JP2002221872A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is very difficult to arrange plural thermostats in a miniaturized fixing device. SOLUTION: In the fixing device having a fixing roller 1 having heat sources 2 and 3 at inside, a rotary body 4 brought into press-contact with the fixing roller 1, plural temperature detecting elements 7 and 8 arranged on the fixing roller 1 and to detect the surface temperature of the fixing roller 1 and safety devices 14 and 15 to detect temperature and to fix toner on paper fed between the fixing roller 1 and the rotary body 4, positional relations between the several temperature detecting elements 7 and 8 and the safety devices 14 and 15 are made symmetrical to the center of the paper in an advancing direction.

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 toner on paper and an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art In recent years, in an image forming apparatus such as a copying machine, a printer, a facsimile, etc., a quick start-up product having a quick start as ecologically compatible (power saving) has been desired, and the image forming speed has been increased to 30 or more. It is required that a machine with a speed of 10 sheets / minute be started in 10 seconds or more. Here, when the image forming apparatus starts up quickly, it is possible to turn off the mechanical power supply in a normal state.

[0003] In response to the demand for a product having such a fast start-up, the image forming apparatus has been required to reduce the weight of the fixing device (reducing the diameter and thickness of the fixing roller) and complicated temperature control. Today, in a fixing device of an image forming apparatus, a safety device for avoiding a fire due to runaway of software tends to be replaced with a thermostat instead of a temperature heat. In addition, a plurality of thermostats are being mounted in anticipation of double safety.

[0004]

As described above, in the image forming apparatus, it is necessary to reduce the weight of the fixing device and to mount a plurality of thermostats. It is very difficult to place a thermostat. SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus in which a plurality of safety devices can be easily arranged even if the size is reduced.

[0005]

Means for Solving the Problems To achieve the above object, an invention according to claim 1 comprises a fixing roller having a heat source therein, a rotating body pressed against the fixing roller, and a fixing roller disposed on the fixing roller. A fixing device that detects a surface temperature of the fixing roller and a safety device that detects the temperature, and fixes toner on a sheet conveyed between the fixing roller and the rotating body. In the apparatus, a positional relationship between the plurality of temperature detecting elements and the safety device is symmetrical with respect to a center in a traveling direction of the sheet.

According to a second aspect of the present invention, in the fixing device according to the first aspect, the safety device is disposed at a position sandwiching a position that is symmetrical with the temperature detecting element with respect to the center of the sheet in the traveling direction. It has a plurality of safety devices. According to a third aspect of the present invention, in the fixing device according to the first or second aspect, the temperature detection element and the safety device are configured such that an area through which sheets of all sizes pass and a sheet through which large-size sheets pass. This is provided in the region where Claim 4
The invention according to the third aspect has the fixing device according to the first, second, or third aspect.

[0007]

FIG. 1 shows an embodiment of the present invention.
The fixing device of this embodiment is incorporated in an image forming apparatus,
The toner on the sheet conveyed from the image forming unit as the image forming means in the image forming apparatus is fixed on the sheet.
As the image forming unit, an image forming unit that forms a toner image on paper by, for example, charging, exposure, development, transfer, or the like is used. The image forming section uniformly charges a photoconductor as an image carrier by a charging device, and then performs image exposure on the photoconductor by an exposure device such as a writing device to form an electrostatic latent image. After developing the electrostatic latent image on the body by a developing unit to a toner image,
The toner image on the photoreceptor is transferred to a sheet fed from a sheet feeding device by a transfer unit and sent to the fixing device.

In the above fixing device, the fixing roller 1
Are rotatably supported and are rotationally driven by a drive mechanism (not shown). A plurality of fixing heaters (here, two fixing heaters) 2 and 3 as heat sources having different light distributions are arranged inside the fixing roller 1, and the fixing roller 1 is heated by the fixing heaters 2 and 3. As shown in FIG. 2A, the fixing heater 2 has a central light distribution which is flat at the center of the fixing roller 1 with respect to the center (paper center) in the paper traveling direction. The heater 3 has a light distribution at both ends where the light distribution is flat at both ends of the fixing roller 1.

Therefore, as shown in FIG. 2C, the fixing roller 1 is heated uniformly by the fixing heater 2 alone so that the central surface thereof is at the set temperature of 180 ° C. In heating, the surface at both ends is the set temperature of 180 ° C
In the heating by both of the fixing heaters 2 and 3, the entire surface is uniformly heated so as to reach the set temperature of 180 ° C. The pressing roller 4 as a rotating body is pressed against the fixing roller 1 by a pressing lever 5 as a pressing unit.

The pressure lever 5 is made of an elastic material, one end of which is rotatably supported and the other end of which is pulled by a pressure spring 6 to press the pressure roller 4 and apply the pressure to the fixing roller 1. It is pressed elastically. The pressure roller 4 is rotatably supported and rotates with the rotation of the fixing roller 1. As shown in FIG. 2, the fixing roller 1 has a plurality of thermistors (here, two thermistors) as temperature detecting elements.
The thermistors 7 and 8 detect the surface temperature of the fixing roller 1.

On the paper entrance side of the fixing roller 1 and the pressure roller 4, entrance guides 9, 10 are provided.
A separation claw 11 is installed on the paper outlet side of the fixing roller 1 so as to contact the surface of the fixing roller 1. The cleaning roller 12 as a cleaning unit is in contact with the pressure roller 4 to clean the pressure roller 4. The paper is fed in the feed roller 13
And the like, and sent to the fixing device.

A fixing temperature control means (not shown) controls the energization of the fixing heater 2 based on the output value of the thermistor 7 so that the central surface of the fixing roller 1 is uniformly at a set temperature of 180 ° C. The energization of the fixing heater 3 is controlled based on the output value such that the surfaces of both ends of the fixing roller 1 are uniformly at the set temperature of 180 ° C.

The thermistors 7 and 8 feed the paper in the sheet width direction perpendicular to the sheet traveling direction so as not to be affected by a problem on the conveyance path (a problem that paper powder is likely to be generated during sheet conveyance by the sheet feeding roller 13). At a position between the rollers 13 and
The fixing roller 1 heated by the fixing heaters 7 and 8 is disposed at a position where the surface temperature distribution at the center and both ends of the fixing roller 1 becomes flat. For example, the thermistor 7 is located at a position between the paper feed rollers 13 in the sheet width direction and at a position where the surface temperature distribution of the central portion of the fixing roller 1 heated by the fixing heater 7 becomes flat, and It is located slightly behind. The thermistor 7 is located at a position between the paper feed rollers 13 in the paper width direction and at a position where the surface temperature distribution at both ends of the fixing roller 1 heated by the fixing heater 8 is flattened. 1 is disposed at one of the two end portions.

The thermostat 14, which constitutes the safety device,
Reference numeral 15 is arranged symmetrically with respect to the positions of the thermistors 7 and 8 with respect to the center in the sheet traveling direction. That is, the thermostat 14 is disposed close to (or in contact with) the surface of the fixing roller 1 at a position symmetrical to the position of the thermistor 7 with respect to the center of the sheet in the sheet traveling direction. The fixing roller 1 is disposed near (or in contact with) the surface of the fixing roller 1 at a position symmetrical to the position of the thermistor 7 with respect to the reference.

The thermostats 14 and 15 may be in contact with the fixing roller 1 or not in contact with the fixing roller 1. When the thermostats 14 and 15 are brought into contact with the fixing roller 1, the thermostats 14 and 15 whose surfaces are treated with a Teflon (registered trademark) coat or the like to prevent toner from adhering are used. The left-right symmetrical positional relationship between the thermostats 14 and 15 and the thermistors 7 and 8 depends on the light distribution characteristics of the fixing heaters 2 and 3. In this case, it is desirable that the distance is within a range of 30 mm left and right.

The paper conveyed from the image forming unit by the paper feed roller 13 or the like passes through the nip between the fixing roller 1 and the pressure roller 4 while being guided by the entrance guides 9 and 10, and at this time, heat and The toner is fixed by pressing. The sheet is separated from the fixing roller 1 by the separation claw 11, and is discharged to a discharge tray 18 by a discharge drive roller 16 and a discharge driven roller 17.

The thermostats 14 and 15 detect that the surface temperature of the fixing roller 1 or a temperature in the vicinity thereof has risen to an abnormal temperature equal to or higher than the upper limit temperature, and supply power to the fixing device (power supply to the fixing heaters 2 and 3). To turn off). A paper discharge sensor 19 detects a sheet before the paper discharge drive roller 16 and the paper discharge driven roller 17, and a fullness detection sensor 20.
Detects that the discharge tray 18 is full of paper.

According to this embodiment, the positional relationship between the thermistors 7, 8 as a plurality of temperature detecting elements and the thermostats 14, 15 as a safety device is symmetrical with respect to the center of the sheet in the traveling direction. When the heaters 2 and 3 are energized, the surface temperature distribution of the fixing roller 1 is the same on the left and right, so that the detected temperatures of the thermistors 7 and 8 and the thermostat 14 and
The temperature of the fixing device 15 becomes the same, so that it is possible to avoid restrictions on the layout of the fixing device (such as a space margin, malfunction due to the arrangement of two or more types of temperature detecting elements and safety devices, etc.) Can be easily arranged.

According to the present embodiment, the thermistors 7 and 8 serving as temperature detecting elements and the thermostats 14 and 15 serving as safety devices are provided in an area through which sheets of all sizes pass (the central portion of the fixing roller 1). ) And in the area through which large-size paper is passed (both ends of the fixing roller 1),
The safety of the fixing device can be improved.

FIG. 3 shows a part of another embodiment of the present invention.
In this embodiment, in the above embodiment, the thermostats 21 and 22 constituting the safety device are a plurality of thermostats (here, two thermostats) to be installed in the same place. The thermostat 14 is a thermostat having two or more thermostats. The thermostats 21 and 22 are located at positions symmetrical with respect to the position of the thermistor 7 with respect to the center of the sheet traveling direction (a position separated by the same distance 1 from the center of the sheet traveling direction to the left and right with respect to the center of the sheet traveling direction). It is arranged close to (or in contact with) the surface of the fixing roller 1. The thermostats 21 and 22 detect that the surface temperature of the fixing roller 1 or a temperature in the vicinity thereof has risen to an abnormal temperature equal to or higher than the upper limit temperature, and shut off a power supply for the fixing device.

According to this embodiment, the safety device is provided with a thermistor 7 as a temperature detecting element with respect to the center of the sheet in the traveling direction.
Since there are a plurality of thermostats 21 and 22 as safety devices arranged at positions sandwiching a position symmetrical to the left and right, errors in the detected temperatures of the plurality of safety devices can be reduced.

[0022]

As described above, according to the first aspect of the present invention, the temperature detected by the temperature detecting element and the temperature of the safety device become the same, and the restriction on the layout of the fixing device (a space margin. The above malfunctions due to the arrangement of the temperature detecting elements and the safety devices, etc.) can be avoided, and a plurality of safety devices can be easily arranged even if the size is reduced. According to the second aspect of the invention, the safety of the fixing device can be improved.

According to the third aspect of the present invention, it is possible to reduce errors in the detected temperatures of the plurality of safety devices. According to the fourth aspect of the present invention, the temperature detected by the temperature detecting element and the temperature of the safety device become the same, and the restriction on the layout of the fixing device (a space margin, two or more types of temperature detecting elements,
Malfunction due to the arrangement of safety devices, etc.) can be avoided, and a plurality of safety devices can be easily arranged even if the device is downsized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating a light distribution of a fixing heater, an arrangement position of a thermistor and a thermostat, and a temperature distribution of each fixing heater of a fixing roller in the embodiment.

FIG. 3 is a schematic view showing a part of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2, 3 Fixing heater 4 Pressure roller 7, 8 Thermistor 14, 15, 21, 22 Thermostat

Claims (4)

[Claims] A fixing roller having a heat source therein; a rotating body pressed against the fixing roller; a plurality of temperature detecting elements disposed on the fixing roller for detecting a surface temperature of the fixing roller; A fixing device for fixing toner on paper conveyed between the fixing roller and the rotating body, wherein the positional relationship between the plurality of temperature sensing elements and the safety device is A fixing device characterized in that it is symmetrical with respect to the center of the sheet in the traveling direction. 2. The fixing device according to claim 1, wherein the safety device has a plurality of safety devices arranged at positions sandwiching a position symmetrical with the temperature detecting element with respect to the center of the sheet in the traveling direction. A fixing device characterized by the above-mentioned. 3. The fixing device according to claim 1, wherein the temperature detecting element and the safety device are arranged in an area through which sheets of all sizes are passed and an area through which sheets of large size are passed. A fixing device characterized by being provided. 4. An image forming apparatus comprising the fixing device according to claim 1, 2 or 3.