JPH10145596A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and properly control the density characteristic of image data without increasing the number of reference patches so as to prevent a density jump by forming the plural reference patches so as to permit the reference patches with continuous densities in order of density to be adjacently positioned and evading that the positions of the reference patches with adjacent densities are largely separated. SOLUTION: When the plural reference patches with the different densities are formed in a paper sheet, formation is executed so as to permit the reference patches with the adjacent densities to be adjacent. Thus, the positions of the reference patches with the adjacent densities are not largely separated so that the jump in the measured density in the reference patch is prevented from occurring in spite of an in-screen nonuniformity. That is, a smooth density curved line is obtained, a density conversion table without the density jump is generated and, as a result, smooth image density control without the density jump is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a method for forming a plurality of reference patches having different densities on a non-image portion on a photoreceptor, based on the densities of the formed plurality of reference patches. The present invention relates to an image forming apparatus that creates a density conversion table and performs image density control for converting density characteristics of image data based on the created density conversion table.

[0002]

2. Description of the Related Art Conventionally, a plurality of reference patches having different densities are formed on a non-image portion on a photosensitive member, and a density conversion table is created based on the densities of the formed plurality of reference patches.
Many techniques relating to image density control for converting the density characteristics of image data based on the created density conversion table have been proposed.

When forming a plurality of reference patches having different densities, it is necessary to form each reference patch at a different position on the photoreceptor. However, in general, the photoreceptor has in-plane unevenness in its charging property and light sensitivity. In addition, even when uniform charging, exposure, and development are performed, the density varies depending on the location. FIG. 13 is a diagram illustrating an example of the variation in density on the surface of the photoconductor, in which the density range is divided into a plurality of ranges, and the surface of the photoconductor is divided into regions having the same density. I have.

On the other hand, conventionally, when a plurality of reference patches are formed, they are often formed over a plurality of rows or columns. FIG. 12 shows an example of a reference patch generally used in the related art. When a plurality of reference patches having different densities are formed over a plurality of rows, as shown in FIG. If the reference patches are arranged in the same direction in each row in the order of density, the positions of the reference patches (for example, 65% and 60%, 25% and 20%) whose densities are adjacent to each other greatly differ between rows. As shown in FIG. 13 described above, the in-plane unevenness of the photoconductor is distributed like contour lines. Therefore, if the position of the reference patch is greatly separated, the influence of the in-plane unevenness becomes large, and the plurality of reference in FIG. As shown in the graph of the patch density measurement result, there is a possibility that a density jump as indicated by the arrow Y1 and the arrow Y2 may occur. Also, the density conversion table created based on the density of such a reference patch is affected by the density jump, and there is a possibility that a jump may occur in the gradation characteristic of the image whose density is finally converted. .

Therefore, in order to reduce the error of image density control due to the reference patch density error caused by the in-plane unevenness of the photosensitive member, a plurality of reference patches having the same density are formed, and the plurality of reference patch densities are determined. Techniques for reducing the error by averaging have been proposed in JP-A-8-9178, JP-A-64-41375, and the like.

[0006]

However, when a plurality of reference patches having the same density are formed as described above, the total number of reference patches to be formed becomes very large, the amount of toner consumption increases, and the production of a copy increases. This has the effect of reducing the properties. Further, for one density, an error can be reduced by averaging a plurality of measured density values. However, since the reference patches adjacent to each other in density are formed on the photoconductor at greatly separated positions, However, the problem that the jump of density occurs as described above remains unsolved.

On the other hand, when an image density is controlled by creating a density conversion table, the stability of each reference patch density is also important, but the smoothness of the entire gradation characteristic is also important.
When the density jump occurs as shown in FIG. 15, there is a possibility that an inconvenience such as an unnecessary boundary line being noticeable as a false contour may appear particularly in a highlight area (low density area).

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made without increasing the number of reference patches.
It is an object of the present invention to provide an image forming apparatus capable of easily creating a density conversion table without a density jump and consequently performing image density control without a density jump.

[0009]

In order to achieve the above object, an image forming apparatus according to the present invention forms a plurality of reference patches having different densities on a plurality of rows or columns in order of density on an image carrier. Reference patch forming means, density measuring means for measuring the density of the formed reference patch, and an image based on a predetermined target value of the density of the reference patch and a measured value of the density of the formed reference patch. Density conversion means for converting density characteristics of data, wherein the reference patch forming means is arranged such that reference patches having a continuous density in the order of density are located adjacent to each other on the image carrier. And forming the plurality of reference patches.

In the image forming apparatus according to the first aspect, the reference patch forming means forms a plurality of reference patches having different densities on the image carrier over a plurality of rows or columns in the order of density. In addition, at this time, in the present invention, a plurality of reference patches are formed such that reference patches having continuous densities are located adjacent to each other on the image carrier in the order of density. This allows
The positions of the reference patches having continuous densities (that is, adjacent densities) in the order of densities do not greatly separate from each other. The image carrier on which the reference patch is formed may be a recording medium such as paper, or may be a photoconductor or a transfer belt.

The density of the reference patch thus formed is measured by density measuring means, and based on the measured density and a predetermined target value of the density of the reference patch, image data is obtained as follows. Is converted by the density conversion means.

For example, a density conversion table is created based on the measured density and the target density of the reference patch. In the present invention, since the positions of the reference patches having adjacent densities do not greatly separate from each other, a jump in the measured density of the reference patches (arrow Y1 portion, It is possible to avoid the occurrence of the arrow Y2), obtain a smooth density curve as shown in the graph of FIG. 16, and create a density conversion table without a density jump. Further, the density characteristic of the image data is converted by the density conversion means based on the density conversion table having no density jump.

As described above, according to the present invention, it is possible to easily control the density characteristic of image data easily without changing the number of reference patches and merely by changing the arrangement of the reference patches so that there is no density jump. it can.

An example of forming a plurality of reference patches such that reference patches having adjacent densities are adjacent to each other as in the present invention is shown in FIG. Are arranged in the order of density. In addition, a plurality of reference patches may be formed so that reference patches having adjacent densities are adjacent to each other in an oblique direction, as indicated by broken lines in FIG.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

[Overall Configuration of Color Copier] FIG. 1 is an overall configuration diagram of a color copier to which the present invention is applied, and FIG. 2 is a block diagram of a color copier to which the present invention is applied.

As shown in FIGS. 1 and 2, the color copier 1
Numeral 0 denotes a reading unit 20 for reading a document, an image processing unit 30 for processing read image data, a ROS optical unit 40 for driving a laser according to the processed image data to irradiate a light beam to a photoconductor, and forming an image. And an image forming unit 60.

As shown in FIG. 2, in the reading section 20, a document G placed at a predetermined position on the table 12 (see FIG. 1) is irradiated by an exposure lamp 22 and reflected light thereof is reflected by a CCD image sensor (hereinafter referred to as a CCD image sensor). ). The image signal read by the CCD 24 is amplified to an appropriate level by an amplifier 26, and the amplified image signal is A / D
The data is converted by the converter 28 into 8-bit digital image data. The shading correction and the gap correction are sequentially performed on the digital image data. The digital image data subjected to these corrections is converted into density data by the density converter 29 and sent to the image processing unit 30.

The image processing section 30 performs basic image processing as a color copying machine, that is, color signal conversion, black reproduction (UC
R), MTF processing and the like are performed, and the image data is converted into image data of four colors of yellow, magenta, cyan, and black. The converted image data of each color is subjected to gradation conversion in accordance with the gradation of the reading unit 20 and the image forming unit 60. Further, the image processing unit 30 receives image data (for example, image data (CG image data) created by computer graphics, image data stored in a CD-ROM, etc.) from an external image processing device or the like. External data input means 33 and an image density control means 31 for creating a density conversion table for converting the density characteristics of the image data. The image density control means 31 performs the gradation conversion. Image data or the external image data is subjected to density conversion based on a density conversion table. The external data input means 33 is, for example, a floppy disk reader,
It can be constituted by a CD-ROM reading device, a communication processing device for receiving data from an external image processing device or the like via a network, or the like.

The image data subjected to the density conversion is D / D
The data is converted into analog image data by the A converter 32 and sent to the comparator 39 via the selector 34. In the comparator 39, pulse width modulation is performed by comparing the sent analog image data with a signal of a predetermined period output from the triangular wave generator 38, and the analog image data is converted into binary image data. Is converted. In the pulse width modulation here, for example, as shown in FIG. 3, the input analog image data A is compared with the triangular wave B from the triangular wave generator 38, and the portion where the analog image data A is larger than the triangular wave B is " 0 "
(Laser off), and binary image data in which the portion of the analog image data A smaller than the triangular wave B is "1" (laser on) is generated, and sent from the comparator 39 to the ROS optical unit 40.

The image processing section 30 is provided with a patch signal generating means 36 for generating image signals (hereinafter referred to as patch image signals) of a plurality of image density control patches (reference patches) having different densities. I have. The selector 34 selects the analog image data from the D / A converter 32 at the time of normal copying, and, when receiving an instruction to create a reference patch from the arithmetic unit 84 of the image forming unit 60 described later, generates a patch signal generating means. The patch image signal from 36 is selected, sent to the comparator 39, and binarized by the pulse width modulation as described above.

The ROS optical unit 40 is controlled by a laser drive circuit 42 for controlling on / off of the laser 46 based on the binary image data sent from the comparator 39, and under the control of an arithmetic unit 84 of the image forming unit 60 described later. And a laser light amount varying device 44 for variably controlling the laser light amount. The laser light is deflected by the polygon mirror 48 and f
Image forming unit 60 via θ lens 50 and reflection mirror 52
To the photoreceptor 62.

As shown in FIGS. 1 and 2, the image forming section 6
0, a photoconductor 62 is provided.
Around the charging device 68, an electrometer 70 for measuring the potential on the photoconductor for controlling the potential of the photoconductor, a rotary developing device 72, and measuring the patch density on the photoconductor for controlling the toner dispensing. An optical sensor 74, a transfer device 80, a cleaner device 64, and a discharge lamp 66 are provided. Further, the image forming unit 60 includes a toner dispensing device 76 that supplies toner to the developing devices of the respective colors of the rotary developing device 72, a fixing device 88, and a sheet conveying device 9.
2 is also provided.

Further, the image forming section 60 includes an arithmetic unit 84 for controlling the entire image formation and controlling the image forming conditions according to the outputs of the electrometer 70 and the optical sensor 74, and an arithmetic unit 84.
And a developing bias variable device 78 that changes the developing bias under the control of the arithmetic device 84. The arithmetic unit 84 includes the patch signal generator 3
6 and the selector 34 are instructed to create a reference patch.

[Outline of Image Forming Process] Next, an outline of the image forming process executed by the image forming section 60 will be described. In the image forming section 60, the following image forming processing is executed according to a well-known xerographic process. That is, the photoconductor 62 rotating clockwise in FIG.
8, the first black latent image of the first color is formed on the photoconductor 62 by the laser light from the ROS optical unit 40. This latent image is developed with black toner by the black developing device of the rotary developing device 72. The developed black toner image is transferred by a transfer corotron 80 </ b> A to a sheet (not shown) that is transported from a paper tray 90 by a paper transport device 92 and wound around a transfer drum 80. The toner image remaining on the photoconductor 62 without being transferred is removed by the cleaner device 64, and the photoconductor 6 is removed.
2 is discharged by the discharge lamp 66.

Then, the photosensitive member 62 is uniformly negatively charged again by the charging device 68, and the second color yellow image is subsequently formed. In this manner, the toner images of a total of four colors from the third color magenta to the fourth color cyan are sequentially transferred to the paper wound around the transfer drum 80. The paper to which the four color toner images have been transferred is separated from the transfer drum 80 by the separation corotron 80B, and
The color toner image is fixed on the paper, and a color copy is formed. After the transfer of each color or the peeling of the paper, the extra charge on the paper and the transfer drum 80 is discharged by the charge removing corotron 80C.
The charge is removed.

[Overview of Photoconductor Potential Control] Next, the photoconductor 6
The control of the photoconductor potential by the charge amount varying device 82, the developing bias varying device 78, and the laser light amount varying device 44 by the electrometer 70 for measuring the potential on 2 will be briefly described.

In the present embodiment, the arithmetic unit 84 of the image forming unit 60 is provided immediately before the power of the color copier 10 is turned on and before the copy is started, and thereafter, every 30 minutes before the start of the copy.
Thus, the photoconductor potential control is performed according to the flowchart of FIG. The memory of the arithmetic unit 84 stores in advance a target dark potential VHS, a target exposure partial potential VLS, and a fog prevention potential difference VC from the target dark potential VHS to the developing bias potential VB.

First, at step 152 in FIG.
8 is applied to the voltage VG by the charge amount varying device 82.
The dark potential VH1 when set to 1 and the dark potential VH2 when set to the voltage VG2 are detected by the electrometer 70. In the next step 154, the target dark potential VH is calculated using the following equation (1).
The grid voltage VGS for obtaining S is calculated.

VGS = VG1 + ((VG2−VG1) × (VHS−VH1) / (VH2−VH1)) (1) In the next step 156, the photosensitive member 62 is moved to the above step 1
It is charged with the grid voltage VGS obtained in 54. And
Laser light amount LD by laser light amount variable device 44
1. The laser drive circuit 42 is driven by two kinds of laser light amounts LD1 and LD2 so that two kinds of laser light amounts L
A reference patch is formed by D1 and LD2. Further, the exposure partial potential VL of each of the two formed reference patches
1. VL2 is measured by the electrometer 70. In the next step 158, a laser light amount LDS for obtaining the target exposure partial potential VLS is calculated using the following equation (2).

LDS = LD2-((LD2−LD1) × (VLS−VL2) / (VL1−VL2)) (2) In the next step 160, development is performed using the following equation (3). Calculate the bias potential VB. VC indicates a fog prevention potential difference.

VB = VHS-VC (3) In the next step 162, the grid voltage VGS obtained as described above is developed into the charging amount varying device 82, and the laser light amount LDS is developed into the laser light amount varying device 44. The bias potential VB is set in the developing bias variable device 78, and the process ends.

[Overview of Toner Dispensing Control]
Dispensing control of each color toner for the rotary developing device 72 will be described. The toner dispensing control is realized by measuring the patch density for toner dispensing control on the photoconductor 62 by the optical sensor 74 and controlling the operation of the toner dispensing device 76 by the arithmetic unit 84 based on the measured patch density. I do. The toner dispensing control patch is instructed to be created by the arithmetic unit 84.

When an instruction to create a patch is issued from the arithmetic unit 84, the selector 34 selects a patch image signal for each color for toner dispensing control with an image area ratio of 50% from the patch signal generating means 36 and sends it to the comparator 39. Then, a reference patch for each color having an image area ratio of 50% is formed on a non-image portion on the photoconductor 62 in the same procedure as the above-described image forming process of the color copying machine.

The optical sensor 74 for measuring the patch density on the photoconductor 62 irradiates the reference patch P on the photoconductor 62 with light from the LED 74A as shown in FIG. 4, and measures the reflected light with the photodiode 74B. The patch density is measured based on the measured reflected light amount.

If the measured patch density is lower than the target value, the arithmetic unit 84 sets the toner dispensing unit 76
Is driven to increase the toner density so that the patch density approaches the target value. Conversely, when the measured patch density is higher than the target value, the arithmetic unit 84 stops the toner dispensing device 76 and brings the patch density closer to the target value.

[Outline of Image Density Control] Next, a plurality of reference patches having different densities are formed, a density conversion table is created based on the density measurement results, and density characteristics of image data are determined based on the created density conversion table. Will be described with reference to a flowchart of a density conversion table creation process in FIG. 6 and a schematic diagram of image density control in FIG.

As shown in FIGS. 6 and 7, when creating the density conversion table, the arithmetic unit 84 sends a signal for creating a correction color patch to the patch signal generating means 36, and each color selector 34 sets the patch signal generating means 36. The correction color patch image signal is selected and sent to the comparator 39, and the correction color patch is printed and output on paper in the same image forming procedure as that of the above-described color copying machine (step S1).
Here, for example, as shown in FIG. 12 and FIG. 14, a correction color patch print composed of 24 tone patches having different densities for each of the four colors of yellow, magenta, cyan, and black is output. In FIGS. 12 and 14, Y in the upper row indicates yellow, M indicates magenta, C indicates cyan, and K indicates black.

Next, the reading unit 20 of the color copying machine 10
Is used as a density measuring device for correction color patch prints, the operator sets the correction color patch prints on the mounting table (platen) 12 (step S).
2). The density measuring device for the color patch print for correction may use a densitometer other than the reading unit 20 of the color copying machine 10.

Next, the reading section 20 measures the density of 24 color patches of each color to determine the current gradation (step S3). The result of the density measurement is sent to the image density control means 31, and it is determined whether or not the measurement result has a problem (step S4). If there is no problem here, the image density controller 31 compares the current gradation with a predetermined target gradation, and creates a density conversion table based on the comparison result and stores it in the memory (step S5). On the other hand, if there is a problem with the measurement result in step S4, a warning is displayed to the operator and the processing is stopped because there is a possibility that the correction color patch print is not properly placed (step S4).
6).

After the density conversion table has been prepared as described above, at the time of image output, the original image data sent from the reading unit 20 is subjected to color conversion by the image processing unit 30 as shown in FIG. After the gradation conversion processing, the density of the image is converted based on the created density conversion table so that the gradation of the image matches the target gradation.
Similarly, when printing image data transmitted from the outside, based on the created density conversion table, an external image data is output so that the gradation of the image matches the target gradation. Density conversion is performed on the image data.

[Execution Result of Image Density Control] The execution result of the above-described image density control will be described with reference to FIGS. FIG. 8 (B) shows 24 different black densities.
A patch conversion result (curve K11), a target value of 24 patches (curve K12), and a density conversion table (curve K) created to match the measurement result of 24 patches to the target value
13) is shown. FIG. 8A shows a density gradation (curve K01) before density control for black, a target value of the density gradation (curve K02), and the density conversion table (FIG. 8).
The density gradation (curve K03) after density control based on the curve K13) of (B) is shown. Obviously, the curve K03 is closer to the curve K02 than the curve K01. That is, by performing the density control, the density gradation can be made closer to the target value.

Similarly, for yellow, FIG.
, Measurement results of 24 patches having different densities (curve Y11),
FIG. 9A shows a target value of 24 patches (curve Y12) and a density conversion table (curve Y13) for matching the measurement result of the 24 patches to the target value, and shows a density gradation before density control shown in FIG. (Curve Y01) is changed to a target value (curve Y0).
In order to approach 2), the density conversion table (FIG. 9)
Density control is performed based on the curve Y13) of (B), and a density gradation (curve Y03) after the density control can be obtained.

FIG. 10B also shows magenta.
, Measurement results of 24 patches having different densities (curve M11),
A density conversion table (curve M13) for matching the target value of 24 patches (curve M12) and the measurement result of 24 patches to the target value is shown, and the density gradation before density control shown in FIG. (Curve M01) is changed to a target value (curve M0).
In order to approach 2), the density conversion table (FIG. 10)
Density control is performed based on the curve M13) of (B), and a density gradation (curve M03) after the density control can be obtained.

FIG. 11B shows the measurement results of 24 patches with different densities (curve C11).
A density conversion table (curve C13) for matching the target value of four patches (curve C12) and the measurement result of 24 patches to the target value is shown, and the density gradation before density control shown in FIG. (Curve C01) is changed to the target value (curve C0).
In order to approach 2), the density conversion table (FIG. 11)
Density control is performed based on the curve C13) of (B), and a density gradation (curve C03) after the density control can be obtained.

[Operations and effects of this embodiment] Next, operations and effects of this embodiment will be described. In the present embodiment, when forming a plurality of reference patches having different densities on a sheet, FIG.
As shown in FIG. 4, the reference patches having adjacent densities are formed so as to be adjacent to each other. As a result, the positions of the reference patches having adjacent densities do not greatly separate from each other, and even if there is in-plane unevenness of the photoconductor, a jump in the measured density of the reference patches (arrow Y1 portion) as shown in the graph of FIG. , Arrow Y2
) Can be avoided. That is, a smooth density curve as shown in the graph of FIG. 16 is obtained, and a density conversion table without a density jump can be created.

As described above, according to the present embodiment, a density conversion table having no density jump can be easily created by merely changing the arrangement of the reference patches without increasing the number of reference patches. Smooth image density control can be performed.

In this embodiment, an example has been described in which a plurality of reference patches having different densities are formed on a sheet and a density conversion table is created based on the results of these density measurements. A plurality of reference patches having different densities may be formed on the belt body, these densities may be measured, and a density conversion table may be created from the measurement results. Similar effects can be obtained even when the reference patches are formed on the photoreceptor or the transfer belt.

[0049]

According to the first aspect of the present invention, a plurality of reference patches are formed such that reference patches having continuous densities (adjacent densities) are located adjacent to each other when viewed in order of density.
Since the positions of the reference patches having the adjacent densities are prevented from being largely separated from each other, the density characteristics of the image data can be easily and appropriately controlled without increasing the number of the reference patches without causing a density jump. Is obtained.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a color copying machine according to an embodiment.

FIG. 2 is a block diagram of the color copying machine of FIG.

FIG. 3 is a diagram illustrating binarization of image data by pulse width modulation.

FIG. 4 is a diagram illustrating a configuration of an optical sensor.

FIG. 5 is a flowchart showing a processing routine of photoconductor potential control.

FIG. 6 is a flowchart showing a procedure for creating a density conversion table.

FIG. 7 is a diagram for explaining an outline of image density control.

8A is a graph showing the density gradation before black density control, the target value of the density gradation, and the density gradation after density control for black, and FIG. 8B is a graph showing the density of 24 patches for black. It is a graph which shows a measured value, a target value of 24 patches, and a density conversion table.

9A is a graph showing a density tone before density control, a target value of density tone, and a density tone after density control for yellow, and FIG. 9B is a graph showing density of 24 patches for yellow. It is a graph which shows a measured value, a target value of 24 patches, and a density conversion table.

10A is a graph showing density gradation before magenta density control, a target value of the density gradation, and density gradation after magenta density control, and FIG. 10B is a graph showing the density of 24 patches for magenta. It is a graph which shows a measured value, a target value of 24 patches, and a density conversion table.

11A is a graph showing density gradation before density control, a target value of density gradation, and density gradation after density control for cyan, and FIG. 11B is a graph showing density of 24 patches for cyan. It is a graph which shows a measured value, a target value of 24 patches, and a density conversion table.

FIG. 12 is a diagram showing a conventional arrangement of 24 patches.

FIG. 13 is a diagram illustrating in-plane unevenness of a photoconductor.

FIG. 14 is a diagram showing an arrangement of 24 patches in the present invention.

FIG. 15 is a graph showing density measurement values of reference patches arranged in a conventional manner.

FIG. 16 is a graph showing density measurement values of a reference patch to which the present invention has been applied.

FIG. 17 is a diagram illustrating another example in which a plurality of reference patches are formed such that reference patches having adjacent densities are adjacent to each other.

[Explanation of symbols]

 Reference Signs List 10 color copying machine (image forming apparatus) 20 reading unit 30 image processing unit 31 image density control means 60 image forming unit 84 arithmetic unit

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H04N 1/46 H04N 1/46 Z

Claims (1)

[Claims] 1. A reference patch forming means for forming a plurality of reference patches having different densities on a plurality of rows or columns in order of density on an image carrier; a density measuring means for measuring the density of the formed reference patches; A density conversion unit that converts density characteristics of image data based on a determined target value of the density of the reference patch and a measured value of the density of the formed reference patch. An image forming apparatus, wherein the patch forming unit forms the plurality of reference patches so that reference patches having continuous densities are located adjacent to each other on the image carrier when viewed in order of density.