Patent Description:
An inkjet recording apparatus according to Patent Literature (PTL) <NUM> includes a plurality of heads, each having a plurality of nozzles that eject ink. PTL <NUM> also discloses a measurement method of nozzle overlapping width in a main scanning direction, in increments of one pixel.

The inkjet recording apparatus according to PTL <NUM> is unable to measure the nozzle overlapping width, in increments smaller than one pixel.

The present invention has been accomplished in view of the foregoing situation, and provides a measurement method of nozzle overlapping width, in increments smaller than one pixel.

In an aspect, the present invention provides a measurement method of nozzle overlapping width, in a main scanning direction intersecting a conveying direction of a recording medium, in an inkjet recording apparatus including an image forming device, including a first head having a plurality of first nozzles aligned in a straight row, and a second head having a plurality of second nozzles aligned in a straight row, the image forming device being configured to eject ink on the recording medium thereby forming an image, and a controller that controls the image forming device. The measurement method includes a first step, a second step, and a third step. In the first head, the plurality of first nozzles are aligned along the main scanning direction. In the second head, the plurality of second nozzles are aligned in a same direction in which the plurality of first nozzles are aligned. The first head and the second head are arranged such that a part of the plurality of first nozzles and a part of the plurality of second nozzles are located adjacent to each other, with a spacing in the conveying direction. The first step includes causing the image forming device to form an image for measurement on the recording medium, using image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction. The second step includes causing the controller to select the block having uniform density along the main scanning direction, in the image for measurement. The third step includes causing the controller to determine the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block.

In another aspect, the present invention provides an inkjet recording apparatus including an image forming device that ejects ink on a recording medium, thereby forming an image, a storage device, and a controller. The image forming device includes a first head having a plurality of first nozzles aligned in a straight row, and a second head having a plurality of second nozzles aligned in a straight row. The plurality of first nozzles in the first head are aligned along the main scanning direction, and the plurality of second nozzles in the second head are aligned in a same direction in which the plurality of first nozzles are aligned. The first head and the second head are arranged such that a part of the plurality of first nozzles and a part of the plurality of second nozzles are located adjacent to each other, with a spacing in the conveying direction. The storage device contains, in advance, image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction. The controller (i) causes the image forming device to form the image for measurement on the recording medium, using the image data stored in the storage device, (ii) selects the block having uniform density along the main scanning direction, in the image for measurement, and (iii) determines the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block.

With the arrangement according to the present invention, the measurement method of nozzle overlapping width, in increments smaller than one pixel, can be obtained.

Referring to <FIG>, an inkjet recording apparatus <NUM>, to which a measurement method of nozzle overlapping width according to an embodiment of the present invention can be applied, will be described hereunder. <FIG> is a schematic cross-sectional view showing the inkjet recording apparatus <NUM>.

As shown in <FIG>, the inkjet recording apparatus <NUM> includes a conveyance device <NUM>, a cassette <NUM>, an output tray <NUM>, an image forming device <NUM>, and a reading device <NUM>.

The conveyance device <NUM> includes a paper feeding device <NUM>, a sheet conveyance path <NUM>, a first belt conveyance section <NUM>, a second belt conveyance section <NUM>, a first conveyance path <NUM>, a reverse conveyance path <NUM>, a branching section <NUM>, a reversing section <NUM>, and a second conveyance path <NUM>.

The cassette <NUM> is for accommodating sheets P therein. The paper feeding device <NUM> includes, for example, a pickup roller, and draws out the sheet P from the cassette <NUM> by driving the pickup roller, and delivers the sheet P to the sheet conveyance path <NUM>. Examples of the usable sheet P include a plain paper, a thick paper, an OHP sheet, an envelope, and a postcard. The sheet P exemplifies the "recording medium" in the present invention.

The sheet conveyance path <NUM> includes various types of rollers, and guides the sheet P to the image forming device <NUM>, by driving those rollers. To be more detailed, the sheet conveyance path <NUM> guides the sheet P delivered from the cassette <NUM> to the image forming device <NUM>, through the first belt conveyance section <NUM>. The image forming device <NUM> ejects the ink onto the sheet P, thereby forming an image on the sheet P. The second belt conveyance section <NUM> conveys the sheet P, on which the image has been formed by the image forming device <NUM>.

The first conveyance path <NUM> includes various types of rollers, and guides the sheet P delivered from the second belt conveyance section <NUM> to the output tray <NUM>, by driving those rollers. As result, the sheet P is delivered to the output tray <NUM>.

The reverse conveyance path <NUM> is branched from the first conveyance path <NUM>. The sheet P conveyed from the first conveyance path <NUM> toward the reverse conveyance path <NUM> is delivered to the branching section <NUM>. The branching section <NUM> is located on the reverse conveyance path <NUM>, and serves to guide the sheet P to the reversing section <NUM>.

The reversing section <NUM> includes various types of rollers, and reverses the moving direction of the sheet P so as to deliver the sheet P to the branching section <NUM>, by driving those rollers. The branching section <NUM> guides the sheet P delivered from the reversing section <NUM>, to the second conveyance path <NUM>. The second conveyance path <NUM> includes various types of rollers, and guides the sheet P to the sheet conveyance path <NUM>, by driving those rollers. Accordingly, the sheet P that has passed the image forming device <NUM> is guided to a return position 11a, through the second conveyance path <NUM>. The return position 11a is set on the sheet conveyance path <NUM>, at a position upstream of the image forming device <NUM>, in the conveying direction X of the sheet P. The conveying direction X of the sheet P refers to the direction in which the sheet P moves, when the image forming device <NUM> forms an image on the sheet P.

The sheet P guided to the return position 11a is again conveyed to the image forming device <NUM>. At this point, the front face and the back face of the sheet P, guided to the return position 11a, are reversed. Accordingly, the image forming device <NUM> forms an image on the back face of the sheet P.

The reading device <NUM> is located between the image forming device <NUM> and the return position 11a. The reading device <NUM> scans the sheet P, thereby reading the image on the sheet P. The reading device <NUM> is, for example, constituted of a contact image sensor (CIS) unit. The reading device <NUM> is located under the sheet conveyance path <NUM>.

Referring to <FIG> and <FIG>, the image forming device <NUM> will be described hereunder. <FIG> illustrates the image forming device <NUM> viewed from below. In other words, <FIG> illustrates the image forming device <NUM> viewed from the side of the first belt conveyance section <NUM>.

As shown in <FIG>, the image forming device <NUM> includes a housing <NUM>, and a plurality of head units. The housing <NUM> supports the plurality of head units. The plurality of head units include, for example, a first head unit <NUM>, a second head unit <NUM>, a third head unit <NUM>, and a fourth head unit <NUM>. The plurality of head units are each opposed to the first belt conveyance section <NUM>. The plurality of head units are aligned along the conveying direction X. To each of the plurality of head units, ink is supplied. The ink color differs with respect to each of the head units. To the first head unit <NUM>, for example, black ink is supplied. To the second head unit <NUM>, for example, cyan ink is supplied. To the third head unit <NUM>, for example, magenta ink is supplied. To the fourth head unit <NUM>, for example, yellow ink is supplied.

The plurality of head units, namely the first head unit <NUM>, the second head unit <NUM>, the third head unit <NUM>, and the fourth head unit <NUM>, have the same structure as each other. Therefore, the structure of the first head unit <NUM> will be described hereunder, and the description of other head units will be skipped.

The first head unit <NUM> includes a plurality of heads and a plurality of nozzles. The plurality of heads include, for example, a first head 42a, a second head 42b, and a third head 42c. The plurality of heads are aligned along a main scanning direction Y, in a checkerboard pattern. The main scanning direction Y refers to a direction intersecting the conveying direction X of the sheet P. The plurality of heads each include the plurality of nozzles. The plurality of nozzles include, for example, a plurality of first nozzles 46a, a plurality of second nozzles 46b, and a plurality of third nozzles 46c. The first head 42a includes the plurality of first nozzles 46a. The second head 42b includes the plurality of second nozzles 46b. The third head 42c includes the plurality of third nozzles 46c. The plurality of nozzles are each opposed to the first belt conveyance section <NUM>. The first head 42a, the second head 42b, and the third head 42c exemplify the "plurality of heads" in the present invention. The plurality of first nozzles 46a, the plurality of second nozzles 46b, and the plurality of third nozzles 46c each exemplify the "plurality of nozzles" in the present invention.

The plurality of first nozzles 46a and the plurality of second nozzles 46b include a first overlapping width Y1. The first overlapping width Y1 refers to the size in the main scanning direction Y, of the respective portions of the plurality of first nozzles 46a and the plurality of second nozzles 46b overlapping in the main scanning direction Y. The plurality of second nozzles 46b and the plurality of third nozzles 46c include a second overlapping width Y2. The second overlapping width Y2 refers to the size in the main scanning direction Y, of the respective portions of the plurality of second nozzles 46b and the plurality of third nozzles 46c overlapping in the main scanning direction Y. The first overlapping width Y1 and the second overlapping width Y2 each exemplify the "nozzle overlapping width" in the present invention.

The plurality of first nozzles 46a are aligned along the main scanning direction Y. One of the plurality of first nozzles 46a at the leading position is located at the left end in <FIG>. The trailing one of the first nozzles 46a is located at the right end in <FIG>. Accordingly, the plurality of first nozzles 46a are aligned from the left end toward the right end in <FIG>. With respect to the main scanning direction Y, the left side in <FIG> will be defined as a leading side, and the right side in <FIG> will be defined as a trailing side.

The plurality of second nozzles 46b are aligned in the same direction as the plurality of first nozzles 46a. Accordingly, the leading one of the plurality of second nozzles 46b is located at the left end in <FIG>. The trailing one of the plurality of second nozzles 46b is located at the right end in <FIG>. Therefore, the plurality of second nozzles 46b are aligned from the left end toward the right end, in <FIG>.

A part of the plurality of second nozzles 46b on the leading side, and a part of the plurality of first nozzles 46a on the trailing side, are located adjacent to each other in the conveying direction X, with a spacing therebetween. Here, the expression "adjacent in the conveying direction X with a spacing" refers to a state where the nozzles are located at different positions in the conveying direction X, and at the same position in the main scanning direction Y.

The plurality of third nozzles 46c are aligned in the same direction as the plurality of second nozzles 46b. Accordingly, the leading one of the plurality of third nozzles 46c is located at the left end in <FIG>. The trailing one of the plurality of third nozzles 46c is located at the right end in <FIG>. Therefore, the plurality of third nozzles 46c are aligned from the left end toward the right end, in <FIG>.

A part of the plurality of third nozzles 46c on the leading side, and a part of the plurality of second nozzles 46b on the trailing side, are located adjacent to each other in the conveying direction X, with a spacing therebetween.

The plurality of heads, namely the first head 42a, the second head 42b, and the third head 42c are each configured to transmit a pressure, generated by deformation of a piezoelectric element, to the ink in each of the nozzles, thereby oscillating a meniscus and generating an ink droplet. As result, the plurality of nozzles, namely the plurality of first nozzles 46a, the plurality of second nozzles 46b, and the plurality of third nozzles 46c each eject the ink.

The respective nozzles of the plurality of head units, namely the first head unit <NUM>, the second head unit <NUM>, the third head unit <NUM>, and the fourth head unit <NUM> eject the ink onto the sheet P, adsorbed to the first belt conveyance section <NUM>. As result, a color image, composed of the four color inks of cyan, magenta, yellow, and black superposed on each other, is formed on the sheet P.

Referring now to <FIG> and <FIG>, an electrical configuration of the inkjet recording apparatus <NUM> will be described hereunder. <FIG> is a functional block diagram showing the electrical configuration of the inkjet recording apparatus.

As shown in <FIG>, the inkjet recording apparatus <NUM> also includes an input device <NUM>, a display device <NUM>, a storage device <NUM>, and a controller <NUM>.

The input device <NUM> receives instructions from the user, directed to the inkjet recording apparatus <NUM>. The input device <NUM> includes, for example, a touch panel or physical keys including operating keys.

The display device <NUM> is, for example, constituted of a liquid crystal display (LCD), or an organic electroluminescence display (ELD). The display device <NUM> may be unified with the input device <NUM>. In this case, the input device <NUM> and the display device <NUM> are constituted of a touch panel.

The storage device <NUM> includes memory units. The memory units include main memory units (e.g., semiconductor memory) such as a Read-Only Memory (ROM), and a Random-Access Memory (RAM), and may further include an auxiliary memory unit (e.g., hard disk drive). The main memory unit contains various computer programs, to be executed by the controller <NUM>.

The control device <NUM> includes a processor, a RAM, a ROM, and so forth. The processor is, for example, a central processing unit (CPU), an application-specific integrated circuit (ASIC), or a microprocessing unit (MPU). The control device <NUM> acts as the controller <NUM>, when the processor executes the control program stored in the ROM or the storage device <NUM>.

The controller <NUM> controls the overall operation of the inkjet recording apparatus <NUM>. The control device <NUM> is connected to the conveyance device <NUM>, the image forming device <NUM>, the reading device <NUM>, the input device <NUM>, the display device <NUM>, and the storage device <NUM>. The controller <NUM> controls the operation of the cited constituent elements, and transmits and receives signals and data to and from the constituent elements. The controller <NUM> controls each of the constituent elements of the inkjet recording apparatus <NUM>. More specifically, the controller <NUM> controls the conveyance device <NUM>, the image forming device <NUM>, the reading device <NUM>, the input device <NUM>, the display device <NUM>, and the storage device <NUM>.

Referring to <FIG> and <FIG>, image data <NUM>, generated by the controller <NUM> and stored in the storage device <NUM>, will be described hereunder. <FIG> illustrates an example of the image data <NUM>. <FIG> is an enlarged view of partial data <NUM> in <FIG>.

The controller <NUM> generates the image data <NUM>, in a form illustrated in <FIG>. As shown in <FIG>, the image data <NUM> is formed so as to operate all of the plurality of first nozzles 46a, the plurality of second nozzles 46b, and the plurality of third nozzles 46c, in a predetermined pattern. The image data <NUM> is generated by defining virtual positions of the plurality of first nozzles 46a and the plurality of second nozzles 46b, so as to cancel the first overlapping width Y1 (i.e., make the first overlapping width Y1 "<NUM>") between the plurality of first nozzles 46a and the plurality of second nozzles 46b, and defining virtual positions of the plurality of second nozzles 46b and the plurality of third nozzles 46c, so as to cancel the second overlapping width Y2 (i.e., make the second overlapping width Y2 "<NUM>") between the plurality of second nozzles 46b and the plurality of third nozzles 46c.

The image data <NUM> is, for example, divided into a plurality of blocks each including four lines. Each of the blocks corresponds to an image of a belt-like shape, extending along the main scanning direction Y. As examples of the blocks, a first block A, a second block B, a third block C, a fourth block D, a fifth block E, a sixth block F, a seventh block G, an eighth block H, a ninth block I, and a tenth block J are illustrated in <FIG>.

The image data <NUM> includes partial data <NUM>. The partial data <NUM> represents the data corresponding to a predetermined number of first nozzles 46a (e.g., <NUM>) on the trailing side, out of the plurality of first nozzles 46a, and a predetermined number of second nozzles 46b (e.g., <NUM>) on the leading side, out of the plurality of second nozzles 46b, in each of the first block A to the sixth block F.

As shown in <FIG>, in the portion of the partial data <NUM> included in the first block A, a large droplet size L is allocated to a trailing pixel group <NUM> corresponding to the first nozzle 46a, and the large droplet size L is also allocated to a leading pixel group <NUM> corresponding to the second nozzle 46b. This combination of the droplet size will be referred to as "LL pattern".

In the portion of the partial data <NUM> included in the second block B, the large droplet size L is allocated to the trailing pixel group <NUM>, and a medium droplet size M is allocated to the leading pixel group <NUM>. This combination of the droplet size will be referred to as "LM pattern".

In the portion of the partial data <NUM> included in the third block C, the medium droplet size M is allocated to the trailing pixel group <NUM>, and the medium droplet size M is also allocated to the leading pixel group <NUM>. This combination of the droplet size will be referred to as "MM pattern".

In the portion of the partial data <NUM> included in the fourth block D, the medium droplet size M is allocated to the trailing pixel group <NUM>, and a small droplet size S is allocated to the leading pixel group <NUM>. This combination of the droplet size will be referred to as "MS pattern".

In the portion of the partial data <NUM> included in the fifth block E, the small droplet size S is allocated to the trailing pixel group <NUM>, and the small droplet size S is also allocated to the leading pixel group <NUM>. This combination of the droplet size will be referred to as "SS pattern".

In the portion of the partial data <NUM> included in the sixth block F, the large droplet size L is allocated to the trailing pixel group <NUM> corresponding to the first nozzle 46a, and a blank is allocated to a leading pixel group <NUM> corresponding to the second nozzle 46b. Further, the large droplet size L is allocated to a second pixel group <NUM> corresponding to the second nozzle 46b.

Though not illustrated, the LL, LM, MM, MS, and SS patterns are respectively allocated, with a blank row interposed therein, in the sixth block F to the tenth block J. Further, in the case where the image data includes an eleventh block to a fifteenth block, the LL, LM, MM, MS, and SS patterns are respectively allocated, with two blank rows interposed therein.

The portion of the image data <NUM> including the boundary between the trailing side of the plurality of second nozzles 46b, and the leading side of the plurality of third nozzles 46c, also includes combination patterns of the droplet size, which are different with respect to each of the blocks extending along the main scanning direction Y.

To the remaining pixels included in the image data <NUM>, the large droplet size L is allocated.

Referring now to <FIG> and <FIG>, an image for measurement <NUM>, formed on the sheet P by the image forming device <NUM>, on the basis of the image data <NUM> under the control of the controller <NUM>, will be described hereunder. <FIG> is a schematic drawing showing an example of the image for measurement <NUM>. <FIG> is an enlarged view of a partial image <NUM> in <FIG>.

In the inkjet recording apparatus <NUM> according to the embodiment, as shown in <FIG>, the plurality of first nozzles 46a and the plurality of second nozzles 46b define a first overlapping width Y1. Likewise, the plurality of second nozzles 46b and the plurality of third nozzles 46c define a second overlapping width Y2. For example, the first overlapping width Y1 corresponds to <NUM> times of the pixel pitch, and the second overlapping width Y2 corresponds to <NUM> times of the pixel pitch, which can be expressed as Y1 = <NUM> pixel, and Y2 = <NUM> pixel.

The image for measurement <NUM> includes the partial image <NUM>. The partial image <NUM> represents the image corresponding to four first nozzles 46a on the trailing side, out of the plurality of first nozzles 46a, and five second nozzles 46b on the leading side, out of the plurality of second nozzles 46b, in each of the first block A to the sixth block F.

As shown in <FIG>, a trailing pixel group <NUM> corresponding to the first nozzles 46a and a leading pixel group <NUM> corresponding to the second nozzles 46b largely overlap, in a portion of the partial image <NUM> corresponding to the first block A to the fourth block D, and therefore the density is increased in the overlapping portion, compared with the remaining portion. The portion of the higher density is recognized as a black line, by the user.

In the portion of the partial image <NUM> corresponding to the sixth block F, a blank portion is left between the trailing pixel group <NUM> corresponding to the first nozzles 46a and a second leading pixel group <NUM> corresponding to the second nozzles 46b. The blank portion is defined by a leading pixel group <NUM> corresponding to the second nozzles 46b. The blank portion is recognized as a white line, by the user.

In the portion of the partial image <NUM> corresponding to the fifth block E, in contrast, the image is formed (printed) in uniform density along the main scanning direction Y, without the black line and the white line. Accordingly, the user can select the fifth block E, to which the SS pattern is allocated, as the block having uniform density along the main scanning direction Y, in the image for measurement <NUM>.

Upon receipt of the notice that the fifth block E, to which the SS pattern is allocated, has been selected, the controller <NUM> determines the nozzle overlapping width according to the following equation [<NUM>], using the droplet size ratio adopted to form the image for measurement <NUM>: <MAT>.

On the assumption that, as an example, the droplet size ratio L/M/S is specified as <NUM>/<NUM>/<NUM>, the nozzle overlapping width Y1 is determined as <NUM> pixel, as calculated with the equation [<NUM>] as below: <MAT>.

When the droplet size ratio L/M/S is specified as <NUM>/<NUM>/<NUM> as above, the nozzle overlapping width Y1 is determined as <NUM> pixel with respect to the LM pattern, as <NUM> pixel with respect to the MM pattern, and as <NUM> pixel with respect to the MS pattern, according to the equation [<NUM>].

In addition, the user can select the seventh block G, as the block having uniform density along the main scanning direction Y in the image for measurement <NUM>, with respect to the overlapping portion between the plurality of second nozzles 46b and the plurality of third nozzles 46c. In the seventh block G, the LM pattern is allocated with one blank row interposed therein.

In this case, the controller <NUM> adds "one pixel" corresponding to the blank row, to <NUM> pixel calculated as the nozzle overlapping width Y2 according to the equation [<NUM>], thereby determining the nozzle overlapping width Y2 as <NUM> pixel.

An operation of the controller <NUM> will now be described, with reference to <FIG> is a flowchart showing an example of the operation performed by the controller <NUM>.

Step S110: As shown in <FIG>, the controller <NUM> generates the image data <NUM> including the combination patterns of the droplet sizes, which are different with respect to each of the blocks extending along the main scanning direction Y, and stores the image data <NUM> in the storage device <NUM>.

Step S120: The controller <NUM> causes the image forming device <NUM> to form the image for measurement <NUM> on the sheet P, using the image data <NUM> stored in the storage device <NUM>.

Step S130: The user selects the block having uniform density along the main scanning direction, in the image for measurement <NUM> that has been formed. The result of the user's selection is notified to the controller <NUM>, through the input device <NUM>. The controller <NUM> selects, according to the notice, the block having uniform density along the main scanning direction, in the image for measurement <NUM>.

Step S140: The controller <NUM> determines the first overlapping width Y1 and the second overlapping width Y2, using the droplet size ratio adopted for the image forming (printing) of the image for measurement <NUM>, on the basis of the position of the selected block.

The arrangement according to this embodiment enables the nozzle overlapping width, namely the first overlapping width Y1 and the second overlapping width Y2, to be measured, for example, in increments of <NUM> pixel. Therefore, the measurement method of the nozzle overlapping width, in increments smaller than one pixel, can be obtained.

By utilizing the measurement result obtained through the measurement method of the nozzle overlapping width described as above, each of the first overlapping width Y1 and the second overlapping width Y2 can be adjusted to "<NUM>", without the need to adjust the respective positions of the plurality of heads, namely the first head 42a, the second head 42b, and the third head 42c.

To be more detailed, when the result "Y1 = <NUM> pixel" is obtained as above with respect to the first overlapping width Y1, the controller <NUM> performs, thereafter, gradation correction based on the overlapping width corresponding to <NUM> pixel, with respect to the trailing one of the plurality of first nozzles 46a and the leading one of the plurality of second nozzles 46b. As result, the first overlapping width Y1, between the ink ejected from the plurality of first nozzles 46a and the ink ejected from the plurality of second nozzles 46b, can be adjusted to "<NUM>" on the sheet P, without the need to adjust the respective positions of the first head 42a and the second head 42b. Likewise, when the result "Y2 = <NUM> pixel" is obtained as above with respect to the second overlapping width Y2, the controller <NUM> thereafter restricts the leading one of the plurality of third nozzles 46c from ejecting the ink, and performs the gradation correction based on the overlapping width corresponding to <NUM> pixel, with respect to the trailing one of the plurality of second nozzles 46b and the second leading one of the plurality of third nozzles 46c. As result, the second overlapping width Y2, between the ink ejected from the plurality of second nozzles 46b and the ink ejected from the plurality of third nozzles 46c, can be adjusted to "<NUM>" on the sheet P, without the need to adjust the respective positions of the second head 42b and the third head 42c.

According to the foregoing embodiment, in addition, the image data <NUM> includes the combination patterns of the three droplet sizes of large, medium, and small, with respect to a part of the plurality of first nozzles 46a (four on the trailing side) and a part of the plurality of second nozzles 46b (four on the leading side), and also a part of the plurality of second nozzles 46b (four on the trailing side) and a part of the plurality of third nozzles 46c (four on the leading side). Accordingly, when a droplet size ratio appropriate for the type of the sheet P is determined, the nozzle overlapping width can be accurately measured, using the image for measurement <NUM> formed on the basis of the image data <NUM>.

Here, the user may be exempted from deciding the density, and instead the reading device <NUM> may read the image for measurement <NUM>, and the controller <NUM> may decide the density. In this case, referring to <FIG>, the sheet P on which the image for measurement <NUM> has been formed (printed) is guided to the return position 11a, through the second conveyance path <NUM>. Then the reading device <NUM> reads the image for measurement <NUM> formed on the sheet P. The controller <NUM> selects the block having uniform density along the main scanning direction Y, in the image for measurement <NUM> read by the reading device <NUM>. For example, the controller <NUM> may decide the density with respect to each of the first block A to the fifth block E, in the partial image <NUM> shown in <FIG>, read by the reading device <NUM>, and identify the block having uniform density along the main scanning direction Y, thereby selecting the fifth block E to which the SS pattern is allocated, as the block having uniform density along the main scanning direction Y in the image for measurement <NUM>.

The embodiment of the present invention has been described as above, with reference to the drawings. However, the present invention is not limited to the foregoing embodiment, but may be implemented in various manners without departing from the scope of the present invention. The plurality of constituent elements disclosed in the foregoing embodiment may be combined as desired, to achieve various inventions. For example, some constituent elements may be excluded, from those disclosed in the foregoing embodiment. The drawings each schematically illustrate the essential constituent elements for the sake of clarity, and the number of pieces of each of the constituent elements illustrated may differ from the actual ones, depending on the convenience in making up the drawings. Further, the constituent elements described in the foregoing embodiment are merely exemplary, and may be modified in various manners without substantially departing from the effects expected from the present invention.

For example, although the controller <NUM> generates the image data <NUM> in the foregoing embodiment, a different arrangement may be adopted. The controller <NUM> may retrieve the image data <NUM>, from outside of the inkjet recording apparatus <NUM>.

Although the image data <NUM> according to the embodiment includes the combination patterns of the three droplet sizes of large, medium, and small, a different combination pattern may be adopted. The image data <NUM> may include the combination patterns of four or more droplet sizes.

Further, although each of the blocks in the image data <NUM> is composed of four lines in the foregoing embodiment, a different arrangement may be adopted. In the case where the blocks are each composed of five or more lines, the image data <NUM> may be modified such that the alphabets are displayed as the block identification mark, with respect to each of such blocks.

Claim 1:
A measurement method of nozzle overlapping width, in a main scanning direction intersecting a transport direction of a recording medium (P), in an ink jet recording apparatus (<NUM>) including an image forming device (<NUM>), including a first head (42a) having a plurality of first nozzles (46a) aligned in a straight row, and a second head (42b) having a plurality of second nozzles (46b) aligned in a straight row, the image forming device (<NUM>) being configured to eject ink on the recording medium (P) thereby forming an image, and a controller (<NUM>) that controls the image forming device(<NUM>),
the plurality of first nozzles (46a) in the first head (42a) being aligned along the main scanning direction,
the plurality of second nozzles (46b) in the second head (42b) being aligned in a same direction in which the plurality of first nozzles (46a) are aligned,
the first head (42a) and the second head (42b) being arranged such that a part of the plurality of first nozzles (46a) and a part of the plurality of second nozzles (46b) are located adjacent to each other, with a spacing in the transport direction,
characterized in the measurement method comprising:
a first step including causing the image forming device (<NUM>) to form an image for measurement on the recording medium (P), using image data including combination patterns of droplet sizes, different with respect to each of blocks extending along the main scanning direction;
a second step including causing the controller (<NUM>) to select the block having uniform density along the main scanning direction, in the image for measurement; and
a third step including causing the controller (<NUM>) to determine the nozzle overlapping width using a droplet size ratio adopted to form the image for measurement, on a basis of a position of the selected block.