JP3130916B2 - Multicolor image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multicolor image in which a multicolor image is formed by superimposing a plurality of color images on an intermediate transfer body and transferring them at once to a transfer material. The present invention relates to a forming apparatus.

2. Description of the Related Art Conventionally, as a device for preventing color misregistration and color unevenness of a multicolor image forming apparatus using an intermediate transfer member, for example, Japanese Patent Application Laid-Open No.
As described in Japanese Patent Application Laid-Open No. 673, there is an apparatus in which belt meandering of an intermediate transfer member is prevented.

Also, examples of successful maintenance of the precise resist control required for full-color machines by color multiplexing using relatively inexpensive components include U.S. Pat.Nos. 4,652,115 and 4,788,572, A method of synchronizing the photosensitive belt and the intermediate transfer belt is used.

[Problems to be Solved by the Invention] However, when a multicolor image is formed by forming a toner image of each color on an intermediate transfer member and then collectively transferring the toner image from the intermediate transfer member to a copy sheet, the following problems arise. There is.

(1) Since there are two transfer steps, compared with a system requiring only one transfer step, color unevenness and
Color shift easily occurs.

(2) uniform speed control of the intermediate transfer body, accuracy of resist control,
Color unevenness and color misregistration occur depending on the meandering condition.

(3) Color unevenness and color misregistration occur due to vibration of mechanical elements of an engine constituting the printer.

Such a drawback increases as the accuracy of uniform movement of the intermediate transfer member, the degree of registration control deviation, belt meandering, mechanical vibration, and the like become worse.

Therefore, in order to reduce image quality deterioration depending on such factors, it is necessary to improve control accuracy and perform complicated control. Also, in order to minimize mechanical vibration, the rigidity of the device must be increased.

 Therefore, there is a disadvantage that the cost of the apparatus is increased.

In addition, among the images of the respective colors transferred to the intermediate transfer body, particularly for the first and last transferred colors, the cleaner that erased the previous image is separated from the intermediate transfer body immediately before the transfer of the first color. May be performed, and at the time of the last color transfer, the cleaner may be in contact with the intermediate transfer member. There is a problem that deviation is highly likely to occur.

The present invention, in a multi-color image forming apparatus that transfers each color image to an intermediate transfer body and collectively transfers it to copy paper, reduces color unevenness due to the first or last transferred color image and color change for each print. It is intended to be.

[Means for Solving the Problems] According to the present invention, a multi-color image is formed by superimposing a color image composed of four color components on an intermediate transfer member and transferring the color image to the transfer member at a time. In the color image forming apparatus, input means for inputting image data of each color component, and forming an image of each color component on the intermediate transfer body in a frame-sequential manner in accordance with the image data input by the input means And an image forming means for forming the color image, wherein the first color component of the four color components to form an image at the beginning or end of image formation by the image forming means is Has a screen angle of 1,
The image formed by the second color component and the image formed by the third color component of the four color components have a common second screen angle different from the first screen angle. And

[Operation] In the present invention, when each color image is superimposed on the intermediate transfer member, the image formed at the first or last color is formed at a screen angle different from the screen angle in the image formation of another color. By doing so, it is possible to suppress the occurrence of color misregistration of the first color or the last color, the occurrence of color unevenness, and the change in tint every time printing is performed, thereby obtaining stable image quality.

For example, as shown in FIG. 4 (a), a color shift occurs in a pattern of each color image due to mechanical vibration or the like, and a long-period color unevenness that is easily visible to the naked eye is generated. As shown in FIG. 4 (b), the overlapping portion and the non-overlapping portion of each color image are finely dispersed, and the color unevenness has a short cycle and becomes less noticeable.

Therefore, especially for the first and last color images in which color misregistration due to mechanical factors is likely to occur, the screen angle is changed from that of the other color images, thereby preventing color unevenness and color change for each print.

Embodiment FIG. 1 is a configuration diagram showing an embodiment of a color image forming apparatus.

In the figure, a pre-exposure lamp 7, a corona primary charger 8, a laser scanner 1 for irradiating a laser beam according to each color signal, a first mirror 2 and a second mirror 3 are provided around an OPC photosensitive drum 5. And a developing unit 4 having four developing units for accommodating magenta, cyan, yellow, and black toners.

Each color developing device is composed of a developing cylinder (not shown) and a non-magnetic blade.

The developer is composed of a toner and a carrier, and is mixed at a fixed ratio. The toner and the carrier are triboelectrically charged, so that the toner is negatively charged and the carrier is positively charged. This developer, by the magnetic field of the fixed magnet,
The brush is raised on the surface of the cylinder and formed into a uniform developer layer by a blade.

A developing bias is simultaneously applied to the developing cylinder. Therefore, the negative component of the developing bias is larger than the positive component. Then, the toner is attracted to the light portion of the photosensitive drum by the negative component of the drum surface potential and the developing bias, and turns the electrostatic latent image into a visible image. For example, when a magenta latent image is formed, the developing unit 4 moves, the magenta developing device comes to the developing position, and only magenta color development is performed. The magenta toner image formed on the photosensitive drum 5 is electrostatically transferred onto the intermediate transfer belt by applying a positive voltage to a counter electrode and a primary transfer electrode of the photosensitive drum.

At the time of this transfer, the paper feed roller 13 on the paper feed box
Is released, the magenta toner image is not transferred to the copy paper, and is conveyed to the transfer section again with the movement of the intermediate transfer belt 18 while being held on the intermediate transfer belt 18.

In this way, the magenta toner image is transferred to the intermediate transfer belt.
After being transferred onto the photosensitive drum 18, the residual toner on the photosensitive drum 5 is completely cleaned by the drum cleaner 6.

Further, before the formation of a latent image of the next color, light from the pre-exposure lamp 7 is applied to the surface of the photosensitive drum 5 to erase residual charges on the surface of the drum.

The above-described series of processes of pre-exposure, primary charging, laser exposure, development, primary transfer, and drum cleaner are similarly repeated for cyan toner, yellow toner, and black toner. , A four-color image of a magenta toner image, a cyan toner image, a yellow toner image, and a black toner image.

When the four-color image is formed on the intermediate transfer belt 18 in this way, the paper feed roller is operated, and the copy paper 19 passes through the register rollers 10 and 11 and synchronizes with the position of the four-color image. It is sent to the transfer roller 13. At this time, when the copy paper 19 approaches the second transfer portion, the bias roller 13 is urged, and the intermediate transfer belt and the copy paper 19 are sandwiched between the two secondary transfer rollers.

At this time, a positive voltage is applied to the secondary transfer roller 13, the bonding force between the transfer paper and the toner becomes stronger than the bonding force between the transfer belt and the toner, and the toner adheres to the transfer paper.

The copy paper is further moved to the fixing unit. Each fixing roller 14
Each has a built-in heater lamp. When the copy paper passes through the fixing roller 14 by heat and pressure,
The color toner images are fixed simultaneously.

FIG. 2 is a schematic diagram showing an image forming pattern of each color formed by the full-color copying material of the present embodiment.

In this embodiment, a four-color full-color image is formed by superimposing formed images of the respective colors using four color toners. Then, as shown in FIG. 2, the screen angle (45 °) and the final color (ie, the fourth color) black (Bk) in the magenta (M) image forming pattern of the first color
Are different from the screen angles of the second color cyan (C) and the third color yellow (Y) (both are 0 °).

FIG. 3 is a block diagram showing the image forming pattern generating apparatus of the present embodiment.

First, a multicolor image signal A (in this embodiment, M,
C, Y, and Bk digital signals) are D / D for each color component.
The signal is converted into an analog signal a by the A converter 21.

On the other hand, using a clock frequency-divided from the high-speed clock by the pulse pattern generator 22, a reference signal b (a triangular wave in this embodiment) determined for each color component is generated under the control of the CPU 23. Further, the reference signal b
Is input to the delay line 26 and is delayed. The delay line 26 has eight kinds of delay patterns in the present embodiment, and one of them is selected by the selector 27. In addition, as shown in FIG.
Eight types were prepared with 1/4 pixel delay as one unit of delay amount. The selector 27 reads the delay pattern information from the phase change pattern generator 24 line by line by the CPU 23.

In the present embodiment, the phase change amount pattern generator 24
It is a RAM and contains delay pattern information to be selected for each line for each color.

The counter 25 counts a horizontal synchronization signal. Every time the counter 25 performs a counting operation, the selector 27 sequentially selects a delay pattern according to the delay pattern written in the pattern generator 24 and outputs it as a reference signal c. The unit of the triangular wave is 2 as shown in FIG.
It is assumed that one pixel corresponds to one unit, that is, the cycle of the triangular wave corresponds to two pixels, and the delay amount is one unit for 1/4 pixel. The analog signal a is compared with the reference signal c by the comparator 28, becomes a PWM signal d, is amplified by the amplifier 29, and is output as the processed signal B.

The above operation is performed for each color component, and the image formation is performed at a screen angle of 45 ° by delaying the M component by 4/4 pixels with respect to the odd lines and not delaying the even lines by {4}. a)｝. The C and Y components are image-formed at no screen delay for all lines, that is, at a screen angle of 0 ° (FIGS. 2B and 2C). Further, the Bk component has no delay for the (i + 1) th line (i = 0, 1, 2...), A delay of 2/4 pixels for the (i + 2) th line, and the (i + 3) th.
An image is formed at a screen angle of 26.6 ° with a 4/4 pixel delay for the line and a 6/4 pixel delay for the (i + 4) th line (FIG. 2 (d)).

In this way, each color is output as a multiplex image by the above-described full-color copying machine.

By making the screen angles of the first and fourth images different from the screen angles of the second and third colors in this manner, the screen angles of the conventional image shown in FIG. As shown in b), color unevenness and the like can be eliminated.

[Effects of the Invention] As described above, according to the present invention, when each color image is superimposed on the intermediate transfer member, the screen angle of the color for which image formation is performed first or last is changed to the screen angle of another color. In a multi-color image forming apparatus using an intermediate transfer member, a color shift of the first color and the last color that occurs at the time of transfer, the occurrence of color unevenness, and a change in color tone every time printing is performed by setting differently from Can be suppressed, and the image quality can always be stabilized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing the overall configuration of a full-color copying machine using an intermediate transfer member according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an image forming pattern of each color in the present embodiment. FIG. 3 is a block diagram showing a circuit configuration for forming the image forming pattern shown in FIG. FIG. 4 is a schematic diagram for explaining an image generated by the embodiment in comparison with a conventional image. 1 ... laser scanner, 2 ... first mirror, 3 ... second mirror, 4 ... developing unit, 5 ... photosensitive drum, 6 ... drum cleaner, 7 ... pre-exposure lamp, 8 ... primary Charger, 9: Primary transfer electrode, 10, 11: Registration roller, 12: Tension roller, 13: Secondary transfer roller, 14: Fixing roller, 15: Fixed roller, 16: Motor, 17: Motor control / drive circuit, 18: Intermediate transfer belt, 19: Copy paper, 21: D / A converter, 22: Pulse pattern generator, 23: CPU, 24: Phase change pattern Generator, 25 ... Counter, 26 ... Shift register, 27 ... Selector, 28 ... Comparator, 29 ... Amplifier.

Continuation of front page (56) References JP-A-62-42693 (JP, A) JP-A-1-92771 (JP, A) JP-A-1-273080 (JP, A) JP-A-1-282571 (JP) , A) JP-A-61-225971 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/525 B41J 2/44 G03G 15/01

Claims (1)

(57) [Claims] 1. A multicolor image forming apparatus for forming a multicolor image by superimposing a color image composed of four color components on an intermediate transfer member and transferring the color image to the transfer member at a time. Input means for inputting the image data of the components; and forming the color image on the intermediate transfer body in a face-sequential manner in accordance with the image data input by the input means. An image forming unit, wherein the image formed by the first color component of the four color components formed at the beginning or end of the image formation by the image forming unit has a first screen angle. The image formed by the second color component and the image formed by the third color component of the four color components have a common second screen angle different from the first screen angle. Characteristic Multicolor image forming apparatus.