JPH0514559A - Image forming method - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent noise images from being mixed into the output results of inspection pattern images. A filter 1100 that detects a position and a size of density from an image formation result in which a noise image is mixed and determines filter characteristics based on the detection result is used to filter a read image signal of a subsequent inspection pattern image. Apply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in the technical field of digital electrophotographic copying machines, and more particularly to an image forming method for adjusting an image forming condition by reading an output image with a document reading section. ..

[0002]

2. Description of the Related Art An image formed by an electrophotographic method is susceptible to changes over time, environmental conditions, etc., and stabilizing the output image density is extremely important for practical use.

First, the main factors affecting the quality of an image formed on the basis of the electrophotographic method are listed. The characteristics of the photosensitive member, the characteristics of the charging means for sensitizing, the characteristics of the exposure source and the exposure amount, the characteristics of development, There are transfer characteristics, transfer material characteristics, residual developer cleaning characteristics, and the like.

Since each of these characteristics is influenced and changed by temperature, humidity, contamination of dust or the like, aging, etc., the image quality also has a complicated influence change.

Conventionally, in order to stabilize this image quality change,
Although a method of independently stabilizing each of the above characteristics has been taken, it has not yet reached a state where it can be said to be sufficiently satisfactory. Also, as a method of stabilizing an electrophotographic image, an electrostatic latent image is formed by charging and exposing on a xerographic photoreceptor.
A Carlson process is known in which the electrostatic latent image is developed and then the developed image is transferred. In this Carlson process, the light amount of the original image to be exposed, the potential of the formed electrostatic latent image, or the density of the developed image is detected, and the detection signal is fed back to the charging / exposure means of the process. In order to stabilize the image, for example, US Pat. No. 2,956,487 is described.

In the so-called potential control by the surface electrometer in this method, the output voltage of the developing bias is determined in advance to freely set the contrast of the image forming system. This method includes measuring the potential (V light) (see FIG. 12) of the non-exposed portion (V dark) and the exposed portion of a certain amount of light, or (for example, placing copy paper on the platen to measure the potential. In many cases, the output fixed image is placed on a document table and the latent image potential formed by the image is read.

Further, the developed image density is detected, and not only one point of the image density but also the development density at a plurality of standard exposures, the amplitude / frequency / DC of the AC component of the AC bias voltage applied to the developing means are detected. The method of stabilizing the image by sequentially changing the minute voltage is Japanese Patent Publication No. S57-4027.
9 are described.

In the method of detecting and controlling the image density on the photosensitive drum, since the output image density is substantially determined by the contrast of development, the image forming state is measured by measuring the developed image density on the photosensitive drum. To get information.

Further, in the digital type electrophotographic copying machine, there have been proposed some methods of adjusting the output image density by reading the output fixed image by the document reading unit.

[0010]

In any of the image density control methods described above, when the output image density is read in order to control the image density, the latent image potential on the photoconductor and the visible image on the photoconductor are determined. The problem is that noise (local density of image density, height of latent image potential) included in an image or an output fixed image is picked up and erroneous control is performed.

In particular, the noise image is an endless track member such as a belt included in image forming means, that is, image signal generating means, photoconductor charging means, optical information exposing means, developing means, transfer means, fixing means, and the like, and It often occurs at the pitch of a rotating body such as a roller or a polygon mirror (see FIG. 13). Noise is mixed in the image signal read when the noise is generated.

However, none of the above-mentioned conventional image density control means takes any measures against the noise due to the pitch of the endless track member and the rotating polyhedron. There is a problem that the image density control is performed based on the read data of the region having a unique image density, and most of the output image density becomes an abnormal density.

In view of the above points, the present invention provides an image forming method in which a noise image is not mixed in the image forming result of the inspection pattern image executed when setting the image forming conditions. To aim.

[0014]

In order to achieve such an object, the present invention reads a document on which an inspection pattern image is described, or generates an inspection pattern by an internal signal to form an image, and In an image forming method for variably setting subsequent image forming conditions by reading the image forming result again, the frequency of the pitch noise image due to the image forming process appearing in the image carrier traveling direction of the image forming result is determined in advance, When the document is read to set the image forming condition for the next time and thereafter, the image signal of the read is subjected to a filtering process for weakening the frequency of the pitch noise image.

[0015]

According to the present invention, the drive system of the image forming apparatus is driven from the reading start position and the recording start position of the original, and the noise generated by the drive system has a constant cycle. The generation frequency of pitch noise is determined in advance from the result of image formation. When a document is read for setting image forming conditions, noise is removed from the image signal by performing a filtering process for weakening the frequency component of the pitch noise in the noise-containing portion of the read image signal. ..

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> An embodiment of the present invention will now be described in detail with reference to the drawings.

The image forming apparatus will be described prior to the description of the present invention.

FIG. 2 shows the main structure of the first embodiment of the present invention. In FIG. 2, reference numeral 1 denotes an original illumination lamp (hereinafter referred to as a lamp) including a halogen lamp or the like, and the reflected light of the original 3 on the original table glass 2 illuminated by the lamp 1 scans through mirrors 4a and 4b. To be done.

The lamp 1 and the mirror 4a integrally constitute a scanning unit, and the scanning unit reciprocates in the horizontal direction at a predetermined speed according to the set magnification by driving a motor (not shown).

Reference numeral 5 denotes an optical lens, which is a reflection image scanned through the mirrors 4a and 4b at a predetermined magnification, such as a CCD.
It is positioned at a position where an image is formed on the image pickup device 6 such as (a charge coupled device or a linear image pickup device) before image formation.

The image density of the original is converted into an analog electric signal by the CCD 6, and then the analog electric signal is converted into a digital electric signal by the image processing device 7.
At the same time, various image processings are performed. An image of the original document is, for example, 400
It is converted into an 8-bit (bit) digital electric signal with a resolution of dpi (dots / inch).

Reference numeral 8 is a laser driver circuit for driving the semiconductor laser unit 9 according to an image signal. The laser light emitted from the semiconductor laser 9 is redirected by the rotary polygon mirror 10 and imaged on the photosensitive drum 11 via the mirror 4c. The above is the optical information exposure means.

A charge eliminating lamp 12 removes residual charges on the photosensitive drum 11 in preparation for the image forming process. A primary charger 13 uniformly charges the photosensitive drum 11.

Reference numeral 14 denotes a developing device, which contains, for example, a black developer (hereinafter referred to as toner) and develops the electrostatic latent image formed on the photosensitive drum 11 into black.

Reference numeral 15 denotes a transfer charger, which conveys the toner image developed on the photosensitive drum 11 through a conveying guide 19, stops at the position of the registration roller 20 and temporarily ends the image formed on the photosensitive drum 11. After being synchronized with
The image is transferred onto the re-fed recording paper 21.

A cleaner 16 collects the toner remaining on the photosensitive drum 11. A conveyor belt 17 conveys the recording paper 21 after the transfer process to the position where the fixing device 18 is provided. The fixing device 18 pressurizes the toner image transferred onto the recording paper 21 with a heat roller and a pressure roller to thermally fix the toner image on the recording paper 21.

FIG. 1 is a functional block diagram in which the image processing according to the present invention executed in the image processing apparatus 7 of FIG. 2 is expressed in hardware.

In FIG. 1, a representative image density signal obtained by averaging the image density signals for one line in the main scanning direction read from the inspection pattern original is created in the image processing device 7,
The representative image density signal sequentially created along the conveyance direction (sub-scanning direction) of the test pattern document is the Fourier transformer 1.
000 is entered.

The Fourier transformer 1000 subjects the input signal to Fourier transform.

The filter 1100 has a filter characteristic B shown in FIG.
And removes the frequency component of the pitch noise from the Fourier transform result of the Fourier transformer 1000.

The inverse Fourier transformer 1200 transforms the filtered Fourier transform result into an inverse Fourier transform to convert it into a representative image density signal. The converted representative image density signal is used for various parameter setting processing of the image forming process.

The noise removal processing performed on the representative image density signal of the inspection pattern original with the above configuration will be described in more detail.

FIG. 3 shows the transfer paper advancing direction and the length Lp of the inspection pattern proposed in the present invention. FIG. 4 shows the relationship between the rotation period of the rotating body or the endless track member included in each image forming process and the length of the output image appearing in the traveling direction by the conveyance of the image holding body. In this embodiment, the diameter (outer diameter) of the heat roller of the fixing device 18 is 40 [mm], and the peripheral length is 125.7 [mm]. Photoconductor drum 1
The diameter of 1 is 30 [mm] and the perimeter is 94.2 [m].
m]. The diameter of the developing roller facing the photosensitive drum of the developing device 14 is 20 [mm], and the circumference is 62.8.
[Mm]. However, in this developing roller, when the peripheral speed Vs of the developing roller and the peripheral speed Vd of the photosensitive drum are different, the pitch at which the nonuniformity of the developing roller appears in the output image is 62.8 × Vd / Vs. When it is desired to read the output image density by removing the influence of the developing roller, the value of the above expression is the length that appears in the traveling direction of the output image due to the conveyance of the image carrier. Assuming that Vd: Vs = 2: 3, the length of the rotation cycle of the developing unit that appears in the traveling direction of the transfer sheet of the output image is 41.9 [m].
m]. The number of faces of the rotary polygon mirror in the optical information exposure means is “10”, one face of the rotary polygon mirror corresponds to one scanning line, and 400 dpi (= 16 pel (line / m)
Since the resolution is m)), the length in which the rotation period of the rotary polygon mirror appears in the traveling direction of the transfer sheet of the output image is 0.625 [mm].

In FIG. 2, the maximum length of the movement cycle of various rotary members or endless track members included in each image forming process in the traveling direction by the conveyance of the transfer sheet of the output image is 125 of the heat roller of the fixing device 18. It becomes 7 [mm]. Therefore, the length L of the inspection pattern in the transfer paper traveling direction is
By making p equal to or longer than 125.7 [mm], it is possible to remove noise due to the pitch of the rotor or the endless track member during each image forming process included in the output image of the inspection pattern. is there.

FIG. 5 shows an example of the waveform of the representative image density signal collected from the inspection pattern image.

Strictly speaking, the actual representative density signal data is discrete data, but it is shown as continuous data in FIG. 5 for convenience of explanation. It can be seen that the image density signal of the read inspection pattern vibrates due to the difference in position in the traveling direction (sub-scanning direction) due to the conveyance of the image carrier.

The frequency spectrum characteristic A of FIG. 6 shows the result of the Fourier transform of the representative image density signal of FIG. It can be seen that the frequency component corresponding to the rotating body or the endless track member pitch in each image forming process included in the output image is included as a noise frequency component.

The filter characteristic of the filter 1100 of FIG. 1 is shown by the characteristic B of FIG.

In the present embodiment, the filter characteristic is set so that the frequency component known to generate pitch noise becomes weak. That is, the filter characteristic is set so that the frequency component corresponding to the pitch of the fixing roller, the photosensitive drum, the developing sleeve, and the rotary polygon mirror becomes weak.

The degree of weakening depends on experimental data and the like.
The magnitude of the influence of the pitch of each member on the image may be examined and then determined.

The frequency spectrum characteristic of the representative image density signal after filtering the representative image density signal after the Fourier transform is shown in characteristic C of FIG.

The actual process of passing through the filter can be realized by integrating the same frequency components of the characteristic A and characteristic B data. It can be seen that pitch noise is removed by such filter processing.

The image density signal after the Fourier transform obtained by the above filter processing is subjected to the inverse Fourier transform to return it to the data string of the typical image density signal along the normal sub-scanning direction. After that, if the averaging process is performed by the image processing device 7, a single image density signal that is a representative value for the image data of one screen can be obtained.

Since the above filter processing is performed, the obtained representative image density signal does not include pitch noise due to the image forming process.

Such filter processing is executed every time the inspection pattern original is read thereafter. FIG. 7 shows an algorithm for feedback-controlling the image forming condition based on the representative image density signal. According to the read image data, the setting condition of each image forming process is changed based on this algorithm.

The conditions for each image forming process for changing the set value are as follows.

(1) Voltage and current of photoconductor charging means (2) Light quantity of optical information exposing means (3) DC voltage of AC bias applied to developing means,
AC voltage component, AC voltage component frequency <Second embodiment> The filter used in the first embodiment is set to remove only the frequency component corresponding to the noise pitch of each image forming process. But,
In the actually read image density signal, there are many noises of relatively high frequency components such as noise during reading, noise due to the surface roughness of the transfer paper, and noise peculiar to the digital image. Therefore, if the filter is provided with the high frequency component removal characteristics as shown in FIG. 7, various high frequency component noises can be removed.

<Third Embodiment> In the above first embodiment, 1
Although the solid image inspection pattern of the density signal of one level is put on the sheet of transfer paper, the solid image inspection pattern of the density signals of plural kinds of levels may be placed as shown in FIG. The signal obtained by reading the inspection pattern changes as shown in FIGS. 5 to 10, but if Fourier transform is performed, a frequency spectrum distribution close to the characteristic A of FIG. 6 can be obtained. However, when there are large differences in the density signal levels of multiple types, the Fourier transform result of the read density signal and the Fourier transform result of the virtual ideal output density signal are subtracted, and the subtraction result is filtered. .. Next, for the concentration signal of the virtual ideal output,
It is necessary to add the result of the Fourier transform to the filter processing result, and then perform the inverse Fourier transform.

[Other Embodiments] In the above-described first embodiment, the length Lp of the inspection pattern in the transfer paper traveling direction is set to the image of the output image when the rotation cycle of the cylinder or the endless track member or the rotating polyhedron in the image forming means is set. The length was made longer or equal to the maximum length among the lengths appearing in the traveling direction due to the conveyance of the holding body, but Lp is not limited to this and is shorter than this due to transfer paper limitation, developer saving, and the like. May be length.

Image Formation In the above-described first embodiment, the charging means and the transfer means in the image forming process did not include the rotating body or the endless track member, but both of them include the charging roller and the transfer roller. In some cases, the rotating body or the endless track member is included. In this case,
The length of the rotation cycle of the rotating member or the endless track member included in the charging unit or the transfer unit that appears in the traveling direction of the transfer sheet of the output image is the maximum during each image forming process, or both If the rotation cycle of the rotating body or the endless track member appears in the traveling direction due to the conveyance of the transfer sheet of the output image, and noise (unevenness in the shade of the output image) is likely to occur, the transfer sheet traveling direction of the inspection pattern It is necessary to make the length Lp equal to or longer than the length in which the rotation cycle of the rotating body or the endless track member in the both appears in the traveling direction of the transfer sheet of the output image.

Further, in the above-described first embodiment, only the developing roller is focused on as the rotary member or the endless track member in the developing means, but the rotary member of the developer stirring member or the endless track member is rotated. When noise (unevenness in the density of the output image) is likely to occur in the length in which the cycle appears in the traveling direction of the transfer sheet of the output image, the transfer sheet traveling direction length Lp of the inspection pattern is set equal to this length. May be longer.

[0052]

As described above, according to the present invention, since the image signal in which noise is mixed is filtered, a normal image signal is obtained, and the image forming result for this image signal is inspected on the original. A density distribution faithful to the pattern image can be obtained. Therefore, the image forming conditions do not change remarkably due to the influence of noise as in the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration of a noise processing circuit according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the main structure of the embodiment of the present invention.

FIG. 3 is a plan view showing an inspection pattern image of an example of the present invention.

FIG. 4 is an explanatory diagram showing a noise generation period according to the embodiment of the present invention.

5 is a characteristic diagram showing a density distribution in a read image signal of the inspection pattern of FIG.

FIG. 6 is a characteristic diagram showing a frequency spectrum distribution in an image signal before and after filtering according to the embodiment of the present invention.

FIG. 7 is a flowchart showing an image forming process setting procedure according to the embodiment of the present invention.

FIG. 8 is a characteristic diagram showing another filter characteristic of the filter according to the embodiment of the present invention.

FIG. 9 is a plan view showing another inspection pattern image of the embodiment of the present invention.

10 is an explanatory diagram showing a density distribution of a read image signal of the inspection pattern image of FIG.

11 is a characteristic diagram showing a density distribution of a virtual image signal used for noise removal of the pattern image of FIG.

FIG. 12 is a characteristic diagram showing potential characteristics of an electrostatic latent image used for forming a latent image in a conventional example.

FIG. 13 is a perspective view showing a noise source of a conventional image forming apparatus.

[Explanation of symbols]

1 Document illumination lamp composed of, for example, a halogen lamp 2 Document platen glass 3 Document 4 Mirror 5 Optical lens 6 Imaging device such as CCD (charge coupled device, linear imaging device) 7 Image processing device 8 Laser driver circuit 9 Semiconductor Laser 10 Rotating polygon mirror 11 Photoreceptor drum 12 Eliminating lamp 13 Primary charger 14 Developing means 15 Transfer charger 16 Cleaner 17 Conveying belt 18 Fixing device 19 Conveying guide 20 Registration roller 21 Recording paper

Claims (1)

Claim: What is claimed is: 1. A document on which an inspection pattern image is described is read, or an inspection pattern is generated by an internal signal to form an image, and the image formation result is read again to form the subsequent image formation. In an image forming method in which conditions are variably set, a frequency of a pitch noise image due to an image forming process appearing in an image holding body advancing direction of the image forming result is determined in advance, and for the setting of image forming conditions for the next time and thereafter, When reading a document,
An image forming method, which comprises performing a filtering process for weakening the frequency of the pitch noise image.