JPS63279276A - Image forming device - Google Patents

Abstract

PURPOSE:To simplify a device and to enhance the reduction of cost by detecting the picture density of the measuring pattern and the dislocation of each color with one photosensor and providing at least one dotted line pattern in the main scanning direction of the edge of the pattern. CONSTITUTION:As for reference patterns 28BK, 28C, 28M and 28Y for detecting the picture density and dislocation, a 25% zigzag type is a standard and one dotted line or some dotted line is provided in the main scanning direction in the edge of the pattern. When the line pattern of the edge of the standard pattern of each color is read, an output from a sensor rises all at once and after that the pattern for detecting the picture density is read and outputted. The detection of dislocation is executed with a line pattern and the picture density is detected with an output voltage following the detection. Therefore, the picture density and the dislocation can be detected with one photosensor 27 and the simplification of the device and the reduction of cost can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a color image forming apparatus having a plurality of photoreceptor drums and a transfer belt, and particularly to a positional deviation detection device therefor.

(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 in which the writing timing of each color is obtained by detecting the transfer paper using a sensor installed in front of each transfer position. It has been difficult to guarantee the positional shift limit (about 0.15 m) for color images because of variations in the mounting positions of the sensors and variations in the detection positions of each sensor.

For this purpose, a technique has already been proposed in which a measurement pattern for each color is created on a transfer belt, and a photo sensor is used to detect the measurement pattern to detect positional deviation.

On the other hand, there is also a method of creating a measurement pattern on a transfer belt and controlling toner density according to the output of a photosensor.

(The present invention was made based on this background, and by detecting each color image once with one photosensor and also detecting positional deviation at the same time, it is possible to reduce costs,
The purpose is to simplify the device.

(Structure) For this purpose, the present invention forms a standard latent image for image flatness detection on each photoreceptor at a predetermined location outside the original image area, develops the latent image, and sequentially processes the developed images. After the image is transferred to the transfer belt and transferred to the final recording device, a means is provided for detecting the density of the image using one photosensor and for detecting positional deviation using the output of the photosensor. This method is characterized by using a standard pattern having at least one dot line pattern in the main scanning direction at the leading edge of the pattern.

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.

FIG. 1 shows a color copying machine as an example of an image recording device. The copying machine includes a scanner section 1 for reading originals, an image processing section 2 that electrically processes image signals output as digital signals from the scanner section 1, and image recording of each color from the image processing section 2. It has a printer section 3 that forms an image on copy paper based on the information. 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 the 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, CGD 11R for red. , CCDIIG for green, and ccDI IB for blue. Each CCDIIR, IIG
.

11B converts the incident light into a digital signal and outputs it, and the output is subjected to necessary processing in the image processing section 2 to record color information of each color, such as black (hereinafter abbreviated as Bk), cyan (C), etc. The signals are converted into signals for recording of each color: magenta (abbreviated as M), and yellow (abbreviated as Y).

Although FIG. 1 shows an example of forming four colors, Bk, C, M, and Y, 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,
12 to each color laser beam emitting device ff1128
Sent to C, 12M, 12Y.

In the example shown in the figure, there are four sets of inscriptions in the printer section. Fitted W113Y
, 13M, 13C, and 138k 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. In addition, for each value, the same parts are given the same reference numerals, and in order to distinguish the composition of each color, a subscript indicating each color is added to the reference number.

The recording device 13G is a laser beam emitting device! In addition to '12G, a photoreceptor 14C1, for example, a photoreceptor drum is provided.

A charger 15c, an exposure device including a laser beam emitting device 12G, a developing device 16G, a transfer charger 17C, and the like are attached to the photoreceptor 14C in the same manner as in a known copying apparatus.

Photoreceptor 1 uniformly charged by charger 15C
4C forms a cyan latent image by exposure with a laser beam emitting device '1112C, and develops it with a developing device ff16G to form a developed image. The paper feed section 1 is fed by the paper feed roller 18.
9. For example, the copy paper supplied from either of the two paper feed cassettes is aligned with its leading edge by the nozzle roller 20 and sent to the transfer belt 21 at the same timing. The copy paper conveyed by the transfer belt 21 is placed on the photoreceptor 148 on which a developed image is formed, respectively.
The images are sequentially sent to , and a developed image is transferred under the action of a transfer charger 17 . The transferred copy paper is fixed by a fixing roller 22 and discharged by a paper discharge 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 the belt drive roller 24 and the driven roller 25 and moves in the A direction! 11 and convey the transfer paper. Further, the cleaning unit 26 removes toner adhering to the belt. ! A reflective sensor 27 is provided on the downstream side of the eight-light body 14 in the belt movement direction as a pattern image detection means for measuring image density and positional deviation.

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

The measurement pattern images visualized outside the transfer paper area by the signals from the measurement pattern image signal generating means in each recording device are transferred to the transfer belt 21, and as shown in FIG. The distance between them is a (home). The measurement pattern images 288kPC, M, and Y pass through the sensor 27 in sequence as the belt moves, and the 0 image leading edge interval a detected by the sensor 27 is determined by setting the exposure timing for each recording device in advance. is a numerical value that can be arbitrarily selected, and if the linear velocity of the transfer belt is V, (Tsuru/5ec), then the difference in each image detection time is a/Vz (see).

FIG. 4 is an explanatory diagram of setting the image leading edge interval a.

The length from the exposure position to the transfer position for each photoreceptor 14 is j! I (IIIm), photoreceptor linear velocity is V, (1 serving/
sec), the distance between the photoconductors is j! g (m) and the linear velocity of the transfer belt is Vt (fl/sec), the time required from exposure to transfer is 1. is the same value for each photoconductor, t+ -1+ /v+ (see) If the time to move between each photoconductor is t□, then tf times l
x/V! (sec) That is, when it is desired to form a pattern at an interval of a, the signal generation timing from the measurement pattern image signal generating means is set to Bk as a reference, tc'' (1! + a) / Vt (see)
tM”2 (1! +3) /V2 (sec)t
It is sufficient to generate the signal with a delay of v −13 (122”a) /Vt (sec).

However, in reality, due to variations in the position τ of each photoconductor, variations in the exposure position with respect to the photoconductor, and variations in the linear speed of the photoconductor and transfer belt 21, the distance between the leading ends of the measurement pattern image transferred onto the belt is relative to a. As a result, color shift occurs in the overlapping images on the transfer paper as well.

The measurement patterns are shown in Figure 5 (a), (b), (C
1. As shown in (d), it is based on a 4 x 4 matrix, and which of the 4 x 4-16 dots is made black and white is related to the detection sensitivity of the photosensor. The %chidori type is used. In addition, Cal,
(bl is 50% concentration and chidori type tearing, (C1, (d
) is 25% concentrated and chidori type.

An example of a standard pattern for detecting image density and detection deviation of the present invention is shown in FIGS. 6(a), (bl, (C1, d)).

This standard pattern is basically a 25% square pattern as described above, and is characterized by having one dot line or several dot lines in the main scanning direction at the leading edge of the pattern. This pattern allows the photosensor to detect image density at 25% increments, and detects positional deviations at one dot line or several dot lines.

FIG. 7 is an example showing the output of the standard pattern photosensor 27 of the present invention. The sensor output rises at once when the line pattern at the tip of each color standard pattern is read, and then the image density detection pattern is read and output.

A circuit diagram of the photosensor is shown in FIG. 8. 5V is applied to the phototransistor for photodetection of the photosensor, and the reference voltage is adjusted to 4 to 5V using a variable volume.

Image density detection will now be explained. First, as shown in Figure 5, set the threshold value V, reset the first detected sensor output, and read the sensor output voltage after counting at a certain interval (the average value of the interval is also acceptable). It is sufficient that the image density detection pattern is output at intervals equal to or greater than the interval at which the sensor outputs the line pattern.This sensor output voltage corresponds to the image density of the image density detection pattern part of the standard pattern. The toner replenishment signal is turned on and off depending on the output voltage.
This is done for each color interval.

Next, positional deviation detection will be explained. In order to detect positional deviation, a threshold value ■ is set, and the first detected sensor output is regarded as Bk, and the output of this sensor 27 is sent to the counter
, Y), and the detection signal on the Bk pattern 288 causes the power output (29C).

M, Y) are reset and start counting.

Next, the counter 29C is activated by the detection signal of the C pattern 28C.
stops counting. Hereinafter, the amount of deviation between the counter value and the set value for each color in the 0th order is calculated in the same manner for M and Y by the comparison calculation circuit.

(In case of C) (1) Counter value: KC (2) Count value for set value tKC: Kcs (3)
Amount of deviation: K (c-cs) -K c -Kcs This value changes the number of clocks relative to the image signal generation timing. This makes it possible to change the image writing timing in accordance with the amount of positional deviation after transfer.

FIG. 9 is a block diagram thereof.

Further, a timing chart is shown in FIG.

The present invention is characterized in that it uses a standard pattern that emphasizes edges, thereby improving the accuracy of positional deviation detection.

(Effects) The present invention is as described above, and by transferring a standard pattern for image density control in a line to a specific location on a transfer belt, it is possible to detect the image density of each color with one photosensor. On the other hand, the detection signal can also be used to detect positional deviations, and other sensors for detecting positional deviations are not required, making it possible to reduce costs and simplify the apparatus.

Furthermore, by using a pattern with edges emphasized in addition to the standard pattern, it is possible to improve the accuracy of detecting positional deviation.

[Brief explanation of the drawing]

FIG. 1 is a schematic 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, FIG. 3 is a system block diagram according to an embodiment of the present invention, and FIG. 4 is a schematic diagram of a digital color image forming apparatus to which the present invention is applied. Explanatory diagram for setting the delay time of image data, Fig. 5 (a
), ('b), (01, (d) are diagrams showing the image density pattern matrix, FIGS. 6(a), (b). (Q), (d) are the image density and image density patterns used in the present invention. A diagram showing a positional deviation detection pattern, FIG. 7 is a diagram showing the output waveform and time interval of the sensor, and FIG. 8 is a circuit diagram of the sensor.
Figure 9 is a block diagram of image output timing control,
Figure 0 is an overall timing chart. 21... Transfer belt, 27... Detection means, 28...
・Pattern image for image density and positional deviation measurement. Figure 3 Figure 5 (a) (b) (C
) (d) Figure 6 (O)
(b) □ Sohisagi (C)
(d) Figure 7 Figure 8

Claims (1)

[Claims] a photoreceptor; a charger that uniformly charges the surface of the photoreceptor;
A recording device includes an exposure means for projecting image light on a photoreceptor according to recording information, a developing means for developing an electrostatic latent image on the photoreceptor, and a transfer means for transferring the developed image on the photoreceptor onto a transfer paper. In an image recording device in which a plurality of sheets are arranged and images are overlaid and transferred by sequentially conveying transfer paper to each recording device using a transfer belt,
A standard latent image for detecting image density is formed on each photoreceptor at a predetermined location outside the original image area, the latent image is developed, and the developed images are sequentially transferred to a transfer belt and processed by a final recording device. After completion of the transfer, a means is provided to detect the density of the image using one photosensor and to detect positional deviation using the output of the photosensor, and a line of at least one dot in the main scanning direction at the tip of the image density detection pattern is provided. An image forming apparatus characterized in that a standard pattern having a pattern is used.