JPH09185286A - Temperature controller for fixing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the abnormality of a thermistor such as disconnection and short-circuiting before energization is started or during preheating or a fixing operation, at a low cost by detecting the coincidence of a first temp./voltage conversion signal for controlling a preheating temp. and a second temp./voltage conversion signal for controlling a fixing temp., so as to detect the abnormality of the thermistor. SOLUTION: When the fixing roller is adjusted to the preheating temp., the first temp./voltage conversion signal Vad1 is used and when the fixing roller is adjusted to the fixing temp., the second temp./voltage conversion signal Vad2 is used. The A/D conversion values of both signals Vad1 and Vad2 by an A/D converter 5 are compared and when the A/D conversion values coincide, it is judged that the thermistor Rt is abnormal and a heater 23 is turned off to prevent abnormal heat generation. When the thermistor Rt is normal, both signals Vad1 and Vad2 never have the same voltage with respect to the same temp. Therefore, when both signals Vad1 and Vad2 at the same point of time show the same voltage, that the thermistor Rt has any abnormality can be judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for controlling the temperature of a fixing device by controlling the electric power supplied to a heater for heating the fixing device.

[0002]

2. Description of the Related Art A fixing device used in an image recording apparatus such as a copying machine is required to have a predetermined high temperature (fixing temperature) in order to heat-fix a toner image transferred onto a recording paper on the recording paper. . Therefore, in the conventional fixing device temperature control device, a thermistor is arranged in the vicinity of the fixing device, and a change in the resistance value according to the temperature of the fixing device of the thermistor is converted into a change in voltage and detected. The temperature of the container is detected, and the amount of electric power supplied to the heater for heating the fixing device is controlled so that the detected temperature becomes the fixing temperature.

However, if the temperature control device cannot correctly detect the actual temperature of the fixing device due to disconnection of the thermistor or the like, not only cannot the temperature of the fixing device be maintained at the fixing temperature, but power is supplied to the heater. The fixing device may continue to have an abnormally high temperature and a fire may occur.

Therefore, knowing whether the thermistor is functioning normally is very important not only for the temperature control device of the fixing device to reliably fix the toner image but also to ensure the safety of the device. is important.

Therefore, as shown in "Temperature control device for heat fixing device in electrophotographic printer" described in Japanese Patent Laid-Open No. 2-69791, the thermistor is disconnected before the heater of the heat fixing device is energized. Also, by performing a check for a short circuit, the risk of fire is avoided and the inconvenience of not functioning as a fixing device is prevented.
As seen in the "fixing device" described in Japanese Patent Publication No. 267987, a series thermistor and a voltage dividing resistor are connected in series with a switch unit for checking the disconnection of the thermistor, and further in parallel with the voltage dividing resistor and the switching unit. By connecting a resistor, it is possible to know the disconnection of the thermistor by software, and as shown in the "image recording device" described in JP-A-6-242699, a plurality of thermistors are provided. Therefore, various proposals have been made, such as disconnection of the thermistor detecting the temperature of the fixing unit and instant determination of low temperature.

[0006]

However, the above-mentioned JP-A-2-69791 and JP-A-3-267987.
The one disclosed in Japanese Patent Laid-Open Publication No. 2003-242242 detects an abnormality such as a wire break or short circuit of the thermistor before the energization of the heater is started, and has a drawback that an abnormality of the thermistor occurring during preheating or fixing operation cannot be identified.

Further, the one disclosed in Japanese Patent Laid-Open No. 6-242699 has a drawback that the cost becomes high because it is necessary to provide a plurality of thermistors for detecting the temperature of the fixing portion.

The present invention has been made in view of the above circumstances, and detects an abnormality in the thermistor such as a wire break or a short circuit at low cost regardless of whether the heater is energized, preheating, or fixing operation is being performed. It is an object of the present invention to provide a temperature control device for a fixing device that can be used.

[0009]

In order to achieve the above object, a temperature control device for a fixing device according to claim 1 controls the temperature of the fixing device by controlling the electric power supplied to a heater for heating the fixing device. In a temperature control device controlling to a preheating temperature or a fixing temperature, a thermistor whose resistance value changes according to a temperature change of the fixing device, a first voltage dividing resistor, and a second voltage dividing resistor are connected in series. A first temperature / voltage characteristic of a temperature / voltage characteristic suitable for temperature detection near the preheating temperature, which is obtained from a connection point between the thermistor of the combined resistance having a predetermined voltage applied to both ends thereof and the first voltage dividing resistor. A temperature suitable for detecting the temperature near the fixing temperature, which is obtained from the connection point between the voltage conversion signal and the first voltage dividing resistor and the second voltage dividing resistor.
A signal switching means for receiving the second temperature / voltage conversion signal having the voltage characteristic and selectively outputting one of those signals;
The output signal from the signal switching means is input, and the A / D converted value from the digital lower limit value to the digital upper limit value is output corresponding to the input voltage signal from the predetermined lower limit voltage to the upper limit voltage, while the predetermined signal is output. For an input voltage signal equal to or higher than the upper limit voltage, an A / D converter that outputs the digital upper limit value, and when controlling the temperature of the fixing device to the preheat temperature, the signal switching means is set to the first temperature / The temperature is controlled on the basis of the first temperature / voltage conversion signal converted to the A / D conversion value by the A / D converter and output by switching to the voltage conversion signal side, while the temperature of the fixing device is changed to the fixing unit. When the temperature is controlled, the signal switching means is switched to the second temperature / voltage conversion signal side, and the second temperature / voltage converted into an A / D converted value by the A / D converter and output. A fixing device temperature control means for temperature control based on the signal, the said signal switching means a first temperature /
A / D conversion value from the A / D converter obtained by switching to the voltage conversion signal side, and A from the A / D converter obtained by switching the signal switching means to the second temperature / voltage conversion signal side. A thermistor abnormality detecting means for detecting abnormality of the thermistor by comparing the / D converted value at any time and detecting the coincidence of those signal values.

A temperature control device for a fixing device according to claim 2 is
The temperature control device of the fixing device according to claim 1, wherein one end of the second voltage dividing resistor, which is not connected to the first voltage dividing resistor, is connected to the same potential as the third voltage dividing resistor. When the power source of the apparatus is turned on, the connection between the first voltage dividing resistor and the second voltage dividing resistor is temporarily released, and the first connection is released.
One end of the voltage dividing resistor is connected to the other end of the third voltage dividing resistor so that the first temperature / voltage conversion signal obtained from the connection point between the thermistor and the first voltage dividing resistor is temporarily higher than room temperature. A voltage dividing resistance switching means for switching to a temperature / voltage characteristic suitable for detecting a low temperature, and the thermistor abnormality detecting means is suitable for detecting a temperature lower than room temperature by the voltage dividing resistance switching means when the device power is turned on. The A / D conversion value from the A / D converter obtained by switching the signal switching means to the side of the first temperature / voltage conversion signal temporarily switched to the temperature / voltage characteristic is below a predetermined level. Is detected to detect an abnormality of the thermistor.

According to a third aspect of the present invention, there is provided a temperature control device for a fixing device.
In the temperature control device of the fixing device according to claim 1, a resistor is connected in parallel to the thermistor.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described in detail.

FIG. 1 shows a schematic structure of a fixing device which is built in an image recording device and whose temperature is controlled by a temperature control device according to the present invention. In the figure, the recording paper 25 onto which the visible image is transferred from a not-shown photosensitive drum is guided by the guide plate 24 in the direction of arrow B, and the fixing roller 21 as a fixing device and the outer peripheral surface thereof contact the fixing roller 21. It moves while being held by a roller pair composed of a pressure roller 22 arranged so as to be in contact with each other. At that time, the visible image is fixed on the recording paper by the heat from the fixing roller 21 heated to a predetermined temperature by the heater 23 in the fixing roller 21 and the pressure received by the roller pair.

In order to surely and consistently fix the visible image on the recording paper, the temperature of the fixing roller 21 must be maintained at a predetermined fixing temperature (180 ° C. in the present embodiment) during the fixing operation. In addition, the temperature of the fixing roller 21 is not always maintained at the fixing temperature, but when the fixing operation is not performed,
In order to reduce power consumption and the like, it is necessary to maintain the preheating temperature (100 ° C. in the present embodiment) lower than the fixing temperature. Therefore, near the fixing roller 21, a thermistor Rt, which is an element having a characteristic that the resistance changes with a change in temperature, is arranged.

A change in the resistance value of the thermistor Rt according to a change in the temperature of the fixing roller 21 is converted into a voltage signal and processed by the temperature control device 1 according to the present invention shown in FIG. Then, the temperature control device 1 keeps the temperature of the fixing roller 21 constant by controlling ON / OFF of the heater 23 according to the voltage signal.

In the image processing apparatus including the temperature control apparatus 1 according to the first embodiment of the present invention shown in FIG.
The analog video signal obtained by reading the original image with the scanner 2 is input to the analog video processing unit 3, and the analog video processing unit 3 removes the DC component contained in the input analog video signal and normalizes the peak value. The analog video signal subjected to the processing such as shading correction is input to the multiplexer 4 which is the signal switching means.

Analog sensor signals from various sensors such as the paper end sensor 11 are also input to the multiplexer 4. Further, a first temperature / voltage conversion signal Vad1 and a second temperature / voltage conversion signal Vad2, which will be described later, are also input to the multiplexer 4 as analog sensor signals. Any one of the analog sensor signals or the analog video signals input to the multiplexers 4 is
The signal is selected by the selection signal SEL from the device control unit 8, output from the multiplexer 4, and input to the A / D converter 5. The A / D converter 5 uses the reference voltage Vt (2V in the present embodiment) output from the reference voltage generator 6 as a reference, and inputs the analog signal in a predetermined range from 0V to the reference voltage Vt (2V). A / D conversion is performed with accuracy (8 bits in this embodiment). Of the converted A / D converted values, the digital video signal is input to the digital video processing unit 7, subjected to MTF correction, edge processing and the like, and input to the device control unit 8. On the other hand, the digital sensor signal is directly input to the device control unit 8. The device control unit 8
The input A / D converted value is processed.

Switching of the multiplexer 4 by the selection signal SEL from the device control unit 8 is required for the scanner 2 to read one line of the original image within the period T, where T is the original reading scanning period of the scanner 2. During the time T1 shorter than the cycle T, the multiplexer 4 is switched to the analog video signal, and the time other than the time T1 (T-T1).
During this time, by sequentially switching the multiplexer 4 to each analog sensor signal. In addition, the multiplexer 4 may be switched to only one of the analog sensor signals at a time (T-T1) for each scanning cycle, and may be sequentially switched to all of the analog sensor signals in a plurality of cycles.

As described above, the image recording apparatus according to the present embodiment performs A / D conversion processing on the analog sensor signal during the period in which the analog video signal is periodically output from the scanner 2, and thereby the analog video signal is processed. Although one A / D converter 5 is shared by the signal and the analog sensor signal, when viewed as the temperature control device 1, the scanner 2, the analog video processing unit 3, the digital video processing unit 7, and the paper end sensor are used. 11 is not directly related to the present invention.

The configuration of the temperature control device 1 shown in FIG. 2 will be described in detail below. In the same figure, as shown in FIG. 1, the thermistor Rt arranged near the fixing roller 21.
And a resistor R1 which is a first voltage dividing resistor and a resistor R2 which is a second voltage dividing resistor are connected in series.
A first temperature / voltage conversion signal Vad1 obtained from a connection point between the resistor R1 and the thermistor Rt, which is a combined resistance in which 5V is applied as a predetermined voltage to one end on the t side and one end on the resistor R2 side is grounded, The second temperature / electric conversion signal obtained from the connection point between R1 and the resistor R2 is input to the multiplexer 4 which is the signal switching means, as described above.

The first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 input to the multiplexer 4 are Vad1 = 5 · (R1 + R2) / (R1 + R2 + Rt) Vad2 = 5 · R2 / (R1 + R2 + Rt) Is represented.

Generally, the resistance of the thermistor has a characteristic that it exponentially decreases as the temperature rises and exponentially increases as the temperature lowers. Now, the thermistor Rt according to the present embodiment has the following characteristics. It is assumed that the temperature / resistance characteristics shown in the graph of FIG. 3B are shown in the table of temperature vs. resistance of FIG. 3A. The resistance R
The resistance value of 1 is 1.3 kΩ, the resistance value of the resistor R2 is 1.1 k
Ω.

As described above, the temperature-voltage conversion characteristics of the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2, which are functions of the respective resistance values, have the characteristics shown in FIG.

As described above, the A / D converter 5 uses the reference voltage Vt (2V) output from the reference voltage generator 6 as a reference, and inputs the analog signal in the range of 0V to the reference voltage Vt (2V). A / D conversion is performed with an accuracy of 8 bits. That is, the input analog signal of 0V to 2V is converted into a digital value of 256 levels from 00H to FFH. Further, the A / D converter 5 is a general A / D converter.
As with D converters, the lower limit voltage is 0V
To an upper limit voltage of 2V, a digital value proportional to the input voltage is output, while when the input voltage is equal to or higher than the upper limit voltage of 2V,
Output FFH.

Therefore, the A / D converter 5 is shown in FIG.
As shown in, when the first temperature / voltage conversion signal Vad1 is input, the temperature range of 0 to 150 ° C. can be detected,
0 to 260 if the temperature / voltage conversion signal Vad2 is input
It is possible to detect the temperature range of ° C. As is apparent from FIG. 4, the first temperature / voltage conversion signal Vad1 cannot detect the temperature near the fixing temperature (180 ° C.), but its inclination is large near the preheating temperature (100 ° C.),
The temperature near the preheating temperature can be detected accurately.
On the other hand, the second temperature / voltage conversion signal Vad has a small inclination in the vicinity of the preheating temperature (100 ° C.), and the temperature in the vicinity of the preheating temperature cannot be accurately detected, but the fixing temperature (18
The inclination is large near 0 ° C., and the temperature near the fixing temperature can be accurately detected.

Therefore, the apparatus controller 8 controls the fixing roller 21.
When controlling the temperature of the
To the first temperature / voltage conversion signal Vad1 by the SEL signal.
To detect the temperature of the fixing roller 21, and in order to control the temperature to the preheating temperature (100 ° C.), the heater controller 9 is instructed whether or not to supply power to the heater 23. The heater control unit 9 turns on / off the electric power supplied to the heater 23 according to the command. Also,
When controlling the temperature of the fixing roller 21 to the fixing temperature, the multiplexer 4 is switched to the second temperature / voltage conversion signal Vad2 by the SEL signal, the temperature of the fixing roller 21 is detected, and the temperature is set to the fixing temperature (180 ° C.). ), A similar command is issued to the heater control unit 9.

As described above, when the thermistor Rt is operating normally, the first temperature / voltage conversion signal Vad1 is used when the temperature of the fixing roller 21 is controlled to the preheating temperature, and when the temperature is controlled to the fixing temperature. By using the second temperature / voltage conversion signal Vad2 having a temperature / voltage characteristic different from that of the first temperature / voltage conversion signal Vad1, the preheating temperature or the fixing temperature can be accurately controlled.

Let us now consider the case where some abnormality occurs in the thermistor Rt. As can be seen from FIG. 4, when the thermistor Rt is normal, that is, when the temperature / resistance characteristics thereof maintain the characteristics shown in FIGS. 3A and 3B, the first temperature / Voltage conversion signal Vad
1 and the second temperature / voltage conversion signal Vad2 do not have the same voltage with respect to the same temperature except for around 0 ° C. In other words, at the same time point (the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 are both caused by a change in resistance of the thermistor Rt, which is the only element that detects the temperature of the fixing roller 21). Since the signals are signals, the conversion signals at the same time point are voltage signals for the same temperature.) When the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 indicate the same voltage It can be determined that some abnormality has occurred in the thermistor Rt.

Abnormalities occurring in the thermistor Rt include
There is a disconnection or omission in the connection, in which case the thermistor Rt
Has a substantially infinite resistance value, and the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 are also substantially 0 V, and the A / D converter 5 has an A / D conversion value of any temperature / voltage. It is also 00H for the converted signal. That is, they match.

Further, as another mode of the abnormality occurring in the thermistor Rt, there is a case where the harness of the thermistor Rt is short-circuited with GND, and in that case also, the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2. Becomes almost 0V, and the 5A / D conversion value of the A / D converter becomes 00H for any temperature / voltage conversion signal. That is, they match.

On the other hand, when the thermistor Rt becomes defective in the short circuit mode and when the harness of the thermistor Rt is shorted to 5V, the first temperature / voltage conversion signal Vad1 is 5V and the second temperature / voltage conversion signal Vad2 is The voltage becomes 2.3 V, and all of these voltages exceed the upper limit voltage of the A / D converter 5, so that the A / D converted value thereof becomes the upper limit value FFh. That is, they match.

In this way, the first temperature / voltage conversion signal Vad
1 and the A / D conversion value of the second temperature / voltage conversion signal Vad2 are compared, and if they match, it is judged that the thermistor is abnormal,
By performing the process of turning off the heater, abnormal heat generation of the heater can be prevented.

Here, the procedure of temperature control of the fixing roller 21 after the power source of the apparatus is turned on in the temperature control apparatus 1 according to the first embodiment will be described with reference to FIGS. 5 and 6.

First, the device control unit 8 causes the multiplexer 4 to receive the first temperature / voltage conversion signal Vad according to the SEL signal.
A / D output from the A / D converter 5
After reading the first temperature / voltage conversion signal Vad1 by reading the D conversion value (process 101), the multiplexer 4 is switched to the second temperature / voltage conversion signal Vad2,
The second temperature / voltage conversion signal Vad1 is read by reading the A / D conversion value output from the A / D converter 5 (process 102).

Then, the first temperature / voltage conversion signal Vad1
And whether the second temperature / voltage conversion signal Vad2 matches (decision 103). If they match (Yes in judgment 103)
In s), the thermistor abnormality handling processing 109 is executed. In the thermistor abnormality handling process, in order to inform the operator of the image recording apparatus that the thermistor Rt has an abnormality such as a disconnection or a short circuit, an indicator lamp indicating the abnormality is lit or a message is displayed on the liquid crystal display as a message. After that, the operation of the apparatus is stopped without turning on the heater 23.

Now, if the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 do not match (No in decision 103), that is, if the thermistor Rt is normal, then the second temperature / Voltage conversion signal Vad2
Is determined to be the voltage Ve or higher (decision 104). This voltage V
As shown in FIG. 4, the temperature e of the fixing roller 21 is 26
It is a voltage of 2V corresponding to the case of 0 ° C., and it means that the second temperature / voltage conversion signal Vad2 is equal to or higher than the voltage Ve.
It can be determined by checking whether the A / D converted value of the D converter 5 or FFH.

The second temperature / voltage conversion signal Vad2 is the voltage V
If it is equal to or larger than e (Yes in determination 104), it is determined that the fixing roller 21 is at an abnormally high temperature, and an abnormal high temperature handling process is performed (process 110). This abnormal high temperature treatment
This is an emergency cutoff of the power source of the apparatus for preventing the fixing roller 21 from catching fire. The second temperature / voltage conversion signal Vad2 is the voltage Ve
If not (No in determination 104), the preheating temperature control process is performed next.

That is, the first temperature / voltage conversion signal Vad1
Is less than or equal to the voltage Va (determination 105), and if less than or equal to the voltage Va (Yes in determination 105), the heater 23
Is turned on (process 106), and if the voltage is equal to or higher than Va (No in determination 105), the heater 23 is turned off (process 107).
Then, it is determined whether the image recording is started (determination 10
8). If the image recording is not started (No in determination 108), in order to maintain the fixing roller 21 at the preheating temperature,
It returns to processing 101. The voltage Va is the output (0.7V) of the first temperature / voltage conversion signal Vad1 corresponding to the preheating temperature of 100 ° C., as shown in FIG.

Through the above processing, the temperature of the fixing roller 21 is controlled to the preheating temperature while constantly monitoring whether the thermistor Rt is abnormal or the fixing roller 21 is abnormally high temperature, and the thermistor Rt is abnormal. If there is a problem or the fixing roller 21 has an abnormally high temperature, no electric power is supplied to the heater 23.

When image recording is started by a copy operation by the operator of the image recording apparatus (decision 108), the temperature control apparatus 1 sets its control mode to control the fixing roller 21 to the fixing temperature. The preheating mode up to then is changed to the fixing mode.

That is, the device control section 8 causes the multiplexer 4 to receive the first temperature / voltage conversion signal Vad by the SEL signal.
A / D output from the A / D converter 5
After reading the first temperature / voltage conversion signal Vad1 by reading the D conversion value (process 111), the multiplexer 4 is switched to the second temperature / voltage conversion signal Vad2,
The second temperature / voltage conversion signal Vad1 is read by reading the A / D conversion value output from the A / D converter 5 (process 112).

Then, the first temperature / voltage conversion signal Vad1
And the second temperature / voltage conversion signal Vad2 match (determination 113). If they match (Yes in judgment 113)
In s), the thermistor abnormality handling processing 119 is executed. The thermistor abnormality handling processing is the same as the processing 109, and in order to notify the operator of the image recording apparatus that the thermistor Rt has an abnormality such as a disconnection or a short circuit, an indicator lamp indicating the abnormality is turned on or the liquid crystal is displayed. After displaying as a message on the display, the heater 2
This is a process for stopping the device operation without turning ON 3.

Now, if the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 do not match (No in judgment 113), that is, if the thermistor Rt is normal, then the second temperature / Voltage conversion signal Vad2
Is determined to be the voltage Ve or higher (decision 114).

The second temperature / voltage conversion signal Vad2 is the voltage V
If it is equal to or greater than e (Yes in determination 114), it is determined that the fixing roller 21 is at an abnormally high temperature, and an abnormal high temperature handling process is performed (process 120). This abnormal high temperature treatment
This is the same as the processing 110, and is an emergency cutoff of the power source of the apparatus for preventing the fixing roller 21 from being ignited. When the second temperature / voltage conversion signal Vad2 is not equal to or higher than the voltage Ve (determination 114
No) indicates that the thermistor Rt has no abnormality and the temperature of the fixing roller 21 has no abnormality.
Next, the process proceeds to the fixing temperature control process.

That is, the second temperature / voltage conversion signal Vad2
Is less than or equal to the voltage Vc (determination 115), and if less than or equal to the voltage Vc (Yes in determination 115), the heater 23
Is turned on (process 116), and if the voltage is Vc or more (No in determination 115), the heater 23 is turned off (process 117).
Then, it is determined whether the image recording is completed (decision 118).
If the image recording is not completed (No in judgment 118),
In order to maintain the fixing roller 21 at the fixing temperature, the process 11
Return to 1. The voltage Vc is, as shown in FIG. 4, the second temperature / voltage conversion signal Vad corresponding to the fixing temperature of 180 ° C.
2 output (1.35V).

Through the above processing, the temperature of the fixing roller 21 is controlled to the fixing temperature while the thermistor Rt is constantly monitored for any abnormality and the fixing roller 21 is not abnormally high temperature. If there is a problem or the fixing roller 21 has an abnormally high temperature, no electric power is supplied to the heater 23.

When the image recording operation due to the copy operation by the operator of the image recording apparatus is completed (decision 118), the heater 23 is turned off (process 12).
The process returns from step 1) to step 101 to return to the preheat mode.

FIG. 7 shows an example of the temperature change of the fixing roller 21 with the passage of time when image recording is started a predetermined time after the power source of the apparatus is turned on by the above procedure. In this case, it is assumed that the abnormality of the thermistor Rt and the abnormal high temperature of the fixing roller 21 are not detected. As is clear from the figure, it is the preheating temperature after power-on 1
The heater is kept in the ON state until the temperature reaches 00 ° C., the temperature of the fixing roller 21 rises rapidly, and after reaching the temperature of 100 ° C., the temperature is kept at 10 ° C. until the image recording operation is started.
Maintained at 0 ° C. When the image recording operation is started, the heater is kept in the ON state until the fixing temperature of 180 ° C. is reached, and the temperature of the fixing roller 21 rapidly rises.
After reaching 180 ° C, the temperature is maintained at 180 ° C.

According to the first embodiment described above,
In the temperature control of the fixing roller 21 in both the preheating mode and the fixing mode, the soundness of the thermistor Rt is always checked, and the electric power is not continuously supplied to the heater 23 after the abnormality is detected. It is possible to reliably prevent the ignition of 21.

Although the temperature control device according to the first embodiment described above has the above advantages, as can be seen from FIG. 4, when the power source of the image recording device is turned on,
When the installation environment of the image recording apparatus is around 0 ° C., which is much lower than the normal room temperature, the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad1 almost match, and the difference between them. If the difference is less than or equal to the conversion accuracy of the A / D converter 5, the A / converted values are both 00H and coincide with each other. In that case, the determination result of the determination 103 in the processing procedure shown in FIG.
The thermistor abnormality handling process of 9 is performed, and there remains a problem that the preheat temperature control cannot be performed although the thermistor Rt is normal. The temperature control device according to the second embodiment of the present invention described below solves that problem.

FIG. 8 shows a part of an image recording apparatus including the temperature control device 1 according to the second embodiment. In FIG.
The difference from the temperature control device 1 according to the first embodiment shown in FIG. 2 is that one end is connected to the same potential as one end of the resistor R2 that is not connected to the resistor R1, that is, is grounded. The connection between the resistor R1 and the resistor R2, which is provided with the resistor R3 that is the third voltage dividing resistor, is temporarily disconnected, and one end of the disconnected resistor R1 is connected to the other end of the resistor R3. For this reason, a switch S1 as a voltage dividing resistance switching means is provided.

With the above configuration, the resistance value of the resistor R1 is 1.3.
The resistance value of kΩ and the resistance R2 is 1.1 kΩ, which is the same as that of the first embodiment, and the resistance R3 is 51 kΩ. Therefore, when the switch S1 is switched to the R3 side (low temperature detection mode), the temperature of the first temperature / voltage conversion signal Vad1 −
The voltage characteristic is not suitable for temperature detection near the preheating temperature (100 ° C.), but is a temperature-voltage characteristic capable of detecting a low temperature of 0 ° C. or lower.

In the second embodiment, the switch S1 is switched to the resistor R3 side to perform a predetermined process only when the power source of the image recording apparatus is turned on, so that the thermistor can be used even in an extremely low temperature environment. It is possible to correctly detect whether Rt is normal or abnormal.
This will be described with reference to FIG.

In the figure, the device control section 8 switches the switch S1 to the resistance R3 side to select the resistance R3 (process 201), and the multiplexer 4 is set to the first position by the SEL signal.
By switching to the temperature / voltage conversion signal Vad1 and reading the A / D conversion value output from the A / D converter 5, the first temperature / voltage conversion signal Vad1 is read (process 202), and the read low temperature detection mode. It is determined whether the first temperature / voltage conversion signal Vad1 in is less than or equal to the voltage Vf (decision 203). This voltage Vf is the output (0.2 V) of the first temperature / voltage conversion signal Vad1 in the low temperature detection mode corresponding to the case where the temperature of the fixing roller 21 is −10 ° C., and −10 ° C. is the image recording apparatus. Since the installation environment is so low as to be impossible, when such an impossible temperature is detected, it is determined that the thermistor Rt is abnormal without determining that the installation environment is that temperature.

Therefore, the first in the low temperature detection mode
When the temperature / voltage conversion signal Vad1 is equal to or lower than the voltage Vf (Yes in the determination 203), the thermistor abnormality handling processing 2
06. The thermistor abnormality handling processing is the same as the processing 109 shown in FIG. 5 and the processing 119 shown in FIG. 6, and is for notifying the operator of the image recording apparatus that an abnormality such as disconnection or short circuit has occurred in the thermistor Rt. After turning on the indicator lamp indicating that, or displaying as a message on the liquid crystal display, the heater 2
This is a process for stopping the device operation without turning ON 3.

When the first temperature / voltage conversion signal Vad1 in the low temperature detection mode is equal to or higher than the voltage Vf (decision 203)
No.), assuming that the thermistor Rt normally detects the temperature of the fixing roller 21, the switch S2 is switched to the second resistance side and the second resistance is selected (process 204).
Switch to the preheat mode and turn on the heater 23 (Process 2
05). By turning on the heater here, even if the fixing roller 21 is at a low temperature of 0 ° C. or less, the temperature of the fixing roller 21 is A / D of the first temperature / voltage conversion signal Vad1 switched to the preheating mode. The temperature rises to such a value that the converted value becomes greater than 00F.

Therefore, after the processing 205, the processing shifts to the processing 101 shown in FIG. 5 and the processing shown in FIGS. 5 and 6 is continuously executed as in the temperature control apparatus according to the first embodiment. The abnormality of the thermistor Rt can be reliably detected not only in the preheating mode and the fixing mode, but also when the installation environment is extremely low when the power of the apparatus is turned on.

Next, a temperature control device according to the third embodiment will be described. The temperature control device according to the third embodiment solves the problem left in the temperature control device according to the first embodiment by a configuration different from that of the temperature control device according to the second embodiment. To do.

FIG. 11 shows a part of an image recording apparatus including the temperature control device 1 according to the third embodiment. In FIG. 11, the temperature control device 1 according to the first embodiment shown in FIG. 2 is shown. 2 is that a resistor R4 is connected in parallel with the thermistor Rt. It is desirable to arrange the resistor R4 as close to the thermistor Rt as possible.

With the above configuration, the resistance value of the resistor R1 is 1.3.
The resistance value of kΩ and the resistance R2 is 1.1 kΩ, which is the same as that of the first embodiment, and the resistance R4 is 100 kΩ.

When the respective resistance values are set as described above, the temperature-voltage characteristics of the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 are as shown in FIG. 12 and shown in FIG. As is clear from the comparison with the temperature-voltage characteristics according to the first embodiment, the first temperature / voltage conversion signal Va is generated even when the temperature of the fixing roller 21 is extremely low.
d1 and the second temperature / voltage conversion signal Vad2 are A / D
Converted to A / D converted value of converter 5 00H (0V)
It does not become. Specifically, the temperature of the fixing roller 21 is −
When the temperature is 10 ° C., the first temperature / voltage conversion signal Vad1 is 0.1
3V (converted to A / D converted value is 10H), second temperature / voltage converted signal Vad2 is 0.06V (converted to A / D converted value is 07H), and the installation environment of the image recording apparatus is -10.
Even when the temperature is ° C, the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal have different A / D conversion values, in other words, the same temperature, assuming that the thermistor Rt is normal. However, if the same A / D conversion value is obtained, it can be determined that the thermistor Rt is abnormal.

Therefore, similarly to the temperature control apparatus according to the first embodiment having the configuration shown in FIG. 11, by executing the processing shown in FIGS. 5 and 6, not only in the preheating mode and the fixing mode, The abnormality of the thermistor Rt can be reliably detected even when the installation environment is extremely low when the power of the device is turned on. Further, the configuration and procedure required therefor are much simpler than those of the temperature control device according to the second embodiment.

In each of the embodiments described above, the first temperature / voltage conversion signal Vad1 and the second temperature / voltage conversion signal Vad2 for controlling the temperature of the fixing roller 21 are converted to analog video signals from the scanner 2, The analog signal from another analog signal source such as the paper end sensor 11 is input to the multiplexer 4 to input the A / D converter 5 to
Although the present invention is applied to those shared with the respective analog signals, the first temperature / voltage conversion signal V is applied to the multiplexer 4.
Only ad1 and the second temperature / voltage conversion signal Vad2 are input, and the A / D converter 5 is dedicated to those conversion signals.
It goes without saying that the present invention can be applied to a configuration in which another analog signal is processed by another A / D converter.

[0064]

According to the first aspect of the present invention, the first temperature / voltage conversion signal for controlling the preheating temperature of the fixing device, which is obtained from the common thermistor by the voltage division by the simple resistance, and the fixing temperature control. Since it is possible to detect the anomaly of the thermistor by detecting the coincidence of the digital conversion value with the second temperature / voltage conversion signal, it is possible to detect whether the heater is energized, preheated, or fixed. Regardless of this, abnormality in the thermistor such as disconnection or short circuit can be detected at low cost.

According to the second aspect of the invention, when the power source of the apparatus is turned on, the first temperature / voltage conversion signal is temporarily switched to the temperature / voltage characteristic suitable for detecting a temperature lower than room temperature, and the first temperature / voltage characteristic is changed. / If the A / D converted value of the voltage conversion signal is detected as a value below a predetermined level value that is not possible at normal room temperature, it is detected as an abnormality in the thermistor and detected as a value above the predetermined level value. If done,
Since the temperature of the fixing device is detected as such a temperature, it is possible to correctly detect the abnormality of the thermistor even when the temperature is extremely low.

According to the third aspect of the present invention, the resistance is connected in parallel with the thermistor Rt, so that the first temperature / voltage conversion signal and the second temperature /
If the thermistor is normal, the difference is maintained between the A / D converted values of the voltage conversion signals, and if the thermistor Rt is abnormal, the difference disappears. The thermistor abnormality can be detected correctly.

[Brief description of the drawings]

FIG. 1 is a diagram showing a fixing device whose temperature is controlled by a temperature control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a part of an image recording apparatus including the temperature control device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing temperature / resistance characteristics of a thermistor used by the temperature control device according to the embodiment of the present invention to detect the temperature of the fixing roller.

FIG. 4 is a diagram showing temperature-voltage characteristics of a first temperature / voltage conversion signal and a second temperature / voltage conversion signal in the temperature control device according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a fixing roller temperature control procedure in the temperature control device according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a temperature control procedure of the fixing roller in the temperature control device according to the first embodiment of the present invention together with FIG.

FIG. 7 is a diagram showing an example of temperature change with time from the time of power-on of the fixing roller whose temperature is controlled by the temperature control device according to the embodiment of the present invention.

FIG. 8 is a diagram showing a part of an image recording device including a temperature control device according to a second embodiment of the present invention.

FIG. 9 is a first diagram in a low temperature detection mode and a preheating mode in the temperature control device according to the second embodiment of the present invention.
It is a figure which shows the temperature-voltage characteristic of a temperature / voltage conversion signal and the 2nd temperature / voltage conversion signal in a fixing mode.

FIG. 10 is a diagram showing a temperature control procedure of a fixing roller in a temperature control device according to a second embodiment of the present invention.

FIG. 11 is a diagram showing a part of an image recording device including a temperature control device according to a third embodiment of the invention.

FIG. 12 is a diagram showing temperature-voltage characteristics of a first temperature / voltage conversion signal and a second temperature / voltage conversion signal in a temperature control device according to a third embodiment of the present invention.

[Explanation of reference numerals] 1 temperature control device 2 scanner 3 analog video processing unit 4 multiplexer 5 A / D converter 6 reference voltage generation unit 7 digital video processing unit 8 device control unit 9 heater control unit 11 paper end sensor 21 fixing roller 22 addition Pressure roller 23 Heater 24 Guide plate 25 Recording paper R1, R2, R3, R4 Resistance Rt Thermistor S1 switch

Claims (3)

[Claims] 1. A temperature control device for controlling the temperature of the fixing device to a preheating temperature or a fixing temperature by controlling the electric power supplied to a heater for heating the fixing device, wherein the resistance of the fixing device changes according to the temperature change of the fixing device. A thermistor having a variable value, a first voltage-dividing resistor, and a second voltage-dividing resistor connected in series, and the thermistor and the first voltage-dividing resistor being a combined resistor having a predetermined voltage applied to both ends thereof. Is obtained from a connection point between the first voltage dividing resistor and the second voltage dividing resistor, and a first temperature / voltage conversion signal having a temperature / voltage characteristic suitable for temperature detection near the preheating temperature. , A signal switching means for inputting a second temperature / voltage conversion signal having a temperature / voltage characteristic suitable for temperature detection near the fixing temperature and selectively outputting one of these signals, and a signal switching means from the signal switching means. With the output signal as input, The A / D converted value from the digital lower limit value to the digital upper limit value is output corresponding to the input voltage signal from the lower limit voltage to the upper limit voltage of When controlling the temperature of the A / D converter that outputs a digital upper limit value and the fixing device to the preheat temperature, the signal switching means is switched to the first temperature / voltage conversion signal side to perform the A / D conversion. When the temperature of the fixing device is controlled to the fixing temperature while the temperature is controlled on the basis of the first temperature / voltage conversion signal which is converted into the A / D converted value and output by Switching to the second temperature / voltage conversion signal side, and the A / D converter
A fixing device temperature control means for controlling the temperature based on the second temperature / voltage conversion signal converted into the D conversion value and output;
A / D conversion value from the A / D converter obtained by switching the signal switching means to the first temperature / voltage conversion signal side, and switching the signal switching means to the second temperature / voltage conversion signal side. The thermistor abnormality detecting means for detecting abnormality of the thermistor by comparing the obtained A / D converted value from the A / D converter at any time and detecting the coincidence of the signal values. And the temperature control device of the fixing device. 2. A third voltage dividing resistor whose one end is connected to the same potential as one end of the second voltage dividing resistor which is not connected to the first voltage dividing resistor, and the first voltage dividing resistor when the power source of the device is turned on. The connection between the voltage dividing resistor and the second voltage dividing resistor is temporarily released, and one end of the first voltage dividing resistor whose connection is released is connected to the other end of the third voltage dividing resistor, Voltage dividing resistance switching means for temporarily switching the first temperature / voltage conversion signal obtained from the connection point of the thermistor and the first voltage dividing resistor to a temperature / voltage characteristic suitable for detecting a temperature lower than room temperature, The thermistor abnormality detecting means, when the power source of the device is turned on, is temporarily switched to the temperature / voltage characteristic suitable for detection of a temperature lower than room temperature by the voltage dividing resistance switching means on the first temperature / voltage conversion signal side. A // obtained by switching the signal switching means to
2. The temperature control device for a fixing device according to claim 1, wherein an abnormality of the thermistor is detected by detecting that the A / D conversion value from the D converter is below a predetermined level. 3. A temperature control device for a fixing device according to claim 1, further comprising a resistor connected in parallel to the thermistor.