JP2000075696A - Fixing device and image forming device - Google Patents

Abstract

(57) [Abstract] [Problem] Even if the pressure roller diameter increases due to thermal expansion,
The transfer material is transported at a constant speed. SOLUTION: A heating body fixed and held, a film material sliding on the heating body, a pressure roller forming a heating nip with the heating body with the film material interposed therebetween,
A fixing member that presses a heating element holding member that holds and holds the heating element toward the pressure roller 1; the film material is moved and driven by the rotation of the pressure roller 1; In the apparatus, a speed adjusting means (2, 3, 4) for canceling a change in the transport speed due to an increase or a decrease in the diameter of the pressure roller 1 due to thermal expansion in conjunction with an axial expansion and contraction generated by the thermal expansion of the pressure roller 1. , 6).

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 an electrophotographic apparatus represented by a copying machine and an LBP, and a fixing device.

[0002]

2. Description of the Related Art FIG. 7 is a schematic diagram showing a conventional image forming apparatus. The image forming apparatus according to the present embodiment is a platen-moving copying machine using a transfer type electrophotographic process.

In FIG. 7, reference numeral 22 denotes a platen as a platen glass; and 21, a photosensitive drum for an electrophotographic apparatus as an image carrier, which rotates at a predetermined peripheral speed (process speed) clockwise as indicated by an arrow. Driven.

The photosensitive drum 21 is subjected to a primary charging process to a predetermined polarity and potential uniformly by a charging roller 25 during the rotation process, and the charged surface is irradiated with exposure light emitted by exposure illumination 23 via an optical system 24. As a result, an electrostatic latent image corresponding to the image information of the document is formed.

The latent image is developed as a toner image by the developing device 26, and the toner image reaches a transfer nip between the photosensitive drum 21 and the transfer roller 27.

On the other hand, the transfer material P, which is the recording material in the paper feed tray 28, is fed one by one by the paper feed roller 29, and passes through the sheet path at predetermined timing.
0 is transferred to the transfer nip by the transfer roller 27.
As a result, an electric field having a polarity opposite to that of the toner is applied from the back surface of the transfer material P, and the toner image on the photosensitive drum 21 side is transferred to the surface of the transfer material P.

The transfer material P, which has received the transfer of the toner image and passed through the transfer nip, is separated from the surface of the photosensitive drum 21 and enters a fixing device, where the toner image is heated and fixed. It is discharged outside.

The fixing device in the image forming apparatus is a device that heats an unfixed toner image on the surface of the transfer material P formed in the image forming unit onto the surface of the transfer material P.

In recent years, a film heating type heating device, that is, a heating device of a film heating type, which has features of low power consumption, shortened wait time, and quick start property (on-demand fixing property),
A heating member fixed and held, a film member slidingly moved on the heating member, and a pressing member forming a heating nip portion with the heating member with the film member interposed therebetween; A heating device that introduces a material to be heated between a film material and a pressing member, holds the material to be conveyed, and heats the material to be heated by heat from the heating body via the film material is practically used as a fixing device of an image forming apparatus. It has come to be.

Referring again to FIG. In FIG. 7, reference numeral 31 denotes a first stay member, which is also a heater holding member and a film guide member, and is a heat-resistant resin molded article having a substantially U-shaped cross section facing upward.

Reference numeral 32 denotes a ceramic heater as a heating element, which is fixed and held to the lower surface of the bottom plate portion of the first stay member 31 by using a heat-resistant adhesive or the like.

Reference numeral 33 denotes a second stay member as a pressing member of the first stay member 31, which is a substantially U-shaped metal material formed with a downward cross section.

Reference numeral 34 denotes a cylindrical fixing film having an endless shape in the circumferential direction. The first stay member 31 and the second stay member 33 are provided.
It is loosely fitted outside the outside.

The first stay member 31, the heater 32,
Each of the second stay member 33 and the cylindrical fixing film 34 is a horizontally long member whose longitudinal direction is perpendicular to the drawing.

In the case of such a film heating type heating apparatus, the pressure roller 1 is driven by the driving means M to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by the arrow.

By the rotational driving of the pressure roller 1, a rotational force acts on the fixing film 34 by the contact friction force between the pressure roller 1 and the outer surface of the fixing film 34 in the fixing nip portion, and the fixing film 34 The outer surface of the first stay member 31 and the second stay member 33 is rotated clockwise as indicated by an arrow while the inner surfaces of the first stay member 31 and the second stay member 33 are slidably contacted with the lower surface of the heater 32 at the fixing nip.

[0017]

However, in the above-mentioned prior art, the pressure roller 1 is driven to rotate at a predetermined peripheral speed in the counterclockwise direction indicated by the arrow by the driving means M, so that the fixing film 34 rotates and the transfer is performed. The material P is pinched and transported. Therefore, there has been a fact that the transport speed of the transfer material P depends on the peripheral speed of the surface of the pressure roller 1.

On the other hand, the configuration of the pressure roller 1 is such that a silicon rubber elastic layer is provided on a cored bar, and a composite resin layer containing a fluororesin or a PFA resin and a PTFE resin as a releasable surface layer on the outside thereof. Is provided, so when the temperature is increased by heating, the outer diameter expands and increases.

Therefore, there is a problem that the conveying speed of the transfer material P increases with the expansion of the outer diameter.

In the experiment, when the diameter of the pressure roller 1 is φ16 mm and the temperature control temperature of the heater is 180 ° C. to 200 ° C., the transfer speed of the transfer material P by the pressure roller 1 is about 1.5. It has been confirmed that the percentage increases.

Due to this, the continuous copy image has many problems as described below because the transfer material P is conveyed while being pulled by the pressure roller 1 at the transfer portion. That is, 1. Transfer failure caused by the transfer material P being pulled.

2. Pitch fluctuation image that appears when vibration of the drive system is transmitted to the transfer process.

3. Immediately after the trailing end of the transfer material P comes off the registration roller, the transfer material P is pulled by the pressure roller 1 and a transfer deviation caused by a rapid change in speed.

There are various problems.

An object of the present invention is to offset the increase in the diameter of the pressure roller due to the thermal expansion, so that the transfer speed of the transfer material is always maintained at a constant speed regardless of the thermal expansion of the pressure roller. A fixing device and an image forming apparatus.

[0026]

SUMMARY OF THE INVENTION In order to achieve the object of the present invention, a fixing device comprises a fixedly-heated heating element, a film material sliding on the heating element, and a film material. A pressure roller that forms a heating nip portion with the heating element with the heating element interposed therebetween, and a pressing member that presses a heating element holding member that fixes and holds the heating element toward the pressure roller, and the rotation of the pressure roller In a fixing device that moves and drives the film material and heats the transfer material while nipping and transferring the transfer material, a change in the conveyance speed due to an increase or decrease in the diameter of the pressure roller due to thermal expansion is caused by an axial direction generated by thermal expansion of the pressure roller. It has a speed adjusting means for canceling out in conjunction with expansion and contraction.

According to the above configuration, the transfer speed of the transfer material conveyed by the pressure roller is utilized by utilizing the expansion and contraction in the axial direction generated when the pressure roller thermally expands, regardless of the thermal expansion of the pressure roller itself. Since it can be kept constant, even in a film material that slides and moves on a heating element and a pressure roller sandwiching the film material, for example, in an on-demand type fixing device, the increase in the diameter of the pressure roller due to thermal expansion And the transfer speed of the transfer material can always be maintained at a constant speed without depending on the thermal expansion of the pressure roller. Therefore, as a result, various problems caused by this which could not be completely prevented conventionally, that is, 1. 1. Transfer failure caused by the transfer material being pulled, 2. A pitch blurring image that appears when the vibration of the drive system is transmitted to the transfer process; The transfer material was pulled by the pressure roller at the moment when the rear end of the transfer material came off the registration roller, and the transfer blurring caused by the rapid change in speed could be eliminated.

Further, the speed adjusting means changes the number of rotations of the pressure roller in accordance with a change in the longitudinal dimension of the pressure roller. According to this configuration, according to the expansion and contraction of the pressing roller in the axial direction caused by the thermal expansion,
By changing the number of rotations of the pressure roller so as to offset the expansion of the diameter, the transfer speed of the transfer material can be kept constant.

The speed adjusting means changes the pressing force of the pressure roller by operating in response to a change in the longitudinal dimension of the pressure roller. According to this configuration, according to the expansion and contraction in the axial direction caused by the thermal expansion,
For example, by changing the nip of the pressure roller, such as changing the position of the bearing in the height direction, the rotation of the roller in conjunction with the extension of the core metal of the pressure roller in the axial direction due to the thermal expansion of the pressure roller The number can be reduced, and the transfer speed of the transfer material can be kept constant regardless of thermal expansion.

Further, the speed adjusting means includes a fixed pulley member rotatably disposed at a predetermined position on the axis of the pressure roller so as not to be movable in the axial direction, and a pressure roller fixed on the pressure roller axis. A movable pulley member that rotates integrally with the fixed pulley member and the movable pulley member. A facing surface of the movable pulley member is formed with a tapered rotating surface. This is a V-belt type continuously variable transmission system in which a V-belt for driving transmission is suspended. According to this configuration, the rotational speed can be automatically reduced by an amount corresponding to the expansion of the pressure roller by the mechanical speed adjusting means based on the V-belt type continuously variable transmission system, thereby offsetting the influence of heat of the fixing device. This makes it possible to suppress fluctuations in the transfer speed of the transfer material. In particular, the object can be solved without adding a servo circuit, and a great effect can be obtained without increasing the cost.

The structure of an image forming apparatus for realizing the object of the present invention is such that one of the above-described fixing devices is provided in an image fixing section.

[0032]

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

<First Embodiment> FIGS. 1, 2 and 3 show a first embodiment of the present invention.

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.

Since the configuration is the same as that of the conventional copy machine using a transfer table using a transfer type electrophotographic process, the description of the configuration of the main body is omitted.

In the present embodiment, unlike the conventional example, the driving from the driving means M is performed by the V-belt 4 on the way to the pressing roller 1.
Speed adjusting means by a V-belt type continuously variable transmission system transmitted to the vehicle.

The pressure roller 1 has a structure in which an elastic layer of silicon rubber is provided on a cored bar, and a composite resin layer in which a fluorine resin or a mixture of a PFA resin and a PTFE resin is provided as a releasable surface layer outside the elastic layer. Therefore, when the temperature is increased by heating, the outer diameter expands and increases.

Accordingly, the transfer speed of the transfer material P increases with the expansion. In the experiment, when the pressure roller diameter was φ16 mm and the temperature control temperature of the heater was 180 ° C. to 200 ° C. and continuous copying was performed, the transfer speed of the transfer material P by the pressure roller 1 was about 1 due to the expansion of the outer diameter. .5% increase.

FIG. 2 is a perspective view of the V-belt type speed adjusting means provided on the pressure roller as viewed from the drive system side.

In FIG. 2, reference numeral 5 denotes a bearing for rotatably holding the pressure roller 1 with respect to a main body (not shown).

Reference numerals 2 and 3 denote a fixed pulley member and a movable pulley member for transmitting the drive of the V-belt 4, respectively. Both pulley members constitute one pulley. Fixed pulley member 2
The movable pulley member 3 and the movable pulley member 3 are disposed so as to oppose the inner tapered portion, and are coaxially disposed with respect to the metal core extending to the end of the pressure roller 1, and are separately installed. The thrust position of the fixed pulley member 2 is fixed to the main body by a thrust positioning member 6 fixed to the main body.

On the other hand, the movable pulley member 3 is disposed on the metal core of the pressure roller 1, and is positioned in the thrust direction with respect to the metal core by two kings (not shown).

Therefore, when the core of the pressure roller 1 expands due to expansion, the movable pulley member 3 moves in the thrust direction in conjunction therewith, and the distance to the fixed pulley 2 changes. That is, the inner diameter formed by the tapered surfaces of the two members changes.

In FIG. 3, the elongation of the pressure roller 1 due to the thermal expansion of the metal core and the number of rotations of the pulleys 2 and 3 by the V-belt 4 will be described in detail.

FIG. 3A shows that the inside of the machine main body is in a normal temperature state (20
(° C).

As described above, the fixed pulley member 2 positioned by the thrust determining member 6 integrated with the main body.
The V-belt 4 is driven by the two pulley members 2, 3 and the movable pulley member 3 positioned on the axis of the pressure roller 1.

The cross section and the thrust interval of both pulley members 2 and 3 are set to 1.2 mm as shown in FIG.
The pulley pitch diameter at normal temperature is φ23.65 mm.

FIG. 3B shows that the pressure roller 1 has a temperature of about 180 ° C.
Shows the state where the temperature was raised.

The thrust of the pressing roller 1 is determined on the side opposite to the driving side. The movable pulley member 3 is arranged at a position 261 mm from that position.

The core of the pressure roller 1 is made of hard steel and has a coefficient of linear thermal expansion of about 0.0000107 / ° C., so that it extends about 0.5 mm from the state shown in FIG. Therefore, only the movable pulley member 3 moves to the left in the figure integrally with the extension of the cored bar, and the distance between the fixed pulley 2 and the movable pulley 3 becomes 1.7 mm.

As a result, the hooking depth of the V-belt 4 with respect to the pulley changes, and the actual pulley pitch circle diameter becomes φ2.
It will be 3.3. Therefore, while being driven by the same motor at the same speed, the number of rotations of the pressure roller is substantially reduced by about 1.5%.

The rotational speed can be automatically reduced by the amount corresponding to the expansion of the pressure roller diameter by the mechanical speed adjusting means based on the V-belt type continuously variable transmission system which operates as described above. As a result, the influence of the heat of the fixing device is offset, and the fluctuation of the transport speed of the transfer material P can be suppressed.

In particular, according to the present embodiment, the object can be solved without adding a servo circuit, so that a great effect can be obtained without increasing the cost.

<Second Embodiment> As means for reducing the number of rotations by the expansion of the diameter of the pressure roller 1, FIG.
The configuration shown in FIG.

That is, a motor 11 for exclusively driving the pressure roller 1 is provided, and a control circuit 10 for operating the motor 11 is provided.

The control circuit 10 has an expansion detecting means for detecting the expansion of the pressure roller 1.

The expansion detecting means is configured as shown in the circuit diagram of FIG. 4. A plate-like member is used as the resistance member 9 and can be configured in the same manner as a general slide type variable resistor. It is.

A rotating body 7 having a tapered rotating surface is attached to the shaft end of the pressure roller 1, and one end of a substantially L-shaped arm member 16 is slidably contacted with the rotating surface. The slide member 8 provided at the other end of the arm member 16 is slidably brought into contact with the resistance member 9.

Therefore, as shown in FIG. 4B, the contact position of the slide member 8 with respect to the resistance member 9 changes while the arm member 16 is tilted with the expansion of the pressure roller 1, so that the measurement device 14 detects the position. The current applied changes.

The current value information is input to the control circuit 10, based on which the control circuit 10 controls the rotation speed so as to offset the increase in the transport speed due to the expansion of the pressure roller 1 and drives the motor 11. Is to be done.

With the above configuration, even if the pressure roller 1 expands, the transfer speed of the transfer material P can be kept constant.

<Third Embodiment> FIGS. 5 and 6 show a third embodiment.

The method for keeping the transfer speed of the transfer material P by the pressure roller 1 constant irrespective of the thermal expansion is not limited to controlling the number of rotations.

This can also be achieved by changing the center position of the pressure roller 1 and changing the pressing force between the heating member and the pressure roller 1 acting on the film material.

FIG. 5 shows a structure as a means for changing the center position of the pressure roller 1.

A positioning cam 12 is rotatably arranged below the pressure roller 1, and the cam surface of the positioning cam 12 comes into contact with the bearing 5 that supports the pressure roller 1,
The position of contact with the bearing 5, that is, the height of the pressure roller 1 can be determined to a predetermined position in accordance with the rotation of.

The positioning cam 12 extends in the longitudinal direction of the pressure roller 1, has a shaft rotatably supported by a main body (not shown), and supports the two bearings 5 in a similar state. .

The positioning cam 12 is adapted to move in conjunction with the rotation of a lever 13. The lever 13 rotates about an axis projecting from the main body, and a tension spring 15 as an elastic member. Thus, the pressure roller 1 is always urged to abut against the end face of the core metal.

Thus, the core of the pressure roller 1 is rotated in conjunction with expansion and contraction due to thermal expansion.

With the above arrangement, when the temperature inside the apparatus rises during copying and the pressure roller 1 expands, the core metal extends, and the lever 13 rotates with the rotation, whereby the positioning cam 12 rotates.

Along with this, the height of the pressure roller 1 is reduced by a small amount, and the pressing force with the heating element is reduced, so that the transfer speed of the transfer material P per rotation is reduced so as to offset the expansion. . Therefore, the transport speed of the transfer material P during the copying operation is eventually maintained to be constant.

[0072]

According to the first and fifth aspects of the present invention, the thermal expansion can be achieved even in an on-demand type fixing device having a film material which slides and moves on a heating element and a pressure roller sandwiching the film material. By acting to offset the increase in the diameter of the pressure roller caused by the pressure roller, the transfer paper transport speed can always be maintained at a constant speed without depending on the thermal expansion of the pressure roller. Therefore, as a result, various problems caused by this which could not be completely prevented conventionally, that is, 1. 1. Transfer failure caused by the transfer material being pulled, 2. The vibration of the drive system is transmitted to the transfer process, and a pitch blurring image appears. The transfer material was pulled by the pressure roller 1 at the moment when the rear end of the transfer material came off the registration roller, and the transfer blurring caused by the rapid change in speed could be eliminated.

According to the second and fifth aspects of the present invention, the number of rotations of the pressure roller is offset by the expansion of the diameter in accordance with the axial expansion and contraction of the pressure roller caused by the thermal expansion. , The transfer speed of the transfer material can be kept constant.

According to the third and fifth aspects of the present invention, the nip of the pressure roller is changed, for example, by changing the position of the bearing in the height direction according to the axial expansion and contraction caused by the thermal expansion. By changing it, the number of rotations of the roller can be reduced in conjunction with the elongation of the core metal of the pressure roller in the axial direction accompanying the thermal expansion of the pressure roller, and the transfer speed of the transfer material is always constant regardless of the thermal expansion. Can be constant.

According to the fourth and fifth aspects of the present invention, the mechanical speed adjusting means based on the V-belt type continuously variable transmission system
The number of rotations can be automatically reduced by an amount corresponding to the expansion of the pressure roller diameter, thereby canceling out the influence of heat of the fixing device and suppressing the fluctuation of the transfer speed of the transfer material. In particular, the object can be solved without adding a servo circuit, and a great effect can be obtained without increasing the cost.

[Brief description of the drawings]

FIG. 1 is a main cross-sectional view of a first embodiment of the present invention according to the present application.

FIG. 2 is a perspective view of a first embodiment of the invention according to the present application.

FIGS. 3A and 3B show the operation of the first embodiment of the present invention, in which FIG. 3A is a cross-sectional view showing the pulley portion when the inside of the machine body is at room temperature (20 ° C.), and FIG. Sectional view showing a state where the pressure roller is heated to about 180 ° C.

FIGS. 4A and 4B show an operation description of a second embodiment of the invention according to the present application, in which FIG. 4A is a cross-sectional view showing the pulley portion when the inside of the machine body is at room temperature (20 ° C.), and FIG. Sectional view showing a state where the pressure roller is heated to about 180 ° C.

FIG. 5 is an operation explanatory diagram of a third embodiment of the invention according to the present application.

FIG. 6 is an operation explanatory diagram of a third embodiment of the invention according to the present application.

FIG. 7 is a sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pressurizing roller 2 ... Fixed pulley member 3 ... Movable pulley member 4 ... V belt 5 ... Bearing 6 ... Thrust determining member 7 ... Umbrella wheel 8 ... Slide member 9 ... Resistance member 10 ... Control circuit 11 ... Motor 12 ... Positioning cam 13 Lever 14 Measuring device 15 Tension spring 16 Arm member

Claims (6)

[Claims] A heating member fixedly held; a film member slidingly moved on the heating member; a pressure roller forming a heating nip with the heating member with the film member interposed therebetween;
A fixing member that presses a heating element holding member that holds and holds the heating element toward a pressure roller side, and that drives the film material to move by rotating the pressure roller, and heats the transfer material while nipping and transporting the transfer material. The fixing device according to claim 1, further comprising a speed adjusting unit configured to cancel a change in a conveying speed due to an increase or a decrease in the diameter of the pressure roller due to thermal expansion in synchronization with an axial expansion and contraction generated by thermal expansion of the pressure roller. apparatus. 2. The fixing device according to claim 1, wherein the speed adjusting unit changes the number of rotations of the pressure roller in accordance with a change in a longitudinal dimension of the pressure roller. 3. The fixing device according to claim 1, wherein the speed adjusting unit changes the pressing force of the pressure roller by operating in response to a change in the longitudinal dimension of the pressure roller. 4. The pressure adjusting means comprises: a fixed pulley member rotatably disposed at a predetermined position on the axis of the pressure roller so as to be axially immovable; and a pressure roller fixed on the pressure roller axis. A movable pulley member that rotates integrally with the fixed pulley member and the movable pulley member. A facing surface of the movable pulley member is formed with a tapered rotating surface. 4. The fixing device according to claim 1, wherein a V-belt type continuously variable transmission system in which a V-belt for driving transmission is suspended. 5. The fixing device according to claim 1, wherein the speed adjusting unit changes the number of rotations of the pressure roller by electrical control. 6. An image forming apparatus, comprising the fixing device according to claim 1, provided in a fixing unit for fixing an image.