JPH05127757A - Heating device - Google Patents

Abstract

PURPOSE:To reduce overshooting after electricity begins to be fed and the ripple in constant-temperature control by providing an electric feeding control means which controls electric power supplied to a heating body according to the temperature gradient of the heating body and the temperature difference from specific temperature. CONSTITUTION:The heating device which has the heating body 5 held at the specific temperature and heats an image on a recording material with the heat from the heating body 5 is equipped with the electric feeding control means 3 which controls the electric power supplied to the heating body 5 according to the temperature gradient of the heating body 5 and the temperature difference from the specific temperature. Further, an arithmetic means l1 which calculates the time required to reach the specific temperature from the temperature gradient after the heating body 5 begins to be fed with the electricity is provided and the electric feeding to the heating body 5 is stopped after the time found by the arithmetic means 1 is elapsed to perform the constant- temperature control at the specific temperature thereafter. Thus, control is so performed as to output an optimum electric feeding pattern according to the temperature difference and temperature gradient, and then the overshooting with respect to the target temperature in the beginning of the control is reduced to reduce subsequent temperature variation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device used in an image forming apparatus such as an electrophotographic device and an electrostatic recording device.
Particularly, the present invention relates to an image forming apparatus suitable for heat fixing of an unfixed image.

[0002]

2. Description of the Related Art A heating method, especially a heat roller fixing method, is widely used for fixing an unfixed image.

Basically, a pair of a heating roller that is maintained at a constant temperature and a pressure roller that is in pressure contact with the heating roller is used to perform fixing by passing a recording material supporting an unfixed image therebetween.

FIG. 22 shows an example of a heating roller temperature control circuit.

Reference numeral 5 is a halogen heater provided inside the heating roller, and 9 is a thermistor provided on the surface of the heating roller.

Reference numeral 6 denotes a comparator, which is a voltage V _T (= R _T / (R ₁ + R ₂ ) × V obtained by the resistance change of the thermistor 9.
compares the _cc) and the control target voltage V _ret, the voltage V _T ON signal does not reach the target voltage V _ret, the voltage V _T outputs an OFF signal if reached V _ret. A heater driving circuit 4 supplies an AC voltage S5 to the halogen heater 5.

FIG. 23 is a flow chart of the operation of the temperature control circuit shown in FIG.

First, the comparator 6 compares the input voltages V _T and V _ret (100). If the target voltage V _ret is not reached (101), the halogen heater 5 is turned on (1).
03), if the target voltage V _ret is reached (101), the halogen heater 5 is turned off (102).

[0009]

FIG. 24 shows the temperature change of the heating roller.

ΔT ₁ is a temperature target, an overshoot amount with respect to T _ret , and ΔT ₂ is an undershoot amount. Q1 is a section from the start of the temperature control until the target temperature T _ret is reached, and Q2 is the subsequent temperature control section.

It can be seen from the figure that in the section Q1, the power supply becomes excessive and a large overshoot ΔT ₁ occurs. On the other hand, a considerable undershoot ΔT ₂ also occurs in the section Q2.

As described above, since the temperature changes ΔT ₁ and ΔT ₂ with respect to the temperature control target temperature are large, a uniform temperature distribution cannot be obtained in the recording paper conveying direction, and the quality deterioration of fixing unevenness is likely to occur.

[0013]

DISCLOSURE OF THE INVENTION The present invention for solving the above problems includes a heating device having a heating body maintained at a predetermined temperature, and heating an image on a recording material with heat from the heating body, A temperature gradient of the heating body, having a power supply control means for controlling the power supply to the heating body based on the temperature difference between the predetermined temperature, and a heating body maintained at a predetermined temperature, In the heating device for heating the image on the recording material with the heat from the heating body, there is a calculation means for calculating the time from the temperature gradient after the start of energization to the heating body until the temperature reaches a predetermined temperature. After the lapse of the required time, the energization of the heating body is stopped, and the constant temperature control at a predetermined temperature is performed later.

[0014]

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

FIG. 21 is a sectional view of an image heating apparatus for carrying out heat fixing according to the embodiment of the present invention.

The recording paper 12 which is conveyed from the direction of the arrow and which supports the unfixed powder toner image is conveyed to the conveying belt 13 and is conveyed to the nip portion between the heating roller 10 and the pressure roller 11.

Numeral 5 is a halogen heater which generates heat by supplying electric power, and the energization is controlled so that the resistance value of the thermistor 9 which is a temperature detecting element provided in contact with the surface of the heating roller is constant.

FIG. 1 shows a temperature control circuit of a heating device according to an embodiment of the present invention.

The same members as those in FIG. 23 are designated by the same reference numerals.

Reference numeral 6 denotes an AD converter for obtaining the digital value S1 from the voltage V _T obtained by the voltage dividing ratio of the thermistor 5 and the resistor R1. _{Reference numeral} 7 is an A / D converter for obtaining the digital value S2 from the control target voltage V _ret . The A / D converter 6 and the A / D converter 7 output digital values S1 and S2, respectively, to the control unit 1, which will be described later, at regular intervals.

Reference numeral 1 is a control unit for transferring the arithmetic data and selecting a control table stored in the ROM 2 which is a storage means.

A ROM 2 serving as a storage means stores a control table for the relationship between the temperature gradient and the power energization pattern.

Reference numeral 3 denotes a power energization pattern generator, which outputs a heater control signal S4 to the heater drive circuit 4 based on the energization pattern selection signal S3 from the control section 1.

Details of this control will be described later.

The heater driving circuit 4 drives the halogen heater 5 with an alternating current based on the heater control signal S4.

FIG. 2 shows a heater control signal S4 output from the pattern generator 3, which drives the heater control signal S4 having a different pulse width on the basis of the pattern selection signal S3 of the arithmetic processing unit 1 every predetermined period T _0. Output to circuit 4.
Here, the predetermined period T ₀ is divided into eight equal parts, but it is not always necessary to fix it to this value. When the power supplied to the fixing device in the full lighting and W _0, the power from the energizing Patan P ₀ to P ₈ is _{0, W 0 / 8,2W 0/} 8, ..., 7W 0/8, W 0
Becomes

FIG. 3 shows an example of a temperature gradient near the target temperature obtained when the energization pattern of FIG. 2 is output to the heater drive circuit 4. Assuming that the temperature gradient is k _i , k _i is proportional to the energization pattern and is as shown in FIG. This figure is a graph that is almost the same as a heating device for the same product.

K ₊₄ is a temperature gradient when the halogen heater is energized with an energization pattern P ₈ which is all lighting, and k ₊₃ is P ₇ ,
k ₊₂ is P ₆ , k ₊₁ is P ₅ , k ₀ is P ₄ , k _-1 is P ₃ , k _-2 is P ₂ , k _-3 is P ₁ , and k _-4 is deenergized P. It is ₀ .

In the energization pattern of P _{7 to} P ₅ , the temperature rises,
At P ₄ , the temperature change becomes almost zero.

The temperature is lowered by energization in the energization pattern of P _{3 to} P ₁ .

FIG. 4 is a table of FIG. The following control table is created based on this figure.

FIG. 5 is a control table stored in the storage means 2. In FIG. 5, ΔT _-3 , ΔT _-2 , and ΔT in the column direction
_-1 is the area where the difference between the measured temperature and the target temperature is negative,
ΔT ₀ is a region where the temperature difference is close to zero, and ΔT ₊₁ ,
ΔT ₊₂ and ΔT ₊₃ are regions where the temperature difference is positive. Further, k ₊₂ and k ₊₁ in the row direction are regions where the temperature gradient is positive, k
₀ is a region close to zero, and k ₋₁ and k ₋₂ are regions where the temperature gradient is negative.

FIG. 12 shows a flowchart of the operation of the control unit 1 described above.

The control modes of the control unit 1 are five modes 0 to 4.

In mode 0, the halogen heater 5 is not energized while waiting for a temperature control start instruction from the main controller of the image forming apparatus in which the present heating device is used.

Mode 1 is a state in which the maximum electric power is supplied to the halogen heater 5 by instructing the start of temperature control. This mode is performed for a time calculated by the control unit 1 which is determined not to overshoot.

Mode 2 is a state in which the power supply to the heater 5 is stopped.

Mode 3 is a control state when the surface temperature of the heating roller is higher than or equal to the target temperature for temperature control.

Mode 4 is a control state when the heating roller surface temperature is lower than the temperature control target temperature.

Next, the control operation based on FIG. 12 will be described.

In the figure, the control of the control unit 1 is 5 from 0 to 4.
There are two pattern modes.

In mode 0, the heater 5 is not energized while waiting for a temperature control start instruction from the main controller of the printing apparatus (not shown).

The mode 1 is a mode in which the temperature control is started in response to an instruction to start the temperature control from the main controller of the printing apparatus (not shown), and the maximum power is supplied.

This mode is performed for a predetermined time when it is determined that the temperature does not overshoot the target temperature.

The mode 2 is a state in which the power supply to the heater 5 is stopped and is used for preventing overshoot, and is performed for a predetermined time after the end of the mode 1.

Mode 3 is a control mode when the temperature detected by the thermistor is equal to or higher than the temperature control target.

Mode 4 is a control mode when the temperature detected by the thermistor is lower than the temperature control target temperature.

First, the difference between the target temperature and the temperature detected by the thermistor (hereinafter referred to as ΔT) is calculated (200).

Next, a temperature gradient (hereinafter referred to as K) is obtained (201).

The temperature gradient is the temperature (referred to as T _n-1 ) corresponding to S1 obtained by the A / D converter 6 last time and the current A / D.
The temperature (T _n corresponding to S2 obtained by the converter 6
, And the sampling period of the A / D converter 6 (called t _AD ), and K = (T _n −T _n−1 ) /
It is determined whether there is an instruction to stop the control from the main control unit of the recording device (not shown) calculated by the control unit 1 as t _AD (202).

If false, the control mode is judged (20
5) If true, the control mode is set to 0 (203), and the heater is energized to the minimum power (duty0) at which the heater is off.
%) And execute the following processing.

The control mode is judged (205).

If the control mode is 0, MODE-0 is executed (300), if the control mode is 1, MODE-1 is executed (400), and if the control mode is 2, MODE-2 is executed (500). , If the control mode is 3, MODE-3
Is executed (600), and if the control mode is 4, MODE-
4 is executed (700).

9 and 10 show the temperature change of the heating roller after the start of energization of the heater.

.. correspond to modes 1 to 4, respectively.

FIG. 9 shows a case where the temperature control target temperature is reached at the end of the mode 2, and FIG. 10 shows a case where the temperature control target temperature is not reached.

In the example shown in FIG. 9, the mode 3 is controlled after the mode 2, and in the example shown in FIG. 10, the mode 4 is controlled after the mode 2.

T ₁ is the time from when the heater is fully energized until the control temperature T ₁ is reached, and T ₂ is the predetermined time for ending the mode 2.

FIG. 11 shows the temperature differences ΔT _{-3 to} ΔT _-1 , Δ shown in FIG. 5 in the control modes shown in FIGS. 9 and 10.
Each section of T ₀ , ΔT _{1 to} ΔT ₃

[0060]

[Outer 1] It is a diagram showing the selection of the energization pattern when

[0061]

[Outside 2] In the above, P ₈ and P ₀ are selected respectively, and other than that, one of the energization patterns shown in FIG. 5 is selected according to the magnitude of the temperature gradient.

Next, each mode will be described in detail.

FIG. 13 is a flow chart for explaining the operation of mode 0. It is determined whether the temperature control is started (30
1) If true, set control mode to 1. If false, end without doing anything.

FIG. 14 is a flow chart for explaining the operation of mode 1. First, the maximum power (duty 100%)
Selection signal S of energization pattern (P8) for supplying the heater to the heater
5 is output to the pattern generator 3 (401).

It is judged whether or not the time k _t required to reach the target temperature has been obtained by the proportional calculation using the previously obtained temperature gradient (402).

If false, it is determined whether or not a predetermined time has elapsed from the start of temperature control, and if this determination is true, k _t is obtained and the next process (405) is executed.

If k _t is obtained, a timer (TM
The counting of time by R1) is started (409), and the next processing (405) is executed.

Next, it is judged whether or not the count value of TMR1 has reached k _t (405). If it is false, it is ended, and if it is true, the energization pattern (P0) selection signal S5 is set to turn off the energization of the heater. It is output to the pattern generator 3 (406). Then, TMR1 is cleared to prepare for the next processing (407), the control mode is set to 2 (408), and the processing is ended.

FIG. 15 is a flow chart for explaining the operation of mode 2. The counting of time by TMR1 is started again (501), and it is judged whether or not the count value of TMR1 reaches k _t (502). If it is false, the processing ends, and if true, TMR.
1 is cleared to prepare for the next process (503), the control mode is set to 3 (504), and the process ends.

FIG. 16 is a flow chart for explaining the operation of mode 3. It is determined whether the temperature ΔT is positively equal or negative (601), and if true, the process of lowering the temperature (hereinafter PWRD
WN) is performed (610), and if it is false, the control mode is set to 4 and FIG. 17 shows the process PWRDW described in FIG.
It is a flow chart explaining operation of N. Here, the selection signal S for selecting the energization pattern from the control table shown in FIG. 5 and selecting the energization pattern P _{0 to} P ₈ is used.
The PTRNO of 5 is selected and output to the pattern generator 3. In the figure, i indicates the row direction in FIG. 5, that is, the number of the temperature gradients k _{-2 to} k _{0 to} k ₊₂ , and j indicates the column direction in FIG. 5, that is, the number of the temperature differences ΔT _{-3 to} ΔT _{0 to} ΔT ₊₃ . Indicates.

First, 2 is substituted for i as an initial value (6
11) and 0 are substituted for j (612). It is determined whether or not j exceeds the maximum value of the number of columns, which is 3 (613). If true, the process ends, and if false, the next process (614) is performed.

Next, it is judged whether or not the temperature difference ΔT is larger than the maximum value ΔT ₃ of the temperature difference in the control table (61
4) If true, PTRNO is set to 0 (621), and if it is false, it is determined whether the temperature ΔT is ΔT _j ≦ ΔT <ΔT _{j + 1} (615). If the result of the determination in (615) is true, the following process (616) is executed, and if false, j
Is incremented by 1 (625), and the above-mentioned processing (613) is repeated again.

Next, it is judged whether or not i is larger than 2. If true, i is set to 2 (622) and the above-mentioned processing (61) is executed.
The PTRNO selected by j obtained as a result of 5) is output to the pattern generator 3 as the energization pattern selection signal S5 (620), and if false, the following process (617) is executed.

Subsequently, it is judged whether or not the temperature gradient k is larger than the maximum value k ₊₂ of the temperature gradient in the control table (61
7), if true, i is set to 2 (622) and the PTRNO selected by j obtained as a result of the above-mentioned processing (615)
Is output to the pattern generator 3 as the energization pattern selection signal S5 (620), and if false, the next process (61)
Execute 8).

Further, it is judged whether or not the temperature gradient k is larger than the minimum value k _-2 of the temperature gradient in the control table (61
8), if true, i is set to -2 (623) and the PTRN selected by j obtained as a result of the above-mentioned processing (615)
Pattern generator 3 with O as energization pattern selection signal S5
Is output to (620), and if false, the next processing (61
Execute 9).

Subsequently, it is judged whether or not k _i ≤k <k _{i + 1} (619). If the result of the determination in (619) is true, the PTRNO selected by (i, j) in the control table.
Is output as the energization pattern signal S5 to the pattern generator 3 (620), and the process ends. If false, i is incremented by 1 (62
5), the above-mentioned processing (616) is repeated again.

FIG. 18 is a flow chart for explaining the operation of mode 4. It is determined whether the temperature ΔT is negative (70
1) If true, a process for raising the temperature (hereinafter referred to as PWRUP) is performed (710), and if false, the control mode is set to 3 and the process ends.

FIG. 19 shows the process PWRUP described in FIG.
3 is a flowchart illustrating the operation of the above. This selects the energization pattern from the control table shown in FIG. 5 of the above P ₀ to P selection signal S5 for selecting the energization pattern of ₈
PTRNO is selected and output to the pattern generator 3.

In the figure, i indicates the row direction in FIG. 5, that is, the number of the temperature gradients k _{-2 to} k _{0 to} k ₊₂ , and j indicates the column direction in FIG. 5, that is, the temperature difference ΔT _{-3 to} ΔT _{0 to} ΔT. Indicates the number of ₊₃ .

First, as an initial value, -2 is substituted for i (711) and -3 is substituted for j (712). It is determined whether or not j exceeds the maximum value 0 of the number of columns (713). If true, the process ends. If false, the next process (714) is performed.

Next, it is judged whether or not the temperature difference ΔT is smaller than the minimum value ΔT _-3 of the temperature difference in the control table (71
4) If true, set PTRNO to 8 (721) and terminate. If false, it is determined whether temperature ΔT is ΔT _j ≦ ΔT <ΔT _{j + 1} (715). If the result of the determination in (715) is true, the following process (716) is executed, and if false, j
Is incremented by one (724) and the above-mentioned processing (713) is repeated again.

Next, it is judged whether or not i is larger than 2, and if true, i is set to 2 (722) and the above-mentioned processing (71) is performed.
The PTRNO selected by j obtained as a result of 5) is output to the pattern generator 3 as the energization pattern selection signal S5 (720), and if it is false, the following process (717) is executed.

Subsequently, it is determined whether or not the temperature gradient k is larger than the maximum value k ₊₂ of the temperature gradient in the control table (71
7), if true, i is set to 2 (722) and the PTRNO selected by j obtained as a result of the processing (715) described above.
Is output to the pattern generator 3 as an energization pattern selection signal S5 (720), and if false, the next process (71
Execute 8).

Further, it is judged whether or not the temperature gradient k is smaller than the minimum value k _-2 of the temperature gradient in the control table (71
8), if true, i is set to -2 (723) and the PTRN selected by j obtained as a result of the above-mentioned processing (715)
Pattern generator 3 with O as energization pattern selection signal S5
Is output to (720), and if it is false, the next process (71
Execute 9).

Subsequently, it is judged whether or not k _i ≤k <k _{i + 1} (719).

If the result of the determination of (719) is true, the PTRNO selected by (i, j) in the control table is output to the pattern generator 3 as the energization pattern signal S5 (720).
Then, if false, i is incremented by 1 (725), and the above-mentioned processing (716) is repeated.

FIG. 20 shows the temperature characteristics of the halogen heater 5 used in this embodiment.

As shown in the figure, the control is performed so as to output the optimum energization pattern based on each temperature difference and temperature gradient. Therefore, the overshoot at the initial stage of the control is small with respect to the control target temperature, and the temperature change thereafter is small. ing.

(Second Embodiment) In the above-mentioned embodiment, one control table for the temperature gradient and the temperature difference is stored in the memory, but a plurality of control tables can be selected according to the material and thickness of the storage material. It is also preferable to store the control table in memory.

When the state of the fixing device changes and it is difficult to control by the control table shown in FIG. 5, two kinds of control tables are prepared in the storage means 2 and used properly according to the state of the fixing device. May be.

For example, when the temperature gradient as shown in FIG. 7 occurs because the thickness of the recording paper is different and the amount of heat taken from the fixing device to the recording paper is different, the control table as shown in FIG. Is prepared and selected, and the same processing as that of the first embodiment is performed, it is possible to control with less temperature fluctuation.

Although the embodiment of the present invention has been described with reference to the heat roller fixing device, the present invention can be applied to other heating devices.

[0093]

As described above, according to the present invention, there is little overshoot when the temperature is raised to the target temperature after the start of constant temperature control, and the temperature change during constant temperature control can be reduced.

[Brief description of drawings]

FIG. 1 is a temperature control circuit diagram of a heating device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an energization pattern according to an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an energization pattern and a temperature gradient.

FIG. 4 is a table of FIG. 3.

FIG. 5 is a diagram showing a control table used in the first embodiment of the present invention.

FIG. 6 is a diagram showing a control table used in the second embodiment of the present invention.

FIG. 7 is a diagram showing a relationship between an energization pattern and a temperature gradient according to a second embodiment of the present invention.

FIG. 8 is a table of FIG. 7.

FIG. 9 is a diagram showing a control mode and a temperature change.

FIG. 10 is a diagram showing control modes and temperature changes.

FIG. 11 is a diagram showing a control mode and a temperature change.

FIG. 12 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 13 is a flowchart showing an operation in mode 0.

FIG. 14 is a flowchart showing an operation in mode 1.

FIG. 15 is a flowchart showing an operation in mode 2;

FIG. 16 is a flowchart showing an operation in mode 3;

FIG. 17 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 18 is a flowchart showing an operation in mode 4;

FIG. 19 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 20 is a diagram showing a temperature change in the example of the present invention.

FIG. 21 is a schematic cross-sectional view of a heat roller fixing device that is a heating device according to an embodiment of the present invention.

FIG. 22 is a diagram showing an example of a temperature control circuit.

23 is a flowchart illustrating an operation of the temperature control circuit of FIG.

FIG. 24 is a diagram showing a temperature change by the temperature control circuit of FIG. 22.

[Explanation of symbols]

 1 arithmetic processing device 2 storage means 3 pattern generator 4 between heater driving 5 halogen heater 6,7 AD converter 8 pull-up resistor 9 thermistor 10 target voltage source S1 measured voltage (digital value) S2 target voltage (digital value) S3 pattern selection Signal S4 Heater drive signal S5 Heater drive AC signal S6 Table creation data S7 Table data S8 Measurement voltage (analog value)

Claims (4)

[Claims] 1. A heating device having a heating body maintained at a predetermined temperature and heating an image on a recording material with heat from the heating body, wherein a temperature difference between a temperature gradient of the heating body and the predetermined temperature. A heating device comprising an energization control means for controlling energization power to the heating element based on the above. 2. The device according to claim 1, wherein the device has a plurality of energization patterns depending on a temperature difference according to a temperature gradient.
Heating device. 3. A heating device having a heating body maintained at a predetermined temperature and heating an image on a recording material with heat from the heating body, wherein the temperature gradient from the start of energization of the heating body to the predetermined temperature is increased. A heating device having a calculating means for calculating the time until reaching, and stopping the energization to the heating body after the time obtained by the calculating means elapses and then performing a constant temperature control at a predetermined temperature. .. 4. The heating device according to claim 3, wherein the power supply to the heating element is stopped for a predetermined time.