JPH0954469A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form plural reference patches developed on a photoreceptor even in the case there is limitation on the place or timing capable of forming the reference patch. SOLUTION: In this image forming device, an image is formed according to image information given to the rotating photoreceptor 42, and the formed image is transferred to a transfer medium; and plural reference patches having different density are formed by the patch forming part 29 of an image processing part 2 and given to an image forming part 4, so that plural patch images divided into prescribed number of groups and having the different density are formed at the nonimage part of the photoreceptor 42 synchronously with the rotation of the photoreceptor 42 for every group, and the density of the patch image formed on the photoreceptor 42 is detected by a photosensor 48, then the image forming condition of the image forming part 4 is controlled by an image forming condition control part 41, based on the detected density.

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 which develops a latent image on a photoconductor according to an image to obtain an image,
In particular, the present invention relates to an image forming apparatus that detects the density of a reference patch image formed on a photoconductor or a transfer medium, and forms an image while controlling image forming conditions based on the detected density.

[0002]

2. Description of the Related Art Conventionally, a reference patch density developed on a photosensitive member is measured and compared with a target reference patch density, and toner replenishment and other image forming conditions are controlled according to the comparison result. Therefore, the final on-paper density is often maintained at a predetermined target density.
Among them, for example, as disclosed in Japanese Patent Laid-Open No. 4-126462, a plurality of reference patch densities having different densities are measured by a density detecting means, and this is compared with a target reference patch density, and the comparison is made. Recently, a method of creating gradation correction data according to the result and correcting the gradation has been widely used.

[0003]

In the case of this method,
It is necessary to measure a plurality of reference patch densities having different densities, but there is a limitation on the place or timing at which the developed reference patch can be formed on the photoconductor. For example, in order to create a reference patch during image formation, it is necessary to create it in a non-image portion, and therefore, it is created between images as disclosed in, for example, Japanese Patent Application Laid-Open No. 56-128977. It will be. In this case, in order not to affect the image creation speed, the length between the images cannot be made too long, and therefore there is a limit to the range in which multiple reference patches with different densities can be created. Occurs.

Further, in a color image forming apparatus for sequentially transferring images of respective colors sequentially formed on a photoconductor to a sheet on a sheet conveying body such as a transfer drum to form a color image, a reference image formed on the photoconductor is used. There is a problem that the film of the paper transport body gets dirty with the patch. Transfer drums are generally disclosed in
As disclosed in Japanese Patent Publication No. 149086 (in particular, FIG. 4), a frame body in which metal wheels at both ends are connected by metal tie bars is used.
It has a cylindrical shape and is wound with a dielectric film.
Further, Japanese Patent Laid-Open No. 6-149086 discloses a device for removing the transfer drum from the photoconductor, a film cleaning device for the transfer drum, and a toner recovery device for the transfer drum, as a method for preventing film contamination.

In any case, a special means is required to freely create a plurality of reference patches having different densities, and if these special means are not provided, the reference patch can be created without contaminating the film on the transfer drum. The position on the photoconductor is only the position corresponding to the tie bar of the transfer drum where the transfer drum does not come into contact with the photoconductor. Therefore, there is a problem in creating a plurality of reference patches developed on the photoconductor because the location or timing at which the reference patch can be created is limited.

The present invention has been made in view of the above problems, and an object of the present invention is to develop a photoconductor on a photoconductor even if the place or timing at which a reference patch can be formed is limited. To provide an image forming apparatus capable of creating a plurality of created reference patches.

[0007]

An image forming apparatus according to the present invention forms an image according to image information provided on a rotating photoconductor and transfers the formed image onto a transfer medium. Then, the reference patch image information is given to the image forming means, and a plurality of patch images having different densities, which are grouped into a predetermined number of groups in advance, are synchronized with the rotation of the photoconductor to the non-image portion of the photoconductor. A patch image forming unit for forming each group, a patch image detecting unit for detecting the density of the patch image formed on the photoconductor or the transfer medium, and an image based on the density detected by the patch image detecting unit. The image forming condition control unit controls the image forming condition of the forming unit.

In the image forming apparatus having the above-mentioned structure, the patch image forming means gives the image forming means a plurality of reference patch image information having different densities which are grouped in a predetermined number of groups in advance, and the plurality of patch images are exposed. It is formed for each group in the non-image portion of the photoconductor in synchronization with the rotation of the body. The patch image detecting means detects the density of the patch image formed on the photoconductor or the transfer medium. The image forming condition control unit controls the image forming condition of the image forming unit based on the density detected by the patch image detecting unit.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of a color copying machine to which the present invention is applied, and FIG. 2 is a block diagram showing a configuration of a first embodiment of the present invention. First, Fig. 1
In a color copying machine, a color copying machine is roughly divided into a scanner unit 1 for reading a document, an image processing unit 2 for processing image data read by the scanner unit 1, and a laser according to image data processed by the image processing unit 2. ROS (Raster Output) that drives the
(Scanner) An optical unit 3 and an image forming unit 4 for finally forming an image.

The details of each section will be described below with reference to FIG. In addition, in FIG. 1 and FIG. 2, the same parts are designated by the same reference numerals. First, in the scanner unit 1, the original 11 is irradiated with the reading light from the exposure lamp 12, and the reflected light is reflected by the CCD image sensor 1.
It is read by being incident on 3. The image data output from the CCD image sensor 13 is amplified to an appropriate level by the amplifier 14, and then converted into 8-bit digital image data by the A / D converter 15. Then, the shading correction device 16 performs shading correction, the gap correction device 17 performs gap correction, the density conversion device 18 converts the reflectance data into density data, and the data is sent to the image processing unit 2.

In the image processing section 2, the first stage color converter 2
1, the basic image processing as a color copying machine, that is, color signal conversion, black color reproduction (UCR; Under Color Removal), M
By performing TF (Modulation Transfer Function) processing, etc., Y (Yellow), M (Magenta), C (Cyan), B
Converted to image data of 4 colors of k (Black). Next, the gradation correction (1) circuit 22 corrects the gradation of each color according to the gradation of the scanner unit 1 and the image forming unit 4. In the gradation correction (2) circuit 23 in the next stage, gradation correction is performed based on gradation correction data that is created by the gradation correction data generation unit 24 and that compensates for gradation variation of the image forming unit 4. .

The gradation-corrected data is D / A
After being converted into an analog image signal by the converter 25, the analog image signal is supplied to the comparator 27 via the selector 26. Comparator 27
Performs pulse width modulation by comparing the analog image signal with a triangular wave signal of a predetermined period sent from the triangular wave generator 28, and converts the analog image signal into binary image data. FIG. 3 is a waveform diagram for explaining binarization of image data by this pulse width modulation. As is apparent from this waveform diagram, the input analog image data is compared with the triangular wave, and the part where the analog image data is larger than the triangular wave is "0", that is, the laser is OFF, and the part where the analog image data is smaller than the triangular wave is ". 1 ”, that is, converted into binary image data in which the laser is turned on. This binary image data is sent from the comparator 27 to the ROS optical section 3.

Further, the image processing section 2 is provided with a patch creating section 29 for creating a plurality of reference patches having different densities. The patch signal created by the patch creating unit 29 is supplied to the comparator 27 via the selector 26.
The selector 26 selects analog image data at the time of normal copying, and is instructed by the image forming condition control unit 41 of the image forming unit 4 to generate a patch, thereby selecting and comparing the patch signal from the patch forming unit 29. Send to vessel 27.
This patch signal is also used in the comparator 2 as in the analog image signal.
It is binarized in 7.

Next, the ROS optical section 3 includes an image forming section 4
Laser light amount varying device 31 for changing the laser light amount by being controlled by the image forming condition control unit 41 of
And a laser drive circuit 32. The laser driving circuit 32 controls ON / OFF of the laser light source 33 based on the binarized data sent from the comparator 27. The laser light emitted from the laser light source 33 is deflected by the polygon mirror 34 and guided to the photoconductor 42 of the image forming unit 4 via the fθ lens 35 and the reflection mirror 36.

In the image forming section 4, a charging device 43, a rotary developing device 44, a cleaner device 45, a charge eliminating lamp 46, an electrometer 47 for measuring the potential on the photoconductor 42, and an optical sensor 48 are provided around the photoconductor 42. It is provided. The optical sensor 48 has a function as a patch density detecting unit that detects (measures) the patch density on the photoconductor 42. In addition, a toner dispensing device 49 that supplies toner to each color developing device of the rotary developing device 44, the fixing device 50 and the sheet conveying device 51 shown in FIG. The above-described image forming condition control unit 41 that controls the toner dispense and the image forming condition according to the output of the optical sensor 48, and the charge amount changing device 52 that is controlled by the image forming condition control unit 41 and changes the charge amount of the charging device 43. A developing bias changing device 53 for changing the developing bias is provided.

Then, image formation is performed according to the well-known xerographic process. That is, the rotating photoconductor 42 is uniformly negatively charged by the charging device 43, and the first latent image is formed by the laser beam. This latent image is the first color (B
Black, which is negatively charged by the developing device
The portion of the toner that has been written with laser light is developed. The developed image is carried by the paper carrying device 51 from the paper tray 54 shown in FIG. 1, and is transferred by the transfer corotron 56 onto the paper (not shown) wound around the transfer drum 55. The image remaining on the photoconductor 42 without being transferred is removed by the cleaner device 45.

The photoconductor 42 is neutralized by the static elimination lamp 46, and is again uniformly negatively charged by the charging device 43.
Image formation for the second color (Yellow) is subsequently performed.
In this way, when the four color development images up to the third color (Magenta) and the fourth color (Cyan) are sequentially transferred to the paper on the transfer drum 55, the paper is separated from the transfer drum 55 by the separation corotron 57. And the fixing device 50
A color copy image is formed by being fixed by.
A static elimination corotron 58 is provided around the transfer drum 55, and the static elimination corotron 58 eliminates excess charges on the paper and the film on the transfer drum 55 after the transfer of each color or the separation of the paper.

Next, in the color copying machine having the above structure,
The densities of a plurality of reference patches having different densities are measured by an optical sensor 48 which is a patch density detecting means, and this is compared with a target reference patch density, and tone correction data is created based on the comparison result, and tone correction is performed. The method for doing so will be briefly described. The multiple patches used for this gradation correction are 0-2 for each color.
Of the 256 gradations of 55, the image area is 15%, 20%,
38/256, 51/25 equivalent to 30% and 50%
There are four patches of 6,76 / 256,128 / 256 levels. The details of the four patch creation methods according to this embodiment will be described later.

First, when the mode for executing the gradation correction is entered, the image forming condition control unit 41 of the image forming unit 4 outputs a patch forming instruction to the patch forming unit 29 of the image processing unit 2. As a result, the patch creating section 29 generates a patch signal having a plurality of densities, while the selector 26 selects the patch signal and sends it to the comparator 27. This comparator 27
The binarized data is sent to the laser drive circuit 32 of the ROS optical section 3. As a result, multiple density patches are exposed on the photoconductor 42 and developed by the rotary developing device 44. The density of the developed four reference patches of each color is measured by the optical sensor 48. The measurement result and the target density of each predetermined patch density are sent from the image forming condition control unit 41 to the gradation correction data generation unit 24.

Next, regarding the procedure for creating the gradation correction data of 256 gradations in the gradation correction data generator 24,
Description will be given along the flowchart of FIG. First, for each color, the image area (Cin) 15, 20, 30,
The measurement result of 50% patch density is obtained, and the difference of the target density of each predetermined patch density, Radc Delta (CIN) is calculated (step S11). Note that the gradation correction data generation unit 24 has the Radc shown in FIG. Table data indicating the relationship between the delta and the gradation offset amount is stored.

Then, referring to this table, Ra
dc Table N of each Cin from delta (CIN)
o. Is obtained (step S12). At this time, Cin10
0% causes the same change as the concentration change of Cin 50%. Is Radc delta
Calculate from (50%). Next, according to the table, the table No. According to each Cin (15, 20, 30, 5
A gradation offset amount of 0,100%) is obtained for each of the photo mode and the character mode (step S13). Next, the correction amount PT at each Cin point TRC [CI
N] is calculated (step S14).

This PT The calculation of TRC [CIN] is performed by the formula of Expression 1 for each Cin, and the value of the Cin is set to each Ci.
This is performed by adding n gradation offset amounts.

[Equation 1] PT TRC [CIN] = (each Cin) + gradation offset amount [each CIN] For example, when the gradation offset amount of Cin 15% (38/255 level) is +3, PT TRC [15] = 3
8 + 3 = 41 levels.

Next, PTs of adjacent Cins Gradation correction data P of 0 to 255 from TRC data LUT (0-2
55) is calculated by first-order approximation (step S15). The straight line connecting each point is obtained by the equation (2). The linear expression passing through two points (x1, y1) / (x2, y2) is

[Formula 2] P LUT (0-255) = (y2-y1) /
(X2-x1) xX + (x2y1-x1y2) / (x2
-X1). Then, the gradation correction data P LUT (0 to 25
If 5) is 255 or more, it is set to 255, and if it is 0 or less, it is set to 0 (step S16).

From the above, the gradation correction data, that is, 0 to 2
Output 256 gradation P for 55 input 256 gradations LU
T (0 to 255) is obtained. The characteristics of the gradation correction data of 256 gradations are shown in FIG. This gradation correction data is transferred from the gradation correction data generation unit 24 to the gradation correction (2) circuit 23. As a result, the image data is corrected by the gradation correction data as described above to form an image.

Next, a method of creating a plurality of reference patches having four different densities for each color, which are necessary for the above-described gradation correction, will be described. As described above, the color image forming apparatus to which the present exemplary embodiment is applied includes the transfer drum that is a sheet conveying body, and is particularly used for removing the transfer drum from the photoconductor and for cleaning the reference patch toner. Since no device such as a film cleaning device and its toner collecting device is provided, as shown in FIG. 7, a portion on the photosensitive member where a reference patch can be formed is a position where the transfer drum does not come into contact with the photosensitive member.
That is, it is only the position corresponding to the tie bar of the transfer drum.

FIG. 8 is an enlarged view of the tie bar portion of the transfer drum. In the figure, the portion where the substantial reference patch can be formed, that is, the portion that does not contact the photoconductor is the film cutout portion of the portion where the films on the tie bar are stacked and attached,
If the notch is made large, the films cannot be stacked and evenly mounted, and therefore, the length in which the reference patch can be created is 20 mm in the image forming apparatus to which the present embodiment is applied.
On the other hand, the measurement area of the optical sensor 48 for measuring the density of the developed reference patch has a diameter of 3.0 mm, and a stable measurement result can be obtained in consideration of variations in sensor mounting, patch edge unevenness, patch unevenness, and the like. In order to obtain it, it is necessary to measure and average at least twice, and the length of one reference patch needs to be at least 10 mm.

Therefore, it is not possible to simultaneously create reference patches of four different densities for each color, which are necessary for gradation correction. Therefore, in the present embodiment, first, as shown in FIG. 9, four patches each having an image area of each color of 15%, 20%, 30%, and 50% are set to a set of 15% and 50%, and a set of 20%.
And 30% of the two groups. Then, as shown in FIG. 10, a set of reference patches of 15% and 50% at the beginning of each color is created on the photoconductor at the position corresponding to the tie bar. Next, 20% and 30% sets of reference patches are formed on the photoconductor at positions corresponding to tie bars. Then, for each image area patch, as shown in FIG. 9, the results obtained by measuring twice with the optical sensor (measurement diameter is 3 mm, for example) are averaged, and the gradation correction described above is performed.

In this way, by grouping a plurality of required reference patches into a predetermined number of sets and sequentially creating the reference patches for each set at positions where the reference patch can be created on the photoconductor in synchronism with the rotation of the photoconductor. , A predetermined number of reference patches can be created in a limited area. Further, as in the present embodiment, when one set of reference patches is composed of a plurality of patches having different densities, the patches on the front side have a large amount of toner by arranging so as to be formed in order from the patch image with the lowest density. The development unevenness at the density boundary portion due to development is reduced, the area inside the patch where stable density is obtained is widened, and the length of the reference patch can be reduced.

Next, a second embodiment of the present invention will be described. In the second embodiment, a set of 15% and 50%,
It has two modes: an operation mode in which two sets of reference patches are grouped into two sets of 20% and 30%, and an operation mode in which only one of the two sets is created. Then, in the gradation correction mode performed immediately after the image forming apparatus is powered on (ON) or the gradation correction mode by a serviceman,
Since there is a possibility that the gradation of the image forming apparatus is greatly changed, both the group of 15% and 50% and the group of 20% and 30% are created in the same manner as in the first embodiment. The first gradation correction mode for gradation correction is set.

On the other hand, in the second gradation correction mode, which is performed periodically (every 30 minutes in this embodiment) during copying, only the reference patches of 15% and 50% are created.
Then, from the measured densities of 15% and 50%, the densities of 20% and 30% that are not created in the second gradation correction mode are calculated. Hereinafter, a method of obtaining the 20% and 30% concentrations will be described. FIG. 11 shows the relationship between the reference patch of each image area ratio density on the photoconductor and the density of the reference patch. This relationship is different in the transfer and fixing states between the image forming apparatuses, or the optical sensor itself or the mounting variation thereof, and the absolute value relationship is not constant. But,
Regarding the shape of the curve, the difference between the image forming apparatuses is small at the density before the output is saturated when the image area ratio is 75% or more.

Therefore, in the second embodiment, the shape data of this curve is stored in the image forming condition control unit 41 of FIG. 2, and as shown in FIG.
Density is obtained from the curve shape data stored in the image forming condition control section 41, and 50% to 30% density is obtained from the curve shape data stored in the image forming condition control section 41. Of course, measured 15% and 50%
20% and 30% by using the shape data of the curve stored in the image forming condition control unit 41 from the difference between both values of the density of
You may make it calculate | require the density | concentration of%.

A procedure for creating tone correction data using a plurality of reference patch densities on the photoconductor created / measured in the second tone correction mode will be described with reference to the flowchart of FIG. First, for each color, create a patch of Cin15% and 50% density pairs,
The patch density is measured (step S21). Next, Ci
n patch densities of 20% and 30% are calculated with the coefficients A and B stored in the image forming condition control unit 41 in step S2.
It is calculated from the Cin 15% and 50% patch density measured in 1 (step S22). Here, Cin 20% patch (calculation) density = Cin 15% (measurement) density * A, Cin
30% patch (calculated) density = Cin 50% (measured) density * B.

Then, the measured or calculated Cin15,
Difference between 20%, 30%, 50% patch density and target density of each Cin, Radc delta (CIN) is calculated (step S23). After that, the same processing as the processing of steps S12 to S16 in the flowchart of FIG. 4 is executed. That is, according to the table (see FIG. 5) stored in the gradation correction data generation unit 24, Radc delta
(CIN) to the table No. of each Cin. Is determined (step S24), and this table No. According to this, the gradation offset amount of each Cin (15, 20, 30, 50, 100%) is obtained for each of the photo mode / character mode (step S25).

Next, the correction amount P at each Cin point
T TRC [CIN] is calculated by the equation (1) (step S26). Next, the PT of the adjacent Cin TR
0 to 255 gradation correction data P from C data LUT
(0 to 255) is calculated by first-order approximation (step S2
7). The straight line connecting each point is obtained by the equation (2). Then, the gradation correction data P LUT (0 to
If 255) is 255 or more, it is set to 255, and if it is 0 or less, it is set to 0 (step S28).

As described above, in the second embodiment, all the grouped reference patches are not created, but the measurement results of the reference patches of one group are stored in the image forming condition control unit 41. Since the reference patch results of other groups not created are calculated and obtained from the reference patch of each image area ratio density and the relationship curve of the reference patch densities, the time required for patch creation can be shortened.
At this time, as in the case where the groups of 15% and 50% are always created in the present embodiment, a set having the maximum or minimum density in all the required reference patches is created as a set of reference patches that are always created. Then, when the result of the patch not created from the created patch is calculated, interpolation calculation can be performed by measuring the end of the fluctuation of the image forming apparatus that is most likely to change, so that the accuracy can be improved.

[0036]

As described above, according to the present invention,
Group the required multiple reference patches into a predetermined number of sets,
By forming each group in the non-image area of the photoconductor in synchronization with the rotation of the photoconductor, it is possible to create a desired number of reference patches in a limited area.
Even in the case where the location or timing at which the reference patch can be created is limited, a plurality of reference patches developed on the photoconductor can be created.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a color copying machine to which the present invention is applied.

FIG. 2 is a configuration diagram showing a first embodiment of the present invention.

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

FIG. 4 is a flowchart of tone correction data creation using a plurality of reference patch densities on a photoconductor created / measured in the first embodiment.

FIG. 5 Radc It is a figure which shows the table data of the relationship of delta and a gradation offset amount.

FIG. 6 is a characteristic diagram of gradation correction data of 256 gradations.

FIG. 7 is a diagram showing a relationship between a patch creatable position and a tie bar portion.

FIG. 8 is an enlarged view of a tie bar portion of a transfer drum.

FIG. 9 is a diagram showing reference patches grouped into two sets.

FIG. 10 is a diagram showing a corresponding position of a reference patch on a transfer drum.

FIG. 11 is a diagram showing a relationship between a reference patch on a photoconductor and the density of the reference patch.

FIG. 12 is a flowchart of gradation correction data creation using a plurality of reference patch densities on a photoconductor created / measured in a second gradation correction mode of the second embodiment.

[Explanation of symbols]

1 Scanner Section 2 Image Processing Section 3 ROS Optical Section 4 Image Forming Section 22 Gradation Correction (1) Circuit 23 Gradation Correction (2) Circuit 25 Gradation Correction Data Generation Section 29 Patch Creation Section 41 Image Forming Condition Control Section 48 Light sensor

Claims (6)

[Claims] 1. An image forming unit for forming an image according to image information given on a rotating photosensitive member, and transferring the formed image on a transfer medium; and reference patch image information for the image forming unit. A patch image forming means for forming a plurality of patch images each having a different density and grouped in a predetermined number of groups in advance in each group in a non-image portion of the photoconductor in synchronization with rotation of the photoconductor; A patch density detecting unit that detects the density of a patch image formed on the photoconductor or the transfer medium; and an image forming condition of the image forming unit based on the density detected by the patch density detecting unit. And an image forming condition control means for controlling the image forming condition. 2. The image forming condition control means compares the density detected by the patch density detecting means with a preset target value, and controls the image forming condition of the image forming means based on the comparison result. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises: 3. The image forming apparatus according to claim 1, wherein a plurality of patch images forming each group are arranged so as to be formed in order from a patch image having a low density. 4. The image forming means includes a rotary drum having a tie bar, which holds a transfer sheet and rotates in synchronism with the rotation of the photoconductor. The patch image forming means includes a tie bar of the transfer drum. The image forming apparatus according to claim 1, wherein a color patch image is formed on a non-image portion of the corresponding photoconductor. 5. A first operation mode in which patch images of a first predetermined number of groups are formed and image forming conditions are controlled based on the detected densities, and a second operation mode which is smaller than the first predetermined number. The image forming apparatus according to claim 1, further comprising a second operation mode in which a predetermined number of groups of patch images are formed and image forming conditions are controlled based on the detected densities. 6. The image forming apparatus according to claim 3, wherein the patch images of the second predetermined number of groups include a patch image having a maximum or minimum density in the plurality of patch images.