Printing apparatus and printing method

The present application claims priority from Japanese Patent Application No. 2020-116400 filed on Jul. 6, 2020, the disclosure of which is incorporated herein by reference in its entirety.

The present disclosure relates to a printing apparatus configured to discharge ink from nozzles and a printing method.

There is known an ink-jet head driving apparatus including: actuators provided corresponding to respective nozzles and configured to discharge ink from the nozzles by amounts corresponding to respective driving signals; a storage configured to store correction data by which ink discharge amounts from the respective nozzles are leveled; a selecting section configured to select one of the driving signals based on the correction data; and a driving section configured to output the selected driving signal to one of the actuators (see Japanese Patent Application Laid-open No. 2008-162261). In this ink-jet head driving apparatus, the nozzles of the ink-jet head are classified into groups depending on characteristics of ink discharge amount from the nozzles. Driving voltage is corrected for each of the groups.

However, a density difference between dots formed by the nozzles that belong to the same group is not considered in the above ink-jet head driving apparatus.

An object of the present disclosure is that, in a printing apparatus including an ink-jet head in which nozzles are classified into groups depending on discharge characteristics, a density difference between dots formed by nozzles belonging to the same group is reduced and a density difference between two groups adjacent to each other is reduced.

According to a first aspect of the present disclosure, there is provided a printing apparatus, including:

a plurality of power supply circuits including at least a first power supply circuit and a second power supply circuit, the power supply circuits having mutually different output voltages;

a head including a plurality of nozzles, the nozzles forming a plurality of groups arranged in a first direction, each of the nozzles being associated with any one of the power supply circuits;

wherein the groups include a first group and a second group adjacent to each other in the first direction,

the first group is formed by a plurality of nozzles associated with the first power supply circuit and a plurality of nozzles associated with the second power supply circuit, and

the second group is formed by a plurality of nozzles associated with the first power supply circuit and a plurality of nozzles associated with the second power supply circuit.

According to a second aspect of the present disclosure, there is provided a printing method using a printing apparatus that includes: a plurality of power supply circuits including at least a first power supply circuit and a second power supply circuit, the power supply circuits having mutually different output voltages; a head including a plurality of nozzles, the nozzles forming a plurality of groups arranged in a first direction, each of the nozzles being associated with any one of the power supply circuits, the method including:

discharging a liquid on a print medium from the nozzles of the head; and

moving the print medium relative to the nozzles,

wherein the groups include a first group and a second group adjacent to each other in the first direction,

the first group is formed by a plurality of nozzles associated with the first power supply circuit and a plurality of nozzles associated with the second power supply circuit, and

the second group is formed by a plurality of nozzles associated with the first power supply circuit and a plurality of nozzles associated with the second power supply circuit.

According to the first and second aspects of the present disclosure, it is possible to reduce the density difference between the dots formed by the nozzles that belong to the same group and to reduce the density difference between the two groups adjacent to each other, without adjusting the output voltages of the power supply circuits.

FIG. 1 is a plan view of an exemplary main configuration of a printing apparatus according to this embodiment.

FIG. 2 is a bottom view of an exemplary head according to this embodiment.

FIG. 3 is a block diagram of an exemplary configuration including a second substrate included in the head and a flexible circuit board connected to the second substrate according to this embodiment.

FIG. 4 depicts an exemplary circuit configuration provided in a driver IC.

FIG. 5 depicts an exemplary configuration of a waveform generating circuit provided in the driver IC.

FIG. 6 is a flowchart indicating an outline of printing executed by the printing apparatus according to this embodiment.

FIG. 7 depicts a state in which nozzles are classified into groups in a temporary setting process according to this embodiment.

FIG. 8 depicts an example of information stored in a non-volatile memory of the head according to this embodiment.

FIG. 9A depicts a state where association of power supply circuits with some of the nozzles is changed in a setting adjustment step according to this embodiment, and FIG. 9B depicts part of a dot array formed by discharging ink droplets from all the nozzles in the head after the change in association of the power supply circuits with the nozzles.

FIG. 10 depicts a modified example of the head of this embodiment.

FIG. 11 depicts another modified example of the head of this embodiment.

FIG. 12 is a plan view of still another modified example of the head of this embodiment.

Referring to FIGS. 1 to 9 , explanation is made about a printing apparatus according to an embodiment of the present disclosure.

In FIG. 1 , an upstream side in a conveyance direction of a print medium P is defined as a front side of a printing apparatus 1 , and a downstream side in the conveyance direction of the print medium P is defined as a rear side of the printing apparatus 1 . Further, a direction parallel to a surface on which the print medium P is conveyed (a surface parallel to the sheet surface of FIG. 1 ) and orthogonal to the conveyance direction is defined as a medium width direction. A left side in FIG. 1 is a left side of the printing apparatus 1 , and a right side in FIG. 1 is a right side of the printing apparatus 1 . A direction orthogonal to the conveyance surface of the print medium P (a direction orthogonal to the sheet surface of FIG. 1 ) is defined as an up-down direction of the printing apparatus 1 . A fore side (front side) of the sheet surface of FIG. 1 is defined as up (upper side), and a far side (the other side) of the sheet surface of FIG. 1 is defined as down (lower side). In the following, explanation is made by appropriately using the front, rear, left, right, up (upper), and down (lower). The medium width direction is an exemplary “first direction” of the present disclosure, and the conveyance direction is an exemplary “second direction” of the present disclosure.

As defined in FIG. 1 , the printing apparatus 1 includes a casing 2 , a platen 3 , four line heads 4 , two conveyance rollers 5 A, 5 B, and a controller 7 .

The platen 3 is placed flatly in the casing 2 . The print medium P is placed on an upper surface of the platen 3 . The four line heads 4 are provided above the platen 3 such that they are arranged in a front-rear direction. The conveyance roller 5 A is disposed on the front side of the platen 3 and the conveyance roller 5 B is disposed on the rear side of the platen 3 . The two conveyance rollers 5 A and 5 B are driven by a motor (not depicted) to convey the print medium P on the platen 3 rearward. Although the printing apparatus 1 includes the four line heads 4 in this embodiment, the number of the line heads 4 is not limited to four.

As depicted in FIG. 3 , the controller 7 includes a first substrate 71 . The first substrate 71 includes a Field Programmable Gate Array (FPGA) 771 , a Read Only Memory (ROM, not depicted in FIG. 3 ), a Random Access Memory (RAM, not depicted in FIG. 3 ), an Electrically Erasable Programmable Read-Only Memory (EEPROM) 712 , and the like. The controller 7 interacts or intercommunicates with an external apparatus 9 , such as a personal computer. When the controller 7 receives an instruction from the external apparatus 9 or an operation section (not depicted) provided for the printing apparatus 1 , the controller 7 controls operation of the line heads 4 and operation of the conveyance rollers 5 A, 5 B in accordance with a program(s) stored in the ROM. A Central Processing Unit (CPU) or a Microprocessor Unit (MPU) may be used instead of the FPGA 711 .

For example, the controller 7 controls the motor, which drives the conveyance rollers 5 A and 5 B, to cause the conveyance rollers 5 A and 5 B to convey the print medium P in the conveyance direction. Further, the controller 7 controls each line head 4 to discharge ink onto the print medium P. Accordingly, an image is printed on the print medium P. The print medium P may be a roll-shaped print medium including a supply roll that has an upstream end in the conveyance direction and a recovery roll that has a downstream end in the conveyance direction. In this case, the supply roll may be attached to the conveyance roller 5 A at the upstream side in the conveyance direction. The recovery roll may be attached to the conveyance roller 5 B at the downstream side in the conveyance direction. Or, the print medium P may be a roll-shaped sheet only including the supply roll that has the upstream end in the conveyance direction. In this case, the supply roll may be attached to the conveyance roller 5 A at the upstream side in the conveyance direction.

The casing 2 includes four head holding portions 8 corresponding to the four line heads 4 . The head holding portions 8 are arranged above the platen 3 in a position between the conveyance rollers 5 A and 5 B. The head holding portions 8 are arranged in the front-rear direction. Each of the head holding portions 8 holds the corresponding one of the line heads 4 .

The four line heads 4 respectively discharge inks of four colors of cyan (C), magenta (M), yellow (Y), and black (K). Each of the inks is supplied from corresponding one of ink tanks (not depicted) to corresponding one of the line heads 4 .

As depicted in FIG. 1 , each line head 4 of this embodiment includes ten heads 11 . The ten heads 11 are arranged zigzag in the medium width direction to form two arrays. Since one color of ink is supplied to one line head 4 , said one color of ink is discharged from the ten heads 11 included in said one line head 4 . In this embodiment, the line head 4 includes the ten heads 11 . The number of the heads 11 , however, is not limited to ten.

As depicted in FIG. 2 , 112 nozzles 11 a are opened in a bottom surface of each head 11 in this embodiment. The 112 nozzles 11 a form 28 nozzle arrays c 01 to c 28 arranged in the medium width direction. Each nozzle array is formed by four nozzles 11 a arranged zigzag in a direction intersecting with the conveyance direction and the medium width direction. Positions in the conveyance direction of the respective nozzles 11 a are defined as r 1 to r 4 from the front side toward the rear side in the conveyance direction. Each head 11 includes two manifolds (not depicted). Ink is supplied from one of the two manifolds to the nozzles 11 a forming the nozzle arrays r 1 and r 2 . Ink is supplied from the other of the two manifolds to the nozzles 11 a forming the nozzle arrays r 3 and r 4 . The position of each nozzle 11 a in each head 11 is uniquely specified by the nozzle array to which each nozzle 11 a belongs and the position in the conveyance direction. Although each head 11 includes the 112 nozzles 11 a in this embodiment, the number of nozzles 11 a is not limited to 112. Further, the number of nozzle arrays is not limited to 28, and the number of nozzles included in each nozzle array is not limited to four. The number of manifolds provided in each head 11 is not limited to two. One manifold may be provided for the nozzle arrays r 1 to r 4 , or each of the manifolds may be provided for the corresponding one of the nozzle arrays r 1 to r 4 (i.e., four in total).

Each head 11 includes the same number of driving elements 111 (described below) as the nozzles 11 a , a second substrate 50 , and a flexible circuit board 60 . The printing apparatus 1 of this embodiment includes the four line heads 4 . Each line head 4 includes the ten heads 11 . The printing apparatus 1 thus includes 40 heads 11 . Accordingly, the number of the second substrates 50 is 40, and the number of flexible circuit boards 60 connected to the second substrates 50 is 40. Although only one second substrate 50 and one flexible circuit board 60 are depicted in FIG. 3 for convenience, the first substrate 71 of the controller 7 is connected to the 40 second substrates 50 .

The second substrate 50 includes: a FPGA 51 , a non-volatile memory 52 such as an EEPROM, a D/A converter 20 , power supply circuits 21 to 26 , and the like. Although the second substrate 50 includes the six power supply circuits 21 to 26 in this embodiment, the number of the power supply circuits is not limited to six. The flexible circuit board 60 includes a non-volatile memory 62 such as an EEPROM, a driver IC 27 , and the like.

Under control of the FPGA 711 provided in the first substrate 71 , the FPGA 51 outputs, to the D/A converter 20 , a digital setting signal for setting an output voltage of each of the power supply circuits 21 to 26 .

The D/A converter 20 converts the digital setting signal output from the FPGA 51 into an analog setting signal, and then outputs it to each of the power supply circuits 21 to 26 .

Each of the power supply circuits 21 to 26 may be configured as a DC/DC converter made using electronic components, such as a FET, an inductor, a resistance, and an electrolytic capacitor. Each of the power supply circuits 21 to 26 outputs, to the driver IC 27 , the output voltage designated by the setting signal. All of the power supply circuits 21 to 26 are set to have different output voltages in this embodiment. Specifically, the output voltage of the power supply circuit 21 is 22 V, the output voltage of the power supply circuit 22 is 21 V, the output voltage of the power supply circuit 23 is 20 V, the output voltage of the power supply circuit 24 is 19 V, the output voltage of the power supply circuit 25 is 18 V, and the output voltage of the power supply circuit 26 is 24 V.

The power supply circuit 21 is connected to the driver IC 27 via a trace VDD 1 . The power supply circuit 22 is connected to the driver IC 27 via a trace VDD 2 . The power supply circuit 23 is connected to the driver IC 27 via a trace VDD 3 . The power supply circuit 24 is connected to the driver IC 27 via a trace VDD 4 . The power supply circuit 25 is connected to the driver IC 27 via a trace VDD 5 . The power supply circuit 26 is connected to the driver IC 27 via a trace HVDD. The power supply circuit 26 is connected to each driving element 111 described below via a trace VCOM. The traces HVDD and VCOM are branched from an intermediate portion of a trace that is pulled out from the power supply circuit 26 .

The power supply circuits 21 to 26 are respectively connected to waveform generating circuits 30 ( 1 ) to 30 ( n ) in the driver IC 27 (n is a natural number equal to or greater than 2, and n is equal to the number of the driving elements 111 in the head 11 (i.e., 112 ) in this embodiment).

The waveform generating circuits 30 ( 1 ) to 30 ( n ) are provided corresponding to n pieces of the driving element 111 in each head 11 . That is, the waveform generating circuits 30 ( 1 ) to 30 ( n ) are provided corresponding to n pieces of the nozzle 11 a in each head 11 . The driver IC 27 is connected to n pieces of signal line 34 ( 1 ) to 34 ( n ). The driver IC 27 is connected to n pieces of the driving element 111 via n pieces of the signal line 34 ( 1 ) to 34 ( n ). Each signal line 34 is connected to an individual electrode of the corresponding driving element 111 .

The driver IC 27 includes n pieces of selector 90 ( 1 ) to 90 ( n ) provided corresponding to n pieces of the driving element 111 . The respective selectors 90 are components of hardware that is configured, for example, by a plurality of FETs formed in the driver IC 27 .

The power supply circuit 26 can be used as a power supply voltage for the VCOM of the driving elements 111 , or can be used as a high-side back gate voltage (HVDD) of PMOS transistors 311 to 315 described below.

The non-volatile memory 62 stores nozzle IDs for identifying the respective nozzles 11 a , group IDs for identifying nozzle groups (described below) formed by the nozzles 11 a , column IDs for identifying the nozzle arrays, row IDs for identifying positions in the conveyance direction of the nozzles 11 a , and the like. Further, for example, as depicted in FIG. 8 , a correspondence between n pieces of the nozzle 11 a and the five power supply circuits 21 to 25 , a correspondence between n pieces of the nozzle 11 a and the groups (group IDs) g 10 to g 70 , a correspondence between n pieces of the nozzle 11 a and the nozzle arrays (columns IDs) c 01 to c 70 , a correspondence between n pieces of the nozzle 11 a and the positions in the conveyance direction (row IDs) r 01 to r 24 , and the like are stored as a table T in the non-volatile memory 52 . The table T may be stored in the non-volatile memory 62 provided in the flexible circuit board 60 instead of being stored in the non-volatile memory 52 .

The driver IC 27 is connected to the FPGA 51 via a control line 40 and n pieces of control line 33 ( 1 ) to 33 ( n ). The control lines 33 ( 1 ) to 33 ( n ) are provided corresponding to n pieces of the waveform generating circuit 30 ( 1 ) to 30 ( n ). A signal for controlling the FET provided for each waveform generating circuit 30 is transmitted to each control line 33 . Each waveform generating circuit 30 generates a driving signal for driving each driving element 111 in accordance with the above signal, and the driving signal generated is output to each driving element 111 via the corresponding signal line 34 .

A control signal for controlling n pieces of the selector 90 ( 1 ) to 90 ( n ) in the driver IC 27 is transmitted to the control line 40 . The FPGA 51 controls n pieces of the selector 90 ( 1 ) to 90 ( n ) and selects a power supply circuit for generating the driving signal to be output to each signal line 34 .

Referring to FIG. 4 , an exemplary configuration of the circuit in the driver IC 27 is explained below. As depicted in FIG. 4 , the driver IC 27 includes n pieces of the waveform generating circuit 30 ( 1 ) to 30 ( n ), and n pieces of the selector 90 ( 1 ) to 90 ( n ) provided corresponding to the waveform generating circuits 30 ( 1 ) to 30 ( n ), respectively.

The driver IC 27 includes n pieces of the above configuration, the number of which is the same as the number of nozzles. Thus, the configuration of the circuit disposed between the control line 33 ( 1 ) and the signal line 34 ( 1 ) is explained below, as a representative. In the driver IC 27 , the selector 90 ( 1 ) and the waveform generating circuit 30 ( 1 ) are formed between the control line 33 ( 1 ) and the signal line 34 ( 1 ).

The control line 33 ( 1 ) from the FPGA 51 is connected to the selector 90 ( 1 ). The control line 33 ( 1 ) is branched from an intermediate portion of a route connecting the FPGA 51 and the selector 90 ( 1 ), and a control line SB( 1 ) branched from the intermediate portion of the control line 33 ( 1 ) is connected to the waveform generating circuit 30 ( 1 ).

The selector 90 ( 1 ) is connected to the waveform generating circuit 30 ( 1 ) via five control lines S 1 ( 1 ), S 2 ( 1 ), S 3 ( 1 ), S 4 ( 1 ), and S 5 ( 1 ). The selector 90 ( 1 ) selects any one of the five control lines S 1 ( 1 ), S 2 ( 1 ), S 3 ( 1 ), S 4 ( 1 ), and S 5 ( 1 ) in accordance with an instruction from the FPGA 51 , and connects the selected line to the control line 33 ( 1 ).

The waveform generating circuit 30 ( 1 ) is connected to five traces connected to the traces VDD 1 to VDD 5 , a trace connected to the trace HVDD, and a trace connected to a trace GND.

Referring to FIG. 5 , an exemplary circuit configuration of the waveform generating circuits 30 ( 1 ) to 30 ( n ) provided for the head 11 according to this embodiment is explained below. Since the waveform generating circuits 30 ( 1 ) to 30 ( n ) have the same configuration, only the waveform generating circuit 30 ( 1 ) is explained. The waveform generating circuit 30 ( 1 ) includes five P-type Metal Oxide Semiconductor (PMOS) transistors 311 to 315 (only two transistors are depicted in FIG. 5 ), a N-type Metal Oxide Semiconductor (NMOS) transistor 32 , a resistance 35 , and the like. The waveform generating circuit 30 ( 1 ) is connected to the individual electrode of the driving element 111 via the signal line 34 ( 1 ).

Each driving element 111 of this embodiment is a piezoelectric element including a first active portion interposed between the individual electrode and a first constant potential electrode and a second active portion interposed between the individual electrode and a second constant potential electrode. Each of the driving elements 111 corresponds to one of pressure chambers. Each driving electrode 111 thus includes a capacitor 111 b and a capacitor 111 b′.

Five source terminals 311 a to 315 a of the PMOS transistors 311 to 315 are connected to the traces VDD 1 to VDD 5 . A source terminal 32 a of the NMOS transistor 32 is connected to ground. That is, the PMOS transistor 311 is connected to the power supply circuit 21 via the trace VDD 1 . The PMOS transistor 312 is connected to the power supply circuit 22 via the trace VDD 2 . The PMOS transistor 313 is connected to the power supply circuit 23 via the trace VDD 3 . The PMOS transistor 314 is connected to the power supply circuit 24 via the trace VDD 4 . The PMOS transistor 315 is connected to the power supply circuit 25 via the trace VDD 5 .

The control line S 1 ( 1 ) is connected to a gate terminal 311 c of the PMOS transistor 311 . The control line S 2 ( 1 ) is connected to a gate terminal 312 c of the PMOS transistor 312 . The control line S 3 ( 1 ) is connected to a gate terminal 313 c of the PMOS transistor 313 . The control line S 4 ( 1 ) is connected to a gate terminal 314 c of the PMOS transistor 314 . The control line S 5 ( 1 ) is connected to a gate terminal 315 c of the PMOS transistor 315 . The control line SB( 1 ) is connected to a gate terminal 32 c of the NMOS transistor 32 .

Drain terminals 311 b to 315 b of the five PMOS transistors 311 to 315 are connected to a first end of the resistance 35 . A drain terminal 32 b of the NMOS transistor 32 is connected to the first end of the resistance 35 . A second end of the resistance 35 is connected to the individual electrode of the driving element 111 (a second end of the capacitor 111 b ′ and a first end of the capacitor 111 b ). The first constant potential electrode of the driving element 111 (a first end of the capacitor 111 b ′) is connected to the VCOM, and the second constant potential electrode of the driving element 111 (a second end of the capacitor 111 b ) is connected to ground.

When the FPGA 51 outputs a low-level signal (L signal) to the control line 33 ( 1 ), any one of the PMOS transistors 311 to 315 connected to the signal line selected by the selector 90 ( 1 ) becomes an on state. The capacitor 111 b is charged with a voltage supplied from any one of the power supply circuits 21 to 25 , and the capacitor 111 b ′ is discharged. When the FPGA 51 outputs a high-level signal (H signal) to the control line 33 ( 1 ), the NMOS transistor 32 becomes an on state. The capacitor 111 b ′ is charged with a voltage output from any one of the power supply circuits 21 to 25 , and the capacitor 111 b is discharged. The driving element 111 is deformed by alternatingly charging and discharging each of the capacitors 111 b and 111 b ′, which discharges or ejects ink from an opening of the corresponding nozzle 11 a.

That is, the driving signal for driving the driving element 111 is output to the control line 34 ( 1 ). The selector 90 ( 1 ) selects any one of the five control lines S 1 ( 1 ) to S 5 ( 1 ) as the control line to be connected to the control line 33 ( 1 ), which allows any one of the five power supply circuits 21 to 25 to be selected as the power supply circuit for generating the driving signal.

Subsequently, a printing method using the printing apparatus 1 of this embodiment is explained below. As depicted in FIG. 6 , the printing method using the printing apparatus 1 of this embodiment mainly includes a temporary setting step S 10 , a test printing step S 20 , a setting adjustment step S 30 , and a main printing step S 40 .

In the temporary setting step S 10 , as depicted in FIG. 7 , the 112 nozzles 11 a are classified into the seven groups g 10 to g 70 for every 4 nozzle arrays. That is, the nozzles 11 a belonging to the nozzle arrays c 01 to c 04 are associated with the group g 10 . The nozzles 11 a belonging to the nozzle arrays c 05 to c 08 are associated with the group g 20 . The nozzles 11 a belonging to the nozzle arrays c 09 to c 12 are associated with the group g 30 . The nozzles 11 a belonging to the nozzle arrays c 13 to c 16 are associated with the group g 40 . The nozzles 11 a belonging to the nozzle arrays c 17 to c 20 are associated with the group g 50 . The nozzles 11 a belonging to the nozzle arrays c 21 to c 24 are associated with the group g 60 . The nozzles 11 a belonging to the nozzle arrays c 25 to c 28 are associated with the group g 70 . The group g 10 is adjacent to the group g 20 in the medium width direction. The group g 30 is adjacent to the group g 20 in the medium width direction at a side opposite to the group g 10 . In this embodiment, the number of the power supply circuits 21 to 26 is six, which is smaller than the number of groups g 10 to g 70 (i.e., seven). The number of the power supply circuits, however, may be the same as the number of the groups.

Subsequently, any of the power supply circuits 21 to 25 is associated with each of the groups so that the seven groups have uniform density of dots formed by ink droplets discharged from the nozzles 11 a . For example, the power supply circuit 21 is associated with the nozzles 11 a forming the groups g 10 , g 20 , g 60 , and g 70 , the power supply circuit 22 is associated with the nozzles 11 a forming groups g 30 and g 50 , and the power supply circuit 23 is associated with the nozzles 11 a forming the group g 40 . The discharge characteristics of 112 nozzles 11 a are affected by a slight error in a diameter of the nozzles 11 a , a manufacturing error in the driving elements 111 , residual stress in the heads 11 generated at the time of manufacture, and the like, which gradually changes the discharge characteristics of 112 nozzles 11 a depending on the positions in the medium width direction and the conveyance direction. Thus, even if the same power supply circuit is associated with the nozzles 11 a forming all the groups (i.e., the groups g 10 to g 70 ), the density of dots formed by ink droplets is not necessarily uniform.

Then, as depicted in FIG. 8 , information about the positions (column ID, row ID) of the nozzle 11 a , the group to which the nozzle 11 a belongs, and the power supply circuit associated with the nozzle 11 a is stored in the non-volatile memory 52 for each of the 112 nozzles 11 a . In FIG. 8 , v 01 to v 05 indicate identifies of the power supply circuits 21 to 25 .

In the test printing step S 20 , test printing is executed on the print medium P in accordance with the association of the power supply circuit with each nozzle 11 a set in the temporary setting step S 10 . Specifically, a voltage is supplied from the power supply circuit 21 to the driving elements 111 corresponding to the nozzles 11 a included in the group g 10 . A voltage is supplied from the power supply circuit 22 to the driving elements 111 corresponding to the nozzles 11 a included in the group g 20 . A voltage is supplied from the power supply circuit 23 to the driving elements 111 corresponding to the nozzles 11 a included in the groups g 30 to g 50 . A voltage is supplied from the power supply circuit 24 to the driving elements 111 corresponding to the nozzles 11 a included in the group g 60 . A voltage is supplied from the power supply circuit 25 to the driving elements 111 corresponding to the nozzles 11 a included in the group g 70 . Test printing is executed on the print medium P by discharging ink droplets from the 112 nozzles 11 a included in the groups g 10 to g 70 .

In the setting adjustment step S 30 , the association of the power supply circuit with each nozzle 11 a set in the temporary setting step S 10 is corrected based on the printing result in the test printing step S 20 . In the temporary setting step S 10 , the power supply circuits are associated with the nozzles for each group. Thus, in two groups adjacent to each other in the medium width direction, a density difference that can be seen with the naked eye may be caused between dots formed by ink droplets discharged from the nozzles 11 a belonging to one of the two groups and dots formed by ink droplets discharged from the nozzles 11 a belonging to the other. In view of this, in the setting adjustment step S 30 , a user observes the printing result in the test printing step S 20 with the naked eye, and determines whether the density difference is generated in the two groups adjacent to each other in the medium width direction. When such a density difference is not generated (when the user sees no density difference with the naked eye), the association of the power supply circuits with the nozzles executed in the temporary setting step S 10 is maintained, and the main printing step S 40 is executed. When the density difference is generated (when the user sees the density difference with the naked eye), the association of the power supply circuits with the nozzles executed in the temporary setting step S 10 is adjusted. A specific example thereof is explained below.

For example, when the user notices that the density difference is generated between the groups g 10 and g 20 and between the groups g 20 and g 30 depicted in FIG. 7 by observing the printing result in the test printing step S 20 with the naked eye, the association of the power supply circuits with the nozzles 11 a belonging to the groups g 10 , g 20 , and g 30 is adjusted. For example, as depicted in FIG. 9A , in the group g 10 , the power supply circuit 21 associated with the nozzles 11 a forming the nozzle array r 4 is changed to the power supply circuit 22 having an output voltage that is the next smallest after the power supply circuit 21 . In the group g 20 , the power supply circuit 21 associated with the nozzles 11 a forming the nozzle array r 3 and the nozzle array r 4 is changed to the power supply circuit 22 . In the group g 30 , the power supply circuit 22 associated with the nozzles 11 a forming the nozzle array r 1 is changed to the power supply circuit 21 . As described above, the output voltages of the power supply circuits 21 to 25 are different from each other. The output voltage is sequentially decreased in the order of the power supply circuits 21 , 22 , 23 , 24 , and 25 (i.e., the power supply circuit 21 has the largest output voltage). Thus, in this embodiment, different natural numbers are associated with the power supply circuits 21 to 25 . For example, a natural number n is associated with the power supply circuit 21 , a natural number m different from the natural number n is associated with the power supply circuit 22 , and a natural number I different from the natural numbers n and m is associated with the power supply circuit 23 . Specifically, natural numbers 1 to 5 are associated with the power supply circuits 21 to 25 . In FIG. 9A , a number in each circle indicating one of nozzles 11 a indicates a natural number associated with the power supply circuit that is associated with the one of nozzles 11 a . The power supply circuit associated with the nozzle is changed by rewriting a power supply circuit ID of the corresponding nozzle 11 a . The power supply circuit ID is stored in the non-volatile memory 52 depicted in FIG. 8 .

That is, in the setting adjustment step S 30 , the association of the power supply circuits with the nozzles is adjusted so that each of the groups g 10 to g 30 is formed by the nozzles 11 a associated with the power supply circuit 21 and the nozzles 11 a associated with the power supply circuit 22 . Specifically, the group g 10 includes 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 and four nozzles 11 a forming the nozzle array r 4 . The power supply circuit 21 is associated with the 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 , and thus the natural number 1 is associated with the 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 . The power supply circuit 22 is associated with the four nozzles 11 a forming the nozzle array r 4 , and thus the natural number 2 is associated with the four nozzles 11 a forming the nozzle array r 4 . As a result, an average value A1 of the natural numbers associated with 16 nozzles 11 a forming the group g 10 is 1.25 (=(12+8)/16).

The group g 20 includes eight nozzles 11 a forming the nozzle arrays r 1 and r 2 and eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . The power supply circuit 21 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 , and thus the natural number 1 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 . The power supply circuit 22 is associated with eight nozzles 11 a forming the nozzle arrays r 3 and r 4 , and thus the natural number 2 is associated with the eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . As a result, an average value A2 of the natural numbers associated with 16 nozzles 11 a forming the group g 20 is 1.5 (=(8+16)/16).

The group g 30 includes four nozzles 11 a forming the nozzle array r 1 and 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 . The power supply circuit 21 is associated with the four nozzles 11 a forming the nozzle array r 1 , and thus the natural number 1 is associated with the four nozzles 11 a forming the nozzle array r 1 . The power supply circuit 22 is associated with 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 , and thus the natural number 2 is associated with the 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 . As a result, an average value A3 of the natural numbers associated with 16 nozzles 11 a forming the group g 30 is 1.75 (=(4+24)/16).

In the above setting adjustment step S 30 , the average value A1 (=1.25) of the values associated with the nozzles 11 forming the group g 10 is different from the average value A2 (=1.5) of the values associated with the nozzles 11 forming the group g 20 , and an absolute value of a difference between the average value A1 and the average value A2 is less than one. Further, the average value A2 (=1.5) of the values associated with the nozzles 11 a forming the group g 20 is different from the average value A3 (=1.75) of the values associated with the nozzles 11 a forming the group g 30 , and an absolute value of a difference between the average value A2 and the average value A3 is less than one. The average value A2 is a value between the average values A1 and A3.

In the main printing step S 40 , a voltage is supplied to the driving element 111 corresponding to each nozzle 11 a in accordance with the association information of the power supply circuit stored in the non-volatile memory 52 . Then, printing is executed on the print medium P by discharging ink droplets from the 112 nozzles 11 a included in the groups g 10 to g 70 .

For example, one dot array extending in the medium conveyance direction as depicted in FIG. 9B is formed on the print medium P by discharging ink droplets from the nozzles 11 a belonging to the groups g 10 to g 30 . In FIG. 9B , one dot formed by an ink droplet discharged from one nozzle 11 a is indicated by one circle. White circles indicate dots formed by ink droplets discharged from the nozzles 11 a with which the natural number 1 is associated (hereinafter referred to as “dot 1”). Hatched circles indicate dots formed by ink droplets discharged from the nozzles 11 a with which the natural number 2 is associated (hereinafter referred to as “dot 2”).

As depicted in FIG. 9B , the group g 10 includes patterns (hereinafter referred to as “patterns 1112 ”) each of which is formed by three dots 1 and one dot 2. The pattern 1112 is repeated (periodically) four times in the medium width direction so that the patterns 1112 are arranged in the medium width direction. The group g 20 includes patterns (hereinafter referred to as “patterns 12 ”) each of which is formed by one dot 1 and one dot 2. The pattern 12 is repeated (periodically) eight times in the medium width direction so that the patterns 12 are arranged in the medium width direction. The group g 30 includes patterns (hereinafter referred to as “patterns 1222 ”) each of which is formed by one dot 1 and three dots 2. The pattern 1222 is repeated (periodically) four times in the medium width direction so that the patterns 1222 are arranged in the medium width direction. In this embodiment, the pattern 1112 is repeated every 0.084 mm in the group g 10 , the pattern 12 is repeated every 0.042 mm in the group g 20 , and the pattern 1222 is repeated every 0.084 mm in the group g 30 . Experiments performed by the inventors(s) revealed that human beings can not notice the patterns repeated periodically when the patterns are repeated every 0.16 mm or less. However, it is desired that the patterns are repeated every 0.1 mm or less.

In the above specified example, the group g 10 is an exemplary “first group” of the present disclosure, the group g 20 is an exemplary “second group” of the present disclosure, and the group g 30 is an exemplary “third group” of the present disclosure. In the temporary setting step S 10 , the power supply circuit 21 associated with the groups g 10 and g 20 is an exemplary “first power supply circuit” of the present disclosure, and the power supply circuit 22 associated with the group g 30 is an exemplary “second power supply circuit” of the present disclosure. A dot array formed by discharging ink droplets from all the nozzles 11 a forming the group g 10 is an exemplary “first dot array” of the present disclosure. A dot array formed by discharging ink droplets from all the nozzles 11 a forming the group g 20 is an exemplary “second dot array” of the present disclosure. Further, the pattern 1112 is an exemplary “first pattern” of the present disclosure, and the pattern 12 is an exemplary “second pattern” of the present disclosure.

In the above embodiment, when the user notices that the density difference is generated in two groups adjacent to each other in the medium width direction by observing the printing result in the test printing step S 20 with the naked eye, the association of the power supply circuits with some of the nozzles forming each group is changed. Specifically, in each group, a certain power supply circuit associated with some of the nozzles 11 a in the temporary setting step S 10 is changed to a power supply circuit in which output voltage is the next smallest after the certain power supply circuit, or to a power supply circuit in which output voltage is the next largest after the certain power supply circuit. This reduces a density difference between dots formed by nozzles belonging to the same group and reduces a density difference between two groups adjacent to each other in the medium width direction without changing the output voltage of each power supply circuit.

In the above embodiment, in two groups adjacent to each other in the medium width direction, the average value A1 of the values of the natural numbers associated with the nozzles 11 a forming one of the two groups is different from the average value A2 of the values of the natural numbers associated with the nozzles 11 a forming the other. The absolute value of the difference between the average value A1 and the average value A2 is less than one. Thus, it is possible to execute the adjustment more accurately than a case where the same power supply circuit is associated with the nozzles 11 a forming each group (i.e., the case of the temporary setting step S 10 ).

In the above embodiment, when the first group, the second group, and the third group are adjacent to each other in the medium width direction in this order, the average value A2 of the values of the natural numbers associated with the nozzles 11 a forming the second group is a value between the average value A1 of the values of the natural numbers associated with the nozzles 11 a forming the first group and the average value A3 of the values of the natural numbers associated with the nozzles 11 a forming the third group. This can smoothly alleviate distribution tendency of the density difference in the head 11 .

In the above embodiment, for example, the pattern 1112 is repeated at the interval of 0.084 mm in the group g 10 , the pattern 12 is repeated at the interval of 0.042 mm in the group g 20 , and the pattern 1222 is repeated at the interval of 0.084 mm in the group g 30 . That is, in each group, the patterns are repeated periodically at intervals of equal to or less than 0.1 mm. Thus, even when the patterns are repeated periodically, it is not perceptible as density unevenness by human vision.

The embodiment as described above is merely an example of the present disclosure, and may be modified as appropriate. For example, in each group, the number of the nozzles 11 a for which the exchange of the power supply circuits is executed and the positions of the nozzles 11 a for which the exchange of the power supply circuits is executed may be changed appropriately. In the above embodiment, the pattern 1112 is repeated four times in the group g 10 , and the pattern 12 is repeated eight times in the group g 20 . The present disclosure, however, is not limited thereto. The pattern 1112 may be repeated in at least part of the dot array formed by discharging ink droplets from all the nozzles forming the group g 10 , and the pattern 12 may be repeated in at least part of the dot array formed by discharging ink droplets from all the nozzles forming the group g 20 .

In the above embodiment, the 112 nozzles 11 a included in each head 11 are classified into the seven groups in the medium width direction. The present disclosure, however, is not limited thereto. The 112 nozzles 11 a included in each head 11 may be further divided in the conveyance direction. For example, as depicted in FIG. 10 , the 112 nozzles 11 a included in each head 11 may be divided into groups g 10 to g 70 at the front side in the conveyance direction and groups g 80 to g 140 at the rear side in the conveyance direction by further dividing the 112 nozzles 11 a included in each head 11 in the conveyance direction. That is, the groups g 10 to g 70 are respectively adjacent to the groups g 80 to g 140 in the conveyance direction. In this case, it is possible to reduce the density difference between two groups adjacent to each other in the conveyance direction by adjusting the association of the power supply circuits with the nozzles similarly to the above embodiment, not only in the two groups adjacent to each other in the medium width direction but also in the two groups adjacent to each other in the conveyance direction. In this modified example, the group g 10 is an exemplary “first group” of the present disclosure, the group g 20 is an exemplary “second group” of the present disclosure, the group g 80 is an exemplary “fourth group” of the present disclosure, and the group g 90 is an exemplary “fifth group” of the present disclosure.

In the modified example depicted in FIG. 10 , the group g 10 includes eight nozzles 11 a forming the nozzle arrays r 1 and r 2 . The power supply circuit 21 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 , and thus the natural number 1 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 . As a result, the average value A1 of the natural numbers associated with the eight nozzles 11 a forming the group g 10 is 1 (=8/8). The same is applied to the group g 20 , that is, the average value A2 of the natural numbers is 1 (=8/8). The group g 30 includes four nozzles 11 a forming the nozzle array r 1 and four nozzles 11 a forming the nozzle array r 2 . The power supply circuit 21 is associated with the four nozzles 11 a forming the nozzle array r 1 , and thus the natural number 1 is associated with the four nozzles 11 a forming the nozzle array r. Further, the power supply circuit 22 is associated with the four nozzles 11 a forming the nozzle array r 2 , and thus the natural number 2 is associated with the four nozzles 11 a forming the nozzle array r 2 . As a result, the average value A3 of the natural numbers associated with the eight nozzles 11 a forming the group g 30 is 1.5 (=(4+8)/8). The group g 80 includes eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . The power supply circuit 21 is associated with four nozzles 11 a forming the nozzle array r 3 , and thus the natural number 1 is associated with the four nozzles 11 a forming the nozzle array r 3 . Further, the power supply circuit 22 is associated with four nozzles 11 a forming the nozzle array r 4 , and thus the natural number 2 is associated with the four nozzles 11 a forming the nozzle array r 4 . As a result, the average value A4 of the natural numbers associated with the eight nozzles 11 a forming the group g 80 is 1.5 (=(4+8)/8). The group g 90 includes eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . The power supply circuit 21 is associated with two nozzles 11 a forming the nozzle array r 3 , and thus the natural number 1 is associated with the two nozzles 11 a forming the nozzle array r 3 . The power supply circuit 22 is associated with two nozzles 11 a forming the nozzle array r 3 and four nozzles 11 a forming the nozzle array r 4 , and thus the natural number 2 is associated with the two nozzles 11 a forming the nozzle array r 3 and the four nozzles 11 a forming the nozzle array r 4 . As a result, the average value A5 of the natural numbers associated with the eight nozzles 11 a forming the group g 90 is 1.75 (=14/8). The group g 100 includes eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . The power supply circuit 22 is associated with the eight nozzles 11 a forming the nozzle arrays r 3 and r 4 , and thus the natural number 2 is associated with the eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . As a result, the average value A6 of the natural numbers associated with the eight nozzles 11 a forming the group g 100 is 2 (=16/8). Thus, a difference between the average values A4 and A1 and a difference between the average values A5 and A2 have the same code (positive values in this modified example). Further, the difference between the average values A5 and A2 and a difference between the average values A6 and A3 have the same code (positive values in this modified example).

In the above embodiment, only one color of ink is discharged from one head 11 . The present disclosure, however, is not limited thereto. For example, as depicted in FIG. 11 , one head 11 may include eight nozzle arrays arranged in the conveyance direction. The black ink may be discharged from four nozzle arrays r 1 to r 4 positioned at the front side in the conveyance direction and the cyan ink may be discharged from four nozzle arrays r 5 to r 8 positioned at the rear side in the conveyance direction. In this case, the head 11 includes a first manifold, a second manifold, a third manifold, and a fourth manifold (the manifolds are not depicted in the drawings). The black ink is supplied from the first manifold to the two nozzle arrays r 1 and r 2 . The black ink is supplied from the second manifold to the two nozzle arrays r 3 and r 4 . The cyan ink is supplied from the third manifold to the two nozzle arrays r 5 and r 6 . The cyan ink is supplied from the fourth manifold to the two nozzle arrays r 7 and r 8 . Similar to the above embodiment, the nozzles 11 a forming the four nozzle arrays positioned at the front side in the conveyance direction may be classified into seven groups g 10 to g 70 in the medium width direction, and the nozzles 11 a forming the four nozzle arrays positioned at the rear side in the conveyance direction may be classified into seven groups g 80 to g 140 in the medium width direction. Then, the association of the power supply circuits with the groups g 10 to g 70 may be adjusted similarly to the above embodiment, and the association of the power supply circuits with the groups g 80 to g 140 may be adjusted similarly to the above embodiment. In this modified example, the black ink is an exemplary “first liquid” of the present disclosure, and the cyan ink is an exemplary “second liquid” of the present disclosure. In this modified example, the magenta ink may be used instead of the black ink, and the yellow ink may be used instead of the cyan ink.

In the modified example depicted in FIG. 11 , the group g 10 includes 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 and four nozzles 11 a forming the nozzle array r 4 . The power supply circuit 21 is associated with the 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 , and thus the natural number 1 is associated with the 12 nozzles 11 a forming the nozzle arrays r 1 to r 3 . The power supply circuit 22 is associated with the four nozzles 11 a forming the nozzle array r 4 , and thus the natural number 2 is associated with the four nozzles 11 a forming the nozzle array r 4 . As a result, the average value A1 of the natural numbers associated with the 16 nozzles 11 a forming the group g 10 is 1.25 (=(12+8)/16). The group g 20 includes eight nozzles 11 a forming the nozzle arrays r 1 and r 2 and eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . The power supply circuit 21 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 , and thus the natural number 1 is associated with the eight nozzles 11 a forming the nozzle arrays r 1 and r 2 . The power supply circuit 22 is associated with the eight nozzles 11 a forming the nozzle arrays r 3 and r 4 , and thus the natural number 2 is associated with the eight nozzles 11 a forming the nozzle arrays r 3 and r 4 . As a result, the average value A2 of the natural numbers associated with the 16 nozzles 11 a forming the group g 20 is 1.5 (=(8+16)/16). The group g 30 includes four nozzles 11 a forming the nozzle array r 1 and 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 . The power supply circuit 21 is associated with the four nozzles 11 a forming the nozzle array r 1 , and thus the natural number 1 is associated with the four nozzles 11 a forming the nozzle array r 1 . The power supply circuit 22 is associated with the 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 , and thus the natural number 2 is associated with the 12 nozzles 11 a forming the nozzle arrays r 2 to r 4 . As a result, the average value A3 of the natural numbers associated with the 16 nozzles 11 a forming the group g 30 is 1.75 (=(4+24)/16). The group g 80 includes four nozzles 11 a forming the nozzle array r 5 and 12 nozzles 11 a forming the nozzle arrays r 6 to r 8 . The power supply circuit 21 is associated with the four nozzles 11 a forming the nozzle array r 5 , and thus the natural number 1 is associated with the four nozzles 11 a forming the nozzle array r 5 . The power supply circuit 22 is associated with the 12 nozzles 11 a forming the nozzle arrays r 6 to r 8 , and thus the natural number 2 is associated with the 12 nozzles 11 a forming the nozzle arrays r 6 to r 8 . As a result, the average value A4 of the natural numbers associated with the 16 nozzles 11 a forming the group g 80 is 1.75 (=(4+24)/16). The group g 9 ) includes 12 nozzles 11 a forming the nozzle arrays r 5 to r 7 and four nozzles 11 a forming the nozzle array r 8 . The power supply circuit 22 is associated with the 12 nozzles 11 a forming the nozzle arrays r 5 to r 7 , and thus the natural number 2 is associated with the 12 nozzles 11 a forming the nozzle arrays r 5 to r 7 . The power supply circuit 23 is associated with the four nozzles 11 a forming the nozzle array r 8 , and thus the natural number 3 is associated with the four nozzles 11 a forming the nozzle array r 8 . As a result, the average value A5 of the natural numbers associated with the 16 nozzles 11 a forming the group g 90 is 2.25 (=(24+12)/16). The group g 100 includes eight nozzles 11 a forming the nozzle arrays r 5 and r 6 and eight nozzles 11 a forming the nozzle arrays r 7 and r 8 . The power supply circuit 22 is associated with the eight nozzles 11 a forming the nozzle arrays r 5 and r 6 , and thus the natural number 2 is associated with the eight nozzles 11 a forming the nozzle arrays r 5 and r 6 . The power supply circuit 23 is associated with the eight nozzles 11 a forming the nozzle arrays r 7 and r 8 , and thus the natural number 3 is associated with the eight nozzles 11 a forming the nozzle arrays r 7 and r 8 . As a result, the average value A6 of the natural numbers associated with the 16 nozzles 11 a forming the group g 100 is 2.5 (=(16+24)/16). Thus, a difference between the average value A4 and the average value A1, a difference between the average value A5 and the average value A2, and a difference between the average value A6 and the average value A3 have the same code (positive values in this modified example). According to this modified example, also in a head capable of discharging two inks that are greatly different in physical properties such as viscosity from each other, it is possible to reduce a density difference between two groups adjacent to each other in the medium width direction. In this modified example, the power supply circuit 23 associated with the natural number 3 is an exemplary “third power supply circuit” of the present disclosure.

In the above embodiment, the association of the power supply circuits with the nozzles is temporarily set in the temporary setting step S 10 , and test printing is executed in the test printing step S 20 . Then, in the setting adjustment step S 30 , the association of the power supply circuits with the nozzles is adjusted based on the printing result of the test printing step S 20 . The present disclosure, however, is not limited thereto. For example, after the temporary setting step S 10 , the main printing step S 40 may be executed without executing the test printing step S 20 and the setting adjustment step S 30 . During the main printing step S 40 , the association of the power supply circuits with the nozzles may be adjusted depending on the printing result. In this case, a density sensor may be provided at a downstream side of the four line heads 4 in the conveyance direction, and the density sensor may detect density at positions in the medium width direction during main printing. When a density difference between two groups adjacent to each other in the medium width direction exceeds a predefined threshold value, the association of the power supply circuits with some of the nozzles belonging to said two groups may be changed.

In the above embodiment and the modified examples, the nozzle arrays are arranged in the conveyance direction in the head 11 . The present disclosure, however, is not limited thereto. For example, as depicted in FIG. 12 , only one nozzle array may be formed along the medium width direction in the head 11 . The one nozzle array may be divided into seven groups g 10 to g 70 in the medium width direction.

In the above embodiment, the printing apparatus 1 executes printing on the print medium P by a line head system in which ink is discharged from the line heads 4 that are fixed to the printing apparatus 1 and that are long in the medium width direction. However, the printing apparatus 1 may execute printing on the print medium P by a serial head system in which the heads 11 are carried on a carriage to move in the medium width direction together with the carriage.

In the above embodiment, the print medium P is conveyed with the line heads 4 being fixed to the printing apparatus 1 . The present disclosure, however, is not limited thereto. It is only required that the print medium P moves relative to the line heads 4 . For example, the line heads 4 may be configured to move relative to the fixed print medium P.