JPH0664388B2 - Multicolor image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus that forms an image using an electrophotographic method.

[Background of the Invention]

Conventionally, mainly proofing from color separation film etc.
As a simple and quick way to create prints for
A method of utilizing a color electrophotographic copying machine or the like has been proposed.

In this method, four sheets, a color plate (for yellow development), a red plate (for magenta development), an eye plate (for cyan development), and a sumi plate (for black development), such as a color separation film, are used as originals. Are placed at the same position on the platen glass one after another to make a copy, and directly on the electrophotographic photosensitive sheet or on a transfer material such as transfer paper (hereinafter collectively referred to as transfer paper).
A full-color image is formed with color toners and is used for calibration.

However, in order to accurately place the above color separation film or the like at the same position on the platen glass, a register pin for normal printing is used.Align the punch hole of the color separation film or the like with this register pin. It takes some time to remove it. Therefore, in general, a color electrophotographic copying apparatus for subjecting a single color original to color separation copying is used to make a full-color copy from this single color original in order to make a proof copy in the same sequence. Was required to replace the original such as the color separation film in a short time between four original illuminations in the full-color copy mode, which was not practical in terms of operability.

In addition, after the toner image of one color is formed on the transfer paper in the monochrome copy mode, the apparatus is stopped, the color separation positive document on the platen is replaced, and the monochrome image of another color is copied. There was a way to overlap.

However, in this method, when the apparatus is stopped, a part of the toner image on the transfer paper comes into contact with the peripheral members of the transfer paper such as the photosensitive drum, the transfer paper conveyance guide, the separation claw support plate, and the transfer paper pressing member. In some cases, a partial pressure is applied to the toner image locally to cause offset, and when the apparatus is stopped or the next time it is started, rubbing may occur between the transfer paper and peripheral members to disturb the image. These results,
There is a problem in that the misregistration of the transfer paper is likely to occur between the transfer of the color-separated toner images, which causes a color misregistration in the full-color image.

In order to solve the above problems, the transfer drum carrying the transfer paper is idly rotated in the transition process from one image transfer to the next image transfer. However, when the transfer drum idles, the transfer sheet carrying the unfixed toner image passes through the transfer position without performing the transfer, so that the unfixed toner is offset to the photosensitive drum.

[Object of the Invention]

In view of this, the present invention is capable of forming a good image without causing the above-mentioned offset in an apparatus in which a transfer material carrying an unfixed toner image may pass a transfer position when transfer is not performed. An object is to provide a color image forming apparatus.

SUMMARY OF THE INVENTION The present invention for achieving the above object includes an image carrier and
An image forming unit that sequentially forms toner images of a plurality of colors on the image carrier, a rotatable transfer material support that carries and conveys a transfer material to a transfer position, and the transfer material support from the image carrier at the transfer position. In a multicolor image forming apparatus, comprising: a transfer charging unit that superimposes and transfers the toner image onto the transfer material carried on a body, after the transfer of the toner image onto the transfer material, the transfer from the image carrier is performed. A means for idly rotating the transfer material support without performing image transfer to the material,
When the transfer material having the toner image passes through the transfer position during the idle rotation, the transfer charging means is charged.

Example of Invention

 The present invention will be described below based on embodiments shown in the drawings.

FIG. 1 is a schematic diagram of the configuration of a color electrophotographic apparatus to which the present invention is applied.

In FIG. 1, reference numeral 1 denotes an image carrier having an electrophotographic photosensitive member of a three-layered structure including a transparent insulating layer, a CdS photoconductive layer and a conductive layer on the surface thereof, a photosensitive drum in this example, which is rotated by a shaft 2. It is supported freely and rotated in the direction of arrow 3 by a drive mechanism (not shown).

Reference numeral 4 denotes a platen glass 4, which has a white coating part 41 for reflecting the illumination light from the halogen lamp 5 at one end and a register pin 42 for positioning the document on its upper surface, as shown in the perspective view of FIG. And a support plate 43 having The white coating part 41 is for preventing the plate 43 from being copied. Reference numeral 44 is a color separation net positive (film) original having an image area 45, and a punch hole 47 formed at one end of a non-image area 46 is fixed to the original glass 4 in alignment with the register pin 42, and An original pressure plate 49 having a white surface in contact with the image area 45 is placed on the upper side. Also,
The non-image area 46 of the color separation net positive (film) original 44
Punch holes 481 and 482 for document identification are formed in the document, and light from light sources 483 and 485 provided under the document table glass 4 penetrates through the punch holes 481 and 482 to press the document compression plate 49. The reflected light is reflected by the optical sensors 484 and 486. That is, as shown in FIG. 5 (a), in the case where two punch holes for identifying the original are provided, the two optical sensors 484 and 486 both sense the light (1,
The sensor output of 1) is output. Further, as shown in FIG. 5B, in the case where the punch hole 482 for identifying the original is provided only at the position corresponding to one optical sensor 486, the optical sensor 4
Since 84 does not detect light, it outputs a sensor output of (0, 1). Therefore, the color separation net positive originals are (1, 1),
Judged as (0,1), (1,0) and (0,0),
It is possible to identify a four-color halftone positive document.

Then, the corresponding latent image formation and document process are automatically selected by these four sensor outputs. The original identification is performed prior to the exposure of the original, and the half-positive original is detected on the original table glass 4 within a predetermined time.
If the original cannot be identified because it was not placed on the top,
The latent image formation and the document process corresponding to the document are omitted, and immediately after the transfer process, the transfer paper is separated from the transfer drum described later and handled as a miscopy.

Next, regarding the configuration and operation of the electrophotographic apparatus, the first stage operation performed using the plate of the color separation network positive film described above will be described as a representative. First, not shown in the drawing provided outside the machine body of the electrophotographic copying apparatus. When the copy start button is pressed, the photosensitive drum 1 starts rotating in the direction of arrow 3 in the figure. When the drum 1 rotates to a fixed position, a plate 0 of a color separation halftone positive film (hereinafter, halftone positive) placed on the platen glass 4 is illuminated by a halogen lamp 5.

Then, the reflected light from the document illuminated by the halogen lamp 5 is reflected by the first scanning mirror 6 and the second scanning mirror 7, and further passes through the lens 8, the third mirror 9, and the fourth mirror 10 and is exposed by the exposure unit 12. An image is formed on the photosensitive drum 1.

The photosensitive drum 1 is first uniformly discharged by the pre-charging device 13 and the pre-exposure lamp 14, and then charged by the primary charging device 15 to a positive polarity. Slit exposure) is applied, and at the same time, negative polarity static elimination is performed.

Next, the entire surface is exposed by the entire surface exposure lamp 17 to form an electrostatic latent image of a printing plate on the photosensitive drum. The potential of this electrostatic latent image is, for example, about +350 V for the dark portion potential and −8 for the light portion potential.
It is possible to prevent the excessive development by giving a sufficient potential difference of about 0 V and by applying a uniform exposure on the photosensitive drum through the secondary charger 16 by the blank exposure lamp 11 to the portion exceeding the size of the plate original. Good.

The electrostatic latent image on the photosensitive drum is then visualized as a yellow toner image by the developing device 18a having a negative polarity yellow toner in the developing device group 18.

In addition to the above, the developing device group 18 includes magenta 18b and cyan 18
C and black 18d developing devices are provided, and corresponding to the electrostatic latent image of the color separation net positive of the red plate, the eye plate, and the sumi plate respectively, only the specified developing device works and the required monochromatic The toner image of is obtained on the photosensitive drum.

As described above, in the case of yellow copy, the optical sensor 484
And the developing device 18a having yellow toner according to the sensor output of 486, for example, (1, 1), is prepared for the developing operation state, and the photosensitive drum 1 is rotated in accordance with the movement of the document exposure device and the rotation of the photosensitive drum 1. A yellow toner image is formed on the original plate glass 4 corresponding to the halftone positive plate, and the yellow toner image is transferred to the position shown in FIG. 1 as the photosensitive drum rotates. It moves to the contact portion of the drum 24.

Next, a mechanism that is driven in synchronization with the various mechanisms for forming the toner image and conveys the transfer paper to the transfer material support, which is the transfer drum in this example, to receive the transfer of the toner image will be described.

The transfer paper 20, which is plain paper in the cassette 19, is fed into the machine by the paper feed roller 21, is roughly timed by the first register roller, and is then accurately timed by the second register roller. It is carried while being wound around the surface of 24. This holding is performed when the gripper cam solenoid of the transfer drum 24 operates.
Is opened and closed to grip the front end of the transfer paper 20.

FIG. 3 is a perspective view of the transfer drum 24. The transfer drum 24 has a mesh screen 242 carrying a transfer paper and a large cutout opening which is a supporting member for supporting the screen at its edge. And a gripper 241 for gripping the front end of the transfer paper. This mesh screen is, for example, polyester or nylon. It is made by knitting fibers such as polypropylene and silk, or punched and pressed into a sheet such as polyester and polypropylene. A mesh screen (generally about 50 to 100 mesh) is used.

As described above, the transfer paper whose tip is gripped by the gripper 241 is
Along with the rotation of the transfer drum 24, the transfer drum 24 is conveyed while being wound around a mesh screen 242 stretched in a large cutout opening of the transfer drum, and is a transfer charger as a transfer charging means.
While the transfer paper 20 passes through the transfer position between the 243 and the photosensitive drum 1, the yellow toner image on the photosensitive drum 1 is transferred, and at the same time, the transfer paper 20 is attracted to the surface of the mesh screen 242 by electrostatic attraction. Retained.

When the exposure of the original on the plate is completed, a lamp (not shown) for instructing the operator to replace the original lights up on the operation plate, and the operator opens the original pressure plate 49 to remove the original on the original platen glass 4, Instead, the red plate original is fixed by aligning the punch hole 47 with the register pin 42 and closing the pressure plate 49.

The red plate original is illuminated by the halogen lamp 5, a latent image of the red plate original is formed on the photosensitive drum 1 in the same manner as in the case of the aforementioned black original, and the magenta toner image developed by the magenta developing device 18b is converted into a magenta toner image. The yellow toner image on the transfer paper held by the transfer drum 24 is aligned and transferred.

In this embodiment, while the transfer of the yellow toner image on the photosensitive drum 1 to the transfer paper is completed and the transfer of the next magenta toner image is started, the photosensitive drum 1 is rotated 1.5 times and the transfer drum 24 is moved. The transfer is rotated three times during idle rotation, and halftone positive originals are exchanged during that period.

The transfer charger is continuously operated even during this idle rotation to electrostatically attract the transfer paper to the surface of the screen of the transfer drum 24 to prevent color misregistration.

That is, after the toner image is transferred onto the transfer paper, the transfer paper 2
When the transfer drum 24 performs idle rotation without transferring the toner image from the photosensitive drum 1 to 0, when the transfer paper 20 carrying the toner image passes the transfer position, the transfer charger 243
Is electrostatically attracted to the transfer drum 24 by operating. Further, by attracting the toner image to the transfer paper 20, it is possible to prevent the toner from being offset to the photosensitive drum 1.

As described above, the magenta toner image is transferred while being accurately aligned with the yellow toner image on the transfer paper held by the transfer drum 24.

Similarly, the cyan toner image and the black toner image are respectively formed on the photosensitive drum 1 by placing the eye plate document and the sum plate document on the platen glass 4 when the photosensitive drum and the transfer drum are idly rotated in sequence. After the transfer of the black toner image, which is the final color, is completed, the gripper cam solenoid operates to open the gripper 241, and the tip of the transfer paper is moved to the gripper 241. The gripping is released, and the separation claw solenoid (not shown) operates, the separation claw approaches the surface of the transfer drum 24, the transfer paper 20 is separated, and the transfer belt 27 passes through the conveyance belt 27.
It is heated and fixed by the heat roller fixing device 28, and the discharge tray 2
It is designed to be discharged to 9.

In the figure, 31 is a cleaner provided downstream of the transfer portion with respect to the photosensitive drum 1, 243 is a transfer charger, and 36 and 37 are transfer material separation chargers.

A series of control including idle rotation control of the photosensitive drum 1 and the transfer drum 24 in the present embodiment as described above is performed by the control circuit described in the block diagram of FIG.

That is, a microcomputer output is used to select the operation of the corresponding developing device, the start and stop of the operation of the developing device, etc. by the sensor output that is output according to the method of opening the punch holes for identifying the original provided in the color separation original for each color. Is specifically controlled by a predetermined sequence set in advance, and a signal from a pulse generator as rotation amount detection selection of the drum driving main motor. In the case of the present embodiment, after the transfer of the toner image to the transfer paper, the photosensitive drum is rotated 1.5 times and the transfer drum is rotated 3 times respectively, during which the color separation original is exchanged, and the final color toner image (black) is transferred. When the process is completed, the transfer paper is separated, conveyed to the fixing device 28, and fixed.

In this embodiment, during full-color copying, image forming conditions at the time of forming toner images of respective colors, such as primary charging high-current, secondary charging high-current, halogen lamp voltage or developing bias voltage, are optimally set, and each color is also set. It is provided so that the image forming condition can be finely adjusted by the image forming condition adjusting volume (total of four) provided for each. FIG. 7 shows the above-mentioned No. 6
6 is a timing chart of multicolor multiplex copying performed from the first color (yellow) to the fourth color (black) by the control circuit in the figure. However, the ratio of the diameter of the photosensitive drum 1 to the diameter of the transfer drum 24 is 360 mm / 180 mm =
It is 2/1 and the transfer paper size is A3 size. Further, one rotation of the transfer drum is displayed as 360 °.

As can be understood from the timing chart of FIG. 7, in the color electrophotographic copying apparatus of this embodiment, the diameter ratio of the photosensitive drum and the transfer drum is 2/1, and the transfer of the yellow image of the first color is performed. After the transfer onto the paper and immediately before the transfer of the magenta image of the second color, the transfer paper contacts the surface of the photosensitive drum three times.

The toner image that has already been transferred until a full-color image is formed in this manner contacts the surface of the photosensitive drum many times while the toner images of other colors are being transferred, and at that time, the toner image that has already been transferred is transferred. It is desirable to prevent the image from being offset on the surface of the photosensitive drum to reduce the density of the full-color image.

Therefore, in the present embodiment, in the latent image forming step when the photosensitive drum 1 is idling, the blank exposure lamp 11 is turned on so that the surface potential of the photosensitive drum 1 is changed to the background potential of the document (for example, the toner has a negative polarity). About 0
V to −120 V) is preferably provided so as to minimize the above-mentioned offset generation.

Further, as shown in FIG. 7, the transfer charger 24 is also operated during idle rotation.
3, the transfer paper carrying the unfixed toner is charged with a polarity opposite to the polarity of the toner to prevent the toner from being offset on the photosensitive drum 1.

In addition, since the transfer paper is electrostatically attracted to the mesh screen of the transfer drum and rotates during idling, it is desirable to prevent the occurrence of a memory image or a ghost image that adversely affects the transfer image.

Therefore, in this embodiment, when the photosensitive drum is idle,
It is preferable to prevent the memory image and the ghost image from being generated by turning off the halogen lamp 5 and performing pre-charging, primary charging, secondary charging and overall exposure. The latent image formed when the halogen lamp is turned off is not developed.

Further, in the present embodiment, the half-tone positive original is replaced when the photosensitive drum is idle (1.5 rotations). However, since the peripheral speed of the photosensitive drum is approximately 145 mm / sec, the replacement of the original is about 12.
It should be done within a second. Therefore, a sufficient document exchange time can be secured for the experienced operator.

During the above-described color separation image formation, the sequence operation corresponding to the image formation for three colors was performed for 1.5 rotations of the photosensitive drum (three rotations of the transfer drum). It may be four rotations of the transfer drum) or five colors (2.5 rotations of the photosensitive drum, five rotations of the transfer drum) or six or more colors. However, making the number of sequence operations more than necessary increases the offset of the transferred toner image to the photosensitive drum surface or the occurrence of image disturbance at the time of separation of the transfer paper from the photosensitive drum surface to a non-negligible level. It is preferable that the number of colors is 5 or less, in terms of good image formation.

Of course, if the process speed (peripheral speed of the photosensitive drum) is slow, the original may be exchanged for one color during the formation of each color separation image.

Also, three color separation start buttons may be provided in combination with the full color copy start button so that the respective color separation image formations can be selected among three colors, four colors, and five colors, for example, and the operator can select them. .

As described above, according to the present embodiment, it is possible to easily replace the color separation original on the original table and obtain a high-quality full-color image for proofreading without offset or color misregistration.

Further, since the identification mark provided on the color separation original can be detected and the latent image formation and development steps can be determined based on the detection signal, an arbitrary color superposition order can be easily obtained, and various color calibration can be performed. You can check the color reproduction effect. Alternatively, a correct full-color image can be obtained even if the originals are replaced in the wrong order, and miscopy can be eliminated.

Further, since image forming conditions such as charging conditions, exposure conditions or developing conditions can be adjusted during image formation for each color, color balance, fog, etc., which are likely to change due to fluctuations or deterioration of toner density of each color developer, can be easily corrected.

In this embodiment, the case where a color separation halftone original is used has been described. However, even when a color separation halftone original is used, a known full-color image can be obtained by using known reversal development. It goes without saying that it is good.

Further, in the present embodiment, a punch hole for identifying an original is provided in the non-image area of the original to identify the original, but the present invention is not limited to this, and an identification mark such as a bar code or a color mark May be provided in the non-image area of the document to identify the document.

Further, in the present embodiment, when the original is not placed on the original platen glass within a predetermined time and the mark cannot be detected, it is treated as a miscopy. The sequence may be configured to continue idling.

〔The invention's effect〕

As described above, according to the present invention, after the transfer of the toner image to the transfer material, there is provided means for idling the transfer material support without performing image transfer from the image carrier to the transfer material. When the transfer material with the toner image passes through the transfer position during rotation,
By charging the transfer charging means, the toner image carried on the transfer material can be electrostatically adsorbed to the transfer material support side, and the offset to the image carrier can be prevented. Therefore, good image formation is possible.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is a schematic view of the structure of a color electrophotographic copying apparatus, FIG. 2 is a perspective view of a glass platen of a document table, and FIG. 3 is a perspective view of a transfer drum. Fourth
FIG. 5 is a perspective view of a color separation net positive document, FIGS. 5 (a) and 5 (b) are sectional views showing a placed state of the color separation net positive document, FIG. 6 is a block diagram of a control circuit, and FIG. FIG. 8 is a diagram showing a time chart of a sequence by the control circuit. 1: Photosensitive drum 2: Axis 4: Original plate glass, 5: Halogen lamp 6: First scanning mirror, 7: Second scanning mirror 8: Lens, 9: Third mirror 10: Fourth mirror, 11: Blank exposure Lamp 12: Exposure unit, 13: Pre-charger 14: Pre-exposure lamp, 15: Primary charger 16: Secondary charger, 17: Full exposure lamp 18: Developing device group 18a, 18b, 18c, 18d: Developing device 19: Cassette, 20: Transfer Paper 21: Paper Feed Roller, 22: First Register Roller 23: Second Register Roller, 24: Transfer Drum 27: Conveyor Belt, 28: Fixing Device 29: Paper Ejection Tray, 31: Cleaner 36 , 37: Separation charger, 41: White coating part 42: Register pin, 43: Plate 44: Color separation net positive document, 45: Image area 46: Non-image area, 47: Punch hole 49: Crimping plate, 241: Gripper 242: Memory disk Over emissions, 243: transfer charger 481 and 482: punching, 483,485: a light source 484, 486: optical sensor

Claims (1)

[Claims] 1. An image carrier, image forming means for sequentially forming toner images of a plurality of colors on the image carrier, a rotatable transfer material support for carrying and transporting a transfer material to a transfer position, and the transfer position. In a multicolor image forming apparatus, comprising: a transfer charging unit configured to transfer the toner image from the image carrier to the transfer material carried on the transfer material support in a superimposed manner. After the transfer, there is provided a means for idling the transfer material support without performing image transfer from the image carrier to the transfer material, and during the idling, the transfer material having the toner image is at the transfer position. When passing through
A multicolor image forming apparatus characterized in that the transfer charging means is charged.