JP6667694B2 - Fixing device - Google Patents

Description

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

  A fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or a printer is a recording material that carries an unfixed toner image in a nip formed by a heating rotator and a pressure roller that contacts the rotator. In general, the toner image is fixed on the recording material by heating while transporting the toner image.

  2. Description of the Related Art In recent years, a fixing device of an electromagnetic induction heating type capable of generating heat in a conductive layer of a heating rotator has been developed and put into practical use. The electromagnetic induction heating type fixing device has an advantage that the warm-up time is short.

  Patent Literature 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-A-2014-026267

  Also in the fixing device disclosed in Japanese Patent Application Laid-Open No. H11-157, there is a problem of raising the temperature of the non-sheet passing portion when performing fixing processing on a small-sized recording material.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a fixing device that can easily control the temperature of a region of a rotating body through which a recording material passes while forming a heat generation distribution according to the size of the recording material.

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems includes 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 converter for driving the resonance circuit, the magnetic flux generated by the coil causes the conductive layer to generate electromagnetic induction, and the image formed on the recording material by the heat of the rotating body. In the fixing device that fixes the recording material to the recording material, the number of coils disposed inside the rotating body is one, and the conductive layer is formed of the same material and the same thickness from one end to the other end in the generatrix direction. cage, a switch member for controlling the power supplied to the converter peripheral to set the drive frequency of the converter according to at least one of the temperature of the non-sheet passing portion of the size of the recording material and the rotating member The number control unit, the controls said switch member in accordance with the temperature of the sheet passing portion of the rotary member, have a, a power control unit for controlling the power supplied to said converter, said to lower the driving frequency When the frequency control unit controls the converter, the heat generation distribution of the conductive layer changes such that the heat generation of the conductive layer at the end in the bus direction decreases .

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

Schematic sectional view of an image forming apparatus Sectional view of fixing unit Front view of fixing unit Perspective view of the coil unit provided in the fixing unit Coil unit drive circuit diagram of Embodiment 1 Diagram showing relationship between drive frequency and heat distribution of fixing sleeve Diagram for explaining triac voltage waveform Flow chart of the first embodiment Embodiment 2 Coil unit drive circuit diagram Diagram for explaining FET voltage waveform Flowchart of Embodiment 2

  Hereinafter, embodiments of the present invention will be illustratively described in detail based on embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment should be appropriately changed 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 configuration diagram of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 of the present 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 includes a CPU (central processing unit) 32 having a ROM 32a, a RAM 32b, a timer 32c, and the like, and various input / output control circuits (not shown). Reference numeral 101 denotes a rotating drum type electrophotographic photosensitive member (hereinafter, referred to as a photosensitive drum) serving as an image carrier, which is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow. The photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by the contact charging roller 102 during the rotation process. Reference numeral 103 denotes a laser beam scanner, which outputs a laser beam L on / off-modulated according 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 light 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) to the surface of the photosensitive drum 101 from the developing roller 104a and develops the electrostatic latent image on the surface of the photosensitive drum 101 as a toner image. Reference numeral 105 denotes a sheet cassette in which a recording material P is stored. Reference numeral 107 denotes a registration roller that conveys the recording material P so that the leading end of the toner image formed on the photosensitive drum is aligned with a predetermined position of the recording material. When a paper feed start signal is input, the paper feed roller 106 is driven to feed the recording materials P in the paper feed cassette 105 one by one. The fed recording material is introduced into a transfer portion 108 </ b> T where the photosensitive drum 101 and the transfer roller 108 abut after the conveyance timing is adjusted by the registration roller 107. A transfer bias is applied to the transfer roller 8 from a power source (not shown) while the recording material P is nipped and conveyed at the transfer portion 108T. The toner image on the photosensitive drum 101 is transferred to the recording material P by applying a transfer bias having a polarity opposite to the charge polarity of the toner to the transfer roller 108. Thereafter, the recording material P to which the toner image has been transferred is separated from the surface of the photosensitive drum 101, and is introduced into the fixing unit A through the conveyance guide 109. The toner image on the recording material is heated by a fixing unit and fixed on the recording material. The recording material P that has passed through the fixing unit is discharged onto a discharge tray 112 through a 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 a fixing device of an electromagnetic induction heating type. Specifically, this is a fixing device that causes a conductive layer of a rotator to generate electromagnetically induced heat by a magnetic flux generated by a coil, and fixes an image formed on the recording material to the recording material by the heat of the rotator. 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 pressing member 8, and sandwiches and conveys a recording material P carrying an unfixed toner image between the heating unit and the pressing member. A fixing nip portion N is formed.

  The pressing roller 8 as a pressing member has a cored bar 8a, an elastic layer 8b formed of silicone rubber or the like, and a release layer 8c formed of fluororesin or the like. Both ends of the cored bar 8a are rotatably held between bearings (not shown) of the fixing unit via a bearing. Further, pressing springs (compression springs in this example) 17a and 17b are provided between both ends of the pressing stay (metal reinforcing member) 5 shown in FIG. 3 and the spring receiving members 18a and 18b on the apparatus chassis side, respectively. By providing this, a pressing force is applied to the pressing stay 5. In the fixing unit A of this embodiment, a pressing force of a total pressure 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 a heat-resistant resin (PPS or the like) and the pressing roller 8 are pressed against each other with the fixing sleeve 1 interposed therebetween to form a fixing nip portion N. The pressing roller 8 is driven in a direction indicated by an arrow by a driving unit (not shown), and the fixing sleeve 1 rotates following the rotation of the pressing roller. Reference numerals 12a and 12b denote flange members which rotate following the rotation of the fixing sleeve. The flange member is rotatably arranged at the longitudinal end of the sleeve guide 6. When the fixing sleeve moves toward the generatrix during rotation, the fixing sleeve abuts on the flange member, and the flange member pushed by the fixing sleeve abuts on the regulating member 13a (13b). Thereby, the shift movement of the fixing sleeve is regulated by the regulating member. The flange member is formed of a material having good heat resistance such as LCP (Liquid Crystal Polymer).

  The fixing sleeve 1 as a rotatable cylindrical rotating body preferably has a diameter of 10 to 50 mm, and includes a heat generating layer (conductive layer) 1a serving as a base layer, an elastic layer 1b laminated on the outer surface thereof, 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 preferably has a thickness of 10 to 50 μm. The elastic layer 1b is formed of silicone rubber, and preferably has a hardness of about 20 degrees (JIS-A, 1 kg weight) and a thickness of 0.1 mm to 0.3 mm. The release layer is a tube of a fluororesin, and preferably has a thickness of 10 to 50 μm. An induced current is generated in the heat generating layer 1a by the action of an alternating magnetic flux described later. The heat generation layer generates heat by the induced current, and the heat is transmitted to the elastic layer 1b and the release layer 1c, so that the entire circumferential direction of the fixing sleeve 1 is heated. The temperature detecting elements 9, 10, and 11 for detecting the temperature of the fixing sleeve will be described later.

  Next, a mechanism for generating an induced current in the heating layer 1a will be described in detail. FIG. 4 is a perspective view of the coil unit provided in the heating unit. The coil unit has a helical portion disposed inside the rotator (fixing sleeve) and having a helical axis substantially parallel to the generatrix direction of the rotator, and generates an alternating magnetic field for causing the conductive layer of the rotator to generate electromagnetically induced heat. It has a coil 3 to be formed. Furthermore, it has a core 2 arranged in the helical portion for inducing magnetic flux. The magnetic core 2 as a magnetic core material is arranged so as to penetrate the 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 an end shape, and the magnetic flux generated by the coil forms an open magnetic path. The core is made of a material having a small hysteresis loss and a high relative permeability, for example, a sintered ferrite, a ferrite resin, an amorphous alloy (amorphous alloy), an oxide or an alloy having a high permeability such as permalloy. Ferromagnetic materials are preferred. In this example, a sintered ferrite having a relative magnetic permeability of 1800 is used. The core of this example has a cylindrical shape, and preferably has a diameter of 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 conductive wire around the magnetic core 2 in the hollow portion of the fixing sleeve 1. At this time, the core is wound so that the interval is closer at the end than at the center. The exciting coil 3 is wound around the magnetic core 2 having a longitudinal dimension of 240 mm 18 times. The winding interval is 10 mm at the end, 20 mm at the center, and 15 mm at the middle. Thus, the coil is wound in a direction intersecting the axis X of the core.

  When a high-frequency current is applied to the exciting coil 3 by the high-frequency converter via the power supply contacts 3a and 3b, a magnetic flux is generated. In the apparatus of this example, most (70% or more, preferably 90% or more, and 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 passes through the other part of the core. Designed to return to the end. For this reason, an induced current that flows in the circumferential direction is generated in the heat generating layer of the fixing sleeve so that a magnetic flux that cancels the magnetic flux that passes outside the sleeve is generated. As a result, the entire heat generating layer in the circumferential direction generates heat. If the configuration is such that the induced current flows in the circumferential direction of the fixing sleeve, the entire area of the fixing sleeve in the circumferential direction generates heat, so that there is an advantage that the time for warming up the fixing device to a temperature at which fixing can be performed can be shortened. Further, the core 2 has an end shape, and is configured such that most of the magnetic flux passes outside the heat generating layer by the open magnetic path. For this reason, there is also an advantage that the size can be reduced as compared with an apparatus having a configuration in which a closed magnetic path is formed by using a core as a loop.

  As shown in FIG. 2, the temperature detecting elements 9, 10, and 11 of the fixing unit A are disposed upstream of the fixing nip N in the fixing sleeve rotation direction, and detect the surface temperature of the fixing sleeve. Further, in the longitudinal direction of the fixing unit, as shown in FIG. 3, the temperatures at the center and both ends of the fixing sleeve are detected. The temperature detecting elements 9, 10, 11 are constituted by thermistors and the like. Power supply to the coil is controlled so that the temperature detected by the temperature detecting element 9 at the center maintains a control target temperature suitable for fixing. Further, the temperature detecting elements 10 and 11 disposed near the end of the fixing sleeve 1 can detect the temperature rise in the non-sheet passing area of the fixing sleeve when the small-sized recording material P is continuously printed. . The temperature detecting 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-sized recording material P is continuously printed. Is also good.

  FIG. 4 is a block diagram showing the relationship between the CPU 32, which is control means for controlling the printer, the printer controller 41, and the host computer. The printer controller 41 communicates with a host computer 42 to be described later, receives image data, and develops the received image data into information printable by the image forming apparatus 100. Further, it exchanges signals with the engine control unit 43 and performs serial communication. The engine control unit 43 exchanges signals with the printer controller 41, and further controls the units 44 to 46 of the image forming apparatus 100 via serial communication. The fixing temperature control unit 44 controls the temperature of the fixing unit A based on the temperatures detected by the temperature detecting elements 9, 10, and 11, and detects an abnormality of the fixing unit A. The frequency control unit 45 as a frequency control unit controls the driving frequency of the high frequency converter 16, and the power control unit 46 controls the power of the high frequency converter 16 by turning on and off the driving of the high frequency converter 16. Specifically, the drive of the high-frequency converter 16 is turned ON / OFF so that the temperature detected by the temperature detecting element 9 maintains the control target temperature. The host computer 42 transfers image data to the printer controller 41 and sets various printing conditions such as the size of the recording material P in the printer controller 41 in response to a request from a user.

  FIG. 5 is a circuit diagram for explaining a drive circuit including the high-frequency converter 16 in the present embodiment. The commercial power supply 50 is a commercial power supply (AC power supply) for connecting the image forming apparatus 100, and supplies AC power to the image forming apparatus 100 via the inlet 51. This circuit includes a primary side directly connected to the commercial power supply 50 and a secondary side connected to the commercial power supply 50 in a non-contact manner. The waveform of the commercial power supply 50 is a waveform like the waveform 1 when the horizontal axis represents time and the vertical axis represents voltage. The electric power input from the commercial power supply 50 is input to the diode bridges 81 to 84 as an example of the rectification unit via the inlet 51, the AC filter 52, and the triac 161 as an example of the switch member, and is rectified. The rectified voltage is charged in the capacitor 85. Subsequently, it is input to a high-frequency converter (current resonance control circuit) 16 composed of FETs 86 and 87 and a voltage resonance capacitor 88. Thus, power is supplied to a resonance circuit (current resonance circuit) 191 including the equivalent inductance L and the equivalent resistance R of the fixing unit A and the resonance capacitor 89.

  Reference numeral 71 denotes a power supply unit (power supply unit) which receives electric power from the commercial power supply 50 via the AC filter 52 and outputs a predetermined voltage to a secondary load (motor or the like) (not shown). The CPU 32 is also used for the operation of the high-frequency converter 16 and includes input / output ports, a ROM 32a, a RAM 32b, and the like. The power supply (power supply unit) 71 for supplying power to the high-frequency converter 16, the resonance circuit 191, and the secondary side is directly connected to the commercial power supply 50 before the primary winding of the transformer in the power supply device (power supply unit) 71. It is a primary side circuit. Further, after the secondary winding of the transformer in the power supply device 71, for example, a motor or a unit (not shown) for rotating the photosensitive drum 101, a motor or a unit operating at the time of image formation, such as a laser scanner 103, are not connected to the commercial power supply 50 It is connected to a contact and is electrically a secondary circuit.

  On the other hand, the power of the commercial power supply 50 is input to the ZEROX generation circuit 75 via the AC filter 52. The ZEROX generation circuit 75 outputs a high-level (or low-level) signal when the commercial power supply voltage is lower than a certain threshold voltage near 0 V, and otherwise outputs a low-level (or high-level) signal. Is output. Then, a pulse signal having a cycle substantially equal to the cycle of the commercial power supply voltage is input to the input port PA1 of the CPU 32 via the resistor 76. The CPU 32 detects an edge of the ZEROX signal that changes from High to Low or from Low to High, and uses this as a trigger for driving the drive circuit 160 described later.

  Next, the drive circuit 160 for power control will be described. The drive circuit 160 is controlled by the power control unit 46 of the CPU 32 (see FIG. 4). When the output port PA2 goes high at the timing determined by the CPU 32, the transistor 165 via the base resistor 67 turns on. When the transistor 165 turns on, the phototriac coupler 162 turns on. The phototriac coupler 162 is a device for ensuring a creepage distance between the primary circuit and the secondary circuit. The resistor 166 is a resistor for limiting the current flowing to the light emitting diode in the photo triac coupler 162.

  The resistors 163 and 164 are bias resistors for the triac (switch member) 161. The triac 161 turns on when the phototriac coupler 162 turns on. Once turned on, the triac 161 is an element that keeps the on state until the next ZEROX point of the commercial power supply 50, so that power according to the on timing is supplied to the fixing unit A via the high frequency converter 16.

  Next, the high-frequency converter 16 will be described. When the CPU 32 outputs a pulse signal having a frequency described later from the output port PA3 to the Hi-gate drive circuit 77, the Hi-gate drive circuit 77 outputs a gate waveform to the switching element 86. The switching element 86 turns on between the drain and source while the gate waveform is Hi and turns off while the gate waveform is Lo. Similarly, when the CPU 32 outputs a pulse signal having the same frequency as the pulse signal to the Hi-gate drive circuit 77 from the output port PA4 to the Lo-gate drive circuit 78, the Lo-gate drive circuit 78 causes the switching element 87 to output. The gate waveform is output. The switching element 87 turns on between the drain and source while the gate waveform is Hi and turns off during the Lo time. The switching elements 86 and 87 are alternately turned on at the frequency of the pulse signal, and supply a square wave to the resonance circuit 191. Thereby, the equivalent inductance L of the fixing unit A and the resonance capacitor 61 resonate, and the rotating body 1 of the fixing unit A generates heat. The ON duty ratio of the pulse signal to the Hi-gate driving circuit 77 (ON time ratio per one cycle of the pulse signal) and the ON duty ratio of the pulse signal to the Lo-gate driving circuit 78 are determined by the frequency of the pulse signal. Regardless, it is set at about 50%. When the pulse signals to the switching elements 86 and 87 are stopped, the heat generation of the fixing unit A is stopped.

  The temperature detecting element 9 arranged in the fixing unit A has one end connected to the power supply Vcc1 via the ground and the other end via the resistor 73, and further connected to the analog input port AN0 of the CPU 32 via the resistor 74. . The outputs of the temperature detecting elements 10 and 11 for detecting the temperature at the end of the fixing unit are also input to the analog input port of the CPU 32 (not shown in FIG. 5), similarly to the temperature detecting element 9. The thermistor used as the temperature detecting element 9 has a characteristic that the resistance value decreases when the temperature becomes high. The CPU 32 detects the temperature of the fixing unit A (more precisely, the temperature of the fixing sleeve) by converting the divided voltage with the fixed resistor 73 into a temperature according to a preset temperature table (not shown). As will be described later, the CPU 32 controls the drive circuit 160 such that the temperature of the fixing unit A (the temperature detected by the temperature detecting element 9) maintains a predetermined temperature (control target temperature) during the fixing process.

  By the way, so that an induced current flowing in the circumferential direction of the sleeve is generated in the conductive layer of the sleeve, almost all of the magnetic flux emitted 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. It has been found that the designed fixing device has the following problems.

  In a general fixing device of the electromagnetic induction type, a high-frequency converter for driving a resonance circuit including a coil is provided. In a fixing device of a type in which magnetic flux generated by a coil is coupled to a conductive layer of a rotating body and an eddy current is generated in the conductive layer to generate heat, a driving frequency of a high-frequency converter (described above) is maintained in order to keep a sleeve temperature constant. The frequency of the generated pulse signal) is adjusted to adjust the heat generation.

  However, it has been found that in a fixing device in which an induced current flows in the circumferential direction of the sleeve as in this example, when the driving frequency of the high-frequency converter is changed, the heat generation distribution in the generatrix direction of the sleeve changes. FIG. 6 shows the temperature distribution of the sleeve when the driving frequency of the high-frequency converter is changed in the range of 21 kHz to 50 kHz so that the center of the rotating body (sleeve) in the generatrix direction (longitudinal direction) maintains 200 ° C. . It can be seen that the lower the driving frequency, the lower the amount of heat generated at both ends of the sleeve. Therefore, for example, in the case where the drive frequency must be set to 21 kHz in order to keep the temperature at the center at 200 ° C., the heat generation at both ends of the sleeve is insufficient. As a result, when a large-sized recording material is fixed, the images on the recording material corresponding to both ends of the sleeve are insufficiently fixed.

  Therefore, in this embodiment, the driving frequency is not set according to the temperature at the center of the fixing sleeve, but is set according to the size of the recording material P or the temperature of the non-sheet passing area of the fixing sleeve 1 (hereinafter referred to as the driving frequency). Frequency fk) is set. The non-sheet passing area is an area where a recording material having a maximum size usable by the apparatus passes but a recording material having a size smaller than the maximum size does not pass. By setting the driving frequency fk in this manner, when fixing a large-sized recording material, the entire length of the fixing sleeve 1 in the longitudinal direction is uniformly heated, and when fixing a small-sized recording material, the sleeve is fixed. The heat generation distribution can be set such that the heat generation amount at the end is suppressed. Further, by controlling the above-described drive circuit 160 in accordance with the temperature at the center of the fixing sleeve, the power supplied to the high-frequency converter 16 is controlled so that the temperature at the center of the fixing sleeve maintains the control target temperature. I have.

  Each operation waveform during four cycles of the commercial power supply voltage when 50% power is applied will be described with reference to FIG. The CPU 32 of this embodiment sets power corresponding to the temperature detected by the temperature detecting element 9 for each control cycle, with four cycles of the commercial power supply voltage as one control cycle.

  In FIG. 7, a voltage 701 of the commercial power supply 50, a ZEROX signal waveform 702, a voltage waveform 703 of the triac 161, a gate waveform 704 of the switching element 86, and a gate waveform 705 of the switching element 87 are represented by time on the horizontal axis. . When a voltage 701 is input from the commercial power supply 50, a ZEROX signal 702 is generated by the ZEROX generation circuit 75 and input to the CPU 32. The switching elements 86 and 87 are alternately switched at a drive frequency fk determined according to the paper size and the degree of temperature rise of the non-sheet passing portion as shown by gate waveforms 704 and 705.

  When supplying 50% of the power, the CPU 32 determines the supplied power for each half-wave so that the average applied power of four cycles becomes 50%. In FIG. 7, the input power pattern of the triac 161 is 50% input power in all half-waves.

  The ROM 32a in the CPU 32 stores a table of lighting timing coefficients for phase control according to the input power ratio. The CPU 32 calculates the lighting timing using the table, the ZEROX signal 702, and the information of the temperature detecting element 9. The table is, for example, as shown in Table 1. The lighting timing coefficient 0 is when the phase of the voltage waveform 701 of the commercial power supply 50 is 0 °, and 1 is when it is 180 °.

  The CPU 32 determines the timing for turning on the drive circuit 160 using the temperature detected by the temperature detecting element 9 and the table shown in Table 1. For example, in the case of the commercial power supply 50 of 50 Hz, the ON timing of the triac 161 for supplying 50% power is 5.0 ms (= 20 ms / 2 × 0) from the falling edge (or rising edge) of the zero-cross signal waveform 702. .50) later. In the case of the odd-numbered waveforms D1, D3, D5, and D7 shown in FIG. 7, the CPU 32 outputs the High level to the output port PA2 5 ms after the time when the ZEROX signal 702 changes from High to Low, thereby reducing the 50%. Power will be supplied. Thus, it is possible to supply 50% input power to the rectifier circuits 81 to 84 in four cycles of the commercial power supply voltage. In this embodiment, four cycles are defined as one control cycle, and power control is performed using phase control every four cycles. However, one control cycle may be other than four cycles. Also, the control waveform may be a control waveform other than the phase control, such as a wave number control or a control combining the phase control and the wave number control.

  The flow of the power-on sequence by the CPU 32 will be described with reference to the flowchart of FIG. First, when the power supply sequence is started, the input power duty ratio D by the triac 61 is determined from the detected value of the temperature detecting element 9 and the control target temperature in S101. Next, in S102, the drive frequency fk of the switching elements 86 and 87 is determined according to at least one of the size of the recording material P and the temperature at the end of the sleeve 1. Subsequently, in step S103, the counter k (the number of half cycles of the commercial power supply voltage) is initialized (k = 1), and the rising or falling edge of the ZEROX signal 702 is monitored in step S104. At the timing when the rising or falling edge of the ZEROX signal 702 is detected, the counter k is incremented (S105), and the triac 161 supplies half-wave power to the fixing unit A at a phase angle of D% (S106). If the counter k is less than 8 in S107, one control cycle (four cycles) has not been reached, so S104 to S106 are repeated. On the other hand, when the counter k has reached 8 in S107, power supply in one control cycle ends. Until it is determined in S108 that power-on is completed, S101 to S107 are repeated, and power-on is performed while switching the power-on duty ratio every four cycles.

  As described above, the triac 161 is arranged before the diode bridges 81 to 84, and the triac 161 adjusts the effective voltage to be input to the subsequent circuit, so that the switching frequency can be changed without changing the drive frequency fk of the switching elements 86 and 87. The power can be adjusted. In the present embodiment, an example has been described in which the triac 161 is disposed in front of the diode bridges 81 to 84 as a power control switch member. However, the switch member may be any switchable component such as an FET, an IGBT, or a relay, and is not limited to a triac.

(Example 2)
In the present embodiment, an example will be described in which FETs are arranged downstream of the diode bridges 81 to 84 and power is controlled by turning on and off the FETs. Hereinafter, the present embodiment will be described mainly with respect to differences from the first embodiment, and the same reference numerals will be given to the common components, and description thereof will be omitted.

  FIG. 9 is a circuit diagram including the high-frequency converter 16 in the present embodiment. The input effective voltage input to the high-frequency converter 16 is adjusted by turning on and off the FET 93 which is an example of a switch member disposed after the rectifier circuits 81 to 84 and before the high-frequency converter 16. When the CPU 32 outputs a signal for turning on the FET from the output port PA5, the FET drive circuit 95 outputs a gate waveform to the FET 93. With this configuration, power adjustment can be performed without changing the driving frequency of the switching elements 86 and 87.

  In FIG. 10, the voltage 701 of the commercial power supply 50, the ZEROX signal waveform 702, the voltage waveform 1001 of the FET 93, the gate waveform 704 of the switching element 86, and the gate waveform 705 of the switching element 87 are represented by time on the horizontal axis. When a voltage 701 is input from the commercial power supply 50, a ZEROX signal 702 is generated by the ZEROX generation circuit 75 and input to the CPU 32. The switching elements 86 and 87 are alternately switched at a drive frequency fk according to the paper size and the degree of temperature rise of the non-sheet passing portion as shown by gate waveforms 704 and 705.

  When supplying 50% of the power, the CPU 32 determines the supplied power for each half-wave so that the average applied power of four cycles becomes 50%. In the case of the example of FIG. 10, the power is supplied by the FET 93 for each half-wave in the order of 100% → 0% → 0% → 100% → 100% → 0% → 0% → 100% from the first half-wave. . As a result, the average input power in one control cycle (4 cycles) becomes 50%. In the present embodiment, power control is performed using wave number control. However, the phase control described in the first embodiment or a control waveform in which phase control and wave number control are mixed may be used.

  The flow of the power supply sequence by the CPU 32 will be described with reference to the flowchart of FIG. 8 are assigned the same reference numerals and explanations thereof will be omitted. The ON-OFF (D1 to D8) for each half-wave is set from the ON-OFF table for each half-wave corresponding to each input power duty ratio prepared in advance and the applied power duty ratio D determined according to the detected temperature ( S201). After the rising or falling edge of the ZEROX signal 702 is detected, it is determined in S202 whether the FET 93 is ON or OFF for each half-wave. If Dk = ON based on the ON-OFF setting value for each half-wave set in S201, the FET 93 is turned on in S203. If Dk = OFF, the FET 93 is turned off in S204. In step S205, the counter k is incremented, and steps S104 to S205 are repeated until the counter k becomes 8. As described above, the FET 93 is arranged at the subsequent stage of the diode bridges 81 to 84, and the effective voltage input to the subsequent circuit is adjusted by the FET 93. This makes it possible to adjust the input power without changing the driving frequency of the switching elements 86 and 87. In this embodiment, the example in which the FET 93 is arranged as the switch member has been described. However, the parts to be arranged are not limited to this embodiment, and may be any parts that can be turned on and off, such as an IGBT and a relay.

  In the first embodiment, power control is performed using phase control, and in the second embodiment, power control is performed using wave number control. However, both the configuration of the first embodiment and the configuration of the second embodiment can apply any of the phase control, the wave number control, and the control pattern in which the phase control and the fraction control are mixed, and are limited to the first and second embodiments. It is not something to be done.

86, 87 Switching element 89 Resonant capacitor 161 Triac 81-84 Diode bridge 93 FET

Claims (9)

A cylindrical rotating body having a conductive layer, a coil disposed inside the rotating body and having a spiral axis substantially parallel to the generatrix direction of the rotating body, and a resonance circuit having a resonance capacitor,
A converter for driving the resonance circuit;
A fixing device that causes the conductive layer to generate electromagnetically induced heat by a magnetic flux generated by the coil, and fixes an image formed on the recording material to the recording material by the heat of the rotating body.
The number of coils arranged inside the rotating body is one,
The conductive layer is formed of the same material and the same thickness from one end to the other end in the bus direction,
A switch member for controlling power supplied to the converter,
A frequency control unit that sets a drive frequency of the converter according to at least one of a size of a recording material and a temperature of a non-sheet passing portion of the rotating body;
A power control unit that controls the switch member according to a temperature of a paper passing unit of the rotating body and controls power supplied to the converter;
Have a,
When the frequency control unit controls the converter so as to reduce the driving frequency, the heat generation distribution of the conductive layer changes so that the heat generation amount of the conductive layer at the end in the bus direction decreases. apparatus.   The fixing device according to claim 1, wherein the power control unit controls the switch member such that a temperature of a paper passing unit 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, further comprising a rectifying unit that rectifies a commercial power supply voltage, wherein the switch member is provided at a stage preceding the rectifying unit.   The fixing device according to claim 4, wherein the switch member is a triac.   The fixing device according to claim 1, further comprising a rectifying unit that rectifies a commercial power supply voltage, wherein the switch member is provided between the rectifying unit and the converter.   The fixing device according to claim 6, wherein the switch member is an FET or an IGBT.   The helical portion of the coil has a core for inducing magnetic flux, and an induced current flowing in a circumferential direction of the rotating body is generated in the conductive layer. The fixing device according to claim 1.   The fixing device according to claim 8, wherein the core has an end shape.