JPH08220904A - Color image forming device - Google Patents

Abstract

PURPOSE: To eliminate complication and to selectively obtain an unglossy copy and a glossy copy by reversely carrying a recording sheet with a fixed image thereon to a different sheet-feed system, and then subjecting the recording sheet to refixing. CONSTITUTION: When the device detects the rear end of the recording sheet which has passed through a fixing device 17 and has finished the fixing of a toner image on its one side, a heat roller 17A and carrying rollers R1-R3 start to rotate reversely all at once, the pressing of the pressure roller 17B is released, and a guide member 51 turns clockwise. Consequently the recording sheet is reversely carried between the heat roller 17A and pressure roller 17B which are apart from each other, and is carried into an inversion sheet feed passage 15B. In this passage 15B, the heat roller 17A and carrying rollers R1-R3 once stop and then return to normal rotations. A carrying roller R4 also starts to rotate reversely, and the pressure roller 17B, separated from the heat roller 17A, is brought into contact with the heat roller 17A. Then, the recording sheet is ejected onto a tray at the top of the device after repressed between the heat roller 17A and pressure roller 17B pressed against each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus in which a color toner image is transferred onto a recording sheet by an electrophotographic method, and the color toner image is fixed to obtain a color copy. The present invention relates to a color image forming apparatus capable of giving gloss to an image.

[0002]

2. Description of the Related Art As a method for forming a multicolor image, a monochromatic toner image formed on each of the photoconductors is transferred by using a photoconductor, a charging device, a developing device and the like as many images as necessary. A device (A) that creates a color image by superimposing it on
A device (B) for forming a color image by repeating charging, image exposure and development for each color by rotating one photosensitive member a plurality of times, or similarly, charging, image exposure for each color and image exposure within one rotation of one photosensitive member. An apparatus (C) or the like is known in which development is sequentially performed to form a color image.

However, the above-mentioned device (A) has a drawback that the volume of the device becomes large because it requires the conveyance of a plurality of photosensitive members and transfer members. On the other hand, the device (B) has only one charging unit, image exposing unit, and one photoconductor, so that the volume can be reduced.

Although the device (C) enables high-speed image formation, the diameter of the photoconductor is large because it is necessary to dispose a plurality of sets of chargers, image exposing means and developing devices within one circumference of the photoconductor. There is a tendency that the device becomes large and the device becomes large.

For the purpose of avoiding the drawbacks of the above-mentioned obstacles in the apparatus (C), the substrate of the image forming body is made of a transparent material, and a plurality of image exposing means are housed therein to form an image. An apparatus has been proposed in which the photosensitive layer formed on the outer periphery of the substrate is exposed through the substrate (for example, JP-A-5-307307).

The present invention relates to the above-mentioned apparatuses (B) and (C), and relates to a color image forming apparatus for collectively transferring the toner images superposed on the image forming body to a recording sheet and then fixing the toner images. It is a thing.

[0007]

In any of the color image forming apparatuses according to the present invention, the photoconductor and the fixing device are in close proximity to each other, the color toner image is transferred from the photoconductor onto the recording sheet, and the heating roller is used. The provided fixing means presses and heats the color toner image adhering to the recording sheet to fuse and fix it onto the recording sheet.The recording sheet on which the color toner image is fixed is placed on the tray outside the apparatus. Is discharged. When observing the color toner image fixed on the recording sheet with a low-power microscope, the spherical or granular toner is melted and deformed, and the toner adheres firmly to the recording sheet, but it is in the fixed state. Unevenness of the adhered toner is recognized in the portion. When a color toner image is fixed by using a transparent sheet for an overhead projector (OHP) as a recording sheet, the unevenness causes damage and the color toner image portion that should be in color when projected over OHP is projected in black. It When a plain paper is used as the recording sheet and a color toner image is fixed on the plain paper, the obtained color image is in a non-glossy state due to the unevenness of the surface of the fixed toner. Non-glossy text images are easier to read, but photographic images are preferably glossy. To obtain a glossy image, the recording sheet once fixed is re-fixed to make the toner image portion in the uneven state smooth. Further, in the case of a transparent sheet for OHP, re-fixing is performed to smooth the toner image portion which is in a concavo-convex state, so that a clear color image is projected when observed over OHP.

It is an object of the present invention to provide a color image forming apparatus capable of selectively obtaining a non-glossy and glossy color image copy while eliminating the complication of the apparatus and the process.

[0009]

SUMMARY OF THE INVENTION The above-described object is to dispose a color toner image on an image forming body by superimposing a color toner image on the image forming body by disposing a charging device, an image exposure device and a developing device. In a color image forming apparatus in which an image is transferred onto a recording sheet and then fixed, the recording sheet once fixed by a fixing device is reversely fed, and after being fed back to a different paper feeding system through the fixing device, it is again fed. It is achieved by a color image forming apparatus which is fed and re-fixed by a fixing device.

As a preferred embodiment of the present invention, the fixing condition at the time of re-fixing may be changed such that the conveyance speed of the recording sheet is reduced or the fixing condition is improved as compared with the fixing condition at the time of fixing. Further, the fixing device has a function of pressing and releasing the pressure of the heat roller, and it is preferable that the fixing device is in the pressure-bonding state at the time of fixing or re-fixing the recording sheet and is in the pressure-release state at the time of reverse feeding of the recording sheet. It is an embodiment. Further, in the present invention,
The recording sheet once fixed by the fixing device is reversely fed, and after being reversely fed to a different paper feeding system through the fixing device,
It is sent again and re-fixed by the fixing device,
In a preferred embodiment, the different paper feed system is a reverse paper feed path for double-sided image formation. It is a preferred embodiment that the length of the reverse sheet feeding path from the fixing position to the transfer position of the different sheet feeding system is set longer than that of the recording sheet.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus capable of double-sided copying showing an embodiment of the present invention. FIG. 2 is a sectional view of a main part of the color image forming apparatus of FIG. FIG. 4
FIG. 2 is a block diagram showing a control system of the color image forming apparatus shown in FIG.

In the color image forming apparatus of this embodiment, an operation panel 70 (not shown) is provided on the upper surface of the apparatus, and the operation panel 70 has a start button 71, a single-sided / double-sided copy selection button 72, and a gloss / non-gloss selection button 73. , A numeric keypad 74 and the like are provided. Single-sided / double-sided copy selection button 72 and gloss / non-gloss selection button 73
By selecting the mode with, non-glossy / single-sided mode, non-glossy / double-sided mode, glossy / single-sided mode,
The four image recording modes of the gloss / double-sided mode and the separately set double-sided mode / paper surface alignment mode are selected.

The ROM 64 stores the above-mentioned image recording programs, and the control section 61 calls the corresponding image recording program from the ROM 64 based on the selected image recording mode, and is set by the ten key 74 according to this program. Image recording is performed for the number of copies.

In the color image forming apparatus shown in FIG. 1, 10 is a drum-shaped image forming body, that is, a photosensitive drum, and a transparent conductive material is formed on the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin. Layer, organic photosensitive layer (O
PC) a-Si is provided.

In this embodiment, in the photoconductor layer of the photoconductor drum, which is the image forming point of the exposure beam for image exposure, a proper contrast is obtained with respect to the light attenuation characteristics (photocarrier generation) of the photoconductor layer. It suffices that the exposure light amount has a wavelength that can be applied. Therefore, the light transmissivity of the transparent substrate of the photosensitive drum in the present embodiment does not have to be 100%, and may have a characteristic that some light is absorbed when the exposure beam is transmitted. As the material of the light-transmitting substrate, various light-transmitting resins such as soda glass, Pyrex glass, borosilicate glass and fluorine, polyester, polycarbonate, polyethylene terephthalate used for general optical members can be used. Further, as the translucent conductive layer, indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, N
A metal thin film made of i, Al or the like and maintaining a light-transmitting property is used.
Various sputtering methods, various CVD methods, dip coating methods, spray coating methods and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer,
Amorphous selenium alloy photosensitive layer and various organic photosensitive layers (O
PC) can be used.

A flange 10A at one end of the photosensitive drum 10 has a guide pin 30 provided in a cartridge 30 described later.
The flange 10B at the other end is supported by P, and the flange 10B at the other end is fitted into a plurality of guide rollers 40R provided in the substrate 40 of the apparatus main body to mesh the outer gear 10G with the drive gear 40G. Rotated clockwise with the layers grounded.

Reference numeral 11 denotes a scorotron charger, which is a photosensitive drum 10.
The above-mentioned organic photoconductor layer is charged by a grid held at a predetermined potential and corona discharge by a discharge wire to give a uniform potential to the photoconductor drum 10.

Reference numeral 12 designates PL, LEDs in which light emitting elements arranged in the axial direction of the photoconductor drum 10 are arranged in a line in an array, and LISA, PLZT, LC in which light emitting elements are arranged in a line.
In an exposure optical system composed of S and an image forming lens such as a self-occlusion lens, image signals of respective colors read by a separate image reading device are sequentially taken out from a memory to be supplied to the respective exposure optical systems 12 described above. It is input as an electric signal.

Each of the exposure optical systems 12 is attached to a cylindrical support member 20 which is fixed to the substrate 40 of the apparatus main body by using the guide pin 40P1 as a guide, and the exposure optical system 12 is attached to the photosensitive drum 10.
Is housed inside the base body of.

Reference numerals 13Y to 13K denote developing units for accommodating yellow (Y), magenta (M), cyan (C) and black (K) developers, respectively, each having a predetermined gap with respect to the peripheral surface of the photosensitive drum 10. Development sleeve 13 that keeps the same and rotates in the same direction
It has 0.

Each of the developing devices is in a non-contact state by applying a developing bias voltage to the electrostatic latent image formed on the photosensitive drum 10 formed by the charging by the charging device 11 and the image exposure by the exposure optical system 12 described above. Reverse development with.

The photosensitive drum 10 and each charger 1
1. Each developing device 13 and further the cleaning device 19 are accommodated in a cartridge 30 and integrated with each other, and a supporting member 20 having an optical system 12 without giving a load or a shock to the image exposure means.
It is configured so that it can be attached to and detached from the main body of the device while leaving. The structure in which the supporting member 20 is left when attaching / detaching is achieved by fixing the heater 201, the heat pipe 202, the lead wire 203 for operating the LED, and the optical system 12 to the supporting member 20 in spite of the rotation of the photoconductor and the attachment / detachment of the photoconductor. It has a feature that can be set,
It can also be used to determine the axis of the photosensitive drum 10.

Next, the process of the color image forming apparatus in this apparatus will be described.

In the image reading apparatus which is a separate body from this apparatus, the original image is once read as an image signal for each color of Y, M, C and K by using the image read by the image pickup device or the image edited by the computer. Stored and stored in memory.

By the start of the image recording, the drive gear 40G is rotated by the start of the photoconductor drive motor to rotate the photoconductor drum 10 in the clockwise direction, and at the same time, the photoconductor is charged by the charging device 11 (Y). Application of electric potential to the drum 10 is started.

After a potential is applied to the photosensitive drum 10,
In the exposure optical system 12 (Y), the exposure by the electric signal corresponding to the first color signal, that is, the yellow (Y) image signal is started, and the yellow (Y) of the original image is formed on the photosensitive layer on the surface by the rotational scanning of the drum. ) Form an electrostatic latent image corresponding to the image.

The latent image is reversal-developed by the developing device 13 (Y) with the developer on the developing sleeve in a non-contact state, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is further given a potential on the yellow (Y) toner image by the charging action of the charger 11 (M), and the second color signal of the exposure optical system 12 (M), that is, Exposure with an electric signal corresponding to the magenta (M) image signal is performed, and non-contact reversal development by the developing device 13 (M) causes a magenta (M) toner image on the yellow (Y) toner image. Will be sequentially stacked.

By the same process, a cyan (C) toner image corresponding to the third color signal is further generated by the charging device 11 (C), the exposure optical system 12 (C) and the developing device 13 (C), and also the charging device. 11 (K), exposure optical system 12 (K) and developing unit 13
By (K), a black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed, and a color toner image is formed on the peripheral surface of the photosensitive drum 10 within one rotation.

Photoreceptor drum 10 by each of these exposure optical systems
The exposure to the organic photosensitive layer is conducted through the transparent substrate from the inside of the drum. Therefore, the exposure of the images corresponding to the second, third and fourth color signals is performed without any influence of the toner image previously formed.
It is possible to form an electrostatic latent image equivalent to the image corresponding to the color signal of. The stabilization of the temperature inside the photosensitive drum 10 and the prevention of the temperature rise due to the heat generation of each exposure optical system 12 use a material having good thermal conductivity for the supporting member 20, and use a heater 201 when the temperature is low, When the temperature is high, it can be suppressed to a level without any trouble by taking measures such as radiating heat to the outside through the heat pipe 202. Further, in the developing action by each developing device, a developing bias in which a direct current or an alternating current is applied to the developing sleeve 130 is applied, and jumping development is performed by the one-component or two-component developer accommodated in the developing device, and the transparent A DC bias having the same polarity as that of the toner is applied to the photosensitive drum 10 having the conductive layer grounded so that the toner is attached to the exposed portion and non-contact reversal development is performed.

The color toner image thus formed on the peripheral surface of the photoconductor drum 10 is conveyed from the paper feed cassette 15 in the transfer device 14A, passes through the paper feed path 15A, and then the photosensor S3 and the timing roller 16 are driven. Is transferred to a recording sheet that is fed in synchronization with.

(1) When the non-glossy / single-sided copy mode is designated, the recording sheet to which the toner image has been transferred is separated from the peripheral surface of the drum by being removed of the charge in the static eliminator 14B. When the transfer belt 14C is conveyed, the fixing roller 17 is sandwiched between the heat roller 17A and the pressure-bonding roller 17B which is pressure-bonded to the heat roller 17A via the guide member 51, and is heated. Later,
The sheet is ejected onto the tray on the upper part of the apparatus through the sheet ejection roller 18 via the conveyance rollers R1, R2 and R3.

On the other hand, a photosensitive drum in which a recording sheet is separated
A cleaning device 19 removes and cleans residual toner to continue forming a toner image of a document image, or temporarily stops to form a toner image of a new document image.

(2) When the non-glossy / duplex copy mode is designated, the photo sensor S1 which detects the trailing edge of the recording sheet which has passed through the fixing device 17 and has finished fixing the toner image on one side is detected. In response to the signal, the heat roller 17A and the above-mentioned transport rollers R1, R2 and R3 all turn in the opposite direction at the same time, and at the same time, the guide member 51 rotates in the clockwise direction with the support shaft 51A as the fulcrum, and is indicated by the broken line. It is placed in the state shown.

Therefore, the recording sheet having the toner image fixed on one side is fed back while the heat roller 17A and the pressure contact roller 17B, which will be described later, are separated in the fixing device 17 and is fed in reverse by the guide of the guide member 51. The sheet is conveyed to the timing roller 16 via the sheet feeding path 15A again via the path 15B. At this time, the toner image surface is inverted downward and the toner image is transferred to the back surface at the transfer portion.

Prior to this, the heat roller 17A and the respective conveying rollers R are detected by the detection signal of the photo sensor S2 which detects the trailing edge of the recording sheet conveyed to the reverse sheet feeding path 15B.
1, R2 and R3 are simultaneously returned to the normal rotation, and at the same time, the guide member 51 is also returned to the state shown by the solid line.

Therefore, the toner image on the back side is held between the heat roller 17A and the pressure contact roller 17B which are in pressure contact with each other in the fixing device 17 to fuse the toner and fix the toner. It is discharged to the tray on the upper part of the device.

The reversing sheet feeding path 15B is provided with the transfer roller 14A without providing a space for the apparatus.
Since it can be constructed in a space formed between the sheet feeding cassette 15 and the sheet feeding cassette 15, it is not necessary to increase the height of the apparatus.

That is, in this apparatus, the exposure optical system 12 is included so that the photosensitive drum 10 having a small diameter can be used. Further, the developing devices 13 are arranged in the manner shown in FIG. 3 so that the cartridge 30 can be balanced. As shown in FIG. 3, they are symmetrically arranged on the left and right sides of a vertical line MOM passing through the center of the drum, and are arranged above the photosensitive drum in consideration of feeding, transferring and fixing of the transfer paper.

Therefore, the transfer and cleaning means are arranged below the drum due to the space distribution on the peripheral surface of the drum. That is, as shown in FIG. 3, a vertical line M-M passing through the center of the photosensitive drum 10 of a small-diameter drum having an outer diameter φ of 60 mm to 160 mm is used as a target axis, and two exposure optical systems 12 and two developing devices 13 are provided on the left and right sides thereof. By arranging the transfer device 14A on one side below the horizontal line N-N passing through the center of the photosensitive drum 10 and the cleaning device 19 on the other side, the left and right balance is maintained, and the handling operation is extremely easy. Become.

As confirmed in the present embodiment, the exposure optical system 12 and the developing device 13 are positioned substantially opposite to each other on the left and right sides of the vertical line MM as shown in the drawing, and the center of the transfer device 14A is located below the horizontal line NN. The angle θ1 on the upstream side of rotation of the photoconductor drum 10 from the vertical line MM is 5 to 40 degrees, while the contact portion of the cleaning device 19 is also below the horizontal line N-N from the vertical line M-M. Rotation angle θ2
Are arranged at respective positions of 10 degrees to 50 degrees, and the angles θ3 and θ4 formed between the center of each developing sleeve of the pair of left and right developing devices 13 and the horizontal line N-N are ± 20 up and down respectively. The angles θ5 and θ6 formed with respect to the pair of left and right developing devices 13 arranged further above within 4 degrees are 4 respectively.
By setting it within the range of 5 degrees to 75 degrees, it was possible to effectively utilize the periphery of the photoconductor and obtain a layout having an external shape balance and a vertical balance. The transfer roller 14A, which is a part of the transfer belt described above, and the cleaning device 1
9 is installed at the positions of angles θ1 and θ2 on the upstream and downstream sides of the drum rotation with respect to the vertical line OM below the drum, and as a result, the recording sheet is fed at an inclination angle with a slight dip to the transfer portion. After the transfer, the sheet is conveyed at the inclination angle.

Therefore, in the case of this apparatus, the means for feeding the recording sheet linearly to the transfer portion is not taken, and the paper feed cassette 15 is accommodated in the bottom of the apparatus to bend the transfer paper into a U-shape. Then, the so-called double-sided unit composed of the guide member 51, the reversing sheet feeding path 15B and the like can be accommodated in the sheet feeding path.

The fixing device 17 of this embodiment comprises a heat roller 17A which is driven at a fixed position and a pressure roller 17B which is pressed against the heat roller 17A from below and is driven to rotate.
B is rotatably supported at one end of an L-shaped crank member 52 having both shaft ends erected with a shaft 52A as a fulcrum of rotation, and the crank member 52 is caused by the tension of a tension spring 53. Is pressed against the heat roller 17A by the urging force in the clockwise direction.

The other end of the crank member 52 is connected to the solenoid 54 so that the solenoid 54 operates or turns on.
Thus, the tension spring 53 is rotated counterclockwise against the tension of the tension spring 53.

The solenoid 54 is turned on by the detection signal of the rear end of the transfer sheet by the photo sensor S1 described above,
The crank member 52 is rotated counterclockwise to move the pressure-bonding roller 17B downward to release the pressure-bonding action with respect to the heat roller 17A, and the transfer paper is re-transferred to the image transfer portion without deterioration of image quality. It is fed. It is also possible to suspend the heating of the heat roller 17A or set it to a low temperature together with this release.

The solenoid 54 releases the crank member 52 until the toner image on the back surface of the recording sheet starts to be fixed after the recording sheet passes through the fixing roller section 17 to press the pressure roller 17B.
Is switched to OFF in order to return to the pressure contact state. The length of the reverse sheet feeding path from the heat roller 17 of the fixing device, which is the fixing position, to the sheet feeding position for re-feeding the recording sheet to the image transfer section, that is, the distance from the photosensor S2 in FIG. 1 to the timing roller 16. Since the length of the recording sheet conveyance path is set to be slightly longer than the maximum length of the recording sheet to be used, the detection signal of the trailing edge of the recording sheet by the photosensor S2 can be used. By the signal, the above-mentioned rotation direction of each roller and the position of the guide member 51, the pressure contact of the pressure roller 17B, the reheating of the heat roller 17B, and the like can be operated. Instead of the photo sensor S2, the photo sensor S3 may be installed in front of the timing roller 16 to control the leading edge of the recording sheet and perform similar control.

Thus, the recording sheet on which the toner image on the back side is transferred and fixed by reversing the front and back is ejected to the tray at the upper part of the apparatus through the ejection rollers 18 through the respective conveyance rollers R1, R2 and R3.

(3) When the gloss / single-sided copy mode is designated, the toner image is first fixed on one side by the same process as the non-glossy / single-sided copy mode. That is, the recording sheet, to which the toner image has been transferred by the transfer device 14A, is separated from the drum peripheral surface by being removed of the charge by the static eliminator 14B, and is conveyed by the transfer belt 14C through the guide member 51 and then the heat roller in the fixing device 17. 17A and the pressure-bonding roller 17B, which is pressure-bonded thereto, are sandwiched and heated, and the toner adhering to one surface is fused and fixed.

The heat roller 17A and the conveying rollers R1, R2, and R3 are all reversed at the same time by the detection signal of the photo sensor S1 which detects the rear end of the recording sheet which has passed through the fixing device 17 and which has fixed the toner image on one side. When the pressure roller 17B is released from the pressure, the guide member 51 is rotated clockwise about the support shaft 51A as a fulcrum and placed in a state indicated by a broken line.

Therefore, the recording sheet having the toner image fixed on one side is fed back between the heat roller 17A and the pressure-bonding roller 17B which are separated from each other, and is fed into the reverse paper feed path 15B by the guide of the guide member 51. In the reverse sheet feeding path 15B, the heat roller 17A and each of the transport rollers R are detected by the detection signal of the photo sensor S2 that detects the trailing edge of the recording sheet.
1, R2, R3 stop once and then return to normal rotation. Further, in accordance with this operation, the conveyance roller R4, which has been rotating in the reverse sheet feeding direction 15B in the reverse sheet feeding direction, also turns to reverse rotation, and the pressure-bonding roller 17B in the separated state is pressure-bonded to the heat roller 17A.

The recording sheet once placed in the reversing paper feeding path 15B is re-pressed between the heat roller 17A and the pressure roller 17B in the pressure-bonded state, and then the transport rollers R1 and R.
2 and R3, and is discharged onto a tray on the upper part of the apparatus via a discharge roller 18. The above-mentioned re-fixing may be carried out under the same fixing conditions as those of the above-mentioned fixing, but in order to make the gloss effect larger, (a) the conveyance linear velocity of the recording sheet at the time of re-fixing is made lower than the linear velocity at the fixing And (b) changing the set fixing temperature at the time of re-fixing to a temperature higher than the set temperature at the time of fixing. Make it stronger, etc.
Further, in parallel with the change of (a), (b) and (c), the heat roller 17
It is desirable to increase the amount of applied oil such as silicone oil supplied to the heat roller 17A via the oil pad 17C that is in contact with A at the time of re-fixing. As a means for increasing the applied oil or the like at the time of re-fixing, for example, an oil pad 1
Oil pad 1 that contains much applied oil compared to 7C
7D is separately provided, and the oil pad 17D is brought into contact with the heat roller 17A only at the time of re-fixing, so that the amount of applied oil at the time of re-fixing can be increased as compared with that at the time of re-fixing, and offset at the time of re-fixing. And the effect of increasing the gloss of the fixed image can be obtained.

In order to reduce the size of the color image forming apparatus of the present invention, the feeding distance from the transfer position where the transfer device 14A transfers the image onto the recording sheet to the fixing position where the fixing device 17 fixes the recording sheet is It is set shorter than the length. Therefore, when the recording sheet whose one side has been fixed is reversely fed for re-fixing, the reverse feeding direction cannot be conveyed toward the transfer portion.The present invention reverse feeds to a different paper feeding system for reverse feeding. After that, the sheet is re-fed and re-fixed by the fixing device. In the present embodiment, the reverse sheet feeding path 15B is used as a different sheet feeding system, and a different sheet feeding system is newly added in the double-sided color image forming apparatus. Re-fixing is possible without providing.

(4) When the gloss / duplex copy mode is designated, the toner image is fixed on both sides of the recording sheet by the same process as the above non-gloss / duplex copy mode, and then the both sides of the recording sheet are fixed. Will be re-established. That is, the recording sheet, to which the toner image has been transferred by the transfer device 14A, is separated from the drum peripheral surface by being removed of the charge by the static eliminator 14B, and is conveyed by the transfer belt 14C through the guide member 51 and then the heat roller in the fixing device 17. 17A and a pressure-bonding roller 17B, which is pressure-bonded thereto, are sandwiched and heated, and the toner adhering to one surface is fused and fixed.

A photo sensor S for detecting the trailing edge of the recording sheet which has passed through the fixing device 17 and has finished fixing the toner image on one side.
In response to the detection signal of 1, the heat roller 17A and the above-mentioned transport rollers R1, R2 and R3 all turn in the reverse direction at the same time, and at the same time, the guide member 51 rotates clockwise about the support shaft 51A as a fulcrum. It is placed in the state shown by the broken line.

Therefore, the recording sheet on which the toner image is fixed on one side is fed back between the heat roller 17A and the pressure-bonding roller 17B which are separated in the fixing device 17, and the guide sheet 51 guides the reverse sheet feeding path 15B. Via the above paper feed path again
It is conveyed to the timing roller 16 via 15A. At this time, the toner image surface is inverted downward and the toner image is transferred to the back surface at the transfer portion.

Prior to this, the heat roller 17A and the respective conveying rollers R are detected by the detection signal of the photo sensor S2 which detects the trailing edge of the recording sheet conveyed to the reverse sheet feeding path 15B.
1, R2 and R3 all return to the forward rotation at the same time, the pressure roller 17B is also pressure-bonded, and at the same time, the guide member 51 is also returned to the state shown by the solid line. Therefore, the toner image on the back is
At 17, the toner is fused and fixed.

The heat roller 17A and the respective conveying rollers R1, R2 and R3 are simultaneously operated by the detection signal of the photo sensor S1 which detects the rear end of the recording sheet which has passed through the fixing device 17 and which has fixed the toner images on both sides. Turning to the opposite direction,
The pressure contact of the pressure contact roller 17B is released, and the guide member 51 is rotated clockwise about the support shaft 51A as a fulcrum and placed in the state indicated by the broken line.

Therefore, the recording sheet on which the toner images on both sides are fixed is fed back between the heat roller 17A and the pressure-bonding roller 17B which are separated from each other, and is guided into the reverse paper feed path 15B by the guide of the guide member 51. In the reverse sheet feeding path 15B, the heat roller 17A and each of the transport rollers R are detected by the detection signal of the photo sensor S2 that detects the trailing edge of the recording sheet.
1, R2, R3 stop once and then return to normal rotation. Further, in accordance with this operation, the transport roller R4 also reversely rotates, and the pressure-bonding roller 17B in the separated state is the heat roller 1.
Press on 7A.

By this operation, the reverse sheet feeding path 15 is once
The recording sheet in B is re-fixed on the toner images on both sides between the heat roller 17A and the pressure roller 17B in the pressure-bonded state, and the recording sheet is conveyed through the transport rollers R1, R2, and R3, and is ejected via the paper discharge roller 18. It is discharged onto the upper tray. As a result, the recording sheets are stacked with the image surfaces in the page order. In the case of double-sided printing, the page order is maintained by forming an image from the back side. In this way, both sides of the recording sheet are re-fixed and discharged onto the tray. Regarding re-fixing, the fixing conditions of (a), (b), and (c) described above and the amount of applied oil are increased. Action is taken.

(5) Double-sided copy mode / paper surface alignment mode In addition to the page order, when it is desired to stack the front and back surfaces of the paper in order, the paper is transferred again after the double-sided fixing (mode or mode) is completed. I will pass through the system.

Specifically, when the rear end of the recording sheet on which the double-sided toner images have been re-fixed is detected again by the photosensor S1, the second detection signal from the photosensor S1 causes the heat roller 17A and the conveying rollers R1 to be detected. , R2 and R3 again rotate in the opposite directions, and the pressure roller 17B is switched to the state of releasing the pressure contact.

Therefore, the recording sheet is fed back into the fixing device 17 again, and is guided by the guide member 51 to be conveyed to the timing roller 16 via the paper feed path 15B and again via the paper feed path 15A. .

Thus, when the trailing edge of the recording sheet re-fed to the reverse feeding path is detected again by the photo sensor S2, the pressure detection roller 17B is caused by the second detection signal.
The heat roller 17A and the transport rollers R1, R2, and R3 are simultaneously returned to the forward rotation while maintaining the pressure contact state, and at the same time, the guide member 51 is also returned to the state shown by the solid line, while the image forming body is formed. 10 and transfer means 14A, 14C
, But the functions of image formation and transfer bias application are suspended.

Therefore, the recording sheet is conveyed again to the fixing device 17 in a state where only the front and back sides are reversed and the first transferred toner image is directed upward, and after the surface is fixed again,
Is discharged. At this time, the fixing device may be released. Further, the image output is different from the previous embodiment (4), and the page order is maintained by forming the image from the surface.

[0065]

According to the present invention, a copy of a non-glossy image can be selectively obtained on general recording paper without enlarging the apparatus, and a transparent sheet for OHP can be obtained. Thus, a color image forming apparatus having a light-transmitting property and capable of obtaining a clear color image when projected by an OHP is provided. Further, the present invention is applied to a color image forming apparatus capable of performing double-sided copying as shown in the embodiment, and the reverse sheet feeding path for double-sided image formation is also used as a different sheet feeding system for reverse feeding. The effects obtained by the invention became extremely remarkable.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram of a color image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of essential parts of the color image forming apparatus shown in FIG.

FIG. 3 is an explanatory view of a main part of the color image forming apparatus shown in FIG.

4 is a block diagram showing a control system of the color image forming apparatus shown in FIG.

[Explanation of symbols]

 10 Photoconductor drum 14A Transfer roller 14B Static eliminator 14C Transfer belt 15A Paper feed path 15B Reverse feed path 16 Timing roller 17 Fixing device 17A Heat roller 17B Crimping roller 17C, 17D Oil pad 18 Paper ejection roller 51 Guide member 52 Crank member 54 Solenoid 72 Single-sided / double-sided copy selection button 73 Glossy / non-glossy selection button

Claims (5)

[Claims] 1. A charger, an image exposure device, and
In a color image forming apparatus in which a developing device is arranged and a color toner image is formed on an image forming body in a superimposed manner, and the color toner image is transferred onto a recording sheet and then fixed, the recording is once fixed by the fixing device. A color image forming apparatus characterized in that a sheet is fed backward, fed back to a different paper feeding system through a fixing device, fed again, and re-fixed by the fixing device. 2. The color image forming apparatus according to claim 1, wherein the fixing condition at the time of re-fixing is such that the conveying speed of the recording sheet is decreased or the fixing condition is improved. 3. The color according to claim 1, wherein the fixing device has a function of pressing and releasing the heat roller, and is in a pressure-bonded state during fixing and in a pressure-released state during reverse feeding. Image forming apparatus. 4. The color image forming apparatus according to claim 1, wherein the different paper feed system is a reverse paper feed path for double-sided image formation. 5. The color image forming apparatus according to claim 1, wherein the length of the reverse sheet feeding path from the fixing device to the sheet feeding position in the different sheet feeding system is set longer than that of the recording sheet. .