Inkjet printer

In an inkjet printer, from one side of a main scanning direction, first through fourth ultraviolet irradiation devices arrayed in the main scanning direction at least partially overlap first and second recording heads. A distance in the main scanning direction between a middle position in the main scanning direction of the first recording head and a middle position in the main scanning direction of the first ultraviolet irradiation device is equal to a distance in the main scanning direction between the middle position of the first recording head and a middle position in the main scanning direction of the second ultraviolet irradiation device. A distance in the main scanning direction between a middle position in the main scanning direction of the second recording head and a middle position in the main scanning direction of the third ultraviolet irradiation device is equal to a distance in the main scanning direction between the middle position of the second recording head and a middle position in the main scanning direction of the fourth ultraviolet irradiation device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inkjet printer.

2. Description of the Related Art

Conventionally, an inkjet printer is known including a recording head injecting ink that is cured when being irradiated with ultraviolet rays (hereinafter, referred to as “ultraviolet-curable ink”) toward a recording medium such as a recording paper sheet or the like and an ultraviolet irradiation device irradiating the ultraviolet-curable ink injected onto the recording medium with ultraviolet rays (e.g., Japanese Laid-Open Patent Publication No. 2011-93179 and Japanese Patent No. 4457622).

Also known is an inkjet printer100shown inFIG. 8including a first recording head141, a second recording head142, a first ultraviolet irradiation device151, and a second ultraviolet irradiation device152. In the inkjet printer100, the recording medium is located below the first recording head141and the second recording head142. The first recording head141and the second recording head142inject ultraviolet-curable ink toward the recording medium while moving in a direction, of a main scanning direction Y, from one side to the other side (hereinafter, such a direction will be referred to as a “forward direction Y1”) and a direction, of the main scanning direction Y, from the other side to the one side (hereinafter, such a direction will be referred to as a “backward direction Y2”). The second recording head142is provided on the one side of the main scanning direction Y with respect to the first recording head141. The first ultraviolet irradiation device151is provided on the other side of the main scanning direction Y with respect to the first recording head141. The second ultraviolet irradiation device152is provided on the one side of the main scanning direction Y with respect to the second recording head142. The ultraviolet-curable ink injected by the first recording head141and the second recording head142while the first recording head141and the second recording head142are moving in the forward direction Y1is cured by ultraviolet rays provided by the second ultraviolet irradiation device152. In contrast, the ultraviolet-curable ink injected by the first recording head141and the second recording head142while the first recording head141and the second recording head142are moving in the backward direction Y2is cured by ultraviolet rays provided by the first ultraviolet irradiation device151.

In the inkjet printer100, distance D101in the main scanning direction Y between middle position L101in the main scanning direction Y of the first recording head141and middle position L103in the main scanning direction Y of the first ultraviolet irradiation device151, and distance D102in the main scanning direction Y between middle position L101of the first recording head141and middle position L104in the main scanning direction Y of the second ultraviolet irradiation device152, are different from each other. Similarly, distance D103in the main scanning direction Y between middle position L102in the main scanning direction Y of the second recording head142and middle position L103of the first ultraviolet irradiation device151, and distance D104in the main scanning direction Y between middle position L102of the second recording head142and middle position L104of the second ultraviolet irradiation device152, are different from each other. Therefore, for example, the time until the ultraviolet ink injected onto the recording medium from the first recording head141moving in the forward direction Y1is cured, and the time until the ultraviolet ink injected onto the recording medium from the first recording head141moving in the backward direction Y2is cured, are different from each other. As the time until the ultraviolet ink is cured is longer, a dot of the ultraviolet ink has a longer diameter. Therefore, in this case, the ink dots of the ultraviolet ink injected onto the recording medium may be different in accordance with whether the ink is injected in the forward direction Y1or the backward direction Y2. This may result in printing unevenness caused as a result of printing.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide an inkjet printer capable of significantly reducing or preventing printing unevenness.

An inkjet printer according to a preferred embodiment of the present invention includes a guide rail, a first recording head, a second recording head, a first ultraviolet irradiation device, a second ultraviolet irradiation device, a third ultraviolet irradiation device, and a fourth ultraviolet irradiation device. The guide rail extends in a main scanning direction. The first recording head is slidably in engagement with the guide rail. The first recording head injects ultraviolet-curable ink toward a recording medium at least either while moving in a forward direction from one side to the other side of the main scanning direction or while moving in a backward direction from the other side to the one side of the main scanning direction. The second recording head is provided on the one side or the other side of the main scanning direction with respect to the first recording head. The second recording head is slidably in engagement with the guide rail. The second recording head injects ultraviolet-curable ink toward the recording medium at least either while moving in the forward direction or while moving in the backward direction. The first ultraviolet irradiation device is provided on the other side of the main scanning direction with respect to the first recording head, and irradiates the ultraviolet-curable ink injected onto the recording medium with ultraviolet rays. The second ultraviolet irradiation device is provided on the one side of the main scanning direction with respect to the first recording head, and irradiates the ultraviolet-curable ink injected onto the recording medium with ultraviolet rays. The third ultraviolet irradiation device is provided on the other side of the main scanning direction with respect to the second recording head, and irradiates the ultraviolet-curable ink injected onto the recording medium with ultraviolet rays. The fourth ultraviolet irradiation device is provided on the one side of the main scanning direction with respect to the second recording head, and irradiates the ultraviolet-curable ink injected onto the recording medium with ultraviolet rays. The first recording head includes a first nozzle line, a second nozzle line, a third nozzle line and a fourth nozzle line each including a plurality of nozzles arrayed in a sub scanning direction perpendicular to the main scanning direction. The first nozzle line and the second nozzle line inject first ink. The third nozzle line and the fourth nozzle line inject second ink. As seen from the one side of the main scanning direction, each of the first ultraviolet irradiation device, the second ultraviolet irradiation device, the third ultraviolet irradiation device and the fourth ultraviolet irradiation device at least partially overlaps the first recording head and the second recording head. A distance in the main scanning direction between a middle position in the main scanning direction of the first recording head and a middle position in the main scanning direction of the first ultraviolet irradiation device is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and a middle position in the main scanning direction of the second ultraviolet irradiation device. A distance in the main scanning direction between a middle position in the main scanning direction of the second recording head and a middle position in the main scanning direction of the third ultraviolet irradiation device is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the second recording head and a middle position in the main scanning direction of the fourth ultraviolet irradiation device. The first nozzle line and the third nozzle line are located on the one side of the main scanning direction with respect to the middle position in the main scanning direction of the first recording head. The second nozzle line and the fourth nozzle line are located on the other side of the main scanning direction with respect to the middle position in the main scanning direction of the first recording head. A distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the first nozzle line is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the second nozzle line. A distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the third nozzle line is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the fourth nozzle line.

According to a preferred embodiment of an inkjet printer, the distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the middle position in the main scanning direction of the first ultraviolet irradiation device is equal to the distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the middle position in the main scanning direction of the second ultraviolet irradiation device. For example, the ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the forward direction is cured by being irradiated with the ultraviolet rays provided by the second ultraviolet irradiation device. The ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the backward direction is cured by being irradiated with the ultraviolet rays provided by the first ultraviolet irradiation device. Therefore, the time after the ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the forward direction arrives at the recording medium until the ultraviolet-curable ink starts to be cured by ultraviolet rays is equal to the time after the ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the backward direction arrives at the recording medium until the ultraviolet-curable ink starts to be cured by ultraviolet rays. Thus, the diameter of a dot of the ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the forward direction is equal to the diameter of a dot of the ultraviolet-curable ink injected by the first recording head while the first recording head is moving in the backward direction. This significantly reduces or prevents printing unevenness on a printed item created by the ultraviolet-curable ink injected by the first recording head onto the recording medium.

A distance in the main scanning direction between a middle position in the main scanning direction of the second recording head and a middle position in the main scanning direction of the third ultraviolet irradiation device is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the second recording head and a middle position in the main scanning direction of the fourth ultraviolet irradiation device. For example, the ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the forward direction is cured by being irradiated with the ultraviolet rays provided by the fourth ultraviolet irradiation device. The ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the backward direction is cured by being irradiated with the ultraviolet rays provided by the third ultraviolet irradiation device. Therefore, the time after the ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the forward direction arrives at the recording medium until the ultraviolet-curable ink starts to be cured by ultraviolet rays is equal to the time after the ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the backward direction arrives at the recording medium until the ultraviolet-curable ink starts to be cured by ultraviolet rays. Thus, the diameter of a dot of the ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the forward direction is equal to the diameter of a dot of the ultraviolet-curable ink injected by the second recording head while the second recording head is moving in the backward direction. This significantly reduces or prevents printing unevenness on a printed item created by the ultraviolet-curable ink injected by the second recording head onto the recording medium.

According to a preferred embodiment of an inkjet printer, a distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the first nozzle line is equal to a distance in the main scanning direction between the middle position in the main scanning direction of the first recording head and the second nozzle line. Therefore, the time until the ink injected from the nozzles of the first nozzle line is cured by ultraviolet rays is equal to the time until the ink injected from the nozzles of the second nozzle line is cured by ultraviolet rays. Thus, the diameters of dots of the ink injected from the nozzles of the first nozzle line and the nozzles of the second nozzle line are equal to each other. Similarly, the diameters of dots of the ink injected from the nozzles of the third nozzle line and the nozzles of the fourth nozzle line are equal to each other. This significantly reduces or prevents printing unevenness on a printed item created by the ink injected by the first recording head onto the recording medium.

Various preferred embodiments of the present invention provide an inkjet printer capable that significantly reduces or prevents printing unevenness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, inkjet printers (hereinafter, referred to individually as a “printer”) according to preferred embodiments of the present invention will be described. The preferred embodiments described below are not intended to specifically limit the present invention in any way. Elements, portions and features having identical functions bear identical reference signs, and the same descriptions may be omitted appropriately or simplified.

First Preferred Embodiment

First, a printer1according to a first preferred embodiment of the present invention will be described.FIG. 1is a perspective view of the printer1according to the first preferred embodiment.FIG. 2is a plan view showing an inner structure of the printer1. In the drawings referred to below, reference signs F, Rr, L and R respectively represent front, rear, left and right. These directions are provided merely for the sake of convenience, and do not limit the form of installment of the printer1in any way. Reference sign Y represents a main scanning direction. Reference sign X represents a sub scanning direction perpendicular to the main scanning direction Y. There is no limitation on the directions used as the main scanning direction Y and the sub scanning direction X. The main scanning direction Y and the sub scanning direction X may be appropriately set in accordance with the form or the like of the printer1.

As shown inFIG. 1, the printer1performs printing on a recording paper sheet5. The recording paper sheet5is anon-limiting example of a recording medium. The recording paper sheet5preferably is a rolled recording medium, for example. The recording paper sheet5is a so-called rolled paper sheet. The recording medium according to various preferred embodiments of the present invention is not limited to the recording paper sheer5. The recording medium may be, for example, a resin sheet. The recording medium is not limited to a flexible sheet. The recording medium may be, for example, a hard recording medium formed of glass or the like.

In this preferred embodiment, the printer1includes a printer main body10extending in the main scanning direction Y and a leg11supporting the printer main body10. To the right of the printer main body10, an operation panel12is provided. Although not shown, the operation panel12includes a display portion and an input portion. The display portion displays information on printing, for example, whether monochrome printing or color printing is to be performed, resolution, darkness of ink, and the like. The input portion is usable by a user to input information to be displayed on the display portion.

The printer main body10is provided with a cover15. In this example, the cover15is attached to a top portion of the printer main body10. The cover15is openable/closable. In a bottom portion of the printer main body10, a discharge opening13, through which the recording paper sheet5is discharged, is provided. At a position to the front of, and below, the discharge opening13, a guide14is provided to guide the recording paper sheer5discharged through the discharge opening13in an obliquely frontward and downward direction.

Now, the inner structure of the printer main body10will be described. As shown inFIG. 2, the printer1includes a guide rail20and a platen25. The guide rail20is located inward of the printer main body10. The guide rail20extends in the main scanning direction Y.

The platen25supports the recording paper sheet5while the printer1performs printing on the recording paper sheet5. The printing on the recording paper sheet5is performed on the platen25. The platen25is located to the front of a central portion of the guide rail20. The platen25extends in the main scanning direction Y.

In the vicinity of aright end of the guide rail20, a pulley21is provided. In the vicinity of a left end of the guide rail20, a pulley22is provided. An endless belt23is wound around, and extends between, the pulley21and the pulley22. The pulley21is coupled with a servo motor24. When the servo motor24drives the pulley21, the belt23runs between the pulley21and the pulley22. In this preferred embodiment, the pulley21is driven. Alternatively, the printer1may be configured such that the pulley22is driven. In this case, the servo motor24is coupled with the pulley22.

A carriage30is attached to the belt23. Although not shown, the carriage30is in engagement with the guide rail20. Therefore, the carriage30moves in the main scanning direction Y along the guide rail20as the belt23runs.

At each of a left end and a right end of the platen25, a pair of, namely, upper and lower rollers26are provided (inFIG. 2, only the upper rollers26are shown). The upper and lower rollers26are not limited to being located at each of the left end and the right end of the platen25. One of the upper and lower rollers26of each pair is a driving roller rotating by itself. The other roller of the upper and lower rollers26of each pair is a pinch roller pinching the recording paper sheet25together with the driving roller. The pinch roller, among the rollers26, is configured such that the position thereof in a top-down direction is changeable in accordance with the thickness of the recording paper sheet5, and thus is operable by a user.

In this preferred embodiment, the printer1includes a first recording head41and a second recording head42. The first recording head41and the second recording head42inject ink downward toward the recording paper sheet5. The ink is cured when being irradiated with ultraviolet rays, namely, is ultraviolet-curable ink.

The first recording head41and the second recording head42are slidably in engagement with the guide rail20. The first recording head41and the second recording head42are movable in the main scanning direction Y. In this preferred embodiment, the first recording head41and the second recording head42are attached to the carriage30. The first recording head41and the second recording head42inject the ink toward the recording paper sheet5while moving in a forward direction Y1and a backward direction Y2of the main scanning direction Y. InFIG. 2and the like, the forward direction Y1represents a direction from the right to the left. The backward direction Y2represents a direction from the left to the right. In the following description, the forward direction Y1will be also referred to as a “leftward direction Y1”. The backward direction Y2will be also referred to as a “rightward direction Y2”. In this preferred embodiment, the printer1is able to print in both directions. Although not shown, an ink cartridge filled with the ink is provided to the rear of the printer main body10. The first recording head41and the second recording head42are connected with the cartridge via a tube (not shown) or the like. The first recording head41and the second recording head42are supplied with the ink from the ink cartridge. In this preferred embodiment, while the first recording head41and the second recording head42are moving in the leftward direction Y1and the rightward direction Y2of the main scanning direction Y, only one of the first recording head41and the second recording head42injects the ink. Namely, while the ink is injected from the first recording head41, no ink is injected from the second recording head42. While the ink is injected from the second recording head42, no ink is injected from the first recording head41.

FIG. 3is a plan view schematically showing the first recording head41, the second recording head42, a first ultraviolet irradiation device51, a second ultraviolet irradiation device52, a third ultraviolet irradiation device53and a fourth ultraviolet irradiation device54. As shown inFIG. 3, the first recording head41and the second recording head42are independent of each other. In this example, the first recording head41is coupled with the second recording head42via a coupling member48. Alternatively, the first recording head41and the second recording head42may be integrally formed. The first recording head41and the second recording head42are located at positions shifted from each other in the main scanning direction Y. In this preferred embodiment, the first recording head41is provided to the left of the second recording head42. Alternatively, the first recording head41may be provided to the right of the second recording head42. The first recording head41and the second recording head42are arrayed in the main scanning direction Y. In this example, the first recording head41and the second recording head42are located at positions completely matched to each other in the sub scanning direction X. Alternatively, the first recording head41and the second recording head42may be located at positions shifted from each other in the sub scanning direction X. There is no specific limitation on the size of each of the first recording head41and the second recording head42. The first recording head41and the second recording head42may have the same size as each other or may have different sizes from each other. For example, the first recording head41and the second recording head42may each have a length of about 30 mm in the main scanning direction Y. The first recording head41and the second recording head42may each have a length of about 40 mm in the sub scanning direction X.

The ink injected from the first recording head41is, for example, cyan ink (C), magenta ink (M), yellow ink (Y) and black ink (B). Each of the cyan ink, the magenta ink, the yellow ink and the black ink is ink usable to form a color image, and is so-called process color ink. There is no specific limitation on the types and the number of types of the ink injected from the first recording head41. For example, the first recording ink41may inject six types of ink including the cyan ink, the magenta ink, the yellow ink and the black ink described above and light cyan ink and light magenta ink. In this example, for example, the cyan ink corresponds to “first ink”, and the magenta ink corresponds to “second ink”.

FIG. 4schematically shows injection portions43C,43M,43Y and43K of the first recording head41, and shows the first recording head41as seen from a bottom surface thereof. As shown inFIG. 4, the first recording head41includes a plurality of injection portions each including an array of a plurality of nozzles located in the sub scanning direction X. The first recording head includes two injection portions43C injecting cyan ink, two injection portions43M injecting magenta ink, two injection portions43Y injecting yellow ink, and two injection portions43K injecting black ink.

The injection portions43C,43M,43Y and43K each include an array of a plurality of nozzles45located in the sub scanning direction X. InFIG. 4, each of the injection portions43C,43M,43Y and43K includes eight nozzles45. In actuality, however, each of the injection portions43C,43M,43Y and43K includes a large number of (for example, eight or more) nozzles45. The injection portions43C,43M,43Y and43K are arrayed in the main scanning direction Y. One of the injection portions43C, one of the injection portions43M, one of the injection portions43Y, and one of the injection portions43K are located on one side, namely, on the right side, of the main scanning direction Y, with respect to middle position L1in the main scanning direction Y of the first recording head41. The other of the injection portions43C, the other of the injection portions43M, the other of the injection portions43Y, and the other of the injection portions43K are located on the other side, namely, on the left side, of the main scanning direction Y, with respect to middle position L1in the main scanning direction Y of the first recording head41. In this example, for example, the right injection portion43C of the two injection portions43C corresponds to a “first nozzle line”. The left injection portion43C of the two injection portions43C corresponds to a “second nozzle line”. For example, the right injection portion43M of the two injection portions43M corresponds to a “third nozzle line”. The left injection portion43M of the two injection portions43M corresponds to a “fourth nozzle line”.

Distance D11abetween middle position L1in the main scanning direction Y of the first recording head41and middle position L11ain the main scanning direction Y of the left injection portion43C is equal to distance D11bbetween middle position L1in the main scanning direction Y of the first recording head41and middle position L11bin the main scanning direction Y of the right injection portion43C. Similarly, distance D12abetween middle position L1of the first recording head41and middle position L12ain the main scanning direction Y of the left injection portion43M is equal to distance D12bbetween middle position L1of the first recording head41and middle position L12bin the main scanning direction Y of the right injection portion43M. Distance D13abetween middle position L1of the first recording head41and middle position L13ain the main scanning direction Y of the left injection portion43Y is equal to distance D13bbetween middle position L1of the first recording head41and middle position L13bin the main scanning direction Y of the right injection portion43Y. Distance D14abetween middle position L1of the first recording head41and middle position L14ain the main scanning direction Y of the left injection portion43K is equal to distance D14bbetween middle position L1of the first recording head41and middle position L14bin the main scanning direction Y of the right injection portion43K.

In this example, in both of the leftward direction Y1and the rightward direction Y2, the plurality of injection portions of the first recording head41are located in the order of the injection portions43C,43M,43Y,43K,43K,43Y,43M and43C. In this preferred embodiment, as seen in a plan view, the injection portions43C,43M,43Y and43K are located so as to be linear-symmetrical, with middle position L1in the main scanning direction Y of the first recording head41being the axis of symmetry. It should be noted that there is no specific limitation on the order of the positions of the injection portions43C,43M,43Y and43K. In this example, the injection portions43C,43M,43Y and43K are arrayed in the main scanning direction Y at an equal interval. In this preferred embodiment, the injection portions43C,43M,43Y and43K are independent of each other. Alternatively, the injection portions43C,43M,43Y and43K may be integral with each other partially or entirely. In each of the injection portions43C,43M,43Y and43K, the nozzles45may be located in one line as shown inFIG. 4, or may be located in two or more lines. In this example, among the plurality of nozzles45of the injection portions43C,43M,43Y and43K, nozzles45adjacent to each other in the main scanning direction Y are located linearly in the main scanning direction Y. For example, the nozzles45located at one end of the injection portions43C,43M,43Y and43K are located linearly in the main scanning direction Y. Alternatively, among the plurality of nozzles45of the injection portions43C,43M,43Y and43K, nozzles45adjacent to each other in the main scanning direction Y may be located to be shifted from each other in the sub scanning direction X. Namely, the nozzles45may be located in a zigzag manner.

The ink injected from the second recording head42is, for example, gloss ink (G), white ink (W) and primer ink (P). The gloss ink is ink mainly injected toward a surface of the process color ink injected onto the recording paper sheet5. The gloss ink is transparent ink, and is used to provide a printed item with a glossy surface. The white ink is used to print the recording medium white. The white ink may be used to provide underlying printing when, for example, the recording paper sheet5is of a color different from white. The process color ink is injected toward the recording paper sheet5already having the white ink injected thereon, so that the recording paper sheet5is printed with the color of the process color ink with no influence of the original color of the recording paper sheet5. The primer ink is a so-called under-layer processing agent. The primer ink is injected toward the recording paper sheet5before the process color ink is injected toward the recording paper sheet5. The gloss ink, the white ink and the primer ink are so-called spot color ink. The spot color ink is ink other than the process color ink. The spot color ink is used together with the process color ink. In this example, for example, the gloss ink corresponds to “third ink”, and the white ink corresponds to “fourth ink”.

FIG. 5schematically shows injection portions44G,44W and44P of the second recording head42, and shows the second recording head42as seen from a bottom surface thereof. As shown inFIG. 5, the second recording head42includes a plurality of injection portions each including an array of a plurality of nozzles located in the sub scanning direction X. The second recording head42includes two injection portions44G injecting gloss ink, two injection portions44W injecting white ink, and two injection portions44P injecting primer ink.

The injection portions44G,44W and44P each include an array of a plurality of nozzles46located in the sub scanning direction X. InFIG. 5, each of the injection portions44G,44W and44P preferably includes eight nozzles46, for example. In actuality, however, each of the injection portions44G,44W and44P includes a large number of nozzles46. The injection portions44G,44W and44P are arrayed in the main scanning direction Y. One of the injection portions44G, one of the injection portions44W, and one of the injection portions44P are located on one side, namely, on the right side, of the main scanning direction Y, with respect to middle position L2in the main scanning direction Y of the second recording head42. The other of the injection portions44G, the other of the injection portions44M, and the other of the injection portions44P are located on the other side, namely, on the left side, of the main scanning direction Y, with respect to middle position L2in the main scanning direction Y of the second recording head42. In this example, for example, the right injection portion44G of the two injection portions44G corresponds to a “fifth nozzle line”. The left injection portion44G of the two injection portions44G corresponds to a “sixth nozzle line”. For example, the right injection portion44W of the two injection portions44W corresponds to a “seventh nozzle line”. The left injection portion44W of the two injection portions44W corresponds to an “eighth nozzle line”.

Distance D21abetween middle position L2in the main scanning direction Y of the second recording head42and middle position L21ain the main scanning direction Y of the left injection portion44G is equal to distance D21bbetween middle position L2in the main scanning direction Y of the second recording head42and middle position L21bin the main scanning direction Y of the right injection portion44G. Similarly, distance D22abetween middle position L2of the second recording head42and middle position L22ain the main scanning direction Y of the left injection portion44W is equal to distance D22bbetween middle position L2of the second recording head42and middle position L22bin the main scanning direction Y of the right injection portion44W. Distance D23abetween middle position L2of the second recording head42and middle position L23ain the main scanning direction Y of the left injection portion44P is equal to distance D23bbetween middle position L2of the second recording head42and middle position L23bin the main scanning direction Y of the right injection portion44P.

In this example, in both of the leftward direction Y1and the rightward direction Y2, the plurality of injection portions of the second recording head42are located in the order of the injection portions44G,44W,44P,44P,44W and44G. In this preferred embodiment, as seen in a plan view, the injection portions44G,44W and44P are located so as to be linear-symmetrical, with middle position L2in the main scanning direction Y of the second recording head42being the axis of symmetry. It should be noted that there is no specific limitation on the order of the positions of the injection portions44G,44W and44P. In this example, the injection portions44G,44W and44P are arrayed in the main scanning direction Y at an equal interval. In this preferred embodiment, the injection portions44G,44W and44P are independent of each other. Alternatively, the injection portions44G,44W and44P may be integral with each other partially or entirely. In each of the injection portions, the nozzles46may be located in one line as shown inFIG. 5, or may be located in two or more lines. In this example, among the plurality of nozzles46of the injection portions44G,44W and44P, nozzles46adjacent to each other in the main scanning direction Y are located linearly in the main scanning direction Y. For example, the nozzles46located at one end of the injection portions44G,44W and44P are located linearly in the main scanning direction Y. Alternatively, among the plurality of nozzles46of the injection portions44G,44W and44P, nozzles46adjacent to each other may be located to be shifted from each other in the sub scanning direction X. Namely, the nozzles46may be located in a zigzag manner.

As shown inFIG. 2, a container16opened upward and wipers17aand17bare located to the right of the platen25. The container16receives the ink injected from the first recording head41and the second recording head42when the first recording head41and the second recording head42arrive at a home position HP, which is a wait position. When the ink in the first recording head41and the second recording head42makes contact with the air, the viscosity of the ink is increased. When the viscosity of the ink is increased, the injection performance of the first recording head41and the second recording head42may be undesirably changed. Thus, the first recording head41and the second recording head42inject the ink toward the container16when necessary in order to improve the reliability of the injection performance thereof. The container16recovers the ink injected from the first recording head41and the second recording head42when such an operation is performed. The container16recovers the process color ink injected from the first recording head41and the spot color ink injected from the second recording head42. In this example, the process color ink injected from the first recording head41toward the container16is not easily attached to the second recording head42. The spot color ink injected from the second recording head42toward the container16is not easily attached to the first recording head41.

The wiper17acleans a nozzle surface (a surface on which the injection portions are provided) of the first recording head41. The wiper17bcleans a nozzle surface of the second recording head42. While moving toward the home position HP, the first recording head41and the second recording head42are appropriately slid by the wiper17aand the wiper17b, respectively. This removes the ink or the like unnecessarily attached to the first recording head41and the second recording head42. In this preferred embodiment, the wiper17bremoves the spot color ink on the second recording head42, and thus the spot color ink is prevented from being attached to the nozzle surface of the first recording head41. The wiper17aremoves the process color ink on the first recording head41, and thus the process color ink is prevented from being attached to the nozzle surface of the second recording head42. In this example, the operation of injecting the ink toward the container16made by the first recording head41and the second recording head42and the operation of cleaning the nozzle surfaces of the first recording head41and the second recording head42made respectively by the wipers17aand17bare comprehensively referred to as “head cleaning”.

As shown inFIG. 3, the printer1includes a first ultraviolet irradiation device51, a second ultraviolet irradiation device52, a third ultraviolet irradiation device53, and a fourth ultraviolet irradiation device54. The ultraviolet irradiation devices51,52,53and54irradiate the ink injected onto the recording paper sheet5with ultraviolet rays. In this preferred embodiment, the ultraviolet irradiation devices51,52,53and54each include a plurality of ultraviolet emitting diodes, for example. The ultraviolet irradiation devices51,52,53and54may each include, for example, a halogen lamp or the like.

Now, the positional relationship among the first recording head41, the second recording head42, the first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54will be described. The ultraviolet irradiation devices51,52,53and54move together with the first recording head41and the second recording head42. As seen from the one side and the other side of the main scanning direction Y, each of the first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54at least partially overlaps the first recording head41and the second recording head42. The ultraviolet irradiation devices51,52,53and54may overlap the first recording head41and the second recording head42entirely or only partially. The ultraviolet irradiation devices51,52,53and54each have a length in the sub scanning direction X that is longer than, or equal to, a length between the most front end of the first recording head41and the second recording head42and the rearmost end thereof. The ultraviolet irradiation devices51,52,53and54may each have a length of, for example, about 60 mm in the sub scanning direction X. The ultraviolet irradiation devices51,52,53and54may each have a length of, for example, about 10 mm in the main scanning direction Y. In this example, the length of each of the ultraviolet irradiation devices51,52,53and54in the sub scanning direction X is longer than, or equal to, each of the length of the first recording head41in the sub scanning direction X and the length of the second recording head42in the sub scanning direction X. In this preferred embodiment, the ultraviolet irradiation devices51,52,53and54preferably have the same size as each other. Alternatively, the ultraviolet irradiation devices51,52,53and54may have different sizes from each other.

The first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54are arrayed in the main scanning direction Y. The first ultraviolet irradiation device51and the third ultraviolet irradiation device53are located to the left of the first recording head41and the second recording head42. The third ultraviolet irradiation device53is located between the first ultraviolet irradiation device51and the first recording head41. The first ultraviolet irradiation device51is attached to the left of the third ultraviolet irradiation device53via a coupling member58a. The third ultraviolet irradiation device53is attached to the left of the first recording head41via a coupling member58b. The second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54are located to the right of the first recording head41and the second recording head42. The second ultraviolet irradiation device52is located between the second recording head42and the fourth ultraviolet irradiation device54. The second ultraviolet irradiation device52is attached to the right of the second recording head42via a coupling member58c. The fourth ultraviolet irradiation device54is attached to the right of the second ultraviolet irradiation device52via a coupling member58d.

Distance D1in the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and middle position L3in the main scanning direction Y of the first ultraviolet irradiation device51is equal to distance D2in the main scanning direction Y between middle position L1of the first recording head41and middle position L4in the main scanning direction Y of the second ultraviolet irradiation device52. Now, among the plurality of injection portions of the first recording head41, the injection portions injecting the same color of ink will be referred to. The distance between the middle position in the main scanning direction Y of the left injection portion and middle position L3of the first ultraviolet irradiation device51is equal to the distance between the middle position in the main scanning direction Y of the right injection portion and middle position L4of the second ultraviolet irradiation device52. For example, inFIG. 4, the injection portions43C injecting the cyan ink will be referred to. The distance between middle position L11aof the left injection portion43C and middle position L3of the first ultraviolet irradiation device51is equal to the distance between middle position L11bof the right injection portion43C and middle position L4of the second ultraviolet irradiation device52.

As used herein in describing the various preferred embodiments of the present invention, the term “equal” encompasses “completely equal” and “substantially equal”. Even if there is a small error between the above-described distances, if the difference is sufficiently small to make it difficult to cause printing unevenness as described below, such distances are encompassed in being “substantially equal”. This is applicable also to the following description.

As shown inFIG. 3, distance D3in the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and middle position L5in the main scanning direction Y of the third ultraviolet irradiation device53is equal to distance D4in the main scanning direction Y between middle position L2of the second recording head42and middle position L6in the main scanning direction Y of the fourth ultraviolet irradiation device54. In this preferred embodiment, distance D1, distance D2, distance D3and distance D4are equal to each other. Now, among the plurality of injection portions of the second recording head42, the injection portions injecting the same type of ink will be referred to. The distance between the middle position in the main scanning direction Y of the left injection portion and middle position L5of the third ultraviolet irradiation device53is equal to the distance between the middle position in the main scanning direction Y of the right injection portion and middle position L6of the fourth ultraviolet irradiation device54. For example, inFIG. 5, the injection portions44G injecting the gloss ink will be referred to. The distance between middle position L21aof the left injection portion44G and middle position L5of the third ultraviolet irradiation device53is equal to the distance between middle position L21bof the right injection portion44G and middle position L6of the fourth ultraviolet irradiation device54. In this example, middle positions L3through L6in the main scanning direction Y of the ultraviolet irradiation devices51through54are respectively the middle positions in the main scanning direction Y of ranges over which the ultraviolet irradiation devices51through54emit the ultraviolet rays. Middle positions L1and L2in the main scanning direction Y of the first recording head41and the second recording head42are respectively the middle positions in the main scanning direction Y of ranges over which the first recording head41and the second recording head42inject the ink.

In this preferred embodiment, the first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54are independent from each other. Alternatively, the first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54are may be integral with each other entirely or partially. For example, the ultraviolet irradiation devices located to the left of the first recording head41and the second recording head42, namely, the first ultraviolet irradiation device51and the third ultraviolet irradiation device53may be integral with each other. The ultraviolet irradiation devices located to the right of the first recording head41and the second recording head42, namely, the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54may be integral with each other. For example, an assembly of the first ultraviolet irradiation device51and the third ultraviolet irradiation device53may include a light emitting diode (LED) array-type ultraviolet irradiation device including an array of a plurality of LEDs, and an assembly of the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54may include an LED array-type ultraviolet irradiation device including an array of a plurality of LEDs. In this case, a controller60described below controls the LEDs provided in light emitting areas respectively corresponding to the ultraviolet irradiation devices51,52,53and54so as to be selectively lit up or lit off. In this manner, the number of components of the printer1is decreased.

FIG. 6is a block diagram showing a portion of elements of the printer1. As shown inFIG. 6, the printer1includes the controller60. The controller60includes a microcomputer and is provided in the printer1. The controller60is configured or programmed to control the servo motor24running the belt23, the driving roller among the rollers26, the first recording head41, the second recording head42, the first ultraviolet irradiation device51, the second ultraviolet irradiation device52, the third ultraviolet irradiation device53, and the fourth ultraviolet irradiation device54. The controller60controls, for example, the moving speed of the carriage30(seeFIG. 2) by controlling the servo motor24. The controller60controls the movement of the recording paper sheet5in the sub scanning direction X by controlling the operation of the driving roller among the rollers26. The controller60controls the ink injection operation of the first recording head41and the second recording head42. The controller60controls the timing at which the ink injected onto the recording paper sheet5is irradiated with the ultraviolet rays by controlling the light emitting diodes of the ultraviolet irradiation devices51,52,53and54. The controller60includes a first printing controller61and a second printing controller62. The first printing controller61and the second printing controller62may be realized by software or hardware. For example, the first printing controller61and the second printing controller62may be executable by a processor or may be incorporated into a circuit.

The first printing controller61moves the first recording head41and the second recording head42in the main scanning direction Y. When the first recording head41injects ink toward the recording paper sheet5, the first printing controller61causes the first ultraviolet irradiation device51or the second ultraviolet irradiation device52to provide the ultraviolet rays. Specifically, when the first recording head41injects ink while moving in the leftward direction Y1, the first printing controller61causes the second ultraviolet irradiation device52to provide the ultraviolet rays. When the first recording head41injects ink while moving in the rightward direction Y2, the first printing controller61causes the first ultraviolet irradiation device51to provide the ultraviolet rays.

When the second recording head42injects ink toward the recording paper sheet5, the first printing controller61causes the third ultraviolet irradiation device53or the fourth ultraviolet irradiation device54to provide the ultraviolet rays. Specifically, when the second recording head42injects ink while moving in the leftward direction Y1, the first printing controller61causes the fourth ultraviolet irradiation device54to provide the ultraviolet rays. When the second recording head42injects ink while moving in the rightward direction Y2, the first printing controller61causes the third ultraviolet irradiation device53to provide the ultraviolet rays.

The second printing controller62moves the first recording head41and the second recording head42in the main scanning direction Y. The second printing controller62performs printing at a speed higher than the first printing controller61. In this example, the speed at which the second printing controller62moves the first recording head41and the second recording head42in the main scanning direction Y is higher than the speed at which the first printing controller61moves the first recording head41and the second recording head42in the main scanning direction Y. For example, the speed at which the first printing controller61moves the first recording head41and the second recording head42preferably is about 500 mm/sec. In contrast, the speed at which the second printing controller62moves the first recording head41and the second recording head42preferably is about 1,000 mm/sec, for example. In the following description, the printing performed by the first printing controller61will be referred to as “low speed printing”, and the printing performed by the second printing controller62will be referred to as “high speed printing”. When the first recording head41or the second recording head42injects ink toward the recording paper sheet5, the second printing controller62causes the first ultraviolet irradiation device51and the third ultraviolet irradiation device53, or the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54, to provide the ultraviolet rays. Specifically, when the first recording head41or the second recording head42injects ink while moving in the leftward direction Y1, the second printing controller62causes the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54to provide the ultraviolet rays. When the first recording head41or the second recording head42injects ink while moving in the rightward direction Y2, the second printing controller62causes the first ultraviolet irradiation device51and the third ultraviolet irradiation device53to provide the ultraviolet rays.

Now, a printing operation of the printer1in this preferred embodiment will be described. In this preferred embodiment, preferably there are two printing modes, namely, the low speed printing performed by the first printing controller61of the controller60and the high speed printing performed by the second printing controller62of the controller60. Alternatively, there may be three or more printing modes between which the moving speed of the first recording head41and the second recording head42is different. For example, a user operates the operation panel12(seeFIG. 1) to choose whether the printer1is to perform the low speed printing or the high speed printing.

In the low speed printing, the first printing controller61performs the printing. For example, the controller60controls the servo motor24to move the carriage30along the guide rail20. At this point, the first recording head41, the second recording head42, and the ultraviolet irradiation devices51,52,53and54move in the main scanning direction Y along the guide rail20. After the first recording head41and the second recording head42makes one cycle of scanning in the forward direction Y1or the backward direction Y2, makes one cycle of round trip scanning, or makes a plurality of cycles of round trip scanning, the controller60drives the driving roller26to transport the recording paper sheet5in the sub scanning direction X. To perform the printing on the recording paper sheet5with the process color ink, the first printing controller61causes the first recording head41to inject the ink toward the recording paper sheet5while the first recording head41is moving in the leftward direction Y1and the rightward direction Y2. While the first recording head41is moving in the leftward direction Y1, the first printing controller61causes the first recording head41to inject the ink from the nozzles45of the injection portions43C,43M,43Y and43K provided on the right side among the plurality of injection portions of the first recording head41. Then, the controller60controls the first recording head41, the second recording head42, and the ultraviolet irradiation devices51,52,53and54to further move in the leftward direction Y1. At this point, the first printing controller61causes the second ultraviolet irradiation device52to emit light and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, none of the first ultraviolet irradiation device51, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54emits light.

While the first recording head41is moving in the rightward direction Y2, the first printing controller61causes the first recording head41to inject the ink from the nozzles45of the injection portions43C,43M,43Y and43K provided on the left side among the plurality of injection portions of the first recording head41. Then, the controller60controls the first recording head41, the second recording head42, and the ultraviolet irradiation devices51,52,53and54to further move in the rightward direction Y2. At this point, the first printing controller61causes the first ultraviolet irradiation device51to emit light and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, none of the second ultraviolet irradiation device52, the third ultraviolet irradiation device53and the fourth ultraviolet irradiation device54emits light.

To perform the low speed printing on the recording paper sheet5with the spot color ink, the first printing controller61causes the second recording head42to inject the ink toward the recording paper sheet5while the second recording head42is moving in the leftward direction Y1and the rightward direction Y2. While the second recording head42is moving in the leftward direction Y1, the first printing controller61causes the second recording head42to inject the ink from the nozzle46of any one of the injection portions44G,44W and44P provided on the right side among the plurality of injection portions of the second recording head42. Then, the controller60controls the first recording head41, the second recording head42, and the ultraviolet irradiation devices51,52,53and54to further move in the leftward direction Y1. At this point, the first printing controller61causes the fourth ultraviolet irradiation device54to emit light and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, none of the first ultraviolet irradiation device51, the second ultraviolet irradiation device52and the third ultraviolet irradiation device53emits light.

While the second recording head42is moving in the rightward direction Y2, the first printing controller61causes the second recording head42to inject the ink from the nozzle46of any one of the injection portions44G,44W and44P provided on the left side among the plurality of injection portions of the second recording head42. Then, the controller60controls the first recording head41, the second recording head42, and the ultraviolet irradiation devices51,52,53and54to further move in the rightward direction Y2. At this point, the first printing controller61causes the third ultraviolet irradiation device53to emit light and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, none of the first ultraviolet irradiation device51, the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54emits light.

In the high speed printing, the second printing controller62performs the printing. To perform the printing on the recording paper sheet5with the process color ink and to perform the printing on the recording paper sheet5with the spot color ink, the operation performed until the ink is injected toward the recording paper sheet5is the same as that in the low speed printing and thus will not be described in detail. To perform the printing with the process color ink or the spot color ink in the leftward direction Y1, after the ink is injected toward the recording paper sheet5, the second printing controller62causes the second ultraviolet irradiation device52and the fourth ultraviolet irradiation device54to emit light, and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, neither the first ultraviolet irradiation device51nor the third ultraviolet irradiation device53emits light. By contrast, to perform the printing with the process color ink or the spot color ink in the rightward direction Y2, after the ink is injected toward the recording paper sheet5, the second printing controller62causes the first ultraviolet irradiation device51and the third ultraviolet irradiation device53to emit light, and thus causes the ink injected onto the recording paper sheet5to be irradiated with the ultraviolet rays. At this point, neither the second ultraviolet irradiation device52nor the fourth ultraviolet irradiation device54emits light.

As described above, in this preferred embodiment, as shown inFIG. 3, distance D1in the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and middle position L3in the main scanning direction Y of the first ultraviolet irradiation device51is equal to distance D2in the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and middle position L4in the main scanning direction Y of the second ultraviolet irradiation device52. In, for example, the low speed printing, the ink injected by the first recording head41while the first recording head41is moving in the leftward direction Y1is cured by being irradiated with the ultraviolet rays by the second ultraviolet irradiation device52. The ink injected by the first recording head41while the first recording head41is moving in the rightward direction Y2is cured by being irradiated with the ultraviolet rays by the first ultraviolet irradiation device51. Therefore, the time after the ink injected by the first recording head41while the first recording head41is moving in the leftward direction Y1arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays is equal to the time after the ink injected by the first recording head41while the first recording head41is moving in the rightward direction Y2arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays.

Distance D3in the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and middle position L5in the main scanning direction Y of the third ultraviolet irradiation device53is equal to distance D4in the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and middle position L6in the main scanning direction Y of the fourth ultraviolet irradiation device54. In, for example, the low speed printing, the ink injected by the second recording head42while the second recording head42is moving in the leftward direction Y1is cured by being irradiated with the ultraviolet rays by the fourth ultraviolet irradiation device54. The ink injected by the second recording head42while the second recording head42is moving in the rightward direction Y2is cured by being irradiated with the ultraviolet rays by the third ultraviolet irradiation device53. Therefore, the time after the ink injected by the second recording head42while the second recording head42is moving in the leftward direction Y1arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays is equal to the time after the ink injected by the second recording head42while the second recording head42is moving in the rightward direction Y2arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays.

FIG. 7shows a timewise change of ink A injected onto the recording paper sheet5. As shown inFIG. 7, the ink A injected onto the recording paper sheet5by the first recording head41and the second recording head42has a dot diameter thereof increased as the time passes in the state where the ink A is not irradiated with the ultraviolet rays. In other words, the area size of the ink A, injected onto the recording paper sheet5, that is in contact with the recording paper sheet5increases as the time passes in the state where the ink A is not irradiated with the ultraviolet rays. The ink A injected onto the recording paper sheet5expands in a horizontal direction on the recording paper sheet5as the time passes. For example, the dot diameter of the ink A at time t1is shorter than the dot diameter of the ink A at each of time t2, time t3and time t4, which have a longer time than time t1after the start. As described above, the time after the ink injected by the first recording head41or the second recording head42while the first recording head41or the second recording head42is moving in the leftward direction Y1arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays is equal to the time after the ink injected by the first recording head41or the second recording head42while the first recording head41or the second recording head42is moving in the rightward direction Y2arrives at the recording paper sheet5until the ink starts to be cured by the ultraviolet rays. Therefore, in this preferred embodiment, the dot diameter of the ink injected by the first recording head41while the first recording head41is moving in the leftward direction Y1is equal to the dot diameter of the ink injected by the first recording head41while the first recording head41is moving in the rightward direction Y2. Similarly, the dot diameter of the ink injected by the second recording head42while the second recording head42is moving in the leftward direction Y1is equal to the dot diameter of the ink injected by the second recording head42while the second recording head42is moving in the rightward direction Y2. This significantly reduces or prevents printing unevenness on a printed item created by the ink injected by the first recording head41and the second recording head42onto the recording paper sheet5.

In this preferred embodiment, as shown inFIG. 4, the injection portions43C,43M,43Y and43K of the first recording head41preferably are arrayed in the main scanning direction Y so as to be line-asymmetrical with middle position L1in the main scanning direction Y of the first recording head41being the axis of symmetry. For example, distance D11ain the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and the left injection portion43C is equal to distance D11bin the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and the right injection portion43C. Distance D12ain the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and the left injection portion43M is equal to distance D12bin the main scanning direction Y between middle position L1in the main scanning direction Y of the first recording head41and the right injection portion43M. Because of such an arrangement, for example, the distance between the left injection portion43C and the first ultraviolet irradiation device51is equal to the distance between the right injection portion43C and the second ultraviolet irradiation device52. Therefore, the time until the ink injected from the left injection portion43C is cured by the ultraviolet rays is equal to the time until the ink injected from the right injection portion43C is cured by the ultraviolet rays. Thus, the dot diameters of the ink injected from the two injection portions43C are equal to each other. Similarly, the dot diameters of the ink injected from the two injection portions43M are equal to each other. The dot diameters of the ink injected from the two injection portions43Y are equal to each other. The dot diameters of the ink injected from the two injection portions43K are equal to each other. This significantly reduces or prevents printing unevenness on a printed item created by the ink injected by the first recording head41onto the recording paper sheet5.

In this preferred embodiment, as shown inFIG. 5, the injection portions44G,44W and44P of the second recording head42are preferably arrayed in the main scanning direction Y so as to be line-asymmetrical with middle position L2in the main scanning direction Y of the second recording head42being the axis of symmetry. For example, distance D21ain the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and the left injection portion44G is equal to distance D2lb in the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and the right injection portion44G. Distance D22ain the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and the left injection portion44W is equal to distance D22bin the main scanning direction Y between middle position L2in the main scanning direction Y of the second recording head42and the right injection portion44W. Because of such an arrangement, for example, the distance between the left injection portion44G and the third ultraviolet irradiation device53is equal to the distance between the right injection portion44G and the fourth ultraviolet irradiation device54. Therefore, the time until the ink injected from the left injection portion44G is cured by the ultraviolet rays is equal to the time until the ink injected from the right injection portion44G is cured by the ultraviolet rays. Thus, the dot diameters of the ink injected from the two injection portions44G are equal to each other. Similarly, the dot diameters of the ink injected from the two injection portions44W are equal to each other. The dot diameters of the ink injected from the two injection portions44P are equal to each other. This significantly reduces or prevents printing unevenness on a printed item created by the ink injected by the second recording head42onto the recording paper sheet5.

In this preferred embodiment, for example, while the first recording head41is moving in the leftward direction Y1, the first printing controller61causes the right injection portion43C to inject the ink and causes the second ultraviolet irradiation device52to provide the ultraviolet rays. While the first recording head41is moving in the rightward direction Y2, the first printing controller61causes the left injection portion43C to inject the ink and causes the first ultraviolet irradiation device51to provide the ultraviolet rays. Because of such an arrangement, the dot diameter of the ink injected from the right injection portion43C of the first recording head41by the printing performed in the leftward direction Y1is equal to the dot diameter of the ink injected from the left injection portion43C of the first recording head41by the printing performed in the rightward direction Y2. This significantly reduces or prevents printing unevenness on a printed item created by the ink injected by the first recording head41onto the recording paper sheet5.

In this preferred embodiment, in the low speed printing and the high speed printing performed in the leftward direction Y1and the rightward direction Y2, any ultraviolet irradiation device passing over the recording paper sheet5before the ink is injected toward the recording paper sheet5does not emit light. In the printing performed in the leftward direction and the printing performed in the rightward direction, the ultraviolet irradiation devices to emit light are switched. This decreases the electric power consumed to cause the ultraviolet irradiation devices51,52,53and54to emit light. In this example, the ultraviolet irradiation devices51,52,53and54each include a light emitting diode. Therefore, it is easy to switch the ultraviolet irradiation device to emit light.

Now, a printer according to a modification of a preferred embodiment of the present invention will be described. In the above-described preferred embodiments, while the first recording head is moving in the leftward direction Y1, the first printing controller61and the second printing controller62cause the ink to be injected from the right injection portions43C,43M,43Y and43K among the injection portions43C,43M,43Y and43K of the first recording head41. While the first recording head41is moving in the rightward direction Y2, the first printing controller61and the second printing controller62cause the ink to be injected from the left injection portions43C,43M,43Y and43K among the injection portions43C,43M,43Y and43K of the first recording head41. Alternatively, in the printing performed in the leftward direction Y1and the printing performed in the rightward direction Y2, the injection portions43C,43M,43Y and43K to inject the ink may be opposite to the above. For example, while the first recording head is moving in the leftward direction Y1, the first printing controller61and the second printing controller62may cause the ink to be injected from the left injection portions43C,43M,43Y and43K. While the first recording head41is moving in the rightward direction Y2, the first printing controller61and the second printing controller62may cause the ink to be injected from the right injection portions43C,43M,43Y and43K. Still alternatively, in the printing performed in the leftward direction Y1and the printing performed in the rightward direction Y2, the ink may be injected from the left and right injection portions43C,43M,43Y and43K. Still alternatively, in the printing performed in the leftward direction Y1and the printing performed in the rightward direction Y2, the first printing controller61and the second printing controller62may be controlled to select the injection portions43C,43M,43Y and43K from which the ink is to be injected, namely, the left injection portions43C,43M,43Y and43K or the right injection portions43C,43M,43Y and43K, for each cycle of printing. This allows the printing quality to be changed for each cycle of printing. The above-described modifications are applicable to the printing performed by the second recording head42.