JPH06282198A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To provide a fixing unit for an image forming device that eliminates the need for the operation of releasing the energizing force of an energizing means, such as a coil spring, at the time of fixing roller replacement. CONSTITUTION:The device is provided with first and second levers 21 and 22 that are energized by the coil spring 14 to press a second fixing roller 2 against a first fixing roller 1; and a stopper 25 which restricts a limit on the rotation of the second lever 22. The stopper 25 is disposed in such a position that when the first and second fixing rollers 1 and 2 are expanded with heat, the second lever 22 is permitted to rotate until the second fixing roller 2 is pressed against the first fixing roller 1, and when the fixing rollers 1 and 2 are contracted at room temperature, the second lever 22 is prevented from rotating until the second fixing roller 2 is pressed against the first fixing roller 1.

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 an image forming apparatus such as an electrophotographic printer or a copying machine.

[0002]

2. Description of the Related Art An image forming apparatus such as an electrophotographic printer or a copying machine is provided with a fixing device having a fixing roller for fusing and fixing a transferred toner image on a sheet by heat and pressure. .

FIG. 4 is a sectional view of a fixing device of a conventional image forming apparatus. Reference numeral 1 is a first fixing roller, and 2 is a second fixing roller, which are pressed against each other. A heater lamp 3 as a heating means is built in at least one fixing roller. The peripheral surfaces of the first and second fixing rollers 1 and 2 are coated with silicone rubbers 4 and 5. The bosses 6 and 7 at both ends of the first and second fixing rollers 1 and 2 are rotatably supported by bearings 8 and 9.

Reference numeral 11 denotes a lever disposed below the bearing 7, one end of which is rotatably attached to a pin 12. At the free end of the lever 11, the threaded portion 1 of the step screw 13
3a is screwed. A coil spring 14 is attached to the step screw 13, and is arranged between the stop plates 15 and 16. The coil spring 14 is a compression spring and has a spring force in the arrow Q direction.

The lever 11 has a coil spring 14 for pin 1
The bearing 9 is biased in a counterclockwise direction of rotation about the second bearing 2, and the bearing 9 is pushed upward by this biasing force, so that the second fixing roller 2 is pressed against the first fixing roller 1.
The magnitude of the pressure bonding force varies depending on the printing speed, and the higher the speed, the larger the pressure bonding force is required.

When the first fixing roller 1 or the second fixing roller 2 is replaced, if the above-mentioned pressure bonding force is applied, it is difficult to perform the replacement work, and therefore the pressure bonding force is released at the time of replacement. As a conventional method for releasing the crimping force, an operator manually turns the step screw 13 to release the biasing force of the coil spring 14, and a method in which a driving mechanism is provided and the driving mechanism is driven to automatically release the pressing force. It is roughly divided into.

[0007]

However, the method of manually releasing it by a worker is troublesome because it needs to be performed twice before and after the replacement, and the method of providing the drive mechanism complicates the apparatus and increases the cost. There was a problem that became.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device for an image forming apparatus which makes it unnecessary to release the urging force of an urging means such as a coil spring when replacing the fixing roller.

[0009]

To this end, according to the present invention, there is provided a second lever which presses one fixing roller against the other fixing roller by the biasing means and presses the fixing roller, and the rotation limit of the second lever. And a second lever is rotated by the urging force of the urging means until one fixing roller presses against the other fixing roller when the fixing roller is in a heat expansion state. When the fixing roller is in a contracted state at room temperature, it is arranged at a position that prevents the second lever from rotating until one fixing roller is pressed against the other fixing roller.

[0010]

According to the above construction, the first means is heated by the heating means.
In a state where the fixing roller and the second fixing roller are heated and expanded, the first fixing roller and the second fixing roller are urged by the urging means to press each other. When the first fixing roller and the second fixing roller are contracted at room temperature,
Since the lever of hits the stopper and rotation is blocked,
The first fixing roller and the second fixing roller are in a non-pressurized state, and the replacement work of the first fixing roller and the second fixing roller can be performed without particularly performing the operation of releasing the urging force by the urging means.

[0011]

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

FIG. 1 is a sectional view of a fixing device of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view of a bearing portion shown in FIG. The same components as those of the conventional one shown in FIG. 4 are designated by the same reference numerals. 1 and 2, 1 is a first fixing roller, 2 is a second fixing roller, and a first lever 21 and a second lever 22 are arranged at an end of the second fixing roller 2. It is set up. The shape of the first lever 21 is substantially U-shaped, and one end of the first lever 21 is rotatably attached to the pin 23 so as to be pressed against the lower side of the bearing 9.
10 is a fixed frame.

The second lever 22 is longer than the first lever 21, and its left end is rotatably supported by a pin 24. The free end 22 of the right end of the second lever 22
The threaded portion 13a of the stepped screw 13 is screwed onto a. 1
Reference numeral 4 is a coil spring mounted on the step screw 13, and is a stop plate 1
5 and the stopper 25. The stopper 25 is fixed to the frame 26. The coil spring 14 is a compression spring and has a spring force in the direction of arrow Q, and the second lever 22 is urged by the spring force in a direction rotating counterclockwise about the pin 24. .

The second lever 22 is located below the first lever 21, and has a rib 27 projecting from the pin 24 near the pin 24. The rib 27 is a lower surface of the free end portion of the first lever 21. Is engaged with. Therefore, the second lever 22 is urged counterclockwise by the spring force of the coil spring 14 in the direction of arrow Q, so that the first lever 21 engaged with the rib 27 rotates clockwise around the pin 23. Is urged in the direction of arrow R to push the bearing 9 upward, and the second fixing roller 2 is pressed against the first fixing roller 1.

FIG. 3 is an explanatory view of the pressure-bonding force of the second fixing roller 2 to the first fixing roller 1. Here, assuming that the pressure force required for the second fixing roller 2 is F, the force FA required for the coil spring 14 is FA = L ₁ / L ₂ × L ₃ / L ₄ × F / _2, which is small. A large pressure force F can be obtained with the force FA. Here, L ₁ is the distance from the center of the second fixing roller 2 to the pin 23, and L ₂ is the rib 27 to the pin 23.
, L ₃ is the distance from the pin 24 to the rib 27,
L ₄ is the distance from the pin 24 to the center of the coil spring 14.

When the power is turned on, the heater lamp 3 (see FIG. 1)
As a result, the first fixing roller 1 is heated to a predetermined temperature,
At the same time, the second fixing roller 2 is also heated by heat transfer. The heating temperature is generally about 170 ° C. In this heating state, the outer diameters of the first fixing roller 1 and the second fixing roller 2 are larger than those at room temperature due to thermal expansion. Power off again
At times, the first fixing roller 1 and the second fixing roller 2 are cooled to room temperature and their outer diameters are reduced.

Here, the first when the power is turned on (when heated and expanded)
The outer diameter of the fixing roller 1 is DH1, the outer diameter of the second fixing roller 2 is DF1, the outer diameter of the first fixing roller 1 when the power is OFF (at room temperature contraction) is DH2, and the second fixing roller 2 is Assuming that the outer diameter is DF2, the center-to-center distance between the first fixing roller 1 and the second fixing roller 2 is 1/2 when the power is on compared to when the power is off {(DH1-DH2) + (DF1-DF2)} Only grows. The amount of movement of the free end portion 22a of the second lever 22 at this time is amplified doubled _{(L 2 / L 1 × L} 4 / L 3). That is, assuming that the movement amount is Δd, Δd = 1/2 × L ₂ / L ₁ × L ₄ / L ₃ × 1/2 × {(DH1-DH2)
+ (DF1-DF2)}.

When the power is turned on, the gap d between the free end 22a of the second lever 22 and the stopper 25 is set to d <Δ.
When set to d, the first lever 21 and the second lever 22 are allowed to rotate until the second fixing roller 2 is pressed against the first fixing roller 1 when the power is turned on. Further, when the power is off, the free end 22a of the second lever 22 contacts the stopper 25, and the first lever 21 and the second lever 22 remain in contact until the second fixing roller 2 presses against the first fixing roller 1. Since it is prevented from rotating, the pressing force between the first fixing roller 1 and the second fixing roller 2 is released, and they are in a no-load state. Therefore, the first fixing roller 1 and the second fixing roller 2 can be exchanged without performing an operation of releasing the biasing force of the coil spring 14.

In principle, the first lever 21 is unnecessary, and the pressing force can be released only by the second lever 22. The first fixing roller 1 and the second fixing roller 1 against the change
Since there is a slight variation in the distance between the center of the fixing roller 2 and the fixing roller 2, it is necessary to increase the lever lever ratio in order to perform crimping / releasing crimping as required, and the lever becomes considerably long and the apparatus becomes large. Invite. Therefore, in the present invention, two levers, that is, the first lever 21 and the second lever 22 are provided, and the amount of change is amplified by a combination of these two steps, enabling compact and reliable crimping / releasing crimping. Is.

[0020]

According to the fixing device of the image forming apparatus of the present invention, when the fixing roller is replaced, the operator does not need to release the pressing force, and the driving for releasing the pressing force is performed. Since no mechanism is required, the replacement work can be performed easily and safely, and a fixing device having a simple structure and a small size can be realized.

[Brief description of drawings]

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

2 is a vertical cross-sectional view of the bearing portion of FIG. 1 of the fixing device of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is an explanatory view of a pressure force of a fixing roller of a fixing device of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 4 is a sectional view of a fixing device of a conventional image forming apparatus.

[Explanation of symbols]

 1 First Fixing Roller 2 Second Fixing Roller 3 Heater Lamp 8 Bearing 9 Bearing 14 Coil Spring 21 First Lever 22 Second Lever 23 Pin 24 Pin 25 Stopper

Claims (1)

[Claims] 1. A first fixing roller and a second fixing roller, both ends of which are rotatably supported by bearings and pressed against each other, and a heating means incorporated in at least one fixing roller to heat the fixing roller. A first lever which is rotatably arranged around a pin at one end of one fixing roller and rotates in a direction in which the one fixing roller is pressed against the other fixing roller; and a first lever A second lever that is fitted and rotatable about a pin, and urges the second lever in a direction in which the first lever presses the one fixing roller to the other fixing roller. Urging means and a stopper that defines the rotation limit of the second lever by the urging force of the urging means, and the fixing roller is heated and expanded by the heating means. when, The second lever is allowed to rotate by the urging force of the urging means until one fixing roller is pressed against the other fixing roller, and when the fixing roller is in a contracted state at room temperature, The second fixing roller is pressed until the second fixing roller presses the second fixing roller.
A fixing device for an image forming apparatus, wherein the fixing device is arranged at a position that prevents the lever of the rotation.