JPH0243584A - Fixation device - Google Patents

Abstract

PURPOSE:To sufficiently execute cooling operation even when images are formed on many sheets at a high speed and at one time by providing plural cooling rollers and selectively using the cooling rollers having a prescribed temperature or under with the aid of the working of a control means receiving the output of a sensor which detects the temperature of the cooling rollers. CONSTITUTION:The plural cooling rollers 35 and 36 come into contact with a 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 temperatures of the respective cooling rollers 35 and 36 are detected by the sensors 61 and 62 and the control means receiving the detection output by the sensors 61 and 62 works so that the cooling roller having the prescribed temperature or under out of the plural cooling rollers 35 and 36 is selectively used. Thus, the cooling operation can be sufficiently executed by effectively using the plural cooling rollers 35 and 36 even when the images are formed on many sheets at a high speed and at one time.

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 unattended, the heat dissipation in the tray L that receives the fixed and discharged sheets will not be in time, and heat will accumulate in the sheets that are successively discharged. 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 conventional solution to this problem, the
Publication No. 186447, Publication of Utility Model Application No. 58-36745,
There is one known from 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. In the second type, at least one of a pair of paper ejection rollers provided after the fixing device is a heat vibrator to obtain a cooling effect. In the third type, a large number of heat radiation fins are provided at one end of a heat vibrator 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 into 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.

Still another method is to raise 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 above object, the present invention includes a plurality of cooling rollers provided after a heat fixing device so as to contact the sheet after the fixing process and cool it. , a sensor that detects the temperature of each cooling roller, and a sensor that receives the detection output from each sensor.
The present invention is characterized by comprising a control means for selectively using a cooling roller having a temperature below a predetermined temperature.

(Function) The plurality of cooling rollers can cool the sheet after thermal fixing by coming into contact with the sheet after thermal fixing sent out from the thermal fixing device, absorbing the heat, and dissipating the heat to the surroundings. However, the temperature of each cooling roller is detected by a sensor, and a control means that receives a detection output from this sensor operates to selectively use one of the plurality of cooling rollers whose temperature is below a predetermined temperature.

Therefore, since the unused cooling roller is separated from the heat-fixed sheet coming out of the heat fixing device, it does not receive heat from the heat-fixed sheet. Therefore, since the cooling roller that is not in use only radiates heat, heat radiation is actively promoted and the temperature can be lowered rapidly.

On the other hand, since the temperature of the cooling roller used is below the specified temperature,
By bringing it into contact with the heat-fixed sheet sent out from the heat fixing device, it is possible to sufficiently remove heat from the heat-fixed sheet and cool it.

As a result, the rollers whose temperature is below a predetermined temperature are used to cool the sheet after fixing and are sufficiently cooled, and those whose temperature exceeds the predetermined temperature are not used and only radiate heat to rapidly lower the temperature below the predetermined temperature. Since the temperature decreases, it can be reused quickly, and by effectively utilizing multiple cooling rollers, the cooling effect can be sufficiently exerted even when multiple images are formed at high speed at once. .

(Example) An embodiment of the present invention shown in the drawings 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 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 drum 2 is developed and visualized by the developing device 5, and when it reaches the transfer/separation charger 6, it is applied to the transfer sheet 11 that is being conveyed in synchronization with the image. transcribed. 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 charger 3 to be used for image formation again.

The sheet 11 is fed from either the first or second paper feed section 12, 13 provided at the inner bottom of the machine body 1, or from the manual paper feed section 14 of the machine body 1, and the timing is adjusted by the register roller 15. The transfer part number is sent through the transfer unit and undergoes the transfer.

After the transfer, the sheet 11 is conveyed by a suction conveyor belt 16 and sent to a 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 re-feed 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 thereto. Sheet 1 in refeed tray 19
When the sheet No. 1 is fed again, it is subjected to timing adjustment by the register roller 15 and then 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 body 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 cooling roller 35, 36 is combined with a lower cooling roller 37, 38 that receives the cooling rollers from below.
is sandwiched between them to remove heat and cool it down.

The lower cooling rollers 37, 38 are provided in a fixed position, whereas the cooling rollers 35, 36 are each mounted on a lever 42a, 42b pivoted by a shaft 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 3 is rotated around a and 41b.
7.38.

The levers 42a and 42b each have a spring 4 attached to one end thereof.
Cooling rollers 35 and 36 are activated by the urging of 3a and 43b.
are urged to come into pressure contact with the lower cooling rollers 37, 38.

A drive circuit 6 is provided at the other end of the levers 42a and 42b, respectively.
Solenoid 44a driven by 6a, 66b,
44b is connected, and when the solenoid 44a144b operates, the cooling roller 3 resists the springs 43a and 43b.
5.36 is rotated away from the lower cooling roller 37.38.

Note that the lever 42 is used instead of the solenoids 44a and 44b.
A and 42b may be provided with cams that come into contact with each other, and the cams may be rotated by a motor to bring the cooling rollers 35 and 36 into and out of contact.

Here, the cooling rollers 35 and 36 have good thermal conductivity, for example,
It is preferable to use 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 to facilitate heat dissipation.

Further, above the cooling rollers 35 and 36, a cooling block 46 made of aluminum, for example, which also has good thermal conductivity is installed. 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 removes heat from the heat dissipating fins 46c. Cooling rollers that only radiate heat when not in use because they radiate heat 35.36
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. These springs 45a, 45b are connected to cooling rollers 35.36 by solenoids 44a, 44b to lower cooling rollers 37.38.
The recesses 46a and 4 of the cooling block 46 are separated from each other.
6b to reduce the impact when it comes into contact with it.

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 1 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 re-feed 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.

A thermistor 61, 62 for detecting the temperature of each cooling roller 35, 36 is provided in contact with the cooling roller 35, 36 at a position that does not interfere with the passage of the sheet 11. These thermistors 61 and 62 are connected to the cooling roller 35 as shown in FIG.
．． It is connected to the CPU 63 along with solenoids 44a and 44b for moving the cooling roller 37 and 36 toward and away from the lower cooling rollers 37 and 38. CPU 63 is a host CPU that controls the operation of the copying machine.
When the print switch 65 is turned on, one of the cooling rollers 35 and 36 is selectively operated, and when the temperature exceeds a predetermined temperature, the cooling roller to be used is switched to another one. 66a and 66b are drive circuits for the solenoids 44a and 44b.

According to the inventor's first experiment, in a conventional device with one cooling roller, process speed: 380 sec/sec, copy speed: 60 sheets/win, fixing upper 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.

As copying continued, when the sheets were separated, the toner fixed on one sheet remained on the back side of the other sheet, 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 temperature of the cooling roller reaches 80°C or higher.

Therefore, in this embodiment, the cooling rollers 35 and 36 are switched and used, but they are used only when the temperature is below 70°C, and when the temperature exceeds 70°C, they are switched to another one.

The switching operation control in this case is as shown in the flowchart shown in FIG.
6, for example, the cooling roller 35 is used preferentially. After that, it is difficult to determine which of the cooling rollers 35 and 36 is being used.Step #1)
5, the cooling roller 35 is set to 70' in step #2.
It is determined whether or not the temperature has reached C or higher, and if it is below 70 C, the cooling roller 35 is returned and the use of the cooling roller 35 is continued.

When the temperature exceeds 70°C, the process moves to step #3, in which 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 roller 36.

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 being used in step #1, the process moves to step #4, and if the temperature of the cooling roller 36 is 70° C. or lower, the process returns to continue using the cooling roller 36. If the temperature of the cooling roller 36 is higher than 70''C, the process moves to step #5, in which the cooling roller 36 is separated from the lower cooling roller 38 to be in an unused state, and the cooling roller 35 is brought into pressure contact with it to be in a used state.

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 Figure 7, the cooling roller 35 is used first, and the rollers 35 and 36 are switched and used each time one of them reaches 70°C, and when the temperature exceeds 70°C, they are no longer used. It can be seen that the temperature of the one that was stopped returns almost to the temperature before use, just when the temperature of the one that was used instead reached 70°C or higher.

As a result of the second result, no blocking phenomenon occurred even when copying was performed continuously.

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

When using the cooling block 46, it is advantageous to bring the rollers 35, 36 into contact with the cooling block 46 at the end of copying so that they can be cooled quickly before the next copy. In this case, when copying is resumed, it is preferable to use the cooling rollers 35 and 36 with lower temperatures first. This is because the next copy may be restarted early and the previously used roller may not have cooled down completely.

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 thus affected by the environmental temperature, it is preferable to automatically set the temperature at which the cooling rollers 35 and 36 are switched based on the environmental temperature.

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

(Effects of the Invention) According to the present invention, a plurality of cooling rollers are provided, and cooling rollers having a temperature below a predetermined temperature are selectively used by the control means that receives the output of a sensor that detects the temperature of the cooling rollers. Since the cooling roller when not in use only dissipates heat that has risen above a predetermined temperature, heat dissipation is actively promoted and the temperature can be lowered rapidly. By bringing it into contact with the heat-fixed sheet sent out from the heat fixing device, it can sufficiently remove heat from the heat-fixed sheet and cool it down, resulting in a temperature below the predetermined temperature of the multiple rollers. The sheet is used to cool the sheet after fixing and is sufficiently cooled, and once the temperature exceeds the specified temperature, it is not used and only radiates heat and rapidly lowers the temperature to below the specified temperature, so it must be reused as soon as possible. The cooling effect can be sufficiently developed even when a plurality of cooling rollers are effectively used to form a large number of images at once at high speed.

[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. 17−・−・−−−−−・−−１−−・・・−・−・−
・-----1--Fixing device 32--・--Fixing roller 34----------1--
−・・−・−・・−・Lower fixing roller 35.36−・
−・−・・−・−−−−−−−−−・− Cooling roller 44a 44b −−−−−−−・−・−−−−1.・Solenoid 61, −・・−・・−・−・−・・−・−・Thermistor 63
．． 64−・−・−・−

Claims (1)

[Claims] (1) A plurality of cooling rollers are provided after the thermal fixing device to contact and cool the sheet after the fixing process, a sensor detects the temperature of each cooling roller, and a sensor receives the detection output from each sensor. , and a control means for selectively using a cooling roller whose temperature is below a predetermined temperature.