JP5018468B2 - Fixing device and coil unit - Google Patents

Description

The present invention relates to an electromagnetic induction heating type fixing device. This type of electromagnetic induction heating type fixing device is typically incorporated in an image forming apparatus such as a copying machine or a printer, and is used to fix toner on a sheet such as paper. The present invention also relates to a coil unit that constitutes a part of such a fixing device.

  Conventionally, as an electromagnetic induction heating type fixing device, for example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 2001-43965), a fixing roller and a pressure roller that are pressed against each other so as to form a nip portion, And an exciting coil disposed along the fixing roller. The fixing roller is heated by electromagnetic induction by the exciting coil, and a sheet (recording paper) to which a toner image is attached is conveyed through the nip portion to fix the fixing roller. A toner image is melted and fixed on a sheet by heat generated by a roller. In this document, a degaussing coil is provided along an exciting coil in a region corresponding to the axial end of the fixing roller. When the maximum size sheet is passed, the degaussing coil is open. On the other hand, when a small-size sheet is passed, by closing the degaussing coil, the change in magnetic flux due to the exciting coil is canceled in the area where the degaussing coil is arranged, and the axial end of the fixing roller It is designed to prevent excessive temperature rise.

In the conventional example, an inverter circuit for supplying power to the exciting coil is provided. In the temperature control of the fixing roller, the surface temperature of the fixing roller is detected by a temperature sensor, and the output frequency of the inverter circuit is varied so that the surface temperature of the fixing roller becomes a predetermined target temperature. This is performed by increasing or decreasing the power supply (feedback control).
JP 2001-43965 A

However, as the degaussing coil is opened and closed, as illustrated in FIG. 9, for example, a load viewed from the power supply side (inverter circuit) with respect to the exciting coil, that is, the exciting coil and the degaussing coil and the fixing electromagnetically coupled thereto. The impedance of the equivalent circuit created by the roller changes. Accordingly, the frequency characteristic when the degaussing coil is open (shown by a solid line. The resonance frequency is f ₀₁ ) is different from the frequency characteristic when the degaussing coil is closed (shown by a broken line. The resonance frequency is f ₀₂ ). Shift to high frequency side. For this reason, for example, when the power P to be applied to the fixing roller is 1200 W, when the degaussing coil is switched from open to closed, an excessive power of 1200 W or more (which causes damage) is input immediately thereafter. In order to prevent this, the output frequency f of the inverter circuit is first set higher than the assumed output frequency (f _{1 in} FIG. 9) and gradually shifted to a lower output frequency (f _{2 in} FIG. 9). Possible control methods. In such a control method, since the frequency characteristic is instantaneously greatly shifted when the degaussing coil is opened and closed, there is a problem that the response time until returning to the steady state becomes long and the fixing quality is impaired.

Therefore, an object of the present invention is to prevent excessive temperature rise at the end of the fixing member when passing through a small size sheet, to uniformly control the temperature distribution of the fixing member, and to solve the fixing quality problem caused by the response time. An object of the present invention is to provide a fixing device that can be used. Another object of the present invention is to provide a coil unit that constitutes a part of such a fixing device.

In order to solve the above problems, the fixing device of the present invention is:
A fixing member in which the conveyed sheet is pressed against the outer peripheral surface;
An excitation coil disposed elongated along the outer circumferential surface of the fixing member in the width direction of the conveyed sheet;
A capacitor connected to the excitation coil and equivalently constituting a resonance circuit;
A demagnetizing coil disposed along the exciting coil in a region corresponding to the end of the fixing member in the width direction of the sheet on the opposite side of the fixing member with respect to the exciting coil;
A high-frequency power supply unit that induction-heats the fixing member via the excitation coil by applying an AC voltage to the resonance circuit;
A first temperature detection unit that detects a temperature of a central portion other than the end portion in the width direction of the sheet among the fixing member;
A second temperature detector for detecting the temperature of the end of the fixing member;
A magnetic flux adjusting member made of a magnetic material provided so as to be able to enter and exit the inter-coil gap layer between the exciting coil and the degaussing coil;
A magnetic flux adjusting member moving mechanism that is movable in a direction in which the magnetic flux adjusting member is inserted into the inter-coil gap layer or a direction in which the magnetic flux adjusting member is pulled out from the inter-coil gap layer;
The output frequency of the high frequency power supply unit is variably set so that the temperature of the central portion of the fixing member detected by the first temperature detection unit matches a predetermined target temperature, and the first temperature detection unit The magnetic flux adjusting member via the magnetic flux adjusting member moving mechanism so that the detected temperature of the center portion of the fixing member and the temperature of the end portion of the fixing member detected by the second temperature detecting portion coincide with each other. And a control unit that performs control to move the coil in a direction to be inserted into the inter-coil gap layer or to be pulled out from the inter-coil gap layer.

  In this control method, the output of the high frequency power supply unit is variably set so that the temperature of the central portion of the fixing member detected by the first temperature detecting unit matches a predetermined target temperature. The temperature of the central portion is controlled to the target temperature. At the same time, the magnetic flux adjustment is performed so that the temperature of the central portion of the fixing member detected by the first temperature detecting unit matches the temperature of the end of the fixing member detected by the second temperature detecting unit. Since the magnetic flux adjusting member is moved through the member moving mechanism in a direction to be inserted into the inter-coil gap layer or to be pulled out from the inter-coil gap layer, the temperature of the fixing member is uniformly controlled in the sheet width direction. The That is, when the magnetic flux adjusting member is at a position where it is inserted into the inter-coil gap layer (referred to as “first position”), most of the magnetic flux generated by the exciting coil is the magnetic flux adjusting Since it returns to the exciting coil through the member, it does not penetrate the degaussing coil. Therefore, the degaussing coil does not function so much and does not significantly affect the temperature of the end portion of the fixing member. On the other hand, when the magnetic flux adjusting member is at a position where it is drawn out from the inter-coil gap layer (this is referred to as a “second position”), most of the magnetic flux generated by the exciting coil is the demagnetizing coil. To penetrate. Therefore, the degaussing coil can effectively cancel the change in magnetic flux caused by the exciting coil, and the excessive temperature rise at the axial end of the fixing roller can be effectively prevented. As a result, it is possible to prevent overheating of the end portion of the fixing member when passing through the small size sheet. Further, since the magnetic flux adjusting member is moved gradually by the magnetic flux adjusting member moving mechanism, the frequency of the equivalent resonance circuit formed by the exciting coil and the capacitor is different from the method of opening and closing the demagnetizing coil described above. The characteristic is not greatly shifted instantaneously. Therefore, according to this control method, the steady state can be maintained at any time, and the fixing quality can be kept good. That is, the problem of fixing quality caused by the response time can be solved.

  In the fixing device according to an embodiment, when the magnetic flux adjusting member is moved in a direction to be pulled out from the inter-coil gap layer by the magnetic flux adjusting member moving mechanism, after being pulled out from the inter-coil gap layer, the demagnetizing coil is further removed. The demagnetizing coil is moved to a position corresponding to the side opposite to the exciting coil.

  In the fixing device according to this embodiment, when the magnetic flux adjusting member is in a position corresponding to the opposite side of the excitation coil with respect to the demagnetization coil, most of the magnetic flux generated by the excitation coil passes through the demagnetization coil. Extend toward the magnetic flux adjusting member (and return to the exciting coil through the magnetic flux adjusting member). Therefore, the degaussing coil can effectively cancel the change in magnetic flux caused by the exciting coil, and the excessive temperature rise at the axial end of the fixing roller can be effectively prevented.

  In the fixing device according to an embodiment, the magnetic flux adjusting member includes a first magnetic flux adjusting member and a second magnetic flux adjusting member which are arranged symmetrically with respect to a plane perpendicular to the inter-coil gap layer and passing through the center of the exciting coil. It is characterized by including.

  In the fixing device according to this embodiment, the magnetic flux adjusting member moving mechanism moves the first and second magnetic flux adjusting members symmetrically with respect to the plane, so that most of the magnetic flux generated by the exciting coil is the above. A state where the demagnetizing coil does not penetrate (first position) and a state where the majority of the magnetic flux generated by the exciting coil penetrates the degaussing coil (second position) are easily created. In this case, the distance for moving each of the first and second magnetic flux adjusting members from the first position to the second position is substantially halved as compared with the case where the magnetic flux adjusting member is an integral member. Is done.

  In the fixing device according to one embodiment, the first and second magnetic flux adjusting members are moved by the magnetic flux adjusting member moving mechanism in a direction of being inserted into the inter-coil gap layer or a direction of being pulled out of the inter-coil gap layer. In this case, it is translated parallel to the plane.

  In the fixing device according to this embodiment, the gaps between the first and second magnetic flux adjusting members are always uniform. Therefore, the demagnetizing coil functions equally in the region of the fixing member facing the demagnetizing coil. Become. Therefore, the temperature of the area of the fixing member facing the demagnetizing coil can be evenly reduced.

  Here, in the actual fixing member, the demagnetization is such that, for example, the excessive temperature rise on the far side is larger than the side (outer end) near the end of the excitation coil in the region facing the demagnetization coil. There are cases where the degree of excessive temperature rise differs in the region where the coils face each other.

  Therefore, in the fixing device according to an embodiment, the first and second magnetic flux adjusting members are moved in a direction to be inserted into the inter-coil gap layer or to be pulled out from the inter-coil gap layer by the magnetic flux adjusting member moving mechanism. When rotating, it is rotationally moved symmetrically with respect to the plane.

  In the fixing device according to this embodiment, for example, when the excessive temperature rise on the far side is larger than the side near the end of the exciting coil in the region facing the degaussing coil in the fixing member, the first The second magnetic flux adjusting member is rotationally moved symmetrically with respect to the plane, so that the side close to the end of the exciting coil in each magnetic flux adjusting member within the plane along the inter-coil gap layer is On the other hand, the side close to the center of the exciting coil is opened wide. At this time, among the magnetic fluxes generated by the exciting coil and penetrating the degaussing coil, the magnetic flux penetrating the side near the end of the exciting coil is small, while the magnetic flux penetrating the side near the central portion of the exciting coil. Will be more. Therefore, the side closer to the center of the exciting coil than the side closer to the end of the exciting coil in the degaussing coil effectively cancels the change in magnetic flux caused by the exciting coil. Therefore, even in the case where the excessive temperature rise on the side near the center of the exciting coil is larger than the side near the end of the exciting coil in the region facing the degaussing coil in the fixing member, The temperature distribution of the fixing member becomes uniform. Thus, according to the fixing device of this embodiment, the temperature distribution of the fixing member is made uniform even when the degree of overheating differs in the fixing member in the region where the degaussing coil faces. Can be controlled.

  Further, as described above, when the magnetic flux adjusting member is moved in the direction of insertion into the inter-coil gap layer or the direction of pulling out from the inter-coil gap layer, the equivalent member produced by the fixing member, the excitation coil, and the demagnetization coil The frequency characteristic of the circuit shifts. For this reason, the temperature of the central portion of the fixing member tends to deviate from the target temperature.

Therefore, in the fixing device of an embodiment, the control unit controls the output frequency of the high-frequency power supply unit to be variable and sets the magnetic flux adjusting member to the inter-coil gap layer via the magnetic flux adjusting member moving mechanism. It is characterized in that the control of insertion or withdrawal is repeated in sequence.

  In the fixing device of this embodiment, the temperature of the central portion of the fixing member is accurately controlled to the target temperature, and the temperature of the fixing member is uniformly and accurately controlled in the sheet width direction.

In the fixing device of one embodiment,
For each of a plurality of positions of the magnetic flux adjusting member with respect to the excitation coil, the power to be supplied to the fixing member via the excitation coil and the output frequency of the high-frequency power supply unit corresponding to the power are stored in association with each other. A storage unit,
The control unit sets an initial value of an output frequency of the high frequency power supply unit based on the stored contents of the storage unit at the start of the control.

In the fixing device of this embodiment, the control unit sets an initial value of the output frequency of the high-frequency power supply unit based on the stored contents of the storage unit at the start of the control. Therefore, control can be started from an assumed output frequency or a frequency sufficiently close thereto. As a result, the time from the start of the control until the temperature of the fixing member reaches the target temperature uniformly in the width direction of the sheet can be shortened.
The coil unit of the present invention is used to constitute a fixing device that presses a sheet to which toner is adhered and is conveyed against the outer peripheral surface of the fixing member, and fixes the toner to the sheet according to the temperature of the fixing member. A coil unit,
An exciting coil that is arranged elongated along the outer circumferential surface of the fixing member in the width direction of the conveyed sheet;
A demagnetizing coil disposed along the exciting coil in a region corresponding to an end of the fixing member in the width direction of the sheet on the opposite side of the fixing member with respect to the exciting coil;
A magnetic flux adjusting member made of a magnetic material movably provided in a direction inserted in an inter-coil gap layer between the exciting coil and the degaussing coil or in a direction pulled out from the inter-coil gap layer. Features.
In the coil unit according to the present invention, the exciting coil is arranged elongated along the outer peripheral surface of the fixing member with respect to the width direction of the conveyed sheet. The degaussing coil is disposed along the excitation coil in a region corresponding to the end of the fixing member in the width direction of the sheet, on the opposite side of the fixing member with respect to the excitation coil. When the magnetic flux adjusting member is located at a position where the magnetic flux adjusting member is inserted into the inter-coil gap layer (this is referred to as a “first position”), most of the magnetic flux generated by the exciting coil Since it passes through and returns to the exciting coil, it does not penetrate the degaussing coil. Therefore, the degaussing coil does not function so much and does not significantly affect the temperature of the end portion of the fixing member. On the other hand, when the magnetic flux adjusting member is at a position where it is drawn out from the inter-coil gap layer (this is referred to as a “second position”), most of the magnetic flux generated by the exciting coil is the demagnetizing coil. To penetrate. Therefore, the degaussing coil can effectively cancel the change in magnetic flux caused by the exciting coil, and the excessive temperature rise at the axial end of the fixing roller can be effectively prevented. As a result, it is possible to prevent overheating of the end portion of the fixing member when passing through the small size sheet.
A coil unit according to an embodiment includes a capacitor connected to the exciting coil and equivalently forming a resonance circuit.
The coil unit according to an embodiment includes a magnetic flux adjusting member moving mechanism that is movable in a direction in which the magnetic flux adjusting member is inserted into the inter-coil gap layer or a direction in which the magnetic flux adjusting member is pulled out from the inter-coil gap layer.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 shows a block configuration of a fixing device according to an embodiment of the present invention. The fixing device is provided so as to be able to enter and leave the fixing unit 10, a demagnetizing unit 30 provided separately from the fixing unit 10, and an inter-coil gap layer 60 between the fixing unit 10 and the demagnetizing unit 30. Magnetic flux adjusting member 61A, 62A, 61B, 62B, and magnetic flux adjusting member moving mechanism 33 for moving the magnetic flux adjusting members 61A, 62A, 61B, 62B relative to the units 10, 30 relative to the Y direction; A power supply device 11 as a high frequency power supply unit and a system control unit 20 as a control unit are provided.

  The fixing unit 10 includes a fixing roller 1 as a fixing member, a pressure roller 2 as a pressure member, an excitation coil 3, and two temperature detection sensors 4A and 4B as first and second temperature detection units. Are respectively positioned and attached.

  The fixing roller 1 and the pressure roller 2 are pressed against each other by a biasing means such as a spring (not shown) so as to form a nip 5 through which a sheet 6 such as paper passes. However, when a jam occurs, the pressure roller 2 can be removed in the right direction (+ Y direction) in FIG. 1 while leaving the exciting coil 3 and the fixing roller 1. Further, when replacing the parts, the fixing roller 1 and the pressure roller 2 can be removed in the right direction in FIG. 1 while leaving the exciting coil 3.

  As shown in FIG. 1, with the components 1, 2, 3, 4A, and 4B attached to the fixing unit 10, the fixing roller 1 is moved in the direction of arrow a (in FIG. 1) by a drive source (such as a motor) not shown. The pressure roller 2 is rotated in the direction of arrow b (clockwise in FIG. 1). During the fixing operation, the sheet 6 having the toner 9 attached to one side 6a is conveyed from below to above through the nip 5 in FIG. As a result, the toner 9 is fixed to the sheet 6. A direction (X direction) perpendicular to the paper surface of FIG. 1 corresponds to the width direction of the sheet 6. Note that the fixing roller 1 may be driven to rotate and the pressure roller 2 may be driven to rotate. That is, the relationship between driving and driven may be reversed.

  The fixing roller 1 includes, for example, a 5 mm thick Si (silicon) sponge rubber layer, a 50 μm thick Ni (nickel) and Cr (chromium) alloy layer, and a 1 mm thick Si core on an iron core. A rubber layer and a surface layer made of PFA (a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) having a thickness of 20 μm are provided. Further, the pressure roller 2 is configured by providing a Si foam rubber layer having a thickness of 5 mm and a PFA surface layer having a thickness of 30 μm on an iron cored bar.

  For example, as shown in FIG. 4A, the exciting coil 3 is elongated above the fixing roller 1 in the axial direction of the fixing roller 1 (corresponding to the X direction in FIG. 1). Specifically, the exciting coil 3 is formed by winding an electric wire bundle into an oval shape a plurality of times so as to form a layer. The layer is supported by a holder (not shown) and is disposed close to the outer peripheral surface of the fixing roller 1. As a result, by passing an alternating current through the exciting coil 3, the NiCr alloy layer included in the fixing roller 1 is directly heated by electromagnetic induction. One conductive wire bundle is formed by bundling a few hundred dozens of strands (copper wires having a diameter of about 0.18 mm to 0.20 mm, which are insulated and coated with enamel) in order to increase the energization efficiency. It is a known stranded wire having a diameter of about several mm.

  Further, as shown in FIG. 4A, the temperature detection sensor 4A as the first temperature detection unit is arranged to face the central part A in the axial direction on the outer peripheral surface of the fixing roller 1, and is fixed by a known infrared method. The surface temperature of the central portion A of the roller 1 (this is called temperature Ta) is detected. The temperature detection sensor 4B as a second temperature detection unit is disposed opposite to the end B in the axial direction on the outer peripheral surface of the fixing roller 1, and the surface temperature of the end B of the fixing roller 1 by a known infrared method ( This is called temperature Tb.). The temperatures Ta and Tb detected by these temperature detection sensors 4A and 4B are sent to the system control unit 20 shown in FIG.

  Two demagnetizing coils 31A and 31B are positioned and attached to the demagnetizing unit 30. As shown in FIG. 4A, the degaussing coils 31A and 31B are arranged along the exciting coil 3 in areas corresponding to the end portions B and B on both sides in the axial direction of the fixing roller 1 above the exciting coil 3, respectively. ing. Each of the degaussing coils 31A and 31B is shorter than the exciting coil 3, but is formed by winding a wire bundle in an elliptical shape a plurality of times in the same manner as the exciting coil 3.

  In FIG. 4A, the inter-coil gap layer 60 between the fixing unit 10 and the demagnetizing unit 30 is shown enlarged in the Z direction for easy understanding. Here, the Z-direction dimension of the inter-coil gap layer 60 is indicated by Z1. In a region corresponding to the left end B in FIG. 4A, a magnetic flux adjustment member 61A as a first magnetic flux adjustment member and a magnetic flux adjustment member 62A as a second magnetic flux adjustment member are provided. On the other hand, a magnetic flux adjusting member 61B as a first magnetic flux adjusting member and a magnetic flux adjusting member 62B as a second magnetic flux adjusting member are provided in a region corresponding to the right end B in FIG. 4A. These magnetic flux adjusting members 61A, 62A; 61B, 62B have substantially the same dimensions as the corresponding demagnetizing coils 31A, 31B in the longitudinal direction (X direction) of the exciting coil 3, respectively.

  In the arrangement shown in FIG. 4A (this arrangement is referred to as “first position”), the magnetic flux adjusting members 61A and 62A are XY planes along the inter-coil gap layer 60, similarly to the magnetic flux adjusting members 61B and 62B. Are arranged in parallel to each other along the longitudinal direction (X direction) of the exciting coil.

  In the arrangement shown in FIG. 4B (this arrangement is referred to as a “second position”), the magnetic flux adjusting members 61A and 62A are arranged in the XY plane along the inter-coil gap layer 60 with respect to the magnetic flux adjusting members 61A and 62A. Among them, the side close to the end of the exciting coil 3 (+ X side) is narrow, while the side close to the central part of the exciting coil 3 (−X side) is wide open. The magnetic flux adjusting members 61B and 62B are narrower on the side near the end of the exciting coil 3 (−X side) of the magnetic flux adjusting members 61A and 62A in the XY plane along the gap layer 60 between the coils. The side close to the center of 3 (+ X side) is wide open. That is, the magnetic flux adjusting members 61A and 62A, together with the magnetic flux adjusting members 61B and 62B, are opened in an eight shape toward the center of the exciting coil 3 in a plane along the inter-coil gap layer 60.

  These magnetic flux adjusting members 61A and 62A, together with the magnetic flux adjusting members 61B and 62B, are moved from the first position shown in FIG. 4A to the second position shown in FIG. 4B by the magnetic flux adjusting member moving mechanism 33 shown in FIG. In the opposite direction, it is moved symmetrically with respect to the ZX plane passing through the center of the exciting coil 3. Specifically, when the magnetic flux adjusting members 61A and 62A are moved from the first position to the second position, the magnetic flux adjusting members 61A and 62A are arranged around a rotation center (not shown) provided on the + X side of these members 61A and 62A. , Rotated as indicated by arrows d1 and d2, respectively, and opened in the shape of an eight. Conversely, when the magnetic flux adjusting members 61A and 62A are moved from the second position to the first position, the magnetic flux adjusting members 61A and 62A are respectively rotated in the opposite direction around the rotation center and closed in parallel. . On the other hand, when the magnetic flux adjusting members 61B and 62B are moved from the first position to the second position, the magnetic flux adjusting members 61B and 62B are respectively arranged around the rotation centers (not shown) provided on the −X side of these members 61B and 62B. It is rotated as indicated by arrows e1 and e2 and is opened in the shape of an eight. Conversely, when the magnetic flux adjusting members 61B and 62B are moved from the second position to the first position, the magnetic flux adjusting members 61B and 62B are respectively rotated in the opposite direction around the rotation center and closed in parallel. . In this example, the rotation of the magnetic flux adjusting members 61A and 62A and the rotation of the magnetic flux adjusting members 61B and 62B are interlocked, and the opening angle between the magnetic flux adjusting members 61A and 62A and the opening angle between the magnetic flux adjusting members 61B and 62B are Are always the same.

  As shown in FIG. 1, the magnetic flux adjusting member moving mechanism 33 has a stepping motor 34 controlled by a demagnetizing unit movement control signal SigC from the system control unit 20 and a gear 35 driven by the stepping motor 34. is doing. By rotating the gear 35 as shown by the arrow c, the magnetic flux adjusting members 61A, 62A; 61B, 62B are moved through the transmission mechanisms 38A, 38B to the first position shown in FIG. 4A and the second position shown in FIG. 4B. Moved between positions.

  For example, when the magnetic flux adjusting members 61A and 62A are in the first position shown in FIG. 4A, most of the magnetic flux MF generated by the exciting coil 3 is substantially equal to the magnetic flux adjusting member 61A, as schematically shown in FIG. , 62A and return to the exciting coil 3, so that it does not penetrate the degaussing coil 31A. Therefore, the degaussing coil 31A does not function so much and does not affect the temperature of the corresponding end B of the fixing roller 1 so much. In this case, as shown in FIG. 4A, the power input at the end B of the fixing roller 1 is, for example, Qb. It is assumed that the power Qb is smaller than the power Qa supplied to the central portion A of the fixing roller 1.

  On the other hand, when the magnetic flux adjusting members 61A and 62A are in the second position shown in FIG. 4B, most of the magnetic flux MF generated by the exciting coil 3 is demagnetized coil 31A as schematically shown in FIG. 5B. To penetrate. Therefore, the degaussing coil 31A effectively cancels the change in the magnetic flux MF caused by the exciting coil 3. That is, the demagnetizing force of the degaussing coil 31A is increased. As a result, compared with the case where the magnetic flux adjusting members 61A and 62A are at the first position shown in FIG. 4A, the electric power applied at the corresponding end B of the fixing roller 1 is small, for example, Qb ′ (<Qb) It becomes.

  Therefore, even if the sheet 6 shown in FIG. 1 is a small size sheet that passes only through the central portion A of the fixing roller 1, the magnetic flux adjusting members 61A, 62A; 61B, 62B are in the first position shown in FIG. 4B to the second position shown in FIG. 4B, it is possible to prevent excessive temperature rise at the end B of the fixing roller 1.

  Here, FIG. 6A shows the temperature distribution generated in the actual fixing roller 1 (the vertical axis indicates the temperature, and the horizontal axis indicates the position in the axial direction (X direction) of the fixing roller 1). The broken line P0 in FIG. 6A illustrates the temperature distribution when there is no magnetic flux adjusting member and the degaussing coil is open, and the solid line P1 illustrates the temperature distribution when there is no magnetic flux adjusting member and the degaussing coil is closed. As can be seen from these examples, in the actual fixing roller 1, the side closer to the center of the exciting coil 3 than the side (outer end) closer to the end of the exciting coil 3 in the region B facing the degaussing coil. In some cases, the degree of overheating is different in the region B where the degaussing coil faces, such that the overheating is large. On the side (outer end) near the end of the excitation coil 3 in the region B where the degaussing coil faces, the temperature decreases due to the difference in magnetic flux density between the center and the end of the excitation coil 3 and natural heat dissipation. Because it does.

  If such temperature distribution occurs, suppose that the magnetic flux adjusting member moving mechanism 33 translates the magnetic flux adjusting members 61A, 62A; 61B, 62B symmetrically with respect to the ZX plane passing through the center of the exciting coil 3. As indicated by a dotted line P2 in FIG. 6A, the temperature of the end B of the fixing roller 1 can be suppressed to a target temperature Tt or less to prevent excessive temperature rise. However, since the input power is uniformly reduced in the region B where the degaussing coil faces, temperature drop is a problem on the side (outer end) near the end of the exciting coil 3 in the region B where the degaussing coil faces. May be.

  Therefore, in this example, when the magnetic flux adjusting members 61A, 62A; 61B, 62B are in the second position shown in FIG. 4B, the magnetic flux adjusting members 61A, 62A together with the magnetic flux adjusting members 61B, 62B In the plane along the line 60, it opens in the shape of an eight character toward the center of the exciting coil 3. As a result, among the magnetic flux MF generated by the exciting coil 3 and penetrating the demagnetizing coils 31A and 31B, the magnetic flux penetrating the side near the end of the exciting coil 3 is small, while the side near the center of the exciting coil 3 is located. The magnetic flux that penetrates increases. Accordingly, the demagnetizing coils 31A and 31B that are closer to the center of the exciting coil 3 than the side closer to the end of the exciting coil 3 effectively cancel the magnetic flux change caused by the exciting coil 3. Therefore, as shown in FIG. 6A, in the fixing roller 1, in the region B where the degaussing coils 31 </ b> A and 31 </ b> B face each other, the excess on the side closer to the center of the exciting coil 3 than the side closer to the end of the exciting coil 3. Even when the temperature rise is large, the temperature distribution of the fixing roller 1 becomes uniform as shown by the solid line P3 in FIG. 6B.

  The power supply device 11 shown in FIG. 1 converts commercial power into a high frequency having a frequency corresponding to the excitation control signal SigE from the system control unit 20 (hereinafter referred to as “output frequency”), The voltage (power) is output to the exciting coil 3. As a result, an alternating current is passed through the exciting coil 3 to inductively heat the NiCr alloy layer included in the fixing roller 1. At the same time, the power supply device 11 opens and closes the degaussing coils 31A and 31B by turning off and on a switch (not shown) according to the demagnetization control signal SigD from the system control unit 20. If the degaussing coil is in the “open” state, no induced current flows through the degaussing coil, so degaussing is not performed. If the degaussing coil is in the “closed” state, an induced current flows through the degaussing coil, and degaussing becomes possible. In a control example described later, the degaussing coil is kept in the “closed” state.

  FIG. 2 specifically shows the configuration of an inverter circuit included in the power supply device 11 in order to cause an alternating current to flow through the exciting coil 3. As a configuration of the inverter circuit, a parallel resonance circuit and a series resonance circuit are conceivable. FIG. 2 shows an example of a preferable series resonance circuit.

  In FIG. 2, the exciting coil 3 shown in FIG. 1 is represented by a series equivalent circuit 43 including an inductance Ls43 and an effective resistance Rs43. This series equivalent circuit 43 includes contributions of the fixing roller 1 and the demagnetizing coils 31A and 31B coupled to the exciting coil 3 by electromagnetic induction in addition to the exciting coil 3. The values of the inductance Ls43 and the effective resistance Rs43 are obtained by connecting an impedance measuring instrument generally called an LCR meter to both ends of the exciting coil 3 and measuring.

A resonance capacitor 44 as a capacitor is connected in series to the IH unit 43, actually the exciting coil 3, thereby forming a series resonance circuit 42. The resonance frequency f ₀ (unit: Hz) of the series resonance circuit 42 is given by the following equation (1).
f ₀ = 1 / (2π (LsC) ^1/2 ) (1)

    However, Ls is the value of inductance Ls43 (unit; H (henry)), and C is the capacity of resonance capacitor 44 (unit: F (farad)).

  The inverter circuit includes a diode bridge DB41 connected to a commercial power supply (AC power supply) 12, a rectifier circuit 41 including a smoothing coil Lf41 and a smoothing capacitor Cf41, a pair of switching elements 45A and 45B each including a power transistor, and It comprises flywheel diodes D45A and D45B for protecting the switching elements 45A and 45B from overvoltage.

The pair of switching elements 45 </ b> A and 45 </ b> B are on / off controlled at an output frequency f corresponding to the excitation control signal SigE from the system control unit 20. As a result, power is supplied to the fixing roller 1 via the IH unit 43.
In this embodiment, the IH unit 43, the demagnetizing unit 30 shown in FIG. 1, the magnetic flux adjusting members 61A, 62A, 61B, and 62B, and the magnetic flux adjusting member moving mechanism 33 constitute a coil unit. .

FIG. 3 shows a drive waveform of the series resonance circuit 42. I _Ls represents the current through the IH unit _{43, V CE} is the respective switching elements 45A, shows the collector-emitter voltage of 45B, also, T is shows a switching element on period.

  FIG. 7 shows the frequency characteristics of the series resonance circuit 42, that is, the relationship between the output frequency f of the inverter circuit and the power P input to the fixing roller 1, between the magnetic flux adjusting members 61A and 62A and the magnetic flux adjusting members 61B and 62B. Angular positions C1, C2, C3, C4, and C5 representing the opening angle between them are shown as parameters (for ease of understanding, each opening angle and the corresponding frequency characteristic are indicated by the same reference numerals). In the series resonance circuit 42, when the output frequency f coincides with the resonance frequency (frequency that gives the peak of the graph), the impedance Z is minimized and the current flows most. Accordingly, the power value P input to the fixing roller 1 is maximized. As can be seen from FIG. 7, the angle position between the magnetic flux adjusting members 61A and 62A and between the magnetic flux adjusting members 61B and 62B is from the angular position C5 having the minimum opening angle (= 0 °) to the maximum opening angle (= 180 °). As it changes to C1, the frequency characteristic of the series resonant circuit 42 gradually shifts to the high frequency side. In FIG. 7, the frequency characteristics are shown only for the five angular positions C1, C2, C3, C4, and C5. However, the opening angles between the magnetic flux adjusting members 61A and 62A and the magnetic flux adjusting members 61B and 62B are continuous or It can be varied substantially continuously in multiple stages.

  The system control unit 20 shown in FIG. 1 outputs an excitation control signal SigE based on the temperatures Ta and Tb detected by the temperature detection sensors 4A and 4B so that the temperature of the outer peripheral surface of the fixing roller 1 becomes the target temperature. Then, the power supply device 11 is feedback-controlled (details will be described later). In the control example described later, the degaussing coils 31A and 31B are kept in the “closed” state by the degaussing control signal SigD. The system control unit 20 includes, for example, a CPU (Central Processing Unit) 21 and a storage unit 23 that stores processing programs and various data. The system control unit 20 may be a circuit that controls only the fixing device, or may be a part of a circuit that controls the entire upper apparatus, for example, the entire image forming apparatus in which the fixing device is incorporated. There may be.

  In this example, the storage unit 23 includes the power P to be supplied to the fixing roller 1 and the output of the power supply device 11 corresponding to the power P for each of the angular positions C1 to C5 of the magnetic flux adjusting members 61A and 62A; 61B and 62B. The frequency f is stored in association with each other.

  FIG. 8 shows a specific control flow by the system control unit 20.

  It is assumed that the system control unit 20 has previously recognized the angular positions (within the range of C1 to C5) of the magnetic flux adjusting members 61A and 62A; 61B and 62B. Then, the system control unit 20 sets the power P to be input to the fixing roller 1, and sets the output frequency f of the power supply device 11 according to the power P and the Z-direction position where the demagnetizing coils 31A and 31B exist. It is assumed that it is set.

For example, as shown in FIG. 7, the electric power P to be supplied to the fixing roller 1 is 1200 W (watts), and the angular positions of the magnetic flux adjusting members 61A, 62A; 61B, 62B are C3, and accordingly Assume that the output frequency f of the power supply device 11 is set to f ₃ = about 43 kHz as an initial value.

  First, in step S1 of FIG. 8, the temperature detection sensor 4A detects the temperature Ta of the central portion A of the fixing roller 1. Next, in step S <b> 2, the temperature Ta is compared with the target temperature Tt corresponding to the power P to be input to the fixing roller 1. Here, if Ta <Tt, the process proceeds to step S3 and the output frequency f of the power supply device 11 is decreased. As a result, the actual power supplied to the fixing roller 1 increases according to the slope of the frequency characteristic C3 in FIG. 7, and the temperature Ta at the central portion A of the fixing roller 1 increases. On the other hand, if Ta> Tt in step S2, the process proceeds to step S4 to increase the output frequency f of the power supply device 11. As a result, the actual power supplied to the fixing roller 1 increases according to the slope of the frequency characteristic C3 in FIG. 7, and the temperature Ta at the central portion A of the fixing roller 1 decreases. Thus, the system control unit 20 performs feedback control so that the temperature Ta of the central portion A of the fixing roller 1 matches the target temperature Tt (steps S1 to S4).

  If the temperature Ta of the central portion A of the fixing roller 1 coincides with the target temperature Tt in step S2 of FIG. 8, the process proceeds to step S5, and the temperature Tb of the end portion B of the fixing roller 1 is detected by the temperature detection sensor 4B. To do. Next, in step S6, the temperature Tb is compared with the temperature Ta detected earlier. Here, if Ta <Tb, the process proceeds to step S7, and the magnetic flux adjusting member moving mechanism 33 moves the magnetic flux adjusting members 61A, 62A; 61B, 62B in a direction to draw out from the inter-coil gap layer 60. In this example, the opening angle between the magnetic flux adjusting members 61A and 62A and between the magnetic flux adjusting members 61B and 62B is increased. As a result, the demagnetizing force of the degaussing coils 31A and 31B is increased, and the temperature Tb at the end B of the fixing roller 1 is relatively lowered with respect to the temperature Ta at the center A. On the other hand, if Ta> Tb in step S6, the process proceeds to step S8 where the magnetic flux adjusting member moving mechanism 33 moves the magnetic flux adjusting members 61A, 62A; 61B, 62B in the direction in which they are inserted into the inter-coil gap layer 60. In this example, the opening angle between the magnetic flux adjusting members 61A and 62A and between the magnetic flux adjusting members 61B and 62B is reduced. Thereby, the demagnetizing force of the degaussing coils 31A and 31B is reduced, and the temperature Tb of the end B of the fixing roller 1 is relatively increased with respect to the temperature Ta of the center A. Thus, the system control unit 20 performs feedback control so that the temperature Tb at the end B of the fixing roller 1 matches the temperature Ta at the center A (steps S5 to S8).

  When the process of step S7 or S8 is performed, the frequency characteristic of the series resonance circuit 42 shifts from the frequency characteristic C3 in FIG. 7 toward C2 or C4, respectively. For this reason, if the same output frequency f is maintained, the temperature Ta at the central portion A of the fixing roller 1 tends to deviate from the target temperature Tt. Therefore, the process returns to step S1 after the process of step S7 or S8, and the feedback control of steps S1 to S4 is performed to make the temperature Ta of the central portion A of the fixing roller 1 coincide with the target temperature Tt.

  As described above, the feedback control (steps S1 to S4) for matching the temperature Ta of the central portion A of the fixing roller 1 with the target temperature Tt, and the temperature Tb of the end B of the fixing roller 1 match the temperature Ta of the central portion A. The feedback control (steps S5 to S8) is repeated.

  If the temperature Tb at the end B of the fixing roller 1 matches the temperature Ta at the center A in step S6, the process returns to another control.

  In this way, thanks to the degaussing coils 31A and 31B, even if the sheet 6 shown in FIG. 1 is a small size sheet that passes only through the central portion A of the fixing roller 1, the end B of the fixing roller 1 Overheating can be prevented. At the same time, the uniformity of the temperature distribution in the axial direction of the fixing roller 1 can be accurately controlled.

  Further, since the magnetic flux adjusting members 61A and 62A; 61B and 62B are moved gradually by the magnetic flux adjusting member moving mechanism 33, the frequency characteristic of the series resonance circuit 42 is instantaneously changed unlike the method of opening and closing the demagnetizing coil described above. There is no significant shift. Therefore, according to this control method, the steady state can be maintained at any time, and the fixing quality can be kept good. That is, the problem of fixing quality caused by the response time can be solved.

  Moreover, since the initial value of the output frequency f of the power supply device 11 is set based on the stored contents of the storage unit 23 at the start of the control, the control can be started from an assumed output frequency or a frequency sufficiently close thereto. As a result, it is possible to shorten the time from the start of control until the temperature of the fixing roller 1 reaches the target temperature uniformly in the sheet width direction.

  In the above-described embodiment, the magnetic flux adjusting member moving mechanism 33 rotates the magnetic flux adjusting members 61A and 62A; 61B and 62B, respectively, and opens them in an eight-letter shape. However, the present invention is not limited to this. As already mentioned, the magnetic flux adjusting member moving mechanism 33 may translate the magnetic flux adjusting members 61A, 62A; 61B, 62B symmetrically with respect to the ZX plane passing through the center of the exciting coil 3.

  Further, as shown in FIG. 10A, one integral magnetic flux adjusting member 91 may be provided corresponding to each end B of the fixing roller 1. Also in this case, the magnetic flux adjusting member moving mechanism 33 moves the magnetic flux adjusting member 91 in the direction in which the magnetic flux adjusting member 91 is inserted into or pulled out from the inter-coil gap layer 60, so that the temperature of the fixing roller 1 is axially increased. It can control uniformly regarding (X direction in FIG. 1). As a result, it is possible to prevent an excessive temperature rise at the end B of the fixing roller 1 when passing through the small size sheet.

  Further, when the magnetic flux adjusting member 91 is moved in the direction of drawing out from the inter-coil gap layer 60, the magnetic flux adjusting member 91 is related to the degaussing coil (only 31A is shown in this example) as shown in FIG. It may be moved to a position corresponding to the side opposite to the exciting coil 3. In this case, when the magnetic flux adjusting member 91 is moved from, for example, the position shown in FIG. 10A, the magnetic flux adjusting member 91 is first drawn from the inter-coil gap layer 60, and further turns around the degaussing coil 31A. It is moved to the position shown inside. When the magnetic flux adjusting member is in the position shown in FIG. 10B, most of the magnetic flux MF generated by the exciting coil 3 passes through the degaussing coil 31A and extends toward the magnetic flux adjusting member 91 (and magnetic flux adjustment). Return to the exciting coil 3 through the member 91). Therefore, the degaussing coil 31A can effectively cancel the change in the magnetic flux MF caused by the exciting coil 3, and the excessive temperature rise at the axial end B of the fixing roller 1 can be effectively prevented.

  In the above-described embodiment, the case where the fixing roller 1 as a fixing member is directly subjected to electromagnetic induction by the exciting coil 3 and is heated by eddy current (this is referred to as a direct heating method) has been described. It is not limited to. The present invention is also preferably applied to a case where the fixing member is indirectly heated via another heat generating member that receives electromagnetic induction from the electromagnetic induction coil and generates heat by eddy current (this is referred to as an indirect heating method). Is done.

  In the above-described embodiment, the exciting coil 3 and the resonant capacitor 44 are connected in series to form the series resonant circuit 42. However, the present invention is not limited to this. The present invention can also be applied to a case where a parallel resonance circuit is configured by an exciting coil and a capacitor.

  Further, in the above-described embodiment, the temperature detection sensor 4B as the second temperature detection unit is provided corresponding to only one end portion B of both end portions in the axial direction of the fixing roller 1, but the present invention is not limited thereto. It is not something that can be done. A second temperature detection unit is provided corresponding to each of the ends B and B on both sides in the axial direction of the fixing roller 1, so that the temperature Ta at the center A of the fixing roller 1 and the temperatures Tb and B at both ends B and B are Control may be performed so that Tb matches.

1 is a block diagram of a fixing device according to an embodiment of the present invention. It is a figure which shows the structure of the inverter circuit contained in the power supply device in FIG. It is a figure which shows the drive waveform of the series resonance circuit by the inverter circuit in FIG. It is a figure which shows the state arrange | positioned in the position where the degaussing coil approached with respect to the exciting coil. It is a figure which shows the state by which the degaussing coil was arrange | positioned in the position spaced apart with respect to the exciting coil. (A) is a state in which the first and second magnetic flux adjustment members are in the first position inserted in the inter-coil gap layer, and (B) is a state in which the first and second magnetic flux adjustment members are more than the first position. It is a figure which shows the state which exists in the 2nd position away from the gap layer between coils. FIG. 6 is a diagram illustrating a temperature distribution in the axial direction of the fixing roller. FIG. 6 is a diagram illustrating a temperature distribution in the axial direction of the fixing roller. It is a figure which shows the frequency characteristic of the series resonance circuit in FIG. 2 using the position of the said degaussing coil as a parameter. It is a figure which shows the flow of control by the system control part of the said fixing device. It is a figure which illustrates the frequency characteristic of a series resonance circuit at the time of opening and closing a degaussing coil. (A) is a state in which one magnetic flux adjusting member is in the first position inserted in the inter-coil gap layer, and (B) is a second state in which one magnetic flux adjusting member corresponds to the side opposite to the exciting coil with respect to the demagnetizing coil. It is a figure which shows the state in the position.

DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 3 Excitation coil 4A, 4B Temperature detection sensor 5 Nip 11 Power supply device 12 Commercial power supply 20 System control part 23 Memory | storage part 31A, 31B Demagnetizing coil 60 Inter-coil gap layer 61A, 61B 1st magnetic flux adjustment member 62A, 62B Second magnetic flux adjusting member 91 Magnetic flux adjusting member

Claims (10)

A fixing member in which the conveyed sheet is pressed against the outer peripheral surface;
An excitation coil disposed elongated along the outer circumferential surface of the fixing member in the width direction of the conveyed sheet;
A capacitor connected to the excitation coil and equivalently constituting a resonance circuit;
A demagnetizing coil disposed along the exciting coil in a region corresponding to the end of the fixing member in the width direction of the sheet on the opposite side of the fixing member with respect to the exciting coil;
A high-frequency power supply unit that induction-heats the fixing member via the excitation coil by applying an AC voltage to the resonance circuit;
A first temperature detection unit that detects a temperature of a central portion other than the end portion in the width direction of the sheet among the fixing member;
A second temperature detector for detecting the temperature of the end of the fixing member;
A magnetic flux adjusting member made of a magnetic material provided so as to be able to enter and exit the inter-coil gap layer between the exciting coil and the degaussing coil;
A magnetic flux adjusting member moving mechanism that is movable in a direction in which the magnetic flux adjusting member is inserted into the inter-coil gap layer or a direction in which the magnetic flux adjusting member is pulled out from the inter-coil gap layer;
The output frequency of the high frequency power supply unit is variably set so that the temperature of the central portion of the fixing member detected by the first temperature detection unit matches a predetermined target temperature, and the first temperature detection unit The magnetic flux adjusting member via the magnetic flux adjusting member moving mechanism so that the detected temperature of the center portion of the fixing member and the temperature of the end portion of the fixing member detected by the second temperature detecting portion coincide with each other. And a control unit that performs control to move the lens in a direction to be inserted into the inter-coil gap layer or to be pulled out from the inter-coil gap layer. The fixing device according to claim 1,
When the magnetic flux adjusting member is moved in the direction to be pulled out from the inter-coil gap layer by the magnetic flux adjusting member moving mechanism, after being pulled out from the inter-coil gap layer, the magnetic flux adjusting member is further rotated around the demagnetizing coil and demagnetized. A fixing device, wherein the fixing device is moved to a position corresponding to a side opposite to the exciting coil with respect to the coil. The fixing device according to claim 1,
The magnetic flux adjusting member includes a first magnetic flux adjusting member and a second magnetic flux adjusting member arranged symmetrically with respect to a plane perpendicular to the inter-coil gap layer and passing through the center of the exciting coil. apparatus. The fixing device according to claim 3.
The first and second magnetic flux adjusting members are symmetrical with respect to the plane when moved by the magnetic flux adjusting member moving mechanism in the direction of insertion into the inter-coil gap layer or the direction of drawing out from the inter-coil gap layer. A fixing device that is translated in parallel. The fixing device according to claim 3.
The first and second magnetic flux adjusting members are symmetrical with respect to the plane when moved by the magnetic flux adjusting member moving mechanism in the direction of insertion into the inter-coil gap layer or the direction of drawing out from the inter-coil gap layer. And a fixing device that is rotated and moved. The fixing device according to claim 1,
The control unit sequentially repeats control for variably setting the output frequency of the high frequency power supply unit and control for inserting or extracting the magnetic flux adjusting member into the inter-coil gap layer via the magnetic flux adjusting member moving mechanism. A fixing device. The fixing device according to claim 1,
For each of a plurality of positions of the magnetic flux adjusting member with respect to the excitation coil, the power to be supplied to the fixing member via the excitation coil and the output frequency of the high-frequency power supply unit corresponding to the power are stored in association with each other. A storage unit,
The fixing device, wherein at the start of the control, the control unit sets an initial value of an output frequency of the high-frequency power supply unit based on stored contents of the storage unit. A coil unit used to constitute a fixing device that presses a sheet to which toner is attached and is conveyed against an outer peripheral surface of a fixing member, and fixes the toner to the sheet according to a temperature of the fixing member;
An exciting coil that is arranged elongated along the outer circumferential surface of the fixing member in the width direction of the conveyed sheet;
A demagnetizing coil disposed along the exciting coil in a region corresponding to an end of the fixing member in the width direction of the sheet on the opposite side of the fixing member with respect to the exciting coil;
A magnetic flux adjusting member made of a magnetic material movably provided in a direction inserted in an inter-coil gap layer between the exciting coil and the degaussing coil or in a direction pulled out from the inter-coil gap layer. Features coil unit. The coil unit according to claim 8, wherein
A coil unit comprising a capacitor connected to the excitation coil and equivalently constituting a resonance circuit. The coil unit according to claim 8 or 9,
A coil unit comprising a magnetic flux adjusting member moving mechanism that is movable in a direction in which the magnetic flux adjusting member is inserted into the inter-coil gap layer or a direction in which the magnetic flux adjusting member is pulled out from the inter-coil gap layer.

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