JPH10177314A - Fixing device - Google Patents

Abstract

(57) [Summary] [Purpose] A fixing device that can solve the problem of image blurring, abrasion of an entrance guide, and the occurrence of roller marks on a sheet material, and can also prevent the sheet material from winding around a pressure roller. To provide. A fixing roller having a heater therein is provided.
And a pressure roller 34 in contact with the fixing roller 29; an entrance guide 28 for guiding the sheet material S to the fixing roller 29 and the pressure roller 34; a pressure separation guide 51; Fusing discharge roller 4 for transporting to paper path
3, an output roller 42 that rotates in contact with the fixing output roller 43, and an envelope that switches the contact pressure of the pressure roller 34 during normal sheet material transport and during transport of thick paper, envelopes, and the like. In the fixing device 4 having a lever (switching means), the entrance guide 28 can be retracted in conjunction with the operation of the envelope lever 60, and the position of the pressure separation guide 51 is changed so that the discharge roller 42 It is configured to change the contact pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser beam printer, a developing device for developing a latent image drawn by a laser beam or the like, a transfer device for transferring the developed toner image to a sheet material, and a transfer device A fixing device for fixing a toner image formed on a sheet material is mainly used.

A fixing device for fixing a transferred toner image on a sheet material includes a fixing roller which rotates while being maintained at a predetermined temperature by a heater and a temperature sensor, and is brought into contact with the fixing roller at a predetermined pressure. The fixing roller and the pressure roller melt the toner as a developer with heat and pressure to fix a toner image on a sheet material.

Here, a configuration of a conventional laser beam printer will be described as a typical example of an image forming apparatus with reference to FIG.

FIG. 7 is a sectional view of a conventional laser beam printer. As shown in FIG. 7, a laser scanner 2, a photosensitive drum 3, a primary charger 16, and a developing device are provided in a printer main body (image forming apparatus main body). A process cartridge 1 including a transfer roller 9, a transfer roller 9, a fixing device 4, a pair of transport rollers 8, a paper feed cassette 6, a paper feed roller (pickup roller) 7, and the like are provided.

The sheet material S stacked and stored in the sheet cassette 6 is fed by a sheet feeding roller 7 rotating in a counterclockwise direction, guided to a sheet material guide 18 and fed to a nip portion of a pair of conveying rollers 8. Sent. Next, the sheet material S is sent to the transfer nip portion between the photosensitive drum 3 and the transfer roller 9 by the conveying roller pair 8.

The photosensitive drum 3 rotates counterclockwise and is uniformly charged by the primary charger 16, and an electrostatic latent image is sequentially formed on the outer peripheral surface thereof by laser light from the laser scanner 2. Then, this electrostatic latent image is
7 and developed as a toner image.

The toner image on the photosensitive drum 3 is sequentially transferred to the sheet material S sent to the transfer nip between the photosensitive drum 3 and the transfer roller 9 by the transfer roller 9.
The sheet material S to which the toner image has been transferred is sent to the fixing device 4, where the sheet material S is heated and pressed to receive the toner image.

Thereafter, the sheet material S is sent to the paper discharge roller 5 by the transport roller pair 10, discharged by the paper discharge roller 5, and stacked on the sheet material discharge tray 19 on the upper surface of the printer main body.

By the way, a paper ejection cover 1 is provided on the printer body.
2 is provided so as to be openable and closable about a fulcrum 15. A face-up discharge roller 14, guides to face-down and face-up discharge paths, and guides to the face-up and face-up discharge paths A flapper 11 for switching a path is provided.

In the conventional laser beam printer configured as described above, the units such as the process cartridge 1 and the fixing device 4 and the roller parts such as the paper feed roller 7 and the transfer roller 9 are consumables. Some exchanges are needed during life. Among them, the fixing device 4 is a unit that is usually replaced about two to four times during the life of the product.

Thus, in the conventional laser beam printer, the fixing device 4 can be replaced with the discharge cover 12 of the printer main body opened in the direction of arrow A in FIG. The fixing device 4 is positioned by the positioning protrusion 13 of the main stay 20 in a state where the fixing device is mounted, and is fixed to the printer main body by a fixing lever 31.

Here, the configuration of the fixing device 4 will be described in detail with reference to FIG.

FIG. 8 is a cross-sectional view of the fixing device 4. The fixing device 4 includes a fixing roller 29, a pressing roller 34, a fixing frame 35 supporting the fixing roller 29 and the pressing roller 34, and a sheet material S entering. An inlet guide 28 serving as a guide, a separation upper guide 30 and a separation lower guide 32 serving as a guide of a paper discharge port,
The fixing device 4 includes a fixing lever 31 for fixing the fixing device 4 to the printer body.

The sheet material S enters the interior of the fixing device 4 in the direction of arrow C from the entrance guide 28 side, and after the toner image is fixed at the nip between the fixing roller 29 and the pressure roller 34. The sheet is guided between the upper separation guide 30 and the lower separation guide 32, and is conveyed out of the fixing device 4 by the fixing discharge roller 43 and the discharge roller 42.

A fixing / discharge detection sensor lever 45 is provided in the middle of the conveying path of the sheet material S.
The presence / absence of the sheet material S between the fixing roller 29 and the sheet ejection roller 43, the sheet material stagnant jam in the sheet ejection unit, and the sheet material conveyance delay jam to the fixing device 4 are detected by the fixing sheet ejection detection sensor lever 45. It is configured to be able to.

When a sheet jam in the sheet discharge section (accordion jam or the like between the fixing roller 29 and the sheet discharge roller 43) occurs, the separation lower guide 32 is opened in the direction of arrow B in FIG. The sheet material S is configured to be removed.

The fixing device 4 shown in FIG. 8 has means (envelope mode switching means) for switching the contact pressure of the pressure roller 34 between the time of normal sheet material conveyance and the time of conveyance of thick paper or an envelope. ing. The envelope mode switching means includes an envelope mode lever 60, a pressure table 61, a pressure bearing holder 62,
It is composed of a pressure roller bearing 63.

When the envelope mode lever 60 is rotated, the pressing table 61 pressed by the pressing spring 44 is pressed down, and the pressing force acting on the pressing roller 34 is reduced. In this state, the pressing roller 34
Moves in a direction away from the fixing roller 29, and the surface pressure of the contact portion (nip portion) between the fixing roller 29 and the pressure roller 34 is reduced.

The conventional fixing device 4 includes a pressing roller 34
A pressure separation guide 51 for separating the sheet material S wrapped around the side, a gap is provided between the tip of the pressure separation guide 51 and the pressure roller 34, and the pressure separation guide 51 The contact roller 53 provided in the
The gap can be managed by contacting the surface of the gap.

Next, the structure around the pressure separation guide 51 of the fixing device 4 will be described with reference to FIG. FIG. 9 is a perspective view of the fixing device 4 in which the fixing upper cover 57, the separation upper guide 30, the separation lower guide 32, and the like are removed, and only main components such as the pressure roller 34, the fixing roller 29, and the fixing frame 35 are shown. .

As shown in the figure, the pressure separation guides 51 are provided at two locations in the longitudinal direction, and each independently contacts the pressure roller 34. Each of the pressure separation guides 51 is attached to the fixing frame 35 so as to be rotatable around a rotation fulcrum 58 by a pressure leaf spring 52, and two rollers 53 are attached to the pressure leaf spring 52 by a shaft 59. It is rotatably supported.

The pressure separation guide 51 is positioned at a total of three positions by the rotation fulcrum 58 and the two rollers 53, and is pressed against the pressure roller 34 by the pressure leaf spring 52. The pressure leaf spring 52 is a pressure separation guide 51.
The shaft 59 of the roller 53 abutting at two places is held at the same time as the rotation fulcrum 58 is held, and the shaft 59 is pressed against the pressing roller 34 side.

[0024]

However, the above-mentioned conventional laser beam printer has the following problems which occur when the fixing device 4 conveys thick paper or envelopes.

Since thick paper, envelopes and the like are stiff, they are squeezed by the entrance guide 28, causing problems such as blurring on the image and friction of the entrance guide 28. Further, in the case of double-sided printing or the like, the lower sheet surface is rubbed against the entrance guide 28, so that a problem that toner adheres to the tip of the entrance guide 28 also occurs. For this reason, it was necessary to replace the entrance guide 28 periodically.

Further, when thick paper, an envelope, or the like is pulled by the fixing discharge roller 43, the contact pressure of the discharge roller 42 increases due to the thickness of the paper, and there is also a problem that roller marks are formed on the paper. .

Further, the configuration of the conventional envelope mode restricts the position of the pressure roller 34 when the envelope is used, and when the contact pressure of the pressure roller 34 is to be extremely reduced as in the case of a thick envelope. Although good, there is a problem that it is not suitable when it is desired to slightly change the contact pressure of the pressure roller 34 as in the case of passing thick paper.

There are also the following problems when used in the envelope mode.

In a configuration in which the contact pressure of the pressure roller 34 is weakened as in the envelope mode, unfixed residual toner tends to remain on the fixing roller 29 or the pressure roller 34 during fixing.
There is a problem that the residual toner stains the next sheet material S. For this reason, conventionally, a cleaning pad had to be attached to the fixing roller 29 or the pressure roller 34, and the cleaning pad had to be periodically replaced because it was a consumable item. The replacement cleaning pad is composed of a pad member (felt or the like) and a pad holding member (heat-resistant material), and has a problem of high replacement cost.

The pressure roller 34 of the fixing device 4 is formed by winding a rubber around a metal core, and is pressed against the fixing roller 29 by a pressure spring 44. For this reason, the pressure roller 34 is crushed to form a portion (nip portion) that is in close contact with the fixing roller 29, and the nip portion has a shape along the outer diameter curvature of the fixing roller 29.

Normally, the conveyed sheet material S is curled toward the fixing roller 29, but when the sheet material S is in a bad condition (the storage condition is bad and the sheet material S is moist or an impurity is attached). Case) In rare cases, the sheet material S may curl toward the pressure roller 34 and stick to the pressure roller 34. In some cases, the sheet material S is wound around the pressure roller 34 without being peeled off from the pressure roller 34.

Therefore, the pressure separation guide 51 is provided on the pressure roller 34 side, but has the following problem in the envelope mode.

FIGS. 10A and 10B are diagrams for explaining the envelope mode. FIG. 10A shows a state in which the pressure roller 34 is in a normal position, and FIG. This shows a state where the contact pressure with the roller 29 is reduced.

When the pressure separation guide 51 is used in a fixing device having a configuration in which the position of the pressure roller 34 is variable, the rotation fulcrum of the pressure separation guide 51 is fixed to the fixing frame 35. The gap E between the tip of the pressure separation guide 51 and the pressure roller 34 changes at the position of the pressure roller 34 shown in FIG.
<E2). Therefore, in the envelope mode, there is a problem that the sheet material is easily wound around the pressure roller 34.

The present invention has been made in view of the above problems, and has as its object to solve the problem of image blur, abrasion of the entrance guide, and the problem of roller marks on the sheet material. It is an object of the present invention to provide a fixing device capable of preventing the wrapping around the pressure roller.

[0036]

In order to achieve the above object, the present invention is directed to a fixing roller having a heater therein, a pressure roller contacting the fixing roller, a fixing roller and a pressure roller. Guide for guiding the sheet material to the sheet, a pressure separation guide for separating the sheet material wrapped around the pressure roller, and a discharge path downstream for the sheet material discharged from the fixing roller and the pressure roller. And a discharge roller that is driven to rotate in contact with the fixing discharge roller, and that the pressing roller contacts the normal sheet material and the conveyance of thick paper or an envelope. In a fixing device having switching means for switching the contact pressure, the entrance guide can be retracted in conjunction with the operation of the switching means, and the position of the pressure separation guide is changed to change the contact pressure of the paper discharge roller. Configured as It is characterized in.

According to a second aspect of the present invention, in the first aspect of the present invention, the switching means is means for switching the strength of the urging means for urging the pressure roller. It is characterized in that two kinds of springs having different pressures are used to switch the springs.

According to a third aspect of the present invention, in the first aspect of the invention, the entrance guide has a cleaning member for cleaning the surface of the pressure roller, and is configured to be replaceable. It is characterized by.

Therefore, according to the present invention, since the entrance guide can be retracted in conjunction with the operation of the switching means, the entrance guide is retracted during the transportation of thick paper, envelopes, etc., thereby causing problems such as image blur and wear of the entrance guide. Can be solved. Also, since the position of the pressure separation guide is changed when transporting thick paper or envelopes, the contact pressure of the discharge rollers is changed,
It is possible to solve the problem of roller traces on the sheet material and prevent the sheet material from winding around the pressure roller.

[0040]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a sectional view of a fixing device according to a first embodiment of the present invention.
(B) is an explanatory view of the operation of the identification fixing device. In these drawings, the same members as those of the conventional fixing device shown in FIG. The description is omitted.

In this embodiment, the entrance guide 28 can be retracted in conjunction with the operation of the envelope mode switching means, the fulcrum position of the pressure separation guide 51 is changed, and the contact pressure of the discharge roller 42 is changed. Features.

The fixing device 4 according to the present embodiment is provided with an envelope lever 60 as an envelope mode switching means, and as shown in FIG.
When the envelope lever 60 is rotated in the direction, the envelope lever 60 pushes down the pressing table 61, and the pressing table 61 rotates about the fulcrum 71, and the pressure pressing the pressure bearing holder 62 is reduced. As a result, the pressure roller 34 moves in a direction away from the fixing roller 29 (arrow F direction), and the contact pressure between the pressure roller 34 and the fixing roller 29 decreases (this state is referred to as an envelope position).

The entrance guide 28 is mounted so as to be rotatable about a fulcrum 65 and is pressed upward by a spring 66. The movement of the entrance guide 28 is regulated by the stopper 72 and the abutting portion 73 provided on the pressing table 61.

As shown in FIG. 2B, when the envelope is in the position of the envelope, the pressing table 61 is rotated, and the abutting portion 73 is rotated.
Is also lowered, and the spring 66 is also weak. When thick paper or an envelope is passed in this state, the entrance guide 28 can be rotated around the fulcrum 65 and retracted at the waist of the paper, and the friction between the entrance guide 28 and the paper can be reduced. it can.

Further, the pressure separation guide 51 is mounted so as to be rotatable about a rotation fulcrum 64 provided on the pressure table 61, whereby the pressure separation guide 51 is pressed as in the conventional example (see FIG. 10). In the present embodiment, the tip gap has changed due to the vertical movement of the roller 34 (E <> E2).
As shown in (b), the fulcrum 64 moves up and down in conjunction with the movement of the envelope lever 60, so that the tip gap of the pressure separation guide 51 can be set to E = E3.

In this embodiment, the discharge rollers 42 are pressed by a discharge roller spring 70, and the discharge roller spring 70 is supported by a discharge roller pressing bar 69.
The ejection roller pressing bar 69 is provided rotatably about a fulcrum 68 and is connected to the pressing table 61 by a connection bar 67. As described above, since the press table 61 and the discharge roller press bar 69 are connected by the connection bar 67, FIG.
As shown in (b), the connection bar 67 is pulled in the direction of arrow I in conjunction with the movement of the envelope lever 60, and the discharge roller pressing bar 69 rotates in the direction of arrow H, and the pressing force of the discharge roller spring 70 is applied. As a result, the contact pressure of the discharge rollers 42 when passing an envelope or thick paper is weakened.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. In addition, FIG.
(B) is an operation explanatory view of the fixing device according to the second embodiment of the present invention. In this figure, the same members as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and structurally and functionally. The description of the same components is omitted.

In this embodiment, the envelope mode switching means is constituted by means for switching the strength of the urging means for urging the pressure roller 34. As the switching method, two different types of pressing force are used. The springs 44 and 81 are used to switch between them.

That is, in the fixing device 4 according to the present embodiment, as shown in FIG. 3, a first pressing spring 44 and a second pressing spring 81 are provided as two types of pressing springs.
The first pressing spring 44 has a stronger pressing force than the second pressing spring 81.

As shown in FIG. 3A, normally, the first pressure spring 44 presses the pressure bearing holder 80 in the same manner as in the conventional example. However, as shown in FIG. In the position, since the pressing table 61 presses down the first pressing spring 44, only the second pressing spring 81 is pressed by the pressing bearing holder 8.
0 is pressurized. Therefore, the envelope lever 6
By switching 0, two types of pressing force are applied to the pressing springs 44,
It can be determined only by the pressing force of 81.

The structure of the conventional envelope mode regulates the position of the pressure roller when the envelope is used. When the contact pressure of the pressure roller is extremely reduced as in the case of a thick envelope, it is good. There is a problem in that it is not suitable for slightly changing the contact pressure of the pressure roller as in the case of paper passing. According to the present embodiment, such a problem can be solved.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIGS. 4 is a sectional view of a fixing device according to Embodiment 3 of the present invention, FIG. 5 is a perspective view of an entrance guide of the identification attaching device, and FIG. 6 is a plan view of an end of the entrance guide. 8, the same members as those shown in FIG. 8 are denoted by the same reference numerals, and the description of those having the same structure and function is omitted.

In this embodiment, the entrance guide 28 is formed integrally with a cleaning member (cleaning pad) 90 for cleaning the surface of the pressure roller 34, and this is used as a regular replacement part replaceable for the fixing device 4. It is characterized by being.

As shown in FIG. 4, a cleaning pad 90 is attached to the entrance guide 28, and the cleaning pad 90 is in contact with the surface of the pressure roller 34, and the residual toner on the surface of the pressure roller 34. To clean. Thereby, contamination of the sheet material S by the residual toner is prevented.

As shown in FIG. 5, the entrance guide 28 is positioned in the fixing device main body by a boss 93 projecting from the center in the width direction, and as shown in FIG. Are attached to the fixing frame 35 by engaging with the fixing frame 35. Therefore, as shown in FIG. 6, the entrance guide 28 can be removed from the fixing device 4 by pushing the knob 91 in the direction of arrow K.

By the way, since thick paper and envelopes have strong stiffness,
In the conventional fixing device, there is a problem that the thick paper or the envelope is squeezed by the entrance guide and the entrance guide is worn. In addition, in the case of double-sided printing or the like, the lower sheet surface is rubbed against the entrance guide, so that a problem that toner adheres to the tip of the entrance guide has also occurred. For this reason, the entrance guide had to be replaced periodically.

In a configuration in which the contact pressure of the pressure roller is weakened as in the envelope mode, unfixed residual toner tends to remain on the fixing roller or the pressure roller during fixing, and the residual toner stains the next sheet material. Problem. For this reason, conventionally, it was necessary to attach a cleaning pad to the fixing roller or the pressure roller. Further, since the cleaning pad is a consumable item, it has to be periodically replaced. The replacement cleaning pad is composed of a pad member (felt or the like) and a pad holding member (heat-resistant material), and has a problem that the replacement cost is high.

In the fixing device 4 according to the present embodiment, the entrance guide 28 and the cleaning pad 90 are integrally formed as a replacement part.
Because it also serves as a holding member, cost reduction is also achieved,
The conventional problem can be solved.

[0060]

As is apparent from the above description, according to the present invention, according to the present invention, the entrance guide can be retracted in conjunction with the operation of the switching means. By retracting the guide, the effect of solving the problem of image blur and the wear field of the entrance guide can be solved.

Further, according to the present invention, since the position of the pressure separating guide is changed at the time of transporting a thick paper or an envelope, and the contact pressure of the discharge rollers is changed, there is a problem that roller marks are formed on the sheet material. In addition to the above, it is possible to obtain an effect that the winding of the sheet material around the pressure roller can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is an operation explanatory view of the fixing device according to the first embodiment of the present invention.

FIG. 3 is an operation explanatory view of a fixing device according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a fixing device according to a third embodiment of the present invention.

FIG. 5 is a perspective view of an entrance guide of a fixing device according to a third embodiment of the present invention.

FIG. 6 is a plan view of an entrance guide end of a fixing device according to a third embodiment of the present invention.

FIG. 7 is a sectional view of a laser beam printer.

FIG. 8 is a sectional view of a conventional fixing device.

FIG. 9 is a perspective view of a main part of a fixing device showing a pressure separation guide of a conventional fixing device.

FIG. 10 is a cross-sectional view illustrating an envelope mode in a conventional fixing device.

[Explanation of symbols]

 4 Fixing Device 28 Entrance Guide 29 Fixing Roller 34 Pressure Roller 42 Discharge Roller 43 Fixing Discharge Roller 44 First Pressure Spring (Biasing Means) 48 Heater 51 Pressure Separation Guide 60 Envelope Lever (Switching Means) 81 Second Pressure spring (biasing means) 90 Cleaning pad (cleaning member) S Sheet material

Claims (3)

[Claims] A fixing roller having a heater therein;
A pressure roller contacting the fixing roller, an entrance guide for guiding the sheet material to the fixing roller and the pressure roller, a pressure separation guide for separating the sheet material wound around the pressure roller, A fixing discharge roller for conveying the sheet material discharged from the rollers and the pressure roller to a downstream discharge path, a discharge roller that rotates in contact with the fixing discharge roller, and a normal sheet material conveyance A fixing device having a switching means for switching the contact pressure of the pressure roller between the time when the sheet is conveyed and a thick paper or an envelope. A fixing device, wherein a position of a separation guide is changed to change a contact pressure of the discharge roller. 2. The switching means is a means for switching the strength of an urging means for urging the pressure roller. As the switching method, the spring is switched by using two kinds of springs having different pressing forces. The fixing device according to claim 1, wherein: 3. The fixing device according to claim 1, wherein the entrance guide includes a cleaning member that cleans the surface of the pressure roller and is replaceable.