JPH0996990A - Heat-fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-fixing device capable of obtaining stable generation of heat and a rise of temp., and executing the quick start with efficiency, by varying frequency of AC current made to flow to an exciting coil, corresponding to the surface temp. of a rotary body. SOLUTION: To the high frequency AC current is made to flow to the exciting coil 12, the eddy current is made to flow so as to prevent the change of magnetic flux on the ferromagnetic conductive layer of a fixing film 11. By this eddy current, Joule heat corresponding to skin resistance of the conductive layer on the fixing film 11 is generated. Inside the exciting coil 12, a thermistor is embedded, by which the surface temp. of the fixing film 11 is detected, an oscillator of the AC power source is set to the optimum frequency, and thus the exciting coil 12 is controlled so that the AC current of the optimum frequency is allowed to flow. In this way, the surface temp. of the fixing film 11 is controlled to a specified value, on which the toner image is made heat- fixing. Namely, the frequency of AC current supplied to the exciting coil 12 is increased corresponding to the temp. rising of the fixing film 11, therefore the quick start is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device for heating and fixing a toner image on a transfer material by generating an eddy current by utilizing electromagnetic induction, and an electrophotographic apparatus equipped with this heat fixing device. The present invention relates to an image forming apparatus such as an electrostatic recording device.

[0002]

2. Description of the Related Art As a heat fixing device, a contact roller fixing device such as a heat roller fixing device and a film heating fixing device have been widely used.
These devices heat the toner image through a roller or film by passing an electric current through a halogen lamp or a heating resistor to heat the toner image, and transfer or transfer heat from the heating member to the nip portion where the transfer material passes. It is a heating method that supplies heat.

However, in the case of these heating methods, there is a problem that the heat radiation effect is large and the heat conversion efficiency is suppressed to a low level. Therefore, quick start of the fixing device is difficult,
Power consumption was also large.

As a means for solving these problems, Japanese Patent Publication No. 5-9027 discloses a method of generating an eddy current in a core metal portion of a fixing roller by a magnetic flux and generating heat by Joule heat. Details of the fixing device using this heating method will be described with reference to FIG. In FIG. 6, 50 is a fixing roller formed of a ferromagnetic material in a cylindrical shape and heated by induction heating. As the heating means, a high-frequency alternating current is caused to flow in the exciting coil 52 wound on the exciting iron core 51 to generate the magnetic field indicated by the arrow in the figure, thereby generating an eddy current on the fixing roller 50. is there. Here, reference numeral 53 is an auxiliary iron core arranged to face the exciting iron core 51 with the fixing roller 50 interposed therebetween so as to form a closed magnetic path. Further, 54 is a pressure roller having elasticity, which is pressed to the fixing roller 50 side by a pressure means (not shown) and forms a nip portion for fixing the toner image on the transfer material. There is.

By utilizing the generation of the eddy current as described above, the fixing roller 50 as a heating member can directly generate heat and the heat generation position can be made closer to the toner, which consumes less energy than a heat roller using a halogen lamp. Increased efficiency can be achieved.

[0006]

However, in the above-mentioned conventional method, since the fixing roller having a large heat capacity is heated, the efficiency cannot be said to be the best and the quick start is not sufficient. There wasn't. In particular, a heat fixing device using electromagnetic induction that satisfies both requirements of maintaining mechanical strength that can withstand pressure contact with a pressure roller and suppressing heat capacity to a quick start has not yet been achieved. .

For example, in the method disclosed in Japanese Patent Publication No. 5-9027, an eddy current is generated in a cylindrical body to generate Joule heat, but the exciting coil winding and the exciting iron core are heated and the amount of magnetic flux is increased. May decrease and the heat generation may become unstable. Furthermore, the specific resistance increases as the temperature of the fixing roller rises, so the surface heat generation decreases, the penetration depth of the induced current becomes deep, and the absorbed power cannot be obtained as expected, and the temperature rise of the fixing roller surface does not occur. There were times when it suddenly deteriorated. Also, when fixing the toner image at the nip part,
Since the transfer material draws heat from the fixing roller, it may be difficult to keep the fixing roller at a constant temperature when the absorbed power is not obtained.In particular, the mechanical strength of the fixing roller is satisfied for the purpose of quick start. If the heat capacity is set to be as small as possible within the range, the heating of the fixing roller may not catch up with the heat radiation to the transfer material, resulting in defective fixing. Further, from these reasons, it may be very difficult to realize a device with low power and to increase the speed of the device.

When the thermistor element is brought into contact with the surface of the fixing roller to adjust the temperature of the fixing roller, the thermistor itself is heated by the magnetic field generated by the exciting coil.
Accurate temperature detection sometimes became impossible.
In addition, the generation of noise due to the alternating magnetic field may make accurate temperature detection difficult.

Further, in the apparatus having the above-described structure in which the heat capacity of the fixing roller is made as small as possible, it may be difficult to keep the temperature of the nip portion constant due to the temperature of the pressure roller and the surrounding members. It was sometimes difficult to prevent offset and the like.

For example, FIG. 7 is a schematic diagram showing changes over time in the surface temperature of the fixing roller, the discharge temperature of the transfer material, and the surface temperature of the pressure roller during fixing. As shown in FIG. Even when the target temperature is adjusted to 190 ° C, the pressure roller has a large heat capacity, so the surface temperature gradually rises.
Similarly to the surface temperature of the pressure roller, the discharge temperature of the continuously conveyed transfer material gradually rises. Then, when the transfer material discharge temperature becomes β ° C. or lower, fixing failure occurs, and when it becomes α ° C. or higher, high temperature offset occurs.

However, in order to prevent fixing failure, if the fixing roller is heated so that the discharge temperature of the transfer material becomes β ° or more on the first sheet, the pressure roller is abnormally warmed by continuous conveyance, and several sheets are heated. There was a case where a high temperature offset was generated during the transportation. On the contrary, if the temperature of the initial fixing roller is controlled to be low in order to prevent high temperature offset, fixing failure may occur on the first sheet of the pressure roller which is cold. This is a phenomenon that occurs when the heat capacity of the fixing roller is set as small as possible, and is an essential matter to be solved in the quick start heat fixing device.

Therefore, according to the present invention, even when the method of generating heat using eddy current is adopted, stable heat generation and good temperature rise can be obtained, the efficiency is high, and the heat fixing device capable of quick start, and , Even when the temperature is detected by the thermistor while generating heat using eddy current,
A heat-fixing device capable of accurately detecting temperature, and further, a heat-fixing device capable of preventing an offset due to the stability of the nip temperature even when the heat capacity of a member for generating heat by using an eddy current is reduced, and heating of these devices. An object is to provide an image forming apparatus including a fixing device.

[0013]

According to the first invention of the present application, the above object is to provide a hollow rotor, an exciting coil provided inside the rotor, and a pressure contact with the rotor. A heating member disposed in the heating fixing device, wherein an eddy current is generated in the rotating body by applying an alternating current to the exciting coil, and the eddy current causes the rotating body to generate heat. This is achieved by making the frequency of the alternating current flowing through the exciting coil variable according to the surface temperature of the rotating body.

According to a second aspect of the present invention,
The above-mentioned object is achieved in the above-mentioned first invention by increasing the frequency of the alternating current flowing through the exciting coil as the surface temperature of the rotating body rises.

Further, according to a third invention of the present application, the above object is that in the first invention, the fixing target temperature is determined according to the rising speed of the surface temperature of the rotating member. To be achieved.

According to a fourth aspect of the present invention,
The above-mentioned object is achieved in the above-mentioned first invention by setting the frequency of the alternating current flowing through the exciting coil to be lower when the temperature is controlled to a constant temperature than when the rotor is started. It

Further, according to the fifth invention of the present application, the object is to provide a hollow rotating body, an exciting coil provided inside the rotating body, and an exciting coil arranged in pressure contact with the rotating body. A pressing member and a temperature detecting member for detecting the temperature of the rotating body, and an eddy current is generated in the rotating body by passing an alternating current through the exciting coil, and the rotating body is driven by the eddy current. In a heat fixing device that causes heat to be generated and maintains the surface temperature of the rotating body at a predetermined set temperature based on the temperature detected by the temperature detecting member, when the transfer material is not present in the heating portion, the energization of the exciting coil is stopped. In addition, it is achieved by having temperature determining means for determining the set temperature according to the temperature detected by the temperature detecting member at the time of stop.

According to the sixth aspect of the present invention,
The above-mentioned object is achieved in the above-mentioned fifth invention by the temperature determining means determining the set temperature based on the change in the temperature detected by the temperature detecting member when the energization of the exciting coil is stopped.

Further, according to the seventh invention of the present application, the above object is to provide a hollow rotating body, an exciting coil provided inside the rotating body, and a pressure contact with the rotating body. An image forming apparatus having a heat fixing device for generating an eddy current in the rotating body by causing an alternating current to flow through the exciting coil, and heating the rotating body by the eddy current. This is achieved by making the frequency of the AC voltage applied to the exciting coil variable according to the surface temperature of the rotating body.

Therefore, according to the first invention of the present application, the resistance value of the rotating body, which is the member to be heated, changes, and the amount of heat generated by the induced current increases or decreases. Also, by varying the frequency of the AC voltage applied to the exciting coil, the amount of heat generated is made desired, and highly efficient direct heating is performed.

According to the second aspect of the present invention,
Even if the resistance value of the rotating body increases due to the increase of the surface temperature of the rotating body and the degree of surface concentration of the induced current decreases, and the amount of heat generated by the induced current generated in the heated part decreases, Since the frequency of the alternating current flowing through the exciting coil is increased, the induced current itself is increased to compensate for the decrease in the heat generation amount.

Further, according to the third invention of the present application, the fixing target temperature is lowered when the rising speed of the surface temperature of the rotating body is fast, but in this case, the heat radiation amount from the rotating body is reduced. Since the amount is small, the temperature of the heated portion becomes an appropriate temperature. on the other hand,
When the surface temperature of the rotating body rises slowly, the fixing target temperature is increased. In this case, however, since the amount of heat radiated from the rotating body is large, the temperature of the heated portion is also an appropriate temperature.

According to a fourth aspect of the present invention,
The frequency of the alternating current flowing through the exciting coil is set to be lower when the temperature is controlled to be constant than when the rotating body is started up.However, when the frequency of the alternating current is low,
Since the change of the calorific value due to the induced current with respect to the change of the frequency is good, the calorific value is finely adjusted to reduce the temperature ripple.

Further, according to the fifth invention of the present application, the high-frequency alternating current flowing through the exciting coil is temporarily stopped when the transfer material is not passed, so that heat is generated by the induced current of the conductive temperature detecting member itself having a low heat capacity. And the generation of noise due to the alternating electric field are prevented, so that the temperature of the rotating body is accurately detected and the optimum temperature is set.

According to the sixth aspect of the present invention,
According to the fifth aspect of the invention, when the energization of the exciting coil is stopped, the temperature detecting member accurately detects the temperature,
Optimum temperature setting is performed.Furthermore, the temperature that changes depending on the heating condition is temporarily detected by the temperature detection member by temporarily stopping the energization of the excitation coil, and the optimum temperature is set according to the change in the detected temperature. Temperature control is performed.

Further, according to the seventh invention of the present application, in the heat fixing device of the image forming apparatus, the resistance value of the rotating body changes due to the surface temperature change of the rotating body which is the member to be heated, Even if the amount of heat generated by the induced current increases or decreases, the frequency of the AC voltage applied to the exciting coil is made variable to obtain the desired amount of heat generation, and direct heating with high efficiency is performed to perform a good image forming operation. .

[0027]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. FIG.
FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

In FIG. 1, 1 is a photosensitive drum, and O
A photosensitive material such as PC, amorphous Se, and amorphous Si is formed on a cylindrical substrate made of aluminum, nickel, or the like. 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, according to the image information,
Scanning exposure is performed by the laser beam 3 controlled to be N / OFF, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As a developing method, a jumbing developing method, a two-component developing method, an FEED developing method, or the like is used, and image exposure and reversal developing are often used in combination.

The visualized toner image is transferred from the photosensitive drum 1 onto the transfer material P conveyed at a predetermined timing by the transfer roller 5 as a transfer device. At this time, the transfer material P is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5 with a constant pressure. Transfer material P on which this toner image is transferred
Is transported to the fixing device 6 and fixed as a permanent image. On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

Next, the structure of the heat fixing device 6 according to the present invention will be described with reference to FIG. In FIG. 2, reference numeral 10 denotes a fixing member, and the fixing member 10 includes a fixing film 11, which is a rotating body, an exciting coil 12, and a stay 13.

The fixing film 11 is made of polyimide, polyamideimide, PEEK, PES, PPS, PFA, PT.
10μ thick with single or composite resin such as FE and FEP
A film base material having a thickness of m to 100 μm is formed, and Fe, Co, ferrite, which is a ferromagnetic member, or a metal such as Cr, Cr, or an alloy composed of these is formed on the film base material with a thickness of 1 μm to 100 μm, PF on the outermost layer
A heat-resistant resin having good releasability such as A, PTFE, FEP and silicone resin is coated alone without being mixed.
The fixing film 11 is loosely fitted onto the stay 13 made of liquid crystal polymer, phenol resin, etc. with a margin, and is rotatably arranged in the direction of the arrow.

The exciting coil 12 is fixed to the stay 13 so as to contact the inner surface of the fixing film 11, and heats the fixing film 11 by electromagnetic induction as described later.

A pressure member 20 such as a pressure roller is disposed below the fixing member 10, and the pressure member 20 is pressed by a pressure means (not shown) toward the fixing member 10.
Is sufficiently pressed from both ends in the longitudinal direction to form a nip portion necessary for heat fixing, and is rotated in the direction of the arrow from the end in the longitudinal direction through a cored bar 21 by a rotation driving means (not shown). Driven. As a result, the fixing film 11 is driven to rotate outside the stay 13.

The pressing member 20 is provided with an elastic layer 22 formed by foaming heat resistant rubber such as silicone rubber or fluororubber or silicone rubber on the outside of the cored bar 21, on which PFA, PTFE, A release layer such as FEP may be formed.

Next, details of the exciting coil 12 are shown in FIG. In FIG. 3, 12a is a core made of a ferromagnetic material such as ferrite. Typical shapes of cores generally used for switching power supplies are I type, E type,
Although there is a U type or the like, in the present embodiment, an I type core is used as shown in FIG. However, the core of the exciting coil applicable to the present invention is not limited to this,
Other shapes can be substituted. Further, on the fixing film 11 side of the core 12a, a glass layer having a small frictional resistance or a releasing layer such as PFA or PTFE may be provided as a heat insulating layer.

A conductor wire 12b is wound around the core 12a, and is connected to a power source 16 whose frequency is variable in the oscillation circuit from the end portion in the longitudinal direction. Therefore, the power source 16
High frequency alternating current of 0 kHz to 1 MHz, preferably 20
Excitation coil 1 for high-frequency alternating current of kHz to 800 kHz
When the magnetic field is applied to 2, the exciting coil 12 forms a magnetic field, and at this time, an eddy current flows in the ferromagnetic conductive layer of the fixing film 11 as if hindering the change in the magnetic field. This eddy current generates Joule heat according to the skin resistance of the conductive layer of the fixing film 11.

Further, a low heat capacity conductive chip thermistor 14 is embedded in the exciting coil 12 as a temperature detecting member with a part thereof protruding outside the core 12a.
The surface temperature of the fixing film 11 is detected by the chip thermistor 14, and the detected surface temperature information of the fixing film 11 is sent to the CPU via an A / D converter (not shown).
Based on this, the CPU 15 sets the oscillator of the AC power supply 16 to the optimum frequency, and controls so that the winding 12b of the exciting coil 12 is supplied with the AC current of the optimum frequency. As described above, the surface temperature of the fixing film 11 is controlled to a predetermined value, and the toner image on the transfer material conveyed to the fixing nip portion is heated and fixed.

Here, the eddy current I flowing on the fixing film 11 almost concentrates on the exciting coil 12 side surface of the conductive layer due to the skin effect, and is proportional to the skin resistance of the conductive layer of the fixing film 11. Although heat is generated by the generated electric power, when the temperature of the member to be heated rises due to heating, the rise of the temperature in the fixing nip portion may be abruptly deteriorated.

This is because there is a strong relationship between the penetration depth δ of the induced current I generated in the heated member and the resistivity ρ of the heated member.
If the resistivity ρ rises as the temperature of the heated member rises,
This is because the penetration depth δ increases and the absorbed power due to the induced current generated in the heated member decreases. Here, the penetration depth δ is a value indicating the degree of surface concentration of the induced current I,
The smaller this value, the more concentrated the eddy current I is on the surface.

Therefore, in this embodiment, the fixing film is efficiently heated by the following configuration and algorithm.

As the fixing film 11 of the member to be heated, a ferromagnetic conductive layer containing Ni as a main component and having a thickness of 50 μm is formed on a polyimide-based film having a thickness of 40 μm, and PTFE is further coated with a thickness of 20 μm as a release layer. . The ferromagnetic conductive layer is a member having a stable relative magnetic permeability in the operating temperature range and in the operating frequency range of 1.5 MHz or less, and the relative magnetic permeability μr thereof is about 200.
Further, the resistivity of the ferromagnetic conductive layer is about 7 × at room temperature of 20 ° C.
It is a member of 10 ⁻⁸ Ωm and about 10 × 10 ⁻⁸ Ωm at 100 ° C., which increases substantially proportionally with temperature rise.
The power consumption of the exciting coil 12 during use was controlled to be constant. The fixing film 11 was induction-heated with an initial power consumption of 200W. Pressurizing member 20 has an outer diameter of 1
Silicone rubber having a thickness of 3 mm was formed on a cored bar 21 having a diameter of 4 mm, and FEP was coated as a release layer to obtain an outer diameter of 20 mm and a hardness of 45 ° C. (Asker-C).

The heating algorithm for the fixing film 11 is shown below.

After the image forming apparatus receives the print command, the temperature of the fixing film 11 is detected by the chip thermistor 14.

Refer to the table below according to the detected temperature of
The oscillation frequency of the oscillator of the AC power supply 16 applied to the exciting coil 12 is determined, and energization is started.

The set frequency is changed every 0.1 seconds according to the temperature detected by the chip thermistor 14 with reference to the following table.

[0047]

[Table 1]

By repeating the above, the fixing film 11 is heated under the conditions that the room temperature is 20 ° C. and the surface temperature of the pressing member 20 is also 20 ° C., and the fixing film 1 reaches the target temperature of 190 ° C.
FIG. 4 shows the relationship between the heating time when 1 is started and the surface temperature of the fixing film 11. Further, for comparison, heating was also performed at a constant frequency while maintaining the initial 200 kHz.

In FIG. 4, the horizontal axis represents the measurement time after the start of the AC application, and the vertical axis represents the temperature detected by the chip thermistor 14 for the fixing film 11. From the figure, when an alternating current is applied at a constant frequency, the temperature rise rate deteriorates as the temperature of the fixing film 11 rises, and the temperature of the fixing film 11 reaches 150 ° C. in about 12 seconds, but it takes 1 minute. Also did not reach the target temperature of 190 ° C. On the other hand, in the present embodiment, the initial rise is the same as when the frequency is constant, but since the temperature rise rate does not change and rises in the same manner as the initial rise, it takes about 7 seconds to reach 150 ° C., and the target temperature reaches 190 ° C. Got up in about 10 seconds.

As described above, by increasing the frequency of the alternating current applied to the exciting coil 12 as the temperature of the fixing film 11 rises, the power absorbed by the fixing film 11 is not reduced, and it is suitable for quick start. It has become possible to start up.

By the way, when the print command is transmitted to the image forming apparatus, the temperature of the fixing roller 11 is not always room temperature, and the temperature of the pressing member 20 also greatly differs depending on the previous printing condition. Therefore, when the fixing film 11 is heated by the above algorithm, for example, when the pressure member 20 is sufficiently heated, the heat radiation from the fixing film 11 to the pressure member 20 is small and the fixing film 11 rapidly reaches the target temperature. Be heated. As a result, excessive heating is performed in the nip portion to fix the toner image on the transfer material. Therefore, high temperature offset or the like may occur.

On the other hand, as in the above experiment, the pressure member 20
Fixing film 1 when is not sufficiently heated.
Even when 1 reaches the target temperature, the amount of heat radiated to the pressure member 20 side is large, and there is a possibility that fixing failure may occur.

Therefore, as a means for solving these problems, in the present embodiment, the following algorithm is added between the above algorithms.

After the energization of the exciting coil 12 is started, 0.2
The temperature of the fixing film 11 after a second is measured by the chip thermistor 14
Detected with, measure the temperature rise speed and refer to the table below,
Set the target fixing temperature.

[0055]

[Table 2]

By the above algorithm, the pressing member 20
It was possible to prevent problems such as improper fixing and high temperature offset depending on the heating conditions. Further, in the above configuration, the fixing target temperature is determined by the temperature rising rate within a fixed time,
In this case, the target temperature can be determined by the same algorithm even if the time required for the temperature to rise is measured. Further, the temperature rising rate may be calculated by judging how many times the predetermined temperature range is detected within a fixed time.

As described above, the fixing film 11
By increasing the frequency of the alternating current applied to the exciting coil 12 as the temperature rises, the startup suitable for quick start can be performed without reducing the power absorbed by the fixing film 11, and further, after the startup, Since heating is performed with the largest absorbed power, sufficient heat can be generated compared to heat dissipation to the transfer material even when the transfer material is continuously conveyed, and problems such as poor fixing and low temperature offset occur even during continuous heat fixing. It is possible to carry out stable heat fixing without causing any trouble. This is a method suitable for increasing the speed of the image forming apparatus as compared with the conventional apparatus that applies a constant frequency. Further, by setting the fixing target temperature in each situation by measuring the rate of temperature rise due to energization of the exciting coil 12, good heat fixing can be performed without causing fixing failure, high temperature offset, and the like.

Further, the above configuration and heating method can be carried out without complicating the apparatus, and are a method with no cost.

(Second Embodiment) The second embodiment of the present invention will be described below. The structure of the entire apparatus is the same as that of the first embodiment shown in FIG. 1, and the structure of the heat fixing device is also the same as that of the first embodiment shown in FIGS. .

In this embodiment, the transfer material on which the toner image is printed is conveyed through the nip portion formed by the fixing film 11 and the pressure member 20, and applied to the exciting coil 12 in the process of fixing the toner image. The present invention implements a temperature control system that provides the optimum frequency of the alternating current that is generated and that has a small fluctuation in power consumption.

As shown in the first embodiment, the relationship between the temperature of the fixing film 11 and the absorbed power is as follows.
It depends largely on the frequency of the alternating current applied to No. 2 and by increasing the frequency in accordance with the rise in temperature, it was possible to prevent the rise of temperature from deteriorating, but after the fixing film 11 has risen to the target temperature, transfer In order to heat and fix the toner image on the material, the fixing film 11 must be kept at a constant temperature.

Therefore, first, in the structure of the first embodiment, the frequency of the alternating current applied to the exciting coil 12 is set to a lower frequency side than the frequency at which the absorbed power of the fixing roller 11 peaks, and a high frequency. The change in absorbed power was compared between the case of setting to the side.

As a result, 20 kHz to 3 on the low frequency side.
About 7% to about 98% of the absorbed power at 310 kHz at which the absorbed power of the fixing film 11 reaches a peak with a fluctuation of 00 kHz.
The amount of change up to% was obtained. Moreover, it was found that the absorbed power increased substantially proportionally with the increase of the frequency in this frequency range. On the other hand, 320 kHz on the high frequency side
Only a variation of about 70% to about 99% was obtained with a variation of 1 MHz.

This is because the relationship between the frequency of the alternating current applied to the exciting coil 12 and the absorbed power of the fixing film 11 is high in contrast to the abrupt change of the absorbed power in the frequency region lower than the frequency at which the absorbed power reaches its peak. This is because it is changing gently in the frequency domain. Therefore, by applying an alternating current to the exciting coil 11 at a frequency lower than the peak, which is a region in which the change of the absorbed power with respect to the frequency change is good, the temperature of the fixing film 11 is maintained at a constant temperature by adjusting the temperature with arbitrary power. I decided.

The results of measuring the overshoot and temperature change (ripple) of the fixing film when the fixing film 11 is temperature-controlled to a constant temperature in a frequency range lower than the frequency at which the absorbed power reaches its peak are shown below. In the experiment, the fixing target temperature was set to 190 ° C., and after the temperature of the fixing film 11 rose, the toner image on the transfer material was continuously fixed. Also,
The set frequencies are as shown in the table below.

[0066]

[Table 3]

[0067]

[Table 4]

The measurement results are shown in FIG. In FIG. 5, the absorbed power of the fixing film 11 has a peak for comparison.
The results of performing temperature control by controlling on / off of the applied alternating current at 10 kHz are also shown.

As can be seen from the figure, when the power is turned on / off at the frequency at which the absorbed power reaches the peak, the overshoot and the ripple are large, whereas both are suppressed in the temperature control method according to the present embodiment. It can be seen that temperature control close to constant temperature control is performed.

This indicates that the temperature control of the chip thermistor 14 after the temperature detection is properly performed by changing the absorbed power of the fixing film 11 little by little. Furthermore, when the toner image on the transfer material was heated and fixed by each of the above temperature control methods, when the applied alternating current was turned on and off, there was uneven fixing property in the transfer material conveyance direction. On the other hand, in this embodiment, uniform fixability was obtained.

As described above, the temperature of the fixing film 11 is controlled by changing the frequency little by little in a frequency region lower than the frequency at which the absorbed power of the fixing film 11 reaches the peak, so that the toner image on the transfer material is nipped. Even during continuous fixing, uniform fixing property can be obtained by stable temperature control with small ripple.

(Third Embodiment) The third embodiment of the present invention will be described below. The structure of the entire apparatus is the same as that of the first embodiment shown in FIG. 1, and the structure of the heat fixing device is also the same as that of the first embodiment shown in FIGS. 2 and 3. Omit the explanation.

In this embodiment, it is possible to detect the accurate fixing film temperature by preventing the detected temperature from being different from the actual fixing film temperature due to the heat generation of the chip thermistor due to the induction heating and the influence of the noise due to the alternating magnetic field by the exciting coil. The method to do is presented.

That is, the chip thermistor 1 in FIG.
Since 4 is formed of a conductive member, the chip thermistor 14 is also heated by induction heating in the same manner as the fixing film 11 is heated by induction heating.
The detected temperature is slightly higher than the temperature of 1. Also,
The thermistor 14 picks up noise due to the generation of the alternating magnetic field.

Therefore, the fixing film 11 and the pressing member 20
When the transfer material is not conveyed through the nip portion consisting of, the high-frequency alternating current applied to the exciting coil 12 is momentarily stopped to prevent heat generation of the chip thermistor 14 due to induction heating, and to prevent generation of an alternating magnetic field. Prevented noise components from being generated.

When the chip thermistor 14 is prevented from self-heating in this way, the temperature of the fixing film 11 is reached immediately because the chip thermistor 14 has a low heat capacity, and
Since it does not pick up noise, the chip thermistor 1 at this time
The detected temperature of 4 is an accurate surface temperature of the fixing film.

The temperature control method in this embodiment will be described below. First, the AC application to the exciting coil is turned off during the standby for waiting the print command, and after the image forming apparatus receives the print command, energization to the exciting coil is started according to the following algorithm.

Before the energization of the exciting coil 12 is started, the temperature of the fixing film is detected by the chip thermistor 14.

Based on the detected temperature of, the controlled temperature shown in the following table is determined as the fixing target temperature.

[0080]

[Table 5]

The application of the high frequency alternating current to the exciting coil 12 is started and the fixing target temperature is heated.

When the fixing film reaches the target temperature, the exciting coil is de-energized and the chip thermistor 14 measures the accurate temperature again.

The control temperature is corrected on the basis of the temperature measured in step.

After the toner image on the transfer material is fixed by heating, the procedure returns to and the next transfer material is prepared.

As described above, the fixing film 11 is accurately affected by the chip thermistor 14 having a low heat capacity without being affected by the alternating magnetic field.
The temperature of the toner image on the transfer material can be fixed by heating at the optimum temperature control temperature according to the heating condition of the pressure roller and the like by the temperature detection before the start-up.
As a result, appropriate heat fixing can be performed without causing low temperature offset, poor fixing, and high temperature offset.

(Fourth Embodiment) The fourth embodiment of the present invention will be described below. The structure of the entire apparatus is the same as that of the first embodiment shown in FIG. 1, and the structure of the heat fixing device is also the same as that of the first embodiment shown in FIGS. 2 and 3. Omit the explanation.

In the present embodiment, a method for accurately detecting the natural cooling speed, which changes according to the heating condition of a device such as a pressure roller, with a chip thermistor to determine the optimum temperature controlled temperature is presented.

Generally, in a heat fixing device in which the heat capacity of the fixing member 10 is suppressed and the pressure member 20 has a certain heat capacity, the device temperature of the pressure member 20 or the like largely changes according to the number of fixed sheets. Therefore, in the initial stage, the pressure member 20 is not warmed up, and conversely, when the number of fixed sheets is increased, the pressure member 20 is sufficiently heated. When heat fixing is performed in such a situation, low temperature offset, poor fixing, high temperature offset,
This will cause wrinkles on the transfer material.

In order to avoid this, it is effective to set a multi-step temperature control target temperature as shown in the third embodiment. However, it is difficult to limit the warming condition of the pressing member 20 only by detecting the temperature when the transfer material is not in the nip. That is, when the number of fixings is small, the temperature gradient of the pressure member 20 is large, and there is a possibility that the warming state of the pressure member 20 may be erroneously detected depending on the detection timing. Therefore, in this embodiment, the warming condition of the device such as the pressure roller is accurately grasped and the target temperature for temperature control is determined by the following method.

The algorithm for setting the temperature control target temperature according to this embodiment will be described below.

After the transfer material passes through the fixing nip, the excitation coil 12 is forcibly turned off for 0.5 seconds.

The temperature drop of the fixing film for 0.5 second after turning off the power is measured with a chip thermistor.

The temperature control target temperature is determined from the rate of temperature decrease of the fixing film based on the following table.

[0094]

[Table 6]

By the above method, the chip thermistor 14
It is possible to accurately estimate the warming condition of the pressure roller 20 from the temperature lowering speed of the fixing film 11 without being affected by the noise due to the self-heating of the fixing film and the alternating magnetic field, and to change the set temperature of the fixing film accordingly. As a result, problems such as low temperature offset, poor fixing, high temperature offset, and wrinkles can be solved. That is, the target temperature of the fixing film 11 can always be switched at an appropriate timing regardless of whether the heat fixing device is sufficiently cold or sufficiently warm.

The target temperature may be determined every two sheets, every three sheets, or every predetermined number of sheets, but it is preferable to perform it every time. However, since the apparatus temperature is saturated when continuous printing is continued, this algorithm does not have to be performed after heat-fixing the specified number of sheets.

Next, another fixing target temperature setting algorithm of this embodiment will be described below.

After the transfer material passes through the fixing nip, the excitation coil 12 is forcibly turned off for 1.5 seconds.

The temperature reached by the detection of the chip thermistor is measured 1.5 seconds after the power is turned off.

The fixing target temperature is determined in the following table according to the measured temperature.

[0101]

[Table 7]

Another method will be described.

After the transfer material passes through the fixing nip, the energization of the exciting coil 12 is forcibly turned off.

After the power is turned off, the elapsed time until the temperature reached by the detection of the chip thermistor reaches 155 ° C. is also measured.

The fixing target temperature is determined in the following table according to the elapsed time. However, even if the power is turned off for 1.7 seconds or more, 1
If the temperature does not reach 55 ° C, the temperature should be adjusted to 160 ° C.

[0106]

[Table 8]

According to this algorithm, when the pressure roller is not heated too much, the energization of the exciting coil is off for a short time, and conversely, when the pressure roller is overheated. Since the time during which the energization to the exciting coil is turned off becomes long, there is an effect of reducing the temperature difference of the device such as the pressing member 20 in both cases.

[0108]

As described above, according to the first invention of the present application, an optimum magnetic field is generated by the exciting coil according to the change in resistance value due to the temperature of the rotating body of the member to be heated. It became possible to perform high-speed direct heating, and to realize a quick start. Furthermore, even when the transfer material is continuously heated, it uses a rotating body with a small heat capacity,
Since the AC voltage is optimally applied to the exciting coil, it is possible to fix the image on the transfer material at a constant temperature without causing problems such as low temperature offset and fixing failure due to the temperature decrease of the rotating body.

According to the second invention of the present application,
Since the frequency of the alternating current flowing through the exciting coil is increased as the surface temperature of the rotating body rises, it is possible to prevent a sharp rise in the temperature rise and to realize a highly efficient quick start, which allows the device to operate at high speed. Can be converted.

Further, according to the third invention of the present application, the fixing target temperature is set according to the rising speed of the surface temperature of the rotating member, so that it is optimal regardless of the temperature conditions of the pressing member and the surroundings. Temperature control can be performed, high temperature offset and low temperature offset can be reliably prevented, and good fixing operation can be performed.

According to the fourth invention of the present application,
The frequency of the alternating current flowing through the exciting coil is set to be lower when the temperature is controlled to a constant temperature than when the rotor is started, so the amount of heat generated can be finely adjusted and the temperature ripple By reducing the temperature, it became possible to fix the image on the transfer material with constant temperature control.

Further, according to the fifth invention of the present application, the high-frequency alternating current flowing through the exciting coil is temporarily stopped when the transfer material is not passed, so that heat is generated by the induced current of the conductive temperature detecting member itself having a low heat capacity. And the generation of noise due to the alternating electric field is prevented, so that the temperature of the rotating body can be accurately detected and the optimum temperature can be set.

According to the sixth invention of the present application,
According to the fifth aspect of the invention, when the energization of the exciting coil is stopped, the temperature detecting member can accurately detect the temperature, and the optimum temperature can be set. It is possible to accurately detect the temperature to be detected by the temperature detecting member, and perform optimum temperature control according to the change in the detected temperature.

Further, according to the seventh invention of the present application, in the heat fixing device of the image forming apparatus, the resistance value of the rotating body changes according to the change of the surface temperature of the rotating body which is the member to be heated. By varying the frequency of the AC voltage applied to the exciting coil, it is possible to perform highly efficient direct heating and perform a favorable image forming operation.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a heat fixing device according to the first embodiment of the present invention.

FIG. 3 is an enlarged view of a heating unit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an AC application time and a surface temperature of a fixing film in the first embodiment of the present invention.

FIG. 5 is a diagram showing a temperature change of a fixing film according to each temperature control method in the first embodiment of the present invention.

FIG. 6 is a configuration diagram of a heat fixing device according to a conventional example.

FIG. 7 is a diagram showing the relationship between the number of fixed sheets and the transfer material discharge temperature.

[Explanation of symbols]

 11 Fixing Film (Rotating Body) 12 Exciting Coil 14 Chip Thermistor (Temperature Detecting Member) 20 Pressurizing Member P Transfer Material

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Yuko Ogama Inventor Yuko Ogama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Hiroshi Kataoka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (7)

[Claims] 1. A hollow rotating body, an exciting coil provided inside the rotating body, and a pressurizing member arranged so as to be in pressure contact with the rotating body, and an alternating current is applied to the exciting coil. In a heat fixing device that generates an eddy current in the rotating body by flowing the heat and causes the rotating body to generate heat by the eddy current,
A heating and fixing device, wherein the frequency of an alternating current flowing through the exciting coil is variable according to the surface temperature of the rotating body. 2. As the surface temperature of the rotating body rises,
The heat fixing device according to claim 1, wherein the frequency of the alternating current flowing through the exciting coil is increased. 3. According to the rising speed of the surface temperature of the rotating body,
The heating and fixing apparatus according to claim 1, further comprising means for determining a fixing target temperature. 4. The frequency of the alternating current flowing through the exciting coil is
The heating and fixing device according to claim 1, wherein the temperature is set lower when the temperature is controlled to be constant than when the rotating body is started. 5. A hollow rotator, an exciting coil provided inside the rotator, a pressure member arranged so as to be in pressure contact with the rotator, and temperature detection for detecting the temperature of the rotator. And a member to generate an eddy current in the rotating body by causing an alternating current to flow through the exciting coil, the eddy current causes the rotating body to generate heat, and the surface temperature of the rotating body is detected by the temperature detecting member. In a heat fixing device that maintains a predetermined set temperature based on the temperature, when the transfer material is not present in the heating section, the energization to the exciting coil is stopped, and the setting is made according to the temperature detected by the temperature detecting member at the time of stop. A heat fixing device having a temperature determining means for determining the temperature. 6. The heat fixing device according to claim 5, wherein the temperature determining means determines the set temperature based on a change in the temperature detected by the temperature detecting member when the energization of the exciting coil is stopped. 7. An alternating current to the exciting coil, comprising a hollow rotating body, an exciting coil provided inside the rotating body, and a pressurizing member arranged so as to be in pressure contact with the rotating body. In an image forming apparatus equipped with a heating and fixing device for generating an eddy current in the rotating body by causing the eddy current to flow, and applying an eddy current to the exciting coil according to the surface temperature of the rotating body. An image forming apparatus characterized in that a frequency of an alternating voltage to be changed is variable.