WO2022093194A1

WO2022093194A1 - Test patterns

Info

Publication number: WO2022093194A1
Application number: PCT/US2020/057536
Authority: WO
Inventors: Nestor LUID PINOL; Javier CASTRO SORIANO; Guillem MONTERO COSTA
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2022-05-05

Abstract

In an example, a method comprises controlling a fluidic die to print a test pattern to a print media by moving the fluidic die sequentially in a forward and reverse direction across a width of a print media. The test pattern is printed, according to the example method, by moving the fluidic die in the forward direction and discharging printing fluid toward the print media to print a first pattern portion to the print media, advancing a print media underneath the fluidic die, and moving the fluidic die in the reverse direction and discharging printing fluid toward the print media to print a second pattern portion to the print media. The second pattern portion is shifted by a predetermined amount relative to the first pattern portion each time the fluidic die moves in the reverse direction.

Description

TEST PATTERNS

BACKGROUND

[0001] Some example print apparatuses are to print an image to a substrate by discharging printing fluid from a fluidic die of the print apparatus.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Examples will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which:

[0003] Figure 1 is a flowchart of an example method;

[0004] Figures 2A and 2B are simplified schematic diagrams of an example test pattern;

[0005] Figure 3 is a flowchart of an example method;

[0006] Figure 4 is a simplified schematic diagram of an example test pattern; [0007] Figure 5 is a simplified schematic diagram of an example test pattern;

[0008] Figure 6 is a simplified schematic diagram of an example machine- readable medium in association with a processor; and

[0009] Figure 7 is a flowchart of an example method.

DETAILED DESCRIPTION

[0010] In some example print apparatuses, the distance travelled by a fluidic droplet from a fluidic die to a print media, or substrate, is referred to the “pen to media space” or “printhead to media space” (or PMS for short). In some examples it may be referred to as fluidic die to media space or nozzle to media space. When the print apparatus is intended for use such that the print media advances horizontally (or parallel to the ground) (spanning x and y axes) the PMS is therefore the vertical (or z-axis, being perpendicular to the plane of the substrate and to the z-axis) distance between a platen of the print apparatus and the nozzles of the fluidic die that discharge the printing fluid. Herein, by platen it is meant a surface over which the print media advances, or which supports a substrate or print media, for example during a print operation). For some print apparatuses, the width of the platen (its length in the direction perpendicular to both the vertical direction and to the direction of advancement of the print media) is relatively long and the platen may therefore be composed of a number of panels, or segments, e.g. that may be secured together to form the platen. The PMS for such print apparatuses is therefore proportional to height of the platen, and the height of each segment of the platen across its width in examples where the platen is formed in segments. The width in some examples may extend in the direction of the printing scan axis.

[0011] In some examples, the PMS is measured at the time of manufacture and may not be measured again. At this stage in the manufacture, the PMS is measured across the platen (and the number of panels thereof) and the different platen segments are adjusted (e.g. their height is adjusted) so as to produce a uniform PMS across the whole platen, across the printing scan access. There may be movement of some parts of the print apparatus in between the completion of its manufacture and its first use (e.g. during transportation) which, if those movements affect parts of the print platen, could cause variations in the PMS along the width of the platen. These variations can have an adverse effect on the quality and uniformity of any image printed by the apparatus to the substrate. For example, such variations can produce inconsistencies in the final image along the printzone, and across the width of the platen and print media.

[0012] Some examples herein relate to the printing of a test pattern that can allow the PMS of a print apparatus to be determined, and corrected for if necessary, after a print apparatus has been transported to its end-destination following its manufacture. According to these examples, the test pattern allows a user, e.g. a service engineer, to determine in which locations across the platen there are variations in the PMS, when compared to the PMS at manufacture. This means that a user can determine PMS variations effectively on-the-fly, and by eye from examining the test pattern, without using a special tool such as a laser (such tools can be expensive, complex to use, and the results they yield can be complicated to interpret).

[0013] As will be described below with specific reference to the Figures, in some examples the test pattern comprises a series of images printed down the length of a print media (the length here being the distance of the print media in the media advance direction, or the direction in which the print media advances during a print operation. The width of the print media may be defined as the distance of the print media perpendicular to the length, and parallel to the scan axis direction, the scan axis direction being the fluidic die movement direction). In these examples, the series of images comprises a first set of images that are printed in a first pass of the fluidic die and a second series of images that are printed in a second pass of the fluidic die. The substrate may be advanced in between passes. In yet other examples, the first set of images may be instructed to be printed such that there is no offset between them (and in this way the set of first images act as a reference), while the second set of images may be instructed to be printed such that there is an offset between them, and therefore an offset between each image in the second set and any image in the first set, but with a different offset amount each time. In some examples, the offset amount of each image in the second set may be changed, or adjusted, by a predetermined amount. In some examples, the offset amount of each image in the second set may be changed, or adjusted, incrementally (e.g. based on a number of pixels). This effectively creates a map (a column) down the print media consisting of the test pattern. Either one of the first and second passes may be made in the forward direction with the other being made in the reverse direction. Therefore, according to some examples, the test pattern comprises a plurality of first images, not offset from one another, printed in a forward pass of the fluidic die and a plurality of second images, offset from each of the first images and offset from one another by a predetermined amount, printed in a reverse pass of the fluidic die. Of course, in some examples, the test pattern comprises a plurality of first images, not offset from one another, printed in a reverse pass of the fluidic die and a plurality of second images, offset from one another by a predetermined amount, printed in a forward pass of the fluidic die. [0014] Herein, the term fluidic die is intended to comprise any number of dies (which may comprise one die or which may comprise a plurality of dies). For example, a print apparatus may comprise a number of fluidic dies retained in a carriage of the print apparatus and the term ‘fluidic die’ is meant to encompass a carriage retaining any number of fluidic dies. A fluidic die may comprise a printhead die and therefore may comprise any number of printheads. [0015] The examples described in the preceding paragraphs may result in a test pattern comprising a column of patterns printed down the length of the print media, but in some examples, each set of images comprises a plurality of images (e.g. image portions or image segments) that extend across the width of the print media (the “crossweb” direction). As stated above, the direction of the width of the print media (the crossweb direction) is parallel to the axis of movement of the fluidic die (or carriage when a carriage retains the die) which may be referred to as the die movement direction, carriage movement direction, or scan axis direction. Therefore, in some examples the test pattern comprises a series of rows and columns of images, or a grid of images printed across the print media. The test pattern may therefore comprise a number of images segments, printed in a forward and reverse pass extending across the surface of the print media, e.g. in both the advance and crossweb directions. In these examples, each portion, or segment, of the test pattern may correspond to a portion, or segment, of the print platen. Since one of the first and second images are offset from one another be a predetermined, different, amount this produces a pattern of different offsets down the length of the print media, for each segment of the platen. In certain individual locations, as will be explained below, one (offset) pattern segment may match another corresponding not offset pattern segment and this indicates to a user or service engineer that, in that location, the PMS distance differs from its manufactured distance by an amount proportional to that offset.

[0016] In some examples, the set of images printed in the first pass are lines but in other examples the may be bracket-shaped. In some examples, the set of images printed in the second pass may be lines but in other examples the may be bracket-shaped. The images printed in the second pass may be mirrorimages of the first images, or may comprise a reflection of the first images. Each of the images printed in the second pass may be below each of the images printed in the first pass on the print media. In one example, the image printed in the first pass may comprise a U-shaped bracket and the image printed in the second pass may comprise an upside-down U-shaped bracket; or the image printed in the first pass may comprise an upside-down U-shaped bracket and the image printed in the second pass may comprise a U-shaped bracket (e.g. a semi-circular or half oval shape). In either of these examples, each of the two images may combine to form a closed shape (for example, a square, circular or oval) shape which easily allows an engineer to identify the amount of PMS variation across the platen.

[0017] For example, in the example of a test pattern comprising one row printed down the print media, a first image may be printed in a forward pass of the fluidic die, then a second image may be printed in a reverse pass of the die. The second image may be printed so as to be offset from the first image, e.g., by +1 , with the image offset of the first image being 0. Here, +1 may refer to 1 pixel shifted in a first direction with respect to the 0 position of the first image. Then, the first image may be printed again in a forward pass of the die and the second image may be printed again in a reverse pass of the die, such that the second image now has a different offset from the first image (e.g. an offset of 0). Finally, this may be repeated one further time with the second image having a different offset (e.g. of -1 ). The print media may be advanced in between each sequential pass such that the images are not overlying one another. In this way, the test pattern in this example may comprise three sets of first and second images, with the second image being offset by +1 , 0 and -1 from the first images in each set. The first and second images in one set may align, for example the first image and second image offset by -1 may be aligned, and a service engineer correlate that the images align when the second pattern is shifted (e.g. by -1 ) to the PMS of the print platen. This may indicate that a number of shims proportional to the offset of -1 may be needed to “prop up” the height of the print platen in that area. These, and other examples, will now be described with reference to the drawings.

[0018] Figure 1 is a flowchart of an example method 100, which may comprise a computer-implemented method, and which may be performed by a processor executing instructions stored by a machine-readable medium, for example a processor of a print apparatus. The method 100 may comprise a method of printing a test pattern to a print media. The method 100 may comprise a diagnostic method. The method 100 may comprise a method of determining a print-to-media space, or of determining a space (or distance) between a fluidic die of a print apparatus and a surface (e.g. a platen) that supports a print media. [0019] At block 101 , the method 100 comprises controlling, e.g. by a processor, a fluidic die to print a test pattern to a print media by moving the fluidic die sequentially in a forward and reverse direction across a width of the print media. The forward direction may be opposite to the reverse direction. Each of the forward and reverse directions may represent opposite directions along a fluidic die movement axis. For example, the fluidic die may be movable in a reciprocating fashion along a movement axis and the forward and reverse directions may each comprise an opposing direction along that axis. The fluidic die movement axis, and therefore the forward and reverse directions, may be parallel to the width of the print media.

[0020] At block 102, the method 100 comprises moving, e.g. by a processor, the fluidic die in the forward direction and discharging printing fluid toward the print media to print a first pattern portion to the print media. At block 104, the method 100 comprises advancing, e.g. by a processor, the print media underneath the fluidic die. At block 106, the method 100 comprises moving, e.g. by a processor, the fluidic die in the reverse direction and discharging printing fluid toward the print media to print a second pattern portion to the print media. The second pattern portion is shifted by a predetermined amount relative to the first pattern portion each time the fluidic die moves in the reverse direction. For example, each time the second pattern portion is printed it may be shifted relative to the first pattern portion by a different, predetermined, amount, and therefore shifted relative to the previously printed second pattern portion by a different, predetermined amount. To produce the shift in the reverse pattern, the method 100 may comprise adjusting, e.g. by a processor, a firing time of the nozzles of the fluidic die. In other words, block 106, each time it is performed, may comprise calibrating a firing time of the nozzles of the fluidic die.

[0021] Referring to Figure 2A, there is shown one example test pattern 200 which may be printed to a substrate according to the method 100 as described above. The test pattern 200 comprises a first pattern portion 201 (which may be generated according to block 102 of the method 100 when the fluidic die moves in the forward direction) and a second pattern portion 202 (which may be generated according to block 106 of the method 100 when the fluidic die moves in the reverse direction). As the pattern portions 201 , 202 are not overlapping the print media has been advanced between the printing of each portion (e.g., block 104 of the method 100). In other examples, however, the second pattern portion 202 may be generated according to block 102 of the method 100 when the fluidic die moves in the forward direction and a first pattern portion 201 may be generated according to block 106 of the method 100 when the fluidic die moves in the reverse direction.

[0022] The test pattern 200 in this example comprises first and second pattern portions that, when aligned, form a square. In other words, in this example, the first and second pattern portions each comprise a bracket-shape or half-square shape. In this example, and in other examples, the second pattern portion may be a reflection of the first pattern portion, e.g. a reflection in an axis parallel to the width of the print media. Since (e.g., see block 106 of the method 100) the second pattern portion 202 is printed so as to be shifted relative to the first pattern portion 201 by a predetermined amount, an offset O may exist between the two pattern portions. The term “may” is used here since the actual amount of the offset O depends on the PMS, or distance between the die and the print media, and this may be 0 if the PMS is the same as the PMS at manufacture; alternatively, the offset O may be 0 if the shifted distance of the second pattern portion 202 is an amount perfectly proportional to the varying PMS. Such an example is shown in Figure 2B. The test pattern 200 in Figure 2B may arise in an example where the second pattern portion 202 is not shifted relative to the first pattern portion 201 (the predetermined amount being 0 in this example) and the PMS has not changed since manufacture, or in the example where the PMS has changed since manufacture but the second pattern portion 202 has been shifted by a corresponding amount (e.g. by a number of pixels in the forward or reverse direction). This will be explained in more detail with reference to later figures. A user, such as an engineer, can therefore examine the test pattern 200 and can determine the PMS distance, and therefore any PMS variation, by examining the offset amount O. It will also be appreciated that even though the second pattern portion 202 is shifted, if the PMS is different to manufacture but by an amount proportional to the sift, then the offset amount 0 may be substantially 0 and the pattern 200 may take on the appearance as shown in Figure 2, even though the second pattern portion 202 was printed with an offset. [0023] Figure 3 is a flowchart of an example method 300, which may comprise the method 100 of Figure 1. At block 301 , the method 300 comprises controlling, e.g. by a processor, a fluidic die to print a test pattern to a print media by moving the fluidic die sequentially in a forward and reverse direction across a width of the print media, for example as described with reference to block 101 of the method 100. At block 302, the method 300 comprises moving, e.g. by a processor, the fluidic die in the forward direction and discharging printing fluid toward the print media to print a first pattern portion to the print media, for example as described with reference to block 102 of the method 100. At block 304, the method 300 comprises advancing, e.g. by a processor, the print media underneath the fluidic die, for example as described with reference to block 104 of the method 100. At block 306, the method 300 comprises moving, e.g. by a processor, the fluidic die in the reverse direction and discharging printing fluid toward the print media to print a second pattern portion to the print media, for example as described above with reference to block 106 of the method 100. At block 308, the method 300 comprises advancing, e.g. by a processor, the print media underneath the fluidic die. As for the second pattern portion of Figure 1 , the second pattern portion generated at block 306 is shifted by a predetermined amount relative to the first pattern portion each time the fluidic die moves in the reverse direction. For example, as indicated by the looping arrow, the method 300 comprises moving, e.g. by a processor, the fluidic die in the forward and reverse direction sequentially a plurality of times (each repetition of blocks 302 and 306) and advancing, by a processor, the print media underneath the fluidic die after each movement of the fluidic die (e.g. each repetition of blocks 304 and 308), and each time the second pattern portion is printed it may be shifted relative to the first pattern portion by a different, predetermined, amount, and therefore shifted relative to the previously printed second pattern portion by a different, predetermined amount. For example, the second pattern portion may be shifted by a different, predetermined, amount each time it is printed. Each time the fluidic die moves in the forward direction (each repetition of block 302), the method 300 comprises printing, by a processor, the first pattern portion to the print media and each time the fluidic die moves in the reverse direction (each repetition of block 306), the method 300 comprises printing, by a processor, the second pattern portion to the print media.

[0024] At block 310 the method 300 comprises determining, e.g. by a processor, the distance in the width direction of the print media between the first pattern portion and the second pattern portion. Block 310 of the method 300 may be performed by a user in some examples. In other examples, block 310 may be performed automatically, e.g. by a measuring device such as a sensor such as an optical sensor that can scan the pattern on the print media. With reference again to Figure 2, block 310 may comprise determining, e.g. manually or automatically as described above, the offset O (which, as described above, may be zero or nonzero). Block 310 may comprise determining, e.g. automatically, e.g. by a processor, a PMS profile across the print media and/or a PMS profile of a printzone of a print apparatus comprising the fluidic die. For example, where block 310 comprises automatically determining the PMS profile (e.g. the distances, or offsets, between patterns), e.g. by a processor, the block may comprise scanning the print media, using an optical sensor for example an optical sensor proximate the fluidic die (e.g. in a print carriage retaining the die), or another optical instrument may be used to measure the profile automatically.

[0025] As stated above with respect to the method 100, to produce the shift in the second pattern portions, the nozzles of the firing die may be adjusted, e.g. by a processor, so that they fire at different times. Therefore, block 302 and/or block 306 may comprise adjusting, by a processor, the firing time of the nozzles of the fluidic die such that they fire according to their calibration (which may, in this example, be their current, or previous, calibration, e.g. at manufacture) (each time block 302 is performed) or such that they fire to produce the offset in the second pattern portion (each time block 306 is performed) which, as stated above, varies each time the second pattern portion is printed. [0026] Referring to Figure 4, there is shown one example test pattern 400 (the right-hand “result” column, to be explained below) which may be printed to a substrate according to the method 300 as described above. The pattern 400 of the Figure 4 example comprises a plurality of first pattern portions 401 a-g and a plurality of second pattern portions 402a-g. Figure 4 is a schematic diagram showing the plurality of first pattern portions 401 in the extreme left-hand side of the diagram (labelled “forward”) and the plurality of second pattern portions 402 in the middle of the diagram (labelled “reverse”). Each of the first pattern portions 401 are printed in a forward pass of the die, e.g. when the die moves in the forward direction, and each of the second pattern portions 402 are printed in a reverse pass of the die, e.g. with the die moves in the reverse direction. The “result” column on the extreme right of the schematic diagram shows the test pattern 400 as printed on the print media. In other words, to achieve the test pattern 400 (which may be generated according to the method 300), first pattern portion 401a is printed by the die moving in the forward direction, the print media is advanced, second pattern portion 402a is printed by the die moving in the reverse direction such that it is shifted by +3 relative to the first pattern, the print media is advanced, the first pattern portion 401 b is printed by the die moving in the forward direction, the print media is advanced, second pattern portion 402b is printed by the die moving in the reverse direction such that it is shifted by +2 relative to the first pattern, the print media is advanced. This continues, the fluidic die moving sequentially in the forward and reverse directions to print the plurality first and second pattern portions until, in this example, the second pattern portion 402g is printed by the die moving in the reverse direction such that it is shifted by -3 relative to the first pattern. In this example a shift of + indicates a shift in the forward direction and a shift of - indicates a shift in the reverse direction, although in other examples + and - may indicate a shift in the reverse and forward direction, respectively. As stated above, the + or - amounts may indicate a number of pixels shifted in the forward or reverse direction from the 0 position, or position of the first pattern portion, which may in some examples be according to calibration at manufacture. [0027] As can be seen in Figure 4, the first and second pattern portions 401 d, 402d align. The second pattern portion 401 d is shifted by a 0 amount relative to the first pattern portion 401 d (in other words, there is no offset). This represents an instance where there is no PMS variation in the print apparatus since its manufacture, since the 0 position of the offset (e.g. no offset), which corresponds to the position that all of the first pattern portions 401 are to be printed. In these such examples, after doing a nozzle health firing calibration (e.g. a die or printhead alignment, etc.), a user may expect to have a match when printing patterns in the forward and reverse direction with 0 offset (along the whole printzone), e.g. shown in Figure 2B. In other words, in these such examples, what is printed is what was expected since, as stated above, different PMS values for the printzone will result on some patterns matching and others not matching.

[0028] According to Figure 4, each of the first pattern portions 401 are printed so as not to be offset with respect to each other (they are all printed in the ‘0’ position) whereas each of the second pattern portions 402 are printed so as to be offset with respect to each other by a different predetermined amount for each pattern portion, and therefore to be offset with respect to each of the first pattern portions 401 by a different predetermined amount.

[0029] Referring to Figure 5, there is shown one example test pattern 500 which may be printed to a substrate according to the method 300 as described above. The pattern 500 of the Figure 5 example comprises a plurality of first pattern portions 501 a-i and a plurality of second pattern portions 502a-i (not all of which are labelled in Figure 5 for brevity). However, in the Figure 5 example each one of the first pattern portions 501 a-i and the second pattern portions 502a-i comprises a plurality of segments, such that each one of the first and second pattern portions extends substantially along the width of the print media (and along the width of the print platen, e.g. its direction in the fluidic die, or carriage, movement direction, or crossweb direction, or scan axis direction, etc.). In other words, each pattern portion being printed a plurality of times means that the test pattern 500 extends the length of the print media (e.g. the test pattern 400) but in the figure 5 example the test pattern 500 extends the width of the print media as well. In this way, the test pattern 500 substantially spans the print media (or a surface thereof). In other words, each of the first pattern portions 501 comprise a row of segments and each of the second pattern portions 502 comprise a row of segments, such that the plurality of first and second pattern portions form a grid, or array, of pattern segments.

[0030] Each pattern portion in the Figure 5 example comprises 9 segments, which will be denoted by the integer n. Adopting this convention, 501a denotes the top (with reference to Figure 5) first pattern portion and its 9 segments are denoted 501a1-a9 (not all of which are labelled in Figure 5 for brevity). With this notation, 501 mn denotes the nth segment of the mth first pattern portion, etc., and similarly for the second pattern portions 502mn, etc. To print the pattern 500, which may be done by performing the method 300 as described above with reference to Figure 3, the first pattern portion 501a may be printed in segments (put another way, each of 501a1-a9 may be printed) in a forward pass of the fluidic die, and the print media may be advanced. Then, the second pattern portion 502a may be printed in segments (put another way, each of 502a1-a9 may be printed) in a reverse pass of the fluidic die, the second pattern portion 502a (and therefore all of the segments 502a1-a9 thereof) being shifted from the first pattern portion by +4. The process then repeats, as described above with reference to Figure 4, as the test pattern 500 is printed down the print media.

[0031] Figure 5 is a schematic diagram and shows, in lines 550 (a plurality of which are shown but only three of which are labelled) a division of area across the print media. The lines 550 may be drawn to indicate the segments of the print platen but it will be understood that they may not be used in some examples. For example, whilst the line 550 may provide an instance visibility in the differing height across the print platen (the PMS profile across the platen) in some examples this line may not be used. For instance, the lines divide the width of the print media up into nine zones, labelled 511-519. In this way, the print platen (the surface which underlies the print media when the test pattern 500 is printed to the print media) may be divided also into nine zones and the different segments of the test pattern 500 may be used to determine the PMS for each zone of the print platen. This may be done as follows.

[0032] As described above with reference to the test patterns 200 and 400, each of the second pattern portion segments 502mn are printed so as to be offset by a different amount each time that they are printed from the first pattern portion segments. Each of the first pattern portion segments are not offset with respect to each other (they are all, in this example, printed so as to have a 0 shift). Each of the second pattern portion segments are offset with respect to the first pattern portion segments each time they are printed. However, as described above, each time the fluidic die prints a second pattern portion 502a-i it prints the nine segments across the page in the reverse pass of the die. In this way, the grid of first and second pattern portion segments is formed and the offsets, resulting from the shifted segments, in each grid of the pattern, can be used to determine the PMS for each zone of the print platen.

[0033] Referring to the first column of the test pattern (first zone 511 ), there is alignment between the first pattern portion segment 501 g1 and the second pattern portion segment 502g1 (which was printed with a shift of -2, or -2 in the reverse direction in this example). Referring to the second column of the test pattern (second zone 512), there is alignment between the first pattern portion segment 501 f2 and the second pattern portion segment 502f2 (which was printed with a shift of -1, or -1 in the reverse direction in this example), and the same is true of the third column (third zone 513). By contrast, referring to the fourth column of the test pattern (fourth zone 514), there is alignment between the first pattern portion segment 501 e4 and the second pattern portion segment 502e4 (which was printed with no shift, or a shift of 0).

[0034] The line 560 is a line that connects aligning pairs of first and second pattern portion segments. As shown in Figure 5, the forward and reverse patterns will “match” (e.g. align) in different positions, and this will depend on the PMS in each zone 511-519. The line 560, which may be drawn by a user, connects the two pattern portion segments across the width of the print media that match (align) and therefore this line 560 is indicative of the “shape” of the PMS along the width of the print media and hence along the printzone. The relative differences between adjacent patterns (e.g. -2 for the pattern segments 501 g1 , 502g1 vs -1 for the adjacent segments 501f2, 502f2) shows the relative PMS differences of the whole printzone. The PMS may therefore be easily determined, and compensated for (e.g. calibrated or adjusted) easily, improving the ease of troubleshooting and reducing the need for, and amount of, visits by a service engineer.

[0035] Regarding correcting for the PMS differences, a service engineer may use shims to prop up various areas of the printzone (e.g. the surface of the print platen) to correct for the PMS differences. For instance, the -1 measurement may indicate that a certain amount of shims should be used to correct for the PMS difference in that zone (e.g. zone 512, 513, and 516), but the -2 measurement may indicate that twice as many shims should be used for that zone (e.g. zones 511 , 517, 518, and 519), whereas a 0 measurement indicates that no compensation should made in that zone (e.g. zones 514 and 515).

[0036] As shown in Figure 5, each segment of the pattern portions (and therefore each pattern portion) may be bracket shaped, or U-shaped, with the first pattern portions in this example being U-shaped and the second pattern portions behind upside-down U-shaped. The second pattern portions may, as they are in the test pattern 500, be reflections of the first pattern portions. Having the first and second portions (and their segments) being reflected brackets in shape means that when two pattern portion segments align, or match, a perfect square is formed, allowing a more ready identification of those patterns that match. For example, in the Figure 5 example, a service engineer can map the PMS along the printzone by connecting the squares. However, in some examples, each of the first and second pattern portions (or pattern portion segments) may comprise dots or lines, and the aforementioned determination of the PMS profile of the printzone applies to these examples. In other examples, each of the patterns may be half-moon, or half-oval or semi-circular shaped. In these examples, rather than two aligning patterns forming a square they may form a circle or oval.

[0037] In some examples (and with reference again to block 310 of the method 300), determining the difference, or offset or shift, between first and second pattern portions may comprise determining the difference between first and second pattern segments. A measuring device such as a sensor, for example an optical sensor, may scan (e.g. using projected and reflected light) the test pattern 500 to determine those areas where the first and second pattern portions segments align or match.

[0038] Figure 6 shows an example non-transitory machine-readable medium, or computer-readable medium, 600, comprising a set of instructions 604 stored thereon. The medium 600 is shown in Figure 6 in association with a processor 602. The instructions 604, when executed by the processor 602, may cause the processor 602 to perform the method 100 or 300 (e.g. any of the blocks thereof) as described above with respect to Figures 1 and 3. The instructions 604, when executed by the processor 602, may cause the processor 602 to cause a fluidic die of a printing apparatus to print the test patterns 200, 400, or 500 as described above with reference to Figures 2, 4, or 5. The instructions, 604, when executed by the processor 602, are to cause the processor 602 to control a fluidic die to print a test pattern to a print media by actuating the fluidic die to move sequentially in a forward and reverse direction across a width of a print media by moving the fluidic die in the forward direction and discharging printing fluid from the fluidic die toward the print media to print a first pattern portion to the print media, advancing the print media, moving the fluidic die in the reverse direction and discharging printing fluid from the fluidic die toward the print media to print a second pattern portion to the print media. The instructions 604, when executed by the processor 602, are to control the fluidic die to print the second pattern portion on the print media such that the second pattern portion is offset from the first pattern portion by a predetermined offset distance each time the fluidic die moves in the reverse direction, e.g. as shown by the test patterns 200, 400 and 500 as described above with reference to Figures 2, 4, and 5.

[0039] In some examples, the instructions, 604, when executed by the processor 602, are to cause the processor 602 to control the fluidic die to move in the forward direction a plurality of times, and to print the first pattern portion to the print media each time, control the fluidic die to move in the reverse direction a plurality of times, and to print the second pattern portion to the print media each time, advance the print media in between each movement of the fluidic die. In these examples, the instructions 604, when executed by the processor 602, are to cause the processor 602 to print the test pattern 400 or 500 as described above with reference to Figures 4 and 5.

[0040] The instructions 604, when executed by the processor 602, may be to cause each of the first pattern portions to be printed so as not to be offset with respect to each other. The instructions 604, when executed by the processor 602, are to cause each of the second pattern portions to be printed so as to be offset with respect to each other by a different predetermined amount for each pattern portion. The first pattern portion and the second pattern portion may extend substantially across the width of the print media, e.g. as shown in Figure 5. The first pattern portion and second pattern portion may extend substantially down the length of the print media (e.g. as shown in Figures 4 and 5). Each of the first pattern portion and the second pattern portion comprises a plurality of segments, e.g. as shown in Figure 5.

[0041] Figure 7 is a flowchart of an example method 700, which may comprise a computer-implemented method, and which may be performed by a processor executing instructions stored by a machine-readable medium, for example a processor of a print apparatus. The method 700 may comprise a method of printing a test pattern to a substrate. The method 700 may comprise a diagnostic method. The method 700 may comprise a method of determining a print-to-media space, or of determining a space (or distance) between a fluidic die of a print apparatus and a surface (e.g. a platen) that supports a substrate.

[0042] At block 701 the method 700 comprises printing, e.g. by a processor, a test pattern on a substrate. The test pattern printed according to the method 700 may comprise any of the test patterns 200, 400, 500 as described above. To print the test pattern the method comprises block 702 at which the method comprises moving, e.g. by a processor, a fluidic die of a print apparatus in a first pass in a first direction along a movement direction of the fluidic die. At block 704 the method comprises printing, by the fluidic die, a first image to a substrate as the fluidic die moves in the first direction. At block 706, the method comprises moving, e.g. by a processor, the fluidic die of a print apparatus in a second pass in a second direction along the movement direction, the second direction being opposite to the first direction. At block 708, the method comprises printing, by the fluidic die, a second image to a substrate as the fluidic die moves in the second direction. At block 710, the method comprises moving, e.g. by a processor, the fluidic die in a third pass in the first direction. At block 712, the method comprises printing, by the fluidic die, the first image to a substrate as the die moves in the first direction, such that the first image printed in the third pass is offset from the first image printed in the first pass.

[0043] In one example, the first direction may comprise the forward direction as described above in which example the second direction may comprise the reverse direction. In another example, the first direction may comprise the reverse direction as described above in which example the second direction may comprise the forward direction.

[0044] In some examples, each of the first and second images printed to the substrate extends substantially the width of the substrate, for example as shown in Figure 5. As discussed above, in these examples, PMS variations along the width of the substrate, and therefore along the width of the platen and therefore the print zone may be determined. Each of the first and second images may be printed a plurality of times down the length of the substrate (e.g. as shown in Figures 4 and 5). Each of the first and second images may comprise a number of image segments, e.g. as shown in Figure 5 such that individual segment pairs of the first and second images may be matched (e.g. aligned) to determine the PMS variation of the printzone. In the latter examples, block 702 may comprise printing the plurality of image segments of the first image, and block 706 may comprise printing the plurality of segments of the second image, etc.

[0045] As indicated by the dotted box, the method 700 may, in some examples, comprise block 714 which comprises, in examples where the first and second images extend across a width of the substrate, measuring, e.g. by a processor, the distance between the second image and the first image printed in the first or third pass, across the width of the substrate, to determine an offset between the fluidic die and the substrate. In these examples, block 714 may comprise using a measuring device or sensor to measure the distance between the second image and the first image printed in the first or third pass. Block 714 may therefore be performed automatically. Block 714 may therefore comprise determining, e.g. by a processor, the PMS profile of a printzone (e.g. as shown by the line 560 in Figure 5).

[0046] Examples in the present disclosure can be provided as methods, systems or machine readable instructions, such as any combination of software, hardware, firmware or the like. Such machine readable instructions may be included on a computer readable storage medium (including but is not limited to disc storage, CD-ROM, optical storage, etc.) having computer readable program codes therein or thereon.

[0047] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart. It shall be understood that each flow and/or block in the flow charts and/or block diagrams, as well as combinations of the flows and/or diagrams in the flow charts and/or block diagrams can be realized by machine readable instructions.

[0048] The machine readable instructions may, for example, be executed by a general purpose computer, a special purpose computer, an embedded processor or processors of other programmable data processing devices to realize the functions described in the description and diagrams. In particular, a processor or processing apparatus may execute the machine readable instructions. Thus functional modules of the apparatus and devices may be implemented by a processor executing machine readable instructions stored in a memory, or a processor operating in accordance with instructions embedded in logic circuitry. The term ‘processor’ is to be interpreted broadly to include a CPU, processing unit, ASIC, logic unit, or programmable gate array etc. The methods and functional modules may all be performed by a single processor or divided amongst several processors. [0049] Such machine readable instructions may also be stored in a computer readable storage that can guide the computer or other programmable data processing devices to operate in a specific mode.

[0050] Such machine readable instructions may also be loaded onto a computer or other programmable data processing devices, so that the computer or other programmable data processing devices perform a series of operations to produce computer-implemented processing, thus the instructions executed on the computer or other programmable devices realize functions specified by flow(s) in the flow charts and/or block(s) in the block diagrams.

[0051] Further, the teachings herein may be implemented in the form of a computer software product, the computer software product being stored in a storage medium and comprising a plurality of instructions for making a computer device implement the methods recited in the examples of the present disclosure.

[0052] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above-mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims.

[0053] The word “comprising” does not exclude the presence of elements other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0054] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.

Claims

1 . A method comprising: controlling a fluidic die to print a test pattern to a print media by moving the fluidic die sequentially in a forward and reverse direction across a width of a print media, by: moving the fluidic die in the forward direction and discharging printing fluid toward the print media to print a first pattern portion to the print media; advancing a print media underneath the fluidic die; moving the fluidic die in the reverse direction and discharging printing fluid toward the print media to print a second pattern portion to the print media, wherein the second pattern portion is shifted by a predetermined amount relative to the first pattern portion each time the fluidic die moves in the reverse direction.

2. The method of claim 1 comprising: moving the fluidic die in the forward and reverse direction sequentially a plurality of times; advancing the print media underneath the fluidic die after each movement of the fluidic die; and wherein each time the fluidic die moves in the forward direction: printing the first pattern portion to the print media; and wherein each time the fluidic die moves in the reverse direction: printing the second pattern portion to the print media.

3. The method of claim 2 wherein each of the first pattern portions are printed so as not to be offset with respect to each other.

4. The method of claim 2 wherein each of the second pattern portions are printed so as to be offset with respect to each other by a different predetermined amount for each pattern portion.

5. The method of claim 1 wherein each of the first pattern portion and the second pattern portion comprises a plurality of segments extending substantially across the width of the print media.

6. The method of claim 1 further comprising: determining the distance in the width direction of the print media between the first pattern portion and the second pattern portion.

7. A non-transitory machine-readable medium comprising a set of machine- readable instructions stored thereon which, when executed by a processor, cause the processor to: control a fluidic die to print a test pattern to a print media by actuating the fluidic die to move sequentially in a forward and reverse direction across a width of a print media by: moving the fluidic die in the forward direction and discharging printing fluid from the fluidic die toward the print media to print a first pattern portion to the print media; advancing the print media; moving the fluidic die in the reverse direction and discharging printing fluid from the fluidic die toward the print media to print a second pattern portion to the print media; wherein the instructions, when executed, are to control the fluidic die to print the second pattern portion on the print media such that the second pattern portion is offset from the first pattern portion by a predetermined offset distance each time the fluidic die moves in the reverse direction.

8. The medium of claim 7 wherein the instructions, when executed by the processor, are to cause the processor to: control the fluidic die to move in the forward direction a plurality of times, and to print the first pattern portion to the print media each time; control the fluidic die to move in the reverse direction a plurality of times, and to print the second pattern portion to the print media each time; advance the print media in between each movement of the fluidic die.

9. The medium of claim 7 wherein the instructions, when executed by the processor, are to cause each of the first pattern portions to be printed so as not to be offset with respect to each other.

10. The medium of claim 7 wherein the instructions, when executed by the processor, are to cause each of the second pattern portions to be printed so as to be offset with respect to each other by a different predetermined amount for each pattern portion.

11 . The medium of claim 7 wherein each of the first pattern portion and the second pattern portion extends substantially across the width of the print media.

12. The medium of claim 7 wherein each of the first pattern portion and the second pattern portion comprises a plurality of segments.

13. A method comprising: printing a test pattern on a substrate, comprising: moving a fluidic die of a print apparatus in a first pass in a first direction along a movement direction of the fluidic die; printing, by the fluidic die, a first image to a substrate as the fluidic die moves in the first direction; moving the fluidic die of a print apparatus in a second pass in a second direction along the movement direction, the second direction being opposite to the first direction; printing, by the fluidic die, a second image to a substrate as the fluidic die moves in the second direction; moving the fluidic die in a third pass in the first direction; and printing, by the fluidic die, the first image to a substrate as the die moves in the first direction, such that the first image printed in the third pass is offset from the first image printed in the first pass.

14. The method of claim 13, wherein each of the first and second images printed to the substrate extends substantially the width of the substrate.

15. The method of claim 13, wherein the first and second images extend across a width of the substrate, and wherein the method further comprises: measuring the distance between the second image and the first image printed in the first or third pass, across the width of the substrate, to determine an offset between the fluidic die and the substrate.