Inkjet Head

Abstract

Provided is an inkjet head that suppresses the generation of small droplets. The inkjet head includes: a pressure chamber that contains ink; a nozzle plate that includes a nozzle that communicates with the pressure chamber; an actuator that is provided corresponding to the pressure chamber and displaces the volume of the pressure chamber; and a drive circuit that drives the actuator. The drive circuit drives the actuator with a drive waveform that includes an expansion waveform, a contraction waveform, a first weak contraction waveform, and a second weak contraction waveform.

Description

Technical Field

[0001] An embodiment of the present invention relates to an inkjet head. Background Art

[0002] In an inkjet head, small droplets called satellite droplets or ink mist are sometimes generated along with the main ink droplets (main droplets) ejected from the nozzle. Such small droplets lead to a decrease in print quality. Therefore, it is required to develop an inkjet head that suppresses the generation of small droplets. Summary of the invention

[0003] Technical problem to be solved by the invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide an inkjet head that suppresses the generation of small liquid droplets.

[0005] Technical solutions to solve problems

[0006] In one embodiment, the inkjet head includes: a pressure chamber that contains ink; a nozzle plate that includes a nozzle that is connected to the pressure chamber; an actuator that is arranged corresponding to the pressure chamber and displaces the volume of the pressure chamber; and a drive circuit that drives the actuator. The drive circuit drives the actuator with a drive waveform, and the drive waveform includes an expansion waveform, a contraction waveform, a first weak contraction waveform, and a second weak contraction waveform. The expansion waveform is a waveform that drives the actuator in the direction of expansion of the volume of the pressure chamber. The contraction waveform is a waveform that drives the actuator in the direction of contraction of the volume of the pressure chamber. The first weak contraction waveform is located between the expansion waveform and the contraction waveform. The first weak contraction waveform is a waveform that drives the actuator in the direction of contraction of the volume of the pressure chamber weaker than the contraction caused by the contraction waveform. The second weak contraction waveform is located after the contraction waveform. The second weak contraction waveform is a waveform that drives the actuator in the direction of contraction of the volume of the pressure chamber weaker than the contraction caused by the contraction waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a perspective view showing an inkjet head according to one embodiment.

[0008] Figure 2 It is a top view showing the main body of the inkjet head.

[0009] Figure 3 This is an AA longitudinal cross-sectional view of the main body of the inkjet head.

[0010] Figure 4 It is a BB longitudinal cross-sectional view of the main body of the inkjet head.

[0011] Figure 5 This is a diagram for explaining the operating principle of the inkjet head.

[0012] Figure 6 This is a block diagram showing the hardware structure of an inkjet printer.

[0013] Figure 7 This is a diagram showing the circuit configuration of a main part of a head driving circuit in the inkjet printer.

[0014] Figure 8 1 is a block diagram showing a circuit configuration of a main part of a waveform generating circuit included in the head driving circuit.

[0015] Fig. 9 1 is a diagram showing the correspondence between the state data and the drive pattern data related to the waveform generating circuit.

[0016] Fig.10 It is an explanatory diagram of the driving waveform used in this embodiment.

[0017] Fig.11 It is a timing chart showing a driving waveform, a pressure waveform of a pressure chamber, and a flow velocity waveform of ink.

[0018] Fig.12 This is an explanatory diagram of a driving waveform used when forming one dot with 1 to 3 droplets.

[0019] Fig.13 It is a photograph in lieu of a drawing showing a flying state of ink according to the embodiment.

[0020] Description of Reference Numerals

[0021] 2…nozzle, 3…head body, 4…head driver, 14, 141, 142…piezoelectric component, 16…nozzle plate, 21…electrode, 24, 241, 242, 243…pressure chamber, 25, 251, 252, 258…actuator, 100…inkjet head (head), 101…head drive circuit, 102…channel group, 200…inkjet printer (printer), 201…processor, 202…ROM, 203…RAM, 204…operation panel, 205…communication interface, 206…conveying motor, 207…motor drive circuit, 208…pump, 209…pump drive circuit, 300…charge and discharge circuit, 400…waveform generating circuit, 401…time setting register, 402…selector, 403…timer, 404…state counter, 405…drive mode memory, 500…power supply circuit. DETAILED DESCRIPTION

[0022] Hereinafter, the embodiments will be described using the drawings.

[0023] In the present embodiment, a piezoelectric inkjet head is exemplified as an on-demand inkjet head.

[0024] Figure 11 is a perspective view showing a piezoelectric inkjet head 100. The inkjet head 100 is a shear mode shared wall type. Hereinafter, the inkjet head 100 is referred to as a head 100.

[0025] The head 100 is composed of a head body 3 having a plurality of nozzles 2 for ejecting ink, a head driver 4 generating a drive signal, and a manifold 7 having an ink supply port 5 and an ink discharge port 6. The head driver 4 has two driver ICs 41 and 42. The circuit structure of each driver IC 41 and 42 is the same. Each driver IC 41 and 42 includes a head drive circuit 101 described later.

[0026] The head 100 ejects ink supplied from the ink supply port 5 as ink supply means from the nozzle 2 according to a drive signal generated from the head driver 4. The head 100 also ejects the ink that has flowed in from the ink supply port 5 but has not been ejected from the nozzle 2 from the ink ejection port 6.

[0027] Figure 2 3 is a top view of the head body 3. Figure 3 yes Figure 2 The AA longitudinal sectional view of the head body 3 shown, Figure 4 yes Figure 3 A cross-sectional view of the head body 3 taken along line BB is shown.

[0028] like Figure 2 As shown in FIG. 1 , the head body 3 is composed of a piezoelectric component 14, a base substrate 15, a nozzle plate 16, and a frame member 17. The head body 3 is based on the base substrate 15. The frame member 17 is bonded to the base substrate 15, and the piezoelectric component 14 is bonded to the frame member 17. The head body 3 has the nozzle plate 16 bonded to the frame member 17. Figure 3 As shown, the head body 3 uses the space in the central portion surrounded by the base substrate 15, the piezoelectric component 14, and the nozzle plate 16 as an ink supply path 18. In addition, the head body 3 uses the space in the peripheral portion surrounded by the base substrate 15, the piezoelectric component 14, the frame member 17, and the nozzle plate 16 as an ink discharge path 19. The nozzle plate 16 is formed with a plurality of nozzles 2 in a predetermined pattern.

[0029] like Figure 3 As shown, the base substrate 15 has a hole 22 communicating with the ink supply path 18 and a hole 23 communicating with the ink discharge path 19. The hole 22 communicates with the ink supply port 5 through the manifold 7. The hole 23 communicates with the ink discharge port 6 through the manifold 7.

[0030] like Figure 4 As shown, the piezoelectric member 14 is formed by laminating a second piezoelectric member 142 having a polarity opposite to that of the first piezoelectric member 141 on a first piezoelectric member 141. The first piezoelectric member 141 and the second piezoelectric member 142 are bonded to each other.

[0031] like Figure 3 As shown in FIG. 1 , the piezoelectric member 14 is formed in parallel with a plurality of long grooves 26 that are connected from the ink supply path 18 to the ink discharge path 19. Figure 4 As shown in FIG. 2 , electrodes 21 are provided on the inner surface of each long groove 26. Figure 2 As shown, each electrode 21 is connected to the head driver 4 via a wiring 20. The space surrounded by each long groove 26 and the back surface of the nozzle plate 16 bonded to the second piezoelectric member 142 so as to cover each long groove 26 is a pressure chamber 24. The nozzle 2 is connected to each pressure chamber 24 in a one-to-one correspondence.

[0032] like Figure 4 As shown, the piezoelectric component 14 forming the partition wall between adjacent pressure chambers 24 is sandwiched by the electrodes 21 of each pressure chamber 24. The head body 3 is composed of the piezoelectric component 14 and the electrodes 21 on both sides thereof to form an actuator 25. When an electric field is applied to the actuator 25 by the drive signal generated by the head drive circuit 101, the actuator 25 is shear-deformed into a "く" shape with the joint between the first piezoelectric component 141 and the second piezoelectric component 142 as the top. Due to the deformation of the actuator 25, the volume of the pressure chamber 24 is displaced, and the ink inside the pressure chamber 24 is pressurized. The pressurized ink is ejected from the nozzle 2 connected to the pressure chamber 24. That is, the head drive circuit 101 functions as a drive circuit for driving the actuator 25.

[0033] A group of one pressure chamber 24, an electrode 21 disposed in the pressure chamber 24, and a nozzle 2 communicating with the pressure chamber 24 is referred to as a channel. That is, the head 100 has channels corresponding to the number of pressure chambers 24. Hereinafter, the number of channels corresponding to the number of pressure chambers 24 is referred to as a channel group 102 (see Figure 6 ).

[0034] Next, use Figure 5 The operating principle of the head 100 configured as described above will be described.

[0035] Figure 5 (a) shows a state where the potential of the electrodes 21 on the walls of the pressure chamber 242 and the two adjacent pressure chambers 241 and 243 adjacent to the pressure chamber 242 are both at the ground potential GND. In this state, the actuator 251 sandwiched between the pressure chamber 241 and the pressure chamber 242 and the actuator 252 sandwiched between the pressure chamber 242 and the pressure chamber 243 are not subjected to any deformation.

[0036] Figure 5(b) shows a state where a negative voltage -V is applied to the electrode 21 of the central pressure chamber 242, and a positive voltage +V is applied to the electrodes 21 of the two adjacent pressure chambers 241 and 243. In this state, an electric field twice the voltage V is applied to each actuator 251 and 252 in a direction orthogonal to the polarization direction of the piezoelectric components 141 and 142. Through this action, each actuator 251 and 252 is deformed outward in a manner that expands the volume of the pressure chamber 242.

[0037] Figure 5 (c) shows a state where a positive voltage +V is applied to the electrode 21 of the central pressure chamber 242, and a negative voltage -V is applied to the electrodes 21 of the two adjacent pressure chambers 241 and 243. In this state, each actuator 251 and 252 is driven to the same voltage as the actuator 251. Figure 5 In (b), an electric field twice the voltage V acts in the opposite direction. Due to this action, the actuators 251 and 252 are deformed inwardly so that the volume of the pressure chamber 242 is contracted.

[0038] When the volume of the pressure chamber 242 expands or contracts, pressure vibration occurs in the pressure chamber 242. The pressure in the pressure chamber 242 increases due to the pressure vibration, and ink droplets are ejected from the nozzle 2 communicating with the pressure chamber 242.

[0039] In this way, the actuator 251 that separates the pressure chamber 241 from the pressure chamber 242 and the actuator 252 that separates the pressure chamber 242 from the pressure chamber 243 apply pressure vibrations to the inside of the pressure chamber 242 having the two actuators 251 and 252 as walls. That is, the pressure chamber 242 shares the actuator 25 with the pressure chamber 241 and the pressure chamber 243 that are adjacent to each other. Therefore, the head driving circuit 101 cannot drive each pressure chamber 24 individually. The head driving circuit 101 divides each pressure chamber 24 into (n+1) groups for every n (n is an integer greater than 2) pressure chambers 24 and drives them. In the present embodiment, the head driving circuit 101 divides each pressure chamber 24 into three groups for every two pressure chambers 24, which is a so-called three-split drive. In addition, the three-split drive is just an example, and it may also be a four-split drive or a five-split drive.

[0040] Next, the inkjet printer 200 using the head 100 will be described. Hereinafter, the inkjet printer 200 will be referred to as a printer 200.

[0041] Figure 62 is a block diagram showing the hardware structure of the printer 200. The printer 200 includes a processor 201, a ROM (Read Only Memory) 202, a RAM (Random Access Memory) 203, an operation panel 204, a communication interface 205, a conveying motor 206, a motor driving circuit 207, a pump 208, a pump driving circuit 209, and a head 100. In addition, the printer 200 includes a bus 210 such as an address bus and a data bus. In addition, the printer 200 connects the processor 201, the ROM 202, the RAM 203, the operation panel 204, the communication interface 205, the motor driving circuit 207, the pump driving circuit 209, and the driving circuit 101 of the head 100 to the bus 210 directly or via an input / output circuit.

[0042] The processor 201 corresponds to the core of the computer and controls each unit according to the operating system and application programs to realize various functions of the printer 200. The processor 201 is, for example, a CPU (Central Processing Unit).

[0043] The ROM 202 corresponds to the main storage unit for reading of the above-mentioned computer. The ROM 202 stores the above-mentioned operating system and application programs. The ROM 202 may also store data necessary for the processor 201 to execute processing for controlling each unit.

[0044] RAM 203 corresponds to the rewritable main storage part of the computer. RAM 203 stores data required for the processor 201 to execute the process. In addition, RAM 203 is also used as a work area for the processor 201 to rewrite information as appropriate. The work area includes an image memory for developing print data.

[0045] The operation panel 204 includes an operation unit and a display unit. The operation unit includes function keys such as a power key, a paper feed key, and an error cancel key. The display unit can display various states of the printer 200.

[0046] The communication interface 205 receives print data from a client terminal connected via a network such as a LAN (Local Area Network) or the like. For example, when an error occurs in the printer 200 , the communication interface 205 transmits a signal notifying the error to the client terminal.

[0047] The motor drive circuit 207 controls the driving of the conveying motor 206. The conveying motor 206 functions as a driving source of a conveying mechanism for conveying recording media such as printing paper. When the conveying motor 206 is started, the conveying mechanism starts conveying the recording medium. The conveying mechanism conveys the recording medium to the printing position of the head 100. The conveying mechanism discharges the recording medium after printing from a discharge port not shown to the outside of the printer 200.

[0048] The pump driving circuit 209 controls driving of the pump 208. When the pump 208 is driven, ink in an ink tank (not shown) is supplied to the head 100.

[0049] The head driving circuit 101 drives the channel group 102 of the head 100 based on the printing data.

[0050] Figure 7 1 is a diagram showing the circuit structure of the main part of the head driving circuit 101. The head driving circuit 101 includes a charging and discharging circuit 300, a waveform generating circuit 400, and a power supply circuit 500. The charging and discharging circuit 300 electrically connects the waveform generating circuit 400 and the power supply circuit 500. In addition, the waveform generating circuit 400 and the power supply circuit 500 may not be included in the head driving circuit 101, but may be located at a position physically separated from the head 100 and electrically connected to the charging and discharging circuit 300.

[0051] The power supply circuit 500 connects the first voltage source 501 and the second voltage source 502 in series. In detail, the power supply circuit 500 connects the negative electrode of the first voltage source 501 to the positive electrode of the second voltage source 502, and grounds the connection point to the ground of zero [V]. The first voltage source 501 and the second voltage source 502 both output a DC voltage E / 2 [V] which is half of the maximum voltage E [V] that is the charging target of the charge and discharge circuit 300. Therefore, the power supply line La connected to the positive electrode of the first voltage source 501 becomes a positive power supply line of +E / 2 [V]. The power supply line Lb connected to the negative electrode of the second voltage source 502 becomes a negative power supply line of -E / 2 [V]. The power supply line Lc connected to the connection point of the negative electrode of the first voltage source 501 and the positive electrode of the second voltage source 502 becomes a ground line of zero [V].

[0052] The charge and discharge circuit 300 is connected to the first voltage source 501 and the second voltage source 502 of the power supply circuit 500 via the power supply lines La, Lb, and Lc. The charge and discharge circuit 300 is also connected to a +24 [V] reference power supply VBG via the power supply line Ld.

[0053] The charge and discharge circuit 300 connects a plurality of switch series circuits between the positive power line La and the negative power line Lb. Specifically, the charge and discharge circuit 300 connects a switch series circuit of switch elements 611 and 612, a switch series circuit of switch elements 621 and 622, ..., a switch series circuit of switch elements 691 and 692 between the positive power line La and the negative power line Lb.

[0054] In addition, the charge and discharge circuit 300 connects the switch element 613, the switch element 623, ..., and the switch element 693 between the connection points of the switch elements of each switch series circuit and the ground line Lc. Furthermore, the charge and discharge circuit 300 connects the electrostatic capacitive actuators 251, 252 (not shown), ..., 258 composed of piezoelectric elements between the connection points of the switch elements of adjacent switch series circuits.

[0055] In this way, the actuators 251, 252, ..., 258 are connected between the interconnection points of the switch elements of the adjacent switch series circuits, so the number of actuators 251, 252, ..., 258 is less than the number of the switch series circuits by "1". In addition, as symbols representing the switch elements of the switch series circuits, "611", "612", ..., "613", "621", "622", ..., "623", "691", "692", ..., "693" are used, but the number of switch series circuits is not limited to 9, and the number of actuators represented by the symbols "251", "252", ..., "258" is of course not limited to 8.

[0056] The switch elements 611, 621, ..., 691 connected to the positive power line La among the switch elements of each switch series circuit are P-type channel MOS transistors. The switch elements 612, 622, ..., 692 connected to the negative power line Lb among the switch elements of each switch series circuit are N-type channel MOS transistors. Therefore, the charge and discharge circuit 300 has a series circuit between the source / drain of a plurality of P-type channel MOS transistors and the source / drain of N-type channel MOS transistors connected between the positive power line La and the negative power line Lb.

[0057] The switch elements 613, 623, ..., 693 are N-channel MOS transistors. Therefore, the charge and discharge circuit 300 connects the source / drain of the N-channel MOS transistors between the connection point of the switch elements of each switch series circuit and the ground line Lc.

[0058] The back gate of the P-channel MOS transistor (switch elements 611, 621, ..., 691) is connected to the reference power line Ld of +24 [V]. The back gate of the N-channel MOS transistor (switch elements 612, 622, ..., 692 and switch elements 613, 623, ..., 693) is connected to the negative power line Lb of -E / 2 [V]. The gates of the P-channel MOS transistor (switch elements 611, 621, ..., 691) and the gates of the N-channel MOS transistor (switch elements 612, 622, ..., 692 and switch elements 613, 623, ..., 693) are all connected to the waveform generating circuit 400.

[0059] The waveform generation circuit 400 generates a control waveform for controlling the switching of the switching elements 611, 621, ..., 691, 612, 622, ..., 692 and 613, 623, ..., 693 to be turned on and off. The switching elements 611, 621, ..., 691, 612, 622, ..., 692 and 613, 623, ..., 693 are switched on and off according to the control waveform output from the waveform generation circuit 400. By the switching of the switching on and off, the actuators 251, 252, ..., 258 are charged and discharged.

[0060] Here, the switch element 611, the switch element 612, and the switch element 613, and the switch element 621, the switch element 622, and the switch element 623, which are connected to each other via the actuator 251, form a current path for charging and discharging the actuator 251. In addition, although not shown in the figure, the switch element 621, the switch element 622, and the switch element 623, and the switch element 631, the switch element 632, and the switch element 633, which are connected to each other via the actuator 252, form a current path for charging and discharging the actuator 252. The same is true for the other actuators 253 to 258. Therefore, the following description of this embodiment continues with a focus on the actuator 251 and the six switch elements 611, 612, 613, 621, 622, and 623 that form the current path to the actuator 251.

[0061] Figure 8 4 is a block diagram showing a circuit configuration of a main part of the waveform generating circuit 400. The waveform generating circuit 400 includes a time setting register 401, a selector 402, a timer 403, a state counter 404, and a drive mode memory 405.

[0062] The time setting register 401 includes a first setting register 4011, a second setting register 4012, a third setting register 4013, a fourth setting register 4014, a fifth setting register 4015, a sixth setting register 4016, and a seventh setting register 4017. Time Ta is set in the first setting register 4011. Time Tb is set in the second setting register 4012. Time Tc is set in the third setting register 4013. Time Td is set in the fourth setting register 4014. Time Te is set in the fifth setting register 4015. Time Tf is set in the sixth setting register 4016. Time Tg is set in the seventh setting register 4017.

[0063] The selector 402 sequentially selects the time Ta, time Tb, time Tc, time Td, time Te, time Tf, and time Tg set in the first to seventh setting registers 4011 to 4017, respectively, according to the state data ST output from the state counter 404. The selector 402 sets the selected time in the timer 403.

[0064] The timer 403 counts the time set by the selector 402. When the time is finished, the timer 403 outputs a state update signal SA to the state counter 404.

[0065] The state counter 404 is an octal counter, and in the initial state, the state data ST is reset to "0". In this state, when a trigger signal for starting waveform output is input from the printer 200, the state counter 404 increments the state data ST by "1". Thereafter, each time a state update signal SA is input from the timer 403, the state counter 404 increments the state data ST by "1". Then, when the state data ST is counted to the upper limit value ("7" because it is an octal counter), the state counter 404 resets the state data ST to "0" through the subsequent input of the state update signal SA. The state counter 404 outputs the state data ST to the selector 402 and the drive mode memory 405.

[0066] Hereinafter, the state data ST of the initial state is set as the state data STa. The state data ST after the increment count "1" is set as the state data STb. Thereafter, the state data after each increment count "1" is set as the state data STc, STd, STe, STf, and the state data ST after the increment count to the upper limit value "7" is set as the state data STh.

[0067] The drive mode memory 405 stores drive mode data corresponding to the state data STa to STh. The drive mode data is data for controlling the on / off of the six switch elements 611, 612, 613, 621, 622, and 623 that form a power path to the actuator 251. The drive mode data is also data for controlling the on / off of the six switch elements 621, 622, 623, 631, 632, and 633 that form a power path to the actuator 252.

[0068] Whenever state data STa to STh is input from the state counter 404, the drive mode memory 405 generates a drive waveform for controlling the switching of on and off of each switching element 611, 612, 613, 621, 622, 623, ... according to the drive mode data corresponding to the state data STa to STh.

[0069] Fig. 9 The diagram shows the correspondence between state data STa to STh and drive mode data. In the initial state of state data STa, the drive mode data is data that switches 623 and 613 are turned on, and switches 621, 622, 611, and 612 are turned off.

[0070] In this state, a trigger signal for starting waveform output is input to the state counter 404, and when the state data is updated from STa to STb (time point ta), the switch element 613 is turned off and the switch element 612 is turned on according to the drive waveform of the drive mode data corresponding to the state data STb output from the drive mode memory 405. At this time, a closed circuit of the first voltage source 501 → the switch element 611 → the actuator 251 → the switch element 623 → the first voltage source 501 is formed. As a result, the actuator 251 is forwardly energized with a voltage of E / 2 [V] and charged.

[0071] Thus, in the first half of charging, the actuator 251 is charged halfway with the intermediate voltage E / 2 [V] which is half of the maximum voltage E [V] as the charging target, using the positive polarity first voltage source 501 .

[0072] When the state data is updated from STa to STb, the selector 402 selects the first setting register 4011. As a result, the timer 403 counts the time Ta. Then, the time Ta is counted, and when the timer 403 times out, the state data is updated from STb to STc.

[0073] When the state data is updated from STb to STc (time point tb), according to the driving waveform of the driving mode data corresponding to the state data STc, the switch element 623 is turned off and the switch element 622 is turned on. At this time, a closed circuit is formed of the first voltage source 501 → the switching element 611 → the actuator 251 → the switching element 622 → the second voltage source 502 → the first voltage source 501. As a result, the actuator 251 is forwardly energized at the maximum voltage E [V] and is further charged.

[0074] Thus, in the second half of charging, the actuator 251 is charged with the maximum voltage E [V] using the positive first voltage source 501 and the negative second voltage source 502. By charging the actuator 251 with the maximum voltage E [V], the actuator 251 is fully charged.

[0075] When the state data is updated from STb to STc, the selector 402 selects the second setting register 4012. As a result, the timer 403 counts the time Tb. Then, the time Tb is counted, and when the timer 403 times out, the state data is updated from STc to STd.

[0076] When the state data is updated from STc to STd (time point tc), according to the driving waveform of the driving mode data corresponding to the state data STd, the switch element 622 is turned off and the switch element 623 is turned on. At this time, a closed circuit is formed of the actuator 251 → the switch element 611 → the first voltage source 501 → the switch element 623 → the actuator 251. As a result, the actuator 251 is discharged.

[0077] In this way, in the first half of discharge, the electric charge is returned from the actuator 251 to the first voltage source 501 of positive polarity, the first voltage source 501 is charged, and the actuator 251 is discharged.

[0078] When the state data is updated from STc to STd, the selector 402 selects the third setting register 4013. As a result, the timer 403 counts the time Tc. Then, the time Tc is counted, and when the timer 403 times out, the state data is updated from STd to STe.

[0079] When the state data is updated from STd to STe (time point td), according to the driving waveform of the driving mode data corresponding to the state data STe, the switch element 611 is turned off and the switch element 613 is turned on. At this time, a closed circuit of the actuator 251 → the switching element 613 → the switching element 623 → the actuator 251 is formed. As a result, the actuator 251 continues to discharge.

[0080] In this way, in the second half of the discharge, the actuator 251 is completely discharged by circulating between the terminals of the actuator 251.

[0081] Through the above charging and discharging actions, the head 100 expands the volume of the pressure chamber to replenish the ink, and then restores the volume of the pressure chamber. This action generates pressure vibration in the pressure chamber, so that ink droplets are ejected from the nozzle. The timing of ejection is the discharge action.

[0082] When the state data is updated from STd to STe, the selector 402 selects the fourth setting register 4014. As a result, the timer 403 counts the time Td. Then, the time Td is counted, and when the timer 403 times out, the state data is updated from STe to STf.

[0083] When the state data is updated from STe to STf (time point te), according to the driving waveform of the driving mode data corresponding to the state data STf, the switch element 623 is turned off and the switch element 621 is turned on. At this time, a closed circuit is formed of the first voltage source 501 → the switch element 621 → the actuator 251 → the switch element 613 → the first voltage source 501. As a result, the actuator 251 is reversely energized at E / 2 [V] and charged.

[0084] Thus, in the first half of reverse charging, the actuator 251 is charged from the reverse direction to half the charge using the first voltage source 501 of positive polarity with the intermediate voltage E / 2 [V] which is half the maximum voltage E [V].

[0085] When the state data is updated from STe to STf, the selector 402 selects the fifth setting register 4015. As a result, the timer 403 counts the time Te. Then, the time Te is counted, and when the timer 403 times out, the state data is updated from STf to STg.

[0086] When the state data is updated from STf to STg (time point tf), according to the driving waveform of the driving mode data corresponding to the state data STg, the switch element 613 is turned off and the switch element 612 is turned on. At this time, a closed circuit is formed of the first voltage source 501 → the switch element 621 → the actuator 251 → the switch element 612 → the second voltage source 502 → the first voltage source 501. As a result, the actuator 251 is further charged by reverse current E [V].

[0087] Thus, in the second half of reverse charging, the actuator 251 is charged from the reverse direction at the maximum voltage E [V] using the first voltage source 501 with positive polarity and the second voltage source 502 with negative polarity. By charging the actuator 251 from the reverse direction at the maximum voltage E [V], the actuator 251 is completely charged from the reverse direction.

[0088] When the state data is updated to STf-STg, the selector 402 selects the sixth setting register 4016. As a result, the timer 403 counts the time Tf. Then, the time Tf is counted, and when the timer 403 times out, the state data is updated from STg to STh.

[0089] When the state data is updated from STg to STh (time point tg), according to the driving waveform of the driving mode data corresponding to the state data STh, the switch element 612 is turned off and the switch element 613 is turned on. At this time, a closed circuit of the actuator 251 → the switch element 621 → the first voltage source 501 → the switch element 613 → the actuator 251 is formed. As a result, the actuator 251 is discharged.

[0090] In this way, in the first half of discharge, the electric charge is returned from the actuator 251 to the first voltage source 501 of positive polarity, the first voltage source 501 is charged, and the actuator 251 is discharged.

[0091] When the state data is updated from STg to STh, the selector 402 selects the seventh setting register 4017. As a result, the timer 403 counts the time Tg. Then, the time Tg is counted, and when the timer 403 times out, the state data returns from STh to STa.

[0092] When the state data returns from STh to STa (time point th), according to the driving waveform of the driving pattern data corresponding to the state data STa, the switch element 621 is turned off and the switch element 623 is turned on. At this time, a closed circuit of the actuator 251 → the switching element 623 → the switching element 613 → the actuator 251 is formed. As a result, the actuator 251 continues to discharge.

[0093] In this way, in the second half of the discharge, the actuator 251 is completely discharged by circulating between the terminals of the actuator 251.

[0094] Through the above reverse charge / discharge operation, the head 100 shrinks the volume of the pressure chamber and then restores it. This operation eliminates the residual vibration of the pressure chamber.

[0095] Thereafter, the waveform generating circuit 400 repeatedly performs the same operation each time a trigger signal for starting waveform output is input to the state counter 404. Through the operation of the waveform generating circuit 400, the charge-discharge circuit 300 switches the six switching elements 611, 612, 613, 621, 622, and 623 that form the current path to the actuator 251 on and off.

[0096] Here, the electrode 21 to which the voltage is applied is controlled by turning on and off the three switching elements 621, 622, and 623, and is the electrode of one channel (hereinafter referred to as the ejection channel Ch.X) that ejects ink. The electrode 21 to which the voltage is applied is controlled by turning on and off the remaining three switching elements 611, 612, and 613, and is the electrode of a channel adjacent to the ejection channel Ch.X (hereinafter referred to as the adjacent channel Ch.X-1). The actuator 251 is sandwiched between the electrode 21 of the ejection channel Ch.X and the electrode 21 of the adjacent channel Ch.X-1. Therefore, the actuator 251 is repeatedly charged or discharged and driven according to the difference between the voltage applied to the electrode 21 of the ejection channel Ch.X and the voltage applied to the electrode 21 of the adjacent channel Ch.X-1. By appropriately controlling the drive of the actuator 251, one drop of ink can be ejected from the nozzle 2 of the ejection channel Ch.X. In this way, the waveform that controls the drive of the actuator 251 is called a drive waveform.

[0097] Fig.10 1 and 2 are explanatory diagrams of drive waveforms used in the present embodiment. In the present embodiment, a first drive waveform (I) and a second drive waveform (II) are used as drive waveforms.

[0098] The first drive waveform (I) includes an expansion waveform in section D, a holding waveform in section R, and a contraction waveform in section P. The expansion waveform applies a first pulse Pa that changes from a stable state of 0 [V] to a negative maximum voltage -E [V] to the actuator 251. By applying the first pulse Pa to the actuator 251, the actuator 251 is driven in a direction to expand the pressure chamber 24 of the ejection channel Ch.X.

[0099] The expansion waveform becomes a stable state of 0 [V] after a time Dt corresponding to the interval D has passed. By making the voltage applied to the actuator 251 become a stable state of 0 [V], the actuator 251 is driven in a direction to restore the pressure chamber 24.

[0100] Thus, in the interval D, the pressure chamber 24 of the ejection channel Ch.X first expands, and then recovers after maintaining its expanded state. By such a volume change of the pressure chamber 24, ink droplets are ejected from the nozzle 2 connected to the pressure chamber 24. In addition, when the time Dt for maintaining the expanded state of the pressure chamber 24 corresponding to the interval D is set to 1 / 2 of the pressure vibration period 2AL (Acoustic Length) of the pressure chamber 24, the ejection volume of the ink becomes maximum. The time Dt can be adjusted by adjusting the time Ta set in the first setting register 4011 and the time Tb set in the second setting register 4012. Here, the expansion waveform of the interval D is called a compression pulse, an ejection pulse, etc.

[0101] When the expansion waveform becomes a stable state of 0 [V], the first drive waveform (I) becomes a holding waveform. The holding waveform holds the stable state of 0 [V] for a time Rt corresponding to the interval R. When the stable state of 0 [V] is held for a time Rt, the first drive waveform (I) becomes a contraction waveform.

[0102] The second pulse Pb whose contraction waveform changes from a steady state of 0 [V] to a positive maximum voltage +E [V] is applied to the actuator 251. By applying the second pulse Pb to the actuator 251, the actuator 251 is driven in a direction to contract the pressure chamber 24 of the ejection channel Ch.X.

[0103] When the time Pt ​​corresponding to the interval P elapses, the contraction waveform becomes a stable state of 0 [V]. By making the voltage applied to the actuator 251 become a stable state of 0 [V], the actuator 251 is driven in a direction to restore the pressure chamber 24.

[0104] In this way, in the interval P, the pressure chamber 24 of the ejection channel ch.x contracts first, and then recovers after maintaining the contracted state. By such a change in the volume of the pressure chamber 24, the residual vibration of the pressure chamber 24 can be eliminated. In detail, by adjusting the time Rt corresponding to the interval of the holding waveform and the time Pt ​​corresponding to the interval P of the contraction waveform to appropriate values, the residual vibration of the pressure chamber 24 is eliminated at the trailing edge of the contraction waveform. The time Rt can be adjusted by adjusting the time Td set in the fourth setting register 4014. The time Pt ​​can be adjusted by adjusting the time Te, Tf, Tg set in the fifth setting register 4015, the sixth setting register 4016 and the seventh setting register 4017. Here, the contraction waveform of the interval P is referred to as a contraction pulse, an elimination pulse, etc.

[0105] In this way, the first driving waveform (I) can eliminate the residual vibration of the pressure chamber 24 in the ejection channel ch.x, so that good ejection efficiency can be obtained. In addition, the landing performance of the ink droplets is also excellent.

[0106] However, the head 100 usually ejects ink droplets from the nozzle 2 in a trailing state when the ink droplets are ejected from the nozzle 2. Moreover, when the ink droplets separate from the ink in the nozzle 2, the trailing portion, i.e., the so-called liquid column, is called a spherical satellite droplet, and it flies after the main ink droplets (main droplets). Since the satellite droplets are tiny droplets, their flying speed is slower than that of the main ink droplets. Therefore, sometimes the satellite droplets leave the main ink droplets and land on the recording medium, resulting in a decrease in printing quality such as uneven concentration and ghosting. In addition, there is so-called ink mist in the satellite droplets that is stalled and floats in the printer 200. When the ink mist adheres to the head 100 or the circuit components around it, it may cause the printer 200 to malfunction. The first drive waveform (I) cannot suppress the generation of small droplets such as the above-mentioned satellite droplets and ink mist.

[0107] The second drive waveform (II) includes an expansion waveform in interval D, a holding waveform in interval R', a first weak contraction waveform in interval H, a contraction waveform in interval P', and a second contraction waveform in interval W. The expansion waveform is the same as the expansion waveform of the first drive waveform (I). That is, the expansion waveform applies a first pulse Pa that changes from a stable state of 0 [V] to a negative maximum voltage -E [V] to the actuator 251, and after a time Dt corresponding to interval D, it becomes a stable state of 0 [V].

[0108] In the second driving waveform (II), in the interval D, the pressure chamber 24 of the ejection channel Ch.X first expands, maintains the expanded state, and then recovers. Due to the volume change of the pressure chamber 24, ink droplets are ejected from the nozzle 2 connected to the pressure chamber 24. In addition, when the time Dt for maintaining the expanded state of the pressure chamber 24 corresponding to the interval D is set to 1 / 2 of the pressure vibration period 2AL of the pressure chamber 24, the ejection volume of the ink becomes the maximum.

[0109] When the expansion waveform becomes a stable state of 0 [V], the second drive waveform (II) becomes a holding waveform. The holding waveform holds the stable state of 0 [V] for a time R't corresponding to the interval R'. When the time R't corresponding to the interval R' of the holding waveform has passed, the second drive waveform (II) becomes the first weak contraction waveform.

[0110] The first weak contraction waveform applies a third pulse Pc that changes from a stable state of 0 [V] to an intermediate voltage +E / 2 [V] that is half of the positive maximum voltage to the actuator 251. By applying the third pulse Pc to the actuator 251, the actuator 251 is driven in a direction to contract the pressure chamber 24 of the ejection channel Ch.X. However, the degree of this contraction is smaller than the degree of contraction of the pressure chamber 24 due to the second pulse Pb of the first drive waveform (I). Hereinafter, the degree of contraction of the pressure chamber 24 caused by the third pulse Pc is referred to as weak contraction, and the state of this weak contraction is referred to as a weak contraction state.

[0111] When the time Ht corresponding to the interval H of the weak contraction waveform has passed, the second drive waveform (II) becomes a contraction waveform. The contraction waveform applies the fourth pulse Pd that changes from the intermediate voltage +E / 2 [V] to the positive maximum voltage +E [V] to the actuator 251. By applying the fourth pulse Pd to the actuator 251, the actuator 251 is driven in the direction of further contracting the pressure chamber 24 of the ejection channel Ch.X. The degree of this contraction is equal to the degree of contraction of the pressure chamber 24 by the second pulse Pb of the first drive waveform (I).

[0112] When the time P't corresponding to the interval P' of the contraction waveform has passed, the second drive waveform (II) becomes a second weak contraction waveform. The second weak contraction waveform applies the fifth pulse Pe that changes from the maximum voltage +E[V] to the intermediate voltage +E / 2[V] to the actuator 251. By applying the fifth pulse Pe to the actuator 251, the actuator 251 is driven in the direction of restoring the pressure chamber 24 of the ejection channel Ch.X. However, the pressure chamber 24 is not completely restored. By making the voltage applied to the actuator 251 the intermediate voltage +E / 2[V], the pressure chamber 24 is in a weak contraction state.

[0113] When the time Wt corresponding to the interval W of the second weak contraction waveform has passed, the second drive waveform (II) becomes a stable state of 0 [V]. When the voltage applied to the actuator 251 becomes a stable state of 0 [V], the pressure chamber 24 in the weak contraction state is completely restored.

[0114] The second driving waveform (II) of this structure can suppress the generation of small droplets such as satellite droplets and ink mist. In detail, the time R′t corresponding to the interval R′ of the holding waveform, the time Ht corresponding to the interval H of the first weak contraction waveform, the time P′t corresponding to the interval P′ of the strong contraction waveform, and the time Wt corresponding to the interval W of the second weak contraction waveform are adjusted to appropriate values. In this way, the generation of small droplets such as satellite droplets and ink mist can be suppressed. The time R′t can be adjusted to the time Td set in the fourth setting register 4014. The time Ht can be adjusted to the time Te set in the fifth setting register 4015. The time P′t can be adjusted to the time Tf set in the sixth setting register 4016. The time Wt can be adjusted to the time Tg set in the seventh setting register 4017.

[0115] Therefore, next, appropriate values ​​of the time R′t, the time Ht, the time P′t, and the time Wt will be described.

[0116] The time R′t is the time from the time point tc when the actuator 251 charged with the negative maximum voltage -E[V] by the first pulse Pa starts to discharge to the time point te when the actuator 25 starts to charge with the intermediate voltage E / 2[V] by the third pulse Pc. The time Ht is the time from the time point te when the actuator 25 starts to charge with the intermediate voltage E / 2[V] by the third pulse Pc to the time point tf when the actuator 25 starts to charge with the positive maximum voltage +E[V] by the fourth pulse Pd. The time P′t is the time from the time point tf when the actuator 25 starts to charge with the positive maximum voltage +E[V] by the fourth pulse Pd to the time point tg when the actuator 25 starts to discharge by the fifth pulse Pe. The time Wt is the time from the time point tg when the actuator 25 starts to discharge by the fifth pulse Pe to the time point th when the discharge ends.

[0117] By setting these time elements so as to have the relationship of the following equations (1) to (3), the generation of small droplets such as satellite droplets and ink mist can be suppressed.

[0118] R′t+Ht=Rt+(0.4~0.6)…(1)

[0119] Wt=Dt+(-0.5~0.5)…(2)

[0120] P′t=4*Dt-(R′t+Ht)-Wt...(3)

[0121] In the formula (1), Rt is the time corresponding to the interval R of the holding waveform in the first drive waveform (I).

[0122] That is, the total time of time R′t and time Ht is set to the time obtained by adding 0.4μs to 0.6μs to time Rt. Time Wt is set to the time obtained by adding or subtracting -0.5μs to 0.5μs from time Dt corresponding to the interval D of the expansion waveform. Time P′t is set to the time obtained by subtracting the total time of time R′t and time Ht and time Wt from the time 4 times time Dt.

[0123] Fig.11 This is a timing diagram showing the pressure waveform of the pressure chamber 24 in the ejection channel Ch.X and the flow rate waveform of the ink when the second drive waveform (II) is applied to the actuator 251, where the total time of the time R′t and the time Ht is set to the time Rt+0.5μs and the time Wt is set to the time Dt+0.1μs. Fig.11In the figure, the solid line "driving voltage" is the voltage waveform of the second driving waveform (II). The single-point dashed line "pressure" is the pressure waveform generated in the pressure chamber 24. The double-point dashed line "flow rate" is the flow rate waveform of the ink flowing into the nozzle 2. The horizontal axis represents the passage of time (μs). The vertical axis represents the driving voltage, pressure, flow rate and the size of the waveform, and the values ​​are standardized.

[0124] like Fig.11 As shown in FIG. 1 , the pressure in the pressure chamber 24, which is reduced by the expansion of the leading edge (first pulse Pa) of the expansion waveform in the second driving waveform (II) at time points ta and tb, rises while maintaining the expansion state. Furthermore, when the pressure chamber 24 recovers at the trailing edge of the expansion waveform at time points tc and td, the pressure rises sharply. As a result, ink droplets are ejected from the nozzle 2 connected to the pressure chamber 24.

[0125] After the ink droplets are ejected, the pressure reaches a positive peak at the time point te of the leading edge (third pulse Pc) of the first weak contraction waveform in the second drive waveform (II). The pressure reaching the positive peak decreases and turns into negative pressure while the pressure chamber 24 maintains a weak contraction state, and increases again after reaching the negative peak. Then, the pressure turns into positive pressure at the time tf of the leading edge (fourth pulse Pd) of the contraction waveform in the second drive waveform (II). The pressure turned into positive pressure reaches a second positive peak while the pressure chamber 24 maintains a contraction state, and then decreases again and turns into negative pressure. Then, the pressure reaching the second negative peak rises again and turns into positive pressure. The pressure turned into positive pressure becomes negative pressure at the time point tg of the leading edge (fifth pulse Pe) of the second weak contraction waveform in the second drive waveform (II). The pressure that becomes negative pressure rises while the pressure chamber 24 maintains a weak contraction state and turns into positive pressure again.

[0126] On the other hand, the flow rate of the ink flowing into the nozzle 2 is a positive peak after the ink droplets are ejected. After that, the flow rate decreases, and reaches a negative peak at the time tf of the leading edge of the contraction waveform in the second drive waveform (II) (the fourth pulse Pd). When the negative peak is reached, the flow rate turns to rise, and while the pressure chamber 24 maintains the contraction state, it reaches a second positive peak, and then decreases again, reaching a second negative peak at the time point tg of the leading edge of the second weak contraction waveform in the second drive waveform (II) (the fifth pulse Pe). When the negative peak is reached, the flow rate turns to rise. Then, at the time point th when the flow rate becomes zero, that is, the time point th when the discharge of the actuator 25 ends, the pressure chamber 24 completely recovers from the weak contraction state. At this time, the pressure in the pressure chamber 24 that has turned into a positive pressure decreases to approximately zero.

[0127] In this way, the second drive waveform (II) sets the pressure chamber 24 to a weak contraction state only at time Ht after the ink droplets are ejected. In addition, in order to eliminate the residual vibration of the pressure chamber, after the pressure chamber 24 is set to a contraction state, it is also set to a weak contraction state only at time Wt. By such a change in the state of the pressure chamber 24, the curved liquid surface of the ink in the nozzle 2 connected to the pressure chamber 24 bulges to such an extent that no ink droplets are ejected. By the bulge of the curved liquid surface, the tail, which is the main reason for the generation of satellite droplets, becomes shorter. As a result, the generation of small droplets that become satellite droplets or ink mist can be suppressed. In addition, the residual vibration of the pressure chamber 24 is also eliminated by the state of the pressure chamber 24 being restored from the contraction state. In this way, by using the second drive waveform (II) as the drive waveform for controlling the drive of the actuator 25, the residual vibration can be suppressed, and the generation of small droplets can also be suppressed. As a result, there is no risk of satellite droplets landing on the recording medium and causing uneven density or ghosting, which may reduce print quality, or ink mist adhering to the head 100 or peripheral circuit components and causing printer 200 to malfunction.

[0128] However, the second drive waveform (II) has a longer waveform length than the first drive waveform (I). Therefore, in the case of grayscale printing by a multi-ink droplet method in which one dot is formed by a plurality of ink droplets ejected continuously, when the second drive waveform (II) is intended to cope with the ejection of all ink droplets, since it takes time to form one dot, it is possible that the drive frequency is affected.

[0129] Therefore, in the case of the multi-droplet method, the ink droplets ejected by the first drive waveform (I) and the ink droplets ejected by the second drive waveform (II) are combined to form one dot. Fig.12 A combination of driving waveforms for a multi-ink droplet method with a maximum of three drops will be described.

[0130] Fig.12 This is a data table in a matrix format with columns as drop numbers and rows as frame numbers. Since there are a maximum of 3 drops, the number of drops is 1Drop, 2Drop, and 3Drop. The frame number is 1Frame for the first drop of 3 drops, 2Frame for the second drop of 3 drops, and 3Frame for the third drop of 3 drops.

[0131] When one dot is formed by one drop, that is, in the case of "1 drop", the one drop corresponds to "3 frames" which is the third drop among three drops. In this embodiment, "3 frames" of ink droplets are ejected using the second drive waveform (II).

[0132] In the case of forming one dot by two drops, that is, in the case of "2 drops", the first drop is equivalent to "2 frames" that become the second drop among the three drops, and the second drop is equivalent to "3 frames" that become the third drop among the three drops. In this embodiment, the second drive waveform (II) is used to eject the ink drops of "2 frames" and "3 frames" of ink drops respectively. In this way, even if the second drive waveform (II) is used to eject all two drops, the time required to form one dot will not affect the drive frequency.

[0133] On the other hand, in the case of forming one dot with three drops, that is, in the case of "3 drops (3Drop)", "1 frame (1Frame)" of ink droplets as the first drop are ejected using the first drive waveform (I). "2 frames (2Frame)" as the second drop and "3 frames (3Frame)" as the third drop are ejected using the second drive waveform (II) respectively. Even if the first drop is ejected using the first drive waveform (I), the satellite droplets generated by the ejection are extremely small compared to the case where all three drops are ejected using the first drive waveform (I). In addition, ink mist sometimes adheres to the second or third drop of ink and lands on the recording medium. Therefore, it does not lead to a decrease in print quality. Moreover, the time required to form one dot can be suppressed to a level that does not affect the drive frequency.

[0134] Fig.13 It is a substitute photograph for the accompanying drawing showing the flying state of the ink. In this figure, the photograph PHa shows the flying state of the ink when the first drive waveform (I) is applied to print in a single drop mode of 1 drop. The photograph PHb shows the flying state of the ink when the first drive waveform (I) is applied to print in a multi-ink drop mode of 2 drops. The photograph PHc shows the flying state of the ink when the first drive waveform (I) is applied to print in a multi-ink drop mode of 3 drops. The photograph PHd shows the flying state of the ink when the second drive waveform (II) is applied to print in a single drop mode of 1 drop. The photograph PHe shows the flying state of the ink when the second drive waveform (II) is applied to print in a multi-ink drop mode of 2 drops. The photograph PHf shows the flying state of the ink when printing in a multi-ink drop mode of 3 drops, in which the first drive waveform (I) is applied to eject the first drop, and then the second drive waveform (II) is applied to eject the second and third drops.

[0135] If we compare the photos PHa and PHd, the photos PHb and PHe, and the photos PHc and PHf, we can see that when the second drive waveform (II) is not applied, a large number of satellite droplets separate from the main ink droplets and land on the recording medium, resulting in a decrease in print quality such as uneven concentration and ghosting. In contrast, when the second drive waveform (I) is applied, the generation of satellite droplets is almost suppressed. Therefore, the decrease in print quality such as uneven concentration and ghosting will not occur, and the print quality can be improved. In addition, since the generation of ink mist is also suppressed, the printer 200 will not malfunction.

[0136] As mentioned above, although embodiment of an inkjet head was described, this embodiment is not limited to this.

[0137] In the above embodiment, the time elements of the holding time R't, the first weak contraction time Ht, the contraction time P't, and the second weak contraction time Wt are respectively set to have the relationship of the above equations (1) to (3). As another embodiment, the above equation (1) may also have the relationship of the following equation (4).

[0138] Ht=Rt+(0.4~0.6)…(4)

[0139] That is, according to the second driving waveform (II), the time R't of the holding interval shown in the interval R' can also be set to "0". Even with such a driving waveform, the amount of satellite droplets attached to the ink droplets ejected from the nozzle can be suppressed by adjusting the respective time elements of the first weak contraction time Ht, the contraction time P't, and the second weak contraction time Wt.

[0140] In the above embodiment, in the case of a multi-ink droplet method in which one dot is formed by three drops, the first drive waveform (I) is applied to the first droplet, and the second drive waveform (II) is applied to the second and third drops. In this regard, the first drive waveform (I) may be applied to the first and second drops, and the second drive waveform (II) may be applied to the third droplet. This technical concept is also the same in a multi-ink droplet method with more than four drops.

[0141] The first driving waveform (I) is not limited to Fig.10 Even when the other drive waveform is set to the first drive waveform (I), by applying the second drive waveform (II) to at least the ejection of the final drop of ink droplets, the generation of small droplets such as satellite droplets and ink mist can be suppressed.

[0142] The head 100 is not limited to the shear mode shared wall type, and the present embodiment can also be applied to other types of piezoelectric inkjet heads.

[0143] In addition, several embodiments of the present invention are described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the main purpose of the invention. These embodiments and their variations are included in the scope of the invention and are included in the invention described in the scope of the claim and its equivalent.

Claims

1. An inkjet head, comprising: a pressure chamber, containing ink; a nozzle plate having a nozzle in communication with the pressure chamber; an actuator, disposed corresponding to the pressure chamber and causing the volume of the pressure chamber to displace; as well as a driving circuit, driving the actuator, The drive circuit drives the actuator with a drive waveform, the drive waveform comprising: an expansion waveform, driving the actuator in a direction of expanding the volume of the pressure chamber; a contraction waveform, driving the actuator in a direction of contracting the volume of the pressure chamber; a first weak contraction waveform, between the expansion waveform and the contraction waveform, driving the actuator in a direction in which the volume of the pressure chamber contracts weaker than the contraction caused by the contraction waveform; and a second weak contraction waveform, after the contraction waveform, driving the actuator in a direction in which the volume of the pressure chamber contracts weaker than the contraction caused by the contraction waveform. the drive circuit drives the actuator with a drive waveform further including a holding waveform for holding the volume of the pressure chamber in a stable state between the expansion waveform and the first weak contraction waveform, The holding time based on the holding waveform is set to R′t, the first weak contraction time based on the first weak contraction waveform is set to Ht, the contraction time based on the contraction waveform is set to P′t, and the second weak contraction time based on the second weak contraction waveform is set to Wt. Each time element is adjusted to have the relationship of the following equations (1) to (3): R′t+Ht=Rt+(0.4~0.6)…(1) Wt=Dt+(-0.5~0.5)…(2) P′t=4*Dt-(R′t+Ht)-Wt...(3) Here, Dt is the expansion time based on the expansion waveform, and Rt is the holding time of the holding waveform in other driving waveforms including the expansion waveform, the contraction waveform, and the holding waveform between the expansion waveform and the contraction waveform.

2. The inkjet head according to claim 1, wherein: When the driving circuit drives the actuator in a multi-ink droplet manner to form one dot by continuously ejecting ink droplets from the nozzle, the driving circuit applies a driving waveform including the expansion waveform, the contraction waveform, the first weak contraction waveform and the second weak contraction waveform to at least the last ejected ink droplet.

3. The inkjet head according to claim 1, wherein: The inkjet head is a piezoelectric inkjet head.

4. The inkjet head according to claim 2, wherein: The inkjet head is a piezoelectric inkjet head.

5. The inkjet head according to claim 1, wherein: The inkjet head further includes a manifold including an ink supply port and an ink discharge port.

6. The inkjet head according to claim 2, wherein: The inkjet head further includes a manifold including an ink supply port and an ink discharge port.

7. The inkjet head according to claim 3, wherein: The inkjet head further includes a manifold including an ink supply port and an ink discharge port.

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