13B is disposed on the upper surface of the vibration plate 13A. Each of the individual electrodes 13C is disposed on the upper surface of the piezoelectric layer 13B so as to overlap with one of the pressure chambers P in the vertical direction.

In the vibration plate 13A and the piezoelectric layer 13B, a portion of the vibration plate 13A and a portion of the piezoelectric layer 13B which are sandwiched between one of the individual electrodes 13C and one of the pressure chambers P function as a piezoelectric element 13X. In other words, one piezoelectric element 13X is disposed with respect to each of the pressure chambers P. Further, since each of the pressure chambers P communicates with one nozzle N, one piezoelectric element 13A can be considered as corresponding to each of the nozzles N. Each of the piezoelectric elements 13X can be independently deformed according to a potential applied to one of the individual electrodes 13C.

The vibration plate 13A and the individual electrodes 13C are electrically connected to a driver IC 14. The driver IC 14 maintains the potential of the vibration plate 13A at the ground potential while changing the potential of each of the individual electrodes 13C. The vibration plate 13A functions as a common electrode common to the piezoelectric elements 13X. The driver IC 14 generates a driving signal based on a control signal from the controller 5 and supplies the driving signal to each of the individual electrodes 13C. The driving signal changes the potential of each of the individual electrodes 13C between a predetermined driving potential and the ground potential.

Next, a driving method of the piezoelectric elements 13X by the controller 5 will be described with reference to FIG. 3 and FIG. 5. In the respective ejecting periods (periods in each of which an ink droplet is ejected from each of the nozzles N to form one dot on the medium M), the controller 5 shifts the driving timings of corresponding piezoelectric elements 13X each corresponding to one of the nozzles N by a predetermined amount of time in accordance with a dispose position of each of the nozzles N in the lower surface 12a of the channel member 12.

Specifically, in each of the ejecting periods, the controller 5 drives piezoelectric elements 13X included in the driving elements 13X and corresponding to non-black painted nozzles N included in the nozzles N in FIG. 5 at a first timing. The non-black painted nozzles N are, in other words, odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR3. On the other hand, in each of the ejecting periods, the controller 5 drives piezoelectric elements 13X included in the driving elements 13X and corresponding to black-painted nozzles N in FIG. 5 at a second timing which is delayed from the first timing by the predetermined amount of time. The black-painted nozzles N are, in other words, even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR4. In the present embodiment, the delay time is uniform (one type) which is, for example, 2.0 μs. In the following, the piezoelectric elements 13X driven at the first timing are also referred to as precedingly-driven piezoelectric elements 13X, and the piezoelectric elements 13X driven at the second timing are also referred to as subsequently-driven piezoelectric elements 13X.

At the first timing, the controller 5 drives the precedingly-driven piezoelectric elements 13X, without driving the subsequently-driven piezoelectric elements 13X; at the second timing, the controller 5 drives the subsequently-driven piezoelectric elements 13X, without driving the precedingly-driven piezoelectric elements 13X. Note that in order to shift the driving timing of the precedingly-driven piezoelectric elements 13X with respect to the driving timing of the subsequently-driven piezoelectric elements 13X, for example, in one discharge period, the driving waveform of the driving signal supplied to the precedingly-driven piezoelectric elements 13X and the driving waveform of the driving signal supplied to the subsequently-driven piezoelectric elements 13X may be changed. Specifically, the timing for changing the potential of each of the individual electrodes 13C may be changed between the driving waveform of the precedingly-driven piezoelectric elements 13X and the driving waveform of the subsequently-driven piezoelectric elements 13X.

Next, the influence of crosstalk between the two nozzles N adjacent to each other in the medium-width direction will be described, with a nozzle N11 and a nozzle N12 depicted in FIG. 5 as an example. First, the controller 5 drives a piezoelectric element 13X corresponding to the nozzle N11 at the first timing. Here, as described above, the distance D1 between two connection ports C11 and C12 adjacent to each other in the medium-width direction is 500 [μm]. Therefore, in a case where the velocity of the pressure wave in the ink is 500 [m/s], a time required for the pressure wave generated by driving of the piezoelectric element 13X corresponding to the nozzle N11 to reach the connection port C12 from the connection port C11 is 1.0 [μs] (=500 [μm]/500 [m/s]). Then, the controller 5 drives a piezoelectric element 13X corresponding to the nozzle N12 at the second timing delayed by 2.0 [μs] from the first timing. That is, the controller 5 drives the subsequently-driven piezoelectric element 13X, after 1.0 [μs] (=2.0 [μs]-1.0 [μs]) since the pressure wave caused by driving the precedingly-driven piezoelectric elements 13X has reached the connection port C12. Accordingly, the influence of crosstalk corresponding to a substantial delay time 1.0 [μs] obtained by subtracting the arrival time 1.0 [μs] of the pressure wave from the actual delay time 2.0 [μs] occurs in the nozzle N12.

Next, the influence of crosstalk between two nozzles N adjacent to each other in the crossing direction will be described, with a nozzle N31 and a nozzle N41 depicted in FIG. 5 as an example. First, the controller 5 drives a piezoelectric element 13X corresponding to the nozzle N31 at the first timing. Here, as described above, the distance D2 between two connection ports C31 and C41 adjacent to each other in the crossing direction is 800 [μm]. Therefore, in a case where the velocity of the pressure wave in the ink is 500 [m/s], a time required for the pressure wave generated by driving of the piezoelectric element 13X corresponding to the nozzle N31 to reach the connection port C41 from the connection port C31 is 1.6 [μs] (=800 [μm]/500 [m/s]). Then, the controller 5 drives a piezoelectric element 13X corresponding to the nozzle N41 at the second timing delayed by 2.0 [μs] from the first timing. That is, the controller 5 drives the subsequently-driven piezoelectric element 13X after 0.4 [μs] (=2.0 [μs]-1.6 [μs]) since the pressure wave caused by driving the precedingly-driven piezoelectric elements 13X has reached the connection port C41. Accordingly, the influence of crosstalk corresponding to a substantial delay time of 0.4 [μs] obtained by subtracting the arrival time of the pressure wave of 1.6 [μs] from the actual delay time of 2.0 [μs] occurs in the nozzle N41.

In this way, in the present embodiment, the actual delay time is uniform (one type) between the two nozzles N adjacent to each other in the medium-width direction and the two nozzles N adjacent to each other in the crossing direction, while the substantial delay time can be made different. As a result, the influence of crosstalk, i.e., the ejecting velocity of the ink droplet, the volume of the ink droplet, the separation state of the ink droplet, and the like, can be made different between the two nozzles N adjacent to each other in the medium-width direction and the two nozzles N adjacent to each other in the crossing direction. Further, as depicted in FIG. 5, the nozzles N are disposed so that the positions thereof in the medium-width direction are mutually different, and each of the nozzles corresponds to one of the pixels aligned in the medium-width direction on the medium M. Accordingly, pixels corresponding to the nozzles N with the same substantial delay time (i.e., nozzles N affected by the same level of the crosstalk) can be prevented from being continuous in the medium-width direction. In other words, the pixels, on which the ink droplets ejected from the nozzles N affected by the same level of the crosstalk land, can be dispersed in the medium-width direction. As a result, the occurrence of periodic unevenness in the result of printing can be reduced.

In the above-described embodiments, the lower surface 12a of the channel member 12 is an example of an “ejection surface”. The medium-width direction is an example of a “first direction”, the crossing direction is an example of a “second direction”, and the conveying direction is an example of a “third direction”. The nozzle N11 is an example of a “first nozzle”, the nozzle N12 is an example of a “second nozzle”, the nozzle N31 is an example of a “third nozzle”, and the nozzle N41 is an example of a “fourth nozzle”. The individual channel 12B communicating with the nozzle N11 is an example of a “first individual channel”, the individual channel 12B communicating with the nozzle N12 is an example of a “second individual channel”, the individual channel 12B communicating with the nozzle N31 is an example of a “third individual channel”, and the individual channel 12B communicating with the nozzle N41 is an example of a “fourth individual channel”. The connection port C11 is an example of a “first connection port”, the connection port C12 is an example of a “second connection port”, the connection port C31 is an example of a “third connection port”, and the connection port C41 is an example of a “fourth connection port”. Further, the piezoelectric element 13X corresponding to the nozzle N11 is an example of a “first driving element”, the piezoelectric element 13X corresponding to the nozzle N12 is an example of a “second driving element”, the piezoelectric element 13X corresponding to the nozzle N31 is an example of a “third driving element”, and the piezoelectric element 13X corresponding to the nozzle N41 is an example of a “fourth driving element”. The actual delay time is an example of a “predetermined amount of time”.

Furthermore, the nozzle row NR1 is an example of a “first nozzle row”, the nozzle row NR2 is an example of a “second nozzle row”, the nozzle row NR3 is an example of a “third nozzle row”, and the nozzle row NR4 is an example of a “fourth nozzle row”. The nozzle row NR1 and the nozzle row NR2 are an example of a “first nozzle row group”, and the nozzle row NR3 and the nozzle row NR4 are an example of a “second nozzle row group”.

In the above-described embodiment, in each of the ejecting periods, the piezoelectric elements 13X corresponding to the non-black painted nozzles N in FIG. 5 are driven at the first timing, and the piezoelectric elements 13X corresponding to the black-painted nozzles N in FIG. 5 are driven at the second timing. However, the driving timing of the piezoelectric elements 13X is not limited to this.

For example, in FIG. 6, piezoelectric elements 13X each corresponding to one of non-black painted nozzles N may be driven at the first timing, and piezoelectric elements 13X each corresponding to one of black-painted nozzles N may be driven at the second timing. The non-black painted nozzles N are, in other words, even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR4. The black-painted nozzles N are, in other words, odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing nozzle row NR3.

Alternatively, the piezoelectric elements 13X corresponding to the odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, the odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR4 may be driven at the first timing, and the piezoelectric elements 13X corresponding to the even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, the even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR3 may be driven at the second timing.

Still alternatively, the piezoelectric elements 13X corresponding to the even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, the even-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR3 may be driven at the first timing, and the piezoelectric elements 13X corresponding to the odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR1, the odd-numbered nozzles N from the right in the medium-width direction of the nozzle row NR2, and all the nozzles N constructing the nozzle row NR4 may be driven at the second timing.

In either one of the above-described cases, pixels corresponding to the nozzles N with the same substantial delay time (i.e., nozzles N affected by the same level of the crosstalk) can be prevented from being continuous in the medium-width direction. In other words, the pixels, on which the ink droplets ejected from the nozzles N affected by the same level of the crosstalk land, can be dispersed in the medium-width direction. As a result, the occurrence of the periodic unevenness in the result of printing can be prevented.

Further, for example, the head 1 as depicted in FIG. 5 (hereinafter referred to as a “first head 1”) and the head 1 as depicted in FIG. 6 (hereinafter referred to as a “second head 2”) may be prepared, and the first head 1 and the second head 2 may be disposed in the conveying direction. Specifically, the first head 1 and the second head 2 may be disposed in the conveying direction such that the positions in the medium-width direction of the nozzles N included in the first head 1 and the positions in the medium-width direction of the nozzles N included in the second head 2 match one another. That is, in the medium-width direction, the position of the nozzle row NR1 of the first head 1 matches the position of the nozzle row NR1 of the second head 2, the position of the nozzle row NR2 of the first head 1 matches the position of the nozzle row NR2 of the second head 2, the position of the nozzle row NR3 of the first head 1 matches the position of the nozzle row NR3 of the second head 2, and the position of the nozzle row NR4 of the first head 1 matches the position of the nozzle row NR4 of the second head 2. In this case, one nozzle N of the nozzles N included in the first head 1 and one nozzle N of the nozzles N included in the second head 2 correspond to each of the pixels aligned in the medium-width direction. Then, an ink of a first color may be supplied to the first head 1, and an ink of a second color different from the first color may be supplied to the second head 2. Further, in the first head 1, the driving timing of the piezoelectric elements 13X each corresponding to one of the black-painted nozzles N in FIG. 5 may be delayed, and in the second head 2, the driving timing of the piezoelectric elements 13X each corresponding to one of the black-painted nozzles N in FIG. 6 may be delayed. In this case, as can be appreciated by comparing FIG. 5 and FIG. 6, the influence of crosstalk is different between the nozzles N each corresponding to one of the pixels of the first head 1 and the nozzles N each corresponding to one of the pixels of the second head 2. For example, as depicted in FIG. 5, the nozzle N11 of the first head 1 corresponds to a first pixel from the right in the medium-width direction, and the nozzle N11 of the first head 1 has no delay time and is not affected by the influence of crosstalk. In contrast, as depicted in FIG. 6, the nozzle N11 of the second head 2 also corresponds to the first pixel from the right in the medium-width direction, and the substantial delay time of the nozzle N11 of the second head 2 is 1.0 [μs]. In other words, the nozzle N11 of the second head 2 is influenced by the crosstalk (e.g., the reduction in the volume of ink droplet, etc.) corresponding to the substantial delay time of 1.0 [μs]. Accordingly, the occurrence of such a situation can be prevented that ink droplets, respectively, of the two colors each ejected from one of two nozzles N influenced by the crosstalk to the same extent land on the same pixel and allowing the influence of crosstalk to be overlaid in this pixel and making the pixel conspicuous.

Further, in the above-described embodiment, although the nozzle row NR3 and the nozzle row NR4 are shifted by one-quarter of the pitch NP to the left in the medium-width direction, respectively, with respect to the nozzle row NR1 and the nozzle row NR2, the present teaching is not limited to this. For example, in FIG. 5, the positions in the medium-width direction of the nozzles N constructing the nozzle row NR3 may each match one of the positions in the medium-width direction of the nozzles N constructing the nozzle row NR1, and the positions in the medium-width direction of the nozzles N constructing the nozzle row NR4 may each match one of the positions in the medium-width direction of the nozzles N constructing the nozzle row NR2. In this case, one nozzle N among the nozzles N constructing the nozzle rows NR1 and NR2 and one nozzle N among the nozzles N constructing the nozzle rows NR3 and NR4 correspond to each of the pixels aligned in the medium-width direction. Furthermore, the ink of the first color may be supplied to one of the two common channels 12A with which the nozzles N constructing the nozzle rows NR1 and NR2 communicate, and the ink of the second color, which is different from the first color, may be supplied to the other of the two common channels 12A with which the nozzles N constructing the nozzle rows NR3 and NR4 communicate. Moreover, the driving timing of each of the piezoelectric elements 13X corresponding to one of the black-painted nozzles N in FIG. 5 may be delayed. In this case also, the influence of crosstalk differs between one nozzle N and the other nozzle N corresponding to each of the pixels. For example, in FIG. 5, the nozzle N22 and the nozzle N42 correspond to the same pixel. Further, the nozzle N22 is influenced by the crosstalk corresponding to the substantial delay time of 1.0 [μs], whereas the nozzle N42 is influenced by the crosstalk corresponding to the substantial delay time of 0.4 [μs]. Accordingly, the occurrence of such a situation can be prevented that ink droplets, respectively, of the two colors each ejected from one of two nozzles N influenced by the crosstalk to the same extent land on the same pixel and allowing the influence of crosstalk to be overlaid in this pixel and making the pixel conspicuous.

Second Embodiment

Next, a second embodiment of the present teaching will be described. A head 1 of the second embodiment is different from the head 1 of the first embodiment in the numbers and located positions of the common channels 12A, the individual channels 12B, and the piezoelectric elements 13X. The following description will focus on the difference from the head 1 of the first embodiment.

As depicted in FIG. 7, the channel member 12 has four common channels 12A and individual channels 12B.

Each of the individual channels 12B is connected to one of the four common channels 12A. Each of the individual channels 12B includes a nozzle N, a pressure chamber P communicating with the nozzle N, and a connection port C with respect to one of the four common channels 12A.

Nozzles N each of which belongs to one of the individual channels 12B construct eight nozzle rows NR1 to NR8 disposed side by side in the conveying direction. Each of the eight nozzle rows NR1 to NR8 is constructed of nozzles N aligned at equal spacing distances (each of which is a pitch NP) therebetween in the medium-width direction.

In the second embodiment, in the nozzle rows NR1 to NR8, the positions of the nozzles N in the medium-width direction are different. For example, nozzles N constructing the nozzle row NR2 are shifted by half the pitch NP to the left in the medium-width direction with respect to nozzles N constructing the nozzle row NR1, and nozzles N constructing the nozzle row NR4 are shifted by half the pitch NP to the left in the medium-width direction with respect to nozzles N constructing the nozzle row NR3.

Further, the nozzles N constructing nozzle row NR3 are shifted by one-quarter of the pitch NP to the left in the medium-width direction with respect to the nozzles N constructing nozzle row NR1, and the nozzles N constructing nozzle row NR4 are shifted by one-quarter of the pitch NP to the left in the medium-width direction with respect to the nozzles N constructing nozzle row NR2.

Furthermore, the nozzles N constructing each of the nozzle rows NR5 to NR8 are shifted by one-eighth of the pitch NP to the left in the medium-width direction with respect to the nozzles N constructing one of the nozzle rows NR1 to NR4.

Moreover, in the second embodiment, in each of the ejecting periods, the controller 5 drives piezoelectric elements 13X each corresponding to one of non-black painted nozzles N in FIG. 7 at the first timing. The non-black painted nozzles N are, in other words, odd-numbered nozzles N from the right in the medium-width direction of each of the nozzle rows NR1 and NR2, even-numbered nozzles N from the right in the medium-width direction of each of the nozzle rows NR5 and NR6, and all the nozzles N constructing each of the nozzle rows NR3 and NR8. On the other hand, the controller 8 drives piezoelectric elements 13X each corresponding to one of black-painted nozzles N in FIG. 7 at the second timing which is delayed by a predetermined amount of time from the first timing. The black-painted nozzles N are: even-numbered nozzles N from the right in the medium-width direction of each of the nozzle row NR1 and the nozzle row NR2, odd-numbered nozzles N from the right in the medium-width direction of each of the nozzle rows NR5 and the nozzle rows NR6, and all the nozzles constructing the nozzle row NR4 and the nozzle row NR7.

Further, by driving each of the piezoelectric elements 13X at the above-described timing, as depicted in FIG. 7, pixels corresponding to the nozzles N with the same substantial delay time (i.e., nozzles N affected by the same level of the crosstalk) can be prevented from being continuous in the medium-width direction. In other words, the pixels, on which the ink droplets ejected from the nozzles N affected by the same level of the crosstalk land, can be dispersed in the medium-width direction. As a result, the occurrence of the periodic unevenness in the result of printing can be prevented. Namely, an effect similar to the effect obtained in the first embodiment can be obtained.

In the second embodiment, the nozzle row NR5 is an example of a “fifth nozzle row”, the nozzle row NR6 is an example of a “sixth nozzle row”, the nozzle row NR7 is an example of a “seventh nozzle row”, and the nozzle row NR8 is an example of an “eighth nozzle row”. The nozzle row NR5 and the nozzle row NR6 are an example of a “third nozzle row group”, and the nozzle row NR7 and the nozzle row NR8 are an example of a “fourth nozzle row group”.

In the second embodiment, the nozzle rows NR5 and NR6 may be omitted, and the nozzle rows NR7 and NR8 may be omitted, in the channel member 12 of the head 1. In other words, the channel member 12 of the head 1 may include the nozzle rows NR1 to NR4 and the nozzle rows NR7 and NR8; or the channel member 12 of the head 1 may include the nozzle rows NR1 to NR6.

Further, the piezoelectric elements 13X driven at the first timing in the second embodiment may be driven at the second timing, and the piezoelectric elements 13X driven at the second timing in the second embodiment may be driven at the first timing. In other words, the order of driving the piezoelectric elements 13X in the second embodiment may be reversed.

Third Embodiment

Next, a third embodiment of the present teaching will be described. A head 1 of the third embodiment is also different from the head 1 of the first embodiment in the numbers and located positions of the common channel 12A, the individual channel 12B, and the piezoelectric element 13X. The following description will focus on the difference from the head 1 of the first embodiment.

As depicted in FIG. 8, the channel member 12 of the head 1 has one common channel 12A and individual channels 12B. Each of the individual channels 12B is connected to the common channel 12A. Each of the individual channels 12B includes a nozzle N, a pressure chamber P communicating with the nozzle N, and a connection port C with respect to the common channel 12A.

The nozzles N construct two nozzle rows NR1 and NR2 disposed side by side in the conveying direction. Each of the nozzle rows NR1 and NR2 is constructed of nozzles N aligned at equal spacing distances (each of which is a pitch NP) in the medium-width direction. The nozzles N which construct the nozzle row NR2 are shifted to the left in the medium-width direction by half the pitch NP with respect to the nozzles N which construct the nozzle row NR1. Note that in FIG. 8, a distance D3 between a connection port C11 and a connection port C22 is longer than the distance D1 and the distance D2, and the distance D3 is, for example, 1100 [μm].

In the third embodiment, in each of the ejecting periods, the controller 5 drives piezoelectric elements 13X each corresponding to one of non-black painted nozzles N in FIG. 8 at the first timing. The non-black painted nozzles N are, in other words, the first, third and fifth to eighth nozzles N from the right in the medium-width direction of the nozzle row NR1, and the fifth and seventh nozzles N from the right in the medium-width direction of the nozzle row NR2. On the other hand, the controller 5 drives piezoelectric elements 13X each corresponding to one of black-painted nozzles N in FIG. 8 at the second timing, delayed by a predetermined amount of time from the first timing. The black-painted nozzles N are, in other words, the second and fourth nozzles N from the right in the medium-width direction of the nozzle row NR1, and the first to fourth, sixth and eighth nozzles N from the right in the medium-width direction of the nozzle row NR2.

Here, the influence of crosstalk in two nozzles N in a positional relationship such as the nozzle N11 and the nozzle N22 depicted in FIG. 8 will be described, with the nozzle N11 and the nozzle N22 as an example. First, the controller 5 drives a piezoelectric element 13X, included in the piezoelectric elements 13X and corresponding to the nozzle N11, at the first timing. Here, as described above, the distance D3 between the two connection ports C11 and C22 is 1100 [μm]. Accordingly, in a case where the velocity of the pressure wave in the ink is 500 [m/s], the time required for a pressure wave generated by driving of the piezoelectric element