JP2001348131A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device providing superior image formation by uniformly heating a sheet stored in a sheet stack means. SOLUTION: The sheet stored in the sheet stack means is heated by a heating means having a heat radiation face 62a for heating the sheet. The heat radiation face 62a is disposed in such a position that shortest distances between the respective ends of the maximum size sheet Smax stackable on the sheet stack means and the respective ends of the heat radiation face 62a become approximately same and the temperature difference in the temperature distribution of the heat radiation face 62a is set to a prescribed quantity or less so that the sheet can be uniformly heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus provided with a sheet heating device for heating sheets contained in sheet stacking means and removing moisture from the sheets.

[0002]

2. Description of the Related Art In a conventional image forming apparatus such as a copying machine or a printer, a sheet stored in a sheet stacking means is conveyed to an image forming section, and a toner image formed on an image carrier is transferred. There is one in which the transferred toner image is fixed on a sheet by a fixing unit.

In such an image forming apparatus, when the sheet absorbs a large amount of moisture, that is, when the water content of the sheet increases, the volume resistivity decreases. If it is grounded at a position other than the above, the transfer current may not satisfactorily flow in the sheet and transfer failure may occur. If the sheet absorbs a large amount of moisture, wrinkles are likely to occur when the sheet passes through the fixing unit.

Therefore, in order to solve such a problem,
2. Description of the Related Art Conventionally, there is an image forming apparatus provided with a sheet heating device that is a heating unit that heats a sheet stored in a sheet stacking unit and removes moisture from the sheet. Here, the sheet heating device is disposed below the sheet stacking means 7c indicated by a dashed line containing the sheet S, for example, as shown in FIG. 9, and the sheet heating device 60 is a heat source indicated by a broken line. A heater 61 and a heat radiating plate 62 which is a heat radiating member indicated by a two-dot chain line are provided.

The heater 61 is fixed to a heat radiating plate 62 as shown in FIG. 10, and the heat radiating plate 62 has a heater mounting surface on the lower side and a bottom plate 101 of an image forming apparatus having an escape hole 101A for a heater. Is fixed to the screw.

In FIG. 1, reference numeral 63 denotes an AC code line from a power supply (not shown) or an external power supply incorporated in the image forming apparatus.
Is supplied to the power supply. In recent years, an environment detection sensor (not shown) has been installed near the sheet stacking means,
Controlling ON / OFF of the heater 61 according to temperature and humidity information is also considered.

[0007]

By the way, in a conventional image forming apparatus provided with such a sheet heating device,
In recent years, due to the demands of users for miniaturization and energy saving, it is often necessary to install the heater 61 near the lower portion of the sheet stacking means 7c as shown in FIGS. 9 and 10 from the viewpoint of space and efficiency. .

As a result, the temperature of the surface (heat radiating surface) of the heat radiating plate 62 directly affects the sheet S immediately above the heat radiating plate, and when the sheet S is locally heated, the temperature gradient of the sheet S decreases. This has caused a problem that the transfer becomes poor and transfer failure occurs.

Here, this problem is caused, for example, by the heater 61.
When the surface of the heat radiating plate (heat radiating surface) is uniformly heated and the temperature distribution is small, when the size of the heat radiating surface 62a of the heat radiating plate 62 is smaller than the sheet S as shown in FIG. When the heat radiating surface 62a of the sheet 62 is not provided at a position symmetric with respect to each side and each corner of the sheet S as shown in FIG. 12 (L1） L2), FIGS.
In the state where the states of
2, the size of the heat radiation surface 62a is smaller than the sheet S,
Further, it is likely to occur when the sheet S is not provided at a position symmetrical with respect to each side and each corner of the sheet S.

In this state, the sheet S is locally heated through the bottom plate of the sheet stacking means 7c by the heat radiating surface 62a of the heat radiating plate 62 whose surface is uniformly heated, and the water content of the sheet S is reduced. Is different depending on the location. When the moisture content is different depending on the location as described above, a portion that thermally expands and a portion that contracts are generated in one sheet, and the sheet becomes as shown in FIG. This is because the waves deform. If the sheet is conveyed in such a wavy shape, there occurs a problem that the transfer is not performed well and a good image cannot be formed.

Incidentally, in order to prevent such a problem from occurring, a heat radiating plate 62 having a heat radiating surface 62a corresponding to the size of the sheet S may be provided, for example. Generally, a universal type sheet stacking tray that enables the heat radiation plate having a good position and size for a sheet of a certain size may not be good for a sheet of another size.

As another method, when a heat radiating plate 62 having a small heat radiating surface 62a is used, the heat radiating plate 62 is arranged at a position distant from the sheet and the heater temperature is increased in order to uniformly heat large-size paper. However, such a configuration not only leads to an increase in the size of the apparatus, but also results in poor heating efficiency, and furthermore, for example, heating the image carrier and the toner, which may cause adverse effects. is there.

When the temperature of the heat radiating plate (heat radiating surface) is not uniform and the temperature distribution is large, the heat radiating surface of the heat radiating plate
Regardless of the size and position of “a”, if the sheet S is locally heated, there will be portions that thermally expand and contract in the sheet S, and the sheet will undulate, resulting in poor transfer. To cause.

Accordingly, the present invention has been made in view of such circumstances, and provides an image forming apparatus capable of uniformly heating sheets stored in sheet stacking means and forming a good image. The purpose is to do so.

[0015]

According to the present invention, there is provided an image forming apparatus for conveying a sheet stored in a sheet stacking unit to an image forming unit to form an image on the sheet, the sheet stored in the sheet stacking unit. A heating means having a heat radiating surface for heating the sheet, the shortest distance between each end of the sheet of the largest size that can be stacked on the sheet stacking means and each end of the heat radiating surface is substantially the same. Wherein the heat radiating surface is disposed so that a temperature difference in a temperature distribution of the heat radiating surface is equal to or less than a predetermined amount.

Further, the present invention is characterized in that the size of the heat radiating surface is the same as the size of the sheet having the maximum size.

Further, according to the present invention, the heating means includes a heat radiating member installed substantially parallel to the sheet and having the heat radiating surface, and a heat source for heating the heat radiating member. In the case where the heat radiating surface of the heat radiating member is smaller than the sheet of the maximum size, when the sheet stacking means is attached to the apparatus main body, each end of the sheet of the maximum size and the The heat radiating member is disposed at a position where the shortest distance from each end of the heat radiating surface is substantially the same.

According to another aspect of the present invention, there is provided an image forming apparatus for conveying a sheet stored in a sheet stacking unit to an image forming unit to form an image on the sheet, wherein the sheet stored in the sheet stacking unit is heated. A heating unit having a heat-dissipating surface, wherein when the heat-dissipating surface is larger than the maximum-size sheet stored in the sheet stacking unit, the heat-dissipating position is set at a position where the maximum-size sheet does not come off the heat-dissipating surface. The surface is arranged.

Further, according to the present invention, the heating means includes a heat radiating member provided substantially parallel to the sheet and having the heat radiating surface, and a heat source for heating the heat radiating member. And if the heat radiating surface of the heat radiating member is larger than the maximum sized sheet, the maximum sized sheet is detached from the heat radiating surface when the sheet stacking means is mounted on the apparatus main body. The heat radiating member is arranged at a position where no heat is generated.

Further, the present invention is characterized in that a heat source for heating the heat radiating member is provided at a position where a temperature difference in a temperature distribution of the heat radiating surface is equal to or less than a predetermined amount.

Further, the present invention is characterized in that the heat radiating member is formed of a material having a high heat transfer coefficient.

Further, the present invention is characterized in that the size of the heat source is equal to or smaller than that of the heat radiating member.

Further, in the present invention, the sheet stacking means is a paper feed cassette, and the heating means is arranged below the paper feed cassette in the order of a heat radiating member and a heat source. is there.

[0024]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 100A denotes an image forming apparatus. The image forming apparatus 100A is a station 100 (100a, 100a) which is four image forming units arranged side by side to form yellow, cyan, magenta and black images.
100b, 100c, 100d), image reading section 1R, sheet feeding means 50, 51, transfer belt 21, and transfer blade 4
(4a, 4b, 4c, 4d), a transfer unit 20, a fixing unit 11, and the like.

Here, the station 100 (100a, 100a,
100b, 100c, and 100d) are photosensitive drums 1 (1a, 1a, 1b) as image carriers that are driven to rotate clockwise.
1b, 1c, 1d) and the photosensitive drums 1a to 1d.
Exposure device 6 (6a, 6b, 6c, 6d) and developing device 3 arranged in order in the rotation direction opposite to the outer peripheral surface of 1d
(3a, 3b, 3c, 3d), and a cleaning and charging device 2 (2a, 2b, 2c, 2d).

Then, such a station 100a
1 to 100d, at the time of image formation, first, the chargers 2a to 2d apply a uniform amount of charge to the surfaces of the photosensitive drums 1a to 1d, and then, in response to a recording image signal from the image reading unit 1R. The photosensitive drums 1a to 1d are exposed by exposing the photosensitive drums 1a to 1d by the exposure devices 6a to 6d.
d to form an electrostatic latent image.

Next, the electrostatic latent images are visualized by the developing devices 3a to 3d containing developers (toners) of four colors of yellow, cyan, magenta, and black, respectively, and the toner images are formed on the respective photosensitive drums 1a to 1d. It is formed on top.

On the other hand, the paper feeding means 50, 51
00B, cassettes 7a and 7b as sheet storage means for storing sheets S, manual trays 36 provided on side surfaces of the main body for loading special paper such as thick paper, cassettes 7a and 7b, or manual trays The apparatus includes a pickup roller 8 and a feeding roller 39 for feeding out the sheets S stored in the tray 36 one by one, a registration roller 10 for sending out the sheets S in synchronization with the toner image forming timing, and the like.

Next, an image forming operation of the image forming apparatus 100A thus configured will be described.

When the image forming operation start signal is issued, first, in each of the stations 100a to 100d, the charger 2a
The surfaces of the photosensitive drums 1a to 1d whose surfaces have been charged by the exposure devices 6a to 6d are exposed by the exposure devices 6a to 6d in accordance with the recorded image signals from the image reading unit 1R. An image is formed. Next, the electrostatic latent images are developed by the developing devices 3a to 3d, and yellow, cyan, magenta, and black toner images are formed on the respective photosensitive drums 1a to 1d.

On the other hand, in parallel with such a toner image forming operation, the sheet S is fed out one by one from the cassettes 7a and 7b or the manual feed tray 36 by the pickup roller 8 and the feeding roller 39. Then, the sheet S sent out in this manner is fed to the conveying roller pairs 41, 43, 4
4 and 45, the sheet is conveyed to the registration roller pair 10 through the conveyance paths 31 and 33.

At this time, the registration roller pair 10 is stopped, so that the leading end of the sheet is
And the skew is corrected. And
After correcting the skew of the sheet S in this manner, the registration roller pair 10 starts rotating at a timing at which the toner image is transferred to a predetermined position of the sheet S, whereby the sheet S is placed on the transfer belt 21 and is It is electroadsorbed and transported in the direction of arrow A.

Thereafter, the sheet S adsorbed on the transfer belt 21 is transferred to each of the photosensitive drums 1a to 1d by the transfer belt 21.
The transfer blades 4a to 4c are sequentially transported to the transfer units Ta, Tb, Tc, and Td facing each other, and are disposed at the transfer units Ta, Tb, Tc, and Td, and are applied with a voltage having a polarity opposite to that of the toner.
The toner images of the respective colors on the photosensitive drums 1a to 1d are superimposed and transferred on the sheet S by the action of d. As a result, a color image is formed on the sheet S by superimposing the four color toner images of yellow, magenta, cyan, and black.

Next, the sheet S on which the four color toner images are transferred is separated from the transfer belt 21 at the leading end in the transport direction and transported to the fixing device 11, where it is fixed by receiving heat and pressure. As a result, the toners of the respective colors are melted and mixed to form a full-color print image fixed on the sheet S, and then discharged outside the apparatus by a discharge conveyance unit 63 provided downstream of the fixing device 11.

By the way, below the cassettes 7a and 7b, a sheet heating device having a heater 61 and a heat radiating plate 62 as shown in FIG. 9 is provided. Here, in the present embodiment, the heat radiating plate 62 of the sheet heating device is used.
Are installed substantially parallel to the cassettes 7a and 7b (sheets), and have a heat radiation surface 62a of substantially the same size as the maximum size sheet Smax, as shown in FIGS.

Here, FIG. 2 shows the radiation surface 62a of the radiation plate 62.
Is larger than the maximum size sheet Smax. In this case, the radiator plate 62 is replaced with the cassettes 7a and 7b loaded with the maximum size sheet Smax.
When set to 00B, the sheet Smax of the maximum size is provided at a position where the sheet Smax does not come off from the heat radiation surface 62a of the heat radiation plate 62 as shown in FIG.

By providing the heat radiating plate 62 at such a position and providing the heater 61 at a position where the temperature difference in the temperature distribution of the heat radiating plate 62 becomes a predetermined amount or less as described later, the sheet Smax is formed. Local heat can be prevented from being applied.

FIGS. 4 and 5 show the cassettes 7a and 7b.
A3, A4, A4R size sheets S that can be stacked
3 shows the positional relationship between the heat radiating plate 62 and the heat radiating surface 62a. In any case, the heat radiating surface 62a of the heat radiating plate 62 is located at a position that does not deviate from the maximum size sheet Smax. Since each side of the sheet is inside of each side of the surface 62a, the entire lower surface of the sheet S comes to face the heat radiation surface 62a. For this reason, even if these sheets S (and the sheet Smax of the maximum size) are heated, local heat is not applied to the sheets S.

By preventing local heat from being applied to the sheet S, the sheet S is not deformed even when heated to dehumidify the sheet S. It is possible to transfer a toner image without causing any trouble and to form a good copy image.

The heat radiating plate 62 is connected to the cassettes 7a and 7b.
When the sheet is set in the main body of the apparatus, the largest sheet Sm
By providing ax at a position where it does not deviate from the heat radiating surface 62a, the degree of design freedom of the cassettes 7a and 7b, and furthermore, the sheet feeding means 50 is increased, and an optimal arrangement is possible.

FIG. 3 shows a case where the size of the heat radiating surface 62a of the heat radiating plate 62 is smaller than the maximum size sheet Smax. In this case, the heat radiating plate 62 is a cassette on which the maximum size sheet Smax is loaded. For example, L1 {L2 {L3} such that the shortest distances L1 to L4 between the ends of the sheet Smax of the maximum size and the ends of the heat radiation surface 62a are substantially the same when the sheets 7a and 7b are set in the apparatus main body.
It is provided at a position such that L4 ≦ about 20 mm.

By providing the heat radiating plate 62 at such a position, if the size of the heat radiating surface 62a is smaller than the maximum size sheet Smax, the maximum size sheet Smax is uniformly heated as described above. In addition, it is possible to prevent the occurrence of transfer failure and to reduce the size of the apparatus. The same effect can be obtained even when the size of the heat radiation surface 62a is the same as the maximum size sheet Smax.

Also, by making the shortest distances L1 to L4 of each end of the sheet Smax of the maximum size and each end of the heat radiation surface 62a substantially the same, compared with the case where the shortest distances L1 to L4 are different. The heat of the sheet S can be uniformly heated by separating the heat radiating plate 62 from the sheet S by a small distance. Thus, the distance between the heat radiating plate 62 and the sheet S can be shortened, and the heat radiating plate 62 to be used can be reduced, so that the cost of the apparatus can be reduced. In addition, the size of the heater 61 can be reduced accordingly, and the cost and size of the device can be reduced.

Next, an example of this embodiment will be described.

In the present embodiment, an aluminum plate having a thickness of 0.8 mm, which is a material having a high heat transfer rate, is used as the radiator plate 62, and the temperature difference in the temperature distribution of the radiator surface 62a of the radiator plate 62 is reduced by a predetermined amount. As shown in FIG. 6, the heater 61 was fixed to the center of the heat radiating plate 62 (aluminum plate) as described below. Further, the distance between the sheet and the heat sink 62 is about 16 m.
and heated at room temperature about 20 ° C. for about 24 hours.

FIG. 7 shows the radiating plate surface (radiating surface 6) at this time.
2A shows the temperature distribution. In addition, ○ indicates a measurement point, and a number inside the ○ indicates a temperature at the measurement point.

Here, the heater 61 is provided at the center of the heat radiating plate 62.
Is fixed, as shown in the figure, the temperature of the heat sink surface is 10 deg or more with respect to room temperature, there is no place where the temperature changes rapidly, and the temperature distribution difference is about 10 deg or less. And such a temperature distribution difference is 10 de.
As a result of using the heat radiating plate 62 of about g or less, the cassette 7a,
The difference in surface temperature distribution of the lowermost sheet stacked on 7b was about 5 deg or less, and a good copy image was obtained.

As described above, the heat radiating surface 62a equivalent to the maximum size sheet Smax that can be loaded on the cassettes 7a and 7b
The sheet S is heated uniformly by heating the sheet S by the sheet heating device 60 having the heat radiating plate 62 configured so that the temperature difference in the temperature distribution of the heat radiating surface 62a is equal to or less than a predetermined amount. Good image formation can be performed.

By forming the heat radiating plate 62 heated by the heater 61 from a material having a high heat transfer rate such as an aluminum plate as in this embodiment, the heat radiation member surface temperature can be reduced with a small amount of heat, that is, with a small power consumption. The distribution difference can be reduced, the sheet can be efficiently dehumidified, and the running cost can be reduced.

Further, in the present embodiment, the heat radiating plate 62 and the heater 61 are arranged so that the temperature difference in the temperature distribution of the heat radiating surface 62a as shown in FIG.
, That is, such that the heater 61 is located substantially at the center with respect to the heat sink 62,
If the heat sink surface temperature distribution as shown in FIG. 7 can be obtained, the heater 61 may be provided at a position other than substantially at the center as shown in FIG. 8B.

Further, in the above description, the case where the sheet heating device 60 is installed below the cassettes 7a and 7b has been described. However, the present invention is not limited to this, and the sheet heating device 60 may be installed above the cassettes 7a and 7b. May be provided.

[0054]

As described above, according to the present invention, a sheet can be uniformly heated, and a good image can be formed without deforming the sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a top view showing a positional relationship between a sheet and a heat radiating surface when a heat radiating surface of a heat radiating plate of a sheet heating device provided in the image forming apparatus is larger than a sheet having a maximum size.

FIG. 3 is a top view showing the positional relationship between the sheet and the heat radiating surface when the heat radiating surface of the heat radiating plate of the sheet heating device is smaller than the maximum size sheet.

FIG. 4 is a top view showing a positional relationship between various sheets and a heat radiating surface when the heat radiating surface of the heat radiating plate is larger than a sheet having a maximum size.

FIG. 5 is another top view showing the positional relationship between the various sheets and the heat radiating surface when the heat radiating surface of the heat radiating plate is larger than the maximum size sheet.

FIG. 6 is a view for explaining the positional relationship between the heat sink and the heater.

FIG. 7 is a view showing a temperature distribution on a heat radiation surface of the heat radiation plate.

FIG. 8 is a diagram showing a positional relationship between a heat sink and a heater according to another embodiment of the present invention.

FIG. 9 is a perspective view illustrating a sheet heating device provided in a conventional image forming apparatus.

FIG. 10 is a diagram illustrating a configuration of the conventional sheet heating apparatus.

FIG. 11 is a view showing a state in which the heat radiating plate of the conventional sheet heating device is smaller than a sheet.

FIG. 12 is a diagram showing a state where the heat radiating plate of the conventional sheet heating device is not provided at a position symmetrical with respect to each side and each corner of the sheet.

FIG. 13 is a diagram showing a wavy deformation of a sheet locally heated by a radiator plate of the conventional sheet heating apparatus.

[Explanation of symbols]

 7a, 7b Cassette 60 Sheet heating device 61 Heater 62 Heat radiating plate 62a Heat radiating surface 100A Image forming device 100B Device main body S Sheet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H072 AA23 AA30 BB01 HB01 HB03 3F343 FA02 FB01 FC19 FC20 GA01 GB01 GC01 GD01 HC28 LC04 MA26 MC14

Claims (9)

[Claims] 1. An image forming apparatus for conveying a sheet stored in a sheet stacking unit to an image forming unit to form an image on the sheet, wherein a heat radiating surface for heating the sheet stored in the sheet stacking unit is provided. Comprising a heating means having the heat dissipating surface at a position where the shortest distance between each end of each sheet of the maximum size that can be stacked on the sheet stacking means and each end of the heat dissipating surface is substantially the same, An image forming apparatus, wherein a temperature difference in a temperature distribution of the heat radiating surface is equal to or less than a predetermined amount. 2. The size of the heat radiating surface is the same as the size of the sheet having the maximum size.
The image forming apparatus as described in the above. 3. The heating means is provided substantially parallel to the sheet and has a heat radiating member having the heat radiating surface, and a heat source for heating the heat radiating member, and the sheet stacking means is detachable from the apparatus main body. In addition, when the heat radiating surface of the heat radiating member is smaller than the sheet of the maximum size, when the sheet stacking means is mounted on the apparatus main body, each end portion of the sheet of the maximum size and the heat radiating surface 3. The image forming apparatus according to claim 1, wherein the heat radiating member is disposed at a position where the shortest distance from each end is substantially the same. 4. An image forming apparatus for conveying a sheet stored in a sheet stacking unit to an image forming unit and forming an image on the sheet, wherein a heat radiating surface for heating the sheet stored in the sheet stacking unit is provided. When the heat radiating surface is larger than the maximum size sheet accommodated in the sheet stacking means, the heat radiating surface is arranged at a position where the maximum size sheet does not deviate from the heat radiating surface. An image forming apparatus comprising: 5. The heating means is provided substantially parallel to the sheet and has a heat radiating member having the heat radiating surface, and a heat source for heating the heat radiating member, and the sheet stacking means is detachable from the apparatus main body. And when the heat radiating surface of the heat radiating member is larger than the sheet of the maximum size, the sheet of the maximum size does not come off from the heat radiating surface when the sheet stacking means is mounted on the apparatus main body. The image forming apparatus according to claim 4, wherein the heat radiating member is disposed at a position. 6. The heat source according to claim 3, wherein a heat source for heating the heat radiating member is provided at a position where a temperature difference in a temperature distribution of the heat radiating surface is equal to or less than a predetermined amount. The image forming apparatus as described in the above. 7. An image forming apparatus according to claim 1, wherein said heat radiating member is formed of a material having a high heat transfer coefficient. 8. The image forming apparatus according to claim 7, wherein the size of the heat source is equal to or smaller than that of the heat radiating member. 9. The sheet stacking means is a paper feed cassette, and the heating means is disposed below the paper feed cassette in the order of a heat radiating member and a heat source. The image forming apparatus as described in the above.