JP2000275998A - Thermal fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute excellent fixing by stably controlling temperature by mitigating the temperature change of a fixing body during fixing in on/off duty ratio control regardless of the existence of a condition affecting temperature control. SOLUTION: Upper limit temperature Ts+β and lower limit temperature Ts-α are set above and under set temperature Ts, and temperature control is executed based on an on/off duty ratio in the case that the detected temperature Th of the fixing body is set to be in areas B and C. In this case, the on/off duty ratio at each temperature area every time the detected temperature of the fixing body is set to be equal to or higher than the upper limit temperature (area D) is changed so as to reduce a ratio to turn on heating electric power, and the on/off duty ratio at the temperature areas B and C every time the detected temperature of the fixing body is set to be equal to or lower than the lower limit temperature (area A) is changed so as to increase the ratio to turn on the heating electric power, so that it is automatically adjusted so as to obtain an optimum on/off duty ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for use in an image forming apparatus such as a printer, a facsimile, a copying machine or the like utilizing an electrophotographic process, for heating and fixing a toner image transferred to a transfer medium.

[0002]

2. Description of the Related Art In this type of heat fixing device, for example, a fixing roller is heated by a heater, and the toner image transferred onto a transfer sheet is heated and pressed by the fixing roller and a pressure roller to fix the toner image. In such a heat fixing device, it is required to stably fix an unfixed toner image on transfer paper. For this reason, it is necessary to keep the temperature of the fixing roller constant, and a temperature control device for keeping the temperature of the fixing roller constant is provided.

As a heat fixing device provided with such a temperature control device, one disclosed in Japanese Patent Application Laid-Open No. 8-146816 is known. This device stops energizing the heater when the detected temperature T obtained by detecting the fixing roller with the temperature detecting element is equal to or higher than the set temperature upper limit value TfL during fixing, and the detected temperature T is equal to or lower than the set temperature lower limit value TfU. And the detected temperature T is TfU ≧ T ≧ T
At fL, the power supply to the heater is controlled based on the ON / OFF duty ratio.

In addition, the on / off duty ratio control is performed under the static conditions inherent to a heating device (for example, the heat capacity of a heated fixed body composed of a fixing pipe and a fixing film, and the self-heating type fixed body composed of a fixing pipe and a fixing film). And thermal conditions (eg, ambient temperature, size and weight of transfer paper, density of recorded images transferred to transfer paper, etc.)
Is determined by the product of the coefficients set by

According to such an apparatus, the temperature change of the fixing body during fixing is moderated, and the heater is turned on and off at a set temperature during fixing, so that the temperature of the fixing body moves up and down in a short cycle. Good fixing can be performed by reducing the temperature ripple.

[0006]

When the on / off duty ratio control is performed in the above-described apparatus, it is necessary to determine the on / off duty ratio coefficients in advance, which has an effect on the temperature control. Extract such conditions (static and dynamic conditions) and turn them on,
It was necessary to determine the coefficient of the off-duty ratio in advance.

However, it is difficult to extract all conditions. In addition, since a method of determining the on / off duty ratio coefficient in accordance with the type of the condition must be determined in advance, the more the extracted conditions, the more time is required to determine the coefficient. . Therefore, it is not enough to obtain a good effect in all environments where various conditions affecting the temperature control exist.

[0008] Therefore, the present invention provides a method for controlling the temperature control in any environment regardless of the presence or absence of a condition affecting the temperature control.
An on / off duty ratio control is intended to provide a heating / fixing device that moderates a temperature change of a fixing body during fixing, can perform a more stable temperature control with a small temperature ripple, and can perform good fixing. Things.

[0009]

According to a first aspect of the present invention, a toner image transferred to a transfer medium by an electrophotographic process is provided.
In a heat fixing device that heats and fixes by a fixing body, a temperature control means for controlling on / off of heating power of the fixing body to control a fixing temperature during fixing is provided, and the temperature control means has an upper limit temperature higher than a set temperature. And setting a lower limit temperature lower than the set temperature, if the detected temperature of the fixing body is equal to or higher than the upper limit temperature, turns off the heating power, and if the detected temperature of the fixing body is lower than the lower limit temperature, controls the heating power on, When the detected temperature of the fixing body is in the temperature range between the lower limit temperature and the upper limit temperature, the temperature range between the upper limit temperature and the set temperature is higher than the temperature range between the set temperature and the lower limit temperature. A heating fixing device characterized in that temperature control is performed based on an on / off duty ratio changed according to a history of detected temperatures of a fixing member so that a ratio of turning on power is increased.

According to a second aspect of the present invention, during the fixing, the heating power is set to an on / off duty ratio in each temperature region each time the detected temperature of the fixing body becomes equal to or higher than the upper limit temperature. Changed the on / off duty ratio to a lower ratio, and each time the detected temperature of the fixing body becomes lower than the lower limit temperature, the on / off duty ratio in each temperature region is increased to increase the ratio of heating power to on / off. 2. The heat fixing device according to claim 1, wherein the duty ratio is changed to a duty ratio.

According to a third aspect of the present invention, when the detected temperature of the fixing member is in each temperature range between the lower limit temperature and the upper limit temperature during fixing, the detected temperature of the fixing member is present. Each time the temperature area changes, the on / off duty ratio of the temperature area where the detected temperature of the fixing body existed before the change is calculated.
3. The heat fixing device according to claim 2, wherein the difference in the ratio of turning on the heating power of the on / off duty ratio in each temperature region is reduced.

According to a fourth aspect of the present invention, when the detected temperature of the fixing member is in each temperature range between the lower limit temperature and the upper limit temperature during the fixing, the temperature control means controls the on / off duty of each temperature range. 4. The heat fixing device according to claim 3, wherein the difference between the ratios at which the heating power is turned on does not exceed a preset minimum value.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG. In the heat fixing device according to the present embodiment, as shown in FIG. 1, a heater 11 heats a fixing roller 12 as a fixing body. The heater 11 is connected to a VB power supply via the solid state relay 18.

Also, the fixing roller 12 is connected to the reference voltage VE.
A series circuit of a temperature detecting element 13 such as a thermistor for detecting the temperature of the sensor 13 and a reference resistor 14 is connected, and a voltage at a connection point between the temperature detecting element 13 and the reference resistor 14 is supplied to an A / D converter 15. . This A / D converter 15
The input voltage is converted into a digital signal and supplied to the CPU (central processing unit) 16 as data of the detected temperature Th.

The CPU 16 compares the data of the reference temperature for temperature judgment and the data of the detected temperature stored in a ROM (read only memory) 17 and controls the solid state relay 18 to turn on the heater 11. The fixing roller 12 is turned off to maintain the temperature of the fixing roller 12 within a predetermined temperature range.

The data of the temperature judgment reference temperature stored in the ROM 17 is an upper limit temperature (Ts) higher than the set temperature Ts.
+ Β) and the lower limit temperature (Ts-α) lower than the set temperature. Here, α and β are determined in consideration of the overshoot / undershoot with respect to the set temperature. It is not necessary that α = β.

The set temperature Ts and the upper limit temperature (Ts +
FIG. 2 shows the relationship between β) and the lower limit temperature (Ts−α), and each temperature region is divided by these. The temperature range below the lower limit temperature (Ts-α) is A, and the lower limit temperature (Ts
The temperature range from −α) to the set temperature Ts is B, the temperature range from the set temperature Ts to the upper limit temperature (Ts + β) is C, and the temperature range from the upper limit temperature (Ts + β) is D.

In this embodiment, when the detected temperature Th is in the temperature range C or B, which is a range above and below the set temperature, the solid state relay 18 is turned on and off and on and off based on the off duty ratio. The average power applied to the heater 11 is controlled. FIG. 3 shows an example of the ON / OFF duty ratio in that case.

For example, to set the average power to 50%,
The on / off cycle is controlled with a one-to-one duty ratio. Specifically, when zero-cross control is performed at a commercial frequency of 50 Hz, counting is performed in units of a half cycle (10 ms). When the control is performed in units of 5%, 20 cycles are defined as one cycle and an integral multiple of 1 to 20 (1/20, 2/20).
20, ...).

In the present embodiment, the control is performed with different on / off duty ratios depending on the temperature range in which the detected temperature Th is located. In this case, control is performed such that the ON ratio of the ON / OFF duty ratio increases as the temperature region increases. The initial value of the average power in each of the temperature regions A to D is set as follows, for example. That is, 100% in the temperature region A, 70% in the temperature region B,
The temperature region C is set to 30%, and the temperature region D is set to 0%.

The CPU 16 stores a to d in the RAM 19.
, And the current values of the ON / OFF duty ratios in the respective temperature regions A to D are stored, and the heater temperature is controlled based on these current values.

The CPU 16 performs the temperature control shown in FIGS. 4 to 8 based on the program data stored in the ROM 17. FIG. 4 shows a main routine, and FIGS. 5 to 8 show subroutines. This temperature control may be performed by interrupt processing. In these temperature controls, whether or not the detected temperature Th is in each of the temperature ranges A to D is stored in the RAM 19 or the like using status signals a to d, respectively. For example, when a = 1, it indicates that the detected temperature Th is in the temperature region A, and a =
A value of 0 indicates a case where the detected temperature Th is not in the temperature range A.

The CPU 16 first executes the ST shown in FIG.
(Step) It is determined in step 1 whether printing is in progress or waiting. At this time, if it is determined in ST1 that the apparatus is on standby, ST1
At 2, a = 0, b = 0, c = 0, and d = 0, and at ST3, the heater 11 is turned off, that is, the heating power is turned off, and the process returns to ST1.

If it is determined in ST1 that printing is being performed, the detected temperature Th is raised to the upper limit temperature (Ts + T) in ST4.
β) It is determined whether or not it is greater than or equal to. If it is determined in ST4 that the detected temperature Th is equal to or higher than the upper limit temperature (Ts + β),
At T5, control in the temperature region D is performed.

In the control in the temperature region D, the heater is turned off in ST11 as shown in FIG. continue,
In ST12, it is determined whether or not the status signal c = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature range C. If it is determined in ST12 that the immediately preceding detected temperature Th was in the temperature region C, the status signal is changed from a case where the detected temperature Th is in the temperature region C to a case where it is in the temperature region D in ST13. That is, if the status signal is c =
0, d = 1.

Subsequently, in ST14, the on / off duty ratio in the temperature ranges B and C is changed to the on / off duty ratio in which the ratio of turning on the heating power is reduced.
The process returns to ST1 shown in FIG. This is because when the detected temperature Th rises from the temperature region C to the temperature region D, it is considered that the heating was excessive in the ON / OFF duty ratio in the temperature regions B and C immediately before. Specifically, the average power DB in the temperature region B is set to DC, and the average power DC in the temperature region C is set to DC-10%. Thus, the on / off duty ratio in each of the temperature ranges B and C is automatically adjusted.

If it is determined in ST12 that the immediately preceding detected temperature Th was not in the temperature range C, it is determined in ST15 whether the status signal is d = 0, that is, whether the immediately preceding detected temperature Th was not in the temperature range D. Determine whether or not. ST1
5 when it is determined that d = 0 is not satisfied, that is, when it is determined that the immediately preceding detected temperature Th was in the temperature range D, FIG.
When it is determined that d = 0, that is, when it is determined that the immediately preceding detected temperature Th is not in the temperature range D, an error such as turning off the heater and displaying an error in ST16 is performed in ST16. The process is performed, and the temperature control process ends.

Since it is considered that the temperature gradually rises and enters the temperature range D in the normal state, the immediately preceding detected temperature T
If h is supposed to be in the temperature area C or D, but the immediately preceding detected temperature Th is not in the temperature area C or D, it is considered that some abnormality has occurred. It is decided to do.

At ST4 shown in FIG. 4, the detected temperature Th is set to (T
If it is determined that the temperature is not equal to or higher than (s + β), it is determined in ST6 whether the detected temperature Th is equal to or higher than the set temperature Ts.
If it is determined in ST6 that the detected temperature Th is equal to or higher than the set temperature Ts, control in the temperature region C is performed in ST7.

In the control in the temperature region C, as shown in FIG. 6, the heater is driven and controlled at a duty ratio of the average power DC in ST21. Subsequently, in ST22, it is determined whether or not the status signal b = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature range B. If it is determined in ST22 that the immediately preceding detected temperature Th was in the temperature range B,
At time T23, the status signal is detected.
Is changed from when it is in the temperature range C to when it is in the temperature range C. That is, the status signals are set to b = 0 and c = 1.

Subsequently, in ST24, the average power DB-DC
Is greater than 15%. D at ST24
If it is determined that B-DC is 15% or less, the process returns to ST1 shown in FIG. In this case, the on / off duty ratio is not changed.

This means that each time the temperature control is repeated, the on / off duty ratios of the temperature regions B and C converge so as to decrease, but the heating power is turned on so as not to excessively converge. This is because the ON / OFF duty ratio is changed only when the minimum value of the ratio difference is provided and the difference is larger than the minimum value. Although the minimum value is set to 15% here, it is not necessarily limited to this.

In ST24, average power DB-DC is 15%
When it is determined that the heating power is greater than the above, the on / off duty ratio in the temperature region B is changed so that the ratio of turning on the heating power is reduced. Specifically, the average power DB in the temperature region B is set to DB-5%, and the process returns to ST1 shown in FIG. Thus, the difference between the on / off duty ratio of the temperature region C and the ratio of turning on the heating power is reduced. This is because when the detected temperature Th rises from the temperature range B to the temperature range C, the detected temperature T
This is because when h returns to the temperature region B, the heating is performed less than in the previous time, so that overshoot when the temperature again enters the temperature region C is suppressed.

If it is determined in ST22 that the immediately preceding detected temperature Th is not in the temperature range B, it is determined in ST26 whether or not the status signal d = 1, that is, the immediately preceding detected temperature T
It is determined whether or not h is in the temperature range D. If it is determined in ST26 that the immediately preceding detected temperature Th was in the temperature region D, the status signal is changed from a case where the detected temperature Th is in the temperature region D to a case where it is in the temperature region C in ST27. That is, the status signals are set to d = 0 and c = 1, and the process returns to ST1 shown in FIG.

If it is determined in ST26 that the immediately preceding detected temperature Th was not in the temperature region D, it is determined in ST28 whether or not the status signal c = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature region C. to decide. If it is determined in ST28 that the immediately preceding detected temperature Th was in the temperature range C, the process returns to the processing of ST1 shown in FIG.
If it is determined that h is not in the temperature range C, error processing such as turning off the heater and displaying an error is performed in ST29, and the temperature control processing ends.

This is because the immediately preceding detected temperature Th is in the temperature range B,
This is a case where neither C nor D exists, and it is considered that some abnormality has occurred. Therefore, in such a case, error processing is performed.

If it is determined in ST6 shown in FIG. 4 that the detected temperature Th is not higher than the set temperature Ts, it is determined in ST8 whether the detected temperature Th is higher than the lower limit temperature (Ts-α). In ST8, the detected temperature Th is lower than the lower limit temperature (Ts−
If it is determined to be larger than α), control in the temperature region B is performed in ST9.

In the control in the temperature region B, as shown in FIG. 7, in ST31, the heater is driven and controlled at the duty ratio of the average power DB. Subsequently, in ST32, it is determined whether or not the status signal c = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature range C. If it is determined in ST32 that the immediately preceding detected temperature Th was in the temperature range B,
At T33, the status signal is detected.
Is changed from the case where it is in the temperature range B to the case where it is in That is, the status signals are set to c = 0 and b = 1.

Subsequently, in ST34, the average power DB-DC
Is greater than 15%. D at ST34
If it is determined that B-DC is 15% or less, the process returns to ST1 shown in FIG. In this case, the on / off duty ratio is not changed. This is to prevent the on / off duty ratios in the temperature regions B and C from excessively converging as in the process of ST24 in the temperature region C.

In ST34, average power DB-DC is 15%
If it is determined that the heating power is higher, the on / off duty ratio in the temperature region C is changed to the on / off duty ratio in which the ratio of turning on the heating power is increased. Specifically, the average power DC in the temperature region C is set to DC + 5%, and the process returns to ST1 shown in FIG. Thus, the difference between the on / off duty ratio of the temperature region B and the ratio of turning on the heating power is reduced. This is because when the detected temperature Th falls from the temperature area C to the temperature area B, the next time the detected temperature Th returns to the temperature area C, a larger amount of heating is performed than in the previous time. This is to suppress the undershoot when entering the temperature range B again.

If it is determined in ST32 that the immediately preceding detected temperature Th is not within the temperature range C, then in ST36, it is determined whether or not the status signal a = 1, that is, the immediately preceding detected temperature T
It is determined whether or not h is in the temperature range A. If it is determined in ST36 that the immediately preceding detected temperature Th was in the temperature region A, the status signal is changed from ST in the temperature region A to ST in the temperature region B in ST37. That is, the status signals are set to a = 0 and b = 1, and the process returns to ST1 shown in FIG.

If it is determined in ST36 that the immediately preceding detected temperature Th was not in the temperature region A, it is determined in ST38 whether or not the status signal b = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature region B. to decide. If it is determined in ST38 that the immediately preceding detected temperature Th was in the temperature range B, the process returns to the process of ST1 shown in FIG.
If it is determined that h is not in the temperature range B, error processing such as turning off the heater and displaying an error is performed in ST39, and the temperature control processing is ended.

This is because the immediately preceding detected temperature Th is in the temperature range A,
This is the case where none of B and C exist, and it is considered that some abnormality has occurred. Therefore, error processing is performed in such a case.

If it is determined in ST8 shown in FIG. 4 that the detected temperature Th is lower than the lower limit temperature (Ts-α), the process proceeds to ST1.
At 0, control in the temperature region A is performed. This temperature range A
8, the heater 11 is turned on in ST41, that is, the heating power is turned on (continuously) as shown in FIG. Subsequently, in ST42, it is determined whether or not the status signal b = 1, that is, whether or not the immediately preceding detected temperature Th was in the temperature range B. If it is determined in ST42 that the immediately preceding detected temperature Th was in the temperature range B, the status signal is changed from ST in the temperature range B to ST in the temperature range A in ST43. That is, the status signals are set to b = 0 and a = 1.

Subsequently, in ST44, the on / off duty ratio in the temperature regions B and C is changed to the on / off duty ratio in which the ratio of turning on the heating power is increased, and the process returns to ST1 shown in FIG. This is because when the detected temperature Th drops from the temperature region B to the temperature region A, it is considered that heating was insufficient at the on / off duty ratios in the temperature regions B and C immediately before. Specifically, the average power DC in the temperature region C is set to DB, and the average power DB in the temperature region B is set to DB + 10%. Thus, the on / off duty ratio in each of the temperature ranges B and C is automatically adjusted.

If it is determined in ST42 that the immediately preceding detected temperature Th was not in the temperature region B, it is determined in ST45 whether or not the status signal is a = 0, ie, whether the immediately preceding detected temperature Th was not in the temperature region A. Determine whether or not. ST5
If it is determined in step 5 that the status signal is not a = 0,
That is, when it is determined that the immediately preceding detected temperature Th was in the temperature region A, the process returns to ST1 shown in FIG. 4, and when it was determined that the status signal was a = 0, that is, when the immediately preceding detected temperature Th was in the temperature region A. If it is determined that the status signal has not been set, it is considered that the state of the status signal is still the initial value.
In ST47, average powers DB and D in temperature regions B and C, respectively.
C is set to 70% and 30%, respectively, and the process returns to ST1 shown in FIG. Note that ST4 to ST10 constitute temperature control means.

In the embodiment of the present invention having such a configuration, during standby, the solid state relay 18
Is turned off, the power supply to the heater 11 is stopped, and the heating power is turned off.

On the other hand, when printing is started, the detection temperature Th from the A / D converter 15 is continuously monitored during printing, and the temperature range in which the detection temperature Th is located is determined by the immediately preceding detection temperature. Temperature control is performed according to the temperature range (history) in which Th was.

That is, when the detected temperature Th is in the temperature range A, the solid state relay 18 is turned on (100%), and the heater 11 is energized. At this time, when the immediately preceding detected temperature Th is in the temperature region B, the on / off duty ratio in the temperature regions B and C where the heating is insufficient is changed to the on / off duty ratio in which the ratio of turning on the heating power is increased. The ratio is automatically adjusted (based on the processing shown in FIG. 8). Thus, when the detected temperature Th rises to the temperature regions B and C next time, more heating than before is performed, so that more appropriate temperature control can be performed.

When the detected temperature Th is in the temperature range B, the temperature is controlled by the on / off duty ratio. At this time, if the immediately preceding detected temperature Th is in the temperature region C, the on / off duty ratio in the temperature region C is automatically adjusted to the on / off duty ratio that increases the ratio of turning on the heating power ( (Based on the processing shown in FIG. 7). Accordingly, when the detected temperature Th returns to the temperature range C next time, by performing heating more than the previous time, it is possible to suppress the undershoot when the temperature T enters the temperature range B again.

When the detected temperature Th is in the temperature range C, the temperature is controlled by the ON / OFF duty ratio. At this time, if the immediately preceding detected temperature Th is in the temperature region B, the on / off duty ratio in the temperature region B is automatically adjusted to the on / off duty ratio in which the ratio of turning on the heating power is reduced ( (Based on the processing shown in FIG. 6).

Thus, when the detected temperature Th returns to the temperature range B next time, by performing heating slightly less than the previous time, it is possible to suppress the overshoot when the temperature T enters the temperature range C again. .

When the detected temperature Th is in the temperature range D, the solid state relay 18 is turned on (100%), and the heater 11 is energized. At this time, if the immediately preceding detected temperature Th is in the temperature range C, the ON in the temperature ranges B and C where the heating is excessive,
The off duty ratio is automatically adjusted to an on / off duty ratio in which the ratio of turning on the heating power is reduced (FIG. 5).
). As a result, the detected temperature Th
When the temperature rises to the temperature regions B and C, the heating is performed less than in the previous time, so that more appropriate temperature control can be performed.

By repeating such control,
For example, as shown in FIG. 9, even if the on / off duty ratio remains at the initial value (average power DB = 70%, DC = 30%), it falls between the upper limit temperature (Ts + β) and the lower limit temperature (Ts−α). Even in a normal temperature environment, the control of the temperature ranges B and C is repeatedly performed, so that the difference between the average powers of the on / off duty ratios is reduced so that the temperature ripple is reduced. , It is possible to perform ideal temperature control such that the temperature becomes gradually smaller, so that good fixing can be performed.

As shown in FIG. 10, the on / off duty ratio is set to the initial value (average power DB = 70%, DC = 30).
%), In a low-temperature environment where the temperature tends to decrease, each time the detected temperature Th decreases from the temperature range B to A, the ON / OFF ratio at which the heating power is turned ON is increased from the previous time. Since the duty ratio is changed, the automatic amount is gradually adjusted to an appropriate ON / OFF duty ratio. Thereafter, the power converges so that the difference between the average powers of the ON and OFF duty ratios is reduced, so that it is possible to perform ideal temperature control such that the temperature ripple is gradually reduced. be able to.

Further, as shown in FIG. 11, the on / off duty ratio is set to an initial value (average power DB = 70%, DC = 3).
0%), in a high-temperature environment where the temperature tends to rise, every time the detected temperature Th rises from the temperature range C to D, the rate at which the heating power is turned on is reduced from the previous time. Since the duty ratio is changed to the off duty ratio, the automatic amount is gradually adjusted to the appropriate on / off duty ratio also in this case. Thereafter, the power converges so that the difference between the average powers of the ON and OFF duty ratios is reduced, so that it is possible to perform ideal temperature control such that the temperature ripple is gradually reduced. be able to.

As described above, according to the heat-fixing apparatus according to the present embodiment, the detection temperature Th is continuously monitored during printing, and the detected temperature Th is set to the upper limit temperature (Ts + β), the set temperature Ts, and the lower limit temperature. Depending on which of the temperature regions A to D divided by (Ts-α), the detection of the fixing member is performed such that the higher the temperature region, the smaller the ratio of turning on the heating power becomes in each temperature region. By controlling the temperature based on the on / off duty ratio changed according to the temperature history, regardless of the conditions that affect the temperature control, regardless of the conditions under which the conditions exist, Without investigating, it is possible to moderate the temperature change of the fixing body during fixing in the on / off duty ratio control, reduce the temperature ripple, and perform stable temperature control. That.

In the embodiment of the present invention, the case where the on / off duty ratio in the temperature ranges B and C is adjusted in units of 5% or 10% average power has been described, but the present invention is not necessarily limited to this. Not something.

[0059]

As described above in detail, according to the present invention, according to the history of the detected temperature of the fixing member, the higher the temperature range, the smaller the ratio of turning on the heating power becomes. By controlling the temperature based on the on / off duty ratio that has been changed by the above, regardless of the presence or absence of the condition that affects the temperature control, regardless of the environment in which the condition exists, without investigating the condition In the on / off duty ratio control, the change in the temperature of the fixing member during fixing is moderated, the temperature fluctuation is small, and a more stable temperature control can be performed, and good fixing can be performed.

Further, when the detected temperature of the fixing member is in each temperature range between the lower limit temperature and the upper limit temperature, each time the temperature region in which the detected temperature of the fixing member exists changes, the detected temperature of the fixing member is changed before changing. By changing the ON and OFF duty ratios of the temperature regions where there was the ON and OFF duty ratios in each temperature region so that the difference in the ratio of turning ON the heating power of the ON and OFF duty ratios is reduced, this is repeated, Since it is possible to converge so that the difference between the average powers of the ON and OFF duty ratios is reduced, it is possible to perform ideal temperature control in which the temperature ripple is gradually reduced, and it is possible to perform good fixing. .

Further, when the detected temperature of the fixing member is in each temperature range between the lower limit temperature and the upper limit temperature, the difference between the ON and OFF duty ratios of the heating power of each temperature range is set in advance. By not exceeding the minimum value, it is possible to prevent the difference between the average powers of the on / off duty ratios from excessively converging.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a heat fixing device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating each temperature region when temperature control is performed in the embodiment.

FIG. 3 is a diagram showing an example of an on / off duty ratio in the embodiment.

FIG. 4 is a flowchart showing temperature control performed by the CPU shown in FIG. 1;

FIG. 5 is a flowchart showing control in a temperature region D shown in FIG. 4;

FIG. 6 is a flowchart showing control in a temperature region C shown in FIG. 4;

FIG. 7 is a flowchart showing control in a temperature region B shown in FIG. 4;

FIG. 8 is a flowchart showing control in a temperature region A shown in FIG. 4;

FIG. 9 is a diagram showing an example in the case where temperature control is performed in the embodiment.

FIG. 10 is a view showing another example when temperature control is performed in the embodiment.

FIG. 11 is a diagram showing another example when temperature control is performed in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Heater 12 ... Fixing roller 13 ... Temperature detection element 16 ... CPU 17 ... ROM 18 ... Solid state relay 19 ... RAM

Claims (4)

[Claims] 1. A heating and fixing device for heating and fixing a toner image transferred to a transfer medium by an electrophotographic process by a fixing member, wherein heating power of the fixing member is controlled on and off to control a fixing temperature during fixing. A temperature control unit that sets an upper limit temperature higher than a set temperature and a lower limit temperature lower than the set temperature, and turns off heating power when the detected temperature of the fixing body is equal to or higher than the upper limit temperature. When the detected temperature of the fixing body is equal to or lower than the lower limit temperature, the heating power is turned on.When the detected temperature of the fixing body is in a temperature range between the lower limit temperature and the upper limit temperature, the upper limit temperature and the set temperature are set. The on-state changed in accordance with the history of the detected temperature of the fixing member so that the ratio of turning on the heating power is higher in the temperature range between the set temperature and the lower limit temperature than in the temperature range between the set temperature and the lower limit temperature. ,off Based on Yuti ratio, heat fixing apparatus characterized by controlling the temperature. 2. The image forming apparatus according to claim 1, wherein the temperature control unit includes:
Each time the detected temperature of the fixing body becomes equal to or higher than the upper limit temperature, the on / off duty ratio in each temperature region is changed to an on / off duty ratio in which the ratio of turning on the heating power is reduced, and the detected temperature of the fixing body is changed. 2. The heat fixing apparatus according to claim 1, wherein the on / off duty ratio in each temperature region is changed to an on / off duty ratio in which the ratio of turning on the heating power is increased every time the temperature becomes equal to or lower than the lower limit temperature. . 3. The fixing device according to claim 1, wherein the temperature control unit is configured to:
When the detected temperature of the fixing member is in each temperature region between the lower limit temperature and the upper limit temperature, each time the temperature region in which the detected temperature of the fixing member exists changes, the detected temperature of the fixing member exists before the temperature changes. 3. The heating according to claim 2, wherein the on / off duty ratios of the temperature regions are changed so that the difference between the on / off duty ratios in which the heating power is turned on in each temperature region is reduced. Fixing device. 4. The fixing device according to claim 1, wherein the temperature control unit includes:
When the detected temperature of the fixing member is in each temperature range between the lower limit temperature and the upper limit temperature, the difference between the ratio of turning on the heating power of the on / off duty ratio of each temperature range exceeds a preset minimum value. 4. The heat fixing device according to claim 3, wherein the heat fixing device is not provided.