JPH07242028A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To sufficiently correct produced density irregularity even when minue image recording is performed by making the width of an ink jet nozzle used in recording by one scanning variable and obtaining the density correction data corresponding thereto to correct the density of a recording pattern. CONSTITUTION:A printer control part CPU 102 taking charge of the control operation of a printer part 20, a reader control part CPU 104 taking charge of reading control operation, a main image processing part 106 processing image display operation and an operation part 108 due to an operator are connected to a main CPU 100. The printer control part CPU 102 and the reader control part CPU 104 perform the operation control of a printer 20 and a reader part and are set to the relation of a master and a slave with respect to the master CPU 100. The main image processing part 106 performs image processing such as masking, black extraction, quaternization or r-correction. A synchronous memory 110 is connected to the printer control part CPU 102 and the main image processing part 106 and the output thereof is connected to a recording head 56.

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 for forming an image by scanning a recording head having a predetermined width in the sub-scanning direction, and more particularly to density correction of the recorded image.

[0002]

2. Description of the Related Art In a conventional image forming apparatus for scanning a recording head to record on a recording medium such as recording paper, a plurality of recording elements (heat generation) are formed in a sub-scanning direction orthogonal to the main scanning direction of the recording head. Elements, ink jet nozzles, etc.) and scans the print head in the main scanning direction to record an image for one band (width printed by one scan of the print head in the main scanning direction). There is.

Generally, a printhead of this type has a large number of print elements, and if the entire image area can be printed by one scan, the throughput of image formation is increased, but on the other hand, such a printhead is not manufactured. Difficult and disadvantageous in terms of product yield and manufacturing cost. Therefore, in general, an image is formed by repeating the operation of scanning the recording head of a predetermined width in the main scanning direction and then moving the recording head or the recording paper by one band in the sub scanning direction. FIG. 20 shows this recording operation. Reference numeral 300 denotes a recording medium such as recording paper, and 301 denotes a recording head.

Further, when such a recording head 301 is used to record the density of the image recorded by all the recording elements of the recording head as the same density, the actually recorded image does not have a uniform density, Density unevenness occurs. For example,
When the recording head 301 is an inkjet head,
As shown in FIG. 21 as an example, even when an attempt is made to print a uniform pattern with an image density of 50%, density unevenness occurs depending on the nozzle position of the print head 301.

As a means for correcting such density unevenness, a technique called head shading has been proposed. This is to detect the density unevenness when printing is performed by driving all print elements of the print head based on the image data of the same density, and adjust the density of the image data output to each nozzle according to the density unevenness. Is.

For example, as shown in the head width A of FIG.
At the nozzle position where the recorded density appears higher than the density of the image data, the density level of the image output to those nozzles is lowered in advance. On the other hand, on the contrary, as shown in B of the same figure, in the nozzle portion where the actual recording density is lower than the image signal, the level of the image data output to those nozzles is raised beforehand. By doing so, it is possible to suppress the print density unevenness of the print head to a considerably low level.

As a means for discriminating and correcting such recording density unevenness, the recorded image pattern is read by a scanner or the like provided in the recording device,
Auto head shading (AHS) that automatically determines and corrects the density unevenness in the device, and a manual head that determines the correction value by the user by visually observing the recorded image pattern and determining the density unevenness. There is shading (hereinafter referred to as MHS).

In any case, a density pattern of a predetermined density such as 50% as shown in FIG.
The data of one band in the center is read and corrected. In addition to the actual use for correction, the reason why the image for one band is additionally printed before and after is to perform density unevenness correction including the influence of the connecting portion between the bands.

[0009]

However, the image forming apparatus as described above has the following problems. That is, FIG. 23A shows an example of reading and recording a non-scaled image by the above-mentioned image forming apparatus.
An image of 256 pixels is read by the reading head 302 having a width of 6 pixels, and an image having a width of 256 pixels is recorded by a recording head having 256 nozzles. Further, the scanning speeds of the read head 302 and the recording head 301 are the same.

However, when the read image is to be reduced in size and recorded, the following occurs. The reduction in the main scanning direction changes the scanning speeds of the read head 302 and the recording head 301, for example, at the time of 50% reduction, the read head is scanned at double speed to thin out images and perform read reduction processing.

As shown in FIG. 23B, the reduction in the sub-scanning direction is, for example, in the case of 50% reduction, the read head 30.
In step 2, an image having a width of 256 pixels is read, the image is thinned to 128 pixels, and then printing is performed using 128 nozzles of the head. The reading width of the image differs depending on the reduction ratio, but the result of thinning is controlled so that it is always 128 pixels.

As a concrete image forming sequence, as shown in FIG. 24 (a), an image is formed in the upper half of the head in the first scan, and then in the second scan as shown in FIG. 24 (b). An image is recorded using the lower half, and an image is formed by two scans.

[0013] Here, a 1-band image is formed by one scan for a normal-size image, whereas a reduced-band image is recorded (printed) in half by dividing the 1-band image into two scans. The problem that is different from the unevenness at the time of double image occurs. The possible causes are as follows. For example, in the case of a bubble jet type ink jet head, the ink jet nozzle is heated for each nozzle in order to eject ink. However, when recording is performed using the entire area of the nozzle, only half the area is used. Depending on the case, the heat distribution of the head changes, and this appears as a difference in density unevenness.

However, the conventional head shading corresponds to the case where one band is printed in one scan by using the print elements in the entire area of the print head, so that all the print elements of the print head are not used as described above. The correction of the density unevenness that occurs when an image is recorded in No. 2 cannot obtain a sufficient effect.

The present invention has been made in view of the above situation, and when recording is performed without using the recording elements in the entire area of the recording head, for example, when reducing recording, 1
It is an object of the present invention to provide density unevenness correction means that can deal with density unevenness that occurs when only half of the recording elements are used for scanning.

[0016]

Therefore, according to the present invention, in an image forming apparatus for forming an image by scanning a recording head having a predetermined width in the sub-scanning direction in the main scanning direction, a recording medium having a predetermined density is formed. An image pattern is recorded, and a correction unit for photoelectrically reading the recorded image to detect and correct density unevenness thereof is provided, and the width of the recording element used for recording in one scan is variable. It is intended to achieve the above-mentioned object by providing a correction means for performing density correction corresponding to each recording pattern by obtaining density correction data corresponding to each of them.

[0017]

According to the apparatus configuration of the present invention as described above,
For example, it is possible to deal with the density unevenness that occurs when only half of the entire area recording elements of the recording head are used in one scan such as reduction recording.

[0018]

The present invention will be described below based on a plurality of embodiments. FIG. 1 is an external perspective view of a digital color copying machine as a preferred embodiment according to the present invention.

The digital color copying machine 10 is mainly composed of two elements 12, 20 which are a first element and a second element. That is, the first large-scale element 12 is a color image scanner unit (hereinafter, referred to as a color image scanner unit) that reads a document image located above in color and outputs digital color image data.
It is abbreviated as "leader unit"). The reader unit 12 includes a controller unit 14 that performs various image processing of digital color image data and has a processing function such as an interface with an external device.

The second major element 20 is the reader unit 1.
A printer unit 20 located below the printer unit 2 for recording color digital image signals output from the controller unit 14 of the reader unit 12 on recording paper.

The reader unit 12 is an image of a document of various shapes and sizes such as a three-dimensional, sheet-shaped or large-sized sheet document placed downward on a document table (not shown) below the document pressing plate 16. It also has a built-in mechanism for reading information.

An operating portion 18 connected to the controller portion 14 is provided on one side of the upper surface of the reader portion 12. The operation unit 18 is for inputting various information and operation instructions for the copying machine.

Further, the controller unit 14 includes an operation unit 18
It is configured to give an operation instruction to the reader unit 12 or the printer unit 20 according to the information input via the. When it is necessary to perform complicated editing processing, a digitizer or the like is attached instead of the document holding plate 16.
This can be connected to the controller unit 14, which enables more advanced image processing.

On the other hand, in the printer section 20 of the present embodiment, a full color ink jet using a recording head of an ink bubble jet recording system as described in, for example, Japanese Patent Laid-Open No. 54-59936 is used. A printer is used.

The above-mentioned first and second major elements 12, 20
Are separable from each other, and can be installed at locations distant from each other by extending the connection cable.

Below, these major elements 12 and 20 will be explained in detail. 2 is a side sectional view schematically showing the internal structure of the digital color copying machine 10 shown in FIG.

(Reader Unit 12) First, the schematic configuration of the reader unit 12 of the copying machine 10 will be described. In the reader unit 12, an exposure lamp 22, a lens 24, and an image sensor 26 capable of reading a line image in full color.
The image of the original placed on the original glass 28, the projected image by the projector, or the image of the sheet-like original by the sheet feeding mechanism 30 is read by (the CCD sensor is adopted in this embodiment).

Next, various image processing is performed on the image information read by the reader unit 12 in this way by the reader unit 12 and the controller unit 14, and then the read and image-processed information is printed by the printer unit. 20 and is to be recorded on the recording paper here.

FIG. 3 shows a schematic mechanism of the reader unit 12, which is a view of the reader unit 12 viewed from above. Reference numeral 80 denotes a read head unit, which is the exposure lamp 2 in FIG.
2, a lens 24, an image sensor 26, a gain circuit, an offset circuit, and the like, and is mounted on the main scanning carriage rail 81 and moves in the main scanning direction.
This movement is performed by a main scanning motor and a drive belt (not shown). Both ends of the main scanning rail 82 are fixed to the sub scanning carriage, and the sub scanning carriage moves on the sub scanning carriage rail 83 in the sub scanning direction. This movement is performed by a sub-scanning motor and a drive belt (not shown).

(Printer Unit 20) Next, in the printer unit 20 shown in FIG. 2, the recording paper is a small-sized standard size (in the present embodiment, A4 to A3 size) cut paper, and a large paper feed cassette 32. Size (A2-A1 in this embodiment)
It is selectively supplied from the roll paper 34 for recording up to size.

Paper feed is started by a print start instruction from the controller unit 14, and is first conveyed to the position of the first paper feed roller 44 through the following path. In the present embodiment, it is also possible to perform manual paper feeding (paper feeding from outside the apparatus) by manually inserting the recording paper one by one from the manual feeding port 36 along the paper feeding unit cover 38. ing.

When the recording paper is fed from the paper feed cassette 32 installed in the printer unit 20, the cut paper from the paper feed cassette 32 is placed on the upper surface of the recording paper setting surface of the paper feed cassette 32. A pick-up roller 40 for picking up one by one is provided. Therefore, by driving the pick-up roller 40, the paper feed cassette 32
The uppermost recording sheet set in (1) is taken out, sent to the cut sheet feeding roller 42, and further conveyed by the roller 42 to the sheet feeding first roller 44.

On the other hand, in the case of the roll paper 34, it is continuously fed by the roll paper feed roller 46, and the cutter 48
Is cut into a fixed length by the
It is transported to 4 positions. Similarly, when the paper feed is manual feed from the manual feed port 36, the manually fed recording paper is conveyed to the paper feed first roller 44 by the manual feed roller 50.

Here, the pick-up roller 40, the cut paper feed roller 42, the roll paper feed roller 46, the first paper feed roller 44, and the manual feed roller 50 are a paper feed motor (not shown) (DC in this embodiment). It is driven by a servo motor), and an electromagnetic clutch attached to each roller can be used to perform on / off control of the rotational drive at any time.

The recording paper sheet thus selectively fed from one of the above-mentioned paper feed paths is conveyed to the first paper feed roller 44. In order to remove the skew (skew) of the recording paper, at the time of this paper feeding, after forming a predetermined amount of paper loop on the recording paper, the paper feeding first roller 44 is turned on and driven to rotate, The recording paper is conveyed to the second paper feed roller 52.

Further, between the first sheet feeding roller 44 and the second sheet feeding roller 52, a sheet feeding roller 64 disposed above the recording head 56 and a sheet feeding first roller disposed below the recording head 56. In order to perform an accurate paper feeding operation with the two rollers 52, the recording paper is slackened by a predetermined amount to form a buffer.
Then, in this buffer, a buffer amount detection sensor 54 for detecting a buffer amount as a slack amount of the recording paper.
Is provided. By constantly forming the buffer on the recording paper during the paper conveyance as described above, it is possible to reduce the load on the paper feed roller 64 and the second paper feed roller 52 particularly when the large-sized recording paper is conveyed. Various paper feeding operations are possible.

As described above, in the printer section 20 having the recording paper conveyance system, when the recording head 56 prints, the scanning carriage 58 on which the recording head 56 is mounted moves on the carriage rail 60. The scanning motor 62 is reciprocated in the front and back directions in the drawing to scan the recording paper in the main scanning direction. Then, in the forward scan, the image is printed on the recording paper by the recording head 56, and in the backward scan, the paper feeding roller 64 performs the feeding operation in the sub-scanning direction to feed the recording paper by a predetermined amount.

Here, the feed amount in the sub-scanning direction is
It is defined as a constant movement amount described later, and here, a length corresponding to the width of the recording head 56 in the sub-scanning direction, that is, although not shown, the recording head 56 is attached to the platen 74.
Is formed over the surface portion facing to and is set to a length corresponding to the arrangement width of the suction line. This suction line is for bringing the recording paper into close contact with the platen 74.

Further, in the recording paper drive control by the scanning motor 62 during the backward scanning, the buffer amount is detected by the buffer amount detection sensor 54, and the control is always performed so that the predetermined buffer amount is obtained. And
The printed recording paper is discharged to the discharge tray 66,
The series of printing operations described above is completed.

Next, the structure around the scanning carriage 58 will be described in detail with reference to FIG. 4; in FIG. 4, 68 is a paper feed motor as a drive source for intermittently feeding the recording paper in the sub-scanning direction. Is. The rotation amount of the paper feed motor 68 can be arbitrarily set and changed, and the paper feed second roller 52 is driven via the paper feed roller 64 and the paper feed second roller clutch 70. There is. Further, the above-mentioned scanning motor 62 is provided as a drive source for reciprocally scanning the scanning carriage 58 carrying the recording head 56 via the scanning belt 72 along the main scanning direction shown by the arrows A and B. In the present embodiment, pulse motors are used for the paper feed motor 68 and the scanning motor 62 because accurate paper feed control with an arbitrary feed amount is required.

In this embodiment, a paper pressing member (not shown) is arranged at a position facing the lower end of the platen 74, and the paper pressing member fixes the recording paper to the platen during scanning of the main scanning carriage 58. By doing so, the movement of the recording paper is controlled so as not to occur.

When the recording paper reaches the second paper feed roller 52, the second paper feed roller clutch 70 and the motor 68 are provided.
Is turned on, and the leading edge of the recording paper is conveyed on the platen 74 until it is held by the pair of paper feed rollers 64.
Then, the conveyed recording paper is detected by the paper detection sensor 76 provided on the platen 74 to have passed through the platen 74, and the sensor information is used for position control, jam control, and the like.

When the leading edge of the recording paper reaches the paper feed roller 64, the second feeding roller clutch 70 and the paper feed motor 6
8 is turned off, and then the inner space of the platen 74 is set to a negative pressure by the activation of a suction motor (not shown) to start the suction operation. By such a suction operation, the recording paper is attracted onto the platen 74.

Here, prior to the image printing operation on the recording paper, the scanning carriage 58 is moved to the position where the home position sensor 78 is arranged, and then the forward scanning is performed in the direction of arrow A. Be seen. In this forward scan, cyan (C), magenta (M), yellow (Y), and black (K) inks are appropriately ejected from the recording head 56 from a predetermined position to record (print) an image.
Is done. When the image recording operation for a predetermined length in the main scanning direction is completed, the rotation direction of the scanning motor 62 is reversed to move the scanning carriage 58 in the reverse direction, that is, the arrow B.
The carriage is moved in the direction indicated by and the backward scan is started. This time,
The scanning motor 62 is reversely driven until the scanning carriage 58 returns to the position where the home position sensor 78 is provided.

During this backward scan, the paper feed motor 6
By driving 8 to rotate the paper feed roller 64, the paper feed operation is performed by the length in the sub-scanning direction (the width of the print head 56) recorded by the print head 56 indicated by the arrow C. . In this embodiment, the paper feed amount, that is, the movement amount in the sub-scanning direction is not limited to the constant movement amount corresponding to the width of the recording head 56 described above, but is defined by the final line width. It may be set to the one-sided movement amount.

In this embodiment, the recording head 56 is made of ink.
It is a jet nozzle with a total of 256 nozzles Y,
It is assembled for each color of M, C and K.

On the other hand, when the scanning carriage 58 stops at the home position defined by the home position sensor, the recovery operation of the recording head 56 is performed. This recovery operation is a process for performing a stable recording operation,
This is a process for preventing unevenness at the start of ejection, which is caused by a change in viscosity of ink remaining in the nozzles of the recording head 56. In this process, a pressurizing operation is performed on each nozzle of the recording head 56 according to pre-programmed conditions such as a sheet feeding time, a temperature inside the apparatus, and an ejection time, and an idle ejection operation of ink is performed from each nozzle.

By repeating the operation described above, desired image recording can be performed over the entire surface of the recording paper.

(System Configuration) Next, the processing and control of the image signal of the control system in the digital color copying machine 10 of this embodiment will be described with reference to the configuration block diagram of FIG.

In FIG. 5, reference numeral 100 denotes a main CPU that controls the apparatus main body. The main CPU 100 has a printer control CP that controls the printer unit 20.
U102, reader control CPU 10 that controls the reading control operation
4, the main image processing unit 106 for processing the image display operation,
An operation unit 108 as an input unit for the operator is connected.

The printer control unit CPU 102 and the reader control CPU 104 are respectively the printer unit 20.
And the operation of the reader unit 12 is controlled by the main CP.
U100 is set to have a master-slave relationship.

The main image processing unit 106 described above performs image processing such as masking, black extraction, quaternarization, and γ correction.
Further, the printer control CPU 102 and the main image processing unit 1
The synchronous memory 110 is connected to 06. The synchronous memory 110 is for performing suction correction of time variations in input operation and delay correction due to the mechanical arrangement of the recording head 56 described above with reference to FIG. The output of the synchronous memory 110 is connected to the recording head 56 of a bubble jet (BJ).

The printer control CPU 102 is the printer unit 2
It is connected to a printer unit drive system 114 that controls 0 input drive. Further, the reader control CPU 104 is connected to an input system image processing unit 116 that performs necessary correction processing in a reading system such as color correction γ correction, and a reader unit drive system 118 that controls input driving of the reader unit 12. There is. further,
The input line image processing unit 116 includes a CCD line sensor 26.
Are connected, and the input system image processing unit 116 is connected to the main image processing unit 106.

Here, the reader unit 12 is the main CPU 10
0, reader control CPU 104, main image processing unit 10
6, operation unit 108, input system image processing unit 115, reader unit drive system 118, and CCD as an image sensor
It is composed of a line sensor 26. The printer unit 20 includes a printer control CPU 102, a synchronous memory 1
10, recording head 56 and printer drive system 114
It consists of and.

Next, with reference to FIG. 6 to FIG. 13, the constitutional operation of the main image processing unit 106 which is particularly related to the present embodiment will be described.

FIG. 6 is a block diagram showing the configuration of the image processing unit 106 in FIG. In FIG. 6, 200
Is an image memory unit for inputting and recording the image data from the input system image processing unit 116, and the main CPU 100 can read the image data stored in the image memory unit 200. Reference numeral 201 denotes a masking processing unit that performs masking processing on the input image data, and 202 denotes γ
A gamma correction unit 203 for performing correction, an HS processing unit 203 for performing head shading (HS), and a binarization processing unit 204 for performing binarization processing.

Reference numeral 205 is a signal line, and 206 is a backup RAM for storing various parameters required for control by the CPU, which is a non-volatile RAM. The main CPU 100 is connected to the data bus 10 for these image processing units.
Various parameters are read from the backup RAM 206 via 0 and set, and each image processing unit executes various image processes using the set parameters.

FIG. 7 is a block diagram showing the configuration of the HS processing unit 203 of this embodiment in more detail. In FIG.
210 is a table ROM, and the input image signal is converted according to the contents of the table ROM 210. The image signal 216 from the γ correction unit 202 in FIG. 6 is input to the lower address of the table ROM 210, and the corresponding value is output via the look-up table in the table ROM 210. The table ROM 210 is
A plurality of tables having such a data group are provided, and one of these tables is selected by the table selection signal 215 connected to the upper address of the table ROM 210.

In this embodiment, the density level of the image signal 216 is "0" to "255" and the number of tables included in the table ROM 210 is "64". Therefore, the image signal 216 is input to the lower 8 bits of the address of the table ROM 210, and the table selection signal 215 is input to the upper 6 bits.

FIG. 8 is a diagram concretely showing the data structure of each table data stored in the table ROM 210. As described above, this table ROM 210
Has a total of 64 tables, and each table is numbered "0" to "63". For example, the table with the number "31" is a table for data through, and when this table is selected, the input data and the output data have a one-to-one relationship. Next, tables "30" and "2"
When a table having a number smaller than the table “31” is selected, such as 9 ”, ..., The level of the image signal output from the table ROM 210 becomes lower than the level of the input image signal 216. .

On the contrary, when a table having a number larger than the table "31", such as the tables "32", "33", ... Is selected, the table ROM 210 outputs a signal level higher than the signal level of the input image signal 216. The output image signal level becomes high. Although not shown in the figure, the smallest table is the table “0” and the largest table is the table “63”.

Reference numeral 211 in FIG. 7 is an HSRAM (head shading RAM) for generating the selection signal 215.
The HSRAM 211 stores selection signals corresponding to each nozzle. This will be described with reference to FIG.

Data is stored in the HSRAM 211 at addresses 0 to 255, and this address corresponds to each nozzle number of the recording head 56 in FIG. For example, data for selecting the table “31” at address 0 and data for selecting the table “33” at address 1 are stored. Writing of data to the HSRAM 211 is performed via the gate 213 of the main CPU 10 of FIG.
It is written by inputting data from 0. The selector 212 is switched to the address bus side of the main CPU side when writing data to the HSRAM 211 by the select signal from the main CPU 100, and selects the address data from the address generation unit 214 when actually printing. The address of the HARAM 211 is selected for the image data corresponding to each nozzle.

In the above description, of the recording heads 56, only the recording heads for one color have been described. However, since the recording heads for four colors of C, M, Y and K are actually used, this recording head is used. The HS processing unit 203 (FIG. 6) has four systems corresponding to each color. However, since there is no difference between the respective colors in the actual processing, for convenience of description, the recording with one color will be described below.

Next, referring to the flowchart of FIG. 12, the main CPU 100 relating to the main part of this embodiment of FIG.
Reader control CPU 104 and printer control CPU 102
The content of the head shading controlled by is explained. FIG. 12 is a flowchart showing the head shading sequence in the color copying machine of this embodiment.

Now, when the head shading pattern output key is pressed from the operation unit (not shown), step S1
In, make head shading through. Specifically, "31" is written in all addresses of the HSRAM 211 of FIG. 5, and the through table "31" of the table ROM 210 is selected for each nozzle. Next, in step S2, as shown in FIG. 10, one band of an image pattern having a uniform density of 50% is recorded.

FIG. 10 shows a head shading pattern. The pattern of C, M, Y, and 50% density is printed on the upper stage by a sequence of equal magnification (100% magnification).
The four colors K are printed. That is, these patterns are printed for three bands by using all 256 nozzles of the head in one scanning.

The lower part is a pattern with a density of 50% printed by a sequence at a reduction ratio, and has four patterns of C, M, Y and K.
The colors are printed. That is, these patterns are printed by using the 128 nozzles in the upper half of the head in the first scan and the 128 nozzles in the lower half of the head in the second scan to form an image for one band in the second scan. . Finally, a pattern for 3 bands is printed. In addition, in order to clarify how the pattern is formed in the drawing, a solid line or a dotted line is added to a band break or the like in the pattern, but such a line naturally does not exist on the actually printed uniform pattern.

Next, in step S3 in FIG. 12,
A message is displayed on the operation unit for the user to place the recorded image (image pattern) printed in step S2 on the document table. In this way, the recorded paper is set on the document table, and when the user presses the start key of the operation unit, the process proceeds to step S4. First, a predetermined pattern on the same size printing pattern C (FIG. 10) of the paper is set. The image pattern of the area is read, input, and recorded in the image memory unit. Here, as shown in FIG. 9, the predetermined area is a length including one band width in the sub-scanning direction and 256 dots in the main scanning direction with respect to the output pattern.

After the image reading is completed in step S4, the process proceeds to step S5, and shading data 1 is created. This processing will be described with reference to FIG.

In FIG. 11, Vd in the equation (A)
[I] and [j] are portions corresponding to the central one band of the data read from the image memory unit 200 (FIG. 6), where the preceding and following one band data are truncated. here,
i indicates the sub-scanning, that is, the nozzle component of the head, and j corresponds to the pixel row in the main scanning direction. The formula (B) in FIG. 11 is the average value Vdm of 256 pixels of the image data in the main scanning direction.
The formula for calculating [i] is shown. Next, in the formula (C) of FIG. 11, the average value of the density levels of the respective nozzles of the recording head that has recorded in the sub-scanning direction is obtained. In the following equation (D), the head shading correction value Hd [i] is calculated. That is, the average value VM of the print densities of each nozzle obtained by the formula (C) and the image data Vdm output to each nozzle.
The ratio between the difference from [i] and the average value VM is calculated. Since the table to which the image signal 216 is directly output is the table "31", the numerical value "31" is multiplied by the ratio to standardize.

The head shading data for the C pattern of the same size is first calculated by the above method.
Then, this data is stored in a predetermined area of the backup RAM 206. In a succeeding step S6, it is determined whether or not the data creation for all the patterns is completed, and No is determined.
If so, the process returns to step S4, and if Yes, that is, when the shading data has been created for the eight types of patterns, the sequence ends.

FIG. 13 is a flow chart showing the operation in the actual copy sequence. First, step S7
Backup data for data corresponding to copy ratio
Read from and set in the HSRAM211. Then, the copy operation is started from step S8. According to the method as described above, there is an effect that head shading can be performed with the optimum correction data for each of different image recording sequences such as equal size and reduction.

(Second Embodiment) In the above embodiment,
For example, the same-size shading data is set in the HSRAM 211 when copying at the same size.
It is also possible to increase the capacity of and to preset both the same size and reduction patterns. FIG. 14 shows another example of the state in the HSRAM 211 as the second embodiment, in which addresses 0 to 255 are set to bank 1 and head shading data corresponding to the same-magnification sequence is set. Then, the addresses 256 to 511 are set to the bank 2, and the head shading data corresponding to the reduction sequence is set.

FIG. 15 is a block diagram of the configuration of the head shading processing unit 203 (FIG. 6) in this embodiment (FIG. 7).
(Corresponding figure). The bank switching signal 217 is input to the most significant bit of the address of the HSRAM 211.
Switches the bank of the HSRAM 211. The bank switching signal 217 is output from the output port of the CPU 100,
When copying is the same size system, it is switched to the bank 1 side, and when it is reduced, it is switched to the bank 2 side.

The present embodiment is particularly effective in the following cases. FIG. 16 is an explanatory view of the function of the inset combination of the digital color copying machine to which the present invention is applied. That is, the image of (a) is fitted into the image of (b) to form the image of (c). Specifically, the image of (c) is formed by a synthesis sequence as shown in FIG. In the image formation in the band including the image to be fitted, the image of the outer portion, that is, the portion 1 in the figure is first performed. At this time, the portion where the image is fitted is printed out in white. Subsequently, image formation is performed on the inset image portion and the portion 2 in the figure. Below 3,
Images are formed in the order of 4. At this time, the magnification of the inset image is not necessarily the same as the outer part,
For example, there is a case where the outside is the same size and the fitted image is reduced.

In such a case, in the first embodiment, it is necessary to rewrite the contents of the HSRAM 211 for each scan, which is disadvantageous in terms of copy throughput, but in the present embodiment, only bank switching is required. This is an advantage because it can be handled.

(Third Embodiment) In each of the above-mentioned embodiments, an example in which head shading data is provided only for two patterns of equal size and reduction has been described.
The present invention is not limited to this. For example,
In an image forming apparatus that forms an image by scanning the recording head in the main scanning direction and the recording paper in the sub scanning direction, depending on the image size, it may not be divisible by the head width as shown by the hatched portion in FIG. The part comes out. This half is (a)
There are cases where it comes to the end of the image, as shown in (b), where it comes to the middle part, and where it comes further to the beginning. The method (b) of bringing the half-end portion in the middle is an extremely effective method because it has the effect of simplifying the structure of the paper transport system.

However, in any case, in the half-edge portion, as shown in FIG. 18 (c), since the printing is performed using a specific area instead of the entire area of the head, the state of uneven density is different from the normal case. Come on.

In order to deal with this, for example, as shown in FIG. 19, a pattern including a half end portion can be printed to create head shading data corresponding to the half end portion. The difference from the above-described embodiment is that the print pattern is different, and the size of the area when the print pattern is read, specifically, the number of pixels in the sub-scanning direction is different.

For example, in an ink jet head having 256 nozzles, there are 255 possible odd patterns, but if shading data is provided for all these patterns, the scale of the circuit and the processing time are disadvantageous. In addition, since the half length of the difference in density unevenness does not change to the extent that it differs by several pixels, it is appropriate to create data for typical several patterns as shown in FIGS. 19 (a), (b), and (c). Is.

When pursuing a high-definition image,
Since the half length is uniquely determined when the copy mode such as the magnification is fixed, head shading data corresponding to the half length can be created at this point. In this case, it is necessary to perform head shading for each copy, but higher quality image formation can be realized.

As described above, the head shading according to the present invention is not only compatible with equal magnification and reduction magnification, but also
It can also be applied to any odd band pattern that is less than the entire head area in the image.

(Other Embodiments) In each of the above-described embodiments, the case where the present invention is applied to the digital color copying machine has been described, but it goes without saying that the present invention can also be applied to a printer having a similar configuration. Is. Further, it goes without saying that the recording head is not limited to the bubble jet head.

The present invention is particularly effective in a recording apparatus using an inkjet recording head for recording by forming flying droplets by utilizing thermal energy among the inkjet recording methods.

Regarding the typical structure and principle thereof, see, for example, US Pat. No. 4,723,129 and US Pat. No. 4,740.
What is done using the basic principles disclosed in 796 is preferred. This method is a so-called on-demand type,
It can be applied to any of the continuous type, but especially in the case of the on-demand type, it can be applied to the sheet holding the liquid (ink) or the electrothermal converter arranged corresponding to the liquid path. By applying at least one drive signal that gives a rapid temperature rise exceeding the film boiling corresponding to the recording information, heat energy is generated in the electrothermal converter, and film boiling is caused on the heat acting surface of the recording head. Liquid (ink) corresponding to this drive signal in a one-to-one correspondence
It is effective because bubbles can be formed inside. Due to the growth and contraction of the bubbles, the liquid (ink) is ejected through the ejection opening to form at least one droplet. It is more preferable to make this drive signal into a pulse shape because bubbles can be immediately and appropriately grown and contracted, so that liquid (ink) ejection with excellent responsiveness can be achieved. As the pulse-shaped drive signal, those described in US Pat. Nos. 4,463,359 and 4,345,262 are suitable. If the conditions described in US Pat. No. 4,313,124 of the invention relating to the rate of temperature rise on the heat acting surface are adopted, more excellent recording can be performed.

As the constitution of the recording head, in addition to the combination constitution of the discharge port, the liquid passage, and the electrothermal converter (the linear liquid passage or the right-angled liquid passage) as disclosed in the above-mentioned respective specifications. US Pat. No. 4,558,333, US Pat. No. 4,558,333, which discloses a configuration in which a heat acting portion is arranged in a bending region.
The structure using the specification of No. 59600 is also included in the present invention. In addition, Japanese Unexamined Patent Publication No. 59-123670 discloses a configuration in which a common slit is used as a discharge portion of the electrothermal converter for a plurality of electrothermal converters, and an opening for absorbing a pressure wave of thermal energy is provided. The effect of the present invention is effective even if the configuration corresponding to the ejection portion is disclosed in JP-A-59-138461. That is, according to the present invention, recording can be surely and efficiently performed regardless of the form of the recording head.

Furthermore, the present invention can be effectively applied to a full-line type recording head having a length corresponding to the maximum width of a recording medium that can be recorded by the recording apparatus. Such a recording head may have a configuration that satisfies the length by a combination of a plurality of recording heads or a configuration as one recording head integrally formed.

In addition, even in the case of the serial type as in the previous example, the recording head fixed to the apparatus main body, or the apparatus main body, is electrically connected to the apparatus main body and ink is supplied from the apparatus main body. The present invention is also effective when a replaceable chip type recording head capable of performing the above or a cartridge type recording head in which an ink tank is integrally provided in the recording head itself is used.

Further, as the constitution of the recording apparatus of the present invention, it is preferable to add ejection recovery means of the recording head, preliminary auxiliary means and the like because the effects of the present invention can be further stabilized. Specifically, heating is performed by using a capping means, a cleaning means, a pressure or suction means for the recording head, an electrothermal converter or another heating element or a combination thereof. Examples include a preheating means for performing the preheating, and a preejection means for performing ejection other than recording.

Regarding the type and number of recording heads mounted, two or more recording heads may be provided corresponding to a plurality of inks having different recording colors and densities. That is, for example, the recording mode of the recording apparatus is not limited to the recording mode of only the mainstream color such as black, but it may be either the recording head is integrally formed or a plurality of combinations may be used. The present invention is also extremely effective for an apparatus provided with at least one of full-color recording modes by color mixing.

In addition, in the above-described embodiments of the present invention, the ink is described as a liquid, but an ink that solidifies at room temperature or lower and that softens or liquefies at room temperature may be used. Or, in the inkjet system, it is common to control the temperature of the ink itself within the range of 30 ° C. or higher and 70 ° C. or lower to control the temperature so that the viscosity of the ink is within the stable ejection range. Sometimes, a liquid ink may be used. In addition, the temperature rise due to thermal energy is positively prevented by using it as the energy of the state change of the ink from the solid state to the liquid state, or in order to prevent the evaporation of the ink, it is solidified and heated in the standing state. You may use the ink liquefied by. In any case, by applying thermal energy such as ink that is liquefied by applying thermal energy according to the recording signal and liquid ink is ejected, or that begins to solidify when it reaches the recording medium. The present invention can be applied to the case where an ink having a property of being liquefied for the first time is used. In this case, the ink is
JP-A-54-56847 or JP-A-60-7
As described in Japanese Patent No. 1260, it may be configured to face the electrothermal converter in a state of being held as a liquid or a solid in the concave portion or the through hole of the porous sheet. In the present invention, the most effective one for each of the above-mentioned inks is to execute the above-mentioned film boiling method.

In addition, as the form of the ink jet recording apparatus of the present invention, in addition to the one used as an image output terminal of an information processing apparatus such as a computer, a copying apparatus combined with a reader or the like, and a facsimile apparatus having a transmitting / receiving function are provided. It may be a form or the like.

[0094]

As described above, according to the present invention,
In an image forming apparatus that forms an image by scanning a recording head having a predetermined width in the sub-scanning direction in the main scanning direction, an image pattern having a predetermined density is recorded on a recording medium, and the recorded image is photoelectrically read. In an image forming apparatus having means for detecting and correcting unevenness in density, the density correction data corresponding to each printing element width used for printing in one scan is provided, and the density corresponding to each print pattern is thereby obtained. By providing a means for performing correction, even when the printing is performed without using the printing elements in the entire area of the print head, for example, density unevenness that occurs when only one half of the printing elements is used in one scan such as reduction printing is used. The effect is extremely large because it is possible to deal with it.

[Brief description of drawings]

FIG. 1 is an external perspective view of a digital color copying machine according to an embodiment.

FIG. 2 is a schematic side sectional view of the internal configuration of FIG.

FIG. 3 is a top view of a schematic configuration of a reader unit.

FIG. 4 is a schematic configuration diagram around a scanning carriage.

FIG. 5 is a configuration block diagram of a control system

FIG. 6 is a configuration block diagram of a main image processing unit.

FIG. 7 is a configuration block diagram of an HS processing unit 203.

FIG. 8: Table data configuration example

FIG. 9 shows an example of the internal state of the HSRAM 211.

FIG. 10: Example of HS pattern

FIG. 11 Shading data creation processing

FIG. 12 is a sequence flowchart of head shading.

FIG. 13 is an actual copy sequence operation flowchart.

FIG. 14 shows another example of the internal state of the HSRAM 211.

FIG. 15 is a configuration block diagram of an HS processing unit according to a second embodiment.

FIG. 16 is an explanatory diagram of a fitting synthesis function.

FIG. 17 is an explanatory diagram of the sequence of FIG.

FIG. 18 is an example of a half portion of a formed image

FIG. 19 is a pattern example including a half end portion.

FIG. 20 is an explanatory diagram of recording operation.

FIG. 21 is an example of uneven density.

FIG. 22: Example of read density pattern

FIG. 23 Example of image reading and recording

FIG. 24 is an example of an image forming sequence

[Explanation of symbols]

 10 digital color copying machine (image forming apparatus) 12 reader section 20 printer section 56 recording head 100 main CPU 200 image memory section 203 HS processing section 211 HSRAM 300 recording paper (recording medium)

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Claims (4)

[Claims] 1. An image forming apparatus for forming an image by scanning a recording head having a predetermined number of recording elements in the sub-scanning direction in the main scanning direction, recording an image pattern of a predetermined density on a recording medium, and recording the image pattern. And a correction means for photoelectrically reading the image to detect and correct density unevenness of the image, and the number of printing elements used for printing in one scan is variable, and density correction data corresponding to each is made variable. An image forming apparatus comprising: a correction unit for performing density correction corresponding to each recording pattern by obtaining the above. 2. The image forming apparatus according to claim 1, further comprising storage means for storing a plurality of density correction data corresponding to the number of recording elements used. 3. The image forming apparatus according to claim 1, wherein the recording element ejects ink. 4. The image forming apparatus according to claim 3, wherein the recording element ejects ink by using thermal energy.