JP2011146862A - Zero-cross detecting device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zero-cross detecting device which can excellently detect a zero-cross point even when the waveform of an AC voltage is distorted and departs from a sinusoidal wave, and an image forming apparatus provided with the zero-cross detecting device. <P>SOLUTION: A low active zero-cross signal 1 is output when the absolute value of the AC voltage becomes lower than a threshold Vt1, and a low active zero-cross signal 2 is output when the absolute value becomes lower than a threshold Vt2 (Vt1>Vt2). The point of time later than the start point of the zero-cross signal 2 by the time calculated by an expression Tw2*Ta/(Ta+Tb) is calculated as a zero-cross point, provided that Tw1 is the pulse width of the zero-cross signal 1, Tw2 is the pulse width of the zero-cross signal 2, Ta is the time from the start point of the zero-cross signal 1 to the start point of the zero-cross signal 2, and Tb is the time from the end point of the zero-cross signal 2 to the end point of the zero-cross signal 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zero-cross detection device that detects a zero-cross point at which the absolute value of an AC voltage becomes zero. Specifically, the zero-cross point can be detected well even when the waveform of the AC voltage is distorted and deviates from a sine wave. The present invention relates to a zero cross detection device and an image forming apparatus having the zero cross detection device.

  Conventionally, a zero cross detection device that detects a so-called zero cross point as a timing at which the absolute value of the AC voltage becomes zero has been proposed. The detected zero cross point is applied to various controls in various electric devices, such as setting the heater ON / OFF timing. In addition, this type of zero-cross detection device outputs a zero-cross pulse corresponding to a period in which the absolute value of the AC voltage is less than a predetermined threshold value, and detects the central point between the start point and the end point of the zero-cross pulse as the zero-cross point. (See, for example, Patent Document 1).

JP-A-10-186908

  However, when the center time point between the start point and the end point of the zero cross pulse is detected as the zero cross point as in Patent Document 1, an accurate zero cross point may not be detected as follows. For example, when the AC voltage waveform is distorted and deviates from the sine wave, and the slope of the AC voltage waveform differs before and after the zero cross point, the zero cross point detected as described above is the slope of the waveform from the accurate zero cross point. Will shift to the loose side.

  Therefore, the present invention provides a zero-cross detection device that can detect a zero-cross point satisfactorily even when the waveform of an AC voltage is distorted and deviates from a sine wave, and an image forming apparatus having the zero-cross detection device. It was made as a purpose.

  The zero-cross detection device of the present invention made to achieve the above object is a zero-cross detection device that detects a zero-cross point where the absolute value of the AC voltage output from the AC power supply becomes zero, and the absolute value of the AC voltage is First zero cross pulse output means for outputting a first zero cross pulse corresponding to a period that is less than a preset first threshold, and the absolute value of the AC voltage is preset to a value smaller than the first threshold A second zero cross pulse output means for outputting a second zero cross pulse corresponding to a period that is less than the second threshold; a start point and an end point of the first zero cross pulse output by the first zero cross pulse output means; and the second zero cross. Based on the four time points consisting of the start point and the end point of the second zero cross pulse output by the pulse output means, the zero cross point It is characterized by comprising a zero-cross point detecting means for detecting.

  In the zero cross detection device of the present invention configured as described above, the first zero cross pulse output means outputs a first zero cross pulse corresponding to a period in which the absolute value of the AC voltage is less than the first threshold, and the second zero cross pulse. The output means outputs a second zero cross pulse corresponding to a period during which the absolute value of the AC voltage is less than the second threshold value. Here, the first threshold value and the second threshold value may be values that are appropriately set in advance so that the second threshold value is smaller than the first threshold value. There is no need to have.

  In this case, when the AC voltage changes from the maximum value or the minimum value to the minimum value or the maximum value through the zero cross point, the start point of the first zero cross pulse, the start point of the second zero cross pulse, the end point of the second zero cross pulse, The four time points are arranged in time series in the order of the first zero cross pulse end point. Therefore, the zero cross point detecting means detects the zero cross point at which the absolute value of the AC voltage becomes zero based on the four time points. For this reason, the zero cross detection device of the present invention can detect the zero cross point satisfactorily even when the waveform of the AC voltage is distorted and deviates from the sine wave.

  For example, the slope of the waveform before the zero cross point is reflected in the time from the start point of the first zero cross pulse to the start point of the second zero cross pulse, and the slope after the zero cross point is from the end point of the second zero cross pulse. It is reflected in the time until the end point of 1 zero cross pulse. Therefore, the zero cross point can be accurately estimated (detected) by referring to the four time points. The zero cross point may be estimated by other methods.

  Further, the present invention is not limited to the following configuration, but the time from the start point of the first zero cross pulse to the start point of the second zero cross pulse and the end point of the second zero cross pulse are the first to the first zero cross pulse. An error notification means for notifying an error may be further provided when the ratio of the time until reaching the end point of the zero cross pulse is out of a predetermined range set in advance.

  The ratio of the time from the start point of the first zero cross pulse to the start point of the second zero cross pulse and the time from the end point of the second zero cross pulse to the end point of the first zero cross pulse is, for example, normal When a predetermined range that can be taken by secular change is out of the predetermined range, any of the zero cross pulse output means has failed, or octopus leg wiring is performed, or a device that consumes large power Some abnormality such as being used nearby is assumed. Therefore, if an error notification means for notifying an error in such a case is further provided, it is possible to satisfactorily cope with the abnormality of the zero cross pulse output means, the abnormality of the AC power supply, and the like.

  When either the first zero cross pulse output means or the second zero cross pulse output means does not output the first zero cross pulse or the second zero cross pulse, the zero cross point detection means Alternatively, the center point between the start point and the end point of the zero cross pulse may be detected as the zero cross point.

  Either the first zero cross pulse or the second zero cross pulse may not be output due to the secular change of the zero cross pulse output means or the voltage change of the AC power supply. For example, since the luminous intensity of a light emitting diode gradually decreases with time, a zero cross pulse output means using a photocoupler or the like using a light emitting diode may not output any of the above zero cross pulses due to change over time. Therefore, in such a case, if the zero cross point detecting means detects the central time point between the start point and the end point of the output zero cross pulse as the zero cross point, the zero cross point cannot be detected. This can prevent other controls from being hindered.

  Further, the zero cross point detection means is a start point of the first zero cross pulse based on a difference between a time from the start point to the end point of the first zero cross pulse and a time from the start point to the end point of the second zero cross pulse. The time from the start point of the second zero cross pulse to the start point of the second zero cross pulse is divided by the time from the start point of the second zero cross pulse to the end point. The zero cross point may be detected. In this case, as described above, the detection of the zero cross point reflecting the inclination of the waveform before and after the zero cross point can be executed by a simple arithmetic process.

  The image forming apparatus of the present invention is an image forming apparatus having any one of the above-described zero-cross detection devices, wherein an AC voltage is applied from an image forming unit that forms an image on a recording medium and the AC power source. And a heating unit that heats the image formed on the recording medium by the image forming unit, and controls the heating unit based on a zero cross point detected by the zero cross detection device. And a heating control means.

  In the image forming apparatus of the present invention configured as described above, when an image is formed on a recording medium by the image forming unit, a fixing device including a heating unit that heats by applying an AC voltage from the AC power source. Then, the image formed on the recording medium is heat-fixed. Moreover, a heating control means controls the said heating part based on the zero cross point which the said zero cross detection apparatus detects. For this reason, in the image forming apparatus of the present invention, the heating unit can be controlled based on the zero cross point accurately detected as described above. For example, when the heating control unit switches energization / non-energization to the heating unit in accordance with the detected zero cross point, the occurrence of flicker can be suppressed very well.

It is explanatory drawing which represents roughly the structure of the laser printer to which this invention was applied. It is a circuit diagram showing the structure for controlling the heater of the laser printer. It is explanatory drawing showing an example of the zero cross pulse produced | generated by the circuit. It is a flowchart showing the zero cross point detection process performed with the circuit. It is explanatory drawing showing the other example of the zero cross pulse produced | generated by the circuit. It is a flowchart showing the warm-up process performed with the circuit.

[Laser printer configuration]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram schematically showing the configuration of a laser printer 1 as an image forming apparatus to which the present invention is applied. As shown in FIG. 1, the laser printer 1 according to the present embodiment includes an image forming unit 10 as an example of an image forming unit that forms an image on a sheet P as an example of a recording medium by an electrophotographic method. .

  The image forming unit 10 forms a toner image on the sheet P while the sheet P is sandwiched between the photosensitive drum 11 and the transfer roller 12 and conveyed in the arrow direction. The photosensitive drum 11 is grounded and a positively charged photosensitive layer is formed on the surface thereof. The photosensitive drum 11 is supported by the laser printer 1 so as to be rotatable counterclockwise in FIG.

  Further, on the outer periphery of the photosensitive drum 11, a charger 13, a laser scanner unit 14, and a developing unit 15 are sequentially disposed along the rotation direction of the photosensitive drum 11 from a portion facing the transfer roller 12. . The charger 13 is a positively charged scorotron charger that generates corona discharge from a charging wire such as tungsten, and is configured to uniformly charge the surface of the photosensitive drum 11 to a positive polarity. The laser scanner unit 14 emits a laser beam L corresponding to image data input from the outside from a light source (not shown), and the laser beam is reflected by a mirror surface of a polygon mirror (not shown) rotated by a polygon motor. This is a well-known one that scans L and irradiates the surface of the photosensitive drum 11.

  The developing unit 15 includes a developing roller 16 at a portion facing the photosensitive drum 11. The developing unit 15 is triboelectrically charged by a well-known supply roller, a layer thickness regulating blade, etc. (not shown) of a positively chargeable non-magnetic one-component polymer toner (not shown) accommodated in the developing unit 15. However, the toner is supplied to the surface of the photosensitive drum 11 through the developing roller 16.

  For this reason, the surface of the photosensitive drum 11 is first uniformly charged positively by the charger 13 along with the rotation of the photosensitive drum 11, and then by high-speed scanning of the laser light L from the laser scanner unit 14. It is exposed to form an electrostatic latent image corresponding to the image data.

  Next, when a positively charged toner is supplied from the developing unit 15 to the photosensitive drum 11, the toner is an electrostatic latent image formed on the surface of the photosensitive drum 11, that is, a uniform positive toner. The charged surface of the photosensitive drum 11 is supplied to the exposed portion exposed to the laser beam L and the potential is lowered, and is selectively carried to be visualized, thereby forming a toner image. Is done.

  The transfer roller 12 is supported by the laser printer 1 so as to be rotatable in the clockwise direction in FIG. The transfer roller 12 is configured such that a metal roller shaft is covered with a roller made of an ion conductive rubber material, and a transfer bias (transfer forward bias) is applied during transfer. Therefore, the toner image carried on the surface of the photosensitive drum 11 is transferred to the paper P while the paper P passes between the photosensitive drum 11 and the transfer roller 12. The sheet P after the toner image has been transferred is conveyed to a fixing device 20 having a heating roller 21 and a pressure roller 22, and the toner image is thermally fixed.

[Circuit configuration for controlling the heater]
Here, the fixing device 20 includes a halogen heater 23 as an example of a heating unit for heating the surface of the heating roller 21, and a thermistor 25 as an example of a temperature detection unit for detecting the surface temperature of the heating roller 21. (Refer to FIG. 2). Next, a circuit configuration for controlling the halogen heater 23 will be described with reference to FIG.

  As shown in FIG. 2, the 100V AC power supply 100 to which the laser printer 1 is connected has a diode bridge D1 for full-wave rectification of the AC voltage from the AC power supply 100 by four diodes via a resistor R1. It is connected. The AC voltage that has been full-wave rectified by the diode bridge D1 is applied to the light emitting diode PC1a of the photocoupler PC1.

  The phototransistor PC1b of the photocoupler PC1 has a collector connected to the DC power supply Vcc via resistors R3 and R2 connected in series, and an emitter grounded. The potential between the resistors R3 and R2 is input to the inverting buffer IC1 as an example of the first zero cross pulse output means, and the potential of the collector of the phototransistor PC1b is input to the inverting buffer IC2 as an example of the second zero cross pulse output means. Have been entered. Therefore, the inverting buffer IC1 outputs a low active zero cross signal 1 (an example of a first zero cross pulse) corresponding to a period in which the absolute value of the AC voltage is less than a predetermined threshold value Vt1 (an example of a first threshold value). The inverting buffer IC2 outputs a low-active zero cross signal 2 (an example of a second zero cross pulse) corresponding to a period in which the absolute value of the AC voltage is less than a predetermined threshold value Vt2 (an example of a second threshold value) (FIG. 3). The generation principle of the zero cross signals 1 and 2 will be described in detail later.

  These zero cross signals 1 and 2 are input to a microcomputer 60 having a ROM, a RAM and the like built therein. The microcomputer 60 includes a heater control circuit 70 that is connected in series to the above-described AC power source 100 and the above-described halogen heater 23, controls the energization of the halogen heater 23, the thermistor 25, and the housing surface of the laser printer 1. Is connected to a display panel 80 as an example of an error notifying means provided in.

  Although not shown, a well-known main switch is provided between the AC power supply 100, the diode bridge D1, and the halogen heater 23. In FIG. 2, the AC power supply 100 is divided into two for convenience, but both are the same (more specifically, for example, the same outlet). The configuration from the resistor R1 and the diode bridge D1 to the microcomputer 60 corresponds to an example of the zero cross detection device of the present invention.

  Next, the principle of generating the zero cross signals 1 and 2 will be described. As the absolute value of the AC voltage increases, a larger amount of current flows through the phototransistor PC1b, the potential input to the inverting buffer IC1 decreases, and the potential input to the inverting buffer IC2 further decreases. For this reason, when the absolute value rises above the threshold value Vt1 determined according to the voltage of the DC power supply Vcc, the characteristics of the inverting buffer IC1, the characteristics of the photocoupler PC1, and the resistance values of the resistors R2 and R3, the inverting buffer IC1 becomes H A level signal is output, and when the absolute value falls below the threshold value Vt1, an L level signal is output as the zero cross signal 1 (see FIG. 3). Similarly, the inverting buffer IC2 has the absolute value above the threshold Vt2 (Vt1> Vt2) determined according to the voltage of the DC power supply Vcc, the characteristics of the inverting buffer IC2, the characteristics of the photocoupler PC1, and the resistance values of the resistors R2 and R3. When the value increases, an H level signal is output, and when the absolute value decreases below the threshold value Vt2, an L level signal is output as the zero cross signal 2 (see FIG. 3).

[Processing in this embodiment]
Next, processing executed by the microcomputer 60 (an example of a zero cross point detection unit and a heating control unit) based on a program stored in a built-in ROM will be described. FIG. 4 is a flowchart showing a zero cross point detection process that is executed when the main switch is turned on and is repeatedly executed periodically.

  In this process, first, in S1 (S represents a step: the same applies hereinafter), it is determined whether or not the zero cross signal 1 is detected. In S1, a negative determination is made if the output of the inverting buffer IC1 has been at the L level from the start of processing (during the output of the zero cross signal 1), and the output of the inverting buffer IC1 is practically from the H level to the L level. It is determined whether or not it has been switched to. When the zero cross signal 1 is not detected (S1: N), the process proceeds to S2, and it is determined whether the zero cross signal 2 is detected. Even in S2, a negative determination is made if the output of the inverting buffer IC2 has been at the L level from the start of processing (while the zero cross signal 2 is being output), and the output of the inverting buffer IC2 is practically from the H level to the L level. It is determined whether or not it has been switched to. If the zero cross signal 2 is not detected (S2: N), the process proceeds to S1 described above.

  In this way, normally, the zero cross signal 2 is detected after the zero cross signal 1 is detected while the loop processing of S1 and S2 is repeatedly executed. Therefore, when the zero cross signal 1 is detected during the execution of the loop process (S1: Y), the process proceeds to S3, and the first timer built in the microcomputer 60 is started, whereby the zero cross signal 1 is detected. Measurement of the pulse width Tw1 (see FIG. 3) is started. In subsequent S4, it is determined in the same manner as in S2 whether the zero-cross signal 2 is detected. When the zero cross signal 2 is not detected (S4: N), the process waits at S4. When the zero cross signal 2 is detected (S4: Y), the process proceeds to S5. In S5, the measurement of the pulse width Tw2 (see FIG. 3) of the zero-cross signal 2 is started by starting the second timer built in the microcomputer 60.

  As illustrated in FIG. 3, normally, when the AC voltage changes from a maximum value (a maximum value on the + side) or a minimum value (a maximum value on the − side) to a minimum value or a maximum value via a zero cross point, the zero crossing is performed. Detection of signal 1, detection of zero cross signal 2, end of detection of zero cross signal 2 (change from inverted buffer IC2 output from L level to H level), end of detection of zero cross signal 1 (from L level of inverted buffer IC1 output to H level) The four points in time are arranged in time order.

  Therefore, in S6 following S5, the process waits until the detection of the zero-cross signal 2 is completed (S6: N). When the detection of the zero-cross signal 2 is completed (S6: Y), the process proceeds to S7. In S7, the measurement of the zero cross signal 2 is ended by stopping the second timer, and the pulse width Tw2 of the zero cross signal 2 is calculated. In the subsequent S8, the process waits until the detection of the zero cross signal 1 is completed (S8: N). When the detection of the zero cross signal 1 is completed (S8: Y), the process proceeds to S9. In S9, the measurement of the zero cross signal 1 is terminated by stopping the first timer, and the pulse width Tw1 of the zero cross signal 1 is calculated. In S10 following S9, the zero cross point at which the absolute value of the AC voltage becomes zero is calculated as follows.

  Here, if the AC voltage from the AC power supply 100 is an accurate sine wave, the centers of the zero cross signals 1 and 2 coincide with each other, and the center becomes the zero cross point. However, when the AC voltage from the AC power supply 100 is distorted and not an accurate sine wave, the centers of the zero cross signals 1 and 2 are shifted from the zero cross point. For example, as illustrated in FIG. 3, when the gradient of the waveform of the AC voltage is different before and after the zero cross point, the centers of the zero cross signals 1 and 2 (that is, the centers of the pulse widths Tw1 and Tw2) are determined from the accurate zero cross points. The inclination of the waveform shifts to the gentle side.

  Therefore, in S10, a time point that is later than the start point of the zero cross signal 2 by the time calculated by the equation Tw2 * Ta / (Ta + Tb) is calculated as the zero cross point, and the process is temporarily ended. In the above equation, as illustrated in FIG. 3, Ta is the time from the start point of the zero cross signal 1 to the start point of the zero cross signal 2, and Tb is from the end point of the zero cross signal 2 to the end point of the zero cross signal 1. Is the time. The slope of the waveform before the zero cross point is reflected in time Ta, and the slope after the zero cross point is reflected in time Tb. For this reason, if the above formula is used, it is possible to accurately estimate the zero cross point by a simple calculation process. For this reason, in this embodiment, the zero cross point can be detected well even when the waveform is distorted and deviates from the sine wave.

  In S10, the ratio between the time Ta and the time Tb is calculated before the zero cross point is calculated. If the value of the ratio is not in the range of 1/2 <Ta / Tb <2, the display panel 80 is displayed. An error may be notified via That is, the value of the ratio changes due to the aging of the photocoupler PC1 and the distortion of the AC voltage, but if it is not in the range of 1/2 <Ta / Tb <2, it is assumed that some abnormality has occurred. . For example, some abnormality is assumed such that the inversion buffer IC1 or IC2 is out of order, octopus wiring is performed, or a device that consumes a large amount of power is being used nearby. Therefore, if an error is notified in such a case, it is possible to cope with an abnormality of the inversion buffer IC1 or IC2 or an abnormality of the AC power supply.

  Further, since the luminous intensity of the light emitting diode PC1a gradually decreases due to the secular change, the current flowing through the phototransistor PC1b also decreases, and the zero cross signal 1 may not be output as illustrated in FIG. Similarly, the zero cross signal 1 may not be output even when the AC voltage drops for some reason. Therefore, in this embodiment, in such a case, the zero cross point is detected based only on the zero cross signal 2 as follows.

  Returning to FIG. 4, in this case, since the zero cross signal 2 is detected (S1: N) before the zero cross signal 1 is detected (S1: N), the process proceeds to S15 and is the same as S5 described above. Then, measurement of the pulse width Tw2 of the zero cross signal 2 is started. In subsequent S16, the process waits until the detection of the zero cross signal 2 is completed (S16: N). When the detection of the zero cross signal 2 is completed (S16: Y), in S17, the pulse of the zero cross signal 2 is the same as in S7 described above. A width Tw2 is calculated. In subsequent S20, the time point later than the start point of the zero cross signal 2 by the time calculated by the equation Tw2 / 2, that is, the center of the zero cross signal 2 is calculated as the zero cross point, and the process is temporarily ended. For this reason, in this Embodiment, it can suppress that the detection of a zero crossing point becomes impossible and troubles other control.

  Next, FIG. 6 is a flowchart showing a warm-up process executed after the main switch is turned on and the zero cross point is first calculated by the zero cross point detection process. As shown in FIG. 6, in this process, first, in S50, the halogen heater 23 is turned on in accordance with the calculated zero cross point.

  In subsequent S51, it is determined whether or not the surface temperature of the heating roller 21 (hereinafter also referred to as the temperature of the fixing device 20) detected via the thermistor 25 has reached a predetermined temperature set in advance for warm-up. The If the specified temperature has not been reached (S51: N), the process proceeds to S52, and it is determined whether or not a preset warm-up timeout time T has elapsed. If the warm-up timeout time T has not elapsed (S52: N), the process proceeds to S51 described above.

  If the temperature of the fixing device 20 reaches the specified temperature while the processes of S51 and S52 are repeated (S51: Y), the process proceeds to S53, and the halogen heater 23 is turned off at the zero cross point. , The process ends. On the other hand, before the temperature of the fixing device 20 reaches the specified temperature (S51: N), if the warm-up timeout time T elapses (S52: Y), a fixing device error indicating that the fixing device 20 has an abnormality in S54. After being displayed on the display panel 80, the process ends. In the processes of S50 and S53, the timing at which the zero cross point is calculated next is predicted based on the zero cross point calculated so far by the zero cross point detection process (a known AC frequency may also be referred to). As a result, the on / off of the halogen heater 23 is adjusted to the zero cross point.

[Effects and modifications of this embodiment]
Thus, in the present embodiment, the zero cross point can be detected well even when the waveform of the AC voltage is distorted and deviates from the sine wave. For this reason, if the halogen heater 23 is switched on / off in accordance with the zero cross point detected (calculated) in the present embodiment, the occurrence of flicker can be suppressed extremely well. Further, in the present embodiment, since the zero cross point can be detected only by the zero cross signal 2 even if the zero cross signal 1 is not output due to secular change or the like, it is controlled that the zero cross signal 1 cannot be detected. Can be prevented.

  In addition, this invention is not limited to the said embodiment at all, It can implement with a various form in the range which does not deviate from the summary of this invention. For example, as a form for estimating the zero cross point based on the start point and end point of the zero cross signals 1 and 2, it is also conceivable to use a calculation formula, a map or the like other than the above. Further, the zero cross point calculated as described above can be applied to other than the control of the halogen heater 23, and the present invention can be applied to other than the image forming apparatus such as the laser printer 1.

DESCRIPTION OF SYMBOLS 1 ... Laser printer 10 ... Image forming part 11 ... Photosensitive drum 14 ... Laser scanner unit 15 ... Developing unit 20 ... Fixing device 21 ... Heating roller 22 ... Pressure roller 23 ... Halogen heater 70 ... Heater control circuit 80 ... Display panel 100 ... AC power supply D1 ... Diode bridge IC1, IC2 ... Inversion buffer L ... Laser beam P ... Paper PC1 ... Photocoupler PC1a ... Light emitting diode PC1b ... Phototransistors R1, R2, R3 ... Resistors

Claims (5)

A zero cross detection device that detects a zero cross point at which the absolute value of the AC voltage output from the AC power source becomes zero,
First zero cross pulse output means for outputting a first zero cross pulse corresponding to a period in which the absolute value of the AC voltage is less than a preset first threshold;
Second zero cross pulse output means for outputting a second zero cross pulse corresponding to a period in which the absolute value of the AC voltage is less than a second threshold value set in advance to a value smaller than the first threshold value;
Based on four time points consisting of the start point and end point of the first zero cross pulse output from the first zero cross pulse output means and the start point and end point of the second zero cross pulse output from the second zero cross pulse output means, A zero cross point detecting means for detecting the zero cross point;
A zero-cross detection device comprising: A ratio between the time from the start point of the first zero cross pulse to the start point of the second zero cross pulse and the time from the end point of the second zero cross pulse to the end point of the first zero cross pulse is preset. Error notification means for notifying an error when the predetermined range is exceeded,
The zero cross detection device according to claim 1, further comprising:   When either the first zero cross pulse output means or the second zero cross pulse output means does not output the first zero cross pulse or the second zero cross pulse, the zero cross point detection means outputs the zero cross of the output one. 3. A zero-cross detection device according to claim 1, wherein a time point in the center between a start point and an end point of a pulse is detected as the zero-cross point.   The zero cross point detection means is a difference between a time from the start point to the end point of the first zero cross pulse and a time from the start point to the end point of the second zero cross pulse, and from the start point of the first zero cross pulse to the end point. The time until reaching the start point of the second zero cross pulse is divided, and the time point that is later than the start point of the second zero cross pulse is multiplied by the time from the start point of the second zero cross pulse to the end point. It detects as a point, The zero cross detection apparatus of any one of Claims 1-3 characterized by the above-mentioned. An image forming apparatus comprising the zero-cross detection device according to claim 1,
Image forming means for forming an image on a recording medium;
A fixing unit that includes a heating unit that is heated by applying an AC voltage from the AC power source, and thermally fixes an image formed on the recording medium by the image forming unit;
Based on a zero cross point detected by the zero cross detection device, heating control means for controlling the heating unit,
An image forming apparatus comprising:

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