JP2002214961A - Heat fixing device and image forming device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optimum fixing condition automatically set regardless of the kind of papers in an on-demand fixing device and the image forming device provided with the fixing device. SOLUTION: This fixing device and the image forming device perform control of an optimum fixing temperature by monitoring a heater temperature, heater power supply and a paper temperature after fixing. Concretely, when the heater power supply is lower or the paper temperature after fixing is lower than the prescribed level, the heater temperature is raised. Or, when the heater power supply is constant and the paper temperature after fixing is lower than the prescribed level, the amount of the heater power supply is increased. At this time, the upper limit value and the lower limit value are set in the heater temperature and the heater temperature is controlled so as not exceed these values.

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 (fixing device) used for an electrophotographic recording device and the like and an image forming apparatus having the same.

[0002]

2. Description of the Related Art Conventionally, many electrophotographic copying machines, printers, etc. employ a contact heating type heat roller fixing system having good thermal efficiency and safety and an energy saving type film heating system as fixing means. .

[0003] The heat fixing device of the heat roller fixing system basically has a heating roller (fixing roller) as a heating rotating body and an elastic pressure roller as a pressing rotating body pressed against the heating roller. An unfixed image (toner image) is formed and held in a pressure contact nip portion (fixing nip portion) of the pair of rollers by rotating the rollers, and a recording material (transfer material sheet, electrostatic recording paper, By introducing facsimile paper, printing paper, etc., and nipping and transporting the press-contact nip, the unfixed image is recorded on a recording material (hereinafter referred to as a transfer material) by the heat from the heating roller and the pressure of the press-contact nip. ) Is fixed by heat and pressure as a permanent fixed image on the surface.

Further, a film heating type fixing device (on-demand fixing device) is disclosed in, for example, JP-A-63-313182.
Gazette, JP-A-2-1577878, 4-44075-4
4083, 4-204980-2044984, etc., wherein a heat-resistant film (fixing film), which is a heating rotating body, is used as a heating element, and a pressing rotating body (elastic roller) is used.
A transfer material carrying an unfixed image is introduced into a press-contact nip formed by a heating element and a pressure member with the heat-resistant fixing film interposed therebetween, and is conveyed together with the heat-resistant film. This is an apparatus for fixing an unfixed image as a permanent image on a transfer material by heat from a heating body applied via a heat-resistant film and a pressing force of a press-contact nip portion.

A film heating type heating apparatus can use a linear heating element having a low heat capacity as a heating element and a thin film having a low heat capacity as a film, thereby saving power and shortening a wait time (quick start property). Is possible. Further, a film heating type heating device is known as a method for driving a film by providing a driving roller on the inner surface of the film as a film driving method, or a method of driving a film by a frictional force with a pressing roller using a pressing roller as a driving roller. In recent years, a pressure roller driving method having a small number of components and a low cost has been widely used.

[0006]

In the above-mentioned heat fixing device, it is known that the fixability of a toner image on a transfer material is greatly affected by the thickness and surface properties of the transfer material. In particular, the fixing property is significantly impaired with a paper type having a rough surface.

This is because a sufficient amount of heat is not supplied to the toner on the transfer material because the contact area between the heating member and the transfer material in the fixing nip is reduced.

As a result, it is necessary to increase the fixing pressure and the fixing temperature in order to obtain good fixing properties even for paper types having poor surface properties.

However, the method of increasing the fixing pressure tends to increase the driving torque of the fixing device and increase the cost of the apparatus. In particular, since a heating film as a heating rotating body slides at a fixing nip portion with respect to a heating heater as a heating body, the rotation torque tends to increase, so that it is difficult to increase the pressing force, and the total pressure is at most 147N. (15 kg) is set as the limit, and the linear pressure in the fixing nip region is set to be low. Therefore, in order to improve the fixing property of a paper type having poor surface properties, the fixing temperature must be increased.

However, if the fixing temperature is simply increased, an excessive amount of heat is supplied to thin paper or paper having a good surface property, which may cause hot offset or increase the curl amount of the paper. Evils occur.

In a film-type heat fixing device of a pressure roller driving system, when thin paper having high smoothness is passed,
If it absorbs moisture, etc., if the fixing operation is performed at a high fixing temperature, a large amount of water vapor will be generated, and a water vapor layer will be generated between the pressure roller and the paper. And the paper slips and stops in the fixing nip.

In addition to the fixing temperature, not only the fixing temperature but also the fixing nip width are important parameters for the opposing phenomena such as the fixability of the toner image on the transfer material and the curl of the transfer material, the hot offset of the toner, and the slip of the transfer material. Become. That is, if the fixing nip width is large, even if the fixing temperature is low, the amount of heat is easily transferred to the transfer material, so that it is possible to exhibit a good fixing property.On the contrary, phenomena such as curl, hot offset and slip occur. It will be easier.

The fixing nip width mainly depends on the hardness of the pressure roller and the pressing force of the pressure spring, but these have some variation, and the fixing nip width differs for each fixing device. Therefore, if the fixing temperature is set in consideration of the variation in the fixing nip width, phenomena such as fixability, curl, hot offset, and slip will occur for various paper types as described above with only one type of temperature setting. It is very difficult to satisfy everything.

As described above, it is difficult to achieve optimum fixing conditions for both a paper type having a rough surface and a paper type having a good smoothness. Conventionally, a user selects a fixing temperature setting according to the paper type. Although it has been supported, it is difficult to set the fixing mode with the parameter that is difficult for the user to understand, such as surface roughness. The optimum fixing temperature is automatically set according to the paper type (particularly the surface roughness). Was desired.

[0015] The present invention meets this need.
It is an object of the present invention to be able to automatically set an optimum fixing condition regardless of a paper type.

[0016]

According to the present invention, there is provided a nip formed by a heating rotator and a pressing rotator for an unfixed toner image formed and carried on a recording material. In the heating and fixing device for performing permanent fixing by passing through the inside of the unit, the heating rotating body is made of an endless film, and in the nip portion, a heating heater that is in contact with the inner peripheral surface of the film facing the nip portion is fixedly arranged on the film. And a means for measuring the temperature of the recording material after passing through the nip portion. By fixing at least one of them at the time of fixing according to the recording material temperature, only low power is supplied to paper types with a rough surface at the same fixing temperature. Automatically controls the appropriate fixing temperature according to the surface roughness of the recording material by, for example, correcting the fixing target temperature according to the amount of supplied power, and measures the recording material temperature after passing through the nip By doing so, the temperature of the recording material is low for thick paper having a large heat capacity, and the temperature of the recording material is high for thin paper having a small heat capacity, so that the paper thickness can be estimated. Fixability can be obtained.

As a more specific control method, there is a heating method in which an unfixed toner image formed and carried on a recording material passes through a nip formed by a heating rotator and a pressing rotator to permanently fix the toner image. In the fixing device, the heating rotator is made of an endless film, and in the nip portion, a heating heater in contact with the inner peripheral surface of the film facing the nip portion is fixed to the film, and the recording material after passing through the nip portion Has means for measuring temperature,
When controlling the energization of the heating heater or the heating rotator so that the temperature of the heating heater becomes the target temperature, the amount of power supplied to the heating heater and the temperature of the recording material after passing through the nip portion are monitored and monitored. By correcting the target temperature according to the result, it is possible to set an optimum fixing temperature according to the surface roughness and thickness of the paper as described above.

As another specific control method, an unfixed toner image formed and carried on a recording material is passed through a nip formed by a heating rotator and a pressing rotator to permanently fix the toner image. In the heat fixing device, the heating rotator is made of an endless film,
In the nip portion, a heater for heating, which is in contact with the inner peripheral surface of the film facing the nip portion, is fixedly arranged on the film, and has means for measuring the temperature of the recording material after passing through the nip portion. In controlling the energization of the heating heater so that the temperature of the heating rotator becomes the target temperature, the amount of power supplied to the heating heater is set in advance with respect to the target temperature, and the power is supplied to the heating heater. The same effect as described above can be obtained by correcting the target temperature and the amount of power supplied to the heater for heating in accordance with the temperature of the recording material supplied and passed through the nip.

In short, for an on-demand fixing device and an image forming apparatus equipped with the fixing device, the heater temperature
The power supply of the heater and the paper temperature after fixing are monitored, and the optimum fixing conditions can be automatically set irrespective of the paper type to perform the optimum fixing temperature control. Specifically, when the heater supply power is small or the paper temperature after fixing is low, the heater temperature is raised. Alternatively, the power supplied to the heater is fixed, and when the paper temperature after fixing is low, the power supplied to the heater is increased. At this time, upper and lower limit values are set for the heater temperature, and control is performed so as not to exceed the upper and lower limit values.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (1) Example of Image Forming Apparatus FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 1 denotes a photosensitive drum having a structure in which a photosensitive material such as OPC or amorphous Si is formed on a cylindrical substrate such as aluminum or nickel.

The photosensitive drum 1 is driven to rotate in the direction of the arrow, and its surface is first uniformly charged by a charging roller 2 as a charging device.

Next, a laser scanner 3 as exposure means
In response to 0, laser beam scanning exposure 3 which is ON / OFF controlled according to image information is performed, and an electrostatic latent image is formed on the photosensitive drum 1.

This electrostatic latent image is developed by the developing device 4,
Be visualized. As a developing method, a jumping developing method, a two-component developing method, or the like is used, and in many cases, a combination of image exposure and reversal developing is used.

On the other hand, a transfer material P as a recording material is separated and fed from the paper feeding unit 8 and passes through a sheet path 81 to form a pressure nip between the transfer roller 5 as a transfer device and the photosensitive drum 1. Paper is fed and transferred to the transfer section at a predetermined timing,
The visualized toner image on the photosensitive drum 1 is transferred onto the transfer material P.

The transfer material P holding the toner image is conveyed to the heat fixing device 6, where it is heated and pressed at the nip portion of the fixing device 6 and fixed on the transfer material to form a permanent image. The transfer material P that has exited the fixing device 6 is discharged to a paper discharge unit 83 through a sheet path 82.

On the other hand, the transfer residual toner remaining on the photosensitive drum 1 after the transfer is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

Reference numeral 100 denotes a control system of the printer.

(2) Heat fixing device 6 The heat fixing device 6 in this embodiment is disclosed in
878, 4-44075-44083, 4-20498
A pressure roller driving type film heating type fixing device disclosed in Japanese Patent Application Publication No. 0-204984 and the like.

FIG. 2 is a schematic cross-sectional model diagram of the film heating type fixing device of this embodiment. Reference numeral 10 denotes a thin flexible endless belt-like fixing film having a thickness of 20 to 150 μm as a heating rotating body, and a release layer is formed on a surface layer. This endless belt-shaped fixing film 1
Numeral 0 is externally fitted to the semicircular film guide member (stay) 13 with a margin in the circumferential length.

The film 10 has a total thickness of 100 μm in order to reduce the heat capacity and improve the quick start property.
m, preferably 60 μm or less and 20 μm or more, and a heat-resistant resin film such as polyimide or PEEK or a metal film such as a Ni electroformed film or a stainless seamless film is used. In the case of a metal film, since its thermal conductivity is good, its thickness is sufficiently practical if it is 150 μm or less.

Reference numeral 11 denotes a pressure roller as a pressure rotating body, which has a PFA tube layer as a release layer on a silicone rubber layer on a core metal such as iron or aluminum.

By rotating the pressure roller 11, the film 10 is brought into close contact with the surface of the heating element (heating heater) 12 in the clockwise direction indicated by an arrow, at least during execution of image fixing, while sliding on the surface of the heating element. It is rotationally driven without wrinkles at a peripheral speed, that is, substantially the same peripheral speed as the transport speed of the transfer material P carrying the unfixed toner image T transported from the image forming unit (not shown).

The heating element 12 is, for example, a ceramic heater and includes an energized heating element (resistance heating element) 12a as a heat source that generates heat by supplying power, and the temperature is increased by the heat generated by the energized heating element 12a.

When the heating element 12 is heated by supplying power to the energizing heating element 12a and the film 10 is driven to rotate, the elastic layer 11b of the pressure roller 11 is rotated.
The transfer material P is introduced into the press-contact nip portion N (fixing nip portion) formed between the heating member 12 and the transfer member P by the elastic force generated by the deformation of the transfer member P. And passes through the fixing nip N in the overlapping state.

In the process of passing the transfer material P through the fixing nip portion, thermal energy is applied to the transfer material P from the heating body 12 via the film 10 so that the unfixed toner image T on the transfer material P is heated and fused and transferred. After passing through the fixing nip, the material P is separated from the film 10 and discharged.

The fixing film 10 used in the heat fixing apparatus of the present embodiment is obtained by applying a polyimide varnish on a cylindrical mold and then heating and curing to form a polyimide layer having a predetermined thickness, and then applying an adhesive layer thereon. PFA powder is electrostatically coated or PFA, PTFE dispersion is sprayed or dipped, and then fired or PFA
A tube is coated on a polyimide film and welded to form a fluororesin layer having a predetermined thickness.

The pressure roller 11 is a core metal 11 made of iron, aluminum or the like.
After a is subjected to a surface roughening treatment such as blasting and the like, cleaning is performed, and then the core metal 11a is inserted into a cylindrical mold, and liquid silicone rubber is injected into the mold and cured by heating. At this time, in order to form a resin tube layer 11c such as a PFA tube as a release layer on the surface layer of the pressure roller, a tube previously coated with a primer is inserted into the mold, so that the rubber is cured by heat. At the same time, the tube and the rubber layer 11b are bonded. The pressure roller formed in this manner is subjected to secondary vulcanization after demolding.

The heating element 12 serving as a heating heater is
d is alumina (Al ₂ O ₃ ) or aluminum nitride (A
1N), a resistor made of silver / palladium is printed in a thick film on the substrate 12d to form a heating element pattern 12a having a desired resistance value. Further, a glass layer 12b is formed on the heating element as a protective layer and a sliding layer with the fixing film. Thermistor 1 which is a temperature detecting element is located on the back side of the heating element forming surface
2c is adhered and fixed, the heater temperature is monitored, and the monitored temperature information is input to the control circuit unit 20. Control circuit unit 20
Controls the AC driver 21 to maintain the heater temperature (fixing nip portion temperature) at a predetermined temperature, and controls the amount of power supplied from the AC power supply 22 to the heating element 12a of the heating element 12.

When a metal film having high thermal conductivity is used as the fixing film 10, the temperature of the metal film immediately after the fixing nip N is measured by a thermistor 12e as shown in FIG. It is also possible to control the power supply.

A non-contact temperature detecting element (a type incorporating a pyroelectric temperature sensor and a condensing lens) 16 is provided for monitoring the temperature of the transfer material after passing through the fixing nip. Monitor. The monitor temperature information is input to the control circuit unit 20.

The amount of power (supplied power) to the heating element 12a of the heating element 12 is finely supplied by well-known means such as phase control and wave number control based on PI (proportional / integral) control, and at the same time engine control. By storing the phase angle or the wave number information, the unit can know the amount of power supplied.

Here, the PI control determines the supply power amount W according to the following equation.

W1 = A * (T0-T) + IW = (V / V0) * W1 (unit is%, and the electric energy at full energization is 100%) where A is a constant (for example, 5) , T0 is a target temperature, T is a thermistor detection temperature, and this portion corresponds to P control.

If I is lower than the target temperature as a result of monitoring the heater temperature at regular intervals (for example, 500 msec), the supply power is increased by 5%, and if it is higher, the supply power is reduced by 5%. This corresponds to the I control.

W1 obtained as a result is supplied power obtained by the PI control, and W corrected to the ratio between the power supply voltage V monitored by the image forming apparatus and the standard voltage V0 (for example, 100 V) is supplied to the heating heater. Power. Here, the power supply voltage is monitored by a voltage detection circuit (not shown).

FIG. 4 is a graph showing a heating heater control temperature table according to this embodiment. The laser beam printer to which this control is applied has a maximum size width of letter size (width 216 mm), a print speed of 20 sheets per minute in letter size, and a transfer material feed speed of 120 mm / sec.
In the present embodiment, an algorithm for reducing the heater control temperature according to the number of continuous prints is employed. This is because the temperature of the pressure roller rises during continuous printing, so that the fixing temperature required to obtain sufficient fixability can be lowered.

In the case of intermittent printing, the intermittent printing 2
A control method is employed in which the number of sheets counted at intermittent times, such as the eleventh sheet during continuous printing, is increased by a certain amount with respect to the continuous time. The determination of intermittent printing / continuous printing is made by measuring the printing interval. In the present embodiment, the number of increased sheets during intermittent printing is set to 10.

Further, at the time of the first printing, the heater temperature is monitored at the start of printing, and the number of sheets at the start is determined according to the temperature.

More specifically, when the heater temperature at the time of printing the first sheet is 85 ° C. or less, the process starts from the set temperature of the first sheet. When the heater temperature at the time of printing the first sheet is higher than 85 ° C. Starting from the set temperature of the 21st sheet, the count is increased to 22 sheets and 23 sheets during continuous printing thereafter.

The heater temperature at the time of printing the first sheet is 1
When the temperature is 00 ° C. or higher, the temperature starts from the set temperature of the 41st sheet, and thereafter, during continuous printing, the number of sheets is increased to 42 sheets or 43 sheets.

In FIG. 4, three lines a, b, and c are a
Is set for thick paper, b is set for plain paper, and c is set for thin paper. The control circuit unit 20 selects which line is in the temperature control mode according to the transfer material temperature monitoring result.

Specifically, when the transfer material temperature monitor value is higher than the predetermined value T1, a line for thin paper is selected.
If the transfer material temperature monitor value is lower than T2, which is lower than the predetermined value T1, a line for thick paper is selected, and otherwise, a line for plain paper is selected.

In this embodiment, the basis weight for cardboard is 135 g /
m ² or more, for plain paper having a basis weight of less than 60～135G / m ^2,
For thin paper, the fixing temperature is set to a basis weight of less than 60 g / m ² and to correspond to special paper such as OHP paper and coated paper.

FIG. 5 is a graph showing the relationship between the paper weight after fixing and the paper basis weight and the heater temperature kept constant. From this graph, it can be seen that the paper temperature after fixing changes according to the paper thickness.

FIG. 6 is a graph showing a target power supply amount table corresponding to the set temperature table shown in FIG. These values substitute values obtained from required power supply for each set temperature of the representative paper type in each fixing mode by experiments.

FIG. 7 is a flowchart showing a fixing temperature control method according to this embodiment. After receiving the print command (step S1), after confirming the set fixing mode (the fixing mode set in the previous printing for continuous printing, and the default plain paper mode for the others) (S2), the temperature of the thermistor 12c is checked. Is monitored, the first number of sheets is set at the start of printing, and the target temperature is determined (S3).

Thereafter, the heater temperature is raised at a constant inclination. The supply power W1 at this time is determined by PI control.

Next, when the heater temperature reaches the target temperature, the rising slope of the heater temperature is controlled so that the transfer material enters the fixing device. When the transfer material enters the fixing nip area, the heater temperature is controlled by PI control. The supply power W1 is controlled so as to reach the target temperature.

At this time, a predetermined time (100 ms in this embodiment)
ec) Monitor the supplied electric energy (the average value of the electric energy determined to be necessary during the PI control) and make it correspond to the table of the target supplied electric power W0 with respect to the target temperature shown in FIG. At this time, the supplied power amount recognized by the image forming apparatus is merely an average value of the wave number or the phase angle, and the absolute value of the power amount cannot be recognized. Therefore, the power supply voltage supplied to the image forming apparatus is monitored, and a value converted by a ratio with respect to a standard voltage (for example, 100 V) is the amount of power actually supplied to the heater. That is, it is necessary to compare the product W of the measured power supply voltage V and the ratio V / V0 of the standard voltage V0 with the supplied power amount W1 to the target supplied power amount W0.

As a result, when the supplied power amount W is smaller than the target supplied power amount W0, it is determined that the surface roughness of the transfer material is large, the contact area between the fixing film and the transfer material is small, and the fixing property is not good. Increase the temperature.

More specifically, in the case of the plain paper mode, if the power amount differs by 3% or more from the target supply power amount, the target control temperature is increased by 5 ° C. If the power amount differs by 6% or more, the target control temperature is raised by 10 ° C., and this temperature is set as the upper limit temperature.

As a result, when PPC paper having good smoothness (surface roughness Ra: 3.1 μm, basis weight 75 g / m ² ) is supplied at a target set temperature of the first sheet, for example, the supplied power amount is 670 W Therefore, there is no change in the set temperature since the target supply power amount is larger than 660 W.

Also, a paper having a rough surface called so-called bond paper (surface roughness Ra: 4.0 μm, basis weight 75 g / m 2)
^{In 2} ), the power supply amount under the same condition is 635 W, which is lower than the target supply power amount 660 W by 3% or more, so the set temperature is increased by 5 ° C.

Further, a paper type called a laid paper having a further rough surface (surface roughness Ra: 4.54 m, basis weight 75 g / m ² )
In this case, the supplied electric energy is further reduced to 615 W, which is lower than the target supplied electric energy 660 W by 6% or more.

This is a phenomenon that occurs because the area of the paper type having a large surface roughness in contact with the fixing film in the fixing nip portion is small, so that the heat flow becomes small.

The reason why the amount of supplied power can be monitored in real time is that the temperature of the heater for heating is directly controlled in the nip portion, and the control as in this embodiment cannot be performed by the heat roller fixing device. It is.

Further, the paper temperature is monitored when the leading end of the paper passes through the measurement area of the paper temperature measuring sensor after passing through the fixing nip portion. When the paper temperature is between 90 and 100 ° C., it is determined that the paper is plain paper, and the above control is continued. I do.

If the paper temperature is lower than 90 ° C. (T2), the paper is determined to be a thick paper and a thick paper mode is set, and the heater target temperature is automatically increased by 10 ° C. with respect to the target temperature correction value based on the supplied electric power.

On the other hand, when the paper temperature is higher than 100.degree. C. (T1), it is determined that the paper is thin and the thin paper mode is set, and the heater target temperature is similarly reduced by 10.degree.

At the time of continuous printing, the temperature table for thick paper, plain paper, and thin paper is selected according to the previous paper temperature monitor value, and under this state, the heater target temperature correction based on the supplied electric power is performed. If the paper mode is the thick paper mode during continuous printing, the mode shifts to the plain paper mode when the paper temperature is higher than 100 ° C. (T1).

When the continuous printing is in the thin paper mode, when the temperature is lower than 90.degree.

As described above, in this embodiment, the amount of power supplied to the leading end of the transfer material is monitored, the target control temperature is made variable in accordance with the monitored value, and at the same time, the temperature of the sheet after fixing is monitored. In order to change the temperature control table, the heater control temperature is automatically increased for a paper type having a rough surface or thick paper, and the heater control temperature is automatically decreased for a thin paper type.

Further, in this embodiment, by monitoring the amount of power supply at the leading end of the transfer material, the amount of power supply can be monitored in many cases in an area where a toner image is not formed. It also has the advantage of wanting.

As described above, in this embodiment, the target supply power is set, and the fixing temperature is increased only when the target supply power falls below the target supply power. Conversely, the target supply power is set according to the type of paper having poor surface properties. However, it is also possible to lower the fixing temperature when the temperature exceeds the temperature.

Further, it is also possible to combine control such that the fixing set temperature is increased when the power supply falls below the target supply electric power, and the fixing set temperature is lowered when the power supply exceeds the target supply power.

[Second Embodiment] FIG. 8 is a flowchart for explaining this embodiment. This control is applied to a laser beam printer under the same conditions as in the first embodiment, and the target temperature setting table (FIG. 4) and the target supply power setting table (FIG. 5) are the same as those in the first embodiment. Is used.

After receiving the print command (step S
1) After confirming the set fixing mode (for continuous printing, the fixing mode set in the previous printing, and other default plain paper modes) (S2), monitor the temperature of the thermistor 14 and print one sheet at the start of printing. The number of eyes is set and the target temperature is determined (S3).

Thereafter, the heater temperature is raised at a constant inclination. The supply power W at this time is determined by PI control.

Next, the heater temperature rising slope is controlled so that the transfer material enters the fixing device when the heak temperature reaches the target temperature, and according to the target power supply table when the transfer material enters the fixing nip area. Supply power. At this time, the supplied power is determined by a wave number or a phase angle corrected according to a power supply voltage value supplied to the image forming apparatus.

Thereafter, the constant power is continuously supplied, and the heater temperature is monitored by the thermistor 14. Here, when the heater temperature fluctuates by a fixed amount with respect to the target temperature table of FIG. 4, the supply power is corrected.

More specifically, when the monitor temperature of the heater becomes 10 ° C. higher than the target temperature (5 ° C. in the cardboard mode), the target temperature is + 10 ° C. (+ 100 ° C. in the cardboard mode).
PI control is performed to maintain the temperature of 5 ° C).

Similarly, when the monitor temperature becomes lower than the target temperature by 10 ° C. (5 ° C. in the thin paper mode), the target temperature−
PI control is performed so as to maintain a temperature of 10 ° C. (target temperature−5 ° C. in the thin paper mode).

Further, the paper temperature is monitored when the leading edge of the paper passes through the measurement area of the paper temperature measuring sensor after passing through the fixing nip portion. When the paper temperature is between 90 and 100 ° C., the paper is determined to be plain paper and the above control is performed. continue.

If the paper temperature is lower than 90 ° C. (T 2), it is determined that the paper is thick paper, and the mode becomes the thick paper mode, and the heater power supply is automatically switched according to the power supply table in the thick paper mode.

The subsequent temperature control is performed in the same manner as described above.

On the other hand, when the paper temperature is higher than 100 ° C. (T1), it is determined that the paper is thin, and the thin paper mode is set. Similarly, the heater power supply is automatically switched according to the power supply table in the thin paper mode.

At the time of continuous printing, the temperature table for thick paper, plain paper, and thin paper is selected according to the previous paper temperature monitor value, and the amount of power supply is determined under that state.

If the paper mode is the thick paper mode during continuous printing, the mode shifts to the plain paper mode when the paper temperature is higher than 100 ° C. (T1). When the continuous printing is in the thin paper mode, the mode is changed to the plain paper mode when the temperature is lower than 90 ° C.

By performing such control, the first
In the same manner as in the embodiment, the heater control temperature is automatically lowered for the paper type having good smoothness because the supplied power amount is constant, while the heater is automatically heated for the paper type having a rough surface. Since the control temperature is increased, it is possible to avoid problems such as curling and hot offset while maintaining good fixing properties according to the type of paper.

When the heater temperature is monitored and the target temperature deviates from the target value by a certain value or more, the control is switched from the constant power supply control to the control for keeping the heater temperature constant so that the printing rate of the solid paper is good and solid black. In the case of fixing a high pattern, for example, the power supply tends to increase.Therefore, the heater temperature drop is likely to increase with simple constant power control alone. By adopting such an algorithm, it is possible to minimize such adverse effects.

Similarly, in the case of thin paper having a rough surface smoothness, power is unlikely to be consumed. Therefore, the amount of heater temperature rise is likely to be increased only by simple constant power control, which may cause hot offset. In some cases, such an adverse effect can be minimized by employing an algorithm such as this control. Further, by monitoring the paper temperature after fixing, it is possible to estimate the paper thickness, and control accuracy is greatly improved.

[0093]

As described above, according to the heat fixing apparatus of the present invention and the image forming apparatus having the same, only low power is supplied to the paper type having a rough surface at the same fixing temperature. It is possible to automatically control the appropriate fixing temperature according to the surface roughness of the recording material by correcting the target fixing temperature according to the conditions, and always obtain good fixing performance regardless of the surface properties Can be. Even when the fixing nip width differs for each fixing device, the fixing target temperature can be corrected to be lower in a fixing device having a wide nip width in which electric power is easily supplied to the recording material. In a fixing device having a narrow nip width that is difficult to be supplied to the material, it is possible to correct the fixing target temperature to be higher, and it is possible to minimize the fixing property variation between the fixing devices. As a result, the precision of the parts can be reduced, and the cost of the fixing device can be reduced.

Further, by monitoring the temperature of the recording material after fixing, the target temperature correction amount based on the result of monitoring the amount of supplied electric power is made variable according to the thickness of the recording material, whereby the supplied power varies. It is possible to set the optimal fixing temperature for the thickness of the recording material, which is another parameter,
More precise fixing temperature control becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a schematic cross-sectional view of the heat fixing device of the embodiment (part 1).

FIG. 3 is a schematic cross-sectional view of a heat fixing device according to an embodiment (part 2).

FIG. 4 is a graph showing a fixing control temperature table according to the embodiment.

FIG. 5 is a graph showing paper thickness and paper temperature after fixing.

FIG. 6 is a graph showing a power supply table according to the embodiment;

FIG. 7 is a flowchart showing heater temperature / supply power control according to the first embodiment;

FIG. 8 is a flowchart showing heater temperature / supply power control according to the second embodiment.

[Explanation of symbols]

1 photoconductor drum, 2 charging roller, 6 heat fixing device, 10 fixing film (rotating body for heating), 11
回 転 Rotating body for pressurization

Claims (6)

[Claims] A heat fixing device for permanently fixing an unfixed toner image formed and carried on a recording material by passing it through a nip formed by a heating rotator and a pressing rotator; The rotating body is made of an endless film, and in the nip portion, a heater for heating, which is in contact with the inside of the film facing the nip portion, is fixed to the film and has means for measuring the temperature of the recording material after passing through the nip portion. At the time of fixing, at least one of the target temperature and the target supply power amount of the preset heating heater or the heating rotating body is corrected according to the temperature of the recording material after passing through the nip portion. Heat fixing device. 2. A heating and fixing device for permanently fixing an unfixed toner image formed and carried on a recording material by passing it through a nip formed by a heating rotator and a pressure rotator. The rotating body is made of an endless film, and in the nip portion, a heater for heating, which is in contact with the inside of the film facing the nip portion, is fixed to the film and has means for measuring the temperature of the recording material after passing through the nip portion. When controlling the energization of the heating heater or the heating rotator so that the temperature of the heating rotator reaches the target temperature, the amount of electric power supplied to the heating heater and the temperature of the recording material after passing through the nip portion are controlled. A heating and fixing device which monitors and corrects the target temperature according to the monitoring result. 3. A heating and fixing device for permanently fixing an unfixed toner image formed and carried on a recording material by passing it through a nip formed by a heating rotator and a pressure rotator. The rotating body is made of an endless film, and in the nip portion, a heater for heating, which is in contact with the inner peripheral surface of the film opposite to the nip portion, is fixedly arranged on the film. When controlling the energization of the heating heater or the heating rotator so that the temperature of the heating heater or the heating rotator becomes the target temperature, the power supply amount to the heating heater is set in advance with respect to the target temperature. In addition, the power is supplied to the heating heater, and the target temperature and the amount of power supplied to the heating heater are corrected according to the temperature of the recording material after passing through the nip portion. Heat fixing device. 4. The heat fixing device according to claim 1, wherein the film has a thickness of 20 to 150 μm, and a release layer is formed on a surface layer. 5. An image forming means for forming and supporting an unfixed toner image on a recording material, and forming the unfixed toner image formed and supported on the recording material by a heating rotating body and a pressing rotating body. A heating and fixing device that performs permanent fixing by passing through the nip portion, wherein the heating rotary member is made of an endless film, and a heating heater that contacts a film inner peripheral surface facing the nip portion in the nip portion. The recording medium is fixed to the film, and has means for measuring the temperature of the recording material after passing through the nip portion. An image forming apparatus having a heating and fixing device, wherein at least one of them is corrected at the time of fixing in accordance with the temperature of a recording material after passing through a portion. 6. The image forming apparatus according to claim 5, wherein the film has a thickness of 20 to 150 μm, and a release layer is formed on a surface layer.