JPH04238372A - Color printer - Google Patents

Abstract

PURPOSE:To correct the positional deviation of an image and to improve image quality by setting the rotational period of an image forming medium to integer part of the rotational period of a transfer medium. CONSTITUTION:The rotational period T1 of the image forming medium 1i is set at one part of an integer of the rotational period T2 of the transfer medium 2, so that the periods of transfer positional deviation fluctuations as the least common multiples of the T1 and T2 are shortest, and equalized to the period of one rotation of the transfer medium 2. Therefore, when a transfer positional deviation is corrected, it is corrected within the range of the period of one rotation of the transfer medium 2. In other words, the positional deviation value of the image transferred from each image forming medium 1i on the position of the equal rotational angle of the transfer medium 2, is measured, and stored in a position storage means 4, at each image forming medium 1i. A correcting means 5 outputs a signal that the interval of scanning is corrected based on the data of the positional deviation, and the corrected image is formed on each image forming medium 1i.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has a plurality of image forming media which are composed of rotary bodies that rotate at a predetermined period and form images by scanning at predetermined intervals, and these image forming media are arranged around the The present invention relates to a color printing apparatus including a transfer medium including a rotating body that forms one image by superimposing and transferring images formed on respective image forming media.

0002

2. Description of the Related Art As a color printing apparatus using electrophotography, as shown in FIG.
After the toner images formed on the photosensitive drums 11y, 11m, 11c, and 11k of each color are sequentially superimposed and transferred onto the transfer drum 12, the printing paper 6 is placed around the transfer drum 12.
An apparatus for obtaining color images by printing on images has been proposed. Such a multi-drum type color printing device is suitable for high-speed printing because it is easy to increase the printing speed.

0003

[Problems to be Solved by the Invention] However, in the above-mentioned color printing apparatus, as shown in FIG. 6(b), for example, due to eccentricity of each photosensitive drum 11, the peripheral speed (speed of the outer circumference of the photosensitive drum) is lower than that of the photosensitive drum. It fluctuates during a period of 11 revolutions. This variation in the circumferential speed of the photosensitive drum 11 causes positional deviation during image formation. Furthermore, due to fluctuations in the peripheral speed of the transfer drum 12, these fluctuations are combined in the transfer of the image from the photosensitive drum 11, and as shown in the figure, the toner image is transferred over one cycle (corresponding to four rotations of the transfer drum 12). There is a problem in that the positions fluctuate irregularly and the registration of images of each color shifts, leading to a decrease in image quality in color printing.

The present invention has been made in view of the above problems, and an object of the present invention is to improve the image quality in color printing by correcting the positional deviation of images.

[0005]

[Means for Solving the Problems] As shown in FIG. 1, the first means of the present invention for solving the above-mentioned technical problems consists of a rotating body that rotates at a predetermined period and scans at a predetermined interval. A plurality of image forming media 1i for forming an image are provided, these image forming media 1i are arranged around the image forming medium 1i, and images formed on each image forming medium 1i are superimposed and transferred to form one image. In a color printing device equipped with a transfer medium 2 consisting of a rotating body, the image forming medium 1
The rotation period of i is set to an integral fraction of the rotation period of the transfer medium 2.

[0006] Also, since it is set to 1/integer above, the second
The means includes a rotation signal output means 3 that outputs a signal corresponding to the rotation angle of the transfer medium 2, and a rotation signal output means 3 that outputs a signal corresponding to the rotation angle of the transfer medium 2, and a rotation signal output means 3 that outputs a signal corresponding to the rotation angle of the transfer medium 2.
When forming an image on the image forming medium 1i based on the positional deviation amount stored in the position storage means 4; The present invention also includes a correction means 5 for correcting the scanning interval.

[0007]

[Operation] In the present invention, as shown in the above means, the rotation period T1 of the image forming medium 1i is set to an integer fraction of the rotation period T2 of the transfer medium 2, so that the transfer position deviation is the least common multiple of T1 and T2. The period of fluctuation is the shortest and equal to the period of one rotation of the transfer medium 2. Therefore, when correcting the transfer position shift, it is sufficient to correct the transfer position within the period of one rotation of the transfer medium 2.

Therefore, in order to correct the positional deviation by setting the above-mentioned period, first, the amount of positional deviation of the image transferred to the transfer medium 2 over one rotation of the transfer medium 2 is measured. That is, the amount of positional deviation of the image transferred from each image forming medium 1i at positions of equal rotation angle of the transfer medium 2 is measured. This operation is then performed on all the image forming media 1i, and the results are stored in the position storage means 4 for each image forming medium 1i.

[0009] Next, printing is performed by rotating both media at the same rotation period as in the measurement described above. When printing is started and both media start rotating, the rotation signal output means 3 sequentially outputs signals corresponding to the rotation angle of the transfer medium 2, and reads the positional deviation amount data stored in the position storage means 4. put out. Then, the correction means 5 creates a signal in which the scanning interval is corrected based on the data, and this signal is applied to the image forming medium 1.
i to form a corrected image on the image forming medium 1i.

The images thus formed on each image forming medium 1i are transferred to a transfer medium 2, and these images are superimposed. These images are corrected so that they overlap each other, so there is no positional shift between the images. The image transferred to this transfer medium 2 is then transferred to printing paper 6.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. FIG. 2 shows a color printing apparatus applied to an embodiment of the present invention. The diameters of the photosensitive drums 11y, 11m, 11c, and 11k as the image forming medium 1i in this printing apparatus are 1/3 of the diameter of the transfer drum 12 as the transfer medium 2. Transmission is transmitted between these two drums using gears, and the drums are driven at a rotational speed ratio of 3:1 so that the circumferential speeds match. Therefore, the rotation period of the photosensitive drum 11 is one-third (1/3) of the rotation period of the transfer drum 12.

FIG. 3 shows a block diagram of a color printing apparatus according to this embodiment. This printing device includes a rotary encoder 13, a frequency divider 14, and a rotary encoder 1.
3, and a pulse counter 15 for counting the increment output pulses outputted by 3, and counters 19, 20, 21, 22 for each color (yellow Y, magenta M, cyan C, black K), and image data. Image memories 23, 24, 25, and 26 in which are stored, and LED arrays 27, 28, 29, and 30 that expose each photosensitive drum 11y, 11m, 11c, and 11k to light are provided. The data in the image memory is shifted and stored in consideration of the exposure and transfer delay time due to the transfer positional relationship of each color.

Furthermore, in this embodiment, since images of other colors are corrected using the yellow image as a reference, a ROM 16 for magenta correction, which stores exposure timing correction data for each color of magenta, cyan, and black; R for cyan correction
It has an OM 17 and a ROM 18 for black correction.

On the other hand, in this embodiment, the resolution of print dots is 400 dpi, and the diameter of the transfer drum 12 is 410 m.
At m, the rotary encoder 13 is directly connected to the axis of the transfer drum 12 and outputs a pulse signal of 81,000 pulses per rotation. The frequency divider 14 divides the signal of 81,000 pulses per revolution, that is, the pulse signal obtained by equally dividing one revolution into 81,000 pulses, into 1/4, ie, 20,250 pulses, and outputs pulses that serve as the light emission timing of the LED array. The pulse counter 15 receives the 1 output from the rotary encoder 13.
It counts 81,000 pulse signals per rotation, and is reset by a zero signal generated when the rotary encoder 13 rotates once.

By the way, the above ROMs 16, 17, 18
The correction data stored in is created as follows.

First, as shown in the block diagram of FIG. 4, all four LED arrays 27, 28, 29, and 30 are caused to emit light using the same light emission timing clock. and,
In the direction of rotation of the drum, print the points where the dots of other colors, magenta MT, cyan CT, and black KT should match, using the yellow dot YT as a reference, and then enlarge the printed state of the dots of each color. To check. As a result, the printing state of each color dot is different from that shown in Fig. 5 (
As shown in a), the dots of each color, which should originally be lined up in a row, are shifted in the drum rotation direction due to the eccentricity of each photosensitive drum 11. Therefore, using the yellow dot YT as a reference, it is determined how many pulses the deviation amount of the dots of other colors corresponds to with respect to the output pulse interval of the rotary encoder 13.

In FIG. 5A, the magenta toner dot MT lags the reference yellow toner dot YT by three output pulses from the rotary encoder 13. In FIG. Therefore, in order to correct the position to the original position where printing should occur, it is necessary to advance the light emission timing of the LED by three pulses. Initially, data '0' is written in all addresses of the correction ROM 16. Then, the absolute rotational position of the transfer drum when this magenta toner dot is exposed,
That is, if the output of the counter 12 is m, data '1' is stored at the address (m-3) of the ROM 16 as shown in FIG. 5(b).
'Write. Such an operation is performed at dozens of locations evenly distributed over one rotation of the transfer drum 12, and each measurement point is similarly corrected and data '1' is written at the corresponding address.

Other cyan and black ROMs 17 and 18
Similarly, correction information for the exposure position for one revolution of the transfer drum 12 is written.

When the writing of the correction information into each ROM is completed through the above operations, printing is performed next. First, the pulse counter 15 counts the output pulses of the rotary encoder 13 that are output in synchronization with the rotation of the transfer drum 12. this,
Each ROM1 uses the output of the pulse counter 15 as an address.
Access data 3, 14, and 15. In this way, the exposure timing clock corresponding to the rotation angle of the transfer drum 12 is output from each ROM 13, 14, 15 as data '1'.

[0020] Each LED array 28, 29, 30 has an RO
Using the corrected clock signals from M16, 17, and 18 as timing clocks, image memories 24, 25, and
Based on the data of 26, light is emitted and the photosensitive drums 11m, 11
c, 11k is exposed. Then, the output pulses of each ROM are counted by counters 20, 21, and 22 (counter 19
(counts the output pulses of the frequency divider 14), the addresses of the image memories 23, 24, 25, 26 to be read are incremented, and the image information of each color is transferred line by line to each LED array 27, 28, 29, 30. sent to.

As a result, the photosensitive drums 11m, 11c,
When forming an image on 11k, writing is performed by shifting the exposure timing back and forth so as to cancel out the positional deviation of the image.

Therefore, according to this embodiment, the photosensitive drum 11
The diameter of the photosensitive drum 11 is set to 1/3 of the diameter of the transfer drum 12, and the rotation period of the photosensitive drum 11 is set to 1/3 of the rotation period of the transfer drum 12, as shown in FIG. 6(a). The period of transfer position shift fluctuation is the shortest, and is equal to the period of one rotation of the transfer drum 12. Therefore, since the correction only needs to be made for one rotation of the transfer drum 12, the correction can be easily performed.

On the other hand, since the images of each color overlap each other on the transfer drum 12, a good image with no misregistration of the images of yellow, magenta, cyan, and black can be obtained, and the image quality of color printing is improved. effective.

[0024]

As explained above, in the color printing apparatus according to the present invention, the rotation period of the image forming medium 1i is set to be an integer fraction of the rotation period of the transfer medium 2, and the rotation period of the image forming medium 1i is set to be an integer fraction of the rotation period of the transfer medium 2. A rotation signal output means 3 that outputs a signal, and a positional shift amount of an image transferred to the transfer medium 2 at a predetermined rotation angle of the transfer medium 2 over one rotation of the transfer medium 2 is stored for each image forming medium 1i. Since it is provided with the position storage means 4 and the correction means 5 for correcting the scanning interval when forming an image on the image forming medium 1i based on the amount of positional deviation stored in the position storage means 4, fluctuations in positional deviation can be reduced. Since the cycle can be minimized and the correction only needs to be made for one rotation of the transfer medium 2, the correction can be easily performed. In addition, by making corrections based on the correction information for one rotation, when the images formed on each image forming medium 1i are transferred to the transfer medium 2, the overlapping positions of each image are aligned, so the height is high enough to avoid color shift. This produces high-quality images and improves the image quality of color printing.

[Brief explanation of the drawing]

[Fig. 1] Principle configuration diagram according to the present invention

FIG. 2 A color printing device according to an embodiment of the present invention.

[Figure 3]
Block diagram according to an embodiment of the present invention

[Fig. 4] Block diagram when measuring positional deviation according to the embodiment of the present invention

[Fig. 5] Explanatory diagram according to an embodiment of the present invention

[Figure 6] Diagram showing the pattern of positional deviation

[Explanation of symbols]

1i (11) Image forming medium (photosensitive drum) 2 (12
) Transfer medium (transfer drum) 3 Rotation signal output means 4 Position storage means 5 Correction means

Claims (2)

[Claims] 1. An image forming medium (
1i, i=1, ~m), these image forming media (1i) are arranged around the image forming medium (1i), and each image forming medium (
A color printing device comprising a transfer medium (2) consisting of a rotating body that forms one image by superimposing and transferring images formed on the image forming medium (1i).
A color printing device characterized in that the rotation period of i) is set to an integral fraction of the rotation period of the transfer medium (2). 2. Rotation signal output means (3) for outputting a signal corresponding to the rotation angle of the transfer medium (2); a position storage means (4) for storing, for each image forming medium (1i), the amount of positional deviation of the image transferred to the transfer medium (2) in terms of angle; and the amount of positional deviation stored in the position storage means (4). 2. The color printing apparatus according to claim 1, further comprising a correction means (5) for correcting a scanning interval when forming an image on the image forming medium (1i) based on the above.