JPH0728354A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the deformation of a fixing belt for preventing a failure in fixing and an offset and simultaneously, to easily remove the paper sheet jammed in a pressure roller part by releasing the pressure of the pressure roller of a fixing device, in a state where a device is not used. CONSTITUTION:The pressurizing lever 53 imparting prescribed pressure to the roller 25 for pressurizing a transfer material on a heating element 21a and a releasing lever 57 releasing the pressurizing force of the pressurizing lever 53 are provided. The releasing lever 57 is supported so as to vertically slide on a front side plate 51 by a stepped screw 66 attached thereto and fitted into an oblong hole 57b provided on the releasing lever 57. Then, the releasing lever 57 is pulled upward (a releasing position side) by the taut force of a releasing spring 64 extended between the top end of the lever 57 and an immobile part, in the state where the transfer material is not made to pass. Thus, the pressurization of the pressure roller 25 on the heating element 21a is released. The value of the taut force of the releasing spring 64 is set larger than that of a pressurizing spring 55.

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 such as a copying machine or a printer having a fixing device for fixing an unfixed toner image on a transfer material by heating and melting the toner.

[0002]

2. Description of the Related Art Generally, a fixing device in an image forming apparatus of this type comprises an unfixed toner by a heating roller maintained at a predetermined temperature and a pressure roller rotated by pressing an elastic layer against the heating roller. A fixing method is often used in which a transfer material on which an image is formed is held and conveyed, and toner is heated and melted to fix an unfixed toner image on the transfer material.

However, in the fixing device based on this fixing method, a low temperature offset and a high temperature offset of the toner are apt to occur due to a variation in the fixing temperature due to insufficient heat capacity of the heating roller. Therefore, in this type of fixing device, normally, the heat capacity of the heating roller is set large to prevent toner offset, but when the heat capacity is set large in this way, the heating roller rises (warm-up). ) Takes a long time, and there is a problem that the standby time becomes long at the beginning of use of the device.

Therefore, in order to solve such a problem of the fixing device, conventionally, there is provided an image forming means for forming an unfixed image on a transfer material by a toner made of a heat-meltable resin or the like, and the transfer is performed. An image constituted so that the unfixed toner is fixed to the transfer material by a heating element (thermal head) that generates heat in a pulsed manner and a pressure roller via a heat resistant sheet (fixing belt) that moves at the same speed as the material. A forming apparatus has been proposed (Japanese Patent Laid-Open No. 63-313182). Further, as a related technique, Japanese Patent Laid-Open No. 62-22228.
No. 1, "Fixing Method", JP-A-64-38775.
A "fixing device" described in Japanese Patent Publication is known.

[0005]

By the way, in the fixing device using the thermal head in the conventional image forming apparatus, since the heating portion of the thermal head is formed in a convex shape, the state where the apparatus is not used is long-term. If this happens, the fixing belt sandwiched between the thermal head and the pressure roller may be deformed, resulting in defective fixing and offset during the fixing. The invention according to claim 1 is made in view of the above-mentioned point, and an object thereof is to release the pressure of the pressure roller when the apparatus is not used to prevent the fixing belt from being deformed, and to prevent fixing failure and An object is to provide an image forming apparatus capable of preventing offset.

As described above, in this type of image forming apparatus,
By releasing the pressure of the pressure roller when not in use,
The fixing belt can be prevented from deforming, but this fixing belt
Usually, since it is in a stretched state, if it is left unused for a long period of time, the fixing belt is deformed due to the stretching of the belt, and the mechanical life of the fixing belt is shortened. Further, due to the elongation of the belt, the thickness of the fixing belt becomes non-uniform, so that temperature unevenness occurs at the time of fixing, resulting in defective fixing and offset. The invention according to claim 2 is made in view of this point, and an object thereof is to release the pressure of a belt driven roller that drives the fixing belt when the apparatus is not used, and to prevent the expansion deformation of the fixing belt. Another object of the present invention is to provide an image forming apparatus capable of preventing the fixing belt from having a reduced life, fixing failure and offset.

Further, in this type of image forming apparatus, as a pressure releasing mechanism of the pressure roller, as shown in FIGS. 8 and 9, a pressure roller for pressing the transfer material against the heating roller 100 is used. The pressure lever 300 for applying a predetermined pressure to 200, the release lever 160 for releasing the pressure force of the pressure lever 300, and the release lever 160 at the release position for releasing the pressure force of the pressure lever 300. A pressure release mechanism having a release lever displacing means (solenoid 150) for displacing is proposed. However, in the conventional image forming apparatus having the pressure release mechanism, the pressure springs 400 and 180 for applying a predetermined pressure to the pressure roller 200 are provided with the pressure lever 300 and the release lever 16.
0, so that the pressure applied by the pressure roller 200 to the heating roller 100 fluctuates due to variations in the pressure applied by these two springs 400, 180, and the heating roller 100 and the pressure roller 200 The nip width between and changed, and uneven fixing and offset may occur during the fixing. The invention according to claim 3 is
It was made in view of the above points, and its purpose is
An object of the present invention is to provide an image forming apparatus capable of stabilizing the pressure applied by a pressure roller to a thermal head and preventing uneven fixing and offset.

[0008]

The invention according to claim 1 is
In order to solve the above-mentioned problems, a heat-resistant sheet that has an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-meltable resin or the like, and moves at the same speed as the transfer material is provided. In the image forming apparatus in which the unfixed toner is fixed to the transfer material by the heating element that heats up in a pulsed manner, the predetermined pressure of the pressure roller for pressing the transfer material against the heating element is applied to the image. The pressure roller is released only when the forming device is turned on, and is provided with a pressure roller pressure releasing means for releasing the pressure of the pressure roller otherwise.

In order to solve the above-mentioned problems, the invention according to claim 2 has an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-meltable resin or the like. A belt driven roller for moving the heat resistant sheet in an image forming apparatus in which an unfixed toner is fixed to the transfer material by a heating element that is energized and heated in a pulse shape through a heat resistant sheet that moves at the same speed as the material. The predetermined pressure is applied only when the image forming apparatus is turned on, and at other times, the belt driven roller pressure releasing means for releasing the pressure of the belt driven roller is provided.

In order to solve the above-mentioned problems, the invention according to claim 3 has an image forming means for forming an unfixed image on the transfer material with a toner made of a heat-meltable resin or the like. In an image forming apparatus in which an unfixed toner is fixed to the transfer material by a heating element that is energized and heated in a pulse shape through a heat resistant sheet that moves at the same speed as the material, in order to press the transfer material against the heating element. A shaft provided on a pressure lever for applying a predetermined pressure to the pressure roller, a long hole into which the shaft provided on a release lever for releasing the pressure of the pressure lever fits, The shaft is engaged with the first end of the oblong hole and the release position where the pressing force of the pressure lever is released by the engaging movement of the shaft and the first end and the second end of the oblong hole. Do not change the release lever that displaces the release lever to the pressure position. And means, the distance between the first end of the shaft and the elongated hole in the pressing position L1,
When the distance between the shaft and the second end of the elongated hole at the pressing position is L2, and the amount of displacement of the release lever by the release lever displacement means is S, the relationship of L1 <S <L2 is satisfied. The configuration is

[0011]

According to the first aspect of the invention, the predetermined pressure of the pressure roller for pressing the transfer material against the heating element is
The pressure is applied only when the image forming apparatus is turned on, and otherwise the pressure of the pressure roller is released.

According to the second aspect of the present invention, the predetermined pressure of the belt driven roller for moving the heat resistant sheet is applied only when the image forming apparatus is turned on, and in other cases, the belt driven roller is pressed. Pressure is released.

According to the third aspect of the present invention, the pressure applied to the pressure roller when the transfer material is passed is biased only by the pressure applied by the pressure lever.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view of the entire image forming apparatus according to the embodiment of the present invention. In FIG. 1, the transfer material P stored in a cassette 2 below the apparatus main body 1 is separated and fed by a paper feed roller 3 and sent to a registration roller 5 via a conveyance roller 4.

On the other hand, the image of the original O set on the contact glass 6 of the apparatus main body 1 is read by the scanner 7 and written as an electrostatic latent image on the photosensitive drum 9 by the writing device 8, and thereafter, An unfixed image is formed (transferred) on the transfer material P fed by the registration roller 5 in synchronism with the electrostatic latent image on the photoconductor drum 9 by toner made of heat-meltable resin or the like.

The unfixed toner image is formed on the transfer material P by a cleaning unit 1 arranged around the photosensitive drum 9 for removing residual toner on the photosensitive drum 9.
0, a discharge lamp 11 for removing the residual charge on the photoconductor drum 9, a charger 12 for uniformly charging the surface of the photoconductor drum 9, and an electrostatic latent image written on the photoconductor drum 9 with toner. The developing unit 13 for forming an image, the transfer charger 14 for transferring the unfixed image formed on the photosensitive drum 9 onto the transfer material P, and the separation for separating the transfer material P on which the unfixed image is transferred from the photosensitive drum 9. Charger 1
This is performed by a well-known electrophotographic process by an image forming unit including 5 or the like.

The transfer material P on which the unfixed toner image is formed and separated from the photosensitive drum 9 in this manner is sent to the fixing unit 17 by the transport guide unit 16 to fix the unfixed toner, and then a pair of Paper discharge rollers 18 and 1
9, the discharge tray 2 arranged on the side of the apparatus main body 1
Is discharged above zero.

The fixing unit 17 in this embodiment is
As shown in FIG. 2, the thermal head 21 and the fixing belt 2
2, a belt driving roller 23, a belt driven roller 24, a pressure roller 25, and transfer material guides 26 and 27.

The fixing belt 22 is made of a transparent heat-resistant sheet made of a resin material such as Teflon having a high heat resistance against heat generation during fixing and a high releasability for the heat-melted toner. Is formed in.

Further, the fixing belt 22 is endlessly rotated clockwise in FIG. 2 by the belt driving roller 23 and the belt driven roller 24 at a speed substantially the same as the conveying speed of the transfer material P.

The thermal head 21 has a heating element 21a.
Inside the fixing belt 22, that is, the fixing belt 22
The transfer material P is disposed so as to face the transfer path of the transfer material P.

The heating element 21a is maintained at a temperature (180 ° C.) higher than the normal toner fixing temperature (120 ° C.), and the fixing belt 22 allows the toner to pass through the heating portion of the heating element 21a at a speed of 8 ms. The rotation speed is set so that it will pass at. As described in JP-A-1-263679, when the fixing temperature of the heating element is set to 180 ° C., it takes a long time to heat the toner until sufficient fixing property is obtained. It costs.

Belt drive roller 2 of thermal head 21
A sliding contact portion 21b with which the fixing belt 22 abuts and slides is provided on the third side portion.

The pressure roller 25 is rotatably arranged so as to sandwich the transfer path of the transfer material P and the fixing belt 22 and to come into pressure contact with the heating element 21a of the thermal head 21.

The transfer material guide 26 is used as the fixing belt 2.
It is arranged so as to guide the transfer material P toward the nip portion between the pressure roller 25 and the pressure roller 25. Furthermore, the transfer material guide 27
Is arranged so as to guide the transfer material P carried out from the nip portion between the fixing belt 22 and the pressure roller 25 toward the nip portion between the pair of paper discharge rollers 18 and 19.

FIG. 3 shows a pressure roller 25, a thermal head 21, a heating element (heating section) 21a, and a fixing belt 22.
FIG. 6 is a state diagram at the time of fixing. As is apparent from FIG. 3, in this fixing state, the fixing belt 22 is pushed by the heating element 21a by the pressure applied by the pressure roller 25 to the thermal head 21 and bites into the pressure roller 25 side. Become. Therefore, in the conventional apparatus which is in the state as shown in FIG. 3 when the driving is stopped, the fixing belt 22 is deformed by being left in this state for a long time.

In order to eliminate such a problem, in this embodiment, a predetermined pressure is applied to the pressure roller 25 for pressing the transfer material P against the heating element 21a as shown in FIG. And a long hole 57a provided in a release lever 57 for releasing the pressing force of the pressure lever 53 with which the shaft 53a is fitted, and a first hole 57a of the long hole 57a. A release position where the shaft 53a is engaged with the first end to release the pressing force of the pressure lever 53, and a press position where the shaft 53a does not engage the first end and the second end of the slot 57a. And a release lever displacing means (solenoid 58) for displacing the release lever 57.
The distance between the a-axis and the first end of the elongated hole 57a is L1, the distance between the shaft 53a and the second end of the elongated hole 57a at the pressure position is L2, and the amount of displacement of the release lever 57 by the solenoid 58 is When S is set, a pressure release mechanism for the pressure roller that satisfies the relationship of L1 <S <L2 is provided.

That is, in FIG. 4, the release lever 57
Is supported slidably in the vertical direction with respect to the front side plate 51 by a step screw 66 attached to the front side plate 51 fitted into another elongated hole 57b provided therein. Further, the release lever 57 is pulled upward (to the release position side) by the contraction force of the release spring 64 stretched between the upper end of the transfer material P and the immovable portion when the transfer material P is not passed. Has been raised.

As a result, when the transfer material P is not passed, the shaft 53a of the pressure lever 53 is provided with the elongated hole 57a.
Is moved upward by engaging with the first end (lower end) of the shaft 53a, and the upward movement of the shaft 53a causes the pressing lever 53 to be stretched between its free end and the front plate 51. The pressure roller 25 is rotated counterclockwise about the pressure lever shaft 54 against the contraction force of the pressure spring 55, and the pressure roller 25 is lowered by its own weight.

As a result, the pressure applied to the heating element 21a by the pressure roller 25 is released. Here, the elastic force of the release spring 64 is set to a value larger than the elastic force of the pressure spring 55.

On the other hand, when the image forming apparatus is turned on,
For example, as shown in FIG. 5, when the copy start button of the copying machine is turned on, the solenoid 58 is turned on by the on signal and the release lever resists the tightening force of the release spring 64 by turning on the solenoid 58. 57
Is displaced to the pressurizing position side shown in FIG.

At this time, as described above, the pressure releasing mechanism of the pressure roller according to the present embodiment is arranged so that the pressure roller 53a at the pressing position is 53a.
The distance between the shaft and the first end (lower end) of the slot 57a is L
1, L1 <S <L, where L2 is the distance between the shaft 53a and the second end (upper end) of the slot 57a at the pressing position, and S is the amount of displacement of the release lever 57 by the solenoid 58.
Since the solenoid valve 58 is turned on, the shaft 53a provided on the pressure lever 53 is connected to the first end portion of the elongated hole 57a provided on the release lever 57 when the solenoid 58 is turned on. And a free position where the second end is not engaged.

Therefore, the pressure lever 53 in the present embodiment.
4 is rotated clockwise in FIG. 4 about the pressure lever shaft 54 only by the contraction force of the pressure spring 55, the pressure roller 25 is pulled upward against its own weight, and the thermal head 21 The heating element 21a is brought into pressure contact with a stable and constant pressure.

As a result, the toner of the transfer material P is fixed, the transfer material P, which has been fixed, is discharged, and the paper discharge sensor 28 (FIG. 2) arranged in the paper discharge section is turned on. Then
After that, as shown in FIG. 5, it is determined whether or not there is a continuous paper feed signal. When it is determined that there is no continuous paper feed signal, the solenoid 58 is turned off based on the signal, and the fixing roller 2
5 is returned to its initial state (released position).

FIG. 6 shows a drive system of the pressure roller 25. Drive from the device body is performed from the idler gear 33 to the connecting gear 3
2 is transmitted to the fixing gear 31. Connecting gear 32
Is rotatably attached to an arm 36, and is pulled upward in FIG. 6 by an arm spring 34 about an arm shaft 37 and connected to an idler gear 33 and a fixing gear 31. The position of the connecting gear 32 is regulated by the arm 36 contacting the stopper 35. By using the drive system configured as described above, the pressure roller 25 can be driven according to the above-described change in the vertical position of the pressure roller 25.

By the way, since a constant tension is constantly applied to the fixing belt of the conventional image forming apparatus, as described above, when the apparatus is left for a long time, the belt is stretched and the belt thickness is reduced. There is a changing bug.

Therefore, in this embodiment, when the apparatus is not turned on, the driven lever 71 moves the belt spring 7
7, the driven shaft 52 is rotated in the clockwise direction in FIG. 7 to push the bearing 74, move the belt driven roller 24 to the left, and loosen the fixing belt 22.

The driven lever 71, when the apparatus is not turned on, is similar to the case of the pressure lever 53 described above.
When the solenoid 75 is turned on, the driven shaft 52 is rotated in the counterclockwise direction against the belt spring 72.

As a result, the belt driven roller 24 moves the bearing 74 thereof to the right in FIG. 7 along the long hole 51a formed in the front plate 51 by the driven spring 73, so that the fixing belt 22 is fixed. Make me nervous again.

[0040]

According to the first aspect of the present invention, the pressure of the pressure roller is released when the apparatus is not in use, so that the fixing belt can be prevented from being deformed, and the fixing failure and the offset can be prevented. It is possible to easily remove the jammed paper generated in the pressure roller unit.

According to the second aspect of the present invention, since the pressure of the belt driven roller with respect to the fixing belt can be released in the unused state of the apparatus, extension deformation of the fixing belt can be prevented and the life of the fixing belt can be extended. In addition, the fixing failure and the offset can be prevented.

According to the third aspect of the invention, since the pressing force of the pressure roller at the time of passing the transfer material is given only by the contraction force of the pressing spring, the pressing force of the pressure roller is stabilized. It is possible to prevent uneven fixing and offset.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a fixing unit in the image forming apparatus according to the embodiment of the invention.

FIG. 3 is a state diagram during fixing of the pressure roller, the thermal head, the heating element, and the fixing belt in the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 4 is a schematic side view of a pressure release mechanism of the pressure roller in the image forming apparatus according to the embodiment of the present invention.

FIG. 5 is a flowchart showing a control operation in the image forming apparatus according to the embodiment of the present invention.

FIG. 6 is a schematic side view of a drive system of a pressure roller in the image forming apparatus according to the embodiment of the invention.

FIG. 7 is a schematic side view of a pressure releasing mechanism of the fixing belt in the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 8 is a schematic side view of a pressure release state of a pressure release mechanism of a pressure roller in a conventional image forming apparatus.

FIG. 9 is a schematic side view of a pressure release mechanism of a pressure roller in a conventional image forming apparatus in a pressed state.

[Explanation of symbols]

 17 fixing unit 21 thermal head 21a heating element 22 fixing belt 23 belt driving roller 24 belt driven roller 25 pressure roller 28 paper ejection sensor 51 front plate 52 driven shaft 53 pressure lever 53a shaft 54 pressure lever shaft 55 pressure spring 57 Release lever 57a Long hole 58 Solenoid 64 Release spring 71 Driven lever 72 Belt spring 73 Driven spring 74 Bearing 75 Solenoid P Transfer material

Claims (3)

[Claims] 1. A pulse is provided through a heat resistant sheet having an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-fusible resin or the like and moving at the same speed as the transfer material. In an image forming apparatus in which an unfixed toner is fixed on the transfer material by a heating element that heats up like a current, the image forming apparatus turns on a predetermined pressure of a pressure roller for pressing the transfer material against the heating element. An image forming apparatus comprising: a pressure roller pressure releasing means for releasing the pressure of the pressure roller only when the pressure roller is applied and otherwise releasing the pressure of the pressure roller. 2. A pulse is provided through a heat resistant sheet which has an image forming means for forming an unfixed image on a transfer material with a toner made of a heat-meltable resin or the like, and which moves at the same speed as the transfer material. In an image forming apparatus in which an unfixed toner is fixed on the transfer material by a heating element that heats like a current, a predetermined pressure of a belt driven roller for moving the heat resistant sheet is applied only when the image forming apparatus is turned on. An image forming apparatus comprising a belt driven roller pressure releasing means for releasing the pressure of the belt driven roller at other times. 3. A pulse is provided through a heat resistant sheet which has an image forming means for forming an unfixed image on a transfer material by a toner made of a heat-meltable resin or the like, and which moves at the same speed as the transfer material. In an image forming apparatus in which an unfixed toner is fixed to the transfer material by a heating element that heats like a current, a pressure lever for applying a predetermined pressure to a pressure roller for pressing the transfer material against the heating element. And a long hole into which the shaft provided in the release lever for releasing the pressing force of the pressure lever is fitted, and the first end of the long hole engages with the shaft. Release lever displacement for displacing the release lever to a release position for releasing the pressing force of the pressure lever and a pressure position where the shaft does not engage the first end and the second end of the elongated hole. Means for providing the shaft and the length in the pressure position. Distance between the first end portion of the L1,
When the distance between the shaft and the second end of the elongated hole at the pressing position is L2, and the amount of displacement of the release lever by the release lever displacement means is S, the relationship of L1 <S <L2 is satisfied. An image forming apparatus comprising: