JP2925364B2 - Image heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating apparatus which is used in an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus and which heats an image on a recording material to fix or improve the surface properties.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 63-313182 and Japanese Patent Application Laid-Open No.
No. 7878 proposes a device using a heating element and a thin film which heat up quickly.

FIG. 1 shows an example of such a film heating apparatus.
It is shown in FIG.

[0004] Thin heat-resistant film 1 (or sheet)
Moving and driving means 11 for the film 1;
And a heater 6 that is fixedly supported and disposed on one surface side of the heater 6 and is disposed opposite to the heater 6 on the other surface side via the film 1 with respect to the heater 6. The film 1 has a pressure member 2 for bringing the visible image bearing surface of the recording material P to be image-fixed into close contact, and the film 1 is conveyed and introduced between the film 1 and the pressure member 2 at least when image fixing is performed. Moving the recording material P to be fixed in the forward direction at substantially the same speed, and passing through the nip portion as a fixing portion formed by pressing the heater 6 and the pressing member 2 across the moving film 1. Thus, the developed image carrying surface of the recording material is heated by the heater 6 via the film 1 to apply thermal energy to the developed image (unfixed toner image) to soften and melt the image, and then, after passing through the fixing unit. Separating the film 1 from the recording material P at the separation point A heating device for a basic.

[0005] Reference numeral 12 denotes a tension roller for applying tension to the film 1.

In such a film heating method, a heating element having a very small heat capacity and a rapid temperature rise can be used, and the time required for the heater to reach a predetermined heating temperature can be greatly reduced.

The temperature of the heater 6 is controlled by a thermistor 4.
So that the temperature detected by the heater 6 by the heater 6 becomes constant.
To control the energization of

[0008]

However, if the input voltage fluctuates and the resistance value of the heating element varies, the resistance value of the heating element changes, and the temperature control accuracy deteriorates significantly.

For this reason, it is conceivable to switch the energized power by detecting the input voltage or the resistance value of the heating element, but it requires a special detection circuit and unnecessary time for detection.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a heating element, a temperature detecting member for detecting the temperature of the heating element, and raising the heating element when the temperature detected by the temperature detecting member is lower than a predetermined temperature. Energization control means for supplying a first power to be heated to the heating element and supplying a second power to lower the temperature when the power is high;
In the image heating apparatus having the above, according to the temperature rising rate of the heating element detected during the period from the start of energization to the heating element to the predetermined temperature, during the constant temperature control after the predetermined temperature is reached. And an energizing power setting means for setting the first and second powers to be supplied to the heating element.

[0011]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic sectional view of a film heating apparatus according to the present invention and a block diagram of a control unit for controlling a heater surface temperature.

In this embodiment, the A4 size is set to 8 per minute at a recording material feeding speed (process speed) of 50 mm / sec.
This embodiment is applied to a heat fixing device of a laser beam printer (not shown) that outputs sheets.

The basic configuration of this heat fixing device is the same as that of FIG. 11, and a detailed description thereof will be omitted.

The heater 6 is provided along a direction substantially perpendicular to the direction of movement of the film, and is composed of a 1 mm-thick ceramic having good thermal conductivity and a resistance heating element provided on the lower surface of the ceramic and having a resistance value of 34Ω. .

A thermistor 4 as a temperature detecting element is provided on the upper surface of the ceramic.

The output signal of the thermistor 4 is input to the CPU 8 via an A / D converter. The CPU 8 controls the power supplied to the heating element 5 via the AC driver 9 based on the input signal, and adjusts the surface temperature of the heater to 180 ° C. As a method of determining the energizing power, a full energization with a duty of 100% at the time of rising is performed, and the thermistor 4 is heated from 160 ° C. to 17 ° C.
Detect the speed up to 0 ° C. From this speed, the power supply ratio (a%) of W is determined so that the power (W) at the time of full power supply to the heater 6 is assumed to be the optimum power ( _Wo ) for controlling the temperature to 180 ° C. .

FIG. 2 shows a flowchart of the temperature control method according to the present embodiment. 1) When energization (full wave) of the image forming apparatus having the film heat fixing device of the present embodiment is started, a reset signal is input to the CPU 8 and 2) measurement of the surface temperature of the heater 6 is started. Next, 3) the heater surface temperature is from 160 ° C. to 17
4) Temperature rise speed and 180 ° C
From the table showing the relationship between the optimum power values for the temperature control, the energization ratio wave number corresponding to the energization power is determined, and 5) the temperature control is started.

Here, the table for determining the energization ratio wave number will be described in detail.

Electric power supplied to heater 6 and heater surface 1
As shown in FIG.
One-to-one correspondence is provided. Thus, the input power can be known by measuring the heater heating rate.

Also, from this figure, the electric power (W _o ) for maintaining the temperature control at 180 ° C. can be found. This is when the heating rate is zero, and is 170 W in this embodiment. That is, 17
The heating element is maintained at 180 ° C. by continuously applying 0 W. The ratio (a%) of input power (W) to proper power ( _Wo ) is

[0022]

[Outside 1] It is made to appear.

Since the relationship between the heating rate and the input power is known from FIG. 3, the relationship between the heating rate and the energization ratio a (%) is also determined as shown in FIG. This is a basic table for power correction based on the temperature rise rate detection. In this embodiment, since the wave number control in which 16 half waves are one cycle is adopted, the wave number output from the heating rate is as shown on the left side of the vertical axis.

A heater 6 for detecting a heating rate is provided.
Is preferably around 180 ° C. This is because the change in resistance value due to the temperature of the thermistor 4 is not linear and changes exponentially, so that the sensitivity cannot be increased in a wide temperature range. Therefore, the maximum sensitivity is obtained near the temperature range actually controlled. in in order to set the value of R ₁ of the control circuit shown in FIG. Therefore, the rate of temperature rise is 100
C. or higher is preferred. Further, when the temperature approaches 180 ° C., the overshoot becomes large.
The time when the surface temperature of the sample reached 160 ° C. to 170 ° C. was detected, and the temperature was taken as the temperature rising rate.

By executing the above algorithm, the optimum energizing power at the time of temperature control for maintaining the heater 6 at a constant temperature is determined only by detecting the speed at which the surface temperature of the heater 6 rises.

(Second Embodiment) FIG. 6 shows a schematic sectional view of a film heating and fixing apparatus to which a second embodiment of the present invention is applied, and a block diagram of a control unit. In this embodiment, the thermistor 4
Correction value input unit 10 to correct the temperature measurement variation of
have. The correction value is input beforehand by measuring the temperature measurement error of each thermistor 3 and measuring the difference between the output value of the typical thermistor in the temperature range where data is input, or by installing the heater in a state where it is incorporated in the film heating and fixing device. 6, a rising temperature curve of the surface is obtained, and there is a method of obtaining a difference from an output voltage to be output by a typical thermistor in the same manner as described above. After the temperature measurement error of the thermistor 4 is determined by the above method, correction information is input to the CPU 8 using, for example, a dip switch. Based on this correction information, the CPU 8 shifts the wave number value in the table indicating the relationship between the temperature rising speed and the wave number as a whole, thereby enabling more stable temperature control regardless of the apparatus.

(Third Embodiment) FIG. 7 illustrates a further preferred embodiment of the present invention.

In the first and second embodiments, the constant power is continuously applied to the heating element when the temperature of the heating element is controlled to a constant value. It may be different from the temperature.

Therefore, in this embodiment, the temperature of the heating element is maintained at a constant temperature by repeatedly raising and lowering the temperature of the heating element.

That is, the heater temperature is detected by the thermistor even during the constant temperature control, and when the detection output of the thermistor is lower than a predetermined value corresponding to a predetermined fixing temperature, electric power for raising the temperature is applied to the heater, and the heater power is higher than the predetermined value. In this case, electric power for lowering the temperature is applied to the heater.

In the flowchart of FIG. 7, 1) to 3) are the first.
The description is omitted because it is the same as that of the embodiment.

In 4), the wave number H ₁ that gives a larger power than the wave number (solid line in the figure) that theoretically maintains the power at 180 ° C. in the table of FIG. 8 based on the heating rate between 160 ° C. and 170 ° C. _Two wave numbers of the wave number H ₂ that gives a small power are determined.

In 5), the temperature detected by the thermistor is 1
When a temperature higher than 80 ° C. is detected, the heater is energized by the wave number of H ₂ to lower the heater, and when a temperature lower than 180 ° C. is detected, the heater is energized by the wave number of H ₁ to perform the heater. Raise the temperature.

In this embodiment, electric power is also applied to the heater when the temperature of the heater during the constant temperature control is lowered. However, since the heat capacity of the heater is small, when the power is turned off, the temperature drops extremely, and the temperature control is performed. This is because the ripple becomes large.

As described above, according to this embodiment, the heater can be controlled at a constant temperature with a small ripple.

(Fourth Embodiment) In a state where the apparatus is cold and a state where it is sufficiently warm, the energy required to maintain the same temperature is not the same.

That is, when the apparatus is cold, for example, a large amount of heat is taken by the pressure roller, and the regulated temperature cannot be maintained unless a large amount of heat is given to the heater.

On the other hand, since the apparatus is warmed up after continuous paper feeding, the amount of heat taken by the heater is reduced.
The amount of heat required for the regulated temperature is reduced.

FIG. 10 shows this. FIG.
The optimum input power required after continuous paper feeding is 8
0W. At this time, the relationship between the power and the heating rate shifts to the left as the optimal power decreases.

In order to satisfy these two systems, in the table of FIG. 9, the binary conduction wave numbers H ₁ and H ₂ ′ are set so that H is slightly higher than the optimum power when the apparatus is cold, that is, 170 W. The wave number H ₁ is set so as to be the supplied power, and the wave number H ₂ ′ is set such that the supplied power is slightly lower than the optimum power required after passing H ₂ ′, that is, 80 W.

In this manner, even when the apparatus is cold, it is possible to control the temperature at a controlled temperature of 180 ° C. even in the re-feeding mode immediately after continuous feeding.

In the first to fourth embodiments, the wave number is controlled to control the power supply. However, the pulse width may be changed in the case of phase control or pulse power supply.

When the heat capacity of the heating element is small, it can be used as a heating roller or the like.

[0044]

As described above, according to the present invention, the heating element can be set at an appropriate set temperature without requiring a special detection circuit for detecting the input voltage or the resistance value of the heating element or a special time for the detection. The temperature can be controlled to a certain level.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image heating apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a heater heating rate and supply power.

FIG. 4 is a diagram showing a relationship between a heating rate and an optimum energizing power.

FIG. 5 is a diagram showing a temperature detection circuit.

FIG. 6 is a sectional view of a second embodiment of the present invention.

FIG. 7 is a flowchart of a third embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a heating rate and an optimum energizing power according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a relationship between a heating rate and an optimum energizing power according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a relationship between a heater heating rate and an optimum energizing power according to a fourth embodiment of the present invention.

FIG. 11 is a sectional view of a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film 2 Pressure roller 4 Thermistor 5 Heating element 6 Heater

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Daizo Fukuzawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Shunji Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo In Non-corporation (72) Inventor Yasumasa Otsuka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-3-12685 (JP, A) JP-A-57-70575 ( JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 13/20 G03G 15/20

Claims (4)

(57) [Claims] 1. A heating element, a temperature detecting member for detecting a temperature of the heating element, and a first electric power for raising the temperature of the heating element when the detected temperature of the temperature detecting member is lower than a predetermined temperature, the first electric power being supplied to the heating element to be high. And an energization control means for supplying a second electric power that sometimes lowers the temperature. In the image heating apparatus, the heating rate of the heating element detected during a period from the start of energization to the heating element until the predetermined temperature is reached is reduced. And an energizing power setting means for setting the first and second powers to be supplied to the heating element during the constant temperature control after the temperature reaches the predetermined temperature. 2. The apparatus according to claim 1, further comprising a film that moves together with the recording material supporting the visible image, wherein the visible image is heated by heat from the heating body via the film. Image heating equipment. 3. The heating element is used in a stationary state, and the film slides on the heating element.
Image heating equipment. 4. The method according to claim 1, wherein the heating rate is detected when the temperature of the heating element is 10 or less.
2. The image heating apparatus according to claim 1, wherein the heating is performed when the temperature is equal to or higher than 0 [deg.] C. and lower than the predetermined temperature.