JP4685514B2 - Fixing apparatus, image forming apparatus, and heating control method of fixing apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an image forming apparatus, an image forming apparatus using the fixing device, and a heating control method for a heater for the fixing device.

  As this type of technology, for example, the inventions described in Patent Documents 1 and 2 are known. Among these, the invention described in Patent Document 1 is made for the purpose of speeding up the fixing device and suppressing a drop in the fixing temperature and overshoot, and the first rotation having the first heat source. An image forming apparatus including a fixing device that sandwiches a recording sheet between a member and a second rotating member having a second heat source, and thermally fixes a toner image formed on the recording sheet. A first temperature detecting device that is installed in contact with the first rotating member to detect the temperature of the member; and a first temperature detecting device that is installed in contact with the second rotating member to detect the temperature of the member. Immediately after power input to the image forming apparatus, the second heat source is controlled by the detection output of the second temperature detection apparatus. After the control, the first or second temperature detection apparatus The first heat source can be controlled by the detection output.

  In the invention described in Patent Document 2, a fixed image having a desired glossiness can be easily and stably formed over a long period of time, and a fixed image having a desired glossiness can be reliably formed regardless of changes in the operating environment or the like. For the belt-fixing type fixing device, the glossiness of the fixed image to be formed is set, the temperature of the pressure roller is detected, and at least the glossiness of the set fixed image is added. The target heating roller temperature is calculated based on the pressure roller detection temperature, the load nip time, the pseudo nip time, and the load nip surface pressure, and the operation state of the heating source in the heating roller is controlled based on the target heating roller temperature. It is a thing.

That is, the invention described in Patent Document 1 is configured to control the heater of the heating roller based on the detection output of the temperature detection device of the heating roller or the temperature detection device of the pressure roller. The target heating roller temperature is calculated based on the pressure roller detection temperature, and the heating source of the heating roller is controlled based on the calculated target heating roller temperature and the heating roller detection temperature.
Japanese Patent Laid-Open No. 2002-221871 JP2003-149987A

  Both of the above two known documents control the heating source of the heating roller based on the temperature detected by the pressure roller. However, in any case, the heating source of the heating roller is merely turned on and off based on the detected temperature of the pressure roller (input is reduced in Patent Document 1).

  In addition, there is a conventional fixing control using PID control, but the control is performed using the detection temperature of a single temperature detection element corresponding to the heating source.

  According to the present invention, in a fixing device including a pair of rotating bodies, the temperature of the second rotating body having the first rotating body and the third heating source heated by the first and second heating sources is precisely controlled. The purpose is to do.

To achieve the above object, the first means heats the central portion of the first rotating body in the fixing device that fixes the image on the recording medium by passing the recording medium between the pair of rotating bodies. to a first heat source, a second heat source for heating the end portion of the first rotating body, and a third heating source to heat the second rotating body, a center of the first rotating part a first temperature detecting means for detecting the temperature of parts, said second temperature detecting means for detecting a first temperature of the end portion of the rotary member, a third for detecting the temperature of the second rotary member Temperature detection means; first calculation means for calculating a lighting ratio at a predetermined control period of the first heating source based on the detected temperature detected by the first temperature detection means; and the second temperature. Lighting of the second heating source at a predetermined control cycle based on the detected temperature detected by the detecting means Second calculating means for calculating a total, and third calculating means for calculating a lighting ratio at a predetermined control period of the third heating source based on the detected temperature detected by the third temperature detecting means; , based on the lighting ratio of the highest heating amount greater heating source of the heating source of the first to third, comprising a correction means for reducing the turn-on rate of the other two heat sources, a large of the most heating amount The heating source is heated at the lighting ratio calculated by the calculating means, and the other two heating sources are heated at the lighting ratio corrected by the correcting means .
The second means is the first means in which the lighting ratio of the other two heating sources is reduced by the lighting ratio of the heating source having the largest heating amount and the lighting of each of the other two heating sources. It is calculated from a ratio based on a predetermined formula .
According to a third means, in the first means, the amount of reduction of the lighting ratio of the other two heating sources is the lighting ratio of the heating source having the largest heating amount and the lighting of each of the other two heating sources. It is stored as a table based on the ratio .
A fourth means is characterized in that, in the second means, a plurality of the predetermined formulas are stored depending on whether the fixing device is in a standby state or a paper passing state .
A fifth means is characterized in that, in the third means, a plurality of the tables are stored depending on whether the fixing device is in a standby state or a sheet passing state .
A sixth means, characterized in that the fixing device according to any one of the means in the first to fifth image forming apparatus.
The seventh means is a heating control method of a fixing device for fixing an image on a recording medium by passing the recording medium between a pair of rotating bodies, and is a first heating source heated by a first heating source. Detecting the temperature of the central portion of the rotating body, detecting the temperature of the end of the first rotating body heated by the second heating source, and heating the second rotating body. Detecting the temperature of the first heating source, calculating the lighting ratio of the first heating source at a predetermined control period based on the temperature of the first heating source, and Calculating a lighting ratio of the second heating source in a predetermined control cycle based on the temperature; and lighting the third heating source in a predetermined control cycle based on the temperature of the third heating source A step of calculating a ratio, and the most heating amount of the first to third heating sources. The step of reducing the lighting ratio of the other two heating sources based on the lighting ratio of the threshold heating source, the heating source having the largest heating amount is heated at the calculated lighting ratio, and the other two heating sources And a step of heating at a lighting rate after being reduced.

  In the embodiments described later, the first rotating body is the fixing belt 330, the first and second heating sources are the first and second heating (halogen) heaters 321 and 322, and the second rotating body. Are the pressure roller 340, the third heating source is the third heater 341, the first to third temperature detecting means are 351, 352, 350, the control means is the I / O control plate 740, respectively. Correspond.

According to the present invention, precise control can be performed while suppressing the temperature from rising and falling .

  Embodiments of the present invention will be described below with reference to the drawings.

<overall structure>
FIG. 1 is a diagram showing a schematic configuration of a color printer as a color image forming apparatus according to an embodiment of the present invention. In FIG. 1, the color printer basically includes an image forming unit 100, a paper feed unit 200, a fixing unit 300, and a paper discharge unit 400.

  The image forming unit 100 includes CMYK photosensitive drums 101C, 101M, 101Y, and 101K, a writing unit for each color (not shown) that performs optical writing on the photosensitive drums 101C, 101M, 101Y, and 101K, and a photosensitive drum. Contact with the body drums 101C, 101M, 101Y, and 101K, and face each of the photosensitive drums 101C, 101M, 101Y, and 101K with the transfer belt 102 stretched between the driving pulley and the driven pulley and the transfer belt 102 interposed therebetween. The transfer roller 103C, 103M, 103Y, 103K provided at the position where the transfer is performed, and the transfer roller 105 provided downstream of the black transfer portion and sandwiching the vertical conveyance path 105 are mainly configured.

  The sheet feeding unit 200 conveys the first and second sheet feeding trays 210 and 220 and the transfer sheets 212 and 222 fed from the sheet feeding trays 210 and 220 by the sheet feeding rollers 211 and 221 to the longitudinal conveyance path 105. A transfer sheet conveyance path 106 for manual transfer, and a manual feed tray 230 for manually feeding the transfer sheet to the vertical conveyance path 105.

  A fixing unit (hereinafter, referred to as a fixing device) 300 is provided on the downstream side of the longitudinal conveyance path 105 in the transfer sheet conveyance direction, and includes a fixing roller 310, a heating roller 320, a fixing belt 330, and a pressure roller 340.

  The paper discharge unit 400 is provided on the downstream side of the fixing device 300 in the transfer paper conveyance direction, and includes a paper discharge roller 410 and a paper discharge tray 420.

  In the color printer configured as described above, the transfer paper fed from the paper feed trays 210 and 220 or the manual feed tray 230 is sent out to the vertical conveyance path 105 and is formed by the image forming unit 100 that performs development and transfer. The full-color image superimposed on the surface of the transfer belt 102 is transferred onto the transfer paper by the transfer roller 104. The unfixed image transferred onto the transfer paper is sent to the fixing device 300 and is formed by a fixing roller 310 and a pressure roller 340 that are driven and driven inside the fixing belt 330 whose surface is heated by a heat source such as a heater. As a result, the sheet is fixed on the surface of the transfer paper and becomes a semi-permanent image, and is discharged to the discharge tray 420.

  2A and 2B are diagrams showing a detailed configuration of the fixing device 300. FIG. 2A is a cross-sectional view seen from the front, and FIG. 2B is a plan view. It is stretched between the fixing roller 310 and the heating roller 320, and is maintained at an appropriate tension by a tension adjusting means (not shown). In addition, an appropriate pressure is applied between the fixing roller 310 and the pressure roller 340, which are located on the inner side of the fixing belt 330 and formed of an elastic body, thereby causing a nip between the fixing belt 330 and the pressure roller 340. Is formed.

<Fixing device>
First and second heaters 321 and 322 are provided inside the heating roller 320, and the heating roller 320 is heated from the inside by the heaters 321 and 322 to heat the fixing belt 330. First and second temperature detection sensors 351 and 352 are provided on the outer peripheral portion of the heating roller 320, and detect the surface temperature of the center portion and the end portion of the fixing belt 330 (heating roller 320) in contact or non-contact, respectively. The energization of the first and second heaters 321 is controlled based on the detected surface temperature of the fixing belt 330, and the surface temperature of the fixing belt 330 is controlled within an appropriate temperature range. A heating heater (hereinafter referred to as a pressure heater) 341 is also provided inside the pressure roller 340, and the surface of the pressure roller 340 is detected by a third temperature detection sensor 350 provided on the outer periphery of the pressure roller 340. The temperature is detected, energization of the pressure heater 341 is controlled based on the detected surface temperature of the pressure roller 340, and the surface temperature of the pressure roller 340 is controlled within an appropriate temperature range.

  In this embodiment, the fixing side rotating body (fixing belt 330) side is the image surface side of the transfer paper P, and the pressure side rotating body (pressure roller 340) side is the non-image side, and the unfixed image formed on the transfer paper is As described above, the toner image is fixed on the transfer paper while passing through the heated nip portion. That is, the fixing toner image adheres to the surface of the transfer paper and is fixed.

<Control circuit>
FIG. 3 is a block diagram illustrating a configuration of a control circuit of the image forming apparatus according to the present embodiment. The control circuit includes a reading control board 710, a system control board 720, a writing control board 730, an I / O control board 740, and an operation / display unit 750, and a toner sensor (T sensor) via the I / O control board 740. 760, an image forming I / O 770, and a high voltage power supply (PSU) 780.

  The reading control board 710 includes a CCD for reading document information, generates the reading timing of the CCD, and transfers the read output (image data) as a digital signal to the system control board.

  The system control board 720 includes a CPU, a ROM, a RAM, a nonvolatile RAM, and a chip having a calendar function. The system control board 720 controls the timing of the entire system, controls the input / output of the operation / display unit 750, and other applications (FAX, printer, not shown) , Scanner) interface, control of these operations, image information data image processing (magnification, filter, γ), and image information data storage / accumulation control using an image memory. .

  The writing control plate 730 includes an LD for exposure and a driving unit thereof, and causes the photosensitive drum 101 to perform optical writing based on image data input from the system control plate 720.

  The I / O control board 740 is an aggregation portion of input signals of various sensors and actuators of the entire system (scanner unit, printer unit), and output signals of motors, solenoids, clutches, high voltage power supplies, etc. The thermistor output is input to the ADC, and the CPU of the system control board 720 performs various controls based on this I / O data. This control includes control of paper feed tray and manual feed tray paper presence / absence information, size information, transfer paper transfer registration sensor, and the like.

  The operation / display unit 750 includes a display unit using key inputs for setting various modes, an LED, an LCD, a touch panel, and the like, and is controlled by a system control board 720.

<Fixing device drive circuit>
FIG. 4 is a block diagram of a drive circuit for driving the fixing heater. In this embodiment, a halogen heater is used as a heating source. In the figure, the heater drive circuit includes an I / O control board 740, a power supply unit (PSU—corresponding to a high voltage power source in FIG. 3) 780, the first and second heaters (halogen heaters) 321, 322, A pressure heater (heated halogen heater) 341, first and second temperature detection sensors 351 and 352, and a third temperature detection sensor 350 are configured.

  On the PSU 780, a circuit for generating power and a circuit for driving the fixing halogen heater are arranged. The heater drive is composed of a relay for AC power cut-off, a triac that turns ON / OFF at a specific cycle, a snubber circuit, and the like. The relay / triac ON / OFF processing is executed via the port of the I / O control board 740 according to the judgment of the CPU on the system control board 720. Each of the fixing heaters (halogen heaters) 350, 351, and 352 can be independently driven (ON / OFF) by each triac. Inside the heating roller 320, there are provided two heaters, a first heater (central heater) 321 whose light distribution is close to the center and a second heater (end heater) 322 which is close to the end as described above. One pressure heater 341 having a flat light distribution is provided inside the pressure roller 340.

<control>
In order to fix the toner on the recording paper, it is necessary to maintain the temperature of the fixing nip portion at a temperature necessary for toner fixing.

  In order to keep the temperature of the fixing nip portion optimal, the target temperatures T of the heating roller 320 and the pressure roller 340 are set in advance.

  The belt-type fixing device shown in FIG. 2 has a temperature detecting element 350 not only on the heating roller 320 side but also on the pressure roller 340 side. As the temperature detection element, a thermistor is usually used. However, of course, the invention is not limited to this, and other contact type and non-contact type temperature detection elements can naturally be used.

  In the temperature control, the target temperature of each temperature detection element, Ta: heating roller center, Tb: heating roller end, and Tc: pressure roller are set in advance. FIG. 5 shows an example of a fixing control circuit using conventional PID control. PID control is a control method based on P: proportional, I: integration, D: differentiation, and each heater uses the detection temperature of each temperature detection element, and the heater lighting ratio ( Control amounts Mva, Mvb, Mvc) are obtained by the PID control units Pa, Pb, Pc. Since PID control itself is a known technique, description thereof is omitted here.

<Control example 1>
FIG. 6 is a block diagram showing a first example of a control method according to the present embodiment. In this control example, any one of the first to third main heating sources is controlled by PID control, and the heating amount of other heating sources is corrected in consideration of the heating state of the main heating source.

  The process until the control amount Mv is obtained by the PID from the difference from the target temperature using the detected temperatures of the temperature detecting elements 351, 352, and 350 is equivalent to the conventional control. In the present embodiment, the control amount Mv is not used as it is for control, but is corrected to the control amount Mv of the other heaters 322 and 341 from the result of the heating source with the largest heating amount (heating center 321 in this example). , Am2.

The corrections Am1 and Am2 change according to the degree of influence. For example, when the heating end heater 322 is affected by about 20% of the lighting of the heating central heater 321, a value obtained by multiplying the control amount Mva of the heating central heater 321 by 0.2 (Am1 = 0.2) is heated. The amount is reduced from the control amount Mvb of the end heater 322. Similarly, when the influence of the pressure roller 340 is about 10%, a value obtained by multiplying the control amount Mva of the heating central heater 321 by 0.1 (Am2 = 0.1) is the control amount of the pressure heater 341. Reduce from Mvc. That is,
Heating end lighting ratio (Mvb ′) = PID calculated value (Mvb)
-Heating center lighting ratio (Mva) x 0.2
Pressurization lighting ratio (Mvc ′) = PID calculation value (Mvc)
-Heating center lighting ratio (Mva) x 0.1
It becomes. Of course, the main heating source may not be the heating center. Further, the correction ratio is not limited to this.

  When controlled in this way, the PID control of the first heating source is performed based on the temperature detected by the first temperature detector, and the second heating source is controlled based on the temperature detected by the second temperature detector, as in the prior art. In the case of only individual control such as PID control, there are concerns that the temperature may rise excessively by turning on two or more heating sources at the same time, and there is a concern that temperature fluctuations become severe. Then, based on the temperature detected by the first, second, and third temperature detectors, the heating amounts of the first, second, and third heating sources are calculated by PID, and the calculated results are corrected. Since the heating source is controlled, the heating amount of each heating source can be taken into consideration, and the temperatures of the first and second rotating bodies can be precisely controlled.

<Control example 2>
FIG. 7 is an explanatory diagram showing a second example of the control method according to the present embodiment. In this control example, the heating amount of each heating source is obtained by PID control from the detected temperature by each temperature detecting unit, and then the time is shifted so as not to be heated simultaneously with other heating sources.

  Although the detection temperatures of the temperature detection elements 351, 352, and 350 are used and the control amount Mv of the heater is obtained from the difference from the target temperature by the PID, it is the same as the control example 1, but each PID control unit Pa, Pb , Pc, a delay unit Dy1 is provided so that each control amount can be delayed with respect to Mva, Mvb, Mvc.

  The control amount Mv is a heater lighting time during a preset control cycle (interval). For example, when the control cycle is 1 second and Mv = 0.8, the heater is lit for 0.8 seconds. Normally, even when a plurality of heaters are controlled, the control cycle is the same, so the heaters are simultaneously turned on as shown in the timing chart of FIG. On the other hand, in this control example 2, as shown in the timing chart of FIG. 9, for example, the heating center 321 is the main heater, and the other heaters 322 and 341 are turned on after the main heater 321 is turned off.

  When the lighting time of the heating center 321 and other heaters (the heating end heater 322 in this control example 2) exceeds the control period of the main heater 321, the time for simultaneously lighting a plurality of heaters is shortened as much as possible. Lighting control is performed as shown in the timing chart. As a matter of course, the main heater is not limited to the heating center 321.

  If the heating sources are heated at the same time, the temperature may rise more than necessary, but this control avoids heating at the same time by shifting the heating timing, and the temperature rises too much. Can be prevented.

<Control example 3>
FIG. 11 is an explanatory diagram showing a third example of the control method according to the present embodiment. This control example is an example in which the heating state of the main heating source is considered and the heating amount of the other heating source is corrected, and the time is shifted so as not to be heated simultaneously with the other heating sources.

  In this control example 3, the configuration itself is the correction unit Am3 instead of the delay unit Dy1 of the control example 2, but is substantially the same. In this control example 3, first, after the lighting amount of the other heaters with respect to the main heater is corrected in the control example 1, the lighting control is executed at the timing shown in FIG. 9 or FIG. 10 in the control example 2 so that the lighting times do not overlap. To do. Of course, since the influence level is different from the case of lighting simultaneously, the influence degree of the main heater is changed according to the situation.

  Since the control example 3 has both functions of the control examples 1 and 2, it is possible to more reliably avoid the temperature increase more than necessary.

<Control example 4>
In this control example, after obtaining the heating amount of each heating source by PID control from the temperature detected by each temperature detection unit, a table (table) stored in the storage means in consideration of the heating amount of other heating sources is used. It is an example which corrects the amount of heating using it.

  This control example 4 has the same configuration as that of the control example 3 shown in FIG. In this control example 4, the detected temperatures of the temperature detecting elements 351, 352, and 350 are used, and until the control amount Mv of the heaters 321, 322, and 341 is obtained from the difference from the target temperature by PID, the control examples 1 to 3 Is equivalent to In this control example 4, not only the heating center value is used for other control corrections, but also corrections are made in consideration of the control amounts of the three heaters. For example, correction is performed using a table as shown in FIG. This table is stored in a storage means mounted on the system control board 720 as a table.

  In this control example 4, the control amounts (Mva, Mvb) by the PID calculation of the heating central heater 321 and the heating end heater 322 are each divided into three, and the corrections in the table are added to the calculation results Mva ′, Mvb ′. The heater is controlled using the control amount. Further, Mva ′ and Mvb ′ are used as Mvc correction values to obtain Mvc ′.

  Note that the correction values in the table of FIG. 12 are examples and are not limited to the correction contents. In this control example 4, a 3 × 3 table is used, but it may naturally be divided more finely. Further, Mvc may be used instead of the combination of Mva and Mvb. Of course, it is possible to add Mvc to a table to make a three-dimensional table.

  In the present control example 4, the control amount obtained by the PID control is not used as it is, but is corrected in consideration of the heating amount of another heating source, so that an excessive temperature rise can be prevented.

<Control example 5>
In this control example, after obtaining the heating amount of each heating source by PID control from the temperature detected by each temperature detecting unit, the heating amount is corrected using a table in consideration of the heating amount of the other heating source. This is an example in which the time is shifted so as not to be heated simultaneously with other heating sources.

  In this control example 5, the configuration itself is the same as that in the control example 4, and the same control as in the control example 4 is performed to correct the heater lighting time. Then, lighting control is executed at the timing shown in FIGS. 9 and 10 of the control example 2 so that the lighting times do not overlap. Naturally, the degree of influence may differ from that when the lamps are lit at the same time. Therefore, by adjusting the correction value of Control Example 5 instead of the correction value as it is, better temperature control becomes possible.

  In the present control example 5, since the function of the control example 2 is also provided with respect to the control example 4, an unnecessarily high temperature rise can be avoided more reliably.

<< Control Example 6 >>
In this control example, after obtaining the heating amount of each heating source by PID control from the temperature detected by each temperature detecting unit, the heating amount is corrected using an equation in consideration of the heating amount of the other heating source. This is an example.

  The present control example 6 has the same configuration as that of the control example 3. In the present control example 6, the control amount of each heating source is obtained from the PID. The heating roller 320 has two heating sources. Therefore, the influence of the heating central heater 321 on the end is referred to as a coefficient A, and the influence of the heating end heater 322 on the center is referred to as a coefficient B. Since the influence from the pressure heater 340 is minute, it is not considered here.

The control amounts Mva and Mvb obtained from the PID of the heating central heater 321 and the heating end heater 322 are actually controlled amounts Mva ′ and Mvb ′.
Mva = Mva ′ + Mvb ′ × B
Mvb = Mvb ′ + Mva ′ × A
It can be expressed as Expanding the above formula,
Mva ′ = (Mva−Mvb × B) / (1−A × B)
Mvb ′ = (Mvb−Mva × A) / (1−A × B)
Thus, the actual control amount can be obtained.

When the influence from the heating roller to the pressure roller is a coefficient C,
Mvc ′ = Mvc− (Mva ′ + Mvb ′) * C
It can be obtained from. Of course, the heating source is not limited to the above combination.

  Of course, it is also possible to adopt an equation that takes into account the influence of each of the three heating sources.

  In the present control example 6, the control amount obtained by the PID control is not used as it is, but is corrected in consideration of the heating amount of the other heating source, so that the temperature rise more than necessary can be prevented. Further, since the correction is made by the calculation formula, even when the control target is different, the same control can be performed only by changing the coefficient.

<Control example 7>
In this control example, after obtaining the heating amount of each heating source by PID control from the temperature detected by each temperature detection unit, the heating amount is corrected using an equation in consideration of the heating amount of the other heating source. This is an example in which the time is shifted so as not to be heated simultaneously with other heating sources.

  In this control example 7, the configuration itself is the same as that of the control example 6, and the same control as in the control example 6 is performed to correct the heater lighting time. In addition, the control in FIGS. 9 and 10 of the control example 2 is performed so that the lighting times do not overlap.

  Naturally, the degree of influence may differ from that when the lamps are turned on at the same time. Therefore, the coefficient of the control example 6 is not used as it is, but is adjusted to use a coefficient that enables better temperature control.

  According to the present control example 7, by having the function of the control example 2 in addition to the control example 6, it is possible to more reliably avoid the temperature increase more than necessary.

<Control example 8>
In this control example, the temperature used for the PID control is corrected from the temperatures detected by the plurality of temperature detection units, and the lighting source is controlled to be turned on using the correction value for the PID control.

  In the present control example 8, as shown in FIG. 13, a correction unit Am4 is provided in the subsequent stage of the temperature detection elements 351, 352, and 350 with respect to the control example 1, and the temperatures detected by the temperature detection elements 351, 352, and 350 are set. The corrected temperature data is not used for PID control as it is but for control.

  In this control example, the detected temperatures of the two temperature detecting elements 351 and 352 used to control the two heaters 321 and 322 provided in the heating roller 320 are corrected. In this control example, for example, a table as shown in FIG. 14 is used for correction. The table is a matrix of differences between the target temperatures Ta and Tb at the center and end of the heating roller 320, and a correction value is selected from the difference between the detected temperature and the target temperature.

  For example, when the heating center is the target temperature -5 ° C and the heating end is the target temperature + 1 ° C, the center: + 1 ° C and the end: 0 ° C are selected from FIG. The center is + 1 ° C. and the target temperature is −4 ° C., and the end portion remains at the target temperature + 1 ° C. In this control example, only the heating center and the end portion are shown as a table, but it is naturally possible to use a three-dimensional table including the detected temperature of the pressure roller. Of course, it is possible to add or subtract by the arithmetic expression without using the table.

  As described above, in the present control example 8, the temperature data used for the PID control is not used as it is, but correction based on other temperature data can avoid an unnecessary temperature rise.

  In the control examples 1 to 8, the state of the fixing device is not particularly defined. Therefore, in this embodiment, a coefficient for each PID is prepared for each state of the fixing device such as paper passing or standby, and a correction formula or table is prepared. For example, when paper with a width narrower than the width of the fixing roller is passed, the heat is taken away by the paper at the center, but the edge is left as it is. It becomes possible to adjust. By changing the coefficients, formulas, and tables used more, it is possible to perform optimal control for each state.

  Further, in the present embodiment, for example, a coefficient, an expression, and a table for controlling each heater so that a temperature change is minimized in the sheet passing state, and a coefficient, an expression, and a table that are controlled in consideration of power saving in the standby state. It is possible to control more flexibly in the form of a table. For example, the correction table in the control example 4 is a correction value suitable for a state such as a standby state, when a paper having a fixing roller width is passed, or when a paper having a width smaller than the fixing roller width is passed. Prepare multiple tables. Similarly, in the control example 6, the coefficient is set to a value suitable for the state such as when the paper is passed in the standby state, when the paper of the fixing roller width is passed, or when the paper narrower than the width of the fixing roller is passed. Prepare several.

  Furthermore, the heat capacity of the first and second rotating bodies of the fixing device is not specified. In order to save power, the first rotating body is made of a material having a small heat capacity and immediately warms up, and the second rotating body is made of a material having a large heat capacity and which is difficult to cool even when paper is passed. Then, it is possible to obtain good fixability by adjusting the coefficients, formulas, and values in the table shown in each control example so as to match the above-described state. Of course, even when a heat capacity different from that described above is adopted for each rotating body, good fixability can be obtained by adjusting the values of the coefficients, equations, and tables.

  Furthermore, even when the heat capacities of the first rotating body and the second rotating body are different, control can be performed by using a table and coefficients in consideration thereof. To save power, the first rotating body uses a material that has a small heat capacity and quickly warms, and the second rotating body uses a material that has a large heat capacity and is difficult to cool even when paper is passed through. It is possible to obtain good fixability.

1 is a diagram illustrating a schematic configuration of a color printer as a color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a detailed configuration of a fixing device. 3 is a block diagram illustrating a configuration of a control circuit of the image forming apparatus according to the present exemplary embodiment. FIG. It is a block diagram of a drive circuit for driving a fixing heater. It is a block diagram showing an example of a fixing control circuit using conventional PID control. It is a block diagram which shows the structure of the control example 1 which concerns on this embodiment. It is a block diagram which shows the structure of the control example 2 which concerns on this embodiment. It is a timing chart which shows the conventional lighting timing. 6 is a timing chart showing lighting timings in Control Example 2. 6 is a timing chart showing another lighting timing of Control Example 2. It is a block diagram which shows the structure of the control example 3 which concerns on this embodiment. It is a figure which shows the correction content of the control example 4 which concerns on this embodiment in a table format. It is a block diagram which shows the structure of the control example 8 which concerns on this embodiment. It is a figure which shows the correction content of the control example 8 which concerns on this embodiment in a table | surface form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming part 105 Vertical conveyance path 200 Paper feed part 212 Transfer paper 300 Fixing device (fixing part)
310 Fixing roller 320 Heating roller 321, 322 Heating heater 330 Fixing belt 340 Pressing roller 341 Pressing heater 350 First temperature detection sensor 351 Second temperature detection sensor 400 Paper discharge unit 710 Reading control plate 720 System control plate 730 Writing Control board 740 I / O control board 780 PSU
Am1, Am2, Am3, Am4 Correction unit Dy1 Delay unit Pa, Pb, Pc PID control unit

Claims (7)

In a fixing device that fixes an image on a recording medium by passing the recording medium between a pair of rotating bodies,
A first heating source for heating the central portion of the first rotating body ;
A second heating source for heating the end of the first rotating body;
A third heating source for heating the second rotating body;
A first temperature detecting means for detecting the temperature of the central portion of the first rotating body,
A second temperature detecting means for detecting the temperature of the end portion of the first rotating body,
A third temperature detection means for detecting a temperature of the second rotating body,
First calculating means for calculating a lighting ratio at a predetermined control cycle of the first heating source based on the detected temperature detected by the first temperature detecting means;
Second calculating means for calculating a lighting ratio at a predetermined control period of the second heating source based on the detected temperature detected by the second temperature detecting means;
Third calculating means for calculating a lighting ratio at a predetermined control period of the third heating source based on the detected temperature detected by the third temperature detecting means;
Correction means for reducing the lighting ratio of the other two heating sources based on the lighting ratio of the heating source having the largest heating amount among the first to third heating sources;
With
The fixing device according to claim 1, wherein the heating source having the largest heating amount is heated at the lighting rate calculated by the calculating unit, and the other two heating sources are heated at the lighting rate corrected by the correcting unit. The amount to reduce the lighting ratio of the other two heating sources is calculated based on a predetermined formula from the lighting ratio of the heating source with the largest heating amount and the lighting ratio of each of the other two heating sources. the fixing device according to claim 1, characterized in that it is. The amount of reduction of the lighting rate of the other two heating sources is stored as a table based on the lighting rate of the heating source with the largest heating amount and the lighting rate of each of the other two heating sources. The fixing device according to claim 1, wherein: 3. The fixing device according to claim 2 , wherein a plurality of the predetermined formulas are stored in accordance with whether the fixing device is in a standby state or a sheet passing state . 4. The fixing device according to claim 3 , wherein a plurality of tables are stored depending on whether the fixing device is in a standby state or a paper passing state . The image forming apparatus you further comprising a fixing device according to any one of claims 1 to 5. A heating control method of a fixing device for fixing an image on a recording medium by passing the recording medium between a pair of rotating bodies,
Detecting the temperature of the central portion of the first rotating body heated by the first heating source;
Detecting the temperature of the end of the first rotating body heated by the second heating source;
Detecting a temperature of a third heating source for heating the second rotating body;
Calculating a lighting ratio in a predetermined control cycle of the first heating source based on the temperature of the first heating source;
Calculating a lighting ratio at a predetermined control period of the second heating source based on the temperature of the second heating source;
Calculating a lighting ratio at a predetermined control period of the third heating source based on the temperature of the third heating source;
Reducing the lighting ratio of the other two heating sources based on the lighting ratio of the heating source having the largest heating amount among the first to third heating sources;
The heating source with the largest heating amount is heated at the calculated lighting rate, and the other two heating sources are heated at the lighting rate after being reduced; and
A heating control method for a fixing device, comprising:

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