JP2020152070A - Liquid discharge head and liquid discharge device - Google Patents

Abstract

To restrain the occurrence of small droplets.SOLUTION: A liquid discharge head in an embodiment includes a pressure chamber for storing liquid, an actuator for changing a pressure of the liquid in the pressure chamber in response to an applied driving signal, and an application unit. The application unit applies a driving signal for discharging the liquid multiple times from a nozzle in communication with the pressure chamber. The driving signal includes a first signal for discharging liquid once and a second signal which is applied later than the first signal and discharges liquid once. The first signal includes a first pulse for driving the actuator so as to reduce the pressure of the liquid in the pressure chamber and a second pulse for driving the actuator so as to increase the pressure of the liquid in the pressure chamber. The second signal includes a third pulse with a longer application time than the first pulse for driving the actuator so as to reduce the pressure of the liquid in the pressure chamber and a fourth pulse for driving the actuator so as to increase the pressure of the liquid in the pressure chamber.SELECTED DRAWING: Figure 10

Description

Embodiments of the present invention relate to a liquid discharge head and a liquid discharge device.

An inkjet head (liquid ejection head) that ejects a liquid such as ink from a nozzle is known. Further, a liquid ejection device such as an inkjet printer equipped with such a liquid ejection head is known.
In the liquid discharge device, small droplets called satellites or the like may be generated in association with the main dots (main droplets) discharged from the nozzle of the liquid discharge head. Such small droplets lead to deterioration of print quality and the like.

JP-A-2018-202763

An object to be solved by the embodiment of the present invention is to provide a liquid discharge head and a liquid discharge device that suppress the generation of small droplets.

The liquid discharge head of the embodiment includes a pressure chamber, an actuator and an application part. The pressure chamber houses the liquid. The actuator changes the pressure of the liquid in the pressure chamber according to the applied drive signal. The application unit applies the drive signal for ejecting the liquid a plurality of times from the nozzle communicating with the pressure chamber to the actuator. The drive signal includes a first signal for discharging the liquid once, and a second signal applied after the first signal to discharge the liquid once. The first signal is a first pulse that drives the actuator to reduce the pressure of the liquid in the pressure chamber and a second pulse that drives the actuator to increase the pressure of the liquid in the pressure chamber. And include. The second signal increases the pressure of the liquid in the pressure chamber with a third pulse, which has a longer application time than the first pulse, which drives the actuator to decrease the pressure of the liquid in the pressure chamber. Includes a fourth pulse that drives the actuator so as to.

The perspective view which shows the part of the inkjet head which concerns on embodiment disassembled. The vertical sectional view in the front part of the inkjet head which concerns on embodiment. FIG. 3 is a cross-sectional view of the front portion of the inkjet head according to the embodiment. The figure for demonstrating the operation principle of the inkjet head which concerns on embodiment. The figure for demonstrating the operation principle of the inkjet head which concerns on embodiment. The figure for demonstrating the operation principle of the inkjet head which concerns on embodiment. The block diagram which shows an example of the structure of the inkjet printer which concerns on embodiment. The block diagram which shows an example of the structure of the head drive circuit in FIG. The figure which shows an example of the drive waveform which concerns on embodiment. The figure which shows an example of the drive waveform which concerns on embodiment. The figure which shows an example of the conventional drive waveform. The figure which shows an example of the conventional drive waveform. The graph which shows the ejection speed of the ink droplet ejected by the drive waveform in FIG. The graph which shows the ejection speed of the ink droplet ejected by the drive waveform in FIG. The graph which shows the ink ejection speed when the ink is ejected by changing the application time of an extended pulse variously. A drawing substitute photograph of landing dots when ink is ejected by changing the application time of the extended pulse in various ways. The figure which shows an example of the precursor waveform which concerns on embodiment. The figure which shows the waveform applied to each electrode when the precursor is not applied. The figure which shows the waveform applied to each electrode when a precursor is applied.

Hereinafter, the inkjet head according to the embodiment will be described with reference to the drawings. In each drawing used for the description of the following embodiments, the scale of each part may be changed as appropriate. In addition, each of the drawings used in the following embodiments may be omitted in configuration for the sake of explanation. Further, in each drawing and the following description, the same reference numerals indicate similar elements.

First, the configuration of the inkjet head according to the embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a perspective view showing a part of the inkjet head 100 according to the embodiment in an exploded manner. FIG. 2 is a vertical cross-sectional view of the front portion of the inkjet head 100. FIG. 3 is a cross-sectional view of the front portion of the inkjet head 100. The inkjet head 100 is an example of a liquid ejection head.

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

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

The inkjet head 100 has a large number of elongated grooves 3 from the front end side to the rear end side of the first piezoelectric member 1 and the second piezoelectric member 2 that have been joined. The grooves 3 are regularly spaced and parallel. The front end of each groove 3 is open, and the rear end is inclined upward.

The inkjet head 100 includes electrodes 4 on the side walls and the bottom surface of each groove 3. The electrode 4 has, for example, 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 method for forming the electrode 4 is not limited to the plating method, and may be a sputtering method, a vapor deposition method, or the like.

The inkjet head 100 includes a drawer electrode 10 from the rear end of each groove 3 toward the rear upper surface of the second piezoelectric member 2. The drawer electrode 10 extends from the electrode 4.

The inkjet 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 inkjet 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 a shape having, 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 pressure chamber 15 stores a liquid such as ink.

The top plate 6 is provided with a common ink chamber 5 behind the inside. A nozzle 8 is bored in the orifice plate 7 at a position facing each groove 3. The nozzle 8 communicates with the facing groove 3, that is, the pressure chamber 15. The nozzle 8 has a tapered shape from the pressure chamber 15 side toward the ink ejection side on the opposite side. The nozzles 8 are formed as a set corresponding to three adjacent pressure chambers 15 and are displaced at regular intervals in the height direction of the groove 3 (vertical direction of the paper surface in FIG. 2).

In the inkjet head 100, a printed circuit board 11 on which a conductive pattern 13 is formed is bonded to the upper surface on the rear side of the base substrate 9. The inkjet head 100 mounts a drive IC 12 on which the head drive circuit 101 described later is mounted on the printed circuit board 11. The drive IC 12 is connected to the conductive pattern 13. The conductive pattern 13 is bonded to each of the leader electrodes 10 by wire bonding with a conducting wire 14.

The set of the pressure chamber 15, the electrode 4, and the nozzle 8 included in the inkjet head 100 is referred to as a channel. That is, the inkjet head 100 has channels ch.1, ch.2, ..., Ch.N by the number N of the grooves 3.

Next, the operating principle of the inkjet head 100 configured as described above will be described with reference to FIGS. 4 to 6. 4 to 6 are diagrams for explaining the operating principle of the inkjet head 100. Note that FIGS. 4 to 6 show pressure chambers 15a to 15c as examples of the pressure chamber 15. Further, the electrode 4 on the wall surface of the pressure chamber 15a is the electrode 4a, the electrode 4 on the wall surface of the pressure chamber 15b is the electrode 4b, and the electrode 4 on the wall surface of the pressure chamber 15c is the electrode 4c.

FIG. 4 shows a state in which a positive voltage V is applied to each of the electrodes 4a to 4c. In this state, since the electrodes 4a to 4c all have the same potential, no electric field is applied to the partition walls 16a and 16b. Therefore, neither 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 deformed.

FIG. 5 shows a state in which a ground voltage GND is applied to the central electrode 4b and a positive voltage V is applied to the electrodes 4a and 4c on both sides. In this state, a potential difference is generated between the central electrode 4b and the adjacent electrodes 4a and 4c. As a result, the partition wall 16a and the partition wall 16b are sheared and deformed outward so as to generate an electric field due to the applied potential difference and expand the volume of the pressure chamber 15b. As the volume of the pressure chamber 15b expands, the pressure of the liquid in the pressure chamber 15b decreases.

FIG. 6 shows a state in which a positive voltage V is applied to the central electrode 4b and a ground voltage GND is applied to the electrodes 4a and 4c on both sides. In this state, a potential difference opposite to that in FIG. 5 occurs between the central electrode 4b and the adjacent electrodes 4a and 4c. As a result, the partition wall 16a and the partition wall 16b are sheared and deformed inward so as to generate an electric field in the direction opposite to that in FIG. 5 due to the applied potential difference and contract the volume of the pressure chamber 15b. As the volume of the pressure chamber 15b contracts, the pressure of the liquid in the pressure chamber 15b increases.

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 (droplets) are ejected from the nozzle 8 communicating with the pressure chamber 15b.

From the above, the partition wall 16a and the partition wall 16b are examples of actuators that change the volume of the pressure chamber 15b having the partition wall 16a and the partition wall 16b as a wall surface. That is, each pressure chamber 15 shares an actuator with the adjacent pressure chamber 15. Therefore, the head drive circuit 101 cannot drive each pressure chamber 15 individually. Therefore, the head drive circuit 101 is a (n + 1) divided drive in which each pressure chamber 15 is divided into (n + 1) groups every n (n is an integer of 2 or more) and driven. In the present embodiment, the case of so-called three-division drive in which the head drive circuit 101 divides and drives each pressure chamber 15 into three groups every two is illustrated. The 3-split drive is just an example, and may be a 4-split drive, a 5-split drive, or the like.

The method of applying a voltage for ejecting ink from the nozzle corresponding to the central pressure chamber 15b is not limited to the examples of FIGS. 4 to 6. For example, the inkjet head 100 may be in a state in which the pressure chamber 15b is not deformed by applying the same voltage such as the ground voltage GND to each of the electrodes 4a to 4c. For example, the inkjet head 100 may expand the volume of the pressure chamber 15b by applying a negative voltage −V to the central electrode 4b and applying a ground voltage GND to the electrodes 4a and 4c on both sides. For example, the inkjet head 100 expands the volume of the pressure chamber 15b by applying a negative voltage −V / 2 to the central electrode 4b and applying a positive voltage V / 2 to the electrodes 4a and 4c on both sides. You may. For example, the inkjet head 100 may contract the volume of the pressure chamber 15b by applying a ground voltage GND to the central electrode 4b and applying a negative voltage −V to the adjacent electrodes 4a and 4c. For example, the inkjet head 100 reduces the volume of the pressure chamber 15b by applying a positive voltage V / 2 to the central electrode 4b and applying a negative voltage −V / 2 to the adjacent electrodes 4a and 4c. You may.

Next, the configuration of the inkjet printer 200 will be described with reference to FIG. 7. FIG. 7 is a block diagram showing an example of the configuration of the inkjet printer 200.
The inkjet printer 200 is, for example, an office printer, a bar code printer, a POS printer, an industrial printer, or the like. The inkjet printer 200 forms an image by ejecting ink or the like onto an image forming medium. The inkjet printer 200 realizes gradation expression by changing the amount of droplets that land on one pixel. The image forming medium is, for example, sheet-shaped paper or the like.
The inkjet printer 200 includes a processor 201, a ROM (read-only memory) 202, a RAM (random-access memory) 203, an operation panel 204, a communication interface 205, a transfer motor 206, a motor drive circuit 207, a pump 208, and a pump drive circuit 209. And an inkjet head 100. Further, the inkjet printer 200 includes a bus line 211 such as an address bus and a data bus. The inkjet printer 200 directly or directly inserts the processor 201, ROM 202, RAM 203, operation panel 204, communication interface 205, motor drive circuit 207, pump drive circuit 209, and head drive circuit 101 of the inkjet head 100 into the bus line 211, respectively. Connect via the output circuit. The inkjet printer 200 is an example of a liquid ejection device.

The processor 201 corresponds to the central part of the computer. The processor 201 controls each part in order to realize various functions as the inkjet printer 200 according to the operating system and the application program. The processor 201 is, for example, a CPU (central processing unit) or the like.

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 processor 201 to execute a process for controlling each unit.

The RAM 203 corresponds to the main storage portion of the computer. The RAM 203 stores data necessary for the processor 201 to execute the process. The RAM 203 is also used as a work area where information is appropriately rewritten by the processor 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 arranged 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 inkjet printer 200.

The communication interface 205 receives print data from a client terminal connected via a network such as a LAN (local area network). When an error occurs in the inkjet printer 200, for example, the communication interface 205 transmits a signal notifying the error to the client terminal.

The motor drive circuit 207 controls the drive of the transfer motor 206. The transfer motor 206 functions as a drive source for a transfer mechanism that conveys the image forming medium. When the transport motor 206 is driven, the transport mechanism starts transporting the image forming medium. The transport mechanism transports the image forming medium to the printing position by the inkjet head 100. The transport mechanism discharges the printed image-forming medium from the discharge port to the outside of the inkjet printer 200.

The pump drive circuit 209 controls the drive of the pump 208. When the pump 208 is driven, the ink in the ink tank is supplied to the inkjet head 100.

The inkjet head 100 ejects droplets onto an image forming medium based on print data. The inkjet head 100 includes a head drive circuit 101, a channel group 102, and the like.

The head drive circuit 101 will be described with reference to FIG. FIG. 8 is a block diagram showing an example of the configuration of the head drive circuit 101. As described above, the head drive circuit 101 is in the drive IC 12.

The head drive circuit 101 drives the channel group 102 of the inkjet head 100 based on the print data. The head drive circuit 101 inputs a drive signal to the channel group 102. The head drive circuit 101 is an example of an application unit that applies a drive signal to the actuator 16.
The channel group 102 is composed of a plurality of channels (ch.1, ch.2, ..., Ch.N) including a pressure chamber 15, an electrode 4, a nozzle 8, and the like. That is, the channel group 102 ejects liquid drops by the operation of each pressure chamber 15 in which the actuator 16 expands and contracts based on the control signal from the head drive circuit 101.

As shown in FIG. 8, the head drive circuit 101 includes a pattern generator 301, a frequency setting unit 302, a drive signal generation unit 303, a switch circuit 304, and the like.

The pattern generator 301 uses a waveform pattern of an expansion pulse that expands the volume of the pressure chamber 15, a release period that releases the volume of the pressure chamber 15, and a waveform pattern of a contraction pulse that contracts the volume of the pressure chamber 15. Generate various waveform patterns.

The drive signal generation unit 303 generates a pulse for each channel based on the waveform pattern generated by the pattern generator 301 and the drive frequency set by the frequency setting unit 302 according to the print data input from the bus line. .. The pulse for each channel is output from the drive signal generation unit 303 to the switch circuit 304.

The switch circuit 304 switches the voltage applied to the electrode 4 of each channel according to the pulse for each channel output from the drive signal generation unit 303. That is, the switch circuit 304 applies a voltage to the actuator 16 of each channel based on the energization time of the expansion pulse or the like set by the pattern generator 301.

The switch circuit 304 expands or contracts the volume of the pressure chamber 15 of each channel by switching the voltage, and continuously ejects droplets from the nozzle 8 of each channel for several gradations.

Hereinafter, the waveform of the drive signal (hereinafter referred to as “drive waveform”) will be described with reference to the drawings.
FIG. 9 is a diagram showing an example of a drive waveform applied to the electrode 4 of the ink ejection channel (ejection channel ch.x). The vertical axis of FIG. 9 indicates the voltage [V] of the electrode 4. The voltage of the electrode 4 is the potential of the electrode 4 with respect to the adjacent electrodes 4. The horizontal axis of FIG. 9 is the time axis.
The drive waveform W1 shown in FIG. 9 is a waveform that ejects ink from the nozzle 8 once. The drive waveform W1 includes the expansion pulse PL1 and the contraction pulse PL2 in this order. The expansion pulse PL1 is applied at the same time as the application of the drive waveform W1 is started. By applying the expansion pulse PL1, the volume of the corresponding pressure chamber 15 is expanded as shown in FIG. The application time T1 of the expansion pulse PL1 is 1.5AL, where 1AL (acoustic length) is half the time of the natural vibration cycle of the ink in the pressure chamber 15. Here, as an example, 1AL = 1.60 μsec. The contraction pulse PL2 is started to be applied when the application of the expansion pulse PL1 is completed. By applying the contraction pulse PL2, the volume of the corresponding pressure chamber 15 is contracted as shown in FIG. Along with this, droplets are ejected from the nozzle 8. The application time T2 of the contraction pulse PL2 is 2AL. The contraction pulse PL2 ends when the drive waveform W1 is applied. When the application of the drive waveform W1 is completed, the volume of the corresponding pressure chamber 15 returns to the state of neither expansion nor contraction as shown in FIG. The waveform that is a combination of the expansion pulse PL1 and the contraction pulse PL2 that follows it is hereinafter referred to as a "first discharge waveform".
The first discharge waveform is an example of the first signal. Further, the extended pulse PL1 included in the first discharge waveform is an example of the first pulse that drives the actuator 16 so as to reduce the pressure of the liquid in the pressure chamber 15. The contraction pulse PL2 included in the first discharge waveform is an example of a second pulse that drives the actuator 16 so as to increase the pressure of the liquid in the pressure chamber 15.

FIG. 10 is a diagram showing an example of a drive waveform applied to the electrode 4 of the channel for ejecting ink. The vertical axis of FIG. 10 indicates the voltage [V] of the electrode 4. The horizontal axis of FIG. 10 is the time axis.
The drive waveform W2 shown in FIG. 10 is a waveform that ejects ink from the nozzle 8 three times in a row. The drive waveform W2 includes pulses in the order of expansion pulse PL1, contraction pulse PL2, expansion pulse PL3, contraction pulse PL2, expansion pulse PL3, and contraction pulse PL2. The waveform that is a combination of the expansion pulse PL3 and the contraction pulse PL2 that follows it is hereinafter referred to as a "second discharge waveform". Therefore, the drive waveform W2 is a waveform in which the first discharge waveform is followed by two second discharge waveforms. The expansion pulse PL3 of the second discharge waveform is applied at the same time as the application of the second discharge waveform is started. By applying the expansion pulse PL3, the volume of the corresponding pressure chamber 15 is expanded as shown in FIG. The application time T3 of the extended pulse PL3 is 1AL. The contraction pulse PL2 of the second discharge waveform is started to be applied when the application of the expansion pulse PL3 is completed. By applying the expansion pulse PL1, the volume of the corresponding pressure chamber 15 is contracted as shown in FIG. Along with this, droplets are ejected from the nozzle 8. The drive waveform W2 is a waveform in which ink is ejected from the nozzle 8 once for each of the first ejection waveform or the second ejection waveform. The first applied second discharge waveform of the drive waveform W2 is started to be applied when the application of the first discharge waveform is completed. The second discharge waveform applied to the drive waveform W2 starts to be applied when the application of the first second discharge waveform ends.
The second discharge waveform is an example of the second signal. Further, the expansion pulse PL3 included in the second discharge waveform is an example of a third pulse that drives the actuator 16 so as to reduce the pressure of the liquid in the pressure chamber 15. The contraction pulse PL2 included in the second discharge waveform is an example of a fourth pulse that drives the actuator 16 so as to increase the pressure of the liquid in the pressure chamber 15.

Similarly, the waveform for continuously ejecting ink from the nozzle 8 k times is composed of a first ejection waveform and (k-1) second ejection waveforms following the first ejection waveform. In addition, k is an integer of 2 or more.

The conventional drive waveform is as shown in FIGS. 11 and 12. 11 and 12 are diagrams showing an example of a conventional drive waveform. Further, the vertical axis of FIGS. 11 and 12 shows the voltage [V] of the electrode. The horizontal axis of FIGS. 11 and 12 indicates the time axis.
The drive waveform W3 shown in FIG. 11 is a waveform that ejects ink once from the nozzle. The drive waveform W3 is a second discharge waveform.
The drive waveform W4 shown in FIG. 12 is a waveform that ejects ink from the nozzle three times in a row. The drive waveform W4 is a waveform in which the second discharge waveform continues three times.

Therefore, in the drive waveform W1 and the drive waveform W2 of the present embodiment, it can be seen that the first expansion pulse PL3 replaces the expansion pulse PL1 as compared with the conventional drive waveform W3 and drive waveform W4.

FIG. 13 shows the ejection speed of the ink droplets ejected by the drive waveform W2 of the present embodiment. FIG. 13 is a graph showing the ejection speed of the ink droplets of the first to third drops ejected by the drive waveform W2. The vertical axis of FIG. 13 indicates the ink droplet ejection speed [m / s]. Further, the horizontal axis of FIG. 13 indicates the number of drops.
Further, FIG. 13 shows the ejection speeds when the inkjet head 100 is driven by single nozzle drive and when the inkjet head 100 is driven by multiple nozzle simultaneous drive. The single nozzle drive is a drive for ejecting ink droplets from only one nozzle. The double nozzle simultaneous drive is a drive in which ink droplets are simultaneously ejected from a plurality of nozzles every n nozzles. Here, since it is divided into three parts, it is every two. That is, here, the double nozzle simultaneous drive is a drive in which ink droplets are simultaneously ejected from the m (m is an integer), m + 3, m + 6, m + 9 ... th nozzle.

Further, FIG. 14 shows the ejection speed of the ink droplets ejected by the conventional drive waveform W4. FIG. 14 is a graph showing the ejection speed of the ink droplets of the first to third drops ejected by the drive waveform W4. The vertical axis of FIG. 14 indicates the ejection speed of ink droplets. Further, the horizontal axis of FIG. 14 indicates the number of drops.
Further, FIG. 14 shows the ejection speeds when the inkjet head 100 is driven by a single nozzle drive and when the inkjet head 100 is driven by a double nozzle simultaneous drive.

As shown in FIG. 14, in the conventional drive waveform W4, the discharge speed of the first drop is faster than the discharge speed of the two drop names in both the single nozzle drive and the double nozzle simultaneous drive. On the other hand, as shown in FIG. 13, in the drive waveform W2 of the present embodiment, the discharge speed of the second drop is faster than that of the first drop. In this way, the ink droplets of the second drop that are ejected later are faster than the ink droplets of the first drop, so that the ink droplets of the second drop are combined with the ink droplets of the first drop during flight. Cheap. By combining the ink droplets in this way, the impact dots that land on the image forming medium are less likely to be split. Further, by combining the ink droplets in this way, satellites and the like are less likely to be generated. Therefore, the image quality is improved by the coalescence of the ink droplets.

FIG. 15 shows the discharge speeds of the first to third drops when the application time of the extended pulse PL1 is variously changed for the drive waveform W2. FIG. 15 is a graph showing the ejection speed of the ink ejected by the drive waveform W2 when the application time of the extended pulse PL1 is variously changed. The vertical axis of FIG. 15 indicates the ejection speed of ink droplets. Further, the horizontal axis of FIG. 15 indicates the application time of the extended pulse PL1 by a difference α [μsec]. The difference α is a value obtained by subtracting 1AL from the application time of the extended pulse PL1. For example, if α = 0.4, the application time of the extended pulse PL1 is 1AL + 0.4 μsec. Since AL = 1.60 [μsec] here, if α = 0.4, the application time of the extended pulse PL1 is 2.0 μsec.

From FIG. 15, it can be seen that when α is −0.4 μsec to 0.4 μsec, the ejection speed of the ink droplet of the first drop is faster than the ejection speed of the second drop. Further, from FIG. 15, it can be seen that when α is 0.6 μsec to 0.8 μsec, the ejection speed of the ink droplet of the second drop is faster than the ejection speed of the ink droplet of the first drop. Therefore, the application time of the extended pulse PL1 is preferably 1AL + 0.6 μsec (= 2.2 μsec) or more. That is, the application time of the extended pulse PL1 is preferably about 1.4AL or more.

FIG. 16 is a photograph of landing dots when the ink is ejected once to three times in succession by varying the application time of the extended pulse PL1. Note that FIG. 16 shows photographs of each landing dot when α is changed from −0.4 μsec to 0.8 μsec in 0.2 μsec increments. As can be seen from FIG. 16, when α is 0.2 μs, the landing dots when the ink is ejected twice in succession are closer to a perfect circle than when α is 0 μs. It can also be seen that when α is 0.4 μs, there are fewer satellite dots than when α is 0.2 μs. The satellite dot is a small dot in the vicinity of the main dot. Further, it can be seen that when α is 0.6 μsec, the number of satellite dots is further smaller than when α is 0.4 μsec. In particular, it can be seen that the number of satellite dots is reduced when the ink is ejected only once. Further, it can be seen that when α is 0.8 μsec, the number of satellite dots is further smaller than when α is 0.6 μsec. Therefore, the application time of the extended pulse PL1 is preferably 1AL + 0.2 μsec (= 1.8 μsec) or more, more preferably 1AL + 0.4 μsec (= 2.0 μsec) or more, and 1AL + 0.6 μsec. It is more preferably (= 2.2 μsec) or more, and most preferably 1AL + 0.8 μsec (= 2.4 μsec). That is, the application time of the extended pulse PL1 is preferably about 1.1AL or more, more preferably about 1.3AL or more, further preferably about 1.4AL or more, and 1.5AL. Is most preferable.

Although not shown in FIG. 16, when α was 1.0 μs, worse results were obtained than when α was 0.8 μs. Therefore, α is preferably less than 1 μsec. That is, the application time of the extended pulse PL1 is preferably less than about 1.6 AL.

Further, in general, in the (n + 1) split drive inkjet head, the ejection performance changes between the m-th nozzle, the m + 1-th nozzle, ..., The m + n-th nozzle. Therefore, in order to suppress the influence of such split driving as much as possible, a micro-vibration pulse called a precursor is applied to the electrode 4. The precursor is a micro-vibration pulse that does not eject droplets.

An example of the waveform of the precursor is shown in FIG. FIG. 17 is a diagram showing an example of the precursor waveform W11. The precursor waveform W11 includes a contraction pulse PL11. The contraction pulse PL11 is started to be applied after T11 from the start of application of the precursor waveform W11. By applying the contraction pulse PL11, the volume of the corresponding pressure chamber 15 is contracted as shown in FIG. The application time of the contraction pulse PL11 is T12. T11 is 2.25AL as an example. T12 is 0.75AL as an example. The voltage of the precursor waveform is 0 from the start of application of the precursor waveform W11 to the elapse of T11. That is, the period from the start of application of the precursor waveform W11 to the elapse of T11 is the release period. Therefore, during this period, the volume of the corresponding pressure chamber 15 is in a state of neither expansion nor contraction as shown in FIG.

Assuming that the maximum number of continuous discharges is, for example, p times, the head drive circuit 101 applies the precursor waveform W11 after applying the drive waveform in which the number of continuous discharges is less than p times. Note that p is an integer of 2 or more.
For example, the head drive circuit 101 applies the precursor waveform W11 (pq) times after applying the drive waveform in which the number of continuous discharges is q times. Note that q is an integer less than or equal to p.
When the number of continuous discharges differs between the nozzles, the residual vibration generated after discharge differs between the nozzles. Therefore, by inserting the precursor waveform as described above, the difference in residual vibration can be made uniform. This improves the print quality.

18 and 19 show examples of waveforms applied to each electrode 4 with and without a precursor. FIG. 18 is a diagram showing a waveform applied to each electrode 4 when a precursor is not applied. FIG. 19 is a diagram showing a waveform applied to each electrode 4 when a precursor is applied. In addition, in FIG. 18 and FIG. 19, the maximum number of discharges p is set to 3 times. As can be seen from FIG. 19, the precursor waveform W11 is applied after the drive waveform that is less than the maximum number of discharges is applied.

The above embodiment can be modified as follows.
In the above embodiment, in the inkjet printer 200, the pressure chambers 15 are continuously arranged. However, the liquid discharge device of the embodiment may include an air chamber. In this case, in the liquid discharge device of the embodiment, for example, pressure chambers and air chambers are alternately arranged.

In addition to the above embodiment, the inkjet head 100 may have a structure in which the diaphragm is deformed by static electricity to eject ink. In this case, the diaphragm is an actuator that changes the pressure of the liquid in the pressure chamber 15.

The inkjet printer 200 of the embodiment is an inkjet printer that forms a two-dimensional image with ink on an image forming medium. However, the liquid discharge device of the embodiment is not limited to this. The liquid discharge device of the embodiment may be, for example, a 3D printer, an industrial manufacturing machine, a medical machine, or the like. When the liquid discharge device of the embodiment is a 3D printer, an industrial manufacturing machine, a medical machine, or the like, the liquid discharge device of the embodiment is, for example, a substance to be a material or a binder for solidifying the material. A three-dimensional object is formed by ejecting from the inkjet head.

In addition, the inkjet printer 200 can also eject transparent glossy ink, ink that develops color when irradiated with infrared rays, ultraviolet rays, or the like, or other special inks. Further, the inkjet printer 200 may be capable of ejecting a liquid other than ink. The liquid discharged by the inkjet printer 200 may be a dispersion liquid such as a suspension. Examples of the liquid other than the ink ejected by the inkjet printer 200 include a liquid containing conductive particles for forming a wiring pattern of a printed wiring substrate, a liquid containing cells for artificially forming a tissue or an organ, and the like. Examples include binders such as adhesives, waxes, and liquid resins.

Each numerical value in the above-described embodiment and its modification allows an error within a range in which the object of the present invention is achieved.

Although some 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 embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

4 ... Electrodes, 8 ... Nozzles, 15 ... Pressure chambers, 16 ... Actuators, 100 ... Inkjet heads, 101 ... Head drive circuits, 200 ... Inkjet printers

Claims (5)

A pressure chamber that houses the liquid and
An actuator that changes the pressure of the liquid in the pressure chamber according to the applied drive signal,
The actuator is provided with an application unit that applies the drive signal to the actuator to discharge the liquid a plurality of times from a nozzle communicating with the pressure chamber.
The drive signal includes a first signal for discharging the liquid once and a second signal applied after the first signal to discharge the liquid once.
The first signal is a first pulse that drives the actuator to reduce the pressure of the liquid in the pressure chamber and a second pulse that drives the actuator to increase the pressure of the liquid in the pressure chamber. Including with pulse
The second signal is a third pulse having an application time shorter than that of the first pulse, which drives the actuator so as to reduce the pressure of the liquid in the pressure chamber, and the pressure of the liquid in the pressure chamber. A liquid discharge head that includes a fourth pulse that drives the actuator to increase. The application time of the first pulse is 1.1 AL or more, where AL is half the time of the natural vibration cycle of the liquid in the pressure chamber.
The liquid discharge head according to claim 1, wherein the application time of the third pulse is 1AL. The liquid discharge head according to claim 2, wherein the application time of the first pulse is less than 1.6 AL. The liquid discharge head according to any one of claims 1 to 3, wherein the application unit applies a signal including a precursor waveform after the drive signal to the actuator. A liquid discharge head and a liquid supply device for supplying a liquid to the liquid discharge head are provided.
The liquid discharge head
A pressure chamber for storing liquid and
An actuator that changes the pressure of the liquid in the pressure chamber according to the applied drive signal,
The actuator is provided with an application unit that applies the drive signal to the actuator to discharge the liquid a plurality of times from a nozzle communicating with the pressure chamber.
The drive signal includes a first signal for discharging the liquid once and a second signal applied after the first signal to discharge the liquid once.
The first signal is a first pulse that drives the actuator to reduce the pressure of the liquid in the pressure chamber and a second pulse that drives the actuator to increase the pressure of the liquid in the pressure chamber. Including with pulse
The second signal is a third pulse having an application time longer than that of the first pulse, which drives the actuator so as to reduce the pressure of the liquid in the pressure chamber, and the pressure of the liquid in the pressure chamber. A liquid discharge device comprising a fourth pulse that drives the actuator to increase.