JP2005257746A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent fixing failure while restricting consumption power to a permissible range even in the event that power sufficient to keep all detected temperatures corresponding to a plurality of heaters at their respective target temperatures cannot be obtained (consumed) in a fixing device that controls the supply of power to the plurality of heaters that heat a fixing heater and a pressing heater. <P>SOLUTION: Control is exerted such that, on the basis of the detection result of a plurality of temperature sensors 81a to 83a corresponding to the plurality of heaters 81 to 83 which heat the fixing roller 71 and the pressing roller 71, determination is made whether or not power needs to be supplied to each of the heaters 81 to 83 after the initiation of heat fixing. In addition, when power is supplied to one or more of the heaters 81 to 83, the proportion of power supplied to each heater to the total power allowed to be consumed by all the heaters is controlled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a fixing device that heat-fixes an unfixed image transferred to a sheet, and an image forming apparatus including the same.

In general, an electrophotographic image forming apparatus presses a recording paper (sheet) on which an unfixed toner image is formed against a rotating fixing roller (also referred to as a heating roller) by a pressure roller or the like, thereby unfixed toner. A fixing device that heat-fixes an image on a sheet such as recording paper is provided.
Here, the heater for heating the fixing roller mainly heats a main heater (first heater) that is included in the fixing roller and mainly heats a predetermined area including the axial center of the fixing roller, and areas on both ends thereof. Some include a sub-heater (second heater). In addition, there is a heater provided with a heater (hereinafter referred to as a pressure heater) for heating the pressure roller from the inside or the outside in order to heat the back side of the sheet (the side opposite to the side where the unfixed image is formed). .
The plurality of heaters that heat the fixing roller and the pressure roller are subjected to energization control according to the detection results of a plurality of temperature sensors (temperature detection means) corresponding to each of the heaters. That is, the main heater has a surface temperature near the center in the axial direction of the fixing roller, the sub heater has a surface temperature near the end in the axial direction of the fixing roller, and the pressure heater has a surface temperature of the pressure roller and the pressure roller outside. The detected temperature of each temperature sensor that measures the surface temperature of the external heating roller to be heated is maintained at a target temperature (usually about 200 ° C. to 210 ° C.) sufficient to melt the unfixed toner and fix it on the sheet. Control to switch between energization / non-energization is performed. As a result, the fixing roller and the pressure roller are maintained at a high temperature, and the unfixed image is heated and fixed on the sheet.
Here, it is ideal to maintain the detected temperatures of all of the temperature sensors at the target temperature, but since the power consumption of the heater necessary to maintain all of the temperature sensors at the target temperature is large, supply to these multiple heaters When no limitation is imposed on the power, the power consumption exceeds the total heater power permitted to be consumed for all of the plurality of heaters. As a result, the power consumption permitted for the entire image forming apparatus (usually 1500 W) is reduced. It will exceed.
For this reason, in the conventional fixing device, the supply power when energizing each heater is fixed, and the total supply power is set in advance so as to be within the total heater power permitted to be consumed for the plurality of heaters as a whole. Is set. That is, the ratio of the electric power supplied to each heater with respect to the total heater electric power when energizing each heater is fixed. Thereby, even if all the heaters are energized, the power consumption does not exceed the total heater power.
Japanese Patent Application Laid-Open No. 2004-26883 discloses that the power consumption of the entire image forming apparatus is allowed by controlling the exposure lamp of the document reading unit and the heater of the fixing device that consume large power in the image forming apparatus so as not to operate simultaneously. Techniques for preventing the above from being exceeded are shown.
Japanese Patent Laid-Open No. 08-286554

Here, a method for controlling each heater of the conventional fixing device and an example of the control result will be described.
FIG. 6 shows a control pattern table of conventional heater control after the start of heat fixing.
In FIG. 6, “OK” in the column for each heater corresponding temperature (temperature sensor detection temperature) represents a case where the temperature is equal to or higher than the target temperature (210 ° C. in this case), and “NG” represents a case where the temperature is lower than the target temperature. . In addition, “xx%” in the DUTY column of supply power represents a duty ratio (time ratio of power supply ON per cycle of the AC power supply) when the phase control of the supply power to each heater is performed. "%" Represents a power supply stoppage.
As shown in FIG. 6, in the conventional fixing device, each heater is energized (DUTY> 0%) when the temperature detected by the corresponding temperature sensor is lower than the target temperature (NG), and is higher than the target temperature (OK). Is controlled so as not to energize (DUTY = 0%). Further, the supplied power when energized is a predetermined power (that is, a power corresponding to a predetermined DUTY). In the example of FIG. 6, the supplied power when energizing each of the main heater, the sub heater, and the pressurizing heater is 100%, 60%, and 40% in terms of DUTY. And these total electric power is electric power set beforehand so that it may become less than the total heater electric power to which consumption with respect to the whole several heater in a fixing device is accept | permitted.
In the example shown in FIG. 6, the rated power of each heater (power consumption when DUTY is 100%) is 820 W for the main heater, 480 W for the sub heater, and 480 W for the pressurizing heater. In this case, 820 × 1 + 480 × 0.6 + 480 × 0.4 = 1300 W is the allowable total heater power.

FIG. 7 shows the trend of the detected temperature of the temperature sensor corresponding to each of the main heater, the sub heater and the pressurizing heater (hereinafter referred to as heater corresponding temperature) when the conventional heater control (according to the control pattern table of FIG. 6) is performed. Represents a graph.
Here, in the conventional heater control, the heater control is performed with the same control pattern as the control pattern shown in FIG. 6 even in the warm-up state until the heat fixing is started.
When a print request is detected while the image forming apparatus is in a pause state (power saving mode state), power supply to the fixing device is started. At this time, since the heater corresponding temperatures T1 to T3 are usually lower than the target temperature, the control pattern Pt1 of FIG. 6 is applied, and all the heaters are energized (the state of St1 in FIG. 7). Thereby, each heater corresponding temperature T1-T3 continues a raise.
Eventually, after the main heater corresponding temperature T1 exceeds the target temperature, the control patterns Pt3 and Pt1 in FIG. 6 are switched according to the state of the main heater corresponding temperature T1 (state of St2 in FIG. 7). Here, in the example of FIG. 7, the pressurizing heater-corresponding temperature T3 remains below the target temperature, but when this exceeds the target temperature, the control pattern Pt5 may be switched.
Then, heat-fixing is started by passing the sheet on which the unfixed image is transferred between the fixing roller and the pressure roller, and then heat-fixing is continuously performed on a plurality of sheets by performing continuous printing. Then, since the heat is taken away from the fixing roller and the pressure roller to the sheet and unfixed toner, the heater corresponding temperatures T1 to T3 are lowered, and the control pattern Pt1 is continuously applied (FIG. 7). St3 state). At this time, the temperature corresponding to the sub heater T2 is lower than the temperature corresponding to the sub heater T1, and the temperature corresponding to the pressurizing heater T3 is further decreased more than that.
However, as the entire fixing device warms up, the roller corresponding temperatures T1 to T3 stop decreasing or turn upward (state of St4 in FIG. 7).
In addition to warming the entire fixing device, the printing operation is temporarily interrupted and the heat fixing is interrupted every time the maximum number of continuous prints (99 sheets in the example of FIG. 7) is heat-fixed. (Because of the non-sheet-passing state: the state of St5 'in FIG. 7), the control pattern Pt3 and Pt1 in FIG. 6 is again switched to the control state depending on the state of the main heater corresponding temperature T1 (the state of St5 in FIG. 7). ).

As a result of performing the conventional control as described above, the sub-heater corresponding temperature T2 becomes substantially lower than the target temperature (state of St4 in FIG. 7) for a relatively long time after the start of heating and fixing. As a result, there is a problem that unfixed toner at a position corresponding to the sub-heater is not sufficiently fixed on the sheet and fixing failure occurs.
In addition, even if the technique disclosed in Patent Document 1 is applied, if the total heater power that is allowed in the first place is less than the power required to maintain all the temperatures corresponding to each roller at the target temperature, a fixing failure may occur. The problem does not go away.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a plurality of heaters in a fixing device that controls energization of the plurality of heaters that heat the fixing heater and the pressure heater. A fixing device capable of preventing occurrence of a fixing failure while suppressing power consumption within an allowable range even when sufficient power for maintaining all corresponding detection temperatures at a target temperature cannot be obtained (cannot be consumed); An object of the present invention is to provide an image forming apparatus having the same.

In order to achieve the above object, the present invention is directed to transferring a sheet on which an unfixed image is transferred between a fixing roller and a pressure roller, which are heated and opposed by a plurality of heaters, to the fixing roller side. The unfixed image is heated and fixed on the sheet by passing through the surface and performing energization control of each of the plurality of heaters based on detection results of a plurality of temperature detection means corresponding to each of the plurality of heaters. In the fixing device, on the basis of the detection results of the plurality of temperature detecting means, control whether to energize each of the plurality of heaters after starting the heat fixing and one of the plurality of heaters is performed. Or control of the ratio of the power supplied to each heater with respect to the total heater power allowed to be consumed by all of the plurality of heaters when energizing a plurality of heaters. It is constituted as a fixing device characterized by comprising comprises a heater power supply control means.
As a result, it is possible to flexibly control the balance of power supply when each heater is energized according to the state of power supply to each of the plurality of heaters, and the ratio of power supply to the heater that has a small effect on fixing performance. It is possible to perform control such as reducing the power supply ratio and increasing the power supply ratio to the heater that has a large influence on the fixing performance. As a result, even if sufficient power to maintain all the detected temperatures corresponding to the plurality of heaters at the target temperature cannot be obtained (cannot be consumed), fixing failure while keeping power consumption within an allowable range. Can be prevented.
More specifically, the heater power supply control unit controls whether to energize each of the plurality of heaters based on the detection results of the plurality of temperature detection units, and based on the number of heaters energized. It is possible to change the ratio of the supplied power to the total heater power.
Conventionally, even when all the heaters are energized, the ratio of the power supplied to each heater with respect to the total heater power is fixed so as not to exceed the allowable total heater power. However, with the above configuration, for example, when energizing more than a predetermined number of heaters (for example, all heaters), the power supply ratio to the heater that has a small influence on the fixing performance is reduced, and in other cases, the original power is reduced. Flexible control such as power supply at a ratio is possible, and the occurrence of fixing failure can be prevented while keeping the total power consumption of all heaters within the allowable total heater power.

More specifically, the plurality of heaters are included in the fixing roller, and a first heater that mainly heats a predetermined area including the center in the axial direction of the fixing roller, and a second heater that mainly heats areas on both ends thereof. And a third heater that heats the pressure roller from the inside or the outside, and the heater power supply control means applies the current to all of the first to third heaters and the second case in other cases. It is conceivable to change the ratio of the supplied power to the total heater power when the heater is energized.
Here, the first heater, the second heater, and the third heater correspond to the main heater, the sub heater, and the pressurizing heater, respectively.
As a result of various experiments, in the conventional control result shown in FIG. 7, a decrease in temperature corresponding to the second heater (sub-heater) (fixing roller temperature (temperature on the unfixed image side)) is the main cause of deterioration in fixing performance. It turned out to be a cause. Therefore, according to the above configuration, when at least one of the first heater (main heater) or the third heater (pressing heater) is de-energized (corresponding to the “other cases”), The ratio of the power supplied to the second heater can be changed (increased) so as to lead to an increase in the power supplied to the two heaters (sub-heaters). As a result, it is possible to prevent the occurrence of fixing failure while keeping the total power consumption of all heaters within the allowable total heater power.
In this case, the heater power supply control means, the heater power supply control means, the detected temperatures of the first temperature detection means and the second temperature detection means corresponding to the first heater and the second heater, respectively, are set to a predetermined target temperature. The first heater and the second heater are switched according to whether or not the first heater and the second heater are energized, and further, the first temperature detector to the third temperature detector corresponding to the first to third heaters, respectively. Whether each detected temperature is lower than the target temperature and the detected temperature of the third temperature detecting means is lower than a preset lower limit temperature lower than the target temperature, and then is higher than the preset lower limit temperature by a predetermined margin temperature. It is conceivable to switch whether or not to energize the third heater depending on whether or not the current state is reached.
If the supplied power when energizing each heater is a fixed ratio as in the prior art, as shown in FIG. 7, the temperature corresponding to the sub-heater (second heater) is significantly lowered after the start of heating and fixing. Here, the main cause of the occurrence of fixing failure is a decrease in temperature corresponding to the sub heater (second heater), and the temperature corresponding to the pressurizing heater (third heater) decreases to a relatively low temperature. However, it was found that the effect on fixing performance was small.
Therefore, according to the above configuration, when both the first heater and the second heater need to be energized (that is, when the detected temperatures of the first and second temperature detecting means are both lower than the target temperature), The three heaters are de-energized until the corresponding temperature (detected temperature of the third temperature detecting means) falls below the set lower limit temperature lower than the target temperature on the fixing roller side, so that the amount of electric power that has a margin is generated. Can be used to increase the ratio of power supplied to the second heater (sub-heater). As a result, the temperature drop corresponding to the second heater (sub-heater) can be kept to a minimum, and the occurrence of fixing failure can be prevented.
In this case, for example, it is conceivable to set each of the target temperatures in the detected temperatures of the first temperature detecting means and the second temperature detecting means within a range of about 200 ° C. to about 210 ° C. Further, it is conceivable that the set lower limit temperature at the detected temperature of the third temperature detecting means is set to about 160 ° C. The marginal temperature may be about 10 ° C.

Further, as a specific configuration for changing the power supply to the heater by the heater power supply control means, the power supply to the heater is changed by phase control, that is, by duty control of energization and non-energization per unit period in the power supply. What to do is conceivable.
The present invention may be an image forming apparatus characterized by including the fixing device.

  According to the present invention, energization of each of the plurality of heaters after the start of heat fixing based on the detection results of the plurality of temperature detecting means corresponding to the plurality of heaters for heating the fixing roller and the pressure roller, respectively. And control of the ratio of the power supplied to each heater with respect to the total heater power allowed to be consumed by all of the plurality of heaters when energizing one or more of the plurality of heaters Thus, according to the energization state to each of the plurality of heaters, it is possible to flexibly control the balance of the supplied power when energizing each heater. As a result, it is possible to perform control such as lowering the power supply ratio to the heater having a small influence on the fixing performance and increasing the power supply ratio to the heater having a large influence on the fixing performance. Even when sufficient power for maintaining the detected temperature at the target temperature cannot be obtained (cannot be consumed), it is possible to prevent the occurrence of fixing failure while keeping the power consumption within an allowable range.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
1 is a side sectional view showing the overall configuration of an image forming apparatus Z on which the fixing device X according to the embodiment of the present invention is mounted, FIG. 2 is a schematic sectional view of the fixing device X, and FIG. 3 is a fixing device. 4 is a schematic cross-sectional view of a fixing roller included in X, FIG. 4 is a diagram showing a control pattern table of heater control in the fixing device X, and FIG. 5 is detection of temperature sensors corresponding to each heater when heater control is performed by the fixing device X. FIG. 6 is a diagram showing a control pattern table of heater control in a conventional fixing device, and FIG. 7 is a trend of detected temperature of a temperature sensor corresponding to each heater when heater control is performed by the conventional fixing device. It is a graph.

First, the configuration of the image forming apparatus Z on which the fixing device X according to the embodiment of the present invention is mounted will be described with reference to the sectional side view of FIG.
The image forming apparatus Z has a copier mode (copying mode), a printer mode, and a FAX mode as print modes. Operation input from an operation unit (not shown) and print job from an external host device such as a personal computer are performed. A print mode corresponding to reception (an example of an image formation request) is selected by a control unit described later.
As shown in FIG. 1, the image forming apparatus Z is roughly divided into a document reading unit 10, a paper feeding unit 20, a printing unit 30, and a paper discharge unit 40, and the document reading unit 10 is arranged above the paper feeding unit 20. A paper discharge unit 40 is provided at an intermediate position between the document reading unit 10 and the paper supply unit 20.
Hereinafter, the copier mode will be described from the above processing modes.
After the user places a document on the platen glass 11 of the document reading unit 10 (scanner unit), the sheet (recording paper) is placed on the sheet feeding cassette 21 of the sheet feeding unit 20 or the manual feed tray 23 provided on the side of the apparatus. After inputting the condition input key (number of printed sheets / printing magnification, etc.) on the operation panel (not shown) placed on the front surface of the apparatus, the start key on the operation panel is used as an operation for making an image formation request. When the operation is performed, the copy operation is started.
When the start key is operated, a main drive motor (not shown) starts and each drive gear rotates. Thereafter, the paper feed roller 22 or 22a rotates to feed (feed) the paper into the apparatus, and the fed paper reaches the registration roller 31 (roller pair) and is captured. The registration roller 31 temporarily stops the paper so as to synchronize with the leading edge (image formation start portion) of the image formed on the photosensitive drum 32, and the leading edge of the paper is uniformly pressed against the registration roller 31. Thus, the leading edge position of the paper is corrected.

On the other hand, in the document reading unit 10, the copy lamp 12a (light source) is turned on, and the exposure starts when the copy lamp unit 12 moves in the direction of the arrow. Irradiation light applied to the document by the copy lamp 12a becomes reflected light (reflected light from the document) including image information of the document, and the reflected light is transmitted from the first mirror 12b provided in the copy lamp unit 12 to the second light. Reading is performed by inputting to the CCD 16 from the mirror 13, the third mirror 14, and the optical lens 15.
The image information read in this way is converted into an electrical signal by a CCD circuit (not shown), and the image information signal is subjected to image processing under a set condition, and the laser scanner unit. 33 as print data.

On the other hand, the entire photosensitive drum 32 is charged to a predetermined charging potential by the charging unit 34.
In the laser scanner unit 33, the laser beam emitted from the semiconductor laser 33a is irradiated to the photosensitive drum 32 while being deflected by the rotating polygon mirror 33c and various lenses. As a result, the laser beam is scanned on the photosensitive drum 32, and an electrostatic latent image is formed on the photosensitive drum 32. Thereafter, the toner on the MG roller 35a in the developing tank 35 is attracted onto the surface of the photosensitive drum 32, and the electrostatic latent image is visualized by the toner according to the potential gap on the photosensitive drum 32.
In addition, paper (recording paper) to be imaged is conveyed in the direction of the photosensitive drum 32 by the registration roller 31 in time, and the toner image on the photosensitive drum 32 is transferred to the paper by the transfer unit 36 (corona charger). Transferred as an unfixed toner image. The toner remaining on the photosensitive drum 32 is scraped off by the cleaning blade 37 a of the drum unit and collected by the cleaner unit 37.

Further, the sheet (sheet) on which the unfixed toner image is transferred passes between the fixing roller 71 and the pressure roller 72 provided in the fixing device X, and heat and pressure are applied to the unfixed toner on the sheet. Is fixed (melted / fixed) to the sheet, and is discharged to the discharge tray 42 by the discharge roller 41. The fixing roller 38a is heated by a plurality of heaters 81 and 82 provided (enclosed) therein.
In addition, when it is detected by a predetermined sensor that a document is placed on the document tray 19 included in the document reading unit 10, the paper feed roller 51 rotates when a predetermined start key operation is performed. Then, the document placed on the document tray 19 is sent into the document reading unit 10 and is transported through a predetermined transport path Rt1. A registration roller 53 is provided on the conveyance path Rt1, and the original is captured by the registration roller 53 and positioned at the leading end of the original, and then conveyed to the original reading position at a predetermined timing.
On the other hand, the document being conveyed is exposed while the copy lamp unit 12 is stopped at a predetermined stop position (document reading position). The process of reading the document image by the reflected light from the document obtained by this exposure is as described above.
The document whose image has been read in this way is discharged to the document discharge unit 18.

Next, the configuration of the fixing device X according to the embodiment of the present invention will be described using the cross-sectional view of FIG.
The fixing device X includes a fixing roller 71 and a pressure roller 72 that are heated by a plurality of heaters 81, 82, and 83 so as to face each other, and a driving unit 50 such as a motor that rotationally drives the fixing roller 71. Between the rollers 71 and 72, the sheet 1 on which the unfixed image has been transferred is passed through the transfer surface (the upper surface of the sheet 1 in FIG. 2) of the unfixed image toward the fixing roller 71. Further, the fixing device X includes a plurality of temperature sensors 81a, 82a, 83a such as thermistors corresponding to the plurality of heaters 81, 82, 83, and the detection results of the temperature sensors 81a-83a. And a control unit 60 that controls energization of each of the plurality of heaters 81, 82, and 83 and controls the driving unit 50 that is a rotational driving source of the fixing roller 71.
The fixing roller 71 and the pressure roller 72 that is driven to rotate while being pressed against the peripheral surface thereof form a nip portion Pn, and the sheet 1 on which an unfixed image (toner image) is transferred passes through the nip portion Pn. As a result, the unfixed toner image is fused (heat-fixed) to the sheet.
The controller 60 inputs the surface temperatures of the fixing roller 71 and the pressure roller 72 detected by the temperature sensors 81a to 83a through the input circuits 81b, 82b, and 83b, and sets each surface temperature to a predetermined temperature. Energization control to each of the heaters 81 to 83 is performed through the drivers 81c, 82c, and 83c so as to be maintained. The control unit 60 includes a CPU, a ROM, a RAM, and the like (not shown), and executes each control according to a predetermined program stored in the ROM. The image forming apparatus Z on which the fixing device X is mounted. You may also use as a control part which controls.

FIG. 3 is a sectional view of the fixing roller 71 in the axial direction.
As shown in FIG. 3, the heaters 81 and 82 for heating the fixing roller 71 are mainly included in the hollow portion of the cylindrical fixing roller 71 and mainly heat a predetermined area W <b> 1 including the axial center of the fixing roller 71. Main heater 81 (an example of the first heater), and a sub-heater 82 (an example of the second heater) that mainly heats the regions W2 on both ends thereof.
The temperature sensors 81a and 82a detect the surface temperature of the fixing roller 71 in the regions W1 and W2 corresponding to the main heater 81 and the sub heater 82, respectively. Hereinafter, the temperatures detected by the temperature sensors 81a and 82a are referred to as a main heater corresponding temperature and a sub heater corresponding temperature.
In the example shown in FIG. 3, the heating regions (regions where the heaters are formed) of the main heater 81 and the sub-heater 82 are basically configured not to overlap, but this is not restrictive.
For example, a configuration in which a part of both heating regions overlap each other, or a heater having a smaller output than the region W1 is arranged in the region W2 for the main heater 81 while substantially overlapping the entire heating regions. (Substantially heating the region W1), conversely, the sub-heater 82 may be configured such that a heater having a smaller output than the region W2 is disposed in the region W1 (mainly heating the region W2). Conceivable.
On the other hand, although not shown in FIG. 3, the other heater 83a (hereinafter referred to as a pressure heater) has a cylindrical shape that rotates in contact with the entire surface of the pressure roller 72 in the axial direction. It is included in the hollow portion of the external heating roller 73 and externally heats the surface of the pressure roller 72 over its entire axial direction. The temperature sensor 83a detects the surface temperature of the pressure roller 72 in the region heated by the pressure heater 83 (for example, near the central portion in the axial direction). Hereinafter, the temperature detected by the temperature sensor 83a is referred to as a pressurizing heater corresponding temperature.
In this embodiment, an example of heating from the outside of the pressure roller 72w is shown. However, the pressure roller 72 is a cylindrical roller, and the pressure heater 73 is included in a hollow portion thereof, whereby the pressure is increased. The roller 72 may be heated from the inside.

The configuration of the fixing device X described above is not particularly different from the conventional fixing device.
The fixing device X is different from the conventional fixing device in the control method of the heaters 81 to 83 by the control unit 60.
FIG. 4 shows a control pattern table for heater control after the heat fixing by the fixing device X is started.
Also in FIG. 4, “OK” in the column of the heater corresponding temperatures T1 to T3 (detected temperatures of the temperature sensors 81a to 83a) represents a case where the temperature is equal to or higher than the target temperature Ts, as in FIG. "Represents a case where the temperature is lower than the target temperature. The example shown in FIG. 6 is an example in the case where the target temperature is 210 ° C. In general, the temperature is preferably about 200 ° C. to 210 ° C. in order to ensure the fixing performance.
However, in the column of the temperature corresponding to the pressurizing heater T3, “specific” means that the temperature corresponding to the pressurizing heater T3 (corresponding to the temperature detected by the third temperature detecting means corresponding to the third heater) is the target temperature Ts. This represents a state (hereinafter referred to as a specific state) from when the temperature falls below a lower preset lower limit temperature Tx until it reaches a temperature Tm higher than the preset lower limit temperature Tx by a predetermined margin temperature. “OK” and “NG” indicate states whether or not the temperature is equal to or higher than the target temperature Ts in cases other than the specific state.
In addition, “xx%” in the DUTY column of the supplied power indicates a duty ratio (AC) when the control unit 60 performs phase control of the supplied power to the heaters 81 to 83 via the drivers 81 c to 83 c. (Time ratio of power supply ON per power supply cycle), and “0%” indicates power supply stop.
In the fixing device X, the rated power (power consumption when DUTY is 100%) of the heaters 81 to 83 is 820 W for the main heater 81, 480 W for the sub heater 82, and 480 W for the pressure heater 83. Then, 820 W × 1 + 480 W × 0.6 + 480 W × 0.4 = 1300 W is the total heater power that can be consumed by all of the plurality of heaters 81 to 83 included in the fixing device X.

As shown in FIG. 4, the control unit 60 (an example of the heater power supply control unit) is based on the detection results (temperatures corresponding to the heaters T1 to T3) of the plurality of temperature sensors 81a to 83a (temperature detection units). , After starting heat fixing, control whether to energize each of the plurality of heaters 81-93 (duty ratio> 0%) and 2 out of the plurality of heaters 81-83. Control of the power supplied to the heater (duty ratio) when energizing the two heaters 82 and 83 (that is, the ratio of the power supplied to the heaters 82 and 83 to the total heater power allowed to be consumed by all the heaters 81 to 83) Control).
At that time, the control unit 60 controls whether to energize each of the plurality of heaters 81 to 83 based on the detected temperatures of the plurality of temperature sensors 81a to 83a (temperature detection means), Control is performed to change the ratio of the supplied power to the total heater power based on the number of heaters 81 to 83 that are energized.
More specifically, for the main heater 81 and the sub heater 82, the control unit 60 sets the main heater corresponding temperature T1 (the detected temperature of the first temperature detecting means corresponding to the first heater) and the sub heater. When the corresponding temperature T2 (detected temperature of the second temperature detecting means corresponding to the second heater) is lower than the predetermined target temperature Ts, energization is performed (duty ratio> 0%), and the target temperature Ts or higher is applied. Is switched to stop energization (duty ratio = 0%).
That is, the main heater 81 is ON (energized) when T1 <Ts, OFF (non-energized) when T1 ≧ Ts, and the sub-heater 82 is ON when T2 <Ts, and OFF when T2 ≧ Ts. To do.

Further, the controller 60 deenergizes the pressurizing heater 83 when the pressurizing heater corresponding temperature T3 (detected temperature of the third temperature detecting means) is equal to or higher than the target temperature Ts (control). Patterns Pt13, Pt15, Pt17, and Pt19). In other cases, when at least one of the temperature corresponding to the main heater T1 and the temperature corresponding to the sub heater T2 (detected temperature of the first and second temperature detecting means) is equal to or higher than the target temperature Ts, the pressurizing heater 83 is energized (duty ratio> 0%) (state of control patterns Pt14, Pt16, Pt18).
On the other hand, the control unit 60 (an example of the heater power supply control unit) is configured such that both the main heater corresponding temperature T1 and the sub heater corresponding temperature T2 (the detected temperatures of the first and second temperature detecting units) are the target temperature. When the temperature is less than Ts, the pressurizing heater-corresponding temperature T3 falls below the specific state (the set lower limit temperature Tx (a predetermined temperature lower than the target temperature Ts)) and then a predetermined margin from the set lower limit temperature Tx. When the temperature (e.g., a state until reaching a temperature Tm that is higher by 10 ° C.), energization is performed (the state of the control pattern Pt12).

Further, as shown in FIG. 4, the control unit 60 always fixes the duty ratio of the main heater 81 when energization is performed (duty ratio> 0%) to 100%, and the total heater is energized. The ratio to the heater power is fixed (control patterns Pt11 to 13, Pt16 and 17).
On the other hand, when energizing the sub-heater 82 and the pressurizing heater 83, the control unit 60 selects all of the three (plural) heaters 81 to 83 (an example of a predetermined number (three) or more). The duty ratio is changed between when the heater is energized and in other cases (that is, the ratio of the supplied power to the total heater power is changed).
More specifically, the controller 60 sets the duty ratio of energization to 60% when the three heaters 81 to 83 are energized (the state of the control pattern Pt12). In other cases, the duty ratio when energizing is set to 100% (states of control patterns Pt11 and Pt13 to 15).
Further, the controller 60, when energizing the three heaters 81 to 83 with respect to the pressurizing heater 83, sets the duty ratio of energization to 40% (the state of the control pattern Pt12), In other cases, the duty ratio when energizing is set to 100% (states of control patterns Pt14, Pt16, and Pt18).

FIG. 5 shows the corresponding temperatures T1 to T1 of the main heater 81, the sub heater 82, and the pressurizing heater 83 when the heater control is performed by the fixing device X that executes control according to the control pattern shown in FIG. The trend graph of T3 is represented. In the fixing device X, in the warm-up state until the heat fixing is started, the heater control is performed with the same control pattern as the conventional control pattern shown in FIG. 6 and is almost the same as the situation described in FIG. Since there is, explanation is omitted here.
In the fixing device X, heat fixing is started for allowing the sheet 1 on which the unfixed image has been transferred to pass between the fixing roller 71 and the pressure roller 72, and then a plurality of heat fixings are performed by performing continuous printing. When the sheet 1 is continuously executed, heat is removed from the fixing roller 71 and the pressure roller 72 to the sheet 1 and the unfixed toner, and the heater corresponding temperatures T1 to T3 start to decrease.
However, at that time, the control unit 60 sets the control state of the heater to the control pattern Pt11 shown in FIG. As a result, the power supply to the pressurizing heater 83 is turned off, while the duty ratio of the power supplied to the sub heater 82 is increased from 60% to 100%. As a result, the pressurizing heater-corresponding temperature T3 is significantly lower than that of the conventional one (FIG. 7), but the corresponding decrease in the main heater-corresponding temperature T1 and the sub-heater-corresponding temperature T2 is minimized (FIG. 7). (St11 state of 5).

Then, after the temperature corresponding to the pressurizing heater T3 falls below the specific state (the set lower limit temperature Tx (a predetermined temperature lower than the target temperature Ts)), a predetermined margin temperature (for example, 10 ° C.) from the set lower limit temperature Tx. The control unit 60 starts energizing the pressurizing heater 83 and subtracts the supplied power from the supplied power to the sub-heater 82. Switching to the control pattern Pt12 (FIG. 4) (state of St12 in FIG. 5). As a result, the temperature corresponding to the pressurizing heater T3 rises.
Thereafter, the pressurizing heater corresponding temperature T3 goes back and forth between the specific state and the released state, and the control unit 60 changes the control state of each heater according to the state change to the control pattern Pt11. And Pt12 (a state of St13 in FIG. 5). As a result, the power supplied to the pressurizing heater 83 is suppressed to such an extent that the corresponding temperature T3 is maintained at the minimum necessary temperature (Tx to Tx + α) that does not affect the fixing performance. Is supplied to the sub-heater 82 (the duty ratio is changed from 60% to 100%). As a result, as can be seen from the graph of FIG. 5, the decrease in the sub-heater corresponding temperature T2 can be suppressed to a very small extent as compared with the conventional case (FIG. 7).
As a result of various experiments, it is preferable for securing the fixing performance that the set lower limit temperature Tx at the pressurizing heater corresponding temperature T3 (the temperature detected by the third temperature detecting means) is about 160 ° C.
Further, while performing such control (St13), in addition to the entire fixing device X being warmed by continuous operation, every time heat fixing for the maximum continuous print number (99 sheets in the example of FIG. 5) is performed. Temporarily interrupting the printing operation and interrupting heat fixing (non-sheet passing state → no heat transfer to sheet or the like: state St13 ′ in FIG. 5), the pressurizing heater corresponding temperature T3 Will also turn upward.

  As a result of various experiments, in the conventional control result shown in FIG. 7, there is a decrease in the sub heater corresponding temperature T2 (temperature corresponding to the second heater), which is the temperature of the fixing roller 71 on the side that directly heats the unfixed image. , It was found to be the main cause of fixing performance deterioration. Therefore, as described above, when the pressurization heater 83 (third heater) is de-energized, the pressurization heater 83 is connected to the pressurization heater 83 so as to increase the power supplied to the subheater 82 (second heater). By changing (increasing) the ratio of supply power (duty ratio), it is possible to prevent the occurrence of fixing failure while keeping the total power consumption of all heaters within the allowable total heater power.

Further, assuming that the supply power at the time of energizing each heater is a fixed ratio as in the prior art, as shown in FIG. 7, the temperature corresponding to the sub-heater T2 (corresponding temperature of the second heater) is greatly increased after the start of heating and fixing. To drop. Here, the main cause of the occurrence of fixing failure is a decrease in the sub heater corresponding temperature T2, and the fixing heater corresponding temperature T3 (temperature corresponding to the third heater) is fixed even if the temperature is lowered to a relatively low temperature. It was found that the effect on performance was small.
Therefore, in the present fixing device X, as described above, when the main heater 81 (first heater) and the sub heater 82 (second heater) need to be energized (that is, the main heater corresponding temperature T1 and the sub heater corresponding). When the temperature T2 (the temperature detected by the first and second temperature detecting means) is less than the target temperature Ts), the pressurizing heater (third heater) is set to the pressurizing heater corresponding temperature T3. A non-energized state is set when in a specific state, and an amount of power generated by this is used to increase the ratio of power supplied to the sub heater 82 (second heater) (duty ratio 60% → 100%). As a result, as shown in FIG. 7, the decrease in the temperature corresponding to the sub-heater T2 can be suppressed to a very small extent, and the occurrence of fixing failure can be prevented.

In the embodiment described above, the heater for heating the fixing roller 71 and the pressure roller 72 is composed of the three heaters 81 to 83. However, the present invention is not limited to this, and two heaters or four or more heaters are used. The thing which consists of can also be considered.
For example, instead of the main heater 81 and the sub heater 82, one heater (fixing heater) for heating the fixing roller 71 in the entire axial direction thereof is provided, and the energization to the pressurizing heater 83 is performed. In some cases, it is conceivable to change the ratio of the supplied power to the total heater power to the fixing heater.
Similarly, the main heater 81 and the sub-heater 82 that heat the fixing roller 71 may be replaced with a plurality of heaters that heat each of the heating regions divided into a plurality of regions, and similar power supply control may be performed. It is done.
In this case, for example, according to the size (sheet width) in the roller axial direction of the sheet to be heat-fixed, only the heater that heats the passage area of the sheet is controlled to be energized, and according to the number of energized heaters It is conceivable to change the ratio of the supplied power to the total heater power to the energized heater. As a result, it is possible to increase the power supplied to the energized heater when heating and fixing a narrow sheet while suppressing the heater power consumption within the total heater power. As a result, it is possible to increase the heat fixing speed (peripheral speed of each roller) while securing the fixing performance for a narrow sheet.
In the embodiment described above, the ratio of the power supplied to the sub-heater 82 (ratio to the total heater power) in the case of energizing all three heaters 81 to 83 (three or more) and in other cases. For example, when four or more heaters are provided, the ratio of the power supplied to a specific heater (in other cases, when energizing three or more heaters and in other cases) Other embodiments in which the ratio of the power supplied to each heater is changed based on the number of heaters to be energized, such as changing the ratio of the total heater power).

  The present invention can be used for a fixing device in an image forming apparatus.

1 is a side sectional view showing an overall configuration of an image forming apparatus Z on which a fixing device X according to an embodiment of the present invention is mounted. 2 is a schematic sectional view of the fixing device X. FIG. 3 is a schematic cross-sectional view of a fixing roller provided in the fixing device X. FIG. FIG. 6 is a diagram illustrating a control pattern table of heater control in the fixing device X. 6 is a trend graph of temperature detected by a temperature sensor corresponding to each heater when heater control is performed by the fixing device X. FIG. The figure showing the control pattern table | surface of the heater control in the conventional fixing device. The trend graph of the temperature detected by the temperature sensor corresponding to each heater at the time of performing heater control by the conventional fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image reading part 18 ... Document discharge part 20 ... Paper feed part 30 ... Printing part 32 ... Photosensitive drum 35 ... Developing tank 36 ... Transfer unit 40 ... Paper discharge part 50 ... Drive part 60 ... Control part 71 ... Fixing roller 72 ... Pressure roller 81 ... Main heater (first heater)
82 ... Sub heater (second heater)
83 ... Pressurizing heater (third heater)
81a ... Temperature sensor corresponding to the main heater (first temperature detecting means)
82a ... Temperature sensor corresponding to the sub-heater (second temperature detecting means)
83a ... Temperature sensor corresponding to the pressurizing heater (third temperature detecting means)
81b to 83b ... drivers 81c to 83c ... input circuit W1 ... heating area W2 of main heater ... heating area X of sub heater ... fixing device Z ... image forming apparatus T1 ... temperature corresponding to main heater T2 ... temperature corresponding to sub heater T3 ... corresponding to heater for pressurization Temperature Ts ... Target temperature Tx ... Set adjustment Pt1, Pt2, ... Control pattern

Claims (8)

A sheet on which an unfixed image is transferred between a fixing roller and a pressure roller that are heated and opposed to each other by a plurality of heaters is passed toward the fixing roller with the transfer surface of the unfixed image directed, and the plurality of sheets A fixing device that heats and fixes the unfixed image on the sheet by performing energization control of each of the plurality of heaters based on detection results of a plurality of temperature detection units corresponding to each of the heaters;
Control whether to energize each of the plurality of heaters after starting heat-fixing based on the detection results of the plurality of temperature detecting means, and energization of one or more of the plurality of heaters And a heater power supply control means for controlling the ratio of the power supplied to each heater with respect to the total heater power allowed to be consumed by all of the plurality of heaters.   The heater power supply control unit controls whether to energize each of the plurality of heaters based on detection results of the plurality of temperature detection units, and based on the number of heaters energized, The fixing device according to claim 1, wherein the power supply ratio is changed. The plurality of heaters are included in the fixing roller and include a first heater that mainly heats a predetermined area including an axial center of the fixing roller, a second heater that mainly heats areas on both ends thereof, and the pressure roller. A third heater for heating from the inside or the outside,
The heater power supply control means changes the ratio of the supplied power to the total heater power when energizing the second heater depending on whether energizing all of the first to third heaters or otherwise. The fixing device according to claim 2. The heater power supply control means
Depending on whether the detected temperatures of the first temperature detecting means and the second temperature detecting means corresponding to the first heater and the second heater are lower than a predetermined target temperature, respectively, the first heater and the second heater are supplied to the first heater and the second heater, respectively. Whether or not energization is performed is switched, and whether or not each detected temperature of the first temperature detecting means to the third temperature detecting means corresponding to each of the first to third heaters is lower than the target temperature, and the third temperature The third heater depends on whether or not the temperature detected by the detection means falls below a predetermined set lower limit temperature lower than the target temperature and reaches a temperature that is higher than the set lower limit temperature by a predetermined margin temperature. The fixing device according to claim 3, wherein whether or not energization is performed is switched.   5. The fixing device according to claim 4, wherein each of the target temperatures at temperatures detected by the first temperature detection unit and the second temperature detection unit is set in a range of about 200 ° C. to about 210 ° C. 6.   The fixing device according to claim 5, wherein the set lower limit temperature at the temperature detected by the third temperature detecting means is set to about 160 ° C. 6.   The fixing device according to claim 1, wherein the heater power supply control unit changes power supplied to the heater by phase control.   An image forming apparatus comprising the fixing device according to claim 1.

Images