JP2007140330A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of not only preventing peripheral members from being heated by a leakage magnetic flux but also preventing the temperature rise of a heating member end part where no paper passes. <P>SOLUTION: The image forming apparatus having such a mechanism that a heating member made of a conductive magnetic material is induction-heated by a magnetic field generation means for generating a magnetic field by an excitation coil, includes; a magnetic flux detection means which is disposed so as to face the magnetic field generation means via the heating member and detects a leakage magnetic flux from the heating member, which is generated when the temperature of the heating member reaches a Curie point; and a control means which concentrates electric power applied to the excitation coil to only the center part of the heating member when detecting the leakage magnetic flux by the magnetic flux detection means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a heating mechanism by induction heating as a heating mechanism of a magnetic material.

  Conventionally, in an image forming apparatus, a fixing device that fixes a toner image transferred onto a sheet such as recording paper or a transfer material as a recording medium to the sheet, the periphery of the image forming device is used to stabilize an output image. Various heating devices such as a heating device for making the environment constant are provided.

  Among these, for example, the fixing device includes, for example, a fixing roller, which is also referred to as a heating roller that thermally melts toner on the sheet, and a pressure roller that presses against the fixing roller and sandwiches the sheet. The fixing roller is formed in a hollow shape, and a heating element is held by a holding unit on the central axis of the fixing roller.

  The heating element is composed of, for example, a tubular heating heater such as a halogen lamp, and generates heat when a predetermined voltage is applied. Since the halogen lamp is located on the center axis of the fixing roller, the heat generated from the halogen lamp is uniformly radiated to the inner wall of the fixing roller, and the temperature distribution on the outer wall of the fixing roller is uniform in the circumferential direction.

  The outer wall of the fixing roller is heated until the temperature reaches a temperature suitable for fixing (for example, 150 to 200 ° C.). In this state, the fixing roller and the pressure roller rotate in opposite directions while being pressed against each other, and sandwich the sheet with the toner attached thereto. At the pressure contact portion (hereinafter also referred to as “nip portion”) between the fixing roller and the pressure roller, the toner on the sheet is melted by the heat of the fixing roller and is fixed to the sheet by the pressure acting from both rollers.

  However, in the above-described fixing device having a heating element composed of a halogen lamp or the like, the fixing roller is heated using radiant heat from the halogen lamp, so that the temperature of the fixing roller is suitable for fixing after the power is turned on. It took a relatively long time to reach the predetermined temperature (hereinafter referred to as “warm-up time”). Meanwhile, there is a problem that the user cannot use the copying machine and is forced to wait for a long time.

  On the other hand, if a large amount of power is applied to the fixing roller in order to shorten the warm-up time and improve the operability for the user, there is a problem that the power consumption in the fixing device increases and this is contrary to energy saving. For this reason, in order to increase the value of products such as copiers, more attention and emphasis are placed on achieving both energy saving (low power consumption) of the fixing device and improved user operability (quick print). It is coming.

  As an apparatus that meets such a demand, an induction heating type fixing apparatus using high frequency induction as a heating source has been proposed. In this induction heating fixing device, a coil is concentrically disposed inside a hollow fixing roller made of a metal conductor, and an induction eddy current is generated in the fixing roller by a high frequency magnetic field generated by flowing a high frequency current through the coil. The fixing roller itself generates Joule heat by the skin resistance of the fixing roller itself. According to the induction heating type fixing device, since the electric-heat conversion efficiency is extremely improved, the warm-up time can be shortened (for example, Patent Document 1).

  The heating by the induction heating method can be used without being limited to the fixing device, and can be used as various heating devices.

  However, in the invention according to Patent Document 1, even the electromagnetic induction heating type fixing device operates so as to fix the entire area of the maximum transfer material by fixing it at the fixing temperature. Further, depending on the size of the transfer material, an area that is not a sheet passing area is abnormally heated, causing temperature rise in the apparatus, thermal deterioration of the heated member, and the like.

  Therefore, in the invention according to Patent Document 2, by using two or more exciting coils having different heating distributions, control is performed so that the respective exciting coils are not energized at the same time, thereby preventing abnormal temperature rise in the non-sheet passing region. .

  However, in the present invention, the temperature rise in the non-sheet passing area is monitored using temperature detecting means such as a thermistor, and the size of the recording sheet to be passed by the image forming apparatus is various, and the mounting position Depending on the accuracy, the reaction rate may be slow, and the variation in detected temperature may increase.

  As a countermeasure, a fixing roller having a Curie point near the fixing temperature has been proposed.

Japanese Patent Application Laid-Open No. H10-228561 uses a leakage magnetic flux as means for determining whether or not the Curie point has been reached. In Patent Document 3, leakage magnetic flux is induced by another magnetic induction member arranged outside the heating member, and an abnormal temperature increase due to a device failure or the like is detected by detecting a temperature increase of the magnetic induction member by a temperature detection sensor. is doing.
JP 59-033787 JP 2001-332377 A JP 2001-267050 A

  However, even with a roller having a Curie point, the peripheral member is heated by the leakage magnetic flux after reaching the Curie point, and an unheated area of the fixing roller is heated due to an increase in the ambient temperature, which may cause image defects. There is sex. In addition, power consumption occurs due to the magnetic flux absorbed by the peripheral members.

  The present invention has been made in view of the above-described problems, and the intended process is to prevent heating of peripheral members due to leakage magnetic flux and to prevent temperature rise at the end of the heating member that has become a non-sheet passing region. An object is to provide an image forming apparatus.

  In order to solve the above-described problem, an image forming apparatus according to claim 1 has a mechanism for inductively heating a heating member made of a conductive magnetic material by a magnetic field generating means for generating a magnetic field by an exciting coil. A magnetic flux detecting means disposed opposite to the magnetic field generating means across the heating member and detecting leakage magnetic flux from the heating member generated when the temperature of the heating member reaches the Curie point; and It has a control means which concentrates the electric power applied to an exciting coil, when a magnetic flux detection means detects a leakage magnetic flux only to the center part of a heating member.

  3. The image forming apparatus according to claim 2, wherein the magnetic field generating means has two or more exciting coils in the longitudinal direction of the heating member, and during normal heating, power is applied to all the exciting coils, and the magnetic flux detecting means. Is characterized in that electric power is supplied to an exciting coil that heats only the central portion when leakage magnetic flux is detected.

  4. The image forming apparatus according to claim 3, wherein the magnetic flux detecting means starts operating after detecting the leakage magnetic flux, and operates at a predetermined time, and the exciting coil that heats only the central portion by the timing generating means. And a switching means for switching whether to supply power only to all of the exciting coils or not.

  5. The image forming apparatus according to claim 4, wherein a paper size detecting unit that detects a paper size of a recording paper on which an image is formed, and a magnetic flux detecting unit detects a leakage magnetic flux, and only a central portion is detected depending on the paper size of the recording paper. It is characterized in that it is determined whether or not to switch between supplying power to only the exciting coil that heats the coil and supplying power to all the exciting coils.

  The image forming apparatus according to claim 5 is characterized in that at least three of the exciting coils are arranged in the longitudinal direction inside the heating member.

  According to the present invention, in an image forming apparatus that heats a heating member having a Curie point by an induction heating method in the image forming apparatus, it is determined whether or not the heating member has reached a Curie point by detecting leakage magnetic flux. By detecting the leakage magnetic flux at the end of the heating member, by changing the orientation of the exciting coil and switching to heating only at the center, heating of the peripheral member due to the leakage magnetic flux is prevented and the heating member becomes a non-sheet passing region It becomes possible to prevent the temperature rise at the end. Furthermore, by switching the excitation coil according to the timer or the paper size through which the paper is passed, it is possible to prevent the fixing property from being deteriorated due to the temperature drop at the end.

  The magnetic flux detection means for capturing the leakage magnetic flux only needs to be arranged at a place where the leakage magnetic flux is captured, and high accuracy is not required at the mounting position such as the thermistor.

  In general, by energizing all the exciting coils, it is possible to shorten the start-up time to the target temperature.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
A simple configuration of a general image forming apparatus is shown in FIG.

  A main body image output unit 10 that outputs a document image on a recording sheet, a main body image input unit 11 that reads data of the original image, and an automatic document feeder 12 are provided above the main body image input unit 11. An operation such as setting a copy mode by the user can be performed by the display unit 14. Further, it is possible to display various setting values of the apparatus, current job status, processing instruction contents at the time of error or jam.

  The main body image output unit 10 is provided with paper feed stages 34, 35, 36, and 37 in which recording paper is stored, and the user can freely sort the recording paper according to the paper size of the recording paper. A large capacity paper deck 15 can be connected to the outside of the main body image output unit 10. The recording paper is conveyed to the image forming unit by paper feeding and conveying rollers 38, 39, 40, 41, and 42 driven by a motor (not shown).

  The main body image input unit 11 emits light from a light source 21 that scans a document placed on a document table on the upper surface of the input unit (not shown) in the left-right direction in FIG. The light is reflected by the document, and an optical image is formed on the CCD 26 through the mirrors 22, 23, 24 and the lens 25. In the CCD 26, the image formed is converted into an electric signal and becomes digital image data. The image data is subjected to image conversion such as enlargement / reduction in response to a user request, and is stored in an image memory (not shown).

  At the time of outputting an image, image data stored in the image memory is called in the main body image output unit 10, reconverted from a digital signal to an analog signal, and scanned from the optical irradiation unit 27 as an optical signal of a laser beam 28 and a lens 29. Then, the light is irradiated onto the photosensitive drum 31 through the mirror 30 to scan the photosensitive drum 31.

  An enlarged view of the vicinity of the fixing roller 32 from the photosensitive drum 31 will be described in detail with reference to FIG.

  The photosensitive drum 31 has a photoconductive layer made of an organic photoconductor on its surface, and is driven to rotate in the direction of arrow A at a constant speed during a copy job. The developing and transferring methods will be described. First, after the charge remaining on the photosensitive drum 31 is removed by the exposure device 52, the primary charger 51 uniformly applies the charge to the photosensitive drum 31. The polarity of the charge at this time is determined by the charging property of the toner, and the material of the photosensitive drum 31 must also be selected so as to have a polarity opposite to that of the toner.

  The laser scanner unit 50 outputs a laser beam modulated in accordance with digital image data obtained by scanning an original with the image input device 11, and electrostatic latent image so as to remove the electric charge of the photoconductive layer on the photosensitive drum 31. An image is launched. Thereafter, the toner is attached to the electrostatic latent image on the photosensitive drum 31 from the developing unit 33 to make the electrostatic latent image a visible image.

  On the other hand, the recording paper 58 is conveyed from the paper supply units 34, 35, 36, and 37 through the paper conveyance path, and passes below the photosensitive drum 31 in accordance with the visible image. The transfer charger 55 starts discharging at the timing when the recording paper 58 passes, charges the recording paper 58, and copies the visible image on the photosensitive drum 31 onto the recording paper 58. Thereafter, in order to improve the separation between the photosensitive drum 31 and the recording paper 58, the recording paper 58 is charged by the separation charger 54. The recording paper 58 separated from the photosensitive drum 31 is transported by the transport belt 59 and introduced between the fixing roller 32 and the pressure roller 43. The unfixed toner image is welded and discharged to the outside of the output device 10 through the paper discharge sensor 56.

  On the other hand, the toner remaining on the photosensitive drum 31 without being transferred is scraped off by a drum cleaner 53 formed by a cleaning roller or a blade, and the charge on the photosensitive drum 31 is made zero by the pre-exposure device 52. Prepare for the next copy.

  Further, the fixing roller 32 may not be completely fixed on the recording paper 58 depending on the image density. At this time, the toner that could not be fixed on the recording paper 58 adheres to the surface of the fixing roller 32. When the next recording paper that has adhered toner moves to the recording paper and may contaminate the image, a web 60 that wipes off the adhering toner is adhered to the fixing roller 32 and disposed. Since the web 60 is contaminated by the adhered toner, the web roller 70 is intermittently rotated by a driving source (not shown in FIG. 2) to wind the web.

  FIG. 3 shows a cross-sectional view of the fixing roller 32 using the electromagnetic induction heating method.

  The heating means of the fixing roller 32 of the present invention is an electromagnetic induction heating method. In the fixing roller 32, a holder 66 containing magnetic cores 61 to 63 and exciting coils 64 and 65 is contained. In the holder 66, T-shaped magnetic cores 611 to 63 are arranged. The magnetic cores 61 to 63 are high magnetic susceptibility members, and are preferably selected using a material with little loss. As shown in FIG. 4, the exciting coils 64 and 65 are wound in the longitudinal direction of the fixing roller 32 and are held by the inner wall of the holder 66 and the magnetic cores 61 and 62.

  As shown in FIG. 5, a pickup coil 80 is disposed outside the fixing roller 32. A plurality of pickup coils 80 may be provided depending on the size of the sheet passing recording paper. The pickup coil 80 is disposed in a direction in which the magnetic flux generated from the excitation coils 64 and 65 of the fixing roller 32 can be efficiently captured.

  FIG. 5 shows a block diagram of a control circuit of the electromagnetic induction heating device.

  The control circuit of the electromagnetic induction heating device includes a rectifying circuit 101 that rectifies an AC input, a drive circuit 102 that switches energization to the excitation coils 64 and 65, and a resonance output that provides a switching signal to the drive circuit 102 for the excitation coils 64 and 65. There is a control circuit 103 and a main body control circuit 104 that supplies input power values and circuit on / off signals to the resonance output control circuit 103. The resonance control circuit 103 controls the resonance frequency by detecting the phase of the voltage waveform energized by the drive circuit 102.

  The pickup coil 80 induces leakage magnetic flux when the fixing roller 32 reaches the Curie point by electromagnetic induction heating. The Curie point is a temperature at which a magnetic material such as a ferromagnetic material transitions to paramagnetism. The magnetic permeability of the ferromagnet gradually decreases during heating, but rapidly decreases when the Curie point is reached. Therefore, the magnetic flux passes through the fixing roller 32 and leaks to the outside of the roller. The pick-up coil 80 conductive flow flows due to the leakage magnetic flux.

  By detecting that the current has started to flow, it can be detected that the fixing roller 32 has reached the Curie point. In FIG. 6, the horizontal axis represents the temperature of the fixing roller 32, and the vertical axis represents the current value Ic flowing through the pickup coil 80. Below the Curie point Tc (for example, 200 ° C.), the current Ic flowing through the pickup coil 80 is substantially zero. However, when the Curie point Tc is reached, the current value Ic flowing through the pickup coil 80 increases rapidly and saturates at a substantially constant value. To do. The current value at this time is Idtc.

  The main body control circuit 104 determines whether or not the current Ic flowing through the pickup coil 80 has become Idtc. This determination method may be compared with a threshold value set between 0 and Idtc using a comparator, and may detect that Idc has been reached as an analog signal. When the main body control circuit 104 detects Idtc, the main body control circuit 104 outputs a signal for cutting the exciting coil 64 to the drive circuit 102 via the power control circuit 103. The excitation coil 64 is cut by this signal, and only the excitation coil 65 is energized. As shown in FIG. 5, the exciting coil 65 is a coil that heats only the central portion of the fixing roller 32, so that the end portion of the fixing roller is gradually naturally cooled.

  The main body control circuit 104 has a timer circuit therein, and starts the timer when the current Ic flowing through the pickup coil 80 reaches Idtc. The timer operating time is set in advance (T = Toff). The set time is a time period from when the exciting coil 64 is cut to a temperature at which the fixing property at the end of the fixing roller 32 is impaired, and is a value experimentally verified. When this timer reaches the set time, the coil 64 is energized again and energized again until the pickup coil 80 detects the leakage magnetic flux.

  FIG. 11 shows the timing of the pickup coil 80 signal, the excitation coil 64 on signal, and the excitation coil 65 on signal.

  Immediately after the start of image formation, energization of both the exciting coils 64 and 65 is started. When the pickup coil 80 detects the leakage magnetic flux, the energization of the excitation coil 64 is cut off. At the same time, a timer is set and the exciting coil 64 is disconnected until T = Toff. After T = Toff, the excitation coil 64 is energized again. When the pickup coil 80 detects the leakage magnetic flux, the same operation is repeated.

  Control of the main body control circuit 104 at this time will be described with reference to the flowchart of FIG.

  When a user operates the main switch of the apparatus and no trouble is found in the main body immediately after the main body is activated, the fixing roller 32 is heated by energizing the exciting coils 64 and 65. When the main body is in a standby state, the user performs an image forming operation by operating the display unit 14 to perform a copying operation or printing out via a network (S1000).

  When the user selects a small size paper and performs a large number of copy or print operations, the temperature at the end of the fixing roller rises and reaches the Curie point. At this time, the pickup coil 80 detects leakage magnetic flux generated when the end of the fixing roller 32 reaches the Curie point. When the copying or printing operation is not completed (S1001), the main body control circuit 104 detects the output current of the pickup coil 80 and determines whether or not the Curie point has been reached based on whether or not it has reached Idtc ( S1002) If the Curie point has been reached, the coil to be energized is switched to the exciting coil 65 only (S1003), and then the timer is started to operate (S1004).

  When the copy or print operation is completed before the timer reaches T = Toff (S1005), the state is changed after the excitation coil is switched so that both 64 and 65 can be energized in order to set the state of the image forming apparatus to standby. (S1009). If the copying or printing operation is not completed in S1005, when the timer reaches a predetermined time T = Toff (S1006), switching is performed so that both the exciting coils 64 and 65 can be energized (S1007), and again. It is determined whether the copying or printing operation has been completed (S1001), and if not, the detection current of the pickup coil 80 is monitored (S1002). S1001 to S1007 are repeated until one image forming operation is completed (S1008).

  As described above, it is possible to switch to heating only at the center by detecting that the end of the fixing roller 32 has reached the Curie point when passing small-size paper, and heating the peripheral members accompanying the temperature rise at the end. It is possible to prevent in-flight temperature rise and image degradation due to.

<Embodiment 2>
The second embodiment is characterized in that in the image forming apparatus of the first embodiment, the switching is performed according to the paper size at which the timing of switching the energization method of the excitation coils 64 and 65 is passed.

  It is not necessary to heat the end of the fixing roller 32 during the passing of the small size paper. However, when recording sheets having different paper sizes (for example, A4 portrait size and A4 landscape size) are alternately fed, the temperature drop at the end of the fixing roller 32 causes deterioration of fixability. Therefore, the leading edge is predicted in advance, and the energization method of the exciting coils 64 and 65 is switched in advance based on the information on the paper size to be passed.

  Information on the sheet passing recording paper size is stored in the main body control circuit 104 according to the setting value of the user. The timing of raising the end of the fixing roller 32 also depends on the internal temperature at that time, so it is necessary to monitor it with the pickup coil 80.

  Control of the main body control circuit 104 of the present embodiment will be described with reference to the flowchart of FIG.

  An image forming operation is performed by a user operation (S2000). The main body control circuit 104 determines whether or not the copy or print job has been completed (2001). If not, the main body control circuit 104 monitors the output current of the pickup coil 80 to determine whether or not the Curie point has been reached. (S2002). If the Curie point has been reached, the energized coil is switched to the exciting coil 65 only (S2003).

  It is always determined whether or not the copy or print job is completed (S2004). At the same time, the paper passing paper size is checked by a predetermined number (S2005), and if the paper size is equal to or larger than the predetermined size (this embodiment) In the embodiment, A4 size or larger) is switched so that both the exciting coils 64 and 65 can be energized (S2006), and it is determined again whether the copying or printing operation is completed (S2001). The detected current is monitored (S2002). S2001 to S2006 are repeated until one image forming operation is completed (S2007).

  As described above, by switching the energization method of the exciting coils 64 and 65 depending on the paper size, it is possible to avoid wasting power consumption during copying and to suppress the temperature rise in the apparatus.

<Embodiment 3>
As a third embodiment, the arrangement of the exciting coils in the fixing roller 32 is as shown in FIG. The exciting coil 67 heats only the central portion of the fixing roller 32, and the exciting coils 68 and 69 are disposed at symmetrical positions at the longitudinal ends of the fixing roller 32.

  A block diagram of the control circuit at this time is shown in FIG.

  Excitation coils 67 to 69 are disposed in the fixing roller 32, and the driver unit 102 has a circuit capable of switching the excitation coil 67 and the excitation coils 68 and 69. Here, the exciting coils 68 and 69 are controlled to be switched simultaneously, but may be switched individually.

  The pickup coil 80 monitors the leakage magnetic flux at the end of the fixing roller 32. Here, since the fixing roller 32 is heated uniformly when heated by all the excitation coils 67 to 69, it is only necessary to monitor only one end. However, since it is necessary to monitor both ends when uniform heating is not possible, the number of pickup coils 80 is not limited to one.

  When the pickup coil 80 detects the leakage magnetic flux, as in the first embodiment, the energization of the exciting coils 68 and 69 for heating the end portions is switched, and only the coil 67 for heating the central portion is energized. Usually, all the exciting coils 67 to 69 are used to heat the fixing roller 32 as a whole.

  From the above, it is possible to suppress the temperature rise at the end by arranging a plurality of coils in the longitudinal direction and switching the energization method of the excitation coil by detecting leakage magnetic flux, and the number of turns of the excitation coil at the end is appropriate. Since it can be set to any value, various heating members can be flexibly supported.

1 is an overall schematic diagram of a general image forming apparatus. FIG. 2 is an enlarged view of a vicinity of a fixing unit from a transfer unit of a general image forming apparatus. It is an expanded sectional view of a fixing roller including an electromagnetic induction heating device used in the present invention. FIG. 3 is an internal perspective view in a longitudinal direction of a fixing roller used in the present invention. It is a control circuit block diagram of the electromagnetic induction heating device in Embodiment 1 of the present invention. It is an output characteristic figure of the magnetic coil in Embodiment 1 of this invention. It is the flowchart which showed the control sequence in Embodiment 1 of this invention. It is the flowchart which showed the control sequence in Embodiment 2 of this invention. FIG. 10 is an internal perspective view in the longitudinal direction of a fixing roller used in Embodiment 3 of the present invention. It is a control circuit block diagram of the electromagnetic induction heating apparatus in Embodiment 3 of this invention. It is the figure which showed the timing of each control signal in Embodiment 1 of this invention.

Explanation of symbols

32 Fixing roller 43 Pressure roller 61-63 Magnetic core 64, 65 Excitation coil 66 Holder 67-69 Excitation coil 70 Web roller 80 Pickup coil

Claims (5)

In an image forming apparatus having a mechanism for inductively heating a heating member made of a conductive magnetic material by a magnetic field generating means for generating a magnetic field by an exciting coil.
A magnetic flux detecting means disposed opposite the magnetic field generating means with the heating member interposed therebetween, and detecting a leakage magnetic flux from the heating member generated when the temperature of the heating member reaches a Curie point; and the magnetic flux detection An image forming apparatus comprising control means for concentrating power applied to the exciting coil only at the center of the heating member when the means detects leakage magnetic flux.   The magnetic field generating means has two or more exciting coils in the longitudinal direction of the heating member. During normal heating, power is applied to all the exciting coils, and when the magnetic flux detecting means detects leakage magnetic flux, The image forming apparatus according to claim 1, wherein electric power is supplied to an exciting coil that only heats.   The magnetic flux detection means starts operating after detecting the leakage magnetic flux, and operates at a predetermined time, and supplies power only to the excitation coil that heats only the central portion by the timing generation means or all the excitation coils. The image forming apparatus according to claim 2, further comprising a switching unit that supplies or switches power to the apparatus.   The paper size detecting means for detecting the paper size of the recording paper on which an image is formed, and the magnetic flux detecting means detects the leakage magnetic flux, and then power is supplied only to the excitation coil that heats only the central portion according to the paper size of the recording paper. The image forming apparatus according to claim 2, wherein it is determined whether to switch between supplying power and supplying power to all exciting coils.   The image forming apparatus according to claim 2, wherein at least three of the exciting coils are arranged in the longitudinal direction inside the heating member.

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