JP2004004205A - Fixing device and image forming device - Google Patents

Abstract

A dielectric heating type fixing device and an image forming apparatus capable of maintaining a wide power control range while absorbing voltage fluctuations.
Power control and temperature control are performed by two systems of frequency modulation and duty control, and constant frequency power is supplied to a series resonance circuit by performing frequency modulation with a signal from a voltage detection circuit. Temperature control is performed by control.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to an induction heating type fixing device for heating an unfixed image formed and carried on a recording material to form a permanent fixed image, and a copy machine or a printer including such a fixing device. The present invention relates to an image forming apparatus using an electrophotographic method or an electrostatic recording method.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus, a heat roller type fixing device has been widely used as a fixing device for heating an unfixed image formed on a recording material, that is, a toner image to form a permanent fixed image.
[0003]
The fixing device of the heat roller type basically has a heating roller having a built-in halogen heater as a heat source, that is, a fixing roller, and a pressing roller pressed against the fixing roller. The fixing of the toner image is performed by applying heat and pressure while nipping and conveying a recording material (recording medium) into the section.
[0004]
In recent years, a film heating type fixing device has been widely used. In this type of fixing device, heat of a heat source is applied to a recording material via a film to fix a toner image. As a heat source, a so-called ceramic heater, in which a metal oxide film resistor is printed on a ceramic substrate and heat is generated by applying an electric current to the printed resistor, is often used.
[0005]
This ceramic heater has a low heat capacity and has a characteristic of rapidly rising in temperature, thereby achieving a reduction in first print time and energy saving.
[0006]
However, although this conventional film heating method functions effectively in mono-color fixing, when performing color and high-speed fixing, a temperature and a pressure that can simultaneously perform the synthesis processing of each color are required. In this system using a ceramic heater having a heat capacity, it was difficult to function effectively.
[0007]
Therefore, an induction heating type fixing device has been proposed as a fixing device capable of overcoming these problems. This induction heating type fixing device uses a magnetic field such as a metal wire or a conductive material by magnetic field generating means such as a wire loop, a heating coil, and an exciting coil to generate a magnetic material such as an eddy current generated in the magnetic material. Is heated to perform fixing.
[0008]
This induction heating type fixing device can reduce the heat capacity similarly to the film heating type and can obtain a high-speed temperature rising characteristic, and is close to direct heating which generates heat at a portion near the fixing nip portion. By adopting the system, excellent temperature rising characteristics, excellent thermal response characteristics, and excellent thermal efficiency can be realized, and it is suitable for performing color fixing at high speed.
[0009]
Conventionally, in a fixing device using this induction heating, a single voltage resonance converter is used as a fixing power supply circuit, a parallel resonance circuit including a resonance capacitor and an exciting coil is connected as a load, and the fixing power supply circuit is disposed to face the fixing pressure roller. A rotating body (heating element) made of magnetic metal is formed around the exciting coil, temperature is detected by a thermistor as a temperature detecting member pressed against the heating element, and the ON time width is fixed with the OFF time fixed to the control of the switch element. The temperature control is performed by using the power control by the on-duty control means that changes the temperature.
[0010]
With such a configuration, a heating means close to direct heating and excellent thermal responsiveness and controllability have been achieved.
[0011]
[Problems to be solved by the invention]
However, the circuit using voltage resonance as described above has two problems described below.
[0012]
The first problem is that the flyback voltage of the resonance circuit generated when the switch element is turned off is applied to the switch element as it is, so that a high breakdown voltage switch element is required and the cost is increased.
[0013]
The second problem is that in a single voltage resonance circuit, temperature control, that is, it is necessary to perform on-time width control with fixed off-time for power control, but in on-time width control, if the time width is too short, The flyback voltage becomes too small, and the voltage applied to the switch element cannot be reduced to 0 or less. As a result, the switching element is turned on in a state where a high voltage is applied when a current is flowing, so that switching loss is increased, efficiency is deteriorated, and the switching element may be broken.
[0014]
In particular, in the latter case, as the input voltage increases, the switching element is turned on while a large voltage is applied, so that the loss increases in proportion to the voltage.
[0015]
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a dielectric heating type fixing device and an image forming apparatus capable of maintaining a wide power control range while absorbing voltage fluctuations.
[0016]
Another object of the present invention is to stabilize image quality by maintaining a uniform fixing property and expanding a controllable area without changing the apparatus even in regions where power supply voltages are different. An object of the present invention is to provide a dielectric heating type fixing device and an image forming apparatus.
[0017]
Another object of the present invention is to provide a dielectric heating type fixing apparatus and an image forming apparatus which are low cost, have small switching loss, and are efficient.
[0018]
[Means for Solving the Problems]
The above object is achieved by a fixing device and an image forming apparatus according to the present invention. In summary, the present invention is a fixing device for fixing an image by a developer to a recording medium,
A conductive heating element,
A series resonance circuit including an excitation coil and a resonance capacitor for heating the conductive heating element,
Switching control means including a half-bridge type current resonance converter including at least two switch elements for supplying power to the series resonance circuit,
Temperature detection means including a detection member for detecting the temperature of the conductive heating element,
Voltage detection means for detecting an AC voltage input to the series resonance circuit;
The power control for controlling the maximum power supplied to the fixing device and the temperature control for controlling the power supplied to the fixing device so as to keep the temperature of the fixing device constant are performed by two systems of frequency modulation and duty control. A fixing device characterized in that:
[0019]
According to one embodiment of the present invention, the switching control means performs the power control based on frequency modulation by a signal from the voltage detection means, and supplies constant power to the series resonance circuit; Control means for performing the temperature control based on duty control in accordance with a signal from the means.
[0020]
According to another embodiment of the present invention, the switching control unit performs the power control based on a duty control based on a signal from the voltage detection unit, and supplies a constant power to the series resonance circuit. Control means for performing the temperature control based on frequency modulation by a signal from the detection means.
[0021]
According to another embodiment of the present invention, the switching control unit performs the power control based on frequency modulation based on a signal from the voltage detection unit, and supplies a constant power to the series resonance circuit. Control means for performing the temperature control based on the frequency modulation and the duty control in accordance with a signal from the detection means.
[0022]
According to another embodiment of the present invention, the conductive heating element is a rotating body, and the conductive heating element is a film body.
[0023]
According to a second aspect of the present invention, there is provided an image forming apparatus including the fixing device.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the fixing device and the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.
[0025]
Example 1
A first embodiment of the present invention will be described with reference to FIGS.
[0026]
First, an electrophotographic laser beam printer, which is an image forming apparatus of the present embodiment, will be described with reference to FIG.
[0027]
As shown in FIG. 1, the image forming apparatus of the present embodiment has an electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 101 as an image carrier substantially at the center of the apparatus main body, and around the photosensitive member. , A primary charger 102, a developing device 104, a transfer roller 108, a cleaning device 109, and the like.
[0028]
The photosensitive drum 101 is driven to rotate at a predetermined peripheral speed, ie, a process speed, in the direction of the arrow in the drawing, and is uniformly charged to a predetermined polarity and potential by the primary charger 102 during the rotation process.
[0029]
The laser beam scanner 103 outputs a laser beam L modulated corresponding to a time-series electric digital pixel signal of target image information input from a host device (not shown) such as a host computer, a word processor, and an image reading device. An electrostatic latent image corresponding to the target image information is formed on the surface of the photosensitive drum 101 uniformly charged. The electrostatic latent image is developed by a developer of the developing device 104 to be a toner image.
[0030]
On the other hand, the recording material (recording medium) P stacked on the paper feed tray 105 is fed out one by one by the paper feed roller 106, and the registration roller 107 is synchronized with the toner image on the photosensitive drum 101, It is introduced into a transfer nip T formed by the transfer roller 101 and the transfer roller 108. In the transfer nip portion T, the toner image carried on the photosensitive drum 101 is transferred to the recording material P by the transfer bias applied to the transfer roller 108.
[0031]
After the transfer, the toner remaining on the photosensitive drum 101 is removed by the cleaning device 109, and the photosensitive drum 101 is provided for the next image formation.
[0032]
The recording material P to which the toner image has been transferred is conveyed to the fixing device 110, where the toner image is fixed by applying heat and pressure, and is discharged to the discharge tray 111.
[0033]
Next, the fixing device 110 of this embodiment will be described. The fixing device 110 of this embodiment is of an induction heating type using a magnetic induction heat-generating film (metal film).
[0034]
First, the overall configuration of the fixing device 110 will be described with reference to FIG.
[0035]
The fixing device 110 includes a heating member 110A and a pressure roller 110B that presses against the heating member 110A to form a fixing nip N.
[0036]
The heating element 110A has a film inner surface guide stay 111 of a semicircular trough-shaped upward cross section, and an excitation coil as a wire loop, that is, a heating coil 112, and a core material 113 as an excitation core are provided inside thereof. It is arranged. A cylindrical or endless magnetically induced heat generating film 114 is loosely fitted outside the guide stay 111. Further, a cover plate 115 is placed over the upper opening of the guide stay 111, and a pressing stay 116 is further provided thereon.
[0037]
The pressure roller 110B is composed of a core bar 117a and an elastic layer 117b of silicone rubber or fluorine rubber coated around the core bar 117a, and is pressed against the lower surface of the guide stay 111 with a predetermined pressing force with the film 114 interposed therebetween. I have.
[0038]
The pressing roller 110A is rotated by the driving means M in the direction of the arrow in the figure. Due to the frictional force between the pressure roller 110A and the outer surface of the film 114 by this rotation drive, the film 114 is brought into close contact with the lower surface of the guide stay 111 to rotate around the guide stay 111.
[0039]
Further, a thermistor 118 as a temperature detecting member is disposed at a portion corresponding to the fixing nip portion N on the lower surface of the guide stay 111 on the inner surface of the film 115.
[0040]
Further, a power supply device 120 for applying a high-frequency current to the exciting coil 111 is connected.
[0041]
Next, the magnetically induced heat generating film 114 of the present embodiment will be described with reference to FIG.
[0042]
The film 114 has, in order from the inside to the outside, a three-layer structure of a heating element layer 114a, an elastic layer 114b, and a release layer 114c made of a magnetic metal, a metal, a magnetic material, or the like. Note that the layer configuration is not limited to this, and is appropriately set.
[0043]
When a high-frequency current is applied to the exciting coil 112 by the power supply device 120, the magnetic induction heating element layer 114a of the film 114 generates heat mainly by the magnetic induction heating in the area of the fixing nip N.
[0044]
More specifically, when a high-frequency current is applied from the power supply device 120 to the exciting coil 112, the magnetic flux indicated by the arrow H around the exciting coil 112 repeats generation and disappearance. This magnetic flux H crosses the magnetic induction heating element layer 114 a of the film 114. When a fluctuating magnetic field crosses the magnetic induction heating element layer 114a, which is a magnetic material, an eddy current indicated by an arrow A is generated in the magnetic induction heating element layer 114a so as to generate a magnetic field that hinders a change in the magnetic field.
[0045]
Due to the skin effect, the eddy current flows almost concentratedly on the surface of the magnetic induction heating element layer 114a on the side of the excitation coil 112, and generates heat (Joule heat) with electric power proportional to the skin resistance of the magnetic induction heating element layer 114a. .
[0046]
The temperature of the fixing nip portion N is detected by a thermistor 118, and the detected temperature information is input to a control circuit of the power supply device 120, and the power supply device 120 excites the temperature so that the temperature of the fixing nip portion N becomes a predetermined fixing temperature. The high frequency current applied to the coil 112 is controlled.
[0047]
Next, the power supply device 120, which is a feature of the present invention, will be described.
[0048]
As shown in FIG. 4, the power supply device 120 includes a line filter 1, a bridge diode 2, a filter capacitor 3, a resonance capacitor 4a forming a series resonance circuit 4, and an exciting coil 4b (described with reference to FIG. 2). The first and second switch elements Q1 and Q2, the first and second reverse blocking diodes 6, 7 and the switching control circuit 8, which constitute the switching control means 5, A voltage detection circuit 9 as voltage detection means and a temperature detection circuit 10 as temperature detection means connected to the thermistor 118 are provided. As described later in detail, the switching control unit 5 supplies a constant power to the series resonance circuit 4 irrespective of the magnitude or fluctuation of the AC input voltage which is the power supply voltage.
[0049]
The voltage input from the AC line is double-wave rectified by the bridge diode 2 via the line filter 1 and applied to the first and second switch elements Q1 and Q2. When the first switch element Q1 is turned on, a current starts to flow in the series resonance circuit 4. If the first switch element Q1 is kept on as it is, the current becomes a peak current determined by the series resonance circuit (LC circuit) 4 and the resistance of the circuit. Decrease.
[0050]
Next, when the first switch element Q1 is turned off and then the second switch element Q2 is turned on, the coil current and the current due to the charges stored in the resonance capacitor 4a flow to GND through the second switch element Q2, This current also increases with time, and after reaching a peak value determined by the circuit constant, the current decreases. At this time, the current flowing through the series resonance circuit 4 becomes a sine wave.
[0051]
If the second switch element Q2 is turned on while the first switch element Q1 is on, a large current flows through the first and second switch elements Q1 and Q2, so that the first switch element Q1 is turned on. Is on, the second switch element Q2 must be in the off state. Further, even if the gate of the first switch element Q1 is set to Low to turn off the first switch element Q1, the switch cannot be turned off immediately. It is necessary to turn on the second switch element Q2 after ns. This time is called dead time. The first and second switch elements Q1 and Q2 are turned on alternately with a dead time therebetween.
[0052]
Next, a gate drive (gate drive) circuit 80 in the switching control circuit 8 for turning on and off the first and second switch elements Q1 and Q2 will be described with reference to FIG. In this embodiment, the gate drive circuit 80 is a half-bridge type current resonance converter.
[0053]
As shown in the figure, in the half-bridge circuit constituting the gate drive circuit 80, the configuration of the upper gate drive circuit requires some contrivance. Usually, driving is performed using a bootstrap circuit or floating is performed by a gate transformer. In this embodiment, a gate transformer is used to insulate the secondary circuit from the line.
[0054]
Outputs from regulator control circuits (drive circuits) 81 and 82 are input to transformers 83 and 84, and diodes 85 and 86 are used to turn on the switches quickly. Transistors 87 and 88 are used to quickly release the stored charge.
[0055]
Next, the temperature detection circuit 10 will be described with reference to FIG.
[0056]
The temperature detection circuit 10 compares the voltage V1 of the detection circuit 60 having the thermistor 118 and the detection resistors 61 and 62 and a predetermined reference voltage Vr from the constant voltage power supply 64 with an operational amplifier (comparator) having a feedback resistor 63. Compare at 65. The output Vs controls the transistor circuit 68 having the transistors 66 and 67 to control the OFF width of the duty control circuit 84 provided in the switching circuit 8, that is, the duty width.
[0057]
Next, the voltage detection circuit 9 will be described with reference to FIG. In this embodiment, photocouplers 91 and 92 are used to detect the input voltage.
[0058]
Further, the voltage detection circuit 9 is provided with resistors 93a to 93e, diodes 94a and 94b, and zener diodes 95a to 95c, as shown in FIG. Then, the time required to reach the reference voltage is transmitted to the secondary side by the photocouplers 91 and 92. On the secondary side, the time is measured, converted into a power supply voltage, and compared with a power supply voltage table to estimate the power supply voltage. This output is transmitted to a frequency modulation circuit 82 provided in the switching circuit 80 to modulate the switching frequency.
[0059]
In other words, when the power supply voltage is high, the switching frequency is increased to increase the impedance of the system to reduce the power supplied to the power supply voltage, and when the power supply voltage is low, the frequency is reduced by conversely. By lowering the impedance and increasing the supply power for the voltage, constant power can always be supplied independently of the voltage.
[0060]
In a current resonance circuit, when driving at a frequency lower than the resonance point (capacitor area), the impedance of the resonance circuit increases when the frequency is lower than that, and the power decreases even if the frequency is lowered below that. It is necessary to avoid frequencies below the point. Here, a current flowing through the resonance circuit is compared with the gate pulse, and a limiter, that is, a resistor 93a is provided to the gate pulse so that the gate pulse is turned off before the current reversal.
[0061]
As described above, in the fixing device of the present embodiment, the resonance circuit is changed from a conventional parallel resonance circuit to a series resonance circuit, and the drive by the herb bridge circuit is performed, so that the voltage applied to the switch element is suppressed to about the power supply voltage. Further, a current resonance type converter for performing a switching operation when the current is zero is constituted, and further, power control for controlling the maximum power supplied to the fixing device and supply to the fixing device so as to keep the temperature of the fixing device constant. The temperature control for controlling the power to be performed is divided into two systems of frequency modulation and duty control, so that it is possible to use a relatively low-cost, low-voltage, large-current switching element and to control the temperature. It is possible to provide a wide power range, and the stable operation region can be expanded.
[0062]
More specifically, in the present invention, the power supply device (inverter) 120 is different from the fixing device 110 in that a series resonance circuit including a capacitor 4a having a fixed capacitance and a coil 4b (excitation coil 112) having a fixed inductance is provided. 4 is supplied with a power supply voltage and switching is performed to supply power. The power supply voltage varies depending on, for example, a region or a country, and it is necessary to perform power control by controlling the duty or frequency according to the power supply voltage. In other words, power control is performed, that is, by applying a power limiter operation, so that current does not flow too much.
[0063]
On the other hand, according to the present invention, the control to narrow down the power supplied to the series resonance circuit, that is, the power supplied to the fixing device by the temperature, that is, the temperature control is performed, and the temperature of the fixing device is controlled to be constant.
[0064]
Example 2
Next, a second embodiment of the present invention will be described with reference to FIG.
[0065]
According to the present embodiment, as in the first embodiment, the power supply device 120 includes the line filter 1, the bridge diode 2, the filter capacitor 3, the resonance capacitor 4a forming the series resonance circuit 4, and the exciting coil 4b. The first and second switching elements Q1 and Q2, the first and second reverse blocking diodes 6, 7 and the switching control circuit 8, which constitute the switching control means 5, the voltage detection circuit 9 as voltage detection means, and the thermistor 118 And a temperature detection circuit 10 as a connected temperature detection means.
[0066]
Further, according to the present embodiment, the switching control circuit 8 is connected to the gate drive circuit 80 connected to the switching elements Q1, Q2, the frequency modulation circuit 82 connected to the temperature detection circuit 10, and the voltage detection circuit 10. The duty control circuit 84 is provided.
[0067]
In the present embodiment, unlike the first embodiment, the frequency modulation control is performed by detecting the temperature of the temperature detection circuit 10, and the duty control is performed by detecting the voltage by the voltage detection circuit 9, and the power control is performed.
[0068]
In this embodiment, the same effects as in the first embodiment can be obtained.
[0069]
Example 3
Next, a third embodiment of the present invention will be described with reference to FIG.
[0070]
According to the present embodiment, as in the first embodiment, the power supply device 120 includes the line filter 1, the bridge diode 2, the filter capacitor 3, the resonance capacitor 4a forming the series resonance circuit 4, and the exciting coil 4b. The first and second switching elements Q1 and Q2, the first and second reverse blocking diodes 6, 7 and the switching control circuit 8, which constitute the switching control means 5, the voltage detection circuit 9 as voltage detection means, and the thermistor 118 And a temperature detection circuit 10 as a connected temperature detection means.
[0071]
Further, according to the present embodiment, the switching control circuit 8 includes the gate drive circuit 80 connected to the switching elements Q1 and Q2, the frequency modulation circuit 82 connected to the voltage detection circuit 9 and the temperature detection circuit 10, and the temperature detection circuit. It has a duty control circuit 84 connected to the circuit 10.
[0072]
In the present embodiment, unlike the first and second embodiments, frequency modulation is performed based on signals from the voltage detection circuit 9 and the temperature detection circuit 10, and the temperature is controlled when power control over a frequency modulation width is required. Duty control is performed based on a signal from the detection circuit.
[0073]
That is, power control based on frequency modulation can be performed by a signal from the voltage detection circuit 9, and temperature control based on frequency modulation and duty control can be performed by a signal from the temperature detection circuit 10.
[0074]
In this embodiment, the same effects as in the first embodiment can be obtained.
[0075]
In the above-described embodiment, the description has been given of the case of the fixing device using the magnetic induction heating film as the conductive heating element. However, it goes without saying that the present invention can be applied to the fixing device using the magnetic induction heating roller.
[0076]
【The invention's effect】
As is apparent from the above description, the fixing device and the image forming apparatus of the present invention include a conductive heating element, a series resonance circuit including an exciting coil and a resonance capacitor for generating heat from the conductive heating element, and a series resonance circuit. Control means provided with a half-bridge type current resonance converter including at least two switch elements for supplying power to the power supply, temperature detection means including a detection member for detecting a temperature of the conductive heating element, and a series resonance circuit Voltage control means for detecting the AC voltage input to the fixing device, and controlling the maximum power supplied to the fixing device and controlling the power supplied to the fixing device so as to keep the temperature of the fixing device constant. Since the temperature control is performed by two systems of frequency modulation and duty control,
(1) It is possible to maintain a wide power control range while absorbing voltage fluctuations.
(2) Even in regions where the power supply voltage is different, it is possible to stabilize the image quality by keeping the fixing property uniform and expanding the controllable area without changing the apparatus.
(3) Low cost, low switching loss and good efficiency.
Such an effect can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a cross-sectional view showing one embodiment of a fixing device according to the present invention.
FIG. 3 is a schematic diagram for explaining heat generation due to magnetic flux.
FIG. 4 is a diagram illustrating an embodiment of a control circuit of the fixing device.
FIG. 5 is a diagram showing a gate drive circuit in the control circuit of FIG. 4;
FIG. 6 is a diagram illustrating a temperature detection circuit in the control circuit of FIG. 4;
FIG. 7 is a diagram illustrating a voltage detection circuit in the control circuit of FIG. 4;
FIG. 8 is a diagram showing another embodiment of the control circuit in the fixing device according to the present invention.
FIG. 9 is a diagram showing another embodiment of the control circuit in the fixing device according to the present invention.
[Explanation of symbols]
Reference Signs List 4 series resonance circuit 4a resonance capacitor 4b exciting coil 5 switching control means 6 reverse blocking diode 8 switching control circuit 9 voltage detection circuit (voltage detection means)
10. Temperature detection circuit (temperature detection means)
110 Fixing device 114 Magnetically induced heat-generating film (film)
118 Thermistor (Temperature detecting member)
120 power supply device Q1, Q2 switch element

Claims (7)

In a fixing device for fixing an image by a developer to a recording medium,
A conductive heating element,
A series resonance circuit including an excitation coil and a resonance capacitor for heating the conductive heating element,
Switching control means including a half-bridge type current resonance converter including at least two switch elements for supplying power to the series resonance circuit,
Temperature detection means including a detection member for detecting the temperature of the conductive heating element,
Voltage detection means for detecting an AC voltage input to the series resonance circuit;
The power control for controlling the maximum power supplied to the fixing device and the temperature control for controlling the power supplied to the fixing device so as to keep the temperature of the fixing device constant are performed by two systems of frequency modulation and duty control. A fixing device, comprising: The switching control means performs the power control based on frequency modulation based on a signal from the voltage detection means, and supplies constant power to the series resonance circuit; and a duty control based on a signal from the temperature detection means. 2. The fixing device according to claim 1, further comprising control means for performing the temperature control. The switching control means performs the power control based on the duty control based on a signal from the voltage detection means, and supplies a constant power to the series resonance circuit. The switching control means is based on frequency modulation based on a signal from the temperature detection means. 2. The fixing device according to claim 1, further comprising control means for performing the temperature control. The switching control means controls the power control based on frequency modulation based on a signal from the voltage detection means, and supplies a constant power to the series resonance circuit. 2. The fixing device according to claim 1, further comprising control means for performing the temperature control based on the duty control. The fixing device according to claim 1, wherein the conductive heating element is a rotating body. The fixing device according to claim 1, wherein the conductive heating element is a film. An image forming apparatus comprising the fixing device according to claim 1.

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