JP2019091087A - Fixation device - Google Patents

Abstract

To provide a fixation device of an electromagnetic induction heating system, which facilitates temperature control of an area of a rotor, through which a recording material passes, while forming heat generation distribution according to the size of the recording material.SOLUTION: A fixation device includes: a first converter driving a resonance circuit; a second converter controlling electric power supplied to the first converter; a frequency setting unit setting the drive frequency of the first converter according to at least one of the size of a recording material and the temperature of the paper non-passing part of a rotor; and an electric control unit controlling the second converter according to the temperature of the paper passing part of the rotor, and controlling electric power supplied from the second converter to the first converter.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or printer.

  A fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or a printer is a recording material carrying an unfixed toner image at a nip portion formed by a heating rotating body and a pressure roller in contact therewith. In general, the toner image is fixed on the recording material by heating while conveying the toner image.

  In recent years, a fixing device of an electromagnetic induction heating system capable of causing the conductive layer of the heating rotator to generate heat has been developed and put into practical use. The fixing device of the electromagnetic induction heating system has an advantage that the warm-up time is short.

  Patent Document 1 discloses a fixing device in which restrictions on the thickness of the conductive layer and the material of the conductive layer are small.

JP, 2014-026267, A

  Also in the fixing device disclosed in Patent Document 1, the temperature rise of the non-sheet-passing portion at the time of fixing the recording material of a small size becomes an issue.

  An object of the present invention is to provide a fixing device in which temperature control of a region through which a recording material of a rotating body passes is easy while forming heat generation distribution according to the size of the recording material.

  The present invention for solving the above-mentioned problems comprises: a cylindrical rotating body having a conductive layer; a coil disposed inside the rotating body and having a helical axis substantially parallel to the generatrix direction of the rotating body; And a first converter for driving the resonant circuit, the conductive layer is caused to generate heat by electromagnetic induction by magnetic flux generated by the coil, and the recording material is formed by heat of the rotating body. And a second converter for controlling power supplied to the first converter, and at least a size of the recording material and a temperature of the non-sheet-passing portion of the rotating body. A frequency setting unit configured to set a drive frequency of the first converter according to one, and controlling the second converter according to a temperature of a sheet passing portion of the rotating body; The co A power control unit for controlling the power supplied to the converter, and having a.

  It is possible to provide a fixing device that can easily control the temperature of the area through which the recording material of the rotating body passes while forming the heat generation distribution according to the size of the recording material.

Schematic cross-sectional view of the image forming apparatus Cross section of fixing unit Front view of fixing unit A perspective view of a coil unit provided in a fixing unit and a block diagram of a drive circuit Drive circuit diagram Diagram showing the relationship between the drive frequency and the temperature distribution of the fixing sleeve Diagram showing the operation of the first converter Diagram showing the operation of the first converter when the drive frequency is switched Diagram showing the operation of the second converter A diagram representing the operation of the second converter when the ON duty ratio of the switch element in the second converter is switched Diagram showing the difference in the amount of heat generation of the rotating body when the ON duty ratio of the switch element in the second converter is switched Explanatory drawing of Example 2

  Hereinafter, with reference to the drawings, a mode for carrying out the present invention will be exemplarily described in detail based on examples. However, the dimensions, materials, shapes, etc. of the components described in this embodiment should be changed as appropriate depending on the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments.

Example 1
FIG. 1 is a schematic block diagram of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 of this embodiment is a laser beam printer using an electrophotographic process.

  Reference numeral 31 denotes a controller which is a control unit of the image forming apparatus, and comprises a CPU (central processing unit) 32 equipped with a ROM 32a, a RAM 32b, a timer 32c and the like, various input / output control circuits (not shown) and the like. Reference numeral 101 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier, which is rotationally driven at a predetermined circumferential speed in the clockwise direction indicated by the arrow. The photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by the contact charging roller 102 in the process of its rotation. Reference numeral 103 denotes a laser beam scanner, which outputs laser light L on / off modulated corresponding to image information input from an external device such as an image scanner or a computer (not shown). The charged surface of the photosensitive drum 101 is exposed by the laser beam L, and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 101. A developing device 104 supplies a developer (toner) from the developing roller 104a to the surface of the photosensitive drum 101 and develops the electrostatic latent image on the surface of the photosensitive drum 101 as a toner image. A paper feed cassette 105 accommodates the recording material P therein. A registration roller 107 conveys the recording material P so that the front end of the toner image formed on the photosensitive drum and the predetermined position of the recording material are aligned. When a feed start signal is input, the feed roller 106 is driven to feed the recording materials P in the feed cassette 105 one by one. After the conveyance timing of the fed recording material is adjusted by the registration roller 107, the recording material is introduced to the transfer portion 108T where the photosensitive drum 101 and the transfer roller 108 abut. While the recording material P is nipped and conveyed at the transfer site 108T, a transfer bias is applied to the transfer roller 8 from a power supply (not shown). A toner image on the photosensitive drum 101 is transferred onto the recording material P by applying to the transfer roller 108 a transfer bias having a polarity opposite to the charging polarity of the toner. Thereafter, the recording material P to which the toner image has been transferred is separated from the surface of the photosensitive drum 101 and introduced into the fixing unit A through the conveyance guide 109. The toner image on the recording material is heated by the fixing unit and fixed on the recording material. The recording material P having passed through the fixing unit is discharged onto the discharge tray 112 via the discharge port 111. On the other hand, the surface of the photosensitive drum 101 after the recording material P is separated is cleaned by the cleaning unit 110.

  The fixing unit A is an electromagnetic induction heating type fixing device. Specifically, the fixing device is configured to cause the conductive layer of the rotating body to generate electromagnetic induction heat by magnetic flux generated by the coil, and fix the image formed on the recording material to the recording material by the heat of the rotating body. 2 is a sectional view of the fixing unit, FIG. 3 is a front view of the fixing unit, and FIG. 4 is a perspective view of a coil unit provided in the fixing unit. The fixing unit A includes a heating unit having a fixing sleeve 1 and a coil unit, which will be described later, and a pressure member 8, and nips and conveys a recording material P carrying an unfixed toner image between the heating unit and the pressure member. A fixing nip portion N is formed.

  The pressure roller 8 as a pressure member has a cored bar 8a, an elastic layer 8b formed of silicone rubber or the like, and a release layer 8c formed of fluorocarbon resin or the like. Both ends of the cored bar 8a are rotatably held between the unshown device chassis of the fixing unit via bearings. Further, pressure springs (in this example, compression springs) 17a and 17b are respectively provided between both ends of the pressure stay (metal reinforcing member) 5 shown in FIG. 3 and the spring receiving members 18a and 18b on the apparatus chassis side. By providing the pressure stay 5, a pressing force is applied to the pressure stay 5. In the fixing unit A of this embodiment, a pressing force of about 100 N to 250 N (about 10 kgf to about 25 kgf) is applied. As a result, the lower surface of the sleeve guide member 6 made of heat resistant resin (PPS or the like) and the pressure roller 8 are pressed against each other with the fixing sleeve 1 interposed therebetween to form the fixing nip portion N. The pressure roller 8 is driven in the direction of the arrow by driving means (not shown), and the fixing sleeve 1 is rotated by the rotation of the pressure roller. Reference numerals 12a and 12b denote flange members that rotate following the rotation of the fixing sleeve. The flange member is rotatably disposed at the longitudinal end of the sleeve guide 6. When the fixing sleeve is displaced in the generatrix direction while rotating, it abuts against the flange member, and the flange member pressed by the fixing sleeve abuts against the regulating member 13a (13b). Thus, the shift movement of the fixing sleeve is restricted by the restricting member. The flange member is formed of a heat-resistant material such as LCP (Liquid Crystal Polymer: liquid crystal polymer).

  The fixing sleeve 1 as a rotatable cylindrical rotary member preferably has a diameter of 10 to 50 mm, and a heat generating layer (conductive layer) 1a as a base layer, an elastic layer 1b laminated on the outer surface, and a release layer 1c on the sleeve surface Have. The heat generating layer 1a is a metal film (the material of the sleeve in this example is stainless steel), and the film thickness is preferably 10 to 50 μm. The elastic layer 1 b is formed of silicone rubber and preferably has a hardness of about 20 degrees (JIS-A, 1 kg load) and a thickness of 0.1 mm to 0.3 mm. The release layer is a fluorocarbon resin tube, and the thickness is preferably 10 to 50 μm. An induced current is generated in the heat generating layer 1a by the action of the alternating magnetic flux described later. The heat generation layer generates heat due to the induction current, and the heat is transmitted to the elastic layer 1 b and the release layer 1 c, and the entire circumferential direction of the fixing sleeve 1 is heated. The temperature detection elements 9, 10, 11 for detecting the temperature of the fixing sleeve will be described later.

  Next, the mechanism for generating an induced current in the heat generating layer 1a will be described in detail. FIG. 4 is a perspective view of a coil unit provided in the heating unit. The coil unit has a spiral-shaped portion disposed inside the rotating body (fixing sleeve) and having a helical axis substantially parallel to the generatrix direction of the rotating body, and generates an alternating magnetic field for electromagnetically generating heat in the conductive layer of the rotating body. It has the coil 3 to form. Furthermore, a core 2 is provided which is disposed in the spiral shape and which guides the magnetic flux. A magnetic core 2 as a magnetic core material is disposed through a hollow portion of the fixing sleeve 1 by fixing means (not shown). NP and SP indicate the magnetic poles of the core 2. The core 2 has a shape which does not form a loop (i.e., an end shape) outside the rotating body, and the magnetic flux generated by the coil forms an open magnetic circuit. The core material is composed of a material having a small hysteresis loss and a high relative permeability, such as a fired ferrite, a ferrite resin, an amorphous alloy (amorphous alloy), an oxide of high permeability such as permalloy, an alloy, etc. Ferromagnetics are preferred. In the present example, a fired ferrite of relative permeability 1800 is used. The core of this example has a cylindrical shape, and the diameter is preferably 5 to 30 mm. In the case of a fixing device mounted on an A4 printer, the length of the core is preferably about 240 mm. The core 2 around which the coil 3 is wound is covered with a cover 4 made of resin.

  The exciting coil 3 is formed by spirally winding a single conducting wire around the magnetic core 2 in the hollow portion of the fixing sleeve 1. At that time, it is wound so that the spacing is closer at the end than at the center of the core. The exciting coil 3 is wound 18 times on the magnetic core 2 having a longitudinal dimension of 240 mm. The winding distance is 10 mm at the end, 20 mm at the center, and 15 mm in the middle. Thus, the coil is wound in a direction intersecting the axis X of the core.

  When a high frequency current is supplied to the exciting coil 3 by the high frequency converter through the feeding contact portions 3a and 3b, a magnetic flux is generated. In the device of this example, most (70% or more, preferably 90% or more, more preferably 94% or more) of the magnetic flux emitted from the end of the core 2 passes outside the heat generating layer of the fixing sleeve and the other It is designed to return to the end. For this reason, an induced current flowing in the circumferential direction is generated in the heat generating layer of the fixing sleeve so as to generate a magnetic flux which cancels out the magnetic flux passing through the outside of the sleeve. As a result, the entire circumferential direction of the heat generating layer generates heat. As described above, when the induction current flows in the circumferential direction of the fixing sleeve, the entire circumferential direction of the fixing sleeve generates heat, so that the time for warming up the fixing device to a temperature at which the fixing device can fix can be shortened. Further, the core 2 is formed into an end shape, and most of the magnetic flux passes through the outside of the heat generating layer by the open magnetic circuit. For this reason, there is also a merit that the core can be miniaturized as compared with a device configured to form a closed magnetic path with a loop shape.

  The temperature detection elements 9, 10, 11 of the fixing unit A are disposed upstream of the fixing nip N in the rotational direction of the fixing sleeve as shown in FIG. 2, and detect the surface temperature of the fixing sleeve. Further, as shown in FIG. 3, the temperatures of the center and both ends of the fixing sleeve are detected in the fixing unit longitudinal direction. The temperature detection elements 9, 10, 11 are constituted by thermistors or the like. Power supply to the coil is controlled such that the temperature detected by the temperature detection element 9 at the central portion maintains a control target temperature suitable for fixing. Further, the temperature detection elements 10 and 11 disposed near the end portion of the fixing sleeve 1 can detect the temperature rise condition of the non-sheet passing area of the fixing sleeve when the small size recording material P is continuously printed. . The temperature detection elements 10 and 11 are disposed at the axial end of the pressure roller 8 to detect the temperature rise of the non-sheet passing area of the pressure roller when the small size recording material P is continuously printed. It is also good.

  FIG. 4 also shows a block diagram showing the relationship between the CPU 32, which is a control unit that performs printer control, the printer controller 41, and the host computer 42. The printer controller 41 communicates with the host computer 42, receives image data, and expands the received image data into information that can be printed by the image forming apparatus 100. Further, exchange of signals with the engine control unit 121 and serial communication are performed. The engine control unit 121 exchanges signals with the printer controller 41, and further controls each unit of the image forming apparatus 100 via serial communication. The engine control unit 121 performs temperature control of the fixing unit A based on the temperatures detected by the temperature detection elements 9, 10 and 11 and performs abnormality detection of the fixing unit A and the like.

  By the way, most of the magnetic flux from the end of the core passes outside the heat generating layer of the fixing sleeve and returns to the other end of the core so that an induced current flowing in the circumferential direction of the sleeve is generated in the conductive layer of the sleeve. It was found that the designed fixing device had the following problems.

  In a general electromagnetic induction type fixing device, a high frequency converter is provided which drives a resonant circuit including a coil. Then, in a fixing device of a system in which the magnetic flux generated by the coil is coupled to the conductive layer of the rotating body and the conductive layer generates the eddy current to generate heat, the driving frequency of the high frequency converter is adjusted to keep the temperature of the sleeve constant. And adjust the calorific value.

  However, it has been found that the heat generation distribution in the generatrix direction of the sleeve changes when the driving frequency of the high frequency converter is changed in the fixing device in which the induced current flows in the sleeve circumferential direction as in this example. FIG. 6 shows the temperature distribution of the sleeve when the drive frequency of the high frequency converter is changed in the range of 20 kHz to 50 kHz so that the center of the generator (sleeve) in the generatrix direction (longitudinal direction) is maintained at 200.degree. . It can be seen that the amount of heat generation at both ends of the sleeve decreases as the drive frequency decreases. Therefore, for example, in the case where the drive frequency has to be set to 20 kHz in order to keep the temperature of the central portion at 200 ° C., the amount of heat generated at both ends of the sleeve is insufficient. As a result, the image on the recording material corresponding to both ends of the sleeve is insufficiently fixed.

  Therefore, in the present embodiment, as shown in FIGS. 4 and 5, in addition to the high frequency converter 16 (first converter) for driving the resonant circuit 191, a second for controlling power supplied to the first converter is used. A converter 15 is provided. The resonant circuit 191 has a cylindrical rotating body having a conductive layer, a coil disposed inside the rotating body, a coil whose helical axis is substantially parallel to the generatrix direction of the rotating body, and a resonant capacitor 1113. R shown in FIG. 5 is the equivalent resistance of the fixing unit A, and L is the equivalent inductance of the fixing unit A. The resonance circuit 191 of this example is a current resonance circuit. Further, a frequency setting unit 120 is provided which sets the driving frequency of the first converter 16 in accordance with at least one of the size of the recording material and the temperature of the non-sheet-passing portion of the rotating body. Furthermore, a power control unit 119 is provided which controls the second converter in accordance with the temperature of the sheet passing portion of the rotating body and controls the power supplied from the second converter to the first converter.

  More specifically, the frequency setting unit 120 sets the drive frequency of the converter 16 in accordance with the detected temperature of the temperature detection elements 10 and 11 so that the temperature of the rotating body in the region which becomes the non-sheet passing portion of small size paper becomes too high. Set The power control unit 119 controls the output voltage of the second converter 15 so as to maintain the control target temperature at which the temperature of the sheet passing portion of the rotating body (the detected temperature of the temperature detection element 9) is a fixable temperature. The driving frequency of the converter 16 may be set according to the size information of the recording material.

  Next, the drive circuit shown in FIG. 5 will be described in detail. Reference numeral 50 denotes a commercial power supply (AC power supply) connecting the image forming apparatus 100, and supplies AC power to the image forming apparatus 100. The waveform of the commercial power supply 50 is a waveform like the waveform 1 when the horizontal axis is time and the vertical axis is voltage. The power input from the commercial power supply 50 is input to the diode bridge 1102 via the AC filter 1101 and full-wave rectified. The rectified voltage becomes a voltage waveform such as the waveform 2 when the horizontal axis is time and the vertical axis is voltage after being charged in the capacitor 1103.

  A power supply unit 71 generates a direct current voltage, and outputs a predetermined voltage to a load (motor, CPU, etc.) on the secondary side (not shown).

  First, the first converter 16 will be described. As will be described later, the first converter 16 is connected to the output of the second converter 15. The half bridge circuit of the first converter 16 is configured by the switch elements 1108 and 1109. Reference numeral 1110 denotes a voltage resonance capacitor, which is connected between the drain (D) and the source (S) of the switch element 1109 in this embodiment (between the collector and the emitter when the switch element is an IGBT). Reference numeral 1118 denotes a drive circuit of the switch elements 1108 and 1109. Reference numeral 191 denotes a series resonance (current resonance) circuit configured by an equivalent inductance L, an equivalent resistance R, and a current resonance capacitor 1113. The equivalent resistance R is a resistance that represents the resistance of the rotating body 1 and the exciting coil 3 as a series equivalent resistance viewed from the exciting coil 3.

  FIG. 7 shows the voltage between the gate (G) and the source (S) of the switch element 1108, the voltage between the gate (G) and the source (S) of the switch element 1109, the drain (D) voltage of the switch element 1109, the current of the coil 3, And the voltage of the capacitor 1113. Since the current resonance circuit is used, the switch elements 1108 and 1109 are alternately driven with a duty ratio of about 50% in period 1 + period 2 + period 3 + period 4. Specifically, the ON period of the switch element 1108 is period 1, and (period 1 / (period 1 + period 2 + period 3 + period 4)) ≒ 50%. The ON period of the switch element 1109 is period 3, and (period 3 / (period 1 + period 2 + period 3 + period 4)) ≒ 50%. The reason for driving at a duty ratio of 50% is that a voltage half of the voltage input to the first converter 16 needs to be charged in the current resonance capacitor 1113. In the case of not driving at a duty ratio of 50%, the voltage amplitude acceptable to the current resonance capacitor 1113 is reduced, and the power that can be output to the coil 3 is reduced. Further, in order to avoid conduction of both of the switch elements 1108 and 1109, a dead time is necessarily provided as a period in which the switch elements 1108 and 1109 are simultaneously turned off (period 2 and period 4 in FIG. 7).

  A voltage resonant capacitor 1110 is connected between the drain (D) and source (S) terminals of the switch element 1109. When the switch element 1108 is turned on and current flows from the capacitor 1107, the voltage of the capacitor 1110 becomes substantially the same as that of the capacitor 1107, and thereafter current starts to flow to the exciting coil 3 and the capacitor 1113 in the fixing unit A (FIG. Period 1). The current flowing through the coil 3 and the capacitor 1113 is sinusoidal. The switch element 1109 is turned off while the current of the coil 3 is charging the capacitor 1113. In order to continue current flow in the exciting coil 3, current flows in a reverse conducting diode (not shown) provided in the capacitor 1113 and the switch element 1109 (period 2 in FIG. 7).

  The drain (D) voltage of the switch element 1109 is lower than the source (S) voltage by the forward voltage of the reverse conducting diode. The frequency setting unit 120 turns on the switch element 1109 via the switch element drive circuit 1118 while the reverse conduction diode of the switch element 1109 is conductive in period 2 of FIG. 7. The current flowing through the exciting coil 3 decreases with time. The voltage stored in the capacitor 1113 becomes the highest voltage, after which current starts to flow in the reverse direction (period 3 in FIG. 7).

  Next, the switch element 1109 is turned off before the current flowing in the reverse direction reaches 0A. Then, the current that has been flowing starts charging the capacitor 1110, and the drain (D) voltage of the switch element 1109 rises (period 4 in FIG. 7). When the drain (D) voltage of the switch element 1109 becomes higher than the voltage of the capacitor 1107, current starts to flow in a reverse conducting diode (not shown) provided in the switch element 1108.

  The voltage of the capacitor 1110 is the sum of the voltage of the capacitor 1107 and the forward voltage of a reverse conducting diode (not shown) provided in the switch element 1109. While the reverse conduction diode of the switch element 1108 is energized, the frequency setting circuit 120 turns on the switch element 1108 through the switch element drive circuit 1118 (period 1 in FIG. 7). Thereafter, the switch control of period 1 to period 4 described above is repeated.

  As described above, by appropriately setting the capacitance of the voltage resonance capacitor 1110, the current at the turn-off, and the dead time (period 2 and period 4), the switch elements 1108 and 1109 perform soft switch operation and achieve high efficiency. It is possible to keep.

  The switch frequency (drive frequency) of the current resonance circuit 191 is controlled by the frequency setting unit 120. The frequency setting unit 120 controls the drive frequency of the resonance circuit 191 based on the detected temperature of the temperature detection element 10 or 11 provided in the area (non-sheet passing area) where the recording material P of the rotating body 1 does not pass. The non-sheet passing area is an area through which the recording material of the largest size available in the apparatus passes but the recording material of a size smaller than the largest size does not. For example, when the detection temperature of the temperature detection elements 10 and 11 reaches a predetermined upper limit temperature, the drive frequency of the resonance circuit 191 is decreased to suppress heat generation in the non-sheet passing portion of the rotating body, and temperature rise in the non-sheet passing portion Is limited. In this way, the heat generation distribution that matches the size of the recording material is formed. FIG. 8 shows gate (G) -source (S) voltage waveforms of the switch element 1108 and the switch element 1109 when the drive frequency is set to 36 kHz and 50 kHz. At any frequency, the ON duty ratio of the switch element 1108 and the ON duty ratio of the switch element 1109 are about 50%. Thus, by switching the drive frequency of the first converter, it is possible to form a heat generation distribution as shown in FIG. 6 that matches the size of the recording material. In this embodiment, since the drive frequency is controlled so that the detection temperature of the temperature detection elements 10 and 11 does not exceed the upper limit temperature, the drive frequency fluctuates during the fixing process of one recording material. Sometimes. On the other hand, when setting the drive frequency of the resonant circuit according to the size information of the recording material without providing the temperature detection elements 10 and 11, a predetermined drive frequency may be set for each recording material size. This will be described in the second embodiment.

  Next, the operation of the second converter 15 will be described. The second converter 15 is provided to control the power supplied to the first converter 16, and the temperature of the sheet passing portion of the rotating body through which the recording material passes regardless of the size of the recording material The power supplied to the first converter is controlled according to the detected temperature). Specifically, the power control unit 119 sends a signal to the drive circuit 1117 according to the temperature detected by the temperature detection element 9 to control the ON duty ratio of the switch element 1104. Thereby, the power (output voltage of the second converter 15) supplied to the first converter 16 is controlled.

  The second converter 15 is composed of a switch element 1104, a diode 1105, a coil 1106, a capacitor 1107, and the like, and is a step-down converter. When a voltage is applied between the gate (G) and the source (S) of the switch element 1104 and the switch element 1104 is turned on, a voltage is applied to the coil 1106. The voltage difference between the capacitor 1103 and the capacitor 1107 is applied to both ends of the coil 1106. The slope of the current flowing through the coil 1106 is determined by the inductance of the coil 1106 and the voltage applied to the coil 1106.

  The current flowing in the coil 1106 charges the capacitor 1107. When the voltage of the capacitor 1107 rises, the voltage applied to the coil 1106 decreases even if the switch element 1104 is turned on. As described above, although the current flowing through the coil 1106 is changed by the voltage applied to the coil 1106, the current flowing through the coil 1106 rises almost linearly if the voltage rise of the capacitor 1107 is slow. This period is period 1 in FIG.

  When the switch element 1104 is turned off, current flows continuously to the coil 1106 through the diode 1105. Capacitor 1107 is charged by the power stored in coil 1106 in the form of a magnetic field. If the capacity of the capacitor 1107 is sufficiently large, the current of the coil 1106 decreases due to the substantially linear characteristic. When a current flows through the coil 1106 when the switch element 1104 is turned on, the current value becomes an initial value when the switch element 1104 is turned on. The second converter 15 operates by repeating the above series of operations.

  PWM control is used as a method of driving the switch element 1104. When it is desired to increase the output power of the second converter 15 in order to maintain the temperature of the sheet passing portion of the rotating body at the control target temperature, the ON time ratio of PWM, ie, the ON duty ratio (period 1 / (period of FIG. Increase 1+ period 2)). Conversely, when it is desired to reduce the output power of the second converter 15, the ON duty ratio is reduced.

  In PWM control, the current flowing through the coil 1106 does not become zero. FIG. 9 shows the current of the coil 1106 and the voltage of the K terminal of the diode 1105 when PWM control is performed. As described above, the switch element 1104 is a hard switch operation that performs turn-on and turn-off operations while current is flowing. The voltage of the capacitor 1107 in FIG. 9 is the output voltage of the second converter.

  FIG. 10 is a comparison diagram when the ON duty ratios are set to 80% and 50%. As shown in FIG. 10, when the ON duty ratio changes, the voltage of the capacitor 1107 changes, and the output voltage of the second converter changes. Thereby, the power supplied to the first converter 16 changes.

  Note that noise may occur depending on the ON / OFF timing of the switch element 1104. In such a case, a critical mode may be used in which the switch element 1104 is kept off until the current flowing through the coil 1106 reaches 0 A during the off period of the switch element 1104.

  Since the source (S) terminal of the switch element 1104 is a contact point with the coil 1106 and the diode 1105, the voltage becomes equal to the voltage at the negative terminal of the capacitor 1103 when turned off. When turned on, the voltage is equal to the positive terminal voltage of the capacitor 1103. As described above, since the voltage at the source (S) of the switch element 1104 largely fluctuates, in order to continue applying a voltage between the gate (G) and the source (S) of the switch element 1104, it is driven by transformer coupling or not shown. It is necessary to use a bootstrap circuit.

  The switch element 1104 is connected to the commercial AC power supply 50 without being insulated. In this embodiment, in order to apply the apparatus to which the insulation is required according to the safety standard, the drive circuits 1117 and 1118 are configured to ensure the insulation as an example.

  As described above, the power control unit 119 controls the ON duty ratio of the above-described PWM control based on the detected temperature of the temperature detection element 9. PI control or PID control is used as a control method. Then, the power control unit 119 drives the drive circuit 1117 to control the ON duty ratio of the switch element 1104 so as to maintain the control target temperature at which the temperature detected by the temperature detection element 9 is the fixable temperature. When the ON duty ratio of the switch element 1104 is changed, the voltage of the capacitor 1107 is changed, and the power supplied to the first converter 16 is changed.

  As described above, in order to maintain the temperature of the sheet passing region (the temperature detected by the temperature detection element 9) at the control target temperature, the output voltage of the second converter is controlled instead of controlling the driving frequency of the first converter 16. Do.

  FIG. 11 is a diagram comparing the amount of heat generation of the rotating body when the ON duty ratio of the switch element 1104 of the second converter 15 is set to 80% and when it is set to 50%. As described above, the heat generation distribution of the rotating body in the generatrix direction is determined by the frequency setting unit 120 using the first converter 16 according to the detected temperature of the temperature detection element 10 or 11 that detects the temperature of the non-sheet passing region of the rotating body. It is adjusted by setting the drive frequency of. Then, the power control unit 119 controls the output voltage of the second converter 15 in accordance with the detected temperature of the temperature detection element 9 that detects the temperature of the sheet passing portion, thereby controlling the temperature of the sheet passing portion to be constant. To be executed. In the case where the ON duty ratio of the second converter 15 is set to 80% and the case where it is set to 50%, as shown in FIG. 11, the voltage of the capacitor 1113 is different. The amount of heat generation of the rotating body is adjusted using this difference in voltage.

  As described above, in the present embodiment, the drive frequency of the first converter 16 is set according to the temperature of the non-sheet passing portion of the rotating body, and the driving frequency of the second converter 15 is set according to the temperature of the sheet passing portion of the rotating body. Control the output voltage. Thus, the temperature of the sheet passing portion can be maintained at the control target temperature while maintaining the heat generation distribution of the rotating body at the heat generation distribution according to the size of the recording material.

(Example 2)
While the drive frequency of the first converter is set in accordance with the temperature of the non-sheet passing portion in the first embodiment, the drive frequency of the first converter 16 is set in accordance with the size of the recording material P. It is to set.

  As described above, as the drive frequency of the first converter 16 is lowered, the calorific value of the longitudinal end of the rotating body becomes smaller than that of the central portion. In this embodiment, the drive frequency of the first converter 16 is set lower as the width of the recording material P (width in the direction orthogonal to the transport direction) becomes narrower by utilizing this property. Table 1 shows the drive frequency for each recording material size.

  In this embodiment, the frequency setting means 120 sets the driving frequency in accordance with the size information of the recording material P designated by the user via the host computer 42.

  The driving frequency used when fixing a recording material of one size may be switched alternately between the first driving frequency and the second driving frequency lower than the second frequency. FIG. 12 shows the temperature distribution in the rotation axis direction of the rotating body 1 when the ratio per unit time of the drive period at the drive frequency of 20 kHz and the drive period at 50 kHz is changed. For example, in the case of the A5 size, the driving time ratio of 20 kHz: 50 kHz is 10: 0. In the case of the B5 size, the driving time ratio of 20 kHz: 50 kHz is 5: 5. In the case of A4 size, the drive time ratio of 20 kHz: 50 kHz is 1: 9, and in the case of letter size, the drive time ratio of 20 kHz: 50 kHz is 0:10.

  In Examples 1 and 2 described above, a film-like one was used as a rotating body (fixing sleeve). However, the present invention is also applicable to a fixing device using a hard rotating body with little flexibility as a rotating body in which the core and the coil are disposed.

1 Rotor 2 Magnetic Core 3 Excitation Coil 16 First Converter 15 Second Converter

The present invention for solving the above-mentioned problems comprises: a cylindrical rotating body having a conductive layer; a coil disposed inside the rotating body and having a helical axis substantially parallel to the generatrix direction of the rotating body; And a first converter for driving the resonant circuit, the conductive layer is caused to generate heat by electromagnetic induction by magnetic flux generated by the coil, and the recording material is formed by heat of the rotating body. In the fixing device for fixing the recorded image on the recording material , there is one coil disposed inside the rotating body, and the conductive layer has the same material and the same thickness from one end to the other end in the generatrix direction A second converter for controlling the power supplied to the first converter, the first converter in accordance with at least one of the size of the recording material and the temperature of the non-sheet-passing portion of the rotating body; Converter's Power control for controlling the power supplied from the second converter to the first converter by controlling the second converter according to the frequency setting unit that changes the dynamic frequency and the temperature of the sheet passing unit of the rotating body and parts, was closed, when said frequency setting to decrease the driving frequency unit controls the first converter, the conductive layer as heat generation amount of the conductive layer at the end portion of the generatrix direction is reduced It is characterized in that the heat generation distribution changes .

Claims (6)

A resonant circuit including: a cylindrical rotating body having a conductive layer; a coil disposed inside the rotating body and having a helical axis substantially parallel to a generatrix direction of the rotating body; and a resonant capacitor.
A first converter for driving the resonant circuit;
A fixing device for fixing the image formed on the recording material to the recording material by the heat of the rotating body by causing the conductive layer to generate electromagnetic induction heat by the magnetic flux generated by the coil;
A second converter for controlling power supplied to the first converter;
A frequency setting unit configured to set a drive frequency of the first converter according to at least one of the size of the recording material and the temperature of the non-sheet-passing portion of the rotating body;
A power control unit configured to control the second converter in accordance with the temperature of the sheet passing portion of the rotating body and to control the power supplied from the second converter to the first converter;
A fixing device characterized by having:   The fixing device according to claim 1, wherein the power control unit controls the second converter such that a temperature of a sheet passing portion of the rotating body maintains a target temperature.   The fixing device according to claim 1, wherein the resonance circuit is a current resonance circuit.   The fixing device according to any one of claims 1 to 3, wherein the second converter is a step-down converter.   The spiral shaped portion of the coil has a core for inducing a magnetic flux, and an induced current flowing in the circumferential direction of the rotating body is generated in the conductive layer. The fixing device according to any one of the preceding claims.   The fixing device according to claim 5, wherein the core has an end shape.

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