JP2012088443A - Image forming apparatus - Google Patents

Abstract

Provided is a heater power control of a fixing heating device that can suppress flicker and harmonic current distortion and can reduce uneven glossiness of an image in power supply control to a heater of a fixing heating device of an image forming apparatus. To do.
A pre-fixing sensor for detecting a conveyance position of a recording medium, a control unit for controlling an energization amount to a fixing heating device, and a memory for storing a plurality of heater power control tables for the fixing heating device. The control unit 113 switches between the energization control table while the recording medium 101 passes the fixing heating device 109 and the energization control table when the recording medium 101 does not pass based on the detection result of the pre-fixing sensor 116. Take control.
[Selection] Figure 1

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer apparatus, a facsimile apparatus, and a multifunction machine having a plurality of functions, and more particularly to a heater power control method for a fixing heating apparatus and image formation using the heater power control method. Relates to the device.

  2. Description of the Related Art Conventional image forming apparatuses are provided with a fixing heating device for fixing an unfixed toner image on a recording medium such as recording paper or an OHP sheet by melting it with heat in order to make it a fixed image. As this fixing heating device, a heat roller type heat fixing device using a halogen heater as a heat source or a film fixing type heat fixing device using a ceramic heater as a heat source is used. Above all, the film fixing type fixing heating apparatus that heats a film having a very small heat capacity from the inside has high energy efficiency and a high rate of temperature increase. Therefore, it is sufficient to heat only at the time of printing, and there is an advantage that the time from when the power is turned on until it becomes ready for printing is short, and the power consumption during standby is small.

  In general, the heater of the fixing heating device is connected to an AC power source via a switching element such as a triac, and power is supplied from the AC power source. The fixing heating device is provided with a temperature detection element such as a thermistor. The temperature of the fixing heating device is detected by the temperature detection element, and the engine controller controls the switching element on / off based on the detected temperature information, thereby turning on / off the power supply to the heater and fixing heating. The temperature of the device is controlled to the target temperature. The on / off control of the ceramic heater is performed by phase control (see Patent Documents 1 to 3) or wave number control (see Patent Document 4) of the AC power source, or a combination of phase control and wave number control (see Patent Document 5). The phase control is a power control method in which the heater is turned on at an arbitrary phase angle within one half wave of the AC power supply. The wave number control is a power control method in which a plurality of half waves are set as one control cycle and the heater is turned on / off in units of half waves of the AC power supply. Control in which phase control and wave number control are combined is a power control method in which a plurality of half waves are set as one control period, some half waves are wave number controlled, and other half waves are phase controlled.

  The reason why the phase control is selected is to suppress so-called flicker and temperature ripple of the fixing heating device. Flicker is a change in the load current of the device and the influence of the internal impedance of the AC power supply connected to the device and the impedance of the indoor power distribution network. This refers to phenomena such as flickering lighting equipment. In the phase control, since a current flows every half wave, a change amount and a change period of the current are small, and the occurrence of flicker can be suppressed. Further, since the electric power can be controlled every half wave, there is an advantage that the temperature adjustment control of the fixing heating device is quick and the temperature ripple of the fixing heating device can be reduced. On the other hand, in the phase control, since the heater is turned on at an arbitrary phase angle within one half wave of the AC power supply, a sudden current fluctuation occurs. A current waveform having a rapid current fluctuation is a current waveform including a large number of frequency components of the fundamental frequency (for example, 50 Hz or 60 Hz) of the AC power supply, that is, a current waveform including a large amount of so-called harmonic current distortion. For this reason, the harmonic current distortion may cause malfunction between electronic devices or distortion of the AC power supply voltage waveform.

  The reason for selecting wave number control is suppression of harmonic current distortion. In wave number control, heater on / off control is always performed when the power supply voltage is near 0V (zero cross point), so there is less sudden current fluctuation and harmonic current distortion than phase control that turns on the heater halfway through the AC power supply. Is unlikely to occur. However, although effective in suppressing the harmonic current distortion, the load current fluctuation for each half wave is large, so that there is a problem that the voltage fluctuation of the AC power supply becomes large and flicker is likely to occur.

  The reason for selecting control that combines phase control and wave number control is that it is advantageous for suppressing harmonic current distortion compared to phase control alone, and that it is advantageous for suppressing flicker compared to only wave number control. Can be given. Higher harmonic current distortion tends to occur more when the voltage of the AC power supply used is higher. Therefore, the heater control method is fixed to either one according to the AC power supply voltage in the area where the image forming apparatus is used. For example, a phase control method that is advantageous for flicker is used for an AC power supply voltage region of 100 to 127 V, and a wave number control method that is advantageous for harmonic current distortion is used for an AC power supply voltage region of 220 V to 240 V. However, with the recent increase in heater power of the fixing heating device due to the speeding up of the image forming apparatus, there are cases where the harmonic current distortion regulation cannot be satisfied only by phase control and the flicker regulation cannot be satisfied only by wave number control. . In that case, the control combining the phase control and the wave number control is effective as the control satisfying both the harmonic current distortion regulation and the flicker regulation.

JP 60-117273 A Japanese Patent Laid-Open No. 09-101718 JP 09-106215 A JP 2000-268939 A JP 2003-123941 A

  In recent image forming apparatuses, a full-color image is formed, and the printing speed is increased, the image quality is improved, and the first printout time (the time from when the print is waiting until one recording medium is ejected (hereinafter, referred to as “printing time”) FP))) Shortening is important. Therefore, the heater power in the fixing heating device in the image forming apparatus tends to increase. The tendency for the heater power to increase means that the resistance value of the heater is decreasing. The decrease in the resistance value of the heater means an increase in the current of the AC power supply when the heater power is supplied, and causes further harmonic current distortion and flicker.

  There is also a demand for a reduction in temperature ripple of the fixing heating device. While the recording medium passes through the fixing heating device, the fixing heating device is controlled to a target temperature that can satisfy the fixing property of the recording medium. The period of the temperature ripple with respect to the target temperature of the fixing and heating apparatus that has not affected the image in the past tends to appear as a period of uneven gloss in the image as the printing speed increases. In order to prevent the gloss unevenness due to the temperature ripple, there is a method of increasing the heat capacity of the fixing heating device. However, the thermal response of the fixing heating device is delayed, and the FPOT of the device is increased. For this reason, the heat capacity of the fixing heating device for increasing the printing speed and shortening the FPOT cannot be increased, and a fixing heating device having a low heat capacity and a fast thermal response may have to be used. .

  As described above, in the phase control that is advantageous for the temperature ripple, the harmonic current distortion increases due to the decrease in the heater resistance value. In particular, regulations on harmonic current distortion have been strengthened for more efficient use of energy, and not only integer multiple harmonic current distortion of the fundamental frequency of AC power supply, but also non-integer multiple harmonic current distortion (harmonic between orders). Suppression of waves) is required. For this reason, the current situation is that high-speed machines with high printing speeds cannot satisfy the harmonic current distortion standard by heater control using only conventional phase control. In order to satisfy the harmonic current distortion standard, when using heater control with only wave number control that is most advantageous for harmonic current distortion suppression, when performing heater power on / off in half wave units of AC power supply Temperature ripple occurs in the fixing heating device. In addition, there is a method that uses heater control that combines phase control and wave number control, but this method also uses wave number control during one control cycle, so temperature ripple similar to heater control with only wave number control occurs, and the image is glossy. It was causing unevenness.

  The present invention has been made in view of the above problems, and in a film fixing type heat fixing apparatus using a ceramic heater as a heat source, both flicker and harmonic current distortion can be suppressed, and temperature ripple can be reduced. It is an object of the present invention to provide heater power control for a fixing heating apparatus.

  In order to solve the above problems, the present invention has the following configuration.

  (1) Image forming means for forming a toner image on a recording medium, fixing heating means for heating and fixing the toner image to the recording medium, conveying means for conveying the recording medium to the fixing heating means, A conveyance detection unit that detects a conveyance position of the recording medium, an electronic switch unit that supplies power from the AC power source to the fixing heating unit, a zero cross detection unit that detects a zero cross of the AC power source, and a fixing heating unit. Using the storage means for storing a plurality of heater power control tables for power supply, the detection result of the zero cross detection means, and any heater power control table stored in the storage means, the fixing heating means An image forming apparatus comprising: a control unit configured to control a supply power of the recording medium, wherein the control unit detects whether the recording medium is based on a detection result of the conveyance detection unit. Determining whether or not the passed the Chakukanetsu means, an image forming apparatus and performs control to switch the heater power control table based on the result of the judgment.

  (2) Image forming means for forming a toner image on a recording medium based on image information, fixing heating means for heating and fixing the toner image to the recording medium, and transport for transporting the recording medium to the fixing heating means Means, a conveyance detection means for detecting a conveyance position of the recording medium, an electronic switch means for supplying power from the AC power source to the fixing heating means, a zero cross detection means for detecting a zero cross of the AC power supply, and the fixing Using storage means for storing a plurality of heater power control tables for supplying power to the heating means, detection results of the zero cross detection means, and any heater power control table stored in the storage means, An image forming apparatus comprising: a control unit configured to control power supplied to the fixing heating unit, wherein the control unit is configured to control the recording medium based on the image information. A print region and a print region are determined, and based on a detection result of the conveyance detection unit, it is determined whether or not the recording medium is passing through the fixing heating unit, and the printing region of the recording medium is the fixing heating unit The heater power control table used while the sheet is being passed, while the recording medium is not passing the fixing heating means, or while the non-printing area of the recording medium is passing the fixing heating means An image forming apparatus that performs control to switch to another heater power control table.

  According to the present invention, in a film fixing type heat fixing apparatus using a ceramic heater as a heat source, it is possible to suppress both flicker and harmonic current distortion, and to control heater power of a fixing heating apparatus capable of reducing temperature ripple. Can be provided.

1 is a configuration diagram of an image forming apparatus and a fixing heating device according to a first exemplary embodiment. 1 is a diagram illustrating a drive circuit of a fixing heating device according to a first embodiment. The figure for demonstrating the control which combined phase control of Example 1, wave number control, phase control, and wave number control The figure which shows the switching flow of the heater electric power control table of Example 1. FIG. The figure which shows the timing chart of the switching of the heater power control table of Example 1. The figure which shows the switching flow of the heater electric power control table of Example 2. FIG. The figure which shows the timing chart of the switching of the heater power control table of Example 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the embodiment described below, an image forming apparatus having a fixing heating device (on-demand fixing device) using a ceramic heater (hereinafter referred to as a heater) shown in FIG. 1A will be described as an example. However, the present invention can be applied to all apparatuses using a fixing heating apparatus, and is not particularly limited to an image forming apparatus. The technical scope of the present invention is defined by the scope of the claims, and is not limited by the following individual embodiments.

  In this embodiment, heater power control capable of reducing gloss unevenness in an image forming apparatus having a film fixing type fixing heating device using a heater as a heat source will be described.

[Configuration of Image Forming Apparatus]
FIG. 1A is a configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus 100 feeds the recording medium 101 by the feeding roller 102 and conveys the recording medium 101 toward the intermediate transfer member 103. The photosensitive drum 104 is driven to rotate counterclockwise at a predetermined speed by the power of a drive motor (not shown), and is uniformly charged by the primary charger 105 during the rotation process. Laser light modulated in accordance with image information is output from the laser beam scanner 106, and selectively scans and exposes the photosensitive drum 104 to form an electrostatic latent image. The developing device 107 attaches powder toner, which is a developer, to the electrostatic latent image to visualize it as a toner image. The toner image formed on the photosensitive drum 104 is primarily transferred onto the intermediate transfer member 103 that rotates in contact with the photosensitive drum 104. Thereafter, the recording medium 101 conveyed at an appropriate timing synchronized with the rotation of the intermediate transfer member 103 is pressed against the intermediate transfer member 103 by the transfer roller 108 to which a transfer bias is applied, and the toner image is recorded on the recording medium 101. Secondary transferred on top.

  The photosensitive drum 104, the primary charger 105, the laser beam scanner 106, and the developing unit 107 are arranged for four colors of black, yellow, magenta, and cyan, respectively, and the toner images for the four colors are secondary on the recording medium 101. Transcribed. The fixing heating device 109 includes a fixing roller 111 having a built-in heater 110 and a pressure roller 112 for press-contacting the fixing roller 111, and the toner image is fixed by heating and pressing the recording medium 101. It is discharged outside. The control unit 113 manages the conveyance position of the recording medium 101 by a conveyance sensor 114, a registration sensor 115, a pre-fixing sensor 116, and a fixing paper discharge sensor 120 that are conveyance detection elements on the conveyance path of the recording medium 101. In addition, the control unit 113 includes a storage unit that stores a temperature control program and a temperature control table of the fixing heating device 109. The power supply device 118 connected to the AC power supply 117 has a power supply circuit to the fixing heating device 109 and a rectification circuit from AC to DC, and the power consumed in the above process is supplied from the power supply device 118 to the image forming apparatus. 100 parts are supplied.

  FIG. 1B is a schematic sectional view of the fixing heating device 109. The heater holder 200 is a heat-resistant and heat-insulating rigid body member that fixes the heater and guides the inner surface of the film, and is a horizontally long member whose longitudinal direction is a direction crossing the conveyance path of the recording medium 101 (a direction perpendicular to the drawing). The heater 110 is a horizontally long member that is inserted into a groove formed along the length of the lower surface of the heater holder 200 and has a length in a direction crossing a transfer material conveyance path fixed and supported by a heat resistant adhesive. A cylindrical heat-resistant film material (hereinafter referred to as a fixing film 201) is loosely fitted on a heater holder 200 to which a heater 110 is attached. The stay 202 is a rigid member whose longitudinal direction is the vertical direction in the figure, and is disposed inside the heater holder 200. The pressure roller 112 is disposed so as to be in pressure contact with the heater 110 and the fixing film 201 interposed therebetween. A range indicated by an arrow N is a fixing nip portion N formed by the press contact. The pressure roller 112 is rotationally driven at a predetermined peripheral speed in the direction of arrow B by a fixing motor (not shown). The rotational force of the pressure roller 112 directly acts on the fixing film 201 due to the frictional force between the pressure roller 112 and the outer periphery of the fixing film 201 at the fixing nip portion N, and the fixing film 201 slides against the lower surface of the heater 110 in pressure contact. While being rotated in the direction of arrow C. The heater holder 200 functions as an inner surface guide member of the fixing film 201 and facilitates the rotation of the fixing film 201. Furthermore, in order to reduce the sliding resistance between the inner surface of the fixing film 201 and the lower surface of the heater 110, a small amount of lubricant such as heat-resistant grease may be interposed therebetween.

  First, the driven rotation of the fixing film 201 due to the rotation of the pressure roller 112 becomes steady, and the temperature of the heater 110 rises to a target temperature for making an unfixed image a fixed image. Next, the recording medium 101 to be fixed is introduced into the fixing nip portion N between the fixing film 201 and the pressure roller 112 and is nipped and conveyed, so that the heat of the heater 110 is transferred onto the recording medium 101 via the fixing film 201. Applied to unfixed images. As a result, the unfixed image on the recording medium 101 is heat-fixed on the surface of the recording medium 101. The recording medium 101 that has passed through the fixing nip N is separated from the surface of the fixing film 201 and conveyed. Note that an arrow A in FIG. 1B indicates the conveyance direction of the recording medium 101. Further, the fixing heating device 109 has a thermistor 203 that is an element for detecting the temperature of the heater 110. The thermistor 203 is pressed against the heater 110 with a predetermined pressure that can always be sensed by a spring (not shown) or the like, and detects the temperature of the heater 110.

[Heater drive circuit]
FIG. 2 shows a drive circuit for the heater 110 of the fixing heating apparatus according to this embodiment. A commercial AC power source 117 is connected to the fixing heating device 109, and the control unit 113 supplies the input voltage from the AC power source 117 to the heater 110, thereby causing the heater 110 to generate heat. Power supply to the heater 110 is performed by energizing / cutting off the triac 301 that is an electronic switch. The resistors 302 and 303 are bias resistors for the triac 301, and the phototriac coupler 305 is a device for ensuring a creepage distance between the primary and secondary. Then, the triac 301 is turned on by energizing the light emitting diode 304 of the phototriac coupler 305. The resistor 306 is a resistor for limiting the current of the phototriac coupler 305, and turns on / off the phototriac coupler 305 by turning on / off the transistor 307. The transistor 307 operates according to the heater drive signal from the control unit 113 via the resistor 308.

  The input power supply voltage from the AC power supply 117 is also input to the zero cross detection circuit 309. The AC voltage from the AC power source 117 is half-wave rectified by the rectifiers 310 and 311. This half-wave rectified AC voltage is input to the base of the transistor 316 via the resistors 312 and 313, the capacitor 314, and the resistor 315. Thus, the transistor 316 is turned on when the neutral side potential is higher than the hot side potential, and the transistor 316 is turned off when the neutral side potential becomes lower than the hot side potential. The photocoupler 317 is an element for securing a creepage distance between the primary and secondary, and the resistors 318 and 319 are resistors for limiting the current flowing through the photocoupler 317. When the neutral side potential becomes higher than the hot side potential, the transistor 316 is turned on, so that the light emitting diode 320 of the photocoupler 317 is turned off, the phototransistor 321 is turned off, and the output voltage of the photocoupler 317 becomes high. On the other hand, when the neutral side potential becomes lower than the hot side potential, the transistor 316 is turned off, so that the light emitting diode 320 of the photocoupler 317 emits light, the phototransistor 321 is turned on, and the output voltage of the photocoupler 317 becomes low. The output of the photocoupler 317 is notified to the control unit 113 through the resistor 322 as a zero cross signal.

  The zero-cross signal is a pulse signal having a signal period equal to the frequency of the AC power supply, and the signal level changes according to the potential polarity of the AC power supply. The control unit 113 detects the rising and falling edges of the zero-cross signal, and controls the power supply to the heater 110 by turning on / off the triac 301 at an arbitrary timing. The temperature detected by the thermistor 203 is detected as a partial pressure between the resistor 323 and the thermistor 203 and input to the A / D port as a TH signal to the control unit 113. In the above configuration, the temperature control of the fixing heating device 109 is performed as follows. That is, the control unit 113 monitors the TH signal, and stops the energization of the heater 110 using the heater drive signal when the target temperature for setting the unfixed image as the fixed image is reached. Further, when the TH signal falls below the target temperature, the control unit 113 keeps the temperature of the fixing heating device constant by energizing the heater 110.

[Power control method]
Next, phase control, wave number control, and control combining phase control and wave number control, which are power control methods when the heater 110 is energized, will be described. FIG. 3A shows an example of heater power control by phase control. The logic of the zero cross signal 4b is switched at a point where the AC power supply voltage waveform 4a is switched from positive to negative and from negative to positive. Then, when the heater drive signal 4c is turned on after Ta time from the rising and falling edges, the heater 110 is energized and supplied with power at the hatched portion of the heater applied voltage 4d. Since the heater 110 is turned off at the next zero cross point after the heater 110 is turned on, the heater drive signal 4c is turned on again after a time Ta from the edge of the zero cross signal 4b, so that the next half wave The same electric power is supplied to the heater 110. Further, when the heater drive signal 4c is turned on after a time Tb different from the time Ta, the energization time to the heater 110 changes, so that the power supplied to the heater 110 can be changed. In this way, the power supplied to the heater 110 can be controlled by changing the time for which the heater drive signal 4c is turned on from the edge of the zero cross signal 4b for each half wave. In the phase control, as shown in FIG. 3A, the energization of the heater 110 is turned on in the middle of the half wave of the AC power supply voltage waveform 4a, so that the current flowing through the heater 110 suddenly rises and the harmonic current flows. This harmonic current increases as the rising amount of the current increases, and becomes maximum when the phase angle is 90 °, that is, when the supplied power is 50%. For example, consider the total harmonic current distortion value under the condition of a heater resistance value of 100Ω and an AC power supply 117 of 230 V / 50 Hz. The total harmonic current distortion values from the second to the 40th when the phase is controlled at a fixed phase angle at each of the phase angles 30 °, 60 °, 90 °, 120 °, and 150 ° are the phase angles of 60 ° and 120 °. In this case, the total harmonic current distortion value is about 85% as compared with the case of the phase angle of 90 °. In the case of the phase angle of 30 ° and 150 °, the total harmonic current distortion value is about 45% compared to the case of the phase angle of 90 °. In addition, since a rising edge of this current occurs every half-wave, many harmonic currents flow, and it is essential to comply with harmonic regulations. Therefore, circuit components such as a filter are often required. On the other hand, since a current smaller than one half wave flows for each half wave, the amount of change in current for each half wave is small, and the change period is also fast, so the effect on flicker is small.

  FIG. 3B shows an example of heater power control by wave number control. In the wave number control, the on / off control is performed in units of half wave of the AC power supply voltage waveform 5a. Therefore, when turning on, the heater drive signal 5c is turned on together with the edge of the zero cross signal 5b. The heater application voltage 5d to the heater 110 is controlled by changing the number of half waves that are turned on in one control cycle, for example, by setting eight half waves as one cycle. In FIG. 3B, since four half waves of the eight half waves are turned on, the power supplied to the heater 110 is 50%. In this way, the energization control pattern obtained by dividing the heater supply power from 0% to 100% into 12 is determined in advance, and the control unit 113 can perform heater power control based on the energization control pattern. Here, when turning on, two consecutive half waves are turned on. In the wave number control, the heater 110 is always turned on / off at zero crossing, so there is no sharp rising edge of current as in phase control, and the harmonic current is very small. On the other hand, since the current flows in half-wave units, the amount of change in current for each half-wave is large and the change cycle is long compared to phase control, so the effect on flicker is large. Therefore, by devising the half-wave position (energization control pattern) that is turned on within one control cycle, the influence of the current fluctuation cycle on flicker is minimized.

  FIG. 3C shows an example of heater power control in which phase control and wave number control are combined. FIG. 3C shows a case where 8 half-waves are set as one control cycle, 2 half-waves of which are controlled by wave number control, and 2 half-waves are controlled by phase control, and the heater supply power ratio is duty 4/12 (= 33.3%). Indicates. The control unit 113 transmits an ON signal to the transistor 307 after the time Tc of the heater driving signal 6c from the edge of the zero cross signal 6b to the transistor 307 so that the power duty of the first wave and the second half wave becomes 33.3%. The phase of the AC power supply voltage waveform 6a is controlled. Then, 2 half of the remaining 6 half-waves are turned on by wave number control, and the other 4 half-waves are all turned off, so that the heater applied voltage 6d of about 33.3% is supplied in one control cycle. In this way, the energization control pattern obtained by dividing the heater supply power from 0% to 100% into 12 parts is determined in advance, and the control unit 113 can perform heater energization control based on the energization control pattern. Flicker is suppressed because phase control is included compared to wave number control, and harmonic current distortion is suppressed because it includes wave number control compared to phase control.

[Heater control sequence]
A heater control sequence that does not cause gloss unevenness in an image and can reduce harmonic current distortion and flicker using the heater control will be described. For the description, the flowchart of FIG. 4, the detection result 8a of the pre-fixing sensor 116 of FIG. 5A, the status 8b of the heater power control table used, and the timing chart of the heater applied voltage 8c are used. Further, the detection result 9a of the pre-fixing sensor 116 in FIG. 5B and the timing chart of the state 9b of the heater power control table to be used are also used. In this embodiment, three types of heater power control tables are recorded in a recording unit (not shown) in the control unit 113, and the control unit 113 switches each heater power control table. These three types of tables are a phase control table 1, a wave number control table 2, and a control table 3 combining phase control and wave number control.

  FIG. 4 shows a switching flow of the heater power control table when a print job is executed. The control unit 113 selects an energization control pattern for starting up and fixing the fixing heating device from the table 3 (S700). Table 3 is a table of energization control patterns in which phase control and wave number control, which are effective for both harmonic current distortion suppression and flicker suppression, although temperature ripple is disadvantageous. The energization control pattern is a combination of phase control and wave number control for one control cycle of 8 half-waves. The temperature of the fixing heating device 109 is controlled by the temperature detected by the thermistor 203, and the control unit 113 performs optimum energization for each cycle. A control pattern is selected from Table 3. Next, the control unit 113 determines whether or not the first recording medium 101 is in the fixing nip N during the next energization control pattern (S701). When determining that there is no control unit 113, the control unit 113 continues to select the energization control pattern from the table 3 (S700). If the control unit 113 determines that the first recording medium 101 is in the fixing nip N during the next energization control pattern, the control unit 113 determines whether the recording paper is in the fixing nip N during the next energization control pattern. Is determined (S702).

  If the control unit 113 determines that the recording paper is in the fixing nip N during the next energization control pattern, the control unit 113 selects the energization control pattern from the table 1 (S703). Here, the control unit 113 can determine whether or not the recording medium 101 is in the fixing nip N during the next energization control pattern from the frequency of the AC power supply and the time Td from the pre-fixing sensor 116 to the fixing nip N. Table 1 is a phase control table that is a control that can reduce the temperature ripple most, although it is disadvantageous to the harmonic current distortion of the fixing heating device 109. The selection of the table 1 is maintained while the recording medium 101 passes through the fixing nip N (S702, S703). If it is determined that the recording medium 101 is not in the fixing nip N during the next energization control pattern (S702) and it is determined that the recording medium 101 currently in the fixing nip N is not the final recording medium 101 (S705), Take control. That is, while the recording medium 101 passes through the fixing nip N, the control unit 113 selects the next energization control pattern from the table 2 (S704). Here, Table 2 is wave number control which is the most advantageous control for suppressing harmonic current distortion, although it is disadvantageous for flicker suppression and temperature ripple. The energization control pattern by the table 2 is maintained while the next recording medium 101 arrives at the fixing nip N (S704, 705, 702). When it is determined that the recording medium 101 currently in the fixing nip N is the final recording medium 101 (S705), the control unit 113 selects the next energization control pattern from the table 3 (S706).

  FIG. 5A shows changes in the heater applied voltage when the heater power control table is switched from the table 3 to the table 1. It can be seen that the table 1 is switched to the table 1 starting from the last one control cycle of the table 3 before the timing when the recording medium 101 enters the fixing nip N. FIG. 5B shows an outline of switching of the heater power control table when three recording media are passed through the apparatus. The heater power control table is changed Td time after the recording medium 101 passes the pre-fixing sensor. The table 1 is selected when the recording medium 101 passes through the fixing nip N, the table 2 is selected when the recording medium 101 passes through the fixing nip N, and the table 3 is selected otherwise. .

  As described above, when the temperature ripple reduction of the fixing and heating apparatus having high thermal response is demanded as the apparatus speeds up, the fixing temperature ripple and flicker are suppressed while the recording medium 101 passes through the fixing nip portion N. Use advantageous phase control. Then, wave number control advantageous for harmonic current distortion is used while the recording medium 101 passes through the fixing nip portion N. Further, by using control in which phase control and wave number control are combined while the recording medium 101 is not passing through the other fixing nip portion N, temperature ripple reduction, harmonic current distortion suppression, and flicker reduction of the fixing heating device 109 are used. It is possible to provide a fixing heating apparatus that can satisfy the following three conditions.

  Although the present embodiment has been described with respect to the case where there are three types of heater power control tables stored in the recording unit, this is merely an example, and two or more types of tables may be stored in the recording unit. For example, when the AC power supply voltage is a high voltage (for example, 220V to 240V), there is often a relatively margin with respect to the flicker standard. In that case, only the two tables of Table 1 and Table 2 may be used without using the control in which the phase control and the wave number control of Table 3 are combined. Further, for example, when the AC power supply voltage is a low voltage (for example, 100 V to 127 V), there is often a relatively margin with respect to the harmonic current distortion standard. In that case, only the two tables of the table 1 and the table 3 may be used without using the wave number control of the table 2.

  Note that the arrival time Td from the detection result of the presence of paper by the pre-fixing sensor 116 of the recording medium 101 to the fixing nip N is obtained as follows. That is, the conveyance distance between the pre-fixing sensor 116 and the fixing nip N is divided by the conveyance speed of the recording medium 101, and the output delay time of the pre-fixing sensor 116 including the chattering removal of the control unit is subtracted. Can do. The arrival times Td corresponding to several transport speeds possible with the apparatus may be recorded in advance in the recording unit of the control unit. In addition, the conveyance sensor 114, the registration sensor 115, the pre-fixing sensor 116, and the fixing paper discharge sensor 120 on the recording medium conveyance path calculate the speed including a minute speed fluctuation due to a change in the stability of the start-up of the apparatus or an environmental change. Alternatively, interpolation calculation may be performed. The control unit 113 can know the frequency of the AC power supply 117 from the zero cross signal from the zero cross detection circuit 309, and the control unit 113 detects that the recording medium 101 is in the fixing nip portion N during the next energization control pattern from the arrival time Td and the frequency. It can be predicted whether or not there is. Further, the switching timing of the energization control pattern does not necessarily have to be between the recording medium 101 passing through the fixing nip portion N and may be between the non-printing areas of the recording medium. Considering the variation in detection of the zero cross signal of the AC power source 117 (generally ± 0.5 ms or less), the variation in the length of the fixing nip portion N, and the variation in the transport distance from the pre-fixing sensor 116 to the fixing nip portion N (several mm). The control error is ± 1 to 2 half waves in total. Therefore, this control can sufficiently satisfy the desired switching timing of the energization control pattern.

  According to the image forming apparatus of the present embodiment, in a film fixing type heat fixing apparatus using a ceramic heater as a heat source, it is possible to suppress both flicker and harmonic current distortion, and to reduce a temperature ripple. Heater power control can be provided.

  In the second embodiment of the present invention, the configuration of the image forming apparatus, the configuration of the heater, the phase control, the wave number control, the control combining the phase control and the wave number, and the like are the same as those in the first embodiment, and thus the description thereof is omitted. As the apparatus speed increases, the moving distance of the recording medium in one wave of the AC power supply (for example, 20 msec for 50 Hz) becomes several mm. For example, in the first embodiment, when one cycle of 8 half-waves control is used for the pattern 3, if the table is switched at the time of updating the energization control pattern, a table switching preceding a maximum of 8 half-waves occurs, resulting in a significant switching timing shift. Occurs. The energization control pattern may be controlled not only with 8 half waves but also with 12 half waves or 16 half waves, and this shift in the switching timing may not be negligible for optimal fixing temperature control. For example, the time of the pattern 2 between the recording media 101 becomes too short, and the harmonic current distortion generated in the pattern 1 may not be sufficiently suppressed. In addition, when the recording medium 101 reaches the fixing nip portion N, the temperature of the heater 110 changes rapidly. In particular, the temperature drop tends to increase as the printing speed of the apparatus increases. Accordingly, it is possible to perform appropriate power control by making the timing at which the recording medium 101 arrives at the fixing nip N accurate. For example, it is possible to perform heater power control in preparation for a decrease in heater temperature at a more accurate timing when the recording medium 101 reaches the fixing nip portion N.

[Heater control sequence]
Here, in addition to the first embodiment, the heater control sequence in which the accuracy of the switching timing of the heater power control table is improved using the flowchart of FIG. 6 and the timing chart of the pre-fixing sensor 116 and the heater power control table of FIG. I will explain. In this embodiment, three types of heater power control tables (table 1: phase control, table 2: wave number control, table 3: control combining phase control and wave number control) are recorded in the recording unit in the control unit 113. The control unit 113 switches between the heater power control tables.

  The control unit 113 selects an energization control pattern for starting and fixing the fixing heating device 109 from the table 3 (S1000). Table 3 has an energization control pattern that combines phase control and wave number control, which are effective for both harmonic current distortion suppression and flicker suppression, although temperature ripple is disadvantageous. Then, the energization control pattern is made up of phase control and wave number control with 8 half-waves as one control cycle, and the temperature of the fixing heating device 109 is controlled by the temperature of the heater 110 by the thermistor 203. An optimum energization control pattern is selected from Table 3. When the pre-fixing sensor 116 detects that there is paper (S1001), the control unit 113 calculates the wave number n until the recording medium 101 reaches the fixing nip N (S1002). The wave number n can be obtained by dividing the time Td from the pre-fixing sensor 116 to the fixing nip N by the frequency of the AC power supply. At this time, the control unit 113 sets the wave number count value to zero (S1002). Here, the wave number count value is monitored for each wave, and the count value is incremented by 1 for each wave (S1003). When the wave number count value is equal to the wave number n (S1004), the heater power control table is switched to the table 1 and at the same time the energization control pattern is updated (S1005 to S1007). Table 1 is a phase control table that is a control that can reduce the temperature ripple most, although it is disadvantageous to the harmonic current distortion of the fixing heating device 109. The selection of Table 1 is maintained while the recording medium 101 passes through the fixing nip N, and the wave number count value is maintained at zero (S1005, S1009). If the pre-fixing sensor 116 detects that there is no paper (S1009), the wave number n until the recording medium reaches the fixing nip N is counted (S1010). When the wave number count value becomes equal to the wave number n, the energization control pattern is updated simultaneously with switching the heater power control table to Table 2 (S1011 to S1015). Here, the table 2 is a wave number control table which is the most advantageous control for suppressing harmonic current distortion although it is disadvantageous for flicker suppression and temperature ripple. The energization control pattern by the table 2 is maintained while the next recording medium 101 arrives at the fixing nip N (S1013, S1017). When it is determined that the recording medium is the final recording medium (S1012), the control unit 113 selects the next energization control pattern from the table 3 (S1018).

  FIG. 7 shows changes in the heater applied voltage when the heater power control table is switched from table 2 to table 1. Here, an example is shown in which the pre-fixing sensor 116 determines that there is a recording medium and the recording medium reaches the fixing nip N at the 16th wave. It can be seen that the heater power control table is switched from Table 2 to Table 1 when the recording medium enters the fixing nip N, that is, when the wave number count value is 16. As described above, in addition to the effects of the first embodiment, the timing at which the recording medium reaches the fixing nip portion N can be realized with higher accuracy.

  Here, the heater power control table stored in the recording unit has been described in the present embodiment for three types as in the first embodiment, but is merely an example, and two or more types of multiple tables are stored in the recording unit. If there is, application is possible. For example, when the AC power supply voltage is a high voltage (for example, 220V to 240V), there is often a relatively margin with respect to the flicker standard. In that case, only two of the table 1 and the table 2 may be used without using the control in which the phase control and the wave number control of the table 3 are combined. Further, for example, when the AC power supply voltage is a low voltage (for example, 100 V to 127 V), there is often a relatively margin with respect to the harmonic current distortion standard. In that case, only the two of Table 1 and Table 3 may be used without using the wave number control of Table 2.

  According to the image forming apparatus of the present embodiment, in a film fixing type heat fixing apparatus using a ceramic heater as a heat source, it is possible to suppress both flicker and harmonic current distortion, and to reduce a temperature ripple. Heater power control can be provided.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 109 Fixing heating apparatus 110 Heater 113 Control part 116 Sensor before fixing

Claims (5)

Image forming means for forming a toner image on a recording medium, fixing heating means for heating and fixing the toner image to the recording medium, and conveying means for conveying the recording medium to the fixing heating means;
To the conveyance detection means for detecting the conveyance position of the recording medium, the electronic switch means for supplying power from the AC power source to the fixing heating means, the zero cross detection means for detecting the zero cross of the AC power supply, and the fixing heating means Storage means for storing a plurality of heater power control tables for power supply of
An image forming apparatus comprising: a detection result of the zero cross detection means; and a control means for controlling power supplied to the fixing heating means using any heater power control table stored in the storage means. ,
The control means determines whether or not the recording medium passes the fixing heating means based on the detection result of the conveyance detection means, and performs control for switching the heater power control table based on the result of the determination. An image forming apparatus. Image forming means for forming a toner image on a recording medium based on image information, fixing heating means for heating and fixing the toner image to the recording medium, conveying means for conveying the recording medium to the fixing heating means,
To the conveyance detection means for detecting the conveyance position of the recording medium, the electronic switch means for supplying power from the AC power source to the fixing heating means, the zero cross detection means for detecting the zero cross of the AC power supply, and the fixing heating means Storage means for storing a plurality of heater power control tables for power supply of
An image forming apparatus comprising: a detection result of the zero cross detection means; and a control means for controlling power supplied to the fixing heating means using any heater power control table stored in the storage means. ,
The control means determines a non-printing area and a printing area of the recording medium based on the image information, and whether the recording medium passes the fixing heating means based on a detection result of the conveyance detection means. Judging
The heater power control table used while the printing area of the recording medium passes through the fixing heating means is used while the recording medium does not pass through the fixing heating means, or the non-printing area of the recording medium. The image forming apparatus is characterized in that control is performed to switch to the other heater power control table while the toner passes through the fixing heating means.   The heater power control table is either a heater power control table using only phase control, a heater power control table using only wave number control, or a heater power control table using both phase control and wave number control. The image forming apparatus according to claim 1, wherein at least two types of the heater power control tables are stored in the storage unit.   The control unit controls power supplied to the fixing heating unit by a heater power control table using only wave number control while the recording medium is not passing through the fixing heating unit. Item 3. The image forming apparatus according to Item 1 or 2.   The control unit controls power supplied to the fixing heating unit by a heater power control table using only phase control while the recording medium passes through the fixing heating unit. Item 3. The image forming apparatus according to Item 1 or 2.

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