JPH07104608A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device equipped with a thermal fixing device capable of obtaining excellent fixing image quality by keeping surface temperature in the paper passing area of a fixing roller at set temperature more precisely than in the conventional device and at hardly fluctuated temperature as an image forming device forming the image by thermally fixing a toner image on transfer paper. CONSTITUTION:In the image forming device equipped with the thermal fixing device 8 thermally fixing an unfixed toner image on the transfer paper 7; the thermal fixing device 8 is provided with a heating roller 1 incorporating a heating source 3, a pressure roller 2 press-contacting with the roller 1, a non-contact temperature detecting element 4 arranged in the paper passing area of the roller 1 and measuring the surface temperature in the paper passing area of the roller 1 while the transfer paper 7 is allowed to pass, and a contact temperature detecting element 5 arranged outside the paper passing area of the roller 1 and measuring the surface temperature outside the paper passing area of the roller 1 directly in contact with the roller 1 while the paper 7 is not allowed to pass, and the image forming device is provided with a temperature controller 6 controlling the temperature of the roller 1 based on output from the detecting element 4 or 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a heat fixing device such as an electrophotographic copying machine, a laser beam printer and a plain paper FAX.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus,
The toner image transferred on the recording paper is heated by a thermal fixing device,
The image is fixed by applying pressure. In an image forming apparatus having a conventional thermal fixing device, a non-contact temperature detecting element is arranged in a paper passing area of a transfer paper between a fixing roller pair (a pressure roller and a heating roller), and the transfer paper of the fixing roller pair is detected. A contact temperature detection element that is in direct contact with the fixing roller is placed outside the paper passing area, and the temperature of the fixing roller is measured.
The temperature of the fixing roller is controlled (Japanese Patent Laid-Open No. 4-296).
889). However, since the temperature of the fixing roller is controlled based on the temperature measured by a contact temperature detection element such as a thermistor that is in direct contact with the fixing roller and has a slow response speed, the temperature of the fixing roller inside the sheet passing area is set to the set temperature. On the other hand, there is a problem that it is difficult to control accurately and with little fluctuation, and it is not possible to form a high quality image.

[0003]

In an image forming apparatus having a conventional heat fixing device, the temperature control of the fixing roller is performed by a response of a thermistor or the like which is in direct contact with the fixing roller outside the paper passing area of the fixing roller. This has been done using a slow contact temperature sensing element. Therefore, the temperature of the inner surface of the fixing roller in the paper passage area can be set accurately with respect to the set temperature.
In addition, the fluctuation cannot be kept small, and as a result, a high quality image cannot be formed.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention is to solve such a problem. That is, according to the present invention, the temperature of the inner surface of the fixing roller in the paper passing area is determined while the transfer paper is being passed.
The temperature of the inner surface of the fixing roller in the paper passing area is controlled more accurately than the conventional one by controlling using a non-contact temperature detection element arranged in the paper passing area of the fixing roller It is an object of the present invention to provide an image forming apparatus having a heat fixing device that can obtain a good fixed image quality by keeping the above.

[0005]

In order to achieve the above object, the present invention provides an image forming apparatus equipped with a heat fixing device for heat fixing an unfixed toner image on a transfer paper, wherein the heat fixing device is a heating device. A heating roller having a built-in heat source, a pressure roller that comes into pressure contact with the heating roller, and a temperature of the inner surface of the heating roller in the paper passing area, which is arranged in the paper passing area of the heating roller while the transfer paper is being passed. A non-contact temperature detecting element for measuring the temperature of the surface outside the paper passing area of the heating roller, which is placed outside the paper passing area of the heating roller and is in direct contact with the heating roller while the transfer paper is not being passed. The image forming apparatus includes a contact temperature detecting element to measure, based on the output of the non-contact temperature detecting element or the contact temperature detecting element, a temperature control device for controlling the temperature of the heating roller, The response speed of the non-contact temperature detecting element is at least faster than the response speed of the contact temperature detecting element, and the temperature measured by the contact temperature detecting element and the non-contact temperature detection immediately before the transfer paper is passed. According to the temperature measured by the element, a warning is given that the measured temperature of the non-contact temperature detecting element is corrected or the fixing roller is cleaned or replaced.

[0006]

In the image forming apparatus constructed as described above, the temperature of the inner surface of the fixing roller in the paper passing area is detected by the non-contact temperature detection which is arranged in the paper passing area of the fixing roller while the transfer paper is being fed. The temperature of the inner surface of the fixing roller in the paper passage area is controlled more accurately than the conventional one by controlling it through an element.
An image forming apparatus having a thermal fixing device capable of obtaining a good fixed image quality by maintaining the temperature with little fluctuation can be provided. Further, it is possible to issue an alarm notifying the operator of cleaning and replacement of the fixing roller without adding a special device.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an explanatory view of a main part of a heat fixing device of an electrophotographic image forming apparatus to which the present invention is applied. The transfer paper 7 on which a toner image on a photoconductor (not shown) is transferred by a transfer device (not shown) is a fixing device. 8 is carried, and is sandwiched between the heating roller 1 and the pressure roller 2 and sent. A heating source 3 is built in the heating roller 1, and a pressure roller 2 that is brought into pressure contact with the heating roller 1 for passing the transfer paper 7 is arranged. 0.8 mm to 3 mm for heating roller 1
Rollers made of iron or aluminum with a moderate thickness are used so that the heat necessary for fixing can be stored with sufficient heat capacity. In addition, in order to set the heating roller 1 to a temperature necessary for fixing and to maintain the temperature,
The non-contact temperature detecting element 4 is arranged in a non-contact state with the heating roller 1 in the paper passing area of the heating roller 1 (in the path through which the transfer paper passes), and the contact temperature detecting element 5 is provided outside the paper passing area. 1, the temperature control circuit 6 is controlled to reach the set temperature by inputting the output of the measured temperature to the temperature control circuit 6.

The temperature control circuit 6 controls the temperature of the heating roller 1 based on the data relating to the measured temperature from the contact temperature detecting element 5 while the transfer paper 7 is not being passed, and the transfer paper 7 is passed. Non-contact temperature detection element 4 during the period
Heating roller 1 based on the measured temperature data from
The temperature of is controlled to the set temperature. The temperature control circuit 6 determines whether the temperature difference between the temperature measured by the contact temperature detection element 5 and the temperature measured by the non-contact temperature detection element 4 is within a specified value immediately before the transfer paper 7 is passed. Correction of the temperature measured by the non-contact temperature detection element 4 or heating roller 1
It is designed to judge whether or not to warn that the cleaning and replacement of the above is in a state of being cleaned.

Further, the present invention is also characterized in that the response speed of the non-contact temperature detecting element 4 is made faster than at least the response speed of the contact temperature detecting element 5. For example, as the contact temperature detecting element 5, a thermistor excellent in absolute temperature measurement is used, and as the non-contact temperature detecting element 4, one having a high response speed using infrared light is used. Since the temperature sensing element using infrared light can be used without contact and has a fast response speed,
It is most suitable for temperature monitoring during a period in which the temperature of the transfer paper 7 is drastically changed. In the present invention, during the period when the transfer paper 7 is being fed (during fixing), the measurement of the non-contact temperature detecting element 4 such as the temperature detecting element utilizing the infrared light arranged in the paper passing area of the heating roller 1. Since the temperature control device 6 controls the surface temperature in the paper passing area of the heating roller 1 on the basis of the temperature, the amount of the paper passing through the transfer paper 7 and the surface stain of the heating roller 1 which influence the temperature drop of the heating roller 1 can be prevented. Regardless of the degree, it works to keep the temperature in the paper passing area, which is the most important for temperature control of the heating roller 1, constant.

FIG. 2 is a diagram showing an example of temperature control according to the present invention. When the heating source 3 described in FIG. 1 is energized and turned on, the surface of the heating roller 1 located outside the sheet passing area described in FIG. The temperature rises as shown by a curve a in the figure, and the measured temperature of the contact temperature detecting element 5 described in FIG.
As shown in, the response is followed with a delay.

Although the target temperature at which the heating source 3 is to be turned on and off is Ts shown in the figure, it actually has a hysteresis characteristic due to the temperature control circuit 6 described in FIG. 1 and the relay included therein, The illustrated temperature T-on for turning on the heating source 3 and the illustrated temperature T-off for turning off the heating source 3 are the target temperature T-s.
The temperature is deviated as shown in FIG. The heating source 3 is turned off when the value of the curve b becomes T-off (time t-off), and at that time, the surface temperature of the heating roller 1 outside the paper passing area can be understood from the locus of the curve a. It has risen to T-aup shown. Next, the surface temperature of the heating roller 1 decreases and the heating source 3 is turned on again when the value of the curve b is T-on (time to
n), at that time, the surface temperature of the heating roller 1 drops to T-adw shown in the figure. Thereafter, the above range T-aup to T
-It becomes the repetition of adw. This repeated state is called ripple. After the illustrated time t-cg, the non-contact temperature detecting element 4 described in FIG. 1 is faster than the response speed of the contact temperature detecting element 5.
When it is operated to control at the measured temperature of
A curve c shown by a solid line after t-cg is a surface temperature in the sheet passing area of the heating roller 1, and a curve d shown is a non-contact temperature detecting element 4.
Is the measured temperature. From the above description, it is clear that the surface temperature of the heating roller 1 similarly repeats the range T-cup to T-cdw shown in the figure, and the ripple becomes smaller according to the speed of the response speed.

FIG. 3 is a diagram showing a change in temperature in the fixing device of the present invention. A curved line a shown by a thick line shows a surface temperature of the heating roller 1 outside the sheet passing area, and a solid line c shown by the drawing shows a heating roller. The surface temperature in the paper passing area of 1 is shown. The curves a and c correspond to the curves a and c shown in FIG. The illustrated preheating period t-1 is the time until the temperature of the heating roller 1 reaches the illustrated target temperature T-s, and the temperature of the heating roller 1 is controlled by the measured temperature of the contact temperature detection element 5 described in FIG. It After that, the transfer paper 7 described in FIG. 1 is always available.
The state of the waiting period t-2 shown in FIG. The heating temperature during the waiting period t-2 is also controlled on the basis of the temperature measured by the contact temperature detecting element 5, and has a large ripple as shown by the curve a in FIG. Preheating period t-1
The curve c indicating the surface temperature of the heating roller 1 in the sheet passing area follows almost the same locus as the curve a from the waiting period t-2 to the waiting period t-2, and therefore is not drawn in this figure. When the sheet passing period t-3 of the transfer sheet 7 shown in the figure is reached, the temperature control is changed to the temperature control by the non-contact temperature detecting element 4 described in FIG. 1, and as a result, the ripple is small and the set temperature is accurately approached and fluctuates. The temperature is kept low. This is one of the main effects of the present invention.

When the amount of the transfer paper 7 that passes is large, the temperature of the inner surface of the heating roller 1 in the paper passing area is deprived, or the temperature of the heating roller 1 decreases due to dirt on the inner surface of the paper passing area. The difference between the surface temperature inside the paper area and the surface temperature outside the paper passing area causes curve a to become higher than curve c. At the time when the state of the waiting period t-2 is changed to the state of the paper passing period t-3 of the transfer paper 7, the paper passing is performed due to the difference between the measurement temperature of the contact temperature detecting element 5 and the measurement temperature of the non-contact temperature detecting element 4. The measured temperature of the non-contact temperature detecting element 4 that controls the temperature in the period t-3 is corrected. In the figure, the difference in the surface temperature of the heating roller 1, which should be called an ideal correction value, is indicated by ΔT-1 in the figure (the same applies to ΔT-2 and ΔT-3 in the figure). However, in the present invention, the difference between the measurement temperature of the contact temperature detection element 5 and the measurement temperature of the non-contact temperature detection element 4, which is the easiest to measure as described above, is used as the correction value. However, the difference between the surface temperature inside the paper passing area of the heating roller 1 and the surface temperature outside the paper passing area is so small that there is no practical problem, and the measurement of the contact temperature detecting element 5 of the present invention is performed. Even if the difference between the temperature and the temperature measured by the non-contact temperature detecting element 4 is used as the correction value, the essential effect does not change.

Next, when the sheet passing period t-3 of the transfer sheet 7 ends and the state of the waiting period t-4 shown again is entered, the temperature of the heating roller 1 is controlled by the temperature measured by the contact temperature detecting element 5, When the temperature approaches the target temperature T-s, the temperature is controlled so that the ripple is large as indicated by the curve a shown in FIG. 2, the temperature drop due to the passing of the transfer paper 7 disappears, and There is no difference between the temperature and the temperature of the surface outside the paper passing area, and the curves a and c approach each other, and the surface temperature of the heating roller 1 becomes constant.

After that, the transfer sheet 7 normally repeats the state of the sheet passing period t-3 and the waiting period t-4, but as a peculiar example, the curve a and the curve are shown in the state of the waiting period t-6 shown in the figure. The illustrated temperature difference ΔT-3 of c may show a large value. This peculiar situation is highly likely not due to the temperature decrease due to the passage of the transfer paper 7, but due to some abnormality in the surface state of the heating roller 1. For example, there may be a case where toner adheres to the surface of the heating roller 1 or the surface of the heating roller 1 is scraped off. As a result, it is considered that the temperature remains low. If this decrease value is large, normal thermal fixing cannot be performed, so in the present invention, the transfer paper 7 is used.
Immediately before passing the sheet, it is checked whether the value exceeds the specified value, and if it exceeds the value, some kind of alarm is issued to prompt cleaning of the heating roller.

FIG. 4 shows a flow chart for explaining the temperature control operation of the heating roller 1 after the end of the preheating period t-1. In step S1, it is determined whether or not a transfer start switch (not shown) is pressed by the operator, and if not pressed, it is determined that the switch is on standby, and the temperature control circuit 6 measures the contact temperature detection element 5. The temperature output operates to control the temperature of the heating roller 1 (S1
2). The temperature control circuit 6 judges whether the output of the measured temperature of the contact temperature detecting element 5 is lower than the temperature T-on (S13) or higher than the temperature T-off (S14), and the temperature T-on is determined.
If it is lower than the temperature T-off, the heating source 3 is turned on (S16), and if it is higher than the temperature T-off, the heating source 3 is turned off (S17). The operation in the standby mode is continued if the standby completion signal is not output due to the transfer start switch being pressed (S15).

When the transfer start switch is pressed by the operator in step S1, the temperature control circuit 6 determines that the paper is being passed and the non-contact temperature detection element 4 controls the temperature of the heating roller 1. So that (S
2) At the same time, the correction value ΔT at the measured temperature of the non-contact temperature detecting element 4 is calculated (S3). It is determined whether or not this correction value ΔT exceeds a specified value (S4), and if it exceeds the specified value, for example, the heating source 3 is turned off (S1).
0), an alarm indicating that the heating roller 1 is abnormal is issued so that the operator can know the abnormality (S11). If the correction value ΔT is within the specified value in step S4, the measured temperature of the non-contact temperature detection element 4 is corrected to be lower than the temperature T-on (S5) or the temperature T-off.
If it is higher than the temperature T-on, the heating source 3 is turned on (S8), and if it is higher than the temperature T-off, the heating source 3 is turned off (S9). This state is continued until the sheet passing completion signal is output (S7).

[0018]

In the image forming apparatus of the present invention configured as described above, the temperature of the inner surface of the fixing roller in the paper passing area is set within the paper passing area of the fixing roller while the transfer paper is being passed. The temperature of the inner surface of the fixing roller in the paper passing area is controlled more accurately and less than the set temperature compared to the conventional one by controlling it through a non-contact temperature detecting element. It has become possible to provide an image forming apparatus having a heat fixing device capable of obtaining a fixed image quality. It is now possible to issue an alarm notifying the operator of cleaning and replacement of the fixing roller without adding any special device.

[Brief description of drawings]

FIG. 1 is a front perspective view of a main part of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of temperature control of a main part of the image forming apparatus of the embodiment of FIG.

3 is an explanatory diagram of a temperature state of a main part of the image forming apparatus of the embodiment of FIG.

FIG. 4 is a flowchart showing a main operation of a main part of the image forming apparatus according to the exemplary embodiment of the present invention.

[Explanation of symbols]

1 ... Fixing roller, 2 ... Pressure roller, 3 ... Heat source, 4 ... Non-contact temperature detecting element, 5 ... Contact temperature detecting element, 6 ... Temperature control device, 7 ... Transfer paper, 8
... Fixing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaro Chino 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd.

Claims (3)

[Claims] 1. An image forming apparatus comprising a heat fixing device for thermally fixing an unfixed toner image on a transfer sheet, wherein the heat fixing device comprises a heating roller having a built-in heating source, and a pressure contacting the heating roller. A roller, a non-contact temperature detecting element arranged in the paper passage area of the heating roller to measure the temperature of the inner surface of the paper passage area of the heating roller during the passage of the transfer paper, and a paper passage of the heating roller. The image forming apparatus is provided with a contact temperature detection element that is arranged outside the zone and directly contacts the heating roller during a period in which the transfer sheet is not passed, and measures the temperature of the surface of the heating roller outside the sheet passing area. An image forming apparatus comprising a temperature control device that controls the temperature of the heating roller based on the output of the non-contact temperature detection element or the contact temperature detection element. 2. The response speed of the non-contact temperature detecting element is
The image forming apparatus according to claim 1, wherein the response speed of the contact temperature detection element is at least faster than that of the contact temperature detection element. 3. The correction of the temperature measured by the non-contact temperature detecting element or the correction of the temperature measured by the non-contact temperature detecting element according to the temperature measured by the contact temperature detecting element and the temperature measured by the non-contact temperature detecting element immediately before the transfer paper is passed. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to warn that the fixing roller is being cleaned or replaced.