JPH06258968A - Image forming device - Google Patents

Abstract

PURPOSE:To perform en excellent transfer regardless of the thickness of a recording sheet by varying the ratio of the moving speed of the surface of an image carrier to that of the surface of a transfer device. CONSTITUTION:The image carrier 1 is rotated while being brought into contact with a transfer roller 2 and their drive sources are separately driven by the image carrier driving motor 3 of a variable speed and the transfer roller driving motor 4 of a uniform speed, respectively. Moreover, a cardboard mode changeover switch in a control part 7 is usually turned off. At this time, the image carrier 1 and the transfer roller 2 are driven so as to make the circumferential speeds uniform, respectively. Therefore, a recording sheet is usually a thin paper and the blurring of an image and a void in a transfer are not generated. When a user makes a copy on the cardboard such as a postcard, etc., the cardboard mode changeover switch is turned on. In the cardboard mode, the image carrier driving motor 3 is controlled so that the surfaces of the image carrier 1 and the transfer roller 2 has a difference in speed at the time of making the copy. Thus, the void in the transfer on the cardboard can be prevented.

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 equipped with a transfer device for transferring a toner image formed on an image carrier onto a recording sheet.

[0002]

2. Description of the Related Art An electrostatic latent image is formed on an image bearing member, the electrostatic latent image is developed to obtain a toner image on the image bearing member, and the toner image is transferred onto a recording sheet for copying. Electronic copying methods for obtaining images are well known.

To transfer a toner image onto a recording sheet,
A method has been proposed in which a transfer member formed in a belt shape or a roller shape and the surface of which is covered with a dielectric is used.
That is, such a transfer member is
The surface of the transfer member is disposed so as to be very close to or in contact with the image carrier, the surface of the transfer member is charged at the time of transfer, and the recording sheet is sandwiched between the transfer member and the image carrier at the transfer section. While moving the surface of the image carrier in the same direction to convey the recording sheet, the toner image is transferred from the image carrier to the recording sheet by the electric force of the electric charge applied to the surface of the transfer member.

[0004]

However, since the above-mentioned contact charging method has a weak transfer force, there is a transfer failure in which the toner image transferred from the image carrier to the recording sheet is transferred to the image carrier again. Occurred when using thick paper.

As a means for preventing the transfer omission, the image carrier is rubbed against the recording sheet, and the moving speed of the surface of the image carrier is changed with respect to the moving speed of the surface of the transfer member in order to forcibly transfer.

However, there is a problem in that the image is blurred by thin paper or the like that does not cause transfer omission.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus provided with a transfer device by the contact charging method, in which good transfer is performed regardless of the thickness of a recording sheet.

[0008]

According to a first aspect of the present invention, a toner image obtained by developing an electrostatic latent image formed on an image carrier is transferred from the image carrier to a recording sheet. An image forming apparatus including a transfer device has a transfer device whose surface is covered with a dielectric and is formed into a belt shape or a roller shape, and holds a recording sheet together with an image carrier at a predetermined transfer portion during transfer, In the transfer device, in which the surface of the transfer device moves in the same direction as the image carrier in the transfer part and transfers the toner image onto the recording sheet while conveying the recording sheet, the moving speed of the surface of the image carrier is The image forming apparatus is characterized in that the ratio of the moving speed of the surface of the transfer device is variable.

A second invention of the present invention is the image forming apparatus according to the first invention, wherein the image carrier has a dedicated drive source.

A third invention of the present invention is the image forming apparatus according to the first invention, characterized in that the drive system for driving the image carrier has a speed change mechanism.

A fourth invention of the present invention has a mode for switching the speed of the surface of the image carrier according to the thickness of the recording sheet, and any one of the first to third inventions is featured. The image forming apparatus according to the invention.

[0012]

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

[First Embodiment] FIG. 5 shows an example of an image forming apparatus to which the present invention is applied. In the figure, an original on the original table glass 21 that reciprocates is illuminated by an illumination lamp 22, and its reflected image light passes through a short focus lens array 24 and is exposed on a photosensitive drum, that is, the image carrier 1 rotating in the direction of the arrow in the figure. .
The image carrier 1 is uniformly charged by the primary charging device 23, a latent image is formed by the exposure, and then developed by the developing device 26, and the latent image becomes a developed image. On the other hand, the recording sheet sent out from the sheet feeding cassette 27 by the sheet feeding roller 28 is passed through the conveying path 29 and is moved to the position of the transfer roller 2 by the registration roller 31 in time with the developed image on the image carrier 1. The fed developed image is transferred and separated from the image carrier 1, and is fed to the fixing device 34 by the conveyor belt 33, and the fixing roller 34a and the pressure roller 3 of the fixing device 34 are fed.
The unfixed image on the recording sheet is fixed by being pinched by 4b and fed, and is ejected to the outside of the apparatus by the paper ejection roller 35.
On the other hand, after the transfer, the residual toner on the image carrier 1 is removed by the cleaning device 36 so that the image can be repeatedly formed.

In the above description, the image carrier 1 rotates while being in contact with the transfer roller 2. As shown in FIG. 1, the drive sources thereof are a variable speed image carrier drive motor 3 and a constant speed transfer roller drive motor 4, respectively. Are driven separately by. Further, FIG. 2 shows an operation unit 7 of the image forming apparatus main body of this embodiment, which has a thick paper mode changeover switch 8. In the normal state, the thick paper mode selection switch 8 is off. At this time, the image carrier 1 and the transfer roller 2 are driven so that their peripheral velocities become constant. Normally, the recording sheet is a thin paper, and the transfer blur does not occur even when the image blurs.

When a user makes a copy on thick paper such as postcards, the thick paper mode selection switch 8 is turned on. In the thick paper mode, the image carrier driving motor 3 is controlled so that the surface of the image carrier 1 and the surface of the transfer roller 2 have a speed difference at the time of copying, so that the transfer omission on the thick paper can be prevented.

Here, for example, the peripheral speed of the image carrier 1 is set to 10
At 0 mm / s, when the recording material sheet is thick paper, the peripheral speed of the transfer roller 2 is 102 mm / s.

[Second Embodiment] FIGS. 3 and 4 show a second embodiment. In this embodiment, the rotation speed of the image carrier 1 is switched by the speed change mechanism provided in the drive system. This drive system uses a motor 5 as a drive source. A motor output gear 9 fixed to the motor shaft of the motor 5 meshes with an input gear 12 of a gear train driving the image carrier 1 and an input gear 13 of a gear train driving other units. The rotation speed of the motor 5 is constant.

The shaft 6 of the input gear 12 is supported by a bearing 14 provided on a frame 25 of the main body so as to be movable in the axial direction. The movable rod 10a of the solenoid 10 is loosely fitted in a hole at one end of a link 11 which is swingably attached to a fixed support pin 15.
6 connected. The slider 17 at the other end of the link 11 is in sliding contact with a shifter 18 fixed to the shaft 6. Movable rod 10a
The shaft 6 moves due to the forward / backward movement, and the two-stage gears 19-1 and 19-2 fixed to the shaft 6 move accordingly. The two-stage gears 19-1 and 19-2 are gears 2 fixed to the image carrier 1.
The image carrier 1 is driven by selectively meshing with 0-1 and 20-2.

Here, the number of teeth of the gears 19-1 and 19-2 is Z
₁ and Z _2, and the number of teeth of the gears 20-1 and 20-2 is Z ₃ ,
When Z ₄ is set, Z ₁ > Z ₂ and Z ₃ <Z _4, and the rotation of the motor 5 rotating at a constant speed is transmitted from the motor output gear 9 to the input gear 12 of the gear train that drives the image carrier 1. The shaft 6 is rotated, and in the state of FIG. 3, the rotation is transmitted from one of the two-stage gears 19-1 to the gear 20-1 to rotate the image carrier 1 while driving the other units. The input gear 13 of the gear train is rotated. In this case, the number of teeth Z ₁ , Z is set so that the peripheral speeds of the image carrier 1 and the transfer roller 2 become equal.
₃ is selected. In this way, image blurring and transfer omission do not occur when copying thin paper.

When copying thick paper, the solenoid 10 is urged to pull the movable rod 10a as shown in FIG. This causes the link 11 to rotate counterclockwise about the support pin 15,
The shaft 6 moves via the link 11 and the gears 19-2 and 20
-2 is engaged. The peripheral speed of the image carrier 1 is lower than the peripheral speed of the transfer roller 2. As a result, even if the thick paper is copied, the transfer omission does not occur.

[Embodiment 3] An image forming apparatus having a plurality of image forming portions, each of which forms a toner image having a different color, and the toner images are sequentially transferred to the same transfer material. Although various so-called color image forming apparatuses have been proposed,
Among them, a color recording apparatus using a multicolor electrophotographic method is often used.

An example of such a color electrophotographic recording apparatus will be briefly described with reference to FIG. 6. In the main body of the color electrophotographic recording apparatus, the first, second, third and fourth image forming portions Pa, Pb, Pc, and Pd are provided side by side, and images of different colors are formed through the processes of latent image, development, and transfer.

The structure of the main body will be described. Image forming unit Pa,
Pb, Pc, and Pd are dedicated image carriers, and in this example, the electrophotographic photosensitive drums 1a, 1b, 1 are used as image carriers.
electrophotographic photosensitive drums 1a, 1b, 1 which are formed by the image forming portions Pa, Pb, Pc and Pd and which have c and 1d.
The images on c and 1d are transferred onto the recording sheet P that is carried and carried on the transfer belt 42 of the transfer material carrier that moves adjacent to each image forming unit. Furthermore, the fixing device 34 is heated and pressurized, and the fixed transfer material P is discharged.

The latent image forming section will be described below. The outer circumferences of the photosensitive drums 1a, 1b, 1c and 1d are exposed to the exposure lamp 3
7a, 37b, 37c, 37d, primary charger 23a, 2
3b, 23c, 23d, a light source device (not shown), a polygon mirror 38 for scanning the light emitted from the light source device, and potential sensors 39a, 39b, 39c, 39d are provided. Laser light emitted from a light source device (not shown) is scanned by rotating the polygon mirror 38, and scanning light obtained by deflecting the light flux by the reflection mirrors 41a, 41b, 41c, 41d is exposed on the photosensitive drums 1a, 1b, 1.
A latent image corresponding to an image signal is formed via an fθ lens that focuses on the generatrixes of c and 1d.

The developing section will be described below. Developing unit 26
a, 26b, 26c and 26d are cyan (hereinafter C
Abbreviated), magenta (hereinafter abbreviated as M), yellow (hereinafter abbreviated as Y), and black (hereinafter abbreviated as BK) color developers by a predetermined amount by a supply device (not shown).
The developing device 26a, 26b, 26c, 26d
Depending on the latent image formed by the scanning light, the photosensitive drums 1a, 1b,
A visible image is formed on 1c and 1d.

The transfer section will be described below. The recording sheet P, which was in the paper feed cassette 27, is transferred to the registration roller 31.
And is sent by the transfer belt 42.

Here, the transfer belt 42 is wound around the driving roller 43 and the driven roller 44, and the upper stretched portion is in contact with the photosensitive drums 1a to 1d. The transfer belt 42 is a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet,
A dielectric resin film such as a polyurethane resin film sheet is used, which is an endless shape obtained by superposing both ends of each other on each other and joining them, or a seamless belt is used.

When it is confirmed that the transfer belt 42 rotates and is in a predetermined position, the recording sheet P is conveyed from the registration roller 31 onto the transfer belt 42. At this time, the image writing signal is turned on, and an image is formed on the first photosensitive drum 1a at a certain timing. Then, the visible image on the photosensitive drum 1a is transferred by the transfer brush transfer charger 2a, which is in contact with the transfer belt 42 under the first photosensitive drum 1a, applying an electric field or electric charge. At this time, the recording sheet P is held on the transfer belt 42 by an electrostatic attraction force, and is conveyed and transferred to the second image forming portion Pb and thereafter. Hereinafter, the transfer material P on which the images formed by the second and third image forming portions are transferred to the recording sheet P by the same method as described above and the image is formed by the fourth image forming portion Pd is not shown. The charge is removed by the separation charging device and the peeling charging device, and the electrostatic charging force is attenuated to separate from the transfer belt 42.
The recording sheet P, which is conveyed to the fixing device 34 and fixed, is carried out of the apparatus.

In the case of such multicolor recording, if the transfer of each color is not performed reliably and a color drop occurs, the partial color development differs from the other parts and the desired color cannot be obtained. . Therefore, in this embodiment, a driving device that rotates the driving roller 43 at a constant speed and a driving device that can shift the photosensitive drums 1a, 1b, 1c, and 1d according to the thickness of the recording sheet are provided. When the recording sheet is thin paper, the photosensitive drum 1a is provided. , 1
By matching the peripheral speeds of b, 1c, and 1d with the peripheral speed of the transfer belt 42 and providing a difference between these speeds when the recording sheet is thick paper, color loss of the recorded image is prevented.

In the embodiment, the case where the image carrier is drum-shaped is solid, but the same is true when the image carrier is sheet-shaped, for example, endless belt.

In the embodiment, the speed of the surface of the image bearing member is switched by the operation section, but a sheet thickness detecting means may be provided in the conveying path for supplying the recording sheet to automatically switch the speed.

[0032]

According to the first aspect of the present invention, the ratio of the moving speed of the surface of the image carrier to the moving speed of the surface of the transfer device is made variable so that when the recording sheet is thin, the image carrier is usually used. The transfer member can be made to have a constant speed to prevent image blurring, and in the case of thick paper, the transfer member can be made to have a non-uniform speed to prevent transfer omission.

According to a second aspect of the present invention, in the first aspect, since the image carrier has a dedicated drive source, the speed can be adjusted steplessly according to the thickness of the recording sheet. Can be easily achieved.

In the third aspect of the present invention, since the drive system for driving the image carrier in the first aspect has a speed change mechanism, a variable speed motor is not used and a variable speed control device is not required.

A fourth invention of the present invention is the first invention to the third invention.
In any one of the inventions described above, since the speed of the surface of the image carrier is switched according to the thickness of the recording sheet, the speed can be easily switched manually, and no operation is required when switched automatically.

[Brief description of drawings]

FIG. 1 is a perspective view of a drive unit according to a first embodiment of the present invention.

FIG. 2 is a plan view of an operation unit according to the first embodiment of the present invention.

FIG. 3 is a plan view of a drive unit according to a second embodiment of the present invention.

FIG. 4 is a plan view of a drive unit according to a second embodiment of the present invention.

FIG. 5 is a vertical sectional view of an example of an image forming apparatus to which the present invention is applied.

FIG. 6 is a vertical sectional view of an example of an image forming apparatus to which the present invention is applied.

[Explanation of symbols]

 1 image carrier 2 transfer roller 3 image carrier drive motor 4 transfer roller drive motor 5 motor 6 axis 10 solenoid 11 link

Claims (4)

[Claims] 1. An image forming apparatus comprising a transfer device for transferring a toner image obtained by developing an electrostatic latent image formed on an image carrier onto the recording sheet from the image carrier, It has a transfer device that is covered with a dielectric material and is formed into a belt or roller shape.
In a transfer device, which sandwiches a recording sheet with an image carrier, and in which the surface of the transfer device moves in the same direction as the image carrier in the transfer section and transfers the recording sheet while transferring the toner image onto the recording sheet. An image forming apparatus, wherein a ratio of a moving speed of the surface of the image carrier to a moving speed of a surface of the transfer device is variable. 2. The image forming apparatus according to claim 1, wherein the image carrier has a dedicated drive source. 3. The image forming apparatus according to claim 1, wherein a drive system for driving the image carrier has a speed change mechanism. 4. The image forming apparatus according to claim 1, further comprising a mode in which the speed of the surface of the image carrier is switched according to the thickness of the recording sheet.