JP2013213887A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents unnecessary temperature rise of an end part in a rotation center line direction of a heating member of a fixing device during printing operation, can suppress the occurrence of UFPs from the end part, and can quickly stabilize the temperature of the heating member to be a temperature appropriate to toner image fixing processing while suppressing waste of energy when shifting from a waiting state to printing operation.SOLUTION: An image forming apparatus 10 employs a fixing device 4 including a heating roller 41 that includes a plurality of heaters h1 and h2 therein, and a pressure roller 42 that opposes to the heating roller 41. During printing operation, the image forming apparatus 10 controls lighting of only the first heater h1 having a heating value at the central part of the heater larger than that of the end part of the heater. During waiting time, the image forming apparatus 10 controls lighting of the second heater h2 having a heating value at the end part of the heater larger than that of the first heater.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these, which can form a toner image on a recording sheet such as recording paper, and in particular, fixing a toner image on a recording sheet This is related to the fixing device.

  In an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these that can form a toner image on a recording sheet, an electrostatic latent image is formed on an image carrier in an electrostatic latent image forming process. Formed (for example, an electrostatic latent image is formed on an image carrier such as a photoreceptor in an exposure process), the electrostatic latent image is developed in a development process to form a visible toner image, and a visible toner is formed in a transfer process. The image is transferred to a recording sheet, or is temporarily transferred to an intermediate transfer member such as an intermediate transfer belt and then secondarily transferred from the intermediate transfer member to the recording sheet. The toner image thus transferred to the recording sheet in the fixing process is transferred to the recording sheet. It can be fixed on a recording sheet.

  A fixing device is used to fix the unfixed toner image formed on the recording sheet onto the recording sheet in the fixing process. Various types of fixing devices are known.

  For example, a rotatable heating member (for example, a heating roller) having a built-in heater as a member for forming a fixing nip portion (a nip portion for fixing the toner image to the recording sheet through a recording sheet carrying an unfixed toner image). And a rotatable pressure member (for example, a pressure roller) opposite to the heating member.

  In this type of fixing device, the toner image can be fixed to the recording sheet under heat and pressure by passing a recording sheet holding the toner image through a nip formed by the heating member and the pressing member. .

  In addition, a plurality of (for example, two) heaters with different heating value distributions in the heating member rotation center line direction are incorporated in the heating member, and the recording sheet size is passed through the fixing nip portion (particularly, the rotation center of the heating member). It has also been proposed to control the temperature of the heating member with these heaters according to the sheet width in the linear direction.

  Japanese Patent Application Laid-Open No. 2011-118261 discloses that the heater is switched between the sub heater and the main heater according to whether or not the heating member temperature detected by the temperature detection unit is equal to or lower than the heater switching temperature. It is described that another heater switching temperature is set depending on whether the working member is stopped or rotating.

JP 2011-118261 A

  A conventional fixing device of the type including a rotatable heating member (for example, a heating roller) incorporating a heater and a rotatable pressing member (for example, a pressure roller) facing the heating member. In the case of a fixing device equipped with one heater inside the heating member, heat escapes from the heater end in the direction of the rotation center line of the heating member during standby when the recording sheet is not passed. It may be set high so that the end temperature does not drop.

  In such a fixing device, when a recording sheet is continuously passed through the fixing nip portion in order to form a plurality of continuous images, heat moves to the recording sheet passing through the fixing nip portion in the recording sheet width range. In this case, the heater lighting time is lengthened because the temperature of the heating roller tends to decrease.

  At this time, near the end of the heating roller in the axial direction outside the recording sheet width, the temperature is unlikely to decrease due to heat transfer from the center of the heating roller. It tends to be hot.

  This is not limited to the fixing device provided with one heater, and the same applies to a fixing device provided with a plurality of heaters corresponding to the size of the recording sheet to be conveyed.

  Incidentally, in recent years, attention has been paid to UFP (ultrafine particles of 100 nm or less) generated from an image forming apparatus.

As for the fixing device, more UFP generated from a fixing device using silicon rubber (for example, a fixing device using silicon rubber in the surface layer portion of a heating member such as a heating roller) is generated at a high temperature. . In order to suppress the amount of UFP generated, it is required to suppress the end of a heating member such as a heating roller from becoming high temperature.

  In this respect, in Japanese Patent Application Laid-Open No. 2011-118261, the heater switching is performed between the sub heater and the main heater depending on whether or not the heating member temperature detected by the temperature detection unit is equal to or lower than the heater switching temperature. It seems that the end of the heating member such as a heating roller can be prevented from becoming high temperature.

  However, in the fixing device described in the publication, the temperature distribution in the heating member such as a heating roller changes before and after the heater switching, and the heat of the end heated by the sub heater before the switching may be wasted. is there. In addition, when the heater switching temperature is different between when the fixing member such as the heating roller is rotated and when it is stopped, it may not be able to cope with the required temperature change at the fixing nip passage timing of the recording sheet. .

  Accordingly, the present invention is an image forming apparatus capable of forming a toner image on an image carrier, transferring the toner image onto a recording sheet, and fixing the image with a fixing device, and the fixing device includes a plurality of heaters. A recording sheet holding a toner image in a nip formed by the heating member and the pressurizing member, and including a rotatable heating member and a rotatable pressurizing member facing the heating member. Thus, the image forming apparatus is a fixing device that fixes the toner image to the recording sheet under heat and pressure, and the end portion of the heating member in the rotation center line direction is at the time of printing operation, even in continuous printing operation. It is a first object to provide an image forming apparatus capable of suppressing the generation of UFP from the end portion in the rotation center line direction of the heating member without causing an increase in temperature.

  The present invention is an image forming apparatus that can solve the first problem, and the temperature of the heating member is reduced in the toner image fixing process while suppressing energy waste when shifting from the standby state where the printing operation is not performed to the printing operation. A second problem is to provide an image forming apparatus that can be quickly stabilized at a suitable temperature.

In order to solve the first problem, the present invention provides:
An image forming apparatus capable of forming a toner image on an image bearing member, transferring the toner image onto a recording sheet, and fixing the image on a recording sheet, and the fixing apparatus is a rotatable heating unit including a plurality of heaters. A recording sheet containing a toner image passing through a nip formed by the heating member and the pressurizing member. An image forming apparatus which is a fixing device for fixing to the recording sheet under heat and pressure,
A power supply for energizing the heater;
A temperature detector for detecting the temperature of the heating member;
A control unit of the power supply unit,
The plurality of heaters includes a first heater that generates a larger amount of heat at the heater center than at the heater end in the rotation center line direction of the heating member,
The controller turns on at least one of the plurality of heaters based on a difference between a temperature detected by the temperature detector and a target temperature of the heating member so that the temperature of the heating member approaches the target temperature. A control unit for controlling the power supply unit to control,
The controller provides an image forming apparatus that controls lighting of only the first heater during a printing operation.

  According to the image forming apparatus of the present invention, a toner image can be formed on the image carrier, and the toner image can be transferred to a recording sheet and fixed by the fixing device. In the fixing device, a recording sheet holding a toner image is passed through a nip portion formed by a rotatable heating member incorporating the plurality of heaters and a rotatable pressure member facing the heating member. The toner image can be fixed on the recording sheet under heat and pressure.

  According to the image forming apparatus of the present invention, in the fixing device, the control unit controls the power supply unit, that is, based on the difference between the temperature detected by the temperature detection unit and the target temperature of the heating member. The heating member temperature is controlled to go to the target temperature by controlling the power supply unit to control lighting of at least one of the plurality of heaters so that the heating member temperature goes to the target temperature. The

Here, the “target temperature” is a target temperature set in advance according to the operation state of the fixing device,
In the so-called warming-up of the fixing device, it is “temperature for achieving the warming-up of the fixing device”. Is a “fixing temperature” suitable for the toner image fixing process.

  The controller controls to turn on only the first heater that generates a larger amount of heat at the heater center than at the heater end in the rotation center line direction of the heating member during the printing operation. As a result, the heating member is heated at the center in the direction of the rotation center line, and can compensate for the temperature drop at the center due to the passage of the recording sheet. Further, the end of the heating member is also heated by the heat from the center. Thus, the heating member is set to the target temperature (fixing temperature).

  Since the heating member end is heated by the heat transfer from the central portion, the heating member end is easily changed even during the printing operation, even if the lighting time of the first heater is long in the continuous printing operation. There is no temperature rise. Therefore, generation | occurrence | production of UFP from the rotation center line direction edge part of the said heating member can be suppressed. For example, even when the surface layer portion of the heating member is made of silicon rubber or the like that easily generates UFP at a high temperature, UFP generation can be suppressed.

  In the image forming apparatus according to the present invention, the plurality of heaters may include a second heater in which the amount of heat generated at the heater end in the rotation center line direction of the heating member is greater than the first heater. . When such a second heater is included, the control unit may perform lighting control only on the second heater at the time of standby when the printing operation is not performed.

  When waiting for no printing operation, the control unit controls the lighting of only the second heater so that when the transition from the standby state to the printing operation is performed, the heating member end is already warmed to some extent by the lighting control of the second heater. Starting from this state, while suppressing wasteful energy of the second heater, the temperature of the heating member is quickly stabilized to a temperature suitable for the toner image fixing process by switching lighting control to the first heater. be able to.

  The control unit obtains a timing at which the recording sheet holding the toner image passes through the nip portion for fixing the toner image, and from the second heater to the first heater when shifting from the standby to the printing operation. The lighting control switching timing may be determined in accordance with the timing at which the recording sheet passes through the nip portion and so that the fixing process of the toner image to the recording sheet can be performed.

  As a specific example of the “lighting control switching timing from the second heater to the first heater” described above, on the premise that the fixing process of the toner image to the recording sheet can be performed, The timing may be selected from “when the nip portion enters”, “a certain time before the nip portion enters the recording sheet tip”, and “immediately after the nip portion enters the recording sheet tip”.

Regarding the effective heat generation length in the rotation center line direction of the heating member of the first heater, the sheet in the rotation center line direction of the heating member when passing through the nip portion of a standard recording sheet capable of toner image fixing processing A case where the width is made smaller than the sheet width of the maximum recording sheet can be exemplified.
By doing so, it is possible to prevent excess heat from escaping to the outside of the recording sheet width (hereinafter sometimes referred to as “sheet passing width”).

An example in which the power distribution to the first heater by the power supply unit is larger than the power distribution to the second heater by the power supply unit can be given. Power distribution to the second heater is as follows:
It is not necessary to consider the heat transfer from the heating member to the recording sheet. You may prevent it.

  A plurality of the temperature detectors may be provided, but one temperature detector may be provided. As the position when one temperature detection unit is provided, for example, within the range of the sheet width when the recording sheet having the maximum sheet width in the rotation center line direction of the heating member when passing through the nip portion passes through the nip portion. Position. When providing one said temperature detection part, the said control part should just employ | adopt the temperature information which this one temperature detection part detects as the temperature information of the said heating member.

  As described above, according to the present invention, there is provided an image forming apparatus capable of forming a toner image on an image carrier, transferring the toner image onto a recording sheet, and fixing the image with a fixing device. Including a rotatable heating member having a built-in heater and a rotatable pressure member facing the heating member, wherein a toner image is held in a nip formed by the heating member and the pressure member An image forming apparatus that is a fixing device that fixes a toner image to a recording sheet under heating and pressure by passing a sheet, and a rotation center line of the heating member during a printing operation, even in a continuous printing operation It is possible to provide an image forming apparatus capable of suppressing the occurrence of UFP from the end portion in the rotation center line direction of the heating member without causing the temperature increase in the direction end portion.

  Further, the present invention is an image forming apparatus having the above-described advantages, and the temperature of the heating member is a temperature suitable for the toner image fixing process while suppressing waste of energy when shifting from the standby state where the printing operation is not performed to the printing operation. It is possible to provide an image forming apparatus that can be quickly stabilized.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 2 is a block diagram illustrating an outline of a control circuit of the image forming apparatus in FIG. 1. FIG. 2 is a schematic sectional view of a fixing device employed in the image forming apparatus of FIG. FIG. 4 is a diagram illustrating an outline of a configuration of a heating roller of the fixing device illustrated in FIG. 3 extending in a rotation axis direction. It is a figure which shows the other example of a heating roller. It is a figure which shows the further another example of a heating roller. It is a figure which shows lighting control of the 1st, 2nd heater and heating roller surface temperature of the type of heating roller shown in FIGS. It is a figure which shows the surface temperature distribution in the rotation center line direction at the time of continuous printing of the type of heating roller shown in FIGS. It is a figure which shows surface temperature distribution in the rotation center line direction at the time of continuous printing of the conventional example heating roller which employ | adopts the long heater with the long heat generation length of a heating roller rotation center line direction.

Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention. FIG. 2 schematically shows a control circuit of the image forming apparatus shown in FIG.
An image forming apparatus 10 shown in FIG. 1 is a printer that forms a monochrome image by an electrophotographic method and prints it on a recording sheet such as a recording sheet.

  The printer 10 includes an image forming unit 1 that forms a toner image by an electrophotographic method, a sheet supply unit 2 that supplies a recording sheet S to the image forming unit 1, and a toner image that is formed by the image forming unit 1 from the sheet supply unit 2. The transfer unit 3 for transferring to the supplied recording sheet S, the fixing device 4 for fixing the toner image transferred to the recording sheet S to the sheet S, and the sheet discharge for discharging the recording sheet S holding the fixing toner image to the discharge tray 50 The apparatus 5 etc. are included.

  The printer 10 also includes a control unit Cont that controls its operation. The operation of each unit of the printer 10 is performed under the instruction of the control unit Cont. An operation panel PA operated by a user is also connected to the control unit Cont. The operation panel PA includes a numeric keypad for setting the number of prints, a key for specifying a recording sheet size to be used, a key for instructing start of printing, and the like.

  The image forming unit 1 includes a drum-type photoconductor 11 that is rotationally driven as an electrostatic latent image carrier. Around the photoconductor 11, a charger 12, a developing device 14, a cleaner 15 and the like are arranged in this order. An image exposure device 13 that performs image exposure on the photosensitive member 11 from between the charger 12 and the developing device 14 is also provided.

  The image exposure device 13 is supplied with image information from a scanner, a computer, etc. (not shown), and performs image exposure on the photoconductor 11 with a laser beam.

  The transfer unit 3 includes a transfer roller 31 that can apply a transfer bias from a transfer power supply (not shown). The transfer roller 31 faces the photoconductor 11 on the downstream side of the developing device 14 and the upstream side of the cleaner 15 in the rotation direction (counterclockwise direction) of the photoconductor 11.

  The transfer roller 31 is pressed by a pressing means (not shown) to form a nip portion between the transfer roller 31 and the recording sheet driven by the rotation of the photosensitive member 11 or fed into the nip portion as will be described later. It can be rotated by being driven or driven.

The sheet supply unit 2 includes a cassette 200 on which the recording sheets S are stacked and stored, and a sheet supply device 20 that pulls out and supplies the sheets one by one from the cassette 200.
The fixing device 4 will be described in detail later.

 The sheet discharge device 5 includes a discharge roller pair 51 that discharges the recording sheet S sent out from the fixing device 4 to the discharge tray 50. Although not shown, a recording sheet reverse circulation path known per se may be provided so that printing (image formation) can be performed on both sides of the recording sheet.

  According to the printer 10, when the print start key is pressed on the operation panel PA connected to the control unit C, the supply of the recording sheet S is started from the recording sheet supply unit 2.

  When the recording sheet S supplied from the recording sheet supply unit 2 is detected by a sensor (not shown), image formation is started by the image forming unit 1, and the recording sheet S is temporarily stopped by the timing roller pair 6.

  When image formation is started in the image forming unit 1, the photoconductor 11 is rotationally driven counterclockwise in the figure, the surface of the photoconductor is charged to a predetermined potential by the charger 12, and an image exposure device is placed in the charged area 13 is subjected to image exposure according to the image to be formed. As a result, an electrostatic latent image is formed on the photoconductor 11, and in this example, the latent image is reversely developed with negatively charged toner in the developing unit 14 to become a visible toner image.

  The recording sheet S waiting on the timing roller pair 6 is sent to the transfer section 3 by the roller pair 6 so that the transfer of the toner image on the photoconductor 11 to the image forming area is transferred from a transfer power supply (not shown). The toner image on the photoconductor 11 is transferred by the transfer roller 31 to which a bias is applied. The recording sheet S to which the toner image has been transferred is continuously fed to the fixing device 4 where the toner image is fixed under heat and pressure, and further directed to the discharge roller pair 51 and discharged to the discharge tray 50 by the discharge roller pair 51. The

  The transfer residual toner remaining on the photoconductor 11 after the toner image transfer is removed and cleaned by a cleaner 15.

Next, the fixing device will be described.
(1) Regarding the Fixing Device 4 FIG. 3 is a schematic sectional view of the fixing device 4 employed in the printer 10. FIG. 4 schematically shows a configuration of the heating roller 41a of the fixing device 4 over the rotational axis direction.

  The fixing device 4 shown in FIG. 3 includes a heating roller 41a and a pressure roller 42 facing the heating roller 41a.

  Here, the heating roller 41a includes a roller body in which an elastic layer 412 made of silicon rubber is provided on a core metal 411 and a first heater ah1 and a second heater ah2 that are parallel to each other. The heating roller 41 a is a member that contacts the carrying surface of the unfixed toner image t on the recording sheet S. The elastic layer 412 may be covered with a release layer made of PFA (perfluoroalkoxy) or the like.

  Here, the pressure roller 42 is a core metal covered with a sponge layer obtained by foaming silicon rubber.

  Each of the rollers 41a and 42 is rotatably supported by a bearing portion (not shown). The heating roller 41a is driven to rotate counterclockwise in FIG. 3 by a drive motor (not shown) at the timing of the toner image fixing process under the instruction of the control unit Cont.

  The pressure roller 42 is rotated in the clockwise direction in FIG. 3 while being elastically pressed against the heating roller 41a by a pressing device (not shown).

  With the heating roller 41a heated to the toner image fixing temperature, the recording sheet holding the toner image in the nip portion N formed by the heating roller 41a and the pressure roller 42 is passed in the arrow direction α to pass the toner image. The recording sheet can be fixed under heat and pressure.

  The heating roller 41a is warmed by two heaters ah1 and ah2 arranged in the heating roller. Lighting control by ON / OFF by the power supply unit PW (see FIG. 2) of these heaters is performed under the instruction of the control unit Cont with reference to the temperature detected by the thermistor SM facing the heating roller 41a.

  Heat other than the heat transferred with the recording sheet stays in the printer 10, and a part thereof raises the temperature at both ends of the heating roller. The remaining part warms the components and air around the fixing device, and the air is sucked by the exhaust fan and discharged outside the printer 10.

  FIG. 4 shows a schematic configuration in the direction of the rotation center line of the heating roller 41a (hereinafter sometimes referred to as “axial direction”), under the instruction of the control unit Cont (in other words, During “image formation”), the filament portion having a length shorter than the sheet passing width (recording sheet passing width) of the first heater ah1 generates heat and heats the heating roller 41a. During standby, the filament portion of the second heater ah2 having a length longer than the sheet passing width generates heat so that the temperature near both ends of the sheet passing width does not drop even if heat escapes from the space between the ends of the heating roller 41a. I have to. At this time, the power of the first heater ah1 is 800 W, and the power of the second heater is 400 W.

  Since the power distribution of the first heater ah1 is thus increased, the necessary amount of heat can be supplied to the toner by the lighting control of only the first heater ah1 even if continuous printing is performed, and the toner image is fixed on the recording sheet S. Can be made.

  Since the second heater ah2 is turned on only when the fixing apparatus 4 is not in the standby state when the recording sheet is not passed, the temperature necessary for promptly shifting to the printing operation can be maintained even if the power is small. The effective heat generating portion of the second heater ah2 has a substantially uniform heat generation amount over almost the entire axial direction.

FIG. 5 shows another example of the heating roller.
In the fixing device that employs the heating roller 41b instead of the heating roller 41a, the filament portion of the second heater-bh2 having a length longer than the sheet passing width generates heat during standby, and is a space between both ends of the heating roller 41b. Even if heat escapes, the temperature near both ends of the sheet passing width is not lowered.

  Further, although the filament portion at the center in the axial direction of the second heater bh2 hardly generates heat, heat does not escape from the center of the heating roller, and no heat is transferred by the recording sheet during standby. Therefore, it is possible to ensure a sufficient temperature only by the heat generation of the filament portions at both ends. At this time, the power of the first heater bh1 is 800W, and the power of the second heater bh2 is 300W.

FIG. 6 shows still another example of the heating roller.
In the fixing device employing the heating roller 41c instead of the heating roller 41a, the filament portion having a length longer than the sheet passing width of the second heater ch2 emits light during standby, and heat is generated from the space between the heating roller and both ends. Even if it escapes, the temperature in the vicinity of both ends of the sheet passing width is not lowered. In particular, the amount of heat generated near the end in the axial direction where the heat easily escapes and the temperature tends to decrease is made larger than that in the central portion so that the temperature distribution is uniform in the axial direction. At this time, the power of the first heater ch1 is 800 W, and the power of the second heater ch2 is 400 W.

FIG. 7 shows the lighting control of the first heaters ah1, bh1, and ch1 and the second heaters ah2, bh2, and ch2 in the heating rollers 41a, 41b, and 41c, and the transition of the heating roller-surface temperature.
Hereinafter, the heating rollers 41a, 41b, and 41c are “heating roller 41”, the first heaters ah1, bh1, and ch1 are “first heater h1”, and the second heaters ah2, bh2, and ch2 are “second heater h2”. Sometimes referred to generically.

  At the time of sleep before warm-up when the heat of the fixing device 4 does not remain in the printer 10, the heaters are not lit and the detected temperature of the thermistor SM is the same as the room temperature as in the power-off state. When an instruction is received from the operation panel PA of the printer 10 to enter a warm-up state, both the first heater h1 and the second heater h2 are in the lighting control state, and the detected temperature of the thermistor also rises. Since both heaters are turned on, the temperature rise rate is high, and it is possible to quickly shift to a printable state.

  The thermistor SM is not in contact with the surface of the heating roller 41, and the temperature detected by the thermistor SM is input to the control unit Cont. The control unit Cont is different from the actual surface temperature of the heating roller. The surface temperature of the heating roller is estimated by correcting the detected temperature of Mr. SM. When the warm-up is completed and there is no print instruction, the process shifts to a standby state. At this time, under the instruction of the control unit Cont, the lighting control of the first heater h1 is stopped, and the lighting control state of only the second heater h2 is set.

  The second heater h <b> 2 is repeatedly turned on / off so that the target temperature of the surface of the heating roller 41 is 150 ° C. during standby. In addition, ON / OFF on FIG. 7 has shown whether it is in a control state, and is not ON / OFF of actual heater lighting. When the printing instruction is received, the target temperature on the surface of the heating roller is changed from 150 ° C. to 170 ° C., and the lighting control of the second heater h2 is stopped in accordance with the timing when the recording sheet passes through the fixing nip portion N. Lighting control is started. The first heater is repeatedly turned on / off so that the target temperature at the time of printing on the surface of the heating roller is 170 ° C.

  Note that the timing of switching from the second heater h2 to the first heater h1 may be the same as the print instruction, but regardless of the print instruction, the timing at which the recording sheet passes through the fixing nip N is calculated, It may be controlled to switch before a certain time. This timing may be the same as the timing when the leading edge of the recording sheet S enters the fixing nip N, or may be delayed from the timing when the leading edge of the recording sheet enters the fixing nip N. The timing is determined by the power distribution of each heater.

  When printing (image formation) is completed, the printer enters a standby state for a predetermined time, and enters a sleep state after a predetermined time has elapsed. The waiting time can be freely changed by setting. If the sleep time is short, when the warm-up state is entered next, only the second heater h2 is lit. Whether or not the first heater h1 is lit is determined by counting the sleep time. For warm-up when the sleep time is, for example, 5 minutes or more, both the first heater and the second heater are controlled to light, and the sleep time is 5 minutes. When the warm-up is less than the value, only the second heater is turned on.

  This selection may be determined by the detected temperature of the thermistor SM. In addition, two thermistors SM are arranged in the axial center and near the axial end, the first thermistor is controlled by the central thermistor, and the second heater is controlled by the thermistor near the end. However, only one thermistor may be arranged in the central portion in the axial direction to control lighting of both the first heater and the second heater in order to switch the heater to be turned on depending on the operation state.

  In the fixing device described above, the number of heaters built in the heating roller is two, but three or more heaters may be arranged. For example, it is possible to exemplify a case where another heater that can be used during warm-up is arranged in order to perform quicker warm-up.

FIG. 8 shows the heating roller surface temperature distribution in the axial direction of the heating roller 41 (41a, 41b, 41c) during continuous printing. Note that the maximum sheet passing width is 216 mm.
As can be seen from FIG. 8, the filament portion having a length shorter than the maximum sheet passing width of the first heater h1 generates heat, and heat is further diffused from both ends of the filament portion to both ends. The temperature distribution is almost uniform, and the temperature outside the sheet passing width does not greatly exceed 170 ° C.

FIG. 9 shows the surface temperature distribution in the rotation center line direction during continuous printing of the conventional heating roller employing a long heater having a long heat generation length in the heating roller rotation center line direction.
In this conventional control, a long heater with a long heat generation length is mainly used. Therefore, the long heater is lit even during printing, and the temperature outside the maximum sheet passing width rises. A lot of UFP was generated from the end.

The advantages of the fixing device 4 described above are summarized below.
During the printing operation, only the first heater h1 with high power distribution is controlled to be turned on, so that the heat at the center moves to the recording sheet S, and the temperature drop at the center of the heating roller 41 can be compensated.
In addition, by making the heat generation width of the first heater h1 smaller than the paper width, the amount of excess heat escaping outside the paper passage width is reduced, preventing the heating roller end temperature from rising during continuous printing, The amount of UFP generated due to temperature rise can be suppressed.
At the time of warming up, both the first heater h1 and the second heater h2 are turned on, so that the temperature raising speed is increased and the time until printing can be shortened. However, the warm-up in the case where the time after both heaters are turned off is short, and only the second heater h2 is lit, the temperature rises sufficiently and the warm-up does not take time.
During standby, only the second heater h2 is controlled to light up, thereby increasing the temperature of the end of the heating roller and preventing the end temperature from decreasing due to heat radiation from the end of the heating roller. At this time, since there is no heat transfer to the recording sheet due to printing, it is not necessary to increase the power of the second heater h2, and the minimum is required.
Further, efficient power consumption can be achieved by switching the lighting of the heater at the time of printing, standby, and warm-up, instead of selectively using the recording sheet size. In particular, the effect is large in an image forming apparatus applied to a recording sheet size of about A4.

  The image forming apparatus (printer) described above is a monochrome image forming apparatus. However, the present invention can also be applied to a color image forming apparatus of a tandem type, a four-cycle type, and the like. The present invention can also be applied to a multifunction machine in which two or more of a facsimile machine, a copying machine, a facsimile machine, a printer, and the like are combined.

  The present invention forms a toner image on an image carrier, transfers the toner image to a recording sheet, and a rotatable heating member incorporating a plurality of heaters and a rotatable pressurizing member facing the heating member. An image forming apparatus that can be fixed by a fixing device that includes a member, and the rotation center line of the heating member does not increase in temperature at the end of the heating member in the rotation center line direction during a printing operation. Generation of UFP from the end of the direction can be suppressed, and when shifting from the standby state to the printing operation, the temperature of the heating member is quickly stabilized to a temperature suitable for the toner image fixing process while suppressing energy waste. The present invention can be used to provide an image forming apparatus capable of performing the above.

10 Printer (an example of an image forming apparatus)
DESCRIPTION OF SYMBOLS 1 Image formation part 11 Photoconductor 12 Charger 13 Image exposure apparatus 14 Developer 15 Cleaner 2 Sheet supply part 3 Transfer part 31 Transfer roller 4 Fixing apparatus 41 (41a, 41b, 41c) Heating roller 42 Pressure roller h1 (ah1, ah1) bh1, ch1) 1st heater h2 (ah2, bh2, ch2) 2nd heater N Nip part PW Power supply part SM Thermistor Cont Control part S Recording sheet t Toner image

Claims (6)

An image forming apparatus capable of forming a toner image on an image bearing member, transferring the toner image onto a recording sheet, and fixing the image on a recording sheet, and the fixing apparatus is a rotatable heating unit including a plurality of heaters. A recording sheet containing a toner image passing through a nip formed by the heating member and the pressurizing member. An image forming apparatus which is a fixing device for fixing to the recording sheet under heat and pressure,
A power supply for energizing the heater;
A temperature detector for detecting the temperature of the heating member;
A control unit of the power supply unit,
The plurality of heaters includes a first heater that generates a larger amount of heat at the heater center than at the heater end in the rotation center line direction of the heating member,
The controller turns on at least one of the plurality of heaters based on a difference between a temperature detected by the temperature detector and a target temperature of the heating member so that the temperature of the heating member approaches the target temperature. A control unit for controlling the power supply unit to control,
The image forming apparatus, wherein the control unit controls lighting of only the first heater during a printing operation.   The plurality of heaters includes a second heater that has a heat generation amount at the heater end in the direction of the rotation center line of the heating member that is greater than the first heater, and the control unit is in a standby state when no printing operation is performed. The image forming apparatus according to claim 1, wherein only the second heater is controlled to be turned on.   The control unit obtains a timing at which the recording sheet holding the toner image passes through the nip portion for fixing the toner image, and from the second heater to the first heater when shifting from the standby to the printing operation. 3. The image forming apparatus according to claim 2, wherein the lighting control switching timing is determined in accordance with the timing at which the recording sheet passes through the nip portion and so that the fixing process of the toner image to the recording sheet can be performed.   The effective heat generation length in the rotation center line direction of the heating member of the first heater is the sheet width in the rotation center line direction of the heating member when passing through the nip portion of a standard recording sheet capable of fixing a toner image. The image forming apparatus according to claim 1, wherein is smaller than the sheet width of the largest recording sheet.   5. The image forming apparatus according to claim 1, wherein power distribution to the first heater by the power supply unit is larger than power distribution to the second heater by the power supply unit. The temperature detection unit is provided within the range of the sheet width when the recording member having the maximum sheet width in the rotation center line direction of the heating member when passing through the nip portion passes through the nip portion, and the control unit 6. The image forming apparatus according to claim 1, wherein temperature information detected by the one temperature detection unit is adopted as temperature information of the heating member.

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