JPH01156272A - Device for correcting curled sheet - Google Patents

Abstract

PURPOSE:To reduce the chance for jamming, and thereby prevent the occurence of erroneous correction in curl by letting a curl correction means be composed of three rollers each of which is brought in contact with each other with pressure, and shortening the distance from the different nip sections of these rollers to a sheet conveying reference line. CONSTITUTION:A curl correction means is composed of three rollers 15a, 15b and 17 each of which is brought in contact with each other with pressure, the distance from the different nip sections A and B of these rollers 15a, 15b and 17 to a sheet reference line C is constituted to be shortened in such a way that the rotating direction of a driving roller 17 is interlocked with the switchover direction of a guiding means 13. As a result, when a sheet is guided by the guiding means 13, friction between the sheet and the guiding means 13 can be lessened so that the jamming of the sheet caused by the friction of the guiding means 13 can be reduced. In addition, a device constituted to be interlocked allows the sheet to be positively conveyed toward the direction to be guided, thereby making it possible to prevent the occurence of erroneous correction in curl.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a sheet curl straightening device attached to an image forming apparatus such as a copying machine and a laser beam printer. The present invention relates to a sheet curl correction device that can correct curls.

(B) Prior Art Conventionally, an image forming apparatus, for example, a laser beam printer (hereinafter abbreviated as LBP), has a supply section IA as shown in FIG.
, print section IB, double-sided section IC.

It consists of the discharge unit ID. The image formed on the photosensitive drum 3 by the laser scanning optical system 2 is transferred to a developing device 5.
The image is developed, transferred to the sheet supplied from the supply section IA by the transfer separation/charging device 6, fixed by the fixing device 7, and further conveyed to the double-sided section 1C or the discharge section ID. Then, in the duplex section IC, the sheets after the image fixation are once stacked and aligned on the intermediate tray 9, and then conveyed to the printer 1 part IB again. Incidentally, the direction of curl that occurs in the sheet material varies depending on the thickness, moisture content, etc. of the sheet. For example, in a fixing roller in which a heat roller is disposed on the upper side and a pressure roller is disposed on the lower side, if the sheet is thick, heat is not sufficiently transmitted to the lower surface, and a large amount of moisture evaporates from the upper surface. As a result, the upper surface of the sheet shrinks due to evaporation of water, causing the sheet to curl in a concave shape toward the upper surface. On the other hand, with a thin sheet, heat is transmitted to the bottom surface, so the amount of water evaporation is usually the same on both sides, but if a large amount of toner adheres to the top surface, the evaporation of water from the toner surface is limited. The amount of water evaporation on the bottom side increases, causing the sheet to curl downward in a concave shape. This phenomenon is particularly noticeable in sheets left in a humid environment. Furthermore, even if either an upper curl or a lower curl occurs, the possibility of jamming increases. For example, in the case of upper curl, when printing the second side during double-sided printing, the image on the drum 3 becomes curled downward, resulting in poor adhesion to the photosensitive drum 3, as shown in FIG. The image transferred onto the sheet will be incomplete, and in the worst case, the leading edge of the sheet will stick into the transfer separation charger 6, causing a jam. On the other hand, in the case of downward curl, the second side during double-sided printing becomes an upward curl, and the time in contact with the drum 3 becomes longer, so that the toner transferred onto the sheet is transferred onto the drum 3 again. A so-called retransfer phenomenon may occur, or the material may become too close to the drum and cannot be separated, resulting in a jam. Furthermore, as printer speeds increase, the amount of heat in the fixing device increases and the cooling and moisture absorption time decreases, resulting in an increase in the amount of sheet material curling.
Equipped with a reversing mechanism, etc., sheet material conveyance has become even more complicated, and the possibility of jamming has become extremely large. Furthermore, the amount of loading at the discharge section increases as the speed increases, and curling of sheet materials has a large effect on alignment of the loading. Therefore, under these circumstances, it is necessary to correct both the upper and lower curls.

Therefore, the present applicant has devised a sheet curl correction device shown in FIG. 8.

The curl straightening device 10' is disposed on the downstream side of the pair of fixing rollers 7a and 7b of the fixing device 7, and
)', 12, flapper 13', drive rollers 14a, 14
b and driven rollers 15a and 15b. Then, depending on the curl direction of the sheet, flapper 1
3', and if the sheet is upwardly curled, the sheet is curled downward by the sheet drive roller 14a and the driven roller 15a, and the curl is corrected. If the sheet is curled downward, the sheet material is curled upward by the driving roller 14b and the driven roller 15b to correct the curl.

(C) Problems to be Solved by the Invention Incidentally, in the sheet straightening device 10' described above, since the curl straightening position is far from the sheet conveyance reference line, friction with the flapper 13' occurs when changing the course of the sheet. It was easy to jam due to the rapid increase in .

(c) Means for Solving the Problems The present invention aims to solve the above-mentioned problems, and the curl correction means is constituted by three rollers that are in pressure contact with each other, and these rollers are 0- The sheet is configured to be inserted into different nips of the roller and straightened in the front and back directions of the girder 1-, and also includes a guide means for guiding the sheet to either one of the different nips. The feature is that the distance from the conveyance reference line to each nip portion is shortened.

(E) Function Based on the above structure, the curled sheet conveyed from upstream is guided by the guide means to the nip portion of the roller pair whose curl is to be corrected in the curl correction means, and is inserted into the nip portion of the roller pair. The curls are corrected.

(F) Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Note that the same parts as those described above are given the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 2, the curl straightening device 10 includes a fixing M7.
The thickness detection sensor 21 is disposed on the downstream side of the roller pair 2 and is composed of an ultrasonic sensor, an eddy current sensor, a magnetic sensor, etc. to detect the thickness of the sheet.
It is attached to 0.

As shown in detail in FIG. 1, the curl straightening device 1o is swingably supported by a pair of guides, guide plates 1), 1), a shaft with a vertical width as small as possible, and a shaft 3a. a flapper 13, a drive roller 17 with a radius r, and upper and lower driven rollers 15a, 1 with a radius R disposed above and below the roller 17.
5b, the surface of the driving roller 17 is made of a material with relatively high hardness (for example, metal, resin, etc.), and the surface of the driven rollers 15a, 15b is made of a material with relatively low hardness (for example, metal, resin, etc.). It is made of foamed silicone rubber, foamed urethane rubber, etc.). Also, the driving roller 17 and each driven roller 15a.

The center distance flJ1 with respect to the drive roller 15b is l (r + R, and the drive roller 17 is the respective driven roller) 5a.

15b. As a result, the driving roller 17 and each driven roller 15a.

The nips A and B with respect to the sheet 15b are located very close to the sheet conveyance reference line C.

Further, the drive unit 19 of the sheet curl correction device 10 has a third
As shown in the figure, it has a gear 22 that is connected to a motor and always rotates to the left, and a rod 2 is attached to the shaft 22a of the gear 22.
3 is swingably supported. Furthermore, a small-diameter gear 25 that meshes with the gear 22 and a large-diameter gear 26 that rotates together with the gear 25 are rotatably supported on the rod 23. A gear 27 that meshes with the large diameter gear 26 is rotatably supported.

A gear 29 connected to the drive roller 17 is disposed near the gear 27 and the large diameter gear 26, and the gear 29 and the large diameter gear=7=26 or the gear 27 are selectively connected to each other. It is designed to mesh with the Also, a rod 31 is attached to the other end E of the rod 23.
One end of the rod 31 is rotatably connected, and the other end F of the rod 31 is connected to the flapper 13. Further, a solenoid 30 is connected to the flapper 13, and the solenoid 3o is turned ON and OFF in response to a signal from the thickness sensor 21.

Since this embodiment has the above configuration, the supply section IA
The sheet fed from the sheet comes into contact with the pair of registration rollers 20, and the skew is corrected (see ta+ in FIG. 4).

At this time, the thickness sensor 21 detects the distance X between the axes of the upper roller 20a and the lower roller 20b of the registration roller pair 20 as a reference distance. Then, the sheet is held between the pair of registration rollers 20 and conveyed in synchronization with the image on the photosensitive drum 3. At this time, when the registration 1-roller pair 20 holds the sheet, the upper roller 20a and the lower roller 20b
The distance dx of movement obtained by subtracting the reference distance gx from the distance between the axes x + d
) or more, that is, if the sheet is thick, the sensor 20
Solenoid 30 turns flapper 1 at 0FFtz due to the signal.
3 swings in the direction of arrow G (see FIG. 3) by a spring (not shown). As a result, the rod 23.degree. 31 moves in the direction of arrow H, the large diameter gear 26 and the gear 29 mesh with each other, the gear 29 rotates to the left, and the drive roller 17 also rotates to the left. Then, the sheet conveyed to the photosensitive drum 3 by the registration rollers 20 has the image on the photosensitive drum 3 transferred by the transfer separation charger 6, and is separated from the drum 3.

Then, the image is fixed on the sheet by the fixing device 7, and at this time, the heat of the fixing device 7 causes both ends of the sheet to curl upward. Further, the sheet is
The upper surface of the flapper 13 moving in the direction and the upper guide plate 1
), the drive roller 17 and the driven roller 15a are guided to the nip A between the drive roller 17 and the driven roller 15a.
As a result, both ends of the sheet are curled downward, and the curl is corrected. Then, the curl-corrected sheets are conveyed to the duplex section IC and re-fed to the printer section IB, or are discharged to the discharge section ID and stacked.

Further, in the case of a thin sheet having a thickness of 100 μm or less, the solenoid 30 is turned on in response to a signal from the thickness detection sensor 21 that detects the thickness of the sheet, and the flapper 13 is rotated in the direction of arrow 1. As a result, the rod 23 is connected to the shaft 22.
The large-diameter gear 26 and the gear 29 are disengaged from each other, and the gear 29 and the gear 27 are engaged to rotate the gear 29 clockwise, and the drive roller 17 also rotates clockwise. do. Then, the lower curl of the sheet is corrected by the same operation as described above, and the sheet is conveyed to the double-sided section IC or the discharge section ID.

In addition, in the above-mentioned embodiment, the switching of the flapper 13 is as follows.
Although the thickness sensor 21 performs this for each sheet, the present invention is not limited to this, and it may also be possible to detect the first one or more consecutive sheets and use the detection result.

In addition, in the above embodiment, the reference value of the sheet thickness was set to 1.
00μmaro, but it is not limited to this, 100μ or 6120μ
Any value between is fine.

If the amount of squeezing of the driven rollers 15a, 15b is made variable by an actuator, the amount of squeezing can be controlled in accordance with the amount of curl to achieve more appropriate curl correction.

Further, in the above embodiment, the driven roller 15a.

15b and the drive roller 17 are always in contact with each other, but the fifth
As shown in the figure, the driven roller 15a is
, 15 b and the driving roller 17 are configured to be separated from each other, deformation of the driven rollers 15 a, 15 b,
Wear can be reduced.

(G) As described in detail, according to the present invention, the curl correction means is constituted by three rollers that are in pressure contact with each other, and the distance between the different nip portions of these rollers and the sheet conveyance reference line is Since the length is shortened, when the sheet is guided by the guide means, the friction between the sheet and the guide means can be reduced, and jamming of the sheet due to friction with the guide means can be reduced.

Furthermore, if the rotational direction of the drive roller is configured to be interlocked with the switching direction of the guide means, the sheet can be reliably guided in the direction in which it should be guided, thereby preventing the occurrence of curl correction errors due to errors in the guide direction.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a sheet curl correction device according to the present invention, FIG. 2 is a front schematic view showing an image forming apparatus equipped with the sheet curl correction device according to the present invention, and FIG. FIG. 2 is a front view showing the drive system of the invention. FIGS. 4(a) and 4(b) are front views showing the detection operation of the thickness sensor. Moreover, FIG. 5 is a front view showing another embodiment of the present invention. Further, FIG. 6 is a schematic front view showing a conventional image forming apparatus, and FIG. 7 is a front view showing a jam state thereof. FIG. 8 is a front view showing a sheet curl correction device devised by the applicant. 10.10' sheet curl correction device, 13゜1
3'・Guiding means, 14ZL, 14b, 15a. 1.5b, 17 Curl correction means, 14a. 14b, 17-・Drive roller, 15a, 15b・
- Driven rollers, A, B...Nip section, C...Conveyance reference line.

Claims (4)

[Claims] (1) A sheet curl straightening device equipped with a curl straightening means for straightening the curl of a sheet, wherein the curl straightening means is constituted by three rollers that are in pressure contact with each other, and the sheet is inserted into different nips of these rollers. The present invention is constructed so that the sheet can be straightened in the front and back directions, and is provided with a guide means for guiding the sheet to one of the different nips, thereby shortening the distance from the sheet conveyance reference line to each nip. Features: Seat curl correction device. (2) The three rollers include one driving roller and two driven rollers, the driving roller having high hardness and being able to rotate forward and backward, and the driven roller having low hardness. The sheet curl correction device according to item 1. (3) If the radius of the driving roller is r, the radius of the driven roller is R, and the distance between the axes from the driving roller to the driven roller is l, then l<r+R always or selectively holds true. The sheet curl correction device according to item 2. (4) The sheet curl correction device according to claim 2, wherein the rotational direction of the drive roller is interlocked with the switching direction of the guide means.