Liquid dispensing device

Abstract

To solve the problem that mist is easily produced when increasing the speed of succeeding droplets.SOLUTION: A liquid discharge device 1 includes a discharge part 10 for discharging droplets from a nozzle N, and a drive signal generation part 60 for generating drive signals. A drive signal comprises a plurality of discharge pulses in one cycle. The plurality of discharge pulses includes a final discharge pulse Pw3 corresponding to a final droplet, and a preceding discharge pulse Pw1 corresponding to a preceding droplet discharged from the nozzle before the final droplet. The final discharge pulse comprises an expansion element a3 for expanding a pressure chamber, an expansion maintaining element b3 for maintaining the expansion of the pressure chamber, a contraction element c3 for contracting the pressure chamber, and a damping element e3 for weakening residual oscillation of a liquid in the pressure chamber. A time width combining the expansion element and the expansion maintaining element of a final discharge pulse is longer than a length that is 0.5 times a natural oscillation period Tc of a discharge part, and shorter than a length that is 1.0 times the natural oscillation period Tc.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to a liquid ejection device. [Background technology]

[0002] The liquid ejection device described in Patent Document 1 supplies a drive signal to a drive element to generate pressure fluctuations in the liquid in a pressure chamber, thereby ejecting droplets from a nozzle. This liquid ejection device causes a first ink droplet and a second ink droplet ejected from the nozzle to combine before landing on a medium. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-95814 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional liquid ejection devices supply a driving signal including multiple ejection pulses with different waveforms to a driving element in order to combine multiple droplets before they land on a medium. In order to combine multiple droplets ejected by multiple ejection pulses before they land on a medium, it is necessary to make the speed of the subsequent droplets faster than the speed of the preceding droplets. However, if the speed of the subsequent droplets is increased, a problem occurs in that mist is more likely to be generated. [Means for solving the problem]

[0005] The liquid ejection device according to the present invention includes an ejection section having a nozzle that ejects liquid to be landed on a medium, a pressure chamber that communicates with the nozzle, and a drive element that generates a pressure fluctuation in the liquid in the pressure chamber when a drive signal is supplied, and a drive signal generation section that generates a drive signal. The drive signal includes a plurality of ejection pulses for ejecting a plurality of droplets during one period. The plurality of droplets generated by the plurality of ejection pulses are combined before landing on the medium. The plurality of ejection pulses include a final ejection pulse corresponding to a final droplet that is ejected last from the nozzle among the plurality of droplets, and a preceding ejection pulse corresponding to a preceding droplet that is ejected from the nozzle before the final droplet among the plurality of droplets. The preceding ejection pulse includes a first expansion element that expands the pressure chamber, a first expansion maintaining element that maintains the expansion of the pressure chamber by the first expansion element, a first contraction element that contracts the pressure chamber expanded by the first expansion element, and a first vibration suppression element that expands the pressure chamber after the pressure chamber is contracted by the first contraction element to weaken residual vibration of the liquid in the pressure chamber. The final ejection pulse includes a second expansion element that expands the pressure chamber, a second expansion maintaining element that maintains the expansion of the pressure chamber by the second expansion element, a second contraction element that contracts the pressure chamber expanded by the second expansion element, and a second vibration damping element that expands the pressure chamber after the pressure chamber is contracted by the second contraction element to weaken residual vibration of the liquid in the pressure chamber. The combined time width of the second expansion element and the second expansion maintaining element of the final ejection pulse is longer than 0.5 times the natural vibration period Tc of the ejection unit and shorter than 1.0 times the natural vibration period Tc of the ejection unit. [Brief description of the drawings]

[0006] [Figure 1] 1 is a schematic diagram of a liquid ejection device according to an embodiment. [Diagram 2] FIG. 1 is a block diagram showing a liquid ejection device. [Diagram 3] FIG. [Figure 4] FIG. 1 is a diagram showing the behavior of ink droplets according to the prior art. [Diagram 5] 11 is a waveform diagram showing a square wave for expanding the volume of a pressure chamber. FIG. [Figure 6]6 is a diagram showing the behavior of the meniscus when a signal including the square wave shown in FIG. 5 is applied to a driving element. [Figure 7] 11 is a waveform diagram showing a square wave for expanding and contracting the volume of a pressure chamber. FIG. [Figure 8] 8 is a diagram showing the behavior of the meniscus when a signal including the square wave shown in FIG. 7 is applied to a driving element. [Figure 9] FIG. 4 is a waveform diagram showing a drive signal including an ejection pulse. [Figure 10] 13 is a table showing ejection pulse conditions for Models 1 to 3. [Figure 11] 11 is a diagram showing the behavior of ink droplets due to ejection pulses in models 1 to 3. FIG. [Figure 12] 5 is a waveform diagram showing a waveform of a drive signal according to the embodiment. FIG. [Figure 13] 1 is a diagram showing a plurality of ink droplets ejected from a nozzle N. FIG. [Figure 14] 1 is a table showing the results of a simulation of the behavior of a plurality of ink droplets ejected when drive signals according to Examples 1 to 6 and Comparative Examples 1 and 2 are supplied. [Figure 15] 13 is a table showing the results of a simulation of the behavior of a plurality of ink droplets ejected when drive signals according to Examples 7 to 15 are supplied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. However, in each drawing, the dimensions and scale of each part are appropriately different from the actual ones. In addition, since the embodiments described below are preferred specific examples of the present invention, various technically preferable limitations are attached, but the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0008] Fig. 1 is a schematic perspective view showing the internal configuration of a liquid ejection device 1 according to an embodiment. Fig. 2 is a block diagram showing the liquid ejection device 1. The liquid ejection device 1 shown in Fig. 1 ejects ink droplets from an ejection section 10, causing the ink droplets to land on a medium PA. The medium PA is, for example, printing paper. The liquid ejection device 1 includes a liquid ejection section 20 having the ejection section 10, a carriage 3 on which the liquid ejection section 20 is mounted, a carriage transport mechanism 4 that transports the carriage 3, and a medium transport mechanism 5 that transports the medium PA.

[0009] The carriage 3 is equipped with an ink cartridge 6 that stores ink. The ink cartridge 6 is an ink container that stores ink. The carriage 3 can be equipped with a plurality of ink cartridges corresponding to, for example, four colors of ink. The four colors of ink include, for example, cyan, magenta, yellow, and black. The ink container does not necessarily have to be equipped on the carriage 3. The ink stored in the ink cartridge is supplied to the liquid ejection unit 20.

[0010] The liquid ejection device 1 includes a transport mechanism 7. The transport mechanism 7 includes a carriage transport mechanism 4 and a medium transport mechanism 5. The carriage transport mechanism 4 has a transport belt 4a and a motor for transporting the carriage 3. The medium transport mechanism 5 has a transport roller 5a and a motor for transporting the medium PA. The liquid ejection device 1 ejects ink droplets onto the medium PA to perform printing, by transporting the medium PA using the carriage transport mechanism 4 while transporting the medium PA using the medium transport mechanism 5. The liquid ejection device 1 forms dots on the medium PA according to the print data Img.

[0011] The liquid ejection device 1 includes a linear encoder 8. The linear encoder 8 is provided at a position where it can detect the position of the carriage 3. The linear encoder 8 obtains information regarding the position of the carriage 3. The linear encoder 8 outputs an encoder signal to the control unit 30 as the carriage 3 moves.

[0012] The liquid ejection section 20 includes a plurality of recording heads 22. FIG. 3 is a cross-sectional view showing the ejection section 10 of the recording head 22. The recording head 22 includes a plurality of ejection sections 10 and common liquid chambers 23, 24. The ejection section 10 includes an individual flow path 11, a pressure chamber 12, a communicating flow path 13, and a nozzle N. The liquid ejection section 20 includes a nozzle plate 25 in which a plurality of nozzles N are formed. The bottom surface of the nozzle plate 25 is a nozzle surface 25a. The ejection section 10 includes a vibration plate 14 and a driving element 50.

[0013] The common liquid chambers 23, 24 communicate with the multiple pressure chambers 12 and store ink before being supplied to the pressure chambers 12. The common liquid chamber 24 is connected downstream of the common liquid chamber 23. The individual flow paths 11 communicate between the common liquid chamber 24 and the pressure chambers 12. The individual flow paths 11 are provided for each pressure chamber 12. The communication flow paths 13 communicate between the pressure chambers 12 and the nozzles N.

[0014] The vibration plate 14 constitutes a part of the wall surface of the pressure chamber 12. The vibration plate 14 is provided in common to the multiple pressure chambers 12. The multiple driving elements 50 are provided for each of the multiple pressure chambers 12. The driving element 50 includes an electrode 51, an electrode 52, and a piezoelectric layer 53. The electrode 51 is a lower electrode, and the electrode 52 is an upper electrode. The electrode 51 is a common electrode, and the electrode 52 is an individual electrode. The common electrode is an electrode common to the multiple driving elements 50. The individual electrodes are provided for each of the multiple driving elements 50. The electrode 51 may be an individual electrode, and the electrode 52 may be a common electrode. The piezoelectric layer 53 is disposed between the electrode 51 and the electrode 52.

[0015] The electrode 51 is electrically connected to the power supply line Lb. The power supply line Lb is set to a potential VBS. A drive signal Com is supplied to the electrode 52. When the drive signal Com is supplied and a voltage is applied between the electrodes 51 and 52, the drive element 50 is displaced in the thickness direction in response to the applied voltage. This causes the drive element 50 and the diaphragm 14 to vibrate. As the diaphragm 14 vibrates, the volume of the pressure chamber 12 and the pressure within the pressure chamber 12 change, and the ink filled within the pressure chamber 12 flows into the communicating flow path 13. The ink within the communicating flow path 13 is pushed out to the nozzle N, and ink droplets are ejected from the nozzle N.

[0016] As shown in FIG. 2, the liquid ejection device 1 includes a control unit 30. The control unit 30 includes one or more CPUs 31. The control unit 30 may include an FPGA instead of or in addition to the CPU 31. The control unit 30 includes a storage unit 40. The storage unit 40 includes, for example, a RAM 42 and a ROM 41. The storage unit 40 may include an EEPROM or a PROM. The storage unit 40 can store print data Img supplied from a host computer. The storage unit 40 stores a control program for the liquid ejection device 1.

[0017] CPU is an abbreviation for Central Processing Unit. FPGA is an abbreviation for field-programmable gate array. RAM is an abbreviation for Random Access Memory. ROM is an abbreviation for Read Only Memory. EEPROM is an abbreviation for Electrically Erasable Programmable Read-Only Memory. PROM is an abbreviation for Programmable ROM.

[0018] The control unit 30 generates signals for controlling the operation of each part of the liquid ejection device 1. The control unit 30 can generate a print signal SI and a waveform designation signal dCom. The print signal SI is a digital signal for designating the type of operation of the ejection unit 10. The print signal SI can designate whether or not to supply a drive signal Com to the ejection unit 10. The waveform designation signal dCom is a digital signal that defines the waveform of the drive signal Com. The drive signal Com is an analog signal for driving the ejection unit 10.

[0019] The liquid ejection device 1 includes a drive signal generation circuit 60. The drive signal generation circuit 60 is an example of a drive signal generation section. The drive signal generation circuit 60 is electrically connected to the control section 30. The drive signal generation circuit 60 includes a DA conversion circuit. The drive signal generation circuit 60 generates a drive signal Com having a waveform defined by a waveform designation signal dCom. When the control section 30 receives an encoder signal from the linear encoder 8, the control section 30 outputs a timing signal PTS to the drive signal generation circuit 60. The timing signal PTS defines the generation timing of the drive signal Com. The drive signal generation circuit 60 outputs the drive signal Com every time it receives the timing signal PTS.

[0020] The liquid ejection section 20 includes a drive circuit 21. The drive circuit 21 is electrically connected to the control section 30 and the drive signal generation circuit 60. The drive circuit 21 switches whether or not to supply the drive signal Com to the ejection section 10 based on the print signal SI. The drive circuit 21 can select the drive element 50 of the ejection section 10 to which the drive signal Com is supplied based on the print signal SI, latch signal LAT, and change signal CH supplied from the control section 30. The latch signal LAT specifies the latch timing of the print data Img. The change signal CH specifies the selection timing of the drive pulse included in the drive signal Com.

[0021] Next, the behavior of an ink droplet according to the conventional technology will be described with reference to Fig. 4. Fig. 4 is a diagram showing the behavior of an ink droplet according to the conventional technology. Fig. 4 illustrates the state of an ink droplet 100 as time progresses, from time t101 to time t105. At time t101, the ink droplet 100 is ejected from the nozzle N. The ink droplet 100 pushed out from the nozzle N forms a liquid column. At time t101, the leading edge 100a of the ink droplet 100 is ejected from the nozzle N, and the trailing edge of the ink droplet 100 has not yet been ejected from the nozzle N.

[0022] At time t102, the rear end 100b of the ink droplet 100 is ejected from the nozzle N. The portion of the ink droplet 100 corresponding to the rear end 100b is pulled toward the nozzle N due to the surface tension between the ink remaining in the nozzle N and the rear end 100b of the ink droplet 100. When the speed of the rear end 100b becomes 0 m / s from the state where it is pulled by the ink remaining in the nozzle N, the ink remaining in the nozzle N and the rear end 100b of the ink droplet 100 ejected from the nozzle N are separated. The rear end 100b is torn off from the ink remaining in the nozzle N, and the rear end 100b is ejected from the nozzle N. In this state, the front end 100a has a larger volume than the rear end 100b.

[0023] A speed difference occurs between the speed Va of the leading edge 100a of the ink droplet 100 and the speed Vb of the trailing edge 100b. The speed Va of the leading edge 100a is faster than the speed Vb of the trailing edge 100b. In this state, the leading edge 100a and the trailing edge 100b are separated in the traveling direction of the ink droplet 100. With the leading edge 100a and the trailing edge 100b separated, the ink droplet 100 forms a liquid column. At time t103, the portion including the leading edge 100a is separated from the cylindrical portion.

[0024] The cylindrical middle portion 100c is unstable. The middle portion 100c is an intermediate portion between the leading end 100a and the trailing end 100b. At time t104, the middle portion 100c starts to separate into multiple droplets. Some of the separated droplets are held together by surface tension. At time t105, the ink droplet 100 is separated into a main droplet 101 including the leading end 100a, multiple satellite droplets 100d and 100e, a fine mist 100f, and a satellite droplet 100g including the trailing end 100b. For example, some of the fine mist 100f may be held together by surface tension to become the satellite droplets 100d and 100e. In this way, the ink droplet 100 is separated by the speed difference between the leading end 100a and the trailing end 100b, and the fine mist 100f is generated.

[0025] Next, referring to Fig. 5 and Fig. 6, the behavior of the meniscus in the nozzle N when a drive signal including a square wave is supplied to the drive element will be described. Fig. 5 is a waveform diagram showing a square wave for expanding the volume of the pressure chamber 12. Fig. 6 is a diagram showing the behavior of the meniscus when a signal including the square wave shown in Fig. 5 is applied to the drive element. In Fig. 5 and Fig. 6, the horizontal axis shows the passage of time. The passage of time is shown based on the natural vibration period Tc of the ejection section 10. In Fig. 5, the vertical axis shows the electric potential, and in Fig. 6, the vertical axis shows the position of the meniscus in the nozzle N. In Fig. 6, the upper side shows the inside of the nozzle N, and the lower side shows the outside of the nozzle N.

[0026] The natural vibration period Tc of the ejection portion 10 may be measured by performing an experiment, or may be calculated by a simulation. The natural vibration period Tc may be the natural vibration period of the vibration of the ink inside the pressure chamber 12.

[0027] The natural vibration period Tc may be calculated, for example, using the following formula (1). In formula (1), Mn is the mass of ink per unit length in the nozzle N [kg / m]. The direction of the unit length is, for example, along the vibration direction of the ink. Ms is the mass of ink per unit length in the individual flow channel 11 that supplies ink to the pressure chamber 12 [kg / m]. Cc is the change in volume of ink per unit pressure in the pressure chamber 12 [m 3 / N]. Tc=2π〔{(Mn×Ms) / (Mn+Ms)}×Cc〕 1 / 2 …(1)

[0028] At time t=0, the meniscus is present on the nozzle surface 25a. At time t=0, a signal including a square wave is applied to the driving element 50. This causes the volume of the pressure chamber 12 to expand. When the volume of the pressure chamber 12 expands, the ink in the nozzle N is drawn inside the nozzle N. The inside of the nozzle N is the side closer to the pressure chamber 12. The meniscus moves away from the nozzle surface 25a and closer to the pressure chamber 12, and an ink flow occurs in the nozzle N.

[0029] At time t=0.5Tc, the displacement of the meniscus due to the natural vibration of the ejection section 10 reaches a maximum and is farthest from the nozzle surface 25a. Thereafter, the meniscus is displaced by the natural vibration of the ejection section 10 so as to approach the nozzle surface 25a.

[0030] Next, the behavior of the meniscus in the nozzle N when a drive signal including a square wave is supplied to the drive element will be described with reference to Figures 7 and 8. Descriptions that are the same as those in Figures 5 and 6 above will be omitted.

[0031] In the square wave shown in FIG. 7, the volume of the pressure chamber 12 is contracted at time t=0.5Tc when the phase of the meniscus vibration caused by the natural vibration of the ejection unit 10 is inverted. This applies an ejection force to the ink, and the meniscus vibration caused by the natural vibration of the ejection unit 10 resonates, doubling the amplitude, and the ink droplet is efficiently ejected from the nozzle N. At time t=0.75Tc, the ink is ejected from the nozzle surface 25a. Then, the velocity Vb of the rear end 100b of the ink droplet 100 decreases monotonically until time t=1.0Tc when the ink flow in the nozzle N is reversed again, so that a velocity difference occurs between the front end 100a and the rear end 100b of the ink droplet 100, and the ink droplet 100 forms a liquid column. A velocity difference occurs from the front end 100a to the rear end 100b of the ink droplet 100, forming a velocity gradient.

[0032] Considering such a speed difference between the leading end 100a and the trailing end 100b of the ink droplet 100, by applying an ejection force to the ink in the nozzle N in time with the time t = 1.0Tc, it is possible to suppress the speed difference between the leading end 100a and the trailing end 100b of the ink droplet 100 and eject the droplet so as to suppress the formation of a liquid column. In this case, the absolute value of the speed Va of the leading end 100a also decreases, but the speed Va can be increased by compensating for the displacement of the vibration plate 14.

[0033] Next, a reference example of the behavior of an ink droplet ejected from a nozzle N will be described with reference to Figs. 9 to 11. The results of verifying the behavior of ink droplets according to models 1 to 3 by simulation will be described. The ink droplets according to models 1 to 3 have different speed differences between the leading and trailing ends of the ink droplets. Fig. 9 is a waveform diagram showing the waveform of the ejection pulse Pw of the driving signal Com. Fig. 10 is a table showing the conditions of the ejection pulse Pw according to models 1 to 3. Fig. 11 is a diagram showing the behavior of an ink droplet 100 caused by the ejection pulse Pw according to models 1 to 3. By supplying the driving signal Com shown in Fig. 9 to the driving element 50, an ink droplet 100 is ejected from the nozzle N. As shown in Fig. 10, when the conditions of the ejection pulse Pw are changed, the behavior of the ink droplet 100 differs as shown in Fig. 11.

[0034] The ejection pulse Pw shown in FIG. 9 includes an expansion element a1, an expansion maintaining element b1, a contraction element c1, a contraction maintaining element d1, and a vibration damping element e1. The expansion element a1 is an element that expands the volume of the pressure chamber 12. The expansion maintaining element b2 is an element that maintains the volume of the pressure chamber 12 expanded by the expansion maintaining element a1. The contraction element c1 is an element that contracts the volume of the pressure chamber 12 maintained by the expansion maintaining element b2. The contraction maintaining element d1 is an element that maintains the volume of the pressure chamber 12 contracted by the contraction element c1. The vibration damping element e1 is an element that expands the volume of the pressure chamber 12 maintained by the contraction maintaining element d1, thereby weakening the residual vibration of the ink in the pressure chamber 12.

[0035] The ejection pulse Pw changes potential between potential V1 and potential V2. The expansion component a1 starts from a reference potential VB. The reference potential VB is a potential between potential V1 and potential V2. The expansion component a1 starts from the reference potential VB at time t11 and reaches potential V1 at time t12.

[0036] The expansion maintaining element b1 is maintained at potential V1. The expansion maintaining element b1 is maintained at potential V1 from time t12 to time t13. The contraction element c1 changes potential from potential V1 to potential V2. The contraction element c1 starts at potential V1 at time t13 and reaches potential V2 at time t14.

[0037] The contraction maintaining element d1 is maintained at potential V2. The contraction maintaining element d1 is maintained at potential V2 from time t14 to time t15. The vibration damping element e1 changes potential from potential V2 to reference potential VB. Note that the period Tab shown in FIG. 9 is the total length of the expansion element a1 and the expansion maintaining element b1. By changing the length of the period Tab, the speed of the rear end 100b of the ink droplet 100 ejected from the nozzle N can be changed.

[0038] As shown in Fig. 10, the ejection pulse Pw for models 1 to 3 was set so that the speed difference between the front end and rear end of the ink droplet was different. In the ejection pulse Pw for models 1 to 3, the time length t11 to t12 of the expansion element a1 and the time length t13 to t14 of the contraction element c1 were set to be the same, and the potential difference between V1 and V2 was adjusted so that the speed Vm1 of the ink droplet tip was the same in all models. In the ejection pulse Pw for models 1 to 3, the time length t12 to t13 of the expansion maintenance element b1 is different from one another, so the time length t11 to t13 of the period Tab is different from one another, and the speed difference Vd between the front end 100a and rear end 100b of the ink droplet 100 is different from one another.

[0039] In model 1, the time length of the expansion element a1 is 1.6 [μs], and the time length of the expansion maintenance element b1 is 2.2 [μs]. The length of the period Tab1 in model 1 is 0.48 times the natural vibration period Tc. In model 1, the time length of the contraction element c1 is 2.75 [μs], and the speed Vm1 of the front end 100a of the ink droplet 100 is 8.5 [m / s]. The speed difference Vd between the front end 100a and the rear end 100b of the ink droplet 100 in model 1 is "large."

[0040] In model 2, the time length of the expansion sustaining element b1 is 3.8 [μs], and the length of the period Tab1 is 0.68 times the natural vibration period Tc. The speed difference Vd between the leading end 100a and the trailing end 100b of the ink droplet 100 in model 2 is "medium". In model 3, the time length of the expansion sustaining element b1 is 5.4 [μs], and the length of the period Tab1 is 0.88 times the natural vibration period Tc. The speed difference Vd between the leading end 100a and the trailing end 100b of the ink droplet 100 in model 3 is "small". The speed difference Vd in model 1 is larger than the speed difference Vd in model 2. The speed difference Vd in model 2 is larger than the speed difference Vd in model 3.

[0041] FIG. 11 shows the state of an ink droplet ejected from nozzle N over time. In model 1, at time t201, the leading edge 100a of the ink droplet 100 is ejected from nozzle N. At time t202, the trailing edge 100b of the ink droplet 100 is ejected from nozzle N. At time t203, a liquid column-like intermediate portion 100c is formed due to the difference in speed between the leading edge 100a and the trailing edge 100b of the ink droplet 100. At time t204, the intermediate portion 100c splits into satellite droplets 100d and 100e. At time t205, a portion of the ink droplet 100 becomes a fine mist 100f with almost no speed.

[0042] In model 2, at time t201, the leading end 100a of an ink droplet 100 is ejected from the nozzle N, and at time t202, the trailing end 100b is ejected from the nozzle N. The leading end 100a and the trailing end 100b form one main droplet 101 from time t203 to t205.

[0043] In model 3, at time t201, the leading end 100a of the ink droplet 100 is ejected from the nozzle N, and at time t202, the trailing end 100b is ejected from the nozzle N. In model 3, almost no liquid column was generated. The leading end 100a and the trailing end 100b form one main droplet 101 from time t203 to t205.

[0044] Thus, in model 1, a fine mist 100f was formed, but the mist 100f was not formed in models 2 and 3. In models 2 and 3, only the main droplet 101 flies.

[0045] Next, referring to FIG. 12, a waveform diagram showing the waveform of the driving signal Com1 according to the embodiment is shown. In FIG. 12, the horizontal axis indicates the passage of time, and the vertical axis indicates the potential. The driving waveform included in the driving signal Com1 includes a plurality of ejection pulses Pw1, Pw2, and Pw3 during one period T1. The ejection pulse Pw1 is an example of a leading ejection pulse, and the ejection pulse Pw3 is an example of a final ejection pulse. The ejection pulse Pw2 is supplied to the driving element 50 after the ejection pulse Pw1. The ejection pulse Pw3 is supplied to the driving element 50 after the ejection pulse Pw2. One period T1 may be, for example, a length from when a timing signal PTS is received until when the next timing signal PTS is received. One period T1 may be, for example, a length from when a latch signal LAT is received until when the next latch signal LAT is received.

[0046] The ejection pulse Pw1 includes an expansion element a1, an expansion maintaining element b1, a contraction element c1, a contraction maintaining element d1, and a vibration damping element e1. The expansion element a1 is an element that expands the volume of the pressure chamber 12. The expansion element a1 is an example of a first expansion element. The expansion maintaining element b2 is an element that maintains the volume of the pressure chamber 12 expanded by the expansion element a1. The expansion maintaining element b1 is an example of a first expansion maintaining element. The contraction element c1 is an element that contracts the volume of the pressure chamber 12 maintained by the expansion maintaining element b2. The contraction element c1 is an example of a first contraction element. The contraction maintaining element d1 is an element that maintains the volume of the pressure chamber 12 contracted by the contraction element c1. The vibration damping element e1 is an element that expands the volume of the pressure chamber 12 maintained by the contraction maintaining element d1, thereby weakening the residual vibration of the ink in the pressure chamber 12. The vibration damping element e1 is an example of a first vibration damping element.

[0047] The ejection pulse Pw1 changes potential between potential V1 and potential V2. The expansion component a1 starts from a reference potential VB. The reference potential VB is a potential between potential V1 and potential V2. The expansion component a1 starts from the reference potential VB at time t11 and reaches potential V1 at time t12.

[0048] The expansion maintaining element b1 is maintained at potential V1. The expansion maintaining element b1 is maintained at potential V1 from time t12 to time t13. The contraction element c1 changes potential from potential V1 to potential V2. The contraction element c1 starts at potential V1 at time t13 and reaches potential V2 at time t14.

[0049] The contraction maintaining element d1 is maintained at the potential V2. The contraction maintaining element d1 is maintained at the potential V2 from time t14 to time t15. The damping element e1 changes potential from the potential V2 to the reference potential VB. The damping element e1 starts at the potential V2 at time t15 and reaches the potential VB at time t16.

[0050] The driving waveform includes a connection element f1 that connects the ejection pulse Pw1 and the ejection pulse Pw2. The connection element f1 is maintained at the reference potential VB. The connection element f1 is maintained at the reference potential VB from time t16 to time t21.

[0051] The period Tab1 of the combined expansion element a1 and expansion maintaining element b1 of the ejection pulse Pw1 is longer than 0.5 times the natural vibration period Tc of the ejection section 10. The period Tab1 of the combined expansion element a1 and expansion maintaining element b1 of the ejection pulse Pw1 is shorter than 1.0 times the natural vibration period Tc of the ejection section 10. The period Tab1 of the combined expansion element a1 and expansion maintaining element b1 of the ejection pulse Pw1 is an example of the combined time width of the first expansion element and the first expansion maintaining element of the preceding ejection pulse. The period Tab1 is from time t11 to time t13.

[0052] The ejection pulse Pw2 includes an expansion element a2, an expansion maintaining element b2, a contraction element c2, a contraction maintaining element d2, and a damping element e2. The relationship between the expansion element a2, the expansion maintaining element b2, the contraction element c2, the contraction maintaining element d2, and the damping element e2 and the expansion and contraction of the volume of the pressure chamber 12 is similar to that between the expansion element a1, the expansion maintaining element b1, the contraction element c1, the contraction maintaining element d1, and the damping element e1 of the ejection pulse Pw1.

[0053] The ejection pulse Pw2 changes potential between potential V1 and potential V2. The expansion component a2 starts from a reference potential VB. The reference potential VB is a potential between potential V1 and potential V2. The expansion component a2 starts from the reference potential VB at time t21 and reaches potential V1 at time t22.

[0054] The expansion maintaining element b2 is maintained at potential V1. The expansion maintaining element b2 is maintained at potential V1 from time t22 to time t23. The contraction element c2 changes potential from potential V1 to potential V2. The contraction element c2 starts at potential V1 at time t23 and reaches potential V2 at time t24.

[0055] The contraction maintaining element d2 is maintained at the potential V2. The contraction maintaining element d2 is maintained at the potential V2 from time t24 to time t25. The damping element e2 changes potential from the potential V2 to the reference potential VB. The damping element e2 starts at the potential V2 at time t25 and reaches the potential VB at time t26.

[0056] The driving waveform includes a connection element f2 that connects the ejection pulse Pw2 and the ejection pulse Pw3. The connection element f2 is maintained at the reference potential VB. The connection element f2 is maintained at the reference potential VB from time t26 to time t31.

[0057] The period Tab2 of the combined expansion element a2 and expansion maintaining element b2 of the ejection pulse Pw2 may be longer than 0.5 times the natural vibration period Tc of the ejection section 10. The period Tab2 of the combined expansion element a1 and expansion maintaining element b1 of the ejection pulse Pw2 may be shorter than 1.0 times the natural vibration period Tc of the ejection section 10. The period Tab2 of the combined expansion element a2 and expansion maintaining element b2 of the ejection pulse Pw2 is an example of the time width of the preceding ejection pulse. The period Tab2 is from time t21 to time t23.

[0058] The ejection pulse Pw3 includes an expansion element a3, an expansion maintaining element b3, a contraction element c3, a contraction maintaining element d3, and a vibration damping element e3. The expansion element a3 is an element that expands the volume of the pressure chamber 12. The expansion element a3 is an example of a second expansion element. The expansion maintaining element b3 is an element that maintains the volume of the pressure chamber 12 expanded by the expansion element a3. The expansion maintaining element b3 is an example of a second expansion maintaining element. The contraction element c3 is an element that contracts the volume of the pressure chamber 12 maintained by the expansion maintaining element b3. The contraction element c3 is an example of a second contraction element. The contraction maintaining element d3 is an element that maintains the volume of the pressure chamber 12 contracted by the contraction element c3. The vibration damping element e3 is an element that expands the volume of the pressure chamber 12 maintained by the contraction maintaining element d3, thereby weakening the residual vibration of the ink in the pressure chamber 12. The vibration damping element e1 is an example of a second vibration damping element.

[0059] The ejection pulse Pw3 changes potential between potential V1 and potential V2. The expansion component a3 starts from a reference potential VB. The reference potential VB is a potential between potential V1 and potential V2. The expansion component a3 starts from the reference potential VB at time t31 and reaches potential V1 at time t32.

[0060] The expansion maintaining element b3 is maintained at potential V1. The expansion maintaining element b3 is maintained at potential V1 from time t32 to time t33. The contraction element c3 changes potential from potential V1 to potential V2. The contraction element c3 starts at potential V1 at time t33 and reaches potential V2 at time t34.

[0061] The contraction maintaining element d3 is maintained at the potential V2. The contraction maintaining element d3 is maintained at the potential V2 from time t34 to time t35. The damping element e3 changes potential from the potential V2 to the reference potential VB. The damping element e3 starts at the potential V2 at time t35 and reaches the potential VB at time t36.

[0062] The period Tab3 of the combined expansion element a3 and expansion maintaining element b3 of the ejection pulse Pw3 is longer than 0.5 times the natural vibration period Tc of the ejection section 10. The period Tab3 of the combined expansion element a3 and expansion maintaining element b3 of the ejection pulse Pw3 is shorter than 1.0 times the natural vibration period Tc of the ejection section 10. The period Tab3 of the combined expansion element a3 and expansion maintaining element b3 of the ejection pulse Pw3 is an example of the combined time width of the second expansion element and the second expansion maintaining element of the final ejection pulse. The period Tab3 is from time t31 to time t33. The period Tab3 may be 0.56 to 0.68 times the natural vibration period Tc.

[0063] The period Tab1 is shorter than the period Tab3. In other words, the length from time t31 to time t33 is longer than the length from time t11 to time t13.

[0064] The amount of potential change per unit time of the contraction element c3 of the ejection pulse Pw3 is greater than the amount of potential change per unit time of the contraction element c1 of the ejection pulse Pw1. The slope of the contraction element c3 is steeper than the slope of the contraction element c1.

[0065] Moreover, by shortening the total time of the ejection pulses Pw1 to Pw3, the period T1 of the drive signal Com1 can be shortened, thereby enabling the liquid ejection device 1 to print at a higher speed.

[0066] FIG. 13 is a diagram showing a plurality of ink droplets 26A, 26B, and 26C ejected from a nozzle N. When a drive signal Com1 is supplied to a drive element 50, a pressure fluctuation occurs in the ink in the pressure chamber 12, the ink in the pressure chamber 12 is pushed out, and the ink droplets 26A, 26B, and 26C are ejected from the nozzle N. The ink droplet 26A is ejected by supplying an ejection pulse Pw1 to the drive element 50. The ink droplet 26B is ejected by supplying an ejection pulse Pw2 to the drive element 50. The ink droplet 26C is ejected by supplying an ejection pulse Pw3 to the drive element 50. After the ink droplet 26A is ejected, the ink droplet 26B is ejected. After the ink droplet 26B is ejected, the ink droplet 26C is ejected. The ink droplet 26C is an example of a final droplet that is ejected last among the plurality of ink droplets 26A to 26C. The ink droplets 26A and 26B are an example of preceding droplets that are ejected before the final droplet among the multiple ink droplets 26A to 26C.

[0067] The velocity Vm3 of the subsequent ink droplet 26C is faster than the velocity Vm1 of the preceding ink droplet 26A. The velocity Vm3 of the subsequent ink droplet 26C is faster than the velocity Vm2 of the preceding ink droplet 26B. The ink droplets 26A to 26C combine in the air. The combined ink droplet lands on the medium PA. The ink droplet 26C can combine with the ink droplets 26A and 26B at a distance of, for example, 0.5 mm from the nozzle surface 25a. The ink droplet 26C may combine with the ink droplets 26A and 26B at a distance of, for example, 0.5 mm or less from the nozzle surface 25a. The ink droplet 26C can combine with the ink droplets 26A and 26B at a distance of, for example, less than 1 / 2 the distance from the nozzle surface 25a to the medium PA. The distance from the nozzle surface 25a to the medium PA may be, for example, 2 mm or more and 3 mm or less. As a result, even if mist is generated by the ejection of ink droplets 26A, 26B by the ejection pulse Pw1 and the ejection pulse Pw, the ink droplet 26c absorbs the mist and prevents the mist from diffusing into the apparatus, and by combining, the weight of the ink droplet is increased, ensuring the straightness of the ink droplet and preventing landing deviation.

[0068] In the liquid ejection device 1, in order to combine the ink droplets 26A to 26C, the potential change amount per unit time of the contraction element c3 of the ejection pulse Pw3 is made larger than the potential change amount per unit time of the contraction element c1 of the ejection pulse Pw1, thereby making the velocity Vm3 of the ink droplet 26C faster than the velocity Vm1 of the ink droplet 26A. Even if the velocity Vm3 of the ink droplet 26C is made faster than the velocity Vm1 of the ink droplet 26A, the length of the period Tab3 of the ejection pulse Pw3 is set to be 0.5 to 1.0 times the natural vibration period Tc, thereby suppressing the generation of mist due to the ejection of the ink droplet 26C by the ejection pulse Pw3. As a result, in this embodiment, it is possible to suppress the generation of mist from the ink droplets 26A to 26C. In the liquid ejection device 1, even if the velocity Vm3 of the ink droplet 26C is increased, the difference in velocity between the leading end and trailing end of the ink droplet 26C can be suppressed, so the ink droplet 26C is prevented from forming a liquid column. This suppresses the generation of satellite droplets and mist. The liquid ejection device 1 can suppress the generation of mist, so it is possible to suppress a decrease in print quality.

[0069] In this embodiment, in order to combine the ink droplets 26A to 26C, the contraction element c3 of the ejection pulse Pw3 has a larger potential change amount per unit time in changing the potential from potential V1 to potential V2 than the contraction element c1 of the ejection pulse Pw1, but the velocity Vm3 of the ink droplet 26C may be made faster than the velocity Vm1 of the ink droplet 26A by setting the final potential of the contraction element c1 of the ejection pulse Pw3 to a potential higher than the potential V2. The potential at the end of the contraction element c3 of the ejection pulse Pw3 may be higher than the potential at the end of the contraction element c1 of the ejection pulse Pw1. The potential of the contraction maintenance element d3 of the ejection pulse Pw3 may be higher than the potential of the contraction maintenance element d1 of the ejection pulse Pw1.

[0070] The velocities Vm1 to Vm3 of the ink droplets 26A to 26C ejected from the nozzles N can be improved by increasing the amount of potential change of the ejection pulses Pw1 to Pw3 or by increasing the amount of potential change per unit time. However, there is a limit to the pulse correction due to the characteristics of the ejection unit 10 and the performance of the drive signal generation circuit 60. Therefore, there is an upper limit to the velocities Vm1 to Vm3.

[0071] Next, with reference to Fig. 14 to Fig. 15, a simulation result when the condition of the ejection pulse Pw3 is changed will be described. As shown in Fig. 14 and Fig. 15, a simulation was performed by changing the length of the period Tab3 which is the sum of the expansion element a3 and the expansion maintenance element b3 of the ejection pulse Pw3. In the simulation, as shown in Fig. 12, the behavior of the ink droplets ejected from the nozzle N was verified when the drive signal Com1 was supplied to the drive element 50.

[0072] As the verification, the judgment of the mid-air coalescence of the ink droplets, the judgment of the tailing, the judgment of the mist, and the overall judgment were performed. In the judgment of the mid-air coalescence, the case where the ink droplets 26A to 26C coalesce before the preceding ink droplet 26A lands on the medium PA and the coalescence position is within 0.5 mm from the nozzle surface 25a was judged as "A". The case where the ink droplets 26A to 26C coalesce before the preceding ink droplet 26A lands on the medium PA and the coalescence position is more than 0.5 mm but less than 1.0 mm from the nozzle surface 25a was judged as "B". The case where the ink droplets 26A to 26C coalesce before the preceding ink droplet 26A lands on the medium PA and the coalescence position is more than 1.0 mm from the nozzle surface 25a was judged as "C". The case where the ink droplets 26A to 26C do not coalesce before the ink droplet 26A lands on the medium PA was judged as "D". If the ink droplets 26A to 26C do not combine before landing on the medium PA, the landing positions of the ink droplets 26A to 26C will be shifted.

[0073] In the determination of the trailing of the ink droplet, the case where the trailing portion is absorbed into the main droplet or the satellite droplet immediately after the ink droplet 26C is discharged from the nozzle N is determined as "A". For example, the model 3 shown in FIG. 11 is determined as "A" in the determination of the trailing. In FIG. 11, the main droplet 101, the satellite droplets 100d and 100e, the trailing portion 103, and the mist 100f are illustrated. In FIG. 13, only the main droplet 101 is illustrated. As shown in FIG. 11, the main droplet 101 includes the tip 100a of the ink droplet 100, is rounded, and has a predetermined volume. At time t204 of the model 1, the satellite droplets 100d and 100e are generated. The satellite droplets 100d and 100e proceed behind the main droplet 101 and have a smaller volume than the main droplet 101.

[0074] The tailing portion 103 includes a portion that extends, for example, linearly backward from the main droplet 101 or the satellite droplets 100d, 100e. The linearly extending portion may be, for example, columnar or thread-like. For example, the tailing portion 103 is formed at time t203 in model 1. The tailing portion 103 is formed at time t202 in model 2. The tailing portion 103 is narrower in width than, for example, the main droplet 101 or the satellite droplets 100d, 100e. The "width" here refers to the length in a direction perpendicular to the traveling direction of the main droplet.

[0075] In the determination of ink droplet tailing, a case where the tailing portion becomes a small amount of mist together with satellite droplets is determined as "B". For example, a case where the length of the tailing portion 103 from the main droplet 101 or the satellite droplets 100d, 100e is 100 μm or less may be determined as "B". Model 2 shown in FIG. 11 is determined as "B" in the tailing determination.

[0076] In the determination of ink droplet tailing, a case where the tailing portion becomes a large amount of mist together with satellite droplets is determined as "C". For example, a case where the length of the tailing portion 103 from the main droplet 101 or the satellite droplets 100d, 100e exceeds 100 μm may be determined as "C". Model 1 shown in FIG. 11 is determined as "C" in the tailing determination.

[0077] In the mist judgment, cases where almost no mist was generated were judged as "A." Models 2 and 3 were judged as "A" in the mist judgment. Cases where mist was generated but within an acceptable range were judged as "B." For example, cases where a small amount of mist was generated but did not interfere with normal use were judged as "B." Cases where mist was generated and caused a malfunction were judged as "C." For example, if the generation of mist caused the mist to scatter within the liquid ejection device 1, a malfunction would occur.

[0078] The overall assessment was based on the results of the assessment of mid-air merging, tailing, and mist. If the liquid ejection device 1 was optimal with almost no malfunction or poor image quality caused by mist during printing, it was assessed as "A." If the liquid ejection device 1 could potentially malfunction or poor image quality caused by mist during printing but this was within the acceptable range and there were no particular problems in practical use, and it could be used, it was assessed as "B." If it could not be used as a liquid ejection device 1, it was assessed as "C."

[0079] 14 shows the results of simulation verification for Examples 1 to 6 and Comparative Examples 1 and 2. The periods Tab3 of the final ejection pulse Pw3 in Examples 1 to 6 are 0.50Tc, 0.60Tc, 0.70Tc, 0.80Tc, 0.90Tc, 1.00Tc, and 1.10Tc, respectively. The periods Tab3 in Comparative Examples 1 and 2 are 0.40Tc and 1.10Tc.

[0080] In Example 1, the aerial fusion was judged as "A", the trailing was judged as "B", and the mist was judged as "B". The overall judgement for Example 1 was "B". In Example 2, the aerial fusion was judged as "A", the trailing was judged as "B", and the mist was judged as "A". The overall judgement for Example 2 was "A". In Example 3, the aerial fusion was judged as "B", the trailing was judged as "B", and the mist was judged as "A". The overall judgement for Example 3 was "A". In Examples 4 to 6, the aerial fusion was judged as "C", the trailing was judged as "A", and the mist was judged as "A". The overall judgement for Examples 4 to 6 was "B".

[0081] In Comparative Example 1, the mid-air merging was judged as "A", the trailing was judged as "C", and the mist was judged as "C". The overall judgement for Comparative Example 1 was "C". In Comparative Example 2, the mid-air merging was judged as "D", the trailing was judged as "B", and the mist was judged as "B". The overall judgement for the Comparative Example was "C".

[0082] 15 shows the results of verification by simulation for Examples 7 to 16. The periods Tab3 of the final ejection pulse Pw3 in Examples 7 to 16 were 0.53Tc, 0.56Tc, 0.59Tc, 0.62Tc, 0.65Tc, 0.68Tc, 0.71Tc, 0.74Tc, and 0.77Tc, respectively.

[0083] In Example 7, the aerial fusion was judged as "A", the trailing was judged as "B", and the mist was judged as "B". The overall judgement of Example 7 was "B". In Examples 8 to 12, the aerial fusion was judged as "A", the trailing was judged as "B", and the mist was judged as "A". The overall judgement of Examples 8 to 12 was "A". In Example 13, the aerial fusion was judged as "B", the trailing was judged as "B", and the mist was judged as "A". The overall judgement of Example 13 was "B". In Example 14, the aerial fusion was judged as "B", the trailing was judged as "B", and the mist was judged as "A". The overall judgement of Example 14 was "B". In Example 15, the aerial fusion was judged as "C", the trailing was judged as "A", and the mist was judged as "A". The overall judgement of Example 15 was "B".

[0084] Examples 2, 3, and 8 to 12 were given an overall rating of "A" and were optimal for the liquid ejection device 1. Examples 1, 4 to 7, and 13 to 15 were given an overall rating of "B" and were within the allowable range for the liquid ejection device 1.

[0085] In the liquid ejection device 1, even if mist is generated from the preceding ink droplets 26A and 26B, the mist is absorbed by the final ink droplet 26C.

[0086] In the liquid ejection device 1, the ink droplets 26A to 26C combine before landing on the medium PA, so the weight of the combined droplet can be made equal to or greater than a certain amount. In the liquid ejection device 1, the weight of the combined droplet can be increased. In the liquid ejection device 1, by making the weight of the combined droplet equal to or greater than a certain amount, the straightness of the combined droplet is increased. This prevents the ink droplets from flying in a curved direction, improving the accuracy of the landing position of the ink droplets.

[0087] In the liquid ejection device 1, the generation of mist is suppressed while the speed of the subsequent ink droplet 46C is increased, so that the multiple ink droplets 46A to 46C can be merged.

[0088] It should be noted that the above-described embodiment merely illustrates a typical form of the present invention, and the present invention is not limited to the above-described embodiment, and various modifications and additions are possible without departing from the gist of the present invention.

[0089] In the above embodiment, the liquid ejection device 1 is described as a serial inkjet printer, but the liquid ejection device 1 is not limited to a serial inkjet printer. The liquid ejection device 1 may be a line-type inkjet printer in which a plurality of liquid ejection units 20 are linearly arranged.

[0090] In the above embodiment, the drive signal is configured to include a plurality of ejection pulses Pw, but the drive signal may also include a plurality of drive pulses that do not eject ink from the nozzle N. For example, the drive signal may include a non-ejection pulse that does not eject ink between the ejection pulse Pw1 and the ejection pulse Pw2.

[0091] In the above embodiment, the driving signal Com1 is described as including the ejection pulses Pw1 to Pw3, but the driving signal Com1 is not limited to this. For example, the driving signal Com1 may include the ejection pulses Pw1 and Pw3, or may include the ejection pulses Pw2 and Pw3. The number of the preceding ejection pulses may be one, or three or more.

[0092] In the above embodiment, the period Tab1, which is the combined time width of the expansion element a1 and the expansion maintaining element b1 of the ejection pulse Pw1, and the period Tab2, which is the combined time width of the expansion element a2 and the expansion maintaining element b2 of the ejection pulse Pw2, are illustrated as being longer than 0.5 times the natural vibration period Tc, but the period Tab1 and the period Tab2 may be shorter than 0.5 times the natural vibration period Tc. In the above embodiment, the period Tab1 and the period Tab2 are illustrated as being shorter than 1.0 times the natural vibration period Tc, but the period Tab1 may be longer than 1.0 times the natural vibration period Tc. The lengths of the periods Tab1 and Tab2 can be set so that the weights of the ink droplets of the ejection pulse Pw1 and the ejection pulse Pw2 are desired. As a result, even if satellite droplets or mist are generated by the ejection of ink droplets by the ejection pulses Pw1 and Pw2, the satellite droplets or mist are absorbed by the ejection pulse Pw3 to form a combined droplet, thereby suppressing the generation of the satellite droplets or mist. In particular, by making the period Tab1 of the ejection pulse Pw1 and the period Tab2 of the ejection pulse Pw2 shorter than the period Tab3 of the ejection pulse Pw3, the weight of the ink droplets is ensured by the preceding ejection pulse, and the satellite droplets and mist are suppressed by the final ejection pulse, resulting in a combined droplet with reduced impact position deviation and mist.

[0093] The liquid ejection device 1 exemplified in the above embodiment can be used in various devices such as facsimile machines and copy machines, in addition to devices dedicated to printing. However, the use of the liquid ejection device of the present invention is not limited to printing. For example, a liquid ejection device that ejects a solution of a color material is used as a manufacturing device that forms a color filter of a display device such as a liquid crystal display panel. Also, a liquid ejection device that ejects a solution of a conductive material is used as a manufacturing device that forms wiring and electrodes of a wiring board. Also, a liquid ejection device that ejects a solution of an organic substance related to a living body is used as a manufacturing device that manufactures, for example, a biochip. [Explanation of symbols]

[0094] 1...liquid ejection device, 10...ejection section, 12...pressure chamber, 20...liquid ejection section, 26A...ink droplet (preceding droplet), 26B...ink droplet (preceding droplet), 26C...ink droplet (final droplet), 50...driving element, 60...driving signal generating circuit (driving signal generating section), a1...expansion element (first expansion element), b1...expansion maintenance element (first expansion maintenance element), c1...contraction element (first contraction element), e1...vibration damping element (first vibration damping element), a3...expansion element (second expansion element), b3...expansion maintenance element (second expansion maintenance element), c3...contraction element (second contraction element), e3...vibration damping element (second vibration damping element), N...nozzle, PA...medium, Pw1...ejection pulse (preceding ejection pulse), Pw3...ejection pulse (final ejection pulse).

Claims

1. a discharge unit including a nozzle that discharges liquid to be landed on a medium, a pressure chamber that communicates with the nozzle, and a drive element that generates a pressure fluctuation in the liquid in the pressure chamber when a drive signal is supplied thereto; a drive signal generating unit that generates the drive signal; the drive signal includes a plurality of ejection pulses for ejecting a plurality of droplets from the nozzle during one period, The droplets generated by the ejection pulses are combined before landing on the medium, The plurality of ejection pulses include a final ejection pulse corresponding to a final droplet that is ejected last from the nozzle among the plurality of droplets; a preceding ejection pulse corresponding to a preceding droplet that is ejected from the nozzle prior to the final droplet among the plurality of droplets; The preceding ejection pulse is A first expansion element that expands the pressure chamber; a first expansion maintaining element that maintains the expansion of the pressure chamber by the first expansion element; a first contraction element that contracts the pressure chamber expanded by the first expansion element; a first vibration damping element that expands the pressure chamber after the pressure chamber is contracted by the first contraction element to damp residual vibration of the liquid in the pressure chamber, The final ejection pulse is A second expansion element that expands the pressure chamber; a second expansion maintaining element that maintains the expansion of the pressure chamber by the second expansion element; a second contraction element that contracts the pressure chamber expanded by the second expansion element; a second vibration damping element that expands the pressure chamber after the pressure chamber is contracted by the second contraction element to damp residual vibration of the liquid in the pressure chamber, a time width of the second expansion element and the second expansion maintaining element of the final ejection pulse is longer than 0.5 times the natural vibration period Tc of the ejection portion and shorter than 1.0 times the natural vibration period Tc of the ejection portion; A liquid ejection device, wherein a combined time width of the first expansion element and the first expansion maintenance element of the advance ejection pulse is shorter than a combined time width of the second expansion element and the second expansion maintenance element of the final ejection pulse.

2. The liquid ejection device according to claim 1 , wherein a potential change amount per unit time of the second contraction element of the final ejection pulse is greater than a potential change amount per unit time of the first contraction element of the preceding ejection pulse.

3. a discharge unit including a nozzle that discharges liquid to be landed on a medium, a pressure chamber that communicates with the nozzle, and a drive element that generates a pressure fluctuation in the liquid in the pressure chamber when a drive signal is supplied thereto; a drive signal generating unit that generates the drive signal; the drive signal includes a plurality of ejection pulses for ejecting a plurality of droplets from the nozzle during one period, The droplets generated by the ejection pulses are combined before landing on the medium, The plurality of ejection pulses include a final ejection pulse corresponding to a final droplet that is ejected last from the nozzle among the plurality of droplets; a preceding ejection pulse corresponding to a preceding droplet that is ejected from the nozzle prior to the final droplet among the plurality of droplets; The preceding ejection pulse is A first expansion element that expands the pressure chamber; a first expansion maintaining element that maintains the expansion of the pressure chamber by the first expansion element; a first contraction element that contracts the pressure chamber expanded by the first expansion element; a first vibration damping element that expands the pressure chamber after the pressure chamber is contracted by the first contraction element to damp residual vibration of the liquid in the pressure chamber, The final ejection pulse is A second expansion element that expands the pressure chamber; a second expansion maintaining element that maintains the expansion of the pressure chamber by the second expansion element; a second contraction element that contracts the pressure chamber expanded by the second expansion element; a second vibration damping element that expands the pressure chamber after the pressure chamber is contracted by the second contraction element to damp residual vibration of the liquid in the pressure chamber, a time width of the second expansion element and the second expansion maintaining element of the final ejection pulse is longer than 0.5 times the natural vibration period Tc of the ejection portion and shorter than 1.0 times the natural vibration period Tc of the ejection portion; A liquid ejection device, wherein a potential change amount per unit time of the second contraction element of the final ejection pulse is greater than a potential change amount per unit time of the first contraction element of the preceding ejection pulse.

4. A liquid ejection device described in any one of claims 1 to 3, wherein the combined time width of the second expansion element and the second expansion maintenance element of the final ejection pulse is 0.56 to 0.68 times the natural vibration period Tc of the ejection section.

5. A liquid ejection device described in any one of claims 1 to 4, wherein the combined time width of the first expansion element and the first expansion maintenance element of the advance ejection pulse is longer than 0.5 times the natural vibration period Tc of the ejection section and shorter than 1.0 times the natural vibration period TC of the ejection section.

Images