JPH0234885A - Thermal fixing device for image forming device - Google Patents

Abstract

PURPOSE:To prolong the service life of a roller by switching the connections of a core temperature detecting means and a cover temperature detecting means respectively with a roller temperature controller, controlling temperature based on the surface temperature of a elastic body during a copying stand-by time, and controlling the temperature based on the surface temperature of a metal core during a copying time. CONSTITUTION:The core temperature detecting means 5 and the cover temperature detecting means 6 are connected switchably with the temperature controller. During rising, the temperature is controlled based on the surface temperature of a core 3 so that the temperature of the core 3 is controlled to be below a bonding limit temperature. When the surface temperature of the cover 4 reaches a temperature prescribed in consideration of a fixing lower limit temperature, temperature control is switched so as to be performed by the surface temperature of the cover 4. When copying is started, the temperature is controlled based on the surface temperature of the cover 4. Thus, all during rising, standing by and copying, the core 3 is maintained to be below the bonding limit temperature, while the cover 4 is maintained to be above the fixing lower limit temperature. The service life of the roller can be thereby prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal fixing device for an image forming apparatus such as a copying machine, facsimile machine, or printer.

[Prior art]

In a heat roller fixing device that has an internal heat source, the fixing roller is formed from a metal core and a rubber layer covering the surface of the core, and the temperature is controlled by detecting the surface temperature of the fixing roller. is conventionally done.

Conventional methods for controlling the temperature of the fixing roller in thermal fixing devices include detecting the surface temperature of the rubber coating and controlling the temperature based on the detected temperature, and detecting the temperature of the core metal and controlling the temperature based on the detected temperature. How to do it.

In the method of controlling the temperature by detecting the surface temperature of the rubber coating,
As shown by curve A in Figure 7, the surface temperature of the rubber coating is kept constant while the paper is passing through the paper, for example, due to the thickness of the rubber coating layer and the low thermal response due to poor thermal conductivity of the material. Considering that the surface temperature temporarily decreases at the start of paper feeding, the temperature is maintained at, for example, 180° C. so that the fixing performance does not deteriorate. At this time, due to the poor thermal conductivity of the rubber 171 layer, the core bar generates a temperature difference with the rubber coating layer as the speed increases and the number of copies per minute (C, P, ?I) increases. As shown by curve B in FIG. 7, the temperature rises to, for example, about 205° C. and becomes stable. Start copying 1. During the standby period, the temperature of the core metal is maintained at, for example, about 190°C. Here, the data is based on the assumption that the thickness of the rubber coating layer is 1 mm and the minimum fixing temperature is 175.degree.

Currently, the adhesion limit temperature between the core metal and the rubber coating layer is 2.
Since the temperature is set at 00°C to 230°C, in this conventional temperature control, the core metal temperature exceeds the adhesion limit temperature, the rubber coating layer peels off, and the life of the roller is shortened.

Since the thermal response of the rubber coating is low at the start of copying, the surface temperature drops to 175 degrees Celsius after passing several sheets of paper, and when that temperature is detected, the heater turns on and heats up, and after that the temperature goes down to 175℃.
Temperature controlled at 80°C.

On the other hand, in the control method using the temperature of the core metal, the temperature is controlled at a temperature that can guarantee the adhesion of the rubber coating, and the core metal temperature is controlled to, for example, 200"C, as shown by curve B in Figure 8. Peeling of the rubber layer does not occur, but as the number of sheets passes increases when copying starts, the surface temperature of the rubber coating decreases as shown by curve A in Figure 8.This temperature decrease also causes fixing. In order to prevent the temperature from dropping beyond the lower limit of 175°C, it is necessary to maintain the surface temperature of the rubber coating at, for example, 190°C during standby.

In this case, the core metal temperature and the rubber coating surface temperature during standby are about 10°C higher than in the temperature control method using the rubber coating surface temperature. In the case of rubber, a difference in temperature of 10 degrees Celsius affects the lifespan by a factor of 2, and in the case of copying machines, the waiting time is long, so the lifespan of the rollers is shortened.

In addition to the above-mentioned problems during standby and copying, the two conventional temperature control methods also have problems when heating the fixing device when the main switch is turned on.

In other words, in the temperature control method based on the surface temperature of the rubber coating, when the rubber coating surface temperature is controlled to 180 degrees Celsius as shown in curve MA at the time of reloading, which is ready for copying as shown in Fig. 9, the thickness of the rubber coating and the conductivity are Due to the poor response, the surface temperature of the core metal reaches 220°C as shown in curve B. In this case, the bonding limit temperature will be exceeded, and the life of the roller will be shortened.

On the other hand, in the temperature control method based on the core metal temperature, if reloading is performed when the core metal temperature reaches 200°C as shown in curve B of FIG. 'C, and the fixing performance is not yet stable. Considering that the fixing property will reach a stable state a little while after reloading, this method has little effect on the life of the roller at startup. However, since the waiting time of the rubber coating is as high as 190° C., the life of the roller will be shortened in copying machines with long waiting times.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide a heat fixing device in which the rubber layer does not peel off from the core metal and the service life does not decrease due to high temperatures.

[Means for Solving the Problems] The present invention solves the above problems by providing a core metal temperature detection means for detecting the surface temperature of the core metal and a coating temperature detection means for detecting the surface temperature of the elastic coating. A feature is that the connection of the temperature detection means to the roller temperature control device is switchable, and the temperature is controlled based on the surface temperature of the elastic body during copy standby, and the temperature is controlled based on the surface temperature of the metal core during copying. The problem was solved by a heat fixing device of an image forming apparatus.

Further, the present invention solves the above problem by controlling the temperature during warm-up based on the surface temperature of the metal core, and controlling the temperature during standby after a certain period of time has passed based on the surface temperature of the elastic body. This problem was solved by a heat fixing device for an image forming apparatus that is characterized by the following.

[Effect]

According to the present invention, during startup, the temperature is controlled based on the core metal surface temperature, the core metal temperature is controlled to be below the bonding limit temperature, and the coating surface temperature is set to a predetermined temperature determined in consideration of the fixing lower limit temperature, for example, 180". When reaching C, the temperature control is switched to based on the coating surface temperature, and at the start of copying, the temperature control is switched to based on the coating surface temperature.This allows the core metal to be kept at a temperature as low as possible below the bonding limit temperature during startup, standby, and copying. and maintain the coating above the minimum fixing temperature.

〔Example〕

The details of the present invention will be explained based on embodiments shown in the drawings.

In FIG. 1, a heat generating heat source 2 is disposed inside at least one of the rollers 1 that are pressed against each other in the heat fixing device.

The roller 1 has a metal core 3 made of iron or aluminum, etc., and an elastic coating 4 made of silicone rubber or the like having heat resistance and mold releasability (non-viscosity). The surface is coated and bonded, for example, with an adhesive called a primer.

The fixing device is further provided with a core temperature detection means 5 for detecting the surface temperature of the metal core 3 and a coating temperature detection means 6 for detecting the surface temperature of the elastic coating 4. It is possible to arbitrarily select whether to use a contact temperature detection means such as a thermistor or a non-contact temperature detection means for both of the and coating temperature detection means 6, for example.

The core metal temperature detection means 5 and the coating temperature detection means 6 are each connected to a temperature control device.

If the coating temperature detection means 6 is a contact type temperature detection means that presses the surface of the elastic coating 4, paper dust, offset toner, etc. may accumulate between the surface of the coating 4 and the temperature detection means 6. This may damage the surface of the relatively weak elastic body and shorten the life of the roller. In particular, when there is a fluororesin coat or RTV silicone coat 71 on the surface of the elastic body, the layer is often as thin as 10 to 50 microns, which may pose a problem in terms of service life. In such a case, it is effective to use a non-contact type temperature detection means as the coating temperature detection means 6. On the other hand, since the core metal temperature detection means 5 detects the temperature of the non-contact paper portion and the other party is metal, no problem occurs whether the core metal temperature detection means 5 is a contact type or a non-contact type.

Temperature control of fixing device? When the ear is on standby, that is, when a copy command is not issued, the temperature is controlled based on the temperature detected by the coating temperature detection means 6, and when copying is started, that is, a copy command is issued, the temperature is controlled by the core metal temperature detection means. 5 to control the temperature of the fixing device based on the surface temperature of the core metal.

While copying continues, temperature control is continued based on the surface temperature of the core metal, and when copying is finished, switching is made to the coating temperature detection means 6 along with a copy end signal, and temperature control is performed based on the surface temperature of coating 4. . While the standby continues, the temperature is controlled based on the surface temperature of the coating 4.

In such control n, as shown in FIG.
The surface temperature of the metal core 1 changes as shown by curve A, and the surface temperature of the core bar 1 changes as shown by curve B. That is, while waiting until the copy start time t, the coating is maintained at, for example, 180°C, and the core metal, that is, the boundary between the core metal and the coating, is maintained at, for example, 190°C.
At the start of copying, temperature control is switched to based on the core metal surface temperature, and the core metal surface temperature is controlled to, for example, 200°C.

With this control, the heat source 2 is immediately turned on, and even when copy paper passes through it, the coating surface temperature does not fall below 175°C, and the core metal surface temperature does not fall below 200°C. For this reason, the bonding temperature of the rubber layer does not reach 200°C, which is said to be the limit temperature for adhesion, so there is no problem with the bonded area.

The life of the roller was extended, and a stable and highly reliable fixing device was obtained.

In FIG. 3, during standby, the temperature is controlled to, for example, 180'C based on the surface temperature of the coating 4, but when an image forming apparatus such as a copying machine is started, that is, when the main switch ONI is
If the temperature is controlled based on the coated surface temperature even during standby, the temperature of the core metal will exceed 200°C and reach 220°C, for example.

At startup, the heater 2 of the fixing device is turned on by turning on the main switch, and heating of the roller 1 is started.

Therefore, after the main switch is turned on, the temperature is detected by the core metal temperature detection means 5, and the temperature is controlled based on the temperature of the core metal 3, so that the core metal temperature is controlled to a predetermined temperature, for example, 200°C.

8 When the temperature of the machine reaches 200°C, it becomes ready to be reloaded, that is, to copy. The response of the temperature rise of the coating 4 is lower than that of the core metal 3 due to the properties and thickness of the material of the coating, so there is a difference in temperature rise.

So when reloading 1. t2 for a more certain period of time, i.e. while the surface of the coating 4 rises to the desired temperature, e.g. 180°C.
After the time elapses, the temperature detection is switched from the core metal temperature detection means 5 to the coating temperature detection means 6, and during the standby time after time L2, the temperature control is switched to the temperature control based on the coating surface temperature.

In FIG. 3, curve A shows the change in coating surface temperature, and curve B shows the change in core metal temperature. By controlling the core metal temperature, the core metal 3 is kept at a predetermined temperature, for example, 200°C, at the time of reloading t.
, and then the temperature of the coating 4 is, for example, 160°C. At this time, if the control is switched to the coating surface temperature, the coating 7f1
Heating with the heater is continued until 4 reaches the desired temperature, e.g. 80°C, and the coating changes along the curve A' shown by the broken line. The temperature will change along curve B', and the core metal temperature will exceed 200'C, exceeding the adhesion limit temperature of the coating. This means that when loading 1. The heater 2 is controlled by continuing control based on the core metal temperature until a time point L□ after a more constant time Δt, for example about IO seconds, has elapsed. In this case, even if the heater 2 is OFF, the coating is heated and the temperature rises. By switching to temperature control based on the coating temperature when the temperature reaches approximately 180°C at time Lt, the core metal is maintained at approximately 190°C during standby, and the coating temperature is maintained at approximately 190°C.
It can be maintained at 80°C.

By determining the temperature at the time of start-up based on FIG. 3 as described above, it is possible to prevent the roller from breaking at the time of start-up of an elastic roller with a built-in heat source, and the durability of the roller can be improved. Ta.

In an image forming apparatus, when the paper reference is a one-sided reference, the copy paper is passed not to the center of the roller but to one side and is fixed thereon. Since the contact position of the paper with respect to the fixing roller is uneven, when the paper is small, the area where the paper does not come into contact is uneven, and the temperature of the roller tends to be higher in the area where the paper does not make contact. In order to avoid this, as shown in FIG. 4, the first heater 2a as a heat source built inside the roller 1 is placed at a position 5-t-i on the left side of the figure, as shown in FIG. As shown by curve C, the range through which a copy sheet of approximately the minimum size passes on the reference side is 100%, and the heat distribution on the non-reference side is formed so as to decrease in a slope to about 30%. In contrast to the first heater 2a, the second heater 2b has a heat generation distribution as shown in the curve shown in FIG. and are installed in the roller l.

The core metal surface detection means 5' and the coating surface detection means 6' are respectively arranged near both ends of the roller, and the coating surface temperature detection means 6' is located inside the reference position, and the core metal surface temperature detection means 5' is disposed near both ends of the roller.
is placed outside the reference position. Note that the roller 1 has a core bar 3 and an elastic covering 4 as in the example shown in FIG. As in the example shown in FIG. 1, it is preferable to use non-contact temperature detection means as the coating surface temperature detection means 6'a and 6'b in order to prevent damage and wear on the roller surface.

In the example shown in FIG. 4, two core metal surface temperature detection means 5
' is used to distinguish the one placed on the reference side from the first metal core surface temperature detection means 5'a, and the one placed on the non-reference side from the second metal core surface temperature detection means 5'b. The temperature detection means distinguishes the reference side as the first coating surface temperature detection means 51a, and the non-reference side as the second coating surface temperature detection means 6'b.

In the temperature control during standby of the roller in FIG. 4, the first heater 2a is controlled based on the temperature detected by the first coating surface temperature detection means 5'a, and the second coating surface temperature detection member 6'
The second heater 2b is controlled based on the temperature detected by 'b. At this time, the core metal 3 of the roller l is curved by the curves A and B in FIG.
As shown in , the coating 4 is maintained at approximately 180°C, and the core bar 3 is maintained at approximately 190''C.The temperature at which fixing performance can be guaranteed is 170°C.The temperature in the axial direction of the roller It is assumed that the distribution is approximately uniform due to the two heaters.

Temperature detection is performed from the copy start time L0, and from the coating surface temperature detection means 6a' and 6b' to the core metal surface temperature detection means 5.
Switch to a', 5b'. At this time, the first heater 2a is controlled based on the temperature detected by the first metal core surface temperature detection means 5a', and the second heater 2b is controlled based on the temperature detected by the second metal core surface temperature detection means 5b'. Control. With this control B, the core metal surface temperature increases to 200% as shown by curve B in Fig. 6.
Due to this control based on the core metal temperature, the surface temperature of the coating 4 decreases as the paper passes through the paper, but it does not decrease beyond the lower limit fixing temperature of 170°C.

For reference, if temperature control is continued using the coating temperature after copy start L6 in the same way as during standby, the coating surface temperature will decrease as the first few sheets pass, as shown by the chain line A' in Figure 6. However, due to the poor response depending on the thickness and material of the coating, the temperature decreases to, for example, 175°C, and this temperature drop is detected by the coating surface temperature detection means 6a' and, in some cases, 6b', and the heaters 2a and 2b are turned on and off. Heat and maintain the coating surface temperature at, for example, 180'C. At this time, the core metal temperature rises to 210°C, as indicated by the chain line B', and stabilizes at 210°C. At 210° C., the bonding limit temperature is exceeded, so the lifespan of the roller becomes a problem.

In anticipation of this temperature rise, the control temperature of the coating surface temperature was adjusted to 10%.
If the temperature is lowered by .degree. C., a problem will arise in fixing performance due to the drop in temperature immediately after the sheet is fed at the start of copying.

Temperature control from standby based on core metal surface temperature, mainly based on adhesion limit temperature? When n is performed, curve B shown by the broken line in FIG.
As shown in #, the core metal surface temperature does not exceed 200°C, and can be controlled so as not to exceed the adhesion limit temperature, and the roller life based on the adhesion limit is extended. As shown by the broken line B', the coating surface temperature decreases to nearly 170° C., which is the minimum fixing temperature, as paper is continuously passed. In this case, when waiting,
The coating surface temperature of the elastic body is 190° C., and the standby temperature is 10° C. higher than when the temperature is controlled based on the coating surface temperature during standby. The lifespan of rubber depends on the temperature
If they are different, the difference will be a factor of 2, so the lifespan of the rollers will be extremely short in copying machines and the like that have long standby times. Therefore, a problem arises in terms of service life.

From this, it can be seen that the present invention, which performs temperature control based on the coating surface temperature during standby and performs temperature control based on the core metal surface temperature during copying, is superior in terms of life and fixing performance. I understand.

As in the case of the roller shown in FIG. 1, there is a problem in that even during standby, the temperature control based on the coating surface temperature causes the core metal temperature to become too high when the main switch is turned on. In order to solve this problem, it is preferable to perform temperature control based on the core metal surface temperature until reloading and for a certain period of time after reloading, for example, until the temperature reaches 180°C. In this case, the first core metal surface temperature detection means 5a' detects the temperature. The first heater 2a is controlled based on the temperature, and the second heater 2b is controlled based on the temperature detected by the second core metal surface temperature detection means 5b'.

The temperature change during startup is as shown in FIG.

After the predetermined time has elapsed after reloading, the temperature control is switched to the standby temperature control described above. In other words, it switches to temperature control based on the coating surface temperature.

If copying is started immediately after reloading, control based on the core metal surface temperature continues as it is.

〔effect〕

According to the present invention, the surface temperature of the elastic coating can be kept as low as possible above the fixing minimum temperature, and the core metal temperature can be kept below the bonding limit temperature, thereby improving the life of the roller. .

Further, according to the present invention, it is possible to control the temperature rise of the core metal at the time of startup after the main switch is turned on, and it is possible to prevent roller breakage at the time of startup.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a roller of a heat fixing device according to the present invention, and FIG. 2 is a diagram showing changes in surface temperature of the core metal and coating of the roller.
FIG. 3 is a diagram showing changes in the surface temperature of the core metal and coating during startup, FIG. 4 is a sectional view of a modified example of the fixing roller of the thermal fixing device according to the present invention, and FIG. 5 is a heat generation distribution diagram of the heater. So, A
is a heat distribution diagram of the first motor, B is a heat generation distribution diagram of the second heater, FIG. 6 is a diagram showing changes in surface temperature of the core metal and coating in the roller of FIG. 4, and FIGS. 7 and 8 are respectively the conventional temperature Figures 9 and 10 show changes in the surface temperature of the core metal and coating during standby and copying in control, respectively, and Figures 9 and 10 respectively show changes in the surface temperature of the core metal and coating during startup in the conventional temperature control '4n. FIG. ■... Roller 2... Heater 3... Core metal 4... Coating 5... Core metal surface temperature detection means 6... Coating surface temperature detection means (one other person) Figure 5 A Nitrogen R1 Figure 5B Roller's It, 1 Figure 7: /lL degree °C 1 degree @C Figure 9 Figure 10

Claims (2)

[Claims] (1) Image formation that has fixing rollers that are pressed against each other and a heat source placed inside at least one of the fixing rollers, where the fixing roller is composed of a metal core and a heat-resistant elastic coating that covers the surface of the metal core. In the heat fixing device of the apparatus, a core metal temperature detection means for detecting the surface temperature of the core metal and a coating temperature detection means for detecting the surface temperature of the elastic coating are provided, and a fixing roller temperature control device for both temperature detection means is provided. The image forming apparatus is characterized in that the connection with the metal core is switchable, and the temperature is controlled based on the surface temperature of the elastic body during image formation standby, and the temperature is controlled based on the surface temperature of the metal core during image formation. Heat fusing device of equipment. (2) Image formation that has fixing rollers that are in pressure contact with each other and a heat source placed inside at least one of the fixing rollers, where the fixing roller is composed of a metal core and a heat-resistant elastic coating that covers the surface of the metal core. In the heat fixing device of the apparatus, a core metal temperature detection means for detecting the surface temperature of the metal core metal and a coating temperature detection means for detecting the surface temperature of the elastic coating are provided, and the fixing roller temperature of both temperature detection means is controlled. The connection with the device can be switched, and temperature control during warm-up is based on the surface temperature of the metal core, and after a certain period of time, temperature control during standby is based on the surface temperature of the elastic coating. A heat fixing device for an image forming apparatus, characterized in that: