JPH0527624A - Image forming device - Google Patents

Abstract

PURPOSE:To shut off a fixing device by operating a fixing device only at the time of the passing of a transfer material at the time of copying a color image, and stopping the operation always except on this time. CONSTITUTION:On transfer material carry-in and ejection guide plates 8A and 8B of the fixing device photosensors PS2 and PS3 are provided respectively and when color copy mode is selected, the fixing device is brought into an operating condition by operating a heat belt 1 and fans F1 and F2 only during a period of time from the time when the front end of the transfer material is detected by the photosensor PS2 and to the time when its rear end is detected by the photosensor PS3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus provided with a fixing device for fixing a toner image by moving a belt-shaped member.

[0002]

2. Description of the Related Art In the fixing process of toner images for electrophotography, heat roller fixing is the most common. In the recent electrophotographic process for handling color images, color reproducibility and glossiness of images after fixing are ensured and
It is required that the toner be sufficiently melted in order to ensure the transparency when the P transfer material is used. If the melting conditions of the polyester toner that is widely used are set to the above-mentioned level, it becomes necessary to apply a large amount of low-viscosity silicone oil as a release agent because of the problem of high temperature offset. There is.

When a large amount of silicone oil is used in this way, problems such as spillage of silicone oil and adhesion of silicone oil to a transfer material occur. In particular, when OHP is used, since the transfer material is not impregnated with silicon oil, the user's hands are soiled with silicon oil, or the permeability of OHP itself is significantly reduced. Due to this problem, a general polyester toner, that is, a wax-based toner is used, but it is difficult to obtain a sufficient molten state under the present circumstances. Further, as described above, color images are often required to have gloss after fixing. As a means in that case, in the range of the prior art, as described above, a large amount of a releasing agent is applied or a wax-based wax is used. When the above toner is used, an image once fixed is fixed again by the option unit.

As a fixing device satisfying such various fixing conditions, there has been proposed a fixing device of a type in which a transfer material on which a toner image is transferred is conveyed by a belt-like member to melt and fix the toner image.

The belt-shaped member controls the heating temperature of the transfer material during its conveyance by the cooling action of the fan in accordance with the fixing conditions, so that it corresponds to each type of color image, monochrome image or transfer material. The obtained image is fixed.

[0006]

However, such a fixing device is slightly larger than the heat roller fixing because of the electric power of the heater for heating, the conveyance of the belt-shaped member, the operation of the cooling fan, and the like. Power is required, there is concern about the durability of the members, and there is a problem in terms of energy saving.

The present invention solves this problem and improves the result.
An object of the present invention is to provide an image forming apparatus equipped with a fixing device which can reduce power consumption by suspending or lowering the operation of members except during the fixing operation.

[0008]

The above-mentioned object has a color copy mode and a monochrome copy mode, and uses a moving belt-like member to fix a toner image to a transfer member by heating / cooling means. In an image forming apparatus equipped with a device, the fixing device is continuously operated in the monochrome copy mode during continuous printing, and the operating member of the fixing device is stopped when the transfer material does not pass during color copying. To be done.

[0009]

1 is a sectional view showing an example of a color image forming apparatus according to the present invention. This image forming apparatus comprises an image reading system A, a laser writing system B, an image forming section C and the like.

An original table made of a transparent glass plate or the like is provided above the image forming apparatus, and an original D placed on the original table.
There is a document placing section 11 composed of a document cover or the like for covering the first mirror unit below the document table and inside the apparatus main body.
12, second mirror unit 13, main lens 20, color CCD 23
An image reading system A including the above is provided. The first mirror unit 12 is provided with an exposure lamp 14 and a first mirror 15, and is mounted parallel to the document table and linearly movable in the left-right direction in the drawing, and optically scans the entire surface of the document D. The second mirror unit 13 integrally includes a second mirror 16 and a third mirror 17, and linearly moves in the same direction in the left and right directions at a speed of 1/2 of that of the first mirror unit 12 so as to always maintain a predetermined optical path length. Of course, the movement of the second mirror unit 13 is parallel to the platen like the first mirror unit 12. The image of the document D on the document table illuminated by the exposure lamp 14 is converted by the main lens 20 into a first mirror 15, a second mirror 16,
An image is formed on the color CCD 23 through the third mirror 17. When the scanning is completed, the first mirror unit 12 and the second mirror unit 13 return to their original positions and wait for the next copy.

The image data of each color obtained by the color CCD 23 is image-processed and output from the laser writing system B as an image signal.

The image forming section C includes a charger 35, an image exposing section 55, which is arranged around the photosensitive drum 30 which is an image forming body.
Developing device 36Y, 36M, 36C, 36BK, transfer device 37, separator 38,
The cleaning device 39 and the photosensitive drum 30 are provided with a paper feed cassette 40, a conveyor belt 44, and a fixing device 45.

The developing devices 36Y, 36M, 36C and 36BK are provided with a developing device 36Y at the most upstream part of the peripheral edge of the photosensitive drum 30 and a developing device 36BK containing black toner BK at the most downstream part. Well-known color toners and black toners BK accommodated in the developing units 36Y, 36M, 36C, and 36BK are used, and thus description thereof will be omitted.

The image forming apparatus has two copy modes, that is, a color image copy mode and a monochrome image copy mode, and either copy mode is arbitrarily selected by operating a button provided outside the apparatus.

When the original D is a color image and the color copy mode is selected, the processes of the image reading system A, the laser writing system B and the image forming section C described above are activated by pressing the copy button. To form a color copy image. That is, the image signal from the image reading system A is controlled by the CPU of the control unit so that the drive motor 31 and the polygon mirror
When 32 is input to a laser writing system B including a semiconductor laser, an fθ lens, a correction lens, and the like (not shown), the copying operation is started. That is, the photosensitive drum 30 rotates clockwise as shown by the arrow, is uniformly charged by the charger 35, and the yellow (Y) image corresponding to the image of the document D is written in the image exposure unit 55. The electrostatic latent image of the Y image is formed by the laser beam from the laser writing system B. The electrostatic latent image on the photosensitive drum 30 is subjected to reversal development with the Y toner by the developing device 36Y to become a visible Y toner image. That is, a DC or further AC bias voltage is applied to the developing sleeve of the developing device 36Y having a built-in magnet roll, and non-contact development is performed by a two-component developer which is a developing means to form a Y toner image. . The photoconductor drum 30 on which the Y toner image is formed passes under the retracted cleaning device 39, and the photoconductor drum 30 is charged by the charger 35 and laser writing system B after the second rotation.
Laser beam writing of the magenta (M) image is performed, and an electrostatic latent image of the magenta (M) image is formed on the Y toner image. This latent image is subjected to reversal development by a developing device 36M containing magenta toner to form an M toner image. Subsequently, a cyan (C) toner image and a black (BK) toner image are similarly formed in an overlapping manner.

On the other hand, when the original D is a monochrome image or a color image and the monochrome copy mode is selected, the charger 35 uniformly applies an electric charge onto the photosensitive drum 30, and then the laser writing system. B is scanned by a monochrome laser beam to form a monochrome latent image. No bias voltage is applied to the developing devices 36Y, 36M, and 36C, and only the developing device 36BK operates to cause black toner BK. Only a toner image is formed.

Next, the transfer papers P fed out one by one by the paper feed roller 41 from the paper feed cassette 40 accommodating the transfer paper P as the transfer material are synchronized with the toner image on the photosensitive drum 30. It is delivered onto the photoconductor drum 30 by an operating timing roller 42. The toner image on the photosensitive drum 30 is transferred to the transfer paper P by the action of the transfer device 37.
After being separated from the photoconductor drum 30 by the separator 38, the toner image is sent to the fixing device 45 via the conveyor belt 44 with the toner image facing upward.

The transfer sheet P, which has been subjected to the fixing action in the fixing device 45, is discharged to the outside of the apparatus via the discharge roller 46,
On the other hand, the photoconductor drum 30 continues to rotate, and the toner remaining on the surface of the photoconductor drum 30 without being transferred is collected and cleaned by the cleaning device 39 having the cleaning blade 39A or the like that has been retracted, and stands by for the next copy.

FIG. 2 shows the details of the fixing device 45. The fixing device 45 is incorporated in the main body of the image forming apparatus in a united state by being housed in an independent container, and a driving portion on the main body side of the apparatus and It is operated by connecting to the power supply.

In FIG. 2, reference numeral 1 denotes a heating belt, which is a moving belt-shaped member for fixing, and is stretched between a heating roller 2 and a separation roller 3 by a tension roller 4 urging the heating roller 2. Is circulated in the clockwise direction by the driving rotation of.

Reference numeral 5 denotes a roller member which is in pressure contact with the outer peripheral surface of the heating belt 1 around which the heating roller 2 is wound, that is, a pressure roller, which is driven in the counterclockwise direction or driven and rotated at the same speed as the heating roller 2 to heat the belt 1. The transfer material is sandwiched between and conveyed.

The pressure roller 5 has a lower hardness than the heating roller 2 and presses the heating belt 1 toward the heating roller 2 side to form the first nip region N1. The second nip region N2 is formed between the heating belt 1 and the heating belt 1 as shown by being located at the downstream side of the conveyance of the heating belt 1 by θ.

In addition, the first nip region N1 and the second nip region N1 formed by the pressure contact between the heating roller 2 and the pressure roller 5 are formed.
The corresponding perimeters and angles of the nip area N2 of FIG.
As shown in (b), they are l ₁ , l ₂ and α ₁ , α ₂ .

The heating roller 2 and the pressure roller 5 have the same outer diameter, and the heaters H having the same heat generation amount.
1 and H2 are built-in, the temperature of the outer peripheral surface is controlled and managed by the temperature detection of the respective temperature sensors S1 and S2.

Further, F1 and F2 are cross-flow type fans (hereinafter simply referred to as "fans") which are cooling means arranged on the front and back sides of the conveying surface of the heating belt.
Regarding the fan F1, the air sucked from the outside of the apparatus via A and 7B is directly passed through the plurality of slit holes 6A formed in the conveyance guide plate 6 and directly to the lower surface of the transfer material.
For No. 2, the upper surface of the transfer material is indirectly cooled by spraying it on the back surface of the heating belt 1.

Further, the cleaning belts 1A and 5A for cleaning the toner adhering to the outer peripheral surfaces of the heating belt 1 and the pressure roller 5 which wind the heating roller 2 are
An oil impregnated roller 1B is further pressed against the heating belt 1 to prevent toner from adhering.

The fixing operation of the toner image on the transfer material by the transfer material by the fixing device 45 will be described.

A transfer material having a toner image transferred on its upper surface is indicated by an arrow A.
When it is conveyed from the direction into the apparatus, the front portion thereof is sandwiched between the heating belt 1 and the pressure roller 5 via the carry-in guide plate 8A and conveyed.

At this time, the transfer material is simultaneously heated from the upper surface and the lower surface by the heating belt 1 and the pressure roller 5, so that the toner is melted.

That is, the toner on the transfer material is the above-mentioned first toner.
In the nip region N1, the heating belt 1 uniformly presses and heats it to be in a molten state, but since the heating is for a relatively short time, the toner image is not disturbed and the deterioration of the image quality is suppressed.

After passing through the first nip region N1, the transfer material is heated by the pressure roller 5 from the back surface in the above-mentioned second nip region N2, but is in a molten state because it is sequentially performed for a relatively long time. The toner sufficiently penetrates into the transfer material and adheres firmly, and there is no risk of offset, so that a toner image with rich gloss can be obtained.

If the second nip region N2 is made too large, the toner will be excessively melted and the image quality will be deteriorated, and the curling and wrinkles of the transfer material will be more likely to occur and the load on the drive system will be increased. 3 for the first nip area N1 for the reason
It is desirable to make it about twice or less.

The transfer material in which the toner is melted is transferred to the fan F on the lower surface in the process of being transferred along the transfer guide plate 6.
1, the toner image on the upper surface of one side is cooled by the fan F2, gradually changes from the semi-molten state to the fixed state, and is separated from the heating belt 1 by the separation roller 3.

The transfer material separated from the heating belt 1 passes through a paper discharge guide plate 8B, a paper discharge roller 9 and a charge eliminating brush BR2.
The electricity is discharged by and is discharged from the direction of the arrow B to the outside of the apparatus main body.

On the other hand, the heating belt 1 from which the transfer material has been separated is neutralized by the static elimination brush BR1, the toner transferred from the transfer material is cleaned by the cleaning roller 1A, and the oil is impregnated by the oil impregnating roller 1B. The transfer action of the transfer material is started. On the other hand, with respect to the pressure roller 5, the toner transferred from the heating belt 1 is simultaneously removed and cleaned by the cleaning roller 5A. When the heating belt 1 moves in the axial direction during conveyance and becomes a so-called skewed state, the photosensors PS1 arranged on both side edges detect the heating belt 1 and tilt the tension roller 4. The heating belt 1 is automatically returned in the normal conveying direction.

Control of fixing temperature in the fixing device 45
Management is performed as follows.

3 and 4 show the temperature sensors S1 and S.
2 shows the temperature control circuit and process according to No. 2, in which the heaters H1 and H2 remain in the ON state when the apparatus is "warm up", and the fans F1 and F2,
Both the heating belt 1 and the pressure roller 5 are in the stopped state (OF
Therefore, the pressing action of the pressure roller 5 is also released (OFF).
Has been done.

When the "warm-up" is completed and the heating roller 2 and the pressure roller 5 reach the predetermined peripheral surface temperatures and the fixing is possible, that is, the "ready" stage, the fixing temperature of the transfer material is maintained constant. Therefore, the heaters H1 and H2 are
At the same time, the heating belt 1 and the pressure roller 5 start to rotate and start rotating after repeating ON / OFF.

When "printing" is performed in the image forming apparatus at the "ready" stage, the pressure roller 5 is in a pressure contact state (O
N), the fans F1 and F2 are rotated (ON), and the transfer material carried in and the toner image fixing action are carried out.

In the fixing device 45, the toner image on the transfer material is melted by sandwiching the heating belt 1 and the pressure roller 5, and then the interface temperature between the heating belt 1 and the toner image is adjusted to the transfer material itself. By providing a temperature difference that is lower than the temperature of 1), the surface layer member of the toner image is solidified, and at the same time, the affinity of the toner image for the transfer material is incorporated to prevent offset at the time of separation.

That is, the above-mentioned fan F2 is arranged at a position closer to the heating roller 2 on the upstream side of the transfer material conveyance than the fan F1 and, if necessary, has a larger air volume than the fan F1.

FIG. 5 shows an example of the relationship between the temperature curve C2 on the transfer material side indicated by the temperature T2 and the temperature curve C1 on the back surface of the heating belt 1 indicated by the temperature T1 which change due to the cooling action of the fans F1 and F2. It is shown.

As shown in the figure, after the toner image is melted, the heating belt 1 at a temperature lower than the temperature of the transfer material itself.
As a result, the surface layer portion is quickly cooled and solidified, so that the surface layer portion is conveyed in close contact with the heating belt 1 and then easily separated in the separation portion.

On the other hand, the transfer material itself is kept at a temperature higher than the interface temperature of the heating belt 1 until it is separated from the belt surface, so that the affinity for the toner image is maintained and, as a result, there is no offset during the separation and the gloss is maintained. Is fixed as a rich image of.

According to experiments, it is sufficient that the difference between the temperature T1 on the back side of the heating belt 1 and the temperature T2 on the transfer material side is within 5 ° C., so that even a transfer material onto which an image having a particularly high density is transferred is transferred. It has been confirmed that they can be separated without causing an offset.

Further, the fixing device 45 is switched to the continuous fixing operation state in the case where monochrome copy is selected according to the selection of the copy mode and a monochrome image is formed.

When the monochrome copy mode is selected and continuous copying is performed, the fixing device 45 operates simultaneously with the start of copying because the interval until the start of fixing is short, and the operation is connected until the end of copying. In the case of copying, the photoconductor drum 30 is rotated many times to form an image, and then transfer is performed.Therefore, since the interval until the start of fixing is long, the fixing device 45 operates only when fixing the transfer material. The fixing operation is controlled to be stopped from the start to the start of fixing.

That is, photo sensors PS2 and PS3 are installed on the carry-in guide plate 8A and the paper discharge guide plate 8B of the fixing device 45, and the tip of the transfer material carried into the fixing device 45 is detected by the photo sensor PS2. The respective signals are input to the CPU when the photo sensor PS3 detects the trailing edge of the ejected transfer material. The photo sensor PS2 may be replaced by the rotation start timing of the timing roller 42.

When the color copy mode is set, the heating belt 1 and the fans F1 and F2 are kept stopped even when copying is started, and the fixing device 45
Is in a dormant state.

When the above-mentioned signals are input to the CPU from this state, the photo sensor PS as shown in the time chart of FIG.
At the timing when the leading edge of the transfer material 2 is detected, the driving of the fans F1 and F2 or the fans F1 and F2 and the heating belt 1 is started, the fixing device 45 is switched to the operating state, and the transfer material is transferred. The fixing action of is performed.

Next, at the timing when the photosensor PS3 finishes fixing and detects the trailing edge of the discharged transfer material, the operation of the heating belt 1 and the fans F1 and F2 is stopped, and the fixing device 45 returns to the rest state. The resting state is maintained until the transfer material is carried into the fixing device 45 again. Of course, the fans F1 and F2 may continue to operate during the above-mentioned rest state.

[0052]

According to the present invention, the fixing operation can be automatically stopped and the fixing device can be stopped except when the image is fixed. As a result, the power consumption is low and the durability of the fixing device is improved. Therefore, an image forming apparatus having excellent practicability has been provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus of the present invention.

FIG. 2A is a sectional configuration diagram of a fixing device included in the device, and FIG. 2B is an enlarged view of a main part thereof.

FIG. 3 is a control circuit diagram of the fixing device.

FIG. 4 is an explanatory diagram showing an operating state of each member in the fixing device.

FIG. 5 is a graph showing temperature changes of a belt and a transfer material.

FIG. 6 is a time chart showing an operation of the fixing device in a color copy mode.

[Explanation of symbols]

1 heating belt 2 heating roller 3 separation roller 4 Tension roller 5 pressure roller 6 Transport guide plate 8A carry-in guide plate 8B Paper ejection guide plate 9 Paper ejection roller 30 photoconductor drum 35 charger 36 Developer 37 Transfer device 38 Separator 39 Cleaning device 40 paper cassettes 42 Timing roller 44 Conveyor belt 45 fixing device PS1, PS2, PS3 photo sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasuhiko Tanaka             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company (72) Inventor Kiyoaki Kawamoto             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company (72) Inventor Tetsuko Omoto             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company (72) Inventor Toshinori Yamazaki             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company

Claims (3)

[Claims] 1. A moving belt-shaped member having a color copy mode and a monochrome copy mode is used.
In an image forming apparatus equipped with a fixing device for fixing a toner image to a transfer body by heating / cooling means, the fixing device is continuously operated in the monochrome copy mode during continuous printing,
An image forming apparatus characterized in that an operating member of a fixing device is stopped when a transfer material does not pass in a color copy mode. 2. The image forming apparatus according to claim 1, wherein the stopping of the actuating member is a stop of movement of the belt-shaped member. 3. The image forming apparatus according to claim 1, wherein the operation member is an operation stop of a cooling unit of the fixing device.