Recording apparatus, method of controlling recording apparatus and computer readable recording medium

Positions of flushing candidate pixels are provided in standard areas S formed from pixels arranged in a matrix pattern. A reference area formation section forms a reference area Ref by arranging two standard areas S adjacently to each other in both a main scan direction and a conveyance direction. In a range where there are overlaps with virtual pixel rows 84 not associated with image dots for a virtual flushing area F virtually arranged at a randomly-determined position in the reference area Ref, an extraction section extracts pixels overlapping flushing candidate pixels in the reference area Ref. A head control section controls inkjet heads such that image dots and flushing dots corresponding to the extracted pixels are formed on a sheet P.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2009-084155, which was filed on Mar. 31, 2009, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a recording apparatus having a liquid ejection head for ejecting a liquid, a method of controlling the recording apparatus and a computer readable recording medium storing a program.

A plurality of nozzles for ejecting ink droplets to a recording medium, such as a print sheet, are formed in an inkjet head provided in an inkjet printer. In such an inkjet head, viscosity of ink in the nozzles increases with elapse of a time, thereby sometimes causing a change in an ink ejection characteristic and an ejection failure. A hitherto known technique for preventing them is to produce image dots pertaining to an image on a recording medium in such a way that ink droplets are ejected from all nozzles before elapse of a predetermined time and to produce flushing dots on the recording medium by causing nozzles, which do not contribute to image production, to eject ink droplets. An increase in the viscosity of the ink in the nozzles can thereby be prevented without wasting the recording medium.

SUMMARY

According to the foregoing technique, in order to reduce visibility of flushing dots produced on a sheet, positions of the flushing dots are determined so as not to overlap each other or adjoin each other. However, according to the technique, positions of the flushing dots are previously determined, the probability of flushing dots being produced at the same locations on a plurality of sheets is high, so that flushing dots become prone to being noticeable. Meanwhile, when an attempt is made to store positions of flushing dots produced on one sheet or a plurality of sheets and individually determine positions of the respective flushing dots such that the flushing dots are not produced at the stored positions of the flushing dots in order to prevent production of flushing dots at the same positions on a plurality of sheets, amounts of arithmetic processing become enormous.

An object of the present invention is to provide a recording apparatus that can quickly determine positions of spare ejection dots through processing involving small amount of arithmetic processing and that can inhibit production of the spare ejection dots at the same positions on any recording medium.

In order to achieve the object, an exemplary embodiment of the present invention provides a recording apparatus comprising:

a conveyance mechanism which conveys a recording medium in a conveyance direction;

a liquid ejection head including a plurality of ejection ports which eject droplets toward the recording medium conveyed by the conveyance mechanism, to produce image dots, and which are arranged at intervals commensurate with a first resolution in a direction orthogonal to the conveyance direction;

an image data storage which stores image data showing, in a recording area defined in the recording medium, positions of image dots produced at intervals commensurate with the first resolution in the orthogonal direction and a second resolution in the conveyance direction;

a flushing area size storage which stores the number of virtual pixels arranged in the conveyance direction in a virtual flushing area in which a flushing area is represented in a virtual space, wherein the flushing area occupies a whole area of the recording area in the orthogonal direction and occupies at least a part of the recording area in the conveyance direction, and the flushing area includes a plurality of element rows having spatial elements arranged in the conveyance direction, the plurality of element rows being arranged in the orthogonal direction;

a standard flushing data storage which stores standard flushing data showing a standard flushing pattern within a standard area, wherein the standard area includes a plurality of elements rows having spatial elements arranged in the conveyance direction and has the same matrix shape as the virtual flushing area, and the standard flushing pattern includes flushing coordinate elements which are selected at least one from the spatial elements of each of the element rows of the standard area;

a reference area formation unit which repeatedly arranges the plural standard areas in at least one of the conveyance direction and the orthogonal direction to form a reference area;

an extraction unit which virtually arrange the virtual flushing area on an arbitrary position within the reference area, and selects the element row, in which the image dot is not included, from the element rows of the flushing area when the recording area is arranged on the flushing area, and extracts the coordinate element within the reference area in the selected element row as a flushing element; and

an ejection controller which controls the ejection ports to eject droplets based on the image data and the flushing element extracted by the extraction unit.

Further, the exemplary embodiment of the present invention provides a method of controlling a recording apparatus which includes a conveyance mechanism which conveys a recording medium in a conveyance direction; and a liquid ejection head including a plurality of ejection ports which eject droplets toward the recording medium conveyed by the conveyance mechanism, to produce image dots, and which are arranged at intervals commensurate with a first resolution in a direction orthogonal to the conveyance direction, the method comprising:

storing image data showing, in a recording area defined in the recording medium, positions of image dots produced at intervals commensurate with the first resolution in the orthogonal direction and a second resolution in the conveyance direction;

storing the number of virtual pixels arranged in the conveyance direction in a virtual flushing area in which a flushing area is represented in a virtual space, wherein the flushing area occupies a whole area of the recording area in the orthogonal direction and occupies at least a part of the recording area in the conveyance direction, and the flushing area includes a plurality of element rows having spatial elements arranged in the conveyance direction, the plurality of element rows being arranged in the orthogonal direction;

storing standard flushing data showing a standard flushing pattern within a standard area, wherein the standard area includes a plurality of elements rows having spatial elements arranged in the conveyance direction and has the same matrix shape as the virtual flushing area, and the standard flushing pattern includes flushing coordinate elements which are selected at least one from the spatial elements of each of the element rows of the standard area;

repeatedly arranging the plural standard areas in at least one of the conveyance direction and the orthogonal direction to form a reference area;

virtually arranging the virtual flushing area on an arbitrary position within the reference area;

selecting the element row, in which the image dot is not included, from the element rows of the flushing area when the recording area is arranged on the flushing area, and extracts the coordinate element within the reference area in the selected element row as a flushing element; and

controlling the ejection ports to eject droplets based on the image data and the extracted flushing element.

Further, the exemplary embodiment of the present invention provides a computer readable recording medium storing a program which causes a recording apparatus, which includes a conveyance mechanism which conveys a recording medium in a conveyance direction; and a liquid ejection head including a plurality of ejection ports which eject droplets toward the recording medium conveyed by the conveyance mechanism, to produce image dots, and which are arranged at intervals commensurate with a first resolution in a direction orthogonal to the conveyance direction, to perform:

storing image data showing, in a recording area defined in the recording medium, positions of image dots produced at intervals commensurate with the first resolution in the orthogonal direction and a second resolution in the conveyance direction;

storing the number of virtual pixels arranged in the conveyance direction in a virtual flushing area in which a flushing area is represented in a virtual space, wherein the flushing area occupies a whole area of the recording area in the orthogonal direction and occupies at least a part of the recording area in the conveyance direction, and the flushing area includes a plurality of element rows having spatial elements arranged in the conveyance direction, the plurality of element rows being arranged in the orthogonal direction;

storing standard flushing data showing a standard flushing pattern within a standard area, wherein the standard area includes a plurality of elements rows having spatial elements arranged in the conveyance direction and has the same matrix shape as the virtual flushing area, and the standard flushing pattern includes flushing coordinate elements which are selected at least one from the spatial elements of each of the element rows of the standard area;

repeatedly arranging the plural standard areas in at least one of the conveyance direction and the orthogonal direction to form a reference area;

virtually arranging the virtual flushing area on an arbitrary position within the reference area;

selecting the element row, in which the image dot is not included, from the element rows of the flushing area when the recording area is arranged on the flushing area, and extracts the coordinate element within the reference area in the selected element row as a flushing element; and

controlling the ejection ports to eject droplets based on the image data and the extracted flushing element.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A preferred embodiment of the present invention is hereunder described by reference to the drawings.

As shown inFIG. 1, an inkjet printer101includes a parallelepiped housing1a. A sheet output section31is provided in an upper portion of the housing1a. An interior of the housing1ais divided, in sequence from top, three spaces A, B, and C. Four inkjet heads1that respectively eject magenta ink, cyan ink, yellow ink, and black ink and a conveyance unit20are arranged in the space A. A sheet feed unit1bremovably attached to the housing1ais disposed in the space B, and an ink tank unit1cis disposed in the space C. In the embodiment, a sub-scan direction is a direction parallel to the conveyance direction in which a sheet P is conveyed by means of a conveyance unit20. A main scan direction is a direction that is orthogonal to the sub-scan direction and that is aligned to a horizontal plane.

A sheet conveyance path along which the sheet P is to be conveyed from the sheet feed unit1bto the sheet output section31is formed in the inkjet printer101(as designated by an arrow of medium width shown inFIG. 1). The sheet feed unit1bincludes a sheet feed tray23capable of housing a plurality of sheets P and a sheet feed roller25attached to the sheet feed tray23. The sheet feed roller25feeds the topmost sheet P among a plurality of sheets P stocked in a piled manner in the sheet feed tray23. The sheet P fed by the sheet feed roller25is fed to the conveyance unit20while being guided by guides27aand27band nipped between a pair of feed rollers26.

The conveyance unit20includes two belt rollers6and7; an endless conveyance belt8wrapped around the rollers so as to extend between the rollers6and7; and a tension roller10. The tension roller10is downwardly forced while remaining in contact with an internal peripheral surface of a lower loop of the conveyance belt8, to thus impart tension to the conveyance belt8. The belt roller7is a drive roller and rotated in a clockwise direction inFIG. 1when imparted with drive force from a conveyance motor M through two gears. The belt roller6is a driven roller and rotated by rotation of the belt roller7in the clockwise direction inFIG. 1along with travel of the conveyance belt8.

An outer peripheral surface8aof the conveyance belt8is subjected to silicon treatment and exhibits adhesiveness. A nip roller4is disposed at a position along the sheet conveyance path so as to oppose the belt roller6with the conveyance belt8sandwiched therebetween. The nip roller4presses the sheet P fed out of the sheet feed unit1bagainst the outer peripheral surface8aof the conveyance belt8. The sheet P pressed against the outer peripheral surface8ais conveyed in a rightward direction inFIG. 1while held on the outer peripheral surface8aby means of adhesiveness of the outer peripheral surface.

A separation plate5is disposed at a position on the sheet conveyance path where the separation plate opposes the belt roller7with the conveyance belt8sandwiched therebetween. The separation plate5separates the sheet P from the outer peripheral surface8a. The thus-separated sheet P is conveyed while guided by guides29aand29band nipped by two feed roller pairs28and output to the sheet output section31from an opening30formed in the upper portion of the housing1a.

Four inkjet heads1are supported by the housing1athrough a frame3. The four inkjet heads1extend along the main scan direction and are arranged in parallel to each other along the sub-san direction. The inkjet printer101is a line-type color inkjet printer in which an ejection area extending in the main scan direction is formed. A lower surface of each of the inkjet heads1is an ejection surface2athrough which ink droplets are ejected.

A platen19is arranged in the loop of the conveyance belt8and is opposed to the four inkjet heads1. An upper surface of the platen19remains in contact with an internal peripheral surface of an upper loop of the conveyance belt8and supports the conveyance belt8from its inner peripheral side. The outer peripheral surface8aof the upper loop of the conveyance belt8is opposed the lower surfaces of the inkjet heads1, namely, the ejection surfaces2a, in parallel to each other, whereby clearance of predetermined interval suitable for producing an image is created. The clearance makes up a portion of the sheet conveyance path. When the sheet P conveyed by the conveyance belt8passes by positions located immediately below the respective heads1, respective colors of ink are sequentially ejected toward an upper surface of the sheet P from the respective heads1, whereupon a desired color image is produced on the sheet P.

The respective inkjet heads1are connected to respective ink tanks49set in the ink tank unit1cprovided in the space C. The four ink tanks49store ink to be ejected by the corresponding ink jet heads1, respectively. Ink is supplied from each of the ink tanks49to the corresponding inkjet head1through a tube (not shown), or the like.

The inkjet heads1are now described in detail by reference toFIGS. 2 and 3. A lower housing87is omitted fromFIG. 3.

As shown inFIG. 2, each of the inkjet heads1includes a reservoir unit71; a head main body2including a flow channel unit9and an actuator unit21; and a COF (Chip On Film: a flat flexible substrate)50that is connected at its one end to the actuator unit21and that is equipped with a driver IC52; and a control substrate54to which the other end of the COF50is connected. The inkjet head1includes the reservoir unit71; an upper housing86and the lower housing87that make up a box surrounding the flow channel unit9; and a head cover55that encloses the control substrate54at a position above the upper housing86.

The reservoir unit71is a flow channel formation member that is fixed to an upper surface of the head main body2and that supplies the head main body2with ink. The reservoir unit71is a multilayered substance formed by stacking four mutually positioned plates91to94. An unillustrated ink inflow channel, the ink reservoir72, and ten ink outflow channels73are formed in the reservoir unit so as to mutually communicate with each other. Only one of the ink outflow channels73is shown inFIG. 2. The ink inflow channel is a channel into which ink flows from the ink tank49. The ink reservoir72temporarily stores an inflow of ink from the ink inflow channel. The ink outflow channel73is a flow channel through which ink flows from the ink reservoir72and that is in mutual communication with an ink supply port105bformed in an upper surface of the flow channel unit9. Ink from the ink tank49flows into the ink reservoir72through the ink inflow channel, passes through the ink outflow channel73, and is supplied from the ink supply port105bto the flow channel unit9.

An indentation94ais formed in a lower surface of the plate94. The indentation94creates clearance90between the lower surface of the plate and an upper surface of the flow channel unit9. The four actuator units21on the flow channel unit9are arranged at equal intervals in the clearance90along the longitudinal direction of the flow channel unit9. In a side surface of the multilayered substance, four openings90aof the clearance90are formed at equal intervals in a staggered pattern and along the longitudinal direction of the reservoir unit71.

Protuberances (areas other than the indentation94a) on the lower surface of the plate94are adhered to the flow channel unit9. The ink outflow channels73are formed in the respective protuberances.

A neighborhood of one end of the individual COF50is connected to an upper surface of the corresponding actuator unit21. The COF50extends from the upper surface of the actuator unit21in a horizontal direction and passes through the opening90a. The COF thus passed through the opening is then curved and bent at substantially right angles in an upward direction. The thus-bent COF passes through a cutout53formed in an interior wall surface of the upper housing86and the lower housing87and is pulled to a position above the reservoir unit71. The COF50further extends in a leftward direction inFIG. 2at a position above the reservoir unit71and pulled to a position above the upper housing86through a slit86aformed in the upper housing86. The other end of the COF50is connected to the corresponding control substrate54through a connector54aat a position above the upper housing86. A driver IC52is mounted at an arbitrary position on the COF50. The driver IC52is affixed to the upper surface of the reservoir unit71and thermally coupled to the reservoir unit71. Heat given off by the driver IC52thereby propagates to the reservoir unit71, whereupon the driver IC52is cooled. On the other hand, ink in the reservoir unit71is heated, to thus hinder an increase in viscosity of ink.

The control substrate54is placed at a position above the upper housing86and controls actuation of the actuator unit21through the driver IC52of the COF50. The driver IC52is for generating a drive signal for actuating the actuator unit21.

The head main body2is now described with reference toFIGS. 3 and 4. Pressure chambers110, apertures112, and ejection ports108, which are located beneath the actuator unit21and which are to be drawn in broken lines, are drawn in solid lines inFIG. 4for the sake of explanation.

As shown inFIG. 3, the head main body2is a multilayered substance in which the four actuator units21are fixed to the upper surface9aof the flow channel unit9. As shown inFIGS. 3 and 4, ink flow channels, including the pressure chambers110, are formed in the flow channel unit9. Each of the actuator units21includes a plurality of actuators assigned to the respective pressure chambers110and has a function of selectively imparting ejection energy to ink stored in the respective pressure chambers110.

The flow channel unit9assumes the shape of a rectangular parallelepiped having substantially the same planar shape as that of the plate94of the reservoir unit71. A total of ten ink supply ports105bare formed in the upper surface9aof the flow channel unit9in correspondence with the ink outflow channels73of the reservoir unit71(seeFIG. 2). As shown inFIG. 3, there are formed in the flow channel unit9a manifold flow channel105remaining in mutual communication with the ink supply ports105b, a sub-manifold105abranched off from the manifold flow channel105, and a plurality of individual ink flow channels132branched off from the sub-manifold flow channel105a. As shown inFIG. 1, the ejection surfaces2aare formed on a lower surface of the flow channel unit9, and as shown inFIG. 4, the plurality of ejection ports108are arranged in the ejection surfaces in a matrix pattern. The plurality of pressure chambers110are also arranged in a matrix pattern in the upper surface9aof the flow channel unit9(i.e., the surface to which the actuator units21are fixed). The ejection ports108are arranged, along the main scan direction, at an interval of 600 dpi that is a resolution achieved in the main scan direction.

In the embodiment, sixteen rows of the pressure chambers110that are equally spaced along the longitudinal direction of the flow channel unit9are arranged in parallel to each other along a widthwise direction. The number of pressure chambers110included in each of the rows of pressure chambers becomes gradually smaller from a long side (a lower bottom side) to a short side (an upper bottom side) in correspondence with the outer shape (a trapezoidal shape) of the actuator unit21to be described later. The ejection ports108are also arranged correspondingly.

The flow channel unit9is a multilayered substance made by mutually positioning a plurality of metal plates made of stainless steel. Formed in the flow channel unit9are a plurality of individual ink flow channels132that extend from the manifold flow channel105to the sub-manifold flow channels105aand from exits of the sub-manifold flow channels105ato the ejection ports108through the pressure chambers110.

Ink flow in the flow channel unit9is now described. As shown inFIGS. 3 and 4, the ink supplied from the reservoir unit71into the flow channel unit9through the ink supply port105bis distributed from the manifold flow channel105to the sub-manifold flow channels105a. The ink in the sub-manifold flow channels105aflows into the individual ink flow channels and reaches the ejection ports108through the pressure chambers110.

The actuator units21are unimorph actuators. The unimorph actuator is made up of lead zirconate titanate (PZT)-based piezoelectric c sheet made of ceramic exhibiting ferroelectricity. Upon receipt of an input of a drive signal, the actuator unit21selectively imparts pressure (ejection energy) to the ink in a target pressure chamber110, thereby ejecting an ink droplet from the corresponding ejection port108.

The controller16is now described by reference toFIG. 5. The controller16includes a CPU (Central Processing Unit); EEPROM (Electrically Erasable and Programmable Read Only Memory) that rewritably stores a program to be executed by the CPU and data used for the program; and RAM (Random Access Memory) that temporarily stores data at the time of execution of the program. Respective operation parts making up the controller16are built as a result of these hardware parts and software in the EEPROM acting synergistically. As shown inFIG. 5, the controller16controls the entirety of the inkjet printer101and includes an image data storage section41, a flushing area size storage section42, a flushing data storage section43, a standard area formation section44, a reference area formation section45, an extraction section46, a head control section47, and a conveyance control section48.

The conveyance control section48controls a conveyance motor M of the conveyance unit20such that the sheet P is conveyed along a conveyance direction.

The image data storage section41stores image data pertaining to an image to be printed in a print area defined on the sheet P. The image data allocate volumes of ink droplets used for producing respective image dots, which make up an image, to the respective ejection ports108of the respective inkjet heads1at every print cycle. Ink droplets to be ejected from the ejection ports108in the present embodiment correspond to any selected from ink droplets having three types of volumes of ink droplets (large ink droplets, medium ink droplets, and small ink droplets). The print cycle corresponds to a period of time required to convey the sheet P only over a unit distance commensurate with a print resolution achieved in the conveyance direction.

The image data represent positions of virtual pixels (spatial elements), which are associated with image dots to be produced at intervals commensurate with a resolution for the main scan direction (a first resolution: a distance between the ejection ports108achieved in the main scan direction) and a resolution for the conveyance direction (a second resolution) with respect to the main scan direction and the conveyance direction, on a virtual sheet P′ (seeFIG. 10) that shows the print area of the sheet P in a data space. The virtual sheet P′ is formed as a result of a plurality of virtual pixels being arranged in a matrix pattern within a two-dimensional space defined by an axis extending along the main scan direction and another axis extending along the conveyance direction. A distance on the virtual sheet P′ between virtual pixels achieved in the conveyance direction is a distance on the sheet P commensurate with the resolution for the conveyance direction. A distance on the virtual sheet P′ between virtual pixels achieved in the main scan direction is a distance on the sheet P commensurate with the resolution for the main scan direction. The respective virtual pixels on the virtual sheet P′ are located at positions associated with any of the ejection ports108of the respective inkjet heads1with respect to the main scan direction.

A flushing area overlapping the print area is defined on the sheet P. The flushing area is an area where flushing dots are created through flushing (preliminary ejection) processing for ejecting ink before ink in the ejection ports108becomes degenerated. The flushing area is a range that occupies the entirety of the print area in the main scan direction and that occupies at least a portion of the print area in the conveyance direction. The flushing area can be arbitrarily determined by the user. In the present embodiment, the flushing area is assumed to match the print area of the sheet P. As shown inFIG. 10, a virtual flushing area F is a virtual area that depicts the flushing area in the data space. The virtual flushing area F is made up of a plurality of virtual pixels arranged in a matrix pattern in both the conveyance direction and the main scan direction.

In the embodiment, a length of the virtual flashing area F in the main scan direction may correspond to a length of an area, in which the plurality of ejection ports108are arranged, in the main scan direction.

The flushing area size storage section42stores the number of virtual pixels in the virtual flushing area F corresponding to the flushing area in the conveyance direction. As mentioned previously, the flushing area is determined in the form of the area that occupies at least a portion of the print area of the sheet P in the conveyance direction. Therefore, the number of virtual pixels in the virtual flushing area F in the conveyance direction is equal to or smaller than a quotient determined by dividing the length of the print area achieved in the conveyance direction by a unit distance commensurate with the resolution for the direction of the conveyance. A degree of freedom of setting of a data size pertaining to flushing is thereby increased, so that a storage capacity can be reduced. In the present embodiment, the flushing area matches the print area. The flushing area size storage section42stores, as the number of pixels, a quotient determined by dividing the length of the print area achieved in the conveyance direction by the unit distance commensurate with the resolution for the conveyance direction.

The flushing data storage section43stores flushing data for each color of ink used. Flushing data include data that show four base flushing patterns in correspondence with colors of ink. Each of the base flushing patterns is a layout pattern for a plurality of flushing candidate pixels achieved in a base area S0. The base flushing pattern corresponds to a layout of virtual pixels corresponding to positions where flushing dots can be produced.

The base area S0is a virtual area made as a result of a plurality of virtual pixels being arranged in a matrix pattern. The base area S0is made up of virtual pixels that are equal in number to the virtual flushing area F in the main scan direction and at least one flushing candidate pixel selected from the respective rows of virtual pixels in the conveyance direction. As will be described later, the standard area S is formed from the base area S0, and the base area S0can be said to be a unit virtual area where flushing candidate pixels are arranged in a flushing dot arrangement pattern. The flushing data storage section43stores the data pertaining to the base area S0, and the data include information about the number of virtual pixels making up the base area S0(achieved in both the main scan direction and the conveyance direction) and a unit arrangement location for a flushing candidate pixel in the base area S0. Detailed explanations are given to the flushing data stored in the flushing data storage section43by further referring toFIGS. 6 and 7.

As shown inFIG. 6, the base area S0is made up of a 4961×3508 matrix of virtual pixels81. The number of the virtual pixels81arranged in the base area S0along the main scan direction; namely, 4961, is a number equal to a result of the length of the print area of the sheet P in the main scan direction being divided by a unit distance (about 42 micrometers) commensurate with a resolution of 600 dpi for the main scan direction. The number of the virtual pixels81arranged in the base area S0along the conveyance direction; namely, 3508, is a number equal to a result of the length of the print area of the sheet P in the conveyance direction being divided by a unit distance (about 84 micrometers) commensurate with a resolution of 300 dpi for the conveyance direction. As mentioned above, in the present embodiment, the base area S0is a virtual area specified by the lowest resolution of 300 dpi (which will be described later) at least with respect to the conveyance direction. In the base area S0, 3508 virtual pixels81arranged along the conveyance direction make up one virtual pixel row82, and 4961 virtual pixel rows82arranged along the main scan direction make up the base area S0.

The inkjet printer101takes a resolution of 300 dpi as the lowest resolution for the conveyance direction and can print an image at any one of four resolutions that increase in steps of 100 dpi. A resolution of 600 dpi is the highest resolution for the conveyance direction at which the inkjet printer101can produce a print. A distance between adjacent virtual pixels81in the base area S0acquired with respect to the conveyance direction is equivalent to the unit distance commensurate with the resolution for the conveyance direction. A distance between adjacent virtual pixels81in the base area S0acquired with respect to the main scan direction is equivalent to the unit distance commensurate with the resolution for the main scan direction.

The virtual pixels81that are flushing candidate pixels are depicted by reference numerals81ato81d, to thus be distinguished from virtual pixels that are not the flushing candidate pixels. The virtual pixel81arepresents a flushing candidate pixel pertaining to a black flushing pattern. The virtual pixel81brepresents a flushing candidate pixel pertaining to a magenta flushing pattern. The virtual pixel81crepresents a flushing candidate pixel pertaining to a cyan flushing pattern. The virtual pixel81drepresents a flushing candidate pixel pertaining to a yellow flushing pattern.

One virtual pixel row82in the base area S0is brought in correspondence with one ejection port108. Each of the virtual pixel rows82includes four virtual pixels81ato81dthat are flushing candidate pixels. In each of the virtual pixel rows82, the virtual pixels81ato81dare placed at this time at mutually-different positions.

The present embodiment provides a configuration in which the flushing area matches the print area as mentioned above. The number of virtual pixels81(=3508) arranged in the base area S0along the conveyance direction is determined from the lowest resolution of 300 dpi at which the printer can produce a print. The flushing data storage area43stores the number of virtual pixels81arranged along the conveyance direction; namely, 3508, as the number of the virtual pixels81arranged in the base area S0along the conveyance direction.

As shown inFIGS. 7 and 8, the standard area formation section44produces a standard area S from the number of virtual pixels81arranged in the virtual flushing area F along the conveyance direction stored in the flushing area size storage section42, by enlarging the base area S0in the conveyance direction. The base area S0is enlarged at this time in such a way that the number of virtual pixels81arranged in the base area S0matches the virtual flushing area F with respect to the conveyance direction.

When the resolution required by image data is now assumed to be 300 dpi, the number of virtual pixels81arranged in the virtual flushing area F along the conveyance direction is equal to the number of virtual pixels81arranged in the base area S0along the conveyance direction. Accordingly, the standard area formation section44sets, as the standard area S, the base area S0where 4961 virtual pixels81are arranged along the main scan direction and where 3508 virtual pixels81are arranged along the conveyance direction. In this case, the standard area S has the same arrangement pattern as that of the base area S0in connection with the virtual pixels81and the flushing candidate pixels.

When the resolution required by image data is 600 dpi, the standard area formation section44first calculates a scale-up factor of 200% that is a ratio of 600 dpi to 300 dpi. On the basis of the base flushing pattern, the standard area formation section44doubles the number of virtual pixels in each of the virtual pixel rows of the base area S0except the flushing candidate pixels [processing for increasing the number of continual virtual pixel groups (which will be described later)]. Further, the standard area formation section44adds virtual pixels, which are equal in number to the flushing candidate pixels included in the virtual pixel row and which are not flushing candidate pixels, to each of the virtual pixel rows (processing for enlarging flushing candidate pixels themselves). Virtual pixels to be added are arranged; for instance, in such a way that each of the flushing candidate pixels is followed by one virtual pixel. When the scale-up factor is not an integral multiple as mentioned in connection with the foregoing embodiment, the number of virtual pixels included in the virtual pixel row is adjusted so as to obtain an integral multiple closest to a product resultant from multiplication of the scale-up factor.

Specifically, the standard area formation section44calculates a scale-up factor (130% inFIGS. 7 and 8) that is a ratio of a resolution for the virtual flushing area F achieved in the conveyance direction to a resolution for the base area S0achieved in the conveyance direction (the lowest resolution achieved in the conveyance direction). In relation to each of the virtual pixel rows82of the base area S0in the conveyance direction, the standard area formation section44multiplies, by the scale-up factor, the number of continual virtual pixels81in the virtual pixel group consisting of one or a plurality of virtual pixels81that are defined by the virtual pixels81ato81dcorresponding to flushing candidate pixels and that are not flushing candidate pixels, thereby calculating a new number of continual virtual pixels81in each of the virtual pixel groups. An integral closest to a product determined by multiplying the number of continual virtual pixels81by the scale-up factor is taken as a new number of continual virtual pixels81. The standard area formation section44inserts one or a plurality of virtual pixels81into a virtual pixel group in each of the virtual pixel row82in such a way that the calculated number of continual virtual pixels81that are not the flushing candidate pixels comes to a newly calculated number of continual virtual pixels, thereby forming the standard area S. The thus-formed standard area S is stored in the flushing data storage section43. Thus, the flushing data storage section43stores flushing data including four flushing patterns pertaining to the standard area S.

For instance, when four virtual pixels81are adjacently arranged in the virtual pixel row82as shown inFIG. 8, we have 4×130%=5.2; hence, an integer closest to the product is five. Therefore, one virtual pixel81is inserted into the virtual pixel group including four virtual pixels81. When only one virtual pixel81is arranged in the virtual pixel row82, we have 1×130%=1.3, and an integer closest to the product is one. Therefore, the virtual pixel81is not newly inserted in this case. When three virtual pixels81are arranged adjacently to each other, we have 3×130%=3.9, and an integer closest to the product is four. Therefore, one virtual pixel81is inserted into the virtual pixel group including the three virtual pixels81. When eight virtual pixels81are arranged adjacently to each other, we have 8×130%=10.4, and an integer closest to the produce is 10. Therefore, two virtual pixels81are inserted into the virtual pixel group including eight virtual pixels81. Even in this case, the standard area formation section44adds, to each of the virtual pixel group, virtual pixels that are equal in number to the flushing candidate pixels included in the virtual pixel row and that are not fluxing candidate pixels, as in the case where the scale-up factor is an integral multiple. The standard area formation section44finally brings the number of virtual pixels included in the virtual pixel row in agreement with the standard area S. Processing for increasing the number of continual virtual pixels and processing for enlarging flushing candidate pixels themselves have already been performed thus far. An excess or a deficiency of virtual pixels occurred at this time may also be collectively placed at the had of the virtual pixel row. Alternatively, the excess or deficiency of virtual pixels may also be placed at the end of the virtual pixel row. A flushing area matching the print area can be subjected to flushing processing.

The reference area formation section45forms a reference area Ref from the standard area S produced by the standard area formation section44, as shown inFIG. 9. In the reference area Ref, two standard areas S are adjacently arranged in both the main scan direction and the conveyance direction. The expression “adjacently arranged” signifies that the outermost virtual pixels81of each of the adjacent standard areas S are spaced apart from each other by a distance commensurate with the resolution for the conveyance direction and the resolution for an orthogonal direction. The virtual pixels81of the standard area S are repeatedly arranged twice in the reference area Ref in a line along the main scan direction and in units equal in number to the virtual pixels81arranged in the standard area S along the main scan direction. The virtual pixels81of the standard area S are also repeatedly arranged twice in the reference area Ref in a line along the conveyance direction and in units equal in number to the virtual pixels81arranged in the standard area S along the conveyance direction. The reference area Ref is thus made up of 9922 (=4961×2) virtual pixel rows arranged in the main scan direction, each of which includes 7016 (=3508×2) virtual pixels81arranged in the conveyance direction.

The extraction section46extracts flushing candidate pixels (flushing pixels) used for producing flushing dots from flushing candidate pixels (the virtual pixels81ato81d) included in the reference area Ref formed by the reference area formation section45.

Specifically, the extraction section46virtually arranges a virtual flushing area F at a randomly determined position in the reference area Ref in such a way that all pixels of the virtual flushing area F overlap the virtual pixels81of the reference area Ref.FIG. 10shows a state of the reference area achieved at this time. When respective image dots are associated with any pixel rows arranged along the conveyance direction, the extraction section46selects, in the virtual flushing area F, virtual pixel rows84not associated with the image dots. In an area where overlaps with the selected virtual pixel rows84are achieved, the extraction section46extracts, as flushing pixels for the virtual flushing area F, pixels overlapping the flushing candidate pixels (the virtual pixels81ato81d) in the reference area Ref. In the virtual flushing area F, there are actually produced the virtual area made up of only the virtual pixel rows84not associated with the image dots corresponds to the flushing area where flushing dots. Each of the virtual pixel rows84includes four flushing pixels in correspondence with the respective virtual pixels81ato81d. The flushing data storage section43stores flushing data pertaining to an arrangement pattern of the flushing pixels achieved at this time as a flushing pattern.

The virtual flushing area F completely overlaps one standard area S or straddles two or four standard areas S within the reference area Ref. The reference area Ref is formed by arranging the four standard areas S so as to become adjacent to each other. Hence, even when the virtual flushing area F straddles two or four standard areas S, only one pixel overlapping any of the flushing candidate pixels (the virtual pixels81ato81d) is present in each of the virtual pixel rows arranged in the conveyance direction within the reference area Ref. Therefore, even when the virtual flushing area F is virtually arranged at any location within the reference area Ref, flushing pixels can be extracted from each of the virtual pixel rows84without fail.

The head control section47controls ejection of ink droplets from the ejection ports108of the inkjet head1through the control substrate54. The head control section47determines whether or not a time elapsed since purging-and-wiping operation (which will be described later) was performed or flushing was performed has exceeded a predetermined time T. When determined that the elapsed time has not exceeded the predetermined time T, the head control section47controls ejection of ink droplets from the ejection ports108of the respective ink jet heads1in such a way that only image dots pertaining to image data stored in the image data storage section41are formed on the sheet P without formation of the flushing dots on the sheet P. The predetermined time T is a time that is shorter than a period of time during which speed of an ink droplet ejected from the ejection port108decreases from a reference speed to a predetermined percentage of the reference speed as a result of the ink stored in the ejection ports108being degraded by drying, or the like. The predetermined time T is set to a time that is shorter than a period of time during which a change in image quality is visibly recognized.

When determined that the elapsed time exceeds the predetermined time T, the head control section47produces a logical OR between image pixels relevant to the image dots included in image data and flushing pixels extracted by the extraction section46(ejection data that are a logical OR between image data and flushing data stored in the flushing data storage section43). The head control section47controls ejection of ink droplets from the ejection ports108of the respective inkjet heads1in such a way that the image dots included in the logical OR (the ejection data) and flushing dots corresponding to the flushing pixels are formed on the sheet P conveyed to the conveyance unit20. Ink droplets are ejected at least one from all of the ejection ports108of the respective inkjet heads1every time the predetermined time T elapses.

Operation procedures of the controller16are now described by reference toFIG. 11. As shown inFIG. 11, upon receipt of a print start command from a host computer, the controller performs purging-and-wiping operation (S101). The purging-and-wiping operation means operation for forcefully supplying ink from an unillustrated ink supply pump to the respective inkjet heads1, purging (ejecting) ink from the respective ejection ports108, and wiping the ejection surfaces2aby means of unillustrated wipers. It becomes possible to discharge ink having increased viscosity and impurities in the inkjet heads1to the outside by means of performing purging-and-wiping operation and to hold meniscuses formed in the ejection ports108in good condition. The head control section47resets an internal timer T0(S102).

The head control section47subsequently determines whether or not the value of the internal timer T0has exceeded the predetermined time T (S103). When determined that the value of the internal timer T0has not exceeded the predetermined time T (NO in S103), the head control section47controls ejection of ink droplets from the ejection ports108of the ink jet head1in such a way that only image dots relevant to image data are produced on the sheet P (S104). When the sheet P has finished undergoing printing, the controller16determines whether or not to subject the next sheet P to printing (S105). When the next sheet P is subjected to printing (YES in S105), processing again proceeds to S103, where the next sheet P undergoes printing. When the next sheet P is not subjected to printing (NO in S105), processing pertaining to a flowchart shown inFIG. 11is completed.

When the head control section47determines that the value of the internal timer T0has exceeded the predetermined time T (YES in S103), the standard area formation section44forms the standard areas S from the base area S0, and the reference area formation section45forms the reference area Ref from the standard areas S (S106). The extraction section46randomly, virtually arranges the virtual flushing area F within the reference area Ref in such a way that all of the pixels of the virtual flushing area F overlap the virtual pixels81of the reference area Ref (S107). Further, when the respective image dots are associated with any of the pixel rows arranged along the conveyance direction within the virtual flushing area F, the extraction section46extracts, as flushing pixels relevant to the virtual flushing area F, the pixels overlapping the virtual pixels81ato81dof the reference area Ref corresponding to the flushing candidate pixels within the range where there are overlaps with the virtual pixel rows84not associated with the image dots (S108). The extraction section46generates flushing data at this time from the extracted flushing pixels and an arrangement pattern of the flushing pixels (the flushing pattern). Simultaneously, flushing data are stored in the flushing data storage section43.

The head control section47controls ejection of ink droplets from the ejection ports108of the respective inkjet heads1in such a way that the image dots included in image data and flushing dots corresponding to flushing pixels extracted by the extraction section46are formed on the sheet P conveyed to the conveyance unit20(S109). The head control section47generates ejection data from the image data and flushing data in the flushing data storage section43and controls ejection of ink droplets in accordance with the ejection data. Ink droplets are ejected from all of the ejection ports108of the respective inkjet heads1at least once every time the predetermined time T elapses. When the sheet P has finished undergoing printing, the controller16determines whether to subject the next sheet P to printing (S110). When the next sheet P is subjected to printing (YES in S110), processing again proceeds to S102, and the internal timer TO is reset. Thus, the next sheet P is subjected to printing. When the next sheet P is not subjected to printing (NO in S110), processing pertaining to the flowchart shown inFIG. 11is completed.

In the inkjet printer101of the present embodiment, the extraction section46can appropriately extract flushing pixels for the respective virtual pixel rows84even when the virtual flushing area F is virtually arranged at any location in the reference area Ref as mentioned above. Therefore, the virtual flushing area F is virtually arranged at a randomly-determined position within the reference area Ref, whereby it is possible to avoid formation of flushing dots at the same positions on all sheets P, to thus make the flushing dots less conspicuous. Positions of flushing dots can quickly be determined through processing involving small amount of arithmetic operation, such as virtually arranging the virtual flushing area F in the reference area Ref and extracting pixels overlapping the virtual pixels81ato81d, which are the flushing candidate pixels, in the reference area Ref as flushing pixels for the virtual flushing area F within the range where there are overlaps with the virtual pixel rows84not associated with the image dots for the virtual flushing area F.

Flushing data stored in the flushing data storage section43include four flushing patterns compliant with the respective inkjet heads1. Four pixel rows for four flushing patterns placed at the same positions with respect to the main scan direction have the virtual pixels81ato81dthat are flushing candidate pixels located at different positions with respect to the conveyance direction. When the flushing dots are formed, ink droplets ejected from the respective inkjet heads1do not arrive at the same locations in a record area on the sheet P. An increase in diameters of the flushing dots can thereby be prevented.

The extraction section46virtually arranges the virtual flushing area F at a randomly-determined position in the reference area Ref. Hence, positions where flushing dots are to be formed can readily be changed from one sheet P to another sheet P.

In addition, the reference area formation section45arranges two standard areas S adjacently to each other in both the main scan direction and the conveyance direction, thereby creating the reference area Ref. It is, therefore, possible to efficiently change positions where flushing dots are to be formed from one sheet P to another sheet P.

The standard area formation section44generates, from the base area S0stored in the flushing data storage section43, a plurality of standard areas S commensurate with mutually-different resolutions for the conveyance direction. It is not necessary to store the plurality of standard areas S in the flushing data storage section43, so that the storage capacity of the flushing data storage section43can be made small. Further, the flushing data storage section43stores the base area S0commensurate with the lowest resolution among the plurality of resolutions for the conveyance direction at which the inkjet printer101can produce a print, so that the storage capacity of the flushing data storage section43can be reduced to a much greater extent.

In relation to each of the virtual pixel rows82arranged in the base area S0along the conveyance direction, the standard area formation section44calculates a new number of continual pixels by multiplying, by a scale-up factor, the number of continual virtual pixels81in the pixel group that is grouped by the virtual pixels81ato81dand that includes one or a plurality of virtual pixels81that are not flushing candidate pixels. The standard area formation section44forms the standard areas S in such a way that the number of continual pixels in each of the pixel groups becomes equal to the calculated number of continual pixels. Therefore, the plurality of standard areas S commensurate with the plurality of resolutions for the conveyance direction can readily be formed.

Example Modification

Example modifications of the present invention are now described. In the foregoing embodiment, the flushing data storage section43is configured so as to store flushing data including flushing patterns for four colors black, magenta, cyan, and yellow having a plurality of flushing candidate pixels as pixels. The flushing data storage section, however, can store flushing data including only one flushing pattern. The extraction section at this time virtually arranges the virtual flushing area F, for each inkjet head1, at a randomly-determined position within the reference area Ref for the flushing data. Further, in the range where there are overlaps with the virtual pixel rows84not associated with the image dots of the virtual flushing area F, the extraction section extracts, as flushing pixels for the virtual flushing area F, pixels overlapping pixels that are flushing candidate pixels in the reference area Ref.

The essential requirement for the flushing data storage section43is to store flushing data including the flushing pattern pertaining to one inkjet head1, so that the storage capacity of the flushing data storage section43can be reduced.

The preferred embodiment of the present invention has been described thus far. However, the present invention is not limited to the foregoing embodiment and susceptible to various alterations within the scope of claims. In the foregoing embodiment, each of the pixel rows, which is made up of a plurality of pixels arranged in the conveyance direction for the four flushing patterns included in the flushing data stored in the flushing data storage section43, is configured so as to include, at mutually-different locations with respect to the conveyance direction, the virtual pixels81ato81dthat are flushing candidate pixels. However, each of the pixel rows can have pixels, which are the flushing candidate pixels, at the same locations with respect to the conveyance direction.

In the foregoing embodiment, the extraction section46is configured in such a way that the virtual flushing area F is virtually arranged at a randomly-determined position in the reference area Ref. The extraction section can also be configured in such a way that the virtual flushing area F is virtually arranged at a position determined on the basis of a previously-stored pattern. The pattern can also change periodically.

In the foregoing embodiment, the reference area formation section45is configured so as to form the reference area Ref by arranging two standard areas S adjacently to each other in both the main scan direction and the conveyance direction. However, the reference area formation section can also be configured so as to form the reference area Ref by arranging an arbitrary number of standard areas S adjacently to each other in both the main scan direction and the conveyance direction. For instance, the reference area Ref can also be formed by arranging two standard areas S adjacently to each other in both the main scan direction and the conveyance direction. Alternatively, the reference area Ref can also be formed by letting the virtual pixels81of a standard area S repeatedly appear in at least the main scan direction or the conveyance direction and in units equal in number to the virtual pixels81arranged in the standard area S in the same direction, in such a way that the virtual pixels81arranged from one end of the standard area S become adjacent to virtual pixels81arranged toward the other end of the standard area S with respect to the same direction.

In the foregoing embodiment, the flushing data storage section43is configured so as to store the base area S0commensurate with the lowest resolution among the resolutions for the conveyance direction at which the inkjet printer101can produce a print. However, The flushing data storage section can also be configured so as to store the base area S0commensurate with another resolution for the conveyance direction.

In the foregoing embodiment, the standard area formation section44is configured so as to form the standard area S by means of inserting virtual pixels81into each of the pixel groups in each of the virtual pixel rows82arranged in the base area S0along the conveyance direction, in such a way that each of the pixel groups that is grouped by the virtual pixels81ato81dand that includes one or a plurality of virtual pixels81which are not flushing candidate pixels assumes a new number of continual pixels determined by multiplying, by a scale-up factor, the number of continual virtual pixels81in the pixel group. However, the configuration of the standard area formation section for forming the standard area S from the base area S0can be arbitrary.

In the foregoing embodiment, each of the virtual pixel rows82of the base area S0is configured so as to include one flushing candidate pixel in one inkjet head1. However, each of the virtual pixel rows82can also be configured so as to include two or more flushing candidate pixels in one inkjet head1.

In the embodiment, the number of pixels arranged in the virtual flushing area F along the conveyance direction is equal to a quotient obtained by dividing the length of the print area achieved in the conveyance direction by the distance equivalent to the resolution for the conveyance direction. However, the number of pixels arranged in the virtual flushing area F along the conveyance direction can also be smaller than the quotient.

In the embodiment, the flushing data storage section43stores a number equal to the number of the virtual pixels in the virtual flushing area F as the number of virtual pixels for the base area S0to be arranged in the main scan direction. The flushing data storage section can also store instead a number equal to or smaller than a quotient obtained by dividing the length of the flushing area (the print area) achieved in the main scan direction by a unit distance commensurate with the resolution for the main scan direction. When the standard area S is formed, the flushing data storage section43enlarges virtual pixels in such a way that a virtual pixel row repeatedly appears in units equal to the previously-stored number of virtual pixels to be formed in the base area S0with respect to the main scan direction. The flushing data storage section43performs enlargement processing until virtual pixel rows required to make up the virtual flushing area F are arranged. Small memory capacity is sufficient in this case.

In the foregoing embodiment, the base area S0is a virtual area defined at the lowest resolution for the conveyance direction. However, the base area S0must be specified at the highest resolution at least for the conveyance direction. The same also applies to the base area in connection with the other direction as well. However, in view of small memory capacity, it is much better to specify the base area at the smallest resolution for both directions.

In the foregoing embodiment, when the standard area formation section44forms a standard area S by enlarging the base area S0, addition of virtual pixels commensurate with enlargement of the respective flushing candidate pixels is performed by adding one virtual pixel so as to immediately follow each of the flushing candidate pixels. However, the virtual pixel can be placed at an arbitrary position, so long as the position is in the same virtual pixel row. For instance, in order to add one pixel corresponding to the flushing candidate pixel, the pixel can also be interposed between the flushing candidate pixel and the next flushing candidate pixel. The standard area S can thereby be formed in a pattern analogous to an arrangement pattern of flushing candidate pixels in the base flushing pattern. Further, all virtual pixels to be added can also collectively be arranged before the head or after the end of the virtual pixel row.

In the foregoing embodiment, the flushing area and the print area are configured so as to match each other. However, as mentioned previously, the essential requirement is that the flushing area should match the print area in the main scan direction and occupy a portion of the print area in the conveyance direction. All the standard area formation section44has to do is to enlarge each of the virtual pixel rows by multiplying, by a scale-up factor, the number of continual virtual pixels in the virtual pixel group made up of the virtual pixels that are not the flushing candidate pixels. The standard areas S are formed from the base area S0by means of simple processing. Processing for enlarging flushing candidate pixels themselves and processing for adjusting an excess or deficiency in virtual pixels in each of virtual pixel rows for letting the flushing area match the print area are not necessary at this time.

Although the base area S0and the standard areas S have been described as including only one of the virtual pixels81ato81din each of the virtual pixel rows for each color, the plurality of virtual pixels81ato81dcan also be included.

When the scale-up factor is not an integral multiple in the foregoing embodiment, processing for enlarging the area by use of an integral multiple closest to the value of the scale-up factor is performed. However, an integral multiple obtained by rounding up a value of a product may also be used. Alternatively, an integral value obtained by rounding down a value of a product may also be used.

The present invention is also applicable to a recorder that ejects a liquid other than ink. The present invention is not limited to the printer but is also applicable to a facsimile, a copier, and the like. Further, the present invention is also applicable to a computer readable recording memory storing a program which causes the recorder to function as described above. In the above exemplary embodiments, the EEPROM storing the program is employed as an example of the computer readable recording medium according to the invention. However, the computer readable recording medium according to the invention is not limited to the EEPROM. The computer readable recording medium according to the invention may be any computer readable recording medium, such as a hard disk, an optical disk (CD-ROM, DVD-ROM, etc.), flash memory and the like, storing the program.