JP2003066766A - 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 preponderantly monitoring an abnormal temperature rise on the basis of a simplified technique which considers such a case that the deterioration of the fixing unit is developing. SOLUTION: The image forming apparatus has two resistance value detecting means connected to a second temperature detecting means for detecting different abnormalities and a means to count the hour of use of the apparatus. The image forming apparatus is further provided with a table which has at least one set of parameters to a difference to determine the output of a switching means outputted so as to connect the second temperature detecting means to one of the two resistance value detecting means when the counted hour of use exceeds the predetermined value, and a control means to control the output of the switching means on the basis of the parameter corresponding to the difference.

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. 11 and 5 to 7, the circuit configuration, operation and function of the thermistor for abnormality monitoring are capable of detecting two abnormalities, that is, an abnormal temperature rise and a thermistor disconnection. .

[0005]

However, when such a configuration is adopted, as shown in FIG. 10 (a), the temperature (T1) initially detected by the temperature adjusting thermistor is initially set.
And the real temperature (T real) match, and a temperature difference occurs because the arrangement is different from the temperature (T2) by the anomaly monitoring thermistor. Then, as shown in FIG. 10B, 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.

Further, 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.

The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to prevent abnormal temperature rise and thermistor disconnection when the operating time of the device reaches a predetermined value. The thermistor circuit for anomaly monitoring to be monitored is controlled to focus on the anomalous temperature rise, and it is possible to instantly detect the occurrence of anomaly, and image formation with dramatically improved safety. It is to provide equipment.

[0008]

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

(1) An image forming section for forming an image on a recording medium, a fixing means for fixing the image formed on the recording medium by heating the image on the recording medium, 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.
The first abnormality determination means for determining the second abnormality when the resistance value detection means detects the resistance value of the second temperature detection means is higher than the second resistance value, and the usage time of the device. To connect either one of the two resistance value detecting means output by the switching means to the second temperature detecting means when the counting means for counting and the value counted by the counting means reach a predetermined value. A table having, in correspondence with the difference between the first temperature information and the second temperature information, the time parameter for connecting the one of the resistance value detecting means of the switching signal of
When the value counted by the counting means reaches a predetermined value, the control means controls the switching means so as to output the switching signal according to the parameter of the table corresponding to the usage time. Image forming apparatus.

(2) The switching means includes a switching signal generating means for generating a switching signal for connecting either 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) Parameter replacement means is provided for returning the parameters changed by the addition means to the initial values after the fixing means or the components arranged therein are completely replaced and cleaned. 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.

[0014]

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 arranged below the optical system 6, and the image forming section 7 includes a photosensitive drum 7a rotatably arranged 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, in the lower part of the apparatus main body 3, there is provided a paper feed 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 sheet feeding section for feeding a 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, conveyance rollers 12a, 12b, 12c, 12d are arranged in a vertical conveyance 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 transport belt 15 for transporting the image-formed sheet material S downstream is disposed downstream of the image forming section 7. A toner image is formed on the downstream side of the transport 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 includes a fixing roller 16a heated to a predetermined fixing temperature, a lower roller 16b facing the fixing roller 16a and contacting 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 conveyance path 20 for the sheet material S to be double-sided and for multiple copying.
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 disposed 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 in each of the above-mentioned transport paths.
2, 53, 54, 55, 56, 57, 58 are arranged.

FIG. 2 shows a block diagram of the control device 100 of the present 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 on the apparatus main 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 to interrupt 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 the switches 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".

5 (b) and 5 (c) is abnormal (abnormal temperature rise or disconnection), the voltage at point A becomes higher than Vref, and the output of the comparator 409 is 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 a change in the voltage at the 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).

FIG. 8 shows the switching signal 40 after the use time has elapsed.
2 shows a flowchart for changing the duty ratio of 1.

It is determined whether or not the counter for counting the usage time of the device has counted a predetermined time (S801). When the predetermined time is counted, the change flag for determining whether the switching signal 401 has already been changed is checked (S802). If the change flag is already 1, this flow ends. If the change flag is 0, the H level time of the switching signal 401 is replaced with the value set in the table (double the initial value in this embodiment) by referring to the table (S803). Then, the change flag indicating that this flow is completed is set to 1 (S80).
4).

FIG. 9 shows a flow chart for releasing an abnormality after cleaning the fixing device and replacing the parts.

First, the change flag is set to 0 (S90).
1). Then, the H level time of the switching signal 401 is initialized (S902).

[0051]

As described above, when the operating time of the device reaches a predetermined time, it is possible to focus on the abnormal temperature rise. As a result, it is possible to instantly detect the occurrence of an abnormal temperature rise, and it is possible to provide a device with dramatically improved safety.

[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

4A, 4B, and 4C are schematic configuration diagrams of an abnormality monitoring circuit.

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

FIG. 6A is an output of a switching signal 401 (point B).
However, when it is "L", b) is the output of the switching signal 401 (B
A diagram showing changes in the voltage at the point A of the abnormality monitoring circuit when the point) is "H"

[Fig. 7] Flow chart for abnormality monitoring

FIG. 8 is a flowchart of changing the duty ratio of the switching signal 401 after the usage time has elapsed.

FIG. 9 is a flowchart of initialization when the abnormality is cleared.

10A and 10B are temperature characteristic graphs showing conventional problems.

11 (a), (b), and (c) are schematic configuration diagrams of a prior art 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

Continued front page    F-term (reference) 2H027 DA12 DA38 DE04 DE07 DE09                       EA12 EE07 EK03 EK06 GA23                       GB07 HA04 HA17                 2H033 AA23 AA42 BA30 BA32 BA34                       BB01 BB28 CA06 CA24 CA34                       CA57

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 detection means to connect to the second temperature detection means, and the resistance value of the second temperature detection means by the first resistance value detection means is lower than the first resistance value. 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 value is detected. Of the two resistors output by the switching 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. Either one of the value detecting means is used as the second temperature detecting means. A table having a parameter of time for connecting to one resistance value detecting means of the switching signal for connecting, corresponding to the difference between the first temperature information and the second temperature information, and counted by the counting means. And a control means for controlling the switching means so as to output the switching signal according to the parameter of the table corresponding to the usage time when the value reaches a predetermined value. 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.