JP3204490B2 - Temperature control method for thermal fixing device - Google Patents

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 provided in an electrophotographic image forming apparatus such as a facsimile, a printer, a copying machine, etc., and more particularly to a method for controlling the temperature of a heat generating portion.

[0002]

2. Description of the Related Art As a conventional temperature control method of a heat fixing device, there is a heat roller fixing device disclosed in Japanese Patent Application Laid-Open No. 61-228484. The heat roller fixing device according to this publication detects the initial temperature of the heat roller, predicts an overshoot amount from a difference between the initial temperature and the target temperature, and subtracts the predicted overshoot amount from the target temperature. When the temperature of the heat roller rises and reaches the set temperature, the power supply to the heater is turned off, and thereafter, the target temperature is spontaneously reached by the accumulated heat, thereby causing overshoot. It is to try to prevent.

As another conventional method for controlling the temperature of a thermal fixing device, there is a method of controlling the temperature of a fixing device disclosed in Japanese Patent Application Laid-Open No. 5-333944. The temperature control method of the fixing device according to this publication detects the amount of temperature rise (temperature gradient) with respect to time of the heat fixing device, predicts the amount of overshoot based on the detected amount, and subtracts the predicted amount of overshoot from the target temperature. The temperature is set, and when the temperature of the heat fixing device rises and reaches the set temperature, the power supply to the heater is turned off, and thereafter, the target temperature is spontaneously reached by the accumulated heat, and the overshoot is performed. This is intended to prevent the occurrence of the problem.

[0004]

However, in the former of the prior art, the amount of overshoot is predicted only by the initial temperature of the heat roller. Since the amount of overshoot also varies due to factors such as temperature, the amount of overshoot cannot be uniformly predicted based on the initial temperature. Therefore, even if the temperature is controlled based on the uniformly predicted overshoot amount, overshoot still occurs, or if the temperature of the heat roller cannot reach the target temperature for a long time and a long fixing waiting time is required. There is a problem that there is.

Further, in the latter case of the prior art, the overshoot amount is predicted by the temperature gradient, so that the variation of the overshoot amount in the former sense of the former case is included in the temperature gradient. This may be the result, for example, when the fuser cover is opened and the flow of air changes, or the temperature of the air conditioner in the room where the fuser is placed is changed by someone to change the indoor temperature. In addition, not only does the amount of overshoot delicately vary due to changes in the environment, but the temperature rise curve of the fixing device is non-linear (it does not necessarily change linearly), so the temperature gradient is not constant. The amount of shoot cannot be uniformly predicted by the temperature gradient. For this reason, there is a problem that overshoot may occur or the temperature of the fixing device may not reach the target temperature for a long time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a temperature control method for a heat fixing device that can accurately reach a target temperature without overshooting itself and can shorten the time required to reach the target temperature. Is what you do.

[0007]

In order to solve the above-mentioned problems, a temperature control method for a heat fixing device according to the present invention is configured as follows.

[0008]

Means for Solving the Problems (1) A feedback correction control area is set between a target temperature of a heat generating portion of a heat fixing device and a set temperature which is set lower than the target temperature by a predetermined temperature difference. After the start of energization to the heating unit whose temperature is lower than the set temperature, the temperature of the heating unit is increased by continuous energization, and after the temperature of the heating unit enters the feedback correction control area, the heating is started. Until the temperature of the unit reaches the target temperature, or until a predetermined time elapses after the temperature of the heating unit enters the feedback correction control area,
The temperature of the heating part reaches the target temperature by intermittent energization
When performing feedback control for the holding and,
The feedback amount of the temperature difference between the temperature of the heat generating part and the target temperature during this control is determined by the temperature gradient immediately before the temperature of the heat generating part enters the feedback correction control area, and the heat generation from the start of energization. temperature parts is corrected using the time elapsed until entering said feedback correction control area, the fee
The target temperature and the setting for setting the feedback correction control area
The predetermined temperature difference from the constant temperature is determined by the
Do not make the correction until the target temperature is reached from the temperature of the hot zone.
Overshoot caused by feedback control
Value greater than the difference between the maximum temperature during
You .

(2) A feedback correction control area is set between a target temperature of the heat generating portion of the heat fixing device and a set temperature set lower than the target temperature by a predetermined temperature difference , and the temperature is lower than the set temperature. After the start of energization to the heating unit, the temperature of the heating unit is increased by continuous energization, and after the temperature of the heating unit enters the feedback correction control area, until the temperature of the heating unit reaches the target temperature. Or, until the predetermined time elapses after the temperature of the heating unit enters the feedback correction control area, the feedback control for maintaining and maintaining the temperature of the heating unit at the target temperature by intermittent energization. when performing, issued at the time of this control
The feedback amount of the temperature difference between the temperature of the heating section and the target temperature, the temperature gradient immediately before the temperature of the heating section enters the feedback correction control area, the temperature of the heating section and the target temperature at the start of energization. the difference is corrected using the said full
Before setting the feedback correction control area and the target temperature
The predetermined temperature difference between the predetermined temperature and
The correction is performed until the target temperature is reached from the temperature of the heating section.
Over when feedback control is performed without
With a value larger than the difference between the maximum temperature during shooting and the target temperature
I do .

(3) In the temperature control method for a thermal fixing device according to the above (1) or (2), the predetermined temperature used for setting the feedback correction control area is determined from a temperature of the heat generating portion at the start of energization. It is characterized in that the temperature is made larger than the amount of overshoot when feedback control is performed until the target temperature is reached.

According to the temperature control method of the thermal fixing device having the above-described configuration, when the temperature of the heat generating portion of the thermal fixing device rises due to continuous energization and enters the feedback correction control region between the target temperature and the set temperature. By performing feedback control for maintaining the temperature of the heat generating unit at the target temperature by intermittent energization, and performing feedback correction control for correcting the temperature error feedback amount during the control using a predetermined parameter, the heat generating unit is controlled. Can accurately reach the target temperature without causing overshoot, and since the target temperature can be reliably reached in this way, the time required to reach the target temperature can be reduced.

That is, for example, instead of predicting the amount of overshoot and completely turning off the energization at a temperature just before the target temperature by the predicted amount as in the conventional example, the heat generating portion is set to the target temperature in the feedback correction control region. By performing intermittent energization by feedback correction control so that overshoot does not occur until the target temperature is reached, the heating unit can accurately reach the target temperature without overshoot, and until the target temperature is reached. Time can be shortened.

When the heat generating portion reaches the target temperature, the correction of the temperature error feedback amount is turned off (feedback correction control is turned off), and only the feedback control is continued to maintain the target temperature. In addition, even when the heating unit does not reach the target temperature even if a predetermined time has elapsed after the temperature of the heating unit has entered the feedback correction control area, the correction of the feedback amount is turned off and only the feedback control is continued. In addition, it is possible to quickly reach the target temperature and to prevent the arrival time from being delayed.

Further, the predetermined temperature used for setting the feedback correction control area is larger than the amount of overshoot when feedback control is performed from the temperature of the heat generating portion at the start of energization to the target temperature. By doing so, it is possible to prevent the amount of heat storage from becoming excessive, and to reliably prevent the occurrence of overshoot due to the amount of heat storage being excessive.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 7 are views for explaining a temperature control method of the heat fixing device according to the first embodiment of the present invention.

FIG. 1 is a block diagram showing a configuration of a temperature control circuit of the heat fixing device. In the figure, reference numeral 11 denotes a heater (heating unit) of a heat roller (not shown) of the heat fixing device, and the heater 11 is provided with a thermistor 12 used for detecting the heat generation temperature. Both terminals of the heater 11 are connected to the power supply circuit C in series with the power supply 15.

An energization control device 16 for controlling energization of the heater 11 is connected in series with the power supply circuit C, and a zero-cross detector 18 used for an interrupt operation described later is connected in parallel with the heater 11. Have been. This zero-cross detector 18 is a CPU (Central Processing Unit)
20 while the CPU 20 is connected to the thermistor 1
2 is connected to a temperature detector 21, and the output of the temperature detector 21 is taken in by an A / D conversion circuit built in the CPU 20 for temperature information.

FIG. 2 is a flowchart showing the main routine operation of the CPU 20. When the power is turned on (Po
First, hardware initialization is performed (step S1). Next, a command for a heater temperature control command is set (step S2), permission is given to an interrupt using a zero-cross signal from the zero-cross detector 18 (step S3), and an interrupt operation as shown in the flowchart of FIG. Do.

In FIG. 3, after an interrupt is started, an interrupt initial process is performed (step S1), and then the temperature Ti of the heater 11 is detected (read) (step S2). Then the detected temperature value to determine the command branch (step S3), and the detected temperature Ti proceeds to the flow of heat-up in the case of low temperature T ₀ than the set temperature T1, which will be described later shown in Fig.

In FIG. 4, Tr is a heater 11
T1 is a set temperature that is set lower than the target temperature Tr by a predetermined temperature TA. A feedback correction control area is set between the set temperature T1 and the target temperature Tr with a width corresponding to the predetermined temperature TA. As an example, the target temperature Tr is 150 ° C.
It is conceivable that the predetermined temperature TA is 8 ° C. and the set temperature T1 is 142 ° C. However, it is needless to say that other specific values are used depending on various conditions such as the model and the energization start temperature. Nor.

The predetermined temperature TA is selected to be slightly larger than the amount of overshoot when feedback control is performed from the temperature of the heater 11 at the start of energization to the target temperature. For example, when the predetermined temperature TA is 8 ° C. as described above, it is conceivable that the overshoot temperature amount is about 6 ° C. or 7 ° C.

By selecting the predetermined temperature TA as described above, it is possible to reliably prevent the heat storage amount from becoming excessive and inevitably causing overshoot. The above-mentioned overshoot amount is a unique map determined according to the energization start temperature by various factors such as the thickness of the heat roller, the material, the heat capacity, the thermal conductivity of the rubber layer outside the heat roller, The predetermined temperature TA is selected as described above based on the specific overshoot amount corresponding to the power supply start temperature.

Referring again to FIG. 3, the heat-up flow is first timed out, that is, it is determined whether a predetermined time has elapsed since the start of energization (step S4). Next, it is determined whether the temperature Ti of the heater 11 is lower than (Tr-TA) of FIG. 4, that is, T1 (step S5). YE
In the case of S, the power value er to be energized to the heater 11 is set to the maximum value (step S6), whereby the CPU 20 outputs a signal to the energization control device 16 after the power conversion, and continuously energizes to the maximum power value (full power). Heater 1
1 is heated (step S7).

The temperature Ti of the heater 11 rises due to the full power supply, and in step S5 in FIG.
If it is determined that the temperature Ti is not lower than the set temperature (Tr-TA), a transient command is set, a correction flag is set, and a correction timer is started (step S8).

In the flowchart showing the operation of the main routine in FIG.
In step S4, a report from the heater temperature control by interruption is received in the form of status, and other processing is performed until the heater reaches the target temperature by the heater temperature control (step S4 in FIG. 2).
5) Waiting. In FIG. 3, after step S8, a heat storage amount estimation calculation value described later is calculated based on the correction parameter (step S9).

After step S9, the process proceeds to step S11 of the transient (transient state) flow in the command branch determination in step S3. In the transient flow, first, it is determined whether the same heat-up as in step S4 has timed out (step S11). If YES, an error process is performed. If NO, however, it is next determined whether the correction flag is set (step S11). S1
2). If YES, it is determined whether the correction timer has timed out (step S13). If NO, it is next determined whether the temperature Ti of the heater 11 is equal to or higher than the target temperature Tr (step S14).

If NO in step S14 of FIG. 3, it is determined whether or not the temperature Ti of the heater 11 is within the stable range between the temperatures TrH and TrL on both the upper and lower sides of the target temperature Tr (step S16). In this case, next, feedback calculation accompanied by correction of the temperature error feedback amount is performed (step S17), control is performed so that the temperature Ti of the heater 11 falls within the stable region, and the power amount of the calculation result is supplied. The energization ratio to the heater 11 by the energization control device 16 is changed (step S18).

Here, the feedback control (feedback correction control) based on the feedback calculation in step S17 in FIG. 3 will be described with reference to the flowchart in FIG. 5 and the temperature control block diagram in FIG. As shown in FIG. 6, the temperature Ti of the heater 11 is detected by the temperature detector 21 via the thermistor 12, and the detected temperature Ti is C
The data is input to the PU 20 and A / D converted.

Then, using the detected temperature data obtained by the A / D conversion, the CPU 20 performs a temperature error feedback operation on the target temperature Tr as shown in the following equation (1) (step S1 in FIG. 5). This calculated value er is the temperature error (Tr
−Ti) is a basic calculated value of the amount of power required to make zero. In the following equation (1), Ti is a detected temperature of the heater 11 that changes little by little at every sampling from the set temperature T1 to the target temperature Tr. As can be seen from the following equation (1), the feedback control basically uses a proportional control method of calculating the electric energy er by a value obtained by multiplying the temperature error by a proportional constant Kp. er = (Tr-Ti) · Kp (1)

Next, a feedback compensation operation is performed (FIG. 5).
Step S2). This calculation is performed based on the feedback of the electric energy at the time of the previous correction calculation and the feedback of the temperature rise data at the time of the current calculation to stabilize the control system. This calculation is as shown in the following equation (2), and er after the calculation in the following equation (2) is a compensation calculation value of the electric energy required to make the temperature error zero. In the following equation (2), x · h is a feedback compensation value. er = er−x · h (2)

Next, it is determined whether the correction flag is set (step S3 in FIG. 5), and if YES, a correction operation is performed (step S4 in FIG. 5). This calculation is performed to calculate the electric energy er corresponding to the heat storage amount up to that time by correcting using the heat storage amount estimation calculation value.

This calculation is as shown in the following expression (3), and er after the calculation in the following expression (3) is a correction calculation value of the electric energy required to make the temperature error zero. The following equation (3)
ΔT indicates that the temperature Ti of the heater 11 is equal to the set temperature T1.
Ts is the temperature gradient (temperature rise rate with respect to time) immediately before the temperature reaches the temperature T.
The time elapsed until i reaches the set temperature T1 (enters the feedback correction control area TA), K is a proportionality constant, and the product ΔT · ts · K thereof is a heat storage amount estimation calculation value. er = er−ΔT · ts · K (3)

As shown in FIG. 6, the heater 1
The time elapsed until the temperature Ti reaches the set temperature T1 is detected by the timer 20a, and the heat storage amount estimating calculation is performed based on the temperature gradient based on the temperature data after the A / D conversion and the proportional constant K. In the figure, reference numeral 20b is a correction timer started in step S8 of FIG.

In the case of NO in step S12 of FIG. 3, the process directly proceeds to step S16. Step S13, S
In the case of YES at 14, the correction flag is cleared (step S15), and the process proceeds to step S16. If YES in step S16, the heat-up completion status is set (step S1).
9) Set a follow command (step S2)
0) Go to step S22.

When the correction timer in step S13 in FIG. 3 times out, the timer 20b in FIG. 6 outputs a signal to perform correction control, and the correction based on the heat storage amount estimation calculation value is turned off. Since the feedback control is performed without accompanying, it is possible to quickly reach the target temperature and to prevent the arrival time from being delayed.

When the flow branches to the follow flow in the determination of the command branch in step S3 of FIG. 3, it is first determined whether or not the temperature Ti of the heater 11 is within the stable region (step S21). Is done. In the case of YES, next, feedback control without correction of the feedback amount is performed so that the temperature Ti of the heater 11 is controlled to be maintained in the stable region (step S22), and the power amount of the calculation result is supplied. Control of the energization ratio to the heater 11 is continued (step S2).
3).

FIG. 7 is a diagram showing the change in the energizing pulse width at each of the positions A, B, and C in the graph showing the temperature change of the heater 11 in FIG. 4. For example, at the position A, the energizing pulse width is W1 ( 7A, the energizing pulse width at position B is W2 (FIG. 7B), and at position C the energizing pulse width is W3 (FIG. 7C). Since the width W1 of the energizing pulse is the largest, the width W2 of the energizing pulse is the next largest, and the width W3 of the energizing pulse is the smallest, the supplied electric energy, that is, the energizing ratio, gradually increases from the position A toward B and C. Then, the temperature Ti of the heater 11 finally reaches the target temperature Tr.

As described above, according to the temperature control method for the thermal fixing device according to the first embodiment, the power is intermittently supplied until the temperature reaches the target temperature Tr without being completely turned off. By efficiently controlling the energization ratio in the decreasing direction, the heater 11 can accurately reach the target temperature Tr without overshooting, and therefore, the time required to reach the target temperature can be reduced. Can be.

FIGS. 8 and 9 are diagrams showing a method of controlling the temperature of the heat fixing device according to the second embodiment of the present invention. Steps S1 to S3 in FIG. 8 are the same as those in FIG. 5 showing the feedback correction control calculation routine in the temperature control method of the first embodiment, but the heat storage amount estimation calculation value used in the correction calculation in step S4 is different.

That is, in the temperature control method according to the first embodiment, the heat storage amount estimation calculation value includes a temperature gradient ΔT
And the temperature Ti of the heater 11 from the start of energization is equal to the set temperature T1.
In the temperature control method according to the second embodiment, the heat storage amount estimation calculation value includes the temperature gradient ΔT and the temperature gradient ΔT and the heater 11 at the start of energization. The difference is that a difference Ts between the temperature T ₀ and the target temperature Tr is used. As described above, in the temperature control method according to the second embodiment, since time is not used for the correction parameter, FIG.
Is different in that the timer 20a used in is not provided.

In the temperature control method according to the second embodiment, similarly to the temperature control method according to the first embodiment, the target temperature Tr is maintained without completely turning off energization in the middle. By intermittently energizing until reaching the temperature and controlling the energizing ratio, the heater 11 can accurately reach the target temperature Tr without overshooting, and can shorten the time required to reach the target temperature. .

In the above embodiment, the heater 1
Although the case where the energization is started when the initial temperature of No. 1 is lower than the set temperature T1 has been described, the initial temperature is set as in the case where the heat fixing device is used for a certain time, then turned off once, and then immediately turned on again. When the energization is started from a value higher than the temperature T1, the object of the present invention can be sufficiently achieved by feedback control without correction.

In the above embodiment, the duty control method of changing the pulse width is used to change the energization ratio. However, any other method such as a frequency control method can be used as long as the energization ratio per time can be changed. Such a control method may be used.

[0044]

As described above, according to the temperature control method for a heat fixing device according to the present invention, the temperature of the heat generating portion of the heat fixing device rises due to continuous energization, and the temperature between the target temperature and the set temperature is increased. Once in the feedback correction control area, feedback control is performed to maintain the temperature of the heat generating portion at the target temperature by intermittent energization, and to correct a temperature error feedback amount during the control using a predetermined parameter. By performing the above, the heating section can accurately reach the target temperature without causing overshoot, and since it is possible to reliably reach the target temperature in this way, the time until the target temperature is reached is reduced. Can be shortened.

When the heat generating section reaches the target temperature, the correction of the temperature error feedback amount is turned off (feedback correction control is turned off), and only the feedback control is continued to maintain the target temperature. In addition, even when the heating unit does not reach the target temperature even if a predetermined time has elapsed after the temperature of the heating unit has entered the feedback correction control area, the correction of the feedback amount is turned off and only the feedback control is continued. In addition, it is possible to quickly reach the target temperature and to prevent the arrival time from being delayed.

Further, the predetermined temperature used for setting the feedback correction control area is larger than the temperature amount that overshoots when the feedback control is performed from the temperature of the heat generating portion at the start of energization to the target temperature. By doing so, it is possible to prevent the amount of heat storage from becoming excessive, and to reliably prevent the occurrence of overshoot due to the amount of heat storage being excessive.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a temperature control method for a heat fixing device according to the present invention.
FIG. 3 is a block diagram illustrating a configuration of a temperature control circuit according to the embodiment.

FIG. 2 is a flowchart showing a main routine operation of a CPU 20 shown in FIG.

FIG. 3 is a flowchart showing an interrupt routine operation of the CPU 20 with respect to the main routine operation of FIG. 2;

FIG. 4 is a graph showing a change in temperature of the heater 11 with respect to time.

FIG. 5 is a flowchart showing a feedback correction control calculation routine operation of the temperature control method according to the first embodiment.

FIG. 6 is a temperature control block diagram of a temperature control method according to the first embodiment.

7 is a waveform chart showing a change in an energizing pulse width at each position of A, B, and C in a graph showing a temperature change of the heater 11 in FIG. 4, and FIG. 7B is a waveform diagram at a position B, and FIG. 7C is a waveform diagram at a position C.

FIG. 8 is a flowchart showing a feedback correction control calculation routine operation of the temperature control method according to the second embodiment.

FIG. 9 is a temperature control block diagram of a temperature control method according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Heater 12 Thermistor 15 Power supply 16 Energization control device 18 Zero-cross detector 20 CPU 20a, 20b Timer 21 Temperature detector C Power supply circuit Tr Target temperature TA Predetermined temperature T1 Set temperature

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 13/20 G03G 15/20

Claims (2)

(57) [Claims] 1. A feedback correction control area is set between a target temperature of a heat generating portion of a heat fixing device and a set temperature set lower than the target temperature by a predetermined temperature difference, wherein the heat generation temperature is lower than the set temperature. After the start of energization of the unit, the temperature of the heating unit is increased by continuous energization, and after the temperature of the heating unit enters the feedback correction control area, until the temperature of the heating unit reaches the target temperature. Alternatively, the temperature of the heat generating section reaches the target temperature by intermittent energization until the predetermined time elapses after the temperature of the heat generating section enters the feedback correction control area, and is maintained. When performing the feedback control, the feedback amount of the temperature difference between the temperature of the heat generating unit and the target temperature at the time of this control is set to the temperature immediately before the temperature of the heat generating unit enters the feedback correction control area. Devil Distribution and the temperature of the heat generating portion from the energization start is corrected using the time elapsed until entering said feedback correction control region, the target temperature for setting the feedback correction control region
The predetermined temperature difference between the temperature and the set temperature is determined by
Until the target temperature is reached from the temperature of the heat generating part.
Occurs when feedback control is performed without correction
-Larger than the difference between the maximum temperature during bar chute and the target temperature
A method for controlling the temperature of the heat fixing device. 2. A feedback correction control area is set between a target temperature of a heat generating section of a heat fixing device and a set temperature set lower than the target temperature by a predetermined temperature difference, wherein the heat generation temperature is lower than the set temperature. After the start of energization of the unit, the temperature of the heating unit is increased by continuous energization, and after the temperature of the heating unit enters the feedback correction control area, until the temperature of the heating unit reaches the target temperature. Alternatively, the temperature of the heat generating section reaches the target temperature by intermittent energization until the predetermined time elapses after the temperature of the heat generating section enters the feedback correction control area, and is maintained. When performing the feedback control, the feedback amount of the temperature difference between the temperature of the heat generating unit and the target temperature at the time of this control is set to the temperature immediately before the temperature of the heat generating unit enters the feedback correction control area. Devil Distribution and the corrected using the difference between the temperature of the heating portion of the energization start time and the target temperature, the target temperature for setting the feedback correction control region
The predetermined temperature difference between the temperature and the set temperature is determined by
Until the target temperature is reached from the temperature of the heat generating part.
Occurs when feedback control is performed without correction
-Larger than the difference between the maximum temperature during bar chute and the target temperature
A method for controlling the temperature of the heat fixing device.