JP2002182517A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly detect any damage on a thermister and to eliminate any erroneous detection of the damage on the thermister in a fixing control device. SOLUTION: Voltage inputted from a thermister 3 is detected 32 times at a cycle of 10 ms from turning on of a heater 4 by using a temperature control part and a comparison part 1 and digital conversion is carried out. Judgement of whether the digitally converted value indicates a value that is greater than a specified value more than 17 times is carried out and, when not, it is judged that the thermister is disconnected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat fixing device in an image forming apparatus such as an electrophotographic printer.

[0002]

2. Description of the Related Art A conventional heat fixing device includes, for example, a heat roller for heat fixing an unfixed image, a heater for heating the heat roller, and a thermistor for detecting the temperature of the heat roller. . In such a heat fixing device, as a method for preventing the heat roller from heating to a predetermined temperature or more when the thermistor is broken, a temperature detected by the thermistor a predetermined time after turning on the heater and a reference stored in advance. The output of the comparing means for comparing with the value was detected.

[0003]

A conventional heat fixing device is
Only when the time required for the heat roller to reach the temperature required for fixing after the heater starts heating, it is possible to accurately detect thermistor breakage. If the time required to reach the temperature required for fixing after the heater starts heating is short, the heat roller heats more than necessary before detecting that the thermistor is damaged by the conventional detection, and the bearings etc. Peripheral parts may be melted or give off odors, which may cause breakage.Delay in the thermistor responsiveness will detect a low fixing temperature and break the thermistor even though the thermistor is not damaged. There is a problem that it is erroneously detected.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a fixing device having a fixing unit for thermally fixing an unfixed image and a heating unit for heating the fixing unit is provided. A temperature detecting sensor for detecting a temperature of the fixing unit, a comparing unit for comparing the temperature of the fixing unit with a pre-stored reference value, and repeating the comparison by the comparing unit at a predetermined cycle during a predetermined time. A fixing unit that counts the number of times the temperature of the fixing unit exceeds the reference value, and a determining unit that determines that the temperature detection sensor is in a damaged state when the counting unit is equal to or less than a predetermined number. It is a device.

[0005] With such a configuration, by adjusting a predetermined cycle and a count number within a predetermined time, it is possible to detect the initial or unexpected damage of the thermistor in a short time, and eliminate erroneous detection due to damage of the thermistor function. Will be able to do it.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a fixing device according to an embodiment of the present invention. The fixing device includes a temperature control unit and a comparison unit 1, a heater lighting circuit 2, a thermistor 3, a heater lamp 4, a power supply 5, a storage unit 6, and a heat roller 7. It is configured.

[0007] The temperature control unit and the comparison unit 1 include a thermistor 3
The input voltage of the thermistor 3 is detected, and when heating is necessary, a signal is sent to the heater lighting circuit 2 to turn on the heater 4.
Is compared with the reference value stored.

Hereinafter, the operation of this embodiment will be described in detail with reference to FIGS. When the power supply 5 is turned on, the temperature control unit and the comparison unit 1 detect the input voltage of the thermistor 3, and if heating is necessary, the temperature control unit and the comparison unit 1 send a signal to the heater lighting circuit 2 to send a signal to the heater lighting circuit 2. 4 is turned on (step 1).

After the heater 4 is turned on, the thermistor is disconnected (breakage).
It is determined whether or not this is the case (steps 2 to 9). First, determination A is performed (step 2). In the determination A, the temperature control unit and the comparison unit 1 detect the input voltage from the thermistor 3 32 times in a period of 10 [ms] after the heater 4 is turned on and perform digital conversion, and the digitally converted value is 17 times or more. "
It is determined whether the above value is shown. The numbers “2” and “1” described later indicate that the input voltage of the thermistor 3 is 2
It is a number corresponding to one voltage of the value divided into 56.

In this embodiment, the voltage (analog data) output from the thermistor 3 and proportional to the fixing temperature is converted into a digital value. Thereby, the storage unit 6 corresponding to the voltage value and the temperature output from the thermistor 3 and the required temperature
The heater lighting is controlled so that the temperature is determined by a software program, based on a conversion table showing the relationship between the digital values in the table. The digital value is a value ultimately required for performing the software control. With such a control, when the CPU has an AD conversion function, the effect that the circuit can be simplified and the cost can be reduced can be obtained. .

As described above, the numbers “2” and “1” appearing below indicate that the input voltage of the thermistor 3 is 256.
If a value corresponding to one voltage value of the divided values is “2”> “1”, where the value is “2”> “1”, the position of the 256 divided value may be appropriately selected. In the thermistor disconnection detection control according to the present embodiment, since a determination is made based on a value that has been converted into a digital value and based on a relative value from the value, “1” indicates that the input voltage from the thermistor 3 is almost constant for a certain period of time. What is necessary is just to show that it has not changed, and to prevent erroneous detection due to an AD conversion error.

In this embodiment, the detection is performed 32 times at a cycle of 10 [ms] to determine whether the value indicates a value equal to or greater than 2 for 17 times or more. By adjusting the detection cycle and the number of determinations, it is possible to prevent erroneous detection as to whether or not the sensor 3 is in a disconnected state. For example, if the number of detections and the cycle are only for the purpose of preventing erroneous detection, it is preferable to increase the number of detections as much as possible and to perform detection in a short cycle. More is preferred. However, the temperature is 0
In the vicinity of ° C., accurate temperature cannot be detected due to the problem of the decomposition performance of AD conversion. Therefore, it is necessary to determine the final control method by evaluating the temperature rise at a low temperature or the like.

Next, when the value of "2" or more is shown 17 times or more in step 2, the process shifts to normal heater control at that time (step 7). "2" 17 times or more in step 2
If the above value is not shown, the determination A is repeated for 5 seconds. If the condition of the determination A is not continuously satisfied during that time (steps 3 to 5), it is determined that the thermistor is initially disconnected (step 6) and the satisfaction is satisfied. If so, the process shifts to normal heater control at that time (step 7).

If there is no disconnection of the thermistor in steps 3 to 5, it is best that the machine be ready for printing as early as 1 second, and the determination A is repeated for 5 seconds, during which the machine is continuously operated for 5 seconds. If there is no failure in the first determination A, the normal temperature control is started at that time. Conversely, if the result of the first determination is NG,
In order to prevent erroneous detection, the determination A is repeated for 5 seconds, and the determination is made continuously for 5 seconds. As described above, the detection can be performed in a short time by continuously performing the detection in the predetermined cycle during the predetermined time.

Next, after satisfying the condition of the judgment A, the judgment B
(Step 8). In the judgment B, after entering the normal control (that is, the control after reaching the standby temperature), the input voltage from the thermistor 3 is detected 32 times at a cycle of 10 [ms] from the lighting of the heater 4 and the digital conversion is performed. If the value is less than "1" for all 32 times, it is determined that the thermistor is disconnected (step 9).

[0016]

As described above, according to the fixing device of the present invention, the counting means for counting the number of times that the temperature of the fixing means exceeds the reference value by repeating the comparison by the comparing means at a predetermined cycle during a predetermined time. A determination means for determining that the temperature detection sensor is in a damaged (disconnected) state when the count means is equal to or less than a predetermined number. Can detect a failure of the thermistor without destroying the fixing device, and can eliminate erroneous detection of thermistor breakage, thereby accurately detecting thermistor breakage. Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a fixing device of the present invention.

FIG. 2 is a flowchart illustrating an operation of the fixing device of the present invention.

[Explanation of symbols]

 1: Temperature control unit and comparison unit (CPU) 2: Heater lighting circuit 3: Thermistor 4: Heater lamp 5: Power supply 6: Storage unit 7: Heat roller

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keisuke Koyama 704, Matabe, Noshino, Tamaki-cho, Tamaki-cho, Mie Prefecture 19 F-term (reference) 2F027 DA12 DA41 DE04 DE07 DE09 EC06 EC15 ED25 EE08 EF04 EF09 HA10 HA15 2H033 AA24 AA35 AA42 BA30 CA07 CA24

Claims (1)

[Claims] 1. A fixing device comprising a fixing unit for thermally fixing an unfixed image and a heating unit for heating the fixing unit, wherein a temperature detecting sensor for detecting a temperature of the fixing unit, and a temperature of the fixing unit. A comparison unit that compares the comparison unit with a reference value stored in advance, a counting unit that counts the number of times the temperature of the fixing unit exceeds the reference value by repeating the comparison by the comparison unit at a predetermined cycle during a predetermined time, A determining unit that determines that the temperature detecting sensor is in a damaged state when the counting unit is equal to or less than a predetermined number.