SHEET CONVEYING DEVICE AND IMAGE FORMING APPARATUS

Abstract

A spring is bridged between a pair of press levers, and a pair of driven rollers is pressurized uniformly, so that clamping and conveying force of the sheet of paper P on the front side and rear side by conveying rollers and the driven rollers is made equal such as Pf=Pr, the sheet of paper P are prevented from being skewed, while the sheet of paper P are clamped and conveyed by a conveying device, and the good conveying of the sheet of paper P is improved, thus the image quality is improved.

Description

FIELD OF THE INVENTION

The present invention relates to a sheet-conveying device for conveying sheet such as paper and film and an image forming apparatus.

DESCRIPTION OF THE BACKGROUND

In an image forming apparatus such as an electrophotographic copier, a facsimile, and a printer, there is a sheet-conveying device, when supplying sheet such as sheet of paper and sheet-like films from a paper supply cassette device or a paper supply tray, for clamping the sheet by a separation sheet and a conveying roller or a separation roller and a conveying roller and supplying only the top of sheet. Further, there is a sheet-conveying device for clamping the sheet supplied and separated from the paper supply cassette device or paper supply tray by the conveying roller and a driven roller and conveying them in a predetermined direction. In such a sheet-conveying device, to stably convey sheet, in Japanese Patent Application 2002-356242, to pressurize a roller pair symmetrical left and right composed of a conveying roller and a driven roller, a constitution of pressuring the left and right shafts of the driven roller separately from each other using two springs is disclosed.

However, like the conventional device, when the driven roller is pressurized to the conveying roller using the left and right separate pressing means, the pressure of the driven roller to the conveying roller becomes imbalance due to variations in the left and right pressing means and the clamping and conveying force by the left and right conveying roller and driven roller pair becomes imbalance. Therefore, during conveyance, sheet is skewed, and conveying defects such as jamming and bending of front ends are caused, or the sheet must be greatly repositioned by an aligning roller. And when the repositioning by the aligning roller is not sufficient, a problem arises that the image quality is decreased due to image displacement. The same may be said with the conveying roller for separating and conveying only the top sheet.

Therefore, a sheet-conveying device and an image forming apparatus for causing no skewing when clamping and conveying sheet by the conveying roller and driven roller or the conveying roller and separating member, preventing conveying defects, repositioning surely the front ends of sheet at the position of the aligning roller, thereby obtaining good images are desired.

SUMMARY OF THE INVENTION

Accordingly, an advantage of the present invention is to provide a sheet-conveying device and an image forming apparatus for preventing skewing when clamping and conveying sheet, repositioning surely the front ends of the sheet by the aligning means, and causing no jamming and image displacement.

To achieve the above advantage, one aspect of the present invention is to provide a sheet-conveying device comprising a fixing roller member having a fixed shaft, a load roller clamping sheet together with said fixing roller member, a pair of first and second pressure units to press between said fixing roller member and said load roller member, by applies load to said fixing roller member, and a elastic member bridged between said pair of pressure units to elastic uniformly said pair of pressure units.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing the copier of the first embodiment of the present invention;

FIG. 2 is a schematic perspective view showing the conveying device of the first embodiment of the present invention;

FIG. 3 is a schematic arrangement diagram showing the conveying device of the first embodiment of the present invention;

FIG. 4 is a schematic block diagram showing to be supported condition of the driven roller shaft on the front side of the first embodiment of the present invention;

FIG. 5 is an illustration showing the principle of making the pressure of the driven roller to the conveying roller uniform on the front side and rear side of the first embodiment of the present invention,

FIG. 6-1 is a schematic perspective view showing the separation and conveying device of the second embodiment of the present invention,

FIG. 6-2 is a schematic arrangement diagram showing the separation and conveying device of the second embodiment of the present invention, and

FIG. 7 is a schematic block diagram showing the support condition of the driven roller shaft on the front side of the second embodiment of the present invention

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the first embodiment of the present invention will be explained in detail with reference to the accompanying drawings. FIG. 1 is a schematic block diagram showing a copier 10, which is an image forming apparatus using the sheet-conveying device, which is an embodiment of the present invention. The copier 10 has a cassette mechanism 3, which is a paper supply unit having paper supply cassettes 3a and 3b for storing sheet of paper P, which are sheet supplied toward an image forming unit 2, which is an image forming portion. Further, the copier 10 has a manual paper supply mechanism 4 having a manual separation and conveying device 4c for taking out sheet of paper P from a paper supply tray 4a, which is a paper supply unit by a manual pickup roller 4b and then separating and conveying the top of sheet of paper P. Further, the copier 10 has a reversing conveying path 5 for reversing sheet of paper P during double-side image forming. On the top of the copier 10, a scanner 6 for reading a document image is mounted.

The scanner 6 has a platen glass 61, a platen 62 for covering the platen glass 61, an optical unit 63 for irradiating light onto a document and focusing reflected light from the document, and a CCD scanner unit 64 for reading light from the optical unit 63.

The image forming unit 2, around a photosensitive drum 11, which is an image carrier, has a main charger 12 for uniformly charging the photosensitive drum 11, an exposure position 13a of a laser exposure device 13 for forming a latent image on the charged photosensitive drum 11 on the basis of image data from the scanner 6, a developing unit 14, a transfer charger 16, which is a transfer unit, a separation charger 17, a cleaner unit 18, and a discharging LED 19 according to the rotation of the photosensitive drum 11 in the direction of the arrow q.

On the downstream side of the image forming unit 2 in the direction of sheet of paper P, a fixing device 22, which is a fixing unit for clamping and conveying the sheet of paper P by a heat roller 20 having a built-in heater lamp 20a and a press roller 21 and heating, pressurizing, and fixing a toner image is mounted. On the downstream side of the fixing device 22, a paper ejection roller 24 for ejecting the sheet of paper P after fixing to a paper ejection tray 23 is mounted.

On supply conveying paths 7a and 7b from the paper supply cassettes 3a and 3b to the transfer charger 16, pickup rollers 30a and 30b for taking out sheet of paper P, first and second separation-conveying devices 31a and 31b, which are sheet-conveying devices, first and second conveying devices 32a and 32b, which are sheet-conveying devices, and furthermore an aligning roller 33, which is an aligning means are mounted. The supply conveying path 7a neighboring the image forming unit 2 has a first conveying path cover 8 indicated by hatching and the supply conveying path 7b neighboring the cassette mechanism 3 has a second conveying path cover 9 indicated by hatching. The first conveying path cover 8 rotates in the direction of the arrow m around a fulcrum 8a, thus the supply conveying path 7a can be opened. The second conveying path cover 9 rotates in the direction of the arrow n around a fulcrum 9a, thus the supply conveying path 7b can be opened.

Next, the first and second conveying devices 32a and 32b will be described in detail. Further, the first and second conveying devices 32a and 32b have the same structure, so that one of them will be explained. For example, the first conveying device 32a, as shown in FIGS. 2 and 3, has a pair of conveying rollers 40f and 40r, which is a fixing roller member on the front side and rear side of a conveying roller shaft 40c, which is a fixed shaft linked with a drive motor (not drawn). At the opposite positions to the pair 0f conveying rollers 40f and 40r, a pair of driven rollers 41f and 41r, which is a load roller member is mounted on the front side and rear side. The pair of conveying rollers 40f and 40r, for example, is made of synthetic rubber and the pair of driven rollers 41f and 41r, for example, is made of metal or resin. By the pair of conveying rollers 40f and 40r and the pair of driven rollers 41f and 41r, sheet of paper P are clamped and conveyed.

The pair of driven rollers 41f and 41r is attached free rotation at a driven roller shaft 41c, which is a load shaft. As shown in FIG. 4, for example, on the front side, the driven roller shaft 41c is supported by a slit 50a formed in a frame 8b in the first conveying path cover 8 and can slide in the slit 50a. At both ends of the driven roller shaft 41c, a guide 51a is formed. The guide 51a is inserted through the slit 50a, thus the rotation of the driven roller shaft 41c is fixed. By doing this, the pair of driven rollers 41f and 41r can be driven to rotate stably by the pair of conveyer rollers 40f and 40r.

In the positions at the same distance from the centers of the driven rollers 41f and 41r on the front side and rear side, a pair of press levers 42f and 42r in an L shape, which is a pair of first and second pressure units in the same shape on the front side and rear side, is arranged respectively. The pair of press levers 42f and 42r is arranged possible rotation respectively around fulcrums 43f and 43r. An L-shaped free end 44f of the pair of press levers 42f and 42r on the front side makes contact and applies load with the driven roller shaft 41c at a pressure unit 45f on the front side, and a free end 44r on the rear side makes contact and applies load with the driven roller shaft 41c at a pressure unit 45r on the rear side, and the two free ends press the driven roller shaft 41c in the direction of the arrow x, which is the direction toward the pair of conveying rollers 40f and 40r.

At hooks 46f and 46r formed on the pair of press levers 42f and 42r, one spring 47, which is an elastic member is bridged. The spring 47 stretches the hook 46f on the front side in the direction of the arrow and the hook 46r on the rear side in the direction of the arrow t with the uniform force and gives the uniform press to the free ends 44f and 44f of the pair of press levers 42f and 42r in the direction of the arrow x.

Here, to convey the sheet of paper P in the direction of in parallel with the arrow r, which is the conveying direction by the first conveying device 32a, the conveying force by the pair of conveying rollers 40f and 40r and the pair of driven rollers 41f and 41r on the front side and rear side must be equal. To make the conveying force by the pair of conveying rollers 40f and 40r and the pair of driven rollers 41f and 41r on the front side and rear side equal, pressure F on the pair of conveying rollers 40f and 40r by the pair of driven rollers 41f and 41r on the front side and rear side must be equal.

Namely, for example, as shown in FIG. 5, on the basis of the center of the sheet of paper P in the conveying direction (hereinafter, abbreviated to PC), assumed the distance up to the center of a first fixing roller member A, which is the first position as L₁, the distance up to the center of a second fixing roller member B, which is the second position on the basis of the PC as L₂, the pressure applied between the first fixing roller member A and the load roller member C by the first pressure unit at center of the first fixing roller member A as F₁, and the pressure applied between the second fixing roller member B and the load roller member D by the second pressure unit at center of the second fixing roller member B as F₂, a formula of F=F₁L₁=F₂L₂ must be held.

Therefore, in this embodiment as shown in FIG. 3, on the basis of the PC, the pair of conveying rollers 40f and 40r and the pair of driven rollers 41f and 41r on the front side and rear side are laid out at the same distance toward the front and rear of the copier 10. Further, the pair of press levers 42f and 42r on the front side and rear side are laid out at the same distance toward the front and rear of the copier 10.

Namely, assumed the distance up to the center of the conveying roller 40f and the driven roller 41f from the PC on the front side as Lf, and the distance up to the center of the conveying roller 40r and the driven roller 41r from the PC on the rear side as Lr, a formula of Lf=Lr is held. Further, assumed the distance up to the free end 44f from the PC on the front side as If, and the distance up to the free end 44r from the PC on the rear side as Ir, a formula of If=Ir is held. Furthermore, the pair of press levers 42f and 42r on the front side and rear side is attracted uniformly by one spring 47 and the force pressurizing the driven roller shaft 41c by the press levers 42f and 42r is equal on the rear side and front side.

And, the distance from the center of the driven roller 41f on the front side to the press lever 42f on the front side and the distance from the center of the driven roller 41r on the rear side to the press lever 42r on the rear side are equal, so that the pressure on the front side and the rear side on the pair of conveying rollers 40f and 40r by the pair of driven rollers 41f and 41r by the pair of press levers 42f and 42r are equal. Namely, on the basis of the PC, the clamping and conveying force Pf of the sheet of paper P between the conveying roller 40f and the driven roller 41f on the front side and the clamping and conveying force Pr of the sheet of paper P between the conveying roller 40r and the driven roller 41r on the rear side are the same, that is, Pf=Pr.

Next, the operation of the present invention will be described. When the image forming process starts, the scanner 6 reads a document. In the image forming unit 2, the photosensitive drum 11 rotates in the direction of the arrow q, thereby is uniformly charged by the main charger 12, then is irradiated with a laser beam according to the document image by the laser exposure device 13, and forms an electrostatic latent image. Next, the developing unit 14 develops the electrostatic latent image and a toner image is formed on the photosensitive drum 11.

On the other hand, in the cassette mechanism 3 or the manual paper supply mechanism 4, by the pickup rollers 30a and 30d or the manual pickup roller 4b, predetermined sheet of paper P are picked up. Then, while the picked-up sheet of paper P pass the separation-conveying devices 31a and 31b or the manual separation-conveying device 4c, only the top of sheet of paper is separated and is fed toward the first or second conveying device 32a or 32b.

Then, the sheet of paper P separated by the first or second separation-conveying device 31a or 31b one by one reaches the first or second conveying device 32a or 32b and is clamped and conveyed in the direction of the arrow r, which is the direction toward the aligning roller 33. In the first or second conveying device 32a or 32b, the pair of conveying rollers 40f and 40r are rotated in the direction of the arrow y, which is a conveying direction of the sheet of paper P by driving by the conveying roller shaft 40c by the drive motor and the pair of driven rollers 41f and 41r making contact with the pair of conveying rollers 40f and 40r under pressure are driven to rotate and clamp and convey the sheet of paper P.

At this time, the pair of conveying rollers 40f and 40r and the driven rollers 41f and 41r are arranged symmetrically on the basis of the PC and the pair of press levers 42f and 42r are arranged symmetrically on the basis of the PC. So that, contact area of conveying rollers 40f and 40r and driven rollers 41f and 41r are arranged symmetrically on the basis of the PC. Furthermore, by the common spring 47, the pair of press levers 42f and 42r is given uniform tensile strength. Therefore, the clamping and conveying force Pf of the sheet of paper P by the conveying roller 40f and the driven roller 41f on the front side and the clamping and conveying force Pr of the sheet of paper P by the conveying roller 40r and the driven roller 41r on the rear side are the same, so that the sheet of paper P are not skewed, are kept straight, and reach the aligning roller 33.

As mentioned above, during conveyance by the first or second conveying device 32a or 32b, the sheet of paper P are not skewed, so that generally, the sheet of paper P are skewed little, and the dependence on repositioning of the sheet of paper P at the position of the aligning roller 33 is reduced, thus the aligning roller 33 can reposition the front ends of the sheet of paper P easily and surely.

After repositioning by the aligning roller 33, the sheet of paper P is conveyed to the position of the transfer charger 16 in synchronization with a toner image on the photosensitive drum 11 and after transfer of the toner image, is separated from the photosensitive drum 11 by the separation charger 17. After separation of the sheet of paper P, the photosensitive drum 11 is cleaned residual toner by the cleaner unit 18, is removed the residual charge by the discharging LED 19, and waits for the next image forming process. The sheet of paper P separated from the photosensitive drum 11 and having an unfixed toner image is inserted through the heat roller 20 and the press roller 21 of the fixing device 22 and after the toner image is heated, pressurized, and fixed, is ejected to the paper ejection tray 23.

In this embodiment structured like this, in the first or second conveying device 32a or 32b, on the basis of the PC, Lf=Lr and If =Ir and the tensile strength of the spring 47 bridged between the press levers 42f and 42r is the same. From this, the clamping and conveying force Pf of sheet of paper P by the conveying roller 40f and the driven roller 41f on the front side and the clamping and conveying force Pr of sheet of paper P by the conveying roller 40r and the driven roller 41r on the rear side are the same, that is, Pf=Pr.

Therefore, the sheet of paper P clamped and conveyed by the first or second conveying device 32a or 32b is not skewed by the first or second conveying device 32a or 32b and the good conveying can be improved. Further, the dependence on repositioning skewing of the sheet of paper P by the aligning roller 33 can be reduced, and the sheet of paper P can be repositioned surely before image forming, thus an image forming apparatus free of image displacement and of high image quality is obtained.

Next, the second embodiment of the present invention will be explained. The second embodiment is different in the constitution of the separation-conveying device from the first embodiment. Therefore, in the second embodiment, the same numerals are assigned to the same parts as those of the constitution explained in the first embodiment and the detailed explanation will be omitted. The first and second separation-conveying devices 31a and 31b of this embodiment have the same structure, so that one of them will be explained. As shown in FIG. 6-1 and FIG. 6-2, the separation device has a separation roller 60, which is a load roller member on a separation roller shaft 60c, which is a load shaft. The separation roller 60 is rotated in the direction of the arrow f, which is a separating direction of the sheet of paper P by prescribed driving force when the sheets of paper P are separated, to return the sheets of paper P picked up from the paper supply cassettes 3a or 3b by the pickup rollers 30a or 30b toward the paper supply cassettes 3a or 3b.

At the opposite positions to the separation roller 60, a paper supply roller 61, which is a fixing roller member is mounted. The paper supply roller 61 is rotated by a paper supply motor (not drawn) in the direction of the arrow g, which is a conveying direction of the sheet of paper P and supplies the top of the sheet of paper P picked up from the paper supply cassette 3a or 3b toward the first or second separation-conveying device 31a or 31b. The paper supply roller 61 is carried out to the paper supply roller shaft 61c, which is a fixed shaft driven in the direction of arrow g. As shown in FIG. 7, the separation roller shaft 60c is supported by a slit 103a formed in a frame 103 in the cassette mechanism 3 and can slide in the slit 103a. Therefore, the separation roller shaft 60c, although it slides in the slit 103a, is connected to the driving force via a link mechanism.

As shown in FIG. 6-2, a center of contact area of the separation roller 60 and the paper supply roller 61 will be defined if it is on the PC. In the positions at the same distance (If=Ir) from the centers of the separation roller 60, a pair of press levers 62f and 62r in an L shape, which is a pair of first and second pressure units in the same shape on the front side and rear side, is arranged respectively. The pair of press levers 62f and 62r is arranged possible rotation respectively around fulcrums 63f and 63r. An L-shaped free end 64f of the press lever 62f on the front side makes contact and applies load with the separation roller shaft 60c at a pressure unit 65f on the front side, and a free end 64r of the press lever 62r on the rear side makes contact and applies load with the separation roller shaft 60c at a pressure unit 65r on the rear side. And the two free ends of the press levers 62f and 62r press the separation roller shaft 60c in the direction of the arrow i, which is the direction toward the paper supply roller 61.

At hooks 66f and 66r formed on the pair of press levers 62f and 62r, one spring 67, which is an elastic member is bridged. The spring 67 stretches the hook 66f on the front side in the direction of the arrow j and the hook 66r on the rear side in the direction of the arrow k with the uniform force and gives the uniform press to the free ends 64f and 64f of the pair of press levers 62f and 62r in the direction of the arrow i.

To supply the sheet of paper P separated one by one in parallel toward the first or second conveying device 32a or 32b, the separation roller 60 and the paper supply roller 61 are arranged symmetrically on the basis of the PC. Further, the pair of press levers 62f and 62r on the front side and rear side is also arranged symmetrically on the basis of the PC. Furthermore, the pair of press levers 62f and 62r is attracted uniformly by one spring 67, so that the force pressurizing the separation roller shaft 60c by the pair of press levers 62f and 62r is equal on the rear side and front side. Therefore, the pressure of the pair of press levers 62f and 62r on the front side and rear side on the paper supply roller 61 of the separation roller becomes equal.

In the first or second separation-conveying device 31a or 31b, when separating the sheet of paper P picked up by the pickup rollers 30a or 30b, the separation rollers 60 is rotated in the direction of the arrow f so as to return the lower sheet of paper P toward the paper supply cassettes 3a or 3b. The separation roller 60 makes contact with the paper supply roller 61 by the pressure of the pair of press levers 62f and 62r. On the other hand paper supply roller 61 is rotated in the direction of the arrow g by driving by the paper supply roller shaft 61c by the paper supply motor, and supply only the top of the sheet of paper P toward the first or second conveying device 32a or 32b.

At this time, the paper supply roller 61, the separation roller 60, and the pair of press levers 62f and 62r are arranged symmetrically on the basis of the PC. Furthermore, by one spring 67, uniform tensile strength is given to the pair of press levers 62f and 62r. Therefore, the separation-conveying force of the sheet of paper P by the supply roller 61 and the separation roller 60 on the front side and the rear side become equal, and the sheet of paper P are not skewed, are kept straight, and reach the first or second conveying device 32a or 32b.

As mentioned above, during conveyance by the first or second separation-conveying device 31a or 31b, the sheet of paper P are not skewed, so that the dependence on repositioning of the sheet of paper P at the position of the aligning roller 33 is reduced, thus the aligning roller 33 can reposition the front ends of the sheet of paper P easily and surely. Hereafter, the sheet of paper P, in the same way as with the first embodiment aforementioned, are clamped and conveyed toward the aligning roller 33 by the first or second conveying device 32a or 32b.

In this embodiment structured like this, in the first or second separation-conveying device 31a or 31b, the paper supply roller 61, the separation roller 60, and the press roller pair 62f and 62r are arranged symmetrically on the basis of the PC and the tensile strength of the spring 67 applied between the press levers 62f and 62r is the same. From this, the separation-conveying force of the sheet of paper P by the paper supply roller 61 and the separation roller 60 on the front side and the rear side become equal.

Therefore, the sheet of paper P separated and conveyed by the first or second separation-conveying device 31a or 31b are not skewed by the first or second separation-conveying device 31a or 31b and the good conveying can be improved. Further, the dependence on repositioning skewing of the sheet of paper P by the aligning roller 33 can be reduced, and the sheet of paper P can be repositioned surely before image forming, thus an image forming apparatus free of image displacement and of high image quality is obtained.

Further, the present invention is not limited to the aforementioned embodiments and can be changed within a range, which is not deviated from the object of the present invention. For example, if the pressure unit can give uniformly the pressure between the fixing roller member and the load roller member, the shape and structure thereof are not restricted. Further, the number of the fixing roller member or the load roller member is not limited. Further, the elastic member is not limited to the spring and it may be rubber or a steel wire bridged between the pair of pressure units. Furthermore, the sheet-conveying device is not limited to the use location if it is a place requiring conveyance of sheet, that is, it may be used in the reversing path or for conveying sheet by the scanner, and is not limited to the copier.

As described above in detail, according to the present invention, the fixing roller member and the load roller member stably can clamp and convey sheet or can separate and convey sheet without skewing them. Therefore, conveying defects such as jamming and bending in the conveying path of sheet are prevented, and a sheet-conveying device of good conveying is obtained, and the dependence on repositioning skewing of the sheet by the aligning means can be reduced, and the sheet can be repositioned surely by the aligning roller, thus an image forming apparatus free of image displacement and of high image quality is obtained.

Claims

1. A sheet-conveying device comprising: a conveying roller member having a fixed shaft;a load roller member pressing said conveying roller member and clamping sheet together with said conveying roller member;a pair of first and second press levers that applies a load to said load roller member; anda spring bridged between said pair of press levers to provide a uniform elastic force to said pair of press levers and to uniform said load by said first and second press levers.

2. The sheet-conveying device according to claim 1, wherein said conveying roller member is driven to rotate in a conveying direction of said sheet, and said load roller member is a driven roller, which is driven by said conveying roller and convey said sheet in said conveying direction together with said conveying roller.

3. The sheet-conveying device according to claim 2, wherein said driven roller is attached to a load shaft such as to allow for free rotation of the driven roller, and said pair of press levers applies pressure to said load shaft towards said conveying roller.

4. The sheet-conveying device according to claim 2, wherein contact area of said conveying roller and said driven roller, and said pair of press levers are arranged symmetrically on the basis of a center of said sheet in said conveying direction.

5. The sheet-conveying device according to claim 2, wherein said conveying roller consists of independent plural rollers, which are arranged at said fixed shaft.

6. The sheet-conveying device according to claim 1, wherein said conveying roller member is driven to rotate in a conveying direction of said sheet, and said load roller member is a separation roller driven to rotate in a separating direction of said sheet.

7. The sheet-conveying device according to claim 6, wherein contact area of said conveying roller and said separation roller, and said pair of press levers are arranged symmetrically on the basis of a center of said sheet in said conveying direction.

8. An image forming apparatus comprising: an image forming portion;a paper supply unit to supply a sheet toward said image forming portion;a paper eject unit to eject said sheet which passed said image forming portion;a conveying roller member having a fixed shaft positioned between said paper supply unit and said paper eject unit;a load roller member pressing said conveying member and clamping sheet together with said conveying roller member;a pair of first and second press levers that applies a load to said load roller member; anda spring bridged between said pair of press levers to provide a uniform elastic force to said pair of press levers and to uniform said load by said first and second press levers.

9. The image forming apparatus according to claim 8, wherein said conveying roller member is driven to rotate in a conveying direction of said sheet, and said load roller member is a driven roller, which is driven by said conveying roller and convey said sheet in said conveying direction together with said conveying roller.

10. The image forming apparatus according to claim 9, wherein said driven roller is attached to a load shaft such as to allow for free rotation of the driven roller, and said pair of press levers applies pressure to said load shaft towards said conveying roller.

11. The image forming apparatus according to claim 9, wherein contact area of said conveying roller and said driven roller, and said pair of press levers are arranged symmetrically on the basis of a center of said sheet in said conveying direction.

12. The image forming apparatus according to claim 9, wherein said conveying roller consists of independent plural rollers, which are arranged at said fixed shaft.

13. The image forming apparatus according to claim 8, wherein said conveying roller member is driven to rotate in a conveying direction of said sheet, and said load roller member is a separation roller driven to rotate in a separating direction of said sheet.

14. The image forming apparatus according to claim 13, wherein contact area of said conveying roller and said separation roller, and said pair of press levers are arranged symmetrically on the basis of a center of said sheet in said conveying direction.

15. The image forming apparatus according to claim 8, wherein said image forming portion form a toner image on an image carrier.

16. A sheet-conveying method comprising: providing a conveying roller member and a load roller member at an opposite position;pressing between said conveying roller member and said load roller member uniformly with attracting a pair of pressure units which applies a pressure to said load roller member uniformly; andclamping and conveying a sheet by said conveying roller member and said load roller member.