JP6628525B2 - Image forming device - Google Patents

Description

  The present invention relates to a technique for controlling a fixing device included in an image forming apparatus.

2. Description of the Related Art As an image forming apparatus, a film heating type fixing device for thermally fixing a toner image carried on a recording medium by an image forming means such as an electrophotographic process or an electrostatic recording process has been put to practical use. In such a fixing device, a recording medium (for example, paper) is brought into close contact with a heating element supported by a support member via a heat-resistant thin-walled film material, and heat of the heating element is applied to the recording medium to form a toner image. Is fixed on a recording medium.
In addition, the heating element includes a base material having a low heat capacity, for example, a ceramic base material having an insulating property and a good thermal conductivity, and a resistance heating layer provided on the surface of the base material and generating heat by energization. , A so-called ceramic heater can be used. The film material may be a thin film having a low heat capacity.

  When a ceramic heater is used as the heating element, it is not necessary to supply power to the heating element when the image forming apparatus is in a standby state. This is because the heating element can be sufficiently heated to a predetermined temperature before the sheet reaches the fixing nip even if the sheet as the material to be heated is immediately passed. Therefore, when a ceramic heater is used as the heating element, there are advantages that a waiting time can be reduced, power consumption can be reduced, and a temperature rise in the main body of the image forming apparatus can be suppressed.

  Further, the temperature control in a fixing device employing a ceramic heater as a heating element generally employs a method of controlling an energization ratio (an energization / non-energization ratio) per unit time with respect to the heating element. Specifically, a wave number control method for controlling energization / de-energization for each half-wave of a power supply waveform of a commercial AC power supply is generally known.

  For example, in the fixing device disclosed in Patent Document 1, in a wave number control of a fixing device having two or more heaters, a desired energization ratio is generated in one control unit with 20 half waves as one control unit. Then, the even-numbered energization number and the odd-numbered energization number in one control unit are set to the same value, and the positive and negative energizations of the AC input are made equal to prevent occurrence of flicker and the like. Further, assuming a case where the energization ratio is changed before the end of one control unit, the even-numbered energization number and the odd-numbered energization number in the fourth half wave are set to the same value to equalize the positive and negative energizations. Then, the energization numbers of the heaters are made substantially equal, and if they are not equal, the energization ratios of the heaters are set to be reversed by using the adjacent energization ratios. Note that these settings determine the energization of each heater with reference to a predefined table. In this manner, the symmetry of AC positive / negative energization as a measure against flicker and the equivalence of main sub energization are realized.

JP 2006-72235 A

  Main-sub energization equivalence may not always be achieved due to a “shift” at a certain energization ratio. In this case, in the fixing device disclosed in Patent Document 1, a long-term energizing ratio is balanced by reversing the magnitude of the energizing ratio of each heater using adjacent energizing ratios. However, in recent years, as the temperature control of the on-demand heating device has become more sophisticated, the control output to the heater has not always changed continuously, and there is a case where a long-term energization ratio cannot be balanced (balanced). Can occur.

  In addition, when the energization ratio is switched earlier than the end of one control unit (20 half waves), the symmetry of AC positive / negative energization is guaranteed, but it is difficult to accurately achieve a desired energization ratio. Remains. Further, the above-mentioned conventional table is optimized for the case where the main heater and the sub-heater are energized at the same energizing ratio. When an arbitrary energizing ratio is selected for each of the main heater and the sub-heater, flicker countermeasures and the like cannot be sufficiently performed. Sometimes.

  The present invention provides an image forming apparatus capable of accurately guaranteeing a long-period energization ratio with a simple configuration and improving the responsiveness of distributed energization of a plurality of heating elements and a change in energization ratio.

  An image forming apparatus according to the present invention includes an image forming unit that forms a toner image on a recording medium, a plurality of heating units that thermally fix the toner image formed on the recording medium to the recording medium, and an alternating current that is supplied to each heating unit. Control means for controlling energization / de-energization of the power supply input independently for each heating means in units of half-waves, wherein the control means comprises: Cumulative calculation is performed by adding the offset energization ratio, and when the result exceeds 1, an energization start is instructed and an operation of subtracting 1 from the cumulative operation result is performed. The method is characterized in that the polarity is reversed and set for each heating means, and the positive and negative phases are set to be reversed for at least two of the plurality of heating means.

  ADVANTAGE OF THE INVENTION According to this invention, the energization ratio of a long period can be exactly guaranteed with a simple structure, and the responsiveness of the distributed energization of a plurality of heating elements and the change of the energization ratio can be improved. Furthermore, flicker can be sufficiently prevented.

FIG. 1 is a schematic longitudinal sectional view illustrating an example of the configuration of an image forming apparatus. FIG. 2 is a schematic longitudinal sectional view illustrating an example of the configuration of a fixing unit. FIG. 2 is a diagram illustrating an example of a configuration of a fixing device including a fixing unit. 9 is a flowchart illustrating an example of a heater energization control process performed by a CPU. 9 is a flowchart illustrating an example of a power supply control process of the heating element 1 performed by the CPU. 9 is a flowchart illustrating an example of a power supply control process of the heating element 2 performed by the CPU. FIG. 7 is an example of a table defining a relationship between a set number of times and an offset energization ratio k. The figure which shows transition of the offset added to the required energization ratio of each heating element. The figure which shows the mode of energization when the value of the required energization ratio of each heating element is set to 0.1 and the heater energization control according to the present embodiment is performed. The figure which shows the mode of energization when the value of the required energization ratio of each heating element is set to 0.1 and the control of the comparative example 1 is performed. The figure which shows the mode of energization when the value of the required energization ratio of each heating element is set to 0.1 and the control of the comparative example 2 is performed. The figure which shows the energization state when the value of the required energization ratio of the heating element 1 is set to 0.4, the value of the required energization ratio of the heating element 2 is set to 0.2, and the heater energization control according to the present embodiment is performed. . The figure which shows the mode of energization when the value of the required energization ratio of the heating element 1 is set to 0.4, and the value of the required energization ratio of the heating element 2 is set to 0.2, and the control of the comparative example 1 is performed. The figure which shows the mode of energization when the value of the required energization ratio of the heating element 1 is set to 0.4, and the value of the required energization ratio of the heating element 2 is set to 0.2, and the control of the comparative example 2 is performed. (A), (b), and (c) are diagrams showing the results when FFT is performed on the waveform of the energizing current flowing through the heater 13 in which the value of the required energizing ratio of each heating element is set to 0.1. . (A), (b), and (c) show the energizing current flowing through the heater 13 in which the required energizing ratio of the heating element 1 is set to 0.4 and the energizing ratio of the heating element 2 is set to 0.2. The figure which shows the result when performing FFT with respect to a waveform.

Hereinafter, embodiments will be described with reference to the drawings. In the present embodiment, an electrophotographic printer (image forming apparatus) capable of forming a full-color image will be described as an example.

[Example of embodiment]
FIG. 1 is a schematic longitudinal sectional view illustrating an example of the configuration of the image forming apparatus according to the present embodiment.
The image forming apparatus 1 includes a scanner unit B, an image forming unit C, and a sheet deck D in each unit of the image forming apparatus 1. The image forming apparatus 1 has a scanner unit B as image reading means for reading image information of a book document at an upper part thereof, an image forming part C as an image forming means at a lower part thereof, and a sheet deck at a lower part thereof. D is provided.

  The scanner unit B reads image information of a document surface, and includes a scanning system light source 201, a platen glass 202, a document pressure plate 203 that can be opened and closed with respect to the image forming apparatus 1, a mirror 204, a lens 205, and a light receiving element (photoelectric conversion). An image processing unit (not shown).

  In the scanner section B, a book original such as book / thick paper / curled paper, a sheet original, or the like is placed on the platen glass 202 with the original surface facing down, and the back surface is pressed by the original pressing plate 203 to read the object to be read. Set. When an instruction to start reading is received, the scanning light source 201 scans the lower part of the platen glass 202 in the direction of arrow a to read image information on the document surface. Image information of a document read by the scanning light source 201 is converted into an electric signal in an image processing unit. The conversion result is transmitted to the laser scanner 111 of the image forming unit C.

  Here, the image forming apparatus 1 functions as a copier, a printer, a facsimile machine, or the like. That is, when the conversion result of the image processing unit is input to the laser scanner 111 of the image forming unit C, it functions as a copying machine. When an output signal from an external device (for example, a computer) is input, the device functions as a printer. Further, the image forming apparatus 1 functions as a facsimile apparatus when receiving a signal from another facsimile apparatus or transmitting a signal from the image processing unit to another facsimile apparatus.

  On the other hand, a sheet cassette 51 is mounted below the image forming unit C, and sheets (recording medium such as paper) stored in the cassette are transferred to the image forming unit C in synchronization with the image forming operation. Will be fed. The sheet cassette 51 includes two units, a lower cassette 51a and an upper cassette 51b, and is configured as one feeding unit. In the present embodiment, two feeding units U1 and U2 are mounted, and four cassettes are mounted. One upper feed unit U1 is detachably attached to the image forming apparatus 1, and the lower feed unit U2 is detachably attached to the sheet deck D.

The sheets accommodated in the lower cassette 51a and the upper cassette 51b are fed out by the pickup roller 53, and are separated and fed one by one by the cooperation of the feed roller 54 and the retard roller 55. Thereafter, the sheet is conveyed by conveying rollers 104 and 105, guided by a registration roller 106, and fed to the image forming section C by the registration roller 106 in synchronization with the image forming operation.
In addition, the manual feed tray 10 is arranged on the side surface of the image forming apparatus 1 separately from the sheet cassette 51 described above. The sheet placed on the manual feed tray 10 is fed out to the registration roller 106 by the manual feed roller 311.

  The image forming section C forms an image on the sheet surface, and includes a photosensitive drum 112, an image writing optical system 113, a developing device 114, a transfer charger 115, and the like. In the image forming section C, a laser beam corresponding to the image information emitted from the laser scanner 111 is scanned by the image writing optical system 113 on the surface of the photosensitive drum 112 uniformly charged by the transfer charger 115 to form a latent image. Is formed. The developing device 114 forms a toner image for the latent image. The toner image is transferred via the transfer charger 115 to the surface of the sheet conveyed in synchronization with the rotation of the photosensitive drum 112 by the registration roller 106.

  The sheet on which the toner image has been formed is conveyed via a conveying unit 117 to a fixing unit 118 serving as a fixing unit. The sheet on which the toner image is formed by the fixing unit 118 is heated and pressed. Thus, the toner image is heat-fixed to the sheet surface. The sheet on which the image has been formed is conveyed to the outside of the apparatus via the discharge roller 119, discharged to the sorter 120, and stacked.

  When forming an image on both sides of the sheet, the sheet discharged from the fixing unit 118 is held by the discharge roller 119, and the discharge roller 119 is rotated in reverse when the rear end of the sheet passes the branch point 207. Thus, the sheet is temporarily placed on the sheet double-sided tray 121. Thereafter, the sheet is conveyed again via the conveying rollers 104 and 105, reaches the registration roller 106, and the above-described image forming processing is performed on the front surface (here, the back surface) of the inverted sheet. Then, the sheet on which the image has been formed is conveyed to the outside of the apparatus via the discharge roller 119, discharged to the sorter 120, and stacked.

<Structure of fixing unit>
FIG. 2 is a schematic longitudinal sectional view illustrating an example of the configuration of the fixing unit 118.
The fixing unit 118 includes a stay 11, an endless heat-resistant film (hereinafter, referred to as a fixing film) 12, a ceramic heater 13, a thermistor 15, and a pressure roller 18. The ceramic heater 13 is pressed against the pressure roller 18 with the fixing film 12 interposed therebetween. The ceramic heater 13 and the pressure roller 18 are in contact at the nip N. The pressing roller 18 is rotated in the direction of the arrow Rot by receiving a driving force from a driving source (not shown), and drives the fixing film 12.

  The sheet (recording medium) on which the toner image is formed is heated by the ceramic heater 13 when the sheet (recording medium) is conveyed through the nip N in the direction of the arrow Paper, so that the toner image is fixed. The ceramic heater 13 is configured to be able to detect the temperature of the ceramic heater 13 via the thermistor 15. Next, the configuration of the fixing device having the fixing unit 118 will be described.

<Configuration of fixing device>
FIG. 3 is a diagram illustrating an example of a configuration of a fixing device including the fixing unit 118.
The fixing device 300 includes a fixing unit 118, a heater control unit 100 serving as current control means including a CPU (Central Processing Unit) 50 on a control board of the image forming apparatus 1, and an AC driver 6 connected to a commercial power supply. It consists of.

The fixing unit 118 functioning as a fixing unit includes a ceramic heater 13 having heating elements 1 and 2 as a plurality of heating units, and a thermistor (M_TH) 15 for detecting the temperature of the ceramic heater 13 as temperature information.
The fixing unit 118 has a sub thermistor (S_TH) 17 that detects a rise in temperature of the end of the ceramic heater 13. In addition, a thermoswitch (TH_SW) 16 for forcibly shutting off the input of an AC power supply supplied to the ceramic heater 13 when an abnormal temperature rise occurs due to a failure such as a triac described later.

The heater control unit 100 includes a CPU 50, a triac A control circuit 3, a triac B control circuit 4, and a relay control circuit 5 arranged on a control board.
The AC driver 6 includes a triac A7 and a triac B8, which are switching elements, and a zero-cross detection unit 19. The AC driver 6 also has a relay 9 for cutting off the power supply to the ceramic heater 13 from the commercial power supply AC side from the viewpoint of safety.

The CPU 50 of the heater control unit 100 controls the triac A control circuit 3 and the triac B control circuit 4 based on the temperature information detected by the thermistor 15 and the sub thermistor 17.
The CPU 50 also controls the timing of turning on the triac A7 and the triac B8 via the triac A control circuit 3 and the triac B control circuit 4. In this way, the CPU 50 individually controls the alternating current flowing through the two heating elements 1 and 2 on the ceramic heater 13.

  The heating element 1 and the heating element 2 of the fixing unit 118 are electrically connected in parallel. In addition, the amount of electricity to the heating elements 1 and 2 is controlled via a triac A7 and a triac B8. Note that the resistance value ratio between the heating element 1 and the heating element 2 is approximately 1: 1 at the center in the longitudinal direction, and a difference is generated between the heating elements 1 and 2 at the end. Is done.

  The zero-cross detection unit 19 detects a zero-cross detection range set in a range of several volts above and below the zero-cross point of the power supply voltage. Specifically, the zero-cross detection unit 19 outputs a zero-cross detection signal ZC according to the set zero-cross detection range. Note that the zero-cross point is a point (a point where the amplitude becomes zero) where the AC waveform and the power supply voltage 0 [V] intersect in the graph representing the AC waveform.

  The CPU 50 calculates the amount of power to the heating elements 1 and 2 based on the temperature information detected by the thermistor 15. The CPU 50 generates heater control signals HA and HB for performing wave number control based on the calculated energization amount and the zero cross signal ZC. The CPU 50 outputs the generated heater control signal HA to the triac A7 via the triac A control circuit 3, and outputs the heater control signal HB to the triac B8 via the triac B control circuit 4. In this way, the on / off states of the triacs A7 and B8 are controlled based on the heater control signals HA and HB, respectively.

  That is, the heating elements 1 and 2 are controlled so that current flows through the triacs A7 and B8 triggered by the “high” level heater control signals HA and HB generated and output by the CPU 50. The CPU 50 controls the triac A7 via the heater control signal HA to control the current supplied to the heating element 1, and the heater control signal HB controls the triac B8 to control the current supplied to the heating element 2. . The current supplied to the ceramic heater 13 is obtained by adding the current supplied to the heating element 1 and the current supplied to the heating element 2.

Note that, in the fixing device 300 of the present embodiment, the heating elements 1 and 2 have substantially the same resistance value. In this case, as compared with the case where only one of the heating elements is energized, the power consumption is substantially doubled when the two heating elements are energized, and the temperature of the entire ceramic heater 13 can be increased at a high speed.
Hereinafter, a processing procedure of the heater energization control for controlling the temperature of the ceramic heater 13 performed by the CPU 50 will be described with reference to FIGS. 4 to 7.

<Heater energization control processing>
FIG. 4 is a flowchart illustrating an example of the heater energization control process performed by the CPU 50. FIG. 5 is a flowchart illustrating an example of a power supply control process of the heating element 1 performed by the CPU 50. FIG. 6 is a flowchart illustrating an example of a power supply control process of the heating element 2 performed by the CPU 50. FIG. 7 shows an example of a table defining the relationship between the set number of times and the offset energization ratio k.
First, the overall flow of the heater energization control process performed by the CPU 50 will be described with reference to FIG.

  The CPU 50 starts the heater energization control process when the power of the image forming apparatus 1 is turned on. The CPU 50 sets the value of the four-cycle wave number control counter n for counting the number of times of input of the zero cross signal ZC to n = 1 (S401). The CPU 50 determines whether or not the zero cross signal ZC has been input (S402).

  When the zero cross signal ZC is input (S402: Yes), the CPU 50 determines whether or not the current value of the wave number control counter n is n = 1 (S403). When the value of the wave number control counter n is n = 1 (S403: Yes), the CPU 50 sets an offset energization ratio k to be used in energization control of the heating element described later (S404). Otherwise (S403: No), the process proceeds to step S405. If the value of the wave number control counter n is not n = 1, the previous value is used as it is in the power supply control of the heating element without updating the offset power supply ratio. Hereinafter, the offset energization ratio k will be described with reference to FIG.

  The table shown in FIG. 7 is a table in which the set value k is determined according to the set number of times. The CPU 50 sets the value of the offset energization ratio k based on the set value k corresponding to the set number of times. The set number is counted via a counter (not shown). In addition, the CPU 50 refers to the corresponding set value k from the first to fifteenth set times, and refers to the set value k in the fifteenth cycle so that the set number of times is returned to the first time in the table after the sixteenth time.

Returning to the description of FIG. 4, the CPU 50 controls the energization of the heating element 1 (S405). The CPU 50 controls the energization of the heating element 2 (S406). The details of the energization control of the heating elements 1 and 2 will be described later.
After independently controlling the energization of the heating elements 1 and 2 individually, the CPU 50 determines whether the value of the wave number control counter n is 4 (S407). When n is not 4 (S407: No), the CPU 50 adds 1 to the value of the wave number control counter n (S408). Otherwise (S407: Yes), the value of the wave number control counter n is set to n = 1 (S409). The CPU 50 determines whether or not the end of the energization control has been instructed (S410). For example, when the energization control is continued such as when the image forming process is continued (S410: No), the process returns to step S402. Otherwise (S410: Yes), the series of processing ends.
Next, details of the energization control process (S405) of the heating element 1 will be described with reference to FIG.

The CPU 50 determines whether or not the value of the wave number control counter n is n = 1 (S501). When n = 1 (S501: Yes), the required energization ratio of the heating element 1 is determined (S502).
The required energization ratio of the heating element 1 is determined, for example, as described below. The difference between the current temperature of the ceramic heater 13 detected through the thermistor 15 and the target temperature is calculated, and the accumulated difference is multiplied by a control gain. The required energization ratio is determined based on this result and the output result of the sub thermistor 17 that detects the end-portion temperature rise. The required energization ratio is expressed as an energization ratio when the full energization request is set to 1.

The CPU 50 adds the value of the offset energization ratio k set in the process of step S404 to the determined value of the required energization ratio (S503). The addition result (summation result) in the process of step S503 is cumulatively calculated, and the cumulative calculation result is readablely stored in a storage unit (not shown) as a cumulative required ratio.
The CPU 50 adds the sum to the latest cumulative request ratio (S504). The CPU 50 determines whether or not the value of the cumulative request ratio after the processing in step S504 is 1 or more (S505). When the value of the cumulative request ratio is 1 or more (S505: Yes), the CPU 50 outputs a signal indicating an energization instruction ON (ON: energization) for instructing a start of energization (S506). The CPU 50 subtracts 1 from the value of the cumulative request ratio (S507). The CPU 50 performs one half-wave energization of the heating element 1 via the triac A control circuit 3 which has received the energization instruction ON signal (S508). Thus, the AC power input is supplied to the heating element 1.

  When the value of the wave number control counter n is not n = 1 (S501: No), the CPU 50 determines whether or not n = 3 (S509). If n = 3 (S509: Yes), the value of the offset energization ratio k is subtracted from the value of the cumulative required ratio (S510). In this case, the result of subtracting the value of the offset energization ratio k from the value of the cumulative request ratio is the latest cumulative request ratio in the process of step S504. If the value of the wave number control counter n is not n = 3 (S509: No), that is, if the value of the wave number control counter n is n = 2 or n = 4, the process proceeds to step S511.

The CPU 50 determines whether or not the energization instruction is ON (S511). When the energization instruction is ON (S511: Yes), the CPU 50 energizes the heating element 1 for one half-wave via the triac A control circuit 3 (S512). Thereafter, the CPU 50 outputs a signal indicating the energization instruction OFF (OFF: non-energization) (S513).
Next, the details of the energization control process (S406) of the heating element 2 will be described with reference to FIG.

The CPU 50 determines whether or not the value of the wave number control counter n is n = 1 (S601). If n = 1 (S601: Yes), the required energization ratio of the heating element 2 is determined (S602).
The required energization ratio of the heating element 2 is determined, for example, as described below. The difference between the current temperature of the ceramic heater 13 detected through the thermistor 15 and the target temperature is calculated, and the accumulated difference is multiplied by a control gain. In the required energization ratio of the heating element 1, the required energization ratio is determined based on this result and the output result of the sub thermistor 17 that detects the end portion temperature rise. On the other hand, the required energization ratio of the heating element 2 is set so that the influence on the required energization ratio based on the detection result of the sub thermistor 17 acts relatively in the opposite direction to the heating element 1. By doing so, it is possible to provide a difference between the required energization ratios of the heating elements 1 and 2 having different resistance ratios at the ends according to the temperature rise at the ends, so that the temperature rise at the ends can be reduced. .

The CPU 50 subtracts the value of the offset power supply ratio k set in the process of step S404 from the value of the determined required power supply ratio (S603).
The CPU 50 adds the total value to the latest cumulative request ratio (S604). The CPU 50 determines whether or not the value of the cumulative request ratio after the processing of Step S604 is 1 or more (S605). When the value of the cumulative request ratio is 1 or more (S605: Yes), the CPU 50 outputs a signal indicating the energization instruction ON (S606). The CPU 50 subtracts 1 from the value of the cumulative request ratio (S607). The CPU 50 performs one-half-wave energization of the heating element 1 via the triac A control circuit 3 that has received the energization instruction ON signal (S608).

  When the value of the wave number control counter n is not n = 1 (S601: No), the CPU 50 determines whether or not n = 3 (S609). When n = 3 (S609: Yes), the value of the offset energization ratio k is added from the value of the cumulative request ratio (S610). In this case, the result of subtracting the value of the offset energization ratio k from the value of the cumulative request ratio is the latest cumulative request ratio in the process of step S604. If the value of the wave number control counter n is not n = 3 (S609: No), that is, if the value of the wave number control counter n is n = 2 or n = 4, the process proceeds to step S611.

  The CPU 50 determines whether or not the energization instruction is ON (S611). If the energization instruction is ON (S611: Yes), the CPU 50 performs one half-wave energization of the heating element 1 via the triac A control circuit 3 (S612). Thereafter, the CPU 50 outputs a signal indicating the power supply instruction OFF (S613).

  Thus, the energization control process of the heating elements 1 and 2 is performed. FIG. 8 shows the transition of the offset added to the required energization ratio of each heating element. In FIG. 8, the vertical axis represents the value of the addition offset, and the horizontal axis represents time.

  Here, the effect of the heater energization control according to the present embodiment will be described in comparison with a comparative example. In the control of Comparative Example 1, the value of the offset energization ratio k set in the process of step S404 is set to 0.5, and this value is not updated. In the control of the comparative example 2, the value of the offset energization ratio k set in the process of step S404 is set to 0, and this value is not updated. That is, when compared with the heater energization control according to the present embodiment, the difference is that the offset energization ratio is not used in the control of Comparative Examples 1 and 2.

  FIG. 9 is a diagram illustrating a state of energization when the required energization ratio of each of the heating elements 1 and 2 is set to 0.1 and the heater energization control according to the present embodiment is performed. FIG. 10 is a diagram illustrating a state of energization when the control of Comparative Example 1 is performed by setting the required energization ratio of each of the heating elements 1 and 2 to 0.1. FIG. 11 is a diagram illustrating a state of energization when the control of Comparative Example 2 is performed with the value of the required energization ratio of each of the heating elements 1 and 2 set to 0.1. In the graphs shown in the figures, the vertical axis represents the energization ratio, and the horizontal axis represents time.

  FIG. 12 shows a case where the value of the required energization ratio of the heating element 1 is set to 0.4 and the value of the required energization ratio of the heating element 2 is set to 0.2 to perform the heater energization control according to the present embodiment. It is a figure showing a situation of energization. FIG. 13 shows the state of energization when the control of Comparative Example 1 is performed with the required energization ratio value of the heating element 1 set to 0.4 and the required energization ratio value of the heating element 2 set to 0.2. FIG. FIG. 14 shows a state of energization when the control of Comparative Example 2 is performed by setting the value of the required energization ratio of the heating element 1 to 0.4 and the value of the required energization ratio of the heating element 2 to 0.2. FIG. In the graphs shown in the figures, the vertical axis represents the energization ratio, and the horizontal axis represents time.

  FIG. 15 shows the result when FFT (Fast Fourier Transform) is performed on the waveform of the energizing current flowing through the heater 13 in which the required energizing ratio of each of the heating elements 1 and 2 is set to 0.1. FIG. FIG. 15A shows the heater energization control according to the present embodiment, FIG. 15B shows the case of Comparative Example 1, and FIG. 15C shows the case of Comparative Example 2. FIG. 16 shows a case where the FFT is performed on the waveform of the energizing current flowing through the heater 13 in which the required energizing ratio of the heating element 1 is set to 0.4 and the required energizing ratio of the heating element 2 is set to 0.2. It is a figure showing the result of. FIG. 16A shows the case of the heater energization control according to the present embodiment, FIG. 16B shows the case of Comparative Example 1, and FIG. 16C shows the case of Comparative Example 2. In the graphs shown in FIGS. 15 and 16, the vertical axis represents FFT results, and the horizontal axis represents frequency [Hz].

  From FIGS. 9 to 14, it can be seen that, in comparison with Comparative Example 2, in Examples and Comparative Example 1, alternating energization of the heating elements 1 and 2 is realized at various required energization ratios. 15 and FIG. 16, it can be seen that the current-carrying current amplitude in the vicinity of 10 [Hz] where the flicker is more likely to occur in the example, especially in the low current-carrying ratio, than in Comparative Examples 1 and 2, is small.

  As described above, the fixing device 300 of the image forming apparatus 1 according to the present embodiment can accurately guarantee a long-period energization ratio with a simple configuration, and realizes improved responsiveness of distributed energization of a plurality of heating elements and change in energization ratio. In addition, flicker countermeasures can be taken.

In the heater energization control process according to the present embodiment, the energization pattern of the heating element is not determined by a table, but the required energization ratio is accumulated and stored in the storage means, and the control is performed based on the accumulation ratio. Therefore, it is possible to balance the long-period energization ratio including a small fraction, and it is possible to immediately respond to a sudden change in the energization ratio.
Also, energization / de-energization is controlled independently for each heating element 1 and 2 in half-wave units. Specifically, when the value of the wave number control counter n is n = 1 and n = 3, it is determined whether one half-wave energization is possible. In addition, when the value of the wave number control counter n is n = 2 and n = 4, by taking over the case of n = 1 and n = 3, the AC positive / negative energization object can be secured, and the flicker due to the imbalance of the positive / negative phase can be ensured. Occurrence can be prevented.

For the heating element 1, the offset energizing ratio is added when the value of the wave number control counter n is 1 (S503), and is subtracted when the value of the number control counter n is 3 (S510). Therefore, the accumulated demand value tends to be 1 or more on the n = 1 side, and the energization instruction can be easily given on the n = 1 side. On the other hand, for the heating element 2, the addition and subtraction of the heating element 1 are reversed (S603, S610), so that the energization instruction can be easily given on the n = 3 side.
In the heater energization control process according to this embodiment, the offset energization ratio is controlled so that the first value and the second value that are different every quarter wave are mixed, and the heating element 1 and the heating element Between the two, a tendency of alternate energization can be provided. Thereby, even if the heating element 1 and the heating element 2 are independently controlled, the energization timing can be leveled (balanced). That is, regardless of the combination of the energization ratios, flicker caused by unevenness of the energization current of the heater 13 can be reduced.

  In addition, flicker is likely to be affected by fluctuations in the energizing current around 10 Hz. In the heater energization control process according to the present embodiment, a case is provided in which the offset energization ratio k is changed for each set number of times in the process of step S404 in FIG. As a result, even when the required energization ratio is set such that a fluctuation of 10 [Hz] is likely to occur, the ON / OFF frequency of energization to the heater can be varied. Therefore, the frequency around 10 [Hz] can be reduced.

  The embodiments described above are for describing the present invention more specifically, and the scope of the present invention is not limited to these examples.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Heating element, 3, 4 ... Triac control circuit, 7, 8 ... Triac, 12 ... Fixing film, 13 ... Ceramic heater, 15 ... · Thermistor, 17 ··· Sub thermistor, ·································································································································································································· ·· ..Fixing devices.

Claims (5)

Image forming means for forming a toner image on a recording medium;
A plurality of heating means for thermally fixing the toner image formed on the recording medium to the recording medium;
Control means for independently controlling energization / de-energization of an AC power supply input supplied to each heat generation means for each heat generation means in half-wave units,
The control means performs a cumulative operation by adding the required power supply ratio and the offset power supply ratio for setting the full power supply to 1 for every two half-waves. An operation of subtracting 1 from the operation result is performed, and the offset energization ratio is set for each heating means by reversing the sign every two half-waves, and the positive and negative phases are set to be reversed for at least two of the plurality of heating means. Characterized by the fact that
Image forming device. The control unit has a storage unit for storing a result of performing the accumulation operation,
The control means stores a result obtained by performing an operation of subtracting 1 from the cumulative operation result in the storage means and updates the cumulative operation result.
The image forming apparatus according to claim 1. The control means is characterized in that the value of the offset energization ratio is controlled to be in a state in which a first value and a second value that are different for every four half waves are mixed.
The image forming apparatus according to claim 1. First detecting means for detecting the temperature of the heat generating means;
And a second detecting means for detecting an end temperature rise of the heat generating means. The control means determines the required energization ratio based on a detection result of the first and second detecting means. Features,
The image forming apparatus according to claim 1. The control unit determines the offset energization ratio by referring to a table in which a set number indicating the number of times to set the offset energization ratio and a set value of the offset energization ratio corresponding to the set number are defined. And
The image forming apparatus according to claim 1.