Patent Publication Number: US-7219977-B2

Title: Printing apparatus, liquid ejecting apparatus, method of adjusting positions of liquid droplet marks, and liquid ejecting system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of application Ser. No. 10/686,772, filed Oct. 17, 2003, the disclosure of which is incorporated herein by reference. The present application claims priority upon Japanese Patent Application No. 2002-303372 filed on Oct. 17, 2002 and Japanese Patent Application No. 2003-111552 filed on Apr. 16, 2003, which are herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to printing apparatuses, liquid ejecting apparatuses, methods of adjusting positions of liquid droplet marks, and liquid ejecting systems. 
   2. Description of the Related Art 
   (1) In recent years, color inkjet printers that eject several colors of ink from a print head so as to form ink dots on print paper have become popular as output devices for computers. More recently, relatively large color inkjet printers that use a plurality of print heads to print onto print paper such as roll paper have also been achieved (for example, see JP 2000-158735A). Such color inkjet printers eject ink from the print heads while moving a carriage so as to form dots on the print paper for correcting the feed amount by which the print paper is fed by a paper feed roller. 
   When moving the carriage and forming dots for correcting the feed amount on the print paper, vibration occurs in the carriage. Since the print heads are provided in the carriage, that vibration is transmitted to the print heads. 
   Under these circumstances, when ink is ejected from the print heads to form dots for correcting the feed amount on the print paper, desired dots are not obtained, and therefore there is the possibility that correction of the feed amount cannot be carried out appropriately. 
   (2) Inkjet printers that include recording heads (as liquid ejecting section groups) for ejecting ink (as an example of liquid) and that perform printing by forming dots (as liquid droplet marks) on a medium with the ejected ink are known as liquid ejecting apparatuses having a plurality of liquid ejecting section groups (for example, see JP 9-262992A). Some of them are large-sized inkjet printers that perform high-speed printing on large-sized print paper (such as JIS standard A0 sized paper, B0 sized paper, and roll paper) using the plurality of recording heads. Such a large-sized inkjet printer ejects ink to perform printing while a carriage, in which the recording heads are arranged at appropriate intervals to comply with the size of the paper to be printed, is being moved by predetermined moving means. 
   When the carriage is moved by the moving means, an external force is applied to a predetermined position of the carriage. This results in bringing about a difference between the behavior of a recording head that is arranged on the side close to the position to which the external force is applied and the behavior of a recording head arranged on the side away from that position when the carriage being moved. Under these circumstances, there is a possibility that the positions of the dots formed on the print paper by the ink ejected from the recording heads are misaligned from initially-set target positions due to this difference in behavior, and that quality in image deteriorates. 
   SUMMARY OF THE INVENTION 
   The present invention was arrived at in light of the foregoing problems. 
   (1) An object of the present invention is to achieve a printing apparatus with which correction of the feed amount can be carried out appropriately. 
   (2) Another object of the present invention is to achieve a liquid ejecting apparatus that is capable of adjusting positions of liquid droplet marks formed on a medium by each liquid ejecting section group, a method of adjusting the positions of the liquid droplet marks, and a liquid ejecting system that is capable of adjusting the positions of the liquid droplet marks. 
   According to an aspect of the present invention, a printing apparatus comprises: 
   a plurality of print heads; 
   a moving member that can be moved and that is provided with the plurality of print heads; and 
   a feed mechanism for feeding a medium to be printed; 
   wherein dots for correcting a feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed by ejecting ink from a predetermined print head, among the plurality of print heads, while moving the moving member, and 
   wherein the predetermined print head is a print head other than the print head, among the plurality of print heads, that is the most susceptible to vibration caused by moving the moving member. 
   According to another aspect of the present invention, a liquid ejecting apparatus comprises: 
   a moving member that has at least two liquid ejecting section groups and that is capable of moving in a predetermined direction due to an external force, each of the liquid ejecting section groups including at least two liquid ejecting sections for ejecting liquid droplets to form liquid droplet marks on a medium, and each of the liquid ejecting section groups being driven based on a single reference ejection signal for causing the liquid droplets to be ejected from the liquid ejecting sections; 
   a reference liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a predetermined reference timing and that is a liquid ejecting section group other than the liquid ejecting section group, among the liquid ejecting section groups, that is the most susceptible to vibration caused by moving the moving member; and 
   at least one other liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a timing adjusted based on the predetermined reference timing of the reference liquid ejecting section group. 
   Features and objects of the present invention other than the above will become clear by reading the description of the present specification with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to facilitate further understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a perspective view showing an overview of a color inkjet printer  20  according to an embodiment of the present invention; 
       FIG. 2  is a perspective view showing an overview of the color inkjet printer  20 , in which the position of a carriage  28  is different from  FIG. 1 , according to an embodiment of the present invention; 
       FIG. 3  is a conceptual diagram illustrating a platen  26  and a suction mechanism  16  according to an embodiment of the present invention; 
       FIG. 4  is an explanatory diagram for describing print heads  36  according to an embodiment of the present invention; 
       FIG. 5  is a block diagram showing the configuration of a printing system provided with the color inkjet printer  20  according to an embodiment of the present invention; 
       FIG. 6  is a block diagram showing the configuration of an image processing section  38  according to an embodiment of the present invention; 
       FIG. 7  is a transition diagram showing the operation of the printing system according to an embodiment of the present invention; 
       FIG. 8  is a conceptual diagram illustrating how vibration occurs when a carriage  28  is moved according to an embodiment of the present invention; 
       FIG. 9  is a conceptual diagram showing an example of a correction test pattern according to an embodiment of the present invention; 
       FIG. 10  is a perspective view showing an overview of a color printer according to a second embodiment of the present invention; 
       FIG. 11  is a perspective view showing the color printer in  FIG. 10  in a state in which the carriage has been moved; 
       FIG. 12  is an explanatory diagram schematically showing a configuration of a linear encoder; 
       FIG. 13A  and  FIG. 13B  are timing charts showing waveforms of two output signals of the linear encoder; 
       FIG. 14  is an explanatory diagram for illustrating nozzle rows of a print head; 
       FIG. 15  is a diagram for illustrating an arrangement of nozzles among a plurality of adjacent print heads and the center of a section to which an external force is applied; 
       FIG. 16  is a block diagram showing a configuration of a liquid ejecting system provided with the color printer; 
       FIG. 17  is a block diagram showing a configuration of an image processing unit; 
       FIG. 18  is a diagram showing a configuration of a drive signal generating section provided in a head control unit; 
       FIG. 19  is a timing chart for illustrating the operation of the drive signal generating section; 
       FIG. 20  is a diagram for illustrating a print pattern for determining the optimum output timing when printing is carried out using achromatic color ink; and 
       FIG. 21  is a diagram for illustrating a print pattern for determining the optimum output timing when printing is carried out using chromatic color ink. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   At least the following matters will be made clear by the explanation in the present specification and the description of the accompanying drawings. 
   (1) According to an aspect of the present invention, a printing apparatus comprises: a plurality of print heads; a moving member that can be moved and that is provided with the plurality of print heads; and a feed mechanism for feeding a medium to be printed; wherein dots for correcting a feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed by ejecting ink from a predetermined print head, among the plurality of print heads, while moving the moving member, and wherein the predetermined print head is a print head other than the print head, among the plurality of print heads, that is the most susceptible to vibration caused by moving the moving member. 
   It is preferable that the dots for correcting the feed amount by which the medium to be printed is fed are formed using the print head that is the least susceptible to vibration. However, it is still possible to suitably correct the feed amount by which the medium to be printed is fed even if the dots for correction are formed using a print head other than the print head that is the most susceptible to the vibration. 
   Further, it is possible that the predetermined print head is the print head, among the plurality of print heads, that is the least susceptible to the vibration caused by moving the moving member. 
   By adopting the print head, among the plurality of print heads, that is least likely to be susceptible to vibration caused by moving the moving member as the predetermined print head, correction of the feed amount can be carried out more appropriately. 
   Further, it is possible that the printing apparatus further comprises a drive member that is connected to the moving member and that is for driving the moving member; and the predetermined print head is the print head that is located the closest to a connecting section at which the moving member and the drive member are connected to each other. 
   Doing this allows the print head that is the least susceptible to the vibration to be more easily selected. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on both edge sections of the medium to be printed by ejecting ink from the predetermined print head, among the plurality of print heads, while moving the moving member. 
   By doing this, it is possible to find a more accurate correction amount, and therefore more appropriate correction can be implemented. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed by ejecting ink from predetermined nozzles provided in the predetermined print head. 
   By doing this, there is the advantage that error due to changing the nozzles that eject ink will not occur. 
   Further, it is possible that the printing apparatus further comprises: a support member for supporting the medium to be printed; a suction member for sucking the medium to be printed toward the support member; and a first detector for detecting a force by which the suction member sucks the medium to be printed; and that whether or not to form, on the medium to be printed, the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed is determined according an output value of the first detector. 
   Doing this allows the dots for correcting the feed amount by which the medium to be printed is fed by the feed mechanism to be formed on the medium to be printed at an appropriate timing. 
   Further, it is possible that whether or not to form, on the medium to be printed, the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed is determined according at least one of a value of a temperature around the printing apparatus and a value of a humidity around the printing apparatus. 
   Doing this allows the dots for correcting the feed amount by which the medium to be printed is fed by the feed mechanism to be formed on the medium to be printed at an appropriate timing. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed when power is supplied to the printing apparatus. 
   Doing this allows the implementation of appropriate correction to be assured. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed during a printing operation of the printing apparatus. 
   Doing this allows the dots to be efficiently formed on the medium to be printed. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed when the medium to be printed has been exchanged. 
   Doing this allows the implementation of appropriate correction to be assured. 
   Further, it is possible that the printing apparatus further comprises: a second detector for detecting whether or not the medium to be printed has been exchanged; and that when it has been detected by the second detector that the medium to be printed has been exchanged, the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed. 
   In this way, whether or not the medium to be printed has been exchanged can be detected using a simple method. 
   Further, it is possible that the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed are formed on the medium to be printed when a print mode of the printing apparatus has been changed. 
   Doing this allows the implementation of appropriate correction to be assured. 
   Further, it is possible that at least two correction amounts for correcting the feed amount by which the feed mechanism feeds the medium to be printed are obtained based on the dots formed on the medium to be printed, and that, based on an average value of the correction amounts that are obtained, the feed amount by which the feed mechanism feeds the medium to be printed is corrected. 
   Doing this allows more accurate correction to be carried out. 
   It is also possible to achieve a printing apparatus comprising: a plurality of print heads; a moving member that can be moved and that is provided with the plurality of print heads; and a feed mechanism for feeding a medium to be printed; wherein dots for correcting a feed amount by which the feed mechanism feeds the medium to be printed are formed on both edge sections of the medium to be printed by ejecting ink from a predetermined print head, among the plurality of print heads, while moving the moving member; wherein the predetermined print head is the print head, among the plurality of print heads, that is the least susceptible to vibration caused by moving the moving member; wherein the printing apparatus further comprises a drive member that is connected to the moving member and that is for driving the moving member; wherein the predetermined print head is the print head that is located the closest to a connecting section at which the moving member and the drive member are connected to each other; wherein the printing apparatus further comprises: a support member for supporting the medium to be printed; a suction member for sucking the medium to be printed toward the support member; and a detector for detecting a force by which the suction member sucks the medium to be printed; wherein whether or not to form, on the medium to be printed, the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed is determined according an output value of the detector; and wherein whether or not to form, on the medium to be printed, the dots for correcting the feed amount by which the feed mechanism feeds the medium to be printed is determined according at least one of a value of a temperature around the printing apparatus and a value of a humidity around the printing apparatus. 
   In this way, most of the primary effects already mentioned can be obtained, and therefore the object of the present invention is more effectively achieved. 
   (2) Another aspect of the present invention is a liquid ejecting apparatus comprising: a moving member that has at least two liquid ejecting section groups and that is capable of moving in a predetermined direction due to an external force, each of the liquid ejecting section groups including at least two liquid ejecting sections for ejecting liquid droplets to form liquid droplet marks on a medium, and each of the liquid ejecting section groups being driven based on a single reference ejection signal for causing the liquid droplets to be ejected from the liquid ejecting sections; a reference liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a predetermined reference timing and that is a liquid ejecting section group other than the liquid ejecting section group, among the liquid ejecting section groups, that is the most susceptible to vibration caused by moving the moving member; and at least one other liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a timing adjusted based on the predetermined reference timing of the reference liquid ejecting section group. 
   According to such a liquid ejecting apparatus, the timing of the reference ejection signal for each of a plurality of liquid ejecting section groups is adjusted based on a predetermined reference timing of a liquid ejecting section group which is a liquid ejecting section group other than the liquid ejecting section group, among the liquid ejecting section groups, that is the most susceptible to vibration caused by moving the moving member. In other words, adjustment is made based on a liquid ejecting section group whose behavior upon movement is stable. Therefore, the positions at which the liquid droplet marks are formed by the other liquid ejecting section group is adjusted based on liquid droplet marks that are formed at stable positions, and thus, it becomes possible to reduce positional misalignment and variations between the liquid droplet marks formed by the reference liquid ejecting section group and each of the other liquid ejecting section groups. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the reference liquid ejecting section group is positioned on a side, in a direction intersecting with the predetermined direction, that is close to a section, in the moving member, to which the external force is applied. 
   According to such a liquid ejecting apparatus, the timing of the reference ejection signal for each of a plurality of liquid ejecting section groups is adjusted based on a predetermined reference timing of a liquid ejecting section group that is positioned on a side, in a direction intersecting with the predetermined direction, that is close to a section, in the moving member, to which the external force is applied, that is, the liquid ejecting section group that is positioned close to the section where the behavior upon movement is stable. Therefore, the positions at which the liquid droplet marks are formed by the other liquid ejecting section group is adjusted based on liquid droplet marks that are formed at stable positions, and thus, it becomes possible to reduce positional misalignment and variations between the liquid droplet marks formed by the reference liquid ejecting section group and each of the other liquid ejecting section groups. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the reference liquid ejecting section group is positioned on a side that is close to a center of the section to which the external force is applied. 
   According to such a liquid ejecting apparatus, even when the moving member moves, for example, in different directions, the timing adjustment is carried out based on the timing of a liquid ejecting section group that is stable in behavior during movement in both directions. Therefore, it is possible to further reduce the variations in the positions of the liquid droplet marks formed on the medium with each of the liquid ejecting section groups. 
   Further, in the above-described liquid ejecting apparatus, the liquid ejecting section groups may be liquid ejecting section rows, each of the liquid ejecting section rows including the liquid ejecting sections aligned in a row in a carrying direction in which the medium is carried. 
   With this structure, each liquid ejecting section row, in which the liquid ejecting sections are aligned in a row in the carrying direction, is driven based on a single reference ejection signal therefor. Therefore, all of the liquid ejecting section rows can be adjusted based on the timing of the liquid ejecting section row that is positioned on the side close to the section to which the external force is applied and whose behavior is thus stable. Accordingly, by adjusting each of the liquid ejecting section rows, it becomes possible to reduce variations in positions of the liquid droplet marks for the entire liquid ejecting apparatus. 
   Further, in the above-described liquid ejecting apparatus, the liquid ejecting section groups may be liquid ejecting units, each of the liquid ejecting units including at least two liquid ejecting section rows aligned in the predetermined direction, and each of the liquid ejecting section rows including the liquid ejecting sections aligned in a row in a carrying direction in which the medium is carried. According to such a liquid ejecting apparatus, it becomes possible to make adjustments on a liquid ejecting unit basis, and therefore, adjustment can be controlled easily. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the timing for driving the other liquid ejecting section group is adjusted to make a reference liquid droplet mark row that is taken as a reference and that is formed in a carrying direction, in which the medium is carried, by the reference liquid ejecting section group ejecting liquid at the predetermined reference timing while moving and a liquid droplet mark row that is formed by the other liquid ejecting section group ejecting liquid while moving be continuous with each other. 
   According to such a liquid ejecting apparatus, adjustment is carried out such that a reference liquid droplet mark row that is taken as a reference and that is formed in the carrying direction and a liquid droplet mark row formed by the other liquid ejecting section group are continuous with each other. Therefore, visibility of the amount of misalignment with respect to the reference is satisfactory, and thus, adjustment can be carried out easily. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the liquid ejecting apparatus carries the medium between an action of forming the reference liquid droplet mark row and an action of forming the liquid droplet mark row with the other liquid ejecting section group. 
   According to such a liquid ejecting apparatus, the medium is carried between the action of ejecting liquid from the reference liquid ejecting section group and the action of ejecting liquid from the other liquid ejecting section group. Accordingly, it becomes possible to make adjustments taking into account also the positional misalignment between liquid droplet marks that occurs due to factors relating to medium-carrying precision. 
   Further, if ink is adopted as the liquid used in the liquid ejecting apparatus, then it is possible to achieve a printing apparatus that is capable of printing high quality images with liquid ejecting section groups in which the variations in positions of the dots with respect to the medium have been reduced entirely. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that each of the liquid ejecting section groups has an achromatic color liquid ejecting section row for ejecting achromatic color ink as the liquid and a chromatic color liquid ejecting section row for ejecting chromatic color ink; and the timing for driving the other liquid ejecting section group is adjusted differently for when the liquid droplet marks are to be formed on the medium by ejecting ink from the achromatic color liquid ejecting section row, and when the liquid droplet marks are to be formed on the medium using the chromatic color liquid ejecting section row. 
   Achromatic color ink is mainly used for printing texts etc. and is of a single color, and therefore, it is preferable to adjust the timing for ejecting the achromatic color ink. On the other hand, chromatic color ink is mainly used for printing, for example, natural pictures such as photographs, and a plurality of colors of inks are used therefor, and therefore, it is preferable to adjust the timing for ejecting the inks of the plurality of colors. However, the timing to be adjusted is different for when the achromatic color ink is used and for when the chromatic color inks are used. According to the liquid ejecting apparatus described above, it becomes possible to print all types of images, such as texts and natural pictures, with high quality by adjusting the timing differently for when liquid droplet marks are formed using achromatic color ink and for when liquid droplet marks are formed using chromatic color ink(s). 
   Further, in the above-described liquid ejecting apparatus, it is preferable that when the positions of the liquid droplet marks are to be adjusted for performing printing on the medium by ejecting ink from the achromatic color liquid ejecting section row, the timing for driving the other liquid ejecting section group is adjusted according to liquid droplet marks that are formed by the ink ejected from the achromatic color liquid ejecting section row. 
   According to such a liquid ejecting apparatus, the adjustment of the positions of the liquid droplet marks for performing printing using achromatic color ink is carried out by adjusting the timing based on the liquid droplet marks actually formed by ejecting ink from the achromatic color liquid ejecting section row. Therefore, it becomes possible to carry out adjustment for printing using achromatic color ink more appropriately. Accordingly, it becomes possible to print satisfactory images using achromatic color ink. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that each of the liquid ejecting section groups has at least two chromatic color liquid ejecting section rows, each for ejecting a different one of at least two chromatic color inks as the liquid; and when the positions of the liquid droplet marks are to be adjusted for performing printing on the medium by ejecting ink from the chromatic color liquid ejecting section rows, the timing for driving the other liquid ejecting section group is adjusted according to liquid droplet mark rows that are formed by the inks ejected from the chromatic color liquid ejecting section rows. 
   According to such a liquid ejecting apparatus, the adjustment of the positions of the liquid droplet marks for performing printing using chromatic color ink is carried out by adjusting the timing based on the liquid droplet marks actually formed by ejecting ink from the chromatic color liquid ejecting section rows. Therefore, it becomes possible to carry out adjustment for printing using chromatic color ink more appropriately. Accordingly, it becomes possible to print satisfactory images using chromatic color ink. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the liquid ejecting section rows in the same one of the liquid ejecting section groups are driven based on the single reference ejection signal; and the timing for driving the other liquid ejecting section group is adjusted to make a distance, in the predetermined direction, between the liquid droplet mark rows, among the liquid droplet mark rows formed by ejecting the inks from the chromatic color liquid ejecting section rows, that are formed using ink of one predetermined color and a distance, in the predetermined direction, between the liquid droplet mark rows, among the liquid droplet mark rows formed by ejecting the inks from the chromatic color liquid ejecting section rows, that are formed using ink of another predetermined color be approximately equal. 
   According to such a liquid ejecting apparatus, it becomes possible to improve the quality of images printed using chromatic color inks by adjusting the positions of the liquid droplet marks formed using predetermined inks, among the plurality of chromatic color inks, that tend to affect image quality, for example. Particularly, the timing is adjusted such that the distances, in the moving direction, between the liquid droplet mark rows formed using the predetermined inks are approximately equal. Therefore, variations in positions of the liquid droplet marks due to difference in ink color are reduced, and thus, it becomes possible to print further improved images using chromatic color inks. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the inks of the predetermined colors are magenta-type ink and cyan-type ink. 
   According to such a liquid ejecting apparatus, the positions of the liquid droplet marks that are formed using magenta-type ink and cyan-type ink, which tend to affect image quality particularly when natural pictures etc. are printed, are adjusted. Therefore, it becomes possible to further improve the quality of images printed using chromatic color inks. 
   Further, in the above-described liquid ejecting apparatus, it is preferable that the liquid ejecting sections for ejecting the chromatic color ink to adjust the positions of the liquid droplet marks are a portion of the liquid ejecting sections of the chromatic color liquid ejecting section row. 
   When natural pictures, for example, for which chromatic color inks are particularly used are printed, ink is seldom ejected from all of the liquid ejecting sections. Therefore, by forming liquid droplet marks, which are formed for timing adjustment, by ejecting ink from only some of the liquid ejecting sections of a liquid ejecting section row, it is possible to adjust the positions of the liquid droplet marks with substantially the same conditions as those for when actual printing is performed. Accordingly, it is possible to make adjustments that suit printing using chromatic color inks even more. 
   Another aspect of the present invention is a liquid ejecting apparatus comprising: a moving member that has at least two ink ejecting units and that is capable of moving in a predetermined direction due to an external force, each of the ink ejecting units including at least two ink ejecting section rows aligned in the predetermined direction, each of the ink ejecting section rows including at least two ink ejecting sections that are for ejecting ink droplets to form ink droplet marks on a medium and that are aligned in a row in a carrying direction in which the medium is carried, and each of the ink ejecting units being driven based on a single reference ejection signal for causing the ink droplets to be ejected from the ink ejecting sections; a reference ink ejecting unit, among the ink ejecting units, that is driven according to the reference ejection signal therefor at a predetermined reference timing and that is an ink ejecting unit other than the ink ejecting unit, among the ink ejecting units, that is the most susceptible to vibration caused by moving the moving member; and at least one other ink ejecting unit, among the ink ejecting units, that is driven according to the reference ejection signal therefor at a timing adjusted based on the predetermined reference timing of the reference ink ejecting unit, wherein: the reference ink ejecting unit is positioned on a side, in a direction intersecting with the predetermined direction, that is close to a center of a section, in the moving member, to which the external force is applied; each of the ink ejecting units has an achromatic color ink ejecting section row for ejecting achromatic color ink and at least two chromatic color ink ejecting section rows each for ejecting a different one of at least two chromatic color inks; a reference ink droplet mark row that is taken as a reference and that is formed in the carrying direction by the reference ink ejecting unit ejecting ink at the predetermined reference timing while moving and an ink droplet mark row that is formed by the other ink ejecting unit ejecting ink while moving are formed, one of either the reference ink droplet mark row or the ink droplet mark row being formed before a carrying action of the medium, and the other being formed after the carrying action; when the positions of the ink droplet marks are to be adjusted for performing printing on the medium by ejecting ink from the achromatic color ink ejecting section row, the timing for driving the other ink ejecting unit is adjusted according to ink droplet marks that are formed by the ink ejected from the achromatic color ink ejecting section row to make the reference ink droplet mark row and the ink droplet mark row that is formed by the other ink ejecting unit be continuous with each other; and when the positions of the ink droplet marks are to be adjusted for performing printing on the medium by ejecting inks from the chromatic color ink ejecting section rows, the timing for driving the other ink ejecting unit is adjusted to make a distance, in the predetermined direction, between the ink droplet mark rows, among the ink droplet mark rows formed by ejecting the inks from the chromatic color ink ejecting section rows, that are formed using magenta-type ink by a portion of the ink ejecting sections of the ink ejecting section row and a distance, in the predetermined direction, between the ink droplet mark rows, among the ink droplet mark rows formed by ejecting the inks from the chromatic color ink ejecting section rows, that are formed using cyan-type ink by a portion of the ink ejecting sections of the ink ejecting section row be approximately equal. 
   According to such a liquid ejecting apparatus, even when the moving member moves, for example, in different directions, the timing for each of a plurality of ink ejecting units is adjusted based on the timing of an ink ejecting unit that is stable in behavior during movement and that is positioned on a side, in a direction intersecting with the predetermined direction, that is close to a section, in the moving member, to which the external force is applied. Therefore, it is possible to reduce the variations in the positions of the ink droplet marks formed with each of the ink ejecting units for movement in both directions in which the ink ejecting units move. Further, it becomes possible to make adjustments on an ink ejecting unit basis, and therefore, adjustment can be controlled easily. Furthermore, since the medium is carried between the action of ejecting ink from the reference ink ejecting unit and the action of ejecting ink from the other ink ejecting unit, it is possible to make adjustments taking into account also the positional misalignment between ink droplet marks that occurs due to factors relating to medium-carrying precision. 
   Furthermore, it is possible to adjust the timing with substantially the same conditions as those for when actual printing is performed differently for when ink droplet marks are formed using achromatic color ink and for when ink droplet marks are formed using chromatic color ink(s), and particularly, magenta-type ink and cyan-type ink, so that the timing suits each case. As a result, it becomes possible to print texts, natural pictures, and so forth with higher quality. 
   It is also possible to achieve a method of adjusting positions of liquid droplet marks, comprising the steps of: 
   preparing a liquid ejecting apparatus including a moving member that has at least two liquid ejecting section groups and that is capable of moving in a predetermined direction due to an external force, each of the liquid ejecting section groups including at least two liquid ejecting sections for ejecting liquid droplets to form liquid droplet marks on a medium, each of the liquid ejecting section groups being driven based on a single reference ejection signal for causing the liquid droplets to be ejected from the liquid ejecting sections; 
   ejecting liquid to form a liquid droplet mark pattern including liquid droplet marks formed by ejecting liquid from the liquid ejecting sections of a reference liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a predetermined reference timing and that is a liquid ejecting section group other than the liquid ejecting section group, among the liquid ejecting section groups, that is the most susceptible to vibration caused by moving the moving member and liquid droplet marks formed by ejecting liquid from the liquid ejecting sections of one other liquid ejecting section group, among the liquid ejecting section groups other than the reference liquid ejecting section group, that is driven according to the reference ejection signal therefor at a timing different from the predetermined reference timing; and 
   adjusting the timing of the reference ejection signal for the one other liquid ejecting section group based on the liquid droplet mark pattern. 
   It is also possible to achieve a liquid ejecting system comprising: 
   a computer; and 
   a liquid ejecting apparatus that is connected to the computer and that includes:
         a moving member that has at least two liquid ejecting section groups and that is capable of moving in a predetermined direction due to an external force, each of the liquid ejecting section groups including at least two liquid ejecting sections for ejecting liquid droplets to form liquid droplet marks on a medium, and each of the liquid ejecting section groups being driven based on a single reference ejection signal for causing the liquid droplets to be ejected from the liquid ejecting sections;   a reference liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a predetermined reference timing and that is a liquid ejecting section group other than the liquid ejecting section group, among the liquid ejecting section groups, that is the most susceptible to vibration caused by moving the moving member; and   at least one other liquid ejecting section group, among the liquid ejecting section groups, that is driven according to the reference ejection signal therefor at a timing adjusted based on the predetermined reference timing of the reference liquid ejecting section group.
 
First Embodiment
 
Example of an Overview of a Printing Apparatus
       

     FIG. 1  and  FIG. 2  are perspective views showing an overview of a color inkjet printer  20  serving as an example of the printing apparatus. The color printer  20  uses, for example, roll paper or relatively large-sized print paper such as JIS standard A0 sized paper or B0 sized paper, and in the example shown in  FIG. 1  and  FIG. 2 , the color printer  20  is provided with roll paper. It should be noted that the position of the carriage, which is discussed later, is different in the color inkjet printer  20  shown in  FIG. 1  and the color inkjet printer  20  shown in  FIG. 2 . 
   The color inkjet printer  20  shown in  FIG. 1  and  FIG. 2  is provided with a paper feed motor  31 , a paper feed roller  24  (also called a “smap roller”) as an example of the feed mechanism that is driven by the paper feed motor  31  and that is for feeding roll paper P, which is an example of the medium to be printed, in the paper feed direction (hereinafter, this is also called the sub-scanning direction), a roll paper holder  27  on which the roll paper P can be set, paper press rollers  29  for pressing the roll paper P against the paper feed roller  24 , a platen  26  serving as an example of the support member that is capable of supporting the roll paper P, print heads  36  each provided with numerous nozzles, a carriage  28  serving as an example of the moving member that is provided with the print heads  36  and that can be moved in the main-scanning direction, a carriage motor  30 , a pull belt  32  serving as an example of the drive member that is moved by the carriage motor  30 , that is connected to the carriage  28  at a predetermined connecting section  37 , and that is for driving the carriage  28 , a guide rail  34  for guiding the carriage  28 , a CCD camera  40  provided in/on the carriage  28  for capturing an image of the dots formed on the roll paper P by the ink that is ejected from the print heads  36 , a temperature gauge  202  for measuring the temperature around the color inkjet printer  20 , and a humidity gauge  204  for measuring the humidity around the color ink-jet printer  20 . 
   The roll paper P is set in the roll paper holder  27 . The roll paper P is pressed against the paper feed roller  24  by the paper press rollers  29 , and is fed in the paper feed direction over the surface of the platen  26  by rotation of the paper feed roller  24 . The carriage  28  is driven by the pull belt  32  and moved in the main-scanning direction along the guide rail  34 . Then, as the roll paper P is fed in the paper feed direction, the carriage  28  is moved in the main-scanning direction and ink is ejected from the plurality of print heads  36  provided in/on the carriage  28  to carry out printing. 
   Also, the platen  26 , as shown in  FIG. 3 , has numerous suction apertures  302  in its upper surface, and is internally provided with a chamber  304  that is continuous with the suction apertures  302 .  FIG. 3  is a conceptual diagram illustrating the platen  26  and a suction mechanism  16 , which is discussed later. The numerous suction apertures  302  are provided annularly along rim of the upper surface of the platen  26 , and are in communication with the suction mechanism  16 , which is an example of the suction member, via the chamber  304 . The chamber  304  includes inside a pressure sensor  306 , which is an example of the detector, for detecting the pressure inside the chamber  304 . 
   The suction mechanism  16  has a suction blower  310  for sucking in the air within the chamber  304  to cause negative pressure therein and make the chamber  304  a vacuum, a hose  308  connecting the suction blower  310  and the chamber  304 , and a switch valve  312  provided in the hose  308  between the suction blower  310  and the chamber  304 . The switch valve  312  is constituted by an electromagnetic three-way valve that has an air release opening. 
   When the suction blower  310  is driven, the pressure within the chamber  304  drops, and the roll paper P supported by the platen  26  is sucked via the numerous suction apertures  302 . Also, by switching the switch valve  312  in this state, atmospheric air can be released into the chamber  304 . 
   That is, by controlling the suction blower  310  and the switch valve  312 , an appropriate pressure can be established within the chamber so as to suck the roll paper P. Thus, the roll paper P can be kept flat without any bending occurring in the roll paper P. 
   It should be noted that in the above description, the numerous suction apertures  302  were provided annularly along the rim in the upper surface of the platen  26 ; however, they may also be provided at an equal spacing, for example, over the entire surface of the platen  26 . This would allow the roll paper P to be adequately adhered, and has the benefit that cockling, for example, is less likely to occur. 
   Configuration of the Print Heads 
   Next,  FIG. 4  is used to describe the configuration of the print heads  36 .  FIG. 4  is an explanatory diagram for describing the print heads  36 . 
   The print head  36 , as shown in  FIG. 4 , has a black nozzle row, a cyan nozzle row, a light cyan nozzle row, a magenta nozzle row, a light magenta nozzle row, and a yellow nozzle row, arranged in straight lines in the paper feed direction. 
   The black nozzle row has 180 nozzles, nozzles # 1  to # 180 . The nozzles # 1 , . . . , # 180  of the black nozzle row are arranged at a constant nozzle pitch k·D in the sub-scanning direction. Here, D is the dot pitch in the sub-scanning direction, and k is an integer. The dot pitch D in the sub-scanning direction is equal to the pitch of the main scan lines (raster lines), which are lines formed in the main scanning direction by dots. Hereinafter, the integer k expressing the nozzle pitch k·D is referred to simply as the “nozzle pitch k.” In the example of  FIG. 4 , the nozzle pitch k is four dots. The nozzle pitch k, however, may be set to any integer. 
   The above-described matters also apply for the cyan nozzle row, the light cyan nozzle row, the magenta nozzle row, the light magenta nozzle row, and the yellow nozzle row. That is, each of these nozzle rows has 180 nozzles # 1  to # 180  arranged at a constant nozzle pitch k·D in the sub-scanning direction. 
   During printing, droplets of ink are ejected from the nozzles as the print heads  36  are moved at a constant speed in the main-scanning direction along with the carriage  28 . However, depending on the print mode, there are instances in which only some of the nozzles are used and not all the nozzles are used. 
   It should be noted that in  FIG. 4 , the ink colors of the rows were, in order from the left side in the figure, the black nozzle row, the cyan nozzle row, the light cyan nozzle row, the magenta nozzle row, the light magenta nozzle row, and the yellow nozzle row; however, this is not a limitation, and it is also possible for the ink colors of the rows to be arranged in a different order. 
   Example of the Overall Configuration of the Printing System 
   Next, an example of the overall configuration of the printing system is described with reference to  FIG. 5  and  FIG. 6 .  FIG. 5  is a block diagram showing the configuration of a printing system provided with the color inkjet printer  20  described above.  FIG. 6  is a block diagram showing the configuration of an image processing section  38 . 
   The printing system is provided with a computer  90  and the color inkjet printer  20 , which is an example of the printing apparatus. It should be noted that the printing system including the color inkjet printer  20  and the computer  90  can also be broadly referred to as a “printing apparatus.” Although not shown in the diagram, a printing system is made of the computer  90 , the color inkjet printer  20 , a display device such as a CRT  21  or a liquid crystal display device, input devices such as a keyboard and a mouse, and a drive device such as a flexible disk drive device or a CD-ROM drive device. 
   In the computer  90 , an application program  95  is executed under a predetermined operating system. The operating system includes a video driver  91 , and the application program  95 , which is for retouching images, for example, carries out desired processing with respect to an image to be processed, and also displays the image on the CRT  21  through the video driver  91 . 
   When the application program  95  issues a print command, the image processing section  38  provided in the color inkjet printer  20  receives image data from the application program  95  and converts the data into print data PD. As shown in  FIG. 6 , the image processing section  38  is internally provided with a resolution conversion module  97 , a color conversion module  98 , a halftone module  99 , a rasterizer  100 , a UI printer interface module  102 , a raster data storage section  103 , a color conversion lookup table LUT, a correction test pattern supply module  104 , a buffer memory  50 , and an image buffer  52 . 
   The resolution conversion module  97  serves to convert the resolution of the color image data generated by the application program  95  into the print resolution. The image data whose resolution has been thus converted at this point is still image information made of the three color components RGB. The color conversion module  98  references the color conversion look-up table LUT and, for each pixel, converts the RGB image data into multi-gradation data of a plurality of ink colors that can be used by the color inkjet printer  20 . 
   The multi-gradation data that has been color converted has a gradation value of 256 grades, for example. The halftone module  99  executes so-called halftone processing to generate halftone image data. The halftone image data are arranged by the rasterizer  100  into a desired data order, and are output as the final print data PD to the raster data storage portion  103  along with various commands COM. 
   Also, the correction test pattern supply module  104  has a function for outputting, to the buffer memory  50 , print data PD used when executing the operation for forming, on the roll paper P, dots for correcting the feed amount by which the paper feed roller  24  feeds the roll paper P. These print data PD include raster data indicating how the dots are to be formed during each main scan and data indicating the sub-scanning feed amount. 
   On the other hand, the user interface display module  101  provided in the computer  90  functions to display various types of user interface windows related to printing and also functions to receive inputs from the user through these windows. For example, a user could instruct the type and size of the print paper, or the dot recording mode, for example, through the user interface display module  101 . 
   The UI printer interface module  102  functions as an interface between the user interface display module  101  and the color inkjet printer  20 . The UI printer interface module  102  interprets instructions given by the user through the user interface and sends various commands COM to the buffer memory  50 , for example, or conversely, it interprets commands COM received from the buffer memory  50 , for example, and executes various displays on the user interface. For example, the above-mentioned instruction regarding the type or the size of the print paper, for example, that is received by the user interface display module  101  is sent to the UI printer interface module  102 , which interprets this instruction and sends a command COM to the buffer memory  50 . 
   The UI printer interface module  102  also functions as a print mode setting section. That is, the UI printer interface module  102  determines the print mode based on information on the dot recording mode received by the user interface display module  101  and the information of the print data PD output from the rasterizer  100 . 
   More specifically, a high image quality mode and a fast mode are provided as the dot recording modes, and the user can select either one of these modes. For example, the high image quality mode is a mode in which dots are recorded using a so-called overlapping method, and fast mode is a mode in which dots are recorded without using this method. Then, the UI printer interface module  102  determines the print mode based on the dot recording mode that has been selected and the resolution information found in the print data PD. Next, according to the print mode that has been determined, the UI printer interface module  102  outputs, to the raster data storage section  103 , information about the nozzles to be use when printing and information about the data indicating the sub-scanning feed amount. 
   The raster data storage section  103  outputs the final print data PD to the buffer memory  50  together with various commands COM. The print data PD includes raster data indicating how dots are to be formed in each main scan, information about the nozzles to be used when printing, and the data indicating the sub-scanning feed amount. 
   The print data PD and the various commands COM that are output by the raster data storage section  103  and the correction test pattern supply module  104 , and the commands COM output by the UI printer interface module  102 , are temporarily stored in the buffer memory  50 . After the color inkjet printer  20  receives these at the buffer memory  50 , it transmits them to the image buffer  52  or the system controller  54 . The print data PD for the plurality of colors that have been received by the buffer memory  50  are stored in the image buffer  52 . 
   The color inkjet printer  20  is provided with a system controller  54  for controlling the overall operation of the color inkjet printer  20 , a main memory  56 , and an EEPROM  58 , in addition to the image processing section  38  described above. The system controller  54  is connected to a main-scan drive circuit  61  for driving the carriage motor  30 , a sub-scan drive circuit  62  for driving the paper feed motor  31 , a head control circuit  63  for controlling the print heads  36 , a captured image processing section  42  for processing images captured by the above-described CCD camera  40 , the above-described pressure sensor  306 , a pressure control circuit  314  for controlling the suction mechanism  16  described above according to the output value of the pressure sensor  306 , the temperature sensor  322  described above, and the humidity sensor  324  described above. 
   In the color inkjet printer  20 , the system controller  54  reads necessary information from the print data in the buffer memory  50 , and based on this information, sends control signals to the main-scan drive circuit  61 , the sub-scan drive circuit  62 , and the head control circuit  63 , for example. Also, the head control circuit  63  reads print data for the various color components from the image buffer  52  in accordance with the control signal from the system controller  54 , and based on the print data, drives the nozzles for the various color provided in the print heads  36 . 
   The system controller  54  also controls the suction blower  310  and the switch valve  312  according to the output value of the pressure sensor  306  using the pressure control circuit  314 . Accordingly, the inside of the chamber is kept at a desired pressure, and suitable suction of the roll paper P can be achieved. 
   Operation of the Printing System 
   The operation of the above-described printing system is described next using  FIG. 7 .  FIG. 7  is a transition diagram showing the operation of the printing system. 
   First, the user turns the power of the computer  90  and the power of the color inkjet printer  200 N in order to supply power to the printing system (step S 2 ). 
   After power has been supplied to the printing system and before an image is printed to the roll paper P, the color ink-jet printer  20  carries out an operation for forming, on the roll paper P, dots for correcting the feed amount by which the paper feed roller  24  feeds the roll paper P (step S 4 ). Then, based on the correction test pattern, which is a group of the dots thus formed on the roll paper P, the color inkjet printer  20  executes an operation for obtaining a correction amount for correcting the feed amount by which the roll paper P is fed (step S 6 ). Hereinafter, these operations according to step S 4  and step S 6  may also be collectively referred to as the “correction amount obtaining operation”. 
   The operation of step S 4  will be described using  FIG. 8  and  FIG. 9 .  FIG. 8  is a conceptual diagram illustrating how the vibration is generated when the carriage  28  is moved.  FIG. 9  is a conceptual diagram showing an example of a correction test pattern. 
   First, the color injection printer  20  receives the above-mentioned command to turn on the power source, and print data PD about the correction test pattern is sent from the correction test pattern supply module  104  to the buffer memory  50  together with various commands COM. The image processing section  38  sends the print data PD to the image buffer  52  after receiving the data at the buffer memory  50 . 
   The image processing section  38  also sends the above-described commands COM to the system controller  54  after they are received by the buffer memory  50 . The system controller  54  then sends control signals to the main-scan drive circuit  61 , the sub-scan drive circuit  62 , and the head control circuit  63  based on the information received from the buffer memory  50  within the image processing section  38 . 
   The head control circuit  63  reads the print data PD from the image buffer  52  within the image processing section  38  according to the control signals from the system controller  54 . The head control circuit  63  then controls the print heads  36  based on the data that has been read out. 
   Then, while the sub-scan drive circuit  62  controls the paper feed motor  31  so that it feeds the roll paper P, the carriage motor  30  is controlled by the main-scan drive circuit  61  to move the carriage  28  in the main-scanning direction and the print heads  36  are controlled by the head control circuit  63  to eject ink, thereby forming, on the roll paper P, dots for correcting the feed amount by which the roll paper P is fed. 
   It should be noted that at this time, a print head  36 , among the plurality of print heads  36  provided in/on the color ink-jet printer  20 , that is the least susceptible to the vibration caused by moving the carriage  28  is used as the print head  36  that is used when forming these dots onto the roll paper P. 
   In the present embodiment, this print head is the print head that is closest to the connecting section  37  between the carriage  28  and the pull belt  32 . This is described using  FIG. 8 . 
   In  FIG. 8 , the carriage  28  is guided along the guide rail  34  and moved in the main-scanning direction (in the diagram, the direction shown by the white arrow). At this time, vibration occurs in the carriage  28  in the direction shown by the black arrows in the diagram. Also, since the carriage  28  is driven by the pull belt  32 , the vibration becomes larger as the distance from the connecting section  37  becomes greater in the direction perpendicular to the main-scanning direction, as shown in the diagram. 
   Consequently, in this example, as shown in  FIG. 1  and  FIG. 2 , the print head  36   c  is the print head that matches these conditions, and ink is ejected from the print head  36   c  to form, on the roll paper P, dots for correcting the feed amount by which the roll paper P is fed. It should be noted that the print heads  36  have not been shown in  FIG. 8  in order to make the diagram easy to understand. 
   As described above, the color inkjet printer  20  feeds the roll paper P while moving the carriage  28  in the main-scanning direction and ejecting ink from a print head  36  to form, on the roll paper P, dots for correcting the feed amount by which the roll paper P is fed. The group of dots formed on the roll paper P then functions as a test pattern for correction.  FIG. 9  shows an example of the dots that are formed. In  FIG. 9 , four transverse lines L 1 , L 2 , L 3 , and L 4  are shown as the correction test pattern at the both edges of the roll paper P, and these are made of groups of dots lined up in the main-scanning direction. 
   The procedure through which these transverse lines L 1 , L 2 , L 3 , and L 4  are formed is described next. First, the carriage  28  is moved in the main-scanning direction as ink is ejected from predetermined nozzles of the print head  36  to form the transverse line L 1 . Then, when the carriage  28  has arrived at a predetermined position, the ejection of ink is temporarily stopped. With the ejection of ink stopped, the carriage  28  is moved further in the main-scanning direction, and when the carriage  28  has arrived at a predetermined position, ink ejection starts again, and the transverse line L 2  is formed. 
   After the transverse line L 2  has been formed, the roll paper P is fed in the paper feed direction by a feed amount y. Then, while the carriage  28  is being moved in the main-scanning direction, ink is ejected from the nozzles used to form the transverse lines L 1  and L 2 , forming the transverse line L 3 . Then, when the carriage  28  has reached a predetermined position, the ejection of ink is temporarily stopped. With ink ejection stopped, the carriage  28  is carried further in the main-scanning direction, and when the carriage  28  has reached a predetermined position, the ejection of ink is started again. Then, the transverse line L 4  is formed. 
   Next, based on the correction test pattern formed on the roll paper P, the color inkjet printer  20  carries out an operation for obtaining a correction amount for correcting the feed amount by which the paper feed roller  24  feeds the roll paper P. (step S 6 ). 
   This operation is described below. First, the color ink-jet printer  20  moves the carriage  28  in the main-scanning direction and positions the carriage  28  in a position where both the transverse line L 1  and the transverse line L 3  can be captured by the CCD camera  40 . Then, both the transverse line L 1  and the transverse line L 3  are captured by the CCD camera  40 . Next, the color inkjet printer  20  moves the carriage  28  in the main-scanning direction and positions it in a position where the CCD camera  40  can capture both the transverse line L 2  and the transverse line L 4 , and an image of both the transverse line L 2  and the transverse line L 4  is captured. 
   The two images captured in this way are sent to the captured image processing section  42 , and both images undergo image processing. Then, from the result of this image processing, the distance between the transverse line L 1  and the transverse line L 3  is obtained as a feed amount Y 1 , and the distance between the transverse line L 2  and the transverse line L 4  is obtained as a feed amount Y 2 . 
   The information on the feed amount Y 1  and the feed amount Y 2  that have been obtained is sent to the system controller  54 . The system controller  54  then calculates the average value Y of Y 1  and Y 2 , and subtracts the above-mentioned feed amount y from the average value Y, obtaining a correction amount C (C=Y−y) for correcting the feed amount by which the paper feed roller  24  feeds the roll paper P. Then, this correction amount is set in the EEPROM  58  of the color inkjet printer  20 . 
   It should be noted that in parallel with the above correction amount obtaining operation, or before or after this operation, the system controller  54  obtains data on the pressure inside the chamber  304  and the temperature and the humidity around the color inkjet printer  20  from the pressure sensor  306 , the temperature sensor  322 , and the humidity sensor  324 , respectively. The data obtained are set in the EEPROM  58  of the color inkjet printer  20  together with the correction amount. 
   After the correction amount obtaining operation of step S 4  and step S 6  is over, the color inkjet printer  20  enters a standby state (step S 8 ). In this embodiment, this standby state is a state in which the power is on and the correction amount obtaining operation or the printing operation is not being performed. 
   Then, in the standby state, the system controller  54  constantly obtains data on the on the pressure inside the chamber  304  and the temperature and the humidity around the color ink-jet printer  20  from the pressure sensor  306 , the temperature sensor  322 , and the humidity sensor  324 , respectively. These data that are obtained are compared with the data on the pressure, temperature, and humidity already stored in the EEPROM  58 , and the differences between them is obtained. Then, if even one of the obtained difference in pressure, the obtained difference in temperature, and the obtained difference in humidity, exceeds a threshold value that has been respectively determined in advance, then the color inkjet printer  20  carries out the correction amount obtaining operation described above. 
   It should be noted that below, the description is continued under the premise that the correction amount obtaining operation is not performed in step S 8 . 
   Next, when an instruction to perform printing is made by the user in the application program  95 , for example, the color inkjet printer  20  carries out the printing operation (step S 10 ). The printing operation is described below. 
   Having received an instruction to perform printing, the application program  95  issues a print command. Then, the image processing section  38  mentioned above receives image data from the application program  95  and converts the data into print data PD, and the print data PD, together with various commands COMPUTER  90 , are transmitted to the buffer memory  50 . The image processing section  38  receives the print data PD through the buffer memory  50 , and then sends the print data PD to the image buffer  52 . 
   The image processing section  38  also receives the above commands COM through the buffer memory  50  and then sends them to the system controller  54 . Based on the information received from the buffer memory  50  in the image processing section  38 , the system controller  54  sends control signals to the main-scan drive circuit  61 , the sub-scan drive circuit  62 , and the head control circuit  63 . 
   Also, the head control circuit  63  reads the print data for each of the various color components from the image buffer  52  in the image processing section  38  in accordance with the control signal from the system controller  54 . Then, the head control circuit  63  controls the plurality of print heads  36   a ,  36   b ,  36   c ,  36   d ,  36   e ,  36   f ,  36   g , and  36   h  according to the data that have been read out. 
   Then, while the sub-scan drive circuit  62  controls the paper feed motor  31  to feed the roll paper P, the main-scan drive circuit  61  controls the carriage motor  30  to move the carriage  28  in the main-scanning direction, and the head control circuit  63  controls the plurality of print heads  36   a ,  36   b ,  36   c ,  36   d ,  36   e ,  36   f ,  36   g , and  36   h  to make them eject ink and print on the roll paper P. It should be noted that at this time, the operation of the paper feed motor  31  is corrected based on the correction amount that is stored in the EEPROM  58 , that is, that has been set in the EEPROM  58  at step S 6 . 
   When the printing operation of the color inkjet printer  20  is over, the color inkjet printer  20  enters the standby state (step S 12 ). 
   Then, as mentioned above, in the standby state, the system controller  54  constantly obtains data about the pressure within the chamber  304  and the temperature and the humidity around the color inkjet printer  20  from the pressure sensor  306 , the temperature sensor  322 , and the humidity sensor  324 , respectively. These data that are obtained are compared with the data about the pressure, temperature, and humidity already stored in the EEPROM  58 , and any difference between them is found. If even one of the obtained difference in pressure, the obtained difference in temperature, and the obtained difference in humidity, exceeds a threshold value that has been respectively determined in advance, then the color inkjet printer  20  carries out the correction amount obtaining operation described above. 
   It should be noted that in this embodiment, in step S 12 , the operation state of the printer has changed to the correction amount obtaining operation as a result of the type of the print paper being changed. A detailed description of this is as follows. 
   The user, in the standby state of step S 12 , changes the type of the print paper through the user interface display module  101 . These instructions received through the user interface display module  101  are sent to the UI printer interface module  102  provided in the image processing section  38 , and the UI printer interface module  102  interprets the order that has been instructed and sends a command COM to the buffer memory  50 . The image processing section  38  receives this command COM and subsequently transmits it to the system controller  54 . 
   The system controller  54  determines that the print paper type has been changed, and from the standpoint that the roll paper P is to be kept in a flat state, the controller  54  sets, to the pressure sensor control circuit  314 , a value for the pressure within the chamber  304  that is adequate for the new type of print paper. Then, the pressure sensor control circuit  314  controls the suction mechanism  16  so that the pressure within the chamber  304  becomes the pressure value that has been set. 
   As a result of this control, the output value of the pressure sensor changes, and if that change is large, then the color ink-jet printer  20  starts executing the correction amount obtaining operation. Then, in the correction amount obtaining operation, the same operations as those described in step S 4  and step S 6  are executed (step S 14  and step S 16 ), and a new correction amount is set in the EEPROM  58 . The new correction amount that has been set is used for controlling the operation of the paper feed motor  31  in the printing operation that is performed next. 
   In this manner, ink is ejected from the print head, among the plurality of print heads, that is the least susceptible to the vibration generated when the carriage is moved, to form, on the roll paper, dots for correcting the feed amount by which the roll paper is fed by the paper feed roller as the carriage is moved, thereby allowing the feed amount to be suitably corrected. 
   That is, as described in the Description of the Related Art, when dots for correcting the feed amount are formed on the roll paper as the carriage is moved, vibration occurs in the carriage. Since the print heads are provided on the carriage, that vibration is also transmitted to the print heads. 
   Under these circumstances, when dots for correcting the feed amount are formed on the print paper by ejected ink from the print heads, a desired correction test pattern cannot be obtained, and consequently, there is a possibility that the correction amount obtained based on this correction test pattern will be inaccurate. Thus, when the feed amount is corrected based on this correction amount, appropriate correction can no longer be executed. 
   Accordingly, as above, ink is ejected from the print head of the plurality of print heads that is the least susceptible to the vibration generated when the carriage is moved, to form, on the roll paper, dots for correcting the feed amount by which the roll paper is fed by the paper feed roller as the carriage is moved. 
   Thus, if ink is ejected from the print head that is the least susceptible to the vibration, which is caused by moving the carriage, to form, on the print paper, dots for correcting the feed amount, then since the vibration has less of an impact, a desired correction test pattern is obtained, and consequently, the correction amount that is obtained based on that correction test pattern becomes accurate. Then, when the feed amount is corrected based on this correction amount, adequate correction of the feed amount can be implemented. 
   It should be noted that in the above discussion, the number of print heads was set to eight; however, this is not a limitation, and as long as the number is plural, there may be any number of print heads. 
   Also, in the above description, the correction test pattern formed on the roll paper was captured with the CCD camera and image processing was carried out in order to obtain a suitable correction amount; however, this is not a limitation, and for example, it is also possible to form a plurality of correction test patterns on the roll paper and for the user to select from these patterns a suitable correction test pattern so as to obtain a suitable correction amount. 
   Also, in the above description, a correction test pattern was formed on the roll paper by ejecting ink from a print head, and after finishing this process, that correction test pattern was captured by the CCD camera. This is not a limitation, however, and it is for example also possible to form a correction test pattern on the roll paper by ejecting ink from a print head while the CCD camera, which is adjacent to that print head, captures an image of the correction test pattern. 
   Also, in the above description, the image processing section shown in  FIG. 6  was used as an example of a image processing means; however, this is not a limitation, and any means may be adopted, as long as it processes images output by an application, for example, in order to carry out operations such as to send print data to the head control circuit. For example, it is not necessary for the color conversion table to always be referenced when the color conversion module performs color conversion, and it is also not necessary for halftone processing to always be performed when image processing is carried out. It is also possible for the image processing means to not include a function as a user interface, such as the UI printer interface module. 
   Also, in the above description, the print mode was determined from the dot recording mode that was selected and the information on the resolution found in the print data PD. This is not a limitation, however. For example, it is also possible for the print mode to be determined based on only one of either the dot recording mode or the resolution. In the above description, a high image quality mode and a fast mode were described as the dot recording modes, but this is not a limitation. 
   Also, a correction test pattern that is made of a group of dots lined up in the main-scanning direction was shown in the above description, but it is also possible for the correction test pattern to be made of dots. 
   Other Considerations 
   An embodiment of a printing apparatus, for example, according to the present invention has been described above. However, the foregoing embodiment of the invention is for the purpose of elucidating the present invention and is not to be interpreted as limiting the present invention. The invention can of course be altered and improved without departing from the gist thereof and includes functional equivalents. 
   It should be noted that in the above embodiment, print paper was described as the medium to be printed, but as the medium to be printed it is also possible to use film, cloth, or thin metal plates, for example. Also, roll paper was described as an example of the print paper, but it is also possible to use A0 paper or B0 paper, for example, as the print paper. 
   Also, in the above embodiment a color inkjet printer was described, but the present invention is also applicable for monochrome inkjet printers as well. 
   Also, in the above embodiment, ink was ejected from the print head located the closest to the connecting section between the carriage and the pull belt while the carriage was moved so as to form, onto the roll paper, dots for correcting the feed amount by which the paper feed roller feeds the roll paper. However, this is not a limitation. 
   In this case, however, the print head that is the least susceptible to vibration can be easily selected from among the plurality of print heads, and in this regard the above-described embodiment is preferable. 
   Also, in the above embodiment, ink was ejected from a print head while the carriage was moved so as to form, on both edge sections of the roll paper, dots for correcting the feed amount. However, this is not a limitation, and for example, it is also possible for ink to be ejected from a print head while the carriage is moved so as to form dots for correcting the feed amount on only one edge section of the roll paper. 
   In the case of the above-mentioned embodiment, however, two groups of correction test patterns can be obtained, thereby allowing the correction amount to be obtained more accurately. Therefore, from the standpoint that more suitable correction can be carried out, the embodiment described above is more preferable. 
   Also, in the above embodiment, ink is ejected from predetermined nozzles provided in the predetermined print head to form dots for correcting the feed amount on the roll paper; however, this is not a limitation. For example, it is also possible to change the nozzles that eject ink every time dots for correcting the feed amount are formed on the roll paper. 
   However, from the standpoint that error due to changing the nozzles that eject ink does not occur, the configuration of the above-mentioned embodiment is preferable. 
   Also, in the above embodiment, whether or not to form, onto the roll paper, the dots for correcting the feed amount by which the print paper is fed by the paper feed roller was determined according to the output value of the pressure sensor. However, this is not a limitation. 
   When, however, the force by which the roll paper is sucked by the suction mechanism fluctuates, the friction of the roll paper against the platen also fluctuates, and therefore there is a higher possibility that the correction amount appropriate for correcting the feed amount will change. 
   Consequently, from the perspective that dots for correcting the feed amount by which the roll paper is fed by the paper feed roller are formed on the roll paper at an appropriate timing, the above-mentioned embodiment is preferable. 
   Also, in the above embodiment, whether or not to form the dots for correcting the feed amount, by which the paper feed roller feeds the roll paper, onto the roll paper was determined according to at least one of the temperature value and the humidity value around the color inkjet printer. However, this is not a limitation. 
   When, however, the temperature or the humidity around the color inkjet printer fluctuates, the roll paper will expand/constrict or the above-described friction may fluctuate, and therefore there is a high possibility that the correction amount appropriate for correcting the feed amount will change. 
   Consequently, from the perspective that dots for correcting the feed amount by which the roll paper is fed by the paper feed roller are formed on the roll paper at an appropriate timing, the above embodiment is preferable. 
   Also, in the above embodiment, the dots for correcting the feed amount by which the roll paper is fed by the paper feed roller are formed on the roll paper when power is supplied to the color inkjet printer. However, this is not a limitation. For example, it is also possible for dots for correcting the feed amount by which the roll paper is fed by the paper feed roller to not be formed on the roll paper when power is supplied to the color ink-jet printer. 
   However, from the standpoint that execution of appropriate correction can be guaranteed, the embodiment described above is preferable. 
   It is also possible for dots for correcting the feed amount by which the roll paper is fed by the paper feed roller to be formed on the print paper during the printing operation of the color inkjet printer. 
   For example, if those dots may be formed on the print paper when a new page is printed, or if a plurality of sheets of print paper are printed continuously, then it is possible for those dots to be formed on the print paper each time a predetermined number of sheets of the print paper have been printed. 
   Doing this allows the dots to be formed on the print paper efficiently. 
   It is also possible to form dots for correcting the feed amount, by which the roll paper is fed by the paper feed roller, onto the print paper when the print paper has been exchanged. 
   Doing this allows execution of suitable correction to be guaranteed. 
   It is also possible to provide the color inkjet printer with a detector (second detector) for detecting whether or not the print paper has been exchanged, and when it is detected by the detector that the print paper has been exchanged, the dots for correcting the feed amount by which the paper is fed by the paper feed roller may be formed on the print paper. 
   For example, a reflective-type optical sensor can be used as the detector, in which case the light that is emitted from the reflective-type optical sensor toward the print paper is reflected by the print paper and the intensity of that reflected light is measured in order to detect whether or not the print paper has been exchanged. 
   Accordingly, whether or not the print paper has been exchanged can be detected using a simple method. 
   It is also possible for the dots for correcting the feed amount by which the roll paper is fed by the paper feed roller to be formed on the print paper when the print mode, which was discussed above, of the color inkjet printer has been changed. 
   Since the paper feed amount is different for each print mode, this would ensure execution of appropriate correction. 
   Also, in the above embodiment, a plurality of correction amounts for correcting the feed amount by which the roll paper is fed by the paper feed roller were obtained based on the dots formed on the roll paper, and based on the average value of the plurality of correction amounts that were obtained, the feed amount by which the roll paper is fed by the paper feed roller was corrected. However, this is not a limitation. For example, it is also possible to obtain a single correction amount for correcting the feed amount by which the roll paper is fed by the paper feed roller based on the dots formed on the roll paper, and based on the correction amount that is obtained, the feed amount by which the roll paper is fed by the paper feed roller can be corrected. 
   However, from the perspective that more accurate correction can be carried out in the present case, the configuration of the above embodiment is preferable. 
   With the present invention, it is possible to achieve a printing apparatus with which correction of the feed amount can be suitably carried out. 
   Second Embodiment 
   Example of an Overview of a Printing Apparatus 
     FIG. 10  and  FIG. 11  are perspective views showing an overview of a color inkjet printer (referred to as “color printer” in the following)  2020 , which serves as a liquid ejecting apparatus in which ink (as an example of liquid) is ejected from nozzles (as an example of liquid ejecting sections) to perform printing, according to a second embodiment of the present invention. This color printer  2020  is an inkjet printer that is capable of outputting color images and that prints images by forming dots by ejecting colored ink of, for example, the six colors—cyan-type ink such as cyan ink (C) and light cyan ink (pale cyan ink, LC), magenta-type ink such as magenta ink (M) and light magenta ink (pale magenta ink, LM), yellow ink (Y), and black ink (K)—on various kinds of media, such as print paper. It should be noted that the colored inks are not limited to the above-noted six colors, and it is also possible to use, for example, dark yellow (dim yellow, DY) or the like. The color printer  2020  is adapted, for example, to roll paper in which print paper serving as the medium to be printed is wound up in roll-shape, but also to relatively large single-sheet print paper, such as A0 or B0 size paper according to the JIS standard. In the example shown in  FIG. 10  and  FIG. 11 , the color printer  2020  is provided with roll paper. In  FIG. 10  and  FIG. 11 , the position of the carriage  2028  provided on the color printer  2020  is different. This carriage  2028  will be explained further below. 
   As shown in the figures, the color printer  2020  includes a printing section  2003  that ejects ink in order to print on the roll paper P, and a print paper carrying section  2005  for carrying the print paper. 
   The printing section  2003  includes a carriage  2028  which serves as a moving member, a carriage motor  2030 , a pull belt  2032 , two guide rails  2034 , a linear encoder  2017 , and a linear encoder code plate  2019 . The carriage  2028  integrally holds print heads  2036  which serve as ink ejecting section groups, or ink ejecting units, provided with nozzles serving as a plurality of ink ejecting sections. The carriage motor  2030  is for causing the carriage  2028  to move (or scan) back and forth by moving it in a direction (which is referred to as “main-scanning direction” below) that is approximately perpendicular to the direction in which the roll paper P is carried (which is referred to as “sub-scanning direction” below). The pull belt  2032  is made of metal, configures a “moving member (moving means)” in cooperation with the carriage motor  2030 , and is driven by the carriage motor  2030  to move the carriage  2028 . The guide rails  2034  are for guiding the carriage  2028 . The linear encoder  2017  is fixed to the carriage  2028 , and the linear encoder code plate  2019  has slits formed therein at predetermined intervals. 
   The two guide rails  2034  are arranged at the top and the bottom along the main scanning direction with a certain spacing in the sub-scanning direction between them, and are supported at their left and right end sides by a frame (not shown) serving as a base. Of the two guide rails  2034 , the lower guide rail  2341  is arranged more to the front than the upper guide rail  2342 . Thus, the carriage  2028 , which is arranged such that it extends between the two guide rails  2341  and  2342 , moves in a tilted state in which its upper section is positioned to the rear and its lower section is positioned to the front. 
   The linear encoder code plate  2019  is provided on and along the upper guide rail  2342  by which the carriage  2028  is guided. The linear encoder code plate  2019  is arranged such that it is in opposition to a detecting section of the linear encoder  2017  that is fixed to the carriage  2028 , which moves along the guide rails  2034 . The linear encoder  2017  will be described in detail later. 
   The pull belt  2032  is formed in an annular shape, and is extended at a central position between the upper and lower guide rails  2341  and  2342  between two pulleys  2044  and  2045  that are spaced apart from each other by a distance approximately equal to the length of the guide rails  2341  and  2342 . One pulley  2044 , of the two pulleys  2044  and  2045 , is connected to the carriage motor  2030 . 
   The carriage  2028 , which is arranged such that it extends between the two guide rails  2341  and  2342 , has an engaging portion  2046  at which the pull belt  2032  is fixed to the carriage  2028  approximately at the center in the vertical direction. The color printer  2020  prints on the roll paper P, which is fed by the print paper carrying section  2005 , by pulling the carriage  2028  with the pull belt  2032  that is driven by the carriage motor  2030  to move the carriage  2028  in the main-scanning direction along the guide rails  2034 , and by ejecting ink from the eight print heads  2036  provided on the carriage  2028 . At this time, the carriage  2028  moves due to a drive force of the carriage motor  2030  transmitted via the pull belt  2032 . In other words, the engaging portion  2046  is the section of the carriage  2028  to which an external force for moving the carriage  2028  is applied. 
   In the present embodiment, eight print heads  2036  are provided on the carriage  2028 , each of these print heads  2036  includes a plurality of nozzles n as ink ejecting sections for ejecting ink, and ink is ejected from predetermined ones of the nozzles n under the control of a head control unit  2063  (see  FIG. 16 ) described below. The surface of the print head  2036  that is in opposition to the roll paper P has a plurality of nozzle rows N, which serve as ink ejecting section rows. In each of the nozzle rows N, the plurality of nozzles n are arranged in a row in the sub-scanning direction. These nozzle rows N are arranged parallel to each other in the main-scanning direction. The arrangement of the print heads  2036  and the nozzles n will be described later. 
   The print paper carrying section  2005  is arranged on the rear side of the two guide rails  2034 . The print paper carrying section  2005  includes a roll paper holding section  2035 , a roll paper carrying section  2037 , and a platen  2026 . The roll paper holding section  2035  is arranged below the lower guide rail  2341  and holds the roll paper P rotatably together with a holder  2027 . The roll paper carrying section  2037  is arranged above the upper guide rail  2342  and carries the roll paper P. The roll paper P, which is carried between the roll paper holding section  2035  and the roll paper carrying section  2037 , is carried over the platen  2026 . The platen  2026  has a flat surface across the entire width of the roll paper P that is carried. This flat surface is tilted such that it is in opposition to each of the print heads  2036 , which are provided on the carriage  2028  movable in a tilted state, at an equal spacing. 
   The holder  2027  has a shaft  2027   a  which serves as a rotating shaft in a state where the roll paper P is held. Guide disks  2027   b  for preventing undulation of the supplied roll paper P are disposed on both sides of the shaft  2027   a.    
   The roll paper carrying section  2037  has a paper feed roller (SMAP roller)  2024  for carrying the roll paper P, clamping rollers  2029  arranged in opposition to the paper feed roller  2024  and clamping the roll paper P between them and the paper feed roller  2024 , and a carry motor  2031  for rotating the paper feed roller  2024 . A driving gear  2040  is arranged on a shaft of the carry motor  2031 , and a relay gear  2041  meshing with the driving gear  2040  is provided on the shaft of the paper feed roller  2024 . The drive force of the carry motor  2031  is transmitted to the paper feed roller  2024  via the driving gear  2040  and the relay gear  2041 . That is to say, the roll paper P that is held by the holder  2027  is clamped between the paper feed roller  2024  and the clamping rollers  2029 , and the roll paper P is carried along the platen  2026  by the carry motor  2031 . 
   Encoder 
   Next, the linear encoder  2017  provided on the carriage  2028  is described.  FIG. 12  is an explanatory diagram that schematically shows the configuration of the linear encoder  2017  attached to the carriage  2028 . 
   The encoder  2017  shown in  FIG. 12  is provided with a light emitting diode  2017   a , a collimating lens  2017   b , and a detection processing section  2017   c . The detection processing section  2017   c  has a plurality of (for example, four) photodiodes  2017   d , a signal processing circuit  2017   e , and, for example, two comparators  2017   f A and  2017   f B. 
   The light-emitting diode  2017   a  emits light when a voltage VCC is applied to both sides thereof via resistors. This light is condensed into parallel light by the collimating lens  2017   b  and passes through the linear encoder code plate  2019 . The linear encoder code plate  2019  is provided with slits at predetermined intervals (for example, 1/180 inch (one inch=2.54 cm)). 
   The parallel light that has passed through the linear encoder code plate  2019  then passes through stationary slits (not shown) and is incident on the photodiodes  2017   d , where it is converted into electrical signals. The electrical signals that are output from the four photodiodes  2017   d  are subjected to signal processing by the signal processing circuit  2017   e , the signals that are output from the signal processing circuit  2017   e  are compared by the comparators  2017   f A and  2017   f B, and the results of these comparisons are output as pulses. Then, the pulse ENC-A and the pulse ENC-B that are output from the comparators  2017   f A and  2017   f B become the output of the encoder  2017 . 
     FIG. 13A  and  FIG. 13B  are timing charts showing the waveforms of the two output signals of the encoder  2017  when the carriage motor is rotating forward and rotating in reverse, respectively. 
   As shown in  FIG. 13A  and  FIG. 13B , the phases of the pulse ENC-A and the pulse ENC-B are misaligned by 90 degrees both when the carriage motor is rotating forward and when it is rotating in reverse. When the carriage motor  2030  is rotating forward, that is, when the carriage  2028  is moving in the main-scanning direction, then, as shown in  FIG. 13A , the phase of the pulse ENC-A leads the phase of the pulse ENC-B by 90 degrees. On the other hand, when the carriage motor  2030  is rotating in reverse, then, as shown in  FIG. 13B , the phase of the pulse ENC-A is delayed by 90 degrees with respect to the phase of the pulse ENC-B. A single period T of the pulse ENC-A and the pulse ENC-B is equivalent to the time during which the carriage  2028  moves for the slit interval of the linear encoder code plate  2019 . 
   In the present embodiment, the width of each slit (section shown in white) of the linear encoder code plate  2019  is twice the resolution of the color printer  2020 , and here, it is equal to 360 dpi, for example. That is, when the carriage  2028  moves in the main-scanning direction, it is detected that the carriage  2028  has moved for a distance amounting to 360 dpi every time a pulse is output from the encoder  2017 . Therefore, it becomes possible to detect the position, in the main-scanning direction, of the carriage  2028  by first recognizing a home position, which is set in advance as a standby position of the carriage  2028 , at the time of, for example, an initial operation for when the color printer  2020  is turned ON, and then counting the number of pulses that are output from the linear encoder  2017 . 
   It is also possible to detect the position of the carriage  2028  at a higher resolution than that of the slits of the linear encoder code plate  2019  by dividing each of the pulses output from the linear encoder  2017  into equal parts. For example, by dividing a pulse output from the linear encoder  2017  into four, it is possible to detect and control the position of the carriage  2028  at a precision of 1440 dpi. 
   Configuration of the Print Heads 
   Next, the configuration of the print heads  2036  is described using  FIG. 10 ,  FIG. 14  and  FIG. 15 .  FIG. 14  is an explanatory diagram illustrating the arrangement of the nozzles of the print heads  2036 .  FIG. 15  is a diagram showing the arrangement of a plurality of adjacent print heads  2036 , and the positional relationship between the nozzle rows of these print heads  2036 . 
   As shown in  FIG. 14 , each of the print heads  2036  has six nozzle rows N serving as recording portion rows, in which a plurality of nozzles n are arranged on a straight line in the sub-scanning direction. In the present embodiment, a row is arranged for each color of ink that is ejected, that is, there are a black nozzle row Nk, a cyan nozzle row Nc, a light cyan nozzle row Nlc, a magenta nozzle row Nm, a light magenta nozzle row Nlm, and a yellow nozzle row Ny, as the nozzle rows N. However, there is no limitation to this arrangement. 
   The black nozzle row Nk has 180 nozzles, namely nozzles n 1  to n 180 . Each of these nozzles n is provided with a piezoelectric element (not shown) as a driving element for driving the nozzle and making it eject ink droplets. The nozzles n 1 , . . . , n 180  of the black nozzle row Nk are arranged at a constant nozzle pitch k·D in the sub-scanning direction. Here, D is the dot pitch in the sub-scanning direction, and k is an integer of 1 or greater. The dot pitch D in the sub-scanning direction is equal to the pitch of the main scan lines (raster lines). Hereinafter, the integer k expressing the nozzle pitch k·D is referred to simply as the “nozzle pitch k.” In the example of  FIG. 14 , the nozzle pitch k is four dots. The nozzle pitch k, however, may be set to any integer. 
   The above-described explanations also apply for the cyan nozzle row Nc, the light cyan nozzle row Nlc, the magenta nozzle row Nm, the light magenta nozzle row Nlm, and the yellow nozzle row Ny. That is, each of these nozzle rows N has 180 nozzles n 1  to n 180  arranged at a constant nozzle pitch k·D in the sub-scanning direction. 
   During printing, droplets of ink are ejected from the nozzles n as the roll paper P is carried intermittently for a predetermined carry amount by the print paper carrying section  2005  while the carriage  2028  is moved in the main-scanning direction during these intermittent carryings. However, depending on the print mode, that is, when printing is carried out, for example, in the interlace mode for printing natural pictures etc., not all of the nozzles n are used necessarily, and there may also be instances in which only some of the nozzles n are used. 
   Of the eight print heads  2036  on the carriage  2028 , four print heads  2036  are arranged above the pull belt  2032  and the remaining four print heads  2036  are arranged below the pull belt  2032 . The positional relation among the four upper print heads  2036  and the positional relation among the four lower print heads  2036  are the same; therefore, here, only the positional relation of the four upper print heads  2036  is explained as an example. 
   The four print heads  2036  are arranged such that two print heads, i.e., upper-side print heads  2036   a  and  2036   b  positioned on the side further from the section to which an external force for moving the carriage  2028  is applied, that is, from the engaging portion  2046 , and two print heads, i.e., lower-side print heads  2036   c  and  2036   d  positioned on the side close to the engaging portion  2046  are arranged in the vertical direction. The two upper-side print heads  2036   a  and  2036   b , as well as the two lower-side print heads  2036   c  and  2036   d , are spaced apart from each other in the lateral direction at a length that is approximately equal to the width of the print head  2036 . The upper-side print head  2036   b  on the right is located at the right end of the carriage  2028 . The lower-side print head  2036   c  on the left is located at the left end of the carriage  2028 . That is, among the four print heads  2036   a ,  2036   b ,  2036   c , and  2036   d , the two print heads  2036   a  and  2036   c  on the left form a pair and the two print heads  2036   b  and  2036   d  on the right form another pair. In each pair of print heads  2036 , the print heads  2036   c  and  2036   d  on the left are located on the lower side, and the print heads  2036   a  and  2036   b  on the right are located on the upper side; that is, the four print heads  2036  are in a staggered arrangement. The four print heads arranged below the pull belt  2032  are also arranged such that there are two print heads in two layers in the vertical direction. It is needless to say, however, that in the four lower print heads, the upper-side print heads  2036   e  and  2036   f  are positioned on the side close to the engaging portion  2046  in the sub-scanning direction, and the lower-side print heads  2036   g  and  2036   h  are positioned on the side further from the engaging portion  2046  in the sub-scanning direction. 
   Moreover, as shown in  FIG. 15 , as for the four print heads  2036  arranged above the pull belt  2032 , the lowermost nozzle n 180  of each nozzle row N in each of the upper-side print heads and the uppermost nozzle n 1  of each nozzle row N in each of the lower-side print heads are arranged at a pitch equal to the nozzle pitch of each nozzle row N. That is, as for the two print heads  2036   a  and  2036   c  arranged on the left, the distance, in the vertical direction, between the lowermost nozzle n 180  (the rearmost nozzle in the paper carrying direction) of each nozzle row N in the upper right print head  2036   a  and the uppermost nozzle n 1  (the foremost nozzle in the paper carrying direction) of each nozzle row N in the lower left print head  2036   c  is arranged so that it is equal to the nozzle pitch k·D. In the same way, as for the two print heads  2036   b  and  2036   d  arranged on the right, the distance, in the vertical direction, between the lowermost nozzle n 180  of each nozzle row N in the upper right print head  2036   b  and the uppermost nozzle n 1  of each nozzle row N in the lower left print head  2036   d  is arranged so that it is equal to the nozzle pitch k·D. Therefore, assuming that the two left print heads  2036   a  and  2036   c  form a print head group and the two right print heads  2036   b  and  2036   d  form another print head group, when each nozzle row N in each print head group forms dots on the roll paper P at the same position in the main-scanning direction during one scan movement of the carriage, the dots formed by the nozzle rows N of the two print heads  2036  in the same group will form a continuous line at a constant pitch. 
   It should be noted that in  FIG. 14 , the ink colors of each of the nozzle rows N were, in order from the left side in the figure, the black nozzle row Nk, the cyan nozzle row Nc, the light cyan nozzle row Nlc, the magenta nozzle row Nm, the light magenta nozzle row Nlm, and the yellow nozzle row Ny; however, this is not a limitation, and it is also possible for the ink colors of the nozzle rows N to be arranged in a different order. 
   Example of an Overall Configuration of a Liquid Ejecting System 
   Next, an example of an overall configuration of a liquid ejecting system is described with reference to  FIG. 16  and  FIG. 17 .  FIG. 16  is a block diagram showing the configuration of a liquid ejecting system provided with the color printer  2020  described above.  FIG. 17  is a block diagram showing the configuration of an image processing unit  2038 . 
   This liquid ejecting system is provided with a computer  2090  and the color printer  2020 , which is an example of a liquid ejecting apparatus. It should be noted that the liquid ejecting system including the color printer  2020  and the computer  2090  can also be referred to as the “liquid ejecting apparatus” in a broad sense. This system is made of the computer  2090 , the color printer  2020 , a display device such as a CRT  2021  or a liquid crystal display device (not shown), input devices (not shown) such as a keyboard and a mouse, and a drive device (not shown) such as a flexible drive device or a CD-ROM drive device. 
   In the computer  2090 , an application program  2095  is executed under a predetermined operating system. The operating system includes a video driver  2091 , and the application program  2095 , which is for retouching images, for example, carries out desired processing with respect to images to be processed, and also displays the images on the CRT  2021  through the video driver  2091 . 
   The color printer  2020  includes image processing units  2038 , a system controller  2054 , a main memory  2056 , and an EEPROM  2058 . Print data etc. is input from the application program  2095  into the image processing units  2038 , which serve as information generators. The system controller  2054  controls the operation of the overall color printer  2020 . Further connected to the system controller  2054  are a main-scan drive circuit  2061  for driving the carriage motor  2030 , a sub-scan drive circuit  2062  for driving the carry motor  2031 , head control units  2063  serving as controllers for controlling the print heads  2036 , and the linear encoder  2017  for detecting the operation of the carriage  2028 . 
   As shown in  FIG. 10 ,  FIG. 11  and  FIG. 16 , the color printer  2020  has a plurality of print heads  2036 . In the present embodiment, eight print heads  2036  are installed on the carriage  2028 , the print heads  2036  are arranged spaced apart from each other in the vertical and lateral directions on the carriage  2028 , and each print head  2036  is configured to be attachable to and detachable from the printer body. 
   Further, each print head  2036  has an ink tank  2067  for containing the ink that is to be supplied to the nozzles n of that print head  2036 . Each print head  2036  also has the head control unit  2063  and the image processing unit  2038  described above, and thus, it is possible to control the print heads  2036  individually based on a drive signal that serves as a reference. 
   When the application program  2095  issues a print command, the image processing units  2038  provided in the color printer  2020  receive image data from the application program  2095  and convert the data into print data PD. As shown in  FIG. 17 , the image processing units  2038  are internally provided with a resolution conversion module  2097 , a color conversion module  2098 , a halftone module  2099 , a rasterizer  2100 , a UI printer interface module  2102 , a raster data storage section  2103 , a color conversion lookup table LUT, a buffer memory  2050 , and an image buffer  2052 . 
   The role of the resolution conversion module  2097  is to convert the resolution of the color image data formed by the application program  2095  into the corresponding print resolution based on information such as the print mode received with the image data. The image data whose resolution has been thus converted at this point is still image information made of the three color components RGB. Referencing the color conversion lookup table LUT, the color conversion module  2098  converts for each pixel the RGB image data into multi-gradation data of a plurality of ink colors that can be used by the color printer  2020 . 
   The multi-gradation data that has been color converted has, for example, 256 gradation values. The halftone module  2099  executes so-called halftone processing to generate halftone image data. Here, for example, “halftoning” involves dividing an image into regions each made up of a plurality of portions (a pixel can be formed in each of these portions), and expressing the darkness of each region by whether or not to form either a large dot, a medium dot, or a small dot in each of the portions that make up that region. 
   The halftone image data is arranged by the rasterizer  2100  into a desired data order, and is output as the final print data PD to the raster data storage section  2103 . Here, signals instructing to form dots for printing sections of the image in halftone are assigned to print heads  2036  that are positioned on the side close to the pull belt  2032  described above. 
   On the other hand, the user interface display module  2101  provided in the computer  2090  has the function to display various types of user interface windows related to printing and the function to receive input from the user through these windows. For example, the user can specify the type and size of the print paper, or the print mode, for example, using the user interface display module  2101 . 
   The UI printer interface module  2102  functions as an interface between the user interface display module  2101  and the color printer  2020 . It interprets instructions given by users through the user interface and sends various commands COM to the system controller  2054 , for example, or conversely, it interprets commands COM received from the system controller  2054 , for example, and executes various displays on the user interface. For example, the instructions regarding the type or the size of the print paper, for example, that are received by the user interface display module  2101  are sent to the UI printer interface module  2102 , which interprets these instructions and sends commands COM to the system controller  2054 . 
   The UI printer interface module  2102  also functions as a print mode setting section. That is, the UI printer interface module  2102  determines the print mode, which is the recording mode, based on print information received by the user interface display module  2101 , namely, information about the resolution of the printed image and the nozzles used for the printing, and information related to the data indicating the sub-scanning feed amount. Then, print data PD corresponding to the print mode is generated by the halftone module  2099  and the rasterizer  2100 , and is output to the raster data storage section  2103 . The print data PD that is output to the raster data storage section  2103  is temporarily stored in the buffer memory  2050 , converted into data corresponding to the nozzles, and stored in the image buffer  2052 . The system controller  2054  of the color printer  2020  controls the main-scan drive circuit  2061 , the sub-scan drive circuit  2062 , the head control units  2063 , and so forth, based on the information of the commands COM that are output by the UI printer interface module  2102 , and performs printing by driving the nozzles for the various colors that are provided on the print heads  2036  based on the data from the image buffer  2052 . Here, as print modes, there are, for example, a high image-quality print mode in which dots are recorded using the so-called interlace mode, and a high-speed mode in which dots are recorded without using the interlace mode. 
   Driving the Print Head 
   Next, the driving of the print head  2036  is described below with reference to  FIG. 18 . 
     FIG. 18  is a block diagram showing the configuration of a drive signal generating section provided in the head control unit  2063  ( FIG. 16 ).  FIG. 19  is a timing chart of an original signal ODRV, a print signal PRT(i), and a drive signal DRV(i) for illustrating the operation of the drive signal generating section. In  FIG. 18 , the drive signal generating section  2200  includes a plurality of mask circuits  2204 , an original drive signal generating section  2206 , and a drive signal correcting section  2230 . The mask circuits  2204  are provided corresponding to each of the plurality of piezoelectric elements for driving each of the nozzles n 1  through n 180  of the print head  2036 . Note that in  FIG. 18 , the number in parentheses attached to the end of each signal name indicates the number of the nozzle to which the signal is supplied. 
   The original drive signal generating section  2206  generates original drive signals ODRV used in common among the nozzles n 1  through n 180 . The original drive signal ODRV is a signal that includes two pulses—a first pulse W 1  and a second pulse W 2 —during the main scan period for one pixel, and serves as a reference ejection signal for causing each nozzle to eject ink. That is, all of the nozzles of one print head  2036  eject ink based on the same original drive signal ODRV, and when it is detected that the carriage  2028  has reached a predetermined position based on the output of the linear encoder  2017 , outputting of the original drive signal ODRV is started. Therefore, the output timing of the original drive signal ODRV is adjusted such that when dot rows are formed, as liquid droplet mark rows, at the same target position on the print paper by ejecting ink from the nozzle rows of the print heads  2036 , the positions, in the main-scanning direction, of the dot rows coincide with each other. More specifically, before this adjustment is made, a logical value for ejecting ink at a target position on the print paper from the above-described predetermined position is set as an initial value based on the relative position between the carriage  2028  and the print paper, the distance in the main-scanning direction between the print heads, the distance in the main-scanning direction between the nozzle rows of the print heads, etc., and this value (initial value) that has been set is stored in the EEPROM. The method for adjusting the positions of the dot rows formed by the print heads according to the output timing of the original drive signal ODRV will be described later. 
   The drive signal correcting section  2230  can change the positions at which the dots are formed individually by shifting, either forward or backward, the timing of the drive signal waveform that has been shaped by each mask circuit  2204 . By shifting the timing of the drive signal waveform, it is possible to print the print patterns  10  and  12  (see  FIG. 20  and  FIG. 21 ) that are used for adjusting the output timing of the original drive signal ODRV which is supplied to each print head. The print patterns  10  and  12  and the method for printing the print pattern  10  will be described later. 
   As shown in  FIG. 18 , input serial print signals PRT(i) are input to the mask circuits  2204  along with the original drive signal ODRV that is output from the original drive signal generating section  2206 . The serial print signal PRT(i) is a serial signal made of two bits per pixel, and each bit corresponds to the first pulse W 1  and the second pulse W 2 , respectively. Each mask circuit  2204  is a gate for masking the original drive signal ODRV according to the level of the serial print signal PRT(i). That is, if the serial print signal PRT(i) is at level  1 , the mask circuit  2204  lets the corresponding pulse of the original drive signal ODRV pass right through so that the pulse is supplied to the piezoelectric element as a drive signal DRV, whereas if the serial print signal PRT(i) is at level  0 , the mask circuit  2204  cuts off the corresponding pulse of the original drive signal ODRV. 
   As shown in  FIG. 19 , the original drive signal generating section  2206  generates an original drive signal ODRV in which the first pulses W 1  and the second pulses W 2  alternately appear for each of the pixel periods T 1 , T 2 , and T 3 . It should be noted that the term “pixel period” has the same meaning as the main scan period for one pixel. 
   As shown in  FIG. 19 , when the print signal PRT(i) has a waveform corresponding to 2-bit pixel data “1, 0”, then only the first pulse W 1  is output during the first half of the pixel period. Accordingly, a small ink droplet is ejected from the nozzle, and a small dot is formed on the medium to be printed. On the other hand, when the print signal PRT(i) has a waveform corresponding to 2-bit pixel data “0, 1”, then only the second pulse W 2  is output during the latter half of the pixel period. Accordingly, a medium-sized ink droplet is ejected from the nozzle, and a medium-sized dot (medium dot) is formed on the medium to be printed. Further, when the print signal PRT(i) has a waveform corresponding to 2-bit pixel data “1, 1”, then both the first pulse W 1  and the second pulse W 2  are output during the pixel period. Accordingly, a large ink droplet is ejected from the nozzle, and a large dot is formed on the medium to be printed. That is, the drive signal DRV(i) for one pixel period is shaped so that its waveform is in one of the three different shapes according to the three different values of the print signal PRT(i). According to these signals, the print head  2036  is enabled to form dots in three sizes. 
   Method for Adjusting the Positions of Dot Rows formed by Print Heads 
   In the present embodiment, all of the nozzles of a print head  2036  eject ink based on an original drive signal ODRV output at an output timing that is the same within each print head. Therefore, the output timing of the original drive signal ODRV for driving each print head  2036  is adjusted such that the positions, in the main-scanning direction, of the actually-formed dots coincide with each other when liquid droplets are ejected to form dots at the same target position on the roll paper P with each of the print heads. Here, the print heads  2036  are adjusted with respect to an original drive signal ODRV that is output to one of the print heads  2036  that serves as a reference. Further, when ink is ejected according to an original drive signal ODRV output at an output timing that is the same within each print head, the appropriate output timing differs for when printing is carried out using achromatic color ink and for when printing is carried out using chromatic color ink. Therefore, adjustment of the output timing of the original drive signal ODRV differs for the two cases. 
   It is preferable that the print head  2036  serving as the reference (which is referred to as “reference print head” below) is relatively stable in behavior upon scan movement of the carriage  2028  and that the positions of the dots formed thereby do not vary. Therefore, the print head  2036  closest, in the sub-scanning direction, to the engaging portion  2046  to which the external force is applied with respect to the carriage  2028  is adopted as the reference print head. Since the carriage  2028  moves back and forth in the main-scanning direction, the way in which the external force is applied to the engaging portion  2046  differs for when the carriage  2028  moves in the forward pass direction and when the carriage  2028  moves in the return pass direction, and thus, the behavior of the carriage  2028  will be different in each direction. Therefore, the print heads  2036   d  and  2036   e , which are positioned close to the center  2046   a  of the engaging portion  2046 , become the print heads  2036  that are relatively stable in behavior during both the forward and return scan movements. Accordingly, the print heads  2036   d  and  2036   e  are adopted as the reference print heads in order to perform adjustment with improved precision. That is, in the present embodiment, the output timing of the original drive signal ODRV is adjusted, taking the original drive signals ODRV supplied to the print heads  2036   d  and  2036   e  that are positioned closest to the center of the carriage  2028  as the reference. It should be noted that among the eight print heads  2036 , the four print heads  2036  above the pull belt  2032  and the four print heads  2036  below it are arranged in the same way, and therefore, only the upper four print heads will be described below. 
   Adjusting the Output Timing for when Printing is Carried Out Using Achromatic Color Ink 
   The positions, in the main-scanning direction, of dots formed with achromatic color ink, i.e., black ink, are adjusted. More specifically, the output timing of the original drive signal ODRV supplied to the upper right print head  2036   b  is adjusted with reference to the output timing of the original drive signal ODRV supplied to the lower right print head  2036   d  in  FIG. 15  that serves as the reference print head. 
   When the carriage  2028  performs a scan movement in the direction towards the left in  FIG. 10  (which is referred to as “forward pass scan movement” below), the target print head  2036   b , which is installed on the same carriage  2028  as the reference print head  2036   d , will reach a target position after the reference print head  2036   d  forms a first dot row. Therefore, the output timing of the original drive signal ODRV supplied to the target print head  2036   b  is set in advance such that the original drive signal ODRV is output delayed by an amount of time required for the carriage  2028  to move for an ideal distance, in the main-scanning direction, between the black nozzle row Nk of the reference print head  2036   d  and the black nozzle row Nk of the target print head  2036   b , which is the target of output timing adjustment. 
   The adjustment of the output timing of the original drive signal ODRV is performed by printing, during a forward pass scan movement of the reference print head  2036   d  and the target print head  2036   b , a print pattern  10  that includes a reference dot row formed by ejecting ink from the black nozzle row Nk of the reference print head  2036   d  and an adjustment-target dot row formed by ejecting ink from the black nozzle row Nk of the target print head  2036   b  with respect to a predetermined position on the roll paper P as a target position, and determining the optimum output timing based on the print pattern  10  that is printed. Here, the relative position between the carriage  2028  and the roll paper P is detected based on the output of the linear encoder  2017 . 
     FIG. 20  is a diagram for illustrating the print pattern for determining the optimum output timing when printing is carried out using achromatic color ink. 
   In the forward pass scan movement of the carriage  2028 , the reference print head  2036   d  ejects ink from the black nozzle row Nk with respect to the predetermined target position in the main-scanning direction on the roll paper P to thereby form a first dot row  10   a  in the carrying direction. After forming the first dot row  10   a , the reference print head  2036   d  ejects ink, for example, six times at constant time intervals to thereby form a total of seven dot rows  10   a  through  10   g  on the upstream side in the carrying direction at appropriate intervals, as shown in  FIG. 20 . 
   At this time, the target print head  2036   b  forms seven dot rows, i.e., an eighth dot row  10   h  to a fourteenth dot row  10   n , by ejecting ink in order to form dots at the same target positions as those of the reference print head  2036   d . However, the seven dot rows, i.e., the eighth dot row  10   h  to the fourteenth dot row  10   n , are printed by successively changing the ink ejection timing with the drive signal correcting section  2230 . More specifically, ink is ejected to form those dot rows at timings that have been corrected with the drive signal correcting section  2230  such that the eleventh dot row  10   k , which is formed by ejecting ink at the output timing that is set in advance such that ink is ejected at the same target position as the reference print head  2036   d , is positioned at the center (i.e., fourth) of the seven dot rows, and such that the eighth dot row  10   h , the ninth dot row  10   i , the tenth dot row  10   j , the twelfth dot row  10   l , the thirteenth dot row  10   m , and the fourteenth dot row  10   n , which are formed before or after the eleventh dot row  10   k , are successively shifted by a slight amount of time. The slight amount of time for correction is, for example, the amount of time required for the carriage  2028  to move for a distance obtained by dividing the inter-dot distance in the main-scanning direction (= 1/180 inch) into eight, i.e., for 1/180 inch÷8= 1/1440 inch, and this correction is made by the drive signal correcting section  2230 . 
   In the print pattern of  FIG. 20 , the fifth dot row  10   e  formed by the reference print head  2036   d  and the twelfth dot row  10   l  formed by the target print head  2036   b  are printed continuously in the carrying direction. The twelfth dot row  10   l  is the dot row adjacent to the eleventh dot row  10   k , which has been printed at the output timing set in advance to the target print head  36   b . Therefore, the output timing of the original drive signal ODRV supplied to the target print head  2036   b  is adjusted, with respect to the output timing set in advance, by an amount of time required for the carriage  2028  to move for 1/1440 inch. In this way, adjustment is made so that the positions in the main-scanning direction of the dot row formed by the reference print head  2036   d  with respect to the predetermined target position and the dot row formed by the target print head  2036   b  match with each other. 
   The adjustment of the output timing of the original drive signal ODRV can be made easily by providing a user interface for displaying, on displaying means of the computer  2090  when the print pattern is printed, a message etc. that prompts a user, for example, to select the dot rows in the printed print pattern that have been printed continuously in the carrying direction and to enter the number etc. specifying those dot rows, and by making the user carry out operations in accordance with the user interface. 
   It should be noted that the method for adjustment is the same for when the print head  2036   a  is the target print head. 
   Further, the method for adjustment is also the same for when the print head  2036   c  is the target print head. Since, however, the print head  2036   c  and the reference print head  2036   d  are arranged next to each other in the main-scanning direction, the way the print pattern is printed is different. In this case, the print pattern is printed by first printing seven dot rows with either the reference print head  2036   d  or the target print head  2036   c  in either the forward pass scan movement or the return pass scan movement of the carriage  2028 , then carrying the roll paper P for a distance amounting to the length of a dot row, and then printing seven dot rows with the other print head while the carriage  2028  is being moved in the same direction as above. In this case, since the roll paper P is carried between printing of dot rows by one of the print heads and printing of dot rows by the other print head, it becomes possible to adjust the positions, in the main-scanning direction, of the dot rows while taking into account also the precision in carrying the roll paper P. Further, for example, it is possible to print a print pattern in a scan movement of the carriage  2028  in one direction by ejecting ink from half of the nozzles of the reference print head  2036   d  that are positioned on the upstream side in the carrying direction, and ejecting ink from half of the nozzles of the target print head  2036   c  that are positioned on the downstream side in the carrying direction, to thereby print seven dot rows with each print head. 
   Here, the way of dividing the nozzles for ejecting ink in the reference print head  2036   d  and the target print head  2036   c  is not limited to dividing the nozzle row in half. For example, a nozzle row may be divided into four regions, and the reference print head  2036   d  may eject ink from the nozzles positioned in the first and third regions counted from the upstream side in the carrying direction, whereas the target print head  2036   c  may eject ink from the nozzles positioned in the second and fourth regions counted from the upstream side in the carrying direction. It should be noted that, as regards the adjustment of the positions of the dot rows for when the print head  2036   b  was taken as the target print head  2036   b  as described previously, it is also possible to adjust the positions, in the main-scanning direction, of the dot rows while taking into account also the precision in carrying the roll paper P by first forming dot rows with the reference print head  2036   d , then carrying the roll paper P for a distance amounting to twice the length of a dot row, and then printing seven dot rows with the target print head  2036   b.    
   Adjusting the Output Timing for when Printing is Carried Out Using Chromatic Color Ink 
   Images such as natural pictures are mainly printed when printing is performed using chromatic color ink. Therefore, it is necessary to adjust the positions of the dots formed with inks of a plurality of colors ejected from the print heads. If, however, the output timing of the original drive signal ODRV is the same within each print head, then it will be difficult to adjust the positions of all of the dots that are formed by the inks of the plurality of colors. Therefore, when printing is performed using chromatic color ink, the positions, in the main-scanning direction, of the dots formed with light cyan ink and light magenta ink, which tend to affect image quality particularly for images such as natural pictures, are adjusted with respect to dots formed by a reference print head. More specifically, in this example, the output timing of the original drive signal ODRV for a target print head  2036   b  is adjusted so that the amount of positional misalignment in the main-scanning direction between the light cyan dot row formed by the reference print head  2036   d  and the light cyan dot row formed by the target print head  2036   b  and the amount of positional misalignment in the main-scanning direction between the light magenta dot row formed by the reference print head  2036   d  and the light magenta dot row formed by the target print head  2036   b  are both approximately equal. 
     FIG. 21  is a diagram for illustrating a print pattern for determining the optimum output timing when printing is carried out using chromatic color ink. 
   The print pattern  12  is printed by first printing a plurality of dot rows at predetermined target positions with the reference print head and then printing a plurality of dot rows with a target print head by successively changing the ejection timing by a slight amount of time, as with the print pattern described in “Adjusting the output timing for when printing is carried out using achromatic color ink” above. For chromatic color ink, however, two nozzle rows will eject ink at the target position. Below, detailed description on aspects that are in common with those regarding the adjustment of the output timing for when printing is performed using achromatic color ink as described above is omitted. 
   In the forward pass scan movement of the carriage  2028 , the reference print head  2036   d  ejects ink from the light cyan nozzle row Nlc and the light magenta nozzle row Nlm with respect to predetermined target positions in the main-scanning direction on the roll paper P to thereby form a first dot row pair  12   a  in the carrying direction. After forming the first dot row pair  12   a , the reference print head  2036   d  ejects ink, for example, six times at constant time intervals to thereby form a total of seven dot row pairs  12   a  through  12   g  on the upstream side in the carrying direction at appropriate intervals, as shown in  FIG. 21 . 
   On the other hand, the target print head  2036   b  forms seven dot row pairs, i.e., an eighth dot row pair  12   h  to a fourteenth dot row pair  12   n , by changing the ink ejection timing by a slight amount of time and ejecting ink in order to form dots at the same target positions as those of the reference print head  2036   d . That is, the distance between the light cyan dot row and the light magenta dot row that are formed by the target print head  2036   b  and that form a pair is the same, but the distance in the main-scanning direction between the dot row pairs is changed. 
   In the print pattern of  FIG. 21 , the second dot row pair  12   b  formed by the reference print head  2036   d  and the ninth dot row pair  12   i  formed by the target print head  2036   b  are printed such that the amount of positional misalignment in the main-scanning direction between the light cyan dot rows of the dot pairs  12   b  and  12   i  and the amount of positional misalignment in the main-scanning direction between the light magenta dot rows of the dot pairs  12   b  and  12   i  are both approximately equal. The ninth dot row pair  12   i  is the second dot row pair from the eleventh dot row pair  12   k  printed at the output timing to which the target print head  2036   b  was set in advance. Therefore, the output timing of the original drive signal ODRV supplied to the target print head  2036   b  is adjusted, with respect to the output timing set in advance, by an amount of time required for the carriage  2028  to move for  2× 1/1440 inch. In this way, the positions, in the main-scanning direction, of the light cyan and light magenta dot rows formed by the reference print head 2036   d  and the positions, in the main-scanning direction, of the light cyan and light magenta dot rows formed by the target print head  2036   b  will be adjusted to be appropriate. Therefore, it is possible to reduce, as a whole, the positional variation of the dots on the roll paper P and to print images such as natural pictures that are printed using chromatic color ink at a higher image quality. 
   Further, when printing is carried out using chromatic color ink, there are areas, particularly highlight areas, in which the dot density with respect to the paper face is low. These highlight areas are printed using small dots or by ejecting ink from only some of the nozzles of each nozzle row. In this case, the ink ejection velocity differs, for example, due to tension between the ink and the inner surface of the nozzle because when small dots are used for printing the weight of the ink that is ejected for forming dots is small, or due to the difference in the amount of flow of ink that is supplied to the nozzles in the print head when only some of the nozzles in a nozzle row are used. The difference in ink ejection velocity may cause misalignment between the target position and the position at which the dot is actually formed. Therefore, as regards the print pattern used for adjusting the output timing for when printing is carried out using chromatic color ink, it becomes possible to adjust the output timing to a more appropriate timing by forming the dot rows using small dots or by forming the dot rows with only some of the nozzles of each nozzle row. 
   In the foregoing embodiment, an example in which ink is ejected based on an original drive signal ODRV output at an output timing that is the same within each print head  2036  was described. It is possible, however, to regard each nozzle row of each print head as one liquid ejecting section group, and to eject ink based on an original drive signal ODRV output at an output timing that is the same within each nozzle row. In this case, the nozzle row that is driven at the reference output timing of the original drive signal ODRV will be either the black nozzle row Nk of the print head  2036   d , which is closest to the center  2046   a  of the engaging portion  2046 , and the yellow nozzle row Ny of the print head  2036   e , which is also closest to the center  2046   a . By printing a print pattern in which reference dot rows are formed with either one of these nozzle rows Nk or Ny and in which dot rows are formed with another nozzle row at a shifted ink-ejection timing, it is not only possible to adjust the positions of the dot rows that are formed with different print heads, but it is also possible to adjust the positions at which dots are formed even for dot rows formed by the nozzle rows in the same print head. That is, it is possible to adjust the positions of the dots formed by ink ejected from all of the nozzles, and therefore, it becomes possible to print images with higher quality. 
   In the present embodiment, the number of print heads is eight. This, however, is not a limitation, and any number of print heads may be provided as long as the number is more than one. 
   Further, the present embodiment described an example in which the engaging portion  2046  between the pull belt  2032  and the carriage  2028  is positioned approximately at the center of the carriage  2028 . The position of the engaging portion  2046 , however, is not limited thereto. For example, the pull belt  2032  may be provided below all eight print heads  2036  installed to the carriage  2028 , and in this case, the reference print head will be the lowermost print head  2036   h  on the right in  FIG. 10 , and if a nozzle row is to serve as the reference liquid ejecting section group, then the black nozzle row Nk of the print head  2036   h  will serve as the reference. 
   Other Considerations 
   In the foregoing, a liquid ejecting apparatus etc. according to the present invention was explained based on the second embodiment, but the above-described embodiments of the present invention are merely to facilitate the understanding of the present invention, and are in no way meant to limit the present invention. Needless to say, modifications and improvements not parting from the spirit of the present invention are possible, and equivalents thereof are intended to be embraced in the present invention. 
   Further, print paper such as roll paper was described as an example of a medium, but film, cloth, thin metal sheets, and so forth may be used as the medium. 
   Furthermore, in the foregoing embodiment, a printing apparatus was described as an example of a liquid ejecting apparatus, but the present invention is not limited to this. For example, technology like that of the foregoing embodiment can also be applied to, for example, color filter manufacturing devices, dyeing devices, fine processing devices, semiconductor manufacturing devices, surface processing devices, three-dimensional shape forming machines, liquid vaporizing devices, organic EL manufacturing devices (particularly macromolecular EL manufacturing devices), display manufacturing devices, film formation devices, or DNA chip manufacturing devices. It is possible to achieve the effects described above because even when the technology of the present invention is applied to such fields it is possible to eject liquid on a medium. 
   Moreover, in the foregoing embodiment, a color ink-jet printer was described as an example of a liquid ejecting apparatus, but the present invention is not limited thereto, and for example, the present invention can also be applied to monochrome ink-jet printers. 
   Further, in the foregoing embodiment, ink was described as an example of the liquid, but the present invention is not limited thereto. For example, it is also possible to eject, from the nozzles, liquid (including water) such as metallic materials, organic materials (in particular polymeric materials), magnetic materials, conductive materials, wiring materials, film forming materials, machining liquids, and genetic solutions. 
   Although the preferred embodiment of the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from spirit and scope of the inventions as defined by the appended claims.