JPH0816023A - Fixing apparatus - Google Patents

Abstract

PURPOSE:To prevent an image quality from degrading and an image from being blurred on an image forming medium with a simple system and keep good speed controllability without difficulty by installing a contact pressure adjusting means to decrease and adjust the contact pressure between a pair of rotary bodies only for a prescribed period at the time when the tip part of the image forming medium reaches a contact region of the pair of the rotary bodies. CONSTITUTION:A fixing apparatus 50 has a contact pressure controlling means 70 and a reflection-type sensor; the means 70 shifts a pressing roller 59 toward the direction shown as an arrow alpha, that is, the direction toward which the pressing roller 59 is parted from a fixing roller 57 in order to decrease and adjust the contact pressure against the fixing roller 57 and the reflection-type sensor emits light and receives light, for example, and detects the tip part of a paper sheet conveyed in a conveying route in the conveying direction. The sensor is put at a position immediate before the pressing roller 59 in the conveying route. When the tip of a conveyed paper sheet is detected by the sensor, the sensor sends a detection signal to indicate the existence of the paper sheet of a control part. Consequently, the contact pressure of the pressing roller 59 to the fixing roller 57 is temporarily decreased and adjusted, so that the paper sheet moves forward smoothly after the tip of the paper sheet is pinched between both rollers 59, 57.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electronic copying machine or the like.

[0002]

2. Description of the Related Art A copying machine 20 including a conventional fixing device 250.
0 will be described with reference to FIG.

In this copying machine 200, as shown in FIG. 14, by moving the document table 201, the document placed on the document table 201 is exposed and scanned by the light source 202. In this case, the light source 202 emits light. Of the reflected light, the light reflected by the document is reflected by the mirrors 203a, 203b, 203.
After passing through c, it reaches the lens 204 and is reflected by the mirror 205 to form an image on the surface of the photosensitive drum 206.

Since the photosensitive drum 206 starts rotating at a predetermined timing with respect to the start of movement of the original table 201, an electrostatic latent image corresponding to the original image is formed on the surface thereof, and this electrostatic latent image is formed. When passing through the developing unit 207, toner is attached and visualized.

On the other hand, the paper P fed from the paper feed cassette 208 is stopped once it is inserted into the registration roller 209, but the registration roller 209 rotates after a lapse of a predetermined time from the start of rotation of the photosensitive drum 206. By starting, the paper P inserted in the photosensitive drum 2
The toner image on the surface of the photosensitive drum 206 is transferred to the paper P by passing through the transfer unit 210 near the surface of 06.

The sheet P on which the toner image is transferred is separated by the separating claw 2.
11 is peeled off from the photosensitive drum 206, and the guide 2
It is guided by 12 and is conveyed by the conveying force of the registration rollers 209.

Then, the paper P passes between the heating fixing roller 213 and the pressure roller 214 which are in contact with each other at a predetermined pressure of the fixing device 250, and the toner image is fixed on the paper P there. After that, the paper P is discharged from the discharge roller 21.
6 is ejected to a paper ejection tray 217 (Japanese Patent Laid-Open No. 63-
88569).

When such a fixing device 250 is used,
Since the paper P is fixed by heating and pressing by the fixing roller 213 and the pressure roller 214, as shown in FIG. 15, the leading end of the paper P is the fixing roller 213 and the pressure roller 21.
When the sheet P is sandwiched between the sheets 4, the sheet P is impacted, and the impact is transmitted to the transfer section 210, which may cause image blur (transfer deviation).
6, the registration roller 209, the fixing roller 213 and the like are connected to the main motor via a clutch to reduce the conveyance speed of the paper P before and after the leading edge of the paper P passes through the fixing roller 213, and to fix the fixing roller 213 and the pressure roller. The shock when passing through 214 is mitigated to prevent image blurring.

[0009]

However, in the above-mentioned conventional apparatus, since the transfer speed of the paper P is changed, the copy speed is lowered, and the high speed change during the transfer of the paper P causes the paper P to be bent or misaligned. As a result, there is a possibility that an image may be defective in the transfer process.

Further, in the conventional apparatus, when the rotation speed of the photosensitive drum 206 and the conveying speed of the paper P are reduced, the exposure condition of the light reflected on the original on the surface of the photosensitive drum 206 is the same, and therefore, There is a problem that the amount of light on the exposed portion of the surface of the photosensitive drum 206 is increased and the image quality of the formed electrostatic latent image is deteriorated.

Further, in the conventional apparatus, the impact cannot be alleviated unless the conveyance speed reaches a certain level. Therefore, although it is effective for a low speed machine, the speed difference becomes large for a high speed machine, and speed control becomes difficult. There was also.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fixing device which can prevent deterioration of image quality and image blur on an image forming medium with a simple structure without causing difficulty in speed control.

[0013]

According to a first aspect of the present invention, there is provided a fixing device including a pair of rotating bodies which fix a developer adhering to an image forming medium which comes into contact with a predetermined pressure and passes through the contact area.
And a contact pressure adjusting means for reducing the contact pressure between the pair of rotating bodies for a predetermined time when the tip of the image forming medium reaches the contact area of the pair of rotating bodies.

According to a second aspect of the present invention, there is provided a fixing device, a fixing roller and a pressing roller which fix the developer adhering to the image forming medium which comes into contact with a predetermined pressure and passes through the contact area, and the fixing roller and the pressing roller. And a contact pressure adjusting means for reducing the contact pressure of the pressure roller to the fixing roller for a predetermined time when the front end of the image forming medium reaches the contact area of the pressure roller.

According to a third aspect of the present invention, there is provided a fixing device, a fixing roller and a pressure roller for fixing the developer adhering to the image forming medium passing through the contact area at a predetermined pressure, the fixing roller and the pressing roller. Detection means for detecting the tip position of the image forming medium conveyed toward the contact area of the pressure roller;
Based on the detection result of the presence of the image forming medium by the detecting means, at least the tip of the image forming medium reaches 3 m from the time when the tip of the image forming medium reaches the contact area of the fixing roller and the pressure roller.
There is provided a contact pressure adjusting means for displacing the pressure roller 1 in the direction away from the fixing roller only for the time of entering the m contact area to reduce the contact pressure to the fixing roller.

[0016]

The function of the present invention will be described below.

According to the fixing device of the first aspect, when the tip of the image forming medium reaches the contact region of the pair of rotating bodies which are in contact with each other at a predetermined pressure, the contact pressure adjusting means rotates the pair of rotating members. Since the contact pressure between the bodies is adjusted only for a predetermined time, the leading edge of the image forming medium can enter the contact area of the pair of rotating bodies without being impacted, which allows the image forming medium to move smoothly during the fixing operation. Therefore, it is possible to prevent deterioration of image quality and image blurring on the image forming medium. Further, there is no need to temporarily drive the pair of rotating bodies at a low speed, and the difficulty of speed control does not occur.

According to the fixing device of the second aspect, when the front end of the image forming medium reaches the contact area of the fixing roller and the pressure roller which are in contact with each other at a predetermined pressure, the contact pressure adjusting means applies the pressure. Since the contact pressure of the pressure roller 1 with respect to the fixing roller is reduced for only a predetermined time, the leading edge of the image forming medium can enter the contact area of the fixing roller and the pressure roller without being impacted, thereby fixing the image forming medium. Movement during operation becomes smooth, and deterioration of image quality and image blur on the image forming medium can be prevented. Further, it is not necessary to temporarily drive the fixing roller and the pressure roller at a low speed, and the difficulty of speed control does not occur.

According to the fixing device of the third aspect, the detecting means detects the leading end position of the image forming medium conveyed toward the contact area of the fixing roller and the pressure roller, and the image forming by the detecting means. Based on the detection result of the presence of the medium, the contact pressure adjusting means applies the addition only for the time when the tip of the image forming medium reaches the contact area of the fixing roller and the pressure roller at least from the time when the tip reaches the contact area of 3 mm. Since the pressure roller 1 is displaced in the direction away from the fixing roller to reduce the contact pressure to the fixing roller, the leading edge of the image forming medium can enter the contact area of the fixing roller and the pressure roller without being impacted. The movement of the image forming medium during the fixing operation becomes smooth, and the deterioration of the image quality and the image blurring on the image forming medium can be prevented. Further, it is not necessary to temporarily drive the fixing roller and the pressure roller at a low speed, and the difficulty of speed control does not occur.

[0020]

EXAMPLES Examples of the present invention will be described in detail below.

A copying machine 1 including a fixing device 50 of the present embodiment shown in FIG. 1 has a drum-shaped photosensitive member 103 in a substantially central portion of a copying machine main body 1A (hereinafter referred to as main body 1A) in a direction indicated by an arrow a. It is rotatably installed.

The photoconductor 103 has a photoconductive layer on its surface. The following devices are arranged around the photoconductor 103 along the rotation direction thereof.

That is, a charging charger 105 as a charging means for uniformly charging the surface of the photoconductor 103 and a light source of an original image on the charged photoconductor 103 above the charging charger 105 on the downstream side in the rotation direction of the photoconductor 103. As a result, a slit glass 107 for slit exposure is provided. Further, a developing device 109 as a developing means for adhering the toner 110 to the electrostatic latent image on the photoconductor 103 to perform development is installed on the downstream side of the slit glass 107. A toner 110 in which a carrier is mixed as an agent is stored.

Further, in the developing device 109, the stirring roller 2 which stirs the developer by the rotation of the roller and frictionally charges the developer.
A supply roller 22 that supplies the developer agitated by the first and agitating rollers 21 to a developing roller 23 described below is provided. Further, in the developing device 109, the developing roller 23 in which the S poles and the N poles are alternately arranged inside along the rotation direction thereof.
Is provided rotatably in the direction of the arrow e in the figure in a state of approaching the photoconductor 103.

On the downstream side of the developing device 109, a transfer device 111 and a peeling device 113 as a transfer means are provided.

The transfer device 111 transfers the toner image formed by the developing device 109 to an image forming medium (hereinafter referred to as "paper P").
Say. The peeling device 113 is a device that peels the sheet P adsorbed on the surface of the photoconductor 103 by the transfer device 111 from the surface of the photoconductor 103.

On the downstream side of the peeling device 113, the photoconductor 10 is provided.
Of the toner 110 attached to the surface of No. 3, the transfer device 11
A cleaning device 115 that removes the toner 110 remaining on the photoconductor 103 after the transfer is performed by the method described in No. 1 is provided. Between the cleaning device 115 and the charging device 105, a static eliminator 117 for removing the residual potential of the photoconductor 103 is provided.

Further, the main body 1A has an original glass 119 on which an original is placed and an optical system 121 which guides the original on the original glass 119 to light and guides the reflected light onto the surface of the photoconductor 103. .

The optical system 121 is an exposure lamp (hereinafter referred to as “lamp”) 123 which serves as a light source of the exposure scanning means and a mirror 12 for reflecting light emitted from the lamp 123.
4, 125, 127, 129, 131, 133 and a lens unit 135 for forming an image of reflected light.

The lamp 123 and the mirror 124 which constitute the first carriage of the exposure scanning means are provided with the original glass 119.
The mirror 125 and the mirror 127, which form the second carriage of the scanning means, move at a speed half the speed of the lamp 123 in order to keep the optical path length constant. It is like this. The mirror 1
The reflected light from 33 is configured to pass through the slit glass 107 and be guided to the surface of the photoconductor 103.

In the middle of the right side of the main body 1A, the paper P
A paper feed cassette 141 for accommodating the paper feed cassette is detachably provided, and a pickup roller 143 for pulling out the paper stored in the paper feed cassette 141 is provided above the front end of the paper feed cassette 141 in the main body 1A. . A manual feed guide for receiving a manual feed paper is provided on the upper surface cover of the paper feed cassette 141.

Further, on the left side of the main body 1A, a paper discharge tray 171 for discharging the copied paper P is provided. A conveyance path of the paper P, that is, a conveyance path 142 is formed between the paper feed cassette 141 and the paper discharge tray 171, and the conveyance path 142 is shown by a dotted line in FIG.

Upstream of the conveying path 142, two pairs of first and second rollers are attached to the main body 1A. First
The roller pair is adjacent to the paper feed cassette 141 and is composed of two rollers, a paper feed roller 145 and a separation roller 147.

The paper feed roller 145 is rotatable in the direction of the arrow f in the figure, and is a roller for feeding the paper P drawn by the pickup roller 143 to the second roller pair by the rotation of the rollers. The separation roller 147 is provided below the paper feed roller 145 so as to be in contact therewith, and when the number of sheets P sent from the pickup roller 143 is two or more, the separation roller 147 rotates in a direction opposite to the rotation direction of the paper feed roller 145. Then, the excess paper P is pulled back to the paper feed cassette 141. When the number of sheets P sent from the pickup roller 143 is one, the separation roller 147 is rotated by the rotation of the sheet feeding roller 145. The second roller pair is a registration roller 149 composed of an upper roller and a lower roller. The registration roller 149 aligns the paper P by hitting the leading edge of the paper P sent from the paper feed roller 145, and then aligns the paper P with the photoconductor 103 between the photoconductor 103 and the transfer device 111. Send it in synchronization with the toner image above.

At the tip of the peeling device 113, a belt-shaped belt for carrying the paper P, that is, a carrying belt 151 is provided.

Further, on the downstream side of the conveying path 142, the fixing device 50 of the present embodiment for fixing the toner 110 on the paper P by heating and pressing the toner 110 is arranged.

The fixing device 50 has a fixing roller (heat roller) 57 and a pressure roller 59 as a pair of rotating bodies which are rotatable in the directions indicated by arrows c and d, respectively. The fixing roller 57 has a built-in heat lamp 55, which is a heating body, and is partially pressure-bonded to the pressure roller 59 with a predetermined contact pressure.

In the fixing device 50, the pressure roller 59 is further separated from the fixing roller 57, that is, in FIG.
For example, as a contact pressure adjusting means 70 for displacing the contact pressure on the fixing roller 57 by displacing in the direction of the arrow α and a detecting means for detecting the leading end of the sheet P conveyed on the conveying path 142 in the conveying direction. It has a reflection type sensor 60 for emitting and receiving light. The sensor 60 is arranged at a position immediately before the pressure roller 59 in the transport path 142.

Here, the contact pressure adjusting means 70 is shown in FIG.
It will be described with reference to FIGS.

The contact pressure adjusting means 70 is used in the fixing device 50.
A pair of rotation support plates 72 is attached to each inner surface side of the both side plates 71 provided in the above, and a shaft body 72b protruding from one end of the pair of rotation support plates 72 is fitted to the both side plates 71. The pair of rotation support plates 72 are supported so as to be rotatable in the direction of arrow α.

A shaft portion 59a protruding from the end surface of the pressure roller 59 is engaged with a recess 72a provided in the pair of rotation support plates 72 to rotatably support the pressure roller 59. There is.

Further, coil springs 73 are attached between the other ends of the pair of rotation support plates 72 and the upper inner walls of the other ends of the both side plates 71, and the pair of rotation support plates 72 and the pressing force are applied. By urging the roller 59 in the direction of arrow β, the pressure roller 59 is pressed against the fixing roller 57 with a predetermined contact pressure to form a contact area between the pressure roller 59 and the fixing roller 57.

Further, the contact pressure adjusting means 70 is the same as that shown in FIGS.
As shown in FIG. 7, a connecting body 74 that connects the other ends of the pair of rotation support plates 72, and a cam (plate cam) 75 having an arc-shaped contour curve arranged in the vicinity of the substantially central portion of the connecting body 74. , And a pulse motor 76 for rotating the cam 75.

As for the shape of the cam 75, in addition to the shape of the cam 75 shown in FIG. 4 that reaches the maximum displacement point only once in one rotation, as shown in FIG. 5, the maximum displacement point is reached twice in one rotation. It is also possible to use the cam 75A having a shape to reach, or, although not shown, a cam having a shape to reach the maximum displacement point of 4 degrees in one rotation.

Further, downstream of the conveying path 142, the paper discharge roller 1 for discharging the paper P to the paper discharge tray 171.
61 is provided.

FIG. 6 shows a control system for the sensor 60 and the contact pressure adjusting means 70 in the fixing device 50. The sensor 60 is controlled by a control unit 80 which performs a control operation.
While controlling the pulse motor 76, the leading edge of the sheet P reaches the contact area between the pressure roller 59 and the fixing roller 57 based on the detection result of the leading edge of the sheet P by the sensor 60 in the control unit 80. A calculation means 81 for calculating time is connected.

The copying process by the above-mentioned copying machine is as follows.

First, the surface of the photoconductor 103 is uniformly charged by the corona discharge of the charging charger 105. Next, the lamp 123 in the optical system 121 scans under the original glass 119 on which the original is placed, and the original is irradiated with light. When scanning is performed by the lamp 123, the lamp 12
The light emitted from 3 is reflected, and the reflected light is guided to the lens unit 135. The reflected light is inverted by the lens unit 135 and is exposed on the charged photoconductor 103 through the slit glass 107. When the light is exposed,
The charge on the surface of the photoconductor 103 is lost and an electrostatic latent image is formed.

In the developing device 109, the toner 110 and the carrier which are agitated by the agitating roller 21 and frictionally charged are sent to the developing roller 23 by the supply roller 22.

The toner 110 and the carrier sent to the developing roller 23 form a magnetic brush by the lines of magnetic force formed between the S pole and the N pole inside the developing roller 23. The carrier is always attracted by the magnetism of the developing roller 23, and the toner 110 is electrically attracted to this carrier.

When the developing roller 23 and the photoconductor 103 rotate and the magnetic brush and the electrostatic latent image on the photoconductor 103 come close to each other, the toner 110 becomes a carrier by the stronger electrostatic attraction of the electrostatic latent image. Away from and stick to the electrostatic latent image.
The toner 110 attached to the electrostatic latent image forms a toner image. Further, at the time of development, a developing bias is applied to the developing roller 23 and the photoconductor 103 by a voltage device (not shown) to prevent unnecessary toner 110 from adhering to the photoconductor 103.

On the other hand, the paper P stored in the paper feed cassette 141 is pulled out by the pickup roller 143, and the paper feed roller 145 is extracted from the pulled out paper P.
By the rotation of the separation roller 147, only one sheet P is sent to the registration roller 149. Registration roller 14
After aligning the front end of the paper P, the paper 9 is fed between the photoconductor 103 and the transfer device 111, and the photoconductor 1
It is superimposed on the electrostatic latent image of 03. The toner image is formed on the back side of the fed paper P by the action of the transfer device 111.
The sheet P on which the toner image is thus transferred, which is transferred onto a sheet of paper, is peeled from the surface of the photoconductor 103 by the peeling device 113, is conveyed on the conveyance belt 151, and is fixed to the fixing roller 57 of the fixing device 50. It enters the contact area with the pressure roller 59.

In the fixing device 50, the fixing roller 57 and the pressure roller 59, which are heated by the heat lamp 55 built in advance, rotate in their respective rotation directions while partially pressure-bonding.

When the fixing roller 57 and the pressure roller 59 are rotated, the toner image is transferred onto the paper P by passing the paper P through the contact area between the rollers 57 and 59 so that the toner image is on the fixing roller 57 side. It is fixed. That is, the heat of the fixing roller 57 melts the toner 110, the pressure of the pressure roller 59 enhances the heat conduction efficiency, and the toner 110 is made to soak between the fibers of the paper P.

The paper P on which a copy image is formed through the above-described process is discharged through the paper discharge roller 161 to the paper discharge tray 171.
Is discharged to

During the fixing operation by the above-described fixing device 50, the leading edge of the paper P conveyed on the conveyor belt 151 is detected by the sensor 60, and the sensor 60 sends a detection signal indicating the presence of the paper P to the controller 80. . Under the control of the control unit 80, the calculation unit 81 calculates the time for the leading edge of the paper P to reach the contact area between the pressure roller 59 and the fixing roller 57, and sends the result to the control unit 80. As a result, the pulse motor 76 is controlled under the control of the control unit 80.
However, when the front end of the paper P reaches the contact area between the pressure roller 59 and the fixing roller 57, the cam 75 is moved to the position shown in FIG.
One turn is made to the arrow δ shown in FIG. 3 (the shape of the cam 75 is
In the case of the shape shown in FIG. 2), the connecting body 74 and the rotation supporting plate 72 are smoothly changed in the direction of the arrow α, and then the connecting body 74 and the rotation supporting plate 72 are smoothly returned to their original positions.

As a result, the pressure roller 59 supported by the rotary support plate 72 is temporarily moved in the direction of the arrow α when the leading edge of the paper P reaches the contact area between the pressure roller 59 and the fixing roller 57. To the fixing roller 57 as shown in FIG.
The initial axial distance L0 as shown on the left side is set to a larger axial distance L1 as shown on the right side in FIG. 7, and then the original axial distance L0 is restored.

The relationship between the operation of the sensor 60 and the change in contact pressure between the fixing roller 57 and the pressure roller 59 at this time is shown in FIGS.

FIG. 8 shows the case where the paper P is A3 size.
Shows the case where the paper P is A4 size.

As is apparent from FIGS. 8 and 9, the contact pressure between the pressure roller 59 and the fixing roller 57 is such that the leading edge of the paper P is the pressure roller 59 and the fixing roller 5 from the normal pressure P0.
From the time of reaching the contact area with 7, the pressure gradually decreases only to the time t1 to reach the lowest pressure P1, and further gradually increases to return to the normal pressure P0.

The fixing roller 5 of such a pressure roller 59
After the leading edge of the paper P is sandwiched in the contact area between the pressure roller 59 and the fixing roller 57 by temporarily reducing the contact pressure with respect to 7, the impact may be caused within 3 mm from the tip. In this case, unlike the conventional example, the image quality of the image formed on the sheet P and the image blur of the sheet P can be prevented. In addition, the pressure roller 5
9. It is not necessary to temporarily drive the fixing roller 57 and the like at a low speed, and the difficulty of speed control does not occur.

Although the fixing performance is lowered within a range of 3 mm from the front end of the paper P, it is rare that characters are printed on the front end, and the normal paper P is peeled off. Since a blank is provided at the tip and processing can be performed within this range, there is no problem in fixing performance.

In the above-described embodiment, the case where the sensor 60 is arranged immediately before the pressure roller 59 has been described. However, in addition to this, the position where the sensor 60 is arranged is such that the transfer device 111 and the peeling device 113 are provided near the conveyance path. It can be set to an arbitrary position of 142. In such a case, as shown in FIGS. 10 and 11, from the time when the sensor 60 detects the leading edge of the paper P, the pressure roller 59 and the fixing roller 57 are moved. The time t2 required to reach the contact area between them may be calculated by the calculating means 81 to control the drive of the pulse motor 76.

Further, it is of course possible to dispose the fixing roller 57 side by the contact pressure adjusting means 70.

Next, another example of the contact pressure adjusting means 70 is shown in FIG.
2, with reference to FIG.

The contact pressure adjusting means 70A shown in FIG. 12 employs, instead of the mechanism using the cam 75, a mechanism in which an electromagnetic solenoid 92 is arranged on the rotation support plate 72 via a buffer spring 91. is there.

Here, the buffer spring 91 is for buffering the shock of a momentary contact pressure change caused by the ON / OFF operation of the electromagnetic solenoid 92.

Further, the contact pressure adjusting means 70B shown in FIG.
Instead of the mechanism using the cam 75, the rotation support plate 7
2 to rack 93, pinion 94, drive motor 95
It adopts a mechanism that arranges.

Such contact pressure adjusting means 70A, 70B
Also, as in the case of the contact pressure adjusting means 70, after the leading edge of the paper P is sandwiched in the contact area between the fixing roller 57 and the pressure roller 59, the tip is impacted within 2 to 3 mm of the contact area. It is possible to smoothly enter without accompanying, and unlike the conventional example, it is possible to prevent deterioration of the image quality of the image formed on the paper P and image blurring of the paper P. Further, it is not necessary to temporarily drive the fixing roller 57, the pressure roller 59, etc. at a low speed, and the difficulty of speed control does not occur.

According to the fixing device 50 of this embodiment, a wide variety of models having any operation speed can be used.

[0071]

According to the present invention described above, the following effects can be obtained.

According to the first aspect of the present invention, the leading edge of the image forming medium can enter the contact area of the fixing roller and the pressure roller without being impacted, and the image forming medium moves smoothly during the fixing operation. It is possible to provide a fixing device that can prevent image quality deterioration and image blurring on an image forming medium, and that does not require a pair of rotating bodies to be temporarily driven at low speed and that speed control is difficult.

According to the second aspect of the invention, the tip of the image forming medium can enter the contact area of the fixing roller and the pressure roller without being impacted, and the movement of the image forming medium during the fixing operation becomes smooth. As a result, it is possible to provide a fixing device capable of preventing deterioration of image quality and image blurring on an image forming medium, and also eliminating the need to temporarily drive the fixing roller and the pressure roller at a low speed and the difficulty of speed control.

According to the third aspect of the present invention, the movement of the image forming medium during the fixing operation can be made smooth to prevent deterioration of image quality and image blurring on the image forming medium. It is possible to provide a fixing device that does not need to be driven at a low speed temporarily and does not cause difficulty in speed control.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a copying machine including an apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic front view of the device of this embodiment.

FIG. 3 is a schematic perspective view of the device of this embodiment.

FIG. 4 is a front view showing a cam of the apparatus of this embodiment.

FIG. 5 is a front view showing another example of the cam of the device of this embodiment.

FIG. 6 is a block diagram showing a control system of the apparatus of this embodiment.

FIG. 7 is an explanatory diagram showing the operation of the apparatus of this embodiment.

FIG. 8 is a timing chart showing the operation of the apparatus of this embodiment.

FIG. 9 is a timing chart showing the operation of the apparatus of this embodiment.

FIG. 10 is a timing chart showing another example of the operation of the device of this embodiment.

FIG. 11 is a timing chart showing another example of the operation of the device of this embodiment.

FIG. 12 is a schematic front view showing another example of the device of this embodiment.

FIG. 13 is a schematic front view showing another example of the device of this embodiment.

FIG. 14 is a schematic sectional view showing a conventional copying machine.

FIG. 15 is an explanatory diagram showing a fixing device of a conventional copying machine.

[Description of Reference Signs] 1 copier 50 fixing device 57 fixing device 59 pressure roller 60 sensor 70 contact pressure adjusting means

Claims (3)

[Claims] 1. A pair of rotating bodies for fixing a developer adhering to an image forming medium which comes into contact with a predetermined pressure and passes through the contact area, and a tip of the image forming medium in the contact area of the pair of rotating bodies. And a contact pressure adjusting means for reducing the contact pressure between the pair of rotating bodies for a predetermined period of time. 2. A fixing roller and a pressure roller for fixing the developer adhering to the image forming medium which comes into contact with a predetermined pressure and passes through the contact area, and an image in the contact area of the fixing roller and the pressure roller. And a contact pressure adjusting means for adjusting the contact pressure of the pressure roller to the fixing roller when the leading edge of the forming medium reaches for a predetermined time. 3. A fixing roller and a pressure roller for fixing a developer adhering to an image forming medium which comes into contact with a predetermined pressure and passes through the contact area, and a contact area of the fixing roller and the pressure roller. Detecting means for detecting the position of the leading edge of the image forming medium being conveyed, and the leading edge of the image forming medium reaches the contact area of the fixing roller and the pressure roller based on the detection result of the presence of the image forming medium by the detecting means. And a contact pressure adjusting means for displacing the pressure roller 1 in the direction away from the fixing roller and reducing the contact pressure to the fixing roller only at least during the time when the tip penetrates into the contact area of 3 mm. Fixing device.