Printhead, scanning type inkjet image forming apparatus having the same, and method of performing a printing operation with high resolution

A printhead, a scanning type inkjet image forming apparatus having the same, and a method of performing a printing operation with a high resolution. Separate N nozzle units are disposed in the printhead such that images can be printed with higher resolution. In addition, the printing operation can be performed with an actual resolution or a higher resolution while a print medium is fed at a uniform speed such that the printing speed can be increased when the printing operation is performed with the higher resolution. In addition, when a portion of nozzles of a first nozzle unit is damaged or is malfunctioning, the portion of the nozzles is compensated for using a second nozzle unit such that an image quality is not affected by a defective nozzle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2005-44464, filed on May 26, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to an inkjet image forming apparatus, and more particularly, to a scanning type inkjet image forming apparatus which performs a printing operation with high resolution.

2. Description of the Related Art

Scanning type inkjet image forming apparatuses eject ink from a printhead that is reciprocated in a direction that is perpendicular to a feeding direction of a print medium while being spaced apart from a top side of the print medium by a predetermined gap, thereby forming an image. Printing quality is a very important factor in inkjet image forming apparatuses. Thus, the scanning type inkjet image forming apparatuses perform a printing operation using a shingling process, so as to improve printing quality. Here, the shingling process is a technique in which printing is repeatedly and overlappingly performed while finely moving a printing position of the printhead.

In an effort to enhance the printing quality, U.S. Pat. No. 4,999,646 describes a conventional shingling process performed by an image forming apparatus.FIG. 1illustrates dot patterns printed with the conventional shingling process. As illustrated inFIG. 1, a predetermined portion of dot patterns is overlappingly printed using one nozzle unit during a first scanning operation and second scanning operation to enhance uniformity and consistency of dots deposited on a print medium. In this case, a feeding speed and a printing speed of the print medium are substantially reduced. In addition, when portions of nozzles are damaged or certain nozzles are malfunctioning, and a printing operation is performed in a normal mode (i.e., without using the shingling process), a portion of the print medium that corresponds to the portions of the nozzles that are damaged or the malfunctioning nozzles is not printed. As a result, printing defects such as a white line (or the like) may occur.

In the above-described conventional image forming apparatus, a high-speed printing operation cannot be performed. Thus, a scanning type inkjet image forming apparatus having an improved structure to perform high-speed printing operation is needed.

SUMMARY OF THE INVENTION

The present general inventive concept provides a scanning type inkjet image forming apparatus having a high printing resolution and a method of performing a printing operation with the high printing resolution

The present general inventive concept also provides a scanning type inkjet image forming apparatus which increases a printing speed when performing a printing operation with a high resolution and a method of performing a printing operation with the high resolution.

The present general inventive concept also provides a scanning type inkjet image forming apparatus which prevents deterioration of printing quality by compensating for damaged portions of nozzles and/or malfunctioning nozzles, and a method of performing a printing operation with a high resolution.

The foregoing and/or other aspects of the present general inventive concept are achieved by providing a scanning type printhead movable along a main scanning direction, the printhead including N nozzle units having a plurality of nozzles arrayed in a subsidiary scanning direction perpendicular to the main scanning direction such that N nozzle units are adjacent to one another in a subsidiary scanning direction, and the N nozzle units being disposed such that a distance along the subsidiary scanning direction between centers of nozzles of the adjacent nozzle units is about D×M+D/N from a nozzle unit disposed at a first end of the printhead to a nozzle unit disposed at a second end of the printhead, where M is a predetermined integer and D is a nozzle pitch.

Each of the N nozzle units may be spaced apart from one another in the subsidiary scanning direction by a predetermined gap.

Each of the N nozzle units may include the same number of nozzles.

The N nozzle units may be disposed such that a distance along the main scanning direction between centers of the nozzles of the adjacent nozzle units is about d×L+d/N from the first end nozzle unit to the second end nozzle unit, where L is a predetermined integer and d is a diameter of a nozzle.

The N nozzle units may include a first nozzle unit and a second nozzle unit.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a scanning type printhead movable along a main scanning direction, the printhead including N nozzle units having a plurality of nozzles arrayed in a subsidiary scanning direction perpendicular to the main scanning direction, and the N nozzle units being disposed such that a distance along the main scanning direction between centers of nozzles of the nozzle units that are adjacent to each other is about d×L+d/N from a nozzle unit disposed at a first end of the printhead to a nozzle unit disposed at a second end of the printhead, where L is a predetermined integer and d is a diameter of a nozzle.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a scanning type inkjet image forming apparatus, including a printhead movable in a main scanning direction and including N nozzle units having a plurality of nozzles arrayed in a subsidiary scanning direction, a print medium-feeding unit to feed a print medium in the subsidiary scanning direction, and a controller to synchronize an ejection operation of the printhead and a feeding operation of the print medium-feeding unit such that ink ejected from the printhead is deposited at a desired position of the print medium, wherein the N nozzle units are disposed such that a distance along the subsidiary direction between centers of nozzles of the nozzle units that are adjacent to each other is about D×M+D/N from a nozzle unit disposed at a first end of the printhead to a nozzle unit disposed at a second end of the printhead, where M is a predetermined integer and D is a nozzle pitch.

The N nozzle units may include a first nozzle unit and a second nozzle unit.

The scanning type inkjet image forming apparatus may further include a printing environment information unit to store information about a printing resolution when a printing operation is performed with a predetermined resolution, and the controller operates the first and second nozzle units according to the printing resolution stored in the printing environment information unit.

The controller may perform a first scanning operation including a printing operation using the first nozzle unit with an actual resolution and feed the print medium by a width of the first nozzle unit before performing a second scanning operation including another printing operation using the first nozzle unit.

The controller may perform a first scanning operation including a printing operation using the first nozzle unit and the second nozzle unit with a higher resolution and feed the print medium by a width of the first nozzle unit before performing a second scanning operation including another printing operation using the first nozzle unit and the second nozzle unit.

The width of the first nozzle unit may be the same as a width of the second nozzle unit.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a method of performing a printing operation with a high resolution in a scanning type inkjet image forming apparatus including a first nozzle unit and a second nozzle unit having a plurality of nozzles arrayed in a subsidiary scanning direction, and the first nozzle unit and the second nozzle unit are disposed such that a distance between centers of nozzles of the first and second nozzle units is D×M+D/2, where M is a predetermined integer and D is a nozzle pitch, the method including receiving a resolution input from a host, comparing the input resolution with an actual resolution of a printhead including the first and second nozzle units, ejecting ink onto a print medium to print an image, determining whether a printing operation has been completely performed, and if the printing operation has not been completely performed, ejecting ink onto the print medium after the print medium is fed by a predetermined distance in the subsidiary scanning direction.

The ejecting of the ink and the determining of whether the printing operation is complete may include, if the input resolution is higher than the actual resolution of the printhead, performing the printing operation using the first nozzle unit and the second nozzle unit; and if the input resolution is the same as the actual resolution of the printhead, performing the printing operation using the first nozzle unit.

The ejecting of the ink onto the print medium after the print medium is fed by the predetermined distance in the subsidiary scanning direction may include feeding the print medium by a width of the first nozzle unit.

The width of the first nozzle unit may be the same as a width of the second nozzle unit.

The comparing of the input resolution with the actual resolution of the printhead may include sensing whether a defective nozzle exists in the first nozzle unit. Additionally, the ejecting of the ink onto the print medium may include compensating for the defective nozzle using nozzles of the second nozzle unit that correspond to the defective nozzle when the defective nozzle exists in the first nozzle unit.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a printhead movable along a main scanning direction of an image forming apparatus, the printhead including at least one nozzle unit extending along a subsidiary direction that is perpendicular to the main scanning direction. The at least one nozzle unit includes a first sub nozzle unit disposed at a first end of the at least one nozzle unit in the subsidiary scanning direction to eject ink of a predetermined color and having a first plurality of nozzles extending along the subsidiary scanning direction from the first end of the at least one nozzle unit toward a middle of the at least one nozzle unit, and a second sub nozzle unit disposed at a second end of the at least one nozzle unit in the subsidiary scanning direction opposite to the first end to eject ink of the predetermined color and having a second plurality of nozzles extending along the subsidiary scanning direction from the second end of the nozzle unit toward the middle of the at least one nozzle unit.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a printhead unit, including a carriage that is movable along a first direction with respect to a print medium, and a printhead supported by the carriage and having two or more nozzle units extending along a second direction perpendicular to the first direction to eject ink of the same color to the same portion of the print medium.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a printhead unit, including a carriage movable along a main scanning direction of a print medium, and the main scanning direction is perpendicular to a subsidiary scanning direction along in which the print medium is conveyed, and a printhead having at least first and second nozzle units each having a plurality of nozzles arranged along the subsidiary scanning direction such that the first nozzle unit prints to the print medium in a first operation mode, and the first and second nozzle units print to the print medium in a second operation mode.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing an image forming apparatus, including a printhead unit having a carriage that is movable along a first direction, and a printhead supported by the carriage and having two or more nozzle units extending along a second direction that is perpendicular to the first direction to eject ink of a predetermined color that is the same to a predetermined portion of a print medium that is the same.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing an image forming apparatus, including a carriage type printhead having an actual resolution and being moveable in a first direction and having at least two nozzle units disposed adjacent to each other along a second direction perpendicular to the first direction, and a controller to receive information about a selected printing resolution, to compare the selected printing resolution with the actual resolution, to control one of the nozzle units to print when the selected printing resolution is the same as the actual resolution, and to control each of the at least two nozzle units to print when the selected printing resolution is greater than the actual resolution.

The foregoing and/or other aspects of the present general inventive concept are also achieved by providing a method of controlling a printhead unit having a carriage that is movable along a first direction with respect to a print medium and a printhead supported by the carriage and having two or more nozzle units extending along a second direction perpendicular to the first direction to eject ink of the same color to the same portion of the print medium, the method including performing a first printing operation in which a first nozzle unit prints to a first portion of the print medium, and performing a second printing operation in which the first nozzle unit prints to a second portion of the print medium while a second nozzle unit prints to the first portion of the print medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A printhead, a scanning type inkjet image forming apparatus having the same, and a method of performing a printing operation with high resolution according to exemplary embodiments of the present general inventive concept will now be described with reference to the accompanying drawings. For a better understanding of the description, the entire structure of the scanning type inkjet image forming apparatus will be first described and then the method of performing a printing operation with high resolution according to the exemplary embodiments of the present general inventive concept will be described. The thicknesses of lines or the sizes of components shown in the drawings are exaggerated for a better understanding of the description.

FIG. 2is a schematic view illustrating a scanning type inkjet image forming apparatus according to an embodiment of the present general inventive concept. Referring toFIG. 2, the scanning type inkjet image forming apparatus includes a paper feeding cassette120, a printhead unit105, a support member114that faces the printhead unit105, print medium-feeding units113,115,116, and117that feed a print medium P in a subsidiary scanning direction, and a stacking unit140on which discharged print medium P is stacked. The printhead unit105includes a body110, a carriage106, a printhead111disposed a bottom surface of the body110having a nozzle unit112.

The print medium P is stacked on the paper feeding cassette120. The print medium P stacked on the paper feeding cassette120is fed to the printhead111by the print medium-feeding units113,115,116, and117, which will be described later. InFIG. 2, the print medium P is fed in an x-direction which is the subsidiary scanning direction, and the printhead111moves in a y-direction which is a main scanning direction. The subsidiary scanning direction and the main scanning direction may be perpendicular to each other. Alternatively, the subsidiary scanning direction and the main scanning direction may be inclined at a predetermined angle.

The print medium-feeding units113,115,116, and117feed the print medium P stacked on the paper feeding cassette120along a predetermined path. InFIG. 2, the print medium-feeding units113,115,116, and117include a pickup roller117, feeding rollers115and116, and a paper discharging roller113. The print medium-feeding units113,115,116, and117are driven by a driving source131, such as a motor and provide a force to transfer the print medium P. The operation of the driving source131is controlled by a controller130, which will be described later.

The pickup roller117is installed at one side of the paper feeding cassette120and picks up the print medium P stacked in the paper feeding cassette120sheet by sheet, thereby drawing the print medium P from the paper feeding cassette120. The pickup roller117is rotated while pressing a top side of the print medium P, thereby feeding the print medium P out of the paper feeding cassette120.

The feeding roller115is installed at an inlet side of the printhead111and feeds the print medium P picked up by the pickup roller117to the printhead111. In this case, the feeding roller115can also align the print medium P so that ink can be ejected onto a desired portion of the print medium P before the print medium P passes under the printhead111. The feeding roller115includes a driving roller115A that provides a force to transfer the print medium P, and an idle roller115B elastically engaged with the driving roller115A. A pair of feeding rollers116(e.g., auxiliary rollers) that feed the print medium P can be further installed between the pickup roller117and the feeding roller115.

The paper discharging roller113is installed at an outlet side of the printhead111and discharges the print medium P, on which a printing operation has been completed, out of the image forming apparatus. The print medium P discharged out of the image forming apparatus is stacked on the stacking unit140. The paper discharging roller113includes a star wheel113A installed along a widthwise direction of the print medium P, and a support roller113B that faces the star wheel113A and supports a rear side of the print medium P. The printhead111makes a reciprocating motion in the main scanning direction to eject ink on the top side of the print medium P. When the top side of the print medium P is wet by ink, the print medium P may wrinkle. If wrinkling is severe, the print medium P may contact the nozzle unit112or the bottom surface of the body110, undried ink may be spread on the print medium P, and an image printed thereon may be contaminated or smeared. In addition, due to the wrinkling, there is a high probability that a distance between the print medium P and the nozzle unit112may not be maintained. The star wheel113A is used to prevent the print medium P fed underneath the nozzle unit112from contacting the nozzle unit112or the bottom surface of the body110and to prevent the distance between the print medium P and the nozzle unit112from varying. At least a part of the star wheel113A is installed to protrude further than the nozzle unit112and makes point contact with the top side of the print medium P. According to the above structure, the star wheel113A makes point contact with the top side of the print medium P so that an image formed by ink that has been ejected on the top side of the print medium P and has not dried yet, is prevented from being contaminated or smeared. Alternatively, a plurality of star wheels may be installed so as to feed the print medium P smoothly. When the plurality of star wheels are installed to be parallel to the feeding direction of the print medium P, a plurality of support rollers that correspond to the star wheels may also be provided.

In addition, when printing is consecutively performed on more than one sheet of the print medium P, the print medium P is discharged and stacked on the stacking unit140and then, a next sheet of the print medium P is discharged before ink ejected on the top side of a current sheet of the print medium P is dried, and a rear side of the next sheet of the print medium P may be contaminated. To prevent this problem from occurring, an additional drying device (not shown) may be further provided.

The support member114is disposed below the printhead111so that a predetermined distance between the nozzle unit112and the print medium P is maintained, and supports the rear side of the print medium P. The predetermined distance between the nozzle unit112and the print medium P may be about 0.5-2.5 mm.

A sensing unit132senses whether a defective (or malfunctioning) nozzle exists in the nozzle unit112disposed under the printhead111. Here, the defective (or malfunctioning) nozzle may include a damaged nozzle, a missing nozzle, or a weak nozzle that cannot eject ink properly. That is, the defective nozzle exists when ink is not ejected from nozzles due to several causes, or when less than a normal amount of ink is ejected from a nozzle.

The sensing unit132may be installed to sense whether a defective nozzle exists in the nozzle unit112before the printing operation begins, or while the printing operation is being performed. Thus, the sensing unit132may include a first sensing unit132A that senses whether a defective nozzle exists in the nozzle unit112before the printing operation starts, and a second sensing unit132B that senses whether a defective nozzle exists in the nozzle unit112during the printing operation. The first sensing unit132A senses whether nozzles are clogged by radiating light directly onto the nozzle unit112, and the second sensing unit132B senses whether a defective nozzle exists in the nozzle unit112by radiating light onto the print medium P. The structure and operation of the first sensing unit132A may be similar to the structure and operation of the second sensing unit132B. Thus, for explanation purposes, only the structure and operation of the second sensing unit132B will be described here.

In general, a printhead of an inkjet image forming apparatus can be classified according to an actuator that provides an ejecting force to ink droplets. A first type of printhead is a thermal driving printhead that generates bubbles in the ink using a heater, thereby ejecting the ink droplets due to an expansion force of the bubbles. A second type of printhead is a piezoelectric driving printhead that ejects ink droplets using a pressure applied to the ink due to deformation of a piezoelectric device. When the ink is ejected using the thermal driving, the case in which (1) a heater that operates to eject the ink is short-circuited, (2) a driving circuit of the heater breaks down, and (3) defects of nozzles result from damage of electrical components such as a field emission transistor (and the like) can be easily sensed. Similarly, when ink is ejected using the piezoelectric driving, (1) defects of a piezoelectric device and (2) defects of nozzles that results from damage of a driving circuit that drives the piezoelectric device also can be easily sensed. The defects of the nozzles that result from the above causes can be sensed by the first sensing unit132A before the printing operation is commenced.

On the other hand, the causes of a defective nozzle may not be easily sensed when the nozzle is clogged with foreign matters. When the causes of a defective nozzle cannot be easily sensed, a test page should be printed. If a defective nozzle exists in the nozzle unit112, a print concentration of a portion of the print medium P that corresponds to the defective nozzle is lower than a portion of the print medium P printed by a normal (i.e., functioning) nozzle, due to missing dots on the print medium P. Since the portion of the print medium P having the lower print concentration can be sensed by the second sensing unit132B, a position of the defective nozzle can be sensed using the second sensing unit132B. That is, the defective nozzle can be sensed using the above-described methods both while printing a test page printing and/or while performing an actual image printing operation.

An optical sensor may be used as the second sensing unit132B. For example, the optical sensor may include a light-emitting part (not shown), such as a light emitting diode that radiates light onto the print medium P, and a light-receiving sensor (not shown) that receives light reflected from the print medium P. An output signal from the light-receiving sensor is input to the second sensing unit132B. The second sensing unit132B senses whether a defective nozzle exists in the nozzle unit112in response to the output signal, and information about whether the defective nozzle exists in the nozzle unit112is transmitted to the controller130. Accordingly, the sensing unit132senses whether the defective nozzle exists in the nozzle unit112using the above-described operations and/or processes. Here, the light-emitting part and the light-receiving sensor may be formed as a single body, or may be formed as separate components. The structure and operation of the optical sensor is should be known to those skilled in the art to which the present general inventive concept pertains, and thus, a detailed description thereof will not be provided here.

The printhead unit105prints an image by ejecting ink onto the print medium P. The printhead unit105includes the body110, the printhead111disposed on the bottom surface of the body110, the nozzle unit112disposed under the printhead111, and the carriage106on which the body110is mounted. The body110having the printhead111is mounted in a cartridge shape on the carriage106, and a carriage moving unit142, which will be described later, reciprocates the carriage106. The feeding roller115is installed at an inlet side of the nozzle unit112, and the paper discharging roller113is installed at an outlet side of the nozzle unit112. In addition, a cable may be connected to each of the nozzles in the nozzles unit112to transmit a driving signal generated by the controller130, a power used to eject ink, print data, and the like. In this case, a flexible cable such as a flexible printed circuit (FPC) or a flexible flat cable (FFC) may be used.

FIG. 3Ais a bottom side view illustrating the printhead111of the image forming apparatus ofFIG. 2, according to an embodiment of the present general inventive concept, andFIGS. 3B and 3Care bottom side views illustrating the printhead111of the image forming apparatus ofFIG. 2, according to another embodiment of the present general inventive concept. For explanation purposes, like reference numerals represent like elements having similar structure and operation. However, it should be understood that these embodiments may be different from one another in various respects, and that the image forming apparatus ofFIG. 2may use any one of these embodiments and/or other embodiments that achieve the purposes set forth herein. Additionally, the nozzle unit112illustrated inFIGS. 3A to 3Cmay include sub-nozzle units1121,1122, etc. The printhead111may include a plurality of nozzle units112arranged adjacent to one another along the main scanning direction such that the printhead111includes sub-nozzle units extending along both the main and subsidiary scanning directions. For purposes of explanation, the sub-nozzle units1121,1122, etc. are simply referred to as “nozzle units”1121,1122, etc.

The printhead111includes N nozzle units112disposed in a subsidiary scanning direction (x-direction). The printhead111makes a reciprocating motion in the main scanning direction (y-direction) and prints an image by ejecting ink onto the print medium P that is fed in the subsidiary scanning direction (x-direction). The printhead111uses thermal energy, a piezoelectric device, or the like, as a power source to eject the ink, and the printhead111may be manufactured to have a high actual resolution using semiconductor manufacturing processes including, for example, etching, deposition, sputtering, and/or the like.

A plurality of nozzles that print the image by ejecting the ink onto the print medium P are arrayed in each of the N nozzle units112. Each of the N nozzle units112may overlap with one another in either direction to improve resolution. In addition, each of the N nozzle units112may include the same number of nozzles. That is, the width (in the subsidiary scanning direction) of each of the N nozzle units112may be the same. The ejection operation of the N nozzle units112is controlled by the controller130.FIGS. 3A through 3Cillustrate the printhead111to eject one color. However, it should be understood that these embodiments are exemplary and that the present general inventive concept is not limited to these arrangements. A color printhead that ejects two or more colors may be used in the present general inventive concept. In this case, two or more times the number of nozzle units N may be used in the printhead111.

As described above, the printhead111includes the N nozzle units112. As illustrated inFIG. 3A, for explanation purposes, the printhead111having four nozzle units112will be described. However, it should be understood that the description that follows may also be applied to the arrangements ofFIGS. 3B and 3C.

In an embodiment of the present general inventive concept (refer toFIG. 3Afor reference numbers), the N nozzle units112may be disposed so that a distance between centers of each of nozzles of the nozzle units112that are adjacent along the subsidiary scanning direction is increased by D×M+D/N from a nozzle unit1121at a first end of the printhead111(i.e., the first end nozzle unit1121) to a nozzle unit1124at a second end of the printhead111(i.e., the second end nozzle unit1124). Here, M is a predetermined integer, D is a nozzle pitch, and N is 4. M may be one of integers (for example, 0, 1, 2, 3, etc.) so that the term D×M represents a relative distance proportional to the nozzle pitch D by the integer M. If the N nozzle units112are disposed as described above, ink droplets ejected by each nozzle unit112are deposited to be adjacent in the subsidiary scanning direction (x-direction) so that a printing resolution in the subsidiary scanning direction can be improved. That is, if two nozzle units112having an actual resolution of 600 dpi (dots per inch) are disposed adjacent to each other as illustrated inFIGS. 3B and 3C, a printing resolution of 1200 dpi can be realized in the subsidiary scanning direction, since these two nozzle units extend along the printing medium transferring direction, which is the same as the subsidiary scanning direction (x-direction). In a similar manner, if four nozzle units112are disposed as illustrated inFIG. 3A, a printing resolution of 2400 dpi can be realized in the subsidiary scanning direction for the same reasons. These gains in printing resolution can be realized due to the fact that two or more nozzle units are used to print to the same region on the print medium P, and the two or more nozzle units correspond to the same region of the print medium P at two or more different times during the printing operation due to the movement of the carriage106along the main scanning direction (y-direction) and the transferring of the print medium P along the subsidiary scanning direction.

In addition, each of the N nozzle units112may be spaced apart from one another by a predetermined gap in the subsidiary scanning direction. That is, the nozzles of the adjacent nozzle units112may be spaced apart from one another by D/N in the subsidiary scanning direction.

Alternatively, the N nozzle units112may be disposed such that a distance between centers of each of nozzles of the nozzle units112adjacent in the main scanning direction is increased by d×L+d/N from the first end nozzle unit1121to the other-end nozzle unit1124. Here, L is a predetermined integer, d is a diameter of a nozzle, and N is 4. L may be one of integers (for example, 0, 1, 2, 3, etc.) so that the term d×L represents a relative distance proportional to the diameter of a nozzle d by the integer L. If the N nozzle units112overlap with one another along the main scanning direction as described above, the printing resolution can be improved in the main scanning direction. That is, when the two nozzle units112having the actual resolution of 600 dpi are disposed as illustrated inFIG. 3B, a printing resolution of 1200 dpi can be realized in the main scanning direction. Similarly, if four nozzle units112are disposed in the printhead111, as illustrated inFIG. 3A, a printing resolution of 2400 dpi can be realized in the subsidiary scanning direction.

When the N nozzle units112are disposed along the subsidiary scanning direction, the N nozzle units112need not also be disposed along the main scanning direction. Similarly, when the N nozzle units112are disposed along the main scanning direction, the N nozzle units112need not also be disposed along the subsidiary scanning direction. In order to improve the printing resolution in both the main scanning direction and the subsidiary scanning direction, the N nozzle units112may be disposed such that the nozzles of the adjacent nozzle units112may be spaced apart from one another in the subsidiary scanning direction and the main scanning direction (i.e., the adjacent nozzle units112are complementarily disposed), as illustrated in the embodiments ofFIGS. 3A and 3B.

For a better understanding, the arrangement and operation of the printhead111will now be described with reference to the accompanying drawings.

Referring toFIG. 3A, four nozzle units (e.g., sub-nozzle units)1121,1122,1123, and1124each having four nozzles are disposed along the subsidiary scanning direction. W1, W2, W3, and W4are widths of each of the nozzle units1121,1122,1123, and1124and regions to be printed on the print medium P when the printhead111is scanned (i.e., moved across the print medium P) once. The widths W1, W2, W3, and W4of each of the nozzle units1121,1122,1123, and1124may be the same. S1, S2, and S3are distances between each of the nozzle units1121,1122,1123, and1124that are adjacent in the subsidiary scanning direction. S1, S2, and S3may be a distance of D×M+D/4. Here, S1, S2, and S3may be the same. When the nozzle units112are disposed as described above, a printing resolution that corresponds to four times the actual resolution can be realized in the subsidiary scanning direction. X1, X2, and X3are distances in the main scanning direction between centers of each of the nozzles of the nozzle units1121,1122,1123, and1124that are adjacent to each other in the main scanning direction. X1, X2, and X3may refer to a relative offset between the nozzle units1121,1122,1123, and1124, respectively, along the main scanning direction. X1, X2, and X3may be a distance of D×L+d/4. Here, X1, X2, and X3may be the same. When the nozzle units112are arranged as described above, a printing resolution that corresponds to four times the actual resolution can be realized in the main scanning direction.

As described above, since the printhead111exhibits the same effect when nozzles are disposed apart from one another by X1in the main scanning direction, as when the nozzles are disposed apart from one another by D/N in the subsidiary scanning direction, images having a higher resolution can be printed.

As illustrated inFIGS. 3B and 3C, the N nozzle units112may include two nozzle units1121and1122in consideration of a printing speed and a printing efficiency. That is, the N nozzle units112may include a first nozzle unit1121and a second nozzle unit1122. The arrangement and operation of the printhead111illustrated inFIGS. 3B and 3Care similar to those of the printhead111illustrated inFIG. 3A, and thus, a detailed description thereof will not be provided here. In the printhead111ofFIG. 3B, the two nozzle units1121and1122are complementarily disposed in the main scanning direction (y-direction) and the subsidiary scanning direction (x-direction). In the printhead111ofFIG. 3C, the nozzle units1121and1122are complementarily disposed only in the subsidiary scanning direction (x-direction). The printhead111ofFIGS. 3A,3B, and3C illustrate exemplary embodiments of the present general inventive concept, and it should be understood that these embodiments are not intended to limit the scope of the present general inventive concept. The printhead111may have a variety of other shapes according to the present general inventive concept.

Although not illustrated, a storage space to receive ink is disposed in the body110. An ink-storing space is formed in a cartridge shape in the body110to be attachable and detachable. The body110may further include a chamber having a an ejecting unit to communicate with each of nozzles of the nozzle units112and to apply pressure to eject ink, such as piezoelectric device and a thermal driving heater, a passage such as an orifice to supply the ink received in the body110to the chamber, a manifold which is a common passage to supply the ink that flows in via the passage to the chamber, and a restrictor which is a separate passage to supply the ink to each chamber from the manifold, and the like. The chamber, the ejecting unit, the passage, the manifold, the restrictor, and the like should be known to those skilled in the art to which the present general inventive concept pertains, and thus, a detailed description thereof will not be provided here.

FIG. 4is a perspective view illustrating the printhead unit105and a carriage moving unit142of the image forming apparatus ofFIG. 2, according to an embodiment of the present general inventive concept. Referring toFIGS. 2 and 4, the body110is mounted on the carriage106. The printhead111is mounted on the carriage106in a cartridge shape and is connected to the body110. The carriage moving unit142moves the carriage106in a reciprocating motion along the main scanning direction. The carriage moving unit142includes a carriage moving motor144, carriage moving rollers143aand143b, and a carriage moving belt145. A power is supplied from a main body of the image forming apparatus to the carriage moving motor144. One side of each of the carriage moving rollers143aand143bis connected to the carriage moving motor144, and the other side thereof is installed on a main frame (not shown). The carriage moving belt145is supported by the carriage moving rollers143aand143band travels around an endless track. The carriage106is combined with the carriage moving belt145. The carriage106moves to a predetermined position in response to a control signal transmitted from the controller130to the carriage moving motor144. The reciprocating motion of the carriage106is guided by a guide shaft108. The guide shaft108guides the reciprocating motion of the carriage106driven by the carriage moving motor144. A combining unit107into which the guide shaft108is inserted is disposed at one side of the carriage106. The combining unit107is perforated at one side of the carriage106. The guide shaft108is inserted into the combining unit107formed in a hollow shape and guides the reciprocating motion of the carriage106.

FIG. 5is a block diagram illustrating an image forming system according to another embodiment of the present general inventive concept, andFIG. 6is a block diagram illustrating operation of the image forming system ofFIG. 5. Here, the image forming system includes a data inputting unit135and an inkjet image forming apparatus125. The image forming apparatus125of the image forming system ofFIGS. 5 and 6may be similar to the image forming apparatus125ofFIG. 2. Accordingly, similar reference numbers are used, and the image forming system ofFIGS. 5 and 6are described with reference toFIG. 2.

Referring toFIGS. 2,5, and6, the data inputting unit135may be a host system such as a personal computer (PC), a digital camera, or a personal digital assistant (PDA). Image data to be printed is input to the data inputting unit135in an order of pages to be printed. The data inputting unit135includes an application program210, a graphics device interface (GDI)220, an image forming apparatus driver230, a user interface240, and a spooler250. The application program210generates an object that can be output using the image forming apparatus125and edits the object. The GDI220is a program that runs on an operating system (OS) on the host system. The GDI220transmits the object generated by the application program210to the image forming device driver230, and generates commands related to the object that the image forming apparatus driver230requests.

The image forming apparatus driver230is a program that runs on the host system and generates printer commands that can be interpreted by the image forming apparatus125. The user interface240for the image forming apparatus driver230is a program that runs on the host system and provides an environmental variable in which the image forming apparatus driver230generates the printer commands. The spooler250is a program that runs on the operating system in host system and transmits the printer commands generated by the image forming apparatus driver230to an input/output device (not shown) connected to the image forming apparatus125.

The image forming apparatus125includes a video controller170, the controller130, and a printing environment information unit136. In addition, the video controller170includes a non-volatile random access memory (NVRAM)185and a real time clock (RTC)190.

The video controller170interprets and bitmaps the printer commands generated by the image forming apparatus driver230and then transmits the interpreted printer commands to the controller130. The controller130transmits the bitmaps generated by the video controller170to each element of the image forming apparatus125to form an image on the print medium P. A printing operation is performed in the image forming apparatus125using the above-described procedure.

The controller130is disposed on a motherboard of the image forming apparatus125and controls an ejection operation of the nozzle units112disposed under the printhead111, an operation of the print medium-feeding units113,115,116, and117, and an operation of the carriage106. That is, the controller130synchronizes the operation of each element so that ink ejected from the nozzle units112can be deposited on a predetermined portion of the print medium P while the printhead111moves in the main scanning direction when the printing operation is performed with a predetermined resolution. The controller130stores the image data input through the data inputting unit135in a memory137and checks whether the image data to be printed has been completely stored in the memory137.

The printing environment information unit136stores a plurality of printing environment information that correspond to each printing environment when the image data is input from the application program210in a predetermined printing environment. That is, the printing environment information unit136stores printing environment information that corresponds to each type of printing environment input to the user interface240. Here, the printing environment information may include at least one of a printing density, a resolution, a size of the print medium P, a type of the printing medium P, a temperature, a humidity, and a continuous printing. Thus, the printing environment information unit136stores various printing environment information settings to correspond to each type of printing environment that could be input via the user interface240. The controller130controls the operations of the printhead111, the carriage106, and the print medium-feeding units113,115,116, and117in each printing environment stored in the printing environment information unit136that corresponds to the printing environment input via the user interface240.

If the image data has been completely stored in the memory137, the controller130operates the driving source131by generating a control signal that corresponds to the input printing environment. The print medium P is fed by the print medium-feeding units113,115,116, and117driven by the driving source131. The print medium P is transferred along the predetermined path to the nozzle units112. The controller130moves the printhead111in the main scanning direction according to the printing environment stored in the printing environment information unit136that corresponds to the printing environment input via the user interface240. In addition, the controller130generates control signals to control the ejection operation of the nozzle units112, and the nozzle units112print the image data on the print medium P in response to the control signals. The controller130performs the printing operation according to the printing environment information stored in the printing environment information unit136and information about a defective nozzle sensed by the sensing unit132.

A printing method using the printing environment input from the user interface240and the information about the defective nozzle sensed by the sensing unit132will be described with reference to the embodiment illustrated inFIG. 3B. InFIG. 3B, reference numerals1,2,3,4,5, and . . .16, respectively, represent nozzles arrayed in the first nozzle unit1121and the second nozzle unit1122.

The controller130controls the operation of each element so as to use different printing methods according to (1) the printing environment input from the user interface240and (2) whether the defective nozzle is sensed by the sensing unit132.

Referring toFIG. 3B, when the printing operation is performed with an actual resolution or the defective nozzle is not sensed by the sensing unit132, the controller130may perform the printing operation using the first nozzle unit1121. That is, the controller130generates a control signal to drive the first nozzle unit1121so that the printhead111moves in the main scanning direction and prints an image by ejecting ink from the first nozzle unit1121. After a scanning operation has been completely performed as described above, the printhead111moves back to an initial position. The controller130feeds the print medium P in the subsidiary scanning direction before a next scanning operation is performed. In this case, the controller130feeds the print medium P by a width W1of the first nozzle unit1121and then begins the next scanning operation using the first nozzle unit1121. When the printing operation is performed with the actual resolution or the defective nozzle is not sensed by the sensing unit132, the above-described procedure is repeatedly performed and the image is printed.

When the printing environment input via the user interface240indicates a higher resolution printing or the defective nozzle is sensed by the sensing unit132, the printing operation may be performed using processes that are different from the above-described processes.

First, a method of printing with a higher resolution will now be described. If a printing environment indicating a higher resolution printing is input via the user interface240, the operation of the printhead111is controlled according to a printing resolution stored in the printing environment information unit136that corresponds to the higher resolution. Accordingly, the controller130performs the printing operation using both the first nozzle unit1121and the second nozzle unit1122. In this case, the second nozzle unit1122performs the printing operation in a region that has already been printed by the first nozzle unit1121such that the higher resolution can be realized. That is, if the print medium P reaches the printhead111, the first nozzle unit1121moves along the main scanning direction and prints a region that corresponds to the width W1(i.e., a first printing operation is performed on the region). After an initial scanning operation (i.e., including the first printing operation) has been completed as described above, the printhead111moves back to the initial position (e.g., at one side of the print medium P). The controller130then controls the print medium-feeding units113,115,116, and117to feed the print medium P in the subsidiary scanning direction by the width W1of the first nozzle unit1121before the next scanning operation is performed. In the next scanning operation, the first nozzle unit1121prints to another region that corresponds to the width W1, and the second nozzle unit1122performs a second printing operation on the region that has already been printed to by the first nozzle unit1121during a previous scanning operation. In this case, ink droplets ejected by the second nozzle unit1122are deposited at positions that are adjacent to ink droplets ejected by the first nozzle unit1121in both the main scanning direction and the subsidiary scanning direction. That is, the printhead111performs the printing operation with a resolution of X1in the main scanning direction and with a resolution of D/N in the subsidiary scanning direction, since the nozzle units1121,1122, etc. are complementarily arranged. In the present embodiment, the printhead111performs the printing operation with a resolution of d/2 in the main scanning direction and with a resolution of D/2 in the subsidiary scanning direction.

FIG. 7illustrates printing patterns printed by a one-time scanning (e.g., a first scanning operation) performed by the printhead111illustrated inFIG. 3B.FIG. 8illustrates printing patterns printed by a two-time scanning (e.g., first and second scanning operations) performed by the printhead111illustrated inFIG. 3B.FIG. 9illustrates printing patterns in which a defective nozzle exists in the first nozzle unit1121of the printhead111illustrated inFIG. 3Bis compensated for by the second nozzle unit1122. In the drawings,1,2,3,4, . . .8represent ink dots ejected from nozzles1,2,3,4, . . .16, respectively, of the first nozzle unit1121and the second nozzle unit1122. The print medium P is fed in a direction of an arrow. In addition, ink dots deposited during a first scanning operation and ink dots deposited during a second scanning operation are illustrated as having different shapes. For example, the ink dots deposited during the first scanning operation have a shaded circular shape, and the ink dots deposited during the second scanning operation have an un-shaded circular shape.

Referring toFIG. 7, the printhead111moves in the main scanning direction (y-direction) during the first scanning operation and prints a region (i.e., a first region) that corresponds to a width W1of the first nozzle unit1121. After the first scanning operation has been completely performed, the print medium P is fed in the subsidiary scanning direction (x-direction) by the width W1of the first nozzle unit1121. Then, as illustrated inFIG. 8, an image is printed on the print medium P using both the first nozzle unit1121and the second nozzle unit1122. InFIG. 8, second ink droplets ejected by the second nozzle unit1122are deposited to be spaced apart from first ink droplets ejected by the first nozzle unit1121by d/2 in the main scanning direction, and are deposited to be spaced apart from the first ink droplets by D/2 in the subsidiary scanning direction. Thus, by using the printhead111according to the present embodiment, the higher resolution can be realized. In other words, during the first scanning operation, the first nozzle unit1121ejects ink droplets to the first region of the print medium P. During the second scanning operation, the first nozzle unit1121ejects ink droplets to a second region of the print medium that is adjacent to the first region while the second nozzle unit1122ejects ink droplets onto the first region.

A printing method used when a defective nozzle is sensed by the sensing unit132will now be described. A method of sensing a defective nozzle is described above, and thus, a detailed description thereof will not be provided.

When performing the printing operation with an actual resolution, the image forming apparatus125performs the printing operation using the first nozzle unit1121of the printhead111. If a defective nozzle exists in the first nozzle unit1121, since ink has not been deposited in a region that corresponds to the defective nozzle, a missing line, such as a white line may be formed in the main scanning direction. The missing line can be easily seen, and thus should be compensated for.

If the defective nozzle does not exist in the first nozzle unit1121, the controller130operates the first nozzle unit1121so that ink is ejected when the print medium P reaches the printhead111. The controller130generates and outputs control signals for to control the operation of the first nozzle unit1121so that the image data is printed on the print medium P, and the first nozzle unit1121prints the image data on the print medium P in response to the control signals.

If the defective nozzle exists in the first nozzle unit1121, the controller130compensates for the defective nozzle using a nozzle in the second nozzle unit1122that corresponds to a position of the defective nozzle in the first nozzle unit1121. The compensation nozzle may have a position within the second nozzle unit1122that corresponds to a position of the defective nozzle within the first nozzle unit1121. The case in which a nozzle3of the first nozzle unit1121illustrated inFIG. 3Bis defective will now be described. Referring toFIG. 9, ink is not deposited in a line L1printed by the nozzle3of a region S1printed by the first nozzle unit1121during the first scanning operation. After the first scanning operation has been completely performed, the print medium P is fed by the width W1of the first nozzle unit1121in the subsidiary scanning direction (x-direction). The second scanning operation is then performed. In the second scanning operation, a new region S2is printed by the first nozzle unit1121, and ink is not deposited in a line L2printed by the nozzle3. Simultaneously, the line L1of the region S1printed during the first scanning operation is compensated for by a nozzle11of the second nozzle unit1122. That is, the defective nozzle is compensated for using the nozzle of the second nozzle unit1122that corresponds to the defective nozzle that exists in the first nozzle unit1121. The controller130may select the compensation nozzle in the second nozzle unit1122based on a signal received from the sensing unit132.

For a better understanding of the explanation, the above-described processes are illustrated as a flowchart.FIG. 10is a flowchart illustrating a method of printing with high resolution according to an embodiment of the present general inventive concept. The method ofFIG. 10can be performed by the image forming apparatus125ofFIGS. 2 and 5and/or the image forming system ofFIG. 6. Accordingly, for illustration purposes, the method ofFIG. 10is illustrated with reference toFIGS. 2 to 10.

Referring toFIGS. 2 to 10, in operation S10, data to be printed is input from a host. In operation S15, a user selects a resolution using the user interface240. In this case, the selected resolution and the actual resolution of the printhead111may be different. Thus, in operation S20, the image forming apparatus compares the selected resolution with the actual resolution of the printhead111.

When the selected resolution is the same as the actual resolution, the sensing unit132senses whether a defective nozzle exists in the first nozzle unit1121in operation S25. If the defective nozzle exists in the first nozzle unit1121, the defective nozzle is compensated for using the second nozzle unit1122in operation S30and the printing operation is performed as described above with reference toFIG. 9. After determining whether the printing operation has been completely performed in operation S35, if the printing operation has not been completely performed, the print medium P is fed by the width W1of the first nozzle unit1121in operation S40, and accordingly, the above-described processes are repeatedly performed. If the defective nozzle does not exist in the first nozzle unit1121, the printing operation is performed using the first nozzle unit1121in operation S50. After determining whether the printing operation has been completely performed in operation S55, if the printing operation has not been completely performed, the print medium P is fed by the width W1of the first nozzle unit1121in operation S60, and accordingly, the above-described processes are repeatedly performed.

When the selected resolution is higher than the actual resolution, the printing operation is performed using the first nozzle unit1121and the second nozzle unit1122in operation S80as described above with reference toFIG. 8. After determining whether the printing operation has been completely performed in operation S85, if the printing operation has not been completely performed, the print medium P is fed by the width W1of the first nozzle unit1121in operation S90, and accordingly, the above-described processes are repeatedly performed.

In the above-described configuration and methods, N nozzle units are separately disposed so that a second region that is adjacent to a first region that is printed by a first nozzle unit can be printed using a second nozzle unit. Thus, a printing operation can be performed with an actual resolution or a higher resolution while a print medium is fed by a width of the first nozzle unit. In addition, missing dots generated by a defective nozzle can be properly compensated for using the second nozzle unit.

As described above, in a printhead, a scanning type inkjet image forming apparatus having the same, and a method of performing the printing operation with high resolution according to various embodiments of the present general inventive concept, separate N nozzle units are properly disposed such that an image can be printed with a higher resolution than an actual resolution of the nozzle units, which is depends on a nozzle pitch D. For example, the N nozzle units can be disposed apart by D/N in a subsidiary scanning direction and apart by a d/N in a main scanning direction such that the higher resolution is N-times greater than the actual resolution. In addition, a printing operation can be performed with the actual resolution or the higher resolution while the print medium P is fed at a uniform speed such that the printing speed can be increased when the printing operation is performed with the higher resolution. In addition, when a portion of nozzles of a first nozzle unit is damaged, the portion of the nozzles in the first nozzle unit can be compensated for using a second nozzle unit such that an image quality is not affected by a damaged or malfunctioning nozzle.