JP2005284093A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for reducing unevenness in the temperature inside a fixing part. <P>SOLUTION: The image forming apparatus is provided with a heat-fixing means fixing a toner image onto a recording medium, by transporting the recording medium on which the toner image is formed, while applying heat from an exothermic body. The heat fixing means is provided with a plurality of exothermic bodies (H1 and H2). Moreover, the voltage, applied to the plurality of exothermic bodies (H1 and H2), is controlled in many steps by a drive control circuit (203) (VSEL). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having means for heat-fixing a toner image formed on a recording medium.

  This type of device includes laser printers, LED printers, etc., and recording paper is fed from a recording paper storage unit such as a paper cassette in accordance with a printing command from an external device such as a computer, and recorded by synchronous conveyance means such as a registration roller. The paper conveyance timing is conveyed in synchronization with the image information transmission timing from the video controller, and image recording is performed.

  FIG. 1 is a block diagram of a conventional laser printer 101, and FIG. 2 is a timing chart showing its operation. The operation of the laser printer 101 will be described with reference to these drawings.

  When the video controller unit 28 confirms that the RDY signal is TRUE, the video controller unit 28 sets the PRINT signal to TURE. When the PRINT signal becomes TURE, the printer controller 26 starts driving the main motor 23 and the polygon motor 14. When the main motor 23 is driven, the photosensitive drum 17, the fixing roller 9, and the paper discharge roller 11 are rotated. Thereafter, the light amount control and the primary charging 19, the developing device 20, and the transfer charging device 21 are sequentially driven at a high voltage.

  When the rotation of the polygon motor 14 reaches a steady state, the printer controller 26 turns on the paper feed roller clutch 24 for t1 seconds to drive the paper feed roller 5 and feeds the recording paper S toward the registration roller pair 6. The printer controller 26 sends a VSREQ signal to the video controller 28 at the timing when the leading edge of the recording paper S reaches the registration roller pair 6 and turns off the paper feed roller clutch 24 to stop driving the paper feed roller 5. .

  When the video controller unit 28 finishes developing the image information into the dot image and is ready to output the VDO signal, the video controller unit 28 confirms that the VSREQ signal is TURE, sets the VSYNC signal to TURE, and synchronizes with this to tv seconds. Later, output of the VDO signal is started as image data for one page.

  At this time, the printer controller 26 turns on the registration roller clutch and drives the registration roller pair 6 after t3 seconds from the rise of the VSYNC signal. The registration roller pair 6 is driven for a time t4 seconds until the trailing edge of the recording paper S passes the registration roller pair 6.

  During this time, the printer controller 26 sends the HSYNC signal to the video controller unit 28 at a predetermined timing synchronized with the laser scanning, and modulates the laser light that scans the photosensitive drum 17 based on the VDO signal.

  Further, when the next page is printed, the PRINT signal is set to TURE again after t5 seconds. After that, the same operation as the first page is performed.

  By such operations of the printer controller 26 and the video controller unit 28, the recording sheet S is sequentially conveyed to the paper feed roller 5, the registration roller pair 6, the image recording unit 8, the fixing roller 9, and the paper discharge roller 11 to record an image. Made.

  The heat fixing device mounted on the laser printer as described above has one or more heaters as heating elements inside. When there are a plurality of heaters, a plurality of heaters having different light distributions are selectively or simultaneously turned on and used in order to heat a narrow recording paper and a wide recording paper without waste.

  For example, the main heater A having a light distribution distribution at the center in the width direction of the recording medium and the sub-heater B having a light distribution distribution at both ends in the width direction of the recording medium have a small size in the width direction. It is conceivable that only the main heater A is used when printing a recording medium, and the main heater A and the sub-heater B are used in combination when printing a recording medium whose size in the width direction is large (for example, see Patent Document 1). reference.).

Japanese Patent Laid-Open No. 11-84936

  In the case of an image forming apparatus (so-called high-speed machine) that performs printing at a high speed, a large amount of heat is taken because the number of sheets to be passed per unit time is large. For this reason, the power consumption of the heater also increases. However, the power (especially current) of the commercial power supply has an upper limit, and the maximum value of the total power of the heaters that are turned on at the same time is also limited. Due to this limitation, when the power of one heater is increased, simultaneous lighting cannot be performed, and alternate lighting is unavoidable.

  However, when the plurality of heaters are alternately lit, the temperature ripple increases and temperature unevenness occurs in the longitudinal direction of the fixing roller. Moreover, fine alternate lighting also contributes to noise generation.

  Although it is possible to reduce temperature unevenness by suppressing the power of the heater, in this case, for example, during continuous printing of small size paper, the end of the fixing roller (non-sheet passing portion) at the same time as holding the temperature at the center. ) Temperature maintenance becomes a problem. In response to this, it is conceivable to provide a heater with a small electric power for maintaining the temperature. However, the installation of the heater causes an increase in cost and causes the apparatus to become large.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus in which temperature unevenness of a heat fixing unit is reduced.

  The above problems are solved by the image forming apparatus of the present invention. An image forming apparatus according to an aspect of the present invention conveys the toner image on the recording medium by conveying a plurality of heating elements and a recording medium on which a toner image is formed while applying heat from the plurality of heating elements. And a heat fixing unit for fixing the heat generating unit to the heat generating unit, and a voltage control unit for controlling a voltage applied to each of the plurality of heating elements.

  According to the present invention, there is provided an image forming apparatus in which temperature unevenness of a thermal fixing unit is reduced.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 3 is a block diagram illustrating the configuration of the fixing device controller of the image forming apparatus according to the present exemplary embodiment. The image forming apparatus includes a charger, a photosensitive drum, a toner developer, and a recording medium on which a toner image is formed. Although a fixing device as a fixing unit is provided, since these configurations are known, illustration is omitted here.

  The fuser controller shown in FIG. 3 converts the voltage of the commercial power source into a DC voltage by a diode bridge, and then applies the voltage to the heater by a generally known step-down down chopper circuit. This will be specifically described below.

  Reference numeral 201 denotes a diode bridge rectifier circuit that rectifies commercial power. A heater voltage detection circuit 202 detects voltages applied to fixing heaters (hereinafter simply referred to as heaters) H1 and H2 as a plurality of heating elements. The heaters H1 and H2 are, for example, halogen heaters, and are arranged inside the fixing roller so as to extend in the axial direction thereof (that is, in the width direction of the recording medium and perpendicular to the conveyance direction of the recording medium). Not shown). A drive control circuit 203 performs energization drive control of the heaters H1 and H2, and includes a ROM, a one-chip microcomputer with a built-in RAM, a timer, and the like.

  The switching FET Tr1 is energized and driven by a heater enable (HENBL) signal that is a PWM signal having a constant duty ratio. The triacs Tr2 and Tr3 connected in series with the heaters H1 and H2, respectively, are energized and driven by respective fuser drive (FSRD1 and FSRD2) signals. When the triac Tr2 is on, the rectified voltage is applied to the fixing heater H1 via the choke L. The applied voltage is a constant voltage regardless of the input power supply voltage. The applied voltage is detected by the heater voltage detection circuit 202, and a heater monitor (HMON) signal is output. The drive control circuit 203 reads the HMON signal and variably controls the on-duty of the HENBL signal applied to the gate of the switching FET Tr1 according to the detected voltage, so that the voltage applied to the heater H1 can be made constant. The same applies to the heater H2.

  A control signal (VSEL) from the drive control circuit 203 to the heater voltage detection circuit 202 is a signal for switching a voltage to be applied to the heater.

  FIG. 4 is a circuit diagram showing a specific configuration of the heater voltage detection circuit 202 in the present embodiment. In the figure, by providing the resistor R41 and the switch SW41, it is possible to change the voltage division ratio between the reference voltage Vb generated by the shunt regulator IC 42 and the output voltage Vout. The switch SW41 is controlled by the VSEL signal from the drive control circuit 203, whereby the applied voltage Vout to the heater is switched.

  To the input to the + terminal of the operational amplifier IC41, the voltage Vin1 when the switch SW41 is open is expressed by the following equation.

      Vin1 = {(R41 + R42) / (R41 + R42 + R43)} · Vout1

  Further, the voltage Vin2 in a state where the switch SW41 is closed is expressed by the following equation.

      Vin2 = {R42 / (R42 + R43)} · Vout2

  Both of these voltages Vin1 and Vin2 are compared with the reference voltage Vb input to the negative terminal of the operational amplifier IC41, and ON / OFF control of the switching FET Tr1 is performed so as to be substantially the same as Vb.

  As a result, Vin1≈Vin2≈Vb.

Therefore,
Vout2 / Vout1 = (R41 + R42). (R42 + R43) / {(R41 + R42 + R43) .R42}
Thus, the output voltage Vout can be changed by opening and closing the switch SW41.

Further, the halogen heater power (W1 _H1, W2 _H1) and the applied voltage 1.54 square relationship _{W1 H1 / W2 H1 = (Vout2} / Vout1) of the relationship applied voltage ratio ^{(Vout2, Vout1) 1.54 (W1} H1> W2 _H1 , Vout2> Vout1)
It is known that

  Therefore, by setting the value of the resistor R41 for the resistors R42 and R43 so that the desired power value is obtained, and changing the output voltage by switching the switch, for example, the output of the halogen heater is set to 1 kW and 500 W. It becomes possible to do.

  The heater H1 is a halogen heater having a light distribution that intensively heats the central portion in the recording medium width direction, and the heater H2 is a halogen heater having a light distribution that intensively heats both ends of the recording medium. In this case, assuming that the maximum power consumption is within 1 kW as a condition that the general maximum current 15 A of the commercial power supply 100 V (in Japan) does not exceed 15 A, the heater lighting modes are as shown in FIGS. It is possible to set the five modes as follows. When the applied voltage to the heater is not changed, the lighting mode is only one of the combination of (A) and (B) or the combination of (C) to (E). Only the combination of (A) and (B) has the disadvantage that the temperature ripple is large, and the combination of (C) to (E) alone has the disadvantage that the maximum power in one heater is small. On the other hand, according to the present embodiment, since all of (A) to (E) can be combined, the fixing roller can be finely heated.

  Therefore, according to the present embodiment, it is possible to reduce temperature unevenness in the longitudinal direction of the fixing roller, and it is possible to improve the efficiency of overheating and temperature holding of the fixing roller. Thereby, the effect of improving the fixing quality of the toner image on the recording medium and improving the image quality can be improved.

(Second Embodiment)
FIG. 6 is a circuit diagram showing a specific configuration of the heater voltage detection circuit according to the second embodiment.

  The switch SW61 switches the reference voltages Vb1 and Vb2 output from the shunt regulators IC61 and IC62, respectively, according to the VSEL signal from the drive control circuit 203, and inputs it to the negative terminal of the operational amplifier IC41. The difference from the first embodiment (FIG. 4) is that the output voltage Vout is changed by providing two types (Vb1, Vb2) of reference voltages Vb.

The drive control circuit 203 determines that Vb≈ (R41 + R42) / (R41 + R42 + R43) Vout from the output signal of the operational amplifier IC41.
Control is performed as follows.

  Accordingly, the heater voltage Vout can be switched to Vout1 and Vout2 in the same manner as in the first embodiment according to the set Vb1 and Vb2.

  Further, a halogen heater having a light distribution in which the heater H1 intensively heats the central portion in the recording medium width direction, and a halogen heater having a light distribution in which the heater H2 intensively heats both ends of the recording medium are used. In this case, assuming that the maximum power consumption is within 1 kW as a condition that the general maximum current 15 A of the commercial power supply 100 V (in Japan) does not exceed 15 A, the heater lighting modes are as shown in FIGS. It is possible to set the five modes as shown in FIG.

(Third embodiment)
FIG. 7 is a block diagram illustrating a configuration of a fixing device control unit of the image forming apparatus according to the present exemplary embodiment.

  In FIG. 7, reference numeral 201 denotes a diode bridge rectifier circuit that rectifies commercial power, and 202a and 202b denote heater voltage detection circuits that detect voltages applied to the heaters H1 and H2, respectively. The heaters H1 and H2 are, for example, halogen heaters, and are disposed inside the fixing roller so as to extend in the axial direction (that is, the recording medium width direction) (not shown). A drive control circuit 203 performs energization drive control of the heaters H1 and H2, and includes a ROM, a one-chip microcomputer with a built-in RAM, a timer, and the like.

  The switching FETs Tr1 and Tr7 are energized and driven by heater enable signals HENBL1 and HENBL2, which are PWM signals having a constant duty ratio. The triacs Tr2 and Tr3 connected in series with the heaters H1 and H2, respectively, are energized and driven by respective fuser drive (FSRD1 and FSRD2) signals. When the triac Tr2 is on, the rectified voltage is applied to the fixing heater H1 via the choke L. The applied voltage is a constant voltage regardless of the input power supply voltage. This applied voltage is detected by the heater voltage detection circuit 202a, and a heater monitor (HMON1) signal is output. The drive control circuit 203 reads the HMON1 signal and variably controls the on-duty of the HENBL1 signal applied to the gate of the switching FET Tr1 according to the detected voltage, so that the voltage applied to the heater H1 can be made constant. The same applies to the heater H2. When the triac Tr3 is on, the rectified voltage is applied to the fixing heater H2 via the choke L2. The applied voltage is a constant voltage regardless of the input power supply voltage. This applied voltage is detected by the heater voltage detection circuit 202b, and a heater monitor (HMON2) signal is output. The drive control circuit 203 reads the HMON2 signal and variably controls the on-duty of the HENBL2 signal applied to the gate of the switching FET Tr7 according to the detected voltage, so that the voltage applied to the heater H2 can be made constant.

  Control signals (VSEL1, VSEL2) from the drive control circuit 203 to the heater voltage detection circuits 202a, 202b are signals for switching the voltage to be applied to the corresponding heater.

  Thus, the difference from the first embodiment is that the voltage driving units for the heaters H1 and H2 are provided independently.

  As a result, the voltage Vout supplied to the heater H1 and the voltage Voutb supplied to the heater H2 can be set differently.

  According to the present embodiment, the power of the heaters H1 and H2 can be controlled independently. For example, when the power change of the heater H1 is 900W-500W and the power change of the heater H2 is 700W-300W, the commercial power supply 100V (Japan) In the case of (1), the combination of maximum power 1200W (H1: 900W, H2: 300W, or H1: 500W, H2: 700W) is possible with a maximum current of 15A or less, and the drive patterns of the heaters H1, H2 can be further increased. It becomes. For this reason, in the present embodiment, more lighting modes can be set, and the fixing roller can be finely heated.

  Therefore, according to the present embodiment, it is possible to further reduce temperature unevenness in the longitudinal direction of the fixing roller, and it is possible to further improve the efficiency of overheating and temperature holding of the fixing roller. Thereby, the effect of improving the fixing quality of the toner image on the recording medium and improving the image quality can be further expected.

It is a figure which shows the structure of the conventional laser printer. It is a figure explaining operation | movement of the conventional laser printer. FIG. 2 is a block diagram illustrating a configuration of a fixing device control unit of the image forming apparatus according to the first embodiment. It is a circuit diagram which shows the specific structure of the heater voltage detection circuit in 1st Embodiment. It is a figure which shows the lighting pattern of the heater in embodiment. It is a circuit diagram which shows the specific structure of the heater voltage detection circuit in 2nd Embodiment. FIG. 10 is a block diagram illustrating a configuration of a fixing device control unit of an image forming apparatus according to a third embodiment.

Claims (5)

A plurality of heating elements;
Heating and fixing means for fixing the toner image on the recording medium by conveying the recording medium on which the toner image is formed while applying heat from the plurality of heating elements;
Voltage control means for controlling the voltage applied to each of the plurality of heating elements;
An image forming apparatus comprising:   The plurality of heating elements include a first heating element having a light distribution that intensively heats a central portion in the width direction of the recording medium, and a light distribution that intensively heats both ends of the recording medium in the width direction. The image forming apparatus according to claim 1, further comprising: a second heating element including   3. The image according to claim 2, wherein the voltage control unit controls a voltage applied to each of the first and second heating elements based on a size in a width direction of the introduced recording medium. Forming equipment.   The image forming apparatus according to claim 1, wherein the voltage control unit switches a voltage applied to each of the plurality of heating elements in a plurality of stages.   The image forming apparatus according to claim 1, wherein the voltage control unit is provided independently for each of the plurality of heating elements.

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