JPH07311492A - Color image forming device - Google Patents

Abstract

PURPOSE:To prevent color slurring from being caused by faulty synchronism of an image signal. CONSTITUTION:The toner images of respective colors formed on an image forming carrier are successively transferred to an intermediate transfer body to obtain color toner images, which are transferred to a recording supporting body altogether to be formed as a color image. Then, the device is provided with an image signal memory 24 in which the image signal SG4 of each color is stored, an exposure device exposing the image forming carrier corresponding to the image signal SG4, and a controller 21 generating an image plane synchronizing signal SG3 for transferring the image signal SG4 of each color to the exposure device and generating a line synchronizing signal SG2 for transferring the image signal SG4 of each line to the exposure device. The signals SG3 and SG2 are generated synchronously.

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.

[0002]

2. Description of the Related Art Conventionally, a transfer drum system, a tandem transfer system, an intermediate transfer system and the like are known as a transfer system in a color image forming apparatus. The intermediate transfer system is a drum type intermediate transfer system or a belt type intermediate system. A transfer method is known. Among them, the transfer drum method and the drum type intermediate transfer method are superior in terms of registration. In particular, the drum-type intermediate transfer method has attracted attention because it can simplify the structure of the color image forming apparatus and reduce the cost.

By the way, in the drum type intermediate transfer system, an intermediate transfer drum is used as an intermediate transfer member, and a developing device accommodating toner of each color is disposed around the photosensitive drum, and the developing device exposes the photosensitive material. Toner images of respective colors are sequentially formed on the body drum, and in the first transfer step, the toner images of respective colors are transferred to the intermediate transfer drum to form color toner images, and then the color toner images are collectively recorded. I try to transfer it to paper.

FIG. 2 is a schematic view of a conventional color image forming apparatus. In the figure, 53 is a photosensitive drum as an image forming carrier, and 70 is an exposure device. Around the photosensitive drum 53, a charging device 54, a yellow developing device 55,
A magenta developing device 56, a cyan developing device 57, an intermediate transfer drum 73 as an intermediate transfer member that forms a first transfer portion between the photosensitive drum 53, and the cleaning device 61 are provided. Then, yellow, magenta, and cyan toner images are sequentially formed on the photosensitive drum 53 by the yellow developing device 55, the magenta developing device 56, and the cyan developing device 57.

In the first transfer step, the toner images of the respective colors formed on the photoconductor drum 53 are sequentially transferred to the intermediate transfer drum 73 to form a color toner image.
Reference numeral 74 is a cleaning device for removing the toner remaining on the intermediate transfer drum 73. Then, in the second transfer step, the color toner images formed on the intermediate transfer drum 73 are collectively transferred onto the recording paper 76. For that purpose, a recording paper conveyance system 75 is provided, and a second transfer portion is formed between the recording paper conveyance system 75 and the intermediate transfer drum 73. The recording paper conveying system 75 conveys the recording paper 76 to bring it into contact with the intermediate transfer drum 73, and transfers the color toner image of the intermediate transfer drum 73 onto the recording paper 76.

In this case, if the recording paper 76 is constantly in contact with the intermediate transfer drum 73, a part of the toner of the color toner image formed on the intermediate transfer drum 73 will be part of the recording paper 76.
Will be transferred to. Therefore, a recording paper pressing device 77 is provided so that the recording paper 76 is pressed and brought into contact with the intermediate transfer drum 73 only when the color toner images formed on the intermediate transfer drum 73 are collectively transferred. .

In the color image forming apparatus having the above structure, when the toner images of the respective colors are transferred onto the intermediate transfer drum 73, it is necessary to align the respective toner images. Therefore, a mark is attached to the intermediate transfer drum 73, the mark is detected by a sensor, etc., and the exposure device 70 is operated according to the image signal of each color in synchronization with the detection timing.
The photoconductor drum 53 is exposed.

By the way, the operation of the intermediate transfer drum 73 to which the toner images of respective colors are transferred is stable. Therefore,
The exposure device 70 controls the image signals of the respective colors in time series.
Can be operated to expose the photosensitive drum 53. Therefore, the intermediate transfer drum 73 and the photosensitive drum 53 are rotated at a constant speed by a drive motor (not shown) via a drive transmission member. Then, the image signal is transferred to the exposure device 70 in synchronization with the screen synchronization signal. The image signal in the main scanning direction is transferred line by line in synchronization with the line synchronization signal, and the photoconductor drum 53 is exposed by the image signal. The screen synchronization signal is adjusted to the time required for the intermediate transfer drum 73 to rotate once.

In this case, it is not necessary to put a mark on the intermediate transfer drum 73 or to provide a sensor or the like, so that the cost can be reduced.

[0010]

However, the above-mentioned
In the conventional color image forming apparatus, it is formed on the recording paper 76.
Color misregistration will occur in the captured image and the image quality will deteriorate.
U FIG. 3 shows a state of an image by a conventional color image forming apparatus.
FIG. In the figure, 76 is a recording paper,
The recording paper 76 is conveyed in the direction of arrow A. L _Y1, L_M1, L
_C1Are drawn in the main scanning direction and transferred to the recording paper 76.
Yellow, magenta, and cyan toner images. This
In the case of, as an image to clarify the occurrence of color shift
I used a line segment. Also, L_Y2, L_M2, L_C2Respectively
Yellow drawn in the sub-scanning direction and transferred to recording paper 76
-, Magenta, and cyan toner images.

As can be seen from the figure, in the sub-scanning direction
Is the toner image L of each color_Y2, L_M2, L _C2Is almost aligned
Although it is completely performed, in the main scanning direction,
Toner image L_Y1, L_M1, L_C1The alignment of the
As a result, color misregistration occurs in the image. Generally, the color of the image
Misalignment is often caused by defective operation of the recording medium.
Yes. For example, the photoconductor drum 53 (FIG. 2), the intermediate transfer drive
Eccentricity generated in the rotor 73, gears, etc., and movement of the drive motor
And the backlash of the drive transmission member such as the gear.
Due to rotation failure (jitter) etc.
It

Color misregistration also occurs due to poor synchronization of the image signals of the respective colors. FIG. 4 is a diagram showing a relationship between a screen synchronization signal and a line synchronization signal in a conventional color image forming apparatus. As shown, it falls on the screen synchronization signal timing t _A, so that the falls again at the timing t _B to the timing t _A 1-color screen time from T has elapsed.

In this case, the screen synchronizing signal and the line synchronizing signal are independently generated in a CPU (not shown). Therefore, the timing t of the screen synchronization signal
And falling in _A, the time between the fall of the subsequent line synchronization signal to the upstanding edge and .tau.1, and fall at the timing t _B of the screen synchronized signal, and falling of the subsequent line synchronization signal to the upstanding edge If the time between them is τ2, the times τ1 and τ2 have different lengths.

The difference between the time τ1 and the time τ2 is equal to one cycle of the line synchronization signal in the longest case. In this case, when the image is printed, the difference between the time τ1 and the time τ2 corresponds to one line pitch, and a large error occurs in the alignment, causing a color shift. SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus capable of solving the problems of the conventional color image forming apparatus and preventing the occurrence of color shift due to poor synchronization of image signals.

[0015]

Therefore, in the color image forming apparatus of the present invention, the toner images of the respective colors formed on the image forming carrier are sequentially transferred to the intermediate transfer member to form a color toner image, A color image is formed by collectively transferring the color toner images to the recording support.

An image signal memory for storing the image signal of each color, an exposure device for exposing the image forming carrier corresponding to the image signal, and an image signal for each color are transferred to the exposure device. And a controller for generating a screen synchronization signal and a line synchronization signal for transferring an image signal for each line to the exposure device.

Further, the screen synchronizing signal and the line synchronizing signal are generated in synchronization with each other.

[0018]

According to the present invention, in the color image forming apparatus, the toner images of the respective colors formed on the image forming carrier are sequentially transferred to the intermediate transfer member to form a color toner image, and the color toner image is recorded. A color image is formed by transferring them to a support at once.

An image signal memory for storing an image signal of each color, an exposure device for exposing the image forming carrier corresponding to the image signal, and an image signal for each color are transferred to the exposure device. And a controller for generating a screen synchronization signal and a line synchronization signal for transferring an image signal for each line to the exposure device.

Further, the screen synchronizing signal and the line synchronizing signal are generated in synchronization with each other. In this case, the screen synchronization signal is output to the image signal memory, and the image signal of each color is read out in correspondence with the screen synchronization signal and transferred to the exposure device. The image signal is transferred to the exposure device line by line in synchronization with the line synchronization signal.

Then, the exposure device exposes the photosensitive drum in correspondence with the image signal to form an electrostatic latent image of each color on the photosensitive drum. The electrostatic latent image of each color is developed into a toner image, which is sequentially transferred to the intermediate transfer member to form a color toner image. After that, the color toner images are collectively transferred to the recording support.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 5 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention. In the figure, 11
Is a photosensitive drum as an image forming carrier formed in a drum shape, a photoconductive layer is formed on a conductive support, a selenium photosensitive member, an organic photosensitive member, a zinc oxide photosensitive member, Any of amorphous silicon photoconductors and the like can be used. Then, the charging device 12 is disposed so as to face the photoconductor drum 11, and charges the surface of the photoconductor drum 11 uniformly and uniformly. In this embodiment, a contact type charging roller as shown in the figure is used as the charging device 12, and the charging roller is made of, for example, a metal mandrel coated with conductive rubber. In addition, a non-contact type corona discharger can be used as the charging device 12.

The LED head 13 as an exposure device
Irradiates the photosensitive drum 11 with light corresponding to the image signal to expose the photosensitive drum 11 to form an electrostatic latent image. As the LED head 13, a combination of a light source such as a laser and an LED array and an image forming optical system is used. In this embodiment,
An LED array was used as a light source, and a rod lens array was used as an image forming optical system.

Further, developing devices 14Y, 14M, 14C and 14B for accommodating toners of respective colors of yellow, magenta, cyan and black in the toner accommodating tank are provided. Each of the developing devices 14Y, 14M, 14C, 14B is arranged along the rotation direction of the photoconductor drum 11 and selects and operates the developing device containing the toner of the color necessary for forming the toner image. You can Each developing device 14
Each of Y, 14M, 14C, and 14B adsorbs toner on the surface of each toner carrier and conveys the toner to the photosensitive drum 11.
The electrostatic latent image formed on the photosensitive drum 11 is developed to form a toner image of each color on the photosensitive drum 11. Each developing device 14Y, 14M,
As 14C and 14B, any of a two-component magnetic brush developing device, a one-component magnetic brush developing device, a one-component non-magnetic developing device and the like can be used.

Further, facing the photosensitive drum 11,
Further, the intermediate transfer drum 16 as an intermediate transfer member is arranged so as to be in contact with each other, and the first transfer portion T ₁ is formed between the intermediate transfer drum 16 and the photosensitive drum 11. The intermediate transfer drum 16 electrostatically transfers the toner. In the intermediate transfer drum 16, an elastic layer made of rubber or the like is formed on a conductive support made of, for example, an aluminum pipe, A highly non-sticky surface layer is formed on the elastic layer.

In the first transfer step, a necessary transfer potential is formed on the support of the intermediate transfer drum 16 by the transfer potential forming means (not shown). A cleaning device 17 is disposed downstream of the first transfer portion T ₁ in the rotation direction of the photoconductor drum 11 if necessary, and the cleaning device 17 removes toner remaining on the photoconductor drum 11. To do.

A transfer roller 18 is disposed so as to face the intermediate transfer drum 16, and a second transfer portion T ₂ is formed between the transfer roller 18 and the intermediate transfer drum 16. Further, a cleaning device 19 is disposed on the downstream side of the second transfer portion T ₂ in the rotation direction of the intermediate transfer drum 16 as required, and the cleaning device 19 removes the toner remaining on the intermediate transfer drum 16. .

Further, a recording support carrying means is provided for carrying a recording support such as a recording paper (not shown) to the second transfer portion T ₂ . Then, in the recording support conveying means, on the upstream side of the second transfer portion T ₂ in the conveyance direction of the recording support, a recording support cassette 35 in which the recording supports are stacked and accommodated, and the recording support cassette A paper feed roller 36 for feeding the recording support housed in 35, a pair of paper feed guides 37 for guiding the fed recording support, a pair of paper feed rollers 38 for feeding the recording support, and a feeding device. A pair of paper feed guides 3 for guiding the printed recording support to the second transfer portion T _2.
9 are provided.

In addition, the second position in the transport direction of the recording support is
A paper guide 42 and a fixing device 43 are provided on the downstream side of the transfer section T ₂ . The fixing device 43 includes a pair of rollers 43a and 4a arranged to face each other so as to sandwich the recording support.
3b. The one roller 43a facing the color toner image transferred to the recording support has at least a heating means. In this embodiment, the roller 43
For a, a hollow member made of metal and having a halogen lamp as a heating means is used. A roller 43a is formed by forming a heating resistor layer made of Ni-P or the like on a base material such as glass or ceramics, and further forming a protective layer of Ta ₂ O ₅ , fluororesin or the like on the heating resistor layer. You can also do it. At least one of the pair of rollers 43a and 43b is formed of an elastic body in which rubber such as silicone rubber is laminated on a metal pipe.

Next, the operation of the color image forming apparatus of the present invention will be described based on FIG. 1 and FIGS. 6 to 8 together with FIG. 1 is a block diagram of a color image forming apparatus according to the embodiment of the present invention, FIG. 6 is a first time chart of the color image forming apparatus according to the embodiment of the present invention, and FIG.
Is a second time chart of the color image forming apparatus in the embodiment of the present invention, and FIG. 8 is a third time chart of the color image forming apparatus in the embodiment of the present invention.

In this case, the color image is formed by four color toners of yellow, magenta, cyan and black. Then, first, an image signal for forming a yellow toner image is generated, and the image signal is transferred to the LE.
It is transferred to the D head 13. And the LED head 1
Light corresponding to the image signal is applied to the photoconductor drum 11 by 3, and electrostatic latent images corresponding to the toner images of the respective colors are formed on the photoconductor drum 11.

At this time, a portion of the photosensitive drum 11 corresponding to the image is irradiated with light to form an image portion where the charged electric charge is erased and a non-image portion where the charged electric charge is left as it is. Therefore, the controller 21 outputs the print signal SG1, the drive motor 22 is driven based on the print signal SG1, and the intermediate transfer drum 16 and the photoconductor drum 11 are kept constant via the drive transmission member 23 such as a gear. It can be rotated at the peripheral speed and at the same speed.

On the other hand, the screen synchronizing signal SG3 is output from the controller 21 to the image signal memory 24, and the image signal SG for each color is made to correspond to the screen synchronizing signal SG3.
4 is read out and transferred to the LED head 13. In this case, the image signal SG4 is transferred to the LED head 13 line by line in synchronization with the line synchronization signal SG2. Then, the LED head 13 exposes the photosensitive drum 11 in correspondence with the image signal SG4. The LED head 13 is the LED driver 2
5 and an LED array 26, the LED driver 25 receives the image signal SG4 and drives the LED array 26.

By the way, as shown in FIG. 7, a color image is formed by a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image.
Then, first, the controller 21 generates the screen synchronization signal SG3 for forming the yellow toner image at the timing t _{Y and} outputs it to the image signal memory 24. At this time, the first line synchronization signal SG2 for forming the yellow toner image is also synchronized with the screen synchronization signal SG3, and the image signal memory 24 and the LED are synchronized.
It is output to the head 13. As a result, the image signal SG4 for one line becomes L by the line synchronization signal SG2.
Transferred to the ED head 13, the LED head 13 exposes the photosensitive drum 11 in correspondence with the image signal SG4.

Further, the image signal SG4 for one line is similarly generated by the LED head 13 by the next line synchronization signal SG2.
Then, the LED head 13 exposes the photoconductor drum 11 in correspondence with the image signal SG4. By repeating such an operation, an electrostatic latent image for forming a yellow toner image is formed on the photosensitive drum 11. Next, the controller 21 generates a screen synchronization signal SG3 for forming a magenta toner image at the timing t _{M and} outputs it to the image signal memory 24. In this case, one cycle of the screen synchronization signal SG3, that is,
The time between the timing t _Y and the timing t _M is set so as to correspond to one rotation time of the intermediate transfer drum 16.

The first line sync signal SG2 for forming a magenta toner image is also the screen sync signal S.
It is output to the image signal memory 24 and the LED head 13 in synchronization with G3. As a result, the image signal SG4 for one line is transferred to the LED head 13 by the line synchronization signal SG2, and the LED head 13 exposes the photosensitive drum 11 in correspondence with the image signal SG4.

The image signal SG4 for one line is similarly generated by the LED head 13 by the next line synchronization signal SG2.
Then, the LED head 13 exposes the photoconductor drum 11 in correspondence with the image signal SG4. By repeating such operations, an electrostatic latent image for forming a magenta toner image is formed on the photosensitive drum 11. Similarly, an electrostatic latent image for forming a cyan toner image and an electrostatic latent image for forming a black toner image are formed on the photosensitive drum 1.
1 is formed.

As described above, since each screen synchronizing signal SG3 and each line synchronizing signal SG2 are controlled and synchronized by the controller 21, an electrostatic latent image for forming a toner image of each color on the photosensitive drum 11 is formed. Alignment can be done. The screen synchronization signals SG3 and the line synchronization signals SG2 can be synchronized by using a counter circuit, for example.

Subsequently, the electrostatic latent images thus successively formed on the photosensitive drum 11 are developed into toner images of the respective colors, and the toner images of the respective colors are collectively transferred and fixed on the recording support. The operation up to is described. That is, when the electrostatic latent image for forming the yellow toner image is formed on the photoconductor drum 11, the developing device 14Y is advanced in advance and placed at a position where it contacts the photoconductor drum 11.

The developing device 14Y visualizes the electrostatic latent image with yellow toner to form a yellow toner image on the photosensitive drum 11. In this case, since an organic photoconductor is used as the photoconductor drum 11,
The photoconductor drum 11 is charged with a negative polarity, and the toner is adsorbed to the portion where the charge is erased. Therefore, the toner is negatively charged.

Then, facing the photosensitive drum 11,
In addition, the intermediate transfer drum 16 arranged so as to be in contact with each other.
Then, the transfer potential forming means forms a transfer potential having a positive polarity. Therefore, in the first transfer step, the yellow toner image formed on the photosensitive drum 11 is electrostatically transferred to the intermediate transfer drum 16.
In this case, the transfer potential forming means is the intermediate transfer drum 1
The support of No. 6 is connected to a power source (not shown) having a positive polarity, and an electric field is generated from the intermediate transfer drum 16 side to the photosensitive drum 11 side. On the other hand, since the toner is negatively charged, a force in the direction opposite to the direction of the electric field acts on the toner, so that the toner is transferred to the photosensitive drum 1 at the first transfer portion T ₁ .
1 is transferred to the intermediate transfer drum 16. In addition, the photosensitive drum 1 is not transferred to the intermediate transfer drum 16.
The toner remaining on No. 1 is removed by the cleaning device 17 so as not to interfere with the next image formation.

In this way, the toners of yellow, magenta, cyan, and black are transferred to the intermediate transfer belt 16, and the toner images of yellow, magenta, cyan, and black are sequentially transferred to the intermediate transfer drum 16. As a result, a color toner image of a mirror image is formed. On the other hand, the paper feed roller 36 feeds the recording support housed in the recording support cassette 35, and the paper feed guide 37 guides the recording support to the paper feed roller 38. Next, the intermediate transfer drum 16
Top synchronously to move into the second transfer portion T ₂ of the color toner image, the recording support is a sheet conveying the sheet feeding guide 39 by the sheet conveying roller 38, the second by the sheet feeding guide 39 Is guided to the transfer section T ₂ . Then, in the second transfer step, the recording support is superposed on the color toner image on the intermediate transfer drum 16, and is sandwiched and pressed by the intermediate transfer drum 16 and the transfer roller 18.

In this case, the transfer potential forming means forms a negative transfer potential having a polarity opposite to that of the first transfer step on the intermediate transfer drum 16. In this state, an electric field is generated from the transfer roller 18 side to the intermediate transfer drum 16 side.
Since the toner is negatively charged, a force in the direction opposite to the direction of the electric field acts on the toner, and the toner is transferred from the intermediate transfer drum 16 to the recording support at the second transfer portion T ₂ . , A color toner image is transferred to the recording support.

Then, the recording support on which the color toner image is transferred is guided by the paper guide 42 and conveyed to the fixing device 43, where the fixing device 43 fixes the color toner image on the recording support, and the recording support is formed. A color image is formed on the body. On the other hand, the toner remaining on the intermediate transfer drum 16 without being transferred to the recording support is cleaned by the cleaning device 19
Are removed so as not to hinder the next image formation.

Next, the relationship between the screen synchronizing signal and the line synchronizing signal in this embodiment will be described. FIG. 8 is a diagram showing the relationship between the screen sync signal and the line sync signal in the embodiment of the present invention. As shown in the figure, the screen synchronization signal SG
3 falls at a timing t _A, so that the falls again at the timing t _B of one color screen time T has elapsed from the timing t _A.

In this case, the screen synchronizing signal SG3 and the line synchronizing signal SG2 are generated in synchronization with each other in the controller 21 (FIG. 1). Therefore, the time between the trailing edge of the screen synchronizing signal SG3 at the timing t _A and the trailing edge of the line synchronizing signal SG2 following the trailing edge is set to τ3, and the trailing edge of the screen synchronizing signal SG3 at the timing t _B Line sync signal SG following the fall
Let τ4 be the time between the fall of 2 and time τ3,
τ4 has the same length.

Therefore, it is possible to prevent the occurrence of color shift in the image. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0048]

As described in detail above, according to the present invention, in the color image forming apparatus, the toner images of the respective colors formed on the image forming carrier are successively transferred to the intermediate transfer member to obtain the color toner images. Then, the color toner images are collectively transferred to the recording support to form a color image.

An image signal memory for storing the image signal of each color, an exposure device for exposing the image forming carrier according to the image signal, and an image signal for each color are transferred to the exposure device. And a controller for generating a screen synchronization signal and a line synchronization signal for transferring an image signal for each line to the exposure device.

Further, the screen synchronizing signal and the line synchronizing signal are generated in synchronization with each other. Therefore, the toner images of the respective colors can be aligned in both the main scanning direction and the sub-scanning direction, so that the color misregistration of the image can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram of a color image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a schematic view of a conventional color image forming apparatus.

FIG. 3 is a diagram showing an image state of a conventional color image forming apparatus.

FIG. 4 is a diagram showing a relationship between a screen synchronization signal and a line synchronization signal in a conventional color image forming apparatus.

FIG. 5 is a schematic diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 6 is a first time chart of the color image forming apparatus in the embodiment of the invention.

FIG. 7 is a second time chart of the color image forming apparatus according to the embodiment of the invention.

FIG. 8 is a third time chart of the color image forming apparatus according to the embodiment of the invention.

[Explanation of symbols]

 13 LED head 16 Intermediate transfer drum 21 Controller 24 Image signal memory SG2 Line synchronization signal SG3 Screen synchronization signal SG4 Image signal

Claims (1)

[Claims] 1. A color image in which toner images of respective colors formed on an image forming carrier are sequentially transferred to an intermediate transfer member to form a color toner image, and the color toner images are collectively transferred to a recording support. In a color image forming apparatus for forming
(A) An image signal memory for storing image signals of respective colors,
(B) an exposure device that exposes the image forming carrier according to the image signal; and (c) a screen synchronization signal for transferring the image signal for each color to the exposure device, and for each line. And a controller for generating a line synchronization signal for transferring the image signal of (1) to the exposure device, and (d) the screen synchronization signal and the line synchronization signal are generated in synchronization with each other. Forming equipment.