JP4335764B2 - Image forming apparatus and program for image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a digital composite apparatus, etc., and a program for the image forming apparatus, and in particular, measures the density of a density correction patch formed on an image carrier with a density measuring sensor. The present invention relates to an image forming apparatus that corrects image forming conditions related to image density based on the measured density.

  The configuration of an image forming apparatus to which the present invention can be applied will be described using a digital color copying machine (4-cycle color laser printing system) as an example. However, the image forming apparatus of the present invention is not limited to the four-cycle color laser printing method, and can also be applied to a printing method such as a tandem color laser printing method, a monochrome laser printing method, and an ink jet printing method.

FIG. 8 is an explanatory diagram showing the configuration of a digital color copying machine (4-cycle color laser printing system).
As shown in this figure, the digital color copying machine includes a scanner unit 10, a print unit 20, a recording medium transport unit 30, and a control unit (not shown) that controls these operations. Yes.

  The scanner unit 10 includes a contact glass 11 on which a document to be copied is placed, first and second optical system traveling bodies 12 and 13 that travel along the lower surface thereof, and these optical system traveling bodies 12 and 13. And an imaging element 15 such as a CCD that receives the reflected light of the original and converts it into an electrical signal via the condenser lens 14.

  The first optical system traveling body 12 is provided with an exposure lamp 16 that exposes and scans the document, and a first mirror 17 that reflects reflected light from the document toward the second optical system traveling body 13, and the second optical system. The traveling body 13 is provided with a second mirror 18 and a third mirror 19 that reflect the reflected light from the first optical system traveling body 12 toward the condenser lens 14.

  The first optical system traveling body 12 and the second optical system traveling body 13 are traveled by a stepping motor (not shown). The first optical system traveling body 12 is normally in the standby position shown in FIG. 8 and moves in the direction indicated by the arrow F in FIG. 8 during exposure scanning, and the moving direction is switched at a return position determined according to the document size. , Move in the direction of arrow R and return to the standby position. The second optical system traveling body 13 is moved by a distance 1/2 that of the first optical system traveling body 12 at a speed that is 1/2 that of the first optical system traveling body 12.

  The print unit 20 includes a photosensitive drum 21. The photosensitive drum 21 is rotationally driven in the direction of the arrow in FIG. 8 by a main motor (not shown). Around the photosensitive drum 21, in order of the rotation direction, a charger 22 for charging the photosensitive layer of the photosensitive drum 21, a laser unit 23 for forming an electrostatic latent image on the photosensitive layer, and an electrostatic latent image Developing device 24 (C, M, Y, K) for each color (C: cyan, M: magenta, Y: yellow, K: black) and a toner image formed on the photosensitive layer. An intermediate transfer belt (intermediate transfer member) 25 to which toner is transferred and a photosensitive member cleaner 26 for removing residual toner on the photosensitive drum 21 are disposed.

  The intermediate transfer belt 25 is rotationally driven in the direction of the arrow in FIG. 8 by a main motor (not shown). Around the intermediate transfer belt 25, a density measurement sensor 27 (for example, a reflection type optical sensor) that measures the density of the toner image transferred to the intermediate transfer belt 25 and a toner image transferred to the intermediate transfer belt 25 are recorded. A transfer roller 28 for transferring to the medium and a transfer belt cleaner 29 for removing residual toner on the intermediate transfer belt 25 are disposed.

  The recording medium transport unit 30 includes a paper feeding roller 32 that feeds the recording medium in the paper feeding cassette 31, and a registration roller 33 that feeds the recording medium sent by the paper feeding roller 32 to the intermediate transfer belt 25 at a predetermined timing. A conveying belt 35 that sends the recording medium after the toner image is transferred to the fixing roller 34; and a discharge roller 37 that sends the recording medium after the toner image is fixed by the fixing roller 34 to the discharge tray 36. Yes.

  In the four-cycle color laser printing type digital color copying machine configured as described above, four color toner images are formed in four cycles using one photosensitive drum 21 when performing color copying. The toner images of the respective colors are sequentially transferred to the intermediate transfer belt 25, and then transferred collectively from the intermediate transfer belt 25 to the recording medium.

Normally, in this type of digital color copying machine, image density correction is performed in order to stabilize gradation reproducibility (see, for example, Patent Document 1).
A conventional image density correction procedure will be described below.

(1) After the photosensitive layer of the photosensitive drum 21 is charged by the charger 22, the laser unit 23 is driven based on the predetermined density correction patch data, and the density correction patch is placed on the photosensitive drum 21. The electrostatic latent image is formed.
(2) The electrostatic latent image formed on the photosensitive drum 21 is visualized as a toner image using the developing device 24 of the corresponding color.
(3) The toner image of the density correction patch is transferred to the intermediate transfer belt 25 by a predetermined transfer voltage.
(4) The above processing is repeated for each color developing device 24 (C, M, Y, K), and density correction patches for each color are formed on the intermediate transfer belt 25.
(5) The density measurement sensor 27 measures the density of the density correction patch formed on the intermediate transfer belt 25.
(6) The image forming conditions related to the image density are corrected based on the measured density. Examples of the image forming condition relating to the image density include the exposure intensity of the laser unit 23 and the developing bias of the developing device 24.
JP 2003-186278 A

  9A to 9D are explanatory views showing patch formation patterns according to a conventional example. In FIG. 9, the density measurement sensor is depicted as scanning each density correction patch from top to bottom. The density correction patches for each color are arranged in the order C, M, Y, K from the top, but this order is arbitrary.

  9A to 9D, four color correction patches PC, PM, PY, and PK are formed so as to be aligned in the scanning direction of the density measurement sensor. The density correction patches PC, PM, PY, and PK for each color include a plurality of patches Pa to Ph having different color values (density), and the measured values of the density measuring sensor are the patches Pa to Ph. It is sampled with a period narrower than the width.

  The density correction patches PC, PM, PY, and PK shown in FIG. 9A are drawn in order from patches Pa to Ph having the smallest color value. When the density correction patches PC, PM, PY, and PK are configured in this way, since the change in the measured density at the patch head position is small, it is difficult to recognize the patch head position based on the measurement value of the density measurement sensor. Become.

  There is also a method of generating a measurement timing signal based on the formation timing of the density correction patches PC, PM, PY, and PK and starting sampling of the density measurement value in accordance with this signal. Due to slippage of the transfer belt or the like, there is a possibility that a large deviation occurs in the sampling start position.

  The density correction patches PC, PM, PY and PK shown in FIG. 9B are drawn in order from the patches Pa to Ph having the largest color values. When the density correction patches PC, PM, PY, and PK are configured in this way, the change in the measured density at the patch head position becomes large. Therefore, the patch head position can be recognized based on the measurement value change of the density measurement sensor. It becomes possible.

For example, preliminary sampling (sampling for patch position detection) is started from a position sufficiently before the head position of the density correction patches PC, PM, PY, and PK, and the main sampling (density) Sampling for measurement) can be started.
However, this method has a restriction that a patch having a large color value must always be placed at the head of the density correction patches PC, PM, PY, and PK.

  Therefore, as shown in FIGS. 9C and 9D, a trigger patch is formed at a predetermined interval in the vicinity of the head position of the patch row composed of the density correction patches PC, PM, PY, and PK. Proposed to do. When such a trigger patch is formed, the head position of the patch row is recognized with high accuracy regardless of the color value arrangement order in the density correction patches PC, PM, PY, and PK, and the main sampling is started with good timing. Can do.

  However, in the above method, even if the main sampling is started in a timely manner, a slight deviation is accumulated near the rear end of the patch row, and there is a large error in the sampling position and the number of samples in each patch Pa to Ph. As a result, there is a possibility of making an error in the aggregation processing and the representative value calculation based on each sampling measurement data.

  It should be noted that the sampling timing that should have been synchronized once deviates slightly toward the rear end because the image carrier is not moving at a uniform speed due to uneven rotation or slippage. This is because the total circumference of the carrier is not necessarily an integral multiple of the sampling clock, and there are subtle individual differences in the total circumference of the image carrier and the sampling clock.

  The present invention has been considered in view of the above circumstances, and when measuring the density of the density correction patch, by resetting the sampling clock a plurality of times, the accumulated error of the sampling position is suppressed, and the density of the density correction patch is reduced. An object of the present invention is to provide an image forming apparatus and a program for the image forming apparatus that can accurately measure the image quality.

  In order to achieve the above object, the image forming apparatus of the present invention measures the density of the density correction patch formed on the image carrier with the density measuring sensor, and based on the measured density, the image forming condition relating to the image density A patch forming unit that forms a plurality of the density correction patches on the carrier at predetermined intervals in the scanning direction of the density measurement sensor, and the density measurement sensor Are measured using a sampling clock of a predetermined cycle, and density measuring means for extracting or calculating a representative value from a plurality of sampled measurement values, and based on the representative value, image forming conditions relating to image density are determined. Density correction means for correcting, wherein the patch forming means forms a plurality of trigger patches in a patch row composed of a plurality of density correction patches, and the density Constant means detects a patch for the trigger, it is constituted for resetting said sampling clock for each detection of the patch.

  According to this configuration, when measuring the density of the density correction patch, the sampling clock is reset a plurality of times based on the trigger patches formed in the patch row, thereby suppressing the accumulated error of the sampling position, The density of the density correction patch can be accurately measured. Thereby, the accuracy of image density correction is improved, and good gradation reproducibility is obtained.

In the image forming apparatus of the present invention, the trigger patch is formed in the vicinity of the head position of each density correction patch with a predetermined interval.
With this configuration, the formation position of each density correction patch and the sampling position can be synchronized with higher accuracy.

In the image forming apparatus of the present invention, the image carrier is a photosensitive drum, an intermediate transfer member, or a recording medium.
With this configuration, it is possible to measure the patch density on the photosensitive drum, the intermediate transfer member, or the recording medium with high accuracy and improve the accuracy of image density correction.

The image forming apparatus program according to the present invention measures the density of the density correction patch formed on the image carrier with a density measuring sensor and corrects the image forming condition related to the image density based on the measured density. A program for an image forming apparatus, wherein a plurality of the density correction patches are formed on the carrier when a plurality of the density correction patches are formed at predetermined intervals in the scanning direction of the density measurement sensor. A plurality of trigger patches are formed in a patch array composed of patches for sampling, and the measurement values of the concentration measurement sensor are sampled using a sampling clock of a predetermined period, and representative values are extracted from the sampled measurement values or When calculating, the trigger patch is detected and the sampling clock is reset every time the patch is detected, based on the representative value. It is constituted to correct the image forming conditions according to the image density.
With this configuration, the existing image forming apparatus can be operated as the image forming apparatus of the present invention by changing the program.

  As described above, according to the present invention, a plurality of trigger patches are formed in a patch row composed of a plurality of density correction patches, and the sampling clock is reset each time the patch is detected, thereby changing the sampling position. Accumulated errors can be suppressed. As a result, it is possible to accurately measure the density of the density correction patch and correct the image density appropriately.

Embodiments of the present invention will be described below with reference to the drawings.
A configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.

  However, although the image processing apparatus shown in FIG. 1 shows the configuration of a copying machine as a specific example, the image forming apparatus according to the present embodiment is not limited to a copying machine. For example, a printer, a facsimile, a digital composite Device (multifunction peripheral (MFP)) and the like.

  Further, as a printing method of the image forming apparatus according to the present invention, a color laser printing method (including a 4-cycle method and a tandem method), a monochrome laser printing method, an ink jet printing method, a sublimation type thermal transfer printing method, a melt type thermal transfer printing. Method, dot impact printing method, and the like.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a scanner unit 10, a print unit 20, a recording medium transport unit 30, a storage unit 40, and a control unit 50. Yes. For the scanner unit 10, the print unit 20, and the recording medium transport unit 30, the same configuration as that of the image forming apparatus illustrated in FIG. 8 is applied, and the reference numerals and descriptions in FIG. 8 are used.

  The storage unit 40 stores programs and data. The data stored in the storage unit 40 includes image data read by the scanner unit 10 and various image forming condition data related to printing of the image data. Further, the image forming condition data includes parameters relating to image density such as the exposure intensity of the laser unit 23 and the developing bias of the developing device 24, and these parameters are the correction targets of the image density correction process described later. Become.

The control unit 50 includes at least a patch forming unit 51, a density measuring unit 52, and a density correcting unit 53 as a functional configuration realized by a program.
The patch forming unit 51 charges the photosensitive layer of the photosensitive drum 21 with the charger 22, and then drives the laser unit 23 based on the predetermined patch data to electrostatically charge the patch on the photosensitive drum 21. A latent image is formed. The electrostatic latent image formed on the photosensitive drum 21 is visualized as a toner image using the developing device 24 of the corresponding color, and then transferred to the intermediate transfer belt 25 by a predetermined transfer voltage. The The patches formed by the patch forming unit 51 include a density correction patch and a trigger patch, and the position of the density correction patch is specified based on detection of the trigger patch.

  The density measuring means 52 samples the measurement value of the density measuring sensor 27 using a sampling clock having a predetermined period. This sampling includes preliminary sampling for detecting the trigger patch and main sampling for detecting the density of the density correction patch, and the sampling clock is reset when the trigger patch is detected.

The density correction unit 53 corrects parameters related to image density, such as the exposure intensity of the laser unit 23 and the development bias of the developing device 24, based on the measured patch density.
Hereinafter, a procedure of image density correction processing using the patch forming unit 51, the density measuring unit 52, and the density correcting unit 53 will be described.

FIG. 2 is a flowchart showing a procedure of image density correction processing according to the embodiment of the present invention.
As shown in this figure, in the image density correction process, first, the head color (for example, cyan) is set in the patch color variable (S101), and then the patch formation process (S102: patch formation means 51) is executed. In the patch forming process, a patch image including a plurality of types of densities (color values) is formed on the photosensitive drum 21 by using the color developing device 24 set in the patch color variable, and this patch image is intermediately transferred. Transfer to the belt 25.

  When the patch forming process is completed, the next color is set in the patch color variable (S103), and the patch forming process (S102) is executed again. When patch formation processing is completed for all colors (S104), density measurement processing (S105: density measurement means 52) and density correction processing (S106: density correction means 53) are executed, and image density correction processing ends. .

FIG. 3 is an explanatory diagram showing a patch formation pattern according to the embodiment of the present invention.
As shown in this figure, in this embodiment, four color density correction patches PC, PM, PY, and PK are formed at predetermined intervals in the scanning direction of the density measurement sensor 27. The density correction patches PC, PM, PY and PK for each color include a plurality of patches Pa to Ph having different color values (density). Further, a plurality of trigger patches TP are formed in a patch row composed of density correction patches PC, PM, PY, and PK. In the example shown in FIG. 3, trigger patches TP are formed at predetermined intervals in the vicinity of the head positions of the respective density correction patches PC, PM, PY, and PK.

  In this way, the sampling clock can be reset at the head position of each density correction patch PC, PM, PY, PK, and the accumulated error at the sampling position can be refreshed. In the present invention, since at least two trigger patches TP are arranged in the patch row, a conventional patch formation pattern in which one trigger patch TP is arranged near the head of the patch row ((c), (c) in FIG. Compared to d), it is possible to suppress the accumulated error at the sampling position and measure the densities of the density correction patches PC, PM, PY, and PK with high accuracy.

  In FIG. 3, the trigger patches TR are arranged in the vicinity of the head positions of the density correction patches PC, PM, PY, and PK. The number of trigger patches TR is the density correction patches PC, PM, and PY. , Less than the number of PKs. For example, in FIG. 3, the trigger patch TR corresponding to the magenta and black density correction patches PM and PK is omitted, or the trigger patch TR corresponding to the magenta and yellow density correction patches PM and PY is omitted. be able to. When the middle trigger patch TP is omitted, the density correction patches PC, PM, PY, and PK may be left blank, or blanks may be filled.

For the trigger patch TP, it is preferable to select a color value for which a sufficient signal change can be expected. For example, the trigger patch TP may be configured so that the density measurement value changes from the background surface of the image carrier (corresponding to a color value of 0%) to a color value of 100% (solid).
When the trigger patch TP is configured in this way, in the sampling at the front and rear positions of the trigger patch TP, the measurement value of the background level of the image carrier is repeated several times, and then the measurement value of the trigger patch level is several times. After that, the measurement value of the background level of the image carrier is repeated several times. The trigger patch TR can be detected by utilizing the fact that such a change in the measured value does not occur in any place other than the trigger patch TR.

  Specifically, the difference between a plurality of adjacent sampling data is calculated sequentially, the concentration change amount per unit time is calculated, and this is set as a threshold value for the concentration change amount per unit time defined in advance by experiments. By comparing, it is possible to detect a location where the amount of change in density per unit time is equal to or higher than a specified level. When this position is detected, a reset signal is generated and the sampling clock is reset.

Each density correction patch PC, PM, PY, PK is designed to be drawn at a predetermined interval from the trigger patch TP, and is drawn on the image carrier by a command to that effect, so the trigger patch By resetting the sampling timing triggered by the detection of TP, the accumulated error at the sampling position is cleared a plurality of times.
To reset the sampling clock, for example, an FF (flip-flop) circuit is inserted in the previous stage of the sampling signal input circuit, and a reset signal may be input when the trigger patch TP is detected.

  Since the density measurement sensor 27 normally has a relatively wide sensor field of view, a signal sampled in a state of straddling the boundary between adjacent patches has a low data reliability and is often handled as an unnecessary signal. However, since it is difficult to measure the sampling timing so as not to straddle adjacent patches, normally, after sampling at a constant period, signals at necessary places are extracted (or signals at unnecessary places are excluded).

By the way, when the density correction patches PC, PM, PY, and PK formed as shown in FIGS. 3 and 9 are sampled at a constant cycle with good timing, the sensor field of view is the boundary portion in any of the patches Pa to Ph. The number of sampling across the same is the same, and the number of sampling without straddling is the same. Therefore, when continuous sampling is performed at regular intervals, if M is the number of consecutive data to be excluded and N is the number of continuous data to be extracted, theoretically, M pieces of sampling data are continuously collected. After the excluded data, N extracted data are arranged, then M excluded data are arranged again, and then N extracted data are arranged again.
In the following representative value calculation processing, unnecessary data is eliminated or necessary data is extracted based on this rule, and the representative values of the patches Pa to Ph are calculated.

[Comparative Example 1]
4A to 4C are explanatory diagrams of Comparative Example 1, and FIG. 4A is an overall view showing an example of sensor output when the patch shown in FIG. 9D is continuously sampled. b) is an enlarged view of the first half part, and (c) is an enlarged view of the second half part.
However, in these drawings, a white point corresponds to a point corresponding to a patch boundary portion, that is, data to be excluded if sampling is performed normally. The black point corresponds to a point corresponding to a non-boundary part of the patch, that is, a point to be extracted.

The example of sensor output shown in FIG. 4 is that the sampling clock and the width of the patch are designed based on the sensor field diameter, the feed speed of the image carrier, the circumference of the image carrier, the type of patch to be measured, etc. The number of data to be extracted (black dots) corresponding to is six, and the number of data to be excluded (white dots) corresponding to the boundary is four.
In this sensor output example, the sampling timing is appropriate, and the data (white dots) to be excluded when the sensor field of view crotches at the patch boundary is located at the patch boundary and should be extracted. Data (black dots) are in the patch area.

When such a sensor output is obtained, it is possible to perform a representative value calculation process assuming that black dots and white dots are repeated in a predetermined number. Specifically, after removing the white dots, the sensor output representative values for the patches Pa to Ph may be calculated based on the black dot data.
For the calculation of the representative value, for example, a simple addition average, a simple geometric average, a median value, or the like can be used.

[Comparative Example 2]
(A)-(c) of FIG. 5 is explanatory drawing of the comparative example 2, (a) is a general view which shows the sensor output example at the time of continuously sampling the patch shown to (d) of FIG. b) is an enlarged view of the first half part, and (c) is an enlarged view of the second half part.

This sensor output example is a case where the patch shown in FIG. 9D is continuously sampled as in FIG. 4, but includes a slight deviation in the sampling timing. In such a case, there is no problem in the vicinity of the head of the patch row, but a subtle deviation is accumulated toward the vicinity of the rear end of the patch row. As a result, in the vicinity of the rear end of the patch row, the data (white dots) to be excluded when the sensor field of view extends over the patch boundary part is not necessarily located at the patch boundary part and is shifted to the patch part. Yes. Also. The data to be extracted (black dots) is not necessarily in the patch portion, but is shifted to the boundary portion of the patch.
In such a case, if processing is performed assuming that white dots and black dots are repeated as many times as a predetermined design, the density of the patch portion cannot be calculated correctly, and the accuracy of density correction decreases.

[Example 1]
6A to 6C are explanatory diagrams of the first embodiment. FIG. 6A is an overall view showing an example of sensor output when the patch shown in FIG. 3 is continuously sampled. FIG. An enlarged view of the first half part, (c) is an enlarged view of the second half part.

This sensor output example relates to the present invention, and when the patch shown in FIG. 3 is continuously sampled, the trigger patch is detected and the sampling clock is reset every time the patch is detected.
In this way, even if there is some deviation between the drawing position of the patch and the sampling timing, accumulation of deviation is suppressed, and appropriate sampling can be performed. Specifically, since the white and black dots are in their original positions from the beginning to the end of the patch row, the sampling data at the boundary of the patch and the sampling data at the non-boundary can be accurately obtained even with relatively simple processing. Can be separated.

[Comparative Example 3]
(A)-(c) of Drawing 7 is an explanatory view of comparative example 3, (a) is a whole figure showing an example of sensor output at the time of carrying out continuous sampling of the patch shown in Drawing 3, (b) An enlarged view of the first half part, (c) is an enlarged view of the second half part.

  Similar to FIG. 6, this sensor output example is obtained when the patch shown in FIG. 3 is continuously sampled, but the sampling clock is not reset by the trigger patch. As a result, it can be seen that the sampling position deviation is accumulated toward the rear end of the patch row, and the positions of the white point and the black point are disturbed.

[Program for image forming apparatus]
Next, an image forming apparatus program will be described.
The density measurement / density correction function of the computer (image forming apparatus) in the above-described embodiment is realized by an image forming apparatus program stored in a storage unit (for example, ROM).

The program for the image forming apparatus is read by the computer, and sends instructions to each component of the computer to perform predetermined processing, for example, patch forming processing of the patch forming means, density measuring processing of the density measuring means, and density of the density correcting means. Perform correction processing.
As a result, the density measurement / density correction function is realized by the cooperation of the image forming apparatus program that is software and each component means of the computer (control means) that is hardware resources.

The program for the image forming apparatus for realizing the density measurement / density correction function is stored in a ROM or hard disk of a computer, or a computer-readable recording medium such as an external storage device or a portable recording medium. Can be stored.
The external storage device refers to a memory expansion device that incorporates a storage medium such as a CD-ROM and is externally connected to the image forming apparatus. On the other hand, the portable recording medium is a recording medium that can be mounted on a recording medium driving device (drive device) and is portable, and refers to, for example, a flexible disk, a memory card, a magneto-optical disk, and the like.
The program recorded on the recording medium is loaded into a RAM of a computer and executed by a CPU (control means / control unit). By this execution, the function of the image forming apparatus of the present embodiment described above is realized.

Needless to say, the present invention is not limited to the embodiment. For example, the image carrier is not limited to an intermediate transfer belt, but includes an intermediate transfer roller, a photosensitive drum, a recording medium, and the like.
Further, the shape, number, interval, and the like of the density correction patch can be arbitrarily changed.

Needless to say, the present invention is not limited to the embodiment. For example, the image carrier is not limited to an intermediate transfer belt, but includes an intermediate transfer roller, a photosensitive drum, a recording medium, and the like.
Further, the shape, number, interval, and the like of the density correction patch can be arbitrarily changed.

  The present invention is applied to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a digital composite apparatus. In particular, it is suitable for an image forming apparatus that measures the density of a density correction patch formed on an image carrier with a density measuring sensor and corrects image forming conditions related to the image density based on the measured density.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a flowchart which shows the procedure of the image density correction process which concerns on embodiment of this invention. It is explanatory drawing which shows the patch formation pattern which concerns on embodiment of this invention. (A)-(c) is explanatory drawing of the comparative example 1. FIG. (A)-(c) is explanatory drawing of the comparative example 2. FIG. (A)-(c) is explanatory drawing of Example 1. FIG. (A)-(c) is explanatory drawing of the comparative example 3. FIG. It is explanatory drawing which shows the structure of a digital color copying machine (4 cycle color laser printing system). (A)-(d) is explanatory drawing which shows the patch formation pattern which concerns on a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Scanner part 20 Print part 21 Photoconductor drum 22 Charger 23 Laser unit 24 Developing device 25 Intermediate transfer belt 26 Photoconductor cleaner 27 Density measurement sensor 28 Transfer roller 29 Transfer belt cleaner 30 Recording medium conveyance part 40 Storage part 50 Control Unit 51 Patch Formation Unit 52 Density Measurement Unit 53 Density Correction Unit PC, PM, CY, CK Density Correction Patch TP Trigger Patch

Claims (3)

An image forming apparatus that measures the density of a plurality of density correction patches provided for each color formed on an image carrier with a density measurement sensor, and corrects image forming conditions related to the image density based on the measured density Because
Patch forming means for forming the density correction patch for each color at a predetermined interval in the scanning direction of the density measurement sensor on the image carrier;
The density measurement means for sampling the measurement value of the density measurement sensor using a sampling clock having a predetermined cycle for each color, and extracting or calculating a representative value for each color from a plurality of measurement values sampled for each color;
A density correction unit that corrects the image forming condition relating to the image density for each color based on the representative value for each color;
The patch forming unit forms a trigger patch in each of the patch arrays corresponding to at least two colors in the patch array including the density correction patches for each color, and corresponds to each trigger patch. In the vicinity of the head position of the density correction patch, with a predetermined interval ,
The image forming apparatus, wherein the density measuring unit detects the trigger patch and resets the sampling clock every time the patch is detected. The image bearing member is a photosensitive drum, an image forming apparatus according to claim 1, characterized in that an intermediate transfer member or a recording medium. For an image forming apparatus that measures a density of a plurality of density correction patches provided for each color formed on an image carrier with a density measurement sensor and corrects an image forming condition related to the image density based on the measured density The program of
When the density correction patch is formed for each color at a predetermined interval in the scanning direction of the density measurement sensor on the image carrier, a patch in the patch row composed of the density correction patches for each color is formed . In addition, each trigger patch is formed in a patch row corresponding to at least two colors, and each trigger patch is formed at a predetermined interval in the vicinity of the head position of the corresponding density correction patch ,
When the measurement value of the density measurement sensor is sampled for each color using a sampling clock having a predetermined period, and the representative value for each color is extracted or calculated from a plurality of measurement values sampled for each color, the trigger patch And detecting the sampling clock every time the patch is detected,
An image forming apparatus program for correcting an image forming condition relating to an image density for each color based on the representative value for each color.