JP2000029349A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately detect an error by providing a means for detecting the disconnection of a heater lamp based on a comparison between a temperature gradient and a previously set reference temperature gradient and a means for changing the reference temperature gradient in accordance with the surface temperature of a heat roller measured at the start of detecting the temperature gradient. SOLUTION: When a power source is turned on, or reset, the heater lamp 3 is energized so as to start warming up the heat roller 4. After the heater lamp 3 is energized, three checking operations are performed. The first is a temperature gradient checking operation for the heat roller 4, the rising temperature ΔT of the heat roller 4 in a fixed period Δt is detected as the gradient, and in the case ΔT/Δt is equal to or below a certain reference temperature gradient, it is detected that the situation is caused by the disconnection of the heater lamp 3. The second is a checking operation that the heat roller 4 is not ready for printing within a fixed period, and such the error 'heater not ready' is detected. The this is a checking operation for detecting that T>=T6 is established (T; the temperature of the heat roller 4 and T6; reference value).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device applied to an electrophotographic apparatus represented by a laser printer, a copying machine, and the like.

[0002]

2. Description of the Related Art A heat roller type fixing device is known as one form of a fixing device applied to an electrophotographic apparatus. The heat roller type fixing device is schematically shown in FIG.
And a pressure roller 5 pressed against the heat roller 4, and a paper or O
The recording material 6 such as an HP sheet is heated and pressurized while being nipped and conveyed by the heat roller 4 and the pressure roller 5 to fix the toner image on the recording material 6.

In this type of heat roller type fixing device,
Usually, at least one temperature detecting element 2 for monitoring the surface temperature of the heat roller 4 is provided. As the temperature detecting element 2, a thermistor is generally used. As shown in FIG. 6, one end of the thermistor 2 is connected to Vcc, the other end is connected to GND via a resistor 7, and the thermistor 2 and the resistor 7 are connected. The CPU 8 takes in the voltage at the connection point to the CPU 8 and controls the temperature of the heat roller 4 and detects disconnection of the heater lamp 3 and the thermistor 2.

[0004] There are two types of temperature control of the heat roller 4, control at the time of startup and control at the time of printing / standby. Here, the control at the start-up means a control during a period from when power is supplied to the heater lamp 3 when the power of the electrophotographic apparatus is turned on until the surface temperature of the heat roller 4 reaches a specified value or more.
The control during printing / standby means that the surface temperature of the heat roller 4 is detected by the thermistor 2 in order to keep the surface temperature of the heat roller 4 constant during printing and during standby, and a preset upper limit temperature and lower limit temperature are set. Conduction of heater lamp 3 continuously with temperature /
It means the control to repeat the cutoff. Hereinafter, control at the time of startup and control at the time of printing / standby will be described.

[0005] POWE in control at the time of startup (control at startup), as shown in FIGS. 7 and 8, the time t ₀
When RON or RESET is performed, the heater lamp 3 is turned on and the heat roller 4 starts to warm. As time elapses, the temperature of the heat roller 4 starts increasing, and the temperature of the heat roller 4 obtained from the output of the thermistor 2 at time t ₁ after the power is turned on to the heater lamp 3 is based on the disconnection of the heater lamp 3 and the thermistor 2. If the temperature is equal to or lower than T ₀ , an error is detected as disconnection of the heater lamp 3 or the thermistor 2.

When the temperature of the heat roller 4 is equal to or higher than the disconnection reference temperature T ₀ of the heater lamp 3 and the thermistor 2 at time t ₁ , the operation of increasing the temperature of the heat roller 4 is continued, and at time t ₂ , If the surface temperature has reached the reference temperature T ₁ , that is, the temperature at which the electrophotographic apparatus can perform the printing operation, the apparatus enters a standby state. If the temperature of the heat roller 4 has not reached T ₁ , the printing operation can be performed within a predetermined time. "HEATER NOT READY" which means that it did not become a state
Detect errors.

(Control During Printing / Standby) Control during printing / standby will be described with reference to FIGS. 7 and 9. FIG. The electrophotographic apparatus that has been enabled to perform a printing operation needs to keep the temperature of the heat roller 4 constant during standby and during printing. Generally, the upper and lower limits of the surface temperature of the heat roller 4 are set in advance, and the conduction / interruption of the heater lamp 3 is repeated between the upper and lower limits to keep the surface temperature of the heat roller 4 constant. The control to make it happen is adopted.

[0008] Time t ₂ later, when the surface temperature of the heat roller 4 derived from the output of the thermistor 2 has reached the upper limit temperature T ₂ cut off the power supply to the heater lamp 3, when it reaches the lower limit temperature T ₃ Turns on the heater lamp 3 to heat the heat roller 4. If the surface temperature of the heat roller 4 further rises despite reaching the upper limit temperature T ₂ , when the temperature reaches T ₄ in order to prevent damage to the fixing device, “OVER T”
EMP ”error is detected. Further, when the surface temperature of the heat roller 4 that despite further lowering reaches the lower limit temperature T ₃ also, to reach a temperature T ₅ for preventing fixing failure to detect errors in "LOW TEMP".

Conventionally, the disconnection of the heater lamp 3 and the thermistor 2 and the temperature control of the heat roller 4 have been performed by the above control.

[0010]

Next, the drawbacks of the above prior art will be described.

First, detection of disconnection of the heater lamp 3 in control at the time of starting will be described.

POWER while the heat roller 4 is cold
FIG. 10 shows a case where ON or RESET is performed.
This will be described with reference to (a) and (b). FIG. 10A shows a case where the heater lamp 3 is disconnected from the beginning or before the time t ₁ , and the temperature T of the heat roller 4 at the time t ₁ .
Is T ₀ ≧ T, the disconnection error of the heater lamp 3 occurs. However, as shown in FIG. 10 (b), the case where the disconnected heater lamp 3 to time t ₁ since, despite the heater lamp 3 is disconnected, the temperature T of the heat roller 4 at time t ₂ is T "HEATER N" that ₁ ≥ T
An “OT READY” error occurs, and no disconnection error is notified.

Next, while the heat roller 4 is warm, the PO
Figure 1 when WER ON or RESET is performed
Description will be made using 0 (c). Also in this case, since the heat roller 4 is warm from the beginning, even if the heater lamp 3 is disconnected at any time during the warm-up,
Since the temperature T of the heat roller 4 at the time t ₁ is T ₀ ≦ T, a disconnection error of the heater lamp 3 does not occur, and the time t ₂
In this case, an error "HEATER NOT READY" that the temperature T of the heat roller 4 satisfies T ₁ ≧ T is obtained.

Next, detection of disconnection of the heater lamp 3 during printing and during standby will be described.

For example, when the width or thickness of the recording material 6 is large, the temperature of the heat roller 4 is easily taken away by the recording material 6, and as shown in FIG.
₂ and the lower limit temperature T _3.
The interruption is repeated. In this case, if the heater lamp 3 is disconnected, the recording material 6 loses heat, so that the temperature T
Reach ₅ and detect "LOW TEMP" error. However, for example, when the width and the thickness of the recording material 6 are small, the temperature of the heat roller 4 is hardly deprived by the recording material 6, and therefore, FIG.
As FIG. 10 (d) as shown in (e) is connection / disconnection of the heater lamp 3 between the upper limit temperature T ₂ and the lower limit temperature T ₃ of the heat roller 4 is not performed. In this case, if the heater lamp 3 is disconnected, an error of “LOW TEMP” will not be detected for a while even if the heater lamp 3 is disconnected.

Next, thermistor 2 for warming up
Will be described.

POWER while the heat roller 4 is cold
FIG. 11 shows a case where ON or RESET is performed.
This will be described with reference to (a) and (b). 11 (a) is a first or from the time t ₁ earlier when the thermistor 2 is disconnected, since the surface temperature T of the heat roller 4 at time t ₁ is T ₀ ≧ T, the disconnection error of the thermistor 2 . However, when the thermistor 2 is disconnected after the time t _{1 as} shown in FIG. 11B, the temperature T of the heat roller 4 at the time t ₂ is T ₁ ≧ despite the disconnection of the thermistor 2. "HEATER NOT"
READY "error.

In the state where the heat roller 4 is warm, P
The case where ON or RESET is performed will be described with reference to FIGS. FIG. 11 (c) is a case where the thermistor 2 is disconnected first from or time t ₁ earlier, since the temperature T of the heat roller 4 is T ₀ ≧ T at time t _1, the disconnection error of the thermistor 2. However, if the initial temperature of the heat roller 4 is high, the temperature of the heat roller 4 which is output from the thermistor 2 shows a an extremely low value, the actual temperature of the heat roller 4 is extremely high, disconnection at time t ₁ At the time of the error,
In some cases, the heat roller 4 and the pressure roller 5 were welded by heat from the heat roller 4.

Further, as shown in FIG.
_{If the} thermistor 2 is disconnected after ₁
"HEATER that but despite the disconnection, the temperature T of the heat roller 4 at time t ₂ is T ₁ ≧ T
Although the error of the NOT READY ", as if the thermistor 2 is disconnected in time t ₁ earlier" HEATE
At the time when the error of “R NOT READY” occurs, the temperature of the heat roller 4 is extremely high, and the heat from the heat roller 4 may cause the heat roller 4 and the pressure roller 5 to be welded.

The detection of disconnection of the thermistor 2 during printing and during standby will be described with reference to FIG. Thermistor 2 and during waiting print is disconnected, the output of the thermistor 2 is reduced, despite the thermistor 2 is disconnected, it reached a temperature T ₅ to prevent fixing failure "L
OW TEMP ”error is detected. afterwards,
When the RESET or the like is restarted, the heat roller 4 and the pressure roller 5 may be welded as in the case of FIG. 11C or 11D.

As described above, in the prior art, when the temperature of the heater lamp is controlled, an error different from a phenomenon actually occurring may be detected. For this reason, not only is the processing method for the error improper, but also there is a problem that thermal runaway leads to fuming and burning damage due to heat welding between the heat roller and the pressure roller.
Further, there is a disadvantage that it takes a lot of time to find out at which part the abnormality is.

An object of the present invention is to provide a fixing device capable of performing appropriate error detection.

[0023]

An object of the present invention is to provide a heat roller having a heater lamp, a pressure roller pressed against the heat roller, and a temperature detecting means for detecting a surface temperature of the heat roller. Heating and pressurizing the recording material holding the toner image while nipping and transporting the recording material with the heat roller and the pressure roller,
In a fixing device for fixing the toner image to a recording material,
Means for detecting a temperature gradient based on the output of the temperature detecting means during a predetermined period, and detecting disconnection of the heater lamp by comparing the temperature gradient with a preset reference temperature gradient; Means for changing the reference temperature gradient in accordance with the surface temperature of the roller.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1, 2, 3 and 4. The basic configuration of the fixing device is the same as that shown in FIG. 5 and will not be described again.

First, the heater lamp control at the time of startup (at the time of warm-up) will be described with reference to FIGS. When POWER ON or RESET is performed, the heater lamp 3 is turned on to start heating the heat roller 4. After the heater lamp 3 is turned on, three checks are performed.

The first is to check the temperature gradient of the heat roller 4. The temperature gradient check means that the heat roller 4
A temperature ΔT at which the temperature rises as a slope.
If ΔT / Δt is below a certain reference temperature gradient, it is detected as a disconnection of the heater lamp 3. Further, Δt in the temperature gradient check is set sufficiently smaller than the time t ₁ and the time t ₂ , the temperature gradient is checked every time Δt, and monitoring is always performed during warm-up.

The second check is that the heat roller 4 has not become printable within a certain period of time.
NOT READY "error is detected.

The third is to detect the temperature T of the heat roller 4 becomes T ≧ T _6, the operation proceeds to the next routine.

If the temperature T of the heat roller 4 is not T ≧ T ₀ , the above three checks are repeated.

When the process proceeds to the next routine, four checks are performed here. Of these, two are the same as in the previous routine, the temperature gradient check and the "HEATER NOT R"
EADY ". The third is a disconnection check of the thermistor 2. The disconnection check of the thermistor 2 is to check whether or not the temperature T obtained from the thermistor 2 satisfies T ₇ ≧ T, and the heater lamp 3 is turned on once the heat roller 4 satisfies T ≧ T _6. T ₇ as long as
This is because ≧ T does not occur.

The reference values T ₆ and T ₇ have T ₆ ≧ T ₇
And the difference between them is sufficiently taken, and sufficient hysteresis is provided so that erroneous detection is not performed even when the output voltage from the thermistor 2 is influenced by noise or the like and the voltage is slightly fluctuated.

Another check detects whether or not the temperature of the heat roller 4 has become equal to or higher than a temperature at which printing is possible.
In the case of T ₁ electrophotographic apparatus is shifted to the printing stand-by state,
If T ₁ ≧ T, the above four checks are repeated.

Next, heater lamp control during standby and during printing will be described with reference to FIGS. When the temperature of the heat roller 4 obtained from the output of the thermistor 2 to keep the temperature of the heat roller 4 constant reaches the upper limit temperature T ₂ cut off the heater lamp 3, the heater lamp 3 reaches the lower limit temperature T ₆ Conduction is performed to heat the heat roller 4.

If the temperature of the heat roller 4 further rises despite reaching the upper limit temperature T ₂ , when the temperature reaches the temperature T ₄ in order to prevent damage to the fixing device, “OVER”
TEMP "error is detected. Even when the temperature of the heat roller 4 a further despite a lower limit temperature T ₃ descends to detect errors in "LOW TEMP" Once at the temperature T ₅ to prevent fixing failure. Further, a temperature gradient check and a disconnection check of the thermistor 2 are performed as in the warm-up. In this case, the gradient check is performed only while the heater lamp 3 is conducting, and the disconnection check of the thermistor 2 is performed by the same detection method as in the warm-up.

Next, the temperature gradient check will be described. In general, temperature detection is performed by the CPU 8 based on a voltage value obtained from the voltage division of the thermistor 2 and the resistor 7. That is, the temperature gradient check is a voltage gradient check.

FIG. 4 shows a change in temperature / voltage value when a general thermistor 2 is used. When the temperature of the heat roller 4 is low, the gradient of the voltage value is small, and the gradient of the voltage increases as the temperature increases. When the temperature further increases, the gradient of the voltage value decreases again. That is, the gradient of the voltage value changes depending on the temperature of the heat roller 4. Therefore, in order to detect disconnection of the heater lamp 3 by an accurate gradient check, it is necessary to change the gradient of the gradient check of the voltage value output from the thermistor 2.

For this purpose, the voltage value at the start of the gradient check is detected, an appropriate gradient is set, and the gradient check is performed. In addition, since the heater lamp 3 is always in a conductive state during the warming-up, a sufficient time for performing the temperature gradient check can be obtained. Sometimes there is not enough time.

In other words, in order to accurately check the temperature gradient during standby and during printing, a temperature gradient check with a variable detection time is performed. And printing waiting to conduct heater lamp 3 at a temperature T ₃ of the heat roller, because blocked with temperature T ₂ that time Δt is the temperature gradient checked that may fall within a certain period.

[0039]

As described above, according to the fixing device of the present invention, a temperature gradient is detected based on the output of the temperature detecting means during a predetermined period, and the temperature gradient is compared with a preset reference temperature gradient. It has a means for detecting disconnection of the heater lamp and a means for changing the reference temperature gradient according to the surface temperature of the heat roller at the start of the temperature gradient detection. A lamp disconnection error can be detected.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control sequence according to the present invention.

FIG. 2 is a timing chart showing control at the time of startup according to the present invention.

FIG. 3 is a timing chart showing control during standby and during printing according to the present invention.

FIG. 4 is a timing chart when a reference temperature gradient is changed in the temperature gradient check of the present invention.

FIG. 5 is a schematic diagram of a fixing device.

FIG. 6 is a block diagram showing a circuit configuration using a thermistor.

FIG. 7 is a flowchart showing a conventional heat roller temperature control sequence.

FIG. 8 is a time chart showing conventional control at the time of startup.

FIG. 9 is a time chart showing conventional control during standby and during printing.

FIG. 10 is a time chart showing a problem in disconnection detection of a conventional thermistor.

FIG. 11 is a time chart showing a problem in detecting a disconnection of a conventional heater lamp.

[Explanation of symbols]

2 ... Thermistor, 3 ... Heater lamp, 4 ... Heat roller, 5
... pressure roller, 6 ... recording material, 7 ... resistance, 8 ... CPU.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H033 AA42 CA03 CA05 CA30 CA32 3K058 AA12 AA34 AA42 BA18 CA12 CA22 CA61 CB02 CB23 CB27 CF02 5H323 AA36 BB17 CA08 CB04 DA01 EE16 FF03 GG04 HH02 KK05 MM02 Q07 SS

Claims (1)

[Claims] A heat roller having a heater lamp; a pressure roller pressed against the heat roller; and a temperature detecting means for detecting a surface temperature of the heat roller. In a fixing device for fixing the toner image on a recording material by heating and pressing while nipping and transporting by the heat roller and the pressure roller, a temperature gradient is detected based on an output of the temperature detecting unit for a predetermined period, and the temperature gradient is detected. Means for detecting disconnection of the heater lamp by comparison with a preset reference temperature gradient, and means for changing the reference temperature gradient according to the surface temperature of the heat roller at the start of temperature gradient detection. Characteristic fixing device.