JP2006084648A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a belt fixing device of an electromagnetic induction heat system capable of changing the axial heating range of a fixing belt. <P>SOLUTION: The image forming apparatus has the fixing device of the induction heating system including: an exciting coil for inducing an induction field by the application of a high-frequency AC current; a heat generating member disposed near the exciting coil and generating heat by the induction field; the endless fixing belt trained about the heat generating member and a fixing roller and heated with heat generated by the heat generating member; a pressure roller for pressing at least the fixing roller via the fixing belt. The fixing device fixes a toner image on a transfer material by conveying the transfer material while sandwiching it between the fixing belt and the pressure roller. In the image forming apparatus, a magnetic particle storage part for storing magnetic particles for converging induction field on the heat generating member is disposed opposite to the exciting coil. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, and more particularly to a fixing device capable of heating in accordance with the paper width of a transfer material.

  2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive member, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto a recording paper (transfer material), and then the toner image transferred onto the recording paper is fixed.

  As a fixing device for fixing such a toner image, a heating roller incorporating a halogen heater or the like and a pressure roller that pressurizes the heating roller are used to heat and hold the recording paper onto which the toner image is transferred. There is a heat roller fixing type fixing device that pressurizes, and such a fixing device is widely used because it has a simple configuration and good fixability on a transfer material. Further, the heating roller and the pressure roller have a structure in which a rubber layer is provided on the surface of the cored bar.

  However, in such a fixing device, heat is not easily transmitted due to the thick rubber layer, and there is a problem that the warming up time (WUT) becomes long because the heating roller or the like is heated for a long time.

  In order to solve this problem, an electromagnetic induction heating type fixing device has been developed (see, for example, Patent Document 1).

  There is also an electromagnetic induction heating type fixing device using a fixing belt. This belt fixing device has a pressure roller that stretches an endless fixing belt between a heat generating roller and a fixing roller and presses the fixing roller via the fixing belt, and an excitation coil provided in the vicinity of the heat generating roller. The heat generating roller is heated by induction magnetic flux induced by applying a high-frequency alternating current to heat the fixing belt, and the transfer material is transferred by being sandwiched and conveyed by a nip formed between the fixing belt and the pressing roller. In this configuration, the toner image on the material is fixed.

  The electromagnetic induction heating method has high heating efficiency, and the fixing belt has a small heat capacity, so that the warm-up time is shortened. It also saves power (energy saving).

  However, the fixing belt has a small heat capacity, a large temperature drop due to heat radiation, and a low thermal conductivity. For this reason, when recording paper having a width smaller than the width of the fixing belt is passed, the temperature rises because heat is not taken away by the recording material at the end of the fixing belt through which the recording paper does not pass. This temperature rise is promoted by continuous paper feeding.

  For example, when A4R size recording paper with a narrow paper width is continuously passed, the temperature of the end of the fixing belt through which the recording paper does not pass rises, and then when A4 size recording paper is passed, it is formed at the end. There are problems that uneven glossiness occurs in the toner image, the recording paper becomes wrinkled, and the toner at the end is offset to the fixing belt, so that a good fixed image cannot be obtained. Further, the fixing belt may be deformed due to a temperature difference.

  For this purpose, a method of cooling the end of the fixing belt by blowing air from a cooling fan is known.

Such a problem also occurs in an electromagnetic induction heating type fixing device that does not use a fixing belt. Therefore, as a countermeasure, a central coil is disposed in the center of the inside of the heating roller, and end coils are provided at both ends of the inside. There is a fixing device that controls the energization time of three coils in accordance with the width of a recording sheet that is arranged and fixed (see, for example, Patent Document 2).
JP 2004-228043 A JP 2003-215594 A

  In the method of cooling the end portion of the fixing belt by blowing with a cooling fan, electric power for cooling is necessary, which is not preferable. In addition, the method of cooling after heating is strongly required to save energy. Unacceptable.

  Further, in the fixing device described in Patent Document 1, it is difficult to equalize the temperature in the axial direction even though the control of the energization time to the three coils is complicated, and three coils are used. Cost increases.

  The present invention has been made in view of such a problem, and image formation is provided with an electromagnetic induction heating type belt fixing device capable of changing the heating range in the axial direction of the fixing belt using only one excitation coil. An object is to provide an apparatus.

  The above object is achieved by the following means.

  [Claim 1] An exciting coil that induces an induction magnetic field by application of a high-frequency alternating current, a heating member that is disposed in the vicinity of the excitation coil and generates heat by the induction magnetic field, and is stretched between the heating member and the fixing roller An endless fixing belt that is heated by the heat generated by the heat generating member; and a pressing roller that presses at least the fixing roller through the fixing belt, and the transfer material is sandwiched between the fixing belt and the pressing roller. In an image forming apparatus including an induction heating fixing device that conveys and fixes a toner image on a transfer material, a magnetic particle storage unit that stores magnetic particles that converge an induction magnetic field on the heat generating member is An image forming apparatus, wherein the image forming apparatus is disposed to face a coil.

  [Claim 2] A partition wall that is movable in the width direction of the transfer material to be fixed is provided in the magnetic particle storage portion, and the partition wall is moved in accordance with the width dimension of the transfer material, and is opposed to the excitation coil. 2. The image forming apparatus according to claim 1, further comprising control means for controlling the accumulated length of the magnetic particles to be varied.

  According to the image forming apparatus according to claim 1, the magnetic particles are moved in accordance with the width dimension of the transfer material to be fixed, and the heating range in the axial direction of the fixing belt using only one excitation coil. Therefore, even when large-size transfer paper is fed after continuous feeding of small-size transfer paper, gloss unevenness occurs in the toner image formed at the edge as in the past. And the recording paper becomes wrinkled, and the toner at the end is offset to the fixing belt, so that a problem that a good fixed image cannot be obtained does not occur.

  In addition, the use of powdered magnetic particles increases the electrical resistance and reduces the eddy current generated. Therefore, the heat generation of the magnetic particles is significantly reduced compared to the conventional magnetic core, and the heating member generates heat. Efficiency.

  An embodiment relating to an image forming apparatus of the present invention will be described.

  First, an image forming apparatus using an induction heating fixing apparatus according to the present invention will be described with reference to the basic configuration diagram of FIG.

  In FIG. 1, reference numeral 1 denotes a photosensitive drum which is an electrophotographic photosensitive member. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow at a predetermined peripheral speed, and a surface of the photosensitive drum 1 is negatively charged by a charger 2. Uniformly charged to VH.

  An exposure apparatus 3 outputs a laser beam modulated in accordance with a time-series digital pixel signal of image information input from an image reading apparatus (not shown) or a computer. The uniformly charged surface of the photosensitive drum 1 is scanned and exposed by this laser beam. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 1 decreases to become the potential VL, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

  The developing device 4 includes a developing roller 4a that is rotationally driven. The developing roller 4a is disposed opposite to the photosensitive drum 1, and a thin layer of negatively charged toner is formed on the outer peripheral surface thereof. A developing bias voltage whose absolute value is smaller than the potential VH of the photosensitive drum 1 and larger than the potential VL is applied to the developing roller 4a, whereby the toner on the developing roller 4a becomes the potential of the photosensitive drum 1. Reversal development is performed only on the VL portion, and a toner image is formed.

  On the other hand, the recording paper P, which is a transfer material fed from a paper supply unit (not shown), passes through the registration roller 9 and is synchronized with the photosensitive drum 1 and the charged transfer pole 5 at an appropriate timing synchronized with the rotation of the photosensitive drum 1. To the transfer area formed in The toner image on the photosensitive drum 1 is transferred to the recording paper P by the charged transfer pole 5 to which a transfer bias is applied.

  Reference numeral 6 denotes a fixing guide, and the recording paper P onto which the toner image has been transferred is conveyed to the fixing device 7 where the toner image transferred onto the recording paper P is fixed. The recording paper P that has passed through the fixing device 7 and has been fixed with the toner image is discharged onto a paper discharge tray (not shown).

  On the other hand, the photosensitive drum 1 from which the recording paper P has been separated is removed by the cleaning device 8 to remove the transfer residual toner and the like adhering to the surface thereof, and the cleaned photosensitive drum 1 is repeatedly subjected to the next image formation. To be served.

  Although the above-described image forming apparatus is an apparatus that forms a monochrome image, the fixing apparatus of the present invention is also applied to an apparatus that forms a color image.

  Next, the induction heating type fixing device 7 of the present invention will be described. FIG. 2 is a schematic sectional view of an induction heating type fixing device 7.

  The fixing device 7 includes a heat generating roller 71 (heat generating member), a fixing belt 73 stretched around the fixing roller 72, an excitation coil 74 disposed in the vicinity of the heat generating roller 71, and an induction magnetic field disposed in the vicinity of the heat generating roller 71. A magnetic particle storage portion 75 that stores magnetic particles G that converge on the heat generating roller 71, a pressing roller 76 that presses the fixing roller 72 through the fixing belt 73, and the like, and a high-frequency alternating current is applied to the exciting coil 74. The heat generating roller 71 is self-heated by the induced magnetic flux induced by the application, the fixing belt 73 is heated by the heat, and the recording paper P is sandwiched and conveyed by the fixing belt 73 and the pressing roller 76 to thereby record the recording paper. In this configuration, the P toner image is heated and pressurized to be fixed.

  The heat generating roller 71 is formed in a cylindrical shape with a thin magnetic metal. As an example, nickel having a relative magnetic permeability of 180 to 200 is used and coated with PFA (perfluoroalkoxy) having a thickness of 10 μm.

  Instead of the heat generating roller 71, a cross section orthogonal to the axial direction may be fixed in a half-moon shape, and a heat generating member on which the fixing belt 73 slides may be arranged on the outer peripheral surface thereof. In this case, when fixing is performed at a linear speed of 320 mm / sec, the cylindrical diameter needs to be at least 55 mm, and when the linear speed is made higher, it is desirable to further increase the cylindrical diameter.

  The fixing roller 72 is a roller whose surface is made of foamed silicone rubber having elasticity of rubber hardness 40Hs to 80Hs (JIS, A rubber hardness).

  The fixing belt 73 is an endless belt having flexibility, and a metal belt using nickel or the like having a thickness of about 20 to 80 μm or a polyimide or polyamide having a thickness of about 40 to 150 μm is used as a base. The outer peripheral surface of a heat-resistant resin belt is coated with a heat-resistant silicone rubber having a thickness of about 100 to 300 μm, and the outer surface is coated with a PFA coating or tube having a thickness of about 30 to 50 μm as a release layer. Is used.

  The exciting coil 74 is formed using a litz wire obtained by bundling thin wires, and is supported by a coil support member 77 formed in an arc shape. The exciting coil 74 is wound around the central portion 77 a of the coil support member 77 and at equal intervals from the heat generating roller 71.

  The magnetic particle storage unit 75 stores powdered magnetic particles G such as ferrite and Permalloy (registered trademark) in a resin casing 751, and is arranged to face the excitation coil 74. Table 1 shows the characteristics of these magnetic particles G.

  The pressure roller 76 includes a cored bar 76a made of a round bar such as stainless steel, a roller layer 76b formed of heat-resistant fluororubber or silicon rubber having a rubber hardness of 10Hs to 40Hs (JIS, A rubber hardness), and a roller layer. This is a soft roller composed of a release layer 76c having a surface of 76b covered with a PFA tube. Then, the fixing roller 72 is pressed by pressing means (not shown) to form a nip portion between the fixing belt 73 and the fixing roller 72.

  Note that TS is a temperature sensor that detects the temperature of the fixing belt 73.

  In the fixing device 7 having the above configuration, a high frequency alternating current of 20 kHz to 50 kHz is applied to the excitation coil 74 from an excitation circuit (not shown). Then, the induced magnetic field converges on the magnetic particles G and is induced by the current of the exciting coil 74, and an eddy current is generated at the portion of the heat generating roller 71 facing the magnetic particles G, so that the heat generating roller 71 self-heats. As a result, the fixing belt 73 is heated, and heat is accumulated inside the belt, and is conveyed to a nip portion formed by the fixing belt 73 and the pressing roller 76 by rotating. When the recording paper P is conveyed to the nip portion, the toner image on the recording paper P is fixed by being heated and pressed.

  Next, the magnetic particles G will be described in detail with reference to FIGS.

  First, a description will be given with reference to FIG. FIG. 3 is a diagram showing the positions of the magnetic particles G that move according to the width dimension of the recording paper P. FIG.

  In FIG. 3, magnetic particles G are accommodated in a casing 751 and pressed by a partition wall 752 that can move from the right side.

  For example, when fixing a recording paper P having a small width such as a postcard, the magnetic particles G are pressed by a partition wall 752 as shown in FIG. The accumulated length corresponds to the width of the paper P. As a result, the induced magnetic field is converged and induced on the magnetic particles G corresponding to the width of the small size recording paper P, and the range in which the heat generation roller 71 generates heat also corresponds to the width of the small size recording paper P.

  Next, for example, when the recording paper P of medium size is fixed by vertically feeding (A4R) the recording paper P of A4, as shown in FIG. The magnetic particles G are pressed by 752 so that the magnetic particles G have an accumulated length corresponding to the width of the medium-sized recording paper P. As a result, the induction magnetic field converges and is induced on the magnetic particles G corresponding to the width of the medium size recording paper P, and the range in which the heat generation roller 71 generates heat also corresponds to the width of the medium size recording paper P.

  Further, for example, when fixing the recording paper P having a large size by laterally feeding the A4 recording paper P, the magnetic particles G are pressed by the partition wall 752 with a smaller amount as shown in FIG. Then, the magnetic particles G have an accumulation length corresponding to the width of the large size recording paper P. As a result, the induced magnetic field converges and is induced on the magnetic particles G corresponding to the width of the large size recording paper P, and the range in which the heat generation roller 71 generates heat also corresponds to the width of the large size recording paper P.

  In FIG. 4, when the horizontal axis is the heat generation distribution of the heat generating roller 71 and the vertical axis is the heat generation intensity of the heat generating roller 71, the state of FIG. 3A corresponds to the graph of A, and the state of FIG. 3 corresponds to the graph of B, and the state of FIG. According to FIG. 4, as the heat generation distribution is narrower, the heat generation intensity becomes stronger. At this time, the application time of the high-frequency alternating current applied to the exciting coil 74 is shortened.

  Next, an example of a mechanism for pressing the magnetic particles G by the partition wall 752 will be described with reference to FIG.

  The partition wall 752 is supported by a support shaft 753 screwed with a male screw, and the male screw of the support shaft 753 is screwed into a female screw (not shown) screwed inside the gear 754. The gear 754 is restricted in movement in the axial direction by the regulating member 755 and only rotates, and meshes with the gear 756. The gear 756 is connected to the motor 757 via a reduction gear (not shown).

  When the motor 757 is driven by this mechanism, the gear 756 rotates through a reduction gear (not shown), and the gear 755 also rotates. Since the axial movement of the gear 754 is restricted by the restricting member 755, the gear 754 rotates without changing the left-right position, and the internal female screw also rotates. Therefore, the support shaft 753 with which the male screw is screwed is moved to the left. Move to. Accordingly, the partition plate 752 also moves to the left and presses the magnetic particles G as appropriate.

  When the partition plate 752 is also moved to the right, the motor 757 may be driven in reverse.

  In addition, the mechanism for moving the partition plate 752 is not limited to the above mechanism, and various mechanisms using a link mechanism, a helicoid, a cam, and the like are assumed, and any mechanism may be used.

  In addition, as a magnetic core for converging the induction magnetic field induced by the exciting coil 74, conventionally, a sintered ferrite powder is used. However, as described above, by using the powder magnetic particles G, the electrical resistance is increased and the generated eddy current is reduced. Therefore, the core loss, that is, the heat generation of the magnetic particles G, compared with the conventional magnetic core. Is significantly reduced, and the efficiency with which the heat generating roller 71 generates heat is improved.

  In addition, if the magnetic particles G are not uniform in the casing 751, the heat generation intensity is uneven. Therefore, it is desirable to apply vibration to the casing 751 to level the magnetic particles G.

Next, as shown in FIG. 3, a configuration for controlling the magnetic particles G to be pressed by the partition wall 752 and changing the accumulated length of the magnetic particles G will be described based on the block diagram of FIG. Consists of a CPU or the like and controls each part and each means to be described later.

  The operation unit 202 is arranged on the upper part of the image forming apparatus shown in FIG. 1 (not shown in FIG. 1), and the size of the recording paper P used by the user's operation (for example, A3, B4, A4, A4R, B5, Select a postcard, etc.) and set it.

  The paper size detection unit 203 automatically detects the size of the fed recording paper P. For example, the size of the original is detected, and the corresponding recording paper P is selected.

  The operation state detection unit 204 is in a state where the image forming apparatus is operable, in an operation state, during warming up, after a series of image formations under a set condition, during idling, or in a low power mode. Detecting whether the vehicle is returning from idling or low power mode, jamming, and the like.

  The temperature sensor 205 corresponds to the temperature sensor TS illustrated in FIG. 2 and detects the temperature of the fixing belt 73.

  A storage unit 206 is a memory for storing the width dimension of the recording paper P and the state of the image forming apparatus.

  The excitation circuit 207 applies a high-frequency alternating current to the excitation coil 208 corresponding to the excitation coil 74 shown in FIG.

  The partition wall moving unit 209 corresponds to the motor 757 illustrated in FIG. 5 that moves the partition wall 752.

  With the above configuration, the paper size of the recording paper P is set by the user in the operation unit 202 or automatically detected by the paper size detection unit 203 and is input to the control unit 201 to determine the width of the recording paper P. The dimensions are stored in the storage means 205. Further, the status of the image forming apparatus detected by the operating state detection unit 204 is also input to the control unit 201 and stored in the storage unit 206. Then, according to the paper size stored in the storage unit 206 and the state of the image forming apparatus, the control unit 201 drives the partition wall moving unit 209 to move the magnetic particles G to the paper size of the recording paper P to be fixed. The corresponding accumulation length is set. Further, since the heat generation intensity changes corresponding to the paper size, the control unit 201 controls the excitation circuit 207 based on the temperature of the fixing belt 73 detected by the temperature sensor 205 and applies a high-frequency alternating current to the excitation coil 208. Change time.

  During warm-up, after completion of a series of image formation under the set conditions, during idling, during low power mode, during recovery from idling or low power mode, and during jam occurrence, the magnetic particles G are For example, the accumulated length corresponds to the recording paper P having the maximum width as shown in FIG.

1 is a basic configuration diagram of an image forming apparatus. FIG. 3 is a schematic cross-sectional view of an induction heating type fixing device. It is a figure of the magnetic body particle from which accumulation length changes according to the width dimension of recording paper. It is a figure of heat_generation | fever distribution and heat_generation | fever intensity | strength of a heat-generating roller. It is a mechanism figure which moves a magnetic body particle. It is a block diagram which controls the magnetic body particle from which accumulation length changes.

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 Fixing device 71 Heat generating roller 72 Fixing roller 73 Fixing belt 74 Excitation coil 75 Magnetic substance storage part 751 Case 752 Partition wall 76 Pressing roller 201 Control means G Magnetic substance particle

Claims (2)

An exciting coil that induces an induced magnetic field by applying a high-frequency alternating current;
A heating member disposed in the vicinity of the exciting coil and generating heat by an induced magnetic field;
An endless fixing belt stretched between the heat generating member and the fixing roller and heated by the heat generated by the heat generating member;
A pressing roller that presses at least the fixing roller through the fixing belt,
In an image forming apparatus provided with an induction heating fixing device that clamps and conveys a transfer material between the fixing belt and the pressing roller to fix a toner image on the transfer material,
An image forming apparatus, wherein a magnetic particle storage portion storing magnetic particles that converge an induced magnetic field on the heat generating member is disposed to face the excitation coil. A partition wall that is movable in the width direction of the transfer material to be fixed is provided in the magnetic particle storage unit,
2. The control device according to claim 1, further comprising a control unit configured to move the partition wall in accordance with a width dimension of the transfer material and to control the accumulated length of the magnetic particles facing the exciting coil to be variable. The image forming apparatus described.

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