JPS6366580A - Color printer - Google Patents

Abstract

PURPOSE:To prevent the color deviation to obtain the images having high quality by controlling the position in the subscanning direction of write scanning to a photosensitive body by the detection output of the surface potential of the photosensitive body to correct the deviation of relative positions of a light scanning part and the photosensitive body. CONSTITUTION:Prior to the writing of an image, the latent image pattern 58 of one or more lines is formed in the detection range of a potential sensor 57 by scanning a laser beam L. The output of the sensor 57 is binarized by a binarizing circuit 60, and a counter 61 terminates a counting by the binarization output, and the counted value indicates the extent of movement of the peripheral surface of the photosensitive body. Contents of a ROM 62 and the counted value of the counter 61 are compared with each other by a comparator 63 to detect the positional deviation in the subscanning direction of write scanning to the photosensitive body 10. The detected positional deviation is corrected based on the positional deviation information and the driving signal of a resist roller to obtain a write signal. When four kinds of electrostatic latent image are formed, the position in the subscanning direction of write scanning is adjusted and controlled at every latent image to obtain the images having high quality free from color deviation.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a color printer.

(Prior art) Writing scanning is performed with a light beam modulated by an image signal on a photoconductive photoreceptor to form a plurality of electrostatic latent images, and these electrostatic latent images are divided into different colors. An electrophotographic color printer is known in which a color print image is obtained by forming an IJ2 image using toner and transferring the obtained visible images of different colors onto the same recording sheet. Figures 9 and 10 show two typical sides of such a color printer. Below, these figures 9 and 1
In accordance with the color printer shown in FIG. 0, the outline of Color Print 1 to Process will be briefly explained, and the problem to be solved by the present invention will also be explained.

In general, a color printer capable of outputting full-color images receives image signals obtained by separating and reading the image to be output into yellow, magenta, and cyan through an appropriate interface. Based on that signal, a monochromatic image of yellow, magenta, and cyan is generated.

Superimpose them to get a full color image.

The color printer shown in FIG. 9 is of a type having - photoreceptors 10 and a multicolor developing device (i!6).

The optical scanner unit 1 modulates a semiconductor laser (not shown) in accordance with an image signal, deflects the laser beam with a rotating polygon mirror 2, and modulates the laser beam with an imaging lens 3 and a mirror 4.
, a predetermined position on the photoreceptor 10 is scanned through the cylindrical lens 5. This scanning is called main scanning, and the scanning direction is called main scanning direction.

The laser beam is directed onto the photoreceptor 1 by the rotation of the rotating polygon mirror 2.
0'' is repeatedly scanned in the main scanning direction, but as the drum-shaped photoreceptor 10 rotates in the direction of the arrow, the laser beam is also scanned in the circumferential direction of the photoreceptor 10, and the laser beam is , raster scan the photoreceptor 10. This scanning is called sub-scanning. The sub-scanning direction is a direction opposite to the rotation direction of the photoreceptor 10.

The photoreceptor 10 is, for example, an aluminum drum with an organic photoconductor layer formed on its outer circumferential surface. During printing, the photoreceptor 10 rotates in the direction of the arrow, and the surface of the photoconductor layer is made uniform by corona discharge by the charger 9. After being charged, a writing scan is performed by the optical scanner unit 1 as described above, and an electrostatic latent image is formed on the photoreceptor 10 by this scanning.

In the first writing scan, for example, an electrostatic latent image to be visualized with yellow toner is formed, and this electrostatic latent image is visualized with yellow 1-toner by the developing unit 6Y of the developing device 6. The yellow visible image thus obtained on the photoreceptor 10 is transferred onto the transfer paper 21, which is a recording sheet.

The transfer paper 21 is transferred from the cassette 22 to the paper distribution roller 20
The paper is distributed by the registration rollers 19 and supplied to the transfer drum 14 at a predetermined timing.

The transfer drum 14 holds the leading end of the transfer paper 21 by a clamper 18 and rotates in the direction of the arrow in synchronization with the rotation of the photoreceptor 10. Due to this rotation, the transfer paper 21 is held so as to wrap around the outer peripheral surface of the transfer drum 1114. Then, the transfer paper 21 is superimposed on the yellow visible image on the photoreceptor 10 in the transfer section.

At this time, the transfer device [2] performs a corona discharge of opposite polarity to the toner on the back side of the outer circumferential member made of a polyvinyl film or the like of the transfer drum [4] to transfer a yellow visible image onto the transfer paper 21. Transcribe.

After the yellow visible image is transferred, the photoreceptor 10 is neutralized by a static eliminator 7, and then residual toner is removed by a cleaner 8.

The photoreceptor 10 is then uniformly charged by the charger 9, and then written and scanned to form an electrostatic latent image to be developed with cyan toner.

This electrostatic latent image is visualized with cyan toner by the developing unit 6C, and the cyan visible image thus obtained is transferred onto the transfer paper 21 held on the transfer drum 14, superimposed on the yellow visible image. be done.

Similarly, next, an electrostatic latent image to be developed with magenta toner is formed by a writing scan and visualized with magenta toner by the developing unit 6N. When the magenta visible image obtained in this way is transferred onto the transfer paper 21, the transfer paper 21 is separated from the top of the transfer drum j4 by the static eliminator 13 and the minute nail 15, and then fixed by a heat roll type fixing device. The visible image is fixed by the device 16 and discharged onto the tray 23 by the discharge roller 17.

Now, in order to obtain a full-color image, all you need to do is to layer three color toners, yellow, magenta, and white, in appropriate proportions.
Analog color copying machines express colors in this way.

In color printers, which reproduce images using digitally processed image signals that express images as a collection of minute dots, the number of dots produced in a fixed virtual area called one pixel is changed, and the amount of toner is controlled by the amount of dots. It is common to use a pseudo gradation based on the area gradation method or the like, which is controlled by the number, that is, the toner adhesion surface A't.

Note that the developing device 6 in FIG. 1 includes a developing unit 68K that uses black toner. This is to obtain a monochromatic black image in a short time, and to output a black color corresponding to the so-called corner plate used in the printing industry. A color expressed using the three colors yellow, magenta, and cyan contains equal amounts of black corresponding to these three colors, so the same color can be expressed as black, yellow, magenta, and
It can be expressed using any two cyan colors. Removing equal amounts of yellow, magenta, and cyan corresponding to black is undercolor removal, and the replaced black color is corner printing.

1 for yellow, magenta, cyan and black
00% undercolor removal is performed, but generally 0% and 10%
The undercolor removal rate between the edges is set.

In an electrophotographic color printer, removing the undercolor not only improves one-color reproducibility but also has advantages such as a reduction in toner consumption and a reduction in fixing energy consumption due to a reduction in the amount of toner in a visible image. For this reason.

Generally, visible images of different colors are formed four times, including a black visible image using black toner, and therefore, four transfers are performed to obtain one color print image.

The color printer shown in FIG. 1O has drum-shaped photoreceptors 38C, 38M, 38Y, and 388K. These photoreceptors 38C, 38M, 38Y, and 388 are provided with chargers 37C, 37M, 37Y, and 37, respectively.
Uniformly charged by 8K.

Writing is performed by scanning beams 30C, 30M, 30Y, and 308K by scanners 31C, 31M, 31Y, and 378K.

In this way, the photoreceptors 38C, 38M, 38Y,
In 388K, electrostatic latent images to be visualized are formed with cyan toner, magenta toner, yellow toner, and black toner, respectively.

These electrostatic latent images are generated by the developing devices 32C, 32M, and 32Y.
.

According to 328, each of the toners is visualized using cyan toner, magenta toner, yellow toner, and black toner.

The transfer paper 21 is distributed from the cassette 22 by a paper distribution roller 44, fed onto a belt-shaped transfer body 33 by a registration roller 43, and transferred by the transfer body 33.
While being conveyed to the left, first, by the transfer device 398K,
Next, take a black visible image from the photoreceptor 388K.

The yellow visible image is transferred to the photoreceptor 38Y by the transfer device 39Y.
Then, a magenta visible image is sequentially transferred from the photoreceptor 38M by a transfer material 39M, and finally a cyan visible image is transferred from the photoreceptor 38C by a transfer device 39C.

38Y, 38M,
38C is the cleaner 368, 36Y,
36M and 36C remove residual toner.

The transfer paper 21 has four different visible images transferred thereto.

It is separated from the transfer body 33 by the separating claw 40, and the fixing device 4
1, the color visible image is fixed and ejected onto a tray 46 by an ejection roller 42.

After the transfer paper 21 is separated, the transfer body 33 is neutralized by a static eliminator 34 and cleaned by a blade type cleaner 35. The transfer body 33 is made of, for example, the polyester film 11 or the like.

Note that the optical scanner may scan a plurality of laser beams using one or two deflectors.

Now, the positional deviation in the sub-scanning direction, which is a problem to be solved by the present invention, will be explained.

It is known that positional deviation in the sub-scanning direction is caused by unevenness in the pitch of the scanning line due to the tilting of the surface of the rotating polygon mirror, deviation from uniform motion of the circumferential surface of the photoreceptor, and the like. However, in addition to these causes, if the relative position of the photoreceptor and laser beam shifts due to vibrations, thermal expansion, etc. of the device,
A similar effect appears on color printed images.

The apparatus shown in FIG. 9 is equipped with a sensor for detecting the position of the transfer drum 14, for example, a reflective photosensor, and the clamper 18 detects the position just before facing the photoreceptor 10, and detects the entire transfer drum 14. An eccentric cam (not shown) is operated to release the When the operation of the cam is completed, the transfer driver 1214 again comes into close contact with the photoreceptor 10 at the opposing point via the clamped transfer paper.

Therefore, detecting the position of the transfer drum not only provides the timing for the clamper 18 to escape, but also accurately provides the timing for the leading edge of the transfer paper to arrive at the transfer position, which occurs immediately thereafter.

Since the rotations of the transfer drum 14 and the photoreceptor 10 are synchronized, if the positional relationship between the optical scanner unit 1 and the photoreceptor 10 is in a predetermined relationship, it is possible to know exactly when to start scanning with the laser beam. be able to. Therefore, although this timing is normally fixed, the position of the leading edge of the image can be narrowed or extended by advancing or delaying this timing.

However, if the positional relationship between the optical scanner unit 1 and the photoreceptor 10 deviates, since the timing of writing is fixed, the above-mentioned deviation in the positional relationship will cause a deviation in the leading edge position of the image, just like a timing deviation. Become.

In a color printer, this displacement of the leading edge of the image appears as a color shift in the color print image.

Also, in the apparatus shown in FIG. 10, the positional relationship between the registration rollers 43 and each transfer position is fixed, so the timing of arrival from the registration position to each transfer position is accurately known. Therefore, as long as the writing start scanning position of each laser beam on the photoreceptor does not change, it is natural to set each writing start timing to align the positions of the leading ends of the four-color visible images on the transfer paper. Taking these points into consideration, final adjustments are made during assembly.

There is also a method of detecting that the transfer paper has arrived at a certain position in front of each transfer position and giving the timing to start writing the laser beam, but the situation remains the same.

Now, the temperature difference between the time of device adjustment and the time of use is considered to be the cause of the shift in the writing start position of the laser beam in the color printer as described above.

It is actually impossible to use a color printer under the same environmental conditions as during adjustment, and the relative position of the optical scanner unit 1- and the photoconductor may vary due to thermal expansion of each part of the machine due to the temperature difference mentioned above. It is necessary to detect the deviation and perform correction.

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its object is to correct the relative positional deviation between the optical scanner unit and the photoreceptor, and to correct the deviation of one color. This prevents color printing and allows you to obtain high-density, high-quality color printed images.
Our goal is to provide a new color printer.

(composition) The color printer of the present invention will be explained below.

The color printer of the present invention performs writing scanning with a light beam modulated by an image signal on a photoconductive photoreceptor to form a plurality of electrostatic latent images, and these electrostatic latent images are mutually separated. This is an electrophotographic color printer that develops with toners of different colors and transfers the obtained visible images of different colors onto the same recording sheet 1 to obtain a color image.

The plurality of electrostatic latent images may be sequentially formed on the same photoreceptor, or may be formed separately on different photoreceptors. In addition, the number of electrostatic latent images is three in principle, but may be four in addition to the above-mentioned corner plate, two types of electrostatic latent images, or five or more types of electrostatic latent images. The present invention can also be applied to cases where images are visualized with toners of different colors and transferred onto the same recording sheet to obtain a color image.

For example, when obtaining one color image using four types of electrostatic latent images, the number of photoreceptors is two, and two images are placed on each photoreceptor.
Separate electrostatic latent images may be formed.

Now, 1. The color printer of the present invention includes a potential detection means and 1.
and a position control means.

The potential detection means is a means for detecting the surface potential of the photoreceptor, and specifically, a known suitable high-level sensor such as a commercially available capacitance type sensor can be used.

The position control means is means for controlling the position of the photoreceptor in the sub-scanning direction of the write start scan based on the output of the potential detection means.

The position control means may be exclusively electrical, and may control the position in the sub-scanning direction of the write scan by changing the start timing of the write scan based on the output of the potential detection means. It is also possible to control the position of the writing scan in the sub-scanning direction by mechanically changing the incident optical path of the light beam onto the photoreceptor.

Hereinafter, description will be given based on specific examples.

FIG. 1 schematically shows an optical scanner unit and a photoreceptor in an embodiment in which the present invention is applied to the apparatus shown in FIG. The same reference numerals as in FIG. 9 have been used for items for which there is no risk of confusion. 1st
In the figure, reference numeral 55 indicates a mirror, and reference numeral 56 indicates a photosensor. Further, reference numeral 57 indicates a potential sensor serving as potential detection means. What is indicated by the reference numeral 58 will be described later.

In FIG. 1, a laser beam L, which is a light beam emitted from a light source (not shown), is reflected by a rotating polygon mirror 2, followed by an fθ lens 3, a mirror 4, and a cylindrical lens 5.
A spot image is formed on the photoreceptor 10 via the . As the rotating polygon mirror 2 rotates in the direction of the arrow, the laser beam L main-scans the photoreceptor 10, and as the photoreceptor 10 rotates in the direction of the arrow, sub-scanning is performed. The laser beam L is modulated by an image signal.

The photosensor 56 detects the laser beam L via the mirror 55 for each main scan prior to the main scan,
Based on the output of the photosensor 56, timing is set to align the main scanning start positions. Note that after the laser beam is detected by the photosensor 56, it is kept in an off state until the main scanning starts.

Now, control of the writing start scanning position in the sub-scanning direction is performed as follows.

Prior to writing an image, a latent image pattern 58 of one or more lines is formed within the detection range of the potential sensor 57 by scanning with the laser beam L. This latent image pattern 5
8 may be formed anywhere in one image area in the sub-scanning direction as long as it precedes one image, and if it needs to be formed at the same time as the image, it is formed somewhere in the image write-inhibited area. .

Assume now that this latent image pattern is a one-line pattern.

Referring to FIG. 2, in FIG. 2(I), the symbol e indicates a negative charge applied to the photoreceptor 10 by the charger 9. In FIG. FIG. 2 ([) shows that 1
This shows the moment when a line latent image pattern is formed, and this moment is set as 1=0 as a time reference. In addition, using the formation position of one line of latent image pattern as a position reference,
The reference position is set to 0. Then, the surface potential of the peripheral surface area of the photoreceptor including this position reference becomes as shown in FIG. 2(m). As shown in FIG. 2 (1), the angle from the central axis of the photoreceptor 10 to the writing position and the potential sensor 57 is θ. , when the angular velocity of the photoreceptor 10 is ω, the latent image pattern moves to a position facing the potential sensor 57 at t=0°/ω (FIG. 2 (■)). Therefore, the photoreceptor surface potential detected by the potential sensor 57 changes over time.
It changes as shown in Figure 2 (IV).

By the output of the potential sensor 57, the latent image pattern 5 is
8 can be detected to have reached the position of the potential sensor 57.

Reference is now made to FIG. FIG. 4 is a block circuit diagram of a shift detection section in the position control means.

The counter 61 starts counting in response to a pattern forming signal. by patterning signals.

On the one hand, a latent image pattern 58 is formed.

Therefore, the formation of the latent image pattern 58 and the start of counting by the counter 60 are simultaneous.

On the other hand, the output of the potential sensor 57 is binarized by a binarization circuit 60. When the potential sensor 57 detects the latent image pattern, the counter 61 ends counting based on the output of the binarization circuit 60.

Therefore, the moving distance of the circumferential surface of the photoreceptor between the position where the latent image pattern 58 is formed and the position detected by the potential sensor 57 is known as the count number of the counter 61.

On the other hand, the ROM 62 stores the above-mentioned Curran 1-number at the time of device adjustment, that is, when there is no deviation in the mutual positional relationship between the photoreceptor and the optical scanner unit. By comparing the count number counted by the counter 61 with the count number counted by the counter 61 using the comparator 63, it is possible to determine the difference in the sub-scanning direction of the write scan with respect to the photoconductor due to the misalignment of the relative positional relationship between the optical scanner unit and the photoconductor. Positional deviation can be detected.

FIG. 6 is a block circuit diagram of a timing control section in the position control means.

The write signal setting circuit 70 is a delay pulse generation circuit,
The output of the comparator 63 and a registration signal for driving the registration roller 19 are applied.

The comparator 63 provides the write signal setting circuit 70 with the count number corresponding to the positional deviation detected as described above as information.

When a register signal is applied to the write signal setting circuit 70,
Based on the shift information provided from the comparator 63, the amount of delay of the delay pulse is increased or decreased, correcting the position shift detected as described above, and generating a write signal.

Therefore, in the case of the position shown in Fig. 9, cyan, magenta,
When forming four types of electrostatic latent images developed with yellow and black toners, color misregistration can be prevented by adjusting and controlling the position in the sub-scanning direction of the writing scan as described above for each latent image. You can get high quality color printed images.

In addition, in the case of the apparatus shown in FIG. 10, by adjusting the write start scanning position in the sub-scanning direction as described above at the time of each write scan of the photoreceptor 388 for 38Y, 38M, and 38C, It is possible to obtain high-quality color print images without color shift.

By the way, in the case of color printers that aim to achieve high image quality, the latent image width of one line is generally as thin as several tens of microns, and depending on the type of potential sensor, the width of the latent image as shown in Figure 2 (
For a one-line latent image pattern as shown in III), an output as shown in FIG. 2(IV) may not be obtained, and the peak shape of the output may become gentle, resulting in a decrease in detection accuracy.

In such a case, it is preferable to increase the number of lines constituting the latent image pattern for detection to widen the width of the latent image pattern.

For example, when the latent image pattern is composed of three lines, the light amount distribution for exposing the photoreceptor will be as shown in Figure 3 (I), and the formed latent image pattern will be as shown in Figure 3 (n). , the detection potential shown in FIG. 3 (Itr) is obtained, and highly accurate detection becomes possible. Therefore, if the method of providing the ROM data is taken into consideration, deviation detection can be performed with a circuit configuration similar to that shown in FIG.

Incidentally, as a method of increasing the detection accuracy of the latent image pattern, there is also a method in which the detection section of the position control means has a circuit configuration as shown in FIG.

In this case, the binarization circuit 60A detects the rise of a certain threshold level, and the binarization circuit 60B detects the fall of the same level, and generates a pulse signal. And counter 6
1A, 61B and the arithmetic unit 64 calculate the count corresponding to the average value of the rise time and the fall time to the comparator 63.
give to Therefore, if the latent image pattern is composed of a plurality of lines, what is detected is the center portion in the width direction of the plurality of lines, and if the latent image pattern is composed of an odd number of lines, the position of the center line can be detected. Therefore, the method of providing data to the ROM 62 is also simplified, and detection accuracy is improved. Fifth
By using the detection section as shown in the figure, accurate latent image pattern detection is possible even if there is some variation in the output of the potential sensor 57.

In the embodiment described above, the position control of the photoconductor in the sub-scanning direction of the write start scan is performed by electrical timing control. The above position control can also be performed by changing the optical path of the light beam incident on the.

FIG. 7 shows only the main parts of an embodiment in which this method is applied to the apparatus shown in FIG. 9.

In this embodiment, the mirror 4 is attached to the stationary member 80 via piezoelectric elements 81, 82, 81A, 82A.

The piezoelectric elements 81 and 82 are provided in a pair at one end of the mirror 4 in the longitudinal direction (direction perpendicular to the drawing), and the piezoelectric elements 81A and 82A are provided in a pair at the other end.

As shown in FIG. 8, when a signal indicating the amount of deviation (the amount of deviation is detected by a detection circuit as shown in FIGS. 4 and 5) is input to the control circuit 85, the control circuit 85 controls the driver 83.
．． Via 84, piezoelectric elements 81.82° 81A, 82
By driving A and changing the inclination of the mirror 4, the optical path of the laser beam L is changed, and the position of the writing scan in the sub-scanning direction is controlled.

To change the optical path, instead of changing the inclination of the mirror 4, the cylindrical lens 5 may be displaced in the left-right direction in FIG.

Controlling the position of the writing scan in the sub-scanning direction by changing the optical path is of course applicable to the color printer of the type shown in FIG. 10, that is, the type that uses a plurality of photoreceptors.
It can be modified and applied as appropriate.

(Effects) As described above, according to the present invention, a novel color printer can be provided. Since this color printer is configured as described above, it is possible to always obtain high-quality color print images without color shift even when printing is performed under environmental conditions different from those during device adjustment.

There are two types of printers: one is a method in which the image area is exposed to light and the electrostatic latent image is reversely developed (negative-positive method), and the other is a method in which the background area is exposed to light and the electrostatic latent image is developed using a normal development method (positive-positive method). However, the present invention can be applied to any of these methods.

The example described above is a negative-positive method, and the latent image pattern is formed as an exposed area.
In the case of the positive-positive method, a latent image pattern can be formed as a non-exposed area.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing only the essential parts of an embodiment of the present invention;
FIGS. 2 and 3 are diagrams for explaining the present invention, and FIG. 4 is a diagram for explaining the present invention.
5 and 5 are block diagrams showing two examples of the detection unit in the position control means, and FIG. 6 is the timing 10 of the write signal in the above embodiment: photoreceptor, L: laser beam (light beam) , 57... potential sensor (potential detection means), 58... latent image pattern. U2 shaku (I), (I) (DI)
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II) 弗 4 ni snow redundant form c9 口が〦7 口ichi〇prisonπ, EA ni snow q Kuni 1 n phantom procedural amendment November 11, 1985

Claims (1)

[Scope of Claims] Writing scanning with a light beam modulated by an image signal is performed on a photoconductive photoreceptor to form a plurality of electrostatic latent images, and these electrostatic latent images are colored with each other. An electrophotographic color printer that obtains a color print image by developing different colored visible images obtained by developing with different toners onto the same recording sheet, the surface potential of the photoreceptor is What is claimed is: 1. A color printer comprising: a potential detecting means for detecting a potential detecting means; and a position controlling means for controlling a position of a photoreceptor in a sub-scanning direction of a write scan based on an output of the potential detecting means.