JPH0243586A - Fixation device - Google Patents

Abstract

PURPOSE:To always cool a sheet where an image is fixed with heat to the extent of a prescribed temperature or under by providing plural cooling rollers and switching and using them with the aid of the working of a control means every time the number of successive copied sheets reaches a prescribed number of sheets. CONSTITUTION:The plural cooling rollers 35 and 36 come into contact with the sheet, where the image is fixed with heat, sent from thermal fixing units 32 and 34 and absorb the heat thereof. Then, they release the heat of the sheet around and cool the sheet where the image is fixed with heat. The use of the respective cooling rollers 35 and 36 is controlled by the control means and the used cooling roller out of the plural cooling rollers 35 and 36 is switched by the working of the control means every time the count value of a means which counts the number of the successive copied sheets reaches the prescribed number. Thus, the sheet where the image is fixed with heat can be always cooled to the extent of the prescribed temperature or under.

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 and a laser beam printer. It is.

(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 unaddressed, the heat dissipation in the trade that receives the fixed and ejected sheets will not be in time, and heat will accumulate in the sheets that are sequentially ejected. For this reason, the toner constituting the fixed image on the ejected sheet 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. The first one is provided with a heat pipe that serves both to transport and cool the sheet after fixing, after the fixing device. In the second type, at least one of a pair of paper ejection rollers provided after the fixing device is a heat pipe so that a cooling effect can be obtained. In the third type, a large number of heat radiation fins are provided at one end of a heat pipe provided after the fixing device.

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.

(Problems to be Solved by the Invention) In the first to third types, the heat roller comes in contact with the sheet being fed after fixing, absorbs heat, and radiates heat to the surroundings, so the sheet after fixing is removed from the machine. It can be cooled before being discharged. However, when many images are formed at once,
Heat dissipation around the heat roller cannot be done in time, and the temperature of the discharged sheet may increase, causing a blocking phenomenon. It is possible to solve this problem by increasing the heat dissipation of the heat roller, but this is only possible by increasing the heat capacity and surface area of the cooling roller, and there is a limit to this.

In the fourth method, it is possible to constantly suppress the temperature of the discharged sheet to a temperature at which no blocking phenomenon occurs. However, when images are formed on a large number of sheets at once, the fixing temperature is suppressed too much, which causes fixing failure.

There is also another method of raising the glass transition point Tg of the toner, but like the fourth method, it causes poor fixing.

The present invention aims to solve the above-mentioned problems by improving the method of cooling the sheet after fixing.

(Means for Solving the Problems) In order to achieve the object as stated in -1-, the present invention includes a plurality of units provided after a heat fixing device so as to contact the sheet after the fixing process and cool it. The apparatus is characterized by comprising a cooling roller, a means for counting the number of consecutive copies, and a control means for switching the cooling roller to be used when the count value by the counting means reaches a predetermined value.

(Function) The plurality of cooling rollers contact the heat-fixed sheets sent out from the heat fixing device, take away the heat, and radiate the heat to the surrounding area, thereby cooling the heat-fixed sheets 1 to 1. can. However, the use of each cooling roller is controlled by a control means, and each time the count value of the means for counting the number of continuous copies reaches a predetermined value, the control means operates to switch the cooling roller to be used among the plurality of cooling rollers.

Therefore, a plurality of cooling rollers are not used simultaneously, but are used in limited numbers at a time.

The cooling roller used is sent out from the heat fixing device and brought into contact with the sheet after heat fixing.
At first, heat can be sufficiently removed from the sheet after fixing and the sheet can be cooled. When a large number of copies are made in succession, the cooling roller absorbs more heat from the sheets than radiates heat1.
The temperature gradually increases. However, when the count value of the number of consecutive copies reaches a predetermined value, the V control means switches to using another cooling roller, so the cooling roller that was previously used is put out of use and the sheet is removed. Once separated, it no longer absorbs heat, and after that it only radiates heat, rapidly cooling down and waiting until the next use.

The temperature of the cooling roller that is switched to use has been sufficiently lowered and, like the previously used cooling roller, it can sufficiently cool the sheet after heat fixing.

As a result, the plurality of rollers are used sequentially so that the temperature is within a predetermined range, and the sheet after heat fixing can be constantly cooled to a predetermined temperature or lower.

(Example) An embodiment of the present invention shown in FIG. 1J will be described below.

This embodiment shows the case of a copying machine. As shown in FIG. 1, a photosensitive drum 2 is provided within a body 1. As shown in FIG. Around the photosensitive drum 2 are a charging charger 3, an exposure section 4, a developing device 5, a transfer/separation charger 6, and a cleaning device 7.
, eraser lamps 8 are sequentially arranged 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 charging nayajar 3 reaches the exposure section 4, receives the slint 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, the transfer sheet 11 is conveyed in synchronization with the image. transcribed into. After the transfer, the surface of the photosensitive drum 2 is cleaned by a cleaning device 7, and then passed through an eraser lamp 8 and a strip charger 3 to be used for image formation again.

1 and 11 are the first and second holes provided at the inner bottom of the fuselage 1.
The paper is fed from one of the paper feed sections 12 and 13, or from the paper feed section I4 on the - side of the machine L, and is fed from the register roller 1.
After the timing adjustment in step 5, the image is sent to the transfer section and subjected to the transfer.

After the transfer, the sheet 11 is transferred to the suction type conveyor heel 1-16 -9
and is conveyed to the fixing device 17. Fixing device 17
The sheet [1 that passes through is either ejected as it is to the paper ejection tray 18 outside the machine body 1, or is sent to the paper refeed tray 19 inside the machine body 1. The paper re-feeding tray 19 receives the seam l whether the transferred image is face-up facing -1- or face-down. When the sheet 11 in the re-feeding tray 19 is re-fed, it is subjected to timing adjustment by the register roller 15 and is subjected to transfer 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.

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 and 38 that receives the cooling rollers from below.
is sandwiched between them to remove heat and cool it down.

The lower cooling rollers 37.3 are provided in fixed positions, while the cooling rollers 35.36 are respectively mounted on levers 42a and 42b pivoted by shafts 41 as shown in FIG.
The shafts 41 of the levers 42a and 42b are supported at one end of the levers 42a and 42b.
The lower cooling roller 37 is rotated around a and 41b.
．． 38.

The levers 42a and 42b each have a spring 43 acting on one end thereof.
The cooling rollers 35.36 are urged to be brought into pressure contact with the lower cooling rollers 37.38 by the urging of the cooling rollers 35.36 and 43b.

A drive circuit 5 is provided at the other end of the levers 42a and 42b, respectively.
Solenoid 44a driven by 5a, 66b
.

44b 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.

Note that the cooling rollers 35, 36 can be brought into contact with and separated from the lower cooling rollers 37, 38 by using cams instead of the solenoids 44a, 44b.

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 and 36. As shown in FIG. 5, the cooling block 46 has cooling rollers 35, 36 and lower cooling rollers 37, 38.
It has recesses 46a and 46b on its lower surface that receive it when it is lifted upwards and come into contact with about half its circumference, and a large number of heat-radiating fins 46c are formed on its 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. The cooling roller 35.3, which only radiates heat when not in use, radiates heat to
6 to significantly reduce the temperature.

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.

These springs 45a and 45b are connected to the cooling rollers 35 and 36 by solenoids 44a and 44b.
．． 38 and the recess 46a of the cooling block 46
, 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 and to enhance 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.
At first, one of the cooling rollers 35 and 36 is selectively operated, and thereafter, each time the number of copies reaches a predetermined value, the cooling roller to be used is switched to another one. A counter 6 connected to a host CPU 64 for this control.
5 is used. The counter 65 is connected to the first and second paper feed sections 12
．． It counts and memorizes the paper feed signal issued in conjunction with the paper feeding operation from the paper refeed tray 13 or the paper refeed tray 19, and the count signal generated by the host CPt 164 based on the sheet size, and has a bank-up power supply. , even if the main power switch of the copying machine is turned off, the current count value is maintained. Note that the counting method is not limited to the above method; for example, a sensor may be installed in the paper passing path of a copying machine, and counting may be performed based on a signal sent each time the sensor detects the passing of a sheet. good. 66a
, 66b are drive circuits for the solenoids 44a, 44b.

According to the inventor's first experiment, in a conventional type with one cooling roller, process speed: 380 mm/sec, copy speed: 60 sheets/min, upper fixing roller: 190°C setting (surface tetrafluoroethylene) As a result of continuous copying by passing JIS standard A4 size sheet 11 horizontally under the lower fixing roller setting of 140°C (silicon rubber surface), a blocking phenomenon occurred in which the ejected sheets stuck together after the 500th sheet. Ta.

However, if you release it by hand, it will just leave.

When copying was continued, when the sheets were separated, the toner fixed on one sheet stuck to the back side of the other sheet and remained, that is, a state of partial transfer occurred.

When the temperature change of the cooling roller at this time was examined, it was as shown in line A of the graph shown in FIG. This shows that the blocking phenomenon begins to occur when the number of continuous copies exceeds 500.

Therefore, in this embodiment, the cooling rollers 35 and 36 are switched and used, but each time the count value of the counter 65 reaches 400, another one is switched and used.

The switching operation control in this case is as shown in the flowchart shown in FIG. To explain this, first, it is determined whether the count value of the counter 65 has reached 400 (step #l). If it has not reached 400, it returns as is, but if it has reached it, it moves to step #2, and the fully used It is determined which one is the cooling roller 35 or 36.

If it is the cooling roller 35, in step #3, the cooling roller 35 is separated from the lower cooling roller 37, and the cooling roller 3
6 is pressed against the lower cooling roller 38. As a result, the roller 35 used is switched from the cooling roller 35 to the cooling port roller 36. Next, the process moves to step #4, and the count value of the counter 65 is returned to O, so that counting of the number of copies in the next usage state of the cooling roller 36 is started.

The separated cooling roller 35 no longer takes heat from the sheet 11, but only radiates the heat, and since it is in contact with the cooling block 46, it is rapidly cooled by the action of the cooling fan 56, and the next sheet is cooled. Wait until use.

If the cooling roller 36 is used in step #2, the process moves to step #5, and the cooling roller 36 is replaced by the lower cooling roller 38.
At the same time, the cooling roller 35 is brought into pressure contact with the lower cooling roller 37, and the cooling roller 35 is brought into use. Next, in step #4, the counter 36 is returned to 0, and the cooling roller 3
5 is used, the number of copies is counted.

Since the separated cooling roller 36 comes into contact with the cooling block 46, it is rapidly cooled together with the action of the cooling fan 56 and waits until the next use.

When a second experiment was conducted under the same conditions as the first experiment by performing continuous copying under such usage conditions, the cooling roller 3
The temperature change of the cooling roller 36 was as shown by the line B, and the temperature change of the cooling roller 36 was shown by the line C. As can be seen from the graph in FIG. 7, the cooling roller 35 is used first, and each roller 35, 36 reaches a temperature of 70° C. when the number of copies reaches 400 and is switched to the other roller.
If the number of copies reaches 400 and the use is stopped, the temperature of the one used in its place will almost return to the temperature before use just when the number of copies reaches 400 and is switched again. .

As a result, even if copies are made continuously, the cooling roller 35.3
6 did not exceed 70°C and no blocking phenomenon occurred.

Note that the temperature rise of the cooling rollers 35 and 36 is estimated based on the number of copies, but the temperature rise of the cooling rollers 35 and 36 is approximately proportional to the total amount of heat received when the sheet 11 undergoes thermal fixation. , it is necessary to consider the area of the sheet 11, and the area of the sheet 11 that has passed must correspond to the number of copies. Therefore, when the size of the sheet 11 is A3, it is counted as the number of copies 2 to maintain a balance with the case where the sheet 11 is A4. This can also be solved by returning the counter 65 to 0 when continuous copying ends and using another cooling roller different from the previous cooling roller when restarting the next copy. Even if the value of the counter 65 has not reached 400, the counter value and the data of the cooling roller used at the end of copying are saved, and the cooling roller used last time is selected and used when copying is resumed. In that case, if the number of copies is restarted from the previous count, there will be no problem even if the next continuous copy is performed immediately after the continuous copy ends. Note that if the value of the counter 65 is maintained even after copying is completed, and the value of the counter 65 is returned to 0 when the time required for the temperature of the cooling roller to drop sufficiently has elapsed, the value of the counter 65 can be reset to 0. This reduces unnecessary switching operations and is more effective.

Cooling block 46 and cooling fan 5 in this embodiment
6 is not necessarily necessary.

When using the cooling block 46, if both rollers 35 and 36 are brought into contact with the cooling block 46 at the end of copying,
It is advantageous to cool down quickly before the next copy.

Further, if the environmental temperature is high, blocking may occur in some cases even if the temperature of the cooling roller is 70°C or less. Since the blocking phenomenon is affected by the environmental temperature as described above, it is preferable to automatically set the number of continuous copies to be made by switching the cooling rollers 35 and 36 based on the environmental temperature.

In the embodiment described above, two cooling rollers are used by switching, but if the number of cooling rollers is increased by even one, it will take a longer time to stop using the cooling roller whose temperature has risen and wait for the temperature to drop. Can be done.

(Effects of the Invention) According to the present invention, a plurality of cooling rollers are provided, and each time the number of consecutive copies reaches a predetermined number, they are switched and used by the control means, so that the plurality of cooling rollers are not used at the same time. The number of cooling rollers that are used will be used at a time, and the cooling rollers used will first be used to cool the sheet after it has been fixed by being sent out from the heat fixing device (by being brought into contact with the sheet after heat fixation). Sufficient heat can be absorbed and cooled, and when a large number of copies are made in succession, heat absorption from the sheet exceeds heat radiation and the temperature gradually rises, but the count value of the number of consecutive copies When the cooling roller reaches a predetermined value, the control means switches to using another cooling roller, so the cooling roller that was previously used is left unused and separates from the sheet, preventing it from absorbing any more heat. After that, it only radiates heat and waits until the next use while rapidly decreasing the temperature, and the cooling roller used after switching has cooled down enough to cool the sheet after heat fixing as well as the cooling roller used previously. I can do it.

As a result, the plurality of rollers are sequentially used so that the temperature is within a predetermined range, and the sheet after heat fixing can be constantly cooled to a predetermined temperature or lower, thereby preventing the blocking phenomenon from occurring.

[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 perspective view of the cooling block. , 6th
The figure is a block diagram of the control circuit, Figure 7 is a graph showing the temperature change of the cooling roller in continuous copying experiments in the conventional case and the case of the embodiment of the present invention, and Figure 8 is the diagram of an embodiment of the present invention. 12 is a flowchart showing a subroutine for controlling the switching use of cooling rollers. Fixing device 35.36...--44a, 44b 63.64 Upper fixing roller Lower fixing roller Cooling roller Solenoid PU Counter Fig. 1 η

Claims (1)

[Claims] (1) A plurality of cooling rollers provided after the thermal fixing device so as to contact and cool the sheet after the fixing process, a means for counting the number of continuous copies, and a count value by the counting means to a predetermined value. A fixing device comprising: a control means for switching a cooling roller to be used when a cooling roller is reached.