JPH1145030A - Belt-type fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent low-temperature offset by increasing the temperature of a fixing roller to a fixing temperature in a short time in a fixing mode, no matter how long a standby mode lasts. SOLUTION: The fixing roller 3 and a heat roller 4 are provided with a first temperature detection sensor 17 and a second temperature detection sensor 18, respectively, and a control part 19 is provided for controlling the temperature of the heat roller 4 based on the temperature detection information from the sensors 17 and 18. Here, in the fixing mode, the fixing roller 3 is maintained at the fixing temperature based on the temperature detection information the first sensor 17, and in the fixing standby mode, the heat roller 4 is maintained at a temperature higher than the fixing temperature based on the temperature detection information from the second sensor 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt-type fixing device provided in an image forming apparatus such as an electrostatographic copying machine, a facsimile, and a printer.

[0002]

2. Description of the Related Art Before fixing a toner image by a nip, one of the fixing devices preheats the toner image and a recording sheet so that the temperature of a nip portion can be set to be low. There is a device.

More specifically, as shown in FIG. 2, this belt-type fixing device winds an endless fixing belt 5 around a fixing roller 3 and a heating roller 4, and
A pressure roller 7 for pressing the fixing roller 3 via the fixing belt 5 is provided below the fixing roller 3. In general, a fixing mode is set in conjunction with an operation of a print switch, and a fixing process is performed. Based on the detected trailing edge of the recording paper a (in the case of recording many sheets, the trailing edge of the final recording paper a),
The mode can be switched to the stable standby mode.

The fixing belt 5 is driven and rotated at a predetermined timing in conjunction with the operation of the print switch, and the heater 15 is rotated with the rotation of the fixing belt 5.
The heat energy of the heating roller 4 heated by the fixing belt 5 is transmitted to the fixing roller 3 using the fixing belt 5 as a heat transfer medium. In the stable standby mode, the driving of the fixing belt 5 is stopped. I have.

In the belt-type fixing device having such a structure,
In order to control the temperature of the heating roller 4 in the fixing mode and the standby mode, a temperature control unit 16 for the heater 15 of the heating roller 4 is provided.

The temperature control means 16 sets the fixing belt portion 5a wrapped around the fixing roller 3 and the fixing belt portion 5b wrapped around the heating roller 4 as temperature control targets. First and second temperature control sensors 17 and 18 for detecting the target temperature are provided, and a control unit 19 for turning on and off the heater 15 of the heating roller 4 based on the temperature detection information from each of the sensors 17 and 18 is provided. It is provided.

In the temperature control means 16, in the fixing mode, the fixing belt portion 5a wound around the fixing roller 3 is maintained at a predetermined fixing temperature based on the temperature detection information from the first temperature detection sensor 17. In the stable standby mode, the temperature of the fixing belt portion 5b wound around the heating roller 4 is changed based on the temperature detection information from the second temperature detection sensor 18 so that the heater 15 is turned on and off. The heater 15 is controlled to be on / off so as to maintain the temperature slightly lower than the fixing temperature.

[0008]

However, since the set temperature for the control in the standby mode is set lower than the fixing temperature, especially when the standby mode becomes longer in time, the print switch is not used. When the fixing device is switched to the fixing mode by the operation, since the temperature of the fixing roller 3 has been lowered and the set temperature of the heating roller 4 is low, the fixing roller 3 It takes a long time before the temperature rises to the fixing temperature of the recording medium. During this time, a so-called low-temperature offset is applied to the recording paper (the first few recording papers in the case of continuous fixing) supplied to the fixing device. In some cases resulted in poor fixing.

According to the present invention, the temperature of the fixing roller can be immediately raised to a predetermined fixing temperature even when the standby mode is extended for a long time by adopting a unique temperature control mode. An object of the present invention is to provide a belt-type fixing device that does not cause a defect.

[0010]

That is, according to the present invention, an endless fixing belt is wound around a fixing roller and a heating roller, and a pressing roller which presses the fixing roller via the fixing belt is provided as a fixing roller. In a belt-type fixing device provided on the lower side, a fixing roller or a fixing belt portion wound around the roller is set as a first temperature control target, and a heating roller or the fixing belt portion wound around the roller is set as a second fixing target. The first and second sensors for detecting the temperature of the temperature control object, and the temperature of the heating roller based on the temperature detection information from each sensor. The first temperature control target is maintained at the fixing temperature based on the temperature detection information from the first sensor in the fixing mode. Was, in the mode of a fixing stand, the second
It is characterized in that the second temperature control target is maintained at a temperature higher than the fixing temperature based on the temperature detection information from the sensor.

That is, when the temperature of the heating roller or the portion of the fixing belt wound around the roller is maintained higher than the fixing temperature in the stable standby mode, the standby mode is set to be longer in time. However, when the fixing device is switched to the fixing mode, a high heat energy is transmitted to the fixing roller using the fixing belt as a heat transfer medium, so that the fixing roller can be fixed in a predetermined time in a short time. It is possible to raise the temperature to the temperature, thereby preventing fixing defects such as low-temperature offset.

The set temperature in the standby mode is as follows:
If this is increased to a dark cloud, there is a problem that the toner melted by the fixing is heated more than necessary, leading to offset, and if it is too close to the fixing temperature, there is an effect compared to the conventional one, The time required to reach the predetermined fixing temperature is slightly longer, and taking these factors into account,
It is preferable to set the temperature within the range of fixing temperature + 3 ° C. to 10 ° C.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a belt-type fixing device of an electrostatographic copying machine (an example of an image forming apparatus), and a lower case 1.
A fixing roller 3 and a heating roller 4 are provided on an upper case 2 which is configured to be openable and closable with respect to the endless fixing belt 5.
Roller means 6 for applying a release agent such as silicon to the belt surface is provided.

The lower case 2 includes a pressing roller 7 for pressing the fixing roller 3 from below via the fixing belt 5, and the recording paper a after transferring the toner image to the pressing roller 7 and the fixing belt 5.
And a guide member 8 for guiding the nip portion N between the guide member 8 and the lower side of the fixing belt 5. Forming path A and recording paper a after toner image transfer
Preheats the toner image and the recording paper a while passing through the heating roller 4 and the lower side of the winding of the fixing belt 5.

As described above, by preheating the toner image and the recording paper a, it is possible to set the fixing temperature at the nip N low, and since the heat capacity of the fixing belt 5 is small. At the time of fixing at the nip portion N, heat is quickly taken away by the toner and the recording paper a,
When the temperature of the fixing belt 5 is lowered, the molten toner is not heated more than necessary, so that the recording paper a
Is reliably separated from the fixing belt 5, so-called offset is prevented.

The fixing belt 5 has a release layer made of silicon rubber or the like provided on an outer surface of an endless belt made of metal such as metal nickel or an outer surface of an endless belt made of resin such as polyimide resin. The fixing roller 3 and the pressure roller 7 are formed by providing coating layers 11 and 12 made of a heat-resistant elastic material such as silicon rubber on roller cores 9 and 10 made of metal such as aluminum. The hardness of the elastic coating layer 11 on the third side is set equal to or softer than the hardness of the elastic coating layer 12 on the pressure roller 7 side.

The heating roller 4 is made of, for example, a metal roller cylinder 13 made of aluminum or the like, and a coating layer 1 made of Teflon or the like.
4 and a heater 15 built in the roller cylinder 13. A heater is also provided in the fixing roller 3 or the pressure roller 7 as necessary. In this embodiment, the heater 15 is used. The heat energy of the heated roller 4 is transmitted to the fixing roller 3 using the fixing belt 5 as a heat transfer medium.

For example, in conjunction with the operation of the print switch, the fixing mode is set, and the fixing belt 5 is driven and rotated at a predetermined timing, while the rear end of the recording paper a having undergone the fixing process is detected (many In the case of sheet recording, the mode is switched to the stable standby mode based on the detection of the rear end of the last recording sheet a).

In order to control the temperature of the heating roller 4 in the fixing mode and the standby mode of the fixing device, a temperature control means 16 for the heater 15 of the heating roller 4 is provided. Moves the fixing roller 3 to the first position.
The first and second temperature detection sensors 17 and 18 such as a thermistor are provided so as to make the heating roller 4 the second temperature control object and make contact with the surface of these rollers. Temperature detection sensor 1
The control unit 19 controls the heating roller 4 to a predetermined temperature by turning on and off the heater 15 based on the temperature detection information from the sensors 7 and 18.

In the fixing mode, the controller 19 controls the first temperature of the nip portion N of the fixing roller 3 to be maintained at a predetermined fixing temperature (for example, 170 ° C.). On / off control of the heater 15 of the heating roller 4 is performed based on the temperature detection information from the temperature detection sensor 17, and in the stable standby mode, the temperature of the heating roller 4 which is the second temperature control target is set to the fixing temperature. On the basis of the temperature detection information from the second temperature detection sensor 18, the heater 15 of the heating roller 4 is configured to be turned on / off so as to maintain a higher temperature (for example, 173 ° C. to 180 ° C.). .

That is, in the standby mode, the temperature of the heating roller 4 is maintained higher than the fixing temperature, and when the fixing device is switched to the fixing mode, the heat of the fixing roller 3 is reduced within a short time by the high thermal energy. The temperature in the nip portion N is raised to a predetermined fixing temperature so as to prevent the occurrence of a low-temperature offset fixing defect.

Specifically, the nip portion N in the fixing mode
The fixing temperature is set to 170 ° C., which is preferable for the toner in general, so that the molten toner is not heated more than necessary.
For the temperature setting of the heating roller 4 under the stable standby mode, if the temperature is increased to a dark cloud, an offset occurs. If the temperature is too close to the fixing temperature, the time required to reach the predetermined fixing temperature is slightly longer. In addition, the fixing belt 5
The material and fixing speed (number of sheets fixed per unit time) also affect the fixing temperature.
The temperature is set in the range of ° C to 180 ° C.

By the way, according to an experimental value obtained by fixing a sheet at a speed of 22 sheets / minute by a printer having the fixing belt 5 of the above-described material, when the temperature of the heating roller 4 in the stable standby mode is set to 175 ° C. When the mode was shifted to the fixing mode, the nip portion N quickly reached the fixing temperature, and no offset occurred.

In the belt-type fixing device having the above-described structure, the temperature detecting sensors 17 and 18 are arranged in contact with the fixing roller 3 and the heating roller 4, but as shown in FIG. , 4 around the belt portion 5a,
5b.

Therefore, in the present invention, the fixing roller 3 or the fixing belt portion 5a wound around the roller 3 is referred to as a first temperature control object, and the heating roller 4 or the fixing belt wound around the roller 4 The portion 5b is referred to as a second temperature control target, and the first and second temperature detection sensors 17, 18 are provided for these portions. Reference numeral 20 in the figure denotes a static eliminator using a brush or the like.

[0026]

As described above, the present invention is characterized in that a unique temperature control mode for maintaining the temperature of the heating roller higher than a predetermined fixing temperature in the standby mode is adopted. Therefore, even when the standby mode is set to a long time, when the fixing device is switched to the fixing mode, the fixing roller can easily be heated to the predetermined fixing temperature within a short time. This makes it possible to reliably prevent poor fixing of low-temperature offset.

[Brief description of the drawings]

FIG. 1 is a sectional view of a belt-type fixing device according to the present invention.

FIG. 2 is a sectional view of a conventional belt-type fixing device.

[Explanation of symbols]

3 fixing roller, 4 heating roller, 5 fixing belt, 7
... pressure roller, 16 ... fixing temperature control means, 17, 18 ...
Temperature detection sensor, 20 ... control unit.

Claims (2)

[Claims] 1. A fixing roller and a heating roller,
A belt-type fixing device in which an endless fixing belt is wound around and a pressure roller that presses the fixing roller via the fixing belt is provided below the fixing roller.
The fixing roller or the portion of the fixing belt wound around the roller is set as a first temperature control object, and the heating roller or the fixing belt portion set around the roller is set as a second temperature control object. Temperature control means comprises: first and second sensors for detecting the temperature of the temperature control target; and a control unit for controlling the temperature of the heating roller based on the temperature detection information from each sensor. Then, the first temperature control object is maintained at the fixing temperature based on the temperature detection information from the first sensor, and in the fixing standby mode, the second temperature is controlled based on the temperature detection information from the second sensor. A belt-type fixing device configured to maintain a control target at a temperature higher than a fixing temperature. 2. The temperature setting in the fixing standby mode is as follows.
The belt-type fixing device according to claim 1, wherein the fixing temperature is in a range of + 3 ° C to 10 ° C.