JP2010039421A - Image forming apparatus and zero-cross detection control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent worsening of a temperature adjustment ripple resulting from power control of a fixing heater when an AC waveform is distorted, by preventing erroneous detection of a zero-cross signal caused by distortion of the AC waveform. <P>SOLUTION: The image forming apparatus that supplies power to a heating element according to the phase of an AC voltage detects the zero-cross of the AC voltage by comparing the AC voltage and a threshold. The apparatus then generates an ignition signal for turning on the heating element at a predetermined phase in response to the zero-cross signal. Further, based on the ignition signal, the apparatus drives the heating element. It subsequently detects a period in which the zero-cross signal is generated, and changes the threshold from an initial value if the detected period does not fall within a predetermined range. Thus, a noise component overlapping the vicinity of the actual zero-cross of an AC waveform is absorbed. This prevents abnormal power source frequency even when a distorted AC waveform is input, thereby preventing stop of a printing job. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image recording apparatus such as an electrophotographic copying machine or an electrophotographic printer. In particular, the present invention relates to an image forming apparatus including an AC phase power supply unit that supplies power to a power supply target according to the phase of an AC voltage.

  Conventionally, in a recording apparatus using electrophotographic technology such as a printer or a copying machine, toner developed on a photosensitive member is transferred to a sheet and thermally fixed by a fixing device at a predetermined temperature and pressure. This fixing device includes those using a halogen heater as a heat source and those using a ceramic heater. Generally, electric power is supplied to the heater from an AC power supply via a switching element such as a triac.

  A temperature detection element such as a thermistor is provided for the heater. The temperature of the heater is detected by this temperature detection element. Based on this detected temperature, the fixing control circuit turns on and off the switching element to turn on and off the power supply to the heater, and the heater temperature is controlled to be a constant temperature.

  Generally, when a commercial AC power line is viewed from the outside of a power outlet, a relatively small line impedance exists. For this reason, when a current of a high-power component such as a heater used in a fixing device such as a printer flows, a voltage drop due to line impedance occurs in the commercial AC power supply line. This voltage drop causes flickering of a lamp or the like connected to the same line and causes malfunction of other devices.

  For this reason, in the lighting power control of the fixing heater, not the wave number control by full wave lighting but the gentle power control using the phase waveform to cope with the power supply voltage fluctuation by eliminating the steep current change is doing.

When power control using a phase waveform is performed, in order to ignite at a predetermined phase angle, an AC input zero cross is detected, and the zero cross signal is used as a trigger to output the ignition signal after a predetermined time t (ms). In this way, phase control is performed.
Japanese Patent Laying-Open No. 2005-084546

  However, when a device that consumes a large amount of power is operating nearby as often seen in factories, etc., or a device that switches with a large amount of power, such as a refrigerator or an air conditioner, is connected to the same AC power line. In some cases, noise components such as spike noise may be superimposed on the AC power supply line. In such a case, the power supply waveform is not necessarily a sine wave and may be a distorted waveform.

  Due to such distortion of the power supply waveform, the zero cross signal also becomes an abnormal waveform. In the CPU, a trigger is usually applied at the edge of the zero cross signal, and the power supply frequency is detected at a time interval until the edge of the next pulse. For this reason, if noise is superimposed near the zero cross of the AC waveform, it becomes impossible to accurately detect the power supply frequency.

  Japanese Patent Application Laid-Open No. 2004-133260 proposes a technique for controlling the fixing heater ON / OFF regardless of the power supply frequency when the zero-cross signal cannot be accurately obtained. In this control, the temperature regulation ripple of the heater becomes large and fine control cannot be performed, so that the fixing temperature is insufficient, and there is a possibility that quality on the output paper such as fixing failure may be greatly affected.

  The present invention has been made in such a background, and suppresses false detection of a zero-cross signal due to distortion of the AC waveform, and deterioration of temperature regulation ripple due to power control of the fixing heater when the AC waveform distortion occurs. It is an object of the present invention to provide an image forming apparatus and a zero-cross detection control method that can prevent the above-described problem.

  An image forming apparatus according to the present invention detects an AC voltage zero cross by generating a zero cross signal by comparing an AC voltage with a threshold in an image forming apparatus that supplies power to a power supply target according to the phase of the AC voltage. A zero-cross detecting means for generating, an ignition signal generating means for generating an ignition signal for driving the power supply target at a predetermined phase by using the zero-cross signal as a trigger, and the electric power supply based on the ignition signal Drive means for driving a target, and control means for changing the threshold value from an initial value when a cycle in which the zero cross signal is generated is not within a predetermined range.

  “The cycle in which the zero-cross signal is generated is not within a predetermined range” corresponds to a situation in which noise is superimposed on the input waveform of the AC voltage and a large number of zero-cross signals are output. Therefore, the detection of noise is avoided by changing the threshold value.

  The control means may change the threshold value and widen the pulse width of the ignition signal. As a result, it is possible to prevent false ignition such as firing the half wave immediately before the half wave to be driven (lighting a minute power).

  The control means may vary the pulse width of the ignition signal in accordance with a phase angle range for driving the power supply target. Thereby, false ignition is prevented.

  Alternatively, the control unit may narrow the pulse width of the ignition signal when the phase angle for driving the power supply target is a predetermined value or more. False firing due to the firing signal crossing a true zero cross is prevented.

  A zero-crossing detection control method according to the present invention is a zero-crossing detection control method in an image forming apparatus that supplies power to a power supply target according to the phase of an AC voltage, and compares the AC voltage with a threshold value, And generating a zero-cross signal, generating a firing signal for driving the power supply target at a predetermined phase using the zero-cross signal as a trigger, and a cycle of generating the zero-cross signal. A step of detecting, and a step of changing the threshold value from an initial value when the detected period is not within a predetermined range.

  According to the present invention, even in a situation where noise is superimposed on an input waveform of an AC power supply and many zero-cross signals are output, a noise component near the zero-cross can be absorbed by changing the threshold value of the zero-cross detection circuit. Thereby, it is possible to avoid the stop of the print job by detecting the power frequency error.

  In addition, by changing the ignition pulse width of the fixing heater in accordance with this, it is possible to control the power supply target without causing the temperature adjustment failure due to the ignition failure. As a result, false ignition can be prevented, and the temperature control lip can be prevented from deteriorating and excessive temperature rise.

  Further, when the ignition signal is output at a phase angle greater than or equal to a predetermined phase angle, the ignition pulse does not cross the true zero cross by narrowing the widened pulse width. As a result, the phase angle of the half wave of the AC waveform can be fully ignited without limiting the phase angle to be ignited.

  In addition, since it is not necessary to change the power control pattern regardless of whether noise is superimposed or not, it is possible to perform fine power control of a power supply target without causing deterioration of the temperature control ripple.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus to which the present invention is applied.

  The photosensitive drum 101 rotates in the direction of the arrow, and the outer peripheral surface of the photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by a charging roller 102 as a charging unit. The laser scanner 103 outputs a laser beam L modulated in accordance with a time-series electric digital pixel signal of image information, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 101. As a result, a latent image is formed on the photosensitive drum surface. The developing device 104 develops the electrostatic latent image on the photosensitive drum surface as a toner image.

  A transfer roller 105 serving as a transfer unit forms a transfer nip T by contacting the photosensitive drum 101 with a predetermined pressing force. The recording paper P is fed to the transfer nip T from a paper feeding unit (not shown) at a predetermined control timing. A predetermined transfer bias is applied to the transfer roller 105 at a predetermined control timing. As a result, the toner images on the photosensitive drum surface are sequentially electrostatically transferred onto the recording paper P at the transfer nip T.

  The recording paper P that has exited the transfer nip T is separated from the surface of the photosensitive drum 101 and introduced into the fixing device 100. The fixing device 100 heats and fixes the unfixed toner image on the conveyed recording paper P as a fixed image, and discharges and conveys the recording paper P. The photosensitive drum cleaning unit 106 removes transfer residual toner on the photosensitive drum 101 after separation of the recording material. Thereby, the transfer residual toner is removed and the photosensitive drum 101 is cleaned.

  FIG. 2 is a block diagram of the AC phase power supply unit 27 that supplies power to the heating element of the fixing device 100 that is a power supply target according to the present embodiment in accordance with the phase of the AC voltage. The AC power source 21 connected to the image forming apparatus main body diagram generates heat by supplying electric power to a heater 26 that is a heating element. The power supply to the heater 26 is supplied and cut off by the triac 28. The resistors 32 and 33 are triac bias resistors, respectively, and set the gate current of the triac 28. The phototriac 31 is used to ensure primary and secondary insulation. The LED in the photo triac 31 is lit by the firing signal from the CPU 36, and the triac in the photo triac 31 is thereby driven. Further, a bias current flows through the gate of the triac 28, and thereby the triac 28 is driven (ignited).

  A zero cross detection circuit 23 is provided on the AC power supply line. A zero cross of the AC waveform of the power supply voltage is detected and input to the CPU 36 as a zero cross signal. The CPU 36 detects the power supply frequency based on this zero cross signal.

  Note that programs executed by the CPU 36 and fixed data are stored in a ROM 37 which is a nonvolatile memory. The RAM 38 is a memory that provides a work area for the CPU 36 and a temporary storage area for data.

  The CPU 36 constitutes various means (ignition signal generation means, drive means, control means, etc.) in the present invention, and also has a timer function to be described later.

  The dotted line frame in FIG. 2 is an AC phase power supply unit, and the power ratio (heat generation ratio) of the heating element is changed by thinning out the phase waveform at a predetermined ratio along the predetermined power ratio table by the ignition signal from the CPU 36. Let

  FIG. 3 shows a control waveform of the AC phase power supply unit 27 of FIG. The phase power control of the heating element is performed by generating the ignition signal after a predetermined time t (ms) with the zero cross signal ZEROX as the starting point (trigger).

  Further, based on the temperature detected by the temperature detection sensor 24 of the heating element 26, the CPU 36 controls the power control ratio table (not shown) of the heating element stored in the ROM 37 so that the heating element temperature changes at a predetermined temperature. Z)), the phase power control of the heater 26 is performed.

  FIG. 4 is a circuit diagram showing a configuration example of the zero-cross detection circuit 23 in the present embodiment.

  The power supply voltage of the AC waveform input is stepped down by the insulation transformer T1. The stepped-down alternating current waveform is full-wave rectified by the rectifier 41, and then the full-wave rectified waveform is compared with the reference voltage V1 by the comparator 42 to be converted into binary data. This binary data includes a zero cross signal and is input as an interrupt signal to the CPU 36.

  FIG. 5 is an explanatory diagram of an initial value (low voltage value V1) of the threshold value of the comparator shown in FIG. 4, and both waveforms show waveforms of signals at points A and B in FIG. . As shown in FIG. 5, at the normal time, the threshold value of the comparator 42 is set to a low voltage value V1 so that a zero cross signal is generated as close to the true zero cross of the AC waveform as possible. This threshold value is changed to a higher voltage V2 under a predetermined condition described later.

  When a distorted AC waveform as shown in FIG. 6 has been input, if the threshold value remains V1, a large number of zero cross signals are output in the vicinity of each zero cross. At present, when a zero cross signal as shown in FIG. 6 is input to the CPU 36, it is determined that the AC power supply frequency is abnormal, and an error signal is output to stop the print job. Therefore, in the present invention, when a large number of zero-crossing interrupts are detected within a predetermined time, the threshold value of the comparator 42 in the zero-crossing detection circuit 23 is absorbed by the comparator 42 so that the noise component superimposed on the AC waveform is absorbed. Variable. Specifically, the CPU 36 detects the cycle of the zero cross signal, and when the zero cross signal is not input at a predetermined cycle, the threshold value of the comparator 42 of the zero cross detection circuit 23 is changed from V1 as shown in FIG. Switch to V2. When the detected period is not within the predetermined range, the noise component superimposed near the true zero cross of the AC waveform is absorbed by changing the threshold value from the initial value to a level at which the noise does not reach the threshold value. Is possible. As a result, even when a distorted AC waveform is input, the power supply frequency does not become abnormal and it is possible to avoid stopping the print job.

  In addition, the ignition pulse is generated starting from the zero cross signal, while the pulse width of the zero cross signal is widened by changing the threshold value. For this reason, the time error between the ignition pulse and the true zero cross point of the AC waveform increases. As a result, false ignition is likely to occur. In particular, if an ignition signal is output at a normal timing in an attempt to turn on a half-wave, as shown in FIG. 8, the phase angle in the half-wave one minute before the half-wave to be lit (micro power) ) May be fired, and the target power control may not be possible.

  In order to cope with such adverse effects, in addition to changing the threshold value of the zero-crossing detection circuit, as shown in FIG. 9, the width of the ignition pulse applied to the fixing heater driving circuit can be dealt with by expanding it beyond a predetermined time width. Is possible.

  As described above, by expanding the pulse width of the ignition signal in synchronization with the switching of the threshold value, it is possible to avoid an adverse effect (cannot be ignited at the target phase) caused by changing the threshold value as shown in FIG. As a result, the print job can be continued without causing a temperature adjustment error of the apparatus due to insufficient power supply to the heating element.

  Further, as shown in FIG. 10, with respect to the ignition signal with an expanded pulse width, there is a risk of false ignition due to the ignition signal straddling a true zero-cross point. That is, as shown in the figure, when the ignition is started immediately before the true zero cross point, the energization should be terminated at the next zero cross point, so that the ignition signal continues beyond the zero cross point, Accidentally, the next half-wave will be turned on.

  In order to prevent such an adverse effect, a restriction corresponding to the phase angle is provided for the pulse width of the ignition signal. For example, if the time X (corresponding to the phase angle) from the time of zero-crossing interrupt to the leading edge of the ignition signal is less than a predetermined value, the enlarged pulse width of the ignition signal is used as it is and from the time of zero-crossing interruption. If the time X (corresponding to the phase angle) to the leading edge of the ignition signal is equal to or greater than a predetermined value (that is, when the ignition signal is output beyond the predetermined phase angle), Reduce the pulse width. In this example, the initial pulse width is restored. This state is shown as ignition 1 → ignition 2 in FIG. By controlling the ignition pulse width in this way, it is possible to avoid the ignition signal straddling the true zero cross. In addition, it can be ignited with a small amount of power, and it is not necessary to change the power control pattern significantly regardless of whether noise is superimposed or not. As a result, even if noise is superimposed, fine power control of the heating element can be performed without causing deterioration of the responsiveness of the temperature control.

  In addition, if it is allowed for the necessity of actual control, the phase angle to be fired may be limited (for example, limited to 0 to 90 °). This also makes it possible to prevent false ignition due to the ignition signal crossing the true zero cross.

  Hereinafter, processing of the zero cross detection control method of the present invention will be described. First, FIG. 12 shows a processing example for performing a basic threshold setting operation in the present embodiment. This process is realized by the CPU 36 reading and executing a program in the ROM 37. In this example, a threshold setting operation is performed during pre-rotation during a print job, the threshold is fixed during the job, and the threshold setting operation is performed every time the job starts. However, the present invention does not preclude changing the threshold during a job.

  First, the apparatus starts rotation before accepting a print job. At that time, the threshold value of the zero cross detection circuit is set to the initial value V1 (S11). Next, the zero cross signal is detected and it is confirmed whether the cycle is appropriate (S12). If it is determined to be appropriate, the threshold setting is confirmed and the print job is started under normal control.

  If it is determined in step S12 that the zero-cross cycle is not appropriate (NG), the threshold value is switched to V2, which is larger than V1 (S13). In this example, V2 is a predetermined fixed value VH.

  With the processing of FIG. 12, the threshold value of the comparator can be switched according to whether the detected zero-cross signal has an appropriate cycle.

  FIG. 13 shows another processing example for performing the threshold setting operation in the present embodiment. In the process of FIG. 12, the threshold value V2 is set to the fixed value VH, but in this process, V2 is variably set. For variable control of the threshold value V2, a D / A (digital / analog) output port of the CPU can be used instead of using the reference voltage source. Alternatively, it is also possible to use a PWM (Pulse Width Modulation) signal from the CPU. It is also possible to change the threshold value by changing the DUTY ratio with a pulse output at a constant frequency instead of the PWM signal.

  Similar to the processing of FIG. 12, first, the threshold value of the zero cross detection circuit is set to the initial value V1 (S21). Next, a zero cross signal is detected to check whether the cycle is appropriate (S22). If it is determined to be appropriate, the threshold setting is confirmed and the print job is started under normal control.

  If it is determined in step S22 that the zero cross period is NG, the threshold value V1 is increased by the unit amount n as the threshold value V2 (S23). The zero-cross signal is detected again to check whether the cycle is appropriate (S24). In the case of OK, the threshold setting is confirmed and the print job is started under normal control. That is, the width of the triac firing pulse is determined from the value of the zero cross period and the threshold value.

  If the zero cross period is NG, it is determined whether the current threshold value exceeds a certain value (upper limit value m) (S25). If the upper limit value m is not exceeded, the process returns to step S23 to further increase the threshold value.

  When the threshold value exceeds the upper limit value m, the zero-cross cycle is abnormal even if the threshold value is varied to that value. In such a case, the distortion of the waveform is so great that it is uncontrollable and an error is determined, the print job is stopped (S26), and this process is terminated.

  With the processing in FIG. 13, the value of V2 can be set appropriately. That is, it is not necessary to increase V2 more than necessary to increase the pulse width of the zero cross signal.

  14 and 15 show still another example of processing for performing the threshold setting operation in the present embodiment. In FIG. 14, the same steps as those shown in FIG. 13 are denoted by the same reference numerals, and redundant description is omitted.

  In the processing of FIGS. 12 and 13, the width of the ignition pulse is fixed, but in this processing, as described above, the pulse width of the ignition signal is made variable according to the range of the phase angle for starting the heater.

  If it is determined in step S24 that the cycle of the zero cross signal is within the range, the threshold V1 + n and the firing pulse width corresponding to the zero cross cycle are set (S27).

  Next, referring to FIG. 15, the setting of the ignition pulse during the printing operation after the threshold value is determined will be described.

  First, if the timer setting value is within nsec when the ignition signal is output after the zero-cross interrupt is entered, the output is performed with the ignition pulse width when the threshold value of the zero-cross detection circuit is determined.

  When the timer value T from the zero cross interrupt is nsec or more (S28, No), the firing pulse width is returned to the width at the threshold v1 and output (S29). As described above, this is to prevent erroneous firing when the minute power is turned on.

  If the timer value T is less than n (S28, Yes), the current ignition pulse width is maintained as it is (S30).

  While the printing operation continues, steps S28 to S30 are repeated.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, it is assumed that the threshold setting process is performed at the time of pre-rotation. However, for a sheet having a wide space and a detection time, the threshold value of the zero cross detection circuit can be changed for each sheet.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus to which the present invention is applied. FIG. 2 is a block diagram of an AC phase power supply unit of a heating element of the fixing device of the image forming apparatus of FIG. 1. It is a figure which shows the control waveform of the alternating current phase power supply part of FIG. It is the circuit diagram which showed the structural example of the zero cross detection circuit in embodiment of this invention. FIG. 5 is an explanatory diagram of an initial value (low voltage value V1) of a threshold value of the comparator shown in FIG. It is explanatory drawing of the problem in case the distorted alternating current waveform is input. It is explanatory drawing of switching of the threshold value when the distorted alternating current waveform is input. It is explanatory drawing of the bad effect accompanying switching of a threshold value. It is explanatory drawing of expansion of the width | variety of the ignition pulse for solving the trouble demonstrated in FIG. It is explanatory drawing of the bad effect accompanying the pulse width expansion of an ignition signal. It is explanatory drawing of the variable control of the width | variety of the ignition pulse for solving the trouble demonstrated in FIG. It is a flowchart which shows the process example which performs basic threshold value setting operation | movement in embodiment of this invention. It is a flowchart which shows the other process example which performs threshold value setting operation | movement in embodiment of this invention. It is a flowchart which shows the further another process example which performs threshold value setting operation | movement in embodiment of this invention. It is a flowchart of the process following FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 ... AC power source 23 ... Zero cross detection circuit 24 ... Temperature detection sensor 26 ... Heater (heating element)
28 ... Triac 31 ... Phototriac 32 ... Resistor 41 ... Rectifier 42 ... Comparator 100 ... Fixing device 101 ... Photosensitive drum 102 ... Charging roller 103 ... Laser scanner 104 ... Developer 105 ... Transfer roller 106 ... Photosensitive drum cleaning section

Claims (5)

In an image forming apparatus that supplies power to a power supply target according to the phase of an AC voltage,
A zero cross detection means for comparing the AC voltage with a threshold, detecting a zero cross of the AC voltage, and generating a zero cross signal;
An ignition signal generating means for generating an ignition signal for driving the power supply target in a predetermined phase using the zero cross signal as a trigger;
Driving means for driving the power supply target based on the ignition signal;
An image forming apparatus comprising: a control unit configured to change the threshold value from an initial value when a cycle in which the zero cross signal is generated is not within a predetermined range.   The image forming apparatus according to claim 1, wherein the control unit changes the threshold value and widens a pulse width of the ignition signal.   The image forming apparatus according to claim 2, wherein the control unit varies a pulse width of the ignition signal in accordance with a range of a phase angle for driving the power supply target.   The image forming apparatus according to claim 2, wherein when the phase angle for driving the power supply target is equal to or greater than a predetermined value, the control unit narrows a pulse width widened of the ignition signal. A zero-crossing detection control method in an image forming apparatus that supplies power according to the phase of an AC voltage to a power supply target,
Comparing the alternating voltage with a threshold to detect a zero crossing of the alternating voltage and generating a zero crossing signal;
Generating an ignition signal for driving the power supply target in a predetermined phase using the zero-cross signal as a trigger; and
Detecting a period in which the zero-cross signal is generated;
And a step of changing the threshold value from an initial value when the detected cycle is not within a predetermined range.