JP2013200531A - High-frequency power supply device, fixing device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress inrush current at the moment of transition from an off state to an on state in a high-frequency power supply device that supplies high-frequency power to a coil.SOLUTION: A high-frequency power supply device 90 includes: a resonance capacitor Ck that is connected in parallel to an exciting coil 81 to constitute a resonance circuit 96; a switching element IGBT; a rectifying unit 92; a smoothing unit 95 that smooths a rectified DC voltage; a current detection unit 98 that detects a current flowing through a primary-side winding of a chalk transformer CT; and a short circuit unit 99 that comprises a current limiting resistor R0 and a triac TR, and transits from an off state to an on state to set a resistance value between both terminals of the current limiting resistor R0 smaller than a resistance value of the current limiting resistor R0.

Description

  The present invention relates to a high-frequency power supply device, a fixing device, and an image forming apparatus.

  2. Description of the Related Art In recent years, in an electrophotographic image forming apparatus, an induction heating (IH: Inductive Heating) method has been widely adopted as a fixing device. In the induction heating method, high-frequency power is supplied to the coil, a high-frequency magnetic field generated by the coil is applied to the fixing belt, and the fixing belt generates heat due to eddy current loss. The induction heating method can heat the fixing belt in a shorter time than the method of heating using a heater or the like.

  Patent Document 1 discloses an image forming apparatus including a heating member and a coil that generates a high-frequency magnetic field so as to generate the heating member eddy current, and includes a fixing device that fixes a developer image on a recording medium. A rectifier circuit that rectifies the output of the commercial AC power supply, a switching circuit that converts the output rectified by the rectifier circuit into a high frequency of a predetermined frequency and outputs a high frequency to the coil, and a first control that controls the switching circuit A circuit, a second control circuit that is supplied with electric power from the commercial AC power source and controls a portion of the image forming apparatus other than the fixing device, and the first control circuit and the second control circuit are electrically connected. And an interface circuit that relays data transmission / reception between the first control circuit and the second control circuit while being electrically insulated. When the switch is turned on, the first control circuit and the second control circuit perform startup processing in parallel, and the first control circuit supplies a high-frequency output to the coil in advance. An image forming apparatus is described.

JP 2005-134918 A

  An object of the present invention is to suppress inrush current when a high-frequency power supply device that supplies high-frequency power to a coil or the like shifts from an off state to an on state.

The invention according to claim 1 includes a resonance circuit including a capacitor and connected in parallel with an externally provided coil, a switching element connected in series to one terminal of the resonance circuit, and the resonance A smoothing unit connected in series to the other terminal of the circuit; a rectifying unit connected to the smoothing unit; a current detection unit that detects a current flowing through either the resonance circuit or the smoothing unit; and the smoothing unit. When the current detection unit detects a predetermined current value, the current limiting resistor that limits the current supplied to the current limiting resistor and the current limiting resistor is shifted to the on state to detect the current. The high-frequency power supply device includes a short-circuit portion that sets a resistance value between both terminals of the limiting resistor to be smaller than the current limiting resistor.
According to a second aspect of the present invention, the current limiting resistor is provided in a path through which an alternating current supplied to the rectifying unit flows, and the short-circuit unit includes a triac. This is a high-frequency power supply device.
According to a third aspect of the present invention, the current limiting resistor is provided between the rectifying unit and the smoothing unit, and the short-circuit unit includes a thyristor. It is a supply device.
According to a fourth aspect of the present invention, there is provided a fixing belt that is heated by electromagnetic induction, an excitation coil that is disposed opposite to the fixing belt and generates a magnetic field for electromagnetic induction, and a capacitor, A resonance circuit configured in parallel, a switching element connected in series to one terminal of the resonance circuit, a smoothing unit connected in series to the other terminal of the resonance circuit, and a connection to the smoothing unit A rectifying unit, a current detecting unit for detecting a current flowing through one of the resonance circuit and the smoothing unit, a current limiting resistor for limiting a current supplied to the smoothing unit, and the current limiting resistor in parallel. When connected and the current detection unit detects a predetermined current value, the state shifts from the off state to the on state, and the terminals of the current limiting resistor are set to a resistance value smaller than the current limiting resistor. A high frequency power supply section having a short circuit portion of a fixing device, characterized in that it comprises a pressure member which is pressed against the outside of the fixing belt.
According to a fifth aspect of the present invention, there is provided image forming means for forming a toner image, transfer means for transferring the toner image formed by the image forming means to a recording material, a fixing belt heated by electromagnetic induction, A resonance circuit that is arranged opposite to the fixing belt and generates a magnetic field for electromagnetic induction, a capacitor and connected in parallel with the excitation coil, and one terminal of the resonance circuit A switching element connected in series, a smoothing unit connected in series to the other terminal of the resonance circuit, a rectification unit connected to the smoothing unit, and a current flowing through either the resonance circuit or the smoothing unit When a current detection unit to detect, a current limiting resistor for limiting the current supplied to the smoothing unit, and a current limiting unit connected in parallel to the current limiting resistor and the current detecting unit detects a predetermined current value, The high-frequency power supply unit including the short-circuit unit that sets the resistance value smaller than the current limiting resistor is pressed between the two terminals of the current limiting resistor and the outside of the fixing belt. A pressure member, and a fixing unit that fixes the toner image transferred to the recording material to the recording material.

According to the first aspect of the present invention, inrush current at the time of transition from the off state to the on state can be suppressed as compared with the case where no current limiting resistor is provided.
According to the second and third aspects of the invention, the circuit can be reduced in size as compared with the case where this configuration is not provided.
According to the fourth aspect of the present invention, it is possible to suppress the generation of noise due to the inrush current as compared with the case where this configuration is not provided.
According to the fifth aspect of the present invention, image quality deterioration caused by noise due to inrush current can be suppressed as compared with the case where this configuration is not provided.

1 is a diagram illustrating an example of a configuration of an image forming apparatus to which a first exemplary embodiment is applied. FIG. 3 is a diagram illustrating a configuration of a fixing device. It is a figure which shows an example of the high frequency electric power supply apparatus with which 1st Embodiment is applied. It is a timing chart explaining operation | movement of a high frequency electric power supply apparatus. It is a figure which shows an example of the high frequency electric power supply apparatus which is not provided with an electric current detection part and a short circuit part. It is a figure which shows typically the electric current Ih which flows into the exciting coil in the high frequency electric power supply apparatus which is not provided with an electric current detection part and a short circuit part, and the electric current If which flows into a smoothing capacitor. It is a figure which shows an example of a structure of the high frequency electric power supply apparatus with which 2nd Embodiment is applied. It is a figure which shows an example of a structure of the high frequency electric power supply apparatus with which 3rd Embodiment is applied.

  Embodiments of the present invention will be described below. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary. Also, the drawings used are used to describe the present embodiment, and do not represent the actual size.

[First Embodiment]
(Image forming apparatus 100)
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 100 to which the first exemplary embodiment is applied. Here, an intermediate transfer type image forming apparatus generally called a tandem type will be described as an example. An image forming apparatus 100 shown in FIG. 1 includes a plurality of image forming units 1Y, 1M, 1C, and 1K that form toner images of respective color components by electrophotography as an example of an image forming unit. Next, the primary transfer unit 10 as an example of a transfer unit that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the intermediate transfer belt 15. A secondary transfer unit 20 that collectively transfers (secondary transfer) the superimposed toner image transferred above onto a sheet P as an example of a recording material. Further, as an example of the fixing unit, a fixing device 60 that fixes the second-transferred image on the paper P is provided. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  As shown in FIG. 1, each of the image forming units 1Y, 1M, 1C, and 1K includes a photosensitive drum 11 that rotates in the direction of arrow A, a charger 12 that charges the photosensitive drum 11, and a photosensitive drum 11. It has a laser exposure device 13 for writing an electrostatic latent image, and a developing device 14 that accommodates each color component toner and visualizes the electrostatic latent image on the photosensitive drum 11 with the toner. Further, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, a drum cleaner 17 that removes residual toner on the photosensitive drum 11, and Have These image forming units 1Y, 1M, 1C, and 1K are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15.

  The intermediate transfer belt 15 is circulated and driven in the direction of arrow B shown in FIG. 1 by various rolls. As various rolls, a drive roll 31 that drives the intermediate transfer belt 15, a support roll 32 that supports the intermediate transfer belt 15, a tension roll 33 that applies tension to the intermediate transfer belt 15 to prevent meandering, and the secondary transfer unit 20. And a cleaning backup roll 34 provided in a cleaning unit that scrapes off residual toner on the intermediate transfer belt 15.

  The primary transfer unit 10 includes a primary transfer roll 16 that faces the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roll 25 disposed on the back surface side of the intermediate transfer belt 15 as a counter electrode of the secondary transfer roll 22. And a power supply roll 26 that applies a secondary transfer bias to the backup roll 25.

  An intermediate transfer belt cleaner 35 for removing residual toner and paper dust on the intermediate transfer belt 15 is provided on the downstream side of the secondary transfer unit 20. A reference sensor (home position sensor) 42 that generates a reference signal for taking an image forming timing in each of the image forming units 1Y, 1M, 1C, and 1K is disposed upstream of the yellow image forming unit 1Y. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K.

  The paper transport system includes a paper storage unit 50, a pickup roll 51 that takes out and transports the paper P in the paper storage unit 50, a transport roll 52 that transports the paper P, and the paper P to the secondary transfer unit 20. A conveyance unit 53 that feeds the sheet P, a conveyance belt 55 that conveys the sheet P secondarily transferred by the secondary transfer roll 22 to the fixing device 60, and a fixing inlet guide 56 that guides the sheet P to the fixing device 60.

A basic image forming process of the image forming apparatus 100 will be described.
In the image forming apparatus 100 shown in FIG. 1, after image processing is performed on image data output from an image reading device (not shown) or the like, the image data is converted into four color material levels of Y, M, C, and K. It is converted into tone data and output to the laser exposure unit 13. For example, each of the photosensitive drums that rotates the exposure beam Bm emitted from the semiconductor laser in the direction of arrow A of the image forming units 1Y, 1M, 1C, and 1K according to the input color material gradation data. 11 is irradiated. After the surface of each photoconductive drum 11 is charged by the charger 12, the surface is scanned and exposed by the laser exposure device 13 to form an electrostatic latent image. The formed electrostatic latent image is developed as a toner image of each color of Y, M, C, and K by each of the image forming units 1Y, 1M, 1C, and 1K.

Next, the toner image formed on the photosensitive drum 11 is sequentially superimposed on the surface of the intermediate transfer belt 15 in the primary transfer unit 10 to perform primary transfer. The intermediate transfer belt 15 moves in the direction of arrow B and conveys the toner image to the secondary transfer unit 20. The paper transport system supplies the paper P from the paper storage unit 50 in synchronization with the timing of transporting the toner image to the secondary transfer unit 20.
In the secondary transfer unit 20, the unfixed toner image held on the intermediate transfer belt 15 is electrostatically transferred onto the paper P sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. Thereafter, the sheet P on which the toner image is electrostatically transferred is conveyed to the fixing device 60 by the conveying belt 55, and the fixing device 60 processes the unfixed toner image on the sheet P with heat and pressure and fixes it on the sheet P. The sheet P on which the fixed image is formed is discharged from the image forming apparatus 100.

(Fixing device 60)
Next, the fixing device 60 in the present embodiment will be described.
FIG. 2 is a diagram illustrating a configuration of the fixing device 60. The fixing device 60 employs an electromagnetic induction heating method.
As shown in FIG. 2, the fixing device 60 is an example of a fixing belt 61, an induction heating unit 80 that generates heat by the magnetic field generated by an alternating current, and a pressure member that is disposed so as to face the fixing belt 61. The pressure pad 64 is pressed from the pressure roll 62 via the pressure roll 62 and the fixing belt 61.

  The fixing belt 61 has a metal layer and has, for example, a cylindrical shape with a diameter of about 30 mm. The metal layer is, for example, stainless steel. The fixing belt 61 is supported so as to be rotationally driven by a pressure pad 64, a belt guide member 63, and edge guide members (not shown) arranged at both ends of the fixing belt 61. And it is press-contacted to the pressurization roll 62 in the nip part N (pressing part), is driven by the pressurization roll 62, and it drives around in the arrow C direction. The fixing belt 61 may be provided with an elastic layer and a release layer in this order on the outer surface of the cylindrical metal layer. The elastic layer is, for example, silicone rubber, and is made of a material having high heat resistance, low surface tension, and excellent elasticity. Further, the release layer is made of, for example, a fluoro rubber, and is made of a material that exhibits an appropriate release property for the toner image.

  The belt guide member 63 is attached to a holder 65 disposed inside the fixing belt 61. The belt guide member 63 is formed by a plurality of ribs (not shown) directed in the rotational driving direction of the fixing belt 61 to reduce the contact area with the inner peripheral surface of the fixing belt 61. The belt guide member 63 is made of a heat-resistant resin such as polyfluoroalkyl vinyl ether (PFA) or polyphenylene sulfide (PPS) having a low friction coefficient and low thermal conductivity, and sliding resistance with the inner peripheral surface of the fixing belt 61. In order to reduce heat dissipation.

  The pressure pad 64 is pressed from the pressure roll 62 via the fixing belt 61 to form a nip portion N that is a pressing portion. The pressure pad 64 is supported by the holder 65 so as to press the pressure roll 62 with a load of, for example, 35 kgf by a spring or an elastic body. The pressure pad 64 is made of an elastic material such as silicone rubber or fluorine rubber, and the pressure roll 62 side is formed in a flat shape, and a nip pressure is formed at the nip portion N. When the fixing belt 61 moves away from the surface of the pressure pad 64 on the pressure roll 62 side, a sudden change in curvature occurs, and the paper P after fixing is peeled off from the fixing belt 61.

The peeling assisting member 70 disposed on the downstream side of the nip portion N is held by the baffle holder 72 so that the peeling baffle 71 faces in the direction (counter direction) opposite to the rotation direction of the fixing belt 61. Further, a low friction sheet 68 is disposed between the pressure pad 64 and the fixing belt 61 to reduce the sliding resistance between the inner peripheral surface of the fixing belt 61 and the pressure pad 64. In the present embodiment, the low friction sheet 68 is configured separately from the pressure pad 64, and both ends are fixed to the holder 65.
A lubricant application member 67 is disposed in the holder 65 over the longitudinal direction of the fixing device 60. The lubricant application member 67 contacts the inner peripheral surface of the fixing belt 61 and supplies the lubricant to the sliding portion between the fixing belt 61 and the low friction sheet 68. Examples of the lubricant include liquid oils such as silicone oil and fluorine oil; grease in which a solid substance and a liquid are mixed, and a combination thereof.

The pressure roll 62 includes, for example, a solid iron core (columnar core) 621 having a diameter of 16 mm, a rubber layer 622 such as a silicone sponge having a thickness of 12 mm, which covers the outer peripheral surface of the core 621, and the like, for example And a surface layer 623 with a heat-resistant resin coating such as PFA having a thickness of 30 μm or a heat-resistant rubber coating. In addition, as a manufacturing method of the pressure roll 62, for example, a fluororesin tube having a bonding primer applied to the inner peripheral surface of a PFA tube and a solid shaft are set in a molding die, and the fluororesin tube and the solid An example is a method in which after the liquid foamed silicone rubber is injected between the shaft and the silicone rubber is vulcanized and foamed by heat treatment (150 ° C. × 2 hrs) to form an elastic layer.
The pressure roll 62 is disposed so as to face the fixing belt 61, rotates in the arrow D direction at a process speed of, for example, 140 mm / s, and moves the fixing belt 61 in the arrow C direction. Further, the fixing belt 61 is held by the pressure roll 62 and the pressure pad 64 to form a nip portion N, and a sheet P holding an unfixed toner image is passed through the nip portion N to pass heat and Pressure is applied to fix the unfixed toner image on the paper P.

  The induction heating unit 80 has a round shape with a cross section that follows the shape of the fixing belt 61, and is installed with a gap of about 0.5 mm to 2 mm from the outer peripheral surface of the fixing belt 61. The induction heating unit 80 includes an excitation coil 81 that generates a magnetic field, a coil support member 82 that holds the excitation coil 81, and a high-frequency power supply device 90 that is an example of a high-frequency power supply unit that supplies current to the excitation coil 81. Have.

The exciting coil 81 is formed, for example, by winding litz wires in which about 16 to 20 copper wires having a diameter of 0.5 mm that are insulated from each other are bundled in a closed loop shape such as an oval shape, an elliptical shape, or a rectangular shape. Use things. By applying an alternating current having a predetermined frequency to the exciting coil 81 by the high frequency power supply device 90, an alternating magnetic field H is generated around the exciting coil 81. When the AC magnetic field H crosses the metal layer of the fixing belt 61, an eddy current I is generated in the metal layer so as to generate a magnetic field that prevents changes in the AC magnetic field H due to electromagnetic induction. The frequency of the alternating current applied to the exciting coil 81 is set to, for example, 10 kHz to 50 kHz. When the eddy current I flows through the fixing belt 61, Joule heat is generated by electric power W (W = I ² R) proportional to the resistance value R of the metal layer, and the fixing belt 61 is heated.

  The coil support member 82 is made of a heat-resistant nonmagnetic material. Examples of the nonmagnetic material include heat resistant resins such as heat resistant glass, polycarbonate, polyethersulfone, and PPS, or heat resistant resins obtained by mixing glass fibers with these.

  In the fixing device 60, the fixing belt 61 is driven to rotate in the direction of arrow C as the pressure roll 62 rotates in the direction of arrow D, and is exposed to the magnetic field generated by the excitation coil 81. At this time, an eddy current I is generated in the metal layer in the fixing belt 61, and the outer peripheral surface of the fixing belt 61 is heated to a temperature at which fixing can be performed. The fixing belt 61 heated in this way moves to the nip N with the pressure roll 62. When the sheet P having the unfixed toner image provided on the surface thereof is conveyed by the conveying unit and the sheet P passes through the nip N between the fixing belt 61 and the pressure roll 62, the unfixed toner image is transferred to the fixing belt 61. Is heated and fixed on the surface of the paper P. Thereafter, the paper P on which the image is formed is transported by the transport unit and discharged from the fixing device 60. In addition, since the fixing belt 61 having finished the fixing process at the nip portion N and whose surface temperature on the outer peripheral surface has decreased is heated again in preparation for the next fixing process, the fixing belt 61 rotates in the direction of the excitation coil 81. To do.

(High-frequency power supply device 90)
Next, the high frequency power supply apparatus 90 to which the first embodiment is applied will be described.
FIG. 3 is a diagram illustrating an example of the high-frequency power supply apparatus 90 to which the first embodiment is applied.
The high frequency power supply device 90 includes a noise filter 91, a current limiting resistor R0, a rectifier 92, a current detector 93 that detects an alternating current (AC) current supplied to the rectifier 92, and a direct current (rectified by the rectifier 92 ( DC) a voltage detection unit 94 for detecting the voltage, a smoothing unit 95 for smoothing the rectified DC voltage, a resonance capacitor Ck connected in parallel with the excitation coil 81 and constituting a resonance circuit 96, and an npn type insulated gate bipolar transistor. A switching element IGBT, a drive unit 97 for turning on / off the switching element IGBT, a current detection unit 98 for detecting a current flowing in the primary winding of the choke transformer CT, and a short circuit unit 99 including a triac TR are provided.
Here, the exciting coil 81 is also expressed as an inductance Lk. That is, the high-frequency power supply device 90 generates a high-frequency magnetic field by supplying high-frequency power to the exciting coil 81 (inductance Lk), and self-heats the fixing belt 61 that is a heating element.

  The switching element IGBT is a device having a structure in which a MOSFET is connected to a pnp bipolar transistor in a Darlington connection in terms of an equivalent circuit. That is, a gate terminal, an emitter terminal, and a collector terminal are provided, the gate terminal is the gate terminal of the MOSFET, and the emitter terminal and the collector terminal are the emitter terminal and the collector terminal of the pnp bipolar transistor. The source terminal of the MOSFET is connected to the base terminal of the pnp bipolar transistor, and the drain terminal of the MOSFET is connected to the emitter terminal of the pnp bipolar transistor. When a predetermined voltage is applied to the gate terminal, the MOSFET is turned on, and the resistance between the base terminal and the emitter terminal of the pnp bipolar transistor is reduced (transition from the off state to the on state). . As a result, the pnp bipolar transistor becomes conductive.

The triac TR is a device having a configuration in which two thyristors complementary in terms of an equivalent circuit are connected in parallel.
First, the thyristor will be described. A thyristor is a device that combines a pnp bipolar transistor and an npn bipolar transistor in terms of an equivalent circuit. The base terminal of the pnp bipolar transistor is connected to the collector terminal of the npn bipolar transistor, and the collector terminal of the pnp bipolar transistor is connected to the base terminal of the npn bipolar transistor. The thyristor includes an anode terminal (an emitter terminal of a pnp bipolar transistor), a cathode terminal (an emitter terminal of an npn bipolar transistor), a gate terminal (a base terminal of an npn bipolar transistor and a pnp bipolar transistor). Collector terminal).
The threshold voltage, that is, the voltage at which the resistance value between the anode terminal and the cathode terminal of the thyristor shifts from the high off state to the low on state (turn on) is set by the voltage applied to the gate terminal. Note that current flows in one direction in the thyristor in the on state.
On the other hand, in terms of an equivalent circuit, the triac TR is configured by connecting in parallel the thyristor described above and a thyristor obtained by inverting a pnp bipolar transistor and an npn bipolar transistor. The triac TR includes a gate terminal and two current terminals. Then, when a predetermined voltage is applied to the gate terminal, a transition is made from the off state to the on state, and a current flows between the two current terminals. In the triac TR, current flows in both directions.

The connection relationship of the high frequency power supply device 90 will be described.
The noise filter unit 91 includes two input terminals and two output terminals, and the two input terminals are connected to an alternating current (AC) power source. The AC power source is, for example, an AC 100V single-phase commercial power source. One output terminal of the two output terminals is connected to one terminal of the current limiting resistor R0. The other output terminal is connected to the rectifier 92 through the current detector 93.
In the noise filter unit 91, for example, one of the input terminals and one of the output terminals are connected, the other of the input terminals and the other of the output terminals are connected, and a capacitor is provided between each and the ground potential. Configured (Y capacitor) to remove noise entering the high frequency power supply device 90 from the alternating current (AC) power source and noise entering the AC power source from the high frequency power supply device 90.

The rectifying unit 92 includes two input terminals and two output terminals. One input terminal is connected to the other terminal of the current limiting resistor R0, and the other input terminal is connected via the current detection unit 93. The other output terminal of the noise filter unit 91 is connected. One output terminal of the rectifying unit 92 is connected to one terminal of the primary winding of the choke transformer CT in the smoothing unit 95, and the other output terminal is connected to the emitter terminal of the insulated gate bipolar transistor IGBT. Yes. The rectification unit 92 rectifies alternating current (AC) into direct current (DC) by, for example, a bridge rectifier circuit.
A voltage detector 94 that detects the rectified DC voltage is connected between the two output terminals of the rectifier 92.

  The smoothing unit 95 includes a primary winding of the choke transformer CT and a smoothing capacitor C0. One terminal of the primary side winding of the choke transformer CT is connected to one output terminal of the rectifier 92, and the other terminal is connected to the resonance circuit 96 and to one terminal of the smoothing capacitor C0. ing. The other terminal of the smoothing capacitor C0 is connected to the emitter terminal of the switching element IGBT.

The resonance circuit 96 is configured by connecting an exciting coil 81 (inductance Lk) and a resonance capacitor Ck in parallel. The exciting coil 81 (inductance Lk) is connected to the high frequency power supply device 90 through connection terminals S1 and S2.
In the resonance circuit 96, one terminal where the exciting coil 81 (inductance Lk) and the resonance capacitor Ck are connected in parallel is connected to the other terminal of the primary side winding of the choke transformer CT in the smoothing unit 95. The other terminal of is connected to the collector terminal of the switching element IGBT.

The drive unit 97 is connected to the gate terminal of the switching element IGBT. Then, the driving unit 97 applies a voltage to the gate terminal so that the switching element IGBT is repeatedly turned on and off (switched) at a predetermined cycle so that an alternating current flows through the exciting coil 81.
Note that the drive unit 97 receives data related to the AC current detected by the current detection unit 93 (AC current data) and data related to the DC voltage detected by the voltage detection unit 94 (DC voltage data). Although not shown, data (temperature data) related to the temperature of the fixing belt 61 detected by the temperature detection unit that detects the temperature of the fixing belt 61 in the fixing device 60 is input. As a result, the drive unit 97 supplies predetermined power to the excitation coil 81 and controls the fixing belt 61 to a predetermined temperature.

  One current terminal of the triac TR constituting the short circuit portion 99 is connected to one terminal of the current limiting resistor R0, and the other current terminal of the triac TR is connected to the other terminal of the current limiting resistor R0. As will be described later, the resistance value of the current limiting resistor R0 is smaller than the resistance value between the two current terminals of the off-state triac TR, and is smaller than the resistance value between the two current terminals of the on-state triac TR. It is set large. Therefore, when the triac TR shifts from the OFF state to the ON state, the resistance value between the two current terminals shifts from a state larger than the resistance value of the current limiting resistor R0 to a smaller state, and the current limiting resistor R0 is short-circuited. To work.

The current detection unit 98 includes a secondary winding of the choke transformer CT, a capacitor C1, a resistor R1, and a rectifier D1. One terminal of the secondary winding of the choke transformer CT is connected to the anode terminal of the rectifier D1, the cathode terminal of the rectifier D1 is connected to one terminal of the resistor R, and the other terminal of the resistor R is connected to the gate terminal of the triac TR. The The other terminal of the choke transformer CT is connected to the other current terminal of the triac TR. A capacitor C1 is connected between the other current terminal and the gate terminal of the triac TR.
When a current flows through the primary winding of the choke transformer CT, a current is induced in the secondary winding. The induced current is rectified by the rectifier D1 and raises the potential of the capacitor C1. As a result, when the voltage between both terminals of the capacitor C1 (the voltage between the other current terminal of the triac TR and the gate terminal) reaches a voltage that turns the triac TR from the off state to the on state, the triac TR is off. Is turned on and the current limiting resistor R0 is short-circuited.

The current detector 93 only needs to be able to measure the value of the AC current flowing from the noise filter 91 to the rectifier 92, and any method may be used. For example, a resistor (shunt resistor) may be interposed in the current flow path (wiring) to measure the voltage drop that occurs between both terminals. A core is provided around the wiring (conductor), and is generated by electromagnetic induction. The electromotive force may be measured.
The voltage detection unit 94 may use any method as long as the rectified DC voltage can be measured. For example, DC voltage may be measured by dividing the voltage with a resistor connected in series.

Next, the operation of the high frequency power supply device 90 will be described.
FIG. 4 is a timing chart for explaining the operation of the high-frequency power supply apparatus 90. In FIG. 4, the gate voltage Vb applied to the gate terminal of the switching element IGBT by the drive unit 97, the collector current Ic flowing between the collector terminal and the emitter terminal of the switching element IGBT, and the exciting coil 81 (inductance Lk) of the resonance circuit 96 The electric current Ih which flows into is shown.
The horizontal axis represents time, and it is assumed that time elapses in the order of time a, time b, time c,.

Before the fixing device 60 is operated, the triac TR is in an off state. In the off state, the resistance value between the two current terminals of the triac TR is higher than the resistance value of the current limiting resistor R0.
When the gate voltage Vb is shifted from 0 to Von at time a, the switching element IGBT is turned on. Here, Von of the gate voltage Vb is a voltage that sets the switching element IGBT to the ON state. Note that 0 of the gate voltage Vb is a voltage for setting the switching element IGBT to the OFF state, and does not necessarily have to be 0V.
When the switching element IGBT shifts from the off state to the on state, the switching element IGBT flows from the AC power source to the rectifying unit 92 through the noise filter unit 91 through the path α (see FIG. 3) via the current limiting resistor R0. The rectified current flows to the switching element IGBT (collector current Ic) via the primary winding of the choke transformer CT and the exciting coil 81 (inductance Lk) of the resonance circuit 96. Since the collector current Ic flows through the choke transformer CT and the exciting coil 81 (inductance Lk), it cannot follow the waveform of the gate voltage Vb and gradually increases with time. Furthermore, since the current flows through the current limiting resistor R0, the rate of increase (slope) with respect to time is smaller than when the current limiting resistor R0 is not provided.

At this time, the direct current flowing from the rectifying unit 92 to the smoothing unit 95 charges the smoothing capacitor C0. However, immediately after the current starts to flow, since no charge is accumulated in the smoothing capacitor C0, a larger current (inrush current) flows than in the state where the charge is accumulated.
When this inrush current is large, it becomes a surge current, which causes electromagnetic interference (EMI: Electro Magnetic Interference).
Therefore, in the first embodiment, a current (inrush current) flowing into the smoothing capacitor C0 is suppressed by flowing a current from the AC power source to the rectifying unit 92 via the current limiting resistor R0.

When the gate voltage Vb shifts from Von to 0 at time b, the switching element IGBT shifts from the on state to the off state. Then, the collector current Ic does not flow. However, in the resonance circuit 96, the current Ik flows toward the resonance capacitor Ck due to the energy accumulated in the exciting coil 81 (inductance Lk). In FIG. 4, the current Ik is shown together with the collector current Ic.
The current Ik becomes 0 at time c. Thereafter, the electric current accumulated in the resonant capacitor Ck flows in the reverse direction (current value is negative). As the charge accumulated in the resonant capacitor Ck decreases, the current Ik flowing in the reverse direction (current value is negative) decreases.

  The current Ih flowing through the exciting coil 81 (inductance Lk) is the sum of the collector current Ic and the current Ik. That is, the current Ih flowing through the exciting coil 81 (inductance Lk) is composed of a current Ic during a period from time a to time b and a current Ik during a period from time b to time d.

  At time d, when the gate voltage Vc is changed from 0 to Von again, the switching element IGBT shifts from the off state to the on state, and the collector current Ic flows. That is, from time d to time e, the operation from time a to time d is repeated.

  When the collector current Ic flows through the switching element IGBT, the current Ic also flows through the primary winding of the choke transformer CT of the smoothing unit 95. Thereby, a current also flows through the secondary winding of the choke transformer CT. This current is rectified by the rectifier D1 to charge the capacitor C1. When the voltage between both terminals of the capacitor C1 becomes high and the voltage at the gate terminal of the triac TR becomes higher than a predetermined voltage, the triac TR is changed from the off state to the on state. Here, it is assumed that the triac TR shifts from the off state to the on state at time e.

Then, the alternating current flowing from the AC power source via the noise filter unit 91 flows from the path α via the current limiting resistor R0 to the path β via the triac TR (see FIG. 3). Since the resistance value between the current terminals of the triac TR in the on state is smaller than the resistance value of the current limiting resistor R0, the state is the same as when the current limiting resistor R0 is short-circuited.
Thereby, the inclination with respect to time of the collector current Ic in the period from the time e to the time f becomes larger than that in the period from the time a to the time b.
At this time, since the current limiting resistor R0 is short-circuited, the direct current flowing from the rectifying unit 92 to the smoothing unit 95 also increases. However, since charge is accumulated in the smoothing capacitor C0, no inrush current flows.

A period from time f to time g is a period in which the switching element IGBT is in an OFF state, and a current Ik flows in the resonance circuit 96. This current Ik is larger than the period from time b to time d because the collector current Ic is large.
After time g, the same operation as in the period from time e to time g is repeated.

  In addition, since the electric charge is continuously accumulated in the capacitor C1, a current is supplied from the gate terminal of the triac TR, and the triac TR is maintained in the ON state.

In this manner, in the fixing device 60, the fixing belt 61 is heated by the magnetic field generated by the exciting coil 81 (inductance Lk).
In the above description, it is assumed that the triac TR has shifted from the off state to the on state at time e. However, the transition of the triac TR from the off state to the on state may not be at the time e, but may be in the middle of the period from the time a to the time b.
In an initial state where the high-frequency power supply device 90 starts operating (for example, from time a to time e in FIG. 4), that is, in a state where current starts flowing in the high-frequency power supply device 90, current is supplied via the current limiting resistor R0. By doing so, it is only necessary to suppress the inrush current flowing through the smoothing capacitor C0. Therefore, the resistance value of the current limiting resistor R0 is set to be smaller than the resistance value between the two current terminals of the off-state triac TR and larger than the resistance value between the two current terminals of the on-state triac TR. In the initial state in which the high-frequency power supply device 90 starts operation, the setting may be made so as not to cause EMI due to the inrush current.
Note that the timing for shifting the triac TR from the off state to the on state can be set by adjusting the capacitance of the capacitor C1 and the like.

Here, the high-frequency power supply device 90 that does not include the current detection unit 98 and the short-circuit unit 99 will be described.
FIG. 5 is a diagram illustrating an example of the high-frequency power supply device 90 that does not include the current detection unit 98 and the short-circuit unit 99. The high frequency power supply apparatus 90 according to the first embodiment shown in FIG. 3 does not include the current detection unit 98 and the short circuit unit 99. A choke coil CC is used instead of the choke transformer CT. Other configurations are the same as those of the high-frequency power supply device 90 in the first embodiment, and thus detailed description thereof is omitted.

FIG. 6 is a diagram schematically showing a current Ih that flows through the exciting coil 81 (inductance Lk) and a current If that flows through the smoothing capacitor C0 in the high-frequency power supply apparatus 90 that does not include the current detection unit 98 and the short-circuit unit 99. . In FIG. 6, it is assumed that time elapses in the order of time s, time t, time u,.
At time s, switching of the switching element IGBT is started and current Ih starts to flow through the exciting coil 81 (inductance Lk). As shown in FIG. 4, the current Ih flowing through the exciting coil 81 (inductance Lk) is an alternating current whose amplitude changes between positive and negative. In FIG. 6, the current Ih flowing through the exciting coil 81 (inductance Lk) is shown in a pseudo sine wave.

At time s, no charge is accumulated in the smoothing capacitor C0. Since the current limiting resistor R0 is not provided, the current If flowing through the smoothing capacitor C0 becomes a larger current (inrush current) than when charge is accumulated in the smoothing capacitor C0. This inrush current is gradually attenuated while repeating positive and negative vibrations as charges are accumulated in the smoothing capacitor C0. Then, when charge is accumulated in the smoothing capacitor C0, it cannot be seen.
Next, at time t, the current Ih flowing through the exciting coil 81 in the switching element IGBT is stopped. Then, the electric charge accumulated in the smoothing capacitor C0 is discharged and lost.
After that, when the current Ih is passed again through the exciting coil 81 (inductance Lk) at time u, the current If flowing through the smoothing capacitor C0 becomes an inrush current again.
That is, in the initial state where the high frequency power supply device 90 starts operation, inrush currents are generated, and noise is generated by these inrush currents.

The fixing device 60 may stop heating when the temperature of the fixing belt 61 reaches a predetermined temperature. Thereafter, when the temperature of the fixing belt 61 falls below a predetermined temperature, heating is resumed. When resuming heating, an inrush current flows.
The power supplied from the exciting coil 81 to the fixing belt 61 is controlled by a current flowing through the switching element IGBT. However, depending on the characteristics of the switching element IGBT, it may not be possible to set the power smaller than a predetermined power. In such a case, the high frequency power supply device 90 is operated intermittently, and the power supplied from the exciting coil 81 to the fixing belt 61 is set to be equivalently small. That is, a period in which the switching element IGBT is continuously switched to pass a current through the exciting coil 81 and a period in which the switching of the switching element IGBT is stopped and a current is not passed through the exciting coil 81 are provided. For example, in the high-frequency power supply device 90 having a maximum output of 1 kW, the operation is intermittently performed at 40% or less of the maximum output, that is, 400 W or less. In other words, if it is operated at 200 W, a period for operating at 400 W and a period for not operating are alternately provided to realize 200 W equivalently.
In this case, an inrush current flows every time the high-frequency power supply device 90 is operated intermittently.
As described above, in the high frequency power supply device 90 that does not include the current detection unit 98 and the short circuit unit 99, noise due to inrush current is likely to occur.

  On the other hand, in the first embodiment, as shown in FIG. 3, in the initial stage when the high-frequency power supply device 90 starts operating, the alternating current from the alternating current power source is a path α via the current limiting resistor R0. (See FIG. 3), the current flowing through the smoothing capacitor C0 in which no charge is accumulated can be suppressed. That is, the inrush current is suppressed, thereby suppressing the generation of noise. After the electric charge is accumulated in the smoothing capacitor C0, the TRIAC TR shifts from the OFF state to the ON state, and the alternating current is supplied through the path β (see FIG. 3) via the TRIAC TR. The supply device 90 operates in the same manner as when the current limiting resistor R0 is not provided.

  When the high-frequency power supply device 90 stops operating, the triac TR shifts from the on state to the off state, and the charge accumulated in the capacitor C1 is discharged through the secondary winding of the choke transformer CT. . Therefore, in the initial state where the high-frequency power supply device 90 starts to operate again, the alternating current is supplied to the rectifier 92 through the path α via the current limiting resistor R0. Thereafter, the electric charge is accumulated in the capacitor C1, so that the TRIAC TR shifts from the OFF state to the ON state, and the alternating current is supplied through the path β via the TRIAC TR.

In the first embodiment, the capacitor C1 accumulates electric charge by the current induced in the secondary winding by the current flowing through the primary winding of the choke transformer CT. Therefore, after the high-frequency power supply apparatus 90 starts operating and a predetermined amount of current flows through the primary winding of the choke transformer CT, the triac TR shifts from the off state to the on state. As described above, the transition of the triac TR from the off state to the on state does not need to be controlled from the outside.
Note that the timing of shifting the triac TR from the off state to the on state is set by the capacitance of the capacitor C1 and the like.
In addition, since the triac TR, which is a semiconductor element, is used, the circuit becomes smaller than when the inrush current is suppressed by a coil or a resistor.

[Second Embodiment]
In the first embodiment, in the high frequency power supply device 90, the current limiting resistor R 0 is provided between the noise filter unit 91 and the rectifying unit 92. In the second embodiment, in the high frequency power supply device 90, the current limiting resistor R0 is provided between the rectifying unit 92 and the smoothing unit 95.
Since other configurations are the same as those of the high-frequency power supply apparatus 90 of the first embodiment, description of similar parts is omitted, and different parts are described.

(High-frequency power supply device 90)
FIG. 7 is a diagram illustrating an example of the configuration of the high-frequency power supply apparatus 90 to which the second exemplary embodiment is applied. In the second embodiment, as shown in FIG. 7, in the high frequency power supply device 90 of the first embodiment shown in FIG. 3, the current limiting resistor R <b> 0 is interposed between the rectifying unit 92 and the smoothing unit 95. In addition, the triac TR of the short-circuit portion 99 is changed to the thyristor TH.

  One terminal of the current limiting resistor R0 is connected to one output terminal of the rectifier 92, and the other terminal is connected to one terminal of the primary winding of the choke transformer CT. One terminal of the current limiting resistor R0 is connected to the cathode terminal of the thyristor TH, and the other terminal is connected to the anode terminal of the thyristor TH. One terminal of the capacitor C1 is connected to the gate terminal of the thyristor TH.

The operation of the high-frequency power supply device 90 in the second embodiment will be described.
Before the high-frequency power supply device 90 starts operating, no charge is accumulated in the smoothing capacitor C0. In the initial state where the high-frequency power supply device 90 starts to operate, the direct current rectified by the rectifying unit 92 is supplied to the smoothing unit 95 through the path α passing through the current limiting resistor R0. As a result, charges are accumulated in the smoothing capacitor C0.

  When a current flows through the primary winding of the choke transformer CT of the smoothing unit 95, a current is induced in the secondary winding. This current accumulates charge in the capacitor C1 via the rectifier D1 and the resistor R1. As the voltage between the two terminals of the capacitor C1 increases, the threshold voltage of the thyristor TH decreases. When the threshold voltage of the thyristor TH becomes smaller than the potential difference between both terminals of the current limiting resistor R0, the thyristor TH shifts from the off state to the on state. As a result, the current limiting resistor R0 is short-circuited, and the current supplied from the rectifying unit 92 to the smoothing unit 95 flows through the path β via the on-state thyristor TH.

The thyristor TH in the on state does not shift to the off state unless the potential difference between both terminals of the current limiting resistor R0 is smaller than a value that can maintain the on state. Therefore, the thyristor TH is kept on until the high frequency power supply device 90 is stopped.
That is, the high frequency power supply apparatus 90 of the second embodiment operates according to the timing chart of FIG. 4 described in the first embodiment.
Note that since the current flowing through the current limiting resistor R0 is a direct current, a thyristor TH in which the current flows in one direction may be used.
Further, since the thyristor TH, which is a semiconductor element, is used, the circuit becomes smaller than the case where the inrush current is suppressed by a coil or a resistor.

As described above, in the second embodiment, in the initial state in which the high frequency power supply device 90 is operated, a direct current is supplied through the current limiting resistor R0, so that the inrush flowing into the smoothing capacitor C0 of the smoothing unit 95 Current can be suppressed, and generation of noise is suppressed.
The resistance value of the current limiting resistor R0 is set to be smaller than the resistance value between the anode terminal and the cathode terminal of the thyristor TH in the off state and larger than the resistance value between the anode terminal and the cathode terminal of the thyristor TH in the on state. In the initial state in which the high-frequency power supply device 90 starts operating, it may be set so as not to generate EMI due to the inrush current.

[Third Embodiment]
In the second embodiment, in the high-frequency power supply device 90, the current detection unit 98 is supplied to the capacitor C1 by the current induced in the secondary winding by the current flowing through the primary winding of the choke transformer CT. Accumulated charge. On the other hand, in the third embodiment, in the high-frequency power supply device 90, the current detection unit 98 accumulates electric charge in the capacitor C1 using the current flowing through the resonance circuit 96.
Since other configurations are the same as those of the high-frequency power supply apparatus 90 of the second embodiment, description of similar parts is omitted, and different parts are described.

(High-frequency power supply device 90)
FIG. 8 is a diagram illustrating an example of a configuration of a high-frequency power supply device 90 to which the third embodiment is applied. In the third embodiment, the primary side winding of the transformer TF is inserted into the resonance circuit 96 in the high-frequency power supply apparatus 90 of the second embodiment shown in FIG. And the current detection part 98 of the high frequency electric power supply apparatus 90 of 2nd Embodiment is connected to the secondary winding of the transformer TF instead of the secondary side winding of choke transformer CT. The smoothing unit 95 uses a choke coil CC instead of the primary winding of the choke transformer CT in the second embodiment.

The operation of the high-frequency power supply device 90 in the third embodiment will be described.
Before the high-frequency power supply device 90 starts operating, no charge is accumulated in the smoothing capacitor C0. In the initial state where the high-frequency power supply device 90 starts to operate, the direct current rectified by the rectifying unit 92 is supplied to the smoothing unit 95 through the path α passing through the current limiting resistor R0. As a result, charges are accumulated in the smoothing capacitor C0.
The current Ih flowing through the exciting coil 81 (inductance Lk) is an alternating current that changes positively and negatively as shown in FIG. When this current Ih flows through the primary winding of the transformer TF, an alternating current is induced in the secondary winding of the transformer TF. This alternating current is rectified by the rectifier D1, and charges are accumulated in the capacitor C1 via the resistor R. Similar to the second embodiment, the voltage between both terminals of the capacitor C1 increases, and the threshold voltage of the thyristor TH decreases. When the threshold voltage of the thyristor TH becomes smaller than the potential difference between both terminals of the current limiting resistor R0, the thyristor TH shifts from the off state to the on state. As a result, the current limiting resistor R0 is short-circuited, and the current supplied from the rectifying unit 92 to the smoothing unit 95 flows through the path β via the thyristor TH.
That is, the high frequency power supply apparatus 90 in the third embodiment operates in accordance with the timing chart of FIG. 4 described in the first embodiment.
Since the current flowing through the current limiting resistor R0 is a direct current, it may be a thyristor TH in which the current flows in one direction as in the second embodiment.

  As described above, also in the third embodiment, in the initial state in which the high-frequency power supply device 90 starts operating and the smoothing capacitor C0 starts to accumulate electric charge, the direct current is passed through the current limiting resistor R0. Since it is supplied, the inrush current flowing through the smoothing capacitor C0 of the smoothing unit 95 can be suppressed, and the generation of noise is suppressed.

  In the first to third embodiments, the exciting coil 81 (inductance Lk) is provided outside the high-frequency power supply device 90, but may be provided inside.

DESCRIPTION OF SYMBOLS 1Y, 1M, 1C, 1K ... Image forming unit, 11 ... Photosensitive drum, 12 ... Charger, 13 ... Laser exposure device, 14 ... Developer, 15 ... Intermediate transfer belt, 16 ... Primary transfer roll, 17 ... Drum cleaner 20 ... secondary transfer unit, 40 ... control unit, 60 ... fixing device, 61 ... fixing belt, 62 ... pressure roll, 63 ... belt guide member, 64 ... pressure pad, 65 ... holder, 80 ... induction heating unit, DESCRIPTION OF SYMBOLS 81 ... Excitation coil, 82 ... Coil support member, 90 ... High frequency electric power supply apparatus, 91 ... Noise filter part, 92 ... Rectification part, 93 ... Current detection part, 94 ... Voltage detection part, 95 ... Smoothing part, 96 ... Resonance circuit , 97: Drive unit, 98: Current detection unit, 99: Short circuit unit, 100: Image forming apparatus, C0: Smoothing capacitor, CC: Choke coil, Ck: Resonance capacitor, CT: Choke transformer R0 ... current limiting resistor, TF ... transformer, TH ... thyristors, TR ... triac

Claims (5)

A resonance circuit comprising a capacitor and connected in parallel with an externally provided coil;
A switching element connected in series to one terminal of the resonant circuit;
A smoothing unit connected in series to the other terminal of the resonant circuit;
A rectifying unit connected to the smoothing unit;
A current detection unit that detects a current flowing through either the resonance circuit or the smoothing unit;
A current limiting resistor for limiting the current supplied to the smoothing unit;
When connected in parallel with the current limiting resistor and the current detecting unit detects a predetermined current value, the current limiting resistor shifts from the off state to the on state, and the current limiting resistor is connected between both terminals of the current limiting resistor. A high-frequency power supply device including a short-circuit unit set to a small resistance value.   The high-frequency power supply apparatus according to claim 1, wherein the current limiting resistor is provided in a path through which an alternating current supplied to the rectifying unit flows, and the short-circuit unit includes a triac.   The high-frequency power supply apparatus according to claim 1, wherein the current limiting resistor is provided between the rectifying unit and the smoothing unit, and the short-circuit unit includes a thyristor. A fixing belt heated by electromagnetic induction;
An exciting coil disposed opposite to the fixing belt and generating a magnetic field for electromagnetic induction;
A resonance circuit including a capacitor and connected in parallel to the excitation coil; a switching element connected in series to one terminal of the resonance circuit; and a smoothing unit connected in series to the other terminal of the resonance circuit A rectifying unit connected to the smoothing unit, a current detection unit that detects a current flowing through either the resonance circuit or the smoothing unit, and a current limiting resistor that limits a current supplied to the smoothing unit When the current detection unit detects a predetermined current value connected in parallel with the current limiting resistor, the current limiting resistor shifts from the OFF state to the ON state, and the current limiting resistor is connected between both terminals of the current limiting resistor. A high frequency power supply unit with a short circuit set to a smaller resistance value;
A pressure member pressed against the outside of the fixing belt;
A fixing device comprising: An image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the image forming means to a recording material;
A resonance belt comprising a fixing belt heated by electromagnetic induction, an excitation coil disposed opposite to the fixing belt and generating a magnetic field for electromagnetic induction, and a capacitor connected in parallel with the excitation coil A circuit, a switching element connected in series to one terminal of the resonant circuit, a smoothing unit connected in series to the other terminal of the resonant circuit, a rectifier connected to the smoothing unit, and the resonant circuit or A current detection unit that detects a current flowing through one of the smoothing units, a current limiting resistor that limits a current supplied to the smoothing unit, and a parallel connection to the current limiting resistor. When a predetermined current value is detected, a transition is made from an off state to an on state, and a high-circuit portion having a short-circuit portion that sets a resistance value smaller than the current limiting resistor between both terminals of the current limiting resistor. An image forming system comprising: a wave power supply unit; and a pressing member pressed against the outside of the fixing belt, and a fixing unit that fixes the toner image transferred to the recording material to the recording material. apparatus.

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