JP2006136104A - Zero-crossing detector and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect a zero-crossing point using a relatively simple and inexpensive circuit constitution. <P>SOLUTION: A photocoupler 102 (a zero-crossing signal generating circuit) generates a zero-crossing signal for indicating the zero-crossing point in an AC voltage based on an AC power supply 101. A gate signal generating means receives the AC voltage, and generates a gate signal having a pulse width including a range in the vicinity of the nature zero-crossing point, and comprises a combination of a diode bridge 103, a voltage dropping circuit 104, a noise filter 105 and a rectangular wave generating section 106. A logical product circuit 107 acquires a logical product of the gate signal and an output from the photocoupler 102 (the zero-crossing signal generating circuit). A latch circuit 108 (a pulse signal forming circuit) forms a leading edge of a pulse in response to a first signal edge in an output from the logical product circuit 107, and forms a trailing edge of the pulse in response to a trailing edge of the gate signal. The pulse outputted from the latch circuit 108 becomes the desired zero-crossing signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zero-cross detection device that generates a zero-cross signal of an alternating voltage and an image forming apparatus using the same.

  In general, in an image forming apparatus such as a copying machine, a printer, or a FAX, power control is performed using a switching element such as a triac as a method of driving using an AC voltage such as a heater or a light source. This power control includes wave number control and phase control, and as a reference for timing for turning on the switching element, a signal indicating the switching point of the half wave of the AC voltage waveform on the time axis (hereinafter referred to as zero cross signal) is used. Control is based on this.

  FIG. 4 shows an example of a conventional zero-cross signal generation circuit. The light emitting element 33 in the photocoupler 32 is turned on by the AC voltage of the AC power supply 31 connected to the input terminal of the photocoupler 32 via a resistor, and the phototransistor 34 on the output side is turned on / off, so that the collector A zero cross signal can be obtained. That is, the amount of light emitted from the light emitting element 33 changes in proportion to the potential (absolute value) of the alternating voltage, and the amount of light that cannot turn on the phototransistor 34 is reduced by decreasing the potential of the alternating voltage. A signal indicating a zero crossing point is output at.

  Based on this zero-cross signal, it is possible to control the amount of power of a heater, a light source, and the like using a switching element such as a triac. Hereinafter, an example of phase control of a fixing heater or the like in a conventional image forming apparatus will be described.

  FIG. 5 shows an example of a heater control circuit 40 using a triac. Energization of the heater 42 connected to the AC power supply 31 is controlled by ON / OFF of the triac 41. A control signal for turning ON / OFF the triac 41 is controlled by the phototransistor 44 on the output side of the phototriac 43. The phototransistor 44 is controlled by a light emitting diode 45 on the input side of the phototriac 43. The light emitting diode 45 is driven via a driving transistor 46 from a CPU (not shown).

  The CPU receives the zero-cross signal generated by the zero-cross signal generation circuit of FIG. 4 and starts the CPU interrupt process at the rising edge of the zero-cross signal (when High is active). For example, in the case of phase control, the CPU starts a timer by interruption of a zero cross signal, and outputs a triac ON signal after a predetermined time. When the input AC voltage is 50 Hz, the zero cross signal is generated every 10 msec. When the timer time from the generation of the zero cross signal to the output of the triac ON signal is set to 5 msec, for example, the AC voltage waveform applied to the load when the triac is turned on is in a phase angle range of 90 ° to 180 °, 270 ° to 360 °. Thus, the amount of power is 50%.

In this way, by changing the timer setting of the triac ON signal output based on the zero cross signal, the amount of power to the load can be freely controlled.
JP 2002-268450 A JP 2004-212713 A

  In the case of a conventional zero cross generation circuit, there is no problem if the input AC voltage waveform is a clean sine wave without noise or fluctuation. However, when spike noise N as shown in FIG. 3A described later occurs, or when voltage fluctuation V near the zero cross point occurs, a zero cross signal is generated at a position other than the original zero cross point, In addition, a large number of signal changes occur in the vicinity of the zero cross point (FIG. 3-b), which makes it difficult to determine the true zero cross point.

  For such a problem, Patent Document 1 discloses a technique for digitizing an AC voltage to be monitored by an A / D converter and detecting a zero cross correctly by digital signal processing. However, this technique requires a relatively expensive part such as an A / D converter, and has a drawback that the processing load of the processing apparatus increases due to digital signal processing.

  Patent Document 2 discloses a technique for accurately detecting a zero cross point by providing a filter means for filtering an AC waveform on the input side of a photocoupler. However, this technique has a drawback that a phase shift occurs in the zero-cross detection signal due to the influence of filtering. In order to cope with this drawback, it is necessary to provide some phase correction means.

  In addition, for a power supply fluctuation that exceeds the standard value of the power supply, if zero cross detection is performed using a noise filter, a normal zero cross signal may not be detected.

  The present invention has been made in such a background, and an object thereof is to provide a zero-cross detection device capable of accurately detecting a zero-cross point with a relatively simple and inexpensive circuit configuration and an image forming apparatus using the same. There is to do.

  Another object of the present invention is to provide a zero-cross detection device capable of performing normal zero-cross detection even for various power supply situations such as power supply fluctuations exceeding the standard value of the power supply, and an image forming apparatus using the same. There is to do.

  A zero-cross detection device according to the present invention is a zero-cross detection device that detects a zero-cross point of an AC voltage of an AC power source, and generates a zero-cross signal that indicates a zero-cross point of the AC voltage based on the AC power source. A gate signal generating means for generating a gate signal having a pulse width including a range in the vicinity of the original zero cross point of the AC voltage, and an AND circuit for calculating a logical product of the output of the zero cross signal generating circuit and the gate signal; A pulse signal forming circuit for forming a leading edge of a pulse at the first signal edge in the output of the AND circuit and forming a trailing edge of the pulse at the trailing edge of the gate signal.

  In this zero cross detection device, first, a gate signal having a pulse width including a range near the original zero cross point is generated by the gate signal generation means. By obtaining this gate signal, the approximate range of the original zero cross point is narrowed down, and by calculating the logical product of this gate signal and the output of the zero cross signal generation circuit, in a range other than the vicinity of the original zero cross point. Eliminate the effects of generated noise. Thereby, the generation range of the zero cross pulse to be obtained can be limited to the vicinity of the original zero cross point.

  Next, the pulse signal forming circuit forms the leading edge of the pulse at the first signal edge in the output of the AND circuit, and forms the trailing edge of the pulse at the trailing edge of the gate signal. As a result, even if multiple detection signals are generated at the output of the zero-cross signal generation circuit due to power supply voltage fluctuations, etc. within the vicinity of the original zero-cross point, a single signal is generated based on the first level change. The zero cross pulse signal can be generated.

  The gate signal generating means includes a full-wave rectifier circuit connected to the AC power supply, a noise filter for removing noise from the output of the full-wave rectifier circuit, and comparing the output of the noise filter with a predetermined threshold value to obtain a square shape. It can be configured by a square wave generator that generates waves.

  The pulse signal forming circuit can be constituted by a latch circuit that latches the first signal edge in the output of the AND circuit and is reset at the trailing edge of the gate signal. With this configuration, a single zero-cross signal pulse can be output even if a plurality of signal changes occur within the time width of the gate signal.

  A rectification unit that rectifies the AC voltage and a smoothing unit that smoothes the output voltage of the rectification unit may be provided, and the output voltage of the smoothing unit may be used as the predetermined threshold value. As a result, it is possible to cope with power supply fluctuations that exceed the standard value of the power supply.

  The zero-cross detection device according to the present invention can be used in an image forming apparatus that controls at least one of a heater and a light source based on the AC power supply.

  According to the zero-cross detection device of the present invention, it is possible to remove noise based on a gate signal having a position and pulse width including a range near the original zero-cross point, and to simply change a plurality of signal changes within the time width of the gate signal. By performing the two-stage process of conversion into one pulse, it is possible to accurately detect the zero cross point with a relatively simple and inexpensive circuit configuration.

  Further, by using this zero-cross detection device for an image forming apparatus, it is possible to perform appropriate power control of a heater and a light source.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to other drawings.

  FIG. 1 is a block diagram illustrating a circuit configuration of a zero-crossing detection apparatus 100 according to an embodiment of the present invention. In the figure, an AC power source 101 is a commercial AC voltage source, and the AC voltage is applied to a photocoupler 102 as a conventional zero-cross signal generation circuit and a diode bridge 103 as a full-wave rectifier circuit. The output of the diode bridge 103 is input to a step-down circuit 104 and a noise filter (low-pass filter) 105, where step-down and noise removal are performed. The output of the noise filter 105 is input to the square wave generator 106. The square wave generator 106 compares this input signal with a predetermined threshold value and outputs a pulsed gate signal. This gate signal is input to one input terminal (here, an inverting input terminal) of an AND (logical product) circuit 107. The output of the photocoupler 102 is input to the other input terminal (here, the non-inverting input terminal). The output of the AND circuit 107 is input to the latch input terminal of the latch circuit 108. A gate signal from the square wave generator 106 is input to the reset input terminal of the latch circuit 108 as a reset signal.

  In this example, the diode bridge 103, the step-down circuit 104, the noise filter 105, and the square wave generation unit 106 constitute the gate signal generation means in the present invention.

  FIG. 2 shows an example of a specific circuit configuration of the zero-cross detection device 100 of FIG. FIG. 3 shows signals at main points in the circuit of FIG. The symbols in the circuit diagram of FIG. 2 correspond to the symbols of FIG. The step-down circuit 104 and the noise filter 105 are configured by a voltage dividing circuit using resistors 114 and 115 and a parallel capacitor 113. The square wave generator 106 includes a comparator 118 and resistors 116 and 117 that constitute a voltage dividing circuit connected to the inverting input terminal. The voltage dividing circuit generates a reference voltage (threshold value) for comparison by the square wave generator 106. The latch circuit 108 includes transistors 122 and 123 connected to each other in a positive feedback relationship to realize the latch function, a transistor 121 that activates the latch function of the transistor 122 by the output of the AND circuit 107, and a square wave generator 106. It is constituted by a transistor 124 for resetting a latch state by an output. Note that the output of the phototransistor of the photocoupler 102, the output of the AND circuit 107, and the output of the square wave generation unit 106 are connected to the DC voltage Vcc through a pull-up resistor, respectively.

  A description will be made assuming that the AC voltage waveform shown in FIG. 1 is superimposed with a noise component as shown in FIG. For example, as shown in FIG. 4, the zero-cross signal can be obtained on the output side by passing an alternating voltage through a photocoupler 102 as a zero-cross signal generation circuit. However, a signal affected by noise superimposed on the AC voltage is output to this signal (FIG. 3-b).

  Further, the AC voltage is input to the gate signal generating means separately from the photocoupler 102. The AC voltage input to the gate signal generating means is rectified by a full-wave rectifier circuit composed of a diode bridge 103 (FIG. 3-c), and then stepped down by a voltage divider circuit 104. The stepped-down rectified waveform is input to the noise filter circuit 105 and smoothed to remove noise components (FIG. 3D). In the present embodiment, the noise filter circuit 105 is configured by an RC filter circuit, but is not limited to this. The smoothed signal is converted into a square wave via the square wave generation unit 106 in order to obtain a final gate signal (FIG. 3E). In this embodiment, signal processing is performed using a comparator. Next, by taking the product of the two signals generated by the above circuit, it is possible to eliminate the influence of noise generated at a timing other than the zero cross point (FIG. 3-f).

  A signal from which the influence of noise other than the zero cross point is removed (FIG. 3F) is input to the latch circuit 108. In this embodiment, the latch circuit is formed by transistors, but the present invention is not limited to this method. In the example of FIG. 2, the latch circuit 108 holds the level starting from the rising edge of the input signal (FIG. 3-f) (formation of the leading edge of the pulse). The above-mentioned gate signal (FIG. 3-e) is used to reset the latched signal, and the latch circuit 108 is reset by the rising edge of the gate signal (formation of the trailing edge of the pulse). The latch circuit 108 corrects the zero cross signal affected by noise generated near the zero cross point into one square wave (FIG. 3G).

  The zero cross signal from which the noise component has been removed by these processes is input to the CPU, and a control signal is output from the CPU to the heater control circuit 40 shown in FIG. 5 at an appropriate timing.

  FIG. 6 is a block diagram illustrating a control hardware configuration of an image forming apparatus that uses the zero-cross detection apparatus 100 illustrated in FIG. 1. The entire apparatus is controlled by a control unit 200 including a CPU. The control unit 200 operates according to a control program stored in the memory 201. The memory 201 can temporarily store various data such as image data in addition to the control program. The image input unit 202 includes an image scanner in the case of a copying machine, a print data communication unit in the case of a printer, and a line communication unit in the case of a facsimile, and transfers input image data to the control unit 200. The various sensors 203 are sensor groups including various sensors necessary for the operation of the apparatus, and input sensor outputs to the control unit 200.

  The image forming unit 204 is a part that forms a toner image on a sheet by a known electrophotographic method or the like. The fixing unit 208 is a part for fixing the toner image formed by the image forming unit 204 to the paper by heat and pressure, and has a heater control circuit 40 inside, and the zero cross signal obtained by the zero cross detection device 100 is used as a heater. Used for control.

  The paper feed unit 205 is a mechanism that picks up and feeds paper from the paper feed stage under the control of the control unit 200, such as a clutch that selectively transmits the power of the drive source to the pickup roller and the paper feed roller. including. The paper transport unit 206 is a mechanism that transports the fed paper under the control of the control unit 200, and includes a clutch that selectively transmits the power of the drive source to the transport roller. The operation panel unit 207 includes a display unit (such as an LCD) that provides various information to the user and an input unit (such as a numeric keypad and operation buttons) for inputting various instructions. Various instructions include a print instruction, number-of-sheets setting, density setting, paper feed stage selection, mode selection, and the like. In FIG. 6, the AC power supply is not shown.

  Next, another embodiment of the present invention will be described with reference to FIGS. FIG. 7 shows another example of a specific circuit configuration of the zero-cross detection device 100 of FIG. FIG. 8 shows signals at main points in the circuit of FIG. In FIG. 7, the same circuit elements as those shown in FIG. 2 are denoted by the same reference numerals, and redundant description is omitted.

  In the circuit configuration shown in FIG. 2, the reference voltage of the comparator 118 (the waveform in FIG. 3H) is a fixed potential. However, in a power supply situation in which the input AC voltage fluctuates significantly, the pulse width of the square wave (FIG. 3-e) output from the square wave generator 106 fluctuates with the input AC voltage, and the zero cross signal is accurately detected. Can no longer be detected. Therefore, in the present embodiment, as shown in FIG. 7, the output of the rectifier 71 (configured with two diodes here) connected to the AC power supply 101 is smoothed by a smoother 72 made of a capacitor and a resistor. The voltage is used as a reference voltage for the comparator 118.

  When the amplitude of the voltage greatly varies as shown in the waveform of FIG. 8-a, the output of the full-wave rectifier circuit 103 (the waveform of FIG. 8-c) also varies significantly. In the configuration of FIG. 7, the smoothing voltage (FIG. 8-h) of the output of the rectifying unit 71 also changes in accordance with this variation, so the pulse width of the output of the comparator 118 (FIG. 8-e) using this as a reference voltage is changed. Large fluctuations are suppressed. Therefore, the final zero cross signal (FIG. 8G) can be generated with higher accuracy.

  Although the preferred embodiments of the present invention have been described above, various modifications and changes can be made. For example, the detailed configuration of the circuit, the polarity of the signal, and the like are not limited to those illustrated. Although FIG. 6 shows an example used for controlling the heater of the fixing device, it can also be used for controlling the light source.

It is a block diagram showing the circuit structure of the zero cross detection apparatus which concerns on embodiment of this invention. FIG. 2 is a circuit diagram illustrating an example of a specific circuit configuration of the zero-cross detection device in FIG. 1. FIG. 3 is a timing diagram showing signals at main points in the circuit of FIG. 2. It is a figure which shows an example of the conventional zero cross signal generation circuit. It is a figure which shows an example of the heater control circuit using a triac. FIG. 2 is a block diagram illustrating a control hardware configuration of an image forming apparatus that uses the zero-cross detection device illustrated in FIG. 1. It is a circuit diagram which shows the other example of the concrete circuit structure of the zero crossing detection apparatus of FIG. FIG. 8 is a timing diagram showing signals at main points in the circuit of FIG. 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 71 ... Rectification part 72 ... Smoothing part 101 ... AC power supply 102 ... Photocoupler 103 ... Diode bridge 104 ... Step-down circuit 105 ... Noise filter 106 ... Square wave generation part 107 ... AND circuit 108 ... Latch circuit 118 ... Comparator

Claims (8)

A zero cross detection device for detecting a zero cross point of an AC voltage of an AC power source,
A zero cross signal generating circuit for generating a zero cross signal indicating a zero cross point of the AC voltage based on the AC power source; and
Gate signal generating means for generating a gate signal having a pulse width including a range near the original zero cross point of the AC voltage;
A logical product circuit that takes a logical product of the output of the zero-cross signal generation circuit and the gate signal;
And a pulse signal forming circuit for forming a leading edge of a pulse at the first signal edge in the output of the AND circuit and forming a trailing edge of the pulse at the trailing edge of the gate signal. apparatus.   The gate signal generating means includes a full-wave rectifier circuit connected to the AC power supply, a noise filter for removing noise from the output of the full-wave rectifier circuit, and comparing the output of the noise filter with a predetermined threshold value to obtain a square shape. The zero-cross detection device according to claim 1, wherein the zero-cross detection device includes a square wave generation unit that generates a wave.   3. The pulse signal forming circuit is configured by a latch circuit that latches a first signal edge in an output of an AND circuit and is reset at a trailing edge of the gate signal. Zero cross detection device.   The zero cross detection apparatus according to claim 2, further comprising a rectifying unit that rectifies the AC voltage and a smoothing unit that smoothes an output voltage of the rectifying unit, and the output voltage of the smoothing unit is used as the predetermined threshold value. In a zero cross detection device that detects a zero cross point of an AC voltage of an AC power source, and an image forming apparatus that controls at least one of a heater and a light source based on the AC power source,
The zero cross detection device generates a zero cross signal indicating a zero cross point of the AC voltage based on the AC power supply, and a zero cross signal generation circuit,
Gate signal generating means for generating a gate signal having a pulse width including a range near the original zero cross point of the AC voltage;
A logical product circuit that takes a logical product of the output of the zero-cross signal generation circuit and the gate signal;
And a pulse signal forming circuit for forming a leading edge of a pulse at a first signal edge in an output of the AND circuit and forming a trailing edge of the pulse at a trailing edge of the gate signal. apparatus.   The gate signal generating means includes a full-wave rectifier circuit connected to the AC power supply, a noise filter for removing noise from the output of the full-wave rectifier circuit, and comparing the output of the noise filter with a predetermined threshold value to obtain a square shape. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus includes a square wave generating unit that generates a wave.   7. The pulse signal forming circuit includes a latch circuit that latches a first signal edge in an output of an AND circuit and is reset at a trailing edge of the gate signal. Image forming apparatus.   The image forming apparatus according to claim 6, further comprising: a rectifying unit that rectifies the AC voltage; and a smoothing unit that smoothes an output voltage of the rectifying unit, wherein the output voltage of the smoothing unit is used as the predetermined threshold value.

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