JPH11143269A - Fixing device with induction heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device with induction heating capable of accurately/quickly judging heating abnormality without providing a temperature detecting means separately. SOLUTION: The fixing device with the induction heating is provided with a voltage detecting circuit 28 and a current detecting circuit 29 which are for detecting supplied power, a control circuit 27 for making the switching frequency of a high-frequency power source variable so as to keep the detected power constant and an abnormality judging circuit 31 for measuring the shifting time from a first switching frequency in which a variable is arbitrarily set to a second arbitrarily set switching frequency to judge the abnormality of an electromagnetic induction heating part by the measured time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electrophotographic copying machine, a printer, a facsimile, and the like, and more particularly, to an induction heating device for fixing a developer to a recording medium by using electromagnetic induction heating. It relates to a fixing device.

[0002]

2. Description of the Related Art An electrophotographic copying machine, a printer, a facsimile and the like are provided with a fixing device for fixing a developer transferred onto a sheet such as a recording medium or a transfer material as a recording medium to the sheet. .

Conventionally, the temperature of a fixing device is controlled by bringing a temperature detecting element such as a thermistor into contact with a heating medium to detect the temperature, and comparing the temperature with a set temperature to control on / off of a heating source.
Alternatively, while performing duty control, an image forming operation permission signal is issued based on temperature information of the temperature detecting element,
Heating abnormality judgment is performed.

A thermistor, which is a general temperature detecting element,
Because of its own heat capacity and heat transfer delay, feedback control causes a delay in temperature detection. However, no particular problem occurred in a fixing roller system having a large heat capacity that is not so fast.

[0005] However, in a fixing device that heats up at a high speed,
The temperature detection delay by the thermistor particularly affects overshoot during warm-up. Therefore,
A method of predicting the degree of heating based on an increase in the temperature detected by the thermistor has also been considered.

As a high-speed heating technique, the applicants have already proposed an electromagnetic induction heating fixing system in which a rotating body including a metal layer is heated by induction heating.
As disclosed in Japanese Patent Application No. 229934, a means for detecting a temperature by detecting an impedance change due to the temperature of a metal rotating body as a heating medium in an inverter circuit has been proposed.

[0007]

As described above, in the fixing device of the high-speed temperature rise, control responsiveness becomes a problem in the temperature detection system using a contact thermistor in detecting an abnormality at the time of warm-up or performing predicted temperature control. .

When predicting the degree of heating based on the temperature rise of the temperature detected by the thermistor, it is difficult to accurately predict the temperature rise due to the difference in the contact state of the thermistor and the temperature condition of the roller, and it is necessary to obtain stable fixing performance. Can not.

When an abnormality is detected by a thermistor, the abnormality detection timing is delayed due to, for example, a delay in the temperature detection by the thermistor, so that the equipment is not damaged by an abnormal rise in temperature of the heating medium. There is a problem that it is necessary to use a certain member, which leads to an increase in cost.

Further, in the means disclosed in Japanese Patent Application No. 8-229934, which detects the temperature change by detecting the impedance change due to the temperature of a metal rotating body as a heating medium in an inverter circuit, the temperature of the heating medium It is assumed that the control is performed by electric power control, and the current amount is limited when one or both of the electric power and the frequency exceeds a predetermined value stored in advance with respect to the heating abnormality determination. .

Therefore, when constant power control is performed by varying the switching frequency of the high-frequency power supply during warm-up, the amount of current is limited when the frequency exceeds a predetermined value. Unless the body temperature rises to the abnormal temperature, it cannot be determined that the heating is abnormal. Further, in the case where the temperature of the rotating body does not rise due to, for example, damage to the rotating body, it is necessary to separately provide a temperature detecting means in order to determine a heating abnormality.

Accordingly, an object of the present invention is to provide an electromagnetic induction heating fixing device having excellent temperature rising characteristics, in which a heating abnormality can be accurately and quickly determined without separately providing a temperature detecting means. It is in.

Another object of the present invention is to provide an electromagnetic induction heating / fixing apparatus having excellent temperature-rise characteristics, whereby an image forming operation is started at a predetermined temperature by accurately predicting a temperature rise, and an overshoot is generated. An object of the present invention is to obtain stable fixing properties without causing the occurrence.

[0014]

According to a first aspect of the present invention, there is provided a heating medium having a conductive layer, an electromagnetic induction heating source for generating an induction current in the heating medium, and an electromagnetic induction heating source. A fixing device for fixing a developer on a recording medium by inductively heating the heating medium, the electromagnetic induction heating unit having an electromagnetic induction heating unit including a high-frequency power supply for supplying a high-frequency current to the induction heating source; Power detection means for detecting power supplied to the power supply, and switching cycle variable means for varying the switching frequency of the high-frequency power supply so as to keep the power detected by the power detection means constant,
A measuring means for measuring a time in which a frequency variable by the switching cycle variable means shifts from an arbitrarily set first switching frequency to an arbitrarily set second switching frequency, and measuring time by the measuring means. An induction heating fixing device comprising: an abnormality detection unit that determines an abnormality of the electromagnetic induction heating unit.

According to the configuration of the present invention, when performing constant power control by varying the switching frequency of the high-frequency power supply at the time of warm-up, when the power is turned on, a predetermined switching frequency from a predetermined switching frequency to an arbitrary predetermined frequency is set. If the transition time is different from the predetermined value, it is determined to be abnormal, so that the temperature of the metal rotator is not raised to an abnormal temperature, and there is no separate temperature detecting means, so that it is quick and accurate. The abnormality of the heating can be determined.

According to a second aspect of the present invention, there is provided a heating medium having a conductive layer, an electromagnetic induction heating source for generating an induction current in the heating medium, and a high-frequency current supplied to the electromagnetic induction heating source. An electromagnetic induction heating section consisting of a high-frequency power supply for flowing the heat, and in the fixing device for fixing the developer on the recording medium by induction heating the heating medium, the electric power supplied to the electromagnetic induction heating source , A switching cycle varying means for varying the switching frequency of the high frequency power supply so as to keep the power detected by the power detecting means constant, and a frequency varied by the switching cycle varying means being a first frequency. Predicting means for predicting a transition time from the switching frequency to an arbitrarily set second switching frequency; and And an image forming operation controlling means for outputting an image forming operation permission signal, an induction heat fixing apparatus characterized by having a.

According to the configuration of the present invention, a transition time from a predetermined switching frequency after power is turned on to an arbitrarily set predetermined frequency is calculated from the change rate of the switching frequency, and the image forming operation permission is performed based on the predicted value. By issuing the signal, the image forming operation is started at a predetermined temperature, and stable fixing performance can be obtained without occurrence of overshoot.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

Embodiment 1 FIG. 1 is a side view showing an induction heating fixing apparatus to which the present invention is applied.

As shown in FIG. 1, the induction heating fixing device comprises a coil assembly 9 composed of a core 1 and a coil 2 wound around the core 1 and a holder unit 4.
A metal flexible fixing sleeve 5 which is housed inside and which generates heat by the induced current of the coil 2 surrounds the holder unit 4. The rotationally driven pressure roller 6 presses the holder unit 4 across the fixing sleeve 5 to move and pass the recording medium (paper) 8 to the nip portion, and the fixing sleeve 5 is moved together with the recording medium 8. As a result, the toner as a developer on the recording medium is melted and fixed.

The fixing sleeve 5 is preferably made of a ferromagnetic material such as iron or nickel. If a ferromagnetic material is used, a large amount of magnetic flux passes through the fixing sleeve and the heat generation efficiency is improved. Further, in the fixing sleeve 5, for example, the thickness of the metal layer of the fixing sleeve 5 is preferably about 20 to 60 μm. The smaller the thickness of the fixing sleeve 5 is, the smaller the heat capacity thereof is. Therefore, the power consumption for generating heat is reduced. However, if the thickness of the fixing sleeve 5 is too small, the strength of the fixing sleeve 5 is reduced and the fixing sleeve 5 is damaged. Easier to do. In addition, it is difficult to make the thickness uniform when the fixing sleeve 5 is manufactured. On the other hand, when the thickness of the fixing sleeve 5 is too large, the fixing sleeve 5 becomes weak against bending, and the durability against partial bending at the nip portion decreases. Also,
A heat-resistant release layer (not shown) made of a very thin fluororesin is formed on the outer peripheral surface of the fixing sleeve 5.

The fixing sleeve 5 is not fixed to any part of the apparatus, and can freely rotate around the holder unit 4. On the other hand, the holder unit 4 is fixed to the apparatus main body, and the surface thereof, at least a portion in contact with the fixing sleeve 5, is formed of a smooth heat-resistant resin material. The frictional resistance between the holder unit 4 and the fixing sleeve 5 is smaller than the frictional resistance, and the rotation of the pressure roller 6 causes the fixing sleeve 5 to follow the movement of the recording medium 8. Further, the holder unit 4 is provided at its both ends with flanges (not shown) for restricting the fixing sleeve 5 from shifting in the longitudinal direction of the holder unit 4.

The coil assembly 9 has an insulating bobbin 3 around the core 1, and a coil 2 is formed by winding a copper wire around the bobbin 3. The bobbin 3 may be formed of, for example, ceramics or heat-resistant insulating engineering plastic, and the coil 2 is preferably a single or litz copper wire having a fusion layer and an insulating layer on the surface. The core 1 is made of, for example, a ferrite core or a laminated core.

The pressure roller 6 has a shaft core 61 and a silicon rubber layer 62 as a surface releasable heat-resistant rubber layer formed around a shaft core 61. Sliding bearings (not shown) are formed at both ends of the pressure roller 6. The fixing sleeve 5 is sandwiched by the spring material 50 between the fixing unit frame 55 and the like, pressed in the holder unit 4 direction, and rotatably mounted. Further, a drive gear (not shown) is fixed to one end of the pressure roller 6, and is driven to rotate by a drive source (not shown) such as a motor connected to the drive gear.

FIG. 2 is a block diagram showing a control system of the fixing device.

The high frequency current is rectified by the rectifier circuit 22 and the smoothing capacitor 23 of the alternating current of the commercial power supply 21, and the high frequency current is supplied to the coil 2 by the inverter circuit including the coil 2, the resonance capacitor 24 and the switch circuit 25. It has become. The control of the high-frequency current is performed by the control circuit 27 based on the voltage and current detected by the voltage detection circuit 28 and the current detection circuit 29 as described later. The control system of this device includes
Arithmetic circuit 30 for calculating power from voltage and current detected by voltage detection circuit 28 and current detection circuit 29
And an abnormality determination circuit 31 for determining an abnormality from the switching frequency and its change as described later. The operations of the arithmetic circuit 30 and the abnormality determination circuit 31 will be described later in detail. In the case shown, these are divided into blocks for each function and are represented as blocks.
When a microcomputer is used, these can be operated by one microcomputer. The power supply switch 20 is connected to the path from the commercial power supply 21 to the rectifier circuit 22.
Is provided.

The basic control of the high frequency current is performed by the control circuit 2
7, the drive circuit 26 is driven by the control signal
For example, a switch circuit 25 composed of a transistor, an FET, an IGBT, or the like is turned on, whereby a current flows through the coil 2. Then, the arithmetic circuit 30 calculates the input power amount based on the current value detected by the current detection circuit 29 and the voltage value detected by the voltage detection circuit 28, and notifies the control circuit 27 of the result. In the control circuit 27,
The switch circuit 25 is controlled so that the electric energy always becomes a constant value.
And outputs a control signal for turning on and off. Thus, the amount of power supplied to the inverter circuit is always constant. On the other hand, as will be described later, the switching cycle (frequency) tries to keep the input power constant, and as a result, the sleeve 5
Will change as the temperature rises.

Thus, the high frequency (several k) is applied to the coil 2.
When a current of (Hz to several tens of kHz) is applied, a magnetic flux orthogonal to the longitudinal direction of the fixing sleeve 5 is generated from the core 1 in accordance with the "Right-handed screw rule of ampere". Vortex induced current is generated in the fixing sleeve 5 in accordance with "Lenz's law". This induced current is converted into Joule heat by the skin resistance of the fixing sleeve 5, and the fixing sleeve 5 generates heat.

Here, the relationship between the input power, the sleeve temperature, and the switching frequency will be described.

For example, the fixing sleeve 5 used in this embodiment
When a nickel sleeve whose metal layer has a thickness of 20 to 60 μm is used as a heating medium, a high frequency (here, 30 μm) is used.
When the input power is constant, the frequency becomes lower as the temperature becomes higher as shown in FIG. 3, and conversely, a higher frequency is required at the time of low temperature, as shown in FIG. Such a phenomenon has the same tendency even when the input electric energy is changed.

The relationship between the fixing sleeve temperature and the switching frequency is such that if the input power is constant when the fixing sleeve is at a certain temperature, the frequency required to raise the temperature of the fixing sleeve from that temperature is as follows. This leads to the relationship that the same frequency depends on the temperature of the fixing sleeve. Then, the heating time of the fixing sleeve, that is, from a certain temperature to a fixing suitable temperature (for example, 180 to 200).
° C) is the same time each time for the same device.

Therefore, in the first embodiment, utilizing such a relationship, the time from a predetermined frequency f1 after the temperature rise of the fixing sleeve 5 is started to a predetermined frequency f2 is measured, and the time is measured. If the time does not fall within the preset time range, it is determined that there is some abnormality and the power supply is cut off. To shut off the power at this time, the power switch 20 is opened to stop all power supply to the circuit.

FIG. 4 is a drawing for explaining an operation for judging an abnormality from the relationship between the fixing sleeve temperature and the switching frequency. As described above, in order to keep the power constant, the switching frequency is decreased as the temperature of the fixing sleeve 5 rises. Here, the time from a predetermined frequency f1 after the power is turned on to an arbitrarily set frequency f2 falls within a certain range even in the case of a normal operation, even if the influence of the ambient temperature or the like is added.

Here, as specific examples of the values of f1 and f2 and the normal time between them, if a nickel sleeve having a metal layer thickness of 20 to 60 μm is used as the fixing sleeve 5, the f1 The value is, for example, a frequency when the fixing sleeve 5 is about 50 ° C. so as not to be affected by the room temperature.
If the frequency is about the same, the frequency transition time during normal operation during this period is about 5 to 7 seconds.

This abnormality determination is performed by the abnormality determination circuit 31. In order to measure the time from f1 to f2, the abnormality determination circuit 31 detects the switching frequency from the switching operation of the switch circuit 25 via the control circuit 26, and the detected frequency is temporarily stored in a memory in the microcomputer. The stored frequency is stored at a preset frequency.
The time from when the value f1 is reached to when the value f2 is reached is measured. Then, it is determined that there is an abnormality when the time during this time is out of the predetermined time range.

FIG. 5 is a flowchart showing the operation of the abnormality determination circuit 31. Here, a case where the fixing device is used in a copying machine will be described as an example.

First, a memory area for storing a switching frequency in the abnormality determination circuit 31 (specifically, a microcomputer) is cleared (S1). Then, it is determined whether or not a copy start command has been received from a control device (not shown) of the copying machine body (S2). If a copy start command has been received, the temperature rise is started (S3). Then, the abnormality is determined during the temperature rise as described above, and if there is no abnormality (S
4) Waiting for the fixing appropriate temperature (S5), and when the fixing appropriate temperature is reached, a signal for starting the image forming operation is output to the control device of the copying machine main body (S6). Here, whether or not the temperature is suitable for fixing is detected by monitoring the switching frequency from the relationship between the sleeve temperature and the switching frequency as described above (see FIG. 3).

Then, temperature control is performed to maintain the appropriate fixing temperature until the copy end signal is received (S7, S7).
8). When the copy end signal is received, the input power is turned off (S9), and the process ends.

On the other hand, if it is determined in step S4 that there is an abnormality, the power switch 20 is opened to cut off the power to the inverter circuit (S11), and a signal indicating that there is an abnormality is output (S12). This abnormal signal is transmitted to the control device of the copying machine and displayed.

Thus, when an abnormality occurs in the fixing device, the power supply to the fixing device is cut off and the printing operation itself is stopped.

As described above, by determining the abnormality from the change time of the switching frequency, the abnormality can be determined in advance before the temperature of the fixing sleeve becomes high. In addition to the case where the fixing sleeve becomes high temperature due to some abnormality, it is possible to cope with the abnormality that the fixing sleeve does not reach the proper fixing temperature.

Second Embodiment In the first embodiment, the abnormality of the fixing device is determined only from the change time of the switching frequency. However, in the second embodiment, the fixing sleeve temperature when the applied power is constant is set. And the switching frequency are used to predict the time required to reach the fixing suitable temperature, and to control other parts of the image forming apparatus provided with the fixing device. Here, the image forming apparatus is
For example, an electrophotographic printer, a copier, a facsimile, and the like, and the components other than the fixing device in such an image forming apparatus include an image forming unit that forms an electrostatic latent image on a photosensitive drum by a laser or an LED. And a developing unit for developing an electrostatic latent image with toner. Since the configuration of such an image forming apparatus itself is already generally used and is well known, the description thereof will be omitted here. Omitted.

The hardware configuration (including the control system) of the induction heating fixing device according to the second embodiment is the same as that of the first embodiment, and the description thereof is omitted.
Here, a control example in the case where the fixing device to which the present invention is applied is used in a copying machine will be described.

FIG. 6 is a flowchart showing the operation procedure of the fixing device according to the second embodiment.

First, the memory area for storing the switching frequency in the abnormality determination circuit 31 (specifically, the microcomputer) is cleared (S21). Then, it is determined whether or not a copy start command has been received from a control device (not shown) of the copying machine body (S22). If a copy start command has been received, the temperature rise is started (S23).

The time required to reach the fixing suitable temperature during the temperature rise is predicted (temperature rise time prediction).
And a variable Ts for determining the image formation start time as described later (S24). Here, the temperature rise time prediction is performed, for example, at regular time intervals (for example, 0.5
Every second), the switching frequency is detected, the rate of change of the frequency is determined, and the time to reach the previously determined fixing suitable temperature is predicted from the determined rate of change of the frequency. Also, for example, how many seconds after which the temperature reaches the fixing suitable temperature from the frequency change rate may be measured in advance, and this may be stored as table data, and the predicted time may be obtained by referring to this table.

The reason why the variable t is subtracted from the variable T containing the predicted result time in determining the image formation start time Ts is that the start of image formation in a copying machine or the like is started shortly before the appropriate fixing time. For this reason, the time t is determined by the structure of the copying machine or the like, and for example, in image formation, it may be determined by the transport time of the sheet that has passed through the developing process to reach the fixing device.
Compared with the case where the image formation is started after the temperature reaches the suitable fixing temperature as in the first embodiment, it is possible to shorten the time of the entire image forming operation. The prediction of the heating time is performed by the arithmetic circuit 30 detecting the switching frequency of the switch circuit 25 via the control circuit 27 (see FIG. 2, the same applies hereinafter).

Next, a timer is started to count the predicted time (S25). During this time, an abnormality determination is made in the same manner as in the first embodiment, and if there is no abnormality (S2
6) Wait until the timer value reaches Ts, which is a time immediately before the temperature suitable for fixing (S27). When the timer value reaches Ts, the arithmetic circuit 30 outputs an image formation start signal (S28). .

Then, the control waits until the timer value reaches the time T at which the temperature is suitable for fixing (S29). When the timer value reaches T, the temperature control is started (S30). As a result, it is possible to shift to the temperature control without causing overshoot at the time when the temperature reaches the suitable fixing temperature, as compared with the case where the temperature adjustment control is performed after detecting that the fixing appropriate temperature has been reached. .

Then, a temperature control is performed to maintain a suitable fixing temperature until a copy end signal is received (S30, S30).
S31). When the copy end signal is received, the input power is turned off (S32), and the process ends.

On the other hand, when it is determined in step S26 that there is an abnormality, the power to the inverter circuit is cut off (S41), and a signal indicating the abnormality is output (S42).
This abnormal signal is transmitted to the control device of the copying machine and displayed.

Thus, the image forming operation can be started at an appropriate time before the temperature becomes suitable for fixing, and the temperature can be immediately shifted to the temperature control when the temperature becomes suitable for fixing. It is possible to form a clear image without shortening the forming operation time and without causing a problem such as overshoot.

[0053]

According to the present invention described above, the following effects can be obtained for each claim.

According to the first aspect of the present invention, in the electromagnetic induction heating fixing device having excellent temperature-rise characteristics, the temperature of the metal rotating body is not raised to an abnormal temperature, and a separate temperature detecting means is provided. Without this, it is possible to quickly and accurately determine a heating abnormality. Further, according to the present invention, it is possible to prevent occurrence of overshoot and obtain stable fixing performance when performing a prediction start of an image forming operation.

[Brief description of the drawings]

FIG. 1 is a side view showing an induction heating fixing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a control system of the induction heating fixing device according to the first embodiment.

FIG. 3 is a diagram showing a relationship between temperature, frequency, and input power of a nickel (Ni) sleeve.

FIG. 4 is a drawing for explaining the operation principle when an abnormality is determined from the relationship between the temperature and the frequency of a nickel (Ni) sleeve.

FIG. 5 is a flowchart illustrating a control procedure of the fixing device according to the first exemplary embodiment.

FIG. 6 is a flowchart illustrating a control procedure of the fixing device according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Coil, 3 ... Bobbin, 4 ... Holder, 5 ... Fixing sleeve, 6 ... Pressure roller, 20 ... Power switch, 21 ... Power supply, 22 ... Rectifier, 23 ... Smoothing capacitor, 24 ... Resonance capacitor Reference numeral 25: switch circuit, 26: drive circuit, 27: control circuit, 28: voltage detection circuit, 29: current detection circuit, 30: arithmetic circuit, 31: abnormality determination circuit

Claims (2)

[Claims] 1. An electromagnetic induction heating section comprising a heating medium having a conductive layer, an electromagnetic induction heating source for generating an induction current in the heating medium, and a high frequency power supply for supplying a high frequency current to the electromagnetic induction heating source. A fixing device for fixing the developer on the recording medium by induction heating the heating medium, wherein the power detection unit detects power supplied to the electromagnetic induction heating source; and the power detection unit detects the power. Switching cycle variable means for varying the switching frequency of the high frequency power supply so as to keep the power to be kept constant; and a frequency which is arbitrarily set from a first switching frequency arbitrarily set by the switching cycle variable means. A measuring means for measuring a time required to shift to a switching frequency of 2; Induction heat fixing apparatus, characterized in that it comprises an abnormality detecting means for determining the normal, the. 2. An electromagnetic induction heating section comprising a heating medium having a conductive layer, an electromagnetic induction heating source for generating an induction current in the heating medium, and a high frequency power supply for supplying a high frequency current to the electromagnetic induction heating source. A fixing device for fixing the developer on the recording medium by induction heating the heating medium, wherein the power detection unit detects power supplied to the electromagnetic induction heating source; and the power detection unit detects the power. Switching frequency varying means for varying the switching frequency of the high frequency power supply so as to keep the power to be maintained constant; and a second frequency wherein the frequency varied by the switching frequency varying means is arbitrarily set from the first switching frequency.
And an image forming operation control unit that outputs an image forming operation permission signal based on the predicted value of the predicting unit.