drum 1, and the transfer from the photosensitive drum 1 to the intermediate transfer belt 7. The total length L _{i2 of} the color image in the moving direction is the length L ₀ of the sheet 11 in the transport direction. In this image forming apparatus, one of the developing devices 2B, 2Y, 2
Since the toner images developed on the photoconductor drum 1 from M and 2C are immediately and sequentially transferred onto the intermediate transfer belt 7, a desired color image is formed only after the intermediate transfer belt 7 makes four revolutions. In the figure, three-color toner images (black, yellow, and magenta) are already stacked on the intermediate transfer belt 7, and after the development of the cyan image, which is the final color, is completed, the images are primarily transferred to the intermediate transfer belt 7. Shows the way.

The specific start timing of deceleration is the time when the last portion of the cyan toner image is separated from the developing device 2C by about 10 mm. At this time, the intermediate transfer belt 7 is still
The upper toner 9 image has not reached the secondary transfer position. Therefore, the image being transferred from the intermediate transfer belt 7 to the sheet 11 is not affected by the speed change. Then, not only the moving speed V ₂ of the intermediate transfer belt 7 but also the moving speed V ₃ of the photosensitive drum 1 is changed, so that a defect such as a transfer omission of an image during the primary transfer due to the speed change is suppressed. To be done. Here, since the speeds V ₂ and V ₃ are changed at the time of the primary transfer, there is a possibility that the image that has been primary-transferred may be skipped.
As described above, by changing the velocities V ₂ and V ₃ by the control means 22 slowly over 0.2 sec and controlling the primary transfer roll 28 at a constant voltage, transfer omission and the like can be sufficiently suppressed. The reason why the constant voltage control of the primary transfer roll 28 is preferable is the same as the constant voltage control of the secondary transfer roll 10 in the second embodiment. As described above, also in this embodiment, the length L ₂ from the primary transfer position to the secondary transfer position is the length L ₀ of the sheet 11 in the transport direction.
Even when the size is smaller than the above, image defects such as missing of transfer of the image during transfer can be suppressed as much as possible.

In this embodiment, the control for changing the speed is performed on the thick paper. However, if the OHP of A3 size is used.
If there is a sheet, the same control can be performed for this as well. In the present embodiment, when image formation is performed on thick paper or OHP sheet smaller than A3 size, the intermediate transfer belt 7 is used in the same manner as A3 size.
It is conceivable that the velocities V ₂ and V ₃ are reduced during the primary transfer to. Alternatively, it is conceivable to reduce the speeds V ₂ and V ₃ while all the images of the toner 9 are on the intermediate transfer belt 7, just as in the first embodiment shown in FIG.

(5) Fifth Embodiment FIG. 6 shows a fifth embodiment. The configuration of this embodiment is the same as that of the fourth embodiment shown in FIG. 5, but the timing of changing the speeds V ₂ and V ₃ is different when an image is formed on thick paper. In the present embodiment, the dimensions are also the same as those in the fourth embodiment, whereby the length L ₃ along the moving direction of the photosensitive drum 1 from the developing device 2C to the primary transfer position and the secondary transfer position from the primary transfer position. The sum of the length L ₂ to the transfer position and the length L ₁ in the transport direction from the secondary transfer position to the fixing device 15 is larger than the length L ₀ of the sheet 11 in the transport direction. In this case, L ₀ is A3 size sheet 11
L ₀ (420 mm, when the longitudinal direction of the
In FIG. 6, it is shown by a virtual line).

When forming an image on thick paper, the timings at which the speeds V ₂ and V ₃ are changed are the length L _i3 in the moving direction of the image formed on the photosensitive drum 1 and the photosensitive drum 1. When the total length L _{i2 of} the color image transferred to the intermediate transfer belt 7 in the moving direction and the length L _{i1 of} the color image transferred from the intermediate transfer belt 7 to the sheet 11 in the transport direction are 420 mm. Is. In this case, while the primary transfer and the secondary transfer of the image of the toner 9 are being performed, the moving speed V ₂ of the intermediate transfer belt 7 and the photoconductor are adjusted in accordance with the conveying speed V ₁ of the fixing device 15. The moving speed V _{3 of the} drum 1 is changed. Therefore, even when the length L ₂ from the primary transfer position to the secondary transfer position is considerably smaller than the length L ₀ of the sheet 11 in the transport direction, image defects such as transfer omission of the image at the time of transfer are possible. Can be suppressed.

In this embodiment, the speed V of the photosensitive drum 1 is
_{3 is} also changed in accordance with the speed V ₂ as a result of the configuration of the drive system, and thus the disturbance of the transferred image between the photosensitive drum 1 and the intermediate transfer belt 7 at the time of primary transfer is suppressed. Further, the driving force is not exchanged between the photosensitive drum 1 and the intermediate transfer belt 7, and the speed of the intermediate transfer belt 7 is reliably controlled. Further, both of the primary transfer roll 28 that performs the primary transfer and the secondary transfer roll 10 that performs the secondary transfer are subjected to constant voltage control, so that the transferability is prevented from being deteriorated.

Also in the present embodiment, if there is an A3 size OHP sheet, the same control as in the case of thick paper can be performed for this. In the present embodiment, when an image is formed on a thick paper or OHP sheet smaller than A3 size, all the images of the toner 9 are placed on the intermediate transfer belt 7, just as in the first embodiment. In the meantime, it is conceivable to reduce the speeds V ₂ and V ₃ . Further, similarly to the second embodiment, it is possible to reduce the speeds V ₂ and V ₃ during the secondary transfer onto the sheet 11. Alternatively, as in the fourth embodiment, it is conceivable to reduce the speeds V ₂ and V ₃ during the primary transfer to the intermediate transfer belt 7.

(6) Sixth Embodiment FIG. 7 shows a sixth embodiment. This embodiment has a configuration
Similar to the second embodiment of FIG. 3, the primary transfer of the image from the photosensitive drum 1 to the intermediate transfer belt 7 is performed by the primary transfer roll 28.
It is different in that it is done in. Further, when A4 size thick paper or OHP sheet is used as the sheet 11 and the sheet is conveyed with its longitudinal direction aligned with the conveying direction, the same speed control as in the fifth embodiment of FIG. 6 is performed. The length of the sheet 11 in the conveyance direction in this case is L ₀ shown by the solid line in FIG. 7.

(7) Modifications In all the above-mentioned embodiments, the secondary transfer roll 10 is used.
Is rotatable and is driven to rotate as the intermediate transfer belt 7 runs, but the secondary transfer roll 10 can also be driven to rotate independently. In this case, the secondary transfer roll 10 is adjusted in accordance with the change in the rotation speed of the motor 20.
Is also changed so that the peripheral speed of the secondary transfer roll 10 substantially matches the speed V ₂ of the intermediate transfer belt 7. 5 to 7
The same applies to the primary transfer roll 28 of the fourth to sixth embodiments. The pressure roll 17 is also the heating roll 16.
The rotation of the pressure roll 17 is changed by the rotation of the pressure roller 17 in accordance with the change of the rotation speed of the motor 21. The peripheral speed of the pressure roll 17 is made to substantially match the peripheral speed V ₁ of the heating roll 16. Further, in the above embodiment, it is the single control means 22 that controls the speeds V ₁ , V ₂ , and V ₃ , but they may be controlled by separate control means.

[0052]

As described above, according to the present invention,
It is possible to form a high-quality image regardless of the rigidity of the sheet on which the image is transferred from the intermediate transfer member, without increasing the size of the device and delaying the operation.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an example of a conventional image forming apparatus.

FIG. 2 is a schematic side view showing a state at the time of changing the speed of the image forming apparatus according to the first embodiment of the present invention.

FIG. 3 is a schematic side view showing a state when changing the speed of the image forming apparatus according to the second embodiment of the present invention.

FIG. 4 is a schematic side view showing a state during speed change of the image forming apparatus according to the third exemplary embodiment of the present invention.

FIG. 5 is a schematic side view showing a state at the time of changing the speed of the image forming apparatus according to the fourth embodiment of the present invention.

FIG. 6 is a schematic side view showing a state when changing the speed of the image forming apparatus according to the fifth embodiment of the present invention.

FIG. 7 is a schematic side view showing a state at the time of changing the speed of the image forming apparatus according to the sixth embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the speed V ₂ of the intermediate transfer member at the time of secondary transfer and the bias transfer roll voltage required for transfer to the sheet in the image forming apparatus according to the present invention.

[Explanation of symbols]

1 photoconductor drum (image bearing member), 2B, 2Y, 2M, 2C developing device (image forming means), 3, 4, 5, 6 rolls, 7 intermediate transfer belt (intermediate transfer member), 8 primary transfer corotron (primary transfer) Transfer means), 9 toner, 10 secondary transfer roll (secondary transfer means, bias transfer roll), 11 sheets, 1
2, 13 registration rolls, 14 conveyor belts, 15 fixing devices (fixing means), 16 heating rolls,
17 pressure roll, 18 peeling claw, 28 primary transfer roll (primary transfer means, bias transfer roll), 20 motor, 21 motor, 22 control means (first speed control means, second speed control means, third Speed control means)

Claims (10)

[Claims] 1. A movable image carrier, image forming means for forming an image on the surface of the image carrier, a movable intermediate transfer member, and an image on the image carrier, the intermediate transfer member. A primary transfer unit that transfers the image on the intermediate transfer member to a sheet, a secondary transfer unit that transfers the image on the intermediate transfer member to a sheet, and conveys the sheet having the image transferred to the surface by the secondary transfer unit while Fixing means for fixing onto the sheet, and a length L ₁ of the sheet in the carrying direction from the secondary transfer position of the image onto the sheet by the secondary transfer means to the fixing means is a length L of the sheet in the carrying direction. _{In an} image forming apparatus having a size smaller than ₀ , a first speed control unit that changes the sheet conveying speed V ₁ by the fixing unit and a moving speed V ₂ of the intermediate transfer member are set by the fixing unit. To speed V ₁ , An image forming apparatus comprising: a second speed control unit that changes the speeds so that they substantially match. 2. The first speed control means is configured to change the conveying speed V _{1 of the} sheet by the fixing means according to at least one of the material and the thickness of the sheet. The image forming apparatus according to claim 1. 3. The length L ₂ from the primary transfer position where the image on the image carrier is transferred to the intermediate transfer member to the secondary transfer position along the moving direction of the intermediate transfer member is the conveying direction. The length L _{0 of the} sheet, and the length L in the moving direction of the image transferred to the intermediate transfer member.
_{While i2} is the length L _{0 of the} sheet in the transport direction,
The second speed control means sets the moving speed V ₂ of the intermediate transfer member to the transfer speed V of the sheet by the fixing means.
_1, the image forming apparatus according to claim 1 or 2, characterized in that to change to match approximately. 4. A length L ₂ from a primary transfer position where an image on the image carrier is transferred to the intermediate transfer body to the secondary transfer position along a moving direction of the intermediate transfer body, Length L ₁ in the conveyance direction from the next transfer position to the fixing unit
Is larger than the length L _{0 of the} sheet in the transport direction, and the length L in the moving direction of the image transferred to the intermediate transfer body is
_While the sum of _i2 and the conveyance direction length L _i1 of the image transferred from the intermediate transfer member to the sheet is the length L _{0 of the} sheet in the conveyance direction, the second speed control means But,
Wherein the moving speed V ₂ of the intermediate transfer member, said the fixing means conveying speed V ₁ of the said sheet by an image forming apparatus according to claim 1 or 2, characterized in that to change to match approximately. 5. The secondary transfer means is a bias transfer roll whose constant voltage is controlled.
The image forming apparatus according to any one of 2 and 4. 6. A third speed control means for changing the moving speed V ₃ of the image carrier so as to substantially match the speed V ₁ of transporting the sheet by the fixing means. The length L ₃ along the moving direction of the image carrier from the image forming position on the image carrier to the primary transfer position where the image on the image carrier is transferred to the intermediate transfer member, and the primary transfer The total length L ₂ from the position to the secondary transfer position along the moving direction of the intermediate transfer body is larger than the length L _{0 of the} sheet in the transport direction, and is formed on the image carrier. The moving direction length L _{i3 of} the captured image
And the total length L _i2 in the moving direction of the image transferred from the image carrier to the intermediate transfer member is the length L _{0 of the} sheet in the transport direction, the second speed control is performed. Means changes the moving speed V ₂ of the intermediate transfer member so as to substantially match the sheet conveying speed V ₁ by the fixing means, and at the same time, the third speed control means moves the image carrier. The image forming apparatus according to claim 1, wherein the speed V ₃ is changed so as to substantially match the speed V _{1 at} which the sheet is conveyed by the fixing unit. 7. A third speed control means for changing the moving speed V ₃ of the image carrier so as to substantially match the speed V ₁ of conveying the sheet by the fixing means. The length L ₃ along the moving direction of the image carrier from the image forming position on the image carrier to the primary transfer position where the image on the image carrier is transferred to the intermediate transfer member, and the primary transfer A length L ₂ from the position to the secondary transfer position along the moving direction of the intermediate transfer member, and a transport direction length L ₁ from the secondary transfer position to the fixing unit.
Is greater than the length L _{0 of the} sheet in the transport direction, and the moving direction length L _{i3 of} the image formed on the image carrier is
And the total length L _i2 in the moving direction of the image transferred from the image carrier to the intermediate transfer member and the transfer direction length L _i1 of the image transferred from the intermediate transfer member to the sheet are The length of the sheet in the direction L ₀ minutes, while the second
The speed control means of the moving speed V ₂ of the intermediate transfer member,
At the same time that the sheet conveying speed V ₁ by the fixing unit is changed so as to substantially match, the third speed control unit changes the moving speed V ₃ of the image carrier to the sheet conveying speed by the fixing unit. The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus is changed so as to substantially match V ₁ . 8. The image forming apparatus according to claim 6, wherein the primary transfer unit is a bias transfer roll whose constant voltage is controlled. 9. The image forming apparatus according to claim 1, wherein a length L _{0 of the} sheet in the transport direction is about 296 mm. 10. The length L _{0 of the} sheet in the transport direction is
9. It is about 420 mm, and it is characterized by the above-mentioned.
The image forming apparatus according to any one of 1.