JP2005050624A - Induction heating device, fixing device, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating device capable of carrying out high-frequency induction heating with power transmission efficiency maintained in a high level in spite of the temperature change of a heated object, a fixing device and an image forming device equipped with the same. <P>SOLUTION: The induction heating device is provided with a high-frequency power supply HFS outputting a high-frequency alternate current voltage with variable frequencies, an induction coil IC on which the high-frequency alternate current voltage of the high-frequency power supply HFS is impressed, the heated object HR radiating heat by being magnetically coupled with the induction coil for a secondary current to flow, and a control means CC controlling the high-frequency power supply HFS so that an output frequency is changed in accordance with the temperature rise of the heated object HR. For carrying out high-speed heating, frequencies are changed for each given time, and for maintaining a constant temperature, a temperature detecting means of the heated object is arranged at the control means CC and the frequencies are changed in accordance with the temperatures. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an induction heating device, a fixing device including the induction heating device, and an image forming apparatus.
[0002]
[Prior art]
A cylindrical roller body made of a conductive member, that is, a heating roller, a cylindrical bobbin concentrically arranged in the roller body, and a spiral winding around the outer periphery of the bobbin to induce an induced current in the roller body by energization. A high-frequency induction heating roller having an induction coil for heating is already known (see Patent Document 1).
[0003]
In Patent Document 1, the cylindrical roller body is a closed-circuit secondary coil, the induction coil is a primary coil, and a transformer coupling is generated between the two, and the secondary coil of the cylindrical roller body is secondary to the secondary coil. A voltage is induced. Then, a secondary current flows in the closed circuit of the secondary coil based on the secondary voltage, so that a heating method using heat generated by the secondary resistance that generates heat from the cylindrical roller body (hereinafter referred to as “transformer method”). ). The transformer system has advantages in that the magnetic coupling is stronger than the eddy current loss system, so that the steady-state efficiency is high and the entire heating roller can be heated, so that the structure of the fixing device is simpler than the eddy current loss system. . In addition, by increasing the operating frequency to 100 kHz or higher, preferably 1 MHz or higher, it is possible to increase the Q of the induction coil and increase the power transmission efficiency. For this reason, the overall efficiency of heating is increased and power saving can be achieved. Further, there is an advantage that the structure of the fixing device is simplified as compared with the eddy current loss method. Furthermore, the heat capacity can be made considerably smaller than that of the eddy current loss type heating roller. Therefore, the transformer method is suitable for speeding up heat fixing.
[0004]
In the heating roller having a hollow structure that is rotatably supported by the air-core transformer before being coupled to the induction coil, the present inventors have changed the secondary resistance value to a secondary coil composed of a closed circuit substantially equal to the secondary reactance. By forming, the power transmission efficiency from the induction coil to the heating roller is increased, and a transformer-coupled invention is obtained in which a remarkable effect of efficiently heating the heating roller is obtained (see Patent Document 2). According to the present invention, it is possible to save power in induction heating of the heating roller and to easily increase the speed of thermal fixing. The transformer-type induction heating roller device is one of the promising applications for heating an object to be heated using high-frequency power extracted from a high-frequency power supply device.
[0005]
[Patent Literature]
JP 59-33787
[Patent Literature]
JP 2002-222688 A
[Problems to be solved by the invention]
By the way, in the induction heating apparatus as shown in Patent Document 2, the electrical equivalent circuit of the secondary coil formed by the cylindrical roller body in the heating roller that is the object to be heated is a parallel circuit of the secondary resistance and the secondary inductance. Can be represented. The secondary resistance is determined by the resistivity of the material constituting the secondary coil. The resistivity varies depending on the temperature of the heated object. Therefore, the secondary resistance value of the secondary coil changes with the temperature of the heated object.
[0006]
On the other hand, the secondary inductance is determined by the magnetic permeability of the material constituting the heated object. The magnetic permeability varies depending on the temperature of the heated object. Therefore, the inductance of the secondary coil also changes with the temperature of the heated object. Moreover, the manner in which the inductance of the object to be heated changes with respect to temperature does not necessarily match that of the secondary resistance value.
[0007]
As can be understood from the above, in the induction heating apparatus, the power transmission efficiency from the induction coil to the heated object varies with the temperature of the heated object. Further, the difference in power transmission efficiency directly affects the rate of temperature increase of the heated object.
[0008]
On the other hand, in eddy current loss type induction heating, the eddy current loss is proportional to the conductivity of the object to be heated, and the conductivity is the reciprocal of the resistivity, so that it eventually changes with the temperature of the object to be heated.
[0009]
Therefore, as a result of investigation of the temperature rise rate in the heated object during high frequency induction heating, the present inventor shows that when the frequency of the high frequency AC voltage is constant, the temperature rise of the heated object tends to saturate as the energization time elapses. I found out that This is considered to be because the high-frequency power transmission efficiency decreases with the passage of energization time.
[0010]
The present invention relates to an induction heating device capable of performing high-frequency induction heating while maintaining a high rate of temperature increase or power transmission efficiency regardless of a temperature change of a heated object, and a fixing device and an image forming apparatus provided with the induction heating device The general purpose is to provide
[0011]
Another object of the present invention is to provide an induction heating device that maintains high temperature rise rate or high power transmission efficiency and facilitates high-speed heating and high-efficiency constant temperature maintenance, a fixing device including the same, and an image forming apparatus. For other purposes.
[0012]
[Means for achieving the object]
An induction heating device according to a first aspect of the present invention includes a high frequency power supply device that outputs a variable frequency high frequency AC voltage; an induction coil to which the high frequency AC voltage of the high frequency power supply device is applied; and a secondary by magnetically coupling to the induction coil. And a control means for controlling the high-frequency power supply device so that the output frequency changes as the temperature of the heated object rises.
[0013]
Hereinafter, characteristic components and other components of the present invention will be described in detail. The definition and technical meaning of the term shall be applied not only to the present invention but also to each of the following inventions unless otherwise specified.
[0014]
<Regarding the High-Frequency Power Supply Device> In the present invention, the high-frequency power supply device is means for outputting a frequency-variable high-frequency AC voltage and energizing an induction coil to be described later, and the specific configuration therefor is not particularly limited.
[0015]
A high-frequency power supply device can be relatively easily configured by using means for generally converting a low-frequency AC voltage indirectly to form a high-frequency AC voltage. However, if necessary, the low-frequency AC voltage may be directly converted into a high-frequency AC voltage. The low frequency AC voltage can be obtained from, for example, a commercial AC power source. In the present invention, “high frequency” means a frequency of 20 kHz or more. However, if the frequency is a high frequency of 100 kHz or more, not only the high frequency power supply device but also the peripheral circuit to which the high frequency AC voltage is applied can be remarkably reduced in size, which is preferable from the viewpoint of cost reduction and weight reduction of the high frequency power supply device. It is. If the frequency is 4 MHz or less, the high frequency characteristics are excellent, and a relatively inexpensive MOSFET can be used as an active element, and the suppression of high frequency noise is relatively easy. Therefore, in the present invention, the high frequency is preferably in the range of 100 kHz to 4 MHz. Furthermore, when the high frequency power supply device is used as a heating power source for an induction heating roller device of an air-core transformer coupling type, it is possible to increase the Q of the induction coil to further increase the power transmission efficiency. When the power transmission efficiency is increased, the overall efficiency of heating is increased and power saving can be achieved. In this case, the range of 1 to 4 MHz is particularly preferable from the viewpoints of the economical efficiency of suitable active elements (for example, MOSFET) and the ease of suppressing high-frequency noise.
[0016]
When a low frequency AC voltage is indirectly converted to form a high frequency AC voltage, a rectified DC power supply means is interposed between the low frequency AC power supply and the high frequency conversion means. The rectified DC power supply means is means for converting low-frequency alternating current into direct current, and can include smoothing means if necessary, in addition to the rectification means. That is, the DC output voltage may be a smoothed DC voltage formed using a smoothing circuit or a non-smooth DC voltage. However, a non-smooth DC voltage eliminates the need for a smoothing circuit and simplifies the circuit configuration, which is advantageous for reducing the size, weight and cost of the induction heating roller device.
[0017]
On the other hand, the functional part that generates high-frequency power is not limited to a specific circuit system. Circuit elements such as amplifiers and inverters can be used to generate high frequencies. As the amplifier, for example, a class E amplifier with high power conversion efficiency can be used. A half-bridge inverter or the like can also be used. A plurality of main circuit units can be connected in parallel, and the high frequency outputs of the source circuit units can be combined, that is, collectively applied to the induction coil. As a result, the output of each circuit unit may be small while maintaining the desired power, so even if a MOSFET having a relatively small capacity is used as an active element, a high frequency can be generated efficiently at low cost.
[0018]
Further, the frequency of the high-frequency AC voltage output of the high-frequency power supply device is configured to be variable. The purpose of making the frequency variable is to increase the temperature increase rate or the power transfer efficiency by changing the frequency as the temperature of the object to be heated increases, thereby controlling the heating as desired. However, in addition, when the object to be heated is a heating roller, a plurality of induction coils are distributed in the axial direction of the heating roller, and a desired induction coil is selectively energized among the plurality of induction coils. Thus, the heating region in the axial direction of the heating roller can be changed so as to be selectable. That is, by making the frequency of the output of the high frequency power supply device variable, it becomes possible to individually control the high frequency power input to the plurality of induction coils. In addition, if necessary, for example, the input power at the time of startup can be made higher than that at the time of normal operation by changing the frequency of the high-frequency AC voltage, and rapid heating can be performed.
[0019]
Furthermore, the high-frequency power supply device can be configured to output a high-frequency AC voltage that is PWM-controlled by control by a control unit described later if desired. Therefore, the high frequency power supply device intermittently generates a high frequency AC voltage by performing a periodic intermittent operation by the PWM control during the period in which the PWM control is performed by the control means. PWM control is performed to control the heating of the heating roller as desired. And it is performed at a frequency sufficiently higher than the frequency of the low-frequency AC voltage and sufficiently lower than the frequency of the high-frequency AC voltage. As a result, the on / off state cannot be observed in the low-frequency alternating current, and the current flicker is substantially not generated. Further, it is possible to perform a soft start that sequentially increases the high-frequency AC voltage when the high-frequency AC voltage rises by PWM control as desired. As a result, it is possible to avoid flicker caused by sudden changes in power. In addition, the effective value of the high-frequency AC voltage can be increased sequentially by not generating the high-frequency AC voltage by skipping the ON signal several times at the rise of the high-frequency AC voltage by PWM control as a method different from the above for soft start. You can go. Note that the high frequency power supply device is allowed to be configured not to perform PWM control at a desired time, for example, at maximum output.
[0020]
Furthermore, the high frequency power supply apparatus is allowed to include a resonance circuit in order to efficiently output the generated high frequency AC voltage. In addition, by providing the resonant circuit, it is possible to obtain a sine wave by shaping the high-frequency AC voltage, whereby the high-frequency AC voltage can be extracted with high efficiency and the generation of high-frequency noise is reduced.
[0021]
<Regarding the induction coil> The induction coil is disposed so as to face a heated body to be described later and to be magnetically coupled to each other. For example, when the object to be heated is a heating roller, the induction coil is arranged so as to be coaxial with the axis of the heating roller. Then, it is energized or excited by the high frequency power supply device and functions as means for transferring a high frequency AC power to the secondary coil by applying a high frequency AC magnetic field to the heated object. Then, the induction coil is arranged opposite to the object to be heated and functions as a primary coil of the transformer to perform transformer coupling, preferably air-core transformer coupling, with the secondary coil of the object to be heated. Configured as follows. However, if necessary, the induction coil and the object to be heated may be eddy current loss type magnetic coupling. When the object to be heated is a heating roller, the induction coil may be stationary with respect to the rotating heating roller, or may be rotated together with or separately from the heating roller. When rotating, a rotating current collecting mechanism may be interposed between the high frequency power supply device and the induction coil. Further, “air-core transformer coupling” means not only a complete air-core transformer coupling but also a transformer coupling that can be substantially regarded as an air-core. For example, it is the structure which does not have a magnetic body inside the induction coil.
[0022]
Further, the induction coil can be provided with a coil bobbin manufactured using a material having as little dielectric loss as possible in order to maintain a predetermined shape and a predetermined arrangement position thereof. The coil bobbin can be formed with a winding groove for aligned winding and an axial groove for accommodating the feed lead wire. However, the induction coil can be maintained in a predetermined shape and position by directly forming or bonding the induction coil with a synthetic resin or glassy material instead of the coil bobbin.
[0023]
Furthermore, the induction coil can be connected to the high frequency power supply device via a power supply lead wire. The power supply lead wire for supplying high frequency AC power to the induction coil from the high frequency power supply device is preferably disposed at a position close to the inner surface or the outer surface of the induction coil. When passing the power supply lead wire inside the induction coil, if the power supply lead wire is close to the central axis of the induction coil, the amount of magnetic flux interlinking with the power supply lead wire increases. Since efficiency falls, it is not preferable. On the other hand, by configuring as described above, the magnetic flux interlinking with the power supply lead wire is reduced, so that a reduction in power transmission efficiency is relatively suppressed.
[0024]
Furthermore, the induction coil may be composed of a plurality of windings connected in series or in parallel, or a plurality of windings electrically conductively independent from each other.
[0025]
<About a to-be-heated body> A to-be-heated body may be anything, such as cooking utensils, such as a heating roller and a rice cooker. The heated object has a secondary coil forming a closed circuit, and this secondary coil and the primary coil are transformer-coupled as described above, preferably air-core transformer coupling or eddy current loss type magnetic coupling. I do. In the case of air-core transformer coupling, the secondary side resistance value of the closed circuit preferably has a value substantially equal to the secondary reactance of the secondary coil. The secondary resistance value and the secondary reactance are “substantially equal” when the secondary resistance value is Ra, the secondary reactance is Xa, and α = Ra / Xa. The range can be satisfied. Further, the secondary resistance value can be obtained by measurement. The secondary reactance can be obtained by calculation.
25 <α <4
Moreover, a to-be-heated body can be arrange | positioned so that a secondary coil may become a single or several aspect. When there is a single secondary coil, it is desirable that the secondary coil is disposed so as to extend over substantially the entire effective length along the axial direction when the object to be heated is a heating roller. Moreover, when arrange | positioning a some secondary coil, it is desirable to distribute them with respect to a to-be-heated body, for example along the axial direction.
[0026]
Further, when the heated object is composed of a heating roller, the secondary coil can be formed with conductors such as a conductor layer, a conductive wire, and a conductive plate. In order to obtain a desired secondary resistance value, the conductor layer can employ the following materials and manufacturing methods. In the case of forming by thick film formation method (coating + firing), Ag, Ag + Pd, Au, Pt, RuO ₂ And a material mainly composed of a metal selected from the group consisting of C and C. As a coating method, a screen printing method, a roll coater method, a spray method, or the like can be used. On the other hand, in the case of forming by plating, vapor deposition, or sputtering, it is preferable to use a metal material selected from the group of Au, Ag, Ni, and Cu + (Au, Ag). Copper and aluminum can be used for the conductive wire and the conductive plate.
[0027]
In order to obtain a more practical heating roller, it is allowed to add the following configuration as necessary.
[0028]
1. (Regarding Roller Base) In order to support the secondary coil, a roller base made of an insulating material or metal can be used. In this case, the secondary coil can be disposed on the outer surface, the inner surface, or the inside of the roller base. The insulating roller base can be formed using ceramics or glass. In consideration of the heat resistance, strong impact and mechanical strength of the roller base, for example, the following materials can be used. Examples of the ceramic include alumina, mullite, aluminum nitride, and silicon nitride. Examples of the glass include crystallized glass, quartz glass, and Pyrex (registered trademark). In the case of a roller base made of metal, cast iron or the like can be used, for example.
[0029]
2. (Regarding Thermal Diffusion Layer) The thermal diffusion layer can be disposed on the upper side of the conductor layer as necessary as a means for improving the temperature uniformity in the axial direction of the heating roller. For this reason, it is preferable to use a material having good heat conduction in the axial direction of the heating roller for the heat diffusion layer. Substances with high thermal conductivity are often found in metals with high conductivity such as Cu, Al, Au, Ag and Pt. However, the thermal diffusion layer only needs to have a thermal conductivity equal to or higher than that of the material of the conductor layer. Therefore, the heat diffusion layer may be the same material as the conductor layer.
[0030]
Further, when the heat diffusion layer is made of a conductive material, it may be in conductive contact with the conductor layer, but it also has an effect of blocking noise radiation by being disposed through an insulating film. Since the high frequency magnetic field does not act up to the heat diffusion layer, a secondary current that contributes to heat generation is not induced in the heat diffusion layer.
[0031]
3. (Regarding Protective Layer) The protective layer can be disposed as necessary for mechanical protection and electrical insulation of the heating roller, or for improving elastic contact property or toner separation property. As the constituent material of the protective layer for the former, glass can be used, and as the constituent material of the protective layer for the latter, synthetic resin can be used. The glass can be selected from the group consisting of zinc borosilicate glass, lead borosilicate glass, borosilicate glass, and aluminosilicate glass. The latter can be selected from the group consisting of silicone resin, fluororesin, polyimide resin + fluororesin and polyamide + fluororesin. In the case of polyimide resin + fluororesin and polyamide + fluororesin, the fluororesin is disposed on the outside.
[0032]
4). (Regarding the shape of the heating roller) If desired, a crown can be formed on the heating roller. The crown may be either a drum shape or a barrel shape.
[0033]
5. (Regarding Rotation Mechanism of Heating Roller) As a mechanism for rotating the heating roller, a known configuration can be appropriately selected and employed.
[0034]
On the other hand, when the object to be heated is heated by the eddy current loss method, the object to be heated is made of a magnetic material, and the eddy current generated when an AC magnetic field acts on the object to be heated flows in the non-heated object. It generates heat.
[0035]
<Regarding Control Unit> The control unit is a unit that controls the high-frequency power supply device so that the frequency of the high-frequency AC voltage output changes as the temperature of the object to be heated increases. How the frequency is changed is allowed to vary depending on the purpose of heating. For example, in order to perform high-speed heating, the frequency is changed to a frequency at which a high rate of temperature increase or power transfer efficiency is obtained in a certain time period. And the timer function for measuring the elapsed time after power-on to the control means, the table data for determining the frequency adopted every predetermined time and its storage means, and the timer function and the table data for controlling as required A program and its storage means, and an arithmetic means for executing the program can be provided. The control means includes a temperature detection means for the object to be heated and a circuit that feedback-controls the oscillation frequency of the drive signal based on the temperature detection signal, and controls the oscillation frequency feedback circuit according to the difference from the target temperature. It is also possible to perform high-speed heating by configuring as above.
[0036]
Further, in order to perform constant temperature maintenance control at a predetermined temperature, the temperature of the object to be heated is detected, and the output frequency of the high frequency power supply device is feedback controlled. For this purpose, the oscillation frequency feedback circuit can be used. Alternatively, the output frequency at the target temperature is set to the output frequency with the highest rate of temperature increase or power transfer efficiency, and the output voltage of the high-frequency power supply device is PWM controlled using a temperature detection signal obtained from the temperature detection means. By performing output voltage control, high-efficiency constant temperature control can be performed. The temperature detecting means may have any configuration as long as it can detect the temperature of the object to be heated. For example, a thermistor can be used.
[0037]
Therefore, in order to continuously perform the high-speed heating control and the constant temperature maintenance control, it is only necessary to provide both the above-described means and a program for performing each control continuously.
[0038]
On the other hand, in order to control the high frequency power supply device as described above, the control means generates a drive signal that is controlled as desired to be supplied to the high frequency power supply device. The drive signal is for driving the switching means of the high frequency power supply device. Then, the control means is driven every predetermined time according to a preset program or in response to a temperature rise of the heated object in order to make the frequency of the high-frequency AC voltage that is the output of the high-frequency power supply device variable. Operates to change the frequency of the signal.
[0039]
In order to change the frequency of the drive signal, it is preferable to change the oscillation frequency of the oscillator that determines the oscillation frequency of the drive signal. As the oscillator, for example, a crystal oscillator or a voltage controlled oscillator can be used. In the case of using a crystal oscillator, a plurality of crystal resonators having different vibration frequencies may be provided in parallel, and a desired crystal resonator may be selectively switched. In the case of using a voltage controlled resonator, a variable potential source may be used.
[0040]
Further, the control means controls the high frequency power supply device according to the external signal according to an external signal as desired, and the high frequency is PWM controlled at a frequency sufficiently higher than the frequency of the low frequency AC voltage and sufficiently lower than the frequency of the high frequency AC voltage. It is allowed to have a function capable of outputting an AC voltage. The “external signal” means a signal coming from the outside of the induction heating device. For example, in the case of a copying machine equipped with an induction heating device in which an object to be heated is a heating roller, that is, an induction heating roller device, the copying This signal is selectively generated so that the induction heating roller device performs a desired operation in accordance with an operation by a user of the machine. Further, the control means can be configured to generate, for example, a PWM control signal in order to perform the PWM control operation. When the external signal is a digital signal, the external signal may be converted into an analog format using a D / A converter as a pre-stage for performing a process for performing a PWM control operation such as a PWM control signal when the external signal arrives. it can. Further, when the external signal is an analog signal, circuit means for performing waveform shaping can be added. However, if necessary, the PWM control signal may be formed using the external signal as it is.
[0041]
Furthermore, the control means can be provided with a soft start function that sequentially increases the high-frequency AC voltage when the power is turned on, if desired. In order to perform this soft start, a timer circuit that operates when the power is turned on, such as a time constant circuit, a resonance circuit in which the resonance voltage gradually increases, or an on signal of a low-frequency AC voltage is provided. It can be realized by shutting off several times.
[0042]
<About the effect | action of this invention> When the high frequency alternating voltage output from a high frequency power supply device is applied to an induction coil, an induction coil will be energized and excitation will be performed. When the induction coil is excited, the high frequency magnetic field generated in the induction coil is linked to the object to be heated. Therefore, in the case of a transformer method (preferably an air core transformer method), a secondary current flows in the object to be heated. The heated body starts to generate heat, and the temperature of the heated body rises. On the other hand, in the case of the eddy current loss method, when a high-frequency AC magnetic flux is interlinked in a heated body made of a magnetic material, a secondary current, in other words, an eddy current flows around the magnetic flux, so that the heated body is Fever.
[0043]
In order to control the object to be heated by controlling the frequency of the high-frequency AC voltage, the temperature of the object to be heated and the frequency of the high-frequency AC voltage at which the power transfer efficiency increases at that temperature are obtained in advance for each temperature. It is good to leave. In addition, the application time of the high frequency and high frequency voltage and the temperature rise at that time can be obtained in advance.
[0044]
Then, in a state in which the object to be heated is cooled, heating is started by applying a high-frequency AC voltage having a frequency at which a high temperature increase rate or power transmission efficiency is obtained at the initial temperature, for example, room temperature, to the object to be heated. However, if desired, the initial frequency may always be constant regardless of the initial temperature. Due to the application of the high-frequency AC voltage, the temperature of the object to be heated starts to rise. And the ultimate temperature of the to-be-heated body after predetermined time progresses is estimated, and the frequency of a high frequency alternating voltage is changed to the value from which the high temperature increase rate or electric power transmission efficiency is obtained in the ultimate temperature when the predetermined time progresses. Thereafter, by changing the frequency to a preset frequency according to the above procedure when a predetermined time has elapsed, heating is performed while maintaining a high rate of temperature increase or power transmission efficiency, so that high-speed heating control is performed.
[0045]
Also, the constant temperature maintenance control is performed under high transmission efficiency by controlling the frequency of the high-frequency AC voltage so that the temperature of the heated body is substantially constant by feeding back the temperature of the heated body by the control means.
[0046]
<Other Configurations> Although not an essential component of the present invention, a more effective induction heating roller device can be obtained by selectively implementing the following configurations as desired.
[0047]
1. (Warm-up control) During the warm-up period after the start-up, that is, the start of power supply, the heating roller can be controlled to rotate at a lower rotational speed than during normal operation.
[0048]
2. (Conveying sheet) When heating a heated object using a heating roller, the heating roller can be configured to directly contact the heated object, but if necessary, a conveying sheet is interposed between the two. Can be configured as follows. In this case, the conveyance sheet is allowed to take an endless or roll shape. By using the conveyance sheet, it becomes possible to smoothly heat and convey the heated object.
[0049]
According to a second aspect of the present invention, there is provided the induction heating apparatus according to the first aspect, wherein the control means changes the output frequency of the high frequency power supply device at predetermined intervals.
[0050]
The present invention defines a configuration of control means suitable for high-speed heating. That is, in the process of increasing the temperature from the cooled initial state to the target temperature, in order to perform induction heating while always maintaining a high rate of temperature increase or power transfer efficiency, the control means reaches that time every predetermined time. The high-speed heating control with high efficiency is performed by changing the temperature rise rate or the power transmission efficiency in the temperature range that is likely to change to an output frequency that is high each time.
[0051]
According to a third aspect of the present invention, there is provided the induction heating apparatus according to the first or second aspect, wherein the control means includes temperature detection means for detecting the temperature of the object to be heated, and temperature detection sent from the temperature detection means. It is characterized in that feedback control of the output frequency of the high frequency power supply device is performed based on the signal.
[0052]
The present invention defines a configuration of control means suitable for constant temperature maintenance control. That is, constant temperature maintenance control can be performed by changing only the frequency of the high-frequency AC voltage output from the high-frequency power supply device. In this case, the control means has a temperature increase rate or power transfer efficiency that is higher when the temperature is lower than the target temperature, and on the contrary, when the temperature is higher, a higher output frequency has a lower temperature increase rate or power transfer efficiency. Set as follows. If it does so, it will become possible to perform constant temperature maintenance control only by controlling an output frequency according to the temperature of a to-be-heated body. Further, it is possible to perform high-speed heating from the cooling state in which the detection output of the temperature detection means is compared with the target temperature data and PWM control of the high-frequency AC voltage is performed based on the difference to the target temperature.
[0053]
According to a fourth aspect of the present invention, there is provided the induction heating apparatus according to the first aspect, wherein the control means includes a temperature detection means for detecting the temperature of the object to be heated. The output frequency is changed every predetermined time, and then the output frequency of the high-frequency power supply device is feedback-controlled based on a temperature detection signal sent from the temperature detection means, thereby maintaining the predetermined temperature.
[0054]
The present invention is configured to perform high-speed heating control from the cooled initial temperature, for example, from room temperature to the target temperature, and to perform high-temperature maintenance control after reaching the target temperature. .
[0055]
An induction heating device according to a fifth aspect of the present invention is the induction heating device according to any one of the first to fourth aspects, wherein the object to be heated is a hollow heating roller; the induction coil is disposed inside the heating roller. And is wound around the axis of the heating roller;
[0056]
The present invention defines the configuration of an induction heating device suitable for heating by an air core transformer system of a heating roller used in a fixing device incorporated in an image forming apparatus or the like.
[0057]
According to a sixth aspect of the present invention, there is provided a fixing device main body provided with a pressure roller; a heating roller and a pressure roller of the fixing device main body are provided in a pressure contact relationship, and a toner image is formed between the two rollers. 6. An induction heating roller device according to claim 5, wherein the induction heating roller device is disposed so as to fix the toner image while being conveyed with the recording medium interposed therebetween.
[0058]
In the present invention, the “fixing device main body” refers to the remaining portion of the fixing device excluding the induction heating roller device. Further, the pressure roller and the heating roller may be in direct pressure contact, but may be indirectly in pressure contact with each other via a conveyance sheet or the like if necessary. Note that the transport sheet may be endless or roll-shaped.
[0059]
Thus, in the present invention, the toner image can be fixed at high speed while the recording medium on which the toner image is formed is sandwiched between the heating roller and the pressure roller and conveyed.
[0060]
An image forming apparatus according to a seventh aspect of the invention comprises: an image forming apparatus main body provided with an image forming means for forming a toner image on a recording medium; and the toner image on the recording medium disposed on the main body of the image forming apparatus. And a fixing device according to claim 6.
[0061]
In the present invention, the “image forming apparatus main body” refers to the remaining part of the image forming apparatus excluding the fixing device. The image forming means is means for forming an image for forming image information on the recording medium by an indirect method or a direct method. The “indirect method” is a method of forming an image by transfer. Examples of the image forming apparatus include an electrophotographic copying machine, a printer, and a facsimile. Examples of the recording medium include a transfer material sheet, printing paper, an electrofax sheet, and an electrostatic recording sheet.
[0062]
Thus, in the present invention, an image forming apparatus suitable for a high-speed type can be obtained.
[0063]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0064]
1 to 4 show an induction heating roller device as a first embodiment of the induction heating device of the present invention. FIG. 1 is a circuit block diagram of a main part, FIG. 2 is a circuit diagram, and FIG. FIG. 4 is a cross-sectional view of the coil and the heating roller. In each figure, AS is a low-frequency AC power supply, HFS is a high-frequency power supply device, HR is an object to be heated, IC is an induction coil, and CC is a control means.
[0065]
<Low frequency alternating current power supply AS> Low frequency alternating current power supply AS consists of a 100-V commercial alternating current power supply, for example.
[0066]
<High Frequency Power Supply Device HFS> The high frequency power supply device includes a rectified DC power supply means (not shown) and a half-bridge inverter INV using MOSFET, that is, a high frequency conversion means, as shown in FIG.
[0067]
The rectified DC power supply means includes a bridge type rectifier circuit and a smoothing capacitor, and an AC input terminal thereof is connected to the low frequency AC power supply AS, and a DC output terminal is connected to a main circuit part MC described later. Note that a rectified and smoothed DC voltage is generated at the DC output terminal.
[0068]
The inverter INV mainly includes a pair of MOSFETs Q1 and Q2, a pair of capacitors C1 and C2, a DC cut capacitor C3, and a resonance circuit RC. The pair of MOSFETs Q1 and Q2 are connected in series between the DC output terminals of the rectified DC power supply means. The pair of capacitors C1 and C2 are connected in parallel to the pair of MOSFETs Q1 and Q2. The DC cut capacitor C3 is inserted in series so as to cut a DC component when taking out a high-frequency switching voltage appearing between the drain and source of the MOSFET Q2. The resonance circuit RC forms a series resonance circuit of a resonance inductor L1 and a resonance capacitor C4. Thus, a sinusoidal high-frequency AC voltage is output between both ends of the resonant capacitor C4. The high frequency alternating voltage is applied to the induction coil IC. In FIG. 2, ws is the secondary coil of the heating roller HR, and Ra is the equivalent resistance of the secondary coil SC.
[0069]
<To-be-heated body HR> The to-be-heated body HR is composed of a heating roller and includes a roller base 1, a secondary coil ws, and a protective layer 2, and is rotated by a rotation mechanism RM.
[0070]
The roller base 1 is made of a cylindrical body made of alumina ceramic, and has a length of 300 mm and a thickness of 3 mm, for example.
[0071]
The secondary coil ws is composed of a cylindrical one-turn coil in the form of a film made of a vapor deposition film of Cu, and is disposed on the outer surface of the roller base 1 over almost the entire effective length in the axial direction. The thickness of the secondary coil ws is set so that the secondary resistance value in the rotating direction, that is, the equivalent resistance R becomes 1Ω, which is substantially the same value as the secondary reactance.
[0072]
The protective layer 2 is made of a fluororesin and is formed so as to cover the outer surface of the secondary coil SC.
[0073]
The rotation mechanism RM is a mechanism for rotating the heated body HR and is configured as follows. 3 and 4, the first end member 3A, the second end member 3B, the pair of bearings 4, 4, the bevel gear 5, the spline gear 6, and the motor 7 are configured. Yes.
[0074]
The first end member 3A includes a cap portion 3a, a drive shaft 3b, and a pointed end portion 3c. The cap portion 3a is fitted to the left end of the heated body HR from the outside in FIG. 3 and is fixed to the heated body HR using a push screw (not shown), whereby the left end of the heated body HR is fixed. I support it. The drive shaft 3b protrudes outward from the center portion of the outer surface of the cap portion 3a. The pointed portion 3c protrudes inward of the cap portion 3a from the center portion of the inner surface of the cap portion 3a.
[0075]
The second end member 3B includes a ring portion 3d. The ring portion 3d is fitted to the right end of the heating body HR in FIG. 2 from the outside and is fixed to the heating roller HR using a push screw (not shown) to support the right end of the heating body HR. ing.
[0076]
One of the pair of bearings 4 and 4 rotatably supports the outer surface of the cap portion 3a in the first end member 3A. The other supports the outer surface of the second end member 3B rotatably. Therefore, the heating roller HR is rotatably supported by the first and second end members 3A and 3B fixed to both ends thereof and the pair of bearings 4 and 4.
[0077]
The bevel gear 5 is attached to the drive shaft 3b of the first end plate 3A. The spline gear 6 meshes with the bevel gear 5. The motor 7 has a rotor shaft directly connected to the spline gear 5.
[0078]
<Induction Coil IC> As shown in FIGS. 3 and 4, the induction coil IC is wound around a coil bobbin 8 and is distributed in the axial direction of the heated body HR. Moreover, it connects in series between a pair of electric power feeding lead wires 9a and 9b, and both ends are connected to the output terminal of the high frequency power supply device HFS via electric power feeding lead wires 9a and 9b.
[0079]
The coil bobbin 8 is made of a fluororesin cylindrical body, and has a recess 8a, a support portion 8b, and a wire groove 8c. The concave portion 8a is formed at the center of the tip of the coil bobbin 8, and is relatively rotatably locked to the rotation mechanism RM. The support portion 8b is formed at the proximal end of the coil bobbin 8, and is fixed to a fixing portion (not shown). The through-groove 8c is formed in a hook shape along the axial direction in a part of the outer surface of the coil bobbin 8, and accommodates the feed lead wires 9a and 9b therein. As shown in FIG. 4, the power supply leads 9a and 9b are accommodated in the through-groove 8c, led out from the base end side of the coil bobbin 8, and a coaxial cable is connected to the output end of the high frequency power supply device HFS. Connect through.
[0080]
Thus, the induction coil IC is used in a stationary state, and since the feeding lead wires 9a and 9b are housed in the through-groove 8c and are close to the induction coil IC, there is almost no flux linkage. Almost no eddy current loss occurs in the power supply leads 9a and 9b.
On the other hand, the induction coil IC is inserted into the heated body HR from the ring portion 3d of the second end member 3B, and the recess 8a formed at the tip of the coil bobbin 8 has a pointed end of the first end plate 3A. The support portion 8d formed at the base end as described above is engaged with the portion 3c and fixed to the fixed portion, so that it is supported in a coaxial relationship with the heated body HR and the heating roller HR rotates. But still state is maintained.
[0081]
<Control Unit CC> The control unit CC includes a crystal oscillator OSC and a timer TM as shown in FIG. 1, and supplies a drive signal whose frequency is controlled to a pair of MOSFETs Q1 and Q2 of the high frequency power supply device HFS.
[0082]
The crystal oscillator OSC includes a plurality of crystal resonators X1, X2, X3,... Xn and a changeover switch SW. The plurality of crystal resonators X1, X2, X3,... Xn have different resonance frequencies. The changeover switch SW selects a desired crystal oscillator from among the plurality of crystal oscillators X1, X2, X3,... Xn and causes the oscillator of the crystal oscillator OSC to contribute to oscillation.
The timer TM generates a plurality of timer outputs every predetermined time. Then, the selector switch SW is sequentially switched in synchronization with the timer output.
[0083]
<Circuit Operation> Next, circuit operation in the present embodiment will be described. An operation in the case where the heated body HR is heated from a cooled state to a desired temperature necessary for heat fixing will be described.
[0084]
When the low frequency AC power supply AS is turned on, the low frequency AC voltage is converted into a DC voltage rectified and smoothed by the rectified DC power supply means of the high frequency power supply device HFS, and the DC power supply voltage is supplied to the DC input terminal of the inverter INV. .
[0085]
On the other hand, the change-over switch SW of the control means CC is initially in the position shown in FIG. 1, and the crystal resonator X1 is connected to the crystal oscillator OSC. At the same time, the timer TM starts a timed operation, and for a predetermined time, the crystal oscillator OSC starts the temperature increase from the cold state and reaches a predetermined temperature after the predetermined time until the temperature increase rate or The oscillation operation is performed at the first frequency f1 at which the power transfer efficiency is relatively high. As a result, the control means CC alternately supplies the drive signal having the first frequency f1 to the MOSFETs Q1 and Q2 of the inverter INV of the high frequency power supply device HFS. For this reason, the inverter INV outputs a high-frequency AC voltage having the first frequency f1. The voltage is applied to the induction coil IC.
[0086]
The induction coil IC is energized to generate a high frequency magnetic field when a high frequency AC voltage having a first frequency f1 is applied. Since this high-frequency magnetic field is linked to the secondary coil ws of the heated body HR surrounding the induction coil IC, both are air-core transformer coupled. As a result, a secondary voltage is induced in the secondary coil ws of the heated body HR, and the secondary current flows through the secondary coil, so that the heated body HR generates heat under a high temperature increase rate or power transmission efficiency. Thus, the heated body HR starts to rise in temperature.
[0087]
Then, when a predetermined time has elapsed, the changeover switch SW opens the crystal resonator X1 by the time limit operation of the timer TM, and then the crystal resonator X2 is connected to the crystal oscillator OSC. As a result, the crystal oscillator OSC performs an oscillation operation at the second frequency f2 in which the rate of temperature increase or the power transfer efficiency is relatively high in the second temperature zone up to the predetermined temperature after a predetermined time. As a result, the control means CC alternately supplies the drive signal having the second frequency f2 to the MOSFETs Q1 and Q2 of the inverter INV of the high frequency power supply device HFS. For this reason, the inverter INV outputs a high-frequency AC voltage having the second frequency f2. Since the induction coil IC is energized and the heated body HR generates heat, the heated body HR continues to rise in temperature.
[0088]
Hereinafter, since the crystal unit is switched every predetermined time in the same manner as described above, the frequency of the high-frequency AC voltage is switched so as to have a high temperature increase rate or power transfer efficiency in each time zone. High efficiency heating is sustained. As a result, the heated zone HR is heated to a desired temperature at a high speed.
[0089]
Next, the temperature rise test result of the induction heating roller device as the first embodiment in the induction heating device of the present invention will be described with reference to FIGS.
[0090]
FIG. 5 is a graph showing the relationship between the energization time and the temperature rise of the heated object. In the figure, the horizontal axis represents energization time [sec], and the vertical axis represents temperature rise [deg]. The energization time indicates the elapsed time from the start of application of the high-frequency AC voltage to the induction coil. The temperature increase indicates the temperature that has increased with respect to the room temperature of the heated object. The curve in the figure shows the change in the temperature rise of the object to be heated when a high-frequency AC voltage having the same frequency is continuously applied to the induction heating device. A plurality of curves represent variation among a plurality of induction heating devices of the same specification.
[0091]
As can be understood from the figure, when the frequency of the high-frequency AC voltage to be applied is the same, the gradient of the temperature rise of the heated object decreases with time, indicating that there is a saturation tendency. Therefore, it takes about 14 to 18 seconds for the temperature rise of the heated object to reach about 150 ° C. On the other hand, if it is assumed that the gradient of the temperature rise immediately after the start of the application of the high-frequency AC voltage is unchanged as shown by the dotted line in the figure, it should reach 150 ° C. in about 10.5 seconds.
[0092]
FIG. 6 is a graph showing the relationship between the frequency of the high-frequency AC voltage and the temperature increase rate for each energization time zone. In the figure, the horizontal axis represents frequency [MHz], and the vertical axis represents temperature increase rate [mdeg / s · W]. The curve in the figure shows a first time zone consisting of 0 to 4.5 seconds from the start of application of the high-frequency AC voltage to the induction heating roller device in the first embodiment, and a second time zone consisting of 4.5 to 9 seconds. And the relationship between the frequency and the temperature rise rate in the third time zone consisting of 9 to 13.5 seconds.
[0093]
As can be seen from the figure, the highest temperature rise rate and the lowest temperature rise rate are obtained in each time zone when the first time zone is 2.4 MHz, the second time zone and the third time zone. 2.3 MHz. Therefore, if the high-frequency AC voltage is changed with the elapsed time as shown by the arrow A, high-speed heating can be performed while maintaining a high temperature rise rate. On the other hand, when the change is made as shown by the arrow B, the temperature rise slows.
[0094]
7 and 8 show the test results similar to those shown in FIGS. 5 and 6 when the material of the heated object is different.
[0095]
In FIG. 7, it takes about 11.7 to about 12.5 seconds to reach about 150 ° C., and the saturation tendency of the temperature rise of the heated object with respect to the energization time is relatively small, but there is no saturation phenomenon Is reached in about 10 seconds. In FIG. 8, the highest frequency in the first time zone in 0 to 4.5 seconds is 3.1 MHz, and the highest frequency in the second time zone in 4.5 to 9 seconds is 2.9 MHz. . Therefore, if the high-frequency AC voltage is changed with the elapsed time as shown by the arrow A, high-speed heating can be performed while maintaining a high temperature rise rate. On the other hand, when the change is made as shown by the arrow B, the temperature rise slows.
[0096]
Hereinafter, other embodiments of the induction heating apparatus of the present invention will be described with reference to FIGS. 9 and 10. In addition, in each figure, the same part as FIG. 1 thru | or FIG. 4 is attached | subjected, and description is abbreviate | omitted.
[0097]
FIG. 9 is a circuit block diagram of the main part showing an induction heating roller device as a second embodiment of the induction heating device of the present invention. In the present embodiment, the control means CC uses a voltage controlled oscillator VCO instead of the crystal oscillator OSC. The variable control potential source E of the voltage controlled oscillator VCO is configured to be variably operated according to each time zone by the timer TM.
[0098]
FIG. 10 is a circuit block diagram of the main part showing an induction heating roller device as a third embodiment of the induction heating device of the present invention. In the present embodiment, the control means CC is configured such that the variable control potential source E of the voltage controlled oscillator VCO is constituted by the terminal voltage of the thermistor RT which is the temperature detection means, and is variably operated according to the temperature of the heated body HR. It is configured. The thermistor RT has one end connected to the potential source e via the resistor R and the other end grounded.
[0099]
FIG. 11 is a longitudinal sectional view showing an embodiment of the fixing device of the present invention. In the figure, 21 is an induction heating roller device, 22 is a pressure roller, 23 is a recording medium, 24 is toner, 25 is a gantry, and IC is an induction coil.
[0100]
As the induction heating roller device 21, those shown in FIGS. 1 to 4, 9 and 10 can be used.
[0101]
The pressure roller 22 is disposed so as to be in pressure contact with the heating roller HR of the induction heating roller device 21 and conveys the recording medium 23 while narrowly pressing between them.
[0102]
The recording medium 23 forms an image by the toner 24 adhering to the surface thereof.
[0103]
The gantry 25 mounts the above constituent elements (excluding the recording medium 23) in a predetermined positional relationship.
[0104]
In the fixing device, the recording medium 23 on which the toner 24 adheres and forms an image is inserted between the heating roller HR and the pressure roller 22 of the induction heating roller device 21 and conveyed. The toner 24 is heated and melted by receiving heat from the heating roller HR, and heat fixing is performed.
[0105]
FIG. 12 is a conceptual sectional view of a copying machine as an embodiment of the image forming apparatus of the present invention.
[0106]
In the figure, 31 is a reading device, 32 is an image forming means, 33 is a fixing device, and 34 is an image forming device case.
[0107]
The reading device 31 optically reads a base paper to form an image signal.
[0108]
The image forming means 32 forms an electrostatic latent image on the photosensitive drum 32a based on the image signal, attaches toner to the electrostatic latent image to form a reverse image, and transfers this to a recording medium such as paper. To form an image.
[0109]
The fixing device 33 has the structure shown in FIG. 11, and heats and melts the toner adhering to the recording medium.
[0110]
The image forming apparatus case 34 accommodates the above-described devices and means 31 to 33, and includes a transport device, a power supply device, a control device, and the like.
[0111]
【The invention's effect】
According to the first aspect of the present invention, by including the control means for controlling the high frequency power supply device so that the output frequency changes as the temperature of the object to be heated increases, the temperature of the object to be heated is changed. It is possible to provide an induction heating apparatus that can perform high-frequency induction heating while maintaining high power transmission efficiency.
[0112]
According to the second aspect of the invention, in addition, the control means can change the output frequency of the high-frequency power supply device every predetermined time, thereby providing an induction heating device suitable for high-speed heating of the object to be heated.
[0113]
According to the invention of claim 3, in addition, the control means includes temperature detection means for detecting the temperature of the object to be heated, and feedback control is performed on the output frequency of the high frequency power supply device based on the temperature detection signal sent from the temperature detection means. By doing, the induction heating apparatus suitable for constant temperature maintenance can be provided.
[0114]
According to the invention of claim 4, in addition, the control means includes a temperature detection means for detecting the temperature of the object to be heated, and changes the output frequency of the high-frequency power supply device every predetermined time from turning on the power to a predetermined temperature, and thereafter Induction heating apparatus suitable for high-speed heating of the object to be heated and subsequent constant temperature maintenance by feedback control of the output frequency of the high-frequency power supply device based on a temperature detection signal sent from the temperature detection means, thereby maintaining the predetermined temperature. Can be provided.
[0115]
According to the invention of claim 5, in addition, the object to be heated is a hollow heating roller, and the induction coil is disposed inside the heating roller and wound around the axis of the heating roller. An induction heating device suitable for induction heating of a roller can be provided.
[0116]
According to the invention of claim 6, it is possible to provide a fixing device having the effects of claims 1 to 5.
[0117]
According to the seventh aspect of the invention, an image forming apparatus having the effects of the first to fifth aspects can be provided.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram of a main part showing an induction heating roller device as a first embodiment of an induction heating device of the present invention.
[Fig. 2] Circuit diagram
FIG. 3 is a partially cutaway central longitudinal sectional view of the induction coil and heating roller.
FIG. 4 is a cross-sectional view of the same
FIG. 5 is a graph showing the relationship between the energization time and the temperature rise of the heated object.
FIG. 6 is a graph showing the relationship between the frequency of the high-frequency AC voltage and the temperature rise for each energization time period.
FIG. 7 is a graph showing the relationship between the energization time and the temperature rise of the heated object
FIG. 8 is a graph showing the relationship between the frequency of the high-frequency AC voltage and the temperature rise for each energization time period.
FIG. 9 is a circuit block diagram of a main part showing an induction heating roller device as a second embodiment of the induction heating device of the present invention.
FIG. 10 is a circuit block diagram of a main part showing an induction heating roller device as a third embodiment of the induction heating device of the present invention.
FIG. 11 is a longitudinal sectional view showing an embodiment of a fixing device of the present invention.
FIG. 12 is a conceptual cross-sectional view of a copying machine as an embodiment of the image forming apparatus of the present invention.
[Explanation of symbols]
AS ... Low frequency AC power supply, CC ... Control means, HFS ... High frequency power supply device, HR ... Heating roller, IC ... Induction coil, OSC ... Crystal oscillator, SW ... Changeover switch, TM ... Timer, X1, X2, X3, Xn ... Crystal oscillator

Claims (7)

A high frequency power supply that outputs a variable frequency high frequency alternating voltage;
An induction coil to which a high-frequency AC voltage of a high-frequency power supply device is applied;
An object to be heated that generates heat by flowing a secondary current by magnetic coupling to the induction coil;
Control means for controlling the high-frequency power supply so that the output frequency changes as the temperature of the object to be heated increases;
An induction heating device comprising: The induction heating apparatus according to claim 1, wherein the control means changes the output frequency of the high-frequency power supply device at predetermined time intervals. The control means includes temperature detection means for detecting the temperature of the object to be heated, and feedback-controls the output frequency of the high-frequency power supply device based on a temperature detection signal sent from the temperature detection means. 2. The induction heating apparatus according to 2. The control means includes temperature detection means for detecting the temperature of the object to be heated, and changes the output frequency of the high-frequency power supply device every predetermined time from turning on the power to a predetermined temperature, and then a temperature detection signal sent from the temperature detection means The induction heating device according to any one of claims 1 to 3, wherein the temperature is maintained at a predetermined temperature by feedback control of the output frequency of the high-frequency power supply device based on the above. The object to be heated is a hollow heating roller;
The induction coil is disposed inside the heating roller and wound around the axis of the heating roller;
The induction heating device according to any one of claims 1 to 4, wherein A fixing device body provided with a pressure roller;
A heating roller is provided in a pressure contact relationship with the pressure roller of the fixing device main body so as to fix the toner image while conveying a recording medium on which a toner image is formed between both rollers. 5 an induction heating roller device;
A fixing device. An image forming apparatus main body provided with an image forming means for forming a toner image on a recording medium;
The fixing device according to claim 6, wherein the fixing device is disposed in the image forming apparatus main body and fixes the toner image on the recording medium;
An image forming apparatus comprising:

Images