JP6750277B2 - Liquid ejector - Google Patents

Description

The present invention relates to a liquid ejection device.

Conventionally, as a liquid ejection device, a line type ejection head having a plurality of head units arranged in the width direction of a recording medium is known. In this head, each head unit has a plurality of nozzles arranged in the width direction. Further, the two head units adjacent to each other in the width direction are arranged such that their nozzle arrangement regions partially overlap with each other.

In the above head, the nozzles of the two head units are selectively used at a predetermined position in the overlapping range (hereinafter, simply referred to as an overlapping range) of the nozzle arrangement areas of the two head units adjacent to each other in the width direction. .. At that time, due to an assembly error of each head unit, a difference in ejection characteristics between the two head units, and the like, a landing deviation occurs between the droplets ejected from the two head units. This landing deviation causes density unevenness in the image recorded on the recording medium.

In this regard, in the head of Patent Document 1, a portion where ink is ejected from only one head unit, a portion where ink is ejected from only the other head unit, and an area where two head units are ejected are included in the overlapping range of the two head units. A boundary portion (mixed area) for ejecting ink from both is set. At the boundary, the droplets ejected from the two head units are dispersed and land, so that it is possible to suppress density unevenness due to the above factors.

JP, 2005-150824, A

By the way, due to factors such as inclusion of foreign matter in the nozzles and deterioration of a driving element for ejecting liquid droplets from the nozzles, it is not possible to eject liquid droplets to some nozzles, or even if ejection is possible, the ejection amount is small In some cases, defective ejection may occur. Here, in the configuration of Patent Document 1, if the position of the boundary portion within the overlapping range of the two head units is fixed, and if ejection failure occurs in some of the nozzles of the boundary portion, The dots corresponding to the nozzles cannot be formed and streaks occur.

An object of the present invention is to provide a liquid ejecting apparatus capable of preventing the generation of streaks due to the ejection failure even when the nozzle ejection failure occurs in the overlapping area of the two head units.

The liquid ejection device of the present invention has a plurality of first nozzles, each of which is arranged in a predetermined nozzle arrangement direction, and the arrangement area of the first nozzles when viewed from a direction intersecting the nozzle arrangement direction. Ejection failure detection for detecting whether or not ejection failure has occurred for each of the first ejection head including the two first head units, which are arranged so as to partially overlap with each other, and each of the plurality of first nozzles. And a control unit that sets a first boundary part, which is a boundary region to be ejected from each of the two first head units, in a part of a first overlapping range in which the two first head units overlap each other. When the ejection failure detection unit detects that ejection failure has occurred in the first nozzles of the first boundary portion, the control unit determines the position of the first boundary portion as the first boundary portion. If a defective portion is changed to a normal portion having no defective nozzle in the overlapping range and there is a defective nozzle in any of a plurality of ranges obtained by dividing the first overlapping range in the nozzle arrangement direction, It is characterized in that the position is changed to a range in which the arrangement density of defective nozzles is the smallest among the plurality of ranges .

It is a schematic plan view of the printer 1 according to the present embodiment. 3 is a block diagram schematically showing an electrical configuration of the printer 1. FIG. It is a plan view of one inkjet head 4. FIG. 6 is a diagram illustrating ejection control in an overlapping range of two head units 11. FIG. 3 is a diagram showing the positions of the boundaries 16 of the four inkjet heads 4 in the initial state of the printer 1. 7 is a flowchart of a discharge failure detection process. It is a flow chart of boundary change processing. It is a figure explaining the case where only the boundary part 16 of the said head 4 is changed. It is a figure explaining the case where both the boundary part 16 of the said head 4 and the boundary part 16 of the other color head 4 are changed. It is a figure explaining a case where it overlaps with boundary 16 of another color head by changing boundary 16 of the head 4 concerned. It is a figure explaining boundary change processing of a change form. It is a figure explaining the boundary change process of another modification. It is a figure explaining the boundary change process of another modification. 11 is a flowchart of a boundary changing process according to another modification, which is performed according to the number of times the nozzles 12 of the boundary portion 16 discharge. FIG. 11 is a plan view of a serial type inkjet head 24 of another modification.

Next, an embodiment of the present invention will be described. In FIG. 1, the direction in which the recording paper 100 is conveyed is defined as the front-back direction of the printer 1. Further, the width direction orthogonal to the conveyance direction of the recording paper 100 is defined as the left-right direction of the printer 1. Further, the direction perpendicular to the plane of FIG. 1 which is orthogonal to the front-back direction and the left-right direction is defined as the up-down direction of the printer 1.

<Outline of printer configuration>
As shown in FIG. 1, the printer 1 includes a platen 3 housed in a housing 2, four inkjet heads 4, two transport rollers 5 and 6, a controller 7, and the like.

The recording paper 100 is placed on the upper surface of the platen 3. The four inkjet heads 4 are arranged above the platen 3 side by side in the transport direction. Ink is supplied to each inkjet head 4 from an ink tank (not shown). Any of the four colors (black, yellow, cyan, and magenta) of ink is supplied to the four inkjet heads 4. That is, the four inkjet heads 4 eject inks of different colors.

In the following description, for the configurations corresponding to the four color inks of black (K), yellow (Y), cyan (C), and magenta (M), respectively, after the reference numeral, “k” indicating black, In some cases, description will be given with “y” indicating yellow, “c” indicating cyan, and “m” indicating magenta. For example, the inkjet head 4k indicates the inkjet head 4 that ejects black ink.

As shown in FIG. 1, the two transport rollers 5 and 6 are arranged on the rear side and the front side of the platen 3, respectively. The two transport rollers 5 and 6 are respectively driven by a transport motor 8 (see FIG. 2) to transport the recording paper 100 on the platen 3 forward.

The control unit 7 in FIG. 2 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an ASIC (Application Specific Integrated Circuit) including various control circuits. Further, the control unit 7 includes a non-volatile memory 17 that rewritably stores various control parameters. Further, the control unit 7 is connected to an external device 9 such as a PC so as to be capable of data communication, and based on the image data sent from the external device 9, the printer 1 such as the four inkjet heads 4 and the conveyance motor 8 is provided. Control each part of.

More specifically, the control unit 7 controls the transport motor 8 that drives the transport rollers 5 and 6 to cause the two transport rollers 5 and 6 to transport the recording paper 100 in the transport direction. Further, along with this paper conveyance, the control unit 7 controls the four inkjet heads 4 to eject ink toward the recording paper 100. As a result, the image is printed on the recording paper 100.

<Detailed configuration of inkjet head>
Next, the inkjet head 4 will be described in detail. As shown in FIG. 3, each inkjet head 4 includes four head units 11 arranged side by side in the left-right direction. The four head units 11 are attached to the unit holding plate 10.

The four head units 11 are alternately arranged on the front side and the rear side in the transport direction. That is, the four head units 11 are arranged in a zigzag pattern in the front-rear direction along the left-right direction. Each head unit 11 has a plurality of nozzles 12 arranged in the left-right direction and an actuator 13 (see FIG. 2) including a plurality of drive elements for ejecting ink from the plurality of nozzles 12, respectively.

The two head units 11 adjacent to each other in the left-right direction are arranged such that the arrangement regions of the nozzles 12 partially overlap. The range in which the nozzle 12 arrangement regions of the two head units 11 overlap is referred to as an “overlap range A”. In the overlapping range A, the positions of the nozzles 12 of one head unit 11 and the nozzles 12 of the other head unit 11 in the left-right direction match. The four head units 11 are arranged in the left-right direction in a state where the head units 11 are partially overlapped with each other, so that the nozzles 12 of the four head units 11 are arranged at equal intervals in the left-right direction. A line head is configured.

The actuator 13 is not limited to a specific configuration, but for example, a piezoelectric actuator having a piezoelectric element that pressurizes ink by utilizing the deformation of the piezoelectric layer due to the inverse piezoelectric effect is preferably used as the drive element. it can.

As shown in FIG. 2, each head unit 11 includes a drive device 14 that individually drives a plurality of drive elements of the actuator 13. First, the control unit 7 transmits a control signal for instructing from which nozzle 12 ink is to be ejected to the drive device 14 based on the image data input from the external device 9 (see FIG. 1). Then, the drive device 14 individually outputs drive signals to the plurality of drive elements of the actuator 13 based on the control signal from the control unit 7.

In each of the nozzles 12 of the head unit 11, there is a case where an ejection failure occurs such that ink cannot be ejected (non-ejection), the ejection amount is small even when ejected, the ejection speed is slow, or the ejection direction is not straight. is there. Causes of ejection failure include, for example, increase in viscosity of ink in the nozzle 12 due to drying (also referred to as viscosity increase), mixing of foreign matter such as paper powder, mixing of air into ink flow path, deterioration of drive element, etc. Is mentioned.

In this regard, as shown in FIG. 2, each head unit 11 has an ejection failure detection unit 15 that detects whether or not an ejection failure has occurred in each of the plurality of nozzles 12. The configuration of the ejection failure detection unit 15 is not particularly limited, but for example, the following configuration can be adopted. When the drive element of the actuator 13 is a piezoelectric element, residual vibration remains in the piezoelectric element for a while after driving. The magnitude and cycle of this residual vibration differ depending on whether the ink is normally ejected from the nozzle 12 or when ejection failure such as ejection failure occurs. Therefore, it is possible to receive the residual vibration after driving each piezoelectric element in the form of a voltage signal, and detect the ejection failure of each nozzle 12 from the state of the vibration (for example, Japanese Patent Laid-Open No. 2012-045957, (See JP 2013-000958 A).

(Discharge control in the overlapping range)
By the way, due to the positional deviation of the head unit 11 due to an assembly error, the difference in the ejection characteristics of the nozzles 12 between the head units 11, and the like, ejection is performed from each nozzle 12 between two head units 11 that are adjacent in the left-right direction. The misalignment of the deposited ink occurs. Due to this factor, density unevenness is likely to occur at the joint between the two head units 11.

Therefore, in the present embodiment, first, the two head units 11 that are adjacent to each other in the left-right direction are arranged so that the arrangement regions of the nozzles 12 partially overlap. Then, a boundary portion 16 which is a boundary area between the ejection nozzles 12 of the two head units 11 is set in a part of the overlapping range A. In the boundary portion 16, ink is ejected from each of the nozzles 12 of the two head units 11. As a result, the uneven density generated between the two head units 11 is made inconspicuous.

The ejection control in the overlapping range A will be described in more detail with reference to FIG. As shown in FIG. 4, the overlapping range A between the two head units 11 is divided into six ranges (a to f) arranged in the left-right direction. The widths of the six ranges a to f in the left-right direction, that is, the number of nozzles 12 existing in each range is the same. Then, the control unit 7 sets the boundary portion 16 to be ejected from each of the two head units 11 in any one of the above-mentioned six ranges a to f.

In each of the six ranges a to f, it is necessary to change the usage ratio of the nozzles 12 between the two head units 11, so the number of nozzles 12 in each range is three or more. Further, in order to make density unevenness less noticeable, it is better that the number of nozzles 12 in one range is larger, for example, about 20 nozzles. In that case, the number of nozzles 12 in the overlapping range A of FIG. 4 is 20×6=120.

In FIG. 4, as an example, a state in which the boundary portion 16 is set in the range a located at the right end of the overlapping range A is shown. Note that the lower diagram of FIG. 4 shows changes in the usage ratio of the nozzles 12 in the left head unit 11 and the right head unit 11.

On the left side of the range a set in the boundary 16, the nozzle usage rate of the left head unit 11 is 100%, and on the right side of the range a, the nozzle usage rate of the right head unit 11 is 100%. In addition, the nozzle usage ratio changes linearly within the range a that is the boundary portion 16. That is, the nozzle usage rate of the left head unit 11 continuously decreases from left to right.

The “nozzle usage ratio” is a ratio indicating how much of the dots formed in the predetermined area of the recording paper 100 is formed by the nozzles 12 of the one head unit 11. For example, when it is necessary to form 10 dots in a certain area based on the density data of each color ink obtained by performing image processing of RGB image data, the nozzle usage ratio of the left head unit 11 in this area is 70%. It was. In this case, 7 out of 10 dots in the above area are formed by the nozzles 12 of the left head unit 11 and the remaining 3 dots are formed by the nozzles 12 of the right head unit 11.

However, even if the above-described control is performed, the image portion formed by the nozzles 12 of the boundary portion 16 has some density unevenness as compared with the image portion formed by only the nozzles 12 of the single head unit 11. Remains. Therefore, if the positions of the boundary portions 16 are the same among the four inkjet heads 4, the density unevenness occurring at the boundary portions 16 of the four heads 4 may overlap and the density unevenness may be noticeable. ..

Therefore, in the present embodiment, the control unit 7 makes the positions of the boundary portions 16 different among the four inkjet heads 4. For example, in FIG. 5, in the black (K) inkjet head 4k, the boundary portion 16k is set to the range a at the right end. The boundary 16y of the yellow (Y) inkjet head 4y is in the range b on the left side thereof, the boundary 16c of the cyan (C) inkjet head 4c is in the range c of the further left side, and the boundary of the magenta (M) inkjet head 4m. The parts 16m are further set in the range d on the left side.

The position information of the boundary portion 16 of each inkjet head 4, that is, the information of which range of the ranges a to f is set, is stored in the rewritable memory 17 in the control unit 7. When printing an image on the recording paper 100, the control unit 7 reads the position information of the boundary portion 16 from the memory 17 for each of the four inkjet heads 4, and controls ejection in the overlapping range A based on the information.

(Boundary change when defective nozzle is detected)
By the way, in the boundary portion 16 set within the overlapping area A, when ejection failure occurs in some of the nozzles 12, dots are not normally formed by the defective nozzles, so that the dots are formed in the boundary portion 16. A streak appears in the captured image. Therefore, when a defective nozzle occurs in the boundary portion 16, the control unit 7 changes the range of the boundary portion 16 to another range within the overlapping range A in order to prevent the occurrence of streaks.

Hereinafter, the ejection failure detection processing and the boundary changing processing executed when the ejection failure is detected will be described with reference to the flowcharts of FIGS. 6 and 7 and the explanatory views of FIGS. 8 to 10. In the following description, Si (i=1, 2, 3...) Indicates the number of each step.

(Discharge failure detection process)
The ejection failure detection process of FIG. 6 is executed by the control unit 7 when an image is printed on the recording paper 100. When the drive device 14 drives the drive element to eject ink from each nozzle 12, the ejection failure detection unit 15 detects whether or not ejection failure has occurred for each nozzle 12 of the four inkjet heads 4. (S1).

When the ejection failure detection unit 15 detects that ejection failure has occurred in the nozzle 12 of the inkjet head 4 of a certain color (S1: Yes), the control unit 7 causes the inkjet head 4 to perform maintenance (S2). ). The maintenance includes “flushing” for ejecting ink from the nozzle 12, and “purge” for forcibly ejecting ink from the nozzle 12 by using a pressurizing unit or a suction unit such as a pump.

When the ejection failure of the nozzle 12 is eliminated by executing the maintenance (S3: Yes), the process returns to S1. On the other hand, if the ejection failure of the nozzle 12 is not eliminated (S3: No), the nozzle 12 is stored in the memory 17 as a "defective nozzle" (S4). For the nozzles 12 that have once been determined to be defective nozzles, the ejection failure detection unit 15 does not perform ejection failure detection thereafter to prevent the processing of FIG. 6 from being unnecessarily repeated.

If the defective nozzle is the nozzle 12 located at the boundary portion 16 of any of the four inkjet heads 4 (S5: Yes), the boundary changing process described below is executed (S6). On the other hand, if the defective nozzle is not the nozzle 12 located at the boundary portion 16 (S5: No), the process ends.

(Boundary change processing)
Next, the boundary changing process will be described with reference to FIG. First, in the inkjet head 4 having defective nozzles at the boundary portion 16, based on the information of the defective nozzles stored in the memory 17, there is no defective nozzle in the range other than the boundary portion 16 within the overlapping range A. It is determined whether there is a normal portion (S11). For convenience of description, in the following description and FIG. 7, the inkjet head 4 in which the defective nozzle is generated in the boundary portion 16 is referred to as “the relevant head”, and the heads of other colors other than that are referred to as “other color heads”.

When there is no normal portion in the overlapping range A of the head 4, the process returns without changing the boundary portion 16 (S11: No). When there is a normal portion in the overlapping range A of the head 4 (S11: Yes) and the normal portion does not overlap the boundary portion 16 of the other-color head 4 in the transport direction (S12: Yes), the head 4 The boundary portion 16 is changed to a normal portion that does not overlap the boundary portion 16 of the other-color head 4 (S13).

The processes of S11 to S13 will be specifically described with reference to FIG. FIG. 8 shows an example in which a defective nozzle occurs at the boundary portion 16k of the black inkjet head 4k. It is also assumed that the current position of the boundary portion 16k is in the range a, and a defective nozzle has occurred in this range a. In addition, in FIG. 8, x is a defective nozzle.

In FIG. 8, the other ranges b to f within the black overlapping range A are all normal parts in which no defective nozzle exists. That is, the candidates of the change destination of the boundary portion 16k are the ranges b to f. However, since the ranges b, c, and d are ranges that overlap the boundary portions 16y, 16c, and 16m of the other-color heads 4y, 4c, and 4m, the ranges b, c, and d are first excluded from the change destination.

Further, with respect to the remaining two ranges, the range e and the range f, it is preferable to select the range f that is farthest from the range a in which the boundary portion 16k before the change was located. The nozzle 12 located on the tip side of the boundary portion 16k of the head unit 11 on the right side in FIG. 8 is a pause nozzle that has not been used until then. Therefore, when changing the range of the boundary portion 16k, by using as many idle nozzles as possible, it is possible to prevent the specific nozzle 12 from being used frequently. That is, by largely changing the position of the boundary portion 16k to the range farthest from the current position, it becomes possible to newly use many rest nozzles within the overlapping range A. Further, with respect to the left head unit, it becomes possible to suspend many nozzles 12 that have been used so far.

As described above, since the widths of the six ranges a to f in the overlapping range A in the left-right direction are all the same, the position of the boundary portion 16 of the head 4 is changed between the six ranges. In this case, the width of the boundary 16 before the change and the width of the boundary 16 after the change are the same.

Returning to FIG. 7, when there is a normal portion in the overlapping range A of the head 4 but there is no normal portion that does not overlap the boundary portion 16 of the other-color head 4 (S12: No), first, the boundary of the head 4 concerned. The portion 16 is changed to a normal portion that overlaps the boundary portion 16 of the heads of other colors (S14). On the other hand, it is examined whether or not the boundary portion 16 of the other-color head 4 that overlaps the boundary portion 16 of the head 4 can be changed. That is, when there is a normal portion having no defective nozzle in the overlapping area A of the other-color head 4 (S15: Yes), the boundary portion 16 of the other-color head 4 is changed to the normal portion (S16). On the other hand, in the overlapping area A of the other-color head 4, if there is no normal portion having no defective nozzle other than the area where the boundary portion 16 is currently set (S15: No), the boundary of the other-color head 4 The part 16 returns without changing from the current position.

In FIG. 7, after changing the boundary portion 16 of the head 4 to a range overlapping the boundary portion 16 of the other color head 4 (S14), it is determined whether the boundary portion 16 of the other color head 4 can be changed. However, the boundary portion 16 of the other color head 4 and the boundary portion 16 of the other color head 4 are changed after determining whether the boundary portion 16 of the other color head 4 can be changed first. You may do it.

The above-described processing of FIGS. 12 to 16 will be specifically described with reference to FIGS. 9 and 10. In FIG. 9, it is assumed that the current black boundary portion 16k is the range a, and a defective nozzle has occurred in this range a. Here, among the other ranges b to f within the black overlapping range A, ranges b, c, and d are normal parts where no defective nozzle exists, but ranges e and f are defective parts where defective nozzles exist. Is.

Therefore, the black boundary portion 16k is changed to any of the ranges b, c, and d. The range b overlaps the yellow boundary portion 16y, the range c overlaps the cyan boundary portion 16c, and the range d Overlaps with the boundary portion 16m of magenta. That is, even if the black boundary portion 16k is changed to any of the ranges b, c, and d, the black boundary portion 16k overlaps with the other color boundary portion 16. Here, as described above, the black boundary portion 16k is changed to the range d, which is the farthest from the current position range a, from the viewpoint of enabling the use of as many idle nozzles as possible.

When the black boundary 16k is changed to the range d, it overlaps with the magenta boundary 16m. However, in the example of FIG. 9, in the magenta overlapping range A, there is a normal portion that does not overlap the boundary portion 16 of another color (range a, e, f). Therefore, the black boundary 16k is changed to the range d, and the magenta boundary 16m is changed to the range a so that they do not overlap each other.

The example of FIG. 10 is the same as FIG. 9 in that the black boundary portion 16k is changed to the range d overlapping the magenta boundary portion 16m. However, in FIG. 10, in the magenta overlapping range A, there are defective nozzles in the ranges a, b, c, e, and f other than the range d in which the current boundary portion 16 is located, and the overlapping occurs. There is no normal part within the range A. In this case, the magenta boundary portion 16m is used without being changed from the current range d, and the black boundary portion 16k and the magenta boundary portion 16m overlap each other.

As described above, in the present embodiment, the control unit 7 changes the position of the boundary portion 16 within the overlapping range A of the two head units 11 of the inkjet head 4. Specifically, in one head unit 11, when ejection failure occurs in the nozzle 12 located at the boundary portion 16, the position of the boundary portion 16 is changed. By causing the nozzles 12 of the normal head unit 11 to eject at the position where the boundary portion 16 before the change is present, it is possible to prevent the generation of streaks due to missing dots.

Further, when the width of the boundary portion 16 after the change is smaller than that before the change when changing the range of the boundary portion 16 within the overlapping range A, the gradient of the nozzle usage ratio (lower diagram in FIG. 4) at the boundary portion 16 Becomes sudden. The steeper the gradient, the more noticeable the density unevenness is in the image portion formed by the nozzles 12 in the boundary portion 16.

For example, in the head disclosed in Japanese Patent Laid-Open No. 2011-255594, ink is ejected from both head units in the entire overlapping range of the two head units. That is, the entire overlapping region is the boundary. Further, in this document, when ejection failure occurs in some of the nozzles located in the overlapping range in one of the head units, the defective nozzle is complemented by the nozzles of the other head unit. That is, the boundary portion set in the entire overlapping range is changed to a narrow region by excluding the portion where the defective nozzle has occurred. As described above, when the ejection failure occurs, the boundary portion is substantially narrowed, so that the gradient of the nozzle usage ratio in the boundary portion becomes steep.

On the other hand, in the present embodiment, when a defective nozzle occurs in the boundary portion, the defective nozzle is not complemented by the normal nozzle 12 of the other head unit 11, but the range of the boundary portion 16 itself is corrected. change. The width of the boundary portion 16 in the left-right direction is the same before and after the change. That is, since the gradient of the nozzle usage ratio in the boundary portion 16 is the same before and after the change, the density unevenness in the overlapping range is less noticeable than that before the change.

When changing the boundary portion 16 of the head 4, as shown in FIGS. 8 to 10, the boundary portion 16 is moved to a normal portion in the overlapping range A where no ejection failure is detected. As a result, the uneven density due to the defective nozzle does not occur after the boundary portion 16 is changed. In particular, as shown in FIG. 8, if there is a range that does not overlap the boundary 16 of the other-color head 4, the boundary 16 is changed to that range. As a result, since the boundary portion 16 of the head 4 and the boundary portion 16 of the other-color head 4 do not overlap with each other, the density unevenness of the image portion formed at the boundary portion 16 is less noticeable.

When the boundary portion 16 of the head 4 is changed, as shown in FIG. 9, when there is no normal portion other than the range A overlapping the boundary portion 16 of the other color head 4 as shown in FIG. It will be changed to a range overlapping with the boundary portion 16 of. At this time, by changing the range of the boundary portion 16 of the other-color head 4, it is possible to finally prevent the boundary portions 16 from overlapping with each other. However, as shown in FIG. 10, it is not preferable to forcibly change the position of the boundary portion 16 until there is no normal portion other than the current boundary portion 16 in the overlapping area A of the other-color heads 4. In this case, the position of the boundary portion 16 of the other-color head 4 is not changed, and the boundary portion 16 of the head 4 and the boundary portion 16 of the other-color head 4 are used in an overlapping state.

In the embodiment described above, the printer 1 corresponds to the “liquid ejection device” of the present invention. The paper width direction corresponds to the "nozzle arrangement direction" of the present invention, and the transport direction corresponds to the "direction intersecting with the nozzle arrangement direction" of the present invention. The head 4 having the defective nozzle at the boundary portion 16 corresponds to the “first ejection head” of the present invention. The head unit 11 of the head 4 is the “first head unit” of the present invention, and its nozzle is the “first nozzle” of the present invention. Furthermore, the overlapping range A of the head 4 is the “first overlapping range” of the present invention, and the boundary portion 16 of the head 4 is the “first boundary portion 16” of the present invention. On the other hand, the other-color head 4 corresponds to the "second ejection head" of the present invention. The head unit 11 of the other-color head 4 is the “second head unit” of the present invention, and its nozzle is the “second nozzle” of the present invention. Further, the overlapping range A of the other-color head 4 is the “second overlapping range” of the present invention, and the boundary 16 of the other-color head 4 is the “second boundary 16” of the present invention.

Next, a description will be given of a modified form in which various modifications are made to the above embodiment. However, components having the same configurations as those in the above-described embodiment are designated by the same reference numerals, and the description thereof will be appropriately omitted.

1] In the above-described embodiment, by changing the range of the boundary portion 16 of the head 4 in which the defective nozzle is generated, the boundary portion 16 of the other color head 4 can be removed only when it overlaps with the boundary portion 16 of the other color head 4. Have changed. On the other hand, when changing the range of the boundary portion 16 of the head 4, the boundary portion 16 of the other-color head 4 may be changed at the same time.

For example, in FIG. 11, since the defective nozzle occurs in the black boundary portion 16k of the range a, the boundary portion 16k is changed from the range a to the range c. Accordingly, the yellow boundary 16y is changed from the range b to the range d, the cyan boundary 16c is changed from the range c to the range e, and the magenta boundary 16m is changed from the range d to the range f.

2] In the above-described embodiment, as shown in FIG. 8, the width of the boundary 16 before the change and the width of the boundary 16 after the change are the same, but the width of the boundary 16 after the change is changed. It may be larger than the width of the front boundary portion 16. For example, in FIG. 12A, the boundary 16 is changed from the range a to a region obtained by combining the range e and the range f, and the width after the change is twice the width before the change. By increasing the width of the boundary 16 after the change, the gradient of the nozzle usage ratio becomes gentle, and the density unevenness becomes less noticeable in the image portion formed by the boundary 16.

Further, the changed boundary portion 16 may include a region different from the boundary portion 16 before the change, and the changed boundary portion 16 may partially overlap the boundary portion 16 before the change. In FIG. 12B, the boundary portion 16 is changed from the range a to the range b, but the changed boundary portion 16 includes not only the range b but also a region in the range a in which there is no defective nozzle. Has been. In this case, the width of the boundary portion 16 can be widened within the limited area of the two ranges a and b while avoiding the defective nozzle.

2] When the boundary portion 16 is changed, if there is no normal portion having no defective nozzle in another range within the overlapping range A, even if the boundary portion 16 is changed to a range in which the arrangement density of defective nozzles is the smallest. Good. As a result, it is possible to minimize the occurrence of streak-shaped density unevenness due to the defective nozzle. In FIG. 13, the current boundary portion 16 is the range a, and defective nozzles are present in all the other ranges b to f. Among them, the number of defective nozzles in the range f is the smallest, that is, The arrangement density is the smallest. Therefore, the boundary portion 16 is changed to the range f. Even if a defective nozzle occurs at the current boundary portion 16, it is not necessary to forcibly change the boundary portion 16 to another range as long as the arrangement density of the defective nozzle is smaller than the other range.

3] In the above-described embodiment, when a defective nozzle is detected in the boundary portion 16, a process of changing the boundary portion 16 to another range is performed. However, the boundary portion 16 is subjected to a condition different from the condition for detecting the defective nozzle. May be changed.

For example, as the number of ejections from the nozzle 12 increases, the deterioration of the driving element progresses. In the case of a piezoelectric element, when the electric field is applied many times, the piezoelectric layer is settled, and the amount of piezoelectric strain is reduced. Therefore, when the number of ejections from the nozzle 12 reaches a certain number or more, it is considered that there is a high possibility that the drive element corresponding to the nozzle 12 has deteriorated, and the boundary portion 16 may be changed. In this case, it is possible to prevent the ejection failure of the nozzle 12 by changing the boundary portion 16 before the ejection failure due to the deterioration of the driving element occurs.

The above processing will be described with reference to the flowchart in FIG. This processing is executed by the control unit 7 when the image is printed on the recording paper 100. As shown in FIG. 14, first, the number of ejections of each nozzle 12 is integrated (S21). This integration is a total value from the start of using the printer 1. That is, the integrated value at the end of the previous image printing is stored in the memory 17, and the number of ejections is further added to the value stored in the memory 17 at the next image printing.

Next, the integrated value of the number of ejections of each nozzle 12 is compared with a predetermined value (S22). When there is a nozzle 12 whose integrated value n of the number of ejections exceeds a predetermined threshold value n0 (S22: Yes) and the nozzle 12 is located at the boundary portion 16 (S23: Yes), the boundary portion 16 is changed. (S24).

The predetermined threshold value n0 depends on how much the droplet velocity decreases due to deterioration of the driving element (eg, piezoelectric element). For example, when the printer guarantees the droplet velocity within the range of 10±1 m/s, the integrated value n of the number of ejections when the droplet velocity is lower than 9 m/s is the above threshold value n0. The specific value of the ejection frequency threshold value n0 is, for example, 600 million times for a household printer, 1 billion times for an office printer, and 100 billion times for an industrial printer.

In addition, if the integrated value of the number of ejections is stored for each nozzle 12, the number of information to be stored will increase if the number of nozzles 12 is large. Therefore, the high ejection frequency may be determined not by the ejection frequency itself of each nozzle 12 but by another parameter related to the ejection frequency, which increases as the ejection frequency of the nozzle 12 increases. For example, parameters such as the number of printed sheets and the total number of dots recorded on the recording paper are integrated for each of the six ranges a to f of the overlapping range A of FIG. The boundary portion 16 may be changed when the value is exceeded. If the parameter is the number of prints, the boundary portion 16 is changed when the number of prints exceeds 60,000, for example. Even if the number of printed sheets exceeds a predetermined threshold value, the position of the boundary portion 16 may not be changed if the frequency of use of the nozzles 12 in the boundary portion 16 is low.

4] In the above embodiment, the present invention is an example applied to a line type inkjet head, but as shown in FIG. 15, ink is ejected from each nozzle 12 while moving in the paper width direction, serial type It is also possible to apply to the inkjet head 24.

1 Printer 4 Inkjet Head 7 Control Section 11 Head Unit 12 Nozzle 15 Ejection Failure Detection Section 16 Border Section

Claims (7)

Each has a plurality of first nozzles arranged in a predetermined nozzle arrangement direction, and is arranged such that the arrangement regions of the first nozzles partially overlap each other when viewed from a direction intersecting the nozzle arrangement direction. And a first ejection head having two first head units,
An ejection failure detection unit that detects whether or not ejection failure has occurred for each of the plurality of first nozzles;
A control unit that sets a first boundary part, which is a boundary region to be ejected from each of the two first head units, in a part of a first overlapping range in which the two first head units overlap,
The control unit is
When the ejection failure detection unit detects that ejection failure has occurred in the first nozzle at the first boundary portion,
The position of the first boundary portion is changed to a normal portion of the first overlapping range without defective nozzles,
When there is a defective nozzle in any of a plurality of ranges obtained by dividing the first overlapping range in the nozzle arrangement direction, the position of the first boundary portion is set to be the density of defective nozzles in the plurality of ranges. A liquid ejecting apparatus characterized by changing to the smallest range . Each has a plurality of first nozzles arranged in a predetermined nozzle arrangement direction, and is arranged such that the arrangement regions of the first nozzles partially overlap each other when viewed from a direction intersecting the nozzle arrangement direction. And a first ejection head having two first head units,
Each of the plurality of second nozzles is arranged in the nozzle arrangement direction, and two second nozzles are arranged so that the arrangement areas of the second nozzles partially overlap each other when viewed from the intersecting direction. A second ejection head provided with two head units and arranged side by side in the direction intersecting with the first ejection head;
An ejection failure detection unit that detects whether or not ejection failure has occurred for each of the plurality of first nozzles;
A second boundary in which a first boundary portion, which is a boundary area for ejecting from each of the two first head units, overlaps with a part of a first overlapping range in which the two first head units overlap, and a second boundary in which the two second head units overlap each other. A control unit for setting a second boundary portion, which is a boundary area for ejecting from each of the two second head units, in a part of the overlapping range ;
The control unit is
When the ejection failure detection unit detects that an ejection failure has occurred in the first nozzle of the first boundary portion,
A liquid ejecting apparatus , wherein the first boundary portion is changed to a range that does not overlap with the second boundary portion when viewed from the intersecting direction . Each has a plurality of first nozzles arranged in a predetermined nozzle arrangement direction, and is arranged such that the arrangement regions of the first nozzles partially overlap each other when viewed from a direction intersecting the nozzle arrangement direction. And a first ejection head having two first head units,
Each has a plurality of second nozzles arranged in the nozzle arrangement direction, and when viewed from the intersecting direction, the arrangement area of the second nozzles is partially
A second ejection head provided with two second head units arranged so as to overlap with each other, and a second ejection head arranged side by side in the direction intersecting with the first ejection head;
An ejection failure detection unit that detects whether or not ejection failure has occurred for each of the plurality of first nozzles;
A second boundary in which a first boundary part, which is a boundary area for ejecting from each of the two first head units, and a part of a first overlapping range in which the two first head units are overlapped, and the two second head units are overlapped with each other. A control unit that sets a second boundary part, which is a boundary region for ejecting from each of the two second head units, in a part of the overlapping range ;
The control unit is
When the ejection failure detection unit detects that ejection failure has occurred in the first nozzle at the first boundary portion,
The liquid ejecting apparatus is characterized in that the first boundary portion is changed to a range overlapping with the unchanging second boundary portion when viewed from the intersecting direction and the range of the second boundary portion is changed. .. For each of the plurality of first nozzles, an ejection failure detection unit that detects whether or not ejection failure has occurred,
The control unit changes the first boundary portion when the discharge failure detection unit detects that a discharge failure has occurred in the first nozzle of the first boundary portion,
Further, the control unit is
When changing the position of the first boundary portion, in the first overlapping range, in addition to the portion overlapping the second boundary portion when viewed from the intersecting direction, there is a normal portion having no defective nozzle. The liquid ejecting apparatus according to claim 3 , wherein, when it does not exist, the first boundary portion is changed to a range overlapping with the second boundary portion. The ejection failure detection unit detects whether or not an ejection failure has occurred in each of the plurality of second nozzles,
The control unit is
When changing the first boundary portion to a range overlapping with the second boundary portion when viewed from the intersecting direction, a portion of the portion where the second boundary portion is set within the second overlapping range The liquid ejecting apparatus according to claim 4 , wherein the range of the second boundary portion is not changed from the current range when there is no other normal portion. Each has a plurality of first nozzles arranged in a predetermined nozzle arrangement direction, and is arranged such that the arrangement regions of the first nozzles partially overlap each other when viewed from a direction intersecting the nozzle arrangement direction. And a first ejection head having two first head units,
An ejection failure detection unit that detects whether or not ejection failure has occurred for each of the plurality of first nozzles;
A control unit that sets a first boundary part, which is a boundary region to be ejected from each of the two first head units, in a part of a first overlapping range in which the two first head units overlap,
The control unit is
When the ejection failure detection unit detects that ejection failure has occurred in the first nozzle at the first boundary portion,
A liquid ejecting apparatus, wherein the first boundary portion is changed to a portion in the first overlapping range that is farthest from a range before the change . The said control part makes the width|variety of the said 1st boundary part in the said nozzle arrangement direction the width |variety more than the width |variety of the said 1st boundary part before change. Liquid ejector.

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