JP2007095539A - Heating device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent flowing of a peak current more than necessary for an excitation coil and a switching element at the effective time of a shielding plate, in an excitation coil drive device of a fixing unit of an induction heating type with the shielding plate. <P>SOLUTION: The drive frequency control part calculates a time to turn on an switching element based on a temperature monitor signal from a temperature detection means and a temperature instruction value from a controller. In that case, when the temperature monitor signal value is greatly lower than the temperature instruction value, the turning-on time is restricted and a drive signal at the maximum turning-on time is generated. Then, the turning-on time restriction time is changed at the effective time and non-effective time of the shielding plate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heating device of an electromagnetic (magnetic) induction heating system, and an image forming apparatus provided with the heating device as an image heating device such as image fixing.

  For convenience, an image heating and fixing device in an image forming apparatus such as an electrophotographic copying machine, a printer, and a fax machine will be described as an example.

  An image heat fixing apparatus in an image forming apparatus is a toner (developer) made of a heat-meltable resin or the like by an appropriate image forming process means such as electrophotography, electrostatic recording, or magnetic recording in an image forming unit of the image forming apparatus. ) To heat and fix an unfixed toner image formed on the surface of the recording material by a direct method or an indirect (transfer) method as a permanently fixed image on the surface of the recording material.

  In recent years, an electromagnetic induction heating method has been used as such an image heating and fixing device.

  The electromagnetic induction heating method uses an electromagnetic induction heating element as a heating element, and applies a magnetic field to the electromagnetic induction heating element by a magnetic field generating means to generate Joule heating based on eddy current generated in the electromagnetic induction heating element. This is a fixing method in which heat is applied to a recording material to heat and fix an unfixed toner image on the surface of the recording material.

  In general, in a heating device, when a material to be heated having a smaller size width (small size width) than a material to be heated having a maximum size width (large size width) that can be passed through the apparatus is continuously passed through and heated. Heat is heated in the non-sheet passing area of the heated material heating section of the apparatus, that is, in the difference area between the passing area of the heated material having a large size width and the passing area of the heated material having a small size width. There is a “non-sheet-passing portion overheating phenomenon” in which the temperature is raised from the region of the sheet passing portion and is not allowed to be heated, and the overheated state is higher than allowable.

  As a countermeasure technique for preventing the excessive temperature rise phenomenon of the non-sheet passing portion, in an electromagnetic induction heating type heating device, for example, the magnetic flux adjusting means causes the working magnetic flux from the magnetic flux generating means to the induction heating element in the heating portion to be heated. A method of changing the density distribution in the longitudinal direction of the heating unit that intersects the transport direction is known.

  The above method will be described with reference to FIGS.

  7 and 8 are partially cutaway side views of the image heating and fixing apparatus 10, FIG. 9 is a longitudinal front view of the heating assembly, and FIG. 10 is a cutaway perspective view of the heating assembly.

  The fixing device 10 mainly includes a heating assembly 1 and a pressure roller 2 as a rotary pressure member.

  The heating assembly 1 includes a cylindrical film guide member 3, an excitation coil 4 and a magnetic core (high transmittance core) 5 as magnetic flux generating means disposed in the inner space thereof, and a cylindrical film guide member 3 that is loosely fitted outside. Magnetic flux adjusting means arranged to be freely slidable in the vertical directions a and b along the inner circumferential surface of one end side of the cylindrical (seamless) fixing film 6 and cylindrical film guide member 3 as induction heating elements As a pair of left and right arc-shaped magnetic flux shielding plates 7, 7 and the like.

  The exciting coil 4 generates a magnetic flux by the alternating current supplied from the exciting circuit 40 (FIG. 10). The magnetic flux is guided to the magnetic core 5 and acts on the fixing nip portion N. An eddy current is generated in the induction heating layer. The eddy current generates Joule heat by the specific resistance of the electromagnetic induction heating layer. That is, by supplying an alternating current to the exciting coil 4, the fixing film 6 is brought into an electromagnetic induction heat generation state in the fixing nip portion N.

  The temperature of the fixing nip portion N is controlled to a predetermined fixing temperature by controlling the supply alternating current from the exciting circuit 40 to the exciting coil 4 by the temperature control system 100 including a temperature detecting means (not shown).

  The exciting coil 4 is formed by winding an insulation coated electric wire into a horizontally long boat shape whose outer shape substantially corresponds to the inner surface of the cylindrical film guide member 3, and is substantially below the inner surface of the cylindrical film guide member 3. The half surface portion receives the outer surface and is inserted into the cylindrical film guide member 3. The exciting coil 4 must generate a magnetic flux sufficient for heating. For this purpose, it is necessary to make the resistance component low and the inductance component high. In one example, the exciting coil 4 is configured by winding 12 turns so as to go around the fixing nip portion N using a high-frequency φ1 insulated coated electric wire bundled with fine wires as core wires. An excitation circuit 40 is connected to the excitation coil 4, and the excitation circuit 40 can supply a high-frequency alternating current to the excitation coil 4.

  In the following description, it is assumed that the recording material P is introduced into the fixing device 10 by one-side reference sheet feeding.

  9 and 10, O is a one-side paper passing reference line, A is a paper passing area portion of a large size recording material (maximum size recording material that can be passed through the apparatus), and B is a paper passing area portion of a small size recording material. , C are non-sheet passing area portions (AB) when a small size recording material is used.

  The pair of left and right arc-shaped magnetic flux shielding plates 7 and 7 are fitted in a circumferential guide groove 3a provided on the inner surface of the end of the cylindrical film guide member 3 on the side where the non-sheet passing region C is generated. Each of the magnetic cores 5 is slidable in the vertical directions a and b along the circumferential guide groove 3a on the left and right sides of the magnetic core 5, and has a width corresponding to the width of the non-sheet passing region C.

  Then, by being slid and moved downward b, the state is inserted (closed position) between the left and right outer surfaces of the exciting coil 4 and the inner surface of the cylindrical film guide member 3 as shown in FIG.

  Further, by sliding to the upper side a, as shown in FIG. 8, it is in a state of being pulled out from between the left and right outer surfaces of the exciting coil 4 and the inner surface of the cylindrical film guide member 3 (open position).

  When the magnetic flux shielding plates 7 and 7 are in the closed position in FIG. 7, the excitation with respect to the non-sheet passing region C when the small-size recording material is fed in the longitudinal direction (longitudinal direction) of the fixing nip N. The magnetic flux from the coil 4 is interrupted or reduced between the fixing film 6 by the closed magnetic flux shielding plates 7 and 7, and the action density of the magnetic flux acts on the small size sheet passing area B of the fixing nip N. Lower than density. As a result, the fixing film portion corresponding to the small size sheet passing area B in the fixing nip portion generates electromagnetic induction heat almost uniformly and has an optimum temperature distribution for fixing, but corresponds to the non-sheet passing area C. The electromagnetic induction heat generation in the fixing film portion is further reduced, thereby preventing or mitigating the temperature rise phenomenon of the non-sheet passing portion.

  When the magnetic flux shielding plates 7 and 7 are in the open position of FIG. 8, the magnetic flux shielding plates 7 and 7 are not shielded by the magnetic flux shielding plates 7 and 7, and the magnetic flux generated by the exciting coil 4 is large-size sheet passing region portion in the fixing nip portion. The entire fixing film A operates at a predetermined high density, and the entire fixing film portion corresponding to the large-size sheet passing area A in the fixing nip portion generates electromagnetic induction heat almost uniformly in a predetermined temperature distribution to obtain an optimum temperature distribution for fixing. .

  The magnetic flux shielding plates 7 and 7 are connected to the driving means 70 (FIG. 9) via the arm portions 7a and 7a, respectively, and the movement to switch between the closed position and the open position depends on the size of the recording material used for passing the paper through the apparatus. In response, the control circuit 101 and the driving means 70 automatically do so.

  The control circuit 101 switches the magnetic flux shielding plates 7 and 7 to the closed position shown in FIG. 7 when it is detected by a recognition means (not shown) that the recording material P used for paper passing through the apparatus is small. The driving means 70 is controlled. By switching to the closed position of the magnetic flux shielding plates 7, 7, the non-sheet passing portion temperature rise phenomenon is prevented or alleviated as described above.

  The control circuit 101 is driven so as to switch and move the magnetic flux shielding plates 7 and 7 to the open position in FIG. 8 when the recognition means detects that the recording material P used for paper passing through the apparatus is large. The means 70 is controlled. As a result, as described above, the magnetic flux reaching the fixing film in the longitudinal direction of the fixing nip portion is unhindered and generates heat throughout the entire area, so that the temperature distribution is optimal for fixing a large recording material.

  FIG. 11 is a block diagram showing the configuration of the excitation circuit 40 and the temperature control system 100 for exciting the excitation coil 4.

  In FIG. 11, D1 to D4 are AC input power rectifying diodes that supply a pulsating current obtained by rectifying AC power to the power control circuit unit.

  NF1 and C1 form a noise filter, and are set to constants that ensure a sufficient attenuation for the switching frequency of the switching element TR1 and pass through the power supply frequency without attenuation.

  The switching element TR1 is a power switching element MOS-FET, C1 is a resonance capacitor for making a high-frequency alternating current applied to the exciting coil 4 as a load a resonance waveform, and D5 regenerates the electric power stored in L1. It is a flywheel diode.

  A temperature sensitive resistance element such as a thermistor is generally used for the temperature detection element of TH1, and its output is input to the temperature detection means 105.

  The temperature detection means 105 outputs the resistance change of the temperature detection element TH1 as a voltage value, and the output value becomes a temperature monitor signal. The temperature monitor signal is input to the drive frequency control unit 56.

  A temperature command value is input from the controller 61 to the drive frequency control unit 56, the energization operation to the excitation coil 4 of the fixing device is determined by the temperature monitor signal and the temperature command value from the temperature detecting means 105, and the switching element TR1 is driven. A drive signal for generating the signal is generated.

  This drive signal is generally controlled by on-time control with a fixed off-time, that is, frequency modulation.

  Next, the operation will be described.

  When an AC input voltage is applied to the input terminal of FIG. 11, it becomes a pulsating flow rectified by the rectifying elements D1 to D4, and the voltage passes through NF1 and is applied to both ends of C1. Therefore, the voltage across C1 has a waveform obtained by rectifying the AC input voltage.

  The drive frequency control unit 56 determines a time to turn on the switching element TR1 based on the temperature monitor signal from the temperature detection unit 105 and the temperature command value from the controller unit 61, and generates a drive signal.

  The drive signal is applied between the gate and the source of the switching element TR1, and the drain current ID flows through the switching element TR1 to energize the exciting coil 4 during the ON period of the drive signal.

  Since the exciting coil 4 stores a current that flows when the switching element TR1 is turned on, a back electromotive voltage is generated when the switching element TR1 is turned off to charge the coil accumulated current to the resonance capacitor C2.

The resonant capacitor voltage rises due to the flowing coil accumulated current.
The current flowing out of the exciting coil attenuates in inverse proportion to the increase in the voltage of the resonance capacitor C2, and when passing through the moment when the coil current does not flow at a certain point, the charge accumulated in the resonance capacitor C2 is reversed. However, a current flows toward the exciting coil 4.

  After that, the electric charge accumulated in the resonance capacitor C2 returns to the exciting coil 4, and at the same time, the voltage of the resonance capacitor C2 decreases, the drain voltage of the switching element TR1 decreases below the source voltage, and the flywheel diode of D5 turns on. Forward current flows.

  Thereafter, when the switching element TR1 is turned on again, the current flows in the exciting coil 4 and the current is accumulated in the exciting coil 4, so that the induction heating element, which is a load that is electromagnetically coupled to the exciting coil, is also induced current. Flows and is heated.

  FIG. 12 shows the configuration of the drive frequency control unit 56. The drive frequency control unit 56 receives the temperature monitor signal from the temperature detection means 105 and the temperature command value from the controller unit 61. Then, the temperature comparison signal generator 51 generates a temperature comparison signal based on the magnitude relationship and the difference between the two signals. The on-time determining unit 57 determines the time for which the switching element TR1 is turned on based on the temperature comparison signal. Specifically, the on-time is longer as the temperature monitor signal is smaller than the temperature command value and the difference is larger, and the on-time is shortened as the temperature monitor signal is larger than the temperature command value and the difference is larger. Control is performed.

  However, if the on-time is made longer than necessary, a large peak current flows through the switching element TR1, so the on-time determining unit limits the maximum on-time, the temperature monitor signal is smaller than the temperature command value, and the difference When the current value exceeds a predetermined value, a preset maximum on-time is set as the on-time to prevent an unnecessary peak current from flowing through the switching element TR1.

  For example, when the temperature monitor signal value from the temperature detecting means 105 is significantly lower than the temperature command value, such as when the image heating and fixing apparatus is started up, the on-time is increased and the surface temperature of the fixing apparatus is rapidly increased. In such a case, the drive signal is controlled with the maximum on-time described above.

  The drive signal generation unit 54 generates a drive signal for driving the switching element TR1 by frequency modulation with a fixed off time based on the determined on time, and the switching element TR1 is turned on / off to control the excitation coil 4. Excitation current is controlled.

  As a result, the surface temperature of the fixing film is controlled at a constant target temperature.

For example, Patent Document 1 can be cited as a conventional example.
JP 2004-273454 A

  In the conventional induction heating fixing device, the set value of the maximum on-time in the switching element TR1 described above is a fixed value.

  On the other hand, when the magnetic flux shielding plate is closed, the inductance value of the exciting coil 4 as viewed from the exciting circuit is lower than when the magnetic flux shielding plate is opened. As a result, when the shielding plate is closed, the gradient of the excitation current flowing in the excitation coil 4 becomes steeper than when the shielding plate is opened.

  Further, in the image forming apparatus, when the image forming operation is not performed for a certain period of time or longer, the image forming apparatus shifts to the sleep mode, and the controller greatly reduces the temperature command value of the induction heating fixing apparatus or stops the power supply. To work. When shifting from such a state to the image forming operation, the temperature monitor signal value from the temperature detecting means 105 is greatly lower than the temperature command value. Increases the surface temperature of the induction heat fixing device in a state limited by the maximum on-time.

  Further, when shifting from the sleep mode to the image forming operation, if the size of the recording material used in advance is known, the shielding plate is moved to the closed position in advance to increase the surface temperature of the induction heat fixing device.

  FIG. 13 shows the relationship between the drive signal of the switching element and the current flowing through the switching element in each of these states.

  In FIG. 13, a drive signal 1 is a drive signal when the surface temperature of the induction heat fixing device reaches the temperature command value and the temperature is adjusted, and the recording material is large and the shielding plate is opened. This is the current flowing through the switching element at that time.

  It is understood that the drive signal 2 is a state in which the surface temperature of the induction heat fixing device is greatly below the temperature command value when returning from sleep or starting up the apparatus, and the recording material in the next image forming operation is large in advance. Or when the shielding plate is open and the ON time is the maximum ON time, Id2 is the current flowing through the switching element at that time.

  The driving signal 3 is a driving signal when the surface temperature of the induction heat fixing device reaches the temperature command value and the temperature is adjusted, the recording material is small in size and the shielding plate is closed, and Id3 is a switching element at that time Current flowing through the

  Further, the drive signal 4 is a state in which the surface temperature of the induction heat fixing device is greatly below the temperature command value when returning from sleep or starting up the apparatus, and the recording material in the next image forming operation is small in advance. When the shielding plate is closed, the on-time is the driving signal with the maximum on-time, and Id4 is the current flowing through the switching element at that time.

  As shown in the figure, when the shielding plate is closed with respect to the drive signal 1, the on-time is controlled to be narrowed like the drive signal 3. On the other hand, since the inductance value of the exciting coil decreases due to the closing of the shielding plate, the slope of the current flowing through the switching element becomes steep. As a result of temperature control, the peak values of Id-1 and Id-3 are almost equal. However, it is known that the recording material in the next image forming operation is small in advance in a state where the surface temperature of the induction heat fixing device is greatly lower than the temperature command value at the time of returning from sleep or starting up the apparatus. As in the case, when the on-time is maximized (Ton4), a large peak current flows. FIG. 14 shows Id-1 to 4 superimposed on each other.

  As shown in FIG. 14, there is a possibility that a peak current of Id-4 flows through the switching element at the maximum. Therefore, when selecting the switching element TR1, the exciting coil inductance value when the shielding plate is closed and the maximum on-time It was necessary to select the switching element TR1 based on the maximum peak current (Id-4) that can flow through the switching element calculated from the set value.

  However, in a state where the surface temperature of the induction heat fixing device reaches the temperature command value and the temperature is adjusted, the drive signal of the switching element TR1 is turned on as long as there is no malfunction due to noise or the like, or temperature misdetection of the temperature detection means. In the past, when the surface temperature of the induction heat fixing device is significantly lower than the temperature command value, such as when returning from sleep or starting up the device, the next image forming operation is performed in advance. Corresponding to the peak current that flows when the recording material is known to be small, a switching element with a capacity larger than necessary was selected for the required capacity during steady-state temperature control, which hindered low costs. .

  Accordingly, the present invention has been made for the purpose of solving the above-described problems. An electromagnetic (magnetic) induction heating type heating apparatus that solves the above-described problems and enables the optimum selection of switching elements and reduces the cost. And an image forming apparatus provided with the heating device as an image heating device such as image fixing.

  According to the first aspect of the present invention, the magnetic flux generating means, the high frequency power supply device for supplying a high frequency current to the magnetic flux generating means by turning on / off the switching element, and electromagnetic induction by the action of the magnetic flux generated from the magnetic flux generating means. An induction heating element that generates heat, and the introduced material to be heated is brought into contact with the induction heating element directly or via a heat transfer material and conveyed to heat the material to be heated by the induction heating element. And a position of the magnetic flux adjusting means for changing the density distribution of the magnetic flux acting on the induction heating element in the direction intersecting the conveying direction of the heated material from the magnetic flux generating means. Driving means, and the limit value of the maximum ON time of the switching element in the high-frequency power supply device is changed according to the position of the magnetic flux adjusting means.

  According to a second aspect of the present invention, the magnetic flux adjusting means functions according to the size of the material to be heated used in the apparatus.

  According to a third aspect of the present invention, the limit value of the maximum ON time is changed so that the maximum value of the current flowing through the switching element becomes equal regardless of the position of the magnetic flux adjusting means.

  According to a fourth aspect of the present invention, the limit value of the maximum ON time of the switching element is changed when the heating device is started up and when the temperature is adjusted.

  According to a fifth aspect of the present invention, the heated material is a recording material that carries an image, and is an image heating device that heats the image.

  According to a sixth aspect of the invention, there is provided an image heating and fixing device that heats and fixes the image as a permanent image.

  According to a seventh aspect of the present invention, the image heating apparatus according to the fifth aspect or the image heating and fixing apparatus according to the sixth aspect is provided.

  As described above, the maximum on-time is controlled regardless of whether the shield plate is opened or closed by changing the limit value of the maximum on-time of the drive signal for driving the switching element when the shield plate is opened and closed. It is possible to make the peak current values when the switching elements are driven substantially equal to each other, and as a result, it is possible to optimally select the switching elements and reduce the cost, and the heating device of the electromagnetic (magnetic) induction heating method, It is possible to provide an image forming apparatus provided with the heating device as an image heating device such as image fixing.

Example 1
Embodiments of the present invention will be specifically described below with reference to the drawings.

  1 to 5 are views showing a first embodiment of the present invention.

  1 to 5, the same or corresponding members as those in FIGS. 7 to 14 of the above-described conventional example are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus provided with an induction heating type fixing device having the present invention. The image forming apparatus of this example is an electrophotographic 4-color printer.

  Reference numeral 11 denotes an electrophotographic photosensitive drum (image bearing member) made of an organic photosensitive member, which is rotationally driven at a predetermined process speed (circumferential speed) in the clockwise direction indicated by an arrow.

  The photosensitive drum 11 is uniformly charged with a predetermined polarity and potential by a charging device 12 such as a charging roller during the rotation process.

  Next, the charged surface is subjected to scanning exposure processing of target image information by the laser light L output from the laser optical box (laser scanner) 13. The laser optical box 13 scans and exposes the surface of the rotating photosensitive member by outputting laser light L modulated (on / off) corresponding to time-series electric digital pixel signals of target image information from an image signal generator (not shown). Thus, an electrostatic latent image corresponding to the target image information scanned and exposed on the surface of the rotary photosensitive drum 11 is formed by this scanning exposure. A mirror 13 a deflects the output laser beam from the laser optical box 13 to the exposure position of the photosensitive drum 11.

  In the case of full-color image formation, scanning exposure / latent image formation is performed on a first color separation component image of a target full-color image, for example, a yellow component image, and the latent image is subjected to yellow development in the four-color developing device 14. The yellow toner image is developed by the operation of the device 14Y. The yellow toner image is transferred onto the surface of the intermediate transfer drum 16 at the primary transfer portion T1 which is a contact portion (or proximity portion) between the photosensitive drum 11 and the intermediate transfer drum 16. After the toner image is transferred to the surface of the intermediate transfer drum 16, the surface of the rotating photosensitive drum 11 is cleaned by the cleaner 17 after removal of adhesion residues such as transfer residual toner.

  The process cycle of charging, scanning exposure, development, primary transfer, and cleaning as described above is performed when the target full-color image is second (for example, magenta component image, magenta developing unit 14M is activated), and third (for example, cyan component image, Cyan developing unit 14C is operated) and fourth (for example, black component image, black developing unit 14BK is operated) color separation component images are sequentially executed, and yellow toner image / magenta toner image / cyan on the surface of intermediate transfer drum 16 The four color toner images of the toner image and the black toner image are sequentially superimposed and transferred, and a color image corresponding to the target full-color image is synthesized and formed.

  The intermediate transfer drum 16 has a middle resistance elastic layer and a high resistance surface layer on a metal drum. The intermediate transfer drum 16 is in contact with or close to the photosensitive drum 11 at an approximately same peripheral speed as the photosensitive drum 11. The toner image is rotated in the counterclockwise direction shown in the drawing, a bias potential is applied to the metal drum, and the toner image on the photosensitive drum 11 side is transferred to the intermediate transfer drum surface side by the potential difference with the photosensitive drum 11.

  The color toner image synthesized and formed on the surface of the rotating intermediate transfer drum 16 is transferred to the secondary transfer portion T2 at the secondary transfer portion T2 which is a contact nip portion between the rotating intermediate transfer drum 16 and the transfer roller 15. Are transferred onto the surface of the recording material P fed at a predetermined timing from a sheet feeding unit (not shown). The transfer roller 15 supplies a charge having a polarity opposite to that of the toner from the back surface of the recording material P, thereby sequentially transferring the combined color toner images sequentially from the surface of the intermediate transfer drum 16 to the recording material P side.

  The recording material P that has passed through the secondary transfer portion T2 is separated from the surface of the intermediate transfer drum 16 and is introduced into the image heating and fixing device 10, and is subjected to a heat and fixing process for an unfixed toner image to form a color image formed product outside the apparatus. Are discharged to a paper discharge tray (not shown).

  The image heating and fixing device 10 is an electromagnetic induction heating type device.

  The image heating and fixing device 10 is controlled to a predetermined temperature based on a temperature command value from a controller (not shown) and a detection result of the surface temperature.

  After the color toner image has been transferred to the recording material P, the rotating intermediate transfer drum 16 is cleaned by the cleaner 18 after removal of adhering residues such as transfer residual toner and paper dust. The cleaner 18 is always held in a non-contact state with the intermediate transfer drum 16, and is brought into contact with the intermediate transfer drum 16 during the secondary transfer of the color toner image from the intermediate transfer drum 16 to the recording material P. Retained.

  The transfer roller 15 is also always held in a non-contact state with the intermediate transfer drum 16, and the recording material is transferred to the intermediate transfer drum 16 during the secondary transfer of the color toner image from the intermediate transfer drum 16 to the recording material P. The contact state is maintained via P.

  FIG. 2 is a schematic diagram of a high frequency power supply device for supplying a high frequency alternating current to the exciting coil in the image heating and fixing apparatus 10.

  The drive frequency control unit 50 generates a drive signal for driving the switching element TR1, and the drive signal is controlled by frequency modulation with fixed off time and variable on time. The drive frequency controller 50 receives a temperature monitor signal from the temperature detector 105, a temperature command value from the controller 61, and a position signal of the magnetic flux shielding plate.

  The controller unit controls the operation of each unit described with reference to FIG. 1, and when the recording material used for passing the paper through the apparatus is detected by a recognition unit (not shown) as a small size, the magnetic flux shielding plate is shown in FIG. As described above, the shield plate driving means is controlled so as to be switched to the closed position, and a shield plate position signal indicating that the shield plate is closed is output to the drive frequency control unit 50. When the recognizing means detects that the recording material used for paper passing through the apparatus is a large size, the controller unit sets the shielding plate driving means so as to switch the magnetic flux shielding plate to the open position as shown in FIG. In addition to the control, a shielding plate position signal indicating that the shielding plate is open is output to the drive frequency control unit 50.

  The configuration of the drive frequency control unit 50 is shown in FIG.

  The drive frequency control unit 50 receives the temperature monitor signal from the temperature detection means 105, the temperature command value from the controller unit 61, and the shielding plate position signal. Then, the temperature comparison signal generation unit 51 generates a temperature comparison signal based on the magnitude relationship and difference between the temperature monitor signal both signals and the temperature command value. The on-time determining unit 52 determines the time for turning on the switching element TR1 based on the temperature comparison signal. Specifically, the on-time is longer as the temperature monitor signal is smaller than the temperature command value and the difference is larger, and the on-time is shortened as the temperature monitor signal is larger than the temperature command value and the difference is larger. Control is performed.

  However, if the on-time is made longer than necessary, a large peak current flows through the switching element TR1, so the on-time determining unit limits the maximum on-time, the temperature monitor signal is smaller than the temperature command value, and the difference When the current value exceeds a predetermined value, a preset maximum on-time is set as the on-time to prevent an unnecessary peak current from flowing through the switching element TR1.

  The maximum on-time is input from the maximum on-time setting unit 53. The shielding plate signal is input to the maximum on-time setting unit 53, and a maximum on-time that differs depending on whether the shielding plate is opened or closed is output.

  Specifically, when the switching element is driven with the maximum on-time so that the maximum on time when the shielding plate is closed is smaller than when the shielding plate is opened, the peak current value at that time when the shielding plate is opened and closed Are set to be approximately equal to each other.

The drive signal generation unit 54 generates a drive signal for driving the switching element TR1 by frequency modulation with a fixed off time based on the determined on time, and the switching element TR1 is turned on / off to control the excitation coil 4. Excitation current is controlled. As a result, the surface temperature of the fixing film is controlled at a constant target temperature.
FIG. 4 is a diagram illustrating the on-time of the drive signal when the shielding plate is opened and closed and the current flowing through the switching element.

  FIG. 4 shows that the drive signal 1 is a drive signal when the surface temperature of the induction heat fixing device reaches the temperature command value and the temperature is adjusted, and the recording material is large and the shielding plate is opened. Current flowing through the switching element.

  It is understood that the drive signal 2 is a state in which the surface temperature of the induction heat fixing device is greatly below the temperature command value when returning from sleep or starting up the apparatus, and the recording material in the next image forming operation is large in advance. Or when the shielding plate is open and the ON time is the maximum ON time, Id2 is the current flowing through the switching element at that time.

  The driving signal 3 is a driving signal when the surface temperature of the induction heat fixing device reaches the temperature command value and the temperature is adjusted, the recording material is small in size and the shielding plate is closed, and Id3 is a switching element at that time Current flowing through the

  Further, the drive signal 4 is a state in which the surface temperature of the induction heat fixing device is greatly below the temperature command value when returning from sleep or starting up the apparatus, and the recording material in the next image forming operation is small in advance. When the shielding plate is closed, the on-time is the driving signal with the maximum on-time, and Id4 is the current flowing through the switching element at that time.

  As shown in the figure, when the shielding plate is closed with respect to the drive signal 1 that is temperature-controlled when the shielding plate is opened, the inductance value of the exciting coil is lowered due to the closing of the shielding plate. The slope of the flowing current becomes steep. Then, the ON time is controlled to be narrowed as in the case of the drive signal 3. As a result, the peak values of Id-1 and Id-3 are almost equal.

  On the other hand, the maximum on time when the shielding plate is opened is ton2, whereas the maximum on time when the shielding plate is closed is ton4, and ton4 is set to a small value with respect to ton2. Thereby, the peak current flowing through the switching element when the shielding plate is closed can be reduced.

  Here, ton4 is set such that the switching element current Id-2 at the maximum on time ton2 when the shielding plate is opened and the switching element current Id-4 at the maximum on time ton4 when the shielding plate is closed are substantially equal. .

  FIG. 14 shows the switching element currents Id-1 to 4 superimposed in each state.

  As shown in FIG. 14, the maximum peak current that may flow through the switching element is substantially constant regardless of the opening and closing of the shielding plate, and is greatly reduced compared to Ip-3 in FIG. 14 of the conventional example. be able to.

  Therefore, when the switching element TR1 is selected, the switching element TR1 may be selected based on the current value of Ip-2 in FIG. 5. A low-cost element can be used.

  In this example, the adjustment of the maximum on-time when the shielding plate is closed and opened is described. However, in the case where the shielding plate can be switched in various steps according to the size of the recording material. However, by setting multiple maximum on-time settings and setting the maximum on-time according to the size of the shielding area of the shielding plate, the switching element at the maximum on-time regardless of the size of the shielding area of the shielding plate It is possible to make the peak currents flowing through substantially the same, and it is possible to use an optimum switching element, that is, a low-cost switching element in the image heat fixing apparatus.

(Example 2)
Hereinafter, a second embodiment of the present invention will be specifically described with reference to the drawings.

  FIG. 6 is a diagram showing a second embodiment of the present invention.

  In FIG. 6, the same or corresponding members as those in FIGS. 7 to 14 of the conventional example and FIGS. 1 to 5 of the first embodiment are designated by the same reference numerals, and the description thereof is omitted.

  FIG. 6 shows the configuration of the drive frequency control unit in the second embodiment.

  A temperature monitor signal from the temperature detection means 105, a temperature command value from the controller unit 61, a shielding plate position signal, and a mode signal are input to the drive frequency control unit.

  The mode signal is a signal that indicates the state of the image forming apparatus, and is a signal that indicates whether the image forming apparatus is on, in sleep, or in steady state.

  Then, the temperature comparison signal generation unit 51 generates a temperature comparison signal based on the magnitude relationship and the difference between the temperature monitor signal value and the temperature command value. The on-time determining unit 52 determines the time for turning on the switching element TR1 based on the temperature comparison signal. Specifically, the control is such that the ON time is longer as the temperature monitor signal is smaller than the temperature command value and the difference is larger, and the ON time is shortened as the temperature monitor signal is greater than the temperature command value and the difference is larger. Is done.

  However, if the on-time is made longer than necessary, a large peak current flows through the switching element TR1, so the on-time determining unit limits the maximum on-time, the temperature monitor signal is smaller than the temperature command value, and the difference When the current value exceeds a predetermined value, a preset maximum on-time is set as the on-time to prevent an unnecessary peak current from flowing through the switching element TR1.

  This maximum on-time is set by the maximum on-time setting unit 55. The maximum on-time setting unit 55 receives the shielding plate signal and the mode signal, and outputs a maximum on-time that varies depending on when the shielding plate is opened and closed, and depending on the state of the image forming apparatus.

  Specifically, when the switching element is driven with the maximum on-time so that the maximum on time when the shielding plate is closed is smaller than when the shielding plate is opened, the peak current value at that time when the shielding plate is opened and closed Is set so that the maximum on-time is approximately equal, and the maximum on-time is output so that the maximum on-time during steady-state temperature adjustment is smaller than when the image forming apparatus starts up or returns from sleep. Yes.

  As a result, the magnitude of the peak current flowing through the switching element TR when the drive signal is operated with the maximum on-time is almost unrelated when the shielding plate is opened and closed, and further, when the image forming apparatus is started up or in sleep mode. Control is performed so that the temperature during steady-state temperature adjustment is smaller than when returning from.

  The drive signal generation unit 54 generates a drive signal for driving the switching element TR1 by frequency modulation with a fixed off time based on the determined on time, and the switching element TR1 is turned on / off to control the excitation coil 4. Excitation current is controlled. As a result, the surface temperature of the fixing film is controlled at a constant target temperature.

  As described above, by setting the optimum maximum on-time according to the state of the image forming apparatus, even when erroneous control occurs due to noise or abnormal temperature detection means, more stable temperature control is possible.

An image forming apparatus including an induction heating type fixing device according to the present invention. 1 is a schematic diagram of a high frequency power supply device according to the present invention. The block diagram of the drive frequency control part in 1st embodiment of this invention. The figure explaining the waveform in 1st embodiment of this invention. The figure explaining the waveform in 1st embodiment of this invention. The block diagram of the drive frequency control part in 2nd embodiment of this invention. FIG. 3 is a partially cutaway side view of the image heating and fixing apparatus. FIG. 3 is a partially cutaway side view of the image heating and fixing apparatus. FIG. 3 is a longitudinal front view of the heating assembly. FIG. 3 is a cutaway perspective view of a heating assembly. Schematic of the high frequency power supply device in a prior art example. The block diagram of the drive frequency control part in a prior art example. The figure explaining the waveform in 1st embodiment of this invention. The figure explaining the waveform in 1st embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heating assembly 2 Pressure roller 3 Film guide member 4 Excitation coil 5 Magnetic core 6 Fixing film 7 Shielding plate 10 Image heating fixing device 11 Photosensitive drum 12 Charging device 13 Laser optical box 14 Color developing device 15 Transfer roller 16 Intermediate transfer drum 17 Cleaner 18 Cleaner 50, 56 Drive frequency control unit 51 Temperature comparison signal generation unit 52 On-time determination unit 53, 55 Maximum on-time setting unit 54 Drive signal generation unit 60, 61 Controller 70 Driving means 100 Temperature detection unit 101 Control circuit 105 Temperature Detection means

Claims (7)

A magnetic flux generating means, a high frequency power supply device for supplying a high frequency current to the magnetic flux generating means by turning on / off a switching element, an induction heating element that generates electromagnetic induction heat by the action of the magnetic flux generated from the magnetic flux generating means, A heating device of an electromagnetic induction heating system that heats the heated material with the induction heating element by conveying the introduced heating material directly or via a heat transfer material in contact with the induction heating element. ,
Magnetic flux adjusting means for changing the density distribution of the working magnetic flux from the magnetic flux generating means to the induction heating element in the direction intersecting the conveying direction of the heated material, and driving means for displacing the position of the magnetic flux adjusting means,
A heating device, wherein a limit value of a maximum ON time of a switching element in the high frequency power supply device is changed according to a position of the magnetic flux adjusting means.   The said magnetic flux adjustment means functions according to the size of the to-be-heated material used for an apparatus, The heating apparatus of Claim 1 characterized by the above-mentioned.   The heating device according to claim 1 or 2, wherein the limit value of the maximum ON time is changed so that the maximum values of the currents flowing through the switching elements are substantially equal regardless of the position of the magnetic flux adjusting means.   4. The heating device according to claim 1, wherein the limit value of the maximum ON time of the switching element is changed when the heating device is started up and the temperature is adjusted.   5. The heating apparatus according to claim 1, wherein the heated material is a recording material carrying an image and is an image heating apparatus that heats the image.   6. The heating device according to claim 1, wherein the heating device is an image heat fixing device that heats and fixes the image as a permanent image.   An image forming apparatus comprising the image heating apparatus according to claim 5 or the image heating fixing apparatus according to claim 6.

Images