Method of correcting alignment error of array inkjet head

A system and method of correcting an alignment error of an array inkjet head having a plurality of head chips to print a main scanning line can include determining a reference head chip, printing a plurality of reference lines in the main scanning direction to be separated from one another at a reference interval in a sub-scanning direction using the reference head chip, and printing a plurality of test lines which can be offset by a multiple m, where m is an integer, of a test interval with respect to the reference interval using other head chips, and determining one of the plurality of test lines that matches any of the plurality of reference lines of each of the head chips, and determining an amount of offset of the determined test line as an amount of offset of each head chip.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2009-0001600, filed on Jan. 8, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field of the Invention

The present general inventive concept relates to a system and method of correcting an alignment error of an array inkjet printhead having a plurality of head chips, and more particularly to a method of correcting an alignment error in a sub-scanning direction.

2. Description of the Related Art

In general, inkjet image forming apparatuses form an image on paper transferred in a sub-scanning direction by ejecting ink from a shuttle type inkjet printhead that reciprocates in a main scanning direction. The inkjet printhead typically includes at least one inkjet head chip that includes a plurality of nozzles for ejecting ink and an ejection unit providing an ink ejection pressure.

Recently, an effort to enable fast printing by using an array inkjet printhead including a nozzle unit having a length in the main scanning direction corresponding to the width of paper, instead of the shuttle type inkjet printhead, has been made. However, the nozzle unit of the array inkjet printhead is difficult to be embodied in a single head chip. In general, the nozzle unit is embodied by arranging a plurality of head chips, each having a plurality of nozzles, in the main scanning direction. To obtain superior print quality, the head chips must be accurately aligned in the sub-scanning direction. Accordingly, when an offset in the sub-scanning direction is generated during the alignment of the head chips, the offset is directly reflected in a printed image. However, it is very difficult to arrange the head chips without an offset in the sub-scanning direction. Accordingly, the manufacturing costs rise to obtain accuracy in the alignment in the sub-scanning direction in a manufacturing process.

SUMMARY

Example embodiments of the present general inventive concept provide a method of correcting an error in a sub-scanning direction of head chips of an array inkjet printhead.

Example embodiments of the present general inventive concept provide a method of correcting an alignment error of an array inkjet head having a plurality of head chips to print a main scanning line, including determining a reference head chip, printing a plurality of reference lines in the main scanning direction to be separated from one another at a reference interval in a sub-scanning direction using the reference head chip, and printing a plurality of test lines which are offset by a multiple m, where m is an integer, of a test interval with respect to the reference interval using other head chips, and determining one of the plurality of test lines that matches any of the plurality of reference lines of each of the head chips, and determining an amount of offset of the determined test line as an amount of offset of each head chip.

The determining of the amount of offset of each head chip may include determining an amount of offset of a matching test line of a plurality of test lines of a preceding head chip closer to the reference head chip than a corresponding head chip and a plurality of test lines of a corresponding head chip as a relative offset amount of the corresponding head chip with respect to the preceding head chip, and determining a sum of the offset amount of the preceding head chip with respect to the reference head chip and the relative offset amount of the corresponding head chip with respect to the preceding head chip as an amount of offset of the corresponding head chip with respect to the reference head chip.

Assuming the resolution of the array inkjet head is R and a positive integer is n, the test interval may be represented as R/n.

The method may further include storing the offset amount in a memory of the array inkjet head as offset data.

Example embodiments of the present general inventive concept can also provide a method of correcting an offset of an inkjet head having a plurality of head chips, the method including selecting a reference head chip from among the plurality of head chips, printing a plurality of reference lines spaced apart from one another at a reference interval in a sub-scanning direction using the reference head chip, printing a plurality of test lines spaced apart from each other in the sub-scanning direction by a predetermined multiple of the reference interval using the other head chips, and determining an amount of offset of each of the other head chips relative to the reference head chip based on an amount of offset between the test lines and the reference lines.

The method may further include selecting one of the test lines which most closely matches a reference line of the reference head chip in the sub-scanning direction with respect to each of the other head chips, and determining the amount of offset of each of the other head chips relative to the reference head chip based on the reference interval of the matching reference line and the predetermined multiple of the matching test line with respect to each of the other head chips.

The method may further include selecting one of the test lines of a first other head chip which most closely matches a reference line of the reference head chip in the sub-scanning direction, determining the amount of offset of the first other head chip relative to the reference head chip by comparing the predetermined multiple of the selected test line with the reference interval of the matching reference line, and determining the amount of offset of the remaining other head chips based on an amount of offset between the test lines of the remaining other head chips and the selected test line.

The head chips may be arranged in at least one row along a main scanning direction, and a length of the at least one row may be greater than a width of the print media to be printed.

The method may further include scanning the test lines and the reference lines to determine the offset therebetween.

Example embodiments of the present general inventive concept can also provide an inkjet head to print ink on a printing medium, the inkjet head including a plurality of head chips including a reference head chip, and a controller to control the plurality of head chips to print a plurality of reference lines spaced apart from one another at a reference interval in a sub-scanning direction using the reference head chip, to print a plurality of test lines spaced apart from each other in the sub-scanning direction by a predetermined multiple of the reference interval using the other head chips, and to determine an amount of offset of each of the other head chips relative to the reference head chip based on an amount of offset between the test lines and the reference lines.

The controller can select one of the test lines which most closely matches a reference line of the reference head chip in the sub-scanning direction with respect to each of the other head chips, and can determine the amount of offset of each of the other head chips relative to the reference head chip based on the reference interval of the matching reference line and the predetermined multiple of the matching test line with respect to each of the other head chips.

The controller can select one of the test lines of a first other head chip which most closely matches a reference line of the reference head chip in the sub-scanning direction, can determine the amount of offset of the first other head chip relative to the reference head chip by comparing the predetermined multiple of the selected test line with the reference interval of the matching reference line, and can determine the amount of offset of the remaining other head chips based on an amount of offset between the test lines of the remaining other head chips and the selected test line.

The inkjet head can further include an optical reader to read the test lines and the reference lines.

Example embodiments of the present general inventive concept can also provide a computer readable medium having computer readable codes embodied thereon to execute a method of correcting an offset of an inkjet head having a plurality of head chips, the method including selecting a reference head chip from among the plurality of head chips, printing a plurality of reference lines spaced apart from one another at a reference interval in a sub-scanning direction using the reference head chip, printing a plurality of test lines spaced apart from each other in the sub-scanning direction by a predetermined multiple of the reference interval using the other head chips, and determining an amount of offset of each of the other head chips relative to the reference head chip based on an amount of offset between the test lines and the reference lines.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a plan view of an array inkjet printhead100using a method of correcting an alignment error according to an embodiment of the present general inventive concept. Referring toFIG. 1, the array inkjet printhead100can be embodied by arranging a plurality of head chips10in a main scanning direction. The overall length L of the head chips10in the main scanning direction can be greater than the width of the paper to be printed.

The head chip10can have a structure capable of ejecting ink supplied from an ink tank (not illustrated) through a nozzle1by applying pressure to the ink using a predetermined ejection unit (not illustrated). The ejection unit may be a heater (not illustrated) to eject ink by applying heat to the ink in an ink chamber (not illustrated) to generate air bubbles, although the present general inventive concept is not limited thereto. For example, it is possible that the ejection unit may be a piezoelectric body (not illustrated). In such case, the ink may be ejected through the nozzle1due to a change in the volume of the ink in the ink chamber which can be generated by the deformation of the piezoelectric material. Since the principle of ejecting ink of a head chip is well known in the field to which the present general inventive concept pertains, a detailed description thereof will be omitted herein to prevent the general inventive concept from being obscured in unnecessary detail.

Referring toFIG. 5, the head chips10may be arranged linearly in a main scanning direction. In this case, a last nozzle1aof a leading head chip10band a first nozzle1bof a next head chip10ccan be arranged accurately at an interval of resolution R in the main scanning direction. However, when the head chips10are arranged in the main scanning direction in a row, it can be very difficult to satisfy this condition.

Thus, as illustrated inFIG. 1, the head chips10can be arranged in two head chip rows21and22separated from each other in a sub-scanning direction that is perpendicular to the main scanning direction. Here, the head chips10in the head chip rows21and22can be arranged zigzag, which is to say that the last nozzle of a leading head chip and the first nozzle of a next head chip may be arranged accurately at an interval of resolution R in the main scanning direction. There may be a print characteristic between the head chips10, for example, a slight difference in the size of an ink drop that is ejected. To reduce a difference in images printed by the head chips10, the head chips10may be arranged such that the nozzles of the adjacent head chips may be partially overlapped with one another as indicated by a dotted line C ofFIG. 1. AlthoughFIG. 1illustrates the array inkjet printhead100having two head chip rows21and22, the present general inventive concept is not limited thereto. For example, it is possible that three or more head chip rows may be provided without departing from the broader principles and spirit of the present general inventive concept.

Referring again toFIG. 1, each of the head chips10can include a nozzle row2and a plurality of nozzles1can be arranged zigzag in the nozzle row2. The interval between the nozzles that are most adjacent in the main scanning direction represents the resolution R.

As illustrated inFIG. 2, in an array inkjet printhead100ato print a color image, four nozzles rows2a,2b,2c, and2dmay be provided in a head chip10a. In this case, for example, the nozzles rows2a,2b,2c, and2dmay respectively eject ink of black (K), yellow (Y), magenta (M), and cyan (C) colors.

FIG. 3illustrates the structure of an inkjet image forming apparatus using the array inkjet printhead100aofFIG. 2. Referring toFIG. 3, four ink tanks70K,70Y,70M, and70C respectively containing ink of black (K), yellow (Y), magenta (M), and cyan (C) colors can be connected to four nozzle rows2a,2b,2c, and2dof the head chip10ato form the array inkjet printhead100a. Negative pressure regulators71K,71Y,71M, and71C may be interposed between the ink tanks70K,70Y,70M, and70C and the array inkjet printhead100ato adjust the negative pressure of ink and prevent the intrusion of air bubbles into the array inkjet printhead100aand unnecessary leakage of ink by maintaining meniscus of the nozzle1. The inkjet image forming apparatus can include a controller300to control the array inkjet printhead100ato print ink to a printing medium, such as paper, and an optical reading apparatus400, such as a scanner, to read the images printed on the printed medium.

The paper drawn from a paper feeding cassette110by a pickup roller120can be transferred in the sub-scanning direction by a transfer roller130. The paper can maintain a predetermined interval, for example, 0.5-2.0 mm, from the head chip10aof the array inkjet printhead100aby a platen140. The array inkjet printhead100aat a fixed position can print an image on the paper by ejecting ink. After printing, the paper can be exhausted to a paper stacking plate160by an exhaust roller150.

Referring toFIG. 1, when the head chips10are arranged in rows21and22, the interval W between the head chip rows21and22in the sub-scanning direction remains constant. Also, the head chips10in each of the head chip rows21and22are aligned without an offset in the sub-scanning direction. When these conditions are met, an image printed by the head chip row21and an image printed by the head chip row22may be accurately matched to each other. However, it is costly to perform a fine adjustment in the manufacturing process of the array inkjet printhead to maintain such alignment during the manufacturing process. Thus, in accordance with the present general inventive concept it is possible to reduce the manufacturing costs and improve productivity by providing a system and method of correcting an alignment error of the head chips10in order to maintain high print quality of the printed image while at the same time lowering the manufacturing tolerances and alignment accuracy of the head chips10to reduce manufacturing costs.

FIG. 4illustrates a method of correcting an alignment error according to an embodiment of the present general inventive concept. Referring toFIGS. 1 and 4, a method of correcting an alignment error according to an embodiment of the present general inventive concept is described below.

Referring toFIGS. 1 and 4, any one of a plurality of head chips11-16can be selected as a reference head chip. In the present example embodiment, the head chip13located at the center of the head chips11-16is selected as a reference head chip, although it is possible that any head chip may be selected as the reference head chip without departing from the present general inventive concept.

Next, a plurality of reference lines50separated from one another at a reference interval Dr in the sub-scanning direction can be printed using the reference head chip13. Here, the reference interval Dr is not limited to any particular value, and it is possible that any interval may be set, for example, to a value where the reference lines50can be identified with the naked eye.

As the reference lines50are printed, the other head chips11,12,14, and15can simultaneously print a plurality of test lines61,62,64, and65, respectively. Here, the test lines61,62,64, and65can be printed by being offset by an integer multiple m of a test interval Dt with respect to the reference interval Dr in the sub-scanning direction. That is, as illustrated inFIG. 4, five test lines62can be printed by being offset as much as −2 Dt, −1 Dt, −0 Dt, 1 Dt, and 2 Dt with respect to the reference interval Dr. InFIG. 4, the numbers “−2, −1, 0, +1, and +2” respectively denote offsets of −2 Dt, −1 Dt, −0 Dt, 1 Dt, and 2 Dt.

The test interval Dt may be, for example, a value obtained by dividing the resolution R of the array inkjet printhead100by a positive integer n. For example, when the array inkjet printhead100is capable of printing at 1200 dpi (dot per inch), the resolution R is about 21.5 μm. In this case, when the positive integer n is 2, the test interval Dt can be an integer multiple of about 10 μm and an alignment error may be corrected at an interval of about 10 μm. As the positive integer n increases, an interval to correct an alignment error decreases so that the alignment error may be corrected more accurately.

According to an example embodiment of the present general inventive concept, one of the test lines62of the head chip12that matches one of the reference lines50can be sought for. This process may be carried out using the naked eye. Also, the matching test line may be sought for by reading the test lines62and the reference lines50using an optical reading apparatus400(FIG. 3) such as an image scanner. InFIG. 4, for example, the test line62printed by being offset by +1 Dt as indicated by a circle A can be determined to match the reference line. Thus, the amount of the offset in the sub-scanning direction with respect to the reference head chip13of the head chip12can be determined to be +1 Dt. This means that the head chip12can be arranged by being offset by +1 Dt in the sub-scanning direction with respect to the reference head chip13in a manufacturing process. Accordingly, by delaying the ink ejection timing of the head chip12by 1 Dt during printing, printing without an offset from the reference head chip13may be possible, even though an alignment error occurs during manufacturing of the head chip. The amount of offsets of the other head chips11,14,15, and16may be determined in a similar manner.

It is also possible that the determined amounts of offsets of head chips may be stored in a memory (not illustrated), for example, customer replaceable unit monitor (CRUM), of the array inkjet print head100as offset data. For example, in an inkjet image forming apparatus having the array inkjet printhead100, printing with a corrected alignment error may be performed by controlling the ink ejection timing of each of the head chips10by using the stored offset data. Alternatively, the offset data may be stored in a memory (not illustrated) of an inkjet image forming apparatus having the array inkjet printhead100.

As described above, the alignment error in the sub-scanning direction of the head chips generated in the manufacturing process may be corrected by the alignment error correction method according to an example embodiment of the present general inventive concept. When the alignment error correction method is used, the accuracy in the alignment of the head chips10may be reduced in the manufacturing process of the inkjet printhead100. Thus, the manufacturing costs and print defects due to the alignment error of the head chips may be reduced so that superior print quality may be obtained.

In accordance with another example embodiment of the present general inventive concept, it is possible that the amount of offset of each head chip may be obtained as follows. For example, when the amount of offset of the head chip11is determined, after determining the amount of offset of the head chip12located closer to the reference head chip13and preceding the head chip11, as described above, a relative offset amount of the head chip11with respect to the preceding head chip12can be obtained. In this case, the sum of the relative offset amount of the head chip11with respect to the preceding head chip12and the offset amount of the preceding head chip12with respect to the reference head chip13can be an amount of offset of the head chip11with respect to the reference head chip13. For example, it is possible to determine that the amount of offset of the preceding head chip12with respect to the reference head chip13is +1 Dt. Next, one of the test lines61of the head chip11that matches any of the test lines62of the head chip12can be sought for. As illustrated inFIG. 4, one of the test lines61of the head chip11that is offset by −1 Dt can be determined to match one of the test lines62of the preceding head chip12, as indicated by a circle B. In this case, the relative offset amount of the head chip11to the preceding head chip12can be determined to be −Dt. The offset amount of the head chip11relative to the reference head chip13can thus be determined to be 0 (+1 Dt+(−Dt)=0). The same process may be applied to the other head chips14,15, and16.