JPH08220930A - Fixing device - Google Patents

Abstract

PURPOSE: To provide a fixing device having a simple constitution capable of always attaining stable fixing performance by controlling plural heaters heating a fixing roller. CONSTITUTION: This fixing device fixing a transferred image on a recording sheet by making the recording sheet pass through the heated cylindrical fixing roller 1 is provided with a first heater 3 set on a large-sized sheet width area, a first energizing controlling means controlling the energizing of the heater 3, a second heater 5 set on a small-sized sheet width area, a second energizing controlling means controlling the energizing of the second heater 5, and a temperature sensor 7 detecting the surface temperature of the roller at the set part of the heater 5. The carolific power of the heater 5 is so low that it can't feed fixing energy enough to fix the small-sized sheet when it passes through, so that the second heater 5 is consecutively energized, also the heater 3 is energized and controlled by the output of the sensor 7 while the small-sized sheet passes through, and only the heater 3 is energized and controlled by the output of the sensor 7 while the large-sized sheet passes through.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine and a plain paper Fa.
x, a laser printer, or the like, relates to a fixing device for fixing a transferred image on the recording sheet by passing a recording sheet having the transferred image through a heated fixing roller, and particularly, for heating the fixing roller. The present invention relates to a fixing device having a simple structure capable of controlling a plurality of heaters and always obtaining stable fixing performance.

[0002]

2. Description of the Related Art In a fixing device of an image forming apparatus such as a copying machine, a plain paper fax, or a laser printer, if small-sized sheets are continuously fed, the roller surface temperature of a portion where the sheets do not pass may rise. It is generally known (in a center-based machine, the temperature at the end of the fixing roller rises, so the above-mentioned problem is often referred to as an end temperature rise). The increase in the edge temperature is remarkable as the thickness of the sheet to be passed is larger, the sheet passing rate (the number of sheets passed per hour) is larger, the environmental temperature is lower, and the thermal conductivity of the roller material is smaller. Appear in. Further, recently, in order to shorten the waiting time of the user, the thickness of the roller tends to be reduced, but when the thickness of the roller is reduced, the end temperature rise is also increased. If the edge temperature rises, there is a problem that the rollers may be damaged or hot offset may occur when a large size sheet is passed. In addition, there is a problem that wrinkles and curls are caused and sufficient fixing property cannot be satisfied.

In conventional fixing devices, since the fixing roller is relatively thick, the temperature rise at the end portion can be small,
This was not a problem, but recently, from the viewpoint of energy saving, in order to minimize the heat release from the roller during standby, the heater is turned off during standby or the preheating temperature (when the fixing roller is warmed up in advance during standby) There is an increasing tendency to set the temperature of as low as possible. At this time, by making the fixing roller thin and reducing the heat capacity so that the waiting time of the user does not become long,
A method of increasing the temperature rising rate is adopted. As described above, in recent years, there has been a strong demand for energy saving, and the problem of temperature rise at the end has been highlighted.

On the other hand, in the conventional fixing device, in order to prevent the end temperature from rising, a plurality of heating areas (mainly two heating areas) are used.
The heater of (book) was used to take measures to selectively heat. The main methods are as follows. First, as a first method, as shown in FIG. 20, a central heating heater 1 is used.
01 and the full width heating heater 103 are combined to heat only the full width heating heater 103 when passing a large size sheet, and the central heating heater 1 when passing a small size sheet.
Only 01 was used for heating. As the second method, as shown in FIG. 21, the central heating heater 10 is used.
In combination of 1 and the heater for edge heating 105, heating is performed by the central heating heater 101 and the heater for edge heating 105 when a large size sheet is passed, and when a small size sheet is passed.
The heating is performed only by the central heating heater 101. The first method is, as shown in FIG. 20, a heater 101 for a small size sheet and a heater 103 for a large size sheet.
Are separately prepared, and the heater is selected according to the size of the sheet to be passed. One temperature sensor 107 is installed in the central portion, and the temperature of both the large size sheet and the small size sheet is controlled by this sensor.

However, in the first method, since the heat is not supplied to the end portion when the small-sized sheet is continuously fed, the temperature of the end portion of the fixing roller 109 is lower than that of the central portion. Therefore, when a large-sized sheet is passed immediately after passing a small-sized sheet, there is a problem that fixing performance is not satisfied due to defective fixing, wrinkles, curls, and the like at the end portions.

On the other hand, in the second method shown in FIG. 21, both the heaters 101 and 105 are energized at the time of warming up and at the time of passing a large size sheet, and only at the central heating heater 101 at the time of passing a small size sheet. It energizes. The temperature sensors 111 and 113 are installed one each at the central portion and the end portion, and the central sensor 111 controls the central heating heater 101, and the end sensor 113 controls the end heating heater 105. ing. In the second method, if the end temperature of the fixing roller 109 is controlled to an appropriate temperature by the end heating heater 105 even when a small-sized sheet is passed, the above-mentioned temperature decrease of the end may occur. Therefore, the fixing performance can be satisfied even when the large size sheet is passed immediately after the small size sheet is passed. However, an independent control system is required for each (temperature sensor 11 in the figure
1, 113, input circuit 115, driver 117, CPU
119 also requires two input ports.) The structure is complicated and there is a drawback that the cost becomes high.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to control a plurality of heaters for heating a fixing roller to obtain a stable fixing performance at all times. It is an object of the present invention to provide a fixing device having a simple structure capable of performing.

[0008]

To achieve the above object, the invention according to claim 1 is a fixing device for fixing a transfer image on the recording sheet by passing a recording sheet through a heated cylindrical fixing roller. A first heater installed in the paper passing width region of a large size sheet, a first energization control means for controlling the energization of the first heater, and a second heater installed in the paper passing width region of a small size sheet. And a temperature sensor that detects a roller surface temperature in the installation portion of the second heater, and a heat generation capacity of the second heater. However, the capacity is so low that it does not reach the fixing energy required for passing the small size sheet, and the second heater is continuously energized during the passage of the small size sheet, and at the same time the first sensor is output by the output of the temperature sensor. Energize the heater Gyoshi, during large size sheet paper passage, characterized in that energization controlling only the first heater by the output of the temperature sensor.

According to a second aspect of the present invention, in the fixing device of the first aspect, the response of the second heater (the rising characteristic of heat generation) is slower than the response of the first heater. Characterize. According to a third aspect of the present invention, in the fixing device according to the second aspect, the fixing is performed by the first heater during a warm-up period during standby and when a large sheet size is specified after rising. It is characterized in that the roller is heated and the fixing roller is heated by the first and second heaters during warm-up when a small sheet passing size is specified after rising.

According to a fourth aspect of the invention, in the fixing device of the first and second aspects, the duty control means is provided only in the first energization control means. According to a fifth aspect of the invention, in the fixing device according to the second aspect, the power supply to the second heater is turned off before the end of copying (printing). According to a sixth aspect of the invention, in the fixing device according to the second aspect, the second heater is composed of a heating wire, and the heating wire is installed so as to surround the first heater. To do.

According to a seventh aspect of the present invention, in the fixing device according to the sixth aspect, an insulating material is arranged around the second heater to be electrically insulated from the outside. According to an eighth aspect of the invention, in a fixing device in which a recording sheet is passed through a heated cylindrical fixing roller to fix the transferred image on the recording sheet, the fixing device is installed in a sheet passing width range of a large size sheet. No. 1 heater, a first energization control means for controlling the energization of the first heater, and a first heater which is installed in the sheet passing width region of a small size sheet and is inferior in responsiveness (heat rising characteristic) to the first heater. Second heater, second energization control means for controlling energization of the second heater, and the second
A temperature sensor for detecting the roller surface temperature at the heater installation portion, and during the passage of the small size sheet, the first and second heaters are energized by the output of the temperature sensor to pass the large size sheet. The inside is configured to control the energization of only the first heater by the output of the temperature sensor,
The first and second heaters are not turned on at the same time.

[0012]

According to the above construction, the first heater installed in the paper passing width range of the large size sheet, the first energization control means for controlling the energization of the first heater, and the paper passing width range of the small size sheet. A second heater installed in the second heater, a second energization control unit that controls energization of the second heater, and a temperature sensor that detects a roller surface temperature in the installation portion of the second heater.
The heat generation capacity of the second heater is so low that it does not reach the fixing energy required for passing the small size sheet, and the second heater is continuously energized during the passage of the small size sheet. Since the first heater is energized by the output of the sensor, and the first heater alone is energized by the output of the temperature sensor during the passage of the large size sheet, the temperature control for the second heater is performed. The control can be simplified without the need, and the temperature sensor for the end portion is not necessary, and a uniform roller temperature distribution can be obtained with a simple configuration.

Further, by using a heater having poor responsiveness as the second heater for continuously energizing, it is possible to obtain temperature controllability substantially equivalent to that described above and, in many cases, contribute to cost reduction. it can. Also, during warm-up when the paper passing size after stand-by and after rising is specified to be large, the fixing roller is heated by the first heater, and the paper passing size after rising is specified to be small. Since the fixing roller is configured to be heated by the first and second heaters during the warm-up when the sheet is warmed up, the sheet can be heated to the preset fixing temperature in a short time when a small-sized sheet is passed. .

Further, since the duty control means is provided only in the energization control means of the first heater,
Even for a roller having a small heat capacity such as a thin fixing roller, it is possible to obtain a temperature distribution having no temperature ripple over the entire width of the roller with a low cost configuration.

Further, since the power supply to the second heater is turned off before the end of copying (printing), it is possible to prevent the overshoot immediately after the sheet is passed and also the central portion and the end of the roller. The temperature difference between the parts can be reduced. Further, since the second heater is composed of a heating wire and the heating wire is installed so as to surround the first heater, it is possible to contribute to space saving and cost reduction. In addition, since an insulating material is arranged around the second heater to electrically insulate the outside from the outside, it is possible to provide a safe fixing device that is electrically insulated while realizing space saving. You can

Further, in a fixing device for passing a recording sheet through a cylindrical fixing roller heated by a heater and fixing the transferred image on the recording sheet, the first fixing device is installed in the sheet passing area of a large size sheet. A heater, a first energization control unit that controls energization of the first heater, and a second heater that is installed in the sheet passing width region of a small-sized sheet and has a poorer responsiveness (heat generation rising characteristic) than the first heater. And a temperature sensor for detecting the roller surface temperature at the installation portion of the second heater, and a second current control means for controlling the current supply to the second heater. The first and second heaters are energized by the output of the sensor, and only the first heater is energized by the output of the temperature sensor during the passage of the large size sheet.
Since the heaters are controlled so as not to be turned on at the same time, the power capacity distributed to the fixing device can be maximized to perform warm-up, so that the warm-up time is further shortened in comparison with the invention of claim 2. be able to.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. 1 is a schematic side view of a fixing device embodying the present invention, and FIG. 2 is a schematic configuration diagram of the fixing device embodying the present invention. In this fixing device, as shown in FIG. 1, first and second heaters 3 and 5 for heating the fixing roller 1 are installed inside the fixing roller 1, and the surface of the fixing roller 1 is provided. Is equipped with a temperature sensor 7 for detecting the roller surface temperature. Then, the recording sheet is passed between the heated fixing roller 1 and pressure roller 8 to fix the transferred image on the recording sheet.

As shown in FIG. 2, the first heater 3 has a heat generation width substantially the same as the sheet passing width area of a large size sheet, and the second heater 5 has a sheet passing width of a small size sheet. It has the same heat generation width as the area. Further, the temperature sensor 7 is installed within the heat generation width of the second heater 5, and the signal detected by the temperature sensor 7 is taken into the CPU 11 via the input circuit 9. CPU 11
Is configured to control the energization of the heaters 3 and 5 via the driver 13 based on the detected roller surface temperature.

FIG. 3 shows the first and second heaters 3,
It is a figure which shows heat distribution of No. 5. As shown in FIG. 3, the first heater 3 is set to have a heat distribution so that a uniform temperature distribution can be obtained without increasing the end temperature when a large size sheet is passed. In FIG. 3, it is described that the end portion has a slightly higher heat distribution in the heat distribution of the first heater 3, but this is because the heat distribution at the end portion is taken into consideration in consideration of the escape of heat in the axial direction. Is set to be slightly higher than the central portion, which is a method generally used conventionally.
Further, the heat distribution width of the second heater 5 is almost the same as the small size sheet passing width range, and the heat generation amount thereof is set to such an extent that it does not reach the fixing energy required for passing the small size sheet. ing.

As shown in FIG. 4, when passing a large size sheet, only the first heater 3 is energized by the temperature detected by the temperature sensor 7, and when passing a small size sheet, The second heater 5 is continuously energized, and the first heater 3 is controlled to be energized.

That is, as shown in the control flowchart of FIG. 5, first, in step 201, the size of the recording sheet to be passed is judged.
03, the first heater 3 is connected to the temperature sensor 7
ON / OFF energization control is performed according to the detected temperature and the second heater 5 is energized continuously. When it is determined in step 201 that the recording sheet is a large-sized recording sheet, in step 205, ON / OFF energization control is performed on only the first heater 3 according to the temperature detected by the temperature sensor 7. According to the above control flow, when the size of the recording sheet is small, the second heater 5 is turned on.
The flow is simple and the load on the software is small.

Further, the recognition of the paper size may be made, for example, by setting the paper size key of the operation unit or by making a paper size switch preset in the paper feed cassette. The sheet being conveyed may be detected by a sensor such as an optical sensor. By controlling in this way, it is possible to prevent the temperature of the end portion from rising and make the roller temperature uniform regardless of the sheet size.

FIG. 6 is a diagram showing how the roller end temperature rises when the amount of heat generated by the second heater 5 is changed. In FIG. 6, since the roller central temperature is controlled by the detection output of the temperature sensor 7, it is constant at the set temperature. On the other hand, the end temperature changes as shown in the graph, and as the heat generation amount (W number) of the second heater 5 is increased, the end temperature rise becomes smaller, and at a certain point the center is reached. The temperature becomes lower at the edges than at the edges. Therefore, the heat generation amount of the second heater 5 is set to an appropriate value so that the end temperature does not occur.

FIG. 7 is a diagram showing the amount of increase in the end temperature measured by the experiment. As shown in FIG. 7, in this fixing device, the temperature of the end portion can be prevented from rising by setting the second heater 5 to about 110 W. Here, fixing roller: φ40, Fe (t = 0.4), roller control temperature: 1
It is set to 50 ° C. and 45 cpm (linear velocity 270 mm / s). As described above, according to the first embodiment, it is not necessary to control the ON / OFF energization temperature of the second heater 5 (continuous energization is sufficient), and the temperature sensor for the end portion is not necessary. Thus, a uniform roller temperature distribution can be obtained.

There are many sheet sizes to be passed,
If a partial temperature rise still occurs even if the heating region is divided into two, the number of heaters may be further increased to divide the heating region. Like the second heater 5, the third heater (additional heater) in this case has a heating region in the sheet passing width region of the sheet passing size, and the heat generation capacity is appropriate so that it does not reach the fixing energy. If the capacity is set to a certain value and a sheet of that size is passed, the third heater is continuously energized and the temperature is controlled by the first heater 3, so that the roller temperature distribution can be kept uniform. Further, the fourth and fifth heaters may be similarly configured.

Next, a second embodiment of the fixing device of the present invention will be described. First, for example, a thin fixing roller, which has recently received attention as a fixing device having a short warm-up time, has a problem that the temperature ripple becomes severe because the heat capacity of the roller is small. In order to reduce the temperature ripple of the fixing roller, temperature control with excellent responsiveness is required.
There are several causes that cause the above temperature ripple,
One of the measures is a temperature sensor, and the temperature ripple can be reduced by using a temperature sensor having excellent responsiveness. The second is control means, which has a large temperature ripple in the conventional ON / OFF control.
The temperature ripple can be reduced by using the duty control means such as phase control and time division control. The third is a heater, and the temperature ripple can be reduced by using a heater having excellent responsiveness.

Regarding the above-mentioned third fixing heater, for example, a halogen heater which has been used conventionally can be said to be a heater having relatively good response, and a nichrome wire heater or the like can be said to be heater having poor response (depending on the number of W). A little different,
The response of the halogen heater is 200 to 500 ms, while the nichrome wire heater is 20 to 50 sec, which is very slow). Therefore, in the conventional usage method, a heater having a poor response such as a nichrome wire heater cannot be used as the fixing heater. In view of this, in the second embodiment, a heater having poor responsiveness, which cannot be used as the heat source of the fixing device by the conventional control method, can be used. Other structural operations are the same as in the first embodiment. The second embodiment has the same basic structure as that of the first embodiment shown in FIG. 2, but the second heater 5 shown in FIG. 2 is replaced with a heater having a poor response such as the nichrome wire heater. Is what you use.

FIG. 8 shows changes in the end temperature when a heater having a fast response (for example, a halogen heater) and a heater having a slow response (for example, a nichrome wire heater) are used as the second heater 5. As shown in FIG. 8, when a heater having a slow response is used, the rise of heat generation takes a long time, and therefore, a slight increase in the end temperature occurs until sufficient heat is generated. However, when the amount of heat generation reaches a predetermined amount, the end temperature decreases again, and the temperature distribution of the fixing roller 1 becomes uniform. In this way, the second heater 5 is a fine ON / O
Slow responsiveness is not a problem because control is not performed to repeat FF, only continuous energization is performed.

As described above, according to this second embodiment,
By using a heater having poor responsiveness as the second heater 5 that continuously energizes, it is possible to obtain temperature controllability that is substantially the same as that of the first embodiment. As described above, one of the first and second heaters 3 and 5 is more responsive than the conventional configuration that uses a responsive heater (ex. Halogen heater). Bad heater (ex. Nichrome wire heater)
Can be replaced with, and in many cases, it can contribute to cost reduction.

Next, a third embodiment of the fixing device of the present invention will be described. The third embodiment is similar to the second embodiment, but the method of temperature control by the first and second heaters 3 and 5 is different. Therefore, in the following, FIG.
11 to 12, only the temperature control method of the third embodiment different from the second embodiment will be described. In the third embodiment, in the image forming apparatus which stands by at the preheating temperature lower than the fixing temperature, as shown in FIG.
The fixing roller 1 is heated by the first heater 3 until the preheating temperature is reached and during standby.
By doing so, the roller temperature distribution during warm-up and during standby can be made uniform. further,
When the copy button is pressed and the paper feed start command is received, and when the size of the paper to be fed is large, the first heater 3 warms up the temperature until the fixing temperature is reached. Control. Then, after passing the sheet, the standby operation by the first heater 3 is performed again.

When the copy button is pressed and a sheet-passing start command is received, when the sheet size to be fed is small, the first and second heaters 3 and 5 warm up to reach the fixing temperature. After that, the temperature is controlled by both heaters as it is. With this control, when a small-sized sheet is passed, heating is performed by both heaters 3 and 5, so the warm-up time is shortened. Then, when the temperature at the center of the roller reaches the fixing temperature, the temperature at the end portion has not yet reached the fixing temperature, but since the sheet to be passed is a small size, there is no problem in the fixing performance. Further, since the end temperature reaches a temperature equivalent to the central temperature in a short time, the nonuniform state of the roller temperature does not continue.

FIG. 10 and FIG. 11 show an example of a fixing device which does not have a preheating temperature (energization to the heater is turned off during standby). The heater that energizes during warm-up is selected. By doing so, the fixing temperature can be warmed up in the shortest time. Although the warm-up was performed on the assumption that a small size sheet is passed, if the size is changed to a large size and the sheet is to be passed, the roller temperature is not uniform and it is not preferable to pass the sheet as it is. In such a case, if the roller is idled and the energization control is performed only by the first heater 3, the temperature distribution can be made uniform in a short time, so that it is not a big problem (the idle rotation is not performed. If this is the case, heat will be dissipated only by natural cooling, so it will take some time until it becomes uniform).

Next, a fourth embodiment of the fixing device of the present invention will be described. First, in the conventional fixing device, in order to obtain a uniform temperature distribution over the entire width of the roller while passing a small-sized sheet, it has been described above that the structure shown in FIG. 21 is necessary. In order to control the temperature of a roller having a small heat capacity such as a fixing roller, as shown in FIG. 12, a duty control means 15 such as phase control is required for each temperature control system. On the other hand, FIG.
As shown in FIG. 4, in the fourth embodiment, since the second heater 5 may be continuously energized, the duty control means 15 for the second heater 5 is not necessary. Therefore, the temperature can be finely controlled for only the first heater D.
The duty control means 15 may be installed. Other configurations and operations are the same as those in the first embodiment.

As described above, for the roller having a small heat capacity such as the thin fixing roller, if the duty control means 15 is installed only for the first heater 3, the temperature distribution without temperature ripple can be obtained over the entire width of the roller. Obtainable. In addition, the fourth embodiment (FIG. 13) has the following merits as compared with the conventional example shown in FIG.
For example, in duty control means such as phase control, noise occurs at the timing of energization. Noise causes voltage fluctuations in the AC line and adversely affects other devices, but noise countermeasure components such as noise filters are usually used as countermeasures against these. In the conventional configuration shown in FIG. 12, a noise filter is required for each heater system.
In the configuration of the fourth embodiment, only the first heater 3 system is required. In this way, it is possible to reduce the number of parts and realize at low cost.

Next, a fifth embodiment of the fixing device of the present invention will be described. In the fixing device of the second embodiment,
If control is performed so that energization to the fixing heater 5 is terminated at the same time when the copying (printing) of the small size sheet is completed, FIG.
As shown in FIG. 4, overshoot occurs after the copy is completed. This is because a heater having a slow response generally has a large heat capacity, and thus it takes time to cool it.
If the overshoot is large, the roller may be damaged, or offset may occur when the sheet is restarted immediately after that, which may cause a problem. Further, as shown in FIG. 14, the temperature difference between the central portion and the end portion of the roller becomes large, which is not preferable.

Therefore, the fifth embodiment solves such a problem, and the second heater 5 is turned off before the end of copying. This state is shown in FIG. As shown in FIG. 15, by turning off the power to the second heater 5 before the end of copying, it is possible to prevent overshoot and reduce the temperature difference between the central portion and the end portion. At this time, after the second heater 5 is turned off, a small-sized sheet is passed by only the first heater 3, so that an edge temperature rise occurs, but this is not a problem because it is a little time. The other constituent operations are the same as those in the second embodiment.

Next, a sixth embodiment of the fixing device of the present invention will be described. In the second embodiment, the first heater 3 and the second heater 5 are independent of each other, but it is space-consuming to install two heaters inside the roller when the fixing roller diameter becomes small. Becomes difficult. Therefore,
The sixth embodiment solves such a problem, and the first and second heaters 3 and 5 are constructed as shown in FIG.

In FIG. 16, the first heater 3 having a fast response is provided.
A halogen heater is used as the halogen heater, and a nichrome wire heater is used as the second heater 5 having poor response.
A nichrome wire heater is wound around the outside of 7. With this configuration, the two heaters can be installed in a small space.

The other constructional operation is similar to that of the second embodiment. Since a heating wire type heater such as a nichrome wire heater usually has a slow response, even if the heater is constructed as shown in FIG. 16, it cannot be used as a heat source of a fixing device. For this reason, a general method has been to arrange a plurality of gas-filled heaters (for example, halogen heaters) having excellent responsiveness in parallel. Alternatively, an idea-level idea has been made in which a plurality of filaments are installed in one glass tube and the heating area is divided, but it was not feasible in terms of cost and productivity. However, in the sixth embodiment, the combination of the heater with high responsiveness and the heater with slow responsiveness covers the slowness of responsiveness and enables uniform temperature control with small temperature ripple. With such a configuration, space saving and cost reduction can be realized.

Next, a seventh embodiment of the fixing device according to the present invention will be described. In the sixth embodiment, when the second heater 5 is not electrically insulated, it is dangerous if the exposed live part comes into contact with the ground part inside the fixing roller. Therefore, this seventh embodiment solves this problem, and its configuration is shown in FIG. FIG. 17 is a sectional view of the first and second heaters 3 and 5. In addition to the configuration of FIG. 16, a heat-resistant quartz glass tube 19 is added, and the quartz glass is surrounded by the second heater 5. A pipe 19 is installed. With this configuration, it is possible to realize an electrically insulated heater while realizing space saving. The other constituent operations are the same as those in the sixth embodiment. Although not shown here, a heat resistant insulating material or the like may be applied around the heating wire (second heater).

Next, an eighth embodiment of the fixing device according to the present invention will be described. The above-mentioned first to seventh embodiments have a problem that the warm-up time of the apparatus is slightly slow. This is because the electric power that can be used in the fixing device is divided into the first heater 3 and the second heater 5. As shown in the timing chart of FIG. 4, there is a timing when both the first heater and the second heater are turned on at the same time, so that inevitably, the first heater capacity + the second heater capacity = the fixing device. The power capacity is distributed to. Furthermore, since only the first heater 3 is used during warm-up,
The heating is performed with less electric power than the electric power capacity distributed to the fixing device, which requires warm-up time.

The eighth embodiment is intended to solve the above problem and has the same structure as the second embodiment, but the temperature control method is different, and a timing chart of the temperature control is shown in FIG. FIG. 19 shows a flowchart of the temperature control. That is, in the eighth embodiment, the first and second heaters 3 and 5 are controlled so as not to be turned on at the same time. As shown in FIG. 18, when passing a large size sheet, energization control is performed only by the first heater 3. When passing a small-sized sheet, energization is controlled using the first and second heaters 3 and 5. At this time, energization to the second heater 5 is prohibited when the first heater 3 is on, and energization to the second heater 5 is permitted only when the first heater 3 is off. . By controlling in this way, the power capacity distributed to the fixing device is not exceeded, and if the power capacity of the first heater 3 is set to the maximum W number, the warm-up time can be shortened.

Further, the energization of the second heater 5 is not performed all the time when the first heater 3 is off, but an appropriate constant Du
If you set it to ty and restrict it from turning on any more,
It is possible to supply a substantially constant amount of heat from the second heater 5 regardless of the thickness of the paper to be passed or the environmental temperature. For example, in the first embodiment described above, it suffices to set the second heater 5 to about 110 W, but in the eighth embodiment, the capacity of the second heater 5 is set to 110 W or more, and it is appropriate. Na D
The duty may be set so that heat generation equivalent to 110 W can be obtained with this duty (for example, the second heater is set to 440 W, and the duty is limited to 25% or more). In this way, the power capacity of the first heater 3 is set to the first heater capacity = the power capacity distributed to the fixing device (the second heater capacity is arbitrary), and when the warm-up is performed as described above, If only the first heater 3 is used when a large size sheet is passed, both heaters 3 and 5 are used when a small size sheet is passed, and both heaters 3 and 5 are controlled so as not to be turned on at the same time. The warm-up time can be shortened.

[0044]

According to the present invention, the first heater installed in the sheet passing width region of the large size sheet, the first energization control means for controlling the energization of the first heater, and the passage of the small size sheet. A second heater installed in the paper width region, a second energization control means for controlling energization of the second heater, and a temperature sensor for detecting a roller surface temperature in the installation portion of the second heater are provided. However, the heat generation capacity of the second heater is so low that it does not reach the fixing energy required for passing the small size sheet, and the second heater is continuously energized during the passage of the small size sheet, and the temperature sensor Since the first heater is energized by the output and only the first heater is energized by the output of the temperature sensor during the passage of the large size sheet, the temperature control for the second heater is not necessary. Control can be simplified and Temperature sensors also without the need for use, it is possible to obtain a uniform roller temperature distribution with a simple structure.

Further, by using a heater having a poor responsiveness as the second heater for continuously energizing, it is possible to obtain the temperature controllability almost equal to that described above and, in many cases, contribute to cost reduction. it can. Also, during warm-up when the paper passing size after stand-by and after rising is specified to be large, the fixing roller is heated by the first heater, and the paper passing size after rising is specified to be small. Since the fixing roller is configured to be heated by the first and second heaters during the warm-up when the sheet is warmed up, the sheet can be heated to the preset fixing temperature in a short time when a small-sized sheet is passed. .

Further, since the duty control means is provided only in the energization control means of the first heater,
Even for a roller having a small heat capacity such as a thin fixing roller, it is possible to obtain a temperature distribution having no temperature ripple over the entire width of the roller with a low cost configuration.

Further, since the power supply to the second heater is turned off before the end of copying (printing), it is possible to prevent the overshoot immediately after the paper is passed and also the central part and the end of the roller. The temperature difference between the parts can be reduced. Further, since the second heater is composed of a heating wire and the heating wire is installed so as to surround the first heater, it is possible to contribute to space saving and cost reduction. In addition, since an insulating material is arranged around the second heater to electrically insulate the outside from the outside, it is possible to provide a safe fixing device that is electrically insulated while realizing space saving. You can

Further, in the fixing device in which the recording sheet is passed through the cylindrical fixing roller heated by the heater to fix the transferred image on the recording sheet, the first fixing device is installed in the sheet passing area of the large size sheet. A heater, a first energization control unit that controls energization of the first heater, and a second heater that is installed in the sheet passing width region of a small-sized sheet and has a poorer responsiveness (heat generation rising characteristic) than the first heater. And a temperature sensor for detecting the roller surface temperature at the installation portion of the second heater, and a second current control means for controlling the current supply to the second heater. The first and second heaters are energized by the output of the sensor, and only the first heater is energized by the output of the temperature sensor during the passage of the large size sheet.
Since the heaters are controlled so as not to be turned on at the same time, the power capacity distributed to the fixing device can be maximized to perform warm-up, so that the warm-up time is further shortened in comparison with the invention of claim 2. be able to.

[Brief description of drawings]

FIG. 1 is a schematic side view of a fixing device embodying the present invention.

FIG. 2 is a schematic configuration diagram of a fixing device embodying the present invention.

FIG. 3 is a diagram showing a heat distribution of first and second heaters shown in FIG.

FIG. 4 is an ON / OFF diagram of the first and second heaters shown in FIG.
It is a time chart of OFF temperature control.

FIG. 5 is a flowchart of temperature control in the first embodiment of the fixing device of the present invention.

FIG. 6 is a graph showing how the roller end temperature rises when the amount of heat generated by the second heater shown in FIG. 2 is changed.

FIG. 7 is a graph showing the amount of increase in end temperature measured by an experiment.

FIG. 8 is a diagram showing changes in end temperature when a fast response heater and a slow response heater are used as the second heater shown in FIG.

FIG. 9 is a graph of temperature control of a third embodiment of the fixing device of the invention.

FIG. 10 is a graph of temperature control of the third embodiment of the fixing device of the present invention.

FIG. 11 is a graph of temperature control of the third embodiment of the fixing device of the present invention.

FIG. 12 is a schematic configuration diagram showing a configuration of a control unit in a conventional fixing device.

FIG. 13 is a schematic configuration diagram showing a configuration of a control unit in a fourth embodiment of the fixing device of the present invention.

FIG. 14 is an explanatory diagram of roller temperature control when overshoot occurs.

FIG. 15 is an explanatory diagram of roller temperature control in the fifth embodiment of the fixing device of the present invention.

FIG. 16 is a first example of a fixing device according to a sixth embodiment of the invention.
It is a configuration perspective view of and a 2nd heater.

FIG. 17 is a first view of a fixing device according to a seventh embodiment of the invention.
It is a structure sectional view of and a 2nd heater.

FIG. 18 is a time chart of temperature control in the eighth embodiment of the fixing device of the invention.

FIG. 19 is a flowchart of temperature control in an eighth embodiment of the fixing device of the invention.

FIG. 20 is a schematic configuration diagram of a conventional fixing device.

FIG. 21 is a schematic configuration diagram of a conventional fixing device.

[Explanation of symbols]

1, 109 ... Fixing roller, 3 ... First heater, 5 ... Second heater, 7
... Temperature sensor, 9,115 ... Input circuit,
11, 119 ... CPU, 13, 117 ... Driver,
15 ... Duty control means, 17 ... 1st
Glass tube of heater, 19 ... Heat-resistant quartz glass tube, 101 ... Central heating heater, 103
... Full-width heating heater, 105 ... End heating heater,
107, 111 ... Temperature sensor center, 113 ...
Temperature sensor end portion, 201 to 205 ... Each step,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H05B 3/00 335 H05B 3/00 335 370 370 (72) Inventor Jun Yura Nakamagome Ota-ku, Tokyo 1-chome 3-6 Inside Ricoh Co., Ltd.

Claims (8)

[Claims] 1. A fixing device for passing a recording sheet through a heated cylindrical fixing roller to fix the transferred image on the recording sheet, the first fixing device being installed in a sheet passing width range of a large size sheet. A heater, a first energization control means for controlling energization of the first heater, a second heater installed in a sheet passing width region of a small size sheet, and a second energizer for controlling energization of the second heater. And a temperature sensor for detecting the roller surface temperature in the installation portion of the second heater, and the heat generation capacity of the second heater is less than the fixing energy required for passing a small size sheet. The capacity is low, and the second heater is continuously energized during the passage of a small size sheet, and the first heater is energized by the output of the temperature sensor. For sensor output Further, the fixing device is characterized in that only the first heater is energized. 2. The fixing device according to claim 1, wherein the responsiveness of the second heater (heat rising characteristic) is slower than the responsiveness of the first heater. 3. The warming-up at the time of waiting and when the paper passing size after rising is designated as a large size, the fixing roller is heated by the first heater so that the paper passing size after rising is small. 3. The fixing device according to claim 2, wherein the fixing roller is heated by the first and second heaters during warm-up when the size is designated. 4. The fixing device according to claim 1, wherein only the first energization control means is provided with a duty control means. 5. The fixing device according to claim 2, wherein the power supply to the second heater is turned off before the end of copying (printing). 6. The fixing device according to claim 2, wherein the second heater is composed of a heating wire, and the heating wire is installed so as to surround the first heater. 7. The fixing device according to claim 6, wherein an insulating material is arranged around the second heater and is electrically insulated from the outside. 8. A fixing device for feeding a recording sheet through a heated cylindrical fixing roller to fix the transferred image on the recording sheet, the first fixing device being installed in a sheet passing width range of a large size sheet. A heater, a first energization control unit that controls energization of the first heater, and a second heater that is installed in a sheet passing width region of a small-sized sheet and is inferior in responsiveness (heat rising characteristic) to the first heater. Heater, a second energization control unit that controls energization of the second heater, and a temperature sensor that detects a roller surface temperature in the installation portion of the second heater, and a small-sized sheet is being fed. Is configured to energize the first and second heaters by the output of the temperature sensor, and energize only the first heater by the output of the temperature sensor during the passage of a large size sheet. And the second heat A fixing device that does not turn on at the same time.