Sheet moisturizing apparatus and image forming system

A sheet moisturizing apparatus, including a vertical conveyance route in which a sheet is guided upward or downward and paired moisturizing units which are mounted symmetrically to sandwich the vertical conveyance route.

This application is based on Japanese Patent Application No. JP2006-110556 filed on Apr. 13, 2006, with the Japanese Patent Office, the entire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a sheet moisturizing apparatus which applies water to a sheet, and an image forming system in which the same apparatus is provided.

BACKGROUND OF THE INVENTION

As is well known, image formation conducted by an electro-photographic process incorporates the process in which a toner image is formed via electrostatic charge, exposure and development, the formed toner image is transferred onto a recording sheet and the toner image transferred onto the sheet is fixed to form a permanent image.

In this fixing process, when toner is melted by heat and pressure to fix the image onto the sheet, some water evaporates from a paper sheet due to the heat. Further, after the fixing, the sheet is open to the outside air, and thereby reabsorbs water from the outside air.

Since such evaporation and re-absorbance of water between the front and reverse surfaces of the paper sheet tends to occur at a different rate, it results in waving or curling of the sheet, which of course is a major problem.

Generally, a fixed paper sheet shows various phenomena.FIG. 1(a) shows wavy sheet S3in which the printed surface is convexly and concavely curled.FIG. 1(b) shows a sheet which is convexly curled upward, which hereinafter is referred to as “convexly curled sheet S1”, whileFIG. 1(b) shows a sheet in which the printed surface is convexly curled downward, which hereinafter referred to as “concavely curled sheet S2”. The conveyance direction of the sheet is shown by an arrow inFIG. 1(a),1(b) and1(c).

These phenomena generate various problems. In the case of post-processes conducted on the sheet which carries a formed image, problems occur during conveyance and processing of the sheet, and in the case of binding process, a book of bound curled sheets becomes very thick, which result in deterioration in quality of the final product. Further, when such sheets are ejected from the apparatus, they do not stack orderly. Accordingly, measures to count such wavy and curled sheets are required.

In Unexamined Japanese Patent Application Publication 61-23,068, to overcome the problem of the wavy or curled sheets, the sheet is moisturized via a mist of water. A moisturizing apparatus incorporating a moisturizing roller is shown, to effectively control the water supply, to reduce any adverse effects due to the water mist on various sections adjacent to the moisturizing apparatus, and to downsize the apparatus.

Moisturizing flattens wavy and curled sheet, but it curls the sheet again if water is not applied equally to both surfaces of the sheet.

Specifically, if more water is applied onto one surface than the other surface, the former expands more than the latter, and a convex curl is generated on wetter surface.

In U.S. Pat. No. 6,052,553, a moisturizing apparatus is shown in which moisturizing rollers are provided on and under the horizontal conveyance route through which the sheet is fed. The upper and lower moisturizing rollers apply water to both surfaces of the sheet. In this apparatus, water is supplied to the upper and lower moisturizing rollers from respective water tanks.

In the case water is applied onto both surfaces of the sheet, due to the water routes from the surface of the water tank, serving as the water source, to the contact position of the moisturizing roller and the sheet, the upper moisturizing means and the lower moisturizing means are not equal, which makes it very difficult to apply equal amounts of water onto both surfaces of the sheet.

Even if water is equally applied onto both surfaces by adjustment, the supplied water amount changes during operation, which causes curled sheets. Further, in above-mentioned moisturizing apparatus, more than three rollers are required for the water supply route, which result in a larger apparatus.

In Unexamined Japanese Patent Application Publication 2006-8,282, a moisturizing apparatus is proposed in which paired moisturizing rollers convey the sheet horizontally, and apply water onto both surfaces of the sheet. A water tank, provided under the lower moisturizing roller, supplies water to the lower moisturizing roller, but the upper moisturizing roller is via the lower moisturizing roller.

In this apparatus, the applied water amount from the upper roller to the sheet tends to be lower than that of the lower roller, which causes the curled sheet.

In these apparatuses, the sheet is conveyed horizontally as it is moisturized. As shown inFIG. 2, since water applied to the sheet moves vertically due to gravity, the amount of water changes in accordance with the direction of thickness, and curling tends to be generated. InFIG. 2, moisture particles in sheet S are schematically shown by solid black dots w.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a sheet moisturizing apparatus, which includes a vertical conveyance route in which a sheet is guided upward or downward, and paired moisturizing units which are mounted symmetrically to sandwich the vertical conveyance route.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be detailed, while referring to the drawings, which however is not limited to the present embodiment.

FIG. 3is an overall view of sheet moisturizing apparatus B relating to the present embodiments.

Sheet S carrying the image which was formed by an image forming apparatus (which is to be detailed later) is introduced to route HR1from entrance101of sheet moisturizing apparatus B, after sheet S is conveyed through selected route HR2or HR3to be processed, sheet S is discharged from sheet moisturizing apparatus B.

In both a non-decurling mode in which sheet S is not moisturized in sheet moisturizing apparatus B and a first decurling mode in which sheet S is mechanically flattened but is not moisturized, sheet S is conveyed through routes HR1and HR2.

On the other hand, in both a moisturizing mode in which the sheet is moisturized but is not mechanically flattened, and a second decurling mode in which sheet S is moisturized and mechanically flattened, sheet S is conveyed through routes HR1and HR3and a portion of route HR2. Route HR2or HR3is selected by changeover gate102.

Mechanical decurling sections150and160are provided on route HR2. Mechanical decurling section150flattens concavely curled sheet S2, and mechanical decurling section160flattens convexly curled sheet S1. “Convex curl” means that the surface of sheet S is convexly curved upward, while “concave curl” means that the surface of sheet S is convexly curved downward, which are illustrated inFIGS. 1(b) and1(c), as well asFIG. 6.

InFIG. 3, moisturizing unit110is provided on route HR3. Moisturizing unit110can be withdrawn by an operator from sheet moisturizing apparatus B, being guided by rails120A and120B.

In route HR1, sheet S is conveyed by paired rollers R1, while in route HR2, sheet S is conveyed by paired rollers R2-R5. In route HR3, sheet S is conveyed by paired rollers R6-R11.

Main tank130, provided under moisturizing unit110to supply it with water, can be partially pulled out from sheet moisturizing apparatus B, being supported and guided by rails130A and130B.

FIG. 4is an enlarged view of moisturizing unit110of sheet moisturizing apparatus B. Moisturizing apparatus B includes moisturizing unit110and main tank130.

InFIG. 3, after sheet S enters horizontally route HR1, it is directed downward from route HR1to U-shaped route HR3by changeover gate102, and then turns upward at a U-shaped section of rote HR3. Moisturizing unit110is positioned to sandwich a portion of route HR3, through which sheet S is conveyed upward. Moisturizing rollers111A and111B are mounted to contact each other.

Moisturizing unit110, refer toFIG. 4, is formed of paired and opposed moisturizing sections, which are left side moisturizing section110A and right side moisturizing section110B. Left side moisturizing section110A is structured of moisturizing roller111A, water supplying roller112A and water supplying tank114A, serving as a water supplying section, while right side moisturizing section110B is structured of moisturizing roller111B, water supplying roller112B and water supplying tank114B. Moisturizing rollers111A and111B are in contact with each other, and rotate as shown by respective arrows to convey sheet S and to supply simultaneously water to sheet S. In addition, it is also possible to form water supplying sections to supply water to water supply rollers112A and112B by employing water tanks and integral transit rollers, in a such a way that the transit rollers are mounted between water supplying roller112A and water supplying tank114A, and also between water supplying roller112B and water supplying tank114B.

Water supplying roller112A is in contact with moisturizing roller11A, while water supplying roller112B is in contact with moisturizing roller111B. Water supplying roller112A is partially submerged in water W of water supplying tank114A, while water supplying roller112B is partially submerged in water W of water supplying tank114B.

Control member113A squeezes water supplying roller112A to regulate the water content of water supplying roller112A, while control member113B squeezes water supplying roller112B to regulate the water content of water supplying roller112B.

Moisturizing rollers111A and111B, as well as water supplying rollers112A and112B are formed of single layered or double layered elastic members, such as non-foamed solid rubber and foamed rubber, or formed of double layered rubbers on which a textile is wrapped. Moisturizing roller111A is structured of metallic core111Aa and rubber layer111Ab layered on the same, while moisturizing roller111B is structured of metallic core111Ba and rubber layer111Bb layered on the same. Water supplying roller112A is structured of metallic core112Aa and rubber layer112Ab formed on the same, while water supplying roller112B is structured of metallic core112Ba and rubber layer112Bb formed on the same.

Control members113A and113B are round bars which rotate or do not rotate. Flat blades may also be used for control members.

InFIG. 3, water W stored in main tank130is pumped up to water supplying tanks114A and114B by a pump which is not illustrated, and any overflow in each tank returns to main tank130through overflow tube116, whereby an adequate water level in water supplying tanks114A and114B is secured in the same way. In addition, water supplying tanks114A and114B are connected to each other, whereby water in both tanks remains at the same level.

During the water supplying process, moisturizing rollers111A and111B, as well as water supplying rollers112A and112B rotate as shown by arrows to supply water to each side of sheet S.

Moisturizing roller111A and water supplying roller112A are symmetrically arranged with moisturizing roller111B and water supplying roller112B with respect to route HR3as shown inFIG. 4. Therefore, the form and the length of the water supplying path from water supplying tank114A to moisturizing roller111A is the same as those of a water supplying path from water supplying tank114B to moisturizing roller111B.

Accordingly, an equal amount of water is supplied to both sides of sheet S. Further, since sheet S is moisturized in vertical route HR3, an equal amount of water is supplied onto sheet S in the direction of the thickness of sheet S, which preferably maintains the flatness of sheet S.

The moisturizing function of moisturizing unit110will be detailed while referring toFIG. 5.

In moisturizing section110A, water supplying roller112A separates from the water surface at area P1. Moisturizing roller111A comes into contact with sheet S at area P2. Water supplying roller112B separates from the water surface at area P3. Moisturizing roller111B comes into contact with sheet S at area P2. Distance WH1is measured from P1to P2over the moisturized surfaces of water supplying roller112A and moisturizing roller111A. Distance WH2is measured from P3to P2over the moisturized surfaces of water supplying roller112B and moisturizing roller111B. Distance WH1is equal to distance WH2, and the shapes of these distances are the same, but mirror images, which are illustrated by heavy S-curved lines inFIG. 5. Accordingly, the amount of water, which is applied to sheet S by moisturizing roller111A, is equal to that applied by moisturizing roller111B. Further, even when the conditions of moisturizing rollers111A and111B, and the conditions of water supplying rollers112A and112B are changed by duration, the ratio of water absorbance of both surfaces is not changed.

Accordingly, equivalent amounts of water are applied onto both surfaces of sheet S, which conduct long and stable moisturizing process.

InFIG. 4, fans117A and117B blow drying air onto both surfaces of sheet S, which allow extra water in sheet S to evaporate immediately after the water supply so that parts mounted in the conveyance route, such as rollers, are prevented from being covered with water.

In addition, in the above explanation of the embodiment, sheet S is fed vertically upward, and paired and opposed moisturizing sections110A and110B are mounted on both sides of the conveyance route. However, it is also possible to have paired and opposed moisturizing sections110A and110B on both sides of the conveyance route oriented downward. Further, paired moisturizing sections are not necessarily mounted at perfectly symmetrical positions. That is, as long as they are practically symmetrical, small changes can be ignored. For example, the heights of both moisturizing sections need not be absolutely the same.

FIG. 6is an enlarged sectional view of decurling sections150and160.

Decurling section150is structured of small diameter roller151(having a radius of 7 mm, for example), paired belt driven rollers152and153, and belt154entraining about belt driven rollers152and153. Spring156is entrained about shaft155and small diameter roller151, and allows small diameter roller151to press against belt154.

Changeover gate157switches the conveyance routes of sheet S, when changeover gate157exists at the dotted position inFIG. 6, route HR21is selected through which sheet S can not enter decurling section150, while when changeover gate157exists at the solid-line position, route HR22is selected through which sheet S enters decurling section150.

Since route HR21has a large curvature radius, for example 60 mm, as shown inFIG. 6, when sheet S passes through route HR21, no decurling operation is conducted. On the other hand, when sheet S passes through route HR22formed of small diameter roller151and belt154, sheet S is decurled by bending force generated by small diameter roller151and belt154. That is, a concavely curled sheet S2is returned to be a flat sheet.

Next, decurling section160is structured of small diameter roller161(having a radius of 7 mm, for example), paired belt driven rollers162and163, and belt164entraining about belt driven rollers162and163. Coiled spring166is entrained about shaft165and small diameter roller161, and allows small diameter roller161to press against belt164.

Changeover gate167switches the conveyance routes of sheet S, when changeover gate167exists as at the dotted-line position inFIG. 6, route HR23is selected through which sheet S does not enter decurling section160, while when changeover gate167exists as at the solid-line position, route HR24is selected through which sheet S enters decurling section160.

Since route HR23has a large curvature radius for example, 60 mm, as shown inFIG. 6, when sheet S passes through route HR23, no decurling is conducted. On the other hand, when sheet S passes through route HR24, sheet S is decurled by bending force generated by small diameter roller161and belt164. That is, convexly curled sheet S1is returned to its original flat sheet state.

Using sheet moisturizing apparatus B, the operator can select an operation mode from among: a non-decurling mode which does not reform sheet S, a moisturizing mode which moisturizes sheet S without using a bending force, a first decurling mode which flattens sheet S using the bending force, but not moisturizing, and a second decurling mode which flattens sheet S using a bending force after moisturizing.

In the non-decurling mode, route HR2is selected by changeover gate102shown inFIG. 3, and routes HR21and HR23are selected by changeover gates157and167, respectively, through which sheet S is conveyed.

In the moisturizing mode, route HR3is selected by changeover gate102shown inFIG. 3, and routes HR21and HR23shown inFIG. 6are selected by changeover gates157and167, respectively. After sheet S2passes through routes HR1and HR3inFIG. 3, sheet S2is moisturized by moisturizing unit110, then sheet S2enters route HR2through paired rollers R2, and further passes through routes HR21and HR23to be ejected out of sheet moisturizing apparatus B.

The first decurling mode, in which sheet S is mechanically decurled without water, includes a concave-decurling mode which flattens the concavely curled sheet (which is sheet S2inFIG. 6) and a convex-decurling mode which flattens the convexly curled sheet (which is sheet S1inFIG. 6).

In the concave-decurling mode, after route HR2is selected by changeover gate102shown inFIG. 3, route HR22is selected by changeover gate157, and route HR23is selected by changeover gate167shown inFIG. 6.

Accordingly, concavely curled sheet S2passes through the selected routes which are HR2, HR22and HR23, and is reformed to the original flat sheet state by decurling section150, after which flattened sheet S2is ejected out of sheet moisturizing apparatus B.

In the convex-decurling mode, after route HR2is selected by changeover gate102shown inFIG. 3, route HR21is selected by changeover gate157shown inFIG. 6, as well as route HR24is selected by changeover gate167.

Accordingly, convexly curled sheet S1passes through the selected routes which are HR2, HR21and HR24, and is returned to its original flat sheet state by decurling section160, after which flattened sheet S1is ejected out of sheet moisturizing apparatus B.

The second decurling mode in which sheet S is mechanically decurled and water content is controlled, also includes a concave-decurling mode (which decurls sheet S2inFIG. 6) and a convex-decurling mode (which decurls sheet S1inFIG. 6)

In the concave-decurling mode, after route HR3is selected by changeover gate102shown inFIG. 3, route HR22is selected by changeover gate157, and route HR23is selected by changeover gate167shown inFIG. 6.

Accordingly, concavely curled sheet S2passes through route HR3, after which it is moisturized by moisturizing unit110, and is reformed to be its original flat sheet state by decurling section150, then flattened sheet S2is ejected out of sheet moisturizing apparatus B.

In the convex-decurling mode, after route HR3is selected by changeover gate102shown inFIG. 3, sheet S1passes through route HR2and route HR21which is selected by changeover gate157shown inFIG. 6, and further passes through route HR24which is selected by changeover gate167.

Accordingly, convex curled sheet S1passes through route HR3, after which it is moisturized by moisturizing unit110, and is reformed to be its original flat sheet state by decurling section160, then flattened sheet S1is ejected out of sheet moisturizing apparatus B.

FIG. 7shows a total structure of an image forming system including: image forming apparatus A, sheet moisturizing apparatus B and book binding apparatus C which is a sheet post-processing apparatus, relating to the embodiment of the present invention.

Image forming apparatus A incorporates an image forming section which includes: charging section2, image exposure section3(which is a writing section), developing section4, transfer section4, discharging section5B and cleaning section6, all of which are mounted around image carrier1. In the image forming section, after the surface of image carrier1is evenly charged by charging device2, which is scanned by laser beam generated by image exposure device3based on the image data which are read from the document, whereby latent images are formed on the surface of image carrier1. The latent images are developed by developing section4, and form the reversal toner image on the surface of image carrier1.

Sheet S, which is supplied from sheet accommodating section7, is conveyed to a transfer position. At the transfer position, the above toner images are transferred by transfer section5A onto sheet S. After electrical charges on the reverse side of Sheet S are neutralized by discharging section5B, sheet S carrying the toner images separates from image carrier1, and is conveyed to conveyance section7B, further, sheet S is heat-fixed by fixing section8, and then ejected by paired ejecting rollers7C into sheet moisturizing apparatus B.

In addition, fixing section8includes heat roller8A, pressure applying roller8B to press against heat roller8A, and heater8C. The unfixed toner images are heated by heat roller8A, which is heated by heater8C, whereby deposited toner for forming the toner images is melted and fixed on sheet S.

In the case of the double-sided image formation on sheet S, which has been heat-fixed by fixing section8, is branched from an ordinal ejecting route by route changeover plate7D, sheet S is flipped over in reverse conveyance section7E, and again conveyed to the image forming section. After images are formed on the reverse side of sheet S, sheet S is re-conveyed to fixing section8, and ejected by paired ejecting rollers7C from image forming apparatus A into sheet moisturizing apparatus B.

Concerning image carrier1, after the images are processed, any remaining toner on its surface is removed by cleaning section6, and image carrier1stands-by for the next image formation.

In sheet moisturizing apparatus B, sheet S is controlled based on the selected mode, such as the non-decurling mode which does not reform sheet S, the moisturizing mode which moisturizes sheet S but does not use bending force, the first decurling mode which flattens sheet S using bending force without supplying water to sheet S, and the second decurling mode which flattens sheet S using bending force after sheet S is moisturized.

The operator selects any of these modes using an operation section (which is not illustrated) of image forming apparatus A, or instructions sent via a network from an outer apparatus can be used to select the mode.

Book binding apparatus C is structured of sheet conveyance section210, sheet ejecting section220, cover supplying section230, printed sheets accommodating section240, printed sheets conveyance section250, pasting section260, cover attaching section270, cover folding section280, and book ejecting section290, all of which are vertically oriented in book binding apparatus C.

When sheets S are to be ejected without being bound, the route directing to printed sheets accommodating section240is closed, and the route directing to sheet ejecting section220is opened.

When printed sheets S are to be bound, sheets S are sequentially stacked on a predetermined position of printed sheets accommodating section240, whereby a stack of the printed sheets S is formed, which includes predetermined number of pages. The stack of the printed sheets S on sheets accommodating section240is conveyed to stacked sheets supporting section250, and section250rotates and stands vertically, then glue is applied onto the edge of the stacked sheets by pasting section260.

Next, a cover sheet is supplied from cover supplying section230to be attached onto the stack by cover attaching section270, and the cover is folded by cover folding section280to become a book.

The book is then ejected by book ejecting section290from book binding apparatus C.

Additionally, book binding apparatus C is further detailed in JP 2003-209,869.

One or more embodiments of the invention can be provided advantages that, since water is applied to both sides of a vertically conveying sheet, both surfaces of the sheet receive equal amounts of water, resulting in no curling. Further, since water is applied equally to both sides of the sheet over a long term, a moisturizing apparatus capable of stable operation can be realized.