JP3522576B2 - Image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a laser printer, a facsimile and the like, and more particularly to a sheet conveying means of an image forming apparatus using an electrophotographic technique.

[0002]

2. Description of the Related Art Next, a conventional image forming apparatus will be described with reference to FIG. In the figure, the paper feed cassette 1
Sheets fed one by one from the sheet feeding roller 11 from the sheet feeding roller 11 pass through the vertical conveyance path 2 and the leading edge is trimmed by the registration unit 3 and waits, and is transferred to the first image forming unit 6 at a predetermined timing. 4 through which the first image forming means 5 is conveyed.
The toner image formed in 1 is transferred to the first surface of the paper by the first transfer means 55, and the paper on which the unfixed toner image is transferred to the first surface is carried by the paper carrying means 6. After that, the sheet on which the unfixed toner image is transferred to the first surface of the sheet is conveyed to the nip portion between the first fixing roller 72 and the second fixing roller 73 via the pre-fixing guide 71, and the sheet is The unfixed toner image is fixed by being nipped and heated by the first fixing roller 72 and the second fixing roller 72, and is discharged to the paper discharge tray 9 through the paper discharge unit 8.

Next, the sheet conveyance will be described in detail with reference to FIGS. The length of the conveyed sheet in the conveying direction is longer than the length from the transfer portion 55 of the image forming means 5 to the nip portion of the fixing means 7. The leading edge of the sheet stands by at the registration roller 31, and then is conveyed to the image forming unit 5 at a predetermined timing and the first sheet of the sheet is conveyed.
The unfixed toner image is transferred onto the surface, and what is acting on the paper at this time is the conveying force by the registration roller 31 and the rubber roller 32. 7A and FIG. 8A show a state in which the sheet is conveyed by the conveying force of the registration unit 3 as described above, and the leading end of the sheet approaches the conveying unit 6.

Then, when the leading edge of the sheet comes into contact with the conveyor belt 63, the sheet is adsorbed on the surface of the conveyor belt 63 by the suction fan 64, and the conveyor belt 63 is rotationally moved and conveyed. The peripheral speed of the photosensitive drum 51 is Vd, the peripheral speed of the conveyor belt is Vh, and normally Vd = Vh, and therefore, the transfer deviation does not occur at this time. FIG. 9B and FIG.
In (b), the sheet is conveyed by the conveying force of the conveying unit 6 as described above, and the leading end of the sheet is the pre-fixing guide 7
It seems that it is approaching 1.

Further, the front end of the sheet is the pre-fixing guide 7
1 and then hit the heat roller 72 and the heat roller 7
2 and the nip formed by the pressure roller 73.
At this time, the impact of the leading edge of the sheet hitting the heat roller 72 absorbs the bending of the sheet due to the step between the sheet conveying surface of the sheet conveying means 6 and the conveying surface of the pre-fixing guide 71, and the transfer deviation does not occur. .

[0006]

Generally, the peripheral speed of the fixing roller is set to be higher than the peripheral speed of the drum and the peripheral speed of the conveyor belt to prevent the occurrence of wrinkles in the fixing portion of a weakly stiff paper. Therefore, approximately Vt = 1.001 to 1.01
Vh. Under such conditions, as the leading edge of the sheet is clamped and conveyed in the nip portion of the fixing means 5, tension is applied to the deflection of the section A, and when the deflection is eliminated, the sheet is still transferred to the transfer section. Cause a gap. 7 (d) and 7 (e) shows that the deflection of the A part is
Since the peripheral speed of the fixing roller is higher than the peripheral speed of the drum and the peripheral speed of the conveyor belt, the transfer speed of the sheet is lost, and the transfer unit 55
It is shown that tension is applied to the portion passing through and the transfer deviation occurs.

As another example of the fixing means, if the peripheral speed of the fixing roller is equal to or slower than the peripheral speed of the drum and the peripheral speed of the conveyor belt, the wrinkles of the paper easily occur as described above. Further, even if there is a fixing device capable of solving this problem, when a sheet having a strong stiffness is being conveyed, the leading end of the sheet is pinched in the nip portion of the fixing means 5 and looped in the deflection of the section A as being conveyed. When the loop becomes large, the stress is transmitted through the sheet, and when the sheet is still applied to the transfer portion, the transfer deviation occurs. 8 (d) and 8 (e), the loop of the section A gradually increases due to the peripheral speed of the fixing roller being lower than the peripheral speed of the drum and the peripheral speed of the conveyor belt, and passes through the transfer section 55 of the sheet. It is shown that stress is also applied to the part where the transfer is occurring and the transfer deviation occurs.

As described above, in the conventional technique, the length of the conveyed sheet in the conveying direction is longer than the length from the transfer portion 55 of the image forming means 5 to the nip portion of the fixing means 7. In many cases, transfer deviation was caused.

Besides, if the length from the transfer portion 55 of the image forming means 5 to the nip portion of the fixing means 7 is sufficient, the above-mentioned problem can be solved, but it certainly prevents the compactness of the mechanical design. Is.

[0010]

In order to solve the above-mentioned problems, the present invention provides an image forming apparatus having a sheet feeding / conveying means; an image forming means; a sheet conveying means; a fixing means; The image forming unit transfers the unfixed toner image onto the first surface of the sheet conveyed to the image forming unit by the electrophotographic method, and the sheet conveying unit transfers the unfixed toner image onto the sheet by the image forming unit on the upstream side. The sheet on which the unfixed toner image is transferred to the first surface is conveyed so as to be delivered to the fixing unit on the downstream side, and the fixing unit includes a heat roller and a pressure roller, and is conveyed from the sheet conveying unit on the upstream side. The unfixed toner image is fixed by sandwiching and heating the sheet having the unfixed toner image transferred to the first surface conveyed to the nip portion between the heat roller and the pressure roller by the two rollers. and, the sheet transport means The peripheral speed of the conveyor belt that forms a part
Vh is a heat roller and a pressure roller that form part of the fixing unit.
When the peripheral speed Vt is different from the peripheral speed Vt , a step is provided between the sheet conveying surface of the image forming means and the conveying surface of the sheet conveying means so that the conveying surface of the sheet conveying means becomes low. An image forming apparatus is provided, in particular, the step is 3 mm.
An image forming apparatus having a thickness of 12 mm to 12 mm is provided.

[0011]

In addition to the conventional deflection of the paper between the transfer path of the image forming means and the nip part of the fixing means, the paper is not bent between the transfer path and the pre-fixing guide. By forming the flexure, the flexure of the paper at two places can be made, and the tension and the stress transmitted from the fixing means to the transfer part through the paper can be absorbed and the occurrence of the transfer deviation can be eliminated.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus to which an embodiment of the present invention is applied will be described with reference to FIG. In the drawing, the papers fed one by one from the paper feed cassette 1 by the paper feed roller 11 pass through the vertical conveyance path 2 and the leading end thereof is adjusted by the registration unit 3 to stand by, and the image forming means 5 is formed at a predetermined timing. A sheet that has been conveyed to the pre-transfer guide plate 4 and has the toner image formed by the image forming means 5 transferred to the first surface of the paper by the transfer means 55 and the unfixed toner image transferred to the first surface. Are conveyed by the sheet conveying means 6. After that, the sheet on which the unfixed toner image is transferred to the first surface of the sheet is conveyed to the nip portion between the first fixing roller 72 and the second fixing roller 73 via the pre-fixing guide 71, and the sheet is The unfixed toner image is fixed by being nipped and heated by the first fixing roller 72 and the second fixing roller 72, and is discharged to the paper discharge tray 9 through the paper discharge unit 8.

Further, the configuration of the image forming apparatus to which the embodiment of the present invention is adopted will be described in detail with reference to FIG.

The image forming means 5 has a generally used electrophotographic process, and in the embodiment of the present invention, the surface of the photosensitive drum 51 is charged with a positive charge (+ in the figure) by the main charging portion 52. The electrostatic latent image formed by applying (display) and exposed by the laser light of the laser optical system unit 53 is visualized by the positively charged toner (indicated by ● + in the drawing) of the developing device 54. The visible image formed by the positively charged toner is transferred to the first surface of the paper by the transfer unit 55.

Although the transfer portion 55 uses the corotron system in the embodiment of the present invention, a bias roller system,
Any of a transfer belt method or the like may be used.

The separation charger 56 separates the photoconductor drum 51 and the conveyed paper by removing high voltage AC bias. It is not necessary when the transfer portion 55 is of the bias roller type or the transfer belt type.

The transfer guide 57 is a rib that guides the sheet conveyed on the transfer section 55 and the separation charger 56. The material used is a resin with excellent insulation properties such as polycarbonate. This is not necessary when the transfer section 55 is of a transfer belt type or the like.

The cleaning unit 58 scrapes off the toner adhering to the photosensitive member 51 with a rubber blade, and a discharging lamp 59 is provided further downstream to remove the electric charge on the surface of the photosensitive member 51.

The sheet conveying means 6 comprises two rollers 6
1, 62 and a transporting means driving means (not shown) for driving at least one of the two rollers
And a conveyor belt 63 that is stretched around the rollers, and the suction fan 64. The conveyor belt 6
The peripheral surface of 3 is rotationally moved at the peripheral speed of Vh by the driving means, and the sheet conveyed on the sheet conveying means 6 is adsorbed on the surface of the conveying belt 63 by the suction fan 64, and the conveying belt 63 rotates. It is transported by moving. The sheet conveying surface of the sheet conveying means has a length of Ld, and is laid out with a step of Lb from the downstream end of the transfer guide to form a groove in the B section.

The fixing means comprises a pre-fixing guide 71, a heat roller 72, a heater 721, and a pressure roller 73. The fixing guide 72 is provided with ribs at appropriate intervals on the sheet conveying surface to improve the sheet conveying property, guide the leading edge of the sheet passing through the pre-fixing guide to the heat roller, and further convey the sheet. The surface is L and the end on the downstream side of the paper transport surface of the paper transport means 6.
It is laid out with a step of a to make a foot in part A. The peripheral speeds of the heat roller 72 and the pressure roller 73 are rotating at the same Vt. The heat roller 72 is made of aluminum or the like having good heat conductivity, and the outer circumference of which is coated with fluorine, and the heater 721 is incorporated therein to control the temperature to a predetermined temperature necessary for fixing. The pressure roller 73 is also made of a material such as aluminum having good thermal conductivity, the periphery of which is covered with an elastic layer made of heat-resistant urethane rubber, and the outer periphery of which has a release layer of a fluorine resin such as PTFE.

Next, the sheet conveyance according to the present invention will be described in detail with reference to FIGS. The length of the conveyed sheet in the conveying direction is the transfer portion 55 of the image forming unit 5.
It is longer than the length from to the nip portion of the fixing means 7. The leading edge of the sheet stands by at the registration roller 31 and is then conveyed to the image forming means 5 at a predetermined timing to transfer the unfixed toner image onto the first surface of the sheet. What is present is the carrying force by the registration roller 31 and the rubber roller 32. 3A and FIG. 4A show a state in which the sheet is conveyed by the conveying force of the registration unit 3 as described above, and the leading end of the sheet approaches the conveying unit 6.

Then, the leading edge of the paper is transferred to the conveyor belt 63.
When it comes into contact with, the suction fan 64 sucks it onto the surface of the conveyor belt 63, and the conveyor belt 63 is conveyed by being rotationally moved. The peripheral speed of the photosensitive drum 51 is Vd, the peripheral speed of the conveyor belt is Vh, and the normal speed is Vd = V.
Because of h, no transfer deviation occurs at this time. 3B and FIG. 4B show a state in which the sheet is conveyed by the conveying force of the conveying unit 6 as described above, and the leading edge of the sheet is approaching the pre-fixing guide 71.

Further, the front end of the paper is the pre-fixing guide 7
1 and then hit the heat roller 72 and the heat roller 7
2 and the nip formed by the pressure roller 73.
At this time, the impact of the leading edge of the sheet hitting the heat roller 72 is absorbed by the deflection of the portion A of the sheet due to the step between the sheet conveying surface of the sheet conveying means 6 and the conveying surface of the pre-fixing guide 71, and the transfer deviation occurs. Does not occur.

Here, under the condition of Vh (= Vd) <Vt, as the leading edge of the sheet is clamped and conveyed in the nip portion of the fixing means 5, tension is applied to the deflection of the section A, and the deflection of the section A disappears. Thus, tension is applied to the flexure of the B section, but the flexure of the B section is absorbed and the transfer deviation does not occur. FIG. 3D shows that the deflection of the section A disappears when the peripheral speed of the fixing roller is higher than the peripheral speed of the drum and the peripheral speed of the conveyor belt, and the tension is about to be applied to the section B. In FIG. 3E, even if tension is applied to the deflection of the B portion, it is being absorbed to some extent. After that, the transfer deviation does not occur until the bending of the portion B disappears.

Under the condition of Vh (= Vd)> Vt, when a relatively strong sheet is being conveyed, as the leading edge of the sheet is sandwiched and conveyed in the nip portion of the fixing means 5, the above A
A loop is generated in the flexure of the part, and when the loop becomes large, the stress is transmitted to the flexure of the part B and a loop is generated, but the stress is absorbed until the loop of the part B becomes a certain size. Therefore, the transfer deviation is less likely to occur. 4 (d) shows that the loop of the section A is gradually increased due to the peripheral speed of the fixing roller being lower than the peripheral speed of the drum and the peripheral speed of the conveyor belt, and the bending of the section B is about to be stressed. is there. In (e) of FIG. 4, the deflection of the B portion is gradually increased, but is being absorbed to some extent. After that, if the trailing edge of the sheet passes through the transfer portion 55 before the bending loop of the portion B becomes larger, the transfer deviation does not occur.

For the above confirmation, Table 1 shows the results showing the relationship between the embodiments showing specific numerical values and defects such as transfer deviation. The conditions of this confirmation experiment are shown below.・ Photoconductor drum; φ60 mm ・ Conveyance speed (photoconductor drum peripheral speed) Vh (= Vd) = 30
0 mm / sec-Fixing roller peripheral speed; Vt = 330,270 mm / sec -Paper: A3 size (420 mm x 297 mm) plain paper is passed in the longitudinal direction.

[0027]

[Table 1]

As described above, in order to make a bend in the B part, Lb
Is preferably not less than 3 mm and not more than 12 mm, and when a step is provided more than that, when the sheet is transferred from the transfer guide 57 to the conveying unit 6, the sheet is obliquely conveyed or the suction force of the suction fan 64 against the sheet is reduced. Tend to adversely affect paper handling and cause defects. Further, under the condition of Vh ≧ Vt, it seems that it is difficult to avoid wrinkles on the sheet during fixing. Note that these tendencies also differ depending on the transport speed.

[0029]

According to the present invention, the problem of transfer deviation at the trailing edge of a sheet, which occurs when printing on a sheet long in the transport direction, is less likely to occur.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an image forming apparatus that employs the present invention.

FIG. 2 is a schematic view of the vicinity of a conveyance path of an image forming apparatus adopting the present invention.

FIG. 3 shows Vh <Vt of an image forming apparatus adopting the present invention.
FIG. 6 is a schematic view of the paper conveyance movement at that time.

FIG. 4 is a diagram illustrating an image forming apparatus employing the present invention, Vh> Vt.
FIG. 6 is a schematic view of the paper conveyance movement at that time.

FIG. 5 is a schematic diagram of an image forming apparatus according to a conventional technique.

FIG. 6 is a schematic view of the vicinity of a conveyance path of the image forming apparatus according to the related art.

FIG. 7 is a schematic diagram of the sheet conveyance movement when Vh <Vt in the image forming apparatus according to the related art.

FIG. 8 is a schematic diagram of the sheet conveyance movement when Vh> Vt in the image forming apparatus according to the related art.

[Explanation of symbols]

55; Transfer unit 56; Separation charger 57; Transfer guide 61, 62; two rollers of the conveyor belt 63; Conveyor belt 64; Suction fan 71; Pre-fixing guide 72; Heat roller 73; Pressure roller

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Ueno 1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Mita Kogyo Co., Ltd. (56) Reference: JP-A-9-188439 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) B65H 5/38 G03G 15/00 518

Claims (2)

(57) [Claims] 1. An image forming apparatus comprising: paper feeding / conveying means; image forming means; paper conveying means; fixing means; wherein the image forming means is an electrophotographic system. The unfixed toner image is transferred onto the first surface of the conveyed paper, and the paper carrying means transfers the paper having the unfixed toner image transferred onto the first surface of the paper by the image forming means on the downstream side to the downstream side. It is conveyed so as to be delivered to the fixing means of
The fixing unit includes a heat roller and a pressure roller, and an unfixed toner image is transferred onto the first surface that is conveyed from the upstream side sheet conveying unit to a nip portion between the heat roller and the pressure roller. The unfixed toner image is fixed by sandwiching and heating the formed sheet with the two rollers .
The peripheral speed Vh of the conveyor belt that constitutes a part of the paper conveyor is
Peripheral speed V of a heat roller and a pressure roller which form part of the fixing means
When different from t, the sheet conveying surface of the image forming unit,
An image forming apparatus, wherein a step is provided between the transport surfaces of the paper transport means so that the transport surface of the paper transport means is lowered. 2. The image forming apparatus according to claim 1, wherein a step between the sheet conveying surface of the image forming unit and the sheet conveying surface of the sheet conveying unit is 3 mm to 12 mm.