JPS6373277A - Digital color image forming device - Google Patents

Abstract

PURPOSE:To reduce the deviation of each color in the carrying direction of a transfer paper with a simple constitution by adjusting the write timing of each image by a single detecting means provided on a transfer belt. CONSTITUTION:Plural pattern images are formed in one cycle of a photosensitive body, and four images are formed here in a figure. The output timing of Bk(black) pattern (28BK) is set to piD/4v1 where D is the diameter of the photosensitive body and v1 is the linear speed of the photosensitive body (mm/sec), and counted values Kc1-Kc4 are averaged by an averaging circuit 30. The difference between the mean value and a counted value Kcs to a set value tkc is calculated, and the number k9C of clocks to the picture signal generation timing is changed in accordance with this difference value. Thus, the image write timing is changed in accordance with the extent of positional deviation after transfer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a digital color image forming apparatus having a plurality of photoreceptors.

(Prior art) In an image forming apparatus that forms color images using multiple photoreceptors, the factors that cause misalignment in the transfer paper feeding direction (vertical registration) include the installation position and circumferential speed of each photoreceptor, and the exposure to the photoreceptor. The position, linear speed of the transfer belt, etc. were configured to guarantee each component accuracy and assembly accuracy, but this resulted in high component costs and assembly costs, and due to changes in each factor over time and variations due to component replacement. Readjustment is required.

As a method to solve this problem, a method has been proposed (Japanese Patent Laid-Open No. 155870/1983) that detects the transfer paper using a sensor installed in front of each transfer position to obtain the writing timing for each color. Due to variations in the mounting position and variations in the detection position of each sensor, it has been difficult to guarantee a positional shift limit (about 0.15 m) for color images.

(Purpose) The present invention was made based on this background,
To reduce color shift in the transfer paper transport direction of each color with a simple configuration in a color image forming device that obtains one color image by superimposing a plurality of color images on transfer paper conveyed by a transport belt. The purpose of the present invention is to provide a digital color image forming apparatus that can perform the following functions.

(Structure) For this purpose, in the present invention, the writing timing for each image is adjusted by a single detection means provided on the transfer belt.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of the present invention will be explained in detail below based on embodiments shown in the drawings.

First, FIG. 1 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied.

In FIG. 1, a color copying machine is shown as an example of an image recording device.The copying machine includes a scanner part 1 for reading originals and an image signal outputted as a digital signal from the scanner part 1 electrically. It has an image processing section 2 and a printer section 3 that forms an image on copy paper based on image recording information of each color from the image processing section 2. The scanner part 1 includes a lamp 5 that scans and illuminates the document on the document table 4.
, with, for example, fluorescent lights. The reflected light from the document when illuminated by the fluorescent lamp 5 is reflected by the mirror 6.7.8 and enters the imaging lens 9.

The image light is focused on a dichroic prism 10 by the imaging lens 9, and is separated into light of three wavelengths, for example, red R, green G, and blue B, and a light receiver 11 for each wavelength, for example, a red CCDIIR. , CC for green
It is input to DIIG and CCDIIB for blue. Each CG
DIIR, 11G, and IIB convert the incident light into a digital signal and output it, and the output is subjected to necessary processing in the image processing section 2 to record color information of each color, such as plaque (hereinafter abbreviated as Bk), The signals are converted into signals for recording of each color: yellow (abbreviated as Y), magenta (abbreviated as M), and cyan (abbreviated as C).

Although FIG. 1 shows an example of forming four colors, Bk, Y, M, and C, it is also possible to form a color image using only three colors. In that case, the number of recording devices can be reduced by one compared to the example shown in FIG.

The signal from the image processing section 2 is input to the printer section 3,
Laser light emitting devices 12Bk, 12C, 1 for each color
Sent to 2M and 12Y.

In the illustrated example, the printer section includes four sets of recording devices 13C, 1.
3M, 13Y, and 13Bk are arranged side by side. Since each recording device 13 is made of the same constituent members, in order to simplify the explanation, the recording device for C will be explained, and the explanations for other colors will be omitted. Note that for each color, the same parts are given the same reference numerals, and in order to distinguish the configuration of each color, a subscript indicating each color is added to the reference number.

The recording device 13C has a photoreceptor 14G, for example, a photoreceptor drum, outside the laser beam emitting device 12c.

The photoreceptor 14C is provided with a charger 15C, an exposure position by a laser light emitting device ff12c, a developing device 16C, a transfer charger 17C, etc., as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15C
4G forms a cyan latent image through exposure by the laser beam emitting device 12C, and develops it by the developing device 16C to form a developed image. Copy paper is fed by a paper feed roller 18 from a paper feed unit 19, for example, one of two paper feed cassettes, and the leading edge of the copy paper is aligned by a registration roller 20 and sent to a transfer belt 21 at the same timing. Transfer belt 2
The copy paper conveyed by 1 is sequentially sent to photoreceptors 14Bk, 14Y, 14M, and 14C, each having a developed image formed thereon, and the developed image is transferred under the action of a transfer charger 17.

The transferred copy paper is fixed by a fixing roller 22,
The paper is ejected by the paper ejection roller 23.

By being electrostatically attracted to the transfer belt 21, the copy paper can be conveyed with high precision at the speed of the transfer belt.

Next, details of embodiments of the present invention will be described.

FIG. 2 is a front view of the transfer belt section. Transfer belt 21
is supported by a belt drive roller 24 and a driven roller 25, and moves in the A direction to convey the transfer paper. Further, the cleaning unit 26 removes toner adhering to the belt. A reflective sensor 27 is provided as a pattern image detection means on the downstream side of the photoreceptor 14 in the belt movement direction.

The operation will be explained based on specific examples shown in FIGS. 3 and 4.

The pattern image visualized outside the transfer paper area by the signal from the pattern image signal generating means in each recording device is
They are each transferred onto the transfer belt 21 and positioned at intervals of a(lj) in the square shown in FIG. Then, in the pattern image 288, C.

M and Y pass through the sensor 27 sequentially as the belt moves, and the zero image interval a detected by the sensor 27 is recorded in advance! ! It is a value that can be arbitrarily selected by setting the exposure timing for the device, and if the linear velocity of the transfer belt is Vz (mu/5ec), the difference in each image detection time is a / Vz (sec) becomes.

FIG. 4 is an explanation of the setting of the image interval a. Each photoreceptor 14
The length from the exposure position to the transfer position for I! l(t
*), photoconductor linear velocity is V, (xs/sec) % distance between photoconductors is j! z (m), transfer belt linear velocity Vg (m
s/sec), the time required from exposure to transfer is 1. is the same value for each photoconductor, and t+ -j+ /v+ (sec) If the time to move between each photoconductor is t, then t t -11t / V
z (see) That is, when it is desired to form a pattern at intervals of an, the signal generation timing from the pattern image signal generation means is set to Bk as a reference, tc''''C1z +a) /Vz (sec)t,
4-2 C11z +a) /vt (see)
tv −3(ft +3)/vz (sec
) can be generated with a delay.

However, in reality, there are variations in the position of each photoconductor, variations in the exposure position with respect to the photoconductor, and differences between the photoconductor and the transfer belt 210.
Due to variations in linear speed, the interval between pattern images transferred onto the belt deviates from a relative to a, and similarly, color misregistration occurs in overlapping images on the transfer paper.

FIG. 5 is an example showing the output of the sensor 27.

The sensor 27 sequentially detects patterns (288, C, M, Y). The signal of the sensor 27 is sent to the counter (29C, M,
Y), and the detection signal in the Bk pattern 288 causes the counter (29C, M.

Y) is reset and the counter 29C stops counting in response to the detection signal of the 0th order C pattern 28C which starts counting. The same applies to the other M and Y, so C will be explained. Based on the counter value of the counter 29C, the comparison calculation circuit 30 calculates the amount of deviation from the set value. In other words,
Assuming that the clock frequency is M lk and the counter value is , the count value K cs (=
The difference between M-tKc) is calculated.

K (c-cs)” K c K c!'K tc
-cs> represents the amount of deviation from the set interval of the Bk and C pattern images, but this amount of deviation is also influenced by speed fluctuations of the photoreceptor and transfer belt (periodic fluctuations with respect to the set linear speed). When a shift occurs on the image as shown in FIG. 6(a), depending on the position of the pattern image, if the detected value is fed back as it is, there is a risk that the amount of shift will become large. Figure 6(b) shows the deviation on the image when feedback is applied (both figures are
Explanations are given in horizontal lines to make the explanations clearer. (The pattern image is not shown because it is outside the transfer paper).

Regarding periodic speed fluctuations, the longer the period, the larger the amount of deviation for the same speed fluctuation rate, so positional deviations due to speed fluctuations of one cycle of the photoreceptor are likely to occur.

Therefore, in the present invention, as shown in FIG. 7, a plurality of sets of pattern images are formed for one cycle of the photoreceptor.

In the example shown in the figure, four sets are formed for one period of the photoreceptor. The timing for outputting the Bk pattern (288k) may be set to πD/4 v r where D is the diameter of the photoreceptor.

In this way, count (I!tK c (1) ~ K c (
41 is averaged by the averaging circuit 30.

gc −(KC(1)+KC(2)+KC(3)
+KC(4))/4 The difference between this and the count value Keg for the set value tic is calculated.

K <c-cs, -We K cs This value changes □ to the number of clocks for the image signal generation timing (Kl- is the 15 mentioned above in the initial state).
)K' @C”
K @L: K (1 knee e31) This makes it possible to change the image writing timing in accordance with the amount of positional deviation after transfer. The same applies to M and Y.

FIG. 8 is a block diagram, and FIG. 9 is a flow chart.

Although four sets of pattern images were formed for one cycle of the photoreceptor, the number of sets and output timing are arbitrary.

Although a reflective sensor is used in this embodiment, any other means capable of detecting an image, such as a transmissive sensor, may be used, and it is obvious that a timer or other means capable of measuring timing may be used instead of a counter.

The pattern image can be output in various ways, such as outputting it outside the transfer paper area at the time of outputting each image (for each copy), outputting it every set number of sheets, or outputting it at a fixed time interval.

(Effects) As described above, according to the present invention: (1) There is no need to tighten component accuracy and assembly accuracy, resulting in cost reduction.

B) Vertical registration adjustment is no longer required, reducing adjustment costs.

(3) No deviations due to parts replacement or changes over time, etc.
Readjustment becomes unnecessary.

It has the following effects.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a digital color image forming apparatus to which the present invention is applied, Fig. 2 is a front view of a transfer belt section according to the present invention, Fig. 3 is a plan view thereof, and Fig. 4 is an image interval. Fig. 5 is a diagram showing the output of the sensor, Fig. 6 is an explanatory diagram of the settings of a,
a) and (b) are diagrams showing positional deviations on images, Figure 7 is a diagram showing multiple sets of pattern images formed for one cycle of the photoreceptor, Figure 8 is; #1111 block diagram, Figure 9 The figure is a flowchart. 21... Transfer belt, 27... Detection means, 29...
- Counting means, 30... Averaging means, 3... Calculating means, 32... Timing signal generating means. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Concave Figure 7 8 Prisoner 9Y

Claims (2)

[Claims] (1) a photoconductor, a charger that uniformly charges the surface of the photoconductor, an exposure device that projects image light on the photoconductor according to recorded information, and a developing device that develops an electrostatic latent image on the photoconductor; In an image recording apparatus in which a plurality of recording apparatuses each having a transfer means for transferring a developed image on a photoreceptor to a transfer paper are arranged, and the transfer paper is sequentially conveyed to each recording apparatus by a transfer belt and images are superimposed and transferred, pattern image signal generating means for forming a plurality of sets of measurement pattern images for each color on the belt;
A single detection means for detecting passage of each color pattern image, a detection timing counting means for the detection means, an averaging means for averaging the count values by the detection timing counting means, and an average value and set value by the averaging means. What is claimed is: 1. A digital color image forming apparatus comprising: a calculating means for calculating a deviation between the two colors; and a writing start timing signal generating means for each color whose settings can be changed according to the output value from the calculating means. (2) The digital color image forming apparatus according to claim (1), wherein a plurality of sets of measurement pattern images are formed for one period of the photoreceptor.