Inkjet head

Abstract

To stabilize an ejection speed of multi-drop operation, without concern for increase in the amount of heat generated or the like.SOLUTION: An inkjet head includes a pressure chamber that stores ink, a nozzle plate comprising a nozzle communicating with the pressure chamber, an actuator provided to correspond to the pressure chamber, which varies volumes of the pressure chamber, and a driving circuit that drives the actuator. The driving circuit provides, to the actuator, a pulse by which the actuator is driven so as to contract the pressure chamber to increase pressure in the pressure chamber, then a contracted state of the pressure chamber is held until the pressure in the pressure chamber reduces into negative pressure and increases again into positive pressure and thereafter the pressure chamber is restored, as an auxiliary pulse by which ink is not ejected prior to a driving pulse for ejecting ink.SELECTED DRAWING: Figure 9

Description

[Technical field]

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

[0002] There is a type of inkjet head in which the partition walls of adjacent pressure chambers serve as actuators. In this type of inkjet head, when a drive pulse including an expansion pulse and a contraction pulse is applied to the actuator, the partition walls deform in a direction that expands or contracts the pressure chamber, generating pressure vibrations in the pressure chamber. The volume of the pressure chamber changes due to the pressure vibrations, and ink droplets are ejected from a nozzle that communicates with the pressure chamber.

[0003] In this way, the inkjet head ejects ink droplets from the nozzles by deforming the partitions of the pressure chambers, so that adjacent nozzles that are connected to adjacent pressure chambers cannot eject ink droplets simultaneously. Therefore, the inkjet head divides each pressure chamber into, for example, three groups of two, and changes the phase of the drive pulse for each group. For this reason, depending on the image pattern, a state occurs in which only one nozzle ejects ink and the other nozzles do not eject ink (hereinafter referred to as a single-nozzle drive state), a state in which only one nozzle in one group ejects ink and the other nozzles do not eject ink (hereinafter referred to as a multiple-nozzle simultaneous drive state), and a state in which ink is ejected in a time-division manner from nozzles that belong to at least two groups (hereinafter referred to as a multiple-nozzle continuous drive state).

[0004] In recent years, there has been a demand for high-resolution inkjet heads. To achieve high-resolution inkjet heads, it is necessary to make the actuator smaller. To eject ink at a given flying speed using a small actuator, the electric field applied to the actuator must be strong. If the electric field applied to the actuator is strong, the nonlinearity of the actuator cannot be ignored.

[0005] Inkjet heads in which adjacent pressure chambers share each of these actuators, each pressure chamber is divided into three groups of two, and the phase of the drive pulse is changed for each group to drive them sequentially, produce a large difference in ejection speed between the multiple nozzle simultaneous drive state and the multiple nozzle consecutive drive state. This is because, in the multiple nozzle simultaneous drive state and the multiple nozzle consecutive drive state, the direction of the previous drive history of the actuator shared with adjacent pressure chambers is reversed depending on whether ejection occurs from the adjacent pressure chamber.

[0006] To solve this problem, a technology is known in which an auxiliary pulse including an expansion pulse and a contraction pulse that are not strong enough to eject ink droplets from the nozzle is applied to the actuator before the drive pulse that ejects the first drop, thereby resetting the actuator's drive direction history and stabilizing the ejection speed of multiple drops regardless of the drive state.

[0007] However, this technology uses two auxiliary pulses, an expansion pulse and a contraction pulse, which increases the number of drive cycles, raising concerns about increased heat generation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2017-013487 A [Patent Document 2] JP 2018-114642 A Summary of the Invention [Problem to be solved by the invention]

[0009] The problem that the embodiments of the present invention aim to solve is to provide an inkjet head capable of high quality printing by using a single pulse as an auxiliary pulse, thereby eliminating concerns about increased heat generation, and stabilizing the multi-drop ejection speed regardless of the driving state. [Means for solving the problem]

[0010] In one embodiment, the inkjet head includes a pressure chamber that contains ink, a nozzle plate having a nozzle communicating 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 in a direction to contract the pressure chamber to increase the pressure in the pressure chamber, and then maintains the contracted state of the pressure chamber until the pressure decreases and turns negative, increases again and turns positive, as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, and then applies a pulse to the actuator to restore the pressure chamber. The auxiliary pulse causes the pressure chamber to return from the contracted state stepwise in a plurality of times at the trailing edge of the auxiliary pulse. . [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is an exploded perspective view of a part of the inkjet head. [Diagram 2] FIG. 2 is a vertical cross-sectional view of the front portion of the inkjet head. [Diagram 3] FIG. 2 is a cross-sectional view of the front portion of the inkjet head. [Figure 4] 3A and 3B are diagrams for explaining the operation principle of an inkjet head. [Diagram 5] FIG. 1 is a block diagram showing the hardware configuration of an inkjet printer. [Figure 6] FIG. 2 is a block diagram showing a specific configuration of a head driving circuit in an inkjet printer. [Figure 7] 4 is a schematic circuit diagram of a buffer circuit and a switch circuit included in the head drive circuit. [Figure 8] FIG. 4 is a waveform diagram showing an example of a drive pulse for ejecting ink. [Figure 9] FIG. 4 is a schematic diagram of each nozzle of the head as viewed from the print paper transport path side. [Figure 10] FIG. 13 is an explanatory diagram of a multi-nozzle continuous drive state. [Figure 11] FIG. 13 is an explanatory diagram of a multiple nozzle simultaneous driving state. [Figure 12] FIG. 2 is a diagram showing a voltage waveform applied to a PZT test piece. [Figure 13] 13 is a graph showing the charge and displacement when the voltage waveform of FIG. 12 is applied to a PZT test piece. [Figure 14] 13 is a graph showing an example of the ejection velocity for each drop when an auxiliary pulse waveform is not applied. [Figure 15] FIG. 11 is a waveform diagram showing a first embodiment of an auxiliary pulse that is output prior to a drive pulse and does not eject ink. [Figure 16] 16 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 15. [Figure 17] FIG. 11 is a waveform diagram showing a modified example of the auxiliary pulse in the first embodiment. [Figure 18] 18 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulse of FIG. 8 and the auxiliary pulse of FIG. 17. [Figure 19] 18 is a diagram showing another simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 17. [Figure 20] FIG. 11 is a waveform diagram showing a second embodiment of an auxiliary pulse that is output prior to a drive pulse and does not eject ink. [Figure 21] 21 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 20. [Figure 22] FIG. 11 is a waveform diagram showing a modified example of an auxiliary pulse in the second embodiment. [Diagram 23] 23 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulse of FIG. 8 and the auxiliary pulse of FIG. 22. [Figure 24] 23 is a diagram showing another simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 22. [Diagram 25] FIG. 11 is a waveform diagram showing a third embodiment of an auxiliary pulse that is output prior to a drive pulse and does not eject ink. [Figure 26]26 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulse of FIG. 8 and the auxiliary pulse of FIG. 25. [Figure 27] FIG. 13 is a waveform diagram showing a modified example of an auxiliary pulse in the third embodiment. [Figure 28] 28 is a diagram showing a simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 27. [Figure 29] 28 is a diagram showing another simulation result when ink droplets are ejected by a multi-drop method using the drive pulses in FIG. 8 and the auxiliary pulses in FIG. 27. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an inkjet head according to an embodiment will be described with reference to the drawings. In this embodiment, a share-mode shared-wall type inkjet head 100 (see FIG. 1) will be exemplified as the inkjet head.

[0013] First, the configuration of an inkjet head 100 (hereinafter, abbreviated as head 100) will be described with reference to Figures 1 to 3. Figure 1 is a perspective view showing a portion of the head 100 in an exploded state, Figure 2 is a vertical cross-sectional view of the front portion of the head 100, and Figure 3 is a horizontal cross-sectional view of the front portion of the head 100.

[0014] 1 to 3, the head 100 has a base substrate 9. The head 100 has a first piezoelectric member 1 bonded to the upper surface of the front side of the base substrate 9, and a second piezoelectric member 2 bonded on top of the first piezoelectric member 1. The bonded first piezoelectric member 1 and second piezoelectric member 2 are polarized in opposite directions along the plate thickness direction, as shown by the arrows in FIG.

[0015] The base substrate 9 is formed using a material that has a small dielectric constant and a small difference in thermal expansion coefficient from the piezoelectric members 1 and 2. Suitable materials for the base substrate 9 include alumina (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), aluminum nitride (AlN), lead zirconate titanate (PZT), etc. On the other hand, suitable materials for the piezoelectric members 1 and 2 include lead zirconate titanate (PZT), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), etc.

[0016] The head 100 has a large number of long grooves 3 formed from the front end to the rear end of the joined piezoelectric members 1 and 2. The grooves 3 are parallel and spaced at regular intervals. The front end of each groove 3 is open, and the rear end is inclined upward.

[0017] The head 100 has electrodes 4 on the side walls and bottom surface of each groove 3. The electrodes 4 have a two-layer structure of nickel (Ni) and gold (Au). The electrodes 4 are uniformly formed in each groove 3 by, for example, a plating method. The method of forming the electrodes 4 is not limited to the plating method. Other methods such as sputtering and vapor deposition can also be used.

[0018] As shown in Figs. 1 and 3, the head 100 includes a top plate 6 and a nozzle plate 7. The top plate 6 covers the upper portion of each groove 3. The nozzle plate 7 covers the tip of each groove 3. In the head 100, a plurality of pressure chambers 15 are formed by each groove 3 surrounded by the top plate 6 and the nozzle plate 7. The pressure chambers 15 are, for example, 300 µm deep and 80 µm wide, and are arranged in parallel at a pitch of 169 µm. Such pressure chambers 15 are also referred to as ink chambers.

[0019] The top plate 6 is provided with a common ink chamber 5 at the rear inside thereof. Nozzles 8 are drilled into the nozzle plate 7 at positions facing each groove 3. The nozzles 8 communicate with the opposing groove 3, i.e., the pressure chambers 15. The nozzles 8 are tapered from the pressure chamber 15 side towards the ink ejection side on the opposite side. The nozzles 8 are formed in a set corresponding to three adjacent pressure chambers 15, and are offset at a regular interval in the height direction of the groove 3 (the vertical direction on the paper surface of FIG. 2).

[0020] As shown in FIG. 1, the head 100 has an extraction electrode 10 extending from the rear end of each groove 3 toward the rear upper surface of the second piezoelectric member 2. The extraction electrode 10 extends from the electrode 4. The head 100 also has a printed circuit board 11, on which a conductive pattern 13 is formed, bonded to the rear upper surface of the base substrate 9. The head 100 has a drive IC 12 mounted on the printed circuit board 11, on which a head drive circuit 101, described below, is mounted. The drive IC 12 is connected to the conductive pattern 13. The conductive pattern 13 is connected to each extraction electrode 10 with a conductor 14 by wire bonding.

[0021] A set of the pressure chamber 15, the electrode 4, and the nozzle 8 of the head 100 is referred to as a channel. That is, the head 100 has channels ch.1, ch.2, ..., ch.N, the number of which is N, the number of grooves 3.

[0022] Next, the operating principle of the head 100 configured as above will be described with reference to FIG. 4(a) shows a state in which the potentials of the electrodes 4 disposed on the respective wall surfaces of the central pressure chamber 152 and the adjacent pressure chambers 151, 153 on both sides adjacent to this pressure chamber 152 are all at the ground potential GND. In this state, neither the partition wall 161 sandwiched between the adjacent pressure chambers 151, 152 nor the partition wall 162 sandwiched between the adjacent pressure chambers 152, 153 is subjected to any distortion action.

[0023] 4(b) shows a state in which a negative voltage -V is applied to the electrode 4 of the central pressure chamber 152. The potentials of the electrodes 4 of both adjacent pressure chambers 151, 153 remain at the ground potential GND. In this state, an electric field of voltage V acts on each of the partitions 161, 162 in a direction perpendicular to the polarization direction of the piezoelectric members 1, 2. Due to this action, each of the partitions 161, 162 deforms outward so as to expand the volume of the pressure chamber 152.

[0024] FIG. 4(c) shows a state in which a positive voltage +V is applied to the electrode 4 of the central pressure chamber 152. The potentials of the electrodes 4 of both adjacent pressure chambers 151, 153 remain at ground potential GND. In this state, an electric field of voltage V acts on each of the partitions 161, 162 in the opposite direction to that in FIG. 4(b). Due to this action, each of the partitions 161, 162 deforms inwardly so as to contract the volume of the pressure chamber 152.

[0025] When the volume of the pressure chamber 152 is expanded or contracted, a pressure vibration occurs within the pressure chamber 152. Due to this pressure vibration, the pressure within the pressure chamber 152 increases, and ink droplets are ejected from the nozzle 8 that communicates with the pressure chamber 152.

[0026] In this way, the partition 161 separating the pressure chambers 151, 152 and the partition 162 separating the pressure chambers 152, 153 serve as actuators for applying pressure vibrations to the inside of the pressure chamber 152, which has the partitions 161, 162 as its wall surfaces. That is, each pressure chamber 15 shares an actuator with the adjacent pressure chamber 15. For this reason, the head drive circuit 101 cannot drive each pressure chamber 15 individually. The head drive circuit 101 divides each pressure chamber 15 into (n+1) groups for every n (n is an integer of 2 or more) pressure chambers 15 and drives them. In this embodiment, the head drive circuit 101 divides each pressure chamber 15 into three groups for every two pressure chambers 15, so-called three-division drive, is illustrated as an example. Note that the three-division drive is merely an example, and four-division drive or five-division drive may also be used. In the cases shown in (a), (b), and (c) of FIG. 4, voltages -V and +V are applied to the electrode 4 of the central pressure chamber 152 in order to eject ink from the nozzle corresponding to the central pressure chamber 152. The example of ejecting ink from the nozzle corresponding to the central pressure chamber 152 is not limited to this. For example, a voltage -V is applied to the electrode 4 of the central pressure chamber 152, and a voltage +V is applied to the electrodes 4 of the adjacent pressure chambers 151 and 153 on both sides. Conversely, a voltage +V is applied to the electrode 4 of the central pressure chamber 152, and a voltage -V is applied to the electrodes 4 of the adjacent pressure chambers 151 and 153 on both sides. In this case as well, if the applied voltage V is halved, the operation of the actuator will be exactly the same as in the case of FIG. 4.

[0027] Next, the configuration of inkjet printer 200 (hereinafter abbreviated as printer 200) will be described with reference to Figures 5 to 7. Figure 5 is a block diagram showing the hardware configuration of printer 200, Figure 6 is a block diagram showing a specific configuration of head drive circuit 101, and Figure 7 is a schematic circuit diagram of buffer circuit 1013 and switch circuit 1014 included in head drive circuit 101. Printer 200 is applicable to, for example, office printers, barcode printers, POS printers, industrial printers, etc.

[0028] The printer 200 includes a CPU (Central Processing Unit) 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 drive circuit 207, a pump 208, a pump drive circuit 209, and a head 100. The printer 200 also includes a bus line 211 such as an address bus and a data bus. The printer 200 connects the CPU 201, ROM 202, RAM 203, the operation panel 204, the communication interface 205, the motor drive circuit 207, the pump drive circuit 209, and the drive circuit 101 of the head 100 to this bus line 211 directly or via an input / output circuit.

[0029] The CPU 201 corresponds to the central part of the computer. The CPU 201 controls each part to realize various functions of the printer 200 in accordance with an operating system and application programs.

[0030] The ROM 202 corresponds to the 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 CPU 201 to execute processes for controlling each unit.

[0031] The RAM 203 corresponds to the main memory of the computer. The RAM 203 stores data necessary for the CPU 201 to execute processing. The RAM 203 is also used as a work area where information is appropriately rewritten by the CPU 201. The work area includes an image memory where print data is expanded.

[0032] 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, an error reset key, etc. The display section can display various states of the printer 200.

[0033] 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.

[0034] A motor drive circuit 207 controls the drive of the transport motor 206. The transport motor 206 functions as a drive source for a transport mechanism that transports a recording medium such as printing paper. When the transport motor 206 is driven, the transport mechanism starts transporting the recording medium. The transport mechanism transports the recording medium to a printing position by the head 100. The transport mechanism ejects the recording medium after printing from an ejection port (not shown) to the outside of the printer 200.

[0035] A pump drive circuit 209 controls the drive of the pump 208. When the pump 208 is driven, ink in an ink tank (not shown) is supplied to the head 100.

[0036] The head driving circuit 101 drives the channel group 102 of the head 100 based on print data. The head driving circuit 101 includes a pattern generator 1011, a logic circuit 1012, a buffer circuit 1013, and a switch circuit 1014, as shown in FIG.

[0037] The pattern generator 1011 generates waveform patterns such as an ejection target waveform, an ejection adjacent waveforms, a non-ejection target waveform, a non-ejection adjacent waveform, etc. Data of the waveform patterns generated by the pattern generator 1011 is supplied to a logic circuit 1012.

[0038] The logic circuit 1012 accepts the input of print data read out line by line from the image memory. When the print data is input, the logic circuit 1012 sets three adjacent channels ch.(i-1), ch.i, and ch.(i+1) of the head 100 as one set, and determines whether one of the channels, for example, the central channel ch.i, is an ejection channel that ejects ink or a non-ejection channel that does not eject ink. If the channel ch.i is an ejection channel, the logic circuit 1012 outputs pattern data of the ejection target waveform to this channel ch.i, and outputs pattern data of the ejection both adjacent waveforms to the adjacent channels ch.(i-1) and ch.(i+1) on both sides. If the channel ch.i is a non-ejection channel, the logic circuit 1012 outputs pattern data of the non-ejection target waveform to this channel ch.i, and outputs pattern data of the non-ejection both adjacent waveforms to the adjacent channels ch.(i-1) and ch.(i+1) on both sides. Each pattern data output from the logic circuit 1012 is provided to a buffer circuit 1013 .

[0039] The buffer circuit 1013 connects a power supply of a positive voltage Vcc and a power supply of a negative voltage -V. As shown in Fig. 7, the buffer circuit 1013 includes a pre-buffer PB for each of the channels ch.1, ch.2, ..., ch.N of the head 100. Note that Fig. 7 shows pre-buffers PB(i-1), PBi, and PB(i+1) corresponding to three adjacent channels ch.(i-1), ch.i, and ch.(i+1), respectively.

[0040] Each pre-buffer PB has three buffers Ba, Bb, and Bc, namely, first to third buffers Ba, Bb, and Bc. Each of the buffers Ba, Bb, and Bc is connected to a power supply of a positive voltage Vcc and a power supply of a negative voltage -V.

[0041] In each pre-buffer PB, the outputs of the first to third buffers Ba, Bb, and Bc change according to the signal level of the pattern data supplied from the logic circuit 1012. The logic circuit 1012 supplies signals of different levels depending on whether the corresponding channel ch.k (1≦k≦N) is an ejection channel, a non-ejection channel, or a channel adjacent to an ejection channel or a non-ejection channel. The first to third buffers Ba, Bb, and Bc supplied with a high-level signal output a signal at a positive voltage Vcc level. The first to third buffers Ba, Bb, and Bc supplied with a low-level signal output a signal at a negative voltage -V level.

[0042] The output of each pre-buffer PB, that is, the output signals of the first to third buffers Ba, Bb, and Bc, are provided to a switch circuit 1014.

[0043] The switch circuit 1014 connects a power supply of a positive voltage Vcc, a power supply of a positive voltage +V, a power supply of a negative voltage -V, and a ground potential GND. The positive voltage Vcc is higher than the positive voltage +V. As typical values, the positive voltage Vcc is 24 volts and the positive voltage +V is 15 volts. In this case, the negative voltage -V is -15 volts.

[0044] However, the appropriate values ​​for the positive voltage and negative voltage vary depending on the viscosity of the ink. The viscosity of the ink varies depending on the type of ink and the temperature at which it is used. For this reason, the positive voltage +V and the negative voltage -V are selected within a range of about ±15 volts to ±30 volts depending on the type of ink and the temperature at which it is used. In this case, the positive voltage Vcc must be higher than the positive voltage +V, so if the positive voltage +V and the negative voltage -V are a maximum of ±30 volts, then the positive voltage Vcc is set to, for example, 39 volts.

[0045] 7, the switch circuit 1014 has a driver DR for each of the channels ch.1, ch.2, ..., ch.N of the head 100. Note that in FIG. 7, drivers DR(i-1), DRi, and DR(i+1) corresponding to three adjacent channels ch.(i-1), ch.i, and ch.(i+1), respectively, are shown.

[0046] Each driver DR includes a PMOS type field effect transistor Tra (hereinafter referred to as the first transistor Tra) and two NMOS type field effect transistors Trb and Trc (hereinafter referred to as the second transistor Trb and the third transistor Trc). Each driver DR connects a series circuit of the first transistor Tra and the second transistor Trb between a power supply of a positive voltage +V and a ground potential GND, and further connects a third transistor Trc between a connection point of the first transistor Tra and the second transistor Trb and a power supply of a negative voltage -V. Each driver DR also connects a back gate of the first transistor Tra to a power supply of a positive voltage Vcc, and connects the back gates of the second transistor Trb and the third transistor Trc to a power supply of a negative voltage -V. Furthermore, each driver DR connects a first buffer Ba of the corresponding pre-buffer PB to the gate of the second transistor Trb, connects a second buffer Bb to the gate of the first transistor Tra, and connects a third buffer Bc to the gate of the third transistor Trc. Each driver DR applies the potential of the connection point between the first transistor Tra and the second transistor Trb to the electrode 4 of the corresponding channel ch.1, ch.2, . . . , ch.N.

[0047] Therefore, the first transistor Tra is turned off when a signal of the positive voltage Vcc level is input from the second buffer Bb, and is turned on when a signal of the negative voltage -V level is input. The second transistor Trb is turned on when a signal of the positive voltage Vcc level is input from the first buffer Ba, and is turned off when a signal of the negative voltage -V level is input. The third transistor Trc is turned on when a signal of the positive voltage Vcc level is input from the third buffer Bc, and is turned off when a signal of the negative voltage -V level is input.

[0048] The driver DR configured as described above applies a positive voltage +V to the electrode 4 of the corresponding channel ch.1, ch.2, ..., ch.N when the first transistor Tra is turned on and the second transistor Trb and the third transistor Trc are turned off. The driver DR sets the potential of the electrode 4 of the corresponding channel ch.1, ch.2, ..., ch.N to the ground GND level when the first transistor Tra and the third transistor Trc are turned off simultaneously and the second transistor Trb is turned on. The driver DR applies a negative voltage -V to the electrode 4 of the corresponding channel ch.1, ch.2, ..., ch.N when the first transistor Tra and the second transistor Trb are turned off simultaneously and the third transistor Trc is turned on.

[0049] Next, an example of a driving pulse for ejecting ink will be described. The driving pulse is a pulse that is applied to the electrode 4 of the channel that ejects ink (ejection channel ch.x), and further to the actuator.

[0050] FIG. 8 is an explanatory diagram of a DRP waveform, which is an example of a drive pulse. In FIG. 8, the solid line "drive voltage" is a waveform representing the voltage of the drive pulse. The dashed line "pressure" is a waveform representing the change in pressure generated in the pressure chamber 15 by the drive pulse. The dashed line "flow velocity" is a waveform representing the change in the flow velocity of ink flowing into the nozzle 8 by the drive pulse. The dashed line "meniscus" is a waveform representing the change in the position of the ink surface by the drive pulse. The horizontal axis represents the passage of time (s). The vertical axis represents the drive voltage, pressure, flow velocity, waveform, and meniscus size, and the numerical values ​​are normalized. In the following, the natural vibration period 2AL (acoustic length) of the pressure in the pressure chamber 15 is defined as the pressure vibration period T. In this embodiment, the pressure vibration period T is 3.8 μs.

[0051] The drive pulse for ejection includes an expansion pulse (Draw) Pd, a retention time (Release) R, and a contraction pulse (Push) Pp. After applying the expansion pulse Pd from 0V, which is a steady state, the drive pulse maintains 0V for the retention time R, and then applies the contraction pulse Pp. After applying the contraction pulse Pp, the steady state of 0V is maintained.

[0052] The expansion pulse Pd is a pulse for suddenly expanding the pressure chamber 15 of the ejection channel ch.x at its leading edge. The expansion pulse Pd maintains the expanded state of the pressure chamber 15 for a time of T / 2 (1.9 μs) to draw in ink and waits until the pressure of the ink in the pressure chamber 15 changes from negative pressure to positive pressure. After the ink pressure changes from negative pressure to positive pressure, the expansion pulse Pd suddenly returns the pressure chamber 15 from the expanded state at its trailing edge. This return further increases the pressure of the ink, which has become positive pressure, and ink is ejected from the nozzle 8 connected to the pressure chamber 15.

[0053] The retention time R is a time for waiting for the pressure of the ink in the pressure chamber 15 in the restored state to change from positive pressure to negative pressure, reach the maximum negative pressure, and then increase again.

[0054] The contraction pulse Pp, at its leading edge, contracts the pressure chamber 15 in which the ink pressure has started to increase due to the lapse of the retention time R, and at its trailing edge, returns the pressure chamber 15 from the contracted state. This contraction and return cancels the residual vibration of the pressure chamber 15.

[0055] The DRP waveform first puts the pressure chamber 15 into an expanded state, and the ink ejection volume is maximized when the time for which the expanded state is maintained is 1 / 2 the pressure vibration period T of the pressure chamber 15. If the time for which the expanded state is maintained is longer or shorter than 1 / 2 the pressure vibration period T, the ink ejection volume decreases. Therefore, in the DRP waveform, the time for which the pressure chamber 15 is maintained in an expanded state may be shifted from 1 / 2 the pressure vibration period T for the purpose of adjusting the ejection volume, etc. The drive waveform for ejecting ink is not limited to the DRP waveform. Other drive waveform pulse waveforms may be used as the drive pulse.

[0056] Next, the multi-nozzle simultaneous drive state and the multi-nozzle continuous drive state will be explained once again with reference to FIGS. FIG. 9 is a schematic diagram of each nozzle 8 of the head 100 of FIGS. 1 to 4 as viewed from the transport path side of the printing paper PA. As shown in the figure, the head 100 of this embodiment has three rows of nozzles 8 in a staggered arrangement. In this type of head 100, adjacent pressure chambers (151, 152, 153, etc.) share actuators (161, 162, etc.), so that adjacent nozzles 8 cannot simultaneously eject ink droplets. For this reason, the pressure chambers 15 corresponding to each nozzle 8 are divided into a (3n+1)th group, a (3n+2)th group, and a (3n+3)th group, and are sequentially driven in a time-division manner. For example, in FIG. 9, when the printing paper PA is transported in the direction of the arrow, in order to print a horizontal line, the pressure chambers 15 corresponding to the nozzles 8 with the symbol a are driven first, followed by the pressure chambers 15 corresponding to the nozzles 8 with the symbol c, followed by the pressure chambers 15 corresponding to the nozzles 8 with the symbol b. 9, the nozzle 8 with the reference symbol b is the nozzle of interest, and the pressure chamber 15 corresponds to the pressure chamber 152 in FIG 4. The nozzles 8 with the reference symbols a and c are nozzles adjacent to the nozzle of interest, and the pressure chamber 15 corresponds to the pressure chambers 151 and 153 in FIG 4.

[0057] FIG. 10 is an explanatory diagram of the multi-nozzle continuous drive state. The multi-nozzle continuous drive state refers to a state in which ink is ejected in a time-division manner from nozzles belonging to at least two groups. For example, as shown in FIG. 10(a), to obtain a print image of two horizontal lines, the actuators are driven so that the required amount of ink droplets are ejected from the nozzles 8 in the time order of the symbols a, c, and b, as shown in FIG. 10(b). In this case, adjacent actuators are all driven with a time lag. This type of drive mode is called multi-nozzle continuous drive. Here, continuous drive means that nozzles 8 that are continuous in the spatial direction (the direction in which the nozzles are arranged) are driven.

[0058] FIG. 11 is an explanatory diagram of the multi-nozzle simultaneous drive state. The multi-nozzle simultaneous drive state refers to a state in which ink is ejected from nozzles belonging to one of the groups, and ink is not ejected from nozzles belonging to the other groups. For example, to obtain a print image in which multiple dots arranged horizontally are arranged in multiple rows as shown in FIG. 11(a), the actuator is driven so that the required amount of ink is ejected from nozzles belonging to the same group when the group is divided into a (3n+1)th group, a (3n+2)th group, and a (3n+3)th group, as shown in FIG. 11(b). This type of drive mode is called multi-nozzle simultaneous drive.

[0059] Simultaneous driving of multiple nozzles is the simplest behavior of the pressure chambers 15. That is, the actuators belonging to the same group are driven uniformly in the arrangement direction of the nozzles, so the pressure chambers 15 of all channels behave uniformly.

[0060] On the other hand, multi-nozzle continuous driving shows complex behavior in the time domain because when ink droplets are ejected from an adjacent channel, the history of driving one wall of the actuator of that channel, which is shared with the adjacent channel, affects the operation of the actuator of that channel.

[0061] Furthermore, in the continuous nozzle drive state, the direction of the history when the actuator operates is different between the first drop and the second drop and thereafter. This difference in direction is the cause of the large drop in the ejection speed of the first drop. To understand the reason for this, next we will explain the hysteresis characteristics of PZT (lead zirconate titanate) used as the piezoelectric members 1 and 2.

[0062] To explain the hysteresis characteristics, a PZT test piece is used. The test piece is a rectangular parallelepiped with a height of 10 mm, a width of 3 mm, and a thickness of 0.2 mm. The test piece is polarized in the height direction, and a voltage with the waveform shown in Fig. 12 is applied in the thickness direction. The voltage is set to 60 V, since the thickness of the test piece is about 2.3 times the thickness of the partition wall of the head 100.

[0063] When the voltage waveform shown in Fig. 12 was applied and the charge P1 [μC / cm2] injected into the test piece and the displacement d [nm] of the test piece were measured, the results shown in Fig. 13 were obtained. That is, when the actuator had a history in the same direction, a voltage change of 60 [V] caused a displacement of 60 [nm] in the test piece. In contrast, when the actuator had a history in the opposite direction, a voltage change of 60 [V] caused a displacement of 80 [nm] in the test piece. In other words, by having a history in the opposite direction, the displacement increased to 133% compared to when the actuator had a history in the same direction. Thus, the displacement of the test piece was smaller when the actuator had a history in the same direction than when the actuator had a history in the opposite direction. Therefore, it is considered that the ejection speed drops significantly in the first drop in the multi-nozzle continuous driving state with a history in the same direction.

[0064] FIG. 14 shows an example of the ejection speed [m / s] when only one drop or two to five drops are ejected consecutively by the multi-drop method without adding an auxiliary pulse waveform in each of the multiple nozzle simultaneous drive state and the multiple nozzle consecutive drive state. In FIG. 14, the value on the vertical axis of the point plotted corresponding to the value "1" on the horizontal axis is the ejection speed when only one drop is ejected. The value on the vertical axis of the point plotted corresponding to the value "2" on the horizontal axis is the ejection speed of the second drop when two drops are ejected consecutively. The value on the vertical axis of the point plotted corresponding to the value "3" on the horizontal axis is the ejection speed of the third drop when three drops are ejected consecutively. The value on the vertical axis of the point plotted corresponding to the value "4" on the horizontal axis is the ejection speed of the fourth drop when four drops are ejected consecutively. The value on the vertical axis of the point plotted corresponding to the value "5" on the horizontal axis is the ejection speed of the fifth drop when five drops are ejected consecutively. 14, the dashed and dotted line graph indicates the ejection speed [m / s] in the multi-nozzle simultaneous drive state, and the dashed line graph indicates the ejection speed [m / s] in the multi-nozzle continuous drive state.

[0065] When an auxiliary pulse is not applied, in the multi-nozzle simultaneous drive state and the multi-nozzle continuous drive state, the ejection speed when only one drop is ejected and when the first drop is ejected when two or more drops are ejected in succession is slower than the ejection speed of the final drop when two or more drops are ejected in succession, as shown in Figure 14. In particular, in the multi-nozzle continuous drive state, the ejection speed when only one drop is ejected is extremely slow, and stable print quality cannot be obtained.

[0066] This problem can be solved by applying an auxiliary pulse to the actuator prior to the drive pulse for ejecting ink. Next, the auxiliary pulse will be described.

[0067] The auxiliary pulse is a pulse that does not eject ink. If an auxiliary pulse is applied to the actuator immediately before driving the actuator for ejection, and the actuator is driven to a degree that does not eject ink, it will affect the subsequent ejection. The effects include differences in amplitude depending on the actuator's history and residual vibrations remaining immediately before driving. In particular, when ink droplets are ejected using a multi-drop method, the auxiliary pulse has a large effect on the ejection speed of the first and second drops. In order to obtain good ejection characteristics, it is necessary to be able to appropriately control both the differences in amplitude depending on the actuator's history and the residual vibrations remaining immediately before driving for ejection. Therefore, first, an auxiliary pulse that resets the history and leaves no residual vibration thereafter will be described. Next, an auxiliary pulse that is modified to intentionally leave a desired residual vibration immediately before driving will be described.

[0068] [First Example] FIG. 15 is an explanatory diagram of the auxiliary pulse Pa according to the first embodiment. In FIG. 15, the solid line "driving voltage" is a waveform representing the voltage of the auxiliary pulse Pa. The dashed and dotted line "pressure" is a waveform representing the change in pressure generated in the pressure chamber 15 by the auxiliary pulse Pa. The dashed and dotted line "flow velocity" is a waveform representing the change in the flow velocity of ink flowing into the nozzle 8 by the auxiliary pulse Pa. The dashed line "meniscus" is a waveform representing the change in the position of the ink surface by the auxiliary pulse Pa. The horizontal axis represents the passage of time (s). The vertical axis represents the driving voltage, pressure, flow velocity, waveform, and meniscus size, and the numerical values ​​are normalized.

[0069] The auxiliary pulse Pa applies a voltage from 0V, which is a steady state, to contract the pressure chamber 15, and after maintaining the voltage for a certain period of time, gradually reduces the voltage and returns it to 0V. The auxiliary pulse Pa suddenly contracts the pressure chamber 15 at its leading edge and maintains the contracted state. At this time, the pressure generated in the pressure chamber 15 increases abruptly due to the contraction. Then, while the contracted state is maintained, the pressure decreases and turns to negative pressure, eventually reaching the maximum negative pressure. The maximum negative pressure is reached after 1 / 2 the pressure vibration period T has elapsed from the leading edge of the auxiliary pulse Pa. After that, the pressure generated in the pressure chamber 15 increases again and turns to positive pressure. If the contracted state of the pressure chamber 15 were maintained as it is, the pressure generated in the pressure chamber 15 would reach a maximum value when the time of the pressure vibration period T has elapsed from the leading edge of the auxiliary pulse Pa, and the residual vibration would continue. However, if the pressure chamber 15, which was in a contracted state, is gradually restored after the pressure generated in the pressure chamber 15 turns to a positive pressure, the residual vibration can be stopped with the actuator having a history of contraction.

[0070] The auxiliary pulse Pa, at its rear edge, returns the pressure chamber 15 in two stages. The first stage return operation adjusts the magnitude of vibration so that the pressure generated in the pressure chamber 15 due to the pressure change caused by the subsequent second stage return operation becomes zero. The second stage return operation is performed when the ink flow velocity in the pressure chamber 15 becomes zero. The time from the start of the contraction operation, which is its leading edge, to the end of the second stage return operation, which is its trailing edge, is equal to or longer than the pressure vibration period T of the pressure chamber 15, e.g., 4.4 μs.

[0071] The auxiliary pulse Pa having such a configuration is applied to the actuator prior to the drive pulse for ejecting ink. By doing so, the residual vibration of the pressure chamber 15 is cancelled in a state in which the actuator always has a history of contraction. Then, after the actuator always has a history of contraction and after the residual vibration of the pressure chamber 15 has been cancelled, a drive pulse for ejecting ink is applied to the actuator. In other words, regardless of the print contents at the previous drive time, the history of the drive direction of the actuator before ink ejection is always aligned in one direction.

[0072] In this way, the auxiliary pulse Pa in the first embodiment is a signal that first resets the actuator's history and leaves no residual vibration thereafter. In other words, the auxiliary pulse Pa fixes the actuator's history in one direction, thereby eliminating amplitude differences that depend on the history, and also stops the residual vibration before the subsequent ejection.

[0073] Fig. 16 is a diagram showing the results of a simulation in which ink droplets are ejected by a multi-drop method using the drive pulse (PRD waveform) in Fig. 8 and the auxiliary pulse Pa in Fig. 15. The simulation was performed using an LCR equivalent circuit (not shown) that simulates an inkjet head. Fig. 16 shows an example in which the auxiliary pulse Pa is applied once, and then the drive pulse is applied three times.

[0074] In FIG. 16, the solid line "drive voltage" is a waveform that represents the voltage change of the auxiliary pulse Pa and the drive pulse. The drive pulse includes an expansion pulse Pd and a contraction pulse Pp. The dashed and dotted line "pressure" is a waveform that represents the change in pressure generated within the pressure chamber 15. The dashed and dotted line "flow velocity" is a waveform that represents the change in the flow velocity of the ink flowing into the nozzle 8. The dashed line "meniscus" is a waveform that represents the change in the position of the ink liquid surface. In FIG. 16, the horizontal axis represents the passage of time (s), and the vertical axis represents the normalized magnitude of each item.

[0075] 16, by applying an auxiliary pulse Pa prior to a drive pulse for ejecting ink, the history of the drive direction of the actuator before ink ejection becomes the contraction direction. Also, the residual vibration of the pressure chamber 15 is canceled. Thus, ink ejected continuously by the multi-drop method is ejected at a constant ejection speed in the simulation.

[0076] However, in reality, the operation does not exactly follow the simulation, and there are cases where it is desired to adjust the subsequent behavior by leaving residual vibration before ejection. Therefore, next, as a modification of the auxiliary pulse Pa, an auxiliary pulse Pe that intentionally leaves residual vibration after resetting the history will be described.

[0077] Fig. 17 is an explanatory diagram of the auxiliary pulse Pe. In Fig. 17, the vertical axis, horizontal axis, solid line "driving voltage", dashed line "pressure", double-dashed line "flow velocity", and dashed line "meniscus" are the same as those explained in Fig. 15, so the explanation here will be omitted.

[0078] Like the auxiliary pulse Pa, the auxiliary pulse Pe also contracts the pressure chamber 15 by applying a voltage from 0V, which is a steady state, and after maintaining the voltage for a certain period of time, the voltage is gradually reduced and returned to 0V. The auxiliary pulse Pe is a modified version of the auxiliary pulse Pa that intentionally leaves residual vibration. Residual vibration can be left by shifting the timing of the stepwise return operation of the auxiliary pulse Pa. The auxiliary pulse Pe intentionally leaves residual vibration by delaying the timing of the first return step.

[0079] By delaying the timing of the first stage of return, the pressure vibration in the pressure chamber 15 is reduced by the subsequent second stage return operation, but does not become zero. In other words, the pressure vibration in the pressure chamber 15 remains. In this way, while the pressure vibration in the pressure chamber 15 remains, the output of the drive pulse is started. By doing so, it is possible to adjust the ejection speed of the first or second drop.

[0080] Fig. 18 shows the simulation results when the ejection speed of the first drop is increased, and Fig. 19 shows the simulation results when the ejection speed of the second drop is increased. Fig. 18 and Fig. 19 show an example in which the auxiliary pulse Pe is applied once, and then the drive pulse is applied three times.

[0081] The difference between the simulation in FIG. 18 and the simulation in FIG. 19 is the waiting time Ha from the end of the second-stage return operation of the auxiliary pulse Pe to the leading edge of the expansion pulse Pd of the drive pulse. In the simulation in FIG. 18, the waiting time Ha is shorter than that in the simulation in FIG. 19. By shortening the waiting time Ha, when the pressure in the pressure chamber 15 is negative, the pressure chamber 15 of the ejection channel ch.x is suddenly expanded by the leading edge of the expansion pulse Pd. In this way, the negative pressure generated in the pressure chamber 15 is larger than when the auxiliary pulse Pa is applied. Therefore, the positive pressure generated in the pressure chamber 15 when the pressure chamber 15 is suddenly returned to the expanded state by the trailing edge of the expansion pulse Pd is larger than when the auxiliary pulse Pa is applied. As a result, the ejection speed of the first drop is faster.

[0082] On the other hand, in the simulation of Fig. 19, the waiting time Ha is longer than in the simulation of Fig. 18. By lengthening the waiting time Ha, when the pressure in the pressure chamber 15 is positive, the pressure chamber 15 of the ejection channel ch.x is suddenly expanded at the leading edge of the expansion pulse Pd. In this way, the negative pressure generated in the pressure chamber 15 is smaller than when the auxiliary pulse Pa is applied. Therefore, the positive pressure generated in the pressure chamber 15 when the pressure chamber 15 is suddenly returned to the expanded state at the trailing edge of the expansion pulse Pd is smaller than when the auxiliary pulse Pa is applied. As a result, the ejection speed of the second drop is faster than the ejection speed of the first drop.

[0083] For example, for an inkjet head in which the ejection speed of the first drop decreases, the auxiliary pulse Pe that produces the simulation result in Fig. 18 is effective. For an inkjet head in which the ejection speed of the second drop decreases, the auxiliary pulse Pe that produces the simulation result in Fig. 19 is effective.

[0084] In this way, by applying the auxiliary pulse Pa or auxiliary pulse Pe, which does not eject ink, to the actuator prior to the drive pulse for ejecting ink, it is possible to achieve the effect of stabilizing the ejection speed of multi-drops regardless of the drive state, such as the multi-nozzle continuous drive state or the multi-nozzle simultaneous drive state, etc. As a result, it is possible to provide an inkjet head 100 capable of high-quality printing.

[0085] Moreover, the auxiliary pulse Pa or the auxiliary pulse Pe is composed of one pulse signal. Therefore, the number of times of driving is less than when an auxiliary pulse including an expansion pulse and a contraction pulse is output. As a result, there is no concern about an increase in heat generation.

[0086] [Second Example] Fig. 20 is an explanatory diagram of the auxiliary pulse Pb according to Example 2. Note that in Fig. 20 as well, the vertical axis, horizontal axis, solid line "driving voltage", dashed line "pressure", dashed line "flow velocity", and dashed line "meniscus" are the same as those explained in Fig. 15, so explanations thereof will be omitted here.

[0087] The auxiliary pulse Pb has a different leading edge compared to the auxiliary pulse Pa. That is, the auxiliary pulse Pb contracts the pressure chamber 15 in two stages at its leading edge. The auxiliary pulse Pb contracts the pressure chamber 15 in stages by applying a voltage from 0V, which is a steady state, and after maintaining the voltage for a certain period of time, the voltage is reduced stepwise and returned to 0V. The first stage contraction operation contracts the pressure chamber 15 at its leading edge, and maintains the contracted state. At this time, the pressure generated in the pressure chamber 15 increases due to the contraction, but while the contracted state is maintained, the pressure decreases to zero.

[0088] When the pressure generated in the pressure chamber 15 becomes zero, a second-stage contraction operation is performed. This contraction operation causes the pressure generated in the pressure chamber 15 to increase again. Then, while the second-stage contraction state is maintained, the pressure decreases and turns to negative pressure, eventually reaching the maximum negative pressure. The maximum negative pressure is reached after the elapse of 1 / 2 the pressure vibration period T from the second-stage contraction of the auxiliary pulse Pa. After that, the pressure generated in the pressure chamber 15 increases again and turns to positive pressure.

[0089] When the pressure that has turned positive becomes zero, the auxiliary pulse Pb, like the auxiliary pulse Pa, returns the pressure chamber 15 in two stages. The first stage return operation adjusts the magnitude of vibration so that the pressure generated in the pressure chamber 15 due to the pressure change caused by the subsequent second stage return operation becomes zero. The second stage return operation is performed when the ink flow rate in the pressure chamber 15 becomes zero. With this type of auxiliary pulse Pb, the time from the start of the first stage contraction operation, which is its leading edge, to the end of the second stage return operation, which is its trailing edge, is equal to or longer than the pressure vibration period T of the pressure chamber 15, e.g., 4.8 μs.

[0090] The auxiliary pulse Pb having such a configuration is applied to the actuator prior to the drive pulse for ejecting ink. By doing so, the residual vibration of the pressure chamber 15 is cancelled in a state in which the actuator always has a history of contraction. Then, after the actuator always has a history of contraction and after the residual vibration of the pressure chamber 15 has been cancelled, a drive pulse for ejecting ink is applied to the actuator. In other words, regardless of the print contents at the previous drive time, the history of the drive direction of the actuator before ink ejection is always aligned in one direction.

[0091] In this way, the auxiliary pulse Pb in the second embodiment is also a signal that first resets the actuator's history and leaves no residual vibration thereafter. In other words, the auxiliary pulse Pb fixes the actuator's history in one direction, thereby eliminating amplitude differences that depend on the history, and stops the residual vibration before the next ejection.

[0092] Fig. 21 is a diagram showing the results of a simulation in which ink droplets are ejected by a multi-drop method using the drive pulse (PRD waveform) of Fig. 8 and the auxiliary pulse Pb of Fig. 20. The simulation was performed using an LCR equivalent circuit (not shown) that simulates an inkjet head. Fig. 21 shows an example in which the auxiliary pulse Pb is applied once, and then the drive pulse is applied three times.

[0093] In FIG. 21, the solid line "drive voltage" is a waveform that represents the voltage change of the auxiliary pulse Pb and the drive pulse. The drive pulse includes an expansion pulse Pd and a contraction pulse Pp. The dashed and dotted line "pressure" is a waveform that represents the change in pressure generated within the pressure chamber 15. The dashed and dotted line "flow velocity" is a waveform that represents the change in the flow velocity of the ink flowing into the nozzle 8. The dashed line "meniscus" is a waveform that represents the change in the position of the ink liquid surface. In FIG. 21, the horizontal axis represents the passage of time (s), and the vertical axis represents the normalized magnitude of each item.

[0094] As shown in Fig. 21, by applying an auxiliary pulse Pb prior to the drive pulse for ejecting ink, the history of the drive direction of the actuator before ink ejection becomes the contraction direction. Also, the residual vibration of the pressure chamber 15 is canceled. Thus, ink ejected continuously by the multi-drop method is ejected at a constant ejection speed in the simulation.

[0095] However, in reality, the operation does not exactly follow the simulation, and there are cases where it is desired to adjust the subsequent behavior by leaving residual vibration before ejection. Therefore, next, as a modification of the auxiliary pulse Pb, an auxiliary pulse Pf that intentionally leaves residual vibration after resetting the history will be described.

[0096] Fig. 22 is an explanatory diagram of the auxiliary pulse Pf. Note that in Fig. 22, the vertical axis, horizontal axis, solid line "driving voltage", dashed line "pressure", double-dashed line "flow velocity", and dashed line "meniscus" are the same as those explained in Fig. 15, so the explanation here will be omitted.

[0097] The auxiliary pulse Pf is a modified version of the auxiliary pulse Pb so as to intentionally leave residual vibration. In the auxiliary pulse Pf, similar to the auxiliary pulse Pe, residual vibration can be left by shifting the timing of the stepwise return operation. The auxiliary pulse Pf applies a voltage from 0V, which is the steady state, to contract the pressure chamber 15 stepwise, and after maintaining the voltage for a certain period of time, the voltage is reduced stepwise to return to 0V. The auxiliary pulse Pf intentionally leaves residual vibration by delaying the timing of the first return step.

[0098] By delaying the timing of the first stage of return, the pressure vibration in the pressure chamber 15 is reduced by the subsequent second stage return operation, but does not become zero. In other words, the pressure vibration in the pressure chamber 15 remains. In this way, while the pressure vibration in the pressure chamber 15 remains, the output of the drive pulse is started. By doing so, it is possible to adjust the ejection speed of the first or second drop.

[0099] Fig. 23 shows the simulation results when the ejection speed of the first drop is increased, and Fig. 24 shows the simulation results when the ejection speed of the second drop is increased. Figs. 23 and 24 show an example in which the auxiliary pulse Pf is applied once, and then the drive pulse is applied three times.

[0100] The difference between the simulation in FIG. 23 and the simulation in FIG. 24 is the waiting time Hb from the end of the second-stage return operation of the auxiliary pulse Pf until the leading edge of the expansion pulse Pd of the drive pulse. In the simulation in FIG. 23, the waiting time Hb is shorter than that in the simulation in FIG. 24. By shortening the waiting time Ha, the pressure chamber 15 of the ejection channel ch.x is suddenly expanded at the leading edge of the expansion pulse Pd when the pressure in the pressure chamber 15 is negative. In this case, the negative pressure generated in the pressure chamber 15 is larger than when the auxiliary pulse Pb is applied. Therefore, the positive pressure generated in the pressure chamber 15 when the pressure chamber 15 is suddenly returned to the expanded state at the trailing edge of the expansion pulse Pd is larger than when the auxiliary pulse Pb is applied. As a result, the ejection speed of the first drop is faster.

[0101] On the other hand, in the simulation of Fig. 24, the waiting time Hb is longer than in the simulation of Fig. 23. By lengthening the waiting time Ha, when the pressure in the pressure chamber 15 is positive, the pressure chamber 15 of the ejection channel ch.x is suddenly expanded at the leading edge of the expansion pulse Pd. In this way, the negative pressure generated in the pressure chamber 15 is smaller than when the auxiliary pulse Pb is applied. Therefore, the positive pressure generated in the pressure chamber 15 when the pressure chamber 15 is suddenly returned to the expanded state at the trailing edge of the expansion pulse Pd is smaller than when the auxiliary pulse Pb is applied. As a result, the ejection speed of the second drop is faster than the ejection speed of the first drop.

[0102] For example, for an inkjet head in which the ejection speed of the first drop decreases, the auxiliary pulse Pf that produces the simulation result in Fig. 23 is effective. For an inkjet head in which the ejection speed of the second drop decreases, the auxiliary pulse Pf that produces the simulation result in Fig. 24 is effective.

[0103] In this way, by applying the auxiliary pulse Pb or auxiliary pulse Pf, which does not eject ink, to the actuator prior to the drive pulse for ejecting ink, it is possible to achieve the effect of stabilizing the ejection speed of multiple drops regardless of the drive state, such as the multi-nozzle continuous drive state or the multi-nozzle simultaneous drive state, etc. As a result, it is possible to provide an inkjet head 100 capable of high-quality printing.

[0104] Moreover, the auxiliary pulse Pb or the auxiliary pulse Pf is composed of one pulse signal. Therefore, the number of times of driving is less than when an auxiliary pulse including an expansion pulse and a contraction pulse is output. As a result, there is no concern about an increase in heat generation.

[0105] Moreover, the leading edge of the auxiliary pulse Pb or the auxiliary pulse Pf causes the pressure chamber 15 to contract stepwise. By appropriately adjusting the time difference of the stepwise contraction, it is possible to obtain the effect of reducing the maximum pressure of the pressure chamber 15 while maintaining the maximum displacement of the pressure chamber 15 at the same magnitude as in the first embodiment.

[0106] [Third Example] Fig. 25 is an explanatory diagram of the auxiliary pulse Pc according to Example 3. In Fig. 25, the vertical axis, horizontal axis, solid line "driving voltage", dashed line "pressure", dashed line "flow velocity", and dashed line "meniscus" are the same as those explained in Fig. 15, so explanations thereof will be omitted here.

[0107] The auxiliary pulse Pc has different leading and trailing edges compared to the auxiliary pulse Pa or the auxiliary pulse Pb. That is, the auxiliary pulse Pc gradually contracts the pressure chamber 15 at its leading edge. The auxiliary pulse Pc gradually restores the pressure chamber 15 at its trailing edge. The auxiliary pulse Pc gradually applies a voltage from 0V, which is a steady state, to gradually contract the pressure chamber 15, and after maintaining the voltage for a certain period of time, gradually reduces the voltage back to 0V.

[0108] When the pressure chamber 15 is gradually contracted at the leading edge of the auxiliary pulse Pc, the pressure generated in the pressure chamber 15 increases due to the contraction, but reaches a maximum positive pressure during the contraction and then decreases. Then, while the contracted state of the pressure chamber 15 is maintained, the pressure further decreases and turns to negative pressure, eventually reaching the maximum negative pressure. After that, when the pressure chamber 15 is gradually restored, the pressure generated in the pressure chamber 15 turns to a positive pressure during the restoration, but then decreases, and at the point when the ink flow rate in the pressure chamber 15 becomes zero, that is, when the pressure chamber 15 is restored, the pressure generated in the pressure chamber 15 becomes zero. The time F from the start of the contraction operation, which is the leading edge, to the end of the restoration operation, which is the trailing edge, of this auxiliary pulse Pc is equal to or longer than the pressure vibration period T of the pressure chamber 15, for example 6.0 μs.

[0109] Fig. 26 is a diagram showing the results of a simulation in which ink droplets are ejected by a multi-drop method using the drive pulse (PRD waveform) of Fig. 8 and the auxiliary pulse Pc of Fig. 25. The simulation was performed using an LCR equivalent circuit (not shown) that simulates an inkjet head. Fig. 26 shows an example in which the auxiliary pulse Pc is applied once, and then the drive pulse is applied three times.

[0110] In FIG. 26, the solid line "drive voltage" is a waveform that represents the voltage change of the auxiliary pulse Pc and the drive pulse. The drive pulse includes an expansion pulse Pd and a contraction pulse Pp. The dashed and dotted line "pressure" is a waveform that represents the change in pressure generated within the pressure chamber 15. The dashed and dotted line "flow velocity" is a waveform that represents the change in the flow velocity of the ink flowing into the nozzle 8. The dashed line "meniscus" is a waveform that represents the change in the position of the ink liquid surface. In FIG. 26, the horizontal axis represents the passage of time (s) and the vertical axis represents the normalized magnitude of each item.

[0111] 26, by applying an auxiliary pulse Pc prior to the drive pulse for ejecting ink, the history of the drive direction of the actuator before ink ejection becomes the contraction direction. Also, the residual vibration of the pressure chamber 15 is canceled. Thus, ink is ejected continuously by the multi-drop method at a constant ejection speed.

[0112] Even when the auxiliary pulse Pc having such a configuration is applied to the actuator prior to the drive pulse for ejecting ink, it is possible to obtain the same effect as when the auxiliary pulse Pa of the first embodiment or the auxiliary pulse Pb of the second embodiment is applied. Moreover, compared to the auxiliary pulse Pb, the auxiliary pulse Pc has the advantage of being able to further reduce the maximum pressure while maintaining the maximum displacement of the pressure chamber 15 at a predetermined value.

[0113] In this way, the change in pressure generated in the pressure chamber 15 decreases in the order of auxiliary pulse Pa, auxiliary pulse Pb, and auxiliary pulse Pc. And, ejection due to the auxiliary pulses is less likely to occur in that order. However, for ink with thixotropy, there is an advantage that the effect of reducing the viscosity of the ink during ejection is greater in the order of auxiliary pulse Pa, auxiliary pulse Pb, and auxiliary pulse Pc.

[0114] In addition, by adjusting the waveform of the trailing edge of the auxiliary pulse Pc as well, it is possible to intentionally leave residual vibration and adjust the ejection speed of the first or second drop, just like the auxiliary pulse Pe or auxiliary pulse Pf.

[0115] Fig. 27 is an explanatory diagram of an auxiliary pulse Pg that intentionally leaves residual vibration after resetting the history as a modified example of the auxiliary pulse Pc. Note that in Fig. 27, the vertical axis, horizontal axis, solid line "driving voltage", dashed line "pressure", dashed line "flow velocity", and dashed line "meniscus" are the same as those explained in Fig. 15, so the explanation here will be omitted.

[0116] The auxiliary pulse Pc, at its trailing edge, gradually returns the pressure chamber 15. The auxiliary pulse Pg, at its trailing edge, returns the pressure chamber 15 sharply, in the same way as the auxiliary pulses Pe and Pf, leaving a pressure vibration in the pressure chamber 15. The output of the drive pulse is started while this pressure vibration remains. By doing so, it is possible to adjust the ejection speed of the first or second drop. The auxiliary pulse Pg gradually increases the voltage from 0V, which is the steady state, to gradually contract the pressure chamber 15, and after maintaining the voltage for a certain period of time, the voltage is reduced back to 0V.

[0117] Fig. 28 shows the simulation results when the ejection speed of the first drop is increased, and Fig. 29 shows the simulation results when the ejection speed of the second drop is increased. Fig. 28 and Fig. 29 show an example in which the auxiliary pulse Pg is applied once, and then the drive pulse is applied three times.

[0118] The difference between the simulation in Fig. 28 and the simulation in Fig. 29 is the wait time from the end of the stepwise return operation of the auxiliary pulse Pg to the leading edge of the expansion pulse Pd of the drive pulse. By changing the wait time, it is possible to increase the ejection speed of the first drop or the ejection speed of the second drop.

[0119] Above, auxiliary pulse Pa, auxiliary pulse Pb, auxiliary pulse Pc, auxiliary pulse Pe, and auxiliary pulse Pf have been given as examples of auxiliary pulses that do not eject ink and are applied to the actuator prior to the drive pulse for ejecting ink, but the auxiliary pulses are not limited to these.

[0120] For example, when the pressure chamber 15 is contracted at its leading edge, it may be an auxiliary pulse that contracts stepwise like auxiliary pulse Pb, and when the pressure chamber 15 is restored at its trailing edge, it may be an auxiliary pulse that restores gradually like auxiliary pulse Pc. Alternatively, when the pressure chamber 15 is contracted at its leading edge, it may be an auxiliary pulse that contracts gradually like auxiliary pulse Pc, and when the pressure chamber 15 is restored at its trailing edge, it may be an auxiliary pulse that restores stepwise like auxiliary pulse Pa or auxiliary pulse Pb.

[0121] In the case where the pressure chamber 15 in the contracted state is gradually restored by the auxiliary pulse Pa or the auxiliary pulse Pb, the number of stages is not limited to two stages. The pressure chamber 15 may be restored in three or more stages.

[0122] In the case where the pressure chamber 15 is contracted in stages by the auxiliary pulse Pb, the number of stages is not limited to two. The pressure chamber 15 may be contracted in three or more stages.

[0123] The time from the start to the end of the auxiliary pulse Pa, auxiliary pulse Pb, auxiliary pulse Pc, auxiliary pulse Pe, and auxiliary pulse Pf is set to be equal to or longer than the pressure oscillation period T of the pressure chamber 15. In this regard, as long as the value is close to the pressure oscillation period T of the pressure chamber 15, it does not necessarily have to be equal to or longer than the pressure oscillation period T.

[0124] Although several other 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 implemented 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 invention and its equivalents described in the claims. In addition, the claims as originally filed in this application are set forth below. [C1] A pressure chamber that contains ink; a nozzle plate having a nozzle communicating with the pressure chamber; an actuator provided in correspondence with the pressure chamber and configured to change the volume of the pressure chamber; and a drive circuit configured to drive the actuator; Equipped with The drive circuit includes: an inkjet head in which, prior to a drive pulse for ejecting ink, an auxiliary pulse for not ejecting ink is applied to the actuator, which drives the pressure chamber in a direction to contract, thereby increasing the pressure in the pressure chamber, and then maintains the pressure chamber in a contracted state until the pressure decreases and becomes negative pressure, then increases again and becomes positive pressure, and then a pulse for returning the pressure chamber to its original state is applied to the actuator. [C2] 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: An inkjet head that provides the actuator with a pulse that acts as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, drives the pressure chamber in a direction to contract, maintains the contracted state, and then returns to its original state, the time from the start to the end of the pulse being equal to or longer than the pressure vibration period of the pressure chamber. [C3] The inkjet head described in C1 or C2, wherein the drive pulse is a pulse that draws in ink by expanding the pressure chamber, and after the pressure of the ink in the pressure chamber changes from negative pressure to positive pressure, returns the pressure chamber from the expanded state to further increase the pressure and ejects ink, and then contracts and expands the pressure chamber to cancel residual vibration. [C4] The inkjet head according to any one of C1 to C3, wherein the auxiliary pulse contracts the pressure chamber stepwise in a plurality of times at a leading edge thereof. [C5] The inkjet head according to any one of C1 to C3, wherein the auxiliary pulse gradually contracts the pressure chamber at a leading edge thereof. [C6] The inkjet head according to any one of C1 to C3, wherein the auxiliary pulse causes the pressure chamber to return from the contracted state stepwise in a plurality of times at its trailing edge. [C7] The inkjet head according to any one of C1 to C6, wherein the auxiliary pulse reduces residual vibration of the pressure chamber at its trailing edge. [C8] The inkjet head according to any one of C1 to C6, wherein the auxiliary pulse starts outputting the drive pulse at its trailing edge while residual vibration remains in the pressure chamber. [C9] The inkjet head according to any one of C1 to C8, wherein adjacent pressure chambers share the actuator. [Explanation of symbols]

[0125] 4...electrode, 7...nozzle plate, 8...nozzle, 15, 151, 152, 153...pressure chamber, 16, 161, 162...partition wall, 100...inkjet head, 101...head drive circuit, Pa, Pb, Pc, Pe, Pf, Pg...auxiliary pulse, Pd...expansion pulse, Pp...contraction pulse.

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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, driving the pressure chamber in a direction to contract the pressure chamber to increase the pressure in the pressure chamber, and then maintaining the pressure chamber in a contracted state until the pressure decreases and turns to a negative pressure, and then increases again and turns to a positive pressure, and then returning the pressure chamber to its original state; The auxiliary pulse causes the pressure chamber to return from the contracted state stepwise in a plurality of times at a trailing edge of the auxiliary pulse.

2. 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, driving the pressure chamber in a direction to contract the pressure chamber to increase the pressure in the pressure chamber, and then maintaining the pressure chamber in a contracted state until the pressure decreases and turns to a negative pressure, and then increases again and turns to a positive pressure, and then returning the pressure chamber to its original state; The auxiliary pulse gradually contracts the pressure chamber at a leading edge of the auxiliary pulse.

3. 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, driving the pressure chamber in a direction to contract the pressure chamber to increase the pressure in the pressure chamber, and then maintaining the pressure chamber in a contracted state until the pressure decreases and turns to a negative pressure, and then increases again and turns to a positive pressure, and then returning the pressure chamber to its original state; The auxiliary pulse causes the pressure chamber to contract stepwise in a plurality of times at a leading edge of the auxiliary pulse.

4. 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, the pulse being a pulse that drives the pressure chamber in a direction to contract and returns to its original state after maintaining the contracted state, the pulse having a time period from start to finish that is equal to or longer than the pressure vibration period of the pressure chamber; The auxiliary pulse causes the pressure chamber to return from the contracted state stepwise in a plurality of times at a trailing edge of the auxiliary pulse.

5. 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, the pulse being a pulse that drives the pressure chamber in a direction to contract and returns to its original state after maintaining the contracted state, the pulse having a time period from start to finish that is equal to or longer than the pressure vibration period of the pressure chamber; The auxiliary pulse gradually contracts the pressure chamber at a leading edge of the auxiliary pulse.

6. 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 and displacing a volume of the pressure chamber; A drive circuit for driving the actuator; Equipped with The drive circuit includes: a pulse is applied to the actuator as an auxiliary pulse that does not eject ink prior to a drive pulse for ejecting ink, the pulse being a pulse that drives the pressure chamber in a direction to contract and returns to its original state after maintaining the contracted state, the pulse having a time period from start to finish that is equal to or longer than the pressure vibration period of the pressure chamber; The auxiliary pulse causes the pressure chamber to contract stepwise in a plurality of times at a leading edge of the auxiliary pulse.

7. 7. An inkjet head according to claim 1, wherein the drive pulse is a pulse that expands the pressure chamber to draw in ink, and then returns the pressure chamber from the expanded state after the pressure of the ink in the pressure chamber has changed from negative pressure to positive pressure, thereby further increasing the pressure and ejecting ink, and then contracts and expands the pressure chamber to cancel residual vibration.

8. The ink jet head according to claim 1 , wherein the auxiliary pulse reduces residual vibration of the pressure chamber at a trailing edge of the auxiliary pulse.

9. 8. The ink jet head according to claim 1, wherein the auxiliary pulse starts outputting the drive pulse at a trailing edge of the auxiliary pulse while residual vibration remains in the pressure chamber.

10. The ink jet head according to claim 1 , wherein adjacent pressure chambers share the actuator.

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