JP2009229696A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of making a temperature distribution in an axial line direction of a heat roller more uniform compared with the conventional ones. <P>SOLUTION: The fixing device includes a heater for induction heating of one (heat roller) out of a pair of fixing rollers and fixes an image onto a recording medium by bringing the pair of fixing rollers into press contact with the recording medium having the image formed on a surface thereof. The heater includes: a plurality of excitation coils disposed in respective heating blocks into which the heat roller is divided in the axial line direction; at least two or more resonance power sources for selectively supplying AC power of a prescribed frequency to one excitation coil; a temperature detection means for detecting temperatures of the heating blocks; and a control means for controlling the frequency of the AC power in the resonance power sources on the basis of temperatures detected by the temperature detection means so that temperatures of respective heating blocks are uniform. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus.

In Patent Document 1, in order to uniformly heat the heating roller in the axial direction, a plurality of induction coils are distributed in the axial direction of the heating roller, and the heating roller is heated by switching energization to each induction coil. An image forming apparatus that switches areas is disclosed.
Patent Document 2 discloses an induction heating type fixing device that causes each induction coil to generate heat with different amounts of heat by flowing an induction current of a predetermined frequency from a single high-frequency power source to a plurality of induction coils having different resonance frequencies. It is disclosed.
JP 2003-347029 A JP 2004-333733 A

By the way, the technique of the above-mentioned patent document 1 switches the heating region of the heating roller by switching the energization to each induction coil, that is, controls the heating state of the heating roller by turning on / off the energization to each induction coil. Therefore, since linear temperature control cannot be realized, temperature ripple cannot be sufficiently reduced. Therefore, the technique disclosed in Patent Document 1 cannot be applied to color printing, for example.
In the technique disclosed in Patent Document 2, since a single high-frequency power source controls the amount of heat generated by each induction coil by switching the frequency of the induction current, the amount of heat generated by different induction coils cannot be moved up and down simultaneously.

SUMMARY An advantage of some aspects of the invention is that it provides a fixing device and an image forming apparatus capable of making the temperature distribution in the axial direction of a heating roller more uniform than in the related art.
It is intended.

In order to achieve the above object, the present invention includes a heating device that induction-heats one of the pair of fixing rollers (heating roller) as a first solving means related to the fixing device, and the pair of fixing rollers forms a surface on the surface. A fixing device that fixes an image onto a recording medium by pressing the recording medium on which the image is formed. The heating device includes a heating block and a heating block formed by dividing the heating roller into a plurality of portions in the axial direction. A plurality of exciting coils arranged at the same time, at least two or more resonance power supplies that selectively supply AC power of a predetermined frequency to any of the exciting coils, temperature detecting means for detecting the temperature of the heating block, and the temperature detection Based on the detected temperature of the means, a means is provided that includes control means for controlling the frequency of the AC power in the resonant power supply so that the temperature of each heating block becomes uniform.
Further, as a second solving means related to the fixing device, in the first solving means, the control means controls the frequency of each AC power so that the frequency difference of the AC power is outside the audible range. adopt.
As a third solving means relating to the fixing device, in the first or second solving means, the resonance power supply includes a plurality of capacitors having different capacitances, and the DC power stored in any one of the capacitors is changed to AC power. The control means adopts a means for selecting the capacitor so that the frequency of the AC power does not exceed the resonance frequency with the exciting coil that supplies the AC power.
As a fourth solving means related to the fixing device, in any one of the first to third solving means, the number of exciting coils is three and the number of resonant power supplies is two. The AC power is supplied to the central block of the heating roller, and the second resonance power supply supplies AC power to the one end block and the other end block of the heating roller.
In the present invention, a fixing device that employs any one of the first to fourth solutions is provided as a solution for the image forming apparatus, and the image formed on the recording medium is fixed by the fixing device. , Is adopted.

According to the present invention, the heating device includes any one of a plurality of exciting coils disposed in each heating block obtained by dividing the heating roller into a plurality of axial directions in the heating roller, and AC power having a predetermined frequency. Based on at least two or more resonance power supplies selectively supplied to the exciting coil, temperature detecting means for detecting the temperature of the heating block, and the temperature detected by the temperature detecting means, the temperature of each heating block is made uniform. And a control means for controlling the frequency of the AC power in the resonant power supply. Therefore, the temperature of each block can be individually controlled by varying the frequency of the AC power.
Therefore, the temperature ripple in the axial direction of the heating roller can be reduced as compared with the conventional case, and it can be applied to color image formation.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an overall configuration of a fixing device A according to the present embodiment, and FIG. 2 is a block diagram showing a functional configuration of a heating device B in the fixing device A. As shown in FIG. 1, the fixing device A includes a heating roller 1A and a pressure roller 1B, which are metal rollers, and a heating device B that generates heat from the heating roller 1A.

  The heating roller 1A and the pressure roller 1B are arranged to face each other so that their circumferential surfaces are in contact with each other, and are a pair of fixing rollers that press-contact the recording paper P (recording medium) on which an image is formed. is there. Such a fixing device A is incorporated in an image forming apparatus such as a printing machine, a copying machine, or a facsimile machine, and fixes an image formed on the recording paper P as a toner image on the recording paper P.

  The heating device B includes three exciting coils 2 to 4, first and second resonance power supplies 5 and 6, thermistors 7 </ b> A and 7 </ b> B, comparators 8 and 10, a resistor 9, and a power supply controller 11. Of these components, two of the comparators 8 and 10, the resistor 9, and the power supply control unit 11 constitute a control means in the present invention. The heating device B is a characteristic component of the fixing device A.

  As shown in the drawing, the three exciting coils 2 to 4 are provided along the axial direction in the heating roller 1A. That is, the heating roller 1A is equally divided into three heating blocks BL1 to BL3 in the axial direction. Among the three excitation coils 2 to 4, the excitation coil 2 is a heating block located at one end of the heating roller 1A. In BL1, the exciting coil 3 is arranged in the heating block BL2 located in the center of the heating roller 1A, and the exciting coil 4 is arranged in the heating block BL3 located in the other end of the heating roller 1A.

  Of these three exciting coils 2 to 4, the exciting coil 2 induction heats the heating block BL1, the exciting coil 3 inductively heats the heating block BL2, and the exciting coil 4 inductively heats the heating block BL3. Further, the exciting coils 2 and 4 of the two heating blocks BL1 and BL3 located at the end of the heating roller 1A have the same number of windings, and the exciting coil 3 of the heating block BL2 located at the center of the heating roller 1A is The number of windings is set larger than that of the other exciting coils 2 and 4. These three exciting coils 2 to 4 have inductances corresponding to the number of windings.

  The two first and second resonant power supplies 5 and 6 are individually supplied with excitation power P24 and P3 (AC power) having a predetermined frequency based on a commercial power supply (for example, AC100V power supply) under the control of the power supply control unit 11. The excitation powers P24 and P3 are generated and supplied to the excitation coils 2 to 4 connected thereto. The first resonance power supply 5 is connected only to the excitation coil 3 among the three excitation coils 2 to 4, and supplies the excitation power P 3 to the excitation coil 3. On the other hand, the second resonance power source 6 is commonly connected to the two exciting coils 2 and 4 among the three exciting coils 2 to 4 and supplies the exciting power P24 to the exciting coils 2 and 4.

  FIG. 3 is a circuit diagram showing a detailed configuration of the first and second resonance power supplies 5 and 6. As shown in the figure, the first and second resonance power supplies 5 and 6 include a diode block DB for full-wave rectification of a commercial power supply, three capacitors C1 to C3 for storing DC power supplied from the diode block DB, and the capacitors It is composed of three open / close switches SW1 to SW3 that are connected in series to C1 to C3 and select capacitors C1 to C3 for discharging electric charges, and an open / close switch SW4 commonly connected to the three open / close switches SW1 to SW3. Both ends of three capacitors C1 to C3 and three open / close switches SW1 to SW3 directly connected to each other serve as output ends. The capacitances of the three capacitors C1 to C3 are set to different values, for example, C1> C2> C3.

  In such first and second resonance power supplies 5 and 6, the open / close state of the three open / close switches SW 1 to SW 3 is controlled by the power supply control unit 11, so that one of the three capacitors C 1 to C 3 is connected to the excitation coil 2. 4 is selectively connected in parallel, and the open / close cycle of the open / close switch SW4 is controlled by the power supply control unit 11 to adjust the frequency of the excitation power.

  The exciting coils 2 to 4 constitute a parallel resonant circuit with any of the three capacitors C1 to C3 that are selectively connected in parallel by the three open / close switches SW1 to SW3, but the electrostatic capacitances of the three capacitors C1 to C3. When the capacitance is set to C1> C2> C3 as described above, the resonance frequency of the parallel resonance circuit is the lowest when the capacitor C1 is selected, and the next lowest when the capacitor C2 is selected. When the capacitor C3 is selected, the maximum value is obtained.

  The thermistors 7A and 7B are temperature detection means whose resistance value changes according to the ambient temperature, as is well known. The thermistor 7A is provided on the discharge side of the recording paper P in the vicinity of the heating block BL1 of the heating roller 1A, and detects the temperature of the heating block BL1 that is induction-heated by the excitation coil 2. One end of the thermistor 7A is grounded, and the other end is connected to one input terminal of the comparators 8 and 10. On the other hand, the thermistor 7B is provided on the discharge side of the recording paper P in the vicinity of the heating block BL2 of the heating roller 1A, and detects the temperature of the heating block BL2 that is induction-heated by the exciting coil 3. One end of the thermistor 7B is grounded, and the other end is connected to the other input terminal of the comparator 8.

  The comparator 8 compares the voltage between terminals of the thermistor 7A and the thermistor 7B connected as described above to generate a detection signal S1 indicating the temperature difference between the heating block BL1 and the heating block BL2 as the power supply controller 11. Output to. One end of the resistor 9 is grounded, and the other end is connected to the other input end of the comparator 10, and the reference set temperature (target) of the heating roller 1A is compared with the resistance values of the thermistor 7A and the thermistor 7B. Resistance value corresponding to (temperature). The comparator 10 compares the voltage between the terminals of the thermistor 7A and the resistor 9 connected as described above to generate a detection signal S2 indicating the temperature difference between the heating block BL1 and the reference set temperature. 11 is output. Note that a constant bias power needs to flow through the thermistors 7A and 7B and the resistor 9, but this is omitted in FIG.

  The power supply control unit 11 directly controls the first and second resonant power supplies 5 and 6 based on the detection signals S1 and S2 respectively input from the comparators 8 and 10 to thereby provide the first and second resonant power supplies 5. , 6 indirectly control the excitation power P24, P3 supplied to the excitation coils 2-4. That is, the power supply control unit 11 controls the three open / close switches SW1 to SW3 in the first and second resonant power supplies 5 and 6 to control the parallel resonance constituted by the three capacitors C1 to C3 and the exciting coils 2 to 4. The resonant frequency of the circuit is controlled, and the frequency of the excitation powers P24 and P3 is controlled by adjusting the open / close cycle of the open / close switch SW4 commonly connected to the three open / close switches SW1 to SW3.

  Although details will be described later, the difference (frequency difference) between the frequency of the excitation power P24 flowing through the two excitation coils 2 and 4 and the frequency of the excitation power P3 flowing through the excitation coil 3 is outside the audible range. 1. Control the second resonance power sources 5 and 6.

  In this heating device B, as shown in FIG. 1, the second resonance power source 6 is connected in series and connected to the two exciting coils 2 and 4 having the same number of windings. The excitation power flowing through 4 is the same in both level and frequency. On the other hand, the first resonance power supply 5 is connected to a single exciting coil 3. Therefore, the two heating blocks BL1 and BL3 that are induction-heated by the two exciting coils 2 and 4 are similarly heated, but the two heating blocks BL2 that are induction-heated by the exciting coil 3 are the two heating blocks BL1 and BL2. Unlike BL3, it is heated independently.

  Next, the operation of the fixing device A configured as described above, particularly the operation of the heating unit B, will be described in detail with reference to FIG. FIG. 4 is a characteristic diagram showing temperature changes of the heating blocks BL1 to BL3 due to frequency changes of the excitation powers P24 and P3.

  In the heating device B, the same excitation power P24 is supplied from the second resonance power source 6 to the two excitation coils 2 and 4, while the two excitation coils 2 are supplied to the excitation coil 3 from the first resonance power source 5. , 4 is separately supplied with excitation power P3 different from excitation power P24. That is, although the frequency and level of the excitation power P24 flowing through the two excitation coils 2 and 4 for induction heating the two heating blocks BL1 and BL3 located at the end of the heating roller 1A are the same, they are at the center of the heating roller 1A. The frequency and level of the excitation power P3 flowing through the excitation coil 3 for induction heating the heating block BL2 positioned can be individually set for the excitation power P24 of the two excitation coils 2 and 4.

  On the other hand, during the operation of the fixing device A, every time the recording paper P passes between the heating roller 1A and the pressure roller 1B, the heat of the heating roller 1A propagates to the recording paper P, and the heating roller 1A The surface temperature decreases. The length of the heating roller 1A is set to be longer than the width of the recording paper P, and the recording paper P passes through the vicinity of the center of the heating roller 1A, etc. The two heating blocks BL1 and BL3 that are positioned exhibit substantially similar temperature fluctuations, but the amount of heat that propagates to the recording paper P in the two heating blocks BL1 and BL3 and the heating block BL2 that is positioned at the center of the heating roller 1A. Therefore, the temperature variation is also different.

  In view of the principle of induction heating, the power supply control unit 11 variably controls the frequencies of the excitation powers P24 and P3 supplied from the first and second resonance power supplies 5 and 6 to the excitation coils 2 to 4, thereby heating blocks. Based on the two detection signals S1 and S2, the excitation power P24 is set so that the temperatures of BL1 and BL3 are equal to the temperature of the heating block BL2, and the temperatures of all the heating blocks BL1 to BL3 are the target temperatures. , P3, that is, the open / close cycle of the open / close switch SW4 in the first and second resonant power supplies 5 and 6 is controlled.

  As is well known, the amount of heat generated by induction heating depends on the frequency of the excitation power. The temperature of the heating blocks BL1 and BL3 changes as shown by the broken line in FIG. 4 by changing the frequency of the excitation power P24, and the temperature of the heating block BL2 is changed by the frequency of the excitation power P3. As shown by the broken line in FIG.

  The power supply controller 11 opens and closes the second resonant power supply 6 based on the detection signal S2 input from the comparator 10 so that the temperature of the heating blocks BL1 and BL3 becomes the target temperature indicated by the solid line (straight line) in FIG. The switching cycle of the switch SW4, that is, the frequency of the excitation power P24 is set, and in this state, the comparator is set so that the temperature of the heating block BL2 becomes the target temperature indicated by the solid line (straight line) as in the heating blocks BL1 and BL3. On the basis of the detection signal S1 inputted from 8, the open / close cycle of the open / close switch SW4 in the first resonance power source 5, that is, the frequency of the excitation power P3 is set.

  According to such frequency control of the excitation powers P24 and P3 by the power supply control unit 11, it is possible to individually control the temperatures of the three heating blocks BL1 to BL3 and set them to the target temperature. The temperature distribution in the axial direction of 1A can be made more uniform than before.

  Further, the power supply control unit 11 sets the frequency of the excitation power P24 and the excitation power P3 such that the frequency difference is outside the audible range and the frequencies of the excitation power P24 and the excitation power P3 are the first. 1. The first, first, and second so as to satisfy the constraint 2 that the resonance frequency of the parallel resonance circuit constituted by the three capacitors C1 to C3 and the exciting coils 2 to 4 in the second resonance power sources 5 and 6 is not exceeded. Three open / close switches SW1 to SW3 in the second resonance power supplies 5 and 6 are controlled.

  The heating roller 1A vibrates due to the frequency difference and generates noise. The constraint condition 1 is to prevent the vibration noise from being heard by the user of the image forming apparatus. Generally, it is said that the human audible frequency range is about 20 Hz to 20000 Hz. The main control process of the external power supply controller 11 is to feedback control the frequencies of the excitation power P24 and the excitation power P3 based on the two detection signals S1 and S2, but the frequency difference between the excitation power P24 and the excitation power P3. In the frequency region where the frequency exceeds 20000 Hz, the excitation power P24 and the excitation power P3 are variably set.

  On the other hand, if the frequencies of the excitation power P24 and the excitation power P3 exceed the resonance frequency, the excitation coils 2 to 4 and the heating roller 1A may be deteriorated or damaged. The restriction condition 2 is for preventing such deterioration and breakage.

  The main control process of the power supply control unit 11 is to feedback control the frequencies of the excitation power P24 and the excitation power P3 based on the two detection signals S1 and S2. When the frequencies of the excitation power P24 and the excitation power P3 determined by the process approach the situation where the above constraints 1 and 2 are not satisfied, the capacitors connected in parallel to the excitation coils 2 to 4 by controlling the open / close switches SW1 to SW3 Change C1-C3.

  That is, in the state where the power supply control unit 11 supplies the excitation power P3 based on the charge of the capacitor C1 to the excitation coil 3 by closing only the open / close switch SW1, for example, with respect to the first resonance power supply 5. When the frequency of the excitation power P3 changes so as to approach the resonance frequency of the parallel resonance circuit composed of the capacitor C1 and the excitation coil 3, the open / close switch SW1 is opened and the open / close switch SW2 at a frequency slightly lower than the resonance frequency. Is switched to the closed state, so that the capacitor C2 is connected to the exciting coil 3 instead of the capacitor C1.

  In this way, the vibration noise generated due to the frequency difference between the excitation power P24 and the excitation power P3 by controlling the frequencies of the excitation power P24 and the excitation power P3 so as to satisfy the two constraints 1 and 2. Therefore, the operating environment of the image forming apparatus can be improved, and the life of the exciting coils 2 to 4 and the heating roller 1A can be extended.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the heating roller 1A is equally divided into the three heating blocks BL1 to BL3. However, the number of blocks may be more than three or may not be equally divided. What is necessary is just to set suitably the number of heating blocks, a division | segmentation space | interval, and also the number of winding of the exciting coils 2-4 according to the state of the temperature fluctuation of a heating roller.
(2) In the above embodiment, the first and second resonance power supplies 5 and 6 are configured to include the three capacitors C1 to C3. However, the number of capacitors is not limited to three. The number may be increased as necessary, or two.

1 is a schematic diagram illustrating an overall configuration of a fixing device A according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a functional configuration of a heating device B in the fixing device A according to an embodiment of the present invention. It is a circuit diagram which shows the detailed structure of the 1st, 2nd resonance power supplies 5 and 6 concerning one Embodiment of this invention. It is a characteristic view which shows the temperature change of heating block BL1-BL3 by the frequency change of excitation electric power P24 and P3 in one Embodiment of this invention.

Explanation of symbols

A ... fixing device, B ... heating device, 1A ... heating roller, 1B ... pressure roller, 2-4 ... excitation coil, 5 ... first second resonance power source, 6 ... first second resonance power source, 7A, 7B ... Thermistor, 8 ... comparator, 9 ... resistor, 10 ... comparator, 11 ... power supply control unit

Claims (5)

A fixing device including a heating device that induction-heats one of the pair of fixing rollers (heating roller), and presses the recording medium having an image formed on the surface with the pair of fixing rollers to fix the image on the recording medium. Because
The heating device is
In the heating roller, a plurality of exciting coils arranged for each heating block obtained by dividing the heating roller into a plurality of axial directions,
At least two or more resonant power supplies that selectively supply AC power of a predetermined frequency to any of the exciting coils;
Temperature detecting means for detecting the temperature of the heating block;
And a control unit that controls the frequency of the AC power in the resonance power supply so that the temperature of each heating block becomes uniform based on the temperature detected by the temperature detection unit.   2. The fixing device according to claim 1, wherein the control unit controls the frequency of each AC power so that the frequency difference between the AC powers is outside the audible range. The resonant power supply includes a plurality of capacitors having different capacitances, converts DC power stored in any one of the capacitors into AC power,
The fixing device according to claim 1, wherein the control unit selects a capacitor so that a frequency of the AC power does not exceed a resonance frequency with an excitation coil that supplies the AC power. There are 3 exciting coils and 2 resonant power supplies.
The first resonance power supply supplies AC power to a central block of the heating roller, and the second resonance power supply supplies AC power to a block at one end and the other end of the heating roller. The fixing device according to claim 1.   An image forming apparatus comprising the fixing device according to claim 1, wherein an image formed on a recording medium is fixed by the fixing device.

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