JPH05165372A - Fixing device - Google Patents

Abstract

PURPOSE:To provide a control means by which waiting time in the case of warming up is shortened even though the output of a heater is made large in order to make operation speed high and thermal breakage of a member or faulty fixing caused by the deviation of temperature distribution in the longitudinal direction of the surface of a fixing roller in the case that excellent fixing is performed with low power consumption at the time of copying operation is not caused. CONSTITUTION:This device is provided with the heater 2 which has a shorter light distribution area than the maximum paper passing area of the surface of the fixing roller, and whose output is 800W and whose length is 200mm, and the heater 3 whose light distribution area is an area obtained by subtracting the light distribution area of the heater 2 from the maximum paper passing area, whose output is 600W, and whose length is 100mm. In the case of warming up, the heater 2 is turned on until the temperature of the light distribution area becomes a set temperature, and the heater 3 is turned off after (t) seconds from the time when a power source is applied and when it is predicted that the temperature of the light distribution area becomes the set temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus, and more particularly to a heat roller fixing device using a heat roller and a control method therefor.

[0002]

2. Description of the Related Art A heat roller fixing device is widely used in an electrophotographic image forming apparatus. However, a drawback of the heat roller fixing device is that a pair of heat rollers has a heat capacity, so that a so-called warm after the power is first turned on. One reason is that it takes a long time to wait for the process. Therefore, attempts have been conventionally made to reduce this waiting time (wait time), and there are roughly two methods. First, the first is a method of increasing the electric power of the heater, which is a heating element, and the second is a method of thinning the roller to reduce the heat capacity of the roller.

However, according to the first method,
Even if there is a surplus of electric power that can be supplied to the heater during warm-up, it is necessary to supply electric power to parts other than the fixing device during normal image forming apparatus operation, which causes a shortage of electric power supply for the entire image forming apparatus. There was a point. Next, according to the second method, the warm-up time is shortened, but there are the following problems. In the case of an image forming apparatus that can use transfer paper of various widths, the heat generation distribution of the heater is usually set according to the transfer paper of the maximum width. Therefore, when a narrow transfer paper is continuously passed, the end area of the roller surface, which does not pass as compared with the area of the roller surface through which the transfer paper passes, does not radiate heat to the transfer paper, and thus becomes extremely hot. However, there is a problem that the device may be damaged in some cases. This is because the wall thickness of the roller is thin, so that thermal energy is difficult to move in the longitudinal direction of the roller.

On the other hand, as an embodiment of the above first method, two heaters are used, both of which generate heat during warm-up, and only one of the two is used during normal image formation. However, even in this case, if the thickness of the roller is thin, the problem of temperature rise at the end of the roller surface similarly occurs when the transfer paper having a narrow width is continuously used as described above.

Therefore, in order to solve the above problems, the following third method has been proposed.

This is because the heat distribution in the longitudinal direction of the heater is divided into two or more types so that the heat distributions do not substantially overlap with each other, and they are all heated at the same time during warm-up, and during normal image formation. In the case of transfer paper with a narrow width, the temperature is controlled using a heater suitable for the size of the transfer paper to prevent the temperature rise at the end of the roller surface. In the above, the plurality of heaters are sequentially heated in a time-division manner and controlled so that the power consumption is reduced as compared with the warm-up time.

The third method will be described below with reference to FIGS. First, for comparison, assume a heater 1 as shown in FIG. The heater 1 is a single heater, and a single heater 1 can sufficiently fix a toner image on a transfer paper of a maximum size (hereinafter referred to as a full size) used in a general copying machine or the like. Suppose it has output and length. That is, this heater 1 has a light distribution over the entire length L [mm] corresponding to the full size, and its output is Q ₀ [W]. Therefore, the output per unit length in this case is Q ₀ / L [W / mm].
Further, the heater 1 is intermittently controlled by a control means (not shown) so as to repeat lighting and extinguishing based on a signal from a temperature detection means (not shown) such as a thermistor, so that the heater 1 has a constant temperature. The surface temperature of the fixing roller is kept within the range. The lighting sequence is shown in FIG. The cycle for starting the lighting of the heater 1 is S [sec], and the lighting time of the heater 1 is T [sec] and the extinguishing time is S-T [sec] intermittently within the cycle S [sec]. Control. Therefore, the amount of heat supplied per unit length of the heater 1 during the cycle S [sec] is q _0.
[W · sec / mm] = (Q ₀ [W] / L [mm]) ×
It becomes t [sec]. That is, it is assumed that this heat quantity q ₀ is the heat quantity required for fixing the toner image on the full-size transfer paper.

Next, in the third method, two heaters 2 and 3 are used. These two heaters 2 and 3 have a heater light distribution as shown in FIG. In the heater 2, a length l ₁ [m corresponding to a narrow transfer sheet
m] only, and the heater 3 mainly has a light distribution outside the narrow transfer paper area l ₂ [mm]. Output of each of these two heaters 2 and 3 is Q ₁ [W], Q ₂ [W]
Then, the output per unit length of the heater 2 is Q ₁ / l ₁
[W / mm], output per unit length of heater 3 is Q ₂
/ L ₂ [W / mm]. Also in this third method, the intermittent control is performed in the cycle S [sec] as described above, and the total lighting time of the heater 2 in the cycle S [sec] is t ₁ [sec], and the total lighting time of the heater 3 is The lighting time is t ₂ [se
c]. As a result, the amount of heat supplied per unit length in the cycle S [sec] in each of the heaters 2 and 3 is q ₁ [W · sec / mm] = (Q ₁
[W] / l ₁ [mm]) × t ₁ [sec], heater 3 is q
₂ [W · sec / mm] = (Q ₂ [W] / l ₂ [mm])
× t ₂ [sec].

As described above, in order to satisfactorily fix the toner image on the full-size transfer paper, a heat quantity of q ₀ [W · sec / mm] per unit length is required within the cycle S [sec]. Therefore, the heat quantities q ₁ and q ₂ [W ·
sec / mm] is required to be the heat quantity q0 or more. Further, since the sum of the total lighting time t ₂ the total lighting time t ₁ and the heater 3 of the heater 2 exceeds the period S [sec], and the heater 2 and the heater 3 will be present time to simultaneously turned, The power supply of the image forming apparatus main body is insufficient. Therefore, t ₁ [sec] + t ₂ [sec] ≦ S
The control is performed so that it becomes [sec]. Furthermore, when the light distributions of the heater 2 and the heater 3 are overlapped, there is approximately L [mm] ≦ l ₁ [mm] + so that there is no region where the light distribution is lost.
The relationship of l ₂ [mm] is required. In consideration of the above conditions, the total lighting times t ₁ and t ₂ of the heater 2 and the heater 3 within the cycle S [sec] are determined as shown in FIG.

Next, each lighting sequence of the heater 2 and the heater 3 set in this way will be described with reference to FIG. First, the lighting sequence 1 is simply the cycle S [sec].
In this example, the heater 2 and the heater 3 are turned on once. When the thickness of the core metal of the fixing roller exceeds a certain level, the heat capacity is large, and thus such a sequence can be used. Next, the lighting sequence 2 is a cycle S
Each heater 2 and 3 is turned on twice within [sec], and the lighting sequence 2 ′ is an example in which the heater 2 is turned on twice and the heater 3 is turned on three times. further,
The lighting sequence 3 is an example in which the number of times the lighting is switched is five. As described above, in the third method, various different controls are possible.

Next, the third method will be described in more detail by giving specific numerical values to the above variables. As shown in FIG. 6, it is assumed that the heater 1 of 800 [W] is required to satisfactorily fix the toner image on the full-size transfer paper with one heater. The lighting sequence has a cycle of 1 to keep the surface temperature of the fixing roller within a predetermined set temperature.
Lighting time 6 [sec] within 0 [sec], extinguishing time 4
Set to [sec]. At this time, the amount of heat supplied per unit length during the cycle 10 [sec] is q ₀ = (8
00 [W] / 300 [mm]) × 6 [sec] ≈16
[W · sec / mm]. That is, the amount of heat required to fix the toner on the full-size transfer paper is about 1 per unit length during the period of 10 [sec].
This is 6 [W · sec / mm].

On the other hand, in the third method, the light distribution of the heater 2 and the heater 3 is 800 [W] / 200 [m] respectively.
m] and 400 [W] / 100 [mm].

Further, the cycle of the lighting sequence is 10 [se
When the total lighting time of the heater 2 in c] is 4 [sec] and the total time of the heater 3 is 4 [sec], the heaters 2 and 3 per unit length during a cycle of 10 [sec]. The amount of heat supplied is q ₁ = 800 [W] / 200 [mm]
× 4 [sec] = 16 [W · sec / mm], q ₂ = 4
00 [W] / 100 [mm] × 4 [sec] = 16 [W
.Sec / mm], and a heat amount substantially equal to the heat amount q ₀ ≈16 [W · sec / mm] required for one heater is obtained.

Further, the total lighting time of the heater 2 t ₁ = 4
[Sec] and the total lighting time of the heater 3 t ₂ = 4 [sec]
Is 8 [sec], which is smaller than the cycle of 10 [sec].
It does not mean that the heater 3 of [W] is turned on at the same time. Therefore, according to such a third method, it is possible to turn on the heaters 2 and 3 only by the power obtained by subtracting the power supplied to the optical (illumination) system or the main motor during the copy operation or the like.

If the heater 2 and the heater 3 are to be turned on at the same time, the electric power required for the fixing device at that time is 800 [W] +400 [W] = 1200.
[W] is reached, and power cannot be supplied to other operations accompanying the copy operation. In other words, it is usually 15 [A] in Japan.
X100 [V] = 1500 [W] is the limit, so 1
This is because the surplus power is exhausted only at 500 [W] -1200 [W] = 300 W.

Next, an example of a lighting sequence by the two heaters 2 and 3 set in this way will be described with reference to FIG. First, when performing the fixing operation of the full-sized transfer paper over the entire area of the fixing roller, as shown in FIG. 7, the lighting time of the heater 2 is set to 1.3 [sec] and lighting is performed three times in one cycle. Further, as shown in FIG. 7, the heater 3 is turned on three times at intervals of 1.3 [sec] during the turn-off time of the heater 2.

By using such a sequence,
Originally, one heater is used for 1 [1] within 10 [sec] over the entire area.
The amount of heat equivalent to the amount of heat supplied for 6 [W · sec / mm] is supplied by the heater 2 and the heater 3, and the fixing performance of the toner image on the full-size transfer paper is satisfied.

On the other hand, regarding the fixing operation of the transfer paper having a narrow width, as shown in FIG. 7, only the heater 2 is turned on and the heater 3 is kept off. As a result, the temperature rise at the end portion (non-sheet passing area) of the surface of the fixing roller does not occur when the narrow transfer paper is continuously fixed.

Further, since the operation of the optical system of the main body of the apparatus, the main motor and the like are stopped during the warm-up, the heat quantity of 800 [W] +400 [W] = 1200 [W] should be supplied to the fixing apparatus. Therefore, both the heater 2 and the heater 3 can be turned on to heat the fixing roller. As a result, the conventional heater 800
The wait time is remarkably shortened as compared with the case of warming up by [W].

[0020]

However, the third method of the above-mentioned conventional example has the following problems. That is, in the above-mentioned conventional example, in order to satisfactorily fix the toner image on the full-size transfer paper with one heater,
With the output of 00 [W], the lighting time is 6 seconds out of 10 seconds in one cycle, and (800 [W] / 300 [mm]) × 6 [s
ec] = 16 [W · sec / mm], the output of the heaters 2 and 3 and the lighting time are set assuming that the amount of heat is required.
For example, considering the case of increasing the speed of the device, it becomes necessary to supply a larger amount of heat.

Therefore, in the conventional speed, when one heater is used, a sufficient performance can be obtained by lighting for 6 seconds per 10 seconds in one cycle, while, for example, in the case of speeding up, 7 seconds in one cycle. In some cases, lighting for 6 seconds is required. In this case, in the lighting sequence of the two heaters 2 and 3 according to the third method of the conventional example, each heater 2 and 3 is
Since the total lighting time of is set to 4 seconds, in order to obtain the amount of heat corresponding to the lighting time of 6 seconds per 10 seconds in one cycle with 2 heaters, 4 × 2 = 8 seconds There is a problem that the amount of heat is insufficient in a high-speed mode in which one heater requires a lighting time of 6 seconds per 7 seconds per cycle.

In order to solve this, the output of each of the two heaters may be increased.
The value of 00 [W] is the total power supplied (100 [V], 1 except for the heaters 2 and 3 required for the copy operation).
At 5 [A], 100 [V] × 15 [A] = 1500
Since it is determined as a value subtracted from [W]),
The output cannot be increased easily. Therefore, 40
The output of the heater 3 assumed to be 0 [W] is increased. For example, if this is increased to 600 [W], the heater 2 is lit at 800 [W] for 4 seconds {(800 [W] /
200 [mm]) × 4 [sec] = 16 [W · sec /
mm]}, the heater 3 is lit at 600 [W] for 2.7 seconds {(600 [W] / 100 [mm]) × 2.7 [se]
It is possible to take a sequence such as c] ≈16 [W · sec / mm]}, which allows +2.7 seconds for 4 seconds.
Seconds = 6.7 seconds, which makes it possible to satisfy the heat supply required within one cycle of 7 seconds for speeding up. Even in this case, 800 [W] + during warm-up
Lighting of 600 [W] = 1400 [W] is possible. This is because the total supply output is 100 [V] × 15 [A] = 1
This is because the value is less than 500 [W]. However, if such a configuration is adopted, the following problems will occur this time.

The output of the heater 2 per unit length is 800 [W].
/ 200 [mm] = 4.0 [W / mm], whereas the output per unit length of the heater 3 is 600 [W] / 100
[Mm] = 6.0 [W / mm], which is larger than that of the heater 2. Therefore, when the heaters 2 and 3 are simultaneously turned on during so-called warm-up, the light distribution area of the heater 3 is larger than that of the heater 2. There is a problem that the temperature rise rate is higher than that of the above, the temperature of the light distribution region of the heater 3 and its surroundings exceeds the set temperature at the end of warm-up, and the temperature distribution on the surface of the fixing roller becomes the state shown in FIG. It was

This is to detect the temperature on the surface of the fixing roller,
As shown in FIG. 8, the thermistor is mounted at a predetermined position in the light distribution area of the heater 2. When the surface temperature of the abutting part of the thermistor reaches a preset temperature, the warm-up ends. This is because the heater is stopped and the lighting of the heater is stopped. That is, if a thermistor is provided at a location as shown in FIG. 8, the temperature increase rate is higher in the light distribution area of the heater 3 on the far side and its periphery than the light distribution area of the heater 2 where the thermistor is attached. When the location where the thermistor is attached reaches the set temperature, the light distribution area of the heater 3 and its periphery have already largely exceeded the set temperature. As a result, the thermal destruction of the cleaning member in contact with the fixing roller, the thermal destruction of the gear incorporated in the fixing roller, the continuous lighting of the heater when the controller of the fixing device fails, etc. There is a problem that the thermoswitch provided as a safety device to prevent a runaway accident erroneously recognizes that the temperature is abnormal and stops the heater.

In order to avoid such a situation, if the mounting position of the thermistor is moved to the back side in FIG. 8 and set to a predetermined position within the light distribution area of the heater 3, the temperature of the mounting position of the thermistor becomes the set temperature. Even heater 3
Since the surface temperature on the front side, which has a lower rate of temperature rise than the light distribution area, remains lower than the set temperature, it does not reach a temperature sufficient to melt the toner, resulting in image fixing failure. There was a problem.

The present invention solves the above problems and, even when the speed of image formation is increased, the wait time during warm-up can be shortened, and good fixing can be performed with low power consumption during copy operation. It is an object of the present invention to provide a fixing device that does not cause member damage during warm-up due to uneven temperature distribution in the longitudinal direction of the surface of the fixing roller or defective fixing immediately after warm-up.

[0027]

SUMMARY OF THE INVENTION According to the present invention, the above object is to provide a heat-generating region that is substantially the same as the paper-passing region in the longitudinal direction by combining heat-generating regions having different heat-generating distributions in the longitudinal direction of the fixing roller. In a fixing device provided with two or more heating elements to be included therein, and a control means for the heating elements, the control means controls the waiting period from power-on until the surface temperature of the fixing roller is raised to a predetermined set temperature. After the power is turned on, driving of all heating elements is started, and each heating element is set to be stopped or driven independently so that the temperature in the heating area of each heating element is maintained at the above set temperature. It is achieved by being.

[0028]

According to the present invention, when the power is first turned on, all the heating elements are driven in order to raise the temperature of the fixing roller surface to a predetermined set temperature in a short period of time. However, when there is a difference in the amount of heat per unit length of the heating element between the heating elements, the degree of temperature rise in each heating region is biased. Therefore, in order to eliminate the bias, each heating element is independently stopped or driven so that the heating area of each heating element is maintained at the set temperature. Then, the standby state is released when the temperatures in the heating regions of all the heating elements reach the set temperature. Thus, according to the present invention, in the fixing device in which the output of each heating element is large and the speed can be increased, all the heating elements are driven in the waiting period to shorten the waiting time from the power-on to the end of the waiting period. Moreover, since each heating element is independently controlled, the temperature distribution on the surface of the fixing roller is not biased at the end of the waiting period, and thermal destruction and fixing failure of the member are prevented.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment and a second embodiment of the present invention will be described with reference to the drawings. In addition, the same parts as those of the conventional example shown in FIG.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows the lighting and extinguishing times and timings of each heater from the power-on to the end of the warm-up in this embodiment, and the changes in the temperature distribution on the surface of the fixing roller with it. As in the conventional example, the heater of this embodiment has a heater 2 with an output of 800 [W] and a heater length of 200 [mm], and an output of 600.
Two heaters 3 of [W] and heater length 100 [mm] were used. The light distribution of each heater and the mounting position of the thermistor are the same as in the conventional example shown in FIG.

However, this embodiment is different from the conventional example in that the heater 3 is turned off at a predetermined timing before the heater 2 during warm-up. The temperature control during warm-up of this embodiment and the change in the temperature distribution on the surface of the fixing roller due to the temperature control will be described below with reference to FIG.

First, both the heater 2 and the heater 3 are turned on for a while after the power is turned on. Then, heater 3
Since the amount of heat per unit length of is larger than that of the heater 2, the temperature increase in the area on the back side corresponding to the light distribution area of the heater 3 is larger than that on the front side corresponding to the light distribution area of the heater 2. The surface temperature distribution is higher on the back side of the light distribution area of the heater 3 than on the front side of the light distribution area of the heater 2 as in the temperature distribution b in FIG.

Next, only the heater 3 is turned off t seconds after the power is turned on. This time t is the time when the temperature of the light distribution area of the heater 3 reaches the set temperature as shown by the temperature distribution c in FIG. 1, and until the temperature of the light distribution area of the heater 3 reaches the set temperature by experiments or the like. The time is measured and stored in the control means in advance. That is, in the conventional control method, even if the temperature of the light distribution region of the heater 3 has reached the set temperature, the temperature at the mounting position of the thermistor has not yet reached the set temperature, so the lighting of the heaters 2 and 3 is continued. However, in this embodiment, the heater 3 is turned off t seconds after the power is turned on by predicting the time when the surface temperature of the light distribution area of the heater 3 and its surroundings reaches the set temperature of the target temperature. As a result, the surface temperature on the back side, which is the light distribution region of the heater 3, does not rise sharply thereafter.

After that, by keeping only the heater 2 turned on, only the temperature on the front side, which is the light distribution region of the heater 2, rises and when the temperature reaches the set temperature as shown by the temperature distribution d in FIG. 1, warm-up occurs. Upon completion, the heater 2 is also turned off and the paper feed standby state is set.

As described above, according to this embodiment, the temperature distribution on the surface of the fixing roller at the end of the warm-up is the set temperature uniformly in the entire sheet passing area, and thereafter, the transfer sheet of any size is fixed. Good fixing is carried out even if the sheet is conveyed to.

The output during warm-up is 8
00 [W] +600 [W] = 1400 [W], and 100 [V] × 15 [A] = 1500 [W] of the total supply output.
Since a sufficiently large value can be obtained within the range not exceeding, the wait time can be remarkably shortened.

Further, during the copying operation, if the total lighting time of the heater 2 of 800 [W] is 4 seconds, (800
[W] / 200 [mm]) × 4 [sec] = 16 [W
sec / mm], and if the total lighting time of the heater 3 of 600 [W] is 2.7 seconds, (600
[W] / 100 [mm]) × 2.7 [sec] ≈16
The amount of heat of [W · sec / mm] is obtained, which results in 4 seconds + 2.7 seconds = 6.7 seconds, and the heat supply required within one cycle of 7 seconds can be satisfied. Therefore, the speed of the fixing device can be increased. As the lighting sequence, each pattern as shown in FIG. 5 of the conventional example can be applied.

Further, since the heater 3 is turned on and off at any time according to the size of the transfer sheet, excessive heating of the non-sheet passing area is prevented for the small size transfer sheet, and good fixing is performed for the full size. ..

As described above, in the fixing device in which the wait time during warm-up is shortened, the power consumption during the copying operation is suppressed as much as possible, and the edge temperature rise in the case of small size paper is prevented, the fixing device is Even when the speed was increased, it was possible to prevent member damage and fixing failure due to uneven temperature distribution on the surface of the fixing roller during warm-up.

<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.

In the present embodiment, as shown in FIG. 2, when the heater 2 and the heater 3 are turned on at the same time, the second portion is located at the location where the temperature rises most rapidly, that is, the light distribution area of the heater 3 and its periphery. It is different from the first embodiment in that the thermistor 2, which is a thermistor, is added.

In this embodiment, the thermistor 1 and the thermistor 2 simultaneously turn on the heater 2 and the heater 3 while detecting the temperatures of the light distribution regions of both the heater 2 and the heater 3. Then, when the signal of the thermistor 2 reaches the set temperature in the temperature distribution c ′ in FIG. 2, the heater 3 is turned off, and then only the heater 2 is continuously turned on, and the temperature distribution d ′ in FIG. After confirming that the state has been reached, the heater 2 is turned off and the sheet passing state is set.

As described above, in this embodiment, in contrast to the first embodiment in which the heater 3 is turned off by predicting that the light distribution area of the heater 3 and its surroundings have reached the set temperature, the light distribution area of the heater 3 is directly provided. Since the heater 3 is turned off when the temperature of the heater 3 and its surroundings are detected and when the temperature reaches the set temperature, the temperature increase in the light distribution area of the heater 3 and its surroundings can be suppressed more accurately than in the first embodiment.

Depending on the environment where the apparatus is installed, for example, in a place where the temperature is low, during the transition from the state of temperature distribution c'in FIG. 2 to the state of temperature distribution d'in FIG. It is expected that the surface temperature on the back side, which is the light distribution area of the heater 3, will be lower than the set temperature. In such a case, the heater 3 is turned on again to bring the roller surface to the set temperature. It is possible to raise.
That is, in this embodiment, the heater 3 is the thermistor 2
Is controlled only by the signal of (1), and this control is continued until the temperature detection signal of the thermistor 1 reaches a predetermined temperature set value.

The present invention is not limited to the above-described embodiments, but can be realized even when two or more heaters are used and various light distributions are set. is there. In addition, when the transfer paper is not fed by the so-called one-sided reference as in the above-mentioned embodiment, but based on the similar idea, for example, the first heater generates heat only near the center, and the second heater has both ends. It is also possible to use a type that only generates heat and perform the same control as in the case of the one-sided reference before the warm-up. Furthermore, heat may be generated not only by a normal halogen heater but also by a sheet-like heat generating element in which a resistor is printed on an insulator, or by a method of directly utilizing the radiant heat of a lamp. That is, with a configuration having a plurality of heating elements having different light distributions, it is possible to obtain the same effect by performing the same control during warm-up.

[0046]

As described above, according to the present invention,
In a fixing device having two or more heating elements each having a different heat generation distribution, each heating element is driven independently during the so-called warm-up time from when the power is turned on until the temperature of the fixing roller surface reaches a predetermined set temperature. The safety device provided to keep the temperature distribution in the longitudinal direction on the surface of the fixing roller close to a smooth surface at the end of warm-up by controlling the temperature to prevent thermal destruction of components due to excessive temperature rise of the fixing roller, and to prevent excessive temperature rise. It is possible to prevent the malfunction of the image forming apparatus and the image fixing failure due to the insufficient amount of heat on the roller surface.

[Brief description of drawings]

FIG. 1 is a diagram showing a timing chart of each heating element and a change in temperature distribution on the surface of a fixing roller in a first embodiment of the present invention.

FIG. 2 is a diagram showing a timing chart of each heating element and a change in temperature distribution on the surface of the fixing roller in the second embodiment of the present invention.

FIG. 3 is a diagram showing a heat generation distribution of one heat generating element which can satisfactorily fix a transfer sheet of the maximum size used for comparison with a conventional method using two heat generating elements and its driving timing. ..

FIG. 4 is a diagram showing a heat generation distribution of each heating element in a conventional method using two heating elements.

FIG. 5 is a diagram showing a drive timing of each heating element in a conventional method using two heating elements.

6] The heating element of FIG. 3 has an output of 800 W and a length of 300 mm.
Distribution and drive timing in the case of
FIG. 6 is a diagram showing heat generation distributions when the heating elements of FIG.

FIG. 7 shows the heating elements of FIG. 4 each having an output of 800 W and a length of 2
It is a figure which shows the drive timing in case of 00 mm, output 400W, and length 100mm.

8 is a diagram showing the temperature distribution on the surface of the fixing roller and the heat generation distribution of each heating element at the end of the waiting period when the heating element having an output of 400 W and a length of 100 mm in FIG. 6 has an output of 600 W and a length of 100 mm. ..

[Explanation of symbols] 2 heater (heating element) 3 heater (heating element)

Claims (2)

[Claims] 1. A heating roller having two or more heating elements that have different heat generation distributions in the longitudinal direction of the fixing roller so that the heat generation areas of the fixing roller are substantially the same as each other so that substantially the entire sheet passing area in the longitudinal direction is included in the heat generation area. In the fixing device having the control means, the control means starts driving all the heating elements after the power is turned on in a waiting period from the power is turned on until the surface temperature of the fixing roller is raised to a predetermined set temperature. A fixing device, wherein each heating element is set to be independently stopped or driven so that the temperature in the heating region of each heating element is maintained at the set temperature. 2. The fixing device according to claim 1, further comprising two or more temperature detecting means, at least one of which is arranged in a region having a maximum temperature increase rate in a longitudinal direction of the fixing roller.