JP2014232247A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem: when a plurality of temperature-controlled heaters in a fixing unit of an image forming apparatus are turned on/off simultaneously, voltage of an AC power supply is changed due to inrush current or abrupt reduction in current consumed.SOLUTION: An image forming apparatus includes: first and second toner-fixing heaters 33, 34; a control circuit 50 which instructs a timing when an AC voltage is applied to each of the heaters; and an output circuit 49 ant triacs 46, 47 for intermittently applying the AC voltage to the first and second heaters 33, 34 on the basis of the instruction of the control circuit 50. The control circuit 50 has a voltage suppression period for limiting the AC voltage in synchronization with on/off of application timing generated based on temperature information of the heaters 33, 34, so that the voltage suppression periods to be generated for each of the first and second heaters 33, 34 may not overlap each other.

Description

  The present invention relates to an image forming apparatus having a thermal fixing device, and more particularly to thermal control of a thermal fixing device having a plurality of heaters.

  Conventionally, this type of electrophotographic apparatus has three types of power loads: a DC power source as an operating power source for each device such as a control means, a heater for a fixing roller as a heat source, and an exposure lamp. A heater that becomes a large load causes a voltage fluctuation in a commercial power supply (hereinafter referred to as an AC power supply) due to an inrush current when the heater is turned on. As a method for suppressing this voltage fluctuation, a method is known in which the phase of the current supplied to the heater is controlled during a transition period after power-on (see, for example, Patent Document 1). Incidentally, when the voltage fluctuation of the AC power supply is large, problems such as flickering of a fluorescent lamp occur.

  In such a conventional electrophotographic apparatus, in order to suppress fluctuations in the power supply voltage, when the power is supplied to the heater, the control means performs a first predetermined phase angle at a first predetermined phase angle set in advance in the control means. When the soft start-on control is performed to keep all the lights on after holding for a period of time and the power supply to the heater is stopped, the control means turns on the second predetermined phase angle preset in the control means or the first predetermined phase. At the corner, soft start-off control is performed to turn off the light after holding for the second predetermined time or the first predetermined time.

Japanese Patent Laid-Open No. 10-186743 (page 3, FIG. 2)

  However, the conventional image forming apparatus is not compatible with a case where a plurality of heaters are provided. When controlling multiple heaters, there are timings when multiple heaters are turned on and off at the same time. Inrush current or sudden decrease in current consumption when turning on and off at the same time is when turning on or off a single heater. The AC power supply voltage fluctuation caused by this is also increased.

  An object of the present invention is to provide an electrophotographic apparatus that solves the problems of the conventional electrophotographic apparatus described above and can suppress fluctuations in the power supply voltage when the heater is turned on and off in the electrophotographic apparatus. It is in.

An image forming apparatus according to the present invention includes:
A plurality of heaters for toner fixing, a control unit for instructing timing for individually applying an AC voltage to the plurality of heaters, and an AC voltage is intermittently applied to the plurality of heaters based on an instruction from the control unit Switching means for
The control means provides a voltage suppression period for limiting the AC voltage in synchronization with the application timing generated based on the temperature information of the heater at the time of on and / or off,
The voltage suppression periods generated individually for each of the plurality of heaters do not overlap each other.

  According to the present invention, when the AC voltage is applied to a plurality of heaters, the voltage suppression periods generated when the application to each heater is turned on and off do not overlap each other. The influence (voltage fluctuation) at the time of OFF can be suppressed.

1 is a main part configuration diagram showing a main part configuration of an image forming apparatus according to a first embodiment of the present invention; 1 is an external perspective view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an external perspective view schematically showing a main configuration of a fixing unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration of a heater control unit that controls the temperature of the heating roller by energizing the first heater and the second heater in the first embodiment. FIG. 4 is a waveform diagram of each part of the heater control unit in a state where avoidance control is performed in the first embodiment, and (a) shows waveforms of on / off control signals of the first heater and the second heater output by the control circuit. (B) shows the voltage waveform applied to the first heater and the second heater. 5 is a flowchart showing a flow of avoidance control for avoiding an overlap between a rising period of an on / off control signal of a first heater that occurs first and a rising period of an on / off control signal of a second heater that occurs later in the first embodiment. . 4 is a flowchart showing a flow of avoidance control for avoiding an overlap between a rising period of an on / off control signal of a second heater that occurs first and a rising period of an on / off control signal of a first heater that occurs later in the first embodiment. . It is a reference waveform figure with which it uses for operation | movement description of a heater control part. FIG. 10 is a block diagram illustrating a configuration of a heater control unit that controls the temperature of a heating roller by energizing a first heater and a second heater in Embodiment 2. FIG. 6 is a waveform diagram of each part of a heater control unit in a state where avoidance control is performed in Embodiment 2, and (a) shows waveforms of on / off control signals of a first heater and a second heater output by a control circuit. , (B) shows voltage waveforms applied to the first heater and the second heater. 7 is a flowchart illustrating a flow of avoidance control for avoiding an overlap between the first heater on / off control signal falling period and the second heater on / off control signal falling period that occur later in the second embodiment. It is. 7 is a flowchart illustrating a flow of avoidance control for avoiding an overlap between a fall period of an on / off control signal of a second heater that occurs first and a fall period of an on / off control signal of a first heater that occurs later in the second embodiment. It is. It is a reference waveform figure with which it uses for operation | movement description of a heater control part. FIG. 10 is a block diagram illustrating a configuration of a heater control unit that controls the temperature of a heating roller by energizing a first heater and a second heater in Embodiment 3. FIG. 10 is a waveform diagram of on / off control signals for a first heater and a second heater output by a control circuit in a state where avoidance control is being performed in the third embodiment. (A) is a voltage waveform diagram applied to the first heater and the second heater in the rise period in the third embodiment, and (b) is a diagram for the first heater and the second heater in the fall period in the third embodiment. It is an applied voltage waveform diagram. In Embodiment 3, it is a flowchart which shows the flow of the duty control of the rising period of the on-off control signal of the 1st heater which generate | occur | produces previously, and the rising period of the on-off control signal of the 2nd heater which generate | occur | produces later. In Embodiment 3, it is a flowchart which shows the flow of the duty control of the rising period of the ON / OFF control signal of the 2nd heater which generate | occur | produces previously, and the rising period of the ON / OFF control signal of the 1st heater which generate | occur | produces later. In Embodiment 3, it is a flowchart which shows the flow of the duty control of the fall period of the ON / OFF control signal of the 1st heater which generate | occur | produces previously, and the fall period of the ON / OFF control signal of the 2nd heater which generate | occur | produces later. In Embodiment 3, it is a flowchart which shows the flow of the duty control of the falling period of the ON / OFF control signal of the 2nd heater which generate | occur | produces previously, and the falling period of the ON / OFF control signal of the 1st heater which generate | occur | produces later.

Embodiment 1 FIG.
FIG. 1 is a main part configuration diagram showing the main part configuration of the image forming apparatus according to the first embodiment of the present invention, and FIG. 2 is an external perspective view thereof.

  As shown in FIG. 1, the image forming apparatus 100 is roughly divided into a paper feeding unit 1, an image forming unit 2, a fixing unit 3, a double-sided printing unit unit 4, and a paper discharge unit 5, and is divided into black (K), yellow ( Y), magenta (M), and cyan (C) as a color electrophotographic printer capable of printing four colors. The paper feed unit 1 includes a paper feed cassette 6 for setting the recording paper 8, a pick-up roller 7 for picking up the recording paper 8 from the paper cassette 6 and feeding it to the paper conveyance path, and the recording paper 8. 2 includes a pair of registration rollers 10 for transporting to the second position.

  The image forming unit 2 includes four toner image forming units 19K, 19Y, 19M, and 19C arranged in series in order from the upstream side in the conveyance direction of the recording paper 8 (if there is no particular need to distinguish, the toner image forming unit LED heads 15K, 15Y, 15M, and 15C arranged corresponding to the respective toner image forming portions 19 (may be simply referred to as LED heads 15 when there is no need to distinguish between them), And a transfer unit 21 that transfers the toner image formed by the toner image forming unit 19 to the upper surface of the sheet by Coulomb force.

  The toner image forming unit 19K is a black (K) toner image, the toner image forming unit 19Y is a yellow (Y) toner image, the toner image forming unit 19M is a magenta (M) toner image, and the toner image forming unit 19C. Respectively form cyan (C) toner images. Each toner image forming unit 19 has a common configuration except that the toner to be used is different.

  Each toner image forming unit 19 comes in contact with the photosensitive drum 11 and the photosensitive drum 11 whose peripheral surface is made of a photoconductive material, and the charging roller 12 uniformly charges the surface of the photosensitive drum 11 to a high voltage. The LED head 15 disposed on the upper surface of the photosensitive drum 11 is contacted with the developing roller 13 for developing the electrostatic latent image formed on the surface of the photosensitive drum 11 with toner, and the developing roller 13 is brought into contact with the developing roller 13. 13 includes a toner supply roller 14 for supplying toner 13, a cleaner 20 for removing toner remaining on the surface of the photosensitive drum 11 after transfer, and a toner cartridge 16 detachably provided to store and supply toner.

  Each LED head 15 is held by the cover 23 and is disposed at a predetermined position of the corresponding toner image forming unit 19 when the cover 23 is closed, and is charged and rotated in the arrow direction. The surface is selectively exposed to form an electrostatic latent image.

  The transfer unit 21 is disposed opposite to the transfer belt 17 that conveys the recording paper 8 conveyed from the paper supply unit 1 in the direction of the arrow, and the photosensitive drum 11 of each toner image forming unit 19 via the transfer belt 17. The four transfer rollers 18 are provided, and the toner images of the respective colors formed on the photosensitive drums 11 of the respective toner image forming portions 19 are sequentially superimposed and transferred onto the recording paper 8 by Coulomb force.

  The fixing unit 3 includes a heating roller 31 and a pressure roller 32 disposed in pressure contact with the heating roller 31, melts the toner transferred to the recording paper 8 that is nipped and conveyed therebetween, and melts the toner. The image is heat-fixed on the recording paper 8. The recording sheet 8 on which the toner image is fixed by the fixing unit 3 is discharged after being conveyed to the sheet discharge unit 5 or is conveyed to the duplex printing unit unit 4 via the switching plate 22 for duplex printing. The image forming unit 2 again forms an image on the opposite surface of the sheet.

  FIG. 3 is an external perspective view schematically showing a main configuration of the fixing unit 3.

  The fixing unit 3 includes a heating roller 31 as a heating rotation member and a pressure roller 32 as a pressure rotation member. Inside the heating roller 31, two heating heaters as heating means, that is, a first heater 33 and a second heater 34 are arranged, and an upper portion of the heating roller 31 is arranged at a substantially central position in the axial direction of the heating roller 31. A temperature sensor 35 for detecting the surface temperature of the heating roller 31 is provided. The heating roller 31 is rotationally driven in the direction of the arrow by a rotational driving means (not shown).

  The pressure roller 32 includes a fixing belt 36, a fixing roller 37, and a pad 38. The endless fixing belt 36 is stretched around a fixing roller 37 and a pad 38 disposed on the inner side thereof, and rotates as the fixing roller 37 rotates. The fixing roller 37 is pressed against the heating roller 31 via the fixing belt 36 to form a nip portion. Here, the fixing roller 37 rotates following the rotation of the heating roller 31.

  FIG. 4 is a block diagram illustrating a configuration of the heater control unit 40 that controls the temperature of the heating roller 31 by energizing the first heater 33 and the second heater 34.

  As shown in the figure, a zero-cross detection circuit 48 serving as a zero-cross detection means connected between terminals of the AC power supply 41 detects that the polarity of the AC power supply 41 is inverted (zero-crossing). Is output to a control circuit 50 as control means. Further, between the terminals of the AC power supply 41, a first heater 33 and a triac 46 connected in series, and a second heater 34 and a triac 47 connected in series are connected. The triac 46 turns on / off the energization of the first heater 33, and the triac 47 turns on / off the energization of the second heater 34.

  The temperature sensor 35 that detects the surface temperature of the heating roller 31 is connected to the temperature detection unit 45, and the temperature detection unit 45 outputs temperature information detected by the temperature sensor 35 to the control circuit 50.

  In the control circuit 50, as will be described later, a fixing temperature control unit 51 that sets energization (on) time to the first heater 33 and the second heater 34 based on temperature information from the input temperature detection unit 45, and In the rise periods Ta and Tb (FIG. 5) as voltage suppression periods that rise simultaneously with the on-time periods T12 and T22 (FIG. 5), the voltage limit for setting the non-energization (off) periods Ta1 and Tb1 from the zero cross of the AC power supply The on-phase control unit 52 is provided as a unit. The output circuit 49 receives the on / off control signal output from the control circuit 50, generates a triac drive pulse signal based on the on / off control signal, and controls on / off of the triac 46 and the triac 47. The output circuit 49 and the triacs 46 and 47 correspond to switching means.

  FIG. 8 is a waveform diagram for explaining the operation of the heater control unit 40. FIG. 8A shows waveforms of ON / OFF control signals of the first heater 33 and the second heater 34 output from the control circuit 50. FIG. (B) shows voltage waveforms applied to the first heater 33 and the second heater 34. However, the waveform shown in FIG. 8 is a reference waveform diagram in which the overlap avoidance control (hereinafter also referred to simply as avoidance control) of the voltage suppression period, which will be described later, based on the present invention is not performed. The formed waveform will be described later with reference to the waveform diagram shown in FIG.

  For example, as shown in FIG. 8A, the fixing temperature control unit 51 generates a rectangular signal with a duty ratio D1 (T12 / T11) for the first heater 33 in the on-time period T12 in a cycle T11. A rectangular signal with a duty ratio D2 (T22 / T21) of the on-time period T22 is generated for the second heater 34 at a cycle T21, and the duty ratios D1 and D2 are based on temperature information input from the temperature detection unit 45. Control is performed so that the temperature detected by the temperature sensor 35 becomes a predetermined temperature.

  The on-time phase control unit 52 rises at the rise of each on-time control signal for the first heater 33 at the rise of each on-time period T12, and at the rise of each on-time control signal for the second heater 34 at the rise of each on-time period T22. In the period Tb, as shown in FIG. 5B, non-energization (off) periods Ta1 and Tb1 from the preceding zero cross are set between the zero cross points before and after the power supply voltage waveform. Specifically, for example, in the rising period Ta, a pulse Pa is generated at the timing (phase angle) after each non-energization period Ta1 from each zero cross, and in the rising period Tb, the timing (phase) after each non-energizing period Tb1 from each zero cross. A pulse Pb is generated at the angle.

  The output circuit 49 drives the triacs 46 and 47 based on the on / off control signal input from the control circuit 50 and applies the applied voltage having the waveform shown in FIG. 8B to the first heater 33 and the second heater 34. . Specifically, for the triac 46, a drive pulse is generated at the timing from the zero cross to the non-energization period Ta1 in each rising period Ta of the on / off control signal, and continuously in the on-time period T12 other than the rising period Ta. Generated drive pulses. For the triac 47, a drive pulse is generated at the timing from the zero cross to the non-energization period Tb1 in each rising period Tb of the on / off control signal, and a continuous driving pulse is generated in the on-time period T22 other than the rising period Tb. Occur.

  The triacs 46 and 47 are located between the preceding and following zero crosses, and when receiving a drive pulse, the triacs 46 and 47 change from the off (open) state to the on (short circuit) state and turn off again at the next zero cross. Therefore, a voltage is applied to the first heater 33 during the rising period Ta except the non-energized (off) period Ta1, and the voltage of the AC power supply remains unchanged during the on period other than the rising period Ta of the on / off control signal. Applied. Similarly, a voltage is applied to the second heater 34 during the rising period Tb except the non-energized (off) period Tb1, and the voltage of the AC power supply remains unchanged during the on period other than the rising period Tb of the on / off control signal. Applied.

  It should be noted that the application time of the voltage applied to the first heater 33 and the second heater 34 in each rising period Ta, Tb is limited in the first heater 33 and the second heater 34 at a low temperature before heating. This is to prevent a large inrush current from flowing because the value is low.

  As described above, in the description of the waveform diagram of FIG. 8 which is a reference waveform diagram, the fixing temperature control unit 51 has rectangular shapes with predetermined periods T11 and T21 as the first heater on / off signal and the second heater on / off signal, respectively. In this case, the rising period Ta of the first heater on / off signal and the rising period Tb of the second heater on / off signal overlap each other. That is, in FIG. 8, the rising period Tb of the second heater on / off signal rising at time t11 overlaps the rising period Ta of the first heater on / off signal.

  In the rising periods Ta and Tb, although the voltage application time is limited, a spire inrush current flows during each period, particularly when the first voltage is applied. If they overlap, an excessive inrush current superimposed will occur.

  For this reason, in the control circuit 50 of the present embodiment, avoidance control is performed such that the rising period Ta and the rising period Tb do not overlap. As described above, the waveform of the on / off control signal shown in the reference waveform diagram of FIG. 8 indicates a waveform in a state where this avoidance control based on the present invention is not performed, and FIG. It is a wave form diagram of each part of heater control part 40 in the state where the avoidance control based on is performed.

  When the avoidance control according to the present invention is performed, as shown in FIG. 5, each of the ON / OFF control signals of the first heater 33 and the second heater 34 output from the control circuit 50 includes a rising period Ta and a rising period Tb. Generated so as not to overlap. That is, as shown in FIG. 8, when the rising period Ta of the preceding on / off control signal of the first heater overlaps with the rising period Tb of the following on / off control signal of the second heater, this subsequent rising period Tb As shown in FIG. 5, avoidance control is performed in which only the rising timing of the on-time period T22 including “” is shifted backward to a position where they do not overlap.

  FIG. 6 is a block diagram for avoiding the overlap of the rising period Tb of the on / off control signal of the second heater that occurs later with the rising period Ta of the on / off control signal of the first heater that occurs earlier as described above. FIG. 6 is a flowchart showing a flow of avoidance control mainly performed by the fixing temperature control unit 51. Hereinafter, the avoidance control will be described according to this flow with reference to FIGS. 4 and 5.

  The avoidance control processing flow of the on / off control signal of the second heater is periodically performed at a predetermined cycle T21 of the on / off control signal of the second heater. Whether or not the fixing temperature control unit 51 is in the period of the rising period Ta of the on / off control signal of the first heater before starting the on-time period T22 according to the predetermined cycle T21 of the on / off control signal of the second heater. Is confirmed (step S101). Here, when it is not the rising period Ta (No in step S101), the on-time period T22 is immediately started up (step S103). At the same time, the rising period Td also rises.

  On the other hand, if it is determined in step S101 that the first heater ON / OFF control signal is in the rising period Ta (step S101, Yes), wait until the rising period Ta ends (step S102, No). When the rising period Ta ends (step S102, Yes), the on-time period T22 and the rising period Td are started (step S103).

  Once the on-time period T22 rises, this state is maintained until the on-time period T22 elapses (step S104, No). When the on-time period T22 elapses (step S104, Yes), the on-time period T22. (Step S105), and the avoidance control process for the on / off control signal of the second heater is terminated.

  The above processing will be further described with reference to the time chart of FIG.

  For example, the fixing temperature control unit 51 attempts to start up the on-time period T22 at time t11 shown in FIG. 5 according to a predetermined cycle T21 of the on / off control signal of the second heater. Since the on / off control signal is in the rising period Ta, the fixing temperature control unit 51 delays the rising of the on-time period T22 until time t12 when the rising period Ta ends. That is, the fixing temperature control unit 51 controls the phase of the on / off control signal so that the rising period Tb of the on / off control signal of the second heater that occurs later does not overlap the rising period Ta of the on / off control signal of the first heater. To do.

  The fixing temperature control unit 51 tries to raise the on-time period T22 again at time t13 when the period T21 has elapsed from time t11. Here, the period of the rising period Ta of the on-off control signal of the first heater is set. Since it is not in the middle, the on-time period T22 is started at the original timing.

  Further, even when the rise timing of the on-time period T22 is shifted by the avoidance control, the on-time phase control unit 52 starts from each zero cross in the rise period Tb at the rise of the on-time period T22 as described above. The pulse Pb is generated at the timing after the non-energization period Tbo.

  FIG. 7 mainly shows fixing in order to avoid the overlap of the rising period Ta of the first heater on / off control signal that occurs later with the rising period Tb of the first heater on / off control signal that occurs earlier. It is a flowchart which shows the flow of the avoidance control which the temperature control part 51 performs, and this flow is periodically performed with the predetermined period T11 of the on-off control signal of a 1st heater. Hereinafter, the avoidance control will be described according to this flow with reference to FIGS. 4 and 5.

  Whether or not the fixing temperature control unit 51 is in the period of the rising period Tb of the on / off control signal of the second heater prior to starting the on-time period T12 according to the predetermined cycle T11 of the on / off control signal of the first heater. Is confirmed (step S201). If it is not the rising period Tb (step S201, No), the on-time period T12 is immediately started up (step S203).

  On the other hand, if it is determined in step S201 that the second heater on / off control signal is in the rising period Tb (step S201, Yes), wait until the rising period Tb ends (step S202, No). At the stage where the rising period Tb is completed (step S202, Yes), the on-time period T12 is started (step S203).

  Once the on-time period T12 rises, this state is maintained until the on-time period T12 elapses (No in step S204), and when the on-time period T12 elapses (step S204, Yes), the on-time period T12. (Step S205) and the avoidance control process of the on / off control signal of the first heater is ended.

  As described above, the same avoidance control as that of the second heater on / off control signal is performed for the on / off control signal of the first heater, and is generated later with respect to the rising period Tb of the on / off control signal of the second heater. The rising periods Ta of the ON / OFF control signals of the first heater are not overlapped.

  In the present embodiment, the fixing temperature control unit 51 is configured to control the duty ratio of the rectangular signal based on the temperature information. However, the present invention is not limited to this, and the temperature information is simply predetermined. An on / off signal for turning on / off to be a value may be output.

  In the present embodiment, the fixing temperature control unit 51 has been described so as to shift the state change timing so that the rising periods do not overlap with each other. However, the present invention is not limited to this, and the on-phase control is performed. The unit 52 itself may be configured to shift the start timing of the rising periods so that the rising periods do not overlap each other.

  As described above, according to the image forming apparatus of the present embodiment, since the rising periods Ta and Tb of the first and second heaters of the fixing device do not overlap each other, they are generated by an inrush current when the heaters are turned on. It is possible to suppress voltage fluctuations of the commercial power supply (hereinafter referred to as AC power supply). Thereby, for example, an effect of reducing flickering of a fluorescent lamp can be expected.

Embodiment 2. FIG.
FIG. 9 is a block diagram showing a configuration of the heater control unit 140 employed in the image forming apparatus according to the second embodiment based on the present invention.

  The image forming apparatus employing the heater control unit 140 is mainly different from the image forming apparatus according to the first embodiment employing the heater control unit 40 shown in FIG. 4 in the control circuit 150 of the heater control unit 140. This is the point that an off-time phase control unit 153 as a voltage limiting unit is added and the control contents of the fixing temperature control unit 151. Accordingly, in the image forming apparatus employing the heater control unit 140, the same reference numerals are given to the parts common to the image forming apparatus 100 (FIG. 1) of the first embodiment, or the drawings are omitted. Omitted, the differences are emphasized. The main configuration of the image forming apparatus according to the present embodiment is the same as the main configuration of the image forming apparatus 100 according to the first embodiment shown in FIG. 1 except for the fixing temperature control unit 151 and the heater control unit 140. 1 to 3 will be referred to as necessary.

  As shown in FIG. 9, in the control circuit 150, energization (on) time to the first heater 33 and the second heater 34 is set based on temperature information from the input temperature detection unit 45, as will be described later. In the fixing temperature control unit 151 and the rising periods Ta and Tb (FIG. 10) as voltage suppression periods rising simultaneously with the on-time periods T12 and T22 (FIG. 10), the non-energized (off) period Ta1 from the zero cross of the AC power supply , Tb1 (FIG. 5) and the on-state phase control unit 52, and the falling periods Tc, Td (FIG. 10) as voltage suppression periods rising simultaneously with the falling of the on-time periods T12, T22 Is provided with an off-time phase control unit 153 that sets non-energized (off) periods Tc1 and Td1 (FIG. 10). The output circuit 49 receives the on / off control signal output from the control circuit 150, generates a triac drive pulse signal based on the on / off control signal, and controls on / off of the triac 46 and the triac 47.

  FIG. 13 is a waveform diagram for explaining the operation of the heater control unit 140. FIG. 13A shows waveforms of on / off control signals of the first heater 33 and the second heater 34 output from the control circuit 150. FIG. (B) shows voltage waveforms applied to the first heater 33 and the second heater 34. However, the waveform shown in FIG. 13 is a reference waveform diagram in which avoidance control to be described later based on the present invention is not performed, and for the waveform formed based on the present invention, refer to the waveform diagram shown in FIG. It will be described later.

  For example, as shown in FIG. 13A, the fixing temperature control unit 151 generates a rectangular signal with a duty ratio D1 (T12 / T11) for the on-time period T12 in the cycle T11 with respect to the first heater 33. A rectangular signal having a duty ratio D2 (T22 / T21) of the on-time period T22 with a period T21 is generated for the second heater 34, and the duty ratios D1 and D2 are based on temperature information input from the temperature detection unit 45. The temperature detected by the temperature sensor 35 is controlled to be a predetermined temperature.

  As shown in FIG. 13B, the off-time phase control unit 153 performs the falling period Tc of the on / off control signal for the first heater 33 and the falling period Td of the on / off control signal for the second heater 34, as shown in FIG. A non-energization (off) period Tc1, Td1 from the preceding zero cross is set between the zero cross points before and after the power supply voltage waveform. Specifically, for example, in the falling period Tc, the pulse Pc is generated at the timing (phase angle) after the non-energization period Tc1 from each zero cross, and in the falling period Td, the timing after the non-energization period Td1 from each zero cross. A pulse Pd is generated at (phase angle).

  The output circuit 49 drives the triacs 46 and 47 based on the on / off control signal input from the control circuit 150 and applies the applied voltage having the waveform shown in FIG. 13B to the first heater 33 and the second heater 34. . Specifically, for the triac 46, a drive pulse is generated at the timing from the zero cross to the non-energization period Tc1 in each falling period Tc of the ON / OFF control signal, and the ON period other than the rising period Ta and the falling period Tc is turned on. In the time period T12, continuous drive pulses are generated. For the triac 47, a drive pulse is generated at the timing from the zero cross to the non-energization period Td1 in each falling period Td of the on / off control signal, and continuously in the on period other than the rising period Tb and the falling period Td. Generated drive pulses.

  The triacs 46 and 47 are located between the preceding and following zero crosses, and when receiving a drive pulse, the triacs 46 and 47 change from the off (open) state to the on (short circuit) state and turn off again at the next zero cross. Accordingly, a voltage is applied to the first heater 33 during the fall period Tc except the non-energization (off) period Tc1, and during the on period other than the rise period Ta and the fall period Tc of the on / off control signal. The voltage of the AC power supply is applied as it is. Similarly, a voltage is applied to the second heater 34 during the fall period Td except for the non-energization (off) period Td1, and during the on period other than the rise period Tb and the on rise period Td of the off control signal. The voltage of the AC power supply is applied as it is.

  Note that, in each falling period Tc, Td, the application time of the voltage applied to the first heater 33 and the second heater 34 is limited by a sudden change in current consumption in the first heater 33 and the second heater 34. It is to suppress.

  As described above, in the description of the waveform diagram of FIG. 13 which is a reference waveform diagram, the fixing temperature control unit 151 has rectangular shapes of predetermined periods T12 and T22 as the first heater on / off signal and the second heater on / off signal, respectively. Although it has been described that the wave signal is generated, in this case, the falling period Tc of the first heater on / off signal overlaps with the falling period Td of the second heater on / off signal. That is, in FIG. 13, the falling period Td of the second heater on / off signal started at time t22 overlaps with the falling period Tc of the first heater on / off signal.

  When the falling periods Tc and Td overlap, particularly at the timing when the first heater and the second heater are turned off at the same time, the current consumption for the AC power supply decreases sharply. Ascends to cause flickering of fluorescent lamps.

  For this reason, in the control circuit 150 of the present embodiment, avoidance control is performed so that the falling period Tc and the rising period Td do not overlap. As described above, the waveform of the on / off control signal shown in the reference waveform diagram of FIG. 13 shows a waveform in a state where this avoidance control based on the present invention is not performed, and FIG. It is a wave form chart of each part of heater control part 140 in the state where the avoidance control based on is performed.

  When the avoidance control according to the present invention is performed, as shown in FIG. 10, the on / off control signals of the first heater 33 and the second heater 34 output from the control circuit 150 are the fall period Ta and the fall period Td. It is generated so that and do not overlap. That is, as shown in FIG. 13, when the falling period Tc of the on / off control signal of the preceding first heater and the falling period Td of the on / off control signal of the subsequent second heater overlap, As shown in FIG. 10, avoidance control is performed in which only the falling timing of the on-time period T22 preceding the falling period Td extends backward to a position where they do not overlap.

  FIG. 11 avoids the case where the fall period Td of the second heater on / off control signal generated later overlaps the fall period Tc of the first heater on / off control signal generated earlier as described above. Therefore, here is a flowchart showing a flow of avoidance control mainly performed by the fixing temperature control unit 151. Hereinafter, the avoidance control will be described according to this flow with reference to FIGS. 9 and 10. The avoidance control for avoiding the overlap of the rising period Ta of the on / off control signal of the first heater and the rising period Tb of the on / off control signal of the second heater is as described in the first embodiment. The description here is omitted.

  The avoidance control processing flow of the on / off control signal of the second heater is started immediately before the end of the on-time period T22 defined in step S105 of the flowchart of FIG. 6 described in the first embodiment, for example. Prior to ending the on-time period T22, the fixing temperature control unit 151 checks whether or not it is during the falling period Tc of the first heater on-off control signal (step S301). Here, if it is not the falling period Tc (No at Step S301), the on-time period T22 is immediately terminated, and at the same time, the falling period Td is raised by the off-phase control unit 153 (Step S303).

  In the present embodiment, as will be described later, the length of the on-time period T22 may be extended in the course of the avoidance control process, and the initial value of the on-time period T22 before the extension is set to T221. The on-time period T22 may be distinguished as T222.

  On the other hand, if it is determined in step S301 that the first heater on / off control signal falls during the fall period Tc (step S301, Yes), the process waits until the fall period Tc ends (step S302, No). ) When the falling period Tc ends (Yes at Step S302), the on-time period T22 ends, and at the same time, the falling phase control unit 153 raises the falling period Td (Step S303).

  The off-time phase control unit 153 maintains this state until the falling period Td elapses (step S304, No), and ends the falling period Td when the falling period Td elapses (step S304, Yes). Then, the avoidance control process of the on / off control signal for the second heater is terminated.

  The above processing will be further described with reference to the time chart of FIG.

  For example, according to the end of the on-time period T22 defined in step S105 of the flowchart of FIG. 6 described in the first embodiment, the on-time period T22 is to be ended at the time t22 shown in FIG. Since the heater on / off control signal falls during the fall period Tc, the fixing temperature control unit 151 delays the rise of the on-time period T22 until time t23 when the fall period Tc ends. That is, the on-time period T22 is extended from its initial value T221 to T222, and the falling period Td of the second heater on-off control signal generated later is overlapped with the falling period Tc of the first heater on-off control signal. The phase of the on / off control signal is controlled so as not to occur.

  FIG. 12 shows a case where the fall period Tc of the first heater ON / OFF control signal generated later overlaps the fall period Td of the ON / OFF control signal of the second heater that occurs earlier. FIG. 6 is a flowchart showing a flow of avoidance control mainly performed by the fixing temperature control unit 151. Hereinafter, the avoidance control will be described according to this flow with reference to FIGS. 9 and 10.

  The avoidance control processing flow of the first heater on / off control signal is started immediately before the end of the on-time period T12 defined in step S205 of the flowchart of FIG. 7 described in the first embodiment, for example. Prior to ending the on-time period T12, the fixing temperature control unit 151 checks whether or not it is during the falling period Td of the second heater on-off control signal (step S401). Here, if it is not the rising period Td (No in step S401), the on-time period T12 is immediately terminated, and at the same time, the falling period control unit 153 raises the falling period Tc (step S403).

  On the other hand, if it is determined in step S401 that the second heater ON / OFF control signal falls during the falling period Td (step S401, Yes), the process waits until the falling period Td ends (step S402, No). ) When the falling period Td ends (step S402, Yes), the on-time period T12 ends, and at the same time, the falling phase control unit 153 raises the falling period Tc (step S403).

  The off-time phase control unit 153 maintains this state until the falling period Tc elapses (step S404, No), and ends the falling period Tc when the falling period Tc elapses (step S404, Yes). Then, the avoidance control process of the on / off control signal of the first heater is ended (step S405).

  As described above, the avoidance control similar to the on / off control signal of the second heater is performed also on the on / off control signal of the first heater, and later with respect to the falling period Td of the on / off control signal of the second heater. The falling periods Tc of the generated on / off control signals of the first heater are prevented from overlapping.

  In the present embodiment, the fixing temperature control unit 151 is configured to control the duty ratio of the rectangular signal based on the temperature information. However, the present invention is not limited to this, and the temperature information is simply a predetermined value. An on / off signal for turning on / off to be a value may be output.

  In the present embodiment, the fixing temperature control unit 151 has been described so as to shift the state change timing so that the falling periods do not overlap with each other. However, the present invention is not limited to this, and the off-phase The control unit 153 itself may be configured to shift the start timing of the rising periods so that the rising periods do not overlap each other.

  As described above, according to the image forming apparatus of the present embodiment, since the falling periods Tc and Td of the first and second heaters of the fixing device do not overlap each other, rapid consumption when the heaters are turned off. Reduction of current can be suppressed, voltage fluctuation of the AC power supply can be reduced, and flickering of the fluorescent lamp can be suppressed.

Embodiment 3 FIG.
FIG. 14 is a block diagram showing a configuration of the heater control unit 240 employed in the image forming apparatus according to the third embodiment based on the present invention.

  The image forming apparatus employing the heater control unit 240 is mainly different from the image forming apparatus according to the second embodiment employing the heater control unit 140 shown in FIG. 9 in the control circuit 250 of the heater control unit 240. The on-duty control unit 255 is added to the on-phase control unit 252 as a voltage limiting unit, and the off-duty control unit 256 is added to the off-phase control unit 253 as a voltage limiting unit. Accordingly, in the image forming apparatus employing the heater control unit 240, the same reference numerals are given to the parts common to the image forming apparatus 100 (FIG. 1) of the first embodiment described above, or the drawings are omitted. Omitted, the differences are emphasized. The main part configuration of the image forming apparatus according to the present embodiment is the same as that of the main part of the image forming apparatus 100 according to the first embodiment shown in FIG. 1 except for the heater control unit 240. Reference is made to FIG.

As shown in FIG. 14, the on-time phase control unit 252 in the control circuit 250 includes a non-energization period Ta _M from the zero cross of the AC power supply in the rising periods Ta and Tb (FIG. 15) of the on-time periods T12 and T22. (M is 1 to m) and Tb _N (M is 1 to n) (FIG. 16) are sequentially set to have an on-duty control unit 255, and the off-phase control unit 253 in the control circuit 250 includes In the falling periods Tc and Td (FIG. 15) following the on-time periods T12 and T22, the non-energization periods Tc _P (P is 1 to p) and Td _Q (Q is 1 to q) from the zero cross of the AC power supply (FIG. 16) has an off-duty control section 256 that sequentially sets 16).

  FIG. 15 is a waveform diagram of the on / off control signal of the first heater 33 and the on / off control signal of the second heater 34 output from the control circuit 250 of the third embodiment. As shown in the figure, each of these on / off control signals is generated by the rising periods Ta and Tb and the falling edges by the avoidance control by the fixing temperature control unit 151 as described in the first and second embodiments. The periods Tc and Td are formed so as not to overlap each other in time.

  FIG. 16 shows applied voltage waveforms for the first heater 33 and the second heater 34, and FIG. 16 (a) shows applied voltage waveforms in the rising periods Ta and Tb formed before and after. b) shows the applied voltage waveforms in the falling periods Tc and Td, which are formed similarly before and after.

First, the operation of the on-phase control unit 252 will be described with reference to FIG. The on-duty control unit 255 sets the non-energization period Ta _M (M is 1 to m) from each zero cross in the rising period Ta over m times. Specifically, in the rising period Ta, the pulse Pa is generated at a timing (phase angle) after the non-energization period Ta _M (M is 1 to m) from each zero cross.

The rising period Ta here is determined in advance, and is set to a length corresponding to 7.5 cycles of the AC power source, for example, and therefore the set number here is 15 (m = 15). The on-duty control unit 255 is set so that the non-energization period Ta _M is decreased by 5% of the half cycle of the AC power supply here so that the periods decrease sequentially. Accordingly, the energization period for each half wave of the AC power supply in the rising period Ta increases by 5% sequentially from 5% to 75%.

Similarly, the on-duty control unit 255 sets a non-energization period Tb _N (N is 1 to n) from each zero cross in the rising period Tb n times. Specifically, in the rising period Tb, the pulse Pb is generated at the timing (phase angle) after the non-energization period Tb _N from each zero cross.

Here, the rising period Tb is determined in advance, and is set to, for example, a length corresponding to five cycles of the AC power supply. Therefore, the number of times set here is 10 (n = 10). On-time duty control unit 255, the de-energized period Tb _N, as the period is reduced sequentially, here, are set so decreases by 5% of the half cycle of the AC power source. Therefore, the energization period for each half wave of the AC power source in the rising period Tb is increased by 5% sequentially from 5% to 50%.

The output circuit 49 drives the triacs 46 and 47 based on the on / off control signal input from the control circuit 250 and applies the applied voltage having the waveform shown in FIG. 16A to the first heater 33 and the second heater 34. . Specifically, for the triac 46, a drive pulse is generated at the timing of Ta _M (M is 1 to m) from each zero cross in each rising period Ta of the ON / OFF control signal, and the ON period other than the rising period Ta is turned on. In the time period T12, continuous drive pulses are generated. For the triac 47, a drive pulse is generated at the timing of Tb _N (N is 1 to n) from the zero cross in each rising period Tb of the on / off control signal, and in the on time period T22 other than the rising period Tb. Generate continuous drive pulses.

The triacs 46 and 47 are located between the preceding and following zero crosses, and when receiving a drive pulse, the triacs 46 and 47 change from the off (open) state to the on (short circuit) state and turn off again at the next zero cross. Therefore, a voltage is applied to the first heater 33 in a period other than the non-energization (off) period Ta _M (M is 1 to m) in the rising period Ta, and an on period other than the rising period Ta of the on / off control signal. The voltage of the AC power supply is applied as is. Similarly, a voltage is applied to the second heater 34 in a period other than the non-energized (off) period Tb _N (N is 1 to n) in the rising period Tb, and an on period other than the rising period Tb of the on / off control signal. The voltage of the AC power supply is applied as is.

  In FIG. 17, as described above, avoidance control is performed so that the rising period Tb of the second heater on / off control signal generated later does not overlap the rising period Ta of the first heater on / off control signal generated earlier, It is a flowchart showing a flow of duty control for generating a pulse Pb in a rising period Tb. Hereinafter, the duty control will be described with reference to FIGS. 15 and 16A according to this flow.

The timing at which this flow is started and the processing from step S501 to step S503 are exactly the same as the start timing and the processing from step S101 to step S103 described in the flow shown in FIG. That is, the fixing temperature control unit 151 raises the on-time period T22 so that the rise period Tb of the second heater on / off control signal does not overlap the rise period Ta of the first heater on-off control signal. Here, as described above, the rising period Tb is set to a length corresponding to five cycles of the AC power supply, and the non-energization period Tb _N (N is 1 to 10) is sequentially set to 5 of the half cycle of the AC power supply. It is set to decrease by%.

The on-time phase control unit 252 sets the count number N of the duty control counter of the on-time duty control unit 255 to 1 in the rising period Tb that starts simultaneously with the on-time period T22 (step S504), and the non-energization period from zero crossing The _first pulse Pb is generated at a timing of Tb ₁ , that is, 95% of the half cycle of the AC power supply (step S505). After that, it is determined whether or not the rising period Tb of the second heater has ended (step S506). If it does not end (step S506, No), the count number N is incremented by 1 (step S507), and step S505. Return to.

Accordingly, in steps S504 to S507, as shown in FIG. 16A, in the rising period Tb, the non-energization time Tb _{N is set} to 5 of the half cycle of the AC power source from Tb ₁ to Tb ₁₀ for each half wave of the AC power source. In other words, the energization period is increased by 5% sequentially from 5% to 50%.

  Next, the fixing temperature control unit 151 maintains this state until the on-time period T22 started in step S503 elapses (step S508, No), and when the on-time period T22 elapses (step S508, Yes). ), The on-time period T22 ends, and the avoidance control process of the on-off control signal of the second heater ends (step S509).

  In FIG. 18, avoidance control is performed so that the rising period Ta of the first heater on / off control signal generated later does not overlap the rising period Tb of the on / off control signal of the second heater generated earlier as described above. It is a flowchart showing a flow of duty control for generating a pulse Pa in a rising period Ta. Hereinafter, the duty control will be described with reference to FIGS. 15 and 16A according to this flow.

The timing at which this flow is started and the processing from step S601 to step S603 are exactly the same as the start timing and the processing from step S201 to step S203 described with reference to the flow shown in FIG. That is, the fixing temperature control unit 151 raises the on-time period T12 so that the rise period Ta of the first heater on-off control signal does not overlap the rise period Tb of the second heater on-off control signal. Here, as described above, the rising period Ta is set to a length corresponding to 7.5 cycles of the AC power supply, and the non-energization period Ta _M (M is 1 to 15) is sequentially set to the half cycle of the AC power supply. It is set to decrease by 5%.

The on-time phase control unit 252 sets the count number M of the duty control counter of the on-time duty control unit 255 to 1 in the rising period Ta that starts simultaneously with the on-time period T12 (step S604), and the non-energization period from zero crossing The _first pulse Pa is generated at a timing of Ta ₁ , that is, 95% of the half cycle of the AC power supply (step S605). Thereafter, it is determined whether or not the rising period Ta of the first heater has ended (step S606), and if it does not end (step S606, No), the count number M is incremented by 1 (step S607), and step S605 is performed. Return to.

Accordingly, in steps S604 to S607, as shown in FIG. 16A, in the rising period Ta, the non-energization time Ta _{M is set} to 5 to the half cycle of the AC power source from Ta ₁ to Ta ₁₅ for each half wave of the AC power source. Decrease by%, conversely, the energization period is sequentially increased by 5% from 5% to 75%.

  Next, the fixing temperature control unit 151 maintains this state until the on-time period T12 started in step S604 elapses (step S608, No), and when the on-time period T12 elapses (step S608, Yes). ), The on-time period T12 is terminated, and the avoidance control process of the on-off control signal of the first heater is terminated (step S609).

Next, the operation of the off-time phase control unit 253 will be described with reference to FIG. The off-duty control unit 256 sets the non-energization period Tc _P (P is 1 to p) from each zero cross in the fall period Tc p times. Specifically, in the falling period Tc, the pulse Pc is generated at a timing (phase angle) after the non-energization period Tc _P (P is 1 to p) from each zero cross.

The falling period Tc here is determined in advance, and is set to a length corresponding to, for example, 7.5 cycles of the AC power supply. Therefore, the set number here is 15 (p = 15). Off duty control unit 256, the de-energized period Tc _P, as the period is increased sequentially, here, are set so increases by 5% of the half cycle of the AC power source. Accordingly, the energizing period for each half wave of the AC power supply in the falling period Tc decreases by 5% sequentially from 75% to 5%. Here, the initial energization time 75% is calculated and prepared in advance so that the last energization period is 5%.

Similarly, the off-duty control unit 256 sets the non-energization period Td _Q (Q is 1 to q) from each zero cross in the falling period Td q times. Specifically, in the falling period Td, the pulse Pd is generated at the timing (phase angle) after the non-energization period Td _Q from each zero cross.

Here, the falling period Td is determined in advance, and is set to, for example, a length corresponding to five cycles of the AC power supply. Therefore, the set number here is 10 (q = 10). Off duty control unit 256, the de-energized period Td _Q, as the period is increased sequentially, here, are set so increases by 5% of the half cycle of the AC power source. Accordingly, the energization period for each half wave of the AC power supply in the falling period Td is decreased by 5% sequentially from 50% to 5%. Here, the initial energization time 50% is calculated and prepared in advance so that the final energization period is 5%.

The output circuit 49 drives the triacs 46 and 47 based on the on / off control signal input from the control circuit 250 and applies the applied voltage having the waveform shown in FIG. 16B to the first heater 33 and the second heater 34. . Specifically, for the triac 46, a drive pulse is generated at the timing of Tc _P (P is 1 to p) from each zero cross in each falling period Tc of the ON / OFF control signal, and the rising period Ta and the rising period are set. In the on period other than the falling period Tc, continuous drive pulses are generated. For the triac 47, a drive pulse is generated at the timing of Td _Q (Q is 1 to q) from the zero cross in each falling period Td of the on / off control signal, and other than the rising period Tb and the falling period Td. A continuous drive pulse is generated during the ON period.

The triacs 46 and 47 are located between the preceding and following zero crosses, and when receiving a drive pulse, the triacs 46 and 47 change from the off (open) state to the on (short circuit) state and turn off again at the next zero cross. Accordingly, a voltage is applied to the first heater 33 during the fall period Tc except for the non-energized (off) period Tc _P (P is 1 to p), and other than the fall period Tc of the on / off control signal. During the ON period, the voltage of the AC power supply is applied as it is. Similarly, a voltage is applied to the second heater 34 during a period other than the non-energization (off) period Td _Q (Q is 1 to q) in the fall period Td, and other than the fall period Td of the on / off control signal. During the ON period, the voltage of the AC power supply is applied as it is.

  FIG. 19 shows the avoidance control so that the falling period Td of the second heater on / off control signal generated later does not overlap with the falling period Tc of the first heater on / off control signal generated earlier as described above. And is a flowchart showing a flow of duty control for generating a pulse Pd in a falling period Td. Hereinafter, the duty control will be described with reference to FIGS. 15 and 16B according to this flow.

The timing at which this flow is started and the processing from step S701 to step S703 are exactly the same as the start timing and the processing from step S301 to step S303 described in the flow shown in FIG. 11 of the second embodiment. That is, the fixing temperature control unit 151 extends the on-time period T22 so that the falling period Td of the on / off control signal of the second heater does not overlap with the falling period Tc of the on-off control signal of the first heater. Here, as described above, the falling period Td is set to the length of five cycles of the AC power supply, and the non-energization period Td _Q (Q is 1 to 10) is sequentially set to the half cycle of the AC power supply. It is set to increase by 5%.

The off-time phase control unit 253 sets the count number Q of the duty control counter of the off-time duty control unit 256 to 1 in the falling period Td that starts following the falling of the on-time period T22 (step S704), and zero crossing The _first pulse Pd is generated at the non-energization period Td ₁ , that is, at a timing of 50% of the half cycle of the AC power supply (step S705). Thereafter, it is determined whether or not the falling period Td of the second heater has ended (step S706). If it does not end (step S706, No), the count number Q is incremented by 1 (step S707), and step The process returns to S705.

Thus, in this Step S704～S707, as shown in FIG. 16 (b), in the fall period Td, the half cycle of the AC power supply to the non-conduction time Td _Q for each half-wave of the AC power supply to _Td 1 _{~Tb 10} Increasing by 5%, in other words, the energization period is decreased by 5% sequentially from 50% to 5%.

  Next, when the falling period Td ends, the avoidance control process for the on / off control signal of the second heater is ended (step S708).

  FIG. 20 shows the avoidance control so that the falling period Tc of the first heater on / off control signal generated later does not overlap the falling period Td of the on / off control signal of the second heater generated earlier as described above. And is a flowchart showing a flow of duty control for generating the pulse Pc in the falling period Tc. Hereinafter, the duty control will be described with reference to FIGS. 15 and 16B according to this flow.

The timing at which this flow is started and the processing from step S801 to step S803 are exactly the same as the start timing and the processing from step S401 to step S403 described in the flow shown in FIG. That is, the fixing temperature control unit 151 extends the on-time period T12 so that the falling period Tc of the first heater on-off control signal does not overlap the falling period Td of the second heater on-off control signal. Here, as described above, the falling period Tc is set to a length corresponding to 7.5 cycles of the AC power supply, and the non-energization period Tc _P (P is 1 to 15) is sequentially divided into half of the AC power supply. It is set to increase by 5% of the cycle.

The off-time phase control unit 253 sets the count number P of the duty control counter of the off-time duty control unit 256 to 1 in the falling period Tc that starts following the falling of the on-time period T12 (step S804), and zero crossing The _first pulse Pc is generated at a non-energization period Tc ₁ , that is, at a timing of 25% of the half cycle of the AC power supply (step S805). Thereafter, it is determined whether or not the rising period Tc of the second heater has ended (step S806), and if it does not end (step S806, No), the count number P is incremented by 1 (step S807), and step S805 is performed. Return to.

Accordingly, in steps S804 to S807, as shown in FIG. 16B, the non-energization time Tc _{P is set} to Tc ₁ to Tc ₁₅ for the half period of the AC power source for each half wave of the AC power source in the falling period Tc. Increasing by 5%, or conversely, decreasing the energization period by 5% sequentially from 75% to 5%.

  Next, when the falling period Tc ends, the avoidance control process of the on / off control signal of the first heater is ended (step S808).

  In the present embodiment, the fixing temperature control unit 151 is configured to control the duty ratio of the rectangular signal based on the temperature information. However, the present invention is not limited to this, and the temperature information is simply a predetermined value. An on / off signal for turning on / off to be a value may be output.

  Further, in the present embodiment, the fixing temperature control unit 151 has been described so as to shift the state change timing so that the rising periods and the falling periods do not overlap each other, but the present invention is not limited to this. In addition, the on-time phase control unit 252 itself shifts the start timing of the rising period so that the rising periods do not overlap with each other, and the off-time phase control unit 253 itself sets the falling period so that the falling periods do not overlap each other. The start timing may be shifted.

  As described above, according to the image forming apparatus of the present embodiment, the effects of the first and second embodiments described above are obtained, and the application time is gradually increased when a voltage is applied to the first and second heaters. When the voltage application to the first and second heaters is stopped, the application time is controlled to gradually decrease. Can be relaxed. As a result, the voltage fluctuation of the external AC power supply that occurs when the heater is turned on and off can be reduced, and the problem of flickering of the fluorescent lamps connected to the same AC power supply line can be solved more effectively.

  In the above-described embodiment, the present invention has been described using a color electrophotographic printer as an example. However, the present invention is not limited to this, and an image is formed on a recording material using an electrophotographic method. It can also be used for image forming apparatuses such as copying machines, facsimiles, and MFPs. Further, although a color printer has been described, a single color printer may be used.

DESCRIPTION OF SYMBOLS 1 Paper feed part, 2 Image formation part, 3 Fixing part, 4 Duplex printing unit part, 5 Paper discharge part, 6 Paper feed cassette, 7 Pickup roller, 8 Recording paper, 10 Registration roller pair, 11 Photosensitive drum, 12 Charging Roller, 13 developing roller, 14 toner supply roller, 15 LED head, 16 toner cartridge, 17 transfer belt, 18 transfer roller, 19 toner image forming unit, 20 cleaner, 21 transfer unit, 22 switching plate, 23 cover, 31 heating roller , 32 pressure roller, 33 first heater, 34 second heater, 35 temperature sensor, 36 fixing belt, 37 fixing roller, 38 pad, 40 heater control unit, 41 AC power supply, 45 temperature detection unit, 46 triac, 47 triac , 48 Zero cross detection circuit, 49 Output circuit, 50 Control circuit 51 Fixing temperature control unit, 52 On-time phase control unit, 100 Image forming apparatus, 140 Heater control unit, 150 Control circuit, 151 Fixing temperature control unit, 153 Off-time phase control unit, 240 Heater control unit, 250 Control circuit, 252 ON phase control unit, 253 OFF phase control unit, 255 ON duty control unit, 256 OFF duty control unit.

Claims (10)

A plurality of heaters for toner fixing;
Control means for instructing the timing of individually applying an AC voltage to the plurality of heaters;
Switching means for intermittently applying an AC voltage to the plurality of heaters based on an instruction of the control means,
The control means provides a voltage suppression period for limiting the AC voltage in synchronization with the application timing generated based on the temperature information of the heater at the time of on and / or off,
An image forming apparatus, wherein the voltage suppression periods generated individually for each of the plurality of heaters do not overlap each other. Having zero-cross detection means for detecting zero-cross of the AC voltage;
The image forming apparatus according to claim 1, wherein the control unit limits the application time of the AC voltage for each zero cross in the voltage control period. The control means provides the voltage suppression period for limiting the application time of the AC voltage for each zero cross when the timing of applying the AC voltage is on,
The image forming apparatus according to claim 2, wherein the rising periods generated individually for each of the plurality of heaters do not overlap each other. The control means provides the voltage suppression period for limiting the application time of the AC voltage for each zero cross when the timing of applying the AC voltage is off,
The image forming apparatus according to claim 2, wherein the falling periods generated individually for each of the plurality of heaters do not overlap each other.   The control means provides the voltage suppression period for limiting the application time of the alternating voltage for each zero cross at the time of turning on and off the timing of applying the alternating voltage, and is generated individually for each of the plurality of heaters. The image forming apparatus according to claim 2, wherein the voltage suppression period at the time of on and the voltage suppression period at the time of off do not overlap each other.   The image forming apparatus according to claim 2, wherein the control unit gradually changes the application time during the voltage control period.   6. The image forming apparatus according to claim 3, wherein the control unit gradually increases the application time during the voltage suppression period at the on time.   6. The image forming apparatus according to claim 4, wherein the control unit gradually decreases the application time in the voltage suppression period at the off time. The control means includes: a fixing temperature control unit that forms a rectangular signal whose duty ratio changes according to the temperature information; and a voltage limiting unit that generates the voltage limiting period in synchronization with a state change of the rectangular signal. Have
The control means controls the timing of the state change of the rectangular signal so that the voltage suppression periods generated individually for the plurality of heaters do not overlap each other,
The image forming apparatus according to claim 2, wherein the voltage limiting unit generates a rising signal that determines a voltage application period after the zero crossing in the voltage suppression period.   The switching means generates a drive pulse in synchronization with the rising signal in the voltage control period, and continuously generates a pulse in the on period of the rectangular signal other than the voltage control period; and The image forming apparatus according to claim 9, further comprising a triac that is driven by an output circuit and intermittently applies the AC voltage to the heater.

Images