JP5550263B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus including a recording material heating device.

  As a recording material heating device, various methods and configurations have been conventionally known, such as a heat roller method, a hot plate method, a heat chamber method, and a film heating method. Each of these heating apparatuses has a heating body, and the temperature of the heating body is controlled and controlled so that the apparatus temperature is maintained at a predetermined temperature (such as a predetermined image fixing temperature).

  Among various conventional heating devices as described above, a film heating type heating device is effective and practical (see Patent Document 1).

  The heating device of the film heating system is a thin heat-resistant film, a driving means for the film, a heating body that is fixedly supported in the film, and a heating body that is disposed facing the heating body. On the other hand, it has a pressurizing member that adheres the image carrying surface of the recording material through a film. At least at the time of image heating, this film travels and moves at substantially the same speed in the forward direction as the recording material conveyed and introduced between the film and the pressure member, and the heating body and the pressure member are sandwiched between the traveling film. Is passed through a nip portion as an image heating portion formed by the pressure contact portion. As a result, the visible image carrying surface of the recording material is heated by the heating body through the film to thermally fix the visible image. Next, the apparatus is basically configured to separate the film after passing through the image heating unit and the recording material at a separation point. Since such a film heating type heating apparatus can use a heating element or a thin film having a low heat capacity and a rapid temperature increase, it is possible to save power and shorten the wait time (quick start). In addition, there is an advantage that various disadvantages of other conventional heating devices can be eliminated, which is effective.

  In recent years, there has also been proposed a heating device having a configuration in which an elastic layer is provided on a heating film to reduce uneven melting of toner due to unevenness of a recording material (see Patent Document 2).

  In the temperature control in the film heating type heating device, the output of the thermistor provided on the heating body is A / D converted and taken into the CPU. Then, based on the comparison result between the detected temperature and the target temperature, the heater is energized by PID control that performs P (Proportion) control, I (Integral) control, and D (Differential) control based on a predetermined control table. There are many things that control.

At this time, the energization control to the heating body is performed by turning on / off the AC voltage by the triac, but this energization control method uses wave number control or phase control, and the power is finely controlled by controlling the energization ratio. By controlling, the amplitude of the temperature of the heating body is made as small as possible.
Here, the wave number control is a control in which several waves of the input AC voltage are set as a predetermined cycle, and the number of waves is turned on and the number of waves is turned off every predetermined cycle. In this method, the energization ratio is controlled by the ON / OFF duty ratio within the cycle.

  For example, when the power supply frequency of the AC power supply is 50 Hz, 1 half wave = 10 msec, and when the predetermined cycle is 20 half waves = 200 msec = 1 cycle, the power supplied to the heating body is updated every 20 half waves. The minimum power is all OFF (20 half-wave all OFF), the maximum power is all ON (20 half-wave all ON), and the amount of power supplied per cycle is 21 levels from 0 to 20 half-waves ON. It becomes.

  According to this control, when the waveform of the input AC voltage is the waveform shown in FIG. 10, for example, the energization current to the heating element has a waveform as shown in FIG. 11.

  On the other hand, the phase control is a method of controlling the energization angle within one wave of the input AC voltage, and the energization current to the heating body has a waveform as shown in FIG.

  The wave number control has a feature that the harmonic current is small but the flicker noise is large, and the phase control has a feature that the flicker noise is small but the harmonic current is large.

  In addition, since the wave number control controls the energization ratio for each predetermined cycle of several waves, it is necessary to lengthen the update period and increase the wave number during that period in order to finely control the energization ratio. However, since the energization ratio can only be updated every predetermined period, if the update period is made too long, the switching of the energization ratio becomes slow. Then, since it becomes impossible to supply appropriate electric power when necessary, it is necessary to set the balance between the energization ratio and the update cycle.

  On the other hand, the phase control finely controls the energization ratio within one half wave, and the update of the energization ratio is at least one full wave. Therefore, in the phase control, the energization ratio, that is, the power can be renewed more finely, and the temperature ripple of the heating body caused by the control can be reduced. In addition, the phase control requires a noise filter, and the circuit configuration is complicated, which increases the cost of the apparatus. On the other hand, in the case of wave number control, there is a feature that there is no such cost increase.

  Therefore, each control is selected according to the requirements of the apparatus. In particular, when a 200V commercial power supply is used in recent years, not the phase control but the wave number control is often employed to reduce the harmonic current.

  For this reason, for example, an apparatus configured to switch wave number control and phase control between 200 V and 100 V in accordance with an AC input voltage has been proposed (see Patent Document 3).

  Also, combining phase control and wave number control, using phase control for at least one half wave within the wave number control update period, reducing harmonic currents compared to using only phase control, and energizing compared to using only wave number control A method of performing finer control by shortening the update period of the ratio has also been proposed. For example, see Patent Document 4.

  By the way, in the heating apparatus of the above-described film heating method, particularly an apparatus having a configuration in which an elastic layer is provided on the heating film, the heating state of the recording material may become unstable in response to the recording material entering the heating nip portion. is there. This is because when the recording material enters from a stable temperature state, the recording material suddenly loses heat immediately after the recording material enters the heating nip, and when the heating film temperature rapidly decreases and then increases, This is because a large temperature fluctuation occurs in the heating nip due to the occurrence of the chute.

  In order to reduce this phenomenon, a method for correcting the electric power supplied to the heating body before the temperature variation due to the entry of the recording material has been disclosed by the present applicant (see Patent Document 5).

JP-A-4-44075 Japanese Patent Laid-Open No. 11-15303 JP-A-10-333490 JP 2003-123941 A JP 2004-078181 A

  By the way, when the temperature of the heating film rapidly decreases as the recording material enters the heating nip, the temperature remains low when this portion comes into contact with the recording material again after the heating film has made one revolution. That is, a phenomenon occurs in which the temperature of the heating film is lowered at a portion corresponding to the second turn of the heating film on the recording material, and the glossiness of the image is lowered. On the other hand, the temperature of the heating film greatly decreases due to the rush of the recording material only for a moment immediately after the rush when the thermal state suddenly changes due to the rush of the recording material. The decline is eliminated. Accordingly, the glossiness of the image is low only in the portion corresponding to the tip of the second turn even in the portion corresponding to the second turn of the heating film on the recording material.

  However, since the glossiness of the image differs greatly between the portion corresponding to the leading edge of the second turn and the trailing edge of the first turn of the heating film, there may be a case where the difference in glossiness appears clearly at this boundary. This is a remarkable phenomenon particularly when glossy paper is passed.

  In order to reduce the gloss difference, the power correction must be controlled more finely so that the gloss is the same at the joints of the first and second rounds. That is, even if heat is taken away at the tip of the first lap, the temperature drop of the heating film at the tip corresponding to the tip of the second lap is complemented so that the tip of the second lap and the rear end of the first lap are at the same temperature. Must-have.

  The mechanism to compensate for the temperature drop by power correction is as follows. First, the temperature of the heating film surface decreases due to the entry of the recording material. If power correction is not performed, the temperature of this portion remains low, and as described above, a gloss level difference occurs after one rotation of the heating film. On the other hand, if power correction is performed to forcibly apply a predetermined power prior to the recording material entering, even if the surface of the heated film drops once, the power that is forcibly input during one rotation, that is, thermal energy, is heated. It is transmitted to the film surface. Then, the temperature drop is offset, and when the leading edge of the second turn of the heating film corresponding to the recording material entry portion of the heating film comes into contact with the recording material again, the temperature returns to a predetermined temperature.

  As is apparent from this mechanism, the portion where the heat generated by the power correction warms the inner surface of the heating film must be almost completely coincident with the portion where the temperature is lowered due to the entry of the recording material.

  In such a case, stricter accuracy is required than when the temperature control is simply stabilized. Especially for recording materials such as glossy paper, the sensitivity of the glossiness to temperature is very high, and only a slight temperature difference appears as a gloss difference, that is, in this case, a gloss level difference. Becomes narrower.

  In order to make the rear end of the first lap and the tip of the second lap the same temperature, it is necessary to perform power correction that accurately compensates for the temperature drop at the tip of the second lap. High accuracy is also required for the timing of power correction. This is because the level difference is generated in a delta function, and in order to compensate for the decrease in temperature so as to eliminate this, power must be supplemented at a precise timing in a delta function with respect to the timing at which the level difference occurs. is there.

  If the power correction timing slightly deviates from the appropriate correction timing, the temperature drop cannot be sufficiently compensated for due to insufficient power, or excessive power input causes problems such as hot offset. That is, if the timing for starting the power correction is slightly shifted, the effect of the power correction is diminished.

  However, in an apparatus employing wave number control, correction cannot be performed at the timing when power correction should be performed in response to the entry of the recording material, and there is a problem that temperature fluctuation due to the entry of the recording material cannot be sufficiently reduced.

  This is due to the fact that the update frequency of the energization ratio of the wave number control is in units of several waves, so the update frequency is low, and therefore the update timing hardly coincides with the power correction timing.

  FIG. 13 is a timing chart showing the energization ratio update period of the wave number control and the phase control, and the timing of the recording material rush and power correction.

  In this example, the update period of the energization ratio for wave number control is 20 half waves. A is the update timing of the energization ratio of wave number control. B is the update timing of the energization ratio of the phase control. The power correction is executed at timing C, and the recording material enters the heating nip at D. In the example of FIG. 13, the power correction is started 130 msec before the recording material enters the heating nip, and the power correction is completed 30 msec after the recording material enters the heating nip.

  In the wave number control, since the energization ratio update period is long, the deviation of the actual correction timing from the appropriate correction timing becomes large. In the example shown here, since the energization ratio is controlled in units of 20 half-waves, a deviation (delay) of 200 msec at the maximum (in the case of 50 Hz) from when the power correction start command is issued until the actual correction is executed. ) Occurs. In this case, the power correction period is 130 msec before entering the recording material, 30 msec after entering the recording material, and 160 msec in total. Therefore, when it is shifted to the maximum, the power correction is started after the timing of completion of the power correction. Become. That is, the power correction end command is actually issued before the power correction is started, so that the power correction is not performed.

  In the above example, since the energization ratio is changed after a correction start command is issued, a timing shift is a direction in which correction execution is necessarily delayed. On the other hand, since the start timing of power correction is known in advance, if correction is performed when the update ratio of the energization ratio comes at the closest timing before and after the power correction start timing on the assumption that it will deviate, the maximum The amount of deviation can be slightly reduced. However, even in that case, the deviation amount is as large as ± 100 msec with respect to the proper power correction timing.

  When the timing is shifted in this way, the temperature state of the heating film surface is shown in FIGS. In the graphs of FIGS. 14 to 16, the horizontal axis indicates time, and the vertical axis indicates the surface temperature of the heating film. 14 shows a case where power correction is performed at an appropriate timing, FIG. 15 shows a case where the start of power correction deviates before the proper timing, and FIG. 16 shows a case where the start of power correction deviates after the proper timing. Show. Although the temperature of the heating film decreases as the recording material enters the heating nip, in FIG. 14, the difference in surface temperature between the heating film before and after the recording material enters the heating nip is within about Δ2 deg. On the other hand, in FIG. 15, the surface temperature greatly increases before entering the heating nip, so the difference in surface temperature of the heating film before and after entering the heating nip is Δ8 deg. In FIG. 16, the surface temperature greatly decreases due to the recording material entering the heating nip, so the difference in surface temperature is about Δ8 deg.

  As is apparent from FIG. 15, when the power correction is performed with the timing shifted, if the correction is performed before the appropriate timing, the temperature of the heating nip rises too much, resulting in excessive heating. When the recording material carrying the toner image enters here, the toner becomes excessively melted and hot offset occurs. In addition, since the high power is supplied earlier than the appropriate timing, the temperature of the heating film until the recording material rushes becomes too high, and the gloss of the recording material becomes glossy at the portion corresponding to the rear end of the first turn of the film. Get higher. Therefore, a horizontal band-like gloss unevenness is generated so that the step between the rear end of the first round and the tip of the second round is more emphasized. On the other hand, if correction is performed after the appropriate timing as shown in FIG. 16, the decrease in the amount of heat due to the rush of the recording material cannot be compensated, and the temperature greatly decreases. In this case, the gloss corresponding to the second turn of the heating film becomes too low, resulting in uneven luster in which the step difference between the rear end of the first turn and the front end of the second turn appears clearly.

  In order to cope with this problem, it is conceivable to shorten the energization ratio update cycle. In this case, however, the number of waves in the update cycle is reduced, so that the energization ratio cannot be set finely, which hinders temperature control.

  Incidentally, even in the case of phase control, of course, a timing shift itself occurs. The maximum value is 1 full wave = 20 msec (in the case of 50 Hz), but even a deviation of this level does not have any influence at all. However, as a result of examination by the present applicant, it has been found that if this deviation amount, the gloss unevenness is managed within an allowable range. Conversely, if phase control is not used, it is impossible to achieve a level at which timing deviation can be tolerated.

  However, as described above, phase control has a problem of harmonic current, and may not always be adopted. Europe, which is in the 200V range, is particularly strict with harmonic currents, and it is necessary to use wave number control instead of phase control.

  Further, in the control using phase control for at least one half wave within the update period of the energization ratio in the wave number control shown in Patent Document 4, the update period of the energization ratio can be shortened. is there. However, if the number of waves in the update period is reduced to shorten the update period of the energization ratio, the number of wave numbers for which phase control is performed relatively increases, so that the harmonic current increases. Cannot be set. Further, as described above, since all levels are finally allowed by using phase control, there is a limit to improvement.

  The object of the invention relating to the present applicant is to reduce the difference between the timing of performing power correction and the update period of the energization ratio before entering the heating nip of the recording material in a configuration that suppresses the increase in harmonics, The object is to provide a technique for correcting power at an appropriate timing.

  The invention according to the present application has the following configuration in order to solve the above problems.

(1) An image forming unit that forms an unfixed toner image on a recording material, a fixing rotator, a heater that generates heat by electric power supplied from a commercial AC power source and heats the fixing rotator, and the fixing rotator A pressure member that forms a nip portion therebetween, and a temperature detection member that detects the temperature of the fixing rotator or the heater, and conveys the recording material on which the unfixed toner image is formed at the nip portion. And a fixing unit that fixes the unfixed toner image on the recording material by heating, and a power control unit that controls the power supplied from the commercial AC power source to the heater according to the detected temperature of the temperature detecting member. In the image forming apparatus, the power control unit uses the wave number control or a combination of the wave number control and the phase control to supply power corresponding to the detected temperature to the heater for each first period. Supply system Mode and a second power supply control mode for supplying the power corresponding to the detected temperature for each of the first shorter than the period the second period to the heater using a phase control, the power supplied to the heater A third power supply control mode to be increased, and when the unfixed toner image is fixed on the recording material at the nip portion, the first power supply control mode is executed, The third power supply control mode is executed before the tip enters the nip portion, and the second power supply mode is executed from the state in which the first power supply control mode is executed before the third power supply control mode. Switching to a state in which the power supply control mode is executed.
(2) An image forming unit that forms an unfixed toner image on a recording material, a fixing rotator, a heater that generates heat by power supplied from a commercial AC power source and heats the fixing rotator, and the fixing rotator A pressure member that forms a nip portion therebetween, and a temperature detection member that detects the temperature of the fixing rotator or the heater, and conveys the recording material on which the unfixed toner image is formed at the nip portion. And a fixing unit that fixes the unfixed toner image on the recording material by heating, and a power control unit that controls the power supplied from the commercial AC power source to the heater according to the detected temperature of the temperature detecting member. In the image forming apparatus, the power control unit uses the wave number control or a combination of the wave number control and the phase control to supply power corresponding to the detected temperature to the heater for each first period. Supply system A mode, a feasible and a second power supply control mode for supplying the heater power according to the detected temperature for each of the first shorter than the period second period by using the phase control, The first power supply control mode is executed when the unfixed toner image is fixed on the recording material at the nip portion, and the first power supply control is performed before the leading edge of the recording material enters the nip portion. Switching from a state in which the mode is executed to a state in which the second power supply control mode is executed, the power supplied to the heater is increased while the second power supply control mode is being executed. Forming equipment.

  According to the invention of the present application described above, power correction can be executed at an appropriate timing while reducing the harmonic current, so that the temperature fluctuation of the heating nip accompanying the entry of the recording material is suppressed, and the gloss of the image on the recording material is reduced. This has the effect of realizing power correction that reduces unevenness and hot offset.

Schematic configuration diagram of a color image forming apparatus in Embodiments 1 and 2 Sectional drawing of the heating apparatus in Example 1,2. The perspective view which shows the positional relationship of the heater main-thermistor sub-thermistor in Example 1,2. Configuration diagram of ceramic heater as heating element The block diagram of the control circuit part and heater drive circuit part of the heating apparatus of this invention Flowchart showing implementation of power correction in the first embodiment Timing chart of power supply in Embodiment 1 Schematic configuration of media sensor Flowchart showing implementation of power correction in the second embodiment Input AC power waveform Energization waveform by wave number control Energized waveform by phase control Timing chart showing the update period of energization ratio of conventional wave number control and phase control, and the timing of recording material inrush and power correction A graph showing the temperature of the heating film surface when power correction is performed at an appropriate timing Graph showing the temperature of the heating film surface when power correction is performed before the appropriate timing Graph showing the temperature of the heating film surface when power correction is performed after the proper timing

  Embodiments of the present invention will be described.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. It is not intended that the scope of the present invention be limited to the following embodiments.

  FIG. 1 is a schematic configuration diagram showing a color image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus of this example is an electrophotographic tandem type full color printer.

  This image forming apparatus includes four image forming units: an image forming unit 1Y that forms a yellow image, a magenta image forming unit 1M, a cyan image forming unit 1C, and a black image forming unit 1Bk. These are arranged in a line at regular intervals.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively. Around each photosensitive drum 2a, 2b, 2c, 2d, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, drum cleaning device 6a, 6b, 6c and 6d are respectively installed. Exposure devices 7a, 7b, 7c, and 7d are installed above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  An endless belt-shaped intermediate transfer belt 40 as a transfer medium is in contact with each primary transfer portion N of each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 40 is stretched between a drive roller 41, a support roller 42, and a secondary transfer counter roller 43, and is rotated (moved) in the arrow direction (clockwise) by the drive of the drive roller 41.

  The transfer rollers 5a, 5b, 5c, and 5d for primary transfer are in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the intermediate transfer belt 40 at each primary transfer nip portion N.

  The secondary transfer counter roller 43 is in contact with the secondary transfer roller 44 via the intermediate transfer belt 40 to form a secondary transfer portion M. The secondary transfer roller 44 is disposed so as to be able to contact and separate from the intermediate transfer belt 40.

  A belt cleaning device 45 that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 40 is installed in the vicinity of the driving roller 41 outside the intermediate transfer belt 40.

  A heating device 12 is installed on the downstream side of the secondary transfer portion M in the conveyance direction of the recording material P.

In addition, an environmental sensor 50 and a media sensor 51 are installed in the image forming apparatus.
When an image forming operation start signal (print start signal) is issued, the photosensitive drums 2a to 2d of the image forming units 1Y, 1M, 1C, and 1Bk that are rotationally driven at a predetermined process speed are respectively charged by charging rollers 3a to 3d. Uniformly, in this embodiment, the battery is negatively charged.

  Then, each of the exposure devices 7a to 7d converts the input color-separated image signal into an optical signal by a laser output unit (not shown), and each laser beam that is the converted optical signal is charged. Each of the photosensitive drums 2a to 2d is scanned and exposed to form an electrostatic latent image.

  First, yellow toner is charged on the surface of the photosensitive member by the developing device 4a in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied onto the photosensitive drum 2a on which the electrostatic latent image is formed. By electrostatically attracting in accordance with the electric potential, the electrostatic latent image is visualized to be a developed image. This yellow toner image is primary transferred onto the rotating intermediate transfer belt 40 by the transfer roller 5a to which a primary transfer bias (polarity opposite to the toner (positive polarity)) is applied at the primary transfer portion N. Is done. The intermediate transfer belt 40 onto which the yellow toner image has been transferred is rotated toward the image forming unit 1M.

  In the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the intermediate transfer belt 40 and transferred by the primary transfer unit N. Is done.

  Similarly, cyan and black toner images formed on the photosensitive drums of the image forming units 1C and 1Bk are sequentially transferred to the primary transfer unit N on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 40. Overlapping and full-color toner images are formed on the intermediate transfer belt.

  On the other hand, after the recording material P is fed / conveyed by a paper feeding mechanism (not shown), when the leading edge position is detected by the registration sensor 47, the recording material P is stopped in that state and held while being held by the registration roller 46. I'm waiting.

  Then, the recording material (transfer material) P is conveyed to the secondary transfer portion M by the registration roller 46 in accordance with the timing when the front end of the full color toner image on the intermediate transfer belt 40 is moved to the secondary transfer portion M. Then, a full-color toner image is secondarily transferred collectively to the recording material P by a secondary transfer roller 44 to which a secondary transfer bias (opposite polarity (positive polarity) with respect to toner) is applied.

  The recording material P on which the full-color toner image is formed is conveyed to the heating device 12, and the full-color toner image is heated and pressed at the heating nip portion between the heating film 20 and the pressure roller 22 to melt on the surface of the recording material P. After fixing, the image is discharged to the outside and becomes an output image of the image forming apparatus. Then, a series of image forming operations is completed.

  The image forming apparatus has an environment sensor 50, and the charging, developing, primary transfer, secondary transfer bias and fixing conditions can be changed according to the environment (temperature, humidity) in the image forming apparatus. It is used for adjusting the toner image density on the recording material P and achieving optimum transfer and fixing conditions. In addition, the image forming apparatus includes a media sensor 51. By determining the recording material P, the transfer bias and the fixing conditions can be changed according to the recording material. Used to achieve optimal transfer and fixing conditions.

  During the primary transfer described above, the primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and collected by the drum cleaning devices 6a, 6b, 6c, and 6d. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 40 after the secondary transfer is removed and collected by the belt cleaning device 45.

  FIG. 2 is a schematic configuration diagram of the heating device 12 in the present embodiment. The heating device 12 of this example is a heating device of a film heating method and a pressurizing rotating body drive method (tensionless type).

20 is a heating film of a fixing rotator, a cylindrical shape having an elastic layer provided on the film (endless belt, sleeve shape) is a member of.

22 is a pressure roller as a pressure member. Reference numeral 17 denotes a heater holder having heat resistance and rigidity having a substantially semicircular arc shape in cross section as a heating body holding member. Reference numeral 16 denotes a heater as a heating body (heat source). The heater holder 17 has a lower surface along the length of the holder. Arranged. The heating film 20 is loosely fitted on the heater holder 17.

  The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the heater 16 and guiding the heating film 20. In this example, DuPont Zenite 7755 (trade name) was used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755 is about 270 ° C.

  The pressure roller 22 is formed by forming a silicone rubber layer having a thickness of about 3 mm on a stainless steel core by injection molding and coating a PFA resin tube having a thickness of about 40 μm thereon. The pressure roller 22 is disposed such that both ends of the core bar are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, a heating film unit composed of the heater 16, the heater holder 17, the heating film 20 and the like is arranged in parallel to the pressure roller 22 with the heater 16 facing downward. Then, both end portions of the heater holder 17 are urged in the axial direction of the pressure roller 22 by a force of one side 98N (10 kgf) and a total pressure 196N (20 kgf) by a pressure mechanism (not shown). Thus, the downward surface of the heater 16 is brought into pressure contact with the elastic layer of the pressure roller 22 through the heating film 20 with a predetermined pressing force against the elasticity of the elastic layer, and heating with a predetermined width necessary for heat fixing. A nip H is formed. The pressurization mechanism has a pressure release mechanism, and is configured to release the pressurization and easily remove the recording material P at the time of jam processing or the like.

18 and 19 are two thermistors main and sub as temperature Doken known member. The main thermistor 18 as the first temperature detection known member is disposed in a non-contact heater 16 is a heating member, Yes resiliently the contacted to the inner surface of the heating film 20 above the heater holder 17 in the present embodiment, the heating The temperature of the inner surface of the film 20 is detected. Sub thermistor 19 as second temperature detection known member is positioned in a location close to the heater 16 as a heat source than the main thermistor 18, in the present embodiment Yes in contact with the back surface of the heater 16, the temperature of the back surface heater 16 Detect.

  The main thermistor 18 is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17, and even if the movement of the inner surface of the heating film 20 becomes unstable due to the elastic swing of the arm 25, the heating film 20. It is always kept in contact with the inner surface.

  FIG. 3 is a perspective view showing the positional relationship among the heater 16, the main thermistor 18, and the sub-thermistor 19 in the heating apparatus of the present embodiment. The main thermistor 18 is disposed near the longitudinal center of the heating film 20, and the sub-thermistor 19 is disposed near the end of the heater 16, and is disposed so as to contact the inner surface of the heating film 20 and the back surface of the heater 16, respectively.

  The outputs of the main thermistor 18 and the sub-thermistor 19 are connected to a control circuit unit (CPU) 21 via A / D converters 64 and 65, respectively (FIGS. 4 and 5). Then, the control circuit unit 21 determines the temperature control content of the heater 16 based on the outputs of the main thermistor 18 and the sub-thermistor 19, and the heater drive circuit unit 28 (FIG. 2) as a power supply unit (heating means). FIG. 4) controls the energization to the heater 16. That is, the control circuit unit 21 functions as a power control unit.

  In the present embodiment, the main thermistor 18 detects the inner surface temperature of the heating film 20, but it can be arranged on the back surface of the heater 16 in the same manner as the sub-thermistor 19 to directly detect the temperature of the heater 16.

  Reference numerals 23 and 26 in FIG. 2 denote an entrance guide and a paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 guides the transfer material so that the recording material P that has passed through the secondary transfer nip is accurately guided to the heating nip H that is the pressure contact portion between the heating film 20 and the pressure roller 22 in the heater 16 portion. Play a role. The entrance guide 23 of the present embodiment is formed of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is driven to rotate at a predetermined peripheral speed in the direction of the arrow by a driving means (not shown). A rotational force acts on the cylindrical heating film 20 by the pressure frictional force in the heating nip H between the outer surface of the pressure roller 22 and the heating film 20 by the rotational driving of the pressure roller 22. The heating film 20 is driven to rotate in the direction of the arrow around the outer periphery of the heater holder 17 while the inner surface of the heating film 20 slides in close contact with the downward surface of the heater 16. In addition, grease is apply | coated to the inner surface of the heating film 20, and the slidability with the heater holder 17 and the heating film 20 inner surface is ensured.

  The pressure roller 22 is rotationally driven, and the cylindrical heating film 20 is driven and rotated, and the heater 16 is energized. The heater 16 is heated to a predetermined temperature, and the temperature is adjusted. The In this state, the recording material P carrying an unfixed toner image is introduced along the entrance guide 23 between the heating film 20 and the pressure roller 22 in the heating nip H. Then, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the heating film 20 at the heating nip H, and the heating nip H is nipped and conveyed together with the heating film 20. In this nipping and conveying process, the heat of the heater 16 is applied to the recording material P through the heating film 20, and the unfixed toner image t on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the heating nip H is separated from the heating film 20 by the curvature, and is discharged by the paper discharge roller 26.

  In the present embodiment, the heating film 20 is a cylindrical (endless belt-shaped) member formed by providing an elastic layer on the film.

As a film material, for example, a stainless rubber layer (elastic layer) having a thickness of about 300 μm is formed by a ring coating method on an endless belt formed by SUS into a cylindrical shape having a thickness of 30 μm, and then a PFA resin tube having a thickness of 30 μm. (Outermost surface layer) is coated. Measurement of the heat capacity of the heating film 20 that was created in such a configuration was ^{12.2 × 10 -2 J / cm 2} · ℃ ( heat capacity per 1 cm ² of the heating film).

  Although a resin such as polyimide can be used for the base layer of the heating film 20, a metal such as SUS or nickel has a thermal conductivity approximately 10 times larger than that of polyimide. Therefore, since higher on-demand property can be obtained, SUS which is a metal is used for the base layer of the heating film 20 in the present embodiment.

A rubber layer having a relatively high thermal conductivity is used for the elastic layer of the heating film 20. This is to obtain higher on-demand characteristics. The material used in this embodiment has a specific heat of about 12.2 × 10 ⁻¹ J / g · ° C.

  By providing a fluororesin layer on the surface of the heating film 20, the releasability of the surface is improved, and the offset phenomenon that occurs when the toner once adheres to the surface of the heating film 20 and moves to the recording material P again. Can be prevented. Moreover, it becomes possible to form a uniform fluororesin layer more simply by making the fluororesin layer on the surface of the heating film 20 a PFA tube.

Generally, when the heat capacity of the heating film 20 is increased, the temperature rise becomes dull and the on-demand property is impaired. For example, although it depends on the configuration of the heating device, the heat capacity of the heating film 20 needs to be about 4.2 J / cm ² · ° C. or less when assuming a rise within one minute without standby temperature control. I know.

In the present embodiment, it is designed such that when starting from a room temperature state, about 1000 W of power is supplied to the heater 16 so that the heating film 20 rises to 190 ° C. within 20 seconds. The silicone rubber layer is made of a material having a specific heat of about 12.2 × 10 ⁻¹ J / g · ° C. At this time, the thickness of the silicone rubber must be 500 μm or less, and the heat capacity of the heating film 20 is It should be about 18.9 × 10 ⁻² J / cm ² · ° C. or less. On the other hand, if the temperature is set to 4.2 × 10 ⁻² J / cm ² · ° C. or less, the rubber layer of the heating film 20 becomes extremely thin, and the elastic layer is advantageous in terms of image quality such as OHT permeability and gloss unevenness. It becomes equivalent to a heating device of a film heating method that does not have.

In the present embodiment, the thickness of the silicone rubber necessary for obtaining a high-quality image such as OHT permeability and gloss setting is 200 μm or more. The heat capacity at this time was 8.8 × 10 ⁻² J / cm ² · ° C.

In other words, the heat capacity of the heating film 20 in the configuration of the heating device similar to the present embodiment is generally intended to be 4.2 × 10 ⁻² J / cm ² · ° C. or more and 4.2 J / cm ² · ° C. or less. Become. Among them, heating with a heat capacity of 8.8 × 10 ⁻² J / cm ² · ° C. or more and 18.9 × 10 ⁻² J / cm ² · ° C. or less can achieve both on-demand and high image quality. It was decided to use a film.

  As shown in FIGS. 2 and 3, the main thermistor 18 is disposed in the vicinity of the longitudinal center of the heating film 20 and is disposed so as to contact the inner surface of the heating film 20. The main thermistor 18 is used as means for detecting the temperature of the heating film 20 that is closer to the temperature of the heating nip portion. Therefore, in normal operation, temperature control is performed so that the detected temperature of the main thermistor 18 becomes the target temperature. As described above, the main thermistor 18 may be disposed on the back surface of the heater 16, and in this case, the temperature on the back surface of the heater is controlled to the target temperature.

  As shown in FIG. 3, the sub-thermistor 19 is disposed in the vicinity of the end of the heater 16 and is disposed so as to contact the back surface of the heater 16. The sub-thermistor 19 serves as a safety device that detects the temperature of the heater 16 that is a heating element and monitors the heater temperature so as not to exceed a predetermined temperature.

  Further, the sub-thermistor 19 monitors the overshoot of the temperature of the heater 16 at the start-up and the temperature rise at the end. For example, when the temperature at the end of the heater 16 exceeds a predetermined temperature due to the temperature rise at the end, it is used for judgment for performing control such as reducing the throughput so that the end does not further increase in temperature. It is done.

  In this embodiment, the heater 16 is formed by forming a resistance heating element on a substrate of aluminum nitride by applying a conductive paste containing a silver / palladium alloy into a film having a uniform thickness by a screen printing method. A ceramic heater with a glass coating made of pressure-resistant glass is used. FIG. 4 is a structural diagram of an example of such a ceramic heater.

  The heater 16 has a horizontally long aluminum nitride substrate a whose base is a direction orthogonal to the paper passing direction as a base material. Then, the thickness of the conductive paste containing silver palladium (Ag / Pd) alloy that is applied to the surface side of the aluminum nitride substrate a along the length by screen printing in a linear or belt shape and generates heat when current flows. It has a resistance heating element layer b having a width of about 10 μm and a width of about 1 to 5 mm. Further, as the power supply pattern for the resistance heating element layer b, the first and second electrode portions c and d and the extended electric circuit portion e, which are similarly patterned by screen printing of silver paste on the surface side of the aluminum nitride substrate a, are provided. Have. Further, a thin-walled material having a thickness of about 10 μm, which can withstand the rubbing with the heating film 20 formed on the resistance heating element layer b and the extension circuit portion e to ensure protection and insulation. A glass coat g and a sub-thermistor 19 provided on the back side of the aluminum nitride substrate a are provided.

  The heater 16 is supported by being fixed to the heater holder 17 with the surface side exposed downward.

  A power feeding connector 30 is mounted on the first and second electrode portions c and d of the heater 16. Power is supplied from the heater drive circuit section 28 to the first and second electrode sections c and d through the power supply connector 30, so that the resistance heating element layer b generates heat and the heater 16 quickly rises in temperature. The heater drive circuit unit 28 is controlled by a control circuit unit (CPU) 21.

  In normal use, as the pressure roller 22 starts rotating, the driven rotation of the heating film 20 starts, and as the temperature of the heater 16 increases, the inner surface temperature of the heating film 20 also increases. Energization of the heater 16 is controlled by PID control, and the input power is controlled so that the inner surface temperature of the heating film 20, that is, the detected temperature of the main thermistor 18 becomes 190 ° C.

  FIG. 5 is a block diagram of a control circuit section (CPU) 21 and a heater drive circuit section 28 as temperature control means of the fixing means. The power supply electrodes c and d of the heater 16 are connected to the heater drive circuit 28 via a power supply connector (not shown).

  In the heater drive circuit unit 28, 60 is an AC power source, 61 is a triac, 62 is a zero cross detection circuit, and 21 is a control circuit unit (CPU). The triac 61 is controlled by the control circuit unit 21. The TRIAC 61 energizes / blocks the heating resistor layer b of the heater 16.

  The AC power supply 60 sends a zero cross signal to the control circuit unit 21 via the zero cross detection circuit 62. The control circuit unit 21 controls the triac 61 based on this zero cross signal. In this manner, the heater 16 as a whole is rapidly heated by energizing the heating resistor layer b of the heater 16 from the heater drive circuit unit 28.

  Outputs of the main thermistor 18 that detects the temperature of the heating film 20 and the sub-thermistor 19 that detects the temperature of the heater 16 are taken into the control circuit unit (CPU) 21 via the A / D converters 64 and 65, respectively.

  The control circuit unit 21 performs PID control of the power supplied to the heater 16 by the triac 61 based on the temperature information of the heating film 20 from the main thermistor 18 so that the temperature of the heating film 20 is a predetermined control target temperature (set temperature). Control to be maintained.

  The PID control is an output value from an object to be controlled by proportional control (hereinafter referred to as “P control”), integral control (hereinafter referred to as “I control”) and differential control (hereinafter referred to as “D control”). In this control, control values are determined by combining them according to the above.

As a method for controlling the supplied power, in this embodiment, wave number control (on / off control) is used as normal main control, and the wave number control is phase controlled prior to the timing of correcting the supplied power before the recording material P enters. And power correction is performed by phase control. Then, the phase control is switched to the wave number control again at the timing when the power correction is completed. Here, the wave number control mode is the first power supply control mode, and the phase control is the second power supply control mode.

  By switching the wave number control to the phase control prior to the power correction timing, the power correction can be started by the phase control with a short energization ratio update cycle. Therefore, the deviation of the timing of power correction can be minimized, and the unevenness of gloss due to power shortage caused by the deviation of timing and the hot offset due to overshoot can be reduced.

  On the other hand, phase control is used only in a very short power correction period that is performed in accordance with the entry of the recording material into the heating nip, and since most of the power supply control is performed by wave number control, the increase in harmonic current is minimized. can do.

In this embodiment, the PID control is stopped 100 msec before the recording material P enters the heating nip H, and power correction is performed to supply a predetermined amount of power from that point until 0 msec after the recording material has entered.
Further, switching from wave number control to phase control is performed from 300 msec before the recording material P enters the heating nip H to 0 msec after the recording material enters.

  During the period when the predetermined power supply amount is supplied without performing PID control and the recording medium is heated by the heating film 20, heating unevenness (gloss level difference) generated between the first and second peripheral edges of the heating film is generated. Selected to be minimal. The reason why the power correction is started before the recording material P enters at the start of paper feeding is that time is taken into consideration until the temperature of the heater 16 rises after the correction power is actually supplied. That is, since the heater temperature does not completely follow the steep power supply, a slight time lag occurs until the actual power supply is reflected in the temperature. In addition, since there is naturally a contact thermal resistance from the heater 16 to the inner surface of the heating film, heat is not immediately transmitted here. Therefore, if heat is appropriately supplied to the portion corresponding to the leading end of the recording material of the heating film 20, it is slow after the leading end of the recording material P enters the heating nip H.

  Therefore, in consideration of the time lag, the timing for starting the correction of power in the sequence is determined. In this embodiment, the recording material P enters the heating nip H before 100 msec.

By the way, in this embodiment, the timing is set with a margin, although it is a little with respect to the entry timing of the recording material P into the heating nip H. In other words, ideally, it is preferable that the timing at which the heat generated by the heater is reflected in the temperature of the inner surface of the heating film completely coincides with the inrush timing of the recording material, but the power correction is started at a slightly earlier timing. Yes. This is because it is difficult to completely adjust the power correction to the recording material entry timing when considering the variation in heat transfer, so the power correction starts slightly earlier than the power correction delays and the temperature drops, so the temperature is slightly higher. It becomes due to the fact that has chosen to adjust the direction. If it is about this embodiment, there is no problem in practical use, but of course, the risk of hot offset becomes higher as this margin is increased as much as possible. This setting is not limited to the configuration of the present embodiment, and various selections can be made as appropriate.

  In addition, the power correction start timing is set based on the entry timing of the recording material P into the heating nip H, but in actuality, in this embodiment, the conveyance start timing of the recording material P by the registration roller 46 is used as a base point. . That is, at the start of conveyance of the recording material P by the registration roller 46, the leading edge of the recording material P is at the position of the registration sensor 47, and therefore the timing at which the recording material P enters the heating nip H is predicted from this, and based on this The timing is determined. That is, the actual control base point is the start of conveyance of the recording material P by the registration roller 46. In this embodiment, the registration roller 46 is used as a base point. However, a sensor for detecting the conveyance state may be provided on the upstream side of the heating device, and the detection result may be used as the base point.

  In the present embodiment, when the power supplied to the heater 16 is corrected, the difference in heat capacity due to the basis weight of the recording material P is taken into consideration. That is, the power used for the correction is changed according to the basis weight of the recording material P. In the present embodiment, the power supplied to the heater 16 according to the table classified according to the paper mode from the necessary power value obtained by the experiment. to correct. Actually, when the user designates the print mode, the print mode information is received together with the print signal from a host computer (not shown), and the control circuit unit 21 determines the supply power when the paper is passed.

  Table 1 shows a table of each paper mode and correction supply power in the present embodiment.

FIG. 6 shows a flowchart of the power control method in the present embodiment.
The actual correction operation will be described below according to the flow.

In this embodiment, a case where the frequency of the AC power supply (AC power) is 50 Hz will be described.
In FIG. 6, the image forming apparatus starts up in a state where a print signal can be received after the power is turned on (S1). When a print command is received from a host computer (not shown) (S2), the paper mode is read from the print signal (S3). The control circuit unit (CPU) 21 in the printer determines the correction supply power E2 (W) corresponding to the paper mode as shown in Table 1 (S4). Thereafter, the control circuit unit 21 drives the heater drive circuit unit 28 to start the heater 16 startup temperature control in order to control the temperature of the heating film 20 to a predetermined temperature (S5). At this time, power supply control to the heater 16 is performed by wave number control. In this embodiment, the wave number control is performed by updating the energization ratio with 20 half waves (predetermined wave number) as one unit. That is, the energization ratio is in increments of 5% from 0 half wave (0% energization) to 20 half wave (100% energization), and the update period of the energization ratio is 200 msec when the AC power supply is 50 Hz.

  When the heating film 20 is close to a predetermined temperature and the start-up temperature adjustment is completed (S6), the print temperature adjustment temperature of 190 ° C. is set as the target temperature, and the temperature is adjusted to the target temperature by PID control (S7). At this time, the supplied power control is wave number control.

  Thereafter, when 300 msec before the recording material enters, the supply power control is switched from wave number control to phase control. (S8) The phase control here uses an energization angle of 5% for one half wave of the AC waveform supplied from the power supply so as to control in units of 5% according to the energization ratio at the time of wave number control. The energization angle is obtained as the timing at which the triac 61 is turned on starting from when the zero cross signal is detected by the zero cross detection circuit 62. It is also possible to set the energization ratio more finely only during phase control.

  At this time, even if the control circuit unit 21 issues a switching command, it is not possible to immediately switch from wave number control to phase control unless the update period of the energization ratio of wave number control matches this timing. Therefore, in practice, switching from wave number control to phase control is performed after waiting for the update timing of the energization ratio of wave number control.

  After that, it waits at the target temperature while performing PID control using phase control as power control until 100 msec before entering the recording material (S9).

  When 100 msec before the recording material enters, the PID control is stopped, and a predetermined power E2 (W) is output as the correction-time supply power determined at S4 (S10), and continues until 0 msec after the recording material enters, E2 (W) continues to be supplied (S11). At this time, the power control is phase control, and the predetermined power is defined by the energization angle (phase angle) within one half wave of the AC waveform.

  After that, when 0 msec elapses after the recording material rushes, the phase control is switched to wave number control in which the current 20 half-wave is set as one unit and the energization ratio is updated. At the same time, the print temperature adjustment temperature of 190 ° C. is set as the target temperature, and the PID control is resumed (S12, S13).

  The above operation is continued until the end of printing (S14), and when the print job is completed, the temperature control is ended (S15). This correction is performed based on a table (Table 1) of the paper mode and correction supply power E2 (W) provided in the control circuit unit (CPU) 21 in the printer.

  Here, the reason for switching to the phase control 300 msec before the recording material enters the heating nip will be described.

  FIG. 7 shows a timing chart of the supplied power.

  In this embodiment, power correction is started 100 msec before the recording material enters the heating nip. However, if the energization ratio update period does not match, the power correction is not performed properly and gloss unevenness and hot offset occur. If the wave number control continues until this timing, unless the accidental energization ratio update timing coincides with the power correction timing, the phase control cannot be switched to the phase control even if the phase control is used at the power correction timing. Therefore, it is obvious that switching from wave number control to phase control needs to be performed prior to the timing of power correction. Considering that the update timing of the energization ratio of the wave number control does not match the switching timing from the wave number control to the phase control, even if the maximum timing is shifted, the power correction timing is surely switched to the phase control. Must be set to Here, it is not possible to switch to the phase control within the time corresponding to the update period of the energization ratio of the wave number control. Therefore, in order to surely switch to the phase control at the power correction timing, it is only necessary to switch to the phase control at a timing more than the time corresponding to the update period of the wave number control from the power correction timing. In this embodiment, the wave number control is performed to update the energization ratio with 20 half waves, which is a predetermined number of continuous two or more half waves as one unit, and the supply power update cycle is 200 msec. It is only necessary to switch from wave number control to phase control 200 msec before. That is, since the power correction is performed 100 msec before the recording material rushes, the switching to the phase control may be performed 300 msec.

  Of course, this is the minimum value for minimizing the increase in the harmonic current, and may be any time before 200 msec from the start of power correction from the viewpoint of preventing a shift in the timing of power correction.

  Further, the timing for returning from the phase control to the wave number control is also the same as the end of the power correction in the present embodiment. However, from the viewpoint of preventing the deviation of the timing of the power correction, any time after the end of the power correction. Good.

  In this embodiment, the case where the AC power supply is 50 Hz is described. However, since the time per one wave of the AC voltage is different in the case of 60 Hz, the timing of switching from wave number control to phase control may be different. In the case of 60 Hz, since one half wave is about 8.33 msec, in the case of the present embodiment in which the energization ratio update period is 20 half waves, in time, from wave number control to phase control about 166.6 msec before the start of power correction. This means that you can switch to Therefore, when the base point is the entry of the recording material into the heating nip, it is before 266.6 msec.

  Here, the frequency of the AC power supply may be detected, and the set value may be varied according to the frequency. In addition, since the switching timing is faster at 50 Hz at 60 Hz and 50 Hz, the switching timing can be set at the earliest timing regardless of the power frequency in accordance with the lowest power frequency that can be assumed.

  Moreover, this value is because the wave number control of the present embodiment sets 20 half waves as the update period, and is not limited to this. For example, in the case of wave number control in which the energization ratio is updated every 10 half-waves, the update cycle is 100 msec. Therefore, it is only necessary to switch from wave number control to phase control 100 msec before the start of power correction.

In the above example, when the power supplied to the heater 16 is corrected, the difference in heat capacity due to the basis weight of the recording material P is considered as the paper mode. is there. That is, recording materials having a basis weight of 60 to 70 g / m ² and 71 to 90 g / m ² are operated at different normal fixing speeds in a thin paper mode and a normal mode, respectively. On the other hand, a basis weight 91~128g / ^{m 2} of the recording material to operate the device at normal half speed as thick paper mode 1, basis weight 129~220g / ^{m 2} of the recording material is usually 1 as thick paper mode 2 It may be operated at a speed of / 3. In such a case, the correction timing may be varied as well as the case of the correction power.

  As this method, for example, as shown in Table 2, a correction power and correction timing table may be used according to the paper mode, and the power correction parameters may be set when the paper mode is determined from the print signal.

  In this embodiment, the reason for making the correction timing different for each operation speed is that, as described above, the power correction start timing has a slight margin with respect to the timing at which the recording material P enters the heating nip H. Related to. The slower the operating speed of the device, the slower the rotation speed of the heating film. At this time, if the time taken as a margin is the same, the rotation speed is slower and it corresponds to the margin in terms of the travel distance of the heating film. The area becomes narrower. Therefore, when the operation speed of the apparatus is slow, it is necessary to add a portion corresponding to the margin. Of course, this is a case where a margin is expected, and it is not always necessary to change the correction timing for each operation speed, and the description of the present embodiment does not limit this. For example, if the power correction timing is set completely in accordance with the entry of the recording material, the correction start timing is only an amount corresponding to the time lag of heat transfer from the heater to the inner surface of the heating film, and the timing is changed depending on the operation speed. There is no need.

  Of course, when the correction timing is different, the switching timing from the wave number control to the phase control is also different. In the case of Table 2, in this embodiment, the switching timing to the phase control is 310 msec before the entry of the recording material if the correction start timing is 110 msec, and if the correction start timing is 120 msec, the recording material 320 msec before the rush.

  This is because, as described above, it is necessary to switch to the phase control at least a time corresponding to the update period of the wave number control with respect to the correction start timing. In this embodiment, since the wave number control update cycle is 200 msec, switching to phase control is performed 200 msec before each correction start timing.

  Regarding the correction end timing, the thicker the paper, the more heat is taken away when the recording material enters, so the time until the surface temperature of the heating film is stabilized becomes slightly longer than that of the thin paper. Therefore, in the present embodiment, the recording material having a larger basis weight is adjusted by delaying the correction end timing. However, depending on the apparatus configuration such as the heat capacity and heat conductivity of the heating film and heater, it is not always necessary to change the correction end timing depending on the basis weight.

The switching timing from the phase control to the wave number control is the same as the correction end timing, but it may be any time after the correction end timing as described above.
In the above example, only the basis weight is set as the paper mode, but a difference due to the surface property of the recording material P can also be included in the paper mode. The recording material called rough paper with poor smoothness on the surface of the recording material, glossy paper with extremely smooth surface properties, and film-based recording materials such as OHT have heat transfer and heat capacity from the heating device to the recording material P. Since it is different from general print paper, the power used for power correction is different. Therefore, more optimal control can be performed if the power correction value is varied according to the type of the recording material.

  Table 3 shows a table of parameters for each paper mode and power correction including the type of recording material. In addition, since glossy paper gives higher gloss, even if the basis weight is small, the operation speed of the apparatus is decreased and the heating amount per unit time is increased. Further, since rough paper has a rough surface and poor fixability, the operation speed of the apparatus is similarly slowed down to increase the amount of heating per unit time so that fixing can be reliably performed.

  The type of the recording material P can be specified by the paper mode set by the user using the printer driver or the control panel, but can also be determined by the media sensor 51.

  As shown in FIG. 1, a media sensor 51 is arranged in the image forming apparatus of this embodiment. A schematic diagram of the configuration of the media sensor 51 is shown in FIG. The media sensor 51 includes an LED 33 as a light source, a CMOS sensor 34 as a reading unit, and lenses 35 and 36 as imaging lenses. Light having the LED 33 as a light source is irradiated to the recording material conveyance guide 31 or the surface of the recording material P on the recording material conveyance guide 31 through the lens 35. This reflected light is condensed through the lens 36 and imaged on the CMOS sensor 34. Thereby, the surface image of the recording material conveyance guide 31 or the recording material P is read. Thereby, the surface state of the paper fiber of the recording material P is read, and the analog output is A / D converted into digital data. The gain calculation and filter calculation of the digital data are processed in a programmable manner by a control processor (not shown). Then, a video comparison calculation is performed, and the paper type is determined based on the video comparison calculation result.

  By the way, it is so-called glossy paper that is particularly likely to have a level difference due to gloss unevenness due to the recording material P entering the heating nip H. This is because glossy paper has a very high surface smoothness, and a slight temperature difference appears as a difference in gloss. Further, in such glossy paper with a smooth surface, a slight temperature difference also appears as a hot offset, so that extremely high accuracy is required in terms of power correction value and correction timing. In addition, it can be said that a recording material having a large basis weight is relatively easily affected by a large temperature change due to the recording material P entering the heating nip H. Therefore, in Table 3, glossy paper and thick paper are particularly large as power correction values.

On the other hand, generally used printing paper having a basis weight of about 64 to 90 g / m ² is not so high in surface smoothness and has a small basis weight, so that the heating film is formed by the recording material P entering the heating nip H. The temperature change is small.

  Therefore, a normal printing paper with a small basis weight has a small power correction value and the correction timing is not so strict. In addition, rough paper is not glossy because its surface is not smooth. With this type of printing paper, even if correction is not performed, the gloss level difference is not so conspicuous. Therefore, even if the power correction is performed only by the wave number control without using the phase control, the deviation of the correction timing becomes an allowable level.

  Therefore, for example, depending on the basis weight and type of the recording material, a configuration in which switching from wave number control to phase control is not performed may be employed. For this purpose, for example, the table shown in Table 4 may be used when setting the power correction parameter according to the paper mode.

  Note that the power correction timing of the present embodiment is not limited to this value. In this embodiment, the power correction is performed before and after the recording material enters the heating nip. However, the power correction can be ended before the recording material enters. This is apparent from the fact that the power correction period is set on the assumption that a time lag occurs in the temperature rise of the heater with respect to the supply of power to the heater.

  As described above, the PID control is stopped for a certain time before and after the entry timing of the recording material P into the heating nip H, and the power supplied to the heater 16 is corrected to a predetermined value and supplied. At the same time, by switching the wave number control to the phase control prior to the power correction timing, it is possible to minimize the deviation between the power correction timing and the supply power update timing without increasing the harmonic current. Thus, more stable temperature control can be performed without causing temperature fluctuations accompanying the entry of the recording material P.

  In the first embodiment, the wave number control is used for the main control of the energization ratio at the time of power supply. However, in this embodiment, a combination of the wave number control and the phase control is used. This has a waveform that always conducts 100% energization or non-energization (0% energization) for one half wave within a predetermined period like wave number control, and controls the energization angle for one half wave within the same period. Thus, by including a waveform for performing phase control, the energization ratio in a predetermined cycle is controlled. Here, this control is defined as “hybrid control”.

  That is, the hybrid control is basically wave number control in which several half waves of one half wave or more are set as one unit, and phase control is performed with respect to several half waves.

  In hybrid control, since the waveform for performing phase control is included in the control cycle, a fine energization ratio can be set here, and the control cycle can be shortened compared with the case where the energization ratio is controlled only by wave number control. On the other hand, since the phase control is performed only on a part of the waves of the AC voltage, it is possible to make a setting that suppresses the increase of the harmonic current as much as possible compared to the case where the energization ratio is controlled only by the phase control.

  In this embodiment, the control period of the energization ratio is 8 half waves. Here, when the AC power supply is 50 Hz, the control cycle (update cycle) is 80 msec.

  When normal wave number control is performed in units of 8 half-waves, the energization ratio can be controlled only in increments of 12.5%, so the fluctuation range of the power supplied to the heater becomes large. Then, since the temperature ripple of the heater also increases, when the visible image is heated, uneven heating tends to appear as uneven gloss on the image. On the other hand, in the hybrid control used in this embodiment, a small energization ratio can be set even in units of 8 half-waves by including several half-waves for phase control in the 8 half-waves.

  In addition, since the cycle of updating the energization ratio during normal operation can be shortened compared to the case where only the wave number control in units of 20 half-waves is performed, stable control without unevenness can be achieved and flicker noise can be reduced. .

  In hybrid control, the number of waves per unit can be reduced. However, if the number is too small, the ratio of phase control in the whole increases, and the harmonic current increases. Therefore, in this embodiment, balanced eight half waves are set as the energization ratio update period. Of course, this differs depending on the apparatus configuration, and is not limited to this setting.

  In actual control, a waveform pattern of an AC voltage is set in advance for each energization ratio, and energization is performed with a waveform according to each pattern for each energization ratio set by PID control.

  Table 5 shows a waveform pattern for each energization ratio of this example. In this example, the energization ratio was set in increments of 5%, and a total of 21 waveforms were set from 0% to 100%. In this embodiment, including the first embodiment, the energization ratio in increments of 5% is described as an example. Of course, the energization ratio can be made finer, for example, can be set in increments of 1%. Since the hybrid control includes a half-wave that performs phase control, it is not necessary to increase the control unit of the wave number no matter how finely the energization ratio is set.

  In this embodiment, the supply power control is performed by hybrid control using the above waveform pattern, and the hybrid control is changed to phase control prior to the timing of correcting the supply power to the heater before the recording material enters the heating nip. Switching and power correction are performed by phase control.

  FIG. 9 shows a flowchart of the operation of this embodiment. The actual correction operation will be described below according to the flow. In this embodiment, the configuration of the image forming apparatus is the same as that of the first embodiment, as shown in FIG. Moreover, the structure of a heating apparatus is the same as that of Example 1, and is as having shown in FIGS. 2-4, The overlapping description is abbreviate | omitted.

  In FIG. 9, the image forming apparatus starts up in a state where it can receive a print signal after the power is turned on (S101). When a print command is received from a host computer (not shown) (S102), the paper mode is read from the print signal (S103). The control circuit unit (CPU) 21 in the printer determines the correction supply power E2 (W) corresponding to the paper mode as shown in Table 1 (S104). Thereafter, the control circuit unit 21 drives the heater drive circuit unit 28 to start the heater 16 startup temperature control in order to control the temperature of the heating film 20 to a predetermined temperature (S105). At this time, power supply control to the heater 16 is performed by hybrid control using the energization ratio pattern shown in Table 5. In the present embodiment, the update period of the energization ratio is 80 msec when the AC power source is 50 Hz.

  When the heating film 20 is close to a predetermined temperature and the start-up temperature adjustment is completed (S106), the print temperature adjustment temperature 190 ° C. is set as the target temperature, and the temperature is adjusted to the target temperature by PID control using hybrid control. (S107).

  Thereafter, when 180 msec before the recording material enters, the supply power control is switched from the hybrid control to the phase control (S108). At this time, actually, after the control circuit unit 21 issues a switching command, the hybrid control is switched to the phase control when the next energization ratio update timing of the hybrid control comes. Therefore, the actual switching timing varies from 180 msec before entering the recording material to 100 msec.

  The reason why the phase control is switched to 180 msec before the recording material rushes is that the timing when the hybrid control is switched to the phase control is a timing that goes back more than the time corresponding to the update period of the energization ratio from the power correction start timing as in the first embodiment. It is necessary. That is, the update period of the energization ratio of the hybrid control of this embodiment is 8 half waves = 80 msec (in the case of 50 Hz), and 80 + 100 = 180 msec. Of course, as described in the first embodiment, this numerical value may be varied depending on the frequency of the AC power supply.

  After that, as soon as the phase control is switched, the power control waits at the target temperature while performing the PID control using the phase control (S109). The phase control is surely switched to at least 100 msec before entering the recording material. Therefore, the PID control is stopped 100 msec before the recording material rushes, the predetermined power E2 (W) is output as the correction power supply determined at S104 (S110), and continues until 0 msec after the recording material rushes. E2 (W) is continuously supplied by phase control (S111). Thereafter, when the recording material rushes to 0 msec before, the phase control is switched to the hybrid control in which the current ratio is updated with the original 8 waves as one unit. At the same time, the print temperature adjustment temperature of 190 ° C. is set as the target temperature and the PID control is resumed (S112, S113).

  The above operation is continued until the end of printing (S114), and when the print job is finished, the temperature control is finished (S115). This correction is performed based on a table (Table 1) of the paper mode and correction supply power E2 (W) provided in the control circuit unit (CPU) 21 in the printer.

  As described above, by using the hybrid control in which the phase control is combined with the wave number control as described above, it is possible to shorten the energization ratio update period while suppressing the harmonic current to some extent, and to stabilize the normal temperature control.

1M, 1C, 1Y, 1Bk Image forming units 2a, 2b, 2c, 2d Photosensitive drums 3a, 3b, 3c, 3d Charging rollers 4a, 4b, 4c, 4d Developing devices 5a, 5b, 5c, 5d Transfer rollers 6a, 6b, 6c, 6d drum cleaning device 12 heating device 16 ceramic heater motor 18 main thermistor 19 sub thermistor 20 heated fill arm 21 the control circuit 22 the pressure low la 28 heater driving circuit portion 40 the intermediate transfer belt 44 secondary transfer roller 45 belt cleaning 46 registration rollers 47 register sensor 50 environmental sensor 51 media sensor 60 AC power P recording material N 1 transfer portion M 2 transfer portion t toner

Claims (17)

An image forming unit for forming an unfixed toner image on a recording material;
A fixing rotator, a heater that generates heat by electric power supplied from a commercial AC power source and heats the fixing rotator, a pressure member that forms a nip portion between the fixing rotator, and the fixing rotator or the A temperature detecting member that detects the temperature of the heater, and a fixing unit that heats the recording material on which the unfixed toner image is formed at the nip portion while heating the recording material and fixes the unfixed toner image on the recording material. ,
An image forming apparatus comprising: a power control unit that controls power supplied from the commercial AC power source to the heater according to a detection temperature of the temperature detection member.
The power control unit includes a first power supply control mode in which power corresponding to the detected temperature is supplied to the heater for each first cycle by using wave number control or control in which wave number control and phase control are combined . A second power supply control mode in which power corresponding to the detected temperature is supplied to the heater every second cycle shorter than the first cycle using phase control; and a second power supply control mode for increasing the power supplied to the heater. 3 power supply control modes can be executed,
When the unfixed toner image is fixed on the recording material at the nip portion, the first power supply control mode is executed,
From the state in which the third power supply control mode is executed before the leading edge of the recording material enters the nip portion, and the first power supply control mode is executed before the third power supply control mode. An image forming apparatus that switches to a state in which the second power supply control mode is executed.   Before the leading edge of the recording material enters the nip portion, the power supply control to the heater is performed in the order of the first power supply control mode, the second power supply control mode, and the third power supply control mode. The image forming apparatus according to claim 1, wherein: The timing for switching from the first power supply control mode to the second power supply control mode is a timing that is more than the time corresponding to the first period from the timing at which the third power supply control mode is started. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. A first fixing processing mode in which the recording material is transported at a first speed in the nip portion; and a second fixing processing mode in which the recording material is transported at a second speed slower than the first speed in the nip portion. Is feasible, and
The time from the start of execution of the third power supply control mode until the leading edge of the recording paper enters the nip portion is greater in the second fixing processing mode than in the first fixing processing mode. the image forming apparatus according to any one of claims 1 to 3, wherein the longer. The power supplied to the heater during execution of the third power supply control mode in the second fixing processing mode is the same as that during execution of the third power supply control mode in the first fixing processing mode. The image forming apparatus according to claim 4 , wherein the power is larger than the power supplied to the heater. The first fixing processing mode is executed when plain paper is used as the recording material, and the second fixing processing mode is executed when thick paper having a basis weight larger than that of the plain paper is used as the recording material. the image forming apparatus according to claim 4 or 5, characterized in that it is. When glossy paper is used as the recording material, the third power supply control mode is executed before the leading edge of the recording material enters the nip portion, and before the third power supply control mode, the third power supply control mode is executed. the image forming apparatus according to any one of claims 1 to 6, characterized in that switching to a state for executing the second power supply control mode from the state to execute the first power supply control mode. When the rough paper is used as a recording material, before the leading end of the recording material enters into the nip, one of the claims 1 to 7, characterized in that to perform only the first power supply control mode The image forming apparatus according to claim 1. The third power supply control mode, the image forming apparatus according to any one of claims 1 to 8, characterized in that a mode for controlling only the phase control. The fixing rotator image forming apparatus according to any one of claims 1 to 9, characterized in that an endless belt. The image forming apparatus according to claim 10 , wherein the heater is in contact with the belt. The image forming apparatus according to claim 11 , wherein the heater is in contact with an inner surface of the belt and forms the nip portion together with the pressure member via the belt. An image forming unit for forming an unfixed toner image on a recording material;
A fixing rotator, a heater that generates heat by electric power supplied from a commercial AC power source and heats the fixing rotator, a pressure member that forms a nip portion between the fixing rotator, and the fixing rotator or the A temperature detecting member that detects the temperature of the heater, and a fixing unit that heats the recording material on which the unfixed toner image is formed at the nip portion while heating the recording material and fixes the unfixed toner image on the recording material. ,
An image forming apparatus comprising: a power control unit that controls power supplied from the commercial AC power source to the heater according to a detection temperature of the temperature detection member.
The power control unit includes a first power supply control mode in which power corresponding to the detected temperature is supplied to the heater for each first cycle by using wave number control or control in which wave number control and phase control are combined . A second power supply control mode in which power corresponding to the detected temperature is supplied to the heater every second period shorter than the first period using phase control, and the nip portion When the unfixed toner image is fixed on the recording material, the first power supply control mode is executed.
Before the leading edge of the recording material enters the nip portion, the second power supply control mode is switched from the state in which the first power supply control mode is executed to the state in which the second power supply control mode is executed. An image forming apparatus comprising: increasing power supplied to the heater during execution. The timing for switching from the first power supply control mode to the second power supply control mode starts to increase the power supplied to the heater while the second power supply control mode is being executed. The image forming apparatus according to claim 13 , wherein the timing is at least a time before the time corresponding to the first period from the timing. The image forming apparatus according to claim 13 or 14, wherein the fixing rotator is an endless belt. The image forming apparatus according to claim 15 , wherein the heater is in contact with the belt. The image forming apparatus according to claim 16 , wherein the heater is in contact with an inner surface of the belt and forms the nip portion together with the pressure member via the belt.

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