JP2002108040A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of attaining a high speed image processing by suppressing the delay memory of image data between respective color printing units to the irreducible minimum. SOLUTION: As for the image forming device provided with plural printing units 23K to 23C for printing based on the image data, and for forming an image by successively printing by plural printing units 23K to 23C and then overlapping, as for the arrangement of plural printing units 23K to 23C, the black one having resolution higher than that of the others is arranged on the uppermost stream side in terms of printing order. Then, the required capacity of the delay memory is suppressed to the minimum as compared with the case that the high resolution printing unit is arranged on the downstream side. Besides, by having such the arrangement, the efficiency is enhanced, and then, the reduction of the whole image processing speed is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus having a plurality of print units. More specifically, the present invention relates to an image forming apparatus having a plurality of print units having different resolutions.

[0002]

2. Description of the Related Art In the field of an image forming apparatus having a plurality of print units, a system in which a plurality of print units are arranged in series and images are sequentially superimposed on a medium by each print unit is used. In this type of image forming apparatus, for example, Japanese Patent Application Laid-Open No. 9-240058
As disclosed in Japanese Unexamined Patent Application Publication No. H11-107, a technique has been proposed in which apparent resolution is changed by correcting data according to the difference between the resolution of a plurality of print heads and a reference resolution.

[0003]

However, in the above-described conventional image forming apparatus, it is assumed that all of the plurality of print units provided have the same resolution. Since the data output delay differences between the print units are all relatively the same, the delay memories for storing data are all the same. However, in recent years,
In order to satisfy both the demand for higher resolution and the demand for cost reduction, print heads having higher resolution than other colors have been used for specific colors. As a result, it is necessary to provide print units having different resolutions in the image forming apparatus. In such a case, if the capacity of the delay memory is adjusted to the print unit having the highest resolution, the other print units having not so high resolution require an excessive delay memory capacity. Further, there is a problem that the overall image processing speed is reduced.

The present invention has been made to solve the above-mentioned problems of the conventional image forming apparatus. That is, an object of the present invention is to provide an image forming apparatus in which a delay memory between print units is minimized by a necessary amount and an image processing speed is increased.

[0005]

SUMMARY OF THE INVENTION An image forming apparatus according to the present invention, which has been made to solve this problem, has a plurality of print units for performing printing based on image data.
An image forming apparatus that sequentially prints with a plurality of print units to form a superimposed image, wherein the arrangement of the plurality of print units is higher in a print order as the print units are higher in resolution. In this image forming apparatus,
Since each print unit performs printing based on the image data, the image data for which printing has been completed is no longer necessary. Since the arrangement of the print units is as described above, the higher the resolution, that is, the larger the amount of data, the earlier the printing is completed, and the more image data is unnecessary. For this reason, the capacity of the delay memory for storing image data can be minimized.

The image forming apparatus of the present invention also has a delay memory for storing image data to be printed by the print unit for each of the plurality of print units that are in the second or subsequent print order. It is preferable to have a memory capacity necessary for delaying printing by the printing unit by a time difference from printing by the printing unit in the first printing order to printing by the printing unit. In this case, the delay memory only needs to be provided for print units other than the print unit requiring the largest memory capacity, so that the total capacity of the delay memory can be reduced. Here, it does not prevent the print unit having the first print order from having the delay memory. Even in such a case, since the largest amount of image data is unnecessary first, the total capacity of the delay memory does not increase so much.

[0007]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
The image forming apparatus according to the present embodiment embodies the present invention as a copier / printer, and has a main configuration shown in FIG.

That is, four printing units 23K (black), 23Y (yellow), 23M (magenta), and 23C (cyan) are arranged in this order from the upstream side in the paper passing direction.
Color print units are arranged. Each of the print units 23K to 23C is a photoconductor 25K to 25C, respectively.
C and LED heads 24K to 24C. The intervals between the transfer positions of the print units 23K to 23C are uniform. And 24K black LED head
Only has a resolution of 1200 dpi, but the LED heads 24Y to 24C of other colors have a resolution of 600 dpi.
i. The reason that only black has a higher resolution than the others is that black is mainly used for characters and line drawings, and it is desired to form an image clearly in detail by its nature. Known devices such as a charger, a developing device, and a transfer charger are arranged around each of the photoconductors 25K to 25C. However, these devices are not particularly related to the features of the present invention, so that they are illustrated and described. Omitted.

In this image forming apparatus, printing paper supplied from a paper feeding device such as a paper cassette moves along a paper passing path P and passes through each of the print units 23K to 23C. As a result, the four color toner images are superimposed on the printing paper. Thereafter, the printing paper is discharged from the image forming apparatus after the toner image is fixed.

The block configuration of the control system of the image forming apparatus is as shown in FIG. That is, each LED
The heads 24K to 24C are each provided with a delay memory 22K.
Through 22C to the image output control unit 20. The image output control unit 20 receives CMYK image data from the RGB → CMYK conversion unit 30 or the printer output control unit 50 via the copier / printer switching unit 40. The RGB → CMYK conversion unit 30 is connected to the scanner 10 and receives RGB image data obtained by reading a document. The printer output control unit 50 is connected to the LAN via the interface 51. Several host computers are connected to the LAN. As a result, the printer output control unit 50 receives the image data transmitted from the host computer.

Thus, when functioning as a copying machine, image data obtained by reading an original with the scanner 10 is converted to CMYK and sent to the image output control unit 20. When functioning as a printer, CMY transmitted from the host computer
The K image data is sent to the image output control unit 20 via the printer output control unit 50. Then, the image output control unit 20 performs necessary correction on the received image data, and synchronizes with the supply of the printing paper, for each scanning line and for each color, for each LED head 24K.
To 24C as a drive signal. Each drive signal is temporarily stored in the delay memories 22K to 22C, and then stored in each LED.
It is supplied to the heads 24K to 24C. Thus, the toner images of each color are superimposed on the printing paper in the order of K, Y, M, and C. At this time, the image forming operation of each color is executed with a delay in timing from the upstream side to the downstream side so that the toner images are superimposed on the same position of the conveyed printing paper. Each delay memory 22K-22
C is for that.

The time difference between the output times of the respective printer units and the capacity of the delay memory based on the difference will be described with reference to FIG. In FIG. 3, T
1 to T4 indicate the print output timing of each color from the first color black to the fourth color cyan for one scan line. Here, assuming that the print output of the first color black is used as a reference, a delay memory having a capacity indicated by oblique lines is required for each of the second color yellow to the fourth color cyan. That is, the delay time of the third color magenta and the fourth color cyan is twice or three times that of the second color yellow with respect to the first color black. Therefore, the delay memory capacity is twice and three times that of the second color yellow, respectively. Therefore, as a whole, the delay memory capacity of the second color yellow, 6
Double the total capacity is required.

This will be compared with the case of FIG. FIG. 4 shows the conventional resolution, in which all four colors have the same resolution (600
4 is a chart showing the capacity of the delay memory in the image forming apparatus having the resolution (dpi) as in FIG. 3. Comparing FIG. 3 with FIG. 4, it can be seen that the required total capacity of the delay memory does not change even though the resolution of black is increased to 1200 dpi. This is because the first color black having a high resolution and a large data capacity is set as the first print order so that the data is not required at an early stage.

Next, a comparison is made with the case of FIG. FIG.
Sets the resolution of black to 120, as in the present embodiment.
4 is a chart showing the capacity of a delay memory in the image forming apparatus increased to 0 dpi as in FIG. 3. However, the printing order is black for the fourth order. In this case, for the fourth color black, a delay memory having a capacity six times the delay memory capacity of the second color magenta is required.
Therefore, the total capacity of the delay memory of the second color magenta is actually nine times as much as a whole. This is because black data having a high resolution and a large data capacity must be held until the timing of T4. Therefore, in such an image forming apparatus, the overall image processing speed tends to be slow due to the excessive capacity of the delay memory.

Thus, comparing FIG. 3 with FIG. 5, it can be seen that the total capacity of the required delay memory is minimized by setting the printing order of black with high resolution to be the first. Therefore, the case of FIG. 3 (this embodiment)
Thus, the overall image processing speed hardly decreases due to the capacity of the delay memory.

In the case of FIG. 3 (this embodiment), a delay from the transmission of the print drive signal from the image output control unit 20 to the timing T1 is still necessary. Compared with the delay data capacity shown in FIG. 4, it is undeniable that the delay data capacity is increased by increasing the resolution of black to 1200 dpi. However, this is the same in FIG. Therefore, in comparison of FIG. 3 with FIG. 5, the total capacity of the delay memory required in FIG. 3 is relatively reduced to a minimum.

As described in detail above, the image forming apparatus according to the present embodiment has a plurality of print units 23K to 23C for performing printing based on image data, and sequentially prints by the plurality of print units 23K to 23C. This is to form a superimposed image. In this case, the arrangement of the plurality of print units 23K to 23C is set to the uppermost stream in the print order, with the black unit having a higher resolution than the others. This makes it possible to minimize the required capacity of the delay memory as compared with the case where the high-resolution print unit is arranged on the downstream side.
This also improves efficiency and prevents a reduction in overall image processing speed.

The present embodiment is merely an example, and does not limit the present invention. Therefore, naturally, the present invention can be variously modified and modified without departing from the gist thereof.

For example, in this embodiment, an image forming apparatus using an LED head has been described. However, as shown in FIG. 6, the present invention can naturally be applied to an image forming apparatus using a laser head (LD head). . In addition, “P” in FIGS. 1 and 6 may be an intermediate transfer zone instead of a paper passing path.
The present invention is not limited to the tandem type in which a photoconductor and a print head are provided for each color, and the present invention can be applied to an image forming apparatus in which a photoconductor and a print head are shared for each color and only a developing device is provided for each color. Alternatively, the present invention can be applied to an apparatus of another image forming method such as an ink jet method or a silver salt photosensitive method. Further, the present invention is not limited to a multifunction machine of a copying machine and a printer, but may be any one of the multifunction machines.

Further, in the present embodiment, only the black print unit has a resolution of 2 other than the other print units.
It was decided to have a resolution of 1200 dpi, which is twice
The resolution of print units of other colors may be increased according to the application. However, even in this case, the print units are arranged such that the print unit having a higher resolution is positioned closer to the upstream side of the print order. Furthermore, in the present embodiment, an example of a full-color image forming apparatus of four colors has been described, but the number of colors is not limited to four. For example, the present invention may be applied to a two-color image forming apparatus as shown in FIG. FIG. 7 shows a first color print unit having a photoconductor 251 and a print head 241 (1200 dpi), a photoconductor 252 and a print head 2.
And FIG. 14 is an example of an image forming apparatus having a second color print unit having 42 (600 dpi).

[0021]

As is apparent from the above description, according to the present invention, there is provided an image forming apparatus in which the delay memory between each print unit is minimized by the required amount and the image processing speed is increased. Have been.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of an image forming apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating a system configuration of the image forming apparatus according to the embodiment;

FIG. 3 is an explanatory diagram showing output timing of each print unit and a delay memory capacity based on the output timing.

FIG. 4 is an explanatory diagram showing output timing of each print unit and a delay memory capacity based on the output timing (comparative example).

FIG. 5 is an explanatory diagram showing output timing of each print unit and a delay memory capacity based on the output timing (comparative example).

FIG. 6 is an explanatory diagram showing an example in which the present invention is applied to an image forming apparatus using an LD head.

FIG. 7 is an explanatory diagram showing an example in which the present invention is applied to a two-color image forming apparatus.

[Explanation of symbols]

 22K-22C delay memory 23K-23C print unit

Continued on the front page F term (reference) 2C162 AE12 AE21 AE28 AE47 AF16 AF61 FA17 2H030 AA06 AA07 AB02 AD13 AD16 BB02

Claims (2)

[Claims] 1. An image forming apparatus having a plurality of print units for performing printing based on image data and sequentially printing by the plurality of print units to form a superimposed image, the arrangement of the plurality of print units is changed to a high resolution. An image forming apparatus, wherein the image forming apparatus is located on the upstream side of the printing order. 2. The image forming apparatus according to claim 1, wherein a print order of the plurality of print units is two.
For each of the print units following the first print unit, there is a delay memory for storing image data to be printed by the print unit. An image forming apparatus having a memory capacity necessary for delaying by a time difference.