JPH0572937A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To prevent face curl in which a paper curls in a state where a printing surface is inside as to a fixing device having so-called an upper-carrying system in which a pressure roller is arranged on an upper side and a fixing roller is arranged on a lower side in a state where they press-contact each other. CONSTITUTION:The paper guiding surface 5a of a separation pawl 5 installed to a fixing roller 2 is formed to be a projecting state from the top part contacting to the fixing roller 2 to a rear end part. The separation pawl 5 is arranged in a state where an angle formed by a straight line in which the top 5b of the separation pawl is combined with the center of the fixing roller 2 with the straight line in which both centers of the fixing roller 2 and the pressure roller 3 are combined is <=30 deg.. Furthermore, a pair of carrying rollers 10 and 11 provided on a paper ejecting side of a fixing nip part is arranged on an upper part than the tangent of the fixing roller 2 passing through the contact of both rollers 2 and 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a pressure roller on the upper side and a fixing roller on the lower side so as to be in pressure contact with each other.
The present invention relates to a fixing device of an image forming apparatus in which a separating claw is attached to the fixing roller, and a pair of conveying rollers is provided on the sheet exit side of both rollers.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine, a facsimile machine or a printer, a pressure roller is arranged on the upper side of a sheet conveying path and a fixing roller is arranged on the lower side so as to be in pressure contact with each other. It is well known to use a fixing device of the type. In this upper conveyance method, the paper that has come out of the pair of rollers tends to hang down toward the printing surface side, so that there is a drawback that the paper curls up with the printing surface inside, so-called face curl occurs.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks and to provide a top-conveying type fixing device in which face curl does not occur.

[0004]

According to the present invention, the above-mentioned problems can be solved by forming the paper guide surface of the separating claw from the front end portion in contact with the fixing roller to the rear end portion in a convex shape. It

In order to solve the above-mentioned problems, the present invention, in addition to the above-mentioned structure, further comprises a straight line connecting the tip of the separating claw which is in contact with the fixing roller and the center of the fixing roller, the fixing roller and the fixing roller. It is proposed that the angle formed by the straight line connecting both centers of the pressure roller is 30 ° or less.

Further, in order to solve the above-mentioned problems, the present invention proposes, in addition to the above-mentioned constitutions, to arrange a pair of conveying rollers above the tangent line of the fixing roller passing through the contact points of both rollers. To do.

[0007]

The sheet guiding surface of the separating claw attached to the fixing roller has a convex shape from the front end to the rear end in contact with the fixing roller, so that the sheet is guided to this guiding surface. It is transported upward.

Further, the angle formed by the straight line connecting the tip of the separating claw in contact with the fixing roller and the center of the fixing roller with the straight line connecting the centers of both the fixing roller and the pressure roller is 30 °. Since it is as follows, the distance between the tip of the separation claw and the fixing nip portion is short.

Further, since the pair of conveying rollers provided on the paper exit side of the fixing roller and the pressure roller are arranged above the tangent line of the fixing roller passing through the contact points of both rollers, each of the above-mentioned respective In combination with the configuration, prevent paper face curl.

[0010]

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

In FIG. 1, a fixing roller 2 is arranged in a lower side of a fixing frame 1, and a pressure roller 3 is arranged in an upper side thereof in a state of being pressed against each other. Inside the fixing roller 2, there is provided a heater 4 for heating and fixing the sheet passing between the rollers. Further, the fixing roller 2 is provided with a separating claw 5 on the paper exit side thereof, the separating claw 5 is rotatably mounted around a shaft 6, and the fixing roller 2 is attached to the fixing roller 2 by a spring 7. It is given a turning habit in the joining direction. Reference numeral 8 is a thermistor for controlling the fixing roller 2 so as to keep it at a predetermined temperature, and 9 is a paper conveyance path, and the paper is fed in the direction of arrow F.

As shown in the figure, the separating claw 5 has a convex shape from the front end 5b whose paper guide surface 5a contacts the fixing roller to the rear end in the paper conveying direction.

The paper having the toner image formed on its surface advances in the direction of arrow F along the paper conveying path 9 with its printing surface facing down, and passes through the fixing nip portion formed by the fixing roller 2 and the pressure roller 3. It passes and is separated from the fixing roller 2 by the separating claw 5. Then, the paper is guided to the convex paper guide surface 5a of the separation claw 5 and conveyed upward.

In the embodiment shown in FIG. 2, the same parts as those in the embodiment of FIG. 1 are designated by the same reference numerals. In the embodiment shown in FIG. 2, the straight line connecting the tip 5b of the separating claw 5 which contacts the fixing roller 2 and the center 2a of the fixing roller 2 and the center 2 of the fixing roller 2.
angle θ formed by a and a straight line connecting the center 3a of the pressure roller 3
However, the disposition position of the separation claw 5 is determined so as to be 30 ° or less. As a result, the distance that the paper fed through the paper transport path 9 contacts the fixing roller 2, that is, the time is shortened.

Also in the embodiment shown in FIG. 3, the same parts as those in the embodiment of FIG. 2 are designated by the same reference numerals. In Figure 3,
Conveying roller pairs 10 and 11 are provided on the sheet conveying path 9 at the sheet exit side of the fixing nip portion between the fixing roller 2 and the pressure roller 3. The pair of conveying rollers 10 and 11 are arranged above a tangent line T of the fixing roller 2 which passes through a contact point P between the fixing roller 2 and the pressure roller 3. That is, the paper transport path 9 after the fixing nip portion in FIG.
Above.

In FIG. 3, the sheet that has passed through the fixing nip portions of the rollers 2 and 3 is separated from the fixing roller 2 by the separating claw 5. The leading end of the thus separated sheet is guided to the pair of transport rollers 10 and 11 along the convex sheet guide surface 5a of the separation claw 5 and the guide plate 1a of the fixing frame 1, and is sandwiched by the pair of rollers. The transport roller pairs 10 and 11 are fixed rollers.
Since it is set to rotate at a peripheral speed slightly higher than the peripheral speed of the roller 2, the sheet is conveyed in a state of being pulled without slack between the fixing nip portion and the conveying roller-nip portion. In this state, the paper passes through the fixing nip portion and is separated from the fixing roller 2 at the same time, and is conveyed to the paper discharge portion without receiving excess heat.

[0017]

In the fixing device according to the first aspect of the present invention, the sheet that has passed through the fixing nip portion is conveyed obliquely upward by the convex guide surface of the separating claw, so that the face curl of the sheet can be prevented.

According to the second aspect, since the tip of the separating claw is located near the fixing nip portion, it is possible to minimize heat from the fixing roller that causes curling of the sheet. Contributes to the prevention of face curl.

According to the third aspect of the present invention, after the leading edge of the sheet reaches the conveying roller pair nip portion, the sheet is guided upward so that the sheet can be separated from the fixing roller at the same time when passing through the fixing nip portion. As a result, it contributes to curl prevention of the paper.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a sectional view showing yet another embodiment of the present invention.

[Explanation of symbols]

 2 Fixing roller 3 Pressing roller 5 Separation claw 5a Paper guide surface 5b Separation claw tip 10,11 Conveyance roller pair θ angle

Claims (3)

[Claims] 1. A pressure roller on the upper side and a fixing roller on the lower side.
Of the fixing roller and the fixing roller.
A fixing device for an image forming apparatus having a separation claw attached to a roller, wherein a sheet guide surface of the separation claw has a convex shape from a front end portion to a rear end portion in contact with the fixing roller. 2. An angle formed by a straight line connecting the tip of the separating claw in contact with the fixing roller and the center of the fixing roller and a straight line connecting both centers of the fixing roller and the pressure roller. The fixing device according to claim 1, wherein the fixing device is 30 ° or less. 3. The fixing device according to claim 1, wherein a pair of conveying rollers is provided on the sheet exit side of the fixing roller and the pressure roller, and the fixing roller passes through the contact points of both rollers. A fixing device in which the pair of conveying rollers are arranged above a tangent line.