IMAGE FORMING APPARATUS

Abstract

An image forming apparatus includes: an image forming section that forms a toner image on a sheet; a fixing section that fixes the toner image on the sheet; a sheet conveyance path that branches into a first sheet conveyance path and a second sheet conveyance path downstream of the fixing section; a blowing section that guides the sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet; and a controller that controls the blowing air of the blowing section.

Description

This application is based on Japanese Patent Application No. 2008-130550 filed on May 19, 2008, which is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an advancing direction switching section for a sheet that is in a sheet conveyance path of an image forming apparatus.

In general, an image forming apparatus of an electrophotographic type transfers a toner image visualized through toner development onto a sheet, and fixes the toner image on a sheet by pressing and heating the sheet onto which the toner image has been transferred with a fixing section.

The aforesaid sheet which has been subjected to fixing processing by the aforesaid fixing section is guided to the first sheet conveyance path or to the second sheet conveyance path, by a sheet conveyance path switching section that switches advancing directions for a sheet.

The aforesaid first sheet conveyance path is, for example, a sheet conveyance path through which the aforesaid sheet is sent to a sheet ejection tray of the image forming apparatus, or to a sheet finisher that is connected to the downstream side, while, the aforesaid second sheet conveyance path is, for example, a sheet conveyance path through which the aforesaid sheet is sent to a sheet reversing device, or to a sheet re-feeding device that is for forming an image on the reverse side of the aforesaid sheet.

Many of the aforesaid sheet conveyance path switching sections are constructed so that the aforesaid sheet may be guided to the prescribed sheet conveyance path by moving the sheet guide member on which a leading edge portion of the sheet rubs, and therefore by regulating the advancing direction of the sheet (for example, see Unexamined Japanese Patent Application Publication No. 2006-330250).

The sheet conveyance path switching section of this kind can be realized in a simple structure, and it is characterized to be low in cost, but it gives strong stress to the sheet, because the sheet immediately after fixing processing comes in pressure contact with a guide member to be bent.

Further, there are sometimes caused problems wherein toner and wax on the sheet surface stick to the aforesaid sheet guide member, and the sticking toner and wax stick again to the sheet because an image surface of the sheet heated by fixing processing rubs against the sheet guide member.

SUMMARY OF THE INVENTION

The invention has been achieved in view of the situations mentioned above, and its object is to realize an image forming apparatus having a sheet conveyance path that branches into the first sheet conveyance path and the second sheet conveyance path at the downstream side of a fixing unit, wherein there is provided an air sending section that switches the sheet conveyance path for the sheet to the first conveyance path or to the second conveyance path, by blowing air against the sheet.

An aspect for attaining the aforesaid object is as follows.

An image forming apparatus characterized in that an image forming section that forms a toner image on a sheet, a fixing section that fixes the toner image on the sheet, a sheet conveyance path that branches into the first sheet conveyance path and the second sheet conveyance path at the downstream side of the aforesaid fixing section, a blowing section that guides the aforesaid sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet and a controller that controls blowing of the blowing section, are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram of a conventional image forming apparatus.

FIG. 2 is a conceptual diagram of an image forming apparatus in the present embodiment.

FIG. 3 is a block diagram showing relationship for controlling an image forming apparatus.

FIG. 4 is a diagram illustrating relationship of arrangement for a sheet conveyance path and a blowing member.

FIG. 5 is a block diagram illustrating the structure of the blowing section.

Each of FIGS. 6(a)-6(d) shows an example of an air amount changing section.

FIG. 7 is a flow chart showing a flow of blowing control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of the embodiment of the invention will be explained as follows based on drawings. Incidentally, the invention is not limited to the present example.

FIG. 1 is a conceptual diagram of a conventional color image forming apparatus G.

The color image forming apparatus G exemplified in the drawing is one that is called a tandem type color image forming apparatus wherein a plurality of photoconductors 31Y, 31M, 31C and 31K are arranged in tandem to face a single intermediate transfer belt 41, and a full-color image is formed.

This color image forming apparatus G is equipped, on its upper portion, with automatic document feeder ADF.

Documents D placed on document table 103 of the automatic document feeder ADF are separated to be a single sheet to be sent out to a document conveyance path, and is conveyed by conveyance drum 108.

An image of the documents D during conveyance is read by document reading section 1 at document image reading position RP. The document D which has been finished in terms of image reading is ejected to document ejection tray 107 by a plurality of conveyance guides and by document ejection roller 105.

Image forming apparatus G is composed of document reading section 1, exposure sections 2Y, 2M, 2C and 2K, image forming sections 3Y, 3M, 3C and 3K, intermediate transfer section 4, fixing section 5, reversing sheet ejection section 6, sheet re-feeding section 7, sheet feeding section 8 and control section C which are housed in a single casing.

The document reading section 1 illuminates a document image with lamp L at document image reading position RP, and guides its reflected light with first mirror unit 11, second mirror units 12, and lens 13, to cause the reflected light to form an image on a light-receiving surface of charge coupled device image sensor CCD.

Image signals obtained through photoelectric conversion by charge coupled device image sensor CCD undergo processes including A/D conversion by image reading control section 14, shading correction, and compression, which are stored in a memory of control section C as image data.

The aforesaid image data stored in the memory undergo appropriate image processing based on conditions established by a user, and output image data are created.

Each of exposure sections 2Y, 2M, 2C and 2K is composed of a laser light source, a polygon mirror and a plurality of lenses, and it creates a laser beam.

Each of exposure sections 2Y, 2M, 2C and 2K conducts scanning exposure by a laser beam on the surface of each of photoconductors 31Y, 31M, 31C and 31K representing constituent elements for image forming sections 3Y, 3M, 3C and 3K, corresponding to output information outputted based on the aforesaid output image data.

A latent image is formed on each of the photoconductors 31Y, 31M, 31C and 31K through the aforesaid scanning exposure by a laser beam.

Image forming section 3Y is composed of photoconductor 31Y, and of main charging section 32Y, developing section 33Y, first transfer roller 34Y and cleaning section 35Y which are arranged around the photoconductor 31Y. The same is equally true of the photoconductors 31M, 31C and 31K.

Latent images on the photoconductors 31Y, 31M, 31C and 31K are developed by respective developing sections 33Y, 33M, 33C and 33K which correspond to the aforesaid photoconductors, whereby, each toner image is formed on each photoconductor.

The aforesaid toner images formed respectively on photoconductors 31Y, 31M, 31C and 31K are transferred one after another at prescribed positions on intermediate transfer belt 41 representing an intermediate transfer body, by first transfer rollers 34Y, 34M, 34C and 34K of intermediate transfer device 4.

Toner remaining on a surface of the photoconductor from which a toner image has been transferred is removed by each of cleaning sections 35Y, 35M, 35C and 35K.

On the other hand, the aforesaid toner image transferred onto the aforesaid intermediate transfer belt 41 is conveyed by second transfer roller 42 from each of trays PG1, PG2 and PG3 of sheet feeding section 8, or from sheet feeding device S1, and is transferred onto sheet P that is fed out after its timing is controlled by sheet feeding roller 81.

A surface of the intermediate transfer belt 41 on which the transfer of a toner image onto sheet P has been finished is cleaned by belt cleaning section 43, to be ready for the succeeding image transfer.

On the other hand, sheet P carrying a toner image is conveyed to fixing section 5 where the toner image is fixed on the sheet P when it is pressed and heated.

Sheet P that has been finished in terms of fixing processing by fixing section 5 is guided by sheet conveyance path switching section 6 in terms of its advance path, and is ejected to sheet ejection tray 61.

When ejecting sheet P after reversing inside out, the sheet P is guided downward temporarily by sheet ejection guide 62, then, the sheet P is reversed after causing sheet ejection reversing roller 63 to interpose a trailing edge of sheet P, and the sheet is guided to sheet ejection roller 64 by sheet ejection guide 62 to be ejected.

Incidentally, when forming an image also on the reverse of sheet P, sheet P that is finished in terms of image fixing on the obverse is conveyed to sheet re-feeding section 7 located below by sheet guide member 62, and the sheet P is reversed by sending it reversely after causing re-feed reversing roller 71 to interpose a trailing edge, thus, the sheet P is fed out to sheet re-feeding conveyance path 72 to be ready for image forming on the reverse.

FIG. 2 is a conceptual diagram of image forming apparatus G1 in the present embodiment.

Though the image forming apparatus G1 is different from color image forming apparatus G in terms of a structure of sheet conveyance switching section 6 at downstream side of a fixing section, other points are the same. Thus, the overall explanation will be omitted.

FIG. 3 is a block diagram showing relationship for controlling image forming apparatus G1.

Control section C1 of image forming apparatus G1 is a computer system having therein CPU, memory M1, an operation unit, I/O port, an interface for communication and drive circuit.

The control by the control section C1 is carried out by performing the prescribed programs stored in memory M1.

Further, the control section C1 is connected to a network to be capable of exchanging information with other information exchange equipment.

In the present drawing, meanwhile, descriptions of blocks which are not related directly to the explanation of the present embodiment are omitted.

FIG. 4 is a diagram illustrating relationship of arrangement for sheet conveyance path 100 and blowing members 210 and 220.

The sheet conveyance path 100 is one arranged at the downstream side of fixing section 5, and it is a sheet conveyance path through which sheet P that has been finished in terms of fixing processing and has been detected by sheet detection sensor SP in terms of its leading edge is guided to the first sheet conveyance path 101 or to the second sheet conveyance path 102.

At a point where the aforesaid sheet conveyance path 100 is branched into the first sheet conveyance path 101 and to the second sheet conveyance path 102, there are arranged first blowing member 210 and second blowing member 220 both representing a blowing nozzle that blows air against sheet P, in a way to face each other.

Meanwhile, in an example shown in FIG. 2, a conveyance path for conveying sheet P toward sheet ejection tray 61 corresponds to the first sheet conveyance path, and a conveyance path for conveying sheet P toward sheet ejection reversing roller (also referred to as sheet reversing section) 63 or toward sheet re-feeding section 7 corresponds to the second sheet conveyance path.

Furthers with respect to a direction of the blowing nozzle, it is not perpendicular to a plane of sheet P, but it is oblique so that a tip of the nozzle may be in the advancing direction of sheet P as shown in the drawing. By providing the inclination of this kind, air can flow in the advancing direction of sheet P, and conveyance of the sheet is stabilized.

Further, the first blowing member and the second blowing member are arranged so that blown air blowing out of the first blowing member and the second blowing member may advance in the direction toward the leading edge of the sheet after hitting the surface of the advancing sheet.

FIG. 5 is a block diagram illustrating the structure of blowing section 200.

The blowing section 200 is composed of first blowing member 210, air valve 211, second blowing member 220, air valve 221, air tank 230, air pump 240 and air duct 260.

The air pump 240 sends air so that air pressure in the air tank 230 may keep prescribed pressure.

Air in the aforesaid air tank is sent to the first blowing member 210 or to the second blowing member 220, when air valve 211 or air valve 212 which is opened or closed by instruction signals 219 or 229 of control section C1 is opened. Further, air sending to the first blowing member 210 or to the second blowing member 220 is intercepted, when the air valve 211 or the air valve 212 is closed.

Owing to the structure mentioned above, timing of the start of air blowing from the first blowing member 210 or the second blowing member 220, or timing of interception, is controlled by control section C1.

On apical portions respectively of the first blowing member 210 and the second blowing member 220, there are respectively provided the first air amount changing section 251 whose position is changed by instruction signal 218 of control section C1 and the second air amount changing section 252 whose position is changed by instruction signal 228 of control section C1.

Namely, an amount of air blowing against sheet P from forefronts of the first blowing member 210 and the second blowing member 220 per unit time is controlled when the control section C1 controls the first air amount changing section 251 and the second air amount changing section 252.

Each of FIGS. 6(a)-6(d) shows an example of an air amount changing section. Meanwhile, the structure of the first air amount changing section 251 is the same as that of the second air amount changing section 252.

FIG. 6(a) is a conceptual diagram of the first blowing member 210, and air that is conveyed through air duct 260 blows out in the direction of arrow “f” from slit-shaped air blowing outlet 259 of the first blowing member 210.

The first air amount changing section 251 is provided on the blowing outlet of the first blowing member 210. Each of FIGS. 6(b), 6(c) and 6(d) is an example of the first are amount changing section 251.

FIG. 6(b) is an example wherein an amount of air that hits sheet P is changed when member 255 having small holes formed in a staggered pattern is moved to a blowing outlet of the first blowing member 210.

Further, FIG. 6(c) is an example wherein an amount of air that hits sheet P is changed when indented member 256 is moved at a blowing outlet of the first blowing member 210.

Further, FIG. 6(d) is an example wherein an amount of air that hits sheet P is changed when member 257 that is opened and closed symmetrically is caused to open and close at a blowing outlet of the first blowing member 210.

Each of the aforesaid members 255, 256 and 257 is called an opening area adjusting member.

FIG. 7 is a flow chart showing a flow of blowing control.

Control of blowing is one wherein sheet P advancing to sheet conveyance path 100 is guided to the first sheet conveyance path 101 or to the second sheet conveyance path 102 by spraying air against sheet P following specifications of a job established in advance, and sheet P that advances further receives blowing to cool an image plane.

After the leading edge of sheet P is detected by sheet detection sensor SP (step S1: Y), sheet conveyance path selection information that is determined by specifications of the job established on image forming apparatus G1 is acquired. Further, sheet leading edge position information that is a distance by which the leading edge of sheet P advances from a position of the sheet detection sensor SP is calculated one after another from a conveyance speed of sheet P (step S2).

After it becomes clear that the leading edge of sheet P has arrived at the position established in advance by the aforesaid calculated sheet leading edge position information (step S3: Y), the sheet P is judged whether it is sheet P to be sent to the first sheet conveyance path 101 or not, referring to the aforesaid acquired sheet conveyance path selection information (step S4).

If the sheet P is one to be sent to the first sheet conveyance path, second air valve 212 is opened so that air may blow out of second blowing member 220 positioned below the sheet P (step S5). An amount of air blowing out per unit time is determined by the second air amount changing section 252.

When a leading edge portion of sheet P is guided to the first sheet conveyance path 101 by air blowing out of the second blowing member 220 and the leading edge of sheet P arrives at an air amount changing position established in advance (step 6: Y), an amount of air blowing out of the second blowing member 220 is reduced (step S7).

A change of an amount of air blowing out of the second blowing member 220 of this kind reduces problems that contact between an image surface of sheet P and a sheet guide member of the first sheet conveyance path is weakened, toner and wax on the sheet surface stick to the aforesaid sheet guide member.

Meanwhile, in the example stated above, a leading edge portion of sheet P is guided by air blowing out of the second blowing member 220 to the first sheet conveyance path 101, for easy understanding of the explanation. However, it is preferable to construct so that air may blow out of both the first blowing member 210 and the second blowing member 220, and a leading edge portion of sheet P may be guided to the first sheet conveyance path 101 by the difference between an amount of air from the first blowing member 210 and that of air from the second blowing member 220.

By constituting as stated above so that both sides of sheet P are constantly hit by air, air flows constantly on an image surface of sheet P, thus, a toner image heated in fixing device 5 is cooled rapidly, rubbing between sheet P and a sheet guide member is reduced, and a problem that toner and wax on the surface of the sheet stick to the sheet guide member is further reduced.

After the trailing edge of sheet P is detected by sheet detection sensor SP (step S8: Y), or after the passage of prescribed time since the detection, an air valve that has been opened is closed (step 12) to finish the routine.

On the other hand, in step S4, when sending sheet P to second sheet conveyance path 102 (step S4: N), the first air valve 211 is opened (step S9) so that air may blow out of the first blowing member 210 that is located above the sheet P. Meanwhile, an amount of air emitted per unit of time is determined by the first air amount changing section 251.

When a leading edge portion of sheet P is guided to the second sheet conveyance path 102 by air blowing out of the first blowing member 210 and the leading edge arrives at a position for changing an amount of air established in advance (step S10: Y), an amount of air blowing out of the first blowing member 210 is reduced (step S11).

In the example stated above again, a leading edge portion of sheet P is guided by air blowing out of the second blowing member 210 to the second sheet conveyance path 102, for easy understanding of the explanation. However, it is preferable to construct so that air may blow out of both the first blowing member 210 and the second blowing member 220, and a leading edge portion of sheet P is guided to the second sheet conveyance path 102 by the difference between an amount of air from the first blowing member 210 and that of air from the second blowing member 220.

By constituting, as stated earlier, so that both sides of sheet P may be constantly hit by air, air flows constantly on an image surface of sheet P, thus, a toner image heated in fixing device 5 and sheet P are cooled rapidly, and rubbing between sheet P and a sheet guide member is reduced.

As a result, a problem that toner and wax on a surface of the sheet stick to the sheet guide member, and a problem of occurrence of curls which are caused when strong stress is applied on overheated sheet P, are reduced.

After the trailing edge of sheet P is detected by sheet detection sensor SP (step S8: Y), or after the passage of prescribed time since the detection, an air valve that has been opened is closed (step 12) to finish the routine.

In the case of switching of sheet conveyance paths in the present embodiment in the image forming apparatus having a sheet conveyance path that is branched into the first sheet conveyance path and the second sheet conveyance path, at the downstream side of the fixing device, occurrence of curls of sheets can be suppressed, because strong stress is not applied on the sheet immediately after fixing processing, which is different from sheet conveyance path switching in which a sheet conveyance path is switched by a sheet guide member.

Further, it is possible to prevent a problem that toner and wax stick to the sheet guide member and to stick again to the sheet, because an image surface of the sheet heated by fixing processing does not rub strongly against the aforesaid sheet guide member, and is further cooled by air.

Claims

1. An image forming apparatus comprising:

(a) an image forming section that forms a toner image on a sheet;

(b) a fixing section that fixes the toner image on the sheet;

(c) a sheet conveyance path that branches into a first sheet conveyance path and a second sheet conveyance path downstream of the fixing section;

(d) a blowing section that guides the sheet to the first sheet conveyance path or to the second sheet conveyance path by blowing air to the sheet; and

(e) a controller that controls the blowing air of the blowing section.

2. The image forming apparatus of claim 1, wherein the blowing section comprises a first blowing member and a second blowing member which blow air of the blowing section, wherein the first and second blowing members are arranged to face each other.

3. The image forming apparatus of claim 2, wherein each of the first and second blowing members comprises a slit-shaped air blowing outlet.

4. The image forming apparatus of claim 2, wherein the first and second blowing members are arranged so that blown air blowing out each of of the first blowing member and the second blowing member advances toward a leading edge of the sheet after hitting a surface of the advancing sheet.

5. The image forming apparatus of claim 2, wherein the first blowing member comprises a first air amount changing section which changes an amount of blown air blowing out of the first blowing member, and the second blowing member comprises a second air amount changing section which changes an amount of blown air blowing out of the second blowing member.

6. The image forming apparatus of claim 5, wherein each of the first and second air amount changing sections comprises an opening area adjusting member which changes an opening area at the air blowing outlet, and changes the amount of the blown air blowing out of the air blowing outlet by moving the opening area adjusting member.

7. The image forming apparatus of claim 2, wherein the blowing section comprises a first air valve which sends or intercepts air blowing from the first blowing member, and a second air valve which sends or intercepts air blowing from the second blowing member.

8. The image forming apparatus of claim 7, wherein the controller calculates positional information of a leading edge of the conveyed sheet on the basis of a signal sent from a sheet detection sensor that detects the leading edge of the sheet, determines a timing of the sending air or the intercepting air on the basis of the calculated positional information, and changes the amount of the air blowing out of each of the first and second air amount changing sections.

9. The image forming apparatus of claim 1, further comprising:

a sheet ejection tray which receives the sheet ejected from the apparatus; and

a re-feeding section through which the sheet having an image on a front side thereof is re-fed for forming an image on a rear side,

wherein the first sheet conveyance path is a conveyance path through which the sheet is conveyed to the sheet ejection tray, and the second sheet conveyance path is a conveyance path through which the sheet is conveyed to the re-feeding section.

10. The image forming apparatus of claim 1, further comprising:

a sheet ejection tray which receives the sheet ejected from the apparatus; and

a sheet reversing section by which a front and rear sides of the sheet are reversed,

wherein the first sheet conveyance path is a conveyance path through which the sheet is conveyed to the sheet ejection tray, and the second sheet conveyance path is a conveyance path through which the sheet is conveyed to the sheet reversing section.