Inkjet head

Abstract

To improve impact accuracy of ink drops.SOLUTION: A drive circuit driving an actuator gives to the actuator an auxiliary waveform prior to a discharge waveform given to the actuator provided in accordance with a pressure chamber discharging ink drops from a nozzle, and drives the actuator to an extent that ink drops are not discharged. The auxiliary waveform includes: a weak expansion waveform which expands a pressure chamber at intermediate voltage smaller than voltage to be applied to expand the pressure chamber in the discharge waveform and a holding waveform which returns the pressure chamber expanded by the weak expansion waveform to a steady state and holds the same.SELECTED DRAWING: Figure 16

Description

[Technical Field]

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

[0002] In inkjet heads, small droplets called satellites or ink mist may occur in association with the main ink droplet (main droplet) ejected from the nozzle. These small droplets can lead to reduced print quality. The generation of small droplets can be suppressed by adjusting the drive waveform of the actuator that drives the actuator to eject ink droplets from the nozzle. However, if the actuator is driven with a drive waveform that is effective in suppressing small droplets, the landing accuracy of the ink droplets tends to deteriorate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-000785 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the embodiments of the present invention is to provide an inkjet head that can improve the landing accuracy of ink droplets. [Means for solving the problem]

[0005] In one embodiment, the inkjet head includes a pressure chamber that contains ink, a nozzle plate having nozzles that communicate 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 applies an auxiliary waveform to the actuator provided corresponding to the pressure chamber that ejects ink droplets from the nozzle, prior to the ejection waveform being applied to the actuator, which includes a weak expansion waveform that expands the pressure chamber with an intermediate voltage that is smaller than the voltage applied to expand the pressure chamber with the ejection waveform, and a holding waveform that returns and maintains the pressure chamber expanded by the weak expansion waveform to a steady state, thereby driving the actuator to a degree that does not eject ink droplets. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a perspective view showing an inkjet head according to an embodiment. [Figure 2] FIG. 2 is a plan view showing the main body of the inkjet head. [Figure 3] FIG. 3 is a longitudinal cross-sectional view of the main body of the inkjet head taken along the line AA. [Figure 4] FIG. 4 is a longitudinal BB cross-sectional view of the main body of the inkjet head. [Figure 5] FIG. 5 is a diagram used to explain the operating principle of the inkjet head. [Figure 6] FIG. 6 is a block diagram showing the hardware configuration of an inkjet printer. [Figure 7] FIG. 7 is a diagram showing the main circuit configuration of the head drive circuit in the inkjet printer. [Figure 8] FIG. 8 is a block diagram showing the main circuit configuration of a waveform generating circuit included in the head driving circuit. [Figure 9] FIG. 9 is a diagram showing the correspondence between the state data and the drive pattern data related to the waveform generating circuit. [Figure 10] FIG. 10 is an explanatory diagram of the ejection waveform used in this embodiment. [Figure 11] FIG. 11 is an explanatory diagram of the non-ejection waveform used in this embodiment. [Figure 12] FIG. 12 is an explanatory diagram of the auxiliary waveform used in this embodiment. [Figure 13]FIG. 13 is an explanatory diagram of the drive waveform applied to the channel in the case of the binary method. [Figure 14] FIG. 14 is an explanatory diagram of the drive waveforms applied to the channel in the case of a multi-drop system with a maximum of three drops. [Figure 15] FIG. 15 is a diagram showing the results of a simulation in which an actuator is driven by a drive waveform in which an auxiliary waveform is not inserted before the ejection waveform to eject ink droplets. [Figure 16] FIG. 16 shows the results of a simulation in which an actuator is driven by a drive waveform in which an auxiliary waveform is inserted before an ejection waveform to eject ink droplets. [Figure 17] FIG. 17 shows the results of a simulation in which the actuator is driven by a drive waveform in which an auxiliary waveform is inserted before a non-ejection waveform, and no ink droplets are ejected. [Figure 18] Figure 18 is a graph comparing the pressure change in the pressure chamber when the actuator is driven by a drive waveform that does not include an auxiliary waveform before the ejection waveform, and the pressure change in the pressure chamber when the actuator is driven by a conventional non-ejection waveform. [Figure 19] Figure 19 is a graph comparing the pressure change in the pressure chamber when the actuator is driven by a drive waveform in which an auxiliary waveform is inserted before the ejection waveform, and the pressure change in the pressure chamber when the actuator is driven by a drive waveform in which an auxiliary waveform is inserted before the non-ejection waveform. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, the embodiments will be described with reference to the drawings. In this embodiment, a piezo inkjet head is exemplified as an on-demand inkjet head.

[0008] 1 is a perspective view showing a piezoelectric inkjet head 100. The inkjet head 100 is of a shared-wall type. Hereinafter, the inkjet head 100 will be referred to as head 100.

[0009] The head 100 is composed of a head body 3 equipped with multiple nozzles 2 for ejecting ink, a head driver 4 that generates drive signals, and a manifold 7 equipped with an ink supply port 5 and an ink discharge port 6. The head driver 4 is equipped with two driver ICs 41 and 42. Each driver IC 41 and 42 has the same circuit configuration. Each driver IC 41 and 42 includes a head drive circuit 101, which will be described later.

[0010] The head 100 ejects ink supplied from an ink supply port 5, which is an ink supply means, from the nozzles 2 in response to a drive signal generated by a head driver 4. The head 100 also ejects, from an ink outlet 6, any ink that has flowed in from the ink supply port 5 but has not been ejected from the nozzles 2.

[0011] Fig. 2 is a plan view of the head body 3. Fig. 3 is a vertical cross-sectional view of the head body 3 shown in Fig. 2 taken along line AA, and Fig. 4 is a horizontal cross-sectional view of the head body 3 shown in Fig. 3 taken along line BB. As shown in FIG. 2, the head body 3 is composed of a piezoelectric member 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 head body 3 has the frame member 17 bonded onto the base substrate 15, and the piezoelectric member 14 bonded inside the frame member 17. The head body 3 has the nozzle plate 16 bonded onto the frame member 17. As shown in FIG. 3, the central space of the head body 3 surrounded by the base substrate 15, the piezoelectric member 14, and the nozzle plate 16 forms an ink supply channel 18. The peripheral space of the head body 3 surrounded by the base substrate 15, the piezoelectric member 14, the frame member 17, and the nozzle plate 16 forms an ink discharge channel 19. The nozzle plate 16 has a plurality of nozzles 2 formed in a predetermined pattern.

[0012] 3, the base substrate 15 has a hole 22 that communicates with the ink supply path 18 and a hole 23 that communicates with the ink discharge path 19. The hole 22 communicates with the ink supply port 5 via the manifold 7. The hole 23 communicates with the ink discharge port 6 via the manifold 7.

[0013] 4, the piezoelectric member 14 is formed by laminating a first piezoelectric member 141 with a second piezoelectric member 142 having a polarity opposite to that of the first piezoelectric member 141. The first piezoelectric member 141 and the second piezoelectric member 142 are bonded together.

[0014] As shown in FIG. 3, the piezoelectric member 14 has a plurality of parallel long grooves 26 formed therein, which connect the ink supply path 18 to the ink discharge path 19. As shown in FIG. 4, an electrode 21 is disposed on the inner surface of each long groove 26. As shown in FIG. 2, 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, which is bonded onto the second piezoelectric member 142 so as to cover each long groove 26, forms each pressure chamber 24. The nozzles 2 are connected to each pressure chamber 24 in a one-to-one correspondence.

[0015] As shown in FIG. 4, the piezoelectric member 14, which forms a partition between adjacent pressure chambers 24, is sandwiched between the electrodes 21 of each pressure chamber 24. In the head body 3, the piezoelectric member 14 and the electrodes 21 on both sides thereof constitute an actuator 25. When an electric field is applied to the actuator 25 by a drive signal generated by the head drive circuit 101, the actuator 25 undergoes shear deformation into a dogleg shape, with the junction between the first piezoelectric member 141 and the second piezoelectric member 142 at its apex. This deformation of the actuator 25 displaces the volume of the pressure chamber 24, pressurizing the ink inside the pressure chamber 24. The pressurized ink is ejected from the nozzle 2 that communicates with that pressure chamber 24. In other words, the head drive circuit 101 functions as a drive circuit that drives the actuator 25.

[0016] A set of one pressure chamber 24, an electrode 21 disposed in that pressure chamber 24, and a nozzle 2 communicating with that pressure chamber 24 is referred to as a channel. In other words, the head 100 has channels equal to the number of pressure chambers 24. Hereinafter, the channels equal to the number of pressure chambers 24 will be referred to as a channel group 102 (see FIG. 6).

[0017] Next, the operating principle of the head 100 configured as above will be explained with reference to FIG. 5(a) shows a state in which the potentials of the electrodes 21 disposed on the wall surfaces of the central pressure chamber 242 and the pressure chambers 241 and 243 adjacent to this pressure chamber 242 are all at ground potential GND. In this state, neither the actuator 251 sandwiched between the pressure chambers 241 and 242 nor the actuator 252 sandwiched between the pressure chambers 242 and 243 is subjected to any strain.

[0018] 5(b) shows a state in which 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 adjacent pressure chambers 241, 243. In this state, an electric field twice the voltage V acts on each of the actuators 251, 252 in a direction perpendicular to the polarization direction of the piezoelectric members 141, 142. This action causes each of the actuators 251, 252 to deform outward so as to expand the volume of the pressure chamber 242.

[0019] 5(c) shows a state in which 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 adjacent pressure chambers 241, 243. In this state, an electric field that is twice the voltage V acts on each of the actuators 251, 252 in the opposite direction to that in FIG. 5(b). Due to this action, each of the actuators 251, 252 deforms inward so as to contract the volume of the pressure chamber 242.

[0020] When the volume of the pressure chamber 242 is expanded or contracted, a pressure vibration occurs within the pressure chamber 242. This pressure vibration increases the pressure within the pressure chamber 242, causing an ink droplet to be ejected from the nozzle 2 communicating with the pressure chamber 242.

[0021] In this way, the actuator 251 separating the pressure chamber 241 from the pressure chamber 242 and the actuator 252 separating the pressure chamber 242 from the pressure chamber 243 apply pressure vibrations to the inside of the pressure chamber 242, which has the actuators 251, 252 as its wall surfaces. In other words, the pressure chamber 242 shares the actuator 25 with the adjacent pressure chamber 241 and pressure chamber 243, respectively. For this reason, the head drive circuit 101 cannot drive each pressure chamber 24 individually. The head drive circuit 101 drives each pressure chamber 24 by dividing it into (n+1) groups, where n is an integer of 2 or more, and drives the pressure chambers 24. In this embodiment, the head drive circuit 101 divides each pressure chamber 24 into three groups, where every two pressure chambers 24 are divided and driven, which is called three-division driving. Note that three-division driving is merely an example, and four-division driving or five-division driving may also be used.

[0022] Next, a description will be given of an inkjet printer 200 that uses the head 100. Hereinafter, the inkjet printer 200 will be referred to as the printer 200. 6 is a block diagram showing the hardware configuration of printer 200. Printer 200 includes processor 201, ROM (Read Only Memory) 202, RAM (Random Access Memory) 203, operation panel 204, communication interface 205, conveyance motor 206, motor drive circuit 207, pump 208, pump drive circuit 209, and head 100. Printer 200 also includes bus lines 210 such as an address bus and a data bus. In printer 200, processor 201, ROM 202, RAM 203, operation panel 204, communication interface 205, motor drive circuit 207, pump drive circuit 209, and drive circuit 101 of head 100 are connected to this bus line 210 directly or via input / output circuits.

[0023] The processor 201 corresponds to the central part of the computer. The processor 201 controls each part to realize various functions of the printer 200 in accordance with an operating system and application programs. The processor 201 is, for example, a CPU (Central Processing Unit).

[0024] The ROM 202 corresponds to the read-only main memory of the computer. The ROM 202 stores the operating system and application programs. The ROM 202 may also store data necessary for the processor 201 to execute processes for controlling each unit.

[0025] The RAM 203 corresponds to the rewritable main memory of the computer. The RAM 203 stores data necessary for the processor 201 to execute processing. The RAM 203 is also used as a work area where information is rewritten as needed by the processor 201. The work area includes an image memory where print data is expanded.

[0026] The operation panel 204 has an operation section and a display section. The operation section has function keys such as a power key, a paper feed key, and an error reset key. The display section can display various statuses of the printer 200.

[0027] The communication interface 205 receives print data from a client terminal connected via a network such as a LAN (Local Area Network). For example, when an error occurs in the printer 200, the communication interface 205 transmits a signal notifying the client terminal of the error.

[0028] A motor drive circuit 207 controls the driving of the transport motor 206. The transport motor 206 functions as a drive source for a transport mechanism that transports recording media such as printing paper. When the transport motor 206 starts, the transport mechanism begins transporting the recording media. The transport mechanism transports the recording media to a printing position using the head 100. After printing, the transport mechanism ejects the recording media from an ejection port (not shown) to the outside of the printer 200.

[0029] A pump drive circuit 209 controls the driving of the pump 208. When the pump 208 is driven, ink in an ink tank (not shown) is supplied to the head 100.

[0030] A head driving circuit 101 drives a channel group 102 of a head 100 based on print data. 7 is a diagram showing the main circuit configuration of the head drive circuit 101. The head drive circuit 101 includes a charge / discharge circuit 300, a waveform generation circuit 400, and a power supply circuit 500. The charge / discharge circuit 300 electrically connects the waveform generation circuit 400 and the power supply circuit 500. Note that the waveform generation circuit 400 and the power supply circuit 500 may not be included in the head drive circuit 101, but may be located physically separate from the head 100 and electrically connected to the charge / discharge circuit 300.

[0031] The power supply circuit 500 connects a first voltage source 501 and a second voltage source 502 in series. More specifically, the power supply circuit 500 connects the negative electrode of the first voltage source 501 and the positive electrode of the second voltage source 502, and grounds the connection point to zero [V]. Both the first voltage source 501 and the second voltage source 502 output a DC voltage E / 2 [V], which is half the maximum voltage E [V] that is the charging target of the charge / discharge circuit 300. Therefore, the power supply line La connected to the positive electrode of the first voltage source 501 is 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 is a negative power supply line of -E / 2 [V]. The power supply line Lc connected to the connection point between the negative electrode of the first voltage source 501 and the positive electrode of the second voltage source 502 is a ground line of zero [V].

[0032] The charge / 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 line La, the power supply line Lb, and the power supply line Lc. The charge / discharge circuit 300 is also connected to the +24V reference power supply VBG via the power supply line Ld.

[0033] The charge / discharge circuit 300 connects a large number of switch series circuits between the positive power supply line La and the negative power supply line Lb. More specifically, the charge / discharge circuit 300 connects a switch series circuit of switch element 611 and switch element 612, a switch series circuit of switch element 621 and switch element 622, ..., a switch series circuit of switch element 691 and switch element 692 between the positive power supply line La and the negative power supply line Lb.

[0034] Furthermore, the charge / discharge circuit 300 connects a switch element 613, a switch element 623, ..., a switch element 693 between the switch element interconnection point of each switch series circuit and the ground line Lc. Furthermore, the charge / discharge circuit 300 connects capacitive actuators 251, 252 (not shown), ..., 258 made of piezoelectric elements between the switch element interconnection points of adjacent switch series circuits.

[0035] In this way, the actuators 251, 252, ..., 258 are connected between the interconnection points of the switch elements of adjacent switch series circuits, and therefore the number of actuators 251, 252, ..., 258 is one less than the number of switch series circuits. Note that although the symbols "611", "612", ..., "613", "621", "622", ..., "623", and "691", "692", ..., "693" are used to indicate the switch elements of the switch series circuits, it goes without saying that the number of switch series circuits is not limited to nine, and the number of actuators indicated by the symbols "251", "252", ..., "258" is not limited to eight.

[0036] Of the switch elements in each switch series circuit, switch elements 611, 621, ..., 691 connected to the positive power supply line La are P-channel MOS transistors. Of the switch elements in each switch series circuit, switch elements 612, 622, ..., 692 connected to the negative power supply line Lb are N-channel MOS transistors. Therefore, in the charge / discharge circuit 300, a large number of series circuits, each consisting of the source-drain of a P-channel MOS transistor and the source-drain of an N-channel MOS transistor, are connected between the positive power supply line La and the negative power supply line Lb.

[0037] The switch elements 613, 623, ..., 693 are N-channel MOS transistors. Therefore, in the charge / discharge circuit 300, the source-drain of each N-channel MOS transistor is connected between the switch element interconnection point of each switch series circuit and the ground line Lc.

[0038] The back gates of the P-channel MOS transistors (switch elements 611, 621, ..., 691) are connected to a +24 V reference power supply line Ld. The back gates of the N-channel MOS transistors (switch elements 612, 622, ..., 692 and switch elements 613, 623, ..., 693) are connected to a -E / 2 V negative power supply line Lb. The gates of the P-channel MOS transistors (switch elements 611, 621, ..., 691) and the gates of the N-channel MOS transistors (switch elements 612, 622, ..., 692 and switch elements 613, 623, ..., 693) are all connected to the waveform generating circuit 400.

[0039] The waveform generating circuit 400 includes a first waveform generating circuit 4001, a second waveform generating circuit 4002, and a third waveform generating circuit 4003. The first waveform generating circuit 4001, the second waveform generating circuit 4002, and the third waveform generating circuit 4003 all generate control waveforms for controlling the on / off switching of each of the switch elements 611, 621, ..., 691, 612, 622, ..., 692, and 613, 623, ..., 693. Each of the switch elements 611, 621, ..., 691, 612, 622, ..., 692, and 613, 623, ..., 693 is switched on / off by the control waveform output from the first waveform generating circuit 4001, the second waveform generating circuit 4002, or the third waveform generating circuit 4003. This on / off switching charges and discharges each of the actuators 251, 252, ..., 258.

[0040] Here, switch elements 611, 612, and 613, and switch elements 621, 622, and 623, which are connected to each other with actuator 251 in between, form a current path for charging and discharging actuator 251. Although not shown, switch elements 621, 622, and 623, and switch elements 631, 632, and 633, which are connected to each other with actuator 252 in between, form a current path for charging and discharging actuator 252. The same applies to the other actuators 253 to 258. Therefore, hereinafter, the description of this embodiment will continue, focusing on actuator 251 and the six switch elements 611, 612, 613, 621, 622, and 623 that form the current path to this actuator 251.

[0041] The first waveform generating circuit 4001 is a circuit that generates an ejection waveform. The second waveform generating circuit 4002 is a circuit that generates a non-ejection waveform. The third waveform generating circuit 4003 is a circuit that generates an auxiliary waveform. The ejection waveform, non-ejection waveform, and auxiliary waveform will be described later. The first waveform generating circuit 4001, the second waveform generating circuit 4002, and the third waveform generating circuit 4003 all have the same basic circuit configuration. Therefore, the following description of this embodiment will focus on the first waveform generating circuit 4001.

[0042] 8 is a block diagram showing the main circuit configuration of first waveform generating circuit 4001. First waveform generating circuit 4001 includes a time setting register 401, a selector 402, a timer 403, a state counter 404, and a drive pattern memory 405.

[0043] 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. A time Ta is set in the first setting register 4011. A time Tb is set in the second setting register 4012. A time Tc is set in the third setting register 4013. A time Td is set in the fourth setting register 4014. A time Te is set in the fifth setting register 4015. A time Tf is set in the sixth setting register 4016. A time Tg is set in the seventh setting register 4017.

[0044] The selector 402 selects, in order, from the times Ta, Tb, Tc, Td, Te, Tf, and Tg set in the first to seventh setting registers 4011 to 4017, respectively, in accordance with the state data ST output from the state counter 404. The selector 402 sets the selected time in the timer 403.

[0045] The timer 403 counts the time set by the selector 402. When the counting of the time has finished, the timer 403 outputs a state update signal SA to the state counter 404.

[0046] The state counter 404 is an octal counter, and in the initial state, resets the state data ST to "0". In this state, when a trigger signal for starting waveform output is input from the printer 200, the state counter 404 counts up the state data ST by "1". Thereafter, each time a state update signal SA is input from the timer 403, the state counter 404 counts up the state data ST by "1". Then, when the state data ST reaches the upper limit value ("7" because it is an octal counter), the state counter 404 resets the state data ST to "0" in response to the input of the subsequent state update signal SA. The state counter 404 outputs the state data ST to the selector 402 and the drive pattern memory 405.

[0047] In the following, the state data ST in its initial state will be referred to as state data STa. The state data ST after counting up by "1" will be referred to as state data STb. Thereafter, the state data counted up by "1" will be referred to as state data STc, STd, STe, and STf, and the state data ST after counting up to the upper limit value of "7" will be referred to as state data STh.

[0048] The drive pattern memory 405 stores drive pattern data in association with each of the state data STa to STh. The drive pattern data is data for controlling the on / off of six switch elements 611, 612, 613, 621, 622, and 623 that form a current path to the actuator 251. The drive pattern data is also data for controlling the on / off of six switch elements 621, 622, 623, 631, 632, and 633 that form a current path to the actuator 252.

[0049] Each time state data STa to STh is input from the state counter 404, the drive pattern memory 405 generates a drive waveform for controlling the on / off switching of each of the switch elements 611, 612, 613, 621, 622, 623, . . . in accordance with the drive pattern data corresponding to the state data STa to STh.

[0050] 9 is a diagram showing the correspondence relationship between the state data STa to STh and the drive pattern data. In the initial state of the state data STa, the drive pattern data is data that turns on the switch elements 623 and 613 and turns off the switch elements 621, 622, 611, and 612.

[0051] In this state, when a trigger signal to start waveform output is input to state counter 404 and the state data is updated from STa to STb (time ta), switch element 613 is turned off and switch element 612 is turned on by the drive waveform of drive pattern data corresponding to state data STb output from drive pattern memory 405. At this time, a closed circuit of first voltage source 501 → switch element 611 → actuator 251 → switch element 623 → first voltage source 501 is formed. As a result, actuator 251 is energized in the forward direction at a voltage E / 2 [V] and charged.

[0052] In this way, in the first half of charging, the positive polarity first voltage source 501 is used to charge the actuator 251 halfway at an intermediate voltage E / 2 [V] that is half the maximum voltage E [V] that is the charging target.

[0053] 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 measures the time Ta. After the time Ta is measured and the timer 403 times out, the state data is updated from STb to STc.

[0054] When the state data is updated from STb to STc (time tb), the switch element 623 is turned off and the switch element 622 is turned on by the drive waveform of the drive pattern data corresponding to the state data STc. At this time, a closed circuit of the first voltage source 501 → switch element 611 → actuator 251 → switch element 622 → second voltage source 502 → first voltage source 501 is formed. As a result, the actuator 251 is energized in the forward direction at the maximum voltage E [V] and is further charged.

[0055] In this way, in the latter half of charging, the actuator 251 is charged with the maximum voltage E [V] using the positive polarity first voltage source 501 and the negative polarity second voltage source 502. By charging the actuator 251 with the maximum voltage E [V], the actuator 251 is fully charged.

[0056] 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. After the time Tb has been counted, the timer 403 times out, and the state data is updated from STc to STd.

[0057] When the state data is updated from STc to STd (time tc), the switch element 622 is turned off and the switch element 623 is turned on by the drive waveform of the drive pattern data corresponding to the state data STd. At this time, a closed circuit of the actuator 251 → switch element 611 → first voltage source 501 → switch element 623 → actuator 251 is formed. As a result, the actuator 251 discharges.

[0058] In this way, in the first half of the discharge, the charge is returned from the actuator 251 to the positive polarity first voltage source 501, and while the first voltage source 501 is being charged, the actuator 251 is discharged.

[0059] 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. After the time Tc has been counted, the timer 403 times out, and the state data is updated from STd to STe.

[0060] When the state data is updated from STd to STe (time td), the switch element 611 is turned off and the switch element 613 is turned on by the drive waveform of the drive pattern data corresponding to the state data STe. At this time, a closed circuit of the actuator 251 → switch element 613 → switch element 623 → actuator 251 is formed. As a result, the actuator 251 continues to discharge.

[0061] In this way, in the latter half of the discharge, the actuator 251 is completely discharged by looping between the terminals of the actuator 251.

[0062] Through the above charging and discharging operations, the head 100 expands the volume of the pressure chamber, refills it with ink, and then returns the volume of the pressure chamber to its original state. This operation causes pressure vibrations in the pressure chamber, causing ink droplets to be ejected from the nozzle. The ejection occurs during the discharging operation.

[0063] 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. After the time Td has been counted and the timer 403 times out, the state data is updated from STe to STf.

[0064] When the state data is updated from STe to STf (time te), the switch element 623 is turned off and the switch element 621 is turned on by the drive waveform of the drive pattern data corresponding to the state data STf. At this time, a closed circuit of the first voltage source 501 → switch element 621 → actuator 251 → switch element 613 → first voltage source 501 is formed. As a result, the actuator 251 is energized in the reverse direction at E / 2 [V] and charged.

[0065] In this way, in the first half of the reverse charging, the positive polarity first voltage source 501 is used to charge the actuator 251 in the reverse direction up to half the charge at an intermediate voltage E / 2 [V] that is half the maximum voltage E [V].

[0066] 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. After the time Te has been counted, the timer 403 times out, and the state data is updated from STf to STg.

[0067] When the state data is updated from STf to STg (at time tf), the switch element 613 is turned off and the switch element 612 is turned on by the drive waveform of the drive pattern data corresponding to the state data STg. At this time, a closed circuit of the first voltage source 501 → switch element 621 → actuator 251 → switch element 612 → second voltage source 502 → first voltage source 501 is formed. As a result, the actuator 251 is energized in the reverse direction at E [V] and is further charged.

[0068] In this way, in the latter half of the reverse charging, the actuator 251 is charged in the reverse direction at the maximum voltage E [V] using the positive polarity first voltage source 501 and the negative polarity second voltage source 502. By charging the actuator 251 in the reverse direction at the maximum voltage E [V], the actuator 251 is completely charged in the reverse direction.

[0069] When the state data is updated to STf to STg, the selector 402 selects the sixth setting register 4016. As a result, the timer 403 counts the time Tf. After counting the time Tf, when the timer 403 times out, the state data is updated from STg to STh.

[0070] When the state data is updated from STg to STh (time tg), the switch element 612 is turned off and the switch element 613 is turned on by the drive waveform of the drive pattern data corresponding to the state data STh. At this time, a closed circuit of the actuator 251 → switch element 621 → first voltage source 501 → switch element 613 → actuator 251 is formed. As a result, the actuator 251 discharges.

[0071] In this way, in the first half of the discharge, the charge is returned from the actuator 251 to the positive polarity first voltage source 501, and while the first voltage source 501 is being charged, the actuator 251 is discharged.

[0072] 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. After the time Tg has been counted and the timer 403 times out, the state data returns from STh to STa.

[0073] When the state data returns from STh to STa (time point th), the switch element 621 is turned off and the switch element 623 is turned on by the drive waveform of the drive pattern data corresponding to the state data STa. At this time, a closed circuit of the actuator 251 → switch element 623 → switch element 613 → actuator 251 is formed. As a result, the actuator 251 continues to discharge.

[0074] In this way, in the latter half of the discharge, the actuator 251 is completely discharged by looping between the terminals of the actuator 251.

[0075] By the reverse charging and discharging operation described above, the head 100 contracts the volume of the pressure chamber and then returns it to its original state. This operation cancels out any residual vibration in the pressure chamber.

[0076] Thereafter, first waveform generating circuit 4001 repeatedly executes the same operation each time a waveform output start trigger signal is input to state counter 404. By such operation of first waveform generating circuit 4001, charge / discharge circuit 300 switches on and off six switch elements 611, 612, 613, 621, 622, and 623 that form a current path to actuator 251.

[0077] Here, the electrode 21, the applied voltage of which is controlled by turning on and off the three switch elements 621, 622, and 623, is the electrode of one channel capable of ejecting ink, for example, the channel including the pressure chamber 242 in FIG. 5 (hereinafter referred to as the channel Ch.X). The electrode 21, the applied voltage of which is controlled by turning on and off the remaining three switch elements 611, 612, and 613, is the electrode of a channel adjacent to the channel Ch.X, for example, the channel including the pressure chamber 241 in FIG. 5 (hereinafter referred to as the adjacent channel Ch.X-1). The actuator 251 is sandwiched between the electrode 21 of the channel Ch.X and the electrode 21 of the adjacent channel Ch.X-1. Therefore, the actuator 251 is driven by repeated charging and discharging depending on the difference between the voltage applied to the electrode 21 of the channel Ch.X and the voltage applied to the electrode 21 of the adjacent channel Ch.X-1. By appropriately controlling the driving of this actuator 251, it is possible to eject one ink droplet from the nozzle 2 of the channel Ch.X.

[0078] In this way, a waveform that controls the drive of the actuator 251 to eject one ink droplet from nozzle 2 of the channel Ch.X is called an ejection waveform. Also, a waveform that controls the drive of the actuator 251 to prevent ink droplets from being ejected from nozzle 2 of the channel Ch.X is called a non-ejection waveform. Also, a waveform that is inserted before the ejection waveform or non-ejection waveform to improve the ejection performance of the channel Ch.X is called an auxiliary waveform.

[0079] FIG. 10 is an explanatory diagram of the ejection waveform used in this embodiment. The ejection waveform includes an expansion waveform in section SA, a hold waveform in section SB, a first weak contraction waveform in section SC, a contraction waveform in section SD, and a second weak contraction waveform in section SE. The expansion waveform applies a first pulse Pa, which changes from a steady state of 0 [V] to a negative maximum voltage -E [V], to the actuator 251. When the first pulse Pa is applied to the actuator 251, the actuator 251 drives the pressure chamber 24 of the ejection channel Ch.X in a direction that expands it.

[0080] After the time SAt corresponding to the section SA has elapsed, the expansion waveform reaches a steady state of 0 [V]. When the voltage applied to the actuator 251 reaches the steady state of 0 [V], the actuator 251 drives the pressure chamber 24 in a direction to restore its original state.

[0081] Thus, in section SA, the pressure chamber 24 of the ejection channel Ch.X first expands, maintains that expanded state, and then returns to its original state. This change in the volume of the pressure chamber 24 causes an ink droplet to be ejected from the nozzle 2 communicating with this pressure chamber 24. Incidentally, if the time SAt during which the pressure chamber 24 maintains its expanded state corresponding to section SA is set to half the pressure oscillation period 2AL (Acoustic Length) of the pressure chamber 24, i.e., AL, the ink ejection volume will be maximized. The time SAt can be determined by adjusting the time Ta set in the first setting register 4011 and the time Tb set in the second setting register 4012. The expansion waveform of section SA is called a compression pulse, an ejection pulse, etc.

[0082] When the expansion waveform reaches a steady state of 0 [V], the ejection waveform becomes a held waveform. The held waveform holds the steady state of 0 [V] for a time SBt corresponding to the section SB. After the time SBt corresponding to the section SB of the held waveform has elapsed, the ejection waveform becomes a first weak contraction waveform.

[0083] The first weak contraction waveform applies a second pulse Pb to the actuator 251, which changes from a steady state of 0 [V] to an intermediate voltage +E / 2 [V] that is half the positive maximum voltage +E [V]. When the second pulse Pb is applied to the actuator 251, the actuator 251 drives the pressure chamber 24 of the channel Ch.X in a direction to contract. However, the degree of contraction is smaller than the degree to which the pressure chamber 24 contracts when a positive maximum voltage +E [V] is applied by a third pulse Pc, which will be described later. Hereinafter, the degree of contraction of the pressure chamber 24 caused by the second pulse Pb will be referred to as weak contraction, and this weak contraction state will be referred to as a weak contraction state.

[0084] After the time SCt corresponding to the section SC of the weak contraction waveform has elapsed, the ejection waveform becomes a contraction waveform. The contraction waveform applies a third pulse Pc, which changes from an intermediate voltage +E / 2 [V] to a positive maximum voltage +E [V], to the actuator 251. By applying the third pulse Pc to the actuator 251, the actuator 251 drives the pressure chamber 24 of the channel Ch.X in a direction that further contracts.

[0085] After the time SDt corresponding to the section SD of the contraction waveform has elapsed, the ejection waveform becomes a second weak contraction waveform. The second weak contraction waveform applies a fourth pulse Pd, which changes from a maximum voltage +E [V] to an intermediate voltage +E / 2 [V], to the actuator 251. When the fourth pulse Pd is applied to the actuator 251, the actuator 251 drives the pressure chamber 24 of the channel Ch.X in a direction to restore the pressure chamber 24. However, the pressure chamber 24 does not completely restore. When the voltage applied to the actuator 251 becomes an intermediate voltage +E / 2 [V], the pressure chamber 24 enters a weak contraction state.

[0086] After the time SEt corresponding to the section SE of the second weak contraction waveform has elapsed, the ejection waveform becomes a steady state of 0 [V]. When the voltage applied to the actuator 251 becomes a steady state of 0 [V], the pressure chamber 24, which was in a weak contraction state, is completely restored.

[0087] An ejection waveform configured in this manner can suppress the generation of small droplets known as satellites, ink mist, etc. Specifically, the time SBt corresponding to the section SB of the hold waveform, the time SCt corresponding to the section SC of the first weak contraction waveform, the time SDt corresponding to the section SD of the strong contraction waveform, and the time SEt corresponding to the section SE of the second weak contraction waveform are adjusted to appropriate values. By doing so, the generation of small droplets known as satellites, ink mist, etc. can be suppressed. The time SBt can be adjusted by adjusting the time Td set in the fourth setting register 4014. The time SCt can be adjusted by adjusting the time Te set in the fifth setting register 4015. The time SDt can be adjusted by adjusting the time Tf set in the sixth setting register 4016. The time SEt can be adjusted by adjusting the time Tg set in the seventh setting register 4017.

[0088] Thus, the ejection waveform is composed of an expansion waveform in section SA, a hold waveform in section SB, a first weak contraction waveform in section SC, a contraction waveform in section SD, and a second weak contraction waveform in section SE. In other words, the duration of the ejection waveform is the sum of the time SAt corresponding to section SA, the time SBt corresponding to section SB, the time SCt corresponding to section SC, the time SDt corresponding to section SD, and the time SEt corresponding to section SE. Hereinafter, this summed time, i.e., the time from time ta to time th in Figure 10, will be referred to as time DC.

[0089] FIG. 11 is an explanatory diagram of the non-ejection waveform used in this embodiment. The non-ejection waveform includes a weak expansion waveform in section SF and a hold waveform in section SG. The weak expansion waveform applies a fifth pulse Pe to the actuator 251. The fifth pulse Pe changes from a steady state of 0 [V] to an intermediate voltage of -E / 2 [V], which is half the negative maximum voltage -E [V]. When the fifth pulse Pe is applied to the actuator 251, the actuator 251 drives the pressure chamber 24 of the corresponding channel Ch.X in a direction that expands it. However, the degree of expansion is smaller than the degree of expansion of the pressure chamber 24 caused by the application of the negative maximum voltage -E [V] by the first pulse Pa of the ejection waveform. Hereinafter, the degree of expansion of the pressure chamber 24 caused by the fifth pulse Pe will be referred to as weak expansion, and this weak expansion state will be referred to as a weak expansion state.

[0090] The weak expansion waveform reaches a steady state of 0 [V] after the time SFt corresponding to the section SF has elapsed. When the voltage applied to the actuator 251 reaches the steady state of 0 [V], the actuator 251 drives the pressure chamber 24 in a direction to restore its original state.

[0091] Thus, during section SF, the pressure chamber 24 of ejection channel Ch.X first undergoes weak expansion, maintains this weak expansion state, and then returns to its original state. Here, the time SFt during which the pressure chamber 24 maintains the weak expansion state, which corresponds to section SF, is set to 1 / 2 the pressure oscillation period 2AL of the pressure chamber 24, i.e., AL or less (AL≧SFt>0). During time SFt, even if a volume change occurs in the pressure chamber 24 due to the weak contraction waveform, no ink droplets will be ejected from the nozzle 2 communicating with this pressure chamber 24.

[0092] When the weak expansion waveform reaches a steady state of 0 [V], the non-ejection waveform becomes a sustained waveform, which maintains the steady state of 0 [V] for a time SGt corresponding to the section SG.

[0093] In this way, the non-ejection waveform is composed of a weak expansion waveform in section SF and a sustain waveform in section SG. In other words, the required time of the non-ejection waveform is the sum of the time SFt corresponding to section SF and the time SGt corresponding to section SG. This sum time, i.e., the time from time ti to time tk in Figure 11, is equal to the required time DC of the ejection waveform.

[0094] The second waveform generating circuit 4002, which generates a non-ejection waveform for the charge / discharge circuit 300, uses a ternary counter as the state counter 404. The time setting register 401 is composed of a first setting register 4011 and a second setting register 4012. With this configuration, when the state data is updated from STa to STb, the selector 402 selects the first setting register 4011. When the state data is updated from STb to STc, the selector 402 selects the second setting register 4012. Here, the setting time Ta of the first setting register 4011 is the time SFt of the section SF. Similarly, the setting time Tb of the second setting register 4012 is the time SGt of the section SG, that is, the time obtained by subtracting the time SFt from the time DC. This allows the second waveform generating circuit 4002 to generate the non-ejection waveform shown in FIG. 11 for the charge / discharge circuit 300.

[0095] 11, the waveform of the conventional non-ejection waveform in section SF is not a weak contraction waveform, but a holding waveform similar to section SG. In other words, the conventional non-ejection waveform does not cause a volume change in the pressure chamber 24.

[0096] FIG. 12 is an explanatory diagram of the auxiliary waveform used in this embodiment. The auxiliary waveform includes a weak expansion waveform in section SH and a hold waveform in section SI. The weak expansion waveform applies a sixth pulse Pf to the actuator 251. The sixth pulse Pf changes from a steady state of 0 [V] to an intermediate voltage of -E / 2 [V], which is half the negative maximum voltage -E [V]. When the sixth pulse Pf is applied to the actuator 251, the actuator 251 drives the pressure chamber 24 of the corresponding channel Ch.X in a direction to expand. However, the degree of expansion is smaller than the degree of expansion of the pressure chamber 24 caused by the application of the negative maximum voltage -E [V] by the first pulse Pa of the ejection waveform. The degree of expansion is equal to the degree of expansion of the pressure chamber 24 caused by the application of the negative intermediate voltage -E / 2 [V] by the fifth pulse Pe of the non-ejection waveform. Hereinafter, the degree of expansion of the pressure chamber 24 caused by the sixth pulse Pf will also be referred to as weak expansion, and this weak expansion state will be referred to as a weak expansion state.

[0097] The weak expansion waveform reaches a steady state of 0 [V] after the time SHt corresponding to the section SH has elapsed. When the voltage applied to the actuator 251 reaches the steady state of 0 [V], the actuator 251 drives the pressure chamber 24 in a direction to restore its original state.

[0098] Thus, in section SH, the pressure chamber 24 of ejection channel Ch.X first undergoes weak expansion, maintains this weak expansion state, and then returns to its original state. Here, the time SHt during which the pressure chamber 24 corresponding to section SH is maintained in the weak expansion state is set to 1 / 2 the pressure oscillation period 2AL of the pressure chamber 24, i.e., AL or less (AL≧SFt>0). This time SHt may or may not be equal to the time SFt during which the weak expansion state of the non-ejection waveform is maintained, as long as it satisfies the condition of being less than AL. Even if a volume change occurs in the pressure chamber 24 due to the weak expansion waveform during time SHt, ink droplets are not ejected from the nozzle 2 communicating with this pressure chamber 24, just as in the case of a non-ejection waveform.

[0099] When the weakly extended waveform reaches a steady state of 0 [V], the auxiliary waveform becomes a hold waveform. The hold waveform holds the steady state of 0 [V] for a time SIt corresponding to the interval SI.

[0100] As described above, the auxiliary waveform is composed of a weak-expansion waveform in the section SH and a hold waveform in the section SI. In other words, the required time of the auxiliary waveform is the sum of the time SHt corresponding to the section SH and the time SIt corresponding to the section SI. This summed time, i.e., the time from time tl to time tn in FIG. 12 , is the pressure oscillation period 2AL of the pressure chamber 24. Note that the required time of the auxiliary waveform may be set to 4AL, which is twice the pressure oscillation period 2AL, or 6AL, which is three times the pressure oscillation period 2AL, by extending the steady-state hold time SIt by the hold waveform. In other words, the total time of the time SHt during which the auxiliary waveform expands the pressure chamber 24 with the weak-contraction waveform and the time SIt during which the pressure chamber 24 maintains the steady state with the hold waveform may be any integer multiple of the pressure oscillation period of the pressure chamber 24.

[0101] The third waveform generation circuit 4003, which generates a supplemental waveform for the charge / discharge circuit 300, uses a ternary counter for the state counter 404, similar to the second waveform generation circuit 4002. The time setting register 401 is also composed of a first setting register 4011 and a second setting register 4012. With this configuration, when the state data is updated from STa to STb, the selector 402 selects the first setting register 4011. When the state data is updated from STb to STc, the selector 402 selects the second setting register 4012. Here, the set time Ta of the first setting register 4011 is set to the time SHt of the section SH. Similarly, the set time Tb of the second setting register 4012 is set to the time SIt of the section SI, that is, the time obtained by subtracting the time SHt from the time 2AL. This allows the third waveform generation circuit 4003 to generate the supplemental waveform shown in FIG. 12 for the charge / discharge circuit 300. This completes the description of the ejection waveform, non-ejection waveform, and auxiliary waveform used in this embodiment.

[0102] As mentioned above, the ejection waveform shown in Figure 10 can suppress the generation of small droplets known as satellites and ink mist. However, this ejection waveform is prone to leaving residual vibrations after the ink is ejected. As a result, there is a concern that the flight speed of the ink droplets may decrease due to the influence of these residual vibrations, reducing the accuracy of their landing.

[0103] Therefore, in this embodiment, a supplemental waveform is inserted prior to the ejection waveform applied to the actuator 25 provided corresponding to the pressure chamber 24 that ejects ink droplets from the nozzle 2. The supplemental waveform includes a weak expansion waveform that expands the pressure chamber 24 with an intermediate voltage that is smaller than the voltage applied to expand the pressure chamber 24 with the ejection waveform, and a hold waveform that returns the pressure chamber 24 expanded by the weak expansion waveform to a steady state and maintains it. When the actuator 25 is driven with such a supplemental waveform, a pressure change occurs in the pressure chamber 24 corresponding to that actuator 25. However, this pressure change does not cause an ink droplet to be ejected from the nozzle 2. This pressure change has the effect of increasing the ejection speed of ink droplets ejected from the nozzle 2 by the ejection waveform. By increasing the ejection speed of the ink droplets, the landing accuracy of the ink droplets is improved.

[0104] In this embodiment, the non-ejection waveform applied to the actuator 25 provided corresponding to the pressure chamber 24 that does not eject ink droplets from the nozzle 2 is the waveform shown in FIG. 11 . That is, the waveform includes a weak expansion waveform that expands the pressure chamber 24 with an intermediate voltage that is lower than the voltage applied to expand the pressure chamber 24 with the ejection waveform, and a hold waveform that returns the pressure chamber 24 expanded by the weak expansion waveform to a steady state and maintains it. The total time during which the pressure chamber 24 is expanded by the weak contraction waveform and the time during which the steady state of the pressure chamber 24 is maintained by the hold waveform is set to be equal to the duration of the ejection waveform. When the actuator 25 is driven with this non-ejection waveform, a pressure change occurs in the pressure chamber 24 corresponding to that actuator 25. This pressure change is smaller than the pressure change occurring in the pressure chamber 24 when the ejection waveform is applied to the actuator 25, and no ink droplets are ejected from the nozzle 2. By applying the non-ejection waveform to the actuator 25, the actuator 25 vibrates even when ink droplets are not being ejected. This vibration has a positive effect on the drive of the actuator 25 when ejecting ink droplets, making it less likely that erroneous ejection will occur.

[0105] Furthermore, in this embodiment, the auxiliary waveform shown in Figure 12 is inserted prior to the non-ejection waveform. Therefore, the actuator 25 is vibrated even before the non-ejection waveform vibrates the actuator 25. This vibration has a further favorable effect on the driving of the actuator 25 when ejecting ink droplets.

[0106] Incidentally, the insertion of an auxiliary waveform is performed not only when printing using the binary method, in which one dot is formed with one ink droplet, but also when printing in gradation using the multi-drop method, in which one dot is formed with multiple ink droplets ejected in succession.

[0107] 13 is an explanatory diagram of the drive waveform applied to the channel Ch.X in the case of the binary method. As shown in the figure, when the drop count is "0," that is, when no ink droplets are ejected from the channel Ch.X, an auxiliary waveform with a required time of 2AL is applied in the first frame, and a non-ejection waveform with a required time of DC is applied in the second frame. When the drop count is "1," that is, when one ink droplet is ejected from the channel Ch.X, an auxiliary waveform with a required time of 2AL is applied in the first frame, and an ejection waveform with a required time of DC is applied in the second frame.

[0108] In this way, when printing using the binary method, the head 100 applies an auxiliary waveform before each of the ejection waveform and the non-ejection waveform to drive the actuator 25 .

[0109] 14 is an explanatory diagram of the drive waveforms applied to channel Ch.X in the case of a multi-drop method with a maximum of three drops. As shown in the figure, when the number of drops is "0," i.e., when no ink drops are ejected from channel Ch.X, an auxiliary waveform with a required time of 2AL is applied in the first frame, and non-ejection waveforms with a required time of DC are applied in the second, third, and fourth frames. When the number of drops is "1," i.e., when one ink drop is ejected from channel Ch.X, an auxiliary waveform with a required time of 2AL is applied in the first frame, an ejection waveform with a required time of DC is applied in the second frame, and non-ejection waveforms with a required time of DC are applied in the third and fourth frames. When the number of drops is "2," i.e., when two ink drops are ejected from channel Ch.X, an auxiliary waveform with a required time of 2AL is applied in the first frame, an ejection waveform with a required time of DC is applied in the second and third frames, and a non-ejection waveform with a required time of DC is applied in the fourth frame. When the number of drops is "3", i.e., when three ink droplets are ejected from the channel Ch.X, an auxiliary waveform with a required time of 2AL is applied as the first frame, and ejection waveforms with a required time of DC are applied as the second, third, and fourth frames.

[0110] In this way, when performing gradation printing using the multi-drop method, the head 100 applies an auxiliary waveform before the ejection waveform or non-ejection waveform of the first frame to drive the actuator 25.

[0111] FIG. 15 shows the simulation results when an actuator is driven with a drive waveform that does not include the auxiliary waveform of FIG. 12 before the ejection waveform of FIG. 10, thereby ejecting ink droplets. FIG. 16 shows the simulation results when an actuator is driven with a drive waveform that includes the auxiliary waveform of FIG. 12 before the ejection waveform of FIG. 10, thereby ejecting ink droplets. FIG. 17 shows the simulation results when an actuator is driven with a drive waveform that includes the auxiliary waveform of FIG. 12 before the non-ejection waveform of FIG. 11, thereby not ejecting ink droplets. All simulations were performed using an LCR equivalent circuit (not shown) that simulates an inkjet head. The inductance L was set to 0.71 μH, the capacitance C was set to 0.26 Ω, and the resistance R was set to 0.41 μF. In this case, the pressure period specific to the actuator is 3.4 μs (AL = 1.7 μs).

[0112] 15 to 17, the solid line "drive voltage" is a waveform that represents the voltage change of the drive waveform. The dashed-dotted line "pressure" is a waveform that represents the change in pressure generated within the pressure chamber 24. The dashed-two-dotted line "flow velocity" is a waveform that represents the change in the flow velocity of ink flowing into the nozzle 2. The horizontal axis represents the passage of time (μs), and the vertical axis represents the normalized magnitude of each item.

[0113] 15, when an actuator is driven to eject ink droplets using a drive waveform that does not include a supplemental waveform before the ejection waveform, the pressure in the pressure chamber 24 expands due to the expansion waveform in the ejection waveform, and when the expansion waveform restores its original shape at the trailing edge of the expansion waveform, the pressure in the pressure chamber 24 increases rapidly. As a result, an ink droplet is ejected from the nozzle 2 that communicates with the pressure chamber 24.

[0114] After an ink droplet is ejected, the pressure repeats two negative and positive peak values ​​due to the action of the hold waveform, first weak contraction waveform, contraction waveform, and second weak contraction waveform in the ejection waveform. This repetition causes a change in the state of the pressure chamber 24, causing the ink meniscus to swell in the nozzle 2 connected to the pressure chamber 24 to the extent that an ink droplet is not ejected. This meniscus swell shortens the trailing edge, which is the primary cause of satellite formation. As a result, the generation of small droplets that become satellites or ink mist is suppressed. This eliminates concerns about satellites landing on the recording medium and causing print quality degradation such as uneven density or ghosting, and about ink mist adhering to the head 100 or surrounding circuit components, causing malfunction of the printer 200. Furthermore, residual vibrations in the pressure chamber 24 are largely canceled as the pressure chamber 24 returns from its contracted state. However, some residual vibration remains. The residual vibration may reduce the flying speed of ink droplets and reduce the landing accuracy.

[0115] 16, when ink droplets are ejected by driving the actuator with a drive waveform that includes a supplemental waveform before the ejection waveform, the pressure chamber 24 expands due to the expansion waveform in the ejection waveform, and when it returns to its original state at the trailing edge of the expansion waveform, the pressure is significantly greater than when the actuator is driven with a drive waveform that does not include a supplemental waveform before the ejection waveform. This increases the flight speed of the ink droplets, resulting in better landing accuracy.

[0116] A conventional non-ejection waveform does not cause a change in the volume of the pressure chamber 24, and therefore there is no change in the pressure generated within the pressure chamber 24. In contrast, when the actuator is driven by a drive waveform in which an auxiliary waveform is added before the non-ejection waveform of this embodiment, which is made up of a weak expansion waveform and a hold waveform, the pressure generated within the pressure chamber 24 changes as shown by the dashed dotted line in Figure 17. The shape of this pressure change curve is similar to the pressure change curve shown in Figure 16.

[0117] 18 is a graph comparing the pressure change (solid line) in the pressure chamber 24 when the actuator is driven by a drive waveform that does not include the auxiliary waveform of FIG. 12 before the ejection waveform of FIG. 10, with the pressure change (dashed line) in the pressure chamber 24 when the actuator is driven by a conventional non-ejection waveform. As is clear from FIG. 18, there is a large difference in pressure in the pressure chamber 24 between when ink droplets are ejected and when ink droplets are not ejected. If the pressure difference is large, erroneous ejection may occur, such as when ink droplets are not ejected when transitioning from a frame that does not eject ink droplets to a frame that does eject ink droplets. Alternatively, erroneous ejection may occur, such as when ink droplets are ejected when transitioning from a frame that ejects ink droplets to a frame that does not eject ink droplets.

[0118] Fig. 19 is a graph comparing the pressure change (solid line) in the pressure chamber 24 when the actuator is driven by a drive waveform in which the auxiliary waveform of Fig. 12 is inserted before the ejection waveform of Fig. 10, with the pressure change (dashed line) in the pressure chamber 24 when the actuator is driven by a drive waveform in which the auxiliary waveform of Fig. 12 is inserted before the non-ejection waveform of Fig. 11. As is clear from Fig. 19, there is little difference in the pressure change that occurs in the pressure chamber 24 between when ink droplets are ejected and when ink droplets are not ejected. As a result, the above-mentioned erroneous ejection does not occur.

[0119] As described above in detail, according to this embodiment, even when the actuator is driven with a drive waveform that is effective in suppressing small droplets, that is, the ejection waveform shown in FIG. 10, it is possible to improve the landing accuracy of ink droplets.

[0120] Furthermore, by setting the application time of the auxiliary waveform inserted before the ejection waveform to an integer multiple of the pressure vibration period in the pressure chamber 24, it is possible to suppress the influence of the auxiliary waveform on the ejection waveform, which results in easier control of the ejection waveform.

[0121] Furthermore, since the actuator 25 vibrates even when not ejecting, it is possible to reduce erroneous ejections. Furthermore, since an auxiliary waveform is inserted before the non-ejection waveform in the same way as the ejection waveform, there is no deviation in the operation timing between ejection and non-ejection.

[0122] Such an effect is not limited to when the head 100 is driven by the binary method, but can also be achieved when the head 100 is driven by the multi-drop method.

[0123] Although the inkjet head has been described above as an embodiment, the embodiment is not limited to this.

[0124] For example, the ejection waveform is not limited to that shown in Fig. 10. For example, a well-known ejection waveform called a DRP waveform may be used. Applying the auxiliary waveform shown in Fig. 12 to the actuator 25 prior to such an ejection waveform also improves impact accuracy.

[0125] The intermediate voltage for putting the pressure chamber 24 into the weakly expanded state is not necessarily half the maximum voltage E [V] that is the charging target. It is sufficient if the voltage is smaller than the maximum voltage E [V] so that ink droplets are not ejected from the nozzle 2 when the pressure chamber 24 returns from the weakly expanded state to the steady state of 0 [V].

[0126] The head 100 is not limited to the shared wall type, and this embodiment can also be applied to other types of piezo inkjet heads.

[0127] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope of the invention and the scope of the inventions and their equivalents as defined in the claims. The inventions described in the original claims of this application are set forth below. [1] An inkjet head comprising: a pressure chamber that stores ink; a nozzle plate having 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, wherein the drive circuit provides an auxiliary waveform to the actuator, prior to an ejection waveform provided to the actuator that is provided corresponding to the pressure chamber that ejects ink droplets from the nozzle, the auxiliary waveform including: a weak expansion waveform that expands the pressure chamber with an intermediate voltage that is smaller than the voltage applied to expand the pressure chamber with the ejection waveform; and a hold waveform that returns and maintains the pressure chamber expanded by the weak expansion waveform to a steady state, thereby driving the actuator to a degree that does not eject the ink droplets. [2] An inkjet head as described in appendix [1], wherein the total time of the auxiliary waveform, that is, the time during which the pressure chamber is expanded by the weak expansion waveform and the time during which the pressure chamber is maintained in a steady state by the holding waveform, is an integer multiple of the pressure oscillation period in the pressure chamber. [3] An inkjet head according to appendix [1] or [2], wherein the drive circuit includes a weak expansion waveform that expands the pressure chamber with an intermediate voltage that is smaller than the voltage applied to expand the pressure chamber with the ejection waveform, and a hold waveform that returns the pressure chamber expanded by the weak expansion waveform to a steady state and maintains it, for the actuator provided corresponding to the pressure chamber that does not eject ink droplets from the nozzle, and the total time of the time to expand the pressure chamber with the weak expansion waveform and the time to maintain the steady state of the pressure chamber with the hold waveform is equal to the time of the ejection waveform by applying a non-ejection waveform to the actuator, thereby driving the actuator to a degree that does not eject ink droplets. [4] The inkjet head according to appendix [3], wherein the auxiliary waveform is applied to the actuator prior to the non-ejection waveform, and the actuator is driven to an extent that the ink droplets are not ejected. [5] The inkjet head according to appendix [3] or [4], wherein, when driving the actuators in a multi-drop manner in which one dot is formed by successively ejecting ink droplets from the nozzles, the drive circuit applies the ejection waveform to the actuators provided corresponding to the pressure chambers that eject the ink droplets, and applies a non-ejection waveform to the actuators provided corresponding to the pressure chambers that do not eject the ink droplets, and further applies the auxiliary waveform to the actuators before first applying the ejection waveform or the non-ejection waveform to the actuators, thereby driving the actuators to a degree that does not eject the ink droplets. [Explanation of symbols]

[0128] 2...Nozzle, 3...Head body, 4...Head driver, 14, 141, 142...Piezoelectric member, 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...RA M, 204...operation panel, 205...communication interface, 206...conveyor motor, 207...motor drive circuit, 208...pump, 209...pump drive circuit, 300...charge / discharge circuit, 401...time setting register, 402...selector, 403...timer, 404...state counter, 405...drive pattern memory, 500...power supply circuit, 4001...first waveform generating circuit, 4002...second waveform generating circuit, 4003...third waveform generating circuit.

Claims

1. a pressure chamber that contains ink; a nozzle plate having a nozzle communicating with the pressure chamber; an actuator provided corresponding to the pressure chamber, for displacing the volume of the pressure chamber; a drive circuit for driving the actuator; Equipped with the drive circuit includes, prior to an ejection waveform to be applied to the actuator provided corresponding to the pressure chamber that ejects ink droplets from the nozzle, a weak expansion waveform that expands the pressure chamber with an intermediate voltage that is smaller than the voltage applied to expand the pressure chamber with the ejection waveform, and a hold waveform that returns the pressure chamber expanded by the weak expansion waveform to a steady state and maintains it, and the total time of the time to expand the pressure chamber with the weak expansion waveform and the time to maintain the steady state of the pressure chamber with the hold waveform is an integer multiple of the pressure oscillation period in the pressure chamber, and drives the actuator to a degree that does not eject the ink droplets, an inkjet head, wherein the drive circuit further provides to the actuator a non-ejection waveform that includes the weak expansion waveform and the hold waveform for the actuator provided corresponding to the pressure chamber that does not eject ink droplets from the nozzle, the total time of the time to expand the pressure chamber with the weak expansion waveform and the time to maintain the steady state of the pressure chamber with the hold waveform being equal to the time of the ejection waveform, and further provides to the actuator the auxiliary waveform prior to the non-ejection waveform, thereby driving the actuator to a degree that does not eject ink droplets.

2. 2. The inkjet head according to claim 1, wherein, when driving the actuators in a multi-drop system in which one dot is formed by successively ejecting ink droplets from the nozzles, the drive circuit applies the ejection waveform to the actuators provided corresponding to the pressure chambers that eject the ink droplets, and applies a non-ejection waveform to the actuators provided corresponding to the pressure chambers that do not eject the ink droplets, and further applies the auxiliary waveform to the actuators before first applying the ejection waveform or the non-ejection waveform to the actuators, thereby driving the actuators to a degree that does not eject the ink droplets.

Images