JP3899606B2 - Inkjet printer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet printer, and more particularly to an ink jet printer capable of changing the diameter of dots to be printed.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an ink jet printer that can print a multi-valued image by changing the diameter of a dot to be printed is known. In such a printer, a technique is known in which high gradation image data is input and pseudo gradation expression is performed using a dither matrix.
[0003]
FIG. 23 to FIG. 26 are diagrams showing examples of the size of dots printed by an ink jet printer employing such a technique and a 4 × 4 dither matrix. In this example, an image is printed using four types of sizes of the first to fourth stages as dot sizes. Also, image data of 64 gradations that can take a value of 0 to 64 as the density of one pixel is input, and pseudo gradation expression of 64 gradations is performed by a dither matrix.
[0004]
The input image data composed of a plurality of pixels is divided into blocks each composed of 4 × 4 pixels. The density of each pixel in each block is compared with the corresponding threshold value of the dither matrix of FIGS.
[0005]
If the density of the pixel is larger than the threshold value included in the dither matrix, the corresponding size dot is printed.
[0006]
That is, if it is larger than the threshold value of the dither matrix in FIG. 23 and less than or equal to the threshold value of the dither matrix in FIG. Similarly, if the threshold value is larger than the threshold value of the dither matrix shown in FIG. 24 and less than the threshold value of the dither matrix shown in FIG. If the threshold value is smaller than the threshold value of the dither matrix shown in FIG.
[0007]
If it is larger than the threshold value of the dither matrix shown in FIG. 26, a fourth-stage dot is printed. If it is below the threshold value of the dither matrix in FIG. 23, no dot is printed.
[0008]
Specifically, it is assumed that the density of the input pixel has a value of “17” in all the pixels of the block as shown in FIG. In this case, since the density of the upper left pixel is larger than “16” which is the threshold value of the second size dot in FIG. 24, the second level pixel is located at that position as shown in FIG. Size dots are printed. The density of the other pixels is less than or equal to the threshold value of the second stage size dot shown in FIG. 24 and exceeds the threshold value of the first stage size dot shown in FIG. As shown in FIG. 28, dots of the first stage size are printed at the positions.
[0009]
In this manner, an image with 64 gradations can be formed in a pseudo manner by using dots having four sizes.
[0010]
[Problems to be solved by the invention]
However, the above-described conventional technique has a problem that the gradation reproducibility in the low density region is poor.
[0011]
The solid line in FIG. 29 is a graph showing the relationship (density characteristic) between the gradation of the image formed as described above and its density. In this figure, the collapse of the linearity of the density characteristic due to the dither matrix (Bayer array) and the collapse of the linearity of the density characteristic due to the overlapping of dots are omitted.
[0012]
As shown in the figure, the increase in density in the portion of 0 to 16 gradations is more rapid than in other portions. The straight line indicating the relationship between gradation and density starts from a position shifted from the density 0 to the high density side by a predetermined amount.
[0013]
In order to increase the gradation of the image reproduced here, when the number of stages of dot size change is increased and the dots between the first stage and the fourth stage are set in three stages, the density characteristics are as shown in FIG. The characteristic is as shown by the dotted line. In such a case, it is possible to increase the number of gradations in the portion of gradation 16 or higher. However, the number of gradations at gradations 0 to 16 cannot be increased.
[0014]
If the minimum dot diameter can be further reduced, the number of gradations in the low density region can be increased, but the minimum dot diameter that can be printed in an inkjet printer is limited. Therefore, it is easy to increase the number of gradations in the high concentration region, but it is difficult to increase the number of gradations in the low concentration region.
[0015]
The present invention has been made to solve such a problem, and an object thereof is to provide an ink jet printer capable of increasing the number of gradations in a low density region.
[0016]
[Means for Solving the Problems]
To achieve the above object, a dot according to an aspect of the present invention, a first printing means inkjet printer for printing dots by color ink on a recording medium, the white Iroi ink on a recording medium a second print means for printing a so that a first control means for controlling the size of dots to be printed by the color ink, the dot by colored ink excluding white dots of white Iroi ink is overprinted and a second control means for controlling the second control means, only when the size of the dots to be printed by color ink, except for white becomes smallest, a white dot size becomes the smallest a control so that dots of white Iroi ink on dots of colored ink are overprinted rows that have, in colored ink excluding white except Ri except when the size of the printed the dot becomes smallest will dots by white ink row control so as not to be printed.
[0017]
According to the invention, it is possible to print overlapping dots by white Iroi ink on dots of colored ink excluding white, can be lowered optical reflection density of dots by color ink, except for white, the number of gradations Many can be taken. Only when the size of the dots to be printed by color ink, except for white becomes smallest, so that the size of dots dots by white Iroi ink on dots of colored ink excluding the smallest since white is overprinted control is performed, except when the dot size of which is printed by color ink, except for white becomes smallest is tone number because, in the low concentration region control as dots by white ink is not printed is performed Can be increased.
[0020]
Preferably, the size of dots to be printed by the white Iroi ink is smaller than the maximum size of the dots to be printed by the color ink, the minimum is greater than the size of the dots to be printed by the color ink.
[0021]
According to this invention, when the dots of white Iroi ink is overprinted on the dots of colored ink, white Iroi ink onto the positively colored ink even if there is some error in the position to be printed Can be stacked. Further, it is possible to prevent the white Iroi ink mix together in dots adjacent.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an ink jet printer according to one embodiment of the present invention will be described with reference to the drawings.
[0023]
FIG. 1 is a perspective view showing a schematic configuration of an inkjet printer 1 according to one embodiment of the present invention.
[0024]
An inkjet printer 1 includes a recording sheet 2 that is a recording medium (recording material) such as paper or an OHP sheet, an inkjet head 3 that is an inkjet printer head, a carriage 4 that holds the inkjet head 3, and a carriage 4. Swing shafts 5 and 6 for reciprocating the recording sheet 2 in parallel with the recording surface, a drive motor 7 for reciprocating the carriage 4 along the swing shafts 5 and 6, and rotation of the drive motor 7 for rotating the carriage 7 A timing belt 9 for changing to a reciprocating motion and an idle pulley 8 are included.
[0025]
The ink jet printer 1 also includes a platen 10 that also serves as a guide plate for guiding the recording sheet 2 along the conveyance path, and a paper pressing plate 11 that presses the recording sheet 2 between the platen 10 and prevents the recording sheet 2 from floating. A discharge roller 12 for discharging the recording sheet 2, a spur roller 13, a recovery system 14 for recovering a defective ink discharge of the inkjet head 3 to a good state, and a paper for manually transporting the recording sheet 2 A feed knob 15.
[0026]
The recording sheet 2 is fed into a recording unit where the inkjet head 3 and the platen 10 are opposed to each other by a sheet feeding device such as manual feeding or a cut sheet feeder. At this time, the rotation amount of a paper feed roller (not shown) is controlled, and the conveyance to the recording unit is controlled.
[0027]
The inkjet head 3 uses a piezoelectric element (PZT) as an energy source for flying ink. A voltage is applied to the piezoelectric element, causing distortion. This distortion changes the volume of the channel filled with ink. Due to this change in volume, ink is ejected from the nozzles provided in the channel, and recording on the recording sheet 2 is performed.
[0028]
The carriage 4 is main-scanned in the digit direction of the recording sheet 2 (the direction across the recording sheet 2) by the drive motor 7, the idle pulley 8, and the timing belt 9, and the inkjet head 3 attached to the carriage 4 corresponds to one line. Record an image. Each time recording of one line is completed, the recording sheet 2 is sent in the vertical direction and sub-scanned to record the next line.
[0029]
The image is recorded on the recording sheet 2 in this way, and the recording sheet 2 that has passed through the recording unit is discharged by a discharge roller 12 disposed on the downstream side in the transport direction and a spur roller 13 pressed against the discharge roller 12. .
[0030]
2-4 is a figure for demonstrating the structure of the inkjet head 3. As shown in FIG. 2 is a plan view showing a part of the inkjet head 3, FIG. 3 is a sectional view taken along the line III-III in FIG. 2, and FIG. 4 is a sectional view taken along the line IV-IV in FIG.
[0031]
The inkjet head 3 includes a black ink head 301 and a white ink head 302. The black ink head 301 and the white ink head 302 have a configuration in which a channel plate 303, a partition wall 304, a vibration plate 305, and a substrate 306 are integrally stacked.
[0032]
The channel plate 303 is made of metal or ceramic. The surface has a water repellent coating layer. The surface of the channel plate 303 facing the partition wall 304 is finely processed by Ni electroforming or photoresist, and the black ink head 301 and the white ink head 302 each have a plurality of ink channels 308 that contain ink 307 and each ink. An ink inlet 311 that connects the channel 308 to the ink supply chamber 310 is formed.
[0033]
As shown in FIG. 3, the ink channels 308 of the black ink head 301 and the white ink head 302 are formed in a long groove shape extending in parallel with the black ink head 301 and the white ink head 302 facing each other. ing. Further, the ink supply chamber 310 and the ink channel 308 are formed symmetrically with respect to the center line 312 and are connected to an ink tank (not shown).
[0034]
A thin film is used for the partition wall 304 and is fixed between the channel plate 303 and the diaphragm 305. The partition wall 304 is fixed in a state where a predetermined tension is applied.
[0035]
The diaphragm 305 includes PZT315. The processing of the diaphragm 305 is performed by first fixing the diaphragm 305 to the substrate 306 with an insulating adhesive, and then separating and forming separate grooves 318 and 319 by dicer processing. Further, by this division, the PZT 315 corresponding to each ink channel 308, the PZT column portion 316 positioned between the adjacent PZTs 315, and the surrounding wall 317 surrounding them are divided.
[0036]
The operation of the PZT 315 is controlled by the control unit of the inkjet printer 1 via a head driver 56 (see FIG. 5) described later. When a predetermined voltage, which is a print signal, is applied between the two electrodes provided on the piezoelectric element from the control unit, the PZT 315 is deformed in the direction of the arrow D1. The deformation of the PZT 315 is transmitted to the partition wall 304, whereby the ink 307 in the ink channel 308 is pressurized, and the ink droplets fly toward the recording sheet 2 through the nozzle 309.
[0037]
In the inkjet head 3 having the above-described configuration, the ink 307 is supplied from an ink tank (not shown) to the ink supply chamber 310. The ink 307 in the ink supply chamber 310 is distributed to each ink channel 308 via the ink inlet 311.
[0038]
FIG. 5 is a block diagram illustrating the configuration of the control unit of the inkjet printer 1. The main controller 51 receives image data from a computer or the like. The image data is stored in the buffer frame memory 52 in units of one frame. When printing on the recording sheet 2, the main controller 51 drives the drive motor 7 of the carriage 4 and the paper feed motor via the motor drivers 54 and 55.
[0039]
Along with these drive controls, the main controller 51 is included in the black ink head 301 and the white ink head 302 via the driver controller 53 and the head driver 56 based on the image data read from the frame memory 52. Each piezoelectric element 315 is driven and controlled.
[0040]
Next, the operation of the inkjet printer 1 will be described.
FIG. 6 is a diagram showing the relationship between the recording sheet 2 and the inkjet head 3.
[0041]
The ink jet head 3 performs main scanning on the recording sheet 2 in the arrow direction. At this time, the white ink head 302 passes through the point on the recording sheet 2 later than the black ink head 301. Thereby, after printing the dot by black ink on the recording sheet 2, the dot by white ink can be overlaid and printed on it. If the print head 3 has reached the right end of the recording sheet 2, the print head 3 moves to the left. Thereafter, the recording sheet 2 moves upward with respect to the drawing. Thereafter, the print head 3 performs printing while moving rightward again. By repeating such an operation, a two-dimensional image is printed.
[0042]
FIG. 7 is a conceptual diagram for explaining the relationship between the ink 307 in the ink channel 308 and the PZT 315.
[0043]
When a voltage is applied to the PZT 315, the PZT 315 expands in the direction of the arrow. As a result, the volume of the ink channel 308 decreases rapidly. As a result, ink is ejected from the nozzle 309.
[0044]
FIG. 8 is a diagram showing a waveform of a voltage pulse applied to PZT.
The inkjet printer 1 changes the amount of ink ejected from the nozzles 309 by changing the waveform of the voltage pulse applied to the PZT 315. Thereby, the size of the dots printed on the recording sheet 2 can be changed.
[0045]
In the present embodiment, any one of the four types of waveforms (a) to (d) is applied to the PZT 315 of the black ink head 301 so that one of the diameters of 30 μm, 60 μm, 90 μm, and 120 μm is obtained. Dots of black ink having a diameter of 1 mm are printed on the recording sheet 2.
[0046]
By applying the waveform shown in (c) to the PZT 315 of the white ink head 302, dots of white ink having a diameter of 90 μm are printed on the recording sheet 2.
[0047]
FIG. 9 is a flowchart showing print processing of the inkjet printer 1.
[0048]
Referring to the drawing, in the printing process, initialization is first performed in step S100.
[0049]
In step S101, image data is input to the main controller 51 (FIG. 5). In step S102, the input image data is converted into data having a density of 80 gradations per pixel. In step S103, the converted 80-gradation data is converted into dot size data to be printed in each pixel.
[0050]
If the inkjet 3 is scanned in step S104 and the recording sheet 2 is at a desired position, dot printing processing is performed in step S105.
[0051]
It is determined in step S106 whether all the dots have been printed, and the processing from step S104 is repeated until YES is obtained.
[0052]
FIG. 10 is a flowchart showing processing in the conversion processing (S103) to the dot size data of FIG.
[0053]
Referring to the drawing, in the conversion process, first, in step S200, the density data of the pixel to be processed is compared with the corresponding value of the dither matrix.
[0054]
That is, image data having a density of 80 gradations is divided into blocks each consisting of 4 × 4 pixels as shown in FIG. Each block is compared to a 4 × 4 dither matrix.
[0055]
As the dither matrix, five types of matrices shown in FIGS. 12 to 16 are used. 12 to 16 show the first to fifth dither matrices, respectively.
[0056]
Returning to FIG. 10, in step S201, it is determined whether the density value of the pixel has exceeded the threshold value of the first-stage dither matrix.
[0057]
If YES, it is determined in step S202 whether the pixel density value exceeds the threshold value of the second-stage dither matrix.
[0058]
If YES, it is determined in step S203 whether the pixel density value exceeds the threshold value of the third-stage dither matrix.
[0059]
If YES, it is determined in step S204 whether the pixel density value exceeds the threshold value of the fourth-stage dither matrix.
[0060]
If YES, it is determined in step S205 that the pixel density value has exceeded the threshold value of the fifth-stage dither matrix.
[0061]
If YES, in step S206, the dot to be printed is determined as the fifth stage dot.
[0062]
Thereafter, in step S207, it is determined whether or not all the pixels have been converted, and the processing from step S200 is repeated until YES is obtained.
[0063]
If NO in each of steps S201 to S205, the dots to be printed are determined as the 0th to 4th dots in steps S208 to S212, and the processing from step S207 is performed.
[0064]
Here, the determination of the 0th stage dot indicates that no dot is printed at that position.
[0065]
FIG. 17 is a flowchart showing processing performed in the dot printing processing (S105) of FIG.
[0066]
Referring to the figure, in step S301, it is determined how many dots are to be printed.
[0067]
If it is the 0th stage dot, the process returns to the main routine without printing the dot in step S302.
[0068]
If it is the first-stage dot, the dot is printed with black ink on the recording sheet 2 by the pulse (a) shown in FIG. 8 in step S303. Thereafter, dots are printed with white ink by the pulse (c) on the dots with black ink printed in step S304.
[0069]
If it is the second stage, dots are printed with black ink by the pulse (a) in step S305.
[0070]
If it is the third stage, dots are printed with black ink by the pulse (b) in step S306.
[0071]
If it is the fourth stage, dots are printed with black ink by the pulse (c) in step S307.
[0072]
If it is the fifth stage, in step S308, dots are printed with black ink by the pulse (d).
[0073]
As a result of the above processing, the size of the dots printed with black ink is 30 μm in the first stage and the second stage, and both are the same. However, in the first stage, dots of white ink having a diameter of 90 μm are printed on 30 μm dots printed with black ink, so that the color of the dots becomes gray. As a result, it is possible to print dots having a lower reflection optical density than the second-stage dots.
[0074]
FIG. 18 is a graph showing the relationship between gradation and density of an image printed by the inkjet printer according to the present embodiment.
[0075]
In gradations 0 to 16, the density increases as the number of gray dots increases. In gradations 16 to 80, the density increases as the number and size of black dots increase, as in FIG. 29, which is the prior art.
[0076]
As described above, in this embodiment, the gradation of the low density region can be increased as compared with the prior art. In addition, the minimum density that can be expressed can be lowered.
[0077]
In the present embodiment, the white ink is superimposed only on the black dots of the minimum size. This is because even if black ink other than the minimum size is overlaid with white ink and gradation control is performed, the density of white ink and black ink varies due to variations in density and dot diameter. This is because it is difficult to adjust the characteristics.
[0078]
In the present embodiment, the size of the white ink dot is made smaller than the maximum dot size printed with black ink and larger than the minimum dot size printed with black ink. .
[0079]
That is, when the first-stage dots and the fifth-stage dots are printed side by side, the result is as shown in FIG. In FIG. 19, B indicates a black dot, W indicates a white dot, and G indicates a portion that has become gray by overlapping a white dot on the black dot.
[0080]
At this time, as shown in FIG. 20, even if the black dot B is slightly shifted to the left side due to mechanical noise or the like, the white dot W and the black dot B are prevented from overlapping. Further, even if the position of the white dot W and the position of the black dot to be overlaid are slightly shifted, they can be overlaid, and the gray dot G can be printed.
[0081]
That is, referring to FIG. 21, if the size of the first-stage black dot B1 and the white dot W is the same, it is impossible to print gray dots even if a slight deviation occurs.
[0082]
In addition, referring to FIG. 22, when the size of the white dot W is the same as the size of the fifth-stage dot B, the dots are overlapped by a slight shift in the print position, and the desired density is reproduced. I can't.
[0083]
In the present embodiment, problems such as those shown in FIGS. 21 and 22 do not occur, and deterioration in image quality can be prevented.
[0084]
In the present embodiment, the density of the black dots of the minimum size is reduced by the white ink. However, the same effect can be obtained even if the density of the black dots is reduced by using the colorless ink. it can.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a schematic configuration of an ink jet printer according to one embodiment of the present invention.
FIG. 2 is a plan view of the inkjet head 3. FIG.
3 is a cross-sectional view taken along the line III-III in FIG.
4 is a cross-sectional view taken along the line IV-IV in FIG.
FIG. 5 is a block diagram illustrating a configuration of a control unit of the inkjet printer 1;
6 is a diagram illustrating a relationship between the recording sheet 2 and the inkjet head 3. FIG.
FIG. 7 is a conceptual diagram illustrating a mechanism for ejecting ink from a nozzle 309;
FIG. 8 is a diagram showing a waveform of a pulse applied to PZT315.
FIG. 9 is a flowchart of print processing performed by the ink jet printer.
10 is a flowchart of a conversion process (S103) to dot size data in FIG. 9;
FIG. 11 is a diagram illustrating a relationship between input image data and a dither matrix.
FIG. 12 is a diagram showing a first-stage dither matrix.
FIG. 13 shows a second-stage dither matrix.
FIG. 14 shows a third-stage dither matrix.
FIG. 15 is a diagram showing a fourth-stage dither matrix.
FIG. 16 is a diagram showing a fifth-stage dither matrix.
FIG. 17 is a flowchart of the dot printing process (S105) in FIG. 9;
FIG. 18 is a diagram illustrating a relationship between gradation and density that can be reproduced by the ink jet printer of FIG. 1;
FIG. 19 is a first diagram showing the effect of the present invention.
FIG. 20 is a second diagram showing the effect of the present invention.
FIG. 21 is a diagram showing a state when white dots W are made the same as the minimum black dot size.
FIG. 22 is a diagram for explaining a problem when the white dot W is the same as the size of the maximum black dot.
FIG. 23 is a diagram showing a first-stage dither matrix in the prior art.
FIG. 24 is a diagram showing a second-stage dither matrix in the prior art.
FIG. 25 is a diagram showing a third-stage dither matrix in the prior art.
FIG. 26 is a diagram showing a fourth-stage dither matrix in the prior art.
FIG. 27 is a diagram showing a specific example of input image data.
FIG. 28 is a diagram illustrating a state after the image data in FIG. 27 is converted into dot diameter data to be printed.
FIG. 29 is a diagram for explaining the relationship between gradation and density reproduced by an ink jet printer according to a conventional technique.
[Explanation of symbols]
301 Black ink head 302 White ink head

Claims (2)

First printing means for printing dots with colored ink on a recording material;
A second print means for printing dots by white Iroi ink to said recording medium,
First control means for controlling the size of dots printed by the colored ink;
And a second control means for controlling so that the dots by the white Iroi ink on dots of the colored ink excluding white color is overprinted,
The second control means includes
Only when the size of the dots to be printed by the color ink, except for white becomes smallest, dots overlapped by the white Iroi ink on dots of colored ink excluding white size before Symbol dots smallest rows that have the control to be printed Te,
Except when the size of the dots to be printed by the color ink, except for white becomes smallest, the dot will row control so as not to be printed by the white ink, an ink jet printer. The size of the dots to be printed by the white Iroi ink is smaller than the maximum size of the dots to be printed by the color ink, the minimum is greater than the size of the dots to be printed by the color ink, according to claim 1 Inkjet printer.

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