Fixing control device, image forming apparatus, fixing control method, and program

Abstract

To provide a fixation control device and the like which can suppress a flicker when driving a switching element by switching the same in each section by control signals in different duty ratios.SOLUTION: A fixation control device comprises: fixation means 5 which incorporates a heater 52; chopper means 83 which includes a reactor L2, a reflux element D and a switching element 831 and performs chopping of input power; and control means 6 which can control the power supply to the heater by supplying the power to a heater from the chopper means by switching the switching element by a control signal and outputting the control signals in the different duty ratios. When a period for switching the switching element 831 by the control signals in the same duty ratio is one time section, the control means 6 sets the duty ratio such that the power supply to the heater becomes a target value by a combination of the different power supplied in at least three time sections in the first to third time sections with the mutually-different duty ratios of the control signals.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a fixing control device, an image forming apparatus, a fixing control method, and a program that are mounted on an image forming apparatus such as a copying machine, a printer, a facsimile apparatus, and a multifunction machine thereof, switch input power at a predetermined duty ratio, and supply it to a heater built in a fixing device.

Background Art

[0002] In an image forming apparatus, there is provided a fixing unit having a built-in heater, and chopper means including a reactor, a reflux element, and a switching element for chopping input power. A fixing control device that supplies power from the chopper means to the heater by switching the switching element of the chopper means at a high frequency by PWM control or the like has been conventionally known. In this fixing control device, the amount of power supplied to the heater can be controlled by changing the duty ratio of a control signal for switching the switching element. For example, at a duty ratio of 100%, the switching element is always on, and 100% of the rated power is supplied. At a duty ratio of 60%, 60% of the power is supplied.

[0003] However, due to a heater connected as a load, an L component such as a reactor mounted as a noise and inrush current prevention measure, and a C component of the circuit, etc., the switching waveform tends to become dull. Therefore, when operating with a short switching period and a high duty ratio setting, that is, when the target value of power supply to the heater is high, if the switching element continues to open and close, the element will become closed before the current reaches zero at the opening timing, and a state where switching is performed in a continuous current mode in which the current to the heater continues will occur.

[0004] To avoid the occurrence of such a continuous current mode, Patent Document 1 describes how, when the duty cycle required to achieve the power target value results in a high duty cycle that leads to a continuous current mode, the power target value is achieved by alternately switching between a first time period in which the switching element is driven at a 100% duty cycle where it is normally open, and a second time period in which the switching element is driven at a low duty cycle. For example, if a continuous current mode occurs when the duty cycle exceeds 80%, and the power target value can be achieved at a duty cycle of 81%, the duty cycle of 81% is achieved by alternately switching between a first time period in which the element is driven at a 100% duty cycle and a second time period in which it is driven at a 62% duty cycle. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6283845 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when power is supplied continuously at a high duty cycle to ensure the fixing temperature of the fixing device, the switching between the first and second time zones occurs continuously, causing large power fluctuations during the switching cycle, which results in a problem where flicker worsens.

[0007] This invention has been made in view of the above-mentioned technical background, and aims to provide a fixing control device, an image forming apparatus, a fixing control method, and a program that can suppress flicker when a switching element is driven by switching it in intervals with control signals of different duty cycles. [Means for solving the problem]

[0008] The above objectives will be achieved by the following means. (1) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to third time intervals, each with a different duty cycle of the control signal. The control means further sets the duty cycle to 100% for the first time interval, and when the duty cycle at which the system transitions to a continuous current mode in which current is continuously supplied to the heater is used as a threshold, it sets the duty cycle of the second time interval immediately before or after the first time interval to a value less than or equal to the threshold, sets the duty cycle of the third time interval immediately before or after the second time interval to be even smaller than the duty cycle of the second time interval, and the difference between the duty cycles of the first time interval and the third time interval exceeds (100% - threshold) in the fixing control device. (2) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to third time intervals, each with a different duty cycle of the control signal. The control means further includes a fixing control device that sets the switching period of the time interval to less than one period of the input power frequency. (3) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to third time intervals, each with a different duty cycle of the control signal. Furthermore, it includes a selection method between productivity priority mode and flicker reduction priority mode. The control means is a fuser control device that performs power control by setting different duty cycles in the at least three time intervals only when the flicker reduction priority mode is selected. (4) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to third time intervals, each with a different duty cycle of the control signal. The control means further includes a fixing control device that sets the duty cycle such that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold), with the duty cycle at which the heater transitions to a continuous current mode in which current is continuously supplied to the heater being used as a threshold. (5) The fixing control device according to any one of paragraphs 1 to 4 above, wherein the control means switches the switching element with a control signal of a constant duty cycle if the target value of power supply can be achieved with a duty cycle that does not transition to a continuous current mode in which current is continuously supplied to the heater, and sets the duty cycle such that the power supply becomes the target value by a combination of power supplied in at least three time intervals if the target power supply cannot be achieved without transitioning to a continuous current mode. (6) A fixing control device according to any one of paragraphs 1 to 5 above, wherein the control means sets the duty cycle in order from the time interval with the smallest duty cycle to the time interval with the largest duty cycle of 100% when the target value of the power supply switches to an increasing direction, and sets the duty cycle in order from the time interval with the largest duty cycle of 100% to the time interval with the smallest duty cycle when the target value of the supplied power switches to a decreasing direction. (7) The fixing control device according to any one of paragraphs 1, 3 to 6 above, wherein the control means sets the switching period of the time interval to less than one period of the frequency of the input power. (8) The system includes a detection means for detecting the input voltage, Based on the detection results by the detection means, the threshold is changed (as described in paragraph 1 above). or 4 The fixing control device described above. (9) The fixing control device according to any one of paragraphs 1 to 8 above, wherein the control means sets the duty cycle for each time interval to 100% when the target value of power supply is 95 to 99%, and sets the duty cycle for each time interval to the threshold when transitioning to a current continuous mode in which current is continuously supplied to the heater, with the duty cycle at which the target value of power supply is greater than the threshold and is 81 to 86%. (10) The fixing control device according to any one of paragraphs 1 to 9 above, wherein the control means sets different duty cycles so that the power supply reaches the target value by a combination of power supplied in multiple time intervals only when the target value of power supply cannot be achieved by setting only one duty cycle. (11) An image forming apparatus equipped with a fixing control device as described in any of paragraphs 1 to 10 above. (12) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The image forming apparatus equipped with The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is defined as one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. Furthermore, a fixing control method in which, when the duty cycle is set to 100% for the first time interval and the duty cycle when transitioning to a current continuous mode in which current is continuously supplied to the heater is taken as a threshold, the duty cycle of the second time interval immediately before or after the first time interval is set to a value less than or equal to the threshold, the duty cycle of the third time interval immediately before or after the second time interval is set to be even smaller than the duty cycle of the second time interval, and the difference in the duty cycles of the first time interval and the third time interval exceeds (100% - threshold). (13) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The image forming apparatus equipped with The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is defined as one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. A fixing control method for setting the duty cycle such that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold), with the duty cycle at which the system transitions to a current continuous mode in which current is continuously supplied to the heater being used as a threshold. (14) Fixing means with built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The computer of the image forming apparatus equipped with: The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is defined as one time interval, the duty cycle of the control signals is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signals. Furthermore, when setting a duty ratio of 100% for the first time interval and using the duty ratio when shifting to a current continuous mode in which current is continuously supplied to the heater as a threshold value, a value equal to or less than the threshold value is set as the duty ratio of the second time interval immediately before or after the first time interval, the duty ratio of the third time interval immediately before or after the second time interval is set to be even smaller than the duty ratio of the second time interval, and a process is executed in which the difference in the duty ratios between the first time interval and the third time interval exceeds (100% - threshold value). (15) Fixing means incorporating a heater, Chop means including a reactor, a reflux element, and a switching element for chopping input power, To the computer of an image forming apparatus provided with While switching the switching element by a control signal to supply power from the chopping means to the heater, controlling the power supply to the heater by outputting control signals with different duty ratios, and when taking a period in which the switching element is switched by a control signal with the same duty ratio as one time interval, the duty ratio of the control signal is set by different combinations of power supplied in at least three time intervals, namely, a first time interval to a third time interval, each having a different duty ratio, so that the power supply to the heater becomes a target value. When using the duty ratio when shifting to a current continuous mode in which current is continuously supplied to the heater as a threshold value, a program for executing a process of setting the duty ratio so that the difference in the duty ratios set in adjacent time intervals does not exceed (100% - threshold value).

Advantages of the Invention

[0009] According to the invention described in paragraph (1) above, when the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches the target value by a combination of different power supplied in at least three time intervals, the first to the third time intervals, each with a different duty cycle of the control signal. In other words, compared to the conventional control method of alternating switching of the duty cycle between the first and second time intervals, the duty cycle is switched in at least three time intervals, the first to the third time intervals, so the difference in duty cycle between one time interval and the next can be reduced. As a result, power oscillations can be suppressed and power supply flicker can be suppressed. Also, first Time zone in between When a duty cycle of 100% is set and the system transitions to a continuous current mode in which current is continuously supplied to the heater, the duty cycle at which point is set as the threshold, first Immediately before or immediately after the time interval second The duty cycle for the time interval is defined as The threshold Value Below A value is set. The duty cycle of the third time period immediately preceding or following the second time period is set to be even smaller than the duty cycle of the second time period, and the difference between the duty cycles of the first and third time periods exceeds (100% - threshold). Therefore, flicker can be suppressed while avoiding the switching operation that transitions to continuous current mode.

[0010] Previous item ( 4 According to the invention described above, the duty cycle of the control signal is different First hour section to third hour section at least 3 two time zones between The combination of supplied power ensures that the power supply to the heater reaches the target value. Control The duty cycle of your signal is set, so the difference in duty cycles for each time interval is... to small This allows for the suppression of power oscillations and thus reduces power supply flicker. Furthermore, when the duty cycle at which the system transitions to a continuous current mode in which current is continuously supplied to the heater is used as a threshold, the duty cycle is set so that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold). This allows for stable suppression of power oscillations and reduces power supply flicker.

[0011] Previous item ( 5According to the invention described above, if the target power supply can be achieved with a duty cycle that does not transition to a continuous current mode in which current is continuously supplied to the heater, the switching element is switched with a control signal of a constant duty cycle, and if the target power supply cannot be achieved without transitioning to a continuous current mode, at least three Different duty cycles are set so that the power supply reaches the target value depending on the combination of power supplied during the time interval, allowing flicker suppression only when necessary.

[0015] Previous item ( 6 According to the invention described above, when the target value of power supply switches to an increasing direction, the duty cycle is set in order from the time interval with the smallest duty cycle to the time interval with the largest duty cycle of 100%, and when the target value of supplied power switches to a decreasing direction, the duty cycle is set in order from the time interval with the largest duty cycle of 100% to the time interval with the smallest duty cycle. Therefore, the duty cycle can be set in stages in accordance with the switching of the target value of power supply.

[0016] Previous item ( 7 According to the invention described above, the time interval switching period is set to less than one period of the input power frequency, so the power fluctuation period is shortened and the appearance of flicker is reduced.

[0018] Previous item ( 8 According to the invention described above, since the threshold is changed according to the input voltage, even if the input voltage fluctuates, flicker suppression can be performed accurately while avoiding switching operations that transition to continuous current mode.

[0021] Previous item ( 9 According to the invention described above, the target value of the power supply 95-99%When the duty cycle for each time interval is set to 100%, and the duty cycle when transitioning to a continuous current mode in which current is continuously supplied to the heater is set as the threshold, the target value of the power supply is greater than the threshold. 81-86% The threshold is the duty cycle for each time interval. Value By configuring this setting, it becomes unnecessary to switch the duty cycle, and flicker can be suppressed while avoiding the switching operation that transitions to continuous current mode.

[0022] Previous item ( 10 According to the invention described above, only when the target value of power supply cannot be achieved with only one duty cycle setting, different duty cycles are set so that the power supply reaches the target value by combining power supplied in multiple time intervals. Therefore, when the target value of power supply can be achieved with only one duty cycle setting, it is not necessary to switch duty cycles, and unnecessary flicker can be prevented.

[0023] Previous item ( 11 According to the invention described above, compared to the conventional control method which involves alternating switching of the duty cycle between the first and second time intervals, the difference in the duty cycle between each time interval can be reduced, power oscillations can be suppressed, and power supply flicker can be suppressed in an image forming apparatus.

[0024] Previous item ( 12 )or( 13 According to the invention described above, the difference in duty cycles in each time interval can be reduced, power oscillations can be suppressed, and power supply flicker can be suppressed.

[0025] Previous item ( 14 )or( 15According to the invention described above, the computer of an image forming apparatus, which includes a fixing means with a built-in heater and a chopper means including a reactor, a freewheeling element and a switching element for chopping input power, can be made to perform a process that reduces the difference in duty cycles in each time interval when the period for switching the switching element with a control signal of the same duty cycle is defined as one time interval. [Brief explanation of the drawing]

[0026] [Figure 1] This is a diagram showing the overall configuration of the image forming apparatus. [Figure 2] This is a diagram showing the configuration of the fixing control device. [Figure 3] This diagram schematically illustrates the time waveform of the main part of the fixing control device. [Figure 4] Figure 2 illustrates the heater current during the ON period of the switching element in the upper section, and the heater current during the OFF period in the lower section. [Figure 5] Figure 2 illustrates the time waveform of the input current to the heater. [Figure 6] This diagram illustrates the heater current at a low duty cycle in the upper section and the heater current at a high duty cycle in the lower section. [Figure 7] This figure schematically illustrates the time waveform of the main part of the fixing control device in the first energization control. [Figure 8] This diagram schematically shows the time waveforms of the key parts of the fixing control device during the switching between the first and second power supply control modes. [Figure 9] (A) is a diagram showing a conventional control method that switches the duty cycle between the first time interval and the second time interval, and (B) is a diagram for explaining the control method 1 according to this embodiment. [Figure 10] This is a diagram illustrating the control method 3 according to this embodiment. [Figure 11] This is a diagram illustrating the control method 4 according to this embodiment. [Figure 12]This is a diagram illustrating the control method 5 according to this embodiment. [Figure 13] (A) is a diagram showing a conventional control method that switches the duty cycle between the first and second time intervals, and (B) is a diagram for explaining the control method 6 according to this embodiment. [Figure 14] This is a flowchart illustrating the fixing control operation of an image forming apparatus. [Modes for carrying out the invention]

[0027] 《Column 1: Overall Configuration and Printing Operation of Image Forming Apparatus》 In Figures 1 and 2, the image forming apparatus 1 is, for example, a copier, printer, or facsimile, or a multifunction device equipped with these functions, which prints an image onto a sheet-like printing medium M (e.g., paper). To this end, the image forming apparatus 1 broadly comprises a paper feeding unit 2, a pair of registration rollers 3, an image forming means 4, a fixing means 5, a control means 6, and a power supply means 7. Here, at least the fixing means 5, the control means 6, and the power supply means 7 constitute a fixing control device 8. The operation of each component of the image forming apparatus 1 during printing will be described below.

[0028] Unused printing media M are loaded into the paper feed unit 2. The paper feed unit 2 feeds the printing media M one sheet at a time along the transport path FP shown by the dashed line in Figure 1. The registration roller pair 3 is located on the transport path FP, downstream of the paper feed unit 2. The registration roller pair 3 temporarily stops the printing media M fed from the paper feed unit 2, and then feeds it to the secondary transfer area at a predetermined timing.

[0029] The image forming means 4 generates a toner image on an intermediate transfer belt, for example, by a well-known electrophotographic method and a tandem method. This toner image is supported by the intermediate transfer belt and transported toward the secondary transfer region.

[0030] In the secondary transfer area, the printing medium M is fed from the registration roller pair 3, and the toner image is transported from the image forming means 4. In the secondary transfer area, the toner image is transferred to the intermediate transfer area. The data is transferred from the belt to the printing medium M.

[0031] In the fixing means 5, the heating roller 51 and the pressure roller 53 come into contact to form a nip. The heating roller 51 has a heater 52 built into a cylindrical core. The heater 52 is, for example, a halogen heater and is lit by the current supplied from the power supply means 7. The pressure roller 53 rotates under the control of the control means 6. The heating roller 51 rotates in accordance with the rotation of the pressure roller 53. When the printing medium M is fed into the nip, the printing medium M is pressurized by both rollers 51 and 53 and heated by the heating roller 51. As a result, toner is fixed to the printing medium M. After that, the printing medium M is sent towards the output tray.

[0032] The fixing means 5 further includes a first temperature detection means 54, which is, for example, a thermistor. The first temperature detection means 54 detects the temperature of the heating roller 51 (i.e., the fixing temperature) and outputs the detection result to the control means 6.

[0033] In the control means 6, the CPU executes the program stored in ROM, using RAM as a working area. The control means 6 performs various controls, but in this embodiment, the most important is the power supply control of the heater 52. Specifically, the control means 6 sets the duty cycle of the switching element 831, described later, using PWM (Pulse Width Modulation) control or PFM (Pulse Frequency Modulation) control so that the detection result of the first temperature detection means 54 reaches the target temperature. The duty cycle is determined by well-known PID control or PI control, etc. In this embodiment, the power supply control of the heater 52 is provided as a first power supply control and a second power supply control, and the control means 6 further switches between the first power supply control and the second power supply control as appropriate based on predetermined conditions.

[0034] As shown in Figure 2, the power supply means 7 includes at least a rectifier circuit 81, a noise filter 82, and a chopper circuit 83. It also includes a current detection means 84, a voltage detection means 85, and a second temperature detection means 86.

[0035] The rectifier circuit 81 is connected to the commercial power supply. The commercial power supply frequency is, for example, 50Hz or 60Hz in Japan.

[0036] The noise filter 82 is, for example, a π-type filter and is connected in cascading to the output side of the rectifier circuit 81. Specifically, the noise filter 82 includes an inductor L1 and capacitors C1 and C2. The inductor L1 is connected in series with the heater 52, and the capacitors C1 and C2 are connected in parallel with the heater 52.

[0037] The chopper circuit 83 is, for example, a step-down chopper circuit, and is cascaded to the output side of the filter 82. In this case, the chopper circuit 83 includes a coil (reactor) L2, a freewheeling element D, a switching element 831, and a drive circuit 832.

[0038] Coil L2 is connected in series between coil L1 and heater 52.

[0039] The freewheeling element D is, for example, a diode, and is connected in parallel with the heater 52 on the filter 82 side of the coil L2. More specifically, the freewheeling element D is positioned such that its cathode is electrically connected between L1 and L2, and its anode is electrically connected between the heater 52 and the collector of the switching element 831.

[0040] Furthermore, the switching element 831 is, for example, an IGBT (Insulated Gate Bipolar Transistor) or a MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor), and is connected in series with the heater 52 on the filter 82 side of the freewheeling element D. More specifically, the switching element 831 is positioned such that its collector is electrically connected to the heater 52 and its emitter is electrically connected to the output side of the rectifier circuit 81. Drive circuit 832 This is connected to the gate of the switching element 831 and sets the duty cycle and drive frequency of the switching element 831 under the control of the control means 6. The heater 52 is connected between the output terminals of the chopper circuit 83 as described above.

[0041] The current detection means 84 detects the current flowing through the reactor L2 (hereinafter referred to as the reactor current) and periodically transmits a signal representing the current value to the control means 6 (specifically, at intervals much shorter than the first time interval D1 described later).

[0042] The voltage detection means 85 detects the voltage that appears between the output terminals of the rectifier circuit 81 (hereinafter referred to as the terminal voltage) and periodically transmits a signal representing that voltage value to the control means 6 (specifically, at intervals much shorter than the first time interval D1).

[0043] The second temperature detection means 86 detects the temperature of the switching element 831 (hereinafter referred to as the element temperature) and periodically transmits a signal representing the detected temperature to the control means 6 (specifically, at intervals much shorter than the first time interval D1). 《Second column: Second power supply control (general power supply control to heaters)》 This section will explain the general power supply control to the heater 52 using Figures 1 to 6.

[0044] First, the rectifier circuit 81 is supplied with alternating current (AC) from the commercial power supply (see the second row from the top in Figure 3). The top row of Figure 3 shows the commercial power supply voltage. The rectifier circuit 81 generates a DC current by full-wave rectifying the input current. The filter 82 removes noise from the output current of the rectifier circuit 81 and prevents high-frequency components of the pulsed current flowing through the switching element 831 from leaking to the commercial power supply side.

[0045] The control means 6 inputs a control signal (see the third row from the top in Figure 3) to the drive circuit 832 that indicates at least the time interval (i.e., pulse period and duty cycle) for energizing the heater 52. Based on the input control signal, the drive circuit 832 generates a drive signal to turn the switching element 831 on / off (see the bottom row in Figure 3) and supplies it to the gate of the switching element 831. Here, the switching frequency of the switching element 831 is much higher than the frequency of the commercial power supply and is driven at a frequency exceeding the upper limit of the audible range (over approximately 20 kHz).

[0046] When the switching element 831 is turned on, as shown by arrow A in the upper part of Figure 4, a DC current generated by the rectifier circuit 81 flows through the switching element 831 to the coil L2 and heater 52. During this time, the coil L2 stores a portion of the DC current flowing through it as magnetic energy.

[0047] On the other hand, when the switching element 831 is turned off, as shown by arrow B in the lower part of Figure 4, the magnetic energy stored in the coil L2 while the switching element 831 was on is released as a current and begins to flow to the heater 52. This current returns to the coil L2 via the freewheeling element D, which acts as a regenerative diode.

[0048] As a result of the operation of the power supply means 7 as described above, the waveform of the input current to the heater 52 becomes close to a sine wave, as shown in Figure 5. This improves the power factor of the power supply means 7 and reduces harmonic currents from the input current.

[0049] Furthermore, since the input current to the heater 52 is controlled by increasing or decreasing the duty cycle, the power consumption of the heater 52 can be controlled with high precision. Therefore, temperature ripple in the fixing means 5 can also be suppressed, and as a result, the color development during color printing can be stabilized.

[0050] By the way, coil L2 and heater 52 are connected to a rectifier circuit 81, as shown in the upper part of Figure 6. A current flows that is a combination of the input current (shown by the solid line) and the freewheel current (shown by the dotted line) that flows through the freewheel element D when the switching element 831 is turned off, on the time axis. As shown in the current waveform WF2 in the upper part of Figure 6, in the case of a low duty cycle (i.e., when the ratio of pulse width to a predetermined pulse period is low), sufficient time is ensured for the current to decrease after the switching element 831 is turned off. In this embodiment, the low duty cycle is, as an example, 80% or less when the commercial power supply frequency is 50 / 60Hz. In this case, as shown in the circle in the upper part of Figure 6, the current value can be made zero when the pulse period switches. In other words, the current flowing through the coil L2 enters a current discontinuity mode. Therefore, the recovery current (in other words, recovery noise) flowing through the freewheel element D can be suppressed. In this embodiment, driving the switching element 831 with a low duty cycle control signal to control the energization of the heater 52 is called the second energization control.

[0051] In the second power control, the switching element 831 periodically switches on and off based on the control signal. However, if this switching frequency falls below approximately 20 kHz, the coil L2 vibrates, resulting in another problem: noise is generated from the image forming apparatus 1. Therefore, it is preferable that the switching frequency exceeds the upper limit of the audible range. Third column: Details of technical challenges The lower part of Figure 6 shows the waveform WF1 of the current flowing through the heater 52 when the duty cycle (i.e., the ratio of pulse width to the predetermined pulse period) is high in the second power control. In this embodiment, the high duty cycle is, as an example, greater than 80% and less than 100% when the commercial power frequency is 50 / 60Hz. Hereinafter, 80%, which is the boundary value between high and low duty cycles, will be referred to as the predetermined duty cycle. In the case of a high duty cycle, the current flowing through the heater 52 enters a continuous current mode. Here, continuous current mode means a mode in which the current flowing through the heater 52, etc., is not substantially zero. In the continuous current mode, as shown in the current waveform WF1, the current for the next pulse period is supplied from the rectifier circuit 81 before the current for a certain pulse period drops to 0 amperes. In other words, the switching element 831 is switched on while a return current is flowing through the heater 52. Therefore, as shown in the circle in the lower part of Figure 6, the current value does not become zero when the period switches, and a recovery current flows through the freewheeling element D, which tends to increase recovery noise. Also, if the switching element 831 is turned on while current is flowing through the freewheeling element D, switching losses occur, causing the temperature of the switching element 831 to rise. As described above, driving the switching element 831 at a high duty cycle (i.e., supplying a large amount of power to the heater 52) presents several problems. Therefore, using only the second energization control leads to a narrowing of the range of settable fixing temperatures. Considering the above background, in this embodiment, in addition to the second energization control, the first energization control of the switching element 831 is also possible, and both energization controls can be switched as appropriate. 《Column 4: Outline of the First Power Control》 Next, the first energization control will be explained in detail, mainly referring to Figure 7. The following describes the case where a large power of 90% of the rated power is supplied to the heater 52. In this case, when the second energization control is performed, the switching element 831 is driven at a high duty cycle (80-99%), and as a result, a current in continuous mode flows through the heater 52.

[0052] As described above, if the second energization control results in a continuous current mode, the control means 6 periodically performs the first energization control. In the execution period T1 of the first energization control, the first time interval D1 and the second time interval D2 appear at least once each on the time axis. In this example, time intervals D1 and D2 each correspond to the duration of one cycle of the commercial power supply. Here, Figure 7 illustrates the case where the execution period T1 is twice the commercial power supply cycle (i.e., the lower limit). Note that the execution period The upper limit of T1 is twice the thermal time constant of the heating roller 51, which is the object heated by the heater 52. Here, the thermal time constant is the time it takes to reach 50% of the temperature when changing from one temperature to another.

[0053] In the first time interval D1, the control means 6 generates and outputs a control signal with a low duty cycle (i.e., an 80% duty cycle) that results in a current discontinuity mode. As a result, the current flowing through the heater 52 will have a current value equivalent to 80% of its rated power. In contrast, in the second time interval D2, it generates and outputs a control signal with a 100% duty cycle. As a result, the current flowing through the heater 52 will be sinusoidal and have a current value equivalent to 100% of its rated power. Note that since the switching element 831 does not switch the input current on or off, the current flowing through the heater 52 will not, in principle, be in current continuous mode.

[0054] In the execution cycle T1, the time average of the duty cycle is 90%. That is, in this execution cycle T1, the current flowing through the heater 52 has a current value equivalent to 90% of its rated power. Thus, with the first energization control, it is possible to supply a large amount of power to the heater 52, and the fixing temperature can be increased while avoiding the current flowing through the heater 52 entering continuous current mode. 《Column 5: Switching between the first and second power control》 In this embodiment, the control means 6 appropriately switches between the first and second energization control. More specifically, the first energization control is performed when a predetermined variable exceeds a reference value that causes the current flowing through the heater 52 to enter continuous current mode; otherwise, the second energization control is performed. To control the fixing temperature, Figure 8 illustrates the transition from a first time zone Z1, which supplies 90% of the rated power to the heater 52, to a second time zone Z2, which supplies 70% of that power.

[0055] As explained in the third column, if the switching element 831 switches at a high duty cycle to supply 90% of the rated power, various problems will occur. Therefore, in the first time period Z1, the control means 6 performs the first power supply control. More specifically, in the first power supply control, the control means 6 outputs a control signal representing an 80% duty cycle to the switching element 831 in the first time period D1, and a control signal representing a 100% duty cycle in the second time period D2.

[0056] In contrast, if 70% of the rated power is supplied to the heater 52, the current continuous mode that is the issue in this case will not occur, so the control means 6 performs the second power supply control in the second time zone Z2. At this time, the control means 6 outputs a control signal representing a 70% duty cycle to the switching element 831 throughout the entire time zone. 《Column 6: Challenges and Solutions for First-Stage Power Control》 By performing the above control, switching of the switching element 831 under the current continuous mode condition can be avoided, thereby reducing the deterioration of the machine noise level due to increased recovery noise and reducing the temperature rise of the switching element 831.

[0057] However, one problem with this control is that when power control is required by switching the duty cycle at a level that allows for continuous first-energy control (first time zone Z1), a situation occurs where the supplied power oscillates during the control switching cycle between the first time zone D1 and the second time zone D2, as shown in Figure 8. For example, if power supply with a control signal duty cycle of 81% is continued, power oscillations at duty cycles of 62% and 100% will occur at 20 msec intervals, assuming a power supply frequency of 50 Hz and control cycles, i.e., the lengths of the first time zone D1 and the second time zone D2, are each 20 msec. This is a concern as it can cause fixed-period oscillations in current consumption and affect power supply flicker.

[0058] Therefore, in this embodiment, a control method is employed that can suppress flicker caused by power oscillations that occur in such first energization control (first time zone Z1).

[0059] Figure 9(A) shows a conventional control method (hereinafter also referred to as the conventional method) that switches the duty cycle in the first time interval D1 and the second time interval D2 described above, and Figure 9(B) is a diagram for explaining the control method 1 (hereinafter also referred to as the new method) according to this embodiment.

[0060] For example, if the control period is set to 20 msec, the target value for power supply is an 81% duty cycle, and the duty cycle threshold at which the switching element transitions to continuous current mode is 80%, and duty cycles exceeding 80% result in continuous current mode, then the conventional method shown in Figure 9(A) avoids duty cycles exceeding 80% but less than 100% where continuous current mode occurs, and achieves the target power supply of 81% by using the average value of a combination of a first time period D1 with a 62% duty cycle and a second time period D2 with a 100% duty cycle.

[0061] In this case, for example, assuming a 1000W halogen heater 52, the current consumption alternates between levels of 6.2A and 10.0A with a period of 20msec, resulting in a current fluctuation of around 4A. If the wiring impedance is present due to daisy-chaining or similar configurations, this could potentially cause fluctuations in the power supply voltage level.

[0062] In contrast, the new method 1 sets a time interval with a duty cycle of 80% between the time intervals with a duty cycle of 62% and the time intervals with a duty cycle of 100%, which is the same as the threshold for transitioning to continuous current mode. This control suppresses instantaneous fluctuations in current consumption while achieving the target value of power supply at a duty cycle of 81%. In the new method 1, the time interval with a duty cycle of 62% is designated as the first time interval D1, the newly set time interval with a duty cycle of 80% is designated as the second time interval D2, and the subsequent time interval with a duty cycle of 100% is designated as the third time interval D3. In the new method 1, the current fluctuation for each time interval is at the 6.2A → 8A → 10A level, a fluctuation of 2A level, which is a reduction from the 4A level in the conventional method.

[0063] In the new method 1, if the difference in the duty cycle of the control signals between two time intervals D1 and D3 exceeds a certain value (e.g., 20%), an intermediate duty cycle time interval D2 is set during that time interval while avoiding a transition to continuous current mode, thereby suppressing current fluctuations. When an intermediate duty cycle time interval D2 is set, if the difference in the duty cycle between this new time interval D2 and the immediately preceding or succeeding time interval D1 or D3 is still greater than or equal to a certain value, another intermediate duty cycle time interval may be set while avoiding a transition to continuous current mode, thereby creating four or more time intervals. The certain value should preferably be set to the difference between the duty cycle threshold for transitioning to continuous current mode (e.g., 80%) and 100%.

[0064] Furthermore, as shown in the second energization control (second time zone Z2) in Figure 8, if the target power supply can be achieved with a duty cycle that does not transition to a continuous current mode in which current is continuously supplied to the heater 52, then it is sufficient to maintain a constant duty cycle, and in this case, flicker is not a problem. If the target power supply cannot be achieved without transitioning to a continuous current mode, then at least three time intervals D1 to D3 with different duty cycles should be set.

[0065] Next, I will explain the new method 2. In the new method 2, when the duty cycle of the control signal in the first time interval D1 is set, the duty cycle of the control signal in the next second time interval D2 is set so as not to exceed the limit, and further, the duty cycle of the control signal in the next third time interval D3 is set so as not to exceed the limit relative to the duty cycle of the control signal in the second time interval D2.

[0066] For example, if the target value for power supply is a 20% limit and an 81% duty cycle, and the duty cycle for the first time interval D1 is set to 62%, then in the next second time interval D2, a duty cycle is set that is within 20% and does not result in continuous current mode. Here, the same 80% as in New Method 1 is selected. Furthermore, for the next third time interval D3, the duty cycle is set to 100%, maintaining a difference of within 20%. This suppresses instantaneous fluctuations in current consumption. The maximum value of the limit should be set to the difference between 100% and the threshold duty cycle at which the system transitions to continuous current mode, i.e., (100% - threshold). In New Method 2, the combinations of the first to third time intervals D1 to D3 are the same as in New Method 1 shown in Figure 9(B). Note that if the target value for power supply is, for example, 90%, then a repetition of the first time interval D1 with an 80% duty cycle and the second time interval D2 with a 100% duty cycle is also acceptable.

[0067] Next, we will explain the new method 3. As shown in Figure 10, the new method 3 controls current fluctuations by setting the duty cycle of the second time period D2, following the first time period D1 with a 100% duty cycle, to be the same as, or below but close to, the duty cycle threshold for transitioning to continuous current mode. For example, if the system transitions to continuous current mode when the duty cycle exceeds 80% (when the threshold is 80%), the duty cycle of the second time period D2 is set to 80%, or below but close to 80%. Furthermore, the duty cycle of the subsequent third time period D3 is also gradually reduced within a predetermined difference (e.g., 20%) to suppress power fluctuations. By repeating the first time period D1 to the third time period D3, the target power supply value of 81% is achieved as an average value.

[0068] Next, we will explain the new method 4. In the new method 4, when the system transitions to the first power supply control and the target value of power supply switches to a decreasing direction, the duty cycle is set in order from the time period with the largest duty cycle of 100% to the time period with the smallest duty cycle. For example, when the target value of power supply switches from 100% to 81%, as shown in Figure 11, if the duty cycle immediately before transitioning to the first power supply control is 100%, the first time period D1 after the start of the first power supply control will also have a duty cycle of 100%, and the duty cycle will be set to a lower value in the subsequent second time period D2 and third time period D3. After that, it will be set to a higher value in order, and this will be repeated to suppress current fluctuations. For example, as shown in Figure 11, the switching will be 100% → 80% → 63% → 63% → 80% → 100%, and by repeating this, the target value of power supply of 81% will be achieved.

[0069] Furthermore, when transitioning to the first power supply control and the target value of the power supply switches to an increasing direction, it is preferable to set the smallest duty cycle in the first time interval D1 after the start of the first power supply control, set a larger duty cycle in the next second time interval D2, and set the largest duty cycle of 100% in the following third time interval D3. For example, 63% → 80% → 100% → 100% → 80% → 63%.

[0070] Next, we will explain the new method 5. As shown in Figure 12, in the new method 5, when achieving a target power supply value of, for example, 81% which is a continuous current mode, it uses two alternating switching modes, similar to the conventional method, consisting of a first time section D1 with a duty cycle of 62% and a second time section D2 with a duty cycle of 100%. However, by setting the switching period to less than one cycle of the input power frequency, the power fluctuation period is shortened, reducing the appearance of flicker. For example, when the input power frequency is 50 Hz, the time of both the first time section D1 and the second time section D2 is set to less than 20 msec, and the switching period is set to less than 20 msec. Preferably, the switching period is set to less than or equal to half a cycle of the input power frequency. Figure 12 shows the case where the switching period is half a cycle of the input power frequency.

[0071] Furthermore, even when setting and switching between three or more time intervals D1 to D3 with different duty cycles, the switching period can be set to less than one period of the input power frequency, preferably half a period or less, by setting the length of each time interval to less than one period of the input power frequency, thereby reducing the appearance of flicker.

[0072] Furthermore, respecting the user's preferences, a selection button may be displayed on the control panel of the image forming apparatus 1, for example, to allow the user to choose between productivity-priority mode and flicker reduction-priority mode. In this case, if productivity-priority mode is selected, the conventional method should be set, and only if flicker reduction-priority mode is selected should a flicker reduction method, including one of the new methods 1 to 5, be set.

[0073] Furthermore, the threshold duty cycle for continuous current mode may be changed to match the input voltage detected by the voltage detection means 85. When the input voltage is low, the current flowing to the load decreases, so the time it takes for the current to become zero when the switching element 831 is turned off is shortened, and the duty cycle, i.e., the threshold for transitioning to continuous current mode can be changed to a higher value.

[0074] Figures 13(A) and 13(B) are diagrams to explain the new method 6 in comparison with the conventional method. In the new method 6, when the target value of power supply is close to 100%, the duty cycle is set to 100%. When the duty cycle at which the system transitions to continuous current mode is used as the threshold, if the target value of power supply is greater than the threshold but close to the threshold, the duty cycle is set to the threshold or a value that is less than or equal to the threshold but close to the threshold.

[0075] Specifically, when the duty cycle threshold for transitioning to continuous current mode is set to 80%, and the target power supply value is, for example, an 86% duty cycle which is the continuous current mode, conventionally, as shown in Figure (A), the target value was achieved by alternating between a first time period D1 with a 72% duty cycle and a second time period D2 with a 100% duty cycle. In contrast, in the new method 6, as shown in Figure (B), the entire time period is set to a 100% duty cycle.

[0076] Furthermore, when the target power supply value is an 81% duty cycle, which corresponds to continuous current mode, conventionally, as shown in Figure (A), the target value was achieved by alternating between a first time interval D1 with a 62% duty cycle and a second time interval D2 with a 100% duty cycle. In contrast, in the new method 6, as shown in Figure (B), the entire time interval is set to an 80% duty cycle.

[0077] According to this new method 6, it is possible to suppress current fluctuations and reduce flicker while avoiding switching operations that transition to continuous current mode.

[0078] Furthermore, if the target power supply is 81-85%, the duty cycle may be set to 80%, and if the target is 95-99%, the duty cycle may be set to 100%. In addition, although there will be a slight delay in the temperature tracking performance of the fixing means 5, the duty cycle setting may be determined, for example, by the difference from the target temperature.

[0079] By applying the new method described above to the first power supply control (first time zone Z1), compared to the conventional control method which alternately switches between the first time zone D1 and the second time zone D2, where the difference in duty cycles is large, it is possible to switch the duty cycle in multiple time zones while keeping the difference in duty cycles small. This suppresses power oscillations and reduces power supply flicker, and reduces the temperature rise of the switching element 831 and the generation of noise from the switching element 831. Alternatively, if the switching period is shortened, the power fluctuation period can be shortened.

[0080] Figure 14 is a flowchart illustrating the fixing control operation of the image forming apparatus 1. This operation is performed by the CPU of the image forming apparatus 1 executing an operation program stored in a recording medium such as ROM.

[0081] When power-on is detected in step S001, control is started in step S002. Then, in step S003, the target value of the power supply required for the fixing function is set.

[0082] Next, in step S004, it is determined whether the set target power supply value will result in the switching element 831 being in continuous current mode. For example, if it is between 81% and 99%, it is assumed that it will be in continuous power mode (YES in step S004), and the first power supply control in step S006 is selected. If it does not result in continuous power mode (NO in step S004), the second power supply control in step S005 is selected. If the second power supply control is selected, in step S009, the duty cycle that achieves the target power supply value is set.

[0083] If the first power supply control in step S006 is selected, then in step S007, calculation 1 selects a combination of duty cycles that achieve the target value by combining power supply in multiple time intervals. Here, we will explain the case of the new method 1 mentioned above. First, as in the conventional method, each duty cycle is set so that the average of the two time intervals, the first time interval D1 and the second time interval D2, becomes the target value of power supply. For example, if the threshold for transitioning to continuous current mode is 80%, then in order to achieve the target value of 81%, a duty cycle of 62% for the first time interval D1 and a duty cycle of 100% for the second time interval D2 are combined.

[0084] Next, in step S008, calculation 2 is performed to reduce the power step. For example, the power step is reduced by inserting a time interval with a duty cycle of 80%, which is the maximum value that does not result in continuous current mode, between a time interval with a duty cycle of 62% and a time interval with a duty cycle of 100%. In step S009, a control instruction is given with the duty cycle thus set. Once the control is complete, the operation ends in step S010.

[0085] If the target value for power supply is changed, the process will return to step S002 and restart.

[0086] However, when performing the first energization control, for example, if the target value is 95%, the combination to avoid the continuous current mode at calculation 1 in step S007 is 100% → 100% → 100% → 80%, and a state with the minimum power step difference of 20% can be secured, so no recalculation is performed in particular by calculation 2 in step S008.

[0087] The same applies when the target value is 98%: 100% → 100% → 100% → 100% → 100% → 100% → 100% → 100% → 80%.

[0088] Furthermore, the target value for power supply required for fixing (step S003) is changed as appropriate depending on the temperature status of the fixing means 5, the operating mode such as printing, the environment, etc. Therefore, the target value at step S003 is set numerically considering the settings in steps S009 and S008-S009.

[0089] In the aforementioned new method 2-6, the duty cycle setting and other parameters are performed after selecting the first energization control in step S006.

[0090] In the above description of the embodiments, the second power supply control was described as being performed during the printing operation. However, the second power supply control may also be performed during the warm-up of the image forming apparatus 1. [Industrial applicability]

[0091] The fixing control device and image forming apparatus according to the present invention are suitable for copiers, printers, facsimile machines, and multifunction devices equipped with these functions. [Explanation of Symbols]

[0092] 1. Image forming apparatus 5. Fixing means 6. Control means 7 Power means 8. Fixing control device 52 Heater 54 First temperature detection means 81 Rectifier circuit 82 Noise Filter 82 filters 83 Chopper Circuit 84 Current detection means 85 Voltage detection means 86 Second temperature detection means D Refrigeration element L2 Coil (Reactor) 831 Switching element 832 Drive Circuit

Claims

1. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to the third time intervals, each with a different duty cycle of the control signal. The control means further sets the duty cycle to 100% for the first time interval, and when the duty cycle at which the system transitions to a current continuous mode in which current is continuously supplied to the heater is used as a threshold, it sets the duty cycle of the second time interval immediately before or after the first time interval to a value less than or equal to the threshold, sets the duty cycle of the third time interval immediately before or after the second time interval to be even smaller than the duty cycle of the second time interval, and the difference between the duty cycles of the first time interval and the third time interval exceeds (100% - threshold) in the fixing control device.

2. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to the third time intervals, each with a different duty cycle of the control signal. The control means further includes a fixing control device that sets the switching period of the time interval to less than one period of the input power frequency.

3. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to the third time intervals, each with a different duty cycle of the control signal. Furthermore, it includes a selection method between productivity priority mode and flicker reduction priority mode. The control means is a fixing control device that performs power control by setting different duty cycles in the at least three time intervals only when the flicker reduction priority mode is selected.

4. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, A control means that switches the switching element by a control signal to supply power from the chopper means to the heater, and also outputs control signals with different duty cycles to control the power supply to the heater, Equipped with, When the period during which the switching element is switched with a control signal of the same duty cycle is defined as one time interval, the control means is characterized by setting the duty cycle of the control signal such that the power supply to the heater reaches a target value by a combination of different power supplied in at least three time intervals, the first to the third time intervals, each with a different duty cycle of the control signal. The control means further includes a fixing control device that sets the duty cycle such that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold), with the duty cycle at which the heater transitions to a current continuous mode in which current is continuously supplied to the heater being used as a threshold.

5. The fixing control device according to any one of claims 1 to 4, wherein the control means switches the switching element with a control signal of a constant duty cycle if the target value of power supply can be achieved with a duty cycle that does not transition to a continuous current mode in which current is continuously supplied to the heater, and sets the duty cycle such that the power supply reaches the target value by a combination of power supplied in at least three time intervals if the target power supply cannot be achieved without transitioning to a continuous current mode.

6. The fixing control device according to any one of claims 1 to 5, wherein when the target value of power supply switches to an increasing direction, the duty cycle is set in order from the time interval with the smallest duty cycle to the time interval with the largest duty cycle of 100%, and when the target value of supplied power switches to a decreasing direction, the duty cycle is set in order from the time interval with the largest duty cycle of 100% to the time interval with the smallest duty cycle.

7. The fixing control device according to any one of claims 1, 3 to 6, wherein the control means sets the switching period of the time interval to less than one period of the frequency of the input power.

8. The system includes a detection means for detecting the input voltage, The fixing control device according to claim 1 or 4, wherein the threshold value is changed based on the detection result by the detection means.

9. The fixing control device according to any one of claims 1 to 8, wherein the control means sets the duty cycle for each time interval to 100% when the target value of power supply is 95 to 99%, and sets the duty cycle for each time interval to the threshold when transitioning to a current continuous mode in which current is continuously supplied to the heater, with the duty cycle at which the target value of power supply is greater than the threshold and is 81 to 86%.

10. The fixing control device according to any one of claims 1 to 9, wherein the control means sets different duty cycles only when the target value of power supply cannot be achieved by setting only one duty cycle, so that the power supply reaches the target value by a combination of power supplied in multiple time intervals.

11. An image forming apparatus comprising a fixing control device according to any one of claims 1 to 10.

12. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The image forming apparatus equipped with The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is defined as one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. Furthermore, a fixing control method in which, when the duty cycle is set to 100% for the first time interval and the duty cycle when transitioning to a current continuous mode in which current is continuously supplied to the heater is set as a threshold, the duty cycle of the second time interval immediately before or after the first time interval is set to a value less than or equal to the threshold, the duty cycle of the third time interval immediately before or after the second time interval is set to be even smaller than the duty cycle of the second time interval, and the difference between the duty cycles of the first time interval and the third time interval exceeds (100% - threshold).

13. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The image forming apparatus equipped with The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is defined as one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. A fixing control method for setting the duty cycle such that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold), with the duty cycle at which the system transitions to a continuous current mode in which current is continuously supplied to the heater being used as a threshold.

14. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The computer of the image forming apparatus equipped with: The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is considered one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. Furthermore, a program to execute a process where the duty cycle is set to 100% for the first time interval, the duty cycle at which the program transitions to a continuous current mode in which current is continuously supplied to the heater is set as a threshold, the duty cycle for the second time interval immediately before or after the first time interval is set to a value less than or equal to the threshold, the duty cycle for the third time interval immediately before or after the second time interval is set to an even smaller value than the duty cycle for the second time interval, and the difference between the duty cycles of the first time interval and the third time interval exceeds (100% - threshold).

15. A fixing means with a built-in heater, A chopper means for chopping input power, including a reactor, a freewheeling element and a switching element, The computer of the image forming apparatus equipped with: The switching element is switched by a control signal to supply power from the chopper means to the heater, and the power supply to the heater is controlled by outputting control signals with different duty cycles. When the period during which the switching element is switched by a control signal with the same duty cycle is considered one time interval, the duty cycle of the control signal is set such that the power supply to the heater reaches a target value by combinations of different power supplied in at least three time intervals, from the first to the third time interval, each with a different duty cycle of the control signal. A program for executing a process to set the duty cycle such that the difference in duty cycles set in adjacent time intervals does not exceed (100% - threshold), with the duty cycle at which the system transitions to a continuous current mode in which current is continuously supplied to the heater being used as the threshold.

Images