JPH0561380A - Electrophotographic image forming device and fault discriminating method for its fixing unit - Google Patents

Abstract

PURPOSE:To detect the faults of a fixing unit in a short time by comparing the rate of a change at every prescribed times of the output signal of a temperature detecting means with a prescribed value set in advance and discriminating the faults of the fixing unit. CONSTITUTION:When the energization of a heater 11c incorporated in a fixing roller 11a is in the ON-state, a CPU 23 samples a thermistor voltage in proportion to the surface temperature of the fixing roller 11a whenever the prescribed time lapses. and the sampled voltage Vt is compared with the last sampled voltage Vt'. When Vt > Vt' is not obtained, the energization of the heater 11c obtains the OFF-state, and the LCD display of an operational panel 27 has 'fixing unit faults'. In other words. the rate of the change at every prescribed times of the thermistor Vt is compared with the prescribed value set in advance (the output change voltage of one pitch of an A/D converter 22), to discriminate the faults of the fixing unit. Therefore, the faults of the fixing unit are promptly detected, and the melting, fuming, firing, etc., of a part caused by the faults. are suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as an optical printer such as a laser printer, a copying machine and a facsimile machine, and more particularly to a technique for detecting a failure of a fixing device.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus such as a laser printer, in order to fix a toner image transferred from a surface of a photosensitive member onto a transfer sheet, the toner image is fixed by heating and pressure bonding using a fixing roller. A fuser is used.

Then, the fixing roller in the fixing device is heated by energizing a built-in heater to raise the surface temperature of the fixing roller, and the surface temperature is detected by a temperature detector such as a thermistor, and its output is obtained. On / off control of energization to the heater is performed so that the surface temperature of the fixing roller is maintained at a predetermined temperature according to a signal.

By the way, in such an image forming apparatus, there has been conventionally considered a function of self-detecting a failure in which the fixing roller cannot be raised to a predetermined temperature due to a disconnection of a heater or the like. This is because when the surface temperature of the fixing roller does not reach a predetermined temperature (usually an appropriate temperature for fixing) within a predetermined time after the power supply to the heater is started, it is determined that the fixing device is out of order. ..

In the image forming apparatus having such a fixing device failure detection function, the time from the start of energization of the heater to the judgment of the fixing device failure is set to a very long time of about 1 to 2 minutes. Has been done. This is the condition under which the surface temperature rise of the fixing roller is the worst (low heater voltage,
This is to prevent erroneous detection of a failure of the fixing device even when the heat capacity of the roller is large and the environmental temperature is low.

In FIG. 11, the solid line shows the thermistor voltage rise curve (proportional to the temperature rise curve of the fixing roller surface) when the energization of the heater is turned on under normal conditions, and the broken line is as described above. The rising curve of the thermistor voltage under the worst condition is shown. in this case,
When the voltage equivalent to the predetermined temperature Vs has not been reached, for example, 200 seconds after the heater is energized, it is determined that the fixing device is out of order.

[0007]

However, in the electrophotographic image forming apparatus as described above, for example, when there is an abnormality in the temperature detector (for example, a thermistor for contacting the surface of the fixing roller to detect the temperature is used). Even if the surface temperature of the fixing roller actually rises when the roller is separated from the roller surface), the output signal (thermistor voltage) of the temperature detector will remain forever as shown by the chain line in FIG. Since the voltage Vs corresponding to the predetermined temperature is not reached, the heater continues to be energized for 200 seconds until it is determined that the fixing device has failed.

In this case, finally, the surface temperature of the fixing roller far exceeds the normal operating temperature range, and there is a concern that parts may be melted, and even smoke and ignition may occur. The present invention has been made in view of the above points, and an object thereof is to make it possible to detect a failure of a fixing device promptly.

[0009]

In order to achieve the above-mentioned object, the present invention heats a fixing roller in a fixing device by energizing a built-in heater to raise the surface temperature of the fixing roller. A temperature detecting means for detecting the surface temperature of the fixing roller, and a fixing temperature control for controlling on / off of energization of the heater so that the surface temperature of the fixing roller is maintained at a predetermined temperature in accordance with an output signal of the means. In the electrophotographic image forming apparatus including the means, means for comparing the rate of change of the output signal of the temperature detecting means for each predetermined time with a predetermined value while driving the temperature raising means, And a means for determining a failure of the fixing device based on the comparison result.

Further, during the driving of the temperature raising means, the rate of change of the output signal of the temperature detecting means is obtained at predetermined time intervals, and the rate of change is compared with a predetermined value set in advance to determine the failure of the fixing device. It also provides a method for determining the failure of a container.

[0011]

According to the present invention, during the driving of the temperature increasing means, the rate of change of the output signal of the temperature detecting means at every predetermined time is compared with a predetermined value set in advance to determine the failure of the fixing device.
It is possible to promptly detect the failure of the fixing device and minimize the secondary damage due to the failure.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a schematic configuration diagram showing an internal mechanism of a laser printer embodying the present invention.

The laser printer main body 1 is composed of an upper structure (upper frame) 1a and a lower structure (lower frame) 1b. The upper structure 1a can be opened and closed by a shaft 2 with respect to the lower structure 1b. Installed. Further, in the figure of the upper structure 1a, the paper feed cassette 3 is detachably provided on the right side and the paper discharge tray 4 is provided on the left side. As the paper feed cassette 3, various paper feed cassettes containing various papers of different sizes can be used.

A belt-shaped photosensitive member 5 is provided substantially in the center of the printer body 1, and a charging charger 6, a developing unit 7, a transfer charger 8 and a cleaning device are arranged around the photosensitive member 5 in the order indicated by the arrow (rotating direction). The electrophotographic process equipment excluding the laser writing unit of the unit 9 is arranged, the laser writing unit 10 is provided below them and the heater 11 is provided above them.
a fixing roller 11a, a pressure roller 11b, and a thermistor TH as a temperature detecting element (temperature sensor)
Each of the fixing devices 11 is provided with.

The thermistor TH for detecting the surface temperature of the fixing roller 11a has a spring 11 together with a holding member 11d made of sponge for holding the thermistor TH.
It is urged toward the fixing roller 11a by e and is in light contact with its surface. Further, in the printer body 1, there are provided a paper feed unit including a paper feed roller 12 and a pair of registration rollers 13, a conveyance guide plate 14, and a paper ejection unit including a paper ejection roller 15 and a paper ejection guide plate 16. It is equipped.

When a print sequence is started by a command from a host system such as a word processor or a computer, the paper feed roller 12 causes the paper feed cassette 3 to start.
Paper feeding starts from the beginning, and then the registration roller pair 1
At timing 3, the sheet is conveyed to the upper side of the photoconductor 5.

The photosensitive member 5 rotates in the direction of the arrow, and at that time, the surface uniformly charged by the charging charger 6 is exposed to the laser light modulated by the laser writing unit 10 according to the image information signal or the like. Irradiation is performed while performing main scanning in the body width direction to form an electrostatic latent image.

When the toner passes through the developing unit 7, toner is attached to make it visible, and after being transferred by the transfer charger 8 to the lower surface of the paper conveyed to the upper side of the photoconductor 5, it is guided by the conveyance guide plate 14. Fixing roller 1 in the fixing device 11
The toner image is fed between 1a and the pressure roller 11b, and the toner image is fixed there by the heat of the heater 11c. Then, the sheet exiting the fixing device 11 is discharged by the sheet discharging roller 15,
As a result, the sheet is guided by the sheet discharge guide plate 16 and is stacked on the sheet discharge tray 4.

FIG. 3 is a circuit diagram showing an example of a fixing temperature control device in this laser printer. In this fixing temperature control device, the heater 11c is built in the heat roller 11a as described above, and is energized from the AC power supply AC via the heater energization control circuit 21 to fix the fixing roller 1a.
Heat 1a.

The thermistor TH is actually in contact with the surface of the heat roller 11a as shown in FIG. 2, and its resistance value changes according to the surface temperature (the resistance value becomes smaller as the temperature rises). ). Thereby, DC power supply + 5V
To the ground through the thermistor TH and the resistor R, the magnitude of the current I changes. The current I is detected by the resistor R as a temperature detection voltage (hereinafter referred to as “thermistor voltage”) Vt
Is converted into a digital value of 8 bits by the A / D converter 22 and input to a central processing unit (hereinafter abbreviated as “CPU”) 23.

The CPU 23 compares the digital value from the A / D converter 22 with a predetermined value preset and stored in the ROM 24 to keep the surface temperature of the fixing roller 11a at an optimum value (about 160 to 180 ° C.). As described above, the heater energization control circuit 21 outputs an on / off control signal for on / off control of energization of the heater 11c. The heater energization control circuit 21 supplies alternating current from an AC power source (100V) to the heater 11c via a switching element, for example, a solid state relay (SSR) whose opening and closing is controlled by an ON / OFF control signal from the CPU 23.

The ROM 24 is a read-on memory for storing a program for operating the CPU 23 and fixed data, and the RAM 25 is a random access memory used as a working memory of the CPU 23 and a buffer memory for temporarily storing various data. .. The timer 26 is used when determining a failure of the fixing device 11 described later.
The operation panel 27 is provided with various keys and an LCD display or a display such as a 7-segment display, and has a function of displaying the fact on the LCD display or a display such as a 7-segment display when the fixing device fails.

When the fixing device 11 is normal, the heater 1
When the energization of 1c is turned on, the thermistor voltage Vt rises with a certain degree of inclination (rate of change). However, when an abnormality occurs due to a disconnection of the heater 11c, the thermistor voltage Vt has an inclination of "0" or very high. It will be small. In this embodiment, it is possible to determine the failure of the fixing device by utilizing this characteristic.

FIG. 1 is a flow chart showing the processing according to the present invention by the CPU 23 of FIG. This routine starts when called from a main routine (not shown), first starts the timer 26, and then determines whether or not the power supply to the heater 11c is on.

When the heater 11c is energized, the timer count value of the timer 26 is a predetermined value (the surface temperature of the fixing roller 11a is the temperature rise rate under the worst condition as shown by the broken line in FIG. 11). It is determined whether or not the digital value of the thermistor voltage in the case of rising reaches a time slightly larger than the time required to increase 1LSB). However, since the timer 26 has just started, the heater 11
The process returns to the determination as to whether or not the power supply to c is in the on state.

After that, when the timer count value of the timer 26 reaches a predetermined value, the timer 26 is reset, then the thermistor voltage Vt (actually its digital value) is sampled, and the voltage Vt and the previous sampling voltage Vt 'are sampled.
However, the sampling of the thermistor voltage Vt is the first time this time, so the previous sampling voltage is 0V.
As a result, the relation with the sampling voltage this time becomes Vt> Vt ′, the timer 26 is restarted, and the same processing as described above is performed.

After the second sampling of the thermistor voltage Vt, the sampling voltage Vt
And the first sampling voltage Vt ′ are compared, and Vt>
If it is Vt ', the process returns to the judgment as to whether or not the energization to the heater 11c is on, but if it is not Vt>Vt', the energization to the heater 11c is turned off and the LCD panel (not shown) of the operation panel 27 displays "Fuser failure. Is displayed.

That is, if the heater 11c is energized, the thermistor voltage Vt (digital value) for each sampling
Is supposed to increase, so if it is not, it can be judged that the fixing device is out of order.

As described above, according to this embodiment, the rate of change of the thermistor voltage Vt for each predetermined time is compared with a predetermined value (the output change voltage for one pitch of the A / D converter 22) for fixing. Since the failure of the container 11 is determined, the failure of the fixing device can be promptly detected, and the melting of parts due to the failure and the secondary damage such as smoking and ignition can be minimized.

FIG. 4 is a perspective view schematically showing the external appearance of the laser printer. This laser printer can be divided into an upper structure 31a and a lower structure 31b similarly to the above-described laser printer, and when the user opens the upper structure 31a, the laser printer actually uses the fixing device 32 in the lower structure 31b. It can be touched by hand. Therefore, when a jam of the print paper occurs due to the printing operation, the user may open the upper structure 31a as shown in FIG. 4 and remove the jammed paper in the paper transport path.

However, in the fixing device as shown in FIG. 5, when the print sheet P is caught inside the mold cover 33, the user must remove the mold cover 33 to remove the print sheet P. It requires a difficult work to carry out, and it is not easy to remove the jammed print paper P.

Therefore, an improved example of the fixing device is shown in FIGS. FIG. 6 is a perspective view showing an example of a fixing device provided with a detachable lid with respect to the mold cover.

The fixing device 41 has a mold cover 4
Fixing roller 43 and pressure roller 4 having a heater built in 2
4 and. Further, an opening is formed above the mold cover 42, and slide grooves 42a, 42a are further formed inside the mold cover 42 in the longitudinal direction. The slide groove 42a is slidably fitted into the opening to open the opening. A lid 45 for closing is provided.

According to the fixing device 41 constructed as described above,
When a jam of the print paper occurs inside, by sliding the lid 45 in the longitudinal direction and removing it,
You can easily remove the jammed print paper. Further, the fixing roller 43 and the pressure roller 44 can be easily cleaned with respect to dirt caused by toner or paper dust.

FIG. 7 is a perspective view showing an example different from FIG. 6 of a fixing device provided with a lid detachable from the mold cover, and the same parts as those in FIG. 6 are designated by the same reference numerals. Also in this fixing device 51, an opening is formed above the mold cover 52, and a lid 53 is provided to close the opening. Four claws 53a are formed on the back surface of the lid 53, and further, on the outside of the mold cover 52, engaging grooves 52 which engage with the respective claws 53a when the lid 53 is mounted.
a is formed.

According to the fixing device 51 thus constructed,
When a jam of the print paper occurs inside the jammed print paper, the cover paper 53 can be removed upward to easily remove the jammed print paper. Further, the fixing roller 43 and the pressure roller 44 can be easily cleaned.

FIG. 8 is a perspective view showing an example of a fixing device provided with a lid that can be opened and closed with respect to the mold cover, and the same parts as those in FIG. 6 are designated by the same reference numerals. Also in the fixing device 61, an opening is formed above the mold cover 62, and a lid 63 is provided to close the opening.
The lid 63 and the mold cover 62 are connected by a hinge 64, and the lid 63 can be opened and closed with respect to the mold cover 62. Further, the lid 63 has two opening / closing claws 63a.
And a lid 6 is formed on the outside of the mold cover 62.
Engagement grooves 62a are formed to engage with the respective claws 63a when 3 is closed.

According to the fixing device 61 thus constructed,
When a jam of print paper occurs inside the jammed print paper, the jammed print paper can be easily removed simply by opening the lid 63. Further, the fixing roller 43 and the pressure roller 44 can be easily cleaned.

FIG. 9 shows a cover 63 of the fixing device 61 shown in FIG.
It is a perspective view showing an example when the lock mechanism of is provided.
Two stopper hooks 65, 65 are fixed to the lid 63 of the fixing device 61, and are engaged with the stopper hooks 65, 65 near the opening inside the mold cover 62 when the lid 63 is closed. Solenoids 66, 66 with lockable stop bars 66a, 66a are provided.

Each of the solenoids 66 is connected to a microcomputer (hereinafter abbreviated as "CPU") 71 as shown in FIG. 10, and for detecting the surface temperature of the fixing roller 43 with the lid 63 closed. The thermistor TH
When the detected value of exceeds the preset temperature, C
It is energized by the PU 71 and pushes the stop rods 66a, 66a to move in the direction of the arrow. As a result, the locking hook 65 is engaged and locked to the locking rod 66a, and the lid 63 cannot be opened.

On the other hand, when the print sheet is jammed in the printer body and the detected value of the thermistor TH becomes a value below the preset temperature, the energization is turned off by the CPU 71 and the stop rods 66a and 66a are returned to the return positions. Is sucked up to. As a result, the stopper rod 66a is separated from the stopper hook 65, the lock is released, and the lid 63 can be opened.

According to this fixing device, even when a jam of the print paper occurs, the lid 63 can be opened safely and easily and the jam paper inside can be removed. Note that the fixing device as shown in FIGS. 6 and 7 can also be provided with the locking mechanism as described above to improve the safety.

Although the embodiment in which the present invention is applied to the laser printer has been described above, the present invention is not limited to the laser printer, but can be applied to other optical printers such as LED printers and liquid crystal shutter printers, as well as copying machines and facsimile machines. And various other electrophotographic image forming apparatuses.

[0044]

As described above, according to the present invention, since the failure of the fixing device can be detected in a short time, the secondary damage due to the failure can be minimized.

[Brief description of drawings]

FIG. 1 is a flowchart showing a process according to the present invention by a CPU 23 of FIG.

FIG. 2 is a schematic configuration diagram showing an internal mechanism of a laser printer embodying the present invention.

FIG. 3 is a circuit diagram showing an example of a fixing temperature control device in this laser printer.

FIG. 4 is a perspective view schematically showing the outer appearance of a laser printer.

FIG. 5 is a cross-sectional view showing a schematic configuration of a conventional fixing device.

FIG. 6 is a perspective view showing an example of a fixing device provided with a lid that is attachable to and detachable from a mold cover.

FIG. 7 is a perspective view showing an example different from FIG. 6 of a fixing device provided with a lid detachable from a mold cover.

FIG. 8 is a perspective view showing an example of a fixing device provided with a lid that can be opened and closed with respect to a mold cover.

9 is a perspective view showing an example of a case where a lock mechanism of a lid is provided in the fixing device of FIG.

FIG. 10 is a block diagram showing a control circuit for the solenoid of FIG.

FIG. 11 is a diagram showing the relationship between time and the thermistor voltage according to the surface temperature of the fixing roller.

[Explanation of symbols]

1 Laser Printer Main Body 11 Fixer 11a Fixing Roller 11c Heater 21 Heater Energization Control Circuit 22 A / D Converter 23 Central Processing Unit (CPU) 24 ROM 25 RAM 26 Timer 27 Operation Panel TH Thermistor

Claims (2)

[Claims] 1. A temperature raising means for heating a fixing roller in a fixing device by energizing a built-in heater to raise a surface temperature of the fixing roller, and a temperature detecting means for detecting a surface temperature of the fixing roller. An electrophotographic image forming apparatus including: a fixing temperature control unit that controls ON / OFF of energization of the heater so that the surface temperature of the fixing roller is maintained at a predetermined temperature according to an output signal of the unit. In driving the temperature increasing means, means for comparing the rate of change of the output signal of the temperature detecting means with a predetermined value set in advance, and failure of the fixing device based on the comparison result by the means. And an electrophotographic image forming apparatus. 2. A temperature raising means for heating the fixing roller in the fixing device by energizing a built-in heater to raise the surface temperature of the fixing roller, and a temperature detecting means for detecting the surface temperature of the fixing roller. An electrophotographic image forming apparatus including: a fixing temperature control unit that controls ON / OFF of energization of the heater so that the surface temperature of the fixing roller is maintained at a predetermined temperature according to an output signal of the unit. In the driving of the temperature raising means, the rate of change of the output signal of the temperature detecting means at every predetermined time is obtained, and the rate of change is compared with a preset predetermined value to determine the failure of the fixing device. A method for determining a failure of a fixing device.