JPH04173160A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent density variations generated by scanning a record by correcting an image signal at a specified period for each record scanned by a recording head in accordance with the size of a record to a recording medium. CONSTITUTION:The gamma correction curve of a gamma correction part 106 is corrected in such a manner that an area where a density during recording by a recording head is low becomes thick in print and an area where a density during recording by a recording head is high becomes thin contrarily. A disturbance gamma ROM 110 consists of a ROM table and corrects an image signal which is output from HS-gamma 106 at a specified period in a head nozzle direction. The output from the disturbance gamma ROM 110 is sometimes entered or sometimes not entered in synchronized delay memory 115. Then when the format size of a record is A1, A2, the image signal converted by the disturbance gamma ROM 110 is stored in synchronized delay memory 115. If the size of a recording sheet is smaller than A3, A4, a switching operation is performed so that an output from HS-gamma 106 can be entered in synchronized delay memory 115 as it is in the form of data pixels.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that performs printing by serially scanning a print head.

[Conventional technology]

A method for correcting density unevenness during printing in a copying machine that uses a conventional inkjet head is disclosed in Japanese Patent Application Laid-Open No. 1999-1.
-129667. In addition, in facsimile machines and the like that record with a thermal head, printed characters may be affected by variations in the resistance of the heat generating resistor of the thermal head, and variations in temperature caused by areas where there is recording data and areas where there is no recording data. There are variations in density in photos. Such variations in density are corrected by changing the drive current, drive pulse width, and number of drive pulses of the thermal head so that the density of the printed image becomes uniform.

[Problem to be solved by the invention]

However, in the case of a serial scan type recording head using the conventional thermal head or inkjet head mentioned above, density unevenness occurs at the joints of the parts printed by each scan, and the density unevenness becomes a very subtle step. appears as. Such density unevenness poses a problem in that even if temperature correction is performed uniformly on the heating resistor of the thermal head, density unevenness will appear as a step if the recording condition in the thermal head changes even slightly. . In order to prevent density unevenness that appears as such steps, for example, in the case of an inkjet recording head, it is necessary to stabilize the density level of each nozzle of the recording head by equalizing it. This is extremely difficult due to the stability of the surface tension of the ink and the influence of changes in ink viscosity due to temperature, and it has the disadvantage that density unevenness gradually becomes noticeable during recording. , the appearance of density unevenness changes depending on the image size after density unevenness correction, but in the above conventional example, such consideration is not taken, ,
When printing on A2 size recording paper, and when printing on A4 size paper that can be viewed from close up. Even in the case of A3 size recording paper, the same density unevenness correction was performed. The present invention has been made in view of the above-mentioned conventional example, and an object thereof is to provide an image forming apparatus that eliminates density unevenness for each scan by changing the image data correction method according to the size of recording paper. purpose.

[Means for Solving the Problems] In order to achieve the above object, an image forming apparatus of the present invention has the following configuration. That is, the image forming apparatus inputs an image signal to form an image on a recording medium, and includes a recording means for scanning a recording head and recording an image on the recording medium based on the image signal, and a recording means for recording an image on the recording medium based on the image signal. and a first correction means for correcting the image signal at a predetermined period for each scan according to the recording size of the image signal. [Operation] In the above configuration, correction is applied to the image signal at a predetermined period for each scan recording by the recording head, depending on the recording size on the recording medium. This makes it possible to prevent density unevenness caused by recording scanning.

【Example】

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an external perspective view of a digital color copying machine which is an embodiment of the present invention. The entire copier can now be divided into two parts. The upper part of Figure 1 shows a color image scanner section 1 (hereinafter referred to as scanner section 1) that reads an original image and outputs digital color image data, and a color image scanner section 1 (hereinafter abbreviated as scanner section 1) that reads an original image and outputs digital color image data. The controller section 2 includes a controller section 2 that performs image processing and has processing functions such as an interface with an external device (not shown). The scanner section 1 not only reads a three-dimensional object or a sheet document placed downward under the document presser 11, but also has a built-in mechanism for reading a large-sized sheet document. Further, the operation section 10 is connected to the controller section 2, and is used to input various information and operation instructions for the copying machine. The controller section 2 instructs the scanner section 1 and the printer section 3 to operate according to the input information. If it is necessary to perform more complicated editing processing, use the document presser 11.
By attaching a digitizer or the like instead and connecting it to the controller section 2, advanced processing such as specifying the reading area of the document and erasing the image of a specific area becomes possible. At the bottom of FIG. 1 is a printer section 3 for recording the color digital image signal output from the controller section 2 onto recording paper or the like. In this embodiment, the printer section 3 is a full color inkjet printer using a recording head of the inkjet recording method described in Japanese Patent Laid-Open No. 54-59936. The two parts described above are separable and can also be installed at separate locations by extending the connecting cable. <Printer Section> FIG. 2 shows a sectional view of the digital color copying machine shown in FIG. 1, and parts common to those in FIG. 1 are designated by the same numbers. First, an exposure lamp 14, a lens 15, and an image sensor 16 that can read line images in full color.
(C0D in this embodiment) reads the original image placed on the original platen glass 17, the projected image by the projector, or the sheet original image by the sheet feeding mechanism 12. Next, various image processing is performed by the scanner section 1 and the controller section 2, and the image is recorded on recording paper by the printer section 3. In FIG. 2, recording paper is supplied from a paper feed cassette 20 that stores cut paper of small standard sizes (A4 to A3 size in this embodiment), or large size (A2 to A3 size in this embodiment). ~Al size),
It is supplied from roll paper 29. Furthermore, by inserting recording sheets one by one through the manual feed port 22 shown in FIG. 1 along the paper feed unit cover 21, paper can be fed from outside the apparatus (manual paper feed). The cut paper fed by the pickup roller 24 is
The cut paper feed roller 25 transports the cut paper to the 10th feed roller 26 . Further, the roll paper 29 is sent out by a roll paper feed roller 30, cut into a standard length by a cutter 31, and conveyed to the paper feed number 10-ra 26. Similarly,
The recording paper inserted through the manual feed port 22 is transferred to the manual feed roller 3.
2, the paper is conveyed to the 10th feeder 26. The pickup roller 24, the cut paper feed roller 25, the roll paper feed roller 30, the 10th paper feed roller 26, and the manual feed roller 32 are connected to a paper feed motor (not shown in the drawings) (in this embodiment, a DC servo motor is used). ), and can be controlled on and off at any time by electromagnetic clutches attached to each roller. When the printing operation is started in the printer section 3 according to an instruction from the controller section 2, the recording paper selectively fed from one of the above-mentioned paper feeding paths is conveyed to the paper feeding path 26. In order to eliminate the skew of the recording paper, after forming a predetermined amount of paper loops, the 10th paper feeder 26 is turned on and the recording paper is conveyed to the 20th paper feeder 27. Between the 10th paper feed roller 26 and the 20th paper feed roller 27, a predetermined amount of recording paper is fed between the paper feed roller 28 and the 20th paper feed roller 27 in order to perform an accurate paper feeding operation. Create a buffer. The buffer amount detection sensor 33 is a sensor for detecting the buffer amount. In this way,
By constantly creating a buffer during paper conveyance, the load on the paper feed roller 28 and paper feed roller 27 can be reduced, especially when conveying large-sized recording paper, and accurate paper feed operation can be achieved. It becomes possible. When the recording head 37 performs a printing operation, the scanning carriage 34 on which the recording head 37 and the like are mounted is reciprocated on the carriage rail 36 by the scanning motor 35 . Then, in the forward scan, an image is printed on the recording paper, and in the backward scan, the paper feed roller 28 operates to feed the recording paper by a predetermined amount. At this time, the above-described drive system is controlled by the paper feed motor so that the buffer amount is always maintained at a predetermined buffer amount while the buffer amount detection sensor 33 detects the above-described drive system. The recording paper printed in this way is discharged to the paper discharge tray 23, and the printing operation is completed. Next, a detailed explanation of the scanning carriage 3 and the invention will be given using FIG. In FIG. 3, a paper feed motor 40 is a drive source for intermittently feeding recording paper, and a paper feed motor 40 is a driving source for intermittently feeding the recording paper.
The 20th paper feeder 27 is driven via the 0-ra clutch 43. The scanning motor 35 moves the scanning carriage 34 to the scanning belt 34.
This is a drive source for scanning in the directions of arrows A and B. In this embodiment, since accurate paper feeding and scanning control of the carriage 34 are required, stepping motors are used for the paper feeding motor 40 and the scanning motor 35. When the recording paper reaches paper feed number 20-ra 27, the candy paper cylinder 20
- Turn on the clutch 43 and paper feed motor 40 to convey the recording paper over the platen 39 to the paper feed roller 28. The recording paper is detected by a paper detection sensor 44 provided on the platen 39.
The information from this sensor is used for position control,
Used for jam control, etc. The recording paper is moved to the paper feed roller 28
When reaching the position, the paper feed 20th clutch 43 and the paper feed motor 40 are turned off, and a suction operation is performed from inside the platen 39 by a suction motor (not shown) to bring the recording paper into close contact with the platen 39. Prior to the image recording operation on recording paper, the scanning carriage 34 is moved to the position of the home position sensor 41,
Next, the carriage 34 is scanned forward in the direction of arrow A, and cyan C, magenta M, yellow Y, and black inks are ejected from the recording head 37 from predetermined positions to record an image on the recording paper. When the image recording for a predetermined length is completed in this way, the scanning carriage 34 is stopped, and conversely, the arrow B
A return scan is started in the direction of , and the scanning carriage 34 is returned to the position of the home position sensor 41. During this backward scanning, the paper feed motor 40 rotates the paper feed roller 28 by the length recorded by the print head 37, thereby conveying the recording paper in the direction of arrow C. In this embodiment, the recording head 37 is an ink jet nozzle of the above-mentioned type, and each recording head is provided with 256 nozzles, and as shown in FIG.
, Y, M, and C are assembled in this order. Scanning carriage 34 is home position sensor 41
When it stops at the home position detected by , the recording head 37 performs a recovery operation. This is a process to ensure stable printing operation, and in order to prevent unevenness at the start of ejection caused by changes in the viscosity of the ink remaining in the nozzles of the print head 37, paper feeding time, internal temperature of the device, etc. This is a process in which pressure is applied to the recording head 37, ink is idly ejected, etc. according to preprogrammed conditions such as ejection time and the like. By repeating the operations described above, an image is recorded on the entire surface of the recording paper. Next, the operation of the scanner section 1 will be explained using FIGS. 4 and 5. FIG. 4 is a diagram for explaining the internal mechanical mechanism of the scanner section 1. As shown in FIG. The CCD unit 18 is a unit composed of a CCD 16, a lens 15, etc., and is moved on the rail 54 by a drive system in the main scanning direction consisting of a main scanning motor 50, pulleys 51, 52, and wires 53 fixed on the rail 54. The scanner moves and reads the document platen glass 17 in the main scanning direction. The light shielding plate 55 and the home position sensor 56 are connected to the main scanning home position in the correction area 68 in the figure.
It is used for position control when moving the D unit 18. The rail 54 rests on a rail 65.69, and is connected to a sub-scanning motor 60, pulleys 67.68, 71.76, and a shaft 7.
It is moved in the direction of arrow C in FIG. 4 by a drive system in the sub-scanning direction consisting of wires 2.73 and 66.70. Light shielding plate 5
7. The home position sensor 58 moves the rail 54 to the sub-scanning home position during the book mode in which an image of a document such as a book placed on the document table glass 17 is read.
Used for position control when moving. FIG. 5 is an explanatory diagram of the reading operation by the scanner unit 1 in the book mode. In the book mode, the CCD unit 18 is moved to the book mode home position (book mode HP) shown in the correction area 68 in FIG. Start a full-page read operation. First, prior to scanning a document, parameters necessary for processing such as shading correction, black level correction, and color correction are controlled in the correction area 68. Thereafter, scanning in the main scanning direction is started by the main scanning motor 50 in the direction of the illustrated arrow. When the reading operation in the area indicated by ■ in Figure 5 is completed,
The main scanning motor 50 is reversed, and the sub-scanning motor 60 is driven to move to the correction area 68 of the area (■). Subsequently, similarly to the main scanning of the area (2), processing such as shading correction, black level correction, color correction, etc. is performed as necessary, and the reading operation of the area (2) is performed. By repeating the above scanning, the entire area (■ to ■) is read, and after completing the reading operation of the area (■), the CCD unit 18 is switched to book mode, home mode, etc.
Return to position. In this embodiment, the document table glass 17 has a maximum
In order to read an L-sized document, scanning must actually be performed many times, but this explanation is simplified to make the operation easier to understand. Assuming that is a reading operation of the same size, the area read by the CCD unit 18 is the fifth
As shown in the figure, it is actually a wide area. This is because the digital color copying machine of this embodiment has a built-in magnification/reduction function. That is, as explained above (because the area that can be recorded by the recording head 37 is fixed at 256 bits at a time, for example, when performing a 50% reduction operation, the image information of an area of at least twice as much as 512 bits) This is because the scanner unit 1 has a built-in function of reading and outputting image information of an arbitrary image area in one main scan. <Description of overall functional block> Next, The functional blocks of the digital color copying machine of this embodiment will be explained with reference to FIG. It is a circuit and is composed of a microcomputer (CPU), program ROM, data memory, communication circuit, etc. Between the control units 102 and 111 and between the control units 111 and 12
1 are connected by a communication line, and a so-called master-slave control system is adopted in which the control units 102 and 121 operate according to instructions from the control unit 111. When operating as a color copying machine, the control section 111 operates according to input instructions from the operation section 10 and the digitizer 114. As shown in FIG. 7, the operation section 10 uses, for example, a liquid crystal (LCD display section 84) as a display section, and is equipped with a touch panel 85 made of transparent electrodes on its surface, so that color-related information can be displayed. Selection instructions such as specification and editing operation can be made. In addition, keys related to operations, such as a start key 87 for instructing to start a copying operation, a stop key 88 for instructing to stop a copying operation, a reset key 89 for returning the operation mode to the standard state, and a copying key 89 (not shown) There is also a numeric keypad for inputting the number of sheets. Note that the digitizer 114 is for inputting position information indicating processing areas such as trimming, masking processing, color conversion, etc.
Connected as an option when complex editing processing is required. The control unit 102 controls the mechanical drive unit 105 that controls the drive of the mechanism of the scanner unit 1 described above, the exposure control unit 103 that controls the exposure of the lamp during reflective original reading, and the like. The control unit 102 also includes an analog signal processing unit 100 that performs various types of processing related to images, and an input image processing unit 10 that performs various types of processing related to images.
1 is also controlled. The control unit 121 includes a mechanical drive unit 105 that controls the mechanical drive of the blink unit 3 described above, and a mechanical drive unit 105 that absorbs time variations in mechanical operation of the printer unit 3 and compensates for delays due to the mechanical arrangement of the recording heads 117 to 120. Synchronous delay memory 11
5. Next, the image processing block in FIG. 6 will be explained along the flow of the image. The image formed on the CCD 16 is converted into an analog electrical signal by the CCD 16. The converted image information is serially processed in the order of red → green → blue, and then manually input to the analog signal processing unit 100 . The analog signal processing unit 100 performs sample and hold, dark level correction, dynamic range control, etc. for each color of red, green, and blue, and then performs analog-to-digital conversion (A/D conversion) on the image signal. ) and serial multi-value (in this example, each color has 8
The input image processing unit 101 converts the image signal into a digital image signal (bit length) and outputs it to the input image processing unit 101. The input image processing unit 101 performs correction processing such as shading correction, color correction, γ correction, etc. necessary in the reading system as is on the serial multivalued digital image signal. The image data processed in this way is sent to the image processing unit 107 as a serial multi-level digital image signal. The image processing unit 107 performs smoothing processing, edge enhancement,
This circuit performs black extraction, masking processing for color correction of recording ink used in the recording heads 117 to 120, and the like. The serial multivalued digital image signal output is input to the head shading/gamma correction unit 106 (hereinafter referred to as H3-γ). The γ correction curve of the γ correction unit 106 is used to correct areas where the density is low during printing by the print head so that it becomes darker, and vice versa, so that areas where the density is dark are made thinner. There are approximately 64 types of this γ correction curve,
It is stored in the form of a ROM table. In this manner, the γ correction unit 106 performs density correction on the serially inputted image signal using the selected γ correction curve. The nozzle designation ROM 109 (Y, M, C, Bk) determines an appropriate γ correction curve corresponding to the nozzle position of the print head, and exists corresponding to each color print head. The disturbance γROMI 10 is composed of a ROM table, and is used to correct the image signal output from the H8-γ106 at a constant cycle in the head nozzle direction.
The output of 0 may or may not be input to the synchronous delay memory 15. This switching control of the selector 112 is performed by a signal from the control section 111. In this embodiment, the recording size is A2. When the recording paper size is A3, the image signal converted by the disturbance γROMll0 is stored in the synchronization delay memory 115. When the size is small, such as A4 size, the data pixels from H8-γ106 are switched to be input to the synchronous delay memory 115 as they are. The synchronization delay memory 115 of the printer section 3
Absorption of time variations in mechanical operation and recording head 117~
This circuit is for correcting the delay due to the mechanical arrangement of the recording heads 117 to 120, and internally also generates the timing necessary for driving the recording heads 117 to 120. Head driver 116
is an analog drive circuit for driving the recording heads 117-120, and internally generates signals for directly driving the recording heads 117-120. Recording head 117~
120 ejects cyan, magenta, yellow, and black ink, respectively, to record an image on recording paper. In the copying machine configured as described above, the operations of the H3-γ correction unit 106 and the disturbance γROMll0 will be explained. FIG. 8(A) shows an example of recording on A4 size recording paper, and FIG. 8(13) shows an example of recording on Al size recording paper. When recording in A4 size, the input Y of the selector 112 is selected by the control unit 111 and output. In this case, n
Printing is performed by serial scanning, and in this embodiment, the density gradient is as shown by 71 in FIG. 8(A). Although this may be printing in one color or a mixture of colors, here, a case of printing using a single color of black ink will be shown. In the print output example shown at 71, the data that has been flattened by the correction curve in the head shading γ correction unit 106 corresponds to the nozzle position specified by Bk in the nozzle specification ROM 109, and the density gradient is changed for each scan. is occurring. As mentioned above, this is A4. This is because when recording on A3 size recording paper, the image data that has passed through the disturbance γROM 110 is not written to the synchronization delay memory 115, so the cycle of density unevenness is in units of one scan. As a result, the appearance of density unevenness is gradually corrected, so that the image quality is good even when this printed image is viewed up close. Next, an example of printing on Al size recording paper is shown in Figure 8 (B).
Shown below. When recording on this A1 size, the control unit 111
The X input of the selector 112 is selected. As a result, the output of the selector 112 is the disturbance γ correction ROMll0
The image signal is passed through the . The correction characteristics of the disturbance γ correction ROMll0 are as shown by 72 in FIG. 8(B). Here, the images printed by each scan are connected and expressed, but it is sufficient to read out one serial scan for each scan. In this correction example, settings are made so that fine disturbances are applied in the positive and negative directions in one serial scan. The purpose of this is to make the density unevenness look like large undulations for each scan by correcting it at small intervals, since the larger the recording paper size, the more it has to be visually checked. There is. Therefore, for the image output example after H3-γ correction shown in 71, re-correction is performed using the characteristics of the disturbance γ correction ROM as shown in 73, and the print is changed to have high frequency components as shown in 74. This is what gives you the output. In this embodiment, an example using an inkjet type output device has been described, but it is obvious that the present invention can also be applied to other printing devices such as a thermal head output device such as a heat-sensitive type, an electrostatic type output device, etc. Furthermore, although this embodiment has been described using a copying machine as an example, the same applies to a printer or the like. Furthermore, in this embodiment, the correction characteristics in the disturbance γ correction ROMll0 are made to act particularly on the high frequency components of the image signal. However, depending on the visual appearance of the printed image, for example, depending on the instructions from the control unit 111,
The correction characteristics of the disturbance γ correction ROMll0 shown in FIG. 6 may be switched. In addition, the disturbance γ correction memory is stored in RAM.
By configuring and rewriting the contents of this memory,
The correction characteristics may also be changed. Further, in this example, the head shading γ correction unit 10
6, but this may be omitted and only disturbance γ correction may be performed to visually reduce density unevenness. Furthermore, although this embodiment has been explained in the case of a color copying machine, the present invention is not limited thereto, and for example, it is possible to input a monochrome image signal or a color image signal and print an image on a recording medium such as recording paper. It may also be a printer for recording. As described above, according to this embodiment, by changing the disturbance γ correction characteristic depending on the size of the recording paper to be recorded, it is possible to reproduce an image with a visually acceptable image quality.

【Effect of the invention】

As described above, according to the present invention, by changing the image data correction method according to the size of the recording paper, it is possible to eliminate density unevenness for each scan.

[Brief explanation of drawings]

FIG. 1 is an external perspective view of a copying machine according to an embodiment of the present invention, FIG. 2 is a side sectional view of a copying machine according to an embodiment of the present invention, and FIG. 3 is a view around the carriage of a copying machine according to an embodiment of the present invention. FIG. 4 is an external view showing the structure of the scanner section of the copying machine according to the embodiment of the present invention; FIG. 5 is a diagram showing the reading operation in the scanner section of the copying machine according to the embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of a copying machine according to an embodiment of the present invention, FIG. 7 is an external perspective view of a scanner section of a copying machine according to an embodiment of the present invention, and FIG. 8 is a block diagram showing the configuration of a copying machine according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of image output by a copying machine. In the figure, 1... scanner section, 2... controller section,
3... Printer section, 10... Operation section, 11... Document holder, 34... Scanning carriage, 35... Scanning motor, 37... Recording head, 102, 111, 121
...Control unit, 106...Head shading γ correction unit, 106...Nozzle specification ROM, 110...Disturbance γ correction ROM, 112...Selector, 114...
Digitizer, 115... Synchronous delay memory. N/T't

Claims (2)

[Claims] (1) An image forming apparatus that inputs an image signal and forms an image on a recording medium, comprising: a recording unit that scans a recording head and records an image on the recording medium based on the image signal; and the recording medium. An image forming apparatus comprising: a first correction means for correcting the image signal at a predetermined period for each scan according to a recording size of the image forming apparatus. (2) A claim further comprising a second correction means for correcting the density of the image signal so that the density becomes lower in areas where the density is high, and conversely so that the density becomes higher in areas where the density is low. The image forming apparatus according to item 1.