JP2018114642A - Inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet head that can stabilize speed at which multi drops are discharged, regardless of a driving state, so as to make high-quality printing possible.SOLUTION: According to one embodiment, an inkjet head comprises an actuator, a pressure chamber, a plate and a head driving circuit. The head driving circuit imparts a main pulse for discharging ink droplets after resetting a history in a driving direction of an actuator so that the history is alway equalized in one direction by imparting a first auxiliary pulse at level at which ink droplets are not discharged to the actuator through a nozzle, and imparts a second auxiliary pulse for generating pressure vibrations in a direction in which pressure vibrations which are generated by the first auxiliary pulse can be cancelled, prior to imparting the first auxiliary pulse.SELECTED DRAWING: Figure 8

Description

  Embodiments described herein relate generally to an inkjet head.

  There is an ink jet head of a type using partition walls of pressure chambers adjacent to each other as an actuator. In this type of inkjet head, when a drive pulse signal including an expansion pulse and a contraction pulse is applied to the actuator, the partition wall deforms in a direction to expand or contract the pressure chamber, and pressure vibration is generated in the pressure chamber. To do. Due to this pressure vibration, the volume in the pressure chamber changes, and ink droplets are ejected from nozzles communicating with the pressure chamber.

  As described above, since the ink jet head causes the ink droplets to be ejected from the nozzles by deforming the partition walls of the pressure chambers, the ink droplets cannot be ejected simultaneously from the adjacent nozzles respectively communicating with the adjacent pressure chambers. Therefore, the ink jet head divides each pressure chamber into, for example, every third group, and changes the phase of the drive pulse signal for each group. For this reason, depending on the image pattern, there is one nozzle that ejects ink, and either one of the state in which ink is not ejected from the other nozzles (hereinafter referred to as a single nozzle drive state) or the ink is ejected. Nozzles belonging to a set, a state where ink is not ejected from nozzles belonging to another set (hereinafter referred to as a multi-nozzle simultaneous drive state), and a state where ink is ejected in a time-sharing manner from nozzles belonging to at least two sets (Hereinafter referred to as a multi-nozzle continuous drive state) occurs.

The inkjet head employs a multi-drop method that adjusts the number of ink droplets ejected from one nozzle when performing gradation printing. When the multi-drop method is employed, the ejection speed of the ink droplets after the second drop is increased by the residual pressure vibration of the ink droplets ejected immediately before that. However, since the first drop of ink drops is subjected to pressure vibration from a state where the meniscus is stationary, the discharge speed is slower than that of the second drop and thereafter. There is a technique for increasing the discharge speed of the first drop by adding an auxiliary pulse signal for amplifying the pressure vibration of the pressure chamber before the drive pulse signal for discharging the first drop.
Similarly, a technique for increasing the discharge speed of the first drop by adding an auxiliary pulse signal for generating a pressure wave corresponding to the residual pressure wave in the pressure chamber before the drive pulse signal for discharging the first drop. Are known.

  However, when these techniques are applied, when the multiple nozzles are simultaneously driven, the ejection speed of the second drop is slower than the first drop due to the influence of vibration caused by the auxiliary pulse signal, and the second drop is the first drop. There is a harmful effect of landing from separated from.

JP 2007-022073 A JP 2002-137390 A

  The problem to be solved by the embodiments of the present invention is to provide an inkjet head capable of stabilizing the multidrop ejection speed regardless of the driving state and capable of high-quality printing.

  In one embodiment, the ink jet head includes an actuator, a pressure chamber, a plate, and a head driving circuit. The actuator has different displacement amounts with respect to the applied voltage depending on whether the history of the previous drive direction is the same direction as the current drive direction or the opposite direction. The pressure chamber applies pressure to the stored ink by changing the internal volume due to the displacement of the actuator. The plate has a nozzle that communicates with the pressure chamber. The head driving circuit applies a first auxiliary pulse that does not eject ink droplets from the nozzles to the actuator, and resets the history so that the history of the driving direction of the actuator is always in one direction. A second auxiliary pulse for applying a pulse and generating a pressure vibration in a direction to cancel the pressure vibration generated by the first auxiliary pulse is provided prior to the first auxiliary pulse.

The perspective view which decomposes | disassembles and shows a part of inkjet head. The longitudinal cross-sectional view in the front part of an inkjet head. FIG. 3 is a cross-sectional view of the front portion of the inkjet head. The figure for demonstrating the principle of operation of an inkjet head. The block diagram which shows the hardware constitutions of an inkjet printer. FIG. 3 is a block diagram illustrating a specific configuration of a head driving circuit in the ink jet printer. FIG. 3 is a schematic circuit diagram of a buffer circuit and a switch circuit included in the head driving circuit. The wave form diagram which shows the drive pulse signal in one Embodiment. The schematic diagram which looked at each nozzle of the head from the conveyance path side of the printing paper. Explanatory drawing of a multi-nozzle continuous drive state. Explanatory drawing of a single nozzle drive state. Explanatory drawing of a multi-nozzle simultaneous drive state. The graph which shows an example of the discharge speed for every drop when an auxiliary pulse waveform is not added. The graph which shows an example of the discharge speed for every drop when only the 1st auxiliary pulse is added. The graph which shows an example of the discharge speed for every drop when the 1st auxiliary pulse and the 2nd auxiliary pulse are added. The graph which shows an example of the discharge speed for every drop when the pulse width of the 1st auxiliary pulse and the 2nd auxiliary pulse is 0.2 microseconds. The graph which shows an example of the discharge speed for every drop when the pulse width of the 1st auxiliary pulse and the 2nd auxiliary pulse is 0.3 microseconds. The graph which shows an example of the discharge speed for every drop when the pulse width of the 1st auxiliary pulse and the 2nd auxiliary pulse is 0.4 microseconds. The graph which shows an example of the discharge speed for every drop when the pulse width of a 1st auxiliary | assistant pulse and a 2nd auxiliary | assistant pulse is 0.5 microsecond. The graph which shows an example of the discharge speed for every drop when the pulse width of a 1st auxiliary pulse and a 2nd auxiliary pulse is 0.6 microsecond. The figure for demonstrating the operating principle of the actuator in a multi-nozzle continuous drive state. The figure which shows the voltage waveform applied to a PZT test piece. The figure which shows a charge charge and displacement amount when the voltage waveform of FIG. 22 is applied to a PZT test piece. The figure which shows the relationship between the voltage applied to a head, and the charging current of an actuator. The figure which shows the equivalent circuit of a pressure chamber. The graph which shows the result of having performed the simulation by performing the equivalent circuit of FIG. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. FIG. 6 is a waveform diagram showing an example of a drive voltage waveform, an ink pressure waveform, and an ink flow velocity waveform. The figure which shows the example which gives an auxiliary | assistant pulse only when the maximum number of drops is 3 and the number of drops is 1. FIG. The figure which shows the example which gives an auxiliary pulse only when the maximum number of drops is 3 and the number of drops is 2 or less.

  Hereinafter, an inkjet head according to an embodiment will be described with reference to the drawings. Incidentally, in this embodiment, a share mode / shared wall type inkjet head 100 (see FIG. 1) is exemplified as the inkjet head.

  First, the configuration of the inkjet head 100 (hereinafter abbreviated as the head 100) will be described with reference to FIGS. 1 is an exploded perspective view showing a part of the head 100, FIG. 2 is a longitudinal sectional view of the front portion of the head 100, and FIG. 3 is a transverse sectional view of the front portion of the head 100.

  The head 100 has a base substrate 9. In the head 100, the first piezoelectric member 1 is bonded to the upper surface on the front side of the base substrate 9, and the second piezoelectric member 2 is bonded onto the first piezoelectric member 1. The bonded first piezoelectric member 1 and second piezoelectric member 2 are polarized in directions opposite to each other along the thickness direction, as indicated by arrows in FIG.

  The base substrate 9 is formed using a material having a small dielectric constant and a small difference in thermal expansion coefficient from the piezoelectric members 1 and 2. As a material of the base substrate 9, for example, alumina (Al203), silicon nitride (Si3N4), silicon carbide (SiC), aluminum nitride (AlN), lead zirconate titanate (PZT), or the like is preferable. On the other hand, as a material of the piezoelectric members 1 and 2, lead zirconate titanate (PZT), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or the like is used.

  The head 100 is provided with a number of long grooves 3 from the front end side to the rear end side of the joined piezoelectric members 1 and 2. Each groove 3 has a constant interval and is parallel. Each groove 3 is open at the front end and inclined upward at the rear end.

  The head 100 is provided with electrodes 4 on the side walls and the bottom surface of each groove 3. The electrode 4 has a two-layer structure of nickel (Ni) and gold (Au). The electrode 4 is uniformly formed in each groove 3 by, for example, a plating method. The formation method of the electrode 4 is not limited to the plating method. In addition, a sputtering method, a vapor deposition method, or the like can be used.

  The head 100 is provided with an extraction electrode 10 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 includes a top plate 6 and an orifice plate 7. The top plate 6 closes the upper part of each groove 3. The orifice plate 7 closes the tip of each groove 3. The head 100 forms a plurality of pressure chambers 15 by the grooves 3 surrounded by the top plate 6 and the orifice plate 7. The pressure chambers 15 have, for example, a depth of 300 μm and a width of 80 μm, and are arranged in parallel at a pitch of 169 μm. Such a pressure chamber 15 is also referred to as an ink chamber.

  The top plate 6 includes a common ink chamber 5 on the inner rear side. The orifice plate 7 is formed with nozzles 8 at positions facing the grooves 3. The nozzle 8 communicates with the facing groove 3, that is, the pressure chamber 15. The nozzle 8 is tapered from the pressure chamber 15 side toward the opposite ink discharge side. The nozzles 8 are formed as a set corresponding to the three adjacent pressure chambers 15 and are formed at a predetermined interval in the height direction of the groove 3 (the vertical direction of the paper surface of FIG. 2).

  The head 100 joins the printed circuit board 11 on which the conductive pattern 13 is formed on the upper surface on the rear side of the base substrate 9. The head 100 mounts a drive IC 12 on which a head drive circuit 101 described later is mounted on the printed board 11. The drive IC 12 is connected to the conductive pattern 13. The conductive pattern 13 is coupled to each extraction electrode 10 by a conductive wire 14 by wire bonding.

  A set of the pressure chamber 15, the electrode 4, and the nozzle 8 included in the head 100 is referred to as a channel. That is, the head 100 has channels ch.1, ch.2,.

Next, the operation principle of the head 100 configured as described above will be described with reference to FIG.
FIG. 4A shows that the potential of the electrode 4 disposed on each wall surface of the central pressure chamber 15b and the pressure chambers 15a and 15c adjacent to the pressure chamber 15b is the ground potential GND. It shows a certain state. In this state, the partition wall 16a sandwiched between the pressure chambers 15a and 15b adjacent to each other and the partition wall 16b sandwiched between the pressure chambers 15b and 15c adjacent to each other are not subjected to any distortion action.

  FIG. 4B shows a state in which a negative voltage −V is applied to the electrode 4 of the central pressure chamber 15b. The potentials of the electrodes 4 in the pressure chambers 15a and 15c on both sides remain the ground potential GND. In this state, an electric field of voltage V acts on each of the partition walls 16a and 16b in a direction orthogonal to the polarization direction of the piezoelectric members 1 and 2. By this action, the partition walls 16a and 16b are respectively deformed outward so as to expand the volume of the pressure chamber 15b.

  FIG. 4C shows a state in which a positive voltage + V is applied to the electrode 4 of the central pressure chamber 15b. The potentials of the electrodes 4 in the pressure chambers 15a and 15c on both sides remain the ground potential GND. In this state, an electric field of voltage V acts on each of the partition walls 16a and 16b in the direction opposite to that shown in FIG. By this action, the partition walls 16a and 16b are respectively deformed inward so as to contract the volume of the pressure chamber 15b.

  When the volume of the pressure chamber 15b is expanded or contracted, pressure vibration is generated in the pressure chamber 15b. Due to this pressure vibration, the pressure in the pressure chamber 15b increases, and ink droplets are ejected from the nozzles 8 communicating with the pressure chamber 15b.

As described above, the partition wall 16a separating the pressure chambers 15a and 15b and the partition wall 16b separating the pressure chambers 15b and 15c are actuators for applying pressure vibration to the inside of the pressure chamber 15b having the partition walls 16a and 16b as wall surfaces. Become. 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 drives each pressure chamber 15 by dividing it into (n + 1) groups every n (n is an integer of 2 or more). In this embodiment, the head driving circuit 101 exemplifies a case of so-called three-division driving in which each pressure chamber 15 is divided and driven in groups of three every two groups. Note that the three-division driving is merely an example, and may be four-division driving or five-division driving.
Incidentally, in FIGS. 4A, 4B, and 4C, voltages −V and + V are applied to the electrode 4 of the central pressure chamber 15b in order to eject ink from the nozzle corresponding to the central pressure chamber 15b. It was. An example in which ink is ejected from the nozzle corresponding to the central pressure chamber 15b is not limited thereto. For example, the voltage −V is applied to the electrode 4 of the central pressure chamber 15b, and the voltage + V is applied to the electrodes 4 of the pressure chambers 15a and 15c adjacent to each other. Conversely, a voltage + V is applied to the electrode 4 in the central pressure chamber 15b, and a voltage −V is applied to the electrodes 4 in the adjacent pressure chambers 15a and 15c. Also in this case, if the applied voltage V is halved, the operation of the actuator becomes exactly the same as in FIG.

  Next, the configuration of the inkjet printer 200 (hereinafter abbreviated as the printer 200) will be described with reference to FIGS. 5 is a block diagram showing a hardware configuration of the printer 200, FIG. 6 is a block diagram showing a specific configuration of the head drive circuit 101, and FIG. 7 is a buffer circuit 1013 and a switch circuit 1014 included in the head drive circuit 101. FIG. The printer 200 is applied to, for example, an office printer, a barcode printer, a POS printer, an industrial printer, and the like.

  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 transport motor 206, a motor drive circuit 207, a pump 208, and a pump drive. A circuit 209 and a head 100 are provided. The printer 200 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, operation panel 204, communication interface 205, motor drive circuit 207, pump drive circuit 209, and drive circuit 101 of the head 100 to the bus line 211 either directly or via an input / output circuit. Connect.

  The CPU 201 corresponds to the central part of the computer. The CPU 201 controls each unit to implement various functions as the printer 200 in accordance with an operating system and application programs.

  The ROM 202 corresponds to the main storage portion of the computer. The ROM 202 stores the above operating system and application programs. The ROM 202 may store data necessary for the CPU 201 to execute processing for controlling each unit.

  The RAM 203 corresponds to the main storage portion 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 in which print data is expanded.

  The operation panel 204 has an operation unit and a display unit. The operation unit is provided with function keys such as a power key, a paper feed key, and an error release key. The display unit can display various states of the printer 200.

  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 error to the client terminal.

  A motor drive circuit 207 controls driving of the carry 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 the print position by the head 100. The transport mechanism discharges the printed recording medium to the outside of the printer 200 from a discharge port (not shown).

  The 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.

  The head drive circuit 101 drives the channel group 102 of the head 100 based on the print data. As shown in FIG. 6, the head drive circuit 101 includes a pattern generator 1011, a logic circuit 1012, a buffer circuit 1013, and a switch circuit 1014.

  The pattern generator 1011 generates waveform patterns such as a discharge related waveform, a discharge adjacent waveform, a non-discharge related waveform, and a non-discharge adjacent waveform. The waveform pattern data generated by the pattern generator 1011 is supplied to the logic circuit 1012.

  The logic circuit 1012 accepts input of print data read out line by line from the image memory. When 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 one of the channels, For example, it is determined whether the central channel ch.i is an ejection channel that ejects ink or a non-ejection channel that does not eject ink. When the channel ch.i is an ejection channel, the logic circuit 1012 outputs the pattern data of the ejection waveform to the channel ch.i, and the adjacent channels ch. (I−1), ch Output pattern data of the waveform on both sides of the discharge for. (i + 1). When the channel ch.i is a non-ejection channel, the logic circuit 1012 outputs the pattern data of the non-ejection waveform to the channel ch.i, and the channel ch. (I−1), ch adjacent to the channel ch.i. Output pattern data of non-ejection both-side waveform for. (i + 1). Each pattern data output from the logic circuit 1012 is supplied to the buffer circuit 1013.

  The buffer circuit 1013 connects a positive voltage Vcc power source and a negative voltage -V power source. 7, the buffer circuit 1013 includes pre-buffers PB1, PB2,..., PBN for each channel ch.1, ch.2,. In FIG. 7, prebuffers PB (i-1), PBi, PB (i + 1) respectively corresponding to three adjacent channels ch. (I-1), ch.i, ch. (I + 1). ).

  Each pre-buffer PB1, PB2,..., PBN has first to third three buffers B1, B2, B3, respectively. Each of the buffers B1, B2, and B3 is connected to a power source having a positive voltage Vcc and a power source having a negative voltage −V.

  In each of the pre-buffers PB1, PB2,..., PBN, the outputs of the first to third buffers B1, B2, B3 change according to the signal level of the pattern data supplied from the logic circuit 1012. The logic circuit 1012 outputs different levels of signals depending on whether the corresponding channel ch.k (1 ≦ k ≦ N) is an ejection channel, a non-ejection channel, or a channel adjacent to the ejection channel or the non-ejection channel. Supplied. The first to third buffers B1, B2, and B3 supplied with the high level signal output a signal of the positive voltage Vcc level. The first to third buffers B1, B2, and B3 supplied with the low level signal output a negative voltage −V level signal.

  The outputs of the pre-buffers PB1, PB2,..., PBN, that is, the output signals of the first to third buffers B1, B2, B3 are supplied to the switch circuit 1014.

The switch circuit 1014 connects a positive voltage Vcc power source, a positive voltage + V power source, a negative voltage −V power source, and a ground potential GND. The positive voltage Vcc is higher than the positive voltage + V. Typical values thereof are a positive voltage Vcc of 24 volts and a positive voltage + V of 15 volts. In this case, the negative voltage -V is -15 volts.
However, appropriate values of the positive voltage and the negative voltage vary depending on the viscosity of the ink. The viscosity of the ink varies depending on the type of ink and the operating temperature. For this reason, the positive voltage + V and the negative voltage −V are selected in a range of about ± 15 volts to ± 30 volts depending on the type of ink and the use temperature. At that time, since the positive voltage Vcc must be higher than the positive voltage + V, if the positive voltage + V and the negative voltage −V are ± 30 volts at the maximum, the positive voltage Vcc is set to, for example, 39 volts.

  As shown in FIG. 7, the switch circuit 1014 has drivers DR1, DR2,..., DRN for each channel ch.1, ch.2,. In FIG. 7, drivers DR (i−1), DRi, DR (i + 1) corresponding to three adjacent channels ch. (I−1), ch.i, ch. (I + 1), respectively. Indicates.

  Each of the drivers DR1, DR2,..., DRN includes a PMOS type field effect transistor T1 (hereinafter referred to as a first transistor T1) and two NMOS type field effect transistors T2, T3 (hereinafter referred to as second transistors T2, T2). Third transistor T3). Each of the drivers DR1, DR2,..., DRN connects a series circuit of a first transistor T1 and a second transistor T2 between a positive voltage + V power source and a ground potential GND, and further, The third transistor T3 is connected between the connection point of the second transistor T2 and the negative voltage −V power source. Each of the drivers DR1, DR2,..., DRN connects the back gate of the first transistor T1 to the power source of the positive voltage Vcc, and connects the back gates of the second transistor and the third transistor to the power source of the negative voltage −V. To do. Furthermore, each driver DR1, DR2,..., DRN connects the first buffer B1 of the corresponding pre-buffer PB1, PB2,..., PBN to the gate of the second transistor T2, and the second buffer B2 is connected to the first transistor. Connected to the gate of T1, the third buffer B3 is connected to the gate of the third transistor T3. Each of the drivers DR1, DR2,..., DRN applies the potential at the connection point between the first transistor T1 and the second transistor T2 to the corresponding electrodes 4 of the channels ch.1, ch.2,. Apply.

  Therefore, the first transistor T1 is turned off when a signal having a positive voltage Vcc level is input from the second buffer B2, and is turned on when a signal having a negative voltage −V level is input. The second transistor T2 is turned on when a positive voltage Vcc level signal is input from the first buffer B1, and is turned off when a negative voltage −V level signal is input. The third transistor T3 is turned on when a positive voltage Vcc level signal is input from the third buffer B3, and is turned off when a negative voltage −V level signal is input.

  The drivers DR1, DR2,..., DRN configured as described above correspond to the corresponding channels ch.1, ch.2,... When the first transistor T1 is turned on and the second transistor T2 and the third transistor T3 are turned off. A positive voltage + V is applied to the electrode 4 of ch.N. When the first transistor T1 and the third transistor T3 are turned off at the same time and the second transistor T2 is turned on, the drivers DR1, DR2,..., DRN are connected to the corresponding channels ch.1, ch.2,. The potential of the electrode 4 is set to the ground GND level. When the first transistor T1 and the second transistor T2 are simultaneously turned off and the third transistor T3 is turned on, the drivers DR1, DR2,..., DRN are connected to the corresponding channels ch.1, ch.2,. A negative voltage −V is applied to the electrode 4.

  FIG. 8 is a waveform diagram of a drive pulse signal applied to the electrode 4 of the channel (ejection channel ch.x) for ejecting ink. This drive pulse signal is a pulse signal according to the pattern data of the relevant waveform generated by the pattern generator 1011 of the head drive circuit 101. In FIG. 8, a section T1 shows a pulse waveform (ejection pulse waveform) for ejecting one ink droplet from the nozzle 8 of the ejection channel ch.x. The ejection pulse waveform includes an expansion pulse EP in section D and a contraction pulse CP in section P. A section R between the expansion pulse EP and the contraction pulse CP maintains the ground potential GND. The time interval between the center of the expansion pulse EP and the center of the contraction pulse CP is equal to the ink resonance period 2AL. Incidentally, when the second drop is discharged by the multi-drop method, the same discharge pulse waveform as that in the section T1 is repeated in the section T2 following the section T1. The same applies to the third and subsequent drops.

  The extension pulse EP sets the electrode 4 of the ejection channel ch.x to a negative potential. That is, for the driver DRx corresponding to the ejection channel ch.x, the first transistor T1 and the second transistor T2 are simultaneously turned off, and the third transistor T3 is turned on, and is output from the buffer circuit 1013 to the switch circuit 1014. The signal level changes. When the electrode 4 of the discharge channel ch.x becomes a negative potential, the pressure chamber 15 of the discharge channel ch.x expands.

  The contraction pulse CP sets the electrode 4 of the ejection channel ch.x to a positive potential. That is, for the driver DRx corresponding to the ejection channel ch.x, the output is output from the buffer circuit 1013 to the switch circuit 1014 so that the first transistor T1 is turned on and the second transistor T2 and the third transistor T3 are turned off. The signal level changes. When the electrode 4 of the discharge channel ch.x becomes a positive potential, the pressure chamber 15 of the discharge channel ch.x contracts.

  Between the expansion pulse EP and the contraction pulse CP, the electrode 4 of the ejection channel ch.x is at the ground potential GND. That is, for the driver DRx corresponding to the ejection channel ch.x, the first transistor T1 and the third transistor T3 are simultaneously turned off, and the second transistor T2 is turned on, so that the output is output from the buffer circuit 1013 to the switch circuit 1014. The signal level changes. When the electrode 4 of the discharge channel ch.x becomes the ground potential GND, the expanded or compressed pressure chamber 15 of the discharge channel ch.x is restored.

  That is, in the section T1, the pressure chamber 15 of the discharge channel ch.x is first expanded, subsequently restored, then contracted, and restored again. Due to such a change in volume of the pressure chamber 15, ink droplets are ejected from the nozzle 8 communicating with the pressure chamber 15. In the section T2 and thereafter, as in the section T1, ink droplets are ejected from the nozzles 8 by repeating expansion, restoration, contraction, and restoration. Here, the extended pulse EP functions as a main pulse. Further, the contraction pulse CP functions as a cancel pulse.

  In the present embodiment, an auxiliary pulse signal output section T0 is added before the section T1 in which the first drop of ink droplets is ejected. The auxiliary pulse signal includes a first auxiliary pulse SP1 applied immediately before the first drop extended pulse EP, and a second auxiliary pulse SP2 applied before the first auxiliary pulse SP1. The section between the first auxiliary pulse SP1 and the second auxiliary pulse SP2 maintains the ground potential GND. The time interval between the center of the first auxiliary pulse SP1 and the center of the second auxiliary pulse SP2 is equal to the ink resonance period 2AL.

  The first auxiliary pulse SP1 is opposite in polarity to the extended pulse EP and has a pulse width w1. The second auxiliary pulse SP2 is opposite in polarity to the first auxiliary pulse SP1 and has a pulse width w2. The pulse widths w1 and w2 are sufficiently shorter than the pulse width of the expansion pulse EP (section D) and the pulse width of the contraction pulse CP (section P). Here, the pulse width w2 corresponds to a second predetermined time. The pulse width w1 corresponds to a first predetermined time. The time width of the expansion pulse (main pulse) SP corresponds to the third predetermined time, and the time width of the contraction pulse (cancellation pulse) CP corresponds to the fourth predetermined time.

  The second auxiliary pulse SP2 sets the electrode 4 of the ejection channel ch.x to a negative potential. When the electrode 4 of the discharge channel ch.x becomes a negative potential, the pressure chamber 15 of the discharge channel ch.x expands. That is, the second auxiliary pulse SP2 is an extended pulse.

  The first auxiliary pulse SP1 sets the electrode 4 of the ejection channel ch.x to a positive potential. When the electrode 4 of the discharge channel ch.x becomes a positive potential, the pressure chamber 15 of the discharge channel ch.x contracts. That is, the first auxiliary pulse SP1 is a contraction pulse.

  As described above, in the output period T0 of the auxiliary pulse signal, similarly to the period T1, the pressure chamber 15 of the discharge channel ch.x is first expanded, subsequently restored, then contracted, and restored again. However, since the pulse widths w1 and w2 of the first and second auxiliary pulses SP1 and SP2 are sufficiently shorter than the pulse width (section D) of the expansion pulse EP, ink droplets are not ejected from the nozzle 8. In other words, the pulse widths w1 and w2 of the first and second auxiliary pulses SP1 and SP2 are set to such a width that ink droplets are not ejected from the nozzle 8.

Here, before describing the operational effect of adding the auxiliary pulse signal, the single nozzle driving state, the multiple nozzle simultaneous driving state, and the multiple nozzle continuous driving state will be described once again with reference to FIGS.
FIG. 9 is a schematic view of each nozzle 8 of the head 100 as viewed from the conveyance path side of the printing paper PA. As shown in the figure, the head 100 of the present embodiment has a staggered arrangement of nozzles 8 in three rows. This type of head 100 cannot eject ink droplets simultaneously from adjacent nozzles 8. For this reason, the pressure chambers 15 corresponding to the respective nozzles 8 are sequentially driven in a time-sharing manner, divided into a (3n + 1) th group, a (3n + 2) th group, and a (3n + 3) th group. For example, in FIG. 9, when the printing paper PA is conveyed in the direction of the arrow H, in order to print a horizontal line, first, the pressure chamber 15 corresponding to the nozzle 8 with the symbol a is driven, and then the symbol c. The pressure chamber 15 corresponding to the nozzle 8 is driven, and then the pressure chamber 15 corresponding to the nozzle 8 of the symbol b is driven. In FIG. 9, the nozzle 8 with the symbol b is the nozzle of interest, and the pressure chamber 15 corresponds to the pressure chamber 15 b in FIG. 4. The nozzles a and c are adjacent to the nozzle, and the pressure chamber 15 corresponds to the pressure chambers 15a and 15c in FIG.

  FIG. 10 is an explanatory diagram of a multi-nozzle continuous drive state. The multi-nozzle continuous drive state refers to a state in which ink is ejected in a time-sharing manner from nozzles belonging to at least two sets. For example, as shown in FIG. 6A, in order to obtain a horizontal two-line printed image, as shown in FIG. 5B, a necessary amount from the nozzle 8 in the order of the symbols a, c, and b. The actuator is driven so that ink droplets are ejected. In this case, all the adjacent actuators are driven at different times. Such a drive mode is referred to as multi-nozzle continuous drive. Here, the continuous drive means that the nozzles 8 that are continuous in the space direction (nozzle arrangement direction) are driven.

  FIG. 11 is an explanatory diagram of a single nozzle driving state. The single nozzle drive state refers to a state where ink is ejected from any one of the nozzles 8. For example, as shown in FIG. 11A, in order to obtain a print image in which a plurality of points are arranged in the vertical direction, as shown in FIG. The actuator is driven so that ink is ejected. Such a drive mode is referred to as single nozzle drive.

  FIG. 12 is an explanatory diagram of a multi-nozzle simultaneous drive state. The multi-nozzle simultaneous drive state refers to a state in which ink is ejected from nozzles belonging to any one group, and ink is not ejected from nozzles belonging to another group. For example, as shown in FIG. 11A, in order to obtain a print image in which a plurality of points arranged in the horizontal direction are arranged in a plurality of columns, as shown in FIG. When the actuator is divided into the (3n + 2) th group and the (3n + 3) th group, the actuator is driven so that a necessary amount of ink is ejected from the nozzles belonging to the same group. Such a drive mode is referred to as multi-nozzle simultaneous drive.

  Multiple nozzle simultaneous driving is the simplest behavior of the pressure chamber 15. That is, since the actuators belonging to the same group are uniformly driven in the nozzle arrangement direction, the pressure chambers 15 of all the channels have a uniform behavior. On the other hand, the single nozzle drive shows a slightly complicated behavior in the spatial direction. This is because the pressure generated in the pressure chamber of the driven channel is propagated to the surrounding channels because only one channel is driven.

  On the other hand, the multi-nozzle continuous drive exhibits a complicated behavior in the time direction. This is because, when an ink droplet is ejected from an adjacent channel, the history of driving one wall of the actuator of the channel shared with the adjacent channel affects the operation of the actuator of the channel.

  For the above reasons, only one drop is discharged from the same nozzle in each of the three modes of the single nozzle drive state, the multiple nozzle simultaneous drive state, and the multiple nozzle continuous drive state, and the case where two drops or more are continuously discharged. Then, the ink droplet ejection speed is evaluated. Incidentally, the gray scale printing method in which ink droplets are continuously ejected from the same nozzle and the size of the dot diameter on the printing medium is adjusted according to the number of ejections is called a multi-drop method. In the multi-drop method, in order to obtain a stable ejection state, it is desirable that the change in ejection speed due to the number of continuous ink droplets is small.

  Next, the function and effect obtained by adding the auxiliary pulse signal will be described with reference to FIGS. FIGS. 13 to 15 show a state where only one drop or two to five drops are continuously discharged by the multi-drop method in each of the single nozzle driving state, the multiple nozzle simultaneous driving state, and the multiple nozzle continuous driving state. An example of the discharge speed [m / s] is shown. 13 to 15, the numerical value on the vertical axis of the points plotted corresponding to the numerical value “1” on the horizontal axis is the discharge speed when only one drop is discharged. The numerical value on the vertical axis of the points plotted corresponding to the numerical value “2” on the horizontal axis is the discharge speed of the second drop when two drops are continuously discharged. The numerical value on the vertical axis of the points plotted corresponding to the numerical value “3” on the horizontal axis is the discharge speed of the third drop when 3 drops are discharged continuously. The numerical value on the vertical axis of the points plotted corresponding to the numerical value “4” on the horizontal axis is the discharge speed of the fourth drop when 4 drops are discharged continuously. The numerical value on the vertical axis of the points plotted corresponding to the numerical value “5” on the horizontal axis is the discharge speed of the fifth drop when 5 drops are discharged continuously. 13 is a graph when the auxiliary pulse waveform is not added, FIG. 14 is a graph when only the first auxiliary pulse SP1 is added, and FIG. 15 is a graph showing the first auxiliary pulse SP1 and the first auxiliary pulse SP1. It is a graph when two auxiliary pulses SP2 are added. In each figure, the solid line graph shows the discharge speed [m / s] when the single nozzle is driven. The one-dot chain line graph indicates the discharge speed [m / s] when the multi-nozzle simultaneous driving state is set. The broken line graph shows the discharge speed [m / s] in the multi-nozzle continuous drive state.

  When the auxiliary pulse waveform is not added, as shown in FIG. 13, the discharge speed when only one drop is discharged in the single-nozzle driving state and the multiple-nozzle continuous driving state is when two or more drops are discharged continuously. It becomes slower than the discharge speed of the final drop. In particular, in the multi-nozzle continuous drive state, the discharge speed when only one drop is discharged is extremely slow, and stable print quality cannot be obtained.

  When only the first auxiliary pulse SP1 is added as the auxiliary pulse waveform, as shown in FIG. 14, in the single nozzle driving state and the multi-nozzle continuous driving state, the discharge speed when only one drop is discharged becomes faster. It is possible to suppress a change in discharge speed depending on the number of drops that are continuously discharged. Even in the multi-nozzle simultaneous drive state, the discharge speed when only one drop is discharged by the first auxiliary pulse SP1 is increased, but in the multi-nozzle simultaneous drive state, this does not necessarily suppress the change in the discharge speed. Even if a drive waveform without an auxiliary pulse is given in the multi-nozzle simultaneous drive state, as shown in FIG. 13, the second drop is discharged when two drops are discharged continuously with the discharge speed when only one drop is discharged. There is not much difference from the original speed. For this reason, when the first auxiliary pulse SP1 is inserted, the ejection speed of the second drop is relatively slower than the first drop, and the speed balance is lost. If two drops are discharged continuously in this state, the slow second drop is separated from the first drop and landed, and there is a high possibility that the print quality will deteriorate.

  When the first auxiliary pulse SP1 and the second auxiliary pulse SP2 are added as the auxiliary pulse waveform, as shown in FIG. 15, the ejection when only one drop is ejected in the single nozzle driving state and the multi-nozzle continuous driving state. Increases speed. However, the discharge speed when only one drop is discharged in the multi-nozzle simultaneous drive state is not so high, and is almost the same as the discharge speed of the second drop when two drops are discharged continuously. Accordingly, since the speed balance is not lost, the second drop does not land separately from the first drop.

  As described above, in this embodiment, the second auxiliary pulse SP2 having the opposite polarity to the first auxiliary pulse SP1 is provided as the auxiliary pulse signal before the first auxiliary pulse SP1 that performs the same function as the conventional boost pulse. Add By doing so, not only the single nozzle driving state and the multi-nozzle continuous driving state but also the multi-nozzle simultaneous driving state can stabilize the multi-drop ejection speed, and thus an inkjet head capable of high-quality printing. And an ink jet printer using the head.

  Here, the pulse widths w1 and w2 of the first and second auxiliary pulses SP1 and SP2 will be verified with reference to FIGS. The pulse width w1 of the first auxiliary pulse SP1 and the pulse width w2 of the second auxiliary pulse SP2 are the same. Further, the pulse center interval between the first auxiliary pulse SP1 and the second auxiliary pulse SP2 is made equal to the ink resonance period 2AL.

  16 to 20 show the discharge speed [m] for each drop when 5 drops are continuously discharged by the multi-drop method in each of the single nozzle drive state, the multiple nozzle simultaneous drive state, and the multiple nozzle continuous drive state. / s] is an example. FIG. 16 is a graph when the pulse width w1 is 0.2 μs. FIG. 17 is a graph when the pulse width w1 is 0.3 μs. FIG. 18 is a graph when the pulse width w1 is 0.4 μs. FIG. 19 is a graph when the pulse width w1 is 0.5 μs. FIG. 20 is a graph when the pulse width w1 is 0.6 μs. In each figure, the solid line indicates the discharge speed [m / s] when the single nozzle is driven. The alternate long and short dash line indicates the discharge speed [m / s] when the multiple nozzles are simultaneously driven. The broken line indicates the discharge speed [m / s] in the multi-nozzle continuous drive state.

  When the pulse width is 0.2 μs, as shown in FIG. 16, the first drop in the multi-nozzle continuous drive state among the single-nozzle drive state, the multi-nozzle simultaneous drive state, and the multi-nozzle continuous drive state, as shown in FIG. Discharge speed is slow and varies. In addition, in the multi-nozzle continuous drive state, the ejection speed of the first drop is still slower than that of the second drop, so that ejection is unstable.

  When the pulse width becomes 0.3 μs, as shown in FIG. 17, even in the multi-nozzle continuous drive state, the discharge speed of the first drop is increased, and there is no significant difference compared to the second drop. Further, in each state of the single nozzle driving state, the multiple nozzle simultaneous driving state, and the multiple nozzle continuous driving state, the ejection speed of the first drop is substantially the same. Therefore, a stable discharge effect can be obtained in any state.

  When the pulse width becomes 0.4 μs, as shown in FIG. 18, the discharge speed of the first drop is substantially the same in each state of the single nozzle driving state, the multiple nozzle simultaneous driving state, and the multiple nozzle continuous driving state. In addition, the discharge speed of the first drop is not greatly slowed compared to the second drop. Rather, since the discharge speed of the first drop in the multi-nozzle simultaneous drive state is slightly faster than that of the second drop, the speed balance is losing.

  When the pulse width becomes 0.5 μs, as shown in FIG. 19, in the multi-nozzle simultaneous drive state, the discharge speed of the first drop becomes faster than that of the second drop, and the speed balance is lost. This point is also remarkable when the pulse width is 0.6 μs as shown in FIG.

  Therefore, in the case of the example shown in FIGS. 16 to 20, the pulse widths w1 and w2 of the first and second auxiliary pulses are within the range of 0.3 μs to 0.4 μs regardless of the driving state. There is an effect that the discharge speed of the drop can be stabilized.

Next, the principle that produces the effect of this embodiment will be described.
As described in the background section, it has already been attempted to equalize the ejection speed by providing an auxiliary pulse signal, that is, a so-called boost pulse, that does not eject ink droplets before ejecting ink droplets. By giving a boost pulse, the difference between the case where pressure vibration is applied from a state where the meniscus is stationary and the case where pressure vibration is applied in the state where residual pressure vibration of the ink droplet ejected immediately before remains is given. There is an effect to compensate. However, the effect of using the second auxiliary pulse SP2 together with the first auxiliary pulse SP1 cannot be explained only by compensating for this difference. In order to understand the effect of the second auxiliary pulse SP2, it is necessary to understand the hysteresis phenomenon caused by the hysteresis of the actuator. Therefore, first, regarding the difference in operation between the single nozzle driving state and the multiple nozzle simultaneous driving state and the multiple nozzle continuous driving state, a simple driving waveform having no auxiliary pulse, that is, the DRP waveform shown in the section T1 in FIG. The operation will be described.

  In the single-nozzle drive state and the multiple-nozzle simultaneous drive state, ink is not ejected from the adjacent channel between a dot (a collection of a plurality of drops) and the next dot. For this reason, the operation of the actuator always repeats (a) → (b) → (a) → (c) → (a) → (b) → (a) → (c) in FIG. During this repetition, two ink droplets are ejected from the nozzle 8 communicating with the central pressure chamber 15b. The actuator provided corresponding to the pressure chamber 15b always performs an operation of contracting with the contraction pulse CP before expanding with the expansion pulse EP.

On the other hand, it is necessary to consider the movement of the adjacent pressure chambers 15 in the multi-nozzle continuous drive state.
FIG. 21 shows that before ejecting ink droplets from the nozzle 8 communicating with the central pressure chamber 15b, first ink droplets are ejected from the nozzle 8 communicating with the left adjacent pressure chamber 15a, and then into the right adjacent pressure chamber 15c. The operation of the actuator corresponding to each pressure chamber 15a, 15b, 15c when ejecting ink droplets from the communicating nozzle 8 is shown.

A1 to A4 are operations of the actuator when ejecting ink droplets from the nozzle 8 communicating with the pressure chamber 15a adjacent to the left, and when ejecting ink droplets continuously, the operations of A1 to A4 are repeated.
A5 to A8 are operations of the actuator when ejecting ink droplets from the nozzle 8 communicating with the pressure chamber 15c on the right side. When ink droplets are ejected continuously, the operations of A5 to A8 are repeated.
A9 to A16 are operations of the actuator when ejecting ink droplets from the nozzle 8 communicating with the central pressure chamber 15b. A9 to A12 are operations of the first drop, and A13 to A16 are operations of the second drop. . In the case of ejecting ink droplets after the third drop, the operations A13 to A16 are repeated.

  One partition 16a serving as an actuator for applying pressure vibration to the inside of the pressure chamber 15b has a history in the left direction in the figure by the operation of A4. This history is maintained until the operation of A9. On the other hand, the other partition wall 16b, which is the same actuator, has a history in the right direction in FIG. This history is maintained until the operation of A9. Accordingly, when the partition walls 16a and 16b are deformed in the direction in which the partition walls 16a and 16b expand in the operation of A10, the deformation directions are in the same direction as the history.

  However, when the second and subsequent drops are ejected from the nozzle 8 communicating with the central pressure chamber 15b, the situation changes. One partition 16a has a history in the right direction in FIG. This history is maintained until the operation of A13. The other partition 16b has a history in the left direction in the figure by the operation of A12. This history is maintained until the operation of A13. Accordingly, when the partition walls 16a and 16b are deformed in the direction in which the partition walls 16a and 16b are expanded by the operation of A14, the deformation directions are respectively opposite to the history.

  Thus, in the multi-nozzle continuous drive state, the direction of the history when the actuator operates is different between the first drop and the second and subsequent drops. This difference in direction is the cause of a significant drop in the discharge speed at the first drop. In order to understand the reason, next, the hysteresis characteristic of PZT (lead zirconate titanate) used as the piezoelectric members 1 and 2 will be described.

  For the explanation of the hysteresis characteristic, a PZT test piece is used. The test piece is a rectangular parallelepiped having a height of 10 [mm], a width of 3 [mm], and a thickness of 0.2 [mm]. Then, this test piece is polarized in the height direction, and a voltage having a waveform shown in FIG. 22 is applied in the thickness direction. The voltage was set to 60 [V] because the thickness of the test piece was about 2.3 times the thickness of the partition wall of the head 100.

When the voltage having the waveform shown in FIG. 22 was applied and the charge P1 [μC / cm ² ] injected into the test piece and the displacement d [nm] of the test piece were measured, the result shown in FIG. 23 was obtained. That is, when the actuator has a history in the same direction, the test piece has a displacement of 60 [nm] with a voltage change of 60 [V]. On the other hand, in the case of having a history in the reverse direction, the test piece had a displacement of 80 [nm] with a voltage change of 60 [V]. That is, having a history in the reverse direction increases the displacement to 133% compared to when having a history in the same direction. Thus, the amount of displacement of the test piece is smaller when it has a history in the same direction than when it has a history in the reverse direction. Therefore, it is considered that the first drop in the multi-nozzle continuous drive state having a history in the same direction is greatly reduced in the discharge speed.

  As shown in FIG. 23, the displacement profile is similar to the charge charge profile. On the other hand, although it is difficult to measure the displacement of the actuator with the head 100 assembled, the charge charge can be obtained relatively easily from the current waveform. Then, next, the hysteresis characteristic of the actuator assembled to the head 100 is examined using this charged charge. Specifically, a voltage indicated by a waveform V1 in FIG. 23 is applied to the head 100, and the charging current of the actuator is measured. The capacitance of the actuator is about 400 [pF] due to the parallel arrangement of the partition wall 16a and the partition wall 16b.

  The charging current was measured as a waveform I1 in FIG. The area S1 of the waveform I1 represents the charge charged when the history is in the reverse direction, and the area S2 represents the charge charged when the history is in the same direction. Accordingly, when the charge charge was measured from the areas S1 and S2, the charge charge measured from the area S1 was 4.2 [nC], and the charge charge measured from the area S2 was 3.1 [nC]. That is, even when the actuator is assembled to the head 100, the actuator has a history in the reverse direction, so that 133% of the charge is injected relative to the actuator having the history in the same direction.

  From the above results, since the displacement of the actuator is smaller when having the history in the same direction than when having the history in the reverse direction, the first drop in the multi-nozzle continuous drive state having the history in the same direction is It can be seen that the discharge speed drops significantly.

  Thus, it can be said that PZT used as the piezoelectric members 1 and 2 in this embodiment has a hysteresis of about 33% under this test condition. The magnitude of hysteresis of the piezoelectric members 1 and 2 directly affects the magnitude of displacement of the actuator. The magnitude of the actuator displacement affects the ejection speed and ejection amount of the ink droplets. For this reason, hysteresis having a size exceeding 30% cannot be ignored for the print quality. Therefore, when using a piezoelectric member having a hysteresis exceeding 30%, it is preferable to control in consideration of the history so as to always have a history in the reverse direction. By always having a history in the reverse direction, the ejection speed and ejection amount of ink droplets are stabilized, and a highly efficient and high quality printing result can be obtained. For example, a soft piezoelectric member having a small mechanical quality factor Qm and a large piezoelectric strain constant (d constant) generally has a large hysteresis. Rather than trying to avoid using such a piezoelectric member with a large hysteresis, it is possible to increase the displacement of the actuator and obtain a stable displacement by appropriately using the hysteresis as described above. It becomes.

  From the above description, the effects of using the second auxiliary pulse SP2 together with the first auxiliary pulse SP1 in the multi-nozzle continuous drive state are as follows.

  First, by applying the first auxiliary pulse SP1 to the head 100, a history in the reverse direction is added to the actuator before discharging the first drop, so that the effect of increasing the amplitude of the actuator using hysteresis and the liquid in advance are added. The effect of the residual pressure vibration due to the vibration of. However, the effect of adding the reverse history to the actuator only affects the first drop and not the second and subsequent drops. On the other hand, applying the residual pressure vibration changes the pressure vibration at the end of the first drop. For this reason, as described with reference to FIG. 14, only the first auxiliary pulse SP1 causes a speed drop of the second drop.

  Therefore, the second auxiliary pulse SP2 is given to the head 100 before the first auxiliary pulse SP1. The second auxiliary pulse SP2 is a pulse that gives an amplitude having an opposite phase one cycle before the first auxiliary pulse SP1. For this reason, by applying the second auxiliary pulse SP2, the previous vibration applied to the liquid by the first auxiliary pulse SP1 is reduced. However, since the actuator history is determined by the direction of the last pulse, the second auxiliary pulse SP2 is not changed. As a result, as described with reference to FIG. 15, by using the first auxiliary pulse S1 and the second auxiliary pulse SP2 together, the discharge speed of the second drop when two drops are continuously discharged is determined. Depression can be improved.

  With this concept, as described with reference to FIGS. 16 to 20, by adjusting the pulse widths w1 and w2 between the first auxiliary pulse S1 and the second auxiliary pulse SP2, the ejection speed of the second drop can be adjusted. It is possible to increase the discharge speed of the first drop while suppressing the drop.

  In the present embodiment, the pulse widths of the first auxiliary pulse S1 and the second auxiliary pulse SP2 are the same, but the balance between the two effects can be finely adjusted by changing the pulse width. . As its simplest example, a description will be given of how to determine the waveforms of the auxiliary pulses SP1 and SP2 when only canceling hysteresis without giving prior vibration to the liquid. With this method, the auxiliary pulses SP1 and SP2 are temporarily determined, and after canceling the influence of hysteresis, the first auxiliary pulse SP1 can be further adjusted to give the liquid a prior vibration. In this description, an equivalent circuit simulating a pressure chamber is used.

  FIG. 25 shows an equivalent circuit 150 that simulates a pressure chamber. The equivalent circuit 150 has one end of a resistor R (0.17Ω) connected to the positive voltage terminal of the voltage source 151, one end of a capacitor C (0.83 μF) connected to the other end of the resistor R, and the other end of the capacitor C. Is connected to one end of an inductor L (0.7 μH), and the other end of the inductor L is connected to the negative voltage terminal of the voltage source 151. Then, the voltage of the voltage source 151 is measured by the first voltmeter 152, the voltage across the inductor L is measured by the second voltmeter 153, and the circuit current is measured by the ammeter 154. The voltage of the voltage source 151 corresponds to the drive voltage. The voltage across the inductor L corresponds to the pressure of the ink near the nozzle. The circuit current corresponds to the ink flow velocity near the nozzle. However, the numerical values of the drive voltage, the ink pressure, and the ink flow velocity are normalized to 1.

  When simulation is performed using this drive circuit, as shown in FIG. 26, the drive voltage waveform (DRP waveform) can be adjusted so as not to leave pressure vibration after ink ejection. In FIG. 26, the solid line waveform indicates the drive voltage, the alternate long and short dash line waveform indicates the ink pressure, and the broken line waveform indicates the ink flow velocity. The drive voltage waveform has a negative potential period t1 of 2.4 [μs], a ground potential period t2 of 3.25 [μs], and a positive potential period t3 of 0.9 [μs]. Since the pressure vibration cycle of the pressure chamber of the head 100 is 4.8 [μs], the negative potential period t1 is set to the most efficient condition, that is, ½ hour of the pressure vibration cycle. Incidentally, the reason why the ground potential period t2 and the positive potential period t3 are different from the negative potential period t1 is due to the loss of the pressure chamber, that is, the resistance R.

  By the way, the pulse having the negative potential period t1 is the extended pulse EP. As described above, the amplitude of the falling edge of the expansion pulse EP indicates whether the driving direction of the previous actuator is the contraction direction for the channel (the expansion direction for the adjacent channel) or the expansion direction (the contraction for the adjacent channel). Direction). With respect to this point, unless either is unified, there is a problem that the print density changes depending on the previous print history.

  Therefore, in order to unify the previous history in the contraction direction, a pulse in the contraction direction is given to the extent that the ink droplet is not ejected before the drive pulse EP. Such a pulse is referred to as a first auxiliary pulse SP1 in the present embodiment. The reason why the direction of the history is unified not in the expansion direction but in the contraction direction is that, as described above, a larger amplitude can be obtained when the history driving direction and the current driving direction are opposite.

  FIG. 27 is an example of a drive voltage waveform (solid line), an ink pressure waveform (dashed line), and an ink flow velocity waveform (broken line) when the first auxiliary pulse SP1 having a positive potential period t6 of 0.45 μs is applied. . As shown in the figure, even the first auxiliary pulse SP1 that is short enough that the positive potential period t6 does not eject ink is accompanied by residual pressure oscillation thereafter. For this reason, as shown in FIG. 28, when a driving pulse having a DRP waveform for ejecting ink is applied after a period t7 = 0.2 μs immediately after the first auxiliary pulse SP1, a first auxiliary pulse is applied. Pressure vibration due to the pulse SP1 affects the ejection, and residual pressure vibration remains after ejection. In this case, as shown in FIG. 29, when the drive pulse having the DRP waveform of the second drop is continuously applied as shown in FIG. 29, the ejection speed of the second drop drops. Therefore, the second auxiliary pulse SP2 is given before the first auxiliary pulse SP1.

  FIG. 30 shows a drive voltage waveform (solid line), an ink pressure waveform (one-dot chain line), and ink when a second auxiliary pulse SP2 having a negative potential period t4 of 0.4 μs is applied before the first auxiliary pulse SP1. It is an example of a flow velocity waveform (broken line). Here, the magnitude of the residual pressure oscillation after the first auxiliary pulse SP1 can be adjusted by the generation position of the second auxiliary pulse SP2 and the pulse width (period t4). When the pulse width (period t4) of the second auxiliary pulse SP2 is changed from the state shown in FIG. 30 in the direction of increasing, the residual pressure oscillation after the first auxiliary pulse SP1 is canceled as shown in FIG. There is a place. In FIG. 31, the period t4 is 0.8 μs. The ground potential period t5 between the second auxiliary pulse SP2 and the first auxiliary pulse SP1 is 4.25 μs.

  In this way, by adjusting the periods t4, t5, and t6 to appropriate values, it is possible to cancel the residual pressure oscillation at the time when the first auxiliary pulse SP1 ends. However, since there is a loss due to the resistance R, the period t4> the period t6 under the condition that the residual pressure oscillation is canceled when the period t6 ends. The time interval between the centers of the pulses of SP1 and SP2, that is, the period “(t4 / 2) + t5 + (t6 / 2)” is slightly longer than the pressure oscillation period.

  On the other hand, as shown in FIG. 32, when the period t4 is further lengthened, residual pressure oscillation whose phase is inverted remains after the first auxiliary pulse SP1. The residual pressure vibration can be canceled again by adjusting the period t5 and the period t6 again as shown in FIG. In the example of FIG. 33, t4 = 1.2 μs, t5 = 4.25 μs, and t6 = 0.6 μs. Thus, there is a certain degree of freedom in canceling the residual pressure vibration.

  The waveform of the second auxiliary pulse SP2 may be an arbitrary width that is short enough not to eject ink droplets, but if it is too short, the pulse width t6 of the first auxiliary pulse SP1 becomes too small and the actuator does not respond. . Therefore, the period t4 is desirably about 0.8 μs to 1.2 μs.

  Now, as shown in FIG. 34, in the head 100, a drive pulse signal having a DRP waveform is applied following the second auxiliary pulse SP2 and the first auxiliary pulse SP1 in which the residual pressure oscillation has been canceled, and ink droplets are applied. Discharge. In FIG. 34, periods t1, t2, and t3 are the same as the DRP waveform described in FIG.

  Thus, if there is no residual pressure oscillation at the time point t7, the waveform of the pressure and flow velocity generated by the DRP waveform is the same as that generated by the DRP waveform when there is no auxiliary pulse, and only the drive history cancels. It becomes. Thus, as shown in FIG. 35, even if the second DRP waveform is applied subsequent to the DRP waveform to discharge the second drop, the discharge speed of the second drop does not decrease.

  The equivalent circuit shown in FIG. 25 does not simulate history, but in order to determine the drive waveform of the head, discharge observation is performed with reference to this waveform, and the values of periods t4, t5, and t6 are finely adjusted. Good.

  By the way, there is a concern that the time required for the auxiliary pulses SP1 and SP2 may decrease the maximum drive frequency that the head 100 can discharge. The maximum drive frequency is limited by the time required for discharging the maximum number of drops. For this reason, if the auxiliary pulses SP1 and SP2 are added prior to the ejection of the maximum number of drops, the required time becomes longer by the required time of the auxiliary pulse, and the maximum drive frequency is lowered. However, such concerns can be solved by the following devices.

  In general, when the number of drops to be ejected is large, since the droplets flying later merge with the previously ejected droplets, there is no problem even if the first drop is late. On the other hand, the hysteresis of the actuator does not affect the ejection of ink after the second drop. Even if there is an influence of hysteresis, as shown in FIGS. 13 to 20, the discharge speeds after the third and fourth drops are usually stabilized. Therefore, no auxiliary pulse is required when discharging 3 to 4 drops or more continuously.

  From these viewpoints, an auxiliary pulse is added only when discharging only one drop (second driving condition), and no auxiliary pulse is input when discharging two or more drops continuously (first driving condition). ), Control method can be taken. By doing so, while increasing the discharge speed when discharging only one drop and discharging more than two drops, the required time is not increased, so the upper limit of the drive frequency is not lowered.

  When the maximum number of drops is 3 or more, auxiliary pulses SP1 and SP2 are added only when drops of N drops or less are continuously discharged, and when pulses of N + 1 or more are continuously discharged, auxiliary pulses SP1 and SP2 are added. By controlling so as not to be applied, the drive frequency can be increased. However, N is 1 or more and (maximum number of drops-1) or less.

FIG. 36 shows an example in which an auxiliary pulse is given only when the maximum number of drops is 3 and the number of drops is 1. FIG. 37 shows an example where an auxiliary pulse is given only when the maximum number of drops is 3 and the number of drops is 2 or less.
The function of determining the number of drops to be discharged for each channel from the print data and determining the presence or absence of the auxiliary pulse can be realized in the logic circuit 1012.

  In addition, in the said embodiment, the discharge speed for every drop at the time of changing the pulse width of a 1st auxiliary | assistant pulse and a 2nd auxiliary | assistant pulse using FIGS. 16-20 is shown, and 0.3 as a preferable pulse width. However, this value is merely an example, and is not construed as a preferable value of the present invention. This value is changed depending on ink characteristics and the like, and an appropriate value is set for the head 100.

  In addition, 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 implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 4 ... Electrode, 7 ... Orifice plate, 8 ... Nozzle, 15 ... Pressure chamber, 16 ... Partition, 100 ... Inkjet head, 101 ... Head drive circuit, 200 ... Inkjet printer.

Claims (6)

An actuator in which the displacement amount with respect to the applied voltage differs depending on whether the history of the previous drive direction is the same direction as the current drive direction or the opposite direction;
A pressure chamber that applies pressure to the accommodated ink by changing the internal volume by the displacement of the actuator;
A plate having a nozzle communicating with the pressure chamber;
A main pulse for performing ejection after resetting the history so that the actuator has a history of the driving direction always in one direction by giving the actuator a first auxiliary pulse that does not eject ink droplets from the nozzles. And a head drive circuit for providing a second auxiliary pulse for generating a pressure vibration in a direction to cancel the pressure vibration generated by the first auxiliary pulse prior to the first auxiliary pulse;
An inkjet head comprising: A plurality of pressure chambers containing ink;
An actuator provided to sandwich each of the plurality of pressure chambers, and shared between the adjacent pressure chambers;
A plate having nozzles communicating with the plurality of pressure chambers and arranged in three rows in a staggered manner;
The pressure chamber corresponding to the nozzle that ejects ink droplets is expanded and returned at a second predetermined time, and the pressure chamber is at a timing for canceling the pressure vibration generated by the second auxiliary pulse. A first auxiliary pulse that is contracted and returned after a lapse of a first predetermined time, and a main pulse that expands the pressure chamber following the first auxiliary pulse and returns after a lapse of a third predetermined time. A head driving circuit for
Comprising
An inkjet head that ejects ink droplets for each group in the same row from the nozzles arranged in a staggered pattern. The head driving circuit further includes:
The inkjet head according to claim 2, wherein the pressure chamber is contracted at a timing for canceling the pressure vibration generated after the main pulse, and a cancel pulse to be returned after a fourth predetermined time has elapsed is provided.   4. The ink jet head according to claim 3, wherein a signal equivalent to the main pulse and the cancel pulse is given after the main pulse and the cancel pulse, and ink droplets are continuously ejected from the same nozzle. The head drive circuit is
A first drive condition for discharging a plurality of ink droplets from the same nozzle by repeatedly applying the main pulse and the cancel pulse;
A second driving condition for ejecting an ink droplet from the nozzle by applying the main pulse and the cancel pulse at least once following the second auxiliary pulse and the first auxiliary pulse;
The ink-jet head according to claim 3, comprising: The head drive circuit is
The driving is performed under the first driving condition when the number of ink droplets continuously ejected from the same nozzle is a predetermined number or more, and the driving is performed under the second driving condition when the number is less than the predetermined number. 5. The inkjet head according to 5.