JP2018151518A - Image forming apparatus and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can effectively reduce harmonic current distortion.SOLUTION: An image forming apparatus comprises: fixing means that heats a sheet on which a developer image is formed to fix the developer image to the sheet; and control means that controls the fixing means through phase control to an AC power supply and controls the fixing means by changing the phase control to wave number control according to the state of harmonic current distortion.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer device, a facsimile machine, and a multifunction machine, and more particularly, to a fixing unit control method for fixing an image on a sheet.

  The image forming apparatus forms an unfixed toner image on a sheet (recording medium) such as recording paper or an OHP sheet, and then fixes the toner image on the sheet to obtain a fixed image. As a fixing unit for fixing a toner image on a sheet, a heat roller type using a halogen heater as a heat source or a film fixing type using a ceramic heater as a heat source is used. A fixing portion of a film fixing system that heats a film having a very small heat capacity from the inside has high energy efficiency and a high temperature increase rate. For this reason, it is sufficient to heat only at the time of printing, and there is an advantage that the time from the power-on to the printing ready state is short and the power consumption during standby is small.

  In general, the heater of the fixing unit is connected to an AC power source via a switching element such as a triac, and power is supplied by the AC power source. The fixing unit is provided with a temperature detection element such as a thermistor. The controller turns on / off the power supply to the heater by turning on / off the switching element based on the temperature detected by the temperature detecting element, thereby controlling the temperature of the fixing unit to be the target temperature. To do. On / off control of the ceramic heater is performed by phase control, wave number control, or a combination of phase control and wave number control. 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 the heater is turned on / off in units of half wave 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 unit. 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 a phenomenon such as flickering lighting equipment. In the phase control, since the heater is turned on at an arbitrary phase angle of one half wave of the AC power supply, the control cycle is small and the occurrence of flicker can be suppressed. In addition, since the control cycle is small, there is an advantage that the temperature control response of the fixing unit is fast and the temperature ripple of the fixing unit can be reduced. On the other hand, since the phase control is energized 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, malfunctions between electronic devices due to the harmonic current distortion or distortion of the AC power supply voltage waveform may occur.

  The reason for selecting wave number control is suppression of harmonic current distortion. Since the wave number control controls the heater on / off near 0V (zero cross point) of the power supply voltage, there is less sudden current fluctuation, and harmonic current distortion than the phase control that turns on the heater in the middle of the half wave of the AC power supply. Is unlikely to occur. However, although effective in suppressing harmonic current distortion, since the load current fluctuation for each half wave is large, 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, for example, the heater control method is fixed to either one according to the AC power supply voltage in a region 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, as the heater power of the fixing unit increases due to the recent increase in the speed of image forming apparatuses, the harmonic current distortion regulation may not be satisfied only by phase control, and the flicker regulation may not 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.

  In order to further suppress the temperature ripple during printing as described in Patent Document 1, phase control is performed during the printing operation, and wave number control is performed while the printing operation is not performed. Ripple and harmonic current distortion can be suppressed.

JP 2012-88443 A

  However, in the configuration described in Patent Document 1, if the printing operation time is long, the phase control is continued, so that harmonic current distortion may increase.

  The present invention provides an image forming apparatus and a control method capable of effectively suppressing harmonic current distortion.

  According to one aspect of the present invention, an image forming apparatus includes: a fixing unit that heats a sheet on which a developer image is formed to fix the developer image on the sheet; and a phase control of the fixing unit with respect to an AC power source. And control means for switching and controlling the phase control to wave number control according to the state of harmonic current distortion.

  According to the present invention, harmonic current distortion can be effectively suppressed.

1 is a configuration diagram of an image forming apparatus according to an embodiment. The figure which shows the control structure of the fixing part by one Embodiment. Explanatory drawing of a starting current ratio. The figure which shows the relationship between electric power duty and a starting current ratio. 6 is a flowchart of temperature control of a fixing unit according to an embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

  FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus according to the present embodiment. The image forming apparatus includes a main body 100 of the image forming apparatus and an image reading apparatus 200 provided on the upper portion of the main body 100. In the main body 100, a sheet feeding unit 10, an image forming unit 20, a fixing unit 30, and a sheet discharging unit 40 are provided in order from the lower side to the upper side in FIG. A sheet refeeding unit 50 is provided on the right side of the image forming unit 20 and the fixing unit 30.

  The sheet feeding unit 10 feeds the sheets P stacked on the feeding cassette 11 and the manual feed tray 16 to the image forming unit 20. The sheet detection sensor S <b> 1 is a sensor that detects whether or not the sheet P is stored in the feeding cassette 11. The sheet P stored in the feeding cassette 11 is fed to the separation roller pair 13 as the pickup roller 12 rotates. When the sheet P is being double-fed, the sheet P is separated into one sheet by the separation roller pair 13 composed of a normal rotation roller and a reverse roller, and is conveyed to a feeding path PS1 indicated by a solid line. The sheet P conveyed to the feeding path PS1 is further conveyed by the feeding roller pair 14, and the skew of the sheet P is corrected by the registration roller pair 15.

  The pre-registration sensor S <b> 2 detects the timing at which the leading edge of the sheet P reaches the nip of the registration roller pair 15. When the sheet P is fed from the manual feed tray 16, the sheet P is separated into one sheet by the supply roller 17 and the separation pad 18 and pulled into the apparatus. Then, the sheet P is conveyed toward the feeding roller pair 14 by the supply roller pair 19, and the skew is corrected by the registration roller pair 15. The sheet P whose skew has been corrected is conveyed to the image forming unit 20 by the registration roller pair 15 at a predetermined timing.

  The surface of the photosensitive drum 21 of the image forming unit 20 is charged to a uniform potential by the charging roller 22. The laser unit 23 irradiates the photosensitive drum 21 with laser light corresponding to the image information. Note that the image information is information read by the image reading apparatus 200 or information input to the image forming apparatus via a network or a communication line. The portion of the photosensitive drum 21 irradiated with the laser light is removed by the irradiation of the laser light, whereby an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 21. The developing roller 24 attaches toner (developer) to the electrostatic latent image and visualizes it as a toner image (developer image). The transfer roller 25 outputs a transfer bias, and transfers the developer image on the photosensitive drum 21 to the sheet P at the nip portion N1. As a result, an unfixed toner image is formed on the sheet P.

  The sheet P on which the toner image is formed is conveyed to the fixing unit 30. The fixing unit 30 includes a fixing roller 31 and a pressure roller 32 that contacts the fixing roller 31 and presses the fixing roller 31 with a predetermined pressure. The fixing roller 31 and the pressure roller 32 form a fixing nip portion N2. doing. The fixing roller 31 is configured by an aluminum roller or the like that is heated by a heat source such as a halogen lamp disposed inside. The sheet P on which the toner image is formed is sent to the fixing nip portion N2 and is heated and pressed in the process of being nipped and conveyed by the fixing roller 31 and the pressure roller 32, whereby the toner image is fixed on the sheet P. Is done.

  The fixing sensor S3 detects that the leading edge or the trailing edge of the sheet P has passed through the fixing nip portion N2. As the fixing unit 30, an on-demand fixing method can be used instead of the heating roller method in which the fixing roller 31 heats. In the on-demand fixing method, a fixing nip portion N2 is formed by pressurizing a heat source such as a ceramic heater through an endless film with a pressure roller 32. When an image is formed only on one side of the sheet P, the sheet P on which the toner image is fixed is conveyed to the sheet discharge unit 40 and discharged to the discharge tray 42 by the discharge roller pair 41. On the other hand, when images are formed on both sides of the sheet P, the sheet P is sent to the double-sided conveyance path PS2 by the reverse rotation of the discharge roller pair 41, image formation is performed on the other side, and then to the discharge tray 42. Discharged.

  FIG. 2 shows a control configuration of the fixing unit 30 and power supply to the fixing unit 30. The fixing unit 30 includes a heating element 118 and a heating element 119, and a thermistor 120 that detects the temperature of the heating element (fixing temperature). The main power supply unit 112 applies an alternating voltage input from an alternating current (AC) power supply 111 to the heating elements 118 and 119 via triacs (TRIAC) 116 and 117. More specifically, the TRIACs 116 and 117 function as switching units. When the TRIACs 116 and 117 are in the on state, an alternating voltage is applied to the heating elements 118 and 119, and when they are off, the alternating voltage is applied to the heating elements 118 and 119. Stop. The rectifier circuit 124 and the DC-DC converter (DDC) 124 generate a predetermined DC voltage for operating the CPU 121 of the control board 113 from the AC voltage output from the AC power supply 111 and supply the generated DC voltage to the CPU 121. The thermistor 120 detects the temperature of the fixing unit 30 and notifies the CPU 121 of the detected temperature. The CPU 121 performs on / off control of the TRIACs 116 and 117 based on the notified temperature, and thereby controls the heat generation of the heating elements 118 and 119 so that the temperature of the fixing unit 30 becomes the target temperature. The CPU 121 selectively uses phase control and wave number control as temperature control of the fixing unit 30. In the phase control, the CPU 121 drives the TRIACs 116 and 117 from the off state to the on state at an arbitrary timing within the half cycle with the half cycle of the AC voltage from the AC power supply 111 as the minimum control unit. In the wave number control, the CPU 121 changes the state of the TRIACs 116 and 117 at the zero-cross point of the AC voltage, with a period that is an integral multiple of a half cycle of the AC voltage from the AC power supply 111 as the minimum control unit. The zero cross detection circuit 115 notifies the CPU 121 of the timing when the AC voltage from the AC power supply 111 becomes zero. This timing is used to determine the timing when the CPU 121 turns the TRIACs 116 and 117 on and off. The control board 113 is provided with a memory 122 for storing a control program executed by the CPU 121 and data used by the CPU 121 for control.

  In the present embodiment, the CPU 121 switches between phase control and wave number control based on the accumulated value of the “rising current ratio” in the past predetermined period. First, the “rising current ratio” will be described with reference to FIG. The solid line in FIG. 3 shows a current waveform when the TRIACs 116 and 117 are switched from the off state to the on state in the phase control. In this embodiment, the amount of current fluctuation when the TRIACs 116 and 117 are changed from the off state to the on state is referred to as a “rising current value” as shown in FIG. In the present embodiment, the “rising current ratio” is the ratio of the “rising current value” to the maximum value of the “rising current value”. In other words, it is the ratio of the current fluctuation amount to the maximum current fluctuation amount when the TRIACs 116 and 117 are changed from the OFF state to the ON state. In FIG. 3, since the energization is performed at the timing at which the alternating current becomes maximum, the startup current ratio is “1”. In the present embodiment, the relationship between the power duty and the rising current ratio shown in FIG. 4 is stored in the memory 122 in advance. The power duty is the ratio of power supplied to the heating elements 118 and 119 with respect to half-wave power. For example, as shown in FIG. 3, when the alternating current is maximized, 50% of the half-wave power is supplied to the heating elements 118 and 119. Therefore, as shown in FIG. The start-up current ratio when the value is 50% is "1".

  According to experiments by the applicant, it has been found that the harmonic distortion is correlated with the cumulative value of the startup current ratio. Therefore, in this embodiment, the upper limit value of the cumulative value of the startup current ratio in the past predetermined period is experimentally obtained in advance. For example, the phase control with the power duty 50% at which the startup current ratio is maximum is performed only for the first time, and then the phase control with the power duty 100% at which the startup current ratio is minimum is performed for the second time repeatedly. . Then, by measuring the harmonic distortion while changing each of the first time and the second time, a combination of the first time and the second time that satisfies the target value (regulation value) of the harmonic distortion is obtained. For example, a combination in which the sum of the first time and the second time is as large as possible is selected from the obtained combinations, and the sum of the selected combinations can be set as a predetermined past period. Further, the cumulative value of the startup current ratio in the selected combination can be set as the upper limit value. For example, when the AC power source is 50 Hz and the first time and the second time in the selected combination are 500 ms, the past predetermined period is 1 second. Further, since the first time corresponds to the time of 50 half waves, the upper limit value of the cumulative value is 50. In the present embodiment, the upper limit value of the cumulative value is a first threshold value that switches from phase control to wave number control. On the other hand, in the present embodiment, the second threshold value for determining whether the wave number control can be switched to the phase control is set to a value smaller than the first threshold, for example, 40. Hereinafter, this second threshold value is referred to as a lower limit value.

  FIG. 5 is a flowchart of temperature control of the fixing unit 30 according to the present embodiment. In S10, the CPU 121 starts wave number control, and in S11, determines whether to continue temperature control. When the temperature control is not continued (No in S11), the CPU 121 ends the process. On the other hand, when the temperature control is continued (Yes in S11), the CPU 121 determines whether the difference between the detected temperature of the fixing unit 30 and the target temperature is equal to or greater than a threshold value. If the difference between the detected temperature and the target temperature is equal to or greater than the threshold (Yes in S12), the CPU 121 starts phase control in S13. If the difference between the detected temperature and the target temperature is less than the threshold value (No in S12), the CPU 121 determines whether the sheet is passing through the fixing unit 30 in S18. If the sheet is not passing through the fixing unit 30 (No in S18), the CPU 121 repeats the process from S10. That is, the CPU 121 continues wave number control. On the other hand, if the sheet is passing through the fixing unit 30 (Yes in S18), the CPU 121 starts phase control in S13.

  When phase control is started in S13, the CPU 121 determines the state of harmonic distortion by calculating the cumulative value of the startup current ratio in the past predetermined period. For example, as described above, if the past predetermined period is 1 second, the CPU 121 calculates the cumulative value of the startup current ratio from the present to the past 1 second. In step S14, the CPU 121 determines whether the accumulated value is equal to or less than the upper limit value obtained in advance. If the cumulative value is equal to or less than the upper limit value as a result of the determination (Yes in S14), the CPU 121 determines whether or not the sheet is passing through the fixing unit 30 in S19. That is, it is determined whether or not the toner image fixing process on the sheet is being performed. If the sheet is passing through the fixing unit 30 (Yes in S19), the CPU 121 repeats the process from S14. On the other hand, if the sheet is not passing through the fixing unit 30 (No in S19), the CPU 121 determines whether or not to continue the temperature control in S15. If the accumulated value exceeds the upper limit value in S14 (No in S14), the CPU 121 determines whether to continue the temperature control in S15. CPU121 complete | finishes a process, when not continuing temperature control (it is No at S15). On the other hand, when temperature control is continued (Yes in S15), the CPU 121 starts wave number control in S16.

  When temperature control needs to be continued, switching to wave number control when the accumulated value exceeds an upper limit value, which is a predetermined value, is to suppress harmonic distortion within a target value. On the other hand, if the sheet is not passing through the fixing unit 30 even if the accumulated value is less than or equal to the upper limit value, the switching to the wave number control is low even if the phase control is not performed, and the temperature ripple of the fixing unit 30 is low and the wave number control is sufficient. Because there is. When the wave number control is started, the CPU 121 determines whether or not the accumulated value is equal to or less than the lower limit value obtained in advance in S17. In S17, since the wave number control is switched, the cumulative value of the startup current ratio in the past predetermined period decreases. When the decreasing cumulative value is larger than the lower limit value (No in S17), the CPU 121 repeats the process from S16. On the other hand, when the accumulated value is equal to or less than the predetermined value, that is, equal to or less than the lower limit value (Yes in S17), the process is repeated from S11. Therefore, after that, the fixing unit 30 starts the sheet fixing process, or when the difference between the detected temperature of the fixing unit 30 and the target temperature becomes equal to or greater than the threshold value, the phase control is switched.

  As described above, in the present embodiment, the state of the harmonic distortion is determined, and while the state of the harmonic distortion is suppressed within the target value, the temperature of the fixing unit is controlled by the phase control, and the harmonic distortion is equal to or higher than the target value. In this case, the temperature of the fixing unit is controlled by switching to wave number control. With this configuration, it is possible to effectively suppress harmonic distortion when phase control continues.

  In this embodiment, the rising current ratio is an evaluation value for determining the state of harmonic distortion. However, it is also possible to use not the rising current ratio but the rising current value, in other words, the amount of current fluctuation when the TRIACs 116 and 117 are switched from the off state to the on state. Furthermore, without using a condition with a predetermined period in the past, start the calculation of the startup current ratio and the cumulative value of the startup current value each time phase control is started, and switch to wave number control when the upper limit is exceeded You can also. In this case, after switching to wave number control, it can be set as the structure which prohibits returning to phase control until predetermined time passes. The predetermined time is experimentally obtained in advance and stored in the memory 122.

  Furthermore, the rising current ratio and rising current value are not used as evaluation values for determining the state of harmonic distortion, and the upper limit of time during which phase control can be performed continuously while suppressing harmonic distortion within the target value. Can be experimentally determined in advance, and the phase control can be switched to the wave number control when the phase control time exceeds the upper limit value. In this case, after switching to wave number control, it can be configured to return to phase control when the period of wave number control reaches a predetermined time or longer. The predetermined time until returning to phase control is experimentally obtained in advance and stored in the memory 122.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  20: Image forming unit, 30: Fixing unit, 120: Thermistor, 116, 117: Triac, 121: CPU

Claims (11)

Fixing means for fixing the developer image on the sheet by heating the sheet on which the developer image is formed;
The image forming apparatus includes: a control unit configured to control the fixing unit with respect to an AC power source by phase control and switch the phase control to wave number control according to a state of harmonic current distortion. apparatus. A determination means for determining a state of harmonic current distortion based on a period of the phase control performed by the control means;
The control unit switches the phase control to the wave number control when it is determined that the state of the harmonic current distortion exceeds a target value as a result of the determination by the determination unit. The image forming apparatus according to 1.   The image forming apparatus according to claim 2, wherein the determination unit determines that the harmonic current distortion increases as a period of the phase control performed by the control unit is longer.   4. The control unit according to claim 1, wherein after the phase control is switched to the wave number control, the control unit returns to the phase control when a period of the wave number control reaches a predetermined time or more. 5. Image forming apparatus. A determination means for determining a state of the harmonic current distortion based on a power duty of the phase control period performed by the control means;
The control unit switches the phase control to the wave number control when it is determined that the state of the harmonic current distortion exceeds a target value as a result of the determination by the determination unit. The image forming apparatus according to 1.   The said determination means determines that the state of the said harmonic current distortion has exceeded the target value, when the accumulated value of the evaluation value according to electric power duty exceeds a predetermined value. Image forming apparatus.   7. The image forming apparatus according to claim 5, wherein after the phase control is switched to the wave number control, the control unit returns to the phase control when a period of the wave number control reaches a predetermined time or more. 8.   6. The determination unit according to claim 5, wherein the harmonic current distortion is determined to exceed a target value when an accumulated value of an evaluation value according to a power duty for a predetermined period exceeds a predetermined value. The image forming apparatus described.   9. The control unit according to claim 8, wherein after the phase control is switched to the wave number control, the control unit returns to the phase control when an accumulated value of the evaluation value in the predetermined period becomes equal to or less than a second predetermined value. The image forming apparatus described.   The image forming apparatus according to claim 6, wherein the evaluation value is a rising current ratio or a rising current value corresponding to a power duty. A method for controlling the fixing unit in an image forming apparatus in which a sheet on which a developer image is formed is heated by a fixing unit to fix the developer image on the sheet.
A control method comprising: controlling the fixing unit with respect to an AC power supply by phase control; and switching the phase control to wave number control according to a state of harmonic current distortion.

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