JP2001109319A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the abnormal temperature rise of a fixing roller and the rupture of a fixing device by rapidly detecting that recording paper is wound round the fixing roller. SOLUTION: In this fixing device, an image on the recording paper is fixed by making the recording paper pass between the fixing rollers 11 and 12 whose temperature is controlled to specified target temperature. The device is provided with a non-contact temperature sensor 15 detecting the surface temperature of the fixing roller in paper passing width in a non-contact state, and a decision means deciding that the recording paper is wound round the fixing roller when the detected temperature by the sensor 15 becomes equal to or under specified warning temperature. In the case of deciding that the recording paper is wound round the fixing roller, the heater for heating 31 of the roller 11 is turned off and the driving of the rollers 11 and 12 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing an image on a recording sheet by passing the recording sheet between fixing rollers whose temperature is controlled to a predetermined target temperature.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus (copier,
Printer, facsimile, etc.), the toner image transferred onto the recording paper is fixed by thermocompression bonding using a fixing roller whose temperature is controlled to a predetermined target temperature (fixing temperature). Here, in the temperature control of the fixing roller, the temperature of the fixing roller is detected by a temperature sensor, and the heater is controlled so that the detected temperature becomes a predetermined target temperature (eg, on / off control).
It is done.

In some cases, the recording paper is wound around the fixing roller. In this case, the temperature of the recording paper is hindered, and the temperature of the fixing roller is detected to be lower than the actual temperature. As a result, the target temperature control of the fixing roller is hindered, and the temperature of the fixing roller rises abnormally. May occur. In order to eliminate this problem, for example, a thermal fuse or a thermostat is used to cut off a current supply circuit of the heater when overheating occurs.

[0004]

A technique using a thermal fuse or the like has poor thermal responsiveness. For this reason, when the temperature rise characteristics of the fixing roller are good, the temperature of the fixing roller may have already risen abnormally when the thermal fuse or the like operates, and the fixing device may be destroyed. SUMMARY OF THE INVENTION It is an object of the present invention to be able to quickly detect that a recording sheet has been wound around a fixing roller. It is another object of the present invention to prevent an abnormal rise in the temperature of the fixing roller and the destruction of the fixing device.

[0005]

According to a first aspect of the present invention, there is provided a fixing device comprising:
A fixing device for fixing an image on a recording sheet by passing the recording sheet between fixing rollers whose temperature is controlled to a predetermined target temperature, wherein the fixing device detects the surface temperature of the fixing roller within the sheet passing width in a non-contact manner. A temperature sensor; and a determination unit configured to determine that the recording paper has been wound around the fixing roller when the temperature detected by the non-contact temperature sensor is equal to or lower than a predetermined warning temperature. According to a second aspect of the present invention, in the fixing device according to the first aspect,
The predetermined warning temperature is determined as a relative temperature from the detected temperature immediately before the temperature starts to drop sharply. According to a third aspect of the present invention, the fixing device according to the first or second aspect further includes an emergency off unit that turns off the heating unit of the fixing roller when the determination unit determines that the recording paper has been wound around the fixing roller. It is characterized by. According to a fourth aspect of the present invention, there is provided a fixing device according to any one of the first to third aspects, further comprising an emergency stop unit that stops driving of the fixing roller when the determination unit determines that the recording sheet has been wound around the fixing roller. ,
It is characterized by the following.

[0006]

FIG. 1A is a block diagram schematically showing an arrangement of a fixing device and a non-contact temperature sensor 15 and a configuration of a control circuit thereof, and FIG.
FIG. 7 is an explanatory diagram showing a relationship between the sheet width and the sheet passing width.

The fixing device has an upper fixing roller 11, a lower fixing roller 12, and a fixing heater 31 provided inside the upper fixing roller 11. The recording paper on which the toner image has been formed is passed between the upper fixing roller 11 and the lower fixing roller 12 as shown by an arrow in the drawing, whereby an image fixing process by thermocompression is performed.

The temperature of the fixing heater 31 is controlled by the control unit 20 so that the temperature detected by the non-contact temperature sensor 15 becomes a predetermined target temperature (eg, 160 ° C., fixing temperature). That is, the upper fixing roller detected by the non-contact temperature sensor 15
The control unit 20 controls the surface temperature of 11 to a predetermined target temperature.
The fixing heater 31 via the temperature control circuit 21 according to a control signal from
(For example, on / off control) is performed.

A non-contact temperature sensor is a known element that receives infrared rays radiated from an object to be detected and generates an electric signal corresponding to the amount of received light. In the present fixing device, the non-contact temperature sensor 15 is located at a position near the surface of the upper fixing roller 11 (FIG. 1).
(See FIG. 1A), and is provided at a position (see FIG. 1B) within the sheet passing width. The paper passing width refers to the width (the size in the direction perpendicular to the paper passing direction) of the recording paper of the minimum size (A5 paper in the figure) when the fixing device is passed. That is,
The non-contact temperature sensor 15 is provided at a position where the surface of the upper fixing roller 11 should be hidden from the non-contact temperature sensor 15 when the recording paper is wound around the upper fixing roller 11.

FIG. 3 is a flowchart showing an outline of temperature control of the fixing device. Hereinafter, description will be given with reference to the flowchart of FIG. At each temperature detection timing (YES in S11), the temperature detected by the non-contact temperature sensor 15 is taken into the control unit 20 (S13). The temperature detection timing is a timing arbitrarily determined according to the accuracy required by the temperature control. This timing may be set at a fixed time interval, such as every 1 second or every 5 seconds, but it is set to a relatively short time interval when the device is started, and to a relatively long time interval in a steady state. Alternatively, a variable time interval may be set.

The control unit 20 compares the detected temperature with a predetermined warning temperature. As a result, if the detected temperature is higher than the warning temperature (NO in S15), normal temperature control (by the non-contact temperature sensor 15) Controlling the fixing heater 31 so that the detected surface temperature of the upper fixing roller 11 becomes a predetermined target temperature.)
Is continued (S17).

On the other hand, if the detected temperature is equal to or lower than the predetermined warning temperature (YES in S15), it is determined that the recording paper has been wound around the upper fixing roller 11, and a display to that effect is displayed via the display circuit 25 on the display panel. 35 (S21), and the temperature control circuit 21
The fixing heater 31 is turned off via the
The driving of the fixing device is stopped via (S23).

Here, the predetermined warning temperature is determined when the recording paper is wound around the upper fixing roller 11 and the infrared ray radiated from the upper fixing roller 11 is cut off to the non-contact temperature sensor 15.
The detection temperature of the non-contact temperature sensor 15 is determined by utilizing the fact that the detection temperature Tn is sufficiently low as shown by the solid line in FIG.

In other words, if a contact-type temperature sensor is used, even if the recording paper is wound around the upper fixing roller 11, FIG.
Since the response is poor as shown by the dashed line in (b), before the detected temperature is sufficiently lowered (even at the lowest point, the temperature is about Tt).
Since the temperature of the recording paper increases, it is extremely difficult to detect the winding of the recording paper based on the decrease in the detected temperature. However, in the case of the non-contact type temperature sensor, FIG.
As shown by the solid line, the detected temperature is sufficiently lowered (the lowermost point is about Tn). Therefore, a temperature higher than Tn and sufficiently lower than Tt is set as a warning temperature, and recorded based on the detected temperature. It is possible to detect winding of the paper. As a specific example when the target temperature (fixing temperature) Ta is set to 160 ° C., Ta−Tt is about 5 ° C. or less than 5 ° C.
Ta-Tn is about 10 to 15 ° C. Therefore, in this case, the predetermined warning temperature is set to Ta.
By setting the temperature to about 150 ° C., which is about 10 ° C. lower than (160 ° C.), the above-described determination can be accurately performed.

In step S31, recovery from the trouble caused by the recording paper wrapped around the upper fixing roller 11 is awaited, and when the trouble is recovered (YES in S31),
“Recording paper is wound” displayed on the display panel 35
Is turned off (see step S21) (S33),
At the same time, the temperature control of the fixing roller 11 is restarted, and the stop of the driving of the fixing device is released (S35, see step S23). The control is performed as described above.

In the above example, a certain temperature (constant value) lower than the target temperature (fixing temperature) Ta by a predetermined temperature is employed as the predetermined warning temperature. The relative temperature from the temperature immediately before the temperature detected by 15 starts to drop sharply may be adopted. this is,
When a large number of recording papers continuously pass through the fixing device, as shown in FIG. 2A, the heat of the upper fixing roller 11 is taken away, the temperature of the upper fixing roller 11 decreases gradually, and the temperature Tb decreases. , The phenomenon that the temperature gradually rises and recovers to the target temperature Ta is considered.

That is, when the recording paper is wrapped at the target temperature Ta, as described above, there is no problem even if a temperature lower than the target temperature Ta by a predetermined temperature (eg, 10 ° C.) is used as the warning temperature. However, when the recording paper wraps around the temperature Tb near the lowest point, which gradually decreases as shown in FIG. 2A, the temperature Tb and the warning temperature determined as described above are used. It is considered that there is a case where a temperature difference from the above is small and a problem occurs in detection accuracy. With this in mind,
As the warning temperature, a configuration may be adopted in which a relative temperature from the temperature immediately before the temperature detected by the non-contact temperature sensor 15 starts to drop sharply is used. Note that "starting to rapidly decrease" does not mean a gradual decrease as shown in FIG. 2A, but a sudden decrease as shown by a solid line in FIG. 2B. Further, the “temperature immediately before the start of a sharp drop” can be calculated by storing the detected temperature at each detection timing for a certain period of time and monitoring the gradient retroactively.

[0018]

According to the fixing device of the present invention, a non-contact temperature sensor for detecting the surface temperature of the fixing roller within the paper passing width in a non-contact manner, and a recording paper when the detected temperature of the non-contact temperature sensor falls below a predetermined warning temperature. Has a determination means for determining that the recording paper has been wound around the fixing roller, so that the fact that the recording paper has been wound around the fixing roller can be quickly detected. Further, in the invention in which the predetermined warning temperature is determined as a relative temperature from the detected temperature immediately before the temperature starts to drop sharply, the paper generated when the temperature of the fixing roller is temporarily lowered by continuous paper feeding is reduced. Winding can be accurately detected. In addition, when the determination unit determines that the recording paper is wound around the fixing roller, the invention having the emergency off unit that turns off the heating unit of the fixing roller can prevent the fixing roller from abnormally rising in temperature. Further, in the invention having the emergency stop means for stopping the driving of the fixing roller when it is determined that the recording paper is wound around the fixing roller, it is possible to prevent the fixing roller from being broken.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing an arrangement of a fixing device and a non-contact temperature sensor 15 and a configuration of a control circuit thereof, and an explanatory diagram (b) showing a relationship between the non-contact temperature sensor 15 and a sheet passing width. ).

FIG. 2 is a graph (a) schematically illustrating the surface temperature of a fixing roller during continuous paper passing, and a temperature detected by a contact temperature sensor and a temperature detected by a non-contact temperature sensor when a recording sheet is wound around the fixing roller. Graph (b) schematically showing temperature.

FIG. 3 is a flowchart illustrating an outline of temperature control of the fixing device.

[Explanation of symbols]

 11 upper fixing roller 12 lower fixing roller 15 non-contact temperature sensor 31 fixing heater

Continuation of the front page F term (reference) 2H027 DA12 DA32 DC14 EA12 EC10 ED25 EF10 EK03 EK04 GA30 GB06 2H033 BB01 CA02 CA22 CA30 CA34 CA38 CA45 CA57

Claims (4)

[Claims] 1. A fixing device for fixing an image on a recording sheet by passing the recording sheet between fixing rollers whose temperature is controlled to a predetermined target temperature, wherein a surface temperature of the fixing roller within a sheet passing width is not contacted. A non-contact temperature sensor for detecting the temperature of the non-contact temperature sensor and a determining means for determining that the recording paper has been wound around the fixing roller when the temperature detected by the non-contact temperature sensor is equal to or lower than a predetermined warning temperature. 2. The method according to claim 1, wherein the predetermined warning temperature is:
The fixing device is characterized by being determined as a relative temperature from a detected temperature immediately before the temperature starts to drop sharply. 3. The fixing device according to claim 1, further comprising an emergency off unit that turns off the heating unit of the fixing roller when the determination unit determines that the recording paper has been wound around the fixing roller. Characteristic fixing device. 4. The image forming apparatus according to claim 1, further comprising an emergency stop unit that stops driving of the fixing roller when the determination unit determines that the recording paper has been wound around the fixing roller. A fixing device.