JP2010002641A - Fixing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption by supplying power obtained at a high power conversion efficiency to an electromagnetic induction coil. <P>SOLUTION: By setting the frequency of output power in a high-frequency power supply circuit 47 to fixed frequency at which power conversion efficiency is 80% or higher, and changing supply voltage of the high-frequency power supply circuit 47, based on surface temperature of a fixing roller 41 detected by a temperature sensor 49, the output power in the high-frequency power supply circuit 47 is changed so as to vary heating temperature of the fixing roller 41 by the electromagnetic induction coil 43b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electromagnetic induction heating type fixing device and an image forming apparatus including the same.

A fixing device provided in an image forming apparatus such as a printer normally forms a toner image by heating the fixing roller with a heat source while pressing the fixing roller and the pressure roller to secure a fixing nip between the two rollers. By passing the printed paper through the fixing nip, the toner image is heated and pressurized to be fixed on the paper.
Conventionally, many halogen heaters have been adopted as the heat source of the fixing device, but in recent years, an electromagnetic induction heating type that can save energy as compared with the halogen heater has attracted attention.

  In an electromagnetic induction heating type fixing device, a fixing roller having an electromagnetic induction heating layer, a pressure roller that is pressed against the fixing roller to secure a fixing nip between the fixing roller, and an electromagnetic induction heating layer of the fixing roller generate heat. And an electromagnetic induction coil for generating a magnetic flux for generating the magnetic flux. The electromagnetic induction coil is supplied with high-frequency power output from a high-frequency power source that is an inverter circuit.

Patent Document 1 discloses a configuration in which a high frequency power source that supplies electric power of a fixed frequency to an electromagnetic induction coil is controlled to be turned on / off based on the surface temperature of the fixing roller, and the temperature of the fixing roller is higher than a set temperature. When the temperature is low, the high frequency power supply is turned on to output high frequency power to the electromagnetic induction coil to heat the fixing roller. When the temperature of the fixing roller is higher than the set temperature, the high frequency power supply is turned off. By doing so, the supply of high-frequency power to the electromagnetic induction coil is stopped and heating of the fixing roller is stopped.
JP 2007-124370 A

  As disclosed in Patent Document 1, in the configuration in which the temperature of the fixing roller is adjusted by on / off control of a high-frequency power source that generates power supplied to the electromagnetic induction coil, when the heat capacity of the fixing roller is large, Since the fixing roller is gradually heated when the high-frequency power supply is turned on, the surface of the fixing roller can be accurately heated to a predetermined temperature, but there is a problem that the heating time until the predetermined temperature is reached becomes long. In contrast, when the heat capacity of the fixing roller is small, the heating time until the predetermined temperature is reached can be shortened, but the fixing roller is locally heated and reaches the predetermined temperature on the surface of the fixing roller. There is a problem that temperature unevenness occurs where a portion and a portion that does not reach occur, and a fixing defect occurs in a portion where the temperature is low.

Further, when the power consumption in the electromagnetic induction coil is large, the power greatly changes due to the on / off control of the high frequency power supply circuit, so that the influence on other power supply portions in the image forming apparatus becomes large.
When the on / off control is performed with the frequency of the power generated by the high-frequency power supply circuit being changed, if the output power is low, the frequency is changed to reduce the power conversion efficiency and the consumption. There is a possibility that electric power cannot be reduced sufficiently.

  The present invention has been made in view of the above-described problems, and is an electromagnetic induction heating type fixing device capable of reducing power consumption by supplying electric power obtained by high power conversion efficiency to an electromagnetic induction coil. Another object of the present invention is to provide an image forming apparatus including the same.

  In order to achieve the above object, a fixing device according to the present invention secures a fixing nip between a first rotating body having an electromagnetic induction heating layer and the first rotating body by pressing the first rotating body. An unfixed image, comprising: a second rotating body; an electromagnetic induction coil that generates a magnetic flux that generates heat from the electromagnetic induction heat generating layer; and a high-frequency power supply unit that generates high-frequency power having a fixed frequency and outputs the high-frequency power to the electromagnetic induction coil. A fixing device that thermally fixes an unfixed image on the recording sheet to the sheet while the recording sheet on which the recording sheet is formed passes through the fixing nip, and changes the supply voltage to the high-frequency power supply unit A supply voltage variable unit that varies the output power from the power supply unit, and a voltage control unit that controls the supply voltage variable unit based on the surface temperature of the first rotating body.

  An image forming apparatus according to the present invention is an image forming apparatus that thermally fixes an unfixed image formed on a sheet by a fixing unit, and includes the fixing device as the fixing unit.

  In the fixing device of the present invention, the frequency of the output power in the high frequency power supply unit is set to a fixed frequency, and the supply voltage to the high frequency power supply unit is changed to change the output power in the high frequency power supply unit. Since the heating temperature of the rotating body such as the fixing roller is changed, there is no possibility that the power conversion efficiency in the high frequency power supply unit is lowered, and the power consumption can be reduced.

  Preferably, the fixed frequency of the high frequency power supply unit does not include a resonance frequency of a resonance circuit formed by the high frequency power supply unit and the electromagnetic induction coil, and is set to a frequency within a predetermined range before and after the resonance frequency. It is characterized by that. As a result, a fixed frequency at which the power conversion efficiency is 80% or more can be obtained, power consumption can be reliably reduced, and control to a predetermined fixing temperature can be easily performed.

Preferably, the voltage control unit sets the surface temperature of the first rotating body to a predetermined temperature when the surface temperature of the first rotating body is within a predetermined temperature range with respect to a preset fixing temperature. The supply voltage variable unit is controlled so that a supply voltage required for changing only the temperature is output. Thereby, it is possible to reliably control to a predetermined fixing temperature.
Preferably, when the surface temperature of the first rotating body is lower than the predetermined temperature range, the voltage control unit is configured so that the supply voltage becomes a maximum voltage that can be varied in the supply voltage variable unit. And controlling the supply voltage variable section. Thereby, it is possible to quickly control to a predetermined fixing temperature.

  Preferably, when the surface temperature of the first rotating body is higher than the predetermined temperature range, the voltage control unit is set to the supply voltage that stops the output of the high-frequency power supply unit. The supply voltage variable unit is controlled. This also enables quick control to a predetermined fixing temperature.

Hereinafter, embodiments of a fixing device and an image forming apparatus according to the present invention will be described using a tandem color digital printer (hereinafter simply referred to as “printer”) as an example.
FIG. 1 is a diagram illustrating the overall configuration of the printer 1.
As shown in the figure, the printer 1 forms an image by a well-known electrophotographic system, and includes an image processing unit 10, a belt conveying unit 20, a feeding unit 30, a fixing device 40, and a main control. When the main control unit 50 is connected to a network (for example, a LAN) and receives a print (print) job execution instruction from an external terminal device (not shown), the yellow color is generated based on the instruction. (Y), magenta (M), cyan (C), and black (K) color image formation is executed.

  The image processing unit 10 includes image forming units 10Y, 10M, 10C, and 10K corresponding to the colors Y, M, C, and K, respectively. The image forming unit 10Y includes a photosensitive drum 11Y and a charger 12Y, an exposure unit 13Y, a developing unit 14Y, a primary transfer roller 15Y, and a cleaner for cleaning the surface of the photosensitive drum 11Y. A Y-color toner image is formed on the photosensitive drum 11Y through known charging, exposure, and development processes. This configuration is the same for the other image forming units 10M, 10C, and 10K, and corresponding color toner images are formed on the photosensitive drums 11M, 11C, and 11K.

The feeding unit 30 includes a paper feeding cassette 31 that stores paper S as a recording sheet. When a print job is executed, the paper feeding unit 30 feeds the paper S from the paper feeding cassette 31 toward the conveyance path 35 one by one to convey the belt. Send to part 20.
The belt conveyance unit 20 includes a conveyance belt 21 that circulates in the direction of the arrow X, and transfers the photosensitive drums 11Y, 11M, 11C, and 11K in a state where the sheet S from the feeding unit 30 is in close contact with the conveyance belt 21. Convey sequentially to the position. When the sheet S passes through each transfer position, the photosensitive member receives an action of electrostatic force due to an electric field generated between the transfer rollers 15Y, 15M, 15C, and 15K and the photosensitive drums 11Y, 11M, 11C, and 11K at each transfer position. The toner images on the drums 11Y, 11M, 11C, and 11K are multiple-transferred onto the paper S. At this time, the image forming operation for each color is executed at different timings so as to be transferred to the same position on the paper S. After the toner images of the respective colors are transferred, the paper S is separated from the transport belt 21 and sent to the fixing unit 40.

The fixing device 40 is based on an electromagnetic induction heating method, and heats and presses the paper S sent from the transport belt 21 to fix the toner images of the respective colors on the paper S. The sheet S after fixing is discharged onto the discharge tray 39.
The printer 1 is provided with an operation unit 60 into which various data are input by an operator's operation, and a display panel for displaying various information is provided on the operation unit 60. Various data input to the operation unit 60 are sent to the main control unit 50. The main control unit 50 stores various data in the storage unit 51.

  FIG. 2 is a cross-sectional view showing the configuration of the fixing device 40. The fixing device 40 includes a fixing roller 41 that is a first rotating body, a pressure roller 42 that is a second rotating body, and a magnetic flux generator 43. The fixing roller 41 and the pressure roller 42 are rotatably supported at both ends in the axial direction by a frame (not shown) via a bearing member, and the pressure roller 42 is driven by a driving force from a driving motor (not shown). It is rotationally driven in the direction of arrow B. As the pressure roller 42 rotates, the fixing roller 41 is driven to rotate in the direction of arrow A.

The fixing roller 41 includes a roller main body 41a in which a heat insulating layer 41c is formed around a cored bar 41b, and a sleeve 41d fitted on the outer periphery of the roller main body 41a.
The sleeve 41d is formed by laminating a magnetic shunt alloy layer 41e, an electromagnetic induction heating layer 41f, an elastic layer 41g, and a release layer 41h in this order from the heat insulating layer 41c side.
The magnetic shunt alloy layer 41e is made of a magnetic metal layer such as an alloy of nickel and iron, has a thickness of about 30 μm, and has a characteristic of changing to a non-magnetic material when the temperature exceeds a predetermined temperature (Curie temperature).

The electromagnetic induction heat generating layer 41 f is made of nickel or the like having a thickness of about 10 μm, and generates heat by the magnetic flux generated from the magnetic flux generator 43. The material of the electromagnetic induction heat generating layer 41f is not limited to nickel as long as it generates electromagnetic induction heat, and for example, iron or copper can also be used.
The elastic layer 41 g is an elastic member made of heat-resistant silicon rubber having a thickness of about 200 μm, and plays a role of improving the adhesion between the sheet S and the surface of the fixing roller 41.

The outermost release layer 41 h is made of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) having a thickness of about 20 μm and plays a role of improving the release property of the surface of the fixing roller 41.
The pressure roller 42 is formed by laminating a release layer 42c via an elastic layer 42b around a long cylindrical cored bar 42a made of, for example, copper or the like as a low resistance conductive material. The fixing unit 41 is pressed against the fixing roller 41 by the pressing means including the fixing roller 44 to secure the fixing nip 44.

The core metal 42a of the pressure roller 42 is made of aluminum or the like, the elastic layer 42b is made of silicon sponge rubber or the like, and the release layer 42c is made of PFA or PTFE (polytetrafluoroethylene) coat or the like.
The magnetic flux generator 43 includes a coil bobbin 43 a, an electromagnetic induction coil 43 b, a main core 43 c, a hem core 43 d, and a cover 43 f, and is extended along the axial direction of the fixing roller 41.

  The coil bobbin 43a provided in the magnetic flux generation unit 43 is a long member extending in the roller axis direction, and the surface facing the surface of the fixing roller 41 is curved in an arc shape along the circumferential direction of the fixing roller 41. Both ends in the longitudinal direction are fixed to a frame (not shown) or the like so that a predetermined interval, for example, an interval of 3 mm, is opened between the fixing roller 41 and the peripheral surface. On the surface of the coil bobbin 43a opposite to the fixing roller 41 side, an electromagnetic induction coil 43b, a main core 43c, and a hem core 43d are arranged and covered with a cover 43f.

  The electromagnetic induction coil 43b is formed by winding a conducting wire around the coil bobbin 43a so as to extend long along the roller axis direction and to have a circular cross section. The longitudinal length of the electromagnetic induction coil 43b is slightly longer than the axial length of the fixing roller 41. The electromagnetic induction coil 43b generates magnetic flux for generating heat at the electromagnetic induction heat generating layer of the fixing roller 41 when high frequency power is supplied.

  The main core 43c and the bottom core 43d are made of ferrite having high magnetic permeability, and guide the magnetic flux generated from the electromagnetic induction coil 43b to the fixing roller 41. The magnetic flux guided to the fixing roller 41 passes through a portion of the electromagnetic induction heat generating layer of the fixing roller 41 facing the magnetic flux generating portion 43, and an eddy current is generated in the electromagnetic induction heat generating layer to generate heat in the electromagnetic induction heat generating layer. Let The size, shape, and the like of the electromagnetic induction coil 43b, the main core 43c, and the bottom core 43d are set so that the amount of generated heat is substantially uniform at any position in the roller axis direction.

FIG. 3 is a block diagram illustrating a configuration of a control system in the fixing device 40. The electromagnetic induction coil 43b is supplied with output power from the high frequency power supply circuit 47. The AC power supplied from the commercial power supply is rectified by the rectifier circuit 45 and supplied to the high frequency power supply circuit 47. The DC power that is set to a predetermined voltage by the voltage variable circuit 46 is input.
The high frequency power supply circuit 47 converts the DC power of the voltage (supply voltage) output from the supply voltage variable circuit 46 into high frequency power fixed at a predetermined frequency, and outputs it to the electromagnetic induction coil 43b. The electromagnetic induction coil 43 b disposed to face the fixing roller 41 is excited by high frequency power having a fixed frequency supplied from the high frequency power supply circuit 47. The electromagnetic induction coil 43b generates a magnetic flux when excited, and the electromagnetic induction heat generating layer 41f of the fixing roller 41 is heated by the generated magnetic flux.

In the vicinity of the fixing roller 41, a temperature sensor 49 that detects the temperature of the surface of the fixing roller 41 is provided. The output of the temperature sensor 49 is input to a voltage control unit 48 that controls the supply voltage variable circuit 46.
The voltage control unit 48 controls the supply voltage variable circuit 46 based on the output of the temperature sensor 49 so that the high-frequency power circuit 47 can obtain output power with high conversion efficiency, and is supplied to the high-frequency power circuit 47. Change the voltage.

The supply voltage variable circuit 46 includes, for example, a pulse width modulation circuit (PWM) that performs pulse width modulation on the input voltage, and an averaging circuit that averages and outputs the voltage modulated by the pulse width modulation circuit. The pulse width in the pulse width modulation circuit is changed by an instruction from the voltage control unit 48, and thereby the supply voltage output from the supply voltage variable circuit 46 changes.
The supply voltage variable circuit 46 is not limited to the above-described configuration, and includes a variable resistor. The input voltage is varied and output by changing the resistance value of the variable resistor according to an instruction from the voltage control unit 48. A simple configuration may be used.

The fixed frequency of the high frequency power supplied to the electromagnetic induction coil 43b in the high frequency power supply circuit 47 provided in the fixing device 40 is set to a predetermined value at the time of factory shipment, maintenance, or the like. Hereinafter, this fixed frequency will be described.
As shown in FIG. 4, the high frequency power supply circuit 47 usually has a characteristic that the output power value changes as the frequency of the output high frequency power changes. In FIG. 4, the output power value changes in the range of 800 to 1400 W by changing the frequency in the range of 45 to 60 kHz.

  As shown in FIG. 5, the output power from the high frequency power supply circuit 47 changes as the supply voltage to the high frequency power supply circuit 47 changes, and the output power value increases as the supply voltage increases in a specific frequency range. In FIG. 5, when the frequency of the output power is 45 kHz, the output power value of the high frequency power supply circuit 47 can be changed in the range of 800 to 1400 W by changing the supply voltage.

Furthermore, as shown in FIG. 6, the power conversion efficiency of the high-frequency power supply circuit 47 has a characteristic that it significantly decreases as the output power value decreases.
Therefore, the power conversion efficiency in the high-frequency power supply circuit 47 is high, and the output power with high power conversion efficiency is fixed by fixing the frequency so that the output power continuously changes greatly when the supply voltage changes greatly. By setting the fixed frequency in this way, it is possible to easily control to a predetermined output power by changing the supply voltage to the high frequency power supply circuit 47.

  Since the high frequency power supply circuit 47 constitutes a resonance circuit together with the electromagnetic induction coil, the output power greatly changes with respect to the change of the supply voltage at the resonance frequency at which the impedance is the lowest. It becomes difficult to control the power value. For this reason, it is not desirable to make the fixed frequency in the high frequency power supply circuit 47 coincide with the resonance frequency, and it is desirable to set it to a predetermined frequency before and after the resonance frequency. In the high-frequency power supply circuit having the frequency-power characteristics shown in FIG. 5, by fixing the frequency to 45 kHz, which is a frequency slightly higher than the resonance frequency, output power in the range of 800 to 1400 W can be obtained by changing the supply voltage. it can.

FIG. 7 is a graph showing the relationship between the supply voltage and the output power in the high frequency power supply circuit 47. In the high frequency power supply circuit 47, the output power P (W) and the supply voltage V (v) have a relationship of P = V ² / Z (where Z is an impedance (Ω)). The output power characteristic is a characteristic having a curve as shown in FIG. With high output power, the amount of change in output power with respect to the amount of change in supply voltage is large, whereas with low output power, the amount of change in output power with respect to the amount of change in supply voltage is small.

  From such characteristics of the high-frequency power supply circuit 47, when the surface temperature of the fixing roller 41 is within a predetermined temperature range (for example, a range of 10 ° C.) with respect to the target fixing temperature, the supply voltage in that temperature range The surface temperature of the fixing roller 41 is easily set to a predetermined fixing temperature by obtaining the relationship between the output power and the output power in advance, and controlling the supply voltage so as to obtain a desired output power based on the relationship. Can be controlled.

  From the above, the frequency of the output power in the high-frequency power supply circuit 47 is a frequency at which the power conversion efficiency is 80% or more, and does not coincide with the resonance frequency, and is fixed to a frequency around the resonance frequency. The output power with high power conversion efficiency can be supplied to the electromagnetic induction coil 43b. Further, when the surface temperature of the fixing roller 41 is within a predetermined temperature range with respect to the target fixing temperature, the high frequency necessary for eliminating the difference between the fixing temperature and the surface temperature of the fixing roller 41. By setting the supply voltage for obtaining the output power of the power supply circuit 47 based on the supply voltage conversion coefficient A obtained in advance, the surface temperature of the fixing roller 41 can be easily adjusted accurately to a predetermined fixing temperature. Can do.

  The supply voltage coefficient A is a change in output power for changing the surface temperature of the fixing roller 41 by, for example, 1 ° C. when the surface temperature of the fixing roller 41 is within a predetermined temperature range with respect to the target fixing temperature. Therefore, it is necessary to eliminate the temperature difference by multiplying the temperature difference between the current temperature of the surface of the fixing roller 41 and the predetermined fixing temperature by the supply voltage coefficient A. A change amount of the supply voltage that can be a change amount of the output power can be obtained. The supply voltage coefficient A is set based on the relationship between the supply voltage and the output power, the heat capacity of the fixing roller 41, the amount of heat generated by the coil, the roller rotation speed, and the like.

  FIG. 8 is a flowchart for explaining processing for setting a fixed frequency of output power in the high-frequency power supply circuit 47. This process is executed by, for example, a main control unit 50 (see FIG. 1) provided in the printer, by an operation by an operator at the time of assembly work or maintenance of the production line. In the storage unit 51 connected to the main control unit, for example, information indicating the resonance frequency of the high frequency power supply circuit 47 is stored. This resonance frequency is obtained in advance based on the frequency-power characteristics in the high-frequency power supply circuit 47. The operator can select a candidate frequency and input it to the main control unit 50 by operating the operation unit 60.

  When the main control unit 50 receives an input of a candidate frequency (see step S1 in FIG. 8, the same applies hereinafter), the main control unit 50 determines whether or not the input frequency f matches the resonance frequency (step S2). When the input frequency f matches the resonance frequency (“NO” in step S2), the display panel provided in the operation unit 60 displays that it is necessary to input a candidate frequency again. (Step S3). Thereafter, when an input of a new frequency f from the operator is received (step S1), it is determined whether or not the re-input frequency f matches the resonance frequency (step S2).

  Thereafter, steps S1 to S3 are repeated until an input of a frequency f that does not coincide with the resonance frequency is received. When an input of a frequency f that does not match the resonance frequency is received, the input frequency f is set as a fixed frequency of the output power in the high frequency power supply circuit 47 (step S4). The high frequency power supply circuit 47 is fixed at a frequency set by an instruction from the main control unit 50.

Further, the supply voltage conversion coefficient A for the set fixed frequency f is set based on the relationship between the supply voltage of the high frequency power supply circuit 47 and the output power, the heat capacity of the fixing roller 41, the coil heat generation amount, the roller rotation speed, and the like. (Step S5). The set supply voltage conversion coefficient A is stored in the storage unit 51.
For example, a reference table as shown in FIG. 10 is used for setting the supply voltage conversion coefficient A. In this reference table, the supply voltage conversion coefficient A is set for each frequency that is a candidate for a fixed frequency in the high frequency power supply circuit 47 based on the printer model and the type of the fixing device, and is stored in the storage unit 51. In the reference table shown in FIG. 10, in the case of a high-speed printer equipped with a high-speed fixing device, for example, a value of “15” is set as the supply voltage conversion coefficient A so that the fixing roller 41 can be heated quickly. Is set. In the case of a medium-speed printer equipped with a medium-speed fixing device, the same value (“15”) as that of a high-speed printer is set as the supply voltage conversion coefficient A, and the medium-speed fixing device is installed. In the case of a low-speed printer, a lower value (for example, “10”) is set as the supply voltage conversion coefficient A because it does not require a printing speed like a high-speed machine and a medium-speed machine. .

By using such a reference table, for example, regardless of whether the medium speed fixing device is mounted on the medium speed device or the low speed device, the corresponding supply voltage conversion coefficient A can be set, and one fixing device can be set. The degree of freedom that it can be installed in different models will increase, and productivity will improve.
The supply voltage conversion coefficient A is set based on a formula set based on the supply voltage-output power characteristics, the printer model conditions, and the fixing device type without using such a reference table. May be.

  FIG. 9 is a flowchart showing the control contents in the voltage controller 48 provided in the fixing device 40. When a print job is started in the printer, the voltage control unit 48 starts controlling the supply voltage to the high frequency power supply circuit 47 whose frequency is fixed. The voltage control unit 48 first sets initial values (A, To, Vo) for power control in the high frequency power supply circuit 47 (see step S11 in FIG. 9, the same applies hereinafter).

  Specifically, the supply voltage conversion coefficient A is read from the storage unit 51 and set. In addition, an appropriate fixing temperature To for fixing the toner image on the recording sheet by the fixing roller 41 of the fixing device 40 is set by an instruction from the main control unit 50. The fixing temperature To is changed for each type of recording sheet. For example, a table of the fixing temperature To set for each type of recording sheet is stored in the storage unit 51 in advance, and the main control unit 50 However, based on the input data regarding the type of recording sheet and the table stored in the storage unit 51, the fixing temperature To is selected and the voltage control unit 48 is instructed. The voltage control unit 48 sets the instructed fixing temperature To as an initial set value.

When initial values (A, To, Vo) for power control in the high frequency power supply circuit 47 are set, the voltage control unit 48 obtains the surface temperature data of the fixing roller 41 based on the output of the temperature sensor 49. Collected and the surface temperature Ta of the fixing roller 41 is detected (step S12).
Next, it is determined whether the difference (temperature difference) obtained by subtracting the detected temperature Ta from the fixing temperature To is greater than 10 ° C. (step S13). When it is determined that the difference is greater than 10 ° C. (“YES” in step S13), the supply voltage is set so that the supply voltage Vo in the supply voltage variable circuit 46 becomes the maximum value that can be changed in the supply voltage variable circuit 46. The variable circuit 46 is controlled (step S14), and the process returns to step S12.

  In step S14, the supply voltage Vo to the high-frequency power supply circuit 47 is set to the maximum value that can be changed by the supply voltage variable circuit 46, whereby the high-frequency power supply circuit 47 sets the maximum output power that can be varied at the fixed frequency f. The heat generation amount of the electromagnetic induction heat generating layer of the fixing roller 41 by the induction coil 43b is maximized. As a result, the surface temperature of the fixing roller 41 rises quickly.

On the other hand, if it is determined that the difference obtained by subtracting the fixing temperature To from the detected temperature Ta is greater than 10 ° C. (“YES” in step S15), the supply voltage Vo is set to 0 V in the supply voltage variable circuit 46. The variable circuit 46 is controlled (step S16), and the process returns to step S12.
In step S16, when the supply voltage Vo becomes 0V, the high frequency power supply circuit 47 is in an output stopped state, and the heat generation of the electromagnetic induction heat generating layer 41f of the fixing roller 41 by the electromagnetic induction coil 43b is stopped. As a result, the surface temperature of the fixing roller 41 quickly decreases.

In the case of “NO” in step S15, that is, when (To−10) ≦ Ta ≦ (To + 10) is satisfied, the voltage V1 for setting the output power of the high-frequency power circuit 47 corresponding to the target fixing temperature To. Is set to the supply voltage Vo (step S17).
In this state, the surface temperature of the fixing roller 41 is detected by the temperature sensor 49, and is necessary for eliminating the temperature difference between the current surface temperature Ta of the fixing roller 41 and the target fixing temperature To. The voltage fluctuation amount V is calculated using the initially set supply voltage conversion coefficient A. The voltage fluctuation amount V is calculated by (To−Ta) × A (step S18). Then, the calculated voltage fluctuation amount V is added to the supply voltage Vo (= V1), the calculation result (Vo + V) is set to a new supply voltage Vo (step S19), and the newly set supply voltage Vo is set. Thus, the supply voltage variable circuit 46 is controlled.

  The supply voltage variable circuit 46 outputs the supply voltage Vo calculated using the supply voltage conversion coefficient A to the high frequency power supply circuit 47. Thereby, the high frequency power supply circuit 47 supplies the electromagnetic induction coil 43b with electric power necessary for eliminating the temperature difference between the detected temperature Ta on the surface of the fixing roller 41 and the fixing temperature To. As a result, the surface temperature Ta of the fixing roller 41 is induction-heated so as to become the fixing temperature To.

  In step S18, for example, when the detected temperature Ta is higher than the fixing temperature To and 0> (To−Ta), the supply voltage Vo is calculated by (To−Ta) × A. The voltage fluctuation amount V is decreased. Then, the closer to the target fixing temperature To, the smaller the amount of decrease in the voltage fluctuation amount V, so that the surface temperature Ta of the fixing roller 41 can be gradually lowered.

On the other hand, when the detection temperature Ta is lower than the fixing temperature To and (To−Ta)> 0, the supply voltage Vo is a voltage fluctuation calculated by (To−Ta) × A. Increased by the amount V. Then, the closer to the target fixing temperature To, the smaller the increase amount of the voltage fluctuation amount V, so that the surface temperature Ta of the fixing roller 41 can be gradually increased.
Therefore, the hunting phenomenon can be suppressed and accurately controlled to the target fixing temperature To with the surface temperature Ta of the fixing roller 41.

The processes in steps S12 to S19 are repeated until all the fixing processes by the fixing device 40 in the print job are completed (step S20).
In this way, when the absolute value of the temperature difference between the detected temperature Ta and the fixing temperature To exceeds 10 ° C., the fixing roller so that the absolute value of the difference between the detected temperature Ta and the fixing temperature To is within 10 ° C. If the absolute value of the temperature difference between the detected temperature Ta and the fixing temperature To falls within 10 ° C., the surface voltage 41 is set to the supply voltage calculated based on the supply voltage conversion coefficient A. Therefore, the surface temperature of the fixing roller 41 can be controlled to a predetermined fixing temperature reliably and accurately.

  In the fixing device 40 according to the present invention, the frequency of the output power in the high-frequency power supply circuit 47 is fixed to a frequency at which the power conversion efficiency is 80% or more, and the supply voltage of the high-frequency power supply circuit 47 is changed. Since the heating power of the fixing roller 41 by the electromagnetic induction coil 43b is changed by changing the output power in the circuit 47, the output power obtained by high power conversion efficiency in the high frequency power supply circuit 47 is supplied to the electromagnetic induction coil 43b. Can be supplied. Therefore, power consumption can be reduced.

In the above-described embodiment, the fixing roller having the electromagnetic induction heat generating layer is used as the first rotating body. However, the present invention is not limited to such a configuration, and the fixing belt having the electromagnetic induction heat generating layer is used. May be used. Further, although the pressure roller is used as the second rotating body, the configuration is not limited to such a configuration, and a pressure belt may be used.
The image forming apparatus to which the fixing device according to the present invention is applied is not limited to a tandem color digital printer, and may be a color image forming apparatus or a monochrome image forming apparatus. It can also be applied to (Multiple Function Peripheral) devices.

  The present invention can be applied to an electromagnetic induction heating type fixing device, and power consumption can be reduced by supplying electric power obtained by high power conversion efficiency to an electromagnetic induction coil.

1 is a diagram illustrating an overall configuration of a printer equipped with a fixing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a configuration of a fixing device according to an embodiment of the present invention arranged in the printer. It is a block diagram which shows the structure of the control system of the electromagnetic induction coil in the fixing device. It is a graph which shows the frequency-output power characteristic of the high frequency power supply circuit which supplies high frequency output power to an electromagnetic induction coil. It is a graph which shows the frequency-output electric power characteristic in the case where the supply voltage in the high frequency power supply circuit is high and low. It is a graph which shows the output power-conversion efficiency characteristic in the high frequency power supply circuit. It is a graph which shows the supply voltage-output power characteristic in the high frequency power supply circuit. It is a flowchart which shows the setting process of the fixed frequency of the output power in the high frequency power supply circuit. 6 is a flowchart illustrating control in a voltage control unit provided in the fixing device. It is an example of the reference table for setting a supply voltage conversion coefficient.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 40 Fixing part 41 Fixing roller 41a Roller body 41b Core metal 41c Elastic layer 41d Sleeve 41f Electromagnetic induction heating layer 42 Pressure roller 42a Core metal 42b Elastic layer 42c Release layer 43 Magnetic flux generation part 43b Electromagnetic induction coil 44 Fixing nip 45 Rectifier circuit 46 Supply voltage variable circuit 47 High frequency power supply circuit 48 Voltage control unit 49 Temperature sensor 50 Main control unit 51 Storage unit

Claims (6)

A first rotating body having an electromagnetic induction heating layer;
A second rotating body that presses the first rotating body and secures a fixing nip with the first rotating body;
An electromagnetic induction coil that generates magnetic flux that generates heat from the electromagnetic induction heating layer;
A high-frequency power supply unit that generates high-frequency power of a fixed frequency and outputs it to the electromagnetic induction coil,
A fixing device that thermally fixes an unfixed image on the recording sheet to the sheet while the recording sheet on which the unfixed image is formed passes through the fixing nip,
A supply voltage variable unit that changes a supply voltage to the high frequency power supply unit to vary output power from the high frequency power supply unit;
A voltage control unit for controlling the supply voltage variable unit based on a surface temperature of the first rotating body;
A fixing device comprising:   The fixed frequency of the high frequency power supply unit does not include a resonance frequency of a resonance circuit formed by the high frequency power supply unit and the electromagnetic induction coil, and is set to a frequency within a predetermined range before and after the resonance frequency. The fixing device according to claim 1.   The voltage control unit changes the surface temperature of the first rotating body by a predetermined temperature when the surface temperature of the first rotating body is in a predetermined temperature range with respect to a preset fixing temperature. 3. The fixing device according to claim 1, wherein the supply voltage variable unit is controlled so that a supply voltage required for the output is output.   When the surface temperature of the first rotating body is lower than the predetermined temperature range, the voltage control unit supplies the supply voltage so that the supply voltage becomes a maximum voltage that can be varied in the supply voltage variable unit. The fixing device according to claim 3, wherein the voltage variable unit is controlled.   When the surface temperature of the first rotating body is higher than the predetermined temperature range, the voltage control unit is configured to supply the supply voltage so that the supply voltage is set to stop the output of the high-frequency power supply unit. The fixing device according to claim 3, wherein the fixing unit is controlled. An image forming apparatus for thermally fixing an unfixed image formed on a sheet by a fixing unit,
An image forming apparatus comprising the fixing device according to claim 1 as the fixing unit.

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