JPH0836324A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain excellent fixability without overshooting even if a thin roller having a small capacity is used by stepwise raising the temperature of a roller up to a stand-by temperature after a consecutive fixing operation. CONSTITUTION:An image forming device is provided with a fixing roller 11 heating a toner image on a transfer material and a pressure roller 2 pressurizing the transfer paper against the fixing roller 1 and a main heater 3 having a great luminous intensity distribution in the longitudinal direction in the central part and a heater 4 whose end parts are large are disposed in the fixing roller 1. The surface temperature of the fixing roller 1 is detected by a thermistor 5 and controlled to 205 deg.C during a standing by and 190 deg.C during a consecutive copy. When the temperature of the roller is raised to the stand-by temperature from the fixing operation after the consecutive fixing operation, the controlled temp. is raised stepwise in consideration of the heat conduction time in the longitudinal direction of the fixing roller 1, the time constant of the thermistor 5, etc. At this time, it is preferable that the temp. is raised stepwise in accordance with an elapsed time after the fixing operation is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device, and more particularly to a method of controlling a fixing heater of the fixing device.

[0002]

2. Description of the Related Art In a general image forming apparatus, a roller fixing device using heat and pressure is used as a means for fixing a toner image transferred on a transfer paper. Such a general roller fixing device has a fixing roller that heats the toner image on the transfer sheet, and a pressure roller that presses the transfer sheet against the fixing roller. A heater is provided as a heating means for supplying heat to the fixing roller.

A thermistor, which is a temperature detecting means, is arranged in contact with the fixing roller, and the surface temperature of the fixing roller is based on the temperature detected by the thermistor, and the toner image is fixed during copying. The temperature is controlled to be a temperature that is high enough to perform the operation, and in the standby mode, a temperature that can immediately reach the temperature required for copying.

Of the temperature control methods, the most general method is to turn off the heater when the temperature detected by the thermistor is higher than the set temperature, and turn on the heater when the temperature is low. There is a way. By performing such control, the temperature of the fixing roller can be stabilized near the set temperature.

However, since the fixing roller used in the fixing device generally has a thick cored bar, when the temperature control temperature is controlled by such a system, the heater is turned on / off. The reaction time of the thermistor to OFF is very long, and the temperature change is delayed by that time.

Therefore, the temperature of the fixing roller after the completion of copying causes some temperature ripples and overshoots. However, in the case of a thick roller, since the heat capacity is large, the temperature rising gradient with respect to time is very large. It was small and overshoot was not a problem in practice.

[0007]

However, at present, in order to reduce the warm-up time at the time of start-up, fixing using a fixing roller of a thin core metal type (specifically, a wall thickness of about 0.7 mm) is used. The device has been commercialized, and in such a system, since the heat capacity is smaller than that of the conventional thick type, the temperature rise gradient is large. Therefore, even if the time constant (reaction delay time) of the thermistor is small, the control delay caused by it is sensitively reflected on the surface temperature of the fixing roller, resulting in a large overshoot.

For example, when a thick fixing roller is used, even if the temperature control temperature at the time of standby is lower than the temperature control temperature at the time of copying, since the heat capacity is large, the pressure roller or the like at the start of copying is used. The amount of heat that is taken away is sufficiently stored during standby, but when a thin roller is used, if the temperature control temperature during standby is lower than the temperature control during copying, the heat capacity will be too small to copy. Immediately after the start, heat is taken away and the surface temperature drops significantly.

However, when the temperature is rapidly raised to a high temperature in order to compensate for this decrease in temperature, a large overshoot occurs due to the large temperature rise gradient as described above.

Therefore, in order to solve such a problem, there is a method in which the temperature control temperature at the time of standby is made higher than the temperature control temperature at the time of copying to prevent overshoot and prevent temperature decrease at the start of copying. was suggested.

However, even when this method is used, the temperature drop at the start of copying is larger at the end portion than at the roller center portion, and when a wide transfer paper is fixed, a fixing failure due to insufficient temperature occurs. There was a risk of causing it.

This is because the amount of heat escaped from the end of the roller is large, and in the thin-walled roller, the heat conduction speed in the radial direction is high, but the heat conduction speed in the longitudinal direction is low, so that the fixing roller This is because the temperature distribution on the surface becomes non-uniform in the longitudinal direction.

Therefore, in addition to the above method, one heater has a larger central portion and the other heater has a larger end portion in the light distribution distribution in the fixing roller longitudinal direction of the two heaters disposed inside the fixing roller. In this way, a method has been proposed in which the temperature control during standby is mainly performed by using a heater having a light distribution that is larger at the ends.

According to this method, the temperature distribution on the surface of the fixing roller during standby becomes slightly higher at both ends as shown by the curve m in FIG. 9, and the temperature distribution on the surface of the roller during copying is As shown by the straight line k shown in FIG. 9, it becomes substantially uniform in the longitudinal direction.

However, in the case where the two fixing heaters having different light distributions are used and the control is performed such that the standby temperature control temperature is higher than the temperature control temperature during copying, the following problems occur. There was a point.

That is, when the temperature of the central portion is raised to the standby temperature control temperature after the copying is completed, if the temperature is raised at once, the amount of heat supplied to the end portion itself is greater than the amount of heat conducted from the end portion side to the central portion side. 10, the temperature distribution becomes as shown by a curve n in FIG. 10, and overshoots indicated by halftone dots occur, and the overshoots are averaged over time, and the central portion of the fixing roller. However, there was a problem of causing overshoot.

This is because a heater whose light distribution is biased toward the end is used for the temperature control during standby, and the heat conduction time in the longitudinal direction of the fixing roller is the heat conduction time in the radial direction of the fixing roller. Although it is slower than the above, the temperature detection thermistor is placed in the center of the fixing roller in the longitudinal direction, so there is a delay due to the time constant of the thermistor. One of the reasons is that the heater is still energized without being able to detect overshoot.

However, if the thermistor is arranged on the end side of the fixing roller, in the case of fixing a transfer paper having a narrow width, the lighting ratio of the heater whose light distribution is biased to the central part becomes high, so that the roller is turned on. It is not preferable because the temperature cannot be detected accurately.

The first invention according to the present application solves the above problems and uses a thin fixing roller and a heater to make the temperature in standby higher than that in copying, and in the standby distribution of light distribution. It is an object of the present invention to provide an image forming apparatus having a fixing device that does not cause an overshoot during the temperature control after completion of copying even when the temperature control is performed by a heater evenly on the edge side.

In addition to the above object, the second invention of the present application provides an image forming apparatus having a fixing device capable of raising the temperature at the time of standby as quickly as possible while preventing the occurrence of overshoot. It is intended to be provided.

Further, in addition to the above object, the third invention of the present application is to provide an image forming apparatus having a fixing device capable of always accurately detecting the temperature of the roller.

In addition to the above-mentioned object, a fourth invention of the present application is an image forming apparatus having a fixing device capable of shortening the warm-up time at startup and shortening the time lag of temperature detection. To provide a device.

Further, in addition to the above object, a fifth invention of the present application is to provide an image forming apparatus having a fixing device capable of making the temperature distribution in the longitudinal direction of the roller uniform.

In addition to the above object, the sixth invention according to the present application can perform good fixing without causing a temperature rise in the non-sheet passing portion even when the size of the transfer paper is different. An object is to provide an image forming apparatus having a fixing device.

Further, in addition to the above object, the seventh invention of the present application provides an image forming apparatus having a fixing device capable of making the temperature distribution in the longitudinal direction of the roller uniform even when two heaters are provided. To provide.

[0026]

According to the first invention of the present application, the above object is to provide a fixing roller and a pressure roller arranged so as to be in pressure contact with each other, and at least inside the fixing roller. The temperature control means is provided with a heating means provided and a temperature control means for maintaining the temperature of the roller provided with the heating means at a desired temperature by controlling energization to the heating means. In the roller set to switch the temperature of the roller between the fixing temperature during the fixing operation and the standby temperature during standby, which is higher than the fixing temperature,
The temperature control means is achieved by setting the temperature of the roller to be raised stepwise when the temperature of the roller is raised to the standby temperature after the end of the continuous fixing operation.

According to the second invention of the present application,
The above-mentioned object is achieved by the temperature control means according to the first aspect of the invention, which is set to raise the temperature stepwise in accordance with the elapsed time after the end of the fixing operation.

Further, according to a third invention of the present application, the above-mentioned object is, in the above-mentioned first invention or second invention, a temperature detecting means for detecting the temperature of a roller provided with a heating means. , The center of the roller in the longitudinal direction.

According to the fourth invention of the present application,
The above object is any of the first to third inventions, wherein the roller provided with the heating means is a thin roller having a core metal thickness of 1.0 mm or less. The response time is achieved by being within 2 seconds.

Further, according to a fifth invention of the present application, in any one of the above-mentioned first to fourth inventions, the heat distribution of the heating means in the longitudinal direction of the roller is from the central portion. Is also achieved by the large amount of heat generated at the ends.

According to the sixth invention of the present application,
The above-mentioned object is, in the above-mentioned first invention to fifth invention, that two heating means are arranged inside the roller, and the heat generation distribution of one heating means is in the center rather than the end portion in the roller longitudinal direction. The heat generation amount of one portion is large, and the heat generation distribution of the other heating means is achieved by the heat generation amount of the end portion being larger than the center portion in the roller longitudinal direction.

Further, according to a seventh invention of the present application, in the above-mentioned first invention to the sixth invention, the temperature control means is such that the drive ratio of the two heating means in standby is This is achieved by setting the heat generation distribution in which the heat generation amount at the end portion is larger than that at the central portion in the roller longitudinal direction so as to be larger than that of the other heating means.

[0033]

According to the first invention of the present application, when the temperature of the roller is raised from the fixing operation to the standby temperature after the continuous fixing operation, the temperature is raised stepwise, so that the heat capacity is small. Even in the case of a roller, overshoot does not occur and the fixability is not adversely affected.

According to the second invention of the present application,
In the first aspect of the invention, the temperature is raised stepwise according to the time elapsed after the fixing operation is completed, so that the temperature can be raised to the standby temperature within a short time within a range where overshoot does not occur.

Further, according to the third invention of the present application, in the first invention or the second invention, the temperature detecting means is arranged at the center of the roller in the longitudinal direction.
Accurate temperature detection is always performed regardless of the size of the transfer paper, and the occurrence of overshoot is suppressed as described above.

According to the fourth invention of the present application,
In the first to third inventions, the roller is a thin roller having a thickness of 1.0 mm or less, and the response time of the temperature detecting means is within 2 seconds. Therefore, the warm-up time at startup is short, and A time lag during temperature detection is reduced, and even if these rollers and temperature detection means are used, overshoot does not occur due to the temperature control as described above.

Further, according to a fifth invention of the present application, in the above-mentioned first invention to fourth invention, the heat generation distribution of the heating means is such that the heat generation amount at the end portion is larger than that at the central portion in the roller longitudinal direction. Since it is made large, the temperature distribution on the surface of the roller is uniform in the longitudinal direction even when the amount of heat escaped from the roller end is large and the heat conduction speed in the longitudinal direction is slow.

According to the sixth invention of the present application,
Two heating means are arranged inside the roller. One heating means has a larger heat generation amount in the central portion than the end portions in the roller longitudinal direction, and the other heating means has a heat generation distribution in the roller longitudinal direction. Since the amount of heat generated at the end is larger than that at the center, an appropriate heating operation is performed according to the size of the transfer paper.

Further, according to the seventh invention of the present application, the driving ratio of the two heating means in standby has a heat generation distribution in which the heat generation amount at the end portion is larger than at the center portion in the roller longitudinal direction, Since there are more heating means than the other heating means, the temperature distribution in the roller longitudinal direction can be made uniform as in the fifth aspect of the invention.

[0040]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a flow chart showing a temperature control sequence after continuous copying in the image forming apparatus of the first embodiment of the present invention, FIG. 2 is a diagram showing a temperature transition due to the temperature control of the present embodiment, and FIG. 3 is this embodiment. 4 is a sectional view showing the configuration of the fixing device in FIG. 4, FIG. 4 is a view showing the light distribution of the main heater, FIG. 5 is a view showing the light distribution of the sub-heater, and FIG. 6 is a standby state after the completion of copying in this embodiment. It is a figure which shows surface temperature distribution.

As shown in FIG. 3, the fixing device in the image forming apparatus of this embodiment includes a fixing roller 1 for heating the toner image on the transfer sheet and a pressure roller 2 for pressing the transfer sheet on the fixing roller 1. Inside the fixing roller 1, heaters 3 and 4 serving as heating means for supplying heat to the fixing roller 1 are provided. Also, the fixing roller 1
An oil application unit 11 is disposed above the web of the fixing roller 1. The oil application unit 11 pushes the web 10 delivered from the delivery side 8 and wound on the winding side 9 onto the surface of the fixing roller 1. A pressing roller 7 for hitting is provided.

The fixing roller 1 is a thin roller having a core metal of 0.7 mm iron, and the pressure roller 2 is a silicone rubber covered with a PFA tube.
Further, the surface temperature of the fixing roller 1 is the thermistor 5 which is a temperature detecting means arranged at the center of the fixing roller 1 in the longitudinal direction.
It is detected by and is controlled so that the value becomes the controlled temperature. The thermistor 5 has a time constant of about 2 seconds.

The heaters 3 and 4 are arranged inside the fixing roller 1, and the two heaters 3 and 4 are a main heater 3 having a large central light distribution in the longitudinal direction and an end portion. Sub heater 4 with large
It is configured as. Schematic diagrams of the light distribution are shown in FIGS. 4 and 5. The outputs are 700 W and 600 W, respectively.

Both of the two heaters 3 and 4 are not always turned on, and one unit is set for a certain fixed time (5 in this embodiment by a temperature control means such as a CPU).
00 ms), the lighting ratios of the two heaters 3 and 4 are given at the time of copying and standby, the heaters are switched according to the lighting ratio, and the lighting ratio is switched according to the paper size at the time of copying. The lighting ratio of the two heaters 3 and 4 is called a flushing rate.

Since heat escapes from both ends of the fixing roller 1 during standby, the flushing rate of the sub-heater 4 is increased to control the temperature of the end to be slightly higher. Specifically, the flushing rate of the main heater 3 and the sub heater 4 is set to 1: 9.

The flushing rate at the time of copying is changed depending on the paper size. When passing A3 size, it is 7: 3, when passing B4 size is 8: 2, and when passing A4R or smaller size. It is controlled as 10: 0.

In the apparatus of this embodiment as described above,
The standby temperature control temperature is set to 205 ° C. and the temperature control temperature during continuous copying is set to 190 ° C. to perform temperature control. Here, the standby temperature control temperature is set to 205 ° C. because the temperature of the fixing roller 1 is deprived of by the pressure roller 2 immediately after the start of copying and the surface temperature is not affected, and the first fixing temperature is set. It is based on the fact that the minimum temperature required to secure the temperature was 205 ° C.

However, if the conventional control is performed and the temperature until the standby temperature control after continuous copying is measured, an overshoot occurs. Therefore, in order to suppress the overshoot, in the present invention, in the longitudinal direction of the fixing roller 1. In consideration of the heat conduction time and the time constant of the thermistor 5, the temperature control temperature is increased stepwise to control overshoot.

Specifically, as shown in FIG. 1, when the temperature control temperature immediately before the end of copying is 190 ° C., the temperature control is performed at 195 ° C. for 20 seconds after the end of copying (step S1).
-1 to S1-2), temperature control at 200 ° C for the next 20 seconds (steps S1-3 to S1-4), and temperature control at 205 ° C which is the normal standby temperature control (step S1-).
5). That is, as shown in FIG. 2, a control method of gradually increasing the temperature control temperature is adopted, but the number of steps and the duration of each step are not limited to this value, and an optimum value may be adopted depending on the system.

Unless the control for raising the temperature control stepwise is performed in this manner, when the temperature of the central portion in the longitudinal direction of 1: 9 (main: sub) which is the flushing rate during standby is raised. The temperature at the edges rises rapidly, and the temperature at the center slows up. Since the temperature difference in the longitudinal direction causes an overshoot, in the present invention, the temperature control temperature is increased stepwise to provide time for equalizing the temperature difference in the longitudinal direction of the fixing roller 1 for each temperature in each step. There is.

By doing so, the fixing roller 1
The temperature distribution in the longitudinal direction of is uniformed, and the temperature of both ends when the temperature of the central part finally reaches 205 ° C. can be suppressed low,
As shown in FIG. 6, a large overshoot does not occur.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 7 shows a flowchart of the control method in this embodiment. The main body configuration is the same as that of the first embodiment except for the temperature control method described below. First, at the end of continuous copying, the fixing roller surface temperature A is detected by the thermistor (step S7-1), the difference between the temperature A and the standby temperature control temperature is calculated, and the temperature control temperature control from continuous copy to standby is performed. The intermediate temperature control temperature in the process of is set (step S7-2).

Specifically, the standby temperature control temperature, for example, 2
The middle value of the roller temperature after the end of continuous copying is set as 05 ° C. Then, the temperature control is performed at the intermediate temperature control temperature for a set time (for example, 20 seconds) after the end of continuous copying (steps S7-3 to S7-4), and then the temperature is controlled at 205 ° C. which is a normal standby temperature control temperature. Key control is performed (step S7-5).

By performing such control, it is possible to raise the temperature control temperature at an appropriate temperature with respect to the temperature at the end of copying, and it is possible to reduce the overshoot.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The constitution of the main body of this embodiment is almost the same as that of the first embodiment, but the heater inside the fixing roller is
The case of a book is shown.

The light distribution of this fixing heater is shown in FIG. In the case of a system using a single heater, the light quantity at the end is often high in this way. This is because heat easily escapes from both ends. The controlled temperature during standby and copying is the same as in the first embodiment.

Even in the case of such a configuration, similarly to the first embodiment, the temperature control temperature control method until the temperature is increased to the standby temperature control after the continuous copying is performed stepwise.
Since it is possible to prevent the occurrence of overshoot and the cost is reduced as compared with the two-heater system, it is possible to cope with a relatively inexpensive machine.

[0061]

As described above, the first aspect of the present application
According to the invention, when the temperature of the roller is raised from the fixing operation to the standby temperature after the continuous fixing operation, the temperature is raised stepwise, so that even if the roller has a small heat capacity and is thin, It is possible to provide an image forming apparatus having a fixing device that can prevent the occurrence of shoots, have a short warm-up time, and can obtain good fixing properties.

According to the second invention of the present application,
In the first aspect of the present invention, the temperature is raised stepwise according to the elapsed time after the end of the fixing operation, so that it is possible to quickly raise the temperature to the standby temperature while preventing the occurrence of overshoot.

Further, according to the third invention of the present application, in the first invention or the second invention, the temperature detecting means is arranged at the center of the roller in the longitudinal direction.
It is possible to always perform accurate temperature detection regardless of the size of the transfer paper while preventing the occurrence of overshoot.

According to the fourth invention of the present application,
In the first to third inventions, the roller is a thin roller having a thickness of 1.0 mm or less, and the response time of the temperature detecting means is within 2 seconds. Therefore, the warm-up time at startup is short, and It is possible to reduce the time lag during temperature detection and prevent the occurrence of overshoot.

Further, according to the fifth invention of the present application, in the above-mentioned first to fourth inventions, the heat generation distribution of the heating means is such that the heat generation amount at the end portion is larger than that at the central portion in the roller longitudinal direction. Since it is made large, the temperature distribution in the longitudinal direction of the roller can be made uniform while preventing the occurrence of overshoot.

According to the sixth invention of the present application,
Two heating means are arranged inside the roller. One heating means has a larger heat generation amount in the central portion than the end portions in the roller longitudinal direction, and the other heating means has a heat generation distribution in the roller longitudinal direction. Since the amount of heat generated at the end is larger than that at the center, it is possible to perform an appropriate heating operation according to the size of the transfer paper while preventing the occurrence of overshoot.

Further, according to the seventh invention of the present application, the driving ratio of the two heating means in standby has a heat generation distribution in which the heat generation amount at the end is larger than at the center in the roller longitudinal direction, Since there are more heating means than the other heating means, it is possible to make the temperature distribution uniform in the roller longitudinal direction while preventing the occurrence of overshoot.

[Brief description of drawings]

FIG. 1 is a flow chart of temperature control in a first embodiment of the present invention.

FIG. 2 is a diagram showing a transition of a controlled temperature in the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of the fixing device according to the first exemplary embodiment of the present invention.

FIG. 4 is a light distribution distribution diagram of the main heater according to the first embodiment of the present invention.

FIG. 5 is a light distribution distribution diagram of the sub heater in the first embodiment of the present invention.

FIG. 6 is a diagram showing a temperature distribution in a longitudinal direction of a fixing roller when a standby temperature control temperature is reached after completion of copying in the first embodiment of the present invention.

FIG. 7 is a flow chart of temperature control in the second embodiment of the present invention.

FIG. 8 is a light distribution distribution diagram of a fixing heater according to a third embodiment of the present invention.

FIG. 9 is a diagram showing temperature distributions of a main heater and a sub heater of a conventional device.

FIG. 10 is a diagram showing a temperature distribution when the standby temperature control temperature is reached after copying in the conventional apparatus.

[Explanation of symbols]

 1 fixing roller 2 pressure roller 3 main heater (heating means) 4 sub-heater (heating means) 5 thermistor (temperature detection means)

Claims (7)

[Claims] 1. A fixing roller and a pressure roller which are arranged so as to be in pressure contact with each other, a heating means which is arranged at least inside the fixing roller, and the heating by controlling energization to the heating means. A temperature control means for maintaining the temperature of the roller on which the means is arranged at a desired temperature, the temperature control means changing the temperature of the roller to a fixing temperature during the fixing operation and a standby time higher than the fixing temperature. In the case where the temperature control means is set to switch to the standby temperature, the temperature control means gradually increases the temperature when the temperature of the roller is raised to the standby temperature after the end of the continuous fixing operation. An image forming apparatus, wherein the image forming apparatus is set to be raised. 2. The image forming apparatus according to claim 1, wherein the temperature control unit is set to raise the temperature stepwise in accordance with the elapsed time after the end of the fixing operation. 3. The image forming apparatus according to claim 1, wherein the temperature detecting means for detecting the temperature of the roller provided with the heating means is provided at the center of the roller in the longitudinal direction. . 4. The roller provided with the heating means is a thin roller having a core metal thickness of 1.0 mm or less, and the response time of the temperature detecting means is within 2 seconds. The image forming apparatus according to claim 3. 5. The image forming apparatus according to claim 1, wherein the heat generation distribution in the roller longitudinal direction of the heating means is such that the heat generation amount at the end portion is larger than at the central portion. 6. Two heating means are disposed inside the roller, and the heat generation distribution of one heating means is such that the heat generation amount in the central portion is larger than that in the end portion in the roller longitudinal direction, and the other heating means. 6. The image forming apparatus according to claim 1, wherein the heat generation distribution is such that the amount of heat generated at the end is larger than that at the center in the roller longitudinal direction. 7. The temperature control means is such that the driving ratio of the two heating means in the standby state is larger in the one having a heat generation distribution in which the heat generation amount at the end portion is larger than that at the central portion in the roller longitudinal direction than in the other heating means. The image forming apparatus according to claim 6, wherein the image forming apparatus is set so as to be set.