Liquid jet device and driving method of liquid jet device

Abstract

To provide a liquid jet device which achieves stable high-speed printing, and a driving method of the liquid jet device.SOLUTION: A liquid jet device includes a discharge part having a nozzle jetting liquid, a pressure chamber and a driving element, and a driving signal generation part for generating a driving signal, wherein the driving signal includes a first discharge pulse DP1, the first discharge pulse DP1 includes a first contraction element a3 whose potential changes from a first potential V1 to a second potential V2, contracting the volume of the pressure chamber, a first contraction maintaining element a4 for maintaining the second potential V2 after the first contraction element a3, and a first expansion element a5 whose potential changes from the second potential V2 to the third potential V3 after the first contraction maintaining element a4, expanding the volume of the pressure chamber. When the first discharge pulse DP1 is supplied to the driving element, a plurality of droplets split from the nozzle are discharged, the plurality of split droplets land as a plurality of dots separated at a first interval on the medium.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a liquid ejecting apparatus having an ejection section that ejects liquid from a nozzle and a method for driving the liquid ejecting apparatus, and more particularly to an ink jet recording apparatus that ejects ink as the liquid and a method for driving the ink jet recording apparatus. [Background technology]

[0002] 2. Description of the Related Art A liquid ejecting apparatus, typified by an ink jet recording apparatus such as an ink jet printer or plotter, is provided with an ejection unit capable of ejecting liquid such as ink stored in a cartridge or tank as droplets.

[0003] The ejection section includes a nozzle for ejecting liquid, a pressure chamber connected to the nozzle, and a drive element for generating pressure fluctuations in the liquid in the pressure chamber. By supplying a drive signal represented by a drive waveform to the drive element, droplets are ejected from the nozzle (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-63022 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if the drive frequency is increased to create smaller dots or dots at higher densities using a drive waveform that creates one dot per pulse, it becomes difficult to control the pressure vibrations of the liquid inside the nozzle, resulting in a decrease in print quality. [Means for solving the problem]

[0006] An aspect of the present invention that solves the above problem comprises an ejection unit having a nozzle that ejects liquid, 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 unit that generates the drive signal, wherein the drive signal includes a first ejection pulse that ejects a plurality of droplets that form a plurality of dots on a medium, the first ejection pulse including a first contraction element that changes potential from a first potential to a second potential and contracts the volume of the pressure chamber, a first contraction maintenance element that maintains the second potential following the first contraction element, and a first contraction maintenance element that changes potential from the second potential to a third potential following the first contraction maintenance element and contracts the volume of the pressure chamber. and a first expansion element that expands the volume, wherein when the first ejection pulse is supplied to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid to form the plurality of dots begins to protrude from the nozzle as a liquid column, and while the first contraction maintenance element is supplied to the drive element, the liquid column continues to extend, and while the liquid column continues to extend, the first expansion element is supplied to the drive element, and a portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into a plurality of droplets, and the multiple droplets that have broken up land on the medium as a plurality of dots separated by a first interval.

[0007] Another aspect of the present invention is a method for driving a liquid ejection device having an ejection section having a drive element that generates pressure fluctuations in liquid within a pressure chamber that communicates with a nozzle that ejects liquid when a drive signal is supplied, the drive signal including a first ejection pulse that ejects a plurality of liquid droplets that form a plurality of dots on a medium, the first ejection pulse including a first contraction element that changes potential from a first potential to a second potential to contract a volume of the pressure chamber, a first contraction maintaining element that maintains the second potential following the first contraction element, and a first expansion element that changes potential from the second potential to a third potential following the first contraction maintaining element to expand the volume of the pressure chamber. and by supplying the first ejection pulse to the driving element, the first contraction element is supplied to the driving element, and an amount of liquid sufficient to form the plurality of dots begins to protrude from the nozzle as a liquid column, the liquid column continues to extend while the first contraction maintaining element is supplied to the driving element, and while the liquid column continues to extend, the first expansion element is supplied to the driving element, and a portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into a plurality of droplets, and the plurality of droplets that have broken up land on the medium as a plurality of dots separated by a first interval. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of a liquid ejecting apparatus according to a first embodiment. [Figure 2] 3 is a cross-sectional view of a discharge section according to the first embodiment. FIG. [Figure 3] 2 is a block diagram showing the electrical configuration of the liquid ejecting device according to the first embodiment. FIG. [Figure 4] 4 is a diagram showing a drive waveform of a first drive signal according to the first embodiment. [Figure 5] 1 is a cross-sectional view of the vicinity of a nozzle when droplets are ejected according to the first embodiment. [Figure 6] 1 is a cross-sectional view of the vicinity of a nozzle when droplets are ejected according to the first embodiment. [Figure 7] 1 is a cross-sectional view of the vicinity of a nozzle when droplets are ejected according to the first embodiment. [Figure 8] 1 is a cross-sectional view of the vicinity of a nozzle when droplets are ejected according to the first embodiment. [Figure 9] 10 is a graph showing the relationship between the potential difference and the ink weight and flying speed. [Figure 10] 10 is a graph showing the relationship between the potential difference and the first distance. [Figure 11] 10 shows drive waveforms of a first drive signal and a second drive signal according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention will be described in detail below based on embodiments. However, the following description illustrates one aspect of the present invention and can be modified as desired within the scope of the present invention. In each drawing, the same reference numerals indicate the same components, and their description will be omitted as appropriate. In each drawing, X, Y, and Z represent three spatial axes that are orthogonal to each other. In this specification, the directions along these axes are referred to as the X direction, Y direction, and Z direction. In each drawing, the direction indicated by the arrow is the positive (+) direction, and the direction opposite the arrow is the negative (-) direction. The Z direction indicates the vertical direction, the +Z direction indicates a vertically downward direction, and the -Z direction indicates a vertically upward direction. Furthermore, the directions of the three spatial axes, which are not limited to positive and negative directions, will be described as the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0010] (Embodiment 1) FIG. 1 is a diagram showing a schematic configuration of a liquid ejecting apparatus 1 of the present invention.

[0011] As shown in the figure, the liquid ejecting device 1 is a so-called serial printer that includes a discharge unit 2 and prints by conveying a medium S in the X-axis direction while reciprocating the discharge unit 2 in the Y-axis direction and discharging (also called spraying) liquid from the discharge unit 2 toward the medium S in the +Z direction. Note that the medium S can be made of any material, such as recording paper, resin film, cloth, etc.

[0012] The liquid ejecting device 1 includes a discharge unit 2, a liquid storage unit 3, a control unit 4, a transport mechanism 5 that feeds the medium S, and a movement mechanism 6.

[0013] The ejection unit 2 ejects the liquid supplied from the liquid storage unit 3 in the form of droplets in the +Z direction.

[0014] The liquid storage section 3 stores the liquid to be ejected from the ejection section 2. Examples of the liquid storage section 3 include a cartridge that can be attached to and detached from the liquid ejection device 1, a bag-shaped ink pack made of flexible film, and an ink tank that can be refilled with ink. Although not specifically shown, the liquid storage section 3 may store multiple types of ink with different colors, ingredients, etc. individually. The liquid storage section 3 may also be separated into a main tank and a sub-tank. The sub-tank may be connected to the ejection section 2, and the liquid consumed when droplets are ejected from the ejection section 2 may be replenished from the main tank to the sub-tank. The liquid may also be circulated between the liquid storage section 3 and the ejection section 2.

[0015] The control unit 4 includes, for example, a control device such as a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array), and a storage device such as a semiconductor memory. The control unit 4 also includes a power supply device that supplies power from an external power source such as a commercial power source to each element of the liquid ejection device 1. The control unit 4 is electrically connected to the ejection unit 2 via external wiring (not shown). The control unit 4 comprehensively controls each element of the liquid ejection device 1 by the control device executing a program stored in the storage device.

[0016] The transport mechanism 5 transports the medium S in the X-axis direction, and includes, for example, a transport roller 5a that is rotated by a transport motor that is driven under the control of the control unit 4.

[0017] The movement mechanism 6 is a mechanism for reciprocating the discharge unit 2 in the Y-axis direction, and includes a holder 6a that holds the discharge unit 2, and a conveyor belt 6b that is an endless belt that is installed along the Y-axis direction. The control unit 4 controls the driving of a conveyor motor (not shown) to rotate the conveyor belt 6b, and moves the discharge unit 2 reciprocally in the Y-axis direction together with the holder 6a fixed to the conveyor belt 6b.

[0018] The discharge unit 2 performs a jetting operation of jetting ink supplied from the liquid storage unit 3 as droplets in the +Z direction from each of the multiple nozzles 21 (see FIG. 2) under the control of the control unit 4. This jetting operation by the discharge unit 2 is performed in parallel with the transport of the medium S by the transport mechanism 5 and the reciprocating movement of the discharge unit 2 by the movement mechanism 6, thereby applying ink to the medium S, or so-called printing.

[0019] 2 is a cross-sectional view of the discharge unit 2 according to one embodiment of the present invention. The directions of the discharge unit 2 will be described based on the directions when the discharge unit 2 is mounted, i.e., the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0020] As shown in the figure, the ejection section 2 of this embodiment includes a pressure chamber substrate 10, a communication plate 15, a nozzle plate 20 having a plurality of nozzles 21 formed therein, a protective substrate 30, a case member 40, a piezoelectric actuator 300, and a wiring member 110.

[0021] The pressure chamber substrate 10 is made of, for example, a silicon substrate. In the pressure chamber substrate 10, a plurality of pressure chambers 12 are arranged side by side along the X-axis direction. The plurality of pressure chambers 12 are arranged side by side along the X-axis direction so as to be at the same position in the Y-axis direction. Two pressure chambers 12 adjacent to each other in the X-axis direction are separated by a partition wall (not shown). In this embodiment, two pressure chamber rows in which the pressure chambers 12 are arranged side by side along the X-axis direction are provided in the Y-axis direction.

[0022] A communication plate 15 and a nozzle plate 20 are stacked in this order on the surface of the pressure chamber substrate 10 facing the +Z direction. A vibration plate 50 and a piezoelectric actuator 300 are stacked in this order on the surface of the pressure chamber substrate 10 facing the -Z direction.

[0023] The communicating plate 15 is made of a plate-like member bonded to the surface of the pressure chamber substrate 10 facing the +Z direction. The communicating plate 15 is provided with nozzle communicating passages 16 that communicate between the pressure chambers 12 and the nozzles 21. The communicating plate 15 is also provided with a first common liquid chamber section 17 and a second common liquid chamber section 18 that constitute a common liquid chamber 100 that communicates with a plurality of pressure chambers 12. The first common liquid chamber section 17 is provided by penetrating the communicating plate 15 in the Z-axis direction. The second common liquid chamber section 18 is provided by opening onto the surface facing the +Z direction without penetrating the communicating plate 15 in the Z-axis direction. Furthermore, the communicating plate 15 is provided with supply communicating passages 19 that communicate with one end of the pressure chambers 12 in the Y-axis direction, independently for each pressure chamber 12. The supply communication passage 19 communicates the second common liquid chamber portion 18 with the pressure chamber 12, and supplies ink in the common liquid chamber 100 to the pressure chamber 12. As such a communication plate 15, a silicon substrate or the like can be used.

[0024] The nozzle plate 20 is bonded to the surface of the communication plate 15 facing the +Z direction. Nozzles 21 are formed in the nozzle plate 20, which communicate with each pressure chamber 12 via nozzle communication passages 16. In this embodiment, the multiple nozzles 21 are arranged in a row along the X-axis direction. Also, in this embodiment, two nozzle rows, in which the nozzles 21 are arranged side by side along the X-axis direction, are provided spaced apart in the Y-axis direction.

[0025] The material of the nozzle plate 20 is not particularly limited, and for example, a silicon substrate or the like can be used.

[0026] The vibration plate 50 has, for example, an elastic film 51 made of silicon oxide provided on the pressure chamber substrate 10 side, and an insulating film 52 made of zirconium oxide provided on the surface of the elastic film 51 facing the -Z direction.

[0027] The piezoelectric actuator 300 includes a first electrode 60 sequentially stacked in the -Z direction on the diaphragm 50, a piezoelectric layer 70 formed using a piezoelectric material, for example, a composite oxide with a perovskite structure represented by the general formula ABO3, and a second electrode 80. Such a piezoelectric actuator 300 is also referred to as a piezoelectric element, and refers to a portion including the first electrode 60, the piezoelectric layer 70, and the second electrode 80. Furthermore, a portion of the piezoelectric layer 70 where piezoelectric strain occurs when a voltage is applied between the first electrode 60 and the second electrode 80 is referred to as an active portion 310. In contrast, a portion of the piezoelectric layer 70 where no piezoelectric strain occurs is referred to as an inactive portion. In other words, the active portion 310 refers to the portion of the piezoelectric layer 70 sandwiched between the first electrode 60 and the second electrode 80. In this embodiment, an active portion 310 is formed for each pressure chamber 12. In other words, the piezoelectric actuator 300 is formed with multiple active portions 310. The plurality of active portions 310 serve as driving elements that cause pressure changes in the ink within the pressure chambers 12. Generally, one of the electrodes of the active portions 310 is configured as an individual electrode that is independent for each active portion 310, and the other electrode is configured as a common electrode that is common to the plurality of active portions 310. In this embodiment, the first electrode 60 constitutes the individual electrode, and the second electrode 80 constitutes the common electrode.

[0028] Furthermore, lead electrodes 91, which are lead wiring, are drawn out from each electrode of the piezoelectric actuator 300. A wiring member 110 made of a flexible substrate is connected to the end of the lead electrode 91 opposite to the end connected to the piezoelectric actuator 300. The wiring member 110 is mounted with a drive circuit 111 having a plurality of switching elements that select whether or not to supply a drive signal for driving each active portion 310 to each active portion 310. In other words, the wiring member 110 in this embodiment is a COF (Chip On Film). Note that the wiring member 110 does not necessarily have to be provided with the drive circuit 111. In other words, the wiring member 110 may be an FFC (Flexible Flat Cable), an FPC (Flexible Printed Circuits), or the like.

[0029] A protective substrate 30 having approximately the same size as the pressure chamber substrate 10 is bonded to the surface of the pressure chamber substrate 10 facing the -Z direction. The protective substrate 30 has accommodation sections 31, which are spaces for protecting the piezoelectric actuators 300. The accommodation sections 31 are provided independently for each row of piezoelectric actuators 300 arranged side by side in the X-axis direction, with two accommodation sections 31 formed side by side in the Y-axis direction. The protective substrate 30 also has a through hole 32 penetrating in the Z-axis direction between the two accommodation sections 31 arranged side by side in the Y-axis direction. Ends of lead electrodes 91 drawn from each electrode of the piezoelectric actuators 300 extend so as to be exposed within the through hole 32, and the lead electrodes 91 and the wiring member 110 are electrically connected within the through hole 32. Such a protective substrate 30 may be made of, for example, a silicon substrate.

[0030] In addition, a case member 40 that defines a common liquid chamber 100 that communicates with the multiple pressure chambers 12 is fixed on the protective substrate 30. The case member 40 has substantially the same shape as the above-mentioned communicating plate 15 in a plan view, and is bonded to the protective substrate 30 as well as to the above-mentioned communicating plate 15.

[0031] Such a case member 40 has a recess 41 on the protective substrate 30 side that is deep enough to accommodate the pressure chamber substrate 10 and the protective substrate 30. This recess 41 has an opening area that is larger than the surface of the protective substrate 30 that is bonded to the pressure chamber substrate 10. Then, with the pressure chamber substrate 10 and the protective substrate 30 accommodated in the recess 41, the opening surface of the recess 41 on the nozzle plate 20 side is sealed by the communicating plate 15.

[0032] The case member 40 is also provided with a third common liquid chamber 42 that communicates with the first common liquid chamber 17 of the communication plate 15. The first common liquid chamber 17 and second common liquid chamber 18 provided in the communication plate 15 and the third common liquid chamber 42 provided in the case member 40 constitute a common liquid chamber 100 of this embodiment. A common liquid chamber 100 is provided for each row of pressure chambers 12, i.e., two common liquid chambers 100 in total. Each common liquid chamber 100 is provided continuously along the X-axis direction in which the pressure chambers 12 are arranged side by side, and the supply communication paths 19 that communicate each pressure chamber 12 with the common liquid chamber 100 are arranged side by side in the X-axis direction. The case member 40 is also provided with an inlet 44 that communicates with the common liquid chamber 100 and supplies ink to each common liquid chamber 100. The case member 40 is also provided with a connection port 43 that communicates with the through hole 32 of the protection substrate 30 and through which the wiring member 110 is inserted. The case member 40 is made of a material such as a metal material or a resin material.

[0033] Furthermore, a compliance substrate 45 is provided on the surface of the communicating plate 15 on the +Z direction side where the first common liquid chamber portion 17 and the second common liquid chamber portion 18 open. This compliance substrate 45 seals the openings on the ejection surface side of the first common liquid chamber portion 17 and the second common liquid chamber portion 18. In this embodiment, such a compliance substrate 45 includes a sealing film 46 made of a flexible thin film, and a fixed substrate 47 made of a hard material such as metal. The area of ​​the fixed substrate 47 facing the common liquid chamber 100 is an opening 48 that is completely removed in the thickness direction, and therefore one side of the common liquid chamber 100 forms a compliance portion 49 that is a flexible portion sealed only by the flexible sealing film 46.

[0034] The ejection unit 2 described above takes in liquid from the liquid storage unit 3 through the inlet 44 into the common liquid chamber 100, filling the interior from the common liquid chamber 100 to the nozzles 21, and then applies a voltage to each active section 310 corresponding to the pressure chambers 12 in accordance with a recording signal from the drive circuit 111. This causes the active sections 310 and the diaphragm 50 to flex and deform, increasing the pressure of the liquid in each pressure chamber 12 and causing droplets to be ejected from each nozzle 21.

[0035] 3 is a block diagram showing the electrical configuration of the liquid ejection device 1. The control unit 4 is an element that performs overall control of the liquid ejection device 1. The control unit 4 includes an external interface 211 (hereinafter referred to as the external I / F 211), a RAM 212 that temporarily stores various data, a ROM 213 that stores control programs and the like, a control processing unit 214 that includes a CPU and the like, an oscillation circuit 215 that generates a clock signal (CK), a drive signal generation unit 216 that generates a drive signal to be supplied to the ejection unit 2, and an internal interface 217 (hereinafter referred to as the internal I / F 217).

[0036] The external I / F 211 is an interface for transmitting and receiving data to and from a host computer (not shown). Examples of data received by the control unit 4 from the host computer via the external I / F 211 include print data composed of character codes, graphic functions, image data, and the like. Examples of data transmitted by the control unit 4 via the external I / F 211 include a busy signal (BUSY) and an acknowledge signal (ACK). The RAM 212 functions as a receive buffer 212A, an intermediate buffer 212B, an output buffer 212C, and a work memory (not shown). The receive buffer 212A temporarily stores print data received by the external I / F 211, the intermediate buffer 212B stores intermediate code data converted by the control processing unit 214, and the output buffer 212C stores dot pattern data. The dot pattern data is composed of recording data (SI) obtained by decoding (translating) gradation data.

[0037] The drive signal generation unit 216 generates a first drive signal COM1. As will be described in detail later, the first drive signal COM1 is a signal that has a first ejection pulse DP1 within one unit period T, which drives the active unit 310 to eject droplets that are split into multiple pieces from the nozzle 21, and is generated repeatedly for each unit period T. The multiple droplets that are ejected by driving the active unit 310 with the first ejection pulse DP1 land on the medium S at first intervals d1. Note that the unit period T is a repeating unit of the first drive signal COM1, and corresponds to one pixel of an image to be printed on the medium S.

[0038] The ROM 213 stores font data, graphic functions, and the like, as well as control programs (control routines) for causing the control processing unit 214 to perform various data processing operations. The control processing unit 214 reads print data from the receive buffer 212A and converts the print data to generate intermediate code data, which it then stores in the intermediate buffer 212B. The control processing unit 214 also analyzes the intermediate code data read from the intermediate buffer 212B and, referring to the font data and graphic functions stored in the ROM 213, develops the intermediate code data into record data. The control processing unit 214 then performs any necessary decoration processing and stores the developed record data in the output buffer 212C. The control program may be read from a recording medium, such as a floppy disk, CD-ROM, DVD-ROM, or USB memory, connected directly via the external I / F 211 or via the host computer. The control program may also be provided in the host computer as a printer driver.

[0039] Then, during printing, when the control processing unit 214 obtains recording data equivalent to one line of the discharge unit 2, it outputs this one line of recording data to the discharge unit 2 via the internal I / F 217. Furthermore, when one line of recording data is output from the output buffer 212C, the expanded intermediate code data is erased from the intermediate buffer 212B, and expansion processing is performed on the next intermediate code data.

[0040] The ejection unit 2 includes a drive circuit 111. The drive circuit 111 is a circuit that supplies a first drive signal COM1 to the activation unit 310 based on print data (SI) sent from the control unit 4 via the internal I / F 217.

[0041] The print data is composed of a plurality of pixel data to be ejected for each of a plurality of dots that make up one line. For example, the pixel data may be binary, with "1" indicating that a dot is to be formed and "0" indicating that a dot is not to be formed. If the pixel data is "1," the drive circuit 111 supplies a first ejection pulse DP1 to the active unit 310 that ejects a droplet from the nozzle 21 corresponding to that pixel data. If the pixel data is "0," the drive circuit 111 does not supply the first ejection pulse DP1 to the active unit 310.

[0042] In this way, the discharge unit 2 discharges droplets from each nozzle 21 at a timing defined by the recording data and the like under the control of the control unit 4. The control unit 4 then controls the transport mechanism 5 to transport the medium S and the movement mechanism 6 to move the discharge unit 2 back and forth via the internal I / F 217 in parallel with the discharge operation by the discharge unit 2. Printing is performed on the medium S under such control of the control unit 4.

[0043] Fig. 4 is a drive waveform showing the first drive signal COM1. Figs. 5 to 8 are cross-sectional views of the vicinity of the nozzle 21 when droplets are ejected.

[0044] 4, the first drive signal COM1 is repeatedly generated by the drive signal generating unit 216 at each unit period T defined by a clock signal transmitted from the oscillation circuit 215. The unit period T corresponds to one pixel of an image to be printed on the medium S. In this embodiment, a first ejection pulse DP1 is generated at each unit period T.

[0045] In this embodiment, the first drive signal COM1 is supplied to the first electrode 60, which is an individual electrode, with the second electrode 80, which is a common electrode of the active portion 310, serving as a reference potential. That is, the voltage applied to the second electrode 80 by the first drive signal COM1 is expressed as a potential with the reference potential as a reference.

[0046] The first ejection pulse DP1 of the first drive signal COM1 causes multiple dots split into multiple pieces to land on the medium S at a first interval within one unit period T, and has a filling element a1, a filling maintenance element a2, a first contraction element a3, a first contraction maintenance element a4, a first expansion element a5, a first expansion maintenance element a6, a second contraction element a7, a second contraction maintenance element a8, and a second expansion element a9 arranged consecutively in this order in chronological order.

[0047] The following describes how the volume of the pressure chamber 12 and the liquid level 120 of the liquid in the nozzle 21 change when each element of the first ejection pulse DP1 is supplied to the active portion 310.

[0048] The filling element a1 changes the potential from the sixth potential V6 to the first potential V1, thereby expanding the volume of the pressure chamber 12 from the reference volume. In this embodiment, the sixth potential V6 corresponds to the reference potential Vc. As shown in FIG. 5, the filling element a1 draws the liquid level 120 of the liquid in the nozzle 21 toward the pressure chamber 12, and liquid is supplied to the pressure chamber 12 from the common liquid chamber 100 side.

[0049] The filling maintaining element a2 maintains the first potential V1 for a certain period of time. While the filling maintaining element a2 is being supplied, pressure oscillations occur in the liquid within the pressure chamber 12. The period of this pressure oscillation of the liquid within the pressure chamber 12, the so-called natural oscillation period Tc, can generally be expressed by the following equation: Tc=2π [(Mn+Ms)×(Cc+Ci) / (Mn×Ms)] 1 / 2 In the above formula, Mn is the inertance in the nozzle 21 (mass of ink per unit cross-sectional area), Ms is the inertance in the supply communication passage 19, Cc is the compliance of the pressure chamber 12 (volume change per unit pressure, indicating the degree of softness), and Ci is the compliance of the liquid (Ci = volume V / [density ρ × speed of sound c2]).

[0050] The first contraction element a3 changes the voltage from the first potential V1 to the second potential V2, contracting the volume of the pressure chamber 12. The first contraction element a3 causes the liquid to start protruding from the nozzle 21 as a liquid column 121 from the liquid surface 120, as shown in FIG.

[0051] The first contraction maintaining element a4 maintains the second potential V2 for a certain period of time. While the first contraction maintaining element a4 is supplied to the active portion 310, the liquid column 121 continues to extend as shown in FIG.

[0052] The first expansion element a5 changes the potential from the second potential V2 to the third potential V3, expanding the volume of the pressure chamber 12. The portion of the liquid column 121 that continues to extend due to the first contraction maintenance element a4, near the nozzle 21, is pulled back toward the pressure chamber 12 by the first expansion element a5, causing the liquid column 121 to split into multiple droplets as shown in FIG. 8. In this embodiment, the first expansion element a5 splits the liquid column 121 into two droplets. The leading droplet in the +Z direction, which is the ejection direction, is referred to as the main droplet 122, and the trailing droplet is referred to as the satellite droplet 123. Of course, the number of droplets split by the first expansion element a5 is not limited and may be three or more.

[0053] The first expansion maintaining element a6 maintains the third potential V3 for a certain period of time. While the first expansion maintaining element a6 is being supplied to the active portion 310, the liquid level 120 in the nozzle 21 starts to move toward the pressure chamber 12 side.

[0054] The second contraction element a7 changes the voltage from the third potential V3 to the fourth potential V4, thereby contracting the volume of the pressure chamber 12. This second contraction element a7 slows down the speed of movement of the liquid surface 120, which has been moving toward the pressure chamber 12 inside the nozzle 21.

[0055] The second contraction maintaining element a8 maintains the fourth potential V4 for a certain period of time. The second contraction maintaining element a8 causes the liquid level 120 in the nozzle 21 to start moving in the opposite direction from the pressure chamber 12 due to natural vibration.

[0056] The second expansion element a9 changes the potential from the fourth potential V4 to the fifth potential V5, thereby expanding the volume of the pressure chamber 12. In this embodiment, the fifth potential V5 corresponds to the reference potential Vc. This second expansion element a9 slows down the speed of the liquid surface 120, which has been moving toward the opposite side of the pressure chamber 12 within the nozzle 21.

[0057] That is, the second contraction element a7 to the second expansion element a9 have a so-called vibration damping function that damps the vibration of the liquid surface 120 in the nozzle 21 after the droplets are ejected.

[0058] The droplets separated into multiple droplets ejected by such a first ejection pulse DP1, in this embodiment, two droplets, a main droplet 122 and a satellite droplet 123, land on the medium S as multiple dots separated by a first interval d1.

[0059] The first interval d1 changes depending on the ratio of the second potential difference ΔV2 between the second potential V2 and the third potential V3 to the first potential difference ΔV1 between the first potential V1 and the second potential V2 in the first ejection pulse DP1.

[0060] 9 is a graph showing the change in ink weight and flight speed of each of the main droplet 122 and the satellite droplet 123 depending on the ratio of the second potential difference ΔV2 to the first potential difference ΔV1. FIG. 10 is a graph showing the change in the first distance d1 between the main droplet 122 and the satellite droplet 123 depending on the ratio of the second potential difference ΔV2 to the first potential difference ΔV1.

[0061] 9, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is small, the force with which the portion of the liquid column 121, which continues to extend due to the first contraction element a3 and the first contraction maintenance element a4, is pulled back into the pressure chamber 12 near the nozzle 21 becomes weaker, and the flight speed of the satellite droplet becomes relatively faster. Also, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is small, the force with which the first expansion element a5 tears the liquid column 121 apart also becomes weaker, and the ink weight of the satellite droplet 123 also becomes larger. Note that when the force with which the first expansion element a5 tears the liquid column 121 apart becomes weaker, the ink weight of the main droplet 122 also becomes larger.

[0062] In contrast, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is large, the force that pulls the portion of the liquid column 121 that continues to extend, near the nozzle 21, back into the pressure chamber 12 by the first contraction element a3 and the first contraction maintenance element a4 becomes stronger, and the flight speed of the satellite droplet 123 becomes relatively slower. Also, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is large, the force that tears the liquid column 121 apart by the first expansion element a5 also becomes stronger, and the ink weight of the satellite droplet 123 becomes smaller. Note that when the force that tears the liquid column 121 apart by the first expansion element a5 becomes stronger, the ink weight of the main droplet 122 also becomes smaller.

[0063] The main droplet 122 flies relative to such a satellite droplet 123 at a flying speed that depends on at least one of the magnitude of the first potential difference ΔV1 of the first contraction element a3 and the rate of potential change per unit time of the first contraction element a3, i.e., the slope of the first contraction element a3. In other words, even if the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 changes, the flying speed of the main droplet 122 is not affected.

[0064] 10, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is small, the flying speed of the satellite droplets 123 increases, and the first distance d1, which is the amount of deviation in the landing position on the medium S between the main droplets 122 and the satellite droplets 123, becomes relatively small. In contrast, when the ratio of the second potential difference ΔV2 to the first potential difference ΔV1 is large, the flying speed of the satellite droplets 123 decreases, and the first distance d1 becomes relatively large. Therefore, by adjusting the ratio of the second potential difference ΔV2 to the first potential difference ΔV1, the size of the first distance d1 between the main droplets 122 and the satellite droplets 123 on the medium S can be adjusted.

[0065] The first ejection pulse DP1 has a period ΔT1 from the start of the first contraction element a3 to the end of the first expansion element a5, i.e., the total time ΔT1 of the first contraction element a3, the first contraction maintenance element a4, and the first expansion element a5, which is 0.5 times or less of the natural vibration period Tc. For example, if the period ΔT1 is greater than 0.5 times Tc, the droplets will be less likely to split. Therefore, by setting the period ΔT1 to 0.5 times or less of the natural vibration period Tc, the ejected droplets can be split and fly.

[0066] Furthermore, the period ΔT2 from the start of the filling element a1 to the start of the first contraction element a3, i.e., the total time ΔT2 for the filling element a1 and the filling maintenance element a2, is at least 0.2 times the natural vibration period Tc of the liquid in the pressure chamber 12. If the period ΔT2 is shorter than 0.2 times the natural vibration period Tc, the liquid will not follow the volumetric changes of the pressure chamber 12, and the ejection characteristics of the main droplet 122, i.e., the ink weight and flight speed, will decrease. Therefore, by setting the period ΔT1 to at least 0.2 times the natural vibration period Tc, the liquid will follow the volumetric changes of the pressure chamber 12, and the ejection characteristics of the main droplet 122 can be improved.

[0067] The sixth potential V6 and the fifth potential V5 may be the same or different. Furthermore, the reference potential Vc and the sixth potential V6 or the fifth potential V5 may be the same or different.

[0068] In this way, by providing the first expansion element a5 within the unit period T, the liquid column 121 extending from the nozzle 21 can be split into multiple droplets, forming multiple micro dots on the medium. In contrast, for example, if the drive frequency is increased to form smaller dots or dots at higher density using a drive waveform that forms one dot with one ejection pulse, it becomes difficult to control the pressure vibration of the liquid in the nozzle 21, making it impossible to eject droplets at the desired flight speed and weight, resulting in reduced print quality. In other words, to eject two droplets using a drive waveform that forms one dot with one ejection pulse, a unit period T that is simply twice as long is required. If these two ejection pulses are placed within one unit period T in this embodiment, the pressure vibration of the liquid ejected by the previous ejection pulse will affect the subsequent ejection pulse, preventing the droplets from being ejected normally. In this embodiment, multiple split droplets can be ejected using a single first ejection pulse DP1, making it possible to form smaller dots or dots at higher density at a higher frequency.

[0069] (Embodiment 2) 11 shows drive waveforms illustrating the first drive signal COM1 and the second drive signal COM2 according to the second embodiment of the present invention. Note that the same components as those in the first embodiment described above are given the same reference numerals, and redundant explanations will be omitted.

[0070] The drive signal generating section 216 shown in FIG. 3 of the first embodiment described above generates the first drive signal COM1 and the second drive signal COM2.

[0071] The first drive signal COM1 is the same as that in the first embodiment described above, and is a signal having a first ejection pulse DP1 within one unit period T that drives the active portion 310 to eject multiple split droplets from the nozzle 21, and is generated repeatedly for each unit period T. By driving the active portion 310 with the first ejection pulse DP1, the split droplets land on the medium S as multiple dots at a first interval d1.

[0072] The second drive signal COM2 is repeatedly generated by the drive signal generating unit 216 at the same unit period T as the first drive signal COM1. In this embodiment, a second ejection pulse DP2 is generated at the unit period T. The second drive signal COM2 is a signal that has, within one unit period T, a second ejection pulse DP2 that drives the active portion 310 to eject multiple split droplets from the nozzle 21, and is repeatedly generated at each unit period T. By driving the active portion 310 with the second ejection pulse DP2, the multiple split droplets land on the medium S at second intervals d2 that are smaller than the first interval d1, as will be described in detail later. Note that the second interval d2 also includes 0 (zero). In other words, the multiple split droplets include those that land at the same position on the medium S. Hereinafter, when the first drive signal COM1 and the second drive signal COM2 are not distinguished, they will be referred to as the drive signal COM, and when the first ejection pulse DP1 and the second ejection pulse DP2 are not distinguished, they will be referred to as the ejection pulse DP.

[0073] The second ejection pulse DP2 causes multiple dots split into multiple pieces within one unit period T to land on the medium S at second intervals d2 narrower than the first intervals d1. The second ejection pulse DP2 includes a fill element a1, a fill sustain element a2, a first contraction element a3, a first contraction sustain element a4, a third expansion element b1, a second expansion sustain element b2, a third contraction element b3, a second contraction sustain element a8, and a second expansion element a9, arranged in chronological order. In other words, the second ejection pulse DP2 replaces the third potential V3 of the first expansion element a5, the first expansion sustain element a6, and the second contraction element a7 of the first ejection pulse DP1 with a seventh potential V7 different from the third potential V3, resulting in the third expansion element b1, the second expansion sustain element b2, and the third contraction element b3. Elements identical to those in the first ejection pulse DP1 are designated by the same reference numerals, and redundant description will be omitted.

[0074] The third expansion element b1 changes the potential from the second potential V2 to the seventh potential V7, expanding the volume of the pressure chamber 12. The portion of the liquid column 121 that continues to extend due to the first contraction maintenance element a4, near the nozzle 21, is pulled back toward the pressure chamber 12 by the third expansion element b1, causing the liquid column to break up into multiple droplets. In this embodiment, the third expansion element b1 breaks up the liquid column into two droplets. Of course, the number of droplets that break up due to the third expansion element b1 is not limited, and may be three or more.

[0075] The second expansion maintaining element b2 maintains the seventh potential V7 for a certain period of time. While the second expansion maintaining element b2 is being supplied to the active portion 310, the liquid level 120 in the nozzle 21 starts to move toward the pressure chamber 12 side.

[0076] The third contraction element b3 changes the voltage from the seventh potential V7 to the fourth potential V4, contracting the volume of the pressure chamber 12. This third contraction element b3 slows down the movement speed of the liquid surface 120 that has been moving toward the pressure chamber 12 inside the nozzle 21.

[0077] Here, the ratio of the fourth potential difference ΔV4 between the second potential V2 and the seventh potential V7 of the second ejection pulse DP2 to the first potential difference ΔV1 between the first potential V1 and the second potential V2 of the first ejection pulse DP1 is smaller than the ratio of the second potential difference ΔV2 to the first potential difference ΔV1. Therefore, the force of the third expansion component b1, which pulls the portion of the liquid column from the nozzle 21 near the nozzle 21 back toward the pressure chamber 12, is smaller than the first expansion component a5 of the first ejection pulse DP1. Therefore, as described above, the flight speed of the satellite droplets 123 increases, and the second distance d2, which is the amount of deviation in the landing positions of the main droplet 122 and the satellite droplets 123 on the medium S, becomes smaller than the first distance d1.

[0078] The control processing unit 214 selectively supplies the first drive signal COM1 having such a first ejection pulse DP1 and the second drive signal COM2 having such a second ejection pulse DP2 to the activation unit 310 to perform printing.

[0079] Specifically, when ejecting droplets based on the recording data expanded by the control processing unit 214, the control processing unit 214 executes a first print mode that selects the second drive signal COM2 when printing images that require sharpness, such as ruled lines and characters. The control processing unit 214 also executes a second print mode that selects the first drive signal COM1 when images that require graininess, such as photographs. The control processing unit 214 may also drive the active units 310 corresponding to the nozzles 21 that eject black ink in a second print mode that supplies the second drive signal COM2 (second ejection pulse DP2), and drive the active units 310 corresponding to the nozzles 21 that eject color inks other than black, such as cyan, magenta, and yellow, in a first print mode that supplies the first drive signal COM1 (first ejection pulse DP1). Because black ink is often used for ruled lines and characters, sharp images can be printed by driving the active units 310 corresponding to the nozzles 21 that eject black ink in the second print mode. Furthermore, since color inks are often used for photographs and the like, by driving the active portions 310 corresponding to the nozzles 21 that eject color inks in the first print mode, it is possible to print images with graininess.

[0080] The control processing unit 214 may drive the active unit 310 with only either the first drive signal COM1 or the second drive signal COM2 for one image, depending on the ratio of images requiring sharpness to images requiring graininess, for example, whichever has the larger area ratio, among the images to be printed. Furthermore, image portions requiring sharpness may be printed with the second drive signal COM2, and image portions requiring graininess may be printed with the first drive signal COM1. In other words, the first print mode and the second print mode may be mixed for one image to be printed.

[0081] If the control processing unit 214 determines from the print data that the image requires sharpness, the control processing unit 214 forms a selection signal that supplies the second drive signal COM2 to the active unit 310 and stores it in the RAM 212. If the control processing unit 214 determines from the print data that the image requires graininess, the control processing unit 214 forms a selection signal that supplies the first drive signal COM1 to the active unit 310 and stores it in the RAM 212. For example, the selection signal may take two values, "0" or "1." "0" indicates that the first drive signal COM1 is to be used, and "1" indicates that the second drive signal COM2 is to be used. The control processing unit 214 forms such a binary selection signal for each image or each nozzle 21.

[0082] Then, during printing, when the control processing unit 214 obtains recording data equivalent to one line of the discharge unit 2, it outputs this one line of recording data together with a selection signal to the discharge unit 2 via the internal I / F 217. Furthermore, when one line of recording data is output from the output buffer 212C, the expanded intermediate code data is erased from the intermediate buffer 212B, and expansion processing is performed on the next intermediate code data.

[0083] The ejection unit 2 includes a drive circuit 111. The drive circuit 111 is a circuit that selects either the first drive signal COM1 or the second drive signal COM2 and applies it to the active unit 310 based on the print data (SI) and selection signal sent from the control unit 4 via the internal I / F 217. Such selection and application of the drive signal is performed for each active unit 310.

[0084] The print data consists of multiple pixel data to be ejected for each of the multiple dots that make up one line. For example, the pixel data may be binary, with "1" indicating that a dot should be formed and "0" indicating that a dot should not be formed. If the pixel data is "1" and the selection signal is "0," the drive circuit 111 supplies a first drive signal COM1 to the activation unit 310 that causes droplets to be ejected from the nozzle 21 corresponding to that pixel data. If the pixel data is "1" and the selection signal is "1," the drive circuit 111 supplies a second drive signal COM2 to the activation unit 310 that causes droplets to be ejected from the nozzle 21 corresponding to that pixel data. If the pixel data is "0," the drive circuit 111 does not supply any drive signal to the activation unit 310.

[0085] In this way, the liquid ejecting device 1 of this embodiment can select and use the first ejection pulse DP1 or the second ejection pulse DP2 as the ejection pulse that drives the active portion 310 depending on the image to be printed, thereby improving the print quality of the image.

[0086] In this embodiment, the only difference between the first ejection pulse DP1 and the second ejection pulse DP2 is the third potential V3 and the seventh potential V7. In other words, the second ejection pulse DP2 replaces the third potential V3 of the first expansion element a5, the first expansion maintaining element a6, and the second contraction element a7 of the first ejection pulse DP1 with the third expansion element b1, the second expansion maintaining element b2, and the third contraction element b3, which are changed to the seventh potential V7, which is different from the third potential V3. The other elements are the same. Therefore, there is no need to significantly change the waveform shapes of the first ejection pulse DP1 and the second ejection pulse DP2, and both can be easily designed.

[0087] Note that the first ejection pulse DP1 of the first drive signal COM1 and the second ejection pulse DP2 of the second drive signal COM2 have the same unit period, but this unit period does not have to be the same. For example, the unit period of the first drive signal COM1 may be shorter than the unit period of the second drive signal COM2. When only the first drive signal COM1 is supplied to all active units 310, the first drive signal COM1 is used as is, and when only the second drive signal COM2 is supplied to all active units 310, the second drive signal COM2 is used as is.

[0088] On the other hand, when selectively supplying the first drive signal COM1 and the second drive signal COM2 to the active units 310, the shorter unit period is adjusted to match the longer unit period. For example, by providing time between the first ejection pulse DP1 and the next first ejection pulse DP1, the shorter unit period is matched to the unit period of the second ejection pulse DP2. By adjusting the unit period in this manner, when only the first drive signal COM1 is supplied to all active units 310, the unit period is relatively short compared to when the second drive signal COM2 is also supplied, so printing speed is not reduced. Furthermore, when a mixture of the first drive signal COM1 and the second drive signal COM2 is supplied to all active units 310, there is no mismatch in ejection timing between the active units 310 supplied with the first drive signal COM1 and the active units 310 supplied with the second drive signal COM2.

[0089] In the present embodiment, a first drive signal COM1 including a first ejection pulse DP1 and a second drive signal COM2 including a second ejection pulse DP2 are generated, and the control processing unit 214 selects the first drive signal COM1 in the first print mode and the second drive signal COM2 in the second print mode, but this is not particularly limited. For example, a single drive signal including both the first ejection pulse DP1 and the second ejection pulse DP2 may be generated within one unit period T, and the control processing unit 214 may select either the first ejection pulse DP1 or the second ejection pulse DP2 and supply it to the activation unit 310.

[0090] Furthermore, since the first ejection pulse DP1 and the second ejection pulse DP2 differ only in the third potential V3 and the seventh potential V7, when all active sections 310 for an image to be printed are driven with the same ejection pulse, the drive signal generating unit 216 may generate only either the first ejection pulse DP1 or the second ejection pulse DP2 in accordance with the image to be printed.

[0091] (Other embodiments) Although one embodiment of the present invention has been described above, the basic configuration of the present invention is not limited to the above.

[0092] In the above-described embodiments, the first ejection pulse DP1 and the second ejection pulse DP2 are configured to include the second contraction element a7 to the second expansion element a9 for suppressing vibration of the liquid surface 120, but this is not particularly limited, and the second contraction element a7 to the second expansion element a9 do not have to be provided. However, by providing the second contraction element a7 to the second expansion element a9, the unit period T can be shortened, and printing at a high frequency can be achieved.

[0093] In the above-described embodiments, the thin-film piezoelectric actuator 300 is used as the driving element for generating a pressure change in the pressure chamber 12. However, the driving element is not limited to this, and other types of driving elements can be used, such as a thick-film piezoelectric actuator formed by attaching a green sheet or a longitudinal vibration type piezoelectric actuator in which piezoelectric material and electrode forming material are alternately laminated to expand and contract in the axial direction. Furthermore, the driving element can be a so-called electrostatic actuator that uses electrostatic force to deform a vibration plate and eject droplets from the nozzle 21.

[0094] Furthermore, the present invention is broadly applicable to liquid ejection devices in general that include a liquid ejection head. Examples of liquid ejection heads include various inkjet recording heads used in image recording devices such as printers, and colorant ejection heads used in manufacturing color filters for liquid crystal displays and the like. Examples of liquid ejection heads include electrode material ejection heads used in forming electrodes for organic EL displays, FEDs (field emission displays), and the like, and bioorganic material ejection heads used in biochip manufacturing, and the present invention can also be applied to liquid ejection devices that include these liquid ejection heads.

[0095] (Addendum) From the above-described exemplary embodiments, the following configurations can be understood, for example.

[0096] A liquid ejection device according to a first preferred aspect includes an ejection unit having a nozzle that ejects liquid, 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, and a drive signal generation unit that generates the drive signal, wherein the drive signal includes a first ejection pulse that ejects a plurality of droplets that form a plurality of dots on a medium, the first ejection pulse including a first contraction element that changes potential from a first potential to a second potential to contract the volume of the pressure chamber, a first contraction maintenance element that maintains the second potential following the first contraction element, and a second contraction maintenance element that changes potential from the second potential to a third potential following the first contraction maintenance element. and a first expansion element that changes potential and expands the volume of the pressure chamber, and when the first ejection pulse is supplied to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid sufficient to form the multiple dots begins to protrude from the nozzle as a liquid column, and while the first contraction maintenance element is supplied to the drive element, the liquid column continues to extend, and while the liquid column continues to extend, the first expansion element is supplied to the drive element, and the portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into multiple droplets, and the multiple droplets that have broken up land on the medium as multiple dots separated by a first interval.

[0097] According to this, by driving the drive element with the first ejection pulse, it is possible to eject droplets that are split into multiple droplets from the nozzle. Therefore, since multiple droplets can be ejected with a single first ejection pulse DP1, it is possible to form smaller dots and dots with higher density at a high frequency.

[0098] In Aspect 2, which is a specific example of Aspect 1, the dots on the medium land at the first intervals corresponding to the ratio of the second potential difference, which is the potential difference between the second potential and the third potential, to the first potential difference, which is the potential difference between the first potential and the second potential. This allows the size of the first intervals to be adjusted by the ratio of the second potential difference to the first potential difference.

[0099] In Aspect 3, which is a specific example of Aspect 1, the size of the first gap is adjusted by adjusting the ratio of a second potential difference, which is a potential difference between the second potential and the third potential, to a first potential difference, which is a potential difference between the first potential and the second potential. This allows the size of the first gap to be adjusted by the ratio of the second potential difference to the first potential difference.

[0100] In Aspect 4, which is a specific example of Aspect 1, the leading droplet of the split droplets flies at a flight speed that depends on at least one of the magnitude of the first potential difference, which is the potential difference between the first potential and the second potential of the first contraction element, and the rate of potential change of the first contraction element. Thus, since the flight speed of the leading droplet is determined by the magnitude of the first potential difference and the rate of potential change of the first expansion element, the flight speed of the trailing droplet can be changed by the ratio of the second potential difference, which is the potential difference between the second potential and the third potential, to the first potential difference, which is the potential difference between the first potential and the second potential, thereby adjusting the size of the first gap.

[0101] In Aspect 5, which is a specific example of Aspect 1, the first ejection pulse includes, following the first expansion element, a first expansion maintaining element that maintains the third potential, a second contraction element that changes potential from the third potential to a fourth potential and contracts the volume of the pressure chamber following the first expansion maintaining element, a second contraction maintaining element that changes potential from the fourth potential to a fifth potential following the second contraction element, and a second expansion element that changes potential from the fourth potential to a fifth potential following the second contraction maintaining element, and when the first ejection pulse is supplied to the drive element, the first expansion maintaining element is supplied. While the second contraction maintaining element is being supplied, the liquid surface in the nozzle begins to move toward the pressure chamber, and when the liquid surface in the nozzle is moving toward the pressure chamber, the second contraction element is supplied, thereby slowing down the speed at which the liquid surface in the nozzle moves toward the pressure chamber. While the second contraction maintaining element is being supplied, the liquid surface in the nozzle begins to move away from the pressure chamber, and when the liquid surface in the nozzle is moving away from the pressure chamber, the second expansion element is supplied, thereby slowing down the speed at which the liquid surface in the nozzle moves away from the pressure chamber. According to this, by having the first expansion maintaining element, second contraction element, second contraction maintaining element, and second expansion element, the first ejection pulse can suppress vibration of the liquid surface in the nozzle after ejecting multiple split droplets. Therefore, the first ejection pulse enables printing at high frequencies.

[0102] In Aspect 6, which is a specific example of Aspect 1, the period from the start of the first contraction element to the end of the first expansion element is 0.5 times or less the natural vibration period of the liquid in the pressure chamber. By setting the period from the start of the first contraction element to the end of the second expansion element to 0.5 times or less the natural vibration period, droplets ejected from the nozzle can be split and sent flying.

[0103] In Aspect 7, which is a specific example of Aspect 1, the first ejection pulse includes a fill element that changes potential from a sixth potential to the first potential to expand the volume of the pressure chamber, and a fill maintenance element that maintains the first potential between the end point of the fill element and the start point of the first contraction element, and the period from the start of the fill element to the start of the first contraction element is 0.2 times or more the natural vibration period generated in the liquid in the pressure chamber. Accordingly, by making the period from the start of the fill element to the start of the first contraction element 0.2 times or more, the liquid follows the change in volume of the pressure chamber, and the ejection characteristics of the main droplet are improved.

[0104] In aspect 8, which is a specific example of aspect 1, the drive signal includes a second ejection pulse that ejects a plurality of droplets that form one or more dots on the medium, the second ejection pulse including: a first contraction element that changes potential from the first potential to the second potential and contracts the volume of the pressure chamber; a first contraction maintaining element that maintains the second potential following the first contraction element; and a third expansion element that changes potential from the second potential to a seventh potential following the first contraction maintaining element and expands the volume of the pressure chamber; and when the second ejection pulse is supplied to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid that forms the plurality of dots is ejected as a liquid column. and a second ejection pulse is supplied to the driving element without supplying the first ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a first ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the first ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a first ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the first ejection pulse to the driving element, and a second ... first ejection pulse to the driving element, and a first ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element without supplying the first ejection pulse to the driving element, and a second ejection pulse is supplied to the driving element.

[0105] In Aspect 9, which is a specific example of Aspect 8, a ratio of a fourth potential difference, which is a potential difference between the second potential and the seventh potential, to a first potential difference, which is a potential difference between the first potential and the second potential, is smaller than a ratio of a second potential difference, which is a potential difference between the second potential and the third potential, to the first potential difference. This allows the second interval to be smaller than the first interval.

[0106] In Aspect 10, which is a specific example of Aspect 8, the printer includes a plurality of the ejection units, and the drive elements of the ejection units that eject black ink are driven in the second printing mode, and the drive elements of the ejection units that eject color inks other than black are driven in the first printing mode. This allows for printing sharp images using black ink, which is often used for ruled lines and characters, and for printing images with graininess using color inks, which are often used for photographs.

[0107] A preferred embodiment of a method for driving a liquid ejection device according to an eleventh aspect is a method for driving a liquid ejection device including an ejection unit having a drive element that generates pressure fluctuations in liquid in a pressure chamber that communicates with a nozzle that ejects the liquid when a drive signal is supplied, the drive signal including a first ejection pulse that ejects a plurality of liquid droplets that form a plurality of dots on a medium, the first ejection pulse including a first contraction element that changes in potential from a first potential to a second potential and contracts the volume of the pressure chamber, a first contraction maintaining element that maintains the second potential following the first contraction element, and a second contraction maintaining element that changes in potential from the second potential to a third potential following the first contraction maintaining element. and a first expansion element that expands the volume of the pressure chamber, and by supplying the first ejection pulse to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid sufficient to form the multiple dots begins to protrude from the nozzle as a liquid column, and while the first contraction maintenance element is supplied to the drive element, the liquid column continues to extend, and while the liquid column continues to extend, the first expansion element is supplied to the drive element, and the portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into multiple droplets, and the multiple droplets that have broken up land on the medium as multiple dots separated by a first interval.

[0108] According to this, by driving the drive element with the first ejection pulse, it is possible to eject droplets that are split into multiple droplets from the nozzle. Therefore, since multiple droplets can be ejected with a single first ejection pulse DP1, it is possible to form smaller dots and dots with higher density at a high frequency. [Explanation of symbols]

[0109] COM1...first drive signal, COM2...second drive signal, DP1...first ejection pulse, DP2...second ejection pulse, T...unit period, 1...liquid ejection device, 2...ejection section, 3...liquid storage section, 4...control section, 5...transport mechanism, 6...movement mechanism, 10...pressure chamber substrate, 12...pressure chamber, 15...communication plate, 20...nozzle plate, 21...nozzle, 30...protection substrate, 32...through hole, 40...case member, 45...compliance substrate, 50...vibration plate, 60...first electrode, 70...piezoelectric layer, 80...second electrode, 91...lead electrode, 100...common liquid chamber, 110...wiring member, 111...drive circuit, 120...liquid surface, 121...liquid column, 122...main droplet, 123...satellite droplet, 211...external interface, 212A...receiving buffer, 212B...intermediate buffer, 212C...output buffer, 214...control processing unit, 215...oscillating circuit, 216...drive signal generating unit, 217...internal interface, 300...piezoelectric actuator, 310...active unit.

Claims

1. a discharge unit having a nozzle for ejecting liquid, a pressure chamber communicating with the nozzle, and a drive element that generates pressure fluctuations in the liquid in the pressure chamber when a drive signal is supplied; a drive signal generation unit that generates the drive signal; Equipped with the drive signal includes a first ejection pulse that ejects a plurality of droplets that form a plurality of dots on a medium; the first ejection pulse includes a first contraction element that changes in potential from a first potential to a second potential and contracts the volume of the pressure chamber, a first contraction maintaining element that maintains the second potential following the first contraction element, and a first expansion element that changes in potential from the second potential to a third potential following the first contraction maintaining element and expands the volume of the pressure chamber, When the first ejection pulse is supplied to the driving element, the first contraction element is supplied to the drive element, and an amount of liquid that forms the plurality of dots begins to protrude from the nozzle as a liquid column; While the first contraction maintaining element is supplied to the drive element, the liquid column continues to extend, while the liquid column continues to extend, the first expansion element is supplied to the drive element, and the portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into a plurality of droplets, the droplets split into multiple droplets land on the medium as multiple dots separated by a first interval; A liquid ejection device characterized by:

2. the plurality of dots on the medium are landed at the first intervals according to a ratio of a second potential difference, which is a potential difference between the second potential and the third potential, to a first potential difference, which is a potential difference between the first potential and the second potential; The liquid ejection apparatus according to claim 1 .

3. The size of the first gap is adjusted by adjusting a ratio of a second potential difference, which is a potential difference between the second potential and the third potential, to a first potential difference, which is a potential difference between the first potential and the second potential. The liquid ejection apparatus according to claim 1 .

4. a leading droplet of the divided droplets flies at a flying speed corresponding to at least one of a magnitude of a first potential difference, which is a potential difference between the first potential and the second potential of the first contraction element, and a potential change rate of the first contraction element; The liquid ejection apparatus according to claim 1 .

5. the first ejection pulse includes, following the first expansion element, a first expansion maintaining element that maintains the third potential; a second contraction element that changes potential from the third potential to a fourth potential and contracts the volume of the pressure chamber following the first expansion maintaining element; a second contraction maintaining element that maintains the fourth potential following the second contraction element; and a second expansion element that changes potential from the fourth potential to a fifth potential following the second contraction maintaining element, When the first ejection pulse is supplied to the driving element, While the first expansion maintaining element is being supplied, the liquid level in the nozzle begins to move toward the pressure chamber, when the liquid surface in the nozzle is moving toward the pressure chamber, the second contraction element is supplied, thereby weakening the speed at which the liquid surface in the nozzle moves toward the pressure chamber, while the second contraction maintaining element is being supplied, the liquid surface in the nozzle begins to move away from the pressure chamber, When the liquid surface in the nozzle is moving in a direction opposite to the pressure chamber, the second expansion element is supplied, thereby slowing down the speed of the liquid surface in the nozzle moving in a direction opposite to the pressure chamber. The liquid ejection apparatus according to claim 1 .

6. a period from the start of the first contraction component to the end of the first expansion component is 0.5 times or less of a natural vibration period generated in the liquid in the pressure chamber; The liquid ejection apparatus according to claim 1 .

7. the first ejection pulse includes a filling element that changes potential from a sixth potential to the first potential to expand the volume of the pressure chamber, and a filling maintaining element that maintains the first potential between an end point of the filling element and a start point of the first contraction element, a period from the start of the filling element to the start of the first contraction element is 0.2 times or more of a natural vibration period generated in the liquid in the pressure chamber; The liquid ejection apparatus according to claim 1 .

8. the drive signal includes a second ejection pulse that ejects a plurality of droplets that form one or more dots on the medium; the second ejection pulse includes the first contraction element, which changes in potential from the first potential to the second potential and contracts the volume of the pressure chamber; the first contraction maintaining element, which maintains the second potential following the first contraction element; and a third expansion element, which changes in potential from the second potential to a seventh potential following the first contraction maintaining element and expands the volume of the pressure chamber; When the second ejection pulse is supplied to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid that forms the plurality of dots begins to protrude from the nozzle as a liquid column; While the first contraction maintaining element is supplied to the drive element, the liquid column continues to extend, While the liquid column continues to extend, the first expansion element is supplied to the drive element, and the portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into a plurality of droplets, the droplets split into multiple droplets land on the medium at second intervals that are smaller than the first intervals; In a first printing mode, the second ejection pulse is supplied to the driving element without supplying the first ejection pulse to the driving element; In a second printing mode, the first ejection pulse is supplied to the driving element without supplying the second ejection pulse to the driving element. The liquid ejection apparatus according to claim 1 .

9. a ratio of a fourth potential difference, which is a potential difference between the second potential and the seventh potential, to a first potential difference, which is a potential difference between the first potential and the second potential, is smaller than a ratio of a second potential difference, which is a potential difference between the second potential and the third potential, to the first potential difference; The liquid ejection apparatus according to claim 8 .

10. A plurality of the discharge portions is provided, the drive element of the ejection unit that ejects black ink is driven in the second print mode, the drive elements of the ejection units that eject color inks other than black are driven in the first printing mode; The liquid ejection apparatus according to claim 8 .

11. A method for driving a liquid ejection device including a discharge unit having a drive element that generates pressure fluctuations in liquid in a pressure chamber that communicates with a nozzle that ejects liquid when a drive signal is supplied, the method comprising: the drive signal includes a first ejection pulse that ejects a plurality of droplets that form a plurality of dots on a medium; the first ejection pulse includes a first contraction element that changes in potential from a first potential to a second potential and contracts the volume of the pressure chamber, a first contraction maintaining element that maintains the second potential following the first contraction element, and a first expansion element that changes in potential from the second potential to a third potential following the first contraction maintaining element and expands the volume of the pressure chamber, By supplying the first ejection pulse to the drive element, the first contraction element is supplied to the drive element, and an amount of liquid that forms the plurality of dots begins to protrude from the nozzle as a liquid column; While the first contraction maintaining element is supplied to the drive element, the liquid column continues to extend, While the liquid column continues to extend, the first expansion element is supplied to the drive element, and the portion of the liquid column near the nozzle is pulled back toward the pressure chamber, causing the liquid column to break up into a plurality of droplets, the droplets split into multiple droplets land on the medium as multiple dots separated by a first interval; A method for driving a liquid ejection device.

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