JPH11258950A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the whole image forming device from becoming unworkable by restraining from abnormal operation of the fixing device in consequence of a noise from an AC power source, a failure of the phase detecting device, or the like. SOLUTION: This image forming device is provided with controlling means 40 performing control of the turning on by normally applying the AC input from AC power source 28 with respect to a heater 27 from arbitrary phase by a phase angle timer 42, and in the case of the disabling of detecting the phase of the AC input from the AC power source 28, performing the control of turning on by applying the AC input from the AC power source 28 without adopting the phase angle timer 42 with respect to the heater 27 irrespective of its phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device, such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In an image forming apparatus, transfer paper, OH
An image is formed on a sheet such as a P sheet with a developer,
Some devices use a fixing device that applies heat to the sheet when fixing the developer on the sheet to the sheet. In some fixing devices, an AC heater heats a heating member such as a heating roller, and the heating member fuses a developer on the sheet to the sheet, thereby fixing an image on the sheet to the sheet.

In this fixing device, as a control method for controlling the lighting of the AC heater, an on / off control for turning on / off an AC input from a commercial power supply to the AC heater regardless of its phase to turn on the AC heater. A control method and a phase in which the phase of the AC input from the commercial power supply is detected by a phase detection device, the AC input from the commercial power supply is applied to the AC heater from a predetermined phase angle, and the phase angle is controlled to control the AC heater. There is a control method.

In this phase control system, a control device generates a lighting signal at a predetermined phase angle after a specified time from the input of the phase detection signal from the phase detecting device, and the AC signal from the commercial power supply is converted into AC by the lighting signal. A to heater
Turn on the C heater. The specified time is stored in a memory or the like of the control device, and the control device starts the timer circuit in response to the input of the phase detection signal, causes the timer circuit to count the clock, and when the count value matches the specified time. A lighting signal for lighting the AC heater is generated. Further, in order to accurately turn on the AC heater at a target phase angle, the phase detection device detects a point at which an AC input from a commercial power supply becomes 0 V with an element such as a photocoupler, and also detects the 0 V detection signal. At the same time, the phase of the AC input from the commercial power supply is accurately detected.

Japanese Patent Application Laid-Open No. Hei 9-62375 discloses a circuit for detecting an AC input voltage without variation by determining a detection timing of an AC input voltage using a zero-cross signal as a trigger, which varies according to the input voltage. A power supply device that accurately controls power of a fixing device is described. Japanese Patent Application Laid-Open No. 8-66005 describes an image forming apparatus provided with an AC control device for stopping power supply to a fixing heater and improving safety when a zero-cross signal cannot be detected. .

Japanese Patent Application Laid-Open No. Hei 7-234729 describes a power control device which improves control accuracy by detecting and correcting a change in frequency of power supplied from a commercial power supply to a control target. Japanese Patent Application Laid-Open No. Hei 8-286556 describes an image forming apparatus in which a control method of a fixing heater is made variable in accordance with a voltage change of an AC power supply.

[0007]

The image forming apparatus employing the above on / off control method has the advantage that the phase of the AC input from the commercial power supply need not be detected by the phase detecting device, and the structure can be simplified. There is A
In order to control on / off of the AC input to the C heater irrespective of its phase, the rush current from the commercial power supply to the AC heater may increase, and this rush current affects the voltage of the commercial power supply. A phenomenon such as flickering may occur in a light source or the like in a room using the forming apparatus.

In an image forming apparatus employing a phase control method, the phase of an AC input from a commercial power supply is detected, and the AC input from the commercial power supply is supplied to the AC heater from a specific phase angle. It is possible to reduce the inrush current from the power supply to the AC heater and suppress the influence of the inrush current on the commercial power supply.

However, in order to apply the AC input from the commercial power supply to the AC heater from a specific phase angle and control the phase angle, it is necessary to always detect the phase of the AC input from the commercial power supply. If the phase detection signal becomes abnormal due to noise from the device or malfunction of the phase detection device, normal control of the AC heater cannot be performed, and the entire image forming apparatus becomes unusable due to abnormal lighting or non-lighting of the AC heater. There are cases.

The phase detector detects a point at which the AC input from the commercial power supply becomes 0 V by using an element such as a photocoupler to generate a 0 V detection signal. The 0 V detection signal is based on the frequency and voltage value of the commercial power supply. The signal width is liable to change due to the influence of the AC power, which hinders accurate detection of the phase of the AC input from the commercial power supply. If the phase angle cannot be accurately detected in the phase angle control, abnormal lighting or non-lighting of the AC heater may occur. To prevent this, the specified time stored in the memory is usually set to a certain level loose,
Absorbing the error of the phase detection signal prevents abnormal lighting of the AC heater even if the phase detection signal is shifted. However, the AC heater cannot be turned on accurately at the target phase angle. The temperature of the fixing device cannot be accurately controlled.

In the phase detector, a point at which the AC input from the commercial power supply becomes 0 V is detected by a photocoupler, and the point is detected.
When generating a V detection signal, the photocoupler may generate a phase detection signal at a point other than the original 0 V in the AC input from the commercial power supply in response to noise from the commercial power supply. The erroneous phase detection signal is A
C causes abnormal control of the heater, resulting in AC
Phenomena such as abnormal lighting and non-lighting of the heater are generated, and a temperature abnormality of the fixing device is caused, thereby making the entire image forming apparatus inoperable.

If the constant of the input filter provided on the input side of the phase detector is set too large in order to prevent the generation of an erroneous phase detection signal due to noise from the commercial power supply, the characteristic variation of the photocoupler and the like will occur. Due to fluctuations in the voltage of the commercial power supply, not only the erroneous phase detection signal due to noise from the commercial power supply but also the original phase detection signal is attenuated, which may cause an abnormality in the fixing device.
It is also difficult to make the constant of the input filter too large.

According to the first aspect of the present invention, it is possible to prevent an abnormal operation of a fixing device due to noise from an AC power supply, a malfunction of a phase detection device, and the like, thereby preventing the entire image forming apparatus from becoming inoperable. It is an object of the present invention to provide an image forming apparatus capable of performing the following. According to a second aspect of the present invention, there is provided an image forming apparatus capable of more accurately lighting an AC heater at a target phase angle even when the width of a phase detection signal changes according to the frequency or voltage value of an AC power supply. Aim.
According to a third aspect of the present invention, there is provided an image forming apparatus capable of stably generating a phase detection signal, preventing occurrence of an abnormality in a fixing device, and ensuring safe operation of the image forming apparatus. The purpose is to do.

[0014]

According to a first aspect of the present invention, a heating member is heated by a heater, and the developer on the sheet is fused to the sheet by the heating member. An image forming apparatus having a fixing device for fixing the image of the sheet to a sheet, a first control for supplying an AC input from an AC power supply to the heater from an arbitrary phase by a phase angle timer and lighting the heater, On the other hand, without using the phase angle timer, selectively performs the second control to supply and turn on the AC input from the AC power supply regardless of the phase, and usually performs the first control, When the phase of the AC input from the AC power supply cannot be detected, a control unit for performing the second control is provided.

According to a second aspect of the present invention, there is provided a fixing device for heating a heating member by a heater, and fusing the developer on the sheet to the sheet by the heating member to fix an image on the sheet to the sheet. And a phase detection device for detecting the phase of the AC input from the AC input from the AC power supply to the heater using a phase detection signal from the phase detection device from any phase by a phase angle timer An image forming apparatus for supplying and lighting is provided with means for detecting an interval of a phase detection signal from the phase detecting device and changing a control timing of a lighting signal for lighting the heater based on a result of the detection.

According to a third aspect of the present invention, there is provided a fixing device in which a heating member is heated by a heater, and the heating member fuses a developer on the sheet to the sheet to fix an image on the sheet to the sheet. A phase detection device that detects the phase of an AC input from the AC power supply, and an AC input from the AC power supply is supplied to the heater from an arbitrary phase by a phase angle timer using the phase detection signal from the phase detection device. In the image forming apparatus to be turned on, there is provided means for changing a circuit constant of the phase detection device according to the number of phase detection signals per unit time from the phase detection device.

[0017]

FIG. 2 shows a first embodiment of the present invention. The first embodiment is an embodiment of an electrophotographic image forming apparatus including an analog copying machine, and controls an AC heater by a phase control method which usually has little influence on a commercial power supply, and generates noise from the commercial power supply. If the abnormality occurs that the phase of the AC input from the commercial power supply cannot be detected due to an increase in the temperature or a failure of the phase detection device, the abnormality is detected and the control method of the AC heater is automatically controlled. By changing the system to the on / off control system, abnormal operation of the fixing device is prevented, and the entire image forming apparatus is prevented from becoming inoperable.

A document is set on a document table 1 by a document feeder 2 or manually, and a photoconductor drum 3 is used as a photoconductor as an image carrier. This photosensitive drum 3
At the time of image formation, the image forming apparatus is rotated and driven by the driving unit and uniformly charged by the charging device 4, the unnecessary portion of the charge is removed by the eraser 5, and the electrostatic latent image is exposed by the slit exposure device 6 as exposure means. It is formed.

The slit exposure device 6 illuminates the original on the original table 1 with a light source 7 and reflects the reflected light on mirrors 8 to 10.
An image is formed on the photosensitive drum 3 via the lens 11 and the mirror 12, and the original is scanned by moving the light source 7 and the mirrors 8 to 10, thereby exposing the photosensitive drum 3 and exposing the original image to the photosensitive drum. 3, an electrostatic latent image is formed on the photosensitive drum 3.

The electrostatic latent image on the photosensitive drum 3 is
An image (toner image) is formed by developing the sheet 3 and a sheet made of a transfer sheet or an OHP sheet from a selected one of the sheet feeding devices 14 to 16 is fed to the registration roller 17. The registration roller 17 sends out a sheet in accordance with the image on the photosensitive drum 3, and the transfer device 18 as a transfer unit applies a charge to the back of the sheet to transfer the image on the photosensitive drum 3. After the image is formed by the developer (toner), the charge removing device 19 is used.
As a result, the back surface is neutralized and separated from the photosensitive drum 3.

The sheet separated from the photosensitive drum 3 is conveyed by a conveying device 20, an image (toner image) is fixed by a fixing device 21, and sorted by a sorter 22. The photosensitive drum 3 is initialized by removing the residual toner by the cleaning device 23 after the transfer of the toner image and removing the charge by the charge removing device 24.

The fixing device 21 has a heating roller 25 as a heating member for applying heat to the sheet, a pressing roller 26 pressed against the heating roller 25 by a pressing mechanism, an AC heater 27 for heating the heating roller 25, and the like. The heating roller 25 and the pressure roller 26 are driven to rotate by a driving mechanism. The sheet conveyed by the conveying device 20 is heated by a heating roller 25.
The developer (toner) on the sheet is fused to the sheet by the heating roller 25, and the image on the sheet is fixed on the sheet.

FIG. 1 shows a part of the electrical system of the first embodiment. In FIG. 1, 28 is a commercial power supply connected to the first embodiment, 29 is an AC harness for transmitting an AC input from the commercial power supply 28, 30 is a triac as a control element for controlling lighting of the AC heater 27, and 31 is A thermistor 32 serving as a temperature detecting means for detecting the temperature of the fixing device 21 (the surface temperature of the heating roller 25) and converting the temperature into a resistance value. A thermistor 32 detects a point (0V point: zero cross) where the AC input from the commercial power supply 28 becomes 0V. A photocoupler as a detecting element for detecting,
33 and 34 are resistors. Thermistor 31 and resistor 33
Outputs a voltage value corresponding to the temperature of the fixing device 21 (the surface temperature of the heating roller 25) as a temperature detection signal.

Reference numeral 35 to 37 denote a noise removing circuit comprising a noise filter for removing noise from the output signal of the photocoupler 32.
Is a multiplexer that selects any one of the noise filters 35 to 37 and connects its output to the input of the next stage.
Reference numeral 39 denotes a buffer including a transistor and the like as a phase detection circuit for detecting the phase of an input signal from the multiplexer 38. The photocoupler 32, the resistor 34, the noise filters 35 to 37, the multiplexer 38, and the buffer 39 constitute a phase detection device.

Reference numeral 40 denotes a microcomputer (CPU) serving as control means.
And the temperature detection signal from the thermistor 31 are input to the fixing device 21 based on these input signals.
The AC heater 27 is controlled by generating a lighting signal to the triac 30 so that the temperature (surface temperature of the heating roller 25) is kept constant. 41 indicates that the CPU 40
This is a memory element that stores a set value of a timer circuit used for performing phase control of an AC input voltage from the AC heater 27 to the AC heater 27.

Reference numeral 42 denotes a phase which starts at the fall of the phase detection signal from the buffer 39, counts the clock, compares the count value with a specified value, and sends a match signal to the CPU 40 when the count value matches the specified value. A timer circuit as an angular timer, 43 is a timer circuit as a signal interval measuring means for measuring an interval of the phase detection signal from the buffer 39, and 44 starts counting of a clock at a fall of the phase detection signal from the buffer 39. By latching the internal count value at the rising edge of the phase detection signal from the buffer 39 and outputting it to the CPU 40, the timer circuit as a signal width detection means for detecting the time during which the phase detection signal holds a low level is provided. is there.

When the AC input voltage input from the commercial power supply 28 becomes equal to or higher than the predetermined value Vf, the photocoupler 32 emits light in the internal light emitting section 32a, and the light receiving element 32b including a phototransistor in the output section emits light. A 0V point detecting means for detecting a point (0V point) at which the AC input voltage from the commercial power supply 28 becomes equal to or higher than the fixed value Vf by receiving and conducting the light from the 32a.

The output signal of the photocoupler 32 is input to noise filters 35 to 37 to remove noise, and the multiplexer 38 selects one of the noise filters 35 to 37 according to a control signal from the CPU 40 and outputs the selected signal. Side is connected to the input side of the buffer 39. Buffer 3
9 detects the phase of the output signal of one of the noise filters 35 to 37 selected by the multiplexer 38 and outputs a phase detection signal to the CPU 40 and the timer circuits 42 to 44 (output of the noise filter selected by the multiplexer 38) The signal is stabilized at its voltage value and output as a phase detection signal to the CPU 40 and the timer circuits 42 to 44). FIG. 3 shows an example of waveforms of an AC input voltage from the commercial power supply 28, an output signal of the photocoupler 32, and an output signal of the filter 39 as a phase detection circuit.

The CPU 40 has a memory element 41 in advance.
The specified value is read from the timer circuit 42, and the specified value is set in the timer circuit 42. The timer circuit 42 starts the counting operation when the phase detection signal from the buffer 39 falls. The system clock used for the operation of the CPU 40 is input to the timer circuit 42, and the timer circuit 42 counts the system clock. FIG. 5 shows the phase detection signal from the buffer 39, the system clock, the count value of the timer circuit 43, and the CP value from each of the timer circuits 42 to 44.
3 shows an output signal to U40.

The timer circuit 42 compares the count value with a set value (a specified value set by the CPU 40), for example, 7, and outputs a match signal to the CPU 40 when the count value matches the set value. When receiving the coincidence signal from the timer circuit 42, the CPU 40 turns on the control signal to the triac 30, applies a lighting signal to the triac 30, and turns on the triac 30, so that the AC input voltage from the commercial power supply 28 passes through the triac 30. AC heater 27
To be applied.

When turning off the AC heater 27, the CPU 40 turns off the control signal to the triac 30. The triac 30 is turned off when the AC input voltage from the commercial power supply 28 becomes 0 V first after the control signal from the CPU 40 is turned off, and the AC heater 27 is turned off when the triac 30 is turned off and the AC input voltage from the commercial power supply 28 is turned off. Lighting is stopped because no voltage is applied.

A plurality of specified values are stored in the memory element 41, and the CPU 40 sequentially calls a plurality of specified values from the memory element 41 and sets them in the timer circuit 42 when the power is turned on in the first embodiment. The fixing device 21 is heated while the lighting duty ratio of the AC heater 27 is gradually increased by gradually changing the phase angle at which the AC heater 27 is turned on to suppress the rush current to the AC heater 27.

In the first embodiment, in the normal state, the rush current from the commercial power supply 28 to the AC heater 27 is suppressed low by controlling the AC heater 27 by the above-described phase control so that the rush current with respect to the voltage of the commercial power supply 28 is reduced. The image forming operation is performed with the adverse effects reduced. Further, the timer circuit 43 starts the counting operation at the fall of the phase detection signal from the buffer 39 to count the system clock,
When the next phase detection signal from the buffer 39 falls, the count value is output to the CPU 40 and the count value is cleared. The system clock is output until the next phase detection signal is input from the buffer 39 and the phase detection signal falls. , The falling interval of the phase detection signal is detected.

FIG. 6 shows a processing flow of the CPU 40 in the first embodiment. When the commercial power supply 28 is turned on, the CPU 40 reads a temperature detection signal from the thermistor 31, reads an output value of the timer circuit 43 at an arbitrary timing, for example, at a timing when the AC heater 27 is turned on, and outputs the output value of the timer circuit 43. By determining whether the value is within the specified range, it is determined whether the phase detection signal is abnormal.

As shown in FIG. 4, the buffer 39 is provided at a point other than the point where the AC input voltage from the commercial power supply 28 becomes 0 V due to noise on the AC input voltage from the commercial power supply 28 (0 V point).
When the phase detection signal is output from the
Is out of the specified range (below the specified value). Therefore,
The CPU 40 determines that the output value of the timer circuit 43 is out of the specified range, and detects an abnormality of the phase detection signal from the phase detection circuit (buffer) 39.

If the output value of the timer circuit 43 is within the specified range and the phase detection signal from the phase detection circuit (buffer) 39 is normal, the CPU 40 changes the control method of the AC heater 27 to the temperature from the thermistor 31. A fixing phase control routine is called as a phase control method for controlling the lighting of the AC heater 27 based on the detection signal and the phase detection signal from the buffer 39, and the AC heater 27 is controlled by the phase control immediately after the power is turned on by the fixing phase control routine. By controlling the temperature of the fixing device 21 (the surface temperature of the heating roller 25) while controlling the rush current from the commercial power supply 28 to the AC heater 27 to a low level, the adverse effect of the rush current on the voltage of the commercial power supply 28 is reduced. After the temperature of the fixing device 21 rises to a predetermined temperature, the temperature of the fixing device 21 Temperature 1 controls the AC heater 27 by the phase control so as to maintain a constant set temperature.

The CPU 40 determines that the output value of the timer circuit 43 is out of the specified range and the phase detection circuit (buffer) 3
9 is abnormal, the AC heater 27
Is switched to the on / off control method for controlling the lighting of the AC heater 27 only by the temperature detection signal from the thermistor 31, and the fixing on / off control routine is called. An AC input voltage from the commercial power supply 28 to the AC heater 27 is controlled on / off irrespective of its phase so that the temperature of the fixing device 21 is maintained at a constant set temperature by the temperature detection signal from the AC heater 31. 27 is turned on / off.

For this reason, noise from the commercial power supply 28 or abnormality in the phase detection circuit (buffer) 39 causes the AC heater 2
AC heater 27 even when the phase control of
Can be controlled by an on / off control method, so that the operation of the image forming apparatus can be continued, and the function stop of the entire image forming apparatus can be prevented. When the output value of the timer circuit 43 is out of the specified range and the phase detection signal from the phase detection circuit (buffer) 39 becomes abnormal, the CPU 40 displays an abnormal phase detection signal on a display unit such as an operation unit. The fact that the phase detection signal is abnormal is notified to the user or the service person by displaying the fact.

In the first embodiment, an AC heater 27 heats a heating roller 25 as a heating member, and the heating member 25 applies a developer on the sheet to the sheet. A fixing device 21 for fixing an image on a sheet to a sheet by fusing the AC heater 27 to an AC heater 27 receives a AC input from a commercial power supply 28 serving as an AC power supply as a phase angle timer. The first control for supplying and lighting from an arbitrary phase by 42, and supplying the AC input from the AC power supply 28 to the AC heater 27 without using the phase angle timer 42 regardless of the phase. The second control for turning on the light is selectively performed. Usually, the first control is performed. If the phase of the AC input from the AC power supply 28 cannot be detected, the second control is performed. CPU40 as a control means for performing
Therefore, it is possible to prevent abnormal operation of the fixing device due to noise from the AC power supply, malfunction of the phase detection device, and the like, and prevent the entire image forming apparatus from becoming inoperable. Therefore, the stable operation of the image forming apparatus and the reduction of adverse effects such as voltage fluctuations on the AC power supply can be effectively compatible.

Next, a second embodiment of the present invention will be described. In the first embodiment, the width of the phase detection signal from the buffer 39 changes depending on factors such as the voltage value of the commercial power supply 28 input to the image forming apparatus of the first embodiment. For example, as shown in FIG.
When it is as high as 1 rms, the width of the phase detection signal from the buffer 39 becomes narrow like WAVE2 in FIG. 7, and the deviation of the fall of the phase detection signal from the true 0 V point of the input voltage from the commercial power supply 28 is a small value. Fits in T1. However, when the input voltage from the commercial power supply 28 is as low as V2 rms, the width of the phase detection signal from the buffer 39 becomes equal to W in FIG.
AVE1, and the deviation of the fall of the phase detection signal from the true 0 V point of the input voltage from the commercial power supply 28 becomes large as T2.

The timer circuit 42 for generating the lighting signal of the AC heater 27 to the CPU 40 starts counting the system clock from the fall of the phase detection signal from the buffer 39. Even if the lighting signal is generated, the timing for turning on the AC heater 27 is shifted by the time of (T2−T1) due to the difference between the input voltages from the commercial power supply 28, which hinders accurate phase control.

As described above, when the width of the phase detection signal changes, the count start point of the timer circuit 42 deviates from the true 0 V point of the input voltage from the commercial power supply 28,
The CPU 40 generates a lighting signal for the AC heater 27 at a timing different from the intended timing, and the non-lighting or abnormal lighting of the AC heater 27 may occur.

Therefore, in the second embodiment, in the first embodiment, the CPU 40 reads the output value of the timer circuit 44 when the power is turned on, and reads the output value of the commercial power supply 2 based on the output value.
8 is detected. Here, the timer circuit 44 starts counting the system clock at the falling edge of the phase detection signal from the buffer 39, latches the internal count value at the rising edge of the phase detection signal from the buffer 39, and outputs it to the CPU 40. Then, the time during which the phase detection signal holds 0 V is detected.

The CPU 40 detects the signal width of the phase detection signal based on the count value of the timer circuit 44, and stores a half value of the signal width (count value) in the memory element 41 as phase angle correction data. When performing the phase control of the AC heater 27, the CPU 40 reads the specified value for phase control described above from the memory element 41 and sets the specified value for phase control read from the memory element 41 when setting the value in the timer circuit 42. The specified value is corrected by adding the phase angle correction data in the memory element 41, and the corrected specified value is set in the timer circuit 42.

The buffer 39 is composed of the commercial power supply 2
Although the phase detection signal is generated before the true 0 V point of the AC input voltage from 8, the timer circuit 42 sets the value obtained by adding the phase angle correction data to the specified value for phase control, True 0 of the AC input voltage from the commercial power supply 28
The specified value can be counted from the point V, and the lighting signal of the AC heater 27 is sent to the CPU 4 at a more accurate phase angle.
0 can be generated. This makes it possible to more accurately control the phase of the AC heater 27 while preventing the danger of the AC heater 27 not being turned on or being abnormally turned on.
Can be prevented from adversely affecting the voltage.

This second embodiment is an embodiment of the invention according to claim 2, in which a heating roller 25 as a heating member is heated by an AC heater 27, and the developer on the sheet is heated by the heating member 25. A fixing device 21 for fixing an image on a sheet to a sheet by fusing to a sheet, a photocoupler 32 as a phase detecting device for detecting a phase of an AC input from a commercial power supply 28 as an AC power supply, a resistor 34, and a noise filter 35 To 37, a multiplexer 38 and a buffer 39
Using a phase detection signal from the phase detection device, an AC input from the AC power supply 28 is supplied to the heater 27 from an arbitrary phase by a timer circuit 42 as a phase angle timer to light the heater 27. In the image forming apparatus,
Detect the interval of the phase detection signal from the phase detection device,
Based on the result, the timer circuit 4 as means for changing the control timing of the lighting signal for lighting the heater 27
4 and the CPU 40, the AC heater can be more accurately turned on at the target phase angle even if the width of the phase detection signal changes according to the frequency or voltage value of the AC power supply, and accurate control of the fixing device is achieved. Thus, the stable operation of the image forming apparatus can be effectively performed.

Next, a third embodiment of the present invention will be described. In the third embodiment, the input filter circuit 3 including a plurality of noise filters is different from the second embodiment.
The filter constants 5 to 37 are set to different values from each other. For example, the filter constants are set so as to increase in the order of input filter 35 <input filter 36 <input filter 37.

In the first embodiment, if the photocoupler 32 operates at a point other than the 0 V point of the AC input from the commercial power supply 28 due to noise from the commercial power supply 28, the timer circuit 42 accurately supplies the CPU 40 with the AC power. Heater 2
7 cannot be generated, the temperature of the fixing device 21 becomes unstable, and the image forming operation is hindered.

Therefore, in the third embodiment, in the second embodiment, the CPU 40 executes the processing flow shown in FIG. 8 instead of the processing flow shown in FIG. The compatibility between the phase detection device and the commercial power supply 28 is determined based on the number, and the circuit constant of the phase detection device is changed (selection of any one of the input filters 35 to 37 by the multiplexer 38 is changed). Change equipment to optimal condition. That is,
When the AC heater 27 is turned on, the CPU 40 normally selects an input filter 36 having an intermediate filter constant among a plurality of input filters 35 to 37 by a control signal to the multiplexer 38, and buffers the output side of the input filter 36. 39 is connected to the input side.

Then, the CPU 40 reads the output value of the timer circuit 43 to determine whether or not the output value of the timer circuit 43 is within a specified range. If the output value of the timer circuit 43 is smaller than the specified value, the commercial power supply It is determined that the photocoupler 32 is malfunctioning due to the noise from 28 and the input signal of the buffer 39 is selected by the control signal to the multiplexer 38 by selecting the input filter 37 having a larger filter constant and a larger noise removing effect than the input filter 36. Is disconnected from the output side of the input filter 36, and the output side of the input filter 37 is connected to the input side of the buffer 39.

Therefore, the signal passed through the input filter 37 having a large noise removing effect is input to the buffer 39, and the output signal of the photocoupler 32 is removed by the input filter 37 so that the noise having a width equal to or less than the time constant of the input filter 37 is removed. The signal is input to the buffer 39, whereby the buffer 39 can output a normal phase detection signal to the CPU 40 and the timer circuits 42 to 44.

Conversely, the signal width of the phase detection signal (the output signal of the photocoupler 32) is reduced by the characteristics of the photocoupler 32 and the frequency and voltage of the commercial power supply 28, and the input filters 36 and 37 detect the phase detection signal itself. When it is no longer possible (it cannot be passed), the output value of the timer circuit 43 becomes larger than the specified value. So, C
The PU 40 determines that the phase detection signal is abnormal if the output value of the timer circuit 43 becomes larger than the specified value, and determines the input filter 35 having the smallest filter constant and the weakest waveform shaping effect by the control signal to the multiplexer 38. Then, the output side of the input filter 35 is connected to the input side of the buffer 39. As a result, the setting is changed so that the output signal of the photocoupler 32 having a narrower signal width can be passed through the input filter 35 and the buffer 39 can output the phase detection signal.

As described above, by selecting the input filters 35 to 37 provided on the input side of the buffer 39 as the phase detection circuit by the multiplexer 38 and optimizing the filter constant of the input filter, the commercial power supply 28 can be reliably supplied. , The phase control of the AC heater 27 can be stably performed, and the stable operation of the image forming apparatus and the adverse effect on the commercial power supply 28 can be suppressed.

The third embodiment is an embodiment of the third aspect of the present invention, in which a heating roller 25 as a heating member is heated by an AC heater 27, and the developer on the sheet is heated by the heating member 25. A fixing device 21 for fixing an image on a sheet to a sheet by fusing to a sheet, a photocoupler 32 as a phase detecting device for detecting a phase of an AC input from a commercial power supply 28 as an AC power supply, a resistor 34, and a noise filter 35 To 37, a multiplexer 38 and a buffer 39
Using a phase detection signal from the phase detection device, an AC input from the AC power supply 28 is supplied to the heater 27 from an arbitrary phase by a timer circuit 42 as a phase angle timer to light the heater 27. In the image forming apparatus,
Since the CPU 40 and the multiplexer 38 are provided as means for changing a circuit constant of the phase detection device based on the number of phase detection signals per unit time from the phase detection device, compatibility between the phase detection device and the AC power supply is determined. The phase detector can be changed to the optimum state by the operation, the phase detection signal can be generated stably, and the occurrence of abnormality in the fixing device can be prevented. Therefore, it is possible to effectively reduce the adverse effect such as voltage fluctuation of the image forming apparatus, and to guarantee the safe operation of the image forming apparatus.

The present invention is not limited to the above-described embodiment. For example, the present invention can be applied to an image forming apparatus other than the analog copying machine, such as a digital copying machine, a printer, a facsimile, and the like. The present invention is also applicable to an image forming apparatus having a fixing device other than the forming device. Further, the present invention is not only an image forming apparatus having a fixing device for fixing a developer on a sheet to a sheet with a heating roller and a pressure roller, but also a fixing device having a pair of heating rollers and a developer on a sheet. The present invention is also applicable to an image forming apparatus having a fixing device having a heating member such as a heating belt for fixing a sheet.

[0056]

As described above, according to the first aspect of the present invention, abnormal operation of the fixing device due to noise from the AC power supply, malfunction of the phase detection device, and the like can be prevented by the above configuration, and image formation can be prevented. It is possible to prevent the entire device from becoming inoperable. Therefore, the stable operation of the image forming apparatus and the reduction of adverse effects such as voltage fluctuations on the AC power supply can be effectively compatible.

According to the second aspect of the present invention, the AC heater can be more accurately turned on at a target phase angle even if the width of the phase detection signal changes according to the frequency or voltage value of the AC power supply. As a result, accurate control of the fixing device becomes possible, and stable operation of the image forming apparatus can be effectively performed.

According to the third aspect of the present invention, with the above configuration, it is possible to judge compatibility between the phase detection device and the AC power supply and change the phase detection device to an optimum state, thereby stably detecting the phase. A signal can be generated to prevent the occurrence of abnormality in the fixing device, and the safe operation of the image forming apparatus and the reduction of adverse effects such as voltage fluctuations to an AC power supply can be effectively performed. Safe operation can be guaranteed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a part of an electrical system according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the first embodiment.

FIG. 3 is a waveform chart showing waveform examples of an AC input voltage from a commercial power supply, an output signal of a photocoupler, and an output signal of a filter in the first embodiment.

FIG. 4 is a diagram for explaining the first embodiment.

FIG. 5 is a diagram showing a phase detection signal from a buffer, a system clock, a count value of a timer circuit 43, and an output signal from each timer circuit to a CPU in the first embodiment.

FIG. 6 is a flowchart illustrating a processing flow of a CPU according to the first embodiment.

FIG. 7 is a diagram for explaining a second embodiment of the present invention.

FIG. 8 is a flowchart illustrating a processing flow of a CPU according to a third embodiment of the present invention.

[Explanation of symbols]

 21 Fixing Device 25 Heating Roller 27 AC Heater 28 Commercial Power Supply 32 Photocoupler 34 Resistance 35-37 Noise Filter 38 Multiplexer 39 Buffer 40 CPU 42-44 Timer Circuit

Claims (3)

[Claims] An image forming apparatus having a fixing device for heating a heating member by a heater and fusing a developer on the sheet to the sheet by the heating member to fix an image on the sheet to the sheet. On the other hand, the first control in which an AC input from an AC power supply is supplied from an arbitrary phase by a phase angle timer and lighting is performed, and the AC input from the AC power supply is used for the heater without using a phase angle timer. Irrespective of the second control for supplying and lighting, the first control is normally performed, and when the phase of the AC input from the AC power supply cannot be detected, the second control is performed. An image forming apparatus comprising a control unit for performing control. 2. A fixing device for heating a heating member by a heater and fusing a developer on the sheet to the sheet by the heating member to fix an image on the sheet to the sheet, and a phase of an AC input from an AC power supply. And a phase angle timer that supplies an AC input from the AC power supply to the heater from an arbitrary phase using a phase detection signal from the phase detection device to light the heater. The image forming apparatus according to claim 1, wherein said forming apparatus includes means for detecting an interval of a phase detection signal from said phase detecting device and changing a control timing of a lighting signal for turning on said heater based on a result of the detection. 3. A fixing device in which a heating member is heated by a heater, the developer on the sheet is fused to the sheet by the heating member, and an image on the sheet is fixed on the sheet. And a phase angle timer that supplies an AC input from the AC power supply to the heater from an arbitrary phase using a phase detection signal from the phase detection device to light the heater. The image forming apparatus according to claim 1, further comprising means for changing a circuit constant of the phase detecting device based on the number of phase detection signals per unit time from the phase detecting device.