JP2003066759A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve security when the hour of use of an apparatus exceeds a predetermined hour by improving control for operating a circuit which alternately monitors two abnormalities, an abnormal temperature rise and the disconnection of a thermistor, so as to preponderantly monitor abnormal temperature rise on the basis of a simplified technique. SOLUTION: When the hour of use of the apparatus exceeds a predetermined value, control is carried out so as to preponderantly monitor the hour of a switching signal to select one abnormality supervisory circuit. When the hour exceeds the predetermined value, the control is carried out so as to monitor only the abnormal temperature rise during apparatus operation and to detect the disconnection during a predetermined operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a fixing means for fixing an image on a recording medium formed in an image forming section by heating, and an image characterized by a constitution for detecting an abnormality of the fixing means. Forming apparatus

[0002]

2. Description of the Related Art Conventionally, in a so-called electrophotographic image forming apparatus, a toner image is formed on a photosensitive drum,
An image forming unit that transfers the toner image to a recording medium (sheet material) to form an image on the surface of the recording medium, and a toner image formed on the recording medium on the downstream side thereof is heated to transfer the toner to the surface of the recording medium. There is provided a fixing device that is fixed by being welded to.

Regarding the fixing device, the temperature of the heating portion is controlled so that a constant amount of heat is transferred to the recording medium. The temperature of the heating unit is controlled by a thermistor for controlling temperature adjustment arranged in the recording medium passing unit, and an anomaly monitoring unit arranged in the recording medium non-passing unit for further safety pursuant to this. It is done with the thermistor.

As shown in FIGS. 12 and 5 to 7, the circuit configuration, operation, and function of this thermistor for abnormality monitoring can detect two abnormalities, an abnormal temperature rise and a thermistor disconnection. . However, when such a configuration is adopted, the temperature (T1) detected by the temperature adjusting thermistor initially matches the true temperature (T real) as shown in FIG. 11A, and the anomaly monitoring thermistor is detected. Since the arrangement is different from the temperature (T2) due to, a temperature difference occurs. Then, as shown in FIG. 11B, as the use time elapses, the recording medium passing portion is contaminated by the toner, and the heat conduction between the fixing roller and the temperature adjusting thermistor becomes low. Temperature seen (T
1) becomes gradually lower, so that the actually controlled temperature (T
real) is getting higher.

Furthermore, in order to realize energy saving,
Alternatively, the temperature rise tends to be accelerated by reducing the heat capacity of the fixing roller in order to accelerate the startup of the apparatus. Therefore, the temperature ripple frequency and 40 shown in FIG.
When the frequency of one output is the same and the abnormal monitoring temperature is exceeded during disconnection monitoring, it becomes difficult to detect instantaneously.

In order to solve this, the duty ratio is changed by adding a parameter that determines the abnormal temperature monitoring time and subtracting a parameter that determines the disconnection monitoring time according to the operating time of the device. However, it has been configured to focus on abnormal temperature rise monitoring.

[0007]

However, in this configuration, the duty ratio of the abnormal temperature rise monitoring becomes 100% and the duty ratio of the disconnection monitoring becomes 0%, so that the disconnection cannot be detected.

The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to monitor abnormal temperature rise and thermistor disconnection when the operating time of the device reaches a predetermined value. The anomaly monitoring thermistor circuit is controlled to focus on the monitoring of abnormal temperature rises, enabling the instantaneous detection of the occurrence of abnormalities, and also the detection of abnormalities such as disconnection. The purpose of the present invention is to provide an image forming apparatus with dramatically improved safety.

[0009]

The present invention has solved the above problems by having the following constitution.

(1) An image forming portion for forming an image on a recording medium, a fixing means for fixing an image formed on the recording medium on the recording medium by heating, and a temperature of the fixing means is detected. In the image forming apparatus including at least two temperature detecting means whose resistance value changes due to the temperature change, the first monitoring means for monitoring the resistance value of the first temperature detecting means and the first monitoring means. According to the resistance value of the first temperature detection means monitored by the first temperature conversion means for converting into the first temperature information of the fixing means and the resistance value of the first temperature detection means A fixing means temperature control means for controlling the temperature of the fixing means according to the first temperature information converted by the temperature conversion means; a second monitoring means for monitoring the resistance value of the second temperature detecting means; Was monitored by two monitoring means According to the resistance value of the second temperature detecting means, the resistance values of the second temperature converting means and the second temperature detecting means for converting the second temperature information of the fixing means from the first resistance value set in advance. A first resistance value detecting means for detecting a low value, a second resistance value detecting means for detecting that a resistance value of the second temperature detecting means is higher than a preset second resistance value; Switching means for switching either one of the first resistance value detecting means and the second temperature detecting means to connect to the second temperature detecting means, and the resistance value of the second temperature detecting means by the first resistance value detecting means. When it is detected that the resistance value is lower than the first resistance value, it is determined as the first abnormality, and the second abnormality is detected.
When the resistance value detecting means of the second temperature detecting means detects that the resistance value of the second temperature detecting means is higher than the second resistance value, the first abnormality judging means for judging the second abnormality is counted by the counting means. When the measured value reaches a predetermined value, one of the resistance value detecting means outputs a switching signal output by a switching means for connecting one of the two resistance value detecting means to the second temperature detecting means. When the value counted by the addition means and the counting means for adding a predetermined value to the corresponding parameter has reached the predetermined value in order to change the switching signal for connecting to The switching means is controlled so as to output a switching signal according to the parameter changed by the adding means, and when the time added by the adding means exceeds a predetermined value, the second temperature detecting means is connected to two resistors. The switching means is controlled so as to be connected to one of the detecting means, and is controlled so as to monitor the abnormality corresponding to the resistance value detecting means. When a predetermined operation occurs, the second temperature detecting means is switched to the other. An image forming apparatus comprising: a control unit that controls the switching unit so as to be connected to the resistance value comparing unit and controls so as to monitor the other abnormality corresponding to the resistance value detecting unit. .

(2) The switching means includes a switching signal generating means for generating a switching signal for connecting one of the first resistance detecting means and the second resistance detecting means to the temperature detecting means. The 1st and 2nd resistance value detection means have a comparison means used commonly, The detection signal produced | generated by this comparison means is sent to the said 1st abnormality determination means, and the said 1st abnormality determination means. Determines whether the detection signal sent from the comparison means is from the first resistance value detection means or the second resistance value detection means, based on the switching signal generated by the switching signal generation means. The image forming apparatus according to (1).

(3) The above-mentioned (1) or (2), further comprising display means for displaying information corresponding to the first abnormality or the second abnormality judged by the first abnormality judging means. The image forming apparatus according to any one of 1.

(4) A parameter initialization means is provided for returning the parameters changed by the addition means to the initial values after the completion of replacement and cleaning of the fixing means or the components arranged therein. The image forming apparatus according to 1).

(5) The second temperature detecting means is a thermistor having a negative temperature coefficient, and the first resistance value detecting means guides the voltage on one side of the thermistor to the comparing means. A circuit, the second resistance value detection means has a circuit for guiding the voltage on the other side of the thermistor to the comparison means, and the comparison means has the same comparison voltage and one side of the thermistor. The image forming apparatus according to (2) above, wherein the voltage is compared with the voltage on the other side or the voltage on the other side is compared to generate the detection signal to be sent to the first abnormality determining means.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic structure of an electrophotographic copying machine as an example of an image forming apparatus according to the present invention. A copying machine 1 shown in the figure includes a circulating automatic document feeder (hereinafter referred to as RDF) 2 for automatically feeding a document, and an image forming apparatus main body (hereinafter simply referred to as apparatus main body) 3.
The RDF 2 can be freely used in combination with the apparatus body 3.

The apparatus main body 3 is provided with a document table glass 5 as a document table on the upper part thereof. An optical system 6 as an image reading unit is provided below the optical system 6.
Is equipped with an exposure lamp 6a, a zoom lens 6c, and a motor (not shown).
The reflected light from the original is scanned by the scanning mirror 6b and the zoom lens 6c.
Thus, the photoconductor drum 7a is irradiated with the light.

There are the following two methods for irradiating the photosensitive drum 7a with the reflected light from the original. First, a method of moving the exposure lamp 6a with the original fixed on the original glass 5 (hereinafter referred to as fixed reading), and a method of moving the original on the original glass 5 with the exposure lamp 6a fixed. It is a method of moving (hereinafter referred to as non-flow reading).

An image forming section 7 is disposed below the optical system 6, and the image forming section 7 includes a photosensitive drum 7a rotatably disposed in the direction of arrow A1 and the photosensitive drum 7.
A high-voltage unit 7b, a blank exposure unit 7c, and a potential sensor 7 that are sequentially arranged around a along the rotation direction thereof.
d, a developing device 7e, a transfer charging device 7f, a separation charging device 7g, and a cleaning device 7h.

The photosensitive drum 7a is rotationally driven by a main motor (not shown), corona-charged by the high-voltage unit 7b, and then reflected light of the original is irradiated from the optical system 6 to form an electrostatic latent image. Is configured. The electrostatic latent image is developed by the developing device 7e and visualized as a toner image.

On the other hand, at the lower part of the apparatus main body 3, there is provided a paper feeding cassette section 9 having a four-stage structure including a first-stage cassette 9a, a second-stage cassette 9b, a third-stage cassette 9c and a fourth-stage cassette 9d. .

Each cassette is similarly provided with a paper feed section for feeding the sheet material S as a recording medium placed thereon, but as an example, the third-stage cassette 9c.
A schematic configuration of the sheet feeding section will be described. A sheet feeding roller 11a for feeding the sheet material S and a pickup roller 10a are disposed above the leading end of the third-stage cassette 9c.

Further, downstream of them, conveying rollers 12a, 12b, 12c, 12d are arranged in a vertical conveying path H0 for supplying the sheet material S to the image forming section 7,
The sheet material S is configured to be conveyed to the registration roller pair 13 provided near the image forming unit 7. In the vicinity of the image forming unit 7, a multi-manual feed 14 for manually feeding the sheet material S to the image forming unit is arranged.

A conveyor belt 15 for conveying the image-formed sheet material S to the downstream side is disposed downstream of the image forming section 7. A toner image is formed on the downstream side of the conveyor belt 15 by heating. A fixing device 16 is provided as a fixing unit that fixes the surface of the sheet material S.

The fixing device 16 is provided with a fixing roller 16a heated to a predetermined fixing temperature, a lower roller 16b facing and in contact with the fixing roller 16a, and a web (not shown) for cleaning the fixing roller 16a. Thus, the toner image on the surface of the sheet material S conveyed from the image forming section 7 is thermocompression bonded. Further, a thermistor (not shown) as a temperature detecting means for controlling the temperature of the fixing roller 16a is provided so as to come into contact with the fixing roller in this embodiment.

In the vicinity of the fixing device 16, there are provided a path H2 for carrying both sides and multiplex recording, a path H1 for discharging the apparatus main body 3 out of the apparatus, and a paper discharge flapper 17 for switching between them. A pair of discharge rollers 19 is provided on the path H1 when the sheet is discharged from the machine.

Below the fixing device 16, there is provided a conveying path 20 for both sides and a sheet material S to be duplicated.
A discharge roller pair 21 that discharges the sheet material to the temporary storage tray 23 and a discharge sensor 22 that detects the discharge of the sheet material S are disposed downstream thereof. And the discharge sensor 2
In the vicinity of 2, a sheet material re-feeding device 3 that temporarily stores the sheet material S delivered after image formation and then re-feeds the sheet material S sequentially
4 is provided.

The temporary storage tray 23 has an inclined structure in order to assist in reaching the re-feed / separation belt 33, and a re-feed roller 31 is disposed near the leading end thereof, and further downstream thereof. Re-feeding delivery roller 32 and re-feeding separation belt 3
3 are in contact with each other, and the sheet materials S are re-fed one by one.

A multiple flapper 36 is provided near the refeed / delivery roller 32 and the refeed / separation belt 33. Downstream of the multiple flapper 36, there is an upward multiple sheet material S for multiple recording. Reverse conveyance path 3 for reversing the image formation image of
7 downwardly conveys the sheet material S to the image forming unit 7 again and the conveying roller pairs 40a, 40b, 40.
c and 40d are provided respectively.

Further, the sensors 50, 51, 5 for detecting the passage of the sheet material S are provided on each of the above-described transport paths.
2, 53, 54, 55, 56, 57, 58 are arranged.

FIG. 2 shows a block diagram of the control device 100 of this embodiment. The control device 100 includes a CPU 101 that controls the entire copying machine according to a control procedure stored in a read-only memory (ROM) 102, and a read-only memory (that stores a control procedure (control program) of the control device of the apparatus main body 3 ( ROM) 102, a random access memory (RAM) 103, which is a main storage device used as a storage area for input data, a work storage area, and the like, an output of a control signal of the CPU 101 for a load such as a main motor, a sensor, and the like. An interface unit (I / O) 104 for inputting a signal and sending it to the CPU 101 is provided.

Then, the apparatus main body 3 is connected via the I / O 104.
Signals from various devices that are installed in or connected to the CPU 1
It is transmitted between 01. As an example, as shown in a region R1 surrounded by a dashed line, controls such as sorter control, document jam detection, stapling control, and sheet material conveyance are performed.

FIG. 3 shows an arrangement configuration example of the operation panel 200 provided in the apparatus body 3. In FIG. 3, reference numeral 601 denotes a user mode key, which the operator (user)
ON / OFF of automatic sort, ON of takeout in front of sorter
/ OFF, skip both sides ON / OFF, feeder manual feed auto start ON / OFF, cassette auto selection ON / OFF, buzzer ON / OFF setting, slightly smaller mode change, preheat mode setting, specification setting initialization , Standard mode change, auto clear time change, auto power off time change, weekly timer setting, day / time setting, zoom fine adjustment, feeder cleaning, wire cleaning etc.

Reference numeral 602 denotes a guide key, which is used when displaying the explanation of the function of each key on the message display. A clear key 604 is used to cancel the set number of copies.

Reference numeral 605 denotes a copy start key (copy start key), which is pressed when copying is started. Reference numeral 606 denotes an interrupt key, which is interrupted during a copying operation and pressed when another copying is performed. This key is a self-illuminating key that lights up when an interrupt is accepted and lights up during an interrupt.

Reference numeral 607 denotes a preheat key, which is pressed to enter the preheat mode. This key is a self-illuminating key and lights up in the preheat mode. Reference numeral 608 denotes a ten-key pad which is pressed when setting the number of copies.

A stop key 609 is pressed when interrupting continuous copying. After the copying at the time when this key is pressed is completed, the copying operation is stopped. An all reset key 610 is pressed to return to the standard mode.

Reference numeral 615 is an L for displaying information relating to copying as a display means and a warning when an abnormality occurs in the main body of the apparatus.
It is a message display with a CD (liquid crystal) type touch panel and displays characters and figures with 240 × 320 dots. In the standard state, this message display is used to set the standard magnification key, the same size key, the zoom key, the slightly smaller key, the paper selection key, the copy density key, the sorter key for selecting the sorter function, and the mode for double-sided copying. Double-sided key, other, frame erase, binding margin,
Cover / sheet, reduced layout, enlarged layout, OHP
Advanced mode keys for setting the copy mode for advanced copying such as center insertion, page continuous shooting, multiplex, manuscript battle, photo, mode memory, etc. are displayed by touching the part corresponding to each key. Window is displayed. In addition to this, an operation procedure or the like when a paper jam or an error occurs and a warning when the apparatus is abnormal are also displayed.

FIG. 4A shows an abnormality monitoring circuit C1 for monitoring a signal from a thermistor 410 having a negative temperature coefficient arranged in a non-passing portion of the sheet material S in order to detect the temperature of the fixing roller 16a. FIG. 6 is a schematic diagram of a peripheral circuit of a thermistor 412 for temperature adjustment control arranged in a passage portion of the sheet material S. The abnormality monitoring circuit C1 uses a switch signal output 401 from an output port of the I / O 104 as a switch signal generating means to switch 402 as a switch means.
Circuits connected to the thermistor 410 are switched by 403, 404, and 405.

A rectangular wave of a predetermined frequency is output from the I / O 104 as a switching signal output 401 (point B), and when the output is "H", the switches 402 and 405 are turned on,
The switches 403 and 404 are turned off, the thick line circuit (first resistance value detecting means) in FIG. 4B is selected, the resistor 407 is connected between the thermistor 410 and the ground, and the thermistor is connected. The voltage on the ground side as one side of 410 (the voltage between the thermistor 410 and the resistor 407) is the comparator 409 and CP as comparison means.
It is input to the AD converter 413 built in U101. This state is the abnormal temperature rise monitoring state of the thermistor 410 as the first abnormality.

When the switching signal 401 is "L",
Switches 403 and 404 are on, switches 402 and 40
5 is turned off, the thick line circuit (second resistance value detecting means) of FIG. 4C is selected, the resistor 408 is connected between the thermistor 410 and the high voltage side, and the thermistor 410 is connected. The voltage on the high voltage side (the voltage between the thermistor and the resistor 408) is input to the comparator 409 and the AD converter 413 as the comparison means. This state is the disconnection monitoring state of the thermistor 410 as the second abnormality.

Here, 406 is a switch 402 and 40.
5 is an inverting element for inverting the phases of 403 and 404. The output signal of the comparator 409 is
CP that functions as abnormality determination means via I / O 104
The determination is made by U101, and the abnormal state is recognized by the apparatus main body 1.

FIG. 5 shows the switching signal 401 (output H and output L) generated by the I / O 104 and the output of the comparator 409 corresponding to the voltage at the point A of the circuit switched by this signal. 5A is a diagram showing normal operation, FIG. 5B is a diagram showing abnormal temperature rise, and FIG. 5C is a diagram showing disconnection.

In the normal operation of FIG. 5A, the voltage at the point A is lower than Vref, and the output of the comparator 409 is always "L".

5B and 5C, the voltage at the point A becomes higher than Vref at the abnormal time (at the time of abnormal temperature rise or disconnection), and the output of the comparator 409 outputs the switching signal 40.
A rectangular wave with the same frequency as 1 is output, and the output is "H".
When this occurs, it is judged to be abnormal and all operations of the device are stopped and prohibited. Then, looking at the output of the switching signal 401 at that time, when it is “H”, it is determined that the abnormal temperature rise has occurred, the power supply of the apparatus is shut off, and when it is “L”, it is determined that the wire is broken and the display 615 is displayed. Displays the disconnection abnormality of the thermistor.

FIG. 6 shows changes in the voltage at point A of the abnormality monitoring circuit C1. FIG. 6A shows the output of the switching signal 401 (B
6) is the voltage change at the point A with respect to the temperature at the time of monitoring the thermistor disconnection, and FIG. 6B shows when the output (point B) of the switching signal 401 is at the “H”, that is, The change in voltage at point A with respect to the temperature during abnormal temperature rise monitoring of the thermistor is shown. Looking at these, the input voltage of the comparator 409 exceeds Vref in any abnormality (see FIG. 6).
6 (a) is Vc, and FIG. 6 (b) is Vh). The output of the comparator 409 becomes a rectangular wave having the same frequency as the switching signal 401, and shuts off.

FIG. 7 shows a flow chart of abnormality monitoring.
When the output of the comparator 409 is detected to be "H" (S701), all the operations of the device are stopped and prohibited (S702), and the state of the switching signal 401 at that time is checked to find that the output is "H". Is an abnormal temperature rise state, and when "L", it is determined to be a disconnection state (S703). After that, the abnormal state is stored in the memory 103 (S705), and the power of the apparatus is shut off (S704).

FIGS. 8A and 8B are flow charts for monitoring deterioration of the fixing device 16 with time according to the present invention.

First, it is determined whether or not the apparatus has been used for 3 years (S801). If 3 years have passed,
The state of flag 1 is checked (S802). If the flag 1 is 0, the switching signal 401 is changed (described later in FIG. 8B).
Is carried out (S803), and 1 is set in the flag 1 (S
804).

Then, the operating time of the device exceeds 2 years, and 3
If less than a year has passed (S805), the state of flag 2 is checked (S806). If the flag 2 is already 1, this flow ends. If the flag 2 is 0, the switching signal 401 is changed (described later in FIG. 8B) (S80).
7), 1 is set to the flag 2 (S808).

Then, the usage time of the device exceeds 1 year, and 2
If less than a year has passed (S809), the state of flag 3 is checked (S810). If the flag 3 is already 1, this flow ends. If the flag 3 is 0, the switching signal 401 is changed (described later in FIG. 8B) (S81).
1), 1 is set in the flag 3 (S812).

Next, a flow chart for changing the switching signal 401 shown in FIG. 8B will be described. Switching signal 401
Then, a predetermined time T1 (for example, 1 second) is added to the current setting of the H level time of (S813). When the H level time exceeds a predetermined time T2 (for example, 3 seconds) (S814), the switching signal 4
01 is set to H, and the abnormality monitoring circuit C1 is set to the abnormal temperature rise monitoring state (S815).

9 (a) and 9 (b) are flow charts for detecting disconnection of the thermistor for abnormality monitoring. Switching signal 4
When the H level of 01 is set to 100% (S
901 / S905), immediately after the power is turned on (S90
2), set the switching signal 401 to L (S903),
The abnormality monitoring shown in FIG. 7 is performed (S904). Immediately after the front door is opened and closed (S906), the switching signal 401 is set to L (S907), and the abnormality monitoring shown in FIG. 7 is performed (S908).

FIG. 10 shows a flow chart for canceling an abnormality after cleaning the fixing device and replacing parts.

First, the change flag is set to 0 (S100).
1). Then, the H level time of the switching signal 401 is initialized (S1002).

[0056]

As described above, in an apparatus that determines deterioration of a fixing roller over time (dirt, etc.) based on the usage time of the apparatus, when the deterioration progresses and the temperature rises, an abnormal temperature rise is focused on. In the configuration for controlling to monitor the abnormal temperature rise, even when the rate of monitoring the abnormal temperature rise reaches 100%, it becomes possible to detect the disconnection abnormality, and a device with dramatically improved safety is provided. be able to.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus.

FIG. 2 is a block diagram of a control device

[Fig. 3] Layout configuration diagram of operation panel

FIG. 4 is a schematic configuration diagram of an abnormality monitoring circuit.

FIG. 5 is a diagram showing a switching signal 401 (output H and output L) generated by the I / O 104, and an output of a comparator 409 corresponding to the voltage at the point A of the circuit switched by this signal.

FIG. 6 is a diagram showing a change in voltage at point A of the abnormality monitoring circuit.

[Fig. 7] Flow chart for abnormality monitoring

FIG. 8 is a flowchart for monitoring deterioration of the fixing unit with time.

FIG. 9: Flow chart for disconnection monitoring of an anomaly monitoring thermistor

FIG. 10 is a flowchart of initialization at the time of error cancellation.

FIG. 11 is a temperature characteristic graph showing conventional problems.

FIG. 12 is a schematic configuration diagram of a conventional abnormality monitoring circuit.

[Explanation of symbols]

1 Copier (Image Forming Device) 2 RDF 3 Device Main Body 5 Original Plate Glass 6 Optical System 6a Exposure Lamp 6b Scanning Mirror 6c Zoom Lens 7 Image Forming Section 7a Photoreceptor Drum 7b High Pressure Unit 7c Blank Exposure Unit 7d Potential Sensor 7e Developer 7f Transfer charging device 7g Separation charging device 7h Cleaning device 9 Paper feeding cassette part 9a First cassette 9b Second cassette 9c Third cassette 9d Fourth cassette 10a Pickup roller 11a Paper feeding rollers 12a, 12b, 12c, 12d Conveying roller 13 Registration roller 14 Multi-manual feeding 15 Conveying belt 16 Fixing device (fixing means) 16a Fixing roller 16b Lower roller 17 Paper ejection flapper 19 Discharging roller pair 20 Conveying path 21 Discharging roller pair 22 Discharging sensor 23 Storage tray 31 Refeeding roller 32 Re-feeding sending low 33 refeed separation belts 34 re-feeding device 36 multiplex flapper 37 reverse conveying path 39 conveying path 40a, 40b, 40c, 40d conveying roller 50,51,52,53,54,55,56,57,5
8 sensor 100 control device 101 CPU 102 ROM 103 RAM 104 I / O 200 operation panel 401 switching signals 402, 403, 404, 405 switch (switching means) 406 inverting elements 407, 408 resistance 409 comparator 410 thermistor 601 user mode key 602 guide Key 604 Clear key 605 Copy start key 606 Interrupt key 607 Preheat key 608 Numeric keypad 609 Stop key 610 All reset key 611 Message display (display means) C1 Abnormality monitoring circuit S Sheet material H0 Vertical transport path H1, H2 path

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 3/00 H05B 3/00 310D 320 320B F term (reference) 2H033 BA31 BB00 CA01 CA03 CA06 CA07 CA20 CA57 3K058 AA12 AA97 BA18 CA02 CA03 CA12 CA22 CA33 CA61 CA92 5H323 AA36 BB17 CA06 GG04 HH02 NN03 QQ02 QQ05 RR01 RR04 SS01 TT02

Claims (5)

[Claims] 1. An image forming unit for forming an image on a recording medium, a fixing unit for fixing an image formed on the recording medium by heating the image on the recording medium, and a temperature for detecting the temperature of the fixing unit. In the image forming apparatus including at least two temperature detecting means whose resistance value changes according to the temperature change of 1., the first monitoring means for monitoring the resistance value of the first temperature detecting means and the first monitoring means. A first temperature conversion unit that converts the first temperature information of the fixing unit into first temperature information according to the monitored resistance value of the first temperature detection unit and a first temperature according to the resistance value of the first temperature detection unit. A fixing means temperature control means for controlling the temperature of the fixing means according to the first temperature information converted by the converting means; a second monitoring means for monitoring the resistance value of the second temperature detecting means; Monitored by the The resistance values of the second temperature conversion means and the second temperature detection means for converting into the second temperature information of the fixing means according to the resistance value of the temperature detection means are lower than the preset first resistance value. First to detect that
Resistance value detecting means, second resistance value detecting means for detecting that the resistance value of the second temperature detecting means is higher than a preset second resistance value, and the first or second resistance value. Switching means for switching one of the detecting means to connect to the second temperature detecting means, and the resistance value of the second temperature detecting means is lower than the first resistance value by the first resistance value detecting means. If it is detected that it is the first abnormality, and if the second resistance value detecting means detects that the resistance value of the second temperature detecting means is higher than the second resistance value, the second abnormality is detected. Of the two resistance value detecting means when the value counted by the counting means and the counting means for counting the usage time of the device reaches a predetermined value. Switching hand for connecting one to the second temperature detecting means In order to change the switching signal output from the stage so as to lengthen the switching signal for connecting to one resistance value detecting means, counting is performed by the adding means and the counting means for adding a predetermined value to the corresponding parameter. When the calculated value reaches the predetermined value, the switching means is controlled to output the switching signal according to the parameter changed by the adding means, and the time added by the adding means exceeds the predetermined value. In this case, the switching means is controlled so that the second temperature detecting means is connected to one of the two resistance value detecting means, and the abnormality corresponding to the resistance value detecting means is monitored. , The switching means is controlled so that the second temperature detecting means is connected to the other resistance value comparing means when a predetermined operation occurs, and the other abnormality corresponding to the resistance value detecting means is monitored. An image forming apparatus characterized by comprising a control means for controlling to implement. 2. The switching means comprises switching signal generating means for generating a switching signal for connecting one of the first and second resistance value detecting means to the temperature detecting means, The second resistance value detection means has a commonly used comparison means, and sends the detection signal generated by this comparison means to the first abnormality determination means, and the first abnormality determination means The switching signal generated by the switching signal generating means determines whether the detection signal sent from the comparing means is from the first or second resistance value detecting means. 1. The image forming apparatus according to 1. 3. A display unit for displaying information corresponding to the first abnormality or the second abnormality determined by the first abnormality determination unit.
The image forming apparatus according to any one of 1. 4. The apparatus according to claim 1, further comprising a parameter initialization means for returning the parameters changed by the addition means to the initial values after the fixing means or the parts arranged therein are completely replaced and cleaned. The image forming apparatus according to item 1. 5. The second temperature detecting means is a thermistor having a negative temperature coefficient, and the first resistance value detecting means is a circuit for guiding a voltage on one side of the thermistor to the comparing means. The second resistance value detection means has a circuit for guiding the voltage on the other side of the thermistor to the comparison means, and the comparison means has the same comparison voltage and one side of the thermistor. The image forming apparatus according to claim 2, wherein the voltage or the voltage on the other side is compared to generate the detection signal to be sent to the first abnormality determination means.