JP3880174B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a means for detecting an initial disconnection state in a thermal fixing device of an image forming apparatus such as a printer, a fax machine, and a copying machine using an electrophotographic process.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an image forming apparatus, a fixing device having a fixing heater as a heating unit for thermally fixing toner onto a recording medium, a temperature detecting body for detecting the temperature of the fixing heater, and ON / OFF control of the fixing heater are performed. It is well known to have an energization control means.
[0003]
Here, the temperature detector includes a thermistor and outputs an analog signal as a temperature information signal. Also, the energization control means detects the initial disconnection state of the fixing heater after A / D conversion (analog signal-digital signal conversion) of the temperature information signal from the temperature detector, and turns ON if there is no initial disconnection state Shifting to temperature control by / OFF control.
[0004]
A conventional example of this initial disconnection detection method will be described with reference to FIG. The energization control means A / D converts the temperature information signal of the fixing heater from a temperature detection body such as a thermistor, and checks the initial disconnection state of the fixing heater based on the A / D conversion value. That is, within the time for determining whether or not the initial disconnection state is present, the detected temperature of the fixing heater is compared with a set temperature Ts that is a predetermined target temperature, and is equal to or higher than the set temperature Ts (from the set temperature Ts in FIG. If it is detected at least once, it is determined that the initial disconnection state has not occurred, and the process proceeds to temperature control by the next ON / OFF control. On the other hand, if it is not detected that the temperature is equal to or higher than the preset temperature, it is determined that the initial disconnection state has occurred.
[0005]
[Problems to be solved by the invention]
However, in the conventional example shown in FIG. 8, if it is detected even once that the thermistor is equal to or higher than the set temperature within the specified time, it is determined that the initial disconnection state has not occurred. Even if it was detected, it was erroneously determined that the initial disconnection state was not established, and the process shifted to the next temperature control.
[0006]
In particular, due to the characteristics of the thermistor, since the variation in the A / D converted value in the low temperature range is large, there is a possibility of erroneous detection if it is not in the initial disconnection state.
[0007]
As described above, even if the fixing heater is actually in the initial disconnection state, if it is erroneously detected that the fixing heater is not in the initial disconnection state and the next temperature control is performed, thermal stress is applied to the fixing heater.
[0008]
An object of the present invention is to detect the initial disconnection state of the heating means with high accuracy, thereby preventing the shift to the temperature control regardless of the initial disconnection state, thereby preventing the thermal stress applied to the fixing heater. Another object of the present invention is to provide a fixing device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a fixing device according to the present invention comprises:
The recording medium is heated by heating means while passing a sheet-like recording medium carrying an unfixed image through a nip formed between a fixing body and a pressure body pressed against each other. Fixing device,
A temperature detecting member for outputting an analog information corresponding to the detected temperature of the temperature is obtained by detection of the heating means,
An A / D conversion means for converting the analog information into a digital value; an energization control means for sampling the digital value converted by the A / D conversion means and controlling the energization from the commercial power supply to the heating means;
Said heating means based on the detected temperature of the temperature sensing body and a judging means for judging whether the initial disconnection state,
The determination means integrates the difference between the value corresponding to the target temperature or the converted value corresponding to the lowest temperature of the A / D conversion means and the sampled digital value in a predetermined period, and the obtained integration said heating means by comparing the reference value predetermined value to determine whether the initial disconnection state.
[0010]
Further, according to the present application, the object is obtained in the first invention according to the present application, wherein the determining means adds up the difference between the target temperature and the detected temperature of the temperature detector in a predetermined period. It is also achieved by the second invention in which it is determined whether or not the heating means is in an initial disconnection state by comparing the obtained integrated value with a predetermined reference value .
[0011]
In addition, another fixing device according to the present invention is a heating unit that feeds a sheet-like recording medium carrying an unfixed image through a nip formed between a fixing member and a pressure member pressed against each other. A fixing device configured to heat the recording medium by heating,
A temperature detector that outputs analog information corresponding to the detected temperature obtained by detecting the temperature of the heating means;
An A / D conversion means for converting the analog information into a digital value; an energization control means for sampling the digital value converted by the A / D conversion means and controlling the energization from the commercial power supply to the heating means;
Determining means for determining whether or not the heating means is in an initial disconnection state based on the temperature detected by the temperature detector;
When a plurality of set temperatures and different specified times corresponding to each set temperature are determined, and the sampled digital value does not exceed the set temperature within a specified time corresponding to each set temperature, the determination means Determines that the heating means is in an initial disconnection state.
[0013]
Further, preferably, the heating means, the temperature sensing on the other surface with the heating resistor which generates heat is provided on one surface of the thin plate-shaped substrate composed mainly of ceramics by energization from the commercial power source The fixing member is an endless belt that is pressed against the one surface via a recording medium carrying an unfixed image.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS.
[0034]
(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.
[0035]
FIG. 1 shows a fixing heater control circuit of the laser printer of this embodiment.
[0036]
The fixing heater control circuit includes a fixing heater 4, a thermistor 5 that detects the temperature of the fixing heater 4, a triac 7 that switches the fixing heater 4, a phototriac coupler 6 that triggers the gate of the triac 7, The switching transistor Q1 for switching the phototriac coupler 6 and a control unit 3 such as a CPU connected to the base resistor R4 of the switching transistor Q1 are connected to a commercial power source 1 that supplies power to the fixing heater 4. ing.
[0037]
The resistor R1 is connected in series with the power source V1 and the thermistor 5. The limiting resistor R2 limits the current flowing through the light emitting diode of the phototriac coupler 6. The limiting resistor R3 limits the gate current of the triac 7. Both the choke coil L1 and the surge absorbing element 8 are for reducing the switching noise of the triac 7.
[0038]
Here, as the fixing heater 4, for example, a heating resistor that receives heat from the commercial power source 1 and generates heat is applied to one surface of a thin plate-shaped substrate mainly composed of ceramics and the other surface. There is known a ceramic heater in which the thermistor 5 is disposed in contact with or close to the thermistor 5.
[0039]
In addition, as a fixing device provided with such a ceramic heater, for example, a recording medium carrying an unfixed image in a nip portion formed between an endless belt-like fixing member and a rotating member-like pressing member that are pressed against each other is used. It is known that the recording medium is heated by heating a ceramic heater while passing paper.
[0040]
Further, the control unit 3 as an energization control unit is configured to A / D convert the temperature information signal S1 from the thermistor 5 and monitor the temperature state of the fixing heater 4 based on the A / D conversion value. Yes.
[0041]
The thermistor 5 as a temperature detector has a large variation in resistance value in a low temperature region due to its characteristics. Therefore, the variation of the A / D conversion value from the temperature information signal S1 is also large. In the present embodiment, the variation in the A / D conversion value is covered, and the initial disconnection state of the fixing heater 4 is detected with high accuracy. That is, as shown in FIGS. 2 and 3, the control unit 3 according to the present embodiment samples the time t <b> 1 (initial disconnection detection processing time t <b> 1) until the initial disconnection failure is determined at a uniquely determined cycle. At this time, the change from the set temperature Ts, which is the target temperature in the pair of A / D conversion values, is integrated with the detected temperature for each cycle, and the magnitude of the integrated value A and a predetermined reference value B is compared. Accordingly, the initial disconnection state is detected as follows.
[0042]
If (integrated value A) <(predetermined reference value B), it is determined that there is no initial disconnection state, and the process proceeds to the next temperature control.
[0043]
On the other hand, if (integrated value A)> (predetermined reference value B), it is determined that there is an initial disconnection state, and a signal S2 that immediately stops energization of the fixing heater 4 is output. Further, the control unit 3 stores that the fixing heater 4 is out of order, and does not turn on the fixing heater 4 even if a print operation signal is subsequently received.
[0044]
The (predetermined reference value B) is determined from the configuration of the fixing device, the printing speed of the image forming apparatus, and the like. In the present embodiment, (predetermined reference value B) is set to 1. That is, in this embodiment, it is determined that “the integrated value <1” is not in the initial disconnection state, and the process proceeds to the next temperature control. Further, when the accumulated value A within time t1 is 0, the time for detection is further extended to determine and determine the accumulated value.
[0045]
According to the present embodiment configured as described above, the initial disconnection state is detected with high accuracy as follows. The specific control operation of FIG. 1 described above is shown in FIGS.
[0046]
When recognizing the ON state of the print operation signal, the control unit 3 turns on the heater ON signal S2. The temperature information signal S1 from the thermistor 5 is input to the control unit 3 and A / D converted. The controller 3 determines whether or not the fixing heater 4 is in an initial disconnection state based on the A / D conversion value.
[0047]
As described above, in the present embodiment, it is determined that “the integrated value <1” is not in the initial disconnection state, and the process proceeds to the next temperature control. In FIGS. 2 and 3, the upper change (the portion indicated by the fine hatching) with respect to the set temperature Ts is a positive value, and the lower change (the portion indicated by the coarse hatching) is a negative value. Yes.
[0048]
First, in the example of FIG. 2, the integral value of the change from the set temperature Ts in the A / D conversion value of the detected temperature for each cycle within the time t1 is −5.
[0049]
Therefore, “integrated value−5 <1” is established, and it is determined that there is no initial disconnection state, and the process proceeds to the next temperature control.
[0050]
On the other hand, in the example of FIG. 3, the integrated value of the change from the set temperature Ts in the A / D conversion value of the detected temperature for each cycle within the time t1 is 5.
[0051]
Therefore, “integrated value 5> 1” is established, and it is determined that the circuit is in an initial disconnection state, and a signal S2 that immediately stops energization of the fixing heater 4 is output. The control unit 3 stores that the fixing heater 4 has an initial disconnection failure, and does not turn on the fixing heater 4 even if a print operation signal is received thereafter.
[0052]
(Second Embodiment)
Next, a second embodiment of the present invention will be described. 4 and 5 are control operation diagrams of this embodiment. The circuit configuration is the same as in FIG.
[0053]
As shown in FIGS. 4 and 5, the control unit 3 according to the present embodiment, when sampling the initial disconnection failure detection processing time t <b> 1 with a uniquely determined cycle, performs A / D of the detected temperature for each cycle. By integrating the change in the converted value from the FF value (the maximum value of the A / D converted value), and comparing the absolute value of the integrated value X with the absolute value of the predetermined reference value Y, the initial value is obtained. Determine if there is a disconnection.
[0054]
If (the absolute value of the accumulated value X)> (the absolute value of the predetermined reference value Y), it is determined that there is no initial disconnection state, and the process proceeds to the next temperature control.
Conversely, if (the absolute value of the accumulated value X) <(the absolute value of the predetermined reference value Y), it is determined that there is an initial disconnection state.
[0055]
(A predetermined absolute value of the reference value Y) is determined from the configuration of the fixing device, the printing speed of the image forming apparatus, and the like.
[0056]
In the present embodiment, the reference value Y is 40. That is, it is determined that “| integrated value |> | 40 |” is not in the initial disconnection state, and the process proceeds to the next temperature control.
[0057]
According to the present embodiment configured as described above, the initial disconnection state is detected with high accuracy as follows.
[0058]
As described above, in the present embodiment, “| integrated value |> | 40 |” is determined to be not in the initial disconnection state, and the next temperature control control is set. In FIGS. 4 and 5, the integrated value is equal to the area of the portion indicated by hatching.
[0059]
First, in the example of FIG. 4, the integrated value of the change from the set temperature Ts in the A / D conversion value of the detected temperature for each cycle within the initial disconnection state detection processing time t1 is −44.
[0060]
Therefore, “integrated value | −44 |> | 40 |” is determined, and it is determined that there is no initial disconnection state, and the process proceeds to the next temperature control.
[0061]
On the other hand, in the example of FIG. 5, the integrated value of the change from the FF value in the A / D conversion value of the detected temperature for each cycle within the initial disconnection detection processing time t1 is −31.
[0062]
Therefore, “integrated value | −31 | <| 40 |” is established, and it is determined that the initial disconnection state occurs.
[0063]
(Third embodiment)
Next, a third embodiment of the present invention will be described. 6 and 7 are control operation diagrams of this embodiment. The circuit configuration is the same as in FIG.
[0064]
The control unit 3 of the present embodiment gradually increases the set temperature for determining the initial disconnection state along with the time lapses ta, tb, and tc in a plurality of stages Ts1, Ts2, and Ts3 within the initial disconnection detection processing time t1. It is set to change. Then, when sampling is performed at a uniquely determined cycle within the initial disconnection detection processing time t1, if the set temperature Ts1 is exceeded within the first ta time, the temperature is shifted to a higher set temperature Ts2, and then the time When the set temperature Ts2 is exceeded within tb, the temperature is shifted to a higher set temperature Ts3. When the set temperature Ts3 is exceeded within time tc, it is determined that there is no initial disconnection state, and the next It is comprised so that it may transfer to temperature control control.
[0065]
Here, t1 = ta + tb + tc and ta <tb <tc.
[0066]
The reason for setting t1 = ta + tb + tc is to determine that it is in the initial disconnection state within time t1. The reason why ta <tb <tc is set is that it takes more time to reach Ta, Tb, Tc and higher set temperatures.
[0067]
In the present embodiment, the set temperature and the division detection time are set in three stages. However, the present invention is not limited to this, and an arbitrary number may be set.
[0068]
According to the embodiment configured as described above, the initial disconnection state is accurately detected as follows.
[0069]
First, in the example of FIG. 6, since the set temperature Ts1 was exceeded within the first time ta, the set temperature is shifted to a higher Ts2. Then, since the set temperature Ts2 is exceeded within the subsequent time tb, the set temperature is shifted to a higher Ts3. And since it exceeded set temperature Ts3 within the continuing time tc, it transfers to the next temperature control.
[0070]
On the other hand, in the example of FIG. 7, the set temperature Ts1 was exceeded within the time ta, and the set temperature Ts2 was exceeded within the subsequent time tb. However, Ts3 could not be cleared within the subsequent time tc. For this reason, the control unit 3 determines that it is in the initial disconnection state.
[0071]
【The invention's effect】
As described above, according to the present invention, it is possible to accurately detect whether or not the heating means is in an initial disconnection state, and reliably prevent the heating means from being subjected to thermal stress. can do.
[0076]
In addition, according to the present invention, the nip formed between the endless belt-like fixing body and the pressurizing body that are in pressure contact with each other is heated by the ceramic heater, so that the heat capacity of the ceramic heater is reduced. In addition, it is possible to efficiently raise and maintain the target temperature such as the nip portion.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a fixing heater control circuit common to first to third embodiments according to the present application.
FIG. 2 is a graph showing a control operation (in the case of no initial disconnection state) of the first embodiment according to the present application.
FIG. 3 is a graph showing a control operation (when there is an initial disconnection state) of the first embodiment according to the present application;
FIG. 4 is a graph showing a control operation (in the case of no initial disconnection state) of a second embodiment according to the present application.
FIG. 5 is a graph showing a control operation (when there is an initial disconnection state) according to the second embodiment of the present application.
FIG. 6 is a graph showing a control operation (in the case of no initial disconnection state) of the third embodiment according to the present application.
FIG. 7 is a graph showing a control operation (when there is an initial disconnection state) of a third embodiment according to the present application.
FIG. 8 is a graph showing a control operation of a conventional example.
[Explanation of symbols]
3 Control unit (energization control means)
4 Fixing heater (heating means)
5 Thermistor (temperature detector)
S1 Temperature information signal S2 Heater ON / OFF signal t1 Initial disconnection detection processing time Ts Set temperature FF A / D conversion value maximum value ta, tb, tc Division detection time Ts1, Ts2, Ts3 Set temperature

Claims (3)

The recording medium is heated by heating means while passing a sheet-like recording medium carrying an unfixed image through a nip formed between a fixing body and a pressure body pressed against each other. Fixing device,
A temperature detector that outputs analog information corresponding to the detected temperature obtained by detecting the temperature of the heating means;
An A / D conversion means for converting the analog information into a digital value; an energization control means for sampling the digital value converted by the A / D conversion means and controlling the energization from the commercial power supply to the heating means;
Determining means for determining whether or not the heating means is in an initial disconnection state based on the temperature detected by the temperature detector;
The determination means integrates the difference between the value corresponding to the target temperature or the converted value corresponding to the lowest temperature of the A / D conversion means and the sampled digital value in a predetermined period, and the obtained integration A fixing device characterized in that it is determined whether or not the heating means is in an initial disconnection state by comparing a value with a predetermined reference value. The recording medium is heated by heating means while passing a sheet-like recording medium carrying an unfixed image through a nip formed between a fixing body and a pressure body pressed against each other. Fixing device,
A temperature detector that outputs analog information corresponding to the detected temperature obtained by detecting the temperature of the heating means;
An A / D conversion means for converting the analog information into a digital value; an energization control means for sampling the digital value converted by the A / D conversion means and controlling the energization from the commercial power supply to the heating means;
Determining means for determining whether or not the heating means is in an initial disconnection state based on the temperature detected by the temperature detector;
When a plurality of set temperatures and different specified times corresponding to each set temperature are determined, and the sampled digital value does not exceed the set temperature within a specified time corresponding to each set temperature, the determination means Determines that the heating means is in an initial disconnection state.   The heating means is provided with a heating resistor that generates heat upon energization from a commercial power source on one side of a thin plate-shaped substrate containing ceramic as a main component, and the temperature detecting body is in contact with or close to the other side. 3. The ceramic heater disposed as described above, wherein the fixing member is an endless belt-like member that is pressed against the one surface via a recording medium carrying an unfixed image. The fixing device according to any one of the above.

Images