JPH0243585A - Fixation device - Google Patents

Abstract

PURPOSE:To sufficiently cool a sheet even in the case that the sheet has a high temperature when image forming is repeatedly executed on the same sheet by providing a cooling means whose cooling ability can be adjusted behind a thermal fixing unit and controlling it with the aid of a control means. CONSTITUTION:The cooling means 35 and 36 whose cooling ability can be adjusted are provided behind the thermal fixing units 32 and 34 and the sheet where an image is fixed with heat is cooled by them. The cooling means 35 and 36 are controlled by the control means and the ability of the cooling means on and after a second fixing processing time is enhanced more than that at a first time when the image forming is repeatedly executed on the same sheet. That means, they are controlled so that the cooling roller 35 is used for the first copying time and both of the cooling rollers 35 and 36 are used for the second copying time and after. Thus, the sheet can be sufficiently cooled without lowering a fixing temperature even in the case that the sheet has a high temperature when the image forming is repeatedly executed on the same sheet.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a fixing device used in an image forming apparatus that performs thermal fixing processing, such as a copying machine that performs electrophotographic image formation or a laser beam printer. In particular, the present invention relates to a fixing device used in an image forming apparatus having a double-sided image forming mode or a composite image forming mode in which images are repeatedly formed on one sheet.

(Prior Art) In the case of a thermal fixing method, as the image forming speed increases, the temperature required for fixing also increases.

If this is left unattended, the heat dissipation on the tray that receives the fixed and ejected sheets will not be in time, and the heat will accumulate on the sheets that are sequentially ejected.As a result, the fixed image on the ejected sheets will be formed. The toner is not completely solidified and adheres to other sheets, causing a so-called blocking phenomenon in which the sheets stick together.

Therefore, as a solution to this problem, the Utility Model 60-1
Some of them are known from Japanese Utility Model Application No. 86447, Japanese Utility Model Application Publication No. 58-36745, and Japanese Utility Model Application Publication No. 58-92245. In the first type, a heat vibrator is provided after the fixing device, which serves both to transport and cool the sheet after fixing. The second one is installed after the fuser - a pair of paper ejection rollers (one of which is a heat pipe so that a cooling effect can be obtained).The third one is installed after the fuser. A large number of radiation fins are provided at one end of the heat pipe.

Another example is the one described in Japanese Patent Application Laid-Open No. 135870/1983. In this fourth type, a temperature sensor is provided in the conveyance path after the fixing device, and when the temperature is higher than a predetermined temperature, the fixing temperature is lowered.

Furthermore, there is one described in Japanese Patent Application Laid-open No. 168178/1983. The fifth type is a double-sided copying machine, in which a temperature sensor is installed in the paper refeed tray that receives the sheet after copying the first side and refeeds the sheet for copying the second side, and the output temperature of this sensor is set at a certain temperature. In such a case, the fixing temperature when copying the second side is set lower than when copying the first side.

(Problems to be Solved by the Invention) However, in recent years, image forming speeds have been increasing, and copy modes such as double-sided copying and composite copying in which images are repeatedly formed on the same sheet have been adopted. Therefore, in copying in this mode, the temperature increases not only due to the increased speed of the sheet, but also because the same sheet is repeatedly subjected to heat fixing processing, which further increases the temperature. However, the first to third conventional devices utilize a heat roller that has only a certain cooling capacity, and there is a limit to the ability to increase heat dissipation by increasing heat capacity or surface area. Therefore, as mentioned above, when the same sheet is subjected to repeated heat fixing such as double-sided copying or composite copying and the temperature becomes higher, it cannot be dealt with, and a blocking phenomenon may occur.

In the fourth and fifth types, the fixing temperature is controlled so that the temperature of the sheet after heat fixing is within a temperature range that does not cause blocking, so blocking development can be avoided even in the case of double-sided copying or composite copying. . However, since the fixing temperature is further lowered during the second and subsequent fixing processes when the sheet temperature becomes even higher, this may cause fixing failure.

It should be noted that another method is to raise the glass transition point Tg of the toner, but this causes poor fixing like the fourth and fifth methods.

The present invention improves the method of cooling the sheet after heat fixing,
The purpose of this is to solve the above-mentioned problems.

(Means for Solving the Problems) In order to achieve the above-mentioned objects, the present invention includes a cooling means whose capacity can be adjusted and which is provided after a heat fixing device to cool down a sheet after a fixing process, and an image forming apparatus. In the fixing process during the second and subsequent image formation in an image forming mode in which formation is repeatedly performed on one sheet, the control means controls the cooling means to have a higher capacity than the fixing process for the first side. It is characterized by the fact that it is equipped with

(Function) A cooling means whose capacity can be adjusted is provided after the heat fixing device, and can act on the sheet after heat fixing to cool it. In the case of an image forming mode in which the cooling means is controlled by a control means and image formation is repeatedly performed on one sheet,
In the fixing process for the second and subsequent image formations, the ability of the cooling means can be increased compared to the fixing process for the first side, so if the same sheet undergoes repeated image formation without lowering the fixing temperature and becomes hotter. But it can be cooled sufficiently.

(Example) A first example of the present invention shown in FIGS. 1 to 7 will be described below.

This embodiment shows the case of a copying machine capable of double-sided copying and composite copying. As shown in FIG. 1, a photosensitive drum 2 is provided within a body 1. As shown in FIG. Around the photosensitive drum 2, a charging charger 3, an exposure section 4, a developing device 5, a transfer/separation charger 6, a cleaning device 7, and an eraser lamp 8 are arranged in order in the rotational direction of the photosensitive drum 2.

In the exposure section 4, a scanning type exposure optical system 10 provided between the photosensitive drum 2 and the document placement glass 9 on the upper surface of the body 1 slit-exposes the image of the document on the document placement glass 9. After all charges are removed from the photosensitive drum 2 by the eraser lamp 8, the portion uniformly charged by the charger 3 reaches the exposure section 4, receives the slit exposure, and forms an electrostatic latent image corresponding to the original. do.

The electrostatic latent image on the photosensitive tram 2 is developed and visualized by the developing device 5, and when it reaches the transfer/separation charger 6, a transfer seam 1 is conveyed in synchronization with the electrostatic latent image. transcribed into. The surface of the photosensitive drum 2 after the transfer is cleaned by the cleaning device 7, and then
After passing through the eraser lamp 8 and the charger 3, it is used for image formation again.

The seam 1 is fed from either the first or second paper feed section 12, 13 provided at the bottom of the machine body 1, or from the manual paper feed section 14 on one side of the machine body 1, and is fed by the register roller 15. After timing adjustment by , the image is sent to the transfer section and subjected to the transfer.

After the transfer, the sheet 1 is conveyed by the suction conveyor belt 16 and sent to the fixing device 17 . The sheet 11 passing through the fixing device 17 is directly ejected to a paper discharge tray 18 outside the machine body 1, or is sent to a paper refeed tray 19 inside the machine body 1.

The paper refeed tray 19 receives the sheet 11 either in a face-up state with the transferred image facing upward, or in a face-down state opposite to that. When the sheet l in the re-feeding tray 19 is re-fed, the timing is adjusted by the register roller 15 and the sheet is transferred in the same manner as described above. At this time, the paper stored face-up will be transferred face-down, resulting in double-sided copying. Items that were stored face-down will be transferred face-up, resulting in a composite copy.

An automatic document feeder 20 is installed on the top surface of the machine 1. This automatic document feeder 20 feeds out a large number of originals set on a document tray 21 one by one and sequentially copies them, and the copied documents are transferred to the document output tray 2
Discharge to 2.

As shown in detail in FIG. 2, the fixing device 17 includes an upper fixing roller 32 with a built-in heater 31 and a lower fixing roller 34 with a built-in heater 33, which is in pressure contact with the upper fixing roller 32 and forms a thermal fixing device. A cooling section 40 is provided after the upper and lower fixing rollers 32, 34. In the cooling section 40, cooling rollers 35 and 36 are provided in two stages, front and rear. Each of the cooling rollers 35 and 36 is combined with a lower cooling roller 37.3 that receives them from below, and the sheet 11 after heat fixing is installed.
is sandwiched between them to remove heat and cool it down.

The lower cooling rollers 37, 38 are provided in fixed positions, while the cooling rollers 35, 36 are each mounted on a lever 42a pivoted by shafts 41a, 41b as shown in FIG.
, 42b, and the lever 42a.

42b is rotated about the shaft 41 so as to be brought into contact with and separated from the lower cooling rollers 37 and 38. Lever 42
a and 42b are springs 43a and 43a applied to one end thereof;
The cooling rollers 35, 36 are urged to come into pressure contact with the lower cooling rollers 37, 38 by the urging force b.

A drive circuit 6 is provided at the other end of the levers 42a and 42b, respectively.
Solenoid 44a driven by 6a, 66b
144b are connected, and the solenoids 44a, 44
When b operates, the cooling rollers 35, 36 are rotated against the springs 43a, 43b so as to separate them from the lower cooling rollers 37, 38. Incidentally, instead of the solenoids 44a and 44b, cams that come into contact with the levers 42a and 42b may be provided, and the cams may be rotated by a motor to move the cooling rollers 35, 36 toward and away from the lower cooling rollers 37, 38.

Here, the cooling rollers 35 and 36 have good thermal conductivity, for example,
It is suitable to be made of aluminum, and the cross-sectional shape is also the same as the fourth one.
As shown in the figure, it has large hollow parts 35a and 36a for easy heat dissipation.

Furthermore, a cooling block 46 made of aluminum, for example, which also has good thermal conductivity, is installed above the cooling rollers 35, 36. As shown in FIG. 5, the cooling block 46 has recesses 46a and 46b on its lower surface that receive the cooling rollers 35, 36 when they are separated upward from the lower cooling rollers 37, 38 and contact approximately half the circumference thereof. A large number of heat radiation fins 46c are formed on the upper surface. As a result, when the cooling rollers 35 and 36 are in an unused state separated from the lower cooling rollers 37 and 38, the cooling block 46 contacts the half circumferential portions of these rollers with the recesses 46a and 46b, removes heat, and actively uses the heat dissipation fins 46c. 35. 36 Cooling rollers that only radiate heat when not in use.
significantly accelerate the temperature drop.

Each cooling roller 35, 36 further includes a fixed guide cylinder 47a,
Springs 45a and 45b housed in springs 47b are urged in a direction to press against the lower cooling rollers 37 and 38.

The springs 45a, 45b are connected to the lower roller 37.
38 and a recess 46a of the cooling block 46;
46b to reduce the impact when it comes into contact with 46b.

After the cooling section 40 is a paper discharge path 5 having a paper discharge roller 51.
2 and a re-conveying path 54 having a re-conveying roller 53 are formed. A switching claw 55 is provided at the branching point, and by controlling the attitude of the switching claw 55, the sheet 11 that has passed through the cooling section 40 is selectively guided to the paper discharge path 52 or the re-conveyance path 54. The sheet 11 guided to the paper discharge path 52 is discharged to the paper discharge tray 18, and the sheet 11 guided to the re-conveyance path 54
is sent to the paper refeed tray 19.

A cooling fan 56 is installed above the paper ejection roller 51 of the fixing device 17.
is provided to exhaust the atmosphere in the cooling section 40 to the outside of the aircraft body 1, thereby increasing cooling in the cooling section 40.

Solenoids 44a and 44b for moving the cooling rollers 35, 36 toward and away from the lower cooling rollers 37, 38 are connected to the CPU 63 as shown in FIG. The CPU 63 is also connected to a host CPU 64 that controls the operation of the copying machine.
Control is performed so that the cooling roller 35 is used during normal copying and the first copying in duplex and composite copying, and both cooling rollers 35 and 36 are used during second and subsequent copying.

The operation control of the cooling 40 will be described below only for double-sided copying and normal copying. Double-sided copy settings are on the host 1-CPU.
This is done by a double-sided copy selection switch 67 connected to 63 together with a print switch 65.

As shown in FIG. 7, it is first determined whether copying is in progress (step #1), and if copying is not in progress, the cooling roller 35.3
6 are both pulled away from the lower cooling rollers 37, 38 and brought into contact with the cooling block 46 (step #2), so that the cooling rollers 35, 36, even if they have heated up by then, are The temperature can be lowered by removing heat from the air.

While copying, it is determined whether the second side is being copied (
Step #3L: If it is not the second side, and therefore the mode is normal copy mode, or the first side is being copied even if it is double-sided copy mode, the process moves to step #5 and the cooling roller 35
The cooling roller 36 is brought into pressure contact with the lower cooling roller 37 to be in a used state, and the cooling roller 36 is separated from the lower cooling roller 38 to be in an unused state. As a result, only the cooling roller 35 is used to satisfy the required degree of cooling. This prevents the cooling roller 36 from being wasted and causing its temperature to rise, thereby preventing it from working satisfactorily during copying of the second side, where the temperature of the sheet is higher.

If the second side is to be copied in step #3, the process moves to step #4, and the cooling roller 35.36 is moved to the lower cooling roller 37.3.
8, and both cooling rollers 35 and 36 are brought into use. As a result, the cooling capacity of the cooling unit 4o is doubled compared to normal copying and first-side copying, and even the sheet 11, which has become hot due to thermal fixation during second-side copying, can be sufficiently cooled. No blocking occurred in the experiment. In addition, in the case of double-sided copying and composite copying, the re-feeding tray 19 is used, so its maximum capacity is 50.
Since the number of continuous copies is limited to a maximum of 50 sheets, the temperature of the sheets due to continuous copying does not rise to the extent that blocking occurs.

To explain the second embodiment of the present invention shown in FIGS. 8 and 9, a cooling section 40 after the upper and lower fixing rollers 32, 34
includes a cooling roller 35 and a lower cooling roller 3 that are in constant pressure contact.
7 and a fan 71 that directly cools the seat are provided in two stages, front and rear, and this is the only difference in structure from the first embodiment, and the rest is common.

In this embodiment, the cooling capacity is divided into eight cycles depending on whether the cooling roller 35 is used alone or together with the fan 71.

Therefore, in actual copying, as shown in FIG. 9, it is first determined whether copying is in progress (step #1). If copying is not in progress, fan 71 is stopped and the process returns. Also, if copying is in progress, it is determined in step #3 whether or not the second side is being copied, and if it is not the second side, the fan 7 is
Stop 1 and return. This can prevent the fan 71 from operating unnecessarily and increasing power consumption, noise, and the like.

If it is a copy of the second side, the process moves to step #4 and the fan 71 is operated at 160 Qrpm.

By operating this fan 71, not only can the sheet be directly cooled, but also a large cooling effect can be obtained by removing heated air within the conveyance path. According to this embodiment, the cooling roller 35 is operated in any case,
The fan 71 is further operated only when copying the second side, so that the sheet, whose temperature is further increased for copying the second side, can be sufficiently cooled.

In the embodiment shown in FIG. 10, the fan 71 in the second embodiment is driven at different rotation speeds for copying the first side of normal copying and double-sided copying, and for copying the second side of double-sided copying. This allows the cooling capacity to be adjusted.

Specifically, first step #1 is to determine whether copying is in progress.
), if copying is not in progress, the fan 71 is stopped and the process returns (step #2). While copying step #
In step #3, it is determined whether the copy is on the second side, and if it is not a copy on the second side, that is, it is a copy on the first side of a normal copy or double-sided copy, the fan 71 is set to 1200 in step #4.
Make it work with rpai. As a result, the cooling roller 35 and the fan 71 are used together, and the sheet for normal copying or first-side copying can be cooled with more margin than in the first and second embodiments.

If it is determined in step #3 that the second side is to be copied, the process moves to step #5 and the fan 71 is operated at a higher speed of 1600 rpm. As a result, even the sheet that has become hotter on the second side of the copy can be sufficiently cooled down.

In the fourth embodiment of the present invention shown in FIGS. 11 and 12, a cooling section 40 after the upper and lower fixing rollers 32, 34 includes a combination of a cooling roller 35 and a lower cooling roller 37 that are constantly in pressure contact with each other.
A heat radiation roller 81 is provided that comes into contact with the cooling roller 35 and removes heat from the cooling roller 35 and radiates the heat to others.
6 promotes heat dissipation. The rest is the same as the first embodiment.

In this embodiment, the cooling fan 56 also serves as an exhaust fan, so first, in step #1, the fan 56 is driven at a low speed of 160 rpm (step #2) to enable exhaust. If copying is in progress, the process moves to step #3 and it is determined whether or not the second side is being copied. If it is not a copy of the second side, that is, a normal copy or a copy of the first side of double-sided copying, the process moves to step #4, where the fan 56 is driven at a medium speed of 220 Orpm, and the cooling roller 35 and the heat dissipation roller 81 are especially heat dissipated. roller 81
Heat dissipation is promoted by exhausting the surrounding atmosphere, the cooling roller 35 does not rise above a predetermined temperature to cool the sheet 11 during normal copying or first side copying, and the fan 56 cools the sheet 11 sufficiently even though it is not at high speed. To prevent the fan 56 from increasing its speed unnecessarily and increasing power consumption, noise, etc.

If step #3 is the second side copy, step #5
Then, the fan 56 is driven at a high speed of 2800 rpm. This further promotes the heat dissipation of the heat dissipation roller 81, so that the cooling roller 35 comes into contact with the heated sheet of the second side of the copy and removes the heat, but the temperature does not rise above a predetermined temperature and lowers the heated sheet to a predetermined temperature. It can be reliably cooled down to. In addition, in this embodiment, since the exhaust fan normally included in copying machines is used as a cooling fan, no special drive means is required, resulting in space saving and cost reduction. Since there is only a pair of cooling rollers 35 and 37 in the path, troubles such as paper jams are less likely to occur compared to other embodiments.

Note that the cooling means whose capacity can be adjusted is not limited to the scope of each of the embodiments described above, and can be modified in various ways.

(Effects of the Invention) According to the present invention, a cooling means whose capacity can be adjusted is provided after the heat fixing device and is controlled by a control means, and in the case of an image forming mode in which image formation is repeatedly performed on one sheet, from the second time onwards. In the fixing process during image formation, the ability of the cooling means is increased compared to the first fixing process, so even if the same sheet is subjected to repeated image formation and becomes hotter without lowering the fixing temperature, It can be cooled down sufficiently,
It is possible to reliably prevent the blocking phenomenon from occurring without impairing fixing properties.

[Brief explanation of the drawing]

Fig. 1 is a schematic sectional view of a copying machine to which the present invention is applied;
3 is a side view 1 showing the operating mechanism of the cooling roller, FIG. 4 is a sectional view of the cooling roller, and FIG. 5 is a sectional view of the cooling roller. Perspective view,
FIG. 6 is a block diagram of the control circuit, FIG. 7 is a flowchart showing a cooling control subroutine in one embodiment of the present invention, and FIG. 8 is a sectional view of a fixing device showing a second embodiment of the present invention. , FIG. 9 is a flowchart showing a cooling fan control subroutine, and FIG. 10 is a flowchart showing a cooling fan control subroutine showing a third embodiment of the present invention.
FIG. 11 is a sectional view of a fixing device according to a fourth embodiment of the present invention, and FIG. 12 is a flowchart showing a cooling fan control subroutine. 17...--1--・--1---・---1--
−−・−・−−−−−・Fixing device 32−・・−・・−・
・---m---・−・・−・−−1 −・〜Fusing roller 3t−−−−−−−・〜・−−−〜−・−・−・
--- Lower fixing roller 35.36- ・---1--
-------------Cooling rollers 44a, 44
b---------Solenoid 56.71-
・・−−−１−−−−−−−−−−−−−・−・・−・
Cooling fan 63.64 ・-・-・--1-...-CPU Double-sided copy selection switch Cleaning of the 2nd side of the heat radiation roller C (no text "r!!" in the content) Figure 1

Claims (1)

[Claims] (1) A cooling means with adjustable capacity provided after the heat fixing device to cool the sheet after the fixing process, and second and subsequent image formation in an image forming mode in which image formation is repeatedly performed on one sheet. A fixing device comprising: a control means for controlling the cooling means to have a higher capacity in the first fixing process than in the first fixing process.