Printing method using a plurality of ink drop jet instruments of different dimension on one printing head

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a gradation printing method using a liquid ink printing apparatus, and particularly to a printing method using an inkjet printing head having ink droplet ejectors having different dimensions.

【0002】

[Problems to be solved by conventional techniques and inventions]

Liquid ink printers of the type called continuous stream or drop-on-demand, such as piezoelectric, acoustic, phase ahange wax-based, or thermal, have at least one printhead from this printhead. Ink droplets are emitted toward the recording sheet. The ink is contained in a plurality of channels inside the print head. The energy pulse causes the ink droplets to be ejected from the channel end openings or nozzles as needed.

【0003】

Generally, in a thermal inkjet printer, the energy pulse is generated by a heating transducer, that is, a resistance heating element, which is standard equipment for each channel. By operating each resistor individually, the ink in each channel is heated and vaporized. That is, when a voltage is applied across the selected resistor, bubbles are generated in the connected channels. The bubbles first expand and then deflate at the channel opening. At this time, the ink in the channel is retracted inward and separated from the expanding ink, thereby forming ink droplets traveling from the channel opening toward the recording medium. The ink droplets collide with the recording medium to form ink dots or spots. After that, the channel is refilled with ink by capillarity while drawing ink from the liquid ink supply container.

【0004】

The inkjet print head includes one or more thermal inkjet print head dies, each of which includes one independent heater die and one channel die. The channel die comprises a row of flow channels, and the ink is transferred by this flow channel and contacts a resistance heating element installed on each channel on the heater die. Further, the address circuit and the driving transistor may be integrated in this die. In the production of die assemblies with a resolution of about 300 to 600 channels per inch (2.54 cm), the number of channels per die is preferably in the range of 50 to 500 with current technical capabilities. The channel sequence in one die assembly is less than the length of one page. For this reason, either measures are taken to scan the print head between page edges while advancing the paper in between, or to combine a plurality of die assemblies to create a page width print bar. In general, thermal inkjet nozzles form spots or dots of one size, so for high-quality printing, a flow channel created with a high resolution of about 400 to 600 channels per inch and an associated heat generator. is required.

【0005】

The inkjet print head can be incorporated into any of a cartridge printer, a partial width array printer, or a page width printer. Cartridge printers typically have a relatively small print head that houses an ink channel and nozzles. The print head is hermetically mounted on a disposable ink supply cartridge. An assembly that integrates the printhead and cartridge is attached to the carriage, and the carriage reciprocates to print the information sequence (matching the length of the nozzle row) on a fixed recording medium such as paper or OHP film at the same time. Will be done. When the information string is printed, the paper is advanced by a distance equal to the height of the printed information string or a part thereof, and the next printed information string is adjacent to or overlaps with the previous information string. Will be done. This procedure is repeated until the entire page is printed. A page width printer, on the other hand, includes a fixed print head, which has a length capable of simultaneously printing the entire sheet width or length of the recording medium. The recording medium continuously passes through the page width print head at a constant or variable speed in a direction substantially perpendicular to the length direction of the print head during printing. Page width inkjet printers are described, for example, in US Pat. No. 5,192,959.

【0006】

Generally, the information printed by the printer is the information received from an image output device such as a personal computer. Usually, this received information is supplied in the form of a raster scan image such as a bitmap of the entire page, or an image written in a page description language. The raster scan image includes a series of scan lines composed of bits representing pixel information, and based on the information contained in each scan line, one line of information is printed linearly across the page. .. What can be printed by the printer is the received bitmap information or the information after converting the image information written in the page description language into a bitmap composed of pixel information.

【0007】

In a printer having equidistant nozzles and a printing head of a type in which ink spots of the same size are formed by nozzles of the same size, the pixels are arranged on a first square grid of size S. S is the marking on the printhead, as shown in the sample print pattern in FIG. Transducers) or intervals between channels roughly match. The nozzle 60 (schematically represented by a triangle) moves both ends of the recording medium in the scanning direction X as shown in the figure. The nozzles are spaced from each other by a predetermined distance d (also called pitch), which causes ink spots, or groups of ink droplets, to be placed on the pixel center 62 on the grid with grid spacing S in a direction perpendicular to the scanning direction. To adhere to. Needless to say, the grid spacing S depends on the nozzle spacing d. Generally, nozzles and printing conditions are designed or set so that a spot diameter of about 1.414 (square root of 2) times the grid spacing S is formed. As a result, adjacent pixels in the 45-degree direction come into contact with each other, and the blank portion is completely filled. The drawback of this printing method is that the edges of the spot line are jagged and give a bad impression, especially in a straight line or curved portion slightly inclined with respect to the scanning direction as shown in FIG. The first ellipse 64, located outside the second ellipse 66 in FIG. 2, shows in which part of the printed image the bad impression due to the jaggedness is most noticeable. Furthermore, based on this figure, 1) how much blank space remains in the ring defined by the first and second ellipses, and 2) the spot is outside either the first or second ellipse. The print quality is determined by considering how much the ink sticks out and 3) the amount of ink adhered to the recording medium.

【0008】

One way to improve the quality of the edges of the spotline is to improve the address performance of the carriage and place the dots in the middle of the grid in the scanning direction. It is also possible to improve the quality of the edge of the spot line by increasing the resolution. However, in this method, the manufacturing process becomes complicated, the manufacturing price rises, and the number of spots to be printed is added, so that the printing speed generally decreases.

【0009】

In the above-mentioned print head and printing method shown in FIG. 2, if the resolution is increased to 600 channels per inch, for example, an inkjet image having sufficiently high image quality can be printed. However, the print head and the printing method do not always obtain an image of a desired image quality when the number of gradation levels, the ink-saving printing mode, and the printing processing amount are taken into consideration.

【0010】

Since the ink spots, that is, the ink droplets formed by most thermal inkjet printers all have the same dimensions (variation within about 10%), gradation printing cannot be performed. The size of the ink droplets, or spot dimensions, is determined by a variety of factors, such as the area of the thermal converter, the cross-sectional area of the ink ejection channel or nozzle, the conditions under which the pulses required to form the ink droplets, and the ink temperature. There is a physical characteristic of the ink itself. The spot size may change by ± 10% due to pulse generation conditions or changes in the ink temperature during printing, but even if the spot size is intentionally changed, it does not reach a size useful for gradation printing. Then, basically, a predetermined spot size is maintained.

【0011】

Another way to improve print quality, especially gradation printing, is to use nozzles of different dimensions disclosed in US Pat. No. 5,745,131 of Kneezel et al., Cited and incorporated herein by reference. Figure 3 is an example of printing under US Pat. No. 5,745,131. In this figure, a pattern is printed using a printhead having a first plurality of openings 67 and a second plurality of openings 68, each aperture forming spots with diameters of 1.4S and 1.0S, respectively. As in the case of FIG. 2, the distance between the nozzles of the first plurality of openings 67 is a distance d, and the distance between each nozzle of the second plurality of openings 68 is also a distance d. The print grid shown in FIG. 3 has a distance S between pixel centers. In an inkjet printer, each nozzle of a plurality of openings is operated separately, and ink droplets are deposited on the grid points in the scanning direction. Compared with the method shown in FIG. 2 above, it is possible to fill the blank area slightly more effectively at least in terms of the amount of ink used. Between the first ellipse 64 and the second ellipse 66, there are 38 large ink droplet pixels and 16 small ink droplet pixels, which results in less total amount of ink actually used than in Figure 2. Nevertheless, the area between the first ellipse 64 and the second ellipse 66 is more extensively covered with ink. Since the number of nozzles in each of the first plurality of nozzles 67 and the second plurality of nozzles 68 is the same, it is possible to properly fill the blank area by advancing the paper by a distance of half the length of the print head.

【0012】

In addition to this, as various methods and devices for performing gradation printing by a thermal inkjet printer and other inkjet printers, there is creation of a gradation image by changing the ink droplet size. In this case, the ink droplet size is changed by changing the drive signal of the heat generating converter that generates the ink droplet, or by manufacturing a print head having a plurality of different size ink ejection openings.

【0013】

For example, U.S. Pat. No. 5,412,410 of Rezanka's invention discloses a printhead in which nozzles of different dimensions are alternately arranged for each dimension. As shown in FIG. 4, the print head 30 includes large nozzles 32 and relatively small nozzles 34 that are alternately arranged in a row. Each nozzle has a distance S between the centers, and the large and small nozzles have a distance of 2S between the centers. This configuration is effective for gradation printing, but on the other hand, there arises a problem that the amount of ink used increases and the amount of printing processing, that is, the processing speed becomes slow.

【0014】

Therefore, there is a need for an inkjet printing method capable of halftone printing, using a small amount of ink, and having a high processing speed.

【0015】

The present invention solves the above-mentioned problems by providing a printing method of a method of filling blank areas between pixels effectively and efficiently by using print heads having nozzles having different dimensions.

【0016】

[Means for solving problems]

According to the present invention, the printing method is a printing method in which ink droplets are ejected onto a printing substrate by using a printing head provided with a plurality of ink droplet ejectors having different dimensions, and printing is performed by the first printing path (1st printing path (1). The printing pass) activates the first dimension ink droplet ejector, the print head is displaced relative to the printing substrate, and the second printing path activates the second dimension ink droplet ejector. This includes a step of forming spots of different diameters aligned in the printing direction by the emitted ink droplets.

【0017】

As an application example using the present invention, for example, a method of operating an ink droplet ejector by ejecting ink droplets on a printing substrate using a print head provided with a plurality of ink droplet ejectors having different dimensions. However, the step of tilting the print head with respect to the normal direction of the scanning direction, the step of operating the ink droplet ejector of the first dimension in the first printing path, and the second dimension in the second printing path. Including a step of activating the ink droplet ejector of the ink droplet ejector so that the ejected ink droplets form spots having different diameters offset in a direction perpendicular to the scanning direction.

【0018】

Yet another application is, for example, a method of printing ink spots on a print medium using nozzles of at least two different dimensions in a printhead row that includes multiple channels extending in the longitudinal direction. , Each channel has a central axis in the longitudinal direction and an end formed by a nozzle that ejects ink droplets, and each nozzle is offset from the longitudinal axis of the channel connected to the nozzle and is adjacent. The mating nozzles are separated from each other on the opposite side of the adjacent channels, resulting in maximum spacing between adjacent nozzles on one side and minimum spacing between adjacent nozzles on the other side. The printing method is one in which the nozzle of the first dimension is operated in the first printing path, the step of advancing the printing medium by the distance of the odd number of the pixel, and the second in the second printing path. In the process of operating the nozzles of the same size, the nozzles of different sizes are operated in a zigzag pattern to shift the spot of the first size by 1/2 pixel in both directions with respect to the spot of the second size. Including the step of making.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

First, the present invention will be briefly described. Efficient gradation printing is performed by a print head using large and small ink droplet ejectors. The print head is arranged so that large and small nozzles are alternately and closely housed so that the maximum amount of blank space can be covered with the minimum amount of ink emitted. This print head can be operated in either one print path mode or two print path modes. In one print path mode, the odd-numbered jets are activated first, and then the even-numbered jets are activated to completely cover the blank area. Adjusting the position of the small spots with respect to the even numbered jets provides maximum coverage and corrects for misalignment between nozzle centers. It is also possible to operate printheads with nozzles of different dimensions by a staggered emission method using two print paths to offset the spots in the scanning direction. This offset can be obtained by displacing the printhead between the two paths, or by alternating large and small nozzle groups. The image quality can be further improved by displacing the spot in the direction perpendicular to the scanning direction. The displacement of the spot is obtained by tilting the printhead or offsetting the nozzle with respect to the channel on the printhead.

【0020】

FIG. 1 is a schematic partial perspective view of the inkjet printer 10. The printer 10 has an inkjet printing head cartridge 12 mounted on a carriage 14 supported by a carriage rail 16. The printhead cartridge 12 includes a housing 18 that houses ink to be supplied to the thermal inkjet printhead 20. The print head 20 selectively emits ink droplets based on the control of an electric signal received from the controller of the printer 10 through the electric cable 22. The print head 20 includes a plurality of ink channels, through which ink is transferred from the housing 18 to an ink ejector (such as an aperture or nozzle) for each channel.

【0021】

At the time of printing, the carriage 14 reciprocates, that is, scans in the direction of the arrow 24 along the carriage rail 16 in the front-back direction (left-right direction in the drawing). When the print head cartridge 12 reciprocates back and forth (in the left-right direction in the figure) across a recording medium 26 such as printing paper or transparency, ink droplets are directed from any of the selected print head nozzles toward the printing paper 26. Is released. The openings or nozzles that eject the ink are typically arranged in a row perpendicular to the scanning direction 24. The recording medium 26 is held in place while the carriage 14 passes once. After one passage of the carriage, the recording medium 26 is advanced in the direction of arrow 28 by the stepping mechanism under the control of the printer controller. This type of printing head and printing methods using it are described in detail in US Pat. No. 4,571,599 and US Reissue (Reissue) Pat. No. 32,572, which are cited and incorporated herein by reference.

【0022】

The carriage 14 is driven by a belt 38 attached to the carriage and moves in the left-right direction, which is the scanning direction. The belt 38 is driven by a first rotary pulley 40 and a second rotary pulley 42. The first rotary pulley 40 is driven by the reversing motor 44 under the control of the controller of the inkjet printer, and the carriage is further moved by the combination mechanism of the toothed belt and the pulley. The movement of the carriage can also be controlled using a combination of cable and capstan, a lead screw or any other mechanism known in the art.

【0023】

To control the movement and / or position of the carriage 14 along the carriage rail 16, the printer includes an encoder with an encoder strip 46, which contains a series of reference mark patterns 48. The pattern 48 is detected by the sensor 50, and the sensor 50 includes a combination of a photodiode and a light source attached to the print head cartridge 14. The sensor 50 includes a cable 52, through which an electrical signal representing the sensed reference mark pattern 48 is transmitted to the printer controller.

【0024】

The printer controller is one of any well-known control systems, and typically this controller selectively controls nozzle operation based on image information. A typical control system suitable for the present invention is shown in FIG. As shown in the figure, the printer controller, that is, the control system 120 includes the clock 122, and the output unit of the clock 122 is connected to the first counter (rom counter) 124. A second counter (ram counter) 126 is connected in series with the first counter 124. Clock 122 generates a series of clock pulses, which are sent to two counters connected in series. The printer controller 128 controls the first counter 124 and the second counter 126 from separate control lines.

【0025】

Further, the control system 120 includes a RAM 130, to which the data and input lines 132 and the read and write lines 134 connected to the controller 128 are connected. The RAM 130 receives data or input information from the printer interface, and the printer interface is connected to an image creation system such as a personal computer. The RAM 130 stores image information, and this image information includes the image information of the entire document or one line, or the image information of one time loaded on the print head. The output line 136 of the RAM 130 is connected to the ROM 137 containing the bitmap pattern to be printed. The stored bitmap pattern comprises a plurality of halftone cells consisting of alphanumeric characters for text printing or representing various gradation levels.

【0026】

During operation, the clock 122 generates a series of clock pulses, which are sent to the first counter 124 and then to the second counter 126. The second counter 126 transmits one word of information on the plurality of output lines 138. The word information on the plurality of output lines 138 is input to the RAM 130, and the part of the image to be printed is selected. Typically, the word information on output line 138 represents the address of the data stored in RAM. The data stored in RAM contains numbers from 1 to N. N is the number of different gradation levels printed.

【0027】

The first counter 124 includes a plurality of output lines 140 connected to the ROM 137. The counter 124 selects a particular portion of the pattern or halftone cell, which portion is loaded into the printhead based on the output 136 of the RAM 130. Output 136 represents the address of ROM 137 containing the bitmap pattern to be printed. When the first counter 124 selects a specific part of the bitmap pattern to be loaded, the ROM 137 outputs the required data on the first data line 142 connected to the printhead 20, large and small by the printhead 20. Spot is printed.

【0028】

As shown in FIG. 6, the print head 20 has ink droplet ejectors or nozzles of different dimensions in one print head die. The information output to the print head 20 is loaded by a shift register (not shown) in the print head. An example of the shift register and electronic circuit components for a printhead suitable for the present invention is described in US Pat. No. 5,300,968 of the Hawkins invention, which is incorporated herein by reference. After loading the data into the printhead 20, the information is latched while the next data string is loaded into the printhead 20, and ink is ejected from each nozzle. You can also load a few lines of data for each output of RAM 130. In this method, the printer controller 128 does not create a specific bitmap for each density level.

【0029】

FIG. 6 shows a suitable configuration of alternating large and small ink droplet ejectors, with large nozzles 70 arranged in a row adjacent to small nozzles 72 on the printhead. In this configuration, the small nozzles 72 are tightly housed between the first, i.e., the large nozzles 70, and the center points of the nozzles 70 are spaced at a distance S. Therefore, the distance between adjacent nozzle centers is S / 2. There is a distance O offset between the centers of adjacent nozzles. In the tight storage configuration in which the small nozzles are located in the gaps between the large nozzles, the nozzles can be operated in one printing path. Further, due to this close storage configuration, gradation display can be performed while maintaining high productivity. By using the mechanism that is assembled as a whole, for example, with a cycle number of 300dpi (dots / inch), high-quality gradation printing with higher image quality than 300x600dpi and faster than printing with a resolution of 600x600dpi is performed. Can be done.

【0030】

Preferably, for example, when S = 1/300 inch, the width of the large nozzle is at least 40 μm at the maximum, especially 50 μm, and the width of the small nozzle is at least 20 μm at the maximum. In particular, 25 μm is suitable. Channel land between nozzles Land) Sufficient sealing is achieved by providing a width of about 5 to 6 μm. For the triangular nozzle shown in FIG. 6, the width measurement is made at the bottom of the aperture. By combining a large nozzle with a width of 50 μm with low-viscosity ink and a resistance heater of appropriate size, between spots of one type of spot size, which are adhered to the printing substrate at 300 spi (spots / inch). The blank area is completely filled. At 300 spi, the distance S between nozzles of the same size is about 84.5 μm, and within this distance, a large nozzle of 50 μm and a small nozzle of 25 μm fit together. As a result, the center of the heater and the center of the channel are arranged at intervals of 600 spi, but the positions of the large spot and the small spot in one printing path can be used properly as desired. This operation is not possible in prior art configurations where large channels larger than 40-50 μm cannot be used in standard 600 spi printheads. The reason for this is that the center spacing of each channel is 42.3 μm and that the channels need to have a reliable seal.

【0031】

Generally, in a prior art device in which spots of one type of dimension are adhered, the spot dimension D is as shown in FIG. 7 (a) to ensure that adjacent spots in the 45 degree direction overlap. Is 2^1/2 S (ie 1.414S) or 2^1/2 Slightly larger than S. However, according to the tight storage configuration of the present invention, there are two spots to fill the blank area.^1/2 It is not necessary to increase to S. As shown in Fig. 7 (b), the large spot with a spot size of 1.1S and the small spot with a spot size of 0.8S further promote the covering effect, completely fill the blank area, and inaccurately adhere to the spot. Can also be tolerated. In this case, the area of the small spot is about half the area of the large spot. A combination of large and small spots of different dimensions is also possible, for example, as shown in FIG. 7 (c), there is a combination of a large spot of 1.2S and a small spot of 0.6S. In this case, the area of the small spot is about 1/4 of the area of the large spot. In each of the above configurations, small spots hardly protrude from the printing edge, and a high-quality printed image can be obtained. The protrusion of small spots can be ignored in whole or in part.

【0032】

The optimum large spot diameter D for completely covering the blank area with the minimum overlap is determined by the method shown in FIG. By this determination method, an efficient balance between the coverage and the amount of ink used, that is, the maximum range covered by the minimum amount of ink can be obtained. The balance becomes an important parameter in ink adhesion because there is a limit to the amount of ink used due to restrictions on the capacity of the print cartridge and the ink drying time required after printing. Reducing the amount of ink released speeds up ink refilling into the channel and enables faster printing than 300 x 600 spi printing with one type of spot size.

【0033】

An example of saving the amount of ink will be described. The total coverage area (including the overlap) of the four spot groups with a uniform standard spot size of 1.414S shown in Fig. 7 (a) is 2πS.²Is. On the other hand, in the case of the four spots with a diameter of 1.1S and the four spots with a diameter of 0.8S shown in Fig. 7 (b), the total coverage area is 1.85πS.²Is. In the case of the four spots with a diameter of 1.2S and the four spots with a diameter of 0.6S shown in Fig. 7 (c), the total coverage area is 1.8πS.²Is. This indicates that a considerable amount of ink can be saved when viewed on a page-by-page basis or as a printed document as a whole.

【0034】

The minimum size spot that can completely cover the blank area of the paper shown in the prior art example of FIG. 7 (a) is when all jets are completely aimed at the target and all spots have the same size. belongs to. In the examples of FIGS. 7 (b) and 7 (c), the range of overlap due to spots is wider than that of FIG. 7 (a), and as a result, there are spots that are slightly smaller or have slightly inaccurate orientation positions. However, the blank area is completely covered. Nevertheless, both of the examples shown in FIGS. 7 (b) and 7 (c) use less ink than in the prior art of FIG. 7 (a). A more accurate comparison of ink savings can be made by calculating the minimum total area of the two types of spots that can be completely covered and comparing the 1-spot dimensional configuration with the 2-spot dimensional configuration. ..

【0035】

For illustration, the diameter of the large spot in Figure 8 is D = aS (1.0 <a <2).^1/2), And the point of the common part of the three adjacent spots is x = 0.5S (a) from the line connecting the two center points.²-1)^0.5Suppose that it occurs at a distance of. In this case, the minimum radius of the small spot is r = 0.5S (1- (a)²-1)^0.5)become. In order to completely overlap the large and small spots, if the diameter of the large spot is 1.2S, the diameter (2r) of the small spot must be at least 0.34S. The total area of the four large spots and the four small spots is 2πS.²(a²-(a²-1)^0.5) = 1.553πS²become. If the diameter of the large spot is 1.1S, the diameter of the small spot must be at least 0.54S, and the total area in this configuration is 1.503πS.²become. By differentiating the area equation with a and setting the result to 0, the minimum total area has a large spot diameter of 1.25.^0.5It can be seen that S = 1.12S and the small spot diameter is 0.5S. The total area at this time is 1.5πS²Is. From this, it can be seen that ink is saved by 25% compared to D = 1.414S in the case of one type of spot diameter in Fig. 7 (a). In fact, in the case of small spots, the thickness of the adherend ink layer is thin, so the saving of ink droplet capacity is 25% or more.

【0036】

The optimal spot size combination with the lowest ink usage shown in the above calculation assumes that the spot positions are accurate and each spot size is perfectly uniform, but in actual printing. Then there are variations in both the spot position and the spot size. In order to compensate for this, prior art print heads having one type of spot size usually have the spot size slightly larger than the minimum spot size (about 10%). Correspondingly, the optimum combination of spot dimensions at the minimum ink usage in a print head with two types of spot dimensions is used in an actual printing environment including inaccuracies in orientation position and non-uniformity of spot dimensions. The range of suitable spot diameters is 1.12S-5% or more for large spots and 1.12S + 15% or less, and 0.5S-5% or more for small spots and 0.5S + 20% or less. Even in this case, it is clear that a certain amount of ink can form spots of different dimensions on different papers, and that the spot dimensions change due to the influence of the temperature of the inkjet printing head.

【0037】

In particular, printing by print heads with nozzles of different dimensions for gradation printing is performed within two print paths, and the print head is displaced by a distance of one pixel between the two paths to make large and small inks. Make sure that both drops cover the print grid. As shown in FIGS. 9 (a) and 9 (b), in this method, the large and small ink droplets are arranged on the same grid. Pixel displacement can be divided into two types of paper feed distances: one pixel distance from the left to the right path and (N-1) pixel distance from the right to the left path. It is done using. N is the total number of jets in the printhead.

【0038】

Also, if the total number of jets used is divisible by 2 and not divisible by 4, the pixels can be displaced using one type of paper feed distance. For example, if the printhead has 128 jets with alternating large and small channels, then only 126 jets are used. Therefore, the paper feed distance is the sum of 63 jet intervals. This allows large and / or small spots to be printed at any grid point position. The loss of print processing is only 2/128, which is less than 2%. It is also possible to print so that the print head paths are sewn together using auxiliary pixels.

【0039】

As shown in FIGS. 10 (a) and 10 (b), if the small ink droplets are offset in the horizontal (horizontal) direction by a distance of 1/2 pixel with respect to the large ink droplets, the gradation range Can be added further. This addition of the gradation range is obtained by emitting spots by the staggered emission method. By this emission method, all the large ink droplets are first emitted, and then the small ink droplets are emitted, so that the small ink droplets can be offset by a distance of 1/2 pixel. When printing with four jets at the same time with a print head with 128 jets, the jet emission order is 1,3,5,7; 9,11,13,15; ...; 121,123,125,127; 2,4,6. , 8; ...; 122,124,126,128. Printing of all large ink droplets takes place within half the time of the normal printing cycle centered on the ink droplets, and printing of small ink droplets is carried out by the print head moving across the paper by a distance of 1/2 pixel. It starts after you do. As a result, as shown in FIGS. 10 (a) and 10 (b), the ink droplets are automatically offset in the horizontal (horizontal) direction by a distance of 1/2 pixel.

【0040】

Another printing method using the staggered emission method is to operate a group of large and small nozzles alternately. In this method, large (odd) pixel strings and small (even) pixel strings are printed alternately. However, the large and small ink droplets are not adjacent to each other. A row of large ink droplets is first ejected, then the printhead is lowered to an intermediate position and then small ink droplets are ejected. The above procedure is repeated while alternately alternating large and small ink droplets and lowering the print head. After printing the lower row, the large or small nozzles rewrap around above the print head. When the print head is tilted by the distance of one pixel, the small ink droplets are automatically offset by the distance of 1/2 pixel. In this case, the nozzle openings are aligned along the bar, but due to the different nozzle heights, the arrangement is offset by offset O in the direction perpendicular to the scanning direction. This difference in the height of the nozzle center makes the position of the small ink droplet slightly inaccurate with respect to the large ink droplet. Since the difference in height is in the scanning direction, by slightly delaying or advancing the operation of the small ink droplet jet, the misalignment of the nozzle openings is compensated, and ink droplets of different dimensions are accurately covered. You can wear it. The misalignment is compensated by making the small pixels precede the large pixels by the staggered emission method.

【0041】

For example, if the nozzle dimensions are 25 and 50 μm, the difference in center height will be 12 μm (0.0005 inches). For a 300spi printer, running the jet at 6kHz would require a carriage speed of 20 inches per second. In the case of this print head, the difference in center height of 12 μm is compensated in about 25 μsec. Therefore, if the small nozzles are operated 25 μsec ahead or behind the large nozzles (depending on the orientation and scanning direction of the printhead), the pixel placement pattern of FIG. 11 (b), which represents a standard emission procedure, will be obtained. can get. This allows each of the large and small pixels to be placed on the same center. At that time, it is not necessary to emit adjacent pixels at the same time.

【0042】

In order to offset the large and small ink droplets by a distance of 1/2 pixel using any of the above zigzag ejection methods, adjacent small and large jets should be placed in the orientation and scanning direction of the printhead. Therefore, it is necessary to operate at intervals of 83 μsec (1/2 of the printing cycle) ± 25 μsec. This method can be applied to all types of printheads with large and small nozzles, and is not limited to printheads with alternating large and small nozzles.

【0043】

If the small ink droplets are offset in the direction perpendicular to the scanning direction in addition to the scanning direction, the image quality is further improved. As a result, the gradation printing function is enhanced, and the amount of ink required for complete coverage is significantly reduced. As shown in FIG. 11A, normally, by tilting the vertically oriented print head by θ = 45 degrees with respect to the scanning direction, offsets in both orthogonal directions can be generated. The resolution is further increased by increasing the tilt angle. The small spots are automatically offset in both directions by half the distance between the large spots and adhered. Slightly staggered operation of the large and small nozzles is necessary to compensate for the nozzle height offset in the scanning direction.

【0044】

The large nozzles have a distance S spacing on the print head. When the print head is tilted by 45 degrees, the spacing between the large printed spots is (S / 2) 2 as shown in Fig. 11 (b).^1/2become. In order to form large spots with an interval of 300 spi on paper, for example, it is necessary to place a large nozzle in the center at an interval of 84.5 × 1.414 = 119.5 μm and install a small nozzle in the middle.

【0045】

In addition to this, as another method of offsetting the small pixels at right angles to the scanning direction without tilting the print head, the small nozzles are installed off-center with respect to the channel as shown in FIG. 12 (a). May displace large and small ink droplets. For example, for a 300 spi printhead with an S of 84.5 μm, the channel diameter is 70 μm and the two nozzle dimensions are 20 μm and 40 μm, respectively. If the centers of each nozzle are maximally offset from each other, the spacing will be 45 μm. This interval is approximately equal to 1/2 of S. As shown in Fig. 12 (b) and Fig. 12 (c), by advancing the paper by the distance of the odd numbered pixels using two printing paths and then printing large and small ink droplets in a staggered pattern. In addition, the small ink droplets can be displaced with respect to the large ink droplets by a distance of 1/2 pixel in both directions.

【0046】

According to the present invention, it is also possible to operate a print head 20 having large and small nozzles arranged alternately so that printing can be performed in one printing path. The offset amount of the printed pixels (0.5S in the case of this embodiment) is set by the nozzle position. The offset is obtained by first activating all odd-numbered jets (large nozzles) and then all even-numbered jets (small nozzles). For example, if eight jets are activated at the same time, the order of operation in a printhead with 256 ink droplet ejectors (128 large ink droplets and 128 small ink droplets) is 1,3,5,7,9, 11,13,15; ... 241,243,245,247,249,251,253,255; 2,4,6,8,10,12,14,16; ... 242,244,246,248,250,252,254,256. All large ink droplets are printed within half the time of the normal printing cycle at the center of the ink droplets. Printing of small ink droplets begins after the printhead has traveled across the paper by half the distance of a pixel. By this method, the blank part is completely filled and the gradation display on one print head path becomes possible.

【0047】

The position of the small ink droplets can be adjusted by first operating the entire set of large ink droplets and then the entire set of small ink droplets. This feature is extremely useful because the positions of the long large channel centerline and the short small channel centerline are slightly different (only offset O). The offset of the center line can be corrected by delaying or leading the operation of the small channel group to the operation of the large channel group (depending on the scanning direction).

【0048】

The single pass method described above has the same processing speed as printing 300 × 600 spi with a print head having the same number of print cycles and the same dimensions. This difference in printing speed is such that while the above method operates two types of 128 jet sets, in the case of the 300 x 600 spi print head, the same 128 jet sets are 1/300 inch in the scanning direction. Based on being advanced and repeatedly operated twice. For a 600 x 600 spi printhead with the same print length (ie 256 jets) and the same number of cycles, the print processing speed is only half. The reason for this is that the feed distance in the scanning direction after all 256 jets have been activated is limited to 1/600 inches.

【0049】

In addition, applying different pulse generation conditions (pulse width and / or voltage) to the large and small ink droplet ejectors facilitates the sizing of the ejected ink droplets. Since large ink droplets are only activated by the large ink droplet ejector (small ink droplets are only operated by the small ink droplet ejector), there are two types of ink droplet ejector with different sized heaters with different resistors. Can be designed. Since an extremely large number of gradation levels can be obtained by a halftone cell in which various large and small spot dimensions are combined, a reproduced image with smooth image quality can be obtained by combining large and small spots.

【0050】

As yet another printing method, a plurality of printing paths are used to direct either large or small spots to each offset grid point on the print medium, and the small spot rows are aligned with the large spot rows as the print head advances. It may be applied continuously. In the case of this method, the processing speed is slower than that of the single print path method described above.

【0051】

Although the present invention has been described with reference to specific embodiments, it is clear that the prior art allows for many alternatives, modifications and modifications. For example, the present invention includes not only scanning carriage printers, but also partial width scanning print heads, page width print heads, full width array print heads, and the like. It is also possible to apply the present invention to a single-color print head or a segment-divided print head to print each color. Further, in the above-described embodiment, a side shooter type print head is used as an example, but it is clear that the present invention can be applied to a roof shooter type print head in which nozzles are arranged two-dimensionally. is there. Accordingly, the present invention includes all alternatives, modifications, and modifications within the appended claims. In addition, other purposes, effects, and features of the present invention will be clarified by the above description, especially the examination based on the attached figure.

[Simple explanation of drawings]

[Figure 1]

It is a schematic partial perspective view of the inkjet printer including this invention.

[Figure 2]

It is explanatory drawing which shows the position of the ink spot in the test pattern formed by the print head which has the ink discharge nozzle of the same size.

[Fig. 3]

It is explanatory drawing which shows the position of the ink spot in the test pattern formed by the print head which has the ink ejection nozzle of two different dimensions.

[Fig. 4]

It is a front view of a print head having nozzles of different dimensions arranged in an alternating form.

[Fig. 5]

It is a schematic block diagram of the control system by this invention.

[Fig. 6]

It is a schematic diagram of the nozzles of different dimensions arranged alternately by this invention.

[Fig. 7]

It is explanatory drawing which shows the pattern of the spot emitted from the print head which has the nozzle of the same size, and is explanatory drawing which shows the pattern of the spot which showed the pattern of the spot which was emitted from the print head which has the nozzle of a different size according to the present invention.

[Fig. 8]

It is a schematic diagram which shows the method of determining the optimum spacing and overlap condition between spots by this invention.

[Fig. 9]

It is a figure which shows the pattern of the spot formed in each of the 1st and 2nd printing paths by the staggered emission method by this invention.

[Fig. 10]

It is a figure which shows another pattern of the spot formed in each of the 1st and 2nd printing paths by the staggered emission method by this invention.

[Fig. 11]

It is explanatory drawing which shows the inclined printing head used in the ejection method by this invention, and is explanatory drawing which shows the pattern of the spot emitted by said printing head.

[Fig. 12]

A schematic diagram showing a group of nozzles of different dimensions alternately arranged according to the present invention and having nozzles offset with respect to the center of a channel connected to the nozzles, and the first and second groups according to the present invention. It is explanatory drawing which shows the pattern of the spot formed in each of the print paths.

[Explanation of symbols]

10 printers, 12 cartridges, 14 carriages, 20 print heads, 26 recording media, 70 large nozzles, 72 small nozzles, 120 printer controllers.